This invention relates to coating compo¬ sitions and to coated articles having a color coat overlaid with a clear coat. In particular, it is directed toward thermosetting acrylic enamels con- 10 taining ultraviolet light stabilizers, which enamels give a high quality weather resistant coating, especially useful for coating the exterior of auto¬ mobile and truck bodies. The enamels are prepared as disclosed in United States Patent 3,622,651 - 15 Vasta issued November 23, 1971, incorporated herein by reference. The addition of one or -more ultra¬ violet light stabilizers serves to diminish the degradation effects of the ultraviolet radiation in the sunlight. Optionally, the enamels also con- 20 tain one or more antioxidants.

Sunlight is composed of electromagnetic radia¬ tion with energy in the infrared, visible, and ultra¬ violet portions of the spectrum. When the ultraviolet portion of sunlight falls upon a clear surface coating, ²⁵ the energy may be partially or wholly absorbed by the coating. In many instances, the energy absorbed initi¬ ates a photochemical reaction which causes discoloration and/or physical failure of the coating. Pigiπented sur¬ face coatings also suffer from ultraviolet degradation.

30 The inclusion of an ultraviolet light stabilizer can increase the useful life of both clear and pigmented coatings. Ultraviolet light stabilizers protect the coatings by absorbing the destructive, high energy- ultraviolet rays and converting such energy into non¬

35 destructive heat energy.

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Antioxidants are useful in preventing the oxidation of polymers, or for inhibiting oxidation already begun by oxygen, air, ozone, or oxidizing agents of many types. The rate of thermal oxidation of the polymeric systems used in coating compositions is normally rather slow, i.e., a reaction that occurs over weeks, months, or years under ordinary conditions. However, even though the reaction is often slow, pro¬ nounced effects may be readily observable very early in the degradation reaction. Furthermore, more rapid oxidative degradation occurs in the presence of ultra¬ violet radiant energy. Antioxidants can assist ultra¬ violet light stabilizers in effectively retarding this degradatio . Thermosetting acrylic enamel finishes are widely used on the exterior of automobiles and trucks. ¹ It has been found that an excellent appearance along with depth of color and metallic glamour can be ob¬ tained by applying a clear or transparent coat over the . conventional colored or pigmented coat. However, the I weatherability and durability of these clear coats have j been found to be poor. Checking, cracking, and flaking ' of the clear coat occur after relatively short periods of exposure to outdoor weathering, giving the automobile or truck an unsightly appearance. Ee- finishing of these weathered clear coats is difficult and expensivejsince the clear coat must be sanded to remove cracked and flaked clear coat before a refinish coat can be applied. In an effort to retard or substantially re¬ duce checking, cracking and flaking of the clear coat, conventional ultraviolet light stabilizers have been added to the clear coat. Also, the combination of a transparent pigment and an ultraviolet light screener has been added to the clear coat, as suggested by

LaBerge United States Patent 3,407,156 issued October

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22, 1968. In each of the above cases, the durability and weatherability of the clear coat was increased for a relatively small length of time but not to the extent required for a practical automotive or truck finish. There exists a felt need for acrylic enamels effec¬ tively stabilized against ultraviolet radiation for use in a clear coat/dolor coat system. ultraviolet light stabilizers have tradition¬ ally been used only in those coating compositions which are utilized as topcoats. The problem with this pro¬ cedure has been the tendency of the stabilizers to leach out of the topcoat and escape into the atmosphere, leav¬ ing the topcoat susceptible to weathering.

The composition of this invention, containing ultraviolet light stabilizer and, optionally, antioxi- dant, has a preferred utility of being used as a clear coat/color coat finish and particularly as the ^" clear coat of such a finish. ^' It is theorized that the ultra- ^' violet light stabilizer will migrate ^' from the color coat into the clear coat, thereby protecting the ^' clear coat against weathering. The preferred finish is one in which both the clear coat and the color coat contain as additives one or more ultraviolet light stabilizers and one or more antioxidants. Some of the additives will be consumed from the clear surface through leaching, evaporation, and "photochemical reaction. A high con¬ centration of additives in the color coat will serve as a reservoir and replenish the lost additives through diffusion from the color coat to the clear coat. Thermosetting acrylic enamels prepared ac¬ cording to the teachings of United States Patent 3,622,651 - Vasta can be used to provide clear coats of increased flexibility and durability.

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SUMMARY OF TKΞ I VEN ION Substrates are coated with first a color coat then a clear coat containg thermosetting acrylic enamels prepared according to the teachings of united States Patent 3,622,651 - Vasta and at least one ultraviolet light stabilizer. The invention also provides a liquid coating composition con¬ sisting essentially of solvents and (a) 95-50%, by- weight, of a polymer having a backbone of polymerized ethylenically unsat rated monomers and having ester groups attached directly to its backbone, said ester groups comprising about 10 to 75 percent of the total weight of the polymer and consisting essentially of Ester Group (A) 0- -C-O-P^-OH and Ester Group (B) selected from the group consisting of

O 0 0 OH ιι ι it >5 ii i

-C-O-R -0-C-R -C-0-CH--C-H 0

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CH ₂ -0-C-R ^"

or mixtures thereof, wherein the molar ratio of Ester Group (A) ^~ .o

Ester Group (3) is from about 1:1.5 to 1:2.5;

R is a saturated hydrocarbon radical containing

2-10 carbon atoms;

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R is selected from the group consisting of alkyiene, vinylene, aroma-cic carbocyciic

and heteroradicals, and is selected from the group consisting of a saturated aliphatic hydrocarbon radical having one to 26 carbon atoms and an . ethylenically unsaturated aliphatic hydro¬ carbon radical having 12 to 18 carbon atoms; (b) 5-50% by weight, based on the weight of the polymer, of a melamine formaldehyde resin which has been at least partially reacted with an aliphatic monohydric alcohol having from 1-4 carbon atoms; and (c) at least one ultraviolet light stabilizer.

These enamels preferably contain about 1-20% by weight, based on the weight of the film- forming constituents, of ultraviolet light stabilizer. Optionally, they also contain about 0-1-5% by weight of antioxidant, wherein the weight ratio of ultraviolet light stabilizer to antioxidant is about 1:1 to about 50:1. More preferably, about . 5-8% by weight of ultraviolet light stabilizer is used, optionally with about 0.1-1% by weight of antioxidant, wherein the weight ratio of ultraviolet light stabilizer to antioxidant is about 10:1. The specified percentages of ultraviolet light stabilizer or antioxidant may be obtained by combining two or more ultraviolet light stabilizers or' two or more antioxidants as well as by utilizing such additives singularly.

DETAILED DESCRIPTION OF THE INVENTION -It has been found that clear coats of the invention using acrylics with the glycidyl ester "Cardura Ξ" made by Shell Chemical Co. are more flexible and have surprisingly much lower

viscosity than those with similar acrylics but without the "Cardura E". In one test, at about a 60% solids level the polymer of the-invention gave a Gardner Holdt viscosity of J while one without the Cardura E gave a viscosity of Z^.

The acrylic polymer is prepared by conven¬ tional polymerization techniques in which the monomer constituents are blended with solvents and a polymeri¬ zation catalyst and heated to 75-150°C. for about 2-6 hours to form a polymer that has a relative viscosity of about 1.04-1.10 and preferably about 1.06-1.09.

Typical solvents and diluents which are used to prepare the acrylic polymer and the coating composi tion of this invention are toluene, xylene, butyl acetate, acetone, methyl isobutyl ketone, πethyl ethyl ketone, butyl alcohol, and other aliphatic, cycloali- phatic and aromatic hydrocarbons, esters, ethers, ke- tones, and alcohols, such as are conventionally used in coating compositions..

About ^" 0.1-4% by weight, based on the weight of the monomer, of a polymerization catalyst is used to prepare the acrylic polymer. Typical catalysts are di-t-butyl peroxide, cu ene hydroperσxide, azobisiso- butyronitrile and the like.

Typical ultraviolet light stabilizers which are useful in this, invention are as fol¬ lows:

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Benzophenones such as hydroxydodecycloxy- benzophenone, 2,4-dihydroxybenzophenone, hydroxy- benzophenones containing sulfonic acid groups, 2,4- dihydroxy-3' ,5'-di-_t-butylbenzophenone, 2,2' ,4*- trihydroxybenzophenone esters of dicarboxylic acids, 2-hydrσxy-4-acryloxyethoxybenzophenone, aliphatic mono- esters of 2,2' ,4-trihydroxy-4'-alkoxybenzophenone, 2- hydroxy-4—methoxy-2'-carboxybenzophenone;

Triazoles such as 2-phenyl-4- (2*-4'-dihydroxy- ^* benzoyl) riazoles, substituted benzotriazoles such as hydroxyphenyltriazoles such as 2-(2'-hydroxy-5*- me h lphenyl)benzotriazole, 2- (2*-hydroxyphenyl)benzo— triazole, 2-(2'-hydroxy-5 ^? -octylphenyl)naphthotriazole; Triazines such as 3,5-dialkyl-4-hydroxyphenyl derivatives of triazine, sulfur-containing derivatives of diallyl-4-hydroxyphenyltriazines, hydroxyphenyl- 1,3,5-triazines and such triazines containing sulfonic acid groups, aryl-l,3,5-triazines, orthohydroxyaryl-s- triazine; .

Benzoates such as dibenzoate of diphenylolpro- pane, t-butyl benzoate of diphenylolpropane, nonyl ^• phεnyl benzoate, octyl phenyl benzoate, resorcinol dibenzoate. Other ultraviolet light stabilizers that can be used include lower alkyl thiomethylene-containing phenols, substituted benzenes such as l,3-bis(2'- hydroxybenzoyl)benzene, metal derivatives of 3,5,-di-t- butyl-4-hydroxyphenylproρionic acid, asymmetrical oxalic acid diarylamides, alkylhydroxyphenylthioalkanoic acid esters, dialkylhydroxyphenylalkanoic acid esters of di- and tri- pentaerythritol, phenyl- and naphthlene- substituted oxalic acid diamides, methyl- ? - (3,5-di-1- butyl-4-hydroxyphenyl)propionate, ^ , - '-bis (2-hydroxy-

phenyl)diisopropylbenzene, 3,5*-dibromo-2'-hydroxy- - acetophenone, ester derivatives of 4,4-bis (4'-hydroxy¬ phenylJpentanoic acid wherein there is at least one - unsubstituted position ortho to the aromatic hydroxyl groups, organophosphorus sulfides such as bis (diphenyi- phosphinothioyDmonosulfide and bis (diphenylphosphino- thioyl)disulfid , 4-benzoyl-6- (dialkylhydroxybenzyl) resorcinol, bis (3-hydroxy-4-benzoylphenoxy)diphenylsi- lane, bis (3-hydroxy-4~benzoylphenαxy)dialkylsilan , 1 _/ 8-naphthalimides, _--cyano- ,β -diphenylaerylie acid derivatives, bis (2-benzoxazolyl)alkanes, bis(2-napthoxa zolyDalkanes, m hylene alonitriles containing aryl and heterocyclic substitutes, alkylenebis(dithio)car- bamate, 4-benzoyl-3-hydroxyphenoxyethyl aer late, 4- benzoyl-3-hydroxyphenoxye h l methacrylate, aryl- or alkyl-substituted acrylonitriles , 3-methyl-5-isopropyl- phenyl-6-hydroxycoumarone.

Particularly useful ultraviolet light stabil¬ izers that can be used are hindered amines ofbipiperidy derivatives such as those disclosed in Murayama et al., U.S. Patent 4,061,616, issued December 6, 1977, column 2, line 65, through column 4, line 2, and nickel com¬ pounds such as /ϊ-phenyl-3-methyl-4-decanoylρyrazolate

(5)7-Ni, bis/phenyldithiocarbamatoT÷NiCII) , and others li~s ^* ted in the~~above patent, column~ ^" 8, line 44 through line 55. _. Among the available ultraviolet light stabilizers, including screeners and absorbers, it is preferred to use "Tinuvin" 900 absorber and "Tinuvin"

292 hindered amine light stabilizer (free radical scavenger) both produced by Ciba Geigy.

Typical antioxidants are as follows: tetrakis- alkylene dialk lhydroxyaryl alkyl ester alkanes such as tetrakismethylene-3-(3 ^« ,5'-dibutyl-4'-hydroxyphenyl) propionate methane, the reaction product of p-aminodi- phenyla ine and glycidyl methacrylate, the reaction

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product of n-hexyl- '-phenyl ^' -£-phenylene diamine and glycidyl methacrylate, pentaerythritol tetrakis (thio- glycolate) , trimetlxylolpropane tris (thioglycolβ c , tri ethylolethane tris (thioglycolate) , N- (4-anilino- phenyl)acrylamide, N- (4-anilinophenyl)maleamic acid, N-(4-anilinophenyl)maleimide, alkylhydroxyphenyl groups bonded through carboalkoxy linkages to the nitrogen atom of a heterocyclic nucleus containing an imidocarbonyl group or an imidodithiocarbonyl group, 3,5-di-t:-butyl- 4-hydroxycinnamonitrile, ethyl-3,5-di-t-hexyl-4-hydroxy- cinnamate, substituted benzyl esters of β-substituted hydroxyphenylpropionic acids, bis (hydroxyphenylalkylene) alkyl isocyanurate compounds, tetrakishydroxybenzylphos- phonium halides alone or in combination with a dialkyl- thiodialkanoate, thiodimethylidyne tetrakisphenols alone or in combination with a dialkyl thiodialkanoate or phosphite or phosphonate, dihydrocarbylhydroxyphenylaryl or -alkyl phosphonites or phosphonates or phosphates or phosphites or phosphinates or phosphinites or phosphoro- thiσnates or phosphinothionates, diphenylbis (3,5-di-t- butyl-4-hydroxyphenoxy)silane, hydrocarbylhydroxy- phenyldihydrocarbyldithiocarbamate ^' s such as 3,5-di-t- butyl-4-hydroxyphenyldimethyldithiocarbamate and amino- benzylthioether.

Plasticizers can be used in the novel coating composition of this invention in amounts of up to 20% by weight of the film-forming material. Preferably, about 3-8% by weight of a plasticizer is used. Functional polymeric plasticizers which react with the constitu¬ ents in the coating composition can be used, such as epoxidized soya bean oil, oil-free and oil-modified alkyIs and polyesters, such as polyorthophthalate esters, polyalkylene adipate esters or polyarylene adipate esters. Volatile non-functional monomeric plasticizers can also be used.

In the color coat, the enamel con¬ tains pigment in the amount of 0.1-20.0% pigment volume concentration. Preferably, a pigment volume concentration of about 0.3-6.0% is used. Ex- amples of the great variety of pigments which are used in the novel coating composition of this invention are metallic oxides (preferably titanium dioxide, zinc oxide, and the like), metal hydroxides, metal flakes, metal powders, chromates (such as lead chromate), sul- fides, sulf tes, carbonates, carbon black, silica, talc, china clay, iron blues, organic reds, maroons, organic dyes, lakes, and the like. If the enamel is to be employed as a clear coat, it may contain one or more transparent pigments, ^' i.e. , pigments having the same or similar refractive index as the binder of the clear coat with ^' a small particle size of about 0.015- 50 microns.

Two ^' particularly useful additives for both the ^" color coat and clear coat are iron pyrophosphate and finely divided silica. Up to about 10% by weight of iron pyrophosphate and up to about 15% by weight of silica, based on the weight of the film-forming con¬ stituents, can be used. The addition of ironpyrophos¬ phate and silica will improve the overall durability and performance of the finish. Although applicant does not wish to be bound by the following theory, it is believed that iron pyrophosphate creates a synergistic effect with ultraviolet light stabilizers and antioxi¬ dants, yielding a period of outdoor weatherability surpassing that which would cumulatively be expected from a combination of the three types of additives.

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Thermosetting acrylic enamels prepared in the manner described and containing about 1-20% by weight, and preferably about 5-8% by weight, based on the weight of the film-forming constituents, of ultra- violet light stabilizer prove particularly useful in clear coat/color coat finishes. Such enamels may also contain about 0.1-5% by weight, and preferably about 0.1-1% by weight, of antioxidant. Where an antioxidant is used, the weight ratio of ultraviolet light stabil- izer to antioxidant ranges from about 1:1 to about 50:1 and is preferably about 10:1.

The novel coating compositions of this in¬ vention can be applied to a variety of substrates, e.g., metal, wood, glass, and plastics such as polypro- pylene, styrene, and copolymers of styrene, by any of the usual application methods, e.g. , spraying, electro¬ static spraying, dipping, brushing, flow coating, and the like. Preferably, the coating composition is applied over a suitably primed metal substrate. These coatings can be air dried or can be baked to mini¬ mize the drying period. The resulting coating is about 1-5 mils thick, preferably 1-3 mils thick, and can be rubbed or polished in accordance with conven¬ tional techniques, if desired, to ^' improve smoothness or apparent gloss or both.

After the novel coating composition is ap¬ plied, the coating preferably is cured at about 125-175 ^β C. for about ^' 15-30 minutes. By the addition of conventional catalyst to the novel composition, the curing temperature can be reduced to 80-110°C. Typical catalysts that can be used are butyl acid phosphate, paratoluene sulfonic acid _} and the like.

EXAMPLE A steel substrate is coated with a chip-resistant primer and a primer surfacer which is sanded as appropriate to obtain the desired - finish. Then the base coat or color coat is sprayed thereon, to a thickness of 15 ym and allowed to dry a few minutes until it is dry to the touch. Than the clear coat is sprayed on to a dry film thickness of 40-45 ym, let stand for 10 minutes, then baked 20 minutes at 130 ^β C.

Compositions known in the art can be - used for the chip resistant primer and the primer surface. Although the same is true for the color coat, preferably it is made by blending the following ingredients by known techniques and reacting them at reflux:

Weight Parts Dynopol M700 polyester 13.80

Maprenal M650 melamine 4.45 Cellulose acetate butyrate solution (CAB) 29.32

Isobutylacetate 5.26

Uresin B polymeric platicizer

(Hoechst) 2.00 Tinuvin 900 UV stabilizer

(Ciba Geigy) 0.2

Tinuvin 292 UV stabilizer 0.2

EVA Wax 6.53

Aluminum flake millbase 16.86 Butyl cellosolve acetate 4.00

(and desired colorants) This gives a solidscontent for the color coat of 25% solids of:

Polyester 46.9

Mela ine 11.33

CAB 33.83

Wax 6.84 _^ The color coat is reduced 70-100% with butyl- acetate to facilitate spraying.

The clear coat includes an acrylate resin by blending the following ingredients and reacting them by heating I to reflux, about 650°C, then adding II and refluxing for 8 hours.

Weight Parts I Solvesso 100 (Ξxxor. Chemicals) 35.00

Phthalic anhydride 3.60

II Cardura E (Shell Chemical) 6.00 Styrene 6.00

Methyl methacrylate 7.80.

Butyl methacrylate 12.00

Hydroxy ethyl acrylate 11.10

Ethyl hexyl acrylate 12.00 Phthalic anhydride 1.50-

Acrylic acid • 1.50

Solvesso 100 5.00

Tertiary butyl perbenzoate 2.77 to give a solids content of 60.19% and a Gardner- Holdt viscosity of J.

The acrylate resin at 60% solids is then blended with melamine and solvents as follows:

Weight Parts Acrylate resin 43.43 Luwipal 015 melamine resin (BASF) 23.04 Tinuvin 900 UV stabilizer 0.2

Tinuvin 292 UV stabilizer 0.2

Solvents:

3utyl acetate 4.73

X iene 4.55

Butanol 1.20 Solvesso 100 4.35

Butyl cellosolve acetate 2.70 Cellulose acetate 4. 00 and these diluted with xylene 10.00

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