Intermediate coating composition, articles using the same, and methods for manufacturing the articles.

Abstract

A mid-coat coating composition is provided, which can form a mid-coat film exhibiting high adhesion to each layer of a multilayer coating film, and can also form a multilayer coating film exhibiting high adhesion to the coated object, and can form a multilayer coating film with excellent film appearance. The present invention provides a mid-coat coating composition comprising a film-forming resin (A), a film-forming resin (B), and a film-forming resin (C), wherein the film-forming resin (B) and the film-forming resin (C) are acrylic resins, and the glass transition temperatures Tg(A), Tg(B), and Tg(C) exhibit a relationship of Tg(A) < Tg(B) < Tg(C). The glass transition temperature Tg(I) of the mid-coat coating composition is 25°C or higher and 60°C or lower, and under specific conditions comprises film-forming resins (A), (B), and (C) relative to 100 parts by weight of the resin solids component of the mid-coat coating composition.

Description

Technical Field

[0001] This invention relates to intermediate coating compositions, articles using the same, and methods for manufacturing articles. Background Technology

[0002] Multilayer coatings, consisting of multiple coatings with different functions applied to a substrate, are used in various fields. For example, multilayer coatings are sometimes applied to components used for vehicle exterior trim.

[0003] Japanese Patent Application Publication No. 2018-8205 (Patent Document 1) discloses a multilayer coating film obtained by forming an uncured coating film of a primer coating composition on a substrate (object to be coated), applying a topcoat coating composition on the uncured coating film, and using a wet-on-wet coating method. The primer coating composition contains epoxy resin (a1), and the topcoat coating composition (B) is a composition containing acrylic resin (b1) and an active methylene-terminated polyisocyanate compound (b2). The coating composition contains acrylic resin (b1) at a ratio of 60 to 80 parts by mass and active methylene-terminated polyisocyanate compound (b2) at a ratio of 20 to 40 parts by mass, based on a total solid content of 100 parts by mass of acrylic resin (b1) and active methylene-terminated polyisocyanate compound (b2).

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent document 1: Japanese Patent Application Publication No. 2018-8205. Summary of the Invention

[0007] The problem that the invention aims to solve

[0008] Multilayer coatings need to meet performance requirements appropriate to their intended use. For example, multilayer coatings used in vehicle applications also require various physical properties.

[0009] Furthermore, in order to improve the function and appearance of multilayer coatings, coatings that function as transparent coatings have also been studied. For example, a multilayer coating having a base coat disposed on the substrate, a middle coat disposed on the base coat, and a top coat disposed on the middle coat has been studied.

[0010] On the other hand, Patent Document 1 discloses a multilayer coating for vehicle applications, having two coating layers. Compared to the two-layer structure of the multilayer coating shown in Patent Document 1, a multilayer coating with at least three coating layers, having a further layer that functions as a transparent coating, has an increased number of coating layers. Therefore, the number of interlayer interfaces also increases, requiring more effective prevention of peeling between coating layers (coating interfaces).

[0011] Therefore, in order to prevent peeling at the coating interface in a multilayer coating with at least three layers, it is necessary to improve the adhesion between the coatings and also require that the multilayer coating has high adhesion to the coated object.

[0012] This disclosure addresses the aforementioned prior art problems and aims to provide a mid-coat coating composition that forms a mid-coat layer in a multilayer coating comprising a topcoat, a mid-coat, and a basecoat on a substrate, thereby improving the adhesion between the individual coatings constituting the multilayer coating and the adhesion between the multilayer coating and the substrate. Furthermore, it provides vehicle exterior parts using this mid-coat coating composition and a method for manufacturing the same.

[0013] Methods for solving problems

[0014] To address the aforementioned issues, the present invention provides the following solution.

[0015] [1] A mid-coat coating composition, wherein the mid-coat coating is formed in a multilayer coating having a base coat film disposed on a substrate, a mid-coat film disposed on the base coat film, and a top coat film disposed on the mid-coat film.

[0016] The above-mentioned intermediate coating composition comprises a film-forming resin (A), a film-forming resin (B), and a film-forming resin (C).

[0017] The coating film forming resin (B) and the coating film forming resin (C) mentioned above are acrylic resins.

[0018] The glass transition temperature Tg(A) of the coating forming resin (A), the glass transition temperature Tg(B) of the coating forming resin (B), and the glass transition temperature Tg(C) of the coating forming resin (C) satisfy the relationship Tg(A) < Tg(B) < Tg(C).

[0019] The glass transition temperature (Tg(I)) of the mixture of film-forming resin (A), film-forming resin (B) and film-forming resin (C) contained in the above-mentioned intermediate coating composition is 25°C or higher and 60°C or lower.

[0020] Of the total 100% by mass of the above-mentioned film-forming resin (A), the above-mentioned film-forming resin (B), and the above-mentioned film-forming resin (C),

[0021] The coating-forming resin (A) mentioned above is 20% by mass or more and 40% by mass or less.

[0022] The coating-forming resin (B) is 20% by mass or more and 75% by mass or less, and

[0023] The coating-forming resin (C) is 5 parts by mass or more and 45% by mass or less.

[0024] [2][1] The intermediate coating composition, wherein the weight average molecular weight of the film-forming resin (A) is 9000 or more and 90000 or less, the hydroxyl value is 50 mg KOH / g or more and 150 mg KOH / g or less, and the glass transition temperature Tg (A) is -25°C or more and 5°C or less.

[0025] The intermediate coating composition described in [3][1] or [2], wherein the weight average molecular weight of the coating film forming resin (B) is 5,000 or more and 30,000 or less, the hydroxyl value is 20 mg KOH / g or more and 100 mg KOH / g or less, and the glass transition temperature Tg (B) is 20°C or more and 80°C or less.

[0026] The intermediate coating composition described in any one of [4][1] to [3], wherein the weight average molecular weight of the film-forming resin (C) is 5,000 or more and 60,000 or less, the hydroxyl value is 0 mg KOH / g or more and 35 mg KOH / g or less, and the glass transition temperature Tg (C) is 40°C or more and 100°C or less.

[0027] The intermediate coating composition described in any one of [5][1] to [4], wherein the film-forming resin (B) comprises a polymer of monomers, said monomers comprising at least one selected from (meth)acrylic acid, hydroxyethyl (meth)acrylate, methyl (meth)acrylate, ethyl (meth)acrylate and butyl (meth)acrylate.

[0028] The intermediate coating composition described in any one of [6][1] to [5], wherein the film-forming resin (C) comprises a polymer of monomers, said monomers comprising at least one selected from (meth)acrylic acid, hydroxyethyl (meth)acrylate, methyl (meth)acrylate, ethyl (meth)acrylate and butyl (meth)acrylate.

[0029] The intermediate coating composition described in any one of [7][1] to [6] is used for coating a substrate containing a resin component.

[0030] [8][7] The intermediate coating composition is used for coating a substrate containing a polyolefin resin.

[0031] The intermediate coating composition described in any one of [9][1] to [8] is used for coating exterior parts of vehicles.

[0032]

[10] [9] The intermediate coating composition is used for coating exterior vehicle components containing resin components.

[0033]

[11] An article comprising a coated object and a multilayer coating having a base coat disposed on the coated object, a mid-coat coat disposed on the base coat, and a top coat coat disposed on the mid-coat.

[0034] The above-mentioned intermediate coating film is formed from the intermediate coating paint composition described in any one of [1] to [6].

[0035] The thickness of the aforementioned base coating film is 3 μm or more and 15 μm or less.

[0036] The thickness of the aforementioned intermediate coating layer is 10 μm or more and 30 μm or less.

[0037] The thickness of the above-mentioned topcoat layer is 20 μm or more and 40 μm or less.

[0038]

[12]

[11] The article, wherein the coated object comprises a resin component.

[0039]

[13]

[12] The article wherein the resin component comprises a polyolefin resin.

[0040] The articles described in

[14]

[12] or

[13] , wherein,

[0041] The object to be coated is the resin component containing polyolefin resin, and the peel strength T(P) [N / m] of the base coating film relative to the object to be coated and the peel strength T(L) [N / m] of the multilayer coating film relative to the object to be coated satisfy the relationship 0.49 < (T(L) - T(P)) < 4.9.

[0042] The article described in any one of

[15]

[11] to

[14] , wherein the coated object is an exterior component of a vehicle.

[0043]

[16]

[15] The article, wherein the coated object comprises a resin component.

[0044]

[17] A method for manufacturing an article comprising a coated object and a multilayer coating film, wherein the multilayer coating film has a base coat disposed on the coated object, an intermediate coat disposed on the base coat, and a top coat disposed on the intermediate coat.

[0045] The method for manufacturing the article includes the following steps:

[0046] The process of applying a primer coating composition to the above-mentioned object to form an uncured primer coating film;

[0047] The process of applying the intermediate coating composition described in any one of [1] to [7] onto the uncured base coating film to form an uncured intermediate coating film;

[0048] The process of applying a topcoat coating composition onto the aforementioned uncured intermediate coating film to form an uncured topcoat film; and

[0049] The process of simultaneously sintering and curing the uncured base coat, the uncured intermediate coat, and the uncured top coat at a temperature of 60°C or higher and 100°C or lower.

[0050]

[18] A method for manufacturing an article comprising a coated object and a multilayer coating film, wherein the multilayer coating film has a base coat disposed on the coated object, an intermediate coat disposed on the base coat, and a top coat disposed on the intermediate coat.

[0051] The method for manufacturing the article includes the following steps:

[0052] The process of applying a primer coating composition to the above-mentioned object to form an uncured primer coating film, and sintering and curing the uncured primer coating film at a temperature of 60°C or higher and 100°C or lower to form a primer coating film.

[0053] The process of applying the intermediate coating composition described in any one of [1] to [7] onto the above-mentioned base coating film to form an uncured intermediate coating film, and sintering and curing the uncured intermediate coating film at a temperature of 60°C or higher and 100°C or lower to form an intermediate coating film.

[0054] The process of applying a topcoat coating composition onto the above intermediate coating film to form an uncured topcoat film, and then sintering and curing the uncured topcoat film at a temperature of 60°C or higher and 100°C or lower to form a topcoat film.

[0055] The method of manufacturing the article as described in

[19]

[17] or

[18] , wherein the coated object comprises a resin component.

[0056]

[20]

[19] The method of manufacturing the article, wherein the resin component comprises a polyolefin resin.

[0057] A method for manufacturing an article as described in any of

[21]

[17] to

[20] , wherein the object to be coated is an exterior component for a vehicle.

[0058] Invention Effects

[0059] The intermediate coating composition disclosed herein can form an intermediate coating in a multilayer coating film comprising a topcoat film, an intermediate coating film, and a basecoat film on a substrate, thereby improving the adhesion between the individual coating films constituting the multilayer coating film and the adhesion between the multilayer coating film and the substrate. Attached Figure Description

[0060] [ Figure 1 [ ] is a schematic diagram showing the peel strength test. Detailed Implementation

[0061] The process of completing this invention will be described. The inventors conducted various studies to solve the aforementioned problems.

[0062] For example, there is a growing demand for lighter exterior parts for vehicles. Furthermore, there is an increasing demand for highly customizable exterior parts with complex shapes. Based on these considerations, in recent years, research has been conducted on lightweight and easily moldable resin components for such vehicle exterior parts.

[0063] On the other hand, when using a substrate containing resin components as the coating, it is necessary to set the sintering temperature of the multilayer coating within a range that will not adversely affect the resin components used as the coating. For example, when the coating is a substrate containing resin components, it is preferable to set the sintering temperature of the multilayer coating lower than that of a component made only of metal. However, if the sintering temperature of the multilayer coating is set too low, the formation (curing) of the multilayer coating becomes insufficient, and sometimes the adhesion between the individual coatings constituting the multiple coatings and the adhesion between the multilayer coating and the coating (hereinafter, these are sometimes collectively referred to as "adhesion") is poor.

[0064] From this perspective, the inventors, aiming to form a multilayer coating film with good adhesion even in cases where the coated object contains resin, focused on a mid-coat coating composition that forms a mid-coat film for a multilayer coating film having a base coat, a mid-coat, and a top coat, and thus completed the present invention.

[0065] The intermediate coating composition disclosed herein is an intermediate coating composition in which an intermediate coating film is formed in a multilayer coating film having a base coating film disposed on a substrate, an intermediate coating film disposed on the base coating film, and a top coating film disposed on the intermediate coating film.

[0066] The intermediate coating composition comprises a film-forming resin (A), a film-forming resin (B), and a film-forming resin (C).

[0067] The film-forming resin (B) and the film-forming resin (C) are acrylic resins.

[0068] The glass transition temperatures Tg(A) of the film-forming resin (A), Tg(B) of the film-forming resin (B), and Tg(C) of the film-forming resin (C) satisfy the relationship Tg(A) < Tg(B) < Tg(C).

[0069] The glass transition temperature (Tg(I)) of the intermediate coating composition is above 25°C and below 60°C.

[0070] In a total of 100% by mass of film-forming resin (A), film-forming resin (B), and film-forming resin (C),

[0071] The coating-forming resin (A) is 20% by mass or more and 40% by mass or less.

[0072] The coating-forming resin (B) is 20% by mass or more and 75% by mass or less, and

[0073] The coating-forming resin (C) is 5% by mass or more and 45% by mass or less.

[0074] With the above-described configuration, the intermediate coating composition disclosed herein, regardless of the type of topcoat or basecoat, can form an intermediate coating that improves the adhesion between the individual coatings constituting multiple coatings and the adhesion between the multilayer coating and the substrate. Furthermore, the multilayer coating obtained using the intermediate coating composition disclosed herein exhibits superior adhesion to the substrate, even in quality evaluations such as high-temperature water resistance tests for exterior applications, compared to multilayer coatings using conventional intermediate coatings.

[0075] In addition, if it is the intermediate coating composition involved in this disclosure, a multilayer coating film with good conformability can be obtained, so it can be used for highly designable parts with complex shapes, and a multilayer coating film with good appearance can be obtained.

[0076] Furthermore, if it is the intermediate coating composition disclosed herein, even in the case where the substrate is a resin, a multilayer coating film with good adhesion can be formed without compromising the properties of the substrate. In addition, compared with the case where the substrate is a metal, the sintering temperature can be significantly reduced.

[0077] The intermediate coating compositions disclosed herein will now be described in more detail.

[0078] (Intermediate coating composition, intermediate coating film)

[0079] The intermediate coating composition disclosed herein is a coating composition in which an intermediate coating film is formed in a multilayer coating having a base coating film disposed on a substrate, an intermediate coating film disposed on the base coating film, and a top coating film disposed on the intermediate coating film, and the intermediate coating film mainly represents a base layer for adjusting the hue.

[0080] The intermediate coating composition disclosed herein comprises a film-forming resin (A), a film-forming resin (B), and a film-forming resin (C).

[0081] The film-forming resin (B) and the film-forming resin (C) are acrylic resins.

[0082] The glass transition temperatures Tg(A) of the film-forming resin (A), Tg(B) of the film-forming resin (B), and Tg(C) of the film-forming resin (C) satisfy the relationship Tg(A) < Tg(B) < Tg(C).

[0083] The glass transition temperature (Tg(I)) of the intermediate coating composition is above 25°C and below 60°C.

[0084] By ensuring that the film-forming resin (A), film-forming resin (B), and film-forming resin (C) contained in the intermediate coating composition of this disclosure, as well as the glass transition temperature of the intermediate coating composition, satisfy the above-mentioned relationship, an intermediate coating film exhibiting high adhesion to each film of a multilayer coating can be formed. Furthermore, the intermediate coating composition of this disclosure can form a multilayer coating exhibiting high adhesion to the coated object, and can also form a multilayer coating with an excellent coating appearance.

[0085] In one embodiment, the object to be coated comprises a resin component. The object to be coated may, for example, be a vehicle exterior component that may include a resin portion. The object to be coated may, for example, be a vehicle exterior component made of a resin component. In such an embodiment, the primer coating film disposed on the object needs to exhibit high adhesion to the resin component. On the other hand, if it is the intermediate coating composition according to this disclosure, in this embodiment, an intermediate coating film exhibiting high adhesion to the primer coating film can be formed, and high adhesion can also be exhibited to the topcoat coating film disposed on the intermediate coating film.

[0086] Therefore, if it is the intermediate coating composition involved in this disclosure, when the coated object contains a resin component, for example, in the case of a resin component for vehicle exterior, the adhesion between the coated object and the multilayer coating can be maintained to a high degree, and the adhesion between the coatings in the multilayer coating (the adhesion between the interfaces of each coating) can be improved.

[0087] Furthermore, the multilayer coating obtained using the intermediate coating composition disclosed herein can achieve such high adhesion and excellent coating conformability even for resin parts used in vehicle exteriors, and therefore can also be used for parts with high design complexity.

[0088] In one embodiment, the glass transition temperature Tg(I) of the intermediate coating composition may be, for example, above 30°C and below 60°C, above 32°C and below 58°C, or, for example, above 35°C and below 58°C.

[0089] By setting the glass transition temperature of the intermediate coating composition to the conditions described above, the intermediate coating composition disclosed herein can more easily form an intermediate coating film that exhibits high adhesion to each layer of a multilayer coating film.

[0090] Furthermore, multilayer coatings, which are less prone to peeling between individual layers, also exhibit higher adhesion to the substrate more easily. In addition, it is easier to form multilayer coatings with excellent appearance.

[0091] The glass transition temperatures Tg(A) to Tg(C) of the film-forming resins (A) to (C) and the glass transition temperature Tg(I) of the intermediate coating composition can be determined by detecting the thermal changes associated with the glass transition of the resin using a differential scanning calorimeter (DSC). An example of a DSC is the "X-DSC7000" manufactured by SII NanoTechnology Co., Ltd. The glass transition temperature can be obtained, for example, from the baseline and the tangent at the inflection point of the DSC curve obtained using the aforementioned DSC.

[0092] The glass transition temperature Tg(A) of the film-forming resin (A), the glass transition temperature Tg(B) of the film-forming resin (B), and the glass transition temperature Tg(C) of the film-forming resin (C) of the intermediate coating composition disclosed herein satisfy the relationship Tg(A) < Tg(B) < Tg(C).

[0093] Furthermore, the glass transition temperature (Tg(I)) of the mixture of film-forming resin (A), film-forming resin (B), and film-forming resin (C) contained in the intermediate coating composition is 25°C or higher and 60°C or lower.

[0094] Furthermore, in a total of 100% by mass of the film-forming resin (A), the film-forming resin (B), and the film-forming resin (C),

[0095] It contains 20% to 40% by mass of film-forming resin (A).

[0096] It contains 20 parts by weight or more and 75% by weight of film-forming resin (B).

[0097] It contains a film-forming resin (C) in amounts of 5 parts by weight or more and 45% by weight or less.

[0098] By including film-forming resins (A), (B), and (C) in such proportions, a mid-coat layer film exhibiting high adhesion to each layer of a multilayer coating can be formed, and a multilayer coating film that is difficult to peel off at the coating interface can be formed. Furthermore, the mid-coat coating composition according to this disclosure can form a multilayer coating film exhibiting high adhesion to the coated object, and can form a multilayer coating film with an excellent coating appearance.

[0099] In one implementation scheme, preferably:

[0100] The intermediate coating composition disclosed herein comprises, in a total of 100% by mass of film-forming resin (A), film-forming resin (B), and film-forming resin (C),

[0101] It contains 20% to 40% by mass of film-forming resin (A).

[0102] It contains 20% or more and 75% or less of film-forming resin (B).

[0103] It contains film-forming resin (C) in an amount of 5% to 45% by mass or more.

[0104] Furthermore, the contents of film-forming resin (A), film-forming resin (B), and film-forming resin (C) satisfy the relationship that the contents of film-forming resin (A) < the contents of film-forming resin (C) and / or the contents of film-forming resin (B) < the contents of film-forming resin (C).

[0105] By having film-forming resins (A), (B), and (C) in such a relationship, it is easier to form a mid-coat layer that exhibits high adhesion to each layer of a multilayer coating, and it is also easier to form a multilayer coating that is difficult to peel off at the coating interface. Furthermore, the mid-coat coating composition according to this disclosure can more easily form a multilayer coating that exhibits high adhesion to the substrate, and it is also easier to form a multilayer coating with an excellent coating appearance.

[0106] [Coating-forming resin (A)]

[0107] In one embodiment, the coating-forming resin (A) preferably has a weight-average molecular weight of 9,000 or more and 90,000 or less, for example, 9,000 or more and 80,000 or less.

[0108] The weight-average molecular weight can be calculated using polystyrene as a standard, based on the results of gel permeation chromatography (GPC).

[0109] In one embodiment, the hydroxyl value of the coating-forming resin (A) is 50 mg KOH / g or more and 150 mg KOH / g or less, for example, it can be 70 mg KOH / g or more and 130 mg KOH / g or less, for example, it can be 70 mg KOH / g or more and 120 mg KOH / g or less. It should be noted that the above hydroxyl value is a value converted in terms of solid content and is a value obtained by determination according to the method of JIS K 0070.

[0110] In one embodiment, the glass transition temperature Tg(A) of the coating-forming resin (A) is above -25°C and below 5°C, for example, it may be above -20°C and below 5°C. The method for determining the glass transition temperature is as described above.

[0111] While it should not be limited to a specific theory for explanation, it is believed that by setting the glass transition temperature Tg(A) of the coating film forming resin (A) within the above range, cohesive failure of the coating film can be suppressed, and excellent color design can be achieved.

[0112] In one embodiment, the coating forming resin (A) preferably has a weight-average molecular weight of 9,000 or more and 90,000 or less, a hydroxyl value of 50 mg KOH / g or more and 150 mg KOH / g or less, and a glass transition temperature Tg (A) of -25°C or more and 5°C or less.

[0113] By giving the film-forming resin (A) such properties, the intermediate coating composition of this disclosure can more easily form an intermediate coating film that exhibits high adhesion to each layer of a multilayer coating film. Moreover, the intermediate coating composition of this disclosure can more easily form a multilayer coating film that exhibits high adhesion to the coated object, and can more easily form a multilayer coating film with an excellent coating appearance.

[0114] In one embodiment, the weight-average molecular weight, hydroxyl value, and glass transition temperature Tg(A) of the coating-forming resin (A) may be appropriately selected within the scope of this disclosure.

[0115] In one embodiment, the film-forming resin (A) comprises at least one selected from acrylic resins, polyester resins, alkyd resins, polyether resins, polyolefin resins, urethane resins, epoxy resins, and melamine resins. For example, the film-forming resin (A) may comprise at least one selected from acrylic resins, urethane resins, and polyester resins.

[0116] In one embodiment, the film-forming resin (A) comprises an acrylic resin. By including the acrylic resin, the film-forming resin (A), film-forming resin (B), and film-forming resin (C) can be mixed more uniformly, further improving the coating strength. Additionally, by including the acrylic resin, it is easier to form a multilayer coating that exhibits high adhesion to the substrate, and it is also easier to form a multilayer coating with an excellent coating appearance.

[0117] As monomeric components constituting acrylic resins, examples include mixtures of one or more of the following: aromatic vinyl monomers such as styrene, vinyltoluene, 2-methylstyrene, tert-butylstyrene, and chlorostyrene; methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-, iso-, or tert-butyl methacrylate; butyl methacrylate, hexyl methacrylate, 2-ethylhexyl methacrylate, n-octyl methacrylate, decyl methacrylate, and methyl acrylate. Lauryl ester, cyclohexyl acrylate, and other alkyl or cycloalkyl esters of (meth)acrylic acid with 1 to 18 carbon atoms; hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 3-hydroxypropyl acrylate, 4-hydroxybutyl acrylate, and other hydroxyalkyl esters of (meth)acrylic acid with 2 to 8 carbon atoms; N-substituted (meth)acrylamide monomers such as N-hydroxymethyl (meth)acrylamide, N-butoxymethyl (meth)acrylamide, and N-methoxymethyl (meth)acrylamide; (meth)acrylic acid, glycidyl acrylate, etc.

[0118] In this specification, "(meth)acrylic acid" refers to both acrylic acid and methacrylic acid.

[0119] The aforementioned polymers can be manufactured by polymerizing the monomers using conventional methods such as solution polymerization and bulk polymerization. For example, the polymerization of the monomers can be carried out via free radical polymerization using a polymerization initiator. There are no particular limitations on the polymerization initiator; for example, persulfates such as potassium persulfate and ammonium persulfate, and azo compounds such as azobis(cyanopentanoic acid) and azobis(isobutyronitrile) can be used.

[0120] Acrylic resins may be polymers comprising monomers, said monomers comprising at least one selected from (meth)acrylic acid, hydroxyethyl (meth)acrylate, methyl (meth)acrylate, ethyl (meth)acrylate, and butyl (meth)acrylate.

[0121] In one embodiment, the film-forming resin (A) comprises both acrylic resin and urethane resin. In this case, the amount of acrylic resin in the film-forming resin (A) can be in the range of 25% to 99% by mass, and the amount of urethane resin can be in the range of 1% to 75% by mass. It should be noted that when using multiple acrylic resins, the sum of the mass fractions of each acrylic resin can be appropriately adjusted to include them within the above-mentioned range; similarly, when using multiple urethane resins, the sum of the mass fractions of each urethane resin can be appropriately adjusted to include them within the above-mentioned range.

[0122] [Coating-forming resin (B)]

[0123] In one embodiment, the weight-average molecular weight of the coating-forming resin (B) is 5,000 or more and 30,000 or less, for example, it may be 7,000 or more and 25,000 or less.

[0124] In one embodiment, the hydroxyl value of the coating forming resin (B) is 20 mg KOH / g or more and 100 mg KOH / g or less, for example, it can be 30 mg KOH / g or more and 100 mg KOH / g or less.

[0125] In one embodiment, the glass transition temperature Tg(B) of the coating forming resin (B) is above 20°C and below 80°C, for example, it can be above 30°C and below 80°C, for example, it can be above 30°C and below 75°C.

[0126] While it should not be limited to a specific theory for explanation, excellent color design can be achieved by setting the glass transition temperature Tg(B) of the coating film forming resin (B) within the above range, and the coating film strength can be further improved.

[0127] In one embodiment, the weight-average molecular weight of the coating-forming resin (B) may be 5,000 or more and 30,000 or less, the hydroxyl value may be 20 mg KOH / g or more and 100 mg KOH / g or less, and the glass transition temperature Tg (B) may be 20°C or more and 80°C or less.

[0128] By giving the film-forming resin (B) such properties, the intermediate coating composition of this disclosure can more easily form an intermediate coating film that exhibits high adhesion to each layer of a multilayer coating film. Moreover, the intermediate coating composition of this disclosure can more easily form a multilayer coating film that exhibits high adhesion to the coated object, and can more easily form a multilayer coating film with an excellent coating appearance.

[0129] In one embodiment, the weight-average molecular weight, hydroxyl value, and glass transition temperature Tg(B) of the coating-forming resin (B) may be appropriately selected within the scope of this disclosure.

[0130] The acid value of the coating-forming resin (B) can be, for example, above 2.7 mg KOH / g and below 4.7 mg KOH / g. It should be noted that the above acid values ​​are expressed in terms of solid content and are values ​​obtained by measurement according to JIS K 0070.

[0131] In addition, the solubility parameter Sp value of the coating-forming resin (B) can be, for example, 9.0 or higher and 10.0 or lower. The Sp value can be determined by measurement or calculation using known methods.

[0132] The film-forming resin (B) is an acrylic resin. Because the film-forming resin (B) is an acrylic resin, it has the following advantages: the intermediate coating film has high film strength, and it provides high adhesion between the layers of the multilayer coating.

[0133] As monomeric components constituting the acrylic resin as the film-forming resin (B), examples include mixtures of one or more of the following: aromatic vinyl monomers such as styrene, vinyltoluene, 2-methylstyrene, tert-butylstyrene, and chlorostyrene; methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-, iso-, or tert-butyl methacrylate; butyl methacrylate, hexyl methacrylate, 2-ethylhexyl methacrylate, n-octyl methacrylate, decyl methacrylate, etc. Alkyl or cycloalkyl esters of (meth)acrylic acid with carbon numbers from 1 to 18, such as lauryl methacrylate and cyclohexyl methacrylate; hydroxyalkyl esters of (meth)acrylic acid with carbon numbers from 2 to 8, such as hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, 3-hydroxypropyl methacrylate, and 4-hydroxybutyl methacrylate; N-substituted (meth)acrylamide monomers such as N-hydroxymethyl (meth)acrylamide, N-butoxymethyl (meth)acrylamide, and N-methoxymethyl (meth)acrylamide; and (meth)acrylic acid and glycidyl methacrylate.

[0134] The aforementioned polymers can be manufactured by polymerizing the monomers using conventional methods such as solution polymerization and bulk polymerization. For example, the polymerization of the monomers can be carried out via free radical polymerization using a polymerization initiator. There are no particular limitations on the polymerization initiator; for example, persulfates such as potassium persulfate and ammonium persulfate, and azo compounds such as azobis(cyanopentanoic acid) and azobis(isobutyronitrile) can be used.

[0135] As the coating forming resin (B), an acrylic resin may be, for example, a polymer of monomers, said monomers comprising at least one selected from (meth)acrylic acid, hydroxyethyl (meth)acrylate, methyl (meth)acrylate, ethyl (meth)acrylate and butyl (meth)acrylate.

[0136] In one embodiment, the preparation of the acrylic resin in the coating forming resin (B) is preferably a polymer of a monomer mixture containing hydroxyethyl methacrylate among the various monomers mentioned above.

[0137] By including such an acrylic resin in the film-forming resin (B), the intermediate coating composition of this disclosure can form an intermediate coating film that exhibits high adhesion to each layer of the multilayer coating film involved in this disclosure. Moreover, the intermediate coating composition of this disclosure can form a multilayer coating film that exhibits high adhesion to the coated object and can form a multilayer coating film with excellent coating appearance.

[0138] For example, the polymerization of the above monomers can be carried out via free radical polymerization using a polymerization initiator. There are no particular limitations on the polymerization initiator; for example, persulfates such as potassium persulfate and ammonium persulfate, and azo compounds such as azobis(cyanopentanoic acid) and azobisisobutyronitrile can be used.

[0139] [Coating-forming resin (C)]

[0140] In one embodiment, the weight-average molecular weight of the coating-forming resin (C) may be 5,000 or more and 60,000 or less, for example, 9,000 or more and 60,000 or less.

[0141] In one embodiment, the hydroxyl value of the coating forming resin (C) is above 0 mg KOH / g and below 35 mg KOH / g, for example, it can be above 0 mg KOH / g and below 20 mg KOH / g.

[0142] In one embodiment, the glass transition temperature Tg(C) of the coating forming resin (C) is above 40°C and below 100°C, for example, it can be above 50°C and below 100°C.

[0143] While it should not be limited to a specific theory for explanation, by setting the glass transition temperature Tg(C) of the coating film forming resin (C) to within the above range, a mid-coat film with excellent film strength and hardness can be formed.

[0144] In one embodiment, the coating forming resin (C) preferably has a weight-average molecular weight of 5,000 or more and 60,000 or less, a hydroxyl value of 0 mg KOH / g or more and 35 mg KOH / g or less, and a glass transition temperature Tg (C) of 40°C or more and 100°C or less.

[0145] By giving the film-forming resin (C) such properties, the intermediate coating composition of this disclosure can more easily form an intermediate coating film that exhibits high adhesion to each layer of a multilayer coating film. Moreover, the intermediate coating composition of this disclosure can more easily form a multilayer coating film that exhibits high adhesion to the coated object, and can more easily form a multilayer coating film with an excellent coating appearance.

[0146] In one embodiment, the weight-average molecular weight, hydroxyl value, and glass transition temperature Tg (C) of the coating-forming resin (C) may be appropriately selected within the scope of this disclosure.

[0147] Because the coating forming resin (C) is an acrylic resin, the intermediate coating has high coating strength and high adhesion to each layer of the multilayer coating.

[0148] As monomeric components constituting the acrylic resin as the film-forming resin (C), examples include mixtures of one or more of the following: aromatic vinyl monomers such as styrene, vinyltoluene, 2-methylstyrene, tert-butylstyrene, and chlorostyrene; methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-, iso-, or tert-butyl methacrylate; butyl methacrylate, hexyl methacrylate, 2-ethylhexyl methacrylate, n-octyl methacrylate, decyl methacrylate, etc. Alkyl or cycloalkyl esters of (meth)acrylic acid with carbon numbers from 1 to 18, such as lauryl methacrylate and cyclohexyl methacrylate; hydroxyalkyl esters of (meth)acrylic acid with carbon numbers from 2 to 8, such as hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, 3-hydroxypropyl methacrylate, and 4-hydroxybutyl methacrylate; N-substituted (meth)acrylamide monomers such as N-hydroxymethyl (meth)acrylamide, N-butoxymethyl (meth)acrylamide, and N-methoxymethyl (meth)acrylamide; and (meth)acrylic acid and glycidyl methacrylate.

[0149] The aforementioned polymers can be manufactured by polymerizing the monomers using conventional methods such as solution polymerization and bulk polymerization. For example, the polymerization of the monomers can be carried out via free radical polymerization using a polymerization initiator. There are no particular limitations on the polymerization initiator; for example, persulfates such as potassium persulfate and ammonium persulfate, and azo compounds such as azobis(cyanopentanoic acid) and azobis(isobutyronitrile) can be used.

[0150] As the coating forming resin (C), an acrylic resin may be, for example, a polymer of monomers, said monomers comprising at least one selected from (meth)acrylic acid, hydroxyethyl (meth)acrylate, methyl (meth)acrylate, ethyl (meth)acrylate, and butyl (meth)acrylate.

[0151] In one embodiment, the acrylic resin in the coating forming resin (C) is preferably a polymer of a monomer mixture containing ethyl (meth)acrylate among the various monomers described above.

[0152] The film-forming resin (C) comprises such an acrylic resin, for example, a film-forming resin (C) having the above-mentioned properties can be suitably formulated. This provides the advantage that a mid-layer coating film exhibiting high adhesion to each layer of a multilayer coating can be formed.

[0153] [Curing agent]

[0154] In one embodiment, the intermediate coating composition may include a curing agent that appropriately corresponds to the type of curable functional groups possessed by the film-forming resin (A), film-forming resin (B), and / or film-forming resin (C).

[0155] The curing agent can be any known curing agent, such as amino resins, end-capped isocyanate resins, epoxy compounds, aziridine compounds, carbodiimide compounds, etc. Azoline compounds, etc. Considering the various properties and costs of the resulting coating, amino resins and / or end-capped isocyanate resins are typically used.

[0156] There are no particular restrictions on the amino resin in the curing agent; water-soluble melamine resin and / or non-water-soluble melamine resin may be used.

[0157] End-capped isocyanate resins can be formulated by adding end-capping agents with active hydrogen to polyisocyanates such as trimethylene diisocyanate, hexamethylene diisocyanate, phenyl diisocyanate, and isophorone diisocyanate. Such end-capped isocyanate resins are cured by heating to dissociate the end-capping agent, generating isocyanate groups, which then react with functional groups in the resin components.

[0158] For example, relative to a total of 100 parts by weight of film-forming resin (A), film-forming resin (B), film-forming resin (C), and curing agent, the amount of curing agent can be 2 to 50 parts by weight, preferably 3 to 40 parts by weight. By keeping the amount of curing agent within such a range, it is easier to form a mid-coat film with sufficient curability, and it is further possible to prevent the mid-coat film from becoming too hard or brittle.

[0159] [solvent]

[0160] In one embodiment, the intermediate coating composition disclosed herein is a solvent-based coating composition. Examples of organic solvents that can be used in solvent-based coating compositions include: hydrocarbon solvents, ester solvents, ketone solvents, alcohol solvents, ether solvents, and aromatic petroleum solvents.

[0161] The intermediate coating composition disclosed herein is a solvent-based coating composition, thereby allowing the sintering and curing temperature of the multilayer coating film to be within a range of 60°C to 100°C. Therefore, even in embodiments where the coated object is a resin component, a multilayer coating film can be formed without compromising the properties of the resin component.

[0162] [Other Additives]

[0163] As needed, the intermediate coating composition disclosed herein may contain pigments, surface conditioners (defoamers, leveling agents, etc.), pigment dispersants, plasticizers, film-forming aids, ultraviolet absorbers, antioxidants, flame retardants, antistatic agents, antistatic agents, heat stabilizers, light stabilizers, solvents (water, organic solvents), and other additives.

[0164] When a pigment is included in a mid-coat coating composition, the pigment content can be set within a range typically set according to the intended application. For example, the ratio [mass %] (PWC: Pigment Weight Concentration) of the pigment content to the sum of the contents of the coating film-forming resins (A) to (C), the curing agent, and other components that form the coating layer is preferably 0.1 to 50% by mass.

[0165] In one embodiment, the intermediate coating composition disclosed herein may include, in addition to film-forming resins (A), (B), and (C), film-forming resins such as polyester resins, alkyd resins, polyether resins, polyolefin resins, urethane resins, and melamine resins.

[0166] (Primer coating composition, primer coating film)

[0167] The primer coating is applied onto the substrate. The primer coating is formed, for example, from a primer coating composition described below. As described below, the substrate is not particularly limited; for example, it may be a substrate containing a resin component, a substrate containing a metal component, or a substrate containing both a resin component and a metal component.

[0168] The primer coating composition may include anhydride-modified chlorinated polyolefin resin and acrylic-modified alkyd resin. By combining these resins, the primer coating film exhibits better adhesion to resin parts containing polyolefin resins, for example, and is often used effectively as a primer layer for vehicle exterior resin parts containing polyolefin resins, showing superior resistance to high-pressure car washes and superior resistance to ethanol gasoline.

[0169] In one embodiment, the primer coating composition comprises anhydride-modified chlorinated polyolefin and acrylic-modified alkyd resin.

[0170] The mass ratio of anhydride-modified chlorinated polyolefin to acrylic-modified alkyd resin can be 80:20 to 20:80. By including anhydride-modified chlorinated polyolefin and acrylic-modified alkyd resin in this ratio, for example, a base coat film with superior high-pressure car wash resistance can be formed, and, for example, for resin parts containing polyolefin resin, the base coat film can exhibit superior adhesion. Furthermore, such a base coat film and the intermediate coat film formed from the intermediate coat coating composition disclosed herein both exhibit superior adhesion. As a result, it can help improve the adhesion between resin parts containing polyolefin resin and multilayer coatings.

[0171] [Anhydride-modified chlorinated polyolefins]

[0172] For example, the anhydride-modified chlorinated polyolefin can be a propylene-α-olefin copolymer, wherein the propylene content is 50 mol% or more and 99 mol% or less, and it contains at least one α-olefin with 2 or 4 to 6 carbon atoms. Furthermore, the chlorine content can be 15 wt% or more and 24 wt% or less, the anhydride modification amount can be 0.6 wt% or more and 2.0 wt%, and the weight-average molecular weight can be selected from a range of 40,000 or more and 120,000 or less.

[0173] In one embodiment, the copolymerization rate of the α-olefin in the propylene-α-olefin copolymer is in the range of 1 mol% or more and 50 mol% or less, preferably 5 mol% or more and 30 mol% or less. By keeping this copolymerization rate within the above-mentioned range, a base coating composition with better storage stability can be obtained. Moreover, the resulting coating film can exhibit better adhesion to resin parts containing polyolefin resins, for example, it can exhibit better resistance to high-pressure car washes for resin parts for vehicle exteriors containing polyolefin resins.

[0174] The weight-average molecular weight range of the propylene-α-olefin copolymer is, for example, 40,000 or more and 120,000 or less, preferably 50,000 or more and 100,000 or less.

[0175] Chlorination of propylene-α-olefin copolymers can be carried out using conventional techniques. For example, a chloroform solution of a polyolefin can be easily chlorinated by blowing chlorine gas at high temperature. In this disclosure, the chlorination rate is preferably in the range of 15% by mass or more and 24% by mass or less, more preferably 18% by mass or more and 21% by mass or less. By keeping the chlorination rate within the above range, a base coating composition with better storage stability can be obtained. In addition, the resulting coating film can have better resistance to ethanol gasoline.

[0176] Anhydride-modified chlorinated polyolefins can be obtained, for example, by copolymerizing maleic anhydride, itaconic anhydride, or other anhydrides with the aforementioned polyolefins. As a method for this copolymerization, known methods of copolymerizing anhydrides at high temperatures in the presence of a free radical generator can be used. Furthermore, the copolymerization amount of anhydride is preferably 0.6% by mass or more and 2.0% by mass or less, more preferably 1.0% by mass or more and 1.6% by mass or less. By setting the copolymerization amount of anhydride within the above range, the primer coating film can exhibit better resistance to ethanol gasoline. Additionally, a coating film with superior moisture resistance can be formed.

[0177] Thus, both the chlorination process of the polyolefin resin and the anhydride copolymerization process in manufacturing the anhydride-modified chlorinated polyolefin of the present invention are known technologies, and either process can be performed in any order.

[0178] [Acrylic-modified alkyd resin]

[0179] For example, acrylic-modified alkyd resins can be composed of an alkyd resin polymerization part and an acrylic resin polymerization part.

[0180] The preferred oils for alkyd resins are castor oil, soybean oil, dehydrated castor oil, linseed oil, and other oils with an iodine value of 80 or higher. There are no particular limitations on the polyacids; examples include one or more dicarboxylic acids or their anhydrides such as phthalic acid, phthalic anhydride, tetrahydrophthalic acid, and tetrahydrophthalic anhydride. Similarly, there are no particular limitations on the polyols; examples include one or more alcohols with two or more nucleotides such as pentaerythritol, glycerol, and neopentyl glycol.

[0181] Known methods can be used in the manufacture of alkyd resins. For example, under an inert gas atmosphere and at a temperature above 200°C and below 250°C, an alcoholysis reaction is carried out by transesterification of oils and polyols using a lithium hydroxide catalyst. The alcoholysis reaction is then terminated using methanol tolerance, followed by esterification using a polyacid. Polyols can be blended as needed to adjust the OH value of the alkyd resin. In this case, the oil content is set to 35% or more and 70% or less, but preferably 50% or more and 60% or less.

[0182] Acrylic acid modification can be carried out using the alkyd resin described above by known methods. For example, the alkyd resin can be heated to 120°C under an inert gas atmosphere, and a mixed solution of acrylic monomer and peroxide can be added dropwise at a constant rate. After further adding the remaining peroxide, the mixture can be kept at this temperature for a certain period of time, thereby modifying the acrylic resin.

[0183] The glass transition temperature of the acrylic resin polymerization portion is preferably 50°C or higher, more preferably 60°C or higher. If the glass transition temperature is 50°C or higher, the primer coating film can have better resistance to high-pressure car washing.

[0184] Examples of acrylic monomers include acrylate monomers such as methyl acrylate, methyl methacrylate, butyl methacrylate, and 2-hydroxyethyl acrylate, as well as styrene, vinyltoluene, and α-methylstyrene. For example, by using at least one monomer selected from these monomers and polymerizing at a glass transition temperature of 50°C or higher, an acrylic resin polymer can be obtained.

[0185] The mass ratio of the alkyd resin polymerization portion to the acrylic resin polymerization portion can be, for example, 25:75 to 75:25, preferably 40:60 to 60:40. By keeping this mass ratio within the above range, a base coating film with better resistance to ethanol gasoline and superior resistance to high-pressure car washes can be formed.

[0186] Furthermore, the weight-average molecular weight of the acrylic-modified alkyd resin can be, for example, 10,000 or more and 100,000 or less, preferably 15,000 or more and 60,000 or less. By keeping the weight-average molecular weight within this range, the coating strength can be further improved. In addition, by keeping the weight-average molecular weight within the above range, the primer coating can exhibit better resistance to high-pressure car washes, superior resistance to ethanol gasoline, and a better coating appearance.

[0187] Furthermore, by keeping the weight-average molecular weight within the aforementioned range, good compatibility with anhydride-modified chlorinated polyolefins can be maintained, and the coating composition can exhibit better storage stability.

[0188] In addition to anhydride-modified chlorinated polyolefin and acrylic-modified alkyd resin, the primer coating composition may, as needed, contain acrylic resin, polyester resin, epoxy resin, acrylic-modified chlorinated polyolefin resin, cellulose resin, melamine resin, end-capped isocyanate resin, and other resin components.

[0189] In this scheme, relative to a total of 100 parts by mass of anhydride-modified chlorinated polyolefin and acrylic-modified alkyd resin, other resins are blended in amounts exceeding 0 parts by mass and falling below 90 parts by mass. The coating process is centered on aromatic hydrocarbon solvents such as toluene and xylene, and can be achieved using ester solvents such as ethyl acetate and butyl acetate, and ketone solvents such as methyl ethyl ketone and methyl isobutyl ketone. Relative to a total of 100 parts by mass of anhydride-modified chlorinated polyolefin and acrylic-modified alkyd resin, these organic solvents can be blended in amounts exceeding 200 parts by mass and falling below 500 parts by mass.

[0190] In addition, the base coat composition can also be blended with pigments such as titanium dioxide, carbon black, and conductive carbon black, extender pigments such as talc, clay, and barium sulfate, or various organic pigments to improve workability through coloring, or it can be made conductive for electrostatic coating. In such a scheme, relative to a total of 100 parts by weight of anhydride-modified chlorinated polyolefin and acrylic-modified alkyd resin, the above-mentioned pigments can be blended in more than 0 parts by weight and less than 100 parts by weight.

[0191] (Topcoat coating composition, topcoat film)

[0192] In a multilayer coating, the topcoat layer is disposed on top of the intermediate coat layer. The topcoat layer is formed, for example, from the topcoat coating composition described below. Additionally, the topcoat layer can also serve a protective function as a transparent coating.

[0193] The topcoat composition can be solvent-based or water-based. Preferably, the topcoat composition is a two-component (two-liquid) topcoat composition. Examples of two-component topcoat compositions include a two-component topcoat composition comprising a base agent containing a hydroxyl-containing acrylic resin and a polycarbonate diol compound, and a curing agent containing a polyisocyanate compound.

[0194] [Hydroxy-containing acrylic resin]

[0195] In one embodiment, the hydroxyl value of the hydroxyl-containing acrylic resin in the topcoat composition is in the range of 80 mg KOH / g or more and 200 mg KOH / g or less, preferably 90 mg KOH / g or more and 190 mg KOH / g or less, and more preferably 100 mg KOH / g or more and 180 mg KOH / g or less. By making the hydroxyl value of the hydroxyl-containing acrylic resin within the above range, the resulting coating film can have better physical properties.

[0196] In one embodiment, the acid value of the hydroxyl-containing acrylic resin in the topcoat composition is 1 mg KOH / g or more and 20 mg KOH / g or less, preferably 3 mg KOH / g or more and 18 mg KOH / g or less, and more preferably 5 mg KOH / g or more and 10 mg KOH / g or less. By keeping the acid value of the hydroxyl-containing acrylic resin within the above range, the reactivity with the polyisocyanate compound can be controlled within a more appropriate range, and the resulting multilayer coating film can have a superior coating appearance and physical properties.

[0197] In the topcoat coating composition, the hydroxyl-containing acrylic resin is a solution polymer of a monomer mixture containing a hydroxyl-containing alkyl ester monomer of (meth)acrylic acid, and the hydroxyl-containing alkyl ester monomer of (meth)acrylic acid has, for example, 3 or less carbon atoms in the hydroxyl-containing alkyl group.

[0198] By including (meth)acrylic acid hydroxyalkyl ester monomers with 3 or fewer carbon atoms in the monomer mixture, the reactivity with polyisocyanate compounds is adjusted to a more appropriate range, thereby improving the appearance of the resulting multilayer coating.

[0199] Specific examples of monomers containing hydroxyalkyl groups of (meth)acrylic acid with 3 or fewer carbon atoms in the hydroxyalkyl group include: 2-hydroxyethyl (meth)acrylic acid, 2-hydroxypropyl (meth)acrylic acid, 3-hydroxypropyl (meth)acrylic acid, etc.

[0200] Relative to 100 parts by mass of the monomer mixture, the amount of (meth)acrylic acid hydroxyalkyl ester monomers containing 3 or fewer carbon atoms in the hydroxyalkyl group is preferably in the range of 20 parts by mass or more and 60 parts by mass or less, more preferably in the range of 30 parts by mass or more and 50 parts by mass or less.

[0201] As needed, the monomer mixture may contain hydroxyl-containing (meth)acrylic acid monomers other than hydroxyl-containing alkyl (meth)acrylic acid ester monomers with 3 or fewer carbon atoms in the hydroxyl alkyl group. Examples of such monomers include: hydroxyalkyl (meth)acrylic acid esters such as 4-hydroxybutyl (meth)acrylic acid and 2-hydroxybutyl (meth)acrylic acid; Placcel FM-1 (trade name, adduct of 2-hydroxyethyl (meth)acrylic acid and polycaprolactone, manufactured by Daicel Chemical Co., Ltd.); and polyalkylene glycol mono(meth)acrylic acid esters.

[0202] In addition to containing hydroxyalkyl ester monomers of (meth)acrylic acid with 3 or fewer carbon atoms in the hydroxyalkyl group, the monomer mixture preferably also contains other monomers containing olefinic unsaturated groups. There are no particular limitations on other monomers containing olefinic unsaturated groups. Examples include: alkyl methacrylates such as methyl methacrylate, ethyl methacrylate, propyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, 2-ethylhexyl methacrylate, and lauryl methacrylate; monomers containing acid groups such as acrylic acid, methacrylic acid, crotonic acid, isocrotonic acid, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, itaconic acid, maleic anhydride, and fumaric acid; aromatic vinyl monomers such as styrene and vinyltoluene; epoxy monomers such as glycidyl methacrylate; amino monomers such as dimethylaminoethyl methacrylate and diethylaminoethyl methacrylate; acrylamide monomers such as methacrylamide, N-ethyl(meth)acrylamide, N,N-butoxymethyl(meth)acrylamide, and N-methylacrylamide; acrylonitrile, vinyl acetate, acrylic acid, and methacrylic acid. They can be used individually or in combination of two or more.

[0203] Hydroxyl-containing acrylic resins can be prepared by solution polymerization of a monomer mixture. Solution polymerization conditions can be those commonly used in the art.

[0204] The weight-average molecular weight of the hydroxyl-containing acrylic resin is preferably 3,000 or more and 50,000 or less. By keeping the weight-average molecular weight within the above range, it is easier to ensure good workability and curability of the resulting topcoat composition.

[0205] [Polyisocyanate compounds]

[0206] Topcoat coating compositions may contain polyisocyanate compounds. Preferably, the polyisocyanate compounds involved in the topcoat coating composition are included in the curing agent in two-component topcoat coating compositions. There are no particular limitations on the polyisocyanate compounds. Representative polyisocyanate compounds include: aliphatic polyisocyanates (especially aliphatic diisocyanates) such as trimethylene diisocyanate, tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate (HDI), and trimethylhexamethylene diisocyanate; 1,3-cyclopentane diisocyanate, 1,4-cyclohexane diisocyanate, 1,2-cyclohexane diisocyanate, isophorone diisocyanate (IPDI), and norbornene diisocyanate (methyl norbornene diisocyanate). Alicyclic polyisocyanates (especially alicyclic diisocyanates) such as socianenet methyl cyanate; aromatic polyisocyanates such as xylene diisocyanate (XDI), 2,4-toluene diisocyanate (TDI), and 2,6-toluene diisocyanate; and isocyanurate compounds, uretdione compounds, ethyl carbamate compounds, allophanate compounds, biuret compounds, and adducts with trimethylolpropane derived from them.

[0207] The polyisocyanate compound is preferably selected from at least one of aliphatic diisocyanates, alicyclic diisocyanates, and ureate or diketone forms of these diisocyanates. Using a polyisocyanate compound offers the advantages of forming a topcoat film with superior weather resistance and better control over the reaction rate with hydroxyl-containing acrylic resins.

[0208] In the topcoat coating composition, the molar ratio of the isocyanate functional groups of the polyisocyanate compound to the hydroxyl functional groups of the hydroxyl-containing acrylic resin (molar number of isocyanate functional groups / molar number of hydroxyl functional groups) is, for example, in the range of 1.15 or more and 1.35 or less. By using a topcoat coating composition with a molar ratio of isocyanate functional groups to hydroxyl functional groups within the above range, a coating film with good appearance and strength can be formed when forming a multilayer coating film.

[0209] [Polycarbonate diol compounds]

[0210] Topcoat coating compositions may contain polycarbonate diol compounds. For example, polycarbonate diol (A) is preferably a compound represented by the following general formula.

[0211] [Chemical Formula 1]

[0212]

[0213] In the formula, the structure of R is determined by the diol component used to manufacture the aforementioned polycarbonate diol. Examples of such diol components include diols with 2 to 10 carbon atoms, preferably 4 to 8. Specifically, examples include aliphatic diols such as 1,2-propanediol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 2-ethyl-1,6-hexanediol, 2-methyl-1,3-propanediol, 3-methyl-1,5-pentanediol, and neopentanediol; alicyclic diols such as 1,3-cyclohexanediol, 1,4-cyclohexanediol, and 1,4-cyclohexanediol; aromatic diols such as p-phenylenediol and p-tetrachlorophenylenediol; and diethylene glycol and dipropylene glycol. These diols can be used alone or in combination of two or more. The above-mentioned polycarbonate diol can be obtained by reacting the diol with a carbonylating agent such as phosgene.

[0214] In polycarbonate diol compounds, R in the above general formula is preferably a straight-chain alkylene (straight-chain alkyldiyl). In this case, R in the general formula is more preferably a straight-chain alkylene (straight-chain alkyldiyl) having 2 to 40 carbon atoms.

[0215] Furthermore, the polycarbonate diol compound is more preferably a polymer containing a diol component of 1,6-hexanediol and a carbonylating agent. By using such a polycarbonate diol compound (C), the following advantages are achieved: durability and hardness are more easily maintained, while better damage resistance is obtained.

[0216] As a particularly preferred example, a polycarbonate diol compound is obtained by using 1,6-hexanediol as an essential diol component and combining two or more diol components, such as the combination of 1,6-hexanediol and 1,5-pentanediol, the combination of 1,6-hexanediol and 1,4-butanediol, or the combination of 1,6-hexanediol and 1,4-dihydroxymethylcyclohexane, with a carbonylating agent.

[0217] Among these, substances obtained by combining 1,6-hexanediol and 1,5-pentanediol in a molar ratio of 80:20 to 20:80 are preferred. Substances obtained by combining two or more of these substances are preferred for their superior wear resistance.

[0218] As carbonylating agents, one or more commonly used alkylene carbonates, dialkyl carbonates, diallyl carbonates, and phosgene can be used in combination. Among these, preferred examples include ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, dibutyl carbonate, and diphenyl carbonate.

[0219] Preferably, the hydroxyl equivalent of the polycarbonate diol compound is 320 g / eq or more and 2000 g / eq or less, more preferably 350 g / eq or more and 1000 g / eq or less. By setting the hydroxyl equivalent within the above range, the following advantages are achieved: abrasion resistance, stain resistance, water resistance, etc., can be maintained better.

[0220] More preferably, the polycarbonate diol compound has a number average molecular weight in the range of 500 to 6000.

[0221] Commercially available products can be used as polycarbonate diols. Examples of commercially available products include: DURANOL T-5650J, T-5650E, T-5651, T-5652 (diol composition: 1,6-hexanediol and 1,5-pentanediol), T-4671 (diol composition: 1,6-hexanediol and 1,4-butanediol) manufactured by Asahi Kasei Corporation, and ETERNACOLL UM-90 (1 / 1, 1 / 3) (diol composition: 1,6-hexanediol and 1,4-dihydroxymethylcyclohexane) manufactured by Ube Industries, Ltd.

[0222] By including hydroxyl-containing acrylic resin and polycarbonate diol compound in the topcoat composition, especially including hydroxyl-containing acrylic resin and polycarbonate diol compound as the main agent of the two-component topcoat composition, the following advantages are obtained: the topcoat film can absorb external forces and repair damage.

[0223] The content of polycarbonate diol compound is preferably in the range of 0 parts by mass or more and 40 parts by mass or less, more preferably in the range of 5 parts by mass or more and 20 parts by mass or less, relative to 100 parts by mass of the hydroxyl-containing acrylic resin (A) resin solids.

[0224] Topcoat coating compositions may also include tack control agents. Including tack control agents improves coating workability. Tack control agents can be substances that typically exhibit thixotropic properties, such as those already described for water-based coating compositions. Additionally, topcoat coating compositions may include curing catalysts, surface conditioners, etc., as needed. Topcoat coating compositions may also include known UV absorbers, light stabilizers, antioxidants, etc. Furthermore, topcoat coating compositions may include known rheology control agents, other surface conditioners, etc., and solvents such as alcohol-based solvents, aromatic hydrocarbon-based solvents, ester-based solvents, and ketone-based solvents may be used for purposes such as viscosity adjustment. These additives may be included in the main agent and / or curing agent.

[0225] Regarding the timing of mixing the base agent and hardener in the case of a two-component topcoat composition, the base agent and hardener can be mixed before use and applied using a standard coating method. Alternatively, in a two-component mixing gun, the respective components can be fed into the gun and applied using a mixing method at the gun tip.

[0226] Methods for manufacturing multilayer coatings and articles

[0227] By applying the above-described intermediate coating composition, primer coating composition, and topcoat coating composition to a substrate, a multilayer coating film can be formed. The multilayer coating film comprises a primer coating film disposed on the substrate, an intermediate coating film disposed on the primer coating film, and a topcoat coating film disposed on the intermediate coating film.

[0228] (Object to be painted)

[0229] There are no particular limitations on the object to be coated; for example, it may contain resin components or metal components. The object to be coated may also contain both resin components and metal components.

[0230] Examples of metal components include metals such as iron, steel, copper, aluminum, tin, and zinc, as well as alloys containing these metals. The metal substrate may undergo a chemical formation treatment (e.g., zinc phosphate formation treatment, zirconium formation treatment, etc.) as needed before the electrodeposited coating is formed.

[0231] The resin component may include, for example, polyolefin resin, polycarbonate resin, urethane resin, polyester resin, polystyrene resin, ABS resin, vinyl chloride resin, polyamide resin, etc. When the object to be coated is a resin component, the primer coating film is required to have excellent adhesion to the resin component. For such a primer coating film with excellent adhesion to the resin component, as long as the primer coating film is formed from the intermediate coating composition disclosed herein, it can exhibit good adhesion to the primer coating film. From the perspective of physical properties such as strength and weight, the resin component preferably comprises a polyolefin resin.

[0232] The object to be coated can be an exterior component of a vehicle. There is no particular limitation on the vehicle; examples include automobiles, two-wheeled vehicles, and heavy vehicles. Alternatively, the object to be coated can be, for example, a car body with an electrodeposited coating, in which case the car body includes metal components.

[0233] In one embodiment, the object to be coated is a resin component for vehicle exteriors, such as a resin component for vehicle exteriors containing a polyolefin resin.

[0234] In one embodiment, the object to be coated is a resin component for automotive exteriors, such as a resin component for automotive exteriors containing a polyolefin resin.

[0235] (Including the coated object and items with multiple coatings)

[0236] The items covered in this disclosure include:

[0237] The object being painted; and

[0238] A multilayer coating having a base coat disposed on an object to be coated, a mid-coat coat formed of the mid-coat paint composition disclosed herein disposed on the base coat, and a top coat disposed on the mid-coat coat.

[0239] The substrate, the primer coating, and the topcoat coating can be any of the above-mentioned components.

[0240] Because the multilayer coating film has a mid-coat film formed by the mid-coat coating composition of the present disclosure, the multilayer coating film can exhibit high adhesion between the individual coating films and can suppress coating peeling. Moreover, the mid-coat coating composition of the present disclosure can form a multilayer coating film that exhibits high adhesion to the coated object and can form a multilayer coating film with excellent coating appearance.

[0241] Furthermore, multi-layer coatings can conform to complex shapes and exhibit high adhesion to the coated object. Therefore, the articles disclosed herein can be used for articles with high design flexibility.

[0242] In one embodiment, the thickness of the base coat of the multilayer coating is 3 μm or more and 15 μm or less, the thickness of the intermediate coat is 10 μm or more and 30 μm or less, and the thickness of the top coat is 20 μm or more and 40 μm or less.

[0243] Furthermore, since the multilayer coating has a coating film formed by the intermediate coating composition according to this disclosure, in the case where the coated object is a resin component, such as a resin component containing a polyolefin resin, a coating film having the aforementioned various properties can be formed without compromising the properties of the coated object. Moreover, compared with the case where the coated object is a metal, the sintering temperature can be significantly reduced.

[0244] In one embodiment, the peel strength (hereinafter, sometimes referred to as "peel strength of the base coat") T(P) [N / m] of the base coat relative to the resin component containing the polyolefin resin, i.e., the coated object, and the peel strength (hereinafter, sometimes referred to as "peel strength of the base coat") T(L) [N / m] of the multilayer coating relative to the coated object, T(L) < (T(L) - T(P)) < 4.9.

[0245] By ensuring that the peel strength T(P) of the base coat and the peel strength T(L) of the multilayer coating satisfy this relationship, a higher adhesion can be achieved between the substrate and the multilayer coating. Furthermore, higher adhesion can be exhibited between the individual coatings within the multilayer coating, further suppressing interfacial delamination in the multilayer coating. This also allows for the formation of multilayer coatings with a superior appearance.

[0246] Furthermore, in applications where the object being coated has a complex shape, multi-layer coatings can also provide higher adhesion, enabling highly customizable items, such as exterior parts for vehicles.

[0247] In one embodiment, the peel strength T(P) of the base coat and the peel strength T(L) of the multilayer coat satisfy the relationship 0.55 < (T(L) - T(P)) < 4.5, for example, 0.60 < (T(L) - T(P)) < 4.0.

[0248] By ensuring that the peel strength T(P) of the base coat and the peel strength T(L) of the multilayer coating satisfy this relationship, a higher adhesion can be achieved between the substrate and the multilayer coating. Furthermore, higher adhesion can also be observed between the individual coatings within the multilayer coating, more effectively suppressing interfacial delamination in the multilayer coating.

[0249] In one embodiment, the multilayer coating on the object is preferably such that no abnormalities are observed in a visual appearance evaluation even after exposure for 240 hours at a relative humidity of 95% and a temperature of 50°C.

[0250] There are no particular limitations on the manufacturing method of the articles involved in this disclosure. The substrate, the primer coating, and the topcoat coating can be as described above.

[0251] In one embodiment, an article comprising a coated object and multiple layers of coating film can be manufactured by a wet-on-wet process. That is, in one embodiment, the article according to this disclosure can be manufactured by a manufacturing method including the following steps:

[0252] The process of applying a primer coating composition to a substrate to form an uncured primer coating film;

[0253] The process of applying the intermediate coating composition of this disclosure onto an uncured primer coating film to form an uncured intermediate coating film;

[0254] The process of applying a topcoat coating composition onto an uncured intermediate coating film to form an uncured topcoat film; and

[0255] The process of simultaneously sintering and curing uncured base coat, uncured intermediate coat, and uncured top coat at temperatures above 60°C and below 100°C.

[0256] In another embodiment, the articles involved in this disclosure can be manufactured by a manufacturing method including the following steps:

[0257] The process of applying a primer coating composition to a substrate to form an uncured primer coating film, and sintering and curing the uncured primer coating film at a temperature above 60°C and below 100°C to form a primer coating film.

[0258] The process of applying the intermediate coating composition of this disclosure onto the base coating film to form an uncured intermediate coating film, and sintering and curing the uncured intermediate coating film at a temperature of 60°C or higher and 100°C or lower to form an intermediate coating film.

[0259] The process of applying a topcoat coating composition onto an intermediate coating film to form an uncured topcoat film, and then sintering and curing the uncured topcoat film at a temperature above 60°C and below 100°C to form a topcoat film.

[0260] In these embodiments, the intermediate coating composition disclosed herein can be used, and each coating film can be sintered and cured at a low temperature of 60°C or higher and 100°C or lower. Therefore, even on a substrate with poor heat resistance, such as a substrate using resin components, a coating film having the various properties described above can be formed without compromising the properties of the substrate.

[0261] By using the intermediate coating composition disclosed herein to form a multilayer coating film, even when the coating film is sintered and cured at low temperatures, such as above 60°C and below 100°C, a higher adhesion between the coated object and the multilayer coating film can be achieved. Furthermore, higher adhesion can be exhibited between the individual coating films in the multilayer coating film, further suppressing interfacial delamination in the multilayer coating film. And a multilayer coating film with a superior coating appearance can be formed.

[0262] Furthermore, in applications where the object being coated has a complex shape, multi-layer coatings can also provide higher adhesion, enabling highly customizable parts, such as exterior parts for vehicles.

[0263] The primer coating composition can be applied to the substrate to achieve a dry film thickness of 3 μm or more and 15 μm or less. Additionally, before applying the intermediate coating composition, the primer film can be dried at room temperature or under heating conditions (e.g., above 60°C and below 90°C), if necessary.

[0264] The intermediate coating composition disclosed herein can be applied onto the primer coating film to achieve a dry coating film thickness of 10 μm or more and 30 μm or less. Furthermore, the intermediate coating film can be dried at room temperature or by heating before applying the topcoat coating composition.

[0265] The topcoat coating composition can be applied onto the intermediate coating film so that the dried topcoat film has a thickness of 20 μm or more and 40 μm or less.

[0266] By simultaneously sintering and curing the uncured base coat, the uncured intermediate coat, and the uncured top coat at temperatures above 60°C and below 100°C, a multilayer coating can be formed on the object being coated.

[0267] Alternatively, in another approach, a base coat, intermediate coat, and top coat can be applied separately, with each application undergoing sintering and curing. For example, a base coat can be applied to the substrate to form an uncured base coat film. This uncured base coat film is then sintered and cured at a temperature between 60°C and 100°C to form a base coat film. The intermediate coat can then be applied to this base coat film to form an uncured intermediate coat film. This uncured intermediate coat film is then sintered and cured at a temperature between 60°C and 100°C to form a intermediate coat film. Finally, a top coat can be applied to this intermediate coat film to form an uncured top coat film. This uncured top coat film is then sintered and cured at a temperature between 60°C and 100°C to form a top coat film.

[0268] Example

[0269] The invention is further illustrated by the following embodiments, but the invention is not limited thereto. In the embodiments, "parts" and "%" are based on mass unless otherwise specified.

[0270] Preparation of the primer coating composition in Example 1

[0271] (Acid anhydride modified chlorinated polyolefin)

[0272] As an anhydride-modified chlorinated polyolefin, a substance with the following properties was used.

[0273] Molar ratio of propylene to ethylene: 90 / 10

[0274] Maleic anhydride content (%): 1.3

[0275] Weight-average molecular weight: 80,000

[0276] (Preparation of acrylic-modified alkyd resin)

[0277] The alkyd resin polymerization phase was prepared using 50.5 parts by weight of dehydrated castor oil, 27.1 parts by weight of phthalic anhydride, 14.5 parts by weight of pentaerythritol, and 7.9 parts by weight of neopentyl glycol.

[0278] In addition, the acrylic resin polymerization part was prepared using 61.0 parts by weight of methyl methacrylate, 20.0 parts by weight of styrene, 18.4 parts by weight of n-butyl acrylate and 0.6 parts by weight of methacrylic acid.

[0279] The resulting alkyd resin polymer was reacted with the acrylic resin polymer to prepare an acrylic-modified alkyd resin.

[0280] A primer coating composition (a primer composition for polyolefins) was prepared by mixing 7 parts (solid components) of the above-mentioned anhydride-modified chlorinated polyolefin, 7 parts (solid components) of acrylic-modified alkyd resin, 14 parts of pigment (Titan R-820, manufactured by Ishihara Sangyo Co., Ltd.) and 72 parts of toluene.

[0281] Preparation of Topcoat Coating Composition (Example 2)

[0282] (Preparation of hydroxyl-containing acrylic resin)

[0283] 30g of butyl acetate was placed in a container equipped with a stirrer, temperature control device, and reflux cooler, and the temperature was raised to 120°C. Then, over 3 hours, a monomer mixture of the following composition (20 parts styrene, 15.8 parts n-butyl acrylate, 21.8 parts n-butyl methacrylate, 41.1 parts 2-hydroxypropyl methacrylate, 1.3 parts acrylic acid), 12 parts kayaester O, and 6 parts butyl acetate were added dropwise. After standing for 30 minutes, a solution of 0.5 parts kayaester O and 4 parts butyl acetate was added dropwise over 30 minutes. The reaction solution was stirred for 1 hour until the rate of change to resin increased, at which point the reaction was stopped, yielding a hydroxyl-containing acrylic resin with a solid content of 70% by mass, a number-average molecular weight of 3800, a hydroxyl value of 160 mg KOH / g (of which secondary hydroxyl groups accounted for 100%), and an acid value of 10 mg KOH / g.

[0284] (Preparation of the main agent in the topcoat coating composition)

[0285] 245.3 parts of the above-mentioned hydroxyl-containing acrylic resin, 19.0 parts of DURANOL T-5650E manufactured by Asahi Kasei Corporation, 5.6 parts of "Tinuvin 384" ultraviolet absorber manufactured by Ciba-Geigy Corporation, 5.6 parts of "Tinuvin 123" light stabilizer manufactured by Ciba-Geigy Corporation, 5.6 parts of acrylic surface conditioner, 37.0 parts of toluene and 37.0 parts of xylene were added sequentially to a 1L metal container. The mixture was stirred thoroughly using a disperser to obtain the main component of the two-component transparent coating composition.

[0286] (Preparation of curing agent in topcoat coating composition)

[0287] 100.0 parts of "Desmodur N-3300" (22% NCO active ingredient) manufactured by Sumitomo Bayer Polyurethanes Co., Ltd. and 30 parts of 2-ethylethoxypropanol were added sequentially to another metal container and stirred thoroughly to obtain a curing agent for a two-component transparent coating composition.

[0288] The preparation of each component contained in the coating composition in Manufacturing Example 3, etc.

[0289] The components contained in the intermediate coating composition were prepared or obtained as follows.

[0290] [Table 1]

[0291] Coating film forming resin (A)

[0292]

[0293] [Table 2]

[0294] Coating forms resin (B)

[0295]

[0296] [Table 3]

[0297] Coating film forming resin (C)

[0298]

[0299] The glass transition temperatures of the above-mentioned coating-forming resins (A) to (C) were determined based on the baseline and tangent at the inflection point of the DSC curves obtained using a differential scanning calorimeter. The specific measurement sequence is as follows.

[0300] The X-DSC7000 manufactured by SII NanoTechnology Co., Ltd. was used as the instrument for measuring the glass transition temperature.

[0301] To determine the glass transition temperature, resin films were coated and dried to create test pieces for the determination.

[0302] To remove the solvent from the resin solution, pretreatment was performed according to the following guidelines.

[0303] After removing most of the solvent from the test piece by drying it at 60°C under normal pressure for 1 hour (using a desiccator), the test piece was further dried at 25°C under a vacuum of 760 mmHg for 4 hours (using a vacuum desiccator).

[0304] The dryer used was SPHH-100 (manufactured by TABAI ESPEC), and the vacuum dryer used was EYLA VOS-450SD (manufactured by Tokyo Risa Machinery).

[0305] Secondly, as preparation for the test tablet, the mass of the test tablet is approximately 10 mg, measured to 0.1 mg.

[0306] Pour the required amount evenly and smoothly into the container (aluminum tray) without gaps, then cover the container with the lid and secure it.

[0307] The containers were installed in the following order: Containers containing test pieces were installed on one container rack. Empty containers with lids were installed on another container rack.

[0308] The nitrogen flow rate was set to 20 m / min and continued to flow in until the end of the experiment without changing the flow rate.

[0309] The container containing the test piece was placed into the DSC device. In order to match the thermal history, (1) the temperature was increased at 20°C per minute to a temperature about 40°C higher than the end of the glass transition and held for 10 minutes. Then, the temperature was decreased at 10°C per minute to a temperature about 50°C lower than the glass transition temperature and held for 3 minutes. Finally, the temperature was increased at 10°C per minute to a temperature about 30°C higher than the end of the transition, and the DSC curve was generated.

[0310] Next, in the glass transition temperature determination, adjustments are made so that the difference along the vertical axis of the step-like change is at least 10% of the full scale of the recording paper. For the obtained DSC curve, the temperature at the intersection of the straight line extending from the low-temperature side to the high-temperature side and the tangent drawn at the point where the gradient of the curve in the step-like change portion of the glass transition is the greatest is determined. The temperature is calculated to one decimal place and rounded.

[0311] The above operation was performed three times on the same material, and the average temperature was calculated to determine the glass transition temperature.

[0312] The weight-average molecular weights of the film-forming resins (A) to (C) were calculated using polystyrene as a standard based on gel permeation chromatography (GPC) results. The hydroxyl values ​​of the film-forming resins (A) to (C) are expressed as values ​​converted to solids content and were obtained by determination according to JIS K 0070.

[0313] Example 1

[0314] Preparation of intermediate coating composition

[0315] After mixing the film-forming resins (A) to (C) shown in the table below in a mixing bag, 10 parts by weight of DISPARLON paste (manufactured by Kusunoki Kasei Corporation, polyamide wax) as a tackifier were added and the mixture was stirred. Next, 4 parts by weight of DURANATE MF-K60X (manufactured by Asahi Kasei Corporation, end-capped isocyanate) as a curing agent and 6 parts by weight of aluminum paste (manufactured by Toyo Aluminum Corporation, aluminum pigment) as a brightener were added, followed by butyl acetate, xylene, ethyl acetate, and 18 parts by weight of a silicone-based additive (additive 5648, manufactured by Toray Industries, Inc.) as an additive, and the mixture was stirred. Visual inspection confirmed the absence of agglomerates, thus obtaining the intermediate coating composition.

[0316] Formation of multilayer coatings

[0317] As the substrate, Mitsubishi Chemical's BK-211S / FT-28 (3mm thick) was used as the polypropylene substrate. As a pretreatment, the substrate surface was wiped with a cloth coated with IPA (isopropyl alcohol) before use.

[0318] The above-obtained primer coating composition is applied to the object to achieve a thickness of 9 μm, thus forming a primer coating film.

[0319] Next, the above-obtained intermediate coating composition is applied over the obtained base coating film to achieve a thickness of 18 μm, thus forming an intermediate coating film.

[0320] Furthermore, the obtained topcoat coating composition was applied over the obtained intermediate coating film to achieve a thickness of 34 μm. The obtained uncured primer, intermediate, and topcoat films were cured at 80°C for 0.75 hours, forming a multilayer coating on the substrate.

[0321] Examples 2-5

[0322] In Example 1, intermediate coating compositions were prepared by changing the types and / or amounts of components in film-forming resins (A), (B), and (C) to the conditions shown in the table below. Otherwise, the intermediate coating compositions were prepared in the same manner as in Example 1. Using the resulting intermediate coating compositions, multilayer coatings were formed on the substrate in the same order as in Example 1.

[0323] Comparative Examples 1-5

[0324] In Example 1, intermediate coating compositions were prepared by changing the types and / or amounts of components in film-forming resins (A), (B), and (C) to the conditions shown in the table below. Otherwise, the intermediate coating compositions were prepared in the same manner as in Example 1. Using the resulting intermediate coating compositions, multilayer coatings were formed on the substrate in the same order as in Example 1.

[0325] The intermediate coating compositions obtained from the above examples and comparative examples were evaluated as follows. Various evaluation conditions and results are shown in the table below.

[0326] [Determination of peel strength]

[0327] Evaluation coated panels were produced using the following method.

[0328] A 3cm wide masking tape was applied to the edge of a polypropylene (PP) substrate. A primer coating composition was then applied to a thickness of 9μm. After applying the primer coating composition, the substrate was allowed to stand for 5 minutes, and the masking tape was peeled off to create the uncured portion of the coating. Next, a mid-coat coating composition was applied to a thickness of 18μm. After applying the mid-coat coating composition, the substrate was allowed to stand for 5 minutes, and then a clear coating composition was applied as the topcoat to a thickness of 32μm. The substrate was then allowed to stand at room temperature for 5 minutes. The resulting uncured primer, mid-coat, and topcoat coatings were then sintered in an oven at 80°C for 20 minutes to form a multilayer coating.

[0329] After curing at room temperature for 48 hours, a test auxiliary coating (the test auxiliary coating is a coating obtained by mixing curing agent R-271 at a ratio of 40% to 100% of R-278 040MG 100% manufactured by Nippon Paint) with 100-120 μm peel strength was laminated and cured at room temperature.

[0330] The resulting coated panels were cured at room temperature to obtain coated panels for evaluation.

[0331] Using a cutting tool, cuts are made every 10 mm in width on the resulting evaluation coated plate, and the film length is extended by using a reinforcing band to extend it onto the substrate.

[0332] Figure 1 This is a schematic diagram showing a peel strength test.

[0333] The testing machine used was the AG-IS manufactured by Shimadzu Corporation. Figure 1As shown, an evaluation coated plate was held by one chuck and a reinforcing strip was held by the other chuck. The peel strength between the substrate and the primer coating was measured at a peel angle of 180°, a peel speed of 20 mm / min, and a peel length of 15 mm. The tensile test conditions were as follows: tensile speed of 50 mm / min, peel width of 10 mm, peel angle of 180°, and test temperature of 20°C. Three measurements were performed, and the average value was taken as the peel strength.

[0334] Moisture resistance test

[0335] The changes in coating state when test specimens were slowly rotated while suspended in a humidification chamber (model CT-3SUGA) were investigated.

[0336] Holes approximately 5 mm in diameter were made at the corners of test pieces (50 × 50 mm or larger) with multi-layered coatings prepared in the order of the embodiments and comparative examples, so that they could be hung. Two test pieces were prepared for each embodiment and comparative example. One test piece was used for the experiment, and the remaining piece was stored as a comparison plate.

[0337] The procedure was performed according to the humidification chamber usage inspection standards (humidity conditions: 49℃±1℃, relative humidity: above 95%, airflow rate: approximately 3 times the volume of the humidification chamber / h, water: deionized water, rotation speed of the rotating ring: approximately 1 / 3 rotation per minute). The test pieces were suspended on the rotating ring for 240 hours with the coating surfaces not overlapping, spaced at intervals of at least 5mm. Afterward, the test pieces were removed, the water was wiped off, and the coating surfaces were arranged indoors with non-overlapping surfaces.

[0338] Afterwards, the test pieces were removed and left at room temperature for 24 hours before an airtightness evaluation was performed. The order of the airtightness evaluation is as follows.

[0339] [Regarding the assessment of tightness]

[0340] A tightness test was conducted according to JIS K 5400. Cross-cutting was performed using a cutting blade to create 100 1mm seals. 2 Next, the checkerboard pattern was cut into slices. Then, transparent tape was completely attached to the prepared checkerboard pattern, and one end of the tape was lifted and peeled upwards. This peeling action was performed three times on the same area. Afterwards, the number of checkerboard patterns peeled off was determined according to the criteria described below. An evaluation score of 8 or higher is considered acceptable based on the following evaluation criteria.

[0341] 10: No peeling

[0342] 8: Peel into 5 grids or less

[0343] 6: Stripping more than 5 squares but less than 15 squares

[0344] 4: Stripping more than 15 squares but less than 35 squares

[0345] 2: Stripping more than 35 squares but less than 65 squares

[0346] 0: Stripping more than 65 squares but less than 100 squares

[0347] Evaluation of water resistance test

[0348] Test pieces with multi-layer coatings prepared in sequence using the various embodiments and comparative examples were immersed in a constant temperature water bath adjusted to 40°C for 10 days (240 hours) or 20 days (500 hours).

[0349] Afterwards, the test pieces were removed and left at room temperature for 24 hours before an airtightness evaluation was performed. The order of the airtightness evaluation is as follows.

[0350] [Regarding the assessment of tightness]

[0351] A tightness test was conducted according to JIS K 5400. Cross-cutting was performed using a cutting blade to create 100 1mm seals. 2 Cut the checkerboard pattern. Next, completely attach transparent tape to the prepared checkerboard pattern, lift one end of the tape and peel it upwards. Perform this peeling action three times in the same area. Afterwards, determine the number of checkerboard patterns peeled off according to the criteria described below. An evaluation score of 8 or higher is considered acceptable based on the following evaluation criteria.

[0352] 10: No peeling

[0353] 8: Peel into 5 grids or less

[0354] 6: Stripping more than 5 squares but less than 15 squares

[0355] 4: Stripping more than 15 squares but less than 35 squares

[0356] 2: Stripping more than 35 squares but less than 65 squares

[0357] 0: Stripping more than 65 squares but less than 100 squares

[0358] [Table 4]

[0359]

[0360] According to the results of the embodiments, when using the intermediate coating composition of the present disclosure to form an intermediate coating film, the intermediate coating composition of the present disclosure can form an intermediate coating film that exhibits high adhesion to each layer of the multilayer coating film. Furthermore, the intermediate coating composition of the present disclosure can form a multilayer coating film that exhibits high adhesion to the coated object. Moreover, the resulting multilayer coating film has good moisture resistance.

[0361] The aforementioned multilayer coating further exhibits excellent coating appearance and the ability to conform to complex shapes. Therefore, any multilayer coating obtained using the intermediate coating composition disclosed herein can be used for parts with high design flexibility.

[0362] Furthermore, any multilayer coating obtained using the intermediate coating composition disclosed herein can achieve high adhesion between the coated object and the multilayer coating. Moreover, the intermediate coating composition disclosed herein maintains excellent adhesion to raw materials suitable for exterior finishes, etc., compared to conventional primer coatings. Therefore, the intermediate coating composition disclosed herein has the advantage of ensuring improved adhesion even to materials other than primer coatings and / or clear coats (e.g., steel substrates).

[0363] Furthermore, any intermediate coating composition disclosed herein can form a coating film with the aforementioned properties without compromising the properties of the substrate, even in cases where the substrate contains resin. Moreover, any intermediate coating composition disclosed herein allows for sintering (curing of the coating film) at a lower temperature compared to cases where the substrate is metal, even in cases where the substrate contains resin. Furthermore, multilayer coating films formed using the intermediate coating compositions disclosed herein have the advantage of good adhesion to the substrate, even when sintering and curing are performed at low temperatures.

[0364] On the other hand, since Comparative Examples 1 to 3 do not contain any of the film-forming resins (A) to (C), their resistance to hot water is insufficient.

[0365] In Comparative Examples 4 and 5, the glass transition temperature Tg(I) of the mixture of film-forming resins (A) to (C) contained in the intermediate coating composition is outside the scope of this invention. In these cases, the resistance to hot water, etc., is also insufficient.

[0366] Industrial availability

[0367] The intermediate coating composition disclosed herein can form an intermediate coating film that exhibits high adhesion to each layer of a multilayer coating film. Furthermore, the intermediate coating composition disclosed herein also has the advantages of forming a multilayer coating film that exhibits high adhesion to the coated object and forming a multilayer coating film with an excellent appearance.

Claims

1. A midcoat coating composition which is a midcoat coating composition for forming a midcoat coating film in a multilayer coating film having a base coating film disposed on a coated article, a midcoat coating film disposed on the base coating film, and a topcoat coating film disposed on the midcoat coating film, the midcoat coating composition comprises a coating film-forming resin (A), a coating film-forming resin (B), and a coating film-forming resin (C), the coating film-forming resin (B) and the coating film-forming resin (C) are acrylic resins, the glass transition temperature Tg(A) of the coating film-forming resin (A), the glass transition temperature Tg(B) of the coating film-forming resin (B), and the glass transition temperature Tg(C) of the coating film-forming resin (C) satisfy the relationship of Tg(A) < Tg(B) < Tg(C), the glass transition temperature Tg(I) of the mixture of the coating film-forming resin (A), the coating film-forming resin (B), and the coating film-forming resin (C) contained in the midcoat coating composition is 25°C or higher and 60°C or lower, in 100% by mass in total of the coating film-forming resin (A), the coating film-forming resin (B), and the coating film-forming resin (C), the coating film-forming resin (A) is 20% by mass or more and 40% by mass or less, the coating film-forming resin (B) is 20% by mass or more and 75% by mass or less, and the coating film-forming resin (C) is 5% by mass or more and 45% by mass or less.

2. The intermediate coating material composition of claim 1, wherein, the weight average molecular weight of the coating film-forming resin (A) is 9,000 or more and 90,000 or less, the hydroxyl value is 50 mgKOH / g or more and 150 mgKOH / g or less, and the glass transition temperature Tg(A) is -25°C or more and 5°C or less.

3. The intermediate coating material composition of claim 1, wherein, the weight average molecular weight of the coating film-forming resin (B) is 5,000 or more and 30,000 or less, the hydroxyl value is 20 mgKOH / g or more and 100 mgKOH / g or less, and the glass transition temperature Tg(B) is 20°C or more and 80°C or less.

4. The intermediate coating material composition of claim 1, wherein, the weight average molecular weight of the coating film-forming resin (C) is 5,000 or more and 60,000 or less, the hydroxyl value is 0 mgKOH / g or more and 35 mgKOH / g or less, and the glass transition temperature Tg(C) is 40°C or more and 100°C or less.

5. The intermediate coating material composition of claim 1 or 3, wherein, the coating film-forming resin (B) comprises a polymer of a monomer comprising at least one selected from the group consisting of (meth)acrylic acid, hydroxyethyl (meth)acrylate, methyl (meth)acrylate, ethyl (meth)acrylate, and butyl (meth)acrylate.

6. The intermediate coating material composition of claim 1 or 4, wherein, the coating film-forming resin (C) comprises a polymer of a monomer comprising at least one selected from the group consisting of (meth)acrylic acid, hydroxyethyl (meth)acrylate, methyl (meth)acrylate, ethyl (meth)acrylate, and butyl (meth)acrylate.

7. The midcoat coating composition described in any one of claims 1 to 4, which is used for coating a coated article comprising a resin part.

8. The midcoat coating composition described in claim 7, which is used for coating a coated article comprising a polyolefin resin.

9. The midcoat coating composition as claimed in any one of claims 1 to 4, which is used for coating a part for vehicle exterior.

10. The midcoat coating composition as claimed in claim 9, which is used for coating a part for vehicle exterior comprising a resin part.

11. An article which is an article comprising a coated article and a multilayer coating film having a basecoat coating film disposed on the coated article, a midcoat coating film disposed on the basecoat coating film, and a topcoat coating film disposed on the midcoat coating film, the midcoat coating film is formed from the midcoat coating composition as claimed in any one of claims 1 to 6, the basecoat coating film has a film thickness of 3 μm or more and 15 μm or less, the midcoat coating film has a film thickness of 10 μm or more and 30 μm or less, the topcoat coating film has a film thickness of 20 μm or more and 40 μm or less.

12. The article of claim 11, wherein, the coated article comprises a resin part.

13. The article of claim 12, wherein, the resin part comprises a polyolefin resin.

14. The article of claim 12 or 13, wherein, the coated article is the resin part comprising a polyolefin resin, and the peeling strength T(P) [N / m] of the basecoat coating film with respect to the coated article and the peeling strength T(L) [N / m] of the multilayer coating film with respect to the coated article satisfy the relationship of 0.49 < (T(L) - T(P)) < 4.

9.

15. The article of any of claims 11-13, wherein, the coated article is a part for vehicle exterior.

16. The article of claim 15, wherein, the coated article comprises a resin part.

17. A manufacturing method of an article which is a manufacturing method of an article comprising a coated article and a multilayer coating film having a basecoat coating film disposed on the coated article, a midcoat coating film disposed on the basecoat coating film, and a topcoat coating film disposed on the midcoat coating film, the manufacturing method of the article comprises the following steps: a step of applying a basecoat coating composition on the coated article to form an uncured basecoat coating film; a step of applying a midcoat coating composition as claimed in any one of claims 1 to 7 on the uncured basecoat coating film to form an uncured midcoat coating film; a step of applying a topcoat coating composition on the uncured midcoat coating film to form an uncured topcoat coating film; and a step of simultaneously sintering-curing the uncured basecoat coating film, the uncured midcoat coating film, and the uncured topcoat coating film at 60°C or higher and 100°C or lower.

18. A manufacturing method of an article which is a manufacturing method of an article comprising a coated article and a multilayer coating film having a basecoat coating film disposed on the coated article, a midcoat coating film disposed on the basecoat coating film, and a topcoat coating film disposed on the midcoat coating film, the manufacturing method of the article comprises the following steps: a step of applying a basecoat coating composition on the coated article to form an uncured basecoat coating film, and sintering-curing the uncured basecoat coating film at 60°C or higher and 100°C or lower to form a basecoat coating film; a step of applying a midcoat coating composition as claimed in any one of claims 1 to 7 on the basecoat coating film to form an uncured midcoat coating film, and sintering-curing the uncured midcoat coating film at 60°C or higher and 100°C or lower to form a midcoat coating film; a step of applying a top coat paint composition on the intermediate coat paint film to form an uncured top coat paint film, and sinter-curing the uncured top coat paint film at 60°C or higher and 100°C or lower to form a top coat paint film.

19. The method of manufacturing an article of claim 17 or 18, wherein, The object to be coated includes a resin member.

20. The method of manufacturing an article of claim 19, wherein, The resin member includes a polyolefin resin.

21. The method of manufacturing the article of claim 17, 18, or 20, wherein, The object to be coated is an exterior member for a vehicle.

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