Two-component coating composition

Abstract

The present invention provides a two-component coating composition that is suitable for in-mold coating, has excellent high-temperature water resistance, and forms a coating film that can be easily peeled off. [Solution] A two-component coating composition comprising a main component and a curing agent, wherein the main component comprises a polyol and a curing catalyst, the curing agent comprises an isocyanurate compound, the curing catalyst comprises an organotin compound containing 16.0% by mass or more of Sn atoms, and the organotin compound comprises the following general formula (1): TIFF2026166260000009.tif3169 (In the formula, R 1 R is a hydrocarbon group having 1 or more carbon atoms. 2 R is a hydrocarbon group having 4 or more carbon atoms. 3 and R 4 Each of these is independently a monovalent organic group with one or more carbon atoms. A two-component coating composition, wherein the content of the curing catalyst is greater than 0.6 parts by mass and less than or equal to 3.0 parts by mass per 100 parts by mass of the solid content of the two-component coating composition.

Description

[Technical Field]

[0001] The present invention relates to a two-component coating composition. [Background technology]

[0002] The surfaces of industrial products and other objects are coated with paint films that serve various purposes. These films protect the object while simultaneously providing a beautiful appearance and excellent design. Generally, paint films are formed by spray-painting a paint composition containing solvents such as organic solvents and / or aqueous solvents, and then drying it. However, in recent years, issues such as solvent dispersion during spray painting, release of solvents into the atmosphere during the drying process, and CO2 generation have become a concern. Furthermore, because spray painting requires a drying process, productivity tends to decrease.

[0003] Therefore, a method of painting within a mold has been proposed as an alternative to spray painting (for example, Patent Document 1). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2002-292638 [Overview of the project] [Problems that the invention aims to solve]

[0005] Furthermore, in recent years, life cycle assessment, a method for quantifying and evaluating the environmental impact at each stage of a product's lifecycle—from manufacturing, transportation, sales, use, disposal, and reuse—has been attracting attention. Resin-coated articles are typically crushed and reused with the coating still attached. However, these reused articles contain foreign matter (the coating) mixed with the resin, which tends to degrade their physical properties and limits their applications.

[0006] As methods for separating a resin and a coating film, a method of pulverizing a coated article and then scraping off the surface coating film by mechanical polishing, and a method of hydrolyzing and separating the coating film with a dedicated solvent have been proposed. However, all of these methods require much time and energy, and are costly.

[0007] An object of the present invention is to provide a two-component coating composition which is suitable for in-mold coating, has excellent high-temperature water resistance, and forms an easily peelable coating film. [MEANS FOR SOLVING THE PROBLEMS]

[0008] In order to solve the above problems, the present invention provides the following aspects. [1] A two-component coating composition comprising a main agent and a curing agent, wherein the main agent comprises a polyol and a curing catalyst, the curing agent comprises an isocyanurate compound, the curing catalyst comprises an organotin compound containing 16.0% by mass or more of Sn atoms, the organotin compound is represented by the following general formula (1): [Chemical Formula] (In the formula, R 1 is a hydrocarbon group having 1 or more carbon atoms, R 2 is a hydrocarbon group having 4 or more carbon atoms, and R 3 and R 4 are each independently a monovalent organic group having 1 or more carbon atoms.) and the two-component coating composition is represented by the formula, wherein the content of the curing catalyst is more than 0.6 parts by mass and 3.0 parts by mass or less based on 100 parts by mass of the solid content of the two-component coating composition. [2] In the general formula (1), the R 3 is a group represented by -COOR 31 (wherein R 31 is a hydrocarbon group having 1 or more carbon atoms), and the R 4The two-component coating composition described in [1] above, wherein is a hydrocarbon group having 4 or more carbon atoms. [3] A two-component coating composition according to [1] or [2] above, wherein the solvent content is 10.0% by mass or less. [4] The isocyanurate compound is a two-component coating composition of any of the above [1] to [3], comprising a trimer of hexamethylene diisocyanate. [5] The polyol is at least one selected from the group consisting of polyester polyols, polyether polyols, and polycarbonate polyols, in any of the two-component coating compositions described in [1] to [4] above. [6] A two-component coating composition according to any of the above [1] to [5], wherein the ratio (NCO / OH) of the isocyanate group equivalent of the isocyanurate compound to the hydroxyl group equivalent of the polyol is 0.5 / 1.0 to 2.0 / 1.0. [7] A two-component coating composition for in-mold coating, one of the above [1] to [6]. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a two-component coating composition that is suitable for in-mold coating, has excellent high-temperature water resistance, and forms a coating film that can be easily peeled off. [Modes for carrying out the invention]

[0010] For mass production of painted articles using in-mold coating (a coating method that forms a coating film within a mold), the coating composition must be able to cure at low temperatures and in a short time. Coating compositions that can cure at low temperatures and in a short time enable in-mold coating not only on resin substrates but also on composite materials such as sheet molding compounds (SMC) or fiber-reinforced plastics (FRP). In addition, in-mold coating reduces the emission of organic solvents and carbon dioxide compared to spray coating, thus reducing the environmental impact. Furthermore, since there is no need to set up a separate drying oven, productivity is improved.

[0011] In the present disclosure, in a two-component coating composition containing a polyol in the main agent and an isocyanurate compound in the curing agent, an organotin compound is used as a curing catalyst. In the organotin compound, the mass of Sn atoms accounts for 16.0 mass% or more. In addition, the organotin compound is represented by the following general formula (1):

Chemical Formula

[0012] To achieve curing at low temperature in a short time, increasing the amount of the curing catalyst is conceivable. However, in general, increasing the amount of the curing catalyst improves the releasability from the object to be coated, while reducing the water resistance.

[0013] When the organotin compound having the above structure is used in an amount of more than 0.6 parts by mass, the cured coating film can be easily peeled off by immersing the coated article in warm water of 80 to 120°C for 2 hours or more. On the other hand, when immersed in 80°C warm water for about 1 hour, peeling of the coating film does not occur. Hereinafter, the ease of peeling of the cured coating film from the object to be coated after immersing the coated article in warm water of 80 to 120°C for 2 hours or more is referred to as "recyclability", and the difficulty of peeling when immersed in 80°C warm water within 1 hour is referred to as "high-temperature water resistance". Even when immersed in 40°C water, peeling of the coating film does not occur. The difficulty of peeling when immersed in 40°C water is referred to as "water resistance".

[0014] Low temperature in curing refers to, for example, 40-110°C, or 80-100°C. Short time refers to, for example, 20 seconds to 1 minute 30 seconds, or 30 seconds to 1 minute. Hereinafter, the process of curing the two-component coating composition may be referred to as "baking".

[0015] In-mold coating is a method of applying a coating composition to a molded substrate within a mold and curing (baking) the coating without contact with the atmosphere (especially oxygen). Typically, the coating composition is injected into the gap between two molds and cured without contact with the atmosphere (especially oxygen). Specific examples of in-mold coating methods include injection molding, injection compression molding, injection press molding, compression molding, reaction injection molding, and RTM molding. Compared to spray painting, in-mold coating reduces the emission of organic solvents and carbon dioxide. In-mold coating has attracted attention in recent years due to its low environmental impact. In-mold coating is suitable as a coating method for resin substrates.

[0016] The use of the two-component coating composition relating to this disclosure in coating methods other than in-mold coating is not excluded.

[0017] The two-component coating composition according to this disclosure can be used as a material for a clear coating or other coating located on the outermost part of a coated article, a colored coating, an intermediate coating, or a base coat coating interposed between the clear coating and the workpiece.

[0018] A "hydrocarbon group" is a group containing carbon and hydrogen, and refers to a group obtained by removing one hydrogen atom from a hydrocarbon. Examples of hydrocarbon groups include aliphatic hydrocarbon groups having 1 to 24 carbon atoms and aromatic hydrocarbons. Aliphatic hydrocarbon groups may be linear, branched, and / or cyclic, and may be saturated or unsaturated. The hydrogen bonded to the carbon may be substituted with a halogen atom or the like. A hydrocarbon group may have one or more N, O, S, Si, amide, sulfonyl, siloxane, carbonyl, carbonyloxy, etc. at its terminal or in its molecular chain.

[0019] An "organic group" refers to a group containing carbon. An organic group is not particularly limited, but it can be a hydrocarbon group or a group containing a hydrocarbon group.

[0020] [Two-component coating composition] The two-component coating composition according to this disclosure comprises a main component and a curing agent. The main component comprises a polyol and a curing catalyst. The curing agent comprises an isocyanurate compound. The two-component coating composition according to this disclosure is suitable for in-mold coating.

[0021] By mixing the main component and the curing agent and heating, the polyol and isocyanurate compound react to obtain a cured coating film. The main component and / or curing agent may each be heated and / or degassed under vacuum before mixing. This reduces the water content in the two-component coating composition obtained by mixing the two components, which can improve the appearance of the resulting coating film.

[0022] (Main ingredient) The main component comprises a polyol and a curing catalyst. The polyol is a film-forming resin. The polyol reacts with the curing agent, for example, by heating, to form a three-dimensional cured coating film. Hereinafter, the curable resin containing the polyol included in the two-component coating composition may be collectively referred to as the film-forming resin.

[0023] <Curing catalyst> The curing catalyst accelerates the curing reaction. The curing catalyst is represented by the following general formula (1) and contains an organotin compound (hereinafter referred to as a specific organotin compound) containing 16.0% by mass or more of Sn atoms.

[0024] The curing catalyst content is greater than 0.6 parts by mass and less than or equal to 3.0 parts by mass per 100 parts by mass of solid content of the two-component coating composition (0.6 parts < catalyst content ≤ 3.0 parts). If the curing catalyst content is greater than 0.6 parts by mass, water resistance and high-temperature water resistance are improved, as well as recyclability. If the curing catalyst content is 3.0 parts by mass or less, the coating hardens at an appropriate speed, allowing the two-component coating composition to easily spread throughout the mold. In addition, the shrinkage stress when the resin components aggregate is kept low, which improves the adhesion between the coating film and the substrate, and in particular, improves high-temperature water resistance.

[0025] The above-mentioned content of the curing catalyst may be 0.65 parts by mass or more, or 0.7 parts by mass or more. The above-mentioned content of the curing catalyst may be 2.0 parts by mass or less, or 1.5 parts by mass or less. The above-mentioned content of the curing catalyst may be 0.65 to 2.0 parts by mass, or 0.7 to 1.5 parts by mass.

[0026] • Certain organotin compounds Certain organotin compounds contain 16.0% by mass or more of Sn atoms. This improves catalytic activity. The percentage of Sn atoms may be 17.0% by mass or more, or 18.0% by mass or more. The percentage of Sn atoms may be 50.0% by mass or less, or 30.0% by mass or less. The percentage of Sn atoms may be between 17.0% and 50.0% by mass, or between 18.0% and 30.0% by mass. The percentage of Sn atoms can be determined by dividing the molecular weight of the specific organotin compound by the atomic weight of the Sn atom (118.7).

[0027] Certain organotin compounds are given by the following general formula (1): [ka] (In the formula, R 1 R is a hydrocarbon group having 1 or more carbon atoms. 2 R is a hydrocarbon group having 4 or more carbon atoms. 3 and R 4 Each of these is independently a monovalent organic group with one or more carbon atoms. It is represented as follows.

[0028] R 1 -COO- is a group formed by removing a hydrogen atom from the carboxyl group of a monocarboxylic acid. As described above, R 1 The direct bonding of -COO- to the Sn atom improves the curing speed. 1 R is a hydrocarbon group having one or more carbon atoms. 1 R may be a saturated aliphatic hydrocarbon group, including a linear or branched structure. 1 It does not need to contain halogen atoms, N, O, S, Si, amides, sulfonyls, siloxanes, carbonyls, carbonyloxys, etc. 1 The number of carbon atoms may be 2 or more, or 3 or more. 1 The number of carbon atoms may be 15 or less, or 12 or less. 1 The number of carbon atoms may be 1 to 15, 2 to 15, or 3 to 12. 1 -COO- may be derived from, for example, acetic acid, octic acid, 7,7-dimethyloctylic acid (neodecanoic acid), or lauric acid.

[0029] R 2 R is a hydrocarbon group with 4 or more carbon atoms. 2 R may be a saturated aliphatic hydrocarbon group, including a linear or branched structure. 2 It does not need to contain halogen atoms, N, O, S, Si, amides, sulfonyls, siloxanes, carbonyls, carbonyloxys, etc. 2 The number of carbon atoms may be 5 or more, or 6 or more. 2 The number of carbon atoms may be 15 or less, or 10 or less. 2 The number of carbon atoms may be 4 to 15, 5 to 15, or 6 to 10. 2 Examples include the n-butyl group and the octyl group.

[0030] R 3 and R 4 Each of these is independently a monovalent organic group having one or more carbon atoms. 3 -COOR 31 The group represented by (R31 (This is a hydrocarbon group having 1 or more carbon atoms.) That is, the organotin compound may have two groups derived from a monocarboxylic acid. This further improves the chemical stability of the organotin compound. 31 R 1 It is defined similarly to R. 31 and R 1 They may be the same, or they may be different.

[0031] R 4 R may be a hydrocarbon group having 4 or more carbon atoms. That is, a particular organotin compound may have two hydrocarbon groups having 4 or more carbon atoms. This further improves the chemical stability of the particular organotin compound. 4 R 2 It is defined similarly to R. 4 and R 2 They may be the same, or they may be different.

[0032] Among them, R 3 ga-COOR 31 The group represented by (R 31 R is a hydrocarbon group having 1 or more carbon atoms. 4 This may be a hydrocarbon group having 4 or more carbon atoms.

[0033] The proportion of a specific organotin compound in the total amount of the curing catalyst is not particularly limited. The above proportion of the specific organotin compound may be 80% by mass or more, 90% by mass or more, 95% by mass or more, or 100% by mass.

[0034] From a curing standpoint, it is desirable that certain organotin compounds are not included in the main component as reaction products with other compounds (typically ethyl silicates or phthalate diesters). A typical reaction product of certain organotin compounds with ethyl silicates is known as alkali stanosiloxane, CAS No. 93925-42-9.

[0035] Other catalysts The curing catalyst may further contain catalysts other than specific organotin compounds. These other catalysts are not particularly limited. Examples of other catalysts include, for example, at least one organometallic catalyst containing a metal element selected from the group consisting of Bi, Zn, Al, and Zr, or an organotin compound containing less than 16% by mass of Sn atoms.

[0036] Examples of organometallic catalysts containing Bi include bismuth carboxylic acid and its salts. Examples of organometallic catalysts containing Zn include zinc complex catalysts. Examples of organometallic catalysts containing Al include aluminum complex catalysts. Examples of organometallic catalysts containing Zr include zirconium chelate catalysts.

[0037] <Polyol> Polyols are film-forming resins. Polyols react with curing agents, for example, by heating, to form a three-dimensional cured coating. Each polyol molecule contains two or more hydroxyl groups. Polyols can be used individually or in combination of two or more types.

[0038] The main component may contain polyol (A1) having an average of 3 or more hydroxyl groups per molecule. This may increase the hardness of the resulting coating film. The main component may also contain polyol (A2) having an average of 2 hydroxyl groups per molecule along with polyol (A1). The proportion of polyol (A2) is not particularly limited. The proportion of polyol (A2) may be 50% by mass or less, 40% by mass or less, or 30% by mass or less of the total of polyol (A1) and polyol (A2).

[0039] The hydroxyl value of polyols is, for example, 300 to 1,000 mgKOH / g. When the hydroxyl value of the polyol is within this range, the reaction rate between the polyol and the isocyanurate compound increases when the main agent and curing agent are mixed. As a result, the coated product can be quickly released from the mold, improving productivity. In addition, since a certain amount of reaction heat is generated during the reaction, the adhesion of the coating film to the resin substrate can be further improved.

[0040] If two or more polyols are present, the apparent hydroxyl value, calculated based on the hydroxyl value and mass ratio of each polyol, should be between 300 and 1,000 mgKOH / g.

[0041] The hydroxyl value of polyols (including apparent hydroxyl value; the same applies hereinafter) may be 350 mgKOH / g or more, and may be 500 mgKOH / g or more. The hydroxyl value of polyols may be 800 mgKOH / g or less, and may be 700 mgKOH / g or less. The hydroxyl value of polyols may be 350 to 800 mgKOH / g, and may be 500 to 700 mgKOH / g.

[0042] The type of polyol is not particularly limited. Examples of polyols include polyester polyols, polyether polyols, polycarbonate polyols, polyacrylate polyols, and polyhydric alcohols. These can be used individually or in combination of two or more. In particular, the polyol may include at least one selected from the group consisting of polyester polyols, polyether polyols, and polycarbonate polyols.

[0043] Polyester polyols may have a branched structure. Polyester polyols having a branched structure can be prepared, for example, by reacting a polyhydric alcohol of three or more valents with a polycarboxylic acid of two or more valents, and repeating the reaction as needed.

[0044] Examples of polyhydric alcohols with a valency of three or higher include trimethylolpropane, trimethylolethane, pentaerythritol, glycerin, mannitol, and xylitol. These can be used individually or in combination of two or more.

[0045] Examples of polycarboxylic acids with two or more valencies include phthalic acid, phthalic anhydride, tetrahydrophthalic acid, tetrahydrophthalic anhydride, hexahydrophthalic acid, hexahydrophthalic anhydride, methyltetraphthalic acid, methyltetrahydrophthalic anhydride, isophthalic acid, terephthalic acid, succinic anhydride, adipic acid, sebacic acid, maleic acid, maleic anhydride, itaconic acid, fumaric acid, hymic anhydride, trimellitic acid, trimellitic anhydride, pyromellitic acid, pyromellitic anhydride, azelaic acid, succinic acid, succinic anhydride, lactic acid, dodecenyl succinic acid, dodecenyl succinic anhydride, cyclohexane-1,4-dicarboxylic acid, and endo anhydride. These can be used individually or in combination of two or more. In particular, saturated aliphatic carboxylic acids may be used from the viewpoint of weather resistance and resistance to yellowing.

[0046] As raw material monomers for polyester polyols, monoepoxide compounds and / or lactones may also be used. Examples of monoepoxide compounds include the trade name "Cardura E" (manufactured by Ciel Chemical Co., Ltd.). Examples of lactones include β-propiolactone, dimethylpropiolactone, butyrolactone, γ-valerolactone, ε-caprolactone, γ-caprolactone, γ-capryloractone, chlorotractone, δ-valerolactone, and δ-caprolactone.

[0047] Examples of commercially available polyester polyols include desmofen VPLS2249 / 1 (manufactured by Sumika Covestro Urethane Co., Ltd.), desmofen 800 (manufactured by Sumika Covestro Urethane Co., Ltd.), desmofen XP2488 (manufactured by Sumika Covestro Urethane Co., Ltd.), Kuraray Polyol P-510 (manufactured by Kuraray Co., Ltd.), and Kuraray Polyol F-510 (manufactured by Kuraray Co., Ltd.).

[0048] Polyether polyols can be obtained, for example, by addition polymerization of an alkylene oxide such as ethylene oxide, propylene oxide, or tetrahydrofuran to a polyhydric alcohol with two or more hydroxyl groups. Polyether polyols may be polyether diols having two hydroxyl groups in one molecule.

[0049] Examples of polyhydric alcohols with two or more valencies include ethylene glycol, diethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 2,2-diethyl-1,3-propanediol, neopentyl glycol, 1,9-nonanediol, 1,4-cyclohexanediol, glycerin, trimethylolpropane, pentaerythritol, neopentyl glycol ester of hydroxypivalate, 2-butyl-2-ethyl-1,3-propanediol, 3-methyl-1,5-pentanediol, and 2,2,4-trimethylpentanediol. These can be used individually or in combination of two or more.

[0050] Examples of polyetherdiols include polyalkylene glycols such as polyethylene glycol, polypropylene glycol, polyethylene propylene glycol, polytetramethylene ether glycol, polyhexamethylene ether glycol, and polyoctamethylene ether glycol, as well as their block forms.

[0051] Examples of commercially available polyether polyols include the Sannix series manufactured by Sanyo Chemical Industries, Ltd. Specifically, these include Sannix GP-250, Sannix GP-400, Sannix PP-200, and Sannix GP-600.

[0052] Polycarbonate polyols can be obtained, for example, by reacting the above-mentioned polyhydric alcohol with dimethyl carbonate.

[0053] Examples of commercially available polycarbonate polyols include Duranol T5650E (manufactured by Asahi Kasei Corporation), C-590 (manufactured by Kuraray Co., Ltd.), and ETERNACOLL PH-50 (manufactured by Ube Industries, Ltd.).

[0054] The weight-average molecular weight (Mw) of a polyol is not particularly limited. The Mw of the polyol can be set appropriately according to the hydroxyl value, etc.

[0055] The proportion of polyol in the total amount of film-forming resin contained in the main component is not particularly limited. The above proportion of polyol may be 80.0% by mass or more, 90.0% by mass or more, 95.0% by mass or more, or 100% by mass.

[0056] <Other film-forming resins> Other film-forming resins besides polyols may be included. Examples of other film-forming resins include acrylic resins, polyester resins, alkyd resins, polyether resins, polyolefin resins, polyurethane resins, polycarbonate resins, melamine resins, and epoxy resins. These other film-forming resins may be used individually or in combination of two or more.

[0057] Other film-forming resins are preferably present in small amounts due to their ability to cure at low temperatures and in short periods of time. In particular, the amount of monool compound may be 5.0% by mass or less, 2.0% by mass or less, or 0% by mass of the total amount of film-forming resin.

[0058] (Hardening agent) The curing agent crosslinks the film-forming resin, such as polyol, thereby improving the corrosion resistance and durability of the resulting coating. The curing agent content is, for example, 35.0 to 90.0% by mass of the resin solids content of the two-component coating composition. The curing agent content may be 45.0% by mass or more, or 55.0% by mass or more. The curing agent content may be 85.0% by mass or less, or 70.0% by mass or less. The curing agent content may be 45.0 to 85.0% by mass, or 55.0 to 70.0% by mass.

[0059] <Isocyanurate compounds> The curing agent contains an isocyanurate compound. The isocyanurate compound is a trimer of an isocyanate compound and has a ring structure.

[0060] The isocyanate compound is not particularly limited, and examples include those known as curing agents for two-component reactive compositions. Examples of isocyanate compounds include aromatic diisocyanates such as tolylene diisocyanate (TDI), 4,4'-diphenylmethane diisocyanate (MDI), xylylene diisocyanate (XDI), and metaxylylene diisocyanate (MXDI); aliphatic diisocyanates such as hexamethylene diisocyanate (HDI), tetramethylene diisocyanate, 2-methylpentane-1,5-diisocyanate, 3-methylpentane-1,5-diisocyanate, lysine diisocyanate, and trioxyethylene diisocyanate; and alicyclic diisocyanates such as isophorone diisocyanate (IPDI), cyclohexyl diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, norbornane diisocyanate, hydrogenated tolylene diisocyanate, hydrogenated xylene diisocyanate, and hydrogenated tetramethylxylene diisocyanate. These can be used individually or in combination of two or more types.

[0061] In particular, aliphatic diisocyanates and HDIs are suitable due to their relatively low viscosity. Trimers of these isocyanate compounds exhibit particularly high reactivity with polyols. Therefore, they are more suitably used in coating layer formation methods by in-mold coating.

[0062] The ratio (NCO / OH) of the isocyanate group equivalent of the isocyanurate compound to the hydroxyl group equivalent of the polyol may be, for example, 0.5 / 1.0 to 2.0 / 1.0. When the equivalent ratio is within the above range, the curability is high, and it is particularly suitable for use in forming a coating layer by in-mold painting. The ratio (NCO / OH) may be 0.9 / 1.0 to 1.2 / 1.0.

[0063] The proportion of the isocyanurate compound in the total amount of the curing agent is not particularly limited. The above proportion of the isocyanurate compound may be 95.0% by mass or more, 98.0% by mass or more, 99.7% by mass or more, or 100% by mass.

[0064] <Other hardening agents> Other curing agents besides isocyanurate compounds may be included. Examples of other curing agents include amino resins, monomers or dimers of the above isocyanate compounds, biuret derivatives of the above isocyanate compounds, blocked derivatives of the above isocyanate compounds, epoxy compounds, aziridine compounds, carbodiimide compounds, and oxazoline compounds. These may be used individually or in combination of two or more.

[0065] Other curing agents are preferably present in small amounts due to their ability to cure at low temperatures and in a short time. In particular, the amount of carbodiimide compounds may be 1.0% by mass or less, 0.2% by mass or less, or 0% by mass of the total amount of curing agents.

[0066] (solvent) The solvent content in the paint composition is, for example, 10.0% by mass or less. This allows for rapid curing of the coating film. Therefore, a coating film with excellent appearance and physical properties can be obtained by layer formation through in-mold coating. The solvent content may be 5.0% by mass or less, or even 0% by mass.

[0067] The solvent is not particularly limited. The solvent is usually an organic solvent. Examples of organic solvents include ester solvents such as ethyl acetate, butyl acetate, isopropyl acetate, ethylene glycol monoethyl ether acetate, propylene glycol monomethyl ether acetate, and propylene glycol monoethyl ether acetate; ether solvents such as propylene glycol monomethyl ether, ethylene glycol monomethyl ether, methyl methoxybutanol, ethoxypropanol, ethylene glycol isopropyl ether, ethylene glycol-t-butyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, methoxybutanol, and propylene glycol monobutyl ether; alcohol solvents such as methanol, ethanol, butanol, and propyl alcohol; ketone solvents such as acetone, methyl ethyl ketone, and methyl isobutyl ketone; aliphatic hydrocarbon solvents such as Swarzol, Shellzol, and mineral spirits; and aromatic solvents such as xylene, toluene, Solvesso-100 (S-100), and Solvesso-150 (S-150). These can be used individually or in combination of two or more.

[0068] <Pigments> The main component may contain a pigment. Examples of pigments include coloring pigments, luminosity pigments, and extender pigments. The pigment content is not particularly limited. The pigment content should be set appropriately depending on its type and purpose.

[0069] Examples of luminous pigments include metal flakes (aluminum, chromium, gold, silver, copper, brass, titanium, nickel, nickel-chromium, stainless steel, etc.), metal oxide flakes, pearl pigments, glass flakes coated with metal or metal oxide, silica flakes coated with metal oxide, graphite, holographic pigments, and cholesteric liquid crystal polymers. These can be used individually or in combination of two or more.

[0070] Examples of coloring pigments include organic coloring pigments such as azo chelate pigments, insoluble azo pigments, condensed azo pigments, diketopyrrolopyrrole pigments, benzimidazolon pigments, phthalocyanine pigments, indigo pigments, perinone pigments, perylene pigments, dioxane pigments, quinacridone pigments, isoindolinone pigments, and metal complex pigments; and inorganic coloring pigments such as lead yellow, yellow iron oxide, red iron oxide, carbon black, and titanium dioxide. These can be used individually or in combination of two or more.

[0071] Examples of extender pigments include calcium carbonate, barium sulfate, clay, and talc. These can be used individually or in combination of two or more.

[0072] (others) The two-component coating composition may contain other components as needed. Examples of other components include additives commonly used in the coating and paint fields. Specifically, these include various pigments, surface modifiers, viscosity modifiers, antioxidants, UV inhibitors, defoamers, catalyst aids, rust inhibitors, settling inhibitors, and dispersants. These additives may be added to the main component or to the curing agent. The amount of additives is not particularly limited and can be set as needed.

[0073] [In-mold painting] In-mold coating is a method of forming a coating film (hereinafter also referred to as a coating layer) inside a mold. In-mold coating yields a coated body having a coating layer formed on a portion of the surface of the object to be coated. In in-mold coating, the coated body is manufactured by a method comprising injecting the two-component coating composition between the surface of the object to be coated, which is placed on one mold, and the other mold, and then curing (baking) the injected two-component coating composition after closing the molds. Curing may be performed inside the mold as described above.

[0074] With in-mold coating, the coating layer is formed within the mold, which suppresses the adhesion of dust and other debris between the workpiece and the coating layer, as well as the incorporation of dust and other debris into the coating layer. Furthermore, because it is less affected by the surface condition of the workpiece, the mold pattern can be transferred to the coating layer with high precision.

[0075] When the amount of solvent in the coating composition is small, a drying process to remove the solvent is not required, improving productivity. Furthermore, a thick coating layer with suppressed sagging and undercoating can be formed.

[0076] (1) Preparation of the object to be coated The object to be coated may be pre-molded into a predetermined shape. That is, in-mold coating may include, for example, placing a pre-molded object to be coated on the surface of one of the molds before injecting the two-component coating composition. Since the two-component coating composition can be cured at low temperatures, it is particularly suitable for coating resin objects. The resin objects to be coated may be molded in the same mold. That is, in-mold coating may include, for example, injection molding the resin objects to be coated in the mold before injecting the two-component coating composition.

[0077] The resin-coated object may be a thermoplastic resin or a thermosetting resin. Examples of resins that make up the above-mentioned resin-coated object include polypropylene (PP) resin, acrylonitrile-butadiene-styrene copolymer (ABS resin), polycarbonate (PC) / ABS resin, PC / acrylonitrile-ethylene-propylene-diene-styrene copolymer (AES resin), AES resin, PC / polybutylene terephthalate (PBT) resin, PC / polyethylene terephthalate (PET) resin, PC resin, polymethyl methacrylate (PMMA) resin, GF-PBT resin, GF-polyamide (PA) resin, Noryl-GTX resin, polyvinyl chloride (PVC resin), acrylonitrile-styrene-acrylic (ASA) resin, carbon fiber reinforced plastic (CFRP resin), and glass fiber reinforced plastic (GFRP resin).

[0078] (2) Injection of two-component coating composition The above-mentioned two-component coating composition is injected between the surface of the object to be coated, which is placed on one mold, and the other mold.

[0079] The viscosity of the two-component coating composition as it is injected into the mold, measured using a Brookfield rotational viscometer at a temperature of 65–95°C (typically 70–85°C) and a rotational speed of 6 rpm, may be 100–500 mPa·s.

[0080] In mold coating, a low amount of solvent in the coating composition is required. A low amount of solvent tends to increase the viscosity of the coating composition. If necessary, the viscosity may be adjusted by heating the main component and / or curing agent of the two-component coating composition. Heating increases the fluidity of the coating composition, improves the mixability of the main component and curing agent, and can also improve the curability (reactivity) after filling into the mold. The heating for viscosity adjustment is not particularly limited as long as it does not cause the two-component coating composition to harden. The above heating is performed, for example, at a temperature of 65°C or higher but below the curing temperature (e.g., 80°C).

[0081] The time from the start of injecting the two-component coating composition into the mold until the injection of a predetermined amount is completed (or until the mold is closed) (injection time) is, for example, 1 to 15 seconds. In in-mold coating, it is desirable that the fluidity of the two-component coating composition be maintained at least during the injection time. Maintaining fluidity means that the viscosity of the two-component coating composition is within the above range. By maintaining the above fluidity, the two-component coating composition can easily spread throughout the inside of the mold. Because the amount of curing catalyst in the two-component coating composition is small, fluidity is easily maintained during the injection time under conditions below the baking temperature. Hereinafter, the performance of maintaining fluidity during the injection time under conditions below the baking temperature will be referred to as coating workability. The two-component coating composition according to this disclosure also has excellent coating workability.

[0082] (3) Baking After closing the mold, the injected two-component coating composition is heated to cure. The inside of the mold may be degassed using a vacuum pump or the like. The inside of the mold may also be pressurized. After that, the mold is opened and the coated object is removed.

[0083] The two-component coating composition is cured by heating at 80-110°C for 20 seconds to 1 minute 30 seconds, for example. According to the two-component coating composition of this disclosure, even with such low temperature and short heating time, the curability is high, and the resulting coating layer has excellent water-resistant adhesion. The curing temperature may be 80-100°C. The curing time may be 30 seconds to 1 minute.

[0084] The baking temperature is the temperature of the mold (both the fixed mold and the movable mold). The temperatures of the fixed mold and the movable mold may be the same or different. The baking time is the time from when the mold is closed until when it is opened.

[0085] The coating layer formed by the above two-component coating composition has excellent curability and water-resistant adhesion. In addition, the coating layer also has excellent weather resistance. [Examples]

[0086] The present invention will be further illustrated by the following examples, but the present invention is not limited thereto. In the examples, "parts" and "%" are based on mass unless otherwise specified.

[0087] [Example 1] The main component was prepared by mixing 36.3 parts of polyol (desmofen VPLS2249 / 1: manufactured by Sumika Covestro Urethane Co., Ltd., polyester polyol, hydroxyl value 512 mg KOH / g, average number of hydroxyl groups 3 or more) and 0.7 parts of curing catalyst a. Separately, 63.7 parts of an isocyanurate compound (Desmodulo N3300, manufactured by Sumika Covestro Urethane Co., Ltd., a nurate of HDI) was prepared as a curing agent. The NCO / OH ratio was 1.0 / 1.0, and the amount of solvent in the two-component coating composition was 0% by mass. Table 1 shows the details of the curing catalyst.

[0088] [Table 1]

[0089] [Examples 2-18 and Comparative Examples 1-13] The main component and curing agent were prepared using the same procedure as in Example 1, except that the type and amount of curing catalyst were changed as shown in Tables 2 to 4.

[0090] [evaluation] The two-component coating compositions prepared in the examples and comparative examples were evaluated as follows. The evaluation results are shown in Tables 2 to 4.

[0091] Details of the carbodiimide used are as follows: Carbodiimide 1: Product name "Carbodilite V-05", manufactured by Nisshinbo Chemical Co., Ltd. Carbodiimide 2: Product name "Carbodilite V-02B", manufactured by Nisshinbo Chemical Co., Ltd.

[0092] (1) Coating workability The main component of the two-component coating composition was agitated using a planetary mixing system with degassing capabilities. Next, the curing agent was added to the main component and mixed for 15 seconds in the same manner, after which the sample was removed. The point at which the sample was removed was considered the start of the injection time. The removed sample was stirred with a spatula, and the point at which the sample no longer fell from the spatula was considered the end of the injection time. The time from the start to the end of the injection time was calculated and evaluated according to the following criteria. The above procedures were performed at room temperature (20-25°C), and the liquid temperature of the two-component coating composition was also at room temperature.

[0093] The above method evaluates whether the time from when the two-component coating composition begins to be injected into the mold until a predetermined amount is injected (injection time) is sufficient, assuming in-mold coating. An A rating indicates excellent coating workability.

[0094] (Evaluation Criteria) A: More than 5 seconds B: Less than 5 seconds

[0095] (2) Curability The main component and hardener of the two-component coating composition were placed in a polypropylene cup and immediately stirred with a glass rod. The start of stirring was considered the beginning of curing. Subsequently, the mixture was continued to be stirred with the glass rod until it stopped dripping from the rod, which was considered the end of curing. The time from the start to the end of curing was calculated and evaluated according to the following criteria. The above procedure was performed at room temperature (20-25°C), and the liquid temperature of the two-component coating composition was also at room temperature.

[0096] The above method evaluates whether a two-component coating composition cures quickly. A rating of C or higher indicates excellent curing properties.

[0097] (Evaluation Criteria) A: 15 seconds or more but less than 60 seconds B: 60 seconds or more but less than 120 seconds C: 120 seconds or more, less than 180 seconds D: 180 seconds or more, less than 300 seconds E: Less than 15 seconds, or 300 seconds or more.

[0098] (3) Initial adhesion First, we prepared test panel A for evaluation. After injection molding ABS resin, the same mold was heated to 80°C. The gap between the fixed mold and the movable mold was set to 300 μm, and a predetermined amount of two-component coating composition was injected within 1 to 15 seconds. The mold was then heated for 60 seconds to obtain test plate A, which had a 2.0 mm thick ABS plate and a coating layer approximately 300 μm thick formed on its surface.

[0099] A tape peel test was performed on the coating layer of test board A. Specifically, 10 vertical and 10 horizontal cuts were made in the coating layer at 1 mm intervals using a cutter, and then cellophane tape (registered trademark) (manufactured by Nichiban Co., Ltd.) was applied and peeled off. The number of squares in which the coating layer remained was counted out of 100 squares. The more squares in which the coating layer remained, the better the adhesion. The number of counted squares was evaluated according to the following criteria. A rating of B or higher indicates excellent initial adhesion.

[0100] (Evaluation Criteria) A: The number of counted squares is 81 or more. B: The number of counted squares is between 60 and 80. C: The number of counted squares is 59 or less.

[0101] (4) Water-resistant adhesion Test plate A, obtained in the same manner as described above, was immersed in 40°C water for 10 days. Afterwards, test plate A was removed and the water droplets were lightly wiped off. After removal, the painted item was left at room temperature (23°C) for 24 hours. Subsequently, a tape peel test was performed and evaluated in the same manner as described above. A rating of B or higher indicates excellent water-resistant adhesion.

[0102] (5) High temperature water resistance Test plate A, obtained in the same manner as described above, was immersed in 80°C water for 1 hour. Afterwards, test plate A was removed and the water droplets were lightly wiped off. After removal, a tape peel test was performed at room temperature (23°C) in the same manner as described above and evaluated. A rating of B or higher indicates excellent high-temperature water resistance.

[0103] (6) Recyclability Test plate A, obtained in the same manner as above, was immersed in 80°C water for 24 hours. Afterwards, test plate A was removed and the water droplets were lightly wiped off. After removal, the painted item was left at room temperature (23°C) for 24 hours. Subsequently, a tape peel test was performed in the same manner as above, and the number of counted squares was evaluated according to the following criteria. An A rating indicates excellent recyclability.

[0104] (Evaluation Criteria) A: The number of counted squares is 59 or less. B: The number of counted squares is between 60 and 80. C: The number of counted squares is 81 or more.

[0105] [Table 2]

[0106] [Table 3]

[0107] [Table 4] [Industrial applicability]

[0108] The two-component coating composition of the present invention can be suitably used in coating methods different from conventional spray painting, such as in-mold coating for forming a coating layer. Because the two-component coating composition of the present invention provides a coating layer with excellent high-temperature water resistance and recyclability, it is particularly suitable for use in the exterior of reusable automobiles and in building applications.

Claims

1. A two-component coating composition comprising a main component and a curing agent, The main component comprises a polyol and a curing catalyst. The curing agent comprises an isocyanurate compound, The curing catalyst contains an organotin compound containing 16.0% by mass or more of Sn atoms. The organotin compound is given by the following general formula (1): 【Chemistry 1】 (In the formula, R １ R is a hydrocarbon group having 1 or more carbon atoms. ２ R is a hydrocarbon group having 4 or more carbon atoms. ３ and R ４ Each of these is independently a monovalent organic group having one or more carbon atoms. It is represented as, A two-component coating composition in which the curing catalyst content is greater than 0.6 parts by mass and less than or equal to 3.0 parts by mass per 100 parts by mass of solid content of the two-component coating composition.

2. In the above general formula (1), the R ３ is -COOR ３１ The group represented by (R ３１ is a hydrocarbon group having 1 or more carbon atoms. ) and the R ４ The two-component coating composition according to claim 1, wherein is a hydrocarbon group having 4 or more carbon atoms.

3. The two-component coating composition according to claim 1 or 2, wherein the solvent content is 10.0% by mass or less.

4. The two-component coating composition according to claim 1 or 2, wherein the isocyanurate compound comprises a trimer of hexamethylene diisocyanate.

5. The two-component coating composition according to claim 1 or 2, wherein the polyol is at least one selected from the group consisting of polyester polyols, polyether polyols, and polycarbonate polyols.

6. The two-component coating composition according to claim 1 or 2, wherein the ratio (NCO / OH) of the isocyanate group equivalent of the isocyanurate compound to the hydroxyl group equivalent of the polyol is 0.5 / 1.0 to 2.0 / 1.

0.

7. A two-component coating composition according to claim 1 or 2, for use in mold coating.

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