THERMOSET ACRYLIC COATINGS HAVING IMPROVED GLOSS RETENTION

The present invention pertains to acrylic polymers containing hydroxybutyl acrylate and to coat¬ ings prepared therefrom.

Thermoset acrylic coatings have been employed in the automobile industry for top- coatings on automo¬ biles. While these coatings are very durable and withstand extreme variations in temperature and moisture environments, there is a need to improve their weatherability in terms of gloss retention.

The present invention provides a method for improving the gloss retention of thermoset acrylic coatings by replacing at least a portion of the hydroxy functional component with hydroxybutyl acrylate or hydroxybutyl methacrylate or a combination thereof.

One aspect of the present invention concerns an acrylic polymeric composition comprising

(I) a curable polymer resulting from polyermizing a mo'nomer composition consisting of

(A) at least one polymerizable

onoethylenically unsaturated ester of a saturated aliphatic or aromatic monocarboxylic acid in an amount of from 0 to 40, preferably 0 to 14, percent by weight of the total weight of the monomer composition;

(B) at least one polymerizable alkyl or aryl ester of a monoethylenically unsaturated monocarboxylic acid in an

10 amount of from 30 to 60, preferably 40 to 54, percent by weight of the total weight of the monomer composition;

15 (C) at least one polymerizable hydroxyalkyl ester of a monoethylenically unsaturated • monocarboxylic acid in an amount of from 10 to 40, preferably.25 to 39. -

20 percent by weight of the total weight of the monomer composition,

(D) at least one polymerizable monoethylenically unsaturated monocarboxylic acid free of ester

25 groups in an amount of from 0 to 3 _> preferably 1 to 2, percent by weight of the total weight of the monomer composition;

(E) acrylonitrile, methyacrylonitrile or

30 mixture thereof in an amount of from 0 to 15, preferably 0 to 14, percent by weight of the total weight of the monomer composition;

35 (F) at least one polymerizable alkyl or aryl ester of a monoethylenically

unsaturated dicarboxylic acid in an amount of from 0 to 20, preferably 0 to 14, percent by weight of the total weight of the monomer composition; and (G) at least one polymerizable monoethylenically unsaturated aromatic monomer free of acid and ester groups in an amount of from 0 . to 50, preferably 20 to 34, percent by weight of the total weight of the monomer composition; and (II) a suitable solvent or mixture of solvents wherein component(I) is present in an amount of from 40 to 80, preferably 65 to 75., percent by weight of the total weight of the polymeric composition and component • (II) is present in an amount of from 20 to 60, preferably 25 to 35, percent by weight of the total weight of the polymeric composition characterized by employing 2- hydroxybutyl acrylate or 2-hydroxybutyl methacrylate or a combination thereof as at least a portion of component (C) in an amount such that at least 75 equivalent percent of the hydroxyl groups contained in component (C) is derived from 2- hydroxybutyl acrylate, 2-hydroxybutyl methacrylate or a combination thereof.

For the purposes of this application, the terms "aromatic" and "aryl" shall refer to "the six-carbon ring characteristic of the molecules of all organic compounds of benzene and related series, or the

condensed six-carbon rings of naphthalene, anthracene, phenanthrene, etc." as defined by the CONDENSED

CHEMICAL DICTIONARY, Reinhold Publishing Corp., page

108 for "aromatic nucleus" and page 112 for "aryl".

Another aspect of the present invention pertains to an acrylic coating composition comprising

(A) one or more of the aforementioned polymeric compositions and (B) a curing quantity of one or more curing agents for component (A).

Another aspect of the present invention pertains to an article coated with one or more layers of the aforementioned acrylic coating compositions.

The acrylic polymers of the present invention can be prepared by polymerizing a mixture of the monomers in the presence of a suitable catalyst or mixture of catalysts and In the presence of a suitable solvent or mixture of solvents. The temperature can be from 70°C to 165°C, preferably from 125°C to 150°C.

Suitable polymerizable monoethylenically unsaturated monocarboxylic acids which can be employed herein include, for example, acrylic acid, methacrylic acid, crotonic acid, vinyl benzoic acid, or mixtures thereof.

Suitable polymerizable alkyl or aryl esters of monounsaturated monocarboxylic acids which can be employed herein Include, for example, ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, butyl acrylate, butyl methacrylate, amyl acrylate, amyl methacrvlate, hexyl acrylate, hexyl

methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, or mixtures thereof.

Suitable polymerizable monoethylenically unsaturated esters of saturated aliphatic or aromatic monocarboxylic acids which can be employed herein include, for example, vinyl acetate, vinyl propionate, vinyl benzoate, allyl acetate, allyl propionate, allyl benzoate, or mixtures thereof.

Suitable hydroxyalkyl esters of monoethylen¬ ically unsaturated monocarboxylic acids which can be employed herein include, for example, hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxyethyl meth- acrylate, hydroxypropyl methacrylate, 2-hydroxybutyl acrylate, 4-hydroxybutyl acrylate, 2-hydroxybutyl methacrylate, or mixtures thereof.

Suitable polymerizable alkyl or aryl esters of monoethylenically unsaturated dicarboxylic acids which can be employed herein include, for example, diethyl maleate, dibutyl maleate, diethyl fumarate, dibutyl fumarate, di( -ethylhexyl) maleate, di(2-ethyl- hexyl) fumarate, or mixtures thereof.

Suitable polymerizable monoethylenically unsaturated aromatic monomers which can be employed herein include, for example, styrene, a methyl styrene, t-butyl styrene, chlorostyrene, vinyl toluene, or mixtures thereof.

Suitable solvents which can be employed herein include, for example, aliphatic esters, alcohols, ketones, aromatic hydrocarbons, Cg to C- _j aliphatic or cycloaliphatic hydrocarbons, hydroxyethers, glycol ethers,, alkoxycarboxylic esters, or mixtures thereof.

Particularly suitable solvents include, for example, ethyl acetate, propyl acetate, butyl acetate, amyl acetate, octyl acetate, toluene, xylene, methyl ethyl ketone, methyl propyl ketone, methyl butyl ketone, methyl amyl ketone, 2-ethoxyethyl acetate, 1-methoxy- propyl-2-acetate, n-butanol, 1-methoxypropyl-2-propio- nate, 1-methoxypropyl-2-butyrate, 1-methoxy-2-propanol, 2-methoxy-1-propanol, 2-butyoxyethanol, 2-ethoxy- ethanol, octane, nonane, decane, undecane, dodecane, or

10 mixtures thereof.

Suitable polymerization catalysts or initiators which can be employed herein include, for example, organic peroxide and organic azo compounds such as, for

15 example, dicumyl peroxide, t-butyl peracetate, benzoyl peroxide, di-t-butyl peroxide, tertbutylazo(lsovalero- nitrlle) ethyl 3,3-di(t-amylperoxy)butyrate, 2,4- pentane- dione peroxide, 1 , 1 '-azαbis(cyclohexane

20 carbonitrlle) , or mixtures thereof.

Suitable curing agents which can be employed herein include, for example, melamine-formaldehyde resins, particularly the methylated form, hexamethoxy-

_?c- methyl melamine, or the mixed methylated/butylated forms; urea-formaldehyde resins; or poly(isocy- anate)compounds, such as isophorone diisocyanate as the free Isocyanate or in the blocked form, or mixtures thereof. Particularly suitable curing agents Include,

30 for example, hexamethoxymethyl melamine.

The coatings can be cured by heating at temperatures of from 70°C to 150°C, preferably from 100°C to 125°C in the presence of a suitable catalyst. 35

The coating compositions of the present invention can be applied to any suitable substrate which can withstand the curing conditions. They are particularly suitable for coating metals, previously 5 coated metals, composite structures such as polyester- -fiber glass, epoxy resin-fiber glass, •extruded plastic objects having softening points above the bake tempera¬ tures and the like.

10 The coating compositions of the present invention can also ^' contain, if desired, pigments, fillers, dyes, flow and leveling agents, flatting agents, curing 'catalysts, and the like in any combina¬ tion.

¹ 5

The following examples are illustrative of the invention but are not to be construed as to limiting the scope thereof in any manner.

20 EXAMPLE 1

A. Preparation of Polymer

In a conventional glass polymerization vessel

_?c . was charged 257 g of 2-ethoxyethyl acetate solvent.

After heating to reflux temperature (145°C) with stirring, a mixture consisting of 87.6 g of styre-ne,

87.6 g of methyl methacrylate, 265 g of butyl acrylate,

142.5 g( 1 hydroxy equivalent) of hydroxybutyl acrylate,

30 29.4 g of acrylic acid and 18 g of tertbutylazo(iso- valeronitrile) was added dropwise over a period of 6.75 hours at 140°C to 150°C. The mixture was maintained at

150°C for 5.25 hours ^" more and then cooled and stored in a suitable container. 35

The above procedure was repeated substituting one at a time the following hydroxyalkyl acrylate or methacrylate monomers for the hydroxybutyl acrylate.

116.4 g (1 hydroxyl equiv.) of 2-hydroxyethyl acrylate 130.5 g (1 hydroxy equiv.) of 2-hydroxypropyl acrylate 130.5 g (1 hydroxy equiv.) of 2-hydroxyethyl methacrylate 142.5 g (1 hydroxy equiv.) of 2-hydroxypropyl methacrylate

The properties of the resulting copolymers are given in the following Table I.

.,

TABLE I

Hydroxy Alkyl olecular Monomer Appearance Viscosity Non-Vol. M Wt cp/Pa-s % Mw' ^! Mn

2-HEΛ ¹ * clear, 5080/5.08 70.0 9800 2400 yellow

2-HPΛ ^: * clea , 3560/3-56 ^' 69.2 6100 2200 yellow

2-1IBA' clea , 2860/2.86 69.1 5700 2200 I yellow I

2-HEMΛ ¹ * faintly 5050/5.05 70.1 5630 2180 turbid

2-HPMΛ * faintly 5050/5.05 69.8 3880 1540 turbid

*Not an example of the present invention '2-hydroxypropyl methacrylate '2-hydroxyethyl acrylate ^r, Mw = weight average molecular weight - ^' 2-hydroxypropyl acrylate Mn = number average molecular weight '2-hydroxybutyl acrylate '2-hydroxyethyl methacrylate

B. Preparation of White Pigmented Baking Enamel

The copolymer prepared In A above was formu¬ lated Into a white baking enamel by blending in a one pint (237 ml) paint can by means of a high-shear mechanical disperser, known as a Cowels Dissolver, the following components.

ENAMEL RECIPE

Pigment Grind

copolymer solution from A above 146 g

Cymel ^* 325*, curing agent 42.6 g n-butanol, solvent 32.1 g methyl amyl ketone, solvent 17.4 g

Dow-Corning Paint additive #57 0.-.6 g 20, p-toluenesulfonic acid in I-propanol 0.11 g

TiPure R-902 TiO, pigment 111 g

*Cymel ^Θ 325 is hexamethoxy methyl melamine commercially available from American Cyanamid Co.

Diluent

methyl amyl ketone to provide the coating with a viscosity of 120 cp (0.12 Pa"s)

C. Coating Substrate and Baking Enamel

The five enamels prepared as above were air- sprayed onto primed 24-gauge (0.7 mm) Bonderite 40 panels to give dry-film thicknesses of 1.5-2.0 mils (0.0381-0.0508 mm) after baking 20 minutes at 150°C. These coated panels were then exposed outdoors on a rack facing south and inclined 45° to the vertical, in Freeport, Texas. The panels were tested after twenty months' exposure for gloss retention and after thirty months' exposure for gloss retention and chalking. The results are given in the following Tables II and III. The thirty month evaluation was more detailed than the twenty month evaluation. The gloss measurements were taken as is, after rinsing with deionized water, and after washing with- deionized wate and a* soft cotton cloth. Gloss measurements were made at both 60° and 20°C. The coatings were tested for chalking before rinsing and the forward impact resistance was measured for comparison to the original values.

TABLE II TWENTY MONTH EXPOSURE

Hydroxy ou . oss

Alkyl Gl .OSS ! Retention

Monomer of Original

Initial After 20 Mos. %

2-HEA ¹ * 91 41 ^' 45

2-HPA ² * 93 38 41

2-HBA ^"1 91 63 69

2-HEMA ⁴ * 92 61 66

2-HPMA ⁵ * 92 58 63

*Not an example of the present invention ^l 2-hydroxyeth l acrylate -2-hydroxypropyl acrylate ^:t 2-hydrox butyl acrylate ^l 2-hydroxyethyl methacrylate ^-hydroxypropyl methacrylate

TABLE III THIRTY MONTH EXPOSURE

Proper y 2 2_-IHEA ¹ * 2 -HPA-* 2-HBA ¹ 2-HEMA ¹ * 2-HPMA^*

Original 60°

Gloss, % 88 92 94 92 92

Gloss Retention, %

60°

Unrinsed 20 20 31 31 22

Rinsed 20 20 33 34 29

Washed 19 15 24 29 26

20°

Rinsed 3 4 6 12 10

Washed 2 3 3 9 7

Chalking slight ight sliglit none very slight

Forward Impact

Resistance

Original, in-lb/J 16/1.81 12/1.36 14/1.58 14/1.58 16/1.81 Final, in-lb/J 6/0,68 7/0.79 5/0.56 8/0.90 7/0.79

* ot an example of the present invention '2-hydroxyethyl acrylate -2-hydroxypropyl acrylate '2-hydroxylbutyl acrylate '2-hydroxyethyl methacrylate 2-hydroxypropyl methacrylate