CA2082734A1

CA2082734A1 - Heat curable platinum catalyzed silicone coating compositions

Info

Publication number: CA2082734A1
Application number: CA 2082734
Authority: CA
Inventors: Chris A. Sumpter; Larry N. Lewis; Judith Stein; James V. Crivello; Mingxin Fan
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1991-12-20
Filing date: 1992-11-12
Publication date: 1993-06-21
Also published as: US5223344A; JPH05262986A

Abstract

ABSTRACT OF THE INVENTION
The present invention discloses the use of certain silicon hydrides having at least two hydrogen atoms attached to silicon in particular heat curable platinum catalyzed silicone coating formulations, which permits the use of a reduced level of inhibitor and improved cure performance.

Description

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HEAT C:URABLE PLATINUM t::A~ALYZED SILICONE
COATIIIG COMPOSI~IONS
... . ......

The present invention relates to a heat curable silicone coating composition. More particularly, the present invention relates to a heat curable sllicone coating composition having an accelerated cure rate. Most particularly, the pxesent invention relates to the use of small amounts of an additive which contains silicon bound to greater than or equal to two hydrogens to accelerate the rate of cure of addition curable silicone material.

The pre3ent invention relates to heat curable organopolysiloxane fluids well known in the art which utilize a silicon hydride siloxane fluid, silicon vinyl siloxane fluid, an effective amount of a platinum catalyst, an inhibitor which prevents premature gelation and a cure accelerator composed of silicon dihydride and trihydride monomers. More particularly the present invention relates to the use ; of the sLlicon dihydrides and trihydrides which accelerate the cure of addition cur~ silicone formulations. These formulation~ are useful as release coatings an paper, plastic, and similar substrate~. The~e formulations are also useful a~
potting compounds, conformal coati~gs of electronic parts, etc.
Special mention is made of Schilling, Jr., United States Patent No. 4,614,B12 and Lewis, L.N. et al , J Am. Chem. Soc., vol. 108, pp. 7228 (1986) .
which have reported that the use of small quantities of an SiH compound accel~rates the ra e of addition cure silicones.

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Recently it has been shown that platinum catalyzed hydrosilation of R2SiH2 or RSiH3 containing silanes is difficult or nearly impossible to carry out. In Lewis et al., Or~anometallics, vol. 9, pp .
5621-25 (1990), it was reported that the SiH2 or SiH3 poisoned the platinum catalyst.
Surprisingly, contrary to the suggestions of the prior art, the present applicants have now found that the addition of small amounts of SiH~ and/or SiH3 acts to accelerate the rate of cure of platinum catalyzed addi~ion curable silicone materials. This is entirely unexpected ln light of the teachings of the prior art that the di and tri hydride ~ilanes are poisons to the platinum catalyst. As shown in the working examples, hereinbelow, the addition of the R2SiH2 and/or RSiH3 silane additives to a platinum catalyzed addition curable silane system accelerate~
the cure of the silane so that curing i~ effected at faster rates and at lower temperatures than silane curing systems of the prior art.

SUMMARY OF THE INVENTION

According to the present invention there is provided a heat curable sLlicone composLtion comprising ~a) a vinyl containing polydiorganosilicone fluid; tb) an effec~ive amount of a crosslinking silicone hydride containing polydiorganosilicone; (c) an effective amount of a platinum group metal catalyst; and (d) a small effect~ve amount of a silane additive which comprises silicon bound to greater than or equal to two hydrogen atoms. Preferably, the heat curable ~ilicone composition also comprises ~e) an inhibiting agent.

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Also according to ~he present invention there is provided a method for preparing a heat curahle silicone composition comprising mixing (a) a vinyl containing polydiorganosilicone fluid; (b) an effective amount of a crosslinking silicone hydride containing polydiorganosillcone; (c) an effective amount of a platinum group metal catalyst; and (d) a small effective amount of a silane additive which comprises silicon bound to greater than or equal ~o two hydrogen atoms. Preferably, the method also comprises the addition of (e) an effective amount of an inhibiting agent.
In preferred embodiments, the vinyl containing polydiorganosilicone fluid (a) is a vinyl containing polydimethylorganosilicone fluid; the silicone hydride polydiorganosilicone (b) is a polydimethylsilicone fluid; the platinum group metal catalyst (c) comprises a platinum catalyst, said silane additive (d) comprises diphenylsilane or phenylsilane; and the inhibiting agent te) is selected from diallylmaleate, dimethylmaleate and mixtures thereof.

The present invention provides hea~ curable silicone composit~ons. The ~ddition curable composLtions are comprised of a mixture of several ingredients which can be coated upon a substrate such as paper and when cured thereon will form a coating on the substrate. In addit~on, these silicone compo~itions can be cured ln bulk to be used as bumper gels, potting compounds, etc.

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Component (a) of the compositions of the present invention are vinyl containing polydiorgano-siloxane base polymers which are generally comprised of siloxane units having substituent groups including lower alkyl radicals having up to about 8 carbon atoms such as methyl, ethyl, propyl, isopropyl, etc., and monovalent alkenyl radicals of from about 2 to 20 carbon a~oms such as vinyl, allyl, butenyl, etc., including cycloalkenyl. These polymers are prepared by methods known in the art and are commercially available with varying degrees of functionality. They generally have a viscosity ranging from about 50 to about 100,000 centipoise at 25C~
Preferred diorganopolysiloxane base polymers (a) of the present invention are vinyl-chainstopped diorganopolysiloxanes having the general formula:

M~lD MVl or MVlD D
: H
wherein MVl comprises HzC==CH-Si-Oos units, R

D~ compri4eR ( S~ ~ O unit~, Dy comprlse~ ( 5- ~ O

units and wherein R is, independently, a monovalent : 25 hydrocarbon radical free of unsatura~ion having up to about 8 carbon atoms, Rl is a hydrocarbon radical having alkenyl unsaturation of from 2 to 20 carbon atoms, and m and n ar~ positive integer~ such that said vinyl containing sillcone fluid has up to about 20% by weight R' groups. Most prefera~ly ~he R groups .

2~)g273L~

will be methyl, the Rl groups will ~e vinyl, and the viscosity of the polymers will range from about 300 to about 5000 centipoise at 25~C. Most preferred is a vinyl containing polydimethylsilicone.
The SiH-containing polysiloxanes for use herein as crosslinking agen~s are comprised primarily of compounds having the general formula:

MDX~M or MD~yDxM

wherein each M is a unit of the formula R3SiOos wherein each R is independently a~ defined above; where Dx is as described above and where D~ is an SiO- unit R
where R is as described above. ~uch polysiloxanes will include, for example, cyclic polymers such as sym-tetrahydrotetramethylcyclotetrasiloxane, or linear polymers such as alkylhydrogen-siloxane fluids or polydialkyl-alkylhydrogen siloxane copolymers.
Particularly useful as crossllnking agents for the present invention are trimethyl-chainstopped polymethylhydrogen siloxane fluid~ having xom approximately 10~ to 100~ SiH groups and having a viscos~ty in the range of from about 15 to about l,000 centipoise at 25C.
The curing reaction which takes place between the vinyl-functional polysiloxane base polymer and the SiH-containing crosslinking ~gent is an a~dition cure re~ction, Xnown as hydrosilation. The compositions of the present invention may be thermally ~30 cured by means of a platinum group metal catalyzed : crosslinking reaction between ~he vinyl gxoup~ of the base polymer and the SiH reaction si~es of the crosslinker.

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Suitable hydrosilation catalysts to be employed in ~he present invention are known to persons skilled in ~he art and include platinum group metal catalysts utilizing such precious metals as ruthPnium, rhodium, palladium, osmium, lridium and platinum, and complexes of the~e metals. Preferred are platinum metal catalysts. Examples of such hydrosilation catalyst~ arQ described in, inter alia, Lamoreaux, United States Patent No. 3,220~972; Rarstedt, United States Patent Nos. 3,715,334; 3,775,452 and 3,814,730;
Ashby, United States Patent Nos. 4,421,903; and 4,2B8,345; and Saruyama et al., United States Patent No. 5,057,476.
The selection of the particular cataly~t will depend upon such factors as speed of reaction desired, expense, useful shelf-life, useful pot~ fe and the temperature at which the cure reaction is to take place. The amount of catalyst employed is not critical, so long as proper crosslinking i~ achieved;
however, as indicated above, the high cost of these precious metal catalysts makes their conservativ0 use obligatory. A~ with ~ny catalyst, it is preferable to use the smallest effective amount possible, for the coating compositions described herein, enough total catalyst is used to provide from about 5 to about 500 paxts per million of precious metal as precious metalO
; Es~ential to the practice of the instant invent~on is the use of the silane cure accelerator additive. The silane addltives of the present invention are those having at least two hydrogen atoms bonded to the silicone atom. Preferred are those havlng the general formula R22SiH2 and RZSiH3 where R2 is selected from the group consisting of alkyl radicals;
halldes ~uch a~ chlorine, bromine and iodine;
cycloalkyl radicals and phenyl radicals.

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Typically the silane cure accelerator additives are selected fro~ silanes such as, but not limited to, dichlorosilane, dimethylsilane, diethyl-silane, dipropylsilane, dibutylsilane, dipentylsilane, dihexylsilane, diheptylsilane, dioctylsilane, dinonyl silane, didecylsilane, dicyclopentylsilane, dicyclo-h0xylsilane, dicycloheptylsilane, dlphenylsllane, phenylchlorosilane, phenylethylsilane, methyl-octylsilane, methyldecylsilane, phenylmethylsilane, phenylethylsilane, phenylcyclohexylsilane and methylcyclsheptyl~ilane. Preferred are diphenyl-silane, phenyl~ilane, dioctylsîlane, m~thyldecyl-silane, phenylme~hylsilane and didecylsilane. Most preferred is diphenylsilane and phenylsilane.
The silane cure accelerator additives are employed in small efective amounts. Typically the silane cure accelerator additive is present in the compositions of the present invention in amounts ranging ~rom about 0.25 to abou~ 20 moles of silane to moles of catalyst metal, most preferably from about 0.5 to about 5 moles of silane to moles of catalyst metal.
The compo itions of the present invention also may comprise (e) an inhibiting agent. These serve to prevent premature cure in one-package system~
and also extend khe shelf-life of stored products and the pot-life of products in use. That is, at room temperature, the complete sili~one composition will not gel prematurely, as often happens with catalyzed silicone compositions. Especially useful are dialkyl and dialkenylcarboxylic ester inhibitors such as diallylmaleate and dimethylmaleate. These are known to those skilled in ~he art and are described in United States Pa~ent No. 4,256,870.

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Additional inhibitors useful in the practice of the present invention include but are not limited to acetylenic alcohols such as those described in United States Patent No. 3,445,420; amines such as those described in United States Patent No. 4,584,361;
isocyanurates such as those described in United States Patent No. 3,882,0~3; ene-ynes such as those described in United States Patent No. 4,465,818; vinyl acetates such as those described in United States Patent No.
4,476,166; and acetylene ~icarboxylates such as ~hose described in Unlted State~ Patent No. 4,347,346.
Additional ingredients may be added to the curable compositions of_the present invention to lend speciflc properties and allow the composition~ to be tailor~d to an end-user's needs. For example, the compositions may be dispsrsed in a solvent or used in a 100% solids formulation, as required.
Vinyl gum cure accelerators, such as those described in Eckberg, United States Reissue Patent No.
RE 31,727, can be added to the compositions of the present invention. Addlng from about 0.5 to about 10 weight percent based on the total weight of the base polymer of the vinyl gum reduces the required curin~
time.
Other conventional additive~, such as controlled release additives ("CRAs"), anti~microbial agents, anti-foaming agents and other additives familiar to persons skilled in the art are also contemplated by t.he present disclo~ure.
Fillers and additive~ to improve the thermal stability, weather resistance, chemical resistance~
flame retardancy or mechanical strength or to reduce the degree of gas permeatlon can also be added.
Examples of these f~llers and additives include fumed silica, quartz powder, glas~ fiber, carbon black, alumina, metal oxides such a3 Lron oxide and titanium 2~273~

oxide and metal carbonates such as calcium carbonate and magneqium carbonate. Moreover, suitable pigments, dyes, blowing agents or antioxidants can be added within a range which does not interfere with the 5 curing process.
The components of the present invention, along with suitable additives are mixed together. The curable silicone coating compositisns of the present invention will cure to a tack-free, smear-free condition on brief exposure to temperature3 in the range of from about 90 to abou~ 300C. The compositions of the present inventlon remain ungelled at ambient temperatures for at least 24 hour , but hea~ cure on useful substrates at temperakures below about 150C, preferably below about 125C, and most preferably below about 110C. The heat cure reaction can be initiated by many ways such as by infrared ; lamps, but typlcally a forced air oven is most : suitable. The composit$ons of the present invention can be applied to substrates in many ways such as by coating, spraylng, brushing and application by blade or gravure processes. The present invention thus provide~ a method for rendering surfaces abhesive by application of the present coating compositions to a suitable substrate. Such substrates can include, but are not limited to, gl~ss, metal, paper, polyethylene coated kraft (PEK) paper, super-calendered Xraft (SCK) paper, polye~hylene films, polypropylene films and polyester films.
Thesa curable coa~ings thus have a wide variety of useful applications. Examples of such applications are a~ follows: potting materials, coa~ing mater~als and molded product~ for the electrical and electronics lndu~trie~; potting materials, coating materials a~d molded product~ for `` 2082734 general industry; rubber for die molding; perforated sections for civil engineering and construction; seam sealants; molded products for medical applications;
impression materials for dental applications and materials for liqu~d injection molding.

DESCRIP~ION OF THE PREFERRED EMBODIMEN~S

~ he following examples illustrate the present invention. They are not intended to limit the scope of the appended claims in any manner whatsoever.
Cure is defined for the purpo~e of the instant specification and the examples below as a coating which will pass both t~e aggressive rub test and the 3M 610 tape test.

CO~PARATIVE EXAMPLE A

A standard commercial formulation that contains 100 parts of a vinyl end stopped polydimethylsilicone fluid of fonmula MVlDXMVl having a viscosity of 420 cps, 0.25~ by weight diallylmaleate (DAM), 75 ppm Pt as "Karstedt catalyst" (Karstedt, United States Patent No. 3,775,452) and 4 parts by weight polydimethylsilicone fluid of formula MD~XM
having a viscosity of 20-40 cps is cured on super-calendered kraft (SCK) paper. The formulation cured at 115C in 15 ~econds but would not cure at 115C at less than 15 seconds or at 105C for 30 seconds.

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COMPA~ATIVE EXAMPLE B

An experimental commercial formulation containing 100 parts vinyl containing polydimethylsilicone fluid of formula MVlDxMvi having a viscosity of 285 cps, 0.55 percent by weight of DAM, 150 ppm "Ashby platlnum catalyst" (Ashby et al., United States Patent No. 4,288,3~5), and 2.6 parts of an SiH crosslinker vf the formula MDXM having a viscosity of 20-40 cps was cured on SCX paper. The formulation gave a cured coating at 110C in 20 seconds, but did not give a cured coating if cured for less than 20 seconds ~ 110C or for 30 seconds at 100C.

EXA~PLE 1 A formula~ion was prepared co~taining 100 parts of the M~1DXMVl fluid with a viscosity of 420 cps, O.2% DAM, 75 ppm Pt as Kar~tedt catalyst, 0.019 parts of diphenylsilane (Ph2SiH2) and 4 parts MDXM
crosslinker. The formulation became yellow upon addition of the silane. The formulation cured on SCK
paper at 105C in 15 seconds.

EXANP~E 2 A formulation containing 100 parts M~XMl fluid having a viscosity of 285 cps, 0.3% DAM, 150 ppm Ashby catalyst, 0.005 parts phenylsilane ~PhSiH3) and 2.6 parts MD~XM crosslinker. The formulation cured on SCK paper at lOO~C in 20 seconds. This formulation also turned yellow upon the addition of the SiH fluid.

.
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' ' ~ ;- ' ' .

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2~2~34 It can be seen from Examples 1 and 2 and Compaxative Examples A and B that the addition of a catalytic amoun~ o~ the silane cure accelerator additive (Ph2SiH2 and PhSiH3) gave new formulations which were stable at ambient temperatures and unexpectedly gave cured coatings at lower temperatures and sharter curing times. Smaller amounts of maleate inhibitor could be used in the formulations due to additional ambient temperatuxe inhibition provided by the silane additive.

EXAMPL~S 3-9 Various coating formulations are prepared following the procedures of Examples 1 and 2. The formulations were applied to SCK paper via a doctor blade and curing was effected in a forced air oven.
For comparative purposes, sample~ were prepared without the silane cure accelerator additive.
Additionally, several of the samples were subjected to an accelerated agin~ test. A sample was considered to pass the tes~ if the viscosity did not ~ double after 4 hours at 40C.
: The compositional data and the results are set forth below in Table 1.

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oIO~o, ~oIooI~I~I
, o I U~ . ~3 oo o, ~ ~, , , , o O ~ ~ ~ ~D

ow, o ,o,o~.,o o,,o,,~,,~,, In ~O I U') IOIO~IO OIIOII~II~II ~OO~
~`I IoIu~.~ ooII~II II II o~
_~ ~1 0 . _I ~ er o U~
~ U~ I O
IOIo~.Io oIIoII
~I ~ O C~
~`
~r _ H It'S O
U~ I In I ~ ~r In I O I I O I I h I 1 14 1 o 11~ 1 I 1` I ' I N I I N
O _I
~1 ~C U~ ~ IIOII~
E~ ~ I o I ~ I o I o I I
~_I O ----~ O . ,~
O
_I

I o I o m ~D I I O o u~ o Ir) o l~ 4 h 1` 0 I o I ~ I o ~ _1 ~ ~ cr~

U~
* I o I U~ o o 0~ ~4 ~ ~ ~ ~ I I
C~

c ~ u c o O O ~
c o 1~ Ei u~ u~ ~ ~ S o ~ H C4 X O ~ C S~ 0 ~rl :, 2 ~ 8 2 ~ 3 l~

In Table 1 above, the superscript notations have the following meanings.
* = Comparative Example pbw = Parts by weight 5 a = Vinyl end stopped polydimethylsiloxane fluid mixed with a siloxane gum, 420 cps viscosity b = Vinyl end stopped polydimethylsiloxane fluid, 285 cps viscosity = Platinum complex catalys~ prepared according to Ka~stedt, United States Patent No. 3,77~,452, in parts per million d = Platinum complex catalyst prepared according to Ashby et al., Unitè~ Sta~es Patent ~o. 4,288,345, in parts per million 15 e = Diallylmaleate = Polyme~hyl hydrogen siloxane, 20-40 cps viscosity, 1.6% H by weight = Diphenylsilane, Ph2SiH2 h = Phenylsilane, PhSiH3 1 = Some formulations were tested at more than one cure level = P is pass, M i9 marginal pass, F is fail = Measured in a Brookfield vi~cometer Table 1 above demonskrakes the significant increase in the acceleration of cure ra~es obtained upon addition of di- and trihydrosilanes to composi~ions wi~hout any additive.

To demon~trate lmprovemznts over the monohydrlde silicones of the prior art, a sample, 10, is prepared as in Example 6 above and a first co~parative sample, E*, is also prepared as in Exampl~

' ' "

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-lS- 60SI-1473 6 except th~t the- PhSiH3 i~ sub8tituted wlth triphenylsilane (Ph3SiHl at the same molar leval.
A ~econd comparative sample, F~ prQpared a~ in Example 2 except the inhibitor is used at the same level in th~ fir~t comparative sample, E~, without the addltion of any other s~lane.
The result~, are shown below in ~able 2 TAB~E 2 Ex~mple E~ F* 10 Compositio~, pbw Ba~e pol ~ er~lO0 100 100 Cat~lyst 150 150 150 Inhibitor~ 0.~2 0~2 0.32 Silane _D.005d -- 0.005 Cro~slinker~ 4 4 4 Properties Cure Temp., C105 105 lOS
Cure Tlme, se~20 20 20 Rub Test F F P
Tape test F P P
Visco~ity (cpS) initial 292 284 2~3 post-aging gelg gel9 60B
* = Comparative Example = Vinyl end stopped polydimethylsiloxane fluid, 285 cps b = Platinum eomplex ~atalyst (Ashby) in ppm = Diallylmalea'ce = Triphenylsilane (Ph SiH) = Phenyl Silane (PhSi~3) ' = Polymethyl hydro~en siloxane, 20-40 cps, 1.6~ H ~y weight 9 = Gelled in le~3 than 4 hours The d3~a in Table 2 above show~ that sub~titution of phenylsilane of the present invention (10) with the triphenylsilane of ~he prior art ( E~ ) causes a signil~cant lo~s ln the cure acc~leratlon 5 time.

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EX~P~E 11 The following example~ ~how that the accelera~ing effect of the silane cure accelerating additives of the present invention occur in an addition cure silicone cured in ~ulk.

For control purpo~ a formulation, ~*, was prepared which con~ained 48 g of a M ~Dx~ fluid having a viscosity of 4000 cp~, 10 ppm of plat~num a~
Karst~d~ catalyst, 0.02 parts by weight of di~hyl maleate (DMM), and 4 parts by weight of an SiH
cros linker, MD8XDyM, 0.8 percent H, viscosity of 20-40 cpg. The time ~o g~llation was m~a~ured in a Sun~hine gel timer.
lS Exam~le 11 A ~ormulation, Ex~mpl~ 11, wa~ prepared a~
ln control G* above ex~pt that 0.014 parts by weight of DMM were used and 0.006 part~ by weight of phenyl silane were added.
Comparative Example H~
For comparative purpo~es, a formulation, comparative example H~, wa~ prepared as in Control G~, except that 0.01~ p~rts DMM were used and 0.012 parts Ph3SiH were added. The results of the gel time mea~urements are set forth below in Table ~.

Table 3 _____ e G* H 1l Silane accelerator -- Ph3Sl~ P~H3 G~l Time, at 54 in seconds 475 476 398 ~=
= Comparative Example ,: :

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The data in Table 3 above shows that ~he inclusion of the phenyl silane provided a significant improvement i~ cure time, while the Ph3SiH had no accelerating effect.
The above-identified patents and publicatlon~ are hereby incorporated by reference.
Many variations of the present invention will suggest themselves to those skilled in the art in light of the above detailed description. For example, a wide variety of vinyl containing polydiorgano-silicone fluids in addition to polydimethylsilicone fluids can be employed. Further, ins~ead of diphenylsilane, a number of other silane cure accelerating additives such as dioctylsilane, methyldecylsilane, phenylmethylsilane and didecylsilane may be used. In addition, phenyl-silane, octylsilane, decylsilane and the like may be used as the accelerating agent. Also, instead of diallylmaleate~ dimethylmaleate and other similar dialkyl and dialkenylmaleates can be u~ed as the inhibiting agent. It is further within the scope of the instant invention to include conventional additives, in desired amounts, such as gum cure accelerators, controlled release agents, fillers, anti-microbial agen~s, pigments, dye , mixtures thereof and the like, in the present compositions.
All such obvious modifications are within the scope of the appended claims.

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Claims

1. A heat curable silicone composition having extended pot life at low temperatures and rapid curing at elevated temperatures comprising:
(a) a vinyl containing polydiorganosilicone fluid;
(b) a silicone hydride containing polydiorganosilicone;
(c) a platinum group metal catalyst;
and (d) an effective cure accelerating amount of a silane additive which comprises silicone bound to greater than or equal to two hydrogen atoms.

2. A heat curable silicone composition as defined in Claim 1 wherein said vinyl containing polydiorganosilicone fluid (a) comprises compounds having the general formulae:
MviDxMvi or MviDxDyMvi wherein Mvi comprises units, Dz comprises units, Dy comprises units, and wherein R is, independently, a monovalent hydrocarbon radical free of unsaturation having up to about 8 carbon atoms, R1 is a hydrocarbon radical having alkenyl unsaturation of from 2 to 20 carbon atoms, and m and n are positive integers such that said vinyl containing silicone fluid has up to about 20% by weight R1 groups.

3. A heat curable silicone composition as defined in Claim 1 wherein said vinyl containing polydiorganosilicone fluid (a) is a vinyl containing polydimethylorganosilicone fluid.

4. A heat curable silicone composition as defined in Claim 1 wherein said vinyl containing polydiorganosilicone fluid (a) is present in an amount ranging from 50 to 99 parts by weight based on the total weight of the silicone composition.

5. A heat curable silicone composition as defined in Claim 1 wherein said silicone hydride polydiorganosilicone (b) comprises compounds having the general formula:
MDxHM
wherein each M is a unit of the formula R3SiO0.5 wherein each R is independently as defined above and DH is an H

SiO- unit where R is as defined above.
R

6. A heat curable silicone composition as defined in Claim 5 wherein caid silicone hydride polydiorganosilicone (b) is a polydimethylsilicone fluid.

7. A heat curable silicone composition as defined in Claim 2 wherein said sillcone hydride polydiorganosilicone (b) comprises compounds having the general formula MDHyDxM
wherein DH is anunit where R is as defined above; M is a unit of the formula R3SiO0.5 wherein each R is independently as defined above; and Dx is as defined above.

8. A heat curable silicone composition as defined in Claim 1 wherein said silicone hydride polydiorganosilicone (b) is present in an amount ranging from about 0.5 to about 30 percent by weight based on the total weight of the silicone composition.

9. A heat curable silicone composition as defined in Claim 1 wherein said platinum group metal catalyst (c) comprises a platinum-siloxane complex of tetramethyltetravinylcyclotetrasiloxane with platinum.

10. A heat curable silicone composition as defined in Claim 1 wherein said platinum catalyst (c) is a complex of 1,3 divinyltetramethyldisiloxane with platinum.

11. A heat curable silicone composition as defined in Claim 1 wherein said platinum catalyst (c) is present in an amount ranging from about 5 to about 200 parts per million by weight of platinum per mole of silane in said composition.

12. A heat curable silicone composition as defined in Claim 1 wherein said sllane additive (d) comprises compounds having the general formula R22SiH2 or R2SiH3 where R2 i3 selected from the group consisting of alkyl radicals, cycloalkyl radicals and phenyl radicals.

13. A heat curable silicone composition as defined in Claim 12 wherein said silane additive (d) is selected from the group consisting of diphenyl-silane, dioctylsilane, methyldecylsilane, phenylsilane, phenylmethylsilane and didecylsilane.

14. A heat curable silicone composition as defined in Clalm 14 wherein said silane additive (d) is diphenylsilane.

15. A heat curable silicone composition as defined in Claim 13 wherein said silane additive (d) is selected from the group consisting of phenylsilane, octylsilane and decylsilane.

16. A heat curable silicone composition as defined in Claim 15 wherein said silane additive (d) is phenylsilane.

17. A heat curable silicone composition as defined in Claim 1 wherein said silane additive (d) is present in an amount ranging from about 5 to about 200 parts per million based on the total weight of the silane composition.

18. A heat curable silicone composition as defined in Claim 1 further comprising (e) an inhibiting agent.

19. A heat curable silicone composition as defined in Claim 18 wherein said inhibiting agent (e) is selected from the group consisting of dialkenylmaleates, dialkylmaleates, acetylenic alcohols, amines, isocyanurates, ene-ynes, vinyl acetates, acetylene dicarboxylates and mixtures thereof.

20. A heat curable silicone composition as defined in Claim 19 wherein said inhibiting agent (e) is selected from the group consisting of diallyl-maleate, dimethylmaleate, 4-butyne-1-ol, tetramethyl ethylenediamine and mixtures thereof.

21. A heat curable ilicone composition as defined in Claim 18 wherein said inhibiting agent (e) is present in an amount ranging from about 0,05 to about 0.5 percent by weight based on the total weight of the silicone composition.

22. A liquid injection moldable heat curable silcone composition having extended pot life at low temperatures and rapid curing at elevated temperatures with a low viscosity in the uncured state and a high physical strength in the cured state comprising the heat curable silicone composition as defined in Claim 1.

23. A method for preparing a heat curable silicone composition comprising mixing (a) a vinyl containing polydiorganosilicone fluid; (b) a silicone hydride containing polydiorganosilicone; (c) a platinum group metal catalyst; and (d) an effective cure accelerating amount of a silane additive which comprises silicon bound to greatsr than or equal to two hydrogen atoms.

24. A method as defined in Claim 23 wherein said vinyl containing polydiorganosilicone fluid (a) comprises compounds having the general formulae:

wherein M1 comprises units, Dx comprises units, Dy comprises units, and wherein R is, independently, a monovalent hydrocarbon radical free of unsaturation having up to about 8 carbon atoms, R1 is a hydrocarbon radical having alkenyl unsaturation of from 2 to 20 carbon atoms, and m and n are positive integers such that sald vinyl containing silicone fluid has up to about 20% by weight R1 groups.

25. A method as defined in Claim 24 wherein said vinyl containing polydiorganosilicone fluid (a) is a vinyl containing polydimethylorganosilicone fluid.

26. A method as defined in Claim 23 wherein said vinyl containing polydiorganosilicone (a) is added in an amount ranging from about 50 to about 99 parts by weight based on the total weight of the silicone composition.

27. A method as defined in Claim 23 wherein said silicone hydride polydiorganosilicone (b) comprises compounds having the general formula:
MDxHM
wherein each M is a unit of the formula R3SiO0.5 wherein each R is as above defined DxH is an unit wherein R is as above defined.

28. A method as defined in Claim 27 wherein said silicone hydride polydlorganosilicone (b) is a polydimethylsilicone fluid.

29. A method as defined in Claim 24 wherein said silicone hydride polydiorganosilicone (b) comprises compounds having the general formula MDHyDxM
wherein each M is a unit of the formula R3SiO0.5 wherein each R is as above defined, DH is an unit, wherein R is as defined above and Dx is as defined above.

30. A method as defined in Claim 23 wherein said silicone hydride polydiorganosilicone (b) is present in an amount ranging from about 0.5 to about 30 percent by weight based on the total weight of the silicone composition.

31. A method as defined in Claim 23 wherein said platinum catalyst (c) comprises a platinum-siloxane complex of tetramethyltetravinylcyclotetra-siloxane with platinum,

32. A method as defined in Claim 31 wherein said platinum catalyst (c) is a complex of 1,3-divinyltetramethyldisiloxane with platinum.

33. A method as defined in Claim 23 wherein said platinum catalyst (c) is present in amount ranging from about 5 to about 200 parts per million based on the total weight of the silicone composition.

34. A method as defined in Claim 23 wherein said silane additive (d) comprises compounds having the general formula R22SiH2 or R2SiH3 where R2 is selected from the group consisting of alkyl radicals, cycloalkyl radicals and phenyl radicals.

35. A method as defined in Claim 34 wherein said silane additive (d) is selected from the group consisting of diphenylsilane, dioctylsilane, methyldecylsilane, phenylsilane, phenylmethylsilane and didecylsilane.

36. A method as defined in Claim 35 wherein said silane additive (d) is diphenylsilane.

37. A method as defined in Claim 34 wherein said silane additive is selected from the group consisting of phenylsilane, octylsilane and decylsilane.

38. A method a defined in Claim 37 wherein said silane additive is phenylsilane.

39. A method as defined in Claim 23 wherein said silane additive (d) is present in an amount ranging from about 5 to about 200 parts per million based on the total weight of the silicone composition.

40. A method as defined in Claim 23 further comprising (e) an inhibiting agent.

41. A method as defined in Claim 40 wherein said inhibiting agent (e) is selected from the group consisting of dialkenylmaleates, dialkylmaleates, acetylenic alcohols, amines, isocyanurates, ene-ynes, vinyl acetates, aectylene dicarboxylatas and mixtures thereof.

42. A method as defined in Claim 41 wherein said inhibiting agent (e) is selected from the group consisting of diallylmaleate, dimethylmaleate, 4-butyne-1-ol, tetramethyl ethylenediamine and mixtures thereof.

43. A method as defined in Claim 40 wherein said inhibiting agent (e) is present in an amount ranging from about 0.05 to about 0.5 percent by weight based on the total weight of the silicone composition.

44. A coated article comprising a substrate coated with the heat curable silicone composition as defined in Claim 1.

45, A coated article as defined in Claim 44 wherein said substrate is selected from the group consisting of paper, polyethylene coated kraft (PEK) paper, super-calendered kraft (SCK) paper, polyethylene films and polypropylene films.

46. A method for forming a coated article comprising (i) mixing (a) a vinyl containing polydiorganosilicona fluid, (b) a silicone hydride containing polydiorganosilicone, (c) a platinum group metal catalyst, and (d) a silane cure accelerating additive which comprises a silicon bound to greater than or equal to two hydrogen atoms;
(ii) coating a substrate with the mixture formed in step (a); and (iii) curing the coated substrate by heating to a temperature of less than about 150°C.

47. A method as defined in Claim 46 wherein step (i) further comprises mixing (e) an inhibiting agent.

48. A method as defined ln Claim 46 wherein said curing temperature is less than about 125°C.

49. A method as defined in Claim 48 wherein said curing temparature is less than about 110°C.

50. The invention as defined in any of the preceding claims including any further features of novelty disclosed.