CA2062264C - Static dissipative resin composition - Google Patents
Static dissipative resin compositionInfo
- Publication number
- CA2062264C CA2062264C CA002062264A CA2062264A CA2062264C CA 2062264 C CA2062264 C CA 2062264C CA 002062264 A CA002062264 A CA 002062264A CA 2062264 A CA2062264 A CA 2062264A CA 2062264 C CA2062264 C CA 2062264C
- Authority
- CA
- Canada
- Prior art keywords
- resin
- resin composition
- zinc oxide
- static dissipative
- oxide whiskers
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Fee Related
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Classifications
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
- C08K3/00—Use of inorganic substances as compounding ingredients
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
- H01B1/00—Conductors or conductive bodies characterised by the conductive materials; Selection of materials as conductors
- H01B1/20—Conductive material dispersed in non-conductive organic material
- H01B1/24—Conductive material dispersed in non-conductive organic material the conductive material comprising carbon-silicon compounds, carbon or silicon
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
- C08K3/00—Use of inorganic substances as compounding ingredients
- C08K3/01—Use of inorganic substances as compounding ingredients characterized by their specific function
- C08K3/017—Antistatic agents
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
- C08K7/00—Use of ingredients characterised by shape
- C08K7/02—Fibres or whiskers
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
- C08K7/00—Use of ingredients characterised by shape
- C08K7/02—Fibres or whiskers
- C08K7/04—Fibres or whiskers inorganic
- C08K7/08—Oxygen-containing compounds
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
- H01B1/00—Conductors or conductive bodies characterised by the conductive materials; Selection of materials as conductors
- H01B1/20—Conductive material dispersed in non-conductive organic material
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
- H01B1/00—Conductors or conductive bodies characterised by the conductive materials; Selection of materials as conductors
- H01B1/20—Conductive material dispersed in non-conductive organic material
- H01B1/22—Conductive material dispersed in non-conductive organic material the conductive material comprising metals or alloys
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10S524/00—Synthetic resins or natural rubbers -- part of the class 520 series
- Y10S524/91—Antistatic compositions
- Y10S524/912—Contains metal, boron, phosphorus, or silicon
Abstract
A static dissipative resin composition has semiconductor fillers dispersed in the resin with at least some of the fillers in electrical contact with each other to form a conductive path. The .alpha. value representing the degree of nonlinearity of the V-i characteristic at the contact between the semiconductor fillers should be 2-150, and the volume resistivity of the semiconductor filler is desirably 105-1010.OMEGA..cm, whereby, by employment of a conductive filler or a solid lubricant together with the semiconductor filler, various physical properties of the resin composition are improved.
Description
r Static Dissipative Resin Composition The present invention generally relates to a static dissipative resin composition, and, more particularly, to a resin composition having the resistivity (surface resistivity 1. OX105-1 . OX1012Q/O) defined as the static dissipative property according to the U.S. standard ANSI/EIA-541-1988, or a resin composition having the resistivity (surface resistivity 1. OX105-1. 0x109Q/~) defined as the static dissipative property according to the U.S. standard DOD-HDBK-263.
A resin composition of the present invention is used in the form of pellets or powders as a resin compound for injection molding or extrusion molding, etc. and is also offered as a final molded product, such as a part, a plate, a sheet, a film, etc. Moreover, the resin composition may be supplied as a paint, a coating paste, putty or a coated film.
The following acronyms are used throughout this specification.
Acronyms Full Meaning OA Office Automation FA Factory Automation AV Audio Visual (Equipment) VTR Video Tape Recorder TFT Thin Film Transistor ABS Acrylonitrile-Butadiene-Styrene PPE Polyphenylether PP Polypropylene PBT Polybutylene-terephthalate PPS Polyphenylene-sulfide POM Polyoxymethylene For examples of the aforementioned molded final products, there are wall or floor materials (floor tile, floor surfacing and the like), antistatic packaging products for semiconductors (e.g., IC trays, IC magazines, IC carrier tapes, boxes, containers, cabinets, substrate holders, printed * .
.~
`~ 2 2062264 board stands and the like), and other antistatic products, earthing products and sliding parts, or the like, in the OA, AV, FA fields such as computers, copying machines, facsimiles, printers, VTRs, video cassette tapes, compact disk recorders, etc. More specifically, tape guides and guide rollers for the tapes of the AV devices can be manufactured of the resin composition, and such sliding parts as bearings and gears can be formed of a resin composition of the present invention.
Likewise, the resin composition is useful not only for the components of liquid crystal displays, particularly TFT liquid crystal displays, but for the supporting or holding members in the manufacturing process of the displays. The resin composition may be employed to coat the floor and equipment in a clean room.
Resin has been widely employed as a material having a superior insulation property (for instance, 1015Q/O or higher).
In recent years, however, the static electricity generated on an insulating resin has been noticed as an embarrassment to semiconductors, OA or FA devices, and accordingly a resinous material with static dissipative properties (105-1012 or 105-109Q/O) has attracted enthusiastic attention. Although a highly conductive resin (smaller than 105Q/O) is effective to some degree, as far as the prevention of static build-up and static electricity are concerned, it is an imperfect resin, since, because of its highly conductive properties (smaller than 105Q/O), a discharge spark can be caused by the static electricity or a short-circuit can occur.
A static dissipative material has the proper resistance by itself, and therefore the static electricity, if it is generated, can be easily and promptly removed with no accompanying discharge spark. In addition, such a static dissipative material has little possibility for causing an electric shock or a short-circuit in an electric circuit, etc.
In other words, the static dissipative material is regarded as ~statically conductive and electrically insulating".
_ _ 3 _ 2062264 Various developments have targeted a superior static dissipative material, but a fully satisfactory result has not yet been achieved.
For instance, conventionally, an organic and ionic antistatic agent has been mixed into ABS resin or the like.
But this resinous material is strongly dependent on humidity, and it functions poorly in a highly dried condition. Worse still is that the antistatic agent may ooze out of the surface of the resin with time, only a relatively high resistance (e.g. 101-1012Q/O) being achieved by this resinous material.
A resinous material of this kind is therefore unstable.
Moreover, this method is only applicable to a limited number of reslns.
On the other hand, an inorganic conductive filler having more stable characteristics than the above-described antistatic agent has been mixed in some of some resinous materials.
In general, the following is known about a resinous material of the type. When the conductive filler is mixed into a resin to cause the resin to be conductive, the phenomenon in this case is often explained by the "Percolation Theory".
To enable the prior art to be described with the aid of a diagram the figures of the drawings will first be listed.
Fig. 1 is a diagram of the characteristic curve of a prior art composition;
Fig. 2 is a diagram of the nonlinear characteristic curve of ZnO whiskers used in an embodiment of the present invention;
Fig. 3 is a diagram of the relation between the surface resistance and loadings of a ZnO whisker;
Fig. 4 is an electron microscope photograph of a ZnO
whisker;
Fig. 5 is a diagram of the relation between the surface resistance and loadings of a ZnO whisker.
, `~ - 4 - 2062264 The relation between the mixing amount (wt.~) of the filler and the resistance of the prior art resinous material with a conductive filler is schematically represented in Fig. 1. As the conductive filler is mixed in, the resinous material is initially in the originally insulating state (area (I)). When the amount of filler exceeds a certain level, a slight conductivity immediately appears (although this conductivity is unstable) (area (II)). Even if the amount of the filler is increased over a certain level, the conductivity Rs is not changed very much, that is, it enters a stable area (III). A stable conductive resinous composition is thus in the area (III).
The stable point Rso of the conductivity of the resinous composition is greatly dependent upon the conductivity of the conductive filler. Rso becomes no higher than 10-1Q/~ in the case of a metallic conductive filler; and becomes 10-104Q/~ in the case of a carbon filler.
As is apparent from Fig. 1, although it is not impossible to obtain a resinous material having the static dissipative level that exists between the insulation level and Rso, if the resinous material is designed in the area (II), the resultant material is unstable in conductivity and has poor reproducibility.
As such, in order to obtain a static dissipative resinous composition, a conductive filler that had the correct conductivity to bring the stable point Rso into the static dissipative level would be desirable. However, as mentioned before, the stable point Rso is too low in the case of conventional inorganic conductive fillers (either metallic or carbon f1ller) to be used for a static dissipative resin composltlon.
Japanese Patent Laid-Open Publication Tokkaihei 1-225663 (225663/1989) discloses a resin composition with high conductivity (the 10Q cm mark) having highly conductive zinc oxide whiskers mixed into the resin. This prior art is, however, disadvantageous in that it has an extraordinarily low Rso and is unable to achieve a stable static dissipative r ~ .
level, similar to the above-described resinous composition having an inorganic conductive filler mixed therein.
An essential object of the present invention is therefore to provide a resin composition having an inorganic conductive filler, with a stable point of conductivity Rso at the static dissipative level.
A further object of the present invention is to provide a static dissipative resin composition with stable conductivity and less dependency on humidity without causing oozing of the conductive agent.
A still further object of the present invention is to provide a static dissipative resin composition enabling a change of a variety of resins, such as a crystalline thermoplastic resin, into a matrix.
A yet further object of the present invention is to provide a static dissipative resin composition that is highly useful in practical use and suitable to be coloured in various tints, while having superior moldability for injection molding and less abrasion of a molding press or mold.
Another important object of the present invention is to provide a highly efficient static dissipative resin composition that will more readily leak static electricity, while being more insulative against general electricity.
According to a first embodiment the invention provides a static dissipative resin composition having semiconductor fillers dispersed in a resin, wherein a conductive path is formed at least through electrical contact among at least a part of said semiconductor fillers which have the ~ value of 2-150 indicating a nonlinearity of the V-i characteristic as a result of electrical contact among said semiconductor fillers.
The invention also provides a static dissipative resin composition wherein zinc oxide whiskers having an aspect ratio not smaller than 3 and a volume resistivity of 105-101Q.cm are dispersed in a resin to form a conductive path through electrical contact among at least some of said zinc oxide whiskers.
` 2û62264 The invention also provides a static disslpat1ve resin composition wherein zinc oxide whiskers having an aspect ratio not smaller than 3, a volume resistivity of 105-101Q.cm and an ~ value of 2-150 and at least one other kind of conductive filler are dispersed in a resin to form a conductive path through electrical contact among at least some of said zinc oxide whiskers, said zinc oxide whiskers and conductive fillers or said conductive fillers.
The invention also provides a static dissipative resin composition wherein zinc oxide whiskers having an aspect ration not smaller than 3, a volume resistivity of 105-101Q.cm and an ~ value of 2-150 and at least one kind of a solid lubricant are dispersed in a resin to form a conductive path through electrical contact among at least some of said zinc oxide whiskers.
The invention also provides a static dissipative resin composition wherein zinc oxide whiskers having an aspect ration not smaller than 3, a volume resistivity of 105-101Q.cm and an ~ value of 2-150, at least one other kind of conductive filler, and at least one kind of a solid lubricant are dispersed in a resin to form a conductive path through electrical contact among at least some of said zinc oxide whiskers, said zinc oxide whiskers and conductive fillers or said conductive fillers.
In one embodiment of the invention a semiconducter filler having an ~ value 2-150 or a specific volume resistance 105-101Q.cm is employed. Concretely speaking, a semiconductor filler of zinc oxide, barium titanate, selenium, silicon, silicon carbide, etc. which is a main component of a varistor, a semiconductor filler of metallic oxide, such as SnO2, TiO2, Ge2, Cu2O, Ag2O, In2o3, T~2O3, SrTiO3, LaCrO3. WO3, EuO, Ae2o3/
PbCrO4, etc. or InP is mixed in a resin. One or more kinds of the above fillers can be blended with a suitable mixing ratio.
Although the shape of the semiconductor filler is not specifically determined and the filler may be granules, whiskers or flakes or may be formed in a mass, it is desirable to use semiconductor fillers of whiskers, fibers, or flakes, ~ 7 ~ 2062264 particularly, tetrapod-like whiskers in order to facilitate the formation of a conducting path in the resin.
A semiconductor filler of a single crystal is most suitable, but the single crystal may be crushed or a filler of fine particles may be used. Also, a semiconductor filler of a sintered body or a sintered body after having been crushed or turned into fine particles can be used.
It is also possible to cause semiconductor fine particles to be held on other filler material, e.g., conductive or insulating whiskers, flakes, fibers, to produce a semiconductor filler (by means of coating or the like).
Regarding the size or dimension of the semiconductor filler, this will naturally be set within a proper range so that the semiconductor filler is dispersed in the resin to make it conductive. Specifically, the maximum length of a filler will preferably be selected from lOmm - O.l~m, more suitably from 300~m-l~m to 300~m-3~m, and more preferably from 200~m-lO~m. 50~m-lO~m is best. If the maximum length is smaller than O.Ol~m, the ~ value is difficult to set properly.
If it exceeds lOmm, it is hard to disperse the filler uniformly in the resin.
When the aspect ratio (maximum length/minimum length) of the semiconductor filler in the form of whiskers, fibers and flakes is 3-10000 or approximately 3-1000, it is effective and efficient for forming a conducting path. Particularly, 5-50 is most suitable.
According to a preferred form of the present invention, the specific volume resistance of the semiconductor filler is 105-101 Q.cm, especially 106-101Q.cm. A semiconductor filler with 107-109Q.cm specific volume resistance is more preferable to realize the static dissipative resin composition. The resistance of the semiconductor filler is controlled in an adequate manner in respect to oxidization, reduction or the control of valences. The addition of a suitable amount of impurity elements therefor is permissible.
The specific volume resistance of the semiconductor filler is measured in the following manner. Initially, the ~ - 8 - 2062264 semiconductor filler to be measured is collected in an amount of 0.5 g and is held uniformly between a pair of parallel plate electrodes (silver-plated electrodes) of 20mm diameter, to which 5kg/cm2 of pressure is uniformly applied. The resistance between the electrodes is measured by means of a superinsulating resistance meter (High Resistance Meter 4329A
by HP Inc.). The value of the meter 5 seconds after the application of the pressure is read (measuring voltage 25V).
Subsequently, the pressured powdery sample of the semi-conductor filler is taken out, and its thickness is measured.The volume resistivity P is calculated from the thickness of the sample, the area of the sample (3.14 cm2) and the above-measured resistance in accordance with the following formula:
P(Q.cm) = R.S/t wherein R(Q) is the resistance, S(cm2) is the area of the sample, t(cm) is the thickness of the samples, and P(Q.cm) is the volume resistivity. The measurement is performed at 20C
with a humidity of 40~RH.
The ~ value indicative of the nonlinear voltage-current characteristic (V-i characteristic) generated consequent to the contact between the semiconductor fillers should be 2-150.
2-100 and particularly 2.5-40 is desirable to obtain a good static dissipative resin composition. 3-15 is further suit-able from the manufacturing viewpoint. Although a semi-conductor filler with an ~ value smaller than 2 may possiblybe used to form the static dissipative resin composition, the obtained resin composition does not show as good a static dissipative property as the present invention. On the other hand, if the ~ value is over 150, a discharge spark of the static electricity can occur, which is undesirable.
In order to measure the ~ value, the semiconductor fillers are brought into contact with each other, and a lead wire is taken out from both ends. By way of example, two monofilaments of zinc oxide whisker (abbreviated as ZnO
whisker hereinafter) (in the shape of a needle, 50mm long) are placed to intersect in contact with each other, and a lead * Trademark - 9 - 206~264 wire (using a silver paint and a gold wire) is led out from each monofilament. The V-i characteristic at this time is indicated in Fig. 2. There is another measuring method, by which a current is measured by changing the voltage using the parallel plate electrodes and the sample employed for measuring the volume resistivity discussed before. This method is simple and makes it easy to evaluate the results.
The voltage is increased gradually from a low voltage. In this case, it is important to monitor carefully the nonlinearity of the V-i characteristics. Moreover, in the case where the measured current is unstable at each voltage, the value 5 seconds after application of the voltage should be taken. The optimum ~ value for the area where the V-i characteristic changes nonlinearly is obtained according to the equation:
i = a(V-b) a + C
wherein a, b, c are constants. In this case, the least square or computing is quite useful.
As the physical phenomenon causing the nonlinearity from the contact between the semiconductor fillers, there are the tendency not to comply with Ohm's law at the boundary, due to the surface level or a PN junction, and the Zener effect, etc.
The loading of the semiconductor filler into the resin cannot be specifically defined, since it depends on the kind of filler. However, 20-80 weight ~ to the whole of the resin composition is normally suitable, and 30-70 weight ~ is more suitable. If it is smaller than 20 weight ~, the conducting path is not perfectly formed, so that the conductivity is insufficient for dissipation of the static electricity. In contrast, if the filler is mixed in over 80 weight ~, the resin composition becomes undesirably fragile or brittle.
A semiconductor whisker suitable as a semiconductor filler in the present invention is formed of, for example, ZnO, silicon carbide, SnO2, ZnS, silicon, germanium. Among them, ZnO whiskers are most suitable from the viewpoints of productivity, cost, colour, hygienic qualities and the like.
r The ZnO whisker is manufactured by various methods into a simple needle-shaped whisker or tetrapod-like whisker as is shown in the electron microscope photograph in Fig. 4. The tetrapod-like whisker is superior in terms of mass production, forming a resin composition with advantageous characteristics.
Although there are many ways to manufacture a tetrapod-like ZnO whisker, the following method is suitable to fulfil the semiconductor characteristics and specific resistance of the ZnO whisker as well as the mass-productivity. The present invention is not restricted to the following method, so long as the semiconductor characteristics and specific resistance of the ZnO whisker are satisfied.
Specifically, vapour of zinc metal melted at 800-1100C
is introduced into a furnace to react with a burning gas such as propane or the like. At this time, an atmosphere that is reducing to some degree is preferably used and several seconds to several tens of seconds are consumed-for the reaction.
Almost all of the ZnO whiskers obtained under these conditions are like tetrapod, with an apparent specific gravity of 0.02-0.5. Moreover, the whiskers are obtained with a high yield, not smaller than 70 wt.~, i.e., the whiskers are suited for mass production. The ZnO whiskers have electric properties, for example, semiconductor characteristics, specific resistance and the like that suit the present invention. In some cases, not only ZnO whiskers having a quadraxial crystalline part, but those with a triaxial, a biaxial or a uni-axial crystalline part may be mixed, but the triaxial, biaxial or uni-axial part is one that is produced when the quadraxial part is partly broken. Particularly when the ZnO whiskers are kneaded into the resin, the whiskers are mostly broken, resulting in a uni-axial crystalline substance.
A thick part at the bottom of the needle shaped crystal of the ZnO whisker is called the base thereof if the whisker is of simple needle shape. In the case of the tetrapod-like crystal, the coupling part where the four needle-shaped crystals gather is also called the base thereof. The length from the base to the front edge (tip) of the ZnO whisker is ~,~
preferable to be 3-300~m, more deslrably 10-200~m to 10-50~m from the viewpoints of the characteristics and productivity of the resin composition.
The aspect ratio (leg length/base diameter) of the ZnO
whisker better be 3-1000, especially 5-50, so as to form the conducting path. If the length between the base and front edge is smaller than 3~m or the aspect ratio is smaller than 3, the resultant resin composition does not exhibit suffic-iently conductive. If the length is over 300~m or the aspect ratio exceeds 1000, the whisker is not suitable for mass production and may be broken into small parts in the kneading process, because of an excessively increasing viscosity of the resln .
It is generally known that the resistivity of ZnO varies depending on the forming method thereof, or whether other elements are doped into the ZnO (for example, it varies from 10~2-1012Q.cm). 105-101Q.cm, particularly, 106-l01Q.cm is preferably employed for the present invention. Taking into consideration the nonlinear characteristics as well, 107-109Q.cm is most suitable to realize a static dissipative resin composition having appropriate conductive properties. The resistivity of the ZnO whisker can be controlled by changing the manufacturing conditions, that is, oxygen concentration, reaction temperature and the like, or by doping an element in the III group (e.g., aluminum, gallium, indium, etc.) or copper, zinc, lithium, chromium according to the conventional manner. Aluminum or zinc is most suitable for doping.
The specific volume resistance of the ZnO whisker is measured in the same manner as in the case of the semiconductor filler described earlier.
Although the a value which is the index of the semiconductor characteristic of the ZnO whisker, i.e., the nonlinearity of the ZnO whisker resulting from the contact between the ZnO whiskers, is not specified, 2-150, 2-100, more particularly 2.5-40 is suitable. More preferably 3-15 is desired. If the ZnO whisker has an a value smaller than 2, it cannot realize a static dissipative resin composition of the ~ .
~062264 present invention. On the other hand, if the ~ value is over ~ 150, it is difficult to achieve a desired resin composition that avoids spark discharge.
The ~ value is measured according to the method employed for the semiconductor filler.
In a conventional ZnO nonlinear resistor, called a varistor, the nonlinearity is known to be achieved by the action of a special thin layer present at the boundary between the ZnO crystalline particles (for example, a Biz03 or PrzO3 thin layer having a thickness of the order of A-~m). However, the nonlinearity in the present invention derives from the direct contact between the crystalline particles of the ZnO
whisker, and no special thin layer composed of other elements is interposed between the crystalline particles. Therefore, the nonlinearity of the present invention is achieved in a fundamentally quite different manner or mechanism from that of a conventional varistor.
The ZnO whisker is mixed into the resin by 20-80 wt.~, more preferably 30-70 wt.~, to the whole of the resin compo-sition. Particularly, the mixing ratio is desirably over 40wt.~ and not larger than 70 wt.~. If it is below 20 wt.~, the conducting path becomes imperfect, whereby the conductivity is insufficient for dissipation of the static electricity. When the mixing ratio exceeds 80 wt.%, the resin composition becomes fragile. When the mixing ratio is over 40 wt.~, it is particularly suitable, since the ZnO whiskers are kept in stable contact with each other.
The conductivity of a resin composition having a semiconductor filler of the ZnO whiskers or the like dispersed therein is measured pursuant to ASTM-D-257 (measuring voltage is suitably DC500V). The present invention aims at a resin composition having 105-1012Q/~, 105-109Q/~, further 106-109Q/~
and more preferably 107-109Q/~. The stability of the static dissipation is endangered if 1012Q/~ is exceeded. Moreover, if the static dissipative property is lower than 105Q/~, the inconveniences inherent in a highly conductive material, such `1_~
as a spark discharge, a shortcircuiting, an electric shock, etc. can arise.
A static dissipative resin composition of the present invention can be used in the form of pellets, powders, molded product, paint or paste.
Besides a thermoplastic resin, a thermosetting resin can be used for the resin. Regarding the thermoplastic resin, although it is not restricted, a melt flow rate (M.F.R.) from lg/10 min. to lOOg/10 min., particularly, lOg/10 min. or higher is preferred, so as to make the characteristics stable.
The M.F.R. is measured, for instance, according to ASTM-D-1238. In a case where the M.F.R. is lower than lg/10 min., the semiconductor fillers are brought less into contact with each other. If it exceeds lOOg/10 min., the resin composition becomes fragile and is therefore not desirable.
Although a thermoplastic resin with high crystallinity is suitable, a non-crystalline resin can be used.
Specifically, polypropylene resin, polybutylene terephthalate resin, polyacetal resin, polyphenylene sulfide resin, polyamide resin, as well as polyethylene resin, polyvinyl chloride resin, polyvinylidene chloride resin, polyethylene terephthalate resin, polyether etherketone resin, liquid crystal polymer (aromatic liquid crystal polyester, semiaromatic liquid crystal polyester or the like), etc. can be the crystalline resin. Among these resin, copolymer polypropyrene resin is best suited but homopolymer polypropyrene resin can be utilized.
For a non-crystalline resin, although it is not particularly specified, polystyrene resin, ABS resin and denatured PPE resin are most desirable, but polyether imide resin, polyether sulfide resin, polyarylate resin, polysulfone resin, polyvinyl acetate resin, polycarbonate resin, polymethyl methacrylate resin, polybutadiene resin, or polyacrylonitrile resin can be employed. It is possible to use a single kind of resin or a copolymer of two or more kinds of these resins or a mixture of the resins.
`~ - 14 - 2062264 On the other hand, for a thermosetting resin, besides unsaturated polyester resin, epoxy resin, urethane resin, silicone resin, melamine resin, phenol resin, urea resin or the like can be used.
Since it requires special attention when the resin is blended or kneaded with the semiconductor filler, the specific conditions (temperature, number of revolution, viscosity and the like) should be set to achieve effective contact between the semiconductor fillers.
However, an apparatus to mix or knead this type of composite material may be a conventional one. A single-screw or multi-screw extruder, a ribbon blender, a super mixer (Henschel mixer), that is, a mixer of a container fixed type with a screw rotor blade, or a mixer of a container rotary type, such as a horizontal cylindrical mixer, an inclined cylindrical mixer, or a V tumbling mixer can be employed.
Various kinds of molding methods are possible, injection molding being the most suitable in the present invention. In addition, extrusion molding, compression molding, vacuum molding, blow molding can be carried out.
Furthermore, when the resin composition is presented in the form of paint, paste or putty, a solvent may or may not be added.
If the semiconductor filler is used after being subjected to a surface treatment, a silane coupling agent is most suitable. Other kinds of agent, for example, of chromium, titan, silyl peroxide, organic phosphate can be used for the surface treatment.
The conductivity is improved in some cases when the semiconductor filler is used along with a conductive filler.
The conductive filler should have the specific volume resistance smaller than 105Q.cm and be made of metal, carbon or graphite particles, flakes, whiskers or fibers, or conductive ceramics particles, whiskers or fibers. The metal is preferably silver, gold, stainless steel or aluminum, but copper, nickel, palladium, iron, etc. can be employed.
- 15 - 206226~
The conductive ceramics can be conductive potassium titanate (for example, DENTALL BK-200 by Otsuka Chemical Co., Ltd.), zirconium carbide, titanium carbide, silicon carbide, etc.
The total of the semiconductor filler and the conductive filler to the whole of the resin composition should be 5-80 wt.~. Meanwhile, the weight ratio of the semiconductor filler and conductive filler is between 1:50 and 50:1, especially from 1:5 to 5:1. If too much conductive filler is mixed then the interactive effect is reduced and proper static dissipation cannot be realized. Therefore, a ratio from 1:1 to 5:1 is most desirable.
When a solid lubricant is used in the present invention, the static dissipative resin composition gains superior sliding property and abrasion resistance. Fluoride resin, such as polytetrafluoroethylene, high density polyethylene, aromatic polyamide, aromatic polyester, granular phenol or a graphitized substance thereof, graphite, molybdenum disulfide, tungsten disulfide, WSe2, MoSe2, boron nitride, etc. are suited for the solid lubricant. Two or more kinds of the above lubricant may be mixed. The lubricants are usually powder in the form of particles or flakes. From the characteristics' viewpoint, polyfluoroethylene, high density polyethylene and molybdenum disulfide are most suitable. The mixing ratio of the solid lubricant to the whole of the resin composition is 1-30 wt.~, more preferably 5-20 wt.~.
It is possible to blend other kinds of material that do not hurt the characteristics of the resin composition. For instance, reinforcing material or an extender composed of glass fibers or flakes, beads, talc, mica, calcium carbonate, clay, barium sulfate, alumina, silica, diatomaceous earth, wood flour, etc. and fire-proof material, such as aluminum hydroxide, antimony trioxide, phosphoric ester can be added.
Or, a colouring agent such as titanium dioxide, carbon black or the like may be used. Likewise, a suitable amount of an * Trademark ~i `` 2062264 organic antistatic agent, stabilizer or deterioration preventing agent may be blended into the resin.
[Embodiment 1]
Vapour of molten zinc metal at 980C is fed into a furnace to react with burning propane gas in a reducing atmosphere. The degree of reduction is -0.1~-10 O2Vol.~ which is measured by an NGK 2 analyzer (model RE-110:product of Nippon Gaishi Co., Ltd.). As a consequence, tetrapod-like ZnO
whiskers are obtained. The length from the base to the front edge of the whisker is 10-30~m, and the average aspect ratio is 15. The specific volume resistance measured by the parallel plate electrodes is 2xl08Q.cm and the ~ value showing the V-i characteristics measured by the electrodes is 3.9.
Thereafter, 2.5 kg polypropylene resin (Diapolymer Co., Ltd.:Mitsubishi Polypropylene BClE, melt flow rate 33g/lOmin.) is uniformly mixed with the above-obtained 2.5 kg ZnO whiskers in a plastic bag. The mixing ratio is accordingly 50wt.~.
The mixed substance is put into a hopper of a single-screw extruder and kneaded at a cylinder temperature of 240C. The speed of the screw is 40 r.p.m. The kneaded substance is then extruded from a nozzle, cooled by water and cut into pellets.
Each pellet of the resin composition has an average diameter of 3mm~ and an average length 5mm.
The pellets are fed into a hopper of an injection molding press and molded at a resin temperature of 220C and a mold temperature of 52C. A dumbbell specimen and a flat plate (85mmx85mmx3mmt) are obtained. These molded products have superior surface smoothness and beautiful white colour.
The flexural modulus and surface resistivity of the molded products is 20100kg/cm2 and 3x106Q/~, respectively.
The flat plate is then cooled in liquid nitrogen for 30 seconds and cut by nippers. When the cut surface is inspected through an electron microscope (magnification x 1500), it is found that some of the ZnO whiskers are in touch with each other whereby to constitute a conductive path. It is also * Trademark confirmed that a considerable amount of the tetrapod-like ZnO
whiskers are broken into simple needle-shaped whiskers.
[Embodiments 2-10]
Vapour of molten zinc metal at 1020C is allowed to react with burning propane gas in a furnace. The reducing atmos-phere has a degree of reduction -4~-6 O2Vol.~. As a result, the obtained ZnO whiskers are in the tetrapod-like shape.
Using these ZnO whiskers and various kinds of material, kneading and molding are carried out substantially in the same manner as in Embodiment 1. The evaluation results of the physical properties of the final composition are indicated in Tables 1 and 2 below.
[Comparative Examples 1-3]
In conformity with Embodiment 1 above, comparative examples are prepared by kneading and molding various kinds of material, the physical properties of which are also shown in Table 2 below.
It is to be noted that the resin represented in Tables 1 and 2 are respectively:
PP: Mitsubishi polypropylene by Diapolymer Co., Ltd., BClE
PBT: Planac BT-lOOOS01 by Dainippon Ink & Chemicals Inc.
Nylon 12: Diamid A1709P by Daicel-Huls Co., Ltd.
PPS: PPS M2900 by Phillips Petroleum Company POM: Iupital F40-03 by Mitsubishi Gas Chemical Company Inc.
Epoxy: Mixture of 100 parts by weight of Epi-Koat #815 by Shell Kagaku Kabushiki Kaishal Co., Ltd. and 80 parts by weight of HN-2200-1 by Hitachi Kasei Kogyou Co., Ltd.
Trademark Embodiment 2 3 4 5 6 7 Resin Thermoplastic PP(50) PBT(55) Nylon PPS(40) PP(60) PCM(50) (pts. by wt.) 12(50) Th ~ t i ng (pts. by wt.) Semiconductor Kind Tetrapod ZrO Tetrapod ZnO Tetrapod ZnOTetrapod ZnO Tetrapod ZnO Tetrapod ZnO
f i l l er wh i sker wh i sker wh i sker wh i sker wh i skerwh i sker Pts. by wt. (50) (45) (50) (60) (35) (50) Vol. resistivity 8x107 8x107 8x107 8x107 8x107 8x107 -cm) value (parallel 3.8 3.8 3.8 3.8 3.8 3.8 plate electrodes) Aspect ratio 5-50 5-50 5-50 5-50 5-50 5-50 Length (max. ) 10-50~m 10-50~m 10-50~im 10-50~m 10-50~m10-5011im Conductor Kind CF
filler Pts. by wt. (5) Maker Mitsubishi ~~
Rayon Co., Ltd.
Grade TRO6NBZE
Sol id Kind PTFE
lubricant pts. by wt. (Z0) Maker Kitamura Co., Ltd.
Grade KTL610 Electrical Among semiconductor present present presentpresent present present contact f i l lers 1~) Among semiconductor present and conductor fillers r~
Surface resistance (~/~) average 2x107 average 8X106 average 1x107average 3x107 average 2x105 average 3X108 r~) Discharge spark with 1000V probe not present not present not presentnot present not present _~, Kneading t, milure (C) of resin 240 260 300 320 240 190 Molding temperature (C) 220 240 250 300 220 180 Embodiment 8 9 10 Comparative Comparative Comparative example 1 example 2 example 3 Resin Thermoplastic POM (55) PP (30) PP (93) POM (70) POM (100) (pts. by wt.) Th~ 2tling epoxy (60) (pts. by wt.) Semiconductor Kind Tetrapod ZnO Tetrapod Zno Granular silicon filler whisker whisker carbide Pts. by wt. (45) (40) (70) Vol. resistivity 8x107 8x107 3x107 (n-cm) Q value (parallel 3.8 3.8 3.1 plate electrodes) Aspect ratio 5-50 5-50 1-4 Length (max.) 10-50om 10-50~m 30-50~m Conductor Kind conductive CF conductive filler whisker whisker Pts. by wt. (7) (7) (30) Maker Otsuka Chemical Mitsubishi Rayon Otsuka Chemical Co., Ltd. Co., Ltd. Co., Ltd.
Grade BK-200 TRO6NBZE BK-200 Solid Kind MoS2 MoS2 PTFE
lubricant Pts. by wt. (3) (3) (20) Maker Nippon Kokuen Nippon Kokuen Kitamura Co., Kogyou Co., Ltd. Kogyou Co., Ltd. Ltd.
Grade Mori powder Mori powder KTL610 B~5~m) B(5~m) Electrical Among semiconductor present present present contact fillers Among semicor,ductor present r~-and conductor fillers Surface resistance (n/~) 5x105 6x108 7x1o8 3x1o2 3x103 1x1o15 Discharge spark with 1000V probe not present not present present present not present Kneading temperature (C) of resin 190 60 240 240 190 190 Molding temperature (C) 180 80C/15h. 220 220 180 180 (setting condition) - 20 - 20622~4 tEmbodiments 11-17 and Comparative Example 4]
Vapour of molten zinc at 1050C is fed into a furnace for reaction with burning propane gas. The atmosphere is a slightly reducing atmosphere, the degree of reduction of which is -6--8 O2Vol.~. The reaction time is approximately 20 seconds. As a result, ZnO whiskers of the tetrapod-like shape are obtained. A typical ZnO whisker has a length from its base to front edge (tip) of 10-20 ~m and an average aspect ratio of 12. The volume resistivity measured by the parallel plate electrodes is 3xl08n.cm, while the ~ value of the V-i characteristics measured by the electrode system is 4.1.
Various kinds of polypropylene resin having different fluidity are then prepared. Similar to Embodiment 1, the ZnO
whiskers and polypropylene resin are mixed (50 wt.~) and kneaded, from which a flat plate is molded.
Table 3 indicates the results. The surface resistance of the resin plate is greatly dependent on the fluidity (M.F.R.) of the mixed resin. If the resin has 1 g/10 min. or more, this resin is suitable to obtain the static dissipative resin composition. Further, if the M.F.R. is increased to be not smaller than 10 g/10 min., the static dissipation is improved to not larger than 109Q/~, whereby the static dissipative resin composition is stable.
As the fluidity of the resin becomes worse, that is, the M.F.R. is decreased, an intense shearing strength acts on the tetrapod-like ZnO whiskers, and therefore these whiskers are increasingly broken in three dimensions. Therefore, a conductive path is not formed efficiently, thereby increasing the surface resistance of the resin plate.
~ - 21 - 2DS2~
Table 3 Poly~ )lclle resin (grade) M.F.R. (g/10 min.) Average surface e (n Embodiment 11 Sumitomo Noblen 70 Sx106 (trademark) AX674 Embodiment 12 Sumitomo Noblen AX57445 7X106 Embodiment 13 Sumitomo Noblen AX56430 3x107 Embodiment 14 Mitsubishi polypropylene 10 7X108 Embodiment 15 Sumitomo Noblen W531 8 3xlO9 Fml-o~liment 16 Sumitomo Noblen H531 3.5 7xlolo Embodiment 17 Sumitomo Noblen FS1012 1.0 8xloll ivt; Sumitomo Noblen F~1015 0.5 9xlol2 example 4 N.B. The mixing ratio is 50 wt.~ in all cases.
[Embodiment 18]
Polypropylene resin (Mitsubishi polypropylene BClE) and ZnO whiskers surface-treated by epoxy silane (A-187) are prepared. Most of the ZnO whiskers are tetrapod-like, having a length from the base to the front edge (tip) of 3-300~m and an aspect ratio of 5-50. The specific volume resistance is 3xl08n.cm and the ~ value is 4.8 measured by the electrode system. The ZnO whiskers and resin are kneaded in the same manner as in Embodiment 1 and various pellets are formed by changing the mixing ratio. The cylinder temperature at this time is 230C and the speed of the screw is 40 r.p.m.
The substance is then injection molded at a resin temperature of 200UC and a mold temperature of 50C, thereby obtaining a flat plate and an Izod impact test piece. The measured physical properties are shown in Fig. 5 where it is clear that the static dissipative resin composition is ready when the mixing ratio is not smaller than 30 wt.%. However, the properties are still unstable, and finally become stabilized when the mixing ratio exceeds 40 wt.%. On the other hand, if the mixing ratio is over 80 wt.~, the impact strength is significantly decreased. Therefore, not larger than 70 wt.~ is best from the viewpoint of impact strength.
[Embodiment 19]
3kg polybutylene terephthalate resin (Planac BT-lOOS01 by Dainippon Ink & Chemicals Inc.) which has 6.8 g/lOmin. M.F.R.
is mixed with 2kg ZnO whiskers used in Embodiment 1. After mixing in the same manner as in Embodiment 1, the mixture is kneaded (the speed of the screw is 40 r.p.m.), whereby to mold a flat plate. The resin temperature is set at 250C both for kneading and for molding.
The surface resistance of the molded resin plate is considerably favourable 6x106Q/~, i.e., having good static dissipative properties.
[Embodiment 20]
Vapour of molten zinc metal at 950C is fed to react with burning propane gas in a furnace. The atmosphere has a degree of reduction of -0.1~3 02Vol . ~ . Most of the ZnO whiskers are formed in the tetrapod-like shape. The average length from base to front edge of a whisker is 5-20~m, and the aspect ratio varies from 5 to 50. Moreover, the specific volume resistance is 7x107Q.cm and the ~ value indicative of V-i characteristics is 3.3, both measured by the electrode system.
The ZnO whiskers are then put into urethane paint, and calmly stirred until they are sufficiently uniformly mixed.
The composition is:
Chief material: 10kg Ohflex* No. 800N white A by Ohashi Kagaku Kogyou Co., Ltd.
Curing agent: 2.5 g Ohflex hardener E-45 by the same 5.2 g diluent thinner No. 7400 by the same 3g ZnO whiskers The obtained paint composition is applied uniformly onto a plate of urethane rubber, and then dried at 80C/l hr., whereby a coating film with an average thickness of 80~m is formed. This film is pure white and truly beautiful, having Trademark ~ - 23 - ~062264 an average surface resistance 5x107Q/~. Therefore, the film has superior static dissipative properties.
[Comparative Example 5]
In Comparative Example 5, conductive carbon black is used, which has a specific volume resistance of 10Q.cm and an ~ value of the V-i characteristics of 1.2 measured by the same manner (DC 0 - 10 Volt) as in Embodiment 1. The carbon black is kneaded and molded with the same resin in the same fashion as in Embodiment 1. The mixing ratio of the carbon black is 20 wt.~. The surface resistance of the resultant molded plate is highly conductive 4x102Q/~. Therefore, a discharge spark takes place when the plate is brought into contact with an electrode to apply, for example, 1000V or more. Moreover, since shortcircuiting or electrification is feared, even with the application of only a general voltage, the resultant composition is not fit for the static dissipative material.
The substance is black and impossible to be coloured. Due to the small microscopical strength of the substance, a mechanical break can easily lead to drop or fall-off, or transfer of colours and smears. Therefore, the substance is not suitable for use in a clean room and cannot be used as a packaging medium or a holding material of ICs, liquid crystal display devices, etc.
As discussed above, the present invention provides an ideal static dissipative resin composition that could not be realized before in a conventional manner.
In other words, the resin composition of the present invention retains relatively good insulation properties against a general voltage, while allowing static electricity to leak well.
The present invention is applicable not only to the field of OA, FA, AV equipment, semiconductors, and liquid crystal display devices, but also to a wide are of technology.
Although the present invention has been fully described in connection with the preferred embodiments thereof with reference to the accompanying drawings, it is to be noted that various changes and modifications are apparent to those r skilled in the art. Such changes and modifications are to be understood as included within the scope of the present invention as defined by the appended claims unless they depart therefrom.
' ~
A resin composition of the present invention is used in the form of pellets or powders as a resin compound for injection molding or extrusion molding, etc. and is also offered as a final molded product, such as a part, a plate, a sheet, a film, etc. Moreover, the resin composition may be supplied as a paint, a coating paste, putty or a coated film.
The following acronyms are used throughout this specification.
Acronyms Full Meaning OA Office Automation FA Factory Automation AV Audio Visual (Equipment) VTR Video Tape Recorder TFT Thin Film Transistor ABS Acrylonitrile-Butadiene-Styrene PPE Polyphenylether PP Polypropylene PBT Polybutylene-terephthalate PPS Polyphenylene-sulfide POM Polyoxymethylene For examples of the aforementioned molded final products, there are wall or floor materials (floor tile, floor surfacing and the like), antistatic packaging products for semiconductors (e.g., IC trays, IC magazines, IC carrier tapes, boxes, containers, cabinets, substrate holders, printed * .
.~
`~ 2 2062264 board stands and the like), and other antistatic products, earthing products and sliding parts, or the like, in the OA, AV, FA fields such as computers, copying machines, facsimiles, printers, VTRs, video cassette tapes, compact disk recorders, etc. More specifically, tape guides and guide rollers for the tapes of the AV devices can be manufactured of the resin composition, and such sliding parts as bearings and gears can be formed of a resin composition of the present invention.
Likewise, the resin composition is useful not only for the components of liquid crystal displays, particularly TFT liquid crystal displays, but for the supporting or holding members in the manufacturing process of the displays. The resin composition may be employed to coat the floor and equipment in a clean room.
Resin has been widely employed as a material having a superior insulation property (for instance, 1015Q/O or higher).
In recent years, however, the static electricity generated on an insulating resin has been noticed as an embarrassment to semiconductors, OA or FA devices, and accordingly a resinous material with static dissipative properties (105-1012 or 105-109Q/O) has attracted enthusiastic attention. Although a highly conductive resin (smaller than 105Q/O) is effective to some degree, as far as the prevention of static build-up and static electricity are concerned, it is an imperfect resin, since, because of its highly conductive properties (smaller than 105Q/O), a discharge spark can be caused by the static electricity or a short-circuit can occur.
A static dissipative material has the proper resistance by itself, and therefore the static electricity, if it is generated, can be easily and promptly removed with no accompanying discharge spark. In addition, such a static dissipative material has little possibility for causing an electric shock or a short-circuit in an electric circuit, etc.
In other words, the static dissipative material is regarded as ~statically conductive and electrically insulating".
_ _ 3 _ 2062264 Various developments have targeted a superior static dissipative material, but a fully satisfactory result has not yet been achieved.
For instance, conventionally, an organic and ionic antistatic agent has been mixed into ABS resin or the like.
But this resinous material is strongly dependent on humidity, and it functions poorly in a highly dried condition. Worse still is that the antistatic agent may ooze out of the surface of the resin with time, only a relatively high resistance (e.g. 101-1012Q/O) being achieved by this resinous material.
A resinous material of this kind is therefore unstable.
Moreover, this method is only applicable to a limited number of reslns.
On the other hand, an inorganic conductive filler having more stable characteristics than the above-described antistatic agent has been mixed in some of some resinous materials.
In general, the following is known about a resinous material of the type. When the conductive filler is mixed into a resin to cause the resin to be conductive, the phenomenon in this case is often explained by the "Percolation Theory".
To enable the prior art to be described with the aid of a diagram the figures of the drawings will first be listed.
Fig. 1 is a diagram of the characteristic curve of a prior art composition;
Fig. 2 is a diagram of the nonlinear characteristic curve of ZnO whiskers used in an embodiment of the present invention;
Fig. 3 is a diagram of the relation between the surface resistance and loadings of a ZnO whisker;
Fig. 4 is an electron microscope photograph of a ZnO
whisker;
Fig. 5 is a diagram of the relation between the surface resistance and loadings of a ZnO whisker.
, `~ - 4 - 2062264 The relation between the mixing amount (wt.~) of the filler and the resistance of the prior art resinous material with a conductive filler is schematically represented in Fig. 1. As the conductive filler is mixed in, the resinous material is initially in the originally insulating state (area (I)). When the amount of filler exceeds a certain level, a slight conductivity immediately appears (although this conductivity is unstable) (area (II)). Even if the amount of the filler is increased over a certain level, the conductivity Rs is not changed very much, that is, it enters a stable area (III). A stable conductive resinous composition is thus in the area (III).
The stable point Rso of the conductivity of the resinous composition is greatly dependent upon the conductivity of the conductive filler. Rso becomes no higher than 10-1Q/~ in the case of a metallic conductive filler; and becomes 10-104Q/~ in the case of a carbon filler.
As is apparent from Fig. 1, although it is not impossible to obtain a resinous material having the static dissipative level that exists between the insulation level and Rso, if the resinous material is designed in the area (II), the resultant material is unstable in conductivity and has poor reproducibility.
As such, in order to obtain a static dissipative resinous composition, a conductive filler that had the correct conductivity to bring the stable point Rso into the static dissipative level would be desirable. However, as mentioned before, the stable point Rso is too low in the case of conventional inorganic conductive fillers (either metallic or carbon f1ller) to be used for a static dissipative resin composltlon.
Japanese Patent Laid-Open Publication Tokkaihei 1-225663 (225663/1989) discloses a resin composition with high conductivity (the 10Q cm mark) having highly conductive zinc oxide whiskers mixed into the resin. This prior art is, however, disadvantageous in that it has an extraordinarily low Rso and is unable to achieve a stable static dissipative r ~ .
level, similar to the above-described resinous composition having an inorganic conductive filler mixed therein.
An essential object of the present invention is therefore to provide a resin composition having an inorganic conductive filler, with a stable point of conductivity Rso at the static dissipative level.
A further object of the present invention is to provide a static dissipative resin composition with stable conductivity and less dependency on humidity without causing oozing of the conductive agent.
A still further object of the present invention is to provide a static dissipative resin composition enabling a change of a variety of resins, such as a crystalline thermoplastic resin, into a matrix.
A yet further object of the present invention is to provide a static dissipative resin composition that is highly useful in practical use and suitable to be coloured in various tints, while having superior moldability for injection molding and less abrasion of a molding press or mold.
Another important object of the present invention is to provide a highly efficient static dissipative resin composition that will more readily leak static electricity, while being more insulative against general electricity.
According to a first embodiment the invention provides a static dissipative resin composition having semiconductor fillers dispersed in a resin, wherein a conductive path is formed at least through electrical contact among at least a part of said semiconductor fillers which have the ~ value of 2-150 indicating a nonlinearity of the V-i characteristic as a result of electrical contact among said semiconductor fillers.
The invention also provides a static dissipative resin composition wherein zinc oxide whiskers having an aspect ratio not smaller than 3 and a volume resistivity of 105-101Q.cm are dispersed in a resin to form a conductive path through electrical contact among at least some of said zinc oxide whiskers.
` 2û62264 The invention also provides a static disslpat1ve resin composition wherein zinc oxide whiskers having an aspect ratio not smaller than 3, a volume resistivity of 105-101Q.cm and an ~ value of 2-150 and at least one other kind of conductive filler are dispersed in a resin to form a conductive path through electrical contact among at least some of said zinc oxide whiskers, said zinc oxide whiskers and conductive fillers or said conductive fillers.
The invention also provides a static dissipative resin composition wherein zinc oxide whiskers having an aspect ration not smaller than 3, a volume resistivity of 105-101Q.cm and an ~ value of 2-150 and at least one kind of a solid lubricant are dispersed in a resin to form a conductive path through electrical contact among at least some of said zinc oxide whiskers.
The invention also provides a static dissipative resin composition wherein zinc oxide whiskers having an aspect ration not smaller than 3, a volume resistivity of 105-101Q.cm and an ~ value of 2-150, at least one other kind of conductive filler, and at least one kind of a solid lubricant are dispersed in a resin to form a conductive path through electrical contact among at least some of said zinc oxide whiskers, said zinc oxide whiskers and conductive fillers or said conductive fillers.
In one embodiment of the invention a semiconducter filler having an ~ value 2-150 or a specific volume resistance 105-101Q.cm is employed. Concretely speaking, a semiconductor filler of zinc oxide, barium titanate, selenium, silicon, silicon carbide, etc. which is a main component of a varistor, a semiconductor filler of metallic oxide, such as SnO2, TiO2, Ge2, Cu2O, Ag2O, In2o3, T~2O3, SrTiO3, LaCrO3. WO3, EuO, Ae2o3/
PbCrO4, etc. or InP is mixed in a resin. One or more kinds of the above fillers can be blended with a suitable mixing ratio.
Although the shape of the semiconductor filler is not specifically determined and the filler may be granules, whiskers or flakes or may be formed in a mass, it is desirable to use semiconductor fillers of whiskers, fibers, or flakes, ~ 7 ~ 2062264 particularly, tetrapod-like whiskers in order to facilitate the formation of a conducting path in the resin.
A semiconductor filler of a single crystal is most suitable, but the single crystal may be crushed or a filler of fine particles may be used. Also, a semiconductor filler of a sintered body or a sintered body after having been crushed or turned into fine particles can be used.
It is also possible to cause semiconductor fine particles to be held on other filler material, e.g., conductive or insulating whiskers, flakes, fibers, to produce a semiconductor filler (by means of coating or the like).
Regarding the size or dimension of the semiconductor filler, this will naturally be set within a proper range so that the semiconductor filler is dispersed in the resin to make it conductive. Specifically, the maximum length of a filler will preferably be selected from lOmm - O.l~m, more suitably from 300~m-l~m to 300~m-3~m, and more preferably from 200~m-lO~m. 50~m-lO~m is best. If the maximum length is smaller than O.Ol~m, the ~ value is difficult to set properly.
If it exceeds lOmm, it is hard to disperse the filler uniformly in the resin.
When the aspect ratio (maximum length/minimum length) of the semiconductor filler in the form of whiskers, fibers and flakes is 3-10000 or approximately 3-1000, it is effective and efficient for forming a conducting path. Particularly, 5-50 is most suitable.
According to a preferred form of the present invention, the specific volume resistance of the semiconductor filler is 105-101 Q.cm, especially 106-101Q.cm. A semiconductor filler with 107-109Q.cm specific volume resistance is more preferable to realize the static dissipative resin composition. The resistance of the semiconductor filler is controlled in an adequate manner in respect to oxidization, reduction or the control of valences. The addition of a suitable amount of impurity elements therefor is permissible.
The specific volume resistance of the semiconductor filler is measured in the following manner. Initially, the ~ - 8 - 2062264 semiconductor filler to be measured is collected in an amount of 0.5 g and is held uniformly between a pair of parallel plate electrodes (silver-plated electrodes) of 20mm diameter, to which 5kg/cm2 of pressure is uniformly applied. The resistance between the electrodes is measured by means of a superinsulating resistance meter (High Resistance Meter 4329A
by HP Inc.). The value of the meter 5 seconds after the application of the pressure is read (measuring voltage 25V).
Subsequently, the pressured powdery sample of the semi-conductor filler is taken out, and its thickness is measured.The volume resistivity P is calculated from the thickness of the sample, the area of the sample (3.14 cm2) and the above-measured resistance in accordance with the following formula:
P(Q.cm) = R.S/t wherein R(Q) is the resistance, S(cm2) is the area of the sample, t(cm) is the thickness of the samples, and P(Q.cm) is the volume resistivity. The measurement is performed at 20C
with a humidity of 40~RH.
The ~ value indicative of the nonlinear voltage-current characteristic (V-i characteristic) generated consequent to the contact between the semiconductor fillers should be 2-150.
2-100 and particularly 2.5-40 is desirable to obtain a good static dissipative resin composition. 3-15 is further suit-able from the manufacturing viewpoint. Although a semi-conductor filler with an ~ value smaller than 2 may possiblybe used to form the static dissipative resin composition, the obtained resin composition does not show as good a static dissipative property as the present invention. On the other hand, if the ~ value is over 150, a discharge spark of the static electricity can occur, which is undesirable.
In order to measure the ~ value, the semiconductor fillers are brought into contact with each other, and a lead wire is taken out from both ends. By way of example, two monofilaments of zinc oxide whisker (abbreviated as ZnO
whisker hereinafter) (in the shape of a needle, 50mm long) are placed to intersect in contact with each other, and a lead * Trademark - 9 - 206~264 wire (using a silver paint and a gold wire) is led out from each monofilament. The V-i characteristic at this time is indicated in Fig. 2. There is another measuring method, by which a current is measured by changing the voltage using the parallel plate electrodes and the sample employed for measuring the volume resistivity discussed before. This method is simple and makes it easy to evaluate the results.
The voltage is increased gradually from a low voltage. In this case, it is important to monitor carefully the nonlinearity of the V-i characteristics. Moreover, in the case where the measured current is unstable at each voltage, the value 5 seconds after application of the voltage should be taken. The optimum ~ value for the area where the V-i characteristic changes nonlinearly is obtained according to the equation:
i = a(V-b) a + C
wherein a, b, c are constants. In this case, the least square or computing is quite useful.
As the physical phenomenon causing the nonlinearity from the contact between the semiconductor fillers, there are the tendency not to comply with Ohm's law at the boundary, due to the surface level or a PN junction, and the Zener effect, etc.
The loading of the semiconductor filler into the resin cannot be specifically defined, since it depends on the kind of filler. However, 20-80 weight ~ to the whole of the resin composition is normally suitable, and 30-70 weight ~ is more suitable. If it is smaller than 20 weight ~, the conducting path is not perfectly formed, so that the conductivity is insufficient for dissipation of the static electricity. In contrast, if the filler is mixed in over 80 weight ~, the resin composition becomes undesirably fragile or brittle.
A semiconductor whisker suitable as a semiconductor filler in the present invention is formed of, for example, ZnO, silicon carbide, SnO2, ZnS, silicon, germanium. Among them, ZnO whiskers are most suitable from the viewpoints of productivity, cost, colour, hygienic qualities and the like.
r The ZnO whisker is manufactured by various methods into a simple needle-shaped whisker or tetrapod-like whisker as is shown in the electron microscope photograph in Fig. 4. The tetrapod-like whisker is superior in terms of mass production, forming a resin composition with advantageous characteristics.
Although there are many ways to manufacture a tetrapod-like ZnO whisker, the following method is suitable to fulfil the semiconductor characteristics and specific resistance of the ZnO whisker as well as the mass-productivity. The present invention is not restricted to the following method, so long as the semiconductor characteristics and specific resistance of the ZnO whisker are satisfied.
Specifically, vapour of zinc metal melted at 800-1100C
is introduced into a furnace to react with a burning gas such as propane or the like. At this time, an atmosphere that is reducing to some degree is preferably used and several seconds to several tens of seconds are consumed-for the reaction.
Almost all of the ZnO whiskers obtained under these conditions are like tetrapod, with an apparent specific gravity of 0.02-0.5. Moreover, the whiskers are obtained with a high yield, not smaller than 70 wt.~, i.e., the whiskers are suited for mass production. The ZnO whiskers have electric properties, for example, semiconductor characteristics, specific resistance and the like that suit the present invention. In some cases, not only ZnO whiskers having a quadraxial crystalline part, but those with a triaxial, a biaxial or a uni-axial crystalline part may be mixed, but the triaxial, biaxial or uni-axial part is one that is produced when the quadraxial part is partly broken. Particularly when the ZnO whiskers are kneaded into the resin, the whiskers are mostly broken, resulting in a uni-axial crystalline substance.
A thick part at the bottom of the needle shaped crystal of the ZnO whisker is called the base thereof if the whisker is of simple needle shape. In the case of the tetrapod-like crystal, the coupling part where the four needle-shaped crystals gather is also called the base thereof. The length from the base to the front edge (tip) of the ZnO whisker is ~,~
preferable to be 3-300~m, more deslrably 10-200~m to 10-50~m from the viewpoints of the characteristics and productivity of the resin composition.
The aspect ratio (leg length/base diameter) of the ZnO
whisker better be 3-1000, especially 5-50, so as to form the conducting path. If the length between the base and front edge is smaller than 3~m or the aspect ratio is smaller than 3, the resultant resin composition does not exhibit suffic-iently conductive. If the length is over 300~m or the aspect ratio exceeds 1000, the whisker is not suitable for mass production and may be broken into small parts in the kneading process, because of an excessively increasing viscosity of the resln .
It is generally known that the resistivity of ZnO varies depending on the forming method thereof, or whether other elements are doped into the ZnO (for example, it varies from 10~2-1012Q.cm). 105-101Q.cm, particularly, 106-l01Q.cm is preferably employed for the present invention. Taking into consideration the nonlinear characteristics as well, 107-109Q.cm is most suitable to realize a static dissipative resin composition having appropriate conductive properties. The resistivity of the ZnO whisker can be controlled by changing the manufacturing conditions, that is, oxygen concentration, reaction temperature and the like, or by doping an element in the III group (e.g., aluminum, gallium, indium, etc.) or copper, zinc, lithium, chromium according to the conventional manner. Aluminum or zinc is most suitable for doping.
The specific volume resistance of the ZnO whisker is measured in the same manner as in the case of the semiconductor filler described earlier.
Although the a value which is the index of the semiconductor characteristic of the ZnO whisker, i.e., the nonlinearity of the ZnO whisker resulting from the contact between the ZnO whiskers, is not specified, 2-150, 2-100, more particularly 2.5-40 is suitable. More preferably 3-15 is desired. If the ZnO whisker has an a value smaller than 2, it cannot realize a static dissipative resin composition of the ~ .
~062264 present invention. On the other hand, if the ~ value is over ~ 150, it is difficult to achieve a desired resin composition that avoids spark discharge.
The ~ value is measured according to the method employed for the semiconductor filler.
In a conventional ZnO nonlinear resistor, called a varistor, the nonlinearity is known to be achieved by the action of a special thin layer present at the boundary between the ZnO crystalline particles (for example, a Biz03 or PrzO3 thin layer having a thickness of the order of A-~m). However, the nonlinearity in the present invention derives from the direct contact between the crystalline particles of the ZnO
whisker, and no special thin layer composed of other elements is interposed between the crystalline particles. Therefore, the nonlinearity of the present invention is achieved in a fundamentally quite different manner or mechanism from that of a conventional varistor.
The ZnO whisker is mixed into the resin by 20-80 wt.~, more preferably 30-70 wt.~, to the whole of the resin compo-sition. Particularly, the mixing ratio is desirably over 40wt.~ and not larger than 70 wt.~. If it is below 20 wt.~, the conducting path becomes imperfect, whereby the conductivity is insufficient for dissipation of the static electricity. When the mixing ratio exceeds 80 wt.%, the resin composition becomes fragile. When the mixing ratio is over 40 wt.~, it is particularly suitable, since the ZnO whiskers are kept in stable contact with each other.
The conductivity of a resin composition having a semiconductor filler of the ZnO whiskers or the like dispersed therein is measured pursuant to ASTM-D-257 (measuring voltage is suitably DC500V). The present invention aims at a resin composition having 105-1012Q/~, 105-109Q/~, further 106-109Q/~
and more preferably 107-109Q/~. The stability of the static dissipation is endangered if 1012Q/~ is exceeded. Moreover, if the static dissipative property is lower than 105Q/~, the inconveniences inherent in a highly conductive material, such `1_~
as a spark discharge, a shortcircuiting, an electric shock, etc. can arise.
A static dissipative resin composition of the present invention can be used in the form of pellets, powders, molded product, paint or paste.
Besides a thermoplastic resin, a thermosetting resin can be used for the resin. Regarding the thermoplastic resin, although it is not restricted, a melt flow rate (M.F.R.) from lg/10 min. to lOOg/10 min., particularly, lOg/10 min. or higher is preferred, so as to make the characteristics stable.
The M.F.R. is measured, for instance, according to ASTM-D-1238. In a case where the M.F.R. is lower than lg/10 min., the semiconductor fillers are brought less into contact with each other. If it exceeds lOOg/10 min., the resin composition becomes fragile and is therefore not desirable.
Although a thermoplastic resin with high crystallinity is suitable, a non-crystalline resin can be used.
Specifically, polypropylene resin, polybutylene terephthalate resin, polyacetal resin, polyphenylene sulfide resin, polyamide resin, as well as polyethylene resin, polyvinyl chloride resin, polyvinylidene chloride resin, polyethylene terephthalate resin, polyether etherketone resin, liquid crystal polymer (aromatic liquid crystal polyester, semiaromatic liquid crystal polyester or the like), etc. can be the crystalline resin. Among these resin, copolymer polypropyrene resin is best suited but homopolymer polypropyrene resin can be utilized.
For a non-crystalline resin, although it is not particularly specified, polystyrene resin, ABS resin and denatured PPE resin are most desirable, but polyether imide resin, polyether sulfide resin, polyarylate resin, polysulfone resin, polyvinyl acetate resin, polycarbonate resin, polymethyl methacrylate resin, polybutadiene resin, or polyacrylonitrile resin can be employed. It is possible to use a single kind of resin or a copolymer of two or more kinds of these resins or a mixture of the resins.
`~ - 14 - 2062264 On the other hand, for a thermosetting resin, besides unsaturated polyester resin, epoxy resin, urethane resin, silicone resin, melamine resin, phenol resin, urea resin or the like can be used.
Since it requires special attention when the resin is blended or kneaded with the semiconductor filler, the specific conditions (temperature, number of revolution, viscosity and the like) should be set to achieve effective contact between the semiconductor fillers.
However, an apparatus to mix or knead this type of composite material may be a conventional one. A single-screw or multi-screw extruder, a ribbon blender, a super mixer (Henschel mixer), that is, a mixer of a container fixed type with a screw rotor blade, or a mixer of a container rotary type, such as a horizontal cylindrical mixer, an inclined cylindrical mixer, or a V tumbling mixer can be employed.
Various kinds of molding methods are possible, injection molding being the most suitable in the present invention. In addition, extrusion molding, compression molding, vacuum molding, blow molding can be carried out.
Furthermore, when the resin composition is presented in the form of paint, paste or putty, a solvent may or may not be added.
If the semiconductor filler is used after being subjected to a surface treatment, a silane coupling agent is most suitable. Other kinds of agent, for example, of chromium, titan, silyl peroxide, organic phosphate can be used for the surface treatment.
The conductivity is improved in some cases when the semiconductor filler is used along with a conductive filler.
The conductive filler should have the specific volume resistance smaller than 105Q.cm and be made of metal, carbon or graphite particles, flakes, whiskers or fibers, or conductive ceramics particles, whiskers or fibers. The metal is preferably silver, gold, stainless steel or aluminum, but copper, nickel, palladium, iron, etc. can be employed.
- 15 - 206226~
The conductive ceramics can be conductive potassium titanate (for example, DENTALL BK-200 by Otsuka Chemical Co., Ltd.), zirconium carbide, titanium carbide, silicon carbide, etc.
The total of the semiconductor filler and the conductive filler to the whole of the resin composition should be 5-80 wt.~. Meanwhile, the weight ratio of the semiconductor filler and conductive filler is between 1:50 and 50:1, especially from 1:5 to 5:1. If too much conductive filler is mixed then the interactive effect is reduced and proper static dissipation cannot be realized. Therefore, a ratio from 1:1 to 5:1 is most desirable.
When a solid lubricant is used in the present invention, the static dissipative resin composition gains superior sliding property and abrasion resistance. Fluoride resin, such as polytetrafluoroethylene, high density polyethylene, aromatic polyamide, aromatic polyester, granular phenol or a graphitized substance thereof, graphite, molybdenum disulfide, tungsten disulfide, WSe2, MoSe2, boron nitride, etc. are suited for the solid lubricant. Two or more kinds of the above lubricant may be mixed. The lubricants are usually powder in the form of particles or flakes. From the characteristics' viewpoint, polyfluoroethylene, high density polyethylene and molybdenum disulfide are most suitable. The mixing ratio of the solid lubricant to the whole of the resin composition is 1-30 wt.~, more preferably 5-20 wt.~.
It is possible to blend other kinds of material that do not hurt the characteristics of the resin composition. For instance, reinforcing material or an extender composed of glass fibers or flakes, beads, talc, mica, calcium carbonate, clay, barium sulfate, alumina, silica, diatomaceous earth, wood flour, etc. and fire-proof material, such as aluminum hydroxide, antimony trioxide, phosphoric ester can be added.
Or, a colouring agent such as titanium dioxide, carbon black or the like may be used. Likewise, a suitable amount of an * Trademark ~i `` 2062264 organic antistatic agent, stabilizer or deterioration preventing agent may be blended into the resin.
[Embodiment 1]
Vapour of molten zinc metal at 980C is fed into a furnace to react with burning propane gas in a reducing atmosphere. The degree of reduction is -0.1~-10 O2Vol.~ which is measured by an NGK 2 analyzer (model RE-110:product of Nippon Gaishi Co., Ltd.). As a consequence, tetrapod-like ZnO
whiskers are obtained. The length from the base to the front edge of the whisker is 10-30~m, and the average aspect ratio is 15. The specific volume resistance measured by the parallel plate electrodes is 2xl08Q.cm and the ~ value showing the V-i characteristics measured by the electrodes is 3.9.
Thereafter, 2.5 kg polypropylene resin (Diapolymer Co., Ltd.:Mitsubishi Polypropylene BClE, melt flow rate 33g/lOmin.) is uniformly mixed with the above-obtained 2.5 kg ZnO whiskers in a plastic bag. The mixing ratio is accordingly 50wt.~.
The mixed substance is put into a hopper of a single-screw extruder and kneaded at a cylinder temperature of 240C. The speed of the screw is 40 r.p.m. The kneaded substance is then extruded from a nozzle, cooled by water and cut into pellets.
Each pellet of the resin composition has an average diameter of 3mm~ and an average length 5mm.
The pellets are fed into a hopper of an injection molding press and molded at a resin temperature of 220C and a mold temperature of 52C. A dumbbell specimen and a flat plate (85mmx85mmx3mmt) are obtained. These molded products have superior surface smoothness and beautiful white colour.
The flexural modulus and surface resistivity of the molded products is 20100kg/cm2 and 3x106Q/~, respectively.
The flat plate is then cooled in liquid nitrogen for 30 seconds and cut by nippers. When the cut surface is inspected through an electron microscope (magnification x 1500), it is found that some of the ZnO whiskers are in touch with each other whereby to constitute a conductive path. It is also * Trademark confirmed that a considerable amount of the tetrapod-like ZnO
whiskers are broken into simple needle-shaped whiskers.
[Embodiments 2-10]
Vapour of molten zinc metal at 1020C is allowed to react with burning propane gas in a furnace. The reducing atmos-phere has a degree of reduction -4~-6 O2Vol.~. As a result, the obtained ZnO whiskers are in the tetrapod-like shape.
Using these ZnO whiskers and various kinds of material, kneading and molding are carried out substantially in the same manner as in Embodiment 1. The evaluation results of the physical properties of the final composition are indicated in Tables 1 and 2 below.
[Comparative Examples 1-3]
In conformity with Embodiment 1 above, comparative examples are prepared by kneading and molding various kinds of material, the physical properties of which are also shown in Table 2 below.
It is to be noted that the resin represented in Tables 1 and 2 are respectively:
PP: Mitsubishi polypropylene by Diapolymer Co., Ltd., BClE
PBT: Planac BT-lOOOS01 by Dainippon Ink & Chemicals Inc.
Nylon 12: Diamid A1709P by Daicel-Huls Co., Ltd.
PPS: PPS M2900 by Phillips Petroleum Company POM: Iupital F40-03 by Mitsubishi Gas Chemical Company Inc.
Epoxy: Mixture of 100 parts by weight of Epi-Koat #815 by Shell Kagaku Kabushiki Kaishal Co., Ltd. and 80 parts by weight of HN-2200-1 by Hitachi Kasei Kogyou Co., Ltd.
Trademark Embodiment 2 3 4 5 6 7 Resin Thermoplastic PP(50) PBT(55) Nylon PPS(40) PP(60) PCM(50) (pts. by wt.) 12(50) Th ~ t i ng (pts. by wt.) Semiconductor Kind Tetrapod ZrO Tetrapod ZnO Tetrapod ZnOTetrapod ZnO Tetrapod ZnO Tetrapod ZnO
f i l l er wh i sker wh i sker wh i sker wh i sker wh i skerwh i sker Pts. by wt. (50) (45) (50) (60) (35) (50) Vol. resistivity 8x107 8x107 8x107 8x107 8x107 8x107 -cm) value (parallel 3.8 3.8 3.8 3.8 3.8 3.8 plate electrodes) Aspect ratio 5-50 5-50 5-50 5-50 5-50 5-50 Length (max. ) 10-50~m 10-50~m 10-50~im 10-50~m 10-50~m10-5011im Conductor Kind CF
filler Pts. by wt. (5) Maker Mitsubishi ~~
Rayon Co., Ltd.
Grade TRO6NBZE
Sol id Kind PTFE
lubricant pts. by wt. (Z0) Maker Kitamura Co., Ltd.
Grade KTL610 Electrical Among semiconductor present present presentpresent present present contact f i l lers 1~) Among semiconductor present and conductor fillers r~
Surface resistance (~/~) average 2x107 average 8X106 average 1x107average 3x107 average 2x105 average 3X108 r~) Discharge spark with 1000V probe not present not present not presentnot present not present _~, Kneading t, milure (C) of resin 240 260 300 320 240 190 Molding temperature (C) 220 240 250 300 220 180 Embodiment 8 9 10 Comparative Comparative Comparative example 1 example 2 example 3 Resin Thermoplastic POM (55) PP (30) PP (93) POM (70) POM (100) (pts. by wt.) Th~ 2tling epoxy (60) (pts. by wt.) Semiconductor Kind Tetrapod ZnO Tetrapod Zno Granular silicon filler whisker whisker carbide Pts. by wt. (45) (40) (70) Vol. resistivity 8x107 8x107 3x107 (n-cm) Q value (parallel 3.8 3.8 3.1 plate electrodes) Aspect ratio 5-50 5-50 1-4 Length (max.) 10-50om 10-50~m 30-50~m Conductor Kind conductive CF conductive filler whisker whisker Pts. by wt. (7) (7) (30) Maker Otsuka Chemical Mitsubishi Rayon Otsuka Chemical Co., Ltd. Co., Ltd. Co., Ltd.
Grade BK-200 TRO6NBZE BK-200 Solid Kind MoS2 MoS2 PTFE
lubricant Pts. by wt. (3) (3) (20) Maker Nippon Kokuen Nippon Kokuen Kitamura Co., Kogyou Co., Ltd. Kogyou Co., Ltd. Ltd.
Grade Mori powder Mori powder KTL610 B~5~m) B(5~m) Electrical Among semiconductor present present present contact fillers Among semicor,ductor present r~-and conductor fillers Surface resistance (n/~) 5x105 6x108 7x1o8 3x1o2 3x103 1x1o15 Discharge spark with 1000V probe not present not present present present not present Kneading temperature (C) of resin 190 60 240 240 190 190 Molding temperature (C) 180 80C/15h. 220 220 180 180 (setting condition) - 20 - 20622~4 tEmbodiments 11-17 and Comparative Example 4]
Vapour of molten zinc at 1050C is fed into a furnace for reaction with burning propane gas. The atmosphere is a slightly reducing atmosphere, the degree of reduction of which is -6--8 O2Vol.~. The reaction time is approximately 20 seconds. As a result, ZnO whiskers of the tetrapod-like shape are obtained. A typical ZnO whisker has a length from its base to front edge (tip) of 10-20 ~m and an average aspect ratio of 12. The volume resistivity measured by the parallel plate electrodes is 3xl08n.cm, while the ~ value of the V-i characteristics measured by the electrode system is 4.1.
Various kinds of polypropylene resin having different fluidity are then prepared. Similar to Embodiment 1, the ZnO
whiskers and polypropylene resin are mixed (50 wt.~) and kneaded, from which a flat plate is molded.
Table 3 indicates the results. The surface resistance of the resin plate is greatly dependent on the fluidity (M.F.R.) of the mixed resin. If the resin has 1 g/10 min. or more, this resin is suitable to obtain the static dissipative resin composition. Further, if the M.F.R. is increased to be not smaller than 10 g/10 min., the static dissipation is improved to not larger than 109Q/~, whereby the static dissipative resin composition is stable.
As the fluidity of the resin becomes worse, that is, the M.F.R. is decreased, an intense shearing strength acts on the tetrapod-like ZnO whiskers, and therefore these whiskers are increasingly broken in three dimensions. Therefore, a conductive path is not formed efficiently, thereby increasing the surface resistance of the resin plate.
~ - 21 - 2DS2~
Table 3 Poly~ )lclle resin (grade) M.F.R. (g/10 min.) Average surface e (n Embodiment 11 Sumitomo Noblen 70 Sx106 (trademark) AX674 Embodiment 12 Sumitomo Noblen AX57445 7X106 Embodiment 13 Sumitomo Noblen AX56430 3x107 Embodiment 14 Mitsubishi polypropylene 10 7X108 Embodiment 15 Sumitomo Noblen W531 8 3xlO9 Fml-o~liment 16 Sumitomo Noblen H531 3.5 7xlolo Embodiment 17 Sumitomo Noblen FS1012 1.0 8xloll ivt; Sumitomo Noblen F~1015 0.5 9xlol2 example 4 N.B. The mixing ratio is 50 wt.~ in all cases.
[Embodiment 18]
Polypropylene resin (Mitsubishi polypropylene BClE) and ZnO whiskers surface-treated by epoxy silane (A-187) are prepared. Most of the ZnO whiskers are tetrapod-like, having a length from the base to the front edge (tip) of 3-300~m and an aspect ratio of 5-50. The specific volume resistance is 3xl08n.cm and the ~ value is 4.8 measured by the electrode system. The ZnO whiskers and resin are kneaded in the same manner as in Embodiment 1 and various pellets are formed by changing the mixing ratio. The cylinder temperature at this time is 230C and the speed of the screw is 40 r.p.m.
The substance is then injection molded at a resin temperature of 200UC and a mold temperature of 50C, thereby obtaining a flat plate and an Izod impact test piece. The measured physical properties are shown in Fig. 5 where it is clear that the static dissipative resin composition is ready when the mixing ratio is not smaller than 30 wt.%. However, the properties are still unstable, and finally become stabilized when the mixing ratio exceeds 40 wt.%. On the other hand, if the mixing ratio is over 80 wt.~, the impact strength is significantly decreased. Therefore, not larger than 70 wt.~ is best from the viewpoint of impact strength.
[Embodiment 19]
3kg polybutylene terephthalate resin (Planac BT-lOOS01 by Dainippon Ink & Chemicals Inc.) which has 6.8 g/lOmin. M.F.R.
is mixed with 2kg ZnO whiskers used in Embodiment 1. After mixing in the same manner as in Embodiment 1, the mixture is kneaded (the speed of the screw is 40 r.p.m.), whereby to mold a flat plate. The resin temperature is set at 250C both for kneading and for molding.
The surface resistance of the molded resin plate is considerably favourable 6x106Q/~, i.e., having good static dissipative properties.
[Embodiment 20]
Vapour of molten zinc metal at 950C is fed to react with burning propane gas in a furnace. The atmosphere has a degree of reduction of -0.1~3 02Vol . ~ . Most of the ZnO whiskers are formed in the tetrapod-like shape. The average length from base to front edge of a whisker is 5-20~m, and the aspect ratio varies from 5 to 50. Moreover, the specific volume resistance is 7x107Q.cm and the ~ value indicative of V-i characteristics is 3.3, both measured by the electrode system.
The ZnO whiskers are then put into urethane paint, and calmly stirred until they are sufficiently uniformly mixed.
The composition is:
Chief material: 10kg Ohflex* No. 800N white A by Ohashi Kagaku Kogyou Co., Ltd.
Curing agent: 2.5 g Ohflex hardener E-45 by the same 5.2 g diluent thinner No. 7400 by the same 3g ZnO whiskers The obtained paint composition is applied uniformly onto a plate of urethane rubber, and then dried at 80C/l hr., whereby a coating film with an average thickness of 80~m is formed. This film is pure white and truly beautiful, having Trademark ~ - 23 - ~062264 an average surface resistance 5x107Q/~. Therefore, the film has superior static dissipative properties.
[Comparative Example 5]
In Comparative Example 5, conductive carbon black is used, which has a specific volume resistance of 10Q.cm and an ~ value of the V-i characteristics of 1.2 measured by the same manner (DC 0 - 10 Volt) as in Embodiment 1. The carbon black is kneaded and molded with the same resin in the same fashion as in Embodiment 1. The mixing ratio of the carbon black is 20 wt.~. The surface resistance of the resultant molded plate is highly conductive 4x102Q/~. Therefore, a discharge spark takes place when the plate is brought into contact with an electrode to apply, for example, 1000V or more. Moreover, since shortcircuiting or electrification is feared, even with the application of only a general voltage, the resultant composition is not fit for the static dissipative material.
The substance is black and impossible to be coloured. Due to the small microscopical strength of the substance, a mechanical break can easily lead to drop or fall-off, or transfer of colours and smears. Therefore, the substance is not suitable for use in a clean room and cannot be used as a packaging medium or a holding material of ICs, liquid crystal display devices, etc.
As discussed above, the present invention provides an ideal static dissipative resin composition that could not be realized before in a conventional manner.
In other words, the resin composition of the present invention retains relatively good insulation properties against a general voltage, while allowing static electricity to leak well.
The present invention is applicable not only to the field of OA, FA, AV equipment, semiconductors, and liquid crystal display devices, but also to a wide are of technology.
Although the present invention has been fully described in connection with the preferred embodiments thereof with reference to the accompanying drawings, it is to be noted that various changes and modifications are apparent to those r skilled in the art. Such changes and modifications are to be understood as included within the scope of the present invention as defined by the appended claims unless they depart therefrom.
' ~
Claims (17)
1. A static dissipative resin composition, which comprises a resin and zinc oxide whiskers dispersed in the resin, wherein the zinc oxide whiskers each have an aspect ratio of more than 3, a length of more than 3 µm from a base to a front edge thereof, and a volume resistivity of 105 to 1010.OMEGA..cm, whereby a conductive path is formed by electrical contact of the zinc oxide whiskers with each other to dissipate static electricity from the composition.
2. A static dissipative resin composition, which comprises a resin, and zinc oxide whiskers and at least one conductive filler dispersed in the resin, wherein the zinc oxide whiskers each have an aspect ratio of more than 3, a length of more than 3 µm from a base to a front edge thereof, and a volume resistivity of 105 to 1010.OMEGA..cm, whereby a conductive path is formed by electrical contact of the zinc oxide whiskers with each other, the zinc oxide whiskers with the conductive fillers, or the conductive fillers with each other, to dissipate static electricity from the composition.
3. A static dissipative resin composition, which comprises a resin, and zinc oxide whiskers and at least one mechanical solid lubricant dispersed in the resin, wherein the zinc oxide whiskers each have an aspect ratio of more than 3, a length of more than 3 µm from a base to a front edge thereof, and a volume resistivity of 105 to 1010.OMEGA..cm, whereby a conductive path is formed by electrical contact of the zinc oxide whiskers with each other to dissipate static electricity from the composition.
4. A static dissipative resin composition, which comprises a resin, and zinc oxide whiskers, at least one mechanical solid lubricant and at least one conductive filler dispersed in the resin, wherein the zinc oxide whiskers each have an aspect ratio of more than 3, a length of more than 3 µm from a base to a front edge thereof, and a volume resistivity of 105 to 1010.OMEGA..cm, whereby a conductive path is formed by electrical contact of the zinc oxide whiskers with each other, the zinc oxide whiskers with the conductive fillers, or the conductive fillers with each other, to dissipate static electricity from the composition.
5. A static dissipative resin composition as defined in claim 1, 2, 3 or 4, wherein each of the zinc oxide whiskers is in the form of a tetrapod.
6. A static dissipative resin composition as defined in claim 1, 2, 3 or 4, wherein the volume resistivity of each of the zinc oxide whiskers is 107 to 109.OMEGA..cm.
7. A static dissipative resin composition as defined in claim 1, 2, 3 or 4, wherein the resin is a thermoplastic resin.
8. A static dissipative resin composition as defined in claim 7, wherein the resin is a crystalline resin.
9. A static dissipative resin composition as defined in claim 7, wherein the resin has a melt flow rate of more than 1 g/10 min.
10. A static dissipative resin composition as defined in claim 7, wherein the resin has a melt flow rate of more than 3.5 g/10 min.
11. A static dissipative resin composition as defined in claim 7, wherein the resin has a melt flow rate of 10 to 100 g/min.
12. A static dissipative resin composition as defined in claim 1, 2, 3 or 4, wherein the surface resistance value of the resin composition is 105 to 1012.OMEGA./?.
13. A static dissipative resin composition as defined in claim 1, 2, 3 or 4, wherein the surface resistance value of the resin composition is 105 to 109.OMEGA./?.
14. A static dissipative resin composition as defined in claim 1, 2, 3 or 4, wherein the amount of zinc oxide whiskers is 20 to 80 weight % based on the weight of the composition.
15. A static dissipative resin composition as defined in claim 1, 2, 3 or 4, wherein the amount of zinc oxide whiskers is more than 40 % and less than 80 % by weight based on the weight of the composition.
16. A static dissipative resin composition as defined in claim 2 or 4, wherein the conductive filler is selected from the group consisting of particles of carbon, flakes, whiskers and fibers.
17. A static dissipative resin composition as defined in claim 3 or 4, wherein the mechanical solid lubricant is a powder selected from the group consisting of polytetrafluoroethylene, high density polyethylene, aromatic polyamide, aromatic polyester, graphite and molybdenum disulfide.
Applications Claiming Priority (6)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP3037678A JPH0525323A (en) | 1991-03-05 | 1991-03-05 | Electrically conductive thermoplastic resin composition |
| JP3-37678 | 1991-03-05 | ||
| JP4054388A JPH05214158A (en) | 1992-02-04 | 1992-02-04 | Static electricity dissipating resin composition |
| JP4-54388 | 1992-02-04 | ||
| JP4056778A JPH05226092A (en) | 1992-02-07 | 1992-02-07 | Electrostatic diffusion resin complex |
| JP4-56778 | 1992-02-07 |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2062264A1 CA2062264A1 (en) | 1992-09-06 |
| CA2062264C true CA2062264C (en) | 1997-01-14 |
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ID=27289546
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002062264A Expired - Fee Related CA2062264C (en) | 1991-03-05 | 1992-03-04 | Static dissipative resin composition |
Country Status (4)
| Country | Link |
|---|---|
| US (1) | US5276080A (en) |
| EP (1) | EP0502483A3 (en) |
| KR (1) | KR950015027B1 (en) |
| CA (1) | CA2062264C (en) |
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| US20050186438A1 (en) * | 2003-09-24 | 2005-08-25 | Alms Gregory R. | Electrically conductive thermoplastic compositions |
| US20070152195A1 (en) * | 2005-12-30 | 2007-07-05 | Saint-Gobain Performance Plastics Corporation | Electrostatic dissipative composite material |
| US20070155949A1 (en) * | 2005-12-30 | 2007-07-05 | Saint-Gobain Performance Plastics Corporation | Thermally stable composite material |
| US20070154716A1 (en) * | 2005-12-30 | 2007-07-05 | Saint-Gobain Performance Plastics Corporation | Composite material |
| US20070154717A1 (en) * | 2005-12-30 | 2007-07-05 | Saint-Gobain Performance Plastics Corporation | Thermally stable composite material |
| JP4865403B2 (en) * | 2006-05-15 | 2012-02-01 | 株式会社クラレ | Polyvinyl acetal powder coating |
| US7476339B2 (en) * | 2006-08-18 | 2009-01-13 | Saint-Gobain Ceramics & Plastics, Inc. | Highly filled thermoplastic composites |
| US20140142228A1 (en) * | 2012-11-21 | 2014-05-22 | Ticona Llc | Plasticized, Conductive Polyoxymethylene for Fuel Applications |
| CN104693801A (en) * | 2013-12-10 | 2015-06-10 | 合肥杰事杰新材料股份有限公司 | Wear-resisting anti-electrostatic polyphenylene sulfide/semi-aromatic high-temperature-resistant nylon composite material and preparation method thereof |
| CN105330963A (en) * | 2015-11-23 | 2016-02-17 | 常州大学 | Preparation method of wear-resistant and anti-static PP (polypropylene) sheet |
| DE102020118742B4 (en) * | 2020-07-15 | 2022-11-03 | Murat Gündüz | Use of silicone as a sealant in particularly exposed areas |
| CN112922266B (en) * | 2021-02-04 | 2022-09-16 | 安徽森泰木塑科技地板有限公司 | Indoor LVT floor |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE3061159D1 (en) * | 1979-09-14 | 1982-12-30 | Mitsubishi Metal Corp | Electroconductive powder and process for production thereof |
| JPS6113421A (en) * | 1984-06-29 | 1986-01-21 | Fuji Photo Film Co Ltd | Magnetic tape having leader tape |
| US4933109A (en) * | 1985-10-14 | 1990-06-12 | Sumitomo Chemical Company, Limited | Fibrous white electrically conductive material and a white electrically conductive coating composition containing the same |
| EP0267535B1 (en) * | 1986-11-11 | 1990-08-08 | Ishihara Sangyo Kaisha, Ltd. | Acicular electroconductive titanium oxide and process for producing same |
| JPH0618911B2 (en) * | 1987-09-25 | 1994-03-16 | ポリプラスチックス株式会社 | Method for manufacturing electrostatically-coated plastic molded products |
| US5231269A (en) * | 1989-02-17 | 1993-07-27 | Matsushita Electric Industrial Co., Ltd. | Electromagnetic wave energy conversion heat-generating material, heating container for microwave oven, and microwave oven |
| JP2767051B2 (en) * | 1989-02-21 | 1998-06-18 | 住友化学工業株式会社 | Polypropylene resin composition |
| JPH0353253A (en) * | 1989-07-21 | 1991-03-07 | Fuji Photo Film Co Ltd | Electrostatic recording film |
| JPH03162445A (en) * | 1989-11-21 | 1991-07-12 | Mitsubishi Gas Chem Co Inc | Sliding resin composition |
| JPH03289004A (en) * | 1990-04-04 | 1991-12-19 | Matsushita Electric Ind Co Ltd | Conductive resin composite |
-
1992
- 1992-03-03 EP EP19920103630 patent/EP0502483A3/en not_active Ceased
- 1992-03-04 CA CA002062264A patent/CA2062264C/en not_active Expired - Fee Related
- 1992-03-05 KR KR1019920003633A patent/KR950015027B1/en not_active IP Right Cessation
- 1992-03-05 US US07/846,924 patent/US5276080A/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| CA2062264A1 (en) | 1992-09-06 |
| KR920019220A (en) | 1992-10-22 |
| EP0502483A2 (en) | 1992-09-09 |
| US5276080A (en) | 1994-01-04 |
| EP0502483A3 (en) | 1993-01-20 |
| KR950015027B1 (en) | 1995-12-21 |
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| EEER | Examination request | ||
| MKLA | Lapsed |