Water-based resin crosslinking agent, water-based resin crosslinking agent-containing liquid, water-based resin composition, cured film, and article

Abstract

Provided is a crosslinking agent for water-compatible resins which is capable of giving liquids containing said crosslinking agent and having excellent storage stability and cured films (water-compatible-resin coating films) having a sufficiently high gloss (mirror surface glossiness). The crosslinking agent for water-compatible resins comprises polycarbodiimide compound (A) and polycarbodiimide compound (B), wherein the polycarbodiimide compound (A) has a structure in which isocyanate groups at both ends have been respectively blocked with hydrophilic organic compounds, at least one of the hydrophilic organic compounds having a molecular weight exceeding 350, and the polycarbodiimide compound (B) has a structure in which isocyanate groups at both ends have been respectively blocked with compounds represented by formula (1) having a molecular weight of 250 or lower, the amount of the polycarbodiimide compound (A) being 5-95 parts by mass per 100 parts by mass of the sum of the polycarbodiimide compound (A) and the polycarbodiimide compound (B).　Formula (1): R1(OCHR2CH2)mOH (In formula (1), R1 is an alkyl group having 1-13 carbon atoms, a cycloalkyl group, or an aryl group, R2 is a hydrogen atom or a methyl, ethyl, or propyl group, and m is a number of 1-4.)

Description

Technical Field

[0001] The present invention relates to a carbodiimide-based aqueous resin crosslinking agent, an aqueous resin crosslinking agent-containing liquid containing the aqueous resin crosslinking agent and an aqueous resin composition, a cured film formed by the aqueous resin composition, and an article having the cured film formed thereon.

Background Art

[0002] Aqueous resins having water solubility or water dispersibility are excellent in handleability from the viewpoints of the environment and safety, and are therefore used in various applications such as paints, inks, fiber treatment agents, adhesives, and coating agents. In order to impart water solubility or water dispersibility to the resin itself, hydrophilic groups such as hydroxyl groups and carboxyl groups are introduced into the aqueous resin. Therefore, aqueous resins tend to be inferior to oil-based resins in terms of water resistance and durability. Therefore, in order to improve various physical properties such as water resistance, durability, and strength of the aqueous resin, a crosslinking agent is added to the aqueous resin.

[0003] As an example of such a crosslinking agent, polycarbodiimide compounds are known. For example, Patent Document 1 describes that when two polycarbodiimide compounds containing a polycarbodiimide compound having a predetermined hydrophilic group at the terminal are mixed at a predetermined ratio and coexist with an aqueous resin, excellent storage stability is obtained, and even when they coexist for a long period of time, a crosslinking performance is maintained. An aqueous resin crosslinking agent is obtained.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In recent years, with the expansion of various applications of aqueous resins, various physical properties corresponding to the applications have been required for the cured products of aqueous resins. For example, in the application of synthetic leather, the cured product (coating film) of an aqueous resin may have a low gloss (specular glossiness), and a cured product (coating film) of an aqueous resin with a sufficiently high gloss (specular glossiness) has been required.

[0006] In response to such requirements, the present inventors focused on the above-mentioned carbodiimide-based crosslinking agent having excellent storage stability, and repeatedly studied to improve the physical properties of the cured product (coating film) of the aqueous resin, and found an aqueous resin crosslinking agent capable of obtaining a cured product (coating film) of an aqueous resin with a sufficiently high gloss (specular glossiness).

[0007] An object of the present invention is to provide an aqueous resin crosslinking agent, an aqueous resin crosslinking agent-containing liquid and an aqueous resin composition containing the same, a cured film (aqueous resin coating film) having a sufficiently high gloss (specular glossiness), and an article formed with the cured film, which can obtain an aqueous resin crosslinking agent-containing liquid and an aqueous resin composition having excellent storage stability (pot life).

Means for Solving the Problems

[0008] The present invention is based on the finding that, in an aqueous resin crosslinking agent, by using a mixture of specific polycarbodiimide compounds, an aqueous resin crosslinking agent-containing liquid and an aqueous resin composition having excellent storage stability (pot life), and a cured film (aqueous resin coating film) having a sufficiently high gloss (specular glossiness) can be obtained.

[0009] The present invention provides the following means. An aqueous resin crosslinking agent containing a polycarbodiimide compound (A) and a polycarbodiimide compound (B), wherein the polycarbodiimide compound (A) has a structure in which the isocyanate groups at both ends are each blocked with a hydrophilic organic compound, at least one of the hydrophilic organic compounds has a molecular weight exceeding 350, the polycarbodiimide compound (B) has a structure in which the isocyanate groups at both ends are each blocked with a compound having a molecular weight of 250 or less represented by the following formula (1), and the polycarbodiimide compound (A) is 5 to 95 parts by mass in a total of 100 parts by mass of the polycarbodiimide compound (A) and the polycarbodiimide compound (B). R 1 (OCHR 2 CH2) m OH ···(1) (In formula (1), R 1 is an alkyl group, cycloalkyl group or aryl group having 1 to 13 carbon atoms. R 2 is a hydrogen atom, methyl group, ethyl group, or propyl group, and m is a number from 1 to 4.) [2] The aqueous resin crosslinking agent according to [1] above, wherein the hydrophilic organic compound having a molecular weight exceeding 350 is a compound represented by the following formula (A). R 1 (OCHR 2 CH2) n OH (A) (In formula (A), R 1 is an alkyl group, cycloalkyl group or aryl group having 1 to 20 carbon atoms. R 2 is a hydrogen atom or a methyl group, ethyl group, propyl group, and n is a number from 1 to 30.) [3] The aqueous resin crosslinking agent according to [2] above, wherein R 1 in formula (A) is a methyl group and R 2 is a hydrogen atom. [4] The aqueous resin crosslinking agent according to any one of [1] to [3] above, wherein the hydrophilic organic compound has a molecular weight of 400 or more. [5] The aqueous resin crosslinking agent according to any one of [1] to [4] above, wherein m in formula (1) is 4. [6]An aqueous resin crosslinking agent-containing liquid containing the aqueous resin crosslinking agent according to any one of [1] to [5] above and an aqueous medium. [7]The aqueous resin crosslinking agent-containing liquid according to [6] above, wherein the aqueous medium is water or a mixed solvent of water and a hydrophilic solvent. [8]The aqueous resin crosslinking agent-containing liquid according to [7] above, further containing a surfactant. [9]The crosslinking agent-containing liquid for an aqueous resin according to [8] above, wherein the surfactant is an anionic surfactant.

[10] The crosslinking agent-containing liquid for an aqueous resin according to [9] above, wherein the anionic surfactant is at least one selected from alkylbenzene sulfonates, alkyl sulfates, and sodium N-cocoyl methyl taurine.

[11] An aqueous resin composition containing the aqueous resin crosslinking agent according to any one of [1] to [5] above and an aqueous resin.

[12] The aqueous resin composition according to

[11] above, wherein the aqueous resin has a group selected from a carboxy group, an amino group, and a hydroxy group.

[13] The aqueous resin composition according to

[11] or

[12] above, wherein the aqueous resin is at least one selected from polyester resins, acrylic resins, polyurethane resins, epoxy resins, styrene-acrylic resins, melamine resins, polyolefin resins, and fluororesins.

[14] The aqueous resin composition according to any one of

[11] to

[13] above, which is used as an adhesive, a fiber treating agent, a coating agent, an ink, a paint, or an adhesive.

[15] The aqueous resin composition according to any one of

[11] to

[13] above, which is for wet-on-wet coating.

[16] A cured film formed from the aqueous resin composition according to any one of

[11] to

[15] above.

[17] An article in which the cured film according to

[16] above is formed on a substrate.

Advantages of the Invention

[0010] According to the present invention, an aqueous resin crosslinking agent-containing liquid and an aqueous resin composition excellent in storage stability (pot life) can be obtained, and a cured film (aqueous resin coating film) having a sufficiently high gloss (specular glossiness) can be obtained. An aqueous resin crosslinking agent, an aqueous resin crosslinking agent-containing liquid and an aqueous resin composition containing the aqueous resin crosslinking agent, a cured film formed by the aqueous resin composition, and an article having the cured film formed thereon can be provided. [Embodiments for Carrying Out the Invention]

[0011] Hereinafter, the aqueous resin crosslinking agent of the present invention, an aqueous resin crosslinking agent-containing liquid and an aqueous resin composition containing the aqueous resin crosslinking agent, a cured film formed by the aqueous resin composition, and an article having the cured film formed thereon will be described in detail. In the present invention, "aqueous" means having solubility or dispersibility in an aqueous medium. Further, the "aqueous medium" refers to water and / or a hydrophilic solvent. Further, the "polycarbodiimide compound" refers to a compound having two or more carbodiimide groups.

[0012] [Aqueous Resin Crosslinking Agent] The aqueous resin crosslinking agent of the present invention contains a polycarbodiimide compound (A) and a polycarbodiimide compound (B), and the polycarbodiimide compound (A) is 5 to 95 parts by mass in a total of 100 parts by mass of both (A) and (B). That is, the aqueous resin crosslinking agent contains two types of polycarbodiimide compounds, (A) and (B). By using an aqueous resin crosslinking agent having such a composition, an aqueous resin crosslinking agent-containing liquid and an aqueous resin composition excellent in storage stability (pot life), and a cured film (aqueous resin coating film) having a sufficiently high gloss (specular glossiness) can be obtained. Furthermore, by using an aqueous resin crosslinking agent having such a composition, a cured film (aqueous resin coating film) excellent in solvent resistance and interlayer adhesion when forming a multilayer coating film can be obtained.

[0013] (Polycarbodiimide Compound (A)) The polycarbodiimide compound (A) is a polycarbodiimide compound having a structure in which the isocyanate groups at both ends are each blocked by a hydrophilic organic compound, and at least one of the hydrophilic organic compounds has a molecular weight of more than 350.

[0014] <Hydrophilic organic compound> The hydrophilic organic compound preferably has one or more functional groups reactive with an isocyanate group and has one or more heteroatoms in the structure other than the functional group. Examples of the functional group include a hydroxyl group, a primary amino group, a secondary amino group, an epoxy group, an isocyanate group, and a carboxyl group. That is, the hydrophilic organic compound more preferably has any one of the functional groups selected from a hydroxyl group, a primary amino group, a secondary amino group, an epoxy group, an isocyanate group, and a carboxyl group and has one or more heteroatoms in the structure other than the functional group.

[0015] The hydrophilic organic compound is preferably a compound selected from monoamines, monoisocyanates, monoalcohols, monoepoxides, and monocarboxylic acids. More preferably, it is a monoalcohol or monoamine having one hydroxyl group, primary amino group, or secondary amino group as the functional group at the end of the molecular chain and having one or more heteroatoms in the structure other than the functional group. The monoalcohol or monoamine may have an anionic group and / or a cationic group.

[0016] Examples of the hydrophilic organic compound include polyoxyalkylene monoalkyl ether, monohydroxy polyester, monohydroxyalkyl sulfonate, dialkylamino alcohol, hydroxycarboxylic acid alkyl ester, dialkylaminoalkyl amine, polyoxyalkylene monoamine, polyoxyalkylene diamine, polyoxyalkylene glycol, and the like. Among these, polyoxyalkylene monoalkyl ether, monohydroxy polyester, monohydroxyalkyl sulfonate, dialkylamino alcohol, hydroxycarboxylic acid alkyl ester, dialkylaminoalkyl amine, and polyoxyalkylene monoamine are preferable, and polyoxyalkylene monoalkyl ether is more preferable.

[0017] Specific examples of the hydrophilic organic compound include a compound represented by the following formula (A). R 1 (OCHR 2 CH2) n OH (A)

[0018] In formula (A), R 1 is an alkyl group, cycloalkyl group, or aryl group having 1 to 20 carbon atoms, preferably 1 to 10 carbon atoms, more preferably 1 to 5 carbon atoms, and examples thereof include methyl group, ethyl group, propyl group, isopropyl group, n-butyl group, s-butyl group, isobutyl group, t-butyl group, cyclohexyl group, phenyl group, and the like. R 1 is preferably an alkyl group having 1 to 4 carbon atoms. Examples of the alkyl group having 1 to 4 carbon atoms include methyl group, ethyl group, propyl group, isopropyl group, n-butyl group, s-butyl group, isobutyl group, and t-butyl group, and from the viewpoint of improving the gloss of the good coating film of the polycarbodiimide compound (A), a methyl group is preferable. R 2 is a hydrogen atom, methyl group, ethyl group, or propyl group, preferably a hydrogen atom or a methyl group, more preferably a hydrogen atom. n is a number from 1 to 30, and from the perspective of the good hydrophilicity of the polycarbodiimide compound (A), it is preferably from 7 to 30, more preferably from 8 to 20. In addition, the compound represented by the formula (A) may be an aggregate of molecules having different numbers of oxyalkylene groups (OCHR 2 CH2). In this case, the average value of the number of oxyalkylene groups in each molecule is taken as n.

[0019] Specific examples of the polyoxyalkylene monoalkyl ether represented by the formula (A) include polyethylene glycol monomethyl ether (R 1 : methyl group, R 2 : hydrogen atom), polyethylene glycol monoethyl ether (R 1 : ethyl group, R 2 : hydrogen atom), polypropylene glycol monomethyl ether (R 1 : methyl group, R 2 : methyl group), polypropylene glycol monoethyl ether (R 1 : ethyl group, R 2 : methyl group), polypropylene glycol monophenyl ether (R 1 : phenyl group, R 2 : methyl group), etc. Polyoxyalkylene monoalkyl ethers, polyoxyalkylene monophenyl ethers, etc. are mentioned. From the perspectives of handleability, availability, and the good hydrophilicity of the polycarbodiimide compound (A), etc., polyethylene glycol monomethyl ether is particularly preferred.

[0020] In addition, the hydrophilic organic compound is preferably a polyoxyalkylene glycol in which R 1 is a hydrogen atom or a hydroxyalkyl group in the formula (A).

[0021] In addition, when the hydrophilic organic compound is a polyoxyalkylene monoalkyl ether or a polyoxyalkylene glycol, as the hydrophilic organic compound, the polyoxyalkylene group [(OCHR 2 CH2) nIt may also have a structure such as a block copolymer or a random copolymer of polyethylene glycol and polypropylene glycol.

[0022] Specific examples of the monohydroxyalkyl sulfonate include compounds represented by the following formula (B). HOR 3 SO3M (B)

[0023] In formula (B), R 3 is an alkylene group having 1 to 10 carbon atoms, and specific examples include a methylene group, an ethylene group, a propylene group, a tetramethylene group, a pentamethylene group, a hexamethylene group, a heptamethylene group, an octamethylene group, a nonamethylene group, a decamethylene group, and the like. M is an alkali metal atom, preferably Na or K.

[0024] Specific examples of the dialkylamino alcohol include compounds represented by the following formula (C). R 4 2NCH2CHR 5 OH (C)

[0025] In formula (C), R 4 is an alkyl group having 1 to 4 carbon atoms, and specific examples include a methyl group, an ethyl group, a propyl group, an isopropyl group, an n-butyl group, an s-butyl group, an isobutyl group, and a t-butyl group. R 5 is a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. Specific examples of the alkyl group include a methyl group, an ethyl group, a propyl group, an isopropyl group, an n-butyl group, an s-butyl group, an isobutyl group, and a t-butyl group.

[0026] Specific examples of the dialkylamino alcohol represented by formula (C) include N,N-dimethylisopropanolamine, N,N-diethylisopropanolamine, and the like.

[0027] Examples of the hydroxycarboxylic acid alkyl ester specifically include compounds represented by the following formula (D). R 6 OCOCHR 7 OH (D)

[0028] In formula (D), R 6 is an alkyl group having 1 to 3 carbon atoms, and examples thereof include a methyl group, an ethyl group, a propyl group, and an isopropyl group. R 7 is a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, and examples of the alkyl group include a methyl group, an ethyl group, a propyl group, and an isopropyl group.

[0029] Specific examples of the hydroxycarboxylic acid alkyl ester represented by formula (D) include methyl glycolate, methyl lactate, and the like.

[0030] Examples of the dialkylaminoalkylamine specifically include compounds represented by the following formula (E). R 8 2-N-R 9 -NH2(E)

[0031] In formula (E), R 8 is an alkyl group having 1 to 4 carbon atoms, and specifically includes a methyl group, an ethyl group, a propyl group, an isopropyl group, an n-butyl group, an s-butyl group, an isobutyl group, and a t-butyl group. R 9 is an alkylene group having 1 to 4 carbon atoms, and examples thereof include a methylene group, an ethylene group, a propylene group, a tetramethylene group, and the like.

[0032] Examples of the polyoxyalkylene monoamine or polyoxydiamine specifically include compounds represented by the following formula (F). R 10 (OCHR 11 CH2) n OR 12 (F)

[0033] In formula (F), R 10is an alkyl group or aminoalkyl group having 1 to 4 carbon atoms. Specific examples of the alkyl group include a methyl group, an ethyl group, a propyl group, an isopropyl group, an n-butyl group, an s-butyl group, an isobutyl group, and a t-butyl group. R 11 is a hydrogen atom or an alkylene group having 1 to 4 carbon atoms. Specific examples of the alkylene group having 1 to 4 carbon atoms include a methylene group, an ethylene group, a propylene group, a tetramethylene group, and the like. R 12 is an aminoalkyl group having 1 to 4 carbon atoms. Specific examples of the aminoalkyl group include an aminomethyl group, an aminoethyl group, an aminopropyl group, an aminoisopropyl group, an amino-n-butyl group, an amino-s-butyl group, an isoaminobutyl group, and an amino-t-butyl group. n is a number from 1 to 30, which is the same as n in formula (A). Regarding the polyoxyalkylene monoamine or polyoxyalkylene diamine of formula (F), the polyoxyalkylene group [(OCHR 11 CH2) n in formula (F) may have a structure such as a block copolymer or a random copolymer of polyethylene glycol and polypropylene glycol, similar to the polyoxyalkylene group [(OCHR 2 CH2) n in formula (A).

[0034] As the hydrophilic organic compound, among the compounds represented by the above formulas (A) to (F), from the viewpoint of good hydrophilicity of the polycarbodiimide compound (A), the polyoxyalkylene monoalkyl ether represented by formula (A) is preferable. When using a polyoxyalkylene monoalkyl ether in which n is 7 to 30 in formula (A) as the hydrophilic organic compound, it is also preferable to use it in combination with one or more compounds selected from a polyoxyalkylene monoalkyl ether in which n is less than 7 in formula (A), a dialkylamino alcohol represented by formula (C), and a hydroxycarboxylic acid alkyl ester represented by formula (D).

[0035] The polycarbodiimide compound (A) has a structure in which the isocyanate groups at both ends are each blocked by a hydrophilic organic compound, and the hydrophilic organic compound for blocking at least one end isocyanate group has a molecular weight exceeding 350. For at least one end, since the hydrophilic organic compound as the end-capping agent has a molecular weight exceeding 350, the storage stability (pot life) of the aqueous resin cross-linking agent-containing liquid containing the polycarbodiimide compound (A) can be improved. From the viewpoint of better hydrophilicity, it is preferable that the end-capping agents at both ends are both hydrophilic organic compounds with a molecular weight exceeding 350.

[0036] From the viewpoint of good storage stability of the polycarbodiimide compound (A), the molecular weight of the hydrophilic organic compound is preferably 400 or more. Also, from the viewpoint of maintaining good hydrophilicity of the hydrophilic organic compound, it is preferably 3200 or less. As the hydrophilic organic compound with a molecular weight exceeding 350, a polyoxyalkylene monoalkyl ether represented by the formula (A) is preferable. From the viewpoint of storage stability, a polyoxyalkylene monoalkyl ether with a molecular weight of 450 to 600 is more preferable. For example, for both ends of the polycarbodiimide compound (A), it is preferable that the hydrophilic organic compound as the end-capping agent is the same or different polyoxyalkylene monoalkyl ethers with n being 7 to 30 and a molecular weight exceeding 350 in the formula (A). Also, it is preferable that the hydrophilic organic compound as the end-capping agent at one end of the polycarbodiimide compound (A) is a polyoxyalkylene monoalkyl ether with n being 7 to 30 and a molecular weight exceeding 350 in the formula (A), and the hydrophilic organic compound as the end-capping agent at the other end is a polyoxyalkylene monoalkyl ether with m being less than 7 and a molecular weight of 350 or less in the formula (A).

[0037] The hydrophilic organic compound may be used alone or in combination of two or more thereof. That is, the polycarbodiimide (A) may be capped with the same hydrophilic organic compound at both ends or with different hydrophilic organic compounds. From the viewpoint of ease of production, it is preferably a single hydrophilic organic compound.

[0038] <Method for Producing Polycarbodiimide Compound (A)> The method for producing the polycarbodiimide compound (A) is not particularly limited and can be carried out using a known production method. For example, the synthesis methods shown in the following (a1) to (a3) can be mentioned. (a1) A method in which a diisocyanate compound (Da) is subjected to a carbodiimidization reaction in the presence of a catalyst to obtain an isocyanate-terminated polycarbodiimide compound, and then a hydrophilic organic compound (end-capping agent) is added to carry out an end-capping reaction (a2) A method in which a diisocyanate compound (Da) and a hydrophilic organic compound (end-capping agent) are mixed and a carbodiimidization reaction and an end-capping reaction are carried out in the presence of a catalyst (a3) A method in which a diisocyanate compound (Da) and a hydrophilic organic compound (end-capping agent) are reacted to carry out an end-capping reaction of the isocyanate group, and then a carbodiimidization reaction is carried out in the presence of a catalyst Among these synthesis methods, from the viewpoints of controlling the degree of polymerization of the carbodiimide group and production efficiency, etc., the methods of (a1) or (a3) are preferred.

[0039] The diisocyanate compound (Da) used in the production of the polycarbodiimide compound (A) is not particularly limited and may be any of a chain or alicyclic aliphatic diisocyanate compound, an aromatic diisocyanate compound, or a heterocyclic diisocyanate compound, and these may be used alone or in combination of two or more. Examples of the chain aliphatic diisocyanate compound include tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, dodecamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, lysine diisocyanate, and the like. Examples of the alicyclic diisocyanate compound include 1,3-bis(isocyanatomethyl)cyclohexane, 1,4-bis(isocyanatomethyl)cyclohexane, 2,2-bis(4-isocyanatocyclohexyl)propane, isophorone diisocyanate, dicyclohexylmethane-4,4'-diisocyanate, and the like. Examples of the aromatic diisocyanate compound include tolylene diisocyanate, diphenylmethane diisocyanate, 2,4,6-triisopropylbenzene-1,3-diyl diisocyanate, and the like. Examples of the aliphatic diisocyanate compound containing an aromatic ring include xylylene diisocyanate, 1,3-bis(2-isocyanato-2-propyl)benzene (common name: tetramethylxylylene diisocyanate), and the like. Among these, as the diisocyanate compound (Da), from the viewpoints of easy availability, good storage stability of the aqueous resin crosslinking agent, etc., it is preferably a diisocyanate compound having an alicyclic or aromatic ring. Specifically, preferably dicyclohexylmethane-4,4'-diisocyanate, isophorone diisocyanate, 4,4'-diphenylmethane diisocyanate, tetramethylxylylene diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, tetramethylene diisocyanate, tolylene diisocyanate, more preferably tetramethylxylylene diisocyanate, dicyclohexylmethane-4,4'-diisocyanate, and particularly preferably dicyclohexylmethane-4,4'-diisocyanate.

[0040] The carbodiimidization reaction is preferably, for example, polymerization (decarboxylation condensation reaction) in the presence of a carbodiimidization catalyst of the diisocyanate compound (Da) (see U.S. Patent No. 2941956, Japanese Patent Publication No. 47-33279, J. Org. Chem. 28, p.2069-2075 (1963), Chemical Review 1981, Vol.81, No.4, p.619-621, etc.). Examples of the carbodiimidation catalyst include phospholene oxides such as 1-phenyl-2-phospholene-1-oxide, 3-methyl-1-phenyl-2-phospholene-1-oxide, 1-ethyl-2-phospholene-1-oxide, 3-methyl-2-phospholene-1-oxide, and 3-phospholene isomers thereof. Among these, 3-methyl-1-phenyl-2-phospholene-1-oxide is preferred from the viewpoints of reactivity and availability. The amount of the carbodiimidation catalyst used is usually preferably 0.01 to 10 parts by mass, more preferably 0.05 to 5 parts by mass, and even more preferably 0.07 to 1 part by mass with respect to 100 parts by mass of the diisocyanate compound (Da).

[0041] The decarboxylative condensation reaction of the diisocyanate compound can be carried out either in a solvent or without a solvent. Examples of the solvent used include alicyclic ethers such as tetrahydrofuran, 1,3-dioxane, and dioxolane; aromatic hydrocarbons such as benzene, toluene, xylene, and ethylbenzene; halogenated hydrocarbons such as chlorobenzene, dichlorobenzene, trichlorobenzene, perchlorene, trichloroethane, and dichloroethane; and cyclohexanone. These may be used alone or in combination of two or more. When the reaction is carried out in a solvent, the concentration of the diisocyanate compound (Da) is preferably 5 to 80% by mass, more preferably 10 to 60% by mass, from the viewpoint of homogenization of the reaction system.

[0042] The reaction temperature of the decarboxylative condensation reaction is appropriately set according to appropriate reaction promotion, the degree of polymerization of the carbodiimide group, etc. Usually, it is preferably 40 to 250 °C, more preferably 90 to 230 °C, and even more preferably 100 to 200 °C. When the reaction is carried out in a solvent, the temperature is preferably within the range of 40 °C to the boiling point of the solvent. Also, the reaction time is appropriately set according to the reaction temperature, the degree of polymerization of the carbodiimide group, etc. Usually, it is preferably 0.5 to 100 hours, more preferably 1 to 70 hours, and even more preferably 2 to 30 hours. Further, it is preferable to carry out the reaction in an inert gas atmosphere such as nitrogen gas or noble gas.

[0043] In the polycarbodiimide compound (A), the degree of polymerization of the carbodiimide group is not particularly limited, but from the viewpoint of suppressing gelation of the aqueous resin crosslinking agent in an aqueous medium, it is preferably 2 to 20, more preferably 3 to 15. In addition, the "degree of polymerization of the carbodiimide group" in this specification refers to the number of carbodiimide groups generated by the carbodiimidization reaction.

[0044] The terminal blocking reaction can be carried out, for example, in the method of (a1) above, by heating the isocyanate-terminated polycarbodiimide compound and the hydrophilic organic compound (terminal blocking agent). The reaction temperature of the terminal blocking reaction is appropriately set within a range that can suppress side reactions and promote the reaction. Usually, it is preferably 50 to 250 °C, more preferably 90 to 220 °C, and still more preferably 130 to 200 °C. In addition, the reaction time is appropriately set within a range that can suppress the reaction temperature and side reactions. Usually, it is preferably 0.1 to 20 hours, more preferably 0.5 to 10 hours, and still more preferably 0.5 to 5 hours. For example, the polycarbodiimide compound (A) can be obtained by heating the isocyanate-terminated polycarbodiimide compound to 50 to 200 °C, preferably 100 to 180 °C, then adding the hydrophilic organic compound, and reacting at 80 to 200 °C for 0.5 to 5 hours.

[0045] (Polycarbodiimide compound (B)) The polycarbodiimide compound (B) has a structure in which the isocyanate groups at both ends are each blocked by a compound represented by the following formula (1) and having a molecular weight of 250 or less. R 1 (OCHR 2 CH2) m OH (1) In formula (1), R 1is an alkyl group, cycloalkyl group or aryl group having 1 to 13 carbon atoms, preferably 1 to 10 carbon atoms, more preferably 1 to 5 carbon atoms, and examples thereof include a methyl group, ethyl group, propyl group, isopropyl group, n-butyl group, s-butyl group, isobutyl group, t-butyl group, cyclohexyl group, phenyl group and the like. R 1 is preferably an alkyl group having 1 to 4 carbon atoms. Examples of the alkyl group having 1 to 4 carbon atoms include a methyl group, ethyl group, propyl group, isopropyl group, n-butyl group, s-butyl group, isobutyl group, and t-butyl group, and from the viewpoint of improving the gloss of a good coating film of the polycarbodiimide compound (B), a methyl group is preferred. R 2 is a hydrogen atom, methyl group, ethyl group, or propyl group, preferably a hydrogen atom or methyl group, more preferably a hydrogen atom. m is a number from 1 to 4. When the compound represented by the above formula (1) has a molecular weight exceeding 250, its hydrophilicity increases and the pot life decreases. Note that the compound represented by formula (1) may be an aggregate of molecules having different numbers of oxyalkylene groups (OCHR 2 CH2). In this case, the average value of the number of oxyalkylene groups in each molecule is taken as m. Also, the compound represented by the above formula (1) is preferably a compound represented by the following formula (1-1). H3C(OCH2CH2) m OH ···(1-1) (In formula (1-1), m is an integer from 1 to 4.)

[0046] The diisocyanate compound (Db) used in the production of the polycarbodiimide compound (B) is the same as the diisocyanate compound (Da) used in the production of the polycarbodiimide compound (A), but the preferred embodiment of the diisocyanate compound (Db) is different from that of the diisocyanate compound (Da). Specifically, preferably dicyclohexylmethane-4,4'-diisocyanate, isophorone diisocyanate, 4,4'-diphenylmethane diisocyanate, tetramethylxylylene diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, tetramethylene diisocyanate, tolylene diisocyanate, more preferably dicyclohexylmethane-4,4'-diisocyanate, tetramethylxylylene diisocyanate, isophorone diisocyanate, m-xylylene diisocyanate, hexamethylene diisocyanate, tolylene diisocyanate, even more preferably dicyclohexylmethane-4,4'-diisocyanate, tetramethylxylylene diisocyanate, isophorone diisocyanate, m-xylylene diisocyanate, even more preferably dicyclohexylmethane-4,4'-diisocyanate, tetramethylxylylene diisocyanate, isophorone diisocyanate, even more preferably dicyclohexylmethane-4,4'-diisocyanate, tetramethylxylylene diisocyanate, and particularly preferably dicyclohexylmethane-4,4'-diisocyanate.

[0047] <Compound represented by formula (1)> Examples of the compound represented by formula (1) include tetraethylene glycol monomethyl ether (R 1 : methyl group, R 2 : hydrogen atom, m = 4, molecular weight 208), tetraethylene glycol monoethyl ether (R 1 : ethyl group, R 2 : hydrogen atom, m = 4, molecular weight 222), tetraethylene glycol monopropyl ether (R 1 : propyl group or isopropyl group, R 2 : hydrogen atom, m = 4, molecular weight 236), triethylene glycol monomethyl ether (R 1 : methyl group, R 2 : hydrogen atom, m = 3, molecular weight 164), triethylene glycol monoethyl ether (R 1 : ethyl group, R 2: Hydrogen atom, m = 3, molecular weight 178), triethylene glycol monopropyl ether (R 1 : Propyl group or isopropyl group, R 2 : Hydrogen atom, m = 3, molecular weight 192), triethylene glycol monobutyl ether (R 1 : n-butyl group, s-butyl group, isobutyl group or t-butyl group, R 2 : Hydrogen atom, m = 3, molecular weight 206), triethylene glycol monobenzyl ether (R 1 : Benzyl group, R 2 : Hydrogen atom, m = 3, molecular weight 240), diethylene glycol monomethyl ether (R 1 : Methyl group, R 2 : Hydrogen atom, m = 2, molecular weight 120), diethylene glycol monoethyl ether (R 1 : Ethyl group, R 2 : Hydrogen atom, m = 2, molecular weight 134), diethylene glycol monopropyl ether (R 1 : Propyl group or isopropyl group, R 2 : Hydrogen atom, m = 2, molecular weight 148), diethylene glycol monobutyl ether (R 1 : n-butyl group, s-butyl group, isobutyl group or t-butyl group, R 2 : Hydrogen atom, m = 2, molecular weight 162), monoethylene glycol monomethyl ether (R 1 : Methyl group, R 2 : Hydrogen atom, m = 1, molecular weight 76), monoethylene glycol monoethyl ether (R 1 : Ethyl group, R 2 : Hydrogen atom, m = 1, molecular weight 90), monoethylene glycol monopropyl ether (R 1 : Propyl group or isopropyl group, R 2 : Hydrogen atom, m = 1, molecular weight 104), monoethylene glycol monobutyl ether (R 1 : n-butyl group, s-butyl group, isobutyl group or t-butyl group, R 2 : Hydrogen atom, m = 1, molecular weight 118), monoethylene glycol monophenyl ether (R 1 : Phenyl group, R 2: Hydrogen atom, m = 1, molecular weight 138), monoethylene glycol monobenzyl ether (R 1 : Benzyl group, R 2 : Hydrogen atom, m = 1, molecular weight 152), monoethylene glycol monolauryl ether (R 1 : Lauryl group, R 2 : Hydrogen atom, m = 1, molecular weight 230), tripropylene glycol monomethyl ether (R 1 : Methyl group, R 2 : Methyl group, m = 3, molecular weight 206), tripropylene glycol monoethyl ether (R 1 : Ethyl group, R 2 : Methyl group, m = 3, molecular weight 220), tripropylene glycol monopropyl ether (R 1 : Propyl group or isopropyl group, R 2 : Methyl group, m = 3, molecular weight 234), dipropylene glycol monomethyl ether (R 1 : Methyl group, R 2 : Methyl group, m = 2, molecular weight 148), dipropylene glycol monoethyl ether (R 1 : Ethyl group, R 2 : Methyl group, m = 2, molecular weight 162), dipropylene glycol monopropyl ether (R 1 : Propyl group or isopropyl group, R 2 : Methyl group, m = 2, molecular weight 176), dipropylene glycol monoisopropyl ether (R 1 : Isopropyl group, R 2 : Methyl group, m = 2, molecular weight 176), dipropylene glycol monobutyl ether (R 1 : n-Butyl group, s-butyl group, isobutyl group or t-butyl group, R 2 : Methyl group, m = 2, molecular weight 190), monopropylene glycol monomethyl ether (R 1 : Methyl group, R 2 : Methyl group, m = 1, molecular weight 90), monopropylene glycol monoethyl ether (R 1 : Ethyl group, R 2 : Methyl group, m = 1, molecular weight 104), monopropylene glycol monopropyl ether (R 1: A propyl group or an isopropyl group, R 2 : A methyl group, m = 1, molecular weight 118), monopropylene glycol monobutyl ether (R 1 : An n-butyl group, an s-butyl group, an isobutyl group or a t-butyl group, R 2 : A methyl group, m = 1, molecular weight 132), monobutylene glycol monomethyl ether (2-methoxy-1-butanol) (R 1 : A methyl group, R 2 : An ethyl group, m = 1, molecular weight 104), monobutylene glycol monoethyl ether (R 1 : An ethyl group, R 2 : An ethyl group, m = 1, molecular weight 118), monobutylene glycol monopropyl ether (R 1 : A propyl group or an isopropyl group, R 2 : An ethyl group, m = 1, molecular weight 132), monobutylene glycol monobutyl ether (R 1 : An n-butyl group, an s-butyl group, an isobutyl group or a t-butyl group, R 2 : An ethyl group, m = 1, molecular weight 146), etc. may be mentioned. These may be used alone or in combination of two or more. Among these, tetraethylene glycol monomethyl ether (R 1 : A methyl group, R 2 : A hydrogen atom, m = 4, molecular weight 208) is preferable.

[0048] When tetraethylene glycol monomethyl ether (formula (1), R 1 : A methyl group, R 2 : A hydrogen atom, m = 4, molecular weight 208) is used as the terminal blocking agent, in the molecule of the polycarbodiimide compound (B), the concentration of the carbodiimide group that becomes a crosslinking point with respect to the aqueous resin is suppressed from decreasing, and a good crosslinking action can be obtained. Also, the storage stability (pot life) of the aqueous resin crosslinking agent-containing liquid containing the polycarbodiimide compound (B) can be improved, and a cured film (aqueous resin coating film) with improved solvent resistance can be obtained without a decrease in the gloss of the coating film.

[0049] The polycarbodiimide compound (B) is a more hydrophobic polycarbodiimide compound with lower hydrophilicity than the polycarbodiimide compound (A). The monoalcohol compound preferably has one hydroxyl group as a functional group that reacts with an isocyanate group and has no hydrophilic group other than the functional group.

[0050] The polycarbodiimide compound (B) has a structure in which the isocyanate groups at both ends are blocked with a compound (ethylene glycol monomethyl ether) represented by the formula (1).

[0051] The compound (ethylene glycol monomethyl ether) represented by the formula (1) may be used alone or in combination of two or more. That is, the polycarbodiimide (B) may be blocked with the same compound (ethylene glycol monomethyl ether) at both ends or with different compounds (ethylene glycol monomethyl ether). From the viewpoint of ease of production, it is preferably one kind of compound (ethylene glycol monomethyl ether).

[0052] <Method for Producing Polycarbodiimide Compound (B)> The method for producing the polycarbodiimide compound (B) is not particularly limited and can be carried out using a known production method. For example, the synthesis methods shown in the following (b1) to (b3) can be mentioned. (b1) A method in which a diisocyanate compound (Db) is subjected to a carbodiimidization reaction in the presence of a catalyst to obtain an isocyanate-terminated polycarbodiimide compound, and then a compound (ethylene glycol monomethyl ether) (end-capping agent) represented by the formula (1) is added to carry out an end-capping reaction (b2) A method in which a diisocyanate compound (Db) and a compound (ethylene glycol monomethyl ether) (end-capping agent) represented by the formula (1) are mixed, and a carbodiimidization reaction and an end-capping reaction are carried out in the presence of a catalyst (b3) A method in which a diisocyanate compound (Db) and a compound represented by the formula (1) (ethylene glycol monomethyl ether) (terminal blocking agent) are reacted to carry out a terminal blocking reaction of isocyanate groups, and then a carbodiimidization reaction is carried out in the presence of a catalyst Among these synthesis methods, from the viewpoints of controlling the degree of polymerization of carbodiimide groups and production efficiency, etc., the method of (b1) or (b3) is preferable.

[0053] The carbodiimidization reaction and the terminal blocking reaction can be carried out in the same manner as the synthesis method of the polycarbodiimide compound (A). Note that since the reactivity varies depending on the type of raw material compound, the reaction conditions are appropriately adjusted according to the type of raw material compound.

[0054] In the polycarbodiimide compound (B), the degree of polymerization of the carbodiimide group is not particularly limited, but from the viewpoint of good storage stability etc. when the aqueous resin crosslinking agent coexists with an aqueous medium or an aqueous resin, it is preferably 2 to 20, more preferably 3 to 15, still more preferably 5 to 7.

[0055] (Content of polycarbodiimide compound (A) and polycarbodiimide compound (B)) In the aqueous resin crosslinking agent, the content of the polycarbodiimide compound (A) in a total of 100 parts by mass of the polycarbodiimide compound (A) and the polycarbodiimide compound (B) is 5 to 95 parts by mass, preferably 15 to 85 parts by mass, more preferably 20 to 80 parts by mass, still more preferably 30 to 60 parts by mass.

[0056] In the aqueous resin crosslinking agent, the polycarbodiimide compound (A) is a polycarbodiimide compound with high hydrophilicity, and the polycarbodiimide compound (B) is a polycarbodiimide compound with low hydrophilicity and higher hydrophobicity. Therefore, it is considered that the aqueous resin crosslinking agent is in a mode in which the polycarbodiimide compound (A) disperses the polycarbodiimide compound (B) in the aqueous medium. The polycarbodiimide compound (A) contributes to the affinity with the aqueous medium and plays a role of making it easy to uniformly add the aqueous resin crosslinking agent to the aqueous resin. On the other hand, the polycarbodiimide compound (B) can exhibit a stronger crosslinking action on the aqueous resin than the polycarbodiimide compound (A). Therefore, it is presumed that the aqueous resin crosslinking agent can obtain a cured film (aqueous resin coating film) with a sufficiently high gloss (specular glossiness).

[0057] When the content of the polycarbodiimide compound (A) in a total of 100 parts by mass of the polycarbodiimide compound (A) and the polycarbodiimide compound (B) is less than 5 parts by mass, the affinity of the aqueous resin crosslinking agent with the aqueous medium becomes insufficient, and good storage stability cannot be obtained when coexisting with the aqueous medium or the aqueous resin. Also, the crosslinking action on the aqueous resin is not sufficiently exerted, and a cured film (aqueous resin coating film) with improved solvent resistance cannot be obtained. On the other hand, when the content exceeds 95 parts by mass, the affinity of the aqueous resin crosslinking agent with the aqueous medium is too large, and when coexisting with the aqueous medium or the aqueous resin, the viscosity tends to increase or gelation tends to occur, and good storage stability cannot be obtained. Also, in this case, the crosslinking action on the aqueous resin is not sufficiently exerted, and a cured film (aqueous resin coating film) with improved solvent resistance cannot be obtained.

[0058] (Other components) In addition to the polycarbodiimide compound (A) and the polycarbodiimide compound (B), the aqueous resin crosslinking agent may contain a solvent and additives such as an antioxidant, an ultraviolet absorber, and an antifoaming agent, as long as the effects of the present invention are not impaired. In this case, from the viewpoint of sufficiently exerting the crosslinking action by the aqueous resin crosslinking agent, the total content of the polycarbodiimide compound (A) and the polycarbodiimide compound (B) in the aqueous resin crosslinking agent is preferably 85% by mass or more, more preferably 90% by mass or more, and still more preferably 95% by mass or more.

[0059] (Method for producing aqueous resin crosslinking agent) The aqueous resin crosslinking agent can be produced by stirring and mixing the polycarbodiimide compound (A), the polycarbodiimide compound (B), and, if necessary, other components such as additives. Further, an aqueous medium may be used during the mixing, and the aqueous resin crosslinking agent may be produced in advance as an aqueous resin crosslinking agent-containing liquid described later. The method of stirring and mixing for obtaining the aqueous resin crosslinking agent is not particularly limited, and can be carried out by a known method using, for example, a rotating blade or a magnetic stirrer. The conditions such as the temperature and time during mixing vary depending on the types of the polycarbodiimide compound (A) and the polycarbodiimide compound (B), but from the viewpoint of efficiently and uniformly mixing, it is preferably mixed at 60 to 200 °C for 1 to 48 hours, for example.

[0060] [Aqueous resin crosslinking agent-containing liquid] The aqueous resin crosslinking agent-containing liquid of the present invention contains the aqueous resin crosslinking agent and an aqueous medium. By keeping the aqueous resin crosslinking agent as a liquid containing the same, it becomes easy to uniformly add and mix it with the aqueous resin to be crosslinked, and the handleability can be made excellent.

[0061] The concentration of the aqueous resin crosslinking agent in the aqueous resin crosslinking agent-containing liquid is appropriately determined from viewpoints such as handleability when uniformly adding and mixing it with the aqueous resin, and efficiency of the crosslinking reaction, etc., but is preferably 10 to 100% by mass, more preferably 20 to 80% by mass, still more preferably 30 to 50% by mass.

[0062] (Aqueous medium) As the aqueous medium, a medium capable of uniformly dissolving or dispersing each contained component in the aqueous resin crosslinking agent is used, and examples include water and hydrophilic solvents such as alcohols, ethers, ketones, esters, etc. These may be used alone or in combination of two or more. Among these, it is preferably water or a mixed solvent of water and a hydrophilic solvent, and from viewpoints such as environmental consideration and cost, it is preferably only water. Examples of the alcohols include methanol, isopropanol, n-butanol, 2-ethylhexyl alcohol, ethylene glycol, propylene glycol, etc. Examples of the ethers include ethylene glycol monohexyl ether, 3-methoxy-3-methylbutanol, tetrahydrofuran, etc. Examples of the ketones include methyl isobutyl ketone, cyclohexanone, isophorone, acetylacetone, etc. Examples of the esters include ethylene glycol monoethyl ether acetate, ethylene glycol monobutyl ether acetate, etc.

[0063] (Surfactant) The aqueous resin crosslinking agent-containing liquid may contain a surfactant. By using a surfactant, the polycarbodiimide compound (A) and the polycarbodiimide compound (B) can be uniformly dissolved or dispersed in the aqueous medium, and the storage stability of the aqueous resin crosslinking agent-containing liquid can be further improved. Also, the surfactant can contribute to improving the solvent resistance of the cured product of the aqueous resin.

[0064] When the surfactant is contained in the aqueous resin crosslinking agent-containing liquid, its content is preferably 0.1 to 20 parts by mass, more preferably 0.2 to 10 parts by mass, still more preferably 0.3 to 8 parts by mass, based on 100 parts by mass in total of the polycarbodiimide compound (A) and the polycarbodiimide compound (B), from the viewpoints of sufficient improvement effects on the storage stability of the aqueous resin crosslinking agent-containing liquid and the aqueous resin composition using the same, improvement effects on the solvent resistance of the cured product of the aqueous resin, etc.

[0065] As the surfactant, an anionic surfactant or a nonionic surfactant is preferable, and more preferably an anionic surfactant, from the viewpoints of the storage stability of the aqueous resin crosslinking agent-containing liquid and the aqueous resin composition using the same, and the compatibility with the aqueous resin. One of these may be used alone, or two or more thereof may be used in combination. Examples of the anionic surfactant include alkylbenzene sulfonates such as sodium dodecylbenzenesulfonate, alkyl sulfates such as sodium dodecyl sulfate and sodium lauryl sulfate, sodium N-cocoylmethyl taurine, sodium di-2-ethylhexyl sulfosuccinate, sodium 2-ethylhexyl sulfate, sodium α-sulfo fatty acid methyl ester salt, etc. Among these, alkylbenzene sulfonates, alkyl sulfates, and sodium N-cocoylmethyl taurine are preferably used, and sodium dodecylbenzenesulfonate is more preferably used, from the viewpoints of easy availability, etc. Examples of the nonionic surfactant include polyoxyethylene-2-ethylhexyl ether, polyoxyethylene isodecyl ether, etc. The molecular weight of these nonionic surfactants is preferably 100 to 2000, more preferably 100 to 1000, still more preferably 300 to 1000, from the viewpoints of ease of addition and mixing, etc.

[0066] (Other components) The aqueous resin crosslinking agent-containing liquid contains the above-mentioned aqueous resin crosslinking agent, an aqueous medium, and a surfactant added as necessary. As optional components other than these, within a range not impairing the effects of the present invention, in addition to the solvent and additives in the aqueous resin crosslinking agent, a solvent and additives such as an antioxidant, an ultraviolet absorber, and an antifoaming agent may be further added.

[0067] (Method for producing an aqueous resin crosslinking agent-containing liquid) The aqueous resin crosslinking agent-containing liquid can be produced by mixing the above-mentioned aqueous resin crosslinking agent, an aqueous medium, and, as necessary, a surfactant and further additives of other components. The method of stirring and mixing is not particularly limited, and for example, it can be carried out by a known method using a rotary blade, a magnetic stirrer, or the like. The conditions such as the temperature and time during mixing vary depending on the composition of the aqueous resin crosslinking agent and the type of the aqueous medium. From the viewpoint of efficiently and uniformly mixing, for example, when mixing the aqueous resin crosslinking agent and the aqueous medium, it is preferable to stir and mix at 20 to 100 °C for 0.5 to 5 hours.

[0068] [Aqueous resin composition] The aqueous resin composition of the present invention contains the above-mentioned aqueous resin crosslinking agent and an aqueous resin. Since the aqueous resin crosslinking agent of the present invention described above is excellent in storage stability in a state of coexisting with the aqueous resin, the aqueous resin composition can perform a crosslinking reaction well by heating or the like even after at least about one week has passed after production. Further, by using the aqueous resin composition, a cured product of an aqueous resin having good solvent resistance can be obtained.

[0069] (Aqueous resin) The aqueous resin is a resin having water solubility or water dispersibility. The aqueous resin can be crosslinked by the aqueous resin crosslinking agent, and particularly preferably has a crosslinkable group that can be crosslinked by a carbodiimide group. Specifically, the aqueous resin preferably has a functional group selected from a carboxy group, an amino group, and a hydroxyl group as a crosslinkable group, and more preferably has an alcoholic hydroxyl group and / or a carboxy group. Examples of the aqueous resin include polyester resins, acrylic resins, polyurethane resins, epoxy resins, styrene-acrylic resins, melamine resins, polyolefin resins, fluorine resins, etc., which are aqueous resins having such crosslinkable groups. These may be used alone or in combination of two or more. Among these, polyester resins, acrylic resins, and polyurethane resins are particularly preferably used.

[0070] (Aqueous resin crosslinking agent) The content of the aqueous resin crosslinking agent in the aqueous resin composition is appropriately determined according to the type of the aqueous resin and the physical properties required for the cured product of the aqueous resin, etc. From the viewpoints of the balance between crosslinking reactivity and cost, etc., it is preferably 0.5 to 40 parts by mass, more preferably 1 to 30 parts by mass, and further preferably 1.5 to 20 parts by mass with respect to 100 parts by mass of the aqueous resin.

[0071] (Other components) The aqueous resin composition may contain other components within a range that does not impair the effects of the present invention, in addition to the aqueous resin crosslinking agent and the aqueous resin. Specifically, separately from the solvent and additives in the aqueous resin crosslinking agent or the aqueous resin crosslinking agent-containing liquid, depending on the purpose of use and application, etc., if necessary, a solvent and various additives such as a colorant, a filler, a dispersant, a plasticizer, a thickener, an ultraviolet absorber, an antioxidant, etc. may be further added.

[0072] (Method for producing aqueous resin composition) The aqueous resin composition can be produced by adding the aqueous resin crosslinking agent, the aqueous resin, and the other components, etc. in an arbitrary order and stirring and mixing them. The method of stirring and mixing is not particularly limited, and can be carried out by a known method using, for example, a rotary blade or a magnetic stirrer. The conditions such as temperature and time during mixing vary depending on the composition of the aqueous resin crosslinking agent, the type of aqueous resin, etc. From the perspective of efficient and uniform mixing, the mixing temperature is preferably 0 to 100°C, more preferably 10 to 50°C. From the perspective of the reactivity and mixing efficiency of the mixture of the aqueous resin crosslinking agent and the aqueous resin, etc., it is more preferably 20 to 30°C. The mixing time is preferably 0.1 to 2 hours, more preferably 0.3 to 1 hour. In addition, from the perspectives of uniform miscibility with the aqueous resin, ease of handling, etc., the above-mentioned aqueous resin crosslinking agent-containing liquid may be mixed with the aqueous resin to produce the aqueous resin composition.

[0073] (Cured product of the aqueous resin composition) The aqueous resin composition undergoes a crosslinking reaction by heating or the like to produce a cured product of the aqueous resin (aqueous resin composition). The cured product can be formed as a cured film by applying the aqueous resin composition on a predetermined substrate and then heating it to cause a crosslinking reaction. As the coating method of the aqueous resin composition, known methods can be used. For example, brush coating, tampo coating, spray coating, hot spray coating, airless spray coating, roller coating, curtain flow coating, flow coating, dip coating, knife edge coating, etc. can be adopted. The heating method is not particularly limited. For example, an electric heating furnace, an infrared heating furnace, a high-frequency heating furnace, etc. can be used. The heating temperature is appropriately set from the perspective of promoting the crosslinking reaction within a range where the aqueous resin composition does not discolor or thermally decompose according to the composition of the aqueous resin crosslinking agent, the type of aqueous resin, etc.

[0074] By using the aqueous resin composition, a cured product of an aqueous resin having good solvent resistance can be obtained. Therefore, the aqueous resin composition can be suitably used for various applications such as paints, inks, fiber treatment agents, adhesives, coating agents, adhesives, molded articles, etc., and is particularly suitable for adhesives, fiber treatment agents, coating agents, inks, paints, adhesives. For example, by applying the aqueous resin composition as a paint, a cured film (coating film) of an aqueous resin excellent in solvent resistance can be obtained, and an article having such a cured film formed thereon can also be obtained on any substrate. The substrate may be an inorganic material or an organic material, and may be made of any material such as a metal such as aluminum, ceramics, resin, wood, cloth, fiber, etc.

[0075] In addition, the aqueous resin composition can also be suitably applied to wet-on-wet coating. In the case of the wet-on-wet method, the coating film formed of the aqueous resin composition promotes the crosslinking reaction, so that bleeding or poor adhesion between the laminated coating films hardly occurs, and a cured film with good interlayer adhesion can be efficiently formed.

[0076] In addition, the aqueous resin composition can also exhibit various physical properties based on its excellent crosslinkability. For example, an article in which the cured film is formed on a substrate can be applied to applications that require high tensile strength, excellent heat resistance, durability, adhesiveness, adhesion, chipping resistance, scratch resistance, and compatibility. Specifically, it can be suitably applied in fields such as automobiles, construction, heavy anticorrosive coatings, food packaging, and healthcare.

Examples

[0077] Hereinafter, the present invention will be described in detail by way of examples, but the present invention is not limited thereto.

[0078] [Synthesis of polycarbodiimide compound] First, each polycarbodiimide compound used in the following examples and comparative examples was synthesized.

[0079] 〔Raw material compounds〕 The details of the raw material compounds used in the following synthesis examples are as follows. The molecular weights in this specification are calculated values or catalog values. <Diisocyanate compound> ·HMDI: Dicyclohexylmethane-4,4'-diisocyanate (manufactured by Tokyo Chemical Industry Co., Ltd., molecular weight 262.35) ·TMXDI: Tetramethylxylylene diisocyanate (manufactured by Tokyo Chemical Industry Co., Ltd., molecular weight 244.29) ·IPDI: Isophorone diisocyanate (manufactured by Tokyo Chemical Industry Co., Ltd., molecular weight 222.29) ·XDI: m-Xylylene diisocyanate (manufactured by Tokyo Chemical Industry Co., Ltd., molecular weight 188.19) ·HDI: Hexamethylene diisocyanate (manufactured by Tokyo Chemical Industry Co., Ltd., molecular weight 168.19) ·MDI: 4,4'-Diphenylmethane diisocyanate (manufactured by Tokyo Chemical Industry Co., Ltd., molecular weight 250.25) ·TDI: Tolylene diisocyanate (manufactured by Tokyo Chemical Industry Co., Ltd., molecular weight 174.16) <Terminal-blocking compound> ·MP550: Polyethylene glycol monomethyl ether 550 (manufactured by Tokyo Chemical Industry Co., Ltd., molecular weight 525 - 575) ·MP400: Polyethylene glycol monomethyl ether 400 (manufactured by Tokyo Chemical Industry Co., Ltd., molecular weight 380 - 400) ·MP385: Octaethylene glycol monomethyl ether (manufactured by Tokyo Chemical Industry Co., Ltd., molecular weight 385) ·MP350: Polyethylene glycol monomethyl ether 350 (manufactured by Kanto Chemical Co., Inc., molecular weight 350) ·MP252: Pentaethylene glycol monomethyl ether (manufactured by Tokyo Chemical Industry Co., Ltd., m = 5 in formula (1), molecular weight 252) ·MP208: Tetraethylene glycol monomethyl ether (manufactured by Tokyo Chemical Industry Co., Ltd., m = 4 in formula (1), molecular weight 208) ·MP76: Monoethylene glycol monomethyl ether (manufactured by Tokyo Chemical Industry Co., Ltd., m = 1 in formula (1), molecular weight 76) ·iPrP104: Ethylene glycol monoisopropyl ether (manufactured by Tokyo Chemical Industry Co., Ltd., m = 1 in formula (1), molecular weight 104) · BzP152: Ethylene glycol monobenzyl ether (manufactured by Tokyo Chemical Industry Co., Ltd., m = 1 in formula (1), molecular weight 152) · BP206: Triethylene glycol monobutyl ether (manufactured by Tokyo Chemical Industry Co., Ltd., m = 3 in formula (1), molecular weight 206) · BFG132: Propylene glycol monobutyl ether (manufactured by Tokyo Chemical Industry Co., Ltd., m = 1 in formula (1), molecular weight 132) · MFG206: Tripropylene glycol monomethyl ether (manufactured by Tokyo Chemical Industry Co., Ltd., m = 3 in formula (1), molecular weight 206) · MBG104: 2-Methoxy-1-butanol (manufactured by Tokyo Chemical Industry Co., Ltd., m = 1 in formula (1), molecular weight 104) · C3: 1-Propanol (manufactured by Tokyo Chemical Industry Co., Ltd., molecular weight 60.10) · CHI: Cyclohexyl isocyanate (manufactured by Tokyo Chemical Industry Co., Ltd., molecular weight 125.17) · PEG400: Polyethylene glycol 400 (manufactured by Tokyo Chemical Industry Co., Ltd., molecular weight 380 - 420) · ED-900: Polyalkylene glycol diamine; "Jeffamine® ED-900", manufactured by Huntsman Corporation, molecular weight 900 · M-1000: Polyalkylene glycol monoamine; "Jeffamine® M-1000" manufactured by Huntsman Corporation, molecular weight 1000 · AA: N,N-Diethylisopropanolamine (manufactured by Tokyo Chemical Industry Co., Ltd., molecular weight 131.22) · GM: Methyl glycolate (manufactured by Tokyo Chemical Industry Co., Ltd., molecular weight 90.08) <Carbodiimidation catalyst> · 3-Methyl-1-phenyl-2-phospholene-1-oxide (manufactured by Tokyo Chemical Industry Co., Ltd.) <Solvent> · Propylene glycol-1-monomethyl ether-2-acetate (manufactured by Tokyo Chemical Industry Co., Ltd.) · Cyclohexanone (manufactured by Tokyo Chemical Industry Co., Ltd.)

[0080] 〔Analytical Apparatus and Method〕 Each analysis in the following synthesis examples was performed using the following apparatus and method. <Infrared Absorption (IR) Spectrum> · Measuring apparatus: "FTIR-8200PC", manufactured by Shimadzu Corporation <Degree of Polymerization> (1) When synthesizing a polycarbodiimide compound by simultaneously blending a diisocyanate compound and a terminal-capping compound, the degree of polymerization of the carbodiimide group is a value based on calculation. (2) When synthesizing an isocyanate-terminated polycarbodiimide by the polycarbodiimidation reaction of a diisocyanate compound and then performing a capping reaction on the terminal isocyanate groups using a terminal-capping compound to synthesize a polycarbodiimide compound, for the isocyanate-terminated polycarbodiimide, the degree of polymerization of the carbodiimide group was determined by potentiometric titration (using apparatus: automatic titrator "COM-900", manufactured by Hiranuma Sangyo Co., Ltd.). Specifically, a toluene solution of di-n-butylamine with a known concentration was mixed with the isocyanate-terminated polycarbodiimide obtained by the carbodiimidation reaction to react the terminal isocyanate groups with di-n-butylamine, and the remaining di-n-butylamine was neutralized and titrated with a standard hydrochloric acid solution to calculate the remaining amount of isocyanate groups (terminal NCO amount [mass%]). From this terminal NCO amount, the degree of polymerization of the carbodiimide group was determined.

[0081] (Synthesis Example 1-1) 100 parts by mass of HMDI and 0.5 parts by mass of a carbodiimidation catalyst were placed in a reaction vessel equipped with a reflux tube and a stirrer, and stirred at 170 °C for 18 hours under a nitrogen stream to obtain an isocyanate-terminated polycarbodiimide compound having isocyanate groups at both ends (terminal isocyanate group amount 6.20 mass%). By IR spectrum measurement, absorption peaks due to carbodiimide groups around a wave number of 2150 cm -1 were confirmed before and after. 86.0 parts by mass of the obtained isocyanate-terminated polycarbodiimide compound was dissolved at 150 °C, and 69.9 parts by mass of MP550 (the same molar equivalent as the terminal isocyanate groups of the isocyanate-terminated polycarbodiimide compound) was added thereto as a terminal blocking compound. The mixture was heated to 180 °C and reacted for 2 hours with stirring. After confirming by IR spectrum measurement that the absorption of the isocyanate groups at a wavenumber of 2200 to 2300 cm -1 had disappeared, the reaction product was taken out from the reaction vessel and cooled to room temperature (25 °C) to obtain a polycarbodiimide compound (A1) (Mn (theoretical value of number-average molecular weight; the same shall apply hereinafter): 2454, number of carbodiimide groups in one molecule: 5).

[0082] (Synthesis Example 1-2) 100 parts by mass of HMDI and 0.5 parts by mass of a carbodiimidization catalyst were placed in a reaction vessel equipped with a reflux tube and a stirrer, and stirred at 170 °C for 6 hours under a nitrogen stream to obtain an isocyanate-terminated polycarbodiimide compound having isocyanate groups at both ends (amount of terminal isocyanate groups: 9.16% by mass). By IR spectrum measurement, absorption peaks due to carbodiimide groups before and after at a wavenumber of 2150 cm -1 were confirmed. 87.4 parts by mass of the obtained isocyanate-terminated polycarbodiimide compound was dissolved at 150 °C, and 104.8 parts by mass of MP550 (the same molar equivalent as the terminal isocyanate groups of the isocyanate-terminated polycarbodiimide compound) was added thereto as a terminal blocking compound. The mixture was heated to 180 °C and reacted for 2 hours with stirring. After confirming by IR spectrum measurement that the absorption of the isocyanate groups at a wavenumber of 2200 to 2300 cm -1 had disappeared, the reaction product was taken out from the reaction vessel and cooled to room temperature (25 °C) to obtain a polycarbodiimide compound (A2) (Mn: 2017, number of carbodiimide groups in one molecule: 3).

[0083] (Synthesis Example 1-3) 100 parts by mass of HMDI and 0.5 parts by mass of a carbodiimidization catalyst were placed in a reaction vessel equipped with a reflux tube and a stirrer, and stirred at 170 °C for 24 hours under a nitrogen stream to obtain an isocyanate-terminated polycarbodiimide compound having isocyanate groups at both ends (the amount of terminal isocyanate groups: 9.16% by mass). By IR spectrum measurement, the absorption peak due to the carbodiimide groups before and after at a wave number of 2150 cm -1 was confirmed. 84.8 parts by mass of the obtained isocyanate-terminated polycarbodiimide compound was dissolved at 150 °C, and 38.1 parts by mass of MP550 (the same molar equivalent as the terminal isocyanate groups of the isocyanate-terminated polycarbodiimide compound) as a terminal blocking compound was added thereto, and the mixture was heated to 180 °C and reacted for 2 hours with stirring. Regarding the reaction product, after confirming that the absorption of the isocyanate groups at a wave number of 2200 to 2300 cm -1 had disappeared by IR spectrum measurement, it was taken out from the reaction vessel and cooled to room temperature (25 °C) to obtain a polycarbodiimide compound (A3) (Mn: 3546, the number of carbodiimide groups in one molecule: 10).

[0084] (Synthesis Example 1-4) 100 parts by mass of HMDI and 0.5 parts by mass of a carbodiimidization catalyst were placed in a reaction vessel equipped with a reflux tube and a stirrer, and stirred at 170 °C for 32 hours under a nitrogen stream to obtain an isocyanate-terminated polycarbodiimide compound having isocyanate groups at both ends (the amount of terminal isocyanate groups: 9.16% by mass). By IR spectrum measurement, the absorption peak due to the carbodiimide groups before and after at a wave number of 2150 cm -1 was confirmed. 84.3 parts by mass of the obtained isocyanate-terminated polycarbodiimide compound was dissolved at 150 °C, and 26.2 parts by mass of MP550 (the same molar equivalent as the terminal isocyanate groups of the isocyanate-terminated polycarbodiimide compound) as a terminal blocking compound was added thereto, and the mixture was heated to 180 °C and reacted for 2 hours with stirring. Regarding the reaction product, after confirming that the absorption of the isocyanate groups at a wave number of 2200 to 2300 cm -1After confirming that the absorption of the isocyanate groups had disappeared, it was taken out from the reaction vessel, cooled to room temperature (25 °C), and a polycarbodiimide compound (A4) was obtained (Mn: 4638, the number of carbodiimide groups in one molecule: 15).

[0085] (Synthesis Example 1-5) 100 parts by mass of TMXDI and 2.0 parts by mass of a carbodiimidization catalyst were placed in a reaction vessel equipped with a reflux tube and a stirrer, and stirred and mixed at 170 °C for 18 hours under a nitrogen stream to carry out a carbodiimidization reaction, obtaining an isocyanate-terminated polycarbodiimide compound having isocyanate groups at both ends (the amount of terminal isocyanate groups: 6.74% by mass). By IR spectrum measurement, the absorption peak due to the carbodiimide groups before and after was confirmed at a wave number of 2150 cm -1 The absorption peak due to the carbodiimide groups before and after was confirmed. 85.0 parts by mass of the obtained isocyanate-terminated polycarbodiimide compound was dissolved at 150 °C, and 75.0 parts by mass of MP550 (the same molar equivalent as the terminal isocyanate groups of the isocyanate-terminated polycarbodiimide compound) as a terminal blocking agent was added thereto, and the mixture was heated to 180 °C and reacted for 2 hours with stirring. Regarding the reaction product, by IR spectrum measurement, after confirming that the absorption of the isocyanate groups at a wave number of 2200 to 2300 cm -1 had disappeared, it was taken out from the reaction vessel, cooled to room temperature (25 °C), and a polycarbodiimide compound (A5) was obtained (Mn: 2346, the number of carbodiimide groups in one molecule: 5).

[0086] (Synthesis Examples 1-6 to 1-13) In Synthesis Example 1-1, MP550 was changed to MP400 (50.8 parts by mass) (Synthesis Example 1-6), MP385 (48.9 parts by mass) (Synthesis Example 1-7), AA (8.3 parts by mass) and MP550 (34.9 parts by mass) (Synthesis Example 1-8), GM (5.7 parts by mass) and MP550 (34.9 parts by mass) (Synthesis Example 1-9), MP350 (44.5 parts by mass) (Synthesis Example 1-10), PEG400 (50.8 parts by mass) (Synthesis Example 1-11), ED-900 (114.4 parts by mass) (Synthesis Example 1-12), M-1000 (127.1 parts by mass) (Synthesis Example 1-13), and otherwise, in the same manner as in Synthesis Example 1-1, polycarbodiimide compounds (A6) to (A13) were obtained respectively.

[0087] (Synthesis Example 2-1) In Synthesis Example 1-1, MP550 was changed to MP208 (26.5 parts by mass), and otherwise, in the same manner as in Synthesis Example 1-1, polycarbodiimide compound (B1) was obtained.

[0088] (Synthesis Example 2-2) In Synthesis Example 1-3, MP550 was changed to MP208 (39.7 parts by mass), and otherwise, in the same manner as in Synthesis Example 1-3, polycarbodiimide compound (B2) was obtained.

[0089] (Synthesis Example 2-3) In Synthesis Example 1-2, MP550 was changed to MP208 (14.4 parts by mass), and otherwise, in the same manner as in Synthesis Example 1-2, polycarbodiimide compound (B3) was obtained.

[0090] (Synthesis Example 2-4) 100 parts by mass of HMDI and 0.5 parts by mass of a carbodiimidization catalyst were placed in a reaction vessel equipped with a reflux tube and a stirrer, and stirred at 170 °C for 3 hours under a nitrogen stream to obtain an isocyanate-terminated polycarbodiimide compound having isocyanate groups at both ends (the amount of terminal isocyanate groups was 14.24% by mass). The absorption peaks due to the carbodiimide groups before and after were confirmed by IR spectrum measurement at a wave number of 2150 cm -1 The absorption peaks due to the carbodiimide groups before and after were confirmed. 89.9 parts by mass of the obtained isocyanate-terminated polycarbodiimide compound was dissolved at 150 °C, and 63.5 parts by mass of MP208 (equimolar to the terminal isocyanate groups of the isocyanate-terminated polycarbodiimide compound) as a terminal-blocking compound was added thereto. The mixture was heated to 180 °C and reacted for 2 hours with stirring. Regarding the reaction product, after confirming that the absorption of the isocyanate groups at a wave number of 2200 - 2300 cm -1 disappeared by IR spectrum measurement, it was taken out from the reaction vessel and cooled to room temperature (25 °C) to obtain a polycarbodiimide compound (B4) (Mn: 1006, number of carbodiimide groups in one molecule: 1.5).

[0091] (Synthesis Example 2 - 5) In Synthesis Example 1 - 4, MP550 was changed to MP208 (9.9 parts by mass), and otherwise, in the same manner as in Synthesis Example 1 - 4, a polycarbodiimide compound (B5) was obtained.

[0092] (Synthesis Example 2 - 6) 100 parts by mass of HMDI and 0.5 parts by mass of a carbodiimidization catalyst were placed in a reaction vessel equipped with a reflux tube and a stirrer, and stirred at 170 °C for 40 hours under a nitrogen stream to obtain an isocyanate-terminated polycarbodiimide compound having isocyanate groups at both ends (amount of terminal isocyanate groups: 1.81 mass%). By IR spectrum measurement, absorption peaks due to carbodiimide groups before and after a wave number of 2150 cm -1 were confirmed. 84.0 parts by mass of the obtained isocyanate-terminated polycarbodiimide compound was dissolved at 150 °C, and 7.6 parts by mass of MP208 (equimolar to the terminal isocyanate groups of the isocyanate-terminated polycarbodiimide compound) as a terminal-blocking compound was added thereto. The mixture was heated to 180 °C and reacted for 2 hours with stirring. Regarding the reaction product, after confirming that the absorption of the isocyanate groups at a wave number of 2200 - 2300 cm -1 disappeared by IR spectrum measurement, it was taken out from the reaction vessel and cooled to room temperature (25 °C) to obtain a polycarbodiimide compound (B6) (Mn: 5046, number of carbodiimide groups in one molecule: 20).

[0093] (Synthesis Example 2-7) In Synthesis Example 1-5, MP550 was changed to MP208 (28.4 parts by mass), and in other respects, in the same manner as in Synthesis Example 1-5, a polycarbodiimide compound (B7) was obtained.

[0094] (Synthesis Example 2-8) 100 parts by mass of IPDI and 31.2 parts by mass of MP208 were placed in a reaction vessel equipped with a reflux tube and a stirrer, and after stirring and mixing at 150°C for 2 hours under a nitrogen stream to cause a reaction, the temperature inside the vessel was cooled to 25°C. 2.0 parts by mass of a carbodiimidization catalyst was added, and heating was carried out again, followed by stirring and mixing at 150°C for 12 hours to cause a reaction. By IR spectrum measurement, it was confirmed that the height ratio ([NCO] / [NCN]: height ratio of the peaks after baseline correction; hereinafter the same) of the absorption peak of the isocyanate group at a wave number of 2200 to 2300 cm -1 and the absorption peak of the carbodiimide group at a wave number of 2000 to 2200 cm -1 decreased to 0.05 or less. Then, the reaction product was taken out from the reaction vessel and cooled to room temperature (25°C) to obtain a polycarbodiimide compound (B8) (Mn: 1530, number of carbodiimide groups in one molecule: 5).

[0095] (Synthesis Example 2-9) 100 parts by mass of XDI, 36.9 parts by mass of MP208, and 210 parts by mass of cyclohexanone as a solvent were placed in a reaction vessel equipped with a reflux tube and a stirrer, and after stirring and mixing at 150°C for 2 hours under a nitrogen stream to cause a reaction, the temperature inside the vessel was cooled to 25°C. 2.0 parts by mass of a carbodiimidization catalyst was added, and heating was carried out again, followed by stirring and mixing at 150°C for 12 hours to cause a reaction. By IR spectrum measurement, it was confirmed that the height ratio of the absorption peak of the isocyanate group at a wave number of 2200 to 2300 cm -1 and the absorption peak of the carbodiimide group at a wave number of 2000 to 2200 cm -1 decreased to 0.05 or less. Then, the solvent was distilled off under reduced pressure, the reaction product was taken out from the reaction vessel, and cooled to room temperature (25°C) to obtain a polycarbodiimide compound (B9) (Mn: 1326, number of carbodiimide groups in one molecule: 5).

[0096] (Synthesis Example 2-10) 100 parts by mass of HDI, 41.3 parts by mass of MP208, and 210 parts by mass of propylene glycol-1-monomethyl ether-2-acetate as a solvent were placed in a reaction vessel equipped with a reflux tube and a stirrer, and stirred and mixed at 150 ° C for 2 hours under a nitrogen stream for reaction. Then, the temperature inside the vessel was cooled to 25 ° C. 2.0 parts by mass of a carbodiimidization catalyst was added, and the mixture was heated again and stirred and mixed at 150 ° C for 12 hours for reaction. By IR spectrum measurement, the absorption peak of the isocyanate group at a wave number of 2200 to 2300 cm -1 and the height ratio of the absorption peak of the carbodiimide group at a wave number of 2000 to 2200 cm -1 were confirmed to have decreased to 0.05 or less. Then, the solvent was distilled off under reduced pressure, the reaction product was taken out from the reaction vessel, cooled to room temperature (25 ° C), and a polycarbodiimide compound (B10) was obtained (Mn: 1206, number of carbodiimide groups in one molecule: 5).

[0097] (Synthesis Example 2-11) 100 parts by mass of TDI, 39.9 parts by mass of MP208, and 210 parts by mass of cyclohexanone as a solvent were placed in a reaction vessel equipped with a reflux tube and a stirrer, and stirred and mixed at 120 ° C for 2 hours under a nitrogen stream for reaction. Then, the temperature inside the vessel was cooled to 25 ° C. 0.5 part by mass of a carbodiimidization catalyst was added, and the mixture was heated again and stirred and mixed at 120 ° C for 10 hours for reaction. By IR spectrum measurement, the absorption peak of the isocyanate group at a wave number of 2200 to 2300 cm -1 and the height ratio of the absorption peak of the carbodiimide group at a wave number of 2000 to 2200 cm -1 were confirmed to have decreased to 0.05 or less. Then, the solvent was distilled off under reduced pressure, the reaction product was taken out from the reaction vessel, cooled to room temperature (25 ° C), and a polycarbodiimide compound (B11) was obtained (Mn: 1241, number of carbodiimide groups in one molecule: 5).

[0098] (Synthesis Example 2-12) 100 parts by mass of MDI, 27.7 parts by mass of MP208, and 190 parts by mass of cyclohexanone as a solvent were placed in a reaction vessel equipped with a reflux pipe and a stirrer, and stirred and mixed at 120 °C for 2 hours under a nitrogen stream to cause a reaction. After that, the temperature inside the vessel was cooled to 25 °C. 0.5 part by mass of a carbodiimidization catalyst was added, and it was heated again and stirred and mixed at 120 °C for 12 hours to cause a reaction. By IR spectrum measurement, the absorption peak of the isocyanate group at a wave number of 2200-2300 cm -1 and the absorption peak of the carbodiimide group at a wave number of 2000-2200 cm -1 were confirmed to have decreased to a height ratio of 0.05 or less. Then, the solvent was distilled off under reduced pressure, the reaction product was taken out from the reaction vessel, cooled to room temperature (25 °C), and a polycarbodiimide compound (B12) was obtained (Mn: 1241, number of carbodiimide groups in one molecule: 5).

[0099] (Synthesis Examples 2-13 to 2-21) In Synthesis Example 1-1, MP550 was changed to MP76 (9.7 parts by mass) (Synthesis Example 2-13), iPrP104 (13.2 parts by mass) (Synthesis Example 2-14), BzP152 (19.3 parts by mass) (Synthesis Example 2-15), BP206 (78.6 parts by mass) (Synthesis Example 2-16), BFG132 (16.8 parts by mass) (Synthesis Example 2-17), MFG206 (26.2 parts by mass) (Synthesis Example 2-18), MBG104 (13.2 parts by mass) (Synthesis Example 2-19), MP252 (32.1 parts by mass) (Synthesis Example 2-20), C3 (7.6 parts by mass) (Synthesis Example 2-21). Otherwise, in the same manner as in Synthesis Example 1-1, polycarbodiimide compounds (B13) to (B21) were obtained respectively.

[0100] (Synthesis Example 2-22) 100 parts by mass of HMDI, 23.9 parts by mass of CHI, and 0.6 part by mass of a carbodiimidization catalyst were placed in a reaction vessel equipped with a reflux pipe and a stirrer, and stirred at 180 °C for 45 hours under a nitrogen stream to cause a reaction. By IR spectrum measurement, the absorption peak of the isocyanate group at a wave number of 2200-2300 cm -1 and the absorption peak of the carbodiimide group at a wave number of 2000-2200 cm -1It was confirmed that the height ratio of the absorption peak of the carbodiimide group decreased to 0.05 or less. Then, the reaction product was taken out from the reaction vessel, cooled to room temperature (25 °C), and a polycarbodiimide compound (B22) was obtained (Mn: 1080, the number of carbodiimide groups in one molecule: 5).

[0101] [Preparation of Aqueous Resin Crosslinking Agent-containing Liquid] Using each polycarbodiimide compound obtained in the above synthesis example, an aqueous resin crosslinking agent-containing liquid was prepared. Details of the surfactants used in the following examples and comparative examples are as follows. [Surfactant] · LA: Sodium dodecylbenzenesulfonate, anionic

[0102] (Examples 1 to 21, 23, 24, and 26 to 39 and Comparative Examples 1 to 7) The polycarbodiimide compound (A) and the polycarbodiimide compound (B) were stirred and mixed at 160 °C for 4 hours in various types and blending amounts shown in Table 1 below, then cooled to 80 °C, diluted with 150 parts by mass of ion-exchanged water, and stirred and mixed to obtain each aqueous resin crosslinking agent-containing liquid.

[0103] (Examples 22 and 25) 40 parts by mass of the polycarbodiimide compound (A) and 60 parts by mass of the polycarbodiimide compound (B) of various types shown in Table 1 below were stirred and mixed at 160 °C for 4 hours, then cooled to 80 °C, and 3 parts by mass (in terms of active ingredient) of an aqueous solution of a surfactant was added to each, diluted with 150 parts by mass of ion-exchanged water, and stirred and mixed to obtain each aqueous resin crosslinking agent-containing liquid.

[0104] [Table 1]

[0105] [Preparation of Aqueous Resin Composition] (Aqueous Polyurethane Resin Composition) 5 parts by mass of each crosslinking agent-containing liquid for aqueous resin (2 parts by mass as the crosslinking agent) produced in the above Examples and Comparative Examples, and 285 parts by mass (100 parts by mass in terms of resin solid content) of a carboxy group-containing aqueous polyurethane resin ("Hydran (registered trademark) WLS-210", manufactured by DIC Corporation, resin solid content 35% by mass) were stirred and mixed to prepare aqueous polyurethane resin compositions, respectively.

[0106] (Aqueous polyester resin composition) 5 parts by mass of each crosslinking agent-containing liquid for aqueous resin (2 parts by mass as the crosslinking agent) produced in the above Examples and Comparative Examples, and 400 parts by mass (100 parts by mass in terms of resin solid content) of a carboxy group-modified aqueous polyester resin ("Plascoat (registered trademark) Z-730", manufactured by Gohou Chemical Industry Co., Ltd., resin solid content 25% by mass) were stirred and mixed to prepare aqueous polyester resin compositions, respectively.

[0107] (Preparation of aqueous acrylic resin composition) 5 parts by mass of each crosslinking agent-containing liquid for aqueous resin (2 parts by mass as the crosslinking agent) produced in the above Examples and Comparative Examples, and 200 parts by mass (100 parts by mass in terms of resin solid content) of a carboxy group-containing aqueous acrylic resin ("Boncoat (registered trademark) VF-1060", manufactured by DIC Corporation, resin solid content 50% by mass) were stirred and mixed to prepare aqueous acrylic resin compositions, respectively.

[0108] [Evaluation of aqueous resin composition] For each of the aqueous resin compositions prepared above, evaluations were made on the following various items. The evaluation results are shown in Table 2 below.

[0109] [Pot life (storage stability)] The viscosities of the aqueous resin compositions were measured immediately after preparation and after storage at 40 °C for 30 days. The change rate of the viscosity after 30-day storage with respect to the viscosity immediately after production was determined to evaluate the pot life (storage stability). The viscosity was measured using a B-type viscometer ("TVB-10M", manufactured by Toki Sangyo Co., Ltd.; rotor: TM2, sample volume 50 mL, temperature 20 °C, rotation speed 60 rpm). The viscosity change rate was evaluated according to the following evaluation criteria. The closer the viscosity change rate is to 0%, the better the storage stability. In the case of evaluations A to C, it can be said that the storage stability is good. Also, in the case of evaluation D, it can be said that it is within the allowable range. <Evaluation Criteria> A: Viscosity change rate less than 20% B: Viscosity change rate of 20% or more and less than 30% C: Viscosity change rate of 30% or more and less than 50% D: Viscosity change rate of 50% or more and less than 100% E: Viscosity change rate of 100% or more

[0110] 〔Gloss of Coating Film (Specular Gloss)〕 The aqueous resin composition was applied onto an aluminum plate using a bar coater (wire rod No. 32) and dried at 130 °C for 5 minutes to obtain a coating film test piece. For the above coating film test piece, the gloss at 60 °C was measured using a handy gloss meter (PG-1M). The gloss (specular gloss) of the cured film (aqueous resin coating film) was evaluated according to the following evaluation criteria. The higher the gloss, the better the gloss (specular gloss) of the cured film (aqueous resin coating film). In the case of evaluations A to C, it can be said that the gloss (specular gloss) of the cured film (aqueous resin coating film) is sufficiently high. <Evaluation Criteria> A: Gloss increase of 8 or more compared to the blank without carbodiimide addition B: Gloss increase of 5 or more and less than 8 compared to the blank without carbodiimide addition C: Gloss increase of less than 5 compared to the blank without carbodiimide addition D: No change in gloss from the blank without carbodiimide addition E: Gloss decrease compared to the blank without carbodiimide addition

[0111] 〔Solvent Resistance of Coating Film〕 The aqueous resin composition was applied onto an aluminum plate using a bar coater (wire rod No. 32) and dried at 80 °C for 10 minutes to obtain a coating film test piece. Regarding the above coating test piece, a friction test was conducted using a friction tester ("FR-1B", manufactured by Suga Test Instruments Co., Ltd.) with absorbent cotton impregnated with a 70% by mass ethanol aqueous solution (load 900 g / cm 2 ) by double rubbing back and forth 50 times. The coating test piece after the friction test was visually observed, and for each evaluation item of whitening property and the ratio of the remaining coating area, the scores were determined according to the following score criteria, and the average score for 2 coating test pieces was obtained, which was used as the evaluation score. By comprehensively considering these evaluation items, the solvent resistance of the coating was evaluated. <Score Criteria> (1) Whitening Property 5 points: No change 4 points: There are faint rubbing marks or slight whitening 3 points: Partial whitening 2 points: Overall whitening 1 point: Partial dissolution 0 point: Complete dissolution (2) Ratio of the Remaining Coating Area 5 points: 100% 4.5 points: 95% or more and less than 100% 4 points: 85% or more and less than 95% 3.5 points: 75% or more and less than 85% 3 points: 60% or more and less than 75% 2.5 points: 45% or more and less than 60% 2 points: 40% or more and less than 45% 1.5 points: 25% or more and less than 40% 1 point: 10% or more and less than 25% 0 point: Less than 10% Regarding the average score of each evaluation point of the above evaluation items, the solvent resistance of the coating was comprehensively evaluated according to the following evaluation criteria. The higher the score, the better the solvent resistance of the coating. In the case of evaluations A to C, it can be said that the solvent resistance of the coating is sufficiently high. <Evaluation Criteria> A: 5 points B: 4 points or more and less than 5 points C: 3 points or more and less than 4 points D: 2 points or more and less than 3 points E: Less than 2 points

[0112] [Wet-on-Wet Coating] The aqueous resin compositions prepared in the above Examples and Comparative Examples were applied onto an aluminum plate by air spraying (dry film thickness: 30 μm), and setting was carried out for 10 minutes. On top of that, the same aqueous resin composition was applied by air spraying (dry film thickness: 15 μm, total 45 μm), preheated at 80°C for 3 minutes, and primed. On top of the primer coating film (uncured coating film), a two-component curable polyurethane clear paint (“Body Pen Urethane Clear”, manufactured by Soft 99 Corporation) was top-coated (dry film thickness: 30 μm), baked at 80°C, and a multilayer coating film (cured film by wet-on-wet painting) was formed. No abnormality was observed by visual inspection for any of the multilayer coating films using the aqueous resin compositions. Regarding the multilayer coating films prepared by wet-on-wet painting as described above, the interlayer adhesion was evaluated by the method shown below. The evaluation results are also shown in Table 2 below.

[0113] 〔Interlayer Adhesion of Multilayer Coating Film〕 The adhesion between the layer of the primer coating film and the layer of the topcoat film of the multilayer coating film was evaluated by a cross-cut test (checkerboard test) according to ASTM D3359-17. The test conditions were as follows: On the multilayer coating film, a 6×6 checkerboard with a 2-mm interval was created with a cutter, at 25°C, a tape with an adhesive strength of 6.7 N / cm was pasted, and based on the peeling state (peeling area ratio) when the tape was peeled off, the interlayer adhesion was evaluated according to the following evaluation criteria. The smaller the peeling area ratio, the higher the interlayer adhesion. In the case of evaluations A to C, it can be said that the interlayer adhesion is sufficiently high. <Evaluation Criteria> A: Peeling area ratio 0% B: Peeling area ratio 0% or more and less than 5% C: Peeling area ratio 5% or more and less than 15% D: Peeling area ratio 15% or more and less than 35% E: Peeling area ratio 35% or more

[0114]

Table 2

[0115] As can be seen from the results shown in Tables 1 and 2, the aqueous resin crosslinking agent of the present invention is also excellent in the storage stability of the aqueous resin composition prepared using the same. Further, regarding the cured products (aqueous resin coatings) of various aqueous resin compositions, it was confirmed that the gloss (specular glossiness) was sufficiently high. Also, it was confirmed that in wet-on-wet coating, a cured film with a good interlayer adhesion can be formed by a multilayer coating film.

Claims

1. Aqueous resin crosslinking agent containing polycarbodiimide compound (A) and polycarbodiimide compound (B), wherein the polycarbodiimide compound (A) has a structure in which the isocyanate groups at both ends are each blocked by a hydrophilic organic compound, and at least one of the hydrophilic organic compounds has a molecular weight exceeding 350, the polycarbodiimide compound (B) has a structure in which the isocyanate groups at both ends are each blocked by a compound having a molecular weight of 250 or less represented by the following formula (1), the polycarbodiimide compound (A) is 5 to 95 parts by mass in a total of 100 parts by mass of the polycarbodiimide compound (A) and the polycarbodiimide compound (B), wherein the hydrophilic organic compound having a molecular weight exceeding 350 is a compound represented by the following formula (A). R １ (OCHR ２ CH ２ ) ｍ OH...(1) (In formula (1), R １ is an alkyl group, a cycloalkyl group or an aryl group having 1 to 13 carbon atoms. R ２ is a hydrogen atom, a methyl group, an ethyl group, or a propyl group, and m is a number from 1 to 4.) R1(OCHR2CH2)nOH (A) (In formula (A), R1 is an alkyl group, cycloalkyl group or aryl group having 1 to 20 carbon atoms. R2 is a hydrogen atom, methyl group, ethyl group or propyl group, and n is a number from 1 to 30.)

2. R in the formula (A) above １ is a methyl group, and R ２ is a hydrogen atom. The aqueous resin crosslinking agent according to claim 1.

3. The aqueous resin crosslinking agent according to claim 1 or 2, wherein the hydrophilic organic compound has a molecular weight of 400 or more.

4. The aqueous resin crosslinking agent according to any one of claims 1 to 3, wherein m in the formula (1) is 4.

5. An aqueous resin crosslinking agent-containing liquid containing the aqueous resin crosslinking agent according to any one of claims 1 to 4 and an aqueous medium.

6. The aqueous resin crosslinking agent-containing liquid according to claim 5, wherein the aqueous medium is water or a mixed solvent of water and a hydrophilic solvent.

7. The aqueous resin crosslinking agent-containing liquid according to claim 6, further containing a surfactant.

8. The crosslinking agent-containing liquid for aqueous resin according to claim 7, wherein the surfactant is an anionic surfactant.

9. The crosslinking agent-containing liquid for aqueous resin according to claim 8, wherein the anionic surfactant is one or more selected from alkylbenzene sulfonates, alkyl sulfates, and sodium N-cocoylmethyl taurine.

10. An aqueous resin composition containing the aqueous resin crosslinking agent according to any one of claims 1 to 4 and an aqueous resin.

11. The aqueous resin composition according to claim 10, wherein the aqueous resin has a group selected from a carboxy group, an amino group and a hydroxy group.

12. The aqueous resin composition according to claim 10 or 11, wherein the aqueous resin is at least one selected from a polyester resin, an acrylic resin, a polyurethane resin, an epoxy resin, a styrene-acrylic resin, a melamine resin, a polyolefin resin, and a fluororesin.

13. The aqueous resin composition according to any one of claims 10 to 12, which is used in an adhesive, a fiber treatment agent, a coating agent, an ink, a paint, or an adhesive.

14. The aqueous resin composition according to any one of claims 10 to 12, which is for wet-on-wet coating.

15. A cured film formed from the aqueous resin composition according to any one of claims 10 to 14.

16. An article in which the cured film according to claim 15 is formed on a substrate.

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