WO2025162646A1

WO2025162646A1 - Laminate, and method for producing laminate

Info

Publication number: WO2025162646A1
Application number: PCT/EP2024/086705
Authority: WO
Inventors: Etsumi Ito; Hideki SUETSUGU; Hideki Yamashita; Takeshi Tsunoda; Shintaro Sato
Original assignee: BASF Coatings GmbH
Current assignee: BASF Coatings GmbH
Priority date: 2024-01-30
Filing date: 2024-12-17
Publication date: 2025-08-07
Anticipated expiration: 2026-07-30
Also published as: JP2025117413A

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. 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 clear coat layer (II) has a molecular weight between cross-linking points (Mc) of 800 g/mol or less. A method for producing a laminate comprising the above cured layers is furthermore provided.

Description

[Document Name] SPECIFICATION

[Title of the Invention] Laminate, and Method for Producing Laminate [Technical Field]

[0001]

The present invention relates to a laminate as well as a method for producing the laminate, and in particular relates to 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), as well as a method for producing the laminate.

[Background Art]

[0002]

Conventionally, when vehicle parts (such as the bumper) are coated, if the object to be coated is made of resin, a multilayer coating film having a clear coat layer is formed by providing a primer layer on the resin base material, providing a coloured base coat layer on top of that, furthermore applying a two-component clear coat composition comprising a base resin (containing a hydroxy group-containing acrylic resin) and a curing agent (containing an isocyanate compound), for example, onto the coloured base coat layer, and baking the composition at 80 to 100°C.

[0003]

If the object to be coated is made of metal, such as the vehicle body, a multilayer coating film is formed by electrodeposition coating on the metal base material and then forming a coloured base coat layer and clear coat layer thereon in the same manner as for objects made of resin.

[0004]

In the last few years, laminated coating films have had to be thermally cured at lower temperatures such as 60 to 70°C to conserve energy and to address environmental concerns. However, even though the reaction between the hydroxy group-containing acrylic resin and the isocyanate curing agent is facilitated by heat, a potential risk of carrying out thermosetting at low temperatures is that the coating film will not be sufficiently cured.

[0005]

Another potential drawback that may occur when the coating film of the above two- component clear coat composition is thermally cured at a low temperature is that the cured coating film shows poor appearance and has poor gasoline resistance and water resistance.

[0006]

The following Patent Documents 1 to 3 here are examples of prior art documents that disclose conventional art for obtaining cured films by thermally curing a clear coat composition that composes a hydroxy group-containing acrylic resin and an isocyanate curing agent.

[0007]

Patent Document 1 discloses the formation of a multilayer coating film via the formation of first and second coloured coating films on an object to be coated that comprises metal and plastic materials, and the subsequent electrostatic application of a two-component clear coat composition that comprises a hydroxy group-containing acrylic resin (K) having a glass transition temperature (Tg) of -12°C, an isocyanate curing agent, and a hydroxy group-containing polyester resin, which is heated for 30 minutes in an oven at 95°C.

[0008]

Patent Document 2 discloses a coating composition for plastics, wherein said composition comprises a hydroxy group-containing acrylic resin having a glass transition temperature (Tg) of 49 to 79°C, an isocyanate curing agent, and a surface conditioning agent that must include a silicon-type surface conditioning agent and an acrylic-type surface conditioning agent, and the composition is cured by baking for 20 minutes at 80°C.

[0009]

Patent Document 3 discloses a coating method (three-coat, one-bake system) for applying an aqueous primer composition (I), an aqueous base coat composition (II), and a clear coat composition (III), in that order, onto a plastic moulded product, and simultaneously baking and curing the three coating films that have been formed, wherein the clear coat composition (III) comprises a hydroxy group-containing resin (F) and an isocyanate cross linking agent (G); the hydroxy group-containing resin (F) is selected from acrylic resins and polyester resins, for example, that contain hydroxyl groups; and the three coating film layers are baked for 5 to 60 minutes at a temperature in the range of 40 to 110°C.

[Prior Art Documents]

[Patent Documents]

[0010]

[Patent Document 1] Specification of WO 2015/087932 A1

[Patent Document 2] JP 2014-019714 A

[Patent Document 3] Specification of WO 2008/050778 A1 [Summary of the Invention] [Problems to be Solved by the Invention]

[0011]

However, according to the invention of Patent Document 1 , the electrostatically applied two-component clear coat composition is baked at an elevated temperature (95°C for 30 minutes) in the conventional manner, and no low-temperature baking conditions are disclosed. Also, the glass transition temperature (Tg) of the hydroxy group-containing acrylic resin (K) in the invention of Patent Document 1 is a low temperature of -12°C, and it is therefore possible that a cured coating film baked at a low temperature would not be hard enough and would thus have poor gasoline resistance.

[0012]

According to the invention of Patent Document 2, baking is carried out at 80°C in the conventional manner, and there is thus no way to guarantee hardness of the coating film under low-temperature baking conditions, so baking at a low temperature could potentially result in a cured coating film that has unsatisfactory hardness and gasoline resistance.

[0013]

According to the disclosure of the invention in Patent Document 3, the three coating film layers are baked at a low temperature, but in the examples, the three coating film layers are heated for 30 minutes at 90°C, so the properties of cured coating films when baked at a low temperature have not been confirmed. In terms of the clear coat composition (III), neither the combined use of an acrylic resin and a polyester resin as the hydroxy group- containing resin (F) in the clear coat composition (III) nor the glass transition temperature (Tg) of the acrylic resin is disclosed, so no way of guaranteeing properties such as curability of the coating film at a low baking temperature is disclosed, thus suggesting that it would not be possible to obtain a cured coating film that would be thermally cured sufficiently at low temperatures and that would show better appearance and have better gasoline resistance.

[0014]

A cured coating film that has a high degree of hardness and that is also satisfactory in terms of appearance and gasoline resistance as well as water resistance thus has not been obtained when a cured coating film is conventionally produced by thermally curing a clear coat composition (comprising a hydroxy group-containing acrylic resin and an isocyanate curing agent) at a low temperature of 70° C or lower. [0015]

In view of the problems noted above, an object of the present invention is to provide a laminate comprising multiple cured layers, that has a high degree hardness, shows better appearance, and has better gasoline resistance and water resistance, even when a multilayer coating film comprising a coating film of a clear coat composition (comprising at least a hydroxy group-containing acrylic resin and an isocyanate curing agent) is thermally cured at 70°C or below.

[Means for Solving the Problems]

[0016]

The inventors engaged in extensive research to achieve the above object. As a result, the inventors perfected the present invention upon finding that a clear coat composition comprising at least a hydroxy group-containing acrylic resin and an isocyanate curing agent affords a laminate of cured layers that has a high degree of hardness, shows better appearance, and has better gasoline resistance and water resistance, provided that the glass transition temperature (Tg) of the hydroxy group-containing acrylic resin is 20° C to 70° C, a hydroxy group-containing polyester resin is also included, and the cured layer that is formed by heating a coating film of the clear coat composition to 70° C or lower has a molecular weight between cross-linking points (Me) of 800 g/mol or less.

[0017]

Specifically, it was found that the above object of the present invention is achieved by 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), said laminate characterized in that: 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 glass transition temperature (Tg) of 20°C to 70°C ; an isocyanate curing agent (A2); and a hydroxy group-containing polyester resin (D); and the cured clear coat layer (II) has a molecular weight between cross-linking points (Me) of 800 g/mol or less.

[0018]

The hydroxy group-containing polyester resin (D) is also preferably blended in an amount (solids) of 3% by mass to 50% by mass relative to the total mass of the solids of the resin components, excluding the isocyanate curing agent (A2) in the clear coat composition (CC).

[0019]

Furthermore, the mass-average molecular weight (Mw) of the hydroxy group-containing polyester resin (D) is preferably 500 g/mol to 5000 g/mol.

[0020]

The hydroxyl value of the hydroxy group-containing polyester resin (D) is preferably 100 mgKOH/g or more.

[0021]

The hydroxyl value of the hydroxy group-containing acrylic resin (A1) is also preferably 80 mgKOH/g to 200 mgKOH/g.

[0022]

Furthermore, the mass-average molecular weight (Mw) of the hydroxy group-containing acrylic resin (A1) is preferably 2000 g/mol to 10 000 g/mol.

[0023]

The clear coat composition (CC) preferably contains isocyanate groups in the isocyanate curing agent (A2) at a ratio from 0.8 equivalent to 1.6 equivalents per equivalent of the totality of hydroxy groups in both the hydroxy group-containing acrylic resin (A1) and the hydroxy group-containing polyester resin (D). [0024]

The isocyanate curing agent (A2) also preferably comprises a polyisocyanate having an isocyanurate structure.

[0025]

The pencil hardness of the laminate is also preferably 6B or more.

[0026]

The above object of the present invention can also be achieved by a method for producing a laminate, comprising: a base coat layer (I) forming step in which the base coat layer (I) is formed by applying a base coat composition onto an object to be coated; a clear coat layer (II) forming step in which the clear coat layer (II) is formed by applying a clear coat composition (CC) onto the base coat layer (I) obtained in the base coat layer (I) forming step; and a curing step in which the base coat layer (I) and clear coat layer (II) are heated to 70°C and thereby cured to obtain a laminate comprising the cured layers, said method characterized in that the clear coat composition (CC) comprises a hydroxy group-containing acrylic resin (A1) having a glass transition temperature (Tg) of 20° C to 70° C, an isocyanate curing agent (A2), and a hydroxy group-containing polyester resin (D), and the cured clear coat layer (II) obtained in the curing step has a molecular weight between cross-linking points (Me) of 800 g/mol or less.

[Effects of the Invention]

[0027]

According to the laminate and the method for producing a laminate of the present invention, the hydroxy group-containing acrylic resin (A1) comprised in the clear coat composition (CC) has a glass transition temperature (Tg) of 20 °C to 70 °C, and the cured clear coat layer (II) has a molecular weight between cross-linking points (Me) of 800 g/mol or less, thus resulting in a laminate that has a high degree of hardness and better gasoline resistance even when thermally cured at 70 °C or below. The clear coat composition (CC) also comprises a hydroxy group-containing polyester resin (D) along with the hydroxy group-containing acrylic resin (A1) having a higher-than-conventional glass transition temperature (Tg), and the hydroxy group-containing polyester resin (D) therefore acts as a softener component, resulting in a better appearance. Because the cured clear coat layer (II) comprising the hydroxy group-containing acrylic resin (A1) and the hydroxy group-containing polyester resin (D) has a molecular weight between crosslinking points (Me) of 800 g/mol or less, the resulting laminate furthermore has better water resistance.

[Brief Description of the Drawings]

[0028]

[Figure 1] is a flow chart of the method for producing the laminate of the present invention.

[Embodiments of the Invention]

[0029]

The laminate of the present invention is 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), said laminate characterized in that: 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 glass transition temperature (Tg) of 20°C to 70°C ; an isocyanate curing agent (A2); and a hydroxy group-containing polyester resin (D); and the cured clear coat layer (II) has a molecular weight between crosslinking points (Me) of 800 g/mol or less.

[0030]

[Object to be Coated]

Examples of objects to be coated on which the laminate of the present invention can be formed include, but are not particularly limited to, members comprising metals such as iron, zinc, aluminium, and magnesium, members comprising alloys of these metals, members upon which these metals have been plated or vapour-deposited, and members comprising glass, plastic, and foamed articles of various materials, where steel and plastic materials used to construct automobile bodies are preferred. These members can be treated by, for example, degreasing treatments or surface treatments, as needed and appropriate.

[0031]

Members on which an undercoat film has been formed can also be used as objects to be coated in the present invention. Undercoat films are applied to the surface of a member in order to cover up the member surface or to make the member corrosion resistant, rust resistant, or adhesive, for example, and can be formed by applying and curing or drying an undercoat coating. The undercoating coating is not particularly limited, and those that are well known, such as electrodeposition coatings, solvent-borne primers, and water-borne primers, can be used. A primer layer is usually formed on the object that is to be coated when the member is a plastic material that is used to construct automobile bodies. The primer layer here is preferably conductive, as this will allow the base coat composition and the clear coat composition to be electrostatically applied thereon. An electrodeposition coated layer is usually formed on the object that is to be coated when the member is a metal material that is used to construct automobile bodies.

[0032]

In the present invention, the object to be coated can furthermore be an optionally treated member noted above that is made of metal, glass, or plastic on which at least one laminate has been provided. In order to touch up an object to be coated that comprises a laminate of this sort, the base coat layer (I) formation step (S110) through curing step (S130) described below can be carried out to provide yet another laminate, known as recoating.

[0033]

[Cured Base Coat Layer (I)]

The base coat layer (I) is a layer (coating film) that is formed primarily for colouring purposes and is formed by applying a base coat composition onto the object to be coated, and the base coat layer (I) is cured by curing the base coat layer (I), either alone or with layers above and below the base coat layer (I). The base coat layer (I) may be one or more layers.

[0034]

The base coat composition may be a solvent-borne coating composition or a waterborne coating composition, but is in particular preferably a solvent-borne coating composition, and may be a one-component coating composition in which the coating material that has been provided can be used as such, or may be a two-component coating composition in which a main resin and a curing agent are mixed together immediately before use.

[0035]

The base coat composition comprises a resin component and various pigments. [0036]

The resin component of the base coat composition is not particularly limited, provide that the component allows the base coat composition to be formed, and may be a thermosetting resin, where a coating is formed by means of a cross linking reaction that progresses when the resin has been applied and then heated, or may be a thermoplastic resin, where the volatilization of the solvent results in the formation of the coating film.

[0037]

When the base coat composition is a thermosetting resin composition, the base resin is not particularly limited, provided that it is a resin that can be stably dissolved or dispersed in an organic solvent and/or water; examples include acrylic resins, polyester resins, polyurethane resins, polyurea resins, acrylic-urethane resins, and polyurethane-polyurea resins. The base resin also preferably has hydroxy groups as functional groups. These base resins may be used alone or in combinations of two or more.

[0038]

When the base coat composition is a thermosetting resin composition, the curing agent also is not particularly limited, provided that it can be stably dissolved or dispersed in an organic solvent and/or water; examples include amino resins, polyisocyanate compounds, and blocked polyisocyanate compounds. These curing agents may be used alone or in combinations of two or more.

[0039]

Thermoplastic resins that can be used in the base coat composition also are not particularly limited, provided that they can be stably dissolved or dispersed in an organic solvent and/or water; examples include acrylic resins, polyester resins, alkyd resins, urethane resins, polyolefin resins (including those that are chlorinated and/or modified), and epoxy resins, that have a mass-average molecular weight (Mw) of 30 000 g/mol or more.

[0040]

Examples of the various pigments in the base coat composition include colour pigments and lustre pigments. Examples of colour pigments include inorganic pigments such as mixed metal oxide pigments, including titanium oxide pigments, iron oxide pigments, and 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 colour pigments may be used alone or in combinations of two or more.

[0041]

Examples of lustre pigments include coloured or uncoloured aluminium pigments, vapour-deposited metal flake pigments, and interference pigments comprising a transparent or translucent base material coated with a metal oxide. These lustre pigments may be used alone or in combinations of two or more.

[0042]

The base coat composition may furthermore comprise organic solvents, additives such as various coating additives, including surface conditioners, thickeners, rheology modifiers, pigment dispersants, antisettling agents, curing catalysts, defoamers, antioxidants, and UV absorbers, and extender pigments, as needed and appropriate. Examples of organic solvents include organic solvents commonly used in the production of base coat compositions, such as toluene, xylene, aromatic naphtha, and other aromatic hydrocarbons, acetone, methyl ethyl ketone, methyl amyl ketone, and other ketones, ethyl acetate, butyl acetate, 2-butoxyethyl acetate, pentyl acetate, ethyl ethoxypropionate, and other esters, isopropanol, butanol, 2-butoxyethanol, and other alcohols, ethers, chlorohydrocarbons, and other aliphatic hydrocarbons, as well as mixtures thereof.

[0043]

The cured base coat layer (I) is usually a single layer when the object to be coated is a plastic material that is used to construct automobile bodies; however, when the object to be coated is a metal material that is used to construct automobile bodies, the cured base coat layer (I) has a structure in which two cured layers (a lower base coat layer (1-1) and an upper base coat layer (I-2)) are laminated in order to provide shock absorption .

[0044]

In such cases, the lower base coat layer (1-1) serves primarily as a shock absorbing layer, and the upper base coat layer (I-2) serves primarily as a coloured layer. The base coat composition for the lower base coat layer (1-1) and the upper base coat layer (I-2) can be prepared by mixing the above components, as appropriate, depending on the intended purpose.

[0045]

[Cured Clear Coat Layer (II)]

The cured clear coat layer (II) is a cured layer provided on the uppermost layer of the laminate in order to protect the coated object and improve the appearance. The cured clear coat layer (II) is formed by applying the clear coat composition (CC) onto the base coat layer (I) and heating the coating to 70°C or below.

[0046]

As noted above, the clear coat composition (CC) of the present invention comprises a hydroxy group-containing acrylic resin (A1) having a glass transition temperature (Tg) of 20°C to 70° C, an isocyanate curing agent (A2), and a hydroxy group-containing polyester resin (D).

[0047]

(Hydroxy Group-Containing Acrylic Resin (A1) Having a Glass Transition Temperature (Tg) of 20°C to 70°C)

The hydroxy group-containing acrylic resin (A1) having a glass transition temperature (Tg) of 20°C to 70°C (also referred to below as hydroxy group-containing acrylic resin (A1 )) can be obtained by polymerizing a radically polymerizable monomer having hydroxy groups or by co-polymerizing a radically polymerizable monomer having hydroxy groups with another radically polymerizable monomer.

[0048]

Examples of radically polymerizable hydroxy group-containing monomers that can be used include (meth)acrylate 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 (meth)acrylate hydroxyalkyl esters, and E- caprolactone adducts of the above (meth)acrylate hydroxyalkyl esters, all of which may be used alone or in combinations of two or more.

[0049]

Examples of other radically polymerizable monomers include (meth)acrylate alkyl esters 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, as well as acrylic acid, methacrylic acid, styrene, acrylonitrile, methacrylonitrile, acrylamide, and methacrylamide, all of which may be used alone or in combinations of two or more.

[0050]

The glass transition temperature (Tg) of the hydroxy group-containing acrylic resin (A1) can be adjusted to a higher-than-conventional range of 20°C to 70°C by increasing the proportion in which tert-butyl methacrylate, methyl methacrylate, styrene, or cyclohexyl methacrylate, for example, is or are blended.

[0051]

On the other hand, the glass transition temperature (Tg) of the hydroxy group-containing acrylic resin (A1) can be adjusted to a lower temperature by increasing the proportion in which an ester of (meth)acrylic acid and a long-chain aliphatic alcohol such as stearyl methacrylate is blended.

[0052]

The glass transition temperature (Tg) of the hydroxy group-containing acrylic resin (A1) is preferably not lower than 20°C, as the hardness of the cured film (cured layer) and the gasoline resistance will be poorer. On the other hand, the glass transition temperature (Tg) of the hydroxy group-containing acrylic resin (A1) is preferably not higher than 70°C, as the cured film (cured layer) will have poor flexibility at lower temperatures.

[0053]

The glass transition temperature (Tg) of the hydroxy group-containing acrylic resin (A1) is even more preferably 20°C to 50°C.

[0054]

The hydroxy group-containing acrylic resin (A1) is also preferably blended in an amount (solids) of 20% by mass to 80% by mass, and even more preferably 40% by mass to 70% by mass, relative to the total mass of the solids of the resin components, excluding the isocyanate curing agent (A2) in the clear coat composition (CC).

[0055]

The hydroxyl value of the hydroxy group-containing acrylic resin (A1) is also preferably 80 mgKOH/g to 200 mgKOH/g, and in particular preferably 120 mgKOH/g to 200 mgKOH/g Adjusting the hydroxyl value of the hydroxy group-containing acrylic resin (A1) to 80 mgKOH/g or more will further increase the reactivity with the isocyanate curing agent (A2), and adjusting the hydroxyl value of the hydroxy group-containing acrylic resin (A1) to 200 mgKOH/g or less will result in even better compatibility with the hydroxy group-containing polyester resin (D).

[0056]

The hydroxyl value of the hydroxy group-containing acrylic resin (A1) can be set, as appropriate, by adjusting the proportion in which the radically polymerizable monomer having hydroxy groups is blended with the other radically polymerizable monomer when synthesizing the hydroxy group-containing acrylic resin (A1).

[0057]

The mass-average molecular weight (Mw) of the hydroxy group-containing acrylic resin (A1) is also preferably 2000 g/mol to 10 000 g/mol, more preferably 3000 g/mol to 9000 g/mol, and even more preferably 3000 g/mol to 5000 g/mol Ensuring that the massaverage molecular weight (Mw) of the hydroxy group-containing acrylic resin (A1) is 2000 g/mol or more will allow even better coating workability to be achieved, and ensuring that the mass-average molecular weight (Mw) of the hydroxy group-containing acrylic resin (A1) is 10 000 g/mol or less will result in even better compatibility with the hydroxy group- containing polyester resin (D).

[0058]

In the present invention, the mass-average molecular weight (Mw) is determined as the value that is obtained when data, which has been measured at a temperature of 40°C and a flow rate of 1 m/min by gel permeation chromatography (GPC) using tetrahydrofuran (THF) as the eluent, is calculated on the basis of the mass-average molecular weight of polystyrene. A combination of TSKgel G2000HXL, G3000HXL, G4000HXL, and G5000HXL (trade name, manufactured by Tosoh Corporation) was used as the gel permeation chromatography (GPC) columns here. [0059]

(Isocyanate Curing Agent (A2))

The isocyanate curing agent (A2) is not particularly limited, provided that it is a curing agent that cures a coating film by reacting with hydroxy groups to form urethane bonds and can be used in coating applications; a variety of aromatic, aliphatic, alicyclic, or other isocyanate compounds can be used.

[0060]

Examples of such isocyanate curing agents (A2) include aliphatic diisocyanates such as hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, and dimeric 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, as well as compounds comprising uretdiones, allophanates, adducts, biurets, and isocyanurates of the above, or other diisocyanate dimers, trimers, or higher diisocyanates. Aliphatic triisocyanate compounds such as 2-isocyanatoethyl-2,6-diisocyanatocaproate (LTI) and 1 ,8-diisocyanato-4-isocyanatomethyloctane may also be used. Furthermore, some of these isocyanate groups may be modified with an amino group-containing silane coupling agent, for example.

[0061]

Particularly in the interests of the flexibility and hardness of the cured coating (cured layer), the isocyanate curing agent (A2) should preferably comprise a polyisocyanate that is a diisocyanate trimer, and the isocyanate curing agent (A2) should in particular preferably comprise a polyisocyanate that has an isocyanurate structure.

[0062]

These isocyanate curing agents (A2) may be used alone or in combinations of two or more.

[0063]

The isocyanate curing agent (A2) in the clear coat composition (CC) of the present invention is blended in an amount as shown below. Specifically, the clear coat composition (CC) of the present invention preferably contains isocyanate groups in the isocyanate curing agent (A2) at a ratio from 0.8 equivalent to 1.6 equivalents, and more preferably 0.9 equivalent to 1.1 equivalent, per equivalent of the totality of hydroxy groups in both the hydroxy group-containing acrylic resin (A1) and the hydroxy group-containing polyester resin (D).

[0064]

(Hydroxy Group-Containing Polyester Resin (D))

The hydroxy group-containing polyester resin (D) comprises a hydroxy group-containing polyester resin (D1) that is obtained by an ester reaction between a monovalent or higher carboxylic acid and a polyhydric alcohol (also referred to below as hydroxy group- containing polyester resin (D1)) and/or a hydroxy group-containing polyester resin (D2) that can be obtained by a trans-esterification reaction between a fatty acid ester and a polyhydric alcohol (also referred to below as hydroxy group-containing polyester resin (D2)).

[0065]

Examples of monovalent or higher carboxylic acids include C2-20 saturated or unsaturated monocarboxylic acids and C2-12 saturated or unsaturated dicarboxylic acids. C2-12 saturated or unsaturated dicarboxylic acids include both dicarboxylic acids having aromatic rings, such as phthalic acid, isophthalic acid, and terephthalic acid, as well as 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 glycerol 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 products of ester reaction between a polyhydric alcohol noted above and a C2-20 saturated or unsaturated aliphatic monocarboxylic acid among the monovalent or higher carboxylic acids noted above. The C2-20 saturated or unsaturated aliphatic monocarboxylic acids noted above that are used in the ester reaction preferably contain hydroxy groups.

[0068]

In the fatty acid esters noted above, not all of the hydroxy groups of polyhydric alcohols have to react with carboxyl groups, but fatty acid esters in which all of hydroxy groups of the polyhydric alcohol are bonded with carboxyl groups are preferred. Specifically, esters of glycerol and a fatty acid may be fatty acid monoglycerides or fatty acid diglycerides but are preferably fatty acid triglycerides.

[0069]

Furthermore, some compounds that have an epoxy group can also be used instead of a polyhydric alcohol to synthesize the hydroxy group-containing polyester resin (D1). Preferred examples of compounds having epoxy groups include glycidyl esters or glycidyl ethers having one epoxy group per molecule, which are obtained by reacting a C2-16 fatty acid or alcohol with epichlorohydrin. Examples of commercially available products that can be used include Cardura E10P (trade name, by Hexion) and ADEKA GLYCIROL ED-502 (trade name, by ADEKA Co., Ltd.).

[0070]

The mass-average molecular weight (Mw) of the hydroxy group-containing polyester resin (D) is preferably 300 g/mol to 10 000 g/mol.

[0071]

The hydroxyl value of the hydroxy group-containing polyester resin (D) is also preferably 100 mgKOH/g or more, and is in particular preferably 150 mgKOH/g or more.

[0072]

The hydroxy group-containing polyester resin (D) is ideally a mixture of a hydroxy group- containing polyester resin (D1), that is obtained by an ester reaction between a monovalent or higher carboxylic acid and a polyhydric alcohol, and a hydroxy group- containing polyester resin (D2), that can be obtained by a trans-esterification reaction between a fatty acid ester and a polyhydric alcohol.

[0073]

The inclusion of the hydroxy group-containing polyester resin (D1) in the hydroxy group- containing polyester resin (D) will ensure that the laminate has sufficient crosslinking points and a better appearance (SW value). Furthermore, the inclusion of the hydroxy group-containing polyester resin (D2) in the hydroxy group-containing polyester resin (D) will ensure that the laminate has better recoatability and an even better appearance (SW value).

[0074]

The mass-average molecular weight (Mw) of the hydroxy group-containing polyester resin (D1) is, for example, 500 g/mol to 10 000 g/mol, and preferably 800 g/mol to 5000 g/mol. The mass-average molecular weight (Mw) of the hydroxy group-containing polyester resin (D2) is, for example, 300 g/mol to 5000 g/mol, and preferably 300 g/mol to 4000 g/mol.

[0075]

The hydroxy group-containing polyester resin (D) in the present invention is preferably blended in an amount (solids) of 3% by mass to 50% by mass, even more preferably 10% by mass to 50% by mass, and in particular preferably 30 parts by mass to 50 parts by mass, relative to the total mass of the solids of the resin components, excluding the isocyanate curing agent (A2) in the clear coat composition (CC). Ensuring that the hydroxy group-containing polyester resin (D) is blended in an amount (solids) of 3% by mass or more will result in a film after curing (cured coating film) that shows an even better appearance, and ensuring that the hydroxy group-containing polyester resin (D) is blended in an amount (solids) of 50% by mass or less will result in a film after curing (cured coating film) that has an even greater degree of hardness.

[0076]

(Catalyst (E))

The clear coat composition (CC) of the present invention preferably comprises a catalyst (E) that accelerates urethane curing. The addition of a catalyst (E) to the clear coat composition (CC) will facilitate the urethane bond formation reaction between the hydroxy group-containing acrylic resin (A1), the isocyanate curing agent (A2), and the hydroxy group-containing polyester resin (D). Examples of the catalyst (E) include bismuth-based compounds, aluminium-based compounds, tin-based compounds, and zinc-based compounds.

[0077]

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

[0078]

Examples of aluminium-based compounds include aluminium tris(acetylacetonate) and aluminium tris(ethyl acetoacetate).

[0079]

Examples of tin-based compounds include dimethyltin dilaurate, dibutyltin dilaurate, dimethyltin chloride, dibutyltin chloride, and di-n-octyltin dilaurate.

[0080]

Examples of zinc-based compounds include zinc acetylacetonate, zinc propionate, zinc octoate, zinc 2-ethylhexanoate, zinc neodecanoate, zinc laurate, zinc stearate, zinc linoleate, zinc naphthenate, zinc benzoate, and zinc salicylate.

[0081]

The catalyst (E) is blended in an amount (solids) of 2% by mass or less, and preferably 0.001 to 1.5% by mass, relative to the total mass of the solids of the resin components, excluding the isocyanate curing agent (A2) in the clear coat composition (CC).

[0082]

(Rheology Modifier (F))

The clear coat composition (CC) of the present invention preferably comprises a rheology modifier (F). The rheology modifier (F) endows the clear coat composition (CC) with a variety of functions, such as resistance to sagging during the coating process, coating film thickness adjustability, greater ease of application, and better leveling properties.

[0083]

Examples of rheology modifiers (F) for the present invention include internally crosslinked resin microparticles, polyamide wax, polyethylene wax, and hydroxy group- containing acrylic resins having a glass transition temperature (Tg) lower than 10°C.

[0084]

The rheology modifier (F) is blended in an amount (solids), for example, of 0.01% by mass to 10% by mass, and preferably 0.01 % by mass to 8% by mass, relative to the total mass of the solids of the resin components, excluding the isocyanate curing agent (A2) in the clear coat composition (CC). [0085]

The clear coat composition (CC) used in the present invention may also comprise colour pigments, provided that the transparency is not thereby compromised. Examples of colour pigments include inorganic pigments such as mixed metal oxide pigments, including titanium oxide pigments, iron oxide pigments, and 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 colour pigments may be used alone or in combinations of two or more.

[0086]

The total content of colour pigments in the clear coat composition (CC) that are used in the present invention is not particularly limited, but is preferably 10% by mass, and more preferably 0 to 5% by mass, relative to the total mass of the solids of the resin components, excluding the isocyanate curing agent (A2) in the clear coat composition (CC).

[0087]

The clear coat composition (CC) used in the present invention may furthermore comprise, for example, media such as organic solvents, various coating additives such as pigment dispersants, antisettling agents, defoamers, antioxidants, and UV absorbers, and extender pigments, as needed and appropriate. Examples of organic solvents include organic solvents commonly used in the production of clear coat compositions (CC), such as toluene, xylene, aromatic naphtha, and other aromatic hydrocarbons, acetone, methyl ethyl ketone, methyl amyl ketone, and other ketones, ethyl acetate, butyl acetate, 2- butoxyethyl acetate, pentyl acetate, ethyl ethoxypropionate, and other esters, ethers, chlorohydrocarbons, and other aliphatic hydrocarbons, as well as mixtures thereof. However, the use of alcohols is not recommended in cases where alcohol may potentially interfere with the curing reaction.

[0088]

The clear coat composition (CC) used in the present invention can be applied by methods such as electrostatic coating, air spraying, and airless spraying. The clear coat composition (CC) is then commonly allowed to stand at room temperature for 5 to 20 minutes and is then thermally cured.

[0089]

The cured clear coat layer (II) obtained via thermal curing has a molecular weight between cross4inking points (Me) of 800 g/mol or less, preferably a molecular weight between cross-linking points (Me) of 500 g/mol or less, and in particular preferably a molecular weight between cross-linking points (Me) of 200 g/mol to 500 g/mol. Ensuring that the cured clear coat layer (II) has a molecular weight between cross-linking points (Me) of 800 g/mol or less will result in a laminate that has better gasoline resistance and water resistance. The method for determining the molecular weight between cross-linking points (Me) is described in detail in the Examples.

[0090]

The pencil hardness of the resulting laminate is preferably 6B or more, and in particular preferably 3B or more.

[0091]

Figure 1 is a flow chart of the method for producing the laminate of the present invention. As illustrated, the method for producing the laminate of the present invention comprises 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, the base coat layer (I) is formed by applying a base coat composition onto the object to be coated. The object to be coated and the base coat composition in the invention of the laminate have already been described and therefore will not be described again here.

[0093]

The base coat layer (I) is formed by applying the base coat composition using a method such as electrostatic coating, air spraying, or airless spraying. After the base coat composition has been applied, the coating is allowed to stand at room temperature for 3 to 5 minutes in order to allow the solvent contained in the coating to volatilize off. Pre-drying (flash-off) then may or may not be performed under heating conditions that will not result in complete curing, such as 5 minutes at 60°C.

[0094]

The film thickness of the cured base coat layer (I) is not particularly limited, but the base coat composition should be applied in such a way that the film thickness after the heat treatment in the curing step (S130) described below (dry film thickness) will preferably be 2 to 30 pm, and more preferably 5 to 20 pm.

[0095]

This step may also be repeated a second time. For example, when the object to be coated is a steel material that is used to construct automobile bodies, a lower base coat layer (1-1) serving as a shock absorbing layer is first formed and allowed to stand for 3 to 5 minutes at room temperature in this step. Pre-drying (flash-off) then may or may not be performed under heating conditions that will not result in complete curing, such as 5 minutes at 60°C. This step may then be repeated to form an upper base coat layer (I-2) serving as coloured layer. In that case, the base coat coating compositions for the lower base coat layer (1-1) and the upper base coat layer (I-2) can be prepared by mixing, as appropriate, the components of the base coat composition for the invention of the laminate as noted above, depending on the intended purpose (the above is the base coat layer (I) forming step (S110)).

[0096]

[Clear Coat Layer (II) Forming Step (S120)]

The clear coat layer (II) is formed by applying the clear coat composition (CC) onto the (uncured) base coat layer (I) obtained in the base coat layer (I) forming step.

[0097]

The clear coat composition (CC) used to form the clear coat layer (II) in the invention contains a hydroxy group-containing acrylic resin (A1) having a glass transition temperature (Tg) of 20°C to 70° C, an isocyanate curing agent (A2), and a hydroxy group- containing polyester resin (D). The clear coat composition (CC), the hydroxy group- containing acrylic resin (A1) having a glass transition temperature (Tg) of 20°C to 70°C, the isocyanate curing agent (A2), and the hydroxy group-containing polyester resin (D) are the same as those explained in the invention of the laminate and therefore will not be described again here.

[0098]

The clear coat layer (II) is also formed by applying the clear coat composition (CC) using a method such as electrostatic coating, air spraying, or airless spraying in the same manner as the base coat layer (I). After the clear coat composition (CC) has been applied, the coating is commonly allowed to stand at room temperature for 3 to 5 minutes in order to allow the solvent contained in the coating to volatilize off. [0099]

The clear coat composition (CC) is preferably applied in such a way that the dry film thickness of the clear coat layer (II) will preferably be 20 to 50 pm, and more preferably 25 to 45 pm. 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 (the above is the clear coat layer (II) forming step (S120)).

[0100]

[Curing Step (S130)]

In this step, the (uncured) base coat layer (I) and the (uncured) clear coat layer (II) are cured by being heated to a temperature of 70°C or below, and preferably 60°C to 70°C, resulting in a laminate comprising cured layers.

[0101]

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

[0102]

The cured clear coat layer (II) obtained in this step has a molecular weight between cross4inkings points (Me) of 800 g/mol or less, preferably a molecular weight between cross-linking points (Me) of 500 g/mol or less, and in particular preferably a molecular weight between cross-linking points (Me) of 200 g/mol to 500 g/mol (the above is the curing step (S130)).

[0103]

According to the laminate of the present invention, as well as the method for producing the laminate of the present invention above, the resulting laminate has a high degree of hardness and a better appearance, water resistance, and gasoline resistance, as well as better flexibility at lower temperatures and recoat adhesion, even when thermally cured at a low temperature of 70°C or below.

[0104]

The laminate of the present invention and the laminate obtained by the method for producing the laminate of the present invention are suitable for automobile bodies, members, and parts such as in passenger vehicles, trucks, motorcycles, and buses. The invention is especially suitable for use in an automobile body when the object to be coated is metal, and the invention is especially suitable for use in interior and exterior parts of automobiles when the object to be coated is plastic.

[Examples]

[0105]

The present invention is described in detail by the following examples but is not limited to these examples only. Unless otherwise specifically indicated, in the examples, “parts” means “parts by mass,” and “%” relating to amounts blended or to content means “% by mass.”

[Methods for Determining Values of Resin Properties]

The values of resin properties in the present invention were determined by the following methods.

1. Hydroxyl value: This was determined in accordance with JIS-K1557-1 :2007.

2. Acid value: This was determined in accordance with JIS-K5601-2-1 :1999.

[0106]

[Synthesis Example 1]

Into a flask equipped with a dropping funnel, a reflux condenser, a thermometer, a stirrer, and a nitrogen gas feed tube, 57.0 parts of ethyl 3-ethoxypropionate (EEP) and 30.0 parts of ethyl acetate were introduced as solvents, and the contents were heated to 75°C while stirred in a nitrogen stream. 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), and 8.0 parts of 2-ethylhexyl acrylate (EHA) (as the monomers) as well as 5.3 parts of 2,2'-azobis(isobutyronitrile) (as the polymerization initiator) was added dropwise at a constant rate at 75°C while stirred over a 3-hour period, and the contents then continued to be stirred for another 5 hours at 75°C. Confirmation via measurement of the resin solids concentration that the conversion rate was greater than 98% was followed by desolvation at reduced pressure until the solids concentration (NV%) reached 60%, giving a hydroxy group-containing acrylic resin (A1-1) solution. The glass transition temperature (Tg) of the hydroxy group-containing acrylic resin (A1-1) was 23°C.

[0107]

[Synthesis Examples 2 through 5]

Hydroxy group-containing acrylic resin (A1-2 through -5) solutions were obtained in the same manner as the hydroxy group-containing acrylic resin (A1-1), except that the initial solvent amount, the monomer compositions and amounts blended, and the initiator amount were changed as noted in Table 1.

[0108]

The compound abbreviations in Table 1 and [Synthesis Examples 1 through 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

[0111]

[Synthesis Example 6]

Into a flask equipped with a dropping funnel, a reflux condenser, a thermometer, and a stirrer, 47 parts of SOLVESSO 100 (trade name, by Andoh Parachemie Co., Ltd.) was introduced as a solvent, after which 34 parts of hexahydrophthalic anhydride, 22 parts of dodecanoic acid NAA-122 (trade name, by NOF Corporation), 24 parts of pentaerythritol, and 20 parts of Cardura E10P (trade name, by Hexion) were introduced, and the contents were heated to 165°C while stirred. The reaction was continued for 3 hours at 165°C, and after it was confirmed that the acid value was 5 mgKOH/g, the contents were cooled to obtain a hydroxy group-containing polyester resin (D1-1) solution having a solids concentration (NV%) of 65%, a hydroxyl value of 189 mgKOH/g, and a mass-average molecular weight (Mw) of 3000 g/mol.

[0112]

[Synthesis Examples 7 and 8]

Into a flask equipped with a dropping funnel, a reflux condenser, a thermometer, a stirrer, and a nitrogen gas feed tube, refined castor oil LAV (trade name, by Ito Oil Chemicals Co., Ltd.; D11), pentaerythritol (DI2-1), trimethylolpropane (DI2-2), glycerol (DI2-3), and sorbitol (DI2-4) in the parts by mass indicated in Table 2 were introduced, tetrabutyl titanate was added (added in amount of 0.5% by mass of the castor oil) as a catalyst, and the contents were heated to 220°C while stirred. The viscosity was determined every 30 minutes, and after it was confirmed that there was no change in viscosity, the contents were cooled to obtain hydroxy group-containing polyester resins (D2-1 and -2).

[0113]

[Synthesis Example 9]

Into a flask equipped with a dropping funnel, a reflux condenser, a thermometer, a stirrer, and a nitrogen gas feed tube, refined castor oil LAV (trade name, by Ito Oil Chemicals Co., Ltd.; D11 ), sorbitol (DI2-4), and hexahydrophthalic anhydride (DI3-1) in the parts by weight indicated in Table 2 were introduced, and the contents were heated to 220°C while stirred. The reaction was continued for 3 hours, and after it was confirmed that the acid value could no longer be determined, the contents were cooled to obtain a hydroxy group-containing polyester resin (D2-3).

[0114]

[Table 2] [0115]

[Synthesis Example 10]

Into a flask equipped with a dropping funnel, a reflux condenser, a thermometer, and a stirrer, 60 parts of SOLVESSO 100 (trade name, by Andoh Parachemie Co., Ltd.) was introduced as a solvent, and the contents were heated to 155°C while stirred. A mixture of 34 parts of n-butyl acrylate, 21 parts of 2-hydroxyethyl acrylate, 39 parts of styrene, and 2 parts of methacrylic acid (dropwise addition components) with 2 parts of di-tert-butyl peroxide (initiator) was added dropwise over a 2-hour period at 155°C. The reaction was then continued for 3 hours, and after it had been confirmed via measurement of the resin solids concentration that the conversion rate was greater than 98%, the contents were cooled to obtain a rheology modifier (F-1) solution having a solids concentration (NV%) of 60%. The Tg of the rheology modifier (F-1) was 5°C.

[0116]

Preparation of Clear Coat Composition (CC)>

[Preparation Example 1]

48 parts of the hydroxy group-containing acrylic resin (A1-1) solution, 30 parts of the hydroxy group-containing polyester resin (D1-1) solution, 5 parts of the hydroxy group- containing polyester resin (D1-2), 5 parts of the rheology modifier (F-1) solution, 36 parts of the isocyanate curing agent (A2-1) (equal to 1.0 equivalent isocyanate groups in the isocyanate curing agent (A2-1) per equivalent of the totality of hydroxy groups in the clear coat composition (CC-1) described below), and 0.01 part of urethane curing catalyst (E-1) were weighed out, ethyl 3-ethoxypropionate was then used as the solvent to dilute the contents to a Ford #4 cup viscosity of 25 seconds (20°C), and the contents were stirred to homogeneity in a paint shaker. The contents were then filtered through a 350 mesh (wire diameter 30 pm) filter to remove coarse particles, giving a clear coat composition (CC-1).

[0117]

[Preparation Examples 2 through 13]

Clear coat compositions (CC-2 to CC-13) were obtained in the same manner as the clear coat composition (CC-1) except that the components that were mixed and the formulations thereof were changed to the blending proportions shown in Table 3.

[0118]

Test plates of Examples 1 through 10 and Comparative Examples 1 through 3 were prepared by applying the clear coat compositions (CC-1 to 13) onto polypropylene plates using an electrostatic rotary atomizer so as to result in a cured coating film thickness of 35 pm (dry film thickness), allowing the coating films to stand for 7 minutes at room temperature, heating the coatings to 70°C for 10 minutes in a hot air circulation type drying oven, and then peeling of the resulting coating films.

[0119]

Test pieces measuring 5 mm wide 10 mm long were then cut out from the test plates, the dynamic viscoelasticity was determined under the following conditions (storage modulus (E’), loss modulus (E”), loss tangent (tan 5)), and the molecular weight between cross-linking points (Me) was determined using the following Formula 1. The lower the molecular weight between cross-linking points (Me), the denser the cross-linked structure will be.

• Device: Dynamic viscoelasticity analyser RSA3 (by TA Instruments)

• Mode: Non-resonant forced vibration mode

• Heating rate: 3.0°C/min

• Interval: 12/min

• Frequency: 1 .0 Hz

• Temperature range: 30 to 180°C

Molecular weight between cross-linking points (Mc)=3pRT/E'min (Formula 1)

(Molecular weight between cross-linking points (Me): g/mol E’min: Pa p (density) : g/m³

R (gas constant): J/mol • K

T (absolute temperature of E'min: K))

[0120]

The assessment criteria for the molecular weight between cross-linking points (Me) are shown below, where O and A were defined as acceptable ranges.

O : 200<Mc<500 A : 500<Mc<800 x : Mc>800 or Mc<200

[0121]

Production of Laminates for Assessment of Performance>

Plymac No. 1501 (trade name, by BASF Japan Ltd.; conductive primer) was air sprayed, as the primer (Pr), to a dry film thickness of 7pm on a polypropylene test plate and was allowed to stand for 10 minutes at room temperature, and a solvent-borne base coat, Plymac No. 8800 Silver (trade name, by BASF Japan Ltd.; one-component acrylic coating composition), was then electrostatically applied, as the base coat (BC), to a dry film thickness of 15 pm and allowed to stand for 5 minutes at room temperature, giving a base coat layer (I). The clear coat compositions (CC) noted in Table 3 were then electrostatically applied onto base coat layers (I) to a dry film thickness of 35 pm, were allowed to stand at room temperature for 10 minutes, and were then heated to 70°C for 10 minutes, giving test coated plates (laminates) in which the multilayer coating films had been cured. The various tests for assessing the performance of the test coating films are described below.

[0122]

The pencil hardness of the test coated plates (laminates) was determined at a temperature of 25°C and a humidity of 65% RH in accordance with JIS K 5600-5-4 (1999). The pencil hardness assessment criteria are shown below, where O and A were defined as acceptable ranges.

O: 3B or more. Exceptional hardness.

A: 4B to 6B. Usable. x : Indeterminable. Fail.

[0123]

The Long Wave (LW) and Short Wave (SW) values of the test coated plates (laminates) were determined via Wave Scan (trade name, by BYK Gardner) to assess the finish appearance.

[0124]

The LW value is an indicator of smoothness, where the smaller the LW value, the greater the smoothness of the coated surface. The LW assessment criteria are shown below, where O and A were defined as acceptable ranges.

[0125]

O : 0<LW<5

A : 5<LW<10 x: LW>10

[0126]

The SW value is an indicator of vividness, where the lower the SW value, the greater the coated surface vividness. The SW assessment criteria are shown below, where O and A were defined as acceptable ranges.

O: 5<SW<25

A : 3<SW<5, 25<SW<30 x: SW<3, SW>30

[0127]

Test coated plates (laminates) were immersed in 40°C warm water for 10 days, were taken out and dried, and the coated surfaces were then visually observed to assess the occurrence of blisters based on the following criteria. The symbols ©, O, and A were defined as acceptable ranges.

O: Blistering on no more than 10% of total surface area.

A: Blistering on 11 % to 30% of total surface area. x : Blistering on 31 % or more of total surface area.

[0128]

Test coated plates (laminates) were immersed in 40°C warm water for 10 days and were then taken out and dried. A cutter was then used to cut lines reaching to the substrate in the coated surface of the test coated plates to make 100 squares measuring 2 mm x 2 mm, Cellophane Tape (registered trademark) was applied onto the surface, and the tape was rapidly peeled off at a 45° angle and a temperature of 20°C. Assessments were made using the following criteria based on the number of squares in which the coating film remained, where the symbols ©, O, and A were defined as acceptable ranges. ©: 100 squares (no coating film peeled off).

O : 99 squares (some coating film peeled off).

A : 51 to 98 squares. x : 50 squares or less.

[0129]

Gasoline resistance was assessed according to the following criteria by immersing test coated plates (laminates) in unleaded regular gasoline (No. 2, as defined in JISK2202:2012) for 24 hours at 20°C, and then visually observing the appearance. The symbols O and A were defined as acceptable ranges.

[0130] o : No abnormalities.

A : Abnormalities such as slight yellowing and blistering. x : Abnormalities such as yellowing and blistering.

[0131]

Test coated plates (laminates) applied on 5 mm thick polypropylene plates were allowed to stand for 4 hours in the atmosphere at -20 °C and were then bent at a 180 degree angle between iron rods 20 mm in diameter, and the coating film at the bend was observed and assessed using the following criteria. The symbols O and A were defined as acceptable ranges.

O : No change at all.

A : Minute wrinkling. x : Pronounced cracking.

[0132]

A primer (Pr), base coat (BC), and clear coat composition (CC) were applied, in that sequence, and were heated, the resulting laminate was cured to form test coated plates (laminates), which were allowed to stand for 7 days at room temperature, and the surface (surface of the cured clear coat layer obtained by curing the clear coating composition (CC)) was again coated (recoated) with a base coat (BC) and clear coat composition (CC), which were heated to form a multilayer coating film.

[0133]

The resulting multilayer laminates were allowed to stand for 3 days at room temperature and were then tested to assess water resistance (adhesion) in the same manner as described above, and the number of squares in which the coating film remained was counted and assessed using the following criteria. The symbols O and A were defined as acceptable ranges.

O : 100 squares (no coating film peeled off) or 99 squares (some coating film peeled off).

A : 51 to 98 squares. x : 50 squares or less.

[0136]

Isocyanate curing agent (A2):

Isocyanate curing agent (A2-1): Duranate TPA-100 (trade name, by Asahi Kasei Corporation; diisocyanate trimer or higher compound; NCO content: 23.1%) Isocyanate curing agent (A2-2): Duranate TKA-100 (trade name, by Asahi Kasei Corporation; diisocyanate trimer or higher compound; NCO content: 21.7%) Catalyst (E):

Urethane curing catalyst (E-1): K-KAT 348 (trade name, by KING INDUSTRIES) Urethane curing catalyst (E-2): K-KAT XK-614 (trade name, by KING INDUSTRIES)

[0137]

The total resin components in Table 3 are the total solids of the hydroxy group- containing acrylic resin (A1), the hydroxy group-containing polyester resin (D), and the rheology modifier (F), and do not include the solids of the isocyanate curing agent (A2).

[0138]

As shown in Table 3, when coating films of clear coat compositions comprising a hydroxy group-containing acrylic resin and an isocyanate curing agent were cured at a low temperature of 70°C, the resulting laminates that met the following requirements all had passing marks for the degree of hardness, appearance (LW and SW), water resistance (blistering and adhesion), gasoline resistance, flexibility at low temperatures, and recoat adhesion (see Examples 1 through 10), whereas Comparative Example 1 , which did not meet requirement (a) (Tg below lower limit), had a poor appearance (LW and SW) and poor water resistance (blistering), and Comparative Example 2, which similarly did not meet requirement (a) (Tg over the upper limit), had a poor appearance (LW and SW) and poor water resistance (blistering) as well as poor water resistance (adhesion), gasoline resistance, and flexibility at low temperatures:

(a) hydroxy group-containing acrylic resin has a Tg of 20°C to 70°C;

(b) includes a hydroxy group-containing polyester resin (D); and

(c) cured clear coat layer (II) has a molecular weight between cross-linking points (Me) of 800 g/mol or less.

[0139]

The laminate of Comparative Example 3, which met requirement (a) but did not include a hydroxy group-containing polyester resin (D) in the cleat coat composition (specifically, did not meet requirement (b)), also had a poor degree of hardness, appearance (LW and SW), water resistance (blistering and adhesion), gasoline resistance, flexiblity at low temperatures, and recoat adhesion.

Claims

[Document Name] CLAIMS

[Claim 1]

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), said laminate characterized in that: 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 Tg of 20°C to 70°C; an isocyanate curing agent (A2); and a hydroxy group-containing polyester resin (D); and the cured clear coat layer (II) has a molecular weight between cross-linking points (Me) of 800 g/mol or less.

[Claim 2]

The laminate according to Claim 1 , characterized in that the hydroxy group-containing polyester resin (D) is blended in an amount (solids) of 3% by mass to 50% by mass relative to the total mass of the solids of the resin components, excluding the isocyanate curing agent (A2) in the clear coat composition (CC).

[Claim 3]

The laminate according to Claim 1 or 2, characterized in that the mass-average molecular weight (Mw) of the hydroxy group-containing polyester resin (D) is 500 g/mol to 5000 g/mol.

[Claim 4]

The laminate according to Claim 1 or 2, characterized in that hydroxyl group value of the hydroxy group-containing polyester resin (D) is 100 mgKOH/g or more.

[Claim 5]

The laminate according to Claim 1 , characterized in that hydroxyl group value of the hydroxy group-containing acrylic resin (A1) is 80 mgKOH/g to 200 mgKOH/g.

[Claim 6]

The laminate according to Claim 1 or 5, characterized in that the mass-average molecular weight (Mw) of the hydroxy group-containing acrylic resin (A1) is 2000 g/mol to less than 10 000 g/mol.

[Claim 7]

The laminate according to Claim 1 or 2, characterized in that the clear coat composition (CC) contains isocyanate groups in the isocyanate curing agent (A2) at a ratio from 0.8 equivalent to 1.6 equivalents per equivalent of the totality of hydroxy groups in both the hydroxy group-containing acrylic resin (A1) and the hydroxy group-containing polyester resin (D).

[Claim 8]

The laminate according to Claim 1 or 2, characterized in that the isocyanate curing agent (A2) comprises a polyisocyanate having an isocyanurate structure.

[Claim 9]

The laminate according to Claim 1 or 2, characterized in that the pencil hardness of the laminate is 6 B or more.

[Claim 10]

A method for producing a laminate, comprising: a base coat layer (I) forming step in which the base coat layer (I) is formed by applying a base coat composition onto an object to be coated; a clear coat layer (II) forming step in which the clear coat layer (II) is formed by applying a clear coat composition (CC) onto the base coat layer (I) obtained in the base coat layer (I) forming step; and a curing step in which the base coat layer (I) and clear coat layer (II) are heated to 70°C and thereby cured to obtain a laminate comprising the cured layers, said method characterized in that the clear coat composition (CC) comprises a hydroxy group-containing acrylic resin (A1) having a glass transition temperature (Tg) of 20° C to 70° C, an isocyanate curing agent (A2), and a hydroxy group-containing polyester resin (D), and the cured clear coat layer (II) obtained in the curing step has a molecular weight between cross-linking points (Me) of 800 g/mol or less