Classifications

• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
  • C09D123/00—Coating compositions based on homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Coating compositions based on derivatives of such polymers
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
  • C09D163/00—Coating compositions based on epoxy resins; Coating compositions based on derivatives of epoxy resins
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
  • C09D5/00—Coating compositions, e.g. paints, varnishes or lacquers, characterised by their physical nature or the effects produced; Filling pastes

Definitions

• the present invention relates to a method for forming a multi-layer coating film, a multi-layer coating film, and an aqueous primer paint composition.
• Patent Document 1 discloses a water-based primer paint composition.
• the aqueous primer coating composition of Patent Document 1 although it is aqueous, is unable to sufficiently reduce emissions of volatile organic compounds (VOCs).
• the present invention aims to provide a multi-layer coating film with excellent appearance, formed from an all-water-based paint composition, including a primer paint composition that has sufficiently low VOC emissions and excellent storage stability and adhesion to resin substrates.
• the aqueous primer coating composition contains an aqueous polyolefin resin (A), an aqueous epoxy resin (B), a thickener (C), an organic solvent (D) and water (E), and has a solid content of 5% by mass or more and 17% by mass or less;
• the aqueous polyolefin resin (A) has a glass transition temperature of ⁇ 40° C. or higher and ⁇ 10° C.
• the organic solvent (D) includes a slightly water-soluble solvent (D1) that dissolves at less than 1 g in 100 g of water at 20° C., and at least one of an amphipathic solvent (D2) that dissolves at least 1 g but less than 60 g in 100 g of water at 20° C., and a hydrophilic solvent (D3) that dissolves at least 60 g in 100 g of water at 20° C.,
• the proportion of the poorly water-soluble solvent (D1) in the organic solvent (D) is 1 mass% or more and 60 mass% or less
• a method for forming a multilayer coating film wherein the mass of the organic solvent (D) is 30 g/L or more and 500 g/L or less in the organic component mass obtained by subtracting the mass of the water (E) from the total mass of the aqueous primer coating.
• a first undercoat coating film formed on a resin substrate using an aqueous primer coating composition A colored base coating film formed on the first undercoat coating film using an aqueous colored base paint; A clear coating film formed on the colored base coating film by a water-based two-component clear paint,
• the aqueous primer coating composition contains an aqueous polyolefin resin (A), an aqueous epoxy resin (B), a thickener (C), an organic solvent (D) and water (E), and has a solid content of 5% by mass or more and 17% by mass or less;
• the aqueous polyolefin resin (A) has a glass transition temperature of ⁇ 40° C. or higher and ⁇ 10° C.
• the organic solvent (D) includes a slightly water-soluble solvent (D1) that dissolves at less than 1 g in 100 g of water at 20° C., and at least one of an amphipathic solvent (D2) that dissolves at least 1 g but less than 60 g in 100 g of water at 20° C., and a hydrophilic solvent (D3) that dissolves at least 60 g in 100 g of water at 20° C.,
• the proportion of the poorly water-soluble solvent (D1) in the organic solvent (D) is 1 mass% or more and 60 mass% or less
• a multilayer coating film wherein the mass of the organic solvent (D) in the organic component mass obtained by subtracting the mass of the water (E) from the total mass of the aqueous primer coating is 30 g/L or more and 500 g/L or less.
• a first undercoat coating film formed on a resin substrate using an aqueous primer coating composition A colored base coating film formed on the first undercoat coating film using an aqueous colored base paint;
• the composition comprises an aqueous polyolefin resin (A), an aqueous epoxy resin (B), a thickener (C), an organic solvent (D) and water (E), and has a solid content of 5% by mass or more and 17% by mass or less;
• the aqueous polyolefin resin (A) has a glass transition temperature of ⁇ 40° C.
• the organic solvent (D) includes a slightly water-soluble solvent (D1) that dissolves at less than 1 g in 100 g of water at 20° C., and at least one of an amphipathic solvent (D2) that dissolves at least 1 g but less than 60 g in 100 g of water at 20° C., and a hydrophilic solvent (D3) that dissolves at least 60 g in 100 g of water at 20° C.,
• the proportion of the poorly water-soluble solvent (D1) in the organic solvent (D) is 1 mass% or more and 60 mass% or less
• An aqueous primer coating composition wherein the mass of the organic solvent (D) is 30 g/L or more and 500 g/L or less relative to the organic component mass obtained by subtracting the mass of the water (E) from the total mass of the
• the present invention provides a multi-layer coating film with excellent appearance, formed from an all-water-based coating composition, including a primer coating composition that has sufficiently low VOC emissions and excellent storage stability and adhesion to resin substrates.
• the method for forming a multi-layer coating film comprises applying an aqueous primer coating composition onto a resin substrate to form a first undercoat coating film, applying an aqueous colored base coating composition onto the first undercoat coating film to form a colored base coating film, and applying an aqueous two-component clear coating composition onto the colored base coating film to form a clear coating film.
• a method may also comprise applying an aqueous surfacer onto the first undercoat coating film to form a second undercoat coating film.
• the aqueous primer coating composition used in the present disclosure contains an aqueous polyolefin resin (A), an aqueous epoxy resin (B), a thickener (C), an organic solvent (D) and water (E), and has a solid content of 5% by mass or more and 17% by mass or less.
• the aqueous polyolefin resin (A) has a glass transition temperature of -40°C or more and -10°C or less.
• the mass ratio (A/B) of the aqueous polyolefin resin (A) to the aqueous epoxy resin (B) is 60/40 to 95/5.
• the organic solvent (D) includes a poorly water-soluble solvent (D1) that dissolves in an amount of less than 1 g in 100 g of water at 20°C, and at least one of an amphipathic solvent (D2) that dissolves in an amount of 1 g or more and less than 60 g in 100 g of water at 20°C and a hydrophilic solvent (D3) that dissolves in an amount of 60 g or more in 100 g of water at 20°C.
• the proportion of the poorly water-soluble solvent (D1) in the organic solvent (D) is 1% by mass or more and 60% by mass or less.
• the ratio of the organic solvent (D) to the total mass of the organic components, excluding the mass of water (E) from the total mass of the water-based primer paint, is 30 g/L or more and 500 g/L or less.
• the surface tension of a resin substrate is usually 40 mN/m or less.
• the surface tension of water is about 72.7 mN/m. Therefore, water-based paint compositions generally do not wet resin substrates well, making film formation difficult.
• the water-based primer paint composition contains a small amount of poorly water-soluble organic solvent, achieving both low VOC emissions and high adhesion to resin substrates (particularly adhesion after a water immersion test (hereinafter also referred to as water resistance)).
• the water-based primer paint composition is suitable for painting resin substrates.
• Aqueous primer paint compositions are particularly prone to penetrating into minute irregularities (scratches) on the surface of resin substrates. Therefore, when an aqueous primer paint composition is applied to a resin substrate having minute irregularities, repelling and smearing are suppressed and a uniform film is formed. This results in the formation of a smooth undercoat film with high adhesion. As a result, the adhesion and appearance of the entire multi-layer coating film are improved.
• film-forming ability affects the appearance and adhesion of the entire multi-layer coating film.
• the fine irregularities are formed, for example, by polishing.
• the fine irregularities correspond to the irregularities formed by polishing back and forth 20 times with abrasive paper of #1000 to #2000 (typically #1500).
• the arithmetic mean roughness Ra of the fine irregularities may be 0.01 ⁇ m to 0.5 ⁇ m, and may be around 0.1 ⁇ m (0.07 ⁇ m to 0.12 ⁇ m).
• the aqueous primer coating composition contains a specified amount of aqueous epoxy resin (B), and therefore has excellent adhesion to old coating films.
• the aqueous primer coating composition is suitable for painting substrates that are at least partially covered with old coating films.
• the aqueous primer coating composition is suitable for painting components that are partially covered with old coating films and have exposed substrates in other areas.
• the old coating film is a coating film other than the multilayer coating film of the present disclosure that was formed on the substrate before the multilayer 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 undercoat, a base layer, and a clear layer).
• a portion of the old coating film e.g., a damaged portion
• the multilayer coating film of the present disclosure may be formed on the old coating film without removing the old coating film.
• aqueous resin refers to a water-soluble resin or a water-dispersible resin.
• Water-dispersible resins are further divided into dispersion type (generally called colloidal dispersion type) and emulsion type.
• Colloidal dispersion type aqueous resins are typically obtained by semi-dissolving a resin synthesized in an organic solvent in water with a neutralizing agent.
• Emulsion type aqueous resins are typically produced by emulsion polymerization or by mechanical forced emulsification.
• Aqueous 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.
• Aqueous resins may be dispersion type. "Making a resin water-soluble or water-dispersible” refers to making a resin water-soluble or water-dispersible.
• the aqueous coating composition contains 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.
• the resin solids content of an aqueous paint composition is the total solids content of the resin components.
• Resin components are components other than thickeners, various pigments, organic solvents, water, and other inorganic components.
• the resin components of an aqueous primer paint composition are aqueous polyolefin resin (A), aqueous epoxy resin (B), and other resins.
• the weight average molecular weight and number average molecular weight are measured using polystyrene standards by the GPC (gel permeation chromatography) method.
• the glass transition temperature Tg may be calculated from the type and amount of raw material monomers, or may be measured by a differential scanning calorimeter (DSC).
• DSC differential scanning calorimeter
• the acid value and hydroxyl value can be measured by the 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.
• the average particle size is the 50% average particle size (D50) in the volume-based particle size distribution measured using a laser diffraction/scattering particle size distribution measuring device.
• Surface tension is measured by the platinum ring method.
• a dyno meter manufactured by Byck Gardner, Germany is used to measure surface tension.
• the solubility parameter (SP value) may be a known value.
• the SP value may be measured by the following method. (Reference: SUH, CLARKE, J.P.S.A-1, 5, 1671-1681 (1967)).
• the sample used is 0.5 g of the object to be measured, weighed into a 100 ml beaker and dissolved in 10 ml of a good solvent (acetone). A poor solvent is dripped onto this sample using a 50 ml burette at a measurement temperature of 20°C, and the point at which turbidity occurs is recorded as the amount dripped.
• a good solvent acetone
• As poor solvents ion-exchanged water is used as a high SP poor solvent, and n-hexane is used as a low SP poor solvent, and the turbidity point of each is measured.
• the SP value ⁇ of the object to be measured is given by the following formula.
• the aqueous primer coating composition according to the present disclosure contains an aqueous polyolefin resin (A), an aqueous epoxy resin (B), a thickener (C), an organic solvent (D) and water (E).
• the solid content of the aqueous primer paint composition is 5% by mass or more and 17% by mass or less. This provides a balance between film-forming properties, water resistance, and paint workability.
• the solid content of the aqueous primer paint composition may be 7% by mass or more, or 9% by mass or more.
• the solid content of the aqueous primer paint composition may be 14% by mass or less, or 12% by mass or less.
• the solids content of the aqueous primer paint composition is determined as follows.
• the aqueous primer paint composition is placed in an aluminum foil cup with a diameter of approximately 5 cm and weighed. This aluminum foil cup is heated at 110°C for 1 hour, and the mass (g) of the remaining part is weighed. The mass of the remaining part is divided by the mass before heating to obtain the solids content (mass%), expressed as a percentage.
• the proportion of organic solvent (D) in the organic component mass excluding the mass of water (E) from the total mass of the aqueous primer paint composition (hereinafter referred to as the VOC amount) is 30 g/L or more and 500 g/L or less. If the amount of VOC contained in the paint is low, the amount of VOC emitted during the formation of the paint film will also be reduced.
• the amount of VOCs can be calculated from the following formula.
• the concentration of water (E) is obtained by dividing the mass of all water contained in the aqueous primer paint composition by the mass of the aqueous primer paint composition.
• the concentration of organic solvent (D) is obtained by dividing the total mass of organic solvent (D) contained in the aqueous primer paint composition by the mass of the aqueous primer paint composition.
• the VOC amount may be 350 g/L or less, 300 g/L, or 250 g/L.
• the surface tension of the aqueous primer coating composition may be, for example, 26.0 mN/m or more and 30.0 mN/m or less. This further improves the wettability of the aqueous primer coating composition to the resin substrate, making it easier to form a uniform coating film.
• the surface tension of the aqueous primer coating composition may be 26.6 mN/m or more, or 27.0 mN/m or more.
• the surface tension of the aqueous primer coating composition may be 29.5 mN/m or less, or 29.0 mN/m or less.
• the surface tension of the aqueous primer coating composition can be adjusted by the type and amount of the organic solvent (D).
• the aqueous polyolefin resin (A) is not particularly limited and can be produced by a conventionally known method.
• the aqueous polyolefin resin (A) can be obtained, for example, by adding toluene to a polyolefin resin modified with an acid anhydride, heating the mixture to obtain a resin solution, adding a surfactant to the resin solution, and then dropping ion-exchanged water while forcibly stirring at 50 to 60 ° C. to cause phase inversion emulsification.
• the aqueous polyolefin resin (A) can also be obtained by heating an acid anhydride-modified polyolefin resin to dissolve it in a solvent such as tetrahydrofuran, neutralizing the carboxyl group of the resin with an excess of amine, and then dropping ion-exchanged water while forcibly stirring at 50 to 60 ° C. to cause phase inversion emulsification.
• the aqueous polyolefin resin (A) can be obtained by mixing an emulsifier and an amine with the above-mentioned solution, and then dropping ion-exchanged water at about 60 ° C. while forcibly stirring to cause emulsification.
• the aqueous polyolefin resin (A) can also be obtained by dropping a molten or dissolved acid anhydride-modified polyolefin into warm water in which a neutralizing agent such as an amine and/or a surfactant is dissolved, while forcibly stirring, to cause emulsification.
• a neutralizing agent such as an amine and/or a surfactant
• aqueous polyolefin resin (A) examples 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 acid esters, methacrylic acid esters). These may be used alone or in combination of two or more.
• olefin monomers e.g., ethylene, propylene, butene, 3-methyl-1-butene, 3-methyl-1-heptene
• ethylene-propylene copolymers ethylene-propylene-diene copolymers
• the aqueous polyolefin resin (A) may be a homopolymer of propylene, a copolymer of propylene and other olefin monomers, a copolymer of propylene and other unsaturated monomers, or a mixture of these with other polymers. These may be used alone or in combination of two or more. 90% by mass or more of the monomers constituting the aqueous polyolefin resin (A) may be propylene.
• the aqueous polyolefin resin (A) may be a modified product.
• the modified product include an adduct of an unsaturated carboxylic acid anhydride with an aqueous polyolefin resin.
• the unsaturated carboxylic acid anhydride include maleic anhydride, fumaric acid, itaconic anhydride, and (meth)acrylic acid.
• the modified product is usually obtained by reacting polyolefins with an unsaturated carboxylic acid anhydride in the presence of an organic peroxide or the like.
• the glass transition temperature Tg of the aqueous polyolefin resin (A) is -40°C or higher and -10°C or lower.
• the low Tg of the aqueous polyolefin resin (A) improves film-forming properties and facilitates adhesion to the substrate.
• the Tg of the aqueous polyolefin resin (A) may be -30°C or higher.
• the Tg of the aqueous polyolefin resin (A) may be -10°C or lower, or may be -20°C or lower.
• the weight average molecular weight Mw of the aqueous polyolefin resin (A) is, for example, 2,000 or more and 300,000 or less.
• the Mw of the aqueous polyolefin resin (A) may be 10,000 or more, or 30,000 or more.
• the Mw of the aqueous polyolefin resin (A) may be 200,000 or less, 120,000 or less, or 80,000 or less.
• the solid content mass of the aqueous polyolefin resin (A) is, for example, 50 parts by mass or more and 98 parts by mass or less, relative to 100 parts by mass of the resin solid content of the aqueous primer coating composition.
• the solid content mass of the aqueous polyolefin resin (A) is 50 parts by mass or more, the adhesion to the resin substrate can be further improved.
• the solid content mass of the aqueous polyolefin resin (A) is 98 parts by mass or less, the adhesion to the aqueous colored base coating film can be further improved.
• the solid content mass of the aqueous polyolefin resin (A) may be 55 parts by mass or more, or may be 60 parts by mass or more.
• the solid content mass of the aqueous polyolefin resin (A) may be 95 parts by mass or less, may be 90 parts by mass or less, or may be 85 parts by mass or less.
• the aqueous polyolefin resin (A) may be chlorinated or may not be chlorinated. From the viewpoint of environmental conservation, the aqueous polyolefin resin (A) may not be chlorinated.
• the chlorination rate may be, for example, 5% or more and 50% or less. Chlorination is carried out, for example, by heating and dissolving the polyolefin resin in a chlorine-based solvent such as carbon tetrachloride, and blowing in chlorine gas at a temperature of 50 to 120°C.
• water-based polyolefin resins (A) include, for example, the Superclone series and Auroren series (both manufactured by Nippon Paper Industries Co., Ltd.), the Hardlen series (manufactured by Toyobo Co., Ltd.), and the Aptlock series (manufactured by Mitsubishi Chemical Corporation).
• non-chlorinated water-based polyolefin resins (A) include, for example, Auroren AE-301, Superchron E-415, and E-480T (all manufactured by Nippon Paper Chemicals Co., Ltd.).
• Commercially available chlorinated water-based polyolefin resins (A) include, for example, Arrowbase DA-1010 (manufactured by Unitika Ltd.), Hardlen EW-5515, Hardlen EW-5303, and Hardlen EW-5250 (all manufactured by Toyobo Co., Ltd.), and Aptlock (manufactured by Mitsubishi Chemical Corporation).
• the aqueous epoxy resin (B) contributes to improving the water resistance and moisture resistance of the multi-layer coating film. During repair painting, the aqueous epoxy resin (B) contributes to improving the adhesion between the new coating film and the old coating film.
• the aqueous primer coating composition is particularly suitable for repairs.
• the aqueous epoxy resin (B) can be obtained as an aqueous dispersion, for example, by graft polymerizing an epoxy resin with a fatty acid (e.g., a vinyl monomer containing a carboxyl group) and then neutralizing the resulting mixture.
• a fatty acid e.g., a vinyl monomer containing a carboxyl group
• the solid content mass of the aqueous epoxy resin (B) is, for example, 2 parts by mass or more and 50 parts by mass or less, relative to 100 parts by mass of the resin solid content of the aqueous primer coating composition.
• the solid content mass of the aqueous epoxy resin (B) may be 5 parts by mass or more, 10 parts by mass or more, or 15 parts by mass or more.
• the solid content mass of the aqueous epoxy resin (B) may be 45 parts by mass or less, or 40 parts by mass or less.
• the mass ratio (A/B) of the water-based polyolefin resin (A) to the water-based epoxy resin (B) is 60/40 to 95/5. This allows the multi-layer coating film formed from the all-water-based paint to exhibit excellent water resistance.
• the mass ratio (A/B) may be 70:30 to 90:10.
• water-based epoxy resin (B) examples include bisphenol type epoxy resins such as bisphenol A type epoxy resin, bisphenol F type epoxy resin, and bisphenol AD type epoxy resin; epoxy ester resins obtained by modifying the above bisphenol type epoxy resins with dibasic acids, etc.; novolac type epoxy resins such as cresol novolac type epoxy resin and phenol novolac type epoxy resin; alicyclic epoxy resin; polyglycol type epoxy resin; hydrogenated bisphenol A type epoxy resin; ethylene glycol diglycidyl ether, diethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, Examples of such epoxy resins include aliphatic epoxy resins such as glycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, neopentyl glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, trimethylolpropane polyglycidyl
• aromatic epoxy resins bisphenol type epoxy resins, and bisphenol A type epoxy resins may be used.
• Water-based epoxy resin (B) can be obtained, for example, by adding epichlorohydrin to phenol novolac resin.
• Commercially available products of such water-based epoxy resin (B) include Denacol EM150 (manufactured by Nagase Chemtech Co., Ltd.), Epilez 6006W70, 5003W55 (manufactured by Japan Epoxy Resins Co., Ltd.), Watersol series (manufactured by DIC Corporation), and WEX-5100 (manufactured by Tohto Kasei Co., Ltd.).
• the water-based epoxy resin (B) may be obtained, for example, by forcibly emulsifying a bisphenol-type epoxy resin with an emulsifier.
• Commercially available products of such water-based epoxy resin (B) include, for example, Denacol EM101 and EM103 (manufactured by Nagase Chemtech Co., Ltd.), Epilez 3510W60, 3515W6, 3522W60, and 3540WY55 (all manufactured by Japan Epoxy Resins Co., Ltd.).
• the water-based epoxy resin (B) may be, for example, an alkyl type in which epichlorohydrin is added to a polyol such as sorbitol, pentaerythritol, or glycerin.
• a polyol such as sorbitol, pentaerythritol, or glycerin.
• Commercially available products of this type of water-based epoxy resin (B) include, for example, Denacol EX-611, EX-614, EX-411, and EX-313 (all manufactured by Nagase Chemtech Co., Ltd.).
• the water-based epoxy resin (B) may be modified.
• the water-based epoxy resin (B) may be, for example, acrylic-modified, urethane-modified, amine-modified, or ester-modified.
• An example of a commercially available acrylic-modified bisphenol A-type water-based epoxy resin (B) is Modepics 304 (manufactured by Arakawa Chemical Industries Co., Ltd.).
• the thickener (C) increases the viscosity of the aqueous primer coating composition.
• the thickener (C) 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 may be used.
• urethane association thickeners examples include polyurethane thickeners that have hydrophobic chains in the molecule, and urethane-urea thickeners in which at least part of the main chain is a hydrophobic urethane chain.
• urethane associative thickeners include, for example, Adekanol UH-756VF (manufactured by ADEKA Corporation) and BYK-420 (manufactured by BYK Corporation).
• the solid content mass of the thickener (C) is, for example, 0.5 parts by mass or more and 5 parts by mass or less, relative to 100 parts by mass of the resin solid content of the aqueous primer coating composition.
• the solid content mass of the thickener (C) may be 1 part by mass or more, or may be 2 parts by mass or more.
• the solid content mass of the thickener (C) may be 4.5 parts by mass or less, or may be 4 parts by mass or less.
• Organic solvent (D) reduces the surface tension of the aqueous primer coating composition and improves the wettability of the composition to the resin substrate.
• a poorly water-soluble solvent (D1) 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 the organic solvent (D).
• the proportion of the poorly water-soluble solvent (D1) in the organic solvent (D) is 1% by mass or more and 60% by mass or less.
• the poorly water-soluble solvent (D1) effectively reduces the surface tension of the aqueous primer coating composition.
• the above proportion of the poorly water-soluble solvent (D1) may be 5% by mass or more, or 10% by mass or more.
• the above proportion of the poorly water-soluble solvent (D1) may be 50% by mass or less, 40% by mass or less, or 35% by mass or less.
• the organic solvent (D) contains at least one of an amphipathic solvent (D2) and a hydrophilic solvent (D3) together with a poorly water-soluble solvent (D1). This improves the compatibility of the organic solvent (D) with water (E) and improves the storage stability of the aqueous primer coating composition.
• Examples of poorly water-soluble solvents (D1) 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 may be used alone or in combination of two or more.
• Commercially available products of poorly water-soluble solvents (D1) 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).
• amphiphilic solvents (D2) include isoamyl acetate (1.7 g/100 g), methoxypropyl acetate (also known as propylene glycol monomethyl ether acetate, 19.8 g/100 g), ethylene glycol monomethyl ether propionate (18.5 g/100 g), ethoxypropyl acetate (9.5 g/100 g), 3-methoxybutyl acetate (also known as methoxybutyl acetate, 6.5 g/100 g), 3-methyl-3-methoxybutyl Examples include ethyl 3-ethoxypropionate (1.3 g/100 g), dipropylene glycol dimethyl ether (dimethyl propylene diglycol, 37 g/100 g), cyclohexyl acetate (1.4 g/100 g), propylene glycol mono-t-butyl ether (14.5 g/100 g), and propylene glycol monobutyl ether (6.4 g
• hydrophilic solvents examples include ethylene glycol monoethyl ether (also known as cellosolve, 100g or more/100g), isopropyl glycol (also known as ethylene glycol monoisopropyl ether, 100g or more/100g), ethylene glycol monoisobutyl ether acetate (100g or more/100g), ethylene glycol monobutyl ether (also known as butyl cellosolve, 100g or more/100g), 3-methoxy-3-methylbutanol (100g or more/100g), ethylene glycol mono t-butyl ether (100g or more/100g), propylene glycol monopropyl ether (100g or more/100g), diethylene glycol dimethyl ether (100g or more/100g), diethylene glycol diethyl ether (100g or more/100g), and ethylene glycol monoisoamyl ether (100g or more/100g). These may be used alone or in combination of two
• the SP value of the organic solvent (D) may be, for example, 7.90 or more and 9.80 or less. This further improves the wettability of the aqueous primer coating composition to the resin substrate, making it easier to form a uniform coating film.
• the SP value of the organic solvent (D) may be 8.00 or more, or 8.30 or more.
• the SP value of the organic solvent (D) may be 9.70 or less, or 9.30 or less.
• the SP value of organic solvent (D) is calculated from the volumetric mixing ratio (volume %) of each organic solvent and the SP value of each organic solvent. Specifically, the SP value of organic solvent (D) is the sum of (mixture ratio X1 (volume %) of poorly water-soluble solvent (D1) x its SP value Y1), (mixture ratio X2 (volume %) of amphipathic solvent (D2) x its SP value Y2), and (mixture ratio X3 (volume %) of hydrophilic solvent (D3) x its SP value Y3).
• the difference ⁇ SP between the SP value of the organic solvent (D) and the SP value of the polymer that constitutes the surface of the resin substrate is, for example, 2.50 or less. This further improves the wettability of the aqueous primer coating composition to the resin substrate, making it easier to form a uniform coating film.
• ⁇ SP may be 0.00 or more, or 0.40 or more.
• ⁇ SP may be 2.50 or less, or 2.00 or less.
• the polymer that constitutes the surface of a resin-based coated object is a polymer that occupies 50% or more by mass of the surface of the coated object.
• the SP value of the known polypropylene resin can be regarded as the SP value of the polymer that constitutes the surface of the coated object.
• the SP value of the polymer that constitutes the surface of the coated object can be substituted with the SP value of polypropylene resin.
• Polypropylene resin is known to be a resin that is particularly difficult to adhere to, and it is difficult to make a coating film adhere to polypropylene resin. Therefore, it is safe to say that organic solvents (D) with an SP value difference ⁇ SP of 2.5 or less from the SP value of polypropylene resin also have excellent wettability with other polymers.
• the SP value of polypropylene resin is known and is 7.90 (Source: Haneda Masaki, "Surface Modification of Plastic Films," Journal of Printing Science and Technology of Japan, Vol. 47, No. 2 (2010) Review, pp. 78-83).
• Water (E) examples include various types of water such as pure water, ion-exchanged water, tap water, and industrial water.
• the aqueous primer coating composition may contain an aqueous polyurethane resin (F).
• the aqueous polyurethane resin (F) contributes to improving the adhesion between the new coating film and the old coating film.
• the aqueous primer coating composition containing the aqueous polyurethane resin (F) is particularly suitable for repair coating.
• the aqueous polyurethane resin (F) is prepared, for example, by neutralizing an NCO-terminated prepolymer obtained by the method described below, dispersing it in water, and then subjecting it to a chain extension reaction, a method known as the prepolymer mixing method.
• the solids mass of the aqueous polyurethane resin (F) is, for example, 0 parts by mass or more and 10 parts by mass or less, relative to 100 parts by mass of the resin solids of the aqueous primer coating composition.
• the solids mass of the aqueous polyurethane resin (F) may be 2 parts by mass or more, or 3 parts by mass or more.
• the solids mass of the aqueous polyurethane resin (F) may be 7 parts by mass or less, or 6 parts by mass or less.
• the acid value of the aqueous polyurethane resin (F) may be, for example, 0 mgKOH/g or more and 40 mgKOH/g or less.
• the acid value of the aqueous polyurethane resin (F) may be 5 mgKOH/g or more, or 10 mgKOH/g or more.
• the acid value of the aqueous polyurethane resin (F) may be 30 mgKOH/g or less, or 20 mgKOH/g or less.
• the Tg of the aqueous polyurethane resin (F) may be, for example, -50°C or higher and 5°C or lower. This improves film-forming properties and facilitates adhesion to the substrate.
• the Tg of the aqueous polyurethane resin (F) may be -40°C or higher, or -35°C or higher.
• the Tg of the aqueous polyurethane resin (F) may be 0°C or lower, or -10°C or lower.
• Polyurethane resins are prepared, for example, by reacting a polyhydric alcohol, a polyisocyanate compound, and a compound having an active hydrogen group in the molecule.
• the polyhydric alcohol has two or more hydroxyl groups.
• Examples of the polyhydric alcohol include the same compounds as those listed as raw materials for the polyester resin dispersion (F).
• the number average molecular weight of the polyhydric alcohol may be 500 or more and 5,000 or less.
• Polyisocyanate compounds have two or more isocyanate groups in the molecule.
• polyisocyanate compounds 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 diisocyan
• Aromatic diisocyanates such as cyanate, 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.
• the polyisocyanate compound 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.
• alicyclic diisocyanates are preferred. This introduces a cyclic structure into the polyurethane resin (F) molecules, improving weather resistance.
• Compounds that have an active hydrogen group in the molecule are used to block the isocyanate group in a polyisocyanate compound.
• Examples of compounds that have an active hydrogen group in the molecule include monohydric alcohols such as methanol, ethanol, and diethylene glycol monobutyl ether; monovalent carboxylic acids such as acetic acid and propionic acid; monovalent thiols such as ethyl mercaptan; primary amines such as diethylenetriamine and monoethanolamine; secondary amines such as diethylamine; and oximes such as methyl ethyl ketoxime.
• chain extenders In preparing polyurethane resin, chain extenders, monoisocyanate compounds, catalysts, etc. are used as necessary.
• Polyurethane resins are synthesized, for example, by a one-shot method in which each component is reacted at once, or a multi-stage method in which the components are reacted in stages (a part of the active hydrogen-containing compound (e.g., a polymer polyol) is reacted with a polyisocyanate to form an NCO-terminated prepolymer, and then the remainder of the active hydrogen-containing compound is reacted).
• the synthesis reaction is carried out, for example, at a temperature of 40°C or higher and 140°C or lower.
• Water-based polyurethane resins include, for example, the Superflex series, such as Superflex 150, Superflex 420, and Superflex 460 (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), the Neosticker series, and the Evaphanol series (all manufactured by Nicca Chemical Co., Ltd.), the Bayhydrol series, such as Bayhydrol VP LS2952 (manufactured by Sumika Covestro Urethanes Co., Ltd.), VONDIC 2260, VONDIC 2220, Hydran WLS210, and Hydran WLS213 (all manufactured by Dainippon Ink and Chemicals Inc.), and NeoRez R9603 (manufactured by Avecia).
• the Superflex series such as Superflex 150, Superflex 420, and Superflex 460 (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.)
• the Neosticker series and the Evaphanol series (all manufactured by Nicca Chemical
• the aqueous primer coating composition may contain various additives as necessary, such as a surface conditioner, a preservative, an antifungal agent, an antifoaming agent, a light stabilizer, an ultraviolet absorber, an antioxidant, and a pH adjuster.
• the surface conditioner can reduce the surface tension of the aqueous primer paint composition. On the other hand, it can reduce the adhesion of the first undercoat film to the resin substrate. Therefore, the content of the surface conditioner may be 0.1 parts by mass or more and 10 parts by mass or less per 100 parts by mass of the resin solids contained in the aqueous primer paint composition. The content of the surface conditioner may be 5 parts by mass or less, or may be 2 parts by mass or less.
• the aqueous surfacer is, for example, a two-component type, and includes, for example, a first main agent including a hydroxyl-containing resin (a1) and an aqueous solvent (a2), and a first curing agent including a polyisocyanate compound (b1) and an organic solvent not having a hydroxyl group (b2).
• hydroxyl group-containing resin (a1) examples include acrylic polyols, polyester polyols, polyether polyols, polyurethane polyols, and polycarbonate polyols.
• acrylic polyols are preferred because they tend to provide good physical properties such as the appearance, weather resistance, and chemical resistance of the resulting coating film.
• 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 commonly used by those skilled in the art. Specifically, an emulsifier is mixed into an aqueous medium, which may optionally contain an organic solvent such as alcohol, and the resulting mixture is heated and stirred while the raw material monomers and polymerization initiator are dropped into it. Alternatively, an emulsion mixture in which the raw material monomers, emulsifier, and water are previously emulsified may be dropped into the aqueous medium.
• the aqueous medium may be the same as or different from the aqueous solvent (a2).
• An emulsion of acrylic polyol can be obtained, for example, by emulsion polymerization of a raw material monomer mixture containing an alkyl (meth)acrylate monomer, an ethylenically unsaturated monomer containing an acid group, an ethylenically unsaturated monomer containing a hydroxyl group, and a styrene-based monomer.
• Examples of the aqueous solvent (a2) include the same as water (E).
• the first main agent may contain an organic solvent in addition to water.
• Examples of the organic solvent include organic solvents that do not have a hydroxyl group, among those exemplified as organic solvents (D).
• the first main agent and the first hardener are mixed to prepare the water-based surfacer.
• the first main agent and the first hardener are mixed immediately before painting. After being mixed, the first main agent and the first hardener may be supplied to a painting device, or may be mixed within the painting device.
• the first main agent may further contain a pigment (c).
• the content of the pigment (c) may be, for example, 100 parts by mass or more and 300 parts by mass or less, and 120 parts by mass or more and 200 parts by mass or less, relative to 100 parts by mass of the resin solid content contained in the first main agent.
• pigments (c) include color pigments such as titanium dioxide, carbon black, iron oxide, and copper phthalocyanine blue; luster pigments such as aluminum flakes and mica flakes; extender pigments such as calcium carbonate, clay, talc, barium oxide, and silica; and rust-preventive pigments such as aluminum tripolyphosphate, aluminum phosphomolybdate, and zinc phosphate.
• color pigments such as titanium dioxide, carbon black, iron oxide, and copper phthalocyanine blue
• luster pigments such as aluminum flakes and mica flakes
• extender pigments such as calcium carbonate, clay, talc, barium oxide, and silica
• rust-preventive pigments such as aluminum tripolyphosphate, aluminum phosphomolybdate, and zinc phosphate.
• At least a body pigment may be included.
• the proportion of the body pigment may be, for example, 30% by mass or more and 100% by mass or less, and 40% by mass or more and 70% by mass or less, relative to 100 parts by mass of the total of all pigments.
• the water-based surfacer may contain an epoxy group-containing silane coupling agent.
• the epoxy group-containing silane coupling agent has a reactive silyl group and one or more epoxy groups as an organic functional group.
• the epoxy group-containing silane coupling agent may have two or more epoxy groups.
• the epoxy group is a three-membered ring (oxirane ring) with an ether bond.
• the epoxy group has high reactivity and reacts with the hydroxyl group-containing resin (a1) and/or the polyisocyanate compound (b1). This increases the crosslink density of the resulting cured coating film.
• the epoxy group-containing silane coupling agent may be added to at least one of the first base agent and the first curing agent.
• the silane coupling agent is added in an amount of 1 part by mass to 8 parts by mass per 100 parts by mass of the total solid content of the hydroxyl group-containing resin (a1) and the polyisocyanate compound (b1).
• the aqueous colored base coating composition may be a curing type or a lacquer type.
• the aqueous colored base coating composition further contains a pigment.
• the pigment include the color pigments and/or luster pigments exemplified as pigment (c).
• the curable water-based colored base paint composition contains a curable resin (e.g., the first main agent described above) and a curing agent (e.g., the first curing agent described above), and forms a cured coating film by heating.
• the curable water-based colored base paint composition may further contain a silane coupling agent (e.g., an epoxy group-containing silane coupling agent).
• a lacquer-type water-based colored base paint 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.
• concentration of the binder resin There are no particular limitations on the concentration of the binder resin, and it is set appropriately depending on the composition and application.
• the binder resin is not particularly limited.
• binder resins include acrylic resins, amino alkyd resins, alkyd resins, amino resins, isocyanate resins, epoxy resins, vinyl chloride resins, cashew resins, silicone resins, styrene resins, styrenated alkyd resins, cellulose-based resins (e.g., cellulose nitrate, etc.), urea resins, vinyl resins, phenolic resins, phthalic acid resins, fluororesins, polyester resins, unsaturated polyester resins, 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.
• organic solvents include naphtha, xylene, toluene, and acetone.
• the aqueous clear coating composition is, for example, a two-liquid type.
• the aqueous clear coating composition includes a second main agent containing the same hydroxyl group-containing resin (a1) and aqueous solvent (a2) as above, and a second curing agent containing the same polyisocyanate compound (b1) and organic solvent (b2) not having a hydroxyl group as above.
• Each component of the aqueous clear coating composition and each component of the aqueous surfacer may be the same or different.
• the aqueous clear coating composition may contain an epoxy group-containing silane coupling agent similar to that described above.
• the epoxy group-containing 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 (a1) and the polyisocyanate compound (b1).
• At least one of the water-based 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 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 surfacer may be the same or different.
• Each aqueous coating composition can be prepared by a known method.
• Each aqueous coating composition is prepared by mixing the above-mentioned components.
• a commonly used mixing device such as a paint shaker or mixer is used.
• the base agent and the curing agent are usually mixed immediately before use (for example, they are used within 60 minutes after mixing).
• the substrate may have at least a surface made of resin.
• the entire substrate may be made of resin, or at least a portion of the surface of a resin or metal substrate may be coated with resin.
• the resin covering the surface of the substrate may be an old coating film. That is, the substrate made of resin may be made of resin, may have a resin substrate and an old coating film covering at least a portion of its surface, or may have a metal substrate and an old coating film covering at least a portion of its surface.
• the aqueous primer coating composition used in the present disclosure has excellent adhesion to the old coating film as well as to the resin or metal substrate.
• the resin that constitutes the resin-made coated object may be a thermoplastic resin or a thermosetting resin.
• resins include polypropylene (PP) resin, acrylonitrile butadiene styrene copolymer (ABS resin), polycarbonate (PC)/ABS resin, PC/acrylonitrile ethylene-propylene-diene styrene copolymer (AES resin), AES resin, PC/polybutylene terephthalate (PBT) resin, PC/polyethylene terephthalate (PET) resin, PC resin, polymethyl methacrylate (PMMA) resin, GF-PBT resin, GF-polyamide (PA) resin, Noryl GTX resin, polyvinyl chloride (PVC resin), acrylonitrile styrene acrylic (ASA) resin, carbon fiber reinforced plastic (CFRP resin), and glass fiber reinforced plastic (GFRP resin).
• PP polypropylene
• ABS resin acrylonitrile butadiene styren
• metals include iron, copper, aluminum, tin, zinc, and alloys thereof.
• Metallic substrates may be surface-treated. Examples of surface treatments include phosphate treatment, chromate treatment, zirconium conversion treatment, and composite oxide treatment.
• Metallic substrates may be further coated with electrocoating paint after surface treatment.
• the electrocoating paint may be of the cationic type or the anionic type.
• the coated article is produced by a method comprising the steps of applying an aqueous primer paint composition onto a resin substrate to form a first undercoat film, applying an aqueous colored base paint composition onto the first undercoat film to form a colored base paint film, and applying an aqueous two-component clear paint composition onto the colored base paint film to form a clear paint film.
• a water-based surfacer may be applied onto the first undercoat film to form a second undercoat film.
• the amount of the aqueous primer coating composition to be applied is not particularly limited and is set appropriately depending on the performance required of the coating film.
• the aqueous primer coating composition is applied so that the thickness of the first undercoat coating film after curing is 10 ⁇ m or more and 40 ⁇ m or less.
• the method of application of the aqueous primer coating composition is not particularly limited. Examples of application methods include air spray coating, airless spray coating, rotary atomization coating, and curtain coat coating. These methods may be combined with electrostatic coating. In the case of repairs, air spray coating is preferred because it is easy to apply localized coating. Coating may be performed multiple times. In coating methods commonly used in automobile painting (e.g., air spray coating), the aqueous primer coating composition exhibits high film-forming properties even on substrates with fine irregularities.
• aqueous primer coating composition After the aqueous primer coating composition is applied, it is heated to harden the coating (which can also be said to be dried and solidified).
• the curing conditions are set appropriately depending on the amount applied and the composition. Curing is carried out, for example, at a temperature of 40°C to 70°C for about 30 to 60 minutes.
• the coating may be allowed to dry naturally. Natural drying may be performed at room temperature (23°C ⁇ 3°C) for at least 2 hours, at least 24 hours, or even at least 1 week.
• the target area and its surroundings are polished as necessary, and any irregularities are filled in with putty. The area is then polished again.
• Step of forming a second undercoat coating film In this step, a water-based surfacer is applied to the substrate to form a second undercoat coating film.
• the second undercoat coating film is formed as necessary.
• the method of applying the water-based surfacer is not particularly limited, and may be the same as that of the water-based primer paint composition.
• the amount of water-based surfacer applied is not particularly limited, and may be appropriately set according to the performance required of the coating film.
• the water-based surfacer is applied, for example, so that the thickness of the second undercoat coating film after curing is 20 ⁇ m or more and 100 ⁇ m or less.
• the water-based surfacer is cured, for example, by the same method as that of the water-based primer paint composition.
• the first and second undercoat films are usually polished and degreased. Polishing is done using sandpaper or similar.
• Step III Step of forming a colored base coating film
• an aqueous colored base coating composition is applied onto the first or second undercoat coating film to form a colored base coating film.
• the application of the aqueous colored base coating composition may be carried out multiple times.
• the method of applying the aqueous colored base paint composition is not particularly limited, and may be the same as that of the aqueous primer paint composition.
• the amount of the aqueous colored base paint composition applied is not particularly limited, and it is applied, for example, so that the thickness of the colored base paint film after curing is 10 ⁇ m or more and 100 ⁇ m or less. After application, the paint film is cured.
• the curing conditions are appropriately set depending on the composition of the aqueous colored base paint composition.
• Step IV Step of Forming Clear Coating Film
• an aqueous clear coating composition is applied onto the colored base coating film to form a clear coating film.
• the prepared water-based clear coating composition is applied onto the water-based colored base coating film.
• the method of applying the water-based clear coating composition is not particularly limited, and may be the same as that of the water-based primer coating composition.
• the amount of the water-based clear coating composition applied is not particularly limited, and is appropriately set according to the performance required of the coating film.
• the water-based clear coating composition is applied, for example, so that the thickness of the clear coating film after curing is 20 ⁇ m or more and 100 ⁇ m or less.
• the water-based clear coating composition is cured, for example, by the same method as that of the water-based primer coating composition.
• a painted article that has a multi-layer coating film in which a first undercoat coating film, an optional second undercoat coating film, a colored base coating film, and a clear coating film are laminated in this order.
• the multilayer coating film of the present disclosure is disposed on a resin substrate.
• the multilayer coating film comprises a first undercoat coating film formed from the above-mentioned aqueous primer coating composition, a colored base coating film formed from the above-mentioned aqueous colored base paint on the first undercoat coating film, and a clear coating film formed from the above-mentioned aqueous two-component clear paint on the colored base coating film.
• the multilayer coating film may further comprise a second undercoat coating film formed from the above-mentioned aqueous surfacer between the first undercoat coating film and the colored base coating film.
• the first undercoat has excellent adhesion to resin substrates and old coatings.
• the multi-layer coating is suitable for repairing resin substrates with old coatings.
• the thickness of the first undercoat coating film after curing is, for example, 10 ⁇ m or more and 40 ⁇ m or less.
• the thickness of the second undercoat coating film after curing is, for example, 20 ⁇ m or more and 100 ⁇ m or less.
• the thickness of the colored base coating film after curing is, for example, 10 ⁇ m or more and 100 ⁇ m or less.
• the thickness of the clear coating film after curing is, for example, 20 ⁇ m or more and 100 ⁇ m or less.
• Example 1 An aqueous primer coating composition, an aqueous surfacer, an aqueous colored base coating composition, and an aqueous clear coating composition were prepared as described below, and multi-layer coating films were formed.
• the first main agent contains acrylic polyol in the form of an emulsion as the hydroxyl group-containing resin (a1), contains pure water as the aqueous solvent (a2), and further contains a pigment.
• the solid content concentration of the hydroxyl group-containing resin (a1) was 24.4% of the total solid content contained in the first main agent.
• the first curing agent was prepared by mixing 60 parts of polyisocyanate compound (b1) (Burnoc DNW-5500, manufactured by DIC Corporation), 19 parts of ethyl ethoxypropionate, 19 parts of ethylene glycol dimethyl ether, and 2 parts of an epoxy group-containing silane coupling agent (3-glycidoxypropyltriethoxysilane).
• the content of the silane coupling agent was 1.18 parts by mass per 100 parts by mass of the total solid content of the hydroxyl group-containing resin (a1) and the polyisocyanate compound (b1).
• aqueous clear coating composition As the second main agent, a mixture of nax E-CUBE WB (2:1) NN clear (manufactured by Nippon Paint Co., Ltd., solid content approximately 38%) and pure water (aqueous solvent (a2)) was prepared.
• the second main agent contains acrylic polyol in the form of an emulsion as the hydroxyl group-containing resin (a1).
• the solid content concentration of the hydroxyl group-containing resin (a1) was 91.5% of the total solid content contained in the second main agent.
• a second hardener was prepared in the same manner as the first hardener described above.
• a water-based clear coating composition was prepared by mixing 100 parts of the second base agent, 50 parts of the second curing agent, and an appropriate amount of pure water using a disper.
• the content of the silane coupling agent was 1.35 parts by mass per 100 parts by mass of the total solid content of the hydroxyl group-containing resin (a1) and the polyisocyanate compound (b1).
• a polypropylene plate (PP plate) with a smooth surface, a PP plate with fine irregularities, a steel plate with a smooth old coating film, or a steel plate with a finely irregular old coating film was prepared, and a multi-layer coating film was formed on each surface.
• the smooth PP plate and the old coating film were used for adhesion evaluation.
• the finely irregular PP plate and the old coating film were used for appearance evaluation. After preparation of each coating composition, painting work was started within 60 minutes.
• a multi-layer coating film P2 was formed in the same manner as in "(2-1) Formation of a multi-layer coating film on a PP plate with a smooth surface" above, except that a PP plate with fine irregularities was used as the substrate.
• a multi-layer coating film M1 was formed in the same manner as in "(2-1) Formation of a multi-layer coating film on a PP plate with a smooth surface" above, except that a steel plate with a smooth surface and an old coating film was used as the substrate.
• a multi-layer coating film M2 was formed in the same manner as in "(2-1) Formation of a multi-layer coating film on a PP plate with a smooth surface" above, except that a steel plate with an old coating film having irregularities was used as the substrate.
• Examples 2 to 18, Comparative Examples 1 to 9 Except for preparing the aqueous primer coating compositions as shown in Table 1, multi-layer coating films were formed on four types of substrates in the same manner as in Example 1.
• Storage stability 900 ml of the aqueous primer coating composition was filled into a 1 L inner surface coated can and allowed to stand at 23° C. After one month, the state of the aqueous primer coating composition was visually evaluated.
• the evaluation criteria are as follows. If the evaluation is B or higher, it can be said that the storage stability is excellent.
• Adhesion evaluation was performed on multi-layer coating films P1 and M1 formed on PP plates with smooth surfaces or steel plates with old coatings. Since adhesion tends to decrease when the painted surface is smooth, it can be evaluated that if the adhesion of multi-layer coating films P1 and M1 is high, the adhesion of multi-layer coating films P2 and M2 is also high.
• Tape (Nichiban Corporation, Cellotape (registered trademark), 24 mm wide) was applied to cover all the squares, and the tape was firmly attached from above with a fingernail or the like. The tape was then peeled off while being pulled so that the angle between the tape and the coating film was about 45°. After the tape was peeled off, the number of squares where the coating film remained was counted. The more squares that remained, the higher the adhesion.
• the coated article having the multi-layer coating film M1 was subjected to an adhesion evaluation in the same manner as described above.
• the coated article having the multi-layer coating film M2 was subjected to an appearance evaluation in the same manner as described above.
• aqueous primer coating compositions of Examples 1 to 18 had excellent storage stability and film-forming properties, and the resulting coatings had good adhesion and appearance.
• the aqueous primer coating composition of Comparative Example 1 gelled immediately after preparation and lost fluidity, making it impossible to apply. As a result, it was not possible to form a multi-layer coating film, and it was not possible to evaluate the multi-layer coating film.
• the aqueous primer coating compositions of Comparative Examples 2 to 4 showed good results in the film-forming evaluation when a large amount was applied, but the results were poor in the adhesion and appearance evaluations when the composition was applied in an amount close to that of automobile repair paint.
• the aqueous primer coating composition of Comparative Example 5 had poor storage stability.
• the aqueous primer coating compositions of Comparative Examples 6 to 9 showed poor film-forming evaluations and also poor results in the adhesion and appearance evaluations.
• the present invention includes the following aspects.
• the aqueous primer coating composition contains an aqueous polyolefin resin (A), an aqueous epoxy resin (B), a thickener (C), an organic solvent (D) and water (E), and has a solid content of 5% by mass or more and 17% by mass or less;
• the aqueous polyolefin resin (A) has a glass transition temperature of ⁇ 40° C.
• the organic solvent (D) includes a slightly water-soluble solvent (D1) that dissolves at less than 1 g in 100 g of water at 20° C., and at least one of an amphipathic solvent (D2) that dissolves at least 1 g but less than 60 g in 100 g of water at 20° C., and a hydrophilic solvent (D3) that dissolves at least 60 g in 100 g of water at 20° C.,
• the proportion of the poorly water-soluble solvent (D1) in the organic solvent (D) is 1 mass% or more and 60 mass% or less
• a method for forming a multilayer coating film wherein the mass of the organic solvent (D) is 30 g/L or more and 500 g/L or less in the organic component mass obtained by subtracting the mass of the water (E) from the total mass
• a first undercoat coating film formed on a resin substrate using an aqueous primer coating composition A colored base coating film formed on the first undercoat coating film using an aqueous colored base paint; A clear coating film formed on the colored base coating film by a water-based two-component clear paint,
• the aqueous primer coating composition contains an aqueous polyolefin resin (A), an aqueous epoxy resin (B), a thickener (C), an organic solvent (D) and water (E), and has a solid content of 5% by mass or more and 17% by mass or less;
• the aqueous polyolefin resin (A) has a glass transition temperature of ⁇ 40° C. or higher and ⁇ 10° C.
• the organic solvent (D) includes a slightly water-soluble solvent (D1) that dissolves at less than 1 g in 100 g of water at 20° C., and at least one of an amphipathic solvent (D2) that dissolves at least 1 g but less than 60 g in 100 g of water at 20° C., and a hydrophilic solvent (D3) that dissolves at least 60 g in 100 g of water at 20° C.,
• the proportion of the poorly water-soluble solvent (D1) in the organic solvent (D) is 1 mass% or more and 60 mass% or less
• a multilayer coating film wherein the mass of the organic solvent (D) in the organic component mass obtained by subtracting the mass of the water (E) from the total mass of the aqueous primer coating is 30 g/L or more and 500 g/L or less.
• a first undercoat coating film formed on a resin substrate using an aqueous primer coating composition A colored base coating film formed on the first undercoat coating film using an aqueous colored base paint;
• the composition comprises an aqueous polyolefin resin (A), an aqueous epoxy resin (B), a thickener (C), an organic solvent (D) and water (E), and has a solid content of 5% by mass or more and 17% by mass or less;
• the aqueous polyolefin resin (A) has a glass transition temperature of ⁇ 40° C.
• the organic solvent (D) includes a slightly water-soluble solvent (D1) that dissolves at less than 1 g in 100 g of water at 20° C., and at least one of an amphipathic solvent (D2) that dissolves at least 1 g but less than 60 g in 100 g of water at 20° C., and a hydrophilic solvent (D3) that dissolves at least 60 g in 100 g of water at 20° C.,
• the proportion of the poorly water-soluble solvent (D1) in the organic solvent (D) is 1 mass% or more and 60 mass% or less
• An aqueous primer coating composition wherein the mass of the organic solvent (D) is 30 g/L or more and 500 g/L or less relative to the organic component mass obtained by subtracting the mass of the water (E) from the total mass of the
• the present invention provides a multi-layer coating film with excellent appearance formed from an all-water-based paint composition, including a primer paint composition that has sufficiently low VOC emissions and excellent storage stability and adhesion to resin substrates. Therefore, the water-based paint composition is suitable for painting automobiles, particularly for painting automobile repairs.

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  • 2023-12-05 WO PCT/JP2023/043448 patent/WO2025120726A1/ja active Pending
  • 2023-12-05 JP JP2024518433A patent/JP7493696B1/ja active Active

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