WO1992002577A1

WO1992002577A1 - Adhesive compounds

Info

Publication number: WO1992002577A1
Application number: PCT/US1991/005409
Authority: WO
Inventors: Yoshinori Igarashi; Yukihiro Ohjubo; Stephen O. Friend; Robert W. Hausslein; James J. Barber; Paul Nahass
Original assignee: Hyperion Catalysis International
Priority date: 1990-07-30
Filing date: 1991-07-30
Publication date: 1992-02-20
Also published as: AU8322991A

Abstract

Adhesive compositions including a matrix and carbon microfibers having diameters less than 1 micron. Also, compositions including a liquid and an amount of such carbon microfibers sufficient to increase the viscosity and/or yield value of the liquid relative to the values of these properties in the absence of the carbon microfibers.

Description

ADHESIVE COMPOUNDS

BACKGROUND OF THE INVENTION

The present invention concerns adhesive compounds, or more specifically it concerns adhesive compounds with superior adhesion characteristics against oily surfaces.

There is an oil film such as press oil on the surface of steel plate at the edging of an automobile hood or trunk. Therefore, the attaching of an inner panel or parts to such an oily surface requires the use of an adhesive with superior adhesion characteristics to the oily surface (called oil adhesiveness hereinafter).

Although various methods for improving oil adhesiveness have been proposed in the past, conventional oil adhesives had shortcomings associated with storage stability and coating applicability. There was also a problem of insufficient adhesion when the type of oil was changed.

Recently, oil adhesive agents with improved polymer compounds which contain epoxy resins, or with oil absorbing filler (refer to, for example, Patent Early Disclosure SHo59-124972, SHo60-137980, 62-533387, 61-155483, 63-186786) have been proposed. However, these oil adhesive agents required various additives such as viscosity adjusting fillers, dilutants, anti-flow agents, or anti-settling agents.

SUMMARY OF THE INVENTION

A purpose of the present invention is to offer adhesive compounds with superior oil adhesion

characteristics as well as with good storage stability and coating applicability. Accordingly, in one aspect, the invention features an adhesive composition that includes an adhesive matrix and an amount of carbon microfibers having diameters less than 1 micron

sufficient to increase the adhesion of the matrix to an oily surface compared to the adhesion of the matrix to the oily surface in the absence of the microfibers. The extent of adhesion improvement is determined by measuring lap shear and T-peel strength.

In preferred embodiments, the amount of

microfibers is between 0.1 and 30 weight parts per 100 weight parts of matrix, preferably between 0.5 and 10 weight parts, and more preferably between 0.75 and 3 weight parts. Preferred microfibers have diameters no greater than 0.1 micron. Even more preferred are carbon microfibers which are tubes having graphitic layers that are substantially parallel to the microfiber axis and diameters between 3.5 and 70 nanometers, inclusive.

These microfibers are preferably substantially free of a continuous thermal carbon overcoat and have a length to diameter ratio of at least 5.

Preferred matrix materials include thermoset and thermoplastic resins. Examples of preferred resins include, e.g., epoxy resins, polyurethane resins,

polysulfides, phenolic resins, thermoplastic elastomers (such as styrene-butadiene-styrene, styrene-isoprene- styrene, and styrene-ethylene-propylene-styrene triblock copolymers), polyvinylacetate, polyamides, polyvinyl alcohol, vinyl acetate-ethylene copolymer, ethylene-vinyl acrylate copolymer, ethylene-acrylic acid copolymer, polyvinyl acetal, acrylic resins, polycyanoacrylates, animal and fish glues, starch and other cellulosics, polychloroprene, amino resins, anaerobic adhesive

matrices, silicones, polyimides, high temperature

polyaromaticε, and polyethylene imine. Adhesives

prepared using a thermoplastic matrix may be in the form of hot melt adhesives.

One or more rubbers and/or colorants (including white pigments) may also be added to the adhesive

composition. In addition, the composition preferably has an electrical conductivity of at least 10^-8 S/cm which is retained even at elevated temperatures.

We have also discovered that carbon microfibers, when added to liquids, increase the viscosity and/or yield value of the liquid relative to the values of these parameters in the absence of the microfibers. The "yield value" is the shear stress at which a measurable shear rate is obtained. It may be measured by plotting the square root of the shear rate vs. the square root of the shear stress using data obtained from a viscometer, and then extrapolating the shear stress to zero shear rate. The value of the shear stress at zero shear rate is the yield value. In the absence of carbon microfibers, the yield value of the liquid is about zero. Preferably, yield values of at least 5 dynes/cm2 are obtained upon addition of 3 wt.% or less carbon microfibers. The compositions exhibit improved sag resistance compared to the liquids in the absence of the microfibers.

The composition may be in the form of an adhesive (including rubber-metal bonding agents), paint, or sealant. Suitable liquids include organic and aqueous polymer solutions, low molecular weight polymers and resins which are liquids at room temperature, and polymer latices.

The composition may also be in the form of a lubricating grease (e.g., where the liquid is an oil prior to microfiber addition) , ink, or a flame-retardant composition such as an anti-drip paint; the latter takes advantage of the ability of the carbon microfibers to increase the sag resistance of the composition.

The types of microfibers and amounts thereof useful as viscosity and yield value modifiers are set fo^th above. Like the adhesive compositions set forth above, these compositions may contain one or more

colorants and preferably have electrical conductivities of at least 10^-8 S/cm. Again, the electrical

conductivities are retained even at elevated

temperatures.

We have also discovered that adding carbon microfibers to solid polymeric matrices (i.e., matrices which are solid at room temperature) improves the creep resistance of the matrices. Preferred matrices are thermoplastics and elastomers. Preferred carbon

microfibers are described above. The composites may be in the form of a plastic panel.

The invention further features a) an adhesive that includes a matrix to which carbon microfibers and at least one colorant have been added, and b) an adhesive that includes a matrix and carbon microfibers in an amount sufficient to impart an electrical conductivity of at least 10^-8 S/cm.

Other features and advantages of the invention will be apparent from the following description of the preferred embodiments thereof, and from the claims.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Epoxy compounds, phenolic compounds,

polyurethane compounds, etc. (simply called compounds hereinafter), can be mentioned as a curing type (i.e., thermoset) compound used in the adhesive compounds covered by the present invention. Among these curing type resins, epoxy resin is the most preferable due to its superior adhesion to metal.

The compounds covered by the present invention can be prepared by various types of curing such as room-temperature curing, heat curing, and photo-curing

depending on the type of curing compound used, or the curing agent, curing accelerator, and/or bridging agent which are used as required. In addition, they can be prepared either in a single or binary liquid formula depending on the composition of the compound and the type of curing.

A detailed explanation will be made starting from the curing type compounds.

First, as epoxy type compounds which contain epoxy groups, condensation products between epichlorohydrin and polyhydroxy alcohol or polyhydroxy phenol such as

Bisphenol-F, Bisphenol-A, ethyleneglycol, butanediol, glycerine, or erythritol; condensation products between epichlorohydrin and Novolak resin such as phenol Novolak resin, cresol Novolak resin; cyclic hydrocarbon epoxy compounds; glycidylester type epoxy compounds;

glycidylamine type epoxy compounds; heterocyclic epoxy compounds; epoxy compounds derived from polyolefin polymers or co-polymers; epoxy compounds obtained from glycidylmethacrylate polymers or co-polymers; epoxy compounds obtained from glycerides of unsaturated fatty acids; polyalkylene-ether type epoxy compounds; and bromine or fluorine containing epoxy compounds can be listed as specific examples. Among these epoxy

compounds, compounds whose epoxy equivalent is below 6,000, or more preferably 90-6,000 are selected.

Reaction products between isocyanate compounds and active hydrogen compounds can be listed as specific examples of polyurethane based curing type compounds.

Here, as the isocyanate compounds, polyisocyanate prepolymers which contain more than two isocyanate radicals in the molecule can be listed. Various polyisocyanates including aliphatic, aromatic, and alicyclic

polyisocyanates can be used as a polyisocyanate that gives the pre-polymers. It is also possible to use these compounds together with pre-polymers. Polyol compounds and polyamine compounds can be mentioned as examples of active hydrogen compounds. Polyhydroxy alcohols such as ethyleneglycol, 1,4-butanediol, pentaerythritol, glycerine, ethyleneglycol, propyleneglycol, polyetherpolyols obtained by the

substitution polymerization between the aforementioned polyhydroxy alcohols and alkyleneoxides, polyesterpolyols obtained by the condensation reaction between polyhydroxy alcohols and polybasic acids, and polyesterpolyols obtained by other methods, acrylpolyols, castor oil polyol and its derivatives, and epoxypolyols can be listed as polyol compounds.

Various amines such as aliphatic polyamines and aromatic polyamines can be listed as polyamine compounds.

When a phenolic compound is used as the curing type compound, reaction products between phenol compounds and formaldehyde can be listed as specific examples. For example, monovalent or polyvalent phenols such as phenol, cresol, xylenol, para-t-butylphenol, resorcinol,

nonylphenol, hydroquinone, catechol, etc. can be listed.

Epoxy compounds are normally used together with a curing agent. The type of curing agent is selected depending on the intended type of curing.

As a curing agent used with the compounds covered by the present invention, aliphatic polyamines such as ethylenediamine, di-ethylenetriamine, tri-ethylenetetramine, tetra-ethylenepentamine, di-propylenediamine, di-ethylaminopropylamine,

hexamethylenediamine, menthenediamine, isochorondiamine, bis (4-amino-3-methyldicyclohexyl)methane, diamino-dicyclohexylmethane, bis (aminomethyl) cyclohexane, N-aminoethylpiperidine, 3,9-bis (3-aminopropyl)-2,4,8,10-tetraoxa-spiro(5,5)undecan, m-xylenediamine; aromatic polyamines such as methaphenylenediamine,

diaminodiphenylmethane, diamino-diphenylsulfone, diamino-diethyl-diphenylmethane, etc.; secondary or tertiary amines such as benzyldimethylamine, 2- (dimethylaminomethyl) phenol, 2,4,6,-tris (dimethylaminomethyl) phenol, tetramethylguanizine, N,N'-dimethylpiperidine, triethylenediamine, 1,8-diazabiscyclo(5,4,0) undecene, triethanolamine,

piperidine, pyrolysine, polyamidamine, boron-monoethylamine-fluoride complex, etc.; anhydride such as methylnasic anhydride, dodecenylsuccinic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic

anhydride, methylcondomethylene-tetrahydrophthalic anhydride, chlorend acid anhydride, ethyleneglycoltrimeritate anhydride ester, methyltetrahydrophthalic anhydride, methylhexahydrophthalic anhydride, etc.;

imidazole derivatives such as imidazole, 2-methylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 2-undecylimidazole, 2-heptadecylimidazole, 1-benzyl-2-methylimidazole, 1-cyanoethyl-2-methylimidazole, l-cyanoethyl-2- phenylimidazole, 1-cyanoethyl-2-ethyl-4-methylimidazole, 1-cyanoethyl-2-undecylimidazole, 1-cyanoethyl-2-methylimidazole-trimeritate, 1-cyanoethyl-2-phenylimidazole-trimeritate, 2, 4-diamino-6-{2'-methylimidazole-(1')}-ethyl-S-triazine, 2,4-diamino-6- {2'-undecylimidazole-(1')}-ethyl-S-triazine, 2,4-diamino-6-{2'-ethyl-4'- methylimidazole-(1')}-ethyl-S-triazine, 1-cyanoethyl-2-ethyl-4-methylimidazole-trimeritate, 1-cyanoethyl-2-undecylimidazole-trimeritate, 1-dodecyl-2- methyl-3-benzoimidazolium chloride, 1,3 benzyl-2-methylimidazolium chloride, etc.; dicyandiamide or its derivatives; organic acid dihydrazide such as adipic acid dihydrazide; urea derivatives such as 3-(p-chlorophenyl)-1,1-dimethylurea, 3-(3,4-dichlσrophenyl)-1,1-dimethylurea; polymercaptan type curing agents; methylol radical containing compounds such as phenol resins, urea resins, melamine resins; polyisocyanate, etc. can be listed. Particularly, when the compound covered by the present invention is prepared as a single-liquid formula, the use of a latent type curing agent such as dicyan-diamide type compound is desirable.

On the other hand, when the compound covered by the present invention is prepared by photo-curing, the use of aromatic diazonium salts, sulphonium salts, etc. which are known as ultraviolet curing catalysts is desirable.

The amount of these curing agents is normally determined so that the ratio between the amount of active hydrogens contained in these curing agents and the amount of epoxy radicals contained in the epoxy compounds become, for example, 1:0.8-1.2 (equivalent ratio).

Further, a curing accelerator can be used with the compounds covered by the present invention as required. For example, tetriary amines such as 2,4,6-tris (dimethylaminomethyl) phenol, 2- (dimethylaminomethyl), 1,8-diazobicyclo(5,4,0)undecene and its salts, adipic acid dihydrazide, isophthalic dihydrazide, sebacic acid dihydrazide,

dimethylbenzylamine, phenols, sulphines, imidazoles, etc. can be mentioned. The amount of these curing

accelerators is determined depending on the type of accelerator, the curing conditions, etc.

A carbon microfiber whose diameter (D) is within the range of 3.5-70 nm or more preferably 7-25 nm, and whose length (L) is greater than at least 5 times the diameter or L/D>5 is used as the carbon microfiber which is the second component of the compounds covered by the present invention. The desirable range for L/D is 10²-10⁴.

The carbon microfiber consists of an outer layer which is formed by many continuous annular layers made of uniformly aligned carbon atoms and an inner core. It is desirable for the microfiber to be practically in a cylindrical form in which the outer layer and the inner core are aligned concentric to the cylindrical center of the microfiber. Further, it is desirable for the inner core to be hollow, or for the inner core to contain carbon atoms whose alignment is not as uniform as the alignment of the outer layer, for the uniformly aligned carbon to be graphite, and for the inner core to have a diameter greater than about 2 nm. The individual microfibers may form intertwined flocks with each other.

For example, such carbon microfiber can be prepared by the following procedures. Suitable metalcontaining particles such as iron, cobalt, or nickel particles carried on alumina, and suitable carbon

containing organic material such as carbon monoxide or a hydrocarbon are contacted at 500-1200°C under a suitable pressure (for example, 0.1-10 atm.) for a period of 10 seconds to 180 minutes. In this case, it is desirable for the dry weight ratio between the carbon containing organic material and the metal containing particles to be at least 100/1.

Examples of suitable carbon microfibers and methods for preparing them are described in the following patents and patent applications, all of which are

assigned to the same assignee as the present application and are hereby incorporated by reference: Tennent, U.S. Pat. No. 4,663,230; Tennent et al., U.S.S.N. 871,676 entitled "Novel Carbon Fibrils, Method for Producing Same and Compositions Containing Same" filed June 6, 1986; Snyder et al., U.S.S.N. 494,894 entitled "Carbon Fibrils" filed March 13, 1990; Mandeville et al., U.S.S.N. 285,817 entitled "Fibrils" filed December 16, 1988; and Moy et al., U.S.S.N. 487,543 entitled "Fibril Aggregates and Method for Making Same" filed September 28, 1989. The amount of carbon microfiber used against 100 weight parts of the aforementioned curing type compound is in the range of 0.1-30 weight parts, or more

preferably in the range of 0.5-10 weight parts, or most preferably in the range of 0.75-3 weight parts.

The method for uniformly suspending the carbon microfibers in the curing type compound and other

components is not particularly restricted, and a normal method such as a three-roll kneading device can be used. Incidentally, the carbon microfiber can be surfaced- treated with a coupling agent, ultraviolet, plasma, etc. (e.g., as described in McCarthy et al., U.S.S.N. 351.967 entitled "Surface Treatment of Carbon Microfibers" filed May 15, 1989 and assigned to the same assignee as the present application and which is hereby incorporated by reference) prior to use as long as it is to such a degree that it does not adversely affect the oil adhesion effects.

The compounds covered by the present invention can be mixed with rubber as required. The rubber used for this purpose may be butadiene rubber, styrene-butadiene rubber, acrylonitrile-butadiene rubber, ethylene-propylene rubber, isoprene rubber, chloroprene rubber, butylrubber, acryl rubber, etc. Active radicals such as carboxyl radical, epoxy radical, or hydroxy radical may be introduced into these rubbers as required. The method for mixing the rubber is not particularly restricted.

However, preliminary reaction with a curing type compound such as an epoxy compound may be carried out when a rubber with an active radical is used. In "'Edition, the form of the aforementioned rubber is also not

particularly restricted. The addition of rubber into the compound gives resilience to the cured product, and also improves the adhesion characteristics. Further, various additives such a elastomer, pigment, leveling agent, tackiness imparting agent, anti-foam, heat stabilizer, photo stabilizer, fillers, etc. can be added as required to the compounds covered by the present invention. In addition, other electrically conductive or oil absorbing fillers such as carbon black, graphite powder, or carbon fibers can be added together with the carbon microfibers.

Application Example 1

100 weight parts of bisphenol A type epoxy compound with 189 epoxy equivalent (Epicoat 828; Yuka Shell Epoxy (KK), manufacturer, 8 weight parts of dicyandiamide, 50 weight parts of calcium carbonate (Nitto Funka (KK) manufacturer, SS30) , 3 weight parts of carbon microfibers according to the above-mentioned Tennent patent and patent applications (Hyperion Catalysis Inc.

manufacturer), and 1 weight part of N,N-dimethylbenzylamine (DMBA; Wako Junyaku (KK)

manufacturer), were mixed by using a three-roll kneader at 20°C for a period of 30 minutes in order to obtain the compound.

Application Examples 2-4 and Reference Examples 1-5

Various adhesive compounds were prepared using the same procedures as Application Example l by varying the types and mixing ratios of the type of curing compound

(main component and curing agent, carbon microfibers, and additives as shown in Table 1. The following is the list of agents shown in the Table:

• Angamine 1618 (aricyclic polyamine) : A.C.I Japan

Limited manufacturer

• R-1309: ACR Co. manufacturer, acryloritrile-butadiene rubber 30% containing epoxy resin

• Silica powder: AEROSIL-200, Japan Aerosil (KK) manufacturer

• Carbon black: Asahi Carbon manufacturer, HS-500 • Carbon fiber: Hicarbon A-6000, diameter 7μm, length 0.5 mm

Incidentally, the curing conditions for each compound are also listed in Table 1.

Evaluation of the Adhesive Compounds

The following evaluation tests were carried out on each compound, and obtained results are shown in Table 2.

(1) Dispersability

The dispersion characteristics (O: good, X: poor) were evaluated by using a three-roll kneader.

(2) Fluidity

Existence of fluidity at room temperature.

(3) Existence of stringiness

Visual observation of stringiness v/hen the compound is scooped with a wooden spatula.

(4) Form stability during the application

Stability when the compound is coated on a vertical surface (O: good, X: drips)

(5) Pressability

Ease of pressing when the compound is placed between objects and pressed. (0: good, X: poor)

(6) Settlability of fillers

Visual observation after leaving still for 1 month at 20°C. (However, compounds were prepared without catalyst or additives.)

(7) Oily surface adhesiveness

Adhesion objects were prepared by soaking two steel plates with 1.6x25x100 mm and 0.8×25×200 mm

dimensions in rust protecting oil (RL-55; Idemitsu Kosan manufacturer), and then leaving them standing vertically over night. Compounds were coated on these objects, and then two plates were immediately pressed together. The plates were clamped and cured at 180°C for a period of 30 minutes, or 140°C for a period of 60 minutes. The thickness of the compound was adjusted to 0.25 mm. Subsequently, the tensile breaking strength and T-type peeling strength were measured. Incidentally, the tensile speed was 5 mm/min for the measurement of the tensile breaking strength, and 50 mm/min for the

measurement of the T-type peeling strength.

For the purpose of comparison, steel plates with cleaned surface were adhered in the same manner as above, and the tensile breaking strength and T-type peeling strength were measured. The results are shown in Table 2.

As is clear from the results shown in Table 2, the compounds covered by the present invention give superior oily surface adhesion characteristics with a relatively small amount of carbon microfiber addition as compared to the amount of carbon black or carbon fiber conventionally used as oil absorbing filler. Further, the addition of carbon microfiber resulted in the resilience and

prevention of settling of fillers.

Thus, the compounds covered by the present invention have superior oily surface adhesiveness, storage stability, and applicability, and they are, for example, extremely suitable for the adhesion of edging parts of automobiles which contain an oily surface.

Further, since the compounds covered by the present invention contain dispersed carbon microfibers, they have an advantage of improved electric conductivity.

Application Example No. 5

1.4 parts by weight of carbon microfibers as described above were combined with epoxy resin and the sag resistance of the resulting composition evaluated using an accepted test method in which a 0.375 inch wide bead of adhesive was laid down on an aluminum panel. The panel was then placed in an oven at 320°F for two hours to effect cure, oriented such that the panel was vertical and the bead was horizontal. After sample was withdrawn from the oven, no sag was observed in the bead; i.e., the bead had not changed shape or increased in width on the panel. Separate tests of the adhesive strength showed no deterioration relative to a sample without carbon

microfibers. In addition, the sample had good electrical conductivity (110 kohms from bead to panel).

Application Example No. 6

This example demonstrates the improvement in lap shear strength of adhesives upon addition of carbon microfibers.

Araldite AW-105 (an epoxy resin commercially available from Ciba-Geigy) plus an equal volume of HV-953 curing agent (also available from Ciba-Geigy) was combined with 1.4 parts carbon microfibers (as described above) per hundred parts epoxy resin, and cured at 100°C for 10 minutes. It was then applied to (a) the clean surface of a cold rolled steel substrate (substrate thickness = 0.063 in.) and (b) to the same surface coated with WD-40 to make it oily. The bond thickness of the epoxy adhesive was 0.012 in. The lap shear strength of the adhesive bond was then measured and compared to that of the epoxy resin alone applied to identical surfaces. The results are shown below.

WITHOUT MICROFIBERS WITH MICROFIBERS

Clean Surface 2290 PSI 2110 PSI

Oily Surface 1500 PSI 1980 PSI

Application Example No. 6

This example also demonstrates the improvement in lap shear strength of adhesives upon addition of carbon microfibers.

Epon 828 (an epoxy resin commercially available from Shell) plus an equal volume of Epon V-40 curing agent (also available from Shell) was combined with 1.34 parts carbon microfibers (as described above) per hundred parts epoxy resin, and cured at 25 °C overnight, then at 150°C for 1 hour. It was then applied to (a) the clean surface of an aluminum substrate (substrate thickness = 0.125 in.) and (b) to the same surface coated with WD-40 to make it oily. The bond thickness of the epoxy

adhesive was 0.010 in. The lap shear strength of the adhesive bond was then measured and compared to that of the epoxy resin alone applied to identical surfaces. The results are shown below.

WITHOUT MICROFIBERS WITH

MICROFIBERS

Clean Surface 3160 PSI 3010 PSI Oily Surface 1580 PSI 2320 PSI

Application Example No. 7

This example describes the ability of carbon microfibers compared to fumed silica to modify the viscosity and impart yield values to liquids.

Dispersions of carbon microfibers and three types of commercially available fumed silica were prepared in the following media:

Medium Polarity Density

Viscosity

DI Water very high 1.0 g/cc 1.0 cp

Ethyl Acetate high 0.89 g/cc 0.4 cp

DOP¹ moderate 0. ,98 g/cc 70 cp

Toluene low 0.87 g/cc 0.7 cp

¹ DOP is dioctyl phthalate.

The three types of fumed silica (all available from Degussa) were Aerosil 200 (hydrophilic), Aerosil COK 84 (hydrophilic with 15% alumina added), and Aerosil R202 (hydrophobic). In the case of DOP and toluene, only carbon microfiber and Aerosil 200-containing dispersions were prepared.

Each dispersion was prepared by adding the thickening agent (carbon microfibers or fumed silica) to

200 ml of the liquid medium with hand stirring. The mix was then poured into a Waring Blender with a rotor/stator attachment. The blender was run on high speed for 2 minutes to provide sufficient dispersion of thickening agent at the concentrations used. The blender was shut off and restarted if cavitation occurred.

For each medium, 2, 4, 6, 10, and 16 grams of thickening agent were added to 200 ml of liquid medium, with the goal of producing dispersions of 1, 2, 3, 5, and

8 parts thickening agent per hundred parts medium.

Viscosities were measured on a Brookfield

Viscometer 1-2 hours after blending to allow the mixture to cool. Viscosity readings were taken at 5, 10, 20, 50, and 100 rpm using the LV-1, LV-2 , LV-3, and helipath spindles. Viscosity was reported at 50 rpm for most runs, corresponding to a shear rate of about 10 sec^-1.

The following table shows the viscosity results obtained at 50 rpm.

Microfibers (wt.%1

0.0 1.0 2.0

Liquid

DOP 70 1000 4000

Toluene 1 200 900 Water 1 200 600

Ethyl Acetate 0.3 30 200

Viscosity data showed that the thickening effect of the carbon microfibers was independent of the

particular liquid medium. This was not true of fumed silica. Moreover, the carbon microfibers thickened the liquids to a greater extend at lower loadings compared to the fumed silicas. The amount of carbon microfibers required to reach moderate viscosity levels was 37 - 50% less than that of the fumed silicas. Moreover, the carbon microfiber-containing slurries experienced no breakdown in viscosity even after extended exposure to shear (e.g, even after mixing for 5 minutes in the blender).

The yield values of the various thickened media were obtained by plotting the square root of the shear rate vs. the square root of the shear stress using data obtained from the viscometer, and extrapolating the stress value to zero shear rate to determine the yield value. The data demonstrated that the carbon microfibers raised the yield value more efficiently at lower

concentrations than the fumed silicas.

The carbon microfibers were also easier to handle than the fumed silicas because they were more easily wet by the media, had a lower initial viscosity (thereby facilitating pouring and cleaning), and created less of a dusting problem. In turn, this lead to enhanced accuracy in formulation and ease of processing.

Application Example No. 8

This example illustrates the ability of carbon microfibers to increase viscosity.

Mixtures of carbon microfibers (as described above) and EPON 828 epoxy resin were prepared at 25°C using a three-roll mill dispersion. The viscosities of the mixtures were then measured at 25°C using a

Brookfield helipath viscometer. The data are summarized below. Viscosity (poise)

Fibril Concentration (phr) 0.5 rpm 5.0 rpm

0.0 130 130

1.5 11,000 2,400

2.5 80,000 16,500

Other embodiments are within the following claims.

Claims

1. An adhesive composition comprising an adhesive matrix and an amount of carbon microfibers having

diameters less than 1 micron sufficient to increase the adhesion of said matrix to an oily surface compared to the adhesion of said matrix to said oily surface in the absence of said microfibers.

2. The composition of claim 1 wherein the amount of said microfibers is between 0.1 and 30 weight parts per 100 weight parts of said matrix.

3. The composition of claim 2 wherein the amount of said microfibers is between 0.5 and 10 weight parts per 100 weight parts of said matrix.

4. The composition of claim 2 wherein the amount of said microfibers is between 0.75 and 3 weight parts per 100 weight parts of said matrix.

5. The composition of claim 1 wherein the diameter of said microfibers is no greater than 0.1 micron.

6. The composition of claim 1 wherein said microfibers comprise tubes having graphitic layers that are substantially parallel to the microfiber axis and diameters between 3.5 and 70 nanometers, inclusive.

7. The composition of claim 6 wherein said microfibers are substantially free of a continuous thermal carbon overcoat.

8. The composition of claim 1 wherein the length to diameter ratio of said microfibers is at least 5.

9. The composition of claim 1 wherein said matrix is a thermoset resin.

10. The composition of claim 1 wherein said matrix is a thermoplastic resin.

11. The composition of claim 1 wherein said composition further comprises at least one rubber.

12. The composition of claim 1 wherein said composition further comprises at least one colorant.

13. The composition of claim 1 wherein said composition has an electrical conductivity of at least 10^-8 S/cm.

14. A composition comprising a liquid and an amount of carbon microfibers having diameters less than 1 micron sufficient to increase the viscosity of said liquid compared to the viscosity said liquid in the absence of said microfibers.

15. A composition comprising a liquid and an amount of carbon microfibers having diameters less than 1 micron sufficient to increase the yield value of said liquid compared to the yield value of said liquid in the absence of said microfibers.

16. The composition of claim 14 or 15 wherein said composition is in the form of an adhesive.

17. The composition of claim 14 or 15 wherein said composition is in the form of a paint.

18. The composition of claim 14 or 15 wherein said composition is in the form of a sealant.

19. The composition of claim 14 or 15 wherein said composition is in the form of a lubricating grease.

20. The composition of claim 14 or 15 wherein said composition is in the form of a flame-retardant composition.

21. The composition of claim 14 or 15 wherein said composition is in the form of an ink.

22. The composition of claim 14 or 15 wherein the amount of said microfibers is between 0.1 and 30 weight parts per 100 weight parts of said matrix.

23. The composition of claim 22 wherein the amount of said microfibers is between 0.5 and 10 weight parts per 100 weight parts of said matrix.

24. The composition of claim 22 wherein the amount of said microfibers is between 0.75 and 3 weight parts per 100 weight parts of said matrix.

25. The composition of claim 14 or 15 wherein the diameter of said microfibers is no greater than 0.1 micron.

26. The composition of claim 14 or 15 wherein said microfibers comprise tubes having graphitic layers that are substantially parallel to the microfiber axis and diameters between 3.5 and 70 nanometers, inclusive.

27. The composition of claim 26 wherein said microfibers are substantially free of a continuous thermal carbon overcoat.

28. The composition of claim 14 or 15 wherein the length to diameter ratio of said microfibers is at least 5.

29. The composition of claim 15 wherein said yield value of said composition is increased to at least 5 dynes/cm² upon addition of 3 wt.% or less of said carbon microfibers.

30. The composition of claim 14 or 15 wherein said composition further comprises at least one colorant.

31. The composition of claim 14 or 15 wherein said composition has an electrical conductivity of at least 10^-8 S/cm.

32. The composition of claim 14 or 15 wherein said liquid comprises a polymeric latex.

33. A composition comprising a solid polymeric matrix and an amount of carbon microfibers having

diameters less than 1 micron sufficient to increase the creep resistance of said matrix compared to the creep resistance of said matrix in the absence of said

microfibers.

34. The composition of claim 33 wherein said matrix is a thermoplastic.

35. The composition of claim 33 wherein said matrix is an elastomer.

36. The composition of claim 33 wherein the amount of said microfibers is between 0.1 and 30 weight parts per 100 voight parts of said matrix.

37. The composition of claim 36 wherein the amount of said microfibers is between 0.5 and 10 weight parts per 100 weight parts of said matrix.

38. The composition of claim 36 wherein the amount of said microfibers is between 0.75 and 3 weight parts per 100 weight parts of said matrix.

39. The composition of claim 33 wherein the diameter of said microfibers is no greater than 0.1 micron.

40. The composition of claim 33 wherein said microfibers comprise tubes having graphitic layers that are substantially parallel to the microfiber axis and diameters between 3.5 and 70 nanometers, inclusive.

41. T he composition of claim 40 wherein said microfibers are substantially free of a continuous thermal carbon overcoat.

42. The composition of claim 33 wherein the length to diameter ratio of said microfibers is at least 5.

43. The composition of claim 33 wherein said composition is in the form of a plastic panel.

44. An adhesive composition comprising a matrix to which carbon microfibers having diameters less than 1 micron and at least one colorant have been added.

45. An adhesive composition comprising a matrix to which carbon microfibers having diameters less than 1 micron have been added in an amount sufficient to impart an electrical conductivity of at least 10^-8 S/cm.