Water-based primer paint composition for automotive exterior parts, method for producing a water-based primer paint composition for automotive exterior parts, and automotive exterior parts

Abstract

The objective is to provide an aqueous primer coating composition for automotive exterior parts that has film film performance equivalent to conventional primer coating compositions, while also offering superior workability robustness and storage stability. [Solution] (A) A water-soluble polyester resin having a hydroxyl value of 50-100 mgKOH / g and a number-average molecular weight of 2000-5000. (B) Melamine resin, and (C) Chlorinated polyolefin emulsion resin an aqueous primer coating composition for automotive exterior parts, comprising: The chlorinated polyolefin emulsion resin (C) is characterized by being an emulsion of a chlorinated polyolefin resin having a weight-average molecular weight of 20,000 or more, by adding 12 to 18 parts by mass of an emulsifier having an HLB value of 11.5 to 16.5 per 100 parts by mass of the solid content of the chlorinated polyolefin resin salt, thereby forming an aqueous primer coating composition for automotive exterior parts.

Description

Technical Field

[0005] , , , ,

[0001] The present invention relates to an aqueous primer paint composition for automotive exterior parts, a method for producing the aqueous primer paint composition for automotive exterior parts, and automotive exterior parts.

Background Art

[0002] Plastic molded products are lightweight and excellent in mechanical strength and the like, and are widely used in automotive parts such as bumpers. Plastic molded products used in automotive parts are usually coated with a primer paint, a base paint, and a clear paint. Recently, from the perspective of environmental protection, it has been desired to use aqueous paints as the primer paint and the base paint for plastic molded products.

[0003] Regarding the above aqueous primer paint, various resin compositions have been studied in consideration of coating film physical properties such as adhesion to plastic molded products, low-temperature curability, and film hardness (see Patent Documents 1 to 3). On the other hand, the one-component aqueous primer paint composition has problems such as easy thickening over time, deterioration of coating workability, and deterioration of pigment dispersibility. For this reason, the development of an aqueous primer paint having excellent storage stability as well as coating film physical properties has been desired.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0005] In view of the above situation, the present invention aims to provide an aqueous primer coating composition for automotive exterior parts that has performance equivalent to conventional primer coating compositions, while being particularly excellent in terms of storage stability. [Means for solving the problem]

[0006] The present invention relates to (A) an aqueous polyester resin having a hydroxyl value of 50 to 100 mg KOH / g and a number average molecular weight of 2000 to 5000. (B) Melamine resin, (C) Chlorinated polyolefin emulsion resin, and (D) A water-based primer coating composition for automotive exterior parts comprising a dispersion containing at least one (E) selected from the group consisting of conductive materials, coloring pigments, and extender pigments, The above-mentioned chlorinated polyolefin emulsion resin (C) is characterized by being an emulsion of a chlorinated polyolefin resin having a weight-average molecular weight of 20,000 or more, by adding 12 to 18 parts by mass of an emulsifier with an HLB value of 11.5 to 16.5 per 100 parts by mass of the solid content of the chlorinated polyolefin resin, and relates to an aqueous primer coating composition for automotive exterior parts. The above-mentioned aqueous primer paint composition for automotive exterior parts further comprises a dispersion (D) containing at least one (E) selected from the group consisting of conductive materials, coloring pigments, and extender pigments. The dispersion (D) is preferably a mixture in which at least one (E) selected from the group consisting of conductive materials, coloring pigments, and extender pigments is codispersed using an aqueous polyester resin (A). The above-mentioned water-based primer paint composition for automotive exterior parts contains, with 100 parts by mass of resin solids, (A) The solid content of the aqueous polyester resin is 10 to 50 parts by mass, (B) The solid content of the melamine resin is 2 to 15 parts by mass. (C) Preferably, the solid content of the chlorinated polyolefin emulsion resin is 10 to 50 parts by mass.

[0007] The present invention relates to a step (1) of codispersing an aqueous polyester resin (A) having a hydroxyl value of 50 to 100 mgKOH / g and a number average molecular weight of 2000 to 5000 with at least one (E) selected from the group consisting of conductive materials, coloring pigments and extender pigments to obtain a dispersion (D), Step (2) to obtain a chlorinated polyolefin emulsion resin (C) by emulsifying a chlorinated polyolefin resin having a weight-average molecular weight of 20,000 or more with an emulsifier having an HLB value of 11.5 to 16.5 in an amount of 12 to 18 parts by mass per 100 parts by mass of solids of the chlorinated polyolefin resin, and, The present invention relates to a method for producing an aqueous primer coating composition for automotive exterior parts, characterized by comprising a step (3) of mixing the above-mentioned dispersion (D), a chlorinated polyolefin emulsion resin (C), and a melamine resin (B).

[0008] The present invention relates to an automotive exterior part having a plastic molded body and a multi-layer coating, The above multi-layer coating film is characterized by having a primer coating film, a base coating film, and a clear coating film obtained by the above-described aqueous primer coating composition for automotive exterior parts. The above-mentioned plastic molded article is preferably made of polypropylene and / or PC-ABS resin. The above-mentioned automotive exterior part is preferably an automotive bumper. [Effects of the Invention]

[0009] The present invention provides a one-component aqueous primer coating composition that has performance equivalent to conventional primer coating compositions and excellent storage stability. [Modes for carrying out the invention]

[0010] The present invention will be described in detail below. The present invention has found that by including an aqueous polyester resin (A) having a hydroxyl value of 50 to 100 mgKOH / g and a number average molecular weight of 2000 to 5000, and a chlorinated polyolefin emulsion resin (C) emulsified with an emulsifier having an HLB value of 11.5 to 16.5, an aqueous primer coating composition for automotive exterior parts (hereinafter referred to as "aqueous primer coating composition") can be obtained that exhibits particularly excellent storage stability, even if it is a one-component type containing a melamine resin (B).

[0011] The above storage stability can be evaluated, for example, by viscosity change. Conventional primer coatings have shown a viscosity increase of 50% or more after 10 days of storage at 40°C. The aqueous primer coating composition of the present invention can suppress the viscosity increase to preferably 45% or less, more preferably 35% or less. The method for measuring the viscosity increase will be described in detail in the examples below.

[0012] The following describes each component. Water-based polyester resin (A) The aqueous polyester resin (A) used in the present invention is an aqueous polyester resin having a hydroxyl value of 50 to 100 mgKOH / g and a number average molecular weight of 2000 to 5000.

[0013] The hydroxyl value of the above aqueous polyester resin (A) is 50-100 mgKOH / g. In this invention, the hydroxyl value can be determined by a neutralization titration method using an aqueous potassium hydroxide solution as described in JIS K 0070.

[0014] The Mn value of the above-mentioned aqueous polyester resin (A) is between 2000 and 5000. When Mn is within this range, the adhesion to the plastic molded article is improved. In the present invention, the above-mentioned Mn can be calculated, for example, from the measurement results of gel permeation chromatography (GPC) using polystyrene as a standard.

[0015] The aqueous polyester resin (A) is not particularly limited as long as it satisfies the above physical properties, and examples thereof include those known as resin for paints such as condensates of polybasic acids and polyhydric alcohols. Examples of polybasic acids include phthalic anhydride, isophthalic acid, terephthalic acid, adipic acid, succinic anhydride, and the like. Examples of polyhydric alcohols include ethylene glycol, propylene glycol, 1,3-butylene glycol, 1,6-hexanediol, polyethylene glycol, polypropylene glycol, and the like. The above aqueous polyester resin (A) may be only one kind or two or more kinds.

[0016] Among them, a polyester resin (A) obtained by reacting (a) a polyhydric alcohol, (b) a polyvalent carboxylic acid and / or a polyvalent carboxylic acid anhydride, and (c) a monoepoxy compound having a long-chain hydrocarbon group, having a hydroxyl value in the range of 50 to 600 mgKOH / g and a number average molecular weight in the range of 300 to 3,000, and further reacting with (d) a polyvalent carboxylic acid and / or a polyvalent carboxylic acid anhydride, and / or (e) a polyisocyanate compound is particularly preferred.

[0017] The above polyester resin (A) is a polyester resin obtained by synthesizing a polyester polyol (A-1) having a specific monomer composition and further reacting the polyester polyol (A-1) with (d) a polyvalent carboxylic acid and / or a polyvalent carboxylic acid anhydride, and / or (e) a polyisocyanate compound.

[0018] Polyester polyol (A-1) Polyester polyol (A-1) is obtained by reacting (a) a polyhydric alcohol, (b) a polyhydric carboxylic acid and / or a polyhydric carboxylic acid anhydride, and (c) a monoepoxide compound having a long-chain hydrocarbon group. The method for synthesizing polyester polyol (A-1) is not particularly limited and can be carried out according to conventional methods. For example, it can be synthesized by heating each of the above components (a) to (c) in a nitrogen stream at approximately 90 to approximately 250°C for about 5 to 10 hours to carry out esterification reactions between epoxy groups and carboxyl groups and esterification reactions between hydroxyl groups and carboxyl groups. The above reaction components (a) to (c) may be added and reacted all at once, or they may be reacted in a multi-step manner, such as reacting components (a) and (b) first, and then reacting component (c). In this process, known esterification catalysts such as dibutyltin oxide, antimony trioxide, zinc acetate, manganese acetate, cobalt acetate, calcium acetate, lead acetate, tetrabutyl titanate, and tetraisopropyl titanate can be used as catalysts.

[0019] Polyhydric alcohols (a) are compounds having two or more hydroxyl groups in one molecule, for example, ethylene glycol, propylene glycol, diethylene glycol, trimethylene glycol, tetraethylene glycol, triethylene glycol, dipropylene glycol, 1,4-butanediol, 1,3-butanediol, 2,3-butanediol, 1,2-butanediol, 3-methyl-1,2-butanediol, 1,2-pentanediol, 1,5-pentanediol, 1,4-pentanediol, 2,4-pentanediol, 2,3-dimethyltrimethylene glycol, tetramethylene glycol, 3-methyl-4,5-pentanediol, 2,2,4-trimethyl-1,3-pentanediol, 1,6-hexanediol, 1,5-hexanediol, 1,4-hexanediol, 2,5-hexanediol, 2-butyl-2-phenyl Examples include glycols such as 1,3-propanediol, neopentyl glycol, and neopentyl glycol hydroxypivalate; polylactone diols obtained by adding lactones such as ε-caprolactone to these glycols, and polyester diols such as bis(hydroxyethyl) terephthalate; 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, tricyclodecanedimethanol, hydrogenated bisphenol A, hydrogenated bisphenol F, spiroglycol, dihydroxymethyltricyclodecane, glycerin, trimethylolpropane, trimethylolethane, diglycerin, triglycerin, 1,2,6-hexanetriol, pentaerythritol, dipentaerythritol, sorbitol, and mannitol, which can be used individually or in combination of two or more.

[0020] (b) The polycarboxylic acid of component (b) is a compound having two or more carboxyl groups in one molecule, and examples include phthalic acid, isophthalic acid, terephthalic acid, succinic acid, adipic acid, azelaic acid, sebacic acid, naphthalenedicarboxylic acid, 4,4-diphenyldicarboxylic acid, diphenylmethane-4,4'-dicarboxylic acid, hetic acid, maleic acid, fumaric acid, itaconic acid, trimellitic acid, pyromellitic acid, cyclohexane-1,3-dicarboxylic acid, cyclohexane-1,4-dicarboxylic acid, hexahydrophthalic acid, hexahydroisophthalic acid, hexahydroterephthalic acid, tetrahydrophthalic acid, hexahydrotrimellitic acid, methylhexahydrophthalic acid, etc., which can be used alone or in combination of two or more.

[0021] (b) The polycarboxylic acid anhydride of component (b) is a compound having one or more acid anhydride groups in one molecule, for example, the polycarboxylic acid anhydrides mentioned above. Here, since two carboxyl groups are produced from one acid anhydride group, one acid anhydride group is considered to be divalent.

[0022] The monoepoxide compound (c) having a long-chain hydrocarbon group is a monoepoxide compound having a chain or cyclic hydrocarbon group with 4 or more carbon atoms, preferably 6 to 20 carbon atoms. Specifically, examples of the monoepoxide compound (c) include glycidyl esters such as glycidyl pivalate, glycidyl hexanoate, glycidyl cyclohexanecarboxylic acid, glycidyl 2-ethylhexanoate, glycidyl isononanoate, glycidyl decanoate, glycidyl undecanoate, glycidyl laurate, glycidyl myristate, glycidyl palmitate, glycidyl stearate, and Cardura E10 (manufactured by Japan Epoxy Resin Co., Ltd., neodecanoate monoglycidyl ester); glycidyl ethers such as butyl glycidyl ether, phenyl glycidyl ether, and decyl glycidyl ether; and α-olefin monoepoxides such as styrene oxide and AOEX24 (manufactured by Daicel Chemical Industries, Ltd., α-olefin monoepoxide mixture).

[0023] Furthermore, the hydrocarbon group having four or more carbon atoms may have substituents such as hydroxyl groups. Specific examples of monoepoxide compounds having such substituent hydrocarbon groups include 1,2-epoxyoctanol and hydroxyoctylglycidyl ether. These monoepoxide compounds (c) having long-chain hydrocarbon groups can be used alone or in combination of two or more.

[0024] The resulting polyester polyol (A-1) generally has a number-average molecular weight in the range of 300 to 3,000, preferably 400 to 2,000, and more preferably 400 to 1,000, and a hydroxyl value in the range of 50 to 600 mgKOH / g, preferably 150 to 500 mgKOH / g. Note that if the number-average molecular weight of polyester polyol (A-1) exceeds 3,000, high solid differentiation of the coating becomes difficult, and if the hydroxyl value falls below 50 mgKOH / g, curability tends to be insufficient.

[0025] The proportions of components (a), (b), and (c) used are selected so that the hydroxyl value and number-average molecular weight of the resulting polyester polyol (A-1) fall within the ranges described above. In this case, it is preferable to use a bifunctional or trifunctional alcohol as component (a) and a bifunctional or trifunctional carboxylic acid anhydride as component (b). Furthermore, from the viewpoint of wettability, compatibility, etc., it is preferable to use a monoepoxide compound having a hydrocarbon group with 6 or more carbon atoms as component (c), and glycidyl esters, especially cardura E10, are preferred.

[0026] The above-mentioned polyester resin (A) is produced by further reacting the polyester polyol (A-1) produced as described above with (d) a polycarboxylic acid and / or a polycarboxylic acid anhydride and / or (e) a polyisocyanate compound. In the above manufacturing process, the reaction between polyester polyol (A-1) and polycarboxylic acid and / or polycarboxylic acid anhydride (d) can be carried out by a conventional method, for example, by heating both components in a nitrogen stream at approximately 150 to 250°C for 1 to 10 hours to induce a condensation reaction. In this process, the same catalyst described in the manufacturing of polyester polyol (A-1) can be used. As the polycarboxylic acid and / or polycarboxylic acid anhydride (d), the same as those exemplified for component (b) above can be used.

[0027] Furthermore, the reaction between the polyester polyol (A-1) and the polyisocyanate compound (e) can be carried out by conventional methods, for example, by heating both components in a nitrogen stream at approximately 60 to 140°C for 1 to 10 hours to induce an addition reaction between the hydroxyl group and the isocyanate group. In this process, organometallic catalysts (especially organotin catalysts), as described later, can be used as catalysts as needed.

[0028] In polyester resin (A), the polyester resin obtained by reacting polyester polyol (A-1) with polyisocyanate compound (e) has urethane bonds in its resin backbone, which can improve the physical properties of coatings and other materials formed therefrom.

[0029] Examples of polyisocyanate compounds (e) include aliphatic polyisocyanates such as hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, dimer acid diisocyanate, and lysine diisocyanate; biuret-type adducts and isocyanurate ring adducts of these polyisocyanates; isophorone diisocyanate, 4,4′-methylenebis(cyclohexyl isocyanate), methylcyclohexane-2,4-(or-2,6-)diisocyanate, and 1,3-(or 1,4-)di(isocyanate). Alicyclic diisocyanates such as (Tyl)cyclohexane, 1,4-cyclohexane diisocyanate, 1,3-cyclopentane diisocyanate, and 1,2-cyclohexane diisocyanate; biuret-type adducts and isocyanurate ring adducts of these diisocyanates; xylylene diisocyanate, metaxylylene diisocyanate, tetramethylxylylene diisocyanate, tolylene diisocyanate, 4,4′-diphenylmethane diisocyanate, 1,5-naphthalene diisocyanate, 1,4-naphthalene diisocyanate, 4,4′-toluidine diisocyanate, 4,4′-diphenyl ether diisocyanate, (m- or p-)phenylene diisocyanate, 4,4′-biphenylene diisocyanate, and 3,3′-dimethyl-4,4′-biphenylene diisocyanate. Aromatic diisocyanate compounds such as bis(4-isocyanatophenyl)sulfone and isopropylidenebis(4-phenylisocyanate); burette-type adducts and isocyanurate ring adducts of these diisocyanate compounds; polyisocyanates having three or more isocyanate groups in one molecule, such as triphenylmethane-4,4′,4″-triisocyanate, 1,3,5-triisocyanatobenzene, 2,4,6-triisocyanatotoluene, and 4,4′-dimethyldiphenylmethane-2,2′,5,5′-tetraisocyanate; burette-type adducts and isocyanurate ring adducts of these polyisocyanates;Urethane adducts are obtained by reacting polyisocyanate compounds with the hydroxyl groups of polyols such as ethylene glycol, propylene glycol, 1,4-butylene glycol, dimethylolpropionic acid, polyalkylene glycol, trimethylolpropane, and hexanetriol in a ratio that results in an excess of isocyanate groups; examples include biuret-type adducts and isocyanurate ring adducts of these urethane adducts.

[0030] When manufacturing polyester resin (A), if both component (d) and component (e) are reacted with polyester polyol (A-1), either component (d) or component (e) may be reacted with polyester polyol (A-1) first. The reaction can be carried out under the same conditions as described above.

[0031] As described above, polyester resin (A) is obtained by further condensing component (d) and / or component (e) with polyester polyol (A-1) to increase its molecular weight, but its number average molecular weight is preferably 400 to 2,000, and especially 700 to 1,600, greater than that of polyester polyol (A-1).

[0032] The proportions of component (A-1) and components (d) and / or (e) used, as well as the reaction conditions, are adjusted so that the hydroxyl value and number-average molecular weight of the resulting polyester resin (A) fall within the ranges described above. In this case, component (d) is preferably a polycarboxylic acid with three or more functions and / or a polycarboxylic acid anhydride with three or more functions, and among these, at least one compound selected from trimellitic anhydride, ethylene glycol bis(anhydrotrimellitate), 1,3-propanediol bis(anhydrotrimellitate), and pyromellitic anhydride is particularly preferred.

[0033] A polyester resin (A) can be dissolved or dispersed in an aqueous medium containing a basic compound in an amount of typically 0.3 to 1.2 equivalents, preferably 0.5 to 1.0 equivalents, relative to the resin acid value, to prepare an aqueous resin composition. Examples of the basic compound include inorganic basic compounds such as alkali metal hydroxides and aqueous ammonia; and amine compounds such as methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine, isopropylamine, diisopropylamine, diethylenetriamine, triethylenetetramine, monoethanolamine, diethanolamine, 2-amino-2-methylpropanol, morpholine, N-methylmorpholine, N-ethylmorpholine, piperazine, dimethylethanolamine, diethylethanolamine, and dimethyldodecylamine. Among these, triethylamine, dimethylethanolamine, and diethylethanolamine are particularly preferred.

[0034] In the present invention, it is important that the polyester resin (A) is synthesized by first reacting a polyhydric alcohol (a), a polyhydric carboxylic acid and / or a polyhydric carboxylic acid anhydride (b), and a monoepoxide compound having a long-chain hydrocarbon group (c) to synthesize a polyester polyol (A-1), and then further reacting this polyester polyol (A-1) with a polyhydric carboxylic acid and / or a polyhydric carboxylic acid anhydride (d) and / or a polyisocyanate compound (e). For example, it is possible to synthesize a polyester resin having a hydroxyl value and number-average molecular weight within the above range and having a similar monomer composition by methods such as (a) in which each of the above components (a) to (c) reacts with most of component (d), and then reacting the resulting condensation product with the remaining portion of component (d), but when a polyester resin produced by methods such as (a) or (b) is used as the resin in an aqueous primer paint composition, it will not be superior in both coating film performance such as water resistance and finish, nor will it have a wide range of suitability for painting work in response to temperature and humidity fluctuations.

[0035] The content of the above-mentioned aqueous polyester resin (A) is preferably 10 to 50 parts by mass per 100 parts by mass of the resin solids of the aqueous primer coating composition. More preferably, the content is 20 parts by mass or more and 40 parts by mass or less.

[0036] The aqueous polyester resin (A) described above is suitably used as a pigment-dispersing resin. The present invention may also include a dispersion (D) in which at least one (E) selected from the group consisting of conductive materials, coloring pigments, and extender pigments is codispersed using the aqueous polyester resin (A), and the above component (E) can maintain a stable dispersion state in the aqueous primer coating composition. This further enhances the storage stability of the aqueous primer coating composition. Furthermore, the aqueous polyester resin (A) used in the dispersion (D) may be the entire amount or a portion of the aqueous polyester resin (A) contained in the aqueous primer coating composition.

[0037] Melamine resin (B) The aqueous primer coating composition of the present invention contains a melamine resin (B) as a crosslinking agent. The melamine resin is not particularly limited as long as it is a melamine resin having one or more triazine rings in one molecule. Examples include alkoxymethylolmelamines such as methoxymethylolmelamine, n-butoxymethylolmelamine, isobutoxymethylolmelamine, methoxybutoxymethylolmelamine, methoxy / n-butoxy mixed methylolmelamine (in which methoxy and n-butoxy groups are etherified in the melamine skeleton), and condensates thereof. Among these, methoxymethylolmelamine, n-butoxymethylolmelamine, and methoxy / n-butoxy mixed methylolmelamine, which have an average degree of condensation of 1 to 4, are preferred. The melamine resin (B) described above may be just one type, or two or more types may be used in combination.

[0038] The melamine resin content is preferably 2 to 15 parts by mass per 100 parts by mass of resin solids in the aqueous primer coating composition. If the content is less than 2 parts by mass, the water resistance of the resulting coating film will be insufficient, while if it exceeds 15 parts by mass, the storage stability of the coating will deteriorate, and the resulting coating film will tend to be hard and brittle.

[0039] Chlorinated polyolefin emulsion resin (C) The aqueous primer coating composition of the present invention further comprises a chlorinated polyolefin emulsion resin (C). A chlorinated polyolefin emulsion resin modified with acid anhydride is preferred as the chlorinated polyolefin emulsion resin (C). The above-mentioned acid anhydride-modified chlorinated polyolefin emulsion resin is an emulsion of acid anhydride-modified chlorinated polyolefin resin. Since acid anhydride-modified chlorinated polyolefin resin is highly hydrophobic and difficult to disperse stably in water, in this invention, the acid anhydride-modified chlorinated polyolefin resin is emulsified using an emulsifier or a basic substance and used as an emulsion.

[0040] The above-mentioned acid anhydride-modified chlorinated polyolefin resin is a polyolefin derivative comprising a chlorinated polyolefin portion and an acid anhydride portion bonded to the chlorinated polyolefin portion. More specifically, the chlorinated polyolefin portion is a portion consisting of a polyolefin in which chlorine atoms have been substituted, and the acid anhydride portion consists of a group derived from an acid anhydride and is a modified portion obtained by grafting. The above-mentioned acid anhydride-modified chlorinated polyolefin resin can be obtained, for example, by internal modification by reacting a polyolefin with chlorine and an acid anhydride. Here, either chlorine or acid anhydride may be reacted first. The reaction with chlorine can be carried out, for example, by introducing chlorine gas into a solution containing polyolefin. The reaction with acid anhydride can be carried out, for example, by reacting a polyolefin (or chlorinated polyolefin) with an acid anhydride in the presence of a peroxide.

[0041] Examples of the polyolefins mentioned above include polyethylene, polypropylene, ethylene-propylene copolymer, ethylene-propylene-diene copolymer, polybutene, and aqueous additives of copolymers such as styrene-butadiene-isoprene. Among these, polypropylene is preferred due to its availability and excellent adhesion to plastic materials, particularly polypropylene materials. The polyolefins may be one type or two or more types. Examples of the acid anhydrides mentioned above include maleic anhydride, citraconic anhydride, and itaconic anhydride. The acid anhydrides may be one type or two or more types.

[0042] The above-mentioned acid anhydride-modified chlorinated polyolefin resin preferably has a chlorine content in the range of 10 to 30% by mass, and more preferably in the range of 18 to 22% by mass. If the chlorine content is less than 10% by mass, the solvent solubility tends to be low and emulsification becomes difficult, while if it exceeds 30% by mass, the adhesion to plastic materials may decrease. The acid anhydride content of the above-mentioned acid anhydride-modified chlorinated polyolefin resin is preferably in the range of 1 to 10% by mass, and more preferably in the range of 1.2 to 5% by mass. If the acid anhydride content is less than 1% by mass, emulsification becomes difficult and the storage stability of the coating may deteriorate. On the other hand, if it exceeds 10% by mass, the number of acid anhydride groups increases, and the water resistance of the resulting coating film tends to decrease.

[0043] The above-mentioned acid anhydride-modified chlorinated polyolefin resin has a weight-average molecular weight in the range of 20,000 or more, preferably in the range of 20,000 to 200,000. If the weight-average molecular weight is less than 20,000, the film strength of the resulting coating film tends to decrease, and the adhesion also tends to decrease. On the other hand, if it exceeds 200,000, the viscosity increases, making emulsification difficult, and there is a risk that the storage stability of the paint will decrease. There are no particular restrictions on the method of emulsifying the above-mentioned acid anhydride-modified chlorinated polyolefin resin to produce an acid anhydride-modified chlorinated polyolefin emulsion resin, and it can be carried out by conventionally known methods. For example, the above-mentioned acid anhydride-modified chlorinated polyolefin resin may be dissolved by adding an emulsifier, a basic substance as a neutralizing agent, and a solvent if necessary, and then emulsified in water using a commercially available emulsifier, or the above-mentioned acid anhydride-modified chlorinated polyolefin resin may be dissolved by adding an emulsifier and a solvent if necessary, and then emulsified in water to which a basic substance has been added using a commercially available emulsifier. Alternatively, the above-mentioned acid anhydride-modified chlorinated polyolefin resin may be dissolved in an organic phase by adding an emulsifier, a basic substance as a neutralizing agent, and a solvent as necessary, and heating or leaving it as is, and then water may be slowly added under stirring to perform phase inversion emulsification.

[0044] In the present invention, the emulsifier used in the emulsion formation process is characterized by having an HLB value of 11.5 to 16.5. The HLB value is a commonly used value that represents the degree of affinity of a surfactant to water and oil, and can be calculated, for example, by Griffin's formula. The HLB value of the emulsifier is preferably 12.0 or more and 16.0 or less.

[0045] It is presumed that acid anhydride-modified chlorinated polyolefin emulsion resins obtained using such emulsifiers have the effect of suppressing the penetration of solvent into the interior of polymer particles. Emulsified with conventional emulsifiers is thought to swell over time or under high-temperature conditions as the solvent penetrates into the polymer particles, preventing the maintenance of a uniform dispersion state and making aggregation and sedimentation more likely. This is expected to reduce the overall stability of the water-based primer coating composition. To date, no method has been investigated for improving the overall storage stability of a paint composition by adjusting the HLB value of the emulsifier used in the emulsification of chlorinated polyolefin emulsion resins. The present invention sets a suitable HLB value for the emulsifier and has found that by using the resulting chlorinated polyolefin emulsion resin (C) in combination with the polyester resin (A), storage stability can be significantly improved.

[0046] The emulsifiers mentioned above are not particularly limited, but examples include nonionic emulsifiers such as polyoxyethylene alkyl ethers (e.g., polyoxyethylene lauryl ether, polyoxyethylene stearyl ether, etc.), polyoxyethylene alkylphenol ethers (e.g., polyoxyethylene nonylphenol ether, etc.), polyoxyethylene aliphatic esters, polyoxyethylene polyhydric alcohol fatty acid esters, polyhydric alcohol fatty acid esters, polyoxyethylene propylene polyols, alkylolamides, etc.; anionic emulsifiers such as alkyl sulfate salts, dialkyl sulfosuccinates, alkyl sulfonates, polyoxyethylene stearyl ether sulfates, polyoxyethylene nonylphenyl ether sulfates, alkyl phosphates, etc.; amphoteric emulsifiers such as alkyl betaines (e.g., stearyl betaine, lauryl betaine, etc.), alkylimidazolines, etc.; resin-type emulsifiers such as polyoxyethylene group-containing urethane resins, carboxylic acid base-containing urethane resins, etc.; cationic emulsifiers such as imidazoline laurate, lauryltrimethylammonium chloride, distearyldimethylammonium chloride, etc. Among these, nonionic emulsifiers that do not have highly hydrophilic ionic polar groups are preferred because they can impart good water resistance to the resulting coating film.

[0047] The amount of emulsifier used in the above emulsion formation can be appropriately set depending on the amount of acid anhydride-modified chlorinated polyolefin resin and the mixing ratio of basic substances and water. However, in the present invention, the amount is 12 to 18 parts by mass per 100 parts by mass of solids of the acid anhydride-modified chlorinated polyolefin resin. If the amount is less than 12 parts by mass, the storage stability of the paint will decrease, and aggregation and sedimentation may easily occur during emulsion formation. On the other hand, if the amount exceeds 18 parts by mass, a large amount of emulsifier will remain in the resulting coating film, which tends to reduce workability (layering resistance) and water resistance. The basic substance used in the above emulsion formation process either adds to the acid anhydride groups and / or carboxyl groups of the acid anhydride-modified chlorinated polyolefin resin, and / or neutralizes these groups, thereby increasing the hydrophilicity of the acid anhydride-modified chlorinated polyolefin resin and improving the storage stability of the emulsion. The present invention involves incorporating the chlorinated polyolefin emulsion resin (C) emulsified in this manner into an aqueous primer paint composition. In the resulting aqueous primer paint composition, it is preferable that the emulsifier is contained in an amount of 12 to 18 parts by mass per 100 parts by mass of the solid content of the chlorinated polyolefin resin.

[0048] The amount of basic substance used in the above emulsion formation should be appropriately set to adequately neutralize the acidic functional groups contained in the acid anhydride-modified chlorinated polyolefin resin and emulsifier, depending on the amount of acid anhydride-modified chlorinated polyolefin resin and the proportions of emulsifier and water. For example, it is preferable to use 0.5 to 4 equivalents per 1 equivalent of acidic functional groups contained in the acid anhydride-modified chlorinated polyolefin resin. If the amount is less than 0.5 equivalents, the emulsion formation tends to be insufficient, while if it exceeds 4 equivalents, the remaining basic substance may reduce the water resistance of the resulting coating film or accelerate the dechlorination of the acid anhydride-modified chlorinated polyolefin resin. The amount of water used in the above emulsion formation is preferably 50 to 95% by mass of the total emulsion, more preferably 60 to 85% by mass, and most preferably 65 to 80% by mass. If the resin solids content is less than 50% by mass, the amount of resin solids in the emulsion becomes too high, making it prone to aggregation and reducing the storage stability of the emulsion. On the other hand, if it exceeds 95% by mass, the amount of resin solids in the paint becomes too low, which may reduce the workability of the paint.

[0049] There are no particular limitations on the solvents that can be used in the above emulsion formation, but examples include aromatic solvents such as toluene and xylene (commercial products include, for example, Sorbesso 100 from Exxon); ethylene glycol-based or propylene glycol-based solvents such as diethylene glycol monoethyl ether acetate, butyl cellosolve, propylene glycol monomethyl ether, dipropylene glycol monomethyl ether, and propylene glycol-n-propyl ether; and so on. There are no particular limitations on the amount of solvent used in the above emulsion formation, but for example, it is preferable to use 15 to 50 parts by mass per 100 parts by mass of the total of the acid anhydride-modified chlorinated polyolefin resin and the emulsifier. If the amount is less than 15 parts by mass, the viscosity may become too high during emulsion formation, making it difficult to emulsify properly, while if it exceeds 50 parts by mass, the emulsion may gradually fuse together, leading to poor stability.

[0050] The pH of the above acid anhydride-modified chlorinated polyolefin emulsion resin is determined by the basic substance used during emulsification, but is preferably 7 to 10.5, and more preferably 8 to 10. If the pH is less than 7, neutralization may be insufficient, and the storage stability of the emulsion may decrease. On the other hand, if the pH exceeds 10.5, the water resistance of the resulting coating film may decrease, or there may be an excess of free basic substances, resulting in a strong odor and making it difficult to use. The particle size of the polymer particles (the above acid anhydride-modified chlorinated polyolefin resin) in the above acid anhydride-modified chlorinated polyolefin emulsion resin is not particularly limited, but is preferably 0.03 to 5 μm, and more preferably 0.05 to 1 μm. If the average particle size of the polymer particles is less than 0.03 μm, a large amount of emulsifier will be required, which may reduce the water resistance of the resulting coating. On the other hand, if it exceeds 5 μm, the storage stability of the paint tends to deteriorate, and the film formation ability may worsen, potentially resulting in a loss of smoothness in the coating.

[0051] The content of the above-mentioned chlorinated polyolefin emulsion resin (C) is preferably 10 to 50 parts by mass per 100 parts by mass of the resin solids of the aqueous primer coating composition. If it is outside this range, it becomes difficult to obtain sufficient adhesion to plastic materials, especially polypropylene materials, and there is a tendency for correlated adhesion with the topcoat paint to be poor or pigment dispersibility to be poor. The above content is more preferably 20 parts by mass or more and 40 parts by mass or less.

[0052] Other resins The aqueous primer coating composition of the present invention may optionally contain other resins. The other resins are not particularly limited and include, for example, alkyd resins, acrylic resins, urethane resins, epoxy resins, and the like.

[0053] Alkyd resin By including alkyd resin, the pigment dispersibility can be improved, and the resulting coating film can be given flexibility. The above alkyd resin is a polyesterization reaction product of a polyhydric alcohol and a polyfunctional carboxylic acid in which part of the acid component may be a long-chain fatty acid of a vegetable oil. In this invention, the above alkyd resin is limited to those that do not fall under the above aqueous polyester resin (A).

[0054] As the polyhydric alcohol and polyfunctional carboxylic acid mentioned above, those exemplified in the aqueous polyester resin (A) above can be used. The alkyd resin may also be modified by modifying it with various oils. Examples of oils that can be used for modification include tung oil, linseed oil, soybean oil, safflower oil, castor oil, corn oil, cottonseed oil, perala oil, sesame oil, coconut oil, dehydrated castor oil, tall oil, etc.

[0055] Acrylic resin Acrylic resin is an ingredient used to improve pigment dispersion stability and curing reactivity with melamine. Examples of the above-mentioned acrylic resin include acrylic resins containing structural units derived from hydrophilic (meth)acrylic monomers. Examples of the above-mentioned hydrophilic (meth)acrylic monomers include carboxyl group-containing (meth)acrylic monomers such as acrylic acid, methacrylic acid, crotonic acid, and itaconic acid; hydroxyl group-containing (meth)acrylic monomers such as 2-hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, and ring-opening adducts obtained by the reaction of these (meth)acrylates with caprolactone or ethylene oxide; amino group-containing (meth)acrylic monomers such as dimethylaminoethyl (meth)acrylate; and acrylamide monomers such as acrylamide and N-methoxymethylacrylamide. One type or two or more types may be used in combination.

[0056] The above-mentioned acrylic resin may, in addition to structural units derived from hydrophilic (meth)acrylic monomers, optionally contain structural units derived from other (meth)acrylic monomers or styrene-based monomers.

[0057] The above acrylic resin can be obtained by polymerizing hydrophilic (meth)acrylic monomers, but may also be obtained by copolymerizing with other (meth)acrylic monomers or styrene monomers as needed, or by making it water-soluble with acids or alkalis. For example, if the hydrophilic (meth)acrylic monomer is a carboxyl group-containing (meth)acrylic monomer, it can be neutralized with an amine or ammonia, and if it is an amino group-containing (meth)acrylic monomer, it can be neutralized with an organic acid or the like. Furthermore, the acrylic resin may be an aqueous dispersion of acrylic resin dispersed in an aqueous medium, or it may be an emulsion or dispersion, and in the aqueous medium, the acrylic resin may be in particulate form.

[0058] Urethane resin Urethane resin is a type of film-forming resin. The inclusion of urethane resin as a film-forming resin offers the advantage of improved solvent resistance in the primer coating. Urethane resin can be prepared, for example, by reacting polyol compounds, polyisocyanate compounds, or compounds containing active hydrogen groups within their molecules.

[0059] Polyol compounds are not particularly limited as long as they have two or more hydroxyl groups. Specific examples of polyol compounds include, for example, polyhydric alcohols such as ethylene glycol, propylene glycol, 1,4-butanediol, 1,6-hexanediol, 3-methylpentanediol, 2-ethyl-1,3-hexanediol, trimethylolpropane, and glycerin; polyether polyols such as polyethylene glycol, polypropylene glycol, and polytetramethylene ether glycol; polyester polyols obtained from dicarboxylic acids such as adipic acid, sebadic acid, itaconic acid, maleic anhydride, phthalic acid, and isophthalic acid, and glycols such as ethylene glycol, triethylene glycol, propylene glycol, butylene glycol, tripropylene glycol, and neopentyl glycol; polycaprolactone polyols; polybutadiene polyols; polycarbonate polyols; and polythioether polyols. The above polyol compounds may be used individually or in combination of two or more. The number-average molecular weight of the polyol compound is preferably 500 to 5000.

[0060] Polyisocyanate compounds are not particularly limited as long as they have two or more isocyanate groups in their molecule. Specific examples of polyisocyanate compounds include, for example, aliphatic diisocyanates with 2 to 12 carbon atoms, such as hexamethylene diisocyanate, 2,2,4-trimethylhexane diisocyanate, and lysine diisocyanate; alicyclic diisocyanates with 4 to 18 carbon atoms, such as 1,4-cyclohexane diisocyanate, isophorone diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, methylcyclohexylene diisocyanate, and isopropylidenecyclohexyl-4,4'-diisocyanate; and 2,4-toluylene diisocyanate, 2,6-toluylene diisocyanate, diphenylmethane-4,4'-diisocyanate, and 1,5'-naphthenesine diisocyanate. Examples include aromatic diisocyanates such as socianates, toridine diisocyanate, diphenylmethylmethane diisocyanate, tetraalkyldiphenylmethane diisocyanate, xylylene diisocyanate, tetramethylxylylene diisocyanate, 4,4'-dibenzyle diisocyanate, and 1,3-phenylene diisocyanate; and triisocyanates such as lysine ester triisocyanate, triphenylmethane triisocyanate, 1,6,11-undecane triisocyanate, 1,8-diisocyanate-4,4-isocyanate methyloctane, 1,3,6-hexamethylene triisocyanate, and bicycloheptane triisocyanate. The polyisocyanate compound may be a dimer or trimer (isocyanurate bond) of the above polyisocyanate compound, or it may be used as a biuret by reacting the above polyisocyanate compound with an amine. Furthermore, polyisocyanates having urethane bonds, obtained by reacting these polyisocyanate compounds with polyols, can also be used.

[0061] As the polyisocyanate compound, it is more preferable to use aromatic aliphatic diisocyanate compounds, such as isophorone diisocyanate, 1,4-cyclohexane diisocyanate, isophorone diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, methylcyclohexylene diisocyanate, and isopropylidenecyclohexyl-4,4'-diisocyanate. By preparing a urethane resin using the above isocyanate compounds, it is possible to obtain a coating film with high flexibility due to the balance between hard and soft segments.

[0062] Compounds having active hydrogen groups in their molecules are generally used to block isocyanate groups in the polyisocyanate compounds mentioned above. Specific examples of such compounds include monohydric alcohols such as methanol, ethanol, and diethylene glycol monobutyl ether; monohydric carboxylic acids such as acetic acid and propionic acid; monohydric thiols such as ethyl mercaptan; primary amines such as diethylenetriamine and monoethanolamine; secondary amines such as diethylamine; and oximes such as methyl ethyl ketoxime.

[0063] In the preparation of urethane resins, chain extenders may be used as needed. The chain extender is not particularly limited as long as it contains two or more active hydrogen groups, but examples include polyamines. Specific examples of polyamines include ethylenediamine, hexamethylenediamine, diethylenetriamine, hydrazine, xylylenediamine, and isophoronediamine.

[0064] In the preparation of urethane resins, monoisocyanate compounds may be used as needed. Examples of monoisocyanate compounds include methyl isocyanate, ethyl isocyanate, propyl isocyanate, butyl isocyanate, lauryl isocyanate, cyclohexyl isocyanate, phenyl isocyanate, and tolylene isocyanate.

[0065] The reaction method for producing urethane resin may be a one-shot method in which each component is reacted at once, or a multi-stage method in which the reaction is carried out in steps (a method in which a portion of the active hydrogen-containing compound (e.g., a high molecular weight polyol) is reacted with a polyisocyanate to form an NCO-terminated prepolymer, and then the remainder of the active hydrogen-containing compound is reacted). The synthesis reaction of urethane resin is usually carried out at 40°C to 140°C, preferably 60°C to 120°C. To accelerate the reaction, tin-based catalysts such as dibutylsus saturates and tin octoates, or amine-based catalysts such as triethylenediamine, which are commonly used in urethane formation reactions, may be used. Furthermore, the above reaction may be carried out in an organic solvent that is inert to isocyanates (e.g., acetone, toluene, dimethylformamide, etc.), and the solvent may be added during or after the reaction.

[0066] Commercially available urethane resins may be used. Examples of commercially available products include NBC300 (manufactured by Sanyo Chemical Industries, 30% non-volatile content), NBC100 (manufactured by Sanyo Chemical Industries, 40% non-volatile content), IB-465 (manufactured by Sanyo Chemical Industries, 30% non-volatile content), IB-940 (manufactured by Sanyo Chemical Industries, 40% non-volatile content), and IB-700 (manufactured by Sanyo Chemical Industries, 30% non-volatile content).

[0067] epoxy resin Epoxy resin is a component that imparts water resistance and adhesion to the resulting coating film. The epoxy resin mentioned above is not particularly limited as long as it is a resin having one or more epoxy groups in one molecule; conventional epoxy resins used in paints can be used. Specifically, these include bisphenol-type epoxy resins obtained by adding epichlorohydrin to bisphenol, novolac-type epoxy resins obtained by adding epichlorohydrin to phenol novolac resins, and those obtained by adding epichlorohydrin to polyols such as pentaerythritol, sorbitol, and glycerin.

[0068] These are made water-based by methods such as forced emulsification using emulsifiers or by carboxylation followed by neutralization with a basic substance. Examples of commercially available water-based epoxy resins include: for bisphenol-type epoxy resins, Epilets 3510W60, 3515W60, 3522W60, 3540Wy55, 880SAW-65, etc. from Shell Chemical Co., Ltd.; for novolac-type epoxy resins, Denacol EM150 from Nagase Chemtec Co., Ltd., Epilets 6006W70, 5003W55 from Shell Chemical Co., Ltd., and WEX-5100 from Toto Kasei Co., Ltd.; and for polyols with epichlorohydrin added, Denacol EX611, EX614, EX411, EX313, etc. from Nagase Chemtec Co., Ltd.

[0069] The content of the above-mentioned other resins is preferably 5 parts by mass or more and 60 parts by mass or less, and more preferably 15 parts by mass or more and 50 parts by mass or less, per 100 parts by mass of resin solids in the aqueous primer coating composition.

[0070] At least one selected from the group consisting of conductive materials, coloring pigments, and extender pigments (E) The primer coating composition of the present invention contains, as a dispersion (D) obtained by codispersing at least one (E) selected from the group consisting of conductive materials, coloring pigments, and extender pigments using an aqueous polyester resin (A). The above component (E) is added to the aqueous primer paint composition in a state where it is sufficiently and uniformly dispersed within the dispersion (D). This allows component (E) to maintain good dispersibility within the aqueous primer paint composition, and also improves the overall stability of the paint composition. The method for producing the dispersion (D) is not particularly limited, and one example is a method of mixing all or part of the above component (E) and the above aqueous polyester resin (A) using a stirrer such as a disperser or Dynomill.

[0071] The aqueous primer coating composition of the present invention imparts conductivity to a plastic molded body to be coated, and preferably contains a conductive material. The conductive material is not particularly limited and may include conductive carbon black, carbon-based materials such as graphite, milled fiber-based materials which are crushed carbon fibers, or reprocessed recycled carbon fibers, or metal-based materials such as silver, zinc, or iron phosphate. Examples include metal oxide systems in which a conductive layer containing tin oxide, doped with at least one element selected from antimony and phosphorus, is coated on the surface of powdered titanium dioxide or the like. Among these, conductive carbon black is preferred. Such conductive materials may be used alone or in combination.

[0072] The above-mentioned coloring pigments are not particularly limited and include conventionally known coloring pigments such as organic azo lake pigments, insoluble azo pigments, condensed azo pigments, phthalocyanine pigments, indigo pigments, perinone pigments, perylene pigments, dioxazine pigments, quinacridone pigments, isoindolinone pigments, metal complex pigments, etc., and inorganic pigments such as lead yellow, yellow iron oxide, red iron oxide, carbon black, titanium dioxide, etc. The above-mentioned extender pigments are not particularly limited and may include extender pigments such as calcium carbonate, barium sulfate, clay, and talc.

[0073] The aqueous primer coating composition used in the present invention may optionally contain known auxiliary compounding agents such as inorganic fillers, organic modifiers, stabilizers, plasticizers, and additives.

[0074] The proportion of water in the above primer paint composition is preferably 45 to 90% by mass, and more preferably 50 to 80% by mass, relative to the entire primer paint composition. If the proportion of water is less than 45% by mass, the viscosity increases, reducing storage stability and paint workability. On the other hand, if the proportion of water exceeds 90% by mass, the proportion of non-volatile components decreases, reducing painting efficiency and making it easier for cosmetic abnormalities such as drips and blotches to occur. The above primer paint composition may further contain an organic solvent, the proportion of which is usually 40% by mass or less relative to the amount of water contained.

[0075] Examples of the above-mentioned organic solvents include aromatic hydrocarbons such as toluene and xylene; aliphatic hydrocarbons such as hexane, heptane, and octane; alicyclic hydrocarbons such as cyclohexane, methylcyclohexane, and cyclopentane; esters such as ethyl acetate, n-butyl acetate, isobutyl acetate, and amyl acetate; ethers such as n-butyl ether and isobutyl ether; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; alcohols such as methanol, ethanol, isopropanol, n-butanol, 2-butanol, n-propylene glycol, and isopropylene glycol; cellosolves such as ethylene glycol monomethyl ether, ethylene glycol monobutyl ether, and ethylene glycol monoethyl ether acetate; carbitols such as diethylene glycol monoethyl ether; propylene glycol alkyl ethers such as propylene glycol monomethyl ether, propylene glycol monoethyl ether, and propylene glycol monobutyl ether; and other solvents such as dioxane, N-methylpyrrolidone, dimethylformamide, and diacetone alcohol.

[0076] The present invention relates to a method for producing the above-mentioned aqueous primer coating composition, Step (1) to obtain a dispersion (D) by codispersing an aqueous polyester resin (A) having a hydroxyl value of 50 to 100 mg KOH / g and a number average molecular weight of 2000 to 5000 with at least one (E) selected from the group consisting of conductive materials, coloring pigments and extender pigments. Step (2) to obtain a chlorinated polyolefin emulsion resin (C) by emulsifying a chlorinated polyolefin resin with a weight-average molecular weight of 20,000 or more by adding an emulsifier with an HLB value of 11.5 to 16.5 in an amount of 12 to 18 parts by mass per 100 parts by mass of solids of the chlorinated polyolefin resin, and, The present invention also relates to a method for producing an aqueous primer coating composition for automotive exterior parts, characterized by comprising a step (3) of mixing the above-mentioned dispersion (D), a chlorinated polyolefin emulsion resin (C), and a melamine resin (B).

[0077] Furthermore, the present invention also relates to an automotive exterior part having a plastic molded body and a multi-layer coating, wherein the multi-layer coating is characterized in that it has a primer coating, a base coating, and a clear coating obtained by the aqueous primer coating composition of the present invention.

[0078] Plastic molded articles are not particularly limited and can include, for example, automotive exterior parts such as bumpers, spoilers, grilles, and fenders. The materials used are also not particularly limited and can include, for example, polyethylene, polyolefins such as polypropylene, polystyrene, ABS, vinyl chloride, polycarbonate, polyacetal, polyester, polyamide, polyurethane, PPO, polymethyl methacrylate, epoxy resin, phenolic resin, and melamine resin.

[0079] The above-mentioned primer coating is a primer coating obtained by the aqueous primer coating composition of the present invention. The method of applying the above-mentioned primer coating composition to the surface of a plastic molded body is not particularly limited and can be applied by methods such as spray painting or bell painting. Industrially, for example, methods using an air electrostatic spray coating machine commonly known as a "react gun" or a rotary atomizing electrostatic coating machine commonly known as a "micro-micro bell," "micro bell," or "metallic bell" can be mentioned. Furthermore, the above-mentioned plastic molded body may be washed and degreased as necessary.

[0080] The above-mentioned primer coating film preferably has a dry film thickness of 10 to 30 μm. If it is less than 10 μm, the opacity will be insufficient, and if it exceeds 30 μm, blotches and sagging are likely to occur. Preferably, it is 15 to 20 μm. The above dry film thickness can be measured using SANKO's SDM-miniR.

[0081] It is preferable to dry the above-mentioned primer coating before applying the base paint composition. The drying temperature can be set as appropriate, but 40 to 110°C is preferred, and 50 to 100°C is more preferred. There are no particular restrictions on the drying method, and known methods such as hot air drying or infrared drying may be used.

[0082] The above-mentioned base coating is typically obtained from a base coating composition containing a coloring pigment, a film-forming resin, a curing agent, and, if necessary, additives. Examples of coloring pigments contained in the above-mentioned base paint composition include the compounds described above. Furthermore, flat pigments such as aluminum powder and graphite powder may be added. In addition, extender pigments such as calcium carbonate, barium sulfate, clay, and talc may be included. Furthermore, if necessary, luminescent materials such as interference mica pigments and aluminum pigments may be included.

[0083] As the film-forming resin and curing agent of the above-mentioned base coating composition, for example, a film-forming resin such as an acrylic resin, polyester resin, alkyd resin, or fluororesin, and a curing agent such as an amino resin and / or a blocked polyisocyanate compound are used.

[0084] The total pigment concentration (PWC) in the above base coating composition is preferably between a lower limit of 3% by mass and an upper limit of 70% by mass. If it exceeds 70% by mass, the appearance of the coating film deteriorates. The lower limit is more preferably 4% by mass, and even more preferably 5% by mass. The upper limit is more preferably 65% ​​by mass, and even more preferably 60% by mass.

[0085] The above-mentioned base coating composition is generally preferably a solution type, and any of the following types are acceptable: organic solvent type, water-based type (water-soluble, water-dispersible, emulsion), or non-water-dispersible type.

[0086] The film thickness of the coating when using the above base paint composition varies depending on the desired application, but in most cases, 10 to 30 μm is useful. If it is less than 10 μm, the substrate may not be concealed and film breakage may occur, and if it exceeds 30 μm, the clarity may decrease, and problems such as unevenness and flow may occur during painting. In addition, the dry film thickness of the base coating is usually 10 to 30 μm. If it is less than 10 μm, the concealment is poor, and if it exceeds 30 μm, it is not economically viable.

[0087] The method for applying the above-mentioned base coating composition is not particularly limited, and examples include spray painting and electrostatic painting.

[0088] The base coating formed by the above base coating composition may be applied directly to the next clear coating composition without drying by heat, or it may be dried at a temperature of 40°C to 110°C. In particular, with water-based coatings, if the drying temperature is below 40°C, blending with the clear coating may occur and the appearance of the coating may deteriorate. If the temperature is too high, peeling may occur between the base coating and the clear coating.

[0089] The above clear coating composition is used to apply over an uncured base film to form the top layer (uppermost layer) of a three-layer coating, and imparts excellent physical properties such as weather resistance and solvent resistance to the cured coating film.

[0090] The above clear coating composition is not particularly limited, and any conventionally known composition may be used. However, a two-component clear coating (e.g., a two-component curing type urethane coating) is preferred, for example, in which a polyol resin containing hydroxyl groups is used as the main component and an isocyanate is used as the curing agent. This is because the resulting clear coating film has a good appearance and excellent acid resistance. The polyol resin used as the main component is not particularly limited, but for example, polyester polyol, acrylic polyol, polycarbonate polyol, polyurethane polyol, etc., can be used.

[0091] Examples of isocyanates used as curing agents include non-yellowing compounds having two or more isocyanate groups in the molecule (for example, adduct, nurate, or biuret forms of hexamethylene diisocyanate and isophorone diisocyanate). Examples of commercially available curing agents include Desmodule 3600 and Sumijoule 3300 from Sumika Bayer Co., Ltd., Coronate HX from Nippon Polyurethane Co., Ltd., Takenate D-140NL and D-170N from Mitsui Takeda Chemical Co., Ltd., and Duranate 24A-90PX and THA-100 from Asahi Kasei Corporation. The above clear coating composition preferably contains a low molecular weight isocyanate compound as a curing agent that easily penetrates into the underlying layer. By curing with the low molecular weight isocyanate compound penetrating to the base coating or primer coating, the adhesion and strength of the multi-layer coating can be improved. Examples of low molecular weight isocyanate compounds include desmodulus N3900 and desmodulus N3400.

[0092] The above clear coating composition preferably contains a curing accelerator. The inclusion of the curing accelerator allows for smooth curing of plastic molded articles even at low temperatures. Examples of the curing accelerator include ZCAT (dibutyltin dilaurate).

[0093] Furthermore, conventionally known additives such as defoamers, rheology control agents, lubricants, and UV absorbers, as well as organic solvents, are used as needed. Examples of commercially available clear coatings include R2500-1, a two-component curing urethane coating manufactured by Nippon B-Chemical Co., Ltd.

[0094] The method of applying the above clear coating composition is not particularly limited, and for example, air spray painting, airless spray painting, and bell painting can be used.

[0095] As described above, the primer coating composition, base coating composition, and clear coating composition are applied to the surface of the plastic molded body in this order to form three layers of uncured films consisting of each coating component, and then the next baking process is carried out. When selecting a paint composition, it is necessary to choose a paint that can be sufficiently cured and dried during the baking process. If drying is insufficient and water or solvent remains inside the cured paint film, the performance of the cured paint film, such as water resistance and solvent resistance, is likely to deteriorate.

[0096] The dry film thickness of the clear coating is preferably 20 to 50 μm. If it is outside this range, there is a risk of deterioration in appearance such as roughness, and poor workability such as sagging and unevenness.

[0097] The baking process involves simultaneously baking the three uncured layers described above to form a cured coating consisting of three layers: a primer coating, a base coating, and a clear coating.

[0098] The curing temperature is preferably 70 to 130°C, for example, considering the balance between rapid curing and preventing deformation of the plastic molded body. Preferably, it is 80 to 110°C. The curing time is usually 10 to 60 minutes, preferably 15 to 50 minutes, and more preferably 20 to 40 minutes. If the curing time is less than 10 minutes, the curing of the coating film is insufficient, and the performance of the cured coating film, such as water resistance and solvent resistance, deteriorates. On the other hand, if the curing time exceeds 60 minutes, it becomes over-cured, reducing adhesion in recoating, lengthening the total time of the painting process, and increasing energy costs. Note that this curing time refers to the time during which the substrate surface actually maintains the target curing temperature. More specifically, it refers to the time from when the target temperature is reached until that temperature is maintained, without considering the time it takes to reach the target curing temperature.

[0099] Examples of heating devices used to simultaneously bake the uncured paint film include drying ovens that utilize heat sources such as hot air, electricity, gas, and infrared radiation. Furthermore, it is preferable to use a drying oven that uses two or more of these heat sources in combination, as this shortens the drying time. [Examples]

[0100] The present invention will be described below with reference to examples. In the examples, "%" and "parts" in the formulation ratios refer to "mass%" and "parts by mass" unless otherwise specified. The present invention is not limited to the examples described below.

[0101] (Manufacturing Example 1-1) Synthesis of Polyester Resin A In a reaction vessel equipped with a thermometer, stirrer, condenser, nitrogen inlet, water separator, and rectification column, 51.3 parts isophthalic acid, 4.6 parts phthalic anhydride, 6.9 parts trimethylolpropane, 6.5 parts neopentyl glycol, 18.5 parts 16-hexanediol, and 20.6 parts glycidyl neodecanoate (Hexion's "Cardura E10P") were charged. The mixture was heated to 220°C, and the resulting condensation water was removed from the system by distillation. Once the reaction vessel reached 220°C, it was kept warm. After 1 hour of warming, 2.0 parts xylene was gradually added to the reaction vessel as a refluxing solvent, and the reaction was continued in the presence of the solvent. The resin was sampled, diluted with methyl ethyl ketone to a solid content of 71%, and after confirming that the bubble viscosity at 25°C was between W and Y, it was cooled to 135°C. To this, 1.4 parts of trimellitic anhydride were added, and the reaction was continued for 2 hours until the desired acid value was reached. Then, butyl cellosolve was added to adjust the solid content to 88%. To this, 3.2 parts of dimethylethanolamine were added to homogenize the mixture, and 149.8 parts of deionized water were gradually added to perform phase inversion emulsification. A stable emulsion with a particle size of 60 nm was obtained. The resulting polyester resin had an acid value of 200, a hydroxyl value of 50, and a number-average molecular weight of 3000.

[0102] (Manufacturing Example 1-2) Synthesis of Polyester Resin B The same method as in Production Example 1 was used, except that the raw materials were changed to 45.1 parts isophthalic acid, 13.4 parts phthalic anhydride, 14.4 parts trimethylolpropane, 23.0 parts neopentyl glycol, 3.3 parts 16-hexanediol, 9.7 parts glycidyl neodecanoate (Hexion's "Cardura E10P"), and 1.6 parts trimellitic anhydride. The particle size was 60 nm, and a stable emulsion was obtained. The obtained polyester resin had an acid value of 200, a hydroxyl value of 100, and a number-average molecular weight of 2000.

[0103] (Manufacturing Examples 1-3) Synthesis of Polyester Resin C The same method as in Production Example 1 was used, except that the raw materials were changed to 48.3 parts isophthalic acid, 8.6 parts phthalic anhydride, 26.5 parts trimethylolpropane, 10.6 parts neopentyl glycol, 5.2 parts 16-hexanediol, 9.7 parts glycidyl neodecanoate (Hexion's "Cardura E10P"), and 1.6 parts trimellitic anhydride. The particle size was 70 nm, and a stable emulsion was obtained. The obtained polyester resin had an acid value of 200, a hydroxyl value of 150, and a number-average molecular weight of 2000.

[0104] (Manufacturing Example 2) Manufacturing of Chlorinated Polyolefin Emulsion Resin (C) In a reaction apparatus equipped with stirring blades, a thermometer, a temperature control thermistor, and a cooling tube, 100 parts of maleic anhydride-modified chlorinated polypropylene resin ("Hardlen M-500P," manufactured by Toyobo MC Co., Ltd.: chlorine content 20%, weight-average molecular weight 75000), 15 parts of polyoxyethylene (14) oleyl ether as an emulsifier, 50 parts of toluene, 60 parts of isopropyl alcohol, and 250 parts of deionized water were charged. The mixture was heated at 100°C for 1 hour to dissolve the components, then 4 parts of a 90% aqueous solution of 1-amino-2-methyl-1-propanol were added and the mixture was stirred for another hour. After that, the solvent was removed under reduced pressure and the mixture was cooled to room temperature. The resin solid content was adjusted with deionized water, and the mixture was filtered through a 400-mesh sieve to obtain maleic anhydride-modified chlorinated polypropylene emulsion resin (1). The obtained maleic anhydride-modified chlorinated polypropylene emulsion resin (1) had a resin solids content of 30.0%, and the basic substance (1-amino-2-methyl-1-propanol) content was 0.9%. If necessary, the following emulsifiers were used to create any desired emulsion. HLB emulsifiers 11.3 Polyoxyethylene(9) oleyl ether 12.1 Polyoxyethylene(8) lauryl ether 14.0 Polyoxyethylene(14) oleyl ether 15.8 Polyoxyethylene (19) lauryl ether 17.4 Polyoxyethylene (40) oleyl ether

[0105] (Manufacturing example 3) Manufacturing of acrylic resin In a reaction vessel equipped with a stirring blade, thermometer, dropping device, temperature control device, nitrogen gas inlet tube, and condenser tube, 55 parts of propylene glycol monomethyl ether ether were charged, and the temperature was raised to 120°C while stirring and introducing nitrogen gas. Next, a polymerizable monomer mixture consisting of 12 parts 2-hydroxyethyl methacrylate, 9 parts methacrylic acid, 35 parts isobutyl methacrylate, and 44 parts n-butyl acrylate, and a solution of 1 part t-butyl peroxy-2-ethylhexanate dissolved in 8 parts propylene glycol were added dropwise over 3 hours with internal stirring. Next, after the dropwise addition was complete, the reaction was aged at 120°C for 1 hour. Then, a solution of 0.1 parts t-butyl peroxy-2-ethylhexanate dissolved in 4 parts propylene glycol monomethyl ether was added dropwise to the reaction vessel over 1 hour. In all cases, internal stirring and a liquid temperature of 120°C were maintained. After this, the mixture was aged at 120°C for 2 hours with stirring, then the internal liquid temperature was cooled to 70°C, and 9.5 parts dimethylaminoethanol was added dropwise and stirred for 30 minutes. The internal liquid temperature was then maintained at 70°C, and 167 parts deionized water was slowly added dropwise while stirring, and the mixture was cooled to obtain a water-soluble acrylic resin solution. The non-volatile content was adjusted to 30% using deionized water. The pH of the obtained water-soluble acrylic resin solution was 8.2, and the weight-average molecular weight of the acrylic resin was 42,000 (polystyrene equivalent by GPC).

[0106] (Manufacturing Example 4) Manufacturing of epoxy resin In a reaction vessel equipped with a stirring blade, thermometer, dropping device, temperature control device, nitrogen gas inlet tube, and cooling tube, 37 parts of deionized water were charged and the temperature was raised to 80°C. All operations from the temperature rise to the completion of the reaction were carried out while stirring the internal liquid. Meanwhile, in an emulsifier (TK Robomix RM type; manufactured by Primix Co., Ltd.), 21 parts of deionized water, 1 part of surfactant Newcol710, and 1 part of Newcol740 (both surfactants, manufactured by Nippon Emulsifier Co., Ltd.) were charged and uniform dissolution was carried out while stirring. While continuing to stir, a polymerizable monomer mixture consisting of 6 parts n-butyl acrylate, 8 parts ethylhexyl methacrylate, and 14 parts glycidyl methacrylate was gradually added dropwise to the emulsifier to prepare a pre-emulsion solution. Meanwhile, a polymerization catalyst solution was prepared consisting of 7 parts deionized water and 1.1 parts ammonium persulfate (emulsion polymerization catalyst). The pre-emulsion solution and the polymerization catalyst solution were added dropwise to the reaction vessel from separate dropping funnels over a period of 3 hours. The internal temperature of the reaction vessel was maintained at 80°C, and emulsion polymerization was carried out while stirring. The pre-emulsion solution was added dropwise by maintaining its emulsified state in an emulsifier and connecting it directly to the reaction vessel. After 3 hours, only the polymerization catalyst solution consisting of 4 parts deionized water and ammonium persulfate polymerization catalyst was added dropwise over 1 hour while maintaining the internal temperature at 80°C. After that, it was aged at 80°C for 1 hour and then cooled to obtain an epoxy group-containing acrylic emulsion. The non-volatile content of this emulsion was 30%. The amount of epoxy group-containing monomer in 100% by mass of resin solids was 50% by mass.

[0107] (Manufacturing Example 5) Manufacturing of Urethane Resin Stirring blades, thermometer, temperature control, dropping device, reflux apparatus with sample collection port and condenser, nitrogen In a pressure-resistant reaction vessel equipped with an inlet tube, 1100 parts of adipic acid, 900 parts of 3-methyl-1,5-pentanediol, and 0.5 parts of tetrabutyl titanate were charged while passing nitrogen gas through the vessel. The reaction temperature of the liquid in the vessel was set to 170°C, and an esterification reaction by dehydration was carried out, continuing until the acid value was 0.3 mg KOH / g or less. Then, the reaction was carried out for 2 hours under reduced pressure conditions of 180°C and 5 kPa or less to obtain a polyester with a hydroxyl value of 112 mg KOH / g and an acid value of 0.2 mg KOH / g. Next, 500 parts of this polyester polyol, 134 parts of dimethyl 5-sulfosodium isophthalate, and 2 parts of tetrabutyl titanate were charged into another reaction vessel equipped with the same apparatus as described above. The esterification reaction was carried out in the same manner as described above, with nitrogen gas flowing through and the reaction temperature set to 180°C, to obtain a sulfonic acid group-containing polyester with a molecular weight of 2117, a hydroxyl value of 53 mgKOH / g, and an acid value of 0.3 mgKOH / g. 280 parts of the above sulfonic acid group-containing polyester, 200 parts of polybutylene adipate, 35 parts of 1,4-butanediol, 118 parts of hexamethylene diisocyanate, and 400 parts of methyl ethyl ketone were charged into a reaction vessel equipped with a stirring blade, thermometer, temperature control, dropping device, sample collection port, and condenser while passing nitrogen gas through the vessel. The urethane reaction was carried out while stirring and maintaining the liquid temperature at 75°C to obtain a urethane prepolymer with an NCO content of 1%. Subsequently, the temperature inside the reaction vessel was lowered to 40°C, and 955 parts of ion-exchanged water were uniformly added dropwise while stirring thoroughly to perform phase inversion emulsification. Next, the internal temperature was lowered to room temperature, and an aqueous solution of adipic acid hydrazide, prepared by mixing 13 parts of adipic acid hydrazide and 110 parts of ion-exchanged water, was added to perform amine extension. Next, the liquid temperature was raised to 60°C under a slightly reduced pressure to remove the solvent. Upon completion, deionized water was added to the polyurethane dispersion so that the solid content was 35%, thereby obtaining a polyurethane dispersion containing sulfonic acid groups. The acid value was 11 mg KOH / g.

[0108] (Manufacturing Example 6) Manufacturing of Dispersion (D) In a stainless steel cylindrical stirring tank equipped with a stirrer, 30 parts of the polyester resin obtained in Production Example 1 were charged, and 29 parts of deionized water were added while stirring. Next, 8.7 parts of the pigment dispersant SURFYNOL GA (non-volatile content = 78%; manufactured by Evonik) were added while stirring. While stirring thoroughly, 1.4 parts of the defoaming agent Nopco 8034-L (non-volatile content 100%; manufactured by Sun Nopco) were added. While continuing to stir, 14.5 parts of talc Microace P-4 (manufactured by Nippon Talc Co., Ltd.), 8.2 parts of conductive carbon Carbon ECP600JD (manufactured by Lion Corporation), and 52.5 parts of titanium R-960 (manufactured by Chemours Co., Ltd.) were added in order, followed by 35.6 parts of deionized water. The mixture was stirred thoroughly for 15 minutes until the mixture was homogenized to create a pigment mill base. This mill base was dispersed using a sand grinder mill to create dispersion (D). The non-volatile content of this substance was 45%, and the pigment concentration (PWC) was 65%.

[0109] [Example 1] 44 parts of dispersion (D) were placed in a container equipped with a stirrer. Then, while stirring, 6 parts of epoxy resin obtained in Production Example 4, 35 parts of maleic anhydride-modified chlorinated polypropylene emulsion resin obtained in Production Example 2, 8 parts of melamine resin (Cymel 202, manufactured by Mitsui Cytec Co., Ltd.), 6 parts of acrylic resin obtained in Production Example 3, 15 parts of urethane resin obtained in Production Example 5, 1 part of isopropanolamine (primary amine compound) as a pH adjuster, 95 parts of deionized water, and 2.5 parts of thickener ("Acrysol ASE60," manufactured by DOW Corporation) were added, and the mixture was stirred for 1 hour to obtain aqueous primer paint (1).

[0110] Examples 2-9, Comparative Examples 1-9 An aqueous primer was obtained in the same manner as in Example 1, except that the composition was changed to that shown in Tables 1 and 2.

[0111] (Storage stability) The viscosity of the aqueous primers obtained in each example and comparative example was measured at 25°C using a B-type viscometer (initial viscosity). Furthermore, the aqueous primers were stored at 40°C for 10 days, and then the viscosity was similarly measured at 25°C (viscosity after 10 days at 40°C). The viscosity increase was calculated using the following formula (1). Viscosity increase rate = (viscosity after 10 days at 40℃ / initial viscosity -1) x 100 (1) ○: Thickening rate ≤ 30% or less △: Thickening rate ≤ 50% or less ×: Thickening rate 50% or more and 100% or less ××: Thickening rate 100% or more

[0112] (Workability evaluation) The prepared water-based primer was spray-painted onto the surface of the PP material (water-based primer film thickness: 7-11 μm), dried at 60°C for 3 minutes, then the base coat (AR-3020: Nippon Paint) was applied in one stage to achieve a dry film thickness of 20 μm, and the panel was again placed vertically and dried at 80°C for 3 minutes. Clear coat (R-2550: Nippon Paint) was then applied to the painted panel to achieve a dry film thickness of 30-35 μm, and the painted product was baked and cured at 120°C for 20 minutes using the Keep setting. The appearance of the obtained painted product was visually evaluated based on the following criteria. Evaluation criteria: ○: No abnormalities in the base coat. △: There are traces of accumulation near the edge. ×: Drip marks can be seen on the edges. ××: Dripping occurred across the entire surface of the paint film.

[0113] [Table 1]

[0114] [Table 2]

[0115] The results shown in Table 1 demonstrate that the aqueous primer coating composition of the present invention exhibits excellent storage stability, as no significant thickening was observed even after storage at 40°C for 10 days. Furthermore, it was shown that workability was maintained. [Industrial applicability]

[0116] The present invention provides an aqueous primer coating composition for automotive exterior parts that is particularly excellent in terms of storage stability.

Claims

1. (A) A water-based polyester resin having a hydroxyl value of 50 to 100 mg KOH / g and a number-average molecular weight of 2000 to 5000. (B) Melamine resin, and (C) Chlorinated polyolefin emulsion resin an aqueous primer coating composition for automotive exterior parts, comprising: The chlorinated polyolefin emulsion resin (C) is characterized by being an emulsion of a chlorinated polyolefin resin having a weight-average molecular weight of 20,000 or more, by adding 12 to 18 parts by mass of an emulsifier having an HLB value of 11.5 to 16.5 per 100 parts by mass of the solid content of the chlorinated polyolefin resin. This is an aqueous primer paint composition for automotive exterior parts.

2. Furthermore, the material comprises a dispersion (D) containing at least one (E) selected from the group consisting of conductive materials, coloring pigments, and extender pigments, The aqueous primer paint composition for automotive exterior parts according to claim 1, wherein the dispersion (D) is obtained by codispersing at least one (E) selected from the group consisting of conductive materials, coloring pigments and extender pigments using an aqueous polyester resin (A).

3. For every 100 parts by mass of the resin solids in the aqueous primer coating composition for automotive exterior parts, (A) The aqueous polyester resin has a solid content of 10 to 50 parts by mass, (B) The melamine resin has a solid content of 2 to 15 parts by mass. (C) The aqueous primer coating composition for automotive exterior parts according to claim 1 or 2, wherein the solid content of the chlorinated polyolefin emulsion resin is 10 to 50 parts by mass.

4. A step (1) to obtain a dispersion (D) by codispersing an aqueous polyester resin (A) having a hydroxyl value of 50 to 100 mg KOH / g and a number average molecular weight of 2000 to 5000 with at least one (E) selected from the group consisting of conductive materials, coloring pigments and extender pigments. Step (2) to obtain a chlorinated polyolefin emulsion resin (C) by emulsifying a chlorinated polyolefin resin having a weight-average molecular weight of 20,000 or more with an emulsifier having an HLB value of 11.5 to 16.5 in an amount of 12 to 18 parts by mass per 100 parts by mass of solid content of the chlorinated polyolefin resin, and, A method for producing an aqueous primer coating composition for automotive exterior parts, characterized by comprising a step (3) of mixing the dispersion (D), a chlorinated polyolefin emulsion resin (C), and a melamine resin (B).

5. An automotive exterior part having a plastic molded body and a multi-layer coating, The multi-layer coating is characterized by having a primer coating, a base coating, and a clear coating obtained by the aqueous primer coating composition for automotive exterior parts described in claim 1 or 2.

6. The automotive exterior part according to claim 5, wherein the plastic molded body is made of polypropylene and / or PC-ABS resin.

7. The automotive exterior part according to claim 5, which is an automobile bumper.

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