Multilayer coating film

Abstract

To provide a multilayer coating film having satisfactory chipping resistance at low temperatures (e.g., around -20°C).SOLUTION: A multilayer coating film according to the present disclosure comprises a substrate, a clear layer formed over the substrate, and a base layer comprising one or more layers and interposed between the substrate and the clear layer, wherein the base layer includes a layer having a low-temperature stress residual rate, as determined by the following method, of 65% or less. [Low-temperature stress residual rate] When a tensile strain of 1% is applied to the base layer at a temperature of -20°C and this base layer is held for 1,000 seconds, a maximum stress of the base layer is expressed by σb0 and a stress of the base layer after the 1,000-second holding is expressed by σb1. The low-temperature stress residual rate is calculated as σb1 / σb0.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present disclosure relates to multi-layer coatings. [Background technology]

[0002] In coated objects such as automobile bodies, multi-layer coating films are formed to impart corrosion resistance, chipping resistance, design, scratch resistance, etc., and for example, a multi-layer coating film is formed by forming an intermediate coating film, a base coating film, a clear coating film, and, if necessary, a chipping primer layer, etc., on a steel plate that has been subjected to rust prevention treatment such as electrodeposition coating. Chipping is damage such as cracks and peeling that can occur when a small stone or the like hits the painted surface of the outer plate of an automobile. When chipping occurs, water or the like may penetrate through the chipped area, causing rust, etc., on the base material of the outer plate.

[0003] To address chipping, efforts have been made to improve undercoat coatings and develop anti-chipping primers.

[0004] Patent Document 1 describes a cured, isolated coating film with a shrinkage stress of 100 kg / cm when the temperature is lowered from 130°C to 40°C. 2 The document describes a chipping-resistant coating method that includes coating and baking a thermosetting powder coating having a breaking elongation of 10% or more at 20°C.

[0005] Patent Document 2 describes a base coat paint composition containing an acrylic polyol as a main resin, an amino resin curing agent, a luster pigment or coloring pigment, and an organic solvent, in which the acrylic polyol has a hydroxyl value of 40 to 120, contains a graft portion whose distance from the acrylic polyol main chain is within a specified range, and uses a specified amount of a melamine resin having a specified weight average molecular weight, and describes that the internal stress of the base coat paint film obtained by applying and heat curing such a base coat paint composition is 0 to 34 kg / cm. 2 It is stated that: [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-open No. 1988-196872 [Patent Document 2] Japanese Patent Application Publication No. 11-228904 Summary of the Invention [Problem to be solved by the invention]

[0007] The base coating films described in Patent Documents 1 and 2 were not fully satisfactory in terms of chipping resistance at low temperatures. The present disclosure has been made in view of such circumstances, and aims to provide a multilayer coating film having good chipping resistance at low temperatures (for example, around -20°C). [Means for solving the problem]

[0008] The present disclosure includes the following aspects. [1] A substrate; A clear layer laminated on the substrate; a base layer disposed between the substrate and the clear layer, the base layer including one or more layers; The multi-layer coating film, wherein the base layer includes a layer having a low-temperature stress retention rate of 65% or less as measured by the following method. [Low temperature stress retention rate] When a tensile strain of 1% is applied to the base layer at a temperature of -20°C and held for 1,000 seconds, the maximum stress in the base layer is σ b0 , the stress in the base layer after holding for 1,000 seconds is σ b1 When the low-temperature residual stress is σ b1 / σ b0 It is calculated as follows. [2] The multilayer coating film according to [1], wherein the base layer includes two or more layers. [3] When a tensile strain of 1% is applied to the base layer and the clear layer at a temperature of -20°C and held for 1,000 seconds, the maximum stress σ in the clear layer is c0 and the maximum stress in the base layer σ b0 Ratio σ c0 / σ b0 The multilayer coating film according to [1] or [2], wherein is 1 or more. Effect of the Invention

[0009] According to the present disclosure, a multilayer coating film having good chipping resistance at low temperatures can be provided. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] The multilayer coating film of the present disclosure comprises a substrate, a clear layer laminated on the substrate, and a base layer disposed between the substrate and the clear layer and including one or more layers, the base layer including a layer having a low-temperature stress retention rate of 65% or less as measured by the following method. [Low temperature stress retention rate] When a tensile strain of 1% is applied to the base layer at a temperature of -20°C and held for 1,000 seconds, the maximum stress in the base layer is σ b0 , the stress in the base layer after holding for 1,000 seconds is σ b1 When the low-temperature residual stress is σ b1 / σ b0 It is calculated as follows.

[0011] The multilayer coating film of the present disclosure has good chipping resistance at low temperatures because it includes a layer with a low low-temperature stress residual rate between the substrate and the clear layer. Although the present disclosure should not be interpreted as being limited to a specific theory, the reason why the multilayer coating film of the present disclosure has good chipping resistance at low temperatures is thought to be as follows. That is, chipping is thought to occur when a small stone or the like hits the surface of the coating film and the coating film cannot absorb the impact, causing damage to the coating film surface. According to the study by the present inventors, the rigidity of the polymer chain increases in a low-temperature environment, and the hardness of the coating film increases, but at the same time, the brittleness is also thought to increase, and even if chipping is suppressed at room temperature, it does not necessarily mean that chipping is suppressed at low temperatures. The inventors focused on the process by which chipping occurs at low temperatures and discovered that by providing a layer inside the outermost layer (clear layer) that can relatively quickly relieve applied tensile stress even at low temperatures, impacts applied to the coating surface can be absorbed, resulting in good chipping resistance even at low temperatures, and thus completed the present invention.

[0012] In the present disclosure, "on the substrate" does not refer to an absolute direction such as vertically upward as determined by the direction of gravity, but rather refers to the direction toward the outside of the substrate between the outside and inside of the substrate with the surface of the substrate as the boundary. Therefore, "on the substrate" is a relative direction determined by the orientation of the substrate surface. In addition, "above" an element includes not only a position directly above the element (on), but also a position above the element, i.e., a position above another layer that is in contact with the element, or a position above with a gap (above).

[0013] (base material) Typically, the substrate preferably has a base layer including one or more layers selected from a metal layer, a plastic layer, and a foam layer.

[0014] Examples of metals forming the metal layer include iron, copper, aluminum, tin, zinc, and alloys thereof. The metal layer may be in the form of a plate or a molded product. Specific examples of the molded products include automobile bodies and parts such as passenger cars, trucks, motorcycles, and buses. The surface of the metal layer (preferably the surface of the metal layer on the base layer side) may be chemically treated in advance with a phosphate, a zirconium salt, a chromate, or the like.

[0015] Examples of the resin forming the plastic layer include polypropylene resin, polycarbonate resin, urethane resin, polyester resin, polystyrene resin, ABS resin, vinyl chloride resin, and polyamide resin. The foam layer can be a foam of the resin. The plastic layer or foam layer can be a plate or a molded product. Examples of the molded product include automobile parts such as spoilers, bumpers, mirror covers, grilles, and doorknobs.

[0016] The substrate layer may further have an electrodeposition coating layer. The electrodeposition coating layer is typically provided on the metal layer (preferably on the base layer side of the metal layer). Examples of the electrodeposition coating composition used to form such an electrodeposition coating layer include a cationic electrodeposition coating composition and an anionic electrodeposition coating composition.

[0017] The substrate layer may further include a primer layer. The primer layer is typically provided on the plastic layer or foam layer (preferably on the base layer side of the plastic layer or foam layer).

[0018] The substrate may further include an intermediate coating layer. The intermediate coating layer is preferably provided on the base layer.

[0019] The intermediate coating film is formed from an intermediate coating composition containing an intermediate coating film-forming resin, a color pigment, an extender pigment, etc. As the intermediate coating film-forming resin, the resins exemplified as the coating film-forming resin (A) used in the base coating composition described below can be used. As the intermediate coating film-forming resin used in the intermediate coating composition, from the viewpoint of various properties of the intermediate coating film, a combination of an acrylic resin and / or a polyester resin with an amino resin and / or an isocyanate is preferably used.

[0020] Examples of coloring pigments contained in the intermediate coating composition include pigments with no chroma, such as carbon black and titanium dioxide, and pigments with chroma to complement the hue of the base layer, etc. When the intermediate coating composition contains a pigment, the content of the pigment is preferably 0.1 parts by mass or more, preferably 150 parts by mass or less, more preferably 100 parts by mass or less, and even more preferably 50 parts by mass or less, per 100 parts by mass of the resin solids.

[0021] The thickness of the intermediate coating film is, for example, preferably 3 to 50 μm, and more preferably 5 to 30 μm.

[0022] The substrate is preferably a substrate layer only; or a laminate of a substrate layer and an intermediate coating layer. In one embodiment, the substrate layer preferably includes a metal layer, and more preferably may be a metal layer or a laminate of a metal layer and an electrodeposition coating layer. That is, the substrate is preferably a metal layer only; a laminate of a metal layer and an electrodeposition coating layer; or a laminate of a metal layer, an electrodeposition coating layer, and an intermediate coating layer.

[0023] (Base layer) The base layer is disposed between the substrate and the clear layer. The base layer includes one or more layers, and includes a layer (hereinafter also referred to as a "stress relaxation layer") having a low-temperature residual stress rate of 65% or less as measured by the following method. [Low temperature stress retention rate] When a tensile strain of 1% is applied to the base layer at a temperature of -20°C and held for 1,000 seconds, the maximum stress in the base layer is σ b0, the stress in the base layer after holding for 1,000 seconds is σ b1 When the low-temperature residual stress is σ b1 / σ b0 It is calculated as follows.

[0024] The low-temperature stress retention rate of the stress relaxation layer is preferably 60% or less, more preferably 55% or less, and may be 10% or more. When the low-temperature stress retention rate is in this range, the chipping resistance at low temperatures is better.

[0025] The number of layers of the base layer is preferably 1 or 2 or more, preferably 2 or more and 10 or less, more preferably 2 or more and 5 or less, and more preferably 2 or more and 3 or less.

[0026] In one embodiment, the number of base layers may be one, and the low temperature stress retention ratio of such base layer may be within the above range; in another embodiment, the number of base layers may be two or more, and the low temperature stress retention ratio of one of the layers may be within the above range; in yet another embodiment, the total number of base layers may be two or more, and the low temperature stress retention ratio of two or more or all of the layers may be within the above range.

[0027] When the base layer includes two or more layers, the arrangement of the stress relaxation layer is not particularly limited. The layer in contact with the base material may be the stress relaxation layer, and the layer in contact with the clear layer may be the stress relaxation layer. In addition, two base layers that do not correspond to the stress relaxation layer may be arranged above and below the stress relaxation layer, and two stress relaxation layers may be arranged above and below the layer that does not correspond to the stress relaxation layer.

[0028] The base layer may preferably be a cured product of a base coating composition containing a coating film-forming resin (A) and a pigment (B). When the base layer contains two or more layers, the base coating compositions forming the respective layers may be the same or different.

[0029] The above-mentioned coating film-forming resin (A) is a resin that can be the main component of the coating film, and preferably contains one or more selected from acrylic resin, urethane resin, polyester resin, polyether resin, polycarbonate resin and epoxy resin; more preferably contains one or more selected from acrylic resin, urethane resin, polyester resin, polyether resin and polycarbonate resin; further preferably contains one or more selected from acrylic resin and urethane resin; particularly preferably contains acrylic resin and urethane resin. Hereinafter, acrylic resin is also called acrylic resin (A1), and urethane resin is also called urethane resin (A2).

[0030] The acrylic resin (A1) is preferably a polymer of a mixture of ethylenic monomers (monomer mixture).

[0031] Examples of the ethylenic monomer include (meth)acrylic acid esters, polymerizable amide compounds, polymerizable aromatic compounds, polymerizable nitriles, α-olefins, vinyl esters, and dienes. In this specification, "(meth)acrylic" means "acrylic and / or methacrylic".

[0032] Examples of the (meth)acrylic acid ester include aliphatic (meth)acrylic acid esters such as methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and lauryl (meth)acrylate; aromatic acrylic acid esters such as phenyl (meth)acrylate; and alicyclic acrylic acid esters such as isobornyl (meth)acrylate, cyclohexyl (meth)acrylate, t-butylcyclohexyl (meth)acrylate, dicyclopentadienyl (meth)acrylate, and dihydrodicyclopentadienyl (meth)acrylate.

[0033] Examples of the polymerizable amide compound include (meth)acrylamide, N-methylol (meth)acrylamide, N-butoxymethyl (meth)acrylamide, N,N-dimethyl (meth)acrylamide, N,N-dibutyl (meth)acrylamide, N,N-dioctyl (meth)acrylamide, N-monobutyl (meth)acrylamide, N-monooctyl (meth)acrylamide, 2,4-dihydroxy-4'-vinylbenzophenone, N-(2-hydroxyethyl)acrylamide, and N-(2-hydroxyethyl)methacrylamide.

[0034] Examples of the polymerizable aromatic compound include styrene, α-methylstyrene, vinyl ketone, t-butylstyrene, parachlorostyrene, and vinylnaphthalene.

[0035] The polymerizable nitrile may, for example, be (meth)acrylonitrile.

[0036] The α-olefin includes ethylene, propylene, and the like.

[0037] Examples of the vinyl ester include vinyl acetate and vinyl propionate.

[0038] Examples of the diene include butadiene and isoprene.

[0039] The content of the units derived from the ethylenic monomer in the acrylic resin (A1) is preferably 50 mass% or more, more preferably 60 mass% or more, even more preferably 70 mass% or more, and is preferably 99 mass% or less, more preferably 90 mass% or less, even more preferably 85 mass% or less.

[0040] The acrylic resin (A1) preferably contains a unit derived from a monomer having an acid group, which gives the acrylic resin (A1) an acid group and can improve the water dispersibility of the acrylic resin (A1).

[0041] Examples of the monomer having an acid group include (meth)acrylic acid, acrylic acid dimer, 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-acryloyloxyethyl acid phosphate, and 2-acrylamido-2-methylpropanesulfonic acid, with (meth)acrylic acid and acrylic acid dimer being preferred.

[0042] The content of units derived from the monomer having an acid group in the acrylic resin (A1) is preferably 0.5% by mass or more, more preferably 1% by mass or more, even more preferably 2% by mass or more, and is preferably 15% by mass or less, more preferably 12% by mass or less, even more preferably 10% by mass or less.

[0043] The acrylic resin preferably contains units derived from a monomer having a hydroxyl group, which gives the acrylic resin (A1) a hydroxyl group and can improve the crosslinking property in the base coating composition.

[0044] Examples of the monomer having a hydroxyl group include hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxybutyl (meth)acrylate, allyl alcohol, (meth)acrylic alcohol, and an adduct of hydroxyethyl (meth)acrylate and ε-caprolactone, and among these, hydroxyethyl (meth)acrylate, hydroxybutyl (meth)acrylate, and an adduct of hydroxyethyl (meth)acrylate and ε-caprolactone are preferred.

[0045] The content of units derived from the monomer having a hydroxyl group in the acrylic resin (A1) is preferably 1 mass % or more, more preferably 3 mass % or more, even more preferably 5 mass % or more, and is preferably 30 mass % or less, more preferably 20 mass % or less, even more preferably 15 mass % or less.

[0046] The acrylic resin (A1) may contain a unit derived from a crosslinkable monomer. When the acrylic resin (A1) contains a unit derived from a crosslinkable monomer, it becomes easy to control the average particle size of the acrylic resin (A1) (for example, to 100 nm or less).

[0047] The crosslinkable monomer is a compound having two or more radically polymerizable unsaturated groups in one molecule. Examples of the crosslinkable monomer include bifunctional monomers such as divinylbenzene, ethylene glycol di(meth)acrylate, hexanediol di(meth)acrylate, polyethylene glycol di(meth)acrylate, allyl(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexanedi(meth)acrylate, neopentyl glycol di(meth)acrylate, pentaerythritol di(meth)acrylate, and divinylbenzene; triallyl cyanurate, pentaerythritol tri(meth)acrylate, and the like. Examples of the crosslinkable monomer include trifunctional or higher monomers such as trimethylolpropane tri(meth)acrylate, trimethylolpropane tri(meth)acrylate, and dipentaerythritol hexa(meth)acrylate, and allyl(meth)acrylate, ethylene glycol di(meth)acrylate, and divinylbenzene are preferred. One type of the crosslinkable monomer may be used, or two or more types may be used in combination.

[0048] The content of the units derived from the crosslinkable monomer in the acrylic resin (A1) is preferably 0.2% by mass or more, more preferably 0.5% by mass or more, and preferably 20% by mass or less. When the content of the units derived from the crosslinkable monomer is within the above range, it becomes easy to control the particle size of the acrylic resin (A1) (for example, to 100 nm or less).

[0049] The acid value of the acrylic resin (A1) is preferably 3 mgKOH / g or more, more preferably 7 mgKOH / g or more, and is preferably 100 mgKOH / g or less, more preferably 80 mgKOH / g or less.

[0050] The hydroxyl value of the acrylic resin (A1) is preferably 10 mgKOH / g or more, more preferably 20 mgKOH / g or more, and is preferably 180 mgKOH / g or less, more preferably 160 mgKOH / g or less.

[0051] The acid value and hydroxyl value of the acrylic resin (A1) can be calculated based on the composition of the monomer mixture.

[0052] From the viewpoint of mechanical properties, the glass transition temperature of the acrylic resin (A1) is preferably −20° C. or higher and preferably 80° C. or lower. The glass transition temperature of the acrylic resin (A1) can be calculated based on the FOX equation, and for the glass transition temperature of the homopolymer of each monomer contained in the monomer mixture forming the acrylic resin (A1), values ​​described in Polymer Handbook (4th edition, Wiley-Interscience, 1999) can be referenced.

[0053] The average particle size of the acrylic resin (A1) is preferably 300 nm or less, more preferably 150 nm or less, and even more preferably 100 nm or less, and is, for example, 20 nm or more, preferably 30 nm or more, and even more preferably 40 nm or more. The average particle size of the acrylic resin (A1) in the above range makes the obtained coating film have good transparency and light transmittance. The average particle size of the acrylic resin (A1) can be measured as a volume average value by dynamic light scattering.

[0054] The number average molecular weight of the acrylic resin (A1) is preferably 1,000 or more, more preferably 3,000 or more, and further preferably 6,000 or more, and the upper limit may be, for example, 300,000. When the acrylic resin (A1) contains a unit derived from a crosslinkable monomer, the number average molecular weight may be outside the above range.

[0055] In this specification, the number average molecular weight and the weight average molecular weight can be measured by gel permeation chromatography (GPC) using polystyrene as a standard sample.

[0056] The acrylic resin (A1) is preferably in the form of an emulsion.

[0057] The acrylic resin (A1) may be one type of acrylic resin or a mixture of two or more types of acrylic resins. Specifically, the acrylic resin (A1) may contain an acrylic resin (A1-1) present as an emulsion and another acrylic resin (A1-2).

[0058] The average particle size of the emulsion of the acrylic resin (A1-1) is preferably 300 nm or less, and the lower limit may be, for example, 50 nm or more. The average particle size of the emulsion can be measured as a volume average value by a dynamic light scattering method.

[0059] The acid value of the acrylic resin (A1-1) is preferably 3 to 50 mgKOH / g, more preferably 7 to 40 mgKOH / g, and the hydroxyl value of the acrylic resin (A1-1) is preferably 10 to 150 mgKOH / g, more preferably 20 to 100 mgKOH / g.

[0060] The acrylic resin (A1-2) has an acid value of preferably 10 to 100 mgKOH / g, more preferably 20 to 80 mgKOH / g, and a hydroxyl value of preferably 20 to 180 mgKOH / g, more preferably 30 to 160 mgKOH / g.

[0061] The content of the acrylic resin (A1-1) in the acrylic resin (A1) is preferably 50 mass% or more, more preferably 70 mass% or more, even more preferably 75 mass% or more, and is 100 mass% or less, preferably 99 mass% or less, more preferably 95 mass% or less, even more preferably 90 mass% or less.

[0062] The content of the acrylic resin (A1-2) in the acrylic resin (A1) is 0 mass% or more, preferably 1 mass% or more, more preferably 5 mass% or more, even more preferably 10 mass% or more, and is preferably 50 mass% or less, more preferably 30 mass% or less, even more preferably 25 mass% or less.

[0063] When the acrylic resin (A1) has an acid group, the acid group may be neutralized with a base. Neutralization with a base improves the dispersion stability of the acrylic resin (A1). In particular, from the viewpoint of dispersion stability, when the acrylic resin (A1) is an emulsion, it is preferable that the acrylic resin is neutralized with a base so that the pH is 5 to 10. Examples of the base include tertiary amines such as dimethanolamine and triethylamine.

[0064] The content of the acrylic resin (A1) in the solid content of the base coating composition is preferably 15% by mass or more, more preferably 20% by mass or more, and preferably 97% by mass or less, more preferably 80% by mass or less, and even more preferably 70% by mass or less. The content of the acrylic resin (A1) in the coating film-forming resin (A) is preferably 15% by mass or more, more preferably 20% by mass or more, and preferably 97% by mass or less, more preferably 80% by mass or less, and even more preferably 60% by mass or less.

[0065] In this specification, the solid content of a composition refers to the portion of the composition excluding the solvent such as the aqueous medium.

[0066] The acrylic resin (A1) can be produced by polymerizing the monomer mixture, preferably by emulsion polymerization of the monomer mixture. Specifically, the emulsifier is mixed in an aqueous medium, and the monomer mixture and the polymerization initiator are dropped under heating and stirring. The monomer mixture, emulsifier and water may be emulsified in advance and dropped into the aqueous medium. As the aqueous medium, the compounds exemplified below as the aqueous medium can be appropriately used.

[0067] Examples of the polymerization initiator include azo-based oily compounds such as azobisisobutyronitrile, 2,2'-azobis(2-methylbutyronitrile, 2,2'-azobis(2,4-dimethylvaleronitrile); azo-based aqueous compounds such as anionic 4,4'-azobis(4-cyanovaleric acid), 2,2-azobis(N-(2-carboxyethyl)-2-methylpropionamidine, and cationic 2,2'-azobis(2-methylpropionamidine); redox-based oily peroxides such as benzoyl peroxide, parachlorobenzoyl peroxide, lauroyl peroxide, t-butyl perbenzoate; and aqueous peroxides such as potassium persulfate and ammonium persulfate.

[0068] The amount of the polymerization initiator is generally preferably 0.1 to 5 mass %, more preferably 0.2 to 2 mass %, based on 100 parts by mass of the total monomer mixture.

[0069] The emulsifier may be any emulsifier commonly used by those skilled in the art, and is preferably a reactive emulsifier. Examples of the reactive emulsifier include Antox MS-60 (manufactured by Nippon Nyukazai Co., Ltd.), Eleminol JS-2 (manufactured by Sanyo Chemical Industries Co., Ltd.), Adeka Reasoap NE-20 (manufactured by Asahi Denka Co., Ltd.), and Aqualon HS-10 (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.).

[0070] The polymerization may be carried out in the presence of a chain transfer agent, such as a mercaptan compound such as lauryl mercaptan, or an α-methylstyrene dimer.

[0071] The polymerization temperature is, for example, 30 to 90° C., and when an azo-based initiator is used, it is preferably 60 to 90° C., and when a redox-based initiator is used, it is preferably 30 to 70. The reaction time is, for example, 1 to 8 hours.

[0072] The polymerization reaction may be a single-stage polymerization or a multi-stage polymerization. As a multi-stage polymerization, for example, it can be carried out in two stages. The two-stage polymerization is a polymerization method in which a part of the monomer mixture (monomer mixture 1) is first emulsion-polymerized, and the remainder of the monomer mixture (monomer mixture 2) is further added thereto to carry out emulsion polymerization.

[0073] For example, when two-stage polymerization is performed, it is preferable that the monomer mixture 1 contains a monomer having an amide group from the viewpoint of preventing compatibility with the clear coating film. In this case, it is even more preferable that the monomer mixture 2 does not contain a monomer having an amide group. Since the monomer mixture is a combination of the monomer mixtures 1 and 2, the requirements for the monomer mixture shown above are satisfied by the combination of the monomer mixtures 1 and 2.

[0074] The base coating composition preferably contains a urethane resin (A2), which increases the breaking energy of the base layer and makes it easier to absorb impact.

[0075] The urethane resin (A2) is preferably a reaction product of a polyol and a polyisocyanate, and may be a reaction product obtained by further reacting the reaction product of the polyol and the polyisocyanate with a chain extender and / or a terminal terminator.

[0076] The polyol includes polymer polyols, low molecular weight polyols (for example, polyols having a molecular weight of less than 500), polyols having a hydrophilic group, and the like. These may be used alone or in combination of two or more kinds.

[0077] Examples of the polymer polyol include polyether polyol, polyester polyol, polycarbonate polyol, polybutadiene polyol, polythioether polyol, and the like, with polyether polyol being preferred.

[0078] Examples of the polyether polyol include polyethylene glycol, polypropylene glycol, and polytetramethylene glycol.

[0079] Examples of the polyester polyol include a reaction product of a polycarboxylic acid with a polyester raw material polyol, a ring-opening polymer of ε-caprolactone, and copolymers thereof. Examples of the polycarboxylic acid include adipic acid, sebacic acid, itaconic acid, maleic anhydride, phthalic acid, isophthalic acid, and the like, and examples of the polyester raw material polyol include ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, tripropylene glycol, butylene glycol, neopentyl glycol, and the like.

[0080] The weight average molecular weight of the polymer polyol is, for example, 500 or more, preferably 700 or more, more preferably 1,000 or more, and is, for example, 10,000 or less, preferably 7,000 or less. The number of functional groups of the polymer polyol (the number of hydroxyl groups contained in one molecule) is 2 or more, preferably 4 or less, more preferably 3 or less.

[0081] Examples of the low molecular weight polyol include bifunctional or trifunctional or higher aliphatic diols such as ethylene glycol, propylene glycol, 1,4-butanediol, pentanediol, 3-methyl-1,5-pentanediol, 1,6-hexanediol, diethylene glycol, glycerin, and trimethylolpropane.

[0082] Examples of the hydrophilic group in the polyol having a hydrophilic group include anionic groups such as acid groups, cationic groups such as amino groups, and nonionic groups such as polyoxyalkylene groups, and polyols having an anionic group are preferred. By using a polyol having a hydrophilic group, the water dispersibility of the resulting urethane resin can be improved.

[0083] Examples of the polyol having an anionic group include known compounds (for example, the compounds described in JP-B-42-24192 and JP-B-55-41607), and specific examples thereof include dimethylolalkanoic acids such as dimethylolacetic acid, 2,2-dimethylolpropionic acid, and 2,2-dimethylolbutyric acid.

[0084] As the polyol having a cationic group, known compounds (for example, the compounds described in JP-B-43-0-76) can be used.

[0085] As the polyol having the nonionic group, a known compound (for example, the compound described in JP-B-48-41718) can be used. Specifically, a polyol having a polyoxyalkylene unit, an alkyl alcohol alkylene oxide adduct, etc. can be used.

[0086] The polyisocyanate is a compound having two or more isocyanate groups in one molecule, and examples of the polyisocyanate include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, a mixture of 2,4-tolylene diisocyanate and 2,6-tolylene diisocyanate, diphenylmethane-4,4'-diisocyanate, diphenylmethane-2,4'-diisocyanate, and diphenylmethane-4,4'-diisocyanate and diphenylmethane-2,4'-diisocyanate. Mixtures of anates, aromatic polyisocyanates such as naphthalene-1,5-diisocyanate, 3,3'-dimethyl-4,4'-biphenylene diisocyanate, xylylene diisocyanate, diphenylmethylmethane diisocyanate, tetramethylxylylene diisocyanate, 4,4'-dibenzyl diisocyanate, 1,3-phenylene diisocyanate; 1,3-cyclopentane diisocyanate, 1,4-cyclohexane diisocyanate, 1,2-cyclohexane diisocyanate, etc. Alicyclic polyisocyanates such as hydrogenated xylylene diisocyanate, dicyclohexylmethane diisocyanate, isophorone diisocyanate, norbornane diisocyanate, and isopropylidenecyclohexyl-4,4'-diisocyanate; aliphatic polyisocyanates such as tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, and trimethylhexamethylene diisocyanate; lysine ester triisocyanate, triisocyanate, and triisocyanate. triisocyanates such as triphenylmethane triisocyanate, 1,6,11-undecane triisocyanate, 1,8-diisocyanate-4,4'-isocyanate methyloctane, 1,3,6-hexamethylene triisocyanate, and bicycloheptane triisocyanate; and polymers of the above aromatic polyisocyanates, alicyclic polyisocyanates, and aliphatic polyisocyanates (e.g., adducts, biuret, isocyanurates, and uretdione).Among these, from the viewpoint of light resistance, aliphatic polyisocyanates, alicyclic polyisocyanates, and polymers of aliphatic polyisocyanates or alicyclic polyisocyanates are preferred.

[0087] The chain extender may be any compound having two or more active hydrogen groups in one molecule, and examples of the chain extender include low molecular weight polyols and polyamines.

[0088] Examples of the low molecular weight polyol as the chain extender include the same compounds as the low molecular weight polyols exemplified as the polyols. Examples of the polyamine include ethylenediamine, hexamethylenediamine, diethylenetriamine, hydrazine, xylylenediamine, isophoronediamine, etc.

[0089] The above-mentioned terminal terminator is preferably a compound having one active hydrogen group in one molecule or a monoisocyanate compound.

[0090] The compound having one active hydrogen group in one molecule may be a monoalcohol or a monoamine. The monoalcohol may be an alkyl alcohol such as methanol, butanol, or octanol; an alkyl alcohol alkylene oxide adduct, or the like. The monoamine may be an alkyl amine such as butylamine or dibutylamine.

[0091] Examples of the monoisocyanate compound include aliphatic monoisocyanates such as methyl isocyanate, ethyl isocyanate, propyl isocyanate, butyl isocyanate, and lauryl isocyanate; alicyclic monoisocyanates such as cyclohexyl isocyanate; and aromatic monoisocyanates such as phenyl isocyanate and tolylene isocyanate.

[0092] The glass transition temperature of the urethane resin (A2) is preferably −50° C. or lower, more preferably −55° C. or lower, and even more preferably −58° C. or lower, and is, for example, −100° C. or higher, preferably −90° C. or higher. The glass transition temperature of the urethane resin (A2) can be measured by differential scanning calorimetry.

[0093] The urethane resin (A2) may be dispersed in a part of the dispersion medium (C) described below.

[0094] As the urethane resin (A2), commercially available products such as the NeoRez series (Kusumoto Chemical Industries, Ltd.), the HUX series (ADEKA Corporation), the U-coat series, the Permalin series, and the Euprene series (all from Sanyo Chemical Industries, Ltd.) may be used.

[0095] From the viewpoint of increasing the breaking energy of the base layer and absorbing impact, the content of the urethane resin (A2) in the coating resin (A) may be 0% by mass or more, preferably 3% by mass or more and 80% by mass or less, more preferably 5% by mass or more and 75% by mass or less, and even more preferably 10% by mass or more and 70% by mass or less.

[0096] The coating resin (A) may further contain a melamine resin (A3). The melamine resin (A3) may act as a curing agent in the coating resin (A). The melamine resin (A3) may be water-soluble or water-insoluble.

[0097] The water tolerance of the melamine resin (A3) is preferably not less than 3.0. The water tolerance is an index for evaluating the degree of hydrophilicity, and a higher water tolerance indicates a higher hydrophilicity.

[0098] The water tolerance can be measured as the amount (mL) of ion-exchanged water added when 0.5 g of a sample and 10 mL of acetone are mixed and dispersed in a 100 mL beaker at 25°C and ion-exchanged water is added dropwise using a burette until the sample becomes cloudy.

[0099] The melamine resin (A3) is also preferably an alkyl-etherified melamine, and is preferably a melamine resin substituted with a methoxy group and / or a butoxy group.

[0100] Examples of the melamine resin (A3) include methyl etherified melamine (Cymel 325, Cymel 327, Cymel 370, Mycoat 723, etc. (manufactured by Allnex)), methyl ether and butyl etherified melamine (Cymel 202, Cymel 204, Cymel 232, Cymel 235, Cymel 236, Cymel 238, Cymel 254, Cymel 266, Cymel 267, etc. (manufactured by Allnex)); butyl etherified melamine (Mycoat 506 (manufactured by Allnex), U-Van 20N60, U-Van 20SE, etc. (manufactured by Mitsui Chemicals)). These may be used alone or in combination of two or more.

[0101] From the viewpoint of increasing the breaking energy of the base layer and absorbing impact, the content of the melamine resin (A3) in the solid content of the coating film-forming resin (A) is preferably less than 50 mass%, more preferably 35 mass% or less, and even more preferably 25 mass% or less, with the lower limit being 0 mass%. The solid content mass ratio ((A3) / (A2)) of the melamine resin (A3) to the urethane resin (A2) is preferably less than 7, more preferably 5 or less, even more preferably 3 or less, and is preferably 0.01 or more, more preferably 0.05 or more, and even more preferably 0.07 or more.

[0102] The total solids content of the acrylic resin (A1), urethane resin (A2) and melamine resin (A3) in the solids of the coating film-forming resin (A) is preferably 60 mass% or more, more preferably 70 mass% or more, and even more preferably 80 mass% or more, with the upper limit being 100 mass%.

[0103] The coating film-forming resin (A) may further contain other resins (A4) such as polyester resins, polyether resins, polycarbonate resins, etc., as necessary.

[0104] The polyester resin may be a reaction product of a polycarboxylic acid and a polyol; a ring-opening polymer of a lactone compound such as polycaprolactone; or a copolymer thereof. The polycarboxylic acid may be a hydroxy acid such as adipic acid, sebacic acid, isophthalic acid, or dimethylolpropionic acid, or an anhydride thereof. The polyol may be an aliphatic polyol such as ethylene glycol, butanediol, neopentyl glycol, or trimethylolpropane. The solid acid value of the polyester resin is preferably 20 to 80 mgkOH / g, and the number average molecular weight of the polyester resin is preferably 1,000 to 15,000.

[0105] Examples of the polyether resin include polyether polyols having oxyethylene units having 2 to 6 carbon atoms (preferably 2 to 4 carbon atoms) as repeating units, such as polyethylene glycol, polypropylene glycol, and polytetramethylene glycol, and copolymers thereof may also be used.

[0106] Examples of the polycarbonate resin include a reaction product of a polyhydric alcohol with phosgene, and an ester exchange product of a polyhydric alcohol with a carbonate compound.

[0107] The polyhydric alcohols include straight-chain dihydric alcohols, branched-chain dihydric alcohols, and trihydric or higher alcohols.

[0108] Examples of the linear dihydric alcohol include 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,8-octanediol, 1,9-nonanediol, and 1,10-decanediol.

[0109] Examples of the branched dihydric alcohol include 2-methyl-1,3-propanediol, 3-methyl-1,5-pentanediol, neopentyl glycol, 2,2-diethyl-1,3-propanediol, 2-butyl-2-ethyl-1,3-propanediol, 2-methyl-1,8-octanediol, 2,2,4-trimethyl-1,3-pentanediol, 2-ethyl-1,3-hexanediol, 1,4-cyclohexanedimethanol, and tricyclodecane dimethanol.

[0110] Examples of the trihydric or higher alcohol include glycerin, trimethylolethane, trimethylolpropane, a dimer of trimethylolpropane, and pentaerythritol.

[0111] The weight average molecular weight of the other resin (A4) is, for example, 500 to 10,000, preferably 1,000 to 10,000, and more preferably 2,000 to 6,000.

[0112] The content of the other resins in the coating film-forming resin (A) is, for example, 40 mass% or less, preferably 30 mass% or less, more preferably 20 mass% or less, and may be 0 mass% or more, 5 mass% or more, or 10 mass% or more.

[0113] The coating film-forming resin (A) may further contain other curing agents (A5). Examples of the other curing agents (A5) include blocked isocyanate compounds in which a blocking agent having an active hydrogen is added to a polyisocyanate such as trimethylene diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, isophorone diisocyanate, etc.; epoxy compounds; aziridine compounds; carbodiimide compounds; oxazoline compounds; metal ions, etc.

[0114] The coating film-forming resin (A) can be prepared by mixing the acrylic resin (A1), the urethane resin (A2), and, if necessary, the melamine resin (A3), other resins (A4), and other curing agents (A5).

[0115] In the above base coating composition, the solids content of the film-forming resin (A) is preferably 55 mass% or more, more preferably 65 mass% or more, even more preferably 70 mass% or more, and is preferably 95 mass% or less, more preferably 85 mass% or less, even more preferably 80 mass% or less, of the solids of the above base coating composition.

[0116] The pigment (B) preferably includes one or more pigments selected from a luster pigment (B1) and a color pigment (B2).

[0117] In one embodiment, the pigment (B) preferably contains a glittering pigment (B1). By containing the glittering pigment, design properties (particularly glittering properties) are exhibited.

[0118] The above-mentioned luster pigment is a pigment that can reflect light and can impart a specific luster to the coating film. Examples of the luster pigment include metals such as aluminum, copper, zinc, iron, nickel, and tin; alloys of the above-mentioned metals; metal oxides such as aluminum oxide; metal acid salt compounds such as mica (particularly interference mica pigments, white mica pigments, etc.); graphite, etc., and they may be used alone or in combination of two or more kinds.

[0119] From the viewpoint of glittering properties, the average particle size (D50) of the above glittering pigment is preferably from 2 to 50 μm, more preferably from 10 to 35 μm, and the average thickness is preferably from 0.1 to 5 μm.

[0120] The content of the above-mentioned shiny pigment in the entire base layer is preferably 0.1 mass% or more, more preferably 0.5 mass% or more, even more preferably 1 mass% or more, and is preferably 20 mass% or less, more preferably 15 mass% or less, and more preferably 12 mass% or less.

[0121] In one embodiment, the pigment (B) includes a color pigment (B2). By including the color pigment, a color can be imparted to the coating film. The color pigment (B2) may be an organic pigment, an inorganic pigment, or a mixture thereof.

[0122] Examples of the organic pigment include azo chelate pigments, insoluble azo pigments, condensed azo pigments, diketopyrrolopyrrole pigments, phthalocyanine pigments, indigo pigments, perinone pigments, perylene pigments, dioxane pigments, quinacridone pigments, isoindolinone pigments, and metal complex pigments.

[0123] Examples of the inorganic pigment include yellow lead, yellow iron oxide, red iron oxide, carbon black, and titanium dioxide.

[0124] Among them, the color pigment (B2) is preferably a phthalocyanine pigment, a diketopyrrolopyrrole pigment, a perylene pigment, or red iron oxide. By using these color pigments, a coating film having high saturation, high brightness, and excellent color depth can be formed.

[0125] The content of the color pigment (B2) is preferably 0.1 part by mass or more, more preferably 0.5 part by mass or more, and even more preferably 1 part by mass or more, relative to 100 parts by mass of the coating film-forming resin (A), and is preferably 15 parts by mass or less, more preferably 10 parts by mass or less, and even more preferably 8 parts by mass or less.

[0126] In the above base coating composition, when the base coating composition contains the luster pigment (B1) and the coloring pigment (B2), the mass ratio ((B1) / (B2)) of the luster pigment (B1) and the coloring pigment (B2) is preferably 0.8 or more, more preferably 1 or more, even more preferably 1.2 or more, and is preferably 5 or less, more preferably 3 or less, even more preferably 2 or less.

[0127] The pigment (B) may contain other pigments such as an extender pigment (B3).

[0128] The content of the pigment (B) is preferably 0.2 parts by mass or more, more preferably 1 part by mass or more, even more preferably 2 parts by mass or more, and even more preferably 3 parts by mass or more, per 100 parts by mass of the coating film-forming resin (A), and is preferably 35 parts by mass or less, preferably 25 parts by mass or less, even more preferably 20 parts by mass or less, and even more preferably 15 parts by mass or less.

[0129] The base coating composition preferably further comprises a dispersion medium (C). The dispersion medium (C) may be either an aqueous medium or a hydrophobic medium.

[0130] The aqueous medium includes water, a hydrophilic solvent, a mixture of water and a hydrophilic solvent, and the like, with water or a mixture of water and a hydrophilic solvent being preferred.

[0131] Examples of the hydrophilic solvent include alcohol solvents such as methanol, ethanol, n-propanol, and 2-propanol; ketone solvents such as acetone and methyl ethyl ketone; polyhydric alcohol solvents such as ethylene glycol, diethylene glycol, propylene glycol, polyalkylene glycol, and glycerin; and amide solvents such as N-methyl-2-pyrrolidone.

[0132] The water content in the aqueous medium is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more, with the upper limit being 100% by mass.

[0133] Examples of the hydrophobic medium include ether solvents such as ethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol mono-n-propyl ether, and ethyl carbitol.

[0134] In the above base coating composition, the content of the dispersion medium (C) is preferably 40 mass% or more, more preferably 50 mass% or more, even more preferably 55 mass% or more, and preferably 90 mass% or less, more preferably 80 mass% or less, even more preferably 85 mass% or less.

[0135] The base coating composition may further contain a pigment dispersant.

[0136] As the pigment dispersant, a resin having a pigment affinity portion and a hydrophilic portion can be used. The pigment affinity part and hydrophilic part may include, for example, nonionic, cationic, and anionic functional groups depending on the type of pigment, and the pigment dispersant may have two or more of the above functional groups in one molecule. The nonionic functional groups may include, for example, hydroxyl groups, amide groups, and polyoxyalkylene groups, and the cationic functional groups may include, for example, amino groups, imino groups, and hydrazino groups. The anionic functional groups may include, for example, carboxyl groups, sulfonic acid groups, and phosphoric acid groups.

[0137] Specific examples of the pigment dispersant include nonionic pigment dispersants and polymeric pigment dispersants.

[0138] Examples of the nonionic pigment dispersants include dispersants having an alkyl chain with 14 or more carbon atoms, preferably 14 to 30, and more preferably 16 to 25. The hydrophilic-lipophilic balance (HLB) of the nonionic pigment dispersants is preferably 16 or more, more preferably 16 to 20, and even more preferably 17 to 19. Examples of the nonionic pigment dispersants include polyoxyethylene stearyl ether, polyoxyethylene oleyl ether, polyoxyethylene 2-octyldodidecyl ether, and modified products thereof (sulfuric acid ester, phosphate ester, maleic acid ester modified products, etc.).

[0139] The polymer pigment dispersant is not particularly limited, but the following may be suitably used. (1) A comb-structured polymeric pigment dispersant having a pigment-affinity group in the main chain and / or in multiple side chains and having multiple side chains that constitute a solvation moiety. (2) A polymeric pigment dispersant having multiple pigment affinity moieties in the main chain, each of which is made up of a pigment affinity group. (3) A linear polymer pigment dispersant having a pigment affinity portion consisting of a pigment affinity group at one end of the main chain.

[0140] The pigment affinity group referred to here means a functional group having a strong adsorption force to the surface of the pigment, and examples thereof include, in organosols, tertiary amino groups, quaternary ammonium groups, heterocyclic groups having a basic nitrogen atom, hydroxyl groups, and carboxyl groups; and, in hydrosols, phenyl groups, lauryl groups, stearyl groups, dodecyl groups, and oleyl groups.

[0141] The comb-structured polymeric pigment dispersant (1) has a structure in which a main chain and / or a plurality of side chains having the pigment affinity group and a plurality of side chains constituting a solvation portion are bonded to the main chain, and these side chains are bonded to the main chain like the teeth of a comb. In this specification, the above structure is referred to as a comb structure. In the comb-structured polymeric pigment dispersant (1), the pigment affinity group is not limited to the end of the side chain, and may be present in a plurality of groups in the middle of the side chain or in the main chain. The solvation portion refers to a structure having affinity to a solvent. The solvation portion is composed of, for example, a water-soluble polymer chain, a lipophilic polymer chain, or the like.

[0142] The number of pigment affinity groups contained in the comb-structure polymer pigment dispersant (1) is preferably 2 or more, more preferably 25 or more, per molecule from the viewpoint of dispersion stability, and is preferably 3,000 or less, more preferably 1,500 or less, from the viewpoint of the viscosity of the base coating composition and the pigment dispersion described below.

[0143] The number of side chains constituting the solvated portion contained in the comb-structured polymer pigment dispersant (1) per molecule is preferably 2 or more, more preferably 5 or more, from the viewpoint of dispersion stability, and is preferably 1,000 or less, more preferably 500 or less, from the viewpoint of the viscosity of the base coating composition or the pigment dispersion described below.

[0144] The number average molecular weight of the comb-structured polymer pigment dispersant (1) is preferably 2,000 or more, more preferably 4,000 or more, from the viewpoint of dispersion stability, and is preferably 1,000,000 or less, more preferably 500,000 or less, from the viewpoint of the viscosity of the base coating composition and the pigment dispersion described later.

[0145] The polymeric pigment dispersant (2) having a plurality of pigment affinity moieties composed of pigment affinity groups in the main chain has a plurality of pigment affinity groups arranged along the main chain, and the pigment affinity groups are, for example, pendant on the main chain. In this specification, the pigment affinity moiety refers to a portion having one or more pigment affinity groups and functioning as an anchor for adsorption to the pigment surface.

[0146] The number of pigment-affinity groups in the polymeric pigment dispersant (2) is preferably 2 or more, more preferably 25 or more, per molecule from the viewpoint of dispersion stability, and is preferably 3,000 or less, more preferably 1,500 or less, from the viewpoint of the viscosity and saturation of the base coating composition and the pigment dispersion described below.

[0147] The number average molecular weight of the polymer pigment dispersant (2) is preferably 2,000 or more, more preferably 4,000 or more, from the viewpoint of dispersion stability, and is preferably 1,000,000 or less, more preferably 500,000 or less, from the viewpoint of the viscosity of the base coating composition and the pigment dispersion described later.

[0148] The linear polymer pigment dispersant (3) having a pigment affinity portion consisting of a pigment affinity group at one end of the main chain has a pigment affinity portion consisting of one or more pigment affinity groups at only one end of the main chain, but has sufficient affinity for the pigment surface.

[0149] The number of pigment affinity groups in the linear polymer pigment dispersant (3) is preferably 2 or more, more preferably 5 or more, per molecule from the viewpoint of dispersion stability, and is preferably 3,000 or less, more preferably 1,500 or less, from the viewpoint of the viscosity of the base coating composition and the pigment dispersion described below.

[0150] The number average molecular weight of the linear polymer pigment dispersant (3) is preferably 1,000 or more, more preferably 2,000 or more, from the viewpoint of dispersion stability, and is preferably 1,000,000 or less, more preferably 500,000 or less, from the viewpoint of the viscosity of the base coating composition and the pigment dispersion described later.

[0151] As the pigment dispersant, from the viewpoint of the transparency of the resulting coating film, the comb-structured polymer pigment dispersant (1) is more preferred.

[0152] As the pigment dispersant, commercially available products can also be used. Examples of such commercially available products include the following.

[0153] Dispex Ultra FA4404, Dispex Ultra FA4416, Dispex Ultra FA4425, Dispex Ultra FA4431, Dispex Ultra FA4437, Dispex Ultra FA4480, Dispex Ultra FA4483, Dispex Ultra PA4550, Dispex Ultra PA4560, Dispex Ultra PX4575, Dispex Ultra PX4585 (manufactured by BASF). TEGO Dispers 650, TEGO Dispers 651, TEGO Dispers 652, TEGO Dispers 655, TEGO Dispers 660C, TEGO Dispers 715W, TEGO Dispers 740W, TEGO Dispers 750W, TEGO Dispers 752W, TEGO Dispers 755W, TEGO Dispers 760W (all manufactured by Evonik). Solsperse 12000S, Solsperse 20000, Solsperse 27000, Solsperse 40000, Solsperse 41090, Solsperse 43000, Solsperse 44000, Solsperse 45000, Solsperse 46000, Solsperse 47000, Solsperse 53095, Solsperse 64000, Solsperse 65000, Solsperse 66000, Solsperse 67000, Solsperse WV400 (all manufactured by Lubrizol). Floren G-700AMP, Floren G-700DMEA, Floren GW-1500, Floren GW-1640 (all manufactured by Kyoeisha Chemical Co., Ltd.). Disparlon DA-703-50, Disparlon DA-7301, Disparlon DN-900 (all manufactured by Kusumoto Chemicals). ANTI-TERRA-250, DISPERBYK, DISPERBYK-102, DISPERBYK-180, DISPERBYK-184, DISPERBYK-185, DISPERBYK-187, DISPERBYK-190, DISPERBYK- 191, DISPERBYK-192, DISPERBYK-193, DISPERBYK-194N, DISPERBYK-198, DISPERBYK-199, DISPERBYK-2010, DISPERBYK-2012, DISPERBYK-2013, DISPERBYK-2015, DISPERBYK-2096 (manufactured by BYK).

[0154] The pigment dispersion may be used alone or in combination of two or more kinds.

[0155] The amount (solid content) of the pigment dispersant is preferably 50 to 300 parts by mass, more preferably 65 to 250 parts by mass, relative to 100 parts by mass of the pigment (B). By using the pigment dispersant in an amount within the above range, it is easy to obtain good pigment dispersion stability and good coating film properties.

[0156] The base coating composition may further contain a phosphoric acid group-containing organic compound. In particular, when the base coating composition contains a glittering pigment, the inclusion of the phosphoric acid group-containing organic compound makes it difficult for the grinding medium such as mineral spirits and the grinding aid such as oleic acid to peel off from the surface of the glittering pigment, and improves the dispersibility of the glittering pigment, thereby improving the coating film properties such as adhesion of the resulting coating film.

[0157] The phosphate group-containing organic compound may include a phosphate group-containing polymer having a phosphate value of 5 to 300 mgKOH / g and an alkyl phosphate ester having an alkyl group having a carbon number of 4 to 30. The phosphate group-containing organic compound may contain either one of the phosphate group-containing polymer and the alkyl phosphate ester, or may contain both.

[0158] The above-mentioned phosphate group-containing polymer is not particularly limited as long as the phosphate group value is in the range of 5 to 300 mgKOH / g, and conventionally known polymers can be used. Specific examples of the phosphate group-containing polymer include acrylic resins having phosphate groups, polyester resins having phosphate groups, polyether resins having phosphate groups, and epoxy resins having phosphate groups. Among the above-mentioned polymers containing phosphate groups, it is preferable to use acrylic resins from the viewpoint of performance such as weather resistance and water resistance. These polymers containing phosphate groups may be used alone or in combination of two or more kinds.

[0159] Particularly preferred examples of the phosphate group-containing polymer include phosphate group-containing acrylic resins and phosphorus ester type surfactants having polyalkylene oxide groups.

[0160] The phosphate group-containing acrylic resin can be produced, for example, by polymerizing only the phosphate group-containing monomer, or a mixture of the phosphate group-containing monomer and a monomer not containing a phosphate group, with the phosphate group-containing monomer being the essential component.

[0161] Examples of phosphate group-containing monomers include 2-acryloyloxyethyl acid phosphate, 2-(methacryloyloxy)ethyl phosphate (also known as acid phosphooxyethyl methacrylate, Phosmer M, manufactured by Unichemical Co., Ltd.), 3-chloro-2-acid phosphooxypropyl methacrylate, acid phosphooxypolyoxyethylene glycol monomethacrylate (Phosmer PE, manufactured by Unichemical Co., Ltd.), acid phosphooxypolyoxypropylene glycol monomethacrylate (Phosmer PP, manufactured by Unichemical Co., Ltd.), and vinyl phosphonic acid.

[0162] Examples of the monomer not containing a phosphoric acid group include the ethylenic monomers, monomers having an acid group, monomers having a hydroxyl group and crosslinkable monomers used in the production of the above acrylic resin (A1).

[0163] As the phosphorus ester type surfactant having the polyalkylene oxide group, commercially available products can be used, such as AQ-330 (manufactured by Kusumoto Chemical Industries, Ltd., phosphoric acid value 12 mg KOH / g), AQ-320 (manufactured by Kusumoto Chemical Industries, Ltd., phosphoric acid value 14 mg KOH / g), AQ-340 (manufactured by Kusumoto Chemical Industries, Ltd., phosphoric acid value 18 mg KOH / g), and BYK-111 (manufactured by BYK-Chemie, phosphoric acid value 120 mg KOH / g) and BYK-180 (manufactured by BYK-Chemie, phosphoric acid value 90 mg KOH / g), which are phosphoric acid ester type wetting and dispersing agents having polyalkylene oxide groups.

[0164] The number average molecular weight of the above phosphoric acid group-containing polymer is preferably 1000 to 50000. In this specification, the number average molecular weight is a value determined by a GPC method using polystyrene as the standard.

[0165] The phosphate group-containing polymer preferably has a phosphate group value of 5 to 300 mgKOH / g, more preferably 10 to 250 mgKOH / g. When the phosphate group value is in this range, both adhesion and water resistance can be achieved.

[0166] In the present disclosure, the phosphate value of the phosphate group-containing polymer can be calculated based on the definition of acid value in JIS K5601 2-1.

[0167] The alkyl phosphate ester is C 4-30 It is an alkyl phosphate ester having an alkyl group. 4-30 The alkyl phosphate ester having an alkyl group includes a monoalkyl phosphate ester, a dialkyl phosphate ester, and a mixture of a monoalkyl phosphate ester and a dialkyl phosphate ester. In a dialkyl phosphate ester, the two alkyl groups are preferably the same group.

[0168] C 4-30 Specific examples of alkyl phosphate esters having an alkyl group include, for example, butyl acid phosphate (a mixture of monobutyl ester and dibutyl ester), 2-ethylhexyl acid phosphate (a mixture of mono-2-ethylhexyl ester and di-2-ethylhexyl ester), isodecyl acid phosphate (a mixture of monoisodecyl ester and diisodecyl ester), dilauryl acid phosphate, lauryl acid phosphate (a mixture of monolauryl ester and dilauryl ester), tridecyl acid phosphate (a mixture of monoisodecyl ester and diisodecyl ester), dilauryl acid phosphate, lauryl acid phosphate (a mixture of monolauryl ester and dilauryl ester), tridecyl acid phosphate (a mixture of monoisodecyl ester and diisodecyl ester), dilauryl acid phosphate, tridecyl acid phosphate (a mixture of monoisodec ... Examples of the phosphate phosphate include monostearyl acid phosphate, distearyl acid phosphate, stearyl acid phosphate (a mixture of monostearyl ester and distearyl ester), isostearyl acid phosphate (a mixture of monoisostearyl ester and diisostearyl ester), oleyl acid phosphate (a mixture of monooleyl ester and dioleyl ester), and behenyl acid phosphate (a mixture of monobehenyl ester and dibehenyl ester).

[0169] When the base coating composition contains a phosphoric acid group-containing organic compound and a luster pigment, the amount of the phosphoric acid group-containing organic compound is preferably 0.1 to 50 parts by mass, more preferably 5 to 35 parts by mass, per 100 parts by mass of the luster pigment. When the amount of the phosphoric acid group-containing organic compound is within the above range, the dispersibility of the luster pigment is improved, and the resulting coating film is more likely to have excellent design and adhesion.

[0170] The above-mentioned base coating composition may further contain, as necessary, additives used in the coating field, such as surface conditioners, antioxidants, ultraviolet absorbers, defoamers, viscosity control agents, surfactants, etc.

[0171] By including the viscosity control agent, it is possible to prevent the coating layers from becoming intimately familiar with each other, and to ensure the ease of coating work. As the viscosity control agent, generally, a thixotropic agent can be used. Specific examples of the viscosity control agent include crosslinked or non-crosslinked resin particles; polyamide-based viscosity control agents such as swollen dispersions of fatty acid amides, amide-based fatty acids, and phosphates of long-chain polyaminoamides; polyethylene-based viscosity control agents such as colloidal swollen dispersions of polyethylene oxide; organic bentonite-based viscosity control agents such as organic acid smectite clay and montmorillonite; inorganic pigments such as aluminum silicate and barium sulfate; and flat pigments that exhibit viscosity depending on the shape of the pigment.

[0172] The base coating composition can be produced by mixing with stirring the above-mentioned film-forming resin (A), pigment (B), and the above-mentioned components which are used as required.

[0173] Prior to the production of the base coating composition, the film-forming resin (A) may be used in the preparation of the base coating composition as a dispersion in which it is dispersed in at least a part of the dispersion medium (C). When the film-forming resin (A) is present in the form of an emulsion or dispersion, it is possible to obtain a dispersion in which the film-forming resin (A) is dispersed in at least a part of the dispersion medium (C) by sequentially mixing and stirring the emulsion or dispersion.

[0174] In the above base coating composition, the solid content is preferably 10% by mass or more, more preferably 15% by mass or more, even more preferably 20% by mass or more, and preferably 60% by mass or less, more preferably 50% by mass or less, even more preferably 55% by mass or less.

[0175] The above pigment (B) may be dispersed together with at least a part of the dispersion medium (C) and a pigment dispersant, and the resulting pigment dispersion may be used in the preparation of the base coating composition.

[0176] The base layer can be typically formed by applying the base coating composition to form a coating film, and then heat-curing the coating film. In addition, when the base layer includes two or more layers, each layer may be heat-cured after application, or the next layer may be applied without heat-curing the applied layer, and the two or more layers may be heat-cured simultaneously. As an example, when the base layer includes two layers, the first base coating composition may be applied, the coating film may be heat-cured to form the first base layer, and then the second base coating may be applied on the first base layer, and the coating film may be heat-cured; the first base coating composition may be applied, the second base coating composition may be applied without heat-curing the coating film, and the first base coating film and the second base coating film may be simultaneously cured. In the case of applying the next layer without heat-curing the applied layer, after applying the base coating composition, the applied layer may be dried or preheated, if necessary, before applying the base coating composition of the next layer on the coating film.

[0177] Furthermore, the above-mentioned base coating film (the upper coating film in the case of multiple layers) may be heat-cured before forming the layer thereon (clear layer, etc.), or the clear coating composition described below may be applied onto the uncured base coating film (particularly the upper coating film) without heat-curing. In this case, after applying the base coating composition (particularly the upper coating composition), drying or preheating may be performed as necessary before applying the clear coating composition.

[0178] The application of the above-mentioned base coating composition (including multiple layers such as a first base coating composition, a second base coating composition, etc.) can be carried out by multi-stage coating using air electrostatic spray coating, preferably two-stage coating; or by a combination of air electrostatic spray coating and a rotary atomizing type electrostatic coater.

[0179] (Clear layer) The clear layer is a layer located on the surface side of the base layer in the multi-layer coating film, and is preferably the outermost layer of the multi-layer coating film. The clear layer may include two or more layers. When the clear layer includes two or more layers, one layer may be located closer to the substrate than a part of the layers included in the base layer.

[0180] The clear layer is preferably a harder layer than the stress relaxation layer, so that the stress relaxation layer can absorb impacts on the surface of the multilayer coating film, making it easier to suppress chipping.

[0181] For example, in one embodiment, when a tensile strain of 1% is applied to the clear layer and the base layer at a temperature of −20° C., the maximum stress σ c0 and the maximum stress in the base layer σ b0 Ratio to σ c0 / σ b0 may preferably be 1 or more. c0 / σ b0 When the stress relaxation layer has a thickness within this range, an impact on the surface of the multilayer coating film is more efficiently transmitted to and absorbed by the stress relaxation layer, making it easier to suppress chipping.

[0182] The clear layer typically contains a resin. Such resins are not particularly limited, and examples thereof include acrylic resins, polyester resins, urethane resins, and epoxy resins, and may be cured in combination with a curing agent having an isocyanate group, an epoxy group, or the like (also referred to as an "isocyanate curing agent" and an "epoxy curing agent", respectively).

[0183] The thickness of the above-mentioned clear layer is preferably 10 μm or more, more preferably 20 μm or more, from the viewpoint of ensuring the strength of the film itself, and is preferably 80 μm or less, more preferably 60 μm or less, from the viewpoint of suppressing defects such as popping or dripping during painting.

[0184] In a preferred embodiment, the clear layer can be formed as a cured product of a clear coating composition containing a resin such as an acrylic resin, a polyester resin, a urethane resin, or an epoxy resin, and a curing agent having an isocyanate group, an epoxy group, etc. The clear coating composition may be any of a solvent-based, water-based, or powder type.

[0185] Preferred examples of the above-mentioned solvent-based clear coating composition include, from the viewpoints of transparency, acid etching resistance, etc., a combination of an acrylic resin and / or a polyester resin with an amino resin and / or an isocyanate curing agent; or a composition containing an acrylic resin and / or a polyester resin having a carboxylic acid / epoxy curing system and a solvent.

[0186] An example of the water-based clear coating composition is a composition containing a resin used in the solvent-based clear coating composition described above, which is neutralized with a base such as a tertiary amine (e.g., dimethylethanolamine, triethylamine, etc.) to make it water-based, and an aqueous medium. As the aqueous medium, the compounds exemplified as the aqueous medium that can be used in the base coating composition can be appropriately used.

[0187] The above-mentioned solvent-based clear coating composition and water-based clear coating composition preferably contain the above-mentioned viscosity control agent in order to ensure ease of coating work.

[0188] Examples of the powder-type clear coating composition include powder coating compositions used in the coating field, such as thermoplastic powder coating compositions, thermosetting powder coating compositions, etc. Among these, thermosetting powder coating compositions such as epoxy-based, acrylic-based and polyester-based compositions are preferred from the viewpoint of coating film properties.

[0189] The above-mentioned clear coating composition can be applied by a coating method according to the coating form of the clear coating composition used.

[0190] A clear layer can be formed by heat-curing the uncured clear coating film obtained by applying the above-mentioned clear coating composition. When the clear coating composition is applied onto an uncured base layer (particularly the second base layer), both of these uncured coating films are heat-cured by heating. From the viewpoint of curability and physical properties of the resulting multi-layer coating film, the heat-curing temperature is preferably 80 to 180°C, more preferably 120 to 160°C, and the heat-curing time can be set arbitrarily, but for example, when the heat-curing temperature is 120 to 160°C, it is preferably 10 to 30 minutes.

[0191] In a preferred embodiment, when the multi-layer coating film has two base layers (a first base layer and a second base layer) and a clear coating film, the following method can be mentioned as a specific example of the method for forming the multi-layer coating film. (1) A method in which a first base coating composition is applied to form an uncured first base layer, then a second base coating composition is applied to form an uncured second base layer, and then a clear coating composition is applied to form an uncured clear coating film, and the resulting three layers are heated and cured at the same time. (2) A method in which a first base coating composition is applied to form an uncured first base layer, then a second base coating composition is applied to form an uncured second base layer, and the two layers obtained are then heat-cured at the same time. After heat-curing, a clear coating may be provided, if necessary. (3) A method in which a first base coating composition is applied to form an uncured first base coating film, then a clear coating composition is applied to form an uncured clear coating film, and the two resulting layers are heat-cured at once, after which a second base coating composition is applied to form an uncured second base coating film, then a clear coating composition is applied to form an uncured clear coating film, and the two resulting layers are heat-cured at once.

[0192] The multi-layer coating film may further have other layers such as a chipping primer layer in addition to the substrate, base layer, and clear layer. The other layers may be present at any position, such as between the substrate and base layer, or between the base layer and clear layer.

[0193] In the above multilayer coating film, the total film thickness of the base layer and the clear layer is preferably 20 μm or more, more preferably 30 μm or more, from the viewpoint of ensuring the strength of the film itself, and is preferably 300 μm or less, more preferably 250 μm or less, from the viewpoint of maintaining the film properties during cooling and heating cycles, etc.

[0194] The multilayer coating film of the present invention has good chipping resistance at low temperatures and can be suitably used for painting automobile bodies and the like. EXAMPLES

[0195] The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto.

[0196] (Production Example 1) Production of acrylic resin emulsion (film-forming resin) 126.5 parts by mass of deionized water was added to the reaction vessel, and the temperature was raised to 80° C. while mixing and stirring in a nitrogen stream. Next, 100 parts by mass of a monomer mixture of 27.61 parts by mass of methyl acrylate, 53.04 parts by mass of ethyl acrylate, 4.00 parts by mass of styrene, 9.28 parts by mass of 2-hydroxyethyl methacrylate, 3.07 parts by mass of methacrylic acid, and 3.00 parts by mass of allyl methacrylate, 0.7 parts by mass of Aqualon HS-10 (polyoxyethylene alkylpropenyl phenyl ether sulfate, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), 0.5 parts by mass of Adeka Reasoap NE-20 (α-[1-[(allyloxy)methyl]-2-(nonylphenoxy)ethyl]-ω-hydroxyoxyethylene, manufactured by Asahi Denka Co., Ltd.), and 80 parts by mass of a monomer emulsion, 0.3 parts by mass of ammonium persulfate, and an initiator solution consisting of 10 parts by mass of deionized water were dropped into the reaction vessel in parallel over a period of 2 hours. After the dropwise addition, the mixture was aged at the same temperature for 2 hours.Then, the mixture was cooled to 40°C and filtered through a 400 mesh filter, after which 70 parts by mass of deionized water and 0.32 parts by mass of dimethylaminoethanol were added to adjust the pH to 6.5, to obtain a single-layer acrylic resin emulsion 1 having an average particle size of 88 nm, a non-volatile content of 25% by mass, an acid value of the solid content of 20 mgKOH / g, and a hydroxyl value of the solid content of 40 mgKOH / g.

[0197] (Production Example 2) Production of water-soluble acrylic resin 23.89 parts by mass of tripropylene glycol methyl ether and 16.11 parts by mass of propylene glycol methyl ether were added to the reaction vessel, and the mixture was heated to 105° C. while being mixed and stirred in a nitrogen stream. Next, a monomer mixture containing 13.1 parts by mass of methyl methacrylate, 68.4 parts by mass of ethyl acrylate, 11.6 parts by mass of 2-hydroxyethyl methacrylate, and 6.9 parts by mass of methacrylic acid was prepared, and an initiator solution consisting of 100 parts by mass of the monomer mixture, 10.0 parts by mass of tripropylene glycol methyl ether, and 1 part by mass of tertiary butyl peroxy 2-ethylhexanoate was dropped into the reaction vessel in parallel over 3 hours. After the dropwise addition, the mixture was aged at the same temperature for 0.5 hours.

[0198] Further, an initiator solution consisting of 5.0 parts by mass of tripropylene glycol methyl ether and 0.3 parts by mass of tertiary butyl peroxy 2-ethylhexanoate was added dropwise to the reaction vessel over a period of 0.5 hours. After completion of the addition, the mixture was aged at the same temperature for 2 hours.

[0199] After 16.1 parts by mass of the solvent was distilled off at 110°C under reduced pressure (70 torr) using a solvent remover, 204 parts by mass of deionized water and 7.1 parts by mass of dimethylaminoethanol were added to obtain a water-soluble acrylic resin solution. The non-volatile content of the obtained water-soluble acrylic resin solution was 30% by mass, the solid content acid value was 40 mgKOH / g, the solid content hydroxyl value was 50 mgKOH / g, and the viscosity was 140 poise (E-type viscometer 1 rpm / 25°C).

[0200] Example 1 Preparation of the base coating composition As the acrylic resin (A1), 45.0 parts by mass of acrylic resin (A1-1), as the melamine resin (A3), 28.0 parts by mass of melamine resin (A3-1), as the other resin (A4), 6.0 parts by mass of resin (A4-1), 21.0 parts by mass of resin (A4-2), 17.9 parts by mass of pigment (B-1), 5 parts by mass of the phosphate group-containing organic compound of Production Example 3 as a pigment dispersant, 0.4 parts by mass of lauryl acid phosphate, 50 parts by mass of butyl cellosolve as a hydrophilic solvent, Noigen EA-207D (amphiphilic compound, manufactured by Daiichi Kogyo Seiyaku Co., Ltd., number average molecular weight 4,200, solid content 55% by mass), A base coating composition with a solids concentration of 25% by mass and a pigment concentration of 7.8% by mass was prepared by uniformly dispersing 5.5 parts by mass (3 parts by mass in terms of solids content), 3 parts by mass of linoleic acid (manufactured by Kishida Chemical Co., Ltd.), and 1.0 part by mass of Adekanol UH-814N (urethane association type viscosity agent, active ingredient 30% by mass, manufactured by ADEKA Corporation, product name) as a viscosity adjuster, adding dimethylaminoethanol to adjust the pH to 8.1, and diluting with deionized water.

[0201] Multi-layer coating production <Multi-layer coating film formation method> A zinc phosphate-treated dull steel plate 0.8 mm thick, 30 cm long and 40 cm wide was electrodeposited with cationic electrodeposition paint "Power Top U-50" (manufactured by Nippon Paint Co., Ltd.) so that the dry film thickness was 20 μm, and the plate was baked at 160°C for 30 minutes. A pre-diluted gray undercoat paint "Orga OP-30" (polyester-melamine paint manufactured by Nippon Paint Co., Ltd.) was applied to the plate using a No. 4 Ford cup so that the discharge time measured at 20°C was 25 seconds, and then the plate was air-sprayed in two stages so that the dry film thickness was 35 μm, and the plate was baked at 140°C for 30 minutes.

[0202] After cooling, the base coating composition was applied in two stages using a Cartridge Bell at room temperature of 23°C and humidity of 68% to a dry film thickness of 5μm. Between the two applications, an interval of 1 minute 30 seconds was allowed for setting. After the second application, an interval of 1 minute 30 seconds was allowed for setting. Then, the plate was preheated at 80°C for 5 minutes to form an uncured base coating film.

[0203] The resulting coated plate was then cooled to room temperature, and a clear coating of Macflow-O-1810 (a solvent-based clear coating made by Nippon Paint Co., Ltd.) was applied in one stage to a dry film thickness of 35 μm, and the plate was left to set for 7 minutes. The coated plate was then baked in a dryer at 140°C for 30 minutes to obtain a multi-layer coating. The coating appearance was good in both cases.

[0204] Examples 2 to 9, Comparative Examples 1 to 3 A multilayer coating film was formed in the same manner as in Example 1, except that the acrylic resin (A1), the urethane resin (A2), the melamine resin (A3), the other resin (A4) and the polyester resin (A5) in Example 1 were changed as shown in Table 1.

[0205] The materials used in the examples and comparative examples are as follows. Acrylic resin (A1) (A1-1): Mitsubishi Rayon Co., Ltd., "Dianal HR-2050", acrylic resin, solid acid value 24 mg KOH / g, solid hydroxyl value 60 mg KOH / g, glass transition temperature 10°C, number average molecular weight 5280, solid concentration 55% by mass (A1-2): Acrylic resin emulsion of Production Example 1, solid content acid value 20 mg KOH / g, solid content hydroxyl value: 40 mg KOH / g, glass transition temperature: 0°C, non-volatile content 25 mass% (A1-3): Water-soluble acrylic resin of Production Example 2, solid content acid value 40 mgKOH / g, solid content hydroxyl value 50 mgKOH / g, viscosity 140 poise (B-type viscometer 1 rpm / 25°C), glass transition temperature: 10°C, number average molecular weight: 7000, non-volatile content 30% by mass Urethane resin (A2) (A2-1): Avecia Corporation's "Neolet's R-9603" (polycarbonate-based urethane emulsion resin, non-volatile content 33% by mass) Melamine resin (A3) (A3-1): U-BAN 20N60 (butylated melamine resin manufactured by Mitsui Chemicals, solid content 60% by mass) (A3-2): Cymel 327 (mixed alkylated melamine resin, manufactured by Allnex, solid content 90% by mass) Other resins (A4) (A4-1): EPO-150 (manufactured by Nippon Steel Chemical Co., Ltd., "EP-0150", epoxy resin, acid value 140 mg KOH / g, solid content concentration 51% by mass) (A4-2): T5650E (Asahi Kasei Chemicals Corporation, "Duranol T5650E", polyalkylene carbonate diol, hydroxyl value 225 mg KOH / g, number average molecular weight 500, solid content concentration 100% by mass) (A4-3): Primepol PX-1000 (bifunctional polyether polyol manufactured by Sanyo Chemical Industries, Ltd., number average molecular weight 400, hydroxyl value 278 mg KOH / g, solid content concentration 100 mass%, primary / secondary hydroxyl value ratio = 63 / 37) Polyester resin (A5) (A5-1): R-4170 (manufactured by R-4170 Co., Ltd., "R-4170 varnish", polyester resin, acid value 8.7 mg KOH / g, hydroxyl value 210 mg KOH / g, number average molecular weight 1310, solid content concentration 79% by mass) Pigment (B) (B-1) Z0684 (manufactured by Toyo Aluminum Co., Ltd., "Aluminum Paste Z0684N", photoluminescent pigment, average particle size 12 μm, active ingredient 70% by mass)

[0206] The multi-layer coating films obtained in the above Examples and Comparative Examples were subjected to the following measurements.

[0207] (Measurement of low-temperature stress retention rate) The base coating composition in the examples was applied in two stages on a polypropylene film (polypropylene plate, manufactured by TP Giken Co., Ltd.) using a "cartridge bell" so that the dry film thickness was 5 μm under conditions of room temperature 23° C. and humidity 68%. Between the two applications, an interval of 1 minute 30 seconds was set. After the second application, an interval of 1 minute 30 seconds was taken and setting was performed. Then, preheating was performed at 80° C. for 5 minutes. Next, baking was performed in a dryer at 140° C. for 30 minutes to obtain a coating film. Next, the temperature was lowered to room temperature (25° C.) at a temperature drop rate of 10° C. / min.

[0208] Next, the base coating film was peeled off from the polypropylene film and molded into a shape conforming to JIS K7161 to obtain a test piece (film length 50 mm). The test piece was set in an autograph (Shimadzu Corporation, "Autograph ACS-X") and cooled from room temperature (25°C) to -20°C at a temperature drop rate of 5°C / min. Next, at -20°C, the test piece was given a 1% strain (0.5 mm) at a tensile speed of 50 mm / sec and held for 1,000 seconds. The stress change from the start of tension was measured, and the maximum stress was set to σ0, and the stress 1,000 seconds after the 1% strain was given to σ1 was calculated as the residual stress rate σ1 / σ0.

[0209] (Chipping area measurement) The test plates having the multilayer coating film obtained in each of the Examples and Comparative Examples were subjected to a stone chipping test using a Gravello tester KSS-1 (manufactured by Suga Test Instruments, diamond shot type) under the following conditions. <Test conditions> Stone size: 6~8mm Stone quantity: 0.7~0.8g / piece Distance: 35cm Shot speed: 100km / h Shot angle: 25° Test temperature: -20℃

[0210] The area of ​​the coating film peeled off due to the collision was measured using an image processor, and the average value (average value of 10 samples for each) was calculated. The chipping resistance was evaluated according to the following three-level scale. ◎(Excellent): Peeling area 2.5mm 2 less than ○(Good): Peeling area 2.5mm 2 More than 3mm 2 less than △(Poor): Peeling area 3mm 2 End

[0211] [Table 1]

[0212] Examples 1 to 9 are examples of the present disclosure, and exhibited good chipping resistance at low temperatures. In Comparative Examples 1 to 3, the low-temperature residual stress rate of the resulting coating film was less than 65%, and the chipping resistance at low temperature (-20°C) was poor.

Claims

1. A substrate; A clear layer laminated on the substrate; a base layer disposed between the substrate and the clear layer, the base layer including one or more layers; The multi-layer coating film, wherein the base layer includes a layer having a low-temperature stress retention rate of 65% or less as measured by the following method. [Low temperature residual stress rate] When a tensile strain of 1% is applied to the base layer at a temperature of -20°C and held for 1,000 seconds, the maximum stress in the base layer is σ ｂ０ , the stress in the base layer after holding for 1,000 seconds is σ ｂ１ When the low-temperature residual stress is σ ｂ１ / σ ｂ０ It is calculated as follows.

2. The multi-layer coating according to claim 1 , wherein the base layer comprises two or more layers.

3. When a tensile strain of 1% is applied to the base layer and the clear layer at a temperature of −20° C. and maintained for 1,000 seconds, the maximum stress σ in the clear layer is ｃ０ and the maximum stress in the base layer σ ｂ０ Ratio σ ｃ０ / σ ｂ０ The multilayer coating film according to claim 1 or 2, wherein is 1 or more.

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