Low-temperature dissociation water-based blocked polyisocyanate and paint containing same

Abstract

To provide a water-based blocked polyisocyanate in which the blocking agent dissociates at low temperature and has good storage stability when used as a water-based coating, and to provide a coating that contains the same.SOLUTION: The problem is solved by a low-temperature dissociation water-based blocked polyisocyanate, which is a low-temperature dissociation water-based blocked polyisocyanate obtained from an imidazole-based blocking agent (a), an active methylene-based blocking agent (b), a polyisocyanate (c), and a nonionic hydrophilic group-containing compound (d), and in which, characterized, the imidazole-based blocking agent (a) is 2-ethyl-4-methylimidazole, the active methylene-based blocking agent (b) is a malonic acid diester, and the mole ratio of (a) and (b) is 70 / 30 to 10 / 90.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an aqueous blocked polyisocyanate in which the blocking agent dissociates at low temperatures, and a coating material containing the same. [Background technology]

[0002] Blocked polyisocyanates are produced by blocking the free isocyanates of isocyanate-terminated precursors with a blocking agent having an active hydrogen group capable of reacting with the isocyanate group, rendering the isocyanate activity inactive at room temperature. When heated, the blocking agent dissociates, regenerating the isocyanate group.

[0003] Blocked polyisocyanates are widely used in baked coatings, such as those used in automobiles, aircraft, building materials, and pre-coated metals used in home appliances. Common blocking agents used in blocked polyisocyanates include alcohol-based, phenol-based, lactam-based, and oxime-based agents. The dissociation temperature of blocked polyisocyanates varies depending on the type of polyisocyanate, the type of blocking agent, the type of reactant, and the type and amount of catalyst, but is generally around 130-250°C.

[0004] In recent years, for the purpose of reducing costs and carbon dioxide emissions during baking finishes and enabling coating of plastic members, there has been a demand for blocked polyisocyanates in which the blocking agent dissociates at lower temperatures than conventional ones and which cure in a short time. Furthermore, in order to meet social and industrial demands for environmental conservation and work safety, there has been a demand for water-based (aqueous) compositions that do not use organic solvents, and there has been an active shift to blocked polyisocyanates that can be used in water-based coatings.

[0005] Diethyl malonate has been disclosed as a blocking agent for use in low-temperature dissociation blocked polyisocyanates (Patent Document 1), but heating to around 100°C is required to completely cure the coating, making it unsuitable for use on plastic members with low heat resistance. In addition, diethyl malonate blocked polyisocyanates are prone to crystallization and have poor storage stability.

[0006] Imidazole-based blocking agents are known as further low-temperature dissociation blocking agents, some of which provide sufficient coating hardness at 80 to 90°C and can be used to coat plastic materials. However, imidazole-based blocked polyisocyanates are said to have poor stability when used in water-based paints, and it has been proposed to utilize this property in a water-encapsulating gel-forming material (Patent Document 2).

[0007] A method of reacting an acid component has been proposed as a measure to improve the aqueous dispersion stability of imidazole-blocked polyisocyanates (Patent Document 3). However, the acid component may have adverse effects, such as increasing the dissociation temperature of the blocking agent and reducing the reactivity of the isocyanate group regenerated after dissociation of the blocking agent. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 57-121065 [Patent Document 2] Japanese Patent Application Publication No. 56-59832 [Patent Document 3] Japanese Patent Application Publication No. 60-40121 Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention has been made in light of the above circumstances, and an object of the present invention is to provide an aqueous blocked polyisocyanate in which a blocking agent dissociates at low temperatures and which has good storage stability when made into an aqueous paint, and a paint containing the same. [Means for solving the problem]

[0010] As a result of intensive research aimed at solving the above-mentioned problems, the present inventors have found that a blocked polyisocyanate obtained by using a specific imidazole-based blocking agent and an active methylene-based blocking agent in combination can solve the above-mentioned problems, and have thus completed the present invention.

[0011] That is, the present invention includes the following embodiments [1] to [9].

[0012] [1] A low-temperature dissociation water-based blocked polyisocyanate obtained from an imidazole-based blocking agent (a), an active methylene-based blocking agent (b), a polyisocyanate (c), and a nonionic hydrophilic group-containing compound (d), characterized in that the imidazole-based blocking agent (a) is 2-ethyl-4-methylimidazole, the active methylene-based blocking agent (b) is a malonic acid diester, and the molar ratio of (a) to (b) is 70 / 30 to 10 / 90.

[0013] [2] The low-temperature dissociation water-based blocked polyisocyanate according to the above [1], characterized in that the active methylene-based blocking agent (b) is at least one selected from the group consisting of dimethyl malonate, diethyl malonate, di-n-propyl malonate, diisopropyl malonate, di-n-butyl malonate, di-t-butyl malonate, t-butylmethyl malonate, and t-butylethyl malonate.

[0014] [3] The low-temperature dissociation water-based blocked polyisocyanate according to [1] or [2] above, wherein the polyisocyanate (c) is at least one selected from the group consisting of aliphatic diisocyanates and alicyclic diisocyanates.

[0015] [4] The low-temperature dissociation water-based blocked polyisocyanate according to any one of [1] to [3] above, characterized in that the nonionic hydrophilic group-containing compound (d) is at least one selected from the group consisting of polyoxyalkylene alkyl ethers and polyoxyalkylene esters.

[0016] [5] The low-temperature dissociation water-based blocked polyisocyanate according to any one of [1] to [4] above, characterized in that the polyisocyanate (c) is an isocyanurate-modified polyisocyanate derived from hexamethylene diisocyanate.

[0017] [6] The low-temperature dissociation water-based blocked polyisocyanate according to any one of the above [1] to [5], characterized in that the nonionic hydrophilic group-containing compound (d) is polyethylene glycol monomethyl ether.

[0018] [7] A resin composition comprising the low-temperature dissociation water-based blocked polyisocyanate according to any one of [1] to [6] above and a base resin.

[0019] [8] A paint containing the resin composition described in [7] above.

[0020] [9] A coating film obtained from the paint described in [8] above. [Effects of the Invention]

[0021] According to the present invention, it is possible to obtain an aqueous blocked polyisocyanate that has good storage stability when made into an aqueous paint without impairing low-temperature dissociation properties, and a paint containing the same. DETAILED DESCRIPTION OF THE INVENTION

[0022] The present invention will be described in detail below.

[0023] The low-temperature dissociation water-based blocked polyisocyanate of the present invention is a blocked polyisocyanate obtained from an imidazole-based blocking agent (a) (hereinafter also referred to as blocking agent (a)), an active methylene-based blocking agent (b) (hereinafter also referred to as blocking agent (b)), a polyisocyanate (c), and a nonionic hydrophilic group-containing compound (d), characterized in that the blocking agent (a) is 2-ethyl-4-methylimidazole, the blocking agent (b) is a malonic acid diester, and the molar ratio of (a) to (b) is 70 / 30 to 10 / 90.

[0024] By using the blocking agent (a) and the blocking agent (b) in combination within the above range, it is possible to obtain an aqueous blocked polyisocyanate that has excellent storage stability when made into an aqueous paint and in which the blocking agent dissociates even at low temperatures.

[0025] The imidazole-based blocking agent (a) in the present invention is 2-ethyl-4-methylimidazole. Examples of imidazole-based blocking agents other than 2-ethyl-4-methylimidazole include imidazole, 2-methylimidazole, 4-methylimidazole, 2,4-dimethylimidazole, 2-ethylimidazole, 2-propylimidazole, 2-isopropylimidazole, 2-butylimidazole, 2-isobutylimidazole, 2-t-butylimidazole, 4-t-butylimidazole, 4-methyl-2-propylimidazole, 2-isopropyl-5-methylimidazole, 2-phenylimidazole, 4-phenylimidazole, 5-phenylimidazole, 2-methyl-4-phenylimidazole, 2,4-diphenylimidazole, 4,5-diphenylimidazole, 2-undecylimidazole, and 2-heptadecylimidazole. These imidazole-based blocking agents can be used in combination within the scope of the present invention, but from the viewpoints of blocking agent dissociation at low temperatures and storage stability, it is preferable to use 2-ethyl-4-methylimidazole alone.

[0026] The active methylene-based blocking agent (b) in the present invention is a malonic acid diester.

[0027] Examples of malonic acid diesters include dialkyl esters such as dimethyl malonate, diethyl malonate, di-n-propyl malonate, diisopropyl malonate, di-n-butyl malonate, di-t-butyl malonate, t-butylmethyl malonate, and t-butylethyl malonate. Among these, diethyl malonate, di-n-propyl malonate, diisopropyl malonate, and di-n-butyl malonate are preferred.

[0028] In the present invention, the molar ratio of blocking agent (a) to blocking agent (b) is 70 / 30 to 10 / 90, and preferably 60 / 40 to 20 / 80. By setting the ratio within this range, it is possible to achieve both good dissociation of the blocking agent at low temperatures and good storage stability.

[0029] The polyisocyanate (c) in the present invention is preferably a polyisocyanate selected from aliphatic polyisocyanates, alicyclic polyisocyanates, and polyisocyanates formed by combining these. However, aromatic polyisocyanates and aromatic aliphatic polyisocyanates can also be used in combination within the scope of the present invention.

[0030] Examples of the aliphatic polyisocyanate include hexamethylene diisocyanate, tetramethylene diisocyanate, 2-methyl-pentane-1,5-diisocyanate, 3-methyl-pentane-1,5-diisocyanate, lysine diisocyanate, and trioxyethylene diisocyanate.

[0031] Examples of alicyclic polyisocyanates include isophorone diisocyanate, cyclohexyl diisocyanate, hydrogenated diphenylmethane diisocyanate, norbornane diisocyanate, hydrogenated tolylene diisocyanate, hydrogenated xylene diisocyanate, and hydrogenated tetramethylxylene diisocyanate.

[0032] Examples of aromatic polyisocyanates include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, 2,2'-diphenylmethane diisocyanate, 4,4'-diphenylether diisocyanate, 2-nitrodiphenyl-4,4'-diisocyanate, 2,2'-diphenylpropane-4,4'-diisocyanate, 3,3'-dimethyldiphenylmethane-4,4'-diisocyanate, 4,4'-diphenylpropane diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, naphthylene-1,4-diisocyanate, naphthylene-1,5-diisocyanate, and 3,3'-dimethoxydiphenyl-4,4'-diisocyanate.

[0033] Examples of aromatic aliphatic polyisocyanates include 1,3- or 1,4-xylene diisocyanate, 1,3- or 1,4-bis(1-isocyanato-1-methylethyl)benzene, ω,ω'-diisocyanato-1,4-diethylbenzene, and the like.

[0034] Furthermore, allophanate-modified, urea-modified, biuret-modified, uretdione-modified, and isocyanurate-modified polyisocyanates may be used in combination.

[0035] Among these polyisocyanates, it is more preferable to use an isocyanurate-modified polyisocyanate of hexamethylene diisocyanate.

[0036] As the nonionic hydrophilic group-containing compound (d) in the present invention, polyoxyalkylene alkyl ethers, polyoxyalkylene esters, and nonionic hydrophilic group-containing compounds that are combinations thereof can be preferably used.

[0037] Examples of polyoxyalkylene alkyl ethers include polyethylene glycol monomethyl ether, polyethylene glycol monododecyl ether, polyethylene glycol monocetyl ether, polyethylene glycol monooleyl ether, ethylene glycol monododecyl ether, diethylene glycol monododecyl ether, triethylene glycol monododecyl ether, tetraethylene glycol monododecyl ether, pentaethylene glycol monododecyl ether, hexaethylene glycol monododecyl ether, and octaethylene glycol monododecyl ether.

[0038] Examples of polyoxyalkylene esters include polyethylene glycol monolaurate and polyethylene glycol monostearate.

[0039] Among these, polyoxyalkylene alkyl ether is preferred, and polyethylene glycol monomethyl ether is most preferred.The number average molecular weight of these is preferably 400 to 4,000, and most preferably 400 to 1,000.

[0040] The blocked polyisocyanate of the present invention can be produced, for example, by adding the above-mentioned components (a) to (d) to an organic solvent and reacting them according to the urethanization reaction and blocking reaction conditions shown below.

[0041] In the present invention, the reaction first involves urethanization of polyisocyanate (c) with a nonionic hydrophilic group-containing compound (d) to obtain an isocyanate-terminated precursor. The amount of nonionic hydrophilic group-containing compound (d) charged is preferably 1 to 30 mass% relative to the polyisocyanate, and more preferably 1 to 20 mass%. This urethanization reaction proceeds without a catalyst, but can also be accelerated using a known urethanization reaction catalyst. The reaction temperature for the urethanization reaction is typically 20 to 200°C, and the urethanization reaction time is typically 1 to 10 hours, although this varies depending on the presence or absence of a catalyst, the amount added, the type of solvent, the solids concentration, and the temperature.

[0042] During the urethanization reaction, the resulting mixture may be diluted to any solid content with an organic solvent inactive to isocyanate groups. Examples of organic solvents include aromatic solvents such as toluene and xylene, ketones such as acetone, methyl ethyl ketone, and methyl isobutyl ketone, esters such as ethyl acetate and butyl acetate, and glycol ethers such as ethylene glycol monoethyl ether acetate, propylene glycol monomethyl ether acetate, and diethylene glycol diethyl ether. These solvents may be used alone or in combination of two or more.

[0043] Next, the isocyanate group-terminated precursor obtained in the above reaction is subjected to a blocking reaction with blocking agent (a) and blocking agent (b). The reaction temperature for the blocking reaction is usually 20 to 200°C, and the blocking reaction time is usually 1 to 20 hours. The amount of blocking agent charged is 1.0 to 2.0 times, and preferably 1.0 to 1.5 times, the molar amount of free isocyanate groups. If significant heat is generated during the addition of the blocking agent, it is added in several portions or added dropwise to suppress sudden heat generation.

[0044] There is no particular limitation on the order in which the blocking agent (a) and the blocking agent (b) are added, and the blocking agent (a) and the blocking agent (b) may be added separately or in admixture.

[0045] Furthermore, if necessary, pigments, dispersion stabilizers, viscosity modifiers, leveling agents, antigelling agents, light stabilizers, antioxidants, ultraviolet absorbers, heat resistance improvers, inorganic and organic fillers, plasticizers, lubricants, antistatic agents, reinforcing materials, etc. may be added.

[0046] The resin composition of the present invention contains the aqueous blocked polyisocyanate described above. The aqueous (water-based) resin used as the base of the resin composition preferably has an active hydrogen group, and specific examples thereof include polyurethane resins, polyamide resins, saturated or unsaturated polyester resins, alkyd resins modified with saturated or unsaturated fatty acids, acrylic resins, fluororesins, epoxy resins, and cellulose resins. Furthermore, in consideration of film performance such as gloss, thickness, hardness, durability, flexibility, and drying speed, as well as cost, saturated or unsaturated polyester resins, alkyd resins modified with saturated or unsaturated fatty acids, and acrylic resins are preferred.

[0047] The blending ratio of the aqueous blocked polyisocyanate to the base resin in the resin composition of the present invention is a molar ratio of available isocyanate groups in the aqueous blocked polyisocyanate to active hydrogen groups in the base resin of 1 / 9 to 9 / 1, preferably 4 / 6 to 6 / 4. Outside this range, the resin becomes difficult to cure. The available isocyanate groups in the aqueous blocked polyisocyanate are isocyanate groups blocked with a blocking agent, and when the blocking agent dissociates, they become available isocyanate groups that can react with active hydrogen groups.

[0048] The resin composition of the present invention can also be suitably used as a coating material.

[0049] The coating method of the present invention is not particularly limited and may be appropriately selected from known methods. The amount of coating, thickness of the coating film, etc. may be appropriately determined depending on the material of the surface to be coated. The curing conditions of the coating depend on the type of blocking agent and base resin, but the aqueous blocked polyisocyanate of the present invention can be sufficiently cured in 30 minutes in an 80°C environment to obtain a good coating film.

[0050] The aqueous blocked polyisocyanate of the present invention uses an imidazole-based blocking agent, which is generally considered to have insufficient storage stability for aqueous coatings. By using 2-ethyl-4-methylimidazole and a malonic acid diester as specific blocking agents, it is possible to obtain an aqueous coating material with a low blocking agent dissociation temperature and excellent storage stability. Because the curing conditions for coating materials using this aqueous blocked polyisocyanate are mild, less energy is required for heat curing, making it environmentally and cost-effective. Furthermore, it is now possible to apply the coating material to plastic components with low heat resistance. [Example]

[0051] Examples and comparative examples of the present invention will be described in detail below, but the present invention is not limited to these.

[0052] Example 1 [Production of Water-Based Blocked Polyisocyanate 1] A four-necked flask equipped with a stirrer, thermometer, heating device, nitrogen seal tube, and condenser was charged with 350 g of Coronate HXR (Tosoh Corporation, hexamethylene diisocyanate trimer, NCO content 21.8% by mass, trade name), 3 g of polyethylene glycol monomethyl ether 400 (Tokyo Chemical Industry Co., Ltd., number average molecular weight 380-420, trade name), and 400 g of diethyl diglycol (Nippon Nyukazai Co., Ltd., diethylene glycol diethyl ether, trade name). The flask was purged with nitrogen, heated to 80 ° C. with stirring, and reacted at the same temperature for 4 hours to obtain an isocyanate-terminated precursor. Subsequently, the resulting isocyanate-terminated precursor was cooled to 60 ° C., and then 145 g of diethyl malonate (Fujifilm Wako Pure Chemical Industries, Ltd.) and 2 g of 28% sodium methoxide methanol solution (Fujifilm Wako Pure Chemical Industries, Ltd.) were charged and reacted at 75 ° C. for 3 hours. Subsequently, the reaction solution was cooled to 60°C, and 100 g of 2-ethyl-4-methylimidazole (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added. The reaction was carried out at 60°C for 5 hours. In the infrared absorption spectrum (IR measurement), the peak of the NCO group (2270 cm -1 When the color (around 100%) disappeared, the mixture was cooled to room temperature to obtain aqueous blocked polyisocyanate BI-1.

[0053] Example 2 [Production of Water-Based Blocked Polyisocyanate 2] In a manufacturing apparatus similar to that used in Example 1, 334 g of Coronate HXR, 4 g of polyethylene glycol monomethyl ether 400, and 400 g of diethyl diglycol were charged, and the flask was purged with nitrogen. The mixture was heated to 80°C with stirring and allowed to react at the same temperature for 4 hours to obtain an isocyanate-terminated precursor. The resulting isocyanate-terminated precursor was then cooled to 60°C, after which 222 g of diethyl malonate and 2 g of 28% sodium methoxide methanol solution were added, and the mixture was allowed to react at 75°C for 3 hours. The reaction solution was then cooled to 60°C, and 38 g of 2-ethyl-4-methylimidazole was added. The mixture was allowed to react at 60°C for 5 hours, and the NCO group peak (2270 cm) was detected in the infrared absorption spectrum (IR measurement). -1 When the color (around 100%) disappeared, the mixture was cooled to room temperature to obtain aqueous blocked polyisocyanate BI-2.

[0054] Comparative Example 1 [Production of Water-Based Blocked Polyisocyanate 3] In a manufacturing apparatus similar to that used in Example 1, 380 g of Coronate HXR, 4 g of polyethylene glycol monomethyl ether 400, and 400 g of diethyl diglycol were charged, and the flask was purged with nitrogen. The mixture was heated to 80°C with stirring and allowed to react at the same temperature for 4 hours to obtain an isocyanate-terminated precursor. The resulting isocyanate-terminated precursor was then cooled to 60°C, and 216 g of 2-ethyl-4-methylimidazole was added. The mixture was allowed to react at 60°C for 5 hours. In the infrared absorption spectrum (IR measurement), the peak of the NCO group (2270 cm) was observed. -1 When the color (around 100%) disappeared, the mixture was cooled to room temperature to obtain aqueous blocked polyisocyanate BI-3.

[0055] Comparative Example 2 [Production of Water-Based Blocked Polyisocyanate 4] In a manufacturing apparatus similar to that used in Example 1, 366 g of Coronate HXR, 4 g of polyethylene glycol monomethyl ether 400, and 400 g of diethyl diglycol were charged, and the flask was purged with nitrogen. The mixture was heated to 80°C with stirring and reacted at the same temperature for 4 hours to obtain an isocyanate-terminated precursor. The resulting isocyanate-terminated precursor was then cooled to 60°C, after which 61 g of diethyl malonate and 2 g of 28% sodium methoxide methanol solution were charged, and the mixture was reacted at 75°C for 3 hours. The reaction solution was then cooled to 60°C, and 167 g of 2-ethyl-4-methylimidazole was charged. The mixture was reacted at 60°C for 5 hours, and the NCO group peak (2270 cm) was detected in the infrared absorption spectrum (IR measurement). -1 When the color (around 100%) disappeared, the mixture was cooled to room temperature to obtain aqueous blocked polyisocyanate BI-4.

[0056] Comparative Example 3 [Production of Water-Based Blocked Polyisocyanate 5] In a manufacturing apparatus similar to that used in Example 1, 388 g of Coronate HXR, 4 g of polyethylene glycol monomethyl ether 400, and 400 g of diethyl diglycol were charged, and the flask was purged with nitrogen. The mixture was heated to 80°C with stirring and allowed to react at the same temperature for 4 hours to obtain an isocyanate-terminated precursor. The resulting isocyanate-terminated precursor was then cooled to 60°C, and 111 g of 2-ethyl-4-methylimidazole and 97 g of 3,5-dimethylpyrazole (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) were added. The mixture was allowed to react at 70°C for 10 hours. Infrared absorption spectroscopy (IR measurement) revealed a peak for the NCO group (at 2270 cm). -1 When the color (around 100%) disappeared, the mixture was cooled to room temperature to obtain aqueous blocked polyisocyanate BI-5.

[0057] Comparative Example 4 [Production of Water-Based Blocked Polyisocyanate 6] In a manufacturing apparatus similar to that used in Example 1, 394 g of Coronate HXR, 4 g of polyethylene glycol monomethyl ether 400, and 400 g of diethyl diglycol were charged, and the flask was purged with nitrogen. The mixture was heated to 80°C with stirring and allowed to react at the same temperature for 4 hours to obtain an isocyanate-terminated precursor. The resulting isocyanate-terminated precursor was then cooled to 60°C, and 113 g of 2-ethyl-4-methylimidazole was added. The mixture was then reacted at 60°C for 1 hour. Then, 89 g of 2-butanone oxime (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., methyl ethyl ketoxime) was added and allowed to react at 60°C for 5 hours. Infrared absorption spectroscopy (IR measurement) revealed the peak of the NCO group (2270 cm). -1 When the color (around 100%) disappeared, the mixture was cooled to room temperature to obtain aqueous blocked polyisocyanate BI-6.

[0058] The compositions of the aqueous blocked polyisocyanates BI-1 to BI-6 are shown in Table 1.

[0059] [Table 1]

[0060] [Evaluation of storage stability of paint formulation] <Paint P-1> 100 g of aqueous blocked polyisocyanate BI-1, 420 g of Burnock WE-304 (trade name, manufactured by DIC Corporation, acrylic emulsion, solids concentration 45% by mass, hydroxyl value 43 mgKOH / g), and 102 g of water were mixed to obtain paint P-1. 150 g of the resulting paint P-1 was placed in a 200 mL sample bottle and stored in a 40°C thermostatic chamber, after which the paint's appearance was confirmed. If no gelation occurred within 10 days, the paint was considered to be in good condition.

[0061] <Paint P-2~6> Paints P-2 to P-6 were obtained using the compositions shown in Table 2 and the same preparation method as for Paint P-1. The storage stability of the paint formulations for Paints P-2 to P-6 was evaluated using the same evaluation method as for Paint P-1.

[0062] The paint formulation is shown in Table 2, and the storage stability evaluation of the paint formulation is shown in Table 4.

[0063] [Table 2]

[0064] [Evaluation of coating film solvent resistance] <Paint P-7> 100 g of aqueous blocked polyisocyanate BI-1, 226 g of Burnock WE-300 (DIC Corporation, acrylic emulsion, solids concentration 45% by mass, hydroxyl value 80 mgKOH / g), and 78 g of water were mixed to obtain Paint P-7. The solvent resistance of the resulting paint film was evaluated under the following conditions. Test conditions Test piece: Paint P-7 was applied to an SPCC-SB steel plate to a thickness of 100 μm (wet). Curing: The above coating film is left to stand at room temperature for 30 minutes, then baked in a thermostatic chamber at 80°C for 30 minutes. Evaluation: The cured coating film is rubbed with absorbent cotton soaked in methyl ethyl ketone under a load of 500 g, and if there is no damage to the coating film after 50 strokes, it is considered to be good.

[0065] <Paint P8~12> Paints P-8 to P-12 were obtained using the compositions shown in Table 3 and the same preparation method as for Paint P-7. The coating film solvent resistance of Paints P-8 to P-12 was evaluated using the same evaluation method as for Paint P-7.

[0066] The paint formulation is shown in Table 3, and the coating solvent resistance evaluation is shown in Table 4.

[0067] [Table 3]

[0068] [Table 4]

[0069] As shown in Table 4, paints using the aqueous blocked polyisocyanate of the present invention have excellent storage stability, and the blocking agent dissociates well even at temperatures as low as 80°C. In other words, the reaction with the base resin proceeds sufficiently, resulting in a paint film with excellent solvent resistance.

Claims

1. A low-temperature dissociation water-based blocked polyisocyanate obtained from an imidazole-based blocking agent (a), an active methylene-based blocking agent (b), a polyisocyanate (c), and a nonionic hydrophilic group-containing compound (d), The imidazole-based blocking agent (a) is 2-ethyl-4-methylimidazole, the active methylene-based blocking agent (b) is a malonic acid diester; the nonionic hydrophilic group-containing compound (d) is polyethylene glycol monomethyl ether, polyethylene glycol monododecyl ether, polyethylene glycol monocetyl ether, polyethylene glycol monooleyl ether, ethylene glycol monododecyl ether, diethylene glycol monododecyl ether, triethylene glycol monododecyl ether, tetraethylene glycol monododecyl ether, pentaethylene glycol monododecyl ether, hexaethylene glycol monododecyl ether, or octaethylene glycol monododecyl ether, and A low-temperature dissociating water-based blocked polyisocyanate characterized in that the molar ratio of (a) to (b) is 70 / 30 to 10 / 90.

2. 2. The low-temperature dissociation water-based blocked polyisocyanate according to claim 1, wherein the active methylene-based blocking agent (b) is at least one selected from the group consisting of dimethyl malonate, diethyl malonate, di-n-propyl malonate, diisopropyl malonate, di-n-butyl malonate, di-t-butyl malonate, t-butylmethyl malonate, and t-butylethyl malonate.

3. 3. The low-temperature dissociation water-based blocked polyisocyanate according to claim 1, wherein the polyisocyanate (c) is at least one selected from the group consisting of aliphatic diisocyanates and alicyclic diisocyanates.

4. 4. The low-temperature dissociation water-based blocked polyisocyanate according to claim 1, wherein the polyisocyanate (c) is an isocyanurate-modified polyisocyanate derived from hexamethylene diisocyanate.

5. 5. The low-temperature dissociation water-based blocked polyisocyanate according to claim 1, wherein the nonionic hydrophilic group-containing compound (d) is polyethylene glycol monomethyl ether.

6. A resin composition comprising the low-temperature dissociation water-based blocked polyisocyanate according to any one of claims 1 to 5 and a base resin having an active hydrogen group.

7. A paint containing the resin composition described in claim 6.

8. A coating film obtained from the paint described in claim 7.

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