GB2325935A - Hydrophilic resin and water-based paint - Google Patents

Abstract

For providing heat-curable water-based paints with high structural viscosity and improving their resistance to sagging and poping, a copolymer of a carboxyl-terminated (meth)acrylate ester monomer, a hydroxyl-containing ethylenically unsaturated monomer and an acrylic monomer containing a saturated hydrocarbon group containing 6 to 18 carbon atoms, optionally together with another ethylenically unsaturated monomer is grafted onto a hydroxyl-terminated polyester resin by transesterification, the acryl-grafted polyester resin is neutralized with a base and dispersed in an aqueous medium, together with a curing agent and a pigment.

Description

HYDROPHILIC RESIN AND WATER-BASED PAINT FIELD OF THE INVENTION The present invention relates to a hydrophilic resin, a water-based paint comprising the same, a method of coating which comprises applying said composition, and a coated article BACKGROUND ART From the concern about environmental pollution, the interest in paints free of any organic solvent is mounting.

One proposed solution is the use of water-sed paints.

One of the problems intrinsic in water-based paints is that the workability and the appearance of finished surfaces are readily influenced by humidity. Thus, in a high humidity environment, sagging and poping tend to appear. detracting from the finish appearance. This is particularly serious in the field of automobiles, for instance, where high regard is paid to the appearance.

Sagging and poping are related to the viscosity and nonvolatile matter content of the paint at the time of application. Thus, the higher the viscosity or nonvolatile matter content is, the less liable is the occurrence of sagging and poping. However, at the time of coating. the viscosity must be decreased to a level at which coating is possible but such a low viscosity can hardly be reconciled with a high nonvolatile matter content. One means for solving this problem comprises using the vehicle resin in the form of a dispersion system, such as aS emulsion or a sol, to thereby provide for structural viscosity. This leads to a decrease in apparent viscosity coefficient upon application of a shear stress at the time of coating, so that the workability requirement can be satisfied. After covering the article to be coated and removal of the shear stress, the apparent viscosity coefficient increases, making sagging difficult to occur. Since no drastic decrease in nonvolatile matter content is required, the problem of poping can be solved as well. The increase of apparent viscosity of the coating film on the substrate is not dependent on the evaporation of water and therefore the occurrence of sagging and poping is not influenced by the humidity in the painting environment.

A number of water-based paints embodying the above idea have so far been proposed. These can be roughly classified into two categories: in one, a particle suspension comprising a different component is added, as typically disclosed in Japanese Kokai Tokkyo Koho H04-25582 and H08-12925 and, in the other, a resin suspension is used in which cores made of a hydrophobic resin are each coated with a shell made of a hydrophilic resin, as typically disclosed in Japanese Kokai Tokkyo Koho H04-233926 and H07-74320. However, these cannot simultaneously satisfy the requirements concerning the degree of expression of structural viscosity, storage stability of paints1 and performance characteristics of cured coating films inclusive of water resistance.

The water-based paint of the present invention belongs to the latter category, namely the resin suspension type comprising the core of a hydrophobic resin and the shell of a hydrophilic resin and yet can satisfy all the requirements concerning the expression of structural viscosity, storage stability, and performance characteristics of cured coating films. i SUMMARY OF THE INVENTION The present invention provides a hydrophilic resin which comprises 50 to 90% by weight of an acrylic resin (A) and 50 to 10 % by weight of a polyester resin (B), said acrylic resin (A) being graft-bonded to said polyester resin (B) by means of transesterification, wherein said acrylic resin (A) comprises of a carboxyl-terminated acrylic monomer (a), a hydroxylcontaining acrylic monomer (b) and an acrylic monomer (c) containing a saturated hydrocarbon group containing 6 to 18 carbon atoms, and has an acid value of 10 to 100, a hydroxyl value of 50 to 300 and a number average molecular weight of 5,000 to 100,000.

The present invention also provides a water-based paint which comprises said hydrophilic resin and a curing agent, both dispersed in an aqueous medium containing a neutralizing base.

The present invention also provides a method of coating by two coat one bake technique which comprises applying the above water-based paint to a substrate and then applying a clear paint, followed by baking.

In a still further aspect, the present invention provides a coated article having a coat resulting from application of the water-based paint mentioned above.

DETAILED DESCRIPTION OF THE INVENTION.

The above-mentioned carboxyl-terminated acrylic monomer (a) is such that the position of the carboxyl group is remote from the carbon atoms constituting the main chain, and said acrylic monomer (c) containing a saturated hydrocarbon group containing 6 to 18 carbon atoms contains a saturated hydrocarbon group which is bulky and hydrophobic. Therefore, when said hydrophilic resin is neutralized and dispersed in water, the carboxyl group remote fro the main chain of monomer (a) serves to increase the thickness of the hydrated layer of the shell, while the bulky saturated hydrocarbon group of monomer (c) interacts with another such group in water in the manner of mutual repulsion. As a result, said hydrophilic resin acquires a high structural viscosity and the thixotropy index (TI value) increases.

Said hydroxyl-containing acrylic monomer (b) has a hydroxyl group capable of reacting with the curing agent when a water-based paint containing the above hydrophilic resin is constituted. Therefore, said monomer serves to satisfactorily attain the fundamental performance characteristics required of water-based paints.

Said hydrophilic resin contains the hydrophobic resin (B) graft-bonded by transesterification and thus has a structure different from the core/shell structure resulting for mere blending. Therefore, it is stable against phase separation and contributes to the improvement in storage stability as water-based paints and in performance characteristics of coating films.

The acrylic resin (A) to be graft-bonded to polyester resin (B) can be produced by copolymerizing the carboxyl-terminated acrylic monomer (a), the hydroxyl-containing acrylic monomer (b) and the acrylic monomer (c) containing a saturated hydrocarbon group containing 6 to 18 carbon atoms. When necessary, another ethylenically unsaturated monomer (d) may be added as a comonomer in the above copolymerization.

As said carboxyl-terminated acrylic monomer (a), there may be mentioned, among others, half esters resulting from the reaction of a hydroxyalkyl (meth)acrylate and a carboxylic acid anhydride.

The term "(meth)acrylate" as used herein means a methacrylate and/or acrylate.

As said hydroxyalkyl (meth)acrylate, there may be mentioned,1 for example, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate.

Said carboxylic acid anhydride includes succinic anhydride, glutaric anhydride, maleic anhydride, phthalic anhydride, hexahydrophthalic anhydride and trimellitic anhydride, among others.

As other examples of said carboxyl-terminated acrylic monomer (a), there may be mentioned reaction products from a hydroxyalkyl (meth)acrylate-E- caprolactone adduct and a carboxylic acid anhydride and, further, reaction products from a hydroxyalkyl (meth)acrylate-neopentyl glycol carbonate adduct and a carboxylic acid anhydride, among others.

A commercial grade of 2-hydroxyethyl acrylate- -caprolactone is available from Daicel Chemical Industries, Ltd. under the trademark Placcel FA-1, and a commercial grade of a 2-hydroxyethyl methacrylate E -caprolaetone adduct is also available from the same supplier under the trademark Placcel FM-1. Reaction products from a hydroxyalkyl (meth)acrylate-neopentyl glycol carbonate adducts and carboxylic acid anhydrides are disclosed in Japanese Kokai Tokkyo Koho H08-157424.

Said neopentyl glycol carbonate is also called 5.5dimethyl-2-oxo-1,3-dioxane or dimethyl-trimethylene carbonate.

Hexahydrophthalic anhydride is preferred.as said carboxylic acid anhydride. As regards said carboxylterminated acrylic monomer (a), it is preferred that the carboxyl group is remote from the polymerization site.

Therefore, reaction products from hydroxyalkyl (meth)acrylate-neopentyl glycol carbonate adducts and carboxylic acid anhydrides are preferred.

The carboxyl-containing monomer (a) may occur as a single compound or a mixture. For the copolymers to have a sufficieritly high structural viscosity, it is preferred, however, that a monomer comprising an ring-opened form of neopentyl glycol carbonate as disclosed in Japanese Kokai Tokkyo Koho H08-157424 account for at least 30 mole percent of the whole of monomer (a).

Specific examples of monomer (b) are, typically those hydroxyalkyl (meth)acrylates such as hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, 4hydroxybutyl acrylate, Placcel FA-1, Placcel FM-1 and hydroxyalkyl (meth)acrylate-neopentyl glycol carbonate adduct.

Specific examples of monomer (c) are alkyl (meth)aerylates containing 6 to 8 carbon atoms such as hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate and stearyl (meth)acrylate, and cyclohexyl (meth)acrylate. Mention may also be made of adducts of glycidyl (meth)acrylate and an alkanoic acids containing 6 to 18 carbon atoms, such as caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid and stearic acid. Mention may further be made of adducts of (meth)acryl isocyanate and alkanols containing 6 to 18 carbon atoms, such as 2-ethylhexanol, lauryl alcohol and stearyl alcohol.

Specific examples of said another ethylenically unsaturated monomer (d) are (meth)acrylate esters such as methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, t-butyl (meth)acrylate and isobutyl (meth)acrylate, styrene and derivatives thereof, such as styrene, a -methylstyrene and vinyltoluene, nitrile and amide monomers such as acrylonitrile, acrylamide, N,N-dimethyl(meth)acrylamide and N,N- dibutyl(meth)acrylamide, and olefins such as ethylene and propylene.

Since the copolymer should have an acid value of 10 to 100, preferably 20 to 60, and a hydroxyl value of 50 to 300, preiferably 60 to 250, the monomer composition has to meet these requirements. Specifically, a monomer composition with which a desired acid value and hydroxyl value can be obtained may be selected by using 2 to 60% by weight, preferably 4 to 40% by weight, of monomer (a), 2 to 40% by weight of monomer (b), 30 to 80% by weight1 preferably 40 to 60% byweight, of monomer (c), and monomer (d) accounting for the balance.

It is recommended that the copolymer have a number average molecular weight of 5,000 to 100,000, preferably 10,000 to 80,000. The polymerization may be carried out by the solution polymerization technique. The acrylic resin (A) is bound to the polyester resin (B) in the manner of grafting. For that purpose, the polymerization for producing (A) may be carried out in a solution of polyester resin (B) synthesized in advance, or both resins may be separately synthesized and bound together by transesterification. In the latter case. both resins in the form of solutions are mixed together and heated at 130 to 200t.

As is well known, the polyester resin is produced by subjecting a polybasic carboxylic acid and a polyhydric alcohol, as essential components, to polycondensation.

It may contain, as other components, a small proportion of a monocarboxylic acid, a hydroxycarboxylic acid, a lactone and/or the like.

Examples of the polybasic carboxylic acid are aromatic polybasic carboxylic acids and anhydrides, such as phthalic anhydride, isophthalic acid, terephthalic acid, trimellitic anhydride, tetrabromophthalic anhydride, tetrachlorophthalic anhydride and pyromellitic anhydride; alicyclic polybasic carboxylic acids and anhydrides, such as hexahydrophthalic anhydride. tetrahydrophthalic anhydride and 1,4- and 1,3-cyclohexanedicarboxylic acid; and aliphatic polybasic carboxylic acids and anhydrides, such as maleic anhydride, fumaric acid, succinic anhydride, adipic acid, sebacic acid and azelaic acid. These may contain one or more of hydroxybenzoic acid, hydrgxypivalic acid, 12hydroxystearic acid and the like: and monocarboxylic acids, such as benzoic acid and t-butylbenzoic acid, in small proportions.

The polyhydric alcohol includes diols such as ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 2,2diethyl-1,3-propanediol, neopentyl glycol, 1,9 nonanediol, 1,4- cyclohexanedimethano 1, neopentyl glycol hydroxypivalate, 2-butyl-2-ethyl-1,3-propanediol, 3methyl-1,5-pentanediol, 2,2,4-trimethylpentanediol and hydrogenated bisphenol A; and polyols which are at least trihydric, such as trimethylolpropane, trimethylolethane, glycerin and pentaerythritol.

Ifis also possible to react a polyester resin with a monoepoxide compound such as Cardura E10 (glycidyl versatate, product of Shell Chemical Company), YOA10, YOA20 or YOA30 (a-olefin monoepoxide, product of Daicel Chemical Industries, Ltd.).

Preferably, the polyester resin (B) has an acid value of less than 15 and a number average molecular weight of 1,000 to 101000.

The polyester resin with the acrylic resin grafted thereupon should comprise 50 to 90% by weight, preferably 60 to 80% by weight1 of acrylic resin (A) and 50 to 10% by weight, preferably 40 to 20% by weight, of polyester resin (B). Upon neutralization with a base for dispersing in an aqueous medium, these proportions allow the formation of a dispersion with a core/shell structure, which shows a high structural viscosity.

The polyester resin after grafting has a number average molecular weight of 9,000 to 200,000, preferably 40,000 to 150,000 and an acid value of 20 to 90, preferably 30 to 70. Said range of number average molecular weight is the range within which dispersion in water is possible and strong and durable coating films can be formed. Said acid value range, too, is the range within which dispersion in water is possible and a desired high structural viscosity can be attained.

Water-based paint The thus-produced acryl-modified polyester resin is neutralized with a base and dispersed in water. The neutralizing base is used in an amount of 0.3 to 1.4 equivalents, preferably 0.5 to 1.2 equivalents, relative to the acid value of the resin. Usable as the base are inorganic bases such as alkali metal hydroxides and aqueous ammonia; and amines such as methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine. triethylamine, isopropylamine, diisopropylamine, diethylenetriamine, triethylenetetramine. monoethanolamine, diethanolamine, 2-methyl-2aminopropanol, morpholine, N-methylmorpholine, Nethylmorpholine, piperazine, dimethylethanolamine. diethylethanolamine and dimethyldodecylamine. Among these, triethylamine, dimethylethanolamine and diethylethanolamine are preferred.

Paint preparation can be carried out by dispersing a curing agent, a pigment and one or more conventional additives in the aqueous varnish comprising the thusneutralized acryl-modified polyester dispersed in aqueous medium.

Curing agents for polyester resins are well known in the field of paints. One class includes amino resins, more specifically di-, tri-, tetra-, penta- and hexamethylolmelamine and alkyl etherification products derived therefrom (the alkyl being methyl, ethyl, propyl, isopropyl, butyl, isobutyl and the like), ureaformaldehyde condensates, urea-melamine cocondensates and the like. Preferred are melamine resins.

When an amino resin is used as the curing agent, a sulfonic acidr such as paratoluenesulfonic acid, dodecylbenzenesulfonic acid or dinonylnaphthalenesulfonic acid: and a salt of such a sulfonic acid with an amine which dissociates at the baking temperature for coating films can be used as a catalyst.

A blocked polyisocyanate compound derived from the corresponding polyisocyanate by blocking with a blocking agent may also be used as a curing agent.

Examples of the polyisocyanate compounds are aliphatic diisocyanates such as hexamethylene diisocyanate (HMDI) and trimethylhexamethylene diisocyanate; alicyclic diisocyanates such as isophoronediisocyanate (IPDI); araliphatic diisocyanates such as xylylene diisocyanate (XDI): aromatic diisocyanates such as tolylene diisocyanate (TDI) and 4,4'-diphenylmethanediisocyanate (MDI); dimers and trimers of these diisocyanates; and adducts of said diisocyanates with a polyhydric alcohol such as trimethylolpropane or with water.

The blocking agent includes oximes such as methyl ethyl ketoxime, acetoxime, cyclohexanone oxime, acetophenone oxime and benzophenone oxime; phenols such as m-cresol and xylenol; alcohols such as methanol, ethanol, butanol, 2-ethylhexanol, cyclohexanol and ethylene glycol monoethyl ether; lactams such as -caprolactam; diketones such as malonic acid diesters and acetoacetic acid esters; and mercaptans such as thiophenol. Polyisocyanate compounds blocked with diketones (active methylene-containing compounds) are preferred. When blocked polyisocyanate compounds are used, a tin compound such as dibutyltin dilaurate may be added as a catalyst.

The wiater-based paint of the present invention may contain one or more conventional pigments. Examples thereof are color pigments and glitters or luster pigments, such as titanium dioxide, zinc oxide, carbon black yellow iron oxide, various lake pigments1 aluminum flake and titanium mica; and extenders pigment. such as calcium carbonate, barium sulfate and clay. The pigments, together with a resin for dispersion, are worked up into pigment pastes, which are then added, together with another or other ingredients, to water varnishes. Other conventional additives such as antipoping, dispersants and surface modifiers may of course be added.

The water-based paint of the present invention is particularly suited for use in providing base coats which are used in finishing coating of automotive bodies, for instance. In this coating process, the metallic or solid color base paint according to the present invention is applied to the surface provided with an electrodeposition coating and an intermediate coat, and a solution-type, water-based or powder clear coat paint is further applied thereonto in the wet-on-wet manner, whereafter both can be baked simultaneously for finishing.

EXAMPLES In the following production examples and examples, "part(s)" and '1%' are on the weight basis, unless otherwise specified.

Polyester rein (B) Product ion Example 1 A reaction vessel was charged with 613 parts of 1,9-nonanediol, 114 parts of trimethylolpropane, 105 parts of adipic acid and 536 parts of phthalic anhydride, together with 30 parts of xylene. The temperature was raised and the water formed by the reaction was removed by azeotrokic distillation with xylene.

From the beginning of reflux, stirring and dehydration were continued while the temperature was raised to 190t over about 2 hours, until the acid value corresponding to the carboxylic acids amounted to 85.

The reaction mixture was then cooled to 140t. While maintaining this temperature, 205 parts of Cardura E10 (glycidyl versatate, product of Shell Chemical Company) was added dropwise over 30 minutes, followed by 2 hours of stirring for completing the reaction. A polyester resin with an acid value of 5, a hydroxyl value of 120 and a number average molecular weight of 2,350 was obtained.

Carboxyl-terminated acrylic monomer (a) Product ion Example 2 A reaction vessel was charged with 130 parts of 2-hydroxyethyl methacrylate, 154 parts of hexahydrophthalic anhydride and 0.142 g of 4-methoxyphenol, and the contents were heated to 120t while blowing air thereinto. The same temperature was maintained for 30 minutes with stirring and air bubbling and, after confirmation by IR spectrometry of disappearance of the acid anhydride absorption at about 1,800 cm-1, the reaction mixture was cooled. By adding the liquid obtained dropping to methanol, it was confirmed that no gel component was contained. Furthermore, molecular weight calculation was performed based on the measured acid value. whereupon it was confirmed that the calculated value and theoretical value were in agreement.

Production Example 3 A carboxyl-terminated acrylate ester monomer was synthesized from 4-hydroxybutyl acrylate and phthalic anhydride in the same manner as in Production Example 2. i Production Example 4 A carboxyl-terminated methacrylate ester monomer was synthesized from Placcel FM-1 (2-hydroxyethyl methacrylate/ E -caprolactone (1/1) adduct, product of Daicel Chemical Industries, Ltd.) and succinic anhydride in the same manner as in Production Example 2.

Production Example 5 A carboxyl-terminated methacrylate ester monomer was synthesized from a 2-hydroxyethyl methacrylate/neopentyl glycol carbonate (1/1) adduct and hexahydrophthalic anhydride in the same manner as in Production Example 2.

Acrylic resin (A) Production Example 6 A reaction vessel was charged with 40.0 parts of S-150 (aromatic hydrocarbon solvent, product of Shoei Kagaku Kogyo) and 21.3 parts of methyl isobutyl ketone (MIBK), the temperature was raised to 100t with stirring in a nitrogen atmosphere, and a mixture of 7.3 parts of 2-ethylhexyl methacrylate, 48.8 parts of the monomer prepared in Production Example 5 and 1.5 parts of Kayaester O (initiator, product of Kayaku Akzo) was added dropwise at a constant rate over 3 hours. After completion of the dropping, stirring was continued for 30 minutes and then a solution composed of 0.15 part of Kayaester 0 and 20 parts of S-150 was added dropwise at a constant rate over 30 minutes. After completion of the dropping, stirring was continued for 1 hour to drive the reaction to completion. An acrylic resin with an acid value of 46.8, a hydroxyl value of 117.4 and a number molecular weight of 67,000 was obtained.

Production1 Examples 7 to 12 Modifying the formulation, acrylic resins shown in Table 1 were obtained in the same manner as in Production Example 6.

Table 1

Production Example 6 7 8 9 10 11 12 S-150 40.0 30.0 30.0 30.0 30.0 30.0 30.0 MIBK 21.3 13.0 13.0 13.0 13.0 13.0 13.0 HEA1) 21.3 30.0 25.0 12.0 20.8 - 4-HBA2) - - - 18.2 - 40.0 40.0 MAA3) - - 2.0 6.1 - - EHMA4) 71.3 22.0 - - 62.5 50.0 56.3 ST5) - 4.0 48.0 53.0 9.1 21.3 15.0 Monomer of Prodn.Ex. 2 - - - - 29.8 - Monomer of Prodn.Ex. 3 - - - - - 28.3 Monomer of Prodn.Ex. 4 - - - - - - 63.5 Monomer of Prodn.Ex. 5 48.8 44.0 25.0 10.7 - - Kayaester 0 3.0 1.0 1.0 1.1 1.0 0.7 4.0 Acid Value 46.8 59.6 46.9 54.3 48.2 47.0 59.2 Hydroxyl Value 117.4 233.7 194.8 164.4 132.6 111.6 89.2 Number average Molecular weight 22,000 62,000 49,000 55,000 58,000 74,000 10,000 1) HEA : 2-ethlhexyle acrylate 2) 4-HBA: 4-hydroxybutyl acrylate 3) MAA : methacrylic acid 4) EHMA: 2-ethylhexyl mathacrylate 5) ST : styrene Hydronhilic resin Production Example 13 A reaction vessel was charged with 20 parts of S-150, 17 parts of MIBK and 20 parts of the polyester resin prepared in Production Example 1, the temperature was raised to 100or with stirring in a nitrogen atmosphere and a mixture of 17 parts of 2-hydroxyethyl acrylate, 57 parts of 2-ethylhexyl methacrylate, 39 parts of the acrylic monomer prepared in Production Example 5 and 1.2 parts of Kayaester 0 was added dropwise at a constant rate over 3 hours. After completion of the dropping, stirring was continued for 30 minutes and then a solution composed of 0.12 part of Kayaester 0 and 20 parts of S-150 was added dropwise at a constant rate over 30 minutes. After completion of the dropping, stirring was continued at the same temperature for 1 hour. Thereafter, the reaction temperature was raised to 1409 and, while maintaining the temperature, stirring was continued in a nitrogen atmosphere for 4 hours. An acryl-grafted polyester resin with an acid value of 40, a hydroxyl value of 80 and a number average molecular weight of 99,000 was obtained.

The reaction mixture was cooled to 609=, the nitrogen stream was discontinued, and the mixture was neutralized to a neutralization degree of 100% with dimethylethanolamine (DMEA) and stirred for 30 minutes.

Thereto was added deionized water at a constant rate over 1 hour so that the nonvolatile matter content amounted to 25%. Stirring was further continued for 1 hour while maintaining the temperature at 60t to give a water-based varnish. The varnish had a thixotropy index (TI value) of not less than 4, showing a high structural viscosity.

Production Examples 14-18 and Comparative Examples 1 and 2 Modifying the formulation, water varnishes shown in Table 2 were obtained in the same manner as in Production Example 13.

Table 2

Comparative Production Example Example 1 2 13 14 15 16 17 18 Polyester resin 20 20 20 50 20 33 20 20 S-150 28 28 40 28 28 28 28 28 MIBK 12 12 17 12 12 12 12 12 HEA 17 17 17 15 20 8 - 4-HBA - - - - - 12 17 17 MAA 6 6 - - 1.6 5 - EHMA 57 30 57 11 - - 40 45 ST - 27 - 2 38.4 35 17 12 Monomer of Prodn.Ex.2 - - - - - - 22.6 Monomer of Prodn.Ex.3 - - - - - - - 50.8 Monomer of Prodn.Ex.4 - - 39 22 20 7 - Kayaester 0 0.8 0.8 1.2 0.5 0.8 0.7 0.8 0.8 Acid Value 40 40 40 30 40 40 45 55 Hydroxyl Value 100 100 80 75 95 90 65 70 Number average Molecular weight 120,000 101,000 50,000 100,000 102,100 67,000 100,000 45,000 % Neutralization with DMEA 140 140 100 120 100 80 120 90 Viscosity of water Varnish (TI value) 2 1.8 > 4 > 4 > 4 3.7 2.7 2.8 Viscosity of water varnish : expressed in terms of the thixotropy index (TI) value TI value = (viscosity at 6 rpm)/(viscosity at 60 rpm)[20 C type B viscometer] Resin for dispersion Production Example 19 A reaction vessel was charged with 400 parts of diethylene glycol monobutyl ether (BDG) and, under stirring at 100t, a a monomer mixture composed of 100 parts of styrene, 172 parts of methyl methacrylate, 230 parts of lauryl acrylate, 219 parts of methyl acrylate, 218 parts of Placcel FM-1 (product of Daicel Chemical Industries, Ltd.), 61 parts of methacrylic acid and 10 parts of Kayaester 0 was added dropwise at a constant rate over 3 hours and, 30 minutes later, 50 parts of BDG and 3 parts of Kayaester 0 were further added dropwise over 30 minutes. At that temperature, the reaction was further conducted for 1 hour to give an acrylic resin with an acid value of 40, a hydroxyl value of 50 and a number average molecular weight of 17,000 (this is referred to as "resin for dispersion").

The thus-obtained resin for dispersion was heated to 85t with stirring and solubilized in water by adding 87 parts A reaction vessel was charged with 630 parts of xylene and the temperature was raised to 130t. Using a dropping funnel, a mixture of 200 parts of styrene, 450 parts of glycidyl methacrylate, 270 parts of methyl methacrylate, 80 parts of isobutyl methacrylate and 75 parts of Kayaester 0 was added dropwise at a constant rate over 3 hours. After completion of the dropping, the same temperature was maintained for 30 minutes. Then, a solution composed of 1 part of Kayaester 0 and 70 parts of xylene was further added dropwise over 30 minutes.

After completion of the dropping, the reaction was further continued at 130do for 1 hour. The xylene was then removed by distillation under reduced pressure to give an acrylic resin varnish.

2. Powder clear paint In a Henschel mixer (product of Mitsui Miike Machinery Co.), 70 parts of the acrylic resin varnish obtained in the above manner, 19.1 parts of decanedicarboxylic acid, 0.11 part of CF-1056 (product of Toray Dow Corning Silicone) and 0.89 part of. benzoin were dry-mixed. Then, the mixture was melted at 100t for effecting dispersion in a Cokneader PR-46 (product of Buss, Switzerland). After cooling the mixture was ground in a hammer mill and classified using a 150-mesh wire gauze to give a powder acrylic clear paint.

Example 1 to 6 and Comparative Examples 3 and 4 Water-based metallic base paints [1] to (8) were prepared according to the formulations shown in Table 3.

An aluminum pigment (Aluminum Paste NW-91-2061. aluminum metal pigment 62%, product of Toyo Aluminium) was uniformly blended in advance with the resin for dispersion, or with the pigment dispersion paste when it was added. The acryl-grafted polyester resin component and curing agent were mixed together in advance. When the melamine resin was used as the curing agent, it was mixed with the acryl-grafted polyester resin and dissolved in water on the occasion of dissolving said resin in water. Thereafter, the resin-curing agent mixture was uniformly blended with the pigment and other components. Then, the additive was further added, and the water-based metallic base paints were prepared using a stirrer at room temperature. The aluminum pigment was added in an amount of 11.4 to 12.5 parts per 100 parts of the resin solids. In Table 3, C-212 indicates a Mitsui Cytec's methyl/butyl melamine resin curing agent, and BL-116 indicates a Sumitomo Bayer's blocked isocyanate curing agent. BYK-341 indicates a BYK Chemie Japan's silicone antipoping agent.

Table 3

Comparative Production Example Example 3 4 1 2 3 4 5 6 - Water based metallic [1] [2] [3] [4] [5] [6] [7] [8] Base paint Comparative Example 1 66.5 - - - - - - Comparative Example 2 - 66.5 - - - - - Production Example 13 - - 66.5 - - - - Hydrophilic Production Example 14 - - - 66.5 - - - Resin Production Example 15 - - - - 49.5 - - Production Example 16 - - - - - 66.5 - Production Example 17 - - - - - - 66.5 Production Example 18 - - - - - - - 66.5 Curing agent C-212 28.5 - - 28.5 28.5 28.5 28.5 28.5 BL-116 - 28.5 28.5 - - - - Pigment dispersion - - - - 4.1 - - Paste Aluminium pigment 10 10 10 10 10 10 10 10 Resin for dispersion 5 5 5 5 17 5 5 5 Additive BYK-341 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 Viscosity of water varnish(TI value) 1.3 1.1 3.4 3.3 2.9 2.4 2.5 2.4 In the table, the amount of the resins are on the solids basis Viscosity of water vanish : expressed in term of the thixotropy index (TI) value TI value = (viscosity at 6 rpm)/(viscosity at 60 rpm)[20 C ,type B viscometer] Evaluation Tests To the water-based metallic base paints [2] and [3] was added 1 part of Nacure 5225 (amine-blocked acid catalyst, product of King Industries Inc.). The viscosity was then adjusted to 60 seconds (Ford cup No.

4) by dilution with deionized water. The water-based metallic base paints (1] and [4] to [8] were subjected to viscosity adjustment in the same manner without adding the acid catalyst. The thus-viscosity-adjusted water-based metallic base paints [1] to [8] were applied, by spraying to a dry film thickness of 10 to 50 Am, to steel sheets provided beforehand with an intermediate coat, followed by drying at 80t for 10 minutes.

Then, a clear paint was applied to a dry film thickness of 40 tcm. After 5 minutes of setting, the base coat and clear coat were simultaneously baked at 140t for 30 minutes.

The paints of Examples 1 to 6 and Comparative Examples 3 and 4 were evaluated for workability by the method mentioned below. As regards the painting conditions, the temperature was 25t and two levels of humidity, namely 65% and 85t, were employed.

The water-based metallic base paints used were respectively evaluated also for storage stability by the method mentioned below. The results are collectively shown in Table 4.

Evaluation methods 1. Threshold film thickness for sagging The maximum film thickness at which no sagging-due film deficiency was observed on a coating film provided by gradient coating from 10 gm (thinnest portion) to 50 gm (thickest portion) was defined as the threshold film thickness for sagging. When the threshold film thickness for sagging was not less than 25 tLm, the paint was regarded as satisfactory. The paints of Examples 1 to 6 were all satisfactory.

2. Threshold film thickness for poping The maximum film thickness at which no poping-due film deficiency was observed on a coating film provided by gradient coating from 10 I'm (thinnest portion) to 50 gm (thickest portion) was defined as the threshold film thickness for poping. When the threshold film thickness for poping was not less than 25 gm, the paint was regarded as satisfactory. The paints of Examples 1 to 6 were all satisfactory.

3. Storage stability The initial stability immediately after dilution and the state of dispersion of the diluted paint after 10 days of standing at 40t were evaluated by the eye.

Table 4

Comparative Production Example Example 3 4 1 2 3 4 5 6 Clear paint PD O-150 O-150 O-150 O-150 PD PD O-150 Water-based metallic [1] [2] [3] [4] [5] 6] [7] [8] base paint Humidity Sagging limit ( m) 30 35 50 52 55 47 40 43 65% 26 24 30 33 37 36 28 29 Poping limit ( m) Sagging limit ( m) 10 13 45 47 48 44 36 35 Humidity 20 19 26 30 30 29 25 24 85% Poping limit ( m) Storage Stability Initial H H H H H H H H After Standing H PS H H H H H H Clear paint : PD---Powder clear paint O-150---Nippon Paint*s melamine clear paint superlac o-150 Sagging limit : threshold film thickness for Sagging Poping limit : threshold film thickness for Poping H : homogeneous PPS : partially sedimented

Claims (10)

1. A hydrophilic resin which comprises 50 to 90% by weight of an acrylic resin (A) and 50 to 10% by weight of a polyester resin (B), said acrylic resin (A) being graft-bonded to said polyester resin (B) by means of transesterification. wherein said acrylic resin (A) comprises a carboxyl-terminated acrylic monomer (a), a hydroxyl-containing acrylic monomer (b) and an acrylic monomer (c) containing a saturated hydrocarbon group containing 6 to 18 carbon atoms, and has an acid value of 10 to 100, a hydroxyl value of 50 to 300 and a number average molecular weight of 5,000 to 100,000.

2. The hydrophilic resin according to Claim 1, wherein said carboxyl-terminated acrylic monomer (a) comprises a reaction product of one compound (a-1) selected from the group consisting of hydroxyalkyl (meth)acrylates, hydroxyalkyl (meth)acrylate- E caprolactone adducts and hydroxyalkyl (meth)acrylateneopentyl glycol carbonate adducts, with one carboxylic acid anhydride (a-2) selected from the group consisting of succinic anhydride, glutaric anhydride, maleic anhydride, phthalic anhydride, hexahydrophthalic anhydride and trimellitic anhydride.

3. The hydrophilic resin according to Claim 2, wherein at least 30 mole percent of said carboxylterminated acrylic monomer (a) comprises a reaction product oft said hydroxyalkyl (meth)acrylate-neopentyl glycol carbonate adduct, with said carboxylic acid anhydride (a-2).

4. The hydrophilic resin according to Claim 1, 2 or 3, wherein said hydroxyl-containing acrylic monomer (b) comprises at least one compound selected from the group consisting of 2-hydroxyethyl (meth)acrylate, 2hydroxypropyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate.

5. The hydrophilic resin according to Claim 1, 2, 3 or 4, wherein said acrylic monomer(c) containing a saturated hydrocarbon group containing 6 to 18 carbon atoms is one compound selected from the group consisting of alkyl (meth)acrylates containing 6 to 18 carbon atoms, cyclohexyl (meth)acrylate, reaction products of glycidyl (methTacrylate with an alkanoic acid containing 6 to 18 carbon atoms, and reaction products of (meth)acryl isocyanate with an alkanol containing 6 to 18 carbon atoms.

6. The hydrophilic resin according to Claim 1, 2, 3, 4 or 5, wherein said polyester resin (B) has an acid value of less than 15 and a number average molecular weight of 1,000 to 10,000.

7. A water-based paint which comprises the hydrophilic resin according to Claim 1, 2, 3, 4, 5 or 6, a curing agent and pigment, dispersed in an aqueous medium containing a neutralizing base.

8. A method of coating by two coat one bake technique which comprises applying the water-based paint according to Claim 7 to a substrate and then applying a clear paint, followed by baking.

9. A coated article having a coat resulting from application of the water-based paint according to Claim 7.

10. A hydrophilic resin substantially as hereinbefore described with reference to the Examples.