Multilayer coating laminate, coating kit for forming a multilayer coating laminate, and method for forming a multilayer coating laminate

Abstract

To provide a multilayered coating film laminate which has good soaking property to a lower layer of a polyisocyanate component, and is excellent in finished appearance, coating film hardness, scratch resistance and weather resistance.SOLUTION: A multilayered coating film laminate is formed by laminating a first coating film obtained by curing a first coating composition, a second coating film obtained by curing a second coating composition and a third coating film obtained by curing a third coating composition in this order onto an object to be coated, wherein the first coating composition and the second coating composition contain a hydroxyl group-containing resin component, the third coating composition contains a hydroxyl group-containing resin component and a polyisocyanate component, and the polyisocyanate component is distributed at a ratio of 5 mass% or more and 15 mass% or less in the first coating film, a ratio of 12 mass% or more and 20 mass% or less in the second coating film and 80 mass% or less in the third coating film.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a multilayer coating laminate, a paint kit for forming a multilayer coating laminate, and a method for forming a multilayer coating laminate. [Background technology]

[0002] In recent years, the use of water-based paint compositions has been increasing, for example, as base coats for automobile body panels. These water-based paint compositions are suitable from the viewpoint of preventing environmental pollution because they contain almost no organic solvents. For example, Patent Document 1 discloses a water-based paint composition that combines a water-based polyol with a specific melamine.

[0003] Furthermore, in order to improve the chipping resistance required for automobile exterior panels and the like, for example, Patent Documents 2 to 4 disclose a method for forming a coating film in which a base coating that does not harden substantially with heat is applied, then a clear coating that hardens with heat is applied, and then heating is performed to simultaneously harden multiple layers of unhardened coating films. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 7-207220 [Patent Document 2] Japanese Patent Application Publication No. 10-128222 [Patent Document 3] Japanese Patent Publication No. 2001-226626 [Patent Document 4] Japanese Patent Publication No. 2020-192497 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] However, the technology disclosed in Patent Document 1 may have insufficient chipping resistance. In addition, in the technologies disclosed in Patent Documents 2 and 3, chipping resistance and the curability of the resulting multilayer coating film are exhibited, but improvement in the coating film hardness of the resulting multilayer coating film is desired. Further, in order to further improve the curability, improvement in the penetrability of the curing agent in the clear paint-containing layer into the base paint-containing layer is desired. In the technology disclosed in Patent Document 4, the penetrability into the lower layer is good, and the coating film hardness and chemical resistance are exhibited, but improvement in the finish appearance, scratch resistance and weather resistance of the resulting multilayer coating film is desired.

[0006] The present invention has been made in view of the above circumstances, and provides a multilayer coating film laminate excellent in penetrability of a polyisocyanate component into a lower layer, finish appearance, coating film hardness, scratch resistance and weather resistance, and a paint kit for forming the multilayer coating film laminate and a method for forming the multilayer coating film laminate, from which the multilayer coating film laminate is obtained.

Means for Solving the Problems

[0007] That is, the present invention includes the following aspects. (1) A multilayer coating film laminate formed by laminating, in this order, a first coating film formed by curing a first paint composition, a second coating film formed by curing a second paint composition, and a third coating film formed by curing a third paint composition on an object to be coated, wherein the first paint composition and the second paint composition contain a hydroxyl group-containing resin component, the third paint composition contains a hydroxyl group-containing resin component and a polyisocyanate component, and the polyisocyanate component is distributed in the first coating film at a ratio of 5% by mass or more and 15% by mass or less, in the second coating film at a ratio of 12% by mass or more and 20% by mass or less, and in the third coating film at a ratio of 80% by mass or less. (2) The polyisocyanate component contains a polyisocyanate having an isocyanurate group derived from an aliphatic diisocyanate monomer containing 1,6-hexamethylene diisocyanate. The content of components with a number average molecular weight of 700 or less is 70% by mass or more relative to the total mass of the polyisocyanate components. The uretdione dimer content is 2% by mass or more and 30% by mass or less relative to the total mass of the polyisocyanate components. The average number of isocyanate groups in the polyisocyanate component is 2.7 or more, and The multilayer coating laminate according to (1), wherein the uretdione dimer is distributed in the first coating film at a ratio of 10% by mass or more and 40% by mass or less, in the second coating film at a ratio of 1% by mass or more and 10% by mass or less, and in the third coating film at a ratio of 80% by mass or less. (3) The multilayer coating laminate according to (1) or (2), wherein the content of diisocyanate monomer in the polyisocyanate component is 0.10% by mass or less with respect to the total mass of the polyisocyanate component. (4) A multilayer coating laminate according to any one of (1) to (3), wherein in the third coating composition, the ratio NCO / OH of the molar concentration of isocyanate groups of the polyisocyanate component to the molar concentration of hydroxyl groups of the hydroxyl group-containing resin component is 0.8 or more and 3.0 or less. (5) A first paint composition contained in a first container, A second paint composition contained in a second container, A third paint composition contained in a third container, A paint kit for forming a multilayer coating laminate, comprising: The first paint composition and the second paint composition each contain a hydroxyl group-containing resin component. The third paint composition comprises a hydroxyl group-containing resin component and a polyisocyanate component, The polyisocyanate component comprises a polyisocyanate having an isocyanurate group, derived from an aliphatic diisocyanate monomer containing 1,6-hexamethylene diisocyanate. The content of components with a number average molecular weight of 700 or less is 70% by mass or more relative to the total mass of the polyisocyanate components. The uretdione dimer content is 2% by mass or more and 30% by mass or less relative to the total mass of the polyisocyanate components. The average number of isocyanate groups in the polyisocyanate component is 2.7 or more. In the third coating composition, the ratio NCO / OH of the molar concentration of isocyanate groups in the polyisocyanate component to the molar concentration of hydroxyl groups in the hydroxyl group-containing resin component is 0.8 or more and 3.0 or less. A paint kit for forming a multilayer coating laminate, wherein the first paint composition, the second paint composition, and the third paint composition have different compositions from each other. (6) A method for forming a multilayer coating laminate, comprising: applying a first coating composition onto an object to be coated to obtain a first uncured coating film; applying a second coating composition onto the first uncured coating film to obtain a second uncured coating film; further applying a third coating composition onto the second uncured coating film to obtain a third uncured coating film; and then simultaneously curing the first uncured coating film, the second uncured coating film, and the third uncured coating film by heating to form a multilayer coating laminate consisting of three layers: the first coating film, the second coating film, and the third coating film, The first paint composition and the second paint composition each contain a hydroxyl group-containing resin component. The third paint composition comprises a hydroxyl group-containing resin component and a polyisocyanate component, A method for forming a multilayer coating laminate, wherein the polyisocyanate component is distributed in the first coating film at a ratio of 5% by mass or more and 15% by mass or less, in the second coating film at a ratio of 12% by mass or more and 20% by mass or less, and in the third coating film at a ratio of 80% by mass or less. [Effects of the Invention]

[0008] According to the multilayer coating laminate of the above embodiment, the polyisocyanate component has good penetration into the lower layer, and a multilayer coating laminate with excellent finish appearance, coating hardness, scratch resistance, and weather resistance can be provided. According to the paint kit for forming a multilayer coating laminate and the method for forming a multilayer coating laminate of the above embodiment, the polyisocyanate component has good penetration into the lower layer, and a multilayer coating laminate with excellent finish appearance, coating hardness, scratch resistance, and weather resistance can be obtained. [Modes for carrying out the invention]

[0009] The following describes in detail embodiments for carrying out the present invention (hereinafter sometimes simply referred to as "this embodiment"). The following embodiments are illustrative examples for explaining the present invention and are not intended to limit the present invention to the following content. The present invention can be implemented by modifying it as appropriate within the scope of its gist.

[0010] In this specification, "polyisocyanate" means a polymer in which multiple monomers having two or more isocyanate groups (-NCO) are bonded together. In this specification, "hydroxyl group-containing resin" means a compound having two or more hydroxyl groups (-OH), and is also called a polyol. In this specification, unless otherwise specified, "coating film" means a cured product obtained by curing a paint composition. That is, a coating film is obtained by curing an uncured coating film.

[0011] ≪Multilayer coating laminate≫ In this embodiment, the multilayer coating laminate has a first coating film, a second coating film, and a third coating film laminated on the object to be coated in that order.

[0012] The first coating film, the second coating film, and the third coating film are formed by curing the first paint composition, the second paint composition, and the third paint composition, respectively.

[0013] In the multilayer coating laminate of this embodiment, the polyisocyanate component contained in the third coating composition is distributed in the following proportions: 5% by mass or more and 15% by mass or less in the first coating film, 12% by mass or more and 20% by mass or less in the second coating film, and 80% by mass or less in the third coating film. Furthermore, it is preferable that the polyisocyanate component contained in the third coating composition is distributed in the following proportions: 6% by mass or more and 14% by mass or less in the first coating film, 13% by mass or more and 19% by mass or less in the second coating film, and 79% by mass or less in the third coating film. Furthermore, it is more preferable that the polyisocyanate component contained in the third coating composition is distributed in the following proportions: 7% by mass or more and 13% by mass or less in the first coating film, 13% by mass or more and 18% by mass or less in the second coating film, and 78% by mass or less in the third coating film. Furthermore, it is even more preferable that the polyisocyanate component contained in the third coating composition is distributed in the following proportions: 8% by mass or more and 12% by mass or less in the first coating film, 14% by mass or more and 17% by mass or less in the second coating film, and 77% by mass or less in the third coating film. By ensuring that the distribution ratio of polyisocyanate components in the first, second, and third coating films is within the above numerical range, the penetration of polyisocyanate components into the underlying layer is good, resulting in a multi-layer coating laminate with excellent finish appearance, coating hardness, scratch resistance, and weather resistance.

[0014] Furthermore, in the multilayer coating laminate of this embodiment, if the polyisocyanate component contained in the third coating composition contains a uretdione dimer, it is preferable that the uretdione dimer is distributed in the first coating film at a ratio of 10% to 40% by mass, in the second coating film at a ratio of 1% to 10% by mass, and in the third coating film at a ratio of 80% by mass or less. Furthermore, it is more preferable that the uretdione dimer is distributed in the first coating film at a ratio of 14% to 38% by mass, in the second coating film at a ratio of 2% to 9% by mass, and in the third coating film at a ratio of 78% by mass or less. Furthermore, it is even more preferable that the uretdione dimer is distributed in the first coating film at a ratio of 18% to 36% by mass, in the second coating film at a ratio of 3% to 8% by mass, and in the third coating film at a ratio of 76% by mass or less. Furthermore, it is particularly preferable that the uretdione dimer is distributed in the following proportions: 22% to 34% by mass in the first coating film, 4% to 7% by mass in the second coating film, and 74% by mass or less in the third coating film. When the distribution ratio of uretdione dimers in the first, second, and third coating films is within the above numerical range, the penetration of the polyisocyanate component into the lower layer is better, resulting in a multi-layer coating laminate with superior finish appearance, coating hardness, scratch resistance, and weather resistance.

[0015] The distribution ratios of the polyisocyanate component and the uretdione dimer in the first, second, and third coating films are calculated, for example, using the following method. First, a smooth cross-section of the multi-layer coating laminate is obtained. Then, Fourier transform infrared spectroscopy (FT-IR) measurements are performed on the first and second coatings of the cross-section using the total internal reflection (ATR) method. From the measurement results, 1730 ± 50 cm⁻¹ is obtained. -1 (Peak derived from ester bonds in hydroxyl group-containing resin components), 1680±50cm -1 (Peak derived from the isocyanurate group of the polyisocyanate component) and 1760±50cm -1 When the peaks of absorbance (peaks derived from the uretdione group of the polyisocyanate component) are denoted as A, B, and C, respectively, the values ​​of B / A and (B+C) / A are calculated. Furthermore, the first and second coating compositions are forcibly mixed with polyisocyanate components diluted with butyl glycol acetate at concentrations of 1, 2, 5, and 10 mass% / resin, respectively. These are then coated to a dry film thickness of 30 μm to 40 μm, dried at 140°C for 30 minutes, and a control coating laminate is prepared. FT-IR measurements are performed on each coating film using the ATR method, and the values ​​of B / A and (B+C) / A are similarly calculated to create a calibration curve. Based on the created calibration curve and dry film thickness, the distribution ratios of the polyisocyanate component and uretdione dimer in the first and second coating films are calculated. Subsequently, based on the calculated values, the distribution ratios of the polyisocyanate component and uretdione dimer in the third coating film are also calculated. Specifically, it is calculated using, for example, the method described in the examples below.

[0016] The first coating film, the second coating film, and the third coating film may each consist of only one layer, or they may each consist of two or more layers. Furthermore, the third coating is a polyurethane resin coating.

[0017] The lower limit of the cured film thickness for the first, second, and third coating films is preferably 10 μm, and more preferably 15 μm. On the other hand, the upper limit of the cured film thickness is preferably 60 μm, and more preferably 50 μm. By keeping the cured film thickness within the above range, the durability of the multi-layer coating can be further improved.

[0018] <Paint composition> The first paint composition and the second paint composition each contain a hydroxyl group-containing resin component. The third paint composition contains a hydroxyl group-containing resin component and a polyisocyanate component.

[0019] Furthermore, the first paint composition and the second paint composition may further contain a polyisocyanate component.

[0020] The first paint composition, the second paint composition, and the third paint composition have different compositions from each other.

[0021] [Polyisocyanate component] The polyisocyanate component is used as a curing agent to cure the first, second, and third uncured coating films simultaneously.

[0022] The polyisocyanate component preferably includes a polyisocyanate having an isocyanurate group, derived from an aliphatic diisocyanate containing 1,6-hexamethylene diisocyanate (hereinafter sometimes abbreviated as "HDI") (hereinafter sometimes referred to as "isocyanurate-type polyisocyanate").

[0023] If the first and second paint compositions contain a polyisocyanate component, they may also contain an isocyanurate-type polyisocyanate.

[0024] The "isocyanurate group" is a functional group derived from a polyisocyanate composed of three molecules of a diisocyanate monomer, and is a group represented by the following formula (I). A polyisocyanate composed of three molecules of a diisocyanate monomer and having a compound represented by the following general formula (I-1) is referred to as an isocyanurate trimer or an isocyanurate-type polyisocyanate. That is, an isocyanurate trimer or an isocyanurate-type polyisocyanate is a reaction product derived from three molecules of a diisocyanate monomer.

[0025]

Chemical formula

[0026] In the above general formula (I-1), R 11 , R 12 and R 13 are each independently a saturated hydrocarbon group. The number of carbon atoms in the saturated hydrocarbon groups in R 11 and R 12 is preferably 4 or more and 30 or less, more preferably 4 or more and 16 or less, and even more preferably 4 or more and 8 or less. Among them, as R 11 , R 12 and R 13 , a hexamethylene group having 6 carbon atoms is particularly preferable.

[0027] As the diisocyanate monomer used in the production of the isocyanurate-type polyisocyanate, HDI is included as an essential component, and optionally, other aliphatic diisocyanates or alicyclic diisocyanates may be included. <00002​​​As alicyclic diisocyanates, those having 8 to 30 carbon atoms are preferred. Specific examples of alicyclic diisocyanates include isophorone diisocyanate (hereinafter referred to as "IPDI"), 1,3-bis(isocyanatemethyl)-cyclohexane, 4,4'-dicyclohexylmethane diisocyanate, norbornene diisocyanate, and hydrogenated xylylene diisocyanate. These diisocyanates can be used individually or in combination of two or more types.

[0029] In particular, HDI is preferred as the diisocyanate monomer used in the production of isocyanurate-type polyisocyanates from the viewpoint of ease of industrial availability, reactivity during polyisocyanate production, and low viscosity. Alternatively, IPDI is preferred from the viewpoint of weather resistance and ease of industrial availability.

[0030] In the polyisocyanate component, the content of isocyanurate trimers is not particularly limited, but it is preferably 55% to 95% by mass, and more preferably 60% to 95% by mass, relative to the total mass of the polyisocyanate component. A content of isocyanurate trimers above the lower limit allows for a further reduction in the viscosity of the polyisocyanate component. On the other hand, a content of isocyanurate trimers below the upper limit allows for a higher yield of the polyisocyanate component. The isocyanurate trimer content can be measured by gel permeation chromatography (hereinafter sometimes abbreviated as "GPC").

[0031] The polyisocyanate component preferably has a uretdione group in addition to the isocyanurate group. The "uretdione group" is a functional group derived from a polyisocyanate consisting of two diisocyanate monomers, and is represented by the following formula (II). The "uretdione dimer" is a polyisocyanate consisting of two diisocyanate monomers, and is represented by the following general formula (II-1).

[0032] [ka]

[0033] In the above general formula (II-1), R 21 and R 22 These are the R values ​​mentioned above. 11 , R 12 and R 13 It is the same as this.

[0034] The uretdione dimer content is preferably 2% to 30% by mass relative to the total mass of the polyisocyanate components, more preferably 4% to 26% by mass, even more preferably 6% to 23% by mass, and particularly preferably 8% to 20% by mass. By keeping the uretdione dimer content within the above range, the penetration of the polyisocyanate component into the first and second uncured coating films, as well as the finished appearance and scratch resistance of the resulting multilayer coating film, can be improved. The uretdione dimer content can be measured by GPC.

[0035] Methods for controlling the uretdione dimer content within the above range include, for example, the following methods (1) or (2). (1) A method in which the isocyanurate reaction of HDI is carried out to deactivate the catalyst, and then the reaction is carried out at a temperature of approximately 140°C to 160°C (preferably 145°C to 165°C) for several hours (preferably 1 hour to 3 hours); (2) A method in which an isocyanurate reaction of HDI is carried out to obtain a first polyisocyanate component, a uretdione catalyst such as a third phosphine is added separately to HDI, and the reaction is carried out at a temperature of about 20°C to 80°C for several hours to several tens of hours to obtain a second polyisocyanate component, and then a portion of the second polyisocyanate component is mixed with the first polyisocyanate component.

[0036] In particular, the method shown in (1) above is preferred as a method for controlling the uretdione dimer content within the above range, from the viewpoint of ease of availability.

[0037] Furthermore, the polyisocyanate component may further have at least one additional functional group selected from the group consisting of an iminooxadiazinedione group and an allophanate group. Generally speaking, the "iminooxadiadindione group" is a functional group derived from polyisocyanate consisting of three diisocyanate monomer molecules, and is represented by the following formula (III). In general, an "allophanate group" is a functional group formed from the hydroxyl group and isocyanate group of an alcohol, and is represented by the following formula (IV).

[0038] [ka]

[0039] Furthermore, the polyisocyanate component may also have urethane groups, urea groups, biuret groups, carbodiimide groups, and the like, in addition to the functional groups mentioned above.

[0040] Furthermore, regarding the polyisocyanate component, the lower limit of the content of components with a number average molecular weight of 700 or less is preferably 70% by mass, more preferably 72% by mass, even more preferably 74% by mass, and particularly preferably 76% by mass, relative to the total mass of the polyisocyanate component. On the other hand, the upper limit of the content of components with a number average molecular weight of 700 or less is preferably 90% by mass, more preferably 86% by mass, and even more preferably 82% by mass. In other words, the content of components with a number average molecular weight of 700 or less is preferably 70% by mass or more, more preferably 72% by mass or more and 90% by mass or less, even more preferably 74% by mass or more and 86% by mass or less, and particularly preferably 76% by mass or more and 82% by mass or less. By ensuring that the content of components with a number-average molecular weight of 700 or less is above the above lower limit, the penetration of polyisocyanate components into the first and second uncured coating films is improved, allowing the first, second, and third uncured coating films to cure more efficiently. As a result, the finished appearance and scratch resistance of the resulting multi-layer coating film can be improved. The content of components with a number-average molecular weight of 700 or less can be measured by GPC.

[0041] The lower limit of the average number of isocyanate groups is preferably 2.7, and more preferably 2.8 or higher. On the other hand, the upper limit of the average number of isocyanate groups is preferably 4.0, more preferably 3.5, and even more preferably 3.3. In other words, the average number of isocyanate groups is preferably 2.7 or more, more preferably 2.7 to 4.0, even more preferably 2.7 to 3.5, particularly preferably 2.7 to 3.3, and most preferably 2.8 to 3.3. When the average number of isocyanate groups is above the lower limit, the crosslinking properties of the polyisocyanate component can be further improved, resulting in a coating with superior hardness and chemical resistance. On the other hand, when the average number of isocyanate groups is below the upper limit, the penetration of the polyisocyanate component into the lower layers, the first and second uncured coating films, is improved, and as a result, the hardness of the resulting multilayer coating consisting of the first, second, and third coating films tends to be better.

[0042] The average number of isocyanate groups (Fn) of a polyisocyanate component can be calculated using the following formula. In the formula, Mn is the number-average molecular weight of the polyisocyanate component, and the NCO content is the mass percentage of isocyanate groups in the polyisocyanate component.

[0043] Fn=(Mn×NCO content×0.01) / 42

[0044] Furthermore, in the third coating composition, the lower limit of the ratio (NCO / OH) of the molar concentration of isocyanate groups (NCO groups) of the polyisocyanate component to the molar concentration of hydroxyl groups (OH groups) of the hydroxyl group-containing resin component is preferably 0.8, more preferably 0.9, and even more preferably 1.0. On the other hand, the upper limit of NCO / OH is preferably 3.0, more preferably 2.0, and even more preferably 1.5. In other words, in the third paint composition, the NCO / OH ratio is preferably 0.8 to 3.0, more preferably 0.9 to 2.0, and even more preferably 1.0 to 1.5. When the NCO / OH ratio is above the lower limit, the curability of the third coating composition, the penetration of the polyisocyanate component into the first and second uncured coating films, and the hardness of the resulting multilayer coating film tend to be superior. On the other hand, when the NCO / OH ratio is below the upper limit, the crosslinking properties of the coating film in the initial drying stage and the hardness of the resulting multilayer coating film tend to be superior.

[0045] (Method for producing polyisocyanate components) 1. Method for producing isocyanurate-type polyisocyanates Isocyanurate-type polyisocyanates are obtained by reacting diisocyanate monomers with an isocyanuration catalyst and an alcohol as a co-catalyst.

[0046] Examples of isocyanuration catalysts used in the production of isocyanurate-type polyisocyanates include sodium salts, potassium salts, and quaternary ammonium salts of fatty acids.

[0047] Examples of fatty acids include acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, heptanoic acid, caprylic acid, pelargonic acid, capric acid, lauric acid, myristic acid, palmitic acid, and stearic acid. These fatty acids may be linear or branched in structure.

[0048] Examples of quaternary ammonium compounds include tetramethylammonium, tetrabutylammonium, butyltrimethylammonium, benzyltrimethylammonium, dibenzyldimethylammonium, and phenyltrimethylammonium.

[0049] The amount of isocyanurate catalyst used varies depending on the amount of co-catalyst and solvent used, but when HDI is used as a raw material for polyisocyanate, it can usually be 0.001% to 0.05% by mass relative to the mass of HDI.

[0050] As co-catalysts, for example, phenolic hydroxy compounds and alcoholic hydroxy compounds can be used. This further facilitates the isocyanuration reaction. Examples of phenolic hydroxy compounds include phenol, cresol, and trimethylphenol. Examples of alcoholic hydroxy compounds include linear alcohols, branched alcohols, cyclic alcohols, and polyhydric alcohols. Examples of linear alcohols include methanol, ethanol, propanol, n-butanol, and 1-hexanol. Examples of branched-chain alcohols include isobutanol and 2-ethylhexanol. Examples of cyclic alcohols include cyclohexanol. Examples of polyhydric alcohols include ethylene glycol.

[0051] The amount of alcohol used correlates with the amount of allophanate groups present in the polyisocyanate component. When using HDI as a raw material for polyisocyanate, it is preferable to use 500 ppm to 30,000 ppm of alcohol by mass relative to the HDI. By keeping the amount of alcohol below the above upper limit, the proportion of isocyanurate groups in the polyisocyanate component is appropriately maintained, resulting in better weather resistance and chemical resistance. On the other hand, by keeping the amount of alcohol above the above lower limit, the reaction rate is kept higher, resulting in better productivity from an economic standpoint.

[0052] In the production of isocyanurate-type polyisocyanates, the timing of alcohol addition is such that the alcohol is present in the reaction system during the isocyanuration reaction. Specifically, the alcohol may be added before the isocyanuration reaction, simultaneously with the isocyanuration catalyst, or while the isocyanuration reaction is progressing after the isocyanuration catalyst has been added. Furthermore, the alcohol may be added at only one of the above timings, or at all of them. The alcohol may be added all at once or continuously. However, from the viewpoint of controlling the reaction and exothermic reaction, continuous addition is preferred when adding alcohol during the isocyanuration reaction. For alcohol addition before the isocyanuration reaction, all-at-once addition is preferred from an economic standpoint.

[0053] The isocyanurate reaction temperature is preferably 70°C or lower, and more preferably 30°C to 65°C. By setting the isocyanurate reaction temperature below the above upper limit, a polyisocyanate with better color can be obtained. On the other hand, by setting the isocyanurate reaction temperature above the above lower limit, the reaction rate is maintained at a more appropriate level, resulting in better productivity from an economic standpoint.

[0054] The reaction time varies depending on the amount of catalyst, the amount and method of adding the co-catalyst alcohol, and the reaction temperature, but it can usually be between 1 and 6 hours.

[0055] The decrease in isocyanate group content (NCO%) as isocyanuration progresses can be measured by titration, so the reaction can be stopped when the desired NCO% is reached. The NCO% at the time of reaction termination allows for the free adjustment of the NCO% and viscosity of the isocyanurate-type polyisocyanate.

[0056] Acidic compounds can be used as reaction stoppers. Examples of acidic compounds include hydrochloric acid, phosphoric acid, dimethyl phosphate, diethyl phosphate, dibutyl phosphate, di-2-ethylhexyl phosphate, dicyclohexyl phosphate, p-toluenesulfonic acid, benzenesulfonic acid, alkylbenzenesulfonic acid, acetyl chloride, and benzoyl chloride. Similar compounds to these acidic compounds may also be used.

[0057] The amount of reaction stopper used can be between 0.5 and 10 times the molar amount per mole of carboxylic acid in the isocyanurate catalyst, and preferably between 1 and 8 times the molar amount. When using a soluble reaction stopper in a mixed solution of the diisocyanate monomer (the raw material) and the polyisocyanate produced by the reaction, the amount can be around 1 time the molar amount per mole of carboxylic acid in the isocyanurate catalyst. When using an insoluble reaction stopper, the amount can be between 2 and 8 times the molar amount per mole of carboxylic acid in the isocyanurate catalyst.

[0058] After adding the reaction stopper, heat curing may be performed to complete the stopping reaction. If heat curing is performed, the temperature is preferably 80°C to 150°C, more preferably 80°C to 130°C, and even more preferably 90°C to 120°C. By keeping the temperature below the above upper limit, the decrease in 1-nylon compounds in the polyisocyanate component containing the resulting isocyanurate-type polyisocyanate can be further suppressed, and the decrease in color and the increase in viscosity due to the progression of isocyanurate-type polyisocyanate can be further suppressed. By keeping the temperature above the above lower limit, the growth of salts produced by the stopping reaction can be accelerated, and in particular, in the case of a combination of a catalyst that forms insoluble salts and a reaction stopper, salts of a size that can be filtered can be formed more easily, resulting in better productivity from an economic standpoint.

[0059] The optimal heating time varies depending on the temperature, but it can be between 10 and 120 minutes, preferably between 10 and 90 minutes, and more preferably between 10 and 60 minutes. Depending on the temperature, keeping the time below the upper limit can further suppress discoloration and the increase in viscosity due to further meristemization of polyisocyanate. On the other hand, keeping the time above the lower limit allows for more sufficient salt formation and growth, and in the case of insoluble salts, separation by filtration can be made easier.

[0060] 2. Method for producing uretdione dimer Uretidione dimers can be obtained by using a uretidionization reaction catalyst.

[0061] The catalyst for the uretdione reaction is not limited to the following, but examples include tertiary phosphines such as trialkylphosphine, tris(dialkylamino)phosphine, and cycloalkylphosphine. Examples of trialkylphosphines include tri-n-butylphosphine and tri-n-octylphosphine. Examples of tris(dialkylamino)phosphine include tris-(dimethylamino)phosphine. Examples of cycloalkylphosphines include cyclohexyl-di-n-hexylphosphine. Many of these compounds also promote isocyanuration reactions, producing isocyanurate-type polyisocyanates in addition to uretdione dimers.

[0062] Once the desired yield is achieved, the uretdione reaction is stopped by adding a deactivator for the uretdione reaction catalyst, such as phosphoric acid or methyl p-toluenesulfonate.

[0063] The amount of the uretdione reaction catalyst used is preferably 10 ppm to 10,000 ppm by mass ratio relative to the diisocyanate raw material, more preferably 10 ppm to 1,000 ppm, and even more preferably 10 ppm to 500 ppm. The lower limit of the reaction temperature for uretdione formation is preferably 20°C, more preferably 25°C, even more preferably 30°C, and particularly preferably 35°C. On the other hand, the upper limit of the reaction temperature for uretdione formation is preferably 120°C, more preferably 110°C, even more preferably 100°C, and particularly preferably 90°C. In other words, the reaction temperature for uretdione formation is preferably 20°C to 120°C, more preferably 25°C to 110°C, even more preferably 30°C to 100°C, and particularly preferably 35°C to 90°C. By keeping the uretdione reaction temperature below the above upper limit, changes in the properties of the resulting polyisocyanate components, such as coloration, can be more effectively prevented.

[0064] Furthermore, a uretdione group-containing polyisocyanate can also be obtained by heating a diisocyanate monomer without using the above-mentioned uretdione reaction catalyst.

[0065] When the above-mentioned uretdione reaction catalyst is not used, the lower limit of the heating temperature for the diisocyanate monomer is preferably 120°C, more preferably 130°C, even more preferably 140°C, and particularly preferably 145°C. On the other hand, the upper limit of the heating temperature for the diisocyanate monomer is preferably 180°C, more preferably 175°C, even more preferably 170°C, and particularly preferably 165°C. In other words, the heating temperature of the diisocyanate monomer is preferably 120°C to 180°C, more preferably 130°C to 175°C, even more preferably 140°C to 170°C, and particularly preferably 145°C to 165°C.

[0066] When the above uretdione reaction catalyst is not used, the lower limit of the heating time is preferably 0.2 hours, more preferably 0.4 hours, even more preferably 0.6 hours, particularly preferably 0.8 hours, and most preferably 1.0 hour. On the other hand, the upper limit of the heating time is preferably 8 hours, more preferably 6 hours, even more preferably 4 hours, particularly preferably 3 hours, and most preferably 2 hours. In other words, the heating time is preferably 0.2 hours to 8 hours, more preferably 0.4 hours to 6 hours, even more preferably 0.6 hours to 4 hours, particularly preferably 0.8 hours to 3 hours, and most preferably 1.0 hour to 2 hours. By setting the heating time above the lower limit, a lower viscosity can be achieved, and by setting it below the upper limit, the discoloration of the polyisocyanate itself can be further suppressed. When obtaining a polyisocyanate component without using a uretdione reaction catalyst, it is preferable to remove the unreacted diisocyanate monomer after the uretdione reaction by heating alone and the isocyanurate reaction described above have been completed, from the viewpoint of reducing the concentration of unreacted diisocyanate monomer, reducing the rate of change in molecular weight of the obtained polyisocyanate component after storage, and reducing yellowing during high-temperature baking.

[0067] 3. Method for producing polyisocyanates having an iminooxadiazinedione group Polyisocyanates having an imino-oxadiazinedione group (imino-oxadiazinedione group-containing polyisocyanates) can be obtained by using an imino-oxadiazinedione reaction catalyst.

[0068] Examples of imino-oxadiazinedione catalysts include the following: (1) General formula M[F n ], or general formula M[F n (HF) m (Poly)hydrogen fluoride represented by ] (In the formula, m and n are integers satisfying the relationship m / n > 0. M is an n-charged cation (mixture) or one or more radicals with a total charge of n.) Examples of the compound ((poly)hydrogen fluoride) in (1) include, for example, tetramethylammonium fluoride hydrate and tetraethylammonium fluoride. (2) General formula R 1 -CR'2-C(O)O-, or general formula R 2 A compound consisting of a compound represented as =CR'-C(O)O- and a quaternary ammonium cation or a quaternary phosphonium cation. (In the formula, R 1 , and R 2 (R' is a branched, cyclic, and / or unsaturated perfluoroalkyl group having 1 to 30 carbon atoms, and R' is the same or different, selected from the group consisting of a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, and an aryl group, and optionally contains a heteroatom.) Examples of compounds in (2) include, for example, 3,3,3-trifluorocarboxylic acid; 4,4,4,3,3-pentafluorobutanoic acid; 5,5,5,4,4,3,3-heptafluoropentanoic acid; and 3,3-difluoropropaneoic acid.

[0069] The lower limit of the amount of imino-oxadiazinedione catalyst used is not particularly limited, but from the viewpoint of reactivity, it is preferably 5 ppm, more preferably 10 ppm, and even more preferably 20 ppm, in mass ratio relative to the diisocyanate monomer used as a raw material. On the other hand, from the viewpoint of suppressing coloration and discoloration of the product and controlling the reaction, the upper limit of the amount of imino-oxadiazinedione catalyst used is preferably 5000 ppm, more preferably 2000 ppm, and even more preferably 500 ppm, in mass ratio relative to the diisocyanate monomer used as a raw material. In other words, the amount of imino-oxadiazinedione catalyst used is preferably 5 ppm to 5000 ppm by mass ratio relative to the diisocyanate monomer used as a raw material, more preferably 10 ppm to 2000 ppm, and even more preferably 20 ppm to 500 ppm.

[0070] The lower limit of the reaction temperature for imino-oxadiazinedione conversion is not particularly limited, but from the viewpoint of reaction rate, 40°C is preferred, 50°C is more preferred, and 60°C is even more preferred. On the other hand, the upper limit of the reaction temperature for imino-oxadiazinedione conversion is preferred from the viewpoint of suppressing coloration and discoloration of the product, 150°C is preferred, 120°C is more preferred, and 110°C is even more preferred. In other words, the reaction temperature for iminooxadiazinedione formation is preferably 40°C to 150°C, more preferably 50°C to 120°C, and even more preferably 60°C to 110°C.

[0071] The imino-oxadiazinedione reaction can be stopped when the desired imino-oxadiazinedione group content is reached. The reaction can be stopped by adding an acidic compound, such as phosphoric acid, acidic phosphoric acid esters, sulfuric acid, hydrochloric acid, or sulfonic acid compounds, to the reaction solution. This inactivates the imino-oxadiazinedione reaction catalyst by neutralization, thermal decomposition, or chemical decomposition. After stopping the reaction, filtration can be performed if necessary.

[0072] 4. Polyisocyanates having allophanate groups Polyisocyanates having allophanate groups (allophanate-containing polyisocyanates) can be obtained by using HDI in combination with alcohol compounds or the like, and by using an allophanate reaction catalyst.

[0073] The alcohol compound used in the production of allophanate group-containing polyisocyanates is not limited to the following, but alcohols formed only from carbon, hydrogen, and oxygen are preferred. Furthermore, the alcohol compound is preferably 200 or less in molecular weight.

[0074] Examples of alcohol compounds include monoalcohols and dialcohols. Examples of monoalcohols include methanol, ethanol, propanol, butanol, pentanol, hexanol, heptanol, octanol, and nonanol. Examples of dialcohols include ethylene glycol, 1,3-butanediol, neopentyl glycol, and 2-ethylhexanediol. These alcohol compounds may be used individually or in combination of two or more. Among these, monoalcohols are preferred as alcohol compounds.

[0075] The amount of alcohol compound used is not limited to the following, but the molar ratio of isocyanate groups of HDI to hydroxyl groups of the alcohol compound is preferably 10 / 1 or more and 1000 / 1 or less, and more preferably 100 / 1 or more and 1000 / 1 or less. By being above the lower limit above, a more appropriate number of isocyanate groups can be secured in the resulting polyisocyanate.

[0076] The allophanate reaction catalyst is not limited to the following, but examples include alkyl carboxylates of tin, lead, zinc, bismuth, zirconium, zirconyl, etc. Examples of alkyl carboxylates of tin (organotin compounds) include tin 2-ethylhexanoate and dibutyltin dilaurate. Examples of alkyl carboxylates of lead (organic lead compounds) include lead 2-ethylhexanoate. Examples of zinc alkyl carboxylates (organozinc compounds) include zinc 2-ethylhexanoate. Examples of alkyl carboxylate salts of bismuth include bismuth 2-ethylhexanoate. Examples of alkyl carboxylate salts of zirconium include zirconium 2-ethylhexanoate. Examples of alkyl carboxylate salts of zirconyl include zirconyl 2-ethylhexanoate.

[0077] Once the desired yield is achieved, the allophanate reaction can be stopped by adding an allophanate reaction catalyst deactivator such as phosphoric acid or methyl p-toluenesulfonate.

[0078] The amount of the allophanate reaction catalyst used is preferably 10 ppm to 10,000 ppm by mass ratio relative to the diisocyanate raw material, more preferably 10 ppm to 1,000 ppm, and even more preferably 10 ppm to 500 ppm.

[0079] The lower limit of the reaction temperature for allophanate formation is preferably 60°C, more preferably 70°C, even more preferably 80°C, and particularly preferably 90°C. On the other hand, the upper limit of the reaction temperature for allophanate formation is preferably 160°C, more preferably 155°C, even more preferably 150°C, and particularly preferably 145°C. In other words, the reaction temperature for allophanate formation is preferably 60°C to 160°C, more preferably 70°C to 155°C, even more preferably 80°C to 150°C, and particularly preferably 90°C to 145°C.

[0080] By keeping the allophanate reaction temperature below the above upper limit, changes in properties such as discoloration of the resulting polyisocyanate can be more effectively prevented. The lower limit of the reaction time is preferably 0.2 hours, more preferably 0.4 hours, even more preferably 0.6 hours, particularly preferably 0.8 hours, and most preferably 1.0 hour. On the other hand, the upper limit of the reaction time is preferably 8 hours or less, more preferably 6 hours, even more preferably 4 hours, particularly preferably 3 hours, and most preferably 2 hours. In other words, the reaction time for allophanate formation is preferably 0.2 hours to 8 hours, more preferably 0.4 hours to 6 hours, even more preferably 0.6 hours to 4 hours, particularly preferably 0.8 hours to 3 hours, and most preferably 1.0 hour to 2 hours. By setting the allophanate reaction time above the lower limit, a lower viscosity can be achieved, and by setting it below the upper limit, the discoloration of the polyisocyanate itself can be further suppressed.

[0081] Furthermore, the above-mentioned isocyanurate reaction catalyst can be used as an allophanate reaction catalyst. When the allophanate reaction is carried out using the above-mentioned isocyanurate reaction catalyst, isocyanurate-type polyisocyanate is also produced simultaneously. In particular, from the viewpoint of improving productivity from an economic standpoint, it is preferable to use the above-mentioned isocyanurate reaction catalyst as the allophanate reaction catalyst and carry out both the allophanate reaction and the isocyanurate reaction. The above isocyanurate reaction and the above uretdione reaction can be carried out sequentially or in parallel. Furthermore, when an allophanate reaction is involved, it is preferable to simplify the manufacturing process by performing the isocyanurate reaction and the allophanate reaction in parallel, followed by the uretdione reaction.

[0082] The allophanate reaction can be stopped once the desired allophanate group content is reached.

[0083] The allophanate reaction can be stopped by adding an acidic compound, such as phosphoric acid, acidic phosphate esters, sulfuric acid, hydrochloric acid, or sulfonic acid compounds, to the reaction mixture, although this is not limited to the above. This allows the allophanate reaction catalyst to be inactivated by neutralization, thermal decomposition, or chemical decomposition. After stopping the reaction, filtration can be performed if necessary.

[0084] 5. Yield In order to control the content of components with a number average molecular weight of 700 or less in the polyisocyanate component to the above range, the lower limit of the yield is preferably 5% by mass, more preferably 10% by mass, and even more preferably 15% by mass. On the other hand, the upper limit of the yield is preferably 40% by mass, more preferably 35% by mass, and even more preferably 30% by mass. In other words, the yield is preferably 5% by mass or more and 40% by mass or less, more preferably 10% by mass or more and 35% by mass or less, and even more preferably 15% by mass or more and 30% by mass or less. If the yield is above the lower limit mentioned above, productivity can be further improved. On the other hand, if the yield is below the upper limit mentioned above, the content of components with a number average molecular weight of 700 or less can be increased. Furthermore, in order to control the content of components with a number average molecular weight of 700 or less within the above range, it is preferable that the polyisocyanate component includes a polyisocyanate having a uretdione group and an allophanate group.

[0085] 6. Thin-film distillation process and heat treatment process The reaction solution immediately after the reaction stops usually contains unreacted diisocyanate monomers such as HDI, so it is preferable to remove these by thin-film evaporator, extraction, or the like. The thin-film distillation process is a process for improving the separation efficiency of low-boiling components from high-boiling components. Specific countermeasures include, for example, reducing the flow rate and extending the residence time, increasing the distillation temperature, increasing the wiper rotation speed, and increasing the number of distillation cycles. Any of these methods may be selected. Among these, increasing the number of distillation cycles is preferred in order to reduce the thermal history and improve separation efficiency. The number of distillation cycles is preferably between one and five.

[0086] Furthermore, the content of diisocyanate monomers remaining in the polyisocyanate component is preferably 0.50% by mass or less, more preferably 0.40% by mass or less, even more preferably 0.30% by mass or less, particularly preferably 0.20% by mass or less, and most preferably 0.10% by mass or less. By keeping the content of residual diisocyanate monomer in the polyisocyanate component below the above upper limit, the toxicity of the polyisocyanate component can be further reduced, and safety can be further improved. Furthermore, by keeping it below 0.10% by mass, a multi-layer coating film with particularly excellent finished appearance can be obtained.

[0087] (Physical properties of polyisocyanate components) 1. Viscosity The lower limit of the viscosity of the polyisocyanate component at 25°C is preferably 100 mPa·s, more preferably 140 mPa·s, even more preferably 180 mPa·s, particularly preferably 200 mPa·s, and most preferably 220 mPa·s. On the other hand, the upper limit of viscosity is preferably 1500 mPa·s, more preferably 1000 mPa·s, even more preferably 800 mPa·s, particularly preferably 700 mPa·s, and most preferably 600 mPa·s. In other words, the viscosity of the polyisocyanate component at 25°C is preferably 100 mPa·s to 1500 mPa·s, more preferably 140 mPa·s to 1000 mPa·s, even more preferably 180 mPa·s to 800 mPa·s, particularly preferably 200 mPa·s to 700 mPa·s, and most preferably 220 mPa·s to 600 mPa·s. If the viscosity is above the lower limit, the crosslinking properties of the polyisocyanate component can be further improved. On the other hand, if the viscosity is below the upper limit, the solid content concentration of the paint composition using the polyisocyanate component can be increased. Viscosity can be measured using an E-type viscometer (manufactured by Tokimec Co., Ltd.) with a polyisocyanate component purified to 99.5% by mass or more of non-volatile components (solids). Specifically, it can be measured by the method described in the examples below.

[0088] 2. Isocyanate group content The lower limit of the isocyanate group content (NCO content) of the polyisocyanate component is preferably 21.0% by mass, more preferably 21.5% by mass, and even more preferably 22.0% by mass. On the other hand, the upper limit of the NCO content is preferably 25.0% by mass, more preferably 24.0% by mass, and even more preferably 23.7% by mass. In other words, the NCO content of the polyisocyanate component is preferably 21.0% by mass or more and 25.0% by mass or less, more preferably 21.5% by mass or more and 24.0% by mass or less, and even more preferably 22.0% by mass or more and 23.7% by mass or less. By having an NCO content above the lower limit, the resulting multilayer coating can have better properties such as hardness. On the other hand, by having an NCO content below the upper limit, the yield of the polyisocyanate component can be increased. The NCO content can be determined by neutralizing the isocyanate groups of the polyisocyanate component with excess 2N amine, followed by back titration with 1N hydrochloric acid. The NCO content is a value relative to the solid content of the polyisocyanate component. The solid content of the polyisocyanate component can be determined from the amount remaining after heating the polyisocyanate component at 105°C for 3 hours.

[0089] 3.Number average molecular weight The lower limit of the number-average molecular weight of the solids in the polyisocyanate component is preferably 400, more preferably 430, even more preferably 460, and particularly preferably 480. On the other hand, the upper limit of the number-average molecular weight is preferably 1000, more preferably 800, even more preferably 700, and particularly preferably 600. In other words, the number-average molecular weight of the solid content in the polyisocyanate component is preferably 400 to 1,000, more preferably 430 to 800, even more preferably 460 to 700, and particularly preferably 480 to 600. When the number-average molecular weight is above the lower limit, the yield of the polyisocyanate component tends to improve. On the other hand, when the number-average molecular weight is below the upper limit, the penetration of the polyisocyanate component into the lower layers, the first and second uncured coating films, is better, and as a result, the hardness of the resulting multilayer coating film consisting of the first, second, and third coating films tends to be better.

[0090] [Hydroxygroup-containing resin component] The hydroxyl group-containing resin component in the first, second, and third paint compositions preferably contains a compound having two or more hydroxyl groups in its molecule (i.e., a polyol). Examples of polyols include polyester polyols, polyether polyols, acrylic polyols, polyolefin polyols, and fluorine polyols. Among these, acrylic polyols are preferred from the viewpoint of weather resistance, chemical resistance, and hardness, while polyester polyols are preferred from the viewpoint of mechanical strength and oil resistance.

[0091] (Polyester polyol) Polyester polyols can be obtained, for example, by condensing a dibasic acid (either alone or in a mixture) with a polyhydric alcohol (either alone or in a mixture).

[0092] Examples of the aforementioned dibasic acids include succinic acid, adipic acid, dimer acid, maleic anhydride, phthalic anhydride, isophthalic acid, terephthalic acid, and carboxylic acids such as 1,4-cyclohexanedicarboxylic acid. Examples of the aforementioned polyhydric alcohols include ethylene glycol, propylene glycol, diethylene glycol, 1,4-butanediol, neopentyl glycol, 1,6-hexanediol, trimethylpentanediol, cyclohexanediol, trimethylolpropane, glycerin, pentaerythritol, 2-methylolpropanediol, and ethoxylated trimethylolpropane.

[0093] Specific examples of methods for producing polyester polyols include, for instance, a method in which the above-mentioned components are mixed and then heated at a temperature of approximately 160°C to 220°C to carry out a condensation reaction.

[0094] Alternatively, a specific method for producing polyester polyols is to obtain polycaprolactones by ring-opening polymerization of lactones such as ε-caprolactone using a polyhydric alcohol, and these obtained polycaprolactones can be used as polyester polyols.

[0095] These polyester polyols can be modified using aromatic diisocyanates, aliphatic diisocyanates, alicyclic diisocyanates, and polyisocyanates obtained therefrom. In this case, aliphatic diisocyanates, alicyclic diisocyanates, and polyisocyanates obtained therefrom are particularly preferred from the viewpoint of weather resistance and resistance to yellowing.

[0096] When used as a water-based paint, some carboxylic acids, such as dibasic acids, are left in place and neutralized with bases such as amines and ammonia to create a water-soluble or water-dispersible resin.

[0097] (Polyether polyol) Examples of polyether polyols include polyether polyols obtained by randomly or block adding alkylene oxides to polyvalent hydroxy compounds alone or in mixtures using, for example, hydroxides, strongly basic catalysts, or complex metal cyanide compounds; polyether polyols obtained by reacting alkylene oxides with polyamine compounds such as ethylenediamines; and so-called polymer polyols obtained by polymerizing acrylamide or the like using these polyether polyols as a medium.

[0098] Examples of the hydroxides mentioned above include lithium, sodium, potassium, and the like. Examples of the strongly basic catalyst include alcoholates and alkylamines. Examples of the aforementioned complex metal cyanide compounds include metal porphyrins and zinc hexacyanocobaltate complexes. Examples of the alkylene oxides include ethylene oxide, propylene oxide, butylene oxide, cyclohexene oxide, and styrene oxide.

[0099] Examples of the polyvalent hydroxy compounds include diglycerin, ditrimethylolpropane, pentaerythritol, dipentaerythritol, sugar alcohol compounds, monosaccharides, disaccharides, trisaccharides, tetrasaccharides, and the like. Examples of sugar alcohol compounds include erythritol, D-threitol, L-arabinitol, ribitol, xylitol, sorbitol, mannitol, galactitol, and rhamnitol. Examples of monosaccharides include arabinose, ribose, xylose, glucose, mannose, galactose, fructose, sorbose, rhamnose, fucose, and ribodesose. Examples of disaccharides include trehalose, sucrose, maltose, cellobiose, genthiobiose, lactose, and melibiose. Examples of trisaccharides include raffinose, gentianose, and meletitose. Examples of tetrasaccharides include stachyose.

[0100] (Acrylic polyol) Acrylic polyols can be obtained, for example, by copolymerizing a polymerizable monomer having one or more active hydrogen-containing groups in one molecule with another monomer that is copolymerizable with the polymerizable monomer.

[0101] Examples of polymerizable monomers having one or more active hydrogen-containing groups in a single molecule include acrylic acid esters having active hydrogen-containing groups, methacrylic acid esters having active hydrogen-containing groups, (meth)acrylic acid esters having polyvalent active hydrogen-containing groups, monoethers of polyether polyols and the above-mentioned (meth)acrylic acid esters having active hydrogen-containing groups, adducts of glycidyl (meth)acrylate and monobasic acids, and adducts obtained by ring-opening polymerization of lactones to the active hydrogen-containing groups of the above-mentioned (meth)acrylic acid esters having active hydrogen-containing groups. These may be used individually or in combination of two or more.

[0102] Examples of acrylic acid esters having the active hydrogen-containing group include 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, and 2-hydroxybutyl acrylate.

[0103] Examples of methacrylic acid esters having the active hydrogen-containing group include 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, 2-hydroxybutyl methacrylate, 3-hydroxypropyl methacrylate, and 4-hydroxybutyl methacrylate.

[0104] Examples of (meth)acrylic acid esters having the aforementioned polyvalent active hydrogen-containing group include (meth)acrylic acid monoesters of triols such as glycerin and trimethylolpropane.

[0105] Examples of the aforementioned polyether polyols include polyethylene glycol, polypropylene glycol, and polybutylene glycol.

[0106] Examples of the monobasic acid include acetic acid, propionic acid, and p-tert-butylbenzoic acid.

[0107] Examples of the aforementioned lactones include ε-caprolactam and γ-valerolactone.

[0108] Other monomers copolymerizable with the above polymerizable monomers include, for example, (meth)acrylic acid esters, unsaturated carboxylic acids, unsaturated amides, vinyl monomers having hydrolyzable silyl groups, and other polymerizable monomers. These may be used individually or in combination of two or more.

[0109] Examples of the (meth)acrylic acid esters mentioned above include methyl acrylate, ethyl acrylate, isopropyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, n-hexyl methacrylate, cyclohexyl methacrylate, lauryl methacrylate, and glycidyl methacrylate.

[0110] Examples of unsaturated carboxylic acids include acrylic acid, methacrylic acid, maleic acid, and itaconic acid.

[0111] Examples of unsaturated amides include acrylamide, N-methylolacrylamide, and diacetoneacrylamide.

[0112] Examples of vinyl monomers having hydrolyzable silyl groups include vinyltrimethoxysilane, vinylmethyldimethoxysilane, and γ-(meth)acrylopropyltrimethoxysilane.

[0113] Other polymerizable monomers include, for example, styrene, vinyltoluene, vinyl acetate, acrylonitrile, and dibutyl fumarate.

[0114] For example, acrylic polyols can be obtained by solution polymerization of the above monomer components in the presence of known radical polymerization initiators such as peroxides and azo compounds, and then diluting them with organic solvents as needed.

[0115] Water-based acrylic polyols can be produced by known methods such as solution polymerization of olefinic unsaturated compounds and conversion to an aqueous layer, or emulsion polymerization. In this case, water solubility or water dispersibility can be imparted by neutralizing the acidic portion of carboxylic acid-containing monomers such as acrylic acid and methacrylic acid, or sulfonic acid-containing monomers, with amines or ammonia.

[0116] (Fluorine polyol) Fluorine polyols are polyols that contain fluorine in their molecule, and examples include copolymers of fluoroolefins, cyclovinyl ethers, hydroxyalkyl vinyl ethers, monocarboxylate vinyl esters, etc., as disclosed in Japanese Patent Publication No. 57-34107 (Reference 1) and Japanese Patent Publication No. 61-275311 (Reference 2).

[0117] [Hydroxyl value and acid value of polyols] The lower limit of the hydroxyl value of the polyol is not particularly limited, but is preferably 10 mg KOH / g, more preferably 20 mg KOH / g, and even more preferably 30 mg KOH / g. On the other hand, the upper limit of the hydroxyl value of the polyol is preferably 200 mg KOH / g. In other words, the hydroxyl value of the polyol is preferably 10 mg KOH / g or more and 200 mg KOH / g or less, more preferably 20 mg KOH / g or more and 200 mg KOH / g or less, and even more preferably 30 mg KOH / g or more and 200 mg KOH / g or less. The acid value of the polyol is preferably between 0 mg KOH / g and 30 mg KOH / g. The hydroxyl value and acid value can be measured in accordance with JIS K1557.

[0118] [NCO / OH] When the first and second paint compositions contain a polyisocyanate component, the NCO / OH ratio in the first and second paint compositions is preferably 1.0 or less, and more preferably less than 1.0. When the NCO / OH ratio is below the above upper limit, the polyisocyanate component of the third paint composition tends to penetrate the first and second paint compositions (the first and second uncured coating films) more effectively, allowing the first and second paint compositions to cure more efficiently. Note that when the NCO / OH ratio in the first and second paint compositions is 1.0, the NCO / OH ratio in the third paint composition is greater than 1.0.

[0119] [Other ingredients] The first, second, and third paint compositions may further contain other components in addition to the polyisocyanate component and the hydroxyl group-containing resin component.

[0120] Other components include, for example, unsaturated bond-containing compounds, inert compounds, metal atoms, basic amino compounds, carbon dioxide, halogen atoms, etc. These components may be included individually or in combination of two or more.

[0121] In the first, second, and third paint compositions, the lower limit of the content of other components can be 1.0 ppm by mass, 3.0 ppm by mass, 5.0 ppm by mass, or 10 ppm by mass, based on the content of the polyisocyanate component. On the other hand, the upper limit for the content of other components is 1.0 × 10⁻⁶, based on the content of polyisocyanate components. 4 It can be expressed as a mass in ppm, 5.0 × 10 3 It can be expressed as a mass in ppm, 3.0 × 10 3 It can be expressed as a mass in ppm, 1.0 × 10 3 It can be expressed as ppm (parts per million). In other words, in the first, second, and third paint compositions, the content of other components is determined based on the polyisocyanate component content, from the viewpoint of preventing discoloration during long-term storage and improving long-term storage stability, to be 1.0 ppm by mass or more and 1.0 × 10⁻¹⁶. 4 It can be less than or equal to a mass of ppm, and 3.0 mass ppm or more, up to 5.0 × 10⁻¹⁶ 3 It can be less than or equal to 5.0 ppm by mass, and 3.0 × 10¹⁶ or more by mass. 3 It can be less than or equal to 10 ppm by mass, and 1.0 × 10 ppm or more by mass. 3 The mass can be reduced to ppm or less.

[0122] (Compounds containing unsaturated bonds) Compounds containing unsaturated bonds can be compounds in which the unsaturated bond is a carbon-carbon unsaturated bond, a carbon-nitrogen unsaturated bond, or a carbon-oxygen unsaturated bond. From the viewpoint of compound stability, compounds in which the unsaturated bond is a double bond are preferred, and carbon-carbon double bonds (C=C) or carbon-oxygen double bonds (C=O) are more preferred. Furthermore, the carbon atoms constituting the compound can be carbon atoms bonded to three or more atoms. Generally, carbon-carbon double bonds may be the same carbon-carbon double bonds that constitute an aromatic ring, but the unsaturated bonds contained in unsaturated bond-containing compounds in paint compositions do not include the carbon-carbon double bonds that constitute an aromatic ring. Examples of compounds having a carbon-oxygen double bond include carbon dioxide derivatives. Examples of carbon dioxide derivatives include urea compounds, carbon dioxide esters, N-unsubstituted carbamic acid esters, and N-substituted carbamic acid esters.

[0123] (inert compound) Inert compounds are classified into, for example, compounds A to G below. Specifically, hydrocarbon compounds are classified into compounds A and B, ether compounds and sulfide compounds into compounds C to E below, halogenated hydrocarbon compounds into compound F below, and silicon-containing hydrocarbon compounds, silicon-containing ether compounds, and silicon-containing sulfide compounds into compound G below. Note that compounds A to G listed here do not contain unsaturated bonds other than aromatic rings, and compounds having the unsaturated bonds mentioned above are not included. Compound A: A linear, branched, or cyclic aliphatic hydrocarbon compound. Compound B: An aromatic hydrocarbon compound which may be substituted with an aliphatic hydrocarbon group. Compound C: A compound having an ether structure or a sulfide group and an aliphatic hydrocarbon group, wherein the same or different aliphatic hydrocarbon compounds are bonded via an ether structure or a sulfide group. Compound D: A compound having an ether structure or a sulfide group and an aromatic hydrocarbon group, wherein the same or different aromatic hydrocarbon compounds are bonded via an ether structure or a sulfide group. Compound E: A compound having an ether structure or a sulfide group, an aliphatic hydrocarbon group, and an aromatic hydrocarbon group. Compound F: A halogenated compound in which at least one hydrogen atom constituting an aliphatic hydrocarbon compound, or at least one hydrogen atom constituting an aromatic hydrocarbon compound, is substituted with a halogen atom. Compound G: A compound in which some or all of the carbon atoms in compounds A to E above are replaced with silicon atoms.

[0124] (metal atom) Metal atoms may exist as metal ions or as individual metal atoms. They may be a single type of metal atom or a combination of multiple types of metal atoms. Preferably, the metal atoms are those that can have a valence of 2 to 4, and more preferably, one or more metals selected from iron, cobalt, nickel, zinc, tin, copper, and titanium.

[0125] (Basic amino compounds) Basic amino compounds are derivatives of ammonia, including compounds in which one hydrogen atom is substituted with an alkyl or aryl group (primary), compounds in which two hydrogen atoms are substituted (secondary), and compounds in which all three hydrogen atoms are substituted (tertiary). Among these, secondary or tertiary amino compounds are preferred as basic amino compounds, and aliphatic amines, aromatic amines, heterocyclic amines, or basic amino acids are more preferred.

[0126] (carbon dioxide) The carbon dioxide can be dissolved in isocyanate at atmospheric pressure, or it can be dissolved under pressure in a pressure vessel. Since using carbon dioxide containing moisture may cause hydrolysis of the isocyanate, it is preferable to control the amount of moisture contained in the carbon dioxide as needed.

[0127] (Halogen atom) The halogen atom content in the first and second paint compositions is 1.0 × 10¹⁶, from the viewpoint of preventing discoloration. 2 The concentration is preferably less than ppm by mass. The halogen atom is not particularly limited, but at least one of chlorine and bromine atoms is preferred, and at least one ion or compound selected from the group consisting of chloride ions, bromide ions, hydrolyzable chlorine, and hydrolyzable bromine is more preferred. Examples of hydrolyzable chlorine include carbamoyl chloride compounds in which hydrogen chloride is added to an isocyanate group, and examples of hydrolyzable bromine include carbamoyl bromide compounds in which hydrogen bromide is added to an isocyanate group.

[0128] [Melamine-based hardener] The first, second, and third paint compositions may further contain, as needed, a melamine-based curing agent in addition to the polyisocyanate component and the hydroxyl group-containing resin component. Examples of melamine-based curing agents include fully alkyl, methylol-type alkyl, and imino-group-type alkyl.

[0129] [Organic solvents] Furthermore, the polyisocyanate component, the hydroxyl group-containing resin component, the first paint composition, the second paint composition, and the third paint composition can all be mixed with an organic solvent. The organic solvent is preferably one that does not have functional groups that react with hydroxyl groups and isocyanate groups. It is also preferably one that is compatible with the polyisocyanate component. Such organic solvents can be those commonly used as paint solvents, and specifically, examples include ester compounds, ether compounds, ketone compounds, aromatic compounds, ethylene glycol dialkyl ether compounds, polyethylene glycol dicarboxylate compounds, hydrocarbon solvents, aromatic solvents, and the like.

[0130] [Other additives] The first, second, and third paint compositions may, in addition to the polyisocyanate component and the hydroxyl group-containing resin component, further contain, depending on the purpose and application, various additives used in the art, such as curing accelerators, pigments, leveling agents, antioxidants, ultraviolet absorbers, light stabilizers, plasticizers, and surfactants, to the extent that they do not impair the effects of this embodiment. Examples of catalysts for accelerating curing include metal salts and tertiary amines. Examples of metal salts include dibutyltin dilaurate, tin 2-ethylhexanoate, zinc 2-ethylhexanoate, and cobalt salts. Examples of tertiary amines include triethylamine, pyridine, methylpyridine, benzyldimethylamine, N,N-dimethylcyclohexylamine, N-methylpiperidine, pentamethyldiethylenetriamine, N,N'-endoethylenepiperazine, and N,N'-dimethylpiperazine.

[0131] [Method for manufacturing paint composition] The first paint composition and the second paint composition are obtained by mixing the hydroxyl group-containing resin component with the polyisocyanate component and various additive components, if necessary, using a known method. The third paint composition is obtained by mixing the above-mentioned polyisocyanate component and the above-mentioned hydroxyl group-containing resin component with various additive components as needed, using a known method.

[0132] For example, when manufacturing a water-based paint composition, various additives are added as needed to a hydroxyl group-containing resin component or its aqueous dispersion or aqueous solution. Then, the polyisocyanate component or its aqueous dispersion is added as a curing agent, and water or a solvent is further added as needed to adjust the viscosity. Finally, the mixture is forcibly stirred using a stirring device to obtain a water-based paint composition.

[0133] When manufacturing a solvent-based paint composition, first, various additives are added as needed to a hydroxyl group-containing resin component or its solvent dilution. Next, the polyisocyanate component is added as a curing agent, and a solvent is further added as needed to adjust the viscosity. Then, the mixture is stirred by hand or using a stirring device such as a mixer to obtain the solvent-based paint composition.

[0134] <Object to be coated> There are no particular limitations on the object to be coated, and examples include molded products made from materials such as metal (steel plates, surface-treated steel plates, etc.), plastic, wood, and inorganic materials. Furthermore, the shape of these molded products is not particularly limited; for example, they may be thin, such as films, sheets, or boards, or thick, such as cylinders or three-dimensional structures. They may also be hollow, such as tubes. Furthermore, the object to be coated may be a coating film. Examples of coating films include those obtained by coating and curing a main component such as a polyol and a curing agent such as (blocked) polyisocyanate or melamine, as well as uncured coating films before curing. In the method for forming a multilayer coating laminate described later, it is preferable that the object to be coated is an uncured coating film, and by curing the first, second, and third uncured coating films together by heating, the uncured coating films that are the object to be coated can be made into cured coating films.

[0135] <Application> The multi-layer coating laminate of this embodiment is useful as a primer layer (undercoat layer), intermediate coat layer, and topcoat layer for materials such as metals (steel plates, surface-treated steel plates, etc.), plastics, wood, and inorganic materials. It is also useful as a laminate for imparting aesthetic properties, weather resistance, acid resistance, rust prevention, chipping resistance, etc., to pre-coated metals including rust-resistant steel plates, and automotive paints.

[0136] ≪Method for forming a multi-layer coating laminate≫ The method for forming a multilayer coating laminate of this embodiment (hereinafter sometimes simply referred to as "the method for forming this embodiment") includes applying a first coating composition to an object to be coated to obtain a first uncured coating film, applying a second coating composition on the first uncured coating film to obtain a second uncured coating film, further applying a third coating composition on the second uncured coating film to obtain a third uncured coating film, and then simultaneously curing the first, second, and third uncured coating films by heating to form a multilayer coating laminate consisting of three layers: a first coating film, a second coating film, and a third coating film.

[0137] When a third uncured coating is laminated on the first and second uncured coatings, some of the components in the third coating composition migrate to the first and second uncured coatings, and the polyisocyanate component migrates into the first and second uncured coatings from the third uncured coating side toward the object to be coated, forming a concentration gradient. Therefore, the adhesion between the first, second, and third uncured coatings is improved.

[0138] Furthermore, if the object to be coated is an uncured coating, a pre-coat layer is formed by the migration of the first and second coating compositions onto the uncured coating. The hydroxyl group-containing resin component is also present in the pre-coat layer. Therefore, the first and second uncured coatings are cured in a state of closer adhesion to the object via the pre-coat layer. Moreover, it is preferable that the polyisocyanate component that has migrated from the third uncured coating via the first and second uncured coatings is also present in the pre-coat layer, and the adhesion of the coating can be further enhanced by curing the pre-coat layer, the first uncured coating, the second uncured coating, and the third uncured coating all at once in the presence of the polyisocyanate component. Here, the uncured coating film on the substrate preferably contains a polyol as the main component and further contains a melamine-based curing agent. Examples of melamine-based curing agents include those described in the "Paint Composition" above.

[0139] The first, second, and third uncured coating films can be formed by laminating the first, second, and third coating compositions onto a substrate, coating film, or other object to be coated, using methods such as roll coating, curtain flow coating, spray coating, bell coating, or electrostatic coating.

[0140] In the formation method of this embodiment, after obtaining the third uncured coating film, the lower limit of the heating temperature for simultaneously curing the first uncured coating film, the second uncured coating film, and the third uncured coating film is preferably 60°C, and more preferably 80°C. The upper limit of the heating temperature is preferably 160°C, and more preferably 150°C. The lower limit of the heating time is preferably 10 minutes, and more preferably 15 minutes. The upper limit of the heating time is preferably 40 minutes, and more preferably 35 minutes. By using the above-mentioned range for heating temperature and heating time, the curing properties and resistance to yellowing of the multi-layer coating film are improved.

[0141] In the formation method of this embodiment, after obtaining the first uncured coating film and the second uncured coating film, or before applying the first uncured coating film and the second uncured coating film to the substrate, a short preheating period can be performed. Preheating is a low-temperature, short-duration drying process at approximately 70°C to 80°C for approximately 1 minute to 5 minutes, and can be performed under conditions in which the first and second uncured coating films do not harden.

[0142] ≪Paint kit for forming multi-layer coating laminates≫ The first paint composition, the second paint composition, and the third paint composition can also be combined and provided as a paint kit. That is, in one embodiment, the present invention provides a paint kit for forming a multilayer coating laminate comprising the first paint composition, the second paint composition, and the third paint composition. The first paint composition, the second paint composition, and the third paint composition are provided contained in the first container, the second container, and the third container, respectively. The first container, the second container, and the third container can be any known shape and material used for containing paint. With this paint kit, the polyisocyanate component acts as a curing agent, the penetration of the polyisocyanate component into the lower layer is good, and a multilayer coating laminate with excellent finished appearance, coating hardness, scratch resistance, and weather resistance can be obtained. In this embodiment of the paint kit, the first paint composition, the second paint composition, and the third paint composition have different compositions from each other. Furthermore, the first paint composition, the second paint composition, and the third paint composition have the same configuration as described in the "multilayer coating laminate" above, and therefore their description is omitted. The method of using the paint kit of this embodiment is as described in the "Method for Forming a Multilayer Coating Laminate" above, and therefore its explanation is omitted. [Examples]

[0143] The embodiment will be described in more detail below with reference to specific examples and comparative examples, but the embodiment is not limited in any way by the following examples and comparative examples unless it exceeds the gist of the embodiment. The physical properties of the polyisocyanate component and the evaluation of the coating film in the examples and comparative examples were measured and evaluated as follows. Unless otherwise specified, "parts" and "%" mean "parts by mass" and "mass%" respectively.

[0144] <Method for measuring physical properties> [Physical Properties 1] (Viscosity of polyisocyanate component) The viscosity of the polyisocyanate component was measured at 25°C using an E-type viscometer (Tokimec Co., Ltd.). A standard rotor (1°34' × R24) was used for the measurement. The rotation speed was as follows:

[0145] (Rotation speed) 100 rpm (if less than 128 mPa·s) 50 rpm (when the pressure is between 128 mPa·s and 256 mPa·s) 20 rpm (when the pressure is between 256 mPa·s and less than 640 mPa·s) 10 rpm (when pressure is between 640 mPa·s and 1280 mPa·s) 5 rpm (when pressure is between 1280 mPa·s and 2560 mPa·s) 2.5 rpm (when pressure is between 2560 mPa·s and less than 5120 mPa·s)

[0146] [Physical Properties 2] (Isocyanate group (NCO) content of polyisocyanate component) The NCO content (mass%) of the polyisocyanate component was determined by neutralizing the isocyanate groups in the polyisocyanate component with excess 2N amine, followed by back titration with 1N hydrochloric acid.

[0147] [Physical Properties 3] (Average number of isocyanate groups (Fn) of polyisocyanate components) The Fn of the polyisocyanate component was determined using the following formula. In the formula, Mn represents the number-average molecular weight and was measured using the method described in "Physical Properties 4" below.

[0148] Fn={Mn×(NCO content)×0.01} / 42

[0149] [Physical Properties 4] (Content of components with a number-average molecular weight of 700 or less and content of uretdione dimers) The number-average molecular weight (Mn) of the polyisocyanate component was determined as the number-average molecular weight relative to polystyrene by GPC under the following measurement conditions.

[0150] (Measurement conditions) Equipment: Tosoh Corporation's "HLC-8120GPC" (product name) Column: 1 x "TSKgel SuperH1000" (product name) manufactured by Tosoh Corporation. "TSKgel SuperH2000" (product name) x 1 bottle "TSKgel SuperH3000" (product name) x 1 bottle Carrier: Tetrahydrofuran (THF) Detection method: Differential refractometer Sample concentration: 5 wt / vol% Detection method: Parallax refractometer Flow rate: 0.6mL / min Column temperature: 40℃

[0151] Next, using the obtained molecular weights, the content (mass%) of components with a number-average molecular weight of 700 or less was determined from the following formula.

[0152] "Content (by mass) of components with a molecular weight of 700 or less" = (Mass of components with a molecular weight of 700 or less) / (Total mass of polyisocyanate components) × 100

[0153] Furthermore, the uretdione dimer content (mass %) was determined from the peak ratio of the component with a number-average molecular weight of 336.

[0154] [Physical Properties 5] (Residual HDI monomer content (mass%)) The HDI monomer content in the polyisocyanate component was determined as follows: First, a 20 mL sample vial was placed on a digital balance and approximately 1 g of the polyisocyanate component was accurately weighed. Next, 0.03 g to 0.04 g of nitrobenzene (internal standard solution) was added and accurately weighed. Finally, approximately 9 mL of ethyl acetate was added, the lid was tightly closed, and the mixture was thoroughly mixed to prepare the sample. The prepared sample was analyzed by gas chromatography under the following conditions to quantify the HDI monomer content in the sample.

[0155] (Measurement conditions) Equipment: “GC-8A” manufactured by SHIMADZU Column: Shinwa Chemical Co., Ltd. "Silicone OV-17" Column oven temperature: 120℃ Injection / Detector Temperature: 160℃

[0156] [Physical Properties 6] (Confirmation of isocyanurate group) Using the Avance600 (product name) manufactured by BrukerBiospin, 13 The isocyanurate group was confirmed by 13C-NMR measurement. The specific measurement conditions were as follows:

[0157] (Measurement conditions) 13 ¹ Cryoprobe: CP DUL 600S3 C / HD-05 Z (Manufactured by Bruker BioSpin) Resonance frequency: 150MHz Concentration: 60wt / vol% Shift reference: CDCl3 (77 ppm) Total count: 10,000 times Pulse program: zgpg30 (complete proton decoupling method, 2-second waiting time)

[0158] (Characteristic peaks (chemical shift values) in the components) Isocyanurate group: Strong peak around 148.5 ppm

[0159] [Physical Properties 7] (Distribution ratio of polyisocyanate components and uretdione dimers in the coating film) For each example and comparative example, the sample coated plates were processed using a Microtome to obtain cross-sections of the multi-layer coating laminates. During processing, the sample coated plates were cooled as needed to suppress thermal damage. Specifically, the sample coated plates were left in a -20°C cooling device for 12 hours. This resulted in obtaining smooth coating cross-sections. FT-IR (ATR) measurements were performed on the first and second coating layers of the obtained cross-sections, yielding a value of 1730±50 cm². -1 (Peak derived from ester bonds in hydroxyl group-containing resin components), 1680±50cm -1 (Peak derived from the isocyanurate group of the polyisocyanate component) and 1760±50cm -1 When the peaks of absorbance (peaks derived from the uretdione group of the polyisocyanate component) were denoted as A, B, and C, respectively, the values ​​of B / A and (B+C) / A were calculated. Furthermore, polyisocyanate components P-1 to P-3, diluted with butyl glycol acetate, were forcibly mixed into the first and second coating compositions at concentrations of 1, 2, 5, and 10 mass% / resin, respectively. Subsequently, the coatings were applied to a dry film thickness of 30 μm to 40 μm and dried at 140°C for 30 minutes. FT-IR (ATR) measurements were performed on each coating film, and the values ​​of B / A and (B+C) / A were similarly calculated to create a calibration curve. Based on the created calibration curve and dry film thickness, the distribution ratios of the polyisocyanate component and uretdione dimer in the first and second coating films were calculated. Next, based on the calculated values, the distribution ratios of polyisocyanate components and uretdione dimers in the third coating film were also calculated.

[0160] [Physical Properties 8] (Concentration gradient of trimer component in the third coating film) Micro-IR measurements were performed on the smooth coating cross-sections obtained in "Physical Properties 7" (the outermost surface of the third coating, a point 6 μm from the outermost surface in the thickness direction, and a point 23 μm from the outermost surface in the thickness direction), and the B / A value was calculated. In addition, acrylic polyol (Allnex, "SETALUX DA 665 BA / X (product name)") and polyisocyanate components P-1 to P-3 were mixed with isocyanate group / hydroxyl group (NCO / OH) ratios of 0.5, 0.7, 0.9, 1.0, and 1.1, respectively, and then coated to a dry film thickness of 30 μm to 40 μm, and dried at 140°C for 30 minutes. Micro-IR measurements were performed on each coating, and the B / A value was calculated in the same manner to create a calibration curve. Based on the created calibration curve, the concentration gradient of the trimer component in the third coating was calculated.

[0161] <Evaluation Method> [Evaluation 1] Penetration Based on the values ​​calculated in "Physical Properties 7," the permeability of the polyisocyanate component to the lower layer was evaluated according to the following evaluation criteria.

[0162] (Evaluation criteria: Distribution ratio of polyisocyanate components in the third coating film) ◎: 75% by mass or less ○: 76% by mass or more and 80% by mass or less △: 81% by mass or more and 82% by mass or less ×: 83% by mass or more

[0163] [Rating 2] (Finished appearance: Flop value) The flop values ​​of the sample coated plates obtained in each example and comparative example were measured using BYK-MAC. The finished appearance:flop value was evaluated according to the following evaluation criteria.

[0164] (Evaluation Criteria) ○:30 or less ×: 31 or more

[0165] [Rating 3] (Finished appearance: Glossy (20° and 60°)) Using BYK micro-TRI-gloss, the gloss value (%) of sample coated panels obtained in each example and comparative example was measured at incident angles of 20° and 60°. The gloss value at incident angles of 20° and 60° was evaluated according to the following evaluation criteria for the finished appearance: gloss.

[0166] (Evaluation Criteria) ○: 90% or more △:85% or more and 89% or less ×: 84% or less

[0167] [Rating 4] (Finished appearance: DOI) The DOI (distinctness of image) of the sample coated panels obtained in each example and comparative example was measured using BYK WaveScan. The finished appearance: DOI was evaluated according to the following evaluation criteria. (Evaluation Criteria) ◎: 95 or higher ○: 90 or more and 94 or less △: 85 or more and 89 or less ×: 84 or less

[0168] [Rating 5] (Finished appearance: LW and SW) Using BYK WaveScan, the WaveScan values ​​at long wavelength (LW) and short wavelength (SW) were measured for the surface of the sample coated plates obtained in each example and comparative example. The finished appearance (LW and SW) was evaluated according to the following evaluation criteria.

[0169] (Evaluation criteria: LW) ◎: 2 or less ○: 3 or more and 5 or less △: 6 or more and 8 or less ×: 9 or more

[0170] (Evaluation criteria: SW) ◎: 15 or less ○: 16 or more and 20 or less △:21 or more and 40 or less ×: 41 or more

[0171] [Rating 6] (Coating hardness: Koenig) The König hardness (in degrees) of the sample coated panels obtained in each example and comparative example was measured using an Erichsen pendulum hardness tester. The coating hardness: König was evaluated according to the following evaluation criteria.

[0172] (Evaluation Criteria) ◎: 80 times or more ○: 60 times or more and 79 times or less △: 40 times or more and 59 times or less ×: 39 times or less

[0173] [Rating 7] (Coating film hardness: HM) The Martens hardness (HM) of the sample coated panels obtained in each example and comparative example was measured using a FISCHERSCOPE HM2000 (applying a maximum load of 50mN for 30 seconds, maintaining it for 30 seconds, and then reducing the load to zero for 30 seconds). The coating hardness: HM was evaluated according to the following evaluation criteria.

[0174] (Evaluation Criteria) ◎: 100N / mm 2 That's all. ○: 60N / mm 2 99 N / mm² or more 2 below △: 40 N / mm 2 More than 59N / mm 2 below ×: 39N / mm 2 below

[0175] [Rating 8] (Scratch resistance: Crockmeter) The gloss values ​​at an incident angle of 20° were measured using BYK micro-TRI-gloss before and after a Crockmeter test (3M 9μm sandpaper, load: 9N, 10 reciprocations, reflow at 23°C for 24 hours) on sample coated plates obtained in each example and comparative example. The ratio of the gloss value at an incident angle of 20° after the test to the gloss value at an incident angle of 20° before the test was calculated as the 20° gloss retention rate (%), and scratch resistance: Crockmeter was evaluated according to the following evaluation criteria.

[0176] (Evaluation Criteria: Crockmeter) ◎: 60% or more ○: 55% or more and 59% or less △: 50% or more and 54% or less ×: 49% or less

[0177] [Evaluation 9] (Scratch Resistance: AMTEC) For the sample coated plates obtained in each example and comparative example, before and after the Amtec-Kistler-Test (silica aqueous solution concentration: 1.5 g / L, 10 reciprocations), the gloss value at an incident angle of 20° was measured using BYK micro-TRI-gloss. The ratio of the gloss value at an incident angle of 20° after the test to the gloss value at an incident angle of 20° before the test was calculated as the 20° gloss retention rate (%), and the scratch resistance: AMTEC was evaluated according to the following evaluation criteria.

[0178] (Evaluation Criteria: AMTEC) ◎: 81% or more ○: 71% or more and 80% or less<​​​​​​​​​​​​​​​​○: 90% or more △:85% or more and 89% or less ×: 84% or less

[0181] (Evaluation criteria: color difference) ○: 0.4 or less △: 0.5 or more and 0.9 or less ×: 1.0 or higher

[0182] <Synthesis of polyisocyanate components> [Synthesis Example 1] (Synthesis of polyisocyanate components P-1 and P-1') A four-necked flask equipped with a stirrer, thermometer, reflux condenser, nitrogen inlet tube, and dropping funnel was placed under a nitrogen atmosphere. 6000 g of HDI and 7.0 g of isobutanol were charged into the flask, and the reactor temperature was maintained at 80°C for 2 hours under stirring. Next, 5.0 g of a solution of the isocyanuration catalyst trimethyl-2-methyl-2-hydroxyethylammonium hydroxide diluted to 5% by mass with isobutanol was added, and the isocyanuration reaction was carried out. When the NCO content of the reaction solution reached 44.6% by mass, phosphoric acid was added to stop the reaction. The reaction solution was then maintained at 150°C for another 2 hours. After cooling the reaction solution, it was filtered to remove precipitates, and then purified twice using a thin-film evaporator at 160°C and 0.2 Torr to obtain polyisocyanate component P-1. The obtained polyisocyanate component P-1 had a viscosity of 480 mPa·s (25℃), an NCO content of 23.1% by mass, an average number of isocyanate groups of 3.0, a content of 79% by mass of components with a number average molecular weight of 700 or less, a uretdione dimer content of 12% by mass, and a residual HDI monomer content of 0.15% by mass. 13 1C-NMR measurement confirmed the presence of an isocyanurate group.

[0183] Polyisocyanate component P-1 was further purified once using a thin-film evaporator under conditions of 160°C and 0.2 Torr to obtain polyisocyanate component P-1'. The obtained polyisocyanate component P-1' had a residual HDI monomer content of 0.04% by mass.

[0184] [Synthesis Example 2] (Synthesis of polyisocyanate components P-2 and P-2') A four-necked flask equipped with a stirrer, thermometer, reflux condenser, nitrogen inlet tube, and dropping funnel was placed under a nitrogen atmosphere. 6000 g of HDI and 11.0 g of isobutanol were charged into the flask, and the reactor temperature was maintained at 80°C for 2 hours under stirring. Next, 5.0 g of a solution of the isocyanuration catalyst trimethyl-2-methyl-2-hydroxyethylammonium hydroxide diluted to 5% by mass with isobutanol was added, and the isocyanuration reaction was carried out. When the NCO content of the reaction solution reached 45.5% by mass, phosphoric acid was added to stop the reaction. The reaction solution was then maintained at 150°C for another 2 hours. After cooling the reaction solution, it was filtered to remove precipitates, and then purified twice using a thin-film evaporator at 160°C and 0.2 Torr to obtain polyisocyanate component P-2. The obtained polyisocyanate component P-2 had a viscosity of 280 mPa·s (25℃), an NCO content of 23.2% by mass, an average number of isocyanate groups of 2.8, a content of 80% by mass of components with a number average molecular weight of 700 or less, a uretdione dimer content of 14% by mass, and a residual HDI monomer content of 0.18% by mass. 13 1C-NMR measurement confirmed the presence of an isocyanurate group.

[0185] Polyisocyanate component P-2 was further purified once using a thin-film evaporator under conditions of 160°C and 0.2 Torr to obtain polyisocyanate component P-2'. The obtained polyisocyanate component P-2' had a residual HDI monomer content of 0.05% by mass.

[0186] [Synthesis Example 3] (Synthesis of polyisocyanate component P-3) The inside of a four-necked flask equipped with a stirrer, a thermometer, a reflux condenser, a nitrogen inlet tube, and a dropping funnel was made into a nitrogen atmosphere, 1000 g of HDI was charged, and 0.1 g of trimethylbenzylammonium hydroxide was added as a catalyst while stirring at 60°C. After 4 hours, when the NCO content of the reaction solution reached 39.4% by mass, 0.2 g of phosphoric acid was added to stop the reaction. Next, after cooling, the reaction solution was filtered to remove the precipitate, and then purified twice using a thin-film evaporator under the conditions of 160°C and 0.2 Torr to obtain the polyisocyanate component P-3. The obtained polyisocyanate component P-3 had a viscosity of 2700 mPa·s (25°C), an NCO content of 22.2% by mass, an average number of isocyanate groups of 3.4, a content of components with a number-average molecular weight of 700 or less of 53% by mass, a content of uretdione dimer of 0% by mass, and a residual HDI monomer content of 0.14% by mass. Also, 13 It was confirmed by C-NMR measurement that it has an isocyanurate group.

[0187] The physical properties of each obtained polyisocyanate component are shown in Table 1 below.

[0188]

Table 1

[0189] <Manufacture of Multilayer Coating Laminate> [Example 1] (Preparation of Sample Coated Plate T-a1) As a substrate, a cationic electrodeposited steel sheet was used. As the first coating composition, water-based base-1 (gray) was spray-coated to a dry film thickness of 18 μm and allowed to stand at room temperature for 5 minutes to form a first uncured coating film. Then, as the second coating composition, water-based base-2 (black sapphire color) was spray-coated on the first uncured coating film to a dry film thickness of 13 μm, allowed to stand at room temperature for 5 minutes, and then preheated at 70°C for 5 minutes to obtain a laminate in which the substrate, the first uncured coating film, and the second uncured coating film were laminated in this order. A third paint composition was prepared by first blending an acrylic polyol (Allnex, "SETALUX DA 665 BA / X (product name)") and polyisocyanate component P-1 in a molar ratio of isocyanate group / hydroxyl group (NCO / OH) of 1.1. Additives included BYK-331 at 0.10% by mass / resin, TINUVIN 292 at 1.0% by mass / resin, and TINUVIN 384-2 at 1.5% by mass / resin. This mixture was then diluted with propylene glycol monomethyl ether acetate / solvent naphtha (mass ratio 50 / 50) to achieve a spray viscosity of 27 seconds (ISO 5 cup). This third paint composition was spray-coated onto the second uncured paint film after preheating to achieve a dry film thickness of 40 μm. Subsequently, the sample coated plate T-a1, a laminate having a multi-layer coating, was dried at 120°C for 30 minutes.

[0190] [Examples 2-10 and Comparative Examples 1-4] (Preparation of sample coated panels T-a2 to T-a10 and T-b1 to T-b4) Sample coated plates were obtained using the same method as in Example 1, except that the type of polyisocyanate component, the molar ratio of isocyanate group / hydroxyl group (NCO / OH), and the curing temperature were as shown in Tables 2 to 4.

[0191] For each sample coated board obtained, various physical properties were measured using the method described above, and the penetration, finished appearance, coating hardness, scratch resistance, and weather resistance were evaluated. The results are shown in Tables 2 to 4. In Tables 2 to 4, "-" indicates that measurement or evaluation was not performed.

[0192] [Table 2]

[0193] [Table 3]

[0194] [Table 4]

[0195] Tables 2 to 4 show that in sample coated panels T-a1 to T-a10 (Examples 1 to 10), where the polyisocyanate component was distributed in the first coating film at a ratio of 6% to 11% by mass, the second coating film at 13% to 16% by mass, and the third coating film at 80% by mass or less, the penetration of the polyisocyanate component into the first and second coating films, the finished appearance, coating hardness, scratch resistance, and weather resistance were all excellent. Furthermore, in a comparison of sample coated panels T-a6 and T-a8 (Examples 6 and 8), and T-a7 and T-a9 (Examples 7 and 9), which have different NCO / OH ratios in the third coating composition, the penetration of the polyisocyanate component into the first and second coating films was particularly good in sample coated panels T-a8 and T-a9 (Examples 8 and 9), where the NCO / OH ratio in the third coating composition was 1.4. Furthermore, in a comparison of sample coated panels T-a1 and T-a3 (Examples 1 and 3), T-a2 and T-a4 (Examples 2 and 4), T-a6 and T-a8 (Examples 6 and 8), and T-a7 and T-a9 (Examples 7 and 9) with different NCO / OH ratios in the third coating composition, sample coated panels T-a3, T-a4, T-a8, and T-a9, where the NCO / OH ratio in the third coating composition was 1.4, showed better finished appearance and coating hardness. Furthermore, in a comparison of sample coated panels T-a4 and T-a5 (Examples 4 and 5), and T-a9 and T-a10 (Examples 9 and 10), which had different residual HDI monomer content, T-a5 and T-a10 (Examples 5 and 10), which used a polyisocyanate component with a residual HDI monomer content of 0.10% by mass or less, showed particularly good finished appearance.

[0196] On the other hand, in the sample coated panels T-b1 and T-b2 (Comparative Examples 1 and 2), in which the distribution ratio of polyisocyanate components in the first coating film was less than 5% by mass and the distribution ratio of polyisocyanate components in the third coating film was more than 80% by mass, and in the sample coated panels T-b1 and T-b2 (Comparative Examples 3 and 4), in which the distribution ratio of polyisocyanate components in the second coating film was less than 12% by mass and the distribution ratio of polyisocyanate components in the third coating film was more than 80% by mass, no sample was obtained that exhibited superior penetration of the polyisocyanate components into the first and second coating films, excellent finish appearance, coating film hardness, scratch resistance, and weather resistance. [Industrial applicability]

[0197] The multilayer coating laminate of this embodiment exhibits good penetration of the polyisocyanate component into the underlying layer, providing a multilayer coating laminate with excellent finish appearance, coating hardness, scratch resistance, and weather resistance. The paint kit for forming a multilayer coating laminate and the method for forming a multilayer coating laminate of this embodiment also provide a multilayer coating laminate with good penetration of the polyisocyanate component into the underlying layer, resulting in a multilayer coating laminate with excellent finish appearance, coating hardness, scratch resistance, and weather resistance.

Claims

1. On the object to be coated, A first coating film formed by curing a first coating composition; A second coating film formed by curing the second coating composition; A third coating film formed by curing a third coating composition; A multilayer coating film laminate formed by laminating the above in this order, the first coating composition and the second coating composition contain a hydroxyl group-containing resin component, the third coating composition comprises a hydroxyl group-containing resin component and a polyisocyanate component, A multilayer coating film laminate, in which the polyisocyanate component is distributed in a ratio of 5% by mass or more and 15% by mass or less in the first coating film, 12% by mass or more and 20% by mass or less in the second coating film, and 80% by mass or less in the third coating film.

2. the polyisocyanate component includes a polyisocyanate having an isocyanurate group derived from an aliphatic diisocyanate monomer including 1,6-hexamethylene diisocyanate; the content of components having a number average molecular weight of 700 or less is 70% by mass or more relative to the total mass of the polyisocyanate component; the content of the uretdione dimer is 2% by mass or more and 30% by mass or less based on the total mass of the polyisocyanate component, The average number of isocyanate groups in the polyisocyanate component is 2.7 or more, and 2. The multilayer coating film laminate according to claim 1, wherein the uretdione dimer is distributed in a ratio of 10% by mass or more to 40% by mass or less in the first coating film, 1% by mass or more to 10% by mass or less in the second coating film, and 80% by mass or less in the third coating film.

3. The multilayer coating film laminate according to claim 1 or 2, wherein the content of the diisocyanate monomer in the polyisocyanate component is 0.10 mass% or less relative to the total mass of the polyisocyanate component.

4. The multilayer coating film laminate according to any one of claims 1 to 3, wherein the ratio NCO / OH of the molar concentration of the isocyanate group of the polyisocyanate component to the molar concentration of the hydroxyl group of the hydroxyl group-containing resin component in the third coating composition is 0.8 or more and 3.0 or less.

5. a first coating composition contained in a first container; a second coating composition contained in a second container; a third coating composition contained in a third container; A paint kit for forming a multilayer coating film laminate, comprising: the first coating composition and the second coating composition contain a hydroxyl group-containing resin component, the third coating composition comprises a hydroxyl group-containing resin component and a polyisocyanate component, the polyisocyanate component includes a polyisocyanate having an isocyanurate group derived from an aliphatic diisocyanate monomer including 1,6-hexamethylene diisocyanate; the content of components having a number average molecular weight of 700 or less is 70% by mass or more relative to the total mass of the polyisocyanate component; the content of the uretdione dimer is 2% by mass or more and 30% by mass or less based on the total mass of the polyisocyanate component, the average number of isocyanate groups in the polyisocyanate component is 2.7 or more, In the third coating composition, the ratio NCO / OH of the molar concentration of the isocyanate groups of the polyisocyanate component to the molar concentration of the hydroxyl groups of the hydroxyl group-containing resin component is 0.8 or more and 3.0 or less, A paint kit for forming a multilayer paint film laminate, wherein the first paint composition, the second paint composition, and the third paint composition have compositions different from one another.

6. A method for forming a multilayer coating film laminate, comprising: applying a first coating composition onto a substrate to obtain a first uncured coating film; applying a second coating composition onto the first uncured coating film to obtain a second uncured coating film; applying a third coating composition onto the second uncured coating film to obtain a third uncured coating film; and then simultaneously curing the first uncured coating film, the second uncured coating film, and the third uncured coating film by heating to form a multilayer coating film laminate consisting of three layers: the first coating film, the second coating film, and the third coating film; the first coating composition and the second coating composition contain a hydroxyl group-containing resin component, the third coating composition comprises a hydroxyl group-containing resin component and a polyisocyanate component, A method for forming a multilayer coating film laminate, wherein the polyisocyanate component is distributed in a ratio of 5% by mass or more to 15% by mass or less in the first coating film, 12% by mass or more to 20% by mass or less in the second coating film, and 80% by mass or less in the third coating film.