JP2013133445A - Aqueous coating composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an aqueous coating composition which can be cured at a low temperature and which has excellent coating stability and satisfactory crosslink density.SOLUTION: The aqueous coating composition includes: (A) an aqueous resin having a hydroxyl group and a carboxyl group; (B) a polyisocyanate compound; and (C) a hydrophilization modified carbodiimide compound; wherein (A) has, in terms of resin solid content, 80 to 200 mgKOH/g hydroxyl value and 10 to 40 mgKOH/g acid value and the ratio of the hydroxyl value to the value of the acid value of (A) is 3 to 15, the ratio of an equivalent weight of carbodiimide group included in (C) to the equivalent weight of the isocyanate group included in (B) is 0.01 to 0.20, (C) is represented by general formula (I), the ration of the equivalent weight of isocyanate group included in (B) to the equivalent weight of the hydroxyl group included in (A) is 0.6 to 1.5 and the ratio of the equivalent weight of the carbodiimide group included in (C) to the equivalent weight of acid radical included in (A) is 0.1 to 1.0. [ In the formula, X denotes a bifunctional organic group containing at least one carbodiimide group, Y denotes a structure formed by removing hydroxyl groups from the same or different polyalkylene glycol monoalkylether and Z denotes a structure formed by removing hydroxyl groups from a bifunctional polyol having a number average molecular weight of 200 to 5,000].

Description

  The present invention relates to an aqueous coating composition that can be cured at a low temperature.

  In the field of painting, from the viewpoint of environmental protection, there is a demand for switching from solvent-based coating to water-based coating. On the other hand, there is also a need for a paint that can be cured at low temperature for the purpose of energy saving in the painting process and for the purpose of painting with a heat-sensitive substrate. As a material satisfying these requirements, there is a urethane-based water-based paint using a polyol as a binder component and a polyisocyanate compound as a curing agent. However, the urethane-based water-based paint has a problem that the curability at low temperature is not sufficient.

  The use of polycarbodiimide compounds has been studied as one means for achieving the low temperature curability requirement. For example, JP-A-9-510747 (Patent Document 1) discloses a resin (A) having a hydroxyl group and an acid group dilutable in water, a polyisocyanate component (B), and a carbodiimide component having a polyether chain ( An aqueous multicomponent-polyurethane-coating agent containing C) is disclosed (claim 1 etc.). However, since the carbodiimide component (C) used in the coating material of Patent Document 1 does not have sufficient water dispersibility, there is a problem that the stability of the resulting coating material is also poor. Furthermore, the film obtained by using the coating material of Patent Document 1 also has a problem that it is remarkably lower than the crosslinking density required in actual use.

  JP 2011-094102 A (Patent Document 2) includes (A) an aqueous resin having a hydroxyl group and a carboxyl group, (B) a polyisocyanate compound, and (C) -OCONH-X-NHCOOY [ X is a bifunctional organic group containing at least one carbodiimide group, and Y has a structure in which a hydroxyl group is removed from a polyalkylene glycol monoalkyl ether. ] The water-based coating composition containing the hydrophilization modified polycarbodiimide compound which has multiple structural units represented by this is described (Claim 1 etc.). The aqueous coating composition described in Patent Document 2 describes that two performances of excellent coating stability and excellent low-temperature curability are compatible at a high level. However, it has been found that the coating film formed by the aqueous coating composition of Patent Document 2 also does not have the crosslinking density required in actual use.

  In the aqueous coating composition, generally, the coating performance such as water resistance and weather resistance tends to be lower than that of the solvent-based coating composition. This is because, in the preparation of the aqueous coating composition, in order to ensure dispersion stability, an aqueous functional group introduced when the resin component or the like is made aqueous remains in the formed coating film. It is thought to be caused. Therefore, in the aqueous coating composition, in order to improve the weather resistance of the coating film and the adhesion to strong impact and force, securing a sufficient crosslinking density in the formed coating film is one of the important issues. is there. However, simply increasing the reactivity of the resin component for the purpose of ensuring a sufficient crosslinking density results in poor paint stability. For this reason, in the low-temperature curable aqueous coating composition, while ensuring the coating stability and the like, it is possible to increase the crosslinking density of the obtained coating film to ensure excellent water resistance, weather resistance, adhesion, etc. It was extremely difficult.

JP 9-510747 gazette JP 2011-094102 A

  An object of the present invention is to solve the above-described problems of the prior art. More specifically, the present invention provides an aqueous coating composition that is curable at low temperatures and has excellent coating stability, and further provides a coating film having a sufficient crosslinking density. The task is to do.

［Ｘは、少なくとも１個のカルボジイミド基を含有する２官能性有機基であり、Ｙは、同一または異種のポリアルキレングリコールモノアルキルエーテルから水酸基を除いた構造であり、Ｚは、数平均分子量２００〜５０００の２官能ポリオールから水酸基を除いた構造である。］

［Ｘは少なくとも１個のカルボジイミド基を含有する２官能性有機基であり、Ｙは、同一または異種のポリアルキレングリコールモノアルキルエーテルから水酸基を除いた構造であり、Ｒ^０は、水素、メチル基、またはエチル基であり、Ｒ^１は、炭素数４以下のアルキレン基であり、ｎは０または１であり、ｍは０〜６０である。］

［Ｘは、少なくとも１個のカルボジイミド基を含有する２官能性有機基であり、Ｙは、同一または異種のポリアルキレングリコールモノアルキルエーテルから水酸基を除いた構造である。］
を提供するものであり、これにより上記課題が解決される。 The present invention
(A) an aqueous resin having a hydroxyl group and a carboxyl group,
(B) a polyisocyanate compound, and
(C) a hydrophilized modified carbodiimide compound,
An aqueous coating composition comprising:
The aqueous resin having a hydroxyl group and a carboxyl group (A) has a hydroxyl value of 80 to 200 mgKOH / g and an acid value of 10 to 40 mgKOH / g in terms of resin solid content.
The ratio of the hydroxyl value to the acid value of the aqueous resin (A) is 3 to 15,
The ratio of the equivalent of the carbodiimide group of the (C) hydrophilized modified carbodiimide compound to the equivalent of the isocyanate group of the (B) polyisocyanate compound is 0.01 to 0.20,
This (C) hydrophilized modified carbodiimide compound is represented by the following general formula (I), (II) or (III),
The ratio of the equivalent of the isocyanate group of this (B) polyisocyanate compound to the equivalent of the hydroxyl group contained in this (A) aqueous resin is 0.6 to 1.5,
The ratio of the equivalent of the carbodiimide group of the (C) hydrophilized modified carbodiimide compound to the equivalent of the acid group of the (A) aqueous resin is 0.1 to 1.0.
Water-based paint composition,

[X is a bifunctional organic group containing at least one carbodiimide group, Y is a structure obtained by removing a hydroxyl group from the same or different polyalkylene glycol monoalkyl ether, and Z is a number average molecular weight of 200. It is the structure which remove | excluded the hydroxyl group from -5000 bifunctional polyol. ]

[X is a bifunctional organic group containing at least one carbodiimide group, Y is a structure obtained by removing a hydroxyl group from the same or different polyalkylene glycol monoalkyl ether, and R ⁰ is a hydrogen or methyl group. Or an ethyl group, R ¹ is an alkylene group having 4 or less carbon atoms, n is 0 or 1, and m is 0-60. ]

[X is a bifunctional organic group containing at least one carbodiimide group, and Y has a structure in which a hydroxyl group is removed from the same or different polyalkylene glycol monoalkyl ether. ]
This solves the above problem.

  The ratio of the equivalent of the carbodiimide group of the (C) hydrophilized modified carbodiimide compound to the equivalent of the isocyanate group of the (B) polyisocyanate compound is preferably 0.01 to 0.09.

  Moreover, it is preferable that ratio of the equivalent of the carbodiimide group which the said (C) hydrophilization modified carbodiimide compound has with respect to the equivalent of the acid group which said (A) aqueous resin has is 0.1-0.6.

  The (A) aqueous resin preferably contains an acrylic emulsion having a number average molecular weight of 10,000 to 80,000.

［Ｘは、少なくとも１個のカルボジイミド基を含有する２官能性有機基であり、Ｙは、下記（ｉ）または（ii）：
（ｉ）繰り返し数６〜２０のポリエチレンオキサイドユニットの末端に、炭素数１〜３のアルキル基がエーテル結合した、ポリエチレングリコールモノアルキルエーテルから、水酸基を除いた構造、
（ii）繰り返し数４〜６０のポリプロピレンオキサイドユニットの末端に、炭素数１〜８のアルキル基がエーテル結合した、ポリプロピレングリコールモノアルキルエーテルから、水酸基を除いた構造：
から選択される、同一または異種の構造である。］ An embodiment in which the (C) hydrophilized modified carbodiimide compound represented by the above formula (III) is the following compound is preferred.

[X is a bifunctional organic group containing at least one carbodiimide group, and Y is the following (i) or (ii):
(I) a structure in which a hydroxyl group is removed from polyethylene glycol monoalkyl ether in which an alkyl group having 1 to 3 carbon atoms is ether-bonded to a terminal of a polyethylene oxide unit having 6 to 20 repeating units;
(Ii) Structure in which a hydroxyl group is removed from polypropylene glycol monoalkyl ether in which an alkyl group having 1 to 8 carbon atoms is ether-bonded to the terminal of a polypropylene oxide unit having 4 to 60 repeats:
It is the same or different structure selected from. ]

  In the (C) hydrophilized modified carbodiimide compound represented by the above formula (III), any one Y is (i) and the other Y is (ii), and the structures (i) and ( More preferably, the ratio of ii) is within the range of (i) :( ii) = 1: 0.7-1: 8.

  The present invention also provides a coating film obtained by coating the aqueous coating composition.

  The aqueous coating composition of the present invention comprises (A) an aqueous resin having a hydroxyl group and a carboxyl group, (B) a polyisocyanate compound, and (C) a hydrophilized modified carbodiimide compound, and an equivalent ratio of functional groups of each component. Is a specific range. The water-based coating composition of the present invention has excellent coating performance and coating properties that achieve excellent coating stability in a low-temperature curable aqueous coating composition and that the resulting coating film has a high crosslinking density. The membrane performance is achieved.

  The aqueous coating composition of the present invention comprises (A) an aqueous resin having a hydroxyl group and a carboxyl group, (B) a polyisocyanate compound, and (C) a hydrophilized modified carbodiimide compound. In the aqueous coating composition of the present invention, (A) the ratio of the hydroxyl value to the acid value of the aqueous resin is 3 to 15, and (B) the equivalent of the isocyanate group of the polyisocyanate compound (C The ratio of equivalents of carbodiimide groups possessed by the hydrophilized modified carbodiimide compound is 0.01 to 0.20, and (A) the hydrophilized modified carbodiimide compound is equivalent to the equivalent of acid groups possessed by the aqueous resin. The equivalent ratio of the carbodiimide group is 0.1 to 1.0. Hereinafter, each component (A)-(C) and these characteristics are explained in full detail.

(A) Aqueous resin having a hydroxyl group and a carboxyl group (A) The aqueous resin having a hydroxyl group and a carboxyl group is a binder component that undergoes a curing reaction with the later-described (B) polyisocyanate compound and (C) a hydrophilized modified carbodiimide compound. And (A) aqueous resin which has a hydroxyl group and a carboxyl group used in the present invention,
-The hydroxyl value in terms of resin solid content is 80-200 mgKOH / g,
The acid value in terms of resin solids is 10 to 40 mg KOH / g, and
The ratio of the hydroxyl value to the acid value is 3 to 15;
Is a requirement.
The hydroxyl value in terms of resin solid content is more preferably 80 to 160 mgKOH / g, and the acid value in terms of resin solid content is more preferably 15 to 35 mgKOH / g.
The aqueous resin having a hydroxyl group and a carboxyl group (A) used in the present invention has a hydroxyl value of 3 to 15 with respect to the acid value, and the hydroxyl value is much larger than the acid value. It is characterized by. This ratio is more preferably 4-10. By using such an aqueous resin having a hydroxyl group and a carboxyl group (A), a coating film having a sufficient crosslinking density can be obtained while ensuring the coating stability.
If the acid value or hydroxyl value is less than the above range, curability may not be sufficient. On the other hand, when the acid value or the hydroxyl value exceeds the above range, the resulting coating film may not have sufficient water resistance.
On the other hand, when the ratio of the hydroxyl value to the acid value is less than 3, a coating film having a sufficient crosslinking density cannot be obtained. On the other hand, if this ratio exceeds 15, sufficient water dispersibility may not be obtained.

  The (A) water-based resin may be composed of a single resin that satisfies the above requirements for the hydroxyl value and acid value in terms of resin solids, or a combination that satisfies the above requirements for the hydroxyl value and acid value. It may be composed of a plurality of resins.

  The (A) aqueous resin has two types of functional groups, a hydroxyl group and a carboxyl group, as reactive groups involved in curing. In the aqueous coating composition of the present invention, (A) the hydroxyl group of the aqueous resin reacts with (B) the polyisocyanate compound, and (A) the carboxyl group of the aqueous resin reacts with (C) the hydrophilized modified carbodiimide compound.

  The type of the (A) aqueous resin is not particularly limited as long as it satisfies the requirements for the hydroxyl group and carboxyl group, but is preferably an acrylic resin and / or a polyester resin because it is easy to produce and obtain. . From the viewpoint of adjusting the physical properties of the coating film, it is preferable to use an acrylic resin alone or a mixture of an acrylic resin and a polyester resin as the aqueous resin (A).

  (A) The acrylic resin that can be suitably used as the aqueous resin includes, for example, a monomer containing an α, β-ethylenically unsaturated monomer having a hydroxyl group and an α, β-ethylenically unsaturated monomer having a carboxyl group. By subjecting the hydroxyl group and the carboxyl group to acrylic copolymerization in an amount that satisfies the above-mentioned requirements for the hydroxyl value and acid value, the desired resin can be obtained.

  Examples of the α, β-ethylenically unsaturated monomer having a hydroxyl group include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, allyl alcohol, and methacryl. Mention may be made of adducts of alcohol, hydroxyethyl (meth) acrylate and ε-caprolactone. Among these, preferred are 2-hydroxyethyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, and an adduct of 2-hydroxyethyl (meth) acrylate and ε-caprolactone. In this specification, “(meth) acryl” means both acrylic and methacrylic.

  Further, α, β-ethylenically unsaturated monomers having a carboxyl group include acrylic acid, methacrylic acid, acrylic acid dimer, crotonic acid, 2-acryloyloxyethylphthalic acid, 2-acryloyloxyethyl succinic acid, ω- Carboxy-polycaprolactone mono (meth) acrylate, maleic acid, fumaric acid, itaconic acid and the like can be mentioned. Among these, acrylic acid and methacrylic acid are preferable.

  In the acrylic copolymerization for obtaining the (A) aqueous resin, other α, β-ethylenically unsaturated monomers can be used as necessary. 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 Amide etc.).

  Examples of the method for obtaining the aqueous resin (A) include a method for obtaining an acrylic resin after performing solution polymerization and a method for obtaining an emulsion by performing emulsion polymerization in an aqueous medium.

  When the emulsion polymerization is carried out to obtain an emulsion, a crosslinkable monomer can be used as the other α, β-ethylenically unsaturated monomer. The crosslinkable monomer is a compound having two or more radically polymerizable ethylenically unsaturated groups in the molecule, and examples thereof include divinylbenzene, allyl (meth) acrylate, and ethylene glycol di (meth) acrylate. .

  The above-mentioned solution polymerization is generally a method in which a mixture of α, β-ethylenically unsaturated monomers used as raw materials is stirred while being dropped into a solvent together with a polymerization initiator under heating conditions. The conditions for solution polymerization are, for example, a polymerization temperature of 60 to 160 ° C. and a dropping time of 0.5 to 10 hours. The α, β-ethylenically unsaturated monomer used as the raw material can be polymerized in two stages. In this case, it is sufficient that the α, β-ethylenically unsaturated monomer used as a raw material satisfies the requirements for the hydroxyl group and the carboxyl group as a whole.

  The polymerization initiator is not particularly limited as long as it is used for normal polymerization, and examples thereof include azo compounds and peroxides. Generally, the amount of the polymerization initiator with respect to 100 parts by mass of the monomer mixture is 0.1 to 18 parts by mass, preferably 0.3 to 12 parts by mass.

  Moreover, the solvent which can be used here will not be specifically limited if it does not have a bad influence on reaction, For example, alcohol, a ketone, ether, a hydrocarbon solvent, etc. are mentioned. Furthermore, in order to adjust the molecular weight, a mercaptan such as lauryl mercaptan and a chain transfer agent such as α-methylstyrene dimer can be used as necessary.

  Thus, the number average molecular weight of the acrylic resin obtained by solution polymerization is preferably 4,000 to 20,000. In this specification, the number average molecular weight of the acrylic resin obtained by solution polymerization can be measured by gel permeation chromatography (GPC) using a polystyrene standard sample standard.

  Moreover, it is preferable that the glass transition temperature (Tg) of an acrylic resin exists in the range of -20-80 degreeC. The glass transition temperature can be measured by a differential scanning calorimeter (DSC).

  The acrylic resin obtained by the solution polymerization, after removing the solvent as necessary, is made aqueous by adding a basic compound, whereby the above (A) aqueous resin is obtained. Examples of the basic compound include ammonia, methylamine, ethylamine, dimethylamine, diethylamine, trimethylamine, triethylamine, dimethylethanolamine, diethanolamine, diethylaminoethanol, triethanolamine and the like. The amount of the basic compound added is preferably such that the neutralization rate is 60 to 100% with respect to the carboxyl group of the acrylic resin obtained by the solution polymerization. If the neutralization rate is less than 60%, the aqueous solution is not sufficient and the storage stability may be poor. The resin solid content of the (A) aqueous resin thus obtained is generally 25 to 55% by mass.

  The acrylic resin thus obtained can be used as an acrylic water dispersion. Such an acrylic water dispersion preferably has a volume average particle diameter in the range of 0.01 to 1 μm. When the volume average particle diameter is in the above range, there is an advantage that the stability of the aqueous dispersion is improved and the appearance of the obtained coating film is improved. The same applies to the acrylic emulsion described later, and the volume average particle diameter can be adjusted by adjusting the monomer composition and / or the emulsion polymerization conditions.

  In the preparation of the aqueous resin (A), when emulsion polymerization is carried out in an aqueous medium, for example, the emulsifier is dissolved in an aqueous medium containing water or an organic solvent such as alcohol, if necessary, and heated. Under stirring, a mixture of an α, β-ethylenically unsaturated monomer used as a raw material and a polymerization initiator can be added dropwise. What mixed the (alpha), (beta) -ethylenically unsaturated monomer used as a raw material may be previously emulsified using an emulsifier and water.

  Examples of the polymerization initiator that can be suitably used for emulsion polymerization 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-methylpropionamidine and cationic 2,2′-azobis (2-methylpropionamidine)); and redox oily peroxides (eg, benzoyl peroxide, parachlorobenzoyl peroxide, lauroyl peroxide and t-butyl perbenzoate), and aqueous peroxides such as potassium persulfate and persulfate Ammonium and the like).

  As the emulsifier, a general emulsifier usually used by those skilled in the art can be used. As emulsifiers, reactive emulsifiers such as Antox MS-60 (manufactured by Nippon Emulsifier Co., Ltd.), Eleminol JS-2 (manufactured by Sanyo Kasei Kogyo Co., Ltd.), Adekari Soap NE-20 (manufactured by Asahi Denka Co., Ltd.) and Aqualon HS-10 (Daiichi Kogyo Seiyaku Co., Ltd.), Latem PD-104 (Kao Co., Ltd.) and the like are particularly preferable. In order to adjust the molecular weight, a mercaptan such as lauryl mercaptan and a chain transfer agent such as α-methylstyrene dimer can be used as necessary.

  The reaction temperature is determined by the initiator. For example, it is preferably 60 to 90 ° C. for an azo initiator or peroxide, and preferably 30 to 70 ° C. for a redox system. In general, the reaction time is 1 to 8 hours. Generally, the amount of the initiator with respect to 100 parts by mass of the monomer mixture is 0.1 to 5% by mass. The emulsion polymerization can be performed in multiple stages, for example, in two stages. That is, first, a part of the mixture of α, β-ethylenically unsaturated monomers used as the raw material is subjected to emulsion polymerization, and the remainder of the α, β-ethylenically unsaturated monomer mixture is further added to emulsify. Polymerization is performed.

  The said emulsion can be used by pH 5-10 by neutralizing with a basic compound from a storage-stable viewpoint. The basic compound may be the same as that used in making the acrylic resin obtained in the previous solution polymerization aqueous. The neutralization is preferably performed by adding the basic compound to the system before or after emulsion polymerization.

  (A) When an acrylic emulsion is used as the aqueous resin, the number average molecular weight is preferably 10,000 to 80,000. The acrylic emulsion has a hydroxyl value of 80 to 200 mg KOH / g, an acid value of 10 to 40 mg KOH / g, a ratio of the hydroxyl value to the acid value of 3 to 15, and a number average molecular weight of 10 The range of 1,000,000 to 80,000 has the advantage that the crosslink density in the resulting coating film is in a better range while ensuring good paint stability. This is because the number average molecular weight is in a relatively high range of 10,000 to 80,000, and the acrylic emulsion has many hydroxyl groups in the above range, so that (A) the hydroxyl group in the aqueous resin It is considered that the low-temperature curability of the reacting (B) polyisocyanate compound is ensured, whereby the crosslinking density in the resulting coating film is in a better range.

  The number average molecular weight of the acrylic emulsion can be measured by gel permeation chromatography (GPC) using polystyrene standard sample standards after removing water by drying under reduced pressure or the like.

  The (A) aqueous resin may include a polyester resin. (A) A polyester resin that can be used as an aqueous resin is generally prepared by condensing a polyhydric alcohol component and a polybasic acid component so as to satisfy the requirements for the hydroxyl group and carboxyl group. Can do.

  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 Examples thereof include hydroxycarboxylic acid components such as diol, 3-methyl-1,5-pentanediol, and 2,2,4-trimethylpentanediol.

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

  Further, as reaction components, mono-epoxide compounds such as monohydric alcohol, Cardura E (trade name: manufactured by Ciel Chemical), and lactones (β-propiolactone, dimethylpropiolactone, butyrolactone, γ-valerolactone, ε-caprolactone, γ-caprolactone, etc.) may be used in combination.

  In addition to the above components, fatty acids such as castor oil and dehydrated castor oil, and an oil component that is one or a mixture of two or more of these fatty acids may be added to the acid component and the alcohol component. It is also possible to graft an acrylic resin or vinyl resin or to react a polyisocyanate compound as long as the above-mentioned requirements for the hydroxyl group and carboxyl group are satisfied.

  The number average molecular weight of the polyester resin thus obtained is preferably 500 to 20,000, and more preferably 1,500 to 10,000. If the number average molecular weight is less than 500, the storage stability when the polyester resin is dispersed in water may be lowered. On the other hand, when the number average molecular weight exceeds 20,000, the viscosity of the polyester resin increases, so that the solid content concentration in the case of coating is lowered, and the coating workability may be lowered.

  Moreover, it is preferable that the glass transition temperature of the said polyester resin is -20-80 degreeC. When the said glass transition temperature is less than -20 degreeC, there exists a possibility that the hardness of the coating film obtained may fall, and when it exceeds 80 degreeC, there exists a possibility that base concealment property may fall. The glass transition temperature is more preferably 0 to 60 ° C. The glass transition temperature of the polyester resin can be measured by DSC as in the case of the acrylic resin.

  By neutralizing the polyester resin thus obtained with the basic compounds mentioned above, (A) an aqueous resin can be obtained.

(B) Polyisocyanate Compound The aqueous coating composition of the present invention includes two components, (B) a polyisocyanate compound and (C) a hydrophilized modified carbodiimide compound, as the component (A) for curing the aqueous resin. . Here, the (B) polyisocyanate compound may be water-dispersible or hydrophobic. Even if it is hydrophobic, water dispersibility is ensured by the interaction with the (C) hydrophilized modified carbodiimide compound, which is excellent in water dispersibility described later.

  Examples of the above-mentioned (B) polyisocyanate compound that is hydrophobic include tolylene diisocyanate (TDI), 4,4′-diphenylmethane diisocyanate (MDI), xylylene diisocyanate (XDI), metaxylylene diisocyanate (MXDI), and the like. Aromatic diisocyanates; Aliphatic diisocyanates such as hexamethylene diisocyanate (HDI); Cycloaliphatic diisocyanates such as isophorone diisocyanate (IPDI) and hydrogenated MDI; Compounds in a form in which these diisocyanate compounds are made non-volatile and less toxic; Polyisocyanates such as burettes, uretdiones, isocyanurates or allophanates of diisocyanate compounds; relatively low molecular weight urethane prepolymers; Mention may be made of the compound.

  On the other hand, as the (B) polyisocyanate compound having water dispersibility, those obtained by introducing a hydrophilic group into the polyisocyanate compound and those obtained by mixing and emulsifying a surfactant, so-called self-emulsification Can be mentioned.

  Examples of the hydrophilic group include an anionic group such as a carboxyl group and a sulfonic acid group, a cationic group such as a tertiary amino group, and a nonionic group such as a polyoxyalkylene group. Among these, considering the water resistance of the resulting coating film, the hydrophilic group is preferably a nonionic group. As a specific nonionic group, a highly hydrophilic polyoxyethylene group is preferred.

  As the surfactant suitably used for the preparation of the self-emulsifying polyisocyanate compound obtained by mixing and emulsifying the polyisocyanate compound and the surfactant, for example, an anionic interface having an anionic group such as a carboxyl group and a sulfonic acid group Examples thereof include a surfactant, a cationic surfactant having a cationic group such as a tertiary amino group, and a nonionic surfactant having a nonionic group such as a polyoxyalkylene group. Among these, it is more preferable to use a nonionic surfactant in consideration of water resistance of the resulting coating film.

  A commercially available product may be used as the (B) polyisocyanate compound having water dispersibility. Commercially available products include AQUANATE 100, AQUANATE 110, AQUANATE 200, and AQUANATE 210 (manufactured by Nippon Polyurethane Industry Co., Ltd.), Bihydur TPLS-2032, SUB-isocyanate L801, Bihjul VPLS-2319, Bihjur 3100, VPLS. -2336 and VPLS-2150 / 1, Bihijoule 305, Bihijoule XP-2655 (manufactured by Sumika Bayer Urethane Co., Ltd.), Takenate WD-720, Takenate WD-725 and Takenate WD-220 (manufactured by Mitsui Takeda Chemical), Resamine D- 56 (manufactured by Dainichi Seika Kogyo Co., Ltd.).

  In this invention, it is more preferable to use what has water dispersibility as (B) polyisocyanate compound. In addition, as a (B) polyisocyanate compound, 1 type may be used independently and 2 or more types may be used in combination.

(C) Hydrophilized modified carbodiimide compound (C) Hydrophilized modified carbodiimide compound contained in the aqueous coating composition of the present invention contains,
-OCONH-X-NHCOOY
[X is a bifunctional organic group containing at least one carbodiimide group, and Y has a structure in which a hydroxyl group is removed from a polyalkylene glycol monoalkyl ether. ]
One or more structural units represented by By having the above structural unit, it is considered that both excellent water dispersibility and excellent curability are obtained.

There are three types of (C) hydrophilized modified carbodiimide compounds: those having one structural unit, those having two structural units, and those having three structural units.
As what has two said structural units, there exists what is represented with the following general formula (I).

  In the above general formula (I), X is a bifunctional organic group containing at least one carbodiimide group, Y is a structure obtained by removing a hydroxyl group from the same or different polyalkylene glycol monoalkyl ether, and Z is It is a structure obtained by removing a hydroxyl group from a bifunctional polyol having a number average molecular weight of 200 to 5,000.

  Further, the above X can be represented by the following general formula (a).

In the general formula (a), R ² is preferably a hydrocarbon group having 6 to 15 carbon atoms. Specific examples include a phenylene group, a diphenylenemethyl group, a diphenylene (dimethyl) methyl group, a methylphenylene group, a dimethylphenylene group, a tetramethylxylylene group, a hexylene group, a cyclohexylene group, and a dicyclohexylenemethyl group. be able to. Preference is given to a dicyclohexylenemethyl group. The p is 1-10. p is the number of carbodiimide groups present in the structural unit, preferably 2 or more from the viewpoint of curability, and more preferably 8 or less.

  In the present specification, the number of repetitions is expressed as an average value, not limited to p.

  Y can be represented by the following general formula (b) or (c).

In the general formulas (b) and (c), R ³ is preferably an alkyl group having 1 to 20 carbon atoms. Specific examples include a methyl group, an ethyl group, a butyl group, a hexyl group, an octyl group, a decyl group, a dodecyl group, and a stearyl group. R ⁴ is a hydrogen atom or a methyl group, and is preferably a hydrogen atom. q is 4-40. In the general formulas (b) and (c), when R ⁴ is hydrogen, the general formulas (b) and (c) show the same structure.

  In addition, said Z is a polymer structure comprised by the ether bond, the ester bond, or the carbonate bond, and it is difficult to formulate. About this, please refer to the description about the bifunctional polyol of the number average molecular weight 200-5,000 mentioned later.

  The (C) hydrophilized modified carbodiimide compound having two structural units has a raw material carbodiimide compound containing at least two isocyanate groups in one molecule, a hydroxyl group at the molecular end, and a number average molecular weight of 200 to 5,000. To the reaction product obtained by reacting the above bifunctional polyol with a molar ratio of the isocyanate group of the raw material carbodiimide compound exceeding the molar amount of the hydroxyl group of the polyol, and further reacting with a polyalkylene glycol monoalkyl ether Can be obtained.

  The raw material carbodiimide compound containing at least two isocyanate groups in the molecule preferably has isocyanate groups at both ends from the viewpoint of reactivity. The method for producing a raw material carbodiimide compound having an isocyanate group at both ends is well known by those skilled in the art, and for example, a condensation reaction involving decarbonization of an organic diisocyanate can be used.

  Specific examples of the organic diisocyanate include aromatic diisocyanates, aliphatic diisocyanates, alicyclic diisocyanates, and mixtures thereof. Specifically, 1,5-naphthylene diisocyanate, 4,4- Diphenylmethane diisocyanate, 4,4-diphenyldimethylmethane diisocyanate, 1,3-phenylene diisocyanate, 1,4-phenylene diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 2,4-tolylene diisocyanate Mixture with 2,6-tolylene diisocyanate, hexamethylene diisocyanate, cyclohexane-1,4-diisocyanate, xylylene diisocyanate, isophorone diisocyanate, dicyclohexylmethane 4,4-diisocyanate, and the like methylcyclohexane diisocyanate, tetramethylxylylene diisocyanate. From the viewpoint of reactivity, dicyclohexylmethane-4,4-diisocyanate is preferable.

  A carbodiimidization catalyst is usually used for the condensation reaction. Specific examples of the carbodiimidization catalyst include 1-phenyl-2-phospholene-1-oxide, 3-methyl-2-phospholene-1-oxide, 1-ethyl-2-phospholene-1-oxide, 3- Examples thereof include phospholene oxides such as methyl-1-phenyl-2-phospholene-1-oxide and isomers of these 3-phospholenes. From the viewpoint of reactivity, 3-methyl-1-phenyl-2-phospholene-1-oxide is preferable.

  Next, the bifunctional polyol having a hydroxyl group at the molecular end is not particularly limited, but the number average molecular weight is preferably 200 to 5,000 from the viewpoint of reaction efficiency. Specific examples of the bifunctional polyol having a hydroxyl group at the molecular terminal include polyether diol, polyester diol, and polycarbonate diol, such as polyethylene glycol, polypropylene glycol, polyethylene propylene glycol, polytetramethylene ether glycol, Polyalkylene glycols such as polyhexamethylene ether glycol and polyoctamethylene ether glycol, polyethylene adipate, polybutylene adipate, polyhexamethylene adipate, polyneopentyl adipate, poly-3-methylpentyl adipate, polyethylene / butylene adipate, polyneopentyl / Polyester diol such as hexyl adipate, polycaprolactone diol, poly-3- Polylactone diols such as chill valerolactone diol, polycarbonate diols such as polyhexamethylene carbonate diol and mixtures thereof and the like can be exemplified.

  The reaction between the raw material carbodiimide compound containing at least two isocyanate groups in one molecule and the bifunctional polyol having a hydroxyl group at the molecular end and a number average molecular weight of 200 to 5,000 is the reaction of the raw material carbodiimide compound. The reaction is carried out at a ratio in which the molar amount of the isocyanate group exceeds the molar amount of the hydroxyl group of the polyol. When the molar amount of the isocyanate group is less than or equal to the molar amount of the hydroxyl group, the reaction of the polyalkylene glycol monoalkyl ether described later cannot be performed sufficiently.

  The ratio between the molar amount of the isocyanate group of the raw material carbodiimide compound and the molar amount of the hydroxyl group of the polyol having a hydroxyl group at the molecular end is from 1.0: 1.1 to 1.0: 2.0 is preferable. In addition, as for the polymerization degree of the raw material carbodiimide compound and the bifunctional polyol which has a hydroxyl group at the molecular terminal in the reaction product obtained by this process, 1-10 are preferable from a viewpoint of reaction efficiency.

  By further reacting the reaction product thus obtained with a polyalkylene glycol monoalkyl ether, a (C) hydrophilized modified carbodiimide compound having two structural units can be obtained. As the polyalkylene glycol monoalkyl ether, those represented by the following general formula (b ′) or (c ′) are used.

In the general formulas (b ′) and (c ′), the contents described in the general formulas (b) and (c) are applied as they are to R ³ , R ⁴ , and q. The type and q of R ^{4 in} the above unit are appropriately set within the above ranges in consideration of storage stability, water dispersibility, and reactivity after water volatilizes. From the viewpoint of water dispersibility, R ³ in the monoalkoxypolyalkylene glycol is preferably a methyl group and R ⁴ is preferably a hydrogen atom. Furthermore, 4-20 are preferable from the viewpoint of water dispersibility and the reactivity after water volatilizes, and 6-12 are more preferable.

  As the polyalkylene glycol monoalkyl ether, a polyalkylene glycol monoalkyl ether having a number average molecular weight of 200 to 5,000 is preferably used. The alkyl group of the polyalkylene glycol monoalkyl ether is preferably an alkyl group having 1 to 20 carbon atoms. Specific examples of the polyalkylene glycol monoalkyl ether include those composed of polyethylene glycol, polypropylene glycol or a mixture thereof having one end blocked with an alkyl group having 1 to 20 carbon atoms. As more detailed specific examples of such polyalkylene glycol monoalkyl ether, for example, polyethylene glycol monomethyl ether, polyethylene glycol mono-2-ethylhexyl ether, polyethylene glycol monolauryl ether having a number average molecular weight of 200 to 5,000, Examples thereof include polypropylene glycol monomethyl ether, polypropylene glycol mono-2-ethylhexyl ether, and polypropylene glycol monolauryl ether.

  The reaction product and the polyalkylene glycol monoalkyl ether are reacted at a ratio in which the molar amount of the isocyanate group of the reaction product is the same as or higher than the molar amount of the hydroxyl group of the polyalkylene glycol monoalkyl ether. When the molar amount of the isocyanate group is less than the molar amount of the hydroxyl group, the reaction of the polyalkylene glycol monoalkyl ether with the reaction product cannot be sufficiently performed. In addition, the molar amount of the isocyanate group of the reaction product may be obtained by direct measurement, or may be a value calculated from the charged composition.

  In the reaction between the raw material carbodiimide compound and the bifunctional polyol having a hydroxyl group at the molecular end, and the reaction between the reaction product and the polyalkylene glycol monoalkyl ether, a catalyst can be used. Although the temperature at the time of the said reaction is not specifically limited, 60-120 degreeC is preferable from a viewpoint of control of a reaction system or reaction efficiency. In the above reaction, it is preferable to use an organic solvent containing no active hydrogen.

  By undergoing such a two-stage reaction, a (C) hydrophilized modified carbodiimide compound having two structural units can be obtained. The (C) hydrophilized modified carbodiimide compound thus produced does not have the structure of the general formula (I) shown above, but various other reaction products derived from the raw materials used. It is a mixture containing. However, in general, it may be regarded as having the structure of the general formula (I).

  Moreover, as said (C) hydrophilization modified carbodiimide compound, what has three said structural units has what is represented by the following general formula (II).

In the general formula (II), the description of X and Y with respect to those having the above two structural units can be applied to X and Y as they are. R ⁰ is hydrogen, a methyl group, or an ethyl group. R ¹ is an alkylene group having 4 or less carbon atoms, and may be the same or different. Specific examples of the alkylene group include a methylene group, an ethylene group, a propylene group, and a butylene group. n is 0 or 1, and m is 0-60.

R ⁰ , R ¹ , n and m are determined by the trifunctional polyol used in producing the (C) hydrophilized modified carbodiimide compound.

  When m is 11 or more, the ratio of the hydrophilic part to the hydrophobic part is preferably 2.0 to 6.3. The ratio of the hydrophilic part to the hydrophobic part can be determined by dividing the molecular weight of the oxymethylene group or oxyethylene group part present in the carbodiimide compound by the molecular weight of the carbodiimide compound.

  The (C) hydrophilized modified carbodiimide compound having three structural units comprises a raw material carbodiimide compound containing at least two isocyanate groups in one molecule, a polyalkylene glycol monoalkyl ether, and an isocyanate group of the raw material carbodiimide compound. Can be obtained by further reacting a trifunctional polyol with the reaction product obtained at a ratio exceeding the equivalent of the hydroxyl group of the polyalkylene glycol monoalkyl ether.

  For the raw material carbodiimide compound containing at least two isocyanate groups in one molecule, the description of the raw material carbodiimide compound of the (C) hydrophilized modified carbodiimide compound having the two structural units is applied as it is.

  Since the reaction between the raw material carbodiimide compound and the polyalkylene glycol monoalkyl ether is further reacted with the trifunctional polyol after the reaction, the isocyanate group needs to remain. For this reason, in the said reaction, the equivalent of an isocyanate group needs to exceed the equivalent of a hydroxyl group, Preferably, it is preferable that the equivalent ratio of an isocyanate group and a hydroxyl group is 2/1. The reaction can usually be carried out under conditions well known to those skilled in the art, and a tin-based catalyst can be used if necessary.

  As the polyalkylene glycol monoalkyl ether, the description of the polyalkylene glycol monoalkyl ether of the (C) hydrophilized modified carbodiimide compound having two structural units is applied as it is.

  Next, the trifunctional polyol is reacted with the reaction product thus obtained. The amount of the trifunctional polyol used in the reaction is preferably such that the hydroxyl equivalent of the reactant is equal to or greater than the isocyanate equivalent, and more preferably the isocyanate equivalent and the hydroxyl equivalent are equal. In addition, the isocyanate equivalent of the said reaction product can also be calculated | required by calculation from the compounding ratio of the diisocyanate compound and polyalkylene glycol monoalkyl ether in a previous process other than measuring directly. The reaction can be carried out in the same manner as the reaction between the raw material carbodiimide compound and the polyalkylene glycol monoalkyl ether.

  The trifunctional polyol is preferably trimethylolpropane, glycerin, or an alkylene oxide adduct thereof from the viewpoint of easy availability. Examples of the alkylene oxide include ethylene oxide and propylene oxide. The alkylene oxide adduct of glycerin is commercially available as a GP series from Sanyo Chemical. In view of the curing reactivity of the resulting three-chain hydrophilic carbodiimide compound, those having a structure in which an alkylene oxide is added to one hydroxyl group are particularly preferred. Among the previous GP series, those having such a structure include GP-250 and GP-3000.

  By undergoing such a two-stage reaction, a (C) hydrophilized modified carbodiimide compound having three structural units can be obtained. The (C) hydrophilized modified carbodiimide compound thus produced does not have the structure of the general formula (II) as described above, but has the structure of the general formula (II). Can be considered as being.

  As said (C) hydrophilization modified carbodiimide compound, what has one said structural unit has what is represented by the following general formula (III).

［Ｘは、少なくとも１個のカルボジイミド基を含有する２官能性有機基であり、Ｙは、同一または異種のポリアルキレングリコールモノアルキルエーテルから水酸基を除いた構造である。］

[X is a bifunctional organic group containing at least one carbodiimide group, and Y has a structure in which a hydroxyl group is removed from the same or different polyalkylene glycol monoalkyl ether. ]

  X in the general formula (III) is a group that can be represented by the formula (a) in the above general formula (I).

  Y in the general formula (III) has a structure in which a hydroxyl group is removed from the same or different polyalkylene glycol monoalkyl ether. This Y can show the same thing as Y in the above-mentioned general formula (I). By using the (C) hydrophilized modified carbodiimide compound represented by the general formula (III), there is an advantage that the crosslinking density is maintained at a higher level. Possible reasons are that the general formula (I) (II) having a plurality of carbodiimide units has a low reaction efficiency with an acid while the acid value of the aqueous resin is low, and the general formula (III) is a general formula (I) Since it does not have a bulky structure as in (II), it does not hinder the crosslinking of the hydroxyl group and isocyanate of the aqueous resin, so that (C) hydrophilization modification represented by the general formula (III) It is thought that the crosslinking density of the carbodiimide compound has increased.

Y in the general formula (III) is preferably the following (i) or (ii):
(I) Structure obtained by removing a hydroxyl group from polyethylene glycol monoalkyl ether in which an alkyl group having 1 to 3 carbon atoms is ether-bonded to the terminal of a polyethylene oxide unit having 6 to 20 repeats (ii) having 4 to 60 repeats A structure obtained by removing a hydroxyl group from a polypropylene glycol monoalkyl ether in which an alkyl group having 1 to 8 carbon atoms is ether-bonded to the end of a polypropylene oxide unit:
More preferably, they are the same or different structures selected from
More preferably, the number of repetitions of the polypropylene oxide unit (ii) is 15 to 60.
By using the (C) hydrophilized modified carbodiimide compound represented by the general formula (III) having the above (i) and (ii), the water dispersibility is excellent, the stability is improved, and the crosslinking density is higher. There is an advantage of being held at the level.

  The (C) hydrophilized modified carbodiimide compound represented by the general formula (III) is a polyalkylene glycol monoalkyl ether which is the same or different from the raw material carbodiimide compound obtained by the above condensation reaction involving decarbonization of organic diisocyanate. Can be prepared by reacting.

The polyalkylene glycol monoalkyl ether is
-Polyethylene glycol monoalkyl ether in which an alkyl group having 1 to 3 carbon atoms is ether-bonded to the terminal of a polyethylene oxide unit having 6 to 20 repeats, or
-Polypropylene glycol monoalkyl ether in which an alkyl group having 1 to 8 carbon atoms is ether-bonded to the end of a polypropylene oxide unit having 4 to 60 repeats,
It is more preferable that In the preparation of the (C) hydrophilized modified carbodiimide compound represented by the general formula (III), these polyethylene glycol monoalkyl ethers and polypropylene glycol monoalkyl ethers may be used alone or in combination.

Specific examples of the polyethylene glycol monoalkyl ether include polyethylene glycol monomethyl ether, polyethylene glycol monoethyl ether, and polyethylene glycol monopropyl ether, with polyethylene glycol monomethyl ether being particularly preferred.
Specific examples of the polypropylene glycol monoalkyl ether include polypropylene glycol monomethyl ether, polypropylene glycol monoethyl ether, polypropylene glycol monobutyl ether, and polypropylene glycol 2-ethylhexyl ether, and polypropylene glycol monobutyl ether is particularly preferable. is there.

In the (C) hydrophilized modified carbodiimide compound represented by the general formula (III), any one Y is (i), the other Y is (ii), and (i) the number of repetitions 6 The structure which remove | excluded the hydroxyl group from the polyethylene glycol monoalkyl ether which the C1-C3 alkyl group ether-bonded to the terminal of -20 polyethylene oxide units, and (ii) The number of repetitions of the polypropylene oxide unit of 4-60 The ratio of the structure obtained by removing the hydroxyl group from the polypropylene glycol monoalkyl ether having an ether bond with an alkyl group having 1 to 8 carbon atoms at the end is (i) :( ii) = 1: 0.7 to 1: 8 More preferably within the range.
In the (C) hydrophilized modified carbodiimide compound represented by the general formula (III), it is preferable that the periphery of the carbodiimide group is somewhat hydrophobic in order to improve water resistance when a coating film is formed. Moreover, in order to suppress the deactivation of carbodiimide by water and maintain stability, it is preferable that the periphery of the carbodiimide group is hydrophobic to some extent and the contact with water molecules is kept low. On the other hand, the carbodiimide compound represented by the general formula (III) needs to have a certain amount of polyethylene glycol structure in order to maintain hydrophilicity. Here, when the structures of (i) and (ii) above exist within the range of (i) :( ii) = 1: 0.7-1: 8, while ensuring the hydrophilicity of the carbodiimide compound On the other hand, hydrophobicity can be maintained to some extent around the carbodiimide group. Thereby, there exists an advantage that the water-based coating composition which was more excellent in low-temperature curability and was excellent also in coating-material stability is obtained. The ratio (i) :( ii) is more preferably in the range of (i) :( ii) = 1: 0.7 to 1: 1.5.

Aqueous coating composition The aqueous coating composition of the present invention comprises (A) an aqueous resin having a hydroxyl group and a carboxyl group, (B) a polyisocyanate compound, and (C) a hydrophilized modified carbodiimide compound.

  In the aqueous coating composition of the present invention, the ratio of the equivalent of the carbodiimide group of the (C) hydrophilized modified carbodiimide compound to the equivalent of the isocyanate group of (B) the polyisocyanate compound is in the range of 0.01 to 0.20. On condition that As described above, the present invention is characterized in that the equivalent of the carbodiimide group is very small relative to the equivalent of the isocyanate group. In the aqueous coating composition of the present invention, the ratio of the equivalent of the carbodiimide group to the equivalent of the isocyanate group is in the range of 0.01 to 0.20, so that the coating obtained can be obtained while ensuring low temperature curability. There is an advantage that the cross-linking density of the film is increased and good coating properties are ensured. The equivalent ratio is more preferably in the range of 0.01 to 0.09.

As described above, the aqueous resin having a hydroxyl group and a carboxyl group (A) used in the present invention has a hydroxyl value of 3 to 15 with respect to the acid value, and the hydroxyl value is higher than the acid value. It is characterized by a great number. And in addition to using such (A) aqueous resin, the ratio of the equivalent of the carbodiimide group which (C) hydrophilization modified carbodiimide compound has with respect to the equivalent of the isocyanate group which (B) polyisocyanate compound has is 0.01- By being in the range of 0.20, it was possible to obtain a coating film having a sufficient crosslinking density while ensuring the coating stability. For example, when the ratio of the equivalent of the carbodiimide group of the (C) hydrophilized modified carbodiimide compound to the equivalent of the isocyanate group of the (B) polyisocyanate compound is simply reduced without using the aqueous resin as described above (A) There is a possibility that the stability of the paint is greatly reduced. This is because (B) the stability of the polyisocyanate compound in the paint is improved by the presence of (C) the hydrophilized modified carbodiimide compound in the aqueous paint composition.
In the present invention, the ratio of the equivalent of the carbodiimide group of the (C) hydrophilized modified carbodiimide compound to the equivalent of the isocyanate group of the (B) polyisocyanate compound is in the range of 0.01 to 0.20, and the amount of the carbodiimide group In addition to being extremely small, (A) an aqueous resin having a hydroxyl value of 3 to 15 with respect to the acid value is used. The aqueous resin (A) used in the present invention has a very high hydroxyl value relative to the acid value. (A) When the hydroxyl value of the aqueous resin is so high, a high crosslink density is achieved in the resulting coating film. In addition, since the acid value of (A) the aqueous resin is low, suppression of undesirable side reactions that can occur between the acid group of (A) the aqueous resin and the isocyanate group of (B) the polyisocyanate compound is achieved.
As described above, in the present invention, by combining the above requirements, a sufficient crosslinking density can be achieved even after the paint is stored. Thereby, the coating film which has sufficient crosslinking density was obtained, ensuring the coating-material stability.

  In the aqueous coating composition of the present invention, the ratio of the equivalent of the isocyanate group of the (B) polyisocyanate compound to the equivalent of the hydroxyl group contained in the (A) aqueous resin is within the range of 0.6 to 1.5. is there. The hydroxyl group of (A) aqueous resin and the isocyanate group of (B) polyisocyanate compound are groups that react with each other. And when the equivalent ratio of these groups is in the above range, there is an advantage that the curing reaction proceeds well even at a low temperature, whereby a coating film having a desired crosslinking density can be obtained.

  In the aqueous coating composition of the present invention, the ratio of the equivalent of the carbodiimide group of the (C) hydrophilized modified carbodiimide compound to the equivalent of the acid group of (A) the aqueous resin is 0.1 to 1.0. As long as it is in the range. This equivalent ratio is preferably in the range of 0.1 to 0.6. As described above, in the aqueous coating composition of the present invention, the acid groups are present in excess in the equivalents of the carbodiimide groups and acid groups that react with each other. Thereby, while the carbodiimide group basically does not remain in the cured coating film to be formed, the acid group remains and there is an advantage that the adhesion of the coating film to the object is improved. .

  In addition to the above components (A) to (C), the water-based coating composition of the present invention includes a pigment, a curing catalyst, a surface conditioner, an antifoaming agent, a pigment dispersant, a plasticizer, and a film-forming aid as necessary. , UV absorbers, antioxidants and the like can be contained. Since the water-based coating composition of the present invention has excellent reactivity at low temperatures, it is preferable to produce it at a painting site. The aqueous coating composition of the present invention can be obtained by mixing the components (A) to (C).

  In the aqueous coating composition of the present invention, since the (C) hydrophilized modified carbodiimide compound is excellent in water dispersibility, the curing agent composition is used even when the water dispersibility of the (B) polyisocyanate compound is not sufficient. By forming the product, the storage stability of the aqueous coating composition can be enhanced.

  Although the resin solid content concentration of the water-based coating composition of the present invention varies depending on the coating conditions, it is generally preferably set to 15 to 60% by mass.

Coating film obtained from aqueous coating composition A coating film can be formed by coating the above-mentioned aqueous coating composition on an article to be coated. The substrate is not particularly limited, and various substrates can be used. Since the aqueous coating composition of the present invention can be cured at a low temperature, it can be applied to a plastic material in addition to a general metal material. Examples of the metal material include an iron plate, a steel plate, and an aluminum plate. Examples of the plastic material include polyurethane, polycarbonate, polybutylene terephthalate, polyamide, polyphenylene oxide, acrylonitrile / butadiene / styrene copolymer (ABS resin), polypropylene, and unsaturated polyester (SMC resin). These base materials may be surface-treated.

  It is preferable to provide the coating film of this invention in a motor vehicle body. A multilayer coating film is usually formed on the surface of an automobile body. This multilayer coating film is composed of an electrodeposition coating film, a first base coating film, a second base coating film, a clear coating film, etc., but the coating film of the present invention contains many urethane bonds and is resistant to chipping. Therefore, it is preferably used as the first base coating film. The first base coating film has the same meaning as the intermediate coating film, and the second base coating film has the same meaning as the colored base coating film. The first base coating film is formed on an electrodeposition coating film or a coating film formed from a primer or a sealer. The formation of the first base coating film is performed by heating the aqueous coating composition of the present invention after electrostatic coating using air spray, airless spray, or the like. It does not specifically limit as a cured film thickness, For example, it can set so that it may become 10-50 micrometers.

  Heating for curing is set according to the heat resistance of the object to be coated. When the object to be coated is an object having high heat resistance such as a metal material, a temperature exceeding 120 ° C. can be applied. On the other hand, in the case of a plastic material having low heat resistance, the heating temperature is preferably 120 ° C. or lower, and more preferably 80 ° C. or lower. The heating time can be appropriately set according to the temperature.

  After applying the aqueous coating composition of the present invention to form an uncured first base coating film, the second base coating for forming the second base coating film is applied without curing the coating film. The so-called wet-on-wet coating can be performed. The aqueous coating composition of the present invention is characterized by having extremely excellent low-temperature curability. Therefore, in normal wet-on-wet coating, the first base coating film is cured even if the second base coating film is formed without performing the preheating treatment required after the first base coating film is formed. Therefore, there exists an advantage that a multilayer coating film can be formed, without accompanying troubles, such as a mixed layer.

  In addition, in the said wet-on-wet coating, after forming a non-hardened 1st base coating film as needed, you may perform the preheating heated at very low temperature. Since the water-based coating composition of the present invention is excellent in low-temperature curability, there is a feature that a part of the curing proceeds by this preheating and an interface that is not mixed by the coating of the second base coating is formed. Thereby, the multilayer coating film excellent in the coating-film external appearance can be obtained.

  The wet-on-wet coating can be performed between the second base coating film and the clear coating film in addition to the first base coating film and the second base coating film. In this case, the formation of the multilayer coating film is called three-wet coating, and after the clear coating for forming the clear coating film is applied, the first base coating film, the second base coating film, and the clear coating film are simultaneously specified. A multilayer coating film is obtained by baking at a temperature of In addition, about the said 2nd base coating material and clear coating material, and those coating, the coating material and coating method well-known to those skilled in the art can be used.

  Examples of other objects that are suitable as objects to be coated with the aqueous coating composition of the present invention include industrial machines and construction machines. Industrial machines and construction machines are generally large in size and can withstand strong loads, and therefore have a feature that the constituent base material (steel plate) is thicker than automobile bodies and the like. Therefore, when such an industrial machine or construction machine is an object to be coated, there is a problem that the heat capacity of the object to be coated is large and heat is not sufficiently transferred to the object to be coated in a heating furnace. One of the characteristics of the aqueous coating composition of the present invention is that it can be cured at a low temperature and that a coating film having a high crosslinking density can be obtained even when cured at a low temperature. Therefore, the water-based coating composition of the present invention is also suitable for coating with industrial machines and construction machinery to be coated, in which the heat capacity of the object to be coated is large and high-temperature heat curing after coating is difficult. Can be used. In the coating using these as a coating object, the aqueous coating composition of the present invention is coated by a coating method usually used by those skilled in the art according to the shape of the coating object, and then, for example, at 50 to 100 ° C. for 10 minutes. The aspect which forms a cured coating film by heating for -2 hours is mentioned.

  EXAMPLES Hereinafter, although a specific Example is given and this invention is demonstrated in detail, this invention is not limited by a following example. Hereinafter, “part” means “part by mass”.

Production Example 1 Production of acrylic emulsion having hydroxyl group and carboxyl group 1,000 parts of deionized water was charged into a reaction vessel equipped with a stirrer, nitrogen introduction tube, temperature controller, condenser, and dropping funnel, and stirred in a nitrogen atmosphere. The temperature was raised to 80 ° C.
103 parts of styrene, 290 parts of n-butyl methacrylate, 280 parts of n-butyl acrylate, 302 parts of hydroxyethyl acrylate, 26 parts of acrylic acid, 3 parts of dodecyl mercaptan and Latemul PD-104 (produced by Kao Corporation, 20 parts) A pre-emulsion obtained by adding 100 parts of deionized water to 1,000 parts of deionized water was added dropwise over 2 hours together with an initiator aqueous solution in which 3 parts of ammonium persulfate was dissolved in 300 parts of deionized water.
After completion of the dropwise addition, the reaction was further continued at 80 ° C. for 1 hour and then cooled, and 8.2 parts of N, N-dimethylaminoether was added to obtain an acrylic emulsion having a resin solid content of 30% by mass. The hydroxyl value in terms of resin solid content of this acrylic emulsion calculated from the monomer composition was 130 mgKOH / g, and the acid value was 20 mgKOH / g. Moreover, the number average molecular weight by the GPC measurement after the water removal of the acrylic resin in the obtained acrylic emulsion was 45,000.

Production Example 2 Production of Acrylic Emulsion Having Hydroxyl Group and Carboxyl Group The amount of monomers in the monomer mixture of Production Example 1 was changed to 90 parts of styrene, 249 parts of n-butyl acrylate, 403 parts of n-butyl methacrylate, and hydroxyethyl 232 acrylate. , 26 parts of acrylic acid, and 3 parts of dodecyl mercaptan were polymerized in the same manner, and then 8.2 parts of N, N-dimethylaminoethanol was added to obtain an acrylic emulsion having a resin solid content of 30% by mass. . The hydroxyl value in terms of resin solid content of this acrylic emulsion calculated from the monomer composition was 100 mgKOH / g, and the acid value was 20 mgKOH / g. Moreover, the number average molecular weight by GPC measurement after the water removal of the acrylic resin in the obtained acrylic emulsion was 43,000.

Production Example 3 Production of Acrylic Water Dispersion Having Hydroxyl Group and Carboxyl Group Into a reaction vessel equipped with a stirrer, nitrogen introduction tube, temperature controller, condenser, and dropping funnel, 712 parts of 2-methoxy-1-propanol was charged, and nitrogen was added. The temperature was raised to 120 ° C. with stirring under an atmosphere.
A monomer mixture of 50 parts of styrene, 20 parts of 2-ethylhexyl acrylate, 122 parts of 2-ethylhexyl methacrylate, 426 parts of n-butyl methacrylate and 182 parts of hydroxyethyl methacrylate was added to Kayaester O (Tert made by Kayaku Akzo). -Butyl peroxy-2-ethylhexanate) was added dropwise over 1.5 hours together with an initiator solution in which 160 parts of 2-methoxy-1-propanol was dissolved.
After completion of dropping, the mixture is kept at 120 ° C. for 1 hour, and then a monomer mixture of 50 parts of n-butyl methacrylate, 119 parts of hydroxyethyl methacrylate and 31 parts of acrylic acid, and 6 parts of Kayaester O are added to 2-methoxy-1-propanol. It dropped over 1 hour with the initiator solution melt | dissolved in 40 parts.
After the completion of the dropwise addition, the mixture was kept at 120 ° C. for 0.5 hours, and then an initiator solution in which 3 parts of Kayaester O was dissolved in 55 parts of 2-methoxy-1-propanol was added dropwise over 0.5 hours. The mixture was further stirred at 120 ° C. for 1 hour to obtain an acrylic resin having a resin solid content of 50% by mass and a number average molecular weight of 6,000 as measured by GPC.
After distilling off the solvent by heating under reduced pressure, 39 parts of N, N-dimethylaminoethanol was added, and then 1206 parts of deionized water was further added and stirred to disperse the acrylic resin in a water content of 45% by mass. Got the body. Calculated from the monomer composition, the hydroxyl value in terms of resin solid content of this acrylic water dispersion was 130 mgKOH / g, and the acid value was 24 mgKOH / g.

Production Example 4 Production of Polyester Aqueous Dispersion Having Hydroxyl Group and Carboxyl Group In a reaction vessel equipped with a stirrer, nitrogen introduction tube, temperature controller, condenser and decanter, 250 parts of trimethylolpropane, 824 parts of adipic acid, cyclohexanedicarboxylic acid 635 parts were added, the temperature was raised to 180 ° C., and the condensation reaction was carried out until no water was distilled off. After cooling to 60 ° C., 120 parts of phthalic anhydride was added, the temperature was raised to 140 ° C., and this was maintained for 60 minutes to obtain a polyester resin having a number average molecular weight of 2,000 by GPC measurement. By adding 59 parts of dimethylaminoethanol (equivalent to 80% of the acid value of resin (neutralization rate 80%)) at 80 ° C., and further adding 1920 parts of deionized water, the resin solid content of 45% by mass was added. A polyester aqueous dispersion was obtained. The hydroxyl value in terms of resin solid content of this polyester aqueous dispersion was 90 mgKOH / g, and the acid value was 35 mgKOH / g.

Production Example 5 Production of Hydrophilized Modified Carbodiimide Compound (1) 700 parts of 4,4-dicyclohexylmethane diisocyanate and 7 parts of 3-methyl-1-phenyl-2-phospholene-1-oxide were reacted at 170 ° C. for 7 hours, A carbodiimide compound having three carbodiimide groups per molecule and having isocyanate groups at both ends of the structure represented by the general formula (a) was obtained.
Next, 180 parts of 4,4-dicyclohexylmethanecarbodiimide having an isocyanate terminal was added to PTMG-1000 (a polytetramethylene glycol having a number average molecular weight of 1,000 manufactured by Mitsubishi Chemical Corporation, and a tetramethylene calculated from the number average molecular weight. Oxide repeat unit 13.6) 95 parts and dibutyltin dilaurate 0.2 part were added and heated to 85 ° C. and held for 2 hours.
Subsequently, 86.4 parts of methyl polyglycol 130 (polyethylene glycol monomethyl ether manufactured by Nippon Emulsifier Co., Ltd., ethylene oxide repeat number 9 calculated from a hydroxyl value of 130 mgKOH / g) was added and kept at 85 ° C. for 3 hours. The reaction was terminated after confirming that the NCO peak had disappeared by IR measurement, and after cooling to 60 ° C., deionized water was added to the hydrophilized modified carbodiimide compound (1) having a resin solid content of 40% by mass. An aqueous dispersion was obtained. The resulting hydrophilized modified carbodiimide compound was a compound represented by the above general formula (I).

Production Example 6 Production of Hydrophilic Modified Carbodiimide Compound (2) In 90 parts of 4,4-dicyclohexylmethane carbodiimide having an isocyanate terminal produced in Production Example 5, 120 parts of polypropylene glycol monobutyl ether having an average of 19 repeats and methyl polyglycol 130. 43.2 parts and 0.07 part dibutyltin dilaurate were added and kept at 80 ° C. until there was no NCO absorption by IR. After cooling to 60 ° C., deionized water was added to obtain an aqueous dispersion of the hydrophilic modified carbodiimide compound (2) having a resin solid content of 25%. The resulting hydrophilized modified carbodiimide compound was a compound represented by the above general formula (III).
The ratio of (i) the structure obtained by removing the hydroxyl group from polyethylene glycol monoalkyl ether and (ii) the structure obtained by removing the hydroxyl group from polypropylene glycol monoalkyl ether in the resulting hydrophilized modified carbodiimide compound is (i): (Ii) = 1.0: 1.0.

Production Example 7 Production of Hydrophilic Modified Carbodiimide Compound (3) 393 parts of 4,4-dicyclohexylmethane diisocyanate and 8 parts of 3-methyl-1-phenyl-2-phospholene-1-oxide were reacted at 180 ° C. for 16 hours. A carbodiimide compound having four carbodiimide groups per molecule and having an isocyanate group at both ends of the structure represented by the formula was obtained. To this, 130 parts of polyethylene glycol monomethyl ether having a repeating number of oxyethylene groups of 9 and 0.2 part of dibutyltin dilaurate were added, heated at 90 ° C. for 2 hours, and the end of the structure represented by the following formula was A carbodiimide compound which is an isocyanate group and a hydrophilic group was obtained. Furthermore, 300 parts of GP-3000 (a trivalent polyol having a structure in which propylene oxide was added in an average of 17 moles to three hydroxyl groups of glycerin manufactured by Sanyo Chemical Industries, Ltd.) were added and reacted at 90 ° C. for 6 hours. . It was confirmed by IR measurement that the NCO peak had disappeared, and the reaction was terminated to obtain a hydrophilic modified carbodiimide compound (3). Deionized water was added thereto and stirred to obtain an aqueous dispersion of a hydrophilic modified carbodiimide compound (3) having a resin solid content of 30% by mass. The resulting hydrophilized modified carbodiimide compound was a compound represented by the above general formula (II).

Production Example 8 Color Pigment Paste Production Dispersant “Disperbyk 190” (manufactured by Big Chemie) 9.2 parts, ion-exchanged water 17.2 parts, rutile titanium dioxide 73.0 parts premixed, paint conditioner The bead medium was added thereto, and the mixture was dispersed at room temperature until the particle size became 5 μm or less, and the bead medium was removed by filtration to obtain a colored pigment paste.

Production Example 9 Production of Comparative Acrylic Water Dispersion In a reaction vessel equipped with a stirrer, nitrogen introducing tube, temperature control device, condenser, and dropping funnel,
161 parts of 2-methoxy-1-propanol and 239 parts of dipropylene glycol monomethyl ether were charged, and the temperature was raised to 120 ° C. while stirring in a nitrogen atmosphere.
A monomer mixture of 100 parts of styrene, 545 parts of ethyl acrylate, 125 parts of methyl methacrylate, 145 parts of hydroxyethyl acrylate, and 85 parts of methacrylic acid was added to Kayaester O (tert-butylperoxy-2-ethyl produced by Kayaku Akzo Corporation). 20 parts of hexanate) was added dropwise over 3 hours together with an initiator solution dissolved in 100 parts of dipropylene glycol monomethyl ether.
After the completion of dropping, after maintaining at 120 ° C. for 0.5 hour, as an after-shot, an initiator solution in which 3 parts of Kayaester O was further dissolved in 50 parts of dipropylene glycol monomethyl ether was dropped over 0.5 hours, The mixture was stirred at 120 ° C. for 1 hour to obtain an acrylic resin having a resin solid content of 64% by mass and a number average molecular weight of 9,000 by GPC measurement.
After 161 parts of the solvent was distilled off by heating under reduced pressure, 71 parts of N, N-dimethylaminoethanol (corresponding to 100% of the amount of carboxyl groups of the resin) was added, and further 1872 parts of deionized water was added and stirred By doing this, an acrylic resin aqueous dispersion having a resin solid content of 30% by mass was obtained. Calculated from the monomer composition, the hydroxyl value in terms of resin solid content of this acrylic aqueous solution was 70 mgKOH / g, and the acid value was 55.5 mgKOH / g.

Production Example 10 Production of Comparative Acrylic Emulsion The amount of monomer in the monomer mixture of Production Example 1 was changed to 103 parts of styrene, 305 parts of n-butyl acrylate, 219 parts of n-butyl methacrylate, 302 parts of hydroxyethyl acrylate, and acrylic acid. Polymerization was carried out in the same manner except that the content was changed to 71 parts and 2.5 parts of dodecyl mercaptan, respectively, and then 22 parts of N, N-dimethylaminoethanol was added to obtain an acrylic emulsion having a resin solid content of 30% by mass. Calculated from the monomer composition, the hydroxyl value in terms of resin solid content of this acrylic emulsion was 130 mgKOH / g, and the acid value was 55.5 mgKOH / g. Moreover, the number average molecular weight by the GPC measurement after the water removal of the acrylic resin in the obtained acrylic emulsion was 42,000.

Example 1 Production of water-based coating composition (1) 100 parts of the acrylic emulsion obtained in Production Example 1 were mixed with Bihydur 305 (polyisocyanate compound having an ethylene oxide group manufactured by Sumika Bayer Urethane Co., Ltd., ethylene oxide content: 20). (Mass%, isocyanate group content: 16 mass%) 22 parts are added with stirring, and further, 7 parts of an aqueous dispersion of the hydrophilized modified carbodiimide compound (1) obtained in Production Example 5 is added and stirred. A water-based paint composition was obtained. The following evaluation was performed about the obtained water-based coating composition. The results are shown in Table 1.

<Water resistance>
On the test plate subjected to electrodeposition coating, coating was performed by air spray coating so that the dry film thickness was 30 μm, and baking was performed at 80 ° C. for 25 minutes for drying. Next, the test plate on which the coating film was formed was immersed in a water bath at 40 ° C. for 10 days, and then the presence or absence of occurrence of coating film abnormality (bullet) was confirmed visually. This visual evaluation is shown as “film abnormality” in the following table. In addition, one hour after pulling up from the water tank, a 2 mm square grid cut (10 × 10) is made with a cutter knife, and a cellophane tape is applied and peeled off to perform an adhesion test. I counted the number. This evaluation is shown as “adhesiveness” in the following table. In this “adhesiveness” evaluation, the smaller the number of peeled, the better the water resistance.

<Paint stability>
After preparing the aqueous coating composition, it was allowed to stand at room temperature, and the time until a non-flowable lump was formed in the coating liquid or the time until the entire coating liquid was lost was measured. Those exceeding 6 hours are acceptable.

<Crosslink density>
The coating composition just prepared in the examples and comparative examples was air spray-coated on a polypropylene plate so as to have a dry film thickness of 30 μm. After heating this plate at 80 ° C. for 25 minutes, the coating film was peeled off from the polypropylene plate to obtain a free film. The resulting free film was measured for crosslink density by vibron DDV-II-EA type (dynamic viscoelasticity measuring instrument manufactured by Toyo Baldwin, test condition: frequency 11 Hz, temperature rise 2 ° C./min). The crosslink density measured here is shown as “initial crosslink density” in the following table.
The initial crosslink density is evaluated to be 1.0 mmol / cc or higher, and more preferably 1.5 mmol / cc or higher.

<Crosslinking density retention>
A free film was prepared in the same manner as described above using the coating composition after being prepared in Examples and Comparative Examples and allowed to stand at room temperature for 6 hours. The crosslink density of the obtained free film was measured in the same manner as described above. The crosslink density measured here is shown as “6H post-crosslink density” in the table below.
Crosslinking density retention (%) is expressed by the following formula: “6H post-crosslinking density” / “initial crosslinking density” × 100
Calculated by
A crosslinking density retention rate of 80% or more is evaluated as acceptable, and 95% or more is more preferable.

<Pot life>
The pot life of the obtained aqueous coating composition was evaluated based on the crosslink density retention rate. A case where the value of the crosslink density retention rate (%) was 80% or more was evaluated as acceptable. When the crosslink density retention rate reached 80% or more after 6 hours, it was indicated as “pot life> 6H”.

Examples 2 to 10 Production of aqueous coating compositions (2) to (10) Aqueous coating compositions were obtained in the same manner as in Examples, except that the formulations shown in Table 1 were used. Each evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.

Example 11 Production of Aqueous Coating Composition (11) While stirring 74 parts of the color pigment paste obtained in Production Example 8 in a mixed solution of 85 parts of the acrylic emulsion of Production Example 1 and 10 parts of the acrylic dispersion of Production Example 3. After the addition, 22 parts of bihijoule 305 and 7 parts of an aqueous dispersion of the hydrophilized modified carbodiimide compound (2) obtained in Production Example 6 were added and stirred to obtain an aqueous coating composition. Various evaluations were performed in the same manner as in Example 1.
The crosslinking density was 3.5 mmol / cc, and the crosslinking density retention after 6 hours was 97%. The coating stability was also secured for 6 hours or more, and no problem was seen in water resistance.

Example 12 Production of aqueous coating composition (12) An aqueous coating composition was obtained by the same procedure except that the acrylic dispersion of Example 11 was changed to the polyester dispersion obtained in Production Example 4. Various evaluations were performed in the same manner as in Example 1.
The crosslink density was 3.3 mmol / cc, and the crosslink density retention after 6 hours was 91%. The coating stability was also secured for 6 hours or more, and no problem was seen in water resistance.

Comparative Examples 1 to 5 Production of Comparative Aqueous Coating Compositions (1) to (5) A comparative aqueous coating composition was obtained in the same manner as in Example 1 except that the formulation shown in Table 2 was used. It was. Various evaluations were performed in the same manner as in the examples. The results are shown in Table 2.

As shown in the above Examples, it was confirmed that the aqueous coating composition of the present invention was able to obtain a coating film having a high crosslink density by baking and drying at 80 ° C. after being applied to an object. Thus, since a coating film has a high crosslinking density, it is excellent in a weather resistance, and becomes excellent in the chipping property and the adhesiveness with respect to strong force. And the coating film formed using the obtained aqueous coating material composition also had favorable water resistance. In addition, it was confirmed that the water-borne coating composition obtained had a sufficiently long pot life of 6 hours or more, despite being a low-temperature curable coating composition.
In the aqueous coating composition of Comparative Example 1, the ratio of the equivalent of the carbodiimide group of (C) the hydrophilized modified carbodiimide compound to the equivalent of the isocyanate group of (B) the polyisocyanate compound exceeds 0.20, This is an example in which the ratio of the equivalent of the carbodiimide group of the (C) hydrophilized modified carbodiimide compound to the equivalent of the acid group exceeds 1.0. In the aqueous coating composition of Comparative Example 1, it was confirmed that the obtained coating film had a low crosslinking density of less than 1. When the crosslink density of the coating is less than 1, there may be a coating failure such as peeling of the coating when a strong force is applied.
The aqueous coating composition of Comparative Example 2 is an example in which (C) a hydrophilized modified carbodiimide compound is not included. In the aqueous coating composition of Comparative Example 2, it was confirmed that a non-fluid lump was generated after 2 hours at room temperature after production. Further, after 6 hours, the entire coating composition was gelled and could not be applied.
The aqueous coating composition of Comparative Example 3 is an example in which (B) polyisocyanate compound is not included. It was confirmed that the coating film obtained using the aqueous coating composition of Comparative Example 3 has extremely low water resistance.
The aqueous coating composition of Comparative Example 4 is an example in which (A) the hydroxyl value in terms of resin solid content of the aqueous resin is less than 80 mgKOH / g, and the ratio of the hydroxyl value to the acid value is less than 3. In the aqueous coating composition of Comparative Example 4, it was confirmed that the resulting coating film had a low crosslink density of less than 1. When the crosslink density of the coating is less than 1, there may be a coating failure such as peeling of the coating when a strong force is applied. This Comparative Example 4 shows that when the hydroxyl value of the (A) aqueous resin is low, a sufficient crosslinking density cannot be obtained.
The aqueous coating composition of Comparative Example 5 is an example in which (A) the acid value in terms of resin solid content of the aqueous resin exceeds 40 mgKOH / g, and the ratio of the hydroxyl value to the acid value is less than 3. In the aqueous coating composition of Comparative Example 5, it was confirmed that the resulting coating film had a low crosslink density of less than 1. Furthermore, at the time when 2 hours passed at room temperature after production, the generation of lumps having no fluidity was confirmed. Further, after 6 hours, the entire coating composition was gelled and could not be applied. As shown in Comparative Example 5, when the acid value of (A) the aqueous resin is high and the ratio of the hydroxyl value to the acid value is less than 3, it can be seen that the coating stability is significantly reduced. .

Example 13 Formation Method of Multi-layer Coating Film After coating the aqueous coating composition obtained in Example 10 on a steel sheet subjected to electrodeposition coating using an air spray under a condition of a dry film thickness of 30 μm, 10 Setting for a minute. Here, an aqueous metallic base paint AR-2000 manufactured by Nippon Paint Co., Ltd. was applied by air spray, preheated at 80 ° C. for 3 minutes, and then a two-component urethane curable clear paint was applied. After coating, baking was performed at 80 ° C. to obtain a multilayer coating film. When the appearance of the obtained multilayer coating film was visually evaluated, no abnormality was found. Further, when the water resistance test was carried out, there was no abnormality in the appearance of the coating film, the adhesion was 0/100, no peeling, and good results were obtained. Furthermore, the chipping resistance evaluation shown below did not result in peeling reaching the substrate, and good results were obtained.

<Chipping resistance>
The paint plate was installed in the gravel tester so that the stone blown from the nozzle hits the paint plate perpendicularly. After the coated plate was cooled to −20 ° C., 100 g of No. 7 crushed stone (basalt) was sprayed onto the coated plate with 0.3 MPa air. The painted plate after the test was visually evaluated according to the following criteria.
○: Peeling reaching the substrate is not observed Δ: Peeling reaching the substrate is slightly recognized ×: Peeling reaching the substrate is often observed

  The water-based coating composition of the present invention has excellent coating performance and coating properties that achieve excellent coating stability in a low-temperature curable aqueous coating composition and that the resulting coating film has a high crosslinking density. The membrane performance is achieved. The water-based paint composition of the present invention is a case where a plastic material having low heat resistance, an industrial machine / construction machine, etc., in which the heat capacity of the object to be coated is large and high-temperature heat-curing treatment after coating is difficult to be coated Has a feature that a coating film having an excellent crosslinking density can be formed.

Claims (7)

(A) an aqueous resin having a hydroxyl group and a carboxyl group,
(B) a polyisocyanate compound, and
(C) a hydrophilized modified carbodiimide compound,
An aqueous coating composition comprising:
The aqueous resin having a hydroxyl group and a carboxyl group (A) has a hydroxyl value of 80 to 200 mgKOH / g and an acid value of 10 to 40 mgKOH / g in terms of resin solid content,
The ratio of the hydroxyl value to the acid value of the aqueous resin (A) is 3 to 15,
The ratio of the equivalent of the carbodiimide group of the (C) hydrophilized modified carbodiimide compound to the equivalent of the isocyanate group of the (B) polyisocyanate compound is 0.01 to 0.20,
The (C) hydrophilized modified carbodiimide compound is represented by the following general formula (I), (II) or (III):
The ratio of the equivalent of the isocyanate group of the (B) polyisocyanate compound to the equivalent of the hydroxyl group contained in the (A) aqueous resin is 0.6 to 1.5,
The ratio of the equivalent of the carbodiimide group of the (C) hydrophilized modified carbodiimide compound to the equivalent of the acid group of the (A) aqueous resin is 0.1 to 1.0.
Water-based paint composition.

[X is a bifunctional organic group containing at least one carbodiimide group, Y is a structure obtained by removing a hydroxyl group from the same or different polyalkylene glycol monoalkyl ether, and Z is a number average molecular weight of 200. It is the structure remove | excluding the hydroxyl group from -5,000 bifunctional polyol. ]

[X is a bifunctional organic group containing at least one carbodiimide group, Y is a structure obtained by removing a hydroxyl group from the same or different polyalkylene glycol monoalkyl ether, and R ⁰ is a hydrogen or methyl group. Or an ethyl group, R ¹ is an alkylene group having 4 or less carbon atoms, n is 0 or 1, and m is 0-60. ]

[X is a bifunctional organic group containing at least one carbodiimide group, and Y has a structure in which a hydroxyl group is removed from the same or different polyalkylene glycol monoalkyl ether. ] The ratio of the equivalent of the carbodiimide group of the (C) hydrophilized modified carbodiimide compound to the equivalent of the isocyanate group of the (B) polyisocyanate compound is 0.01 to 0.09.
The water-based coating composition according to claim 1. The ratio of the equivalent of the carbodiimide group of the (C) hydrophilized modified carbodiimide compound to the equivalent of the acid group of the (A) aqueous resin is 0.1 to 0.6.
The water-based coating composition according to claim 1 or 2. The aqueous coating composition according to any one of claims 1 to 3, wherein the (A) aqueous resin includes an acrylic emulsion having a number average molecular weight of 10,000 to 80,000. The water-based coating composition in any one of Claims 1-4 whose (C) hydrophilization modified carbodiimide compound represented by the said formula (III) is the following compound.

[X is a bifunctional organic group containing at least one carbodiimide group, and Y is the following (i) or (ii):
(I) a structure in which a hydroxyl group is removed from polyethylene glycol monoalkyl ether in which an alkyl group having 1 to 3 carbon atoms is ether-bonded to a terminal of a polyethylene oxide unit having 6 to 20 repeating units;
(Ii) Structure in which a hydroxyl group is removed from polypropylene glycol monoalkyl ether in which an alkyl group having 1 to 8 carbon atoms is ether-bonded to the terminal of a polypropylene oxide unit having 4 to 60 repeats:
It is the same or different structure selected from. ] In the (C) hydrophilized modified carbodiimide compound represented by the formula (III), any one Y is (i) and the other Y is (ii), and
The ratio of the structures (i) and (ii) is within the range of (i) :( ii) = 1: 0.7-1: 8,
The aqueous coating composition according to claim 5. The coating film obtained by coating the water-based coating composition in any one of Claims 1-6.