CA1243459A - Process for molding formed articles - Google Patents
Process for molding formed articlesInfo
- Publication number
- CA1243459A CA1243459A CA000490461A CA490461A CA1243459A CA 1243459 A CA1243459 A CA 1243459A CA 000490461 A CA000490461 A CA 000490461A CA 490461 A CA490461 A CA 490461A CA 1243459 A CA1243459 A CA 1243459A
- Authority
- CA
- Canada
- Prior art keywords
- pressure
- mould cavity
- resin
- foamed
- mould
- 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
Links
Classifications
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C44/00—Shaping by internal pressure generated in the material, e.g. swelling or foaming ; Producing porous or cellular expanded plastics articles
- B29C44/02—Shaping by internal pressure generated in the material, e.g. swelling or foaming ; Producing porous or cellular expanded plastics articles for articles of definite length, i.e. discrete articles
- B29C44/04—Shaping by internal pressure generated in the material, e.g. swelling or foaming ; Producing porous or cellular expanded plastics articles for articles of definite length, i.e. discrete articles consisting of at least two parts of chemically or physically different materials, e.g. having different densities
- B29C44/0415—Shaping by internal pressure generated in the material, e.g. swelling or foaming ; Producing porous or cellular expanded plastics articles for articles of definite length, i.e. discrete articles consisting of at least two parts of chemically or physically different materials, e.g. having different densities by regulating the pressure of the material during or after filling of the mould, e.g. by local venting
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C44/00—Shaping by internal pressure generated in the material, e.g. swelling or foaming ; Producing porous or cellular expanded plastics articles
- B29C44/02—Shaping by internal pressure generated in the material, e.g. swelling or foaming ; Producing porous or cellular expanded plastics articles for articles of definite length, i.e. discrete articles
- B29C44/10—Applying counter-pressure during expanding
- B29C44/105—Applying counter-pressure during expanding the counterpressure being exerted by a fluid
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29K—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR MOULDS, REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS
- B29K2105/00—Condition, form or state of moulded material or of the material to be shaped
- B29K2105/04—Condition, form or state of moulded material or of the material to be shaped cellular or porous
- B29K2105/043—Skinned foam
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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
- Y10S264/00—Plastic and nonmetallic article shaping or treating: processes
- Y10S264/83—Injection molding of polyolefin-type foam
Abstract
ABSTRACT OF THE DISCLOSURE
An improved process for producing a foamed thermoplastic resin article which consists of a relatively thin non-foamed outer shell with a smooth surface and a foamed core portion, and has excellent dimensional stability, by pressurizing a mould cavity under a gas pressure less than the foaming pressure and not less than the surface smoothing pressure of a foamable resin and simultaneously with completion of the filling of the mould by injection inflow, reducing the gas pressure to atmospheric pressure or lower.
An improved process for producing a foamed thermoplastic resin article which consists of a relatively thin non-foamed outer shell with a smooth surface and a foamed core portion, and has excellent dimensional stability, by pressurizing a mould cavity under a gas pressure less than the foaming pressure and not less than the surface smoothing pressure of a foamable resin and simultaneously with completion of the filling of the mould by injection inflow, reducing the gas pressure to atmospheric pressure or lower.
Description
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This invention relates to an improved process for producing a foamed thermoplastic resin article and more particularly to an improved process for producing a foamed thermoplastic resin article having a foamed core, a non-foamed exterior skin layer, and a smooth surface free from both swirl marks and sink marks.
As a process for producing a foamed article, the short shot process is well known. The process comprises injecting a thermoplastic resin containing a blowing agent in short shot quantity into a mould cavity under atmospheric pressure, filling the mould cavity with said resin through foaming and expansion of the blowing agent in it, and solidifying said resin by cooling within said mould cavity.
The foamad article thus obtained has swirl marks on a surface of the article and is constituted by an exterior skin layer which is substantially non-foamed and a foamed core. As compared with conventional non-foamed injection moulded articles, the article has the following characteristics:
1) higher rigidity relative to weight;
This invention relates to an improved process for producing a foamed thermoplastic resin article and more particularly to an improved process for producing a foamed thermoplastic resin article having a foamed core, a non-foamed exterior skin layer, and a smooth surface free from both swirl marks and sink marks.
As a process for producing a foamed article, the short shot process is well known. The process comprises injecting a thermoplastic resin containing a blowing agent in short shot quantity into a mould cavity under atmospheric pressure, filling the mould cavity with said resin through foaming and expansion of the blowing agent in it, and solidifying said resin by cooling within said mould cavity.
The foamad article thus obtained has swirl marks on a surface of the article and is constituted by an exterior skin layer which is substantially non-foamed and a foamed core. As compared with conventional non-foamed injection moulded articles, the article has the following characteristics:
1) higher rigidity relative to weight;
2) smaller warpage due to relaxation of resi-dual strains in the article during foaming;
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3) no formation of sink marks in thick portion again due to the foaming; and
3) no formation of sink marks in thick portion again due to the foaming; and
4) can be moulded at relatively lower injection pressures and mould clamping pressures, which enables the moulding of large articles by means of an inexpensive machine.
On account of the above characteristics, such conventional foamed articles have been used as a substitute for large structures of wood, but are limited in usefulness for structural parts with external decorative surfaces because of the drawback of surface swirl marks.
Attempts have been made to overcome the drawback of surface swirl marks, whilst retaining the advantageous characteristics Qf the foamed articles described above.
For example, one approach to avoiding swirl marks on the surface of the foamed article is disclosed in U. S. Patent No. 3,268,635 and German OLS 1,504,278, which disclose a process in which a resin is injected into a mould cavity pressurized with a gas, also known as the gas counter pressure process. Speci~ic processes embodyiny this approach are disclosed in U.S. Patents Nos. 3,960,996, 4,096,218 and 4,255,368.
U. S. Patent No. 4,255,368 discloses a process comprising the steps of: plastifying and kneading and then metering and accumulating a molten mixture of a thermoplastic polymer and a soluble gaseous blowing agent at a pressure above the foaming pressure of said mixture, feeding this mixture into a mould cavity maintained at a temperature sufficiently low to cause the outer portion of said mixture to form a self supporting exterior shell in said mould, in a volume sufficient in the unfoamed state to substantially fill said mould cavity: allowing the outer portion of the charge to cool in said cavity to ~2~39LS9 form a self supporting exterior shell while maintaining the mould cavity at a presæure aboYe the foam~ng pre~sure of ~aid mixture; thereafter releasing the pressure within the mould cavity to provide a temperature and pressure gradient such as to cause (i) the thermoplastic material therein to contract and (ii) gas desolubilization and expansion so as to balance the volume contraction of said charge which would otherwise have resulted from said gradients, to produce a foamed core and exterior solid shell; and removing the resultant article from said mould cavity.
However, this process tends to suppress foaming of the resin mixture, which produces a foamed article that has too little foamed core portion and an excessively thick exterior non-foamed solid shell. The resultant -- article may have sink marks on its surfaces of parts in which the thickness is relatively small and warpage by lack of relaxation of residual moulding strains resulting from poor foaming.
It is an object of the present invention to provide an improved process which can form a foamed thermoplastic resin article which has a non-foamed outer shell with a smooth surface free from both swirl marks and sink marks and a foamed core portion.
According to the invention, there is provided a process for producing a foamed article having a non-foamed outer shell with a smooth surface free from both swirl marks and sink marks and a foamed core portion, which comprises the steps of:
plastifying and kneading a foamable resin under a pressure equal to or higher than its foaming pressure and metering and accumulating said resin, injecting the above meter d and accumulated foamable resin into a closed mould cavity pressurized at a ~Z~3~S'~
,~
pressure not lower than a ~urface smoothing pressure and less than the foaming pressure o~ the above foamable resin by applying a pressurized gas to the mould cavity, whereby a non-foamed outer shell is formed from a portion of the resin which contacts a wall defining the mould cavity, simultaneously with inflow of the resin, discontinuing injection of the foamable resin after filling of the mould cavity by the injection and also discontinuing application of the pressurized gas to the mould cavity permitting immediate reduction of the pressure within the mould cavity, so as to allow foaming of the foamable resin enclosed within the already formed non-foamed outer shell in the mould cavity, subsequently allowing the foamable resin within ~5 the above non-foamed outer shell to foam while cooling the resin, and removing the article from the mould cavity after solidification by cooling.
Further features of the invention will become apparent from the following description with reference to the accompanying drawings, in which:
Figure 1 is a graph showing the relationship between pressure and a volume of a foamable resin and a non-foamable resin;
Figure 2 is a graph showing the variation with time of pressure in a mould cavity during injection of a foamable resin;
Figure 3 is a schematic section illustration of an injection moulding machine modified for measuring the pressure volume behaviour and foaming pressure of a foamable resin;
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On account of the above characteristics, such conventional foamed articles have been used as a substitute for large structures of wood, but are limited in usefulness for structural parts with external decorative surfaces because of the drawback of surface swirl marks.
Attempts have been made to overcome the drawback of surface swirl marks, whilst retaining the advantageous characteristics Qf the foamed articles described above.
For example, one approach to avoiding swirl marks on the surface of the foamed article is disclosed in U. S. Patent No. 3,268,635 and German OLS 1,504,278, which disclose a process in which a resin is injected into a mould cavity pressurized with a gas, also known as the gas counter pressure process. Speci~ic processes embodyiny this approach are disclosed in U.S. Patents Nos. 3,960,996, 4,096,218 and 4,255,368.
U. S. Patent No. 4,255,368 discloses a process comprising the steps of: plastifying and kneading and then metering and accumulating a molten mixture of a thermoplastic polymer and a soluble gaseous blowing agent at a pressure above the foaming pressure of said mixture, feeding this mixture into a mould cavity maintained at a temperature sufficiently low to cause the outer portion of said mixture to form a self supporting exterior shell in said mould, in a volume sufficient in the unfoamed state to substantially fill said mould cavity: allowing the outer portion of the charge to cool in said cavity to ~2~39LS9 form a self supporting exterior shell while maintaining the mould cavity at a presæure aboYe the foam~ng pre~sure of ~aid mixture; thereafter releasing the pressure within the mould cavity to provide a temperature and pressure gradient such as to cause (i) the thermoplastic material therein to contract and (ii) gas desolubilization and expansion so as to balance the volume contraction of said charge which would otherwise have resulted from said gradients, to produce a foamed core and exterior solid shell; and removing the resultant article from said mould cavity.
However, this process tends to suppress foaming of the resin mixture, which produces a foamed article that has too little foamed core portion and an excessively thick exterior non-foamed solid shell. The resultant -- article may have sink marks on its surfaces of parts in which the thickness is relatively small and warpage by lack of relaxation of residual moulding strains resulting from poor foaming.
It is an object of the present invention to provide an improved process which can form a foamed thermoplastic resin article which has a non-foamed outer shell with a smooth surface free from both swirl marks and sink marks and a foamed core portion.
According to the invention, there is provided a process for producing a foamed article having a non-foamed outer shell with a smooth surface free from both swirl marks and sink marks and a foamed core portion, which comprises the steps of:
plastifying and kneading a foamable resin under a pressure equal to or higher than its foaming pressure and metering and accumulating said resin, injecting the above meter d and accumulated foamable resin into a closed mould cavity pressurized at a ~Z~3~S'~
,~
pressure not lower than a ~urface smoothing pressure and less than the foaming pressure o~ the above foamable resin by applying a pressurized gas to the mould cavity, whereby a non-foamed outer shell is formed from a portion of the resin which contacts a wall defining the mould cavity, simultaneously with inflow of the resin, discontinuing injection of the foamable resin after filling of the mould cavity by the injection and also discontinuing application of the pressurized gas to the mould cavity permitting immediate reduction of the pressure within the mould cavity, so as to allow foaming of the foamable resin enclosed within the already formed non-foamed outer shell in the mould cavity, subsequently allowing the foamable resin within ~5 the above non-foamed outer shell to foam while cooling the resin, and removing the article from the mould cavity after solidification by cooling.
Further features of the invention will become apparent from the following description with reference to the accompanying drawings, in which:
Figure 1 is a graph showing the relationship between pressure and a volume of a foamable resin and a non-foamable resin;
Figure 2 is a graph showing the variation with time of pressure in a mould cavity during injection of a foamable resin;
Figure 3 is a schematic section illustration of an injection moulding machine modified for measuring the pressure volume behaviour and foaming pressure of a foamable resin;
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- 5 -Figure 4 is a graph showing the relakionship between pressure in the mould and volume change ratio of a foamable resin after diPferent time lapses;
Figure 5 i6 a graph showing the relationship between a weight of the articl~ and pressure in a mould when a foamable resin is in~ected into the mould cavity respectively under atmospheric pr~ssure and under a gas pressure of 9 Kg/cm 2;
Figure 6 is a graph showing the relationship between moulding weight index and pressure within the mould on completion of injection, for articles with moulding thicknesses of 3 mm, 5 mm and 7 mm, respectively;
and Figure 7 is a graph showin~ the relationship between tha retention time for maintenance of gas pressure in the mould cavity, and the foaming ratio of a foamed article, with a moulding thickness of 6 mm at gas pressures in the mould cavity of 6 Xg/cm2, 20 Kg/cm2 and 25 Xg/cm2 respectively, and with a moulding thickness of 5 mm and a gas pressure in the moulfl cavity of 6 Kg/cm2.
The foaming pressure of resins utilized in the present invention is defined and measured as follows.
~ hen the pressure in an accumulator 3 (see Figure 3) is lowered through a high pressure region, the volume of a foamable resin, as in the case of a non-foamable resin, is slightly increased due to slight decompression of the molten resin with decre~se of pressure.
~owever, in a low pressure region below a certain critical pressure, the volume of the foamable molten resin abruptly increases with a decrease in ~, , .
~L2~3~5g pressure and for a given pressure, ~till more abruptly increases with increase of the time lapse over which the change takes place, as ~hown in Figure 4.
This abrupt volume change i6 caused by foaming and expansion of the foamable molten resin.
The critical pressure, at which the volume-pressure behaviour of the foamable resin changes abruptlyl is defined as the foaming pressure (Pf) for the purposes of the present disclosure.
The foaming pressure (Pf) can be determined quantitively by measuring the pressure-volume behaviour of the foamable resin directly, and it is found that the foaming pressure (Pf) varies depending on the blowing agent employed and its amount in the formulation: it changes slightly upwardly as the temperature of the resin is elevated.
The foamable resin is maintained in an unfoamed state when the pressure is not lower than the foaming pressure (Pf). A pressure not lower than the foaming pressure ~Pf) has the same meaning as the expression of "pressure high enough to suppress foaming" in th~ prior art.
In the prior art, for obtaining a foamed article with a smooth surface free from swirl marks, it has been considered necessary to pressurize a mould cavity at a pressure sufficient to suppress foaming of a foamable resin (that is, a pressure higher than the foaming pressure). When a mould cavity is pressurized with a gas having a pressure equal to the foaming pressure or higher, a foamed article with a smooth surface can be obtained, but a thick layer of non-foamed outer shell is formed on the foamed article, and the foaming ratio of the article f i ~L~43459 is reduced. Especially when such a process, in which the mould cavity i~ pres~urized above the foaming pres6ure, is applied to manufacture of an article which is relatively thin and has a complicated shape having latticed or hollow portions, sink marks will be formed on the surface, and warpage may result in loss of the desirable characteristics of a foamed article. On the other hand, a foamed article produced by the process of the present invention can have a relatively thin outer shell with a smooth surface and a substantial foamed core portion, thus overcoming these problems of the prior art.
The pressure of the gas in the mould cavity necessary for obtaining a foamed article with a smooth surface free from both swirl marks and sink marks according to the process of the present invention has been measured (see Reference Example 1 below) and its lowest value is defined as the surface smoothing pressure. The surface smoothing pressure is found to be 50 to 70% of the foaming pressure of the foamable resin.
Figure 1 shows the pressure/volume characteristics of a foamable resin, illustrating the relationship between the above mentioned foaming pressure and the smoothing pressure at a particular temperature appropriate to the foamable resin. P is the pressure (rein pressure, or gas pressure) applied to the resin, V
is the volume of the resin, the solid line shows the P-V
locus of the foamable resin, and the broken line shows the P-V locus of a non-foamable resin.
The preferred volume of resin to be injected is discussed with reference to Figure 2.
Figure 3 shows the pressure in the mould cavity with lapse of time during moulding of the foam. The pressure within the mould is measured by a pressure sensor 1~39LS~3 provided at the mould wall of the mould cavity. The mould cavity is defined by a mould having a structure which can withstand pressurization by a gas. A foamable resin i8 injected and feeding of the gas into the mould cavity i6 discontinued when the mould cavity is filled with resin so as to allow the mould cavity to return to atmospheric pressure. The curve A is the locus of the pressure within the mould when the mould cavity is overfilled with a foamable resin. The curve A may be divided into the sequential time regions t1 : inflow, t2 : filling, t3 :
overfilling and t4 : cooling. In the region t1, the foamable resin flows into the mould cavity until the mould cavity is completely filled up. In the region t2, foamable resin is still forced into the mould cavity, and therefore the pressure in the mould is abruptly elevated, an inflexion point R in the pressure curve being generated. In the region t3, the foamable resin is overfilled and under a high pressure. A firm, thick, self sustaining outer shell is formed in regions t2 and t3. In the region t4, the in-mould resin pressure will gradually drop through volume shrinkage by cooling. The boundary between the regions t3 and t4 is determined as the moment when the foamable resin at the injection nozzle of the mould is solidified by cooling and further injection of foamable resin into the mould cavity is prevented.
In contrast to the pressure curve A, the pressure curve B will be obtained when injection of the foamable resin is stopped between t2 and t3, the pressure curve C when injection is stopped between tl and t2, and the pressure curve D when injection is stopped in the course of t1.
0~ the curves A, B, C and D shown in Figure 2, the preferred locus for the pressure within the mould during the process of the present invention is the curv2 C.
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_ g The above curve C can be obtained by in;ecting a foamable resin into a mould cavity pres6urized with ~ gas and discontinuing injection a~ ~oon as the mould cavity is filled with the resin. The article obtained by achieving in-mould pressures following curve C should have a uniform smooth surface, and a shape which accurately conforms to the shape of the mould cavity.
In contrast, if the pressure follows curve D, a smooth surface will be formed on filled parts of the moulding, but a surface with swirl marks may be formed on the remainder of the surface which is contacted as the resin foams, ~ith a linear concavity on the surface at the boundary, giving a product different from that obtained by the process of the invention. If the pressure follows curve B, the in-mould pressure rises to a peak, without dropping immediately on discontinuation of the injection.
This is an unfavourable characteristic for obtaining desired properties of the article. Pressure rurve A is inappropriate for a foam moulding process.
In implementing the process of the present invention, the foamable resin is subjected to plastifying and kneading and then metering and accumulating at a pressure (back pressure) higher than the foaming pressure.
The density o~ the foamable resin accumulated after metering is that inherent in the resin at that temperature and pressure.
The injection step consists of the following steps:
(i) maintaining a gas pressure not lower than the surface smoothing pressure but less than the foaming pressure of the foamable resin in a mould cavity, (ii) injecting foamable resin into the ~ould cavity until it is completely filled and immediately discontinuing the injection, and ~LZ~3~5~
(iii) diæcontinuing maintaining the gas pressure in said mould cavity simultaneously with discontinuation of the above mentioned injection, and permitting the mould cavity to communicate with atmospheric pressure or lower. Using these procedures, a non-foamed outer shell with uniform smooth surface and a foamed core portion enclosed within the non-foamed outer shell are formed within the mould cavity. The non-foamed outer shell with uniform smooth surface is formed successively as the foamable resin contacts the wall of the mould during the filling of the latter, and the non-foamed outer shell will be completely simultaneously with completion of injection.
The foamable resin of the core portion enclosed within the non-foamed outer shell is released of its pressure to a lower pressure less than the foaming pressure, preferably to the atmospheric pressure or lower by dropping of the gas pressure and pressure within the mould. The release of this pressure permits the foamable resin in the core portion to assume the foamed state.
In the process of the present invention, when the foaming pressure of a foamable resin is sufficiently higher than the pressure in the mould of the foamable resin on completion of filling o~ the mould cavity, it will be appreciated that the foamable resin flowing into the core portion within the non-foamed outer shell formed in the mould cavity enters the foamed state during the injection step.
The quantity of resin injected is preferably such that the mould cavity is completely filled up.
Injection is discontinued simultaneously with completion of filling, and plastifying, kneading and then metering and accumulation of resin for a subsequent injection operation is prepared in the extruder and the injection .:
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cylinder. An extruder or injection cylinder iB maintained at a pressure not lower than the foaming pressure of the ~oamable resin until initiation of injection in a following moulding operation. When the quantity of the resin is th~t which just ~ills the mould on completion of the injection step, the mould clamping force can ~e lower.
For example, when an acrylonitrile-butadien2-styrene copol~mer resin (hereinafter abbreviated as ABS resin) is inj~cted at 240C into a 7 cm thickness mould cavity, the mould pressure is 20 Kg/cm2 at the inflexion point at which the mould cavity is completely filled up; whereas if forced filling is taken to completion, the pressure will exceed 200 Kg/cm2~ Noreover, when the injsction is discontinued at the inflexion point, the pressure in the mould immediately drops and foaming of the foamable resin is promoted. The quanti~y of resin injected is most preferably the quantity injected at said inflexion point at which the gently rising pressure gradient in the mould resin pressure during injection sharply increase, but slightly in excess of that guantity is permissible.
The gas pressure in the mould cavity must be maintained at the smoothing pressure or higher only for a short time whilst the foamable resin in unfoamed state flows into the mould cavity under injection pressure overcoming the gas pressure and contacting the inner wall of the mould, and a non-foamed outer shell is formed so as to restrain foaming of the foamable resin in the vicinity of the inner wall.
The gas pressure is applied to and released from the mould cavity by means of plural openings in the mould wall, which openings permit passage of the gas but inhibit passage of the resin. The gaps are preferably located in portions of the wall in which the shape of the mould cavity is complicated, in which the thickness of the mould cavity is relatively thin, and in portions which are 1, , . . ~ - .
39L5~3 distant from the injecting nozzle ~or the re~in. Early release of the pressure of the gas within the mould cavity immediately after formation of the non-foamed outer shell will assist accurate transfer of the ~hape of the mould cavity to the result moulding. Becau~e the gas ls not retained between the inner wall of the mould and the non-foamed outer shell formed thereat, the non-foamed outer shell is urged by the foaming pressure of the core portion against the inner wall of the mould cavity.
In portions of articles with shapes such that relatively large areas are in contact with the mould cavity such as latticed portions, hollow portion and extremities of the article, wherein the resin in the cavity is cooled relatively more rapidly, thicker outer shells will be formed quickly and may form sink marks, and hence there is advantage in employing a method in which the gas pre~sure in the mould cavity is reduced successively corresponding to the inflow of the resin, as the latter contacts the plural gaps, so as to obtain a foamed article consisting of an outer shell with a uniform smooth surface witho~t surface defects due to sink marks and a foamed core portion, even in articles of complicated shape with a relatively small thickness of 5 to ~ mm, or having lattice portions and hollow portions.
In a moulding process in which the foaming step directly follows completion o~ the injection step as in the process of the present invention, it is not necessary to maintain the gas pressure within the mould cavity until formation of the self maintaining, firm and thick outer shell. The reason is that the foamable resin within the non-foamed outer shell is not migrated or blown as in the processes disclosed in U. S. Patents Nos. 3,960,996 and 4,096,218. Maintenance of the gas pressure within the mould cavity after discontinuance of injection is not desirable, not only because tranfifer of the ~hape of the mould cav~ty i6 worsQned, but Also because the aells formed in the core portion will disappear or be reduced in size to reduce the degree of foaming oP the ~oamed article.
The article in the process of the present invention should desirably have a thickness of approximately 5 to 8 mm as the standard thickness of moulding suitable for a relatively thin article. Further, the process of the present invention may also be applied to a thick article. On the other hand, when the standard thickness of the mould is 3 mm, for example/ in the case of moulding of ABS resin at 240C, the in-mould resin pressure will exceed 150 kg/cm2 during injection, whereby the clear inflection point in the pressure against volume curve will disappear and the degree of foaming of the article becomes also very low.
The cooling step in the process of the present invention should preferably be controlled to occur at a cavity temperature which is not lower than the dew point of steam in the air on the mould cavity surface and at l~ast 10C lower than the heat distortion temperature (JIS
K 6871). ~n the cooling step, the article is removed after the foamed resin of the core portion enclosed within the non-foamed outer shell in the mould cavity has been foamed sufficiently to compensate for volume shrinkage and cooled to a temperature at which it is solidified.
The present invention may be employed with thermoplastic resins such as polymers of olefins, styrenic polymers, acrylic polymers, methacrylic polymers, polyphenylene ether and the mixtures of polyphenylene ether and polystyrene, polycarbonate, polyester, polyamide, polyoxymethylene and the copolymers thereof and graft copolymers thereof, blends of resins comprising the ~2~3~5~
resins described above or mixtures with other compatible resins.
The blowing agents whiah are employed in the present invention are volatil~ blowing agent~ 6uch as nitrogen, carbon dioxide, hydrocarbons, halogenated hydrocarbons, and decomposition type organic or inorganic blowing agents such as sodium dicarbonate, N-nitroso compounds, azo compounds, and sulfonyl hydrazides. They can be employed either alone or in mixtures thereof.
These blowing agents may be either mixed with the foamable resins employed before the mixing process before the injection step, or mixed with the foamable resins employed by injection under pressure into the extruder used in the mixing process. The foamable resin employed may be prepared by diluting the foamable resin mixed with the above mentioned blowing agents with unfoamable resins.
The pressurizing gas to be employed in the present invention is a pressurized gas such as nitrogen and air, which is controlled to a pressure qual or higher than the resin smoothing pressure and less than the foaming pressure of the foamable resin.
By means of a moulding machine having a preplasticating structure as shown in Figur~ 3, a foamable resin was plastified and kneaded by an extruder (1) (40 mm ~) to be metered and accumulated (3) to 830 cc in an injection cylinder (6) under a pressure of 80 kg/cm2, (back pressure) and the position of the injecting piston (2) was read with the lapse of time by a position detection device (4) so as to measure the pressure and the volume change ratio of the foamable resin~
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A foamable resin prepared ~rom a dry blend of 100 parts by weight of a ~tyrene-acrylonitrile copol~mer resin ~hereinafter callsd as SAN resin; Stylac* AS 769, produced by Asahi Kas~i Kogyo Xabushiki Kai~ha), dried at 85C for 3 hours, with 0.3 part by weight o~
azodicarbonamide, was plastified and kneaded at 230C
under a back pressure of 80 kg/cm2, and metered and accumulated in the injection cylinder (6) under a resin pressure of 80 Kg/cm2. The volume of the foamable resin in the injection cylinder (6~ under the pressure of 80 Kg/cm2 was measured initially, the pressure in the injection cylinder (6) was gradually lowered by controlling the pressure which is charged with the injecting piston (2) and the amount of volume change with the change of the pressure was measured, and the volume change ratios ~%) relative to the respective pressures were calculated to give the results graphed in Figure. 4.
As is apparent from Figure 4, the volume of the foamable resin increased by about 1% with decreasing the pressure to 13 Kg/cm2l but there was no further change in volume with the lapse of time. However, in the pressure region below 13 Kg/cm2, tha volume abruptly increased with decrease of the pressure, and the volume further increased with lapse of time. Thus 13 Xg/cm2 was the foamin~
Z5 pressure of this foamable resin at 230C.
Foaming pressures measured similarly by varying the amount of the blowing agent, temperature and parts by weight of the above dried SAN resin, 0.3 part by weight of water and 0.3 part by weight of azodicarbonamide was subjected to measurement of the foaming pressure at 230C.
As a result, it was found to be 17 Kg/cm2, thus being increased by 4 Kg/cm2 in foaming pressure by addition of 0.3 parts by weight of water.
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In order to measure the surface ~moothing pressure Ps, a moulding machine was used in which the injection control system of the injection actuator (5) with a preplasticating structure as shown in Figure 3 waG
replaced with a known hydraulic pressure control system.
The foamabl~ resin was plastified, kneaded and then metered, and injected into a mould (not shown in Figure 3) defining a mould cavity 300 mm x 300 mm x 7 mm thickness, capable of being pressurized with a gas, solidified by cooling as described above and the resulting article was remov~d for observation of its surface. The gas pressure at which the swirl marks disappear from the surface of the moulding (i.e. the surface smoothing pressure Ps as defined above) was measured. Table 1 also shows the measured values of surface smoothing pressures of foamable resin obtained by blending SAN resin, ABS resin (Stylac*
100, produced by Asahi Kasei Kogyo Kabushiki Kaisha) and a modified polyphenylene ether resin (hereinafter abbreviated as PPE resin, Xyron* F200Z) severally with blowing agents. The surface smoothing pressures were found to be in the pressure regions lower than the foaming pressures, respectively.
REFERENCE EXA~IPLE 2 The moulding machine employed i~ Reference Example 1 was equipped with a mould having a mould cavity 300 mm x 100 mm x 7 mm thickness, which could be pressurized with a gas and was provided in its wall surface with a pressure sensor for detection of the pressure in the mould cavity. A foamable resin comprising a dry blend of 100 parts by weight of the ABS resin, dried at 85~C for 3 hours, with 0.3 parts by weight of azodicarbonamide was plastified and kneaded at 240~C to be metered and accumulated under a resin pressure of 80 Kg/cm2 .
* Trade Mark . .
~;Z 434S9 - ~7 -Next, the gas pressure applied to the mould was set at 9 Kgjcm2, inj~ction wa~ perform~d at an injection pressure of 700 Kg/cm2 whilst varying the quantity o~
resin injected for ~ucaessive moulding. Simultaneously with discontinuation of injeckion, the pres~urized gas was released to the atmosphere, followed by cooling of the article in the mould cavity at 40C for 3 minutes, before the article was removed. The same experiment was performed except that the pressure of the gas applied to the mould was atmospheric. The relationships between the weights of the articles and the maximum values of pressure in the cavity during the injection step are shown in Figure 5.
When the pressure of the gas in the mould cavity was 9 Kg/cm2, the weight of the article was increased with increase in the quantity of the resin injected into the mould cavity by injection and the maximum value of pressure in the mould also increased, the increase having a gentle gr~dient in the lower pressure region until the mould was filled. When the quantity of injected resin was further increased, the pressure was abruptly elevated indicating an inflexion point. The inflexion point coincided with the quantity of injected resin which resulted in swirl marks and their boundaries completely disappearing from the surface of moulding to give an article with a uniform smooth surface. The quantity of injected resin required for obtaining a foamed article with a uniform smooth surface free from both swirl marks and sink marks was the quantity which caused the pressure in the mould at least to reach the inflexion point of the pressure curve shown in Figure 5. The most preferred injected resin quantity was substantially that corresponding to the inflexion point, namely that on completion of filling of the mould.
~Z~3459 In contrast, when the pre~sure of the gas in the mould cavity was atmospheric, no clear inflexion point appears in the curve showing the pressure in the mould.
Moreover, rapid increase in the pressure in the mould during injection began at a lighker weight o~ resin than in the case where 9 Kg/cm2 pressure was applied by the gas within the mould cavity, thus indicating the probability that the ~oamable resin is already in a foamed state during injection in the case where the mould cavity is under atmospheric pressure.
Reference Example 2 was repeated except that the thickness of the mould cavity, having a length and width of 300 mm x 100 mm, was varied to 3 mm, 5 mm and 7 mm, and the injection speed was reduced by 1/2. The pressure of the gas in the mould cavity was set at 9 Kg/cm2. The weights of the articles obtained were measured against the pressure in the mould, and the respective weights of the articles were calculated in terms of article weight index on the basis of article weight index of 100 at the inflexion point of the pressure in the mould, namely upon completion of the injection inflow. The results are plotted in Figure 6.
In the case of articles 5 mm and 7 mm thick, inflexion points in the pressure gradient within the mould were generated corresponding to the pressure within the mould on completion of mould filling. ~he pressure at the inflexion point was low and close to the foaming pressure of ~he foamable resin. However, in the case of 3 mm thickness, the in pressure in the mould increased during filling to a higher pressure and the inflection point on completion of filling was not exhibited.
3~59 The same moulding ~achine as in Reference Example 2 was provided ~ith a mould having a mould cavity 300 mm x 100 mm x 6 mm thickness, which could be pressurized with a gas. A foamable resin was prepared by dry blend of 100 parts by weight of SAN resin, dried at 85C for 3 hours, with 0.2 parts by weight of azodicarbonamide. The above foamable resin was plastified and kneaded at 230C, and metered and accumulated under a 10 pressure of 80 Kg/cm2, and the nitrogen gas pressure in the mould cavit6y was set at (i~ 6 ~g/cm2 ~not lower than the surface smoothing pressure or higher and less than the foaming pressure), (ii) 20 Kg/cm2 (above the foaming pressure) and (iii) 25 Kg/cm2 (above the foaming pressure). The above mentioned foamable resin was injected into the mould cavity of 40~C and injection was discontinued on completion of filling of the mould. The duration for which the nitrogen gas pressure was maintained thereafter was varied and the article was removed after cooling for 3 minutes. The articles were found to be transparent and the cellular structure of the core portion could sufficiently be observed with tha naked eye.
The average density of the foamed articles obtained was measured by the water displacement method and the foaming ratio of the articles was calculated from the density ~f 1.07 g/cm2 of the unfoamed resin to give the results shown in Figure 7. From Figure 7, it is clearly apparent that the pressure of the gas in the mould cavity should preferably be at the lower end of the pressure range between the surface smoothing pressure and the foaming pressure in order to obtain an article of higher foaming ratio.
, .
, _ ~ 13~L59 It is also clear that the optimum time ~or releasing the pres~ure o~ the gas in the mould cavity is at the ~ame time as injection i6 discontinued, that i8 the retention time for feeding of nitrogen gas in Figure 7 i6 zero. As ~he retention time for maintaining gas pressure on the mould cavity is prolonged, the number of the foamed cells in the core portion in the foamed article could be clearly seen to be reduced and then disappear. In Figure 7, the mark O indicates an article in which the foamed cells in the core portion in the article can be recognized by the naked eye, and the mark ~ indicates an article in which substantially no foam cells can be recognized by the naked eye in the core portion. As the foamed cells in the core portion of the article disappeared, -sink marks were found to be formed on the artic]e surface, and warpage of the article was found to be increased. As the foamed cells in the core portion were seen to be reduc~d, so as the thickness of the non-foamed outer shell on both surfaces increased, whilst the thickness of the foamed portion was relatively reduced.
The mould cavity was next changed to 300 mm x 300 mm x 5 mm thickness with provision of a relatively fine embossed pattern (HN22; which is a standard embossed pattern produced by Nippon Etching Xabushiki Xaisha) and moulding was carried out similarly under a gas pressure in the mould cavity of 6 Xg/cm2 to obtain the results as shown by the broken line in Figure 7. As can be clearly seen from this Figure, when the thickness of the article is thin, not only the foaming ratio of the foam moulding is lowered, but also the foaming ratio of the foamed article is markedly lowered as the retention tim of the - gas pressure in the mould cavity is prolonged. Also, the embossed pattern was less well transferred onto the article surface as the retention time was prolonged.
~Z~3~5~3 By the use of the same moulding machine as in Example 2 and a mould cavity with a thickness of 7 mm, a foamable resin comprising a dry blend of lO0 parts by weight of ABS rein, predried at 85C for 3 hours, with 0.3 parts by weight of azodicarbonamide was plastified and kneaded at 240C under a resin pressure of 80 Kg/cm2, and metered and accumulated. Injection was carried out under an injection pressure of 600 Kg/cm2 by varying the injection step as described below, whilst applying a gaseous pressure of 8.5 Kg/cm2 to the mould cavity, at 40OC, followed by release of the gaseous pressure into the atmosphere simultaneously with discontinuance of the injection and cooling for 3 minutes to obtain a foamed article.
The injection step was varied as follows:
(i) injection was discontinued on completion of filling of the mould;
(ii) after completion of the filling of the mould, further pressurization was effected before discontinuance of injection;
(iii) after filling, pressure was maintained at 550 Kg/cm2 for 5 seconds before discontinuance of injection;
25(iv~ after filling, pxessure maintained at 550 Kg~cm2 for 10 seconds before discontinuance of injection;
~v) after filling, pressure was maintained at 550 Kg/cm2 for 15 seconds before discontinuance of injection.
30The foaming ratios of the articles obtained by the respective injection s$ep were measured to obtain the results shown in Table 2. From Table 2, it can clearly be seen that employment of pressure maintenance as in conventional injection moulding results in high pressures -- ~LZ~34SS~
~ 22 -in the mould, whereby the ~oaming ra~io of the foamed article is unfavourably lowered, and that dlecontinuation of pressure on completion of filling 1s most pre~erable.
An in-line type injection moulding machine with a mould clamping force of 225 tons was provided with a mould with a structure having a mould cavity of 200 mm x 200 mm x 7 mm thickness which can be pressurized with a gas, and moulding was carried out with the use of the foamable resins and conditions as indicated in Table 3.
Plastifying and kneading and th~n metering and - accumulating were conducted under a back pressure of 80 Xg/cm2, the mould cavity was pressurized with nitrogen gas, the foamable resin was injected, the injection was discontinued with closing of an injection nozzle simultaneously with completion of filling, and at the same time the application of nitrogen gas into the mould cavity, through plural slit-like gaps which could prevent flow of the resin in the mould cavity but permitted passage of a gas, was discontinued. Simultaneously, the mould cavity was communicated to a vacuum source at lO0 mm Hg through said slit-like gaps, followed by cooling of the article in the mould cavity for 3 minutes, and thereafter the article was removed from the mould. The articles obtained has the foaming ratios as shown in Table 3, each consisting of an outer shell with uniform smooth surface and a foamed core portion, without sink marks being obser~ed. When shot moulding of the above mentioned process was repeated for 200 times continuously, stable foamed articles could be obtained .repeatedly with good reproducibility.
lZ4345~
- 23 ~
R~sin Foaming Smoothing ~emp. Pressure Pressure Eoamable Resin ~-5l. _ (Kq/~) (Kg/cm~L
SAN (100 wt. par~s)/azodi-carbonamide (0.3 wt. part) 230 13 8 SAN (100 wt. parts)/azodi-carbonamide (0.3 wt. part) 250 14 10 SAN (lO0 wt. parts)/azodi-10 carbonamide (0.5 wt. part) 270 15 12 SAN (lO0 wt. parts)/azodi-carbonamide (0.7 wt. part) 230 20 14 SAN ~100 wt. parts)/azodi-carbonamide (0.7 wt. part) 230 31 20 ABS (lO0 wt. parts)/azodi-carbonamide (0.3 wt. part) 240 14 7 Modified PPE (200 wt~ parts)/
azodicarbonamide (0.3 wt part) 250 18 9 ~ Z4~591 . .
-- 2~ --~o ~^
C C 0 ~ trl N N
~_/ 0~ U O O O O O
ra 6 ~ . . .
~1 ~ ~ ,~
O ~ 0 1~ h U~ .
~ X
h ~ --
Figure 5 i6 a graph showing the relationship between a weight of the articl~ and pressure in a mould when a foamable resin is in~ected into the mould cavity respectively under atmospheric pr~ssure and under a gas pressure of 9 Kg/cm 2;
Figure 6 is a graph showing the relationship between moulding weight index and pressure within the mould on completion of injection, for articles with moulding thicknesses of 3 mm, 5 mm and 7 mm, respectively;
and Figure 7 is a graph showin~ the relationship between tha retention time for maintenance of gas pressure in the mould cavity, and the foaming ratio of a foamed article, with a moulding thickness of 6 mm at gas pressures in the mould cavity of 6 Xg/cm2, 20 Kg/cm2 and 25 Xg/cm2 respectively, and with a moulding thickness of 5 mm and a gas pressure in the moulfl cavity of 6 Kg/cm2.
The foaming pressure of resins utilized in the present invention is defined and measured as follows.
~ hen the pressure in an accumulator 3 (see Figure 3) is lowered through a high pressure region, the volume of a foamable resin, as in the case of a non-foamable resin, is slightly increased due to slight decompression of the molten resin with decre~se of pressure.
~owever, in a low pressure region below a certain critical pressure, the volume of the foamable molten resin abruptly increases with a decrease in ~, , .
~L2~3~5g pressure and for a given pressure, ~till more abruptly increases with increase of the time lapse over which the change takes place, as ~hown in Figure 4.
This abrupt volume change i6 caused by foaming and expansion of the foamable molten resin.
The critical pressure, at which the volume-pressure behaviour of the foamable resin changes abruptlyl is defined as the foaming pressure (Pf) for the purposes of the present disclosure.
The foaming pressure (Pf) can be determined quantitively by measuring the pressure-volume behaviour of the foamable resin directly, and it is found that the foaming pressure (Pf) varies depending on the blowing agent employed and its amount in the formulation: it changes slightly upwardly as the temperature of the resin is elevated.
The foamable resin is maintained in an unfoamed state when the pressure is not lower than the foaming pressure (Pf). A pressure not lower than the foaming pressure ~Pf) has the same meaning as the expression of "pressure high enough to suppress foaming" in th~ prior art.
In the prior art, for obtaining a foamed article with a smooth surface free from swirl marks, it has been considered necessary to pressurize a mould cavity at a pressure sufficient to suppress foaming of a foamable resin (that is, a pressure higher than the foaming pressure). When a mould cavity is pressurized with a gas having a pressure equal to the foaming pressure or higher, a foamed article with a smooth surface can be obtained, but a thick layer of non-foamed outer shell is formed on the foamed article, and the foaming ratio of the article f i ~L~43459 is reduced. Especially when such a process, in which the mould cavity i~ pres~urized above the foaming pres6ure, is applied to manufacture of an article which is relatively thin and has a complicated shape having latticed or hollow portions, sink marks will be formed on the surface, and warpage may result in loss of the desirable characteristics of a foamed article. On the other hand, a foamed article produced by the process of the present invention can have a relatively thin outer shell with a smooth surface and a substantial foamed core portion, thus overcoming these problems of the prior art.
The pressure of the gas in the mould cavity necessary for obtaining a foamed article with a smooth surface free from both swirl marks and sink marks according to the process of the present invention has been measured (see Reference Example 1 below) and its lowest value is defined as the surface smoothing pressure. The surface smoothing pressure is found to be 50 to 70% of the foaming pressure of the foamable resin.
Figure 1 shows the pressure/volume characteristics of a foamable resin, illustrating the relationship between the above mentioned foaming pressure and the smoothing pressure at a particular temperature appropriate to the foamable resin. P is the pressure (rein pressure, or gas pressure) applied to the resin, V
is the volume of the resin, the solid line shows the P-V
locus of the foamable resin, and the broken line shows the P-V locus of a non-foamable resin.
The preferred volume of resin to be injected is discussed with reference to Figure 2.
Figure 3 shows the pressure in the mould cavity with lapse of time during moulding of the foam. The pressure within the mould is measured by a pressure sensor 1~39LS~3 provided at the mould wall of the mould cavity. The mould cavity is defined by a mould having a structure which can withstand pressurization by a gas. A foamable resin i8 injected and feeding of the gas into the mould cavity i6 discontinued when the mould cavity is filled with resin so as to allow the mould cavity to return to atmospheric pressure. The curve A is the locus of the pressure within the mould when the mould cavity is overfilled with a foamable resin. The curve A may be divided into the sequential time regions t1 : inflow, t2 : filling, t3 :
overfilling and t4 : cooling. In the region t1, the foamable resin flows into the mould cavity until the mould cavity is completely filled up. In the region t2, foamable resin is still forced into the mould cavity, and therefore the pressure in the mould is abruptly elevated, an inflexion point R in the pressure curve being generated. In the region t3, the foamable resin is overfilled and under a high pressure. A firm, thick, self sustaining outer shell is formed in regions t2 and t3. In the region t4, the in-mould resin pressure will gradually drop through volume shrinkage by cooling. The boundary between the regions t3 and t4 is determined as the moment when the foamable resin at the injection nozzle of the mould is solidified by cooling and further injection of foamable resin into the mould cavity is prevented.
In contrast to the pressure curve A, the pressure curve B will be obtained when injection of the foamable resin is stopped between t2 and t3, the pressure curve C when injection is stopped between tl and t2, and the pressure curve D when injection is stopped in the course of t1.
0~ the curves A, B, C and D shown in Figure 2, the preferred locus for the pressure within the mould during the process of the present invention is the curv2 C.
, ~.
i ~ ..~, 1~43~5~
_ g The above curve C can be obtained by in;ecting a foamable resin into a mould cavity pres6urized with ~ gas and discontinuing injection a~ ~oon as the mould cavity is filled with the resin. The article obtained by achieving in-mould pressures following curve C should have a uniform smooth surface, and a shape which accurately conforms to the shape of the mould cavity.
In contrast, if the pressure follows curve D, a smooth surface will be formed on filled parts of the moulding, but a surface with swirl marks may be formed on the remainder of the surface which is contacted as the resin foams, ~ith a linear concavity on the surface at the boundary, giving a product different from that obtained by the process of the invention. If the pressure follows curve B, the in-mould pressure rises to a peak, without dropping immediately on discontinuation of the injection.
This is an unfavourable characteristic for obtaining desired properties of the article. Pressure rurve A is inappropriate for a foam moulding process.
In implementing the process of the present invention, the foamable resin is subjected to plastifying and kneading and then metering and accumulating at a pressure (back pressure) higher than the foaming pressure.
The density o~ the foamable resin accumulated after metering is that inherent in the resin at that temperature and pressure.
The injection step consists of the following steps:
(i) maintaining a gas pressure not lower than the surface smoothing pressure but less than the foaming pressure of the foamable resin in a mould cavity, (ii) injecting foamable resin into the ~ould cavity until it is completely filled and immediately discontinuing the injection, and ~LZ~3~5~
(iii) diæcontinuing maintaining the gas pressure in said mould cavity simultaneously with discontinuation of the above mentioned injection, and permitting the mould cavity to communicate with atmospheric pressure or lower. Using these procedures, a non-foamed outer shell with uniform smooth surface and a foamed core portion enclosed within the non-foamed outer shell are formed within the mould cavity. The non-foamed outer shell with uniform smooth surface is formed successively as the foamable resin contacts the wall of the mould during the filling of the latter, and the non-foamed outer shell will be completely simultaneously with completion of injection.
The foamable resin of the core portion enclosed within the non-foamed outer shell is released of its pressure to a lower pressure less than the foaming pressure, preferably to the atmospheric pressure or lower by dropping of the gas pressure and pressure within the mould. The release of this pressure permits the foamable resin in the core portion to assume the foamed state.
In the process of the present invention, when the foaming pressure of a foamable resin is sufficiently higher than the pressure in the mould of the foamable resin on completion of filling o~ the mould cavity, it will be appreciated that the foamable resin flowing into the core portion within the non-foamed outer shell formed in the mould cavity enters the foamed state during the injection step.
The quantity of resin injected is preferably such that the mould cavity is completely filled up.
Injection is discontinued simultaneously with completion of filling, and plastifying, kneading and then metering and accumulation of resin for a subsequent injection operation is prepared in the extruder and the injection .:
3~15~
cylinder. An extruder or injection cylinder iB maintained at a pressure not lower than the foaming pressure of the ~oamable resin until initiation of injection in a following moulding operation. When the quantity of the resin is th~t which just ~ills the mould on completion of the injection step, the mould clamping force can ~e lower.
For example, when an acrylonitrile-butadien2-styrene copol~mer resin (hereinafter abbreviated as ABS resin) is inj~cted at 240C into a 7 cm thickness mould cavity, the mould pressure is 20 Kg/cm2 at the inflexion point at which the mould cavity is completely filled up; whereas if forced filling is taken to completion, the pressure will exceed 200 Kg/cm2~ Noreover, when the injsction is discontinued at the inflexion point, the pressure in the mould immediately drops and foaming of the foamable resin is promoted. The quanti~y of resin injected is most preferably the quantity injected at said inflexion point at which the gently rising pressure gradient in the mould resin pressure during injection sharply increase, but slightly in excess of that guantity is permissible.
The gas pressure in the mould cavity must be maintained at the smoothing pressure or higher only for a short time whilst the foamable resin in unfoamed state flows into the mould cavity under injection pressure overcoming the gas pressure and contacting the inner wall of the mould, and a non-foamed outer shell is formed so as to restrain foaming of the foamable resin in the vicinity of the inner wall.
The gas pressure is applied to and released from the mould cavity by means of plural openings in the mould wall, which openings permit passage of the gas but inhibit passage of the resin. The gaps are preferably located in portions of the wall in which the shape of the mould cavity is complicated, in which the thickness of the mould cavity is relatively thin, and in portions which are 1, , . . ~ - .
39L5~3 distant from the injecting nozzle ~or the re~in. Early release of the pressure of the gas within the mould cavity immediately after formation of the non-foamed outer shell will assist accurate transfer of the ~hape of the mould cavity to the result moulding. Becau~e the gas ls not retained between the inner wall of the mould and the non-foamed outer shell formed thereat, the non-foamed outer shell is urged by the foaming pressure of the core portion against the inner wall of the mould cavity.
In portions of articles with shapes such that relatively large areas are in contact with the mould cavity such as latticed portions, hollow portion and extremities of the article, wherein the resin in the cavity is cooled relatively more rapidly, thicker outer shells will be formed quickly and may form sink marks, and hence there is advantage in employing a method in which the gas pre~sure in the mould cavity is reduced successively corresponding to the inflow of the resin, as the latter contacts the plural gaps, so as to obtain a foamed article consisting of an outer shell with a uniform smooth surface witho~t surface defects due to sink marks and a foamed core portion, even in articles of complicated shape with a relatively small thickness of 5 to ~ mm, or having lattice portions and hollow portions.
In a moulding process in which the foaming step directly follows completion o~ the injection step as in the process of the present invention, it is not necessary to maintain the gas pressure within the mould cavity until formation of the self maintaining, firm and thick outer shell. The reason is that the foamable resin within the non-foamed outer shell is not migrated or blown as in the processes disclosed in U. S. Patents Nos. 3,960,996 and 4,096,218. Maintenance of the gas pressure within the mould cavity after discontinuance of injection is not desirable, not only because tranfifer of the ~hape of the mould cav~ty i6 worsQned, but Also because the aells formed in the core portion will disappear or be reduced in size to reduce the degree of foaming oP the ~oamed article.
The article in the process of the present invention should desirably have a thickness of approximately 5 to 8 mm as the standard thickness of moulding suitable for a relatively thin article. Further, the process of the present invention may also be applied to a thick article. On the other hand, when the standard thickness of the mould is 3 mm, for example/ in the case of moulding of ABS resin at 240C, the in-mould resin pressure will exceed 150 kg/cm2 during injection, whereby the clear inflection point in the pressure against volume curve will disappear and the degree of foaming of the article becomes also very low.
The cooling step in the process of the present invention should preferably be controlled to occur at a cavity temperature which is not lower than the dew point of steam in the air on the mould cavity surface and at l~ast 10C lower than the heat distortion temperature (JIS
K 6871). ~n the cooling step, the article is removed after the foamed resin of the core portion enclosed within the non-foamed outer shell in the mould cavity has been foamed sufficiently to compensate for volume shrinkage and cooled to a temperature at which it is solidified.
The present invention may be employed with thermoplastic resins such as polymers of olefins, styrenic polymers, acrylic polymers, methacrylic polymers, polyphenylene ether and the mixtures of polyphenylene ether and polystyrene, polycarbonate, polyester, polyamide, polyoxymethylene and the copolymers thereof and graft copolymers thereof, blends of resins comprising the ~2~3~5~
resins described above or mixtures with other compatible resins.
The blowing agents whiah are employed in the present invention are volatil~ blowing agent~ 6uch as nitrogen, carbon dioxide, hydrocarbons, halogenated hydrocarbons, and decomposition type organic or inorganic blowing agents such as sodium dicarbonate, N-nitroso compounds, azo compounds, and sulfonyl hydrazides. They can be employed either alone or in mixtures thereof.
These blowing agents may be either mixed with the foamable resins employed before the mixing process before the injection step, or mixed with the foamable resins employed by injection under pressure into the extruder used in the mixing process. The foamable resin employed may be prepared by diluting the foamable resin mixed with the above mentioned blowing agents with unfoamable resins.
The pressurizing gas to be employed in the present invention is a pressurized gas such as nitrogen and air, which is controlled to a pressure qual or higher than the resin smoothing pressure and less than the foaming pressure of the foamable resin.
By means of a moulding machine having a preplasticating structure as shown in Figur~ 3, a foamable resin was plastified and kneaded by an extruder (1) (40 mm ~) to be metered and accumulated (3) to 830 cc in an injection cylinder (6) under a pressure of 80 kg/cm2, (back pressure) and the position of the injecting piston (2) was read with the lapse of time by a position detection device (4) so as to measure the pressure and the volume change ratio of the foamable resin~
1243~S~
A foamable resin prepared ~rom a dry blend of 100 parts by weight of a ~tyrene-acrylonitrile copol~mer resin ~hereinafter callsd as SAN resin; Stylac* AS 769, produced by Asahi Kas~i Kogyo Xabushiki Kai~ha), dried at 85C for 3 hours, with 0.3 part by weight o~
azodicarbonamide, was plastified and kneaded at 230C
under a back pressure of 80 kg/cm2, and metered and accumulated in the injection cylinder (6) under a resin pressure of 80 Kg/cm2. The volume of the foamable resin in the injection cylinder (6~ under the pressure of 80 Kg/cm2 was measured initially, the pressure in the injection cylinder (6) was gradually lowered by controlling the pressure which is charged with the injecting piston (2) and the amount of volume change with the change of the pressure was measured, and the volume change ratios ~%) relative to the respective pressures were calculated to give the results graphed in Figure. 4.
As is apparent from Figure 4, the volume of the foamable resin increased by about 1% with decreasing the pressure to 13 Kg/cm2l but there was no further change in volume with the lapse of time. However, in the pressure region below 13 Kg/cm2, tha volume abruptly increased with decrease of the pressure, and the volume further increased with lapse of time. Thus 13 Xg/cm2 was the foamin~
Z5 pressure of this foamable resin at 230C.
Foaming pressures measured similarly by varying the amount of the blowing agent, temperature and parts by weight of the above dried SAN resin, 0.3 part by weight of water and 0.3 part by weight of azodicarbonamide was subjected to measurement of the foaming pressure at 230C.
As a result, it was found to be 17 Kg/cm2, thus being increased by 4 Kg/cm2 in foaming pressure by addition of 0.3 parts by weight of water.
* Trade Mark ~ ;
lZ43~5~
In order to measure the surface ~moothing pressure Ps, a moulding machine was used in which the injection control system of the injection actuator (5) with a preplasticating structure as shown in Figure 3 waG
replaced with a known hydraulic pressure control system.
The foamabl~ resin was plastified, kneaded and then metered, and injected into a mould (not shown in Figure 3) defining a mould cavity 300 mm x 300 mm x 7 mm thickness, capable of being pressurized with a gas, solidified by cooling as described above and the resulting article was remov~d for observation of its surface. The gas pressure at which the swirl marks disappear from the surface of the moulding (i.e. the surface smoothing pressure Ps as defined above) was measured. Table 1 also shows the measured values of surface smoothing pressures of foamable resin obtained by blending SAN resin, ABS resin (Stylac*
100, produced by Asahi Kasei Kogyo Kabushiki Kaisha) and a modified polyphenylene ether resin (hereinafter abbreviated as PPE resin, Xyron* F200Z) severally with blowing agents. The surface smoothing pressures were found to be in the pressure regions lower than the foaming pressures, respectively.
REFERENCE EXA~IPLE 2 The moulding machine employed i~ Reference Example 1 was equipped with a mould having a mould cavity 300 mm x 100 mm x 7 mm thickness, which could be pressurized with a gas and was provided in its wall surface with a pressure sensor for detection of the pressure in the mould cavity. A foamable resin comprising a dry blend of 100 parts by weight of the ABS resin, dried at 85~C for 3 hours, with 0.3 parts by weight of azodicarbonamide was plastified and kneaded at 240~C to be metered and accumulated under a resin pressure of 80 Kg/cm2 .
* Trade Mark . .
~;Z 434S9 - ~7 -Next, the gas pressure applied to the mould was set at 9 Kgjcm2, inj~ction wa~ perform~d at an injection pressure of 700 Kg/cm2 whilst varying the quantity o~
resin injected for ~ucaessive moulding. Simultaneously with discontinuation of injeckion, the pres~urized gas was released to the atmosphere, followed by cooling of the article in the mould cavity at 40C for 3 minutes, before the article was removed. The same experiment was performed except that the pressure of the gas applied to the mould was atmospheric. The relationships between the weights of the articles and the maximum values of pressure in the cavity during the injection step are shown in Figure 5.
When the pressure of the gas in the mould cavity was 9 Kg/cm2, the weight of the article was increased with increase in the quantity of the resin injected into the mould cavity by injection and the maximum value of pressure in the mould also increased, the increase having a gentle gr~dient in the lower pressure region until the mould was filled. When the quantity of injected resin was further increased, the pressure was abruptly elevated indicating an inflexion point. The inflexion point coincided with the quantity of injected resin which resulted in swirl marks and their boundaries completely disappearing from the surface of moulding to give an article with a uniform smooth surface. The quantity of injected resin required for obtaining a foamed article with a uniform smooth surface free from both swirl marks and sink marks was the quantity which caused the pressure in the mould at least to reach the inflexion point of the pressure curve shown in Figure 5. The most preferred injected resin quantity was substantially that corresponding to the inflexion point, namely that on completion of filling of the mould.
~Z~3459 In contrast, when the pre~sure of the gas in the mould cavity was atmospheric, no clear inflexion point appears in the curve showing the pressure in the mould.
Moreover, rapid increase in the pressure in the mould during injection began at a lighker weight o~ resin than in the case where 9 Kg/cm2 pressure was applied by the gas within the mould cavity, thus indicating the probability that the ~oamable resin is already in a foamed state during injection in the case where the mould cavity is under atmospheric pressure.
Reference Example 2 was repeated except that the thickness of the mould cavity, having a length and width of 300 mm x 100 mm, was varied to 3 mm, 5 mm and 7 mm, and the injection speed was reduced by 1/2. The pressure of the gas in the mould cavity was set at 9 Kg/cm2. The weights of the articles obtained were measured against the pressure in the mould, and the respective weights of the articles were calculated in terms of article weight index on the basis of article weight index of 100 at the inflexion point of the pressure in the mould, namely upon completion of the injection inflow. The results are plotted in Figure 6.
In the case of articles 5 mm and 7 mm thick, inflexion points in the pressure gradient within the mould were generated corresponding to the pressure within the mould on completion of mould filling. ~he pressure at the inflexion point was low and close to the foaming pressure of ~he foamable resin. However, in the case of 3 mm thickness, the in pressure in the mould increased during filling to a higher pressure and the inflection point on completion of filling was not exhibited.
3~59 The same moulding ~achine as in Reference Example 2 was provided ~ith a mould having a mould cavity 300 mm x 100 mm x 6 mm thickness, which could be pressurized with a gas. A foamable resin was prepared by dry blend of 100 parts by weight of SAN resin, dried at 85C for 3 hours, with 0.2 parts by weight of azodicarbonamide. The above foamable resin was plastified and kneaded at 230C, and metered and accumulated under a 10 pressure of 80 Kg/cm2, and the nitrogen gas pressure in the mould cavit6y was set at (i~ 6 ~g/cm2 ~not lower than the surface smoothing pressure or higher and less than the foaming pressure), (ii) 20 Kg/cm2 (above the foaming pressure) and (iii) 25 Kg/cm2 (above the foaming pressure). The above mentioned foamable resin was injected into the mould cavity of 40~C and injection was discontinued on completion of filling of the mould. The duration for which the nitrogen gas pressure was maintained thereafter was varied and the article was removed after cooling for 3 minutes. The articles were found to be transparent and the cellular structure of the core portion could sufficiently be observed with tha naked eye.
The average density of the foamed articles obtained was measured by the water displacement method and the foaming ratio of the articles was calculated from the density ~f 1.07 g/cm2 of the unfoamed resin to give the results shown in Figure 7. From Figure 7, it is clearly apparent that the pressure of the gas in the mould cavity should preferably be at the lower end of the pressure range between the surface smoothing pressure and the foaming pressure in order to obtain an article of higher foaming ratio.
, .
, _ ~ 13~L59 It is also clear that the optimum time ~or releasing the pres~ure o~ the gas in the mould cavity is at the ~ame time as injection i6 discontinued, that i8 the retention time for feeding of nitrogen gas in Figure 7 i6 zero. As ~he retention time for maintaining gas pressure on the mould cavity is prolonged, the number of the foamed cells in the core portion in the foamed article could be clearly seen to be reduced and then disappear. In Figure 7, the mark O indicates an article in which the foamed cells in the core portion in the article can be recognized by the naked eye, and the mark ~ indicates an article in which substantially no foam cells can be recognized by the naked eye in the core portion. As the foamed cells in the core portion of the article disappeared, -sink marks were found to be formed on the artic]e surface, and warpage of the article was found to be increased. As the foamed cells in the core portion were seen to be reduc~d, so as the thickness of the non-foamed outer shell on both surfaces increased, whilst the thickness of the foamed portion was relatively reduced.
The mould cavity was next changed to 300 mm x 300 mm x 5 mm thickness with provision of a relatively fine embossed pattern (HN22; which is a standard embossed pattern produced by Nippon Etching Xabushiki Xaisha) and moulding was carried out similarly under a gas pressure in the mould cavity of 6 Xg/cm2 to obtain the results as shown by the broken line in Figure 7. As can be clearly seen from this Figure, when the thickness of the article is thin, not only the foaming ratio of the foam moulding is lowered, but also the foaming ratio of the foamed article is markedly lowered as the retention tim of the - gas pressure in the mould cavity is prolonged. Also, the embossed pattern was less well transferred onto the article surface as the retention time was prolonged.
~Z~3~5~3 By the use of the same moulding machine as in Example 2 and a mould cavity with a thickness of 7 mm, a foamable resin comprising a dry blend of lO0 parts by weight of ABS rein, predried at 85C for 3 hours, with 0.3 parts by weight of azodicarbonamide was plastified and kneaded at 240C under a resin pressure of 80 Kg/cm2, and metered and accumulated. Injection was carried out under an injection pressure of 600 Kg/cm2 by varying the injection step as described below, whilst applying a gaseous pressure of 8.5 Kg/cm2 to the mould cavity, at 40OC, followed by release of the gaseous pressure into the atmosphere simultaneously with discontinuance of the injection and cooling for 3 minutes to obtain a foamed article.
The injection step was varied as follows:
(i) injection was discontinued on completion of filling of the mould;
(ii) after completion of the filling of the mould, further pressurization was effected before discontinuance of injection;
(iii) after filling, pressure was maintained at 550 Kg/cm2 for 5 seconds before discontinuance of injection;
25(iv~ after filling, pxessure maintained at 550 Kg~cm2 for 10 seconds before discontinuance of injection;
~v) after filling, pressure was maintained at 550 Kg/cm2 for 15 seconds before discontinuance of injection.
30The foaming ratios of the articles obtained by the respective injection s$ep were measured to obtain the results shown in Table 2. From Table 2, it can clearly be seen that employment of pressure maintenance as in conventional injection moulding results in high pressures -- ~LZ~34SS~
~ 22 -in the mould, whereby the ~oaming ra~io of the foamed article is unfavourably lowered, and that dlecontinuation of pressure on completion of filling 1s most pre~erable.
An in-line type injection moulding machine with a mould clamping force of 225 tons was provided with a mould with a structure having a mould cavity of 200 mm x 200 mm x 7 mm thickness which can be pressurized with a gas, and moulding was carried out with the use of the foamable resins and conditions as indicated in Table 3.
Plastifying and kneading and th~n metering and - accumulating were conducted under a back pressure of 80 Xg/cm2, the mould cavity was pressurized with nitrogen gas, the foamable resin was injected, the injection was discontinued with closing of an injection nozzle simultaneously with completion of filling, and at the same time the application of nitrogen gas into the mould cavity, through plural slit-like gaps which could prevent flow of the resin in the mould cavity but permitted passage of a gas, was discontinued. Simultaneously, the mould cavity was communicated to a vacuum source at lO0 mm Hg through said slit-like gaps, followed by cooling of the article in the mould cavity for 3 minutes, and thereafter the article was removed from the mould. The articles obtained has the foaming ratios as shown in Table 3, each consisting of an outer shell with uniform smooth surface and a foamed core portion, without sink marks being obser~ed. When shot moulding of the above mentioned process was repeated for 200 times continuously, stable foamed articles could be obtained .repeatedly with good reproducibility.
lZ4345~
- 23 ~
R~sin Foaming Smoothing ~emp. Pressure Pressure Eoamable Resin ~-5l. _ (Kq/~) (Kg/cm~L
SAN (100 wt. par~s)/azodi-carbonamide (0.3 wt. part) 230 13 8 SAN (100 wt. parts)/azodi-carbonamide (0.3 wt. part) 250 14 10 SAN (lO0 wt. parts)/azodi-10 carbonamide (0.5 wt. part) 270 15 12 SAN (lO0 wt. parts)/azodi-carbonamide (0.7 wt. part) 230 20 14 SAN ~100 wt. parts)/azodi-carbonamide (0.7 wt. part) 230 31 20 ABS (lO0 wt. parts)/azodi-carbonamide (0.3 wt. part) 240 14 7 Modified PPE (200 wt~ parts)/
azodicarbonamide (0.3 wt part) 250 18 9 ~ Z4~591 . .
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Claims (6)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A process for producing a foamed article comprising a non-foamed outer shell having a smooth surface free from both swirl marks and sink marks and a foamed core portion, which comprises the steps of:
plastifying and kneading a foamable resin under a pressure equal to or higher than its foaming pressure and metering and accumulating said resin, injecting the above metered and accumulated foamable resin into a closed mould cavity pressurized at a pressure of not lower than a surface smoothing pressure and less than the foaming pressure of the above foamable resin by applying a pressurized gas to the mould cavity, whereby a non-foamed outer shell is formed from a portion of the resin which contacts a wall defining the mould cavity, simultaneously with inflow of the resin, discontinuing injection of the foamable resin after filling of the mould cavity by the injection and also discontinuing application of the pressurized gas to the mould cavity permitting immediate reduction of the pressure within the mould cavity, so as to allow foaming of the foamable resin enclosed within the already formed non-foamed outer shell in the mould cavity, subsequently allowing the foamable resin within the above non-foamed outer shell to foam while cooling the resin, and removing the article from the mould cavity after solidification by cooling.
plastifying and kneading a foamable resin under a pressure equal to or higher than its foaming pressure and metering and accumulating said resin, injecting the above metered and accumulated foamable resin into a closed mould cavity pressurized at a pressure of not lower than a surface smoothing pressure and less than the foaming pressure of the above foamable resin by applying a pressurized gas to the mould cavity, whereby a non-foamed outer shell is formed from a portion of the resin which contacts a wall defining the mould cavity, simultaneously with inflow of the resin, discontinuing injection of the foamable resin after filling of the mould cavity by the injection and also discontinuing application of the pressurized gas to the mould cavity permitting immediate reduction of the pressure within the mould cavity, so as to allow foaming of the foamable resin enclosed within the already formed non-foamed outer shell in the mould cavity, subsequently allowing the foamable resin within the above non-foamed outer shell to foam while cooling the resin, and removing the article from the mould cavity after solidification by cooling.
2. A process according to Claim 1, wherein the lowering of the pressure within the mould cavity is carried out:
1) by releasing gas through plural gaps in the wall defining the mould cavity to produce a pressure below the foaming pressure, as said plural gaps are success-ively contacted by the injected resin, the gaps being such as to permit passage of the gas but not the injected resin;
2) discontinuing injection of the resin simultaneously with filling of the mould cavity with the resin; and 3) discontinuing application of pressurized gas to the mould cavity.
1) by releasing gas through plural gaps in the wall defining the mould cavity to produce a pressure below the foaming pressure, as said plural gaps are success-ively contacted by the injected resin, the gaps being such as to permit passage of the gas but not the injected resin;
2) discontinuing injection of the resin simultaneously with filling of the mould cavity with the resin; and 3) discontinuing application of pressurized gas to the mould cavity.
3. A process for producing a foamed article according to Claim 1, wherein the quantity of resin injected into the mould cavity is such that injection thereof is completed just as the mould cavity is completely filled.
4. A process according to Claim 1, 2 or 3, wherein the cooling is controlled by maintaining a cavity temperature which is not lower than the dew point of air reaching the mould cavity surface and at least 10°C lower than the heat distortion temperature of the article produced.
5. A process according to Claim 1, 2 or 3, wherein the temperature in the mould cavity is maintained at 40°C.
6. A process according to Claim 1, 2 or 3, wherein the pressure in the cavity after discontinuance of injection is reduced to atmospheric or below.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP191499/1984 | 1984-09-14 | ||
| JP59191499A JPS6169421A (en) | 1984-09-14 | 1984-09-14 | Molding method of foamed molding |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1243459A true CA1243459A (en) | 1988-10-25 |
Family
ID=16275664
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000490461A Expired CA1243459A (en) | 1984-09-14 | 1985-09-11 | Process for molding formed articles |
Country Status (4)
| Country | Link |
|---|---|
| US (1) | US4952365A (en) |
| JP (1) | JPS6169421A (en) |
| CA (1) | CA1243459A (en) |
| GB (1) | GB2164291B (en) |
Families Citing this family (22)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5604266A (en) * | 1992-10-15 | 1997-02-18 | Ecomat, Inc. | Cured unsaturated polyest-polyurethane highly filled resin materials and process for preparing them |
| US5508315A (en) * | 1992-10-15 | 1996-04-16 | Ecomat, Inc. | Cured unsaturated polyester-polyurethane hybrid highly filled resin foams |
| US5302634A (en) * | 1992-10-15 | 1994-04-12 | Hoppmann Corporation | Cured unsaturated polyester-polyurethane hybrid highly filled resin foams |
| WO1995027752A1 (en) * | 1992-10-15 | 1995-10-19 | Ecomat, Inc. | Cured unsaturated polyester-polyurethane hybrid highly filled resin foams |
| IT1255887B (en) * | 1992-10-19 | 1995-11-17 | Pirelli | MOLDING PROCEDURE AND RELATED EQUIPMENT FOR THE PRODUCTION OF LOW DENSITY AND CLOSED ELASTOMERIC EXPANDED TOROID MANUFACTURES. |
| US5602188A (en) * | 1993-07-13 | 1997-02-11 | Suzuki Sogyo Co., Ltd. | Biodegradable resin foam and method and apparatus for producing same |
| JPH0794008A (en) * | 1993-09-24 | 1995-04-07 | Chiyatani Sangyo Kk | Flat lighting device |
| US5441680B1 (en) * | 1994-05-02 | 1997-04-29 | Milko G Guergov | Method and apparatus for injection molding |
| US6019918A (en) | 1997-01-17 | 2000-02-01 | Guergov; Milko G. | Gas assisted injection molding with controlled internal melt pressure |
| US5558824A (en) * | 1994-05-23 | 1996-09-24 | General Motors Corporation | Gas-assisted plastics injection molding with controlled melt flow and method of controlling melt flow |
| JP3814032B2 (en) * | 1996-11-01 | 2006-08-23 | 本田技研工業株式会社 | Molding |
| US5997797A (en) * | 1997-06-24 | 1999-12-07 | Jac Products, Inc. | Injection mold internal pressure equalization system and method |
| US6103154A (en) * | 1998-02-27 | 2000-08-15 | Reebok International Ltd. | Method of molding cross-linked foamed compositions |
| US5985188A (en) * | 1998-06-09 | 1999-11-16 | Aero Components, Inc. | Method for manufacturing a chair having separate moldable parts |
| JP2002001751A (en) * | 2000-06-16 | 2002-01-08 | Jsr Corp | Method for manufacturing foam and foam manufacturing device |
| KR20020038378A (en) * | 2000-11-17 | 2002-05-23 | 구자홍 | A Bubble Outbreak Device and a Method for Plastic |
| DE10329249A1 (en) * | 2003-06-24 | 2005-01-13 | Volkswagen Ag | Process for acquiring physical and/or chemical parameters during the production of a foamed component comprises positioning a pressure and/or temperature sensor in a volume of the component to be foamed and foaming during the process |
| CA2517995A1 (en) * | 2005-09-02 | 2007-03-02 | Chul B. Park | Apparatus and method for advanced structural foam molding |
| US8048347B2 (en) * | 2008-03-26 | 2011-11-01 | Delta Engineered Plastics | Method of manufacture of a foamed core class “A” article |
| JP5749065B2 (en) * | 2011-04-22 | 2015-07-15 | 住友重機械工業株式会社 | Injection molding machine and injection molding method |
| US11034813B2 (en) * | 2018-03-12 | 2021-06-15 | Nike, Inc. | Foam compositions and uses thereof |
| US11447615B2 (en) * | 2019-09-12 | 2022-09-20 | Nike, Inc. | Foam compositions and uses thereof |
Family Cites Families (16)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2829117A (en) * | 1952-07-31 | 1958-04-01 | Lonza Electric & Chem Works | Process for making closed cell cellular bodies |
| US3268635A (en) * | 1963-02-25 | 1966-08-23 | Robert A Kraus | Arrangement for forming foam plastic article |
| DE1704544A1 (en) * | 1967-08-12 | 1971-05-19 | Huels Chemische Werke Ag | Production of foamed injection molded parts |
| US3694529A (en) * | 1970-04-02 | 1972-09-26 | Allied Chem | Method for molding articles |
| US4096218A (en) * | 1973-07-19 | 1978-06-20 | Asahi-Dow Limited | Method of producing foamed thermoplastic resin articles having smooth and glossy surfaces free from swirl marks and hair cracks |
| US3960996A (en) * | 1973-09-21 | 1976-06-01 | Institut Po Metaloznanie I Technologia Na Metalite | Method of injection molding a thermoplastic article having a cellular core and integral skin involving use of reclaimed material |
| US4129635A (en) * | 1973-12-28 | 1978-12-12 | Asahi-Dow Limited | Method for producing foamed moldings from synthetic resin materials |
| US3988403A (en) * | 1974-07-09 | 1976-10-26 | Union Carbide Corporation | Process for producing molded structural foam article having a surface that reproducibly and faithfully replicates the surface of the mold |
| US4092385A (en) * | 1974-11-25 | 1978-05-30 | Institute Po Metaloznanie I Technologia Na Metalite | Method of producing molded parts with a smooth noncellular skin and a cellular core from foamable thermoplastic material |
| JPS54149774A (en) * | 1978-05-17 | 1979-11-24 | Asahi Chem Ind Co Ltd | Injection molding of thick-wall article |
| US4229395A (en) * | 1976-03-13 | 1980-10-21 | Asahi-Dow Limited | Method for injection molding thick-walled articles |
| JPS52112661A (en) * | 1976-03-18 | 1977-09-21 | Asahi Dow Ltd | Injection molding |
| US4133858A (en) * | 1977-12-14 | 1979-01-09 | Usm Corporation | Injection foam molding process |
| US4208368A (en) * | 1978-07-18 | 1980-06-17 | Gebruder Buhler Ag | Method and apparatus for injection molding foamed plastic articles using a pre-pressurized mold having fixed core members with controlled venting |
| US4255368A (en) * | 1979-07-18 | 1981-03-10 | Union Carbide Corporation | Structural foam molding process |
| JPS581659A (en) * | 1981-03-16 | 1983-01-07 | エリツヒ・ゴルデ | Child-proof screwing cover device |
-
1984
- 1984-09-14 JP JP59191499A patent/JPS6169421A/en active Granted
-
1985
- 1985-09-11 CA CA000490461A patent/CA1243459A/en not_active Expired
- 1985-09-13 GB GB08522684A patent/GB2164291B/en not_active Expired
-
1987
- 1987-03-18 US US07/027,487 patent/US4952365A/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| GB8522684D0 (en) | 1985-10-16 |
| JPS6169421A (en) | 1986-04-10 |
| JPH0533129B2 (en) | 1993-05-18 |
| GB2164291B (en) | 1988-08-03 |
| US4952365A (en) | 1990-08-28 |
| GB2164291A (en) | 1986-03-19 |
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