Multilayer coating film

Abstract

The purpose of the present disclosure is to provide a multilayer coating film having satisfactory chipping resistance at low temperatures (e.g., around -20°C).　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 60% 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.

Description

Multi-layer coating

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

[0002] On coated objects such as automobile bodies, multilayer coatings are formed to impart corrosion resistance, chipping resistance, design properties, scratch resistance, etc. For example, a multilayer coating is formed by forming an intermediate coating, a base coating, a clear coating, and, if necessary, a chipping primer layer, etc. on a steel plate that has been subjected to a rust prevention treatment such as electrodeposition coating. Chipping is damage such as cracks and peeling that can occur when a pebble or the like hits the painted surface of the outer panel of an automobile. When chipping occurs, water or the like can seep in through the chipped area, which can cause rust or the like on the base of the outer panel.

[0003] To address chipping, improvements to the undercoat coating and research into anti-chipping primers have been conducted.

[0004] Patent Document 1 describes a chipping-resistant coating method that involves applying and baking a thermosetting powder coating that produces a cured, isolated coating film with a shrinkage stress of 100 kg / cm2 or less when the temperature is lowered from 130°C to 40°C and 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 color pigment, and an organic solvent, in which the acrylic polyol has a hydroxyl value of 40 to 120, contains a graft moiety 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 / cm2.

[0006] JP-A-58-196872 JP-A-11-228904

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

[0008] The present disclosure includes the following aspects. [1] A multilayer coating film comprising: 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, wherein the base layer includes a layer having a low-temperature stress retention rate of 60% 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 maintained for 1,000 seconds, the maximum stress in the base layer is σb0, and the stress in the base layer after maintaining the temperature for 1,000 seconds is σb1, where σb1 is the stress in the base layer. [2] The multilayer coating film according to [1], wherein the base layer includes two or more layers. [3] The multilayer coating film according to [1] or [2], wherein when a tensile strain of 1% is applied to each of the base layer and the clear layer at a temperature of -20°C and maintained for 1,000 seconds, the ratio σc0 / σb0 of the maximum stress σc0 in the clear layer to the maximum stress σb0 in the base layer is 1 or more.

[0009] According to the present disclosure, a multi-layer coating film having good chipping resistance at low temperatures can be provided.

[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 60% 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 σb0, and the stress in the base layer after holding for 1,000 seconds is σb1, and the low-temperature stress retention rate is calculated as σb1 / σb0.

[0011] The multilayer coating film of the present disclosure includes a layer with a low low-temperature stress retention rate between the substrate and the clear layer, and therefore has good chipping resistance at low temperatures. While the present disclosure should not be interpreted as being limited to a particular 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: It is believed that chipping occurs when a small stone or the like strikes the surface of the coating film and the coating film is unable to fully absorb the impact, causing damage to the coating film surface. According to the inventors' studies, in low-temperature environments, the rigidity of polymer chains increases, increasing the hardness of the coating film, but at the same time, it is thought that brittleness also increases. Therefore, even if chipping is suppressed at room temperature, it does not necessarily mean that chipping will be 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 film 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 outward direction 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. Furthermore, "on" with respect to 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] (Substrate) The substrate preferably has a base layer that typically includes one or more layers selected from a metal layer, a plastic layer, and a foam layer.

[0014] Examples of metals that form 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 product 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 facing the base layer) may be previously chemically treated with a phosphate, zirconium salt, chromate, or the like.

[0015] Examples of resins that form 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 above resin. The plastic layer or foam layer can be in the form of a plate or a molded product. Examples of the molded product include automotive parts such as spoilers, bumpers, mirror covers, grilles, and door knobs.

[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 electrodeposition coating compositions used to form such an electrodeposition coating layer include cationic electrodeposition coating compositions and anionic electrodeposition coating compositions.

[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 have an intermediate coating layer, which is preferably provided on the substrate 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. The intermediate coating film-forming resin can be any of the resins exemplified as the film-forming resin (A) used in the base coating composition described below. From the viewpoint of the performance 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 as the intermediate coating film-forming resin used in the intermediate coating composition.

[0020] Examples of coloring pigments contained in the intermediate coating composition include pigments with no saturation, such as carbon black and titanium dioxide, and pigments with saturation to complement the hue of the base layer. When the intermediate coating composition contains a pigment, the content of the pigment is preferably 0.1 part 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 resin solids.

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

[0022] The substrate is preferably a substrate layer alone, 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 alone, 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, including a layer (hereinafter also referred to as a "stress relaxation layer") having a low-temperature stress retention rate of 60% 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 σb0, and the stress in the base layer after holding for 1,000 seconds is σb1, and the low-temperature stress retention rate is calculated as σb1 / σb0.

[0024] The low-temperature stress retention rate of the stress relaxation layer is preferably 55% or less, more preferably 50% or less, and may be 10% or more. When the low-temperature stress retention rate is in this range, chipping resistance at low temperatures is better.

[0025] The number of the base layers 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 rate of such base layer may be within the above-mentioned range; in another embodiment, the number of base layers may be two or more, and the low-temperature stress retention rate of one of the layers may be within the above-mentioned range; in yet another embodiment, the total number of base layers may be two or more, and the low-temperature stress retention rates of two or more or all of the layers may be within the above-mentioned 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 substrate may be the stress relaxation layer, or 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, or 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 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 film-forming resin (A) is a resin that can be the main component of a 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 will also be referred to as acrylic resin (A1), and urethane resin will also be referred to as 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, dienes, etc. In this specification, "(meth)acrylic" means "acrylic and / or methacrylic".

[0032] Examples of the (meth)acrylic acid esters 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] Examples of the polymerizable nitrile include (meth)acrylonitrile.

[0036] Examples of the α-olefin include ethylene and propylene.

[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% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, and is preferably 99% by mass or less, more preferably 90% by mass or less, even more preferably 85% by 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 the 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, and even more preferably 2% by mass or more, and is preferably 15% by mass or less, more preferably 12% by mass or less, and 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, thereby improving the crosslinkability of 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 hydroxyethyl (meth)acrylate, hydroxybutyl (meth)acrylate, and an adduct of hydroxyethyl (meth)acrylate and ε-caprolactone are preferred.

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

[0046] The acrylic resin (A1) may contain units derived from a crosslinkable monomer, which makes it 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; and trifunctional or higher functional monomers such as triallyl cyanurate, pentaerythritol tri(meth)acrylate, trimethylolpropane tri(meth)acrylate, and dipentaerythritol hexa(meth)acrylate. Of these, allyl (meth)acrylate, ethylene glycol di(meth)acrylate, and divinylbenzene are preferred. One type of 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) or the like 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. When the average particle size of the acrylic resin (A1) is within the above range, the transparency and light transmittance of the resulting coating film are good. The average particle size of the acrylic resin (A1) can be measured as a volume average value by a dynamic light scattering method.

[0054] The number average molecular weight of the acrylic resin (A1) is preferably 1,000 or more, more preferably 3,000 or more, and even more preferably 6,000 or more, and the upper limit may be, for example, 300,000. When the acrylic resin (A1) contains units 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 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 an emulsion.

[0057] The acrylic resin (A1) may be a single acrylic resin or a mixture of two or more 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 dynamic light scattering.

[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 acid value of the acrylic resin (A1-2) is preferably 10 to 100 mgKOH / g, more preferably 20 to 80 mgKOH / g, and the hydroxyl value of the acrylic resin (A1-2) is 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% by mass or more, more preferably 70% by mass or more, even more preferably 75% by mass or more, and is 100% by mass or less, preferably 99% by mass or less, more preferably 95% by mass or less, even more preferably 90% by mass or less.

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

[0066] The acrylic resin (A1) can be produced by polymerizing the monomer mixture, preferably by emulsion polymerization of the monomer mixture. Specifically, an emulsifier is mixed into an aqueous medium, and the monomer mixture and a polymerization initiator are added dropwise under heating and stirring. The monomer mixture, emulsifier, and water may be pre-emulsified and then added dropwise to the aqueous medium. As the aqueous medium, compounds exemplified below as aqueous media can be used as appropriate.

[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% by mass, more preferably 0.2 to 2% by 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, such as Antox MS-60 (manufactured by Nippon Nyukazai Co., Ltd.), Eleminol JS-2 (manufactured by Sanyo Chemical Industries, Ltd.), Adeka Reasoap NE-20 (manufactured by Asahi Denka Co., Ltd.), and Aqualon HS-10 (manufactured by Dai-ichi 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 α-methylstyrene dimer.

[0071] The polymerization temperature is, for example, 30 to 90° C., preferably 60 to 90° C. when an azo initiator is used, and preferably 30 to 70° C. when a redox initiator is used. 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. Multi-stage polymerization can be carried out, for example, in two stages. Two-stage polymerization is a polymerization method in which a portion of the monomer mixture (monomer mixture 1) is first emulsion-polymerized, and then the remainder of the monomer mixture (monomer mixture 2) is further added to the emulsion-polymerized monomer mixture.

[0073] For example, when two-stage polymerization is performed, it is preferable that Monomer Mixture 1 contains a monomer having an amide group in order to prevent compatibility with the clear coating film. In this case, it is even more preferable that Monomer Mixture 2 does not contain a monomer having an amide group. Note that since the combination of Monomer Mixtures 1 and 2 constitutes the above-mentioned monomer mixture, the combination of Monomer Mixtures 1 and 2 satisfies the requirements for the above-mentioned monomer mixture.

[0074] The base coating composition preferably contains a urethane resin (A2). By containing the urethane resin (A2), the breaking energy of the base layer is increased, making 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 a polyol and a polyisocyanate with a chain extender and / or a terminal terminator.

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

[0077] Examples of the polymer polyol include polyether polyol, polyester polyol, polycarbonate polyol, polybutadiene polyol, and polythioether polyol, 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 polymerization product 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. 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 functional 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 anionic groups are preferred. Use of a polyol having a hydrophilic group can improve the water dispersibility of the resulting urethane resin.

[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, compounds described in JP-B-43-0-76) can be used.

[0085] As the polyol having a nonionic group, known compounds (for example, compounds described in the specification of JP-B-48-41718) can be used. Specifically, polyols having a polyoxyalkylene unit, alkyl alcohol alkylene oxide adducts, 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 a mixture of diphenylmethane-4,4'-diisocyanate and diphenylmethane-2,4'-diisocyanate. Aromatic polyisocyanates such as mixtures of diisocyanates, naphthalene-1,5-diisocyanate, 3,3'-dimethyl-4,4'-biphenylene diisocyanate, xylylene diisocyanate, diphenylmethylmethane diisocyanate, tetramethylxylylene diisocyanate, 4,4'-dibenzyl diisocyanate, and 1,3-phenylene diisocyanate; 1,3-cyclopentane diisocyanate, 1,4-cyclohexane diisocyanate, and 1,2-cyclohexane diisocyanate. Alicyclic polyisocyanates such as cyclohexanediisocyanate, 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 the like. Examples of suitable polyisocyanates include triisocyanates such as triphenylmethane triisocyanate, 1,6,11-undecane triisocyanate, 1,8-diisocyanate-4,4'-isocyanatomethyloctane, 1,3,6-hexamethylene triisocyanate, and bicycloheptane triisocyanate; and polymers of the above-mentioned aromatic polyisocyanates, alicyclic polyisocyanates, and aliphatic polyisocyanates (for example, adducts, biurets, isocyanurates, and uretdiones). Among these, from the viewpoint of light resistance, aliphatic polyisocyanates, alicyclic polyisocyanates, and polymers of aliphatic 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 above. Examples of the polyamine include ethylenediamine, hexamethylenediamine, diethylenetriamine, hydrazine, xylylenediamine, isophoronediamine, etc.

[0089] The terminal terminator is preferably a compound having one active hydrogen group per molecule or a monoisocyanate compound.

[0090] The compound having one active hydrogen group per molecule may be a monoalcohol or a monoamine. Examples of the monoalcohol include alkyl alcohols such as methanol, butanol, and octanol; alkyl alcohol alkylene oxide adducts, etc. Examples of the monoamine include alkyl amines such as butylamine and 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 Chemicals), the HUX series (ADEKA), the U-coat series, the Permarin series, and the Euplen series (all manufactured by Sanyo Chemical Industries) 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-forming 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 film-forming resin (A). The melamine resin (A3) may be water-soluble or water-insoluble.

[0097] The water tolerance of the melamine resin (A3) is preferably 3.0 or more. The water tolerance is an index for evaluating the degree of hydrophilicity, and a higher water tolerance indicates higher hydrophilicity.

[0098] The water tolerance can be measured as the amount (mL) of ion-exchanged water dropped 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 dropped using a burette until the sample becomes cloudy.

[0099] The melamine resin (A3) is preferably an alkyl-etherified melamine, and more 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)), and butyl-etherified melamine (Mycoat 506 (manufactured by Allnex), U-Van 20N60, U-Van 20SE, etc. (manufactured by Mitsui Chemicals, Inc.)). 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) is preferably less than 50% by mass, more preferably not more than 35% by mass, and even more preferably not more than 25% by mass, of the solid content of the coating film-forming resin (A), with the lower limit being 0% by mass. The solid content mass ratio of the melamine resin (A3) to the urethane resin (A2) ((A3) / (A2)) is preferably less than 7, more preferably not more than 5, even more preferably not more than 3, and is preferably 0.01 or more, more preferably 0.05 or more, and even more preferably 0.07 or more.

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

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

[0104] Examples of the polyester resin include reaction products of polycarboxylic acids and polyols; ring-opening polymerization products of lactone compounds such as polycaprolactone; and copolymers thereof. Examples of the polycarboxylic acids include hydroxy acids such as adipic acid, sebacic acid, isophthalic acid, and dimethylolpropionic acid, as well as anhydrides thereof. Examples of the polyols include aliphatic polyols such as ethylene glycol, butanediol, neopentyl glycol, and 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 chain dihydric alcohols 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% by mass or less, preferably 30% by mass or less, and more preferably 20% by mass or less, and may be 0% by mass or more, 5% by mass or more, or 10% by mass or more.

[0113] The film-forming resin (A) may further contain another curing agent (A5), such as a blocked isocyanate compound obtained by adding a blocking agent having an active hydrogen to a polyisocyanate such as trimethylene diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, or isophorone diisocyanate; an epoxy compound; an aziridine compound; a carbodiimide compound; an oxazoline compound; or a metal ion.

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

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

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

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

[0118] The above-mentioned luster pigment is a pigment that can reflect light and can impart a unique 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 metals; metal oxides such as aluminum oxide; metal acid salt compounds such as mica (particularly, interference mica pigments, white mica pigments, etc.); graphite; and the like. These may be used alone or in combination of two or more.

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

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

[0121] In one embodiment, the pigment (B) includes a color pigment (B2). The color pigment (B2) can impart a hue 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 these, phthalocyanine pigments, diketopyrrolopyrrole pigments, perylene pigments, and red iron oxide are preferred as the color pigment (B2). Use of these color pigments makes it possible to form a coating film that is excellent in high saturation, high brightness, and color depth.

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

[0126] In the 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) to 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 contains a dispersion medium (C), which 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 base coating composition, the content of the dispersion medium (C) is preferably 40% by mass or more, more preferably 50% by mass or more, even more preferably 55% by mass or more, and preferably 90% by mass or less, more preferably 85% by mass or less, even more preferably 80% by mass or less.

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

[0136] The pigment dispersant can be a resin having a pigment affinity moiety and a hydrophilic moiety. The pigment affinity moiety and hydrophilic moiety can be, for example, nonionic, cationic, or anionic functional groups depending on the type of pigment, and two or more of these functional groups may be present in one molecule of the pigment dispersant. Examples of the nonionic functional groups include hydroxyl groups, amide groups, and polyoxyalkylene groups, while examples of the cationic functional groups include amino groups, imino groups, and hydrazino groups. Examples of the anionic functional groups include carboxyl groups, sulfonic acid groups, and phosphate groups.

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

[0138] Examples of 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 dispersant 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 (such as sulfate ester, phosphate ester, and maleate ester modified products).

[0139] The polymeric pigment dispersant is not particularly limited, but the following can be suitably used: (1) A comb-structured polymeric pigment dispersant having pigment affinity groups in the main chain and / or in a plurality of side chains, and having a plurality of side chains constituting solvation moieties; (2) A polymeric pigment dispersant having a plurality of pigment affinity moieties composed of pigment affinity groups in the main chain; and (3) A linear polymeric pigment dispersant having a pigment affinity moiety composed of a pigment affinity group at one end of the main chain.

[0140] Here, the pigment affinity group refers to a functional group that has a strong adsorptive power to the surface of a 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, together with the main chain and / or multiple side chains having the pigment affinity groups, multiple side chains constituting solvation moieties 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 groups are not limited to being present at the end of the side chains, but may also be present in multiple locations along the side chains or within the main chain. The solvation moiety refers to a structure that has affinity for a solvent. The solvation moiety 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-structured 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 moiety contained in the comb-structured polymer pigment dispersant (1) is preferably 2 or more, more preferably 5 or more, per molecule, 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 and 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 below.

[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 moiety 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 polymeric 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 below.

[0148] The linear polymer pigment dispersant (3) having a pigment affinity moiety consisting of a pigment affinity group at one end of the main chain has a pigment affinity moiety 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 one molecule of the linear polymer pigment dispersant (3) is preferably 2 or more, more preferably 5 or more, 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 below.

[0151] As the pigment dispersant, from the viewpoint of the transparency of the resulting coating film, the comb-shaped structure 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 (all 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). FLORENE G-700AMP, FLORENE G-700DMEA, FLORENE GW-1500, FLORENE GW-1640 (all manufactured by Kyoeisha Chemical Co., Ltd.), DISPARLON DA-703-50, DISPARLON DA-7301, DISPARLON DN-900 (all manufactured by Kusumoto Chemical Co., Ltd.).ANTI-TERRA-250, DISPERBYK, DISPERBYK-102, DISPERBYK-180, DISPER BYK-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, per 100 parts by mass of the pigment (B). By using the pigment dispersant in this range, it is easy to obtain good pigment dispersion stability and good coating film properties.

[0156] The base coating composition may further contain a phosphate group-containing organic compound. In particular, when the base coating composition contains a bright pigment, the inclusion of the phosphate 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 bright pigment, and also improves the dispersibility of the bright pigment, thereby improving the physical properties of the resulting coating film, such as adhesion.

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

[0158] The phosphate group-containing polymer is not particularly limited as long as it has a phosphate group value in the range of 5 to 300 mgKOH / g, and conventionally known polymers can be used. Specific examples of phosphate group-containing polymers 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 phosphate group-containing polymers, acrylic resins are preferred in terms of performance such as weather resistance and water resistance. These phosphate group-containing polymers may be used alone or in combination of two or more.

[0159] Particularly preferred examples of the phosphate group-containing polymer include phosphate group-containing acrylic resins and phosphorus ester 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 an essential component.

[0161] Examples of the phosphate group-containing monomer 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 vinylphosphonic acid.

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

[0163] As the phosphorus ester surfactant having a polyalkylene oxide group, commercially available products can be used, and examples thereof include AQ-330 (manufactured by Kusumoto Chemicals, Ltd., phosphate value 12 mgKOH / g), AQ-320 (manufactured by Kusumoto Chemicals, Ltd., phosphate value 14 mgKOH / g), AQ-340 (manufactured by Kusumoto Chemicals, Ltd., phosphate value 18 mgKOH / g), and phosphate ester wetting and dispersing agents having a polyalkylene oxide group, such as BYK-111 (manufactured by BYK-Chemie, phosphate value 120 mgKOH / g) and BYK-180 (manufactured by BYK-Chemie, phosphate value 90 mgKOH / g).

[0164] The number average molecular weight of the phosphate group-containing polymer is preferably 1,000 to 50,000. In this specification, the number average molecular weight is a value determined by GPC method using polystyrene as a standard.

[0165] The phosphate group value of the phosphate group-containing polymer is preferably 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 group 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 an alkyl phosphate ester having a C4-30 alkyl group. Examples of the alkyl phosphate ester having a C4-30 alkyl group include monoalkyl phosphate esters, dialkyl phosphate esters, and mixtures of monoalkyl phosphate esters and dialkyl phosphate esters. In dialkyl phosphate esters, it is more preferable that the two alkyl groups are the same group.

[0168] Specific examples of alkyl phosphate esters having a C4-30 alkyl group include 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), tri ... Examples of the oleic acid phosphate include monostearyl acid phosphate (a mixture of monoisostearyl ester and diisostearyl ester), 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 phosphate group-containing organic compound and a luster pigment, the amount of the phosphate 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 phosphate 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 properties and adhesion.

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

[0171] The inclusion of the viscosity control agent prevents adhesion between coating films and facilitates coating workability. The viscosity control agent can generally be one that exhibits thixotropy. 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 phosphate salts 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 whose viscosity is determined by the shape of the pigment.

[0172] The base coating composition can be produced by mixing with stirring the film-forming resin (A), pigment (B), and the other optional components described above.

[0173] Prior to the production of the base coating composition, the film-forming resin (A) may be dispersed in at least a portion of the dispersing medium (C) and then used in the preparation of the base coating composition. When the film-forming resin (A) is present in the form of an emulsion or dispersion, these can be mixed and stirred sequentially to form a dispersion in which the film-forming resin (A) is dispersed in at least a portion of the dispersing medium (C).

[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 55% by mass or less, even more preferably 50% by mass or less.

[0175] The pigment (B) may be dispersed together with at least a portion of the dispersion medium (C) and a pigment dispersant, and the resulting pigment dispersion may be used to prepare 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 comprises two or more layers, each layer can be heat-cured after application, or the next layer can be applied without heat-curing the applied layer, and two or more layers can be heat-cured simultaneously.For example, when the base layer comprises two layers, the first base coating composition can be applied, and the coating film can be heat-cured to form a first base layer, and then the second base coating can be applied on the first base layer, and the coating film can be heat-cured; the first base coating composition can be applied, and the second base coating composition can be applied without heat-curing the coating film, and the first base coating film and the second base coating film can be simultaneously cured.When applying the next layer without heat-curing the applied layer, after applying the base coating composition, before applying the next layer of base coating composition on the coating film, if necessary, the applied layer can be dried or preheated.

[0177] Furthermore, the base coating film (or the upper coating film in the case of multiple layers) may be heat-cured before forming the layer thereon (such as a clear layer), or a clear coating composition described below may be applied to 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 layer coating composition), drying or preheating may be carried out as necessary before applying the clear coating composition.

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

[0179] (Clear layer) The clear layer is a layer located on the surface side of the base layer in the multilayer coating film, and is preferably the outermost layer of the multilayer 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 layer included in the base layer.

[0180] The clear layer is preferably a harder layer than the stress relaxation layer, which allows the stress relaxation layer to 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 ratio σc0 / σb0 of the maximum stress σc0 of the clear layer to the maximum stress σb0 of the base layer may preferably be equal to or greater than 1. When the ratio σc0 / σb0 is within this range, impacts on the surface of the multilayer coating film are more efficiently propagated to and absorbed by the stress relaxation layer, making it easier to suppress chipping.

[0182] The clear layer typically contains a resin. Examples of such a resin include, but are not limited to, an acrylic resin, a polyester resin, a urethane resin, and an epoxy resin, 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 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 above-mentioned water-based clear coating composition is a composition containing a resin used in the above-mentioned solvent-based clear coating composition, which has been neutralized with a base such as a tertiary amine (e.g., dimethylethanolamine, triethylamine, etc.) to make it water-soluble, and an aqueous medium. As the above-mentioned aqueous medium, any of the compounds exemplified as the aqueous medium that can be used in the base coating composition can be used as appropriate.

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

[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 application of the above clear coating composition can be carried out by a coating method that conforms to the application 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 to 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 the physical properties of the resulting multilayer coating film, the heat-curing temperature is preferably 80 to 180°C, more preferably 120 to 160°C. The heat-curing time can be set as desired, 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 multilayer coating film has two base layers (a first base layer and a second base layer) and a clear coating film, specific examples of methods for forming the multilayer coating film include the following: (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, then a clear coating composition is applied to form an uncured clear coating film, and the resulting three layers are heat-cured at once. (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 then the resulting two layers are heat-cured at once. After heat-curing, a clear coating film 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, the resulting two layers are heat-cured at once, and then 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 resulting two layers are heat-cured at once.

[0192] The multilayer coating film may further comprise 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.

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

[0196] (Production Example 1) Production of acrylic resin emulsion (film-forming resin) 126.5 parts by mass of deionized water was added to a reaction vessel, and the temperature was raised to 80°C while mixing and stirring in a nitrogen stream. Next, a monomer emulsion consisting of 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 alkylpropenylphenyl ether sulfate, manufactured by Dai-ichi 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 deionized water, and an initiator solution consisting of 0.3 parts by mass of ammonium persulfate and 10 parts by mass of deionized water were added dropwise to the reaction vessel in parallel over 2 hours. After completion of the dropwise addition, the mixture was aged at the same temperature for 2 hours. The mixture was then 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, yielding a single-layer acrylic resin emulsion 1 having an average particle size of 88 nm, a nonvolatile 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 a 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 this monomer mixture, 10.0 parts by mass of tripropylene glycol methyl ether, and 1 part by mass of tertiary butyl peroxy 2-ethylhexanoate was added dropwise to the reaction vessel in parallel over 3 hours. After completion of 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 0.5 hours. After completion of the addition, the mixture was aged at the same temperature for 2 hours.

[0199] Using a solvent remover, 16.1 parts by mass of the solvent was distilled off under reduced pressure (70 torr) at 110°C, and then 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 resulting water-soluble acrylic resin solution had a nonvolatile content of 30% by mass, an acid value of 40 mgKOH / g (solids), a hydroxyl value of 50 mgKOH / g (solids), and a viscosity of 140 poise (E-type viscometer, 1 rpm, 25°C).

[0200] (Production Example 3) Production of Phosphate Group-Containing Organic Compound A 1-liter reaction vessel equipped with a stirrer, a temperature regulator, and a cooling tube was charged with 40 parts by mass of ethoxypropanol, and 121.7 parts by mass of a monomer solution consisting of 40 parts by mass of a solution obtained by dissolving 20 parts by mass of Phosmer PP (acid phosphooxyhexa(oxypropylene)monomethacrylate manufactured by Unichemical Corporation) in 4 parts by mass of styrene, 35.96 parts by mass of n-butyl acrylate, 18.45 parts by mass of ethylhexyl methacrylate, 13.92 parts by mass of 2-hydroxyethyl methacrylate, 7.67 parts by mass of methacrylic acid, and 20 parts by mass of ethoxypropanol was added dropwise at 120°C over 3 hours, and stirring was continued for an additional 1 hour. The resulting phosphate group-containing organic compound had an acid value of 105 mgKOH / g, including a phosphate group value of 55 mgKOH / g, a hydroxyl group value of 60 mgKOH / g, a number average molecular weight of 6,000, and a nonvolatile content of 63 mass %.

[0201] Example 1 Production of Base Coating Composition

[0047] The acrylic resin (A1) was 45.0 parts by mass of acrylic resin (A1-1), the melamine resin (A3) was 28.0 parts by mass of melamine resin (A3-1), the other resins (A4) were 6.0 parts by mass of resin (A4-1) and 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, and Noigen EA-207D (amphiphilic compound, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., number average molecular weight 4,200, solid content 55% by mass). 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 ADEKA NOL UH-814N (urethane associative viscosity agent, active ingredient 30% by mass, manufactured by ADEKA Corporation, trade name) as a viscosity adjuster were uniformly dispersed, and dimethylaminoethanol was added to adjust the pH to 8.1. The mixture was then diluted with deionized water to prepare a base coating composition with a solids concentration of 25% by mass and a pigment concentration of 7.8% by mass.

[0202] Preparation of multi-layer coating film <Method of forming multi-layer coating film> 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.) to a dry film thickness of 20 μm, and baked at 160°C for 30 minutes. A pre-diluted gray undercoat paint "Orga OP-30" (a polyester-melamine paint manufactured by Nippon Paint Co., Ltd.) was then applied to the coated plate using a No. 4 Ford cup in two stages using an air spray so that the drainage time measured at 20°C was 25 seconds, to a dry film thickness of 35 μm, and the plate was then baked at 140°C for 30 minutes.

[0203] After cooling, the base coating composition was applied in two stages using a Cartridge Bell at a room temperature of 23°C and a humidity of 68% to a dry film thickness of 5 μm. A 1 minute 30 second interval was allowed to set between the two applications. After the second application, a 1 minute 30 second interval was allowed to set. The coating was then preheated at 80°C for 5 minutes to form an uncured base coating film.

[0204] The resulting coated panels were then allowed to cool to room temperature, and coated with Macflow-O-1810 (a solvent-based clear coating manufactured by Nippon Paint Co., Ltd.) as a clear coating in one stage to a dry film thickness of 35 μm, and allowed to set for 7 minutes. The coated panels were then baked in a dryer at 140°C for 30 minutes to obtain multi-layer coatings. The coating appearances were good in all cases.

[0205] Examples 2 to 9, Comparative Examples 1 and 2 A multilayer coating film was formed in the same manner as in Example 1, except that the acrylic resin (A1), urethane resin (A2), melamine resin (A3), other resin (A4) and polyester resin (A5) in Example 1 were changed as shown in Table 1.

[0206] 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 mass% (A1-2): Acrylic resin emulsion of Production Example 1, solid acid value 20 mg KOH / g, solid 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 acid value 40 mg KOH / g, solid hydroxyl value 50 mg KOH / 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 mass% Urethane resin (A2) (A2-1): "Neolez R-9603" manufactured by Avecia (polycarbonate-based urethane emulsion resin, non-volatile content 33% by mass). Melamine resin (A3) (A3-1): Uvan 20N60 (butylated melamine resin manufactured by Mitsui Chemicals, Inc., 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 (manufactured by 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% by mass, primary / secondary hydroxyl value ratio = 63 / 37) Polyester resin (A5) (A5-1): R-4170 (manufactured by 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 K.K., "Aluminum Paste Z0684N", glitter pigment, average particle size 12 μm, active ingredient 70% by mass)

[0207] The multi-layer coating films obtained in the above Examples and Comparative Examples were subjected to the following measurements.

[0208] (Measurement of Low-Temperature Stress Residual Rate) The base coating composition in the examples was applied in two stages to a polypropylene film (polypropylene plate, manufactured by TP Giken Co., Ltd.) at a room temperature of 23°C and a humidity of 68% so as to achieve a dry film thickness of 5 μm using a "Cartridge Bell." An interval setting of 1 minute 30 seconds was performed between two applications. After the second application, an interval of 1 minute 30 seconds was taken for setting. Thereafter, the film was preheated at 80°C for 5 minutes. Next, a coating film was obtained by baking at 140°C for 30 minutes using a dryer. Next, the film was cooled to room temperature (25°C) at a temperature decrease rate of 10°C / min.

[0209] 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 defined as σ0, and the stress 1,000 seconds after applying 1% strain was defined as σ1, and the residual stress ratio σ1 / σ0 was calculated.

[0210] (Measurement of Chipping Area) The test plates having the laminated coating film obtained in each Example and Comparative Example were subjected to a stone chipping test using a Gravelo Tester KSS-1 (manufactured by Suga Test Instruments, diamond shot method) under the following conditions: <Test conditions> Stone size: 6 to 8 mm Stone amount: 0.7 to 0.8 g / piece Distance: 35 cm Shot speed: 100 km / h Shot angle: 25° Test temperature: -20°C

[0211] The area of ​​the coating 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. Chipping resistance was evaluated in the following three stages: ◎ (Excellent): Peeled area less than 2.5 mm2 ○ (Good): Peeled area 2.5 mm2 or more but less than 3 mm2 △ (Bad): Peeled area 3 mm2 or more

[0212]

[0213] Examples 1 to 9 are examples of the present disclosure and had good chipping resistance at low temperatures. In Comparative Examples 1 and 2, the low-temperature residual stress rate of the resulting coating film exceeded 60%, and chipping resistance at low temperatures (-20°C) was poor.

Claims

1. A multi-layer coating film comprising: 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 60% 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 multi-layer coating film 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, what is the maximum stress σ in the clear layer? 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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