JPS61268768A - Coating for application to metallic can - Google Patents

Abstract

PURPOSE:To obtain a coating suitable for correcting the side seam section of welded can or for application to inner surface of metallic can, by blending a thermosetting resin and specific liquid polybutadiene. CONSTITUTION:The objective coating of organic solvent base can be obtained by blending (A) 100pts.wt. of a thermosetting resin made up of, pref. either (i) bisphenol type and resol resins or (ii) bisphenol type epoxy and amino resins and (B) 5-100pts.wt. of a liquid polybutadiene containing >=50wt% of 1,4-butadiene unit and having functional groups(s) consisting of epoxy, carboxyl and/or hydroxyl group(s). This coating is especially preferable for application to the inner surface of metallic can.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Field of Application) The present invention is useful as a paint for metal cans, particularly as a correction paint for painting the side seam of welded cans, and as a paint for the inner surface of metal cans. Regarding paints for metal cans.

(Prior Art) Metal cans are stronger than other containers and have the characteristics of being able to preserve the food they contain for a long period of time, and are used in a wide range of applications. In recent years, metal cans have been replaced by paper.

As with other containers such as plastic, can shapes are beginning to be produced in a wide variety of formats to strongly appeal to consumers from an aesthetic point of view. In particular, processes such as bead processing and multi-neck-in processing are being added.

In order to be able to respond to these movements, can manufacturing methods have changed from conventional adhesive cans and solder cans to extremely strong cans (and have the cost advantage of requiring less equipment space. Welded cans are widely used. On the other hand, in order to prevent corrosion and improve processability of can materials, various metal materials such as electroplated steel sheets and tin-free steel are coated with coatings, which can withstand the above processing and further improve the processability of can materials. It is generally difficult to form a coating film with anticorrosion properties that can preserve the contents for a long period of time, and there are many practical problems.

In particular, in the case of welded cans, the end surfaces of both cut surfaces of the two can body materials are overlapped (lap seam) and welded, so the cut surfaces are exposed to the inside of the can without being painted, and the materials are exposed to electroplated tin. If so, the tin will reflow due to the heat during welding, and if it is tin-free steel, corrosion will easily occur from the metal surface that has been shaved to make it easier to weld. To prevent this, it is necessary to apply correction paint to the inner surface of the can, and in some cases to the outer surface of the weld, to form a protective film, but the welding step in such welds is relatively large, and this part is especially thick. It is necessary to form a paint film, and if a paint film has good corrosion resistance, cracks are likely to occur when processed, and it is generally difficult to form a paint film that has both good corrosion resistance and workability. Therefore, the performance of the correction paint is an important factor that affects the performance of welded cans.

In this way, paints for metal cans have recently been developed to withstand severe processing such as beading and multi-neck-in, and to form coatings that can preserve the contents of food products and other items for long periods of time.

In particular, weld can correction paints are required to form a thick coating under the condition of short-term baking.

Several proposals have been made regarding paints to satisfy these various demands. One is one whose main component is a vinyl chloride resin-based organosol composition (Japanese Unexamined Patent Publication No. 55-49174).

Alternatively, metal can paints are known in which a polyester resin is added to various types of epoxy-acrylic, epoxy-amino, or epoxy-phenol thermosetting paints (Japanese Patent Laid-Open Publication No. 32230/1983).

JP-A No. 55-5936).

However, although paints containing thermoplastic resins can form a film in a short time, when the content is beverages or food, they require sufficient acid resistance and sterilization to withstand high-temperature retort processing. It has drawbacks in terms of corrosion resistance and content resistance. In addition, the above-mentioned epoxy resin-based thermosetting paints and polyester resin-containing thermosetting paints generally have a 220 to 260 It does not cure sufficiently even at temperatures as high as ℃, making it difficult to form a coating film with excellent corrosion resistance. Moreover, the processability of thick films is poor, and even thermosetting paints containing polyester resin, which are characterized by relatively excellent processability, have not yet achieved sufficient performance.

(Problem to be solved by the invention) The present invention has been made in view of the above-mentioned current situation.

The purpose is to form a coating film that can withstand severe processing such as beading and multi-neck-in, and can preserve the contents of food products for a long period of time. The purpose of the present invention is to provide a paint for metal cans that can form a thick coating film under the following baking conditions and is capable of forming a coating film with excellent workability and resistance to contents.

[Structure of the invention]

(Means for Solving the Problems) Namely, 2. The present invention has at least one functional group selected from an epoxy group, a carboxyl group, and a hydroxyl group based on 100 parts of a thermosetting resin; 1. Liquid polybutadiene 5 to 100 containing 50% by weight or more of 4-butadiene units
This is an organic solvent-based paint for metal cans containing parts by weight.

As the thermosetting resin in the present invention, epoxy resin,
Phenolic resin, amino resin, alkyd resin.

There are acrylic resins, etc. Preferably, it is a combination of a bisphenol type epoxy resin and a resol resin or an amino resin.

Bisphenol type epoxy resin includes bisphenol A type epoxy resin, hydrogenated bisphenol A type epoxy resin,
This is an epoxy resin typified by bisphenol F type epoxy resin. In particular, epoxy resins obtained by the reaction of bisphenol A and epichlorohydrin and having an average epoxy equivalent of 1,500 to 4,000 can be preferably used. In addition, bisphenol-type epoxy resins such as linoleic acid, linuric acid, l! Those esterified with higher unsaturated fatty acids such as castor oil fatty acids, soybean oil fatty acids, and coconut oil fatty acids can also be used.

Resole resins are those obtained by reacting phenols such as 9-carbolic acid, 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.

Amino resin is a product obtained by reacting urea, melamine, a triazine compound with formaldehyde, or.

This may be etherified using a monohydric alcohol having 1 to 4 carbon atoms.

Alkyd resins are linseed oil, tung oil, and dehydrated castor oil.

It is obtained from fatty acids such as soybean oil, polybasic acids such as phthalic acid, isophthalic acid, maleic acid, and trimellitic acid, and polyhydric alcohols such as glycols.

Examples of acrylic resins include carboxylic acid-containing monomers such as acrylic acid, methacrylic acid, itaconic acid, and (meth)
There are resins obtained from alkyl esters of acrylic acid or styrene monomers, and self-crosslinking acrylic resins containing N-methylol (meth)acrylamide and the like.

The liquid polybutadiene in the present invention has at least one functional group selected from an epoxy group, a carboxyl group, and a hydroxyl group, contains 50% by weight, preferably 70% by weight or more of 1,4-butadiene units, and contains other constituents. is 1.2
-Butadiene units are preferred, but they may also contain monomers other than butadiene, such as α-methylstyrene and styrene. The number average molecular weight is 5
oo-toooo.

Preferably, 1000 to 5000 is used.

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

The epoxy group of liquid polybutadiene can be obtained by modifying the raw material polybutadiene with a peracid such as peracetic acid or performic acid. It can be obtained by reacting acids or their acid anhydrides.

The paint for metal cans of the present invention contains liquid polybutadiene in an amount of 5 to 100 parts by weight, preferably 20 parts by weight or more, per 100 parts of the thermosetting resin. As the proportion of liquid polybutadiene in the coating decreases, there is a tendency for the rapid curing and processability of the coating to deteriorate.

The paint for metal cans 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 solvents include acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, xylene, aromatic compounds such as alkylbenzenes, cellosolves such as methyl cellosolve, ethyl cellosolve, and butyl cellosolve, methyl cellosolve acetate, butyl cellosolve acetate, ethyl acetate, and acetic acid. Esters such as butyl,
Alcohols such as isopropyl alcohol, butyl alcohol, diacetone alcohol, etc., or a mixed solvent thereof can be used.

The paint for metal cans of the present invention has a thermosetting resin and a functional group-containing liquid polybutadiene as main components, but in addition to these solvent-soluble components, a thermoplastic resin is contained within 30% by weight of the total resin components. It can be blended with. Particularly when used as a correction paint, to improve coverage against welded steps and cuts.

Polyamide resin, carboxyl group-modified polyolefin resin, polyester resin, polyvinyl chloride resin.

Fine particles of thermoplastic resin such as polyacetal resin can be used by being dispersed in the paint.

The paint for metal cans of the present invention contains phosphoric acid, phosphoric acid esters, and p-)luenesulfonic acid to accelerate curing.

Acidic substances such as trimellitic acid, salts such as zinc octylate and zinc naphthenate, or aluminum alcoholade,
Organometallic compound-based curing aids such as alkyl titanates, amine catalysts such as trimethylamine, triethylamine, dimethylaminoethanol, etc., or organic peroxides such as benzoyl peroxide as reagents for carbon-carbon double bonds contained as side chains in liquid polybutadiene. A radical generating agent such as a compound or the like can be added.

Other conventional additives such as coloring dyes and pigments, antirust pigments, fillers, surfactants, lubricants, etc. can be added to the paint for metal cans according to the present invention.

A method for applying the paint for metal cans of the present invention is as follows.

Known means such as spraying, roll coating, brush coating, flow coating, etc. can be used.

The present invention will be specifically explained below with reference to nine examples. In the examples, "parts" and "%" indicate "parts by weight" and "% by weight."

(Example) Preparation of epoxy resin solution (a): Epicor) 1009 (Bisphenol A type epoxy resin manufactured by Yuka Shell Epoxy G@, epoxy equivalent: 2650)
100 parts were dissolved in 100 parts of diethylene glycol monoethyl ether acetate at 90°C.

This was referred to as epoxy resin solution (a).

Preparation of epoxy resin solution (b): Epicoat 1007 (bisphenol A type epoxy resin manufactured by Yuka Shell Epoxy ■, epoxy equivalent: 1950)
It was prepared in the same manner as epoxy resin solution (a) except that epoxy resin solution (a) was used instead of Epikote 1009.

Preparation of epoxy ester resin solution (C): AER667
(Bisphenol A type epoxy resin manufactured by Asahi Kasei Industries) 1
00 parts, soybean oil fatty acid 40 parts.

10 parts of xylene was reacted at 220°C for 3 hours, and the acid value was 1.
The reaction is terminated when it becomes 0 or less, and Tsurpets 10
0. Tsurpets 150. 65 parts of diethylene glycol monoethyl ether acetate were added to each and cooled to obtain an epoxy ester resin solution (C).

Preparation of resol resin (d): 108 parts of p-cresol, 40% n of formaldehyde
- 56 parts of butanol solution, 14 parts of 25% ammonia in 1 part
After reacting at 00° C. for 3 hours, 110 parts each of xylene, cyclohexanone and n-butanol were added to extract the resin component, and further dehydrated to obtain a resol resin solution (d) with a solid content of 35%.

Preparation of resol resin (e): 108 parts of p-cresol, 40% n of formaldehyde
- After reacting 56 parts of a butanol solution and 117 parts of a 5% magnesium hydroxide aqueous solution at 100°C for 3 hours, 70 parts each of xylene, cyclohexanone and n-butanol were added, stirred and allowed to stand for 50 hours to form a salt. The aqueous layer containing the water was removed and further azeotropic dehydration was performed.

A resol resin solution (e) with a solid content of 35% was prepared.

Amino resin (f); trade name Beckamine L-105 manufactured by Nippon Reichhold Co., Ltd.
-60 was used.

Preparation of acrylic resin (g) 25 parts of Nibutyro Cellosolve and 25 parts of Swasol 1000° were placed in a flask and heated to 110°C.

20 parts of methyl methacrylate, 20 parts of 2-ethylhexyl acrylate, 10 parts of acrylic acid, and 0.5 part of benzoyl peroxide were placed in a dropping flask, and added dropwise while stirring. When dropping, the temperature inside the flask is 110℃.
Add 2 drops for about 90 minutes, adjusting the amount so that
After 0 minutes, 0.05 part of benzoyl peroxide was further added, heated at 110°C for 90 minutes, and then cooled to obtain an acrylic resin solution with a solid content of 50%.

Terminal hydroxyl group liquid polybutadiene (h): Product name PolybdR-45HT manufactured by Idemitsu Petrochemical Co., Ltd. (1,4-butadiene 80%, 1,2-butashev 20% 1 molecular weight 28
00) was used.

Carboxyl group-containing polybutadiene (i): trade name Po'ly bd R-45MA manufactured by Idemitsu Petrochemical Co., Ltd.
(1,4-butadiene 80%, 1,2-butashev 20%
%3 molecular weight 2800) was used.

Epoxy group-containing polybutadiene (j) Product name PolybdR-45EPI manufactured by Idemitsu Petrochemical Co., Ltd.
(1,4-butadiene 80%, 1,2-butashev 20% 1 molecular weight 2800) was used.

Examples 1 to 13 The above thermosetting resin and functional group-containing liquid polybutadiene were blended to have the composition shown in Table 1, and diethylene glycol monobutyl ether/diethylene glycol monobutyl ether/ Ethylene glycol monoethyl ether acetate/isopropyl alcohol = 40/40/2Q mixed solvent with a viscosity of 25°C for 50 seconds (#4 Ford cup)
This was adjusted to give the metal can base paint of the example.

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

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

Each test method is as follows.

Paint stability test: After storing each paint at room temperature for two months, the state of gelation and separation of the resin was observed.

Bending workability test: The above-mentioned metal can base paint was applied by roll coating to an electroplated tin plate with a thickness of 0.230 so that the film thickness after drying was 5μ, and baked in a gas oven at an ambient temperature of 190°C for 10 minutes. , created painted panels. Cut the painted panel into 3 an x 5 cm pieces and use the mandrel 1
After bending it to a diameter of 78 inches, we sandwiched a steel plate with the same thickness as the painted panel and covered it with polyethylene film to avoid damaging the painted surface.

It was bent with a bending tester (IKg, 30cm height), and the processed part was immersed in a copper sulfate solution to determine the precipitation state (adhesion) of 1jJ.
The bending workability was evaluated.

Punching workability test: The height of the painted panel is 27mm so that the paint film is on the outside.

Punch out a cap with a diameter of 39 dragons and evaluate the processing condition of the coating film.

Pencil hardness test: The coating hardness of the painted panel was evaluated using a pencil hardness test method in accordance with JIS standards.

Contents resistance test: The painted panel was cut into 3cm x 7CI11 pieces, immersed in coffee, retorted at 125°C for 40 minutes, and further heated for 3
It was stored at 7° C. for 3 months, and the corrosion state and whitening state of the coating film were evaluated at 1 gi (coffee). Similarly, it was immersed in tomato juice, heated at 97°C for 30 minutes, and further stored at 37°C for 3 months to evaluate the state of corrosion and the state of whitening of the paint film (tomato juice).

As is clear from Table 2, the paints obtained in Examples 1 to 13 have excellent processability, film hardness, and resistance to contents, whereas Comparative Examples 1 to Although the paint obtained in step 3 has excellent coating hardness and content resistance, it has poor processability, and the paint obtained by the present invention as a metal can base paint has better processability than the comparative paint. It has excellent performance in terms of balance between content resistance and content resistance.

The paints obtained in Examples 1 to 13 were used as correction paints for the welded parts of welded cans, and the paints were baked according to the following method, and physical property tests were conducted.

A tin-plated steel plate with a plate thickness of 0.231 m was coated with an applicator so that the film thickness after drying was 30 μm, and baked for 30 seconds with a gas burner. The board temperature reaches 230℃ after 30 seconds of baking.
It was set to reach .

Next, using the painted panel prepared in this way, a bending workability test similar to the metal can base paint, a pencil hardness test, a content resistance test, and a punching workability test (cap height 9IIm, diameter 36 dragons). In addition to coffee and tomato juice, the contents resistance test was conducted using tuna according to the following method.

Contents resistance test (tuna): A painted panel was cut into 3 mm x 7 mm, immersed in tuna, retorted at 117'C for 90 minutes, and then heated at 50°C.
The specimens were stored for 1.5 months at a storage room, and the state of occurrence of black sulfide discoloration and the state of whitening of the coating film were evaluated.

Table 3 shows the results of a coating film test of the coatings obtained in Examples and Comparative Examples as welded can correction coatings.

The paint obtained in the example has excellent processability,
Although it has excellent coating hardness and resistance to contents, the paint obtained in the comparative example has poor processability and poor balance with resistance to contents, so it cannot be used as a correction paint for welding cans. Not the point.

Examples 14 to 16 To the paint obtained in Example 8, fine nylon 12 powder with an average particle size of 14 μ, fine nylon powder with an average particle size of 2 μ, and PVC base resin (Sumitomo Chemical Co., Ltd.) with an average particle size of 5 μ were added. Fine powder of Sumilift

The welded can correction paints obtained in Examples 14 to 16 were tested in the same manner as above to examine coating film performance.

The results are shown in Table 5.

〔Effect of the invention〕

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

Also, when used as a correction paint for welding cans.

It is possible to dry and bake at a high temperature of 220° C. or higher for 60 seconds, or in some cases for 15 seconds in a short time.

Claims (1)

[Claims] 1. With respect to 100 parts by weight of thermosetting resin, epoxy group,
An organic solvent-based paint for metal cans containing 5 to 100 parts by weight of liquid polybutadiene having at least one functional group selected from carboxyl groups and hydroxyl groups and containing 50% by weight or more of 1,4-butadiene units. 2. The paint for metal cans according to claim 1, wherein the thermosetting resin is selected from a combination of a bisphenol-type epoxy resin and a resol resin, a bisphenol-type epoxy resin and an amino resin. 3. The paint for metal cans according to claim 1, which is a paint for the inner surface of metal cans.