CA1256630A

CA1256630A - Acrylic polyurethane coating composition

Info

Publication number: CA1256630A
Application number: CA000470422A
Authority: CA
Inventors: Joseph A. Vasta; Eric C. Houze
Original assignee: EI Du Pont de Nemours and Co
Current assignee: EIDP Inc
Priority date: 1983-12-19
Filing date: 1984-12-18
Publication date: 1989-06-27
Also published as: AU583486B2; AU3682684A; BE901299A; US4503175A; NZ210597A; ZA849858B

Abstract

Acrylic Polyurethane Coating Composition ABSTRACT
A coating composition in which the binder contains the following:
(1) an acrylic polymer having pendent hydroxyl containing ester groups and (2) a polyisocyanate which has the formula where R4 is a hydrocarbon group having 6 carbon atoms.
The composition can be used as an unpigmented clear finish or can contain convention pigments and be used as a colored finish. The composition is useful for refinishing trucks and automobiles and as an original finish for trucks, automobiles, boats, outdoor equipment and the like since the resulting finish is glossy,durable and weatherable.

Description

TITLE
FF-7856 Acrylic Polyurethane Coating Composition BACKGROUND OF THE INVENTION
This invention is directed to a polyurethane 5 coating composition and in particular to an improved acrylic polyurethane coating composition.
~ crylic polyurethane coating compositions are well known and ha~e been widely used to finish and repair finishes on automobiles and trucks. One 10 particular high quality acrylic polyurethane coating composition described in Vasta U.S. 3,558,564 issued January 26, 1971 has been widely used for finishing, refinishing and repairing automobiles and trucks.
Another high quality polyurethane finish containing 15 metallic flake pigments that provides excellent glamour ~nd a hiqh quality appearance and is used to finish automobiles and trucks is described in Crawley et al. U.S. Patent 4,131,571 issued December 26, 1978. There is a need for compositions with 20 improved durability and weatherability which is provide~
by this invention.
SUMMARY OF THE INVENTION
_ _ _ The coating composition has a binder solids content of 5-75~ by weiqht ~nd contains 95-25~ by weight 25Of an organic liquid; the solids consist essentially of about (1) 50-95% by weight of an acrylic polymer having a backbone of polymerized monomers of the group of styrene, alkyl methacrylate, ~lkyl acrylate or mixtures thereof, each having 1-12 carbon atoms in the alkyl groups and having polymerized ethylenically unsaturated ester units that form ester groups pending from the carbon ~toms of the backbone that ~!
comprise about 10 to 75~ of the total , ~

:~5~
weight of the polymer and are of ester group (A) - C - o ~ ~1 ~H
and ester group (B) which is either O O O OH
~ 2 ~ l - C- O - R ~ O- C- R - C~ O -CH2- C -H 1l 3 O O o ~ OH
~ 2 - C~-O - R - O -C - R ~ C~ C -CH2 o CH2 O~ - R
or a mixture of these groups; wherein the molar ratio of ester group (A) to ester 0 group (B) is from about 1:1.5 to 1:2.5;
and wherein Rl is a saturated hydrocarbon radical having 2-4 carbon ~toms, R2 is an aromatic radical, R3 is a tertiary hydrocarbon group having 8-10 carbon atoms; and

(2) 5-50% by weight of a polyisocyanate of the formula

3 ~2~$~

~R ~-NCO
~N~
~C~ ~C~
., I 1 ' .
OCN-tR~ R4~NCQ
10 . C ,' where R4 is a hydrocarbon group havin~ 6 ~toms.
DESCRIPTION OF THE INVENTION
.. _ . . ..
The composition contains about 5-75% by 20 weight of binder ~olids and ab~ut 95-25% by weight of an organic liquid. The binder solids of the composition are of about 50-95% by weight of an ~crylic polymer and 5-50~ by weight of ~ polyisocy~nate.
The acrylic polymer and the prepar~tion ~5 thereof is.disclosed in ~forementioned Vast~ patent.
Preferably, styrene and me.thylmethac~yla~e are used in the backbone. One particularly useful ~crylic polymer which foxms a high quality inish is ~ polymer of styrene/methyl methacryl~te/hydroxy ethyl acrylate/phthalic anhydride/~ mixed glycidyl ester of synthetic tertiary carboxylic ~cids of the formula /0\ O
CH2 - CH- CH2- 0~ ~R

where R3 is a tertiary aliphatic hydrocarbon of 8-10 carbon atoms; wherein the acrylic polymer has the aforementioned pendent ester groups (A) and (B) in the above molar ratio.
. The polyisocyanate used in the composition has the formula ~R4~-N~o / N \

oCN-(R4) - N~ j N - ~R4~-NCo C
a where R4 is a hydrocarbon group having 6 carbon atoms.
The above polyisocyanate is 1,3,5-tris(6-isocy~nato-~O hexyl)1,3,5-triazine 2,4,6(lH,3H,5H)trione. Commercially ~vailable polyisocyanate composition contain the above polyisocyanate 4nd small amounts of higher molecul~r weight moieties such as dimers, trimers, and hex~mers of the ab3ve polyisocyanate.
The composition can be used ~s ~ clear coat which is unpigmented or contains relatively small ~mounts of pigment having the s~me refractive index as the resulting finish such ~s ilica. These clear coats ~re generally used over ~ base coatO Usually the clear coat lOis applied over the base coat while the base coat i5 still wet ~nd then both coats are cured.
The composition c~n be pigmented in ~ pigment to binder weight ratio of about 0.1/100 to 100/100.
Conventional pigments cnn be used in the composition 15 such as metallic ~xides, preferably titanium dioxide, zinc oxide, iron oxide, and the like, metallic powders, metallic hydroxides, phth~locyanine pigments such as copper phthalocyanine blue or green, quinacridones, sulfates, carbonates, carbon blacks, silica, and 20 other pigments, organic dyes, lakes, and the like.
Metallic flake pigments used in the composition ~re ~ny of those pigments that pro~ide a finish with metallic ~lamour. These pigments include any of the conventional metallic fl~ke pigments, such as 25 aluminum flake, nickel flake, nickel-chrome flake, but also includes ~ire Frost* flake which is a polyester 1ake coated with a layer of vapor-deposited ~luminum ~nd Affl~ir* pigments which are mic~ flakes coat~d with titanium dioxide.
Generally, when metallic fl~ke pigments ~re used in the o~osition, absut 1-15~ ~y weight, kased on the weight of the binder, of cellulose ~cetate butyrate in ~ddi~ion to the akove binder constituents is used. The cellulose ~cetate butyrate used in the composition has a butyryl 35*denotes trade mark content of about 50-60% by weight, a hydroxyl content of 1.0-3~0% by weight and has a viscosity of about 0.02-500 seconds measured at 25~C According to ASTM D-1343-56. One preferred cellulose acetate 5 butyrate that forms a high glamour finish has ~ butyryl content of 53-55~ by weight and a viscosity of about 0.1-0.5 seconds and a hydroxyl content of 1.5~2.5 by weight.
The binder also can contain in addition - labout 0.05-1.0~ by weight, based on the weight of the binder of an alkyl acid phosphate having 1-12 carbon atoms in the alkyl ~roup, Typical alkyl acid phosphates are monoalkyl acid phosphates or mixtures thereof and have an acid No. of about 4-250 and are as follows:
methyl acid phosphate ethyl acid phosphate propyl acid phosphate isopropyl acid phosphate pentyl acid phosphate hexyl acid phosphate 2-ethylhexyl acid phosphate octyl acid phosphate nonyl acid phosphate decyl acid phosphate and lauryl acid phosphate.
Butyl acid phosphate is one preferred compound that provides a proper curing composition.
One technique for preparing this butyl phosphate is to react phosphorus pentoxide with butanol giving a product that has an acid number of about 100-150~
The coating composition can contain in addition to the above components about 0.5-5~ by weight, based on the weight of the binder, of ultraviolet light stabilizers. Preferably a blend of a benYotriazole and a hindered amine light stabilizer.

T~pical ultraviolet light stabilizers that are useful in the additive are as follows:
Benzophenones such as hydroxydodecycl benzophenone~ 2,~-dihydroxybenzo?hen~ne, hyd.roxy-~enzophenones c~ntainin~ sulfon~c aci~ ~roups, 2c4-dihy~roxy-3',5$-di-t-butylbenzo~henone, 2,2',4~-trihydroxybenzophenone esters o~ dicarboxylic acids, 2-hydrD~y~4-acrylo~ye-.hoxy~enzo~henone, aliphati~ mono-esters ~f 2~2~4-~rihydroxy-4l-alkoxybenzophenone~ 2-10 hydro~y-4-methoxy-2!-car~oxy~enzophenon~;
Triazoles such as 2-phenyl-4-t2'-4' dihydroxy-benzoyl)triazoles, subs~ituted ~onzotriazoles such as hydroxyphe~yltriaz~les such as 2-~2 7 hydroxy-5'-m~hylphenyl3benzo~riazole, 2-~2'-hydroxyphen~l)benzo-15 triazole, 2-~2~-hydroxy~ ctylphenyl)naphthotriazole;
Trizzines such as 3,5-aialkyl~4-hydroxyphenyl d~ri~at;~es of triazine, sul~ur-~ontaining ~eriva~ives ~ dialkyl-4-hydro~yphenyltriazines, hydroxyp~enyl-- 1~3,5-triazines and ~uch tria2ines containing sulfonic 20 acid groups, aryl-1,3,5-triazines. orthohydrox~aryl-s-triazine;
Benzoa~es such 2S- di~enzoate of diphenylolpro-pan2,' t-but~l ben~oate oE diph2~ylolpropane, nonyl phenyl benzoa~e, octyl phenyl benzoate, resorcin~l 25 dibenzoate.
Oth~r ultraviolet liskt stabilizers that can be used includ~ lower alkyl.khi~.e,hylene-containing phenols, substi~utea benzenes such as 1,3-bist2'-hydroxybenzoyllben~ene, metal ~erivatlves ~ 3t~,-di-t-30 bu~yl-4-hydro~yphen~rlpropionic acid, asymmetricalox~lic acid ~iaryla~ides, alkylhydroxyp~enylthioalka~oic acid esters~ dialkyl~ydroxyphenylalk2~0ic acid esters of ~i- and tri- pen~aery~hritol, phenyl- and naphthlene-s:~stitu~ed oxalic acid diamides, methyl-~ -t3~5-di-t-.

.

rj~6;~q~

~utyl-4-hyaroxyphenyl)propi~na.e, ~ bist2-hydrox~-phen~l)diisopropyl~enzene, 3,5l-dibromo-2'-hydroxy-acetophenone, ester derivatives of 4,4 bis~4'-hydroxy-ph~yl)pentanoic a~id wherein th2re is at lea5~ one 5 unsubstituted positi~n ~rth~ tv the aro~tic hyaro~yl grou~s, oxgano~hosphorus sulfi~es s~ch as bis(diphenyl-phosphinothioyl)monosulfide and bistdiphenylphosphino-th~oyl)dis~lfide, 4-benz~yl-6-taial~ylhydroxybenzyl) xesorcirlol, bis (3-hydroxy~ 2n.zoylphenoxy~ diphenylsi-:~lan~, bis~3-hydroxy-4-benzoylphenoxy)dial~ylsilane, 1,8-naph~halimides, ~-cyano- ~ dipheny~acrylic acid deri~atives, bis~2-benzoxazolyl)21~anes, bis(2-~apthoxa-20iyl~ al~anes, m~thylene malonitriles containing aryl and hetero yGlic ~ubstitut~s, alkylenebis(dithio~car-l~zma~e~ 4-benzoyl-3-h~dr~xyphenQx~e~hyl acrylate~ 4-b~nzoyl-3-hyaroxyphenoxye~hyl ~et~acryla~e, aryl- ~r alkyl-subs~ituted ~crylonitriles, 3-me~hyl-~-isopropyl-phenyl-6-hy~roxycoumarone. .
Particularly useful ultraviolet light .~ stabilizers that can be used are hindered amine~
of piperidyl deriYatives such as those disclosed in Murayama et al., U.S. Patent 4,061,616, issued December 6, 1g77, ~olumn 2, line 65, through column 4, line 2, and nickel ~ompounds such as 25 ~I-phenyl-3-methyl-4-decanoylpyrazolate(5~]-~i, bisrphenyldithiocarbamato~Ni(II~, and others listed in the abo~e patent, ~olumn 8, line 44 through line 55.
The following ultraviolet light stabilizers 30 are particularly preferred: bis(1,2,2 t 6,6-pentamethyl-

4-piperidinyl)decane dioate a blend of 2-[2'-hydroxy-3',5'-1(1-1-dimethyl-propyl)phenyl~benzotri~zole and bis-14-(1,2,2,6,6-pentamethylpiperidyl)]2-butyl-2-1(3,5-t-butyl-4-hydroxyphenyl)methyl]-propanedioate.
, 35 The stabilizers can be used in any ratio however, a 1:1 ratio of benzotriazole to propanedioate is preferred.

~ 2~g66~

The coating composition can contain in addition to the above components about 0.01-0.10% by weight, based on the weight of the binder, of an organo metal catalyst. Typical organo metal catalyst are stannous dioctoate and alkyl metal laurates, such as alkyl tin laurate, alkyl cobalt laurate, alkyl manganese laurate, alkyl zirconium laurate, alkyl nickel laurate. The alkyl group can have from 1-12 carbon atoms. Particularly useful catalysts are dibutyl tin dilaurate and stannous dioctoate.
The coating composition also can contain in addition to the above components about 0.05-2% by weight, based on the weight of the binder, of poly 2-ethylhexyl acrylate. Another component that can be used in the coating composition is about 0.05-2% by weight, based on the weight of the binder, of polydimethyl siloxane. Both of these compounds are used to reduce surface imperfections in the dried and cured paint film.
Any of the conventional solvents can be used in the composition, such as toluene, xylene, butyl acetate, acetone, methyl isobutyl ketone, methyl ethyl ketone, and other aliphatic cycloaliphatic and aromatic hydrocarbons, esters, ethers, ketones, and the like. These solvents also can be used to reduce the composition to an application viscosity.
The coating composition is applied by conventional techniques such as brushing, spraying, dipping, flow coating and the like, and either dried at ambient temperatures or a elevated temperatures of 50-100C for 2-30 minutes. The resulting acrylic coating layer is about 0.1-5 mils thick. Usually about a 1-3 mil thick layer is applied.
The composition can be applied over a wide variety o~ substrates such as metal, wood, glass, plastics, primed metals, or previous coated or -~r i6~3~

painted met~ls. If used to repair an existing flinish, the cvmposition is usually ~pplied over ~n ~crylic primer ~urfacer. The composition can be ~pplied directly to an acrylic lacquer or enamel finish ~h~t has been sanded ~nd cle~ned with an aliphatic hydroc~rbon solvent. The composition can be applied as an original finish over an epoxy primer or other conventional primers or can be applied directly to bare met~l. It is preferred to have the ~et~l surf~ce tre~ted with ~ phosphate.
The ~ollowing Examples illustrate the invention. The parts and percentages ~re by weight unless otherwise specified.

An acrylic resin solution was prepared 15 following the te~chings of Ex~mple 1 of the afore-mentioned Vasta patent. The resulting acrylic resin solution has a 55% polymer solids content in a solvent blend of 89~ ethylene glycol monoethyl ether acetate, 11% VM and P naphtha of an acrylic polymer of 20 styrene/methyl methacrylate/hydroxyethyl acryl~te/
Cardur~* E ester!phthalic ~nhydride in a weight ratio of 30~15/16.5/25/13.5 ~Cardura" E ester (a mixed ester described in U.S. Patent No. 3,275,583, issued September ~7, 1966, and is a glycidyl ester 25 of ~ F,ynthetic tertiary carboxylic Acid of the formula O\ O
CH2--C~--~CH2--O-- C ~R3 where R3 is ~ terti~ry ~liphatic hydrocarbon ~roup of 8-10 carbon atoms).

*denotes trade mark ; "` 11 ~ ~ 5~
~crylic polym~r 501ution 1 was prepared by bl~ndiny the follot~in~ constituentS:
. Parts hy ~7ei~ht Acrylic resin solution(prepare~ 56.24 (above) : . Ethylene ylycol monoethyl ether 21.50 acetate Toluene 5.42 Ethyl acetate 13.46 Bis-[4-(1,2,2,6,6-pent~methyl 0.31 piperidyl)]-2-bu~yl-2-[(3,5-t-but~1-4-hydroxyphenyl) methyl~-propanedio2te 2-t2'-hydroxy-3',5'~ 1-dimethyl 0.31 propyl)phenyl]benz~triazole 15 Dibutyltindilaurate solutior. (~.2% 1.83 solids in ethyl ~cetate) M~daflow* solution (10% solids of 0.31 poly 2-ethyihe~:yl acrylate~
Polydimethy siloxane solution Q.62 C5% solids in xvlene) Total 100.~0 A pGlyisocyanate solution w~s prepared by blen~ing together the foilowing constituents.
Parts by Weight Desm~d~r* N3390(polyisocy2nate 42.4 havin the ~tructure described previo.~sl~ ~nd is 1,3,5-tris(6-: isocyan~tohexyl)l,3,5-triazine 2,4,6(1~, 3H, 5H trione and small a~ounts of hi~her molecular we~ght moietiQs) Ethyl acetate 57.6 Total 100.0 Clear paint 1 was formulated by blending ,he foilowing:

.

*denotes trade mark Parts by - Weight _ Acrylic polymer solut7On 1 80.2 ~prepared above) Polyisocyanate solution 1 19.8 (prepared above) Total 109.0 The above clear paint 1 was sprayed ~n a steel panel coated with a pi~mented acrylic lacquer b~se coat. The resulting coated panel was dried at ambient temperatures. The resulting coatins had an outstandin~ appearance, excellent gloss measured at 20 and 60 and excellent distinctness OI
imzge. Flexibility,adhesion, chip resistance, recoat properties, chemical resiscance, humidity lS resistance and durability were measured and were at a level acceptable for commercial clear paint.
Acrylic polymer solution 2 was prepared by blending the follo~ing constituents:
Pz~rts by Weight P.crylic resin solution(prepared 48.75 above) Ethylene 31ycol monoethyl ether 21.52 ace~ate Tol~tene 5~4 25 rtnyl ~cetate 13.48 Xylene 7 ~9 Bis-[4-(1,2,2,6,6-pentamethyl 0.27 piperidyl)]~2-butyl-2-[~3,5~t-butyl-4-hydro.Yyphenyl) meth~ propanedioate 2-[2'~.ydro~y-3',5'-1(1-1 dimet~vl- 0O27 propyl)pnenyl3ben~otriazole Dibut~ltindilaurate solution(o.2~ solids 1.59 in eth~l acetate) t'~odaflow" solution(described above)0.27 Po ymethyl siloxane solutior 0.54 3~ ~described above) Total 100.00 .

~ polyisocyanate solution 2 was prep~red by blending the following consti~uents:
Parts by

5 "Desmodur" N 3390 ~described above) 64.7 Ethyl acetate 35.3 _ Total 100.0 Clear paint 2 was fo~mul2ted by blend~ng the followin~ constituerlts:
Parts by Wei~ht Acrylic polymer solu,ion 2 88.3 ~prepared above) Polyisocyanate solution 2 11.7 (prepared above) _ _ Total 100.0 - The abcve clear paint 2 was sprayed on a s~eel panel coated with 2 pig~.ented acrylic enamel base coat. ~he resulting coated panel was dried .at ambient temperatures. The resulting coating h2d an outstanding appearance, excelleni gloss measured ~t 20 and 60~, excellent distinctness of i~;a~e. Flexibility, adhesion, chip r~sistance, recoat properties, chemical res.~stance, humidit~
resistance and durability were r,easured and were at a le~el acceptable for ~ cc~mercial clear pai~t.
~ white pigmented acrylic polymer composition was prepared ~s ollows:
Parts by Portion 1 Weight _ Acrylic polymer solution 8.80 30 (prepared above) Titanium dioxide pigment 26.40 Ethylene glycol monoether ~.76 ether acetate Fumed silica 0.04 Parts by Portion II Wei~ht Acrylic polymer solution 41.10 (prepared above) "Modaflow~' solution (described 0.25 (above~
Polymethyl siloxane solution 0.50 ~described above) Ethyl acetate 12~60 Dibutyltindilaurate solution 1.55 (described above) Total100.00 Portion 1 is premixed ~nd charged into a conventi~nal sand mill and ground to fineness of 0.1 microns. Portion 2 is premixed ~nd then portion 1 is added to portion 2 with mixing to form a white pigmented composition.
Polyisocyan~te solution 3 was formulated by blending the following constituents:
Parts by Weight "Desmodur" N 3390(described 82.6 above) Butyl ~cetate 8.7 Solvess~ lOO(hydrocarbon 8.7 solv~nt) ~ot~l lOOo O
25A white paint was prepared by thoroughly blending the following:
P~rts by ~ei~ht White pigmented acrylic polymer 89.8 composition (prepared above) 30 Polyisocyanate solution 3 10.2 _ Total 100.0 The white paint was reduced to ~ spray viscosity with conventional ~olvents ~nd sprayed onto steel panels primed with a pigmented alkyd resin primer ~nd dried at ambient temperatures. The *denotes trade mark 3~

resulting coating was about 2-3 ~ils thick. The resulting coating had an outstanding appe~rance, excellent gloss and distinctness of image and commercially acceptable chip resistance, humidity resistance, chemical resistance and durability.
A second white paint was formulated using the indentical ingredients as above except the biuret of hexamethylene diisocyanate was substituted for the "Desmodur" N 3390 and the resulting paint was reduced to a spray viscosity and applied to steel panels ha~ing the same ~lkyd resin primer as above~
The resulting coating was dried ~t ambient temperatures and the dried coating was about 2-3 mils in thickness.
The panels coated with the white paint snd panels coated with the second white paint were exposed to weathering in Florida and the % glos~ retain at 20 was measured. The results are ~s follows:

% Gloss Re ~ n (m~Nred at 20 . ~ . _ . . .

6 months 12 months 18 months Ex~osure ExFosure E~sure ~hite Paint 93 85 42 (invention) ~nd White Paint 92 70 22 (prior art3 The panels prepared with white paint of this invention retained substantially higher percent of gloss on weathering in Florida in comparison to the second white paint which is representative of the art.

Claims

1. A coating composition having a binder solids content of 5-75% by weight and 95-25% by weight of an organic liquid; wherein the binder consists essentially of about (1) 50-95% by weight, based on the weight of the binder, of an acrylic polymer having backbone of polymerized monomers selected from the group consisting of alkyl methacrylate, alkyl acrylate each having 1-12 carbon atoms in the alkyl group, styrene or mixtures thereof and having polymerized ethylenically unsaturated ester monomers that form ester groups A and B pending from he carbon atoms of the polymer backbone and comprise about 10 to 75% of the total weight of the acrylic polymer and the ester groups consisting essentially of ester group (A) and ester group (B) selected from the group consisting of or mixtures thereof, wherein the molar ratio of ester group (A) to ester (B) is from about 1:1.5 to 1:2.5; and wherein R1 is a saturated hydrocarbon group having 2-4 carbon atoms, R2 is phenylene, R3 is a tertiary hydrocarbon group having 8 through 10 carbon atoms; and (2) 5-50% by weight, based on the weight of the binder, of a polyisocyanate consisting of a polyisocyanate of the formula where R4 is a hexylene group.

2. The coating composition of claim 1 containing in addition about 0.05-1.0% by weight, based on the weight of the binder, of an alkyl acid phosphate.

3. The coating composition of claim 2 in which the alkyl acid phosphate is butyl acid phosphate.

4. The coating composition of claim 1 containing in addition about 0.01-0.10% by weight, based on the weight of the binder, of an organo metal catalyst.

5. The coating composition of claim 4 in which the catalyst is dibutyltin dilaurate.

6. The coating composition of claim 1 containing in addition about 0.5-5% by weight, based on the weight of the binder, of ultraviolet light stabilizer.

7. The coating composition of claim 6 in which the ultraviolet light stabilizer is a blend of a benzotriazole and a hindered amine light stabilizer.

8. The coating composition of claim 1 containing in addition pigment in a pigment to binder ratio of about 0.1/100 to 100/100.

9. The coating composition of claim 8 in which the pigment contains metallic flake pigments.

10. The coating composition of claim 9 containing in addition 1-15% by weight, based on the weight of the binder, of cellulose acetate butyxate having a butyryl content of about 50-60% by weight, a hydroxyl content of about 1.0-3.0% by weight, and a viscosity of 0.02-5.0 seconds measured at 25°C.
according to ASTM D-1343-56.

11. The coating composition of claim 10 containing in addition about 0.05-1.0% by weight, based on the weight of the binder, of an alkyl acid phosphate, 0.5-5% by weight, based on the weight of the binder, of a blend of ultraviolet light stabilizer of a benzotriazole and a hindered amine light stabilizer and 0.01-0.10% by weight, based on the weight of the binder, of an alkyl tin laurate catalyst.

12. The coating composition of claim 1 wherein (1) the acrylic polymer has a backbone of styrene and methyl methacrylate and ester group A is from hydroxy ethyl acrylate and ester group B
is from hydroxy ethyl acrylate, phthalic anhydride and a mixed glycidyl ester of a tertiary carboxylic acid and wherein R1 is (CH2)2, R2 is phenylene R3 is a tertiary hydrocarbon group having 8 through 10 carbon atoms;
and (2) the polyisocyanate is 1,3,5-tris(6-isocyanatohexyl)1,3,5 triazine 2,4,6(1H,3H,5H)trione, and contains in addition 0.05-1.0% by weight, based on the weight of the binder, of butyl acid phosphate; and 0.01-0.10% by weight, of a dibutyl tin dilaurate catalyst.

13. The coating composition of claim 12 containing in addition 0.5-5% by weight, based on the weight of the binder, of a blend of ultraviolet light stabilizers consisting of 2-[2-hydroxy-31, 51-1(1-1-dimethylpropyl)phenyl3benzotriazole and bis-[4-(1,2,6,6-pentamethylpiperidyl)]2-butyl-2-[(3,5,-t-butyl-4-hydrGxyphenyl)methyl]-propanedioate.

14. The coating composition of claim 13 containing in addition about 0,05-2% by weight, based on the weight of the binder, of polydimethyl siloxane.

15. The coating composition of claim 14 containing in addition about 0.05-2% by weight, based on the weight of the binder of poly 2-ethyl hexyl acrylate.

16. The coating composition of claim 12 containing in addition 0.5-5% by weight, based on the weight of the binder, of an ultraviolet light stabilizer consisting of bis(1,2,6,6-pentamethyl-4-piperidinyl)decane dioate.

17. The coating composition of claim 12 containing in addition pigment in a pigment to binder ratio of about 0.1/100 to 100/100.

18. A substrate coated with a layer of the composition of claim 1 containing pigment in a pigment to binder ratio of about 0.1/100 to 100/100 and having superimposed thereon a layer of a clear composition of claim 1.

19. A substrate coated with a layer of the composition of claim 1 containing pigment in a pigment to binder ratio of about 0.1/100 to 100/100 and having super imposed thereon a layer of a clear composition of claim 1 containing a blend of ultra-violet light stabilizers of a benzotriazole and a hindered amine light stabilizer.