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

Abstract

The present disclosure provides a water-based paint composition which is a single-component, has excellent storage stability, and forms a coating film having excellent workability, crack resistance, and damage resistance. The water-based paint composition of the present disclosure contains 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 5 mgKOH / g or more and 35 mgKOH / g or less, the crosslinking agent (B) contains a peralkyl melamine resin (B1), and the neutralization rate of the acid group of the sulfonic acid compound (C) based on the amine compound (D) is 100% or more and 1,300% or less.

Description

Technical Field

[0001] This disclosure relates to waterborne coating compositions, coating films, and methods for manufacturing coating films. Background Technology

[0002] Coated steel sheets (hereinafter also referred to as "PCM") are produced by coating metal substrates such as cold-rolled steel sheets and galvanized steel sheets before forming. They are used in building components such as roller shutters, skylights, doors, roofs, and wall panels; exterior materials for electrical equipment such as air conditioner outdoor units; and interior materials. These PCMs are typically manufactured by applying a coating composition to the surface of the metal substrate and heating (baking) it at, for example, 200–270°C for 30–60 seconds to form a coating film, which is then used for forming. Therefore, the coating film of PCMs requires workability that prevents cracking and peeling during processing, and hardness that prevents damage and dents.

[0003] Coating compositions exist in both one-component and two-component forms. The one-component composition contains a base agent comprising a film-forming resin and a curing agent comprising a crosslinking agent, both coexisting within the same system. The two-component composition stores the base agent and curing agent separately and mixes them before use. In the two-component composition, the base agent and curing agent are not mixed until just before use; therefore, it exhibits superior storage stability compared to the one-component composition. However, the two-component composition requires mixing and stirring the base agent and curing agent in a specified ratio to achieve homogeneity before use, and has a limited usable time. Sometimes, its handling and application become problematic, leading to the search for one-component coating compositions.

[0004] Furthermore, increased awareness of reducing environmental impact in recent years has led to demands for environmentally friendly products. In the coatings industry, there is also a need to reduce the amount of volatile organic compounds (VOCs), a requirement that can be met by using water-based coating compositions. In other words, the market demand for single-component water-based coating compositions is becoming increasingly high.

[0005] Various solutions have been proposed for such one-component waterborne coating compositions. For example, the following solution has been proposed: in a waterborne coating composition comprising an acrylic copolymer containing hydroxyl and carboxyl groups, a waterborne amino resin, an amine compound, and a hydrophilic organic solvent, an amine compound is used to neutralize the carboxyl groups contained in the acrylic copolymer containing hydroxyl and carboxyl groups (Patent Document 1). Another solution has been proposed: in an acrylic water-soluble coating composition comprising a hydroxyl-containing (meth)acrylate, a carboxyl-containing vinyl monomer, a copolymer of (meth)acrylate and vinyl monomers containing long-chain alkyl groups, a water-soluble amino resin, and an aqueous medium, an amine compound is used to neutralize the carboxyl groups in the acrylic copolymer containing hydroxyl and carboxyl groups (Patent Document 2). Furthermore, the following solution was proposed: In a waterborne coating composition for metal coating containing hydroxyl and carboxyl groups, comprising an acrylic resin with a glass transition temperature in the range of -10°C to 80°C, an acrylic resin with a glass transition temperature in the range of -50°C to 20°C, a waterborne amino resin, an alkaline compound, and a waterborne medium, the carboxyl groups of the acrylic resin containing hydroxyl and carboxyl groups are neutralized using an alkaline compound (Patent Document 3). Additionally, Patent Document 4 proposes a waterborne coating composition comprising a waterborne resin, a melamine resin, and a phosphate ester catalyst as a weak acid catalyst, and proposes using an alkaline compound to neutralize the waterborne resin (Patent Document 4).

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent Application Publication No. 2001-323207

[0009] Patent Document 2: Japanese Patent Application Publication No. 2001-240624

[0010] Patent Document 3: Japanese Patent Application Publication No. 2000-17225

[0011] Patent Document 4: Japanese Patent Application Publication No. 2015-174958 Summary of the Invention

[0012] The problem that the invention aims to solve

[0013] However, the coating film formed by the coating composition described in the aforementioned patent documents 1 to 4 cannot adequately satisfy the processability (adhesion, crack resistance) and damage resistance of the obtained pre-coated steel sheet.

[0014] Furthermore, in one-component coating compositions, since the main agent and curing agent coexist in the same system, the following balancing relationship exists: when the reactivity of the main agent and curing agent is increased to improve the film properties, the storage stability of the coating composition decreases; on the other hand, when the reactivity is decreased to improve the storage stability of the coating composition, the film properties decrease. Therefore, it is very difficult to balance storage stability and film properties in one-component coating compositions.

[0015] In order to solve this problem, the inventors conducted repeated and in-depth research and discovered that by using a fully alkyl melamine resin as a crosslinking agent, and by using sulfonic acid compounds and amine compounds in a manner that exhibits a specific neutralization rate, even single-component compositions can achieve high storage stability. Furthermore, even when coating is performed under the high temperature and short time conditions characteristic of pre-coated steel sheets, good coating properties (especially processability (adhesion, crack resistance) and damage resistance) can be achieved, thereby completing the waterborne coating composition and coating film manufacturing method described in this disclosure.

[0016] The subject of this disclosure is to provide a waterborne coating composition that exhibits excellent storage stability even when formed as a single component, and is capable of forming a coating film with good processability such as bending, crack resistance during processing, and damage resistance.

[0017] Methods for solving problems

[0018] This disclosure provides the following methods. [1]

[0020] A water-based coating composition comprising a film-forming resin (A), a crosslinking agent (B), a sulfonic acid compound (C), and an amine compound (D),

[0021] The aforementioned coating-forming resin (A) includes an acrylic resin (A1).

[0022] The aforementioned coating-forming resin (A) has a hydroxyl value of 5 mg KOH / g or higher and 35 mg KOH / g or lower.

[0023] The aforementioned crosslinking agent (B) comprises a fully alkyl melamine resin (B1).

[0024] The neutralization rate, calculated based on the molar conversion of the acid groups of the aforementioned amine compound (D) and the aforementioned sulfonic acid compound (C), is more than 100% and less than 1,300%.

[0025] [2] According to the waterborne coating composition of [1], wherein the weight average molecular weight of the aforementioned film-forming resin (A) is 100,000 or more.

[0026] [3] The waterborne coating composition according to [1] or [2], wherein, at a temperature of 23°C, the reaction proceeds at a rate of 0.01 s -1 The shear viscosity measured at the shear rate was below 30,000 mPa·s, with a 10s... -1 The shear viscosity measured at the shear rate was below 800 mPa·s, and at 1,000 s⁻¹... -1 The shear viscosity measured at the shear rate was above 150 mPa·s.

[0027] [4] The waterborne coating composition according to any one of [1] to [3] further comprises an organic solvent (E1).

[0028] [5] The waterborne coating composition according to any one of [1] to [4] is used for roll coating.

[0029] [6] A method for manufacturing a coating film, comprising:

[0030] The process of applying the water-based coating composition described in any one of [1] to [5] to a substrate to form a coating film; and

[0031] A process of drying and / or curing the aforementioned coating film under conditions where the maximum temperature reaches 180°C or higher and the drying and / or curing time is less than 120 seconds to form a coating film.

[0032] Invention Effects

[0033] According to this disclosure, a waterborne coating composition can be provided that exhibits excellent storage stability even when formed as a single component, and is capable of forming a coating film with good processability such as bending, crack resistance during processing, and damage resistance. Detailed Implementation

[0034] The waterborne coating composition disclosed herein comprises a film-forming resin (A), a crosslinking agent (B), a sulfonic acid compound (C), and an amine compound (D).

[0035] <Coating Forming Resin (A)>

[0036] The aforementioned coating-forming resin (A) comprises an acrylic resin (A1). The aforementioned acrylic resin (A1) refers to a polymer having units derived from monomers having (meth)acryloyl groups, which can be prepared by polymerizing a monomer mixture containing monomers having olefinic unsaturated bonds. It should be noted that, in this specification, (meth)acrylic acid refers to acrylic acid or methacrylic acid.

[0037] As monomers with olefinic unsaturated bonds, examples include unsaturated carboxylic acids such as (meth)acrylic acid, crotonic acid, isocrotonic acid, 2-acrylic acid, ethylacrylic acid, propylacrylic acid, and isopropylacrylic acid; unsaturated polycarboxylic acids (including their anhydrides) such as maleic acid, fumaric acid, and itaconic acid; monoalkyl esters of unsaturated polycarboxylic acids such as ethyl maleate, butyl maleate, ethyl fumarate, butyl fumarate, ethyl itaconic acid, and butyl itaconic acid; methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, n-pentyl (meth)acrylate, neopentyl (meth)acrylate, and isopentyl (meth)acrylate. Alkyl methacrylates, including sec-amyl methacrylate, 3-pentyl methacrylate, hexyl methacrylate, heptyl methacrylate, n-octyl methacrylate, 2-ethylhexyl methacrylate, nonyl methacrylate, decyl methacrylate, undecyl methacrylate, dodecyl methacrylate, stearyl methacrylate, etc.; cyclopentyl methacrylate, cyclohexyl methacrylate, isobornyl methacrylate, tricyclodecyl methacrylate, adamantyl methacrylate, etc., containing alicyclic hydrocarbon groups; 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, etc. 4-Hydroxybutyl methacrylate and other hydroxyalkyl methacrylates; their lactone adducts (such as ε-caprolactone, etc.) and other hydroxyl-containing methacrylates; monomers having organosilanes such as γ-(meth)acryloyloxypropyltrimethoxysilane, γ-(meth)acryloyloxypropylmethyldimethoxysilane, γ-(meth)acryloyloxypropyltriethoxysilane, γ-(meth)acryloyloxypropylmethyldiethoxysilane, vinyltrimethoxysilane, vinylmethyldimethoxysilane, vinyltriethoxysilane, vinylmethyldiethoxysilane; α-vinylbenzenesulfonic acid, p-(meth)acrylamide propanesulfonic acid, tert-butyl(meth)acrylamide sulfonic acid, etc. Monomers containing sulfonic acid groups; phosphate monoesters of (meth)acrylates containing hydroxyl groups, etc.; (meth)acrylamide monomers such as (meth)acrylamide, N-hydroxymethyl (meth)acrylamide, methoxybutyl (meth)acrylamide, and diacetone (meth)acrylamide; (meth)acrylamide monomers containing amino groups such as aminoethyl (meth)acrylamide, dimethylaminoethyl (meth)acrylamide, and methylaminopropyl (meth)acrylamide; (meth)acrylates containing epoxy groups (epoxyethylene groups) such as glycidyl (meth)acrylate; (meth)acrylonitrile monomers such as α-chloro(meth)acrylonitrile; vinyl acetate, vinyl propionate, and other vinyl carboxylic acid esters;Styrene, α-methylstyrene, α-methylstyrene dimer, vinyltoluene, divinylbenzene, and other styrene monomers; carbonyl monomers; and crosslinking monomers such as multifunctional vinyl monomers not mentioned above.

[0038] The aforementioned monomers with olefinic unsaturated bonds can be used in combination, either by using only one type or by using two or more types in combination.

[0039] The aforementioned acrylic resin (A1) has hydroxyl groups. By giving the aforementioned acrylic resin (A1) hydroxyl groups, a cross-linking reaction can occur between the hydroxyl groups and the reactive groups of the cross-linking agent, thereby curing the coating film. In order to give the aforementioned acrylic resin (A1) hydroxyl groups, when preparing the polymer, only (meth)acrylates having hydroxyl groups can be used as the monomers having olefinic unsaturated bonds.

[0040] The aforementioned acrylic resin (A1) containing hydroxyl groups preferably has a hydroxyl value of 5 mg KOH / g or more, more preferably 7 mg KOH / g or more, even more preferably 10 mg KOH / g or more, and preferably 50 mg KOH / g or less, more preferably 35 mg KOH / g or less, even more preferably 30 mg KOH / g or less, and even more preferably 25 mg KOH / g or less. By falling within the aforementioned range, it has the advantage of being able to obtain a coating film with good processability (adhesion, crack resistance).

[0041] In the aforementioned hydroxyl-containing (meth)acrylates, the number of carbon atoms in the group bonded to the (meth)acryloyl group is preferably 1 to 3, more preferably 2. By including (meth)acrylates with hydroxyl groups and a carbon number of 1 to 3 in the aforementioned (meth)acryloyl group, it is advantageous to obtain a coating film with excellent damage resistance. The content of this (meth)acrylate with hydroxyl groups and a carbon number of 1 to 3 in the hydroxyl-containing (meth)acrylate is preferably 70% by mass or more, more preferably 80% by mass or more, and up to a maximum of 100% by mass.

[0042] The aforementioned acrylic resin (A1) has a weight-average molecular weight of, for example, 50,000 or more, preferably 100,000 or more, more preferably 150,000 or more, for example, 10,000,000 or less, and more preferably 2,000,000 or less. A higher weight-average molecular weight of the acrylic resin (A1) results in better damage resistance and the advantage of obtaining a coating with excellent processability.

[0043] It should be noted that, in this specification, the weight-average molecular weight is a polystyrene conversion value based on gel permeation chromatography (GPC).

[0044] The aforementioned acrylic resin (A1) preferably has acid groups. By having acid groups, the aforementioned acrylic resin (A1) can be imparted with dispersibility in the aqueous medium (E) described later.

[0045] In order to obtain acid groups in the aforementioned acrylic resin (A1), when making the polymer, any monomer with an acid group, such as an unsaturated monocarboxylic acid, an unsaturated polycarboxylic acid, a monoalkyl ester of an unsaturated polycarboxylic acid, a monomer with a sulfonic acid group, or a monomer with a phosphoric acid group, can be used as the monomer with the aforementioned olefinic unsaturated bond.

[0046] As the aforementioned monomers having acid groups, unsaturated monocarboxylic acids, unsaturated polycarboxylic acids, and monoalkyl esters of unsaturated polycarboxylic acids are preferred, more preferably unsaturated monocarboxylic acids and unsaturated polycarboxylic acids, even more preferably unsaturated monocarboxylic acids, and particularly preferably (meth)acrylic acid.

[0047] The aforementioned acrylic resin (A1) preferably has an acid value of 5 mg KOH / g or higher, more preferably 50 mg KOH / g or lower, and more preferably 30 mg KOH / g or lower. Being within the aforementioned range provides the advantage of enabling the acrylic resin (A1) to be stably dispersed in the aqueous medium (E).

[0048] It should be noted that in this specification, the acid value and hydroxyl value of acrylic resin (A1) represent the acid value and hydroxyl value of the solid components, respectively, and can be determined in accordance with JIS K0070:1999.

[0049] The glass transition temperature (Tg) of the aforementioned acrylic resin (A1) is preferably -70°C or higher, more preferably 0°C or higher, further preferably 10°C or higher, even more preferably 15°C or higher, and preferably 95°C or lower, more preferably 90°C or lower, even more preferably 85°C or lower, and even more preferably 80°C or lower. By being within the aforementioned range, it has the advantage of being able to obtain a coating with excellent processability and damage resistance.

[0050] The aforementioned glass transition temperature can be calculated as the reciprocal of the sum of the quotients obtained by dividing the mass fraction of each monomer constituting the acrylic resin (A1) by the Tg (K: Kelvin) value of the homopolymer (homogene) derived from each monomer.

[0051] More specifically, in this specification, the aforementioned glass transition temperature (Tg) can be calculated using the Fox formula (TGFox; Bull.Am.Phys.Soc.,1(3),123(1956)).

[0052] For example, when the resin is a polymer of multiple monomers (monomer A, monomer B, ... monomer N), the Tg shown in the following general formula is set as the Tg of the resin.

[0053] 1 / Tg=wa / Tga+wb / Tgb+…+wn / Tgn

[0054] Here,

[0055] Tga: Glass transition temperature (K) of the homopolymer of monomer A; wa: Mass fraction of monomer A.

[0056] Tgb: Glass transition temperature (K) of the homopolymer of monomer B; wb: Mass fraction of monomer B.

[0057] Tgn: Glass transition temperature (K) of the homopolymer of monomer N; wn: Mass fraction of monomer N.

[0058] wa+wb+…+wn=1.

[0059] In the monomers forming the aforementioned acrylic resin (A1), the monomers having olefinic unsaturated bonds preferably include alkyl (meth)acrylates, more preferably alkyl (meth)acrylates with 1 to 6 carbon atoms, and even more preferably 1 to 4 carbon atoms. By using monomers within the aforementioned range, the resulting coating film exhibits excellent damage resistance. The content of alkyl (meth)acrylates with 1 to 6 carbon atoms is preferably 20% by mass or more, more preferably 30% by mass or more, further preferably 40% by mass or more, and preferably 95% by mass or less, more preferably 85% by mass or less, and even more preferably 80% by mass or less.

[0060] From the viewpoint of weather resistance, the content of styrene monomers in the aforementioned acrylic resin (A1) is preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 3% by mass or less, with a lower limit of 0% by mass.

[0061] When the aforementioned acrylic resin (A1) has acidic groups, the aforementioned waterborne coating composition may contain a basic compound. By including a basic compound in the aforementioned waterborne coating composition, some or all of the acidic groups are neutralized, thereby imparting good water dispersibility to the acrylic resin. Examples of the aforementioned basic compound can be ammonia, amine compounds, alkali metals, etc. Alternatively, a portion of the amine compound (D) described later may also be used as the aforementioned basic compound.

[0062] Alternatively, well-known anionic and / or nonionic surfactants can be used to impart water dispersibility to acrylic resins.

[0063] The content of the aforementioned acrylic resin (A1) in the aforementioned film-forming resin (A) is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 15% by mass or more, with a maximum of 100% by mass.

[0064] The aforementioned acrylic resin (A1) is preferably an aqueous resin, which can be a water-soluble resin that can dissolve in an aqueous medium (E), or a water-dispersible resin that can be dispersed in an aqueous medium (E), such as a colloidal dispersion or an emulsion (emulsion polymerization type, forced emulsification type). The aforementioned 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 based on emulsion polymerization. By giving the aforementioned acrylic resin (A1) acid groups and / or hydroxyl groups, and / or having it coexist with an emulsifier, an aqueous resin can be prepared.

[0065] When the aforementioned acrylic resin (A1) is an emulsion-type water-dispersible resin, the average particle size of the emulsion particles is preferably 500 nm or less, more preferably 300 nm or less, and even more preferably 200 nm or less; for example, it can be 10 nm or more, 30 nm or more, or 50 nm or more. By being within the aforementioned range, it has the advantage of good storage stability of the emulsion particles and the coating composition containing the aforementioned emulsion particles. It should be noted that, in this specification, the average particle size is the average particle size determined using a dynamic light scattering method; specifically, it can be measured using an electrophoretic light scattering spectrophotometer of the ELSZ series (manufactured by Otsuka Electronics Co., Ltd.).

[0066] The minimum film-forming temperature (MFT) of the aforementioned acrylic resin (A1) is preferably 50°C or higher, more preferably 60°C or higher, and even more preferably 70°C or higher. For example, it can be 200°C or lower, 150°C or lower, or 120°C or lower. By being within the aforementioned range, the resulting coating has the advantages of improved damage resistance and suppressed adhesion between coatings. It should be noted that, in this specification, the minimum film-forming temperature refers to the lowest temperature at which a crack-free, uniform film is formed when the aforementioned emulsion-type water-dispersible resin is dried, and can be measured according to JISK6828-2:2003.

[0067] When the aforementioned acrylic resin (A1) is an emulsion-type water-dispersible resin, the emulsion can be an emulsion containing multilayered structural particles including a core and a shell.

[0068] The aforementioned multilayer structure particles can be prepared by, for example, the method described in Japanese Patent Application Publication No. 2002-12816.

[0069] The aforementioned acrylic resin (A1) can be manufactured by polymerizing the aforementioned monomers having olefinic unsaturated bonds. The polymerization reaction can be carried out, for example, by heating the aforementioned monomers having olefinic unsaturated bonds in a partially or entirely aqueous medium (E) under stirring. The aforementioned polymerization reaction is preferably an emulsion polymerization reaction. During the aforementioned polymerization reaction, a polymerization initiator is preferably coexisting, and an emulsifier is preferably coexisting as needed. The reaction temperature is preferably, for example, 30–100°C, and the reaction time is preferably, for example, 1–10 hours.

[0070] Free radical polymerization initiators are preferred as the aforementioned polymerization initiators. Water-soluble free radical polymerization initiators can be persulfates such as potassium persulfate, sodium persulfate, and ammonium persulfate. Alternatively, redox initiators composed of oxidants such as potassium persulfate, sodium persulfate, ammonium persulfate, and hydrogen peroxide combined with reducing agents such as sodium bisulfite, sodium thiosulfate, sodium hydroxide, and ascorbic acid can be used. These free radical polymerization initiators can be dissolved in a portion or all of the aqueous medium (E) and used as aqueous solutions.

[0071] As the aforementioned emulsifiers, anionic or nonionic emulsifiers can be used that have a hydrophobic portion, such as a hydrocarbon group having 6 or more carbon atoms, and a hydrophilic portion, such as a carboxylate, sulfonate, or sulfate ester. Examples of anionic emulsifiers include alkali metal or ammonium salts of sulfate half-esters of alkylphenols or higher alcohols; alkali metal or ammonium salts of alkyl or allyl sulfonates; alkali metal or ammonium salts of sulfate half-esters of polyoxyethylene alkylphenyl ethers, polyoxyethylene alkyl ethers, or polyoxyethylene allyl ethers; and various anionic reactive emulsifiers having groups such as acrylic, methacrylic, propenyl, allyl, allyl ether, and maleic acid, as well as olefinic unsaturated bonds.

[0072] In addition, examples of nonionic emulsifiers include polyoxyethylene alkylphenyl ethers, polyoxyethylene alkyl ethers, or polyoxyethylene allyl ethers; and nonionic reactive emulsifiers with groups such as acrylic, methacrylic, propylene, allyl, allyl ether, and maleic acid, as well as olefinic unsaturated bonds.

[0073] In addition, during polymerization (preferably emulsion polymerization), from the viewpoint of carrying out polymerization (preferably emulsion polymerization), and from the viewpoint of promoting the smooth and uniform formation of the coating film and improving the adhesion to the coated object, it is often preferred to use a combination of thiol compounds, lower alcohols and other auxiliaries (chain transfer agents) for adjusting molecular weight, and so on, depending on the circumstances.

[0074] When performing emulsion polymerization, any emulsion polymerization method can be used, such as the conventional single-stage continuous monomer uniform drop method, the core-shell polymerization method as a multi-stage monomer feeding method, or the dynamic feeding polymerization method in which the monomer composition is continuously changed during polymerization.

[0075] The aforementioned acrylic resin (A1) can be used in the preparation of waterborne coating compositions in the form of an aqueous solution or aqueous dispersion that pre-contains the acrylic resin (A1) and includes a portion of the aqueous medium (E) described later. The aqueous solution or aqueous dispersion may further contain the aforementioned emulsifier.

[0076] Commercially available acrylic resins (A1) can be used as the aforementioned resin. Alternatively, only one type can be used, or two or more types can be used in combination.

[0077] In addition to the aforementioned acrylic resin (A1), the aforementioned coating-forming resin (A2) may also contain other resins (A2).

[0078] Examples of the aforementioned other resins (A2) include hydroxyl-free acrylic resins, urethane resins, vinyl acetate resins, fluoropolymers, and vinyl chloride resins, which are preferably water-based resins, more preferably water-dispersible resins, and even more preferably emulsion-type water-dispersible resins. This other resin (A2) can be used in the preparation of water-based coating compositions in the form of an aqueous solution or aqueous dispersion that pre-contains the other resin (A2) and a portion of the aqueous medium (E). The aqueous solution or aqueous dispersion may contain an emulsifier.

[0079] The aforementioned hydroxyl-free acrylic resins refer to polymers having units derived from monomers having (meth)acryloyl groups, which can be prepared by polymerizing a mixture of monomers without hydroxyl groups among the aforementioned monomers having olefinic unsaturated bonds.

[0080] The aforementioned hydroxyl-free acrylic resin preferably has a weight-average molecular weight of 50,000 or more, more preferably 100,000 or more, further preferably 150,000 or more, and more preferably 10,000,000 or less, more preferably 2,000,000 or less, and further preferably 500,000 or less. Being within the aforementioned range provides the advantage of improved processability of the resulting coating.

[0081] The glass transition temperature of the aforementioned hydroxyl-free acrylic resin is preferably below 80°C, more preferably below 60°C, and even more preferably below 50°C, and preferably above 20°C, more preferably above 30°C, and even more preferably above 40°C. Being within the aforementioned range provides the advantage of good damage resistance.

[0082] The minimum film-forming temperature (MFT) of the aforementioned acrylic resin is preferably 50°C or higher, more preferably 60°C or higher, and even more preferably 70°C or higher. For example, it can be 200°C or lower, 150°C or lower, or 120°C or lower. By being within the aforementioned range, the resulting coating film has the advantages of improved damage resistance and suppressed adhesion between coating films.

[0083] The aforementioned hydroxyl-free acrylic resin preferably has acid groups. The acid value of the aforementioned hydroxyl-free acrylic resin is preferably 5 mg KOH / g or more, more preferably 50 mg KOH / g or less, and more preferably 30 mg KOH / g or less.

[0084] When the acrylic resin containing the aforementioned hydroxyl-free acrylic resin is included, its content in the total of the aforementioned acrylic resin (A1) and the aforementioned hydroxyl-free acrylic resin is preferably 20% by mass or more, more preferably 30% by mass or more, and preferably 90% by mass or less, more preferably 85% by mass or less.

[0085] The aforementioned coating-forming resin (A) has a hydroxyl value of 5 mg KOH / g or more, preferably 7 mg KOH / g or more, more preferably 10 mg KOH / g or more, and is 35 mg KOH / g or less, preferably 30 mg KOH / g or less, more preferably 25 mg KOH / g or less. By being within the aforementioned range, it has the advantage of being able to obtain a coating film with good processability and damage resistance.

[0086] The acid value of the aforementioned film-forming resin (A) is preferably 5 mg KOH / g or more, more preferably 50 mg KOH / g or less, and more preferably 30 mg KOH / g or less. By being within the aforementioned range, it has the advantage of being able to stably disperse the aforementioned film-forming resin (A) in the aqueous medium (E).

[0087] The weight-average molecular weight of the aforementioned coating-forming resin (A) is, for example, 50,000 or more, preferably 100,000 or more, more preferably 150,000 or more, and for example, 10,000,000 or less, preferably 2,000,000 or less. By being within the aforementioned range, it has the advantage of being able to obtain a coating with good processability.

[0088] The glass transition temperature (Tg) of the aforementioned coating-forming resin (A) is preferably -70°C or higher, more preferably 20°C or higher, even more preferably 25°C or higher, and even more preferably 30°C or higher, and preferably 95°C or lower, more preferably 70°C or lower, even more preferably 60°C or lower, and even more preferably 50°C or lower. By being within the aforementioned range, it has the advantage of being able to obtain a coating with excellent processability and damage resistance.

[0089] As the aforementioned film-forming resin (A), only one type may be used, or two or more types may be used in combination. When two or more of the aforementioned film-forming resins (A) are included, the parameters of the aforementioned film-forming resins (A), except for the glass transition temperature, can be calculated as a weighted average based on the parameters and content of each resin. In addition, the glass transition temperature can be calculated by summing the values ​​obtained by dividing the mass basis content of each film-forming resin by the glass transition temperature (K: Kelvin value) and then taking its reciprocal.

[0090] The content of the aforementioned film-forming resin (A) is preferably 50 parts by weight or more, more preferably 70 parts by weight or more, and even more preferably 80 parts by weight or more, and preferably 100 parts by weight or less, more preferably 95 parts by weight or less, and even more preferably 90 parts by weight or less, out of 100 parts by weight of the solid components of the aforementioned water-based coating composition. It should be noted that, in this specification, the content of the film-forming resin (A) refers only to the content of the solid components.

[0091] In this specification, the solid component of a waterborne coating composition refers to the portion remaining after removing the waterborne medium (E) from the entire waterborne coating composition.

[0092] <Crosslinking agent (B)>

[0093] The aforementioned crosslinking agent (B) is a compound having two or more groups in one molecule that can react with the hydroxyl groups contained in the aforementioned film-forming resin (A), and can undergo a crosslinking reaction with the aforementioned film-forming resin (A) to form a coating film. The aforementioned crosslinking agent (B) includes an amino resin, and examples of such amino resins include melamine resin, urea resin, and benzoguanamine. From the viewpoint of the storage stability of the resulting coating composition and the various physical properties (processability, damage resistance) of the resulting coating film, the amino resin preferably includes melamine resin.

[0094] Melamine resin is a thermosetting resin synthesized from melamine and aldehyde, preferably a compound or its condensation polymer having three reactive functional groups as shown in the following formula in a molecule of triazine core.

[0095] -NX1X2

[0096] X1 and X2 each independently represent a hydrogen atom, a hydroxymethyl group, or -CH2-OR. 1 .

[0097] R 1 The alkyl group represents 1 to 8 carbon atoms, preferably a straight-chain or branched alkyl group representing 1 to 8 carbon atoms.

[0098] Multiple -CH2-OR molecules in the same molecule 1 In the case of multiple R1 They can be the same or different.

[0099] Examples of melamine resins that contain only -N(CH2OR) can be shown. 1 )2 is a fully alkyl type with reactive functional groups; containing -N(CH2OR) 1 (CH2OH) is a hydroxymethyl type with reactive functional group; it contains -N(CH2OR) 1 (H) is an imino type with reactive functional group; containing -N(CH2OR) 1 (CH2OH) and -N(CH2OR) 1 These are the four types: (H) or hydroxymethyl / imino containing -N(CH2OH)(H) as a reactive functional group. 1 Preferably, it is an alkyl group having 1 to 4 carbon atoms, and more preferably methyl, n-butyl or isobutyl.

[0100] In this disclosure, the aforementioned melamine resin preferably contains X. 1 and X 2 All are -CH2-OR 1 The compound or its condensation product is a fully alkyl-type melamine resin (B1). Examples of such resins include methylated melamine resin, butylated melamine resin, and isobutylated melamine resin. By including a fully alkyl-type melamine resin, the resulting coating composition has the advantages of good storage stability and good reactivity with acrylic resins (A1) at high temperatures and in the presence of a catalyst.

[0101] The aforementioned all-alkyl melamine resin (B1) has a degree of polymerization of 1 or more, preferably 1.2 or more, more preferably 1.5 or more, and preferably 10 or less, more preferably 5 or less, and more preferably 3 or less.

[0102] The aforementioned all-alkyl melamine resin (B1) preferably has a number average molecular weight of 300 or more, preferably 2,000 or less, more preferably 1,300 or less, further preferably 1,000 or less, and particularly preferably 800 or less.

[0103] It should be noted that, in this specification, the number-average molecular weight is a polystyrene conversion value based on gel permeation chromatography (GPC).

[0104] As for the aforementioned all-alkyl melamine resin (B1), commercially available products can also be used, such as CYMEL303, CYMEL325, CYMEL350, CYMEL370, and Mycot 715 (all methylated melamine resins, manufactured by Ornex Japan Co., Ltd.); CYMEL202, CYMEL235, CYMEL254, and CYMEL112. 3. CYMEL1128, CYMEL1170, and Mycot 212 (all methyl-butylated mixed melamine resins, manufactured by Ornex Japan Co., Ltd.); Smimar M-40S (methylated melamine resin, manufactured by Sumitomo Chemical Co., Ltd.); Amidea J-820-60 and Amidea L-127-60 (both butylated melamine resins, manufactured by DIC Co., Ltd.), etc. Only one type can be used, or two or more types can be used in combination.

[0105] The content of the aforementioned all-alkyl melamine resin (B1) in the aforementioned crosslinking agent (B) is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more, with an upper limit of 100% by mass.

[0106] The aforementioned crosslinking agent (B) may include other crosslinking agents (B2) besides the aforementioned all-alkyl melamine resin (B1). Examples of such other crosslinking agents (B2) include melamine resins other than the aforementioned all-alkyl melamine resin (B1), urea resins, benzoguanamine resins, and other amino resins. The aforementioned amino resins exhibit high reactivity with the aforementioned film-forming resin (A), resulting in a coating film with good appearance and moisture resistance.

[0107] As the aforementioned crosslinking agent (B), only one type can be used, or two or more types can be used in combination.

[0108] The ratio of the content of the aforementioned crosslinking agent (B) to the content of the aforementioned film-forming resin (A) ((B) / (A)) is preferably 5 / 95, more preferably 10 / 90 or more, and more preferably 30 / 70 or less, more preferably 20 / 80 or less, based on a mass standard. By being within the aforementioned range, the resulting coating film has the advantage of good processability and damage resistance.

[0109] <Sulfonic Acid Compound (C)>

[0110] The aforementioned sulfonic acid compound (C) can act as a catalyst to promote the reaction between the aforementioned film-forming resin (A) and crosslinking agent (B). Therefore, it has the advantage of imparting high reactivity to the resulting coating composition.

[0111] The aforementioned sulfonic acid compound (C) can be a monosulfonic acid compound or a polysulfonic acid compound. Examples of the aforementioned sulfonic acid compounds include aliphatic sulfonic acids such as methanesulfonic acid; and aromatic sulfonic acids such as p-toluenesulfonic acid, dodecylbenzenesulfonic acid, dinonylnaphthalenesulfonic acid, and dinonylnaphthalenedisulfonic acid. The aforementioned sulfonic acid compound (C) can be used alone or in combination of two or more.

[0112] The content of the aforementioned sulfonic acid compound (C) is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, and more preferably 5 parts by mass or less, more preferably 3 parts by mass or less, relative to 100 parts by mass of the aforementioned coating forming resin (A). By keeping the content of the aforementioned sulfonic acid compound (C) within the aforementioned range, a coating film with good processability (adhesion, crack resistance) and damage resistance can be formed on the pre-coated steel sheet.

[0113] <Amine Compound (D)>

[0114] The aforementioned amine compound (D) neutralizes the sulfonic acid compound (C). By coexisting with the sulfonic acid compound (C) in a manner exhibiting a specific neutralization rate, it possesses the advantage of balancing the stability of the waterborne coating composition during storage (e.g., 15–50°C) and its high reactivity during post-coating heat drying / curing. A portion of the aforementioned amine compound (D) may exist to form a salt with the sulfonic acid compound (C).

[0115] The aforementioned amine compound (D) is a compound having one or more amino groups, preferably a secondary amine compound or a tertiary amine compound.

[0116] Furthermore, the substituents of the nitrogen atom in the aforementioned amine compound are preferably saturated or unsaturated aliphatic hydrocarbon groups. The hydrogen atoms contained in these saturated or unsaturated aliphatic hydrocarbon groups can be independently replaced by -COOH, -OH, etc., and the -CH2- contained in these saturated or unsaturated aliphatic hydrocarbon groups can be replaced by -O-. Additionally, the substituents of the nitrogen atom in the aforementioned amine compound can bond together to form a ring containing the nitrogen atom.

[0117] Examples of the aforementioned amine compounds (D) include, for instance, 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; and triethylamine, tributylamine, triallylamine, N,N-dimethylethanolamine, N-methyldiallylamine, N,N-di-dimethylethanolamine, etc. Aliphatic tertiary amine compounds such as methylallylamine; 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; and amine compounds such as pyridine and 4-ethylpyridine, which are aromatic compounds.

[0118] The boiling point of the aforementioned amine compound (D) is preferably 50°C or higher, more preferably 70°C or higher, even more preferably 100°C or higher, and preferably 250°C or lower, more preferably 220°C or lower. By being within the aforementioned range, it has the advantage of being able to further improve the storage stability of the aforementioned waterborne coating composition.

[0119] The content of the aforementioned amine compound (D) is such that the neutralization rate of the aforementioned sulfonic acid compound (C) based on the aforementioned amine compound (D), i.e., the neutralization rate calculated by molar conversion using the following formula, is in the range of 100% or more and 1,300% or less.

[0120] Neutralization rate (%) = [(valence of the base of amine compound (D) × number of moles of amine compound (D)) / (valence of the acid of sulfonic acid compound (C) × number of moles of sulfonic acid compound (C))] × 100

[0121] The aforementioned neutralization rate is preferably 200% or more, more preferably 300% or more, and can be set to 1,300% or less, 1,100% or less, 1,000% or less, or 900% or less or 800% or less. Although it should not be limited to a specific theory for interpretation, it can be considered that by being within the aforementioned range, during storage (e.g., 15 to 30°C), the aforementioned amine compound (D) can end-cap the sulfonic acid group of the aforementioned sulfonic acid compound (C), inhibiting catalytic activity, thereby improving storage stability. In addition, during heat drying / curing after coating (e.g., 180°C or more), the end-capping detaches, and the sulfonic acid compound (C) can function as a catalyst.

[0122] It is known that the aforementioned all-alkyl melamine resin (B1) has lower reactivity compared to melamine resins commonly used as crosslinking agents, such as imino-type melamine resin and hydroxymethyl-type melamine resin. However, according to the research results of the inventors, the reactivity of the aforementioned all-alkyl melamine resin (B1) is low at low temperatures (e.g., 60–80°C), and its reactivity increases at high temperatures when the all-alkyl melamine resin (B1) is used with the aforementioned sulfonic acid compound (C) and the aforementioned amine compound (D) at the aforementioned neutralization ratio. By combining the aforementioned all-alkyl melamine resin (B1), the aforementioned sulfonic acid compound (D), the aforementioned amine compound (D), and the aforementioned neutralization ratio, a waterborne coating composition with good storage stability can be obtained, which is particularly suitable for high-temperature / short-time coating. Furthermore, the crosslinking density can be increased, thus providing the advantage of obtaining a coating film with excellent processability (adhesion, crack resistance).

[0123] The aforementioned sulfonic acid compound (C) and amine compound (D) can be used directly to prepare waterborne coating compositions, or they can be used in the preparation of waterborne coating compositions as a mixture obtained by pre-mixing them. In this case, in the aforementioned mixture, the aforementioned sulfonic acid compound (C) and some or all of the aforementioned amine compound (D) can form a salt (e.g., a salt obtained by end-capping the sulfonic acid group contained in the sulfonic acid compound (C) with the amino group contained in the amine compound (D), or the salt of the sulfonic acid compound (C) and some or all of the amine compound (D) can be formed before being mixed into the coating composition. Examples of salts formed by the aforementioned sulfonic acid compound (C) and some 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-capping forms of these amines. Commercially available products can also be used as salts of the aforementioned sulfonic acid compound (C) and some or all of the amine compound (D).

[0124] In one embodiment, it is preferred that the content of 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 film-forming resin (A), and the neutralization rate is 100% or more and 1,300% or less; more preferably, the content of sulfonic acid compound (C) is 0.1 parts by mass or more and 5 parts by mass or less relative to 100 parts by mass of film-forming resin (A), and the neutralization rate is 200% or more and 1,000% or less; even more preferably, the content of 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 film-forming resin (A), and the neutralization rate is 300% or more and 900% or less. By having the coating composition have the aforementioned amounts and neutralization rates of sulfonic acid compound (C) and amine compound (D), high storage stability at low temperatures (storage temperature, for example, 15-30°C) and higher reactivity at high temperatures are achieved, resulting in better processability (adhesion, crack resistance) and damage resistance of the coating film.

[0125] In the solid components of the aforementioned waterborne coating composition, the total content of film-forming resin (A), crosslinking agent (B), sulfonic acid compound (C) and amine compound (D) is preferably 50% by mass or more, more preferably 70% by mass or more, further preferably 80% by mass or more, and the upper limit is 100% by mass or less.

[0126] <Aqueous Media (E)>

[0127] The aforementioned waterborne coating composition comprises an aqueous medium (E). The aforementioned aqueous medium (E) is preferably water, an organic solvent (E1), or a mixture of water and an organic solvent (E1).

[0128] As the aforementioned organic solvent (E1), a hydrophilic organic solvent is preferred, and examples include organic solvents with a solubility of 0.1 g / 100 g H2O or more in water at 25°C. Examples of such organic solvents include glycol solvents such as ethylene glycol, propylene glycol, butanediol, pentanediol, diethylene glycol, dipropylene glycol, and triethylene glycol; glycol ether solvents such as ethylene glycol monobutyl ether (butyl cellosolve), diethylene glycol monobutyl ether, 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 2,2,4-trimethylpentane-1,3-diol monoisobutyrate; ketone solvents such as acetone; and N-methyl-2-pyrrolidone. By using such organic solvents, the resulting coating composition exhibits good wetting properties with the substrate.

[0129] In one embodiment, the boiling point of the aforementioned organic solvent (E1) is preferably 150°C or higher, more preferably 180°C or higher, and preferably 300°C or lower, more preferably 250°C or lower. Examples of such organic solvents include diol-based solvents such as propylene glycol (1,2-propanediol), 1,4-butanediol, 1,5-pentanediol, diethylene glycol, and dipropylene glycol, with diethylene glycol being particularly preferred. Only one or more of these solvents may be used.

[0130] The solubility of the aforementioned organic solvent (E1) in water at 25°C is preferably 0.1 g / 100 g H2O or more, more preferably 1 g / 100 g H2O or more, and even more preferably 5 g / 100 g H2O or more. The aforementioned organic solvent (E1) can be a water-miscible organic solvent.

[0131] The organic solvent (E1) in the aforementioned aqueous medium (E) contains 3% by mass or more, preferably 4% by mass or more, more preferably 5% by mass or more, and preferably 30% by mass or less, more preferably 20% by mass or less, and even more preferably 10% by mass or less. By falling within the aforementioned range, the following advantages are achieved: reduced environmental impact; and good storage stability, good wettability to the substrate, and consequently, good appearance of the resulting coating composition.

[0132] The content of the aforementioned aqueous medium (E) is preferably 40% by mass or more, more preferably 50% by mass or more, even more preferably 55% by mass or more, and preferably 90% by mass or less, more preferably 80% by mass or less, even more preferably 85% by mass or less.

[0133] The aforementioned waterborne coating composition may, as needed, include organic solvents other than the aforementioned waterborne medium (E). Examples of organic solvents other than (E) include diethylene glycol dibutyl ether and 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate (Texanol). The boiling point of the organic solvent other than (E) is preferably 150°C or higher, more preferably 180°C or higher, and preferably 300°C or lower, more preferably 250°C or lower.

[0134] <Other>

[0135] The aforementioned water-based coating composition may further include other additives as needed. These other additives include, for example, extender pigments; colorants such as pigments and dyes; heat-insulating pigments; glossy pigments; aggregates (resin particles, silica particles, etc.); waxes; solvents other than those mentioned above; ultraviolet absorbers (benzophenone-based ultraviolet absorbers, etc.); antioxidants (phenolic, thioether-based, hindered amine-based antioxidants, etc.); plasticizers; coupling agents (silane-based, titanium-based, zirconium-based coupling agents, etc.); anti-sagging agents; viscosity modifiers; pigment dispersants; pigment wetting agents; surface conditioners (organosilicon-based, organic polymer-based, etc.); leveling agents; anti-separation agents; anti-settling agents; anti-flooding agents; defoamers; surfactants; antifreeze agents; emulsifiers; rust inhibitors; corrosion inhibitors; mildew inhibitors; antibacterial agents; and stabilizers. Only one of these additives may be used, or two or more may be used in combination.

[0136] As the aforementioned viscosity modifier (F), examples include associative viscosity modifiers that utilize the bonding forces (interactions) of hydrophilic groups (partially) or hydrophobic groups (partially); and thickening viscosity modifiers that utilize the solubilizing / thickening effect of polymers. As the aforementioned associative viscosity modifiers, examples include hydrophilic associative viscosity modifiers that form hydrogen bonds between themselves or with the matrix resin and utilize their bonding forces (interactions), and hydrophobic associative viscosity modifiers that utilize the interaction between intramolecular hydrophobic groups (partially). As the aforementioned associative viscosity modifiers, examples include alkali-thickening viscosity modifiers that utilize the solubilizing / thickening effect of alkali-based polymers.

[0137] As examples of the aforementioned hydrophilic associative viscosity modifiers, polyamide-type viscosity modifiers can be cited. Commercially available polyamide-type viscosity modifiers can be used, such as (all trade names below): BYK-430, BYK-431 (manufactured by Bickkemi Co., Ltd.); Disparan AQ-580, Disparan AQ-600, Disparan AQ-607 (manufactured by Kusumoto Chemical Co., Ltd.); Chikuzol W-300, Chikuzol W-400LP (manufactured by Kyoeisha Chemical Co., Ltd.), etc.

[0138] As the hydrophobic association type viscosity modifier, commercially available products can be used, and examples thereof include Adenacron UH-420 and Apodacron.ルUH-462, アデカノールUH-472, アデカノールUH-526, UH-540, アデカノールU H-814N (manufactured by ADEKA Co., Ltd.); プライマルRH-1020, プライマルRM-2020 (ダウケミカ(manufactured by Suntec Corporation); SNシックナー612, SNシックナー621, Nノパール700N (manufactured by Suntec Corporation), etc.

[0139] Examples of alkali-thickening viscosity modifiers include viscose cellulose, methylcellulose, ethylcellulose, hydroxyethylcellulose, sodium polyacrylate, polyvinyl alcohol, and carboxymethylcellulose. Alternatively, commercially available products can be used, such as cellulose-based viscosity modifiers like Chirose MH and Chirose H (manufactured by Melk Corporation); Premium ASE-60, Premium TT-615, and Premium RM-5 (manufactured by Dookemical Corporation); and Unicorn Polyform (manufactured by Union Carbide Corporation).

[0140] They can be used in single-type or in combination of two or more types.

[0141] Associative viscosity modifiers (F) are preferred. Including an associative viscosity modifier improves the coating workability (roller coating properties) in a roller coater. Specifically, it enables the viscosity of the coating composition to exhibit Newtonian properties at high shear rates. Furthermore, it is more preferable to use it in combination with a hydrophobic associative viscosity modifier, thereby achieving good water resistance and other physical properties of the resulting coating film.

[0142] The content of the viscosity modifier (F) in the waterborne coating composition disclosed herein is preferably 0.01 to 20 parts by weight, more preferably 0.1 to 10 parts by weight, relative to 100 parts by weight of the total solid components of the film-forming resin (A) and the crosslinking agent (B). By keeping the amount of viscosity modifier (F) within this range, it has the advantages of good coating workability in a roller coater (roller coater coating performance) and good appearance and water resistance of the resulting coating film.

[0143] Examples of pigments that can be used as a base pigment include calcium carbonate, barium sulfate, clay, talc, mica, and glass fiber. Only one type can be used, or two or more can be used in combination.

[0144] In one embodiment, the amount of extender pigment is preferably 1 part by mass and 40 parts by mass or less, more preferably 10 parts by mass and 30 parts by mass or less, relative to the total solid components of the film-forming resin (A) and the curing agent (B) of 100 parts by mass. By keeping the amount of extender pigment within this range, the damage resistance of the coating film is easily improved.

[0145] Examples of coloring pigments mentioned above include inorganic pigments such as titanium dioxide, carbon black, graphite, iron oxide, and coal dust; organic pigments such as phthalocyanine blue, phthalocyanine green, quinacridone, perylene, anthraquinone, carbazole violet, anthraquinone, azo orange, flavanone yellow, isoindoline yellow, azo yellow, indanthrelin blue, dibromoanthrone red, perylene red, azo red, and anthraquinone red; and aluminum powder, alumina powder, bronze powder, copper powder, tin powder, zinc powder, iron phosphide, and micronized titanium dioxide. Only one of these pigments may be used, or two or more may be used in combination.

[0146] The aforementioned heat-insulating pigments refer to pigments that do not absorb light in the near-infrared wavelength region (wavelength: 780nm~2,500nm) or have a low absorption rate of light in the near-infrared wavelength region (wavelength: 780nm~2,500nm). There are no particular limitations on the aforementioned heat-insulating pigments; both inorganic and organic heat-insulating pigments can be used.

[0147] Inorganic heat-insulating pigments include, for example, 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 (e.g., Daipiroki Sid Color Black #9595 manufactured by Dainippon Seika Co., Ltd., and Black 6350 manufactured by Asahii Kasei Kogyo Co., Ltd.), and iron oxide-cobalt oxide-chromium oxide (e.g., Daipiroki Sid Color Black manufactured by Dainippon Seika Co., Ltd.). Composite oxide pigments such as Raa Brown #9290, Daipiroki Sid Color Black #9590, copper oxide-magnesium oxide (e.g., Daipiroki Sid Color Black #9598 manufactured by Dai Nippon Seika Co., Ltd.), manganese oxide-bismuth oxide (e.g., Black 6301 manufactured by Asahie Chemical Industry Co., Ltd.), and manganese oxide-yttrium oxide (e.g., Black 6303 manufactured by Asahie Chemical Industry Co., Ltd.); metallic pigments such as silicon, aluminum, iron, magnesium, manganese, nickel, titanium, chromium, and calcium; and alloy pigments such as iron-chromium, bismuth-manganese, iron-manganese, and manganese-yttrium. They can be used individually or in combination of two or more types.

[0148] Organic heat-insulating pigments include, for example, azo pigments, azomethine pigments, lake pigments, thioindigo pigments, anthraquinone pigments (anthraquinone pigments, diaminoanthraquinone pigments, indanone pigments, flavanone pigments, anthraquinone pigments, etc.), perylene pigments, perylene ketone pigments, diketopyrrolopyrrole pigments, dioxazine pigments, phthalocyanine pigments, quinophthalone pigments, quinacridone pigments, isoindoline pigments, and isoindoline pigments. They can be used individually or in combination of two or more.

[0149] Examples of the aforementioned bright pigments include aluminum foil, bronze foil, tin foil, gold foil, silver foil, titanium foil, stainless steel foil, nickel-copper alloy foil, and foil-shaped phthalocyanine blue, among other foil pigments. Only one type can be used, or two or more can be used in combination.

[0150] As the wax, waxes known to those skilled in the art for use in coatings can be used, such as microcrystalline wax, polyethylene wax, polypropylene wax, paraffin wax, carnauba wax, and their modified forms. Only one type can be used, or two or more can be used in combination.

[0151] The shear viscosity of the aforementioned water-based coating composition is 0.01 s⁻¹ at 23°C. -1 When measuring the shear rate, it is preferably 30,000 mPa·s or less, more preferably 20,000 mPa·s or less, even more preferably 10,000 mPa·s or less, and preferably 3,000 mPa·s or more, more preferably 4,000 mPa·s or more, and even more preferably 5,000 mPa·s or more. (The measurement is performed at 10 s...) -1 When measuring the shear rate, it is preferably 800 mPa·s or less, more preferably 700 mPa·s or less, even more preferably 600 mPa·s or less, and preferably 300 mPa·s or more, more preferably 400 mPa·s or more, even more preferably 500 mPa·s or more. At 1,000 s... -1 When measuring the shear rate, it is preferably 1,000 mPa·s or less, more preferably 150 mPa·s or more, and most preferably 500 mPa·s or less. By being within the aforementioned range, a viscosity suitable for paint pick-up during roller coating is achieved.

[0152] The aforementioned shear viscosity can be set to, for example, a value measured immediately after the coating composition is prepared.

[0153] The aforementioned shear viscosity can be measured using a rotational viscometer, such as the stress-controlled rheometer MCR301 (manufactured by Anton Par Corporation).

[0154] <Preparation Method of Waterborne Coating Composition>

[0155] The method for preparing the waterborne coating composition disclosed herein is not particularly limited, and it can be prepared by mixing the various components. Mixing can be performed using, for example, roller mills, ball mills, bead mills, stone mills, sand mills, can mills, paint agitators or distributors, dispersers, kneaders, etc.

[0156] The coating film formed from the aforementioned water-based coating composition and the method for manufacturing the coating film are also included within the scope of this disclosure.

[0157] <Painted Object>

[0158] Examples of substrates that can be coated using the waterborne coating compositions disclosed herein include galvanized steel sheets, galvanized-aluminum alloy steel sheets, aluminum alloy steel sheets, molten zinc-aluminum-magnesium alloy steel sheets, stainless steel sheets, and cold-rolled steel sheets manufactured by methods such as melt coating or electrolysis. In addition to these steel sheets or coated steel sheets, metal sheets such as aluminum sheets (including aluminum alloy sheets) can also be used as coating targets.

[0159] The aforementioned object to be coated preferably undergoes surface treatment. Specifically, the object to be coated is preferably subjected to a chemical formation treatment after pretreatment such as alkaline degreasing, hot water washing, or water washing. The aforementioned chemical formation treatment can be performed using known methods, including, for example, non-chromate treatments such as chromate treatment or zinc phosphate treatment. As for the aforementioned surface treatment, it can be appropriately selected according to the steel plate used, and a treatment that does not contain heavy metals is preferred. By applying the coating composition disclosed herein to the object to be coated in this manner after chemical formation treatment, the adhesion of the coating film to the metal plate surface is improved, and the corrosion resistance is also improved. Alternatively, a primer film (primer film) can be formed on the metal plate surface after chemical formation treatment, and then the coating can be applied thereon. The thickness of the primer 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.

[0160] <Coating Manufacturing Method>

[0161] The method for manufacturing the coating film disclosed herein includes:

[0162] The process of forming a coating film by applying the disclosed water-based coating composition to a substrate; and

[0163] A process of drying and / or curing the aforementioned coating film under conditions where the maximum temperature reaches 180°C or higher and the drying and / or curing time is less than 120 seconds to form a coating film.

[0164] There are no particular limitations on the method of applying the aforementioned water-based coating composition of this disclosure to the object. Existing known methods such as roller coating, airless spraying, electrostatic spraying, and curtain coating can be used. Roller coating and curtain coating are preferred examples, and roller coating is more preferred.

[0165] The aforementioned maximum temperature reached is preferably 200 seconds or more, for example, it can be 280 seconds or less, 270 seconds or less, or 250 seconds or less. The drying and / or curing time is 120 seconds or less, or it can be set to 60 seconds or less, 30 seconds or less, 10 seconds or less, or 6 seconds or less, preferably 1 second or more.

[0166] There are no particular limitations on the method for drying and / or curing the aforementioned coating film; heating methods such as hot air heating, infrared heating, and induction heating can be used.

[0167] The film thickness (dry film thickness) of the dried and / or cured coating is preferably 1 μm or more, more preferably 5 μm or more, and preferably 30 μm or less, more preferably 25 μm or less.

[0168] A laminate having the aforementioned coated object and the aforementioned coating film formed on the coated object is also included within the scope of this disclosure.

[0169] When the aforementioned object to be coated further has the aforementioned coating film on one side, it may have a coating film formed of a known coating composition such as a coating composition containing epoxy resin on the other side.

[0170] When the waterborne coating composition of this disclosure is applied under conditions that are higher temperature and shorter time than those typically used for coating metal substrates (e.g., drying / curing temperature of 60 to 80°C and drying / curing time of 30 minutes to 1 hour), a coating film with high curability and good film properties (adhesion, crack resistance, and other processability and damage resistance) can be obtained.

[0171] The waterborne coating composition disclosed herein exhibits high storage stability, and the resulting coating film is not easily peeled off from the substrate during bending and other processing, demonstrating good adhesion. Furthermore, cracking is suppressed, resulting in good crack resistance and excellent damage resistance. Therefore, the waterborne coating composition disclosed herein is suitable for coating metals, especially for pre-coating.

[0172] Example

[0173] The present disclosure is illustrated in more detail by means of the following embodiments, but is not limited thereto. The terms “parts” and “%” in the embodiments are based on a mass basis unless otherwise specified.

[0174] <Example of manufacturing film-forming resin (A-1)>

[0175] Dissolve 0.6 parts by weight of surfactant SS-H (manufactured by Kao Corporation) in 60 parts by weight of deionized water. Add to this mixture a monomer mixture comprising 53.0 parts by weight of methyl methacrylate, 39.2 parts by weight of n-butyl acrylate, 5.8 parts by weight of 2-hydroxyethyl methacrylate, and 2.0 parts by weight of methacrylic acid, and stir to prepare 150.5 parts by weight of monomer pre-emulsion. Separately, dissolve 1.0 part by weight of ammonium persulfate as an initiator in 20 parts by weight of deionized water to prepare an initiator aqueous solution.

[0176] 40 parts by mass of ion-exchanged water and 0.4 parts by mass of Perex SS-H were added to a reaction vessel equipped with a thermometer, condenser, and stirrer, and the mixture was heated to 80°C under a nitrogen atmosphere. While maintaining the temperature at 80°C, the aforementioned initiator aqueous solution was added dropwise over 180 minutes. Ten minutes after the start of the dropwise addition, a monomer pre-emulsion was added dropwise over 150 minutes from another opening in the reaction vessel to carry out emulsion polymerization. After the addition of the aforementioned initiator aqueous solution was completed, the mixture was further heated and stirred at 80°C for 60 minutes, then cooled to room temperature. 2.10 parts by mass of dimethylethanolamine were added to prepare an acrylic emulsion (solids concentration: 45% by mass) in which a film-forming resin (A-1) was dispersed in an aqueous medium.

[0177] As shown in Table 1, the monomer type, amount, and initiator dosage were changed, and the same procedures were followed as described above to prepare coating-forming resins (A-2) to (A-11). The characteristic values ​​such as the hydroxyl value of each coating-forming resin are shown in Table 1.

[0178] Details of the components shown in the table below used in the Examples and Comparative Examples are shown below.

[0179] Coating film forming resin (A)

[0180] (A-12) Biolonal MD2000 (manufactured by Toyobo Co., Ltd., polyester resin emulsion); Hydroxyl value: 6 mg KOH / g, Acid value: 2 mg KOH / g, Weight-average molecular weight: 30,000, Glass transition temperature: 67℃, Minimum film-forming temperature: 48℃, Average particle size: 125 nm, Solid content concentration: 40% by mass

[0181] Crosslinking agent (B)

[0182] (B-1)CYMEL303 (manufactured by Ornex Japan Co., Ltd., all-alkyl methylated melamine resin); Solid content concentration: 100% by mass; Number average molecular weight: 455

[0183] (B-2) CYMEL300 (manufactured by Ornex Japan Co., Ltd., all-alkyl methylated melamine resin); Solid content concentration: 100% by mass; Number average molecular weight: 390

[0184] Other crosslinking agents

[0185] (b-1) CYMEL327 (manufactured by Ornex Japan Co., Ltd., imino-type methylated melamine resin); Solid content concentration: 90% by mass; Number average molecular weight: 470

[0186] (b-2) Mickey 508 (manufactured by Ornex Japan Co., Ltd., imino-type butylated melamine resin): Solid content concentration: 80% by mass, number average molecular weight: 1,500 Sulfonic acid compounds (C)

[0187] (C-1) AC400S (manufactured by Teika Co., Ltd., dodecylbenzenesulfonic acid); Solid content concentration: 25% by mass

[0188] (C-2) AC700 (manufactured by Teika Co., Ltd., p-Toluenesulfonic acid); Solid content concentration: 25% by mass

[0189] (C-3) Nacurre-1051 (manufactured by Kusumoto Chemical Co., Ltd., dinonylnaphthalenesulfonic acid); solid content concentration: 51% by mass

[0190] Other acid compounds

[0191] (c-1)Cycat296 (manufactured by Ornex Japan Co., Ltd., phosphate compound); solid content concentration: 50% by mass

[0192] Amine compounds (D)

[0193] (D-1) DMEA (dimethylethanolamine, manufactured by Mitsubishi Gas Chemical Company); Boiling point: 134℃

[0194] (D-2)AMP (2-amino-2-methyl-1-propanol, manufactured by a domestic chemical company); Boiling point: 165℃

[0195] (D-3)TEA (triethylamine, manufactured by Mitsubishi Gas Chemical Company); Boiling point: 90℃

[0196] Aqueous medium (E)

[0197] (E1-1) Diethylene glycol (manufactured by Nippon Shokubai Co., Ltd.); Boiling point: 244℃; Solubility in water: Infinite (miscible with water)

[0198] (E1-2) Propylene glycol (manufactured by Sankyo Chemical Co., Ltd.); Boiling point: 187℃; Solubility in water: infinite (miscible with water).

[0199] (E1-3) Dipropylene glycol (manufactured by Showa Chemical Co., Ltd.); Boiling point: 232℃; Solubility in water: infinite (miscible with water)

[0200] (E1-4)1,4-Butanediol (manufactured by Sankyo Chemical Co., Ltd.); Boiling point: 228℃; Solubility in water: infinite (miscible with water).

[0201] (E1-5)1,5-Pentanediol (manufactured by Ube Industries, Inc.); Boiling point: 242°C; Solubility in water: Infinite (miscible with water)

[0202] Viscosity modifier (F)

[0203] (F-1)SN Sickner 612 (Polyether urethane hydrophobic associative viscosity modifier, manufactured by Sunopco Co., Ltd.); Solid content concentration: 40% by mass

[0204] (F-2)SN Sickner 621 (Polyether urethane hydrophobic associative viscosity modifier, manufactured by Sunopco Co., Ltd.); Solid content concentration: 30% by mass

[0205] (F-3) Adeknor UH-526 (Polyether urethane hydrophobic associative viscosity modifier, manufactured by ADEKA Corporation); Solid content concentration: 30% by mass

[0206] (F-4) Premium RM-2020NPR (Polyether urethane hydrophobic associative viscosity modifier, manufactured by Daikmekal Co., Ltd.); Solid content concentration: 20% by mass

[0207] (F-5) Polymer ASE-60 (Alkali-swellable thickener for polyacrylate emulsions, manufactured by Daikemia Corporation); Solid content concentration: 28% by mass

[0208] <Example of Pigment Dispersion Paste Manufacturing>

[0209] 1.63 parts by weight of Disperbyk190 (manufactured by Big Keme Co., Ltd.) as a dispersant, 0.25 parts by weight of dimethylethanolamine, 0.05 parts by weight of SN-477T (manufactured by Sunopco Co., Ltd.) as an antifoaming agent, 32.9 parts by weight of ion-exchanged water, and 65.2 parts by weight of titanium dioxide (Ti-PureR-706, manufactured by DuPont Co., Ltd.) as a pigment were premixed and dispersed at 1,600 rpm using an SG mill (dispersion medium: glass beads) until the maximum particle size of the pigment coarse particles reached 5 μm, thus obtaining a pigment dispersion paste.

[0210] <Example of manufacturing waterborne coating composition 1>

[0211] 55.1 parts by weight of the pigment dispersion paste obtained in the aforementioned manufacturing example, 80.0 parts by weight of the film-forming resin (A-1) obtained in the aforementioned manufacturing example, 20.0 parts by weight of the film-forming resin (A-8), and 17.6 parts by weight of CYMEL303 as a crosslinking agent (B-1) were mixed, and then 5.4 parts by weight of diethylene glycol (E1-1) and 5.4 parts by weight of propylene glycol (E1-2) as an aqueous medium were mixed and stirred. Next, 1.2 parts by weight of dodecylbenzenesulfonic acid as a sulfonic acid compound (C-1) and 1.9 parts by weight of dimethylethanolamine as an amine compound (D-1) were stirred using a distributor, and then 20.2 parts by weight of sicner SN-61 as a viscosity modifier (F-1) were mixed while stirring to obtain coating composition 1.

[0212] (Coating compositions 2-45, Comparative Examples 1-10)

[0213] The types and amounts of each component are changed as described in Tables 2-7. Otherwise, the coating composition is prepared in the same manner as coating composition 1.

[0214] <Example of manufacturing coated steel sheet>

[0215] After alkaline degreasing of 0.4mm thick molten galvanized steel sheet, phosphate treatment agent Servocote EC2310 (manufactured by Japan Pent Servocote Co., Ltd.) is applied to the surface and back of the steel sheet, thereby performing chromium-free formation treatment and drying.

[0216] Next, using a bar coater, the coating composition 1 obtained in the manufacturing example is applied to the surface of the steel plate with a dry film thickness of 18 μm. The plate is then baked for 30 seconds at a maximum raw material temperature of 230°C to form a surface coating, thus obtaining a coated steel plate.

[0217] 1) Shear viscosity measurement

[0218] Regarding the shear viscosity of the coating compositions obtained in the examples and comparative examples, the shear rate was measured to be 0.1 s using a stress-controlled rheometer MCR301 (manufactured by Anttones, Inc., clamp: 50 mm parallel plate, gap: 0.5 mm). -1 10s -1 And 1,000s -1 The shear viscosity at that time. The measurement temperature was set to 23℃.

[0219] 2) Storage stability

[0220] The evaluation was conducted using Ford Cup No. 4 (made by Uejima Manufacturing Co., Ltd.) according to the method specified in JISK56002-2 (Flow Cup Method).

[0221] Ion-exchanged water was added to the coating compositions obtained in the examples and comparative examples to adjust the viscosity to 60 ± 10 seconds (initial viscosity (seconds)). Specifically, the initial viscosity was set as the viscosity measured immediately after dilution with the aforementioned ion-exchanged water and stirring at 1,000 rpm for 3 minutes using a dispenser. The coating temperature was set to 25°C.

[0222] The coating composition, adjusted to the aforementioned initial viscosity (60 ± 10 seconds (25°C)), was added to 80-90% of a 1 / 5 container and sealed. The container was then left to stand in a constant temperature chamber at 40°C. After 14 days (2 weeks), the mixture was removed and its viscosity (viscosity over time (seconds)) was measured in the same manner as described above.

[0223] The rate of change of viscosity over time relative to the initial viscosity is calculated using the following formula, and storage stability is evaluated according to the following criteria. ○ The above is considered acceptable.

[0224] Viscosity change rate (%) = Viscosity over time (seconds) / Initial viscosity (seconds) × 100

[0225] ◎: Viscosity change rate is 0% or more and less than 30%.

[0226] ○: The viscosity change rate is greater than 30% and less than 50%.

[0227] △: The viscosity change rate is greater than 50% but less than 100%.

[0228] ×: The viscosity change rate is over 100%.

[0229] 5) Coating workability (roller coating performance)

[0230] For the coating compositions obtained in the examples and comparative examples, a small-scale experimental coating machine (manufactured by Enu Kei Tech Co., Ltd.) equipped with three rollers (support roller, coating roller, and pickup roller) was used to coat the substrates under the following conditions, and the coating performance of the roller coating machine was evaluated according to the following criteria. ○ The above is considered acceptable. It should be noted that the test conditions were set at room temperature of 23°C and humidity of 60% RH.

[0231] • Object to be coated: GL steel sheet (manufactured by Nippon Steel Co., Ltd.) with dimensions of 300mm × 2,000mm × 0.35mm.

[0232] • Painting conditions:

[0233] • Linear velocity: 50m / min

[0234] • Roller circumferential speed: Coating roller: 65 m / min (130% of linear speed), Pick-up roller: 20 m / min (40% of linear speed)

[0235] • Support roller pressure: 60 kgf

[0236] • Baseline coating weight: The mass of the dried coating is 28 g / m² 2

[0237] Baking conditions: 30 seconds at a maximum temperature of 230°C on the raw material to be coated.

[0238] ◎: Able to evenly coat the entire surface with the standard coating amount.

[0239] ○: Can be evenly coated on the entire surface, but the coating amount is 20-28 g / m². 2

[0240] △: Can be coated on the entire surface, but the coating amount is less than 20g / m². 2 The film thickness becomes uneven.

[0241] ×: Unpainted areas are present, making it impossible to paint the entire surface.

[0242] It should be noted that in a roller coater, the paint is picked up by the pick-up roller and transferred to the coating roller, and then to the support roller to be coated on the workpiece. When the paint is appropriately picked up by the pick-up roller and transferred to the support roller by the pressure of the coating roller and the support roller, the paint is evenly coated on the workpiece. However, if only a small amount of paint is picked up by the pick-up roller, uneven transfer occurs during the roller-to-roll transfer, resulting in an uneven coating on the workpiece.

[0243] 4) Processability (Sealing properties)

[0244] The coated steel sheets obtained in the examples and comparative examples were cut into 5cm × 3cm pieces and pre-bent using a bending machine (manufactured by Uejima Manufacturing Co., Ltd.) with the coated surface as the outermost side. Two steel sheets of the same thickness (0.4mm) were clamped in the test piece and bent using a press (manufactured by Kyoritsu Industrial Co., Ltd.). A celestial tape (registered trademark) (LP-24, manufactured by Nichiban Co., Ltd.) was applied to the processed part of the coated steel sheet and peeled off in one go. The adhesion of the coating film in the processed part was evaluated. The appearance of the part peeled off due to the tape was evaluated according to the following criteria. A score of 4 or higher was considered acceptable.

[0245] 5: No metal substrate was observed in the peeled-off portion of the tape.

[0246] 4: A metal base was observed in the area of ​​the peeled portion of the tape (more than 0% and less than 20%).

[0247] 3: A metal base was observed in more than 20% but less than 50% of the area of ​​the peeled-off portion of the tape.

[0248] 2: The base of the metal was observed in more than 50% but less than 80% of the area of ​​the peeled-off portion of the tape.

[0249] 1: The base of the metal was observed in more than 80% of the area of ​​the peeled-off portion of the tape.

[0250] 5) Machinability (Crack Resistance)

[0251] The coated steel plates obtained in the examples and comparative examples were cut into 5cm × 3cm pieces and pre-bent using a bending machine (manufactured by Uejima Manufacturing Co., Ltd.) with the coated surface as the outermost side. Five steel plates of the same thickness (0.4mm) were clamped in this test piece and bent using a press (manufactured by Kyoritsu Industrial Co., Ltd.). The coating condition (cracks) of the processed area was observed using a 15x magnifying glass, and the processability was evaluated according to the following criteria. A score of 4 or higher was considered acceptable. It should be noted that the test conditions were set at a temperature of 23°C and a humidity of 60% RH.

[0252] 5: No cracks were observed in the machined parts.

[0253] 4: Cracks were observed in the area of ​​the processed portion (more than 0% and less than 20%).

[0254] 3: Cracks were observed in more than 20% but less than 50% of the area of ​​the processed part.

[0255] 2: Cracks were observed in more than 50% but less than 80% of the area of ​​the processed part.

[0256] 1: Cracks were observed in more than 80% of the area of ​​the machined part.

[0257] 6) Damage resistance

[0258] A continuously weighted scratch strength tester (TYPE: 18 / 18L, manufactured by Shin-Tung Science Co., Ltd.) was used. A diamond needle (a conical scratch needle with a diameter of 0.4 mm) with a radius of 0.4 mm was applied to the coating surface of each coated steel sheet obtained in the examples and comparative examples. A load was applied and the sheet was scratched once at a speed of 300 mm / min and a travel width of 10 cm. The weight of the load at which coating damage and substrate exposure were confirmed was evaluated according to the following criteria. A value of ○ or higher was considered acceptable. It should be noted that the load was 500 gf applied each time, and the test conditions were set at a temperature of 23°C and a humidity of 60% RH.

[0259] ◎: Even with a load exceeding 3,000g, the substrate will not be exposed.

[0260] ○: Load exceeding 2,000 but less than 3,000g

[0261] △: Load exceeding 1,000g but less than 2,000g

[0262] ×: Load below 1,000g

[0263] [Table 1]

[0264]

[0265] [Table 2]

[0266]

[0267] [Table 3]

[0268]

[0269] [Table 4]

[0270]

[0271] [Table 5]

[0272]

[0273] [Table 6]

[0274]

[0275] [Table 7]

[0276]

[0277] Examples 1 to 45 are embodiments of this disclosure, exhibiting high storage stability, excellent processability, and good resistance to damage.

[0278] Comparative Examples 1 and 2 are examples of acrylic resins (A1) with a hydroxyl value of less than 5 mg KOH / g, exhibiting poor damage resistance. Comparative Examples 3 and 4 are examples of acrylic resins (A1) with a hydroxyl value exceeding 35 mg KOH / g, exhibiting poor storage stability and processability. Comparative Examples 5 and 6 are examples of sulfonic acid compounds (C) based on amine compounds (D) with a neutralization rate of less than 100%, exhibiting poor storage stability. Comparative Example 7 is an example of sulfonic acid compounds (D) based on amine compounds (D) with a neutralization rate exceeding 1,300%, exhibiting poor storage stability. Comparative Examples 8 and 9 are examples of melamine resins (B1) without a fully alkyl-type melamine resin as a crosslinking agent (B), exhibiting poor processability. Comparative Example 10 is an example of melamine resins (C) without a sulfonic acid compound (C) and using a phosphoric acid compound, exhibiting poor storage stability and damage resistance.

Claims

1. A waterborne coating composition comprising a film-forming resin (A), a crosslinking agent (B), a sulfonic acid compound (C), an amine compound (D), and a waterborne medium (E). The coating forming resin (A) comprises an acrylic resin (A1) having hydroxyl groups. The hydroxyl value of the coating-forming resin (A) is 5 mg KOH / g or higher and 35 mg KOH / g or lower. The crosslinking agent (B) comprises a fully alkyl melamine resin (B1). The content of the sulfonic acid compound (C) is 0.1 parts by weight or more and 5 parts by weight or less per 100 parts by weight of the film-forming resin (A). The neutralization rate, calculated based on the molar conversion of the acid groups of the amine compound (D) and the sulfonic acid compound (C), is greater than 100% and less than 1,300%. The amine compound (D) has a boiling point above 100°C. The aqueous medium (E) contains an organic solvent (E1). The organic solvent (E1) has a boiling point above 150°C. The content of organic solvent (E1) in the aqueous medium (E) is less than 30% by mass.

2. The water-based coating composition according to claim 1, wherein, The coating-forming resin (A) has a weight-average molecular weight of 100,000 or more.

3. The water-based coating composition according to claim 1, wherein, At a temperature of 23°C, the time is 0.01s. -1 The shear viscosity measured at the shear rate was below 30,000 mPa·s, with a 10s... -1 The shear viscosity measured at the shear rate was below 800 mPa·s, and at 1,000 s⁻¹... -1 The shear viscosity measured at the shear rate was above 150 mPa·s.

4. The waterborne coating composition according to any one of claims 1 to 3, used for roll coating.

5. A method for manufacturing a coating film, comprising: The process of applying the water-based coating composition according to any one of claims 1 to 4 to a substrate to form a coating film; as well as The process of drying and / or curing the coating film under conditions where the maximum temperature reaches 180°C or higher and the drying and / or curing time is less than 120 seconds to form a coating film.

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