JP2819941B2 - Aqueous paint composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

FIELD OF THE INVENTION The present invention relates to an aqueous coating composition,
The present invention relates to an aqueous coating composition having excellent retort resistance, processability, and coatability, and further having excellent pigment dispersibility.

[0002]

2. Description of the Related Art The outer surfaces of beverage cans containing soft drinks and the like and food cans for packaging foods can prevent corrosion of can materials, increase aesthetic merchandise value, and withstand heat treatment steps during food sterilization. It is formed by coating. Conventionally, these paints are coated with an organic solvent solution such as an epoxy / amino resin, an acrylic / amino resin, or a polyester / amino resin using a roll coater, and then baked and cured in a gas oven. However, these paints cause a large amount of solvent evaporation during baking, causing air pollution,
It is not preferable from the viewpoint of resource saving. Therefore, the emergence of a water-based paint capable of solving these problems has been desired.

There are two types of known water-based paints, water-dispersible and water-soluble. Many water-dispersible resins are usually synthesized by emulsion polymerization using a surfactant. Even after the formation of the coating film, it remains in the coating film, and has a drawback of lowering the water resistance. On the other hand, there is also a method of synthesizing in an organic solvent system without using a surfactant, synthesizing a resin containing an acid component (carboxyl group), neutralizing the resin with a volatile base, and making it a dispersion or water-soluble. The paint requires an acid value of 20 or more in the basic resin structure, and has a drawback of poor performance such as water resistance, water adhesion, and retort resistance.

Various epoxy resins have been proposed as a method of improving these disadvantages. For example, there are an epoxy resin in which a carboxyl group is introduced by a polycarboxylic anhydride, and an epoxy phosphate in which an epoxy resin is reacted with phosphoric acid. However, the former has insufficient water resistance, water adhesion and retort properties of the coating film, and the latter has good coating film performance, but has poor compatibility with acrylic resin, and has extremely poor pigment dispersion stability. was there.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above situation, and has as its object to provide a hot water process capable of withstanding the heat treatment step of sterilizing beverage cans and food cans, especially retort processing. The present invention provides a water-based paint composition for outer surfaces of cans, which has a high hardness that is hard to be damaged in the process of transporting the cans, and that is coated with an excellent workability that can be processed into various can shapes, and that has a low amount of organic solvent. Things.

[0006]

The gist of the present invention is that (a)
30 to 65 parts by weight of an aqueous acrylic resin, 30 to 60 parts by weight of an aqueous amino resin (b), and (c) a phosphoric acid-modified epoxy compound obtained by adding a phosphoric acid ester to an epoxy compound, to a carboxyl group-containing ethylenically unsaturated compound. A phosphoric acid-modified aqueous epoxy resin 5 which is obtained by copolymerizing an ethylenically unsaturated monomer containing a saturated monomer and which is adjusted to be water-soluble or water-dispersible.
The present invention relates to a water-based coating composition containing a total of 100 parts by weight of the resin composition as a resin component. That is, the present invention can form a coating film having excellent heat resistance and water resistance by combining the above components (a), (b) and (c).

The component (c), which is one of the features of the present invention, comprises:
The epoxy group of the epoxy resin is reacted with the hydroxyl group of the phosphate ester to form a phosphoric acid-modified epoxy resin, and the phosphoric acid-modified epoxy resin is acrylic-modified to obtain a phosphoric acid-modified epoxy resin containing a free carboxyl group. The acrylic modification means that a carboxyl group-containing ethylenically unsaturated monomer is addition-polymerized to a phosphoric acid-modified epoxy resin. In order to make the resulting free carboxyl group-containing phosphoric acid-modified epoxy resin water-soluble or water-dispersible, a basic compound such as an amine is acted on to neutralize a part or all of the free carboxyl groups. The product thus obtained is a phosphoric acid-modified aqueous epoxy resin.

The present invention will be described in detail. The aqueous acrylic resin used as the component (a) in the present invention includes α / β-monoethylenically unsaturated carboxylic acid monomers such as acrylic acid and fumaric acid, acrylic acid acrylic esters such as methyl acrylate and ethyl acrylate, styrene and vinyl. A wide range of monomers can be used, such as those obtained by appropriately selecting and copolymerizing a styrene-based monomer such as toluene and a hydroxy group-containing monomer such as hydroxyethyl acrylate and hydroxypropyl acrylate. The amount of α-β monoethylenically unsaturated carboxylic acid used is 3.5 relative to the acrylic resin.
% By weight or more, and the optimum range is 5 to 20% by weight.

The aqueous acrylic resin of the present invention is preferably a resin having a weight average molecular weight of 5,000 to 50,000 obtained by synthesizing a mixture of the above monomers in a hydrophilic organic solvent. The acrylic resin in an organic solvent is dissolved in an aqueous medium in the presence of ammonia and an organic amine to make it aqueous. As the organic amine, triethylamine, triethanolamine, diethanolamine, monoethanolamine, monoethylamine, monomethylamine, dimethylaminoethanol and the like can be used. The aqueous acrylic resin is used in an amount of 30 to 65 parts by weight in the resin solid content of the entire coating composition. If the amount is less than 30 parts by weight, the adhesion to the base material is reduced, and the water dispersibility, the storage stability of the paint, and the pigment dispersibility when the pigment is added are poor. If it is more than 65 parts by weight, the hardness is lowered and the water resistance is poor.

The aqueous amino resin used in the component (b) of the present invention is an amino resin that can be dissolved or dispersed in an aqueous medium, and includes a melamine resin, a benzoguanamine resin,
Spilog anamin resin or the like is used. The aqueous amino resin is used in an amount of 30 to 60 parts by weight in the total coating composition. If it is less than 30 parts by weight, the hardness is not sufficient, and if it exceeds 60 parts by weight, the processability of the coating film is reduced.

The phosphoric acid-modified aqueous epoxy resin as the component (c) of the present invention will be described. First, an epoxy resin used to obtain a phosphoric acid-modified epoxy resin is a bisphenol glycidyl ether type, a novolak type epoxy resin, or the like. The phosphate compound used in the present invention is preferably a monohydroxyphosphate diester, and diethyl phosphate, dibutyl phosphate, dioctyl phosphate, and the like can be used. Also, a mixture of dihydrooxyphosphate monoesters such as butyl acid phosphate and isobutyl acid phosphate can be used.

The reaction between the epoxy resin of the present invention and a phosphate ester is carried out in the absence of a solvent or in the presence of an organic solvent at 70 to 15 times.
It is performed in the range of 0 ° C. Since the reaction generates heat, a method of gradually adding a phosphate ester to the epoxy resin over 30 minutes to 2 hours is suitable. The reaction ratio between the epoxy resin and the phosphoric acid ester is preferably such that the acid equivalent of the phosphoric acid ester is in the range of 0.3 to 0.8 per 1 equivalent of the epoxy group. 0.
If it is 3 or less, the adhesion and retort properties decrease. If the ratio is 0.8 or more, unreacted phosphoric acid ester remains, and the stability of the paint decreases. The reaction between the epoxy resin and the phosphoric acid ester is performed until the acid value of the phosphoric acid-modified epoxy resin becomes 10 mgKOH / g or less. When the acid value is 10 mgKOH / g or more, the paint stability decreases. The phosphorus content of the phosphoric acid-modified epoxy resin is preferably from 1 to 10%, more preferably 1% or less,
The retort properties are inferior, and even if it is 10% or more, the effect just added cannot be obtained. More preferably, it is in the range of 3 to 8%. Incidentally, if a large amount of epoxy groups remain after the reaction, esterification having poor hydrolysis resistance occurs when copolymerized with the acrylic monomer, so that the oxirane oxygen content after the reaction is preferably 0.8% or less, If it is 0.8% or more, it may be reacted with an alkylphenol, a tertiary fatty acid, a monocarboxylic acid, or the like.

Next, a carboxyl group-containing ethylenically unsaturated monomer is polymerized on the obtained phosphoric acid-modified epoxy resin in an organic solvent solution in the presence of a free radical generator to produce a carboxyl group-containing phosphoric acid-modified epoxy resin. And A carboxyl group-containing ethylenically unsaturated monomer is an ethylenically unsaturated carboxylic acid containing a carboxyl group as an essential component, and containing other ethylenically unsaturated monomers as necessary. is there. Examples of the ethylenically unsaturated carboxylic acid containing a carboxyl group include acrylic acid, methacrylic acid, and fumaric acid. Other ethylenically unsaturated monomers include acrylics such as methyl acrylate and ethyl acrylate. There are styrene monomers such as acid esters, styrene and vinyl toluene, and hydroxyl group-containing monomers such as hydroxyethyl acrylate and hydroxypropyl acrylate. 3% of ethylenically unsaturated carboxylic acid in carboxyl group-containing ethylenically unsaturated monomer
It is preferable to contain the above. The carboxyl group-containing ethylenically unsaturated monomer is a phosphoric acid-modified epoxy resin 100
10 to 40 parts by weight per part by weight are used.

The acrylic modification of the phosphoric acid-modified epoxy resin of the present invention is carried out by subjecting an acrylic resin obtained by polymerizing an ethylenically unsaturated monomer containing 3% by weight or more of a carboxyl group-containing ethylenic monomer to phosphoric acid. It can also be obtained by reacting in a modified epoxy resin solution. In order to adjust the carboxyl group-containing phosphoric acid-modified epoxy resin to be water-soluble or water-dispersible, the carboxyl group-containing phosphoric acid-modified epoxy resin is neutralized with a basic compound such as amine or ammonia. For this adjustment, the acid value of the carboxyl group-containing phosphoric acid-modified epoxy resin is desirably 30 mg KOH / g or more so that sufficient water solubility or water dispersibility can be obtained. However, the acid value is 150 mg
If KOH / g or more, the water resistance decreases, so the acid value is preferably in the range of 50 to 100 mgKOH / g.

The phosphoric acid-modified aqueous epoxy resin obtained by this method is used in an amount of 5 to 20 parts by weight in the coating composition. 5
When the amount is less than the weight part, the adhesion of the coating film is poor, and the retort resistance and the workability are poor. If the amount is more than 20 parts by weight, the compatibility with other resins is reduced, and the paint stability and paintability are reduced.

The aqueous coating composition of the present invention is obtained by dissolving or dispersing a resin component in an aqueous medium. The aqueous medium contains water as a main component and contains at least 5 parts by weight of a hydrophilic organic solvent. As the hydrophilic organic solvent, butyl cellosolve, hexyl cellosolve, propylene glycol methyl ether, propylene glycol butyl ether, diethylene glycol methyl ether,
And diethylene glycol butyl ether. The content of the hydrophilic organic solvent is preferably 20% by weight or less. The aqueous coating composition of the present invention may optionally contain an amine-blocked acid catalyst such as p-toluenesulfonic acid, dodecylbenzenesulfonic acid, dinonylnaphthalenedisulfonic acid or the like as a curing aid in an amount of 0 to 100 parts by weight of the resin solids. .1
~ 2 parts by weight are added to form a coating.

It is also possible to mix a water-soluble resin or a water-dispersible resin, such as a water-soluble polyester resin, a maleated fatty acid, or a polyol, which is generally used as a water-based coating resin. Similarly, a leveling agent, an antifoaming agent, and a lubricant can be added. Further, a pigment paste can be prepared by pulverizing the pigment with the solution of the acrylic resin, and can be formed into a paint by the same method as described above.

The aqueous paint of the present invention can be applied to a substrate by a known means such as roll coating, spraying and brushing. As the base material, there is a metal base material such as an electro-tin plated steel plate, tin-free steel, and aluminum. Further, the water-based paint of the present invention can be cured under a wide range of baking conditions from baking at 150 to 200 ° C. for about 10 minutes to baking at a high temperature of about 250 ° C. for about 10 seconds for a short time.

[0019]

EXAMPLES The present invention will be described below with reference to examples. In the example,
Parts mean parts by weight, and% means% by weight. Production Example 1 Production of Aqueous Acrylic Resin Solution A1 100 parts of butyl cellosolve was charged into a four-necked flask equipped with a thermometer, a stirrer, a reflux condenser, a dropping tank, and a nitrogen gas injection tube, and the temperature was adjusted to 10 by stirring while introducing nitrogen gas.
5 ° C., 5 parts of benzoyl peroxide was added to 100 parts of a mixture of 30% of styrene, 30% of ethyl acrylate, 10% of butyl acrylate, 10% of 2-hydroxyethyl acrylate, 10% of methyl methacrylate and 10% of acrylic acid. The solution was added dropwise over 3 hours. Thereafter, the mixture was reacted at 105 ° C. for 1 hour, 0.5 part of benzoyl peroxide was added, and the mixture was further reacted for 1 hour to complete the reaction. The butyl cellosolve was distilled off under reduced pressure at 100 ° C. until the non-volatile content became 83%. Thereafter, 14.6 parts of diethanolamine and water were added, and a transparent and viscous aqueous acrylic resin A1 having a solid content of 50% and a residual butyl cellosolve of 10% was added. I got

Production Example 2 Production of aqueous acrylic resin solution A2 According to Production Example 1, styrene 15%, ethyl acrylate 20%, 2-hydroxyethyl acrylate 15%,
Methyl methacrylate 35%, methacrylic acid 15%
In the same manner, polymerization was carried out using the monomer composition described above to obtain an aqueous acrylic resin solution A2.

Production Example 3 Production of phosphoric acid-modified aqueous epoxy resin solution B1 300 parts of Epicoat 828 (epoxy resin epoxy equivalent: 186 g / eq, manufactured by Shell Epoxy Co., Ltd.) was placed in a reactor equipped with a thermometer, a stirrer, a reflux condenser, and a dropping can. And heated to 105 ° C., and 243 parts of dibutyl phosphate are added dropwise over 1 hour. Thereafter, the reaction was continued for another 1 hour to reduce the acid value to 4.
A product having a mgKOH / g, an oxirane oxygen content of 0.3% and a number average molecular weight of 1400 was obtained. Next, 125 parts of butyl cellosolve is added and dissolved at 100 ° C. A mixture of 50 parts of acrylic acid, 30 parts of styrene, and 5 parts of bezoyl peroxide was added dropwise to this solution over 1 hour, and the mixture was further reacted at 100 ° C. to carry out acryl modification. Next, the mixture was neutralized with 62 parts of dimethylaminoethanol and further added with 431 parts of water to obtain a transparent and viscous phosphoric acid-modified aqueous epoxy resin solution B1 having a solid content of 50% and butyl cellosolve of 10%.

Production Example 4 Production of phosphoric acid-modified aqueous epoxy resin solution B2 In the same manner as in Production Example 3, 300 parts of Epikote 828 and 243 parts of dioctyl phosphate were reacted to obtain an acid value of 3 mgK.
After OH / g, the resin was dissolved with butyl cellosolve, and 50 parts of methacrylic acid, 20 parts of styrene,
A mixture of 10 parts of hydroxyethyl acrylate and 3 parts of benzoyl peroxide was dropped and neutralized with 52 parts of dimethylaminoethanol. Water was added to the mixture, and a clear and viscous phosphoric acid having a solid content of 50% and butyl cellosolve of 10% was added. A modified aqueous epoxy resin solution B2 was obtained.

Production Example 5 Production of Aqueous Epoxy Resin Solution C1 In a reactor similar to that of Production Example 3, 300 parts of Epicoat 828 were added with 241 parts of benzoic acid, reacted at 150 ° C. for 5 hours, cooled to 100 ° C., and then cooled to butyl cellosolve. Dissolve in 124 parts, then add 50 parts acrylic acid, 30 parts styrene
And 5 parts of benzoyl peroxide in advance, and a drop reaction is carried out.
The mixture was neutralized with 2 parts and further added with 430 parts of water to obtain an aqueous epoxy resin solution C1 having a solid content of 50% and butyl cellosolve of 10%.

Production Example 6 Production of Aqueous Epoxy Resin Solution C2 In the same reactor as in Production Example 3, Epicoat 828 was charged with 60 parts of 200 butyl cellosolve, heated to 100, and then 100 parts of butyl acid phosphate was added dropwise over 1 hour. Thereafter, the reaction was carried out for 2 hours to obtain an epoxy phosphate having an acid value of 90 mgKOH / g. Next, neutralize with 43 parts of dimethylaminoethanol and add 197 parts of water.
An aqueous epoxy resin solution C2 containing 10% butyl cellosolve was obtained.

Examples 1 to 4 After mixing the respective components according to Table 1, (however, in Example 2, the acrylic resin and the pigment were kneaded first.) Butyl cellosolve and water were added, and the organic solvent in the paint was added. Quantity 10
% And the solid content were adjusted to 40%. (However, in Example 2, the solid content was 60%.) Table 1 shows the solid content ratio of each component in percentage. To this, 0.3% of a p-toluenesulfonic acid amine salt and 0.3% of a leveling agent were added to obtain an aqueous paint. This paint was applied to an electroplated tin plate having a thickness of 0.23 mm using a natural coater.
It was baked and cured at 0 ° C. for 10 minutes. The film thickness was 6-8 μ. Cymel 1123 is a benzoguanamine resin manufactured by Mitsui Cyanamid.

Comparative Examples 1 to 3 Each component was mixed according to Table 1 and water-based paints were obtained in the same manner as in Examples 1 to 4. Using this paint, Examples 1 to
A coated plate was obtained in the same manner as in Example 4. Table 2 shows the results of examining the stability and physical properties of the coatings prepared in the examples and comparative examples.

Each test method in Table 2 is as follows. Paint Test ○ Paint stability test After the paint was stored at room temperature for 2 months, the state of gelation and separation of the resin in the paint was observed. -Coating physical property test An electroplated tin plate having a thickness of 0.23 mm was dried by roll coating and then coated so as to have a coating thickness of 7 µm, and baked in a gas oven at an atmosphere temperature of 190 ° C for 10 minutes to prepare a panel. The scratch resistance was evaluated by preparing a three-piece can formed by molding a coated plate such that the coated surface was the outer surface of the can. -Water resistance test The coated panel was immersed in water and heat-treated at 100C for 30 minutes, and then the whitening state of the coating film was evaluated.

○ Workability test Erichsen test: According to JISZ-2247, after extruding until the base metal plate started to crack, the state of the coating film was evaluated. ○ Impact resistance Using a DuPont impact tester, a 1/2 inch diameter firing pin is brought into contact with the sample, and then a 500 gr weight is dropped. Impact resistance was evaluated based on the height at which cracks did not occur in the coating film. ○ Pencil hardness test JIS standard "pencil scratch test" (JIS No. K54
(00).

○ Adhesion Test A cross-cut peel test was performed. O Scratchability The contents were packed in cans, and the outer surfaces of the cans were brought into contact with each other in warm water at 80 ° C to evaluate the degree of scratchiness of the coating film. ○ Immediately after coating with a flow roll coater, baking was performed in a gas oven to evaluate the leveling state.

[0030]

[Table 1]

[0031]

[Table 2]

[0032]

The aqueous coating composition of the present invention has excellent retort resistance and workability of the coating film. Further, the pigment dispersibility at the time of adding the pigment was excellent, and the storage stability of the coating over time was good.

Continuation of the front page (51) Int.Cl. ⁶ identification code FI (C09D 161/20 133: 04 163: 10) (58) Investigated field (Int.Cl. ⁶ , DB name) C09D 133/04 C09D 161 / 20 C09D 163/00-163/10

Claims (1)

(57) [Claims] 1. A phosphoric acid-modified epoxy obtained by adding a phosphate ester to (a) 30 to 65 parts by weight of an aqueous acrylic resin, (b) 30 to 60 parts by weight of an aqueous amino resin, and (c) an epoxy compound. Compounds are prepared by co-polymerizing an ethylenically unsaturated monomer containing a carboxyl group-containing ethylenically unsaturated monomer with a carboxyl group-containing phosphoric acid-modified epoxy resin, which is adjusted to a water-soluble or water-dispersible phosphoric acid. An aqueous coating composition containing a total of 100 parts by weight of a modified aqueous epoxy resin of 5 to 20 parts by weight as a resin component.