CA1123535A - Photocurable composition for coating - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
A photocurable coating composition suitable for coatings comprising (i) a polythiol, (ii) a polyene, and (iii) a silicone-modified polyester copolymer. These coating compositions are suitable for coating poly-carbonate articles.

Description

1~2353S

~SP~203~ 1 This invention is directed to a photocurable coating composi-, tion suitable for coatings comprising (i) a polythiol, (ii) a ;polyene, and (iii) a silicone modified polyester copolymer.
These coating compositions are suitable for coating polycarbonate articles and have good a~hesion thereto.
Background of the Invention Commercial liquid coating compositions are available. Many ~of these coating compositions are not suitable for coating poly-~` ,carbonate articles since they are not compatible with the polycar-lQ ~bonate. Also, the uncured coating may adversely affect the poly~
carbonate article by stress cracking and crazing it, by causing crack propogation into the polycarbonate as a result of brittle~
''ness of the coating itself and/or by reducing the properties of ;Ithe polymer generally such as, for examPle, impact resistance, 'elongation, tensile strength and so on. Further, several coatings ,while compatible with the polycarbonate have little or no chemical ~ibarrier properties and/or poor adhesion.
Therefore, a successful coating or polycarbonate articles ,must be compatible with the polycarbonate and provide barrier or iother desirable sur~ace properties while maintaining mechanical or other properties of the polymer substrate and themselves 'Iprovide chemically resistant surfaces Also, the cured coating, ~in this particular`application, should particularly provide the ,¦coated polycarbonate article with anti-skid properties in addition¦
~'¦to the chemical barrier properties necessary to prevent crazing of the substrate polycarbonate in chemically aggressive environments and have improved adhesion'to the'polycarbonate substrate.
U.S. 4,082,891 discloses photocurable compositions sultable for coatings comprising a polythiol and two different~polyenes i:
!l ~.23~i35 ~SP-2036 and polycarbonate articles coated therewith. The instant inventionl provides coating compositions having good anti-skid properties and ¦
good adhesion to a polycarbonate substrate.
DE~SCRIPTION OF THE INVENTION
The instant invention is concerned with a hotocurable composition suitable for coating polycarbonate articles comprising:
(i) a polythiol, (ii) a polyene, and (iii) a silicone modified polyester copolymer. These coating compositions are especially suitable for coating polycarbonates~ Upon curing, the coatings have improved adhesion to the polycarbonate substrate and provide ~a polycarbonate article with anti-skid properties, chemical resistance, scratch resistance and chemical barrier properties resulting in stress cra~ing resistance. Also, the coating compo-~ sition of the instant invention allows the polycarbonate substrate;
; 15 ~to retain its inherent desirable physical properties (particularIy,l`` ! ~, ~
impact resistance) by which it is distinguished.
The photocurable coating composition comprises:
(i) a polythiol represented by the general ormula:
,1 0 C-R2SH)a ~0 , wherein Rl and R2 are organic moieties containing no reactive carbon-to-carbon unsaturation and a is 2 to 4; ¦
' (ii) a polyene represented by the general ormula:

~(~oR3C1~=c~l2)3 ,¦ wherein R3 is an organic molety containing no reactive f ~:25 I carbon-to-carbon unsaturation; and 'I (iii) a silicone modi~ied polyester which is the reaction product of a hydroxyl terminated unsaturated polyester ~ , ;

.

- 2 -.

. . . , . .

~_23~3~j of a polycarboxylic acid reactant wherein at least about 65 mole 6 of the poly carboxylic acid reactant ¦ ~ -is an c~ ethylenically unsaturated polycarboxylic acid reactant and an alcohol which contains two 5 ~' terminal hydroxyl groups and allyl ether and/or ~; methallyl ether groups, and an organopolysiloxane containing at least 0~25% by weight of groups reactive , with the hydroxyl functional groups of the polyester.
The polythiols of (i) are prepared by reacting an estér of thiol containing acids of the formula HS-R2^-COOH~wherein R2 is an organic moiety containing no reactive carbon-to-carbon unsatur~
ation, with polyhydroxy compounds of structure R1(OH)a wherein l is an organic moiety containing no reactive carbon-to~carbon ,unsaturation and a is 2 to 4. These components react under -'` :1 ` conditions ]cnown in the art and as are set forth in U.S. Patent

3,661,744, which issued M~y 9, 1972. Preferably, ` the polythiol of (i) has the following general formula:
ol -~ ` '' R~ CH2OC-R2SH) wherein Rl and R2 are straight chain aliphatic moieties contain-1 ing no reactiVe carbon-to-carbon unsaturation and~a is 2 to 4. ¦
, Preferred straight chain aliphatic moieties are those containing from 1 to about 20 carbon atoms.
i The polyenès of ~ii) are prepared by methods known in the art and as set forth in U.S. Patent 3,661i7~4,~which .1 1 25 I issued May 9, 1972. ~Preferred~polyenes of the type (ii) hàve.
~; I the following general formula~

i ~ I : .
~ ~ 3 -_ ~L_ I

~!.Z3~35 ~ iSP--2036 wherein R3 is an organic moiety containiny no reactive carbon-to- ¦
carbon unsaturation. Preferably, R3 is a straight chain aliphatic moiety containing no reactive carbon-to-carbon unsaturation and containing from 1 to about 20 carbon atoms. ', The silicone modified polyesters of (iii) are the reaction ~products of: ' ~
A. a hydroxyl terminated unsaturated polyester of: ..
1. a polycarboxylic acid reactant wherein at least , .
;, about 65 mole cj of the polycarbo~ylic acid 10 : reactant is an ~, ~ -ethylenically unsaturated polycarboxylic acid reactant and up to about 35 mole % of the polycarboxylic acid reactant is a polycarboxylic acid reactant free from :.
~j non-benzenoic unsaturation; and 2. an alcohol reactant containing two terminal '. hydroxyl groups and allyl ether groups and/or ~ methallyl ether groups in an amount sufficient :` j to provide at least 0.1 mole of allyl ether ~ j :: groups and/or methallyl ether groups per mole 20 ~ of said ethylenically unsaturated polycarboxylic ; I acid reactant; and 3. wherein said polyester has an acid number from ', :
. about 10 to about 35; and ; i ~ B. an organopolysiloxane having the average unit formula~
'~ (H)q(R'~rRS~i~g~ ; ~' ;' i~ wherein R is lower alkyl radical having 1 to 3 carbon , .
atoms; and/or cycloalkyl radical havlng 5 to 7 carbon :
atoms in the ring; and/or lower al~enyl radical having .
~, :

.` .' 4 -: :

~L~..2~535 -; 2 to 8 carbon atoms; and/or mononuclear aryl radical;
and/or mononuclear aryl lower alkyl radical having 1 to 6 carbon atoms in the alkyl group; and/or halogenated derivatives of the above radicals; R' is al]cyl containing 5 ' from 1 to 8 carbon atoms per radical; and/or aryl; and/
or acyl of 1 to 8 carbon atoms; s has a value of 1 to 2;`
q has a value of 0 to 1.0, r has a value of 0 to 1.0, ~ and the sum of q + r has a value of 0.01 to 1; and con-:. . !
taining at least 0.25% by weight of silicon-bonded OH and/or OR' groups. , - These siLicone-polyester copolymers and the process for their production are ]cnown in the art and are set forth in U.S. Patent 3,919,43~, which issued November 11, 1975.
,~ The relatlve amounts of unsaturated polyester and organopoly-~
siloxane are generally from about 90 to about 40% by weight of unsaturated polyester and correspondingly from about 10 to about ,~ 60%~by welght of organopolysiloxane based upon the combined weight !
of the polyester and organopolysiIoxane. The preferred relative quantities o~ polyester to organopolysiloxane employed in the 'copolymers of the present invention are from about 70~ to about 50% by weight of unsaturated polyester and correspondingly from about 30 to abou~ 50~ by weight of organopolysiloxane based upon ¦
the combined weight of the polyester and organopolysiloxane.
The copolymers of the present invention are prepared by ¦
copolymerizing a preormed unsaturated polyester o the type ¦
described above with the required polysiloxane to efect a trans-esterification between the reactants. The ester interchange ~reaction is carried out in the presence of a reaction diluent which ,,is inert to the reaction (does not adversely affect either the " ~ , .. ..... .. ....

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reactants or the product). Suitable reaction diluents include aromatic hydrocarbons such as xylene, benæene, and toluene; and esters such as ethyl acetate and Cellosolve acetate.
The preferred diluents are the aromatic hydrocarbons. The ~diluent is usually employed in amounts oE at least about 1 part by weight per 4 parts of reactants and preferably at least about 1 part by welght per 3 parts of reactants. The maximum ~uantity of diluent is limited only by economical and practical considerations such as equipment capacities.
10 ; In addition, it is preferred to carry out the transesterifi- -; cation in the presence of an esterification catalyst. Examples of such eatalysts include the metallic esters of the general formula ;M(oR4)4 wherein M is a titanium atom or a zirconium atom and each R4 is a monovalent hydrocarbon radieal or an acyl radical. The ~; 15 substituents represented by R4 can be alkyl, aryl, alkenyl, aralkyl, alkaryl, and acyl. The ~4 substituents ean be the same ~or different in a particular compound. Illustrative of suitable specific catalysts are M(OC6IIs)4, M(OC3H7)4, M(OC4Hg)4, M(OC2Hs)4,, M~oc2H~)3(oc6Hs)~ M(OCE~3)3(0C2~I3)r M(OCH2C6H5)4~ M(OC5~I4CH3)4/
20 `and M(OCH3)(0C2Hs)(OC6H5)(0C4Hg).
The preferred catalysts are the alkyl titanates wherein the alkyl group contains from 1 to 20 carbon atoms; and the titanium acylates. Some commercially available titanium acylates are represented by the formula (R50)3TioR4 wherein R5 is an alkyl ,, radical or is hydrogen and R4 is an acyl radical. The most '~ preferred transesterification catalyst for the present invention '~ is tetraisopropyltitanate. In addition, various known polymeric ` titanates and zirconates obtained by the partial hydrolysis and eon~ensation of the above~deseribed monomeric titanates or zirconates can be employed.

, ~.Z3535 Generally, the polythiol of (i) and the polyene of ~ are ;used in stoichiometric amounts. The amounts, by weight, of the silicone modified polyester copolymer, the polythiol and the .polyene present in the coating composition generally range from ,about l part by weight of the silicone modified polyester copolymerl 'to about 3 parts by weight of the combined weight of the polythioli : and the polyene to from about 3 parts by weight of the silicone ; modified polyester copolymer to about l part by weight of the ,! combined weight of the polythiol and the polyene; preferably from ~ lO "abo,~t l part by weight of the silicone modified polyester copoly-: , mer to about 2 parts by weight of the combined weight of the. poly-thiol and the polyene to rom about 2 parts by weight of the silicone modified polyester copolymer to about l part by weight of ,!the combined weights of the polythiol and polyene; and more ¦ ;
~; I
; 15 .~preferably from about l part by wei~ht of the silicone modified ' polyester copol~ner to about l part by weight of the combined .
weights of the polythiol and polyene.
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! The photocurable composition may be formulated for use as 100 percent soIidsr or di.sposed in organic solvents,.or as disper-~,slons or emulsions in aqueous media, prior to curin~
The curable coating compositions, if in liquid form, prior to curing may readily be pumped, poured, siphoned, brushed, sprayed, doctored, or otherwise handled as desired. Following application, j, .
`~ curing in place to the polycarbonate article may be effected i ~ .
.~ 25 ', elther very rapidly or extremely slowly as desired by manipulation' of.the compounding ingredients and the method of curing. :
. The curing reaction may be initiated by most actlnic~light i sources that disassociate or abstract a hydrogen atom from an SH ¦
group, or accomplish the equivalent thereofO Generally, the rate¦ 1 :`; i 7 !, .
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~.2;3535 of the curing reaction may be increased by increasing the tempera-ture of the composition at the time of initiation of cure. In many applications, however, the curing is accomplished conveniently ~and economically by operatiny at ordinary room temperature ,conditions.

.. . .
By proper choice of type and concentration of photocuring ~rate accelerator for initiation, the curing period required for conversion of the polythiol-po~yene-silicon modified polyester copolymer composition from the liquid to the solid state may be Ivaried greatly as desired. In combination with suitable accelera-tors or retarders, the curing period may vary from about a second ;jor less to about 30 days or more. In general, short curing periods are achieved in applications where thin films of curable compositions are required, such as in the field of coatings ¦
~whereas the long curing periods are achieved and desired where more massive layers of com~osition are required, such as in the field of elastomeric sealants.
`
j ~ class of actinic llght useful herein ls ultraviolet llght , and other forms of actlnic radlation which are normally found in ~i radiation emitted from the sun or from artificial sources such as ~j Type RS Sunlamps, carbon arc lamps, xenon arc lamps, mercury .!
, vapor lamps, tungsten halide lamps and the like. Ultraviolet radiation may be used most efficiently if the photocurable coatin~
I~ composition contains a suitable photocuring rate accelerator.

~ Curlng periods may be adjusted to be very short and hence commer-cially economical by proper choice of ultraviolet source, photocuring rate accelerator and concentration thereof, tempera- I
1I ture and molecular weight, and reactive group functionality of j!
Il the polyene and polythiol.
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235i~5 Conventional curing inhibitors or retarders which may be used in order to stabilize the components or curable compositions j so as to prevent premature onset of curing may include hydroquinone;
p-tert-~butyl catechol; 2,6-di tert-butyl-p~methylphenoli phenothia-zine; N-phenyl-2-nephthylamine; inert gas atmosphere such as helium, argon, nitrogen and carbon dioxide; vacuum; and the like.
It is understood to be within the scope of this invention ~that the photocuring rate accelerator may be present as a separate ,and distinct component such as azobenzene, as a mixture of two or more separate components, such as benzophenone; benzanthrone;
anlhrone and dibenzosuberoheî carbon tetrachloride and phenan-threne; and the like, or in chemically combined form within the molecular structure o either the polyene or the polythiol.
Specifically useful herein are chemical photocuring rate ,accelerators such as benzophenone, acetophenone, acenaphthene-~uinone, o-methoxy benzophenone, thioxanthen-9-one, xanthen-9-one, 7-H-~enz(de)anthracen-7-one, dibenzosuberone, l~naphthal-dehyde, 4,~'-bis (dimethylamino) benzophenone, fluorene-9-one, , . i ~ '-acetonahpthane, anthraquinone, l-indanone, 2-t`ert-butyl 20 ~ anthraquinone, valerophenone, hexanophenone, 3-phenyl-~utyrophen- ¦
one, p-morpholinopropiophenone, 4-morpholino-benzophenone, p-diacetyl-benzene, 4-amino-benzophenone, 4'-methoxyacetophenone, I'benzaldehyde, ~-tetralone, 9-acetylphenanthrene, 2-acetylphenan-¦- ~,throne, 10-thioxanthenone, 3-acetylphenanthrene, 3-acetylindole, l 1,3,5-triacetylbenzene and the like, including blends thereof, to greatly reduce the exposure times.
The curing rate accelerators are usually added in an amount ranging from about 0.005 to about 50 percent by weight of the ,lphotocurable composition, with a preferred range being from about i;
' _ 9 _ ~ I
i, j.
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`' -~L~..2353~i ~ SP-2036 0.05 to about 25 percent by weight. Preferred photocuring rate accelerators are ~he aldehyde and ketone carbonyl compounds having at least one aromatic nucleus attached directly to the -C- group.
The compositions to be cured, i.e., (converted to solid Iresins or elastomers) in accord with the present invention may, if desired, include such adclitives as antioxidants, accelerators, I
dyes, inhibitors, activators, fillers. pigments, antistatic agents, ;flame--retardant agents, thickeners, thixotropic agents, surace- ' ~actlve agents~ viscosity modifiers, extending oils, plasticizers, ltackifiers and the like within the scope of this invention. Such additives are usually preblended with the polyene or polythiol prior to or during the compounding step. Operable fillers 'include natural and synthetic resins, carbon black, glass fibers, I'wood 10ur, clay, silica, alumina, carbonates, oxides, hydroxides, Isilicates, glass`flakes, glass beads, borates, phosphates, diatomaceous earth, talc, kaolin, barium sulate, calcium sulfate,, ~calcium carbonate, antimony oxide and the like. The aforesaid additives may be present in quantities up to 500 parts or more per lOO parts polymer by weight and preferably about 0. 0005 to ~,about 300 parts on the same basis.
A useful method of compounding is to prepare in an ambient atmosphere by conventional mixing techniques but in the absence of actinic radiation a conposition consisting of polyene, ;,antioxidant (to inhibit spontaneous oxygen-initiated curing), ,, ~. .' `'.~
,polythiol, silicone modiied polyester copolymer, UV sensitizer " or photoinitiator, and other inert additives. This composition 'may be stored in the dark for extended periods of time, but on ¦ ~;

lexposure to actinic radiation (e.g., ultraviolet light, sunlight, ' etc.) will cure controllably and in a very short time period to 'solid polythioether products.

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.
.

~.Z3~35 The coating composition of the instant invention may be applied to the polycarbonate surface by any conventional coating technique such as roll, curtain or spray.
In the practice of this invention, any of the aromatic polycarbonates can be employed herein These are homopolymers and copolymers and mixtures thereof that are prepared by reacting a dihydric phenol with a carbonate precursor. Typical of some of the dihydric phenols that may be employed in the practice of . . .
'~this invention are bisphenol-A, (2,2-bis(4-hydroxyphenyl)propane), ,bis (4-hydroxyphenyl) methane, 2,2-bis(4-hya.roxy-3-methylphenyl) propane, 4,4-bis~4-hydroxyphenyl) heptane, 2,2-(3,5,3',5'-tetra-chloro-4,4'=dihydroxydiphenyl) propane, 2,2-(3,5,3',5'-tetrabromo-~4,~' dihydroxydiphenyl) propane, (3,3'-dichloro-4,4'-dihydroxy-phenyl) methane. Other dihydric phenols of the bisphenol type are also available and are disclosed in U.S. Patents 2,S99,835, 3,028,365 and 3,334,154 It is, of course, possible to employ two or more different ~dihydric phenols or a copolymer of a dihydric phenol with a ~glycol or with hydroxy or acid terminated polyester, or with a ,dibasic acid in the event a carbonate copolymer or interpolymer `rather than a homopolymer is desired for use in the preparation 'of the aromatic carbonate polymers ~f this invention. Also ~employed in the practice of this invention may be blends of any `of the above materials to provide the aromatic carbonate polymer.
`¦ The carbonate precursor may be either a carbonyl halide, a carbonate ester or a haloformate. The carbonyl halides which can be employed herein are carhonyl bromide, carbonyl chloride and mixtures thereof. Typical or the carbonate esters which may be ~employed herein are diphenyl car~onate, di-(halophenyl)carbonates , !
, ., , ., , .,,, , . . _ _ _ _ ~ ............................................ . . ~ .

~ 3~35 ~ ::

such as di-(chlorophenyl) carbonate, di-(bromophenyl) carbonate, di-(trichlorophenyl) carbonate, di-(tribromophenyl) carbonate, etc., di-(alkylphenyl) carbonate such as di(tolyl) carbonate~
jetc., di-(naphthyl) carbonate. di-(chloronaphthyl) carbonate, ,phenyl tolyl carbonate chlorophenyl chloronaphthyl carbonate, etc., or mixtures thereof. The haloformates s-~itable for use herein include bis-haloformates of dihydric phenols (bischloro-formates of hydroquinone, etc.) or glycols (bishaloformates of ethylene glycol, neopentyl giycol, polyethylene glycol, etc.).
~While other carbonate precursors will occur to those skilled in ~the art, carbonyl chloride, also known as phosgene, is preferred.
Also included are the polymeric derivatives of a dihydric phenol, a dicarboxylic acid and carbonic acid. These are ,¦disclosed in U.S. Patent 3,169,121, which issued F~bruary 9, 1965.
, The aromatic carbonate polymers oE this invention may be pre-l ., ~
:pared by employing a molecular wei~ht regulator, an acid acceptor and a catalyst. The molecular weight regulators which can he ~employed in carrying out the process o~ this invention include ,monohydric phenols such as phenol, chroman-T, paratertiary-~
~butylphenyl, parabromophenol, primary and secondary amines, etc.
,!Preferably, phenol is employed as the molecular weight regulator. l -A suitable acid acceptor may be either an organic or an ~inorganic acid acceptor. A suitable organic acid acceptor is a tertiary amine and includes such materials as pyridine, triethyl~
`amine, dimethylaniline, tributylamine, etc. The inorganic acid iacceptor may be one which can be either a hydroxide, a carbonate, a bicarbonate, or a phosphate of an alkali or alkaline earthmetal.
' The catalysts which are employed herein can be any of the i,suitable catalysts that aid the polymerization of bisphenol-A
.'1 1 ' .
1 '.
ii -- 12 -- jl ,1 . I . .
11 . I
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~.23~i35 ~with phosgene. Suitable catalysts include tertiary amines such as,~
for example, triethylamine tripropylamine, N,l~-dimethylaniline;
;quaternary ammonium compounds such as, for example, tetraethyl-ammonium bromide, xetyl triethyl ~nmonium bromide, tetra-n-;heptylammonium iodide, tetra-n-propyl ammonium bromide, tetra-methylammonium chloride, tetramethyl ammonium hydroxide, tetra-n-~butylammonium iodide, benzyltrimethylammonium chloride and ~quaternary phosphonium compounds such as for example, n-butyltri-"phenyl phosphonium bromide and methyltriphenyl phosphonium `~bromide.
Also, included herein are branched polycarbonates wherein a polyfunctional aromatic compound is reacted with the dihydric phenol and carbonate precursor to provide a thermoplastic ,irandomly branched polycarbonate.
I These polyfunctional aromatic compounds contain at least three functional groups which are carboxyl, carboxyllc anhydride, ~,haloformyl or mixtures thereof. Examples of these polyfunctional arornatic compounds which may be employed in the practice of ,this invention include: trimellitic anhydride, trimellitic acid, !trimellityl trichloride, 4--chloroformyl phthalic anhydride, pyromellitic acid, pyromellitic dianhydride, mellitic acid, mellitic anhydride, trimesic acid, benzophenonetetracarboxylic I, -~acid, benzophenonetetracarhoxylic anhydride ancl the like. The ',preferred polyfunctional aromatic compounds are trimellitic ~, anhydride or trlmellitic acid, or their haloformyl derivatives.
Ii Also, included herein are blends of a linear polycarbonate 1, and a branched polycarbonate. ! -i~ DESCRIPTION OF THE_ PREFERRED EMBODIMENT j : ;

Ij The following examples are set Eorth to illustrate more ~` clearly the principle and practice o this invention to those ji - 13 -~3~3~ 1 `skilled in the art Unless otherwise specified, ~here parts or percents are mentioned, they are parts or percents by weight.
EY~IPLE 1 A sample of a polycarbonate of 2,2'-bis-(4-h~droxyphenyl) propane having an intrinsic viscosity or 0.57 deciliters is molded into test specimens of 4" x 4" x 1/4" and tested for ~toughness and stress-crazing.
The toughness of the specimen is dete~lined by moving the fingernails of a hand back and for-th across the test specimen , with mecium pressure and observing whether or not the coating 'scratches.
The stress-crazing of the 4" x 4" specimen is determined by placing it on a material, such as an equivalent size of carpet, iplacing a steel ball in the center of the combination and applying;
ja load plate of 100 lbs. to the steel ball. The sample is '~a]lowed to remain under stress for 7 days. The sample of poly-carbonate is then examined around the stress point for any sign -~
of stress crazing.
The polycarbonate of this example is molded into a test specimen of 10" x 10'l x 1/~" and tested for its anti-skid ~properties. The anti-skid rating is determined bv placing three 7/8" diameter steel balls, welded together to form a triangle, on I
the test specimen and raising one end of the specimen vertically ~ ;
while keeping the opposite end on the horizontal plane. The ` di.stance in inches to which the edge is raised vertically when the ;, weight slides down the sample is recorded. A value of 7-8 is considered acceptable.

The test results are sulNmarized in Table I.
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~X~IPLE 2 Sheets of 4" ~ 4" ~ l/4" and lO" x lO" x l/4", made from the !
polycarbonate of Example l, are coated with a coating which is a mixture of a stoichiometric amount o a thiol of the formula:
., O

CH3CH2C~--CH2OCCH~CH2SH)3 and a polyene of the formula:
O

~'2C~=CH2 COCH2C~=CH2 ., 0 ' 1, in a thickness in the range of 0.5 mils to 2.5 mils and cured with ultraviolet light for 60 seconds The coated s~eets are ,tested as described in Example I and also tested f~r coating adhesion.
The coating adhesion is measurec~ on the coated sheet with scotch tape. In the unscribed coating adhesion test, a strip of ~scotch tape is ap lied to the surface of the coating, taking care to hold one end of the strip away from the surface. The tape is removed rapidly by pulling the free end at a 90 angle ' away from the surface. Removal of the coating with the tape is ; ,~considered adhesion failure. In the scribed coating adhesion !
test, the coating surface is scribed wi~h a shar~ instrument ~such as a razor blade or a Gardner cross-cut (lattice cutting) tester. The scribed area consists o. two sets of parallel ,scribes 1-2 n~ apart, perpendicular to each other. The scotch tape is applied (as above~ over the scribed area and removed in ,,the same manner as above. The coating is then examined for ipartial or complete removal of the s~uares or no change.

;, . I
ii I

~SP-2036 Sheets o ." x 4" x ~ 7 and 10" x 10" x 1/~" made ~rom the polycarbonate of Example 1, are coated with a coating which is a mixture of a stoichiometric amount of the thiol of Example 2 and a - 5 polyene of the formula:
i ~ HO ~C3H6OC~I ~ NCOC3~I6 ~ OCN ~ ~icocH2c~l=c~I2 where n is an integer wherein the molecular weight is @qual to 1000, in a thickness in the range of 0.5 mils to 2 5 mïls and cured with ultraviolet light for 60 seconds. The coated sheets are !
tested as described in Examples 1 and 2. The results are set forth .in Table I.
. .
EX.~IPLE
To a reaction vessel equipped with a stirrer, a fractionation column packed with glass helices, a Dean-Stark trap, and a condenser are added 213.30 parts of maleic anhydride, 202.74 parts of tri-methylolpropane monoalkyl ether, and 183.96 parts of diethylene - !
glycol. The reaction mass is heated under a nitrogen atmosphere to,~
a ma~imum temperature of 200C. After about 4~ hours, a total f 33 parts of water of esterification are collected. The reaction i! ~ ':
mass is cooled to room temperature and about 567 parts of an unsaturated polyester having an acid number of 32 are obtained.
` 169 parts of this polyester and 60 parts of xylene are added to a reaction vessel equipped with a stirrer, a fractionation column packed with glass helices, a Dean--Stark trap, and a condenserl.
The reaction mixture is heated to 110C in about 10 minutès at whi~
time 76 parts o~ a methoxy chain-stopped linear polysiloxane ,fontaining phenyl and methyl groups, 7% by weight silicon-bonded methoxy groups~ and a viscosity of 1500-3000 centistokes at 25C;

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3~35 ~25 parts of xylene and 0.38 parts of tetraisopropyl titanate are added to the reaction vessel. The reaction mass is heated under a~
nitrogen atmosphere to a maximum temperature of 152C. After about~
2~ hours, 6 parts of methanol are collected and external heating !lof the reaction is stopped. The reaction mass is distilled under ¦
;vacuum at a pressure of 20 mm Hg to a maximum temperature of 145C' .;
to remove the xylene. About 239 parts of a clear copolymer containing 70 weight percent of the unsaturated polyester and 30 ~weight percent of the organopolysiloxane are obtained. ~ -, EXA~PLE 5 Sheets of 4" x 4'` x 1/~" and 10" x 10" x l/A" made from the polycarbonate of Example I are coated with a coating which contains a mixture o~ (i) 50 gms. of a mixture of a stoichiometric~

'amount of the thiol of Example 2 and a stoichiometric amount o~ a polyene having the ~ormula '' N l i, ' : , :
~ ~ (OCH2CH=CH2)3 ,andi(ii) 50 gms. of the silicone modified polyester copolymer ,prepared substantially in accordance with Example 4 and cured with~

iultraviolet light for 60 seconds to give a cured coating about ~ 2 mils in thickness. The coated sheets are tested as described ,in Examples 1 and 2. The results are set forth in Table I.

TABLE I

, Example 1 Example 2 Example 3 Example 5 .
~, Toughness Pass Fail Pass Pass 25 ~i Stress Crazing Fail Pass Fail Pass !~ Anti-Skid 3-4 6-8 7-8 7-8 Adhesion N/A Pass Fail Pass I ;~
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~ ~3535 :
~SP-2036 Al~hough the abofe examples have shown various modifications `
of the present invention, other variations are possible in the , ;
light of the ahove teachings. It is therefore to be understood that changes may be made in the particular embodiments of the . ~-invention described which are within the full intended scope of 'the invention as defined by the ap~ended claims~
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Claims (8)

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

1. A photocurable coating composition comprising:
(i) a polythiol represented by the general formula:

wherein R1 and R2 are organic moieties containing no reactive carbon-to-carbon unsaturation and a is 2 to 4;
(ii) a polyene represented by the general formula:

wherein R3 is an organic moiety containing no reactive carbon-to-carbon unsaturation; and, (iii) a silicone modified polyester copolymer which is the reaction product of:
a) a hydroxyl terminated unsaturated polyester of:
1) polycarboxylic acid reactant wherein at least about 65 mole percent of said polycarboxylic acid reactant is an .alpha., .beta.-ethylenically unsatu-rated polycarboxylic reactant and up to about 35 mole percent of said polycarboxylic acid reactant is a polycarboxylic acid reactant free from non-benzenoid unsaturation; and, 2) an alcohol reactant containing two terminal hydroxyl groups and a member selected from the group consisting of allyl ether groups methallyl ether groups and mixtures thereof in an amount sufficient to provide at least 0.1 mole of said ether groups per mole of said ethylenically unsaturated polycarboxylic acid reactant; and, 3) wherein said polyester has an acid number from about 10 to about 35; and, b) an organopolysiloxane having the average unit formula (OH)q(OR')rRsSiO(4-q-r-s)/2 wherein R is selected from the group of lower alkyl radicals having 1 to 8 carbon atoms; cycloalkyl radicals radicals having 5 to 7 carbon atoms in the ring; lower alkenyl radicals having 2 to 8 carbon atoms; mono-nuclear aryl radicals; mononuclear aryl lower alkyl radicals having 1 to 6 carbon atoms in the alkyl group;
and halogenated derivatives of the above radicals; R' is selected from the group of alkyl radicals containing 1 to 8 carbon atoms; mononuclear aryl radicals; acyl radicals of 1 to 8 carbon atoms; s has a value of 1.0 to 2.0; q has a value of 0 to 1.0; r has a value of 0 to 1.0; the sum of q + r has a value of 0.01 - 1.0;
and, said organopolysiloxane containing at least 0.25%
by weight of OH or OR' groups or a mixture of said OH
and OR' groups; said coating composition containing, in parts by weight, from about 1 parts of (iii) to about 3 parts of the combined weights of (i) and (ii) to from about 3 parts of (iii) to about 1 part of the combined weights of (i) and (ii).

2. The coating composition of claim 1 wherein said polythiol is represented by the general formula wherein R1 and R2 are straight chain aliphatic moieties containing no reactive carbon-to-carbon unsaturation and a is 2 to 4.

3. The coating composition of claim 2 wherein R1 and R2 are straight chain aliphatic moieties containing no reactive carbon-to-carbon unsaturation and containing from 1 to about 20 carbon atoms.

4. The coating composition of claim 1 wherein said polythiol is represented by the formula:

.

5. The coating composition of claim 1 wherein said polyene is represented by the formula .

6. The coating composition of claim 5 wherein said polyene is represented by the formula:

.

7. The coating composition of claim 1 wherein said polyene and polythiol are present in stoichiometric amounts.

8. The coating composition of claim 7 wherein said composition contains, in parts by weight, from about 1 part of said silicone modified polyester copolymer to about 2 parts of the combined weights of said polythiol and polyene to from about 2 parts of said silicone modified polyester copolymer to about 1 part of the combined weights of said polythiol and polyene.