JP2006257141A - Two-part curable aqueous coating composition and coating film forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a two-part curable aqueous coating composition having stable pot-life and capable of forming coating film having such physical properties as good appearance, mechanical strength and chemical resistance. <P>SOLUTION: The two-part curable aqueous coating composition comprises (I) an aqueous main agent containing a hydroxyl-containing resin and (II) a curing agent. In this composition, the aqueous main agent(I) comprises an aqueous macromolecular polyol with a hydroxyl number of 50-200 mgKOH/g, an acid value of 10-100 mgKOH/g and a number-average molecular weight of 1,000-100,000, and the curing agent(II) is comprises a water-dispersible polyisocyanate and an organic solvent having a solubility parameter of 8.0-10.0 and inert to isocyanate group. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention relates to a two-component curable aqueous coating composition and a coating film forming method.

In recent years, along with the seriousness of environmental problems, it has been desired to reduce the environmental load in the paint field, and various studies have been made. An important issue that is regarded as a problem in the field of paints is to reduce the amount of organic solvent used. From such a viewpoint, water-based paints are used as paints with reduced organic solvents, and the amount of use is expanding in various fields.

On the other hand, as one of the uses of the paint, there are general industrial uses such as building exteriors, bridges, ships, vehicles, industrial machines, construction machinery, automobiles and the like. Among these general industrial applications, especially when coating large and thick materials, it is difficult to use a baking type paint because the heat capacity of the object to be coated is high. Many are used.

As a room temperature drying paint, an isocyanate curable two-component curable paint is known. This is a two-component curable coating composition comprising a solution of a compound having two or more isocyanate groups and a resin solution having two or more functional groups that react with isocyanate groups such as hydroxyl groups. A coating film is formed by a curing reaction. Since such a reaction occurs at room temperature, a thermosetting step is unnecessary, and it can be used as a room temperature drying type paint.

However, it has been extremely difficult to make such an isocyanate-curable coating material water-soluble because a polyisocyanate compound as a curing agent easily reacts with water. In order to solve such a problem, Patent Document 1 describes a two-part curable aqueous coating composition comprising an emulsified organic polyisocyanate compound and a binder component. The composition described in Patent Document 1 provides dispersibility in water by using a polyisocyanate compound in combination with a resin having a high carboxyl group or sulfonate group content, thereby ensuring pot life. It is. However, in such a composition, it is necessary to use a resin having a relatively high acid value in order to disperse the isocyanate compound, or to blend a large amount of a nonionic surfactant component. When a resin having a high acid value is used, a large amount of reaction between the carboxyl group and the isocyanate compound occurs. When the reaction between the carboxyl group and the isocyanate compound increases, there arises a problem that the appearance of the coating film deteriorates. In addition, when a nonionic surfactant component is added, water resistance and chemical resistance are reduced due to remaining in the film.

Polyisocyanate compounds having water dispersibility are disclosed in Patent Documents 2 to 4. However, when these polyisocyanate compounds having water dispersibility were used, the two components were not sufficiently mixed due to the viscosity of the polyisocyanate compound when the binder liquid and the polyisocyanate compound were mixed during use. It becomes a coating film inferior to various physical properties such as coating film appearance, coating film strength, and chemical resistance.

Japanese Patent Laid-Open No. 2-105879 JP 2003-96390 A JP 10-36767 A Japanese Patent Laid-Open No. 10-140084

In view of the above situation, the present invention is a two-component curable type capable of forming a coating film having a stable pot life and having various physical properties such as excellent coating film appearance, coating film strength, and chemical resistance. The object is to provide an aqueous coating composition.

The present invention is a two-part curable aqueous coating composition comprising an aqueous main agent (I) containing a hydroxyl group-containing resin and a curing agent (II), wherein the aqueous main agent (I) has a hydroxyl value of 50 to 50. 200 mg KOH / g, acid value 10-100 mg KOH / g, containing an aqueous polymer polyol having a number average molecular weight of 1000-100,000, the curing agent (II) is a polyisocyanate having water dispersibility, and solubility It is a two-component curable aqueous coating composition characterized by containing an organic solvent inert to isocyanate groups with a parameter of 8.0 to 10.0.

The boiling point of the solvent is preferably 80 to 250 ° C.
The aqueous polymer polyol is preferably an acrylic polyol.
The water-dispersible polyisocyanate is preferably a modification of a nurate type polyisocyanate.
The aqueous main component (I) is an organic solvent having a solubility parameter of 8.0 to 10.0 and having no hydroxyl group, and containing the same organic solvent as that contained in the curing agent (II). Preferably there is.

The organic solvent contained in the curing agent (II) or the aqueous main component (I) is at least one selected from the group consisting of dipropylene glycol dimethyl ether, methyl isobutyl ketone, butyl acetate, xylene, and propylene glycol methyl ether acetate. Is preferred.

In the two-component curable aqueous coating composition, the aqueous main agent (I) and the curing agent (II) have an isocyanate group of 0.5 to 3.0 (moles) relative to the hydroxyl group in the aqueous main agent (I). The ratio is preferably used in a mixture.

The present invention includes a step (A) of applying a primer paint and a step (B) of forming a coating film on the primer layer formed by the above step (A) by the above-described two-component curable aqueous coating composition. It is also a method for forming a multilayer coating film.

The primer coating is a two-part curable aqueous coating composition comprising an aqueous main agent (X) and a curing agent (Y), and the aqueous main agent (X) is a condensation product of an epoxy compound and an aliphatic polyol compound. The epoxy equivalent contains a condensation product of 100 to 10000 g / mol, and the curing agent (Y) is preferably a two-component curable aqueous coating composition containing a polyamine.

The present invention is also a coated article having a multilayer coating film formed by the above-described multilayer coating film forming method.
Hereinafter, the present invention will be described in detail.

The present invention improves the mixing properties of a two-part curable aqueous coating composition, and thereby enables the formation of a coating film having excellent coating film appearance, coating film strength, chemical resistance and the like. A curable aqueous coating composition is provided.

In the present invention, a two-component curable aqueous solution is added by adding a solvent having a specific solubility parameter to the curing agent (II), preferably by adding a solvent having a specific solubility parameter to the aqueous main agent (I). It has been completed by finding that the mixing properties of the coating composition are significantly improved, thereby improving the coating properties.

That is, in the present invention, the dispersibility of the isocyanate compound in water is improved by the fact that the curing agent (II) contains an isocyanate-inactive organic solvent having a solubility parameter of 8.0 to 10.0. This improves the miscibility of the isocyanate compound in the paint and solves the above-mentioned problems.

When the solubility parameter is less than 8.0, the organic solvent has a problem that the miscibility (compatibility) with the main agent side is lowered, resulting in poor curing and appearance deterioration, and exceeds 10.0. As a result, the miscibility with polyisocyanate is lowered, resulting in problems such as poor curing and poor appearance. The solubility parameter (SP value) is a measure of solubility and is measured as follows. (Reference document SUH, CLARKE [JPSA-1, 5, 1671-1681 (1967)])

As a sample, 0.5 g of resin is weighed into a 100 ml beaker, and 10 ml of acetone is added using a whole pipette and dissolved with a magnetic stirrer. A poor solvent is dropped into the sample at a measurement temperature of 20 ° C. using a 50 ml burette, and the point at which turbidity is generated is defined as the dropping amount. As the poor solvent, ion-exchanged water is used as the high SP poor solvent, and n-hexane is used as the low SP poor solvent, and the muddy point is measured. The SP value δ of the resin is given by the following calculation formula.

δ = (V _ml ^1/2 δ _ml + V _mh ^1/2 δ _mh ) / (V _ml ^1/2 + V _mh ^1/2 )
V _m = V ₁ V ₂ / (φ ₁ V ₂ + φ ₂ V ₁ )
δ _m = φ ₁ δ ₁ + φ ₂ δ ₂ V _i : Molecular volume of solvent (ml / mol)
φ _i : Volume fraction of each solvent at cloud point δ _i : SP value of solvent ml: Low SP poor solvent mixed system mh: High SP poor solvent mixed system

Further, the organic solvent needs to be an isocyanate-inactive one. That is, it must be an organic solvent that does not react with isocyanate groups. This is a property that is naturally required for stably storing the polyisocyanate compound, and means that it does not have a functional group that reacts with the polyisocyanate group. The functional group that reacts with the polyisocyanate group is a hydroxyl group, an amino group, a carboxyl group, or the like, and an organic solvent that does not have these functional groups can be used.

The organic solvent preferably has a boiling point of 80 to 250 ° C. If the boiling point is too low, appearance defects such as cracking and foaming may occur, and if the boiling point is too high, film performance may be deteriorated due to remaining in the coating film.

Examples of such an organic solvent include dipropylene glycol dimethyl ether, methyl isobutyl ketone, butyl acetate, xylene, propylene glycol methyl ether acetate, and the like. Of these, dipropylene glycol dimethyl ether is particularly preferably used. The above-mentioned solubility parameter in the curing agent (II) used in the present invention is 8.0 to 10.0, and the isocyanate-inactive organic solvent contains 10 to 50% by mass with respect to the polyisocyanate resin solid content. Is preferred. By making it within the above range, the miscibility can be improved. Moreover, when adding the said solvent to an aqueous main ingredient, it is preferable that it is 5-50 mass% with respect to the polyol resin solid content in an aqueous main ingredient.

The curing agent (II) contains a polyisocyanate compound having water dispersibility. The polyisocyanate compound having water dispersibility refers to a polyisocyanate compound that can be dispersed without being separated when added to water. As such a compound, for example, by modifying with a hydrophilic compound, Examples thereof include polyisocyanate compounds having a hydrophilic group.

When the above-mentioned polyisocyanate compound having water dispersibility is dispersed in water due to its hydrophilicity, the isocyanate units that are hydrophobic structural units are aggregated inside the particles, and the hydrophilic structural units are directed to the outside of the dispersed particles. It seems to form a micelle structure. As a result, it is presumed to exist relatively stably in water. That is, since an isocyanate group having high reactivity with water is present in a hydrophobic state inside the micelle, it is presumed that the decarboxylation reaction in water can be suppressed and the pot life can be lengthened.

Examples of the hydrophilic compound include polyalkylene glycols, and among them, those modified with polyethylene glycol which is a kind of polyalkylene glycol are preferable. Alternatively, one end may be modified with polyethylene glycol blocked with an alkyl group such as a methyl group, an ethyl group, a propyl group, or a butyl group.

It does not specifically limit as a polyisocyanate compound modified | denatured with the said hydrophilic compound, For example, aromatic polyisocyanate, such as tolylene diisocyanate, 4,4'- diphenylmethane diisocyanate, xylylene diisocyanate, metaxylylene diisocyanate; Examples thereof include aliphatic polyisocyanates such as hexamethylene diisocyanate; alicyclic polyisocyanates such as isophorone diisocyanate; and multimers such as burette type, nurate type, and TMP adduct type. It may be a mixture of these two or more polyisocyanate compounds.

The polyisocyanate compound is preferably a multimer such as a nurate type, a burette type, or a TMP adduct type. Since the polyisocyanate compound that is a multimer is trifunctional or more, it is a compound that modifies at least one of a plurality of isocyanate groups and has at least two isocyanate groups to cause a crosslinking reaction by the isocyanate groups. It is preferable that

The modification of the polyisocyanate compound with the hydrophilic compound is preferably performed at a ratio such that two or more isocyanate groups remain per molecule of the modified polyisocyanate compound on average. If the isocyanate group is less than 2, the crosslinking reaction may not proceed sufficiently.

A commercially available polyisocyanate can also be used as the polyisocyanate having water dispersibility. It does not specifically limit as a commercially available thing, For example, BAYHYDUR VP LS 2319, BAYHYDUR VP LS 2150 / BA (above Bayer AG company make) etc. can be mentioned.

In addition to the polyisocyanate compound and the organic solvent having the specific properties, the curing agent (II) may contain other organic solvents and the like within a range that does not affect the physical properties. The other organic solvent is not particularly limited, and examples thereof include alcohol solvents such as n-butyl alcohol and methoxypropanol; cellosolv solvents such as diethylene glycol monobutyl ether and ethylene glycol monobutyl ether; aromatic solvents such as toluene and xylene. And ketone solvents such as methyl isobutyl ketone and methyl ethyl ketone.

The aqueous main component (I) contains an aqueous polymer polyol having a hydroxyl value of 50 to 200 mgKOH / g, an acid value of 10 to 50 mgKOH / g, and a number average molecular weight of 1000 to 100,000. The aqueous polymer polyol may be any of an emulsification type, a dispersion type, and a water-soluble type, but from the viewpoint that a coating film having a good appearance can be formed, a dispersion-type or water-soluble type aqueous polymer polyol. Is more preferable, and a dispersion type aqueous polymer polyol is most preferable. The dispersion-type aqueous polymer polyol here refers to a dispersion in water by neutralizing part or all of the carboxylic acid groups in the aqueous polymer polyol with a basic compound.

Since the aqueous polymer polyol has the above physical properties, it has the advantages that it is stably hydrated and stabilized in water, and the hydroxyl group cures with the isocyanate group of the curing agent to exhibit excellent film performance. I have it. The molecular weight of the aqueous polymer polyol is preferably 2000 to 50000, and more preferably 5000 to 10,000. The lower limit of the acid value of the aqueous polymer polyol is more preferably 20 mgKOH / g, and the upper limit of the acid value is more preferably 30 mgKOH / g.

The aqueous polymer polyol is not particularly limited, and for example, acrylic polyol, polyester polyol, polyether polyol, polyurethane polyol, polycarbonate polyol and the like can be used. Among them, it is preferable to use an acrylic polyol because various physical properties such as good appearance, weather resistance and chemical resistance are good.

It is not specifically limited as said acrylic polyol, What is necessary is just an acrylic polyol obtained by superposition | polymerization of a radically polymerizable unsaturated monomer composition, and having the said physical property. Examples of the radical polymerizable unsaturated monomer include a hydroxyl group-containing radical polymerizable unsaturated monomer necessary for obtaining the hydroxyl value, and a carboxyl group-containing radical polymerizable unsaturated necessary for obtaining the acid group. It is possible to use a monomer and a mixture of other monomers in such a ratio that the above physical properties can be obtained.

The carboxyl group-containing radical polymerizable unsaturated monomer is not particularly limited, and examples thereof include carboxylic acids such as acrylic acid, methacrylic acid, ethacrylic acid, crotonic acid, maleic acid, fumaric acid, and itaconic acid, or dicarboxylic acids thereof. A monoester etc. can be mentioned. Of these, acrylic acid and methacrylic acid are preferred. These may be used alone or in combination.

The other radical polymerizable monomers are not particularly limited, and examples thereof include styrenes such as styrene and α-methylstyrene; methyl acrylate, ethyl acrylate, propyl acrylate, acrylic acid-n, i, and t- Acrylic esters such as butyl, 2-ethylhexyl acrylate, lauryl acrylate; methyl methacrylate, ethyl methacrylate, propyl methacrylate, methacrylic acid-n, i and t-butyl, 2-ethylhexyl methacrylate, methacrylic acid Examples include methacrylic acid esters such as lauryl acid; amides such as acrylamide and methacrylamide.

The acrylic polyol is synthesized by reaction in the absence of a solvent or in the presence of a suitable organic solvent, and then dropped into water and mixed, and if necessary, an excess solvent is removed to obtain an aqueous acrylic polyol. Can do.
The acrylic polyol can be obtained by a polymerization reaction in the absence of a solvent or in the presence of a suitable organic solvent. The polymerization initiator used here is not particularly limited as long as it is generally used as a radical polymerization initiator. For example, organic peroxides such as benzoyl peroxide, t-butyl peroxide and cumene hydroperoxide, And organic azo compounds such as azobiscyanovaleric acid and azoisobutyronitrile.

The polymerization can be carried out at a temperature of 80 to 140 ° C. for 1 to 8 hours by an operation well known to those skilled in the art. The said polymerization can be performed by dripping a radically polymerizable monomer and a polymerization initiator, for example in the heated organic solvent. The organic solvent is not particularly limited, but preferably has a boiling point of about 60 to 250 ° C. Suitable organic solvents include water-insoluble organic solvents such as butyl acetate, xylene, toluene, methyl isobutyl ketone, propylene glycol, dipropylene glycol dimethyl ether, methyl ether acetate; and tetrahydrofuran, ethanol, methanol, propanol, isopropanol 2-butanol, t-butyl alcohol, dioxane, methyl ethyl ketone, ethylene glycol, ethylene glycol monobutyl ether, 2-methoxypropanol, 2-butoxypropanol, diethylene glycol monobutyl ether, butyl diglycol, N-methylpyrrolidone, ethylene carbonate and propylene carbonate And water-soluble organic solvents such as

Next, a neutralizing agent is added to neutralize at least a part of the acid groups contained in the acrylic polyol. Thereby, water dispersibility is imparted to the acrylic polyol.
The neutralizing agent is not particularly limited as long as it is generally used for neutralizing acid groups contained in the preparation of the water-dispersible resin composition. For example, monomethylamine, dimethyl Examples include organic amines such as amines, trimethylamine, triethylamine, diisopropylamine, monoethanolamine, diethanolamine and dimethylethanolamine, and inorganic bases such as sodium hydroxide, potassium hydroxide and lithium hydroxide. These may be used alone or in combination.

Furthermore, it can be set as the water-dispersible acrylic polyol used for aqueous | water-based main ingredient (I) by carrying out water dispersion by dripping water with respect to neutralized acrylic polyol or dropping neutralized acrylic polyol in water.
Moreover, you may remove an excess organic solvent as needed before neutralizing agent addition or after water dispersion.

A commercially available thing can also be used as said acrylic polyol. It does not specifically limit as a commercially available thing, For example, MACRYNAL VSM6299 / 42WA (made by Surface Specialties), BAYHYDROL XP2470 (made by Bayer AG) etc. can be mentioned.

The aqueous acrylic polyol preferably further contains an isocyanate-inactive organic solvent having a solubility parameter of 8.0 to 10.0. By having the organic solvent, the mixing property can be further improved. The organic solvent may be the same as or different from the organic solvent contained in the curing agent (II), but is more preferably the same.

When mix | blending the said organic solvent in the said aqueous | water-based main ingredient (I), a compounding quantity is 5-50 mass% with respect to resin solid content, Preferably you may be 20 mass% as an upper limit.
When the blending amount is 5% or less, the mixing property becomes insufficient, and when it exceeds 50%, the stability of the main ingredient is lowered.

The aqueous main component (I) preferably has a resin solid content of 30 to 50% by mass. It is preferable that it is in the above range in that it has suitable properties in terms of storage stability, miscibility with the curing agent (II), and the like.

In addition to the above components, the aqueous main component (I) includes a dispersant, an antifoaming agent, a colored pigment, an extender pigment, an ultraviolet absorber, a hindered amine light stabilizer, an antioxidant, a crosslinked resin particle, a surface conditioner, and a film forming agent. Auxiliaries, brightening agents such as aluminum flakes and mica, rust preventive pigments, thickeners and the like may be blended. The aqueous main ingredient (I) is prepared as follows.
First, a dispersant, a pigment, and if necessary, an antifoaming agent are mixed and dispersed with a dispersing machine such as an SG mill until a predetermined particle size is obtained, and then an aqueous acrylic polyol, and if necessary, the above solvent is added. , And other additives are added to prepare an aqueous base.

The two-pack curable aqueous coating composition is used by mixing two liquids immediately before use, but the above mixing is performed in such a way that an isocyanate group is added to 1 mol of hydroxyl group in the aqueous main agent (I). It is preferable to carry out in the ratio which will be 0.5-3.0 mol. If the isocyanate group is less than 0.5 mole, the crosslinking reaction does not proceed sufficiently and the physical properties of the coating film may be reduced. If the isocyanate group exceeds 3.0 mole, the excess isocyanate group reacts with water to cause low molecular weight urea. There is a risk of forming particles and causing the problem of film appearance deterioration.

The two-component curable aqueous coating composition can sufficiently mix two liquids even by stirring with a spatula, but can also be used by mixing using a stirring device such as a disper or a static mixer. It is. Therefore, the present invention does not exclude the case where the two-component curable aqueous coating composition is stirred using a stirring device such as a disper or a static mixer.

The two-component curable aqueous coating composition can be applied by a normal coating method such as spray coating, brush coating, dip coating, roll coating, or flow coating. In addition, the two-component curable aqueous coating composition of the present invention can be applied to the surface of any substrate, for example, wood, metal, glass, cloth, plastic, polystyrene foam, concrete, ceramic materials and the like. . In particular, it can be used in fields such as low-electricity / heavy electrical equipment called general industrial use, construction machinery, agricultural machinery, steel furniture, machine tools, large vehicles, aluminum building materials, ceramic building materials, architecture, and bridges.

When the two-component curable aqueous coating composition of the present invention is applied, a primer paint may be applied in advance, and the primer coating formed thereby may be applied. By having a primer coating film, the adhesion of the coating film can be improved, which is preferable in that the properties such as weather resistance and corrosion resistance can be greatly improved.

When primer coating is performed in the coating of the two-component curable aqueous coating composition of the present invention, it is preferable from the viewpoint of reducing the amount of organic solvent used in primer coating. The primer paint is a two-component curable aqueous primer comprising an aqueous main agent (X) and a curing agent (Y), wherein the aqueous main agent (X) is a condensation product of an epoxy compound and an aliphatic polyol compound. Then, it is preferable to use a two-component curable aqueous primer comprising a condensation product having an epoxy equivalent of 100 to 10,000 g / mol, and the curing agent (Y) containing a polyamine. Since the primer paint having such a composition is a normally dry type, it does not require a curing step, and is water-based in the same manner as the two-component curable aqueous coating composition. It is preferable because it can be reduced and has excellent adhesion. Hereinafter, the preferable primer paint will be described in detail.

In the two-component curable aqueous primer coating, the aqueous main component (X) preferably contains a condensation product of an epoxy compound and an aliphatic polyol compound, and more preferably has an epoxy equivalent of 100 to 10,000 g / mol. It is preferable to contain the condensation product which is.

The condensation product in the aqueous main agent (X) is obtained by subjecting an epoxy compound and an aliphatic polyol compound to a condensation reaction at a mass ratio (epoxy compound / aliphatic polyol compound) 95/5 to 5/95. Preferably there is.

It does not specifically limit as said aliphatic polyol compound, For example, polyether polyol, polyester polyol, polycarbonate polyol, polyurethane polyol etc. can be mentioned, However, Polyalkylene glycol which is polyether polyol is especially preferable. The polyalkylene glycol is preferably a polyalkylene glycol having an alkylene group having 4 or less carbon atoms, and examples thereof include polyethylene glycol, polypropylene glycol, polybutylene glycol, and a block copolymer of ethylene oxide and propylene oxide. Moreover, the mixture, copolymer, etc. of the said polyalkylene glycol can also be used. In addition, it may be partially end-capped with a monohydric alcohol or the like. The polyalkylene glycol may have a partially branched structure, but is preferably a linear polyalkylene glycol.

The aliphatic polyol compound may be a mixture of the polyalkylene glycol and another aliphatic polyol. Examples of the other aliphatic polyols include polyester polyols, polycarbonate polyols, polyamide polyols, polyurethane polyols, and the like, and polyester polyols are particularly preferable. The other aliphatic polyol is preferably 30% or less, more preferably 10% or less in terms of mass in the aliphatic polyol compound.

Examples of the other aliphatic polyols include aliphatic polyester polyols of aliphatic dicarboxylic acids and aliphatic diols, dicarboxylic acids having 3 to 40 carbon atoms, diols having 2 to 20 carbon atoms, and 2 to 40 And compounds obtained by a condensation reaction of a compound selected from primary diamines, polyalkylene polyamines, amino alcohols and the like having the following carbon atoms.

The epoxy compound is preferably a compound having an average of at least two epoxy groups per molecule, and preferably has an epoxy group content of 100 to 5000 g / mol. The thing of the said range has an effect that the thing with the better coating film physical property formed is obtained.

The epoxy compound may be saturated or unsaturated, may be aliphatic, alicyclic, aromatic and / or heterocyclic, and may have a hydroxyl group.

The epoxy compound is preferably polyglycidyl ether having a skeleton based on polyhydric alcohols, phenols, hydrogenated products of phenols and / or novolak phenol resins. The alcohols, phenols, and divalent are preferable.

Examples of the polyhydric phenols include resorcinol, hydroquinone, 2,2-bis (4-hydroxyphenyl) propane (bisphenol A), isomer mixture of dihydroxydiphenylmethane (bisphenol F), tetrabromobisphenol A, 4,4′- Dihydroxydiphenylcyclohexane, 2,2-bis (4-hydroxy-3-methylphenyl) propane, 4,4′-dihydroxybiphenyl, 4,4′-dihydroxybenzophenone, 1,1-bis (4-hydroxyphenyl) ethane, 2,2-bis [4- (2′-hydroxypropoxy) phenyl] propane, 1,1-bis (4-hydroxyphenyl) isobutane, 2,2-bis (4-hydroxy-3-tert.-butylphenyl) Propane, bis (2-hydroxynaphthy ) Methane, 1,5-dihydroxynaphthalene, tris (4-hydroxyphenyl) methane, bis (4-hydroxyphenyl) ether, bis (4-hydroxyphenyl) sulfone, etc., and halogenated and hydrogenated products of the above compounds is there. Of the above compounds, bisphenol A is particularly preferred.

The polyhydric alcohol is not particularly limited. For example, ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol (n = 4-35), 1,2-propylene glycol, polypropylene glycol (n = 2-15), 1 , 3-propylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,2,6-hexanetriol, glycerol, neopentylglycol, trimethylolethane, trimethylolpropane, etc. Can be mentioned. Among the above compounds, polypropylene glycol (n = 8 to 10) is particularly preferable.

As an epoxy compound, polyglycidyl ester obtained by reaction of polycarboxylic acid and epichlorohydrin or its derivative can also be used. The polycarboxylic acid is not particularly limited, and examples thereof include aliphatic, alicyclic or aromatic polycarboxylic acids such as oxalic acid, succinic acid, adipic acid, glutaric acid, phthalic acid, terephthalic acid, hexahydrophthalic acid, Examples include 2,6-naphthalenedicarboxylic acid and dimerized linolenic acid. Of these, diglycidyl adipate, diglycidyl phthalate and diglycidyl hexahydrophthalate are preferable.

A condensation product of the epoxy compound and the aliphatic polyol compound (hereinafter referred to as a condensation product (P)) can be obtained by condensing the aliphatic polyol and the epoxy compound. The condensation product (P) was subjected to a condensation reaction in such a ratio that the ratio z (OH): z (EP) of the number of hydroxyl groups to the number of epoxy groups was 1: 3.6 to 1:10. It is preferable. By carrying out the reaction in the above-mentioned range, it is preferable in that a suitable water dispersibility can be obtained, and it can be used as a paint and can suppress deterioration of physical properties of the paint film when a paint film is formed. The z (OH): z (EP) is more preferably in the range of 1: 4 to 1: 9, and still more preferably in the range of 1: 4.5 to 1: 8.

The condensation product (P) preferably has an epoxy group equivalent in the range of 100 to 10,000 g / mol. If it exceeds 10,000 g / mol, sufficient curability may not be obtained. If it is less than 100 g / mol, there is a risk that the storage stability is poor. The lower limit is more preferably 150 g / mol, and the upper limit is more preferably 2000 g / mol.

The condensation product (P) preferably has a weight average molecular weight in the range of 200 to 100,000 g / mol. If it is out of the above range, there is a possibility of causing a problem of poor film properties. The lower limit is more preferably 500 g / mol, and the upper limit is more preferably 20000 g / mol.

As the two-component curable aqueous primer of the present invention, the one containing the condensation product (P) as the aqueous main component (X) is used. The condensation product (P) is synthesized by a reaction in the absence of a solvent or in the presence of an appropriate organic solvent, and then added dropwise to water and mixed, and an excess solvent is removed as necessary, whereby an aqueous main agent is obtained. (X).

The aqueous main agent (X) may contain a liquid epoxy resin in addition to the condensation product (P). That is, since the condensation product (P) has an emulsifying ability, it can be contained in the aqueous main agent (X) even if it is a hydrophobic epoxy resin when used in combination therewith.

Examples of the liquid epoxy resin include the compounds exemplified as the epoxy resin that can be used in the production of the condensation product (P), and among them, bisphenol type epoxy resins having a bisphenol skeleton such as bisphenol A and bisphenol F. Is preferred. The liquid epoxy resin is preferably contained in a proportion of 100 parts by mass or less with respect to 100 parts by mass of the condensation product (P).

The aqueous main component (X) preferably has a resin solid content of 10 to 90% by mass. It is preferable that it is in the above range in that it has suitable properties in terms of storage stability, miscibility with the curing agent (Y), and the like.

A commercially available product can also be used as the condensation product (P) used in the aqueous main agent (X). It does not specifically limit as a commercially available epoxy resin, For example, Beckopox EP384W / 53WAMP (brand name: Surface Specialties Japan company make) etc. can be mentioned.

In addition to the condensation product, the aqueous main agent (X) may further contain other components used in the coating material. The other components are not particularly limited. For example, film forming aids, ultraviolet absorbers, hindered amine light stabilizers, antioxidants, crosslinked resin particles, extender pigments, colored pigments, rust preventive pigments, curing catalysts, and pigment dispersions. Agents, anti-settling agents, antifoaming agents, surfactants, thickeners, organic solvents, preservatives, surface conditioners, flash rust inhibitors and the like.

In the present invention, it is particularly preferable to contain the film-forming aid in a proportion of 0.1 to 10% by mass in the aqueous main agent (X). The two-component curable aqueous primer of the present invention is a coating in which the aqueous main agent (X) and the curing agent (Y) described in detail below are mixed immediately before use, and these two components are mixed. Then, a reaction occurs at the interface of the emulsion particles in water with the passage of time, thereby causing the resin emulsion particles to become coarse. As a result, the film-forming property is deteriorated, and it may be difficult to form a coating film having good physical properties. Since this causes a decrease in pot life, it is preferable to improve such a problem by adding a film-forming aid.

The film-forming aid is not particularly limited. For example, ethylene glycol monobutyl ether (butyl cellosolve), diethylene glycol monobutyl ether (butyl carbitol), diethylene glycol monobutyl ether acetate (butyl carbitol acetate), propylene glycol monomethyl ether, dipropylene glycol Monomethyl ether, 2,2,4-trimethyl-1,3-pentanediol isobutyrate and the like can be used. Of these, ethylene glycol monobutyl ether is preferable.

The said hardening | curing agent (Y) contains a polyamine.
The polyamine has (1) an active hydrogen equivalent of 50 to 1000 g / mol, a condensation product of an epoxy compound and a polyamine compound (hereinafter referred to as a condensation product (Q)), and / or ( 2) The active hydrogen equivalent is preferably 50 to 1000 g / mol, and is preferably a condensation product of an epoxy compound, an aliphatic polyol compound and a polyamine compound (hereinafter referred to as a condensation product (R)).

A polyamine is a compound used as a curing agent for an epoxy resin in a room temperature curable coating. In the present invention, the condensation product (Q) and / or the condensation product (R) modified with an epoxy as the polyamine is used. By using it, various problems such as deterioration of physical properties of a coating film caused by making an epoxy type room temperature curable coating water-based are improved.

The polyamine compound used for the preparation of the condensation product (Q) and / or the condensation product (R) is a compound having two or more amino groups. It does not specifically limit as said polyamine compound, The polyamine compound used as a hardening | curing agent in normal temperature curable coating material can be used. Examples of the polyamine compound include polyalkyleneamines such as diethylenetriamine, triethylenetetraamine, tetraethylenepentamine, and pentaethylenehexamine; 2,2,4- and / or 2,4,4-trimethylhexamethylenediamine, Bis (3-aminopropyl) amine, 1,4-bis (3-aminopropyl) piperazine, N, N-bis (3-aminopropyl) ethylenediamine, neopentanediamine, 2-methyl-1,5-pentanediamine, Aliphatic diamines such as 1,3-diaminopentane and hexamethylenediamine; 1,2- and 1,3-diaminocyclohexane, 1,4-diamino-3,6-diethylcyclohexane, 1,2-diamino-4-ethyl Cyclohexane, 1-cyclohexyl-3,4-dia Nocyclohexane, isophoronediamine and their reaction products, 4,4'-diaminodicyclohexyl-methane and -propane, bis (4-aminocyclohexyl) -methane and -propane, 3,3'-dimethyl-4,4'- Alicyclic amines such as diaminodicyclohexylmethane, 3-amino-1-cyclohexylaminopropane, 1,3- and 1,4-bis (aminomethyl) cyclohexane; orthoxylylenediamine, metaxylylenediamine, paraxylylenediamine And aromatic diamines. Mixtures of two or more of these can also be used.

Among these, diethylenetriamine, triethylenetetraamine, tetraethylenepentamine, and metaxylylenediamine are preferable, and a mixture thereof may be used. These polyamine compounds are particularly preferable from the viewpoint of obtaining pot life, storage stability, curability, and good coating film properties.

It does not specifically limit as an epoxy compound used for manufacture of the said condensation product (Q) and / or a condensation product (R), and an aliphatic polyol compound, It can be used for manufacture of the said condensation product (P). Examples thereof include epoxy compounds and aliphatic polyol compounds exemplified. Especially, as an epoxy compound, the bisphenol-type epoxy resin which has bisphenol frame | skeletons, such as bisphenol A and bisphenol F, is preferable. It does not specifically limit as an aliphatic polyol compound, For example, polyether polyol, polyester polyol, polycarbonate polyol, a polyurethane polyol etc. can be mentioned, Especially, polyalkylene glycol which is polyether polyol is preferable.

The condensation product (Q) can be obtained by condensing the polyamine compound and the epoxy compound. The condensation product (R) can be obtained by condensing an epoxy compound, an aliphatic polyol compound, and a polyamine compound.

In the condensation product (Q) and the condensation product (R), the ratio z (H): z (EP) of the number of active hydrogens to the number of epoxy groups is 0.1: 1 to 10: 1. It is preferable that the condensation reaction is performed at a ratio. By carrying out the reaction in the above-mentioned range, it is preferable in that a suitable water dispersibility can be obtained, and it can be used as a paint and can suppress deterioration of physical properties of the paint film when a paint film is formed. The z (H): z (EP) is more preferably in the range of 1: 1 to 5: 1.

The condensation product (Q) and the condensation product (R) preferably have an active hydrogen equivalent of 50 to 1000 g / mol. If it exceeds 1000 g / mol, sufficient curability may not be obtained. If it is less than 50 g / mol, the problem of poor water resistance may occur. The lower limit is more preferably 100 g / mol, and the upper limit is more preferably 500 g / mol.

The condensation product (Q) and the condensation product (R) preferably have a weight average molecular weight in the range of 500 to 100,000 g / mol. If it is less than 500 g / mol, the problem of poor film physical properties may occur, and if it exceeds 100,000 g / mol, the problem of poor film physical properties may occur. The lower limit is more preferably 1000 g / mol, and the upper limit is more preferably 20000 g / mol.

The two-component curable aqueous primer preferably contains the condensation product (Q) and / or the condensation product (R) as the curing agent (Y). The condensation product (Q) and / or the condensation product (R) is synthesized by a reaction in the absence of a solvent or in the presence of a suitable organic solvent, and then added dropwise to water and mixed, and if necessary, excess By removing the solvent, the curing agent (Y) can be obtained.

The condensation product (Q) is preferably obtained by a condensation reaction of an epoxy compound and a polyamine compound at a mass ratio (epoxy compound / polyamine compound) 99/1 to 50/50.

As the condensation product (R), an epoxy compound, an aliphatic polyol compound and a polyamine compound are condensed at a mass ratio (epoxy compound / aliphatic polyol compound / polyamine compound) 95/4/1 to 5/45/50. It is preferable that it is obtained by reacting.

The curing agent (Y) preferably has a solid content of 10 to 90% by mass. It is preferable that it is in the above range in that it has suitable properties in terms of storage stability, miscibility with the aqueous resin (X), and the like. The curing agent (Y) is preferably aqueous. Aqueous means water dispersible or water soluble.

In addition to the condensation product, the curing agent (Y) may further contain other components used in the paint. The other components are not particularly limited. For example, a film forming aid, an ultraviolet absorber, a hindered amine light stabilizer, an antioxidant, a crosslinked resin particle, an extender pigment, a coloring pigment, a curing catalyst, a pigment dispersant, and an anti-settling agent. Agents, antifoaming agents, surface conditioners, surfactants, thickeners, organic solvents, preservatives, flash rust inhibitors and the like.

The two-part curable aqueous primer is used by mixing two liquids immediately before use, but the mixture is used in the curing agent with respect to 1 mol of the epoxy group in the aqueous main agent (X). It is preferable to carry out at such a ratio that the active hydrogen is 0.3 to 2.0 mol. If the active hydrogen is less than 0.3 mol, the cross-linking reaction does not proceed sufficiently and the physical properties of the coating film may be reduced. If the active hydrogen exceeds 2.0 mol, the problem of poor water resistance due to unreacted residual amine may occur. is there.

In the two-component curable aqueous primer of the present invention, the structural unit derived from the bisphenol skeleton in the resin solid content in the paint in a state where the two components are mixed is preferably 10 to 90% by mass. Since the structural unit derived from the bisphenol skeleton has a function of improving the adhesion of the coating film, by making it within the above range, properties such as the adhesion of the coating film and chemical resistance are improved. It is preferable. A coating composition obtained by mixing two liquids in the above ratio is also a part of the present invention.

Here, the structural unit derived from the bisphenol skeleton is a ratio occupied by units derived from the bisphenol compound in the resin. For example, when the bisphenol skeleton is bisphenol A, the following general formula (1);

In the case of bisphenol F, the following general formula (2);

The ratio which the structural unit represented by represents in resin.

The two-component curable aqueous primer can be sufficiently uniformly stirred by a usual method such as stirring with a spatula, and does not require a special stirring device.

The present invention includes a step (A) of applying a water-based primer coating, and a step (B) of forming a coating film on the aqueous primer layer formed by the above-described step (A) using the above-described two-component curable aqueous primer. It is also a method for forming a multilayer coating film.

The multilayer coating film formation of the present invention can be used for a substrate to which the two-component curable aqueous primer can be applied, and for use.

In the formation of the multilayer coating film, it is preferable to perform curing or forced drying after the application of the aqueous primer. When curing and forced drying are not carried out, there is a risk of poor appearance (boiled or foamed) due to the reaction of the unreacted amine of the primer and the isocyanate. Curing is preferably performed at room temperature (25 ° C.) for 18 hours or longer, and forced drying is preferably performed under conditions of, for example, about 60 to 100 ° C. × 30 minutes.

In the multilayer coating film, the primer layer is desirably 20 to 100 μm, more preferably 30 to 50 μm thick, and the layer formed by the two-component curable aqueous primer is 20 to 100 μm, more preferably 30 A thickness of ˜50 μm is desirable. When the layer formed by the two-component curable aqueous primer has a thickness of less than 20 μm, the formed coating film cannot sufficiently cover the primer layer, and when it exceeds 100 μm, a sufficient coating film appearance is obtained. There is a risk that it will not be possible.

This invention is also a coated article which has the coating film formed by the said multilayer coating-film formation method.

The two-component curable aqueous coating composition of the present invention has a stable pot life and can form a coating film having various physical properties such as excellent coating film appearance, coating film strength, and chemical resistance. is there.

As an object to be coated, a JIS G 3141 (SPCC to SD) cold rolled steel sheet of 0.8 t × 70 × 150 mm size is solvent degreased, and then Uniepoch 30 primer (trade name, manufactured by Nippon Paint Co., Ltd.) Was coated with a spray gun so that the dry film thickness was 30 to 50 μm, and was naturally dried for 7 days. A test piece was prepared by mixing the main component (I) and the curing agent (II) with a spatula at a predetermined ratio, painting with a spray gun, and forced drying at 60 ° C. for 1 hour. Evaluation was performed. Moreover, the mixing property when mixing the main agent (I) and the curing agent (II) was also evaluated based on the following criteria.

(Examples 1-11, Comparative Examples 1-7)
An aqueous main component (I) and a curing agent (II) having the composition shown in Table 1 were prepared. In addition, the following were used for each raw material in the table.
DISPERBYK-190 (manufactured by BYK Chemie) Dispersant ACW-1001 (manufactured by Nippon Paint) Dispersant BYK-024 (manufactured by BYK Chemie) Antifoaming agent CR97 Taipei CR97 (manufactured by Ishihara Sangyo Co., Ltd.)
MACRYNAL VSM6299 / 42WA (manufactured by Surface Specialties) water-dispersed acrylic polyol, acid value 25, hydroxyl value 135, number average molecular weight 6500
BAYHYDUR VP LS 2319 (manufactured by Bayer AG) Hydrophilized modified product of nurate adduct of isocyanate, isocyanate group content 17.5 to 18.5%

(Mixability)
The ease of mixing when mixing the two liquids was judged based on the following criteria.
A: Can be easily mixed with a spatula.
A: Some force is required, but it can be easily mixed with a spatula.
Δ: Difficult but can be mixed with a spatula ×: Mixer required for mixing

(Appearance of coating film)
The appearance of the coating film was visually observed and evaluated based on the following criteria.
○: Paint leveling is good and the coating film is uniform and no abnormality △: Coating leveling is slightly poor and the coating film is slightly non-uniform ×: Coating leveling is poor and the coating film is non-uniform

(Pencil hardness)
According to JIS K 5600 5-4.

(water resistant)
The appearance of the coating film after water immersion at 40 ° C. for 240 hours was visually observed and evaluated based on the following criteria.
○: No difference in appearance from before testing.
Δ: Appearance abnormality such as lower gloss than before the test.
×: Abnormalities such as blistering and peeling.

(Acid resistance)
The appearance of the coating film was visually observed after being immersed in a 5% HCl aqueous solution at 25 ° C. for 96 hours, and evaluated based on the following criteria.
○: No difference in appearance from before testing.
Δ: Appearance abnormality such as lower gloss than before the test.
×: Abnormalities such as blistering and peeling.

(Alkali resistance)
The appearance of the coating film was visually observed after being immersed in a 5% NaOH aqueous solution at 25 ° C. for 96 hours, and evaluated based on the following criteria.
○: No difference in appearance from before testing.
Δ: Appearance abnormality such as lower gloss than before the test.
×: Abnormalities such as blistering and peeling.

In addition, each solvent kind used in Table 1 is shown in following Table 2.

From the above results, the two-part curable aqueous coating composition of the present invention can form a coating film having excellent miscibility and excellent chemical resistance. On the other hand, what does not use the said solvent in a hardening | curing agent has inadequate mixing property.

(Example 12)
In Example 1 above, coating was performed in the same manner except that the following two-component curable aqueous primer coating was used as a primer. As a result, it was possible to form a coating film having good coating performance as in Example 1.

(Two-part curable aqueous primer)
An aqueous main component (I) having the composition shown in Table 3 and a curing agent (II) shown in Table 4 were prepared. The prepared aqueous main component (I) and curing agent (II) were mixed in a ratio of aqueous main component (I) / curing agent (II) = 80/20 (mass ratio) to prepare a coating material.
In Table 3, Beckopox EP384W is manufactured by Surface Specialties Japan, Inc. (epoxy equivalent = 490-550 g / mol) (condensate of bisphenol A, polyethylene glycol, and polypropylene glycol).
In Table 4, Epilink 701 is manufactured by Air Products Japan (active hydrogen equivalent = 165 g / mol) (condensate of bisphenol A, metaxylylenediamine, and triethylenetetramine).

The two-component curable aqueous coating composition of the present invention can be used for general industrial applications such as building exteriors, bridges, ships, vehicles, industrial machinery, construction machinery, automobiles and the like. The multilayer coating film forming method of the present invention can be applied to general industrial uses as described above.

Claims (10)

A two-part curable aqueous coating composition comprising an aqueous main component (I) and a curing agent (II) containing a hydroxyl group-containing resin,
The aqueous main component (I) contains an aqueous polymer polyol having a hydroxyl value of 50 to 200 mgKOH / g, an acid value of 10 to 100 mgKOH / g, and a number average molecular weight of 1000 to 100,000.
The curing agent (II) contains a polyisocyanate having water dispersibility and an organic solvent which has a solubility parameter of 8.0 to 10.0 and is inert to isocyanate groups. Liquid curable aqueous coating composition. The two-component curable aqueous coating composition according to claim 1, wherein the organic solvent has a boiling point of 80 to 250 ° C. The two-part curable aqueous coating composition according to claim 1, wherein the aqueous polyol is an acrylic polyol. The two-component curable aqueous coating composition according to claim 1, 2, or 3, wherein the polyisocyanate having water dispersibility is a modification of a nurate type polyisocyanate. The aqueous main component (I) is an organic solvent having a solubility parameter of 8.0 to 10.0 and having no hydroxyl group, and containing an organic solvent which is the same as or different from that contained in the curing agent (II). The two-component curable aqueous coating composition according to claim 1, 2, or 3. The organic solvent contained in the curing agent (II) or the aqueous main component (I) is at least one selected from the group consisting of dipropylene glycol dimethyl ether, methyl isobutyl ketone, butyl acetate, xylene, and propylene glycol methyl ether acetate. The two-component curable aqueous coating composition according to 1, 2, 3, 4 or 5. The aqueous main agent (I) and the curing agent (II) are mixed at a ratio such that the isocyanate group of the curing agent is 0.5 to 3.0 (molar ratio) with respect to 1 mol of the hydroxyl group in the aqueous main agent (I). The two-part curable aqueous coating composition according to claim 1, 2, 3, 4, 5 or 6. Step (A) for applying primer paint, and
It comprises the step (B) of forming a coating film on the primer layer formed by the step (A) with the two-component curable aqueous coating composition according to claim 1, 2, 3, 4, 5, 6 or 7. A method for forming a multilayer coating film. Primer paint
A two-component curable aqueous primer comprising an aqueous main agent (X) and a curing agent (Y),
The aqueous main agent (X) is a condensation product of an epoxy compound and an aliphatic polyol compound, and contains a condensation product having an epoxy equivalent of 100 to 10,000 g / mol,
The method for forming a multilayer coating film according to claim 8, wherein the curing agent (Y) is a two-component curable aqueous primer containing a polyamine. A coated article comprising a multilayer coating film formed by the multilayer coating formation method according to claim 8 or 9.