CA1159180A - Highly filled thermally conductive elastomers ii and iii - Google Patents

Abstract

A dispensable precursor composition for highly filled thermally conductive elastomers of improved thermal stability is provided. The composition comprises an intimate admixture of an olefinically unsaturated crosslinkable polysiloxane and a silyl halide functional polysiloxane.

Description

~ 1S'31~1 HIGHLY FILLED THERMALI,Y CONDUCTIVE ELASTOMERS
II & III
The present invention relates -to thermally conductive elastomers.
Elastomers for use in rotary regenerator assemblies are known, e.g., see U.S. Patent 4,148,354 These assemblies comprise ceramic core surrounded by steel ring gear with elastomer kherebetween. The elastomer accommodates differen-tial rates of expansion during assembly and during operation.
Materials proposed in U.S. Patent 4,148,354, while satisfactory, do have certain deficiencies. For example, the materials may not function optimally under certain conditions for as long periods as might be desired.
A particularly acute problem is that these materials tend to degrade during extended high temperature service.
Others have proposed certain filled organosiloxane and other organic polymers for use in making articles that resist degradation when exposed to extreme conditions.
See, for example, U.S. Patents 3,098,836; 3,255,152; 3,274,145;
20 3,506,607; 3,676,420; 3,746,662; 3,791,998; 3,865,784;
3,867,315; 3,911,045; 4,025,485; and 4,069,083.
These patents show that desirable properties may result by loading certain organic polymers with inorganic particulate.
It has been discovered in accordance with this invention that besides enhancing certain physical properties as well as potentially reducing material costs, certain particulates also offer improved thermal stability. Improved thermal stability is insufficient by itself, however, to provide a more acceptable material for applications as ring gear assemblies. Rather, such improved thermal stability, when provided by increased particulate loading, is accompanied typically by higher initial viscosities and shorter working times. The higher initial viscosities and shorter working times can make such materials undesirable for high volume production use.
This invention relates to highly filled, thermally conductive elastomers made from ingredients that include organopolysiloxanes and inorganic particulate. ~y admixing 1 15l318~
these and other essentiaL ingredients in certain ways, there is provision of elastomer precursor compositions that readily fill difflcult to fill mold cavities and yet, when cured, exhibit such physical and thermal properties as to make them admirably suited for high temperature, mechanical service.
In elastomer precursor compositions of this inven-tion, crosslinking occurs between such functional groups as vinyl of one organopolysiloxane and such functional groups as silyl hydride ( _SH) of another organopolysiloxane in the presence of catalyst and certain other ingredients.
Among these other ingredients are thermally conductive particulates that contribute ~o high temperature stability and improved physical properties of the elastomer.
Certain viscosity modifiers serve to facilitate incorporation of high particulate levels into the elastomer precursors while at the same time permitting desired initial viscosities and working times. By selection and control of particulate size and amount as well as viscosity modifier type and amount, there is a net increase in thermal and physical properties. At the same time there is provision thereby of elastomer pEecUrsOrs with such initial viscosities and working ~5, ,~d t1mes as to permlt ready incorporation into difficult to fill mold cavities.
Surprisingly, even though the viscosity modifier is li~uid and may be expected to be non-reactive, the amount of metallic particulate, for example, that it allows to be effectively incorporated gives elastomers which show even less high temperature weight loss than -the same elastomers without any me-tallic particulate and viscosity modifier. Thus, the metal and liquid viscosity difier combination in the elastomer acts, with respect to thermal aging, as if it were a more stable filled, crosslinked polymer than the filled, crosslinked organo-polysiloxane polymer without such combination. With spherical or irregular shaped particles (e.g. L/D ' 8) as the powders of this invention, the above described benefit is particularly notable.
The elastomers of this invention are made by intimately admixing a polymer containing base component (Component I) and an oligomer containing component (Component II). With admixture, the polymer and oligomer in the Components I and II crosslink at room temperature (or elevated temperature r if desired) to provide (with the other ingredients in the components) thermally conductive elastomers. The ingredients of Components I and II prefera-

2~ bly are as follows:
A. Component I. Component I comprises 100parts by weight of a crosslinkable polymer (Polymer I).
Polymer I is of a formula corresponding to ,Rb Ra - (SiO)m Si(Ra)3 Rb wherein at least most of the Ra's and Rb's are independently selected from (A) any one or more of 1. saturated hydro-carbyl groups having from about 1-10 carbon atoms or 2. saturated hydrocarbyloxy groups having from 1 to about 10 carbon atoms that are alkyl or aryl or alkyl and aryl carbons and (B) either or both allyl or vinyl which may be substituted by halo or saturated hydrocarbyl or hydro-carbyloxy groups between about 1-8 carbon atoms that are ,~
.~

1 15~8~) alkyl or aryl or aryl and alkyl carbon atoms and wherein there are up to two substituents oE these substituents per vinyl or allyl Up to about 25% (preferably up to lO~), however, of the total nul~er of Rb's may correspond to the formula:
Rd Rc - (SiO)n - Si(Rc)3 I(a) wherein at least most of the Rc's and Rd's are selected from (A) and (B) above but up to about 10% (preferably 5~) of the total number of Rd's may contain additional siloxane units such as those of formula I(a) above with substituents selected from (A) and (B) above or still additional siloxane units. Provided 7 however, there is ll) an average number of siloxane units (i.e. m plus all n's plus the total number of end groups) per polymer molecule between about 100 and 300 (preferably 150-250) and (2) an average of above about 1.5 but lower than 6 (preferably about 1.5-2.5) crosslinking sites selected from the vinyl, allyl or vinyl and allyl groups per polymer molecule. Preferably, m averages between about 170-200 and n is below 50. More preferably n is below 25 and less than 10% of the Rb's are siloxane units. Also, preferably the vinyl or allyl groups are on end siloxane groups e.g., the vinyl or allyl groups in the position of Ra or Rc. Examples of the saturated hydrocarbyl and the saturated hydrocarbyl of the saturated hydrocarbyloxy include: alkyl, aryl, alkaryl, aralkyl such as straight or branched alkyl, straight or branched alkyl substituted phenyl, phenyl, phenyl substituted straight or branched alkyl including for example methyl, ethyl, butyl, methyl-phenyl, phenylethyl etc., any of which may be substituted by normally unreactive substituents such as halo (e.g.
chloro) or interrupted by oxy l-O-). Examples of commer-cially available polymers for Polymer I are Silastic*
J, E & L RTV silicone elastomers available from Dow Corning Corporation.

* - Trademark ~ t~

Especially preferred polymers for Polymer I
of Component I correspond mostly by weight (e.g. 90%
or higher) to the formula:
R R
A - (SiO)n - Si - A I' R R
wherein each R is independently a monovalent aliphatic or aromatic group or combination thereof up to about 8 carbons and preferably is R'(O)X wherein x is zero or 1, and R' is independently phenyl or alkyl of up to about 6 carbons (more preferably 3) or alkylphenyl (or phenylalkyl) having up to about 6 alkyl carbons (more preferably up to 3 alkyl carbons; A is vinyl; and n averages between 150-200.
Component I also contains silica particulate intimately admixed with the-Polymer I. The silica prefer-ably is a combination of silicas comprising ground and fumed silicas. Preferably the weight ratio of silica to Polymer I is between about 0.3 to 2.5:1, more preferably between about 0.9:1 to 1:0.9.
The silica is-desirably of small particle size so as to not only provide reinforcement bllt also impart thixotropic behavior to the compositions. Preferred Polymer I and silica admixtures have viscosities between about 500-1500 poises at 25C.
As mentioned, it is preferred to have a combination of silicas comprising ground and fumed silica. Normally, the weight of ground silica such as those having an average (i.e. mean) diameter between about 0.1-15 (more preferably 0.5-10) microns will desirably far exceed the weight of fumed silica e.g. a weight ratio of 2:1 or more as preferably between about 5:1 to 19:1. The fumed silica (at an average (i.e. mean) particle diameter of between about 0.005-0.015 microns, more preferably between about 0.010 microns and 0.014 microns) provides reinforcement to the elastomer. The ground silica imparts better flow properties to the uncured elastomer composition. The balance of these two silica types then is of importance -~r ~,~

3 l ~

for control of desired elastomer precursor and cured elastomer properties.
Other inorganic particles that may be added include, for example, glass fibersJ if additional rein-forcement (especially lmproved hot tear resistance) ofthe elastomer is desired. Chopped fiber in lengths of between about 0.34 and 1.25 centimeters especially between about 0.5-1 centimeters are preferred. Improved adhesion of glass fiber in the cured thermally conductive elastomer can be accomplished through coating of the glass fibers with primers which are commercially available. For example, Dow Corning Primer Q 3-6061 (e.g. at 0.15 g primer to 1 kg glass fibers) diluted with methylene chloride may be used to pack and coat the glass fibers. Other fibers such as carbon, graphite, cellulose and metal may be employed together with or in place of the glass fibers.
In addition, still other ingredients such as zinc oxide, lamp black and the like may be included in component I to improve heat stability and the like functions.
Preferably, component I contains a metal catalyst (such as platinum) to reduce cure time and temperature. (See, for example, U.S. Patent 4,076,684, col. 6, lines 49-68, col. 7, lines 1-2, and the paragraph bridging cols.
7 and 8). A preferred catalyst is a platinum complexed silicone oligomer. The oligomer may be of the structure of Polymer I but wherein m averages less than 50 e.g.
15 or less. Additionally it is preferred to use a modifier with these systems that slows increase in viscosity due to crosslinking e.g. snap time modifiers available from Dow Corning Corporation, benzotriazole, etc. Such modifiers are commercially available and are preferably vinyl sili-cones of up to 15 repeating siloxane units with desirably up to about 5 vinyl groups. These vinyl silicones serve to slow down the crosslinking reaction thereby slowing increase in viscosity. Other modifiers available for this purpose include quinoline, triphenyl phosphite, dimethyl sulfoxide, perchloroethylene, etc. known to those in the art. Other catalyst may also be used, e.g.

1 15~31~t) peroxides, alkoxides and the like as well as modifiers as is well known in the art.
Essential to elastomers of this invention are conductive powders which improve t:hermal properties of the elastomer. Among the conductive powders are metal powders of silver, gold, silicon, aluminum, nickel, cadmium, palladium, molybdenum, magnesium, chromium, zinc, rhodium, tungsten and -the ]ike having particle sizes (i.e. mean diameter) between about 40-300 microns. Certain transition metals such as copper are less desirable for high tempera-ture (e.g. 260C) environments of the cured articles during long exposures (e.g. 500 hours) at such temperatures.
In general, however, the conductive powders have a con-ductivity above that of silica and more preferably above about 0.5 cal cm (C cm2 sec) 1 at 68F.
It is found that even better properties are obtained with powders that are alloys, especially single phase alloys, especially in compositions having highest desired conductive powder loading. Examples of these alloys are alloys of at least about 25% by weight first row transition metals including, for example, tungsten-copper, nickel-aluminum, nickel-copper, aluminum-silicon, iron-magnesium-silicon, brasses, bronzes and the like alloys. Commercially available preferred alloys include, for example, Monel, Inconel. The average (i.e., mean) paxticle diameters range is preferably 40-300 microns for such alloys.
The conductive powder is normally at a weight ratio to Polymer I of between about 0.3 to 2.5:1 (prefer-ably about 0.5:1 to 2.0:1) powder to polymer.
The conductive carbon powders preferably comprisegraphite powders such as synthetic graphites, flake graph-ites and crystalline graphites or carbon blacks such as furnace blacks and acetylene blacks.

-I I ~ ~3 L

Artiflci21 graphites ~seful herein include those preferably havlns largest partlcle dimensions ~f between about ; 5-300 microns. These graphites a~e commercially available from sources such as Pocco Graphite, Inc., a division of Union 5 Oil Company, Joseph Dixon Crusible Company, ètc. These artificial graphites comprise hexagonal sheets produced by graphitizing coke or slmilar carbons in electric furnaces at above about 3000C. These graphites have up tc about 99.9% or more graphitic carbons;
Flake graphites have a distinct flaky appearance and preferably for use herein have largest particle dimensions between about 5-300 microns. Crystalline gra~hites suitable herein preferably contain at least about 97% by weight graphitic carbon.
To obtain preferred particle size of between about 5-300 microns in largest particle dimension, the graphite powders may be ground in ball mills.
Smaller particle size graphites ~o.g. synthetic graphite having largest particle dimension less than about 15 20 microns) exhibit ~in elastomer precursor compo~itions of this invehtion) shorter working times and higher thermal conductivities in the cured elastomer as compared to larger particle size graphites in the same circumstances. On the other hand, larger size graphites (e.g., synthetic graphite 25 having largest particle dimensions above abo~t 35 microns) exhibit respectively longer working times an2 lower thermal conductivities. ~lends of larger and smaller graphites, however, permit optimization of these properties.
~lternatively, when longer working times ar~ desired, the 30 elastomer precursors may be formulated to contain, for instance, less than 50 parts by weight s~aller graphite particles per 100 DartS of combined weight of the polysiloxane polymers, i.e., of combined weight of Polymer I and Oligomer I
(which is hereinafter more particularly described).
35 Similarly, inclusion of, for instance, more t~an 50 parts by weight of the lar~er graphite particles (e.g. particles with largest particle dimension above about 35 microns) per 100 parts by weight of combined weight of Polymer I and Oligomer I, leads to longer working times.

O~ the above mentloned graphites, crystalllne graphlte o~fers cured elastomers with generally highest thermal conduetivity.
The carbor bl~cks suitable herein preferably comprise those having largest particle dimenslons below one micron and in the colloidal partlcle size range or below. For example, furnace blacks su-h as N-650 tlargest partlcle dlmension averaging about 0.05 micron), SL-90 (largest p~rticle dimension averagin~ about 0.1 micronj and N-339 (largest 10 particle dimension averaging about 0.05 microns) that are available from ~shland Chemicals Co. yield desirably processable precursor compositions when compounded at about 50 I parts by weight per 100 parts by weight of the polysiloxane Il polymers, i.e., com~ined weight of Polymer I and Oligomer I.
I 15 As with the graphites, smaller particle sizes provide elastomer precursor compositions with shorter working times and vice versa. Additionally, higher structure carbon blacks also shorter working times. Normally, however, desirable working times may ~e maintained by using less than 100 parts 20 by weight of the black per 100 parts by weight of the combined weight of Polymer I and Oligomer I or by increasing the viscosity modifier to greater than 10% by weight of the weight of the precursor co~posltion absent the carbon black.
! The condu~ive carbon particulate may be used at any 25 desired level but ~s normally at a weight ratio to Polymer I
of between about ~:10 to 2.5:1 (preferably about 0.3:1 to 2.0:1) powder to Po~ymer I.
Boron refractory conductive powders also improve 30 thermal properties of the elastomer. These powders preferably are of spherical or irregular shape as distinguished from fibrous with L/D greater than 3/1. Boron nitride constitutes a preferred boronrefractory powder. Another boron refractory 35 is boron carbide. Preferred boron nitride particles have an average largest dinension between about 10-350 microns, more preferably 10-250 ~icrons.

I . } J 1 5'3 3 ~

Boron n;-ride particularly useful in this invention comprises ~lat c~ramic platelets similar to graphite. The powder may be ob~ained by a number of procedures (e,g., see ~Special Ceramics, proceedings of a symposium held at the 8ritish Ceramic R~search Association, Editor P. Popper, 1960).
A number of co~mercial sources are available for boron nitride, includirg, for example, Carbon Products Division of IJnion Carbide Corporation.
The boron refractory powders may be used with other powders such as graphites at any weight ratio, preferably between about 1:~5:1, especially with particles of about the same size. The boron nitride aids thermal conductivity; the graphite aids pro~essability~
The Boron c~nd~ctive powder is normally at a weight ratio to Polymer I of between about 0:3 to 2.5:1 tpreferably about 0;5:1 to 2.~:1) powder to polymer.
Essenti~1 to the addition of high levels of conductive powd~rs is inclusion of cert~in amounts of viscosity modific~rs to control the initial apparent viscosity of these compositions. A careful balance between particulate including condu~tive ~owder and viscositv modifier is importar.t to achieve high thermal conductivit~l without loss of viscosity modifLer and conseauent decrease in thermal stability and physical properties of the cured compounds~ The viscosity modifier is normally at a weight ratio between about 1:20 to 1:~ (more preferably 1:10-1:2) viscosity modifier to the inorganic p~rticulates of silica and ccnductive powder depending upon c~rtain other features as amount and particle size of conductive powder and other particulates as well as viscosity modifier character.
The viscosity modifier prefera~ly comprises a silicone oil having a viscosity of between about 1000-1,000,000 centistokes at 25C, more preferably 5000-1,000,000 centistokes at 25C. Pref~rred viscosity modifiers include those having a formula whlc~ corresponds to formula I above for Polymer I except that the ~inyl group is 11.
replaced ~y yroups simllar to the others on -the backbone, e.g., al~vl or alkoxy of between about 1-10 carbon atoms.
Especially preferred viscosi-ty modifiers are dimethyl silicone oils i.e., polymers of formula I above wherein at least most of the Ra's and Rb's are methyl and particularly wherein there is minimum branching e.g., wherein less than 10% of the Rb's are siloxane units. In addition to dimethyl silicone oils, however, other examples of silicone oils that may be used alone or in combination with dimethyl silicone oils include, for example, methyl phenyl silicone, branched methyl phenoxy silicone, branched chlorophenyl methyl silicone, fluorosilicone, nitrile silicone, methyl hydrogen and methyl vinyl silicone oils.
Especially preferred viscosity modifiers coriespond to the formula:
R R
~m ~m Am-(siO)n Si Am II
Rm Rm wherein Rm and Am comprise alkyl of 1-8 carbons or phenyl or phenyl substituted by alkyl or alkoxy of 1-8 carbons or halo such as chloro; and n is above about 15.
B. Component-II. Component II comprises an oligomer (hereinafter, Oligomer I) that crosslinks with Polymer I through the vinyl groups of Polymer I and silyl hydride groups of Oligomer I. Oligomer I preferably has a formula corresponding to that of formula I except that there are an average of more than 1 and less than about 20 silyl hydride groups --si--H
rather than any vinyl or allyl groups; the total number of siloxy groups (i.e., total of all m and n's~ averages between about 15-50; and there is little, if any, branching e.g., less than about 5% of the Rb's are siloxane units.
Examples of such oligomers include Silastic J curing agent available from Dow Corning Corporation.
Preferred oligomer crosslinking agents correspond to the formula:

., 1 ~59 Rf Re - (SiO~p -- Si(Re)3 III
Ri wherein Re and Rf are selected from hydrogen and saturated hydrocarbyl or hydrocarbyloxy of be-tween ahout 1-10 carbon atoms optionally substituted by halo such as chloro or interrupted by oxy (-0-); p averages between 6-40 and wherein there is an average of at least about two silyl hydrides groups per polymer and up to about one for each siloxy group, more preferably an average between 5 and 15 silyl hydride groups per polymer chain.
Especially preferred crosslinking agents correspond mostly by weight (e.g., 90% or more) to the formula:
R

Ao-(SiO)n-Si Ao III' H H
wherein Ro is alkyl or alkoxy of 1-3 carbons; phenyl or phenoxy, preferably methyl; Ao is alkyl of 1-3 carbon atoms or phenyl, preferably methyl; and n is between about 5-14 on the average.
The crosslinking agent is used at a weight ratio with respect to Polymer. I of between about 1:3 to 1:20, Polymer III to Polymer I and preferably at least about 1 equivalent of silyl hydride for each equivalent of vinyl or other aliphatic unsaturation.
The elastomer precursor compositions of this invention may also contain other such ingredients which are included typically in compositions of the type disclosed herein, e.g., dyes, heat stabilizers, antioxidants, pigments, adhesion promotors, uv absorbers and the like.
The following procedures are used in the examples below to determine working time and physical and thermal properties:

I' f -~

3 1 ~ ~) l3 Working Time: ~fter de-aeration some of mix is poured in a 100 ml beaker for determination of working time with the Brookfield viscometer. A #4 spindle at 0.6 rpm is used for this measurement with the guard in its proper place. The time required for the spindle to mo~e from the starting point to 100 on the instrument scale is called the working time o:E a composition.
A. Physical Properties 1. Tensile testing of dumbbell specimens: ASTM
D 412 procedure is used for determination of tensile strength, 10% modulus and elongation to break. Dumbbell specimens are cut with the standard die from a thin slab (0.32 cm thick) and used for this testing.
2. Durometer Hardness: The hardness of cured silicone rubber is determined according to ASTM D 2240 procedure.
3. Tear Testing: Tear specimens, cut with a die B, are tested according to ASTM D 624 procedure.
Razor-nicked specimens are used for determination of tear resistance.
B. Coefficients of Thermal ExPansion: The coefficients of thermal expansion are determined with the Dupont 942 thermomechanical analyzer. Sensitivity of this instrument is checked with an aluminum metal standard. Sample height is 0.60 cm and temperature was programmed at 5C/mm. In all cases the expansion probe is resting on molded surfaces and has zero load.
The coefficients of expansion are calculated for the temperature ranges of 25-300C and 200-300C.
C. Determination of Thermal Conductivities:
The split bar method is used for determining the thermal conductivities of these elastomeric materials. Two speci-mens are used for these measurements and an average of thermal conductivity is obtained from the two samples.
Typical dimensions of thin specimens are 2.14 cm(W) x

4.80 cm(L) x 0.210 cm(T) and for thick specimen 2.15 cm(W) x 4.80 cmlL) x 0.65 cm(T). Measurements on two samples of different thickness are used to eliminate temperature -~r ,~

3 1 S (~
1'~
drops due to the interfaces between the specimen and copper rod.
~ he Examples below are in~ended to illustrate this invention and not necessarily limit its scope.
Example 1 The following ingredients in amounts indicated are charged into a Hobart mixer.
Component Amount 1. Silastic J RTV Silicone Elastomer 2,268.0 gm 10 and silica particulate (1) 2. Kadox* 15 ZnO 14020 gm 3. Williams 1011 Lampblack7.10 gm 4. Glass Fibers (~" chopped strand 25.00 gm coated with primer) After mixing above ingredients for five minutes, this base is stored for subsequent use in the preparation of thermally conductive elastomer compositions.
In compounding the thermally conductive elastomer material, the above base compound is combined with ingredients below in the following manner:
Component Amount 1. Base Material 400O00 gms 2. Silastic J Curing Agent40.00 gms 3. Cure Modifier E-1990-760.80 gms 25 4. Silicone Fluid 200 (100,000 40.00 gms centistokes at 25C)

5. Silicon Powder (-325 mesh)150.00 gms The silastic J RTV silicone elastomer (base material) and silicon powder are charged in the steel bowl of Ross double planetary mixer. The addition of Silicone Fluid 200 follows with mixing for 4 minutes.
The mix is scraped off the two blades of the mixer and allowed to fall in middle of bowl for better mixing.
Then the silastic J curing agent and viscosity modifier are added and mixing is completed in 6 more minutes.
After de-aeration of mix for 30 minutes, it is ready for molding and determination of working life of compound with the Brookfield viscometer. The working time is ~ . .
* - Trademark ~ 1 5 ~3 ~
lO hours. Molding of mix follows by pouring part of lt in a four cavity mold kept at room temperature. After curing, the compound for 20 minutes (top platen of hydraulic press at 232C and bottom at ambient -temperature) under 5 63 tons press~lre, the rubber slabs are taken out of mold and post cured in an air circulating oven for 3 hours at 202C. (Alternatively, curing can also be done by leaving the charged mold at room temperature for 48 hours).
The molded articles exhibit the following physical 10 properties before and after aging at 260C for 500 hours.
TestHardnessModulus atTensileTearElonga-l~p.Shore A909~ Elong.StrengthStrength tion %
MPa MPa KN/M

25C 63 0.75 4.30 14.20 57 15 232C 63 0.73 2.40 5.05 31 232C*66 0.89 2.10 4.80 22 * Aged at 260C for 500 hours.
Retention of physical properties on aging is excellent with practically no change in hardness. The 20 weight loss on aging is small 3.3 vs. 6.0% compared to materials without the conductive filler. The thermal conductivity is 8.55 x lO 4 cal. sec. l cm. l C l, coef-ficient of linear thermal expansion is 2.7 lO 4 in,~in/C
and weight loss on aging at 260C for 500 hours is 3.3%.
25 The addition of the conductive filler to the elastomer compositions shows no negative effects and doubles the conductivity of base material.
(1) The silica particulate of the base material is about 1093 parts by weight ground crystalline silica 30 (Min-U-Sil*) and about 58 parts by weight fumed silica (Cab-O-Sil* MS-75). Min-U-Sil is a white powder with particles having an average diameter of about 5 microns and a specific * - Trademarks ~, ~'~,...

gravity of a~out 2.6~ Cab-O-Sil ~S-75 has with a specific gravity of 2.2 an~ an average par~lcle dlameter between abo~
0.07-0.1 microns. The b2se materlal or base compound further includes less than about 10 parts by weight of ~ platinum complex catalyst ~hich lS a vinyl siloxane oligo~er modified by plat~num metal (available from Dow Corning Corporation). The bacD compound Wit~, these ingredlen-s h~s a vlscoslty between 700-1300 centlstok~s at 25C.

Exam~le 2 Example 1 is repeated exce?t ~he welght of silicon powder 180.0 gms. After mixlng all ingredients on a 80 x 180 mm two-roll vent~ research mill, the compound has a working time of 7.5 hours. n 5pecimen molded under the same conditions as materials of Exam~le 1 exhibit good physical properties before and after aging at 260C for 500 hours. They also exhibit improved thermal conductivity and lower weight loss as compared to compounds wlthout the silicon.

Examole 3 A base compound prepared as in Example 1 is compounded with the following ingredients:
Component Amount 1. Base compound ~Example 1) 430.00 gms.
2. Silicon powder (-325 mesh) 15~.00 gms.
3. Silicone Fluid 705 10.00 gms.
4. Silastic J Cur ~g Agent 43.00 gms.
5~ Cure Modifier E - 1990 - 76 ~.80 gms.
In this composition the Silicone Fluid ~200 is replaced by base material (30 gms.) 2nd lower viscosity Silicone Fluid 705 110 gms.). After mixing according to proce~ure of Example 1, the physical properties of virgin and aged specimens are as follows:

~ 1~91~

TestHardness ~dulus at Tensile TearElongation Temp.Shore A 106 Elong. Strength Strength ~6 MPa ~a KN/M
25C 70 1.25 5.40 17.50 53 5 232C 69 1.17 2.85 7.20 25 232C*76 1.43 2.10 6.70 16 * Data for aged samples at 260C for 500 hours.
In addition to yood retention of physical proper-ties on aging, these articles exhibit improved thermal 10 conductivities and lower weight losses on heat aging at 260C for 500 hours.
Example 4 A base compound prepared as in Example 1 is combined with the following ingredients according to 15 mixing procedure of Example 1.
Component Amount 1. Base compound (Example 1) 656.00 gms.
2. Aluminum Powder (-325 Mesh)213.00 gms.
3. Silicone Fluid 200 (100,000 centistokes at 25C) 65.60 gms.
4. Silastic J Curing Agent 65.60 gms 5. Cure Modifier E - 1990 - 76 1.30 gms.
The working time of this compound is 10.5 hours.
After molding this silicone elastomer composite 25 according to the conditions described in Example 1, virgin and aged specimens* at 260C for 500 hours have the follow-ing physical properties:
TestHardness~dulus atTensileTearElongation Temp. Shore A10% elong.StrengthStrength %
MPa MPa KN/M
25C 60 0.69 3.15 11.4 43 232C59 0.66 1.54 5.0 25 232C64 0.75 1.91 3.5 10 These materials exhibit also improved thermal conductivity 35 (7.10 10 4 cal. sec. 1 cm. 1 C 1) and lower weight loss on aging at 260C for 500 hours.

~r 3 ~ 8 ~i Æxample 5 A base compound prepared as in Example 1 is mi~ed with the following ingredients:
Cornponent Amount 5 1. Base compound (Example l) 656.00 gms.
2. Aluminum powder (~325 Mesh) 350.00 gms.
3. Silicone Fluid 200 (lO0,000 centistokes at 25C) 65.60 gms.
4. Silastic J Curing Agent 65.60 gm~.
lO 5. Cure Modifier E-1990-76 1.30 gms.
AEter completion of mixing as in Example l, the compound has a working time of 6.0 hours. After de-aeration molded articles of various thicknesses are prepared by molding at 177C for 20 minutes and post curing 15 at 202C for 3 hours in an air-circulated oven.
The test specimens exhibit the following physical properties before and after aging* at 260C for 500 hours.
TestHardness Modulus at Tensile Tear Elongation Teltp. Shore A1096 Elong. Strength 5trength %
MPa MPa KN/M
~ . .
25C 63 0.92 4.20 13.60 45 232C 63 0.88 1.75 6.20 24 232C*68 1.05 l.90 5.15 13 *Upon aging these materials exhibit good retention 25 of physical properties. Thermal conductivity is improved and percent weight loss is lower than in compounds without the aluminum powder.
Example 6 A base compound prepared as in Example 1 is 30 mixed with the same ingredients as in Example 5 but with the exception of weight of aluminum powder. Aluminum powder (450.00 gms. -325 Mesh) is combined with ingredients listed in Example 5. After mixing, the elastomer compo-sition has a working time of 3 hours.

'~.

3 ~

.

Molded ~r~lcles cured according to procedure of example 5 exhib~t good ~hysical properties. Retention of ¦ physlcal propertLes after aging is ~ood. Improvement in thermal conduc.i-rity (10.8 10-4 cal. sec.~1 cm.~l C) and percent weight loss (3.7%) is also found.

Example 7 A base compound prepared as in Example 1 is mixed on a 80 x 180 mm. two-roll vented research mill with the followin~ ingredi~nts:
Componen~ A~ount 1. Base compound (Example 1) 480.00 gms.
2. Iron Powder (-230 Mesh) 480~00 gms.
3. Silicone Flui~ 200 (100,000 centi-stokes at 25~) 48.00 gms.
15 4. Silastic J. C~ring A~ent 48.00 gms.
5. Cure Modifier E - 1990 - 7~ 0.~6 gms.
After 2~ min~tes of mixing at ambient temperature, the ~ix had a working time of 6.20 hours. Up~n completion of de-airation, ~ne mixture is molded according to conditions of 20 Example 1. The p~ysical properties before and after aging* at 260C for 500 hours are listed below.
Test Hardness Modulus at Tensile Tear Elonga-Tem~. Shore A 10% Elong. Strength Strength tion MPa MPa KN~M
25 25C 65 0.97 3.7C 12.9~ 38 ;232C 65 0.74 1.59 5.0~ 20 232C* 77 0.86 1.60 4. 6a 17 *Improve~ents in thermal conductivity (7.85 10-4 cai.
sec.~1 cm.~l oCJ~l and percent weight loss upon aging are ~ observed.

8 l) Example 8 Example 7 is repeated with the exception that lower amounts of iron powder (380 gms.) is used for making the elastomer compound. Af-ter mixing, the material exhibits a working time of 8 hours.
Molded specimens of various thicknesses exhibit improved thermal conductivity and percent weight losses upon aging at 260C for 500 hours.
Example 9 10 Example 7 is repeated with the exception that a higher amount of iron powder (580 gms.) is used for preparing the elastomer compound. Working time of mixture is 4.5 hours. Molded specimens according to conditions of Example 7 exhibited improvement in thermal conductivity and no improvements in weight loss.
Example 10 A base compound prepared as in Example 1 is mixed with the same ingredients as in Example 1 with the exception of silicon powder. Chromium powder is used as follows:
Component Amount 1. Base Compound 400.00 gms.
2. Chromium Powder (-325 Mesh) 300.00 gms 3. Silicon Fluid 200 (100,000 centistokes at 25C) 40.00 gms.
4. Silastic J Curing Agent 40.00 gms.
5. Cure Modifier E - 1990 - 76 0.80 gms.
The ingredients are mixed as in Example 1. Upon completion of mixing, this compound has a working time of 7.0 hours.
Moldings are made according to conditions described in Example 1. The physical properties before and after aging at 260C for 500 hours are as follows:

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Test Hardness ~cdulus at Tensile Tear Elongation Temp. 5hore A 10% Elong. Strength Strength %
MPa Mæa KN/M
. . ~
25~C 63 O.G5 3.G0 12.8 40 232C 63 0.68 1.30 5.10 20 232C* 77 0.00 1.02 4.90 18 Improvement in thermal conductlvity is observed (8.1 cal. sec. 1 cm. 1 C) but no substantial improvement in weight losses upon aging.
Example 11 The procedures of Example 10 are repeated withthe exception that 200 gms. of chromium powder is used (-325 Mesh). Upon mixing the mixture has a working time of 8.5 hours. Molded articles show improvements in thermal conductivities over compounds containing no chromium powder.
Example 12 The procedures of Example 10 are repeated with the exception that 400 gms. of chromium powder are mixed with other ingredients. After molding the mixture under same conditions as in Example 10, the articles exhibit improvements in thermal conductivity.
Example 13 Example 1 is repeated with the exception that 55.0 gms. of the Silicone Fluid 200 is used for preparing the mixture. The molded articles have improved thermal conductivity.
Example 14 Example 1 is repeated with the exception that 30 gms. of the Silicone Fluid 200 are used in preparation of compound. After molding specimens according to procedure of Example 1, they exhibit good properties before and after aging at 260C for 500 hours. Improvement in thermal conductivity and percent weight losses are found.

1 1~9 l~tl Example 15 Example 6 lS repeated wit~ tbe exce~tion of weight ofthe Slllcone ~luld 2G0 (70.00 gms.). The mixture is processable and ~pon molding has ~mprotJed properties.
ExamDle 16 Example 1 is repeated with the exception of Silicone Fluid 200. An e~ual amount of a lower viscosity fluid (60,000 centistokes, 40.00 gms.) is employed. ~pon mixing and molding, the com~ounds have good properties.

Exam~le 17 Example ; is repeated with exceptlon that 40.00 gms.
of a lower viscosity Silicone Fluid (30,000 centistokes at 25C) is used. S~milar results are seen.

Example 18 Examples 1, 2, 4 or 5 are repeated, except for varying the amount of cure modifier E-1990-76 (0.6 to 1.5 gms.). Similar rPsults are seen.

Example 19 Examples 1, 2, 4 and 5 are repeated except Silastic E
RTV Silicone Elastomer is used on an equal weight basis to replace the Silastic J RTV Silicone Elastomer in making the base compound. Similar results are seen.
Example 20 ~ Examples 1, 2, 4 and 5 are repeated, except Silastic L ~TV Silicone Elastomer on an equal weight basis to replace the Silastic J ~V Silicone Elastomer is used in making the base compound. c ~ilar results are seen.

~ .

9 1 8 ( ~letal Allo~ Cc~e~osi~iqns ExamDle 21 __ _ The base compound ~escribed in Ex~mpl~ 1 is combined with the followi~g ir~redients according to mixi~ng procedure of Example 1.
Componen~ Amount .
1. Base r~aterial (Example 1) 400.00 gms.
2. Nickel-Alumin~m Alloy (80/20 by weight) 400.00 gms.
10 3. Silicone Eluid 200 ( 100 ,000 centi-stokes at 25C) 40.00 gms.
4. Curing Agent ~Silastic j) 40.00 gms.
5. Cure ~lodifier E - 1990 - 76 0.80 gms.
After mixing above ingredients, the compound has a 15 working time of 8 hours.
After molding this silicone elastomer composite according to cond~tions described in Example 1, the virgin and aged specimens* ~t 260~C for 500 hours have the following physical properties:
20 Test Hardness Modulus at Tensile Tear Elonga-Temp. Shore A 10% Elong. Strength Strength tion MPa MPa RN/M
25C 60 0.62 3.23 13.30 47 232C 62 0.68 1.35 5.07 20.0 25 232C 62 0.84 1.08 4.65 13.0 These materials exhibit higher thermal conductivity values than compositions with other metal alloy powders (11.70 10-4 cal sec -1 cm.~l . oC~l). Lower weight losses are also found after aging at 260C for 500 hours. Aging at 260C
30 for 500 hours has no effect on hardness.
Exa~le 22 A base compound pre~ared as in Exam~le 2 is mixed with the following ingredients according to procedure of Example 1.

~ 9 1 ~ t) -2~-ComDOne~t A~.ount 1. Base Compoun~ (Example 1) 600.00 gms.
2. Tunqste~-Co?~er (75/25 by weight) Alloy Powder 600.00 gms.
5 3. Sllicone ~-lu.d 200 (100,000 centi-stokes at 25aC) 60.00 gms.
4. Sil3stic J Cur1ng Agent 60.00 gms.
5. Cure Modifle~ E - 1990 - 76 1.20 gms.
The mixture has a longer working ~ime (15 hours).
10 The alloy powder appears to have an effec~ on ~orking time.
After ~olding th lS S il 1cone compound according to conditions described in Example 1, the virgin and aged*
specimens at 260C for 500 hours have the following physical properties:
15 Test ~ardness Modulus at Tensile Tear Elonga-Tem~. Shore A 10% Elong. Strength âtrength tion %
MPa MPa KN/M
25C 60 0.90 3.21 13.90 43 232C 61 0.67 1.22 5.34 1~
20 232C 66 0.89 1.40 4.85 17 These m~lded ~aterials exhibit also improved therm21j~t conductivity (5.98~ cal. sec.~l cm.~1 oC~1) and lower weight loss (aging at 260C for 500 hours~ than materials without the metal alloy powder. Hardness (âhore A) change 25With aging is very insignificant.
. Example 23 To a base compound prepared as in Example 1, the ^following ingredients are added according to procedure of Example 1.
30 COmROnent Amount 1. Base Compoun~ (Example 1) 400.00 gms.
- 2. Nickel-Copper (70/30 by weight) Alloy Powder 400.00 gms.
3. Silicone Flu1d 200 (100,000 centi-35 stokes at 25C) 40.00 g~s.
4. Silastic J Curing Agent 40 .ao gms.
5. Cure Modlfie- E - 1990 - 76 0.80 gms.

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After mixing and de-aeration the mixture has a working time of 8.5 hours.
Following molding of this silicone elastomer composite, the physical, chemical and thermal properties 5 are determined.
TestHardness~idulus atTensileT~ar Elc~gati~
Telrç). Shore A 10% Elong.Strength Strength %
L~Pa MPa KN/M
25C 60 0.67 3.75 12.00 55 10 232C 60 0.81 1.55 7.9 20 232C 62 0.64 1.35 3.2 21 Molded samples exhibit improved thermal con-ductivity (10.2 10 4 cal. sec. 1 cm. . C 1) and lower weight loss on aging at 260C for 500 hours. No change 15 in hardness with aging is observed.
Example 24 Example 23 is repeated with the exception that the nickel-copper alloy is replaced by an equivalent amount of aluminum-silicon (89/11 by weight). After 20 mixing, the elastomer composite has a working time of 4 hours.
Molded articles according to procedure of Example 1 possess good physical properties. They also exhibit improved thermal conductivity and lower weight loss on 25 aging at 260C for 500 hours.
Example 25 Example 23 is repeated with the exception that the nickel-copper alloy powder is replaced by 373 g.
of Iron-Silicon-Magnesium (80/10/10 by weight) alloy 30 powder. After mixing the compound has a working time of 1 hour.
Molded specimens cured according to conditions of Example 1 have the following physical properties:
TestHardness~dulus atTensileTear Elongatia 35 Tenp.5hore A10% Elong.Strength 5trength ~6 MPa MPa KN/M
25C 69 1.09 4.80 10.80 52 232C 72 0.75 2.75 4.72 32 232C 82 1.10 2.70 4.90 12 .~
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~ 3 5~3~8~1 -26- ~lû ~
Impro,e~e~ts in .herm31 co~ductlvity (7.98~cal. sec.
1 . cm.-l C l) and ?ercent welght loss arn found. A small change ln hardne~~ (Shore A) is o~served on aging of materlal at 260C for 500 `iours. ~
Exa~Dle 26 A base Aom~ound ~re~ared as in Exam21e 1 is combined with the following ingredients:
Com~onene A~ount 1. Base Compounc 400.00 gms.
0 2. Inconel~ owder (-325 Mesh, Nickel-Chromium Iron alloy) 380.00 gms.
3. Silicone Flu~ 200 (100,000 CSK at 2506) 40.00 gms.
4. Silastis J Curing Agent 40.00 gms.
15 5. Cure Modifier E - 1990 -76 0.80 gms.
Followir.g mixing and de-aeration the mixture exhibits a working time or 6.5 hours.
The physical, chemical and thermal proper~ies of molded articles cured as in Example 1 ar- determined as 20 described in this document. Physical pr~perties are as follows:
Test Hardness Modulus at Tensile T~ar Elonga-Temp. Shore A 10% Elong. Strength S~rength tion %
MPa MPa KN/M
25 25C 67 1.35 3.00 18.40 31 232C ~7. 1063 1.80 11.7~ 12 232C i5 1.45 1.58 3.80 10 Improvements in thermal conductivLty and percent weight loss are Dbserved. After aging, very small change in 30 hardness is found.
Example 27 To a base compound prepared as ir. Example 1 the following ingredients are added as in Example 1.
~ r~Cle ~`k ~ 1~9~3t~

Component Amount l. Base Compound (Example l) 400.00 gms.
2. Brass powder (#2B-126)(Cu 52~, SN 48%
by weight) 300.00 gms.
3. Sllicone Fluid 200 (lO0,000 CSK at 25C) 40.00 gms.
4. Silastic J Curing Agent 40.00 gms.
5. Cure Modifier E - 1990 - 76 0.80 gms.
After miY~ing and de-aera-tion the mixture has a very long working time (20 hours). After molding compound as in Example l, the molded articles have the following physical properties: -Test Har&ess ~odulus at Tensile TearElongaticn Temp. Shore A 10% Elong. Strength Strength MPa MPa KN/M
_ _ .
25C 39 0.37 1.70 6.10 62 232C 38 0.22 0.67 2.13 28 232C* 37 0.31 0.58 2.20 18 Improved thermal conductivity and percent weight loss are found. The brass powder appears to affect the reaction and results in softer elastomer articles.
Example 28 Example 23 is repeated with the exception that the brass powder (#2 B-226)- is replaced by an equivalent weight of Bronze Powder ~B-402, -lO0 mesh 50-50 Cu/Zn).
After mixing the silicone elastomer composite has a working time of 3.5 hours.
After molding the mixture according to procedure of Example l, the molded articles have good physical properties before and after aging. They also exhibit improved thermal conductivity.
Example 29 In preparing the base for use in compounding thermally conductive silicone elastomers the following ingredients are charged into a Hobart double planetary mixer:

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Component Amount l. Silastic J RTV Silicone Elastomer ~ SiO2 (l) 1134.0 grams 2. Kadox 15 ZnO 7.10 grams 3. Williams 1011 Lampblack3.55 grams 4. Glass Fibres (~" Chopped Strand Coated with Primer)12.50 grams 5. Cure Modifier E-1990-762.10 grams After mixing above ingredients for five minutes the base can be stored for subsequent use in preparing the thermally conductive materials.
In making the thermally conductive material the base is combined with the following ingredients:
Comp~nent Amount l. Base Material 400.00 grams 2. Synthetic Graphite (Part~cle Diameter 15 Microns) 100.00 grams 3. Silicone Fluid (100,000 Centistokes at 25C) 40.00 grams 4. Silastic J Curing Agent40.00 grams After charging the base in a Ross double planetary mixer, the addition of synthetic graphite (15 microns) follows with mixing for 2 minutes. Then the addition of silicone fluid follows with mixing for 4 minutes.
The mix is scraped off the two blades of the mixer and allowed to fall in the middle of steel bowl for improving mixing. Addition of Silastic J curing agent is completed in six minutes with mixing. After de-aeration of the mixture for 30 minutes, it is ready for molding and deter-mination of working time with the Brookfield Viscometer (Model LV, Spindle #4). The working time of this mixtureis l hour.
Molding of mix is carried out by pouring and spreading the mixture in a four cavity, chrome-plated mold kept at ambient temperature. After curing the compound for 20 minutes (top platen of hydraulic press at 232C
and bottom at ambient temperature) under 70 ton pressure, .~
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I1~91~

the rubber slabs are taken out of mold and post cured in an air circulating oven for 3 hours at 202C. Alternately, the mixture can be cured at ambient temperature for 24-48 hours.
The molded articles exhibit the following physical properties berore and after aging* at 260C for 500 hours:
Test Hardness ~dulU5 atTensile Tear Elongatia Temp. Shore A 1096 Elong. Strength Strength %
MPa MPa KN/M
_ 10 25C 68 1.31 3.40 11.60 34 232C 65 0.92 2.35 5.30 28 232C* 70 0.92 1.60 4.40 19 The physical properties after aging are excellent with practically no change in hardness. The weight loss 15 on aging is very small (3.1 vs 6.096) compared to materials containing no graphite powder. The thermal conductivity is also substantially improved (11.1 x 10 4 cal sec.
cm 1 C 1~. The addition of synthetic graphite to the elastomer composition has no negative effects but improves 20 thermal conductivity by a factor of 2.7. These materials also show a smaller expansion than materials without the graphite powder. (2.1 10 4 in / in / C).
(1) The silica particulate of the base material is about 1093 parts by weight ground silica (Min-U-Sil) 25 and about 58 parts by weight fumed silica (Cab-O-Sil MS-75). Min-U-Sil is a white powder with particles having an average diameter of about 5 microns and a specific gravity of about 2.65. Cab-O-Sil MS-75 has a specific gravity of 2.2 and an average particle diameter between 30 about 0.07-0.1 microns. The base material further includes less than about 10 parts by weight of a platinum complex catalyst which is a vinyl siloxane oligomer modified by platinum metal (available from Dow Corning). The base material with these ingredients has a viscosity 35 between 700-1300 poises at 25C.
Example 30 A base RTV silicone elastomer prepared as described in Example 29 is combined with the following ingredients:
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Component Amount l. Base Material 400.00 grams 2. Synthetic Graphite (35-40 Microns~ 85.00 grams 3. Silicone Fluid (lO0,000 Centistokes at 25C) 40.00 grams 4. Silastic J Curing Agent40.00 grams The ingredients are preblended with a spatula and then placed in the Ross double planetary mixer for complete mixing. The mixing was completed in ten minutes.
lO After de-aeration of mix for 30 minutes, it was used for molding and determination of working time with Brook-field Viscometer (Model LV, Spindle #4). The wor~cing time was in desired range (7.4 hours).
After molding this silicone elastomer composite 15 according to conditions described in Example 29, the virgin and aged* specimens at 260C for 500 hours have the following physical properties:
Test Har&es;, ~dulus at Tensile Tear Elongation Temp. Shore A 10% Elong. Strength 5trength %
MPa MPa KN/M
.
25C 60 0.88 - 3.22 14.25 40 232C 61 0.70 1.50 5.40 20 232C* 62 0.75 1.05 4.30 16 The molded articles exhibited improved thermal 25 conductivity (8.3 lO 4 cal sec 1 cm l . C 1) .
Lower weight losses are found after aging at 260C for 500 hours (2.8 vs 6.0). Aging also has absolutely no effect on hardness.
Example 31 The base silicone elastomer of Example 29 is mixed with the following ingredients according to procedure of Example 29.

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Component Amount 1. sase ~aterial 400.00 grams 2. Synthetic ~raphite (Particle Size 35-40 Microns) 100.00 grams 3. Silicone Fluid (100,000 Centlstokes at 25C) 50.00 grams 4. Silastic J Curing Agent40.00 grams The mixture has a working time of 8 hours.
After molding the silicone compound according to conditions 10 described in Example 29, the virgin and aged* specimens at 260C for 500 hours have the following physical proper-ties.
TestHardness ~dulus at TensileTear Elc~gatia Temp.5hore A 10% Elong. StrengthStrength %
MPa MPa KN/M
_ 25C 63 1.00 3.3011.20 50 232C 67 1.10 2.905.93 36 232C*67 0.99 2.003.40 22 Molded articles have a thermal conductivity 20 of 10.50 x 10 4 cal sec 1 . cm-l . oc-l They also exhibit lower weight losses after aging at 260C for 500 hours than the compounds without graphite. Accelerated aging also has no effect on hardness.
Example 32 25 The base material of Example 29 is prepared again as described but no glass fibres and modifier are added to the mixture. The mix is combined with the following inoredients on a 80 x 180 mm two-roll research mill.
Component Amount 30 1. Base Material 400.00 grams 2. Synthetic Graphite (Particle Size 20-45 Microns~ 85.00 grams 3. Silicone Fluid (100,000 Centistokes at 25C) 40.00 grams 35 4. Silastic J Curing Agent 40.00 grams 5. Modifier E-1990-76 0.80 grams ,/

The working time o~ mix is within the desired range.
The physical properties of molded specimens are as follows:
Test Hardness Modulus atTensileTear Elongatia Telrp. Shore A106 Elong.Strength Strer~gth %
MPa MPa KN/M
25C ~0 0.50 3.90 9.80 68 232C 60 0.65 2.95 4.40 38 232C* 62 0.60 2.25 5.00 29 The rectangular specimens exhibit improved thermal conductivity. They also have lower weight losses on aging than samples without the conductive filler.
Accelerated aging has no effect on hardness.
Example 33 The glass fibres and modifier are omitted from the base of Example 29. The base mixture is combined with the following ingredients in a Ross double planetary mixer:
Componeht Amount 1. Base Material -600.00 grams 2. Synthetic Graphite (Particle Size 35-40 Microns) 150.00 grams 3. Silicone Fluid (100,000 Centistokes at 25C) 60.00 grams 4. Silastic J Curing Agent60.00 grams 5. Cure Modifier E-1990-761.20 grams After mixing ingredients according to Example 29, the working time of mixture is 7.0 hours. After 30 curing and post curing the compounds as in Example 29, molded articles exhibit the following properties:
Test Hardness ~dulus atTensileTear ElcIlgatic Tellp. Shore A10% Elong.Strength Strens~th %
MPa MPa KN/M
25C 62 0.66 3.80 9.70 63 232C 62 0.77 3.00 4.70 37 232C* 65 0.68 2.45 2.70 29 * Aged at 260C for 500 hours.

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The thermal conductivity of molded specimens is lO 75 x 10-4 cal s c~l cm-l C~l They also show lower weigh-t losses on aging than specimens without graphite filler. Accelerated aging has no effect on 5 hardness.
Example 34 To the base of Example 29 the following ingre-dients are added acc:ording to mixing procedure of Example 29.
Component Amount l. Base Material 500.00 grams 2. Synthetic Graphite (Particle Size 15 Microns) 102.00 grams 3. Silicone Fluid (100,000 Centistokes at 25C) 50.00 grams 4. Silastic J Curing Agent50.00 grams Upon completion of mixing and de-aeration of mixture, it has a working time of 1.5 hours. Molded specimens exhibit the following physical properties:
20 T~st Hardness ~;dulus atTensile Tear Elongati Tenp. Shore A 10% Elong. StrengthStrength %
MPa MPa KN/M
_ 25C 65 1.25 4.55 17.20 50 232C 68 l.lO 2.60 7.00 25 25 232C* 68 0.99 1.30 4.60 14 * Aged at 260C for 500 hours.
The molded specimens exhibit improved thermal conductivities. Upon accelerated aging the specimens exhibit lower weight losses and hardness changes than 30 specimens without graphite filler.
Example 35 Example 29 is repeated with the exception that 85.00 grams of synthetic graphite and 60 grams of silicone fluid are used. The ingredients are mixed in a Ross double 35 planetary mixer. The working time of mixture is 2.85 hours.
Molding of mix result in specimens with the following properties:
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Test E~rdness ~dulus atTensile Tear Elongati~
Tenp. 5hore A 10% Elong.Strength Strength MPa MPa KN/M
~5C 61 1.10 4.30 14.00 61 S 232C 61 1.40 2.60 6.20 30 232C* 65 0.95 1.60 3.80 18 * Aged at 260C for 500 hours.
The thermal conductivity of molded specimens is improved. Thermal stability is also improved.
Example 36 The base material of Example 29 is mixed in a Hobart mixer with the following ingredients:
Component Amount 1. Base Material 400.00 grams 15 2. Synthetic Graphite (Particle Size 15 Microns) 85.00 grams 3. Silicone Oil (60,000 Centistokes at 25C) 50.00 grams 4. Silastic J Curing Agent40.00 grams 20 After completion of mixing schedule as in Example 29 and de-aeration, the mixture has a working time of 5.00 hours.
The physical properties of virgin and heat aged* specimers has as follows:
25 Test Hædness Modulus at Tensile Tear Elo~gatia Te~. Shore A 10% Elong.Strengt~ Strengt~ %
MPa MPa KN/M
___ __ . , _ 25C 64 0.99 3.50 11.40 46 232C 64 0.94 2.85 5.90 34 30 232C* 68 0.98 1.30 4.00 14 * Heat aged at 260C for 500 hours in an air-circulating oven. The molded specimens exhibit improve-ments in thermal conductivity and stability over the values obtained from samples containing no graphite.
Example 37 Example 36 is repeated with the exception that 60 grams of silicon oil (60,000 centistokes at 25C) is employed. The working time of mixture was 7.20 hours.

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The physical properties of molded specimens are as follows:
Test Hardness Modulus atTensile Tear Elongati~
Tem~. Shore A 10% Elong. Streng~hStrength %
MPa MPa KN/M
.
25C 63 0.8~ 3.71 10.30 68 232C 63 0.89 2.50 5.70 38 232C* 68 0.89 1.70 3.85 20 * Heat aged specimens at 260C for 500 hours 10 in an air circulating oven.
Improved thermal conductivity and heat stability are obtained. Some of physical properties such as tensile strength and elongation determined at 232C are slightly improved.
Example 38 The base of Example 29 without the modifier (working time) is combined with the following ingredients in a Ross double planetary mixer:
Component Amount 20 1. Base Material 400.00 grams 2. Synthetic Graphite- (Particle Size 15 Microns) 85.00 grams 3. Silicone Fluid (lOO,OQO Centistokes at 25C) 80.00 grams 25 4. Silastic J Curing Agent40.00 grams 5. Cure Modifier E-1990-760.80 grams After completion of mixing and de-aeration, the working time of mixture is 8.5 hours.
After molding the resulting articles have the 30 following properties:
Test H~rdness ~ulus atTensile Tear Elongatia TemQ. Shore A 10% Elong. Strength Strength %
MPa MPa ~21/M
25C 57 0.90 2.60 8.95 45 35 23?C 57 0.65 1.30 4.70 20 232C* 62 0.75 1.30 3.70 19 * Heat aged at 260C for 500 hours in an air-circulating oven.
.

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Improvement in thermal conductivity and thermal stability over the values of samples containing no graphite are obtained.
Example 39 The following lngredients are combined with the base of Example 29.
~onent Amount 1. Base Material 400.00 grams 2~ Synthetic Graphite (Particle Size 35-40 Microns) 60.00 grams 3. Synthetic Graphite (Particle Size 15 Microns) 40.00 grams 4. Silastic J Curing Agent40.00 grams 5. Silicone Oil (100,000 Centistokes at 25C) 40.00 grams Following mixing and de-aeration the mixture has a working time of 2.10 hours. Molded specimens have the following properties:
Test Hardness Modulus atTensile Tear El~gatian 20 Te~. Shore A 1096 Elong. Strength Strength %
MPa MPa KN/M
25C 66 1.30 4.70 16.70 47 232C 66 1.35 2.70 6.90 22 232C* 68 1.05 1.50 3.90 14 25 * Aged at 260Cfor 500hours in an air-circulating oven. Samples have improved thermal conductivity and stability.
Example 40 The base of Example 29 without modifier (working 30 time) is mixed with the following ingredients as in Example 29.

~ lS~31~() Component Amount l Base Ma-terial 400.00 grams 2. Synthetic Graphite (Particle Size 35-40 microns) 60.00 grams 3. Synthetic Graphite (Particle Size L5 microns) 30.00 grams 4. Silastic J Curing Agent40.00 grams 5. Silicone Oil (100,000 Centistokes at 25C) 40.00 grams 10 6. Cure Modifier E-1990-760.80 grams After blending ingredients in a Hobart mixer, the working time of mixture is 6.3 hours.
The physical properties of molded articles before and after aging* at 260C for 500 hours are as 15 follows:
Test Hardness M~dulus at Tensile Tear Elongati~
Tellp. Shore A10% Elong.Strength Strength %
MPa ME?a ~W/M
. _ _ .. .. . _ . , 25C 66 1.15 3.40 ~2.10 37 20 232C 66 I.12 1.20 5.70 16 232C* 69 1.10 1.60 3.80 16 The molded specimens exhibit a thermal conductivity of 9.3 x 10 4 cal ~ sec ~ cm C . A lower weight loss and hardness change is also found when compared 25 to similar samples containing no graphite powder.
Example 41 The following ingredients are mixed with base of Example 29 according to procedure of Example 29:
Component Amount 30 1. Base Material 400.00 grams 2. Synthetic Graphite (Particle Size less than 150 microns)130.00 grams 3. Silastic J Curing Agent40.00 grams 4. Silicone Oil (100,000 Centistokes at 25C) 40.00 grams This composition has a working time within the desired range.

1 1591~() The rnolded articles have a -thermal conductivity of 11,4 x 10 cal sec 1 . cm~l . oc~l The exhibit lower weight loss and hardness change than similar materials containing no graphite powder.
Example 42 Example 29 is repeated with the exception that synthetic graphite of particle size less than 45 microns is used. The working time of composition is 6 hours.
The physical properties before and after aging*
10 at 260C for 500 hours are as follows:
TestHardness M~dulus at Tensile Tear Elongatia T~l~.Shore A 10% Elong. StrengthStrength %
MPa MPa KN/M
25C ~3 0.80 2.70 16.00 41 15 232C 64 0.82 2.55 7.10 29 232C*64 0.70 1.15 3.20 15 The thermal conductivity of these samples is 2.5 x 10 4 cal sec 1 cm 1 C 1. Improvements in percent weight loss and hardness change are observed.
Example 43 Example 29 is repeated with the exception that synthetic graphite of particle size less than 75 microns is mixed with other ingredients. The working time of mixture is 15.0 hours. The physical properties before 25 and after aging* at 260C for 500 hours are as follows:
TestHardness Modulus at Tensile Tear Elongaticn Temp.Shore A 10% Elong. StrengthStrength %
MPa MPa KN/M
, _, _, .. ,, ... , . _ . _ . .
25C 65 0.88 4.00 12.80 66 30 232C65 0.90 3.00 5.80 37 232C* 68 0.90 1.65 3.70 19 The thermal properties and hardness change are improved over those of similar materials containing no graphite powder.
35Example 44 The base of Example 29 is mixed with the follow-ing ingredients in a Ross double planetary mixer.

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Component Amount 1. Base Material 400,00 grams 2. Crystalline Graphite ~Particle Size 35-40 microns) 85.00 grams 5 3. Silicone Oil (100,000 Centistokes at 25C) 40.00 grams 4. Silastic J Curing Agent40.00 grams The working time of mix is 9.5 hours.
The physical properties of virgin and aged*
10 samples at 260C for 500 hours are as follows:
TestHar&essModulus atTensileTear Elongatia Temp.Shore A10% Elong.Strength Strength %
MPa MPa KN/M
_ 25C ~4 0.97 3.10 12.30 43 15 232C 64 0.99 2.33 6.30 24 232C* 6~ 0.96 1.70 4.60 14 Molded specimens have a thermal conductivity of 12 9 x 10-4 cal sec~l ~ cm-l oc~l Lower weight loss on aging at 260C for 500 hours is observed. The 0 hardness change on aging is also very small.
Example 45 Example 29 is repeated with the exception that flake graphite is used (particle size 10 microns). The working time of mixture is very short. The physical 25 and thermal properties of molded articles are inferior to those described in Examples 1-16.
Example 46 Repeat Example 29 with the exception that 100 grams of silicone fluid (100,000 centistokes at 25C) 30 is used. Longer working times are obtained. Molded articles exhihit improvements in thermal conductivity.
Example 47 Example 29 is repeated with the exception that 30 grams of siiicone fluid (60,000 centistokes at 25C) 35 are used. The molded articles exhibit improvements in thermal conductivity.

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~o Example 48 Exampl~ 29 is repea-ted with the exception that 15 grams o~ silicone fluid (30,000 centistokes at 25C) used. P~ moldable composition is prepared showing improvement 5 in thermal conductivity.
Example 49 Examples 29-48 are repeated with the exception that 0.6 grams of modifier (working time) are used. Molded specimens exhibit improvements in thermal conductivity.
10Example 50 Examples 29-48 are repeated with the exception that 1.5 grams of modifier are used. Moldable compositions are preparedO
Example 51 15Example 29 was repeated with the exception that synthetic graphite is replaced by 75 grams carbon black (N-650, particle size 0.05 microns). The composition has a 4.0 hour working time. Molded articles show improve-ments in thermal conductivity over materials containing 20 no conductive filler.
Example 52 The amount of carbon black (N-650) in Example 51 is increased to 100.00 grams. The mixture has a shorter working time. Molded specimens have the following physical 25 properties before and after aging* at 260C for 500 hours:
Test Hardness MQdulus atTensile Te~r Elongatia T~ly. Shore A 10% Elong. Strength Strength %
MPa MPa ~W/M
25C 72 1.22 3.22 13.80 32 30 232C 72 0.96 1.50 5.64 17 232C* 81 1.72 1.76 4.20 10 Improvements in thermal conductivity are found.
Example 53 Example 51 is repeated with the exception that 35 75.00grams of SL-90 carbon black is used. The mixture has a working time of 7.0 hours. Molded articles exhibit the following physical properties:

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Test Hardness l~odulus at Tensile Tear ElQnsaticn Temp. Shore A 10~ Elong. Strength Strength MPa MPa KN/M
_ _ 25C 60 0.60 2.1012.2 35 5 232C ~
232C* 60 0.60 0.703.10 12 *Heat aged at 260C for 500 hours in an air circulating oven.
Improvements in thermal conductivity and lower weight loss are found.
Example 54 Example 53 is repeated with the exception that 90.00 and 100 grams of SL-90 carbon black are used. The mixtures have shorter working ties.
Example 55 Example 51 is repeated with the exception that 75.00 grams of N-339 carbon black is used. Moldable mixtures are obtained. Improvements are obtained in thermal properties.
Example 56 Example 51 is repeated with the exception that 75.00 grams of N-765 carbon black are used in preparing the mixture. Moldable materials are obtained.
Example 57 The base RTV silicone elastomer materials is prepared by mixlng the following ingredients in a hobart mixer:
Component Amount 1. Silastic J RTV Silicone Elastomer and silica Particulate (1)2494.80 2. Kadox 15 ZnO 15.60 3. Williams 1011 Lampblack7.80 4. Glass Fibers ( In. Chopped Strand Coated with Primer) 27.50 After mixing the above ingredients for five minutes, this base material was stored for use in preparation of thermally conductive elastomers.

-. 8 In co~poundinq the thermally conductivesilicone elastomers, the above base material is combined with the ingredients below in the following manner:
Component Amount 5 1. Base Material 400.00 grams 2. Boron nitride (diameter:
48-90 Microns) 100.00 grams 3. Silicone Fluid 200 (100,000 centi-stokes at 25) 40.00 grams 10 4. Silastic J Curing Agent 40.00 grams 5. Cure Modifier E-1990-76 0.80 grams The silastic J RTV silicone elastomer (base material) and boron nitride powder are charged in a Ross double planetary mixer. The addition of silicone fluid 15 200 follows with mixing for 4 minutes. The mix is scrapped off in middle of mixing chamber for better mixing. Then the silastic J curing agent and cure modifier are added to the mixture and mixing is completed in six more minutes.
After de-aeration of mix for 30 minutes, it is ready for 20 molding and determination of working time with the Brookfield Viscometer ~Model LV). The working time of mixture is over in 15 hours.
Molding of mix is carried out by pouring and spreading the mixture in a four cavity, chrome-plated mold 25 kept at ambient temperature. After curing the compound for 20 minutes (top platten of hydraulic press at 232C and bottom at ambient temperature) under 70 ton pressure, the rubber slabs are taken out of mold and post cured in an air circulating oven for 3 hours at 202C. (Alternately, the 30 mixture can be cured at room temperature for 24-48 hours)~
The molded articles exhibited the following physical properties before and after aging* at 260C for 500 hours.

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Test ~ dness ~ ulus at Tensile Tear Elongaticn Te~p. Shore A 10~ Elong. Streng~l Strength ~Pa ~Pa KN/M
25C 65 0.82 3.00 12.90 56 5 232C 65 0.93 1.77 6.20 26 232C* 70 1.01 1.44 3.90 16 There is good retention of physical properties on aging at 260C for 500 hours. The weight loss on aging is small (4.4 vs 6.00) compared to silicone materials without boron nitride. The thermal conductivity of molded, rectangular shape is 9.53 x 10 4 cal sec. cm C 1.
The addition of conductive filter to the elastomer compositions shows no negative effects and substantially increases the thermal conductivity of base elastomer material. Improvements in thermal expansion are also found.
(1) The silica particulate of the base material is about 1093 parts by weight ground silica (Min-u-sil) and about 58 parts by weight fumed silica (cab-O-Sil MS-75).
Min-U-Sil is a white powder with particles having an average diameter of about 5 microns and a specific gravity of about 2.65. Cab-O-Sil MS-75 has a specific gravity of 2.2 and an average particle diameter between about 0.07-0.1 microns.
The base material further includes less than about 10 parts by weight of a platinum complex catalyst which is a vinyl siloxane oligomer modified by platinum metal (available from Dow Corning). The base material with these ingredients has a viscosity between 700-1300 centistokes at 25C.
Example 58 The base material prepared as described in Example 57 is compounded with the following ingredien"s as in Example 57.

1 15'~ 3l) Component Amount -1. Base r1aterial 400.00 grams 2. Boron Nitride (Particle Diameter 48~90 Micron) 140.00 grams 3. Silicone FLuid #200 (100,000 centi-stokes at 25C) 40.00 grams 4. Silastic J Curing Agent40.00 grams 5. Cure Modifier E~1990-760.80 grams After mixing all ingredients in a Ross double planetary mixer as in Example 57 the compound has a working time of 11.0 hours.
Articles molded according to procedure of Example 57 exhibit good physical properties before and after aging at 260C for 500 hours. ~igher thermal conductivities and lower weight losses are also found.
Example 59 Example 57 is repeated with the exception that the weight of boron nitride is lowered (75.00 grams, 48-90 microns). After mixing all ingredients on a 80 x 180 mm two-roll vented research mill, the compound has a working time of-over 20.0 hours.
Specimens molded under the same conditions as materials of Example 57 exhibit good physical properties.
Lower weight loss on aging and improvements in thermal conductivity are found.
Example 60 The base RTV silicone material prepared as described in Example 57 is combined with the following ingredients according to mixing procedure and equipment of Example 57.

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~ Amount 1. Base ~aterial (RTV Silicone Elastomer) 400.00 grams 2. Boron nitride (Particle Diameter 25-30 Microns) 100.00 grams 3. Silicone Fluid #200 (100,000 centi-stokes at 25C) 40.00 grams 4. Silastic J Curlng Agent 40.00 grams 5. Cure Modifier E-1990-76 0.80 grams Upon completion of mixing, the mix has a working tlme of less than one hour.
Articles molded according to Example 57 exhibit the following properties before and after aging* at 260C
for 500 hours:
Test Hardness Modulus at Tensile Tear Elongation 15 Temp. Shore A 10% Elong. Strength Strength %
MPa MPa KN/M
25C 68 1.24 3-09 12.50 46 232C 68 1.10 2.19 6.10 22 232C* 77 1.44 1.76 3.75 13 Molded specimens exhibit lower weight losses (4.9%) than materials without boron nitride. The thermal conductivity of these articles (13.90 cal sec. 1 cm C ) is over three times higher than values of material without the conductive filler. The expansion characteristics are also improved.
Example 61 Example 60 is repeated with the exception that lower amounts of boron nitride were used (80 grams, 25-30 microns boron nitride). After mixing according to procedure of Example 57, the mixture had a working time of less than 2.0 hours.
Molded specimens according to procedure of Example 57 had good physical properties before and after aging at 260C for 500 hours. These materials showed improvements in thermal conductivity and lower weight loss on aging.

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Example 62 The base silicone elastomer prepared as described in Example 57 is mixed with the foLlowing ingredients as in Example 57.
Component Amount 1. Base Material 500.00 grams 2. Boron Nitride (Particle Diameter 25-30 Microns) 125.00 grams 3. Silicone Fluid #200 (100,000 centi-stokes at 25C) 65.00 yrams 4. Silastic J Curing Agent60.00 grams 10 5, Cure Modifier E-1990~76 1.00 grams After mixing the ingredients, the mix had a working time of about 3 hours.
Molded specimens according to procedure of Example 57 exhibit good physical properties and improvements in thermal conductivity.
Example 63 Example 62 is repeated with the exception that a larger amount of silicone fluid #200 is used (90.0 gra~ms silicone fluid #200). The mixture has longer working time and was moldable.
Example 64 The base material (RTV silicone base) described in Example 57 is mixed with the following ingredients according to procedure of Example 57.
Component Amount 1. Base Material 400.00 grams 2. Boron Nitride (Particle Diameter 48-90 Microns) 50.00 grams 3. Boron Nitride (Particle Diameter 25-30 Microns) 50.00 grams 4. Silicone Fluid #200 (100,000 Centi-stokes at 25C) 40.00 grams 5. Silastic J Curing Agent40.00 grams

6. Cure Modifier E-1990-76 0.80 grams 1 1591~) After mixing the above components, the mixture has a working time of over 4 hours.
Molded specimens according to procedure of Example 57 show improvements in thermal conductivity and have good physical properties.
Example 55 Example 64 is repeated with the exception that 70 gms. of boron nitride (particle diam. 48-90 microns) are used for preparing the mixture. The mix has a working time of over 3 hours. It shows good thermal conductivity.
Example 66 Example 57 is repeated with the exception that 180 gms. of boron nitride (particle diameter 48-90 microns) is used for preparation of mixture. The compound is moldable and exhibit good thermal conductivity.
Example 67 The base of Example 57 is combined with the following ingredients according to procedure of Example 57.
Component Amount 20 1. Base Material 400.00 grams 2. Boron Nitride (25-30 Microns)100.00 grams 3. Silicone Fluid (30,000 centi-stokes at 25C) 40.00 grams 4. Silastic J Curing Agent 40.00 grams 25 5. Cure Modifier E-1990-76 0.80 grams After combining the ingredients, the mixture is moldable.
Example 68 Example 57 was repeated with the exception that another size grade (on 20 mesh-none, on 325 mesh - 90~) of boron nitride is used for preparing the mixture. Upon mixing the compound is moldable and has good properties.

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Example 69 Examples 57, 58 and 59 are repeated with the exception that 0.6 grams of cure modifier E-1990-76 are used in compounding the ingredients. Similar results are seen.
Example 70 Examples 60, 61 and 62 are repeated with the exception that 1.6 grams of cure modifier E-1990-76 are used for preparing the mixture. Similar results are obtained.
Example 71 In Examples 57-61 silastic J RTV silicone elastomer is replaced by silastic L&E. Similar results are obtained.
In the above Examples 1-71 the Silicone Fluid #200 (viscosity modifier) is a silicone fluid number designation of fluid available from the Dow Corning Corporation. Silicone fluid designated by viscosity are also available from Dow Corning.
The Silastic J, E and L (i.e. crosslinking polymer) as well as Silastic Curing Agent (i.e. crosslinking oligomer) and Cure Modifier E - 1990 - 76 are also available from the Dow Corning Corporation.
Information on the Silicone Fluid #200 used in the 25 above Examples may be obtained from Form No. 22-069C-76 of Dow Corning Corp. Information on Silicone Fluid #705 (Dow Corning 705 Diffusion Pump Fluid described as pentaphenylmethyltrisiloxane) used in the above Examples may be had from Bulletin 22-287 date 8/74 from Dow Corning Corp.
Information on Silastic J RTV Silicone Elastomer (and curing agent) used in the above Examples may be obtained from Form No. 61-080A-76 of Dow Corning Corp. Information on Silastic E and L elastomers used in the above Examples may be obtained from Form No. 61-326-76 of Dow Corning Corp.

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~ 159 ~3 These ingreclients are all deemed ~ithin the scope of the invention as hereinbefore disclosed.
In the above Examples 1-71 the Silicone Fluid 200 and 705 (viscosity modifier) are silicone fluid number designations of f]uids available from the Dow Corning Corporation. Silicone fluid designated by viscosity are also availahle from Dow Corning.
~ he Silastic J, E and L (i.e. crosslinking polymer) as well as Silastic Curing Agent (i.e. crosslinking oligomer) and Cure Modifier E - 1990 - 76 are also available from the Dow Corning Corporation.

,~

Claims (23)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:
1. A dispensible precursor composition for highly filled, thermally conductive elastomers which composition comprises:
I. 100 parts by weight of an olefinically unsatur-ated crosslinkable polysiloxane having the formula:
I
wherein at least most of the Ra's and Rb's are selected from (A) saturated hydrocarbyl or hydrocarbyloxy groups having a total of 1 to about 10 carbon atoms that are alkyl or aryl or alkyl and aryl and (B) allyl or vinyl groups but wherein up to about 25% of the Rb's may be Ia wherein at least most of the Rc's and Rd's are selected from (A) and (B) above but up to about 10% of the Rd's may contain additional siloxane units with substituents selected from (A) and (B) or still additional siloxane units; and still further wherein (1) m and n are integers such that the average number of siloxane units per polymer molecule is between 100 and 300 and (2) there is an average of above about 1.5 but lower than 6 cross-linking sites selected from the vinyl, allyl or vinyl and allyl groups per polymer molecule;
II. about 35-550 parts by weight of finely divided particulate comprising:
(A) silica particulate at a weight ratio to the polysiloxane of I. of between about 1:4 to 3:1 wherein the silica particulate comprises:

1. ground silica having an average particle diameter between about 0.1 and 15 microns; and 2. fumed silica having an average particle diameter between about 0.005 and 0.015 microns;

(B) thermally conductive carbon powder at a weight ratio to the polysiloxane of I. of between about 1:10 to 2.5:1;
III. a viscosity modifier comprising a silicone oil having a viscosity between about 1000-1,000,000 centistokes at 25°C at a weight ratio to the particulate of II of between about 1:20 to 1:4 oil to particulate, and IV. a silyl hydride functional polysiloxane oligomer containing from 5 to 50 siloxane groups that crosslinks with I at a weight ratio with respect to the polysiloxane of I. of between about 1:3 to 1:20, the silyl hydride functional polysiloxane oligomers having an average of up to about 20 silyl hydride groups per polymer chain.

2. The precursor composition in accordance with Claim 1 wherein the crosslinkable polysiloxane is substantially free of branching.

3. The precursor composition in accordance with Claim 1, wherein the viscosity modifier comprises a dialkylpolysiloxane.

4. The precursor composition in accordance with Claim 3 wherein I (B) is vinyl.

5. The precursor composition in accordance with claims 1, 2 or 3 wherein the conductive carbon powder comprises graphite.

6. The precursor composition in accordance with claim 1, 2 or 3, wherein the conductive carbon powder comprises graphite and silicone oil is selected from the group con-sisting of dimethyl silicone, methyl phenyl silicone, branched methyl phenoxy silicone, branched chlorophenyl silicone, fluorosilicone, nitride silicone, methyl hydrogen and methyl vinyl silicone oils and combinations of two or more of them.

7. The precursor composition in accordance with claim 1, 2 or 3, wherein the conductive carbon powder is graphite and the silyl hydride function polysiloxane has the formula:

wherein n averages between about 5 and about 14, Ro and Ao are alkyl or alkoxy groups having 1-3 carbons, phenyl or phenoxy groups.

8. The precursor composition in accordance with claims 1, 2 or 3 wherein the weight ratio of II.A to II.B is greater than about 2:1.

9. An elastomer made from the precursor composition of claims 1, 2 or 3.

10. An elastomer made from the precursor composition of claim 1, 2 or 3, wherein the weight ratio of silica to the polysiloxane of I. is between about 0.9:1 to 1:0.9.

11. The precursor composition in accordance with claim 4 wherein the conductive carbon powder comprises graphite.

12. The precursor composition in accordance with claim 11, wherein the silicone oil is selected from the group con-sisting of dimethyl silicone, methyl phenyl silicone, branched methyl phenoxy silicone, branched chlorophenyl silicone, fluorosilicone, nitride silicone, methyl hydrogen and methyl vinyl silicone oils and combinations of two or more of them.

13. The precursor composition in accordance with claim 11, wherein the silyl hydride function polysiloxane has the formula:
wherein n averages between about 5 and about 14, Ro and Ao are alkyl or alkoxy groups having 1-3 carbons, phenyl or phenoxy groups.

14. The precursor composition in accordance with claim 4 wherein the weight ratio of II.A to II.B is greater than about 2:1.

15. An elastomer made from the precursor composition of claim 4.

16. An elastomer in accordance with claim 15, wherein the weight ratio of silica to the polysiloxane of I. is be-tween about 0.9:1 to 1:0.9.

17. A thick, highly filled, shaped elastomeric body made by filling a cavity with a dispensible elastomer precursor, which comprises:
I. 100 parts by weight of an olefinically-unsaturated crosslinkable polysiloxane having the formula:
I
wherein at least most of the Ra's and Rb's are selected from (A) saturated hydrocarbyl or hydrocarbyloxy groups having 1 to about 10 carbon atoms that are alkyl or aryl or alkyl and aryl and (B) allyl or vinyl groups but wherein up to about 25% of the Rb's may be Ia wherein at least most of the Rc's and Rd's are selected from (A) and (B) above but up to about 10% of the Rd's may contain additional siloxane units with substituents selected from (A) and (B) or still additional siloxane units; and still further wherein (1) m and n are integers such that the average number of siloxane units per polymer molecule is between 150 and 250 and (2) there is an average of above about 1.4 but lower than 2.5 crosslinking sites selected from the vinyl, allyl or vinyl and allyl groups per polymer molecule;
II. about 60-500 parts by weight of finely divided particulate comprising:
(A) silica particulate at a weight ratio to the polysiloxane of I. of between about 0.3 to 2.5:1 wherein the silica particulate comprises:
1. ground silica having an average particule diameter between about 0.5 and 10 microns; and 2. fumed silica having an average particule diameter between about 0.010 and 0.014 microns;
(B) thermally conductive alloy powder at a weight ratio to the polysiloxane of I. of between 0.3 to 2.5:1 wherein the alloy is an alloy of a first row transition metal;

III. a viscosity modifier comprising a silicone oil having a viscosity between about 1000-1,000,000 centistokes at 25°C at a weight ratio to the particulate of II of between about 1:20-1:4 oil to particulate; and IV. a silyl hydride functional polysiloxane oligomer containing be-tween about 5 and about 50 siloxane groups at a weight ratio with respect to the polysiloxane of I. of between about 1:3 to 1:20, the silyl hydride functional polysiloxane oligomer having an average of more than 1 and less than 20 silyl hydride groups per polymer chain.

18. The elastomeric body in accordance with claim 17, wherein the crosslinkable polysiloxane is substantially free of branching.

19. The elastomeric body in accordance with claim 17, wherein the viscosity modifier comprises a dialkylpolysiloxane.

20. The elastomeric body in accordance with claims 17, 18 or 19 wherein I(B) is vinyl.

21. The elastomeric body in accordance with claim 17, 18 or 19 wherein I (B) is vinyl and the silyl hydride function-al polysiloxane has the formula:

wherein n averages between about 5 and about 14, Ro is selected from the group consisting of alkyl or alkoxy groups having 1 to 3 carbons, phenyl and phenoxy groups, and Ao is selected from the group consisting of alkyl groups having 1 to 3 carbons and phenyl.

22. The elastomeric body in accordance with claim 17, 18 or 19 wherein I(B) is vinyl and the weight ratio of ground silica II(A) to fumed silica II(B) is greater than 2:1.

23. The elastomeric body in accordance with claim 17, 18 or 19 wherein I(B) is vinyl, the weight ratio of ground silica II(A) to fumed silica II(B) is greater than 2:1, and the weight ratio of ground silica to the polysiloxane of I is about 0.9:1 to 1:0.9.