JP4289940B2 - Method for forming coating film of water-based paint - Google Patents

Description

 The present invention relates to a method for forming a coating film of a water-based paint, and the obtained coating film has no occurrence of coating film defects such as sagging or flaming, and when the water-based paint is applied on a sealer, there is no repellency, This is a method for obtaining a coating film having excellent concealment properties, and is particularly suitable for coating inner plates in line coating of automobile bodies.

An automobile body is usually coated with a multilayer coating film composed of an undercoating film, an intermediate coating film, and a top coating film by a cationic electrodeposition coating for the purpose of providing corrosion prevention and aesthetics.
Conventional paints mainly use paints that use organic solvents. However, there is always a danger of fire when using organic solvents, and there is concern about the impact on the health of users, especially the environment. Therefore, a paint using safe and harmless water is required.
For this reason, water-based paints are also becoming water-based in terms of automobile paints, and water-based paints have been applied to automobile lines even in intermediate coatings that require a chipping resistance function.

  Conventionally, there is an invention relating to an aqueous intermediate coating material containing urethane-modified polyester resin, blocked isocyanate compound, melamine resin, and flat pigment particles.

. However, with the above invention alone, when the automobile body is line-coated, a coating film defect such as sagging or peeling, or a coating film with excellent concealability when coated on a sealer cannot be obtained.

JP 2003-20441 A

Due to the recent trend of water-based products, users such as automobile manufacturers have received approval for the materials of water-based intermediate coating materials, and they have come to be applied on the painting line.
However, when water-based paint is applied to a complex-shaped object such as an automobile body, the finish of the paint film varies greatly depending on the paint conditions (solid content of paint, viscosity, booth temperature / humidity, coating viscosity). For example, (1) coating film defects such as armpits and sagging occurred on the inner plate of the automobile body (the back of the hood, around the door, the back door, the lid of the gasoline inlet, etc.), which became a problem.

  In addition, in the process of (2) "Electrodeposition coating-Sealer application-Water-based intermediate coating", the colored base is applied after the sealer is exposed without the water-based intermediate coating being sufficiently applied on the sealer. When the coating film is a transparent color such as a pearl coating color, the sealer may not be concealed.

The repair of the above-mentioned coatings (1) and (2) takes a lot of work. For example, if the coating line stops, the productivity will be significantly reduced. It was just trial and error.
Therefore, when water-based paint is line-painted, there are no defects such as cracks and sagging on the inner plate of the automobile body, and defects such as poor concealment properties when painted on the sealer, and chipping resistance, There has been a demand for a method for forming a coating film of a water-based paint having excellent water resistance.

  As a result of intensive studies to solve the above problems, the present inventors have found that coating defects such as cracks and sagging of objects to be coated (particularly inner plates of automobile bodies) occur in the application of water-based paints. Thus, the present inventors have completed the present invention by finding a method for forming a coating film that is excellent in hiding, sealing resistance and chipping resistance and water resistance.

That is, the present invention
1. Using the following water-based paint, (1) the solid content at the time of coating is 45 to 70% by weight, and (2) the water-based paint viscosity at 20 ° C. is 50 to 90 seconds with Ford Cup # 4. (3) Coating booth temperature 15 to 40 ° C., (4) Coating booth formation method for water-based paint, characterized in that the coating booth humidity is 60 to 90%.
1. Water-based paint: containing a hydroxyl group-containing resin (A), a block polyisocyanate compound and / or a curing agent (B) that is a melamine resin, and a flat pigment (C). Furthermore, application | coating of the water-based paint of 1 which comprises 1-30 weight part water-soluble organic solvent (D) with respect to 100 weight part of solid content total of hydroxyl-containing resin (A) and hardening | curing agent (B). Film forming method,
3. A water-based paint is applied to an object to be coated in a thickness of 20 to 35 μm, and the viscosity (η) after 1 minute is 2000 to 6000 mPa · sec (20 ° C., shear rate 2.0 / sec). The method for forming a coating film of the water-based paint according to item 1 or 2,
4). The hydroxyl group-containing resin (A) is a polyester resin, and the proportion of the alicyclic polybasic acid and / or alicyclic polyhydric alcohol is 20 with respect to the total solid content of the polybasic acid and polyhydric alcohol constituting the resin. The method for forming a coating film of a water-based paint according to item 1, comprising a polyester resin (a) that is 70% by weight,
5. Item 5. The method for forming a coating film of an aqueous coating material according to any one of items 1 to 4, wherein the aqueous coating material is an aqueous intermediate coating material for automobiles.
6). The method for forming a coating film of a water-based paint according to any one of claims 1 to 4, wherein the water-based paint is used for coating an inner plate of an automobile body.
It relates to an automobile body obtained by using the method for forming a coating film according to any one of items 7 to 6.

In the method for forming a coating film of a water-based paint according to the present invention, when the inner plate of an automobile body is coated with a water-based paint, (1) the solid content at the time of painting is 45 to 70% by weight, preferably 50 to 55% by weight. (2) Paint viscosity is 50 to 90 seconds in Ford Cup # 4, (3) Paint booth temperature is 15 to 40 ° C., and (4) Paint booth humidity is 60 to 90%.
More preferably, a water-based paint is applied to an object to be coated in a thickness of 20 to 35 μm, and the viscosity (η) 1 minute after the water-based paint is applied is 2000 to 6000 mPa · s (20 ° C., shear rate 2.0). / Sec).

  Under these conditions, there is no occurrence of coating film defects such as sagging or peeling on the coating surface, and excellent concealability when water-based paint is applied on the sealer. Even when the color is transparent (the coated film of the colored base paint is transparent), there is no head of the sealer on the coated film, and good finish can be obtained.

  Hereinafter, the method for forming a coating film of the aqueous paint of the present invention will be described in detail.

  A description will be given by taking a car body painting line as an example. An outline of an example of a coating line of a water-based paint (water-based intermediate paint) is shown in FIG. In FIG. 1, an automobile body (6) passes through a preparation zone (1) and is coated by an electrostatic coating machine (4) in a zone (2) for painting an outer plate, and then a zone (3 for painting an inner plate). ), The inner plate is spray-coated by the worker (5).

  In such line painting, the car body is continuously applied (conveyor speed is usually 4 to 8 m / min) while being sprayed using a spray coating machine or an electrostatic coating machine. In particular, the conveyor speed (6 to 8 m / min) is applied. In a line with a high speed, the inner plate (the back of the hood, around the door, the back door, the lid of the gasoline inlet, etc.) may cause wrinkles or sagging or a concealing coating film defect of the sealer. The present invention eliminates the above-mentioned coating film defects and forms a coating film of a water-based paint excellent in finish, chipping resistance, and water resistance.

The coating conditions in the method for forming a coating film of the present invention are as follows. Condition (1): The solid content of the paint at the time of application of the aqueous paint (Note 1) is 45 to 70% by weight, preferably 50 to 55% by weight. Wrinkles and sagging are unlikely to occur in the coating film. Here, when the solid content of the paint is less than 45% by weight, the sagging of the coating film is likely to occur, and when the solid content of the paint exceeds 70% by weight, the flowability is deteriorated, so
Paint solid content: The measurement of the paint solid content was determined according to the formula (1).

Paint solid content (% by weight) = [(X ₂ −X) / (X ₁ −X)] × 100 Formula (1)
(In the formula, X represents the weight of the container, X ₁ represents the total weight of the paint and the container, and X ₂ represents the total weight of the paint and the container after drying for 60 minutes at 110 ° C. ± 5 ° C.)
Condition (2): In addition to condition (1), as condition (2), the viscosity of the water-based paint may be in the range of 50 to 90 seconds (20 ° C.) in Ford Cup # 4. When the viscosity is within this range, no concealment defect occurs when a water-based paint is applied on the sealer.
Here, when the viscosity is less than 50 seconds in the Ford Cup # 4, the concealability when the aqueous paint is applied on the sealer applied to the inner plate of the automobile body is poor. On the other hand, if it exceeds 90 seconds, water remains in the coating film, so that it is easy to generate cracks.

In addition to these conditions (1) and (2), it is desirable that the coating booth temperature is 15 to 40 ° C. as the condition (3) and the coating booth humidity is 60 to 90% as the condition (4). .
When the temperature and humidity of the coating booth are in the above ranges, the evaporation of moisture proceeds moderately after the inner plate is coated, resulting in good finish. However, if either the temperature of the coating booth or the humidity is out of the above range, coating film defects such as cracking and sagging, and poor concealment when a water-based paint is applied on the sealer will occur.

  In addition to the above conditions (1) to (4), the water-based paint is coated with a film thickness of 20 to 35 μm, preferably 25 to 30 μm, and the viscosity (η) after 1 minute after the paint is applied to the object. Is preferably set to 2000 to 6000 mPa · sec (20 ° C., shear rate 2.0 / sec) from the viewpoints of suppression of occurrence of sagging and sagging of the coating film, concealment, and the like. The viscosity (η) was measured using an RE80 viscometer (trade name, viscosity measuring device manufactured by Toki Sangyo Co., Ltd.).

  Condition (1) to Condition (4), more preferably aqueous having a characteristic in which the viscosity (η) after 1 minute of application is in the range of 2000 to 6000 mPa · sec (20 ° C., shear rate 2.0 / sec). Since the paint does not cause coating film defects such as sagging or peeling, and has excellent sealer hiding properties, the colored base paint to be applied over the water-based paint is a transparent color such as pearl. Even if it is a film | membrane, favorable finish can be obtained.

Next, after the application of the water-based paint, (a) setting at room temperature, (b) preheating at 40 to 100 ° C. for 1 minute to 60 minutes, (c) heat curing at about 100 to 180 ° C., For example, a multilayer coating film can be formed by a coating film forming method such as the method (I) to the method (III) in Table 1 below.

The film thickness of the top coat coloring paint, top coat coloring base paint, top coat first clear paint, and top coat second clear paint in Table 1 is 10 to 70 μm, and the baking temperature in heat curing is about 100 to 160 ° C. for about 10 minutes to 90 minutes. It is.

Aqueous paint The aqueous paint used in the method for forming a coating film of the aqueous paint of the present invention contains a hydroxyl group-containing resin (A), a block polyisocyanate compound and / or a melamine resin curing agent (B), and a flat pigment (C). .

  As the hydroxyl group-containing resin (A), polyester resin, acrylic resin, polyether resin, polycarbonate resin, urethane resin, hydroxyacrylic resin, or the like can be used. The polyester resin is a resin in which a hydroxyl group and a blocked isocyanate group coexist in one molecule obtained by extending a polyisocyanate compound to a part of the hydroxyl group in the hydroxyl group-containing polyester resin by a urethanization reaction to increase the molecular weight. A urethane resin-modified polyester resin in the resin may be used.

When the water-based paint is used as an intermediate paint for automobile paint, a polyester resin, an acrylic resin, a urethane-modified polyester resin, or the like is mainly used.
The polyester resin has two or more hydroxyl groups in one molecule, and can be prepared by an esterification reaction between a polybasic acid and a polyhydric alcohol. A polybasic acid is a compound having two or more carboxyl groups in one molecule. For example, terephthalic acid, isophthalic acid, phthalic acid, naphthalenedicarboxylic acid, 4,4'-biphenyldicarboxylic acid, diphenylmethane-4,4 ' -Aromatic dicarboxylic acids such as dicarboxylic acids and anhydrides; alicyclic dicarboxylic acids such as hexahydroisophthalic acid, hexahydroterephthalic acid, hexahydrophthalic acid, tetrahydrophthalic acid and anhydrides; adipic acid, sebacic acid, Aliphatic dicarboxylic acids such as suberic acid, succinic acid, glutaric acid, maleic acid, chloromaleic acid, fumaric acid, dodecanedioic acid, pimelic acid, azelaic acid, itaconic acid, citraconic acid, dimer acid and the anhydrides thereof; Lower alkyl such as methyl ester and ethyl ester of dicarboxylic acid Ester; trimellitic acid, trimellitic anhydride, pyromellitic anhydride, pyromellitic acid, trimesic acid, methylcyclohexene tricarboxylic acid, such as tri- or more polybasic acids such as tetrachloro hexene tricarboxylic acid and anhydrides thereof.

  The polyhydric alcohol is a compound 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-4,3-pentanediol, 3-methyl-4,5-pentanediol, 2, 2,4-trimethyl-1,3-pentanediol, 1 Dihydric alcohols such as 6-hexanediol, 1,5-hexanediol, 1,4-hexanediol, 2,5-hexanediol, neopentyl glycol, and hydroxypivalic acid neopentyl glycol ester; these dihydric alcohols Polylactone diols obtained by adding lactones such as epsilon-caprolactone to diols; ester diols such as bis (hydroxyethyl) terephthalate; alkylene oxide adducts of bisphenol A, polyether diols such as polyethylene glycol, polypropylene glycol, and polybutylene glycol ;

  Mono-epoxy compounds such as α-olefin epoxides such as propylene oxide and butylene oxide, Cardura E10 [trade name, glycidyl ester of synthetic hyperbranched saturated fatty acid]; glycerin, trimethylolpropane, trimethylolethane, diglycerin , Triglycerin, 1,2,6-hexanetriol, pentaerythritol, dipentaerythritol, sorbitol, mannitol and other trihydric or higher alcohols; to these trihydric or higher alcohols, lactones such as epsilon-caprolactone are added Polylactone polyols; 1,4-cyclohexanedimethanol, tricyclodecane dimethanol, hydrogenated bisphenol A, hydrogenated bisphenol F, hydrogenated bisphenol A and hydrogenated bisphenol F Such as throat alicyclic polyhydric alcohols. The acrylic resin can be produced by normal radical copolymerization of a polymerizable monomer component containing a hydroxyl group-containing monomer and an acrylic monomer.

  A hydroxyl group-containing monomer is a compound having at least one hydroxyl group and one polymerizable unsaturated bond in one molecule. For example, carbon such as hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate, etc. Examples thereof include monoesterified products of glycols of several 2 to 20 and (meth) acrylic acid.

  The acrylic monomer is a monoesterified product of (meth) acrylic acid and a monohydric alcohol having 1 to 22 carbon atoms. For example, methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, butyl Examples include acrylate, butyl methacrylate, hexyl acrylate, hexyl methacrylate, octyl acrylate, octyl methacrylate, lauryl acrylate, lauryl methacrylate, 2-ethylhexyl acrylate, and 2-ethylhexyl methacrylate.

The number average molecular weight of the acrylic resin is 1,000 to 50,000, particularly 2,000 to 20,000, the hydroxyl value is 20 to 200 mgKOH / g, particularly 50 to 150 mgKOH / g, and the acid value is 3 to 100 mgKOH / g, especially. 20-70 mgKOH / g is preferred.
The urethane-modified polyester resin can be obtained by subjecting a part of the hydroxyl group in the hydroxyl group-containing polyester resin to a urethanization reaction with a partially blocked polyisocyanate compound. The hydroxyl group-containing polyester resin has two or more hydroxyl groups in one molecule, and this can be prepared by an esterification reaction between a polybasic acid and a polyhydric alcohol.

  The reaction between the polyisocyanate compound and the blocking agent can be carried out under known conditions. Further, the ratio of both components is particularly limited as long as the obtained partially blocked polyisocyanate compound has at least one free isocyanate group and one blocked isocyanate group in one molecule. There is no.

  A urethane-modified polyester resin is obtained by reacting such a partially-blocked polyisocyanate compound with a part of hydroxyl groups in the hydroxyl group-containing polyester resin. The urethanation reaction between the partially blocked polyisocyanate compound and the hydroxyl group-containing polyester resin can be performed under the conditions of a normal urethanization reaction.

  The urethane-modified polyester resin can also be obtained by blocking the remaining isocyanate groups of the product obtained by reacting a part of the hydroxyl groups in the hydroxyl group-containing polyester resin with a part of the isocyanate groups of the unblocked polyisocyanate compound with a blocking agent. Is obtained.

  The urethane-modified polyester resin thus obtained has a hydroxyl value of 20 to 200 mgKOH / g, particularly 40 to 120 mgKOH / g, an isocyanate group value of 5 to 120 mgKOH / g, particularly 10 to 50, and an acid value of 100 mgKOH / g or less, particularly 10 -60 mgKOH / g, number average molecular weight is 1000-20000, Especially within the range of 1500-10000 is preferable.

  In addition, as the hydroxyl group-containing resin (A) in the water-based paint, an alicyclic polybasic acid and / or an alicyclic polyhydric alcohol is an essential component, and other polybasic acids and other polyhydric alcohols are added as necessary. The polyester resin (a) to contain can also be contained.

  An alicyclic polybasic acid is a compound having one or more alicyclic structures (mainly 4- to 6-membered rings) and two or more carboxyl groups in one molecule. For example, 1,3-cyclohexanedicarboxylic acid 1,4-cyclohexanedicarboxylic acid, hexahydrophthalic acid, hexahydroisophthalic acid, hexahydroterephthalic acid, hexahydrotrimellitic acid, methylhexahydrophthalic acid, and anhydrides thereof. As other polybasic acids, the same polybasic acids as the polyester resin can be used.

  An alicyclic polyhydric alcohol is a compound having one or more alicyclic structures (mainly 4 to 6-membered rings) and two or more hydroxyl groups in one molecule, such as 1,3-cyclohexanedimethanol. 1,4-cyclohexanedimethanol, tricyclodecane dimethanol, hydrogenated bisphenol A, hydrogenated bisphenol F, spiroglycol, dihydroxymethyltricyclodecane, and the like. As other polyhydric alcohols, polyhydric alcohols similar to those of the polyester resin can be used.

  The content of the alicyclic polybasic acid and / or alicyclic polyhydric alcohol in the polyester resin (a) is 20 to 70% by weight, preferably 30%, based on the total solid content of the monomers constituting the polyester resin (a). A range of ˜60% by weight is preferred. If the content of the alicyclic polybasic acid and / or alicyclic polyhydric alcohol is less than 20% by weight, the chipping resistance is not improved, and if it exceeds 70% by weight, the weather resistance is lowered.

  The polyester resin (a) obtained by reacting the above alicyclic polybasic acid and other polybasic acids and / or alicyclic polyhydric alcohols and other polyhydric alcohols has a weight average molecular weight of 1,000 to 1,000. 1,000, preferably 2,000-10,000, hydroxyl value is in the range of 30-200 mgKOH / g, preferably in the range of 50-180 mgKOH / g, acid value is in the range of 5-100 mgKOH / g, preferably in the range of 10-60 mgKOH / g. The inside is suitable.

  Curing agent (B): As the curing agent (B) used as a crosslinking component, a blocked polyisocyanate compound obtained by blocking an isocyanate group of a polyisocyanate compound having an isocyanate group with a blocking agent, or a melamine resin can be used.

Examples of the polyisocyanate species in the block polyisocyanate include aliphatic polyisocyanates such as hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, dimer-acid diisocyanate, and lysine diisocyanate; and burette type adducts of these polyisocyanates, isocyania Nurate ring adducts;
Isophorone diisocyanate, 4,4′-methylenebis (cyclohexyl isocyanate), methylcyclohexane-2,4- (or-2,6-) diisocyanate, 1,3- (or 1,4-) di (isocyanatomethyl) cyclohexane, Alicyclic diisocyanates such as 1,4-cyclohexane diisocyanate, 1,3-cyclopentane diisocyanate, 1,2-cyclohexane diisocyanate; and burette type adducts, isocyanurate cycloadducts of these polyisocyanates;

Xylylene diisocyanate, metaxylylene diisocyanate, tetramethyl xylylene 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, 3,3'-dimethyl-4,4'-biphenylene diisocyanate, bis (4-isocyanatophenyl) sulfone, Aromatic diisocyanate compounds such as isopropylidenebis (4-phenylisocyanate); and burette-type adducts of these polyisocyanates, isocyanu Over preparative ring adducts;
Triphenylmethane-4,4 ', 4 "-triisocyanate, 1,3,5-triisocyanatobenzene, 2,4,6-triisocyanatotoluene, 4,4'-dimethyldiphenylmethane-2,2', Polyisocyanates having three or more isocyanate groups in one molecule, such as 5,5′-tetraisocyanate; and burette type adducts, isocyanurate cycloadducts of these polyisocyanates;

  A polyisocyanate compound is reacted with a hydroxyl group of a polyol such as ethylene glycol, propylene glycol, 1,4-butylene glycol, dimethylolpropionic acid, polyalkylene glycol, trimethylolpropane, hexanetriol and the like in an excess amount of isocyanate groups. And burette type adducts of these polyisocyanates, isocyanurate cyclic adducts, and the like.

  The blocking agent blocks a free isocyanate group and dissociates when heated to, for example, 100 ° C. or higher, preferably 130 ° C. or higher, and can easily react with a hydroxyl group. Examples of such blocking agents include phenols such as phenol, cresol, xylenol, nitrophenol, ethylphenol, hydroxydiphenyl, butylphenol, isopropylphenol, nonylphenol, octylphenol, and hydroxybenzoic acid methyl; ε-caprolactam, δ-valerolactam, γ -Lactams such as butyrolactam and β-propiolactam; aliphatic alcohols such as methanol, ethanol, propyl alcohol, butyl alcohol, amyl alcohol, lauryl alcohol;

  Ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, propylene glycol monomethyl ether, methoxymethanol, etc .; glycolic acid; methyl glycolate, methyl glycolate, ethyl glycolate, glycol Glycolic acid esters such as butyl acid; Lactic acid esters such as lactic acid, methyl lactate, ethyl lactate, butyl lactate; methylol urea, methylol melamine, diacetone alcohol, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate Alcohol system such as;

  Oxime systems such as formamide oxime, acetamide oxime, acetoxime, methyl ethyl ketoxime, diacetyl monooxime, benzophenone oxime, cyclohexane oxime;

  Active methylenes such as dimethyl malonate, diethyl malonate, ethyl acetoacetate, methyl acetoacetate, acetylacetone; butyl mercaptan, t-butyl mercaptan, hexyl mercaptan, t-dodecyl mercaptan, 2-mercaptobenzothiazole, thiophenol, methylthiophenol Mercaptan series such as ethylthiophenol; Acid amide series such as acetanilide, acetanisidide, acetolide, acrylamide, methacrylamide, acetic acid amide, stearamide, benzamide; Imido series such as succinimide, phthalimide, maleic imide; Diphenylamine, phenylnaphthylamine, xylidine, N-phenylxylidine, carbazole, aniline, naphthylamine, butylamine, dibutylamine Emissions, such as butyl phenylamine amine; imidazole, imidazole and 2-ethylimidazole;.

  Pyrazoles; ureas such as urea, thiourea, ethylene urea, ethylene thiourea, diphenylurea; carbamates such as phenyl N-phenylcarbamate; imines such as ethyleneimine and propyleneimine; sodium bisulfite, potassium bisulfite And the sulfite system.

A melamine resin can also be used as the curing agent (B). The melamine resin is a resin in which an average of three or more methylol groups per one triazine nucleus is methyletherified, or a part of the methoxy group is substituted with a monoalcohol having two or more carbon atoms.
Examples of the melamine resin include a methylolated amino resin obtained by a reaction between melamine and an aldehyde. Examples of aldehydes include formaldehyde, paraformaldehyde, acetaldehyde, and benzaldehyde. Moreover, what methylated the methylol group of this methylolated amino resin partially or entirely with monoalcohol can also be used. Examples of monoalcohols used for etherification include methyl alcohol, ethyl alcohol, n-propyl alcohol, i-propyl alcohol, n-butyl alcohol, i-butyl alcohol, 2-ethylbutanol, 2-ethylhexanol and the like. Further, a melamine resin having an imino group and having an average condensation degree of about 2 or less and a mononuclear ratio of about 50% by weight or more can be suitably used.

  Flat pigment (C): The flat pigment (C) is a thin and flat pigment such as talc, aluminum flakes, mica flakes, etc. Among them, talc is preferred. As for the size of the flat pigment (C), the thickness is preferably from 0.1 to 2 μm, particularly preferably from 0.2 to 1.5 μm, and the longitudinal dimension is preferably from 1 to 100 μm, particularly preferably from 2 to 20 μm.

  The composition ratio of the hydroxyl group-containing resin (A), the curing agent (B), and the flat pigment (C) is not particularly limited and can be arbitrarily selected according to the purpose. Specifically, based on the total weight of the hydroxyl group-containing resin (A) and the curing agent (B), the hydroxyl group-containing resin (A) is 45 to 80% by weight, particularly 55 to 75% by weight, and the curing agent (B) is It is preferably in the range of 20 to 55% by weight, particularly 35 to 50% by weight. The flat pigment (C) is suitably 5 to 50 parts by weight, particularly 10 to 30 parts by weight per 100 parts by weight of the total solid content of the hydroxyl group-containing resin (A) and the curing agent (B).

  In addition, the addition of a water-soluble organic solvent (D) to the water-based paint can improve the wettability and the crackiness.

Specific examples include propylene glycol monomethyl ether, dipropylene glycol monomethyl ether, tripropylene glycol monomethyl ether, propylene glycol monopropyl ether, dipropylene glycol monopropyl ether, propylene glycol monobutyl ether, dipropylene glycol monobutyl ether and the like. Among these, tripropylene glycol monomethyl ether is particularly preferable.
The content of the water-soluble organic solvent (D) is 1 to 30 parts by weight, preferably 10 to 25 parts by weight, more preferably 100 parts by weight of the total solid content of the hydroxyl group-containing resin (A) and the curing agent (B). 15 to 20 parts by weight is suitable.

  Neutralization of the water-based paint can be carried out by water dispersion by neutralizing the carboxyl group of the hydroxyl group-containing resin (A) with a neutralizing agent. Examples of such a neutralizing agent include hydroxides of alkali metals or alkaline earth metals such as sodium hydroxide, potassium hydroxide, lithium hydroxide, calcium hydroxide, barium hydroxide; ammonia; ethylamine, propylamine, Primary monoamines such as butylamine, benzylamine, monoethanolamine, neopentanolamine, 2-aminopropanol, 3-aminopropanol; diethylamine, diethanolamine, di-n- or di-iso-propanolamine, N-methylethanol Secondary monoamines such as amine and N-ethylethanolamine; Tertiary monoamines such as dimethylethanolamine, trimethylamine, triethylamine, triisopropylamine, methyldiethanolamine and dimethylaminoethanol And polyamines such as diethylenetriamine, hydroxyethylaminoethylamine, ethylaminoethylamine, and methylaminopropylamine.

  In addition, water-based paints are used for hydroxyl group-containing urethane resins, urethane emulsions, colored pigments, metallic pigments such as aluminum flakes and mica, extender pigments, dispersants, anti-settling agents, organic solvents, and urethanization reactions as needed. A catalyst (for example, an organic tin compound), a catalyst for promoting a crosslinking reaction between a hydroxyl group and a melamine resin (for example, an acid catalyst), an antifoaming agent, a thickener, a rust inhibitor, an ultraviolet absorber, a surface conditioner, etc. Can be blended.

  Further, a curing catalyst can be added to accelerate the crosslinking reaction of the coating film. Specifically, tin octylate, dibutyltin di (2-ethylhexanoate), dioctyltin di (2-ethylhexanoate), dioctyltin diacetate, dibutyltin dilaurate, dibutyltin oxide, monobutyltin trioctate, 2 -Organic metal compounds such as lead ethylhexanoate and zinc octylate can be mentioned.

  Although the usage-amount of a curing catalyst can be selected arbitrarily, it is 0.005-5 weight part per 100 weight part of total solid content of a hydroxyl-containing resin (A) and a hardening | curing agent (B), Especially the range of 0.01-3 weight part. Is suitable.

  Hereinafter, the present invention will be described in more detail with reference to examples. The present invention is not limited thereby. “Parts” and “%” indicate “parts by weight” and “% by weight”.

Production Example 1 Production of polyester resin Neopentyl glycol 0.27 mol, trimethylolpropane 0.33 mol, butylethylpropanediol 0.4 mol, isophthalic acid 0.25 mol, adipic acid 0.3 mol and hexahydrophthalic anhydride After adding 0.05 mol of trimellitic anhydride to the product obtained by reacting 0.3 mol, the solvent is removed, neutralized with dimethylethanolamine, and then mixed with water to obtain an aqueous dispersion. Polyester resin No. 1 was obtained. Polyester resin No. The hydroxyl value of 1 was 130 mgKOH / g, the acid value was 25 mgKOH / g, and the number average molecular weight was 1,800.

Production Example 2 Production of polyester resin (a) 0.27 mol of 4-cyclohexanecarboxylic acid, 0.3 mol of adipic acid, 0.33 mol of trimethylolpropane, 0.27 mol of neopentyl glycol, 1,4-cyclohexanedimethanol After adding 0.05 mol of trimellitic anhydride to the product obtained by reacting 0.19 mol, the solvent is removed, neutralized with dimethylethanolamine, and mixed with water to obtain an aqueous dispersion. Polyester resin No. 2 was obtained. Polyester resin No. 2 had a hydroxyl value of 150 mgKOH / g, an acid value of 35 mgKOH / g, and a number average molecular weight of 2,000.

Production Example 3 Production of Urethane Modified Polyester Resin After reacting 0.2 mol of trimethylolpropane, 0.8 mol of 1,6-hexanediol, 0.4 mol of cyclohexyldicarboxylic acid, and 0.3 mol of adipic acid, Furthermore, a polyester resin (100 parts) obtained by adding 0.05 moles of trimellitic anhydride to polyurethane (30 parts) by reacting 2 moles of 4,4′-methylenebis (cyclohexyl isocyanate) and 1 mole of dimethylolpropionic acid. ) In methyl ethyl ketone to make 130 parts of product.
A half-block polyisocyanate compound (10 parts) obtained by reacting methylethylketone oxime and 4,4′-methylenebis (cyclohexyl isocyanate) at an equimolar ratio is reacted with a part of the hydroxyl group using the above product, and then removed. Solvent, neutralize by adding dimethylethanolamine and mix with water to obtain polyester resin No. 3 was obtained. Polyester resin No. 3 had a hydroxyl value of 90 mgKOH / g, an acid value of 38 mgKOH / g, an NCO value of 10, and a number average molecular weight of 2,000.

Production Example 4 Production of Urethane Modified Polyester Resin According to component (A-1), except that “4,4′-methylenebis (cyclohexyl isocyanate)” in the above component was changed to “tetramethylxylylene diisocyanate”. Polyester resin No. 4 was obtained. Polyester resin No. The hydroxyl value of 4 was 90 mgKOH / g, the acid value was 38 mgKOH / g, the NCO value was 10, and the number average molecular weight was 2,000.

Production Example 5 Production of acrylic resin 0.14 mole of styrene, 0.2 mole of methyl methacrylate, 0.22 mole of ethyl acrylate, 0.14 mole of butyl acrylate, 0.14 mole of hydroxyethyl acrylate
11 mol and 0.07 mol of acrylic acid were polymerized in butyl cellosolve using a polymerization initiator azobisisobutyronitrile to obtain an acrylic resin solution having a resin solid content of 70%. After neutralizing butyl monoamine to this acrylic resin solution, water was added to obtain an aqueous solution of hydroxyl-containing acrylic resin (solid content 55%).

Production Example 6 Production of Block Polyisocyanate 50 parts of hexamethylene diisocyanate was added dropwise to 40 parts of methylketoxime at 40 to 60 ° C., followed by heating at 80 ° C. for 1 hour, and curing agent No. 90 having a solid content of 90%. 1 was obtained.

Production Example 7 Aqueous intermediate coating Production of polyester resin No. 1 1 20 parts (solid content), 20 parts of talc (Note 2), 60 parts of JR-806 (Note 3), 0.6 parts of carbon MA-100 (Note 4), 40 parts of barrita, deionized water and pigment Dispersion gave a 60% pigment dispersion paste.
(Note 2) Talc (thickness is 0.3 to 0.9 μm, longitudinal dimension is 1 to 10 μm, equivalent to flat pigment (C))
(Note 3) JR-806: trade name, titanium white manufactured by Teika Co., Ltd. (Note 4) Carbon black MA-100: trade name, carbon black, manufactured by Mitsubishi Chemical Corporation.

Production Example 8 Water-based intermediate coating material No. 1
234 parts of pigment dispersion paste obtained in Production Example 7, polyester resin no. 1 20 parts (solid content), polyester resin No. 1 2 20 parts (solid content), curing agent no. 1 30 parts (solid content) and Cymel 325 (Note 5) 10 parts, deionized water was added, and water-based intermediate coating no. 1 was obtained.

Production Examples 9-12
In the contents of Table 2, the waterborne intermediate coating No. 2-No. 5 was obtained.

(Note 5) Cymel 325: manufactured by Mitsui Cytec, trade name, imino group-containing melamine resin
(Note 6) Water-soluble organic solvent: Tripropylene glycol monomethyl ether is used.
Corresponds to water-soluble organic solvent (D).

Preparation of test plate Test plate (1): Car body: Palbond # 3020 (manufactured by Nippon Parkerizing Co., Ltd., trade name, zinc phosphate treatment), ELECTRON GT-10LF (manufactured by Kansai Paint Co., Ltd., product) Name, lead-free cationic electrodeposition paint) was electrodeposited and baked at 170 ° C. for 20 minutes, and used as a test plate having a film thickness of about 20 μm.

  Test plate (2): A panel (100 x 300 x 0.8 mm galvanized steel plate) is hung on the back of the hood of the automobile body, and the automobile body and panel are simultaneously subjected to chemical conversion treatment and electrodeposition coating. Used as a plate.

Example 1
In the coating line (conveyor speed 7.5 m / min) as shown in FIG. 1 was used and spray coating was performed for 1 minute and 30 seconds under the following conditions (1) and (2) using the objects to be coated (test plate (1), test plate (2)).
Condition (1): The solid content at the time of coating was adjusted to 50% by weight. Condition (2): The coating viscosity was adjusted to 70 seconds (Ford Cup No. 4, 20 ° C.). At that time, condition (3): painting booth temperature was 25 ° C., condition (4): painting booth humidity was 75%.
Thereafter, the test plate (2) was removed, and the viscosity (η) after 1 minute of the applied coating film was measured. The result was 4,000 mPa · sec (20 ° C., shear rate 2.0 / sec).
On the other hand, the test plate (1) was pre-heated at 80 ° C. for 3 minutes, and then baked at 150 ° C. for 20 minutes. 1 was obtained.

Examples 2-5
In the water-based intermediate coating composition shown in Table 3 and the coating conditions, the test result No. 2-No. 5 was obtained.

Comparative Examples 1-5
In the water-based intermediate coating composition shown in Table 4 and the coating conditions, the test result No. 6-No. 10 was obtained.
Test results Various tests were performed on the aqueous intermediate coating film formed as described above. Table 3 shows the coating conditions and test results of the examples, and Table 4 shows the coating conditions and test results of the comparative examples.

(Note 7) Paint solid content: Performed according to the method of (Note 1).
(Note 8) Paint viscosity: Measured at 20 ° C. using Ford Cup # 4.
(Note 9) Viscosity 1 minute after application: RE80 type viscometer (trade name, manufactured by Toki Sangyo Co., Ltd.), shear rate 2.0 / sec, measured at 20 ° C.
(Note 10) Chipping resistance: 35 μm of each waterborne intermediate coating was applied using the test plate (1), baked at 140 ° C. for 20 minutes, and then Magiclon TB-516 Mica Base (Kansai Paint Co., Ltd.) (Product name) was applied at 15 μm and allowed to stand at room temperature for 3 minutes, then the uncured coated surface was coated with 35 μm thick Maglon KINO 1200 clear (trade name, manufactured by Kansai Paint Co., Ltd.) and heated at 140 ° C. for 30 minutes. Both the coats were cured together.

The above-mentioned coated plate is placed on a specimen holder of a Q-G-R gravelometer (chipping test device) manufactured by Q-PANEL, USA, and compressed at 0.294 MPa (3 kgf / cm ² ) at −20 ° C. 100 g of granite crushed stone with a particle size of 7 was sprayed onto the coated surface with air, and the degree of occurrence of scratches on the coating film was visually observed and evaluated.
◎: Scratch size is quite small and no intermediate coating film is exposed ○: Scratch size is small and intermediate coating film is exposed △: Scratch size is small, but electrodeposition coating The film and the base steel plate are exposed. X: The size of the scratch is considerably large, and the base steel plate is also exposed greatly.
(Note 11) Sagging / peeling property: An automobile body was used as an object to be coated, and an aqueous intermediate coating film coated on the back of the hood was observed.
◎: Good with no problem ○: Slight sagging is observed at the top of the hood, but no problem △ indicates that sagging or sagging is observed at the top of the hood x: No sagging or sagging at the top of the hood The occurrence of the occurrence is remarkable.
(Note 12) Sealer concealment: An automobile body was used as an object to be coated, and a sealer was applied, followed by application of a water-based intermediate coating, baking and curing, and the concealment of the sealer was observed on the back of the hood.
○ is good without problems. Δ is that the intermediate coating film is coated on the sealer, but because the film thickness is thin, cueing of the sealer is observed.
In x, since the intermediate coating film is not painted on the sealer, the sealer is exposed significantly.

  When the method for forming a coating film of a water-based paint of the present invention is applied to line coating of an automobile body, a coating film having excellent concealability can be obtained without coating film defects such as sagging and armpits even when coated on a sealer.

It is a model figure of the water-based intermediate coating of a motor vehicle body.

Explanation of symbols

1. Preparation zone 2. 2. Zone for painting the outer skin of the car body 4. Zone electrostatic coating machine for painting the inner plate of the car body. 5. Workers who perform inner coating by spray painting. Car body

Claims (4)

As an essential component on the inner plate of an automobile body line coating of an automobile body, a curing agent (B) made of a hydroxyl group-containing resin (A), a blocked polyisocyanate compound and / or a melamine resin, and a flat pigment (C) made of talc The aqueous intermediate coating composition contained was (1) 45 to 70 wt% solids, (2) Viscosity of Ford Cup # 4 at 20 ° C for 50 to 90 seconds, (3) Coating booth temperature of 15 to 40 ° C and ( 4) Coating booth, under conditions of 60-90% humidity, coating to a film thickness of 20-35 μm to form an aqueous intermediate coating film, the talc content being a hydroxyl group-containing resin (A) and a curing agent ( 5) to 50 parts by weight per 100 parts by weight of the total solid content of B), and (5) the coating film viscosity (η) 1 minute after coating is 2000 to 6000 mPa · s (20 ° C., shear rate 2. 0 / sec) A method for forming a coating film, characterized by comprising: Furthermore, the coating film formation of Claim 1 which contains 1-30 weight part water-soluble organic solvent (D) with respect to 100 weight part of solid content total of hydroxyl-containing resin (A) and hardening | curing agent (B). Method. The hydroxyl group-containing resin (A) is a polyester resin, and the proportion of the alicyclic polybasic acid and / or alicyclic polyhydric alcohol is relative to the total solid content of the polybasic acid and polyhydric alcohol constituting the resin. It is 20 to 70 weight%, The coating-film formation method of Claim 1. The motor vehicle body obtained using the coating-film formation method of any one of Claims 1-3.

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