JP2920465B2 - Resin for water-based paint and water-based paint using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a base material for a coating film,
Good adhesion to metal, good balance of hardness and impact resistance of coating film, excellent water resistance of coating film can be formed, and resin for water-based paints with excellent storage stability .
And a water-based paint using the same .

[0002]

2. Description of the Related Art Food cans, including beverage cans used in canned coffee, canned juice, canned beer, and the like, include:
It is provided with corrosion resistance to the contents and, in the case of cans containing retort foods, is coated to withstand sterilization treatment.

Conventionally, organic solvent type paints such as epoxy resin / amino resin paint, acrylic resin / amino resin paint and polyester resin / amino resin paint have been used as the paint for cans. For the curing of the coating film, a method of performing a thermal curing treatment in a baking furnace is used. But,
Coating films formed from these solvent-based paints, a large amount of organic solvent volatilizes during the thermosetting treatment, which causes air pollution, and is considered to be problematic from the viewpoint of resource saving. There is a demand for a water-based paint resin free of such disadvantages.

[0004] There are two types of water-based paint resins known so far, water-soluble resins and water-dispersible resins.
The water-dispersible resin is made by an emulsion polymerization method of a vinyl monomer using an aqueous medium containing an emulsifier, and a surfactant used as an emulsifier remains in a coating film formed from the water-dispersible resin. In addition, the water resistance of this coating film is poor,
Further, the paint made of the water-dispersible resin has a drawback that it is difficult to apply the paint by a roll coater due to its structural viscosity.

As the water-soluble resin, an acrylic resin is generally used, but in order to make the resin water-soluble, it is necessary to introduce a carboxyl group into the molecule. However, a coating film formed from a water-soluble resin into which a large amount of a carboxyl group is introduced in order to increase the water solubility of the resin has disadvantages such as insufficient water resistance and insufficient alkali resistance. In order to solve this difficulty, a method of using aminoplast which gives a crosslinked structure to a coating film together with a water-soluble acrylic resin has been adopted.

[0006] A coating film formed from a coating composed of a water-soluble acrylic resin and aminoplast exhibits considerably excellent properties, but has insufficient adhesion to a metal serving as a coating base material. Therefore, a method in which an epoxy resin is used in combination with the water-soluble paint has been adopted.

[0007]

The paints of water-soluble acrylic resin, aminoplast and epoxy resin which have been developed so far have some characteristics, but they have a characteristic that they can be compared with the same kind of organic solvent-based paints. Still, the epoxy resin undergoes phase separation during storage of the waterborne paint. The properties of the coating film formed from the water-based paint are more cloudy than those of the coating film formed from the organic solvent paint, and the properties of the coating film such as water resistance are not yet satisfactory.

[0008]

Means for Solving the Problems In view of the above circumstances, the present inventors have formed a water-soluble paint having excellent storage stability and a coating film having excellent adhesion to a base metal,
Good and has a water-resistant, water-based coating resin and child capable of forming a coating film balanced hardness and impact resistance
As a result of studying to obtain a water-based paint using the same , the present invention has been completed, and the gist of the invention is that an epoxy resin having one or more glycidyl groups in a molecule and two resins having different acid strengths are used. A half-esterification reaction product with an α, β-monoethylenically unsaturated dicarboxylic acid having a carboxylic acid group or an anhydride thereof , and a copolymer having another copolymerizable vinyl monomer as a component are mixed with a base. Sum
And a water-based paint using the same.

The epoxy resin having one or more glycidyl groups in a molecule used in the practice of the present invention is an epoxy resin having an epoxy equivalent of 400 to 3000, particularly a bisphenol A type epoxy resin or bisphenol F
It is preferably a type epoxy resin. Epoxy resin having an epoxy equivalent of less than 400 is subjected to a half-esterification reaction with α, β-monoethylenically unsaturated dicarboxylic acid,
The reaction controllability is poor, the obtained resin is easily gelled, and the gelled half-esterified epoxy resin is difficult to be made water-soluble by a base. On the other hand, an epoxy resin having an epoxy equivalent greater than 3000 has a slow half-esterification reaction with α, β-monoethylenically unsaturated dicarboxylic acid, and tends to make it difficult to produce a resin having good water solubility.

Specific examples of α, β-monoethylenically unsaturated dicarboxylic acids having two carboxylic acids having different acid strengths used in carrying out the present invention include itaconic acid,
α-methylene glutaric acid, methacrylic acid dimer and the like can be mentioned. Since the α, β-monoethylenically unsaturated dicarboxylic acid used in the present invention has two carboxylic acid groups having different acid strengths in the molecule, it is half-esterified without causing gelation in the reaction with the epoxy resin. The obtained epoxy resin can be obtained efficiently. In addition, a water-soluble resin made by using the half-esterified epoxy resin can form a coating having extremely good storage stability without causing phase separation in an aqueous medium. The coating film formed has a great feature that the adhesion to the substrate is good, the hardness of the coating film and the impact resistance are balanced, the retort resistance is good, and the appearance is also good. I have.

[0011] The half ester of an epoxy resin and itaconic acid is obtained by [Chemical Formula 1], and one of the carboxyl groups in itaconic acid is usually kept free.

Embedded image Α, β of the resulting epoxy resin
-To prevent the gelation of the monoethylenically unsaturated dicarboxylic acid half ester, and to impart water solubility to the resin obtained by copolymerizing this half-esterified epoxy resin with another ethylenically unsaturated carboxylic acid. You can. The epoxy resin and the α, β-monoethylenically unsaturated dicarboxylic acid are defined as dicarboxylic acid to 1 equivalent of epoxy.
By reacting at a ratio of 0.8 to 1.2 equivalents, preferably 0.9 to 1.1 equivalents, an α, β-monoethylenic dicarboxylic acid half ester of an epoxy resin can be efficiently produced.

The half-esterification reaction of an epoxy resin with an α, β-monoethylenically unsaturated dicarboxylic acid is preferably carried out as follows. A reaction vessel is charged with a hydrophilic organic solvent, for example, butyl cellosolve, a tertiary amine such as triethylamine is interposed as a reaction catalyst, and a predetermined amount of epoxy resin and α, β-monoethylenically unsaturated dicarboxylic acid are reacted in the reaction vessel. And reacting at 60-150 ° C. for 2-8 hours. In order to prevent the polymerization of the α, β-monoethylenically unsaturated dicarboxylic acid during the reaction, it is preferable that a radical polymerization inhibitor such as hydroquinone is interposed in the reaction system. The half esterification reaction is preferably controlled by measuring the acid value of the reaction system.

Examples of vinyl monomers copolymerizable with a half ester of an epoxy resin and an α, β-monoethylenically unsaturated dicarboxylic acid include carboxyl group-containing vinyl monomers such as (meth) acrylic acid, maleic acid and fumaric acid, and alkyl groups. Alkyl (meth) acrylate having 1 to 18 carbon atoms such as methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, cyclohexyl (meth) acrylate , 2-ethylhexyl (meth) acrylate, lauryl (meth) acrylate, octyl (meth) acrylate, stearyl (meth) acrylate, and the like.

If necessary, aromatic vinyl compounds such as styrene and α-methylstyrene, vinyl esters such as vinyl acetate and vinyl propionate, nitrile group-containing monomers such as (meth) acrylonitrile, 2-hydroxyethyl (meth) )) Commonly used monomers such as hydroxyalkyl (meth) acrylates such as acrylate, glycidyl group-containing monomers such as glycidyl (meth) acrylate, methacrylamides, methylol-modified products of these amides, and benzyl (meth) acrylate Can also be used in combination.

The polymerization catalyst that can be used in the copolymerization of the above-mentioned half-ester of the epoxy resin with a copolymerizable vinyl monomer is not particularly limited, and a known catalyst can be used. For example, peroxides such as lauryl peroxide and benzoyl peroxide, and azo-based compounds such as 2,2′-azobisisobutyronitrile are exemplified. These polymerization initiators are used alone or in combination of two or more.
A known chain transfer agent may be used as needed.
Examples of the chain transfer agent include n-dodecyl mercaptan, n-octyl mercaptan, 2-ethylhexyl thioglycolate, thiophenol, and α-methylstyrene dimer.

The copolymerization of a half esterifying agent of an α, β-monoethylenically unsaturated dicarboxylic acid of an epoxy resin with another copolymerizable monomer is carried out in the presence of a water-soluble organic solvent.
It can be performed by a method such as a batch polymerization method or a drop polymerization method.

The resin solution obtained as described above is neutralized with a basic compound and diluted with water to obtain an aqueous coating. Examples of the basic compound that can be used include alkylamines such as triethylamine, trimethylamine and butylamine, alcohol amines such as 2-dimethylaminoethanol, triethanolamine, diethylethanolamine, dimethylethanolamine and aminomethylpropanol, and morpholine. Can be mentioned.
The amount of these amines used is 50 to 150 of the acid value of the water-soluble resin.
%.

The aqueous resin obtained according to the present invention can be dissolved in an aqueous medium to form an aqueous coating. Further, an aqueous amino resin can be added to form a cross-linkable aqueous coating. Examples of the aqueous amino resin that can be used here include alkyl etherified melamine resins, alkyl etherified benzoguanamine resins, alkyl etherified urea resins, alkyl etherified glycoluril resins, and phenylene nuclei.
And a diguanamine alkyl etherified resin to which three triazine rings are bonded. In particular, it is preferable to use a methyl etherified amino resin having good water solubility. These amino resins are preferably used in a proportion of 10 to 60 parts by weight with respect to 100 parts of the aqueous resin. An aqueous resin made mainly of a half ester of an α, β-monoethylenically unsaturated dicarboxylic acid of an epoxy resin, and a coating film formed from an aqueous paint containing the amino resin, further, stain resistance, hardness,
It has improved solvent resistance, retort resistance and the like.

In order to improve the crosslinking rate of the coating and the crosslinking density of the coating film, an acid catalyst such as p-toluenesulfonic acid, dodecylbenzenesulfonic acid, dinonylnaphthalenesulfonic acid, or these sulfonic acids It is preferable to use an amino blocked product of the above. Also,
Conventionally known leveling agents, defoamers, lubricants, pigments and the like can also be used in combination. In addition, as a coating method, a known method such as a roll coating method, a spray coating method, or a brush coating method can be used.

The paint made from the water-based resin of the present invention has extremely good storage stability, and a coating film formed from the water-based paint has excellent adhesion to a substrate, especially a metal substrate. The coating film has a balance with impact resistance and also has retort resistance, so that it is particularly suitable as a paint for cans.

Hereinafter, the present invention will be described in more detail with reference to examples. The “parts” used in the examples are “parts by weight”.
Is shown.

[Synthesis of Resin (A-1)] In a four-necked flask equipped with a stirrer, a thermometer, a nitrogen inlet tube and a reflux condenser, 49.5 parts of butyl cellosolve was added to an epoxy resin having an epoxy equivalent of 450 (manufactured by Yuka Shell Co., Ltd.). Epicoat # 1001) 3
After dissolving 8.8 parts, heating to 80 ° C., adding 11.2 parts of itaconic acid and reacting for 30 minutes, and after confirming that the reaction solution became transparent, 0.5 ml of triethylamine was added.
The reaction solution was immediately heated to 130 ° C. and reacted for 4 hours until the acid value of the reaction system became constant. The viscosity of the obtained resin solution is V (using a Gardner-Holdt foam viscometer).
(Measured at 25 ° C.), solid content 53.6% by weight, resin obtained (A-
The acid value of 1) was 47.5 mgKOH / g, and the evaluation results are shown in Table 1.

[Production of Resins (A-2) to (A-6)] Using the epoxy resin, carboxylic acid and the like shown in Table 1, in the same manner as in the production method of Resin (A-1), 2)-(A
-6) was obtained, and the characteristics were evaluated. The results are shown in Table 1.
Resin numbers (A-4) to (A-6) are comparative examples.

[Table 1]

In a four-necked flask equipped with a stirrer, thermometer, nitrogen inlet tube and reflux condenser, butyl cellosolve 22.0 was added.
After the temperature was raised to 80 ° C, the above resin solution (A-
1) to (A-5), ethyl acrylate, methacrylic acid, N-butoxymethylacrylamide, styrene, 2-hydroxyethyl methacrylate, and azobisisobutyronitrile, the compositions shown in Table 2 were added dropwise over 3 hours. While polymerizing. One hour after the completion of the dropwise addition, 0.2 parts of azobisisobutyronitrile was added, and the properties of the water-soluble resin and the resin solution obtained by polymerization for 2 hours were shown in Table 2.

[Table 2]

[0025]

Examples 1 to 3 and Comparative Examples 1 to 4 The aqueous resins (B-1) to (B-5) and (C-1) produced as described above.
And 2 parts of a water-soluble methylated melamine resin (manufactured by Mitsui Cyanamid Co., Ltd., Cymel # 303) and 6.8 parts of 2-dimethylethylethanol were added to 100 parts of each and 100 parts of (C-2). In addition, it was diluted so that the viscosity measured by Ford Cup No. 4 became 100 seconds to obtain an aqueous paint. The obtained six water-based paints were applied to a thickness of 0.3
The coated film was coated with a bar coater on an aluminum plate having a thickness of 8 mm so as to have a thickness of 8 to 10 μm and baked in a drying oven at 200 ° C. for 10 minutes. Table 3 shows the results of evaluating the obtained coating films.

[Table 3]

The coatings and coatings in Table 3 were evaluated according to the following criteria. [Appearance of paint] The appearance of paint was visually determined. ○: good transparency; Δ: slightly cloudy; ×: cloudy opacity [Coating film hardness] Measured according to JIS standard using Mitsubishi Uni pencil. [Adhesion] According to JIS standard, the state of the coated plate after peeling off the cellophane tape was observed. …: Good; Δ: some peeling of coating film observed;
×: Peeling is observed on the entire surface. [Impact resistance] Using a Dupont impact tester, a hammer rod was mounted at 1/2 inch, load was 300 kg, and height was 30 cm, and the state of the coating film was observed. ○: good; Δ: some cracks; ×: cracks all over [Retort resistance] Put the coated plate in a pressure cooker tester, immerse it in hot water at 130 ° C for 30 minutes, and then apply The whitening state of the film was visually determined. …: Good; Δ: some whitening observed; ×:
... whitening is observed on the entire surface [Paint stability] The paint was left in an atmosphere at 60 ° C for one month, and the appearance was visually judged. …: Good; Δ: some cloudiness is observed; ×:
… Separation is seen

──────────────────────────────────────────────────続 き Continuation of front page (51) Int.Cl. ⁶ Identification symbol FI // C08G59 / 14 C08G59 / 14 (56) References JP-A-60-245617 (JP, A) JP-A-52-114625 (JP, a) JP Akira 49-25084 (JP, a) Tokuoyake Akira 53-11530 (JP, B2) PCT National flat 1-501482 (JP, a) (58 ) investigated the field (Int.Cl. ⁶ , DB name) C08F 290/00-290/14 C08F 8/00-8/50 C09D 1/00-201/10 C08G 59/00-59/72

Claims (4)

(57) [Claims] 1. Half-esterification of an epoxy resin having one or more glycidyl groups in a molecule with an α, β-monoethylenically unsaturated dicarboxylic acid having two carboxylic acids having different acid strengths or an anhydride thereof. the reaction product, and <br/> copolymerizable other aqueous coating resin obtained by neutralizing a copolymer as a constituent of vinyl monomers in a base. 2. An epoxy resin having an epoxy equivalent of 40
The water-based paint resin according to claim 1, wherein an epoxy resin of 0 to 3000 is used . Wherein α has an acid strength of different two carboxylic acid groups, beta-as monoethylenic dicarboxylic acids, aqueous claim 1 or claim 2, wherein the use of itaconic acid or its anhydride Paint resin. 4. A 100 parts of an aqueous paint resin of claim 1, comprising a water-soluble amino resin 10 to 60 parts by weight of the aqueous medium an aqueous coating.