JP5416473B2 - Multi-layer coating formation method - Google Patents

Description

  The present invention relates to a method for forming a multilayer coating film used for painting automobiles and the like.

  A so-called wet-on-wet painting is performed in automobile painting, in which after one paint is applied, another paint is applied on the paint without curing. Recently, three-wet coating, in which three layers are painted wet-on-wet, has also been adopted. In such a three-wet coating system, another water-based paint may be applied on top of the water-based paint. When wet-on-wet coating is performed between water-based paints in this way, the upper layer and the lower layer are more likely to be mixed, unlike when a solvent-based paint is applied after applying a conventional water-based paint. Has the problem.

  Regarding the prevention of the mixed layer, it is generally known to control the physical properties of the coating film such as the solid content, viscosity, and water absorption (for example, Patent Documents 1 to 4). Further, a method has been proposed in which a coating that cures by irradiating active energy rays is used for the lower layer, and mixing is prevented by irradiating active energy rays (for example, Patent Document 5).

  On the other hand, a carbodiimide compound in which an addition reaction with a carboxyl group proceeds at a low temperature is known as a curing agent for an aqueous coating (for example, Patent Document 6), and an aqueous coating using a carbodiimide compound in combination with a melamine curing agent is disclosed. (For example, Patent Document 7). However, a solvent-type clear paint is applied on the upper layer of the water-based paint, and the carbodiimide compound is not used for the purpose of interlayer control. In addition, since the carbodiimide compound is more reactive than other curing agents, a water-based paint containing the carbodiimide compound has a problem that it lacks storage stability in a heated state such as a high temperature condition in summer. .

JP 2009-028576 A JP 2004-351369 A JP 2004-358462 A JP 2004-097917 A JP 2004-290721 A JP 2000-007642 A JP 2004-351359 A

  The present invention provides an aqueous paint having improved storage stability in a heated state by controlling the reactivity of the carbodiimide compound.

（式中、ｎは１〜５を表し、Ｒ ^１ およびＲ^２は、一般式Ｒ^３−（−Ｏ−ＣＨ_２−ＣＨ_２−）_ｐ−ＯＨ（式中、ｐは６〜２０の整数を表し、Ｒ^３は炭素数１〜３のアルキル基を示す。）で表されるポリエチレングリコールモノアルキルエーテル、および、一般式：

（式中、ｑは１５〜６０の整数を表し、Ｒ^４は炭素数１〜８のアルキル基を示す。）で表されるポリプロピレングリコールモノアルキルエーテルとの混合物の残基を表す。）
で表されるカルボジイミド組成物を層間制御剤として含有することを特徴とする、複層塗膜形成方法を提供する。 That is, the present invention provides a first coating step in which a first aqueous paint is applied on a substrate, and a second coating in which a second aqueous paint is applied without curing the coating film obtained in the first coating step. In the method for forming a multilayer coating film in which the baking process for baking and curing the coating film is performed in this order after the process and the second process,
The first water-based paint is (a) an aqueous binder component having a hydroxyl group and a carboxyl group,
(B) a curing agent, and (c) the following chemical formula (1):

(In the formula, n represents 1 to 5, R ¹ and R ² represent the general formula R ³ — (— O—CH ₂ —CH ₂ —) _p —OH (wherein p represents an integer of 6 to 20). And R ³ represents an alkyl group having 1 to ³ carbon atoms.) And a general formula:

(In the formula, q represents an integer of 15 to 60, and R ⁴ represents an alkyl group having 1 to 8 carbon atoms.) The residue of the mixture with the polypropylene glycol monoalkyl ether represented by )
A carbodiimide composition represented by the formula (1) is contained as an interlayer control agent.

  The mixing molar ratio between the polyethylene glycol monoalkyl ether and the polypropylene glycol monoalkyl ether is preferably 60:40 to 40:60.

（式中、ｎは１〜５を表し、Ｒ ^１ は、一般式Ｒ^３−（−Ｏ−ＣＨ_２−ＣＨ_２−）_ｐ−（式中、ｐは６〜２０の整数を表し、Ｒ^３は炭素数１〜３のアルキル基を示す。）で表されるポリエチレングリコールモノアルキルエーテルからOHを除いた基を示し、Ｒ^２は、一般式：

（式中、ｑは１５〜６０の整数を表し、Ｒ^４は炭素数１〜８のアルキル基を示す。）で表されるポリプロピレングリコールモノアルキルエーテルからOHを除いた基を示す。）
で表されるカルボジイミド化合物を主成分とするものである。 More specifically, the above interlayer control agent is represented by the following chemical formula (1):

(In the formula, n represents 1 to 5, R ¹ represents a general formula R ³ — (— O—CH ₂ —CH ₂ —) _p — (wherein p represents an integer of 6 to 20; R ³ Represents a group obtained by removing OH from the polyethylene glycol monoalkyl ether represented by formula (1), wherein R ² represents a general formula:

(In the formula, q represents an integer of 15 to 60, and R ⁴ represents an alkyl group having 1 to 8 carbon atoms.) A group obtained by removing OH from a polypropylene glycol monoalkyl ether represented by: )
The main component is a carbodiimide compound represented by the formula:

  In the multilayer coating film forming method of the present invention, it is preferable to further include a step of applying a clear paint between the second water-based paint application step and the baking step.

  In the present invention, by using a specific carbodiimide compound (or carbodiimide composition) as an interlayer control agent, even when coating is carried out by so-called wet-on-wet, a mixed layer between two layers is effectively prevented. In the prior art, when such a mixed layer between two layers can be prevented, the storage stability of the water-based paint, particularly the storage stability during heating, may decrease. However, the specific carbodiimide compound of the present invention (or It has been found that the use of a carbodiimide composition) not only prevents mixing between the two layers, but also improves the storage stability in the heated state.

  The reason why such characteristics can be exhibited is not necessarily limited, but the carbodiimide compound (or carbodiimide composition) of the present invention is, for example, compared with the carbodiimide compound described in JP-A-2000-007642 (Patent Document 6). The number of propylene oxide units is quite large. Thus, when the number of propylene oxide units is large, the properties of the carbodiimide compound are slightly shifted to the hydrophobic side. Moreover, when the propylene oxide unit is increased, the reactivity of the carbodiimide compound is slightly reduced. In the present invention, by using a carbodiimide compound (or carbodiimide composition) having a specific structure, a mixed layer between two layers is effectively prevented, and the storage stability in a heated state is also improved.

  The multilayer coating film forming method of the present invention includes a first coating process for coating a first aqueous paint on a substrate, and a second aqueous paint without curing the coating film obtained in the first coating process. A second coating step for coating and a baking step for baking and hardening the obtained two-layer coating film are performed in this order. This method is considered as a so-called two-coat one-bake coating method. In the present invention, a third coating step for coating the clear paint may be provided between the second coating step and the baking step. In that case, the clear coating is also applied wet-on-wet, and the three layers formed are baked and cured at once. First, the paint used in each process will be described.

The first water-based paint The first water-based paint generally corresponds to what is called a water-based intermediate coating in automobile painting. It conceals the base and secures the surface skin appearance after top coating (improves appearance). It is applied in order to impart coating film properties such as impact resistance. The first water-based paint used in the method of the present invention contains a hydroxyl group and carboxyl group-containing acrylic resin emulsion, a curing agent, and a specific interlayer control agent in a state of being dispersed or dissolved in an aqueous medium. The first water-based paint may further contain a pigment and additives usually contained in a water-based intermediate coating for automobile bodies.

  The hydroxyl group- and carboxyl group-containing acrylic resin emulsion functions as a film-forming resin in the first water-based paint (water-based intermediate paint), and comprises (meth) acrylic acid alkyl ester (i), carboxyl group-containing ethylenically unsaturated monomer (ii). ) And a monomer mixture containing a hydroxyl group-containing ethylenically unsaturated monomer (iii) can be obtained by emulsion polymerization. In addition, you may use the compound illustrated below as a component of a monomer mixture, combining suitably 1 type (s) or 2 or more types. In the present specification, “meth (acrylic)” represents both acrylic and methacrylic.

  The (meth) acrylic acid alkyl ester (i) is used for constituting the main skeleton of the acrylic resin emulsion.

  Specific examples of (meth) acrylic acid alkyl ester (i) include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, n-butyl (meth) acrylate, and (meth) acrylic. Isobutyl acid, t-butyl (meth) acrylate, hexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, octyl (meth) acrylate, nonyl (meth) acrylate, decyl (meth) acrylate, ( Examples thereof include dodecyl (meth) acrylate and stearyl (meth) acrylate.

  The carboxyl group-containing ethylenically unsaturated monomer (ii) improves various stability such as storage stability, mechanical stability, stability against freezing of the resulting acrylic resin emulsion, Used to accelerate the curing reaction with the curing agent.

  Examples of the carboxyl group-containing ethylenically unsaturated monomer include acrylic acid, methacrylic acid, crotonic acid, isocrotonic acid, ethacrylic acid, propylacrylic acid, isopropylacrylic acid, itaconic acid, maleic anhydride and fumaric acid.

  The hydroxyl group-containing ethylenically unsaturated monomer (iii) imparts hydrophilicity based on hydroxyl groups to the acrylic resin emulsion and increases the workability and stability against freezing when it is used as a coating material, as well as melamine resin and isocyanate-based curing. Used to impart curing reactivity with the agent.

  Examples of the hydroxyl group-containing ethylenically unsaturated monomer (iii) include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, N-methylolacrylamide, allyl alcohol, Examples include ε-caprolactone-modified acrylic monomers.

  Specific examples of the ε-caprolactone-modified acrylic monomer include “Placcel FA-1”, “Placcel FA-2”, “Placcel FA-3”, “Placcel FA-4”, “Placcel” manufactured by Daicel Chemical Industries, Ltd. FA-5 "," Placcel FM-1 "," Placcel FM-2 "," Placcel FM-3 "," Placcel FM-4 "," Placcel FM-5 "and the like.

  The monomer mixture may contain, as an optional component, at least one monomer selected from the group consisting of a styrene monomer, (meth) acrylonitrile, and (meth) acrylamide. Examples of the styrenic monomer include α-methylstyrene in addition to styrene.

  Emulsion polymerization can be carried out by heating the monomer mixture in an aqueous liquid with stirring in the presence of a radical polymerization initiator and an emulsifier. The reaction temperature is about 30 to 100 ° C., for example, and the reaction time is preferably about 1 to 10 hours, and the reaction temperature is adjusted by batch addition or temporary dropping of the monomer mixture or monomer pre-emulsified liquid in a reaction vessel charged with water and an emulsifier. It is good to do.

  As the radical polymerization initiator, known initiators usually used in emulsion polymerization of acrylic resins can be used. Specifically, as a water-soluble free radical polymerization initiator, for example, a persulfate such as potassium persulfate, sodium persulfate, or ammonium persulfate is used in the form of an aqueous solution. In addition, so-called redox initiators in which an oxidizing agent such as potassium persulfate, sodium persulfate, ammonium persulfate or hydrogen peroxide and a reducing agent such as sodium bisulfite, sodium thiosulfate, Rongalite or ascorbic acid are combined are aqueous solutions. Used in the form of

  As an emulsifier, an anionic system selected from a micelle compound having a hydrocarbon group having 6 or more carbon atoms and a hydrophilic moiety such as a carboxylate, sulfonate, or sulfate partial ester in the same molecule Alternatively, a nonionic (nonionic) emulsifier is used. Among these, as anionic emulsifiers, alkali metal salts or ammonium salts of sulfuric acid half esters of alkylphenols or higher alcohols; alkali metal salts or ammonium salts of alkyl or allyl sulfonates; polyoxyethylene alkylphenyl ethers, polyoxyethylenes Examples thereof include alkali metal salts or ammonium salts of alkyl ether or sulfuric acid half ester of polyoxyethylene allyl ether. Examples of nonionic emulsifiers include polyoxyethylene alkyl phenyl ether, polyoxyethylene alkyl ether, and polyoxyethylene allyl ether. In addition to these general-purpose anionic and nonionic emulsifiers, the molecule has a radically polymerizable unsaturated double bond, that is, acrylic, methacrylic, propenyl, allyl, allyl ether, maleic acid. Various anionic and nonionic reactive emulsifiers having a group such as are also used singly or in combination of two or more.

  In the emulsion polymerization, the use of an auxiliary agent (chain transfer agent) for adjusting the molecular weight such as a mercaptan compound or a lower alcohol promotes the smooth and uniform formation of the coating film from the viewpoint of promoting the emulsion polymerization. From the viewpoint of improving the adhesion to the material, there are many cases where it is preferable, and it is carried out depending on the situation.

  Emulsion polymerization can be performed by any one of the usual one-step continuous monomer uniform dropping method, core-shell polymerization method which is a multi-stage monomer feed method, and power feed polymerization method which continuously changes the monomer composition fed during the polymerization. Can be legal.

  Thus, the hydroxyl group- and carboxyl group-containing acrylic resin emulsion used in the present invention is prepared. Although the weight average molecular weight of the obtained acrylic resin is not particularly limited, it is generally about 50,000 to 1,000,000, for example, about 100,000 to 800,000. In addition, the number average molecular weight and the weight average molecular weight in this specification are styrene standard conversion values by gel permeation chromatography.

  The glass transition temperature (Tg) of the acrylic resin is −50 ° C. to 20 ° C., preferably −40 ° C. to 10 ° C., more preferably −30 ° C. to 0 ° C. By setting the Tg of the resin in this range, when an aqueous intermediate coating containing an acrylic resin emulsion is used in a wet-on-wet system, the affinity and adhesion with the undercoat and the topcoat are improved, and the wet state Fitting at the interface with the upper coating can be suppressed to prevent inversion. Moreover, the moderate softness | flexibility of the coating film finally obtained is acquired, and chipping resistance is improved. As a result, a multilayer coating film having a very high appearance can be formed. If the Tg of the resin is less than −50 ° C., the mechanical strength of the coating film is insufficient and the chipping resistance is weak. On the other hand, if the Tg of the resin exceeds 20 ° C., the coating film becomes hard and brittle, so that it lacks impact resistance and weakens chipping resistance. The type and amount of each monomer component are selected so that the Tg of the resin falls within the above range.

  The acid value of the acrylic resin is 2 to 60 mgKOH / g, preferably 5 to 50 mgKOH / g. By setting the acid value of the resin within this range, various stability such as storage stability, mechanical stability and stability against freezing of the resin emulsion and the water-based intermediate coating material using the resin emulsion are improved. A curing reaction with a curing agent such as a melamine resin at the time of formation sufficiently occurs, and various strengths, chipping resistance, and water resistance of the coating film are improved. When the acid value of the resin is less than 2 mgKOH / g, the above-mentioned various stability is inferior, and the curing reaction with a curing agent such as a melamine resin is not sufficiently promoted, and the coating film has various strengths, chipping resistance, and water resistance. Inferior. On the other hand, when the acid value of the resin exceeds 60 mgKOH / g, the polymerization stability of the resin is deteriorated, the above-mentioned various stability is deteriorated, or the water resistance of the obtained coating film is inferior. The type and amount of each monomer component are selected so that the acid value of the resin falls within the above range. As described above, it is important to use a carboxyl group-containing monomer among the acid group-containing ethylenically unsaturated monomers (b), and among the monomers (b), the carboxyl group-containing monomer is preferably 50% by mass or more, More preferably, it is contained by 80% by mass or more.

  The hydroxyl value of the acrylic resin is 10 to 120 mgKOH / g, preferably 20 to 100 mgKOH / g. By setting the hydroxyl value of the resin within this range, the resin has moderate hydrophilicity, and when used as a coating composition containing a resin emulsion, the workability and stability against freezing are increased, and the melamine resin or isocyanate type is used. The curing reactivity with the curing agent is also sufficient. When the hydroxyl value is less than 10 mg KOH / g, the curing reaction with the curing agent is insufficient, the mechanical properties of the coating film are weak, chipping resistance is poor, and water resistance and solvent resistance are also poor. On the other hand, when the hydroxyl value exceeds 120 mgKOH / g, the water resistance of the obtained coating film is decreased, the compatibility with the curing agent is poor, the coating film is distorted, and the curing reaction is uneven. As a result, the various strengths of the coating film, particularly chipping resistance, solvent resistance and water resistance are inferior. The type and amount of each monomer component are selected so that the hydroxyl value of the resin falls within the above range.

  A basic compound is added to the obtained acrylic resin emulsion in order to neutralize part or all of the carboxylic acid and maintain the stability of the acrylic resin emulsion. As these basic compounds, ammonia, various amines, alkali metals and the like are usually used, and they are also used appropriately in the present invention.

  You may mix | blend a hydroxyl-containing polyester resin with a 1st aqueous coating material as needed. This hydroxyl group-containing polyester resin is added to adjust the flow properties and physical properties of the coating film.

Hydroxyl-containing polyester resin The hydroxyl-containing polyester resin includes an oil-free polyester resin obtained by condensing a polyhydric alcohol component and a polybasic acid component, or castor oil and dehydrated castor in addition to the polyhydric alcohol component and the polybasic acid component. Oil components such as oil, tung oil, safflower oil, soybean oil, linseed oil, tall oil, coconut oil, etc., and a mixture of two or more of these fatty acids are added to the acid component and alcohol component. And oil-modified polyester resins obtained by reacting the three. Moreover, the polyester resin which grafted acrylic resin and vinyl resin can also be used. Furthermore, a urethane-modified polyester resin obtained by reacting a polyisocyanate compound with a polyester resin obtained by reacting a polyhydric alcohol component and a polybasic acid component can also be used.

  The number average molecular weight (Mn) of the hydroxyl group-containing polyester resin is 800 to 10000, preferably 1000 to 8000. When Mn is less than 800, the stability when the polyester resin is dispersed in water is lowered, and when it exceeds 10,000, the viscosity of the resin is increased, so that the solid content concentration in the case of coating is lowered and the coating workability is lowered. To do.

  The hydroxyl value of the hydroxyl group-containing polyester resin is 35 to 170, preferably 50 to 150. When the hydroxyl value is less than 35, the curability of the resulting coating film decreases, and when it exceeds 170, the chipping resistance of the coating film decreases.

  The hydroxyl group-containing polyester resin preferably has an acid value of 15 to 100 mgKOH / g. Preferably it is 20-80. When the acid value is less than 15, the water dispersion stability of the polyester resin is lowered, and when it exceeds 100, the water resistance of the coated film is lowered.

  Moreover, it is preferable that the glass transition temperature of the said hydroxyl-containing polyester resin is -40-50 degreeC. When the said glass transition temperature is less than -40 degreeC, there exists a possibility that the hardness of the coating film obtained may fall, and when it exceeds 50 degreeC, there exists a possibility that base concealment property may fall. More preferably, it is -40-10 degreeC. The glass transition temperature can be measured with a differential scanning calorimeter (DSC) or the like.

  Examples of the polyhydric alcohol component include, for example, ethylene glycol, diethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 2, 2-diethyl-1,3-propanediol, neopentyl glycol, 1,9-nonanediol, 1,4-cyclohexanediol, hydroxypivalic acid neopentyl glycol ester, 2-butyl-2-ethyl-1,3-propane Diols such as diol, 3-methyl-1,5-pentanediol, 2,2,4-trimethylpentanediol and hydrogenated bisphenol A, and trivalent or more such as trimethylolpropane, trimethylolethane, glycerin, pentaerythritol Polyol component of And hydroxycarboxylic acids such as 2,2-dimethylolpropionic acid, 2,2-dimethylolbutanoic acid, 2,2-dimethylolpentanoic acid, 2,2-dimethylolhexanoic acid, 2,2-dimethyloloctanoic acid, etc. An acid component can be mentioned.

  Examples of the polybasic acid component include, for example, aromatic polyvalent carboxylic acids such as phthalic anhydride, isophthalic acid, terephthalic acid, trimellitic anhydride, tetrabromophthalic anhydride, tetrachlorophthalic anhydride, pyromellitic anhydride, etc. And acid anhydrides; alicyclic polycarboxylic acids and anhydrides such as hexahydrophthalic anhydride, tetrahydrophthalic anhydride, 1,4- and 1,3-cyclohexanedicarboxylic acid; maleic anhydride, fumaric acid, succinic anhydride And polybasic acid components such as aliphatic polycarboxylic acids such as adipic acid, sebacic acid and azelaic acid and anhydrides, and anhydrides thereof. A monobasic acid such as benzoic acid or t-butylbenzoic acid may be used in combination as necessary.

  When preparing a polyester resin, as reaction components, monohydric alcohol, monoepoxide compound such as Cardura E (trade name: manufactured by Ciel Chemical), and lactones (β-propiolactone, dimethylpropiolactone, Butyrolactone, γ-valerolactone, ε-caprolactone, γ-caprolactone, γ-caprolactone, crotolactone, δ-valerolactone, δ-caprolactone, etc.) may be used in combination. In particular, lactones are used for ring-opening addition to a polyester chain of a polyvalent carboxylic acid and a polyhydric alcohol to form a polyester chain by itself, and further to improve the chipping resistance of an aqueous intermediate coating composition. These may be contained in 3 to 30%, preferably 5 to 20%, in particular 7 to 15% of the total mass of all reaction components.

  The hydroxyl group-containing polyester resin can be easily made aqueous by adjusting its acid value and neutralizing the carboxyl group with a basic substance (for example, 50% or more). Examples of basic substances used here include ammonia, methylamine, ethylamine, dimethylamine, diethylamine, trimethylamine, triethylamine, dimethylethanolamine, diethanolamine, and triethanolamine. Among these, diethanolamine, dimethylethanolamine, and triethanolamine are included. Ethanolamine and the like are preferred. Moreover, the neutralization rate in the case of the said neutralization is not specifically limited, For example, it is 80 to 120%.

The curing agent blended in the first water-based paint of the curing agent causes a curing reaction with the acrylic resin and the hydroxyl group-containing polyester resin contained as an emulsion, and can be blended in the first water-based paint (water-based intermediate paint). There is no particular limitation as long as it is present, and examples thereof include melamine resins and isocyanate resins. These 1 type (s) or 2 or more types are used in combination as appropriate. It is preferable to contain a melamine resin from the viewpoint of coating performance.

  It does not specifically limit as a melamine resin, What is normally used as a hardening | curing agent can be used. However, hydrophobic melamine resins are preferred. This is because the appearance of the obtained multilayer coating film is improved.

  As the melamine resin, those usually used as a curing agent can be used. For example, an alkyl etherified melamine resin obtained by alkyl etherification is preferable, and a melamine resin substituted with a methoxy group and / or a butoxy group is more preferable. As such melamine resins, those having a methoxy group alone, Cymel 325, Cymel 327, Cymel 370, Mycoat 723; those having both a methoxy group and a butoxy group, Cymel 202, Cymel 204, Cymel 232, Cymel 235, Cymel 236, Cymel 238, Cymel 254, Cymel 266, Cymel 267 (all trade names, manufactured by Mitsui Cytec); My Coat 506 (trade name, Mitsui Cytech, Inc.) having a butoxy group alone Product), Uban 20N60, Uban 20SE (both trade names, manufactured by Mitsui Chemicals) and the like. These may be used alone or in combination of two or more. Of these, Cymel 325, Cymel 327, and My Coat 723 are more preferable.

  The isocyanate resin is obtained by blocking a diisocyanate compound with an appropriate blocking agent. The diisocyanate compound is not particularly limited as long as it has two or more isocyanate groups in one molecule. For example, aliphatic diisocyanates such as hexamethylene diisocyanate (HMDI) and trimethylhexamethylene diisocyanate (TMDI); isophorone Alicyclic diisocyanates such as diisocyanate (IPDI); aromatic-aliphatic diisocyanates such as xylylene diisocyanate (XDI); aromatic diisocyanates such as tolylene diisocyanate (TDI) and 4,4-diphenylmethane diisocyanate (MDI) Hydrogenated diisocyanates such as dimer acid diisocyanate (DDI), hydrogenated TDI (HTDI), hydrogenated XDI (H6XDI), hydrogenated MDI (H12MDI), Adducts of beauty more diisocyanates and isocyanurates thereof, and the like. Furthermore, these 1 type (s) or 2 or more types can be used in combination as appropriate.

  The blocking agent for blocking the diisocyanate compound is not particularly limited. For example, oximes such as methyl ethyl ketoxime, acetoxime, and cyclohexanone oxime; phenols such as m-cresol and xylenol; butanol, 2-ethylhexanol, cyclohexanol, ethylene Alcohols such as glycol monoethyl ether; lactams such as ε-caprolactam; diketones such as diethyl malonate and acetoacetate; mercaptans such as thiophenol; ureas such as thiouric acid; imidazoles; Can be mentioned. Of these, oximes, phenols, alcohols, lactams and diketones are preferred.

から得られるイソシアネート末端ジシクロヘキシルメタンカルボジイミドと、一般式Ｒ^３−（−Ｏ−ＣＨ_２−ＣＨ_２−）_ｐ−ＯＨ（式中、ｐは６〜２０の整数を表し、Ｒ^３は炭素数１〜３のアルキル基を示す。）で表されるポリエチレングリコールモノアルキルエーテル、および、一般式：

（式中、ｑは１５〜６０の整数を表し、Ｒ^４は炭素数１〜８のアルキル基を示す。）で表されるポリプロピレングリコールモノアルキルエーテルとの混合物から合成されるものである。尚、前記式（１）中、ｎは１〜５の整数を表す。 Interlayer Control Agent The interlayer control agent of the present invention is a carbodiimide composition represented by the above general formula (1), and is 4,4′-dicyclohexylmethane diisocyanate.

And an isocyanate-terminated dicyclohexylmethanecarbodiimide obtained from the formula R ³ — (— O—CH ₂ —CH ₂ —) _p —OH (wherein p represents an integer of 6 to 20, and R ³ represents 1 to And a polyethylene glycol monoalkyl ether represented by the general formula:

(Wherein q represents an integer of 15 to 60, and R ⁴ represents an alkyl group having 1 to 8 carbon atoms) and is synthesized from a mixture with a polypropylene glycol monoalkyl ether. In the formula (1), n represents an integer of 1 to 5.

（式中、ｑは１５〜６０の整数を表し、Ｒ^４は炭素数１〜８のアルキル基を示す。）で表されるポリプロピレングリコールモノアルキルエーテルとの混合物とを反応させることにより製造することができる。 More specifically, the carbodiimide composition of the present invention synthesizes isocyanate-terminated dicyclohexylmethane carbodiimide by a condensation reaction involving decarbonization of the above 4,4′-dicyclohexylmethane diisocyanate, and further, this isocyanate-terminated dicyclohexylmethane carbodiimide and And R ³ — (— O—CH ₂ —CH ₂ —) _p —OH (wherein p represents an integer of 6 to 20, and R ³ represents an alkyl group having 1 to ³ carbon atoms). Polyethylene glycol monoalkyl ethers represented by the general formula:

(In the formula, q represents an integer of 15 to 60, and R ⁴ represents an alkyl group having 1 to 8 carbon atoms.) It is produced by reacting with a mixture with a polypropylene glycol monoalkyl ether represented by Can do.

  The above-mentioned isocyanate-terminated dicyclohexylmethane carbodiimide is basically produced by a conventional polycarbodiimide production method (US Pat. No. 2,941,956, Japanese Patent Publication No. 47-33279, J. Org. Chem. 28, 2069-2076 (1963), Chemical Review 1981, vol. 81, No. 4, 619-4, 621).

  The condensation reaction involving decarbonization of the dicyclohexylmethane diisocyanate proceeds in the presence of a carbodiimidization catalyst. Examples of the catalyst include 1-phenyl-2-phospholene-1-oxide, 3-methyl- 2-phospholene-1-oxide, 1-ethyl-2-phospholene-1-oxide, 1-ethyl-3-methyl-2-phospholene-1-oxide, 3-methyl-1-phenyl-2-phospholene-1-oxide Alternatively, phospholene oxides such as these 3-phospholene isomers can be used, and 3-methyl-1-phenyl-2-phospholene-1-oxide is preferable from the viewpoint of reactivity.

  In addition, the reaction temperature in the condensation reaction is preferably in the range of 80 ° C. to 180 ° C. When the reaction temperature falls below this range, the reaction time becomes extremely long, and when the reaction temperature exceeds the above range, Since the reaction occurs, a high-quality carbodiimide cannot be obtained, which is not preferable in any case.

  Further, the degree of condensation is preferably 1 to 5, and when the degree of condensation exceeds 5, the dispersibility when adding aqueous dicyclohexylmethane carbodiimide to the aqueous resin is lowered, and the aqueous dicyclohexylmethane carbodiimide is previously dispersed in an aqueous solution or water. When a liquid is used, a good aqueous solution or aqueous dispersion cannot be obtained due to low dispersibility. In order to complete the reaction quickly, the reaction of 4,4'-dicyclohexylmethane diisocyanate is preferably performed under an inert gas stream such as nitrogen.

It is represented by the general formula R ³ — (— O—CH ₂ —CH ₂ —) _p —OH (wherein p represents an integer of 6 to 20 and R ³ represents an alkyl group having 1 to ³ carbon atoms). Specific examples of the polyethylene glycol monoalkyl ether include poly (ethylene oxide) monomethyl ether, poly (ethylene oxide) monoethyl ether, poly (ethylene oxide) monopropyl ether and the like, and particularly poly (ethylene oxide). ) Monomethyl ether is preferred.

（式中、ｑは１５〜６０の整数を表し、Ｒ^４は炭素数１〜８のアルキル基を示す。）で表されるポリプロピレングリコールモノアルキルエーテルは、具体的にはポリ（プロピレンオキサイド）モノメチルエーテル、ポリ（プロピレンオキサイド）モノエチルエーテル、ポリ（プロピレンオキサイド）モノフェニルエーテル等を挙げることができ、特にポリ（プロピレンオキサイド）モノメチルエーテルが好適である。 General formula:

(In the formula, q represents an integer of 15 to 60, and R ⁴ represents an alkyl group having 1 to 8 carbon atoms.) Specifically, the polypropylene glycol monoalkyl ether represented by poly (propylene oxide) monomethyl Examples include ether, poly (propylene oxide) monoethyl ether, poly (propylene oxide) monophenyl ether and the like, and poly (propylene oxide) monomethyl ether is particularly preferable.

In the present invention, the mixing molar ratio of the polyethylene glycol monoalkyl ether and the polypropylene glycol monoalkyl ether is preferably mixed at a ratio of 60:40 to 40:60, and used at a ratio of 50:50. More preferably. When the ratio is outside the above range, when the proportion of polyethylene glycol monoalkyl ether decreases (the proportion of polypropylene glycol monoalkyl ether increases), the hydrophilicity decreases, and it does not disperse in water. May not be enough. On the other hand, when the proportion of polyethylene glycol monoalkyl ether increases (the proportion of polypropylene glycol monoalkyl ether decreases), the hydrophilicity increases, it becomes easier to have affinity with water, and the carbodiimide group may be deactivated. .

  A catalyst is generally used for the addition reaction of the isocyanate-terminated dicyclohexylmethane carbodiimide, a mixture of the polyethylene glycol monoalkyl ether and the polypropylene glycol monoalkyl ether.

  The reaction temperature for the above reaction is in the range of 60 ° C. to 160 ° C., preferably in the range of 100 ° C. to 150 ° C. When the reaction temperature falls below this range, the reaction time becomes extremely long. When the above range is exceeded, side reactions occur and a high-quality carbodiimide composition cannot be obtained, which is not preferable in any case.

  The aqueous dicyclohexylmethane carbodiimide of the present invention can be isolated from the reaction system according to a usual method, and the structure represented by the general formula (1) is that an infrared absorption (IR) spectrum and a nuclear magnetic resonance absorption ( NMR) supported by spectra.

（式中、ｎは１〜５を表し、Ｒ ^１ は、一般式Ｒ^３−（−Ｏ−ＣＨ_２−ＣＨ_２−）_ｐ−（式中、ｐは６〜２０の整数を表し、Ｒ^３は炭素数１〜３のアルキル基を示す。）で表されるポリエチレングリコールモノアルキルエーテルからOHを除いた基を示し、Ｒ^２は、一般式：

（式中、ｑは１５〜６０の整数を表し、Ｒ^４は炭素数１〜８のアルキル基を示す。）で表されるポリプロピレングリコールモノアルキルエーテルからOHを除いた基を示す。）
で表されるカルボジイミド化合物を主成分とするということができる。
The interlayer control agent used in the present invention can be represented by the following chemical formula (1) by another description method:

(In the formula, n represents 1 to 5, R ¹ represents a general formula R ³ — (— O—CH ₂ —CH ₂ —) _p — (wherein p represents an integer of 6 to 20; R ³ Represents a group obtained by removing OH from the polyethylene glycol monoalkyl ether represented by formula (1), wherein R ² represents a general formula:

(In the formula, q represents an integer of 15 to 60, and R ⁴ represents an alkyl group having 1 to 8 carbon atoms.) A group obtained by removing OH from a polypropylene glycol monoalkyl ether represented by: )
It can be said that a carbodiimide compound represented by

  In the above formula, when p is less than 6, hydrophilicity cannot be imparted and water dispersion cannot be achieved. On the other hand, when p exceeds 20, the effect corresponding to the increase in molecular weight cannot be obtained. Moreover, when q in the formula is less than 15, hydrophobicity cannot be imparted, and stability after water dispersion, particularly storage stability, is deteriorated. When q exceeds 60, the reactivity of the raw material polypropylene glycol monoalkyl ether becomes weak, and the addition reaction with the isocyanate group may not proceed sufficiently.

Other Components The first water-based paint (water-based intermediate paint) used in the present invention can further contain the following components. For example, additional resin components, pigment dispersion pastes, thickeners, other additive components, and the like.

  Although it does not specifically limit as said additional resin component, For example, a urethane resin emulsion, an acrylic resin, a carbonate resin, an epoxy resin etc. can be mentioned.

  The pigment dispersion paste is obtained by previously dispersing a pigment and a pigment dispersant in a small amount of an aqueous medium. The solid content of the pigment dispersant does not contain any volatile basic substance or contains 3% by mass or less. In the aqueous intermediate coating composition used in the present invention, by using such a pigment dispersant, the amount of volatile basic substances in the coating film formed from the aqueous intermediate coating composition is reduced, and the resulting multilayer coating is obtained. Yellowing of the film can be suppressed. Therefore, if the volatile basic substance is contained in the solid content of the pigment dispersant in an amount of more than 3% by mass, the resulting multilayer coating film tends to turn yellow and the finished appearance tends to deteriorate. Absent.

  The volatile basic substance means a basic substance having a boiling point of 300 ° C. or less, and examples thereof include inorganic and organic nitrogen-containing basic substances. As an inorganic basic substance, ammonia etc. are mentioned, for example. Examples of the organic basic substance include linear or branched alkyl having 1 to 20 carbon atoms such as methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine, isopropylamine, diisopropylamine, and dimethyldodecylamine. Group-containing primary to tertiary amines; monoethanolamine, diethanolamine, 2-amino-2-methylpropanol and other linear or branched hydroxyalkyl group-containing primary to tertiary amines having 1 to 20 carbon atoms; dimethylethanolamine A primary or tertiary amine containing a linear or branched alkyl group having 1 to 20 carbon atoms and a linear or branched hydroxyalkyl group having 1 to 20 carbon atoms such as diethylethanolamine; diethylenetriamine , Substitution of 1 to 20 carbon atoms such as triethylenetetramine Unsubstituted chain polyamine; substituted or unsubstituted cyclic monoamine having 1 to 20 carbon atoms such as morpholine, N-methylmorpholine, N-ethylmorpholine; piperazine, N-methylpiperazine, N-ethylpiperazine, N, N-dimethylpiperazine Examples thereof include amines such as substituted or unsubstituted cyclic polyamines having 1 to 20 carbon atoms.

The first water-based paint used in the present invention may contain a volatile basic substance in components other than the pigment dispersant. Accordingly, it is more preferable that the weight of the volatile basic substance contained in the pigment dispersant is suppressed. That is, it is preferable to disperse using a pigment dispersant that does not substantially contain a volatile basic substance. Further, it is more preferable not to use an amine-neutralized pigment dispersion resin generally used conventionally. And it is preferable to use a pigment dispersant so that the volatile basic substance per unit area 1 mm < ² > may be 7 * 10 < ^-6 > mmol or less at the time of multilayer coating film formation.

  The pigment dispersant is a resin having a structure including a pigment affinity part and a hydrophilic part. Examples of the pigment affinity portion and the hydrophilic portion include nonionic, cationic and anionic functional groups. The pigment dispersant may have two or more of the above functional groups in one molecule.

  Examples of the nonionic functional group include a hydroxyl group, an amide group, a polyoxyalkylene group, and the like. Examples of the cationic functional group include an amino group, an imino group, and a hydrazino group. Examples of the anionic functional group include a carboxyl group, a sulfonic acid group, and a phosphoric acid group. Such pigment dispersants can be produced by methods well known to those skilled in the art.

  The pigment dispersant is not particularly limited as long as it does not contain a volatile basic substance in the solid content or has a content of 3% by mass or less. What can disperse | distribute a pigment is preferable. For example, commercially available products (hereinafter, trade names) can also be used. Specifically, Disperbyk 190, Disperbyk 181, Disperbyk 182 (polymer co-polymers), which are anionic and nonionic dispersants manufactured by Big Chemie, Inc., can be used. Polymer), Disperbyk 184 (polymer copolymer), EFKAPOLYMER 4550, an anionic / nonionic dispersant manufactured by EFKA, Solsperse 27000, a nonionic dispersant manufactured by Abyssia, Solsperse 41000, an anionic dispersant, And Solsperse 53095.

  The number average molecular weight of the pigment dispersant is preferably a lower limit of 1000 and an upper limit of 100,000. If it is less than 1000, the dispersion stability may not be sufficient, and if it exceeds 100,000, the viscosity may be too high and handling may be difficult. More preferably, the lower limit is 2000 and the upper limit is 50,000, and even more preferably, the lower limit is 4000 and the upper limit is 50,000.

  The pigment dispersion paste is obtained by mixing and dispersing a pigment dispersant and a pigment according to a known method. It is preferable that the ratio of the pigment dispersant at the time of manufacturing the pigment dispersion paste is a lower limit of 1% by mass and an upper limit of 20% by mass with respect to the solid content of the pigment dispersion paste. If it is less than 1% by mass, it is difficult to disperse the pigment stably, and if it exceeds 20% by mass, the physical properties of the coating film may be inferior. Preferably, the lower limit is 5 mass% and the upper limit is 15 mass%.

  Although it will not specifically limit if it is a pigment used for a normal water-based paint, A colored pigment is preferable from the point which improves a weather resistance and ensures concealment property. In particular, titanium dioxide is more preferable because it is excellent in color concealment and is inexpensive.

  Examples of pigments other than titanium dioxide include azo chelate pigments, insoluble azo pigments, condensed azo pigments, phthalocyanine pigments, indigo pigments, perinone pigments, perylene pigments, dioxane pigments, quinacridone pigments, and isoindolinone. Organic pigments such as pigments, diketopyrrolopyrrole pigments, benzimidazolone pigments and metal complex pigments; inorganic pigments such as yellow lead, yellow iron oxide, Bengala and carbon black. These pigments may be used in combination with extender pigments such as calcium carbonate, barium sulfate, clay and talc.

  As the pigment, a standard gray paint having carbon black and titanium dioxide as main pigments can also be used. In addition, it is also possible to use a paint in which the top coat paint is combined with lightness or hue or a combination of various color pigments.

  Although it does not specifically limit as a thickener, Cellulose type | system | groups, such as viscose, methylcellulose, ethylcellulose, hydroxyethylcellulose, and what is marketed, such as Tyroze MH and Tyroze H (all are the Hoechst company make, brand name), etc. Things; Sodium polyacrylate, polyvinyl alcohol, carboxymethyl cellulose, and commercially available products (all are trade names below) include Primal ASE-60, Primal TT-615, Primal RM-5 (all manufactured by Rohm & Haas) ), Alkali thickening type such as Euker Polyphobe (manufactured by Union Carbide); polyvinyl alcohol, polyethylene oxide, and commercially available products (hereinafter referred to as trade names) include Adecanol UH-420 and Adecanol UH- 4 2, Adecanol UH-472, UH-540, Adecanol UH-814N (Asahi Denka Kogyo Co., Ltd.), Primal RH-1020 (Rohm & Haas), Kuraray Poval (Kuraray Co., Ltd.) be able to. These may be used alone or in combination of two or more.

  By containing the thickener, the viscosity of the first water-based paint can be increased, and the occurrence of dripping can be suppressed when the first water-based paint is applied. Moreover, the mixed layer between an intermediate coating film and a base coating film can be suppressed more. As a result, compared to the case where no thickener is included, the coating workability during coating is improved, and the finished appearance of the resulting coating film can be made excellent.

  Examples of other additives include additives usually added in addition to the above-mentioned components, such as ultraviolet absorbers; antioxidants; antifoaming agents; surface conditioners; pinhole inhibitors. These compounding amounts are within the range known to those skilled in the art.

  The first water-based paint used in the present invention is prepared by mixing the above-mentioned acrylic resin emulsion, curing agent, pigment dispersion paste and the like.

  The curing agent has a lower limit of 2% by mass and an upper limit of 50% by mass, preferably a lower limit of 4% by mass and an upper limit of 40% by mass, more preferably a lower limit of 5% by mass and an upper limit of 30% by mass with respect to the solid content of the curing agent and the acrylic resin emulsion. Use to be. When it is less than 2% by mass, the water resistance of the resulting coating film tends to decrease. Moreover, when it exceeds 50 mass%, there exists a tendency for the peeling property of the coating film obtained to fall.

  Appropriate amounts of the additional resin component, pigment dispersion paste and other additives may be mixed. However, the additional resin component is preferably blended at a ratio of 50% by mass or less based on the solid content of all the resins contained in the first aqueous coating composition. When it exceeds 50% by mass, it is difficult to increase the solid content concentration in the paint, which is not preferable.

  The pigment preferably has a pigment concentration (PWC: pigment weight content) of 10 to 60% by mass with respect to the total mass of the solid content and pigment of all the resins contained in the first water-based paint. If it is less than 10% by mass, the concealability may be lowered. When it exceeds 60 mass%, viscosity increase at the time of hardening will be caused, flow property may fall and a coating-film external appearance may fall.

  The content of the interlayer control agent is preferably 1 to 30 parts by mass with respect to 100 parts by mass of the resin solid content of the first water-based paint (solid content of all resins contained in the first water-based paint). More preferably, it is 5-15 mass parts. When the amount is less than 1 part by mass, the interface is disturbed when the second water-based paint is applied wet-on-wet. When it exceeds 30 mass parts, there exists a possibility that various performances of an external appearance and the coating film obtained may fall.

  The order of adding these components may be before or after adding the curing agent to the emulsion. The form of the first water-based paint is not particularly limited as long as it is water-based. For example, it may be in the form of water-soluble, water-dispersed, aqueous emulsion or the like.

Second aqueous paint The second aqueous paint used in the method for forming a multilayer coating film of the present invention is generally called an aqueous base paint, and contains (a) 0.2 to 20% by mass of a crosslinkable monomer. The acrylic resin emulsion obtained by emulsion polymerization of the monomer mixture has a solid content of 10 to 60% by mass, (b) the water-soluble acrylic resin has a solid content of 5 to 40% by mass, and (c) the melamine resin has a solid content of 20%. -40% by mass and further contains a pigment.

Ingredient (a)
The acrylic resin emulsion of component (a) is a monomer mixture of a crosslinkable monomer and another α, β-ethylenically unsaturated monomer, and the crosslinkable monomer is 0.2 to 0.2% when the mass of the monomer mixture is 100%. Contains 20% by mass. Therefore, the other α, β-ethylenically unsaturated monomer is contained in an amount of 80 to 99.8% by mass.

  The acrylic resin emulsion of component (a) is blended in the aqueous base paint in an amount of 10 to 60% by mass, preferably 15 to 50% by mass. If it is less than 10% by mass, high solid differentiation and good FF properties cannot be obtained. When it exceeds 60 mass%, the solid content at the time of coating will become low.

  The monomer mixture forming the acrylic resin emulsion of component (a) contains 0.2 to 20% by mass, preferably 0.5 to 20% by mass of the crosslinkable monomer. When the crosslinkable monomer is less than 0.2% by mass, the solid content at the time of coating is lowered and sagging occurs. Further, the orientation of the glitter pigment is disturbed and the FF property is lowered. If the crosslinkable monomer exceeds 20% by mass, the resin gels, making it difficult to synthesize the emulsion.

  The crosslinkable monomer is a compound having two or more radically polymerizable ethylenically unsaturated groups in the molecule. For example, divinylbenzene, ethylene glycol di (meth) acrylate, hexanediol di (meth) acrylate, polyethylene glycol Di (meth) acrylate, allyl (meth) acrylate, 1,4-butanediol di (meth) acrylate, 1,6-hexane di (meth) acrylate, neopentyl glycol di (meth) acrylate, pentaerythritol di (meth) acrylate And diaryl compounds such as triallyl cyanurate, pentaerythritol tri (meth) acrylate, trimethylolpropane tri (meth) acrylate, and dipentaerythritol hexa (meth) acrylate. The crosslinkable monomer may be a combination of the above monomers. Preferred crosslinkable monomers are allyl (meth) acrylate, ethylene glycol di (meth) acrylate and divinylbenzene. This is because these crosslinkable monomers are relatively easy to handle. In this specification, “(meth) acryl” means both acrylic and methacrylic.

  The acrylic resin emulsion (a) preferably has an acid value or a hydroxyl value as required. The acid value or hydroxyl value of the acrylic resin is substantially the same as the acid value or hydroxyl value of the monomer mixture in which it is synthesized. The monomer mixture used in the present invention has an acid value of preferably 3 to 50 mgKOH / g, more preferably 7 to 40 mgKOH / g. If the acid value is less than 3 mgKOH / g, the workability cannot be improved, and if it exceeds 50 mgKOH / g, the water resistance of the coating film decreases. On the other hand, when the aqueous base coating material needs to have curability, the monomer mixture needs to have a hydroxyl value of 10 to 150 mgKOH / g, preferably 20 to 100 mgKOH / g. When the hydroxyl value is less than 10 mgKOH / g, sufficient curability cannot be obtained, and when it exceeds 150 mgKOH / g, the water resistance of the coating film is lowered. Moreover, it is preferable from the point of the mechanical physical property of the coating film obtained that the glass transition temperature of the polymer obtained by copolymerizing the said monomer mixture is between -20-80 degreeC.

  The said monomer mixture can have the said acid value and hydroxyl value by including the alpha, beta-ethylenically unsaturated monomer which has an acid group or a hydroxyl group in it.

  Examples of the α, β-ethylenically unsaturated monomer having an acid group include acrylic acid, methacrylic acid, acrylic acid dimer, crotonic acid, 2-acryloyloxyethylphthalic acid, 2-acryloyloxyethyl succinic acid, ω- Carboxy-polycaprolactone mono (meth) acrylate, isocrotonic acid, α-hydro-ω-((1-oxo-2-propenyl) oxy) poly (oxy (1-oxo-1,6-hexanediyl)), maleic acid , Fumaric acid, itaconic acid, 3-vinylsalicylic acid, 3-vinylacetylsalicylic acid, 2-acryloyloxyethyl acid phosphate, 2-acrylamido-2-methylpropanesulfonic acid, and the like. Among these, acrylic acid, methacrylic acid, and acrylic acid dimer are preferable.

  On the other hand, as the α, β-ethylenically unsaturated monomer having a hydroxyl group, hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate, allyl alcohol, methacryl alcohol, (meth) Mention may be made of adducts of hydroxyethyl acrylate and ε-caprolactone. Among these, preferred are hydroxyethyl (meth) acrylate, hydroxybutyl (meth) acrylate, and an adduct of hydroxyethyl (meth) acrylate and ε-caprolactone.

  Furthermore, the monomer mixture may further contain other α, β-ethylenically unsaturated monomers. Examples of the other α, β-ethylenically unsaturated monomers include (meth) acrylate esters (for example, methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, (meth) acrylic). N-butyl acid, isobutyl (meth) acrylate, t-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, lauryl methacrylate, phenyl acrylate, isobornyl (meth) acrylate, cyclohexyl methacrylate, ( (Meth) acrylic acid t-butylcyclohexyl, (meth) acrylic acid dicyclopentadienyl, (meth) acrylic acid dihydrodicyclopentadienyl, etc.), polymerizable amide compounds (for example, (meth) acrylamide, N-methylol ( (Meth) acrylamide, N-butoxymethyl (meth) acrylic N, N-dimethyl (meth) acrylamide, N, N-dibutyl (meth) acrylamide, N, N-dioctyl (meth) acrylamide, N-monobutyl (meth) acrylamide, N-monooctyl (meth) acrylamide 2, 4-dihydroxy-4′-vinylbenzophenone, N- (2-hydroxyethyl) acrylamide, N- (2-hydroxyethyl) methacrylamide, etc.), polymerizable aromatic compounds (for example, styrene, α-methylstyrene, vinyl ketone, t-butylstyrene, parachlorostyrene, vinylnaphthalene, etc.), polymerizable nitriles (eg, acrylonitrile, methacrylonitrile, etc.), α-olefins (eg, ethylene, propylene, etc.), vinyl esters (eg, vinyl acetate, propionic acid) Vinyl), dienes ( Examples thereof include butadiene and isoprene), polymerizable aromatic compounds, polymerizable nitriles, α-olefins, vinyl esters, and dienes. These can be selected depending on the purpose, but (meth) acrylamide is preferably used when hydrophilicity is easily imparted.

  The acrylic resin emulsion contained in the aqueous base paint of the present invention is obtained by emulsion polymerization of the monomer mixture. The emulsion polymerization carried out here can be carried out using a generally well-known method. Specifically, it can be carried out by dissolving the emulsifier in water or an aqueous medium containing an organic solvent such as alcohol as required, and dropping the monomer mixture and the polymerization initiator under heating and stirring. . A monomer mixture emulsified in advance using an emulsifier and water may be similarly dropped.

  Suitable polymerization initiators include azo oily compounds (for example, azobisisobutyronitrile, 2,2′-azobis (2-methylbutyronitrile) and 2,2′-azobis (2,4 -Dimethylvaleronitrile) and the like, and aqueous compounds (for example, anionic 4,4'-azobis (4-cyanovaleric acid), 2,2-azobis (N- (2-carboxyethyl) -2-methylpropion) Amidine and cationic 2,2′-azobis (2-methylpropionamidine)); and redox oily peroxides (eg, benzoyl peroxide, parachlorobenzoyl peroxide, lauroyl peroxide and t-butyl perbenzoate) Etc.), and aqueous peroxides such as potassium persulfate and ammonium persulfate It is below.

  As the emulsifier, those commonly used by those skilled in the art can be used. However, reactive emulsifiers such as Antox MS-60 (manufactured by Nippon Emulsifier Co., Ltd.), Eleminol JS-2 (manufactured by Sanyo Chemical Industries Ltd.) Adekaria soap NE-20 (Asahi Denka Co., Ltd.) and Aqualon HS-10 (Daiichi Kogyo Seiyaku Co., Ltd.) are particularly preferred.

  In order to adjust the molecular weight, a mercaptan such as lauryl mercaptan and a chain transfer agent such as α-methylstyrene dimer may be used as necessary.

  The reaction temperature is determined by the initiator, and for example, it is preferably 60 to 90 ° C. for an azo initiator and 30 to 70 ° C. for a redox system. In general, the reaction time is 1 to 8 hours. The amount of the initiator relative to the total amount of the monomer mixture is generally 0.1 to 5% by mass, preferably 0.2 to 2% by mass.

  The emulsion polymerization can be performed in multiple stages, for example, in two stages. That is, first, a part (monomer mixture 1) of the α, β-ethylenically unsaturated monomer mixture is subjected to emulsion polymerization, and the remainder of the α, β-ethylenically unsaturated monomer mixture (monomer mixture 2) is added thereto. In addition, emulsion polymerization is performed.

  The monomer mixture 1 preferably contains an α, β-ethylenically unsaturated monomer having an amide group from the viewpoint of preventing the compatibility with the clear coating film. At this time, it is more preferable that the monomer mixture 2 does not contain an α, β-ethylenically unsaturated monomer having an amide group. Since the mixture of monomer mixtures 1 and 2 is the monomer mixture, the requirement for the α, β-ethylenically unsaturated monomer mixture described above is the combination of monomer mixtures 1 and 2. Will meet.

  The particle diameter of the acrylic resin emulsion is preferably in the range of 0.01 to 1.0 μm. When the particle diameter is less than 0.01 μm, the effect of improving workability is small, and when it exceeds 1.0 μm, the appearance of the resulting coating film may be deteriorated. The particle size can be adjusted, for example, by adjusting the monomer composition and emulsion polymerization conditions.

  The said acrylic resin emulsion can be used by pH 5-10 by neutralizing with a base as needed. This is because the stability in this pH region is high. This neutralization is preferably carried out by adding a tertiary amine such as dimethylethanolamine or triethylamine to the system before or after emulsion polymerization.

Ingredient (b)
The second water-based paint of the present invention contains a water-soluble acrylic resin (b). The water-soluble acrylic resin is contained in the aqueous base paint in an amount of 5 to 40% by mass, preferably 10 to 30% by mass. If the amount is less than 5% by mass, the solid content tends to decrease too much. If the amount exceeds 40% by mass, good FF properties are not obtained.

  The water-soluble acrylic resin has a number average molecular weight of 3,000 to 50,000, preferably 6,000 to 30,000. If it is less than 3000, workability and curability are not sufficient, and if it exceeds 50000, the non-volatile content at the time of coating becomes too low, and workability is rather deteriorated.

  The water-soluble acrylic resin preferably has an acid value of 10 to 100 mg KOH / g, more preferably 20 to 80 mg KOH / g. When the upper limit is exceeded, the water resistance of the coating film is lowered, and when the lower limit is exceeded, the water dispersibility of the resin is reduced. Decreases. Further, it preferably has a hydroxyl value of 20 to 180 mgKOH / g, more preferably 30 to 160 mgKOH / g. When the upper limit is exceeded, the water resistance of the coating film decreases, and when the lower limit is exceeded, the curability of the coating film decreases.

  This water-soluble acrylic resin has an α, β-ethylenically unsaturated monomer having an acid group described in the previous monomer mixture as an essential component, and performs solution polymerization together with other α, β-ethylenically unsaturated monomers. Can be obtained.

  The water-soluble acrylic resin is usually neutralized with a basic compound, for example, an organic amine such as monomethylamine, dimethylamine, trimethylamine, triethylamine, diisopropylamine, monoethanolamine, diethanolamine, and dimethylethanolamine, and added to water. Although it dissolves and uses, this neutralization may be performed with respect to water-soluble acrylic resin itself, or may be performed at the time of manufacture of the 2nd water-based coating material mentioned later.

Ingredient (c)
The second aqueous paint of the present invention contains melamine resin (c) as a curing agent. The melamine resin may be water-soluble or water-insoluble. Among the melamine resins, it is preferable in terms of stability to use a water tolerance of 3.0 or more. The water tolerance used here is for evaluating the degree of hydrophilicity, and the higher the value, the higher the hydrophilicity. The water tolerance value is measured by mixing 0.5 g of sample in 10 ml of acetone and dispersing in a 100 ml beaker at 25 ° C., and gradually adding ion-exchanged water using a burette until the mixture becomes cloudy. The amount (ml) of ion exchange water required is measured, and this amount (ml) of ion exchange water is used as a water tolerance value.

  It is preferable that content of a melamine resin is 20-40 mass% with respect to the resin solid content in a 2nd aqueous coating material composition. If it is less than 20% by mass, the curability is lowered, and if it exceeds 40% by mass, the stability of the paint may be lowered.

Other Components The second water-based paint of the present invention contains a pigment. Examples of pigments include glitter pigments and colored pigments. The shape of the glitter pigment is not particularly limited and may be colored. For example, the pigment having an average particle diameter (D ₅₀ ) of 2 to ₅₀ μm and a thickness of 0.1 to 5 μm Is preferred. Those having an average particle diameter in the range of 10 to 35 μm are excellent in glitter and are more preferably used. Specific examples include non-colored or colored metallic brightening agents such as aluminum, copper, zinc, iron, nickel, tin, and aluminum oxide, and alloys, and mixtures thereof. In addition, interference mica pigments, white mica pigments, graphite pigments, and the like are included in this.

  On the other hand, as the colored pigment, for example, organic azo chelate pigment, insoluble azo pigment, condensed azo pigment, phthalocyanine pigment, indigo pigment, perinone pigment, perylene pigment, dioxane pigment, quinacridone pigment, isoindo Examples thereof include linone pigments and metal complex pigments. Examples of inorganic pigments include chrome lead, yellow iron oxide, bengara, carbon black, and titanium dioxide.

  The total pigment concentration (PWC) in the second water-based paint of the present invention is preferably 0.1 to 50% by mass. More preferably, it is 0.5-40 mass%, Most preferably, it is 1.0-30 mass%. When the upper limit is exceeded, the appearance of the coating film deteriorates. When a bright pigment is included, the pigment concentration (PWC) is generally preferably 18.0% by mass or less. When the upper limit is exceeded, the appearance of the coating film deteriorates. More preferably, it is 0.01-15.0 mass%, Most preferably, it is 0.01-13.0 mass%.

  Moreover, the said 2nd water-based coating material can contain polyether polyol. By including this polyether polyol, the flip-flop property of the composite coating film obtained from this can be further improved, so that the coating film appearance can be further improved.

  The polyether polyol has at least one primary hydroxyl group in one molecule, has a number average molecular weight of 300 to 3000, a hydroxyl value of 30 to 700 mgKOH / g, and a water tolerance of 2.0 or more. It is preferable to use a certain one. If the above conditions are not satisfied, the water resistance may not be lowered or the target appearance may not be improved.

  As such a polyether polyol, a compound obtained by adding an alkylene oxide such as ethylene oxide or propylene oxide to an active hydrogen-containing compound such as a polyhydric alcohol, a polyhydric phenol, or a polyvalent carboxylic acid can be used. Specific examples include commercial products such as Prime Pole PX-1000, Sanix SP-750 (all of which are manufactured by Sanyo Chemical Industries), and PTMG-650 (manufactured by Mitsubishi Chemical). The polyether polyol is preferably contained in an amount of 1 to 40% by mass, more preferably 3 to 30% by mass in the solid content of the coating resin.

  Furthermore, other viscosity control agents can be added to the second water-based paint of the present invention in order to prevent the familiarity with the top coat and to ensure the coating workability. As the viscosity control agent, those generally showing thixotropy can be used, for example, polyamide-based ones such as crosslinked or non-crosslinked resin particles, swelling dispersions of fatty acid amides, amide fatty acids, and long-chain polyaminoamide phosphates. Viscosity develops depending on the shape of polyethylene, such as colloidal swelling dispersion of polyethylene oxide, organic bentonite such as organic acid smectite clay, montmorillonite, inorganic pigments such as aluminum silicate and barium sulfate, etc. A flat pigment etc. can be mentioned.

  In the second water-based paint used in the present invention, in addition to the above-mentioned components, additives usually added to the paint, such as surface conditioners, thickeners, antioxidants, UV inhibitors, antifoaming agents, etc. You may mix | blend. These compounding amounts are within the range known to those skilled in the art.

  The second water-based paint may contain other curing agent in addition to the melamine resin curing agent of component (c). As such a hardening | curing agent, what is generally used for the coating material can be used. Examples of such compounds include blocked isocyanates, epoxy compounds, aziridine compounds, oxazoline compounds, and metal ions. A blocked isocyanate resin is generally used from the viewpoint of various performances and costs of the obtained coating film.

  The above-mentioned blocked isocyanate can be obtained by adding a blocking agent having active hydrogen to a polyisocyanate such as trimethylene diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, isophorone diisocyanate, etc. Examples include those that dissociate and generate isocyanate groups.

  If necessary, the second water-based paint of the present invention may further contain a polyester resin. The polyester resin is obtained by condensation polymerization of an acid component and an alcohol component. The acid component is not particularly limited, and examples thereof include polyvalent carboxylic acid compounds such as adipic acid, sebacic acid, isophthalic acid, and phthalic anhydride, and anhydrides thereof. Furthermore, as an acid component, a compound having a carboxylic acid group and a hydroxyl group in one molecule such as dimethylolpropionic acid can be used. Moreover, it does not specifically limit as said alcohol component, Polyhydric alcohol compounds, such as ethylene glycol, a trimethylol propane, neopentyl glycol, can be mentioned. The polyester resin preferably has a resin solid content acid value of 20 to 80 mgKOH / g and a number average molecular weight of 1000 to 15000. The polyester resin is added to suppress color unevenness of the obtained coating film. The compounding quantity in the coating material of a polyester resin is 5-30 mass%, Preferably it is 10-20 mass%. If it is less than 5% by mass, the effect of suppressing color unevenness is small, and if it is more than 30% by mass, the flip-flop property may be lowered.

  The method for producing the paint used in the present invention is not particularly limited, including those described later, and all methods well known to those skilled in the art such as kneading and dispersing a compound such as a pigment using a kneader or a roll. Can be used.

Coating Method The multi-layer coating film forming method according to the present invention comprises, as described above, two coats and one bake in which the first aqueous paint and the second aqueous paint are applied wet-on-wet and then the two layers are cured simultaneously. Although this is a coating method, this method can also be a three-coat / one-bake coating method in which a clear paint is further applied wet-on-wet after the second aqueous paint is applied, and then the three layers are simultaneously cured. For explanation, the explanation will focus on the 3-coat / 1-bake coating method, but the 2-coat / 1-bake coating method is considered to be a method in which the clear coating film of the uppermost layer is not formed.

  In the multilayer coating film forming method, first, an article to be coated on which an electrodeposition coating film is formed is provided. The electrodeposition coating film is formed by applying an electrodeposition paint to an object to be coated and baking and curing it. The object to be coated is not particularly limited as long as it is a metal product capable of cationic electrodeposition coating. For example, iron, copper, aluminum, tin, zinc, an alloy containing these metals, and the like can be given.

  The electrodeposition paint is not particularly limited, and a known cationic electrodeposition paint or anion electrodeposition paint can be used. Electrodeposition coating and baking may be performed by a method and conditions usually used for electrodeposition coating of automobile bodies.

  Next, a first aqueous paint (water-based intermediate paint) is applied on the electrodeposition paint film to form a first water paint film. The first water-based paint is, for example, an air electrostatic spray called “react gun”, commonly called “micro-microbell (μμbell)”, “microbell (μbell)”, “metallic bell (metabell)”, etc. It can be applied by spraying using a so-called rotary atomizing electrostatic coating machine.

  The coating amount is adjusted so that the film thickness of the cured coating film is 10 to 40 μm, preferably 15 to 30 μm. If the film thickness is less than 10 μm, the appearance and chipping resistance of the resulting coating film may be reduced, and if it exceeds 40 μm, problems such as sagging during coating and pinholes during baking hardening may occur.

  The first aqueous coating film is preferably pre-dried (preheated) by heating or blowing air before applying the second aqueous coating material (aqueous base coating material). The reason is that when the drying is insufficient, the water remaining in the coating film causes bumping in the step of baking the multilayer coating film, and it is easy to generate a crack. Further, when the base is coated on the first coating film, it tends to be mixed with the base and the appearance may be deteriorated.

  Next, without curing the first coating film, a second aqueous paint and, if necessary, a clear coating are sequentially applied on the first coating by wet-on-wet to form a base coating and, if necessary, a clear coating. Form. Here, wet-on-wet coating refers to coating with a degree of preliminary drying (preheating) without curing a plurality of coating films.

  The coating amount of the second water-based paint (water-based base paint) is usually adjusted so that the film thickness after curing of the coating film is 10 to 30 μm. If the film thickness after curing is less than 10 μm, there is a risk that the underlying layer will be insufficiently concealed and color unevenness may occur. If it exceeds 30 μm, sagging will occur during painting and pinholes will occur during heat curing. There is a risk of doing so.

The coating amount of the clear paint is usually adjusted so that the film thickness after drying and curing of the coating film is 10 to 70 μm. When the film thickness after curing is less than 10 μm, the appearance such as glossiness of the multilayer coating film is deteriorated, and when it exceeds 70 μm, the sharpness is deteriorated or defects such as unevenness and flow occur at the time of coating.

  Next, the first coating film, the second coating film, and the clear coating film formed as necessary are baked and cured simultaneously. Baking is usually performed by heating to a temperature of 110 to 180 ° C, preferably 120 to 160 ° C. Thereby, a cured coating film having a high degree of crosslinking can be obtained. If the heating temperature is less than 110 ° C, curing tends to be insufficient, and if it exceeds 180 ° C, the resulting coating film may be hard and brittle. Although the time to heat can be suitably set according to the said temperature, for example, when temperature is 120-160 degreeC, it is 10 to 60 minutes.

Clear paint The clear paint used in the method of the present invention may be a paint composition usually used as a clear paint for automobile bodies. For example, what contains a film-forming resin, a hardening | curing agent, and another additive in the state disperse | distributed or melt | dissolved in the medium can be mentioned. Examples of the film-forming resin include acrylic resin, polyester resin, epoxy resin, and urethane resin. These may be used in combination with a curing agent such as an amino resin and / or an isocyanate resin. From the viewpoint of transparency or acid etching resistance, it is preferable to use a combination of an acrylic resin and / or a polyester resin and an amino resin, or an acrylic resin and / or a polyester resin having a carboxylic acid / epoxy curing system.

  The coating form of the clear paint may be any of organic solvent type, aqueous type (water-soluble, water-dispersible, emulsion), non-aqueous dispersion type, and powder type. If necessary, a curing catalyst, a surface conditioner, etc. It may be included.

  EXAMPLES Hereinafter, although an Example is hung up and demonstrated in more detail about this invention, this invention is not limited only to these Examples. In the examples, “parts” means “parts by mass” unless otherwise specified.

Production Example 1
Preparation of 2-chain carbodiimide composition A To 250 parts of 4,4-dicyclohexylmethane diisocyanate, 2.5 parts of 3-methyl-1-phenyl-2-phospholene-1-oxide, which is a carbodiimidization catalyst, is added, at 170 ° C. The reaction was continued until the NCO equivalent was 300. The reaction product had an average of 2.8 carbodiimide groups per molecule. To this, 106 parts of polyethylene glycol monomethyl ether having an average of 9 repeats, 295 parts of polypropylene glycol monobutyl ether having an average of 19 repeats and 0.18 part of dibutyltin dilaurate were added, and the reaction was continued at 90 ° C. until there was no NCO absorption by IR. And a two-chain carbodiimide composition A was obtained.

Production Example 2
Production of 2-chain carbodiimide composition B In production of 2-chain carbodiimide composition A (Production Example 1), instead of 295 parts of polypropylene glycol monobutyl ether having an average of 19 repeats, polypropylene glycol mono having an average of 47 repeats Using 696 parts of butyl ether, a 2-chain carbodiimide composition B was obtained in the same manner as in Production Example 1.

Production Example 3
Production of 2-chain carbodiimide composition C In the production of 2-chain carbodiimide composition A (Production Example 1), 106 parts of polyethylene glycol monomethyl ether having an average of 9 repeats and 186 polyethylene glycol monomethyl ether having an average of 16 repeats were prepared. The two-chain type carbodiimide composition C was produced by changing in the same manner as in Production Example 1.

Comparative production example 1
Production of comparative carbodiimide composition 1
In the production of the 2-chain carbodiimide composition A (Production Example 1), instead of 295 parts of polypropylene glycol monobutyl ether having an average of 19 repeats, 61 parts of tripropylene glycol monobutyl ether (3 repeats) were used. The carbodiimide composition 1 for comparison was obtained by the same treatment as in Example 1.

Comparative production example 2
Production of comparative carbodiimide composition 2 (refer to [0081] Production Example 1 Production of Hydrophilized Modified Carbodiimide Compound in JP-A-2001-009357)
700 parts of 4,4-dicyclohexylmethane diisocyanate is reacted with 14 parts of a carbodiimidization catalyst (3-methyl-1-phenyl-2-phospholene-1-oxide) at 180 ° C. for 16 hours to give isocyanate-terminated 4,4-dicyclohexylmethane carbodiimide. (Carbodiimide group content: 4 equivalents) was obtained. Next, 226.8 parts of the obtained carbodiimide was dissolved in 106.7 parts of N-methylpyrrolidone under heating at 90 ° C. Next, after stirring 200 parts of polypropylene glycol (number average molecular weight: 2000) at 40 ° C. for 10 minutes, 0.16 part of dibutyltin dilaurate was added, the temperature was raised again to 90 ° C., and the reaction was performed for 3 hours. Furthermore, 96.4 parts of poly (oxyethylene) mono-2-ethylhexyl ether having 8 oxyethylene units was added and reacted at 100 ° C. for 5 hours to obtain a carbodiimide composition 2.

Comparative production example 3
Production of comparative carbodiimide composition 3 In the production of 2-chain carbodiimide composition A, 106 parts of polyethylene glycol monomethyl ether having an average of 4 repetitions and 51 parts of tetraethylene glycol monomethyl ether were used in the same manner as in Production Example 1. The carbodiimide composition 3 for a comparison was obtained by processing.

Comparative production example 4
Preparation of comparative carbodiimide composition 4 3,930 parts of 4,4-dicyclohexylmethane diisocyanate together with 79 parts of 3-methyl-1-phenyl-2-phospholene-1-oxide as a carbodiimidization catalyst at 180 ° C. for 16 hours The reaction was performed to obtain a carbodiimide compound having four carbodiimide groups per molecule and having isocyanate groups at both ends. To this, 1,296 parts of polyethylene glycol monomethyl ether having an average of 9 repeating units of oxyethylene group and 2 parts of dibutyltin dilaurate are added, heated at 90 ° C. for 2 hours, and the terminal is an isocyanate group and a hydrophilic group. A carbodiimide compound was obtained. Next, 3000 parts of GP-3000 (manufactured by Sanyo Chemical Co., Ltd.) having a structure in which 16.7 moles of propylene oxide corresponding to OR ¹ group was added to the three hydroxyl groups of glycerin on average were added at 90 ° C., Reacted for hours. It was confirmed that the isocyanate group disappeared from the reaction product by IR. To this, 18,800 parts of deionized water was added and stirred to obtain a carbodiimide composition (water dispersion) 4 having a resin solid content of 30% by mass.

Production Example 4: Preparation of hydroxyl group-containing acrylic resin emulsion In a reaction vessel for producing a normal acrylic resin emulsion equipped with a stirrer, a thermometer, a dropping funnel, a reflux condenser, a nitrogen introduction tube and the like, 445 parts of water and New Coal 293 are prepared. 5 parts (manufactured by Nippon Emulsifier Co., Ltd.) were charged and heated to 75 ° C. while stirring. 24.6 parts of a monomer mixture composed of 0.4 parts of methacrylic acid, 2.0 parts of 2-hydroxyethyl acrylate, 8.6 parts of styrene, 9.4 parts of acrylic acid-n-butyl, and 4.2 parts of ethyl acrylate A mixture of 240 parts of water and 30 parts of New Coal 293 (manufactured by Nippon Emulsifier Co., Ltd.) was emulsified using a homogenizer, and the monomer pre-emulsified solution was dropped into the reaction vessel over 3 hours with stirring. Along with the dropping of the monomer pre-emulsified solution, an aqueous solution prepared by dissolving 1 part of APS (ammonium persulfate) as a polymerization initiator in 50 parts of water is uniformly dropped into the reaction vessel until the end of the dropping of the monomer pre-emulsified solution. did. After completion of the dropwise addition of the monomer pre-emulsion, the reaction was further continued at 80 ° C. for 1 hour, and then cooled. After cooling, an aqueous solution in which 2 parts of dimethylaminoethanol was dissolved in 20 parts of water was added to obtain a hydroxyl group-containing acrylic resin emulsion having a nonvolatile content of 40.6% by mass (EmA to EmJ). The pH of the acrylic resin emulsion was adjusted to 7.2 using a 30% aqueous dimethylaminoethanol solution.

Production Example 5: Preparation of hydroxyl-containing polyester resin 25.6 parts of isophthalic acid, 22.8 parts of phthalic anhydride, 5.6 parts of adipic acid, 19.3 parts of trimethylolpropane, 26.7 parts of neopentyl glycol , 17.5 parts of ε-caprolactone and 0.1 part of dibutyltin oxide were added, and the temperature was raised to 170 ° C. with mixing and stirring. Thereafter, while the temperature was raised to 220 ° C. over 3 hours, water produced by the condensation reaction was removed until the acid value reached 8. Subsequently, 7.9 parts of trimellitic anhydride was added and reacted at 150 ° C. for 1 hour to obtain a polyester resin having an acid value of 40. Further, after cooling to 100 ° C., 11.2 parts of butyl cellosolve was added and stirred until uniform, and after cooling to 60 ° C., 98.8 parts of ion-exchanged water and 5.9 parts of dimethylethanolamine were added, and the solid content was 50% by mass. Thus, a hydroxyl group-containing polyester resin having a solid content acid value of 40, a hydroxyl value of 110, a number average molecular weight of 2870, and a glass transition temperature (Tg) of −3 ° C. was obtained. The glass transition temperature (Tg) of the hydroxyl group-containing polyester resin was measured using a differential scanning calorimeter (DSC220C) manufactured by Seiko Instruments Inc. (SII) [Measurement conditions: sample amount 10 mg, rising rate 10 ° C./min, Measurement temperature -20-100 degreeC].

Production Example 6 Preparation of Pigment Dispersion Paste Commercial Dispersant “Disperbyk 190” (Bion Chemie Anionic Nonionic Dispersant, Product Name) 4.5 parts, Antifoam “BYK-011” (Bik Chemie Defoamer) ) 0.5 parts, 22.9 parts of ion-exchanged water and 72.1 parts of rutile titanium dioxide were premixed, and then glass beads medium was added in a paint conditioner, and mixed and dispersed at room temperature until the particle size became 5 μm or less. Obtained pigment dispersion paste

Example 1: Formation of multilayer coating film 24.6 parts of a hydroxyl group-containing acrylic resin emulsion prepared in Production Example 4, 99.9 parts of a hydroxyl group-containing polyester resin prepared in Production Example 5, Cymel 211 (Mitsui Cytec Co., Ltd.) as a curing agent A first aqueous paint prepared by mixing 37.5 parts of imino-type melamine resin, trade name), 33.3 parts of carbodiimide composition A obtained in Production Example 1, and 139 parts of pigment dispersion paste prepared in Production Example 6 (Water-based intermediate coating) was obtained.

  Next, Powernics 110 (Cation Electrodeposition Paint, trade name, manufactured by Nippon Paint Co., Ltd.) was electrodeposited onto the zinc phosphate treated dull steel plate so that the dry coating film would be 20 μm, and was heated at 160 ° C. for 30 minutes. A steel plate substrate was prepared by cooling after heat curing.

  The first substrate was coated with 20 μm of the first water-based paint by air spray coating, preheated at 80 ° C. for 5 minutes, and then subjected to Aqualex AR-2000 Silver Metallic (water-based metallic base paint manufactured by Nippon Paint Co., Ltd., trade name) ) Was applied as a second water-based paint by air spray coating at 10 μm and preheated at 80 ° C. for 3 minutes. Furthermore, as a clear paint on the coated plate, Mac Flow O-1800W-2 Clear (Nippon Paint Co., Ltd. acid epoxy curable clear paint, trade name) was applied by air spray coating to 35 μm, and then heated at 140 ° C. for 30 minutes. Curing was performed to obtain a test piece with 3 coats and 1 bake coating.

  As another test piece, after the second water-based paint was applied by air spraying, it was heat-cured at 140 ° C. for 30 minutes without applying the clear paint to obtain a test piece of 2-coat / 1-bake coating.

  The finished appearance of the multilayer coating film obtained after heat curing was visually evaluated according to the following evaluation criteria. The results are shown in Table 1 below. The first aqueous paint (aqueous intermediate paint), the second aqueous paint (aqueous base paint) and the clear paint were diluted under the following conditions and used for painting.

First aqueous paint thinner: ion-exchanged water 40 seconds / NO. 4 Ford Cup / 20 ° C
The solid content of the paint was 54% by mass.

Second aqueous paint thinner: ion-exchanged water 45 seconds / NO. 4 Ford Cup / 20 ° C

Clear paint thinner: EEP (Ethoxyethyl propionate) / S-150 (Exxon aromatic hydrocarbon solvent, trade name) = 1/1 (mass ratio) mixed solvent 30 seconds / NO. 4 Ford Cup / 20 ° C

Appearance evaluation The finished appearance of the coating film (3 coats and 1 bake coating film) was measured using a wave scan (manufactured by Big Chemie-Gardner) in the medium wavelength region of 800 to 2400 μm (W2 value) and 320 to 800 μm. The measurement in the low wavelength region (W3 value) was performed. The lower these values, the better the appearance.

Color difference (ΔE)
On the coating film obtained by applying and baking the first water-based paint, the color difference from the laminated coating film obtained by 3 coats and 1 bake on the basis of the coating film obtained by 2 coats and 1 bake ( ΔE) was measured using a spectrocolorimeter CM512m3 manufactured by Konica Minolta.

Storage stability The first water-based paint immediately after production and after 1 month storage at 40 ° C, the appearance change when creating a multilayer coating film: ○ ... No change, × ... Deterioration of the appearance Judgment on confirmation.

Example 2
Two types of test pieces were obtained in the same manner as in Example 1 except that the carbodiimide composition A blended in the first aqueous paint was changed to the carbodiimide composition B produced in Production Example 2. The test piece was evaluated in the same manner as in Example 1, and the results are shown in Table 1.

Example 3
Two types of test pieces were obtained in the same manner as in Example 1 except that the carbodiimide composition A blended in the first aqueous paint was changed to the carbodiimide composition C produced in Production Example 3. The test piece was evaluated in the same manner as in Example 1, and the results are shown in Table 1.

Comparative Example 1
Two kinds of test pieces were obtained in the same manner as in Example 1 except that the carbodiimide composition A blended in the first water-based paint was changed to the comparative carbodiimide composition 1 produced in Comparative Production Example 1. . The test piece was evaluated in the same manner as in Example 1, and the results are shown in Table 1.

Comparative Example 2
Two types of test pieces were obtained in the same manner as in Example 1 except that the carbodiimide composition A blended in the first water-based paint was changed to the comparative carbodiimide composition 2 produced in Comparative Production Example 2. . The test piece was evaluated in the same manner as in Example 1, and the results are shown in Table 1.

Comparative Example 3
Two types of test pieces were obtained in the same manner as in Example 1 except that the carbodiimide composition A blended in the first water-based paint was changed to the comparative carbodiimide composition 3 produced in Comparative Production Example 3. . The test piece was evaluated in the same manner as in Example 1, and the results are shown in Table 1.

Comparative Example 4
Two types of test pieces were obtained in the same manner as in Example 1 except that the carbodiimide composition A blended in the first aqueous paint was changed to the comparative carbodiimide composition 4 produced in Comparative Production Example 4. . The test piece was evaluated in the same manner as in Example 1, and the results are shown in Table 1.

Comparative Example 5
Two types of test pieces were obtained in the same manner as in Example 1 except that the carbodiimide composition A blended in the first aqueous paint was not used. The test piece was evaluated in the same manner as in Example 1, and the results are shown in Table 1.

  In the table, PEO is an abbreviation for polyethylene oxide, the number of polyethylene oxide means the number of repeating units of polyethylene oxide in the polyethylene oxide monoalkyl ether, PPO is an abbreviation for polypropylene oxide, and the number of polypropylene oxide is polypropylene oxide. It means the number of repeating units of polypropylene oxide in monoalkyl ether.

  As seen in Examples 1 to 3, the carbodiimide composition works effectively, has an excellent appearance, and has excellent storage stability as long as it is within the scope of the present invention. On the other hand, in Comparative Example 1, the number of polypropylene oxides in the carbodiimide composition is as small as 3, which increases the hydrophilicity and functions as an interlayer control agent. However, when stored at 40 ° C., there is no contact between the carbodiimide group and water. It is likely to occur and the storage stability of the paint is reduced. In Comparative Example 2, since the carbodiimide compound is a chain extension type, the storage stability based on water dispersibility is sufficient, but because of the large number of carbodiimide groups, it reacts with the binder during storage, and the stability of the coating is It's not expensive. In the case of Comparative Example 3, the number of polyethylene oxides in the carbodiimide composition is as small as four, the aqueousity becomes weak and the water dispersibility is inferior, and uniform dispersion in the paint becomes impossible, resulting in poor appearance. In Comparative Example 4, since the carbodiimide composition becomes a three-chain type, the storage stability based on water dispersibility is sufficient, but since the number of carbodiimide groups is large, it reacts with the binder during storage, and the stability of the paint Will not be expensive. Comparative Example 5 does not include a carbodiimide composition as an interlayer control agent, and the interlayer control is not performed. Therefore, the first coating film and the second coating film are mixed and the appearance is poor.

  The multilayer coating film forming method of the present invention can be used for finish coating of automobiles. In the method for forming a multilayer coating film of the present invention, when the first water-based paint (particularly water-based intermediate paint) and the second water-based paint (particularly water-based base paint) are applied wet-on-wet, In addition to the effective prevention of the mixed layer produced in the above, the storage stability of the water-based intermediate coating is improved, and high stability is ensured even when stored in a heated state, particularly at a temperature of about 40 ° C.

Claims (4)

First coating process for coating the first aqueous paint on the substrate, second coating process for coating the second aqueous paint without curing the coating film obtained in the first coating process, and second coating In the method for forming a multilayer coating film in which the baking process for baking and curing the coating film is performed in this order after the process,
The first water-based paint is (a) an aqueous binder component having a hydroxyl group and a carboxyl group,
(B) a curing agent, and (c) the following chemical formula (1):

(In the formula, n represents 1 to 5, R ¹ and R ² represent the general formula R ³ — (— O—CH ₂ —CH ₂ —) _p —OH (wherein p represents an integer of 6 to 20). And R ³ represents an alkyl group having 1 to ³ carbon atoms.) And a general formula:

(In the formula, q represents an integer of 15 to 60, and R ⁴ represents an alkyl group having 1 to 8 carbon atoms.) The residue of the mixture with the polypropylene glycol monoalkyl ether represented by )
A method for forming a multilayer coating film, comprising: a carbodiimide composition represented by the formula:   The method for forming a multilayer coating film according to claim 1, wherein a mixing molar ratio of the polyethylene glycol monoalkyl ether and the polypropylene glycol monoalkyl ether is 60:40 to 40:60. The interlayer control agent has the following chemical formula (1):

(In the formula, n represents 1 to 5, R ¹ represents a general formula R ³ — (— O—CH ₂ —CH ₂ —) _p — (wherein p represents an integer of 6 to 20; R ³ Represents a group obtained by removing OH from the polyethylene glycol monoalkyl ether represented by formula (1), wherein R ² represents a general formula:

(In the formula, q represents an integer of 15 to 60, and R ⁴ represents an alkyl group having 1 to 8 carbon atoms.) A group obtained by removing OH from a polypropylene glycol monoalkyl ether represented by: )
The multilayer coating-film formation method of Claim 1 which has as a main component the carbodiimide compound represented by these.   The method for forming a multilayer coating film according to claim 1, further comprising a step of applying a clear coating between the coating step of the second aqueous coating and the baking step.