CA1247770A - Silicone release coatings and inhibitors - Google Patents

Abstract

SILICONE RELEASE COATINGS AND INHIBITORS

ABSTRACT OF THE DISCLOSURE

A solventless release coating composition is provided as well as a method for rendering materials nonadherent to other materials which would normally adhere thereto. The coating composition is a precious metal catalyzted silicone composition comprising a vinyl functional polysiloxane base polymer and a methylhydrogen cross-linking agent. A blend of diallylmaleate and vinyl acetate is added to the composition in order to extend the useful pot-life of the product by inhibiting premature cross-linking.

Description

SILICONE gELEASE CO~TINGS AND INHIBITORS
BACKGROUND OF THE INVENTTON
The present invention relates to silicone release coating compositions and inhibitors therefor. More particular].y, the present invention relates to a blend of a dialkyl carboxylic ester having carbon to carbon unsaturation and an olefinic carboxylic acid ester of an aliphatic alcohol as an inhibitor for precious metal catalyzed polysiloxane compositions ~hich are particularly well suited for solventless silicone release coating compositions.
Silicone compositions have long been used for rendering surfaces nonadherent to materials which would normally adhere thereto. For a long time it was necessary that these silicone coatings be applied as a dispersion within a solvent in order to control the ~iscosity of the coating material so as to be suitable for coating applications. However, although the solvent aids in the application of the coating, it is a highly inefficient process inasmuch as the solvent must thereafter be evaporated The evaporation of solvents requires large expenditures of energy, and additional].y, pollution control requirements mandate that solvent vapors be prevented from escaping into the environment. Thus, removal and recovery of solvents entails considerable expenditures for apparatus and energy.
Consequently, solventless release coating compositions, sometimes referred to as 100% solids release compositions, have been developed. The absence of a solvent in such compositions .

--~4~7~ ( 1 both lowess the amount of energy requiret to effect curing and eliminates ~he need for expensive pollution contsol equip-mene. However, a problem associated with such silicone release coatings relating to premature gelation must be overcome.
Since a typical composition is made up of a vinyl chain-stopped base polymer, a crosa-linking agent and a plstinum metal catalyst, premature curing or gelation may occur in a short period of time, thus resul~ing in a prsduct with an unsatisfactory pot-life. When the composition is ready for use it is desirable that the catalyzed polymer composition have a sufficiently long pot-life to enable the end-user to carry out the coating application. Accordingly, the coating composition is provided with an inhibitor which effectively retard~ the hydrosilation addition cure reaction of the composition at ambient temperature, but does not retard the cure at elevated temperatures. Examples of inhibitors which have been utilized in prior art solventless release compositions include vinyl acetate, diallylmaleate and triallylisocyanurste tTAIC).

Eckberg in U.S. Patent No. 4,256,870 discloses a silicone composition comprising a base polymer such as a vinyl chain-stopped polydialkyl-alkyl~inyl polys.loxane base copolymer snd a methylhydrogen cros~-linking $1uid. This composition is catalyzed by platinum or a platinum met61 complex which will initiate an addition cure reaction. An inhibitor selected from organic esters of maleic acid is added to the composition in order to selectively retard the cure reaction so as to provide a workable pot-life $or the costing composition.

7~

Eckberg in U.S. Patent No. 4,262,107, issued April 14, 1981 discloses a silicone rubber composition with good pot-life and fast curing at elevated temperatures comprising a silanol end-stopped diorganopolysiloxane polymer, a silicone hydride crosslinker and a rhodium complex catalyst in combination with an inhibitor compound selected from low molecular weight silanol end-stopped diorganopolysiloxanes, certain acetylenic compounds, lo olefinic carboxylic acid esters of aliphatic alcohols such as vinyl acetate, alkenyl isocyanurates and mixtures of such inhibitor compounds.
Eckberg in U.S. Patent No. 4,347,346, issued August 31, 19~ discloses a solventless platinum or rhodium catalyzed addition curable polyorganosiloxane release coating composition containing a dialkylacetylenedicarboxylate inhibitor for preventing premature gelation at ambient temperatures but which will cure at elevated temperature via a hydrosilation reaction to form a coating capable of releasing materials from substrates which would normally adhere thereto.
A novel multi-component solventless silicone release system is disclosed in Grenoble and Eckberg in Canadian Application Serial Number 447,719, filed February 17, 1984, assi~ned to the same assignee as the present invention. Therein it is disclosed that prior art two-component systems, one part of which comprises a vinyl silicone fluid, precious metal catalyst and an inhibitor, and the other part a polymethyl-hydrogensiloxane crosslinker, unduly limit the flexibility of the end-user to formulate solvent-free 1 silicone release coatings which more precisely meet their performance and cost requirements. Accordingly,~ there i8 provided a multi-component system wherein the ingredients are provided the end-user in three or more separate part6 to provide such flexibility. While such a multi-component system substantially eliminates the proble~ of premature gelation over an extended period of ti~e, it is also desirable to further increase the useful pot-life of release coating compositions to extend the period of time during which the end-user can carry out the coating application.

Thus, there is provided by the present invention a solventless silicone release coating composition containing a two-part inhibitor which not only exhibits more effective inhibition than similar concentrations of the individual ingredients, but also improves the solubility of such~inhibitor in silicone fluids. Hence the present invention provides a significant improvement over prior art release coating composi-tions containing a one-part inhibitor.
It is therefore a primary object of the present invention to provide a solventless composition which will render surfaces non-adherent to materials which ~ould normally adhere thereto.

Another object of the present invention is to provide a solventless coating composition which will cure to a coating having satisfactory smear, rub-off, migration and release characteristics.

' 1 A further object of ~he presen~ invention i6 to provide a solventless coating composition which has ~ satisfactory pot-life or baeh-life in its catalyzed for~ when it is ready for use.

Still another object of the present invention i8 to provide a method of rendering materials nonadherent to other materials which would normally adhere thereto.

It is still a further object of the present invention to provide a release coating composition having a two-part inhibitor which effectively retards the catalyzed cross-linking reaction at temperatures below the heat cure te~perature of these compositions and to provide solventless silicone compositions which are particularly well suited for paper release applications.

These and other objects will become apparent to those skilled in the art upon consideration of the present descrip-tion, examples and cl8ims.

Summar~ of the Invention The present invention provides 8 ~ilicone release coating composition containing a two-part inhibitor comprised of blend of a dialkyl casboxylic ester having carbon to carbon unsaturation and an olefinic carboxylic acit ester of an aliphatic alcohol ~hich ic eEfe~tive for retardiDg a precioDs .

-metal catalyzed addition cure hydrosilation reaction at room temperature but which does not interfere with curing at elevated temperatures.
Such two-part inhibitor is especially effective for use with release coating baths containing high concentration and in the multi-component system described by Grenoble and Eckberg in Canadian Patent Application Serial Number 447,719, filed February 14, 1984 and assigned to the same assignee as the present invention. The cured composition provides a silicone coating which will tenaciously adhere to a substrate, such as paper, to which it is applied, but will render such substrate substantially nonadherent to materials, such as pressure sensitive adhesives, which would normally adhere thereto.
The release coating composition containing a two-part inhibitor as provided by the present invention can be a two-component system or, more preferably, is a multi-component system of the type disclosed in Grenoble and Eckberg, Canadian Serial Mo. 447,719. Generally, the release coating composition of the present invention comprises:
(a) an olefinorganopolysiloxane having structural units of the formula:

a b (4-a-b) (I) or a silanol end-stopped organopolysiloxane having the general formula:

1 H0 t lio ~ B (Ia) -(b) an organohydrogenpolysiloxane having structural units - of the formuls:

Ra~bSi(4-a-b) (Il) -S wherein R is an organic radical attached to silicon by a C-Si linkage and is selected from the group consisting of monovalent hydrocarbon radicals, halogen~tet monovalent hydrocarbon radicals and cyanoalkyl rsdicals; ~enerally R contains from 1 to 30 carbon ato,.,s, either in branched or linear chains, - preferably from 1 to 12 carbon atoms and most preferably from 1 to 8 carbon atoms; R is an olefinic hydrocarbon radical attached to silicon by a C-Si linkage and generally contains 1 to 20 aliphatic carbon atoms, either in branched or linear chain6, and preferably l to 12 carbon atoms, linked by multiple bonds (e.g. vinyl, allyl, methallyl, butenyl, pentenyl, ethenyl and the like); a has a value of 0 to 3 inclusive, and preferably from about 0.5 to about 2 inclusive; b has a value from about ~7~

1 0.005 to about 2.0 inclusive, and the 8um uf a snd b equals from 0.8 to 3 inclusive; and wherein the release coating composition is a fluid at rc,om temperature having a viscosity of approximately lO to 5000 centipoise and preferably 30~ to l~00 centipoi~e at 25C;

(c) a cstalytic amount of a precious metal catalyst, preferably a platinum or rhodium compound, to effect the co-reaction of (a) &nd (b); and (d) an amount of a blend of a dialkyl carboxylic ester having carbon to carbon unsaturation and an olefinic carboxylic acid ester of an aliphatic alcohol effec-tive for inhibiting an addition cure hydrosilation reaction between said olefinorganopolysiloxane and said organohydrog2npolysiloxane at room temperature but is not present in an amount sufficient to prevent curing of said coating composition at elevated temperatures.

Description of the Invention In accordance with the presene invention there is provided 8 composition particularly well ~uited for rendering material6 nonadherent to other normally adhèrent materialfi ~uch 85 glue, adhesivell a=d the like. Additicnally the cD=position ca= be applied directly to a substrate without the need for a solvent, thereby avoiding the problems associated with solvent-based release compositions as described above.
The addition curable composition of the present invention can be provided as a mixture of several components wherein at least one component contains more than one ingredient as taught in the prior art. An example of such a system is described in U.S. Patent No. 4,256,870 wherein one part includes a vinyl silicone fluid, a precious metal catalyst and an inhibitor, and a second part comprises a polymethylhydrogensiloxane cross-linker. In such a composition the inhibitor of the present invention exhibits improved solubility, and if the composition has a high platinum content further effects improved bath life. ~owever, it is preferable that the coating composition be provided as a four part system such as that described in Canadian Serial Number 447,719 filed February 17, 1984 to Grenoble and Eckberg and assigned to the same assignee as the present invention, teaches that shelf-life is substantially improved for release coating compositions when the individual ingredients are stored separately, and that low temperature cure performance comparable to that of prior art high platinum content two part systems can be provided with significantly reduced catalyst concentrations as a result of more effective use of the catalyst.
The release coating composition is made up of the above-mentioned ingredients which will thermally cure on the ~:4~7~ ( 1 substrate upon which it is coated and render the substrate substantially nonadherent. More particularly, the olefinor-ganopolysiloxanes having structural units represented by Formula I hereinabove are iDtended to broadly cover low viscosity fluid organopolysiloxanes suitable for coating which preferably, but not necessarily, are free of silanic hydrogen and contain olefinic unsaturation by means of double or triple bonds between two adjacent aliphatic csrbon atoms. Among the radicals which R represents in Formula I hereinabove are included alkyl, such as methyl, ethyl, propyl, isopropyl, butyl, octyl, dodecyl and the like; cycloalkyl, such as cyclopentyl, cyclohexyl, cycloheptyl and the like; aryl, such as phenyl, naphthyl, tolyl, xylyl, and the like; aralkyl such as phenylethyl, phenylpropyl and the like; halogenated derivatives of the aforesaid radicals including chloromethyl, trifluoromethyl, chloropropyl, chlorophenyl, dibromophenyl, tetrachlorophenyl, difluorophenyl and the like; and cvanoalkyl, such as beta-cyanoethyl, ga~a-cyanopropyl, beta-cyanopropyl and the ~ike. Preferably R is ~ethyl. Furthermore, Formula I
is intended to encompass those materials wherein R is a mixture of the aforesaid radicals.

Among the radicals represented by R in Formula I are included alkenyl, such as vinyl, allyl, ~ethallyl, butenyl, pentenyl and the like; snd nlkynyl, such as ethynyl, propynyl, butynyl, pentynyl and the like. Preferably R is vinyl or allyl and ~ost preferably R is vinyl.

77~ ( The olefinorganopolysiloxanes encompassed within the scope of Formula I are well known in the art, for exa~ple, as d;s-1 closed in U.S. Patent ~o. 3,344,111 to Chalk and U.S. Patent : No. 3,436,366 to Modic, Simllarly, their pre~aration andcommercial availability are also well known. Ihe olefinorganopolysiloxanes o~ Formula I can be characterized as copolymers of (1) siloxane units havin~ the formul~:
RCRdsi~_C_d) (IV) where R and Rl are as defined above and c has a value of from 0 to 2 inclusive and the average sum of c and d is equal to from 0.8 to 3.0 inclusive, and (2) organopolysiloxane units having the structural formula:

(R)nSiO4-n (V) where R is as defined above and n has a value of from 0.8 to

2.5 inclusive. Thus, where the olefinorganopolysiloxane employed herein is a copolymer of units within the scope of Formula IV and an organopolysiloxane having an average formula within the scope of Formula V, the copolymer generally contains from 0.5 to 99.5 mole percent of the unit~ of Formula IV and from 0.5 to 99.5 mole percent of unit6 within the scope of Formula V. The preparation of these copolymers i6 well known to those skilled in the art.

A major proportion of the composition is typieally 8 vinyl chain-stopped polysiloxane having the general formula:

o / R ~ ~ R
R t i ~ Rl~ I
wberein R is a monovalent hydroc rbon radical free of unsaturation. Suitsble radicals for R include, for example, methyl, ethyl, propyl, butyl and other similar unsaturated hydrocarbons, but ordinarily wDuld not include phenyl groups for paper release purposes. R i8 a hydrocarbon radical having alkenyl unsaturation. Typically Rl represents vinyl groups but may also represent Qllylic or cycloalkenyl uns~tu-rated groups; x and y are positive integers such that the vinyl chain-stopped polysiloxane has up to approximately 20% by weight of Rl groups. The viscosity of such a polysiloxane ranges from approximately 50 to approximately 100,000 centipoise at 25C. Preferably the vinyl chain-stopped polysiloxane has up to approximately 20~ by weight of vinyl groups and the vîscosity ranges from approximately 300 to approximately 550 centipoise at 25DC. Ihe preferred vinyl chain-stopped polysiloxane has the general formula:
1 ~ l \ ~ l CH3 t CH3 ~x si ~ s CH ~ CH

whesein x and y are as described ove.

.

1 The silanol chain-6topped linear polydiorganosiloxane of Formula Ia can be used with, or in place of, ~the vinyl-containing copolymer of Formula I. Such 6ilanol end~6topped polysiloxanes are preparet by equilibration of cyclic poly-siloxane6 in the presence of sn alksli metal hydroxide catalyst. The desired viscoGity is obtained by ~ontrolling the amount of water added to the reaction. These procedures are described in the literature and are well known to those skilled in the art. Furthermore, silanol chain-6topped polydimethyl-methylvinylsiloxane copolymers can be envisioned which are al50 within the scope of the present invention.

Methylhydrogen fluid is often used by those 3killed in the silicone srt as a cross-linking agent for addition-cured tilicone systems. Particularly useful as a cross-linking agent for the present invention is a trimethyl chain-stopped polymethylhydrogen siloxane fluid having from approximately 10~
to approximately lOO~o SiH groups, any re~2ining groups being dimethylsiloxy units, and having a viscosity in the range o~
&pproximately 15 to approximately 1000 centipoise at 25C.

The organohydrogenpolysiloxanes having structural units represented by For~uls II hereinabove are intended to broadly cover fluid organopolysiloxanes which are preferably, but not necessarily, free of olefinic unsaturation, but which do contain silanic hydrogen. The organohydrogenpolysiloxanes represented by Formuls II are also well known in the art, for example, as described in ~.S. Patent No. 3,344,111 and V.S.
Patent No. 3,436,366.

C

Among the radicals iocluded within R of Formula II are alkyl, such as methyl, ethyl, propyl, isopropyl, butyl, octyl snd the like; cycloalkyl, such as cyclopentyl, cyclohexyl, cycloheptyl and the like; aryl, such a8 phenyl, naphthyl, tolyl, xylyl and the like; sralkyl, such as phenylethyl, phenylpropyl and ehe like; halogenated derivatives of the above radicals, including chloromethyl, trifluoromethyl, chloropro-pyl, chlorophenyl, dibrGmophenyl, tetrachlorophenyl, difluorophenyl and the like; and cyanoalkyl, such as beta-cyanoethyl, gamma-cyanopropyl, beta-cyanopropyl and the like.
Also intended to be included within the scope of Formula II are those materials where R is a mixture of the aforesaid radicals. Preferably the R group of For~ula II is methyl.
Materials specifically encompassed within Formula II
hereinabove include 1,3-dimethyldisiloxane and 1,1,3,3-tetra-methyldisiloxane, as well as higher polymers containing up to 100,000 or more silicon atoms per molecule. Also included within the scope of Formula II are cyclic materials such as cyclic polymers of methylhydrogen siloxane having the general formula:
¦ CH3\
-L iio- _ \~ x wherein x is a whole number equal to from 3 to 10 or more.
Particularly included is sym-tetramethylcyclotetrasiloxane.

~2~

The organohydrogenpolysiloxanes emp;oyed in the practice of the present invention can also be char~cteri~ed ~8 copolymers containing at least one unit per molecule having the formulR
S
RCHd Sio(4-c-d) (VI) with the remaining siloxsne units of the organopolysiloxane being within the scope of Formula V hereinabove, where R, c, d, and n are as defined above.

Within the scope of FormulA VI are siloxane units such as hydrogen siloxane units (HSiO~l 5, methyl hydrogen siloxane units (HSiCH30), dimethyl hydrogen siloxane units (H Si¦CH3]20~, and dihydrogen siloxane units (H25iO). In these copolymers, the siloxane units of For~ulae V and VI are present in proportions so as to form a hydrogenpolysiloxane within the scope of Formula II hereinabove. In general such copolymers coiltain from 0.5 to 99.5 mole percent of siloxane units of Formula V and from 0.5 to 99.5 mole percent of siloxane units of Formula VI.

Ordinarily for release coating purposes it i8 preferred that the organohydrogenpoly6il0xsne cro6slinker be essentially a trimethyl chain-stopped methylhydrogenpolysiloxane fluit having a viscosity of approximately 10 to 500 centipoise at 25C and a hydrogen content of from approximstely 0.1 to 1.67 percent by weight.

The precious metal catalyst component utilized in compositions of the present invention incl~des all of the well known platinum and rhodium catalysts which are effective for catalyzing the reaction between silicon-bonded hydrogen atoms and silicon-bonded olefinic groups, and which are freely miscible insolvent-free silicone polymers. These materials especially include the platinum hydrocarbon complexes described in U.S.
Patent No. 3,159,601 issued December 1, 196~ to Ashby and U.S. Patent No. 3,159,662, issued Decem~er 1, 1964 to Ashby, and the platinum alcoholate catalysts described in U.S. Patent No. 3,220,970, issued November 30, 1965 to Lamoreaux, as well as the platinum catalysts of U.S. Patent ~o. 3,814,730, issued June 4, 1974 to Karstedt. Additionally, the platinum chloride-olefin complexes described in U.S. Patent ~o. 3,516,946, issued June 23, 1970 to Modic are also useful herein.

The curing reaction which takes place between the vinyl-functional polysiloxanes and the polymethylhydrogensiloxane fluid cross-linking agent is an addition cure xeaction, also known as hydrosilation. The composition of the present invention may be the mally cured by means of a platinum catalyzed cross-linking reaction between pendant vinyl groups of a dialkylvinyl chain-stopped polydialkyl-alkylvinylsiloxane copolymer and a trimethyl chain-stopped polymethylhydrogen fluid.

A particularly use~ul catalyst ~or facilitatin~ the hydrosilation reaction is the Karstedt catalyst described in U.S. Patent No 3,814,730. Other platinum metal catalysts can be utilized in the practice of the present invention, however, { ~ ~L~ ~77~ ~

their Eelection depends upon ~uch factos6 85 the required seaceion rate, expense, useful pot-life and the temperature at which the cure reacti~n is to take place. Other metal catalysts useful in the present invention include those which are silicone soluble complexes of the metals rhodium, : ruthenium, palladium, osmium, iridium and platinum. For coat;ng compositions of the present invention, the amount of catalyst ranges from approximately 10 to approximately 500 ppm ~as weight of metal atoms), again depending on Euch factors as Epeed of reaction and c06t requirements. Preferably, the amount of catalyse is approximately 10 to 150 ppm of the precious metal.

In order to substantially eliminate the problem of premature curing or gelation it is desirable to include an inhibitor in the coating composition package. It has surpris-ingly been found that an inhibitor comprising a blend of a dialkyl carboxylic ester having carbon to carbon unsaturation and an olefinic carboxylic acid ester of an aliphatic alcohol is more effective as an inhibitor ehan similar amounts of the individual ingredients utilized alone, especially in high platinum content (i.e. low cure temperature) Eystems. By a high platinum content or low cure temperature sy6tem, it is meant thst the catalyzed bath contains more than 50 ppm of precious metal catalyst, and typically may be more than lOO ppm of precious metal catalyst. Such two-part inhibitor is al60 especially useful in the multi-component packaging sy6tem of ; Grenoble et al., Can. Serial No. y y ~ ~7~9 as it affords the end-user with the cspability of formulating re~ease coating 76) 1 bath compositions suited to his specific need~. Furthermore, the inhibitor of the present invention is used more~advantage-ously in low tempersture curing release coating sy6tem6 than prior art one-part inhibitors since, for exsmple, diallyl-maleste i6 a polar substance which i6 not very soluble in silicone fluids at concentration6 above about 0.3 weight percent. However, in the instant invention vinyl acetate function~ both as sn inhibitor and as a mutual 601vent for diallylmaleate and silicone fluid, snd accordingly, ~ore preferred concentrations of inhibitor can be utilized which would otherwise be impractical.

Eckberg in U.S. Patent No. 4,256,870 discloses that an amount of dialkyl carboxylic ester containing carbon to carbon unsaturation is effective to inhibit the precious metal catslyzed hydrosilation cure reaction at temperatures below the heat cure temperature of the release coating composition. Most preferably such dialkyl carboxylic ester is diallylmaleate which has the formuls: 8 H
~ ~C /

CH2 ~ CHCH2 - O - C l l 2CH CH2 O O
and ordinarily i8 utilized in A ran8e of from spproximstely O.lX to approxi~ately 0.5X by weight. Other preferred diallylic carboxylic e~ters which are preferred include diallylphthalate and diallylsuccinate. Also, satur~ted dialkyl esters of maleic acid, ~uch as diethyl and dimethyl maleate, ~ 247770 and ~ixed esters such as butylallylmaleate or methylethyl-maleate are useful as hydrosilation inh;bitors for solventless release coating compositions. Other useful inhibitors can also be found in the Eckberg patent.

The use of ari olefinic carboxylïc acid ester of an aliphatic alcohol is disclosed in Eckberg as an inhibitor for rhodium catalyzed silicone rubber compositions in U.S. Patent No. 4,262,107. Therein it is taught that such compositions can be utilized at low concentration, such as from 0.1 to 2 parts per 100 parts of the silanol base polymer, but preferably should be utilized in a concentration of 0.5 to 5 parts per 10C
parts of the silanol base polymer. The preferred inhibitor compound is vinyl acetate, however, those olefinic carboxylic acid esters of an aliphatic alcohol wherein the alcohol has from 1 to 4 carbon atom and the olefinic carboxylic acid has from 2 to 10 carbon atoms are within the scope of the disclosed.

The present invention is based on the surprising discovery that a blend of a dialkyl carboxylic ester containing carbon to carbon unsaturation and an olefinic carboxylic acid ester of an aliphatic alcohol results in a blend which is a more effective inhibitor than utilizing similar amounts of the individual compounds, that is, a synergistic effect is obtained by such a blend of inhibitors.

Iq 7~ C-.

The most preferred dialkyl carboxylic e~ter containing carbon to carbon unsaturation is diallylmaleate, however, any of the inhibitor composit;ons within the scope of V.S. Patent No. 4,256,870 can also be utilized in the present invention.
Among the preferred inhibitor compositions which also can be utilized are butylallylmaleate, diallylsuccinate, dimethylmaleate, diethylmaleate and 6ilylmaleates such as bis- ~ -propyltris (methoxy) silylmaleate which has the formula: ~ H
~ f 1 / \ ~ ~

~i(OCH3)3 C C CH2 si (OCH3)3 The most preferred olefinic carboxylic acid ester of an aliphatic alcohol is vinyl acetate, however, any inhibitor compound within the scope of U.S. Patent No. 4,262,107 may also be utilized. More particularly, such compounds are those derived from an aliphatic alcohol having l to 4 carbon atoms and an olefinic carboxylic acit having from 2 to 10 carbon atoms.

The dialkyl carboxylic ester having carbon to carbon unsaturation, preferably diallylmaleate or butylallylmaleate, is blended with the olefinic carboxylic acid ester of an aliphatic slcohol, preferably vinyl acetate, in a r.atio ranging from approximately i:24 to l:l, but most preferably i6 blended 77~ c l in approximately a 1:3 ratio. Accordingly, the most preferred inhibitor for the release coating composition of t~e present invention is a blend comprising 1 pare diallyl~aleate snd 3 I:-rt6 vinyl acetate.

I~ has been discovered that small amounts of such 8 two-par~ inhibitor permit exceptionally long catalyzed pot-life without sacrifice of cure perfo~ance, especially in co~po-sitions having a high platinum content. Ordinarily the effective smount of inhibitor ranges from approximately 0.05 to approximately 2% by weight, and preferably fro~ 0.1 to 1.5% by weight. Use of the present invention results in improved pot-life yet the composition rapidly cures to a smear-free and migration-free nonadherent surface when thermally cured.
1~
The improved inhibitor of the present invention can be provided in a conventional two package system, that is, it can be stored in one container which includes the inhibitor blend, a vinyl silicone fluid and a precious metal cat~lyst, while the polymethylhydrogensiloxane cross-linking agent is stored in a separate container. It is preferred, however, that a three or more component package system as disclosed in Grenoble et al., Can. Serial No. ~ ;7~ ~, be utilized. Thus, it is preferable that each of the ingredients be 6tored ;n separste contfliner6 ~o that in addition to the i~proved pot-life provided by the inhibitor blend of the prebent invention, very long shelf-life is also obtained.

In addition to the foregoing ingredients, it is within the scope of the present invention that other ingredients can be included. One of the preferred additional ingredients is a '~ ~L~ ~ 7 7 0 vinyl-gum cure accelerator of the type disclosed by Eckberg in V.S. Patent No. 4,340,647, issued July 20, 1~82, which is assigned to the same assignee as the present invention. Therein it is disclosed that a dimethylvinyl chain-stopped polydimethylmethylvinylsiloxane polymer gum will accelerate the hydrosilation cure reaction at a relatively low temperature without sacrificing performance. Such vinyl gum may be packaged alone or preferably with the base polymer.

In order that those skilled in the art might be better able to practice the present invention, the following examples are given by way of illustration ana not by way of limitation.

Description of the Preferred Em'oodiments Examples 1 to 14 In the following examples, release coating compositions were prepared from the following ingredients:

(A) a mixture consisting of 100 parts of a linear dimethylvinyl chain-stopped polyaimethylsiloxane fluid having a viscosity of 120 cps at 25 C and 5 parts of a dimethylvinyl chain-stopped linear polydimethyl~ethyl-vinylsiloxane copolymer gum having a molecular weight of approximately 300,000 and containing 0.2 mols percent methylvinyl siloxane units, such mixture having a viscosity of approximately 400 cps at 25 C;

r ~ f~"~L~jL777Q

(B) a solution of a platinum catalyst in a dimethylvinyl end-stopped polydi~eehylsiloxane fluid ~ hsving a viscosity of 300 cps nt 25C, there being sufficient catalyse present to afford 1800 ppm platinu~ (as metal~ in the solution;

- (C) a trimethylsiloxy chain-stopped linear polymethylhydrogensiloxane fluid having 8 viscosity of approximately 20 to 40 cps at 25C as a cross-linking agent; and (D) a blend of 3 parts vinyl acetate to 1 part of diallylmaleate.
Initial experiements were performed by preparing release coating composition baths 8S described in Table 1.

7~
C

Tsble I

Bath _ xample 1 Example 2 Example 3 Ex~mple 4 Ingredient A150.0g 150.0g 150.0g 150.0g Ingredient B 2.1 4.17 8.33 12.51 Ingredient C 6.0 6.0 6.0 6.0 Ingredient D 0.3 0.6 1.2 1.8 ppm Pt 24.0 47.0 91.0 134.0 Total Inhibieor, X 0.2 0.39 0.75 1.10 ViOAc, X 0.15 0.29 0.5S 0.82 DAM, X 0.05 0.10 0.19 0.28 7~

The viscositie6 of the four release coating baths were monitored as a function of time under still condition6 at 25C
over a seven hour period. The results set forth i~ Table II
illustrate that the two-part inhibitor of the present in~ention provides a release coating bath havin a satisfactory pot-life.
Note that for purposes of these experiments, the cross-linking agent W8S added at time zero.

Table II

Bath Example 1 Example 2 Example 3 Example 4 lS Initial 500 cps 495 cps 465 cps 460 cps 2 hours 525 525 490 480 4 hours 530 525 505 480 7 hours 540 550 525 495 Thus it can be seen thae varying a~ounts of the diallyl-maleate/vinyl acetate inhibitor gsve satisfsctory pot-life while effectively controlling the percentage vi6cosity increase of the catalyzed baths regardless of the absolute level of catsly6t.

Examples 5 and 6 In the following examples tWD baths were prepared identically to that of Example 1 with the exception that each contained only one of the inhibitors of the blend utilized in Example 1. The composition of these release coating baths is shown in Table III.

~able III

Bath Example 5 Example 6 Ingredient A 150.0 g 150.0 g Ingredient B 2.1 2.1 Ingredient C 6.0 6.0 2~
ViOAc 0.23 (0.15Z) Not present DAM Not present 0.08 (0.05Z) ppm Pt 24 24 The viscositie6 of the two release coating bathfi were again monitored as a function of time under still conditions at 25C
over a seven hour period. The results are set forth in Table IV.

... . ... .. ....... _ . ... .

~L~7~ ( Table IV

- Bath Exa~ple 5 ExamDle 6 Initial 360 cps 36S cps 2 hours 500 525 4 hours 570 7S0 7 hours 1025 4000 Although the ~iscosity of each bath doubled in approximately four hours, the results are un erarkable in the sense that the total inhibitor concentration in the bath of Example 1 exceeds the total inhibitor load in the bath of either Example 5 or Example 6.

Examples 7 to 9 Experiments were then run to determine the effectiveness of the individual inhibitors at levels comparable to the level of two-part inhibitor utilized in Example 1. The :co~position of these release coating baths is sho~n in Table V.

.

Table V
S
Bath Example 7 Example 8 Ingredient A 150.0 g 150.0 g Ingredient B 2.1 2.1 Ingredient C 6.0 6.0 VioAc 0.31 (0.2X) Not present DAM Not present 0.31 ~0.2%) ppm Pt 24.0 24.0 The viscosities of the release coating baths were once again monitored as a function of time undes still conditions at 25C
over a seven hour period. The result6 are illustrsted in Tsble VI.

C f~ 7~ C

1 Table VI

Bath _ Example 7 Example 8 Initial 335 cps 355 cps 2 hours 480 370 4 hours 620 375 7 hours 900 380 These results sho~ that the combined diallylmaleate/vinyl acetate inhibitor significantly improves upon the inhibitory 15effect of vinyl acetate alone. While the bath composition of Example 8 has a satisfactory bath life, i~ is not useful for a low temperature cure applications, such as those of the bath in Example 4. Moreover, even in those compositions ~hich require high temperature curing, the inhibitor blend of the present 20invention exhibits improved solubility thus enabling more preferred concentrations of inhibitor to be utili2ed~ Next, a release coating bath having a high platinum content, that is, comparsble to that of Example 4, was prepared to determine the effectiveness of diallylmaleate in such A bath. The composition of this bath is set forth in Table VII, 7~

Table VII

Bath Example 9 Ingredient A 150.0 g Ingredient B 12.5 Ingredient C 6.0 DAM 0.49 (0.3%) ppm Pt 134 The viscosity of the bath was monitored as a function of time under still conditions at 25C over a seven hour period, the results being shown in Table VIII.

Table VIII

Bath Example 9 Initial 350 CpB
2 hours 590 4 hours 1200 7 hours GEL

~4~77C:~ ~

1 Thus it can be ~een that diallylmaleate slone i8 not effecti~e for use in high platinum content release coating co~position baths, whereas a bath which inste&d utilizes the two part inhibitor of the present invention pro~ide~ a useful pot-life of 7 hour6 or more.

While the examples and claim~ cited in U.S. Patent No.
4,256,870 in lude references to silicone comp~sitions in which diailylmalea~e alone inhibits premature curing in the presence of high levels of platinum, it should be understood that the cataly6t specified therein is the ~ameroux caealyst of U.S. Patent No.

3,220,972~ The Lameroux catalyst has been found to be ineffective for promoting commercially useful cure rates at temperstures below 250~F, even at platinum concentrations as high a8 200 ppm. For example, U.S. Patent ~o. 4,256,870 discloses that a composition which include~ 200 ppm Lameroux catalyst and O.5X diallylmaleate requires 40 seconds to cure at 250DF. Use of the Rarstedt or As~by type catalysts, on the other hand, permits curing in less than 30 seconds at temperatures as low 88 200F and in the presence of 100 to 200 ppm platinum catalyst. High concentrations ( ~ 3000 ppm) of diallylmaleate by itself i6 incompatible with high concentrations of Karstedt or Ashby platinu~ cntaly6t (i.e. ;~ 100 ppm Pt), and causes rapid precipitation of insoluble plstinum residues. Thu6, further sesearch has cbown that diallylmaleate alone i8 not suitnble a~ an inhibitor for high ~5 platinum content compositions nor for the multi~component system described by Grenoble and Eckberg in Can. Serial No. 4~

Claims (42)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A composition comprising:
(a) an olefinorganopolysiloxane or silanol end-stopped diorganopolysiloxane polymer, (b) an organohydrogenpolysiloxane cross-linking agent, (c) at least 50 ppm of a precious metal or precious metal containing catalyst, and (d) an effective amount of an inhibitor comprising a blend of a dialkyl carboxylic ester having carbon to carbon unsaturation and an olefinic carboxylic acid ester of an aliphatic alcohol.

2. The composition of claim 1 wherein the olefinorganopolysiloxane has structural units of the formula:
and the organohydrogenpolysiloxane has structural units of the formula:
where R is an organic radical selected from the group consisting of monovalent hydrocarbon radicals, halogenated monovalent hydrocarbon radicals, cyanoalkyl radicals and mixtures thereof and which has from 1 to 30 carbon atoms;
R1 is an olefinic hydrocarbon radical having from 1 to 20 carbon atoms; a has a value ranging from 0 to 3 inclusive, b has a value ranging from about 0.005 to about 2.0 inclusive, and the sum of a and b equals 0.8 to 3 inclusive; and wherein the coating composition is a fluid at 25°C having a viscosity ranging from approximately 10 centipoise to 5000 centipoise.

3. The composition of claim 2 where R is methyl.

4. The composition of claim 2 where R1 is vinyl or allyl.

5. The composition of claim 1 wherein the olefinorganopolysiloxane is a dimethylvinyl chain-stopped dimethylmethyl vinylpolysiloxane copolymer fluid having a viscosity of approximately 100 to 1000 centipoise at 25°C and a vinyl content of up to 2.5 weight percent.

6. The composition of claim 1 wherein the organohydrogenpolysiloxane is a trimethyl chain-stopped methylhydrogenpolysiloxane fluid having a viscosity of approximately 10 to 500 centipoise at 25°C and a hydrogen content of approximately 0.1 to 1.67 percent by weight.

7. The composition of claim 1 wherein the precious metal catalyst is selected from the group consisting of platinum metal, rhodium metal, complexes of platinum metal and complexes of rhodium metal.

8. The composition of claim 7 wherein the precious metal catalyst is present in an amount sufficient to provide approximately 50 to 500 parts of catalyst as platinum or rhodium metal per million parts of olefinorgano-polysiloxane.

9. The composition of claim 1 wherein the dialkyl carboxylic ester is selected from the group consisting of diallylmaleate, butylallylmaleate, diallylsuccinate and dialkyl esters of maleic acid selected from the group consisting of dimethylmaleate, diethylmaleate and silylmaleate.

10. The composition of claim 1 wherein the dialkyl carboxylic ester is diallylmaleate.

11. The composition of claim 1 wherein the olefinic carboxylic acid ester of an aliphatic alcohol is formed from an alcohol having from 1 to 4 carbon atoms and an olefinic carboxylic acid having from 2 to 10 carbon atoms.

12. The composition of claim 1 wherein the olefinic carboxylic acid ester of an aliphatic alcohol is vinyl acetate.

13. The composition of claim 1 wherein the dialkyl carboxylic ester is blended with an olefinic carboxylic acid ester of an aliphatic alcohol in a ratio of from approximately 1:24 to approximately 1:1.

14. The composition of claim 1 wherein the dialkyl carboxylic ester is blended with an olefinic carboxylic acid ester of an aliphatic alcohol in a ratio of approximately 1 to 3.

15. The composition of claim 1 wherein diallylmaleate is blended with vinyl acetate in a ratio of approximately 1 to 3.

16. The composition of claim 1 wherein the inhibitor is present in an amount ranging from approximately 0.05 to 2 percent by weight.

17. The composition of claim 1 wherein the inhibitor is present in an amount ranging from approximately 0.1 to 1.5 percent by weight.

18. The composition of claim 1 further comprising a substrate upon which the composition has been coated and thermally cured.

19. The composition of claim 18 wherein the substrate is paper.

20. A composition comprising:
(a) a dimethylvinyl chain-stopped dimethyl-methylvinylpolysiloxane copolymer fluid having a viscosity of approximately 100 to 1000 centipoise at 25°C and a vinyl content of approximately 0.1 to 2.5 weight percent;
(b) a trimethyl chain-stopped methylhydrogen-polysiloxane fluid having a viscosity of approximately 10 to 500 centipoise at 25°C and a hydrogen content of approximately 0.1 to 1.67 percent by weight;
(c) 50 to 500 parts of a precious metal catalyst as precious metal selected from the group consisting of platinum metal, rhodium metal, complexes of platinum metal and complexes of rhodium metal; and (d) 0.05 to 2 percent by weight of an inhibitor comprising a blend of diallylmaleate and vinyl acetate in a ratio of approximately 1 to 3.

21. A process for rendering surfaces nonadherent to materials which would normally adhere thereto, comprising the steps of:
(A) providing a silicone release coating composition by combining:
(a) an olefinorganopolysiloxane or silanol end-stopped diorganopolysiloxane polymer, (b) an organohydrogenpolysiloxane cross-linking agent, (c) at least 50 ppm of a precious metal or precious metal containing catalyst for effecting the co-reaction of (a) and (b), and (d) an effective amount of an inhibitor comprising a blend of a dialkyl carboxylic ester having carbon to carbon unsaturation and an olefinic carboxylic acid ester of an aliphatic alcohol;
(B) applying said silicone release coating on a suitable substrate, and (C) curing said silicone release coating with an amount of heat effective for overcoming the cure retarding ability of said inhibitor.

22. The process of claim 21 wherein the olefinorganopolysiloxane has structural units of the formula:

and the organohydrogenpolysiloxane has structural units of the formula:
wherein R is an organic radical selected from the group consisting of monovalent hydrocarbon radicals, halogenated monovalent hydrocarbon radicals, cyanoalkyl radicals and mixtures thereof and which has from 1 to 30 carbon atoms; R1 is an olefinic hydrocarbon radical having from 1 to 20 carbon atoms; a has a value ranging from 0 to 3 inclusive, b has a value ranging from about 0.005 to about 2.0 inclusive, and the sum of a and b equals 0.8 to 3 inclusive; and wherein the coating composition is a fluid at 25°C having a viscosity ranging from approximately 10 centipoise to 5000 centipoise.

23. The process of claim 22 where R1 is methyl.

24. The process of claim 22 where R is vinyl or allyl.

25. The process of claim 21 wherein the olefinorganopolysiloxane is a dimethylvinyl chain-stopped dimethylmethylvinylpolysiloxane copolymer fluid having a viscosity of approximately 100 to 1000 centipoise at 25°C and a vinyl content of approximately 0.1 to 2.5 percent by weight.

26. The process of claim 21 wherein the organohydrogenpolysiloxane is a trimethyl chain-stopped methylhydrogenpolysiloxane fluid having a viscosity of approximately 10 to 500 centipoise at 25°C and a hydrogen content of approximately 0.1 to 1.67 percent by weight.

27. The process of claim 21 wherein the precious metal catalyst is selected from the group consisting of platinum metal, rhodium metal, complexes of platinum metal and complexes of rhodium metal.

28. The process of claim 27 wherein the precious metal catalyst is present in an amount sufficient to provide approximately 50 to 500 parts of catalyst as platinum or rhodium metal per million parts of olefin-organopolysiloxane.

29. The process of claim 21 wherein the dialkyl carboxylic ester is selected from the group consisting of diallylmaleate, butylallylmaleate, diallylsuccinate, and dialkylester of maleic acid selected from the group consisting of dimethylmaleate, diethylmaleate, and silylmaleate.

30. The process of claim 21 wherein the dialkyl carboxylic ester is diallylmaleate.

31. The process of claim 21 wherein the olefinic carboxylic acid ester of an aliphatic alcohol is formed from an alcohol having from 1 to 4 carbon atoms and an olefinic carboxylic acid having from 2 to 10 carbon atoms.

32. The process of claim 21 wherein the olefinic carboxylic acid ester of an aliphatic alcohol is vinyl acetate.

33. The process of claim 21 wherein the dialkyl carboxylic ester is blended with an olefinic carboxylic acid ester of an aliphatic alcohol in a ration of from approximately 1:24 to 1:1.

34. The process of claim 21 wherein the dialkyl carboxylic ester is blended with an olefinic carboxylic acid ester of an aliphatic alcohol in a ratio of approximately 1 to 3.

35. The process of claim 21 wherein diallyl-maleate is blended with vinyl acetate in a ratio of approximately 1 to 3.

36. The process of claim 21 wherein the inhibitor is present in an amount ranging from approxi-mately 0.05 to 2 percent by weight.

37. The process of claim 21 wherein the inhibitor is present in an amount ranging from approximately 0.1 to 1.5 percent by weight.

33. The process of claim 21 wherein the substrate is paper.

39. A process for rendering surfaces nonadherent to materials which would normally adhere thereto, comprising the steps of:
(A) providing a silicone release coating composition by combining:
(a) a dimethylvinyl chain-stopped dimethyl-methylvinylpolysiloxane copolymer fluid having a viscosity of approximately 100 to 1000 centi-poise at 25°C and a vinyl content of approximately 0.1 to 2.5 percent by weight;
(b) a trimethyl chain-stopped methylhydrogen-polysiloxane fluid having a viscosity of approximately 10 to 500 centipoise at 25°C and a hydrogen content of approximately 0.1 to 1.67 percent by weight;
(e) 50 to 500 parts of a precious metal catalyst as precious metal selected from the group consisting of platinum metal, rhodium metal, complexes of platinum metal and complexes of rhodium metal;
(d) 0.05 to 2 percent by weight of an inhibitor comprising a blend of diallylmaleate and vinyl acetate in a ratio of approximately 1 to 3;
(B) applying said silicone release coating composition on a suitable substrate; and (C) curing said silicone release coating with an amount of heat effective for overcoming the cure retarding ability of said inhibitor.

40. A method for providing a coating bath comprising mixing:
(a) an olefinorganopolysiloxane or silanol end-stopped diorganopolysiloxane polymer, (b) an organohydrogenpolysiloxane cross-linking agent, (c) at least 50 mmp of a precious metal or precious metal containing catalyst, and (d) an effective amount of inhibitor comprising a blend of a dialkyl carboxylic ester having carbon to carbon unsaturation and an olefinic carboxylic acid ester of an aliphatic alcohol.

41. The method of claim 40 wherein the precious metal catalyst is selected from the group consisting of platinum metal, rhodium metal, complexes of platinum metal and complexes of rhodium metal.

42. The method of claim 41 wherein the precious metal catalyst is present in an amount sufficient to provide 50 to 500 ppm of catalyst as platinum or rhodium metal per million parts of olefinorganopolysiloxane.