CA1233290A - Ultraviolet radiation-curable silicone release compositions - Google Patents

Abstract

ULTRAVIOLET RADIATION-CURABLE
SILICONE RELEASE COMPOSITIONS
ABSTRACT OF THE DISCLOSURE
Novel UV-curable silicone release coating compositions and photocatalysts therefor are provided which include mercaptoalkoxyalkyl-functional polysiloxanes and vinyl-functional photoreactive terpolymers, both of which are especially compatable with certain perbenzoate ester photocatalysts. The addition of certain polyaromatic photosensitizers to enhance cure is also disclosed.

Description

. ~233290 SUE

ULTRAVIOLET RADIATION-CURABLE
SILICONE RELEASE COMPOSITIONS

FIELD OF THE INVENTION

This invention relates to ultraviolet radiation-curable silicone release compositions. More particularly it relates to new photo curable selection polymers and new photocatalyst-siloxane polymer combinations. Marquette-alkoxyalkyl-functional polysiloxanes and vinyl-functional selection terpolymers have been discovered which are curable on exposure to ultraviolet radiation in the presence of a photo initiator.

BACKGROUND OF THE INVENTION

Silicone compositions have become widely accepted as release coatings, which are useful to provide a surface or material which is relatively non adherent to other materials which would normally adhere closely thereto. Silicone release compositions may be used as coatings which release pressure sensitive adhesives for labels, decorative laminates, transfer tapes, etc.
Jo Silicone release coatings on paper, polyethylene, Mylar , and other such substrates are also useful to provide non-stick surfaces for food handling and industrial packaging.

Previously developed silicone release products have been heat-curable, however the high one gyp costs and safety and environmental considerations associated with high temperature oven curing has provided the incentive for developing alternative technologies, such as ultraviolet radiation-curable silicones.

Ultraviolet (W) radiation is one of the most widely used types of radiation because of it low cost, ease of maintenance, and low potential hazard to industrial users. Typical curing times are much shorter, and heat-sensitive materials can be safely coated and cured under W radiation where thermal energy might damage the substrate.
I
Three basic Uncurable silicone systems have been developed: ~poxysilicone systems, acrylic-runctional silicone systems, and mercaptofunctional silicone systems.
I
Epoxy silicone systems, such as those described in US. 4,279,717 (Eckberg et Allah and commonly assigned Canadian application Serial Jo. 428,1~2 which was filed May 13, 1983, feature epoxy-functional diorgano selection base polymers catalyzed by opium salt photo initiators.
The compositions exhibit extremely high cure rates but depend on expensive materials which are not widely available.

lZ~3~90 SUE 666 Acrylic-~unctional silicone systems sun as described in commonly assigned cop ending dun Applications Serial Nos. 399,410 filed March 25, 19~2 and 428,142 filed May 13, 1983, and also modified systems described in US. 4,048,036 (Prucnal) and US. 4,017,652 (Grubber), provide serviceable coatings that are W-curable in the presence of free radical-type photo initiators but require complex, multi step preparation.

Many mercapto-functional systems are known: For example, US. 4,064,027 (cant), US. 4,107,390 (Gordon et at.), US. 4,197,173 (Curry et at.), Japan okay Tokyo Kiwi 79 48,854 (to Takamizawa; Chum.
Abstracts 91: 58888r, 1979), US. 3,661,744 (Kerr et at.), US. 4,G70,526 (Colquhoun et at.), US. 4,052,529 (Bokerman et at.), US. 3,873,499 Michael et at.), and US. 3,816,282 (Viventi) disclose Marquette-functional polysiloxane or polythiol compositions which are W -curable when combined with an ethylenically unsaturated organic compounds, which curable csmpusitions also contain, variously, mercaptoalkyl polysiloxane cure accelerators, acetophenone-type photosensitizes, silacyclopentenyl curing agents, cure rate accelerators and gellation inhibitors. These provide a wide range of serviceable release coating compositions, however, the acceptance of this technology has been hindered by several persistent disadvantages including dependence on scarce or expensive starting materials, unserviceably slow curing rates, complex processing, and offensive odors (associated with the mercaptan group) which persist in the cured products. Some of these specific disadvantages have been addressed, for example, in the cant patent, photosensiti~ers such as acetophenone are added to assist radiation curing, in Us 4,171,252 (Fantazier), photo polymerization of unsaturated come , SUE 666 ~Z33Z9(~

pounds is catalyzed by peroxy-napthalenic compounds, and in the aforementioned Kerr et at. and Colquhoun et at.
patents aromatic kittens are employed to accelerate the cure; however, there is still a need for improvement and reduction of costs in mercaptofunctional compositions and related W-cure technologies.

New mercaptoalkoxyalkyl-functional silicones have now been discovered which can be synthesized in a two-step, one-vessel process from readily available, inexpensive lo materials and which do not emit disagreeable odors. In addition, it has been discovered that certain perbenzoate esters are suitable photoinititators for polymerization reactions between mercqptofunctional compounds and vinyl-functional compounds; and the cure characteristics of the novel reactive polysiloxane/photoinitiator blends ox the present invention may be enhanced or modified by certain aromatic photosensitizes or by judicious selection of the molar ratios of reactive ingredients in such Lindsey SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invent lion to provide new mercaptofunctional silicone release coating compositions.

It is a further object of the present invention 25 to provide solvent less silicone release coating compositions which are curable on brief exposure to ultraviolet radiation.

~,~3~9~ SUE 666 It is a further object of the present invention to provide improved reactive polysiloxane/photoinitiator blends which are simply and inexpensively produced.

These and other objects are accomplished herein by a mercaptoalkoxyalkyl-functional polysiloxane capable of curing (i.e., polymerizing or cross linking) to an adhesive polymeric composition on brief exposure to ultraviolet radiation when combined with an organic compound containing ethylenic unsat~ration and a catalytic amount of a photo initiator comprising: A
diorsanopolysiloxane comprising units of the formula RR'SiO, where R is hydrogen or Cal 8) alkyd and R' is hydrogen, Cal 8) alkyd or a monovalent mercaptoalkoxyalkyl-functional organic radical of from 2 to 20 carbon atoms, said diorganopolysiloxane having up to about 50% Marquette-alkoxyalkyl-functional groups and a viscosity of from about 50 to 10,000 centipoise at 25C.

Also contemplated are mercaptoalkoxyalkyl-function~l diorganopolysiloxanes prepared by (1) reacting a dialkyl-hydrogen-chainstopped polydialkyl-alkylhydrogensiloxane copolymer with an ~-halo-alkene in the presence of a precious metal hydrosilation catalyst, and (2) reacting the product of (1) with a hydroxy-functional they'll of the formula HORATIO, where R" is a diva lent alkaline or alkyd kitten radical of from 2 to 20 carbon atoms in the presence of an amine.

Another feature of the present invention is a corbel silicone release composition comprising:

o i~33~9 SUE 666 (A) A diorganopolysiloxane comprising units Of the formula RR'SiO, where R is hydrogen or Cal 8) allele and R' is hydrogen, Cal 8) alkyd or a monovalent mercaptoalkoxyalkyl functional organic radical of from 2 to 20 carbon atoms, said diorganopolysiloxane having up to about 50~ weight mercaptoalkoxyalkyl groups and a viscosity of from about 50 to 10,000 centipoise at 25C;

(B) A polysiloxane consisting of from about 0.5 to 100 mole percent of vinyl-lunctional selection units of the formula (CH2=CH)RnSiO3 n/2' where R is hydrogen or Cal 8) alkyd and n has a value of 0 to 2, inclusive, any non-vinyl-containing selection units having the formula R3mSio4 my where R is hydrogen or Cal 8) alkyd and m has a value of from 0 to 3, inclusive; and (C) A catalytic amount of a photo initiator.

Especially contemplated are W -curable compositions wherein the photGinitiator component is a pe~benzoate ester; and further features include the use of certain aromatic kittens as photosensitizes to assist curing, and the discovery of a vinyl-functional polysiloxane terpolymer which is useful in forming Uncurable release compositions.

Further embodiments of the present invention will become apparent to those skilled in the art upon consider-lion of the following description, examples, and claims.

DOTTED DESCRIPTION OF THE INVENTION

The present invention provides mercaptoalkoxyalkyl-functional silicone compositions and silicone release coaxings made from such compositions, as well as photo-initiators for such compositions and processes for providing the compositions and coatings.

The mercaptofunctional polymers of the present invention are diorganopolysiloxanes comprised of selection units having substituent groups including hydrogen atoms, lower alkyd radicals having up to about 8 carbon atoms such as methyl, ethyl, Ripley, isopropyl, etc., and monovalent mercaptoalkoxyalkyl radicals of from about 2 to 20 carbon atoms. These polymers may be advantageously synthesized from a number of constituent ingredients. The relative proportions of these constituents are not critical and may be varied over a wide range to provide mercaptoalkoxyalkyl-functional polysiloxanes having varied properties. The preferred synthesis, described below, requires only two steps and may be carried out in a single reaction vessel, however it will be recognized that alterations in the synthesis procedure can be readily devised which are within the scope of the present invention.

The preferred mercaptoalkoxyalkyl-functional polymers of the present invention are prepared from a dialkylhydrogen-chainstopped polydialkyl-alkylhydrogen selection copolymer. Such SiH-containing polysiloxanes will ordinarily haze the general formula:
-z33~9c~ SUE 566 _ 8 R , R \ / R R

Ho Slow Sluice R H R y R

in which each R represents, independently, a monovalentalkyl radical of from 1 to 8 carbon atoms, preferably methyl, and zoo is an integer of about 25 to 600 such that the polysiloxane has a viscosity of about 20 to 5000 centipoise at 25C, preferably 100 to 500 centipoise.
Such hydrogen-functional selection fluids are primarily linear and will therefore have an R to So ratio of approximately 2 to 1. These selection fluids will ordinarily have from about 0.5 to 50 percent by weight hydrogen-siloxy functionality and are made by processes well known in the art. Minor amounts of moo- and tri-functional selection units, some of which may also contain hydrogen, may also occur in these fluids but will not seriously detract from their usefulness.

The SiH-containing polysiloxanes are reacted with an ~-halo-alkene, preferably an w-chloro-l-alkene such as ally chloride, methallyl chloride, sheller-butane, 10-chloro-1-decene, and owner analogous unsaturated halogen-containing hydrocarbons. Mixtures of such ~-halo-alkenes will also be useful.

1233Z~3~

_ g The alkene component and the hydrogen-functional polysiloxane component are reacted in a precious metal-catalyzed addition cure reaction. Such catalysts are well known in the silicone art and will ordinarily be a platinum metal complex effective to promote the addition of a -Six moiety to the double bond of an alkene. Examples of such hydrosilation catalysts suitable for the purposes herein are described in United States Patents 3,220,972 (Limericks) issued November 30, 1965; 3,715,334 (Karlstedt) issued February 6, 1973; 3,775,452 (Karlstedt) issued November 27, 1973 and 3,814,730 (Karlstedt) issued June 4, 1974.
The product of the hydrosilation reaction described above is finally reacted with a hydroxy-functional they'll monomer in the presence of an amine.
Suitable thiols have the general formula Horatio in which R is diva lent alkaline of from 2 to 20 carbon atoms or diva lent alkyd kitten radicals, -(Sheehan COO-, of from 2 to 20 carbon atoms.
Preferred compounds are -mercaptoethanol and -mercaptopropionic acid. For the purposes of the present invention, sufficient amounts of the hydroxy-functional they'll monomer should be used to provide a mercaptioalkoxyalkyl-functional polysiloxane having from 0.5 to 50 percent by weight mercaptoalkoxyalkyl sulks functionality. The above-described synthesis may be illustrated as follows: _ _ :.

1~33~

_ 10 _ 1) -Six + CH2=CCH2-C~ -I SiCH2fHCH2-Cl SHEA SHEA
methallyl chloride

2) -SiCH2CHCH2-Cl + HOWE amine _ I

OH

3 -SiCH2CHCH2-O-R-SH

SHEA
o R is preferably CH2CH2 or CCH2CH2 .

W -curable mercaptoalkoxyalkyl-functional silicone composition scan be made by combining the above-described mercaptoalkoxyalkyl-functional polysiloxanes with a catalytic amount of a photo initiator. Any of the numerous photo catalysts known to promote a curing-, it cross linking, reaction between the mercaptofunc-tonal group and the vinyl-functional group of a vinyl-containing cross linking compound, marry of which photo catalysts are discussed n the previously cited United States Patent Numbers are suitable. Especially contemplated are the acetophe-none-type photo initiators such as dimethylhydroxyacetophe-none, which is commercially obtainable under the trade name Darker 1173 term. Chemicals, Inc.) A preferred feature of the present invention, however, stems from the discovery that certain perbenzoate esters hazing the general formula:

Wreck 12332~0 SUE 66~i where R is a monovalent alkyd or aureole group and Z is H, alkoxy, alkyd, halogen, vitro, amino, primary and secondary amino, amino, etc. The nature of the Z
substituent will affect the stability of the proxy bond, an electron-poor substituent stabilizing the proxy bond, and an electron-rich substituent making the proxy bond more reactive. These perbenzoate esters may be synthesized in known ways, such as by reacting bouncily halides with hydroperoxides. (See, e.g., the descriptions in Blomquist and Bernstein, J. Amer. Chum.
So., 73,5546 (1951)). Preferred perbenzoate esters include t-butylperbenzoate and its para-substituted derivatives, t-butylper-p-nitrobenzoate, t-but~lper-p-methoxybenzoate, t-butylper-p-methylbenzoate, and t-butylper-p-chlorobenzoate. T-butylperbenzoate is most preferred.

The amount of photo initiator employed is not critical, so long as proper cross linking is achieved.
As with any catalyst, it is preferable to use the smallest effective amount possible; however, for purposes of illustration, catalyst levels of from about 1% to 5% by weight of the total composition have been found suitable.
In addition to the discovery that t-b~tylperbenzoate (and its derivatives) is an excellent photo catalyst for radical addition of mercaptofunctional selections to vinyl-functional selections, it has been discovered that the effectiveness of t-butylperbenzoate as a photo catalyst is considerably enhanced when it is combined with certain photosensitizes soluble in the silicone polymers of the the instant invention. The use of these photosensitizes leads to advantages in terms of release performance ease of processing and lowering costs. The photosensi-lZ33290 SUE 666~

- 12 _ titers more than double the rate of cure in photoactive compositions under inert conditions and, surprisingly, promotes good cure without inverting, which allows important cost and processing advantages.

The photosensitizes are polyaromatic compounds having at least two Bunsen rings which may be fused or bridged by organic radicals or hetero-radicals such as ox, trio, etc. Preferred among the photosensitizes Lo tested were benzophenone and t-butylanthraquinone.
Anthracene and thioxanthone were unsuccessful as photo-sensitizers due to their limited volubility in silicone solutions. Other photosensitizes compounds related to those already mentioned will suggest themselves to persons skilled in the art and are meant to be included within the scope of the present invention.

In the course of trials testing the effectiveness of the aforementioned perbenzoate esters and photo-sensitizers, previously unknown photo reactive terpolymers were discovered which are capable of curing (on exposure to W radiation) to adhesive compositions in the presence of certain radical photosensitizes and without the use of perbenzoate esters. The terpolymers are mixed dimethylvinyl- and trimethyl-chainstopped linear polydimethyl-methylvinyl-methylhydrogen selection terpolymer fluids and can be synthesized by acid equal-ration of methyl hydrogen selection fluid, tetramethyl-tetravinylcyclotetrasiloxane (methylvinyltetramer~ and octamethylcyclotetrasiloxane (dimethyltetramer), as desk cried Gore completely in the worming examples (infer).

The W -curable silicone compositions which may be prepared from the previously described ingredients can be applied to cellulosic and other substrates including paper, metal, foil, glass, polyethylene coated Crete PUKE), super-,. . .

Swiss calendered raft paper (SUCK), polyethylene films, polyp propylene films and polyester films. A photo initiated reaction will cure the silicone compositions to form an adhesive surface on the coated substrate. Inverting of the cure environment, such as with nitrogen, may be desirable where the presence of oxygen is found to inhibit the curing reaction.

In order that persons skilled in the art may better understand the practice of the present invention, the following examples are provided by way of illustration, and not by way of limitation. All measurements are parts by weight.

EXAMPLES l-10 Sample A
200 parts by weight of a 90 cups dimethylhydrogen-chain stopped linear polydimethyl-methylhydrogen selection fluid having about 9.5% by weight SiH-containing sulks units about 0.31 moles Six total) were combined with 200 parts by weight Tulane and about 31.5 parts by weight metnallyl chloride about 0.36 moles). A small amount of a platinum catalyst was added and the reaction mixture reflexed at 110C for 14 hours, at which time infrared examination detected no unrequited Six functionality. Excess methallyl chloride was removed by distilling about 6 parts by weight of solvent from the mixture at one atmosphere pressure. 33 parts by weight y-mercaptopropionic acid Tao moles) were added to the reaction vessel and a nitrogen atmosphere established prior to drops addition of 40 parts by weight triethylamlne at a temperature of SKYE. A
hazy precipitate taminehydrochloride) formed as the triethylamine was added. The solvent was stripped under a vacuum trout 5 mm pressure) at 158C for 30 minutes.

1~332~0 SUE 666 _ 14 -Filtering the reaction product resulted in 173 parts by weight of a hazy fluid, ~50 cups viscosity.

Sample B
Another mercaptofunctional polysiloxàne material was prepared in the same manner as Sample A except that ~-mercaptoethanol (0.31 moles) was substituted for y-mercaptopropionic acid. 182 parts by weight of a slightly hazy 190 cups fluid product were obtained.
Sample C
250 parts by weight of a 50 cups SiH-containing fluid similar to that used in Samples A & B containing about 6.0 percent by weight SiH-containing sulks units (0.25 moles total Six) were reacted with about 27 parts by weight methallyl chloride by refluxing in 250 parts by weight Tulane for 16 hours in the presence of a platinum catalyst. After removal of excess methallyl chloride, 500 parts by weight hexane and 19.5 parts by weight (0.25 moles) ~-mercaptoethanol were added, followed by drops addition of 20 parts by weight pardon (0.26 moles) under nitrogen at 60C. The precipitate resulting from the amine addition was filtered from the solution and the filtrate stripped of solvent and unrequited mercaptoethanol under a vacuum at 165C for I hours. 226 parts by weight of a clear, pale yellow 130 cups product were obtained.

Sample D
250 parts by weight of a 295 cups SiH-containing fluid having about 7.0 percent by weight SiH-containing sulks units (0.29 moles total Six) were reacted with methallyl chloride, then ~-mercaptoethanol and pardon precisely as in the preparation of Sample C, above.

Stripping the reaction product at 165C for 4 hours yielded 237 parts by weight of a clear, pale yellow fluid product, 830 cups viscosity.

It was noted that the prolonged strip cycle at temperatures above about 160C accomplished the removal of free (unrequited) mercaptoethanol (leaving an odor-free product) and the removal of residual pardon hydrochlorate precipitate by vacuum sublimation (leaving a clear fluid lo product).

The mercaptoalkoxyalkyl-functional silicones produced in the above fashion were used to produce ultra-violet radiation-curable release compositions, as set forth below:

Coating Composition l: 10 parts Sample B
1 part methylvinyltetramer (teiramethyl-tetravinyl cyclotetrasiloxane) 0.5 part dimethylhydroxyaceto-phenone (Darker 1173).

Coating Composition 2: 8 parts Sample B
2 parts methylvinyltetramer US 0.5 part dimethylhydroxyaceto-phenone Coating Composition 3: 8 parts Sample B
2 parts vinyl terminated dimethylpolysiloxane fluid, 200 cups.
0.5 part dimethylhydroxyaceto-phenone.

:3 Z~2~3Q

~16~

Coating Composition 4: 7 parts Sample D
3 parts sym-Letramethyldivinyl-disiloxane 0.4 part dimethylhydroxyaceto-phenone.

Coating Composition 5: 5 parts Sample D
3 parts sym-tetramethyldivinyl-disiloxane 2 parts vinyl terminal dim ethyl-methyl vinyl selection fluid, 200 cups 0.4 part dimethylhydro~yaceto-phenone.

Each coating composition was coated onto 40-lb.
SUCK paper as a thin film with a doctor blade, then exposed to ultraviolet radiation from two focused medium-pressure mercury vapor lamps each operating at 30C watts per square inch mounted in a PUG 1202 SCAN processor.
Exposure times and curing atmosphere were varied to assess the cure performance of the experimental compost-lions. The cure was qualitatively determined by noting the presence or absence of smear, migration, or rub-off, with the following results:

Coating Cure Exposure Cc~position _ Time, Sec. Qualitative Cure 1 No 1.5 No smear, no migration, no rub-off 1 Air 1.5 Slight jar, slight muggier., no n~toff 1 No 0-3 No migration, easy rub-off 1 Air 0.3 Slight migration, easy rub-off 1 No 0-07 No migration, eye rub-off 1 Air 0.07 Migrates, rubs off easily 2 No 0-3 Jo migration, rubs off easily 2 Air 0.3 Slight muggier., rubs off easily 3 No 0-3 Slight muggier., rubs off easily i23329~ SUE 666 3 Air 0.3 NOT CUD

4 1.5 No jar, no migration, no rebuff 4 Air 1.5 Slight err, no migration, slight rub-off

5 5 No 1.5 No smear, no migration, no rub-off Air 1.5 Migrates, no rub-off No 0-3 No migration, easy rub-off These data indicate that a wide range of vinyl-functional selections are suitable cross linkers in the US cure of mercaptoalkoxyalkyl-functional polysiloxanes.
Also, it is apparent that better results are obtained under a nitrogen atmosphere than in air, which is predictable given the radical-initiated nature of the curing reaction. Fully cured (migration-free) coatings are observed with exposure times as brief as 1.5 seconds, although anchorage to the SIX paper (evidenced by rub-off) suffers at shorter exposure times.

It has been previously -sported, in US. 4,139,385 (Crivello), issued on February 13, 1979 , that opium salt photo catalysts promote poIv~lefin-polythiol cross-linking; and the following coating compositions were prepared to test the effectiveness of cat ionic photo-catalysts with the polymers of eke present invention:

Coating Composition 6: 10 parts Sample B
1 part methylvinyltetramer 0.2 part (C12H25Ph)2ISbF6 (bis(dodecylphenyl) ioaonium hexafluoroantimonate photo catalyst).

lZ~3~0 Coating Composition 7: lo parts Sample C
l part methylvinylteramer 0.5 part dimethylhydroxyacetophenone 0.2 part (Classifies 6 Coating Composition 8: 7.5 parts Sample C
0.5 part methylvin~ltetramer 2 parts 1,2-epoxydodecane*
0.4 part dimethylhydroxyacetophenone 0.2 part (Cl2H2sPh)2Isb 6 *I -epoxy monomer added as a cure enhancer (described as to epoxy silicones in Canadian Apply SUN. 428,142 filed May 13, 1983.
The performance of these compositions was tested on super calendered raft paper as in Examples 1-5 with the following results:
Exposure, Composition Aim. Sec. Qualitative Cure

6 Air 1.5 No smear, no migration, no rub-off 6 No 0~3 No smear, no migration, rubs-off

7 Air 0.3 Slight smear, no migration, some rub-off 7 N 0.3 No smear, no migration, easy 2 rub-Off

8 Air 1.5 No smear, no migration, no rub-off 8 No 0 3 No smear, no migration, easy rub-off 30 using the 'opium salt catalyst in this system allows those skilled in the art to add an epoxy monomer reactive delineate (such as the linear epoxide present in Composition 8) to the vinylsiloxane-mercaptoalkoxyalkylsiloxane mixture n =

i;2332~

_ 19 -order to assist anchorage or modify the release character-is tics of the cured coating.

The quantitative release performance was determined for two coating compositions by preparing coating baths as follows: (The Sample compositions were dispersed in solvent in order to obtain even, low silicone depositions) Bath 9: 20 parts Sample B
lo 2 parts methylvinyltetramer l part dimethylhydroxyacetophenone 80 parts hexane.

Bath 10: 20 parts Sample B
2 parts methylvinyltetramer 0.4 part (Cl2H2sPh)2Isb 6 80 parts hexane.

These baths were used to coat SUCK paper using a #3 wire-wound rod, and the coated paper were then exposed to W radiation for 0.3 seconds as described above.
Laminates of the cured coatings were prepared by applying a lo mix coating of Monsanto Gelva 263 aggressive acrylic adhesive on top of the cured silicone coating and then pressing an uncoated sheet of SUCK paper onto the adhesive.
2"x9" strips of the laminates were cut, and the silicone/SCK famine separated from the adhesive/SCR famine at a 180 angle at 400 ft./minute in a Scott tester. The release, in grams force needed to separate Ike two famine, was recorded and the following results obtained:

i ~3Z90 SUE 666 _20 -Qualitative Bath Aim. Cure Release grams

9 Aryan muggier., rubs-off 150-190 9 No No muggier., rubs-off 350-450 Air (poor cure) (not recorded) No No muggier., rubs-off 150-210 Although the cured silicone release coatings did not appear to be well anchored, as evidenced by rub-off, there was no observation of the silicone layer being pulled away preferentially from the SUCK substrate. The results also show a high release (as opposed to "premium" release, usually <100 grams), especially when cured in an inert atmosphere, suggesting that the radicals formed in the silicone coating interact with the acrylic monomers present in the adhesive to raise the observed release.

EXAMPLES 11 & lea The efficacy of t-butylperbenzoate as a photo catalyst so thiol/vinyl addition was demonstrated in the following comparative trial:

Coating Composition 11: go parts Sample D (described previously) . 1.0 parts methylvinyltetramer 0.5 part t-butylperbenzoate.

Coating Composition lea: 9.0 parts Sample D
1.0 part methylvinyltetramer 0.5 parts dimethylhydroxyaceto-phenone (Darker 1173).
These coating compositions were hand-coated on 40-lb.
super calendered raft paper using a doctor blade, exposed to ultraviolet light as described above, and finally 35 qualitatively assessed for cure as a release surface, as 1~3Z90 60S~ 666 - 21_ summarized below:
W Exposure Eye Aim. sec. Qualitative Cure 11 AIR 0.6 Slight sir, no migration, slight rub-off 11 No 0-3 No smear, no migration, no rub-off 11 No 0.15 No or, no migration, slight rub off lea AIR 1.5 Swears, no migration, easily rubbed of lea No 1.5 Slight jar, no migration, slight rebuff lea No 0 3 us no migration, easily rubbed-of From these data, it is apparent that t-butylperbenzoate is superior to the commercially available Darker 1173 photo initiator in this curable mercapto-vinyl silicone system.

EXAMPLES 12-14 & AYE
Further investigation into the photo catalytic qualities of perbenzoate esters was conducted by preparing the following coating compositions:
5 Coating Composition 12: 10 parts vinyl terminal d methyl fluid*
0.6 part trim ethyl terminal methyl hydrogen fluid 0.5 part t-butylperbenzoate.

Coating Composition 13: 10 parts vinyl terminal dim ethyl fluid 1.0 part trim ethyl terminal methyl hydrogen fluid 0.5 part t-butylperben~oate 0.5 part dimethylhydrox~yaceto-phenone.

~Z33~90 SUE 666 _ 22-Coating Composition 14: 10 parts vinyl-functional terpolymer3 0.5 part t-butylperbenzoate.

Coating Composition AYE: 10 parts vinyl-functional terpolymer 0.5 part 2, 5-bis(t-butylperoxy) hexane (control) *Dimethylvinyl terminal dim ethyl polysiloxane, 200 cups viscosity fluid.
-Trim ethyl terminal methyl-hydrogen polysiloxane, about 30 cups viscosity fluid. 3Dimethylvinyl terminal dimethyl-methylvinyl-methylhydrogen polysiloxane fluid, ratio of dim ethyl: methyl vinyl: methyl hydrogen units equals, approximately, 88: 5: 6, 80 cups viscosity fluid.

Because t-butylperbenzoate may be used to promote thermally-activated cross linking reactions, the control composition, AYE, was included in the trial. Bassett-butylperoxy) hexane has similar thermal activity to t-butylperbenzoate, so that if the heat generated by the W curing lamps was responsible for curing the coating compositions (instead of the ultraviolet radiation), then the curing characteristics of compositions 14 and AYE
would be similar.

The cure performance in terms of exposure time required to achieve a tack-free release surface was tested by the following method:

~3Z~0 SUE 666 Each mixture was applied as a thin film to 40-lb.
super calendered raft (SKYE) paper by hand with a doctor blade, then exposed to two Hanovia medium pressure mercury vapor ultraviolet lamps, each operating at 300 watts per square inch focused power, mounted in a PUG QC
1202 AN processor. The following results were observed:
Tack-Free Exposure Coating Composition Atmosphere time, seconds 12 INERT 0.9 12 AIR No Cure (5.0 sec.) 13 INERT 1.5 13 AIR No Cure (5.0 sec.) 14 INERT 0.3 14 AIR No Cure (5.0 sec.) AYE INERT No Cure (5.0 Sec.
AYE AIR --Failure of the control composition to cure even in an inert cure environment indicates that t-butylperbenzoate is a photo catalyst for a wide range of vinyl-nydrogen cross-linking reactions. The cured coating compositions also exhibited typical release surface characteristics, with no migration to Scotch #610 adhesive tape but with a slight tendency to smear. Poor cure in the presence of oxygen indicates the radical nature of the cross linking reaction. It is believed that the proxy group bonded directly to the phenol kitten chromophore through the carbonyl carbon atom is necessary for photoactivity.

Derivatives of t-butylperbenzoate were synthesized to evaluate their performance as photo catalysts.

lZ33Z90 SUE 666 _ I _ Nutria Perbenzoate Derivative 33.4 parts by weight of 70~ aqueous t-butylhydro-- peroxide were placed in a reaction vessel and cooled in an ice bath. 65 parts by weight of a 30% aqueous solution of KOCH and 46.4 parts by weight of p-nitrobenzoylchloride dissolved in 90 parts by weight SCHICK were simultaneously added to the vessel slowly over a 30-minute period. This reaction mixture was stirred for 2 hours at 0C, and then for 3 hours at 25C. The organic layer was separated from the aqueous layer, transferred to a separator funnel and twice washed with a I Nikko solution, thrice washed with water and finally dried over an hydrous McCoy. Removal of ethylene chloride under a vacuum furnished 30.9 parts by weight of a crude yellow product, which was recrystallized from acetone/hexane to furnish yellow crystalline t-butylper-p-nitrobenzoate. This was designated Dun, or nutria derivative.

P-methoxy Perbenzoate Derivative Synthesis of t-butylper-p-methoxybenzoate was carried out in the same manner as the nutria derivative.
Since the product is a liquid at room temperature, purification was achieved by dissolving the crude product in CHICANO, then extracting twice with hexane. The product was obtained from the acetonitrile layer by removing C~3CN under a vacuum, to give a 64% yield of a clear, pale yellow, viscous fluid. This product was designated Do, or p-methoxy derivative.

P-tolyl Perbenzoate Derivative T-butylper-p-methylbenzoate was synthesized and purified precisely as the p-methoxy derivative. Purify-cation gave an 85% yield of a clear, colorless fluid product which was designated Do, or p-tolyl derivative.

P~chloro Perbenzoate Derivative T-butylper-p-chlorobenzoate was synthesized according to the procedure used for the nutria derivative. The tendency of the compound to supercool resulted in the recovery of a product with a melting point of approximately

10-30C, compared to 49C for this compound known from the literature. The solid product slowly melted at room temperature to a clear, pale yellow viscous fluid. No further effort was made to purify this sample, which was designated Do, or p-chloro derivative.

In addition to the foregoing syntheses, a number of reactive silicone terpolymers were prepared by acid-catalyzed IFiltrol 20, acid treated play) equilibration of trimethyl-chainstopped methyl hydrogen polysiloxane, methylvinyltetramer, and dimethyltetramer. Photosensi-titers were added to the terpolymers to enhance cure, according to the discovery discussed previously and demonstrated in Examples 25-56, swooper. These terpolymer compositions are described below:

Silicone TerpolYmer Compositions Photosensi-polymer Wt. D units t. % Do units White D units titer Wt. %
A 75.0 20.0 5.0 A, 0.2 B 77.0 11.3 11.7 BY, 2; A, 0.2 C 88.0 10.0 2.0 BY, 2; A, 0.25 D 48.0 50.0 2.0 BY, 2; A, 0.25 E 45.0 50.0 5.0 BY, 2; A, 0.25 F 45.0 50.0 5.0 BY, 3; A, 0.3 D = dim ethyl sulks units DO = methyl hydrogen sulks units DVi = methyl vinyl sulks units I A = 2-t-butylanthraquinone .

lZ33290 SUE 666 sup = benzophenone The relative W-curing performance of the various para-substituted perbenzoate derivatives was determined by assessing the the speed and quality of cure of a photo-sensitized silicone terpolymer combined with various perbenzoate ester photo catalysts. Low volubility of some of the perbenzoate derivatives necessitated coating and curing the compositions out of solvent.
Two coating baths were prepared, as follows:

Bath 15: 20 pow terpolymer C
80 pow hexane l pow t-butylperbenzoate Bath 16: 20 pow terpolymer C
80 pow hexane l pow Dun.
The coating mixtures were applied to SUCK substrates with a #3 wire-wound rod. Coated samples were exposed to ultraviolet lamps as 600 watts per square inch under inert conditions in a PUG QC 1202 AN processor as previously described until smear- and migra~ion-free adhesive surfaces were obtained. The unsubstituted perbenzoate-catalyzed composition (No. 15) cured after 0.6 seconds W exposure;
the Containing composition required 5.0 seconds W
exposure for the same degree of cure.
Another set of coating baths were prepared as follows:

.,~

Perbenzoate Baths Terpolymer Derivative 17 D Do, 5 Wt. %
18 D Do, 5 Wt.
19 D Do S Wt. %
D Control, 5 Wt.

Control = t-butylperbenzoate ~unsubstituted) Of these solvent less compositions, only the p-methoxy derivative, Do, formed an opaque mixture in terpolymer D, the other mixtures remained clear. The compositions were hand-coated on SIX substrates with a doctor blade, then cured under inert and ambient (air) environments as in Eagles 15 & 16, to give the following results:

Minimum US Exposure Required for Cure I MacWeek R in Terpolymer D

20 Derivative R Aim. Cure time, sec.
Control H AIR 1.5 Control H INERT 0.3 Do Of AIR 1.5 Do Of INERT 0.3 Do Me AIR 0.6 Do Me INERT C.15 Do Owe AIR 0.6 Owe INERT 0.15 From these data is appears that the perbenzoate ester catalysts may be qualitatively ranked (in ascending order of activity): Dun (very low activity), Do roughly eke to unsubstituted t-butylperbenzoate, and Do roughly equal to Do.
This rank roughly corresponds to thermally-induced pyre bond dissociation energies observed in the literature, 33'Z5~0 _28 _ It is believed that higher alkoxy derivatives, e.g., p-butoxy, p-ethoxy, or p-dodecyloxy, etc. might overcome the sublet problems of the p-methoxy derivative, Do.

It was a further discovery during the course of these trials that the photosensitized sit cone terpolymers described above were capable of photo curing tug adhesive coatings without the assistance of a perbenzoate ester photo initiator.
Solvent-free coating baths were prepared as follows:

Bath Composition 1521 Terpolymer F alone (contains photosensitizes: 3 Wt. % BY
and 0.3 Wt. % A) 22 10 pow terpolymer F + 0.5 pow diethoxyacetophenone (DEEP) 2023 10 pow terpolymer F + 0.5 pow Trigonal~ 14 (mixture of isobutyl Bunsen esters;
Norway Chemical Co.) 24 10 pow terpolymer F + 0.5 pow t-butylperbenzoate.
2525 10 pow terpolymer F + 0.5 pow DEEP + 0.5 t-butylper-bonniest.
Baths 21-24 were clear fluids, while bath 25 was hazy and partially opaque due to the limited volubility of DEEP
and t-butylperbenzoate mixtures in non-polar silicone fluids.

The baths were coated on SUCK substrates and cured as in Examples 17-20, and the minimum W exposure time until smear- and migration-free coatings were achieved was recorded lo ~329 SUE 666 Minimum W
sathCure Atmosphere Exposure or Cure sec.
-21 AIR 1. 5 21 INERT O . 6 22 AIR O . 3 5 2 2 INERT O . 3 23 AIR 1.5 24 AIR 1. 3 24 INERT Owe AIR 0.3 1025 INERT O . 3 These date suggest that H-abstraction prom the Sigh bond by the photosensitizes is involved in the curing mechanism. Benzophenone and t-butylanthraquinone are known to produce free radicals following excitation by ultraviolet radiation in the presence of a suitable proton donor.

Combinations of photosensitizes with photo-initiators capable of generating radical pairs via u..imoiecular homolysis after photo excitation are reported to be a means of minimizing oxygen quenching of radical-induced cross linking by Grubber, US. 4,071,652 which issued January 31,,1978, and this effect is evident in comparing the performance of Baths 21 and 22, where DEEP is the photo initiator generating radical pairs.
Also noted is a synergistic effect in combining photo-sensitizers with perbenzoate photo initiators, when comparing the performance of Baths 21, 24 and 25. Although volubility problems evidently interfered with the perform-ante of Bath E, it is believed that enhanced cure will result from combinations including benzophenone, t-butyl-anthraquinone, DEEP and t-butylperbenzoate in a mutually computable medium.

lZ33~0 SUE 666 _ 30-The following compositions were prepared to show the effect of certain polyaromatic photosensitizes:

880 parts by weight dimethyltetramer, 50 pa is by weight methylvinyltetramer, 20 parts by weight of sym-tetramethyldivinyldisiloxane, and 63 parts by weight of trimethyl-chainstopped polymethylhydrogensiloxane fluid (30 cups) were blended together with 5 parts by weight of an acid clay catalyst (Filtrol 20), then agitated under a nitrogen atmosphere at 60C for 15 hours. Removing the catalyst by filtration afforded a mixed dimethylvinyl-and trimethyl-chainstopped linear polydimethyl-methylvinyl-methylhydrogensiloxane terpolymer fluid 570 cups), Wheaties designated Sample G.
300 parts by weight of Sample G were stripped of light ends under a vacuum at 165C for 2 hours. 241 parts by weight of the product were treated with 1.2 parts by weight benzophenone and the mixture stirred at 100C for 30 minutes until a clear solution was obtained. The ben~ophenone remained in solution when the polymer was cooled to room temperature, to give a 340 cups fluid product designated Sample H.

Another terpolymer was prepared exactly as Sample G from the following materials: 1260 parts by weight dimethyltetramer, 92 parts by weight methyl vinyl-tetramer, 15 parts by weight sym-te~ramethyldivinyldi-selection, and 150 parts by weight of the methyl hydrogen fluid. Filtering and stripping the equilibrate afforded 1240 parts by weight of a 1225 cups fluid, designated Sample J.
_.

i23325~0 SUE 666 _ 31 -A composition designated Sample K was prepared con-sitting of 0.5 weight percent solution of benzophenone in the Sample J terpolymer.

A composition designated Sample L was prepared consistilig of a 1.0 weight percent solution of buoyancy-phenone in the Sample J terpolymer.

A composition designated Sample M was prepared con-sitting of a 2.0 weight percent solution of benzophenone in the Sample J terpolymer.

A composition designated Sample N was prepared consisting of a 4.0 weight percent solution of benzophenone in the Sample J terpolymer.

A composition designated Sample P was prepared consisting of a 0.2 weight percent solution of 2-t-butyl-anthraquinone in the Sample J terpolymer.
It was noted that the benzophenone was quite soluble in silicone fluids to at least 4 weight percent.
The limits of volubility of the chemically similar t-butylanthraquinone have not been established, however, simple experimentation will reveal to the persons skilled in this art the useful range of volubility for this and other photosensitizes suitable for the purposes disclosed herein.
Attempts to prepare 0.5 weight percent solutions of anthrax cent and thioxanthone in the Sample J terpolymer were us-successful due to their limited volubility in silicones.

Ultraviolet cure analyses were performed using Samples G-P in the following manner. Each sample was mixed with 5 weight percent p-butylperbenzoate, manually coated as thin films on 40-lb. super calendered raft (SUCK) paper with a doctor blade, then passed through a ~;33 SUE 666 _ 32 -PUG QC 1202 An ultraviolet processor (2 Hanovia medium-pressure mercury vapor US lamps each capable of operating at lo, 200 or 300 watts per square inch focused power).
The degree of cure was qualitatively assessed by noting the presence or absence of smear, migration, and rub-off in irradiated coatings. After curing the test coatings prepared from Samples G-P under various cure conditions, the following results were obtained:
To lamp Ensure to, Cure Eye ale pcwer,-~tts seconds Aim. elite ivy Cure 26 G 600 0.3 No No smear, no micra-lion, slight runoff 27 G 600 1.5 AIR NOT CUD
28 H 400 0.3 No No smear, no micra-lion, slight rough 29 H 600 0.15 No No smear, no micra-lion, slight rub-off H 600 1.5 AIR No smear, no micra-lion, no rub-off 31 J 400 0.3 No No smear, no micra-lion, slight rub-off 32 J 600 0.15 No No or, no micra-lion, moderate rub-off 33 J 600 0.6 AIR NOT CUED
34 K 200 0.6 No No sir, no muggier-lion, slight r off X 400 0.1 No No smear, no micra-lion, moderate rub-off 36 K 600 0.08 No No smear, no micra-lion, easy r off 37 L 200 0.3 No No or, no micra-ton, moderate -off 38 L 400 0.1 No No smear, no micra-lion, moderate nephew - 39 L 600 0.08 No No sneer, no micra-lion, easy rub-off - - 1233291~ SUE 666 _ 33 -queue posture twine, Cure Example ale power, watts seconds Aim. alitative Cure M100 0.3 No No smear, no micra-lion, moderate rub-off 41 M400 0.1 No I seer, my micra-lion, moderate r off 42 M600 0.6 AIR No slrear, no micra-lion, r off 43 N200 0.3 No No smear, no micra-lion, moderate rub-off 44 N600 0.08 No No Of, no micra-lion, easy rebuff N600 0.3 No No en, no micra-lion, no r off 46 N600 0.3 AIR No seer, no micra-lion, no rub-off 47 P200 0.3 No No sir, no micra-lion, moderate r~b-off 48 P600 0.3 No No err, no micra-lion, no rub-off 49 P600 0.3 AIR No smear, no micra-lion, no rub-off P600 0.8 No No smear, no micra-lion, easy nephew It it apparent from these results that the presence of benæophenone or t-butylanthraquinone more than doubles the rate of cure for the photoactive compositions under inert conditions, and, surprisingly, permits good cure (at fairly fast rates) even without inverting the cure environment. The latter observation can be particularly important where the expense of providing an inert atoms-phone for radiation curing is a critical concern of the particular user. The compositions anchor well to SIX
substrates when W lamps are operated at high intensity for at least 0.3 seconds exposure. Shorter exposure provides migration-free adhesive coatings which are ' .

123329~

easily rubbed off, although they are otherwise fully cured.

Several samples were next assessed for release performance against common adhesives The following coating baths were prepared (measurements are in parts by weight):

Bath Q: 20 pow Sample J
1 pow t-butylperbenzoate 79 pow hexane.

Bath R: 20 pow Sample L
1 pow t-butylperbenzoate 79 pow hexane Bath S: 20 pow Sample M
1 pow t-butylperbenzoate 79 pow hexane pa path T: 20 pow Sample N
1 pow t-butylperbenzoate 79 pow hexane Bath U: 20 pow Sample P
1 pow t-butylperbenzoate 79 pow hexane Each of the baths Q-U were coated onto 9"x12"
sheets of SUCK paper with a I wire-wound rod, then exposed to ultraviolet light in the PUG ultraviolet processor as previously described. The cured compost-lions were then coated with a 10 mull layer of Jowl 263 acrylic adhesive (Monsanto) and cured for 15 minutes at 65C. An uncoated SUCK sheet was then affixed to ..

~Z~33Z9Q SUE 666 _ 35 --the adhesive layer. These laminates were cut into strips, and the release in grams recorded as in previous examples, with the following results:
Iota lamp Exposure, Cure ~itative Release, S Example Bath or, watts sec. A Cure go 51 Q 100 0.3 No No migration, 55-80 poor anchorage 52 R 100 0.3 No No migration, 50 85 poor anchorage 53 S 600 0.3 AIR No migration, 210-250 good anchorage 54 S 100 0.3 No No migration, 60-90 good anchorage U 600 0.3 AIR No migration, 110-130 good anchorage 56 U 600 0.3 No No migration, 25-40 good anchorage Examples 51, 52 and 54 indicate that benzophenone con-cent ration has little effect on release. Although some of the cured compositions did not appear to anchor to the sub-striate particularly well, the separated famine showdown evidence that the silicone layer adhered preferentially to the aggressive Gelva adhesive.

Examples 53, 55 and 56 indicate that the nature of 2$ the curing environment does have an effect that is not evident from the previous Examples 26-50: Air cure apparently leads to a higher release than cure of the same composition in an inert environment. This difference in release suggests that varying the amount of nitrogen in the curing chamber may provide a means of controlling the release of a silicone composition. It is also apparent that a low level on anthraquinone (0.2%) is more effective than benzophenone for promoting t-bu~ylperbenzoate-catalyzed US cure of the vinyl-runctional terpolymers of the present invention.

SUE -_ 36 -because t-butylper~enzoate is thermally very stable and can be stored indefinitely at room temperature, the compositions of the present invention can be packaged and sold as l-part systems, eliminating preparatory steps and making the compositions easier to use.

EXAMPLES 57 & 58 Higher alkoxy-substituted perbenzoate photo-catalysts were synthesized to try to overcome thesolubility problems encountered with the p-methoxy and p-tolyl derivatives of t-butylperbenzoate:

T-butylper-p-butoxybenzoate was synthesized by first preparing p-butoxybenzoylchloride according to the procedure described by Rohrmann and Wischniewski, Arch.
Harm., 292, 787 (1959). 29.1 parts by weight of 4-n-butoxybenzoate 4-n-butoxybenzoic acid and 71.4 parts by weight thionylchloride were mixed and agitated at 86C for 1 hour. The resulting clear solution was stripped of excess thionylchloride under a vacuum at 60C, and the product isolated by vacuum distillation.
30.6 parts by weight of clear viscous fluid by 143-147C/
7mm) were obtained (95 yield). This product was added slowly to 18 parts by weight of 70~ aqueous t-butylhydro-peroxide simultaneously with 35 parts by weight of 30%
aqueous potassium hydroxide (also slowly added). Reaction temperature was maintained at 0-5C during this addition.
the p-butoxy derivative was isolated by dissolution in acetonitrile, extracting twice with hexane, and removal of the acetonitrile under a vacuum, resulting in 26.2 parts by weight of a clear, pale yellow fluid product.
the infrared spectrum of the product was consistent with the structure of the p-butoxy derivative of t-butylper-benzoats.

1~3Z9(3 SUE 666 _ 37 _ A p-dodecyloxy derivative was prepared in the same manner as the p-butoxy derivative, using p-dodecyl-oxybenzoyl chloride. The final product was a viscous pale yellow liquid at room temperature, and the infrared spectrum was consistent with the structure of the p-dode-sulks derivative.

Two silicone release coating compositions were prepared using the above derivatives by mixing 5 parts by weight or each derivative, respectively, with 100 parts by weight of a 670 cups linear polydimethyl-methyl-vinyl-methylhydrogen selection fluid with 7 weight percent methylvinylsiloxy units, 5.2 weight percent methyl hydrogen sulks units and the remainder consisting of dim ethyl-sulks units. In each case, an opaque white mixture resulted. Although both compositions could be cured to smear- and migration-free release coatings on SUCK substrates in 0.3 seconds W exposure (at 600 watts/square inch), the apparent poor compatibility of these two derivatives with pure silicone terpolymer solutions suggests that they are not the catalysts of choice for solvent-free release applications.

Further trials were conducted with terpolymers prepared according to the present invention in order to assess cure characteristics and storage stability. Three new terpolymers having different Si-H/Si-vinyl ratios were prepared as in previous examples and compared with terpolymer F (see Examples 15-25):

lZ33~90 _38 -Mole Ratio Example Terpolymer Photosensitizes Si-H/Si-vinyl 59 F 3 White BY, 0.3 Wt.% A 14.0 X 2 White BY 2.80 61 Y 2 Wt.% BY 1.50 562 Z 3 White BY Luke BY = benzophenone A = t-butylanthraquinone The release performance of the above terpolymers was assessed as in previous examples, by preparing coating baths consisting of 20 parts by weight of a terpolymer~
0.6 pow t-butylperbenzoate and 8 a pow hexane, applying each coating composition to SIX paper, curing under US
light at 600 watts/square inch for 0.3 seconds inert atmosphere), and finally preparing laminates using Molly coatings of aggressive SIR adhesive (Coated Products, Inc.
#495G~ and recording the force required to separate the famine (400 ft./minute; 180 angle). Release was tested initially and periodically after aging at 150F. The following data resulted:
Release Release Release Release (grams) (grams) (grams) (grams) Exhume Terpolymer Initial 1 day 1 week 2 weeks 2559 F 30-50 ~500 >500 >500 It is apparent that a large excess of unrequited Sigh functionality relative to Si-vinyl-functionality will affect release, probably due to interaction OX the Sue function with the adhesives. The data suggest that where stable release is desired, the Si-H~Si-vinyl ratio should 35 be held at lower levels, preferably below about 2/1 for the _ 39-terpolymers described herein.

A separate trial to assess storage stability of a l-part W-curable composition was run by preparing a coating composition using 100 pow of Terpolymer X (con-twining benzophenone, I blended with t-butylperbenzoa'e (5 pow The composition was split into two samples, one sample being maintained at room temperature in the dark and the other at 66C also in the dark. The viscosity of these blends was monitored over time Jo obtain an indication of storage stability. The following results were observed:

Storage Tempt Initial 1 Week 2 Weeks 4 Weeks 8 Weeks 25C 560 cups 550 cups 540 cups 550 cups 550 cups 660C 550 cups 4370 cups (golfed) -- --These data suggest that a storage temperature below about 30C it recommendable to prevent cure during storage.
EXAMPLES 64 & AYE

A trial comparing the cure performance of reactive terpolymers prepared according to the present invention to conventional Uncurable vinyl-functional systems was run as follows:

A linear polydimethyl-methylvinyl-methylhydrogen selection terpolymer was prepared having a molar Sue/
Si-vinyl ratio of 2.8 and including 83 weight percent dimethylsiloxy units was prepared in which 2.5 weight percent benzophenone was dissolved. A conventional W-curable, vinyl-functional silicone blend was prepared consisting of 100 parts by weight of a 200 cups dim ethyl-vinyl-chainstopped linear polydimethyl-methylvinyl selection fluid having 5.2 weight percent methyl vinyl sulks units, combined with 3 parts by weight of a 30 cups trimethyl-chainstopped linear polymethylhydrogen selection fluid, also containing 2.5 parts by weight benzophenone.

The cure performance of the two coating blends was qualitatively tested as described in previous examples, with the PUG ultraviolet processor operating with 400 watts/square inch total focused power. The minimum US exposure time (seconds to obtain a smear-and-migration-free release coating on SUCK substrates was recorded:
Exposure Time CompositionCurinq Aim. for Cure, sec.
64 No 0.3 64 AIR 1.5 AYE No 3.0 (control) AYE AIR No cure after (control) 15 sec.
64+3% t-butyl-N~ 0.15 perbenzoate These data indicate that the instant terpolymer compositions ax superior in cure efficiency to known vinyl-functional systems; additionally, there appears to be a synergistic effect from the combination of buoyancy-phenone and perbenzoate catalysts, allowing line speeds 20 times faster than those required to fully cure conventional coatings.

Modifications and variations in the present invention are obviously possible in light of the fore-going disclosure. For example, many polyaromatic ; 35 compounds soluble in a given silicone composition and . ..
.
... . .

1;~33~90 effective as photosensitizes for the purposes described herein will suggest themselves to persons of ordinary skill in this art and may be utilized advantageously with coating compositions prepared in accordance with the present disclosure. It is understood, however, that any such incidental change made in the particular embodiments of the invention are within the full intended scope of the appended claims.

Claims (12)

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

1. An ultraviolet radiation-curable silicone release composition comprising:
(A) an odor-free mercaptoalkoxyalkyl-functional diorganopolysiloxane consisting essentially of units of the formula RR'SiO, wherein R is hydrogen or C(1-8) alkyl and R' is hydrogen, C(1-8) alkyl or a monovalent.
mercaptoalkoxyalkyl-functional organic radical of from 2 to 20 carbon atoms, said diorganopolysiloxane having up to about 50% by weight mercaptoalkoxyalkyl-functional groups and a viscosity of from about 50 to 10,000 centipoise at 25°C;
(B) a polysiloxane consisting of from about 0.5 to 100 mole percent of vinyl-functional siloxane units of the formula (CH2=CH)RnSiO3-n/2, where R is hydrogen or C(1-8) alkyl and n has a value of 0 to 2, inclusive, any non-vinyl-containing siloxane units having the formula R3mSiO4 m/2, where R3 is hydrogen or C(1-8) alkyl and m has a value of from 0 to 3, inclusive; and (C) a catalytic amount of a photoinitiator.

2. A silicone release composition as defined in claim 1, wherein said photoinitiator is a perbenzoate ester having the formula, where R4 is a monovalent alkyl or aryl group and Z is hydrogen, alkoxy, alkyl, halogen, nitro, amino, primary amino, secondary amino, or amido.

3. A silicone release coating composition as defined in claim 2,wherein said perbenzoate ester is selected from the group consisting of t-butylperbenzoate, t-butylper-p-nitrobenzoate, t-butylper-p-methoxy benzoate, t-butylper-p-methylbenzoate, and t-butylper-p-chlorobenzoate.

4. A silicone release coating composition as defined in claim 2, which includes the additional com-ponent (D) a small amount of a polyaromatic photosensitizer or a combination of such photosensitizers effective to enhance the cure of said composition.

5. A silicone release coating composition as defined in claim 4, wherein said photosensitizer component (D) is selected from the group consisting of benzophenone, t-butylanthraquinone, and combinations thereof.

6. A solid substrate coated on at least one surface with the composition of claim 1.

7. The coated substrate of claim 6, wherein said substrate is selected from the group consisting of paper, metal foil, glass, polyethylene coated kraft paper, super-calendered kraft paper, polyethylene film, polypropylene film and polyester film.

8. The coated substrate of claim 7, wherein said composition is cured on said substrate.

9. The coated substrate of claim 8, wherein said cured coating forms an adhesive surface on said substrate.

10. An odor-free mercaptoalkoxyalkyl-functional polysiloxane capable of curing to an adhesive polymeric composition on brief exposure to ultraviolet radiation in the presence of an organic compound contain-ing ethylenic unsaturation and a catalytic amount of a photoinitiator consisting essentially of units of the formula RR'SiO, wherein R is hydrogen or C(1-8) alkyl and R' is hydrogen, C(1-8) alkyl or a monovalent mercaptoalkoxyalkyl-functional organic radical of from 2 to 20 carbon atoms, said diorganopolysiloxane having up to about 50% mercaptoalkoxyalkyl-functional groups and a viscosity of from about 50 to 10,000 centipoise at 25°C.

11. An odor-free mercaptoalkoxyalkyl-functional polysiloxane capable of curing to an adhesive polymeric composition on brief exposure to ultraviolet radiation in the presence of an organic compound containing ethylenic unsaturation and a catalytic amount of a photoinitiator, consisting essentially of the composition obtained by (1) reacting a dialkylhydrogen-chainstopped polydialkyl-alkylhydrogensiloxane copolymer with an .omega.-halo-alkene in the presence of a precious metal hydro-silation catalyst, and (2) reacting the product of (1) with a hydroxy-functional thiol of the formula HO-R"-SH, wherein R" is a divalent alkylene or alkyl ketone radical of from 2 to 20 carbon atoms in the presence of an amine.

12. An odor-free mercaptoalkoxyalkyl-functional diorganopolysiloxane as defined in claim 11, wherein said .omega.-halo-alkene is methallyl chloride and said hydroxy-functional thiol is .beta.-mercaptoethanol or .gamma.-mercaptopropionic acid.