Clear coating composition and method for producing coated article

Abstract

Provided is a clear coating composition which can obtain a coating film having excellent color reversion resistance and has excellent coating workability despite a high solid content. The clear coating composition comprises a hydroxyl-containing acrylic resin (A), a polyisocyanate compound (B), and an organic solvent (C), wherein the hydroxyl-containing acrylic resin (A) comprises a primary hydroxyl-containing acrylic resin (A1) and a secondary hydroxyl-containing acrylic resin (A2), the primary hydroxyl-containing acrylic resin (A1) has a weight average molecular weight of 6,000 or less, the secondary hydroxyl-containing acrylic resin (A2) has a weight average molecular weight of 6,000 or more, the organic solvent (C) contains a specific primary alcohol and / or secondary alcohol, and the solid content concentration during coating is 55% by mass or more.

Description

Technical Field

[0001] The present invention relates to a method for producing a clear coating composition and a coated article. Background Art

[0002] A clear coating film is generally formed as the outermost layer of a car body or the like, and the clear coating film is required to have high design properties and appearance.

[0003] In recent years, however, for environmental protection, it has been sought to reduce the emission of volatile organic compounds (VOC) from factories, etc. One method of reducing VOC emission is to increase the solid content concentration of the coating composition.

[0004] Patent Document 1 describes a coating composition comprising (A) a hydroxyl-containing acrylic resin having an acid value of 0 to 30 mgKOH / g, (B) a hydroxyl-containing acrylic resin having an acid value of 60 to 120 mgKOH / g, and (C) a polyisocyanate compound, wherein the solid content during coating is 50% by mass or more.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: International Publication No. 2022 / 107847 Summary of the invention

[0008] Problems to be solved by the invention

[0009] According to Patent Document 1, a high-solid content coating composition with reduced VOC emission and a coating film with excellent color reversion resistance and appearance can be obtained. However, due to consumers' desire for higher-end products, the demand for higher design and appearance is increasing, and it is not enough to balance these performances with coating workability.

[0010] An object of the present invention is to provide a clear coating composition which can provide a coating film having excellent color reversion resistance and which is excellent in coating workability despite having a high solid content, and a method for producing a coated article using the clear coating composition.

[0011] Means for solving problems

[0012] In order to solve the above-mentioned problems, the present invention provides the following aspects.

[0013] [1] A clear coating composition comprising a hydroxyl group-containing acrylic resin (A), a polyisocyanate compound (B) and an organic solvent (C),

[0014] The aforementioned hydroxyl-containing acrylic resin (A) comprises a primary hydroxyl-containing acrylic resin (A1) and a secondary hydroxyl-containing acrylic resin (A2).

[0015] The weight average molecular weight of the acrylic resin (A1) containing a primary hydroxyl group is 6,000 or less,

[0016] The weight average molecular weight of the acrylic resin (A2) containing a secondary hydroxyl group is 6,000 or more,

[0017] The organic solvent (C) comprises at least one alcohol solvent selected from the group consisting of a linear primary alcohol having 1 to 8 carbon atoms, a branched primary alcohol having 3 to 8 carbon atoms, a linear secondary alcohol having 1 to 8 carbon atoms, and a branched secondary alcohol having 3 to 8 carbon atoms,

[0018] The solid content concentration during coating is 55% by mass or more.

[0019] [2] The clear coating composition according to [1], wherein the acid value of the primary hydroxyl group-containing acrylic resin (A1) is 0 mgKOH / g or more and 40 mgKOH / g or less.

[0020] [3] The clear coating composition according to [1] or [2], wherein the acid value of the secondary hydroxyl group-containing acrylic resin (A2) is 0 mgKOH / g or more and 40 mgKOH / g or less.

[0021] [4] The clear coating composition according to any one of [1] to [3], wherein the glass transition temperature Tg(A1) of the primary hydroxyl group-containing acrylic resin (A1) is -20°C or higher and 60°C or lower.

[0022] [5] The clear coating composition according to any one of [1] to [4], wherein the glass transition temperature Tg(A2) of the secondary hydroxyl group-containing acrylic resin (A2) is -30°C or higher and 35°C or lower.

[0023] [6] The clear coating composition according to any one of [1] to [5], wherein the organic solvent (C) further contains a ketone compound.

[0024] [7] The clear coating composition according to any one of [1] to [6], wherein the mass ratio (A1) / (A2) of the content of the aforementioned primary hydroxyl group-containing acrylic resin (A1) to the content of the aforementioned secondary hydroxyl group-containing acrylic resin (A2) is 1 / 99 to 80 / 20.

[0025] [8] The clear coating composition according to any one of [1] to [7], wherein the alcohol solvent is at least one selected from a linear primary alcohol having 3 to 5 carbon atoms and a branched primary alcohol having 3 to 5 carbon atoms.

[0026] [9] The clear coating composition according to any one of [1] to [8], wherein the weight average molecular weight of the primary hydroxyl group-containing acrylic resin (A1) is 3,000 or more and 6,000 or less.

[0027]

[10] The clear coating composition according to any one of [1] to [9], wherein the organic solvent (C) further comprises an organic solvent, which is at least one organic solvent selected from monocarboxylic acid esters, dibasic ester compounds, cellosolves, and carbitol, and has a boiling point of 200° C. or higher.

[0028]

[11] A method for producing a coated article, comprising:

[0029] A step of applying a base coating composition to an object to be coated to form an uncured base coating film;

[0030] A step of applying a clear coating composition to the uncured base coating film to form an uncured clear coating film; and

[0031] a step of simultaneously curing the uncured base coating film and the uncured clear coating film;

[0032] The clear coating composition comprises a hydroxyl-containing acrylic resin (A), a polyisocyanate compound (B) and an organic solvent (C).

[0033] The aforementioned hydroxyl-containing acrylic resin (A) comprises a primary hydroxyl-containing acrylic resin (A1) and a secondary hydroxyl-containing acrylic resin (A2).

[0034] The weight average molecular weight of the acrylic resin (A1) containing a primary hydroxyl group is 6,000 or less,

[0035] The weight average molecular weight of the acrylic resin (A2) containing a secondary hydroxyl group is 6,000 or more,

[0036] The organic solvent (C) comprises at least one alcohol solvent selected from the group consisting of a linear primary alcohol having 1 to 8 carbon atoms, a branched primary alcohol having 3 to 8 carbon atoms, a linear secondary alcohol having 1 to 8 carbon atoms, and a branched secondary alcohol having 3 to 8 carbon atoms,

[0037] The solid content concentration during coating is 55% by mass or more.

[0038] Effects of the Invention

[0039] According to the present invention, a clear coating composition can be provided which can produce a coating film having excellent color reversion resistance and has excellent coating workability despite a high solid content. According to the present invention, a method for producing a coated article using the clear coating composition can also be provided. DETAILED DESCRIPTION

[0040] [Clear coating composition]

[0041] The transparent coating composition described in the present application comprises an acrylic resin (A) containing a hydroxyl group, a polyisocyanate compound (B) and an organic solvent (C). The acrylic resin (A) containing a hydroxyl group comprises an acrylic resin (A1) containing a primary hydroxyl group and an acrylic resin (A2) containing a secondary hydroxyl group. The weight average molecular weight (Mw) of the acrylic resin (A1) containing a primary hydroxyl group is 6,000 or less. The weight average molecular weight (Mw) of the acrylic resin (A2) containing a secondary hydroxyl group is 6,000 or more. The organic solvent (C) comprises the above-mentioned specific primary alcohol and / or secondary alcohol. The solid content concentration of the transparent coating composition during coating is 55% by mass or more.

[0042] The clear coating composition is a two-component type consisting of a main agent comprising a hydroxyl-containing acrylic resin (A) and a solvent and a curing agent comprising a polyisocyanate compound (B) and a solvent. At least a part of the solvent contained in the main agent is an organic solvent (C) containing the above-mentioned specific primary alcohol and / or secondary alcohol.

[0043] The solid content concentration of the clear coating composition at the time of coating is the solid content concentration of the clear coating composition immediately after the main agent and the curing agent are mixed (within 10 minutes after mixing) and immediately before coating (within 10 minutes before coating). The solid content concentration of the clear coating composition at the time of coating is obtained by measuring the mass of the residue (also referred to as the heating residue) after heating the clear coating composition within 10 minutes after the main agent and the curing agent are mixed at 140° C. for 30 minutes.

[0044] Specifically, the solid content concentration C1 of the clear coating composition during coating can be calculated as follows. First, the mass (initial mass W0) of an aluminum cup of appropriate size is measured. Next, the clear coating composition is added to the aluminum cup within 10 minutes from the time the main agent and the curing agent are mixed, and the mass (W1) is measured within 10 minutes after the addition.

[0045] Next, the aluminum cup is heated at 140°C for 30 minutes, and the mass (W2) is measured again. W2 is the total mass of the solid content (heating residue) of the clear coating composition and the aluminum cup. Finally, the solid content concentration C1 of the clear coating composition at the time of coating is calculated using the following formula. (W1-W0) represents the total mass of the solvent and solid content remaining in the clear coating composition just after coating. (W2-W0) represents the mass of the solid content of the clear coating composition alone.

[0046] Solid content concentration C1 (%) = 100 × (W2-W0) / (W1-W0)

[0047] The viscosity of the above-mentioned clear coating composition during coating can be regarded as the viscosity of the clear coating composition immediately before coating (within 10 minutes before coating). The solid content concentration C1 of the clear coating composition can be 56% by mass or more, 58% by mass or more, or 60% by mass or more. The solid content concentration C1 of the clear coating composition can be 80% by mass or less, or 75% by mass or less.

[0048] In a two-component coating composition, if the solid content concentration is high, the main agent and the curing agent are likely to react, and therefore, the shelf life is usually likely to be shortened. The shelf life refers to the time (usable time) during which the coating composition can be applied and can exert the expected coating performance, final appearance, design, etc. since the main agent and the curing agent are mixed. The viscosity of the coating composition beyond the shelf life is too high, and therefore, the performance and appearance of the coating obtained using it may be reduced. In order to extend the shelf life, it can be considered to control in a manner that no sharp reaction of the main agent and the curing agent occurs, or, even if a reaction is performed before coating, the viscosity can be maintained low.

[0049] In the present application, from the viewpoint of controlling the reaction, as the main agent, an acrylic resin (A1) containing a primary hydroxyl group and an acrylic resin (A2) containing a secondary hydroxyl group are used in combination. Generally, a primary hydroxyl group has a higher reactivity than a secondary hydroxyl group. By using acrylic resins containing hydroxyl groups with different reactivities in combination, the speed of the curing reaction can be controlled.

[0050] Furthermore, in order to maintain the viscosity low, a low molecular weight resin is used as the acrylic resin containing a highly reactive primary hydroxyl group. Thus, even if the acrylic resin (A1) containing a primary hydroxyl group and the polyisocyanate compound (B) react after the main agent and the curing agent are mixed, the viscosity increase of the entire clear coating composition can be suppressed.

[0051] That is, according to the present application, since the molecular weight of the acrylic resin (A1) containing a more reactive primary hydroxyl group is small, the reaction rate can be controlled and the viscosity increase of the clear coating composition can be suppressed. As a result, the shelf life is prolonged, and the coating performance and appearance of the obtained coating film are also improved. The appearance of the coating film can be evaluated by, for example, smoothness.

[0052] On the other hand, from the viewpoint of color reversion resistance, a high molecular weight resin is used as the acrylic resin (A2) containing a secondary hydroxyl group. Color reversion refers to a phenomenon in which the design property is reduced due to the penetration and mixing of the components of the clear coating composition into the coating film (e.g., a colored base coating film or a metal base coating film) in the lower layer. For example, in the case where the lower layer is a metal base coating film having a bright pigment, if the components of the clear coating composition penetrate into the lower layer, the arrangement of the bright pigment is disordered, and the desired FF property (flip flop property) cannot be obtained. This reduction in FF property is an example of color reversion. Color reversion resistance can be said to be a performance that the coating film in the lower layer of the clear coating film can exert a design property that will not be impaired by the clear coating composition. By using an acrylic resin (A2) containing a secondary hydroxyl group having a large molecular weight, the resin itself is not easy to penetrate into the lower layer, and other components with small molecular weight are inhibited from penetrating into the lower layer.

[0053] That is, according to the present application, since the molecular weight of the acrylic resin (A2) containing a secondary hydroxyl group having lower reactivity is large, the color reversion resistance can be improved.

[0054] In the clear coating composition of the present application, by using the above-mentioned primary hydroxyl group-containing acrylic resin (A1) and secondary hydroxyl group-containing acrylic resin (A2), a coating film having a high solid content concentration and excellent design can be obtained. That is, the conflicting properties of high solid content and coating film smoothness are achieved.

[0055] On the other hand, when a high-solid content coating composition developed in this way and achieving the above-mentioned performance is applied using a coating container, it is found that the cleaning ease after the coating is completed is poor. The cleaning ease mentioned here refers to the ease of cleaning work to remove the coating composition attached to the coating container, etc. due to the scattering of the coating in the spray coating, etc. after the coating. For example, in the coating using a reactive coating, sometimes the coating composition attached to the container reacts and solidifies during the coating, and cannot be easily removed during cleaning. And it is known that for the high-solid content coating that is the object of this application, this cleaning ease tends to be particularly poor. Furthermore, it is also known from experiments that the above-mentioned cleaning ease may not be correlated with the shelf life of the two-component coating.

[0056] The present inventors have also studied means for solving the above problems. Furthermore, it has been found through experiments that by using a specific alcohol solvent, the cleaning ease is high and the coating workability is good, thereby completing the clear coating composition of the present application. In this specification, the coating workability is evaluated from the viewpoint of the cleaning ease.

[0057] Hereinafter, each component of the clear coating composition in the present application will be described in detail.

[0058] (A) Hydroxyl-containing acrylic resin

[0059] The hydroxyl group-containing acrylic resin (A) includes a primary hydroxyl group-containing acrylic resin (A1) and a secondary hydroxyl group-containing acrylic resin (A2).

[0060] The acrylic resin (A1) containing a primary hydroxyl group (hereinafter also referred to as the first acrylic resin (A1)) contains a primary hydroxyl group but does not contain a secondary hydroxyl group. The acrylic resin (A2) containing a secondary hydroxyl group (hereinafter also referred to as the second acrylic resin (A2)) contains at least a secondary hydroxyl group and may further contain a primary hydroxyl group. The second acrylic resin (A2) may contain only a secondary hydroxyl group.

[0061] A primary hydroxyl group is a carbon atom that is bonded to only one carbon atom. α The bonded hydroxyl group is represented by "-CR2-C α H2-OH" represents an -OH group. A secondary hydroxyl group refers to a carbon atom C bonded to two carbon atoms. β The bonded hydroxyl group is represented by "-CR2-C β H(R 1 )-OH" represents an -OH group. R independently represents a hydrogen atom or a hydrocarbon group, R 1 It represents a hydrocarbon group.

[0062] The mass ratio (A1) / (A2) of the content of the first acrylic resin (A1) to the content of the second acrylic resin (A2) is, for example, 1 / 99 to 80 / 20. If the ratio of the first acrylic resin (A1) to the total mass of the first acrylic resin (A1) and the second acrylic resin (A2) is 1% by mass or more, the appearance of the resulting coating film can be further improved. If the ratio of the second acrylic resin (A2) to the total mass of the first acrylic resin (A1) and the second acrylic resin (A2) is 20% by mass or more, the color reversion resistance can be further improved.

[0063] If the mass ratio (A1) / (A2) is within the above range, it is easy to achieve both improvement in shelf life, coating film performance and appearance, and improvement in color reversion resistance. The mass ratio (A1) / (A2) may be 20 / 80 to 70 / 30, 30 / 70 to 60 / 40, or 30 / 70 to 50 / 50.

[0064] (A1) Acrylic resin containing primary hydroxyl groups

[0065] The weight average molecular weight (Mw) of the acrylic resin (first acrylic resin) (A1) containing a primary hydroxyl group is 6,000 or less. Thus, the viscosity of the clear coating composition during coating is maintained low. The Mw of the first acrylic resin (A1) may be 5,000 or less, 4,500 or less, or 4,000 or less.

[0066] The Mw of the first acrylic resin (A1) may be 1,000 or more, 2,000 or more, or 3,000 or more. This tends to increase the hardness of the resulting coating film. In one embodiment, the Mw of the first acrylic resin (A1) is 3,000 or more and 6,000 or less.

[0067] The Mw is determined by GPC using polystyrene as standard.

[0068] The acid value of the first acrylic resin (A1) is, for example, 0 mgKOH / g or more and 40 mgKOH / g or less. Thus, the usable time (also referred to as "shelf life") after mixing with the curing agent can be sufficiently prolonged. The acid value of the first acrylic resin (A1) can be 1 mgKOH / g or more, or 3 mgKOH / g or more. The acid value of the first acrylic resin (A1) can be 30 mgKOH / g or less, or 24 mgKOH / g or less, or 10 mgKOH / g or less.

[0069] The hydroxyl value of the first acrylic resin (A1) is, for example, 80 mgKOH / g or more and 250 mgKOH / g or less. Thus, sufficient crosslinking density can be obtained, and the hardness of the resulting coating film can be increased. The hydroxyl value of the first acrylic resin (A1) can be 100 mgKOH / g or more, and can be 120 mgKOH / g or more. The hydroxyl value of the first acrylic resin (A1) can be 220 mgKOH / g or less, and can be 200 mgKOH / g or less.

[0070] The hydroxyl value and the acid value are determined based on the solid content mass. The hydroxyl value and the acid value can be measured by a known method described in JIS K 0070: 1992. The hydroxyl value and the acid value can be calculated based on the amount of the unsaturated monomer in the raw material monomer of the resin (for example, the first acrylic resin (A1)).

[0071] The glass transition temperature (Tg) of the first acrylic resin (A1) is, for example, -20°C or higher and 60°C or lower. This can improve the durability of the obtained coating film, such as hardness and weather resistance. The Tg of the first acrylic resin (A1) may be 0°C or higher, or 5°C or higher. The Tg of the first acrylic resin (A1) may be 50°C or lower, or 40°C or lower.

[0072] Tg can be determined by calculation based on the type and amount of raw material monomers of the resin. Tg can be measured using a differential scanning calorimeter (DSC).

[0073] The first acrylic resin (A1) can be prepared by polymerizing an α,β-ethylenically unsaturated monomer having only a primary hydroxyl group and a third α,β-ethylenically unsaturated monomer having no primary or secondary hydroxyl group by a known method. The first acrylic resin (A1) is prepared, for example, by solution polymerization.

[0074] Examples of the α,β-ethylenically unsaturated monomer having only a primary hydroxyl group include 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 2-hydroxy-1-methyl (meth)acrylate, Placcell FM1 (ε-caprolactone-modified hydroxyethyl methacrylate, manufactured by Daicel Chemical Co., Ltd.), polyethylene glycol mono(meth)acrylate, and polypropylene glycol mono(meth)acrylate. These may be used alone or in combination of two or more.

[0075] Examples of the third α,β-ethylenically unsaturated monomer include (meth)acrylate monomers such as methyl, ethyl, propyl, butyl, hexyl, ethylhexyl, lauryl, phenyl, isobornyl, and cyclohexyl (meth)acrylate; α,β-ethylenically unsaturated monomers containing an acid group such as acrylic acid, methacrylic acid, acrylic acid dimer, crotonic acid, 2-acryloyloxyethylphthalic acid, 2-acryloyloxyethylsuccinic acid, ω-carboxy-polycaprolactone mono(meth)acrylate, maleic acid, fumaric acid, and itaconic acid; vinyl alcohol ester monomers, which are esters of vinyl alcohol and carboxylic acids such as acetic acid and propionic acid; polymerizable unsaturated hydrocarbon monomers such as styrene, α-methylstyrene, vinylnaphthalene, butadiene, and isoprene; polymerizable nitrile monomers such as acrylonitrile and methacrylonitrile; and acrylamide monomers such as acrylamide, methacrylamide, N-hydroxymethylacrylamide, N,N-dimethylacrylamide, and diacetoneacrylamide. These monomers may be used alone or in combination of two or more.

[0076] (Meth)acrylate refers to acrylate and / or methacrylate.

[0077] (A2) Acrylic resin containing secondary hydroxyl groups

[0078] The weight average molecular weight (Mw) of the acrylic resin (second acrylic resin) (A2) containing a secondary hydroxyl group is 6,000 or more. This improves the color reversion resistance of the coating film. In addition, the coating film properties such as hardness, chemical resistance, scratch resistance and weather resistance can also be improved.

[0079] The Mw of the second acrylic resin (A2) may be 20,000 or less, or 12,000 or less. The Mw of the second acrylic resin (A2) may be 6,500 or more, or 7,000 or more.

[0080] The acid value of the second acrylic resin (A2) is, for example, 0 mgKOH / g or more and 50 mgKOH / g or less. The acid value of the second acrylic resin (A2) may be 1 mgKOH / g or more, 5 mgKOH / g or more, or 10 mgKOH / g or more. The acid value of the second acrylic resin (A2) may be 40 mgKOH / g or less, 35 mgKOH / g or less, or 30 mgKOH / g or less. In one embodiment, the acid value of the second acrylic resin (A2) is 0 mgKOH / g or more and 40 mgKOH / g or less.

[0081] The hydroxyl value of the second acrylic resin (A2) is, for example, 80 mgKOH / g or more and 250 mgKOH / g or less. Thus, sufficient crosslinking density can be obtained, and the hardness of the resulting coating film can be improved. The hydroxyl value of the second acrylic resin (A2) can be 100 mgKOH / g or more, and can be 120 mgKOH / g or more. The hydroxyl value of the second acrylic resin (A2) can be 220 mgKOH / g or less, and can be 200 mgKOH / g or less.

[0082] The acid value of the first acrylic resin (A1) and the second acrylic resin (A2) may both be 0 mgKOH / g or more and 40 mgKOH / g or less. The acid value of the second acrylic resin (A2) may be higher than that of the first acrylic resin (A1).

[0083] The glass transition temperature (Tg) of the second acrylic resin (A2) is, for example, -30°C or higher and 35°C or lower. This can improve the durability of the obtained coating film, such as hardness and weather resistance. The Tg of the second acrylic resin (A2) may be -15°C or higher, 0°C or higher, or 5°C or higher. The Tg of the second acrylic resin (A2) may be 30°C or lower, 25°C or lower, or 20°C or lower.

[0084] The glass transition temperature Tg(A1) of the primary hydroxyl group-containing acrylic resin (A1) may be -20°C to 60°C, and the glass transition temperature (Tg) of the second acrylic resin (A2) may be -30°C to 35°C.

[0085] The second acrylic resin (A2) can be prepared by polymerizing an α,β-ethylenically unsaturated monomer having at least a secondary hydroxyl group and a fourth α,β-ethylenically unsaturated monomer having no secondary hydroxyl group by a known method. The second acrylic resin (A2) is prepared by, for example, solution polymerization.

[0086] Examples of the α,β-ethylenically unsaturated monomer having at least a secondary hydroxyl group include 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, and 3-hydroxybutyl (meth)acrylate, and these may be used alone or in combination of two or more.

[0087] Examples of the fourth α,β-ethylenically unsaturated monomer include the aforementioned α,β-ethylenically unsaturated monomer having only a primary hydroxyl group and the third α,β-ethylenically unsaturated monomer.

[0088] (Other hydroxyl-containing resins)

[0089] The clear coating composition may contain other hydroxyl-containing resins. Examples of other hydroxyl-containing resins include hydroxyl-containing polycarbonate resins, hydroxyl-containing urethane resins, hydroxyl-containing polyester resins, and hydroxyl-containing amino resins. These may be used alone or in combination of two or more.

[0090] The solid content of other hydroxyl-containing components in 100 parts by mass of the total solid content of the first and second hydroxyl-containing acrylic resins (A1, A2) and other hydroxyl-containing resins is, for example, 10 parts by mass or less, 5 parts by mass or less, or 3 parts by mass or less.

[0091] (Other resins)

[0092] The clear coating composition may contain other resins. Other resins include resins other than those mentioned above, such as polycarbonate resins, urethane resins, polyester resins, acrylic resins, amino resins, etc., which do not contain hydroxyl groups and do not fall within the above definition. They may be used alone or in combination of two or more.

[0093] (B) Polyisocyanate Compounds

[0094] The polyisocyanate compound (B) is a curing agent, and reacts with the hydroxyl group-containing resin to form a crosslinked structure, thereby curing the clear coating composition.

[0095] The polyisocyanate compound (B) has at least two isocyanate groups in one molecule. As the polyisocyanate compound, for example, aliphatic polyisocyanates, alicyclic polyisocyanates, aliphatic polyisocyanates having an aromatic ring not bonded to an isocyanate group in the molecule (aromatic aliphatic polyisocyanates), aromatic polyisocyanates, and derivatives of these polyisocyanates can be listed. Specifically, aromatic polyisocyanates such as toluene diisocyanate, 4,4'-diphenylmethane diisocyanate, o-phthalylene diisocyanate, and m-phthalylene diisocyanate; aliphatic polyisocyanates such as hexamethylene diisocyanate; alicyclic polyisocyanates such as isophorone diisocyanate; polymers such as their biuret, urate, and adducts, etc. They are used alone or in combination of two or more.

[0096] The equivalent ratio (NCO / OH) of the isocyanate group contained in the polyisocyanate compound (B) to the hydroxyl group contained in the resin containing the hydroxyl group may be 0.7 or more, or 0.8 or more. The equivalent ratio (NCO / OH) may be 2.0 or less, or 1.8 or less, or 1.5 or less. In one embodiment, the equivalent ratio (NCO / OH) is 0.7 or more and 2.0 or less. If the equivalent ratio (NCO / OH) is within this range, a transparent coating film having excellent hardness and weather resistance is easily formed.

[0097] (Other curing agents)

[0098] The clear coating composition may include other curing agents except the polyisocyanate compound (B). As other curing agents, for example, amino resins, epoxy compounds, aziridine compounds, carbodiimide compounds and oxazoline compounds may be listed. They are used alone or in combination of two or more. The content of other curing agents is appropriately set according to the resin containing hydroxyl groups.

[0099] (C) Organic solvents

[0100] The organic solvent (C) contains at least one alcohol solvent selected from the group consisting of a linear primary alcohol having 1 to 6 carbon atoms, a branched primary alcohol having 3 to 8 carbon atoms, a linear secondary alcohol having 1 to 6 carbon atoms, and a branched secondary alcohol having 3 to 8 carbon atoms. The clear coating composition of the present application contains the above-mentioned alcohol solvent, thereby having the following advantages: even a clear coating composition having a high solid content concentration has high cleaning ease and excellent coating workability.

[0101] Examples of the linear primary alcohol having 1 to 6 carbon atoms, which is one type of the alcohol solvent, include methanol, ethanol, propane-1-ol, butane-1-ol, pentane-1-ol, and hexane-1-ol.

[0102] Examples of the branched primary alcohol having 3 to 8 carbon atoms include isobutyl alcohol, 3-methyl-1-butanol, 2-ethyl-1-pentanol, and 2-ethylhexanol.

[0103] Examples of the linear secondary alcohol having 1 to 6 carbon atoms and the branched secondary alcohol having 3 to 8 carbon atoms include propane-2-ol, butane-2-ol, pentane-2-ol, hexane-2-ol and heptane-2-ol.

[0104] From the viewpoint of improving the ease of cleaning, the above-mentioned alcohol solvent is more preferably at least one selected from a straight-chain primary alcohol having 3 to 5 carbon atoms and a branched-chain primary alcohol having 3 to 5 carbon atoms, and more preferably at least one selected from a straight-chain primary alcohol having 4 to 5 carbon atoms and a branched-chain primary alcohol having 4 to 5 carbon atoms.

[0105] The content of the alcohol solvent is preferably 10% by mass or more relative to the total mass of the organic solvent (C). The content of the alcohol solvent may be 12% by mass or more. The content of the alcohol solvent may be 60% by mass or less, or 50% by mass or less.

[0106] The organic solvent (C) preferably further comprises a ketone compound. The ketone compound is more preferably a ketone compound having 7 or more carbon atoms. By making the organic solvent (C) further comprise a ketone compound, there is the following advantage: the viscosity of the clear coating composition having a high solid content concentration can be controlled to an appropriate range during coating. In addition, the ketone compound has little effect on the properties of other components contained in the clear coating composition. Therefore, the properties of the other components contained in the clear coating composition can be fully utilized, and the physical properties of the resulting coating film can be improved.

[0107] When the organic solvent (C) further contains a ketone compound having 7 or more carbon atoms, especially when containing a ketone compound having 7 or more carbon atoms, there is an advantage that the viscosity of the clear coating composition having a high solid content concentration can be controlled to an appropriate range during coating, and as a result, the appearance of the resulting coating film becomes good. In addition, there is an advantage that the coating workability is also improved. Although not bound by a specific theory, it is believed that this is because the ketone compound having 7 or more carbon atoms has a slow evaporation rate and can well disperse the high molecular weight secondary hydroxyl-containing acrylic resin (A2).

[0108] The ketone compound has a -C(=O)- structure. Examples of the ketone compound include methyl amyl ketone (MAK), methyl isoamyl ketone (MIAK), 3-heptanone, 4-heptanone, 2-octanone, diisobutyl ketone, and isophorone. Among them, from the viewpoint of high solubility of the hydroxyl-containing acrylic resin (A), it is desirable that the ketone compound is linear. Examples of the linear ketone compound include MAK and 2-octanone.

[0109] From the viewpoint of evaporation rate, the carbon number of the ketone compound may be 8 or more. From the viewpoint of solubility of the hydroxyl-containing acrylic resin (A), the carbon number of the ketone compound may be 9 or less. The carbon number of the ketone compound may be 7.

[0110] When the organic solvent (C) contains a ketone compound having 7 or more carbon atoms, the viscosity during coating is controlled to a more appropriate range. Therefore, there is an advantage that the appearance of the obtained coating film becomes better even at such a high solid content concentration.

[0111] The ketone compound having 7 or more carbon atoms also has a solid content concentration of 60 seconds after the clear coating composition is spray-coated (hereinafter referred to as the coating solid content concentration C 60 ) is controlled to an appropriate range. The coating solid content concentration C of the clear coating composition described in the present application 60 For example, it is 60% to 80% by mass. By maintaining the solid content concentration not being too high for a predetermined time after the clear coating composition is applied, the self-leveling function of the coating composition is exerted, and the smoothness of the resulting coating film can be further improved.

[0112] During coating, part of the solvent evaporates, so the solid content concentration of the coating after coating usually becomes higher. For previous coatings, in order to increase the solid content concentration during coating and reduce the viscosity during coating, solvents with small molecular weight such as butyl acetate are used. Solvents with small molecular weight are generally highly volatile, so the solid content concentration of the coating just after being applied to the coated object tends to become higher. Therefore, the self-leveling function cannot be exerted, and the smoothness of the resulting coating film is more likely to decrease. It can be considered that the ketone compound with a carbon number of 7 or more that can be suitably used in the clear coating composition described in the present application has a slow evaporation rate, so the coating solid content concentration C can be reduced. 60 Maintain within an appropriate range. Coating solid content concentration C 60 The coating solid content concentration C may be 65% or more, or 70% or more. 60 It may be 79% by mass or less, or 78% by mass or less.

[0113] The coating solid content concentration C of the above-mentioned clear coating composition is 60 The calculation can be performed as follows. First, the mass (initial mass W0) of a substrate of appropriate size (e.g., aluminum film) is measured. Next, the substrate is spray-coated with a clear coating composition. 60 seconds after the spray coating is completed, the substrate is bent with the surface with the clear coating composition attached as the inner side to prevent the solvent from volatilizing. The mass (W0) of the substrate with the uncured clear coating composition is measured. wet ). wetIt is the total mass of the solvent and solid components remaining in the clear coating composition 60 seconds after spray coating, and the substrate.

[0114] Next, the substrate was opened and heated at 140° C. for 30 minutes to cure the clear coating composition. Thereafter, the mass (W) of the substrate having the cured clear coating composition was measured. dry ). dry It is the total mass of the solid content of the clear coating composition and the substrate.

[0115] Finally, the coating solid content concentration C was calculated using the following formula: 60 . (W wet -W0) represents the total mass of the solvent and solid components remaining in the clear coating composition after spray coating for 60 seconds. (W dry -W0) represents the mass of only the solid components of the clear coating composition.

[0116] Coating solid content concentration C 60 (%) = 100 × (W dry -W0) / (W wet -W0)

[0117] The organic solvent (C) may further contain other organic solvents in addition to the above-mentioned alcohol solvents and ketone compounds. Examples of other organic solvents include aromatic hydrocarbons such as benzene, toluene, ethylbenzene, propylbenzene, tert-butylbenzene, o-xylene, m-xylene, p-xylene, tetralin, and decalin; monocarboxylic acid esters such as methyl acetate, ethyl acetate, n-butyl acetate, amyl acetate, and diethylene glycol monobutyl ether acetate (butyl carbitol acetate); dibasic ester compounds; cellosolves such as methyl cellosolve, ethyl cellosolve, n-propyl cellosolve, isopropyl cellosolve, n-butyl cellosolve, isobutyl cellosolve, isopentyl cellosolve, phenyl cellosolve, and benzyl cellosolve. Carbitols such as methyl carbitol, ethyl carbitol, n-propyl carbitol, isopropyl carbitol, n-butyl carbitol, isobutyl carbitol, isoamyl carbitol, carbitol acetate, phenyl carbitol, and benzyl carbitol; ethers such as ethylene glycol monoisopropyl ether, ethylene glycol monoethyl ether, ethylene glycol mono-n-propyl ether, ethylene glycol mono-n-butyl ether, ethylene glycol mono-tert-butyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol mono-n-propyl ether, propylene glycol mono-n-butyl ether, propylene glycol monomethyl ether acetate, propylene glycol monoethyl ether acetate, and dioxane. These may be used alone or in combination of two or more.

[0118] When the organic solvent is added to the curing agent, it is a condition that the organic solvent does not have a hydroxyl group.

[0119] In one embodiment of the present application, the organic solvent (C) may include the above-mentioned alcohol solvent and an organic solvent having a boiling point of 200°C or more. This can further improve the color reversion resistance and appearance of the obtained coating film. In particular, it may include at least one selected from monocarboxylic acid esters, dibasic ester compounds, cellosolves and carbitol having a boiling point of 200°C or more. These organic solvents having a boiling point of 200°C or more may be used alone or in combination of two or more.

[0120] Dibasic ester compounds (also called dibasic acid esters) are obtained by the reaction of dicarboxylic acids and alcohols. Dibasic ester compounds are represented by the following general formula, for example:

[0121] R 3 OOC-R 2 -COOR 4

[0122] (Where R 2 , R 3 and R 4 Each is independently an aliphatic, alicyclic, aliphatic or aromatic hydrocarbon group having an aromatic ring.)

[0123] R 2 It can be an aliphatic hydrocarbon group. 2 In the formula (R), the carbon number of the aliphatic hydrocarbon group may be 1 to 6, 2 to 6, or 2 to 4. 2 In R 2 In the formula (R), the aliphatic hydrocarbon group may be straight chain or branched. 2 It may be a linear saturated aliphatic hydrocarbon group having 1 to 6 carbon atoms.

[0124] R 3 and R 4 It can be an aliphatic hydrocarbon group. 3 and R 4 In the formula (R), the carbon number of the aliphatic hydrocarbon group may be 1 to 6, 1 to 3, or 1 or 2. 3 and R 4 In R 3 and R 4 In the formula (R), the aliphatic hydrocarbon group may be straight chain or branched. 3 and R 4 It may be a linear saturated aliphatic hydrocarbon group having 1 to 6 carbon atoms. 3 and R 4 Can be the same or different. 3 and R 4 Can be the same.

[0125] Specific examples of suitable dibasic ester compounds include dimethyl succinate, diethyl succinate, di-n-propyl succinate, di-n-butyl succinate, di-n-pentyl succinate, di-n-hexyl succinate, dimethyl glutarate, diethyl glutarate, di-n-propyl glutarate, di-n-butyl glutarate, di-n-pentyl glutarate, di-n-hexyl glutarate, dimethyl adipate, diethyl adipate, di-n-propyl adipate, di-n-butyl adipate, di-n-hexyl adipate, Amyl ester, di-n-hexyl adipate, dimethyl pimelate, diethyl pimelate, di-n-propyl pimelate, di-n-butyl pimelate, di-n-pentyl pimelate, di-n-hexyl pimelate, dimethyl suberate, diethyl suberate, di-n-propyl suberate, di-n-butyl suberate, di-n-pentyl suberate, di-n-hexyl suberate, dimethyl azelaic acid, diethyl azelaic acid, di-n-propyl azelaic acid, di-n-butyl azelaic acid, di-n-pentyl azelaic acid, di-n-hexyl azelaic acid. They are used alone, or are used in combination of more than two kinds. For example, the alkyl esters of succinic acid, the alkyl esters of glutaric acid and the alkyl esters of adipic acid can be used in combination.

[0126] In the clear coating composition, when the organic solvent (C) further includes the above-mentioned ketone compound, the content thereof can be, for example, 50 parts by mass or more and 550 parts by mass or less relative to 100 parts by mass of the content of the above-mentioned alcohol solvent. The above-mentioned content of the ketone compound can be 70 parts by mass or more, and can be 75 parts by mass or more. In addition, the above-mentioned content of the ketone compound can be 500 parts by mass or less, and can be 200 parts by mass or less. In addition, when the organic solvent (C) further includes the above-mentioned organic solvent having a boiling point of 200°C or more, the content thereof can be, for example, 30 parts by mass or more and 200 parts by mass or less relative to 100 parts by mass of the content of the above-mentioned alcohol solvent. The above-mentioned content of the organic solvent having a boiling point of 200°C or more can be 40 parts by mass or more. In addition, the above-mentioned content of the organic solvent having a boiling point of 200°C or more can be 180 parts by mass or less, and can be 120 parts by mass or less.

[0127] The organic solvent (C) may contain the alcohol solvent and other organic solvents having a boiling point lower than 200° C. The content of such other organic solvents may be, for example, less than 20 parts by mass, 10 parts by mass or less, 5 parts by mass or less, or 0 parts by mass relative to 100 parts by mass of the alcohol solvent.

[0128] (Other ingredients)

[0129] The clear coating composition may further contain a pigment and various additives. Examples of the additives include ultraviolet absorbers, antioxidants, defoamers, surface conditioners, and anti-pinhole agents.

[0130] [Painted items]

[0131] The clear coating composition described in the present application can be used to obtain a coated article. The coated article includes, for example, a coated article and a multilayer coating film including a base coating film and a clear coating film. The clear coating film is formed by the clear coating composition described in the present application. Thus, the coated article has excellent color fastness and appearance.

[0132] The base coating film is disposed between the object to be coated and the clear coating film. The multilayer coating film may further include a mid-coat coating film disposed between the object to be coated and the base coating film. That is, the coated article may include an object to be coated, and a multilayer coating film in which a mid-coat coating film, a base coating film, and a clear coating film are sequentially laminated.

[0133] (Object to be coated)

[0134] Examples of the material of the coating include metal, resin, and glass. Specifically, examples of the coating include automobile bodies and automobile body parts of cars, trucks, motorcycles, and buses, and automobile parts such as spoilers, bumpers, rearview mirror covers, body grills, and door handles.

[0135] Examples of the metal include iron, copper, aluminum, tin, zinc, and alloys thereof (e.g., steel). Examples of the metal to be coated include cold-rolled steel sheets, hot-rolled steel sheets, stainless steel, electrogalvanized steel sheets, hot-dip galvanized steel sheets, zinc-aluminum alloy plated steel sheets, zinc-iron alloy plated steel sheets, zinc-magnesium alloy plated steel sheets, zinc-aluminum-magnesium alloy plated steel sheets, aluminum plated steel sheets, aluminum-silicon alloy plated steel sheets, tin plated steel sheets, and the like.

[0136] The metal object to be coated may be subjected to surface treatment. Examples of the surface treatment include phosphate treatment, chromate treatment, zirconium chemical treatment, and composite oxide treatment. After the surface treatment, the metal object to be coated may be further coated with an electroplating paint. The electroplating paint may be cationic or anionic.

[0137] Examples of the resin include polypropylene resin, polycarbonate resin, urethane resin, polyester resin, polystyrene resin, ABS resin, vinyl chloride resin, and polyamide resin. The resin coating object may be subjected to a degreasing treatment.

[0138] (Middle coating film)

[0139] The mid-coat film is formed by a mid-coat coating composition. The mid-coat coating composition is described below. The film thickness (dry film thickness) of the mid-coat film after curing is, for example, 5 μm or more and 80 μm or less. The dry film thickness of the mid-coat film can be 10 μm or more. The dry film thickness of the mid-coat film can be 50 μm or less.

[0140] The thickness of the coating film can be measured using an electromagnetic film thickness meter (for example, SDM-miniR manufactured by SANKO Co., Ltd.). The thickness of the coating film is the average value of the coating film thickness at any five points.

[0141] (Base coating)

[0142] The base coating film is formed by a base coating composition. The base coating composition is described below. The base coating film can be a single layer or a laminated coating film of more than two layers. The dry film thickness of each layer in the base coating film is, for example, 5 μm or more and 35 μm or less. The dry film thickness of each layer in the base coating film can be 7 μm or more. The dry film thickness of each layer in the base coating film can be 30 μm or less.

[0143] (Transparent coating)

[0144] The transparent coating film is formed from the transparent coating composition described in the present application. The dry film thickness of the transparent coating film is, for example, 10 μm or more and 80 μm or less. The dry film thickness of the transparent coating film may be 20 μm or more. The dry film thickness of the transparent coating film may be 60 μm or less.

[0145] [Method for producing coated article]

[0146] The aforementioned coated article is manufactured by a method comprising, for example, the following steps: a step of applying a base coating composition on the coated object to form an uncured base coating film; a step of applying the clear coating composition described in the present application to the uncured base coating film to form an uncured clear coating film; and a step of simultaneously curing the uncured base coating film and the uncured clear coating film.

[0147] Before the step of applying the base coating composition, a step of applying the mid-coat coating composition to the object to be coated may be performed. When the base coating composition is applied, the mid-coat coating film may be cured or uncured. When the base coating composition is applied, the mid-coat coating film may be cured.

[0148] That is, the coated article can be manufactured by a method (two-coat one-bake method) having the following steps: a step of applying a mid-coat coating composition to the coated object and curing it to form a cured mid-coat coating film; a step of applying a base coating composition and a clear coating composition in sequence on the cured mid-coat coating film to form an uncured base coating film and a clear coating film in sequence; and a step of curing the uncured base coating film and the clear coating film together.

[0149] In addition, the coated article can be manufactured by a method (three-coat one-bake method) having the following steps: a step of sequentially coating a mid-coat coating composition, a base coating composition and a clear coating composition on the coated object to form an uncured mid-coat coating film, a base coating film and a clear coating film in sequence; and a step of curing the uncured mid-coat coating film, the base coating film and the clear coating film together.

[0150] Hereinafter, each step will be described by taking the case of manufacturing a coated article having a multilayer coating film in which a midcoat film, a base coating film, and a clear coating film are sequentially laminated by a two-coat one-bake method as an example. However, the method for manufacturing a coated article is not limited thereto.

[0151] (I) Step of forming a cured intermediate coating film

[0152] First, the midcoat coating composition is applied to the object to be coated to form an uncured midcoat film. The midcoat film improves the adhesion of the base film to the object to be coated. In addition, the coating surface is made uniform by the midcoat coating, and the unevenness of the base film is easily suppressed.

[0153] As the coating method, for example, a roller coater method, air jet coating, air jet coating, and rotary atomization coating can be listed. These methods can be combined with electrostatic coating. Among them, from the viewpoint of coating efficiency, rotary atomization electrostatic coating is preferably used. Rotary atomization electrostatic coating can use a rotary atomization electrostatic coating machine commonly known as "MICRO MICROBELL (μμBELL)", "MICROBELL (μBELL)", "METALLICBELL (METABELL)", etc.

[0154] Next, the uncured mid-coat film is cured. The mid-coat coating composition can be cured by heating. The curing (heating) conditions are appropriately set according to the composition of the mid-coat coating composition, the material of the coated object, etc. The heating temperature is, for example, above 100°C and below 180°C, and can be above 120°C and below 160°C. The heating time can be appropriately set according to the heating temperature. When the heating temperature is above 100°C and below 180°C, the heating time is, for example, above 10 minutes and below 60 minutes, and can be above 10 minutes and below 30 minutes. The heating time refers to the time when the target temperature is reached in the heating device and the coated object maintains the target temperature, without considering the time until the target temperature is reached. As a heating device, a drying furnace using a heating source such as hot air, electricity, gas, infrared rays, etc. can be listed.

[0155] (Mid-coat coating composition)

[0156] The midcoat coating composition may be water-based or solvent-based. In a water-based coating composition, as a solvent, water is included in an amount of 50% by mass or more of the total solvent. In a solvent-based coating composition, as a solvent, an organic solvent is included in an amount of 50% by mass or more of the total solvent.

[0157] The midcoat coating composition may further include, for example, resins, pigments, and various additives on the basis of various solvents. Examples of the resin include acrylic resins, polyester resins, polyurethane resins, alkyd resins, fluororesins, epoxy resins, and polyether resins. One of these resins may be used alone, or two or more thereof may be used in combination. The midcoat coating composition may further include the above-mentioned curing agent.

[0158] (II) Step of forming an uncured base coating film

[0159] The base coating composition is applied on the cured mid-coat film to form an uncured base coating film. Two or more layers of uncured base coating films can be formed by applying the same or different base coating compositions more than twice. An interval of several minutes can be set between the application of the nth base coating composition and the application of the n+1th base coating composition.

[0160] As a coating method, the same method as the coating method of a mid-coat coating composition can be mentioned, for example.

[0161] After the base coating composition is applied and before the clear coating composition is applied, pre-drying (also referred to as preheating) can be performed. Thus, the dilution component contained in the base coating composition is suppressed from boiling in the curing process, and the generation of gushing out is easily suppressed. And then, the mutual mixing of the uncured base coating film and the clear coating composition is suppressed by pre-drying, and it is difficult to form a mixed layer. Therefore, the smoothness of the obtained coated article can be further improved.

[0162] Examples of the pre-drying method include a method of leaving the mixture at a temperature of 20°C to 25°C for 5 minutes to 15 minutes, and a method of heating the mixture at a temperature of 50°C to 80°C for 30 seconds to 10 minutes.

[0163] (Base coating composition)

[0164] The base coating composition can be water-based or solvent-based. The base coating composition can be water-based. The water-based base coating composition includes, for example, an acrylic resin emulsion, a water-soluble acrylic resin, a curing agent (typically, a melamine resin), and a polyether polyol resin. The base coating composition can also include a pigment and various additives.

[0165] (III) Step of forming an uncured clear coating film

[0166] The clear coating composition described in the present application is applied on an uncured base coating film to form an uncured clear coating film.

[0167] The coating method is not particularly limited. As the coating method, for example, the same method as the coating method of the midcoat coating composition can be cited. Among them, from the viewpoint of coating efficiency, rotary atomization electrostatic coating is preferred. After applying the clear coating composition, pre-drying can be performed in the same manner as described above.

[0168] (IV) Curing process

[0169] The uncured base coating film and the clear coating film are cured together. Each coating film can be cured by heating. The heating conditions can be the same as those of the intermediate coating film.

[0170] Example

[0171] The present invention will be described in more detail by the following Examples, but the present invention is not limited thereto. In the Examples, "parts" and "%" are based on mass unless otherwise specified.

[0172] First, a plurality of first acrylic resins (A1) and second acrylic resins (A2) were produced as described below. Table 1 shows the physical property values ​​of the produced hydroxyl-containing acrylic resins.

[0173] The solid content concentration of the varnish obtained in Production Examples 1-1 to 1-3 and Production Examples 2-1 to 2-5 was determined by measuring the mass of the residue (heating residue) after heating at 150° C. for 60 minutes.

[0174] [Manufacturing Example 1-1] Manufacture of the First Acrylic Resin (A1-1)

[0175] 24.2 parts by mass of butyl acetate were added to an autoclave equipped with a stirrer, a temperature control device, a reflux condenser, a nitrogen inlet pipe and a liquid feeding pump, and the temperature was raised to 170° C. A monomer solution (a mixed solution containing 20 parts by mass of styrene, 13.2 parts by mass of 2-ethylhexyl acrylate, 26.4 parts by mass of 2-ethylhexyl methacrylate, 39.4 parts by mass of 2-hydroxyethyl methacrylate and 1.0 part by mass of methacrylic acid) and a mixed solution of 1.65 parts by mass of di-tert-amyl peroxide and 7.74 parts by mass of butyl acetate were added dropwise to the autoclave using a liquid feeding pump over 3 hours.

[0176] After the dropwise addition was completed, the temperature was maintained at 170° C. for 30 minutes and then cooled to 120° C. over 30 minutes. Then, a mixed solution of 0.2 parts by mass of di-tert-amyl peroxy-2-ethylhexanoate and 2.0 parts by mass of butyl acetate was added dropwise over 30 minutes using a liquid delivery pump.

[0177] Next, after the reaction was continued at 120° C. for 1 hour, 6.4 parts by mass of butyl acetate was added to obtain a varnish having a solid content concentration of 70.0% by mass and containing the first acrylic resin (A1-1) having an Mw of 4,000, a hydroxyl value of 170 mgKOH / g, an acid value of 7 mgKOH / g, and a Tg of 20° C.

[0178] [Manufacturing Example 1-2] Manufacture of the First Acrylic Resin (A1-2)

[0179] The same operation as in Production Example 1-1 was performed except that the amount of di-tert-amyl peroxide added dropwise together with the monomer solution was set to 1.08 parts by mass, thereby obtaining a varnish containing the first acrylic resin (A1-2) having an Mw of 6,000, a hydroxyl value of 170 mgKOH / g, an acid value of 7 mgKOH / g, and a Tg of 20° C. and having a solid content concentration of 70.1% by mass.

[0180] [Manufacturing Example 1-3] Manufacture of the First Acrylic Resin (A1-3)

[0181] A varnish containing a first acrylic resin (A1-3) having a Mw of 4,000, a hydroxyl value of 170 mgKOH / g, an acid value of 25 mgKOH / g, and a Tg of 20° C. and having a solid content concentration of 70.0% was obtained in the same manner as in Production Example 1-1 except that the amount of 2-ethylhexyl acrylate in the monomer solution was 17.4 parts by mass, the amount of 2-ethylhexyl methacrylate was 19.4 parts by mass, and the amount of methacrylic acid was 3.8 parts by mass.

[0182] [Manufacturing Example 2-1] Manufacture of the Second Acrylic Resin (A2-1)

[0183] 38.2 parts by mass of butyl acetate were added to a container equipped with a stirrer, a temperature control device, a reflux condenser and a dropping funnel, and the temperature was raised to 120° C. A monomer solution (a mixed solution comprising 20 parts by mass of styrene, 15.8 parts by mass of n-butyl acrylate, 21.8 parts by mass of n-butyl methacrylate, 41.1 parts by mass of 2-hydroxypropyl methacrylate and 1.3 parts by mass of acrylic acid) and a mixed solution of 11.0 parts by mass of tert-butyl peroxy-2-ethylhexanoate and 5 parts by mass of butyl acetate were simultaneously added dropwise to the container over 3 hours.

[0184] After leaving it for 30 minutes, a mixed solution of 0.5 parts by mass of tert-butyl peroxy-2-ethylhexanoate and 4 parts by mass of butyl acetate was added dropwise over 30 minutes. Then, the reaction was continued at 120° C. for 1 hour, and then 7 parts by mass of butyl acetate was added. Thus, a varnish having a solid content concentration of 64.5% was obtained, which contained a second acrylic resin (A2-1) containing a secondary hydroxyl group having an Mw of 8,000, a hydroxyl value of 160 mgKOH / g, an acid value of 10 mgKOH / g, and a Tg of 20° C.

[0185] [Manufacturing Example 2-2] Manufacture of Second Acrylic Resin (A2-2)

[0186] The same procedures as in Production Example 2-1 were performed except that the amount of tert-butyl peroxy-2-ethylhexanoate added dropwise together with the monomer solution was 4.5 parts by mass, thereby obtaining a varnish having a solid content concentration of 64.8% by mass, comprising a second acrylic resin (A2-2) containing a secondary hydroxyl group having an Mw of 12,000, a hydroxyl value of 160 mgKOH / g, an acid value of 10 mgKOH / g, and a Tg of 20°C.

[0187] [Manufacturing Example 2-3] Manufacture of Second Acrylic Resin (A2-3)

[0188] A varnish having a solid content concentration of 64.2% was obtained by the same procedure as in Production Example 2-1, except that the amount of n-butyl acrylate in the monomer solution was 18.3 parts by mass, the amount of n-butyl methacrylate was 14.8 parts by mass, and the amount of acrylic acid was 5.8 parts by mass. The varnish contained a second acrylic resin (A2-3) containing a secondary hydroxyl group having an Mw of 8,000, a hydroxyl value of 160 mgKOH / g, an acid value of 45 mgKOH / g, and a Tg of 20°C.

[0189] [Manufacturing Example 2-4] Manufacture of Second Acrylic Resin (A2-4)

[0190] The same procedures as in Production Example 2-1 were carried out except that the amount of n-butyl acrylate in the monomer solution was 1.4 parts by mass, the amount of n-butyl methacrylate was 36.2 parts by mass, and the amount of tert-butyl peroxy-2-ethylhexanoate added dropwise together with the monomer solution was 3.0 parts by mass, thereby obtaining a varnish having a solid content concentration of 65.1% by mass, which contained a second acrylic resin (A2-4) containing a secondary hydroxyl group and having an Mw of 15,000, a hydroxyl value of 160 mgKOH / g, an acid value of 10 mgKOH / g, and a Tg of 35°C.

[0191] [Manufacturing Example 2-5] Manufacture of the Second Acrylic Resin (A2-5)

[0192] A varnish having a solid content concentration of 64.7% was obtained by the same procedure as in Production Example 1-1, except that 39.4 parts by mass of 2-hydroxyethyl methacrylate in the monomer solution was replaced with 39.4 parts by mass of 2-hydroxypropyl methacrylate. The varnish contained a second acrylic resin (A2-5) having a Mw of 4,000, a hydroxyl value of 150 mgKOH / g, an acid value of 7 mgKOH / g, and a Tg of 10°C and having a secondary hydroxyl group.

[0193] Table 1

[0194]

[0195] [Example 1]

[0196] (1) Preparation of main agent

[0197] 42 parts by mass of the first acrylic resin (A1-1), 18 parts by mass of the second acrylic resin (A2-1), 2.0 parts by mass of a UV absorber (Tinubin 384, manufactured by BASF), 1.0 parts by mass of a light stabilizer (Tinubin 123, manufactured by BASF), 1.0 parts by mass of an acrylic surface conditioner, 6 parts by mass of isobutyl alcohol, 30 parts by mass of methyl amyl ketone, and 7 parts by mass of DBE (a dibasic ester compound, dimethyl glutarate, boiling point of about 205° C.) were added to a 1 L metal container in this order, and the mixture was stirred thoroughly with a disperser to obtain a main agent. The mass of the compounded parts is the solid content.

[0198] (2) Preparation of curing agent

[0199] In another metal container, 40 parts by mass of a polyisocyanate compound (B-1) (isocyanurate of hexamethylene diisocyanate, Desmogal N-3300, manufactured by Sumika Combustion Laboratories, solid content concentration: 100% by mass) and 12.0 parts by mass of methyl amyl ketone were added in this order and stirred to obtain a curing agent.

[0200] (3) Preparation of clear coating composition

[0201] The main component and the curing agent were mixed to obtain a clear coating composition. The clear coating composition had a solid content concentration of 60% by mass during coating (within 10 minutes after mixing).

[0202] [Examples 2 to 18 and Comparative Examples 1 to 4]

[0203] Clear coating compositions were prepared by the same procedures as in Example 1 except that the types and amounts of the blended components, the solid content during coating, and the like were changed as shown in Tables 2 to 4.

[0204] The details of each component shown in Tables 2 to 4 are as follows.

[0205] (Polyisocyanate compound (B))

[0206] (B-1): SUMIDUL N-3300 (manufactured by Sumika Combustion Laboratories, isocyanurate of hexamethylene diisocyanate, solid content concentration: 100% by mass)

[0207] (B-2): Desmogel N-3600 (manufactured by Sumika Combustrol Reitan Co., Ltd., isocyanurate of hexamethylene diisocyanate, solid content concentration: 100% by mass)

[0208] (B-3): Duranet TKA-100 (manufactured by Asahi Kasei Corporation, isocyanurate of hexamethylene diisocyanate, solid content concentration: 100% by mass)

[0209] (B-4): Dulanet TPA-100 (manufactured by Asahi Kasei Corporation, isocyanurate of hexamethylene diisocyanate, solid content concentration: 100% by mass)

[0210] (Organic solvent (C))

[0211] (Alcohol solvent)

[0212] Alcohol solvent (1): Isobutanol

[0213] Alcohol solvent (2): n-butanol

[0214] Alcohol solvent (3): 1-hexanol

[0215] Alcohol solvent (4): 2-butanol

[0216] Alcohol solvent (5): tert-butyl alcohol

[0217] (Ketone Compounds)

[0218] MAK: Methyl amyl ketone

[0219] (Organic solvent with boiling point above 200℃)

[0220] DBE: dibasic ester (manufactured by Shoei Chemical Co., Ltd., a mixture of dimethyl succinate, dimethyl glutarate and dimethyl adipate, CAS No. 95481-62-2), boiling point: 200°C

[0221] (other)

[0222] UV absorber: Thunbine 384, manufactured by BASF

[0223] Light stabilizer: Thunbine 123, manufactured by BASF

[0224] Surface conditioner: BYK-350, manufactured by ビックケミー・ジャパン Co., Ltd.

[0225] The solid content concentration of the clear coating compositions prepared in Examples and Comparative Examples at the time of coating was determined according to the following procedure.

[0226] (Solid content concentration C1 during coating)

[0227] Measure the initial mass (W0) of an aluminum cup with a diameter of about 6 cm. Add a clear coating composition obtained by mixing a main agent and a curing agent into it, and measure its mass (W1) within 10 minutes after mixing. Use a spray oven to heat it at 140°C for 30 minutes and cool it naturally, then measure the mass again (W2). Finally, use the following formula to calculate the solid content concentration C1 during coating.

[0228] Solid content concentration during coating C1 (mass %) = 100 × (W2-W0) / (W1-W0)

[0229] [evaluate]

[0230] The following evaluations were performed using the clear coating compositions prepared in the above Examples and Comparative Examples. The evaluation results are shown in Tables 2 to 4.

[0231] (1) Film smoothness

[0232] (a) Preparation of Test Plate A

[0233] A zinc phosphate treated matte steel plate having a thickness of 0.8 mm, a length of 30 cm, and a width of 40 cm was electroplated with a cationic electroplating paint "Pavotop U-50" (manufactured by Nippon Payton Automode Coatings Co., Ltd.) in such a way that the dry film thickness became 20 μm, and baked at 160° C. for 30 minutes.

[0234] On the obtained coated plate, a gray mid-coat "Oluga OP-30" (a polyester-melamine paint manufactured by Nippon Paint Automotive Coatings Co., Ltd.) diluted to a viscosity of 25 seconds (measured at 20°C using a No. 4 Ford cup) was applied in two stages by air spraying so that the dry film thickness became 35 μm, and the coating was baked at 140°C for 30 minutes.

[0235] On the obtained coated plate, a water-based base coating was applied in two stages using a cartridge bell at a room temperature of 23°C and a humidity of 68% so that the dry film thickness was 15 μm. An interval of 1 minute and 30 seconds was set between the first and second coatings. After the second coating, a setting of 1 minute and 30 seconds was performed. Then, preheating was performed at 80°C for 5 minutes to form an uncured first base coating film.

[0236] As the aforementioned water-based base paint, a water-based paint produced by Nippon Paint Automotive Coatings Co., Ltd., which has a trade name of "Acarex AR-3000 (black)" and contains a black pigment as a coloring pigment, was used, which was diluted with deionized water to a viscosity of 6,000 mPa·s (measured using a B-type viscometer at 6 rpm and 20° C.).

[0237] On the obtained uncured first base coating film, a water-based metallic base coating was applied in two stages using a cartridge rotary cup. An interval of 1 minute and 30 seconds was set between the first and second coatings. After the second coating, a conditioning was performed for 1 minute and 30 seconds. Then, preheating was performed at 80°C for 5 minutes to form an uncured second base coating film.

[0238] As the water-based metallic base paint, a water-based paint composition containing an aluminum pigment and marketed under the trade name of "Aquarex AR-3000 (metal)" manufactured by Nippon Paint Automotive Coatings Co., Ltd. was used.

[0239] Next, the clear coating composition was applied in one step to the obtained coated plate so that the dry film thickness was 35 μm, and the coating was adjusted for 7 minutes. Next, the plate was baked in a dryer at 140° C. for 30 minutes to obtain a test plate A having a multilayer coating film.

[0240] (b) Determination and evaluation of LW value

[0241] The Long Wave (LW) value of the test plate A was measured using a "wave scanner DOI" (manufactured by BYK Gardner) (measurement wavelength: 1,300 to 12,000 μm), and the smoothness of the resulting coating film was evaluated according to the following criteria. The smaller the LW value, the higher the smoothness of the coating film.

[0242] (Evaluation Criteria)

[0243] A: LW value is less than 10

[0244] C: LW value exceeds 10

[0245] (2) Color fastness

[0246] The L values ​​of the test plate A prepared in the same manner as above were measured at an incident angle of 45 degrees and a light receiving angle of 15 degrees using a multi-angle spectrophotometer "MA-68II" (trade name, manufactured by X-Rite Corporation). * Value (L * 15 value) and the light receiving angle is 110 degrees L * Value (L* 110 value), find the FF value (=L * 15 Value / L * 110 The calculated FF value was used to evaluate the color fastness according to the following criteria. The larger the FF value, the better the color fastness.

[0247] (Evaluation Criteria)

[0248] A: FF value is 5.5 or above

[0249] B: FF value is 5.0 or more and less than 5.5

[0250] C: FF value is less than 5.0

[0251] (3) Validity period

[0252] The main agent and curing agent prepared above were mixed for 1 minute using a disperser, and the obtained mixture was temperature-adjusted to 20°C. Within 5 minutes from the start of mixing of the main agent and curing agent, the initial viscosity V0 at 20°C was measured using Ford Cup No. 4. Next, the mixture was allowed to stand for 1 hour under standard conditions (23°C, humidity 68%). Thereafter, the mixture was temperature-adjusted to 20°C, and the viscosity V1 at 20°C was measured using Ford Cup No. 4.

[0253] The thickening ratio was calculated using the following formula and evaluated according to the following criteria: The lower the thickening ratio, the longer the shelf life.

[0254] Thickening ratio (%) = 100 × (V1-V0) / V0

[0255] (Evaluation Criteria)

[0256] A: Thickening ratio is less than 25%

[0257] B: Thickening ratio is 25% or more and less than 40%

[0258] C: Thickening ratio is more than 40%

[0259] (4) Ease of cleaning

[0260] The clear coating composition was spray-coated on the glass plate according to the following steps and conditions, and the paint scattering (dust) during the spray coating adhered to the glass plate. Then, the paint scattering adhering to the glass plate was wiped off by soot blowing according to the following steps, and the cleaning ease was evaluated according to the following criteria.

[0261] <Air spray coating conditions>

[0262] Discharge: 2 turns from fully closed

[0263] Air pressure: 0.25MPa

[0264] <Painting method>

[0265] The object to be coated is held in a substantially vertical state and coated in accordance with the following steps.

[0266] Step 1. Stand at a position with a gun 150 cm away from the glass plate and tilted 45°, and blow soot for 10 seconds.

[0267] Step 2. Allow to dry at room temperature (23°C) for 10 seconds

[0268] Step 3. After performing steps 1 and 2 a total of 5 times, the mixture was allowed to stand at room temperature (23° C.) for 24 hours.

[0269] Step 4. After leaving the glass plate to stand, the paint splatter adhering to the glass plate in the above step was wiped off with a cloth, and the glass plate was evaluated according to the following criteria.

[0270] Evaluation Benchmarks

[0271] A: Can be easily wiped off

[0272] B: Can be wiped with (cleaning detergent)

[0273] C: Paint splatters solidify on the test plate and are difficult to wipe off even with a cleaning agent.

[0274]

[0275]

[0276]

[0277] The clear coating compositions of the examples all had good color reversion resistance, and the obtained coating films had good appearance. Furthermore, despite being high-solid content coating compositions, they were easy to clean.

[0278] Comparative Example 1 is an example of an alcohol solvent containing a tertiary alcohol as the organic solvent (C). In this example, the ease of cleaning was not sufficiently satisfactory.

[0279] Comparative Example 2 is an example in which the acrylic resin (A2) containing a secondary hydroxyl group is not contained, and the obtained coating film did not have sufficiently satisfactory color reversion resistance.

[0280] Comparative Example 3 is an example in which the acrylic resin (A1) containing a primary hydroxyl group is not contained, and the pot life of the obtained coating composition and the appearance (coating film smoothness) of the obtained coating film were not sufficiently satisfactory.

[0281] Comparative Example 4 is an example in which a resin having a weight average molecular weight of less than 6,000 was used as the secondary hydroxyl group-containing acrylic resin (A2), and the obtained coating film did not have sufficient reversion resistance.

[0282] This application includes the following aspects.

[0283] [1] A clear coating composition comprising a hydroxyl group-containing acrylic resin (A), a polyisocyanate compound (B) and an organic solvent (C),

[0284] The aforementioned hydroxyl-containing acrylic resin (A) comprises a primary hydroxyl-containing acrylic resin (A1) and a secondary hydroxyl-containing acrylic resin (A2).

[0285] The weight average molecular weight of the acrylic resin (A1) containing a primary hydroxyl group is 6,000 or less,

[0286] The weight average molecular weight of the acrylic resin (A2) containing a secondary hydroxyl group is 6,000 or more,

[0287] The organic solvent (C) comprises at least one alcohol solvent selected from the group consisting of a linear primary alcohol having 1 to 8 carbon atoms, a branched primary alcohol having 3 to 8 carbon atoms, a linear secondary alcohol having 1 to 8 carbon atoms, and a branched secondary alcohol having 3 to 8 carbon atoms,

[0288] The solid content concentration during coating is 55% by mass or more.

[0289] [2] The clear coating composition according to [1], wherein the acid value of the primary hydroxyl group-containing acrylic resin (A1) is 0 mgKOH / g or more and 40 mgKOH / g or less.

[0290] [3] The clear coating composition according to [1] or [2], wherein the acid value of the secondary hydroxyl group-containing acrylic resin (A2) is 0 mgKOH / g or more and 40 mgKOH / g or less.

[0291] [4] The clear coating composition according to any one of [1] to [3], wherein the glass transition temperature Tg(A1) of the primary hydroxyl group-containing acrylic resin (A1) is -20°C or higher and 60°C or lower.

[0292] [5] The clear coating composition according to any one of [1] to [4], wherein the glass transition temperature Tg(A2) of the secondary hydroxyl group-containing acrylic resin (A2) is -30°C or higher and 35°C or lower.

[0293] [6] The clear coating composition according to any one of [1] to [5], wherein the organic solvent (C) further contains a ketone compound.

[0294] [7] The clear coating composition according to any one of [1] to [6], wherein the mass ratio (A1) / (A2) of the content of the aforementioned primary hydroxyl group-containing acrylic resin (A1) to the content of the aforementioned secondary hydroxyl group-containing acrylic resin (A2) is 1 / 99 to 80 / 20.

[0295] [8] The clear coating composition according to any one of [1] to [7], wherein the alcohol solvent is at least one selected from a linear primary alcohol having 3 to 5 carbon atoms and a branched primary alcohol having 3 to 5 carbon atoms.

[0296] [9] The clear coating composition according to any one of [1] to [8], wherein the weight average molecular weight of the primary hydroxyl group-containing acrylic resin (A1) is 3,000 or more and 6,000 or less.

[0297]

[10] The clear coating composition according to any one of [1] to [9], wherein the organic solvent (C) further comprises an organic solvent, which is at least one organic solvent selected from monocarboxylic acid esters, dibasic ester compounds, cellosolves, and carbitol, and has a boiling point of 200° C. or higher.

[0298]

[11] A method for producing a coated article, comprising:

[0299] A step of applying a base coating composition to an object to be coated to form an uncured base coating film;

[0300] A step of applying a clear coating composition to the uncured base coating film to form an uncured clear coating film; and

[0301] a step of simultaneously curing the uncured base coating film and the uncured clear coating film;

[0302] The clear coating composition comprises a hydroxyl-containing acrylic resin (A), a polyisocyanate compound (B) and an organic solvent (C).

[0303] The aforementioned hydroxyl-containing acrylic resin (A) comprises a primary hydroxyl-containing acrylic resin (A1) and a secondary hydroxyl-containing acrylic resin (A2).

[0304] The weight average molecular weight of the acrylic resin (A1) containing a primary hydroxyl group is 6,000 or less,

[0305] The weight average molecular weight of the acrylic resin (A2) containing a secondary hydroxyl group is 6,000 or more,

[0306] The organic solvent (C) comprises at least one alcohol solvent selected from the group consisting of a linear primary alcohol having 1 to 8 carbon atoms, a branched primary alcohol having 3 to 8 carbon atoms, a linear secondary alcohol having 1 to 8 carbon atoms, and a branched secondary alcohol having 3 to 8 carbon atoms,

[0307] The solid content concentration during coating is 55% by mass or more.

[0308] Industrial Applicability

[0309] The clear coating composition of the present invention is a clear coating composition that can obtain a coating film having excellent color reversion resistance and has excellent coating workability despite having a high solid content. Therefore, it is suitable for forming various clear coating films, especially clear coating films for automobiles.

[0310] This application claims priority based on Japanese Patent Application No. 2022-206529 filed in Japan on December 23, 2022, the entire contents of which are incorporated herein by reference.

Claims

1. A clear coating composition comprising a hydroxyl-containing acrylic resin (A), a polyisocyanate compound (B) and an organic solvent (C), The hydroxyl-containing acrylic resin (A) comprises a primary hydroxyl-containing acrylic resin (A1) and a secondary hydroxyl-containing acrylic resin (A2), The weight average molecular weight of the acrylic resin (A1) containing primary hydroxyl groups is 6,000 or less, The weight average molecular weight of the acrylic resin (A2) containing secondary hydroxyl groups is 6,000 or more, The organic solvent (C) comprises at least one alcohol solvent selected from the group consisting of a linear primary alcohol having 1 to 8 carbon atoms, a branched primary alcohol having 3 to 8 carbon atoms, a linear secondary alcohol having 1 to 8 carbon atoms, and a branched secondary alcohol having 3 to 8 carbon atoms, a ketone compound, and an organic solvent having a boiling point of 200° C. or higher. The solid content concentration during coating is 55% by mass or more.

2. The clear coating composition according to claim 1, wherein The acid value of the primary hydroxyl group-containing acrylic resin (A1) is 0 mgKOH / g or more and 40 mgKOH / g or less.

3. The clear coating composition according to claim 1 or 2, wherein: The acid value of the secondary hydroxyl group-containing acrylic resin (A2) is 0 mgKOH / g or more and 40 mgKOH / g or less.

4. The clear coating composition according to any one of claims 1 to 3, wherein The glass transition temperature Tg(A1) of the primary hydroxyl group-containing acrylic resin (A1) is -20°C or higher and 60°C or lower.

5. The clear coating composition according to any one of claims 1 to 4, wherein The glass transition temperature Tg(A2) of the acrylic resin (A2) containing a secondary hydroxyl group is -30°C or higher and 35°C or lower.

6. The clear coating composition according to any one of claims 1 to 5, wherein The mass ratio (A1) / (A2) of the content of the acrylic resin (A1) containing a primary hydroxyl group to the content of the acrylic resin (A2) containing a secondary hydroxyl group is 1 / 99 to 80 / 20.

7. The clear coating composition according to any one of claims 1 to 6, wherein The alcohol solvent includes at least one selected from the group consisting of a linear primary alcohol having 3 to 5 carbon atoms and a branched primary alcohol having 3 to 5 carbon atoms.

8. The clear coating composition according to any one of claims 1 to 7, wherein The weight average molecular weight of the primary hydroxyl group-containing acrylic resin (A1) is 3,000 or more and 6,000 or less.

9. The clear coating composition according to any one of claims 1 to 8, wherein The organic solvent (C) further contains at least one selected from the group consisting of monocarboxylic acid esters, dibasic ester compounds, cellosolves, and carbitol having a boiling point of 200° C. or higher.

10. A method for producing a coated article, comprising: A step of applying a base coating composition to an object to be coated to form an uncured base coating film; A step of applying a clear coating composition to the uncured base coating film to form an uncured clear coating film; and a step of simultaneously curing the uncured base coating film and the uncured clear coating film, The clear coating composition comprises a hydroxyl-containing acrylic resin (A), a polyisocyanate compound (B) and an organic solvent (C), The hydroxyl-containing acrylic resin (A) comprises a primary hydroxyl-containing acrylic resin (A1) and a secondary hydroxyl-containing acrylic resin (A2), The weight average molecular weight (Mw) of the acrylic resin (A1) containing primary hydroxyl groups is 6,000 or less, The weight average molecular weight (Mw) of the acrylic resin (A2) containing secondary hydroxyl groups is 6,000 or more, The organic solvent (C) comprises at least one alcohol solvent selected from the group consisting of a linear primary alcohol having 1 to 6 carbon atoms, a branched primary alcohol having 3 to 8 carbon atoms, a linear secondary alcohol having 1 to 6 carbon atoms, and a branched secondary alcohol having 3 to 8 carbon atoms, a ketone compound, and an organic solvent having a boiling point of 200° C. or higher. The solid content concentration during coating is 55% by mass or more.

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