JPH01310773A - Top coat finishing method - Google Patents

Abstract

PURPOSE:To improve finish appearance and scratch resistance by applying thermosetting aqueous coating containing pigment on a surface to be coated and subsequently coating the coated surface with clear coating containing a specific polyisocyanate compound as a crosslinking agent. CONSTITUTION:A clear coating is prepared by using a polyisocyanate compound as a crosslinking agent and adjusting the crosslinking MW of a cured film to <=200 (a value measured based on a xylene swelling method). A surface to be coated is coated with thermosetting aqueous coating containing pigment and dried or cured to be coated with a aforementioned clear coating containing the polyisocyanate compound as the crosslinking agent. By preparing the clear film as mentioned above, scratch resistance and finish appearance are enhanced to a large extent. This clear coating can be pref. obtained based on a composition containing a hydroxyl group-containing resin and the polyisocyanate compound as main components.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a novel top coating finishing method, and more particularly to a coating finishing method that provides a coating film with excellent finished appearance and scratch resistance.

Conventional technology and its problems In finishing methods such as top coating of automobile exterior panels where aesthetic appearance is important, a thermosetting paint (base coat) containing a pigment is applied, dried or hardened, and then a clear coat is applied. A clear coating (top coat) that forms a film is applied, and both coatings or the clear coating are cured by heating. The one-to-one method) is often used.

However, the clear coating film in the two-coat system is easily scratched by collisions with sand and dust while driving or by friction from car wash brushes, etc., which is one of the causes of deterioration in appearance.
This is especially noticeable in dark colors such as black, navy blue, and red, and there is a strong demand for improvement in the scratch resistance of clear coating films in two-coat systems.

On the other hand, base 1 containing a large amount of organic solvent is a two-coat method.
・It is also being made water-based due to the need to save resources and prevent pollution. In such cases, for example, an aqueous base coat mainly composed of a base resin neutralized with a basic compound such as an amine is used, and an organic solvent containing an alkyl etherified melamine resin or a polyisocyanate compound as a crosslinking agent is applied to the coated surface. It is known to apply a type of clear paint (Japanese Unexamined Patent Publication No. 193676/1986). However, with clear paints using melamine resin, the crosslinking and curing reactivity of the clear paint film is inhibited by the basic compounds remaining in the base coat film, resulting in poor weather resistance and
It has been difficult to improve chemical resistance and other properties. On the other hand, clear paints using polyisocyanate compounds show almost no curing inhibition like the melamine resins mentioned above, but have insufficient scratch resistance and finished appearance.

Means for Solving the Problems The present inventors particularly aimed to improve the scratch resistance and appearance of the coating film in a two-coat system using a water-based base coat and a lubcoat containing a polyisocyanate compound as a crosslinking agent. As a result of intensive research, the inventors discovered that the objective could be achieved by reducing the molecular weight between crosslinks of the cured coating film of the top coat to a specific value or less, leading to the completion of the present invention.

That is, the present invention is a method in which a pigment-containing thermosetting water-based paint is applied to a surface to be coated, dried or cured, and then a clear paint containing a polyisocyanate compound as a crosslinking agent is applied to the painted surface, The present invention relates to a method for applying a top coat, characterized in that the clear paint is obtained by adjusting the crosslink molecular weight of the cured paint film to 200 or less (measured based on the xylene swelling method).

First, the clear paint used in the present invention will be explained.

The clear paint preferably uses a hydroxyl group-containing resin as a base resin, a polyisocyanate compound as a crosslinking agent, and has a crosslink molecular weight of 200 or less in a cured paint film measured by a xylene swelling method. It is.

The value of the molecular weight between crosslinks of the cured coating film of the clear paint is a value measured by the xylene swelling method described in the following method.

[Method for measuring molecular weight between crosslinks] ■The clear paint is applied using the same method as the original painting process, except that the object to be coated is a tin plate, and then heated and cured.

(2) Peel off the clear coating film using a tin plate using the mercury amalgam method to obtain a free clear coating film (film) approximately 4 cm x 4 cm in size.

■ Fill a desiccator with xylene, place a film on top of the liquid, and gently swell it with xylene vapor.

■Then, the film was immersed in xylene and heated at 25°C for 2 hours.
Soak for 4 hours to reach swelling equilibrium.

■Remove the film from the xylene and quickly remove the xylene from the surface of the film by placing it between filter papers.

■ Place the film in a weighing bottle that has been weighed in advance and weigh it (the weight of the swollen film is Ws).

■Remove the lid of the weighing bottle and place it in a vacuum drying mold to 10mgH.
Dry at 100°C for 3 hours at a temperature of 100 g or less (the weight of the dried coating film is Wd).

In addition, when the film is easily broken in xylene, it is preferable to place the film in a stainless steel wire mesh, a polyester net, or a porous paper bag and immerse it.

(2) Calculate the molecular weight between crosslinks (MC) using the following formula (F1ory-R1ner formula).

However, here, VR is the volume fraction of the resin in the swollen coating film, and is calculated by the following formula.

Wd Here, ψ is the density of the clear coating film (g/cm3), ψ
Haxylene density (0,8637g/cm"') (2
5°C).

■ O is the molar volume of xylene (123cc/mole
). X is F between xylene and clear coating resin
It is assumed that the Iory-Huggins interaction constant is 0.4.

In the present invention, it is essential that the crosslinking molecular weight of the coating film after heat curing of the clear coating material is 200 or less. As a result, it is possible to carry out a coating finishing method that provides a coating film with excellent finished appearance and excellent scratch resistance. ~50.

The molecular weight between crosslinks of a cured coating film of a clear paint using a polyisocyanate compound as a crosslinking agent, which is used in the conventional two-coat method, was 250 or more when similarly measured by the xylene swelling method.

By adjusting the clear coating film in this way, it is possible to ensure a wide range of improvement in scratch resistance, and a wide range of finished appearance.
was also realized, and the above objective was achieved.

Such a clear paint that forms a cured coating film with a low molecular weight between crosslinks is preferably obtained based on a composition containing a hydroxyl group-containing resin and a polyisocyanate compound as main components, and the hydroxyl group-containing resin has a low molecular weight. More preferably, it is made of an acrylic resin and/or polyester resin containing a polyol and a hydroxyl group, or a rough-modified acrylic resin containing a hydroxyl group. Preferred examples containing each of these components include the following (1), (2), and (2).

(A) A low molecular weight polyol with a weight average molecular weight of 400 to 2,000 and a hydroxyl value of -15 C) -400 mgKOH/g; (B) A hydroxyl group-containing acrylic resin with a weight average molecular weight of 5,000 to 50,000 and a hydroxyl value of 50 to 180 mgKOH/g. , and (C) a curable resin composition comprising a polyisocyanate-1 compound. Furthermore, it is preferable that the molecular weight distribution of the low molecular weight polyol as the component (A) is narrow in order to improve the scratch resistance.
Its weight average molecular weight (M W ) and number average molecular weight ff1 (
The ratio of yn) is preferably about 1.0 to 1.6.

(A) A low molecular weight polyol having a weight average molecular weight of 400 to 2,000 and a hydroxyl value of 150 to 400 mgKOH/g; (B) A low molecular weight polyol having a weight average molecular weight of 2,000 to 50,000 and a hydroxyl value of 50 to b and in the resin. A curable resin composition comprising a hydroxyl group-containing polyester resin having a cyclohexylene ring content of 7% by weight or more, and (C) a polyisocyanate compound.

It is preferable that the molecular weight distribution of the low molecular weight polyol as the component (A) is narrow in order to improve the scratch resistance, and its MW and M
The ratio of n is preferably about 1.0 to 1.6.

Component (A) and (B) of the preferred clear paint described above
) The ratio of components is 35 to 90% by weight of component A) and 6% of component (B) based on the total amount of (A) and (B).
The content is preferably 5 to 10% by weight. Component (C) consists of hydroxyl groups contained in components (A) and (B) and (C)
Based on the molar ratio with the isocyanate) group in the component,
/NGO-〇, 5 to 2.5, particularly preferably 0.7 to 2.0. Since component (C) may react with components (A) and (B) at room temperature and cause crosslinking and curing, it is preferable to separate the component in advance and mix it immediately before use. However, block type polyisocyanate compounds But that's not all.

(2) A curable composition comprising (A) a lactone-modified hydroxyl group-containing acrylic resin having a weight average molecular weight of 5,000 to 50,000° and a hydroxyl value of 50 to 180 mgKOII/g, and (B) a polyisocyanate compound.

The ratio of component (B) in (1) is based on the molar ratio of the hydroxyl group in component (A) and the isocyanate group in component (B),
This is the same range as (■) and (■) above.

The above clear paints ①, ② and ② will have the molecular weight between crosslinks specified above when heated and cured at about 120 to 160'C for about 10 to 30 minutes in the presence of an appropriate catalyst, and will have good scratch resistance and coating properties. A rear coating film with a good finished appearance can be obtained.

The component (B) used in the preparation of the clear paint mentioned in (1) above as a preferred example can be prepared in the same manner as in the synthesis of ordinary acrylic resins for paints.

That is, using various peroxide-based and azo-based initiators,
Solution polymerization or non-aqueous dispersion polymerization may be carried out at a temperature in the range of about 50 to about 180°C. Monomers that can be used include:
Any radically polymerizable unsaturated monomer can be used without particular limitation. Typical examples are as follows.

(a) Esters of acrylic acid or methacrylic acid: for example, methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, butyl acrylate,
Hexyl acrylate, octyl acrylate, lauryl acrylate, stearyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, butyl methacrylate, hexyl methacrylate, octyl methacrylate, -11= lauryl methacrylate , C1-18 alkyl esters of acrylic acid or methacrylic acid such as stearyl methacrylate; glycidyl acrylate, glycidyl methacrylate; 02-8 alkenyl esters of acrylic acid or methacrylic acid such as allyl acrylate and allyl methacrylate; hydroxyethyl acrylate, hydroxyethyl methacrylate , C2-8 hydroxyalkyl esters of acrylic acid or methacrylic acid such as hydroxypropyl acrylate and hydroxypropyl methacrylate; C3-18 alkenyloxyalkyl esters of acrylic acid or methacrylic acid such as allyloxyethyl acrylate and allyloxymethacrylate;

(b) Vinyl aromatic compounds: Examples include styrene, α-methylstyrene, vinyltoluene, p-chlorostyrene, vinylpyridine, and the like.

(C) α, β-ethylenically unsaturated acid; For example, acrylic acid, methacrylic acid, itaconic acid, etc.

(d) amides of acrylic acid or methacrylic acid; for example,
Acrylamide, methacrylamide, n-butoxymethylacrylamide, n-methylolacrylamide, n
-butoxymethylmethacrylamide, n-methylolmethacrylamide, etc.

(e) Others; For example, acrylonitrile, methacrylaterile, methyl isopropenyl ketone; vinyl acetate, beoba monomer
[Manufactured by Shell Chemical Co., Ltd.], vinyl propionate, vinyl pivalate, isocyanate ethyl methacrylate, perfluorocyclohexyl acrylate-1, perfluorocyclohexyl methacrylate, p-styrene sulfonamide, N-methyl-p-styrene sulfonamide, γ
-Methacryloxypropyltrimethoxysilane, etc.

Among these, 01 of (a) acrylic acid or methacrylic acid
It is preferable that the monomer component (B) contains at least 20% by weight of the -18 alkyl ester.

The acrylic resin can be used in the form of a solution type acrylic resin, a non-aqueous dispersion type acrylic resin, or a combination of both.

Component (B) used in the preparation of the clear paint mentioned in (1) above as a preferred example is produced by condensation reaction of polybasic acid and polyhydric alcohol as main components.

Examples of the polybasic acids used in the production of component (B) include phthalic acid, isophthalic acid, terephthalic acid, tetrahydrophthalic acid, tetrahydroterephthalic acid, hexahydrophthalic acid, hexahydroisophthalic acid, hexahydroterephthalic acid, het acid, trimellitic acid, hexahydrotrimellitic acid, pyromellitic acid, cyclohexanetetracarboxylic acid, methyltetrahydrophthalic acid, methylhexahydrophthalic acid, endomethylene hexahydrophthalic acid, methylendomethylenetetrahydrophthalic acid,
Maleic acid, fumaric acid, itaconic acid, succinic acid, glutaric acid, adipic acid, azelaic acid, cepatic acid, decanedicarboxylic acid, speric acid, pimelic acid, dimer acid (
tall oil fatty acid dimer), tetrachlorophthalic acid, naphthalene dicarboxylic acid, 4,4'-diphenylmethanedicarboxylic acid, 4,4'-dicarboxybiphenyl, etc., and their acid anhydrides and dialkyl esters, especially dimethyl ester, etc. can be mentioned.

Among the polyhydric alcohol components, examples of dihydric alcohols include ethylene glycol, propylene glycol, 1,4
-butanediol, 1,3-butanediol, 2,3-
Butanediol, 1,2-15-butanediol, 1,5-bentanediol, 1゜4-
Bentanediol, 2,4-bentanediol, 2,3
-dimethyltrimethylene glycol, 3-methyl-pentane-1,5-diol, 3-methyl-4,5-bentanediol, 2. 2,4-trimethyl-1,3-bentanediol, 1゜6-hexanediol, 1,5-hexanediol, 1,4-hexanediol, 2,5-
Hexanediol, 1,4-cyclohexane dimetatool, diethylene glycol, dipropylene glycol,
triethylene glycol, neopentyl glycol, hydroxypivalic acid neopentyl glycol ester,
Examples include polyalkylene oxide, bishydroxyethyl terephthalate, and alkylene oxide adducts of (hydrogenated) bisphenol A. Furthermore, monoepoxy compounds such as Cardigan E10 (manufactured by Shell Chemical Co., Ltd.), α-olefin epoxide, and butylene oxide can also be used as a type of glycol.

Examples of the trivalent or higher polyhydric alcohol include glycerin, trimethylolpropane, trimethylolethane, diglycerin, pentaerythritol, dipentaerythritol, and sorbitol.

Furthermore, compounds having both carboxylic acid and hydroxyl groups in the molecule can also be used. Examples of such compounds include dimethylolpropionic acid, pivalic acid, 12-hydroxystearic acid, and ricinoleic acid. Also ε−
Lactones such as caprolactone and γ-valerolactone are also cyclic ester compounds and therefore belong to the above-mentioned category of compounds.

In addition, various natural and synthetic higher fatty acids, higher alcohols, benzoic acid, pt-butylbenzoic acid, and other monofunctional raw materials and natural oils can also be used in part.

Among these raw materials, it is best to limit the amount used of natural oils and fats that contain unsaturated bonds in their molecules, maleic acid, fumaric acid, dimer acid, tetrahydrophthalic anhydride, etc. from the viewpoint of weather resistance. .

The polyester resin preferably contains about 7 to 50% by weight of cyclohexylene rings based on the solid content of component (B). In research conducted by the present inventors, it has been found that by containing a cyclohexylene ring within this range, scratch resistance and weather resistance are particularly improved.

Examples of raw materials used to introduce a cyclohexylene ring into the resin include hexahydrophthalic acid (anhydride), hexahydroisophthalic acid, hexahydroterephthalic acid,
Examples include cyclohexane dimetatool, cyclohexene oxide, methylhexahydrophthalic acid (anhydride), and the like. Among these, resins obtained using hexahydroisophthalic acid are particularly preferred.

Examples of the low molecular weight polyol as component (A) in the coating composition of (1) and (2) mentioned above as a preferred clear coating composition include the compounds described below. The molecular weight distribution of the low molecular weight polyol is preferably such that MW/Mn is about 1.0 to 1.6 from the viewpoint of improving scratch resistance.
This doesn't necessarily have to be the case.

(i) A branched low-molecular-weight polyester polyol obtained by condensing organic acid components and alcohol components used in the production of ordinary polyester resins for paints as raw materials.

As the raw materials used in the synthesis of the polyester, all the raw materials used in the synthesis of component (B) in the above-mentioned preferred clear paint (1) can be used.

The low molecular weight polyester polyol is a branched type.

In order to obtain a branched structure, the raw materials used need to contain a trihydric or higher polyhydric alcohol and/or a polybasic acid.

In producing a branched low molecular weight polyester polyol with a narrow molecular weight distribution using raw materials such as those listed in Section 2,
Although there are cases in which it is sufficient to simply adopt a conventional method for producing polyester, in many cases, the following special measures are required regarding the synthesis method, selection of raw materials, purification of the product, etc. As a modification of the synthesis method, for example, in the presence of a suitable catalyst such as p-toluenesulfonic acid or monobutyltin hydroxide, an inert solvent with a high boiling point (for example, an alkylbenzene-based solvent with a boiling point in the range of 130 to 250 °C) is used. is present in a large amount (for example, about 30 to 150 parts by weight per 100 parts by weight of the polyester resin component), and the solvent is refluxed in a solution state for a long period of time (for example, 15 to 40 hours).
It is preferable to synthesize a polyester polyol using the following steps.

By this method, the molecular weight distribution of the resulting polyester polyol can be narrowed to -20. In addition, as a method of selecting raw materials, for example, raw materials that can be synthesized using only addition reactions with a fast reaction rate (for example, Cardura E10 [manufactured by Shell Chemical Co., Ltd.]
and trimellitic acid, phthalic anhydride, trimethylolpropane, etc.), the molecular weight distribution can be sharpened. More specifically, for example, by adding 3 moles of a monoepoxy compound to 1 mole of trimellitic acid,
A polyester polyol with a narrow molecular weight distribution can be obtained. In addition, for product purification, for example, a method of fractional precipitation (cutting off high molecular weight components) in which a suitable poor solvent (e.g. petroleum ether) is added to a solution of a low molecular weight polyester polyol, or a solution of a low molecular weight polyester polyol in a large amount of a poor solvent. A reprecipitation method (cutting of low molecular weight components) in which the resin is precipitated by adding a
It is possible to adopt a method of fractionation that takes advantage of the fact that the solubility of a resin in a medium in its critical state changes greatly depending on pressure and temperature.

The weight average molecular weight of the low molecular weight polyol [component (A)] is preferably in the range of 400 to 2000, and for this purpose, the polybasic acid in the raw material is mixed with the polyhydric alcohol.
What is necessary is just to set it so that it may become a range of about 0.4-0.75 in molar ratio.

Among the low molecular weight branched polyester polyols, suitable ones include, for example, cyclohexane dimetatool synthesized using monobutyltin hydroxide as a catalyst in Suwasol 1500 [manufactured by Cosmo Oil Co., Ltd., aromatic petroleum solvent], trimethylolpropane, and succinic anhydride. Examples include low molecular weight branched polyester polyols made of acid or adipic acid.

(ii) A linear polyester polyol made from raw materials used in the production of ordinary polyester 14'i + resin for paints, and with a weight average molecular weight of 400 to 200.
0 and a molecular weight distribution of Mw/Mn of about 1.0 to 1.6.

As raw materials used for the production of such polyester polyols, any of the raw materials listed in (i) above from which polyhydric alcohols of trihydric or higher valence and polybasic acids have been removed can be used.

When producing a linear polyester polyol with a narrow molecular weight distribution, it is often necessary to simply adopt the method for producing ordinary polyesters, compared to the case (i) above, but the synthesis method and raw materials are The special measures shown in (i) above may be used as appropriate for the selection of the product, purification of the product, etc.

Among the linear polyester polyols, for example, a polyester made of hexahydrophthalic anhydride, adipic acid, and neopentyl glycol is synthesized by a conventional method, and then heated under reduced pressure for a long time at high temperature (specifically, from 230 to 240°C1 about 5-10 hours, about 20mmHg
Examples include polyester polyols whose low molecular weight components are removed by evaporation under the following reduced pressure.

(iii) A ring-opening polyester polyol prepared by ring-opening polymerization of lactones using a divalent or higher polyhydric alcohol as an initiator, and has a weight average molecular weight of 400 to 2000 and a molecular weight distribution of MW/Mn of 1.0 to 1. .6 polyol.

Examples of the lactones used include ε-caprolactone, β-methyl-δ-valerolactone, γ-valerolactone, δ-caprolactone, γ-caprolactone, γ
-Methylvalerolactone, β-propiolactone, γ-
Examples include butyrolactone. Examples of the poly(24)-hydric alcohol as an initiator include ethylene glycol, diethylene glycol, 1,4-butanediol, 1,6
-hexanediol, 3-methyl-pentane-1,5-
Examples include diol, glycerin, trimethylolethane, trimethylolpropane, pentaerythritol, and the like.

Examples of catalysts used in ring-opening polymerization include boron trifluoride-ethyl etherate, sulfuric acid, phosphoric acid, tetraisopropyl titanate, tetrabutyl titanate, dibutyltin oxide, hydroxytitanium stearate,
Examples include isopropyl titanium stearate and litharge.

When producing a ring-opening polyester polyol, it is possible to obtain a polyol with a narrow molecular weight distribution by simply employing the usual ring-opening polymerization method, but the special methods shown in (i) above are necessary for purification of the product. You can also use the ideas of

Among the above-mentioned ring-opened polyester polyols, preferred examples include polyols in which 5 moles of ε-caprolactone are added to 1 mole of ethylene glycol, and polyols in which 6 moles of ε-cabrolactone are added to 1 mole of trimethylolpropane.

(1) Acrylic polyol which is a copolymer of a hydroxyl group-containing monomer and a monomer copolymerizable with it.

Examples of the hydroxyl group-containing monomer include common hydroxyl group-containing monomers such as hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, and hydroxypropyl methacrylate. As monomers that can be copolymerized with the hydroxyl group-containing monomer, monomers that are generally used in the synthesis of acrylic resins for paints can be widely used, such as acrylic acid or methacrylic ester of C1-18 monohydric alcohol, styrene, acrylonitrile, acrylamide. , methacrylamide, N-methylolacrylamide butyl ether, and the like.

Acrylic polyols with a narrow molecular weight distribution can be obtained, for example, by copolymerizing the above monomers and purifying a radical polymerization product by heating under reduced pressure, fractional precipitation, or the like.

Among the above acrylic polyols, suitable ones include, for example, 25 parts by weight of n-butyl methacrylate, 35 parts by weight of n-butyl acrylate, and 40 parts by weight of 2-hydroxyethyl acrylate, mercaptan as a chain transfer agent, and azobis Examples include acrylic polyols that are purified by copolymerizing in a solution using isobutyronitrile as a polymerization initiator, followed by vacuum treatment and fractionation treatment.

The lactone-modified hydroxyl group-containing acrylic resin, which is the component (A) in the coating composition (2) above, has an acrylic resin as its main skeleton, and a heavy body or dimer-hexamer of lactone is bonded to the main skeleton in a pendant manner. The pendant lactone has at least a hydroxyl group at the end. The method for producing it is not particularly limited, and it can be obtained, for example, by copolymerizing an esterified product of a hydroxyl group-containing monomer and a lactone with an acrylic monomer. The esterified product is produced by a reaction between a carboxyl group generated by ring opening of a lactone and a hydroxyl group-containing monomer, and has a hydroxyl group and a polymerizable unsaturated bond at both ends. The reaction ratio of both components in the esterified product can be selected arbitrarily, but preferably 1 to 6 moles of lactone per mole of the hydroxyl group-containing monomer; if the amount of lactone exceeds 2 moles, a multimer of lactones is formed, and the A hydroxyl group-containing monomer is bonded to one end. The acrylic monomer with which the esterified product is copolymerized is not particularly limited, but a radically polymerizable unsaturated monomer containing a hydroxyl group-containing monomer is preferable. ”
As the lactones, hydroxyl group-containing monomers, radically polymerizable unsaturated monomers, etc. mentioned above, those already exemplified can be suitably used, and the copolymerization reaction thereof can also be carried out by methods known per se. Regarding the lactone-modified hydroxyl group-containing acrylic resin, the content of the esterified product of lactone and the hydroxyl group-containing monomer is preferably 5 to 50% by weight in the resin, the weight average molecular weight is 5000 to 50000, and the hydroxyl value is 50 to 18.
0 is suitable. The low molecular weight polyol described in (1) above may be used in combination with these compositions (1).

The polyisocyanate compound used in the preparation of the clear paint of the present invention is a compound having at least two isocyanate groups in one molecule, such as aliphatic diisocyanates such as hexamethylene diisocyanate or trimethylhexamethylene diisocyanate; cycloaliphatic diisocyanates such as isocyanate or isophorone diisocyanate; organic diisocyanates themselves such as tolylene diisocyanate or aromatic diisocyanates such as 4,4'-diphenylmethane diisocyanate-1, or each of these organic diisocyanates. and adducts with polyhydric alcohols, low molecular weight polyester resins, water, etc., polymers of each organic diisocyanate as described above, and isocyanate biuret forms, etc., and examples of typical commercially available products thereof include As for [Parnock D-7
50, -800, DN-950, -970 or 15
-4554 [The above are products of Dainippon Ink and Chemicals Co., Ltd.], [Desmodule L, N, HL.

or ILJ (product of Bayer, West Germany), [Takenate D-102, -202, -11ON or -11
23NJ [Takeda Pharmaceutical Co., Ltd. product], “Coronate LSHL, EH or 203” [Japan Polyurethane Industries Co., Ltd. product] or “Duranate 24A-90C
XJ [Mukasei Kogyo Co., Ltd. products, etc.]

A blocked polyisocyanate compound in which isocyanate groups are blocked with a suitable blocking agent can also be used.

Block polyisocyanates are non-yellowing polyisocyanates, such as isophorone diisocyanate, hexamethylene diisocyanate, lysine diisocyanate).
, synchhexylmethane-4,4'-diisocyanate is made into a blocked polyisocyanate using a conventional blocking agent such as an aliphatic or aromatic monoalcohol oxime, lactam, phenol, etc. For example, [takenate] B-815NJ (Takeda Pharmaceutical Co., Ltd. product), Takenate 13-84ONJ (Takeda Pharmaceutical Co., Ltd. product), r AdductB 1065
J (Veba Chemie), [ADDITO
Examples include L VXL-80J (manufactured by Hoechst Japan Co., Ltd.).

The clear paint used in the present invention preferably contains the above-mentioned hydroxyl group-containing resin and polyisocyanate compound as essential components, and is used in a form in which these are dissolved or dispersed in an organic solvent as necessary.

The organic solvent used in the clear coating composition of the present invention is
Any material can be used as long as it can stably dissolve or disperse the resin or low molecular weight polyol contained therein. In other words, various aromatic solvents, saturated hydrocarbon solvents,
Ketone solvents, ester solvents, ether solvents, glycol ether solvents, alcohol solvents, etc. can be appropriately selected and used.

The clear paint of the present invention may contain known coating surface conditioners, fluidity conditioners, ultraviolet absorbers, light stabilizers, curing catalysts, electrostatic coating workability control agents, etc., as required. Examples of the curing catalyst include dibutyltin diacetate, dibutyltin dioctyl-1., dibutyltin dilaurate, triethylamine, and jetanolamine.

The blending ratio of these curing catalysts is about 0 to 10 parts by weight, preferably 0.05 to 5 parts by weight, per 100 parts by weight of the resin.

As the fluidity modifier, silica-based fine powder, bentonite-based modifier, polyamide-based modifier, intra-particle crosslinked fine particles produced by aqueous emulsion polymerization, intra-particle cross-linked fine particles produced by non-aqueous system, etc. can also be used. As the fluidity modifier to be added to the clear coating composition of the present invention, a diurea fluidity modifier produced from a diisocyanate and a mono-primary amine is preferred from the viewpoint of finished appearance and image clarity.

The water-based base coat that is applied before clear paint is
It is a thermosetting water-based paint containing a pigment, and the essential components are a base resin, a crosslinking agent, a pigment, and water.

Examples of the base resin include water-soluble or water-dispersible acrylic resins and polyester resins. Preferred water-soluble acrylic resins include acids obtained by polymerization using α, β-ethylenically unsaturated acid nialic acid or methacrylic acid 02-8 hydroxyalkyl ester; and other radically polymerizable unsaturated monomers. Value: about 20 to about 10
0 and an acrylic resin with a hydroxyl value of about 20 to about 200,
Ammonia or triethylamine, monoethanolamine, jetanolamine, triethanolamine,
It is obtained by neutralization using basic compounds such as amines such as dimethylaminoethanol or alkali metal hydroxides such as potassium hydroxide and sodium hydroxide.After this, water is added to obtain an appropriate solid content. And if necessary, an organic solvent compatible with water is added to dilute with water.

On the other hand, water-dispersible acrylic resins use ionic or non-ionic or both low-molecular or high-molecular surfactants as dispersion stabilizers, or water-soluble resins, and the above-mentioned raw materials for water-soluble acrylic resins. It is prepared by emulsion polymerization of a polymerizable unsaturated monomer in an aqueous medium by a commonly known method.

Various unsaturated monomers used in the production of these water-soluble or water-dispersible acrylic resins include those listed in the explanation of the clear paint, and known polymerization methods can be employed.

Further, a preferable water-soluble polyester resin is obtained by reacting a polybasic acid and a polyhydric alcohol so that the acid value becomes 20 to 100 and the hydroxyl value becomes 20 to 200, and the polyester resin is neutralized with a basic compound. A water-dispersible polyester resin can be obtained by reducing the acid value or by only partially neutralizing it. As these polybasic acids and polyhydric alcohol components, those listed in the explanation of the clear paint can be used.

Water-soluble or water-dispersible amino resins are suitable as the crosslinking agent, and are obtained by condensation or co-condensation of formaldehyde with melamine, benzoguanamine, triazine compounds, urea, dicyandiamide, etc.
Those modified with -8 alcohol modifiers, carboxyl group-containing amino resins, etc. are also used. Usually, about 0.5 to about 2.0 equivalents of formaldehyde are reacted with 1 equivalent of amino group in alkaline or acidic conditions using a pH adjuster (for example, ammonia, sodium hydroxide, amines) by a known method. It is prepared by Preferred in the present invention is melamine formaldehyde resin.

Regarding the composition ratio of the base resin and the crosslinking agent, the weight ratio of the water-soluble base resin and the crosslinking agent is 50 to 90 parts, particularly 65 parts.
85 parts of the latter, 10 to 50 parts of the latter, especially 35 to 15 parts.For water-dispersible base resins, it is suitable to use a water-soluble base resin in combination.Specifically, water-dispersible base resin 1
0 to 70 parts, especially 20 to 50 parts, 10 to 70 parts of water-soluble base resin
70 parts, especially 30 to 50 parts, and 10 to 50 parts, especially 15 to 35 parts of the crosslinking agent are preferred (the total of each of the above two and three components is 100 parts by weight).

As the pigment, a colored pigment and/or a metallic pigment are used. All of these can already be used, and various organic and inorganic pigments can be used as coloring pigments, and examples of metallic pigments include aluminum, copper, brass, micaceous iron oxide, bronze, stainless steel, and titanium dioxide. Examples include iron oxide or mica coated with iron oxide, and mica coated with iron oxide.

These water-based paints are cured by heating to form colored or metallic paint films with excellent hiding properties.

The top coating finishing method of the present invention is preferably carried out using the above-mentioned thermosetting water-based paint and clear paint by a two-coat method, particularly a two-coat one-bake method as described below. The thermosetting water-based paint (base coat) is applied to the object to be coated, which has been subjected to chemical conversion treatment, primer coating using electrodeposition paint, intermediate coating, etc., as necessary. It is preferable, but not essential, that the primer coating and intermediate coating be cured in advance. The water-based coating is preferably applied by an air spray method, an electrostatic method, an airless method, etc., and the film thickness is suitably 1.0 to 25 μm, particularly 12 to 20 μm, based on the cured coating film.

Next, the coating film of the water-based paint is heated to usually room temperature or about 100%
It is preferable to dry at a temperature below .degree. C. to volatilize part or most of the water in the coating.

It is preferable to dry the water-based paint film so that the water content in the water-based paint film is 5% by weight or less, particularly 2% by weight or less. There is nothing or little to do.

Next, a clear paint is applied to the surface of the water-based paint film. The coating method can be carried out in the same manner as the water-based paint described above, and the suitable film thickness is 10 to 40 μm based on the cured coating film.

After overcoating both of the above coatings, the topcoat finish coating that is the objective of the present invention can be suitably obtained by simultaneously curing both coatings by heating to about 120 to 160°C.

Effects of the invention Since the base coat is a water-based paint, it is easy to impart structural viscosity (thixotropy), and as a result, the viscosity of the paint applied to the coated surface increases, making it difficult for metallic pigments to flow (metallic unevenness). The non-volatile content of the applied paint can be lowered, that is, the difference in film thickness between immediately after application and after curing is large, and the smoothness of the BASECO-1 paint film itself is good. Moreover, since the molecular weight between crosslinks of the cured coating film of the clear paint was adjusted to a specific value or less, which is smaller than that of the conventional coating, the scratch resistance was significantly improved. In addition, since the crosslinking agent of the clear paint is a polyisocyanate-l-compound, even if the basic compound used for neutralization remains in the uncured coating film of the water-based thermosetting paint of the base coat. A clear coating film having the above-mentioned molecular weight between crosslinks can be formed without inhibiting the crosslinking reaction.

In this way, the two-coat finish coating film obtained by the method of the present invention has a uniform metallic feel, excellent finished appearance such as smoothness, sharpness, and gloss, and has significantly improved scratch resistance. Ta. Furthermore, it has excellent weather resistance, chemical resistance, water resistance, moisture resistance, etc.

Therefore, the present invention is preferably applied to base materials that require these performances, such as outer panels of automobile bodies, furniture, architectural exterior materials, etc., and particularly to dark-colored top coatings thereof.

EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to production examples, working examples, and comparative examples. Unless otherwise specified, “Department” and “
%" means 1 part by weight" and "% by weight", respectively.

■ Thermosetting water-based paint containing pigment (base coat)
(1) Base resin aqueous dispersion (B-1) In a reaction vessel, 113 parts of deionized water and 30% rNewc were added.
Add 5 parts of ol 707SFJ (surfactant, manufactured by Nippon Nyukazai Co., Ltd.), 10 parts of a 5% ammonium persulfate aqueous solution, and 20 parts of the following monomer mixture, and heat to 75°C.

80 parts of the monomer mixture described below are then added over a period of 2 hours using a metering pump. After the addition was completed, the mixture was aged at 75°C for 1 hour, and filtered at 30°C using a 200 mesh nylon cloth. The resulting aqueous dispersion had a nonvolatile content of 44%.
, the glass transition temperature (Tg) was 41°C. Deionized water was further added to this and the pH was adjusted to 7.5 with dimethylaminoethanol to obtain an aqueous dispersion with a solid content of 40%.

Monomer mixture methyl methacrylate 50 parts styrene
10//butyl acrylate
27//acrylic acid
3//2-hydroxyethyl methacrylate
1011 (2) Base resin water acid solution (B-2) In a reaction vessel, 140 parts of deionized water, 30% rNewc
Add 2.5 parts of ol 707SFJ and 1 part of the following monomer mixture (1), stir and mix in a nitrogen stream, and heat at 60°C.
Add 3 parts of 30% ammonium persulfate. Then 80
After increasing the temperature to °C, the following monomer mixture (1
) 99 parts, 30% rNewcol 707SFJ 2.
5 parts 3% ammonium persulfate 4 parts deionized water 42 parts
A monomer emulsion consisting of 1.5 ml of monomer emulsion is added to the reaction vessel using a metering pump over a period of 4 hours. After the addition is completed, aging is carried out for 1 hour.

Furthermore, the following monomer mixture (2) was added to the reaction vessel over 1.5 hours at 80°C, and after the addition was completed, it was aged for 1 hour.
It was filtered through a 200 mesh nylon cloth at 0°C. Add deionized water to this mixture, adjust the pH to 7.5 with dimethylaminoethanol, and adjust the pH to 46°C1 solids content 2.
A 0% aqueous dispersion was obtained.

Monomer mixture (1) Methyl methacrylate 55 parts Styrene
1-O1l n-butyl acrylate 9 //2-hydroxyethyl acrylate 5 //methacrylic acid
1 // Monomer mixture (2) Methyl methacrylate 5 parts n-butyl acrylate 7 // 2-ethylhexyl acrylate 5 // Methacrylic acid
31/30%rNevcol 707SF
J 0.5 parts 3% ammonium persulfate aqueous solution
4 // Deionized water 3011
(3) Base resin aqueous solution (B-3) 60 parts of butyl cellosolve and 15 parts of isobutyl alcohol are added to a reaction vessel and heated to 11,500 ℃ in a nitrogen stream. When the temperature reached 115°C, 26 parts of n-butyl acrylate,
A mixture of 47 parts of methyl methacrylate, 10 parts of styrene, 10 parts of 2-hydroxyethyl methacrylate, 6 parts of acrylic acid and 1 part of azoisobutyronitrile is added over a period of 3 hours. After the addition was completed, the mixture was aged at 115°C for 30 minutes, and a mixture of 1 part of azobisisobutyronitrile and 115 parts of butyl cellosolve was added over 1 hour.
Filter through a 200 mesh nylon cloth at °C.

The resulting reaction product had an acid value of 48, a viscosity of Z4 (Gardner foam viscometer), a nonvolatile content of 55%, and a Tg of 45°C. Neutralize this with an equivalent amount of dimethylaminoethanol,
Further, deionized water was added to obtain an aqueous solution with a solid content of 50%.

(4) Base coat■ Base resin aqueous dispersion B-2275 parts Base resin aqueous solution B-3 4071 "Cymel 350" 25/l (manufactured by Mitsui Toatsu Chemical Co., Ltd., amino resin) "Aluminum paste AW-500Bj 4" (Asahi Kasei Metals) Carbon black (manufactured by Columbia Co., Ltd.) Carbon black (manufactured by Columbia Co., Ltd.)
dsAGJ) Butyl cellosolve 2071 deionized water 25.3// mixed and
-1,30BJ (thickener manufactured by Kyoeisha Yushi Kagaku Kogyo Co., Ltd.) was added to Thikusol and adjusted to 300Qcps with a B-type viscometer (rotor rotation speed 6 rpm) to make Baseco-1.
I got ■.

(5) Base coat■ Base resin aqueous dispersion B-1137, 5 parts Base resin aqueous solution B-34011 "Zymel 350" 251/[aluminum paste AW-500BJ 2011 butyl cellosolve 2011 deionized water 4311 was mixed with [Tixol and 130 BJ was added and adjusted to 2500 cps using a B-type viscometer (rotor rotation speed: 6 rpm) to obtain a base coat (2).

(6) Base coat■ Base resin aqueous solution B-340 parts "Phthalocyanine Blue 6900" 1011 carbon flak 3//butyl cellosolve 201/ was dispersed to 5μ or less in a pebble mill, and further, base resin aqueous dispersion] 3-
2 27511 [Cymel 350J
25 parts deionized water
111 was added and the viscosity was adjusted to 2,500 cps in the same manner as above to obtain base coat (2).

(7) Base coat ■ 15 parts of styrene, 20 parts of methyl methacrylate, 30 parts of ethyl acrylate, 21 parts of n-butyl methacrylate, 12 parts of 2-hydroxyethyl methacrylate, and 2 parts of acrylic acid as a polymerization initiator α.

Polymerization was carried out in xylene using α'-azobisisobutyronitrile to obtain an acrylic resin solution having a resin content of 50% and a varnish viscosity of Z1. Using this acrylic resin solution, an organic solvent type base coat was prepared with the following formulation.

160 parts of the above 50% acrylic resin solution 60% [Kneepan 20 S EJ 33 parts (manufactured by Mitsui Toatsu Chemical Co., Ltd., melamine resin) Aluminum paste 3 parts (manufactured by Toyo Aluminum Co., Ltd., "Aluminum paste #49", 9J) Carbon black 1 part of this Baseco-1 was then mixed with 40 parts of toluene and [Swazol-10
00j [manufactured by Cosmo Oil] 30 parts, butyl acetate 20
A mixed solvent consisting of 1 part and 10 parts of n-butanol has a viscosity of 1
The temperature was adjusted to 4 seconds (Ford Cup #4/20°C) and used for painting.

■ Manufacture of clear paint (1) Low molecular weight polyol solution In LMP-1 flask, 53.8 parts of cyclohexane dimetatool, 12.8 parts of trimethylolpropane, 44.3 parts of adipic acid, boiling point 1
440 parts of aromatic petroleum solvent [[Swazole 1500J (manufactured by Cosmo Oil Co., Ltd.]] at 80°C to 220°C and 0.5 part of monobutyltin oxide were charged, and the condensed water was separated under reflux of the solvent. The reaction was carried out while removing it through the vessel. The reaction was stopped when the acid value reached 7, and the mixture was concentrated under reduced pressure.

The solid content concentration of the obtained solution was 80.0%, the hydroxyl value of the solid content was 247, and the weight average molecular weight 1i (MW) was 1170.
, the ratio MW/Mn of MW and number average molecule 1 (yn) is 1.3
And ivy.

(2) Low molecular weight polyol solution 25.0 parts of trimethylolpropane, 25.0 parts of ε-caprolactone and 1-0.1 part of tetrabutyl rapeseed were placed in an LMP-2 flask and heated to 100°C. It was kept at temperature for 1 hour. Next, the temperature was raised to 120°C, and 50.0 parts of ε-caprolactone was added dropwise to this mixture over a period of 1 hour. After that, 18
The temperature was raised to 0°C, and the reaction was continued until there was no change in the refractive index of the reactant. Thereafter, the yarn was subjected to reduced pressure to remove a small amount of unreacted substances and low-molecular substances, and then cooled. The solid content concentration of the obtained product was 100%, the hydroxyl value was 302, and the MW was 1.
010, and Mw/Mn was 1.31.

(3) Hydroxyl group-containing resin solution 0H-A In a normal acrylic resin reaction tank equipped with a stirrer, thermometer, reflux condenser, etc., add “Suwazol-1000j [manufactured by Cosmo Oil Co., Ltd., 150 parts of aromatic solvent, 1 part of Cellosolve Acetate]
5 parts were charged, heated and stirred, and when the temperature reached 132°C, the following monomer mixture was added over a period of 3 hours.

Styrene 20 parts Isobutyl methacrylate 24 parts n-butyl methacrylate 35 parts 2-hydroxyethyl methacrylate 19 parts Acrylic acid
Part 2 α, α′ -Azobisisobutyronitrile
After addition of 2 parts of the above monomer mixture, for an additional 1 hour, 13
After maintaining at 2 DEG C., a mixture of 1 part of tert-butyl peroctoate and 410 parts of Swasol-1000 is added over a period of 1 hour. Thereafter, stirring was continued while maintaining the temperature at -32°C for 2 hours, and then the mixture was cooled.

Swazol-1000J was added to this to obtain a hydroxyl group-containing resin solution 0H-A with a solid content concentration of 50%.The weight average molecular weight MW of this acrylic resin was 19,000, and the hydroxyl value was 82.

(4) Hydroxyl group-containing resin solution 0I (-L) 1.65 parts of cellosolve acetate was charged into an ordinary acrylic resin reaction tank equipped with a stirrer, thermometer, reflux condenser, etc., and heated and stirred to 132°C. Once reached, the following monomer mixture was added over a period of 3 hours.

Methyl methacrylate 20 parts n-butyl methacrylate 15 parts n-butyl acrylate 18 parts hydroxyethyl acrylate
Part 25 “Plaxel FM-3j 20
Part [Monomer manufactured by Daicel Chemical Industries (additive of 3 moles of ε-caprolactone and 1-1 mole of 2-hydroxyethyl methacrylate)] Acrylic acid 2 parts α, α'
-Azobisisobutyronitrile 1.9 parts After addition of the above monomer mixture, the temperature was maintained at 132°C for an additional hour, and then t
- A mixture of 1 part of butyl peroctoate and 10 parts of xylene is added over a period of 1 hour. 132°C for the next 2 hours
After stirring was continued while maintaining the temperature at Add xylene to this to obtain a hydroxyl group-containing resin solution with a solid content concentration of 50%.
H-L was obtained. The weight average molecular weight of this acrylic resin is 2
1,500, and the hydroxyl value was 145.

(5) Hydroxyl group-containing resin solution 0H-P: 42.0 parts of hexahydroterephthalic acid, 22.1 parts of isophthalic acid, 12.0 parts of trimethylolpropane in a flask.
1 part and 37.3 parts of neopentyl glycol,
Heated. The temperature was raised from 160°C to 230°C over a period of 3 hours while removing the generated condensed water from the system via a rectification column.

After keeping it at 230℃ for 2 hours, add a small amount of xylene,
The reaction was carried out by a solvent condensation method at 230° C. under reflux of xylene, and when the acid value reached 6, cooling was performed. Add this to xylene/Swazol 1000j-50150
The mixture was diluted with a mixed solvent to give a solid content concentration of 60% to obtain a hydroxyl group-containing resin solution 0H-P. The obtained polyester resin (solid content) has a hydroxyl value of 125 and a MW of 4010.
, the cyclohexylene ring concentration was 20.2%.

(6) Clear paint The components obtained in (1) to (5) above are mixed in the compounding ratio shown in Table 1, and the mixture is treated with a mixed solvent of cellosolve acetate/xylene = 50150 to a viscosity of 25 seconds (#4 Ford). cup/20°C) and call this “Liquid A”.
And so. [Sumidur Nj (NC0% is 16.5
%, polyisocyanate compound manufactured by Sumitomo Bayer Urethane Co., Ltd. with a solid content concentration of 75%) with ethyl acetate to a solid content concentration of 70%.
% was prepared and designated as "Liquid B".

Clear paints (-1 to C-6) were prepared by mixing liquid A/liquid B in the proportions shown in the same table.

= 55- Notes 1- and 2 in Table 1 indicate the following.

Note 1: Nidodecylbenzenesulfonic acid was used.

Note 22 Cymel-2B5j (methyl/butyl mixed etherified monomeric melamine resin manufactured by Mitsui Toatsu Chemical Co., Ltd.) is used, and its blending amount is shown.

The clear paint C-6 was adjusted to have a viscosity of about 30 seconds using a mixed solvent of xylene/cellosolve acetate-1/n-butanol-40150/10 (weight ratio).

Examples 1 to 6 and Comparative Examples 1 to 6 Epoxy-based cationic electrodeposition paint was electrodeposited on a dull steel plate with a thickness of 0.8 mm that had been subjected to zinc phosphate chemical conversion treatment so that the dry film thickness was 20μ, After baking at 170°C for 20 minutes, air spray paint with an intermediate coating surfacer for automobiles to a dry film thickness of 25μ, and then apply a 140°
It was baked for 30 minutes at C for 30 minutes to prepare a test object.

The above-mentioned base coat and clear paint were applied to this object to be coated, and both coatings were simultaneously cured by heating.

The coating conditions for both coatings are as follows.

Spray gun: [DeVilbiss J GA 502J (manufactured by Nippon DeVilbiss Co., Ltd.) Air pressure: 5 kg/cm2 Gun distance: 35 cm Paint booth temperature = 25°C Wind speed: 0.5 m/sec Humidity near 0% Base coat film Thickness: 15 ± 2μ (based on cured coating) Clear paint film thickness: 35 ± 3μ (based on cured coating) Table 2 shows the combination of base coat and clear coating, presence or absence of air drying, baking temperature for both coatings, etc. As shown.

The performance tests of the obtained coated plates are also listed in the same table.

In Table 2, *1 to 8 indicate the following.

(*1) Air drying: "Dry" indicates that the moisture content in the base coat film was adjusted to 2% by weight or less at a temperature of 50°C, and "wet" indicates that the moisture content was adjusted in the same way. 1
The content was 0 to 15% by weight. In addition, the base coat ■ is 1 at room temperature.
I left it for 5 minutes and then applied clear paint.

(*2) Baking temperature This is the baking temperature for applying two base coats and clear paint and curing both coatings at the same time.

(*3) Molecular weight between crosslinks: A single coat of clear paint is
The coating films cured at the baking temperatures shown in the table were measured according to the xylene swelling method described above.

(*4) Scratch resistance: After a car with a test coating plate attached to its roof was washed 15 times in a car wash, the state of the coating surface of the coating plate was observed. The car wash machine is rPo 20 made by Yasui Sangyo.
FWRCJ was used. The evaluation criteria are as follows.

○: A few scratches were found by visual observation, but the degree of scratches was extremely slight and passed.

△: Scratches were noticeable by visual observation, and the test was rejected.

×: Visual observation clearly showed significant scratches, and the product failed.

(*5) Sharpness: For measuring sharpness [JCRI-GGD-1
66 type Gd meter (sold by Japan Color Research Institute). The measurement was carried out with the angle fixed at 55°.

(0) Gloss = 60 degrees based on specular reflectance.

(*7) Adhesion: After making 100 goblets of size 1 x 1 mm on the coating film with a sharp knife so as to reach the base material, adhesive Seronone tape is pasted on the surface, and it is rapidly peeled off. The number of remaining rough coating films was investigated.

(*8) Weather resistance: 1 on the sunshine weather meter
The coating film after being exposed for 600 hours was observed and evaluated as follows.

○: No abnormality.

△: Slight cracking occurred.

×: Many cracks occurred.

(that's all)

Claims (1)

[Claims] (1) A method in which a pigment-containing thermosetting water-based paint is applied to a surface to be painted, dried or cured, and then a clear paint containing a polyisocyanate compound as a crosslinking agent is applied to the painted surface, the clear paint However, the molecular weight between crosslinks of the cured coating film is 2
000 or less (measured based on the xylene swelling method).