GB2198740A

GB2198740A - U.V. curable olefinic polysiloxane coating composition

Info

Publication number: GB2198740A
Application number: GB08725155A
Authority: GB
Inventors: Richard Paul Eckberg
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1986-12-22
Filing date: 1987-10-27
Publication date: 1988-06-22
Anticipated expiration: 2007-10-27
Also published as: KR880007671A; FR2608617A1; GB2198740B; JPH0692564B2; GB8725155D0; FR2608617B1; KR940011192B1; CA1299802C; JPS63172776A; DE3742000A1

Description

P 1 1 2198740 UV-ACTIVATION OF ADDITION CURE SILICONE COATINGS The present

invention relates to the ultraviolet light activated cure of certain silicone coatings. More particularly, the present invention relates to the ultraviolet light activated cure of platinum catalyzed, addition cured silicone coatings which contain dialkylatetylenedicarboxylate inhibitors.

Silicone compositions which are curable by reaction of SSiH groups with silicon ' -bonded olefinic groups in the presence of a hydrosilation catalyst are well known in the art, for example, as described in U.S. Pat. Nos. 2,813,218; 3,249,581 and 3, 436,366, all of which are incorporated by reference into the present disclosure. Because curing begins upon mixing of the aforesaid ingredients, it is the usual practice to provide addition curable compositions in two packages, one of which contains the olefinically unsaturated polysiloxane and the hydrosilation catalyst, and t.he other the organohydrogenpolysiloxane crosslinking agent.

Wherr it is necessary to extend the pot life of addition curableorganopolysiloxane compositions or provide one-component addition curable organopolysiloxane composition, a cure inhibitor can be included therein. Generally, cure inhibitors are compounds which slow cur- ing at ambient temperatures but do not retard curing at elevated temperatures. Such cure inhibitors are heat deactivated cure inhibitors, or are sufficiently volatile to be expelled from coating compositions at elevated temperature.

Particular heat deactivated cure inhibitors are the dialkylacetylenedicarboxylates. These inhibitors are disclosed in U.S. Pat - No. 4,347,346, and are described by the formula, ROOC EO CCOOR, where R is a monovalent hydrocarbon radical.

It is an object of the present invention to pro- c vide platinum catalyzed, addition cured silicone coating compositions containing dialkylacetylenedicarboxylate inhibitors which are curable with ultraviolet light.

It is a further object of the present invention to provide a method to cure platinum catalyzed, addition curable silicone coating compositions containing dialkylacetylenedicarboxylate inhibitors which contains the step of exposing the coating composition to ultraviolet light. Summary of the Invention

The present invention provides a silicone composi- tion containing a dial kyl acetylenedicarboxyl ate inhibitor agent which is effective for retarding a platinum metal catalyzed a d d i t i o n cure hydrosilation reaction at room temperature but which will effectively cure upon exposure to ultraviolet radiation thereby forming a silicone coati ng w h i c h will tenaciously adhere to a substrate such as paper to whi ch i t i s appl i ed but wi 11 render sai d substrate substantially nonadherent to materials such as pressure sensitive adhesives which would normally adhere thereto.

The release coating composition of the present invention is comprised of:

a. an olefinorganopolysiloxane h a v i n g structural u n i t s of the formula:

R a R b' Sio (4-a-b) T_ (I) and b. an organohydrogenpolysiloxane having structural units of the formula:

R a H b Sio (4-a-b) I- (I I) 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, halogenated monovalent hydrocarbon radicals, and cyanoa] kyl r a d i c a 1 s; general I y, R contains f rom 1-30 carbon atoms, straight or branched chained, prefer- v -3-.

c.

ably from 1-12 carbon atoms, and most preferably I8 carbon atoms; R' is an olefinic hydrocarbon radical attached to silicon by a C--Si linkage and generally contains f rom 1-20 a I i p h a t i c carbons, straight or branch chained, and preferably 1-12 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 0.5 to about 2, inclusive, b has a value from 0.005 to 2.0, inclusive, and the sum of a and b is equal to from 0.8 to 3, inclusive, wherein the release coating composition is a fluid at room temperature having a viscosity of, approximately, 25 to 5000 centipoi.se and preferably 300 to 1000 centipoise at 2 5 0 C, a sufficient amount of platinum metal catalyst to cause the co-reaction of (a.) and (b.), and d. an amount of dialkyl acetylenedicarboxyl ate effective for inhibiting an addition cure hydrosilation reaction between said olefinorganopolysiloxane and said organohydrogenpolysiloxane. The dicarboxylate has the general formula ROOCC -- CCOOR where R is as defined above and is present in an amount to inhibit premature gelation of the catalyzed co-reaction product of (a.) and (b.) but is present in an amount insufficient to prevent curing of said coating composition upon exposure to ultraviolet radiation.

Description of the Invention

The composition of the present invention is par- ticularly well suited for rendering materials nonadherent to other normally adherent materials such as glue and adhesives. Additionally, the composition can be applied directly to a substrate without the need for a solvent, thus avoiding all of the problems associated with coating solvents as described above.

The composition is an organopolysiloxane made up of several constituent ingredients which will adhere to v and thermally cure o n the substrate upon w h i c h i t i S coated, and render the substrate nonadherent.

The olefinorganopolysiloxanes having structural u n i t s represented by Formula I hereinabove are intended to broadly cover low viscosity fluid organopolysiloxanes suitable for coating which preferably, but not necessarily, are free of s i 1 a n i c hydrogen, and contain olefinic unsaturation by means of double or triple bonds between two adjacent aliphatic carbon atoms. Among the radicals which R represents in Formula I hereinabove are i ncl uded al kyl, such as methyl, ethyl, propyl, i sopropyl, butyl, octyl, dodecyl, and the 1 i k e; cycloalkyl, such as cyclopentyl, cyclohexyl, cyclopeptyl, and the like; aryl, s u c h as phenyl, naphthyl, tolyl, xylyl, and the like; aralkyl, such as benzyl, phenylethyl, phenylpropyl, and the 1 i k e; halogenated derivatives of the aforesaid radicals including chloromethyl, trifluoromethyl, chloropropyl, chlorophenyl, dibromophenyl, tetrachlorophenyl, difluorophenyl, and the like; and cyanoalkyl, such as beta-cyano ethyl, gamma-cyanopropyl, beta-cyanopropyl and the like. Preferably R is methyl. Moreover, Formula I is intended to include those materials wherein R is a mixture of the aforesaid radicals.

Among the radicals represented by R' in Formula 1 hereinabove are included alkenyl, such as vinyl, allyl, methallyl, butenyl, pentenyl, and the like; and alkynyl, such as ethynyl, propynyl, butynyl, pentynyl, andthe 1 i k e. Preferably, R' is vinyl or allyl and most prefer ably R' is vinyl.

Thses olefinorganopolysiloxanes encompassed with in the scope of Formula I hereinabove are well known in the art, as particularly manifested by U.S. Patent No.

3,344,111 to Chalk, and U.S. Patent No. 3,436,366 to Modic, which are incorporated herein by reference. Sim ilarly, thei r preparation and commercial availability is also well known.

The olefinorganopolysiloxanes encompassed within 17 -5-.

1 the scope of the present invention can be characteriz.ed as copolymers of (1) siloxane units having the formula:

R c R' dS'4-c-d OV) 7_ where R and R' are as defined above and c has a value of from 0 to 2, inclusive, and the sum of c and d is equal to from 0.8 to 3.0,. inclusive, and (2) organosiloxane units having the structural formula:

(R) n S i 0 4-n 2_ (V) where R is as defined above and n has a value of from 10 0.8 to 2.5, inclusive. Thus, where the olefinorganopolysiloxane employed herein is a copolymer of units within the scope of Formula IV with 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 units of Formula IV, and from 0.5 to 99.5 mole percent of units within the scope of Formula V. The preparation of these copolymers is also well known in the art. A major proportion of the composition is typically a vinyl chainstopped -polysiloxane having the general formula:

R R R 1 1 1 H2C - CH - Si - 0]U Sio Si - CH CH2 - 1 1 11 1 R R XR' R X v wherein. R is a monovalent hydrocarbon radical free of unsaturation. Suitable radicals for R include, for example, methyl, ethyl, propy], buty], and other similar unsaturated hydrocarbons, but ordinarily would not include phenyl groups for paper release purposes. R' is a hydrocarbon radical h a v i n 9 alkenyl unsaturation. Typically, R' represents vinyl groups but may also represent allylic or cycloalkenyl unsaturated groups. X and Y are positive integers so that the vinyl chainstopped p o 1 y s i I o x a n e h a s up to approximately 20% by weight of R' groups. The viscosity of such a polysiloxane ranges from approximately 50 to approximately 100, 000 centipoise at 25'C Preferably, the vinyl chainstopped polysiloxane has up to approximately 20% by weight of vinyl groups represented by R' and the viscosity of this polymer ranges from approximately 300 to approximately 550 centi poise at 250C. The preferred vinyl chainstopped poly siloxane has the general formula:

C H C H C H C H 1 3 ' 1 31 3 1 3 CH 2 CH-Si -0 Sio S10 Si -CH--CH 2 CH C H H 3 11 3 CH) X 2 y C H 3 wherein X and Y are as described above.

Methylhydrogen fluid is often used by those skill e d in the s i 1 i c o n e art as a crosslinking agent for addition-cured silicone systems. Particularly useful as a crosslinking agent for the present invention is a trimethyl chainstopped polymethyl hydrogen siloxane fluid having from approximately 10% to approximately 100% SiH groups with the remainder being essentially dimethylsil- oxy units and having a viscosity in the range of approximately 1,000 centipoise at 25'C.

The organohydrogenpolysiloxanes having structural units represented by Formula II hereinabove are intended to broadly cover fluid organopolysiloxanes whi ch are preferably, but not necessarily, free of olefinic unsat- u r a t i o n, but which contain silanic hydrogen. These org anohydrogenpolysiloxanes represented by Formula 11 herein above are also well known in the art as particularly manifested by U.S. Patent N o. 3,344,111 to Chalk, and U.S. Pat. No. 3,436,366 incorporated herein by reference.

Among the radicals represented by R in Formula II, hereinabove, similarly to R in Formula I hereinabove, are included alky], such as methyl, ethyl, propy], isopropy], buty], octyl and the like; cycloalky], such as cyclopenty], cyclohexy], cycloheptyl and the like; ary], such as phenyl, naphthy], toly], xyly], and the like, aralky], such as benzyl, phenylethy], phenylpropyl, and the like; halogenated derivatives of the above radicals, i n c 1 u d i n 9 chloromethyl, trifluoromethy], chl oropropyl, chlorophenyl, dibromophenyl, tetrachlorophenyl, difluorophenyl and the 1 i ke; and cyanoal kyl, such as beta-cyanoethyl, gammacyanopropy], 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 Formula II is methyl. Materials specifically encompassed within Formula II hereinabove, include 1,3-dimethyldisiloxane, 1,1,3,3,tetramethyldisiloxane, as well as higher polymers con20 taining up to 100,000 or more silicon atoms per molecule. Also included within the scope of Formula II hereinabove are cyclic materials, such as cyclic polymers of methyl hydrogen siloxane having the formula:

(CH3SiHO) X wherein x is a whole number equal to from 3 to 10 or more. Particularly included is tetramethylcyclotetrasiloxane.

The organohydrogenpolysiloxanes employed in the practice of the present invention can also be character- ized as copolymers containing at least one unit per molecule having the formula:

M - R H SiO -c d 4-c-d k (VI) with the remaining siloxane units in the organopolysiloxane being within the scope of Formula V hereinabove, where R, c, d and n are defined above.

V -8-.

Within the scope of Formula VI are siloxane units, such as hydrogen siloxane units (H 2 S i 0) 1.51 methyl hydrogen siloxane units (HSiCH3 0), dimethyl hydrogen siloxane u n i t s, and dihydrogen siloxane units (H 2 sio). In these copolymers, the siloxane units of Formulae V and VI are present in proportions so as to form a hydrogenpolysiloxane within the scope of Formula II hereinabove. In general, these copolymers contain from 0.5 to 99.5 mole percent of the siloxane units of Formula V with from 0.5 to 99.5 mole percent of the siloxane units of Formula Vi.

Ordinarily for release coating purposes it is preferred that the organohydrogenpolysiloxane crosslinker be essentially a trimethyl chainstopped 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 weight percent.

The precious metal catalyst component employed in the compositions of the present invention includes all of the well known platinum-metal catalysts which are effective for catalyzing the reaction between silicon bonded hydrogen groups and silicon-bonded olefinic groups and w h i c h are freely miscible' in solvent-free silicone polymers. These materials i n c 1 u d e, for exam'ple, the platinum hydrocarbon complexes shown in U.S. Patent No.

3,159,601 to Ashby and U.S. Patent No. 3,159,662 to Ashby as well as the platinum alcoholate catalysts described in U.S. Patent N o. 3,220,972 to Lamoreaux. Moreover, the platinum chloride-olefin complexes described in U.S.

Patent N o. 3,516,946 to Modic are also useful herein.

All of the aforesaid U.S. Patents are intended to be incorporated herein by reference.

Small amounts of dialkylacetylenediacraboxylate i n h i b i t o r permit exceptionally long catalyzed pot-life without sacrifice of cure performance in a solventless paper release system. Ordinarily, the effective amount to approx- of i n h i b i t o r ranges from approximately 0.05"C v -g- 4 1 imately 1.0% by weight, and preferably from 0.1 to 0.25% by weight. Use of the inhibitor of the present invention results in adequate pot-life yet the composition rapidly cures to a smear-free and migration-free nonadh-6teff-surface when cured with ultraviolet light.

Dialkylacetylenedicarboxylates result from the diesterification reaction of -2-butynoic dicarboxylic acid with two equivalents of alcohols such as methanol, ethanol, butanol, benzylic alcohol, allyl alcohol or mix- tures of such alcohols. Such reactions can be represented as:

HOOCC = CCOOH + 2 ROH--> ROOCC_ CCOOR + 2 H 2 Ok or HOOCC=-= CCOOH + CCOOH + ROH + RIOH ROOCCm- CCOORI + 2H 20 Useful diesters prepared in this fa.shion include dimethyl- acetylenedicarboxylate, diethylacetylenedicarboxylate, dibutylacetylenedicarboxylate, methylbutylacetylenedicarboxylate, methylethylacetylenedicarboxylate, etc. Particularly useful for the practice of the present invention are those diesters wher-e R represents methyl or ethyl groups.

Effective levels of dimethylacetylenedicarboxyl ate are quite soluble in silicone fluids, and it is not sifnificantly volatile, having a boiling point above 200cC at atmospheric pressure. Additionally, dimethylacetylenedicarboxylate is readily available commercially. Fur- thermore, inasmuch as the total inhibitor concentration in the di methyl acetyl enedi carboxyl ate- i nhi bi ted polysil oxane is quite low, the total cost is significantly reduced. Additionally, the small inhibitory amounts of dimethylacetylenedicarboxylate utilized by the present inventi on will be substantially wholly included within the crosslinked polymer. Thus free dimethylacetylenedi carboxylate is not extant aft er the polymeric composition is cured.

Dimethylacetylenedicarboxyl ate will also effectiv ely inhibit the platinum catalyzed condensation cure V reaction for polysiloxane compositions having silanol functionality as well as inhibit the cure for those compositions exhibiting both silanol and vinyl functionality. A base polymer for such a composition can be, for example, a silanol chainstopped polydiorganosiloxane having pendant vinyl groups along the siloxane chain.

The ingredients described above may be mixed in any order and exposed to ultraviolet radiation for cure. Persons skilled in the art are familiar with ultraviolet light cure and are easily able to determine proper spectrum, flux and exposure time to obtain the cure.

A preferred use of the above described composition is as a release coating on a substrate. The composition is mixed, appl i ed as a t h i n film on a substrate, and cured by exposure to ultraviolet light. The substrate may be non-porous, i.e. g 1 a s s, pl asti c, metal foil etc. but is preferably porous, such as, paper and other fibrous materials.

In order that those skilled in the art might be better a b 1 e to practice the present invention, the following examples are given by way of illustration and not by way of limitation.

Description of the Preferred Embodiments Example 1

A 500 centipoise vinyl-stopped linear polydimethylsiloxane fluid was blended with various amounts of a 5 Karstedt platinum catalyst and dimethylacytylenedicarboxylate (DIMAC). Within two minutes of mixing, an intense orange-yellow col.our was generated in each of the compositions. Table I shows the compositions which were blended and their contents.

Table I

DIMAC Mole Ratio, Composition Pt. conc. ppm conc., ppm Pt/DIMAC 1 25 1000 1/55 2 25 250 1/13.7 3 40 200 1 A/11 4 50 200 2/11 Example 2

A 400 centipoise vinyl-stopped, dimethyl; methyl- vi vinyl, linear silicone polymer with 3.7 wt. % D units was blended with various amounts of a Karstedt platinum catalyst and dimethylacetylenedicarboxylate (DIMAC). Within two minutes of mixing, an intense orange-yellow orod was generated in each of the compositions. Table II shows the compositions which were blended and their contents.

Table II

DIMAC Mole Ratio Composition Pt. conc., ppm conc., ppm Pt/DIMAC 50 200 2/11 6 100 300 4/16.5 1,01 -12-.

Example 3

Each of compositions 1-6 were blended with a 350 centipoise linear, trimethyl siloxy-stopped poly(dimethylmethylhydrogen)siloxane with 50 wt. % DH units present in a weight ratio of 9 to 1. The resultant bath composi t i o n s 1-6 were coated on to aluminum Q panels, polypropylene film, or 40#/ream paper SCK paper substrates. The coated -substrates were exposed in an oven or in air to ultraviolet light as shown in Table III.

4 T a b 1 e Coating Thickness Comp. Substrate Mil 1 paper 2 1 a] umi num 1 paper 1 a] umi num 1 paper 2 paper 2 paper 3 paper 3 paper paper paper 4 paper paper paper 5 polypropylene 5 polypropylene 6 paper 2 thin film 2 4 thin film thin film thin film thin film thin film thin film thin film thin film thin film thin film 1 thin film 6 paper thin film UV_ Oven Exposure Conditions j/CM2 min/'C 1.5 4.5 1.5 5/80 1.5 -- 1.15 0.6 0.48 0.6 0.48 0.96 0.64 1.28 2.9 0.96 0.64 -- Shadow set up across coating "thin films' is approximately 5 microns 1 Qualitative Results - L5/80 1/80 Cured; no smear, no migration, good anchorage Exposed areas cured shadowed areas wet Cured; no migration slight smear 11 Cured; no migration slight smear Undercured, migrates Cured; slight migration Cured; no migration slight smear Undercured; slight migration Curecl; no migration slight smear Undercured; migrates Poor cure; migrates, poor anchorage Cured; no migration, but rubs off Cured; no migration, slight smear Undercured; migrates i 1; t -13-.

The above data shows that -D v i - units present in the base polymers appear to slow cure relative to 0' - functional f 1 u i d s. High Pt concentrations do not enhance cure so long as inhibitory concentrations of DIMAC are _present.

Example 4

This experiment is to verify that ultraviolet light without thermal assist will trigger cure of Pt/ DIMAC addition cured systems. A low intensity ultraviolet light source, (UV Products, Inc. table top lamp, 115 volt, 0.35 amp.) was set up. (unfocused) 1.41 inches away from an aluminum substrate having a 2 mil coating of bath composition 1. UV flux was determined to be 6 J/CM2 hr. No significant difference could be detected between room temperature, 24'C, and the measured tempera- ture of the substrate after 15 minutes exposure to the low intensity source. The coating cured to a smear-free well-anchored rubbery surface in about 2.5 hours exposure, i.e. 15 J/cm2 to.tal flux. This observation coupled with the Experiment 3 "shadow" observation confirms the ultra- violet light nature of this cure mechanism.

Example 5

The pot life of bath compositions 1 and 3-6 was investigated by noting viscosity as a function of time at a given temperature. Table IV shows the time/viscosity relationship at 25"C.

v -14-.

Table IV

COMPOSITION, viscosity, cps.

Time hr. 1 3-6 0 624 2 686 Gelled in less than 30 min.

4 760 6 842 8 1025 24 9000 4'C.

T a b 1 e V shows the time/viscosity relationship at Table V

COMPOSITION, viscosity, cps.

Time hr. 3 4 5 6 0 760 800 600 606 1 890 910 702 730 2 940 1115 860 882 3 1135 1300 980 1925 4 1240 1600 1200 1400 11 f f

Claims

CLAIMS:

1. A silicone release coating composition which can be cured by exposure to ultraviolet light, comprising (a) an olefinorganopolysiloxane having units of the s,tru.ctural formula Ra R' bS'04-a-b2 (b) an organohydrogenpolysiloxane having units of the structural formula R a H b Sio 4-a-b 2 wherein R is selected from a monovalent hydrocarbon radical, a halogenated monovalent hydrocarbon radical, a cyanoalkyl radical and mixtures thereof, R' is an olefinic hydrocarbon radical, wherein a has a value of from 0 to 3, inclusive, b has a value of from 0.005 t,& 2.0, inclusive, and the sum of a and b is equal to from 0.8 to 3, inclusive; (c) a sufficient amount of a platinum metal catalyst to cause the coreaction of (a) and (b); and (d) a dial kyl acetylenedicarboxyl ate having the general formula -ROOCC ' CCOOR where R is as defined above and wherein said dial kylacetylenedicarboxyl ate is present in an amount effective for inhibiting premature gelation but insufficient for preventing cure at elevated temperature; wherein the release coating composition has a viscosity of 25 to 5000 centipoise at 25'C.

2. A composition as claimed in claim 1, wherein R contains from 1-30 carbon atoms and R' contains from 1-20 carbon atoms.

- v -16-.

3. A composition as claimed in claim 1 or 2, wherein R contains from 1-12 carbon atoms and R' contains from 1-12 carbon atoms.

4. A composition as claimed in any preceding claim, wherein the composition is fluid at room temperature and has a viscosity of 25 to 5000 centipoises at 25'C.

5. A composition as claimed in any preceding claim, wherein the alkyl groups in the dialkyl acetylene- dicarboxylate are methyl or ethyl groups.

6. A composition as claimed in any preceding claim, wherein said platinum metal catalyst is a Karstedt catalyst.

7. A composition as claimed in any of claims 1 to 5, wherein said platinum metal catalyst is a Lamoreaux catalyst.

8. A composition as claimed in any preceding claim, wherein said platinum metal catalyst is present in an amount sufficient to provide, approximately, 5 to 500 parts platinum metal per million parts of said olefinorganopolysiloxane.

9. A composition as claimed in any preceding claim, wherein s a i d dialkylacetylenedicarboxylate is present in an amount of, approximately, 0.02 to 1.0 weight percent of the silicone coating composition.

10. A composition as claimed in any preceding claim, wherein said dial kyl acetylenedicarboxylate is sel ected from di methyl acetyl enedi carboxyl ate, diethylacetyl enedicarboxylate, and methylethylacetylenedicarboxylate, dibutylacetylenedicarboxylate, and methylbutylacetylene dicarboxylate. '1 -17-.

f;

ll 1; 11 A composition as claimed in any preceding claim, wherein said olefinorganopolysiloxane is a di methylmethylvinylpolysiloxane copolymer fluid having a viscosity of, approximately, 300 to 1000 centipoise at 25'C and a vinyl content of, approximately, 0.1 to 2.5 weight percent.

12. A composition as claimed in any preceding claim, wherein said organohydrogenpolysiloxane is a tri methyl chainstopped methylhydrogenpolysiloxane fluid having a viscosity of, approximately, 10 to 500 centi poise at 250C at a hydrogen content of, approximately, 0.1 to 1.67 weight percent.

13. A composition as claimed in claim 1, wherein the olefinorganopolysiloxane is a dimethylvinylpolysilox ane having a viscosity of 1000 to 100,000 centipoises at 25"C.

14. A -composition as claimed in any preceding claim and further comprising a substrate upon which said silicone coating composition has been coated.

_1 5. A process for rendering surfaces nonadherent to materials which would normally adhere thereto, wherein a silicone release coating composition as claimed in claim 1 is coated on a suitable surface at a thickness of, approximately, 0.05 to 2.0 mils; and cured with an amount of ultraviolet light effective for overcoming the cure retarding properties of said dialkylacetylenedicar boxylate.

16. A silicone release coating composition substantially as hereinbefore described.

v Pubhshed 1988 P,'. The Patent Office, State House, 6571 High Holborn, London WC IR 4TP. Further cuples may be obtained from The Patent Office, Sales Branch, St Mary Cray. Orpington, Kent BR5 3RD. Printed ky Multiplex techniques Ad, St Mary Cray, Kent. Con. 1/87.