CA1114576A - In-mold coating of sheet molding compound moldings - Google Patents

Abstract

Abstract of the Disclosure Liquid compositions suitable for hot post-mold coating of cured sheet molding compound (SMC) parts com-prise a reaction product of an epoxide and an unsatur-ated carboxylic acid mixed with a low shrink additive.
These liquid compositions are used to smooth surfaces, fill porosity and other voids and to eliminate or reduce sink marks. Coatings typically are cured in less than two minutes and appear able to provide many features of normal painting without paint facilities except possibly those needed for touch-up.
The application method used to date has been to compression mold an SMC part in the usual way, separate the mold halves, inject the liquid composition and re-close the mold for a second cure cycle. A unique feature of the liquid composition is its ability to ad-here to an uncleaned SMC molding.

Description

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BACKGROUND OF THE INVENTION
Field of the Invention The present invention relates to an in-mold coating process for applying coatings to moldings made of sheet molding compounds. -DESCRIPTION OF THE PRIOR ART
SMC is widely used for high-volume moldings of large, rigid parts. Factors favoring this use have been fast cure and easy flow of the SMC, high strength and stiffness, smoothness, low ;
shrinkage, dimensional stability, and relatively low cost.
However, still further improvement in surface quality for ~;;
exterior automotive parts is a major need.
Particularly troublesome are surface pcrosity, waviness and sinks. None of these are effectively filled or masked by normal painting operations. Therefore, it is customary to inspect all parts and recycle dèfective ones throu~h handfilling, sanding, painting and inspection stations until acceptable appearance is obtained. Where no sink can be tolerated, it is common to mold a separate part to act as a skin and bond to it a second part with stiffening and fastening sections~
Other approaches have been to mold a gel coat on parts to hide substrate flaws. In principle, this is done either by coating the hot mold before a charge is molded, see U.S. Patent 3,940,468, or by molding a gel coat on a previously-molded part, ~.' ~X
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see Japanese published publication 34210/62.
None of the above described methods of gel coating other than the urethane, appears to have received significant -testing in hot matched metal SMC m~lding for a variety of reasons. Probably, the major technical obstacle has been lack of coatings which adhere to SMC other than through co-cure. Thus, where such coatings are applied first, the ~`
coating must be cured enough to resist tear during flow of the SMC but still be undercured enough to cross-link with the SMC. Similarly, when the SMC is molded first, it is necessary to open the mold before the SMC is fully cured, which is generally impractical since thin sections of parts are cured long before thick sections are adequately hardened.
One way around the problems described has been the use of resin impregnated foils in place of gel coatings. -Another method has been use of unimpregnated foils wich act as a tiecoat into those opposite sides first SMC and later a ; gel coat can bite. The outstanding benefit with both methods is the ability to obtain surfaces with printed patterns. However, the utility is limited by folding or tearing of foil on many nonflat parts.
Another method has been to bond the gel coat to the substrate through isocyanate reactivity using a two canFonent gel cost. Ihe two psrt systems re~uire .
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-mixing control, see British Patent 1,457,935.
In view of the above difficulties, liquid compositions were sought which could be molded on and which would adhere to cured SMC parts. As a result of this work, coatings were found which could be molded onto SMC parts.
Accordingly, the invention provides in a method of ~;
; coating a rigid automotive part made from sheet molding compound, after the part is formed between two mold halves and cured, by the injection of a liquid coating composition into a space formed by separating one of the mold halves from the part while main-taining the mold in a sealed condition and then curing the coat-ing composition, the improvement characterized by the liquid coating composition consisting essentially of lO0 parts of vinyl ester resin formed by the reaction of a polyepoxide resin with an unsaturated monocarboxylic acid and lO to 50 parts of a low shrink additive.
Thus, the coatings process used is to conventionally compression mold an SMC part, separating the mold half, retaining a seal between the shear edge formed by the upper sides of the mold extending below the upper edge of the top of the lower mold half. The gel coat is then injected and the mold is closed to flow and cure the coating. The coatings injected do not require mixing of reactive components at the time of or im~ediately prior to the time of in,ection. The coatings of the present invention are also cheaper than the prior art isocyanate coatings. The coatings can also be applied to cured SMC parts.
In order to obtain coatings having the physical prop-erties desired by the automobile manufacturers without the dis-advantages of the prior art coating compositions, a mixture of ; 30 two components, generally in a vinyl monomer solvent, are required.
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The first component is a vinyl ester resin.
~, The second component is a material which is incompatible with the vinyl ester resin. Materials commonly used as low shrink additi~es meet this requirement. It is believed that the low shrink additive weakens the - 4a -'c~

tenslle strength o~ the coatlng 90 lt cannot be pulled o~f ln one plece or transmlt force~. Based on lO0 parts of vinyl e~ter resin, the low shrink addltlve 18 present at a level of ~rom lO to 50 parts, preferably from 20 to 40 parts by welght. Both the vlnyl ester and the low shrink additive are normally dis~olvéd in ; styrene.
Vlnyl ester reslns are generally prepared by reactlng about equlvalent proportlons o~ a polyepoxide resln and an unsaturated monocarboxyllc acld whereln ,,, !jj :' i --COCH2fHCH~o--: -linkages are formed and the resulting re~ln ha~ ter-mlnal, polymerlzable unsaturated group6. For example, two equlvalents of methacryllc acld may be reacted wlth two equlvalents of a polyepoxlde resln to produce a vlnyl e6ter resln.
Vlnyl ester reslns are descrlbed ln U.S. Patent 3,367,992 to Bearden whereln dlcarboxyllc acld half esters of hydroxyalkyl acrylates or methacrylates are reacted wlth polyepoxlde reslns. Bowen ln U.S. Patents 3,066,112 and 3,179,623 describes the preparatlon of vlnyl ester reslns from monocarboxylic aclds such as acryllc and methacryllc acld. Bowen also descrlbes an alternate method of preparatlon whereln a glycldyl methacrylate or acrylate 16 reacted wlth~the sodlum salt of a dlhydrlc phenol such as bisphenol A. Vlnyl ~`

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ester reslns based on epoxy novolac reslns are de~crlbed ln U.S. Patent 3,301,743 to Fekete et al, Fekete et al al~o describe ln U.S. Patent 3,256,226 vlnyl ester reslns wherein the molecular welght of the polyepoxlde i8 lncreased by reacting a dicarboxyllc acld with the polyepoxlde resln as well as acryllc acld, etc. Other dlfunctlonal compounds contalnlng a group whlch 18 re-actlve with an epoxlde group, such as an amlne, mercaptan and the llke, may be utlllzed ln place of the dlcarboxy-lic acld. All of the above-descrlbed resins whlch con-taln the characterlstlc linkages ' --COCHzCHCH20--~H

and termlnal, polymerizable unsaturated groups arelclas-~ifled hereln as vlnyl ester reslns. ~he preparatlon o~ ;
vlnyl ester reslns is fully dlsclosed ln the above patents.
Addltlonally, lt ls meant to lnclude wlthln the deflnltlon o~ vinyl ester reslns those reslns whereln the secondary hydroxyl group formed by the lnteractlon of an epoxlde group wlth a carboxylic acld group ha~ been reacted wlth a dlcarboxylic acld anhydrlde to produce pendant carboxylic acid groups. The preparatlon o~ these materla~s ls descrlbed in U.S. Patent 3,466,259 to Jernlgan. A var~ety of saturated and unsaturated anhy-drlde~ slmllar to those descrlbed a~ useful ln preparlng j ` ;

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polyester reslns may be used in proportlons Or at least about 0.1 mole of anhydrlde per equlvalent Or hydroxyl group up to an amount sufflclent to react wlth each hydroxyl. ~ reaction temperature from about 25 to 150C ls sultable and any o~ the well known vlnyl poly-merizatlon lnhibltors may be added to prevent polymer- ;
lzatlon durlng the reaction.
Brlefly, any of the known polyepoxldes may be employed in the preparation Or the vlnyl ester reslns of this lnventlon. Use~ul polyepo~ides are glycldyl polyethers of both polyhydrlc alcohols and polyhydrlc - phenols, flame retardant epoxy re~lns based on tetra-bromo blsphenol A, epoxy novolacs, epoxldlzed ~atty aclds or drylng oll aclds, epoxldlzed dlole~ins, epoxl-dlzed dl-unsaturated acld e~ters as well as epoxidlzed unsaturated polyester~, so long as they contaln more than one oxirane group per molecule. The polyepoxides may be monomerlc or polymeric.
Pre~erred polyepoxldes are glycldyl polyethers ; 20 o~ polyhydrlc alcohols or polyhydrlc phenols having weights per epoxide group of about 150 to 2,000. These polyepoxldes are usually made by reactlng at least about .i ~

2 moles of an eplhalohydrin or glycerol dlhalohydrin wlth one mole of the polyhydric alcohol or polyhydrlc phenol, and a sufflclent amount of a caustlc alkall to comblne wlth the halogen of the halohydrln. The products are characterized by the presence of more than one epoxide group per molecule, l.e., a 1,2-epoxy equivalency greater than one.
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Unsaturated monocarbo~ylic aclds lnclude acrylic acid, methacrylic acid, halogenated acrylic or methacrylic acids, cinnamic acid and the like and mix-tures thereof, and hydroxyalkyl acrylate or methacrylate half esters o~ dicarboxylic acids as described ln U.S.
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Patent 3,367,992 wherein the hydroxyalkyl group prefer-ably has from two to slx carbon atoms.
~ se~ul dlcarboxylic acid anhydrldes to modlfy the vlnyl ester resln lnclude unsaturated anhydrldes such as malelc anhydrlde~ cltraconic anhydrlde, ltaconlc -anhydrlde, the varlous substituted malelc anhydrldes and the llke, as well as a variety Or saturated anhydrldes such as phthalic anhydrlde, chlorendlc anhydrlde, tetrabromophthallc anhydrlde and the llke.
A varlety of copolymerlzable monomers are avallable and sultable and lnclude alkenyl aromatlc monomers, alkyl esters o~ acryllc and methacryllc acld, vlnyl acetate, acrylonltrlle, dlallyl maleate, diallyl phthalate, acrylic and methacryllc acid, and the llke and mixtures;thereof. Pre~erred are the alkenyl aromatlc monomers such as styrene, a-methyl styrene, vlnyl toluene, alkyl substituted styrenes ~uch as t-butyl styrene, etc., halogen substltuted styrenes ~uch as chlorostyrene, dlchlorostyrene and the llke.
The pre~erred low shrlnk additlve or rilm weakening addltive ls polyvinyl acetate. Polyvlnyl acetate copolymers can also be used.

The thermoplastic polymers Or vinyl acetate sultable ~or purposes of thls inventlon contaln an average of O to about 10 and pre~erably an average Or O
to about 3 carboxyl group3 per molecule. On a welght basis, ~uitable thermoplastic polymer~ contain about O to about 5 percent by welght, pre~erably about O to about 2 percent by weight comblned "carboxyl" com-pound. These polymers can be prepared ln a number Or ways, all well known in the art, by: -(1) Polymerizlng vlnyl acetate with a copoly-merizable carboxyllc acld to produoe a copolymer having an average of at least one carboxyl group per molecule.
Sultable copolymerlzable carboxyllc aclds are the un-saturated polycarboxyllc acids previously descrlbed as well as unsaturated monocarboxylic aclds havlng the ;~
~ormula:
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CaH~a-2oz whereln a 18 an integer havlng a value of 3 to 10 inclu- -slve, preferably 3 to 6 incluslve. Exemplary of aclds falllng wlthln the scope o~ the above are the followlng:
acrylic acld, methacrylic acld, crotonic acld, lsocro-tonic acld, vlnyl acetic acid, tlgllc acld, hexenic acid, and the like.
(2) Reacting poly(vlnyl aceta~e) with a co-polymerlzable carboxyllc acld, such as the acids described ln (1) above to form a block copolymer or a gra~ted co-polymer.

(3) Partially hydrolyzing poly(vlnyl acetate) generally to a maxlmum value o~ 20% based on the total number Or ester groups origlnally present and partially or totally esteri~ying the hydroxyl groups with a poly-carboxylic acid or anhydrlde thereof as previouslydescribed in this speciflcation.

(4) Pre~erably the vlnyl acetate i8 a homo-polymer. In formulatlng the compositlons o~ thls in-vention, it is customary to admix wlth the polymers o~
vlnyl acetate, a polymerlzable ethylenloally unsaturated monomer, which serves to cross-link the vlnyl ester re~ln to a thermoset product. Vlnyl monomers have the ; formula:

whereln R 1 a group havlng an un~aturated carbon-to-carbon, carbon-to-oxygen or carbon-to-nltrogen group in conJugatlon wlth the vlnyl group. Groups havlng such unsaturation ln con~ugatlon with the vlnyl group are aryl, ketonic, heterocycllc, nltrlle, carbalkoxy, carboxy and amldo.
Speclflc vlnyl monomers include the following:
Wherein R 18 aryl: 3tyrene, halogenated styrenes such as chlorostyrene, p-iodostyrene, m-fluorostyrene, dl-chlorostyrene and the llke; alkyl sub-stltuted styrenes such as p-methyl styrene, p-ethyl styrene, o-tert-butyl styrene and the llke; alkoxy and aryloxy sub~tituted styrenes such as p-ethoxy styrene, p-propoxy styrene, p-phenoxy styrene and the like;

S'~i Wherein R læ ketonic: ethyl vlnyl ketone, n-propyl vlnyl ketone, phenyl vlnyl ketone and the llke;
Whereln R is heterocycllc: vlnyl pyrldlne, -vinyl qulnoline, vinyl pyrrole, vlnyl carbazole, vlnyl thlophene and the llke;
Whereln R ls nltrlle: acrylonitrlle and the llke;
Whereln R 18 amldo: acrylamlde, blcyclo-heptylacrylamide, dlacetoneacrylamlde and the llke;
Whereln R ls carboxy: acryllc acld and the llke, Whereln R ls carbalkoxy: methyl aorylate, butyl acrylate, octyl acrylate, lauryl acrylate, cyclo-hexyl acrylate, phenyl acrylate, benzyl acrylate and the like.
Also suitable 18 dlallylphthalate and the like.
The amount o~ ethylenically unsaturated mono-mer used can vary over wide limits. For example, the monomer can be used in amounts of about lO to about 60%
by welght ba~ed on the comblned welght of the monomer and the polyvlnyl acetate. It is pre~erred to used about 20 to about 50% by welght ethylenlcally unsaturated mono-mer, based on the comblned weight of the monomer and polyvlnyl acetate. The same unsaturated monomers can be used as solvents for the other low æhrink additlves and the vlnyl ester resln. The unsaturated monomer ls u~ually pre ent at a level of from 50 to 400 parts and pre~erably lO0 to 200 parts based upon 100 parts Or vlnyl ,: :

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ester resin. Preferably from 1 to 3 equlvalents o~ vinyl monomer per equivalent of vlnyl ester un~aturatlon are present.
Other preferred low shrink additlve includes the polydiene rubbers. By polydlene rubbers lt 18 meant to lnclude hereln homopolymers and copolymers o~ con-~ugated dlene monomers such as butadiene. It is ~urther contemplated wlthln thls deflnition to lnclude polymers contalning at least about 30 welght percent Or dlene monomer wlth the balance comprlsing at least one other copolymerlzable monomer such as styrene or acrylonltrlle.
It i8 al~o meant to lnclude random, gra~t and block polymers o~ whlch a wlde varlety are commerclally avall-able or readlly prepared by known polymerizatlon methods.
15Whlle polydlene rubbers wlth as llttle as 30 " ~ .
weight percent of a dlene monomer provide lmprovements accordlng to thls lnventlon better coatlng properties are ~ound when the dlene monomer con~tltutes at least about 40 welght percent of the polymer and polymers at or above this level are preferred ~or this lnvention.
Con~ugated diene monomers lnclude butadiene, isoprene, chloroprene, the various halo and lower alkyl ~-~ substltuted derlvatives thereof and the like monomers.
Mixtures of said dlene monomers are frequently used to impart certain desired propertles to the polydiene rub-bers. Polybutadlene is a preferred polydlene.

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Copolymerlzable monomera u~eful wlth sald d~ene monomers include nltrlle monomers such a~ acryl-onitrile, methacrylonitrlle and the llke and alkenyl aromatlc monomers such as styrene, a-methyl styrene, vinyl toluene, the halo and alkyl substituted styrene~
such as chlorostyrene or t-butyl styrene. Preferred copolymers include styrene-butadlene copolymers and especially block copolymers thereo~.
The unsaturated polydlene rubbers Or thls ln-ventlon may be prepared by a varletg o~ well known pro-cedures, and slnce this inventlon i8 concerned with the utillzation of sald rubbers and not thelr preparatlon, no detalled descrlptlon thereof læ needed. Many text-, .. . .
books and patents are readlly available whlch can be consulted for such preparatlve methods, such as the chapteron butadlene polymers and copolymers by W. Saltman in "Encyclopedia o~ Polymer Science and Technology", Vol. 2, Interscience Publishers, 1965.
The preferred polydlene rubber has an lnherent vlscouity o~ about 0.3 to 1.2 declllters/gram or a molecular welght of at least about 15,000 to 20,000.
; Improvement ln coatlng propertles appear to be related to molecular welght of the polydiene rubber.
Consequently hlgher molecular weight polydiene rubbers when used at the lowest concentratlon shows greater lm-provement than the lower molecular weight~. Accordlngly, lt is preferred to use polydlene rubbers havlng a vl~-cosity of at least about 0.5 decillteræ/gram.

Advantageously, it ha3 been ~ound that the vlsco~lty ranæe can be extended upward to about 2 decl-llters/gram if the system also contain~ at least about 15 parts of an lnert flller such as clay and the llke per 100 parts of resin and rubber. Thls 18 Or parti-cular slgnlflcance because thermosettable resln systems are usually formulated with such ~lllers ln commerclal use ln order to lmpart certaln propertles such as weatherablllty, etc. and ror reason of ec,onomlc~.
Inherent vlscoslty 18 defined as rOllow8:

nlnh = (2.303 loglOnr)/(C) where nr ~ (n/n) and , n ~ tlme for solvent and ~ ~ tlme for a solutlon o~ 0.15 gm of polymer/100 ml of toluene C ~ concentratlon The vlscoslty unlts are ln declliters/gram Other low shrlnk addltlves whlch can be used lnclude polymethylmethacrylate, polyethylene and poly-styrene.
In addltlon to the vlnyl ester resln, an un-saturated pol-yester re~ln can optlonally be pre~ent.
The polyester ls present at a level o~ from O to 100 part~ o~ vinyl ester resin by welght. ,~

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Generally, in the preparation o~ suitable polyesters, an ethylenically unsaturated dicarboxylic acid such as malelc acid, ~umaric acid, itaconic acld or the llke, is lnteresterlfied with an alkylene glycol or polyalkylene glycol having a molecular weight of about 1,000 to 8,ooo or thereabouts. Frequently, di-carboxylic acids free of ethylenic unsaturatlon such as -~
phthallc acid, isophthalic acid, tetrabromophthalic acid, chlorendlc acid, adiplc acid, succinlc acld and the llke may be employed withln a molar range of 0.25 to as much as 15 moles per mole of the a,~-unsaturated dlcarboxyllc acld. It w111 be understood that the appropriate acid anhydrldes when they exlst may be used and usually are preferred when avallable.
The glycol or polyhydric alcohol component of the polyester ls usually stolchlometric or in slleht excess wlth re~pect to the sum o~ the aclds. The exces~
of polyhydrlc alcohol ~eldom will exceed 20-25% and usually ls about 2-10%.
These unsaturated polyesters may be generally prepared by heatlng a catalyzed mixture of the poly-hydrlc alcohol wlth the dicarboxyllc acid or anhydrlde ln the proper molar proportions at elevated temperatures, usually at about 150 to 225C for a perlod of time ranging ~rom about 5 to 15 hours. Polymerizatlon in-hlbltors such as t-butyl catechol may be advantageously added. It is also posslble to prepare unsaturated ' ':
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polyesters directly from the appropriate oxide by co- '~
polymerlzatlon with an anhydrlde, e.g., propylene oxlde can be used in place Or propylene glycol and copoly-merlzed with malelc anhydrlde or a mlxture Or malelc

5 anhydrlde and phthalic anhydrlde. Further descrlptlon of these well known reslns ls unnecessary hereln.
Normally, the gel coatlng composltlon o~ the present lnventlon are dissolved or suspended in a vlnyl monomer such a~ those descrlbed above in con~unctlon wlth the vlnyl acetate. The vlnyl monomer can be pre-sent at a level Or from lO to 200 and pr~Perably 50 to 150 parts based upon lOO parts by welght Or vlnyl ester.
The usual emulslrler, lnhlbltors and rlllers can also be present, see U.S. Patents 3,466,259;
3,548,030; 3,564,074; 3,674,893; 3,836,600 and 3,683,045 or a complete disclosure Or the above materlais.
-~ The prererred S~C's used ln the practlce o~
the present lnvention as substrates rOr in-mold coatlng are those based on vlnyl ester, lsophthallc and propylene glycol fumarate polyester sy~tems.
Chrome-plated, shear edge molds suitable for compresslon molding SMC adequately contain and release in-mold coated parts. Ordinarlly, molds are used whose surraces part evenly when the press iB opened. Further-more, lt must be noted that coating thlckness varieswlth draft angle of substrate surrace; thlcknesse~
typically run from around .01 mm on low draft sur~aces to .07 mm on hlgh drart surraces. This occurs because . :~

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the mold openlng available for coatlng when mea~ured perpendicular to the part surface varles wlth ~he slne of the draft angle.
As mentioned earlier, the principal method 80 far used to apply coating is to ælightly separate ~ the mold halves, inJect onto the SMC part and then re-; close the mold. This method allows a shear edge deslgn to form a liquid seal at all tlmes.
Charge weights giving as much as .5 mm of coating have been used, but an average of .07 to .10 mm of coating has generally been enough to give both opacity and complete coverage. Slnce the usual SMC part averages 2.5 mm in thickness, a typical coating has re-qulred about .03 to .05 gm o~ coating per gm of SMC
used.
Simple coating charge placements, often a single pool or strip formed by high pressure in~ection usually have provided complete coverage.
Mold temperature~ from 140 to 160C have given satl~factory coatings. A minimum cure time of lO to 30 seconds at 150C has been used and even slower cure rates have sometimes been required to prevent too rapid gel-ation and resulting incomplete coverage.
Higher molding presYures, as expected, provlde better coverage of steeper, lower draft surfaces. How-ever, the typical pressures needed to mold the base SMC part have also generally been adequate to give a co~plete coating.
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~he prlncipal aim of gel coatlng ha~ been to rill volds, reduce slnks and act as a replacement ror the primer-~ealer now commonly used by custom molders o~ SMC.
In-mold coated part~ have appeared satlsrac-tory by the automotlve test~ normally u~ed escept ror the Ford Cro~s-Hatch Test. Re~ults are stlll lncomplete as to weatherlng. Gra~elometer values have been partl-cularly good wlth no separatlon o~ in-mold coatlng ~rom ~ubstrate and llttle separatlon Or palnt ~rom ln-mold coating.
Although most work has been directed at re-placlng a prlmlng operatlon, coatlngs have al~o been made whlch appear sultable a~ topcoats, at lea~t, lnso-~ar as h1dln~ power goes. Al~o coatlng~ wlth good conductlvlty havo been made by lncluslon o~ ~ultable cokeo. As thIs lndlcate~, there i8 con~lderable rlex bility in choice Or lngredlent~ and re~ultlng ooatlng properties.
In the rollowing example~ as ol~ewhore ln the ~peoirication and claims, all par~o and p~rcentag~ are by weight unles~ otherwlse ~peclried.

EXAMPLE I
A 1976 Old~mobile grlle wa~ molded u~ing a tandard Rohm and Ha~ un~burated poly~t~r ba~od ~hoet moldlng oompoun~. The part wa~ curod ~n ~he pr~ or l-1/2 mlnute~ at a mold tomp~ratur~ o~ l50¢~ ~h6 top `
mold halr wa~ then r~l~od lO mm whllo ~tnt~inlng ~
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seal with the shear edge of the mold. Ihe following gel coating composition was then injected for 3 seconds through a cooled injection nozzle positioned in the top surface of the mold. m e coating was cured for 1/2 minute. A coating 0.13 mm thick was formed using 80 gms of the coating composition.
m e coating composition used had the following formulation.
Components Parts Vinyl ester resinl in styrene (be- 400 lieved to be 66% copolymer of acrylic acid and diglycidyl ether of bis-phenol A in 44% styrene) 4CP/o polyvinyl acetate containing some 120 carboxyl groups dissolved in 60% -styrene CaCo3 filler 450 Tertiary butyl peroctoate 5 Saturated solution of parabenzoquinone 0.6 in styrene (inhibitor) Dialkyl phosphate 3 (mold release)4.2 Dow SC 9013.01 Union Carbide LP 40 3 Zelac NE trademark of DuPont - 19 - ~.

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The coated grllls were testing uslng the following Chrysler test procedures wlth the following result 8:

REQUIRED TESTING: No aeparation of the paint ~ ~`
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fllm ~rom the base sub~trate or coating.
Thls test lnvolves scorlng the coatlng then taplng with a special adheslve tape then re-- moving the tape.

TEST PASSED REQUIRED TESTINa: No bllsterlng or 1088 of adhe~lon due to condenslng humldlty.
Thls test lnvolves placlng the part ln a 100S humldlty environment at 49C for 250 hours.

FACES PASSED REQUIRED TESTING: Method II
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no bllsterlng, checklngJ cracklng, chlpplng, 108~ of adheslon, 1088 of color, or other effect~ detrlmental to the surface. The test involves 15 heatlng and coollng cycle~.

The coated grllls were also sub~ected to the ~`
SAE J400 Gravelometer test wlth the following re8ult8: r The test i~ performed at -18PC by bombardlng the part with gravel propelled by an air pressure of 483 KPa.
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Chip Resiætance tGravelometer) 2 - Panels (13) A - 5C
B - 6C, 7B
2 - Panels (14) A - 7C
B - 6B, 7C
2 - Panels (15) A - 7B

Passed Requlred Testlng - Ratl~g of 4B or lower are failures.

~he composition of Example I was used to coat SMC substrate~ based on Unlon Carblde, Ashland and Rohm and Haas formulations with equally good results. Sub-strate cure times can be varled from nlnety seconds to : 8iX minutes whlle stlll retalnlng~an acceptable product.
The substrates coated lncluded Oldsmoblle hoods havlng a top surrace area of 2.3 square meters wlth good results.

EXAMPLE II
Example I was repeated wlth the exceptlon that the LP 40 was replaced wlth LP 100. The CaC0, wa~
replaced wlth Feldspar and a 1% of a llght stablllzer and W absorber was added. LP 100 has basically the same ~-compositlon as LV 40 but results ln better plgmentation.
A ~lat panel mold was employed and the panel~ produced - are belng tested for the effects o~ sunllght on the plant roof.

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EXAMPLE III
A gel coatlng compo~ltlon was rormulated uslng the followlng ingredients.

Composltlon - Parts Reslllent polyester (malelc anhydrlde, 70 isophthalic anhydrlde, ethylene glycol and dlethylene glycol) 66 parts of rlgld vlnyl ester re~lnllO
(copolymer of a¢ryllc acld and the dlglycldylether of Blsphenol A
acetate) dlssolved ln 44 parts styrene.

Thermoplastlc styrene-butadlene copolymer 44.4 (purchased from Dow) Styrene monomer 79.6 Tert-butyl perbenzoate 2 Tert.-butyl peroctoate 2 Dlalkyl phosphaté (ZELEC UN) DuPont1.375 mold release agent Feldspar (anhydrouæ sodlum, potasslum 265 alumlnum sillcate) 5% Na 8% K

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HO ~ OH
CH~

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A series of 12 Oldsmoblle hoods havlng an upper surface area of 2.3 square meters were rormed of conventlonal Rohm and Haas based SMC and coated with the above formulation. The hood~ were cured ~or about four mlnutes prlor to the gel coatlng. The gel coat was cured for about 1/2 mlnute. Most o~ the sur~ace lmperfections present ln the uncoated hoods were cor-- rected by the coatlng. The coatlng dld not possess good adhesion to the substrate and even p~orer adheslon to other conventlonal SMC substrate~.
In order to determlne the e~fects Or cure tlme o~ the ~ubstrate on adheslon, substrate cure tlmes of 45 sec., 1 mln., l-l/2 mln. and 3-1~2 mln. (prior to - applylng the coatlng) were employed. The substrate wa~ molded sheet. The coatlng cure tlme was 3-l/2 min.
with a mold temperature o~ 300F ln all cases. The ad-i hesion was very good at substrate cure tlmes of 45 s~ seconds, l mlnute and l-l/2 minute and poor at 3-1/2 mlnutes.
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' 20 EXAMPLE III b ~he Feldspar was replaced wlth calcium car-I bonate with the same results as those obtalned ln ~ r ,~; Example IIIa.

~; EXAMPLE IV
Conductlve coatlng composltlons used ln the i practlce of the pre~ent invention have the followlng formulatlons: -, i . ~.
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:

Components Part~ Parts Vinyl ester reslnl ln styrene400 400 (belleved to be 66% copolymer of acryllc acld and diglycldyl ether :
of bisphenol A in 44% styrene) 40% polyvlnyl acetate dissolved ln 60% styrene2 120 120 ,' ., Petroleum coke (~lnely ground)480 600 Coak Coke (~lnely ground) 600 `~-Tertlary butyl peroctoate 6 : Saturated ~olution Or parabenzoqul- 0-.8 0-.8 ;~ non in styrene (inhibltor) Styrene 0-40 0-40 ~' Dlalkyl phosphate J (mold relea~e) 4 4 ~ *

~ The lnhlbltor and styrene levels are varled -: to control the flow and gel tlme o~ the composltlon.
Generally, large part~ have longer rlow tlmes. The .
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Dow XD 9013.01 2Union Carbide LP 40 ~elac NE DuPont ~ . ', 1~4~'?~i ~

The coating composltlons as outllned above have good conductlvity. The conductlve sur~ace allows roof parts to be chrome-plated preventlng heat build-up ln the pasæenger compartment. The conductive surrace on a hood reduces statlc radio interference. The entlre body can also be made conductive 80 that lt can be electro-sta~ically painted.
The conductive filler can be present at from a small but ef~ectlve amount to lmpart conductlvlty to a level of 300 parts per 100 parts of vlnyl e~ter resin.
The calculatlon throughout lnclude only the vinyl ester and not the monomeric styrene pre~ent in the so-called vlnyl e3ter resln.
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Claims (6)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. In a method of coating a rigid automotive part made from sheet molding compound, after the part is formed between two mold halves and cured, by the injection of a liquid coating composition into a space formed by separating one of the mold halves from the part while maintaining the mold in a sealed con-dition and then curing the coating composition, the improvement characterized by the liquid coating composition consisting es-sentially of 100 parts of vinyl ester resin formed by the reaction of a polyepoxide resin with an unsaturated monocarboxylic acid and 10 to 50 parts of a low shrink additive.

2. The method of claim 1 wherein the polyepoxide resin is the diglycidyl ether of the compound

3. The method of claim 1 wherein the low shrink additive is polyvinyl acetate.

4. The method of claim 1 wherein the low shrink additive is an unsaturated rubber polydiene having a molecular weight of at least 15,000 and containing in polymerized form at least 30 weight percent of a conjugated diene monomer and from 0 to about 70 percent of at least one other copolymerizable monomer, and having an inherent viscosity of about 0.3 to 1.2 deciliters/gram.

5. The method of claim 1 wherein the low shrink additive is selected from the group consisting of polymethyl-methacrylate, polyethylene and polystyrene.

6. The method of claim 1 wherein a conductive filler is present in the coating composition.