Water-based primer surfacer, method for forming multi-layer coating film, and multi-layer coating film

Abstract

The composition comprises a base agent (A) containing a specific water-dispersible hydroxyl-containing resin (a1), a pigment (a2) and a thickener (a3), and a curing agent (B) containing a polyisocyanate compound (b1) and an organic solvent (b2) having no hydroxyl group, the pigment (a2) containing three types of pigments having different Mohs hardnesses and specific gravities, the average Mohs hardness being 3.15 to 4.25 and the average specific gravities being 3.25 to 3.55 g / cm 3 a total content of the pigment (a2) is 100 parts by mass or more and 300 parts by mass or less relative to 100 parts by mass of a resin solid content contained in the main agent (A), and an equivalent ratio (hydroxyl group equivalent / isocyanate group equivalent) of the hydroxyl groups of the water-dispersible hydroxyl-containing resin (a1) to the isocyanate groups of the polyisocyanate compound (b1) is 0.3 to 2.

Description

[Technical field]

[0001] The present invention relates to a water-based primer surfacer, a method for forming a multi-layer coating film, and the multi-layer coating film. [Background technology]

[0002] In recent years, environmental pollution has become more serious, and regulations on organic solvent emissions have been strengthened internationally. In the field of paints, there has been a shift from conventional solvent-based paints to water-based paints using water as a medium. Patent Document 1 discloses a water-based undercoat paint composition. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2018-178082 A Summary of the Invention [Problem to be solved by the invention]

[0004] In automotive repair, the area to be painted and the surrounding area are sanded down as necessary, and any irregularities are filled in with putty. The area is then sanded down again. A primer surfacer is then applied. Further sanding is usually performed.

[0005] In automobile repair, polishing the primer surfacer coating is essential to improve the appearance. If the primer surfacer coating is thin, the base material (such as the base material for the automobile) may be exposed by the polishing process.

[0006] Water-based primer surfacers are prone to causing bubbles when curing. To prevent bubbles from occurring, water-based primer surfacers are usually applied thinly. Therefore, coatings using water-based primer surfacers are more likely to expose the base material when polished compared to coatings using solvent-based primer surfacers.

[0007] An object of the present invention is to provide a water-based primer surfacer for automobile repair that has excellent sanding workability while also being capable of forming a coating film that is sand-resistant. [Means for solving the problem]

[0008] In order to solve the above problems, the present invention provides the following aspects. [1] A base material (A) containing a water-dispersible hydroxyl-containing resin (a1), a pigment (a2), and a thickener (a3), and A curing agent (B) containing a polyisocyanate compound (b1) and an organic solvent (b2) having no hydroxyl group, the water-dispersible hydroxyl-containing resin (a1) has a hydroxyl value of 20 mgKOH / g or more and contains at least one member selected from the group consisting of acrylic polyols, polyester polyols, polyether polyols, polyurethane polyols, and polycarbonate polyols; The pigment (a2) is Mohs hardness is 1.0 to 2.3 and specific gravity is 2.0 to 4.0 g / cm 3 A first pigment (a2-1) which is Mohs hardness is 2.5 to 5.5 and specific gravity is 1.0 to 5.0 g / cm 3 A second pigment (a2-2) which is Mohs hardness is 5.8 to 8.2, and specific gravity is 2.0 to 6.0 g / cm 3 and a third pigment (a2-3) which is The average Mohs hardness is 3.15 to 4.25. Average specific gravity: 3.25~3.55g / cm 3 and a total content of the pigment (a2) is 100 parts by mass or more and 300 parts by mass or less relative to 100 parts by mass of a resin solid content contained in the main agent (A); an equivalent ratio (hydroxyl group equivalent / isocyanate group equivalent) of the hydroxyl group of the water-dispersible hydroxyl-containing resin (a1) to the isocyanate group of the polyisocyanate compound (b1) is 0.3-2; [2] The water-based primer surfacer according to [1] above, wherein the main agent (A) further contains a polyurethane resin having a hydroxyl value of less than 20 mgKOH / g and a glass transition temperature of 0°C or lower. [3] The water-based primer surfacer according to the above [1] or [2], wherein at least one of the base agent (A) and the curing agent (B) contains a silane coupling agent. [4] The water-based primer surfacer according to any one of the above [1] to [3], wherein the first pigment (a2-1), the second pigment (a2-2), and the third pigment (a2-3) each contain at least one type of coloring pigment and at least two types of extender pigments. [5] The coating film formed by the water-based primer surfacer was irradiated with light I at an angle of 45 degrees to the surface of the coating film. 45 Any of the water-based primer surfacers [1] to [4] above, having a maximum spectral reflectance of more than 70% when received at an angle of 110 degrees to specular reflected light. [6] The pigment (a2) comprises at least one black pigment, The coating film formed by the water-based primer surfacer was irradiated with light I at an angle of 45 degrees to the surface of the coating film. 45 Any of the water-based primer surfacers [1] to [4] above, having a maximum spectral reflectance of 4 to 70% when received at an angle of 110 degrees to specular reflected light. [7] Applying any one of the water-based primer surfacers according to [1] to [6] above onto a substrate including an automotive substrate to form a primer surfacer coating film; Applying an aqueous colored base coating composition onto the primer surfacer coating to form a colored base coating; and applying, onto the colored base coating film, a multi-component aqueous clear coating composition comprising a first component containing a hydroxyl-containing resin and an aqueous solvent and a second component containing a polyisocyanate compound and an organic solvent having no hydroxyl groups, to form a clear coating film. [8] The method for forming a multilayer coating film according to [7] above, wherein the substrate comprises the automotive substrate and a coating film other than the multilayer coating film that covers at least a portion of a surface of the automotive substrate. [9] The method for forming a multilayer coating film according to the above item [7] or [8], wherein the substrate comprises a resin automotive substrate and a primer coating film formed from an aqueous primer, the primer coating film covering at least a portion of the surface of the automotive substrate.

[10] A primer surfacer coating film formed on a substrate including an automotive substrate using any one of the water-based primer surfacers [1] to [6] above; A colored base coating film formed on the primer surfacer coating film using an aqueous colored base coating composition; A multi-layer coating film having a clear coating film formed on the colored base coating film from a multi-component aqueous clear coating composition comprising a first liquid containing a hydroxyl group-containing resin and an aqueous solvent and a second liquid containing a polyisocyanate compound and an organic solvent having no hydroxyl groups.

[11] A primer coating film formed by an aqueous primer on a substrate including a resin automotive substrate; a primer surfacer coating film formed on the primer coating film using any one of the aqueous primer surfacers [1] to [6] above; A colored base coating film formed on the primer surfacer coating film using an aqueous colored base coating composition; A multi-layer coating film having a clear coating film formed on the colored base coating film from a multi-component aqueous clear coating composition comprising a first liquid containing a hydroxyl group-containing resin and an aqueous solvent and a second liquid containing a polyisocyanate compound and an organic solvent having no hydroxyl groups. Effect of the Invention

[0009] According to the present invention, there is provided an aqueous primer surfacer which is excellent in polishing workability while being capable of forming a coating film having abrasion resistance. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Primer surfacer coating films are required to have the conflicting properties of being abrasion-resistant so as not to be excessively abraded, and being easily abraded (so that the coating film can be easily made smooth) with ease of abrasion.

[0011] The average Mohs hardness and average specific gravity of all pigments contained in the coating film affect the abrasion resistance and abrasion workability. The average Mohs hardness of pigment (a2) is 3.15 to 4.25, and the average specific gravity is 3.25 to 3.55 g / cm 3 In this case, both abrasion resistance and abrasion workability are achieved.

[0012] It is important not only to keep the average Mohs hardness and average specific gravity of the pigments within a specific range, but also to use three pigments (primary, secondary, and tertiary pigments) with different Mohs hardness and specific gravity.

[0013] The first pigment (a2-1) has a low hardness. The first pigment (a2-1) reduces the average Mohs hardness of the pigment (a2) to improve the polishing workability, but may excessively reduce the polishing resistance. The first pigment (a2-1) has a relatively small specific gravity, so it is likely to be unevenly distributed in the upper part of the coating film. The third pigment (a2-3) has a high hardness. The third pigment (a2-3) increases the average Mohs hardness of the pigment (a2) to improve the polishing resistance, but may excessively reduce the polishing workability. The third pigment (a2-3) has a large specific gravity, so it is likely to be unevenly distributed in the lower part of the coating film. The uneven distribution of these pigments makes it even more difficult to achieve both polishing workability and polishing resistance.

[0014] The second pigment (a2-2) has a medium hardness and a wide range of specific gravity, and can easily balance the polishing workability and polishing resistance by uniformly disposing the first pigment (a2-1) and the third pigment (a2-3) in the coating film.

[0015] By using three types of pigments with different Mohs hardness and specific gravity, it is possible to achieve both excellent polishing workability and high abrasion resistance while suppressing the deterioration of the coating film properties.

[0016] According to the water-based primer surfacer of the present disclosure, a coating film having abrasion resistance to such an extent that the substrate (e.g., steel plate for automobiles, resin substrate for automobiles, existing coating film, paint base including primer coating film and putty, etc.) is not exposed by grinding. The coating film obtained by the water-based primer surfacer of the present disclosure is also excellent in grinding workability. Therefore, a multilayer coating film in which another coating film is laminated on the primer surfacer coating film is smooth and has excellent appearance.

[0017] The water-based primer surfacer of the present disclosure is used for automobile repair (repair painting). Repair painting is painting carried out on the polished and peeled part after removing the existing paint film (old paint film) by polishing. Hereinafter, the term "paint film" may include a paint film (repair paint film) formed by repair painting. The term "painting" may include repair painting.

[0018] The old coating film is a coating film other than the multi-layer coating film of the present disclosure that was formed on the substrate before the multi-layer coating film of the present disclosure was formed. The old coating film may be, for example, a coating film for automobile exteriors (at least one of an intermediate coating film, a base coating film, and a clear coating film). During partial repair, a part of the old coating film (e.g., a damaged part) is removed by grinding, and then the multi-layer coating film of the present disclosure is formed. During repair, the multi-layer coating film of the present disclosure may be formed on the old coating film without removing the old coating film.

[0019] ·Abrasion resistance Abrasion resistance is evaluated by the mass loss of the primer surfacer coating film before and after the abrasion test. If the mass loss is 85 mg or less, it is evaluated as having excellent abrasion resistance. The abrasion test is performed on a test plate having a 60 μm thick primer surfacer coating film formed on a bonded steel plate using a Taber type tester under the following conditions.

[0020] (Polishing test conditions) Abrasive tool: Abrasive wheel (CS-10) with #400 abrasive paper (e.g., Kovacs) attached Load capacity: 1kg Rotation speed: 60 rpm Number of rotations of the test plate: 50 times

[0021] Specifically, the primer surfacer coating film to be evaluated for abrasion resistance is obtained by applying an aqueous primer surfacer to a 110 mm x 110 mm bonded steel plate so that the cured film thickness is 60 μm, and then heating at 60°C for 20 minutes.

[0022] ·Polishing workability The polishing workability is evaluated by a sensory test when the primer surfacer coating film is polished until the surface becomes smooth. If it is felt that the surface can be polished without resistance, it is evaluated as having excellent polishing workability. Polishing is performed by using a polishing tool with #400 abrasive paper (e.g., manufactured by Kovacs) attached to a 60 μm-thick primer surfacer coating film formed on a tin plate.

[0023] Specifically, the coating film to be evaluated for sanding workability is obtained by applying a water-based primer surfacer to a 100 mm x 200 mm tin plate so that the cured film thickness is 60 μm, and then heating at 60° C. for 20 minutes.

[0024] Water-dispersible resins include dispersion type (generally referred to as colloidal dispersion type) and emulsion type. Colloidal dispersion type water-dispersible resins are typically obtained by semi-dissolving a resin synthesized in an organic solvent in water with a neutralizing agent. Emulsion type water-dispersible resins are typically produced by emulsion polymerization or by mechanically forcibly emulsifying. Water-dispersible resins can also be obtained by modifying a hydrophobic resin with a polar compound or by using a polar monomer in the synthesis of the resin. The water-dispersible resin may be a dispersion type.

[0025] Aqueous coating compositions such as aqueous primer surfacers contain water as a solvent. The proportion of water in the total solvent is 50% by mass or more, may be 60% by mass or more, may be 70% by mass or more, or may be 80% by mass or more.

[0026] The resin solid content contained in a coating composition such as an aqueous primer surfacer is the total solid content of the resin components. The resin components are organic components other than thickeners, various pigments, organic solvents, water, and other inorganic components. For example, the resin solid content of an aqueous primer surfacer is the total solid content of the resin components contained in the main agent (A) and the hardener (B). The resin components of an aqueous primer surfacer are a water-dispersible hydroxyl-containing resin (a1), a polyisocyanate compound (b1), and other resins. The resin components of the main agent (A) of an aqueous primer surfacer are typically a water-dispersible hydroxyl-containing resin (a1) and other resins.

[0027] The weight average molecular weight and number average molecular weight are measured with polystyrene standards by the GPC (gel permeation chromatography) method.

[0028] The acid value and hydroxyl value can be measured by a known method described in JIS K 0070:1992. The acid value and hydroxyl value may be calculated from the amount of unsaturated monomer in the raw material monomer of the target resin. The acid value and hydroxyl value are determined based on the solid content.

[0029] The glass transition temperature may be calculated from the types and amounts of raw material monomers, or may be measured by differential scanning calorimetry (DSC).

[0030] (Water-based primer surfacer) The water-based primer surfacer according to the present disclosure is used for automobile repair painting. The water-based primer surfacer contains a base material (A) containing a water-dispersible hydroxyl-containing resin (a1), a pigment (a2), and a thickener (a3), and a curing agent (B) containing a polyisocyanate compound (b1) and an organic solvent (b2) that does not have a hydroxyl group. The water-based primer surfacer is a multi-liquid type (typically, a two-liquid type) coating composition.

[0031] Main component (A) The main agent (A) contains a water-dispersible hydroxyl-containing resin (a1), a pigment (a2), and a thickener (a3). The solid content concentration of the main agent (A) is not particularly limited. The solid content concentration of the main agent (A) is, for example, 30% by mass or more and 60% by mass or less.

[0032] Water-dispersible hydroxyl-containing resin (a1) The water-dispersible hydroxyl-containing resin (a1) (hereinafter sometimes referred to as hydroxyl-containing resin (a1)) is a base resin (film-forming component) of the primer surfacer coating film. The hydroxyl-containing resin (a1) has one or more (typically, two or more) hydroxyl groups and a hydroxyl value of 20 mgKOH / g or more. The hydroxyl-containing resin (a1) reacts with the polyisocyanate compound (b1) to form a crosslinked structure.

[0033] The hydroxyl-containing resin (a1) contains at least one selected from the group consisting of acrylic polyol, polyester polyol, polyether polyol, polyurethane polyol and polycarbonate polyol. Acrylic polyol may be contained in order to further improve the physical properties such as the appearance, weather resistance and chemical resistance of the resulting coating film.

[0034] The hydroxyl value of the hydroxyl-containing resin (a1) is, for example, 20 mgKOH / g or more and 200 mgKOH / g or less. The hydroxyl value may be 30 mgKOH / g or more. The hydroxyl value may be 180 mgKOH / g or less.

[0035] The acid value of the hydroxyl-containing resin (a1) is, for example, 2 mgKOH / g or more and 30 mgKOH / g or less. The acid value may be 3 mgKOH / g or more. The acid value may be 25 mgKOH / g or less.

[0036] The number average molecular weight of the hydroxyl-containing resin (a1) is, for example, 1,000 or more and 100,000 or less. The number average molecular weight may be 2,000 or more. The number average molecular weight may be 50,000 or less.

[0037] The glass transition temperature of the hydroxyl-containing resin (a1) is, for example, 20° C. or more and 80° C. or less. The glass transition temperature may be 30° C. or more. The glass transition temperature may be 70° C. or less.

[0038] The hydroxyl-containing resin (a1) can be obtained, for example, by emulsion polymerization of one or more raw material monomers. The emulsion polymerization is carried out by a method generally used by those skilled in the art. Specifically, an emulsifier is mixed into an aqueous medium containing an organic solvent such as alcohol as necessary, and the resulting mixture is heated and stirred while the raw material monomers and a polymerization initiator are dropped into it. Alternatively, an emulsion mixture in which the raw material monomers, the emulsifier and water are previously emulsified may be dropped into the aqueous medium.

[0039] For example, an emulsion-type acrylic polyol can be obtained by emulsion polymerization of a raw material monomer mixture containing a (meth)acrylic acid alkyl ester monomer, an acid group-containing α,β-ethylenically unsaturated monomer, a hydroxyl group-containing α,β-ethylenically unsaturated monomer, and a styrene-based monomer.

[0040] Examples of (meth)acrylic acid alkyl ester monomers include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, phenyl (meth)acrylate, isobornyl (meth)acrylate, cyclohexyl (meth)acrylate, t-butylcyclohexyl (meth)acrylate, dicyclopentadienyl (meth)acrylate, and dihydrodicyclopentadienyl (meth)acrylate. (Meth)acrylic acid esters represent acrylic acid esters and methacrylic acid esters.

[0041] Examples of hydroxyl group-containing α,β-ethylenically unsaturated monomers include hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxybutyl (meth)acrylate, allyl alcohol, methallyl alcohol, and adducts of these with ε-caprolactone.

[0042] Examples of acid group-containing α,β-ethylenically unsaturated monomers include acrylic acid, methacrylic acid, crotonic acid, 2-acryloyloxyethyl phthalic acid, 2-acryloyloxyethyl succinic acid, ω-carboxy-polycaprolactone mono(meth)acrylate, isocrotonic acid, α-hydro-ω-((1-oxo-2-propenyl)oxy)poly(oxy(1-oxo-1,6-hexanediyl)), maleic acid, fumaric acid, itaconic acid, 3-vinylsalicylic acid, 3-vinylacetylsalicylic acid, 2-acrylamido-2-methylpropanesulfonic acid, p-hydroxystyrene, and 2,4-dihydroxy-4'-vinylbenzophenone.

[0043] Other α,β-ethylenically unsaturated monomers may be used in combination. Examples of other α,β-ethylenically unsaturated monomers include polymerizable amide compounds, polymerizable aromatic compounds, polymerizable nitriles, polymerizable alkylene oxide compounds, polyfunctional vinyl compounds, polymerizable amine compounds, α-olefins, dienes, polymerizable carbonyl compounds, polymerizable alkoxysilyl compounds, and other polymerizable compounds.

[0044] The emulsion-type polyurethane polyol can be obtained, for example, by reacting a polyisocyanate compound with a polyol. Examples of the polyisocyanate compound include the same polyisocyanate compound (b1) as described below.

[0045] Examples of polyols include ethylene glycol, propylene glycol, butylene glycol, neopentyl glycol, 1,6-hexanediol, trimethylolpropane, glycerin, pentaerythritol, polycaprolactone diol, polyester polyol, and polyether polyol.

[0046] ·Pigment (A2) At least three pigments with different Mohs hardness and specific gravity are used. The Mohs scale is a measure of hardness, primarily for minerals. There are 10 levels, with talc being 1 and diamond being 10. Standard minerals are designated for each level, and the hardness is determined in relation to the standard minerals.

[0047] The pigment (a2) has an average Mohs hardness of 3.15 to 4.25 and an average specific gravity of 3.25 to 3.55 g / cm 3 By combining three pigments with different Mohs hardness and specific gravity, excellent abrasion resistance and ease of polishing are achieved.

[0048] The average Mohs hardness of the pigment (a2) may be 3.35 or more, or may be 3.45 or more. The average Mohs hardness of the pigment (a2) may be 4.15 or less, or may be 4.00 or less.

[0049] The average specific gravity of pigment (a2) is 3.30 g / cm 3 or more, and 3 or more, and 3 The average specific gravity of the pigment (a2) may be 3.50 g / cm or more. 3 or less, 3.45 g / cm 3 It may be the following:

[0050] The average Mohs hardness of the pigment (a2) is obtained by multiplying the Mohs hardness of a certain pigment by the volume percentage (%) of that pigment relative to all the pigments in the mixture, and then adding these values ​​together.

[0051] The average specific gravity of the pigment (a2) is obtained by multiplying the specific gravity of a pigment by the mass percentage (%) of that pigment relative to all the pigments that are blended, calculating the value for each pigment, and adding these values ​​together.

[0052] The total content of pigment (a2) is 100 parts by mass or more and 300 parts by mass or less, based on 100 parts by mass of the resin solid content of the main agent (A). When the total content of pigment (a2) is 100 parts by mass or more, the polishing resistance is improved. When the total content of pigment (a2) is 300 parts by mass or less, the polishing workability is improved. The total content of pigment (a2) may be 120 parts by mass or more, 150 parts by mass or more, or 200 parts by mass or more. The total content of pigment (a2) may be 280 parts by mass or less, 260 parts by mass or less, or 250 parts by mass or less.

[0053] The primary particle size of the pigment (a2) is not particularly limited and is appropriately set depending on the hiding power, dispersibility, etc.

[0054] ·First pigment (a2-1) The first pigment (a2-1) has a Mohs hardness of 1.0 to 2.3 and a specific gravity of 2.0 to 4.0 g / cm 3 The first pigment (a2-1) improves the workability of polishing. The first pigment (a2-1) can also increase the film thickness without significantly affecting other physical properties, which can contribute to suppressing exposure of the base material.

[0055] The Mohs hardness of the first pigment (a2-1) may be 2.0 or less, or 1.5 or less. The specific gravity of the first pigment (a2-1) is 3.5 g / cm 3 or less than 3.0 g / cm 3 It may be the following:

[0056] When a plurality of types of first pigments (a2-1) are contained, the Mohs hardness of each of the first pigments (a2-1) is 1.0 to 2.3, and the specific gravity of each of the first pigments (a2-1) is 2.0 to 4.0 g / cm 3 Meet the following.

[0057] The first pigment (a2-1) is mainly a body pigment. Examples of the body pigment corresponding to the first pigment (a2-1) include talc, gypsum, clay, and kaolin. These may be used alone or in combination of two or more.

[0058] The first pigment (a2-1) is a pigment (a2) having an average Mohs hardness of 3.15 to 4.25 and an average specific gravity of 3.25 to 3.55 g / cm 3 The content of the first pigment (a2-1) is, for example, 20 parts by mass or more and 70 parts by mass or less relative to 100 parts by mass of the resin solid content of the main agent (A). When the content of the first pigment (a2-1) is 20 parts by mass or more, the polishing workability can be further improved. When the content of the first pigment (a2-1) is 70 parts by mass or less, the decrease in polishing resistance is suppressed. The content of the first pigment (a2-1) may be 25 parts by mass or more, or may be 30 parts by mass or more. The content of the first pigment (a2-1) may be 60 parts by mass or less, or may be 50 parts by mass or less.

[0059] ·Second pigment (a2-2) The second pigment (a2-2) has a Mohs hardness of 2.5 to 5.5 and a specific gravity of 1.0 to 5.0 g / cm 3 The second pigment (a2-2) has a medium hardness and a wide range of specific gravity, and it uniformly distributes the pigment (a2) and adjusts the average Mohs hardness and average specific gravity. The second pigment (a2-2) can easily balance the polishing workability and the polishing resistance while suppressing the deterioration of the physical properties of the coating film. The second pigment (a2-2) also improves the toughness of the coating film.

[0060] The Mohs hardness of the second pigment (a2-2) may be 2.7 or more, or 3.0 or more. The Mohs hardness of the second pigment (a2-2) may be 5.3 or less, or 5.0 or less, or 4.0 or less. The specific gravity of the second pigment (a2-2) is 1.5 g / cm 3 or more, and 3 The specific gravity of the second pigment (a2-2) may be 4.8 g / cm or more.3 or less, 4.5 g / cm 3 It may be the following:

[0061] When a plurality of types of second pigments (a2-2) are contained, the Mohs hardness of each of the second pigments (a2-2) is 2.5 to 5.5, and the specific gravity of each of the second pigments (a2-2) is 1.0 to 5.0 g / cm 3 Meet the following.

[0062] The second pigment (a2-2) may be a body pigment, an anti-rust pigment, or a color pigment. The body pigment corresponding to the second pigment (a2-2) may be, for example, calcium carbonate, precipitated barium sulfate, or borosilicate glass. The anti-rust pigment corresponding to the second pigment (a2-2) may be, for example, aluminum polyphosphate or zinc phosphate. The color pigment corresponding to the second pigment (a2-2) may be, for example, mica or aluminum. These may be used alone or in combination of two or more.

[0063] The second pigment (a2-2) is a pigment (a2) having an average Mohs hardness of 3.15 to 4.25 and an average specific gravity of 3.25 to 3.55 g / cm 3 The content of the second pigment (a2-2) is set according to the type and content of the first pigment (a2-1) and the third pigment (a2-3). The content of the second pigment (a2-2) is, for example, 100 parts by mass or more and 200 parts by mass or less with respect to 100 parts by mass of the resin solid content of the main agent (A). The content of the second pigment (a2-2) may be 110 parts by mass or more, or may be 120 parts by mass or more. The content of the second pigment (a2-2) may be 190 parts by mass or less, or may be 180 parts by mass or less.

[0064] ·Third pigment (a2-3) The third pigment (a2-3) has a Mohs hardness of 5.8 to 8.2 and a specific gravity of 2.0 to 6.0 g / cm 3 The third pigment (a2-3) has high hardness and a large specific gravity, and improves abrasion resistance.

[0065] The Mohs hardness of the third pigment (a2-3) may be 6.0 or more, and may be 6.5 or more. The Mohs hardness of the third pigment (a2-3) may be 8.0 or less, and may be 7.8 or less. The specific gravity of the third pigment (a2-3) is 2.2 g / cm 3 or more, and 3 The specific gravity of the third pigment (a2-3) may be 5.8 g / cm or more. 3 or less than 5.0 g / cm 3 It may be the following:

[0066] When a plurality of types of third pigments (a2-3) are contained, the Mohs hardness of each of the third pigments (a2-3) is 5.8 to 8.2, and the specific gravity of each of the third pigments (a2-3) is 2.0 to 6.0 g / cm 3 Meet the following.

[0067] The third pigment (a2-3) includes a body pigment and a color pigment. Examples of the body pigment corresponding to the third pigment (a2-3) include diatomaceous earth and silica. Examples of the color pigment corresponding to the third pigment (a2-3) include titanium dioxide and iron oxide. These are used alone or in combination of two or more. The third pigment (a2-3), which is a color pigment, also contributes to improving hiding power.

[0068] The third pigment (a2-3) is a pigment having an average Mohs hardness of 3.15 to 4.25 and an average specific gravity of 3.25 to 3.55 g / cm 3 The content of the third pigment (a2-3) is set according to the type and content of the first pigment (a2-1) and the second pigment (a2-2). The content of the third pigment (a2-3) is, for example, 30 parts by mass or more and 120 parts by mass or less with respect to 100 parts by mass of the resin solid content of the main agent (A). The content of the third pigment (a2-3) may be 50 parts by mass or more, or may be 60 parts by mass or more. The content of the third pigment (a2-3) may be 110 parts by mass or less, or may be 100 parts by mass or less.

[0069] Other pigments (a2-4) The base material may further contain other pigments (a2-4). Examples of the other pigments (a2-4) include carbon black (Mohs hardness 1.5, specific gravity 1.8 g / cm 3 ), zinc oxide (Mohs hardness 4.5, specific gravity 5.62g / cm 3 ) and coloring pigments that do not fall under the first, second, or third pigments.

[0070] The content of the other pigment (a2-4) is set according to the desired hue, etc. The content of the other pigment (a2-4) may be, for example, 20 mass% or less, 10 mass% or less, 5 mass% or less, 1 mass% or less, or 0 mass% of the total content of the pigment (a2). The content of the other pigment (a2-4) may be 0.1 mass% or more, or 0.2 mass% or more.

[0071] The first pigment (a2-1), the second pigment (a2-2) and the third pigment (a2-3) may contain at least one color pigment and at least two extender pigments. This improves the polishability and polish resistance as well as the hiding power. For example, the first pigment (a2-1) and the second pigment (a2-2) are combined with the third pigment (a2-3) as a color pigment.

[0072] The pigment (a2) may include at least one color pigment. The color pigment may be included as a second pigment (a2-2), a third pigment (a2-3), or another pigment (a2-4). The color pigment may be a white pigment such as titanium dioxide, a black pigment such as carbon black, or both.

[0073] ·Thickener (A3) The thickener (a3) ​​increases the viscosity of the aqueous primer surfacer. Examples of the thickener (a3) ​​include inorganic thickeners, cellulose derivatives, urethane association type thickeners, polyamide type thickeners, and alkali swelling type thickeners. These are used alone or in combination of two or more. Among them, from the viewpoint of flowability, the urethane association type thickener is preferable.

[0074] Examples of urethane association type thickeners include polyurethane thickeners having a hydrophobic chain in the molecule, and urethane-urea thickeners in which at least a portion of the main chain is a hydrophobic urethane chain.

[0075] Commercially available urethane association thickeners include, for example, ADEKA NOL UH-756VF (manufactured by ADEKA), BYK-420 (manufactured by BYK), and NOPALL 3303 (manufactured by SAN NOPCO).

[0076] The solid content mass of the thickener (a3) ​​is, for example, 0.5 parts by mass or more and 5 parts by mass or less, based on 100 parts by mass of the resin solid content of the aqueous primer facer. The solid content mass of the thickener (a3) ​​may be 1 part by mass or more, or 1.5 parts by mass or more. The solid content mass of the thickener (a3) ​​may be 4.5 parts by mass or less, or 4 parts by mass or less.

[0077] ·Silane coupling agent The water-based primer surfacer may contain a silane coupling agent. The silane coupling agent may be contained in the main agent (A), may be contained in the curing agent (B), or may be contained in both. The silane coupling agent may be contained in the curing agent (B).

[0078] The silane coupling agent may have at least one of an epoxy group and an isocyanate group as an organic functional group together with a reactive silyl group. The epoxy group has high reactivity and reacts with the hydroxyl group-containing resin (a1) and / or the polyisocyanate compound (b1). The isocyanate group may also react with the hydroxyl group-containing resin (a1). This increases the crosslink density of the resulting cured coating film.

[0079] The epoxy group is a three-membered ring (oxirane ring) having an ether bond. The epoxy group may be alicyclic. An example of the alicyclic epoxy group is an epoxycyclohexyl group.

[0080] The content of the silane coupling agent is, for example, 1 part by mass or more and 8 parts by mass or less with respect to 100 parts by mass of the resin solid content of the aqueous primer facer. The content of the silane coupling agent may be, for example, 1.1 parts by mass or more, or 1.2 parts by mass or more. The content of the silane coupling agent may be, for example, 7 parts by mass or less, or 6 parts by mass or less.

[0081] An example of an epoxy group-containing silane coupling agent is KBM-403 (manufactured by Shin-Etsu Chemical Co., Ltd.). An example of an isocyanate group-containing silane coupling agent is KBE-9007N (manufactured by Shin-Etsu Chemical Co., Ltd.).

[0082] Aqueous solvents The main component (A) may contain an aqueous solvent, such as pure water, ion-exchanged water, tap water, or industrial water.

[0083] The main agent (A) may contain an organic solvent together with the aqueous solvent. Examples of the organic solvent include diethylene glycol dibutyl ether (dibutyl diglycol), dipropylene glycol dimethyl ether, ethyl diglycol acetate, propylene glycol methyl ether acetate, n-butyl alcohol, methoxypropanol, diethylene glycol monobutyl ether, ethylene glycol monobutyl ether, ethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, diethylene glycol monoethyl ether, diethylene glycol diethyl ether, diethylene glycol monoethyl ether acetate, diethylene glycol monobutyl ether, diethylene glycol monobutyl ether acetate, and ethylene glycol monohexyl ether.

[0084] Other resins The main agent (A) may contain other resins having a hydroxyl value of less than 20 mgKOH / g as necessary. The other resins are not particularly limited as long as they have a hydroxyl value of less than 20 mgKOH / g. Examples of the other resins include acrylic resins, polyester resins, polyether resins, polyurethane resins and polycarbonate resins.

[0085] In order to improve adhesion to other coating films, the base agent (A) may contain a polyurethane resin together with the hydroxyl group-containing resin (a1). The base agent (A) may contain an acrylic polyol and a polyurethane resin. The base agent (A) may particularly contain an acrylic polyol and a polyurethane resin having a glass transition temperature of -50°C or more and 0°C or less.

[0086] The polyurethane resin may have a glass transition temperature of -40°C or higher. The polyurethane resin may have a glass transition temperature of -10°C or lower. The polyurethane resin may have an acid value of, for example, 0 mgKOH / g or higher and 40 mgKOH / g or lower. The polyurethane resin may have an acid value of 10 mgKOH / g or higher. The polyurethane resin may have an acid value of 20 mgKOH / g or lower.

[0087] The mass ratio of the hydroxyl-containing resin (a1) (particularly, acrylic polyol) to the polyurethane resin (hydroxyl-containing resin / polyurethane resin) is, for example, 70 / 30 to 30 / 70. The mass ratio (hydroxyl-containing resin / polyurethane resin) may be 60 / 40 to 40 / 60.

[0088] Other Ingredients The main component (A) may also contain various additives as necessary, such as dispersants, antifoaming agents, UV absorbers, hindered amine light stabilizers, antioxidants, viscosity modifiers, surface conditioners, film-forming assistants, curing accelerators, rust inhibitors, and thickeners.

[0089] Preparation method of main agent (A) The main component (A) can be prepared by mixing the above components by a method known to those skilled in the art. The pigment (a2) may be mixed with a pigment dispersant and then mixed with the hydroxyl-containing resin (a1) and the like. Examples of the mixing method include a kneading and mixing method using a kneader or roll, and a dispersion and mixing method using a sand grind mill or disperser.

[0090] Hardener (B) The curing agent (B) contains a polyisocyanate compound (b1) and an organic solvent (b2) that does not have a hydroxyl group. The solid content concentration of the curing agent (B) is not particularly limited. The solid content concentration of the curing agent (B) is, for example, 20% by mass or more and 70% by mass or less.

[0091] Polyisocyanate compounds (b1) The isocyanate compound (b1) reacts with the hydroxyl groups of the hydroxyl-containing resin (a1) in the main component (A) to form a crosslinked structure.

[0092] The content of the polyisocyanate compound (b1) may be, for example, 20 mass % or more, or 30 mass % or more, of the total solid content of the curing agent (B).

[0093] The number average molecular weight of the polyisocyanate compound (b1) may be, for example, 500 or more and 3,000 or less. The number average molecular weight of the polyisocyanate compound (b1) may be 700 or more, or 800 or more. In terms of facilitating an increase in crosslink density, the number average molecular weight of the polyisocyanate compound (b1) may be 2,500 or less, or 2,000 or less.

[0094] The polyisocyanate compound (b1) is not particularly limited as long as it has two or more isocyanate groups on average in one molecule. The polyisocyanate compound (b1) may be hydrophilic from the viewpoint of compatibility with the main component (A).

[0095] Examples of the polyisocyanate compound (b1) include aliphatic diisocyanates having 2 to 12 carbon atoms, such as hexamethylene diisocyanate, 2,2,4-trimethylhexane diisocyanate, and lysine diisocyanate; alicyclic diisocyanates having 4 to 18 carbon atoms, such as 1,4-cyclohexane diisocyanate, isophorone diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, methylcyclohexylene diisocyanate, and isopropylidenecyclohexyl-4,4'-diisocyanate; 2,4-toluylene diisocyanate, 2,6-toluylene diisocyanate, diphenylmethane-4,4'-diisocyanate, and 1,5'-naphthene diisocyanate. Aromatic diisocyanates such as isocyanate, tolidine diisocyanate, diphenylmethylmethane diisocyanate, tetraalkyldiphenylmethane diisocyanate, xylylene diisocyanate, tetramethylxylylene diisocyanate, 4,4'-dibenzyl diisocyanate, and 1,3-phenylene diisocyanate; triisocyanates such as lysine ester triisocyanate, triphenylmethane triisocyanate, 1,6,11-undecane triisocyanate, 1,8-diisocyanate-4,4-isocyanate methyloctane, 1,3,6-hexamethylene triisocyanate, and bicycloheptane triisocyanate.

[0096] The polyisocyanate compound (b1) may be a dimer or trimer (isocyanurate bond) of the above polyisocyanate compound, or a biuret obtained by reacting the above polyisocyanate compound with an amine. A polyisocyanate having a urethane bond obtained by reacting the above polyisocyanate compound with a polyhydric alcohol may also be used.

[0097] (b2) an organic solvent not having a hydroxyl group The organic solvent (b2) improves the storage stability of the polyisocyanate compound (b1), thereby improving the workability in preparing the coating material.

[0098] The organic solvent (b2) is not particularly limited as long as it does not have a hydroxyl group. Examples of the organic solvent (b2) include ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol divinyl ether, diethylene glycol ethyl methyl ether, diethylene glycol isopropyl methyl ether, diethylene glycol butyl methyl ether, triethylene glycol dimethyl ether, triethylene glycol divinyl ether, tetraethylene glycol diethyl ether, propylene glycol dimethyl ether, propylene glycol diethyl ether, propylene glycol di-n-propyl ether, propylene glycol diisopropyl ether, propylene glycol di-n-butyl ether, propylene glycol diisobutyl ether, propylene glycol diallyl ether, propylene glycol diphenyl ether, dipropylene glycol dimethyl ether, dipropylene glycol diethyl ether, dipropylene glycol di-n-butyl ether, dipropylene glycol diisobutyl ether, propylene glycol diallyl ether, propylene glycol diphenyl ether, dipropylene glycol dimethyl ether, dipropylene glycol diethyl ether, dipropylene glycol di-n-butyl ether, dipropylene glycol diisobutyl ether, propylene glycol diphenyl ether, dipropylene glycol diethyl ether, dipropylene glycol di-n-butyl ether, dipropylene glycol diisobutyl ether, di ... glycol ether-based organic solvents such as pyrene glycol diisobutyl ether, dipropylene glycol diallyl ether, tripropylene glycol dimethyl ether, tripropylene glycol diethyl ether, tripropylene glycol di-n-butyl ether, tripropylene glycol diisobutyl ether, tripropylene glycol diallyl ether, butylene glycol dimethyl ether, butylene glycol diethyl ether, butylene glycol di-n-butyl ether, 2-butoxyethyl diethoxyethyl ether, 2-butoxyethyl triethoxy ether, and 2-butoxyethyl tetraethoxyethyl ether; acetate-based organic solvents such as ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, ethylene glycol mono-n-butyl ether acetate, diethylene glycol monoethyl ether acetate, diethylene glycol mono-n-butyl ether acetate, 3-methoxybutyl acetate, and propylene glycol monomethyl ether acetate;Examples of the organic solvent include ketone-based organic solvents such as acetone, methyl ethyl ketone, methyl amyl ketone, and methyl isobutyl ketone; and ester-based organic solvents such as ethyl acetate, butyl acetate, isobutyl acetate, methyl benzoate, ethyl 3-ethoxypropionate, ethyl propionate, and methyl propionate. These may be used alone or in combination of two or more.

[0099] ·others The curing agent (B) may contain a curing agent other than the isocyanate compound (b1). The content of the other curing agent is, for example, 10 mass% or less of the total solid content of all the curing agents. The curing agent (B) may also contain the above-mentioned various additives as necessary.

[0100] - Preparation method of hardener (B) The curing agent (B) can be prepared by mixing the above components by a method known to those skilled in the art. Examples of the mixing method include the same method as that for preparing the base agent (A).

[0101] The water-based primer surfacer is prepared by a method commonly used by those skilled in the art. For example, the water-based primer surfacer is prepared by mixing the respective components in the same manner as in the preparation of the main component (A).

[0102] The equivalent ratio (hydroxyl group equivalent / isocyanate group equivalent) of the hydroxyl group of the hydroxyl-containing resin (a1) to the isocyanate group of the polyisocyanate compound (b1) is 0.3 to 2. In other words, the main agent (A) and the curing agent (B) are mixed so that the equivalent ratio (hydroxyl group equivalent / isocyanate group equivalent) is 0.3 to 2. The equivalent ratio may be 0.4 or more, or 0.5 or more. The equivalent ratio may be 1.8 or less, or 1.6 or less.

[0103] The water-based primer surfacer may further include a diluent. The diluent is used to adjust the viscosity of the water-based primer surfacer. Examples of the diluent include the same aqueous solvent and organic solvent that may be included in the main agent (A). The diluent may be the same as the aqueous solvent and organic solvent of the main agent (A) or may be different.

[0104] The amount of the diluent component to be mixed is appropriately set in consideration of the viscosity of the aqueous primer surfacer, the coating method, etc. The amount of the diluent component to be mixed is, for example, 10 parts by mass or more and 70 parts by mass or less per 100 parts by mass of the resin solid content of the aqueous primer surfacer.

[0105] (Method of forming multi-layer coating film) The multilayer coating film according to the present disclosure is formed by a method comprising the steps of: applying the above-mentioned aqueous primer surfacer onto a substrate, including an automotive substrate, to form a primer surfacer coating film; applying an aqueous colored base coating composition onto the primer surfacer coating film to form a colored base coating film; and applying a multi-component aqueous clear coating composition, including a first liquid containing a hydroxyl-containing resin and an aqueous solvent, and a second liquid containing a polyisocyanate compound and an organic solvent having no hydroxyl groups, onto the colored base coating film to form a clear coating film.

[0106] The water-based primer surfacer according to the present disclosure is suitable for automobile repair painting. Specific examples of the objects of repair include automobile bodies and parts for automobile bodies such as passenger cars, trucks, motorcycles, and buses, and automobile parts such as spoilers, bumpers, mirror covers, grilles, and door knobs.

[0107] ·Object to be coated The substrate to be coated includes an automobile substrate. The automobile substrate may be, for example, a steel plate or a resin. The shape of the substrate to be coated is not particularly limited. The substrate to be coated may be flat or may have a three-dimensional shape.

[0108] The object to be repaired may comprise an automotive substrate and an old paint film covering at least a portion of the surface of the substrate.

[0109] Specific examples of steel sheets include cold-rolled steel sheets, hot-rolled steel sheets, stainless steel, electrolytic galvanized steel sheets, hot-dip galvanized steel sheets, zinc-aluminum alloy-plated steel sheets, zinc-iron alloy-plated steel sheets, zinc-magnesium alloy-plated steel sheets, zinc-aluminum-magnesium alloy-plated steel sheets, aluminum-plated steel sheets, aluminum-silicon alloy-plated steel sheets, and tin-plated steel sheets.

[0110] The steel sheet may be surface-treated. Examples of the surface treatment include phosphate treatment, chromate treatment, zirconium conversion treatment, and composite oxide treatment. After the surface treatment, the steel sheet may be further coated with an electrodeposition paint. The electrodeposition paint may be of the cationic type or the anionic type.

[0111] The steel plate may be blasted, painted with an anti-corrosive paint, painted with a shop primer, or painted with an organic or inorganic zinc-rich primer.

[0112] Examples of the resin include polypropylene resin, polycarbonate resin, polyurethane resin, polyester resin, polystyrene resin, ABS resin, vinyl chloride resin, and polyamide resin. The resin substrate may be degreased.

[0113] The substrate including a resinous automotive substrate may further include a primer coating formed of an aqueous primer and covering at least a part of the surface of the resinous substrate. The application of the aqueous primer and the application of the aqueous primer surfacer may be performed successively.

[0114] Before painting, the area to be repaired and its surroundings are polished as necessary, and any irregularities are filled in with putty. The area is then polished again.

[0115] (I) Formation of primer coating A water-based primer is applied to a resin substrate for an automobile to form a primer coating film. The primer coating film is formed as required.

[0116] The amount of the water-based primer applied is not particularly limited and is appropriately set depending on the performance required for the coating film. For example, the water-based primer is applied so that the thickness of the primer coating film after curing is 10 μm or more and 40 μm or less.

[0117] The method of applying the water-based primer is not particularly limited. Examples of the application method include air spray application, airless spray application, rotary atomization application, and curtain coat application. These methods may be combined with electrostatic application. In the case of repair, air spray application is preferred because it is easy to apply localized coating. Application may be performed multiple times.

[0118] After the water-based primer is applied, the coating is heated to cure. The curing conditions are appropriately set according to the amount applied and the composition. Curing is performed, for example, at a temperature of 40°C or higher and 70°C or lower for about 30 to 60 minutes.

[0119] The coating film may be allowed to dry naturally. Natural drying may be performed at room temperature (23° C.±3° C.) for 2 hours or more, 24 hours or more, or even for one week or more.

[0120] Water-based primer The water-based primer is not particularly limited. The water-based primer contains, for example, water-based polyolefin resin (i), water-based epoxy resin (ii), thickener (iii), organic solvent (iv) and water. The water-based resin refers to a water-soluble resin or a water-dispersible resin.

[0121] Examples of the aqueous polyolefin resin (i) include homopolymers of olefin monomers (e.g., ethylene, propylene, butene, 3-methyl-1-butene, 3-methyl-1-heptene), ethylene-propylene copolymers, ethylene-propylene-diene copolymers, styrene-butadiene-isoprene copolymers, and copolymers of olefin monomers with other unsaturated monomers (e.g., vinyl acetate, butadiene, acrylic esters, methacrylic esters).

[0122] The aqueous polyolefin resin (i) may be a modified product. For example, the modified product may be an adduct of an unsaturated carboxylic acid anhydride with an aqueous polyolefin resin. For example, the unsaturated carboxylic acid anhydride may be maleic anhydride, fumaric acid, itaconic anhydride, or (meth)acrylic acid.

[0123] The aqueous polyolefin resin (i) may have a glass transition temperature of -40°C or more and -10°C or less, and a weight average molecular weight Mw of 2,000 or more and 300,000 or less.

[0124] The aqueous epoxy resin (ii) can be obtained as an aqueous dispersion by, for example, graft-polymerizing an epoxy resin with a fatty acid (e.g., a vinyl monomer containing a carboxyl group) and then neutralizing the resulting mixture. The aqueous epoxy resin (ii) may be an aromatic epoxy resin or a bisphenol-type epoxy resin. The aqueous epoxy resin (ii) may be a bisphenol A-type epoxy resin.

[0125] The mass ratio (A / B) of the aqueous polyolefin resin (i) and the aqueous epoxy resin (ii) may be 60 / 40 to 95 / 5.

[0126] The solids content of the aqueous primer may be, for example, 5% by mass or more and 17% by mass or less.

[0127] Examples of the thickener (iii) include inorganic thickeners, cellulose derivatives, urethane association type thickeners, polyamide type thickeners, and alkali swelling type thickeners. These may be used alone or in combination of two or more. From the viewpoint of flowability, the thickener may be a urethane association type thickener.

[0128] The organic solvent (iv) reduces the surface tension of the aqueous primer coating composition and improves the wettability of the composition to the resin substrate. In particular, by using a poorly water-soluble solvent that dissolves less than 1 g in 100 g of water at 20°C, the wettability of the composition to the resin substrate can be improved with a small amount of organic solvent (iv).

[0129] Examples of poorly water-soluble solvents include 2-ethyl-1-hexanol (0.07 g / 100 g) and normal butyl propionate (also known as normal butyl propionate, 0.2 g / 100 g). The solubility in water at 20°C is shown in parentheses. These are used alone or in combination of two or more. Examples of commercially available poorly water-soluble solvents include A-solvent (manufactured by JX Nippon Oil & Energy Corporation, 0 g / 100 g) and Ipsol TP (manufactured by Idemitsu Kosan Co., Ltd., 0 g / 100 g).

[0130] The water-based primer may further contain a water-based polyurethane resin (v). In repair coating, the water-based polyurethane resin (v) contributes to improving the adhesion between the new coating film and the old coating film. The water-based primer containing the water-based polyurethane resin (v) is particularly suitable for repair coating.

[0131] (II) Formation of primer surfacer coating film The above-mentioned water-based primer surfacer is applied to an object to be coated to form a primer surfacer coating film.

[0132] The method of applying the water-based primer surfacer is not particularly limited, and may be the same as that of the water-based primer. The amount of the water-based primer surfacer applied is not particularly limited, and may be appropriately set according to the performance required for the coating film. The water-based primer surfacer is applied, for example, so that the thickness of the primer surfacer coating film after curing is 20 μm or more and 100 μm or less. The curing of the water-based primer surfacer is performed, for example, by the same method as that of the water-based primer.

[0133] After curing, the primer coating film and the primer surfacer coating film are usually polished and degreased. Polishing is performed using sandpaper or the like.

[0134] (III) Formation of colored base coating The water-based colored base coating composition is applied onto the primer surfacer coating film to form a colored base coating film. The water-based colored base coating composition may be applied multiple times.

[0135] The method of applying the aqueous colored base coating composition is not particularly limited, and may be the same as that of the aqueous primer. The amount of the aqueous colored base coating composition applied is not particularly limited, and for example, the coating is applied so that the thickness of the colored base coating film after curing is 10 μm or more and 100 μm or less. After application, the coating film is cured. The curing conditions are appropriately set according to the composition of the aqueous colored base coating composition.

[0136] Water-based pigmented paint composition The aqueous colored base coating composition may be a curing type or a lacquer type. The aqueous colored base coating composition contains a pigment. The pigment is not particularly limited. Examples of the pigment include color pigments and / or glitter pigments.

[0137] The curable water-based colored base coating composition contains a curable resin and a curing agent, and forms a cured coating film by heating. The curable water-based colored base coating composition may further contain a silane coupling agent (e.g., an epoxy group-containing silane coupling agent).

[0138] A lacquer-type water-based colored base coating composition contains water, an organic solvent, and a binder resin dissolved or dispersed therein, and a cured coating film is formed by the evaporation of the water and the organic solvent. The concentration of the binder resin is not particularly limited and is appropriately set depending on the composition and application.

[0139] The binder resin is not particularly limited. Examples of the binder resin include acrylic resin, aminoalkyd resin, alkyd resin, amino resin, isocyanate resin, epoxy resin, vinyl chloride resin, cashew resin, silicone resin, styrene resin, styrenated alkyd resin, cellulose resin (e.g., cellulose nitrate, etc.), urea resin, vinyl resin, phenol resin, phthalic acid resin, fluororesin, polyester resin, unsaturated polyester resin, and modified resins thereof (e.g., rosin-modified, phenol-modified, epoxy resin-modified, styrene-modified, acrylic-modified, urethane-modified). These may be used alone or in combination of two or more. Examples of the organic solvent include naphtha, xylene, toluene, and acetone.

[0140] (IV) Formation of clear coating A water-based clear coating composition is applied onto the colored base coating to form a clear coating.

[0141] The aqueous clear coating composition is applied onto the aqueous colored base coating film. The method of applying the aqueous clear coating composition is not particularly limited, and may be the same as that of the aqueous primer. The amount of the aqueous clear coating composition applied is not particularly limited, and is appropriately set according to the performance required for the coating film. The aqueous clear coating composition is applied, for example, so that the thickness of the clear coating film after curing is 20 μm or more and 100 μm or less. The curing of the aqueous clear coating composition is performed, for example, by the same method as that of the aqueous primer.

[0142] Water-based clear paint composition The aqueous clear coating composition is a multi-liquid type. The aqueous clear coating composition may be a two-liquid type or a three-liquid type. The aqueous clear coating composition includes at least a first liquid containing a hydroxyl group-containing resin and an aqueous solvent, and a second liquid containing a polyisocyanate compound and an organic solvent having no hydroxyl group.

[0143] Examples of the hydroxyl-containing resin include the same as those exemplified as the hydroxyl-containing resin (a1). The aqueous solvent is typically water. The first liquid may contain an organic solvent together with water. Examples of the organic solvent include the same as those exemplified for the main component (A).

[0144] Examples of the polyisocyanate compound include the same compounds as those exemplified as the polyisocyanate compound (b1). Examples of the organic solvent not having a hydroxyl group include the same compounds as those exemplified as the organic solvent not having a hydroxyl group (b2).

[0145] The components of the water-based clear coating composition and the components of the water-based primer surfacer may be the same or different.

[0146] The first liquid and the second liquid are mixed so that the hydroxyl group equivalent of the hydroxyl group-containing resin and the isocyanate group equivalent of the polyisocyanate compound satisfy the ratio hydroxyl group equivalent / isocyanate group equivalent=0.5 / 1 to 1.5 / 1.

[0147] The aqueous clear coating composition may contain the same silane coupling agent as above. The silane coupling agent is added in an amount of 1.2 parts by mass or more and 10 parts by mass or less per 100 parts by mass of the total solid content of the hydroxyl group-containing resin and the polyisocyanate compound.

[0148] At least one of the water-based primer surfacer and the water-based clear coating composition may contain a silane coupling agent having one or more epoxy groups. This can further improve the water resistance of the entire multi-layer coating film. Both the water-based primer surfacer and the water-based clear coating composition may contain an epoxy group-containing silane coupling agent. The epoxy group-containing silane coupling agents contained in the water-based clear coating composition and the water-based primer surfacer may be the same or different.

[0149] The aqueous clear coating composition may further include a third liquid containing a curing accelerator. The third liquid allows any amount of the curing accelerator to be mixed. In other words, it is possible to control the curing speed according to the curing environment and / or requirements. Since the curing speed is appropriately controlled, defects such as a decrease in gloss of the clear coating film and the occurrence of popping are suppressed, and the appearance of the resulting coating film is further improved. In addition, the storage stability of the first and second liquids is improved, and the function (catalytic function) of the curing accelerator is less likely to be impaired. Furthermore, since an appropriate amount of the curing accelerator is added, a coating film having a desired hardness can be easily obtained.

[0150] The curing accelerator is not particularly limited as long as it accelerates the reaction between the hydroxyl group and the isocyanate group. Examples of the curing accelerator include amine compounds, metal compounds, and acids. Examples of the amine compounds include tertiary amines such as triethylamine and triethylenediamine. Examples of the metal compounds include tin compounds, bismuth compounds, molybdenum compounds, and zinc compounds. Examples of the acids include sulfonic acid, inorganic acids, phosphoric acid esters, oxyacids, and carboxylic acids. Among these, metal compounds are preferred. In particular, molybdenum compounds are preferred because they are easy to control the drying rate and the appearance of the coating film is easily improved. In addition, molybdenum compounds are difficult to react with water, so they can exist stably even in aqueous solvents.

[0151] The water-based clear coating composition may contain various additives (typically, gloss adjusters, diluents, and blurring agents).

[0152] -Preparation method of each water-based paint composition Each aqueous coating composition can be prepared by a known method. Each aqueous coating composition is prepared by mixing the above-mentioned components. For mixing, a commonly used mixing device such as a paint shaker or a mixer is used. The base agent (or the first liquid) and the curing agent (or the second liquid) are usually mixed immediately before use (for example, they are used within 60 minutes after mixing).

[0153] (Multi-layer coating) The multilayer coating film of the present disclosure is disposed on a substrate including an automobile substrate. The multilayer coating film comprises a primer surfacer coating film formed by the above-mentioned water-based primer surfacer, a colored base coating film formed by the above-mentioned water-based colored base coating composition on the primer surfacer coating film, and a clear coating film formed by the above-mentioned multi-liquid water-based clear coating composition on the colored base coating film.

[0154] The multilayer coating film formed on a resinous substrate for an automobile may further comprise a primer coating film formed from the above-mentioned water-based primer between the substrate and the primer surfacer coating film.

[0155] The thickness of the primer coating film after curing is, for example, 10 μm or more and 40 μm or less. The thickness of the primer surfacer coating film after curing is, for example, 20 μm or more and 100 μm or less. The thickness of the colored base coating film after curing is, for example, 10 μm or more and 100 μm or less. The thickness of the clear coating film after curing is, for example, 20 μm or more and 100 μm or less.

[0156] The primer surfacer coating is irradiated with light I at a 45 degree angle to the surface of the coating. 45 The maximum spectral reflectance of the coating film, received at an angle of 110 degrees relative to the specular reflection, may be greater than 70%. The coating film has a hue that is said to be white. A white coating film does not contain black pigment. A white coating film may contain white pigment.

[0157] The primer surfacer coating containing black pigment is irradiated with light I at a 45 degree angle to the surface of the coating. 45 The maximum spectral reflectance of light received at an angle of 110 degrees relative to the specular reflected light may be 4 to 70%. This coating film has a hue called light gray (typically, reflectance of 30 to 70%) or dark gray (typically, reflectance of 4% or more and less than 30%).

[0158] The black pigment may correspond to the first, second, and third pigments. Examples of the black pigment include carbon black; composite metal oxides such as iron chromium and bismuth manganese; perylene pigments; and azomethiazo pigments. These may be used alone or in combination of two or more. The black pigment may be carbon black.

[0159] The primary particle diameter of the black pigment is not particularly limited. From the viewpoint of hiding power, the primary particle diameter of the black pigment may be 20 nm or more and 70 nm or less, or 30 nm or more and 60 nm or less. The primary particle diameter can be measured, for example, from an electron microscope image of the cross section of the primer surfacer coating film using image processing software.

[0160] The white pigment may correspond to the first, second, and third pigments. Examples of the white pigment include titanium dioxide and zinc oxide. These may be used alone or in combination of two or more. The surface of the titanium dioxide may be treated with an inorganic compound such as silica, zirconium, or aluminum.

[0161] The primary particle diameter of the white pigment is not particularly limited. From the viewpoint of hiding power, the primary particle diameter of the white pigment may be 100 nm or more and 500 nm or less, or 200 nm or more and 400 nm or less.

[0162] The spectral reflectance is measured as follows. Using a multi-angle spectrophotometer, the reflectance of the primer surfacer coating film is measured for multiple wavelengths at predetermined intervals set within the visible light wavelength range (for example, wavelengths at 10 nm intervals in the range of 400 to 700 nm). Specifically, light from 400 nm to 700 nm is irradiated onto the primer surfacer coating film surface at an angle of 45 degrees to the coating film surface, and the light is received at an angle of 110 degrees to the specularly reflected light, and the reflectance is measured. The maximum value of the reflectance obtained is adopted as the spectral reflectance of the primer surfacer coating film.

[0163] In order to eliminate the influence of the base, the water-based primer surfacer is applied to a black and white hiding power test paper specified in 4.1.2 (Method B) of JIS K5600-4-1 using a 6 mil (equivalent to 150 μm) applicator, and then dried (e.g., heated at 60°C for 30 minutes) to obtain a primer surfacer coating film. The spectral reflectance is measured at the part of the black and white hiding power test paper that corresponds to the black base. The spectral reflectance can be measured using a multi-angle spectrophotometer (e.g., BYK's "micro-TRI-color"). EXAMPLES

[0164] The present invention will be described in more detail below using examples, but the present invention is not limited to these examples. In the examples, "parts" and "%" are based on mass unless otherwise specified.

[0165] [Example 1] (1) Preparation of coating composition A water-based primer, a water-based primer surfacer, a water-based colored base coating composition, and a water-based clear coating composition were prepared as follows.

[0166] (1-1) Preparation of water-based primer As a water-based primer, nax E-CUBE WB PP primer (main agent, manufactured by Nippon Paint Co., Ltd., solid content approximately 15%) was prepared. nax E-CUBE WB PP Primer contains water-based polyolefin resin (product name: Aurouren AE-301), water-based epoxy resin (product name: Modepix 304), urethane association type thickener (product name: Adekanol UH-756VF), poorly water-soluble solvent (2-ethyl-hexanol), amphiphilic solvent (dipropylene glycol dimethyl ether), and hydrophilic solvent (propylene glycol monopropyl ether).

[0167] (1-2) Preparation of water-based primer surfacer 70.8 parts of pure water (A) and 3.4 parts of acetylene-based defoamer (B) (resin solid content: 1.7 parts) were mixed together, and 13 parts of pigment dispersant (C) (resin solid content: 5.2 parts) were added thereto, followed by stirring for 5 minutes. To this were added 22.5 parts of the first pigment (talc), 8.4 parts of the second pigment (aluminum polyphosphate), 125.6 parts of the second pigment (calcium carbonate), 56.9 parts of the second pigment (precipitated barium sulfate), 34.4 parts of the third pigment (titanium oxide), 2.25 parts of dimethylethanolamine (G), and 2.25 parts of pure water (H), and the mixture was dispersed. To the obtained dispersion, 15.7 parts of amphipathic solvent (I), 111 parts of acrylic polyol (J) (resin solid content 50 parts), 142.9 parts of polyurethane resin (K) (resin solid content 50 parts), 0.19 parts of defoamer (L), 1 part of surface conditioner (M), 4.31 parts of alkali swelling type thickener (N) (resin solid content 0.8 parts), 5 parts of urethane association type thickener (O), 3.19 parts of hydrophilic solvent (P), 35.5 parts of pure water (Q), and 31.25 parts of carbon black dispersion (R) (solid content 12.5 parts) were added and stirred to obtain a base agent (A) with a solid content of 51%. The solid content concentration of acrylic polyol (J) was 13.9% of the total solid content contained in the base agent (A).

[0168] As the hardener (B), nax E-CUBE WB hardener for primer surface (manufactured by Nippon Paint Co., Ltd., solid content approximately 55%) was prepared. The ax E-CUBE WB hardener for primer surface contains hexamethylene diisocyanate, ethyl 3-ethoxypropionate, and an isocyanate group-containing silane coupling agent.

[0169] A water-based primer surfacer was prepared by mixing 100 parts of the base agent, 12.5 parts of the curing agent, and an appropriate amount of pure water using a disper. The hydroxyl group equivalent / isocyanate group equivalent was 0.5. The content of the silane coupling agent was 1.6 parts by mass per 100 parts by mass of the total resin solid content of the water-based primer surfacer.

[0170] (1-3) Preparation of Water-Based Colored Coating Composition A lacquer-type water-based colored base coating composition was prepared by mixing 100 parts of nax E-CUBE WB 412 Silent Black (manufactured by Nippon Paint, solid content approximately 22%), 50 parts of nax E-CUBE WB 911 S-binder (auxiliary agent, manufactured by Nippon Paint, solid content approximately 26%), and 45 parts of nax E-CUBE WB R20 standard diluent (dilution component, manufactured by Nippon Paint).

[0171] (1-4-1) Preparation of Water-Based Clear Coating Composition C1 As the first liquid, nax E-CUBE WB(2:1)NN Clear (manufactured by Nippon Paint, solid content approximately 38%) was prepared. nax E-CUBE WB(2:1)NN Clear contains acrylic polyol in the form of an emulsion as a hydroxyl-containing resin. The solid content of the hydroxyl-containing resin was 91.5% of the total solid content in the base resin.

[0172] As the second liquid, nax E-CUBE WB water-based hardener (manufactured by Nippon Paint Co., Ltd., solid content approximately 55%) was prepared. The nax E-CUBE WB water-based hardener contains hexamethylene diisocyanate, ethyl 3-ethoxypropionate, and an epoxy group-containing silane coupling agent.

[0173] 100 parts of the first liquid, 50 parts of the second liquid, and an appropriate amount of pure water were mixed using a disper to prepare an aqueous clear coating composition C1. The hydroxyl group equivalent / isocyanate group equivalent was 0.7. The content of the silane coupling agent was 1.35 parts by mass relative to 100 parts by mass of the total resin solid content of the aqueous clear coating composition C1.

[0174] (2) Formation of multi-layer coating An electrodeposition-coated steel plate and a polypropylene plate (PP plate) were prepared as substrates, and multi-layer coating film A was formed on the electrodeposition-coated steel plate and multi-layer coating film B was formed on the PP plate as follows. After preparation of each coating composition, painting work was started within 60 minutes.

[0175] (2-1) Formation of multi-layer coating film A on electrodeposition-coated steel sheet (2-1-1) Formation of primer surfacer coating As a coating object, an electrodeposition-coated steel plate cut to 150 mm x 70 mm x 0.8 mm thick was prepared. A water-based primer surfacer was applied to this electrodeposition-coated steel plate using an air spray gun, and air-blow dried until the paint no longer adhered to the plate when touched with a finger. This coating and drying process was repeated two more times. The coated plate was then heated in an oven set at 60°C for 30 minutes to form a primer surfacer coating film (cured film thickness 60 μm). The surface of the primer surfacer coating film was then polished and degreased.

[0176] (2-1-3) Formation of colored base coating The water-based colored base coating composition was applied onto the primer surfacer coating film using an air spray gun, and the coating was dried by air blowing until the coating no longer adhered to the surface when touched with a finger. This coating and drying process was repeated two more times to form a colored base coating film (cured film thickness: 20 μm).

[0177] (2-1-4) Formation of clear coating The water-based clear coating composition C1 was applied three times on the colored base coating film using a spray gun. The interval between each application was 1 minute. This resulted in the formation of an uncured clear coating film. Thereafter, the electrodeposition-coated steel sheet with the uncured clear coating film was left to stand for 15 minutes in an environment with a temperature of 23±2°C and a humidity of 50±2RH%. The electrodeposition-coated steel sheet was then placed in an oven set at 70°C and heated for 40 minutes to cure the clear coating film. The humidity in the oven was 10RH%. In this way, a multi-layer coating film A comprising a primer surfacer coating film, a colored base coating film and a clear coating film was formed on the electrodeposition coated plate.

[0178] (2-2) Formation of multi-layer coating film B on polypropylene plate (2-2-1) Formation of primer coating A PP plate cut to 150 mm x 70 mm x 0.8 mm thick was prepared as the substrate. The water-based primer was applied to the PP plate undiluted with an air spray gun, and the paint was dried with an air blower until the paint film lost its luster, forming a primer coating (cured film thickness 10 μm).

[0179] (2-2-2) Formation of multi-layer coating On the primer coating, coating was carried out in the same manner as in "(2-1) Formation of multi-layer coating film A on electrodeposition-coated steel plate" above. As a result, a multi-layer coating film B comprising a primer coating film, a primer surfacer coating film, a colored base coating film, and a clear coating film was formed on the PP plate.

[0180] [Examples 2 to 9, Comparative Examples 1 to 8] An aqueous primer surfacer was prepared in the same manner as in Example 1, except that the pigments were combined as shown in Table 1, and multi-layer coating film A was formed on an electrodeposition-coated steel plate and multi-layer coating film B was formed on a PP plate.

[0181] [Examples 10 to 12] A water-based primer surfacer was prepared by combining pigments as shown in Table 1, and the water-based clear coating composition C2 prepared as follows (1-4-2) was used instead of the water-based clear coating composition C1. Other than this, the multi-layer coating film A was formed on an electrodeposition-coated steel plate, and the multi-layer coating film B was formed on a PP plate in the same manner as in Example 1.

[0182] (1-4-2) Preparation of Water-Based Clear Coating Composition C2 The first and second liquids were prepared in the same manner as in (1-4-1). As the third liquid, nax E-CUBE WB clear-specific hardening accelerator (containing sodium molybdate, manufactured by Nippon Paint, solids content approximately 1%) was prepared.

[0183] 100 parts of the first liquid, 50 parts of the second liquid, 3 parts of the third liquid, and an appropriate amount of pure water were mixed using a disper to prepare a water-based clear coating composition C2.

[0184] [Table 1]

[0185] Details of each component in Table 1 are as follows. First pigment Talc: extender pigment, product name "RGD-125", manufactured by Fuji Talc Industries Co., Ltd., particle size (D50) 7.88 μm

[0186] Second Pigment Aluminum polyphosphate: Anti-rust pigment, product name "GX-ZN15", manufactured by Guangxi Xinjing Science & Technology Co., Ltd. Calcium carbonate: Extender pigment, product name "heavy calcium carbonate", manufactured by Maruo Calcium Co., Ltd. Precipitated barium sulfate: extender pigment, product name "BARIUM SULPHATE PRECIPITATED NT-BS", manufactured by Beijing Yingwoda Technology Co., Ltd. Borosilicate glass: extender pigment, product name "Spehericel 110P8", manufactured by Potters Barotini

[0187] ·Third pigment Titanium dioxide: color pigment, product name "TIPAQUE UT771", manufactured by Ishihara Sangyo Kaisha

[0188] Other pigments Zinc oxide: Color pigment, product name "Zinc oxide type 2", manufactured by Sakai Chemical Industry Co., Ltd.

[0189] The details of each component used are as follows: Acetylene-based defoamer (B) Product name: Surfynol 104DPM, manufactured by EVONIK Pigment dispersant (C) Product name: "DISPERBYK-190", manufactured by BYK Amphiphilic Solvents (I) Propylene glycol monobutyl ether (SP value: 9.69, specific gravity: 0.88 g / cm 3 )

[0190] Acrylic polyol (J) Product name: "BAYHIDROL A2601", manufactured by Covestro, resin solid content 45%, hydroxyl value 130mgKOH / g, acid value 10mgKOH / g, number average molecular weight 3500, glass transition temperature 51℃

[0191] Polyurethane resin (K) Product name: Hydran WLS-210, manufactured by DIC, resin solid content 35%, hydroxyl value 0mgKOH / g, acid value 28mgKOH / g, glass transition temperature -32℃

[0192] Defoamer (L) Product name: "TEGO FOAMEX 810", manufactured by EVONIK, 100% active ingredient Surface conditioner (M) Product name: Tego Wet 260, manufactured by EVONIC, 100% active ingredient Alkali swelling thickener (N) Product name: "PRIMAL ASE-60", manufactured by Dow, active ingredient 30% Urethane associative thickener (O) Product name: NOPALL 3303, manufactured by San Nopco, active ingredient 15% Hydrophilic solvent (P) Propylene glycol monopropyl ether, SP value: 9.82, specific gravity: 0.885g / cm 3 Carbon black dispersion(R) Product name: "FCW Black 220 (semi-solid)", manufactured by Nippon Paint Co., Ltd., pigment solid content 11%, primary particle size 55 nm,

[0193] [Reflectance measurement] - Preparation of primer surfacer coating A black and white hiding power test paper as specified in JIS K5600-4-1 4.1.2 (Method B) was prepared as a coating material. A water-based primer surfacer was applied to the black and white hiding power test paper using a 6 mil (equivalent to 150 μm) applicator. The coated plate was then heated in an oven set at 60°C for 30 minutes to form a primer surfacer coating. Reflectance measurement Using a multi-angle spectrophotometer (BYK's "micro-TRI-color"), light from 400 nm to 700 nm was irradiated at 10 nm intervals from a 45 degree angle onto the primer surfacer coating surface, and the reflected light received at an angle of 110 degrees to the specular reflected light was measured. The maximum reflectance value was used as the spectral reflectance of the primer surfacer coating.

[0194] [Evaluation of water-based primer surfacer] (1) Polishing workability - Preparation of primer surfacer coating A tin plate cut to 200 mm x 100 mm x 0.8 mm thick was prepared as a coating object. A water-based primer surfacer was applied to the tin plate using an air spray gun, and the plate was air-dried until the paint no longer adhered to the plate when touched with a finger. This coating and drying process was repeated two more times. The plate was then heated in an oven set at 60°C for 30 minutes to form a single layer of primer surfacer coating (film thickness 60 μm).

[0195] Polishing work The surface was polished until it was smooth using an abrasive tool with #400 abrasive paper (e.g., manufactured by Kovacs) and evaluated by a sensory test. A level of 4 or higher is considered to be excellent in terms of polishing workability.

[0196] Evaluation criteria 5. No snagging and no resistance when polishing 4: It may be a little difficult at first, but after that it can be polished without resistance. 3: There is some resistance, but the polishing can be done without much resistance. 2: Difficult to polish due to resistance such as stickiness and stickiness 1: High resistance, cannot be polished

[0197] (2) Abrasive resistance - Preparation of primer surfacer coating A degreased bonded steel plate with a smooth surface and dimensions of 110 mm x 110 mm x 0.8 mm (with a 7 mm hole in the center) was prepared as a coating object. A single layer of primer surfacer coating was formed on the bonded steel plate in the same manner as above.

[0198] Polishing work Abrasion tests were conducted under the following conditions using a Taber tester, and the amount of weight loss of the coating film before and after the test was measured. A rating of level 4 or above indicates excellent abrasion resistance.

[0199] (Polishing test conditions) Abrasive tool: Abrasive wheel (CS-10) with #400 abrasive paper (manufactured by Kovacs) attached Load capacity: 1kg Rotation speed: 60 rpm Number of rotations of the test plate: 50 times

[0200] Evaluation criteria 5: Mass loss 75mg or less 4: Mass loss more than 75 mg and less than 85 mg 3: Mass loss more than 85mg and less than 95mg 2: Mass loss more than 95mg and less than 105mg 1: Mass loss exceeding 105mg

[0201] [Appearance evaluation of multi-layer coating film] The appearance of each of the multi-layer coating films A and B was evaluated visually.

[0202] Evaluation criteria 5: The coating film is smooth and free of irregularities. 4: The coating is smooth with only slight irregularities visible. 3: The coating has some visible unevenness. 2: The coating film is not smooth and has visible bumps and irregularities. 1: The coating has very visible bumps and is not smooth.

[0203] [Table 2]

[0204] [Table 3]

[0205] The pigment contents in Tables 2 and 3 are values ​​based on 100 parts by mass of the solid content of the hydroxyl group-containing resin. [Industrial Applicability]

[0206] According to the present disclosure, there is provided a water-based primer surfacer capable of forming a coating film having excellent polishing workability while having abrasion resistance. The water-based primer surfacer of the present disclosure is suitable for automobile repair painting. According to the present disclosure, there is provided a multi-layer coating film having excellent appearance formed by an all-water-based paint composition.

Claims

1. A main component (A) comprising a water-dispersible hydroxyl group-containing resin (a1), a pigment (a2), and a thickener (a3), and The curing agent (B) contains a polyisocyanate compound (b1) and an organic solvent (b2) that does not have hydroxyl groups. The water-dispersible hydroxyl group-containing resin (a1) has a hydroxyl value of 20 mg KOH / g or more and comprises at least one selected from the group consisting of acrylic polyols, polyester polyols, polyether polyols, polyurethane polyols, and polycarbonate polyols. The aforementioned pigment (a2) is It has a Mohs hardness of 1.0 to 2.3 and a specific gravity of 2.0 to 4.0 g / cm³. ３ The first pigment (a2-1) is, It has a Mohs hardness of 2.5 to 5.5 and a specific gravity of 1.0 to 5.0 g / cm³. ３ The second pigment (a2-2) is, It has a Mohs hardness of 5.8 to 8.2 and a specific gravity of 2.0 to 6.0 g / cm³. ３ It includes a third pigment (a2-3), The average Mohs hardness is 3.15 to 4.

25. The average specific gravity is 3.25 to 3.55 g / cm³. ３ And, The total content of the pigment (a2) is 100 parts by mass or more and 300 parts by mass or less, relative to 100 parts by mass of the resin solids contained in the main component (A). An aqueous primer surfacer for automotive repair, wherein the equivalent ratio (hydroxyl group equivalent / isocyanate group equivalent) of the hydroxyl groups of the water-dispersible hydroxyl group-containing resin (a1) to the isocyanate groups of the polyisocyanate compound (b1) is 0.3 to 2.

2. The aqueous primer surfacer according to claim 1, wherein the main component (A) further comprises a polyurethane resin having a hydroxyl value of less than 20 mg KOH / g and a glass transition temperature of 0°C or lower.

3. The aqueous primer surfacer according to claim 1 or 2, wherein at least one of the main component (A) and the curing agent (B) comprises a silane coupling agent.

4. The aqueous primer surfacer according to claim 1 or 2, wherein the first pigment (a2-1), the second pigment (a2-2), and the third pigment (a2-3) each comprise at least one coloring pigment and at least two extender pigments.

5. The coating film formed by the aqueous primer surfacer is subjected to light I irradiated onto the surface of the coating film at a 45-degree angle. ４５ The aqueous primer surfacer according to claim 1 or 2, wherein the maximum spectral reflectance when the light is received at an angle of 110 degrees to specularly reflected light is more than 70%.

6. The pigment (a2) comprises at least one black pigment, The coating film formed by the aqueous primer surfacer is subjected to light I irradiated onto the surface of the coating film at a 45-degree angle. ４５ The aqueous primer surfacer according to claim 1 or 2, wherein the maximum spectral reflectance when the light is received at an angle of 110 degrees to specularly reflected light is 4 to 70%.

7. Applying the aqueous primer surfacer described in claim 1 or 2 to a substrate containing an automotive base material to form a primer surfacer coating film, The process involves applying an aqueous colored base coating composition onto the primer surfacer coating to form a colored base coating, A method for forming a multilayer coating film, comprising: applying a multi-component aqueous clear coating composition, comprising a first liquid containing a hydroxyl group-containing resin and an aqueous solvent, and a second liquid containing a polyisocyanate compound and an organic solvent that does not contain hydroxyl groups, onto the aforementioned colored base coating film to form a clear coating film.

8. The method for forming a multilayer coating according to claim 7, wherein the object to be coated comprises the automotive substrate and a coating film other than the multilayer coating film that covers at least a portion of the surface of the automotive substrate.

9. The method for forming a multilayer coating film according to claim 7 or 8, wherein the object to be coated comprises a resin-based automotive substrate and a primer coating film formed with an aqueous primer that covers at least a portion of the surface of the automotive substrate.

10. A primer surfacer coating film formed on a substrate containing an automotive base material using the aqueous primer surfacer described in claim 1 or 2, A colored base coating film formed on the primer surfacer coating film with an aqueous colored base coating composition, A multilayer coating film having a clear coating film formed on the aforementioned colored base coating film using a multi-component aqueous clear coating composition comprising a first liquid containing a hydroxyl group-containing resin and an aqueous solvent, and a second liquid containing a polyisocyanate compound and an organic solvent that does not contain hydroxyl groups.

11. A primer coating film formed with an aqueous primer on a substrate containing a resin-based automotive base material, A primer surfacer coating film formed on the primer coating film using the aqueous primer surfacer according to claim 1 or 2, A colored base coating film formed on the primer surfacer coating film with an aqueous colored base coating composition, A multilayer coating film having a clear coating film formed on the aforementioned colored base coating film using a multi-component aqueous clear coating composition comprising a first liquid containing a hydroxyl group-containing resin and an aqueous solvent, and a second liquid containing a polyisocyanate compound and an organic solvent that does not contain hydroxyl groups.