Resin composition for aqueous coating material, aqueous primer coating material, primer coating film, and article

Abstract

Provided is a resin composition for an aqueous coating material which contains a polyurethane (A), a polyolefin (B), and an aqueous medium (C), wherein the ester group concentration of the polyurethane (A) is 2-14 mmol / g and the mass ratio (A / B) of the polyurethane (A) to the polypropylene (B) is 99 / 1 to 50 / 50. The aqueous resin composition has both initial adhesiveness to and releasability from a base material, while having excellent recyclability, and is therefore suitable for use as an aqueous coating material.

Description

Resin composition for water-based paint, water-based primer paint, primer coating film, and article

[0008]

[0001] The present invention relates to a resin composition for water-based paint, a water-based primer paint, a primer coating film, and an article.

[0002] In recent years, in the automotive and home appliance industries, the replacement of metals with plastic materials for the purpose of weight reduction has been progressing, and various paints for plastics with excellent adhesion are used for their painting. On the other hand, from the perspective of recycling, it is required that the plastic substrate and the coating film can be easily peeled off.

[0003] Under such circumstances, a method has been proposed for peeling off a primer layer from a plastic substrate by a simple method by using a specific aqueous urethane resin composition as a primer layer (see, for example, Patent Document 1). However, although the primer layer using this aqueous urethane resin composition is excellent in peelability, there is a problem that the initial adhesion to a plastic substrate, particularly a low-polarity polyolefin substrate, is insufficient.

[0004] Japanese Patent No. 7440003

[0005] The problem to be solved by the present invention is to provide a resin composition for water-based paint having both initial adhesion and peelability to a substrate.

[0006] As a result of intensive studies to solve the above problems, the present inventors have found that a resin composition for water-based paint containing a specific polyurethane (A), a polyolefin (B), and an aqueous medium (C) can solve the above problems, and have completed the invention.

[0007] That is, the present invention relates to a resin composition for water-based paint containing a polyurethane (A), a polyolefin (B), and an aqueous medium (C), wherein the ester group concentration of the polyurethane (A) is 2 to 14 mmol / g, and the mass ratio (A / B) of the polyurethane (A) to the polyolefin (B) is 99 / 1 to 50 / 50.

[0008] The resin composition for water-based paints of the present invention possesses both good initial adhesion to the substrate and excellent peelability, and is highly recyclable, making it suitable for use as a water-based paint.

[0009] The present invention relates to an aqueous coating resin composition comprising polyurethane (A), polyolefin (B), and an aqueous medium (C), wherein the ester group concentration of polyurethane (A) is 2 to 14 mmol / g, and the mass ratio (A / B) of polyurethane (A) to polyolefin (B) is 99 / 1 to 50 / 50.

[0010] The method for producing the aqueous coating resin composition of the present invention is not particularly limited, but a method of mixing an aqueous dispersion of polyurethane (A) and an aqueous dispersion of polyolefin (B) is preferred because a composition containing polyurethane (A), polyolefin (B), and an aqueous medium (C) can be easily obtained.

[0011] The ester group concentration of the polyurethane (A) is 2 to 14 mmol / g, which allows for a balance between initial adhesion and peelability of the resulting coating film. However, 4 to 12 mmol / g is preferred because it further improves the balance between initial adhesion and peelability.

[0012] The ester group concentration of polyurethane (A) in this invention is a value obtained by calculation from the raw material composition.

[0013] The polyurethane (A) is obtained by a reaction between a polyol and a polyisocyanate, and the ester groups of the polyurethane (A) can be easily introduced into the polyurethane (A) by using a polyester polyol as a component of the polyol.

[0014] Examples of the aforementioned polyester polyols include aliphatic polyester polyols and aromatic polyester polyols obtained by esterifying a low molecular weight polyol with a polycarboxylic acid, polyesters obtained by ring-opening polymerization of cyclic ester compounds such as ε-caprolactone, and copolymer polyesters thereof.

[0015] Examples of low molecular weight polyols used in the production of the polyester polyol include ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, 1,2-propanediol, 1,3-propanediol, dipropylene glycol, tripylene glycol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 1,5-pentanediol, neopentyl glycol, 1,5-hexanediol, 1,6-hexanediol, 2,5-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, and 1 Examples include aliphatic polyols with molecular weights of 50 to 300, such as 1,11-undecanediol, 1,12-dodecanediol, 2-methyl-1,3-propanediol, neopentyl glycol, 2-butyl-2-ethyl-1,3-propanediol, 3-methyl-1,5-pentanediol, 2-ethyl-1,3-hexanediol, 2-methyl-1,8-octanediol, glycerin, trimethylolpropane, ditrimethylolpropane, trimethylolpropane, and pentaerythritol; polyols having an alicyclic structure, such as cyclohexanedimethanol and hydrogenated bisphenol A; and polyols having an aromatic structure, such as bisphenol A and bisphenol F.

[0016] Examples of the polycarboxylic acids include aliphatic polycarboxylic acids such as succinic acid, adipic acid, sebacic acid, and dodecanedicarboxylic acid; alicyclic polycarboxylic acids such as 1,4-cyclohexanedicarboxylic acid and cyclohexanetricarboxylic acid; aromatic polycarboxylic acids such as terephthalic acid, isophthalic acid, phthalic acid, and naphthalenedicarboxylic acid; and their anhydrides or esterified products.

[0017] The amount of polyester polyol used is preferably 15 to 100% by mass, and more preferably 30 to 95% by mass, relative to the total amount of polyol used in the production of polyurethane (A).

[0018] Furthermore, from the viewpoint of water dispersibility, the polyurethane (A) preferably has acidic groups. The acidic groups of the polyurethane (A) can be easily introduced into the polyurethane (A) by using a polyol having acidic groups as a component of the polyol.

[0019] Examples of polyols having acidic groups include diols having carboxyl groups or sulfonic acid groups, and it is preferable that they include diols having carboxyl groups. Examples of diols having carboxyl groups include 2,2-dimethylolpropionic acid, 2,2-dimethylolbutanoic acid, 2,2-dimethylolbutyric acid, and 2,2-dimethylolvaleric acid. Among these, 2,2-dimethylolpropionic acid is preferred. Polyester polyols having carboxyl groups obtained by reacting the polyol having carboxyl groups with various polycarboxylic acids can also be used. Examples of polycarboxylic acids include aliphatic polycarboxylic acids such as succinic acid, adipic acid, sebacic acid, and dodecanedicarboxylic acid; alicyclic polycarboxylic acids such as 1,4-cyclohexanedicarboxylic acid and cyclohexanetricarboxylic acid; aromatic polycarboxylic acids such as terephthalic acid, isophthalic acid, phthalic acid, and naphthalenedicarboxylic acid; and acid anhydrides thereof. These polyols can be used individually or in combination of two or more.

[0020] Examples of polyols having sulfonic acid groups include polyester polyols obtained by reacting dicarboxylic acids such as 5-sulfoisophthalic acid, sulfoterephthalic acid, 4-sulfophthalic acid, and 5[4-sulfophenoxy]isophthalic acid, or salts thereof, with low molecular weight polyols exemplified as usable in the production of polyester polyols having the aromatic structure. These polyols can be used individually or in combination of two or more.

[0021] The amount of polyol having the acid group used is preferably 1 to 20% by mass, and more preferably 3 to 15% by mass, relative to the total amount of polyol used in the production of polyurethane (A).

[0022] Other polyols that can be used in combination with the polyester polyol or the polyol having an acid group include, for example, polyether polyols and polycarbonate polyols.

[0023] Examples of the polyisocyanates include aromatic diisocyanates such as phenylene diisocyanate, tolylene diisocyanate, diphenylmethane diisocyanate, and naphthalene diisocyanate; and diisocyanates having an aliphatic or aliphatic cyclic structure such as hexamethylene diisocyanate, lysine diisocyanate, cyclohexane diisocyanate, isophorone diisocyanate, dicyclohexylmethane diisocyanate, xylylene diisocyanate, and tetramethylxylylene diisocyanate. However, from the viewpoint of improving the initial adhesion and peelability of the resulting primer layer, isophorone diisocyanate, tolylene diisocyanate, hexamethylene diisocyanate, and dicyclohexylmethane diisocyanate are preferred. These polyisocyanates can be used individually or in combination of two or more.

[0024] The molar ratio (NCO / OH) of isocyanate groups (NCO) contained in the polyisocyanate to hydroxyl groups (OH) contained in the polyol is preferably 0.9 to 2.

[0025] Furthermore, the polyurethane (A) may be one which has been increased in molecular weight by using a chain extender such as a polyamine.

[0026] The polyamine is preferably used in which the equivalent ratio of the amino groups of the polyamine to the isocyanate groups of the urethane prepolymer is 0.8 to 1.

[0027] The chain extension reaction is preferably carried out by first producing an aqueous dispersion of polyurethane, and then mixing the aqueous dispersion with a chain extension agent such as the polyamine.

[0028] The acid value of the polyurethane (A) is preferably 10 to 70 mg KOH / g, and more preferably 15 to 60 mg KOH / g, as this improves the balance between water dispersibility, initial adhesion, and peelability.

[0029] The acid value of polyurethane (A) in this invention is a value obtained by calculation from the raw material composition.

[0030] The weight-average molecular weight of the polyurethane (A) is preferably 20,000 or more, and more preferably 30,000 or more, from the viewpoint of hydrolysis resistance and stability. Furthermore, from the viewpoint of lower viscosity during water dispersion and productivity, it is preferably 300,000 or less, and more preferably 200,000 or less.

[0031] In this invention, unless otherwise specified, the average molecular weight is the value measured by gel permeation chromatography (GPC) using polystyrene as the standard sample.

[0032] The method for producing the aqueous dispersion of polyurethane (A) is not particularly limited, but one example is to neutralize some or all of the acidic groups of polyurethane (A) with a basic compound and disperse the resulting neutralized product in water.

[0033] Examples of the basic compounds include alkylamines such as monomethylamine, dimethylamine, trimethylamine, monoethylamine, diethylamine, triethylamine, monopropylamine, dipropylamine, and tripropylamine; alkanolamines such as monoethanolamine, diethanolamine, monoisopropanolamine, diisopropanolamine, N-methylethanolamine, N,N-dimethylethanolamine, N,N-diethylethanolamine, 2-amino-2-methylpropanol, 2-(dimethylamino)-2-methylpropanol, and N-methyldiethanolamine; organic amines such as polyhydric amines such as ethylenediamine, diethylenetriamine, triethylenetetramine, and tetraethylenepentamine; and metal hydroxides such as ammonia (water), sodium hydroxide, potassium hydroxide, and lithium hydroxide. These basic compounds can be used individually or in combination of two or more.

[0034] Examples of the polyolefin (B) include polyethylene, polypropylene, polybutadiene, ethylene-propylene copolymer, propylene-butene copolymer, propylene-ethylene-butene copolymer, natural rubber, synthetic isopropylene rubber, ethylene-vinyl acetate copolymer, and the like. Furthermore, if the polyolefin (B) is a copolymer, it may be a random copolymer or a block copolymer. The polyolefin is preferably one containing propylene because it improves initial adhesion. In this invention, modified polyolefins, in which other unsaturated monomers such as acrylic monomers are copolymerized in part, are also included in the category of polyolefins.

[0035] The aforementioned polyolefin (B) is preferably one that contains propylene, and more preferably one that contains 50% by mass or more, because it improves initial adhesion.

[0036] As the polyolefin (B), acid-modified polyolefins and chlorinated polyolefins are preferred, with acid-modified polyolefins being more preferred, due to their excellent water dispersibility and initial adhesion of the resulting coating film. Polyolefin (B) can be used alone or in combination of two or more types.

[0037] The aqueous dispersion of polyolefin (B) can be obtained by dispersing polyolefin (B) in water using a known method, but commercially available products can also be used. Examples of commercially available products include "Aurolene AE-202", "Aurolene AE-301", "Aurolene AE-502", "Superclon E-480T", "Superclon E-415", and "Superclon E-604" from Nippon Paper Industries Ltd.; "Hardren EW5303", "Hardren EH-801J", "Hardren NZ1004", and "Hardren NZ1015" from Toyobo MC Corporation; and "Advantis 510W" from Eastman Chemical Company.

[0038] The mass ratio (A / B) of polyurethane (A) to polypropylene (B) is 99 / 1 to 50 / 50, which allows for a balance between initial adhesion and peelability of the resulting coating film. However, a ratio of 97 / 3 to 60 / 40 is preferred, and a ratio of 95 / 5 to 65 / 35 is more preferred, as this further improves the balance between initial adhesion and peelability.

[0039] Examples of the aqueous medium (C) include water, organic solvents miscible with water, and mixtures thereof. Examples of organic solvents miscible with water include alcohol solvents such as methanol, ethanol, n-propanol, isopropyl alcohol, 1,2-propylene glycol, and 1,3-butylene glycol; ketone solvents such as acetone and methyl ethyl ketone; glycol ether solvents such as ethylene glycol-n-butyl ether, diethylene glycol-n-butyl ether, diethylene glycol monoethyl ether acetate, diethylene glycol dimethyl ether, propylene glycol methyl ether, dipropylene glycol methyl ether, dipropylene glycol dimethyl ether, dipropylene glycol-n-butyl ether, and tripropylene glycol methyl ether; lactam solvents such as N-methyl-2-pyrrolidone and N-ethyl-2-pyrrolidone; and amide solvents such as N,N-dimethylformamide, with ketone solvents being preferred.

[0040] Considering safety and reducing the burden on the environment, the aqueous medium (C) is preferably water only, or a mixture of water and an organic solvent that is miscible with water, and more preferably water only. The water content is preferably 50% by mass or more, and more preferably 70% by mass or more, in the aqueous medium (C).

[0041] The content of the aqueous medium (C) is not particularly limited, but from the viewpoint of workability, it is preferably 30 to 95% by mass, and more preferably 50 to 90% by mass, in the resin composition for aqueous coatings.

[0042] In addition to the above, as other components of the resin composition for aqueous paints of the present invention, additives such as crosslinking agents, defoamers, viscosity modifiers, light stabilizers, weather stabilizers, heat stabilizers, ultraviolet absorbers, antioxidants, leveling agents, pigment dispersants, thickeners, etc. can be used. Also, pigments such as titanium oxide, calcium carbonate, aluminum powder, copper powder, mica powder, iron oxide, carbon black, phthalocyanine blue, toluidine red, perylene, quinacridone, benzidine yellow, etc. can be used.

[0043] Examples of the crosslinking agent include amino resins, aziridine compounds, melamine compounds, epoxy compounds, oxazoline compounds, carbodiimide compounds, isocyanate compounds, silane compounds, etc. These crosslinking agents can be used alone or in combination of two or more.

[0044] Since the resin composition for aqueous paints of the present invention provides a coating film with excellent initial adhesion, it can be suitably used as an aqueous primer paint, and is particularly suitably used as an aqueous primer paint for plastic substrates.

[0045] Examples of the plastic substrate include substrates made of polyolefins such as polyethylene, polypropylene, ethylene-propylene copolymers; substrates made of polyesters such as polyethylene isophthalate, polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate; substrates made of polyamides such as nylon 1, nylon 11, nylon 6, nylon 66, nylon MX-D; substrates made of styrenic polymers such as polystyrene, styrene-butadiene block copolymers, styrene-acrylonitrile copolymers, styrene-butadiene-acrylonitrile copolymers; substrates made of acrylic polymers such as polymethyl methacrylate, methyl methacrylate / ethyl acrylate copolymers; substrates made of polycarbonate, etc.

[0046] The primer coating film of the present invention is obtained by drying the aqueous primer paint on a substrate in the range of 10 to 120°C after coating.

[0047] As coating methods, for example, methods such as spraying, applicator, bar coater, gravure coater, roll coater, comma coater, knife coater, air knife coater, curtain coater, kiss coater, shower coater, whirler coater, spin coater, dipping, screen printing, etc. can be mentioned.

[0048] Also, by applying various topcoat paints on the coating film of the aqueous primer paint of the present invention, various functions according to the use can be imparted to the coating film surface.

[0049] As the topcoat paint, for example, paints mainly composed of ultraviolet curable resins, acrylic resins, polyurethane resins, polyester resins, melamine resins, or epoxy resins, etc. can be used.

[0050] On the other hand, the primer coating film obtained from the aqueous primer paint of the present invention can be easily peeled off from the substrate by immersing it in an alkaline solution, so it also has excellent recyclability.

[0051] The article having the primer coating film of the present invention is not particularly limited, but because it has excellent initial adhesion to a plastic substrate, the housing of electronic devices such as mobile phones, smartphones, tablet terminals, personal computers, digital cameras, game machines, etc.; the housing of home appliances such as televisions, refrigerators, washing machines, air conditioners, etc.; plastic molded products such as automobile bumpers and interior materials of various vehicles such as automobiles and railway vehicles are preferred.

[0052] Hereinafter, the present invention will be described in more detail with specific examples. The ester group concentration and hydroxyl value were determined by calculation from the raw material composition, and the average molecular weight was measured under the following measurement conditions.

[0053] [GPC Measurement Conditions] Measurement device: High-speed GPC device (HLC-8220GPC manufactured by Tosoh Corporation) Column: The following columns manufactured by Tosoh Corporation were used in series. "TSKgel G5000" (7.8 mm I.D. × 30 cm) × 1 "TSKgel G4000" (7.8 mm I.D. × 30 cm) × 1 "TSKgel G3000" (7.8 mm I.D. × 30 cm) × 1 "TSKgel G2000" (7.8 mm I.D. × 30 cm) × 1 Detector: RI (differential refractometer) Column temperature: 40°C Eluent: Tetrahydrofuran (THF) Flow rate: 1.0 mL / min Injection volume: 100 μL (tetrahydrofuran solution with a sample concentration of 4 mg / mL) Standard samples: Calibration curves were prepared using the following monodisperse polystyrene.

[0054] (Monodisperse Polystyrene) TSKgel Standard Polystyrene A-500 (manufactured by Tosoh Corporation) TSKgel Standard Polystyrene A-1000 (manufactured by Tosoh Corporation) TSKgel Standard Polystyrene A-2500 (manufactured by Tosoh Corporation) TSKgel Standard Polystyrene A-5000 (manufactured by Tosoh Corporation) TSKgel Standard Polystyrene F-1 (manufactured by Tosoh Corporation) TSKgel Standard Polystyrene F-2 (manufactured by Tosoh Corporation) TSKgel Standard Polystyrene F-4 (manufactured by Tosoh Corporation) TSKgel Standard Polystyrene F-10 (manufactured by Tosoh Corporation) TSKgel Standard Polystyrene F-20 (manufactured by Tosoh Corporation) TSKgel Standard Polystyrene F-40 (manufactured by Tosoh Corporation) TSKgel Standard Polystyrene F-80 (manufactured by Tosoh Corporation) TSKgel Standard Polystyrene F-128 (manufactured by Tosoh Corporation) TSKgel Standard Polystyrene F-288 (manufactured by Tosoh Corporation) TSKgel Standard Polystyrene F-550 (manufactured by Tosoh Corporation)

[0055] (Synthesis Example 1: Synthesis of Polyester Polyol (1)) In a polyester reaction vessel equipped with a stirrer, nitrogen gas inlet tube, rectification tube, moisture separator, etc., 32 parts by mass of terephthalic acid, 32 parts by mass of isophthalic acid, 13 parts by mass of ethylene glycol, and 23 parts by mass of diethylene glycol were charged. The mixture was gradually heated so that the temperature at the top of the rectification tube did not exceed 100°C, and the internal temperature was maintained at 220°C. When the acid value became 10 mg KOH / g or less, heating was continued under reduced pressure at 100 torr, and when the acid value became 1 mg KOH / g or less, the esterification reaction was terminated, yielding polyester polyol (1) with an ester group concentration of 9.0 mmol / g, a hydroxyl value of 56 mg KOH / g, and a number average molecular weight of 2,000.

[0056] [Method for calculating ester group concentration] The ester group concentration was calculated using the following formula (1).

[0057] Ester group concentration (moles / g) = Amount of ester groups produced (mol) / [Amount of monomer used (g) - Amount of water produced (g)] × 1000 ... (1)

[0058] The method for calculating the ester group concentration will be explained in more detail using the polyester polyol (1) obtained in Synthesis Example 1 as an example. The amount of ester groups produced was calculated assuming that the entire amount of the monomer used in the synthesis undergoes the esterification reaction. Amount of ester groups produced = 0.193 mol terephthalic acid × 2 + 0.193 mol isophthalic acid × 2 = 0.772 mol Next, the amount of water produced was also calculated assuming that the entire amount of the monomer used in the synthesis undergoes the esterification reaction, similar to the amount of ester groups. Amount of water produced = (0.193 mol terephthalic acid × 2 + 0.193 mol isophthalic acid × 2) × 18.02 = 13.9 g From the values ​​obtained above, the ester group concentration of polyester polyol (1) can be calculated using the following formula (2). Ester group concentration (mol / g) = 0.772 / [100 - 13.9] × 1000 = 9.0

[0059] (Synthesis Example 2: Synthesis of Polyester Polyol (2)) In a polyester reaction vessel equipped with a stirrer, nitrogen gas inlet tube, rectification tube, moisture separator, etc., 35 parts by mass of isophthalic acid, 8 parts by mass of adipic acid, 18 parts by mass of sebaciic acid, 7 parts by mass of ethylene glycol, 21 parts by mass of neopentyl glycol, and 12 parts by mass of 1,6-hexanediol were charged. The mixture was gradually heated so that the temperature at the top of the rectification tube did not exceed 100°C, and the internal temperature was maintained at 220°C. When the acid value became 10 mg KOH / g or less, heating was continued under reduced pressure at 100 torr, and when the acid value became 1 mg KOH / g or less, the esterification reaction was terminated, yielding polyester polyol (2) with an ester group concentration of 8.1 mmol / g, a hydroxyl value of 56 mg KOH / g, and a number average molecular weight of 2,000.

[0060] (Synthesis Example 3: Synthesis of Polyester Polyol (3)) In a polyester reaction vessel equipped with a stirrer, nitrogen gas inlet tube, rectification tube, moisture separator, etc., 57 parts by mass of oxalic acid and 43 parts by mass of ethylene glycol were charged, and the mixture was gradually heated so that the temperature at the top of the rectification tube did not exceed 100°C, maintaining the internal temperature at 220°C. When the acid value became 10 mg KOH / g or less, heating was continued under reduced pressure at 100 torr, and when the acid value became 1 mg KOH / g or less, the esterification reaction was terminated, yielding polyester polyol (3) with an ester group concentration of 16.4 mmol / g, a hydroxyl value of 56 mg KOH / g, and a number average molecular weight of 2,000.

[0061] (Production Example 1: Synthesis of an aqueous dispersion of polyurethane (A-1)) In a four-necked flask equipped with a thermometer, a stirrer, a reflux condenser, and a nitrogen inlet tube, 74 parts by mass of polyester polyol (1) obtained in Synthesis Example 1, 6 parts by mass of 2,2-dimethylolpropionic acid, and 139 parts by mass of methyl ethyl ketone were added. Then, 20 parts by mass of isophorone diisocyanate was added, and the mixture was reacted at 75°C for 8 hours. Next, the mixture was cooled to 50°C, and 3 parts by mass of 25% aqueous ammonia was added as a neutralizing agent to obtain polyurethane. Next, 334 parts by mass of deionized water was added, and the mixture was dispersed in water. The obtained reaction product was subjected to reduced pressure at 40-60°C to remove the methyl ethyl ketone, and then deionized water was added to adjust the concentration to obtain an aqueous dispersion of polyurethane (A-1) with a non-volatile content of 23% by mass. The ester group concentration of this polyurethane (A-1) was 6.6 mmol / g, the acid value was 25 mgKOH / g, and the weight-average molecular weight was 35,000.

[0062] (Production Examples 2-4: Synthesis of Aqueous Dispersions of Polyurethanes (A-2) to (A-4)) Except for changing the polyol and polyisocyanate used as shown in Table 1, aqueous dispersions of polyurethanes (A-2) to (A-4) with a non-volatile content of 23% by mass were obtained in the same manner as in Production Example 1.

[0063] (Production Example 5: Synthesis of an aqueous dispersion of polyurethane (A-5)) In a four-necked flask equipped with a thermometer, a stirrer, a reflux condenser, and a nitrogen inlet tube, 62 parts by mass of polyester polyol (1) obtained in Synthesis Example 1, 6 parts by mass of dimethylolpropionic acid, and 42 parts by mass of methyl ethyl ketone were added under a nitrogen stream and mixed uniformly. Then, 30 parts by mass of dicyclohexylmethane diisocyanate was added, followed by 0.01 parts by mass of dibutyltin dilaurate, and the mixture was reacted at 80°C for about 4 hours to obtain a methyl ethyl ketone solution of a urethane prepolymer having isocyanate groups at the molecular ends. Next, 2 parts by mass of triethylamine was added to the obtained methyl ethyl ketone solution of the urethane prepolymer to neutralize the carboxyl groups in the urethane prepolymer, followed by 232 parts by mass of ion-exchanged water, and then 1.4 parts by mass of 80% hydrazine solution was added and the mixture was reacted. After the reaction was complete, methyl ethyl ketone was removed by distillation under reduced pressure to obtain an aqueous dispersion of polyurethane (A-5) with a non-volatile content of 30% by mass. The ester group concentration of this polyurethane (A-5) was 5.5 mmol / g, the acid value was 25 mgKOH / g, and the weight-average molecular weight was 150,000.

[0064] (Production Example 6: Synthesis of an aqueous dispersion of polyurethane (RA-1)) An aqueous dispersion of polyurethane (RA-1) with a non-volatile content of 23% by mass was obtained in the same manner as in Production Example 1, except that the polyol and polyisocyanate used were changed as shown in Table 1.

[0065] Table 1 shows the polyurethane (A-1) to (A-5) and (RA-1) polyol raw materials and polyisocyanate raw materials obtained above.

[0066]

[0067] The polycarbonate polyol (1) in the table is "ETERNACOL UH-200" manufactured by UBE Corporation.

[0068] (Examples 1-8: Preparation and evaluation of water-based paint resin compositions (1)-(8)) The polyurethane aqueous dispersion obtained in the production example and a polypropylene aqueous dispersion (Hardlen NZ-1004, manufactured by Toyobo MC Co., Ltd., acid-modified polypropyn, 30% by mass of non-volatile content) were mixed so that the solid content ratio was as shown in Table 2 or 3 to obtain water-based paint resin compositions (1)-(8).

[0069] (Comparative Examples 1-3: Preparation and Evaluation of Water-Based Paint Resin Compositions (R1)-(R3)) The polyurethane aqueous dispersion obtained in the production example and a polypropylene aqueous dispersion (Harden NZ-1004 manufactured by Toyobo MC Co., Ltd., 30% by mass of non-volatile content) as the aqueous dispersion of polyolefin (B-1) were mixed so that the solid content ratio was as shown in Table 4 to obtain water-based paint resin compositions (R1)-(R3).

[0070] [Preparation of water-based primer paint] The water-based paint resin composition obtained above was adjusted in viscosity with water so that the Iwata cup viscosity was 10 to 12 seconds (at 23°C) to obtain a water-based primer paint.

[0071] [Preparation of Test Panels] A polypropylene substrate was cut to 5 cm x 10 cm, and the mass of the unpainted test panel was measured. Next, the water-based primer paint obtained above was spray-coated to a film thickness of 5 to 15 μm after drying, and after drying at 80°C for 30 minutes, the mass of the painted test panel was measured.

[0072] [Evaluation of Initial Adhesion] The coating film on the test plate after painting, obtained as described above, was subjected to a cross-cut test based on ASTM D3359, and the initial adhesion was evaluated according to the following criteria: ○: 4B or higher △: 3B ×: 2B or lower

[0073] [Preparation of test solution (1)] Test solution (1) was obtained by adding 10 g of sodium hydroxide and 390 g of water to a 1 L container and dissolving them.

[0074] [Preparation of test solution (2)] Test solution (2) was obtained by adding 5 g of sodium hydroxide, 1.5 g of emulsifier (Tritoon X-100, manufactured by Kishida Chemical Co., Ltd.), and 493.5 g of water to a 1 L container and dissolving them.

[0075] [Evaluation of Peelability] A stirring bar was placed in a beaker, 300g of the preheated test solution was added, and the beaker was set in a heater-equipped stirrer and heated until the test solution reached 65°C. The test plate was immersed in the test solution so that it did not touch the bottom of the beaker, and heating and stirring were started at a rotation speed of 100 rpm. After 15 minutes, the test plate was removed, lightly washed with deionized water, air-dried, and its mass was measured. The mass loss rate was calculated using the following formula, and the peelability was evaluated according to the following criteria. Mass loss rate (%) = ("Mass of test plate after peel test" - "Mass of unpainted test plate") / ("Mass of test plate before peel test" - "Mass of unpainted test plate") × 100 ○: Mass loss rate of 80% or more △: Mass loss rate of 50% or more and less than 80% ×: Mass loss rate less than 50%

[0076] The formulations and evaluation results of the water-based paint resin compositions (1) to (7) obtained above are shown in Tables 2 and 3.

[0077]

[0078]

[0079] Table 4 shows the formulations and evaluation results of the water-based paint resin compositions (R1) to (R3) obtained above.

[0080]

[0081] The coating films obtained from Examples 1 to 8, which are aqueous coating resin compositions of the present invention, were confirmed to have excellent initial adhesion and peelability.

[0082] On the other hand, Comparative Example 1, which has a low polyurethane (A) content, was found to have insufficient peelability of the resulting coating film.

[0083] Comparative Example 2 is an example with a high content of polyurethane (A), but it was confirmed that the initial adhesion of the resulting coating film was insufficient.

[0084] Comparative Example 3 is an example in which a polyurethane with a low ester group concentration was used, but it was confirmed that the peelability of the resulting coating film was insufficient.

Claims

1. A resin composition for aqueous coatings comprising polyurethane (A), polyolefin (B), and an aqueous medium (C), wherein the ester group concentration of polyurethane (A) is 2 to 14 mmol / g, and the mass ratio (A / B) of polyurethane (A) to polypropylene (B) is 99 / 1 to 50 / 50.

2. The aqueous paint resin composition according to claim 1, wherein the polyolefin (B) contains propylene.

3. An aqueous primer paint containing the aqueous paint resin composition according to claim 1 or 2.

4. A primer coating obtained from the aqueous primer paint described in claim 3.

5. An article having the primer coating film described in claim 4.

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