GB2399520A

GB2399520A - Forming a coated composite film by a three-coat one-bake method

Info

Publication number: GB2399520A
Application number: GB0406010A
Authority: GB
Inventors: Takayuki Fujita; Takuhiro Kakii; Masakazu Watanabe
Original assignee: Nippon Paint Co Ltd
Current assignee: Nippon Paint Co Ltd
Priority date: 2003-03-18
Filing date: 2004-03-17
Publication date: 2004-09-22
Anticipated expiration: 2024-03-17
Also published as: JP2004275966A; GB0406010D0; GB0405880D0; JP4170805B2; KR20040082338A; CN100339163C; CN1532004A; GB2399520B; TW200427797A

Abstract

A coated composite film having excellent appearance, in particular gloss appearance and excellent in anti-chipping properties is formed by forming an electrocoated film on a substrate, and then successively applying an intermediate paint, a base paint and a clear paint in a wet-on-wet manner, followed by baking and curing the three layers at once, the baking and curing including both a low-temperature heating stage of heating at a temperature which is 25 to 80% of a curing temperature for a time which is 5 to 30% of a curing time and a high temperature heating stage of heating at a temperature which exceeds 80% and is not more than 120% of a curing temperature for a time which is 30 to 130% of a curing time. The intermediate paint may comprise (a) an urethane-modified polyester resin (b) a melamine resin, (c) a blocked isocyanate compound, (d) a non-aqueous dispersion resin having a core-shell structure and (e) a flake pigment.

Description

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METHOD FOR COATED COMPOSITE FILM

FIELD OF THE INVENTION

l0001l The present invention relates to a method for forming a coated composite film and, more particularly, to a method for forming a coated composite film by a three-coat one-bake method.

BACKGROUND OF THE INVENTION

1 Y There are two methods for forming a coated composite film. One is a method in which every coated film is baked and cured after coating. The other is a method in which a coated composite film is formed by coating two or more paints without curing and then cured one time. For example, two-coat one-bake method is generally performed for forming a metallic coating. JP-A No. 11-114489 discloses a method for forming a coated composite film which comprises successively forming a color base coating film, a metallic base coating film and a clear coating film, and then baking and curing the three layers at the same time, in order to enhance film appearance.

100031 When an intermediate coating film, a base coating film and a clear coating film are formed by a three-coat one-bake method, a baking oven for curing the intermediate coating can be eliminated. Accordingly, consumed energy and operation time are reduced, and there is great advantage in economical view and environment compatibility.

100041 However, in the three-coat one-bake method, three layers of coating films are overlaid in wet or damp-dry state. For this reason, escaping ways of solvent are reduced and limited so that a non-volatile content in the coated composite film increases, as compared with conventional successive baking method or two-coat one-bake method. As the result, solvent contained in one coating film is moved to an adjacent coating film, especially when heating.

This solvent movement easily raises phenomenon which is so-called phase mixing at baking and curing, in which adjacent coating films are dissolved in each other and components contained in respective coating films are mixed.

When the phase mixing occurs, appearance of the resulting composite film is remarkably deteriorated. In particular, the phase mixing has remarkable adverse effect on gloss appearance of the coated composite film.

5] On the other hand, JP-A No. 20004463 suggests a method of performing a baking and curing step under two stage heating conditions, as a method for forming a coating film excellent in smoothness using a solution-type thermosetting paint. In this method, roughness of the coating film surface is prevented by mildly evaporating solvent contained in a coated layer.

1 Y However, the three-coat one-bake method has, for example, the following problems.

1 71 Peeling of coating film occurs in some cases by so-called chipping where a running vehicle snaps up pebbles and the pebbles collide with a coating film. In the conventional coated composite film formation method such as baking every application of respective paints and a two-coat onebake method, an undercoating film and an intermediate coating film are baked and cured, independently. Therefore, strategy for chipping could be adopted by forming an anti-chipping coating film on or beneath an intermediate coating film, or forming an intermediate coating film in which chipping is not recognized, by adjusting the brightness of a topcoating film and the brightness of an intermediate coating film.

8] For example, JP-A No.2002-249699 and JP-A No.9-208882 describe a chipping primer coating composition, and formation of an anti-chipping coating film in a coated composite film.

100091 In addition, in JP-A No.6-256714 or JP-A No.6-254482, improvement in the antihipping properties is studied from a viewpoint of a composition of an intermediate paint, but a level of improvement is insufficient for using in a three-coat one-bake method.

OBJECT OF THE INVENTION

100101 The present invention solves the conventional problems, and an object of the present invention is to provide a method of forming a coated composite film having good appearance, especially gloss properties, and excellent anti-chipping properties, by a three-coat one-bake method.

SUMMARY OF THE INVENTION

10011] The present invention provides a method for producing a coated composite film, comprising forming an electrocoated film on a substrate, and then successively applying an intermediate paint, a base paint and a clear paint in a wet-on-wet manner, followed by baking and curing the applied three layers at once, wherein the baking and curing includes both a low-temperature heating stage of heating at a temperature which is 25 to 80% of a curing temperature for a time which is 5 to 30% of a curing time, and a high-temperature heating stage of heating at a temperature which exceeds 80% and is not more than 120% of a curing temperature for a time which is 30 to 130% of a curing time.

DETAILED DESCRIPTION OF THE INVENTION

00121 Coating film formation f In the coated composite-film forming method of the present invention, an intermediate coating film is formed by an intermediate paint, a base coating film is formed by a base paint, and a clear coating film is formed by a clear paint, successively on a substrate in a wet-on-wet manner.

[00131 When an automobile body is used as a substrate, as an anticorrosion film (generally referred to as "undercoating film"), an electrodeposition film is formed on a body steel plate in advance. In a method of applying an intermediate paint, a paint can be applied by multistage coating, preferably, two-stage coating by an air electrostatic spray coating, or can be applied by air electrostatic spray coating and/or with a rotation atomizing electrostatic coating machine called Upp (micro micro) bel", "p (micro) bel" or "metabel".

[00141 A thickness of a dried coating him formed of an intermediate paint varies depending on the desired utility. In many cases, a thickness of 10 to 60,um is useful. When a thickness exceeds an upper limit, sharpness of image is reduced, disadvantage such as ununiformity and sagging occurs at coating in some cases and, when a thickness is below a lower limit, the surface can be hidden and uneven coating occurs.

[00151 In the coated composite film formation method of the present invention, on an uncured intermediate coating film, a base paint and a clear paint are coated in a wet-on-wet manner, to form a base coating film and a clear coating film.

[00161 A base paint used for forming a base coating film can be applied by electrostatic spray coating or with a rotation atomizing electrostatic coating machine such as a metabel, a Isabel, a Abel and the like. A dried thickness of the coating film can be set to be 5 to 35 Am, preferably 7 to 25 m. When a . r I thickness of a base coating film exceeds 35 am, sharpness of image is reduced, and ununiformity or sagging occurs in some cases. When a thickness is less than 5 m, surface hiding properties are insufficient and uneven coating (state of discontinuous film) occurs in some cases.

7] When irregularities resulting from the base coating film are present or when luster color pigments are contained, a clear coating film is formed for protection by hiding fine projections generated therefrom. As a coating method, specifically, it is preferable to form a coating film with the rotation atomizing electrostatic coating machine such as a Ilil bel, a 11 bel and the like.

lO01 al A dry thickness of a clear coating film is preferably about 10 to 80 m, more preferably about 20 to 60 m. When the dry thickness exceeds an upper limit, disadvantage such as popping and sagging occurs at application in some cases. When the thickness is below a lower limit, irregularities of the surface can not be hidden.

lO01 al The thus coated composite films are cured by simultaneous heating.

The method is generally called three-coat one-bake method. A thickness of a coated composite film is, in many cases, 30 to 300,um, preferably 50 to 250 lam.

When the thickness exceeds an upper limit, film physical properties, such as temperature cycle test, is reduced. When the thickness is below a lower limit, strength of a film is reduced.

100201 In order to sufficiently cure a coated layer which is applied on the substrate surface, curing condition is set for a thermosetting paint. When a thermosetting paint is cured under the condition not satisfying the curing condition, cross-linking of a coated composite film is insufficient, and the coated composite film performance is reduced. Generally, as the curing condition of a thermosetting paint, a curing temperature ( C) and a curing time are set.

100211 A curing temperature refers to a temperature of an environment in which a coated composite film is placed when a coated film is baked and cured by a conventional one stage heating method. Generally, it is a temperature arranged for a drying oven in which a coated composite film is inserted. A curing temperature is determined depending on both a temperature for reacting the cross-linking system of a coated composite film and a facility of a practical application line to be applied.

100221 A curing time refers to a time necessary for curing a coated composite film at a curing temperature. As a curing time, an optimal value is empirically determined depending on a kind of a paint and a thickness of a coated composite film. A curing time is determined as a time by which practically necessary coated composite film performance is obtained, taking mode of a facility of a practical application line to be applied and a curing temperature into consideration.

100231 In the method of the present invention, a step of baking-curing coated three layers is divided into a low-temperature heating stage and a high-temperature heating stage, and each stage is performed for a predetermined time. When a low-temperature heating stage is performed in a short time, a total heating time is not fairly long time and working efficacy is not reduced. It is considered that, since a deposited volatile content can be increased by performing a low-temperature heating stage, phase of layers mixing is prevented from occurring.

100241 In a low-temperature heating stage in the present invention, a layer of a thermosetting paint formed on the substrate surface is heated at a temperature which is 25 to 80%, preferably 35 to 60% of a curing temperature, for a time which is 5 to 30%, preferably 10 to 20% of a curing time. When a curing temperature and a curing time are outside the range, technical effects are insufficient. For example, when a curing temperature is 140 C, a low-temperature heating temperature is 35 to 112 C, preferably 49 to 84 C.

When a curing temperature is 100 C, a low-temperature heating temperature is to 80 C, preferably 35 to 60 C. In addition, when a curing time is 30 minutes, a low-temperature heating time is 2 to 9 minutes, preferably 3 to 6 minutes. When a curing time is 60 minutes, a low-temperature heating time is 3 to 18 minutes, preferably 6 to 12 minutes.

l0025l At a high-temperature heating stage, a layer of a thermosetting paint is further heated at a temperature which exceeds 80% and is not more than 120%, preferably 90 to 110% of a curing temperature, for a time which is 30 to 130%, preferably 50 to 100% of a curing time. When a curing temperature and a curing time exceed an upper limit, stress strain is accumulated, and a crack occurs in a coated composite film in some cases. For example, when a curing temperature is 140 C, a high- temperature heating temperature exceeds 112 C and is not more than 168 C, preferably 126 to 154 C. When a curing temperature is 100 C, a high- temperature heating temperature exceeds 80 C and is not more than 120 C, preferably 90 to 110 C. In addition, when a curing time is 30 minutes, a high-temperature heating time is 10 to 40 minutes, preferably 15 to 30 minutes. When a curing time is 60 minutes, a high-temperature heating time is 18 to 78 minutes, preferably 30 to 60 minutes.

l0026l Heating can be performed by using the method known to a person skilled in the art. Generally, an article, on which a thermosetting paint is coated,

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may be held in a drying oven adjusted at a heating temperature.

[00271 Especially the method may include: a procedure of placing an article to be coated, on which a thermosetting paint is coated, in a drying oven controlled at a lower-temperature heating temperature, holding it for a low-temperature heating time and, thereafter, adjusting a temperature of a drying oven to a high-temperature heating temperature, and holding for a high-temperature heating time; a procedure of preparing a tunnel-type dryer in which an inlet and an outlet are opened at both ends, and drying is performed by moving the material therein by a belt conveyer, dividing the interior of a tunnel into a low-temperature region and a high-temperature region, adjusting a temperature of a lowtemperature region at a low-temperature heating temperature and adjusting a temperature of a high-temperature region at a high-temperature heating temperature, first passing the article through a low-temperature region for a low-temperature heating time and, thereafter, passing the article through a high-temperature region for a high-temperature heating time; and a procedure of preparing a first drying oven adjusted at a temperature of a low-temperature heating temperature, and a second drying oven adjusted at a temperature of a high-temperature heating temperature, then holding an article to be coated on which a thermosetting paint is coated, in the first drying oven for a low-temperature heating time and, holding the article in the second drying oven for a high-temperature heating time.

00281 Intermediate coating film In the coating film formation method of the present invention, an intermediate paint is used for forming an intermediate coating film, and the À . intermediate paint contains (at an urethane-modified polyester resin, (b) a melamine resin, (c) a blocked isocyanate compound, (d) a non-aqueous dispersion resin having a coreshell structure, and (e) a flake pigment. The intermediate paint may further contain organic or inorganic various coloring pigments and filler pigments.

100291 The urethane-modified polyester resin (a) can be obtained by reacting a hydroxyl group-containing polyester resin with an aliphatic isocyanate compound.

[00301 Generally, a polyester resin can be prepared by polycondensing an acid component such as carboxylic acid, acid anhydride and acid chloride, with a monohydric or polyhydric alcohol. The hydroxyl group-containing polyester resin used in the present invention contains isophthalic acid in an acid component used in a polycondensation reaction, at 80 mol% or more on the basis of a total mole number of an acid component. When an amount of isophthalic acid in an acid component is lower than 80 mol%, a glass transition temperature (Tg) of the resulting hydroxyl group- containing polyester resin becomes lower than the desired range.

[00311 Examples of an acid component other than isophthalic acid include phthalic acid, phthalic acid anhydride, tetrahydrophthalic acid, tetrahydrophtalic acid anhydride, hexahydrophthalic acid, hexahydrophthalic acid anhydride, methyltetrahydrophthalic acid, methyltetrahydrophthalic acid anhydride, himic acid anhydride, trimellitic acid, trimellitic acid anhydride, pyromellitic acid, pyromellitic acid anhydride, terephthalic acid, maleic acid, maleic acid anhydride, fumaric acid, itaconic acid, adipic acid, azelaic acid, sebacic acid, succinic acid, succinic acid anhydride, dodecenylsuccininc acid, dodecenylsuccininc acid I' . 1 anhydride and the like. Alternatively, as an acid component, acids other than polyvalent carboxylic acid and acidanhydride, which are generally used in preparation of a polyester resin may be contained. Examples of such an acid include monocarboxylic acid and hyroxycarboxylic acid. As an acid used for preparing the hydroxyl group-containing polyester resin, isophthalic acid may be used alone, or may be used by mixing with other acid.

l0032l Examples of the polyhydric alcohol include ethylene glycol, diethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, neopentyl glycol, 1,2-butanediol, 1,3butanediol, 1,4-butanediol, 2,3-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,4-cyclohexanediol, 2,2-dimethyl-3-hydroxypropyl-2,2-dimethyl-3-hydroxypropionate, 2,2,4-trimethyl-1,3-pentanediol, polytetramethylene ether glycol, polycaprolactone polyol, glycerin, sorbitol, annitol, trimethylolethane, trimethylolpropane, trimethylolbutane, hexanetriol, pentaerythritol, dipentaerythritol and the like.

10033] In preparation of the hydroxyl group-containing polyester resin, besides the acid components and polyhydric alcohols, other components which can be reacted with these components may be used. Examples of such other components include acid chloride, acid derivatives of lactones, an epoxide compound, and a drying oil and a semidrying oil and fatty acid derivatives thereof. Lactones can form a graft chain by ring-opening addition to polyester resin of polyvalent carboxylic acid and polyhydric alcohol. Examples of lactones includes,8-propiolactone, dimethylpropiolactone, butyllactone, y-valerolactone, E-caprolactone, ycaprolactone, y-capryllactone, crotolactone, 6-valerolactone, 6-caprolactone and the like. In particular, E- caprolactone is most preferable. Specific examples include monoepoxide compound such as Carjula E (manufactured by Shell Chemical Co., Ltd.), and lactones.

100341 The hydroxyl group-containing polyester resin has a glass transition temperature (Tg) of 40 to 80 C, preferably 45 to 75 C. When the glass transition temperature (Tg) is lower than 40 C, film hardness is reduced.

When the point is higher than 80 C, anti-chipping performance is reduced.

100351 Examples of the aliphatic isocyanate compound include hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, cyclohexane-1,4-diisocyanate, dicyclohexylmethane4,4-diisocyanate, methylcyclohexane diisocyanate and isophorone diisocyanate.

l0036l In particular, it is preferable from a viewpoint of anti-chipping performance and weather resistance of a coated composite film that hexamethylene diisocyanate or trimethylhexamethylene diisocyanate is used.

Buret, isocyanurate and adduct of them may be used.

100371 A reaction of the hydroxyl group-containing polyester resin and the aliphatic isocyanate compound can be performed by a method known to a person skilled in the art.

[00381 The urethane-modified polyester resin (a) has a number average molecular weight (Mn) of 1500 to 3000, preferably 1700 to 2500. When the molecular weight is smaller than 1500, workability and curability are not sufficient. When the molecular weight exceeds 3000, a nonvolatile content is too low when coating, and workability is deteriorated conversely. Herein, a number average molecular weight is determined by a GPC method using polystyrene as a standard.

00391 The urethane-modified polyester resin (a) has a hydroxyl-group value (OHV) of preferably 30 to 180, more preferably, 40 to 160. When a hydroxyl group value exceeds 180, water resistance of a coated composite film is reduced. When the hydroxyl group value is smaller than 30, curability of a coated composite film is reduced. In addition, the resin has an acid value (AV) of preferably 3 to 30 mgKOH/g, more preferably 5 to 25 mgKOH/g. When an acid value exceeds 30 mgKOH/g, water resistance of a coated composite film is reduced. When an acid value is smaller than 3 mgKOH/g, curability of a coated composite film is reduced.

0] An amount of the urethane-modified polyester resin (a) contained in an intermediate paint is, on the basis of a weight of a resin solid content in a paint, to 56% by weight, preferably 43 to 50% by weight. When a content is smaller than 40% by weight, anti-chipping performance becomes insufficient.

When a component exceeds 56% by weight, hardness of a coated composite film is reduced.

1] It is considered that, by inclusion of the urethane-modified polyester resin as a component for an intermediate paint, elasticity of a coated composite film is improved, and anti-chipping properties of a coated composite film is also improved.

2] A melamine resin (b) and a blocked isocyanate compound (c) described below are a component for curing an urethane-modified polyester resin (a).

10043] The melamine resin (b) is not particularly limited, but includes a methylated melamine resin, a butylated melamine resin or a methyl-butyl mixed type melamine resin. Examples include "Cymel-303", "Cymel 254", "U ban 128" and "U ban 20N60" sold by Mitsui Toatsu, and USumimar Series" sold by Sumitomo Chemical Co., Ltd. 100441 An amount of the melamine resin (b) contained in an intermediate paint is 10 to 30% by weight, more preferably 15 to 25% by weight on the basis of a weight of a resin solid content in a paint. When a content of a melamine resin is smaller than 10% by weight, curing of a coated composite film is insufficient.

When a content exceeds 20% by weight, a cured coated composite film is too hard, and brittle.

100451 The blocked isocyanate compound (c) can be obtained by adding a blocking agent to aliphatic isocyanate or a derivative thereof. When the blocked isocyanate compound is heated, a blocking agent is dissociated to generate an isocyanate group, which is reacted with a hydroxy group in the urethane-modified polyester resin to cure the material.

l0046l Examples of the aliphatic isocyanate and a derivative thereof include compounds which are used for preparation of the urethane-modified polyester resin. Examples of the blocking agent include compounds having an active methylene group, such as acetyl acetone, ethyl acetoacetate and ethyl malonate. By using the blocking agent, elasticity of a coated composite film is improved, and anti-chipping of a coated composite film is also improved.

[004n The blocked isocyanate compound is sold, for example, by Asahi Chemical Industry Co., Ltd., as active methylene-type blocked isocyanate "Duranate MF-K60Xn.

l0048l An amount of the blocked isocyanate compound (c) contained in an intermediate paint is 15 to 30% by weight, preferably 17 to 25% by weight on the basis of a weight of a resin solid content in a paint. When a content is smaller than 15% by weight, curability is insufficient and, when a content exceeds 30% by weight, cured film is too hard, and brittle.

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10049] The non-aqueous dispersion resin (d) having a core-shell structure can be prepared by copolymerizing a dispersion stable resin and a copolymerizable monomer in a mixed solution with an organic solvent, to obtain the resin as a non-cross-linked resin particle which is insoluble in the mixed solution. A monomer to be copolymerized in the presence of the dispersion stable resin for obtaining a non-uoss-linked resin particle is not particularly limited as far as it is a radical- polymerizable unsaturated monomer.

100501 In order to synthesize the dispersion stable resin and a nonaqueous dispersion, it is preferable to use a polymerizable monomer having a functional group because the non-aqueous dispersion having a functional group can react with the curing agent together with the dispersion stable resin containing a functional group to form a three- dimensionally cross-linked coated composite film.

10051] The dispersion stable resin is not particularly limited as far as the non-aqueous dispersion can be stably synthesized in an organic solvent.

Specifically, it is preferable to use an acryl resin, a polyester resin, a polyether resin, a polycarbonate resin, polyurethane resin and the like, which have a hydroxyl group value of 10 to 250, preferably 20 to 180, an acid value of 0 to mgKOH/g, preferably 0 to 50 mgKOH/g, and a number average molecular weight of 800 to 100,000, preferably 1,000 to 20,000. When above parameters exceed upper limits, handling properties of the resin are reduced, and handling properties of the non-aqueous dispersion are also reduced. When parameters below lower limits, there is a possibility that the coated film is desorbed off and the stability of a particle is reduced when formulated into a coated composite film. .

l0052l A method of synthesizing the dispersion stable resin is not particularly limited, but include preferably a method of obtaining the resin by radical polymerization in the presence of a radical polymerization initiator, and a method of obtaining the resin by condensation method or an addition reaction.

In addition, a monomer which is used for obtaining the dispersion stable resin can be appropriately selected depending on properties of the resin, but it is preferable to use monomers having a functional group such as a hydroxyl group, an acid group and the like which are possessed by polymerizable monomers described later which are used for synthesizing the non-aqueous dispersion and, further if needed, monomers having a functional group such as a glycidyl group, an isocyanate group and the like may be used.

100531 In addition, a weight ratio of the dispersion stable resin and the polymerizable monomer can be arbitrarily selected depending on the purpose.

For example, it is preferable that the dispersion stable resin is 3 to 80% by weight, particularly 5 to 60% by weight, and the polymerizable monomer is 97 to 20% by weight, particularly 95 to 40% by weight on the basis of a total weight of both components. Further, the total concentration of the dispersion stable resin and the polymerizable monomer in an organic solvent is preferably 30 to 80% by weight, particularly 40 to 60% by weight on the basis of a total weight.

100541 The non-aqueous dispersion can be obtained by polymerizing a radical polymerizable monomer in the presence of the dispersion stable resin. In this non-aqueous dispersion, it is preferable that a hydroxyl group value is 50 to 400, preferably 100 to 300, an acid value is 0 to 200 mgKOH/g, preferably 0 to 50 mgKOH/g, and an average particle diameter (D50) is 0.05 to 10,um, preferably 0.1 to 2 m. When parameters are below lower limits, a particle shape does À À not maintain. When parameters exceed upper limits, stability is reduced when dispersed in a paint.

100551 Representative polymerizable monomers having a functional group used for synthesizing the non-aqueous dispersion include monomers having a hydroxyl group, such as hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxybutyl (meth)acrylate, hydroxymethyl (meth)acrylate, allyl alcohol, and adduct of hydroxyethyl (meth)acrylate and Ecaprolactone.

l0056l On the other hand, examples of monomers having an acidic group include polymerizable monomers having a carboxyl group, a sulfonic acid group or the like. Examples of monomers having a carboxyl group include (meth)acrylic acid, crotonic acid, ethacrylic acid, propylacrylic acid, isopropylacrylic acid, itaconic acid, maleic acid anhydride, fumaric acid and the like. Examples of polymerizable monomers having a sulfonic acid group include t-butylacrylamide sulfonic acid and the like. When polymerizable monomer having an acidic group is used, it is preferable that a part of an acidic group is a carboxylic group.

100571 In addition, examples of polymerizable monomers having a functional group include a glycidyl group-containing unsaturated monomer such as glycidyl (meth)acrylate, and an isocyanate group-containing unsaturated monomer such as m-isopropenyl-a,a-dimethylbenzyl isocyanate, isocyanatoethyl acrylate and the like.

l0058l Examples of other polymerizable monomers include (meth)acrylic acid alkyl ester such as methyl (meth)acrylate, ethyl (meth)acrylate, isopropyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)acrylate, t-butyl (meth)acrylate, isobutyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, noctyl À (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, and tridecyl (meth)acrylate, addition reaction products of oil fatty acid and acrylic add or methacrylic acid ester monomer having an oxirane structure(e.g., addition reaction product of stearic acid and glycidyl methacrylate etc.) addition reaction product of an oxirane compound containing a C3 or higher alkyl group and acrylic acid or methacrylic acid, styrene, amethylstyrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, p-tbutylstyrene, benzyl (meth)acrylate, itaconic acid ester (dimethyl itaconate), maleic acid ester (dimethyl maleate), fumaric acid ester (dimethyl fumarate), as well as other polymerizable monomers such as acrylonitrile, meth acrylonitrile, methylisopropenyl ketone, vinyl acetate, Veoba Monomer (manufactured by Shell Chemical Co., Ltd., trade name), vinyl propionate, vinyl pivalate, vinyl propionate, ethylene, propylene, butadiene, N,N-dimethylaminoethyl acrylate, N,Ndimethylaminoethyl methacrylate, acrylamide, and vinyl pyridine.

[00591 It is preferable that a polymerization reaction for obtaining the non-aqueous dispersion is performed in the presence of a radical polymerization initiator. Examples of the radical polymerization initiator include azo-based initiators such as 2,2'- azobisisobutyronitrile' and 2,2'-azobis(2,dimethylvaleronitrile), benzoyl peroxide, lauryl peroxide, t-butyl peroctoate and the like. It is desirable that an amount of these initiators is 0.2 to 10 parts by weight, preferably 0.5 to 5 parts by weight per a total of 100 parts by weight of a polymerizable monomer. It is preferable that a polymerization reaction for obtaining a non-aqueous dispersion in an organic solvent containing a dispersion stable resin is generally performed in a temperature range of about to 160 C for 1 to 15 hours. '

0] In addition, the non-aqueous dispersion is a particle component in a paint different from a cross-linked polymer particle, but has the characteristic that it does not form a particle structure in a coated composite film. That is, the non-aqueous dispersion is different from a cross-linking polymer particle in that since there is no cross-linking site in a particle, a particle shape is changed in a baking process, and this can be a resin component.

l0061l Further, for example, a resin particle called NAD (Non Aqueous Dispersion) which is described in Coloring Material, vol.48 (1975), pp.2834 and is used in a NAD paint, can be also used.

l0062l An amount of a non-aqueous dispersion resin (d) contained in an intermediate paint is 4 to 15% by weight, preferably 5 to 12% by weight on the basis of a weight of a resin solid content. When a content is smaller than 4% by weight, appearance of a coated composite film is insufficient and, when a content exceeds 15% by weight, anti-chipping performance is reduced.

l0063l By using the non-aqueous dispersion resin (d), prevention of miscibility between coating layers is easy, and appearance is improved.

l0064l The flake pigment (e) includes mica, alumina, talc and silica, talc being preferable from a viewpoint of chipping performance.

0065l It is preferable that the flake pigment (e) has a size of a long diameter of 1 to 10 1lm and a number average particle diameter of 2 to 6 lam. When a long diameter is outside the range, appearance of a film is inferior, and sufficient anti-chipping performance is not obtained. When a number average particle diameter is outside the range, similarly, appearance of a coated composite film is inferior and sufficient anti-chipping performance is not obtained.

[00661 A content of the flake pigment (e) is 0.4 to 2 parts by weight when a weight of a resin solid content in a paint is a 100 parts by weight. A content of 0.5 to 1.5 parts by weight is further preferable. When a content is outside the range, since adhesion properties with an undercoating film are reduced and sufficient chipping performance is not obtained.

l0067l Other resins which can be contained are not particularly limited, but examples thereof include an acryl resin, a polyester resin, an alkyd resin, an epoxy resin and the like. These resins may be used alone or in combination of two or more.

[00681 Examples of the coloring pigment include an azo chelate-based pigment, an insoluble azo-based pigment, a fused azo-based pigment, a phthalocyanine-based pigment, an indigo pigment, a perinone-based pigment, a perylene-based pigment, a dioxane-based pigment, a quinacridone-based pigment, an isoindolinone-based pigment, a metal complex pigment and the like as an organic base. As an inorganic base, chrome yellow, yellow iron oxide, iron oxide red, carbon black, titanium dioxide and the like can be used. In addition, filler pigment may be employed, including calcium carbonate, barium sulfate, aluminum powder, kaolin and the like.

l0069l As a standard, a gray-based coloring pigment containing carbon black and titanium dioxide as a main pigment is used. Further, a coloring pigment having a hue compatible with that of a topcoating, and a combination of various pigments may be also used.

100701 In addition, in order to prevent miscibility of layers with a topcoating film and maintain coating workability, a theological agent can be added to the intermediate paint. Examples of the theological agent include materials which generally exhibit thixotropic properties, for example, polyamide-based agents l.

such as a swollen dispersion of fatty acid amide, amide fatty acid, phosphate of long chain polyaminoamide and the like, polyethylene-based agents such as a colloidal swollen dispersion of polyethylene oxide and the like, organic bentonitbased agents such as organic acid smectite clay, montmorillonite and the like, inorganic pigments such as aluminum silicate, barium sulfate and the like, flake pigments developing viscosity depending on a shape of a pigment, a cross-linked resin particle and the like.

[00711 A total amount of a solid content of an intermediate paint used in the present invention when applying is 30 to 80% by weight, preferably 35 to 65% by weight. When the amount is outside this range, paint stability is reduced.

When the amount exceeds an upper limit, viscosity is too high and appearance of a coated composite film is reduced. When the amount is below a lower limit, viscosity is too low, deteriorated appearance such as miscibility of layers and ununiformity occurs.

100721 In addition to the components, other additives which are generally added to a paint, for example, a surface adjusting agent, an anti-oxidant, an anti-foaming agent and the like may be incorporated in the intermediate paint used in the present invention. An amount of them to be incorporated is within a range known to a person skilled in the art.

100731 In addition, other resin may be contained in the urethane-modified polyester resin. Such a resin is not particularly limited, but include an acryl resin, a polyester resin, an alkyd resin, an epoxy resin and the like. These resins may be used alone or in combination of two or more.

00741 A process for preparing a paint composition used in the present invention including the process described later is not particularly limited, but all . processes which are well known to a person skilled in the art such as kneading and dispersing of a blend of a pigment using a kneader, a roll and a SO mill can be used.

00751 Base coating film The base paint used in the coating film formation methods of the present invention is used for constituting a topcoating film with a clear paint.

The base paint contains a coating film forming resin, a curing agent, a coloring pigment and, if necessary, a luster color pigment and the like.

[00761 The film forming resin contained in the base paint is not particularly limited, but preferable examples thereof include an acryl resin, a polyester resin, an alkyd resin, an epoxy resin, an urethane resin and the like. These resins can be used alone or in combination of two or more.

[00771 The film forming resin can be used by combining with a curing agent.

From a viewpoint of the various performances and the cost of the resulting coating film, an amino resin and/or a blocked isocyanate resin are preferably used.

[00781 A content of the curing agent is preferably 20 to 60% by weight, more preferably 30 to 50% by weight, based on a weight of a solid content of the film forming resin. When a content is smaller than 20% by weight, curability is insufficient. When a content is higher than 60% by weight, a cured film is too hard and brittle.

[00791 In addition, as the coloring pigment, for example, coloring pigments exemplified for the intermediate paint can be contained.

[00801 A shape of the luster color pigment optionally contained in the base paint is not particularly limited. The luster color pigment may be further colored. .

For example, a luster color pigment having an average particle diameter (D50) of 2 to 50 Em, and a thickness of 0.1 to 5 Em is preferable. In addition, a luster color pigment having an average particle diameter in a range of 10 to 35,um is excellent in the luster color pigmenting feeling, and is further suitably used.

The pigment concentration (PWC) of the luster color pigment in the paint is generally 20.0% by weight or less. When the concentration exceeds an upper limit, appearance of a coating film is reduced. The concentration is preferably 0.01 to 18.0% by weight, more preferably 0.1 to 15.0% by weight. When a content of the luster color pigment exceeds 20.0% by weight, appearance of a film is reduced.

1] Examples of the luster color pigment include non-colored or colored metal luster color pigments of metals or alloys such as aluminum, copper, zinc, iron, nickel, tin and aluminum oxide, and a mixture thereof. Further, an interfering mica pigment, a white mica pigment, a graphite and other colored or non-colored flake pigments may be used jointly.

l0082l The total pigment concentration (PWC) of the luster color pigment and other all pigments in a paint is 0.1 to 50% by weight, preferably 0.5 to 40% by weight, more preferably 1.0 to 30% by weight. When the concentration exceeds an upper limit, appearance of a coating film is reduced.

l0083l Further, as in the intermediate paint, in order to maintain coating workability, it is preferable to add a theological agent to the base paint. A rheological agent is used for forming a film having no ununiformity and sag and, generally, agents exhibiting thixotropic properties may be contained. As such an agent, for example, agents exemplified for the intermediate paint can be contained. À

[00841 In addition to the components, additives which are generally added to a paint such as a surface adjusting agent, a theological agent, an antioxidant, an ultraviolet inhibitor and an anti-foaming agent may be incorporated into the base paint used in the present invention. An amount of them to be incorporated is within a range known to a person skilled in the art.

10085] An amount of a total solid content of the base paint used in the present invention at applying is 10 to 60% by weight, preferably 15 to 50% by weight.

When the amount is above an upper limit or below a lower limit, paint stability is reduced. When the amount exceeds an upper limit, viscosity is too high, and appearance of a coating film is reduced. When the amount is below a lower limit, a viscosity is too low, and deteriorated appearance such as miscibility of layers and ununiformity occurs.

0086] Clear coating film For forming the clear coating film, a clear paint is used. The clear paint is not particularly limited, but clear paints containing a film forming thermosetting resin and a curing agent can be utilized. As a form of the clear paint, a solution type, an aqueous type and a powder type are exemplified.

10087] From a viewpoint of transparency and resistance to acid etching, preferable examples of the solution-type clear paint include a combination of an acryl resin and/or a polyester resin and an amino resin, a combination of an acryl resin and/or a polyester resin and an isocyanate compound, and an acryl resin and/or a polyester resin having carboxylic acid-epoxy curing system.

10088] In addition, examples of the aqueous type clear paint include paints containing a resin obtained by neutralizing the film forming resin contained in the exemplified solution-type clear paints with a base so that paints become aqueous. The neutralization can be performed by adding tertiary amine such as dimethylethanolamine and triethylamine before or after polymerization.

1008y On the other hand, as the powder-type clear paint, conventional powder paints such as thermoplastic and thermosetting powder paints can be used.

Since coating films having better physical properties are obtained' thermosetting powder paints are preferable. Examples of the thermosetting powder paints include epoxy-based, acryl-based and polyester resin-based powder clear paints, but acryl-based powder clear paints having the better weather resistance are particularly preferable.

1 9 1 As the powder type clear paint used in the present invention, epoxy-containing acryl resin/polyvalent carboxylic acid-based powder paints are particularly preferable because there is no volatile material at curing, better appearance is obtained and yellowing is scarcely caused.

100911 Further, as in the intermediate paint, in order to maintain coating workability, it is preferable that a theological agent is added to the clear paint.

As a theological agent, agents exhibiting thixotropic properties can be generally contained. As the theological agent, those exemplified for the intermediate paint can be contained. If necessary, a curing catalyst, a surface adjusting agent and the like can be contained.

00921 Substrate The coated composite film formation method of the present invention can be advantageously used for various substrates, for example, metal, plastic, foamed material and the like. Preferred are metal and molded article. The method can be particularly suitably used in metal products which can be cation

electrocoatable.

[00931 Examples of the metal products include iron, copper, aluminum, tin, zinc and the like and alloys containing these metals. Embodiments include vehicle bodies and parts of an automobile, a truck, a motorbike, a bus and the like. It is particularly preferable that metals are chemical-treated with phosphate, chromate or the like in advance.

100941 In addition, in a substrate used in the coated composite film formation method of the present invention, an electrodeposition coating film may be formed on a chemical formation-treated steel plate. As an electrodeposition I paint for forming an electrodeposition coating film, either cation type or anion type may be used, and a cation type electrodeposition paint composition is preferable because it gives a coating him excellent in corrosion resistance.

[00951 EXAMPLES l

The present invention will be explained in detail by way of Examples below, but the present invention is not limited by the following Examples.

Hereinafter, Upart" and U%" are based on a weight.

100961 Prenaration Examnle1 1 Preparation of urethane-modified polyester resin (a) 440 Parts of isophthalic acid, 20 parts of hexahydrophthalic acid, 40 parts of azelaic acid, 300 parts of trimethylolpropane and 200 parts of neopentyl glycol were placed into a 2L reaction vessel equipped with a nitrogen introducing tube, a stirrer, a temperature adjuster, an addition funnel and a cooling tube equipped with a decanter and, when raw materials were dissolved by heating and stirring became possible, 0.2 part of dibutyltin oxide was placed therein, stirring was initiated and a reaction layer temperature was gradually risen from 180 to 220 C for 3 hours. Produced condensation water was distilled off from the system. When a temperature reached 220 C, a temperature was retained for 1 hour, 20 parts of xylene was gradually added to a reaction layer, and a condensation reaction was allowed to proceed in the presence of a solvent. When a resin acid value reached 10 mgKOH/g, the material was cooled to 100 C, and 100 parts of hexamethylene diisocyanate was gradually added over 30 minutes. Further, a temperature was retained for 1 hour, 200 parts of xylene and 200 parts of butyl acetate were added, to obtain an urethane-modified polyester resin having a solid content of 70%, a number average molecular weight of 2000, an acid value of 8 mgKOH/g, a hydroxyl group value of 120 and resin Tg of 60 C.

100971 Preparation Examole 2 Preparation of non-anueous dispersion (a) Preparation of dispersion stable resin Parts of butyl acetate was placed into a vessel equipped with a stirrer, a temperature controller and a refluxing condenser. Then, 20 parts from a solution having the following composition:

00981 Table 1

Methyl methacrylate 38.9 parts Stearyl methacrylate 38.8 parts 2-Hydroxyethyl acrylate 22.3 parts Azobisisobutyronitrile 5.0 parts was added, and a temperature was risen by heating while stirring. 85 Parts of the reminder of the mixed solution was added dropwise at 110 C for 3 hour, and then, a solution of 0.5 part of azobisisobutyronitrile and 10 parts of butyl acetate was added dropwise over 30 minutes. The reaction solution was stirred to reflux for further 2 hours to increase a rate of change to a resin, and the reaction was completed to obtain an acryl resin having a solid content of 50% a À number average molecular weight of 5600 and a SP value of 9.5.

[00991 (b) Preparation of non-aqueous dispersion Parts of butyl acetate and 60 parts of the acryl resin obtained in the (a) Preparation of a dispersion stable resin were placed into a vessel equipped with a stirrer, a condenser and a temperature controller. Then, a solution having the following composition:

O100] Table 2

Styrene 7.0 parts | Methacrylic acid 1.8 parts Methyl methacrylate 12.0 parts Ethyl acrylate 8.5 parts 2-Hydroxyethyl acrylate 40.7 parts Azobisisobutyronitrile 1.4 parts was added dropwise at 1 00 C for 3 hours and, then, a solution of 0.1 part of azobisisobutyronitrile and 1 part of butyl acetate was added dropwise over 30 minutes. Stirring of the reaction solution was continued for 1 hour, to obtain an emulsion having a solid content of 60% and a particle diameter of 180 nm.

This emulsion was diluted with butyl acetate to obtain a core-shell type butyl acetate dispersion having a non-aqueous dispersion content of 40%, a viscosity of 300 cps (25 C) and a particle diameter of 180nm. This nonaqueous dispersion resin had Tg of 23 C, a hydroxyl group value of 162 and a SP value of 11.8, and a difference in SP values of a shell part which is a dispersion stable resin and this whole non-aqueous dispersion resin was 2.3.

0101l Examole 1 Intermediate paint 107 Parts of the urethane-modified polyester resin varnish obtained in the previous Preparation, 280 parts of CR-97 (titanium oxide manufactured by À Ishihara Sangyo Kaisha, Ltd.), 13 parts of MA-100 (carbon black pigment manufactured by Mitsubishi Chemical Co., Ltd.), 7 parts of LMS- 100 (scaly talc manufactured by Fuji Talc), 47 parts of butyl acetate and 47 parts of xylene were placed into a 1 L vessel, the same amount as a charging weight of GB503M (glass beads having a particle diameter of 1.6 mm) was placed, and the materials were dispersed at room temperature for 3 hours using a desk size SO mill to obtain a gray pigment paste. A particle size at completion of dispersion with a grind gauge was 5 1lm or less. Glass beads were filtered to obtain a pigment paste. The pigment paste was prepared into an intermediate paint having a composition shown in Table 3. The paint was diluted to 19 seconds/20 C with a mixed solvent of ethoxyethyl propionate/S-100 (aromatic hydrocarbon solvent manufactured by Exxon) = 1/1 using a No.4 Ford cup. A non-volatile content at application was 49%.

01021 Table 3

Intermediate Pigment paste 100 parts coating Polyester resin 130 parts composition Non-aqueous dispersion 53 parts Melamine resin ("U ban 128 (trade name)" 71 parts manufactured by Mitsui Cyteck) Blocked isocyanate (UDuranate MF-K60X (trade 71 parts name)" manufactured by Asahi Chemical Industry Co., Ltd.) Resin solid Polyester resin/non-aqueous 50/10/20/20 content ratio disoersion/melamine resin/blocked isocyanate Pigment ratio Titanium oxide/carbon black/talc 2811.310.7 PWC 30% 0103l Base paint An acrylmelamine-based metallic base pigment "Orga TO H600 1 8J Green Metallic" manufactured by Nippon Paint Co., Ltd. was diluted to 17 second/20 C with a mixed solvent of ethoxyethyl propionate/S-100 (aromatic r hydrocarbon solvent manufactured by Exxon) /toluene = 1/1/2 using a No.3 Ford cup. A non-volatile content of the paint at application was 31%. A non-volatile content at deposition was 65%.

[01 041 Clear paint An acid epoxy curing-based clear paint "Mack 0-1600 Clear" manufactured by Nippon Paint Co., Ltd. was diluted to 26 seconds/20 C with a mixed solvent of ethoxyethyl propionate/S-100 (aromatic hydrocarbon solvent manufactured by Exxon) = 1/1 using a No.4 Ford cup. A non-volatile content of the paint at application was 50%. In addition, a non-volatile content at deposition was 61%.

[01051 Coated composite film formation method A cationic electrodeposition paint UPower Top V-20" (manufactured by Nippon Paint Co. , Ltd.) was electrodeposition-coated on a SPC steel plate having a thickness of 0.8 mm, a length of 30 cm and a width of 10 cm which had been treated with zinc phosphate, to form a coating having a dry film thickness of 20 m, followed by baking at 160 C for 30 minutes. Then, the steel plate on which the electrodeposition coating film was formed was adhered to a moving body, and coated with the intermediate paint by a "microbe!" (rotation atomizing type electrostatic coating machine) while moving, to form a coating having a dry film thickness of 20 m. Setting was performed by leaving it for 10 minutes.

[01061 Then, the base paint was applied using a "microbe!" and a UmetabelN at 2 stage so that a dry film thickness was 15 m. Between two applications, an interval of 2.5 minutes was taken. After the second application, setting of 8 minutes was performed. Then, the clear paint was coated using a "microbell" at 1 stage so that a dry film thickness was 35,um, and 10 minutes setting was performed. The curing condition of the resulting laminated coated composite film was a curing temperature of 140 C and a curing time of 30 minutes.

lO1 071 The thus prepared coated plate was placed into a first drying oven at 40 C, held for 5 minutes, transferred to a second drying oven set at 140 C, and held for 20 minutes. Thereafter, the coated plate was taken out from the drying oven, and allowed to cool to room temperature.

l0108l (1) Appearance of a cured coated composite film was assessed visually for the presence or the absence of gloss appearance. The test results are

shown in Table 5.

[01091 Table 4

Assessment criteria 3 Gloss appearance is better, and it seems that a clear paint is applied at a sufficient thickness.

2 Gloss appearance is slightly inferior, and it seems that a clear paint thickness is small.

1 Gloss appearance is inferior, and it seems that a clear paint is not coated.

l0110l (2) Then, the state of the surface of a cured coated composite film was tested using a coated composite film appearance measuring apparatus "Wave Scan DOln manufactured by Big Chemie. The test results are shown in Table 5.

1] A measured value Wa means an amount of roughness of 0.1 to 0.3 mm among skin tortuosity, and expresses gloss appearance of a coated composite film. We means an amount of roughness of 1 to 3 mm among skin tortuosity, and expresses the surface hiding properties of a coated composite film. Wd means an amount of roughness of 3 to 10 mm among skin tortuosity of a coated composite film, and expresses the smoothness of a coated composite film. As

-

a numerical grows smaller, each measured value becomes better.

10112] (3) Further, the anti-chipping properties of the resulting coated plate was assessed as follows. The test results are shown in Table 5.

l0113l Using a glabero tester (manufactured by Suga Test Instrument Co., Ltd.), 300 pieces of No.7 ground stones were collided to a film at an angle of 45 from a distance of 35 cm at an air pressure of 3.0 kgf/cm2. After washing with water and drying, a peeling test was performed using an industrial gummed tape manufactured by Nichiban and, thereafter, a degree of peeling of a film in terms of a peeling diameter and the number of peelings was observed and assessed visually.

0114l Examples 2 to 4 According to the same manner as the method described in Example 1 except that a curing temperature and a curing time were changed as shown in Table 5, a cured coated composite film was prepared, and tested. The test results are shown in Table 5.

01151 Comparative ExamnIe 1 According to the same manner as the method described in Example 1 except that a step of baking and curing an uncured coated composite film was performed by heating at one stage at 140 C for 30 minutes, a cured coated composite film was prepared and tested. The test results are shown in Table 6.

011 al Comparative Example 2 According to the same manner as the method described in Example 1 except that a polyester-melamine-based intermediate paint "Orga TO H870 Gray" manufactured by Nippon Paint Co., Ltd. was used as an intermediate paint, and a curing temperature and a curing time were changed as shown in Table 6, a cured coated composite film was prepared and tested. The test results are shown in Table 6.

01171 Reference Example 1 A cationic electrodeposition paint UPower Top V20" (manufactured by Nippon Paint Co., Ltd.) was electrodeposition-coated on a SPC steel plate having a thickness of 0.8 mm, a length of 30 cm and a width of 10 cm which had been treated with zinc phosphate, to form a dry film having a thickness of m, followed by baking at 1 60 C for 30 minutes. Then, the steel plate on which the electrodeposition coating film was formed was adhered to a moving body, and coated with the intermediate paint by a "microbes (rotation atomizing type electrostatic coating machine) while moving, to form a dry film having a thickness of 20 Am and, after application, setting was performed by leaving it for 1 0 minutes.

l0118l This coated plate was placed into a drying oven set at 140 C, and held for 20 minutes. Thereafter, a coated plate was taken out from the drying oven, and allowed to cool to room temperature. A base paint and a clear paint were applied on the coated plate as in Example 1, to obtain a coated composite film.

l011y The thus prepared coated plate was placed into a drying oven at 140 C, and held for 30 minutes. Thereafter, the coated plate was taken out from the drying oven, and allowed to cool to room temperature. According to the same manner as the method described in Example 1, the resulting cured coated composite film was tested. The test results are shown in Table 6.

0120] Reference Example 2 According to the same manner as the method described in Reference Example 1 except that a polyester-melamine-based intermediate paint conga TO H870 Gray" manufactured by Nippon Paint Co., Ltd. was used as an intermediate paint, and a curing temperature and a curing time were changed as in Table 6, a cured coated composite film was prepared, and tested. The test results are shown in Table 6. vv À r

101211 Table 5

Example No. 1 2 3 4 l Intermedi- Kind Example 1 Example 1 Example 1 Example 1 ate coated Baking _ _ _ composite film Coated Low 40 C x 60 C x 60 C x 100 C x composite temperature 5 min. 3 min. 5 min. 5 min. film baking High | 140 C x 140 C x 140 C x 140 C x I temperature 30 min. 30 min. 30 min. 30 min. Appearance 3 3 3 3 (visual asset;ment) Surface Wa 16.3 14.7 13.6 16.6 state Wc 13.4 14.4 12. 2 16.2 Wd 8.7 8.2 7.3 10.3 1 Anti-chipp- Peeling 2 mm 1.8 mm 1.7 mm 2 mm ing diameter Number 20 18 16 19

[01221 Table 6

Example No. Comparative Comparative Reference Reference Example 1 Example 2 Example 1 Example 2 Intermed- Kind Example 1 Orga TO Example Orga TO late coated 1 composite Baking _ _ 140 C x 140 C x film 30 min. 30 min.Coated Low _ 60 C x 5 _ composite temperature min. film baking High 140 C x 140 C x 140 C x 140 C x temperature 30 min. 30 min. 30 min. 30 min. Appearance 2 1 3 3 (visual assesment) Surface Wa 23.1 45.3 13.1 12.9 state Wb 21.0 61.4 11. 5 11.4 Wc 18.5 35.6 8.4 9.1 Anti-chipp- Peeling 2 mm 3.5 mm 2.0 mm 2.5 mm ing diameter Number 20 106 16 30 [0123] In the examples of the present invention, gloss appearance equal to that obtained by a three-coat two-bake method could be attained even when the coated composite film was formed by a three-coat one-bake method. In addition, the coating system performed by the present invention had the anti-chipping properties equivalent to that of a coated composite film obtained by a three-coat two-bake method, although number of baking times was less.

Claims

WHAT IS CLAIMED IS

1. A method for producing a coated composite film, comprising forming an electrocoated film on a substrate, and then successively applying an intermediate paint, a base paint and a clear paint in a wet-on-wet manner, ; followed by baking and curing the applied three layers at once, wherein the baking and curing includes both a low-temperature heating stage of heating at a temperature which is 25 to 80% of a curing temperature for a time which is 5 to 30% of a curing time, and a high- temperature heating stage of heating at a temperature which exceeds 80% and is not more than 120 of a curing temperature for a time which is 30 to 130% of a curing time.

2. The method according to claim 1, wherein said intermediate paint comprises: (a) 40 to 56% by weight of an urethane-modified polyester resin having a number average molecular weight of 1500 to 3000 obtained by reacting an aliphatic isocyanate compound, with a hydroxyl group-containing polyester resin having a glass transition temperature (Tg) of 40 to 80 C.obtained by polycondensation of an acid component containing 80 mol% or more of isophthalic acid and a polyhydric alcohol; (b) 10 to 30% by weight of a melamine resin; (c) 15 to 30% by weight of a blocked isocyanate compound; (d) 4 to 15% by weight of a non-aqueous dispersion resin having a core- shell structure, amounts of (a) to (d) being based on a weight of a resin solid content; and (e) 0.4 to 2 parts by weight of a flake pigment, based on 100 parts by weight of a resin solid content.

3. The method according to claim 2, wherein said blocked isocyanate compound is blocked with a compound having an active methylene group.

4. A coated composite film which is formed by the method according to any one of claims 1 to 3.