JP2611924B2 - Aqueous baking coating composition for metal cans - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

FIELD OF THE INVENTION The present invention relates to an aqueous baking coating composition for metals. More specifically, it relates to an aqueous baking coating composition useful as an outer coating for metal cans.

[0002]

2. Description of the Related Art Metal cans made of tin, tin-free steel, aluminum, etc. are widely used for packaging containers for soft drinks, alcoholic beverages, fruits, processed fish products, etc., and spray cans for cosmetics, insecticides, etc. Have been. The outer surfaces of these metal cans are often coated for the purpose of preventing rust, displaying products or improving design. Hitherto, as an aqueous baking coating composition used for this coating, a composition comprising an aqueous acrylic resin (for example, JP-A-63-230779 and JP-A-63-248874) is known. However, these materials have insufficient post-workability such as retort resistance, bending property, and deep drawability, and their applications are limited. Further, there has been proposed one using a water-soluble urethane resin (for example, JP-A-1-193367), but there is a problem that the retort resistance is insufficient.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to provide an aqueous baking coating composition which has good post-processing properties such as retort resistance, bending property and deep drawability, and is useful as an outer coating for metal cans. Is to do.

[0004]

Means for Solving the Problems The present inventors have made intensive studies to solve the above-mentioned problems, and as a result, have reached the present invention. That is, the present invention comprises an aqueous urethane resin (A) and an aromatic ring-containing epoxy resin (B), wherein (A) is an organic polyisocyanate (a), a polymer polyol (b),
An aqueous polyurethane resin obtained by chain-extending an isocyanate group-terminated prepolymer composed of α, α-dimethylolmonocarboxylic acid (c) and, if necessary, an elongating agent (d) in water after or with neutralization with a base. And the weight ratio of (A) and (B) is (A) / (B) = 50/5
It is an aqueous baking coating composition for metal cans, wherein the composition is 0 to 95/5.

In the present invention, the organic polyisocyanate (a) constituting (A) is described in JP-A-3-9951.
And those described in Japanese Patent Publication No. Of these, preferred are 2,4 and / or 2,6-tolylene diisocyanate (TDI), 4,4'-diphenylmethane diisocyanate (MDI), hexamethylene diisocyanate (HDI), isophorone diisoyanate (IPDI), 4,4′-dicyclohexylmethane diisocyanate (hydrogenated MDI) and α, α, α ′, α ′
-Tetramethylxylylene diisocyanate (TMXD
I), and particularly preferred are HDI, IPDI and hydrogenated MDI.

The polymer polyol (b) includes those described in JP-A-3-9951.
Of these, preferred are polyester polyols and polyether polyols, and particularly preferred are polyester polyols and polyether polyols containing an aromatic ring in the molecule. The OH equivalent of (b) is usually 150 to 3000, preferably 200 to 2500.
It is.

[0007] α, α-dimethylol monocarboxylic acid (c) is an epoxy resin (B) containing an anionic hydrophilic group and an aromatic ring for dispersing the polyurethane resin (A) stably in water. It is a component used for introducing a crosslinking group to be reacted, and specific examples thereof include α,
α-Dimethylolacetic acid, α, α-dimethylolpropionic acid and α, α-dimethylolbutyric acid are preferred, with α, α-dimethylolpropionic acid being preferred.
The amount of (c) in (A) is based on the amount of carboxyl group (-CO
OH) is usually 0.3 to 6% by weight, preferably 0.4 to 6% by weight based on the weight of the isocyanate group-terminated prepolymer.
5% by weight. When the amount of the carboxyl group is less than 0.3% by weight, a stable dispersion cannot be obtained, and when the amount exceeds 6% by weight, the water resistance of the coating film decreases.

If necessary, low-molecular polyols and / or polyamines described in JP-A-3-9951 may be used as the chain extender (d). Preferred low molecular polyols are 1,4-butanediol, 3-methylpentanediol, pentaerythritol and trimethylolpropane. Preferred as polyamines are hexamethylenediamine, isophoronediamine and 4,4'-diaminodicyclohexylmethane.

As the base for neutralizing the carboxyl group of the isocyanate group-terminated prepolymer comprising (a), (b), (c) and, if necessary, (d), an organic base (eg, trimethylamine, triethylamine), an inorganic base ( For example, sodium hydroxide and potassium hydroxide). Preferred among these are organic bases.

Water or diamines (eg, isophorone diamine, hexane) may be used to obtain an aqueous polyurethane resin by extending the chain in water after or while neutralizing the isocyanate group-terminated prepolymer with a base. Methylenediamine) and hydrazine derivatives (eg, hydrazine, adipic dihydrazide) and their 2
Combinations of more than one species may be mentioned.

The method for producing (A) in the present invention is not particularly limited. For example, in the presence of an organic solvent containing no active hydrogen group in the molecule (eg, acetone, methyl ethyl ketone, tetrahydrofuran, N, N-dimethylformamide), or In the absence of (a), (b), (c) and, if necessary, (d), an isocyanate (NCO) group of (a) and an active hydrogen group of (b) + (c) + (d) Equivalent ratio with (NC
O / active hydrogen group) in a range of usually 1.05 to 2.0, preferably 1.1 to 1.6, by a one-shot method or a multistage method, usually at 20 ° C to 150 ° C, preferably at 60 ° C to 1 ° C.
The mixture is reacted at 10 ° C. for 2 to 10 hours to obtain a urethane prepolymer containing a terminal NCO group, and then, after neutralizing the prepolymer with a base or while neutralizing, usually from 10 ° C. to 60 ° C.
C., preferably at 20 ° C. to 40 ° C., mixed with an aqueous solution containing at least one chain extender selected from water, diamine or dividrazidine derivative, and subjected to an emulsion extension reaction until the NCO group disappeared. A specific example is the method of removing.

The aromatic ring-containing epoxy resin (B), which is another essential component of the present invention, includes, for example, bisphenol A, bisphenol F, and novolak type phenol resins (phenol novolak resin, orthocresol novolak resin, etc.). Epoxy resin obtained by condensation reaction with chlorohydrin; alkylene (C2-4) oxide adduct such as bisphenol A, bisphenol F, novolak type phenol resin (phenol novolak resin, orthocresol novolak resin) and epichlorohydrid Epoxy resin obtained by a condensation reaction with phosphorus;
And mixtures of two or more of these. Preferred among these are epoxy resins derived from bisphenol A. The epoxy equivalent of (B) is usually 120-3000, preferably 180-2000. If the epoxy equivalent is less than 120, sufficient coating film hardness cannot be obtained, and if it exceeds 3,000, workability such as bending resistance deteriorates.

In the present invention, (B) is usually used by emulsifying or dispersing in water. The method of emulsifying or dispersing (B) in water is not particularly limited. For example, an emulsifier is usually blended in an amount of 2 to 30% by weight based on the weight of the epoxy resin, and water is added to perform phase inversion emulsification to obtain an aqueous dispersion. Method: A method in which an emulsifier is blended in an amount of 2 to 30% by weight based on the weight of an epoxy resin and self-dispersed in water.
A method in which epichlorohydrin is subjected to a condensation reaction with the mole-added product, and the obtained epoxy resin is self-dispersed or self-emulsified in water. Examples of the emulsifier include a nonionic surfactant such as an ethylene oxide adduct of nonylphenol, an anionic surfactant such as lauryl alcohol sulfate sodium salt, and a mixture thereof.

The aqueous baking coating composition of the present invention may contain, if necessary, additives such as other aqueous resins, pigments, stabilizers, surfactants, antifoaming agents, preservatives, antifreezing agents and thickeners. May be contained. Specific examples of these are as follows. Aqueous resin: acrylic, polyester, and polyolefin emulsions. Pigment: titanium white, calcium carbonate, carbon black, etc. Stabilizer: Hindered phenol, hydrazine, phosphorus, benzophenone, benzotriazole, oxalic acid anilide or hindered amine stabilizer. Surfactant: a nonionic surfactant such as an ethylene oxide adduct of nonylphenol. Anionic surfactants such as lauryl alcohol sulfate sodium salt. Antifoaming agent: silicone-based or fluorine-based antifoaming agent. Preservatives: organic nitrogen sulfur compound-based, organic sulfur halogen compound-based preservatives, etc. Antifreeze: ethylene glycol, propylene glycol, and the like. Thickeners: cellulose derivatives, starch derivatives, polyvinyl alcohol, etc.

The mixing ratio (weight ratio of solid content) of (A) and (B) in the aqueous baking coating composition of the present invention is usually (A) / (B) = 50/50 to 95/5, preferably 6
0/40 to 90/10. When the ratio of (B) is less than 5, the curing of the coating film becomes insufficient, and when it exceeds 50, the coating film becomes brittle and the post-processability decreases.

The metal to be coated with the aqueous baking coating composition of the present invention includes, for example, a tin plate, a tin-free steel plate and an aluminum plate.

The application of the aqueous baking coating composition of the present invention is usually carried out by a roll coating method, and the applied amount is usually 5 to 10 μm in terms of a solid content film thickness. The baking temperature is usually 15
0 ° C. to 240 ° C., preferably 160 ° C. to 220 ° C., and the baking time is usually 5 seconds to 10 minutes, preferably 1 second.
0 seconds to 5 minutes.

[0018]

EXAMPLES The present invention will be further described with reference to the following examples, but the present invention is not limited to these examples. In the following, "parts" indicates parts by weight and "%" indicates% by weight.

Production Example 1 207.7 polycaprolactone diol (number average molecular weight 2015) was placed in a closed reaction vessel equipped with a thermometer and a stirrer.
Part, 1,4-butanediol 15.7 parts, trimethylolpropane 6.4 parts, dimethylolpropionic acid
3 parts, IPDI 149.9 parts and acetone 171.4
After the reaction system was replaced with nitrogen gas, the mixture was reacted at 80 ° C. for 7 hours with stirring, and the NCO% content was 2.5%.
An O-terminal urethane prepolymer was obtained. The obtained acetone solution was cooled to 30 ° C., and 15.3 parts of triethylamine was added. Next, 600.0 parts of water was added to the acetone solution to carry out an emulsification and chain extension reaction,
The acetone is distilled off with a solid content of 40.0% and a viscosity of 450 c.
1000 parts of an aqueous urethane resin dispersion at p / 25 ° C. (A1)
I got

Production Example 2 Polybutylene adipate diol (number average molecular weight 2000) 10 was placed in a closed reaction vessel equipped with a thermometer and a stirrer.
3.7 parts, ethylene oxide adduct of bisphenol A (number average molecular weight 324) 103.7 parts, trimethylolpropane 3.9 parts, dimethylolpropionic acid
8 parts, IPDI 164.8 parts and acetone 171.4
After the reaction system was replaced with nitrogen gas, the mixture was reacted at 80 ° C. for 8 hours with stirring to obtain an NCO% content of 2.2% NC.
An O-terminal urethane prepolymer was obtained. The obtained acetone solution was cooled to 30 ° C., and 17.9 parts of triethylamine was added. Next, 600.0 parts of water was added to the acetone solution, and an emulsification / chain extension reaction was performed.
The acetone is distilled off at 40.0% solids, viscosity 310c
1000 parts of an aqueous urethane resin dispersion at p / 25 ° C. (A2)
I got

Production Example 3 Polybutylene phthalate diol (number average molecular weight 1980) 25 was placed in a closed reaction vessel equipped with a thermometer and a stirrer.
After 0.7 parts, 16.6 parts of 1,4-butanediol, 23.2 parts of dimethylolpropionic acid, 109.5 parts of TDI and 400.0 parts of acetone were charged, the reaction system was replaced with nitrogen gas, and then stirred. NCO at 80 ° C for 8 hours
A 1.5% NCO-terminated urethane prepolymer was obtained. The obtained acetone solution was cooled to 30 ° C., and 17.5 parts of triethylamine was added. Next, 600.0 parts of water was added to the acetone solution to cause an emulsification and chain extension reaction, and then acetone was distilled off at 50 to 60 ° C. under reduced pressure to obtain a solid content of 4%.
There were obtained 1000 parts (A3) of a 0.0% urethane resin aqueous dispersion having a viscosity of 250 cp / 25 ° C.

Production Example 4 Polycarbonate diol (number average molecular weight 1980) 194.2 was placed in a closed reaction vessel equipped with a thermometer and a stirrer.
16.5 parts, 1,4-butanediol 16.5 parts, trimethylolpropane 3.2 parts, dimethylolpropionic acid
8 parts, hydrogenated MDI 162.2 parts and acetone 171.
After charging 4 parts and replacing the reaction system with nitrogen gas, the mixture was reacted at 80 ° C. for 8 hours with stirring to obtain an NCO-terminated urethane prepolymer having an NCO% content of 1.85%. The obtained acetone solution was cooled to 30 ° C. and triethylamine was 17.9.
Parts were added. Next, 5.8 parts of isophorone diamine was added to water 6
The solution dissolved in 08.7 parts was added to the acetone solution, and an emulsification / chain extension reaction was carried out. Thereafter, acetone was distilled off at 50 to 60 ° C. under reduced pressure to obtain a solid content of 40.0% and a viscosity of 420 cp / 2.
1014 parts (A4) of a 5 ° C. urethane resin aqueous dispersion were obtained.

Production Example 5 600 parts of methyl ethyl ketone was charged into a four-necked kolben equipped with a thermometer, a stirrer, a reflux condenser, a dropping funnel and a nitrogen gas inlet tube, and the temperature was raised to 80 to 85 while stirring while introducing nitrogen gas. C., and a mixture of 28.7 parts of methacrylic acid, 285.3 parts of methyl methacrylate, 46 parts of butyl methacrylate, 40 parts of 2-hydroxy methacrylate, and 6 parts of azobisisobutyronitrile was dropped from the dropping funnel over 4 hours. Further, 0.8 parts of azobisisobutyronitrile was added, and the mixture was kept at the same temperature for 2 hours to complete the polymerization. After adding 29 parts of triethylamine to the obtained polymer, it was mixed with 650 parts of water. Then under reduced pressure 60-70
The methyl ethyl ketone was distilled off at 4 ° C., and the solid content was 40.0%.
Acrylic resin water dispersion 100 having a viscosity of 450 cp / 25 ° C.
0 parts (A5) were obtained.

Example 1 Using (A1) obtained in Production Example 1, an aqueous baking paint 1 was prepared according to the following formulation. (A1) 100 parts Epoxy EM-0140A 20 parts (Epoxy emulsion manufactured by Sanyo Kasei: water dispersion of bisphenol A epoxy resin, epoxy equivalent 1150, solid content 47%) Water 45 parts

Example 2 Using (A2) obtained in Production Example 2, an aqueous baking paint 2 was prepared according to the following formulation. (A2) 100 parts Becopox EP122 10 parts (manufactured by Hoechst; self-emulsifying epoxy resin, epoxy equivalent 192) Water 56.7 parts

Example 3 Using (A3) obtained in Production Example 3, an aqueous baking paint 3 was prepared according to the following formulation. (A3) 100 parts Epoxy EM-0140A 20 parts Water 45 parts

Example 4 Using (A4) obtained in Production Example 4, an aqueous baking paint 4 was prepared according to the following formulation. (A4) 100 parts Becopox EP122 10 parts Water 56.7 parts

Comparative Example 1 Using (A1) obtained in Production Example 1, an aqueous baking paint 5 was prepared according to the following formulation. (A1) 100 parts water 33.3 parts

Comparative Example 2 Using (A1) obtained in Production Example 1, an aqueous baking paint 6 was prepared according to the following formulation. (A1) 100 parts Denacol EX-521 10 parts (manufactured by Nagase Kasei Co., Ltd .; polyglycerol polyglycidyl ether, epoxy equivalent 186) Water 56.7 parts

Comparative Example 3 Using (A1) obtained in Production Example 1, an aqueous baking paint 7 was prepared according to the following formulation. (A1) 100 parts Cymel 325 15 parts (Mitsui Cyanamid; high solid type amino resin) Water 58.3 parts

Comparative Example 4 Using (A5) obtained in Production Example 5, an aqueous baking paint 8 was prepared according to the following formulation. (A5) 100 parts Cymel 325 20 parts Water 66.7 parts

Each of the aqueous baking paints 1 to 8 obtained in Examples 1 to 4 and Comparative Examples 1 to 4 was applied to a tin plate with a bar coater so as to have a solid content of 4 to 6 μm.
After baking at 00 ° C. for 2 minutes, the following performance tests were performed. Table 1 shows the results.

[0033]

[Table 1]

<Performance Test Items and Test Methods> Adhesion A cross cut was made in the coating film, Nichiban Solo tape (12 mm width) was applied to the cross cut part, and the application surface condition when one end of this Nichiban cello tape was rapidly peeled off in a direction perpendicular to the application surface was observed. did. Judging criteria ○: No peeling ×: Peeled part is seen

2. Flex resistance Measured according to JIS K5400.8.1. (Diameter of mandrel of bending tester 2 mm, thickness of auxiliary plate 2 mm) Criteria ○: No abnormality in bent part ×: Cracks occur in bent part

3. Retort resistance A test piece was placed in a pressure cooker (manufactured by Hirayama Seisakusho), and the state of the coating film after treatment at 125 ° C. for 90 minutes was observed. Criteria ：: No change in appearance of the coating film ×: Cracks or whitening are observed in the coating film.

[0037]

The aqueous baking coating composition for metal cans of the present invention has the following effects. (1) Since it is water-based, it has high safety and has no problems such as air pollution due to organic solvents. (2) Compared with conventional water-based baking paints, it is particularly excellent in post-workability such as retort resistance, bending resistance and deep drawability. Because of the above effects, the composition of the present invention is extremely useful as a paint for metal cans such as beverage cans, food cans, and industrial cans.

 ──────────────────────────────────────────────────続 き Continuation of the front page Examiner Yoko Nakajima (56) References JP-A-3-195738 (JP, A) JP-A-1-1933367 (JP, A)

Claims (3)

(57) [Claims] 1. An aqueous urethane resin (A) and an aromatic ring-containing epoxy resin (B), wherein (A) is an organic polyisocyanate (a), a polymer polyol (b), α,
α- dimethylol monocarboxylic acid (c) and required by the extender to isocyanate terminated prepolymer consisting of (d), in water with neutralization or after neutralized with a base I aqueous polyurethane resin der that chain extension, And the above (A)
The weight ratio of (B) is (A) / (B) = 50 / 50-95.
Aqueous baking coating composition for metal cans, characterized in that the ratio is / 5 . 2. The coating composition according to claim 1, wherein (B) is an epoxy resin derived from bisphenol A. 3. The epoxy equivalent of (B) is from 120 to 300.
3. The coating composition according to claim 1, which is 0.