GB2456893A

GB2456893A - Clear coating composition for multilayered coating film

Info

Publication number: GB2456893A
Application number: GB0823615A
Authority: GB
Inventors: Hideaki Tsujioka; Junji Shimada; Hisaki Tanabe
Original assignee: Nippon Paint Co Ltd
Current assignee: Nippon Paint Co Ltd
Priority date: 2007-12-25
Filing date: 2008-12-29
Publication date: 2009-08-05
Anticipated expiration: 2028-12-29
Also published as: GB0823615D0; GB2456893B; JP2009155396A

Abstract

The invention relates to a clear coating composition, which comprises an acrylic resin obtainable/obtained by a monomer mixture comprising a (meth)acrylate monomer comprising a long chain of a linear hydrocarbon group having 9 to 15 carbon atoms, a carboxyl group-containing (meth)acrylic monomer, and a hydroxyl group-containing (meth)acrylic monomer. The clear coating composition according to the invention can prevent color reversion in/over a base coating film, and can form an excellent multilayered coating film.

Description

CLEAR COATING COMPOSITION AND

METHOD FOR PROCUCING MULTILAYERED COATING FILM

TECHNICAL FIELD

[0001] The present invention relates to a clear coating composition and a method for producing a multilayered coating film therewith.

BACKGROUND OF THE INVENTION

[0002] Generally, coatings on vehicle bodies such as bodies of automobiles include formation of a coating film comprising a base coating film and clear coating film thereon, i.e., formation of a top coating film.

Particularly, the clear coating film consists in the most outer exterior layer among these coatings on the vehicle body such as automobile body. Therefore, the clear coating film requires various properties such as design properties, acid-resistance, scratch-resistance, etc. [0003] Conventional clear coating compositions to be applied to automobiles include coating compositions in a thermal curing system by means of an acryl-melamine resin.

The system employs a melamine resin as a curing agent.

Therefore, the resulting coating film is inferior in the acid-resistance. Consequently, the resulting coating film would be susceptible to acid rain, and brittle.

Accordingly, it might bring coating failures over the exterior surface.

[0004] In addition to the clear coating compositions in the thermal curing system by means of the acryl-melamine resin, for example, urethane coating compositions are known in the art (see, for example, Patent Literature No. 1: JP-A-2005-787, etc.)

SUMMARY OF THE INVENTION

DISCLOSURE OF THE INVENTION

PROBLEM TO BE SOLVED BY THE INVENTION

[0005] The urethane coating compositions can provide a coating film having good acid-resistance and scratch-resistance. In the case of a so-called two coating and one-baking (2C1B) coating procedure, which includes steps of applying the urethane coating composition on an uncured base coating film to form an uncured clear urethane coating film thereon, and then heating and curing both of the uncured base coating film and the uncured clear urethane coating film thereon to produce a top coating film comprising them, some components therein such as acrylic resin (e.g., acrylic polyol) might migrate, from the clear coating composition, into the uncured base coating film to adversely influence on the design properties thereof.

[0006] In a certain case that the base coating composition comprises luster color pigments, i.e., the base coating composition is a so-called metallic color base coating composition, the migration of some components from the clear coating composition into the uncured base coating film disturbs orientation of the luster color pigments therein. As a result, "color reversion" occurs in/over the base coating film. The color reversion is a phenomenon in/on the base coating film, wherein highlight (top) areas are darkened and shade (oblique) areas are brightened.

Therefore, the design properties thereof might be deteriorated.

[0007] Accordingly, the urethane coating composition fails to provide a coating film having excellent design properties, and therefore the urethane coating composition is not suitable for forming a clear coating film on a vehicle body, particularly on an automobile to which excellent design properties are required in the market.

[0008] In view of the above-described problems, objects of the present invention consist in a provision of a clear coating composition superior in design remaining ability, which can prevent the color reversion in/over the base coating film and maintain inherent excellent design properties of the base coating film, and which can form a multilayered coating film, as well as a provision of a method for producing a multilayered coating film therewith.

MEANS FOR SOLVING THE PROBLEM

(0009] The present invention relates to a clear coating composition, which comprises an acrylic resin obtainable/obtained by a monomer mixture comprising a (meth)acrylate monomer comprising a long chain of a linear hydrocarbon group having 9 to 15 carbon atoms, a carboxyl group-containing (meth)acrylic monomer, and a hydroxyl group-containing (meth)acrylic monomer.

[0010] In a preferable embodiment of the present invention, the clear coating composition further comprises a curing agent which can react with a carboxyl group and/or a hydroxyl group.

[0011] In a preferable embodiment of the present invention, the curing agent is a polyisocyanate compound.

[0012] In a preferable embodiment of the present invention, content of the above-described (meth)acrylate monomer is within a range of from 5 to 15% by weight relative to total weight of monomer solid contents in the monomer mixture.

(0013] In a preferable embodiment of the present invention, the acrylic resin has an acid value, based on the solid content, within a range of from 1 to 10 mgKOH/g.

[0014] Furthermore, the present invention relates to a method for producing a multilayered coating film, which includes steps of (1) applying a base coating composition on a substrate to from an uncured base coating film thereon, (2) applying a clear coating composition on the uncured base coating film (resulted from the step (1)) to form an uncured clear coating film thereon, and (3) heating and curing both of the uncured base coating film (resulted from the step (1)) and the uncured clear coating film thereon (resulted from the step (2)) to form a multilayered coating film, wherein the clear coating composition is one of those described above.

[0015] The method for producing the multilayered coating film according to the present invention may further include, prior to the step (1), a step (p) of applying an intermediate coating composition on the substrate to form an intermediate coating film, or applying a primer surfacer on the substrate to from a primer surface.

EFFECT OF THE INVENTION

[0016] The present invention can prevent color reversion in/over the base coating film, maintain inherent excellent design properties of the base coating film, and form a multilayered coating film.

BRIEF DESCRIPTION OF THE DRAWINGS

(0017] Fig 1 is a schematic view illustrating measurement of L values.

DETAILED DESCRIPTION OF THE INVENTION

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] The present invention is described hereinafter in detail.

(0019] According to the present invention, the clear coating composition comprises an acrylic resin obtainable/obtained by a monomer mixture comprising a (meth)acrylate monomer comprising a long chain of a linear hydrocarbon group having 9 to 15 carbon atoms, a carboxyl group-containing (meth)acrylic monomer, and a hydroxyl group-containing (meth)acrylic monomer.

[0020] The clear coating composition according to the present invention can form a coating film having an excellent acid-resistance and an excellent scratch-resistance. Furthermore, the clear coating composition according to the present invention can prevent color reversion in/over the underlying base coating film, and therefore provide a coating film having excellent design properties. Accordingly, the clear coating composition according to the present invention is preferably suitable for coating vehicle bodies such as bodies of automobiles as a clear coating composition in a two-pack system.

[0021] The clear coating composition according to the present invention can form a coating film having an excellent appearance. The reasons why such film can be formed seem to consist in that the acrylic resin, as described above, has a considerably long side chain of the linear hydrocarbon group having 9 to 15 carbon atoms.

During the two-coating and one-baking coating procedure, which comprises an application of the clear coating composition to an uncured base coating film in order to form a top coating film, it is not allowed for the acrylic resin in the clear coating composition to migrate into the uncured base coating film due to the steric hindrance of the linear hydrocarbon groups therein. Furthermore, the higher acid value of the acrylic resin seems to effectively contribute to the prevention of the migration of the acrylic resin into the uncured base coating film.

(0022] As described above, use of the clear coating composition according to the present invention can prevent migration of the acrylic resin therein into an uncured base coating film. Therefore, it is expected that use of the clear coating composition according to the present invention can prevent color reversion in/over a base coating film formed with a base coating composition comprising luster color pigment(s), i.e., a so-called metallic color base coating composition, since the clear coating composition according to the present invention can not adversely influence on the orientation of the luster color pigment in the base coating composition.

(0023] The acrylic resin is obtainable/obtained by a monomer mixture comprising a (meth)acrylate monomer comprising a long chain of a linear hydrocarbon group having 9 to 15 carbon atoms, a carboxyl group-containing (meth)acrylic monomer, and a hydroxyl group-containing (meth) acrylic monomer.

[0024] The above-described (meth)acrylate monomer includes, for example, a monomer represented by the formula (A)

H R

H C-O CH2 CH3 (A) wherein R is a hydrogen atom or a methyl group; and n is an integer of 8 to 14.

[0025] The (meth)acrylate monomer includes, but is not particularly limited to, a (meth)acrylate monomer comprising a linear hydrocarbon group having 9 to 15 carbon atoms, such as lauryl (meth)acrylate, tridecyl (meth)acrylate, decyl (meth)acrylate, nonyl (meth)acrylate.

One of these (meth)acrylate monomers may be used alone.

Alternatively, two or more of these (meth)acrylate monomers may be used in a combination.

[0026] Content of the (meth)acrylate monomer is preferably within a range of from 5 to 15% by weight relative to total weight of monomer solid contents in the monomer mixture.

When the content is less than 5% by weight, it may be difficult to adequately control the influence of the clear coating film on the base coating film. When the content is more than 15% by weight, there may be a problem that inferior adhesion occurs upon recoating thereon.

[0027] The above-described carboxyl group-containing (meth)acrylic monomer includes, but is not particularly limited to, for example, acrylic acid, methacrylic acid, acrylic acid dimer, crotonic acid, isocrotonic acid and maleic acid. One of the carboxyl group-containing (meth)acrylic monomers may be used alone. Alternatively, two or more of the carboxyl group-containing (meth)acrylic monomers may be used in a combination. Among these carboxyl group-containing (meth) acrylic monomers, acrylic acid and methacrylic acid are preferable.

[0028] Use of the carboxyl group-containing (meth)acrylic monomer can provide a coating film having excellent design properties. Such provision seems to be due to the possible prevention of the migration of the acrylic resin into the base coating film, since association of the carboxyl group with the acryl resin can increase apparent molecular weight of the acrylic resin.

(0029] The above-described hydroxyl group-containing (meth)acrylic monomer includes, but is not particularly limited to, for example, hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxybutyl (meth)acrylate, allylalcohol, methacrylalcohol, adduct of hydroxyethyl (meth)acrylate and c-caprolactone, etc. One of the hydroxyl group-containing (meth)acrylic monomers may be used alone. Alternatively, two or more of the hydroxyl group-containing (meth)acrylic monomers may be used in a combination.

[0030] The above-described monomer mixture comprising the long chain (meth)acrylate monomer, the carboxyl group- containing (meth) acrylic monomer and the hydroxyl group-containing (meth)acrylic monomer, each of which is described above, can provide the acrylic resin. The monomer mixture may further include other unsaturated monomer(s) [0031] The other unsaturated monomers include(s), for example, (meth)acrylates comprising alkyl (meth)acrylates wherein the alkyl moiety having 1 to 8 carbon atoms, such as methyl (meth)acrylate, ethyl (meth)acrylate, i-propyl (meth)acrylate, n-butyl (meth)acrylate, i-butyl (meth)acrylate, t-butyl (meth)acrylate, and 2-ethyihexyl (meth)acrylate; cyclohydrocarbyl (meth)acrylates, such as phenyl (meth)acrylate, and cyclohexyl (meth)acrylate; isoboronyl (meth) acrylates; polyalkyleneglycol (meth)acrylates, such as (poly) ethyleneglycol mono (meth) acrylate, polyethyleneglycol (having polymerization degree within a range of from 2 to 10) mono(meth)acrylate; alkoxyalkyl (having 1 to 3 carbon atoms) (meth) acrylates; etc. The other unsaturated monomer(s) further include(s) (meth) acrylamides; vinyl compounds, such as styrene, a-methylstyrene, vinyl acetate, vinyl propionate, vinyl benzoate, vinyltoluene, and acrylonitrile; crotonates diesters of unsaturated dibasic acid, such as maleic diesters and itaconic diesters; etc. One of the other unsaturated monomers may be used alone.

Alternatively, two or more of the other unsaturated monomers may be used in a combination.

(0032] Polymerization method in order to provide the acrylic resin includes, but is not particularly limited to, polymerization methods known to those skilled in the art, such as solution polymerization, dispersion polymerization, and emulsion polymerization.

(0033] The acrylic resin has an acid value, based on the solid content, preferably within a range of from J. to 10 mgKOH/g.

[0034] In the case that the acid value is within the range, association of the acrylic resin with the carboxyl group can be increased, and therefore apparent molecular weight of the acrylic resin can be also increased. It can prevent the migration of the acrylic resin into the base coating film, and therefore provide a coating film having excellent design properties.

(0035] If the acid value is less than 1 mgKOH/g, such association is decreased, and then it will be difficult to increase the apparent molecular weight of the acrylic resin.

Therefore, in this case, it may be difficult to form a coating film having excellent design properties. If the acid value is more than 10 mgKOH/g, the resulting coating composition may have an excessive viscosity, and then may not allow a higher solid content. It is more preferable that the acid value is within a range of from 2 to 7 mgKOH/g.

[0036] The acrylic resin has a hydroxyl value, based on the solid content, preferably within a range of from 50 to 440 mgKOI-1/g. If the hydroxyl value is less than 50 mgKOH/g, there may be a problem that curability is decreased. If the hydroxyl value is more than 140 mgKOH/g, there may be a problem that the resulting coating film has an inferior water-resistance. it is more preferable that the hydroxyl value is within a range of from 80 to 140 rngKOH/g. Herein, the acid value and the hydroxyl value can be adjusted by varying mixing ratio of the starting monomers.

(0037] The acrylic resin has a number average molecular weight (Mn) preferably within a range of from 2000 to 10000.

If the number average molecular weight (Mn) is less than 2000, the resulting coating composition may have an insufficient curability, If the number average molecular weight (Mn) is more than 10000, the resulting coating composition may have a higher viscosity, and therefore the resulting coating composition may not allow a higher solid content. It is more preferable that the acrylic resin has a number average molecular weight within a range of from 4000 to 6000.

[0038] Herein, the number average molecular weight (Mn) can be determined by a gel permeation chromatography (GPC) as a calculated value by means of a polystyrene standard.

[0039] The acrylic resin has a glass transition temperature (hereinafter which is referred to as a Tg value) preferably within a range of from -30 to 50°C. If the Tg value is less than -30°C, there may be a problem that the resulting coating film has a decreased hardness, and there may be a problem that thickness of the resulting coating film is S 14 variable depending on the varying temperature of the coating composition. If the Tg value is more than 50°C, the resulting coating composition may have an excessive viscosity, and therefore the resulting coating composition may not allow a higher solid content. It is more preferable that the acrylic resin has a Tg value within a range of from --10 to 30°C.

(0040] The Tg value of the acrylic resin can be determined by means of, for example, calculation with known Tg values of the constituting monomers or the homopolymers thereof as well as the formulation thereof.

[0041] The clear coating composition preferably comprises a curing agent which can react with a carboxyl group and/or a hydroxyl group.

(0042] The curing agent includes, for example, polyisocyanate compounds, polycarbodiimide compounds, oxazoline compounds, etc. Among these curing agents, polyisocyanate compounds are preferable.

[0043] The polyisocyanate compounds include, but are not particularly limited to, for example, compounds having at least two isocyanate groups, which include aliphatic isocyanates, such as trirnethylenedilsocyanate, tetramethylenediisocyanate, pentamethylenedi isocyanate, hexamethylenedi isocyanate (HNDI), and trimethylhexamethylenediisocyanate; aliphatic cyclic isocyanates, such as 1,3-cyclopentanediisocyanate, 1, 4-cyclohexanediisocyanate, and 1, 2-cyclohexanediisocyanate; aromatic isocyanates, such as xylilenediisocyanate (XDI), 2,4-trilenediisocyanate (TDI), and 2,6-trilenedi isocyanate; alicyclic isocyanates, such as isophoronedlisocyanate (IPDI), and norbornane diisocyanate methyl; and multimers such as nurates, biurets and adducts thereof, and mixture thereof; etc. Among these polyisocyanate compounds, polyisocyanates in nurate forms are preferable, which can provide a weather-resistance.

[0044] The polycarbodiimide compounds, i.e., carbodlimide group-containing compounds include, but are not particularly limited to, compounds having at least two factional groups to form a crosslinking structure by a reaction with heating, preferably, such as (1) compounds having two isocyanate groups therein, and (2) compounds having at least two carbodiimide groups therein. Such carbodlimide group-containing compounds include compounds derived from the above-described isocyanate compounds via decarboxylat ion.

[0045] (1) The compounds having two isocyanate groups therein (which is hereinafter referred to as an isocyanate group-containing compound (1)) include a compound represented by the formula: OCN-R1-(NCN-R1) rNCO wherein R1 may be identical or different, and represent a residue derived from an organic diisocyanate without isocyanate groups, and n is an integer of 1 or more, which represents a repeating number of carbodilmide group(s) [0046] (2) The compounds having at least two carbodilmide groups therein (which is hereinafter referred to as a carbodlirnide group-containing compound (2)) include a compound represented by the formula: R2-NCN-R1-(NCN-R1) mNCNR2 wherein R1 may be identical or different, and represent a residue derived from an organic diisocyanate without isocyanate groups, R2 may be identical or different, and represent a residue derived from a monoisocyanate compound without isocyanate group, and m is 0, or an integer of 1 or more, which represents a repeating number of carbodiirnide group(s) [0047] The oxazoline compounds, i.e., oxazoline group-containing compounds include compounds comprising a plurality of oxazoline groups therein. The oxazoline group-containing compounds includes, but are not particularly limited to, for example, dioxazoline compounds such as 2,2'-bis-(2-oxazoljne), 2,2'-methylene-bjs-(2-oxazoline), 2,2'-ethylene-bis-(2- oxazoline), 2,2'-trimethylene-bjs-(2-oxazoljne), 2,2'-tetramethylene-bis-(2-oxazoljne), 2,2'-hexamethylene--bjs- (2-oxazoline), 2,2'-octamethylerie-bjs-(2-oxazoljne), 2,2'-ethylene-bis-(4,4-djmethyl_2_oxazo1j) 2,2'-(1,3-phenylene)-bjs-(2-oxazoljne), 212'-(l,3-phenylene)-bis-(414-dimethyl-2-oxazoljne), 212T-(1,4-phenylene)-bis-(2- oxazoline), bis-(2-oxazolinylcyclohexane)sulfjde, bis-(2-oxazolinylnorbornane) sulfide; trioxazoline compounds such as 2,2'-(l,2,4-phenylene)-tris-(2-oxazoline) ; etc. [0048] The above-described curing agent has a functional group which can react with a carboxyl group and/or a hydroxyl group, such as the carboxyl group and/or the hydroxyl group in the above-described acrylic resin, to cure the acryl resin. A stoichiometric ratio of total of the carboxyl group and/or the hydroxyl group in the acrylic resin to the functional group in the curing agent [total of the carboxyl group and the hydroxyl group in the acrylic resin/the functional group in the curing agent] is preferably within a range of from 1/1.5 to 1.5/1. If the stoichiometric ratio is less than 1/1.5, sufficient curability may not be obtained. If the stoichiometric ratio is more than 1.5/1, the resulting cured coating film may be excessively hardened, and brittle. It is more a preferable that the stoichiometric ratio is within a range of from 1.4/1 to 1/1.4.

(0049] The clear coating composition can comprise an ultraviolet ray-absorbing agent, a hindered amine lightstabilizer, an antioxidant, a crosslinked resin particles, a surface conditioner, etc. The crosslinked resin particles are added to the composition within a preferable range of from 0.01% by weight to 10% by weight relative to the solid resin content of the curable resin composition according to the present invention. It is more preferable that the lower limit is 0.1% by weight. It is more preferable that the upper limit is 5% by weight. If the amount of the crosslinked resin particles to be added is more than 10% by weight, the resulting coating film may have deteriorated appearance. If the amount is less than 0.01% by weight, the desired rheology controlling effect may not be achieved.

[0050] The clear coating composition according to the present invention is preferably a coating composition, in a two-pack curing system, which comprises a composition comprising the above-described acrylic resin, and a curing agent which can react with a carboxyl group and/or a hydroxyl group.

[0051] The clear coating composition according to the present invention can be applied by a method such as S 19 spraying, brushing, dipping, roll coating, curtain coating or the like. In the case that the clear coating composition is a coating composition in a two-pack curing system, the two packed-coating compositions can be previously mixed together, immediately before its application, and then the coating composition can be applied according to the above-described coating procedure.

[0052] The clear coating composition according to the present invention can be advantageously applied on a substrate including, for example, woods, metals, glasses, fabrics, plastics, foams, and the like, particularly on surfaces of plastics and surfaces of metals such as steel, aluminum, and alloys thereof. It is more particularly preferable that the clear coating composition according to the present invention can be applied as a clear coating composition for coating a vehicle such as an automobile.

[0053] The method for producing a multilayered coating film according to the present invention includes steps of (1) applying a base coating composition on the substrate to from an uncured base coating film thereon, (2) applying the above-described clear coating composition on the uncured base coating film to form an uncured clear coating film thereon, and (3) heating and curing both of the uncured base coating film and the uncured clear coating film thereon to form a multilayered coating film comprising them. The present method can be particularly preferably applied to coating of a vehicle such as an automobile.

[0054] The substrate may be used, for example, in a metal molded article, a plastic molded article, a foamed article, or the like. The substrate on which the multilayered coating film can be formed, for an automobile, includes metal molded articles of a substrate made of iron, aluminum or zinc, or an alloy thereof, or the like, and plastic molded articles, and the like. The metal molded article is applicable and preferable, to which a cationic electrodeposition coating composition can be applied, in the formation of the multilayered coating film according to the present invention. It is preferable that the substrate is chemically treated on its surface. The substrate may further include an electrodeposition coating film thereon with an electrodeposition coating composition. The electrodeposition coating composition includes the cationic electrodeposition coating compositions and the anionic electrodeposition coating compositions. The cationic electrodeposition coating composition is preferable due to its corrosion-resistance.

[0055] The base coating composition includes a luster color pigment-containing base coating composition, which may comprise a resin component for forming a base coating film, a luster color pigment, a coloring pigment, a filler pigment, a solvent, and the like. The base coating composition may be in an aqueous solvent (i.e., waterborne) type or in an organic solvent type, including a dispersion in an aqueous solvent and a dispersion in an organic solvent. The aqueous solvent and the organic solvent includes, but are not particularly limited to, those conventional solvents known to those skilled in the art.

[0056] The resin component to be added to the base coating composition may be a resin for forming a base coating film, if necessary, which may be used in a combination with a curing agent for the resin. In the luster color pigment-containing base coating composition, the resin component can disperse the luster color pigment, and if necessary, the coloring pigment.

[0057] The resin in order to form a base coating film includes, for example, acrylic resins, polyester resins, polyurethane resins, alkyd resins, epoxy resins, polyether resins, etc. Among these resins, acrylic resins, polyester resins and polyurethane resins are preferable. One of these resins may be used alone. Alternatively, two or more of these resins may be used in a combination.

[0058] Generally, the resin to form a base coating film includes curable type resins and lacquer type resins. The curable type resin is preferable. The curable type resin can be used in a combination with a curing agent for the resin for forming a base coating film, such as a melarnine resin, a (blocked)isocyanate compound, an oxazoline compound, a carbodiimide compound, or the like. The curing agent for the resin can be added to the resin component, and then subjected to a curing reaction with the resin component under heating or without heating, i.e., at an ambient temperature. Herein, the curable type resin may be used in a combination with other type resin than the curable type resin.

(0059] In the case the resin is used in a combination with the curing agent for the resin, weight ratio of the resin to the curing agent [resin/curing agent], based on the solid content of the coating composition, is preferably within a range of from 90/10 to 50/50, more preferably within a range of from 85/15 to 60/40. The weight ratio of the resin to the curing agent is more than 90/10, wherein the content of the curing agent is less than 10, the resulting coating film may have an insufficient crosslinkage. If the weight ratio is less than 50/50, wherein the content of the curing agent is more than 50, the resulting coating composition may have decreased storage stability and an increased curing rate, and therefore provide a coating film with deteriorated appearance. S 23

[0060] Instead of the above-described curing agent, an etherified-melamine resin may be added thereto. The etherjfjed-melamine resin can be obtained by etherifying a rnelamjne resin with an alcohol such as methanol, butanol, or the like.

[0061] The pigment to be added to the base coating composition includes a scaly luster color pigment made of a metal such as aluminum (or aluminum oxide), copper, zinc, iron, nickel, tin, or an alloy thereof, or the like, which may be colored, and a mixture thereof; and a non-colored luster color pigment, but having an inherent color, such as interference color mica powder, color mica powder, white mica powder, graphite, glass flake, or the like; etc. [0062] The other pigment than the above- described luster color pigment includes, for example, filler pigments such as baryta powder, precipitated barium sulfate, barium carbonate, plaster, clay, silica, talc, magnesium carbonate, and alumina white; and coloring pigments, etc. The coloring pigments include, for example, organic pigments such as azo lake pigments, phthalocyanine pigments, indigo pigments, perylene pigments, quinophthalone pigments, dioxazine pigments, quinacridone pigments, isoindolinone pigments, diketopyrrolopyrrole pigments, benzimidazolone pigments, metal complex pigments; and inorganic pigments such as chrome yellow, yellow iron oxide, red iron oxide, titanium dioxide, carbon black.

Content of the pigment can be appropriately determined depending on the desired properties and the development of the desired color. One of these pigments may be used alone.

Alternatively, two or more of these pigments may be used in a combination.

[0063] If necessary, in addition to the above-described component(s), the base coating composition may appropriately comprise a wax such as polyamide wax including a lubricant dispersion comprising an aliphatic amide, and polyethylene wax including a colloidal dispersion comprising a polyethyleneoxide as a main component; a curing catalyst; an ultraviolet ray absorbing agent; an antioxidant; a leveling agent; a surface conditioner such as silicones and organic polymers; an anti-sagging agent; a thickener; an anti-foaming agent; a lubricant; a crosslinkable polymer particles (i.e., microgels); etc. The additive may be added in an amount of 15 parts by weight or less, as a basis of the solid content, relative to 100 parts by weight of the resin component in order to improve the properties of the coating composition and the properties of the resulting coating film therewith.

[0064] Content of the pigment in the base coating composition relative to the solid content of the coating composition, i.e., pigment weight content (PWC) is preferably up to 65% by weight. It is more preferable that the PWC is no less than 5% by weight. Herein, the solid content of the base coating composition is preferably within a range of from 15% by weight to 60% by weight.

[0065] Application of the base coating composition includes, for example, a multistage-, preferably two stage-coating by an air electrostatic spraying or by a rotary atomization electrostatic coating machine. These application procedures can be carried out in order to improve design properties of the resulting coating film. In addition, the base coating composition may be applied, in a combination of the air electrostatic spraying, with the rotary atomization electrostatic coating machine. Thickness of the resulting dried base coating film is preferably within a range of from 5 to 50 pin, per one coating film, and more preferably within a range of from 10 to 30 jim.

(0066] The resulting uncured base coating film can be subjected to preheating. The applied base coating composition can be subjected to preheating to form an uncured base coating film, as a result, which can provide a multilayered coating film having an excellent finished appearance. Herein, the term "uncured" means a state that the applied coating composition is not completely cured, which further includes a state the applied coating composition has been subjected to preheating. The "preheating" can be carried out without heating, i.e., with being left, or with heating for 1 to 10 minutes at a temperature within a range of from room temperature to 100°C which is lower than the temperature in the following heating (i.e., baking) and curing step.

[0067] In the method for producing the multilayered coating film according to the present invention, application of the clear coating composition includes, for example, application by means of a rotary atomization electrostatic coating machine which is a so-called micro-micro-bel or micro-bel. In the case that the clear coating composition is a coating composition in a two-pack curing system, the two packed-compositions can be mixed, before application, and then the resulting clear coating composition can be applied according to the above-described coating procedure.

According to the present invention, the clear coating composition can be applied such that thickness of the dried coating film formed with the clear coating composition in the resulting multilayered coating film is preferably within a range of from 20 jim to 60 jun.

[0068] The uncured base coating film and the uncured clear coating film thereon, which can be formed according to the above- described coating procedures, preferably can be simultaneously heated (i.e., baked) and cured in order to form a multilayered coating film. The heating can be carried out at a temperature preferably within a range of from 100°C to 180°C, and more preferably within a range of from 120°C to 160°C. Time for the heating and curing may vary depending on the conditions such as curing temperature.

In the case that the above-defined temperature for the heating and curing is applied, the time is appropriately within a range of from 10 to 30 minutes.

(0069] Total thickness of the base coating film and the clear coating film of the resulting multilayered coating film is preferably within a range of from 30 jim to 80.tm.

The multilayered coating film obtained/obtainable by the method according to the present invention can provide excellent film properties such as scratch-resistance, acid-resistance and solvent-resistance, and therefore provide excellent design properties.

[0070] Herein, the method for producing the multilayered coating film according to the present invention may further include, prior to the above-described step (1), a step (p) of applying an intermediate coating composition on the substrate to form an intermediate coating film, or applying a primer surfacer on the substrate to from a primer surface.

Accordingly, the method for producing the multilayered coating film according to the present invention can be applied to both cases that a vehicle body is initially coated and that a coated film on the vehicle body is repaired. The intermediate coating composition which can be employed in the step (P) includes conventional intermediate coating composition known to those skilled in the art.

(0071] The intermediate coating composition includes a waterborne coating composition and a solvent-type coating composition. The intermediate coating composition may comprise, as components therein, a resin component for forming an intermediate coating film, a coloring pigment, a filler pigment, and an aqueous solvent and/or an organic solvent. The resin component includes a resin for forming an intermediate coating film, and can be used in a combination with a curing agent for the resin for forming the intermediate coating film, if necessary. The resin component, the curing agent, the coloring pigment, the filler pigment, and the other additive, and the solvent, which may be added to the intermediate coating composition, can be appropriately selected from those listed in the above-described base coating composition.

(0072] Content of the pigment in the intermediate coating composition, relative to the solid content of the coating composition, i.e., pigment weight content (PWC) is preferably within a range of from 30% by weight to 65% by weight. It is more preferable that the PWC is up to 50% by S 29 weight. Herein, the solid content of the intermediate coating composition is preferably within a range of from 35% by weight to 65% by weight.

[0073] Application of the intermediate coating composition can be carried out by means of spraying, roll coater, or the like. For example, coating procedures such as an air electrostatic spraying by means of a so-called "REACT", and a rotary atomization electrostatic coating machine by means of a so-called "micro-micro-bel (p.p. bel)", "micro-bel (p.

bel)", "meta-bel" or the like are preferable. Among others, the coating by means of the rotary atomization electrostatic coating machine is particularly preferable.

Thickness of the dried intermediate coating film is preferably within a range of from 5 to 80 p.m, and more preferably within a range of from 10 to 50 p.m.

[0074] The resulting uncured intermediate coating film can be subjected to baking and curing at a temperature within a range of from 120 to 160°C for a given period in order to form a cured intermediate coating film. On thus obtained cured intermediate coating film, the above-described base coating composition and the above-described clear coating composition can be applied.

[0075] Herein, preferably, on the resulting uncured intermediate coating film, by wet-on-wet, the base coating composition can be applied, and then the clear coating composition can be applied thereon in order to form the uncured intermediate coating film, the uncured base coating film, and the uncured clear coating film in this order. In such case that the clear coating composition is applied by wet-on-wet on the uncured base coating composition, the applied intermediate coating composition may be subjected to preheating in order to form an uncured intermediate coating film. As a result, it can provide a multilayered coating film having an excellent finished appearance.

[0076] Herein, according to the present invention, instead of the intermediate coating composition, a primer surfacer can be applied to the substrate, as a primer coating composition, in order to form a primer surface, i.e., a primer coating film. Herein, the method for producing the multilayered coating film according to the present invention can be applied to repair the coating film applied on the vehicle such as an automobile. Herein, the primer surfacer includes conventional surfacer known to those skilled in the art.

EXAMPLES

[0077] Hereinafter, the present invention is further described in detail referring to the following Examples, but is not limited to these Examples. In the Examples, the term "part(s)" mean(s) "part(s) by weight" unless otherwise specified.

[0078] Preparation Example "a" 446 Parts of propyleneglycol monomethyl ether acetate was added into a reaction vessel equipped with a thermometer, a stirring blade, a nitrogen-introducing tube, a cooling condenser and a dropping funnel, and then heated to 120°C under nitrogen atmosphere. 100 Part of propyleneglycol monomethyl ether acetate, 105 parts of tert-butylperoxy-2-ethyihexanoate, and a monomer mixture consisting of 200 parts of styrene, 270 parts of isobornyl methacrylate, 67 parts of n-butyl acrylate, 100 parts of lauryl methacrylate, 360 parts of 4-hydroxybutyl acrylate and 3 parts of methacrylic acid were added dropwise into the vessel through the dropping funnel at a constant rate over 3 hours.

Subsequently, the mixture was left for 0.5 hour at 120°C.

Parts of tert-butylperoxy-2--ethylhexanoate dissolved in parts of propyleneglycol monomethyl ether acetate was added dropwise to the mixture at a constant rate over 30 minutes. The mixture was left at 120°C with heating for 1 hour. S 32

(0079] Consequently, the resulted product was an acrylic copolymer, hereinafter which was referred to as acrylic copolymer "a", having calculated Tg: 4.8°C, acid value: 2 mgKOH/g and hydroxyl value: 140 mgKOH/g (as a basis of solid content), number average molecular weight (Mn) : 4600 and weight average molecular weight (Mw) : 11600 (calculated by GPC with a polystyrene standard), and solid resin content: 62.5%.

[0080] Preparation Examples b to k As shown in the following Table 1, acrylic copolymers "b" to "k" containing hydroxyl (i.e., OH) groups were prepared according to the Preparation Example "a" with the proviso that formulations were shown in the following Table 1.

(0081] Herein, alkyl rnethacrylate was ACRYESTER SL (produced by MITSUBISHI RAYON CO., LTD.) wherein mixing ratio of lauryl methacrylate to tridecyl methacrylate was 4/6 (lauryl methacrylate/tridecyl methacrylate) as a basis of weight.

(0082] Table 1

SI

Preparation Example a b J c d e g h J i k Styrene 200.0 200.0 200.0 195.5 203.0 200.0 50.0 200.0 200.0 160.0 100.0 n-ButylAcrylate 67.0 67.0 67.0 67.0 67.0 17.0 117.0 142.0 107.0 167.0 g Lauryl Methacrylate 100.0 Tridecyl Methacrylate 100.0 i2 Alkyl Methacrylate* 100.0 100.0 100. 0 150.0 180.0 50.0 25.0 ______ ______ E Isobornyl Methacrylate 270.0 270.0 270.0 270.0 270.0 2700 407.0 270.0 270.0 270.0 370.0 2Ethylhexyl Methacrylate 100.0 4-Hydroxybutyl Acrylate 360.0 360.0 360.0 360.0 360.0 360.0 360.0 360.0 360.0 360.0 360.0 -Methacrylic Acid 3.0 3.0 3.0 7.5 3.0 3.0 3.0 3.0 3.0 3.0 Content of Long Chain (meth)ocrylate monomer (in wt%) 10.0 10.0 10.0 10.0 10.0 15.0 18.0 5.0 2.5 0.0 0.0 Calculated Tg (°C) 4.8 7.9 5.3 5.5 5.2 4.7 3.1 6 6.3 6.8 7.2 W Acid Value (mgKOH/g) 2 2 2 5 0 2 2 2 2 2 2 ° Hydroxyl Value (mgKOH/g) 140 140 140 140 140 140 140 140 140 140 140 Number Average Molecular Weight (Mn) 4600 4500 4600 4600 4500 4400 4600 4500 4300 4400 4500 Weight Average Molecular Weight (Mw) 11600 10400 1 1300 10700 10600 10500 11000 11000 10700 11200 10800 0. __________________________________ _____ ______ _____ ______ ______ ______ _____ ______ ______ -Solid Resin Content (%) 62.5 62.1 62.6 62.8 62.4 62. 5 62 8 62.3 62.6 62.5 62.6 * alkyl methacry].ate: ACRYESTER SL (produced by MITSUBISHI RAYON CO., LTD.) wherein mixing ratio of lauryl methacrylate to tridecyl methacrylate was 4/6 (lauryl methacrylate/tridecyl methacrylate) as a basis of weight [0083] Examples 1 to 7 and Comparative Examples 1 to 4 According to the formulations as shown in the following Table 2, one of acrylic copolymers "a" to "k", each of which comprised hydroxyl (i.e. OH) groups, and an Isocyanate compound in an isocyanurate form (Desmodule N-3300 produced by Sumika Bayer Urethane Co., Ltd.) were combined to prepare clear coating compositions. Hereinafter, these clear coating compositions are respectively referred to as Examples 1-7 and Comparative Examples 1-4.

[0084] A cationic electrodeposition coating composition under a trade name of "POWERTOP U-50" (produced by NIPPON PAINT Co., Ltd.) was applied on a phosphate-treated steel panel, and then heated and cured such that thickness of the resulting dried electrodeposition coating film was 25 jnn.

Subsequently, a gray intermediate coating composition under a trade name of "ORGA P-30" (produced by NIPPON PAINT Co., Ltd.) was applied on the coating film, and then heated and cured, such that thickness of the resulting dried intermediate coating film was 40 jim, to prepare a test panel. A waterborne base coating composition, in a silver metallic color, under a trade name of "AQUAREX AR-2000" (produced by NIPPON PAINT Co., Ltd.) was applied on the test panel to form an uncured base coating film, and then, by wet-on-wet, i.e., on the uncured base coating film, the clear coating composition selected from the Examples 1-7 and Comparative Examples 1-4 was applied. The panel was baked and dried at 140°C for 30 minutes to prepare a coated test panel having the multilayered coating film. Herein, the coated test panel was prepared by a so-called two-coating and one-baking (2C1B) coating procedure. Herein, the multilayered coating film having the base coating film and the clear coating film thereon was applied on the panel such that thickness of the dried base coating film was 15 J.xm and thickness of the dried clear coating film was 40 tm.

Separately, the base coating composition in a silver metallic color was applied on the other test panel such that thickness of the dried base coating film was 15 pm, and then baked and dried at 140°C for 30 minutes to prepare a coated test panel having one single base coating film.

[0085] Evaluations The coated test panel comprising the clear coating film formed with the clear coating composition selected from the Examples 1-7 and Comparative Examples 1-4 was evaluated according to the following evaluation items (1)-(4) Evaluation results are shown in the following Table 2.

[0086] Table 2

Number of C atoms of Exmples CparaiveEamples Neutral Side Chain of Side Chain -(Formulation Based on Solid Content) on Solid content Monomer 1 2 3 4 J 5 6 7 1 2 ---= -Acrylic Copolymer a containing OH groups Cl 2 Linear 68.68 Acrylic Copolymer b containing OH groups Cl 3 Linear 68.68 Acrylic Copolymer c containing OH groups Cl 2/Cl 3 Linear 68.58 Acrylic Copolymer d containing OH groups Cl 2/C 13 Linear 68 68 Acrylic Copolymer e containing OH groups Cl 2/Cl 3 Linear 68 68 Acrylic Copolymer f containing OH groups Cl 2/C 13 Linear 68.68 --Acrylic Copolymor g containing OH groups Cl 2/Cl 3 Linear -68.68 Acrylic Copolymer h containing OH groups Cl 2/C 13 Linear 68.68 Acrylic Copolymer i containing OH groups C12/C13 Linear 6868 Acrylic Copolymer.j containing OH groups C8 Branched 68 68 Acrylic Copolymer k containing OH groups Cl 0 Cyclic 68.68 Isocyanate in Isocyanurete Form 31.32 31.32 31.32 31.32 31.32 31.32 31 32 31 32 31.32 31.32 31.32 L Value Highlight 95.64 95 64 95.56 95.48 95.62 95.71 95 68 9540 95.65 95.66. 95.77 Singly Applied -Base Coating Film Shade 31.97 31.85 31.62 31.91 31.94 31.80 31.89 31.92 32.02 31.79 31.86 L Value Highlight 95.23 95.44 95.22 95.42 9541 95.11 9556 9465 94.81 93.32 93.65 L Value Clear Coating Applied Base Coating Film Shade 33.98 33.92 33.52 32.95 33.86 34.01 32.99 34.59 34.62 35.98 35.78 Highlight -0.41 -0.20 -0.34 -006 -0.21 -0.60 -012 -075 -0.84 -2.34 -2.12 LIL Value ---Shade 2.01 2.01 1.90 1.04 1.92 2.21 1.10 2.67 260 419 3.92 Visually Observed Appearance 0 0 0 0 0 0 � X X Innitial Adherence in Recoating Q 0 0 0 0 0 Water Resistance and Secondary Adherence after Recoating 0 0 0 0 0 0 X S 38 [0087] (1) L value Difference between the metallic color of the multilayered coating film formed in accordance with the 2C1B coating procedure and the metallic color of the corresponding single base coating film was measured.

As schematically illustrated in the appended Fig. 1, the measurement was carried out with CM-512m3 manufactured by MINOLTA. L values were measured at acceptance angles of 25° (hereinafter which is referred to as "highlight") and 75° (hereinafter which is referred to as "shade") . i L value was calculated according to the following equation: L L value = (L value of multilayered coating film) - (L value of single base coating film) (0088] (2) Visually Observed Appearance Design properties of the multilayered coating film was visually observed and evaluated. Evaluation basis is as follows.

Evaluation basis Excellent ( � ) : Surprisingly significant flip-flop properties and extremely excellent design properties Good ( 0) : Significant flip-flop properties and remained inherent design properties of the base coating film with slight miscibility between the base coating film and the clear coating film No Good ( A) : Deteriorated flip-flop properties and deteriorated design properties with miscibility between the base coating film and the clear coating film Terrible ( X) : Extremely deteriorated flip-flop properties and extremely deteriorated design properties with miscibility between the base coating film and the clear coating film (0089] (3) Initial Adherence in Recoating On the heated and cured multilayered coating film, the above-described same waterborne base coating composition was applied again thereon, and then the above-described same clear coating composition was applied thereon. Baking and drying was carried out at 120°C for 30 minutes to prepare a test panel for evaluating the adherence. The resulted test panel was subjected to a cross-cut adhesion test according to JIS K 5600-5-6. Evaluation of the adhesion between films as initial adhesion was carried out.

Evaluation basis is as follows.

Evaluation basis Excellent (0): No peeling of coating films Terrible (X) : Peeling of coating films [0090] (4) Water Resistance and Secondary Adherence after Recoa ting The above-described test panel for evaluating the initial adherence, before cross-cut adhesion test, was immersed into ion-exchange water at 40°C, and then kept at 40°C for days. Immediately after taking up the test panel, water on the surface of the test panel was wiped off. The test panel was subjected to a cross-cut adhesion test according to JIS 1< 5600-5-6. Evaluation of the adhesion between films as secondary adhesion was carried out. Evaluation basis is as follows.

Evaluation basis Excellent (0): No peeling of coating films Terrible (X) : Peeling of coating films [0091] The Examples 1-7 respectively provided small iL values at both of highlight and shade. This means that, in the resulted multilayered coating film therewith, color reversion could be suppressed, and excellent inherent design properties of the base coating film could be maintained.

[0092] Whereas, the Comparative Examples 1-4 respectively provided large L values at both of highlight and shade.

This means that, the resulted multilayered coating film therewith, wherein color reversion was occurred, and could * not provide good design properties.

INDUSTRIAL APPLI CATION

(0093] The clear coating composition according to the present invention is applicable to application on vehicles such as automobiles, particularly automobiles to which excellent design properties are desired in the market. The clear coating composition according to the present invention is preferably applicable to initial coating or repairing the coated film on the automobile. The clear coating composition according to the present invention is preferably applicable to application on a base coating film particularly in a metallic color. a

Claims

WHAT IS CLAIMED IS: 1. A clear coating composition, which comprises an acrylic resin obtainable/obtained by a monomer mixture comprising a (meth)acrylate monomer comprising a long chain of a linear hydrocarbon group having 9 to 15 carbon atoms, a carboxyl group- containing (meth)acrylic monomer, and a hydroxyl group-containing (meth)acrylic monomer.
2. The clear coating composition according to claim 1, which further comprises a curing agent which can react with a carboxyl group and/or a hydroxyl group.
3. The clear coating composition according to claim 2, wherein the curing agent is a polyisocyanate compound.
4. The clear coating composition according to any one of claims 1 to 3, wherein content of the (meth)acrylate monomer is within a range of from 5 to 15% by weight relative to total weight of monomer solid contents in the monomer mixture.
5. The clear coating composition according to any one of claims 1 to 4, wherein the acrylic resin has an acid value, based on the solid content, within a range of from 1 to 10 mgKOH/g. 0 -
6. A method for producing a multilayered coating film, which includes steps of (1) applying a base coating composition on a substrate to from an uncured base coating film thereon, (2) applying a clear coating composition on the uncured base coating film to form an uncured clear coating film thereon, and (3) heating and curing both of the uncured base coating film and the uncured clear coating film thereon to form a multilayered coating film, wherein the clear coating composition is according to any one of claims 1 to 5.
7. The method according to claim 6, which further includes, prior to the step (1), a step (p) of applying an intermediate coating composition on the substrate to form an intermediate coating film, or applying a primer surfacer on the substrate to from a primer surface.