JPH0822980B2 - Inner paint for metal cans for food and drink - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to a paint for the inner surface of a metal can for food and drink, and more particularly to a correction paint for painting the side seam portion of a welding can.

(Prior Art) Metal cans are stronger than other containers and have the characteristic of being able to store food as a content for a long period of time, and are used in a wide range of applications. In recent years, metal cans, like other containers such as paper and plastic, are strongly appealing to consumers from an aesthetic point of view.
In particular, bead processing, multi-neck-in processing, etc. have been added. Welding cans have begun to be widely used because the can manufacturing method can cope with such movements, and the strength of the cans is extremely higher than that of conventional adhesive cans and solder cans, and the equipment space is small, which is a cost advantage. There is. On the other hand, in order to prevent corrosion of the can material and improve workability, a coating film is formed on various metal materials such as electroplated steel sheets and tin-free steel. It is generally difficult to form a coating film that also has corrosion resistance that can be stored for a long period of time, and there are many practically inadequate points.

In particular, in the case of a welded can, the end faces of both cut surfaces of the can body material are overlapped (lap seam) and welded, so that the cut can is exposed unpainted on the inner surface of the can and the material is electroplated. In the case of tin, tin reflows due to the heat during welding, and in the case of tin-free steel, corrosion easily occurs from the metal surface that has been scraped to facilitate welding. In order to prevent this, it is necessary to apply a correction coating to the inner surface of the can, and in some cases the outer surface of the weld, to form a protective film. However, the weld step at such weld is relatively large, and this part is particularly thick. It is necessary to form a coating film. If the coating film has good corrosion resistance when processed, cracks are likely to occur, and it is generally difficult to form a coating film with good corrosion resistance and workability. Therefore, the performance of the correction paint is an important factor that affects the performance of the welding can.

Thus, paints for metal cans have recently been able to withstand severe processing such as beads and multi-neck-ins, and to form coatings that can preserve contents such as foods for a long period of time. However, it is necessary to form a thick coating film under a short baking condition. Several proposals have been made for paints that satisfy such various requirements. One is mainly composed of a vinyl chloride resin-based organosol composition (JP-A-55-49174), or an epoxy-acrylic or epoxy-based composition.
Paints for metal cans are known in which polyester resins are added to various amino-based or epoxy-phenol-based thermosetting paints (Japanese Patent Laid-Open Nos. 50-32230 and 55-593).
No. 6).

However, paints containing thermoplastic resins can form coating films in a short time, but when the contents are beverages and foods, they are only sufficient for high temperature retort treatment due to acid resistance and sterilization. There are drawbacks in terms of corrosion resistance and content resistance. In addition, the epoxy resin-based thermosetting paint and the polyester resin-containing thermosetting paint are generally 220 to 260 in a short baking time of 2 minutes or less, particularly 30 seconds or less, which is a baking condition for welding can correction paint. Even at a high temperature of about ℃, it does not cure sufficiently and it is difficult to form a coating film with excellent corrosion resistance.
Moreover, even a polyester resin-containing thermosetting paint, which is characterized by poor workability in thick film and relatively good workability, has not yet achieved sufficient performance.

(Problems to be Solved by the Invention) The present invention has been made in view of the above-mentioned current situation, and withstands severe processing such as beads and multi-neck-in, and
Metal can inner coating for food and drink forming a coating film capable of long-term storage of contents such as food and drink, particularly thick under baking conditions for a short time, and with excellent processability, It is an object of the present invention to provide a coating material for welding can compensating which forms a coating film excellent in content resistance.

[Structure of Invention]

(Means for Solving Problems) That is, the present invention has 100 parts by weight of a thermosetting resin and at least one functional group selected from an epoxy group, a carboxyl group and a hydroxyl group. 4 butadiene units to 50
It is an organic solvent-based internal coating for metal cans for foods and drinks, which is prepared by mixing 5 to 100 parts by weight of liquid polybutadiene containing at least 1% by weight.

The thermosetting resin in the present invention includes epoxy resin, phenol resin, amino resin, alkyd resin, acrylic resin and the like. A combination of a bisphenol type epoxy resin and a resole resin is preferable.

Bisphenol type epoxy resin is bisphenol A
Type epoxy resin, hydrogenated bisphenol A type epoxy resin, bisphenol F type epoxy resin and the like. Particularly, an epoxy resin obtained by a reaction of bisphenol A and epichlorohydrin and having an average epoxy equivalent of 1500 to 4000 can be preferably used. In addition, bisphenol type epoxy resin, linoleic acid, linolenic acid, dehydrated castor oil fatty acid, soybean oil fatty acid,
Those esterified with higher unsaturated fatty acids such as coconut oil fatty acid can be used in the same manner.

The resole resin is obtained by reacting phenols such as carboxylic acids, cresols, ethylphenols, other alkylphenols or bisphenols with aldehydes such as formaldehyde and acetaldehyde in the presence of a basic catalyst, or , Alkyl etherified phenolic resins obtained by reacting them with alcohols can be used.

The liquid polybutadiene in the present invention is an epoxy group,
It has at least one functional group selected from carboxyl group and hydroxyl group and contains 50% by weight, preferably 70% by weight or more of 1,4-butadiene unit, and other constituents are composed of 1,2-butadiene unit However, in addition to these, monomers other than butadiene such as α-methylstyrene and styrene may be contained. The number average molecular weight used is 500 to 10,000, preferably 1,000 to 5,000.

Functional groups in liquid polybutadiene, especially epoxy groups and carboxyl groups introduced into the raw material polybutadiene by a modifier, react effectively with crosslinkable functional groups in thermosetting resin to form a cured coating film. preferable.

The epoxy group of liquid polybutadiene may be obtained by modifying the raw material polybutadiene with a peracid such as peracetic acid or formic acid, and the carboxyl group may be the unsaturated polybasic acid such as maleic acid, itaconic acid, citraconic acid or fumaric acid. Alternatively, it can be obtained by reacting those acid anhydrides.

The inner surface coating for metal cans for food and drink of the present invention comprises 5 parts by weight to 1 part by weight of liquid polybutadiene per 100 parts of thermosetting resin.
00 parts by weight, preferably 20 parts by weight or more. As the proportion of liquid polybutadiene in the paint decreases, the rapid curing property and the processability of the coating film tend to deteriorate.

The inner coating for metal cans for food and drink of the present invention is used by dissolving a functional group-containing liquid polybutadiene and a thermosetting resin in an organic solvent. Examples of the organic solvent include aromatic compounds such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, xylene and other alkylbenzenes, cellosolves such as methyl cellosolve, ethyl cellosolve and butyl cellosolve, methyl cellosolve acetate, butyl cellosolve acetate, ethyl acetate, butyl acetate. And the like, alcohols such as isopropyl alcohol, butyl alcohol, diacetone alcohol, and the like, or a mixed solvent thereof can be used.

The inner surface coating for metal cans for food and drink of the present invention contains a thermosetting resin and a functional group-containing liquid polybutadiene as main components, and in addition to these solvent-soluble components, a thermoplastic resin is used as a total resin component. Can be compounded within 30% by weight. Especially when used as a correction paint, fine particles of thermoplastic resin such as polyamide resin, carboxyl group-modified polyolefin resin, polyester resin, polyvinyl chloride resin, polyacetal resin, etc. are used in order to improve the covering property against burrs at welded portions and cut portions. It can be used by being dispersed in a paint.

The inner coating for metal cans for food and drink of the present invention includes phosphoric acid, phosphoric acid esters, p-toluenesulfonic acid, acidic substances such as trimellitic acid, zinc octylate, zinc naphthenate, etc. for promoting curing. Organometallic compound type curing aids such as salts or aluminum alcoholates, alkyl titanates, etc., or amine catalysts such as trimethylamine, triethylamine, dimethylaminoethanol, etc. or benzoyl peroxide as a reaction agent for carbon-carbon double bonds contained in liquid polybutadiene as a side chain. Radical generators such as organic peroxides can be added.

The inner coating for metal cans for food and drink according to the present invention contains other conventional additives such as coloring dyes and pigments, rust preventive pigments, fillers,
Surfactants, lubricants, etc. can be added.

As a method for applying the inner coating material for a metal can for food and drink of the present invention, known means such as spraying, roll coating, brush coating, and flow coating can be used.

Hereinafter, the present invention will be specifically described with reference to examples. In the examples, "part" and "%" mean "part by weight" and "% by weight", respectively.

(Example) Preparation of epoxy resin solution (a): 100 parts of Epikote 1009 (bisphenol A type epoxy resin manufactured by Yuka Shell Epoxy Co., Ltd., epoxy equivalent 2650) was added to diethylene glycol monoethyl ether acetate.
It was dissolved in 100 parts at 90 ° C. to obtain an epoxy resin solution (a).

Preparation of Epoxy Resin Solution (b): Similar to Epoxy Resin Solution (a) except that Epicoat 1007 (bisphenol A type epoxy resin manufactured by Yuka Shell Epoxy Co., Ltd., epoxy equivalent 1950) was used instead of Epicoat 1009. It was adjusted.

Preparation of epoxy ester resin solution (c): 100 parts of AER667 (bisphenol A type epoxy resin manufactured by Asahi Kasei Corporation), 40 parts of soybean oil fatty acid, 2 parts of xylene 10 parts
The reaction was terminated at 20 ° C for 3 hours, and when the acid value became 10 or less, the reaction was terminated, and 65 parts each of Solvesso 100, Solvesso 150 and diethylene glycol monoethyl ether acetate were added and cooled, and the epoxy ester resin solution (c) And

Preparation of resole resin (d): p-cresol 108 parts, formaldehyde 40% n-
56 parts of butanol solution, 14 parts of 25% ammonia at 100 ℃ 3
After reacting for a period of time, 110 parts of each of xylene, cyclohexanone and n-butanol were added to extract the resin component, which was further dehydrated to give a resol resin solution (d) having a solid content of 35%.

Preparation of resole resin (e): p-cresol 108 parts, formaldehyde 40% n-
56 parts butanol solution, 5% magnesium hydroxide aqueous solution 11
After reacting 7 parts at 110 ° C for 3 hours, 70 parts each of xylene, cyclohexanone and n-butanol were added, and the mixture was stirred and allowed to stand for 5 hours to remove the aqueous layer containing the produced salt, and further azeotropic dehydration. Was performed to obtain a resol resin solution (e) having a solid content of 35%.

Terminal hydroxyl group liquid polybutadiene (h): trade name Poly bd R-45HT (1,4 manufactured by Idemitsu Petrochemical Co., Ltd.
-Butadiene 80%, 1,2-Butadiene 20%, molecular weight 2800)
It was used.

Carboxyl group-containing polybutadiene (i): Product name Poly bd R-45MA (1,4 manufactured by Idemitsu Petrochemical Co., Ltd.
-Butadiene 80%, 1,2-Butadiene 20%, molecular weight 2800)
It was used.

Epoxy group-containing polybutadiene (j) Product name Poly bd R-45EPI (1,4 manufactured by Idemitsu Petrochemical Co., Ltd.
-Butadiene 80%, 1,2-Butadiene 20%, molecular weight 2800)
It was used.

Examples 1 to 11 The above-mentioned thermosetting resin and functional group-containing liquid polybutadiene were blended so as to have the composition shown in Table 1, and diethylene glycol monobutyl ether / diethylene glycol monobutyl ether / was added without adding phosphoric acid and aluminum diisopropylate as a curing catalyst. A mixed solvent of ethylene glycol monoethyl ether acetate / isopropyl alcohol = 40/40/20 was adjusted to a viscosity of 25 ° C. for 50 seconds (# 4 Ford cup) to obtain a metal can base paint of the example.

In addition, the metal can base paints of Comparative Examples 1 to 3 were prepared in the same manner.

A paint test and a paint test were conducted on the paints obtained in Examples and Comparative Examples, and the results are shown in Table 2.

 Each test method is as follows.

Paint stability test: After each paint was stored at room temperature for 2 months, gelation of resin,
The state of separation was observed.

Bending workability test: Electroless tin plate with a plate thickness of 0.23 mm was coated with the metal can base paint by roll coating to a thickness of 5 μ after drying, and baked in a gas oven at an ambient temperature of 190 ° C for 10 minutes. ， Paint panel was created. Painted panels
After cutting it into 3 cm x 5 cm, bending it with a mandrel 1/8 inch diameter, sandwiching a sheet of steel with the same thickness as the painted panel, covering it with a polyethylene film so as not to scratch the coating surface, and then bending Bending was performed with a tester (1 kg, 30 cm height), the processed part was immersed in a copper sulfate solution, and the bending workability was evaluated from the copper deposition state (adhesion).

Punching workability test: Paint panel is 27 mm high and 3 diameter with the coating on the outside.
The 9 mm cap is punched out and the processing state of the coating film is evaluated.

Pencil hardness test: The coating film hardness of the coated panel was evaluated by the pencil hardness test method according to JIS standard.

Content resistance test: Cut the painted panel into 3cm x 7cm and immerse in coffee.
Retort treatment was performed at 25 ° C for 40 minutes and then stored at 37 ° C for 3 months, and the corrosion state and the whitening state of the coating film were evaluated (coffee). Similarly, it was immersed in tomato juice, heated at 97 ° C for 30 minutes, and stored at 37 ° C for 3 months to evaluate the corrosion state and the whitening state of the coating film (tomato juice).

As is clear from Table 2, the coating materials obtained in Examples 1 to 13 have excellent workability, coating hardness, and content resistance, while Comparative Examples 1 to 1 The paint obtained in No. 3 is excellent in coating hardness and content resistance, but is inferior in processability, and the paint obtained by the present invention as a metal can base paint is more processable than the paint of Comparative Example. And has excellent performance in terms of balance of content resistance.

The paints obtained in Examples 1 to 11 were used as a correction paint for the welded part of a welding can, and the paint was baked according to the following method to perform a physical property test.

Apply a 30 μm coating on a tin-plated steel plate with a plate pressure of 0.23 mm after drying with an applicator, and use a gas burner to apply 30
Baking for a second. The baking was set so that the plate temperature reached 230 ° C after 30 seconds.

Next, using the painted panel created in this way,
The bending workability test, the pencil hardness test, the content resistance test, and the punching workability test (cap height 9 mm, diameter 36 mm) similar to those of the metal can base paint were performed. As a content resistance test, in addition to coffee and tomato juice, a tuna test shown in the following method was performed.

Content resistance test (tuna): Cut the coated panel into 3mm x 7mm, immerse in the tuna, 117 ℃
After 90 minutes of retort treatment and storage at 50 ° C for 1.5 months, the state of occurrence of sulfur blackening and the state of whitening of the coating film were evaluated.

Table 3 shows the results of the coating film tests of the coating materials obtained in Examples and Comparative Examples as the welding can compensating coating material.

The paints obtained in the examples have excellent workability, and also have excellent coating film hardness and content resistance, whereas the paints obtained in the comparative examples have excellent workability. Inferior in properties, poor balance with content resistance, and not practical as welding can correction paint.

Examples 12 to 14 Nylon 12 fine powder having an average particle diameter of 14 μ and nylon fine powder having an average particle diameter of 2 μ were added to the coating materials obtained in Example 8.
And fine powder of vinyl chloride paste resin (Sumitomo Chemical Co., Ltd., trade name Summit X13) with an average particle diameter of 5μ is mixed with high-speed stirring so that the solid content ratio is as shown in Table 4, and a welding can correction paint is obtained. It was

The welding can correction paints obtained in Examples 12 to 14 were tested in the same manner as above to examine the coating film performance.

 Table 5 shows the results.

〔The invention's effect〕

The paint for metal cans of the present invention has content resistance and heat resistance comparable to those of paints containing bisphenol type epoxy resin as a main component, which have been conventionally used as an inner paint for metal cans or a base paint for outer paints. In addition, it also has coating processability due to the flexibility of polybutadiene.
In addition, the coating film hardness required as a paint for the inner surface of metal cans for food and drink is excellent.

When used as a correction paint for welding cans, 220 ℃
With the above, it is possible to dry and bake at a high temperature of 60 seconds, and in some cases at a high temperature of 15 seconds.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-53-88038 (JP, A) JP-A-51-16340 (JP, A) JP-A-53-77297 (JP, A) Actual development Sho-51- 84889 (JP, U) Actually open Sho 51-92888 (JP, U) Japanese Patent Sho 39-13643 (JP, B1)

Claims (1)

[Claims] 1. A thermosetting resin comprising a bisphenol type epoxy resin (A) and a resol type phenol resin (B).
It has at least one functional group selected from an epoxy group, a carboxyl group, and a hydroxyl group per 0 parts by weight, contains 50% by weight or more of 1,4-butadiene unit in one molecule, and has a number average molecular weight. An inner coating material for metal cans for food and drink based on an organic solvent, which is characterized by containing 5 to 100 parts by weight of 1000 to 5000 of liquid polybutadiene (C).