Laminate, and method for producing laminate

Abstract

To provide a laminate comprising multiple cured layers, that has a high degree of hardness, is more attractive, and has better gasoline resistance and water resistance, even when a multilayer coating film comprising a coating film of a clear coat composition containing at least a hydroxy group-containing acrylic resin and an isocyanate curing agent is thermally cured at 70°C or below, and to provide a method for producing the laminate.SOLUTION: There is provided a laminate comprising cured layers of each of a base coat layer (I) on an object to be coated and a clear coat layer (II) on the base coat layer (I). The cured clear coat layer (II) is formed by heating a coating film of a clear coat composition (CC) comprising the following components to 70°C or below: a hydroxy group-containing acrylic resin (A1) having a prescribed glass transition temperature (Tg); an isocyanate curing agent (A2); and a hydroxy group-containing polyester resin (D). The cured layer of clear coat layer (II) has a molecular weight between cross-linking points (Mc) of 800 g / mol or less. There is furthermore provided a method for producing a laminate comprising the above cured layers.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a laminate and a method for producing the laminate, and more particularly to a laminate comprising a cured base coat layer (I) and a cured clear coat layer (II) on an article to be coated, and a method for producing the laminate. [Background technology]

[0002] Conventionally, when painting vehicle parts (bumpers, etc.), in the case of resin products, a primer layer is formed on a resin substrate, a colored base coat layer is formed on top of that, and then a two-component clear coating composition consisting of, for example, a base agent containing a hydroxyl group-containing acrylic resin and a curing agent containing an isocyanate compound is applied on top of the colored base coat layer, and this is then baked, usually at 80 to 100°C, to form a multi-layer coating film having a clear coat layer.

[0003] Furthermore, when the object to be coated is made of metal, such as a vehicle body, electrodeposition coating is applied to the metal substrate, and then, as with plastic products, a colored base coat layer and a clear coat layer are formed on top of that to form a multi-layer coating film.

[0004] In recent years, from the viewpoint of energy conservation and environmental friendliness, there has been a demand for thermally curing laminated coating films at low temperatures, for example, 60 to 70° C. However, although the reaction between the hydroxyl group-containing acrylic resin and the isocyanate curing agent is accelerated by heat, there is a risk that the film will not be sufficiently cured if thermal curing is performed at a low temperature.

[0005] Furthermore, when the coating film of the above two-component clear coating composition was thermally cured at low temperatures, the appearance of the cured film after curing was not good, and furthermore, the gasoline resistance and water resistance of the cured film were insufficient.

[0006] Here, the following Patent Documents 1 to 3 can be cited as prior art documents disclosing conventional techniques for obtaining a cured film by thermally curing a clear coating composition containing a hydroxyl group-containing acrylic resin and an isocyanate curing agent.

[0007] Patent Document 1 discloses a method of forming first and second colored coating films on a substrate containing a metal material and a plastic material, then electrostatically coating the first and second colored coating films on top of the first and second colored coating films with a two-component clear coating containing a hydroxyl-containing acrylic resin (K) with a glass transition temperature (Tg) of -12°C, an isocyanate curing agent, and a hydroxyl-containing polyester resin, and then heating the coating film in an oven at 95°C for 30 minutes to form a multi-layer coating film.

[0008] Patent Document 2 discloses a coating composition for plastics that contains a hydroxyl group-containing acrylic resin with a glass transition temperature (Tg) of 49 to 79°C, an isocyanate curing agent, and a surface conditioner that essentially contains a silicone-based surface conditioner and an acrylic-based surface conditioner, and that is cured by baking at 80°C for 20 minutes.

[0009] Patent Document 3 discloses a coating method (3-coat, 1-bake method) in which an aqueous primer (I), an aqueous base coat paint (II), and a clear coat paint (III) are applied to a plastic molded product in that order, and the three-layer coating film formed is baked and cured simultaneously, in which the clear coat paint (III) contains a hydroxyl group-containing resin (F) and an isocyanate crosslinking agent (G), the hydroxyl group-containing resin (F) is selected from hydroxyl group-containing acrylic resins, polyester resins, etc., and the three-layer coating film is baked at a temperature in the range of 40 to 110°C for 5 to 60 minutes. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] International Publication No. 2015 / 087932 [Patent Document 2] Japanese Patent Application Publication No. 2014-019714 [Patent Document 3] International Publication No. 2008 / 050778 Summary of the Invention [Problem to be solved by the invention]

[0011] However, according to the invention of Patent Document 1, the electrostatically applied two-component clear paint is baked at a high temperature (95°C for 30 minutes) as in the conventional case, and no low-temperature baking conditions are disclosed. Also, because the glass transition temperature (Tg) of the hydroxyl group-containing acrylic resin (K) of the invention of Patent Document 1 is low at -12°C, the hardness of the cured film after low-temperature baking may be insufficient, and therefore the gasoline resistance may also be poor.

[0012] Furthermore, according to the invention of Patent Document 2, baking is carried out at the conventional temperature of 80°C, and no measures are disclosed to ensure film hardness under low-temperature baking conditions. Therefore, when baking is carried out at low temperatures, the hardness and gasoline resistance of the cured film after curing are inferior.

[0013] Furthermore, the invention of Patent Document 3 also discloses baking a three-layer coating film at low temperature, but in the examples, the three-layer coating film is heated at 90°C for 30 minutes, and the physical properties of the cured film after low-temperature baking are not confirmed. Focusing on the composition of the clear coat paint (III), it is not disclosed that the clear coat paint (III) uses an acrylic resin and a polyester resin in combination as the hydroxyl group-containing resin (F), and the glass transition temperature (Tg) of the acrylic resin is not disclosed either. Therefore, no measures are disclosed to ensure physical properties such as the curability of the film after low-temperature baking. Therefore, it is thought that a cured coating film that is sufficiently heat-cured at low temperature and has excellent appearance and gasoline resistance cannot be obtained.

[0014] Therefore, in the past, when a clear coating composition containing a hydroxyl group-containing acrylic resin and an isocyanate curing agent was thermally cured at a low temperature of 70°C or less to produce a cured film, it was not possible to obtain a cured film that had high hardness while also satisfying all of the requirements for appearance, gasoline resistance, and water resistance.

[0015] The object of the present invention, made in view of the above problems, is to provide a laminate comprising multiple cured layers that has high hardness even when a multilayer coating film including a coating film of a clear coating composition containing at least a hydroxyl group-containing acrylic resin and an isocyanate curing agent is heat-cured at 70°C or less, and that has excellent appearance, gasoline resistance, and water resistance, and to provide a method for producing such a laminate. [Means for solving the problem]

[0016] The present inventors have conducted extensive research to achieve the above object, and as a result, have found that in a clear coating composition containing at least a hydroxyl-containing acrylic resin and an isocyanate curing agent, by adjusting the glass transition temperature (Tg) of the hydroxyl-containing acrylic resin to 20°C or higher and 70°C or lower, by adding a hydroxyl-containing polyester resin, and by heating a coating film of the clear coating composition at 70°C or lower to form a cured layer having a molecular weight between crosslink points (Mc) of 800 g / mol or lower, the resulting laminate of the cured layer has high hardness and excellent appearance, gasoline resistance, and water resistance, which led to the completion of the present invention.

[0017] That is, the object of the present invention is to A laminate comprising a base coat layer (I) on an object to be coated and a clear coat layer (II) on the base coat layer (I), The cured layer of the clear coat layer (II) is formed by heating a coating film of a clear coating composition (CC) containing a hydroxyl-containing acrylic resin (A1) having a glass transition temperature (Tg) of 20°C or higher and 70°C or lower, an isocyanate curing agent (A2), and a hydroxyl-containing polyester resin (D) at 70°C or lower, It has been found that this can be achieved by a laminate characterized in that the cured layer of the clear coat layer (II) has a molecular weight between crosslink points (Mc) of 800 g / mol or less.

[0018] In addition, the amount (solid content) of the hydroxyl group-containing polyester resin (D) is preferably 3% by mass or more and 50% by mass or less based on the total mass of the solid content of the resin components excluding the isocyanate curing agent (A2) contained in the clear coating composition (CC).

[0019] Furthermore, the weight average molecular weight (Mw) of the hydroxyl group-containing polyester resin (D) is preferably 500 g / mol or more and 5000 g / mol or less.

[0020] In addition, the hydroxyl value of the hydroxyl-containing polyester resin (D) is preferably 100 mgKOH / g or more.

[0021] The hydroxyl value of the hydroxyl-containing acrylic resin (A1) is preferably 80 mgKOH / g or more and 200 mgKOH / g or less.

[0022] Furthermore, the weight average molecular weight (Mw) of the hydroxyl group-containing acrylic resin (A1) is preferably 2000 g / mol or more and less than 10000 g / mol.

[0023] Furthermore, it is preferable that the clear coating composition (CC) contains 0.8 to 1.6 equivalents of isocyanate groups in the isocyanate curing agent (A2) per 1 equivalent of the total of hydroxyl groups in the hydroxyl-containing acrylic resin (A1) and the hydroxyl-containing polyester resin (D).

[0024] The isocyanate curing agent (A2) preferably contains a polyisocyanate having an isocyanurate structure.

[0025] Furthermore, the laminate preferably has a pencil hardness of 6B or more.

[0026] Furthermore, the object of the present invention is to provide a method for coating a substrate with a base coat paint composition to form a base coat layer (I); a clear coat layer (II) forming step of applying a clear coating composition (CC) onto the base coat layer (I) obtained in the base coat layer (I) forming step to form a clear coat layer (II); a curing step of heating the base coat layer (I) and the clear coat layer (II) at 70°C or less to cure them, thereby obtaining a laminate consisting of the respective cured layers, The clear coating composition (CC) comprises a hydroxyl-containing acrylic resin (A1) having a glass transition temperature (Tg) of 20°C or higher and 70°C or lower, an isocyanate curing agent (A2), and a hydroxyl-containing polyester resin (D), This can also be achieved by a method for producing a laminate, wherein the cured layer of the clear coat layer (II) obtained in the curing step has a molecular weight between crosslinks (Mc) of 800 g / mol or less. [Effects of the Invention]

[0027] According to the laminate and laminate manufacturing method of the present invention, the hydroxyl-containing acrylic resin (A1) contained in the clear coating composition (CC) has a glass transition temperature (Tg) of 20°C to 70°C, and the cured layer of the clear coat layer (II) has a crosslinking molecular weight (Mc) of 800 g / mol or less. Therefore, even when heat-cured at 70°C or less, the laminate has high hardness and excellent gasoline resistance. Furthermore, because the clear coating composition (CC) contains the hydroxyl-containing acrylic resin (A1) having a higher glass transition temperature (Tg) than conventional coatings and the hydroxyl-containing polyester resin (D), the hydroxyl-containing polyester resin (D) acts as a softening component, improving the appearance. Furthermore, because the cured layer of the clear coat layer (II) containing the hydroxyl-containing acrylic resin (A1) and the hydroxyl-containing polyester resin (D) has a crosslinking molecular weight (Mc) of 800 g / mol or less, the resulting laminate also has excellent water resistance. [Brief explanation of the drawings]

[0028] [Figure 1] FIG. 1 is a flow diagram showing a method for producing a laminate of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0029] <Laminate> The laminate of the present invention is A laminate comprising a base coat layer (I) on an object to be coated and a clear coat layer (II) on the base coat layer (I), The cured layer of the clear coat layer (II) is formed by heating a coating film of a clear coating composition (CC) containing a hydroxyl-containing acrylic resin (A1) having a glass transition temperature (Tg) of 20°C or higher and 70°C or lower, an isocyanate curing agent (A2), and a hydroxyl-containing polyester resin (D) at 70°C or lower, The cured layer of the clear coat layer (II) has a molecular weight between crosslink points (Mc) of 800 g / mol or less.

[0030] [Subject to be coated] There are no particular limitations on the substrate on which the laminate of the present invention is formed, and examples thereof include members made of metals such as iron, zinc, aluminum, magnesium, etc., members made of alloys of these metals, members plated or vapor-deposited with these metals, members made of glass, plastics, foams of various materials, etc., and among these, steel and plastic materials that form automobile bodies are preferred. These members can be subjected to appropriate treatments such as degreasing and surface treatments as necessary.

[0031] In the present invention, the above-mentioned member on which a primer coating film has been formed can also be used as the substrate. The primer coating film is applied to the surface of the member to conceal the member surface or to impart corrosion resistance, rust resistance, adhesion, etc. to the member, and can be formed by applying a primer coating and curing or drying it. This primer coating is not particularly limited, and known primers, such as electrodeposition paints, solvent-based primers, and water-based primers, can be used. When the member is a plastic material that constitutes an automobile body, the substrate is usually one on which a primer layer has been formed. Here, if the primer layer is conductive, it is more preferable that the base coat coating composition and clear coating composition to be applied thereon can be electrostatically coated. When the member is a steel material that constitutes an automobile body, the substrate is usually one on which an electrodeposition coating layer has been formed.

[0032] Furthermore, in the present invention, the substrate may be any of the aforementioned metal, glass, and plastic members that have been subjected to any of the above-mentioned treatments and that have at least one laminate formed thereon. For repair purposes, the process of forming a base coat layer (I) (S110) through the curing step (S130) described below is carried out on such a substrate that includes a laminate, thereby forming a further laminate, which is called recoating.

[0033] [Cured layer of base coat layer (I)] The base coat layer (I) is a layer (paint film) formed mainly for coloring, and is formed by applying a base coat paint composition to an object to be coated, and the cured layer of the base coat layer (I) is obtained by curing this base coat layer (I) alone or together with layers above and below the base coat layer (I). The base coat layer (I) may be a single layer or multiple layers.

[0034] The base coat paint composition may be a solvent-based paint composition or a water-based paint composition, but a solvent-based paint composition is particularly preferred.It may be a one-component paint composition in which the paint can be used as supplied, or a two-component paint composition in which the base agent and curing agent are mixed immediately before use.

[0035] The base coat paint composition contains a resin component and various pigments.

[0036] The resin component of the base coat paint composition is not particularly limited as long as it is a component that can form a base coat paint composition, and may be a thermosetting resin that forms a paint film by heating to cause a crosslinking reaction after application, or a thermoplastic resin that forms a paint film by volatilizing the solvent.

[0037] When the base coat paint composition is a thermosetting resin composition, the base resin is not particularly limited as long as it is a resin that can be stably dissolved or dispersed in an organic solvent and / or water, and examples thereof include acrylic resin, polyester resin, polyurethane resin, polyurea resin, acrylic urethane resin, polyurethane polyurea resin, etc. Furthermore, it is preferable that the base resin has a hydroxyl group as a functional group. These base resins may be used alone or in combination of two or more.

[0038] When the base coat paint composition is a thermosetting resin composition, the curing agent is not particularly limited as long as it is stably soluble or dispersible in organic solvents and / or water, and examples thereof include amino resins, polyisocyanate compounds, blocked polyisocyanate compounds, etc. These curing agents may be used alone or in combination of two or more.

[0039] There are no particular restrictions on the thermoplastic resins that can be used in the base coat paint composition, as long as they are stably soluble or dispersible in organic solvents and / or water. Examples include acrylic resins, polyester resins, alkyd resins, urethane resins, polyolefin resins (including chlorinated and / or modified resins), and epoxy resins, all of which have a mass average molecular weight (Mw) of 30,000 g / mol or more.

[0040] Examples of various pigments for the base coat paint composition include color pigments and luster pigments. Examples of color pigments include inorganic pigments such as titanium oxide pigments, iron oxide pigments, and composite oxide pigments such as titanium yellow; organic pigments such as azo pigments, quinacridone pigments, diketopyrrolopyrrole pigments, perylene pigments, perinone pigments, benzimidazolone pigments, isoindoline pigments, isoindolinone pigments, metal chelate azo pigments, phthalocyanine pigments, anthraquinone pigments, dioxazine pigments, threne pigments, and indigo pigments; and carbon black pigments. These color pigments may be used alone or in combination of two or more.

[0041] Examples of bright pigments include uncolored or colored aluminum pigments, vapor-deposited metal flake pigments, and optical interference pigments in which a transparent or translucent substrate is coated with a metal oxide. These bright pigments may be used alone or in combination of two or more.

[0042] The base coat paint composition may further contain, as necessary, organic solvents and additives such as various paint additives such as surface conditioners, thickeners, rheology modifiers, pigment dispersants, anti-settling agents, curing catalysts, antifoaming agents, antioxidants, UV absorbers, extender pigments, etc. Examples of organic solvents include organic solvents commonly used in the production of base coat paint compositions, such as aromatic hydrocarbons such as toluene, xylene, and aromatic naphtha, ketones such as acetone, methyl ethyl ketone, and methyl amyl ketone, esters such as ethyl acetate, butyl acetate, 2-butoxyethyl acetate, pentyl acetate, and ethyl ethoxypropionate, alcohols such as isopropanol, butanol, and 2-butoxyethanol, ethers, aliphatic hydrocarbons including chlorinated hydrocarbons, and mixtures thereof.

[0043] When the substrate is a plastic material that constitutes an automobile body, the base coat layer (I) usually has a single hardened layer. However, when the substrate is a steel material that constitutes an automobile body, the base coat layer (I) has a two-layer hardened layer structure consisting of a lower base coat layer (I-1) and an upper base coat layer (I-2) laminated together to provide impact absorption properties.

[0044] In this case, the lower base coat layer (I-1) mainly serves as an impact absorbing layer, and the upper base coat layer (I-2) mainly serves as a colored layer. The base coat paint compositions for the lower base coat layer (I-1) and the upper base coat layer (I-2) can be prepared by appropriately mixing the above components according to the purpose.

[0045] [Cured layer of clear coat layer (II)] The cured layer of the clear coat layer (II) is a cured layer provided on the top layer of the laminate for protecting the coated object and improving the appearance. The cured layer of the clear coat layer (II) is formed by applying a clear paint composition (CC) onto the base coat layer (I) and heating it at 70°C or less.

[0046] As described above, the clear coating composition (CC) of the present invention comprises a hydroxyl-containing acrylic resin (A1) having a glass transition temperature (Tg) of 20°C or higher and 70°C or lower, an isocyanate curing agent (A2), and a hydroxyl-containing polyester resin (D).

[0047] (Hydroxyl group-containing acrylic resin (A1) having a glass transition temperature (Tg) of 20°C or higher and 70°C or lower) The hydroxyl group-containing acrylic resin (A1) (hereinafter also referred to as hydroxyl group-containing acrylic resin (A1)) having a glass transition temperature (Tg) of 20°C or more and 70°C or less can be obtained by polymerization of a radically polymerizable monomer having a hydroxyl group, or by copolymerization of a radically polymerizable monomer having a hydroxyl group with another radically polymerizable monomer.

[0048] Examples of the radically polymerizable monomer having a hydroxyl group include (meth)acrylic acid hydroxyalkyl esters such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate; unsaturated aliphatic alcohols such as allyl alcohol; ethylene oxide and / or propylene oxide adducts of the above-mentioned (meth)acrylic acid hydroxyalkyl esters; and ε-caprolactone adducts of the above-mentioned (meth)acrylic acid hydroxyalkyl esters, and these can be used alone or in combination of two or more.

[0049] Other radical polymerizable monomers include, for example, alkyl (meth)acrylates such as methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, sec-butyl (meth)acrylate, tert-butyl (meth)acrylate, hexyl (meth)acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, lauryl (meth)acrylate, and stearyl (meth)acrylate; acrylic acid; methacrylic acid; styrene; acrylonitrile; methacrylonitrile; acrylamide; and methacrylamide; and these may be used alone or in combination of two or more.

[0050] The glass transition temperature (Tg) of the hydroxyl group-containing acrylic resin (A1) can be adjusted to a range of 20°C or higher and 70°C or lower, higher than conventional values, by, for example, increasing the blending ratio of tert-butyl methacrylate, methyl methacrylate, styrene, cyclohexyl methacrylate, etc.

[0051] On the other hand, the glass transition temperature (Tg) of the hydroxyl group-containing acrylic resin (A1) can be adjusted to a lower value by increasing the blending ratio of an ester of a long-chain aliphatic alcohol and (meth)acrylic acid, such as stearyl methacrylate.

[0052] If the glass transition temperature (Tg) of the hydroxyl-containing acrylic resin (A1) is less than 20°C, the hardness of the film (cured layer) after curing decreases, which is undesirable, as does the gasoline resistance. On the other hand, if the glass transition temperature (Tg) of the hydroxyl-containing acrylic resin (A1) is more than 70°C, the low-temperature flexibility of the film (cured layer) after curing decreases, which is undesirable.

[0053] The glass transition temperature (Tg) of the hydroxyl group-containing acrylic resin (A1) is more preferably 20°C or higher and 50°C or lower.

[0054] The amount (solid content) of the hydroxyl group-containing acrylic resin (A1) is preferably 20% by mass or more and 80% by mass or less, and more preferably 40% by mass or more and 70% by mass or less, based on the total mass of the solid content of the resin components excluding the isocyanate curing agent (A2) contained in the clear coating composition (CC).

[0055] The hydroxyl value of the hydroxyl-containing acrylic resin (A1) is preferably 80 mgKOH / g or more and 200 mgKOH / g or less, and particularly preferably 120 gKOH / g or more and 200 mgKOH / g or less. When the hydroxyl-containing acrylic resin (A1) has a hydroxyl value of 80 mgKOH / g or more, the reactivity with the isocyanate curing agent (A2) is further improved, and when the hydroxyl-containing acrylic resin (A1) has a hydroxyl value of 200 mgKOH / g or less, the compatibility with the hydroxyl-containing polyester resin (D) is further improved.

[0056] The hydroxyl value of the hydroxyl-containing acrylic resin (A1) can be appropriately set by adjusting the compounding ratio of the radically polymerizable monomer having a hydroxyl group to the other radically polymerizable monomers during the synthesis of the hydroxyl-containing acrylic resin (A1).

[0057] The weight average molecular weight (Mw) of the hydroxyl-containing acrylic resin (A1) is preferably 2000 g / mol or more and less than 10000 g / mol, more preferably 3000 g / mol or more and 9000 g / mol or less, and particularly preferably 3000 g / mol or more and 5000 g / mol or less. When the weight average molecular weight (Mw) of the hydroxyl-containing acrylic resin (A1) is 2000 g / mol or more, better coating workability can be obtained, and when the weight average molecular weight (Mw) of the hydroxyl-containing acrylic resin (A1) is less than 10000 g / mol, better compatibility with the hydroxyl-containing polyester resin (D) can be obtained.

[0058] In the present invention, the mass average molecular weight (Mw) was determined by gel permeation chromatography (GPC) using tetrahydrofuran (THF) as an eluent at a temperature of 40°C and a flow rate of 1 m / min, and the data was converted to the mass average molecular weight of polystyrene as a standard. The gel permeation chromatography (GPC) columns used were a combination of TSKgel G2000HXL, G3000HXL, G4000HXL, and G5000HXL (product names, manufactured by Tosoh Corporation).

[0059] (Isocyanate curing agent (A2)) The isocyanate curing agent (A2) is a curing agent that reacts with hydroxyl groups to form urethane bonds, thereby curing the coating film, and is not particularly limited as long as it is used in coating applications, and various isocyanate compounds such as aromatic, aliphatic, and alicyclic isocyanate compounds can be used.

[0060] Examples of such isocyanate curing agents (A2) include aliphatic diisocyanates such as hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, and dimer acid diisocyanate; aromatic diisocyanates such as xylylene diisocyanate (XDI), tolylene diisocyanate (TDI), and 4,4-diphenylmethane diisocyanate (MDI); alicyclic diisocyanates such as isophorone diisocyanate, hydrogenated XDI, hydrogenated TDI, and hydrogenated MDI; and compounds comprising diisocyanate dimers, trimers, or higher diisocyanates such as uretdione, allophanate, adduct, biuret, and isocyanurate derivatives of these. Alternatively, the compound may be an aliphatic triisocyanate compound such as 2-isocyanateethyl-2,6-diisocyanate caproate (LTI) or 1,8-diisocyanato-4-isocyanatomethyloctane, or a compound in which some of the isocyanate groups have been modified with an amino group-containing silane coupling agent or the like.

[0061] In particular, from the viewpoint of achieving both flexibility and hardness of the cured film (cured layer), it is preferable that the isocyanate curing agent (A2) contains a polyisocyanate that is a trimer of diisocyanate, and it is particularly preferable that the isocyanate curing agent (A2) contains a polyisocyanate having an isocyanurate structure.

[0062] These isocyanate curing agents (A2) may be used alone or in combination of two or more.

[0063] The amount of isocyanate curing agent (A2) in the clear coating composition (CC) of the present invention is as follows: The clear coating composition (CC) of the present invention preferably contains 0.8 to 1.6 equivalents of isocyanate groups in the isocyanate curing agent (A2) per equivalent of the total of hydroxyl groups in the hydroxyl-containing acrylic resin (A1) and the hydroxyl-containing polyester resin (D), and more preferably 0.9 to 1.1 equivalents.

[0064] (Hydroxyl group-containing polyester resin (D)) The hydroxyl group-containing polyester resin (D) includes a hydroxyl group-containing polyester resin (D1) (hereinafter also referred to as hydroxyl group-containing polyester resin (D1)) obtained by an esterification reaction between a monovalent or higher carboxylic acid and a polyhydric alcohol, and / or a hydroxyl group-containing polyester resin (D2) (hereinafter also referred to as hydroxyl group-containing polyester resin (D2)) that can be obtained by an ester exchange reaction between a fatty acid ester and a polyhydric alcohol.

[0065] Examples of monovalent or higher carboxylic acids include saturated or unsaturated monocarboxylic acids having 2 to 20 carbon atoms and saturated or unsaturated dicarboxylic acids having 2 to 12 carbon atoms. Saturated or unsaturated dicarboxylic acids having 2 to 12 carbon atoms include dicarboxylic acids having an aromatic ring, such as phthalic acid, isophthalic acid, and terephthalic acid, and also acid anhydrides, such as phthalic anhydride.

[0066] Examples of polyhydric alcohols include dihydric alcohols such as ethylene glycol and propylene glycol, trihydric alcohols such as glycerin and trimethylolpropane, tetrahydric alcohols such as pentaerythritol and erythritol, pentahydric alcohols such as xylitol, and hexahydric alcohols such as sorbitol and mannitol.

[0067] Examples of fatty acid esters include ester reaction products of saturated or unsaturated aliphatic monocarboxylic acids having 2 to 20 carbon atoms among the above-mentioned monovalent or higher carboxylic acids and the above-mentioned polyhydric alcohols. It is preferable that the above-mentioned saturated or unsaturated aliphatic monocarboxylic acids having 2 to 20 carbon atoms used in the esterification reaction contain a hydroxyl group.

[0068] The fatty acid ester does not necessarily have to have all the hydroxyl groups of the polyhydric alcohol reacted with carboxyl groups, but is preferably a fatty acid ester in which all the hydroxyl groups of the polyhydric alcohol are ester-bonded to carboxyl groups. That is, as long as it is an ester of glycerin and a fatty acid, it may be a fatty acid monoglyceride or a fatty acid diglyceride, but is preferably a fatty acid triglyceride.

[0069] Furthermore, in synthesizing the hydroxyl group-containing polyester resin (D1), a compound having an epoxy group can be used in place of the polyhydric alcohol. Preferred examples of the compound having an epoxy group include glycidyl esters or glycidyl ethers having one epoxy group per molecule, which are obtained by reacting a fatty acid or alcohol having 2 to 16 carbon atoms with epichlorohydrin. Commercially available products that can be used include, for example, Cardura E10P (trade name, manufactured by Hexion) and Adeka Glycirol ED-502 (trade name, manufactured by ADEKA Corporation).

[0070] The weight average molecular weight (Mw) of the hydroxyl group-containing polyester resin (D) is preferably 300 g / mol or more and 10,000 g / mol or less.

[0071] Moreover, the hydroxyl value of the hydroxyl-containing polyester resin (D) is preferably 100 mgKOH / g or more, particularly preferably 150 mgKOH / g or more.

[0072] In particular, the hydroxyl group-containing polyester resin (D) is preferably a mixture of a hydroxyl group-containing polyester resin (D1) obtained by an ester reaction between a monovalent or higher carboxylic acid and a polyhydric alcohol, and a hydroxyl group-containing polyester resin (D2) obtainable by an ester exchange reaction between a fatty acid ester and a polyhydric alcohol.

[0073] When the hydroxyl-containing polyester resin (D) contains the hydroxyl-containing polyester resin (D1), the laminate has sufficient crosslinking points and the appearance (SW value) is improved. Furthermore, when the hydroxyl-containing polyester resin (D) contains the hydroxyl-containing polyester resin (D2), the recoatability of the laminate is improved and the appearance (SW value) is further improved.

[0074] The weight average molecular weight (Mw) of the hydroxyl-containing polyester resin (D1) is, for example, 500 g / mol to 10,000 g / mol, preferably 800 g / mol to 5,000 g / mol, and the weight average molecular weight (Mw) of the hydroxyl-containing polyester resin (D2) is, for example, 300 g / mol to 5,000 g / mol, preferably 300 g / mol to 4,000 g / mol.

[0075] In the present invention, the amount (solid content) of the hydroxyl-containing polyester resin (D) is preferably 3 to 50 mass %, more preferably 10 to 50 mass %, and particularly preferably 30 to 50 mass parts, based on the total mass of the solid content of the resin components excluding the isocyanate curing agent (A2) contained in the clear coating composition (CC). When the amount (solid content) of the hydroxyl-containing polyester resin (D) is 3 mass % or more, the appearance of the film after curing (cured film) is further improved, and when the amount (solid content) of the hydroxyl-containing polyester resin (D) is 50 mass % or less, the hardness of the film after curing (cured film) is further improved.

[0076] (Catalyst (E)) The clear coating composition (CC) of the present invention preferably contains a catalyst (E) that accelerates urethane curing. Addition of the catalyst (E) to the clear coating composition (CC) accelerates the urethane bond-forming reaction between the hydroxyl-containing acrylic resin (A1), the isocyanate curing agent (A2), and the hydroxyl-containing polyester resin (D). Examples of the catalyst (E) include bismuth-based compounds, aluminum-based compounds, tin-based compounds, and zinc-based compounds.

[0077] Examples of the bismuth-based compounds include bismuth bis(acetylacetone), bismuth 2-ethylhexanoate, bismuth neodecanoate, and bismuth salicylate.

[0078] Examples of the aluminum compounds include aluminum tris(acetylacetonate) and aluminum tris(ethylacetoacetate).

[0079] Examples of the tin compounds include dimethyltin dilaurate, dibutyltin dilaurate, dimethyltin chloride, dibutyltin chloride, and di-n-octyltin dilaurate.

[0080] Examples of the zinc-based compounds include zinc acetylacetonate, zinc propionate, zinc octanoate, zinc 2-ethylhexanoate, zinc neodecanoate, zinc laurate, zinc stearate, zinc linoleate, zinc naphthenate, zinc benzoate, and zinc salicylate.

[0081] The amount (solid content) of the catalyst (E) is 2 mass % or less, preferably 0.001 to 1.5 mass %, based on the total mass of the solid content of the resin components excluding the isocyanate curing agent (A2) contained in the clear coating composition (CC).

[0082] (Rheology modifier (F)) The clear coating composition (CC) of the present invention preferably contains a rheology modifier (F), which imparts various functions to the clear coating composition (CC), such as preventing sagging during application, adjusting the coating thickness, improving ease of application, and improving leveling properties.

[0083] In the present invention, examples of the rheology modifier (F) include hydroxyl group-containing acrylic resins having a glass transition temperature (Tg) of less than 10° C., polyethylene wax, polyamide wax, and internally crosslinked resin particles.

[0084] The amount (solid content) of the rheology modifier (F) is, for example, 0.01 mass % or more and 10 mass % or less, preferably 0.01 mass % or more and 8 mass % or less, based on the total mass of the solid content of the resin components excluding the isocyanate curing agent (A2) contained in the clear coating composition (CC).

[0085] The clear coating composition (CC) used in the present invention may also contain a coloring pigment to the extent that transparency is not impaired. Examples of coloring pigments include inorganic pigments such as titanium oxide pigments, iron oxide pigments, and composite oxide pigments such as titanium yellow, azo pigments, quinacridone pigments, diketopyrrolopyrrole pigments, perylene pigments, perinone pigments, benzimidazolone pigments, isoindoline pigments, isoindolinone pigments, metal chelate azo pigments, phthalocyanine pigments, anthraquinone pigments, dioxazine pigments, threne pigments, and indigo pigments, and organic pigments such as carbon black pigments. These coloring pigments may be used alone or in combination of two or more.

[0086] The total content of the color pigments contained in the clear coating composition (CC) used in the present invention is not particularly limited, but is preferably 10 mass % or less, and more preferably 0 to 5 mass %, based on the total mass of the solid content of the resin components excluding the isocyanate curing agent (A2) contained in the clear coating composition (CC).

[0087] The clear coating composition (CC) used in the present invention may further contain, as necessary, various paint additives such as organic solvents, pigment dispersants, anti-settling agents, antifoaming agents, antioxidants, and UV absorbers, and extender pigments. Examples of organic solvents include those commonly used in the production of clear coating compositions (CC), such as aromatic hydrocarbons such as toluene, xylene, and aromatic naphtha; ketones such as acetone, methyl ethyl ketone, and methyl amyl ketone; esters such as ethyl acetate, butyl acetate, 2-butoxyethyl acetate, pentyl acetate, and ethyl ethoxypropionate; ethers; and aliphatic hydrocarbons including chlorinated hydrocarbons, or mixtures thereof. However, the use of alcohol is not recommended if it is expected to interfere with the curing reaction.

[0088] The clear coating composition (CC) used in the present invention can be applied by electrostatic coating, air spray, airless spray, etc. Generally, after application of the clear coating composition (CC), it is left at room temperature for 5 to 20 minutes and then heat cured.

[0089] The cured layer of the clear coat layer (II) obtained after heat curing has an inter-crosslinking molecular weight (Mc) of 800 g / mol or less, preferably an inter-crosslinking molecular weight (Mc) of 500 g / mol or less, and particularly preferably an inter-crosslinking molecular weight (Mc) of 200 g / mol or more and 500 g / mol or less. When the cured layer of the clear coat layer (II) has an inter-crosslinking molecular weight (Mc) of 800 g / mol or less, the gasoline resistance and water resistance of the obtained laminate are improved. The method for measuring the inter-crosslinking molecular weight (Mc) will be described in detail in the Examples.

[0090] The pencil hardness of the resulting laminate is preferably 6B or more, and particularly preferably 3B or more.

[0091] <Method of manufacturing laminate> 1 is a flow diagram showing a method for producing a laminate of the present invention. As shown in the figure, the method for producing a laminate of the present invention includes a base coat layer (I) forming step (S110), a clear coat layer (II) forming step (S120), and a curing step (S130).

[0092] [Base coat layer (I) forming step (S110)] In this step, a base coat paint composition is applied to a substrate to form a base coat layer (I). The substrate and base coat paint composition have already been explained in the laminate invention, so explanations thereof will be omitted here.

[0093] The base coat layer (I) is formed by applying a base coat paint composition by electrostatic coating, air spraying, airless spraying, or other methods. After application of the base coat paint composition, the coating is left at room temperature for 3 to 5 minutes to evaporate the solvent contained in the coating. Thereafter, preliminary drying (flash-off) may or may not be performed under heating conditions that do not complete curing, such as at 60°C for about 5 minutes.

[0094] The thickness of the cured layer of the base coat layer (I) is not particularly limited, but the base coat paint composition is applied so that the film thickness (dry film thickness) after the heat treatment in the curing step (S130) described below is preferably 2 to 30 μm, more preferably 5 to 20 μm.

[0095] This step may also be repeated twice. For example, when the substrate is a steel material constituting an automobile body, a lower base coat layer (I-1) that serves as an impact-absorbing layer is first formed by this step and left at room temperature for 3 to 5 minutes. This may be followed by preliminary drying (flash-off) under heating conditions that do not complete curing, such as at 60°C for about 5 minutes, or may not be performed. This step may then be further performed to form an upper base coat layer (I-2) that serves as a colored layer. In this case, the base coat paint compositions for the lower base coat layer (I-1) and the upper base coat layer (I-2) can be prepared by appropriately mixing the components of the base coat paint composition described in the laminate invention according to the purpose (this is the base coat layer (I) formation step (S110)).

[0096] [Clear coat layer (II) forming step (S120)] In this step, a clear coating composition (CC) is applied onto the (uncured) base coat layer (I) obtained in the base coat layer (I) forming step to form a clear coat layer (II).

[0097] In the present invention, the clear coating composition (CC) used to form the clear coat layer (II) contains a hydroxyl-containing acrylic resin (A1) having a glass transition temperature (Tg) of 20° C. or higher and 70° C. or lower, an isocyanate curing agent (A2), and a hydroxyl-containing polyester resin (D). Note that the clear coating composition (CC), the hydroxyl-containing acrylic resin (A1) having a glass transition temperature (Tg) of 20° C. or higher and 70° C. or lower, the isocyanate curing agent (A2), and the hydroxyl-containing polyester resin (D) are the same as those explained in the laminate invention, and therefore explanations thereof will be omitted here.

[0098] As in the case of the base coat layer (I), the clear coat layer (II) is also formed by applying the clear coating composition (CC) by a method such as electrostatic coating, air spray, airless spray, etc. Furthermore, after applying the clear coating composition (CC), it is generally left to stand at room temperature for 3 to 5 minutes to evaporate the solvent contained in the coating film.

[0099] The clear coating composition (CC) is preferably applied so that the dry film thickness of the clear coat layer (II) is preferably 20 to 50 μm, more preferably 25 to 45 μm. The dry film thickness of the clear coat layer (II) is the film thickness after the heat treatment in the curing step (S130) described below (this is the clear coat layer (II) forming step (S120)).

[0100] [Curing process (S130)] In this step, the (uncured) base coat layer (I) and the (uncured) clear coat layer (II) are cured by heating at 70°C or less, preferably 60°C or more and 70°C or less, to obtain a laminate consisting of each cured layer.

[0101] The heating time varies somewhat depending on the film thickness of the base coat layer (I) and the clear coat layer (II), but is generally 5 to 20 minutes, preferably 8 to 15 minutes.

[0102] The cured layer of the clear coat layer (II) obtained in this step has a molecular weight (Mc) between crosslinking points of 800 g / mol or less, preferably a molecular weight (Mc) between crosslinking points of 500 g / mol or less, and particularly preferably a molecular weight (Mc) between crosslinking points of 200 g / mol or more and 500 g / mol or less (these are the curing steps (S130)).

[0103] As described above, according to the laminate of the present invention and the method for producing the laminate of the present invention, the obtained laminate has high hardness and is excellent not only in appearance, water resistance, and gasoline resistance but also in low-temperature flexibility and recoat adhesion, even when heat-cured at a low temperature of 70°C or less.

[0104] The laminate of the present invention and the laminate obtained by the method for producing a laminate of the present invention are applicable to automobile bodies, members, and parts of automobiles such as passenger cars, trucks, motorcycles, buses, etc. When the substrate is metal, the laminate is particularly effective for automobile bodies, and when the substrate is plastic, the laminate is particularly effective for automobile interior and exterior parts. [Example]

[0105] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. In the examples, "parts" means "parts by mass" unless otherwise specified, and "%" regarding blend amounts and contents means "% by mass." [Method for measuring resin characteristic values] In the present invention, the resin characteristic values were measured by the following methods. 1. Hydroxyl value: Measured in accordance with JIS-K1557-1:2007. 2. Acid value: Measured in accordance with JIS-K5601-2-1:1999.

[0106] <Synthesis of hydroxyl group-containing acrylic resin (A1)> [Synthesis Example 1] A flask equipped with a dropping apparatus, a reflux condenser, a thermometer, a stirrer, and a nitrogen gas inlet tube was charged with 57.0 parts of ethyl 3-ethoxypropionate (EEP) as a solvent and 30.0 parts of ethyl acetate, and heated to 75 ° C. under a nitrogen stream with stirring. A mixture of 15.0 parts of styrene (St), 20.0 parts of 4-hydroxybutyl acrylate (HBA), 25.0 parts of 2-hydroxyethyl methacrylate (HEMA), 32.0 parts of cyclohexyl methacrylate (CHMA), 8.0 parts of 2-ethylhexyl acrylate (EHA), and 5.3 parts of 2,2'-azobis(isobutyronitrile) as a polymerization initiator was added dropwise to the dropping apparatus at a constant rate for 3 hours while maintaining the temperature at 75 ° C., and then stirring was continued for another 5 hours at 75 ° C. After measuring the resin solid content to confirm that the conversion rate exceeded 98%, the solvent was removed under reduced pressure until the solid content (NV%) reached 60%, yielding a solution of hydroxyl-containing acrylic resin (A1-1). The glass transition temperature (Tg) of the hydroxyl-containing acrylic resin (A1-1) was 23°C.

[0107] [Synthesis Examples 2 to 5] Solutions of hydroxyl-containing acrylic resins (A1-2 to A1-5) were obtained in the same manner as the solution of hydroxyl-containing acrylic resin (A1-1), except that the initial solvent amount, monomer composition, blending amount, and initiator amount were changed to those shown in Table 1.

[0108] The compound names shown as abbreviations in Table 1 and [Synthesis Examples 1 to 5] are as follows.

[0109] St: styrene HBA: 4-hydroxybutyl acrylate HEMA: 2-hydroxyethyl methacrylate MMA: methyl methacrylate EHA: 2-ethylhexyl acrylate CHMA: Cyclohexyl methacrylate

[0110] [Table 1]

[0111] <Synthesis of Hydroxyl Group-Containing Polyester Resin (D1)> [Synthesis Example 6] A flask equipped with a dropping device, reflux condenser, thermometer, and stirrer was charged with 47 parts of Solvesso 100 (trade name, manufactured by Ando Parachemie Co., Ltd.) as a solvent, 34 parts of hexahydrophthalic anhydride, 22 parts of dodecanoic acid NAA-122 (trade name, manufactured by NOF Corporation), 24 parts of pentaerythritol, and 20 parts of Cardura E10P (trade name, manufactured by Hexion), and the temperature was raised to 165 ° C. with stirring. The reaction was continued for 3 hours at 165 ° C., and after confirming that the acid value had reached 5 mg KOH / g, the mixture was cooled to obtain a hydroxyl group-containing polyester resin (D1-1) solution with a solids content (NV%) of 65%, a hydroxyl value of 189 mg KOH / g, and a mass average molecular weight (Mw) of 3000 g / mol.

[0112] <Synthesis of Hydroxyl Group-Containing Polyester Resin (D2)> [Synthesis Examples 7 and 8] A flask equipped with a dropping device, reflux condenser, thermometer, stirrer, and nitrogen gas inlet tube was charged with refined castor oil LAV (trade name, manufactured by Ito Oil Mills, Ltd., DI1), pentaerythritol (DI2-1), trimethylolpropane (DI2-2), glycerol (DI2-3), and sorbitol (DI2-4) in the amounts shown in Table 2. Tetrabutyl titanate (addition amount: 0.5% of the castor oil mass) was added as a catalyst, and the temperature was raised to 220°C with stirring. Viscosity measurements were taken every 30 minutes, and after confirming that the viscosity had ceased to change, the mixture was cooled to obtain hydroxyl-containing polyester resins (D2-1-2).

[0113] [Synthesis Example 9] A flask equipped with a dropping device, reflux condenser, thermometer, stirrer, and nitrogen gas inlet tube was charged with refined castor oil LAV (trade name, manufactured by Ito Oil Mills, Ltd., DI1), sorbitol (DI2-4), and hexahydrophthalic anhydride (DI3-1) in the parts by mass shown in Table 2, and the mixture was heated to 220°C with stirring. The reaction was continued for 3 hours, and after it was confirmed that the acid value could no longer be measured, the mixture was cooled to obtain a hydroxyl group-containing polyester resin (D2-3).

[0114] [Table 2]

[0115] <Synthesis of rheology modifier (F-1)> [Synthesis Example 10] A flask equipped with a dropping device, reflux condenser, thermometer, stirrer, and nitrogen gas inlet tube was charged with 60 parts of Solvesso 100 (trade name, manufactured by Ando Parachemie Co., Ltd.) as a solvent and heated to 155 ° C. Next, 34 parts of n-butyl acrylate, 21 parts of 2-hydroxyethyl acrylate, 39 parts of styrene, 2 parts of methacrylic acid, and 2 parts of di-tert-butyl peroxide as an initiator were mixed and added dropwise at 155 ° C. over 2 hours. The reaction was continued for 3 hours, and after confirming that the conversion rate exceeded 98% by measuring the resin solids content, the mixture was cooled to obtain a rheology modifier (F-1) solution with a solids content (NV%) of 60%. The Tg of the rheology modifier (F-1) was 5 ° C.

[0116] <Preparation of clear coating composition (CC)> [Preparation Example 1] 48 parts of hydroxyl group-containing acrylic resin (A1-1) solution, 30 parts of hydroxyl group-containing polyester resin (D1-1) solution, 5 parts of hydroxyl group-containing polyester resin (D1-2), 5 parts of rheology modifier (F-1) solution, 36 parts of isocyanate curing agent (A2-1) (1.0 equivalent of isocyanate groups in the isocyanate curing agent (A2-1) relative to 1 equivalent of all hydroxyl groups in the clear coating composition (CC-1) described later), and 0.01 parts of urethane curing catalyst (E-1) were weighed, and then diluted with 3-ethoxyethyl propionate as a solvent to a Ford Cup #4 viscosity of 25 seconds (20 ° C), and stirred until sufficiently uniform with a paint shaker. Then, the mixture was filtered through a 350 mesh (30 μm wire diameter) filter to remove coarse particles, and a clear coating composition (CC-1) was obtained.

[0117] [Preparation Examples 2-13] The components to be mixed and their blending ratios were changed to achieve the blending ratios shown in Table 3, and clear coating compositions (CC-2 to 13) were obtained in the same manner as for clear coating composition (CC-1).

[0118] <Evaluation of molecular weight between crosslinks (Mc)> The clear coating compositions (CC-1 to 13) were applied to polypropylene plates using a rotary atomizer electrostatic coater to form a cured coating film with a thickness of 35 μm (dry film thickness). The plates were left at room temperature for 7 minutes, heated in a hot air circulating drying oven at 70°C for 10 minutes, and then the resulting coating film was peeled off to produce test plates for Examples 1 to 10 and Comparative Examples 1 to 3.

[0119] Next, test pieces 5 mm wide and 10 mm long were cut out from each test plate and subjected to dynamic viscoelasticity measurements (storage modulus (E'), loss modulus (E'') and loss tangent (tanδ)) under the following conditions, and the molecular weight between crosslinks (Mc) was measured using the following equation 1. The smaller the molecular weight between crosslinks (Mc), the denser the crosslinked structure. Apparatus: Dynamic viscoelasticity measuring device RSA3 (TA Instruments) Measurement mode: Non-resonant forced vibration method Heating rate: 3.0℃ / min Measurement interval: 12 / min Frequency: 1.0Hz Temperature range: 30~180℃ Molecular weight between crosslinking points (Mc)=3ρRT / E'min (Formula 1) (Molecular weight between crosslinking points (Mc): g / mol E'min:Pa ρ (density): g / m 3 R (gas constant): J / mol K T (absolute temperature of E'min: K)

[0120] The evaluation criteria for the molecular weight between crosslinks (Mc) were as follows, with ◯ and △ being in the acceptable range. ○:200≦Mc≦500 △:500 <Mc≦800 ×: Mc>800 or Mc<200

[0121] <Production of laminate for performance evaluation> A polypropylene test panel was air-sprayed with a primer (Pr) of Primac No. 1501 (product name, BASF Japan Co., Ltd., conductive primer) to a dry film thickness of 7 μm, and then left at room temperature for 10 minutes. A solvent-based base coat paint, Primac No. 8800 Silver (product name, BASF Japan Co., Ltd., one-component acrylic paint), was then electrostatically applied as a base coat (BC) to a dry film thickness of 15 μm, and left at room temperature for 5 minutes to form a base coat layer (I). Next, the clear coating composition (CC) listed in Table 3 was electrostatically applied to the base coat layer (I) to a dry film thickness of 35 μm. The coating was then left at room temperature for 10 minutes, and then heated at 70 ° C for 10 minutes to obtain a test panel (laminate) with a cured multilayer coating film. Hereinafter, various performance evaluation tests using this test coating will be described.

[0122] <Evaluation of pencil hardness> The pencil hardness of the test coated plate (laminate) was measured at a temperature of 25°C and a humidity of 65%RH in accordance with JIS K 5600-5-4 (1999). The pencil hardness was evaluated according to the following criteria, with ◯ and △ representing acceptable ranges. 〇: 3B or higher. Excellent hardness. △: 4B or less, 6B or more. Usable. ×: Measurement impossible, failure.

[0123] <Evaluation of finish> The Long Wave (LW) value and Short Wave (SW) value of the test coated plate (laminate) were measured using a Wave Scan (trade name, manufactured by BYK Gardner) and the finished appearance was evaluated.

[0124] The LW value is an index of smoothness, and the smaller the LW value, the smoother the coating surface. The evaluation criteria for LW values are as follows, with ◯ and △ being in the pass range.

[0125] ○:0 <LW<5 △:5≦LW<10 ×:LW≧10

[0126] The SW value is an index of image clarity, and the smaller the SW value, the higher the image clarity of the coating surface. The evaluation criteria for SW values are as follows, with ◯ and △ being in the pass range. ○:5≦SW<25 △:3 <SW<5、25≦SW≦30 ×: SW≦3, SW>30

[0127] <Water resistance (blister) evaluation> The test coated plate (laminate) was immersed in warm water at 40°C for 10 days, then removed and dried. The coated surface was then visually inspected and the occurrence of blistering was evaluated according to the following criteria. ⊚, ◯, and △ were considered acceptable. ◎: No blistering occurred. ◯: The area where blisters occurred was 10% or less of the total area. △: The area where blisters occurred was 11% or more and 30% or less of the total area. ×: The area where blisters occurred was 31% or more of the total area.

[0128] <Evaluation of water resistance (adhesion)> The test coated plate (laminate) was immersed in warm water at 40°C for 10 days, removed, and dried. Subsequently, scores were made with a cutter on the coating surface of the test coated plate so that they reached the substrate, creating 100 2mm x 2mm grids. Cellotape (registered trademark) was attached to the surface and then rapidly peeled off at a 45° angle at 20°C. Evaluation was based on the number of remaining coatings in the grids according to the following criteria, with ⊚, ◯, and △ representing acceptable ranges. ◎: 100 pieces (no peeling). 〇: 99 pieces (some peeling). △: 51 or more and 98 or less. ×: Less than 50 pieces.

[0129] <Evaluation of gasoline resistance> Gasoline resistance was evaluated by immersing the test coated plate (laminate) in unleaded regular gasoline (No. 2 as defined in JIS K2202:2012) at 20°C for 24 hours, visually inspecting the appearance, and evaluating it according to the following criteria. ◯ and △ were considered acceptable.

[0130] ○: No abnormalities were observed. △: Slight yellowing, swelling, and other abnormalities were observed. ×: Abnormalities such as yellowing and swelling were observed.

[0131] <Evaluation of low-temperature flexibility> A 5mm thick polypropylene plate was coated and left to stand in a -20°C atmosphere for 4 hours, then the test plate (laminate) was bent 180° between 20mm diameter iron bars and the coating film at the bent part was observed and evaluated according to the following criteria. ◯ and △ were considered acceptable. O: No change at all. △: Minor wrinkles were generated. ×: Significant cracking occurred.

[0132] <Evaluation of recoat adhesion> The primer (Pr), base coat (BC), and clear paint composition (CC) were applied in that order, and heated to form a test coated plate (laminate) on which the resulting multi-layer coating film had hardened. This test plate was then left at room temperature for 7 days, and the surface (the surface of the cured layer of the clear coat layer obtained by curing the clear paint composition (CC)) was then repainted (recoated) with the base coat (BC) and clear paint composition (CC) and heated to form a multi-layer coating film.

[0133] The multilayer coating film laminate thus obtained was left to stand at room temperature for 3 days, and then subjected to the same water resistance (adhesion) evaluation test as above to check the number of remaining coating films and evaluate them according to the following criteria. ◯ and △ were considered to be within the acceptable range. 〇: 100 pieces (no peeling) or 99 pieces (some peeling). △: 51 or more and 98 or less. ×: Less than 50 pieces.

[0134] [Table 3]

[0135] The specific components of the isocyanate curing agent (A2) and catalyst (E) used in Table 3 are explained below.

[0136] Isocyanate hardener (A2): Isocyanate curing agent (A2-1): Duranate TPA-100 (trade name, manufactured by Asahi Kasei Corporation, diisocyanate trimer or higher compound, NCO content: 23.1%) Isocyanate curing agent (A2-2): Duranate TKA-100 (trade name, manufactured by Asahi Kasei Corporation, diisocyanate trimer or higher compound, NCO content: 21.7%) Catalyst (E): Urethane curing catalyst (E-1): K-KAT 348 (product name, manufactured by KING INDUSTRIES) Urethane curing catalyst (E-2): K-KAT XK-614 (product name, manufactured by KING INDUSTRIES)

[0137] The total resin components in Table 3 is the sum of the solid contents of the hydroxyl-containing acrylic resin (A1), the hydroxyl-containing polyester resin (D), and the rheology modifier (F), and does not include the solid content of the isocyanate curing agent (A2).

[0138] As shown in Table 3, when a coating film of a clear coating composition containing a hydroxyl group-containing acrylic resin and an isocyanate curing agent was cured at a low temperature of 70°C, (a) the Tg of the hydroxyl group-containing acrylic resin is 20°C or higher and 70°C or lower; (b) containing a hydroxyl group-containing polyester resin (D), and (c) the molecular weight between crosslinking points (Mc) of the cured layer of the clear coat layer (II) is 800 g / mol or less; All of the laminates satisfying the above requirements were satisfactory in hardness, appearance (LW, SW), water resistance (blistering, adhesion), gasoline resistance, low-temperature flexibility, and recoat adhesion (see Examples 1 to 10). However, Comparative Example 1 (Tg below the lower limit) which did not satisfy requirement (a) showed poor appearance (LW, SW) and water resistance (blistering), and Comparative Example 2 (Tg above the upper limit) which also did not satisfy requirement (a) showed poor water resistance (adhesion), gasoline resistance, and low-temperature flexibility in addition to poor appearance (LW, SW) and water resistance (blistering).

[0139] Furthermore, in Comparative Example 3, which satisfied requirement (a) but did not contain a hydroxyl group-containing polyester resin (D) in the clear coating composition (i.e., did not satisfy requirement (b)), the hardness, appearance, water resistance (LW, SW), water resistance (blister, adhesion), gasoline resistance, low-temperature flexibility, and recoat adhesion of the laminate were deteriorated.

Claims

1. A laminate comprising a base coat layer (I) on an object to be coated and a clear coat layer (II) on the base coat layer (I), The cured layer of the clear coat layer (II) is formed by heating a coating film of a clear coating composition (CC) containing a hydroxyl group-containing acrylic resin (A1) having a Tg of 20°C or higher and 70°C or lower, an isocyanate curing agent (A2), and a hydroxyl group-containing polyester resin (D) at 70°C or lower, A laminate characterized in that the cured layer of the clear coat layer (II) has a molecular weight between crosslink points (Mc) of 800 g / mol or less.

2. 2. The laminate according to claim 1, wherein the blending amount (solid content) of the hydroxyl group-containing polyester resin (D) is 3% by mass or more and 50% by mass or less relative to the total mass of the solid content of the resin components excluding the isocyanate curing agent (A2) contained in the clear coating composition (CC).

3. 3. The laminate according to claim 1, wherein the hydroxyl group-containing polyester resin (D) has a mass average molecular weight (Mw) of 500 g / mol or more and 5,000 g / mol or less.

4. 3. The laminate according to claim 1, wherein the hydroxyl group-containing polyester resin (D) has a hydroxyl value of 100 mgKOH / g or more.

5. 2. The laminate according to claim 1, wherein the hydroxyl value of the hydroxyl-containing acrylic resin (A1) is 80 mgKOH / g or more and 200 mgKOH / g or less.

6. 6. The laminate according to claim 1, wherein the hydroxyl group-containing acrylic resin (A1) has a mass average molecular weight (Mw) of 2,000 g / mol or more and less than 10,000 g / mol.

7. 3. The laminate according to claim 1, wherein the clear coating composition (CC) contains 0.8 to 1.6 equivalents of isocyanate groups in the isocyanate curing agent (A2) relative to 1 equivalent of the total of hydroxyl groups in the hydroxyl-containing acrylic resin (A1) and the hydroxyl-containing polyester resin (D).

8. 3. The laminate according to claim 1, wherein the isocyanate curing agent (A2) contains a polyisocyanate having an isocyanurate structure.

9. 3. The laminate according to claim 1, wherein the pencil hardness of the laminate is 6B or more.

10. a base coat layer (I) forming step of applying a base coat paint composition to a substrate to form a base coat layer (I); A clear coat layer (II) forming step of applying a clear coating composition (CC) onto the base coat layer (I) obtained in the base coat layer (I) forming step to form a clear coat layer (II); a curing step of heating the base coat layer (I) and the clear coat layer (II) at 70°C or less to cure them, thereby obtaining a laminate consisting of the respective cured layers, The clear coating composition (CC) comprises a hydroxyl-containing acrylic resin (A1) having a glass transition temperature (Tg) of 20°C or higher and 70°C or lower, an isocyanate curing agent (A2), and a hydroxyl-containing polyester resin (D), A method for producing a laminate, wherein the cured layer of the clear coat layer (II) obtained in the curing step has a molecular weight between crosslinks (Mc) of 800 g / mol or less.

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