Coating composition, kit, coated film, and method for forming a coated film

Abstract

A coating composition comprising an organic polyisocyanate (A) and an acrylic polyol (B), the organic polyisocyanate (A) comprising a modified polyisocyanate (a), the modified polyisocyanate (a) being a reaction product of a polyisocyanate component (a1) and a polyol component (a2) or a modified product thereof, the polyisocyanate component (a1) comprising an organic diisocyanate or a modified product thereof, the polyol component (a2) comprising at least one selected from the group consisting of polytetramethylene glycol and polycarbonate polyol having a number average molecular weight of 200 to 750, the acrylic polyol (B) comprising an acrylic polyol (b) having a glass transition temperature of 5 to 30°C and a hydroxyl value of more than 100 mgKOH / g and 150 mgKOH / g or less.

Description

Technical Field

[0001] This invention relates to coating compositions, kits, coating films, and methods for forming coating films. Background Technology

[0002] Hard coating is known to form a coating film with excellent scratch resistance and stain resistance on the surface of molded plastic parts. Hard coating is a method for forming a coating film with high cross-linking density and surface hardness. However, once a scratch occurs on the coating film formed by hard coating, cracks will develop from that location. Furthermore, when hard-coated molded plastic parts are used as exterior automotive components, sand, small stones, etc., can collide with the molded parts during vehicle operation, causing micro-indentations (dents, etc.) on the surface (coated surface). In the case of hard coating, the problem of scratches on the coated surface can be avoided by thickening the coating film, but the increased film thickness leads to a decrease in appearance and a heavier exterior component.

[0003] Therefore, soft coating treatments are gradually becoming more popular as an alternative to hard coating treatments. These soft coating treatments utilize coating compositions that absorb external forces and restore scratches (hereinafter referred to as "self-healing") to form a coating film. For example, Patent Document 1 discloses a coating composition for soft coating treatments comprising: a polycarbonate diol containing specific repeating units and terminal hydroxyl groups, wherein the average carbon number of the specific repeating units is 3.0 to 4.0; a polyol other than the polycarbonate diol; and an organic polyisocyanate. In Patent Document 1, this coating composition yields a coating film that combines high scratch recovery and stain resistance.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2019-137840 Summary of the Invention

[0007] The problem the invention aims to solve

[0008] However, the coating film based on the coating composition of Patent Document 1 has a long scratch recovery time, and its stain resistance cannot be said to be sufficient.

[0009] One aspect of the present invention relates to providing a coating film with good stain resistance and excellent self-healing properties for scratches. Another aspect of the present invention relates to providing a coating film with good smoothness, stain resistance, and adhesion, and excellent self-healing properties for scratches. Furthermore, other aspects of the present invention relate to providing a coating composition that facilitates the preparation of the above-mentioned coating film, a kit for preparing the coating composition, and a method for forming the above-mentioned coating film.

[0010] Solution for solving the problem

[0011] The various embodiments of the present invention include the following [1] to

[11] .

[0012] [1] A coating composition comprising an organic polyisocyanate (A) and an acrylic polyol (B), wherein the organic polyisocyanate (A) comprises a modified polyisocyanate (a), wherein the modified polyisocyanate (a) is a reaction product of a polyisocyanate component (a1) and a polyol component (a2) or a modified thereof, wherein the polyisocyanate component (a1) comprises an organic diisocyanate or a modified thereof, wherein the polyol component (a2) comprises at least one of a polytetramethylene glycol and polycarbonate polyols having a number average molecular weight of 200 to 750, and wherein the acrylic polyol (B) comprises an acrylic polyol (b) having a glass transition temperature of 5 to 30°C and a hydroxyl value greater than 100 mg KOH / g and less than 150 mg KOH / g.

[0013] [2] According to the coating composition of [1], wherein the average number of functional groups of the aforementioned modified polyisocyanate (a) is 4.0 to 6.0.

[0014] [3] The coating composition according to [1] or [2], wherein the aforementioned polyisocyanate component (a1) comprises at least one selected from the group consisting of aliphatic diisocyanates and alicyclic diisocyanates.

[0015] [4] The coating composition according to any one of [1] to [3], wherein the aforementioned modified polyisocyanate (a) comprises urea-formate modified polyisocyanate.

[0016] [5] The coating composition according to [4], wherein the aforementioned modified polyisocyanate (a) further comprises isocyanurate modified polyisocyanate.

[0017] [6] The coating composition according to any one of [1] to [5] further comprises a polydimethylsiloxane compound.

[0018] [7] According to the coating composition of [6], the silicon content converted from SiO2 is 0.001 to 0.1% by mass, based on the total amount of the aforementioned organic polyisocyanate (A), the aforementioned acrylic polyol (B) and the aforementioned polydimethylsiloxane compound.

[0019] [8] The coating composition according to any one of [1] to [7], wherein the ratio of the number of moles of isocyanate groups in the isocyanate-containing compound contained in the coating composition to the number of moles of hydroxyl groups in the hydroxyl-containing compound contained in the coating composition is 0.8 to 1.3.

[0020] [9] A kit for preparing a coating composition as described in any one of [1] to [8], the kit comprising: a first reagent comprising the aforementioned organic polyisocyanate (A) and a second reagent comprising the aforementioned acrylic polyol (B).

[0021]

[10] A coating film comprising a cured product of any one of the coating compositions described in [1] to [8].

[0022]

[11] A method for forming a coating film, comprising: applying the coating composition described in any one of [1] to [8] onto a substrate and curing it thereon.

[0023] The effects of the invention

[0024] According to one aspect of the present invention, a coating film with good stain resistance and excellent self-healing properties for scratches can be provided. Furthermore, according to other aspects of the present invention, a coating film with good smoothness, stain resistance, and adhesion, and excellent self-healing properties for scratches can be provided. Additionally, according to other aspects of the present invention, a coating composition that facilitates the preparation of the above-mentioned coating film, a kit for preparing the coating composition, and a method for forming the above-mentioned coating film can be provided. Detailed Implementation

[0025] The exemplary embodiments for carrying out the various aspects of the present invention will be described in further detail. However, the present invention is not limited to the following embodiments.

[0026] It should be noted that in this specification, the numerical range indicated by "~" represents the range in which the values ​​before and after "~" are respectively the minimum and maximum values. Furthermore, unless specifically stated otherwise, the units of the values ​​before and after "~" are the same. Additionally, the upper or lower limit of the numerical range described in this specification can be replaced with the values ​​shown in the embodiments. Furthermore, the individually stated upper and lower limits can be combined arbitrarily. Also, in this specification, "(meth)acrylic acid" refers to at least one of acrylic acid and its corresponding methacrylic acid.

[0027] <Coating Composition>

[0028] One aspect of the coating composition of the present invention comprises an organic polyisocyanate (A) and an acrylic polyol (B). The organic polyisocyanate (A) comprises a modified polyisocyanate (a), which is a reaction product of the polyisocyanate component (a1) and the polyol component (a2) or a modified thereof. The polyisocyanate component (a1) comprises an organic diisocyanate or a modified thereof. The polyol component (a2) comprises at least one polyol selected from the group consisting of polytetramethylene glycol and polycarbonate polyols with a number average molecular weight of 200 to 750. The acrylic polyol (B) comprises an acrylic polyol (b) with a glass transition temperature of 5 to 30°C and a hydroxyl value greater than 100 mg KOH / g and less than 150 mg KOH / g.

[0029] According to one aspect of the coating composition of the present invention, a coating film with good stain resistance and excellent self-healing properties for scratches can be obtained. Furthermore, according to one aspect of the coating composition of the present invention, a coating film with good smoothness and adhesion can also be obtained. The following describes a coating composition of one aspect of the present invention and details the components that may be contained in the coating composition.

[0030] (Organic polyisocyanate (A))

[0031] Organic polyisocyanate (A) includes modified polyisocyanate (a). Modified polyisocyanate (a) is the reaction product of polyisocyanate component (a1) and polyol component (a2) or a modified form thereof.

[0032] The reaction product can be a urethane-modified polyisocyanate obtained by reacting a polyisocyanate component (a1) with a polyol component (a2), or a urethane-modified polyisocyanate obtained by urethane-modified polyisocyanate by urethane-formaldehyde esterification, or an isocyanurate-modified polyisocyanate obtained by isocyanurate esterification of the urethane-modified polyisocyanate.

[0033] Examples of modified compounds include end-capped modified compounds of the reaction products described above. These end-capped modified compounds have a structure obtained by modifying a portion of the isocyanate group with a capping agent. The capping agent prevents the isocyanate group from reacting with water and active hydrogen groups such as hydroxyl groups by capping the isocyanate group, thereby inhibiting the reaction in the coating composition. Therefore, using end-capped modified compounds, single-component formulation is easily achieved. The modified polyisocyanate (a) used as an end-capped modified compound is a potential curing agent that reacts with active hydrogen groups by heating to dissociate the capping agent and reactivate the isocyanate group. Details of the capping agent will be described later. It should be noted that in the following description, urea-formate modified polyisocyanates and isocyanurate modified polyisocyanates include end-capped urea-formate modified polyisocyanates and isocyanurate modified polyisocyanates.

[0034] The modified polyisocyanate (a) preferably contains a urea-formaldehyde modified polyisocyanate. Since the modified polyisocyanate (a) contains a urea-formaldehyde modified polyisocyanate, it has the effects of obtaining a soft and tough coating film, being able to form a liquid with lower viscosity, and improving workability during coating, thereby further improving the self-healing properties of the coating film.

[0035] From the viewpoint of obtaining a softer and stronger coating film, the modified polyisocyanate (a) may include the urea-formate modified polyisocyanate and the isocyanurate modified polyisocyanate. The inclusion of the isocyanurate modified polyisocyanate in the modified polyisocyanate (a) leads to an increase in the glass transition temperature of the resulting coating film (the polyurethane resin in the coating film), while in order to lower this glass transition temperature, by, for example, increasing the content of structures derived from polycarbonate polyols, it is possible to suppress self-healing damage.

[0036] When modified polyisocyanate (a) contains urea-formate modified polyisocyanate or isocyanurate modified polyisocyanate, the fewer the number of urethane groups in modified polyisocyanate (a), the better the self-healing property of the coating film. From this perspective, modified polyisocyanate (a) can be substantially free of urethane groups. Modified polyisocyanate (a) being substantially free of urethane groups means that, based on the total amount of urea-formate modified polyisocyanate, isocyanurate modified polyisocyanate, and urethane modified polyisocyanate, proton nuclear magnetic resonance (NMR) is used to measure the self-healing property of the coating film. 1 The urethane-modified polyisocyanate content confirmed by H-NMR spectroscopy was less than 0.5 mol%.

[0037] From the perspective of further improving the self-healing properties of the coating, based on the total mass of the modified polyisocyanate (a), the content (total amount) of urea carbamate-modified polyisocyanate and isocyanurate-modified polyisocyanate in the modified polyisocyanate (a) can be above 80% by mass, above 90% by mass, or even 100% by mass.

[0038] When the modified polyisocyanate (a) includes urea-formate modified polyisocyanate and isocyanurate modified polyisocyanate, from the viewpoint of further improving the self-healing properties of the coating, based on the total amount of urea-formate modified polyisocyanate and isocyanurate modified polyisocyanate, the content of isocyanurate modified polyisocyanate can be less than 30 mol%, less than 20 mol%, or less than 10 mol%. From the viewpoint of further improving the stain resistance of the coating, based on the total amount of urea-formate modified polyisocyanate and isocyanurate modified polyisocyanate, the content of isocyanurate modified polyisocyanate can be more than 1 mol%, more than 2 mol%, or more than 3 mol%. From the above viewpoints, the content of isocyanurate modified polyisocyanate can be 1–30 mol%, 2–20 mol%, or 3–10 mol%. The above contents can be determined by proton nuclear magnetic resonance (NMR). 1 The 1H-NMR spectrum was used for confirmation.

[0039] From the viewpoint of obtaining a coating with superior self-healing properties, the average number of functional groups in the modified polyisocyanate (a) can be 4.0 or more, or 4.5 or more. From the viewpoint of viscosity, the average number of functional groups in the modified polyisocyanate (a) can be 6.0 or less, or 5.5 or less. From the above viewpoints, the average number of functional groups in the modified polyisocyanate (a) can be 4.0 to 6.0 or 4.5 to 5.5.

[0040] In this specification, the average number of functional groups in modified polyisocyanate (a) refers to the average number of isocyanate groups (-NCO) contained in each molecule of modified polyisocyanate (a). The average number of functional groups in modified polyisocyanate (a) can be calculated based on the isocyanate group content (NCO content) and number average molecular weight of modified polyisocyanate (a). In the case where the modified polyisocyanate (a) is an end-capped modifier, the average number of functional groups also includes the number of end-capped isocyanate groups.

[0041] The NCO content of the modified polyisocyanate (a) can be 13.0–23.0% by mass, 14.0%–22.0% by mass, or 15.0%–21.0% by mass. When the NCO content of the modified polyisocyanate (a) is below 23.0% by mass, the self-healing properties of the coating film are further improved. When the NCO content of the modified polyisocyanate (a) is above 13.0% by mass, the stain resistance of the coating film becomes good.

[0042] In this specification, the NCO content is determined by the method described in JIS K1603-1 (Test Method for Aromatic Isocyanates in Polyurethane Raw Materials). However, when the modified polyisocyanate (a) is an end-capped modifier, the NCO content of the modified polyisocyanate (a) is measured in the uncapped state (the state in which the end-capping agent is dissociated).

[0043] The number-average molecular weight of the modified polyisocyanate (a) can be 500–8,000, 600–7,500, or 700–7,000. When the number-average molecular weight of the modified polyisocyanate (a) is above 500, the self-healing properties of the coating are further improved. When the number-average molecular weight of the modified polyisocyanate (a) is below 8,000, the smoothness and appearance of the coating are further improved.

[0044] In this specification, the number-average molecular weight is a value determined using GPC (gel permeation chromatography) under the following conditions. Specifically, when the modified polyisocyanate (a) is a capped modifier, the number-average molecular weight of the modified polyisocyanate (a) is measured in its uncapped state (the state in which the capping agent is dissociated).

[0045] [condition]

[0046] • Measuring instrument: "HLC-8120" (manufactured by Tosoh Corporation)

[0047] • Pillar: “TSKguardcolumn HXL-L” (Made by Tosoh Corporation)

[0048] Particle size = 6μm, Size = 6mmID × 30cm × 4 pieces

[0049] • Support: Tetrahydrofuran (THF)

[0050] • Detector: Parallax Refraction

[0051] • Sample: 0.1% THF solution

[0052] Standard curve: Polystyrene

[0053] The viscosity of the modified polyisocyanate (a) at 25°C can be 500–10000 mPa·s, 800–6000 mPa·s, or 1000–3000 mPa·s. When the viscosity of the modified polyisocyanate (a) at 25°C is within the above range, the film-forming properties become better, the smoothness of the film is further improved, and the appearance of the film is further improved. The viscosity of the modified polyisocyanate (a) at 25°C is the value measured using a type B viscometer.

[0054] The organic polyisocyanate (A) may contain only one modified polyisocyanate (a) or a combination of two or more. Furthermore, as long as it does not impair self-healing properties, the organic polyisocyanate (A) may also contain other organic polyisocyanates besides the modified polyisocyanate (a) (e.g., polyisocyanate component (a1) as a reaction raw material). The content of the modified polyisocyanate (a) in the organic polyisocyanate (A) is preferably 80% by mass or more, more preferably 90% by mass, and even more preferably 100% by mass, based on the total mass of the organic polyisocyanate (A). The content of the free polyisocyanate component (a1) may be 1.0% by mass or less, based on the total mass of the organic polyisocyanate (A).

[0055] Next, the polyisocyanate component (a1) and polyol component (a2) used as reaction raw materials for modified polyisocyanate (a), as well as the method for manufacturing modified polyisocyanate (a), will be described.

[0056] [Polyisocyanate component (a1)]

[0057] The polyisocyanate component (a1) is a component composed of an organic compound having multiple isocyanate groups, including an organic diisocyanate or a modified form thereof. An organic diisocyanate is an organic compound having two isocyanate groups. Examples of organic diisocyanates include aromatic diisocyanates, aromatic aliphatic diisocyanates, aliphatic diisocyanates, and alicyclic diisocyanates. The modified form can be a modified form of these organic diisocyanates. Examples of modified forms include urea-formate modified polyisocyanates, isocyanurate modified polyisocyanates, urea-dione modified polyisocyanates, carbamate modified polyisocyanates, biuret modified polyisocyanates, urea-ketimide modified polyisocyanates, acylurea modified polyisocyanates, etc. The polyisocyanate component (a1) can be one selected from the above-mentioned organic diisocyanates and modified forms, or a mixture of two or more selected from the above-mentioned organic diisocyanates and modified forms.

[0058] Examples of aromatic diisocyanates include: 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, mixtures of 2,4-toluene diisocyanate and 2,6-toluene diisocyanate, m-phenylenedimethyl diisocyanate, terephthalic diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, mixtures of 2,4'-diphenylmethane diisocyanate and 4,4'-diphenylmethane diisocyanate, etc. '-Diphenyl ether diisocyanate, 2-nitrodiphenyl-4,4'-diisocyanate, 2,2'-diphenylpropane-4,4'-diisocyanate, 3,3'-dimethyldiphenylmethane-4,4'-diisocyanate, 4,4'-diphenylpropane diisocyanate, isophenyl diisocyanate, terephthalic diisocyanate, naphthalene-1,4-diisocyanate, naphthalene-1,5-diisocyanate, 3,3'-dimethoxydiphenyl-4,4'-diisocyanate, etc.

[0059] Examples of aromatic aliphatic diisocyanates include, for example, 1,3- or 1,4-phenyldimethyl diisocyanate or mixtures thereof, 1,3- or 1,4-bis(1-isocyanate-1-methylethyl)benzene or mixtures thereof, ω,ω'-isocyanate-1,4-diethylbenzene, etc.

[0060] Examples of aliphatic diisocyanates include hexamethylene diisocyanate, tetramethylene diisocyanate, 2-methyl-pentane-1,5-diisocyanate, 3-methyl-pentane-1,5-diisocyanate, lysine diisocyanate, and trioxyethylidene diisocyanate.

[0061] Examples of alicyclic diisocyanates include: isophorone diisocyanate, cyclohexyl diisocyanate, hydrogenated diphenylmethane diisocyanate, norbornene diisocyanate, hydrogenated toluene diisocyanate, hydrogenated diphenylmethylene diisocyanate, and hydrogenated tetramethyldiphenylmethylene diisocyanate.

[0062] From the viewpoint of coating film weather resistance, organic diisocyanates are preferred, and at least one selected from the group consisting of aliphatic and alicyclic diisocyanates is more preferred. Furthermore, from the viewpoint of coating film weather resistance, polyisocyanates without unsaturated bonds are preferred. That is, at least one selected from the group consisting of aliphatic and alicyclic diisocyanates without unsaturated bonds is even more preferred. Among these, hexamethylene diisocyanate is particularly preferred from the viewpoint of obtaining a coating film that is readily available and synthesized and possesses further excellent adhesion and self-healing properties.

[0063] The polyisocyanate component (a1) may contain polyisocyanates other than organic diisocyanates and their modifiers. The content (total) of organic diisocyanates and their modifiers in the polyisocyanate component (a1) is preferably 80% by mass or more, more preferably 90% by mass, and even more preferably 100% by mass, based on the total mass of the polyisocyanate component (a1).

[0064] [Polyol component (a2)]

[0065] The polyol component (a2) is a component composed of organic compounds having multiple hydroxyl groups. The polyol component (a2) includes at least one polyol selected from the group consisting of polytetramethylene glycol and polycarbonate polyols, with a number average molecular weight of 200 to 750.

[0066] Polytetramethylene glycol (PTG) is a compound with an oxytetramethylene group in its molecular backbone, primarily obtained through the ring-opening polymerization of tetrahydrofuran. The number average molecular weight of PTG ranges from 200 to 750, but can be above 220 or 250, below 600 or 500, or between 220 and 600 or 250 and 500. A higher number average molecular weight of PTG generally results in better self-healing properties of the coating, while a lower number average molecular weight generally leads to smoother coatings and a better overall appearance.

[0067] Polycarbonate polyols are compounds having multiple carbonate groups and multiple hydroxyl groups, primarily obtained by the dealcoholization or dephenolization reaction of low molecular weight polyols (e.g., polyols with a molecular weight of less than 500) with carbonates. Examples of polycarbonate polyols include compounds (reaction products) obtained by the dealcoholization or dephenolization reaction of at least one compound selected from the group of compounds shown below (α) with at least one compound selected from the group of compounds shown below (β).

[0068] (α): Ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,8-octanediol, 1,9-nonanediol, 3-methyl-1,5-pentanediol, 3,3-dimethylolheptane, diethylene glycol, dipropylene glycol, neopentanediol, diethylene glycol, dipropylene glycol, cyclohexane-1,4-diol, cyclohexane-1,4-diethanol, dimer glycol, ethylene oxide adduct of bisphenol A, propylene oxide adduct of bisphenol A, bis(β-hydroxyethyl)benzene, benzenediethanol, glycerol, trimethylolpropane, pentaerythritol, and other low molecular weight polyols.

[0069] (β): Dialkyl carbonates such as dimethyl carbonate and diethyl carbonate; alkyl carbonates such as ethylene carbonate and propylene carbonate; diphenyl carbonate, dinaphthalene carbonate, dianthrene carbonate, dianthrene carbonate, diphenanthracene carbonate, diindene carbonate, diindene carbonate, tetrahydronaphthalene carbonate, and other diaryl carbonates.

[0070] From the viewpoint of further improving the stain resistance of the coating film, the preferred material is the substance obtained by the dealcoating reaction of 1,6-hexanediol and dialkyl carbonate (the reaction product of 1,6-hexanediol and dialkyl carbonate).

[0071] The number average molecular weight of polycarbonate polyols ranges from 200 to 750, but can be above 220, 250, or 300, or below 600, 500, or 400, or even 220–600, 250–500, 300–750, or 200–400. The higher the number average molecular weight of the polycarbonate polyol, the easier it is to improve the self-healing properties of the coating; conversely, the lower the number average molecular weight, the easier it is to achieve good smoothness and a good coating appearance.

[0072] The polyol component (a2) may contain polyols other than polytetramethylene glycol and polycarbonate polyols. In other words, the modified polyisocyanate (a) may be a reaction product of the polyisocyanate component (a1) (e.g., an organic diisocyanate or its modifier) ​​with at least one polyol selected from the group consisting of polytetramethylene glycol and polycarbonate polyols with a number average molecular weight of 200 to 750, and other polyols. The content (total amount) of polytetramethylene glycol and polycarbonate polyols in the polyol component (a2) is preferably 80% by mass or more, more preferably 90% by mass, and even more preferably 100% by mass, based on the total mass of the polyol component (a2).

[0073] Other polyols include, for example, ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,8-octanediol, 1,9-nonanediol, 3-methyl-1,5-pentanediol, 2-ethyl-1,3-hexanediol, 3,3-dimethylolheptane, diethylene glycol, dipropylene glycol, neopentanediol, cyclohexane-1,4-diol, cyclohexane-1,4-diethanol, dimer glycol, ethylene oxide adduct of bisphenol A, propylene oxide adduct of bisphenol A, bis(β-hydroxyethyl)benzene, benzenediethanol, glycerol, trimethylolpropane, pentaerythritol, etc. Other polyols may be used as one compound or in combination of two or more compounds.

[0074] Other types of polyols that can be used include polyester polyols, polyether polyols, acrylic polyols, polyolefin polyols, fluorinated polyols, and animal and vegetable oil polyols.

[0075] [Method for manufacturing modified polyisocyanate (a)]

[0076] Modified polyisocyanates (a) can be obtained, for example, through steps 1 to 4 described below.

[0077] Step 1: Add polyisocyanate component (a1) and polyol component (a2) in excess of isocyanate group relative to hydroxyl group to carry out urethane esterification reaction to obtain isocyanate group-terminated prepolymer I.

[0078] • Step 2: Add a catalyst to isocyanate-terminated prepolymer I and ureate it at 70-150°C to produce isocyanate-terminated prepolymer II.

[0079] • Step 3: The reaction is terminated by adding a reaction terminator to isocyanate-terminated prepolymer II.

[0080] • Step 4: Remove the free polyisocyanate component (a1) by thin-film distillation or solvent extraction of isocyanate-terminated prepolymer II to obtain modified polyisocyanate (a).

[0081] In steps 1 through 3 described above, the reaction is carried out under a nitrogen or dry air stream. Steps 1 through 3 described above can be carried out in the presence of an organic solvent or in the absence of an organic solvent.

[0082] As organic solvents, various organic solvents that do not affect the reaction can be used. Examples of organic solvents include: aliphatic hydrocarbons such as octane; alicyclic hydrocarbons such as cyclohexane and methylcyclohexane; ketones such as methyl isobutyl ketone and cyclohexanone; esters such as butyl acetate and isobutyl acetate; glycol ether esters such as ethylene glycol ethyl ether acetate, propylene glycol monomethyl ether acetate, 3-methyl-3-methoxybutyl acetate, and ethyl-3-ethoxypropionate; ethers such as dioxane; halogenated hydrocarbons such as diiodomethane and monochlorobenzene; and polar aprotic solvents such as N-methylpyrrolidone, dimethylformamide, dimethylacetamide, dimethyl sulfoxide, and hexamethylphosphonamide. These organic solvents can be used individually or in combination of two or more.

[0083] Next, taking the manufacturing process of the modified polyisocyanate (a) mainly modified with urea carbamate as an example, the manufacturing method of the modified polyisocyanate (a) of one embodiment will be further explained.

[0084] [Step 1: Step in manufacturing isocyanate-terminated prepolymer I]

[0085] In the first step, isocyanate-terminated prepolymer I is produced by reacting a polyisocyanate component (a1) and a polyol component (a2). The amounts of polyisocyanate component (a1) and polyol component (a2) added are set to an excess of isocyanate groups relative to hydroxyl groups.

[0086] As the "amount of isocyanate groups in excess relative to hydroxyl groups", it can be the number of moles of isocyanate groups (M') in the polyisocyanate component (a1). NCO The number of moles of hydroxyl groups in polyol component (a2) and (M') OH The ratio of R' (=M') to M' NCO / M' OH The amount of R' can reach 6 to 40, or it can be 7 to 30. When the R' is above 6, the excess of isocyanurate-modified polyisocyanate in the obtained modified polyisocyanate (a) can be further suppressed. When the R' is below 40, the increase in the amount of polyisocyanate containing urethane groups in the obtained modified polyisocyanate (a) is further suppressed, the decrease in the number of functional groups is further suppressed, and the productivity and yield are further improved.

[0087] The temperature at which the polyisocyanate component (a1) reacts with the polyol component (a2) (the carbamate reaction temperature) is, for example, 20–120°C, or 20–100°C or 50–100°C. The reaction time of the carbamate reaction varies depending on the presence, type, and temperature of the catalyst, but is usually less than 10 hours, or 1–5 hours.

[0088] In the carbamate reaction, known carbamate catalysts can be used. Examples of carbamate catalysts include organometallic compounds such as dibutyltin diacetate, dibutyltin dilaurate, and dioctyltin dilaurate; organic amines such as triethylenediamine and triethylamine, or their salts; etc. These catalysts can be used alone or in combination of two or more.

[0089] [Step 2: Step in manufacturing isocyanate-terminated prepolymer II]

[0090] In step 2, after the urethane esterification reaction in step 1, a urea-formaldehyde esterification reaction is further carried out to produce isocyanate-terminated prepolymer II. At this time, the urea-formaldehyde esterification reaction can be carried out simultaneously (in parallel) with the urethane esterification reaction, or it can be carried out after the urethane esterification reaction is completed.

[0091] When the carbamate and ureacarbamate reactions are carried out simultaneously (in parallel), the reaction can proceed simply in the presence of both the carbamate catalyst and the ureacarbamate catalyst. Alternatively, if the ureacarbamate reaction is carried out after the carbamate reaction is complete, the carbamate reaction can be performed for a predetermined time in the presence of a carbamate catalyst and in the absence of a ureacarbamate catalyst, followed by the addition of a ureacarbamate catalyst to carry out the ureacarbamate reaction.

[0092] As a catalyst for urea carbamate esterification, a suitable selection from known catalysts can be used. For example, metal salts of carboxylic acids can be used (metal salts of alkali metals such as lithium, sodium, and potassium; metal salts of alkaline earth metals such as magnesium, calcium, and barium; metal salts of other typical metals such as tin and lead; metal salts of transition metals such as manganese, iron, cobalt, nickel, copper, zinc, and zirconium; etc.). Examples of carboxylic acids include monocarboxylic acids and polycarboxylic acids.

[0093] Specific examples of ureocarboxylation catalysts include zirconium octanoate. A single ureocarboxylation catalyst can be used alone, or in combination of two or more catalysts.

[0094] The amount of urea-formylation catalyst used relative to the total mass of the polyisocyanate component (a1) and the polyol component (a2) can be 0.001–0.1% by mass or 0.005–0.03% by mass. When the amount of urea-formylation catalyst used is 0.001% by mass or more, the urea-formylation reaction proceeds more easily, the amount of byproducts of urethane-modified polyisocyanate is suppressed, and the reduction in the number of functional groups of the resulting polyisocyanate is further suppressed. In addition, when the amount of urea-formylation catalyst used is 0.1% by mass or less, the storage stability is further improved.

[0095] The preferred reaction temperature for the urea-formaldehyde esterification reaction is 70–150°C, more preferably 90–130°C. At reaction temperatures above 70°C, urea-formaldehyde-modified polyisocyanates are more readily formed, and the amount of byproducts from urethane-modified polyisocyanates is further suppressed, thus further inhibiting the reduction in the number of functional groups in the resulting polyisocyanate. Furthermore, at reaction temperatures below 150°C, byproducts from isocyanurate-modified polyisocyanates are suppressed, further improving self-healing properties.

[0096] The urea-carbamate esterification reaction is preferably carried out until the urethane group is substantially no longer present. Here, "substantially no longer present" means that, as indicated by proton nuclear magnetic resonance (NMR), the urethane group is no longer present. 1The content of urethane-modified polyisocyanates, as confirmed by H-NMR spectroscopy, is less than 0.5 mol%, based on the total amount of urea-modified polyisocyanates, isocyanurate-modified polyisocyanates, and urethane-modified polyisocyanates.

[0097] The second step described above mainly involves urea-formylation, but as mentioned above, by adjusting the ratio R' (=M') in the first step... NCO / M' OH It can also partially undergo isocyanurate esterification. For example, by making the ratio R' 10 or higher, it is possible to make the content of isocyanurate-modified polyisocyanate (based on the total amount of urea-formate-modified polyisocyanate and isocyanurate-modified polyisocyanate) less than 30 mol%.

[0098] [Step 3: Reaction Termination Step]

[0099] In step 3, after the urethane esterification reaction in step 2, a reaction terminator is added to deactivate the catalyst and terminate the urethane esterification reaction. The reaction terminator can be added after the urethane esterification reaction has ended (after the urethane ester group is no longer present). However, even to suppress side reactions, it is preferable to add the reaction terminator quickly after the urethane esterification reaction has ended.

[0100] Examples of reaction terminators include inorganic acids such as phosphoric acid and hydrochloric acid; well-known compounds such as organic acids having sulfonic acid groups, aminosulfonic acids, their esters, and acyl halides. One of these can be used alone, or in combination of two or more.

[0101] The amount of reaction terminator added varies depending on the type of catalyst, but relative to the amount of catalyst added, it can be 0.5–10 equivalents or 0.8–5.0 equivalents. When the amount of reaction terminator added is 0.5 equivalents or more, the storage stability of the obtained modified polyisocyanate is further improved. When the amount of reaction terminator added is 10 equivalents or less, coloring can be further suppressed. After the reaction is stopped, a purification process can be performed to remove free unreacted polyisocyanate components (a1).

[0102] [Step 4: Purification Step]

[0103] In step 4, free unreacted polyisocyanate components (a1) present in the reaction mixture are removed. Additionally, if organic solvents are used in the reaction process, this purification step can remove them.

[0104] The polyisocyanate component (a1) is preferably removed to a residual content of less than 1.0% by mass, more preferably to a residual content of less than 1.0% by mass. When the residual content is less than 1.0% by mass, the odor is further reduced and the storage stability is further improved.

[0105] The removal of the polyisocyanate component (a1) is preferably carried out by thin-film distillation. Thin-film distillation can be carried out, for example, by thin-film distillation at 120-140°C under a high vacuum of 10-100 Pa.

[0106] The above describes a method for manufacturing modified polyisocyanate (a) according to one embodiment, but the method for manufacturing modified polyisocyanate (a) is not limited to the above embodiment.

[0107] For example, in another embodiment, steps 2 through 4 can be omitted, and the isocyanate-terminated prepolymer I obtained in step 1 can be used as a modified polyisocyanate (a).

[0108] Additionally, in other embodiments, a step of modifying (capping) a portion of the isocyanate group with a capping agent can be performed after step 4. Examples of capping agents include: phenol, cresol, xylenol, nitrophenol, chlorophenol, ethylphenol, p-hydroxybiphenyl, tert-butylphenol, o-isopropylphenol, o-sec-butylphenol, p-nonylphenol, p-tert-octylphenol, hydroxybenzoic acid, and hydroxybenzoate esters, etc.; phenolic capping agents such as ε-caprolactam, δ-valerolactam, γ-butyrolactam, and β-propiolactam, etc.; active methylene capping agents such as diethyl malonate, dimethyl malonate, ethyl acetoacetate, methyl acetoacetate, and acetylacetone; methanol, ethanol, etc. Propanol, isopropanol, n-butanol, isobutanol, tert-butanol, n-pentanol, tert-pentanol, lauryl alcohol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, propylene glycol monomethyl ether, benzyl alcohol, methoxymethanol, glycolic acid, methyl glycolate, ethyl glycolate, butyl glycolate and other glycolate esters; lactic acid, methyl lactate, ethyl lactate, butyl lactate and other lactate esters; hydroxymethylurea, hydroxymethyl melamine, diacetone alcohol, chloroethanol, bromoethanol, 1,3-dichloro-2-propanol, ω-hydroperfluoroalcohol Alcohol-based end-capping agents such as acetone cyanohydrin; thiol-based end-capping agents such as butyl mercaptan, hexyl mercaptan, tert-butyl mercaptan, tert-dodecyl mercaptan, 2-mercaptobenzothiazole, thiophene, toluenethiophenol, and ethylbenzylthiophenol; amide-based end-capping agents such as acetylaniline, methoxyacetylaniline, acetyl-o-toluidine, acrylamide, methacrylamide, acetamide, stearamide, and benzamide; imide-based end-capping agents such as succinimide, phthalimide, and maleimide; and end-capping agents such as diphenylamine, phenylnaphthylamine, xyleneamine, N-phenylxyleneamine, carbazole, and aniline. Amine-based end-capping agents such as naphthylamine, butylamine, dibutylamine, and butylaniline; imidazole-based end-capping agents such as imidazole and 2-ethylimidazolium; urea-based end-capping agents such as urea, thiourea, ethylene urea, ethylene thiourea, and 1,3-diphenylurea; carbamate-based end-capping agents such as phenyl N-phenylcarbamate and 2-oxazolidinone; imine-based end-capping agents such as ethyleneimine and propyleneimine; oxime-based end-capping agents such as formamide oxime, acetamide oxime, acetone oxime, methyl ethyl ketone oxime, diacetyl monooxime, benzophenone oxime, and cyclohexanone oxime; sulfite-based end-capping agents such as sodium bisulfite and potassium bisulfite; etc. These end-capping agents can be used individually or in combination of two or more.

[0109] Furthermore, for example, by using an isocyanurate esterification catalyst instead of a ureacarate esterification catalyst, isocyanurate modification can be primarily performed. The extent of ureacarate modification and isocyanurate modification can be determined by selecting various catalysts and considering the ratio R' (=M') mentioned above. NCO / M' OH Adjust it using ).

[0110] (Acrylic polyols (B))

[0111] Acrylic polyols (B) include acrylic polyols (b). Here, "acrylic polyols" refers to polymers that contain (meth)acrylic monomers as monomer units and have multiple hydroxyl groups.

[0112] Acrylic polyol (b) can be a homopolymer polymerized from one (meth)acrylic monomer, or a copolymer copolymerized from two or more (meth)acrylic monomers. Acrylic polyol (b) may contain monomers other than (meth)acrylic monomers as monomer units, but from the viewpoint of balancing the specified glass transition temperature and hydroxyl value, it is preferable to contain only (meth)acrylic monomers as monomer units.

[0113] Examples of homopolymers formed by the polymerization of a single (meth)acrylic acid monomer include: homopolymers of (meth)acrylic acid hydroxyl compounds. Examples of copolymers formed by the copolymerization of two or more (meth)acrylic acid monomers include: copolymers formed by the copolymerization of (meth)acrylates and (meth)acrylic acid hydroxyl compounds.

[0114] Among them, (meth)acrylate is at least one selected from the group consisting of acrylate and methacrylate. (meth)acrylate hydroxy compound is at least one selected from the group consisting of acrylate hydroxy compound and methacrylate hydroxy compound, which has one or more hydroxyl groups in its molecule that can serve as a reaction site.

[0115] The glass transition temperature (Tg) of acrylic polyol (b) is 5–30°C. When the glass transition temperature of acrylic polyol (b) is below 5°C, its self-healing properties against repeated scratches and its resistance to staining during outdoor use may sometimes decrease. Furthermore, when the glass transition temperature of acrylic polyol (b) is above 30°C, its self-healing properties at room temperature (e.g., 5–35°C) and low temperature (e.g., below 5°C) may sometimes decrease. From the viewpoint of better self-healing properties against repeated scratches and better resistance to staining during outdoor use, the glass transition temperature of acrylic polyol (b) can be above 10°C or above 15°C. From the viewpoint of better self-healing properties at room temperature and low temperature, the glass transition temperature of acrylic polyol (b) can be below 25°C or below 20°C. From the above viewpoints, the glass transition temperature of acrylic polyol (b) can also be 10–25°C or 15–20°C. Polyols (b) with glass transition temperatures within the above range can be synthesized by adjusting the types and mixing ratios of monomer components. For example, when the acrylic polyol (b) is a copolymer, the glass transition temperature can be calculated using the Fox formula, and the mixing ratio of monomer components can be set to obtain acrylic polyols (b) with glass transition temperatures within the above range.

[0116] The glass transition temperature of the above-mentioned acrylic polyol (b) was determined based on the inflection point of DSC measured by JIS K7121.

[0117] The hydroxyl value of acrylic polyol (b) is greater than 100 mg KOH / g and less than 150 mg KOH / g. When the hydroxyl value of acrylic polyol (b) is outside this range, its self-healing properties, stain resistance, and smoothness may sometimes decrease. From the viewpoint of better stain resistance and smoothness, the hydroxyl value of acrylic polyol (b) can be greater than 120 mg KOH / g or greater than 140 mg KOH / g. From the viewpoint of better self-healing properties, the hydroxyl value of acrylic polyol (b) can be less than 130 mg KOH / g or less than 110 mg KOH / g. From the above viewpoints, the hydroxyl value of acrylic polyol (b) can also be 120–150 mg KOH / g, 140–150 mg KOH / g, 120–130 mg KOH / g, greater than 100 and less than 130 mg KOH / g, or greater than 100 and less than 110 mg KOH / g. The hydroxyl value of the aforementioned acrylic polyol (b) was determined according to the method of JIS K1557.

[0118] Acrylic polyols (b) can be obtained, for example, by polymerizing (meth)acrylic monomers by imparting energy (light energy such as ultraviolet light or electron beams, or heat energy) to a mixture of (meth)acrylic monomers and a polymerization initiator. In other words, acrylic polyols (b) can be thermopolymers or photopolymers. From the viewpoint that polymers readily form after polymerization and crosslinking reactions, acrylic polyols (b) can be thermopolymers.

[0119] Acrylic polyol (B) may contain only one type of acrylic polyol (b) or a combination of two or more types. In addition, acrylic polyol (B) may also contain acrylic polyol (b') other than acrylic polyol (b) (acrylic polyols whose glass transition temperature and hydroxyl value are outside the ranges mentioned above).

[0120] From the viewpoint of easily obtaining coatings with better self-healing and stain resistance, the content of acrylic polyol (b') in acrylic polyol (B) can be less than 50% by mass (e.g., 0 to 50% by mass), less than 30% by mass, or less than 10% by mass, based on the total mass of acrylic polyol (B).

[0121] Next, (meth)acrylates and (meth)acrylate hydroxyl compounds, which can be used as reaction raw materials for acrylic polyols (b), as well as polymerization initiators, will be described.

[0122] [(Meth)acrylate]

[0123] Examples of (meth)acrylates include alkyl esters having an alkyl group having 1 to 20 carbon atoms. Examples of such (meth)acrylates include methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, pentyl methacrylate, hexyl methacrylate, 2-ethylhexyl methacrylate, octyl methacrylate, nonyl methacrylate, decyl methacrylate, dodecyl methacrylate, and other alkyl methacrylates; cyclohexyl methacrylates (products based on the esterification reaction of (meth)acrylic acid with alicyclic alcohols) and aryl methacrylates such as phenyl methacrylate and benzyl methacrylate. One type of such (meth)acrylate may be used alone, or a combination of two or more may be used.

[0124] [(Meth)acrylic acid hydroxy compounds]

[0125] (Meth)acrylic acid hydroxy compounds have one or more hydroxyl groups within their molecules that can act as reaction sites with polyisocyanates. Examples of (meth)acrylic acid hydroxy compounds include: 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 4-hydroxybutyl acrylate, 3-hydroxy-2,2-dimethylpropyl acrylate, pentaerythritol triacrylate, and other hydroxyacrylate compounds; 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, 4-hydroxybutyl methacrylate, 3-hydroxy-2,2-dimethylpropyl methacrylate, pentaerythritol trimethacrylate, and other hydroxymethacrylic acid hydroxy compounds; etc. These (meth)acrylic acid hydroxy compounds can be used alone or in combination of two or more.

[0126] [Polymerization initiator]

[0127] Examples of polymerization initiators include thermal polymerization initiators and photopolymerization initiators. The appropriate polymerization initiator can be selected based on the polymerization method.

[0128] Examples of thermal polymerization initiators include: dicarbonates such as di-2-ethylhexyl peroxide; peroxide esters such as tert-butyl peroxide benzoate, tert-butyl peroxide-2-ethylhexanoate, tert-butyl peroxide isopropionate, and tert-hexyl peroxide isopropionate; peroxide ketals such as di(tert-butylperoxide)-2-methylcyclohexane, di(tert-butylperoxide)-3,3,5-trimethylcyclohexane, and di(tert-butylperoxide)cyclohexane; etc.

[0129] Examples of photopolymerization initiators include: acetophenone, methoxyacetophenone, 2,2-diethoxyacetophenone, p-dimethylaminoacetophenone, 2,2-dimethoxy-2-phenylacetophenone, α-hydroxy-α,α'-dimethylacetophenone, 2-hydroxy-2-cyclohexylacetophenone, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinylacetone-1, etc.; benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl butyl ether, etc. Benzoin ethers; ketones such as benzophenone, 2-chlorobenzophenone, p,p'-dichlorobenzophenone, N,N'-tetramethyl-4,4'-diaminobenzophenone, and 4-(2-hydroxyethoxy)phenyl(2-hydroxy-2-propyl) ketone; thioxanthone, 2-chlorothioxanthone, and 2-methylthioxanthone; phosphine oxides such as bisacylphosphine oxide and benzoylphosphine oxide; ketals such as benzoyldimethyl ketal; ketones such as camphene-2,3-dione and phenanthrenequinone; etc.

[0130] (Polydimethylsiloxane compound)

[0131] The coating composition may contain a polydimethylsiloxane compound. By using a polydimethylsiloxane compound, not only can the smoothness and stain resistance of the coating film be further improved, but scratch resistance can also be further improved while maintaining self-healing properties. Therefore, by using a polydimethylsiloxane compound, even when forming a film with a thickness of less than 20 μm obtained by coating, a high degree of balance between self-healing and scratch resistance can be achieved.

[0132] In addition to polydimethylsiloxane (dimethylpolysiloxane), the polydimethylsiloxane compound also includes modified polydimethylsiloxanes. Examples of modified polydimethylsiloxanes include those derived from compounds having at least one hydroxyl group on the polydimethylsiloxane. Such modified compounds have at least one hydroxyl group.

[0133] Examples of polydimethylsiloxane compounds include: dimethylpolysiloxane-acrylic block copolymers having an acrylic portion, dimethylpolysiloxane-polyether block copolymers having a polyether portion, dimethylpolysiloxane-polyester block copolymers having a polyester portion, and dimethylpolysiloxane-polyether-polyester block copolymers having both a polyether portion and a polyester portion. All of the above copolymers may have at least one hydroxyl group in their structure (in the acrylic portion, polyether portion, or polyester portion). By ensuring that the polydimethylsiloxane compound has at least one hydroxyl group in its structure, the additive reacts with the polyisocyanate, resulting in effects such as reduced additive leakage after coating formation, improved stain resistance, and excellent recoatability. It should be noted that polydimethylsiloxane compounds having two or more hydroxyl groups and being acrylic-terminated do not belong to the aforementioned acrylic polyols (B).

[0134] Examples of dimethylpolysiloxane-acrylic acid block copolymers include BYK-SILCLEAN3700 (manufactured by BYK Japan KK, number average molecular weight: 7600, silicon content (SiO2 conversion): 1% by mass).

[0135] Examples of dimethylpolysiloxane-polyether block copolymers include: BYK-377 (number average molecular weight: 1400, silicon content: 18% by mass), BYK-SILCLEAN3720 (number average molecular weight: 1100, silicon content: 17% by mass), BYK-9200 (number average molecular weight: 4600, silicon content: 36% by mass), BYK-9201 (number average molecular weight: 4100, silicon content: 20% by mass), BYK-9204 (number average molecular weight: 5700, silicon content: 26% by mass), BYK-9205 (number average molecular weight: 4800, silicon content: 37% by mass), BYK-9206 (number average molecular weight: 5400, silicon content: 34% by mass), BYK-9210 (number average molecular weight: 4200, silicon content: 14% by mass), and BYK-9211 (number average molecular weight: 49%). 00, Silicon content: 37% by mass), BYK-9215 (Number average molecular weight: 4500, Silicon content: 29% by mass), BYK-9230 (Number average molecular weight: 6000, Silicon content: 20% by mass), BYK-9241 (Number average molecular weight: 6000, Silicon content: 22% by mass), BYK-9242 (Number average molecular weight: 10500, Silicon content: 16% by mass), BYK-9247 ( Number average molecular weight: 5400, silicon content: 25% by mass), BYK-9420 (number average molecular weight: 2500, silicon content: 33% by mass), BYK-9001 (number average molecular weight: 6800, silicon content: 22% by mass), BYK-9004 (number average molecular weight: 6800, silicon content: 17% by mass), BYK-9020 (number average molecular weight: 10500, silicon content: 17% by mass), etc. All of the above products are manufactured by BYK Japan.

[0136] Examples of dimethylpolysiloxane-polyester block copolymers include BYK-370 (manufactured by BYK Japan KK, number average molecular weight: 2100, silicon content: 8% by mass).

[0137] Examples of dimethylpolysiloxane-polyether-polyester block copolymers include BYK-375 (manufactured by BYK JapanKK, number average molecular weight: 2200, silicon content: 15% by mass).

[0138] The number-average molecular weight of polydimethylsiloxane compounds can be 1000–15000, 1500–12000, or 2000–8000. When the number-average molecular weight of the polydimethylsiloxane compound is above 1000, the self-healing properties of the coating are further improved. When the number-average molecular weight of the polydimethylsiloxane compound is below 15000, the smoothness and appearance of the coating are further improved.

[0139] From the viewpoint of further improving the smoothness, slip properties, stain resistance, and scratch resistance of the coating film, the silicon content of the polydimethylsiloxane compound, based on the total mass of the polydimethylsiloxane compound, can be 0.1% by mass or more, or 0.5% by mass or more, or 1.0% by mass or more. From the viewpoint of further suppressing the formation of pinholes and further suppressing the reduction in recoatability, the silicon content of the polydimethylsiloxane compound, based on the total mass of the polydimethylsiloxane compound, can be 50% by mass or less, or 45% by mass or less, 40% by mass or less, 15% by mass or less, 10% by mass or less, or 5.0% by mass or less. From the above viewpoints, the silicon content of the polydimethylsiloxane compound, based on the total mass of the polydimethylsiloxane compound, can also be 0.1–50% by mass, 0.1–15% by mass, 0.5–45% by mass, 0.5–10% by mass, 1.0–40% by mass, or 1.0–5.0% by mass. It should be noted that the silicon content mentioned above is a SiO2 conversion value, which is obtained by thermogravimetric-differential thermal analysis (TG-DTA).

[0140] Polydimethylsiloxane compounds can be used alone or in combination of two or more.

[0141] The amount of polydimethylsiloxane compound added can be adjusted by ensuring that the silicon content (based on the total amount of organic polyisocyanate (A), acrylic polyol (B), and polydimethylsiloxane compound) in the coating composition, converted from SiO2, reaches the range described below.

[0142] Polydimethylsiloxane compounds can be added during the mixing of acrylic polyols (B) and organic polyisocyanates (A). For example, organic polyisocyanates (A), acrylic polyols (B), and polydimethylsiloxane compounds can be mixed and stirred during film formation. Alternatively, if the polydimethylsiloxane compound has at least one hydroxyl group, it can be added to the organic polyisocyanate (A) by pre-reaction with the organic polyisocyanate. In other words, the organic polyisocyanate (A) (e.g., modified polyisocyanate (a)) can also be an organic polyisocyanate modified with a polydimethylsiloxane compound. In this case, the reaction solution obtained from the reaction of the polydimethylsiloxane compound and the organic polyisocyanate can be mixed and stirred with the acrylic polyol (B) during film formation for use.

[0143] (Other ingredients)

[0144] Various coating additives can be used in coating compositions as needed. Examples of coating additives include not only those that impart leveling and stain resistance to the coating film, but also those that further enhance scratch resistance while maintaining self-healing properties. With coating additives, it is easier to balance self-healing and scratch resistance for practical use, even with thin coatings. Examples of additives include: antioxidants such as 2,6-di-tert-butyl-4-methylphenol, UV absorbers, pigments, dyes, solvents, flame retardants, hydrolysis inhibitors, lubricants, plasticizers, fillers, antistatic agents, dispersants, catalysts, storage stabilizers, thickeners, etc.

[0145] As catalysts, well-known carbamate esterification catalysts can be used. Examples include organometallic compounds such as dibutyltin diacetate, dibutyltin dilaurate, and dioctyltin dilaurate; and organic amines and their salts such as triethylenediamine, triethylamine, diazabicycloundecene, and diazabicyclononene. These catalysts can be used alone or in combination of two or more. The catalysts can be mixed during the coating process.

[0146] (M NCO / M OH )

[0147] From the perspectives of further suppressing excess hydroxyl groups, further improving water resistance and damp heat resistance, further suppressing the reduction of crosslinking density, and further improving durability (stain resistance, etc.) and mechanical strength of the coating film, the molar number (M) of isocyanate groups in the isocyanate-containing compound contained in the coating composition is... NCO The molar number of hydroxyl groups in the hydroxyl-containing compound contained in the coating composition (M) OH The ratio of R (=M) NCO / M OHThe specific value (R) can be 0.8 or higher, or 0.9 or higher, or 1.0 or higher. From the viewpoint of further suppressing the excess of isocyanate groups, suppressing the excess formation of isocyanurate groups and urea groups, and further improving the softness and self-healing properties of the coating film, the specific value (R) can be 1.3 or lower, or 1.2 or lower, or 1.1 or lower. From the above viewpoints, the specific value (R) can also be 0.8 to 1.3, 0.9 to 1.2, or 1.0 to 1.1.

[0148] From the same point of view as above, the ratio of the molar number of isocyanate groups in organic polyisocyanate (A) to the sum of the molar numbers of hydroxyl groups in acrylic polyol (B) and polydimethylsiloxane compounds can also be 0.8 to 1.3.

[0149] (Silicon content)

[0150] The silicon content, converted from SiO2, in the coating composition is preferably 0.001 to 0.1% by mass, based on the total amount of organic polyisocyanate (A), acrylic polyol (B), and polydimethylsiloxane compound. When the silicon content is 0.001% by mass or more, the smoothness, slip properties, stain resistance, and scratch resistance of the resulting coating film are further improved. When the silicon content is 0.1% by mass or less, the formation of pinholes can be further suppressed, and the reduction in recoatability can be further suppressed. From the same point of view, the silicon content can be 0.002% by mass or more, 0.005% by mass or more, or 0.01% by mass or more, or 0.09% by mass or less, or 0.05% by mass or less. It should be noted that "the total amount of organic polyisocyanate (A), acrylic polyol (B), and polydimethylsiloxane compound" can be referred to as "the amount of total resin solids".

[0151] The coating composition described above can be prepared by mixing the organic polyisocyanate (A), the acrylic polyol (B), and, as appropriate, a polydimethylsiloxane compound and / or the additives described above in such a way that the ratio of R and the silicon content reaches the range described above.

[0152] As described above, the coating composition according to one aspect of the present invention can yield a coating film that combines high self-healing and stain resistance. Furthermore, it is possible to obtain a coating film that not only exhibits excellent self-healing and stain resistance but also excellent smoothness and adhesion. Particularly when using a polydimethylsiloxane compound, a coating film with a thickness of less than 20 μm that combines high self-healing and stain resistance can be obtained. Therefore, the coating composition according to one aspect of the present invention is suitable for applications involving the formation of surface coatings for automotive exterior parts requiring fine processability, high aesthetics, and lightweight exterior components, as well as for plastic molded articles.

[0153] The coating composition of one aspect of the present invention has been described above, but the coating composition and its manufacturing method are not limited to the above-described aspect. For example, the coating composition may replace the above-described organic polyisocyanate (A) and polydimethylsiloxane compound, or, based on the above-described organic polyisocyanate (A) and polydimethylsiloxane compound, further include the reaction product of the above-described organic polyisocyanate (A) and polydimethylsiloxane compound having at least one hydroxyl group.

[0154] <Reagent Kit>

[0155] One embodiment of the present invention is a kit for preparing the above-mentioned coating composition (a kit for preparing coating compositions), which comprises, for example, a first reagent containing the above-mentioned organic polyisocyanate (A) and a second reagent containing the above-mentioned acrylic polyol (B). The organic polyisocyanate (A) contained in the first reagent includes a modified polyisocyanate (e.g., a reaction product of a polyisocyanate component (a1) and a polyol component (a2) or a modified form thereof with a polydimethylsiloxane compound).

[0156] The kit for preparing coating compositions may also include other reagents besides the first and second reagents. These other reagents may include, for example, the polydimethylsiloxane compound described above.

[0157] The first and second reagents can be prepared by mixing them to obtain the coating composition described above, or by mixing the first reagent, the second reagent, and other agents besides the first and second reagents to obtain the coating composition described above. For example, in preparing a coating composition containing the above-described polydimethylsiloxane compound, the polydimethylsiloxane compound can be blended in the first reagent and / or the second reagent, or it can be blended in other reagents. The above-described additives that can be included in the coating composition can be included in the first reagent, the second reagent, and other agents.

[0158] When using the kit for preparing coating compositions, for example, the first reagent, the second reagent, and any other agents may be mixed in such a way that the ratio R reaches the range described above.

[0159] <Coating>

[0160] One aspect of the coating of the present invention is a self-healing coating comprising a cured product of the aforementioned coating composition. This coating exhibits self-healing properties within one time, for example, at room temperature (e.g., 5–35°C) or by heating to 40–60°C. Furthermore, the coating exhibits good smoothness and good stain resistance under high humidity conditions. The inventors speculate that the improved smoothness is achieved by enhancing drying and moisture resistance, and the improved stain resistance is achieved by increasing crosslinking density.

[0161] The cured coating composition comprises a polyurethane resin having a urethane structure formed by the urethane esterification reaction of an organic polyisocyanate (A) and an acrylic polyol (B). In addition to the urethane group (-CONH-), the urethane structure of the polyurethane resin also contains reactive residues of the organic polyisocyanate (A) and the acrylic polyol (B), and, depending on the application, reactive residues of a polydimethylsiloxane compound (a polydimethylsiloxane compound having at least one hydroxyl group).

[0162] The coating thickness is, for example, 5 to 40 μm. The coating can be a thin film with a thickness of less than 20 μm. When the coating composition contains the above-mentioned polydimethylsiloxane compound (or the reaction product of the above-mentioned organic polyisocyanate (A) and a polydimethylsiloxane compound having at least one hydroxyl group), even if the coating thickness is less than 20 μm (for example, 5 μm), the smoothness, stain resistance and adhesion are good, and the self-healing properties of scratches are also excellent.

[0163] The coating is typically formed on the substrate. That is, one embodiment of the invention includes both the substrate and the coating formed on it. The substrate will be described later.

[0164] <Methods for forming coating>

[0165] One aspect of the coating film formation method of the present invention includes the step of applying the above-described coating composition onto a substrate and curing it. Details of the substrate are as described above.

[0166] Examples of materials that can be bonded include molded bodies made from stainless steel, phosphate-treated steel, zinc steel, iron, copper, aluminum, brass, glass, acrylic polyols, polycarbonate resins, polyethylene terephthalate resins, polyethylene naphthalate resins, polybutylene terephthalate resins, polystyrene resins, AS resins, ABS resins, polycarbonate-ABS resins, 6-nylon resins, 6,6-nylon resins, MXD6 nylon resins, polyvinyl chloride resins, polyvinyl alcohol resins, polyurethane resins, phenolic resins, melamine resins, polyacetal resins, chlorinated polyolefin resins, polyolefin resins, polyamide resins, polyetheretherketone resins, polyphenylene sulfide resins, NBR resins, chloroprene resins, SBR resins, SEBS resins, etc., as well as surface-treated versions of these molded bodies. Surface-treated versions can be molded bodies made from olefin resins such as polyethylene and polypropylene that have undergone surface treatments such as corona discharge treatment (surface-treated molded bodies).

[0167] The adherend may have other coatings on its surface that can serve as intermediate layers. In other words, the coating composition may be applied directly to the surface of the molded body, or it may be applied over other coatings that are primed onto the surface of the molded body. These other coatings may be a single layer or multiple layers.

[0168] The coating composition can be applied by spraying, brushing, dipping, or other methods. According to one aspect of the present invention, even with spray coating which is easily affected by humidity, a coating film with excellent smoothness and self-healing properties can be obtained.

[0169] Curing of the coating composition can be carried out, for example, by heating. The heating used for curing can be the same as heating used for drying. That is, if the coating composition contains a solvent, the coating composition can be cured simultaneously (in parallel) with drying for solvent removal. The heating temperature can be, for example, 60–150°C. The heating time can be, for example, 1–10 hours.

[0170] Example

[0171] The embodiments of the present invention will be described below, but the present invention is not limited to these embodiments.

[0172] <Determination of Number Average Molecular Weight>

[0173] The number-average molecular weight disclosed in this embodiment is a value measured under the following conditions.

[0174] [condition]

[0175] • Measuring instrument: "HLC-8120" (manufactured by Tosoh Corporation)

[0176] • Pillar: “TSKguardcolumn HXL-L” (Made by Tosoh Corporation)

[0177] Particle size = 6μm, size = 6mm ID×30cm×4 pieces

[0178] • Support: Tetrahydrofuran (THF)

[0179] • Detector: Parallax Refraction

[0180] • Sample: 0.1% THF solution

[0181] Standard curve: Polystyrene

[0182] <Determination of NCO content>

[0183] The NCO content disclosed in this embodiment is a value measured according to the method described in JIS K1603-1 (Test Method for Aromatic Isocyanates in Polyurethane Raw Materials).

[0184] <Viscosity Measurement>

[0185] The viscosity disclosed in this embodiment is a value obtained by measuring the viscosity at 25°C using a Type B viscometer (manufactured by Tokyo Keiki Co., Ltd., model "DVL-BII") and a No. 4 rotor.

[0186] <Determination of Free HDI Content>

[0187] The free HDI content disclosed in this embodiment is a value determined by GPC (Tosoh HLC-8120) and calculated from the peak area ratio of hexamethylene diisocyanate in the polyisocyanate composition.

[0188] <Determination of Silicon Content>

[0189] The silicon content disclosed in this embodiment is obtained as follows: the mass residual rate after being held at 500°C for 30 minutes in a nitrogen atmosphere is determined by thermogravimetric-differential thermal analysis (TG-DTA), and this mass residual rate is used as the equivalent value of silicon dioxide residual rate to calculate the SiO2 conversion value.

[0190] <Synthesis of Modified Polyisocyanates>

[0191] (Synthesis example 1)

[0192] In a 1L four-necked flask equipped with a stirrer, thermometer, cooling tube, and dropping funnel, 890g of hexamethylene diisocyanate (manufactured by Tosoh Corporation, NCO content: 49.9% by mass, hereinafter referred to as "HDI") and 110g of PTMG-250 (manufactured by BASF Corporation, polytetramethylene glycol, trade name: Poly THF250, number average molecular weight 250) were added. The reaction was carried out at 80°C for 2 hours under a nitrogen atmosphere. Then, 0.05g of zirconium octoate (trade name: zirconium octoate, manufactured by Daiichi Rare Element Chemical Industry Co., Ltd., hereinafter referred to as "OCtZr") was added, and the reaction was carried out at 110°C for 2 hours for a urea-formaldehyde ester reaction. Once the NCO content reached 37.0% by mass, 0.5g of JP-508 (trade name, manufactured by Jōhoku Chemical Industry Co., Ltd., acidic phosphate) was added to terminate the reaction, and the reaction solution was cooled to room temperature. The reaction solution was subjected to thin-film distillation at 130 °C and 0.04 kPa to remove unreacted HDI, yielding polyisocyanate P1.

[0193] Polyisocyanate P1 has an NCO content of 16.2% by mass, is a transparent liquid, has a number-average molecular weight of 1400, an average number of functional groups calculated based on NCO content and number-average molecular weight of 5.4, a viscosity of 2000 mPa·s at 25°C, and a free HDI content of 0.2% by mass. Proton nuclear magnetic resonance (NMR) was used to analyze the NCO content. 1 ¹H-NMR spectroscopy confirmed that polyisocyanate P1 mainly consists of urethane-modified polyisocyanate, with a small amount of isocyanurate-modified polyisocyanate. Furthermore, the content of isocyanurate-modified polyisocyanate, based on the total amount of urethane-modified and isocyanurate-modified polyisocyanate, is 2 mol%.

[0194] (Synthesis example 2)

[0195] In a 1L four-necked flask equipped with a stirrer, thermometer, cooling tube, and dropping funnel, 880g of HDI and 120g of PCD-250 (polyhexamethylene polycarbonate diol, number average molecular weight 250) were added. The reaction was carried out at 80°C for 2 hours under a nitrogen atmosphere. Then, 0.05g of OctZr was added, and the reaction was carried out at 110°C for 2 hours for ureocarboxylation. Once the NCO content reached 35.9% by mass, 0.05g of JP-508 was added to terminate the reaction, and the reaction solution was cooled to room temperature. The reaction solution was then subjected to thin-film distillation at 130°C and 0.04kPa to remove unreacted HDI, yielding polyisocyanate P2.

[0196] Polyisocyanate P2 has an NCO content of 15.9% by mass, is a transparent liquid, has a number-average molecular weight of 1350, an average number of functional groups calculated based on NCO content and number-average molecular weight of 5.1, a viscosity of 4000 mPa·s at 25°C, and a free HDI content of 0.2% by mass. Proton nuclear magnetic resonance (NMR) was used to analyze the NCO content. 1 ¹H-NMR spectroscopy confirmed that polyisocyanate P2 mainly consists of urethane-modified polyisocyanate, with a small amount of isocyanurate-modified polyisocyanate. Furthermore, the content of isocyanurate-modified polyisocyanate, based on the total amount of urethane-modified and isocyanurate-modified polyisocyanates, is 2 mol%.

[0197] (Synthesis example 3)

[0198] In a 1L four-necked flask equipped with a stirrer, thermometer, cooling tube, and dropping funnel, 870g of HDI and 130g of PCD-500 (polyhexamethylene polycarbonate diol, number average molecular weight 500) were added. The reaction was carried out at 80°C for 2 hours under a nitrogen atmosphere. Then, 0.05g of OctZr was added, and the reaction was carried out at 110°C for 2 hours for a urea-formaldehyde esterification reaction. Once the NCO content reached 39.1% by mass, 0.05g of JP-508 was added to terminate the reaction, and the reaction solution was cooled to room temperature. The reaction solution was then subjected to thin-film distillation at 130°C and 0.04kPa to remove unreacted HDI, yielding polyisocyanate P3.

[0199] The polyisocyanate P3 has an NCO content of 13.2% by mass, a number-average molecular weight of 1450, an average number of functional groups calculated based on the NCO content and number-average molecular weight of 4.6, a viscosity of 6000 mPa·s at 25°C, and a free HDI content of 0.2% by mass. Proton nuclear magnetic resonance (NMR) was used to analyze the NCO content. 1 ¹H-NMR spectroscopy confirmed that polyisocyanate P3 mainly consists of urethane-modified polyisocyanate, with a small amount of isocyanurate-modified polyisocyanate. Furthermore, the content of isocyanurate-modified polyisocyanate, based on the total amount of urethane-modified and isocyanurate-modified polyisocyanates, is 3 mol%.

[0200] <Synthesis of Acrylic Polyols (B)>

[0201] (Synthesis Example 4)

[0202] In a 300 mL four-necked flask equipped with a stirrer, thermometer, cooling tube, and dropping funnel, 70 g of butyl acetate was added, and the temperature was raised to 120 °C. Next, 38.0 g of methyl methacrylate (Mitsubishi Gas Chemical Co., Ltd., hereinafter referred to as "MMA"), 26.0 g of butyl acrylate (Nippon Shokubai Co., Ltd., hereinafter referred to as "BA"), 31.0 g of 2-hydroxyethyl acrylate (hereinafter referred to as "2HEA"), 5.0 g of isobornyl acrylate (Kyoeisha Chemical Co., Ltd., hereinafter referred to as "IBXA"), and 2 g of PERBUTYL O (Nippon Yushu Co., Ltd., tert-butyl peroxide-2-ethylhexanoate) were added to the dropping funnel to prepare a mixture. This mixture was then added dropwise to a reaction vessel over 4 hours. The reaction mixture was then maintained at 120 °C for 1 hour. Next, 30 g of butyl acetate and 1 g of PERBUTYL O were added to a dropping funnel to prepare a mixture, which was then added dropwise to the reaction vessel over 1 hour. The mixture was then maintained at 120°C for 3 hours and cooled to room temperature. This yielded a solution of acrylic polyol 1 (AP1).

[0203] The hydroxyl value of acrylic polyol 1 in AP1 was determined according to JIS K1557, and the result was that the hydroxyl value of acrylic polyol 1 was 150.0 mg KOH / g. Furthermore, AP1 is a transparent liquid, and the solid content (content of acrylic polyol 1) of AP1 is 50% by mass, with the glass transition temperature (hereinafter referred to as "Tg") of acrylic polyol 1 being 15°C.

[0204] (Synthesis Examples 5 to 10)

[0205] Following the raw materials and addition ratios recorded in Table 1, the same operation as in Synthesis Example 4 was performed to obtain a solution of acrylic polyols 2-7 (AP2-7, solid content: 50% by mass).

[0206] [Table 1]

[0207]

[0208] <Examples 1-10 and Comparative Examples 1-5>

[0209] [Preparation of Coating Compositions]

[0210] The materials shown in Tables 2-3 were mixed at the mixing amounts (unit: g) shown in Tables 2-3 to prepare coating compositions 1-15 of Examples 1-10 and Comparative Examples 1-5, respectively. The ratio R in Tables 2-3 represents: the molar number of isocyanate groups in the isocyanate-containing compound (the molar number of isocyanate groups in the organic polyisocyanate) [M]. NCO[M] relative to the number of moles of hydroxyl groups in the hydroxyl-containing compounds in the coating composition (the sum of the number of moles of hydroxyl groups in acrylic polyols and the number of moles of hydroxyl groups in polydimethylsiloxane compounds) OH The ratio of [M] NCO / M OH Additionally, the Si content in Tables 2 and 3 represents the silicon content converted from SiO2 in the coating composition determined by the above method (based on the total amount of organic polyisocyanates, acrylic polyols, and polydimethylsiloxane compounds).

[0211] [Coating Preparation]

[0212] Under the following conditions, coating compositions 1 to 15 were applied to substrates and cured to obtain coatings of Examples 1 to 10 and Comparative Examples 1 to 5, respectively. It should be noted that the substrates used were acrylic resin sheets (manufactured by Kuraray, 2 mm thick) or thermoplastic polyurethane films.

[0213] (Painting conditions)

[0214] • Painting method: Use an applicator

[0215] Humidity conditions: 50% RH

[0216] Temperature conditions: 23℃

[0217] • Drying (curing) conditions: Forced drying at 80℃ for 5 hours

[0218] • Film thickness: Approximately 20 μm

[0219] <Evaluation>

[0220] The coatings of Examples 1-10 and Comparative Examples 1-5 obtained above were evaluated as follows: Evaluation Tests 1, 3 and 4 used coatings made with acrylic resin sheets (manufactured by Kuraray, 2 mm thick) as the substrate, while Evaluation Test 2 used coatings made with thermoplastic polyurethane film as the substrate.

[0221] (Evaluation Test 1: Coating Appearance (Smoothness))

[0222] The gloss of the coating at 60° was measured according to JIS Z8741 using a haze-gloss meter (manufactured by BYK-Additives & Instruments). The appearance of the coating was evaluated according to the following evaluation criteria. If the evaluation is A, the coating appearance is considered good. It should be noted that in this evaluation, good appearance of the coating essentially means good smoothness.

[0223] [Evaluation Criteria]

[0224] • A: Gloss level is 80% or higher

[0225] • B: Gloss level less than 80%

[0226] (Evaluation Test 2: Stain Resistance)

[0227] The coating surface was contaminated with a black marker (Sharpy Corporation), and then left to stand for 1 hour at 23°C and 50% RH. After standing, the contaminated coating surface was wiped with gauze soaked in ethanol, and the color difference before and after contamination was calculated using the following formula using a spectro2guide (BYK-Gardner Corporation).

[0228] Color difference = [(ΔL) ＊ ) 2 +(Δa ＊ ) 2 +(Δb ＊ ) 2 ] 1 / 2

[0229] Stain resistance is evaluated using the following criteria. A rating of A indicates good stain resistance.

[0230] [Evaluation Criteria]

[0231] A: Color difference less than 1

[0232] • B: Color difference is greater than 1 and less than 2

[0233] •C: Color difference of 2 or more

[0234] (Evaluation Experiment 3: Self-Healing)

[0235] At 23°C and 50% RH, the coating was scratched by rubbing it with a brass wire brush. The degree of repair was visually observed, and the time from scratch to complete repair was measured. A rating of A or B indicates good self-healing properties.

[0236] [Evaluation Criteria]

[0237] • A: Scars heal within 1 hour at room temperature.

[0238] • B: The scar did not heal within 1 hour at room temperature, but healed within 1 hour when heated to 50°C.

[0239] • C: The wound did not heal within 1 hour under both room temperature and 50°C heating conditions.

[0240] (Evaluation Experiment 4: Fit)

[0241] Adhesion tests shall be conducted using the cross-cut adhesion test according to JIS 5600-5-6, and the fit shall be evaluated according to the following evaluation criteria. If the evaluation is A, the fit is considered good.

[0242] [Evaluation Criteria]

[0243] • A: Category 0-1

[0244] •B: Categories 2-5

[0245] [Table 2]

[0246]

[0247] [Table 3]

[0248]

[0249] The details of each raw material in Tables 2 and 3 are as follows.

[0250] • Polyisocyanates P1 to P3: Polyisocyanates P1 to P3 synthesized in Examples 1 to 3

[0251] • Polyisocyanate P4: HDI isocyanurate (trade name: coronate HXR, manufactured by Tosoh Corporation)

[0252] • AP1~AP7: Solutions of acrylic polyols synthesized in Examples 4~10, AP1~AP7

[0253] U-CAT SA102: (manufactured by San-Apro, carbamate catalyst, 2-ethylhexanoate of DBU)

[0254] • BYK-SILCLEAN3700: (Manufactured by BYK Japan KK, dimethyl polysiloxane-acrylic acid block copolymer, number average molecular weight: 7600, silicon content (SiO2 conversion): 1%)

Claims

1. A coating composition comprising an organic polyisocyanate (A) and an acrylic polyol (B), The organic polyisocyanate (A) comprises a modified polyisocyanate (a), The modified polyisocyanate (a) is the reaction product of polyisocyanate component (a1) and polyol component (a2) or a modified form thereof. The polyisocyanate component (a1) comprises an organic diisocyanate or a modified form thereof. The polyol component (a2) comprises at least one polyol selected from the group consisting of polytetramethylene glycol and polycarbonate polyols, with a number average molecular weight of 200 to 750. The modified polyisocyanate (a) comprises urea-formate modified polyisocyanate and isocyanurate modified polyisocyanate, wherein, based on the total amount of urea-formate modified polyisocyanate and isocyanurate modified polyisocyanate, the content of isocyanurate modified polyisocyanate is more than 1 mol% and less than 3 mol%. The modified polyisocyanate (a) has an average number of functional groups of 4.0 to 6.

0. The acrylic polyol (B) comprises acrylic polyols (b) with a glass transition temperature of 5 to 30°C and a hydroxyl value greater than 100 mg KOH / g and less than 150 mg KOH / g.

2. The coating composition according to claim 1, wherein, The polyisocyanate component (a1) comprises at least one selected from the group consisting of aliphatic diisocyanates and alicyclic diisocyanates.

3. The coating composition according to claim 1 or 2, further comprising a polydimethylsiloxane compound.

4. The coating composition according to claim 3, wherein, Based on the total amount of the organic polyisocyanate (A), the acrylic polyol (B), and the polydimethylsiloxane compound, the silicon content converted from SiO2 is 0.001 to 0.1% by mass.

5. The coating composition according to claim 1 or 2, wherein, The ratio of the molar number of isocyanate groups in the isocyanate-containing compound of the coating composition to the molar number of hydroxyl groups in the hydroxyl-containing compound of the aforementioned coating composition is 0.8 to 1.

3.

6. The coating composition according to claim 1 or 2, wherein, The polyol component (a2) comprises polytetramethylene glycol with a number average molecular weight of 200 to 750.

7. A kit for preparing the coating composition according to any one of claims 1 to 6. The kit comprises: a first reagent containing the organic polyisocyanate (A) and a second reagent containing the acrylic polyol (B).

8. A coating film comprising a cured product of the coating composition according to any one of claims 1 to 6.

9. A method for forming a coating film, comprising the steps of: applying the coating composition according to any one of claims 1 to 6 onto a substrate and curing it thereon.

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