CN117440996A

CN117440996A - Aqueous coating composition, coating film, and method for producing coating film

Info

Publication number: CN117440996A
Application number: CN202280040929.XA
Authority: CN
Inventors: 岛村健一; 畦地谦作; 南保光孝
Original assignee: Nippon Paint Industrial Coatings Co Ltd
Current assignee: Nippon Paint Industrial Coatings Co Ltd
Priority date: 2021-06-10
Filing date: 2022-04-22
Publication date: 2024-01-23
Also published as: AU2022291046A1; TW202302673A; JP2022189126A; KR20240018566A; WO2022259774A1; JP7101294B1

Abstract

The present disclosure has an object to provide an aqueous coating composition which is excellent in storage stability even in a one-component form and can form a coating film excellent in workability such as bending and crack resistance and mar resistance during processing. The aqueous coating composition of the present disclosure comprises a coating film-forming resin (a), a crosslinking agent (B), a sulfonic acid compound (C), and an amine compound (D), wherein the coating film-forming resin (a) comprises an acrylic resin (A1), the hydroxyl value of the coating film-forming resin (a) is 5mgKOH/g or more and 35mgKOH/g or less, the crosslinking agent (B) comprises a fully alkyl melamine resin (B1), and the neutralization ratio in terms of the mole of the acid groups of the sulfonic acid compound (C) based on the amine compound (D) is 100% or more and 1,300% or less.

Description

Aqueous coating composition, coating film, and method for producing coating film

Technical Field

The present disclosure relates to aqueous coating compositions, coating films, and methods of making coating films.

Background

A coated steel sheet obtained by coating a metal substrate such as a cold-rolled steel sheet or a plated steel sheet and thereafter subjecting the coated steel sheet to a forming process is also called a precoated steel sheet (hereinafter also referred to as "PCM"), and is used for building members such as a roll-up door, a sunroof, a door, a roof, and a siding; an exterior material for electrical equipment such as an air conditioner outdoor unit; interior material, and the like. The precoated steel sheet is usually produced by applying a coating composition to the surface of the metal base material, heating (baking) the steel sheet at 200 to 270 ℃ for 30 to 60 seconds to form a coating film, and then subjecting the steel sheet to a molding process. Therefore, the coating film of the precoated steel sheet is required to have such a degree of workability that cracking and peeling do not occur during processing, and such a degree of hardness that damage and dent do not occur.

The coating composition includes a one-component coating composition in which a main agent containing a coating film forming resin and a curing agent containing a crosslinking agent coexist in the same system, and a two-component coating composition in which the main agent and the curing agent are stored separately and used in combination at the time of use. Wherein the two-component coating composition does not mix the main agent with the curing agent until immediately before use, and therefore, storage stability is superior to that of the one-component coating composition. However, the two-component coating composition requires mixing and stirring the main agent and the curing agent at a predetermined ratio at the time of use so as to be uniform, and has a limited pot life, and the handling and coating workability thereof are sometimes problematic, and a one-component coating composition is demanded.

In addition, in recent years, awareness of reducing environmental load has been increasing, and replacement with environmental protection commodity is demanded. In the coating field, there is also a demand for reducing the amount of, for example, volatile Organic Compounds (VOCs), which can be satisfied by using an aqueous coating composition. That is, in the market, the demand for one-part aqueous coating compositions is becoming increasingly very high.

As such one-part aqueous coating compositions, various proposals have been made, for example, the following proposals have been made: in an aqueous coating composition containing an acrylic copolymer containing hydroxyl groups and carboxyl groups, an aqueous amino resin, an amine compound, and a hydrophilic organic solvent, the carboxyl groups contained in the acrylic copolymer containing hydroxyl groups and carboxyl groups are neutralized with the amine compound (patent document 1). The following schemes are also proposed: in an acrylic water-soluble coating composition comprising a hydroxyl group-containing (meth) acrylate, a carboxyl group-containing vinyl monomer, a copolymer of a long-chain alkyl group-containing (meth) acrylate and a vinyl monomer, and a water-soluble amino resin and an aqueous medium, the carboxyl group of the hydroxyl group-and carboxyl group-containing acrylic copolymer is neutralized with an amine compound (patent document 2). The following scheme is further proposed: in a water-based coating composition for metal covering comprising an acrylic resin having hydroxyl groups and carboxyl groups and having a glass transition temperature in the range of-10 to 80 ℃, an acrylic resin having hydroxyl groups and carboxyl groups and having a glass transition temperature in the range of-50 to 20 ℃, an aqueous amino resin, a basic compound and an aqueous medium, the carboxyl groups of the acrylic resin having hydroxyl groups and carboxyl groups are neutralized with the basic compound (patent document 3). Further, patent document 4 proposes an aqueous coating composition comprising an aqueous resin, a melamine resin, and a phosphate catalyst as a weak acid catalyst, and proposes neutralization of the aqueous resin with a basic compound (patent document 4).

Prior art literature

Patent literature

Patent document 1: japanese patent laid-open No. 2001-323207

Patent document 2: japanese patent laid-open No. 2001-240624

Patent document 3: japanese patent laid-open No. 2000-17225

Patent document 4: japanese patent application laid-open No. 2015-174958

Disclosure of Invention

Problems to be solved by the invention

However, the coating films formed from the coating compositions described in the above patent documents 1 to 4 do not sufficiently satisfy the workability (adhesion, crack resistance) and flaw resistance of the obtained precoated steel sheet.

Furthermore, in the one-component coating composition, since the main agent and the curing agent coexist in the same system, the following relationship of equilibrium with each other exists: when the reactivity of the main agent and the curing agent is improved for the purpose of improving the physical properties of the coating film, the storage stability of the coating composition is lowered, and when the reactivity is lowered for the purpose of improving the storage stability of the coating composition, the physical properties of the coating film are lowered. Therefore, it is very difficult for the one-component coating composition to achieve both storage stability and coating film properties.

The present inventors have conducted intensive studies to solve such problems, and found that: by using the fully alkyl melamine resin as the crosslinking agent and further using the sulfonic acid compound and the amine compound so as to exhibit a specific neutralization rate, a high storage stability can be achieved even in the one-pack type composition, and further, good coating film physical properties (particularly, workability (adhesion, crack resistance) and scratch resistance) can be exhibited even when coating is performed under the condition of high temperature and a short time which is specific to the precoated steel sheet, thereby completing the aqueous coating composition and the method for producing the coating film of the present disclosure.

The present disclosure has an object to provide an aqueous coating composition which is excellent in storage stability even in a one-component form and can form a coating film excellent in workability such as bending and crack resistance and mar resistance during processing.

Means for solving the problems

The present disclosure provides the following manner.

[1]

An aqueous coating composition comprising a coating film-forming resin (A), a crosslinking agent (B), a sulfonic acid compound (C) and an amine compound (D),

the coating film-forming resin (A) contains an acrylic resin (A1),

the hydroxyl value of the coating film-forming resin (A) is 5mgKOH/g or more and 35mgKOH/g or less,

the crosslinking agent (B) contains a fully alkyl melamine resin (B1),

the neutralization rate of the sulfonic acid compound (C) based on the amine compound (D) in terms of the mole of the acid groups is 100% or more and 1,300% or less.

[2] The aqueous coating composition according to [1], wherein the weight average molecular weight of the coating film-forming resin (A) is 100,000 or more.

[3]According to [1]]Or [2]]The aqueous coating composition was prepared at a temperature of 23℃for 0.01s ^-1 The shear viscosity measured at a shear rate of 30,000 mPas or less, at 10s ^-1 The shear viscosity measured at a shear rate of 800 mPas or less, at 1,000s ^-1 The shear viscosity measured at the shear rate of (2) is 150 mPas or more.

[4] The aqueous coating composition according to any one of [1] to [3], further comprising an organic solvent (E1).

[5] The aqueous coating composition according to any one of [1] to [4], which is used for coil coating.

[6] A method for producing a coating film, comprising:

a step of forming a coating film by applying the aqueous coating composition of any one of [1] to [5] to an object to be coated; and

and drying and/or curing the coating film under the conditions that the maximum temperature is 180 ℃ or higher and the drying and/or curing time is 120 seconds or less, thereby forming a coating film.

Effects of the invention

According to the present disclosure, an aqueous coating composition which is excellent in storage stability even in a one-part form and can form a coating film excellent in workability such as bending and crack resistance and mar resistance during processing can be provided.

Detailed Description

The aqueous coating composition of the present disclosure includes a coating film forming resin (a), a crosslinking agent (B), a sulfonic acid compound (C), and an amine compound (D).

< coating film Forming resin (A) >)

The coating film-forming resin (a) contains an acrylic resin (A1). The aforementioned acrylic resin (A1) represents a polymer having a unit derived from a monomer having a (meth) acryloyl group, and can be produced by polymerizing a monomer mixture containing a monomer having an ethylenically unsaturated bond. In the present specification, (meth) acrylic acid means acrylic acid or methacrylic acid.

Examples of the monomer having an ethylenically unsaturated bond include unsaturated carboxylic acids such as (meth) acrylic acid, crotonic acid, isocrotonic acid, 2-acrylic acid, ethacrylic acid, propylacrylic acid, and isopropylacrylic acid; unsaturated polycarboxylic acids (including anhydrides thereof) such as maleic acid, fumaric acid, itaconic acid, and the like; mono-alkyl esters of unsaturated polycarboxylic acids such as ethyl maleate, butyl maleate, ethyl fumarate, butyl fumarate, ethyl itaconate, and butyl itaconate; (meth) acrylic acid alkyl esters such as methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, t-butyl (meth) acrylate, n-pentyl (meth) acrylate, neopentyl (meth) acrylate, isopentyl (meth) acrylate, sec-pentyl (meth) acrylate, 3-pentyl (meth) acrylate, hexyl (meth) acrylate, heptyl (meth) acrylate, n-octyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, nonyl (meth) acrylate, decyl (meth) acrylate, undecyl (meth) acrylate, dodecyl (meth) acrylate, stearyl (meth) acrylate, and the like; (meth) acrylic esters having an alicyclic hydrocarbon group such as cyclopentyl (meth) acrylate, cyclohexyl (meth) acrylate, isobornyl (meth) acrylate, tricyclodecyl (meth) acrylate, and adamantyl (meth) acrylate; hydroxyalkyl (meth) acrylates such as 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, and 4-hydroxybutyl (meth) acrylate; (meth) acrylic esters having a hydroxyl group such as lactone adducts (e.g., epsilon-caprolactone as the lactone); monomers having an organic silyl group, such as γ - (meth) acryloxypropyl trimethoxysilane, γ - (meth) acryloxypropyl methyl dimethoxysilane, γ - (meth) acryloxypropyl triethoxysilane, γ - (meth) acryloxypropyl methyl diethoxysilane, vinyltrimethoxysilane, vinylmethyl dimethoxysilane, vinyltriethoxysilane, vinylmethyl diethoxysilane, and the like; monomers having a sulfonic acid group such as α -vinylbenzenesulfonic acid, p- (meth) acrylamide propane sulfonic acid, and t-butyl (meth) acrylamide sulfonic acid; a monomer having a phosphate group such as a phosphate monoester of the (meth) acrylate having a hydroxyl group; (meth) acrylamide monomers such as (meth) acrylamide, N-methylol (meth) acrylamide, methoxybutyl (meth) acrylamide, diacetone (meth) acrylamide, and the like; amino group-containing (meth) acrylamide monomers such as aminoethyl (meth) acrylamide, dimethylaminoethyl (meth) acrylamide and methylaminopropyl (meth) acrylamide; (meth) acrylic esters having an epoxy group (oxirane group), such as glycidyl (meth) acrylate; (meth) acrylonitrile monomers such as (meth) acrylonitrile and α -chloro (meth) acrylonitrile; vinyl carboxylates such as vinyl acetate and vinyl propionate; styrene monomers such as styrene, α -methylstyrene dimer, vinyltoluene, and divinylbenzene; a carbonyl monomer; crosslinking monomers such as polyfunctional vinyl monomers other than those described above, and the like.

The monomer having an ethylenically unsaturated bond may be used alone or in combination of 1 or more than 2.

The acrylic resin (A1) has a hydroxyl group. By providing the acrylic resin (A1) with hydroxyl groups, a crosslinking reaction between the hydroxyl groups and the reactive groups of the crosslinking agent can be caused to cure the coating film. In order to obtain a hydroxyl group in the acrylic resin (A1), a (meth) acrylate having a hydroxyl group may be used as the monomer having an ethylenically unsaturated bond in the production of a polymer.

The hydroxyl value of the acrylic resin (A1) having a hydroxyl group is preferably 5mgKOH/g or more, more preferably 7mgKOH/g or more, still more preferably 10mgKOH/g or more, and preferably 50mgKOH/g or less, more preferably 35mgKOH/g or less, still more preferably 30mgKOH/g or less, still more preferably 25mgKOH/g or less. When the amount is within the above range, a coating film having excellent processability (adhesion and crack resistance) can be obtained.

In the (meth) acrylate having a hydroxyl group, the number of carbon atoms of the group bonded to the (meth) acryloyl group is preferably 1 to 3, more preferably 2. The (meth) acrylate having a hydroxyl group and having 1 to 3 carbon atoms bonded to the (meth) acryloyl group has an advantage that a coating film excellent in scratch resistance can be obtained. The content of the (meth) acrylate having a hydroxyl group and having 1 to 3 carbon atoms bonded to the (meth) acryloyl group is preferably 70 mass% or more, more preferably 80 mass% or more, and the upper limit is 100 mass% in the (meth) acrylate having a hydroxyl group.

The weight average molecular weight of the acrylic resin (A1) is, for example, 50,000 or more, preferably 100,000 or more, more preferably 150,000 or more, for example, 10,000,000 or less, preferably 2,000,000 or less. The acrylic resin (A1) has an advantage that the higher the weight average molecular weight, the better the scratch resistance, and a coating film excellent in processability can be obtained.

In the present specification, the weight average molecular weight is a polystyrene equivalent based on Gel Permeation Chromatography (GPC).

The acrylic resin (A1) preferably has an acid group. The acrylic resin (A1) has an acid group, so that dispersibility in an aqueous medium (E) described later can be imparted.

In order to obtain an acid group in the acrylic resin (A1), a monomer having an acid group such as an unsaturated monocarboxylic acid, an unsaturated polycarboxylic acid, a monoalkyl ester of an unsaturated polycarboxylic acid, a monomer having a sulfonic acid group, or a monomer having a phosphoric acid group may be used as the monomer having an ethylenically unsaturated bond in the production of the polymer.

The monomer having an acid group is preferably an unsaturated monocarboxylic acid, an unsaturated polycarboxylic acid, or a monoalkyl ester of an unsaturated polycarboxylic acid, more preferably an unsaturated monocarboxylic acid or an unsaturated polycarboxylic acid, still more preferably an unsaturated monocarboxylic acid, and particularly preferably (meth) acrylic acid.

The acid value of the acrylic resin (A1) is preferably 5mgKOH/g or more, and is preferably 50mgKOH/g or less, more preferably 30mgKOH/g or less. When the content is within the above range, the acrylic resin (A1) can be stably dispersed in the aqueous medium (E).

In the present specification, the acid value and the hydroxyl value of the acrylic resin (A1) represent the acid value of the solid component and the hydroxyl value of the solid component, respectively, and can be measured in accordance with JISK 0070:1999.

The glass transition temperature (Tg) of the acrylic resin (A1) is preferably-70 ℃ or higher, more preferably 0 ℃ or higher, still more preferably 10 ℃ or higher, still more preferably 15 ℃ or higher, and is preferably 95 ℃ or lower, more preferably 90 ℃ or lower, still more preferably 85 ℃ or lower, still more preferably 80 ℃ or lower. When the content is within the above range, there is an advantage that a coating film excellent in coating film processability and scratch resistance can be obtained.

The aforementioned glass transition temperature can be calculated as the reciprocal of the sum of the respective quotient obtained by dividing the mass fraction of the respective monomers constituting the acrylic resin (A1) by the Tg (K: kelvin) value of the homopolymer (homopolymer) derived from the respective monomers.

In more detail, in the present specification, the aforementioned glass transition temperature (Tg) can be calculated by Fox formula (t.g. Fox; bull.am. Phys.soc.,1 (3), 123 (1956)).

For example, when the resin is a polymer of a plurality of monomers (monomer a, monomer B, … monomer N), tg shown by the following general formula is defined as Tg of the resin.

1/Tg＝wa/Tga+wb/Tgb+…+wn/Tgn

Here the number of the elements is the number,

tga: glass transition temperature (K), wa) of homopolymer of monomer a: mass fraction of monomer A,

Tgb: glass transition temperature (K), wb) of the homopolymer of monomer B: mass fraction of monomer B,

Tgn: glass transition temperature (K), wn of the homopolymer of monomer N: the mass fraction of the monomer N,

wa+wb+…+wn＝1。

among the monomers forming the acrylic resin (A1), the monomer having an ethylenically unsaturated bond preferably contains an alkyl (meth) acrylate, more preferably an alkyl (meth) acrylate having 1 to 6 carbon atoms, still more preferably 1 to 4 carbon atoms in the alkyl group. By using the monomer in the above range, the obtained coating film has an advantage of excellent scratch resistance. The content of the alkyl (meth) acrylate having 1 to 6 carbon atoms in the alkyl (meth) acrylate is preferably 20 mass% or more, more preferably 30 mass% or more, still more preferably 40 mass% or more, and is preferably 95 mass% or less, more preferably 85 mass% or less, still more preferably 80 mass% or less.

Among the monomers contained in the acrylic resin (A1), the content of the styrene monomer is preferably 10 mass% or less, more preferably 5 mass% or less, still more preferably 3 mass% or less, and the lower limit is 0 mass% from the viewpoint of weather resistance.

In the case where the acrylic resin (A1) has an acid group, the aqueous coating composition may contain a basic compound. By incorporating the basic compound in the aqueous coating composition, a part or all of the acid groups are neutralized, and thus water dispersibility can be imparted to the acrylic resin well. As the basic compound, ammonia, an amine compound, an alkali metal, or the like can be used, for example. In addition, a part of the amine compound (D) described later may be used as the basic compound.

In addition, a known anionic and/or nonionic surfactant may be used to impart water dispersibility to the acrylic resin.

The content of the acrylic resin (A1) in the coating film-forming resin (a) is preferably 5 mass% or more, more preferably 10 mass% or more, still more preferably 15 mass% or more, and the upper limit is 100 mass%.

The acrylic resin (A1) is preferably an aqueous resin, and may be a water-soluble resin that is soluble in the aqueous medium (E), or may be a water-dispersible resin that is dispersible in the aqueous medium (E), such as a colloidal dispersion type, an emulsion type (emulsion polymerization type, forced emulsification type), or the like. The acrylic resin (A1) is preferably a water-dispersible resin, more preferably an emulsion-type water-dispersible resin, and particularly preferably an emulsion-type water-dispersible resin by emulsion polymerization. The acrylic resin (A1) has an acid group and/or a hydroxyl group and/or is allowed to coexist with an emulsifier, whereby an aqueous resin can be produced.

When the acrylic resin (A1) is an emulsion-type water-dispersible resin, the average particle diameter of the emulsion particles is preferably 500nm or less, more preferably 300nm or less, still more preferably 200nm or less, and may be, for example, 10nm or more, 30nm or more, or 50nm or more. When the content is within the above range, there is an advantage that the emulsion particles and the coating composition containing the emulsion particles are excellent in storage stability. In the present specification, the average particle size is an average particle size determined by a dynamic light scattering method, and specifically, measurement can be performed using an electrophoresis light scattering photometer ELSZ series (manufactured by the tsuka electronics company) or the like.

The minimum film forming temperature (MFT) of the acrylic resin (A1) is preferably 50 ℃ or higher, more preferably 60 ℃ or higher, still more preferably 70 ℃ or higher, and may be, for example, 200 ℃ or lower, 150 ℃ or lower, or 120 ℃ or lower. When the amount is within the above range, the resulting coating film has the advantages of improved scratch resistance and suppressed adhesion between the coating films. In the present specification, the minimum film forming temperature means: the minimum temperature at which a uniform coating film free of cracks is formed when the emulsion type water-dispersible resin is dried can be measured in accordance with JISK 6828-2:2003.

When the acrylic resin (A1) is an emulsion-type water-dispersible resin, the emulsion may be an emulsion in which particles having a multilayer structure including a core portion and a shell portion are dispersed.

The multilayered structure particles can be produced by, for example, the method described in Japanese patent application laid-open No. 2002-12816.

The acrylic resin (A1) can be produced by polymerizing the monomer having an ethylenically unsaturated bond, and the polymerization reaction can be carried out, for example, by heating the monomer having an ethylenically unsaturated bond in a part or the whole of the aqueous medium (E) with stirring. The polymerization reaction is preferably emulsion polymerization. In the polymerization reaction, a polymerization initiator is preferably present together, and an emulsifier is preferably present together as needed. The reaction temperature is preferably 30 to 100℃and the reaction time is preferably 1 to 10 hours.

The polymerization initiator is preferably a radical polymerization initiator. As the water-soluble radical polymerization initiator, persulfates such as potassium persulfate, sodium persulfate, ammonium persulfate, and the like can be used. Further, a redox initiator obtained by combining an oxidizing agent such as potassium persulfate, sodium persulfate, ammonium persulfate, hydrogen peroxide, and a reducing agent such as sodium bisulfite, sodium thiosulfate, rongalite, and ascorbic acid may be used. These radical polymerization initiators may be used in the form of an aqueous solution by dissolving them in a part or the whole of the aqueous medium (E).

As the emulsifier, an anionic or nonionic emulsifier having a hydrophobic moiety such as a hydrocarbon group having 6 or more carbon atoms and a hydrophilic moiety such as carboxylate, sulfonate or sulfate partial ester in the same molecule can be used. Examples of the anionic emulsifier include alkali metal salts or ammonium salts of sulfuric acid half esters of alkylphenols or higher alcohols; alkali metal or ammonium salts of alkyl or allyl sulfonates; alkali metal salts or ammonium salts of sulfuric acid half esters of polyoxyethylene alkylphenyl ethers, polyoxyethylene alkyl ethers or polyoxyethylene allyl ethers; various anionic reactive emulsifiers having groups such as acrylic, methacrylic, propenyl, allyl ether, and maleic and ethylenically unsaturated bonds, and the like.

Examples of the nonionic emulsifier include polyoxyalkylene ethers such as polyoxyethylene alkylphenyl ether, polyoxyethylene alkyl ether, and polyoxyethylene allyl ether; nonionic reactive emulsifiers having groups such as acrylic, methacrylic, propenyl, allyl ether, and maleic and ethylenically unsaturated bonds.

In addition, in the polymerization (preferably emulsion polymerization), from the viewpoint of performing the polymerization (preferably emulsion polymerization), and from the viewpoint of promoting smooth and uniform formation of a coating film and improving adhesion to a coating object, it is preferable to use an auxiliary agent (chain transfer agent) for adjusting molecular weight such as a thiol compound and a lower alcohol in combination in many cases, and it is suitably performed according to circumstances.

In the case of performing emulsion polymerization, any emulsion polymerization method such as a usual single-stage continuous monomer homogeneous drop method, a core-shell polymerization method as a multistage monomer feed method, and a dynamic feed polymerization method in which the monomer composition is continuously changed during the polymerization may be used.

The acrylic resin (A1) may be used for the preparation of an aqueous coating composition in the form of an aqueous solution or aqueous dispersion containing the acrylic resin (A1) in advance and containing a part of the aqueous medium (E) described later. The aqueous solution or aqueous dispersion may further comprise the aforementioned emulsifiers.

As the acrylic resin (A1), a commercially available product can be used. In addition, only 1 kind may be used, or 2 or more kinds may be used in combination.

The coating film-forming resin (a) may contain other resins (A2) in addition to the acrylic resin (A1).

Examples of the other resin (A2) include an acrylic resin, a urethane resin, a vinyl acetate resin, a fluororesin, a vinyl chloride resin, and the like which do not contain hydroxyl groups, and are each preferably an aqueous resin, more preferably a water-dispersible resin, and further preferably an emulsion-type water-dispersible resin. The other resin (A2) may be used for the preparation of the aqueous coating composition in the form of an aqueous solution or aqueous dispersion containing the other resin (A2) in advance and containing a part of the aqueous medium (E). The aqueous solution or dispersion may comprise an emulsifier.

The aforementioned hydroxyl group-free acrylic resin means a polymer having a unit derived from a monomer having a (meth) acryloyl group, and can be prepared by polymerizing a mixture of monomers having no hydroxyl group among the aforementioned monomers having an ethylenically unsaturated bond.

The weight average molecular weight of the hydroxyl group-free acrylic resin is preferably 50,000 or more, more preferably 100,000 or more, further preferably 150,000 or more, and is preferably 10,000,000 or less, more preferably 2,000,000 or less, further preferably 500,000 or less. When the amount is within the above range, there is an advantage that the processability of the obtained coating film becomes good.

The glass transition temperature of the hydroxyl group-free acrylic resin is preferably 80 ℃ or lower, more preferably 60 ℃ or lower, further preferably 50 ℃ or lower, and is preferably 20 ℃ or higher, more preferably 30 ℃ or higher, further preferably 40 ℃ or higher. When the amount is within the above range, there is an advantage that damage resistance becomes good.

The minimum film forming temperature (MFT) of the acrylic resin is preferably 50 ℃ or higher, more preferably 60 ℃ or higher, still more preferably 70 ℃ or higher, and may be, for example, 200 ℃ or lower, 150 ℃ or lower, or 120 ℃ or lower. When the amount is within the above range, the resulting coating film has the advantages of improved scratch resistance and suppressed adhesion between the coating films.

The aforementioned hydroxyl group-free acrylic resin preferably has an acid group. The acid value of the hydroxyl group-free acrylic resin is preferably 5mgKOH/g or more, and is preferably 50mgKOH/g or less, more preferably 30mgKOH/g or less.

When the hydroxyl group-free acrylic resin is contained, the content thereof is preferably 20 mass% or more, more preferably 30 mass% or more, and preferably 90 mass% or less, more preferably 85 mass% or less in the total of the acrylic resin (A1) and the hydroxyl group-free acrylic resin.

The hydroxyl value of the coating film-forming resin (A) is 5mgKOH/g or more, preferably 7mgKOH/g or more, more preferably 10mgKOH/g or more, and is 35mgKOH/g or less, preferably 30mgKOH/g or less, more preferably 25mgKOH/g or less. When the content is within the above range, there is an advantage that a coating film having excellent processability and scratch resistance can be obtained.

The acid value of the coating film-forming resin (A) is preferably 5mgKOH/g or more, and is preferably 50mgKOH/g or less, more preferably 30mgKOH/g or less. When the content is within the above range, the coating film-forming resin (a) can be stably dispersed in the aqueous medium (E).

The weight average molecular weight of the coating film-forming resin (a) is, for example, 50,000 or more, preferably 100,000 or more, more preferably 150,000 or more, for example, 10,000,000 or less, preferably 2,000,000 or less. When the content is within the above range, there is an advantage that a coating film having good workability can be obtained.

The glass transition temperature (Tg) of the coating film forming resin (a) is preferably-70 ℃ or higher, more preferably 20 ℃ or higher, still more preferably 25 ℃ or higher, still more preferably 30 ℃ or higher, and is preferably 95 ℃ or lower, more preferably 70 ℃ or lower, still more preferably 60 ℃ or lower, still more preferably 50 ℃ or lower. When the content is within the above range, there is an advantage that a coating film excellent in coating film processability and scratch resistance can be obtained.

As the coating film forming resin (a), only 1 kind may be used, or 2 or more kinds may be used in combination. When the coating film-forming resin (a) contains 2 or more types, each parameter of the coating film-forming resin (a) other than the glass transition temperature may be calculated as a weighted average value based on the parameters and the content of each resin. The glass transition temperature may be calculated by summing up the values obtained by dividing the content of the mass reference of each coating film forming resin by the glass transition temperature (K: kelvin value), and calculating the values as the reciprocal thereof.

The content of the coating film-forming resin (a) is preferably 50 parts by mass or more, more preferably 70 parts by mass or more, still more preferably 80 parts by mass or more, and is preferably 100 parts by mass or less, more preferably 95 parts by mass or less, still more preferably 90 parts by mass or less, based on 100 parts by mass of the solid content of the aqueous coating composition. In the present specification, the content of the coating film forming resin (a) means the content of only solid components.

In the present specification, the solid content of the aqueous coating composition means a portion after the aqueous medium (E) is removed from the entire aqueous coating composition.

< crosslinker (B) >

The crosslinking agent (B) is a compound having 2 or more groups capable of reacting with hydroxyl groups contained in the coating film-forming resin (a) in one molecule, and is capable of crosslinking with the coating film-forming resin (a) to form a coating film. The crosslinking agent (B) contains an amino resin, and examples of the amino resin include melamine resin, urea resin, benzoguanamine, and the like. The amino resin preferably contains a melamine resin from the viewpoints of storage stability of the obtained coating composition and various physical properties (processability, mar resistance) of the obtained coating film.

The melamine resin is a thermosetting resin synthesized from melamine and an aldehyde, and is preferably a compound having 3 reactive functional groups represented by the following formula as reactive functional groups in 1 molecule of triazine core or a polycondensate thereof.

-NX ₁ X ₂

[X ₁ 、X ₂ Each independently represents a hydrogen atom, a hydroxymethyl group or a-CH ₂ -OR ¹ 。

R ¹ An alkyl group having 1 to 8 carbon atoms is preferably a linear or branched alkyl group having 1 to 8 carbon atoms.

Comprising multiple-CH in the same molecule ₂ -OR ¹ In the case of (1), a plurality of R ¹ May be the same or different.]

Examples of melamine resins include melamine resins containing only-N (CH) ₂ OR ¹ ) ₂ A holoalkyl type as a reactive functional group; comprises-N (CH) ₂ OR ¹ )(CH ₂ OH) hydroxymethyl type as reactive functional group; comprises-N (CH) ₂ OR ¹ ) (H) imino as a reactive functional group; comprises-N (CH) ₂ OR ¹ )(CH ₂ OH) and-N (CH) ₂ OR ¹ ) (H) or comprises-N (CH) ₂ OH) (H) as reactive functional groups. R is R ¹ Preferably an alkyl group having 1 to 4 carbon atoms, and more preferably a methyl group, an n-butyl group or an isobutyl group.

In the present disclosure, among the aforementioned melamine resins, X is preferably contained ¹ And X ² Are all-CH ₂ -OR ¹ Examples of the compound (B1) or the peralkylated melamine resin (B1) as a polycondensate thereof include methylated melamine resin, butylated melamine resin, isobutylated melamine resin and the like. The inclusion of the fully alkyl melamine resin has the advantage that the resulting coating composition has good storage stability and good reactivity with the acrylic resin (A1) at high temperatures and in the presence of a catalyst.

The degree of polymerization of the above-mentioned fully alkyl melamine resin (B1) is 1 or more, preferably 1.2 or more, more preferably 1.5 or more, and preferably 10 or less, more preferably 5 or less, more preferably 3 or less.

The number average molecular weight of the fully alkyl melamine resin (B1) is preferably 300 or more, preferably 2,000 or less, more preferably 1,300 or less, still more preferably 1,000 or less, and particularly preferably 800 or less.

In the present specification, the number average molecular weight is a polystyrene equivalent based on Gel Permeation Chromatography (GPC).

Examples of the fully-alkyl melamine resin (B1) include CYMEL303, CYMEL325, CYMEL350, CYMEL370, and mare コ (both of which are methylated melamine resins, available from ladle company); CYMEL202, CYMEL235, CYMEL254, CYMEL1123, CYMEL1128, CYMEL1170, and matrix コ (both of methyl-butylated mixed melamine resin, matrix of crokurtin corporation); a surfactant M-40S (methylated melamine resin, manufactured by sumitomo chemical company); and J-820-60 and L-127-60 (both of butylated melamine resin, DIC Co.) by Di-Di. The number of these may be 1 alone, or 2 or more may be used in combination.

The content of the fully alkyl melamine resin (B1) in the crosslinking agent (B) is preferably 80 mass% or more, more preferably 90 mass% or more, still more preferably 95 mass% or more, and the upper limit is 100 mass%.

The crosslinking agent (B) may contain a crosslinking agent (B2) in addition to the fully alkyl melamine resin (B1). Examples of the other crosslinking agent (B2) include amino resins such as melamine resins, urea resins, and benzoguanamine resins other than the fully alkyl melamine resin (B1). The amino resin has high reactivity with the coating film-forming resin (A), and the obtained coating film has good appearance and moisture resistance.

As the crosslinking agent (B), only 1 kind may be used, or 2 or more kinds may be used in combination.

The ratio ((B)/(A)) of the content of the crosslinking agent (B) to the content of the coating film-forming resin (A) is preferably 5/95, more preferably 10/90 or more, and is preferably 30/70 or less, more preferably 20/80 or less on a mass basis. When the content is within the above range, there is an advantage that the processability and scratch resistance of the obtained coating film become good.

< sulfonic acid Compound (C) >)

The sulfonic acid compound (C) can function as a catalyst for promoting the reaction between the coating film-forming resin (a) and the crosslinking agent (B). Therefore, there is an advantage in that high reactivity can be imparted to the resulting coating composition.

The sulfonic acid compound (C) may be a monosulfonic acid compound or a polysulfonic acid compound. Examples of the sulfonic acid compound include aliphatic sulfonic acids such as methanesulfonic acid; aromatic sulfonic acids such as p-toluenesulfonic acid, dodecylbenzenesulfonic acid, dinonylnaphthalenesulfonic acid, dinonylnaphthalenedisulfonic acid, and the like. As the sulfonic acid compound (C), only 1 kind may be used, or 2 or more kinds may be used in combination.

The content of the sulfonic acid compound (C) is preferably 0.1 part by mass or more, more preferably 0.5 part by mass or more, and preferably 5 parts by mass or less, more preferably 3 parts by mass or less, based on 100 parts by mass of the coating film forming resin (a). When the content of the sulfonic acid compound (C) is in the above range, a coating film having excellent workability (adhesion, crack resistance) and flaw resistance of the precoated steel sheet can be formed.

< amine Compound (D) >)

The amine compound (D) has an effect of neutralizing the sulfonic acid compound (C), and is coexistent with the sulfonic acid compound (C) so as to exhibit a specific neutralization rate, whereby there is an advantage that it is possible to achieve both stability at the time of storage (for example, 15 to 50 ℃) and high reactivity at the time of heat drying/curing after coating of the aqueous coating composition. Part of the amine compound (D) may be present as a salt with the sulfonic acid compound (C).

The amine compound (D) is a compound having 1 or more amino groups, and is preferably a secondary amine compound or a tertiary amine compound.

The substituent of the nitrogen atom of the amine compound is preferably a saturated or unsaturated aliphatic hydrocarbon group, the hydrogen atoms contained in the saturated or unsaturated aliphatic hydrocarbon group may be each independently substituted with-COOH, -OH or the like, and-CH contained in the saturated or unsaturated aliphatic hydrocarbon group ₂ May be replaced by-O-. In addition, the substituents of the nitrogen atom of the amine compound may be bonded to each other to form a ring containing the nitrogen atom.

Examples of the amine compound (D) include aliphatic secondary amine compounds such as diethylamine, di-N-propylamine, diisopropylamine, diisobutylamine, di-N-butylamine, di-sec-butylamine, dipentylamine, N-ethyl-1, 2-dimethylpropylamine, N-methylhexylamine, di-N-octylamine, and diallylamine; aliphatic tertiary amine compounds such as triethylamine, tributylamine, triallylamine, N-dimethylethanolamine, N-methyldiallylamine, and N, N-dimethylallylamine; cyclic secondary amine compounds such as piperidine, 2-methylpiperidine, 3-methylpiperidine, 4-methylpiperidine, 2, 4-dimethylpiperidine, 2, 6-dimethylpiperidine, 3, 5-dimethylpiperidine, and 3-piperidinemethanol; cyclic tertiary amine compounds such as N-methylpiperidine, N-methylpiperazine and N-methylmorpholine; pyridine, 4-ethylpyridine, and the like as an amine compound of an aromatic compound.

The boiling point of the amine compound (D) is preferably 50℃or higher, more preferably 70℃or higher, still more preferably 100℃or higher, and preferably 250℃or lower, more preferably 220℃or lower. When the content is within the above range, the storage stability of the aqueous coating composition can be further improved.

The amine compound (D) is contained in such an amount that the neutralization rate of the sulfonic acid compound (C) based on the amine compound (D), that is, the neutralization rate in terms of a mole calculated by the following formula, is in the range of 100% to 1,300%.

Neutralization rate (%) = [ (valence of base of amine compound (D)/(mole of amine compound (D)/(valence of acid of sulfonic acid compound (C) ×mole of sulfonic acid compound (C) ]×100

The neutralization rate is preferably 200% or more, more preferably 300% or more, and may be, for example, 1,300% or less, 1,100% or less, 1,000% or less, or may be 900% or less, 800% or less. While not being limited to a particular theory, it is believed that: when the amount is within the above range, the amine compound (D) can block the sulfonic acid group of the sulfonic acid compound (C) during storage (for example, 15 to 30 ℃ C.) and inhibit the catalytic action, thereby improving the storage stability, and the blocked end can be released during heat drying/curing (for example, 180 ℃ C. Or more) after coating, whereby the sulfonic acid compound (C) can function as a catalyst.

Known are: the fully alkyl melamine resin (B1) has lower reactivity than melamine resins which are usually used as crosslinking agents, such as imino melamine resins and methylol melamine resins. However, according to the results of the studies by the present inventors, etc., it was found that: the reactivity of the fully alkyl melamine resin (B1) is low in the case of low-temperature reaction (for example, 60 to 80 ℃), and when the fully alkyl melamine resin (B1) is used together with the sulfonic acid compound (C) and the amine compound (D) so as to have the neutralization rate, the reactivity at high temperature becomes high. By combining the above-mentioned all-alkyl melamine resin (B1), the above-mentioned sulfonic acid compound (D), the above-mentioned amine compound (D), and the above-mentioned neutralization ratio, the storage stability is good, and an aqueous coating composition particularly suitable for high-temperature/short-time coating can be obtained, and further, the crosslinking density can be increased, and therefore, there is an advantage that a coating film excellent in coating film processability (adhesion, crack resistance) can be obtained.

The sulfonic acid compound (C) and the amine compound (D) may be used directly for the preparation of the aqueous coating composition, or may be used in the form of a mixture obtained by previously mixing them. In this case, the sulfonic acid compound (C) and a part or all of the amine compound (D) may be formed into a salt (for example, a salt obtained by capping a sulfonic acid group contained in the sulfonic acid compound (C) with an amino group contained in the amine compound (D)) in the mixture, or may be formed into a salt of the sulfonic acid compound (C) and a part or all of the amine compound (D) and then blended into the coating composition. Examples of the salt of the sulfonic acid compound (C) with a part or all of the amine compound (D) include aliphatic sulfonic acids such as methanesulfonic acid; aromatic sulfonic acids such as dinonylnaphthalene disulfonic acid and dinonylnaphthalene sulfonic acid, and end-caps of these amines. The salt of the sulfonic acid compound (C) with a part or all of the amine compound (D) may be commercially available ones.

In one embodiment, it is preferred that: the content of the sulfonic acid compound (C) is 1 part by mass or more and 5 parts by mass or less relative to 100 parts by mass of the coating film-forming resin (A), and the neutralization rate is 100% or more and 1,300% or less; more preferred are: the content of the sulfonic acid compound (C) is 0.1 part by mass or more and 5 parts by mass or less relative to 100 parts by mass of the coating film-forming resin (A), and the neutralization rate is 200% or more and 1,000% or less; further preferred are: the content of the sulfonic acid compound (C) is 2 parts by mass or more and 9 parts by mass or less relative to 100 parts by mass of the coating film-forming resin (A), and the neutralization rate is 300% or more and 900% or less. By providing the coating composition with the amounts and neutralization rates of the sulfonic acid compound (C) and the amine compound (D) as described above, the coating composition has high storage stability at low temperatures (e.g., 15 to 30 ℃) and also has higher reactivity at high temperatures, and the resulting coating film has better processability (adhesion, crack resistance) and mar resistance.

The total content of the film-forming resin (a), the crosslinking agent (B), the sulfonic acid compound (C), and the amine compound (D) in the solid content of the aqueous coating composition is, for example, preferably 50 mass% or more, more preferably 70 mass% or more, still more preferably 80 mass% or more, and the upper limit is 100 mass% or less.

< aqueous Medium (E) >

The aforementioned aqueous coating composition comprises an aqueous medium (E). The aqueous medium (E) is preferably water, an organic solvent (E1), or a mixture of water and an organic solvent (E1).

As the organic solvent (E1), a hydrophilic organic solvent is preferable, and for example, a solubility in water at 25℃of 0.1g/100gH is exemplified ₂ And an organic solvent of O or more. Examples of such organic solvents include glycol solvents such as ethylene glycol, propylene glycol, butylene glycol, pentylene glycol, diethylene glycol, dipropylene glycol, and triethylene glycol; glycol ether solvents such as ethylene glycol monobutyl ether (butyl cellosolve), diethylene glycol monobutyl ether acetate, triethylene glycol monoethyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, and propylene glycol monomethyl ether acetate; alcohol solvents such as methanol, ethanol, isopropanol, and benzyl alcohol; cyclic ether solvents such as dioxane and tetrahydrofuran; alcohol ester solvents such as 2, 4-trimethylpentane-1, 3-diol monoisobutyrate; ketone solvents such as acetone; n-methyl-2-pyrrolidone, and the like. By using such an organic solvent, there is an advantage in that wettability of the resulting coating composition with a substrate becomes good.

In one embodiment, the boiling point of the organic solvent (E1) is preferably 150 ℃ or higher, more preferably 180 ℃ or higher, and preferably 300 ℃ or lower, more preferably 250 ℃ or lower. Examples of such an organic solvent include glycol solvents such as propylene glycol (1, 2-propanediol), 1, 4-butanediol, 1, 5-pentanediol, diethylene glycol, and dipropylene glycol, and diethylene glycol is particularly preferred. Only 1 kind of them may be used, or 2 or more kinds may be used.

The solubility of the aforementioned organic solvent (E1) in water is preferably 0.1g/100gH at 25 DEG C ₂ O or more, more preferably 1g/100gH ₂ O or more, more preferably 5g/100gH ₂ O or more. The aforementioned organic solvent (E1) may be a water-miscible organic solvent.

The content of the organic solvent (E1) in the aqueous medium (E) is 3 mass% or more, preferably 4 mass% or more, more preferably 5 mass% or more, and preferably 30 mass% or less, more preferably 20 mass% or less, and further preferably 10 mass% or less. By being in the aforementioned range, there are the following advantages: the environmental load can be reduced, and the coating composition has good storage stability, wettability to a substrate, and appearance of a coating film obtained.

The content of the aqueous medium (E) is preferably 40 mass% or more, more preferably 50 mass% or more, still more preferably 55 mass% or more, and is preferably 90 mass% or less, more preferably 80 mass% or less, still more preferably 85 mass% or less.

The aqueous coating composition may contain an organic solvent other than the aqueous medium (E) as required. Examples of the organic solvent other than the above (E) include diethylene glycol dibutyl ether, 2, 4-trimethyl-1, 3-pentanediol monoisobutyrate (Texanol), and the like. The boiling point of the organic solvent other than the above (E) is preferably 150℃or more, more preferably 180℃or more, and preferably 300℃or less, more preferably 250℃or less.

< others >

The aforementioned aqueous coating composition may further contain other additives as needed. As the aforementioned other additives, there are, for example, extender pigments; coloring agents such as coloring pigments and dyes; a thermally insulating pigment; a lustrous pigment; aggregate (resin particles, silica particles, etc.); a wax; solvents other than the foregoing; ultraviolet absorbers (benzophenone-based ultraviolet absorbers, etc.); antioxidants (phenol-based, thioether-based, hindered amine-based antioxidants, etc.); a plasticizer; coupling agents (silane-based, titanium-based, zirconium-based coupling agents, etc.); an anti-sagging agent; a viscosity modifier; a pigment dispersant; a pigment wetting agent; surface conditioning agents (silicone-based, organic polymer-based, etc.); a leveling agent; an anti-dichroic agent; an anti-settling agent; an anti-settling agent; a defoaming agent; a surfactant; an anti-freezing agent; an emulsifying agent; an antirust agent; a preservative; a mildew inhibitor; an antimicrobial agent; stabilizers, and the like. These additives may be used in an amount of 1 or 2 or more.

The viscosity modifier (F) may be an associative viscosity modifier using a bonding force (interaction) of a hydrophilic group (moiety) or a hydrophobic group (moiety); thickening viscosity modifier utilizing the solubilization/thickening action of polymer. The associative viscosity modifier includes a hydrophilic associative viscosity modifier that forms hydrogen bonds between the viscosity modifiers or between the viscosity modifiers and the matrix resin and utilizes the bonding force (interaction) of the viscosity modifiers and a hydrophobic associative viscosity modifier that utilizes the interaction of hydrophobic groups (moieties) in the molecule, and the associative viscosity modifier includes an alkali thickening viscosity modifier that utilizes the solubilization/thickening action of an alkali-based polymer.

The hydrophilic-associated viscosity modifier may be a polyamide-based viscosity modifier. As the polyamide-based viscosity modifier, commercially available ones can be used, and examples thereof include BYK-430, BYK-431 (manufactured by the brand company); the duinding is selected from the group consisting of duinding AQ-580, duinding AQ-600, duinding AQ-607 (manufactured by nannik localization corporation); and a copy of the metal, such as copy W-300 and copy W-400LP (manufactured by co-chemical Co., ltd.).

Examples of the hydrophobic-associated viscosity modifier include a commercial product such as a tare UH-420, a tare UH-462, a tare UH-472, a tare UH-526, a UH-540, and a tare UH-814N (manufactured by ADEKA corporation); pan RH-1020, pan RM-2020 (manufactured by pan company); and SN tap 612, SN tap 621, and tap 700N (manufactured by tap コ).

Examples of the alkali thickening viscosity modifier include viscose, methylcellulose, ethylcellulose, hydroxyethylcellulose, sodium polyacrylate, polyvinyl alcohol, and carboxymethyl cellulose. Further, commercially available products may be used, and examples thereof include cellulose-based viscosity modifiers such as zerland MH and zerland H (manufactured by the company phaku); pan ASE-60, pan TT-615, pan RM-5 (manufactured by pan company); the strain is a strain and the strain is a strain; on, inc.) and the like.

The number of these may be 1 alone, or 2 or more may be used in combination.

The viscosity modifier (F) is preferably an associative viscosity modifier. By including the associative viscosity regulator, there is an advantage that the coating workability in a roll coater (roll coater coatability) becomes good. In particular, the viscosity of the coating composition can be caused to exhibit newtonian theory at high shear rates. In addition, more preferable is: the use of the hydrophobic-associated viscosity modifier in combination provides an advantage that the resulting coating film can have good physical properties such as water resistance.

The content of the tackiness adjusting agent (F) contained in the aqueous coating composition of the present disclosure is preferably 0.01 to 20 parts by mass, more preferably 0.1 to 10 parts by mass, relative to 100 parts by mass of the total solid content of the coating film forming resin (a) and the crosslinking agent (B). When the amount of the tackiness adjusting agent (F) is in such a range, there is an advantage that the coating workability in a roll coater (roll coater coatability) and the appearance and water resistance of the obtained coating film become good.

Examples of the extender pigment include calcium carbonate, barium sulfate, clay, talc, mica, and glass fiber. The number of these may be 1 alone, or 2 or more may be used in combination.

In one embodiment, the amount of the extender pigment is preferably 1 to 40 parts by mass, more preferably 10 to 30 parts by mass, based on 100 parts by mass of the total solid components of the coating film forming resin (a) and the curing agent (B). By setting the amount of extender pigment in this range, the scratch resistance of the coating film is easily improved.

Examples of the coloring pigment include coloring inorganic pigments such as titanium dioxide, carbon black, graphite, iron oxide, and coal dust; colored organic pigments such as phthalocyanine blue, phthalocyanine green, quinacridone, perylene, anthrapyrimidine, carbazole violet, anthrapyridine, azo orange, flavanthrone yellow, isoindoline yellow, azo yellow, indanthrene blue, dibromoanthrone red, perylene red, azo red, anthraquinone red, and the like; aluminum powder, aluminum oxide powder, bronze powder, copper powder, tin powder, zinc powder, iron phosphide, micronized titanium and the like. These may be used in an amount of 1 or 2 or more.

The heat-insulating pigment means: a pigment which does not absorb light in the near infrared wavelength region (wavelength: 780nm to 2,500 nm) or has a small absorptivity of light in the near infrared wavelength region (wavelength: 780nm to 2,500 nm). The heat-insulating pigment is not particularly limited, and the following inorganic heat-insulating pigments and organic heat-insulating pigments can be used.

Examples of the inorganic heat-insulating pigment include metal oxide pigments such as titanium oxide, magnesium oxide, barium oxide, calcium oxide, zinc oxide, zirconium oxide, yttrium oxide, indium oxide, sodium titanate, silicon oxide, nickel oxide, manganese oxide, chromium oxide, iron oxide, copper oxide, cerium oxide, and aluminum oxide; iron oxide-manganese oxide, iron oxide-chromium oxide (for example, dyco manufactured by Dairy refining company, dyco #9595, black6350 manufactured by chemical industry company), iron oxide-cobalt oxide-chromium oxide (for example, dyco #9290 manufactured by Dairy refining company, dyco # 9290) a composite oxide pigment such as a dyi-collar, a dyi-collar #9590, a copper oxide-magnesium oxide (for example, a dyi-collar manufactured by dado refinement, a dyi-collar #9598, a dyi-collar, a manganese oxide-bismuth oxide (for example, a Black6301, a dyi-collar, a Black6303, a dyi-collar, a compound industrial company), and a manganese oxide-yttrium oxide; metallic pigments such as silicon, aluminum, iron, magnesium, manganese, nickel, titanium, chromium, and calcium; alloy pigments such as iron-chromium, bismuth-manganese, iron-manganese, manganese-yttrium, and the like. The number of these may be 1 alone, or 2 or more may be used in combination.

Examples of the organic heat-insulating pigment include azo pigments, azomethine pigments, lake pigments, thioindigo pigments, anthraquinone pigments (anthranthrone pigments, diaminoanthraquinone pigments, indanthrone pigments, flavanthrone pigments, anthrapyrimidine pigments, and the like), perylene pigments, diketopyrrolopyrrole pigments, dioxazine pigments, phthalocyanine pigments, quinophthalone pigments, quinacridone pigments, isoindoline pigments, and isoindolinone pigments. The number of these may be 1 alone, or 2 or more may be used in combination.

Examples of the brightening pigment include foil pigments such as aluminum foil, bronze foil, tin foil, gold foil, silver foil, titanium foil, stainless steel foil, alloy foil such as nickel-copper, and foil-like phthalocyanine blue. The number of these may be 1 alone, or 2 or more may be used in combination.

As the wax, a wax known to those skilled in the art for coating applications can be used, and examples thereof include microcrystalline wax, polyethylene wax, polypropylene wax, paraffin wax, carnauba wax, and modified products thereof. The number of these may be 1 alone, or 2 or more may be used in combination.

The shear viscosity of the aqueous coating composition was 0.01s at a temperature of 23 DEG C ^-1 The shear rate of (2) is preferably 30,000 mPas or less, more preferably 20,000 mPas or less, still more preferably 10,000 mPas or less, and is preferably 3,000 mPas or more, more preferably 4,000 mPas or more, still more preferably 5,000 mPas or more. At 10s ^-1 The shear rate of (2) is preferably 800 mPas or less, more preferably 700 mPas or less, still more preferably 600 mPas or less, and is preferably 300 mPas or more, more preferably 400 mPas or more, still more preferably 500 mPas or more. At 1,000s ^-1 The shear rate of (2) is preferably 1,000 mPas or less, more preferably 150 mPas or more, and still more preferably 500 mPas or less. When the viscosity is within the above range, the coating composition exhibits a viscosity suitable for coating pick-up properties in the application by a roll coater.

The aforementioned shear viscosity may be set to, for example, a value measured immediately after the preparation of the coating composition.

The aforementioned shear viscosity can be measured using a rotary viscometer, for example, a strain-controlled rheometer MCR301 (available from the company "Sida" as a whole) manufactured by company), and the like.

< method for producing Water-based coating composition >

The method for preparing the aqueous coating composition of the present disclosure is not particularly limited, and may be prepared by mixing the components. The mixing may be performed using a mixer-disperser, a kneader, or the like, such as a roll mill, a ball mill, a bead mill, a stone mill, a sand mill, a tank mill, a paint stirrer, or a dispenser.

A coating film formed from the aforementioned aqueous coating composition and a method for producing the coating film are also included in the technical scope of the present disclosure.

< coated article >

Examples of the coating material (substrate) to be coated with the aqueous coating composition of the present disclosure include galvanized steel sheets, galvanized aluminum alloy steel sheets, galvanized molten zinc-aluminum-magnesium alloy steel sheets, stainless steel sheets, cold-rolled steel sheets, and the like, which are produced by a fusion method, an electrolytic method, or the like. In addition to these steel plates or plated steel plates, a metal plate such as an aluminum plate (including an aluminum alloy plate) may be used as a coating target.

The substrate is preferably surface-treated. Specifically, the coating material is preferably subjected to pretreatment such as alkali degreasing treatment, hot water washing treatment, and then subjected to chemical conversion treatment. The chemical conversion treatment may be performed by a known method, and includes, for example, a chromate treatment, a zinc phosphate treatment, and other non-chromate treatments. The surface treatment may be appropriately selected depending on the steel sheet used, and is preferably a treatment not containing heavy metals. By applying the coating composition of the present disclosure to the object subjected to the chemical conversion treatment in this way, the adhesion of the coating film to the metal plate surface is improved and the corrosion resistance is also improved. Further, a primer coating film (primer coating film) may be formed on the metal plate surface subjected to the chemical conversion treatment, and the metal plate surface may be coated thereon. The film thickness of the undercoat film is preferably 3 μm or more, more preferably 5 μm or more, and preferably 15 μm or less, more preferably 10 μm or less.

< method for producing coating film >

The method for producing a coating film of the present disclosure comprises:

a step of forming a coating film by coating an object with the aqueous coating composition of the present disclosure; and

The method of applying the aqueous coating composition of the present disclosure to an object is not particularly limited, and conventionally known methods such as a roll coater method, an airless spray method, an electrostatic spray method, a curtain coater method and the like can be employed, and a roll coater method and a curtain coater method are preferable, and a roll coater method is more preferable.

The maximum temperature is preferably 200 seconds or more, and may be 280 seconds or less, 270 seconds or less, or 250 seconds or less, for example. The drying and/or curing time is 120 seconds or less, or 60 seconds or less, 30 seconds or less, 10 seconds or less, or 6 seconds or less, preferably 1 second or more.

The method for drying and/or curing the coated film is not particularly limited, and heating means such as hot air heating, infrared heating, induction heating, and the like may be used.

The film thickness (dry film thickness) of the dried and/or cured coating film is preferably 1 μm or more, more preferably 5 μm or more, and preferably 30 μm or less, more preferably 25 μm or less.

A laminate having the aforementioned object and the aforementioned coating film formed on the object is also included in the technical scope of the present disclosure.

When the object to be coated further has the coating film on one surface, the object to be coated may have a coating film formed from a known coating composition such as a coating composition containing an epoxy resin on the other surface.

The aqueous coating composition of the present disclosure can provide a coating film having high curability and good coating film properties (processability, mar resistance such as adhesion and crack resistance) even when the coating is performed at a high temperature and in a short time as compared with the conditions (for example, a drying/curing temperature of 60 to 80 ℃ and a drying/curing time of 30 minutes to 1 hour) that are generally employed as coating conditions for metal substrates.

The aqueous coating composition of the present disclosure has high storage stability, and the resulting coating film is less likely to peel off from the object to be coated even during processing such as bending, has good adhesion, is suppressed in the occurrence of cracks, has good crack resistance, and is excellent in damage resistance. Thus, the aqueous coating composition of the present disclosure may be suitably used for coating, especially precoating, of metals.

Examples

The present disclosure will be more specifically described by the following examples, but the present disclosure is not limited to them. In the examples, "parts" and "%" are based on mass unless otherwise specified.

< production example of coating film-forming resin (A-1)

0.6 parts by mass of Louis SS-H (surfactant, manufactured by Kao corporation) was dissolved in 60 parts by mass of ion-exchanged water. A monomer mixture containing 53.0 parts by mass of methyl methacrylate, 39.2 parts by mass of n-butyl acrylate, 5.8 parts by mass of 2-hydroxyethyl methacrylate and 2.0 parts by mass of methacrylic acid was added thereto and stirred to prepare 150.5 parts by mass of a monomer pre-emulsion. An aqueous initiator solution was prepared by dissolving 1.0 part by mass of ammonium persulfate as an initiator in 20 parts by mass of ion-exchanged water.

Into a reaction vessel equipped with a thermometer, a condenser, and a stirrer, 40 parts by mass of ion-exchanged water and 0.4 parts by mass of peter SS-H were charged, and the mixture was heated to 80 ℃ under a nitrogen atmosphere. The aqueous initiator solution was added dropwise thereto over 180 minutes while maintaining the temperature at 80℃and, after 10 minutes from the start of the addition, the monomer pre-emulsion was added dropwise from the other port of the reaction vessel over 150 minutes to carry out emulsion polymerization. After the completion of the dropwise addition of the aqueous initiator solution, the mixture was heated and stirred at 80℃for 60 minutes, and then cooled to room temperature, and 2.10 parts by mass of dimethylethanolamine was added thereto to prepare an acrylic emulsion (solid content concentration: 45% by mass) in which the film-forming resin (A-1) was dispersed in an aqueous medium.

Coating film-forming resins (A-2) to (A-11) were prepared in the same manner as described above, except that the types, amounts, and initiator amounts of the monomers were changed as shown in Table 1. The specific values such as hydroxyl value of each coating film forming resin are shown in table 1.

Details of the respective components shown in the following tables used in examples and comparative examples are as follows.

Film-forming resin (A)

(a-12) nanoring MD2000 (polyester resin emulsion manufactured by eastern spinning corporation); hydroxyl number: 6mgKOH/g, acid number: 2mgKOH/g, weight average molecular weight: 30,000, glass transition temperature: 67 ℃, minimum film forming temperature: 48 ℃, average particle size: 125nm, solid content concentration: 40 mass%

Crosslinking agent (B)

(B-1) CYMEL303 (full alkyl methylated melamine resin manufactured by the company of zening); concentration of solid content: 100 mass% number average molecular weight: 455

(B-2) CYMEL300 (full alkyl methylated melamine resin manufactured by the company of zening); concentration of solid content: 100 mass% number average molecular weight: 390

Other crosslinking agents

(b-1) CYMEL327 (an imino methylated melamine resin manufactured by the company of zening); concentration of solid content: 90 mass% number average molecular weight: 470

(b-2) a case コ a case 508 (an iminobutylated melamine resin manufactured by the company of the weak company): concentration of solid content: 80 mass%, number average molecular weight: 1,500Sulfonic acid compound (C)

(C-1) AC400S (dodecylbenzenesulfonic acid, manufactured by tekane corporation); concentration of solid content: 25 mass%

(C-2) AC700 (p-toluenesulfonic acid, manufactured by tecar corporation); concentration of solid content: 25 mass%

(C-3) Nacure-1051 (dinonylnaphthalene sulfonic acid, manufactured by Naku Chemie Co., ltd.); concentration of solid content: 51 mass%

Other acid Compounds

(c-1) a phosphate compound manufactured by Cycat296, a company of the weak corporation; concentration of solid content: 50 mass%

Amine compound (D)

(D-1) DMEA (dimethylethanolamine, mitsubishi gas chemical Co., ltd.); boiling point: 134 DEG C

(D-2) AMP (2-amino-2-methyl-1-propanol, manufactured by domestic chemical company); boiling point: 165 DEG C

(D-3) TEA (triethylamine, mitsubishi gas chemical Co., ltd.); boiling point: 90 DEG C

Aqueous medium (E)

(E1-1) diethylene glycol (manufactured by Japanese catalyst Co., ltd.); boiling point: solubility in water at 244 ℃): infinity (Water miscible)

(E1-2) propylene glycol (manufactured by Sanyoshi Co., ltd.); boiling point: solubility in water at 187 ℃): infinity (Water miscible)

(E1-3) dipropylene glycol (manufactured by Showa chemical Co., ltd.); boiling point: solubility in water at 232 ℃): infinity (Water miscible)

(E1-4) 1, 4-butanediol (manufactured by Sanyoshi Co., ltd.); boiling point: solubility in water at 228 ℃): infinity (Water miscible)

(E1-5) 1, 5-pentanediol (manufactured by Yu Zu Xing Co., ltd.); boiling point: solubility in water at 242 ℃): infinity (Water miscible)

Viscosity modifier (F)

(F-1) SN tap 612 (polyether urethane hydrophobic association adhesive modifier, manufactured by Session コ Co.); concentration of solid content: 40 mass%

(F-2) SN (made by PEGylation type viscosity modifier, session コ Co.) of a late 621; concentration of solid content: 30 mass%

(F-3) a dialects UH-526 (polyether urethane based hydrophobic association type viscosity modifier, manufactured by ADEKA Co.); concentration of solid content: 30 mass%

(F-4) cartridge RM-2020NPR (polyether urethane based hydrophobic association type viscosity modifier, manufactured by dow chemical company); concentration of solid content: 20 mass%

(F-5) cartridge ASE-60 (polyacrylate emulsion alkali swelling thickener, manufactured by dow chemical company); concentration of solid content: 28 mass%

< production example of pigment Dispersion paste >

A dispersion paste was obtained by premixing 1.63 parts by mass of Disperbyk190 (manufactured by the company of bulk, the company of bulk), 0.25 parts by mass of dimethylethanolamine, 0.05 parts by mass of SN-477T (manufactured by the company of nano コ) as a defoaming agent, 32.9 parts by mass of ion-exchanged water, and 65.2 parts by mass of titanium dioxide (manufactured by the company of Ti-PureR-706, the company of DuPont) as a pigment, and dispersing the mixture at 1,600rpm until the maximum particle diameter of the pigment coarse particles became 5. Mu.m, using an SG mill (dispersion medium: glass beads).

< production example of Water-based coating composition 1 >

55.1 parts by mass of the pigment-dispersion paste obtained in the production example, 80.0 parts by mass of the coating film-forming resin (A-1) obtained in the production example, 20.0 parts by mass of the coating film-forming resin (A-8) and 30317.6 parts by mass of CYMEL as the crosslinking agent (B-1) were mixed, and then 5.4 parts by mass of diethylene glycol (E1-1) and 5.4 parts by mass of propylene glycol (E1-2) as aqueous media were mixed and stirred. Then, 1.2 parts by mass of dodecylbenzenesulfonic acid as sulfonic acid compound (C-1) and 1.9 parts by mass of dimethylethanolamine as amine compound (D-1) were stirred with a dispenser, and further, one part by mass of the gum SN-6120.2 parts by mass as viscosity modifier (F-1) was mixed with stirring to obtain coating composition 1.

(coating compositions 2 to 45, comparative examples 1 to 10)

A coating composition was prepared in the same manner as in coating composition 1, except that the types and amounts of the respective components were changed as described in tables 2 to 7.

< production example of coated Steel sheet >

After alkali degreasing is performed on the hot-dip galvanized steel sheet with the thickness of 0.4mm, a phosphate treatment agent コ strain EC2310 (manufactured by petalfrem corporation) was applied to the front and rear surfaces of a steel sheet, and then subjected to a chromium-free chemical conversion treatment and dried.

Next, the coating composition 1 obtained in the production example was applied to the surface of a steel sheet using a bar coater so that the dry coating film became 18 μm, and baked for 30 seconds under the condition that the maximum temperature of the raw material reached 230 ℃ to form a surface coating film, thereby obtaining a coated steel sheet.

1) Shear viscosity measurement

The shear viscosity of the coating compositions obtained in examples and comparative examples was measured at a shear rate of 0.1s using a stress-controlled rheometer MCR301 (clamp: 50mm parallel plate, gap: 0.5mm, manufactured by the company of Takara Shuzo Co., ltd.) ^-1 、10s ^-1 And 1,000s ^-1 Shear viscosity at time. The measurement temperature was set at 23 ℃.

2) Storage stability

Evaluation was performed by using Ford cup No.4 (manufactured by Shimadzu corporation) according to the method specified in JISK56002-2 (flow cup method).

Ion-exchanged water was added to the coating compositions obtained in examples and comparative examples, and the coating compositions were adjusted so that the viscosity became 60.+ -.10 seconds (initial viscosity (seconds)). In detail, the initial viscosity is set as: the viscosity was measured immediately after dilution with the aforementioned ion-exchanged water and stirring at 1,000rpm for 3 minutes using a dispenser. The coating temperature was set at 25 ℃.

The coating composition adjusted to the initial viscosity (60.+ -. 10 seconds (25 ℃ C.) was put into a 1/5 tank, sealed, and then allowed to stand in a constant temperature chamber at 40 ℃ C.) after 8 to 9 times. Thereafter, the sample was taken out after 14 days (2 weeks), and the viscosity (viscosity with time (seconds)) was measured in the same manner as described above.

The rate of change of the viscosity with time from the initial viscosity was calculated by the following formula, and the storage stability was evaluated according to the following criteria. The above test was qualified.

Viscosity change rate (%) =time-lapse viscosity (seconds)/initial viscosity (seconds) ×100

And (3) the following materials: the viscosity change rate is 0% or more and less than 30%.

O: the viscosity change rate is 30% or more and less than 50%.

Delta: the viscosity change rate is 50% or more and less than 100%.

X: the viscosity change rate is 100% or more.

5) Coating workability (coatability of roll coater)

The coating compositions obtained in examples and comparative examples were applied to the objects under the following conditions using a small-sized experimental coater (made by penknife, teku corporation) having 3 rolls (backup roll, coating roll, and pick-up roll), and the coatability of the roll coater was evaluated according to the following criteria. The above test was qualified. The test conditions were set at room temperature of 23℃and humidity of 60RH%.

Coated article: GL Steel plate (manufactured by Nissan Steel plate Co., ltd.) of 300mm×2,000mm×0.35mm size

Coating conditions:

linear velocity: 50m/min

Roll peripheral speed: and (3) coating roller: 65m/min (130% relative to linear velocity), pick-up roller: 20m/min (40% relative to linear velocity)

Backup roll pressure: 60kgf

Reference coating amount: the mass of the dried coating film was 28g/m ²

Baking conditions: under the condition that the maximum reaching temperature of the raw material of the coated object is 230 ℃ for 30 seconds

And (3) the following materials: can be uniformly coated on the whole surface with the reference coating amount

O: can be uniformly coated on the whole surface, but the coating weight is 20-28 g/m ²

Delta: can be applied to the whole surface, but the coating amount is less than 20g/m ² The film thickness becomes uneven

X: an uncoated portion is generated, and the whole surface cannot be coated

In the roll coater, the coating material is rolled up by the pick-up roller, transferred to the coating roller, and further transferred to the backup roller to be coated on the object to be coated. When the paint is properly wound up by the pick-up roller, the paint is properly transferred to the backup roller by the pressure of the coating roller and the backup roller, and thereby the paint is uniformly applied to the object to be coated, the pick-up roller winds up only a small amount of paint, and uneven transfer occurs between the rollers, and the paint is not uniformly applied to the object to be coated.

4) Workability (adhesion)

Each of the coated steel sheets obtained in examples and comparative examples was cut into 5cm×3cm pieces, and pre-bent using a bending machine (manufactured by shimeji corporation) so that the coating film surface was the surface side. 2 steel sheets of the same thickness (0.4 mm) were held by the test piece, and bending was performed by a press machine (manufactured by Co., ltd.). The seta is adhered to a processed portion of a coated steel sheet (registered trademark) (LP-24, manufactured by the company iv) and peeled off at once, and adhesion of the coating film on the processed portion was evaluated. The appearance of the portion peeled off by the tape was evaluated according to the following criteria. And the score of 4 or more is qualified.

5: no metallic substrate was observed at the tape-peeled portion.

4: in the area of the tape peeled portion (more than 0% and less than 20%), a metallic base portion was observed.

3: a metallic base portion was observed at 20% or more and less than 50% of the area of the tape-peeled portion.

2: at 50% or more and less than 80% of the area of the tape-peeled portion, a metallic base portion was observed.

1: at 80% or more of the area of the tape-peeled portion, a metallic base portion was observed.

5) Workability (crack resistance)

Each of the coated steel sheets obtained in examples and comparative examples was cut into 5cm×3cm pieces, and pre-bent using a bending machine (manufactured by shimeji corporation) so that the coating film surface was the surface side. 5 steel sheets of the same thickness (0.4 mm) were held by the test piece, and bending was performed by a press machine (manufactured by Co., ltd.). The state of the coating film (cracks) in the processed portion was observed with a 15-fold magnifying glass, and the processability was evaluated according to the following criteria. And the score of 4 or more is qualified. The test conditions were set at a temperature of 23℃and a humidity of 60RH%.

5: no cracks were observed in the machined part.

4: cracks were observed in the area of the machined portion (more than 0% and less than 20%).

3: cracks were observed at 20% or more and less than 50% of the area of the processed portion.

2: cracks were observed at 50% or more and less than 80% of the area of the processed portion.

1: cracks were observed at 80% or more of the area of the processed portion.

6) Damage resistance

Using a continuous weighted scratch strength tester TYPE:18/18L (New east scientific Co., ltd.) a diamond needle (conical scraping needle with diameter of 0.4mm, which was subjected to R processing) with R of 0.4mm was brought into contact with the coated surfaces of the coated steel sheets obtained in examples and comparative examples, and the coated steel sheets were scraped 1 time under a load of 300mm/min and a movement width of 10 cm. The weight of the load at which damage to the coating surface and exposure of the substrate were confirmed was evaluated according to the following criteria. Let the above pass. The test conditions were set at a temperature of 23℃and a humidity of 60RH% for each 500gf load application.

And (3) the following materials: even if the load exceeds 3,000g, the substrate is not exposed

O: the load exceeds 2,000 and is below 3,000g

Delta: the load exceeds 1,000g and is below 2,000g

X: the load is below 1,000g

TABLE 1

TABLE 2

TABLE 3

TABLE 4

TABLE 5

TABLE 6

TABLE 7

Examples 1 to 45 are examples of the present disclosure, and are high in storage stability, excellent in processability and good in damage resistance.

Comparative examples 1 and 2 are examples in which the hydroxyl value of the acrylic resin (A1) was less than 5mgKOH/g, and the scratch resistance was poor. Comparative examples 3 and 4 are examples in which the hydroxyl value of the acrylic resin (A1) exceeds 35mgKOH/g, and the storage stability and the processability are poor. Comparative examples 5 and 6 are examples in which the neutralization rate of the sulfonic acid compound (C) based on the amine compound (D) was less than 100%, and the storage stability was poor. Comparative example 7 shows that the neutralization rate of the sulfonic acid compound (D) based on the amine compound (D) exceeds 1,300%, and the storage stability is poor. Comparative examples 8 and 9 are examples in which the fully alkyl melamine resin (B1) was not contained as the crosslinking agent (B), and the processability was poor. Comparative example 10 is an example in which a phosphoric acid compound was used without the sulfonic acid compound (C), and the storage stability and the scratch resistance were poor.

Claims

1. An aqueous coating composition comprising a coating film-forming resin (A), a crosslinking agent (B), a sulfonic acid compound (C) and an amine compound (D),

the coating film forming resin (A) comprises an acrylic resin (A1) having a hydroxyl group,

The crosslinking agent (B) comprises a fully alkyl melamine resin (B1),

2. The aqueous coating composition according to claim 1, wherein the weight average molecular weight of the coating film-forming resin (A1) is 100,000 or more.

3. The aqueous coating composition according to claim 1 or 2, wherein the aqueous coating composition is applied at a temperature of 23 ℃ for 0.01s ^-1 The shear viscosity measured at a shear rate of 30,000 mPas or less, at 10s ^-1 The shear viscosity measured at a shear rate of 800 mPas or less, at 1,000s ^-1 The shear viscosity measured at the shear rate of (2) is 150 mPas or more.

4. A waterborne coating composition according to any of claims 1 to 3, further comprising an organic solvent (E1).

5. The aqueous coating composition according to any one of claims 1 to 4 for coil coating.

6. A method for producing a coating film, comprising:

a step of forming a coating film by applying the aqueous coating composition according to any one of claims 1 to 5 to an object to be coated; and

and drying and/or curing the coating film under the conditions that the maximum temperature is 180 ℃ or higher and the drying and/or curing time is 120 seconds or less.