JP5751629B2 - Painting method - Google Patents

Description

  The present invention relates to a coating method capable of forming a multilayer coating film excellent in finish and water resistance without being mixed even if an overcoat is applied to the polyolefin bumper without preheating after applying an aqueous primer.

  The polyolefin bumper is often pre-coated with a primer containing chlorinated polyolefin or the like in order to improve the adhesion between the top coat and the molded product. For this primer, aromatic organic solvents such as toluene and xylene have been used as solvents from the viewpoint of the solubility of chlorinated polyolefins. It has been.

In addition, since the above-mentioned molded article usually has a volume resistivity of about 10 ¹⁰ Ω · cm or more, a top coating is applied to such a plastic molded article using an electrostatic coating method having excellent coating efficiency. Direct coating is difficult, and usually, the primer is imparted with conductivity, and after coating it, a top coating for coloring purposes is electrostatically coated (for example, Patent Document 1 and Patent Document 2). Such).

  As the coating method, for example, as in Patent Document 3 and Patent Document 4, a 3-coat 1-bake method including top coating in which a colored base paint and a clear paint are sequentially applied after applying an aqueous primer has been proposed. When water-based primer is used in such a wet-on-wet system, pre-drying is required even after a few minutes after the water-based primer is applied and before the next coating process is performed in order to ensure the finish after the top coat. (Preheating) was essential.

  However, in the actual painting line, it was required to eliminate the preheating process from the viewpoint of space saving and energy saving, but the preheating process was required from the viewpoint of the coating properties such as finish and water resistance after top coating. It was difficult to omit.

  Therefore, Patent Document 5 proposes that a multilayer coating film excellent in finish, water resistance, etc. can be formed even when top coating is performed without preheating by using an aqueous primer composition having a specific composition. . However, even in this method, in the environment of low temperature and low humidity in midwinter, there are cases where sufficient finish cannot be obtained if the preheating step is omitted.

JP-A-6-165966 International Publication WO2007 / 046532 Pamphlet JP-A-10-296171 JP 2004-331911 A International Publication WO2010 / 016617 Pamphlet

  An object of the present invention is to provide a coating method capable of forming a multi-layer coating film having excellent finish and water resistance without mixing even if a top coat is applied to the polyolefin bumper without preheating after applying an aqueous primer. Is to provide.

  As a result of intensive studies to solve the above-mentioned problems, the inventors of the present invention have heated the polyolefin bumper surface so that its surface temperature is within a specific range before coating a specific aqueous primer. The present inventors have found that the above problems can be solved, and have completed the present invention.

Thus, in the present invention, an aqueous primer is applied to a polyolefin bumper surface heated to a surface temperature of −3 to + 20 ° C. with respect to a coating booth temperature of 15 to 35 ° C., and the coated surface without preheating. A coating method comprising: applying a solvent-based colored base coat paint to the coating, and further applying a solvent-type clear coat paint to the coated surface, and baking these three-layer coating films simultaneously;
The aqueous primer is an aqueous dispersion of modified polyolefin (A), aqueous urethane resin (B), aqueous acrylic resin (C), general formula (1)

[Wherein, R ¹ and R ² independently represent a hydrocarbon group having 4 to 18 carbon atoms, R ³ represents an alkylene group having 2 to 4 carbon atoms, m is an integer of 3 to 20, m R ³ may be the same or different from each other]
Containing the diester compound (D) and the conductive pigment (E), and the blending amounts of the components (A), (B) and (C) are based on the total solid content mass of the three components (A ) Is 15 to 60% by mass, component (B) is 30 to 75% by mass, and component (C) is in the range of 10 to 40% by mass,
The polyolefin bumper surface is heated when a far-infrared heater is installed on both sides and the upper part of the conveyor at the entrance of the painting booth, and the bumper passes,
Furthermore, the present invention provides a coating method characterized by coating an aqueous primer with a film thickness of 3 to 6 μm.

  According to the present invention, even in a low-temperature and low-humidity booth environment, even if a water-based primer is applied to a polyolefin bumper without preheating after coating, it is excellent in finish and water resistance without being mixed even if the next coating is overcoated. A multilayer coating film can be formed.

  In the coating method of the present invention, an aqueous primer is applied to the polyolefin bumper surface, a solvent-based colored base coat paint is applied to the coated surface without preheating, and a solvent-type clear coat paint is further applied to the coated surface. These three-layer coating films are baked simultaneously.

Polyolefin bumper and surface heating :
In the present invention, the polyolefin bumper is usually made of a polyolefin obtained by (co) polymerizing one or more of olefins having 2 to 10 carbon atoms such as ethylene, propylene, butylene and hexene. The surface can be appropriately subjected to a pretreatment such as a degreasing treatment and a water washing treatment by a method known per se prior to the application of an aqueous primer described later.

  In the method of the present invention, the polyolefin bumper surface is −3 to + 20 ° C. with respect to the coating booth temperature of 15 to 35 ° C., preferably −1.5 to + 15 ° C., more preferably before coating the aqueous primer described later. Is heated to a surface temperature of 0 to + 10 ° C. In this case, the surface temperature can be measured using a non-contact type radiation thermometer.

  The polyolefin bumper surface is preferably heated when far-infrared heaters are installed on both sides and the upper part of the conveyor at the entrance of the coating booth, and the bumper passes.

When using a far infrared heater, heat by the heater is generally 500~2,000W / ^{m 2,} preferably set to be within a range of 600~1,800W / ^{m 2,} the distance between the object to be coated is usually 50~500mm The thickness is preferably in the range of 100 to 300 mm. Although the heating time depends on the amount of heat and the distance, it is generally 10 to 300 seconds, preferably about 10 to 100 seconds.

Aqueous primer and its coating :
In the method of the present invention, after heating the polyolefin bumper surface as described above, an aqueous primer is applied. The aqueous primer used contains an aqueous dispersion (A) of a modified polyolefin, an aqueous urethane resin (B), an aqueous acrylic resin (C), a diester compound (D), and a conductive pigment (E).

Modified polyolefin aqueous dispersion (A) :
The aqueous dispersion (A) of the modified polyolefin includes those obtained by dispersing the polyolefin (i) modified with an unsaturated carboxylic acid or acid anhydride in an aqueous medium.

  The unsaturated carboxylic acid or anhydride-modified polyolefin (i) includes, for example, at least one olefin selected from olefins having 2 to 10 carbon atoms, particularly 2 to 4 carbon atoms such as ethylene, propylene, butylene, and hexene. ) The polyolefin obtained by polymerizing is further an unsaturated carboxylic acid (preferably unsaturated monocarboxylic acid) having 3 to 10 carbon atoms, particularly 4 to 8 carbon atoms such as (meth) acrylic acid, maleic acid, fumaric acid, itaconic acid and the like. -Or di-carboxylic acids) or anhydrides of these unsaturated carboxylic acids and can be obtained by graft polymerization according to methods known per se, in particular modified by maleic acid or anhydrides thereof. Those are preferred. The amount of grafting with the unsaturated carboxylic acid or acid anhydride thereof is not strictly limited, and can be appropriately changed according to the physical properties desired for the formed coating film. The range of 1 to 20% by mass, preferably 1.5 to 15% by mass, more preferably 2 to 10% by mass is appropriate.

  The polyolefin used in the unsaturated carboxylic acid or acid anhydride-modified polyolefin (i) is a polymerization catalyst particularly from the viewpoint that the obtained polyolefin has a narrow molecular weight distribution and excellent random copolymerizability. Those produced using a single site catalyst are preferred. The single site catalyst has the same active site (single site), and a metallocene catalyst is particularly preferable among the single site catalysts. The metallocene-based catalyst is usually a metallocene which is a compound having at least one conjugated five-membered ring ligand and containing a group 4-6 or group 8 transition metal compound or a group 3 rare earth transition metal in the periodic table. It is obtained by combining (bis (cyclopentadienyl) metal complex and derivatives thereof), a cocatalyst such as aluminoxane that can activate the same, and an organoaluminum compound such as trimethylaluminum.

  The polyolefin can be produced by a method known per se, for example, by continuously adding an alkylaluminum and a metallocene catalyst while supplying an olefin such as propylene or ethylene and hydrogen to a reaction vessel. Can do.

  The unsaturated carboxylic acid or acid anhydride-modified polyolefin (i) may be further acrylic-modified as necessary. Examples of the polymerizable unsaturated monomer that can be used for the acrylic modification include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, hexyl (meth) acrylate, and cyclohexyl (meth) ), Acrylate, 2-ethylhexyl (meth) acrylate, lauryl (meth) acrylate, alkyl ester of (meth) acrylic acid such as stearyl (meth) acrylate; (meth) acrylic acid, glycidyl (meth) acrylate, 2-hydroxyethyl ( Acrylic monomers such as (meth) acrylate, (meth) acrylamide and (meth) acrylonitrile; styrene and the like can be mentioned, and these can be used alone or in combination of two or more.

  In the present specification, “(meth) acryl” means acryl or methacryl, and “(meth) acrylate” means acrylate or methacrylate.

  As the method for the acrylic modification, for example, an unsaturated carboxylic acid or acid anhydride-modified polyolefin is first reacted with a carboxyl group in the modified polyolefin, for example, glycidyl (meth) acrylate. Examples thereof include a method in which a polymerizable unsaturated group is introduced and then at least one other monomer is copolymerized with an unsaturated carboxylic acid or acid anhydride-modified polyolefin into which a polymerizable unsaturated group has been introduced. The amount of the polymerizable unsaturated monomer used in the acrylic modification is usually based on the solid content mass of the resulting modified polyolefin (i) from the viewpoint of compatibility with other components and adhesion of the formed coating film. It is desirable that the amount be 30% by mass or less, particularly 0.1 to 20% by mass, and more particularly 0.15 to 15% by mass.

  The unsaturated carboxylic acid or acid anhydride-modified polyolefin (i) is modified with a compound having a polyoxyalkylene chain, if necessary, from the viewpoint of water resistance, moisture resistance, gasohol resistance, etc. of the formed coating film. May be. Examples of the polyoxyalkylene chain in the compound having a polyoxyalkylene chain include a polyoxyethylene chain, a polyoxypropylene chain, a block chain of polyoxyethylene and polyoxypropylene, and the like.

  The unsaturated carboxylic acid or acid anhydride-modified polyolefin (i) may be further chlorinated as necessary. The chlorination of polyolefin can be performed, for example, by blowing chlorine gas into an organic solvent solution or dispersion of polyolefin or a modified product thereof, and the reaction temperature at that time is usually in the range of 50 to 120 ° C. it can. The chlorine content in the chlorinated polyolefin (solid content) can be changed according to the physical properties desired for the chlorinated polyolefin. From the viewpoint of adhesion of the formed coating film, the mass of the chlorinated polyolefin In general, it is desirable that the amount be in the range of 35% by mass or less, particularly 10 to 30% by mass, and more particularly 12 to 25% by mass.

  The polyolefin used for the unsaturated carboxylic acid or acid anhydride modified polyolefin (i) is particularly preferably one containing propylene as a polymerization unit, and the unsaturated carboxylic acid or acid anhydride modified polyolefin (i). The mass fraction of propylene is usually 0.5 to 0.99, particularly 0.6 to 0.97, more particularly 0.7 to 0, from the viewpoints of compatibility with other components and adhesion of the formed coating film. It is preferable to be within the range of .95.

The unsaturated carboxylic acid or acid anhydride modified polyolefin (i) obtained as described above is generally 120 ° C. or lower, preferably 50 to 100 ° C., more preferably 60 to 90 ° C., and generally 30 Mass average molecular weight within the range of from 50,000 to 180,000, preferably from 50,000 to 150,000, more preferably from 70,000 to 120,000 (
Mw). If the melting point and the weight average molecular weight of the modified polyolefin deviate from these ranges, the compatibility with other components, the adhesion of the formed coating film to the base material, the interlayer adhesion to the top coating layer, etc. are preferred. Absent. Further, the unsaturated carboxylic acid or acid anhydride-modified polyolefin (i) generally has a heat of fusion within the range of 1 to 50 mJ / mg, particularly 2 to 50 mJ / mg, from the viewpoint of adhesion as described above. desirable.

  Here, the melting point and the heat of fusion were measured by using a differential scanning heat capacity measuring device “DSC-5200” (trade name, manufactured by Seiko Denshi Kogyo Co., Ltd.). It is obtained by heating in minutes and measuring the amount of heat. When it is difficult to obtain the heat of fusion, the sample to be measured may be heated to 120 ° C., cooled at 10 ° C./min, and then allowed to stand for 2 days or more, and the amount of heat may be measured by the above method.

  The melting point of the modified polyolefin (i) can be adjusted, for example, by changing the composition of the polyolefin, particularly the amount of α-olefin monomer.

The mass average molecular weight of the modified polyolefin (i) is a value obtained by converting the mass average molecular weight measured by gel permeation chromatography on the basis of the mass average molecular weight of polystyrene. “HLC / GPC150C” (manufactured by Water) , Trade name, 60 cm × 1), measured at a flow rate of 1.0 ml / min using a column temperature of 135 ° C. and o-dichlorobenzene as a solvent. The injection sample is prepared by dissolving at 140 ° C. for 1 to 3 hours so as to obtain a solution concentration of 5 mg of modified polyolefin in 3.4 ml of o-dichlorobenzene. An example of a column used for gel permeation chromatography is “GMH _HR- H (S) HT” (trade name, manufactured by Tosoh Corporation).

  Furthermore, the unsaturated carboxylic acid or acid anhydride-modified polyolefin (i) is a ratio of the weight average molecular weight to the number average molecular weight (Mw / Mn) from the viewpoint of compatibility with other components and adhesion of the formed coating film. Is generally in the range of 1.5 to 4.0, particularly 2.0 to 3.5, more particularly 2.0 to 3.0.

  The aqueous dispersion (A) of the modified polyolefin can be obtained by dispersing the unsaturated carboxylic acid or acid anhydride modified polyolefin (i) in an aqueous medium, for example, deionized water. Depending on the situation, some or all of the carboxyl groups in the unsaturated carboxylic acid or anhydride modified polyolefin (i) can be neutralized with an amine compound and / or dispersed in water using an emulsifier. When the modified polyolefin (i) has a polyoxyalkylene chain, it is possible to disperse the modified polyolefin (i) in an aqueous medium without using the amine compound or emulsifier or only using a small amount thereof. is there.

  Examples of the amine compound include tertiary amines such as triethylamine, tributylamine, dimethylethanolamine, and triethanolamine; secondary amines such as diethylamine, dibutylamine, diethanolamine, and morpholine; primary amines such as propylamine and ethanolamine. Etc.

  When the amine compound is used, the amount used is usually within a range of 0.1 to 1.0 molar equivalents relative to the carboxyl group in the unsaturated carboxylic acid or anhydride modified polyolefin (i). Is desirable.

Examples of the emulsifier include polyoxyethylene monooleyl ether, polyoxyethylene monostearyl ether, polyoxyethylene monolauryl ether, polyoxyethylene tridecyl ether, polyoxyethylene phenyl ether, polyoxyethylene nonylphenyl ether, polyoxyethylene Nonions such as ethylene octyl phenyl ether, polyoxyethylene monolaurate, polyoxyethylene monostearate, polyoxyethylene monooleate, sorbitan monolaurate, sorbitan monostearate, sorbitan trioleate, polyoxyethylene sorbitan monolaurate Emulsifiers; anio such as sodium and ammonium salts such as alkyl sulfonic acid, alkyl benzene sulfonic acid and alkyl phosphoric acid A polyoxyalkylene group-containing anionic emulsifier having an anionic group and a polyoxyalkylene group such as a polyoxyethylene group or a polyoxypropylene group in one molecule, or the anionic emulsifier in one molecule. A reactive anionic emulsifier having a group and a polymerizable unsaturated group can also be used. These can be used alone or in combination of two or more.

  The amount of the emulsifier used is usually 30 parts by mass or less, particularly 0.5 to 25 parts by mass with respect to 100 parts by mass of the solid content of the unsaturated carboxylic acid or acid anhydride-modified polyolefin (i). It is desirable.

Water-based urethane resin (B) :
The aqueous urethane resin (B) is a water-soluble or water-dispersible resin having a urethane bond in the molecule, and includes a self-emulsifying emulsion having an acid value or an emulsion combined with an emulsifier, a water-soluble resin, and the like. Particularly preferred is a dispersion. Urethane dispersion is usually forced or self-emulsified while dispersing in water the urethane prepolymer obtained by reacting diol and diisocyanate in advance in the presence of an emulsifier, and further dimethylol alkanoic acid as necessary. Is a dispersion obtained by

  Examples of the skeleton of the water-based urethane resin (B) include ethers, carbonates, and esters. Of these, ethers and carbonates are desirable from the viewpoint of water resistance of the formed film. The aqueous urethane resin (B) may contain a hydroxyl group.

Water-based acrylic resin (C) :
The aqueous acrylic resin (C) is usually obtained by copolymerizing a monomer mixture comprising a hydrophilic group-containing polymerizable unsaturated monomer such as a carboxyl group-containing polymerizable unsaturated monomer and other polymerizable unsaturated monomers. A water-soluble acrylic resin having a weight average molecular weight of usually 5,000 to 100,000, preferably 5,000 to 50,000, or a weight average molecular weight of 50,000 or more, preferably 100,000 or more. An acrylic resin emulsion can be used.

  The mass average molecular weight is a value when the mass average molecular weight measured by gel permeation chromatography is converted on the basis of the mass average molecular weight of polystyrene using tetrahydrofuran as a solvent. As a gel permeation chromatography apparatus, HLC8120GPC ”(trade name, manufactured by Tosoh Corporation) can be used, and columns used for gel permeation chromatography include“ TSKgel G-4000H × L ”,“ TSKgel G-3000H × L ”,“ TSKgel ”. Four of “G-2500H × L” and “TSKgel G-2000H × L” (both manufactured by Tosoh Corporation, trade name) can be used.

Examples of the carboxyl group-containing polymerizable unsaturated monomer include (meth) acrylic acid, crotonic acid, maleic acid, fumaric acid, itaconic acid, and half-monoalkyl esterified products of dicarboxylic acids among these, Other hydrophilic group-containing polymerizable unsaturated monomers include, for example, polyalkylene chain-containing polymerizable unsaturated monomers such as polyethylene glycol (meth) acrylate and polypropylene glycol (meth) acrylate; 2-acrylamide-2- Sulfonic acid group-containing polymerizable unsaturated monomers such as methylpropanesulfonic acid and sulfoalkyl (meth) acrylate such as 2-sulfoethyl (meth) acrylate; N, N-dimethylaminoethyl (meth) acrylate, N, N-diethylaminoethyl (Meta) ak Tertiary amino group-containing polymerizable unsaturated monomers such as acrylate; Quaternary ammonium base-containing polymerizable unsaturated monomers such as 2- (methacryloyloxy) ethyltrimethylammonium chloride and 2- (methacryloyloxy) ethyltrimethylammonium bromide; Examples thereof include an ammonium chloride carboxyl group-containing polymerizable unsaturated monomer.

  Examples of the other polymerizable unsaturated monomers include methyl (meth) acrylate, ethyl (meth) acrylate, n- or i-propyl (meth) acrylate, n-, i- or t-butyl (meth) acrylate, C1-C24 alkyl ester or cycloalkyl ester of acrylic acid or methacrylic acid such as 2-ethylhexyl (meth) acrylate, cyclohexyl (meth) acrylate, lauryl (meth) acrylate, isobornyl (meth) acrylate; 2-hydroxyethyl Hydroxyalkyl esters of acrylic acid or methacrylic acid such as (meth) acrylate, 2- or 3-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate; glycidyl (meth) acrylate, Acrylonitrile, acrylamide, styrene, vinyl toluene, vinyl acetate, vinyl chloride, 1,6-hexanediol diacrylate and the like, which may be used alone or in combination.

  The copolymerization of the monomer mixture is not particularly limited and can be performed by a method known per se, for example, a water-soluble acrylic resin can be performed by a solution polymerization method, and an acrylic resin emulsion is It can be produced by an emulsion polymerization method or the like.

  When the aqueous acrylic resin (C) is an acrylic resin emulsion obtained by emulsion polymerization in particular, a multilayer structured particle emulsion obtained by emulsion polymerization in multiple stages using a monomer mixture in the presence of water and an emulsifier It may be.

  An acidic group such as a carboxyl group derived from a hydrophilic group-containing polymerizable unsaturated monomer in the aqueous acrylic resin (C) can be neutralized using a basic substance as necessary. The basic substance that can be used in this case is preferably water-soluble, such as ammonia, methylamine, ethylamine, propylamine, butylamine, dimethylamine, trimethylamine, triethylamine, ethylenediamine, morpholine, methylethanolamine, dimethyl. Ethanolamine, diethanolamine, triethanolamine, diisopropanolamine, 2-amino-2-methylpropanol and the like can be mentioned, and these can be used alone or in combination of two or more.

  The aqueous acrylic resin (C) desirably contains a hydroxyl group, and is generally 20 to 200 mgKOH / g, particularly 20 to 150 mgKOH / g from the viewpoint of water dispersibility, compatibility with other components, curability of the formed coating film, and the like. It is desirable to have a hydroxyl value in the range of g and an acid value in the range of generally 1-100 mg KOH / g, especially 10-70 mg KOH / g.

  In the aqueous primer used in the present invention, the amount of the components (A), (B) and (C) is 15 to 60% by mass based on the total solid mass of the three components, preferably 20-55 mass%, component (B) is 30-75 mass%, preferably 35-65 mass%, and component (C) is in the range of 10-40 mass%, preferably 15-35 mass%. If it is out of this range, the adhesion of the formed coating film to the material, water resistance, gasohol resistance and the like are lowered, which is not preferable.

Diester compound (D) :
The aqueous primer has the general formula (1)

[Wherein, R ¹ and R ² independently represent a hydrocarbon group having 4 to 18 carbon atoms, R ³ represents an alkylene group having 2 to 4 carbon atoms, m is an integer of 3 to 20, m R ³ may be the same or different from each other]
The diester compound (D) shown by these is contained.

In the above formula (1), the hydrocarbon group represented by R ¹ or R ² is preferably an alkyl group having 5 to 11 carbon atoms, more preferably an alkyl group having 5 to 9 carbon atoms, and 6 to 8 carbon atoms. The alkyl group is more preferable. In particular, when R ¹ and R ² are branched alkyl groups having 6 to 8 carbon atoms, even when the paint is applied after being stored for a relatively long period of time, it has excellent film formability in the formed coating film. Can be granted. R ³ is preferably ethylene, and m is particularly preferably an integer of 4 to 10.

  The diester compound (D) can be obtained, for example, by esterifying a polyoxyalkylene glycol having two terminal hydroxyl groups and a monocarboxylic acid having a hydrocarbon group having 4 to 18 carbon atoms.

  Examples of the polyoxyalkylene glycol include polyethylene glycol, polypropylene glycol, block copolymer of polyethylene glycol and polypropylene glycol, and polybutylene glycol. Among these, polyethylene glycol is particularly preferable. These polyoxyalkylene glycols preferably have a weight average molecular weight within the range of generally about 120 to about 800, particularly about 150 to about 600, more particularly about 200 to about 400, from the viewpoint of water resistance and the like.

  Examples of the monocarboxylic acid having a hydrocarbon group having 4 to 18 carbon atoms include pentanoic acid, hexanoic acid, 2-ethylbutanoic acid, 3-methylpentanoic acid, benzoic acid, cyclohexanecarboxylic acid, heptanoic acid, 2 -Ethylpentanoic acid, 3-ethylpentanoic acid, octanoic acid, 2-ethylhexanoic acid, 4-ethylhexanoic acid, nonanoic acid, 2-ethylheptanoic acid, decanoic acid, 2-ethyloctanoic acid, 4-ethyloctanoic acid, Examples include dodecanoic acid, hexadecanoic acid, and octadecanoic acid. Among these, hexanoic acid, heptanoic acid, 2-ethylpentanoic acid, 3-ethylpentanoic acid, octanoic acid, 2-ethylhexanoic acid, 4-ethylhexanoic acid, nonanoic acid, 2-ethylheptanoic acid, decanoic acid, 2- Monocarboxylic acids having an alkyl group having 5 to 9 carbon atoms such as ethyloctanoic acid and 4-ethyloctanoic acid are preferred, and heptanoic acid, 2-ethylpentanoic acid, 3-ethylpentanoic acid, octanoic acid, 2-ethylhexanoic acid Monocarboxylic acids having an alkyl group having 6 to 8 carbon atoms such as 4-ethylhexanoic acid, nonanoic acid, 2-ethylheptanoic acid, etc. are more preferable, 2-ethylpentanoic acid, 3-ethylpentanoic acid, 2-ethylhexane Monocarboxylic acids having a branched alkyl group having 6 to 8 carbon atoms such as acid, 4-ethylhexanoic acid and 2-ethylheptanoic acid. Preferred.

  The diesterification reaction between the polyoxyalkylene glycol and the monocarboxylic acid can be carried out by a method known per se. The polyoxyalkylene glycol and the monocarboxylic acid can be used alone or in combination of two or more.

  The obtained diester compound (D) is generally within the range of about 320 to about 1,000, particularly about 400 to about 800, more particularly about 500 to about 700, from the viewpoints of film formability, finish, water resistance, and the like. It preferably has a molecular weight.

  The content of the diester compound (D) in the aqueous primer is the sum of component (A), component (B) and component (C) from the viewpoints of film formability, finish of the multilayer coating film, water resistance, and the like. Based on 100 parts by mass of the solid content, it is generally 1 to 15 parts by mass, preferably 2 to 13.5 parts by mass, and more preferably 3 to 12 parts by mass.

Conductive pigment (E) :
The aqueous primer also contains a conductive pigment (E). The conductive pigment (E) is not particularly limited as long as it can impart conductivity to the coating film to be formed, and may have any shape such as a particle shape, a flake shape, and a fiber (including whisker) shape. Even things can be used. Specific examples include conductive carbon such as conductive carbon black, carbon nanotube, carbon nanofiber, and carbon microcoil; metal powder such as silver, nickel, copper, graphite, and aluminum, and further doped with antimony. And tin oxide doped with phosphorus, acicular titanium oxide surface-coated with tin oxide and antimony, pigments coated with conductive metal oxides such as antimony oxide, and the like. Or it can be used in combination of two or more. Of these, conductive carbon can be particularly preferably used.

  The content of the conductive pigment (E) is the sum of the component (A), the component (B) and the component (C) in the aqueous primer from the viewpoints of imparting conductivity, adhesion of the formed coating film, water resistance, and the like. Based on the solid content of 100 parts by mass, it is usually desirable to be in the range of 1 to 300 parts by mass, particularly 3 to 250 parts by mass, more particularly 5 to 180 parts by mass. In particular, when conductive carbon is used, its content is usually 1 to 30 mass based on 100 parts by mass of the total solid content of the component (A), component (B) and component (C) in the composition. Part, particularly 3 to 25 parts by weight, more preferably 5 to 25 parts by weight.

  If necessary, the water-based primer may be a pigment other than the above conductive pigment, for example, a colored pigment such as titanium white, bengara, aluminum paste, azo, phthalocyanine; talc, silica, calcium carbonate, barium sulfate, zinc white An extender pigment such as (zinc oxide) can be contained, and these can be used alone or in combination of two or more.

  The water-based primer is, for example, an aqueous dispersion (A) of the modified polyolefin described above, a water-based urethane resin (B), a water-based acrylic resin (C), a diester compound (D), and a conductive pigment (E). It can be prepared by mixing according to the method and appropriately diluting with an aqueous medium such as deionized water, and the solid content at the time of coating is usually 30% by mass or more, particularly 35 to 45% by mass. Is preferred.

  The aqueous primer may further contain a coating additive such as a crosslinking agent, a curing catalyst, a thickener, an antifoaming agent, an organic solvent, and a surface conditioner, if necessary.

  The aqueous primer can be applied by, for example, air spray coating, airless spray coating, brush coating, dip coating, etc., and the aqueous primer coating film thickness is in the range of 3 to 6 μm in terms of dry film thickness. be able to. Outside this range, it is not desirable because if the top coating is applied without preheating, a mixed layer may be formed.

Solvent type colored base coat paint and its coating :
In the method of the present invention, the aqueous primer is applied as described above, and the solvent-type colored base coat paint is applied to the coated surface without preheating. As the solvent-type colored base coat paint, an organic solvent-type paint comprising a hydroxyl group-containing resin, a color pigment / brightness pigment and an organic solvent is usually used.

  The hydroxyl group-containing resin is a film-forming resin having two or more hydroxyl groups in one molecule, and examples thereof include an acrylic resin, a polyester resin, and an alkyd resin that contain a hydroxyl group usually used in paint decomposition. In particular, a hydroxyl group-containing acrylic resin is suitable. The resin generally has a hydroxyl value in the range of 30 to 200, especially 40 to 170, and a number average molecular weight in the range of 3,000 to 50,000, especially 5,000 to 30,000. Is suitable.

  Examples of the color pigment / bright pigment include titanium oxide, zinc white, carbon black, chrome lead, Hansaero, chrome orange, iron oxide, permanent red, fast violet, chrome green, and phthalocyanine blue. And pigments such as flake-like aluminum, mica, and mica coated with a metal oxide such as titanium oxide, and bright pigments such as mica-like iron oxide.

  As the organic solvent, for example, usual paint solvents such as hydrocarbons (aliphatic or aromatic), ketones, alcohols, esters and ethers can be used.

  Solvent-type colored base coat paints, if necessary, extender pigments, crosslinking agents, curing catalysts, thickeners, UV absorbers, light stabilizers, antifoaming agents, rust preventives, plasticizers, surface conditioners, An anti-settling agent or the like can be appropriately contained.

  The solvent-type colored base coat paint is usually applied by electrostatic coating. The electrostatic coating can be performed, for example, by applying an electrostatic force in coating such as spray coating or rotary atomization coating. The coating film thickness is preferably 10 to 30 μm, particularly preferably 10 to 20 μm, in terms of the film thickness after the colored base coat layer is cured.

Solvent type clear coat paint and its coating :
In the method of the present invention, a solvent-type clear coat paint is applied to the coating surface of the colored base coat paint. As the clear coat paint, for example, a base resin such as an acrylic resin, a polyester resin, an alkyd resin, a urethane resin, an epoxy resin, and a fluororesin having a crosslinkable functional group such as a hydroxyl group, a carboxyl group, an epoxy group, and a silanol group; A melamine resin, a urea resin, a polyisocyanate compound which may be blocked, a carboxyl group-containing compound or resin, an epoxy group-containing compound or a resin containing a crosslinking agent such as a resin can be used. Especially, it is especially preferable to use what contains a hydroxyl-containing acrylic resin and the polyisocyanate compound which may be blocked as a resin component.

  If necessary, the clear coat paint may contain a color pigment, a bright pigment, a dye and the like to such an extent that the transparency is not hindered. Furthermore, extender pigments, curing catalysts, thickeners, ultraviolet absorbers, light stabilizers, antifoaming agents, rust inhibitors, plasticizers, organic solvents, surface conditioners, and the like can be appropriately contained.

  The clear coat paint is usually applied by electrostatic coating. The electrostatic coating can be performed, for example, by applying an electrostatic force in coating such as spray coating or rotary atomization coating. The coating film thickness is preferably in the range of usually 15 to 80 μm, particularly 20 to 40 μm in terms of the film thickness after the clear coat layer is cured.

Baking :
In the method of the present invention, the uncured three-layer coating film formed as described above is baked simultaneously. Baking can be performed by a usual baking means of the coating film. For example, it can be cured by heating at a temperature of about 80 to about 170 ° C. for about 15 to 40 minutes by hot air heating, infrared heating, high frequency heating, or the like.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated further more concretely, this invention is not limited only to these Examples. Note that “part” and “%” indicate “part by mass” and “% by mass”, respectively, unless otherwise specified.

Preparation of aqueous primer Preparation Example 1
As an aqueous dispersion of modified polyolefin, “EH-801” (aqueous dispersion of acid-modified chlorinated polyolefin, manufactured by Toyo Kasei Co., Ltd., trade name, chlorination degree: 16%, solid content: 30%) in solid mass is 30. Parts, “U-coat UX-310” (trade name, aqueous urethane dispersion, manufactured by Sanyo Kasei Co., Ltd.) as a water-based urethane resin, 40 parts by weight of solid content, and water-based acrylic resin (C-1) (Note 1) as a solid content mass 30 parts by weight, 5 parts by weight of the diester compound (D-1) (Note 2), 20 parts by weight of “Vulcan XC72” (trade name, conductive carbon black, manufactured by Cabot Specialty Chemicals) as a conductive pigment, and 80 parts of titanium white were mixed according to a conventional method, and diluted with deionized water to a solid content of 40% to obtain an aqueous primer (1).

Production Examples 2-6
In Production Example 1, operations were carried out in the same manner as in Production Example 1 except that the formulation composition was as shown in Table 1, to obtain aqueous primers (2) to (6).

The composition of Table 1 is a solid content display, and (Note 1) to (Note 2) in Table 1 are as follows. (Note 1) Aqueous acrylic resin (C-1): A reactor equipped with a stirrer, a reflux condenser and a thermometer was charged with 40 parts of propylene glycol monomethyl ether, heated to 120 ° C., and 53 parts of cyclohexyl methacrylate. , 20 parts of n-butyl acrylate, 21 parts of 2-hydroxyethyl acrylate, 6 parts of acrylic acid and 5 parts of azobisisobutyronitrile were added dropwise over 3 hours. After dropping, the mixture was aged at the same temperature for 1 hour, and a mixed solution of 1 part of azobisdimethylvaleronitrile and 10 parts of propylene glycol monomethyl ether was added dropwise over 1 hour. After further aging for 1 hour, 7.4 parts of dimethylethanolamine and 193 parts of deionized water was added with stirring to obtain a hydroxyl group-containing acrylic resin solution. This was used as an aqueous acrylic resin (C-1). The obtained resin had an acid value of 47 mgKOH / g, a hydroxyl value of 101 mgKOH / g, and a mass average molecular weight of about 10,000.
(Note 2) Diester compound (D-1): A diester compound of polyoxyethylene glycol and n-hexanoic acid. In the general formula (1), R ¹ and R ² are each a pentyl group, R ³ is an ethylene group, and m is 5. Molecular weight: 434.

Examples and Comparative Examples A far-infrared heater (amount of heat: 1,000 W / m ² , covered with polypropylene (degreased) (surface temperature: 5 ° C.) formed on a bumper and installed on both sides and the upper part of the conveyor at the entrance of the painting booth. Aqueous primer (1) to (6) prepared as described above in a coating booth at a room temperature of 25 ° C. and a relative humidity of 70%. ) Are sprayed by air spray so as to have the coating thicknesses shown in Table 2, and allowed to stand for 30 seconds. Then, "SOFLEX 450" (trade name, solvent type colored base coat paint, manufactured by Kansai Paint Co., Ltd.) is used as a colored base coat paint thereon. ) Is electrostatically coated so that the dry film thickness is about 15 μm, and then “Soflex 7300 Clear” (trade name, acrylic urea, manufactured by Kansai Paint Co., Ltd.) is used as a clear paint. Emissions based solvent-type clear paint) was electrostatically coated to be about 30μm in dry thickness, were prepared each test paint was dried by heating for 30 minutes at 80 ° C..

Performance Test Each test coating prepared as described above was subjected to the following performance test. The results are shown in Table 2.
(* 1) Finished appearance: The finished appearance of the coated film after top coating was visually evaluated according to the following criteria.
○: Finished skin and glossy feeling are good.
Δ: Finished skin is slightly inferior, or gloss is slightly inferior,
X: Finished skin and gloss are inferior.
(* 2) Initial adhesion: Cut lines with a cutter to reach the substrate on the coating surface of each test paint, make 100 squares of 2mm x 2mm size, and adhesive cellophane tape (registered) on the surface (Trademark) is pasted, and the number of residual coatings in the squares after having been abruptly peeled off at 20 ° C. is examined and displayed according to the following criteria.
○ is 100 (no peeling)
△ is 99-50 pieces,
X is 49 or less.
(* 3) Water resistance and adhesion after water resistance: A part of the bumper coated with each test paint was cut out, immersed in warm water at 40 ° C for 10 days, pulled up and dried, and then the initial adhesion test described above. In the same manner, an adhesion test was performed, and the number of remaining coating films was examined and evaluated in the same manner as described above (adhesion after water resistance). In addition, the surface of the coating film is observed, the presence / absence of blistering is examined, and displayed according to the following criteria (water resistance).
○: No occurrence of blister,
×: Blister occurred.

Claims (2)

A water-based primer is applied to a polyolefin bumper surface heated to a surface temperature of -3 to + 20 ° C with respect to a coating booth temperature of 15 to 35 ° C, and a solvent-based colored base coat paint is applied to the coated surface without preheating. A coating method comprising: coating a three-layer coating film at the same time by painting a solvent-type clear coat paint on the coating surface;
The aqueous primer is an aqueous dispersion of modified polyolefin (A), aqueous urethane resin (B), aqueous acrylic resin (C), general formula (1)

[Wherein, R ¹ and R ² independently represent a hydrocarbon group having 4 to 18 carbon atoms, R ³ represents an alkylene group having 2 to 4 carbon atoms, m is an integer of 3 to 20, m R ³ may be the same or different from each other]
Containing the diester compound (D) and the conductive pigment (E), and the blending amounts of the components (A), (B) and (C) are based on the total solid content mass of the three components (A ) Is 15 to 60% by mass, component (B) is 30 to 75% by mass, and component (C) is in the range of 10 to 40% by mass,
The polyolefin bumper surface is heated when a far-infrared heater is installed on both sides and the upper part of the conveyor at the entrance of the painting booth, and the bumper passes,
Furthermore, the coating method characterized by coating a water-based primer with a film thickness of 3-6 micrometers.   The content of the diester compound (C) in the aqueous primer is in the range of 1 to 15 parts by mass based on 100 parts by mass of the total solid content of the components (A), (B) and (C). Painting method.