JPS5811074A - Painting method for inside surface of food can - Google Patents

Abstract

PURPOSE:To improve adhesive strength, working durability and corrosion resistance by coating an aq. soln. of a resin consisting of a copolymer of ethylene or propylene of specific performance and acrylic acid or methacrylic acid on the inside surfaces of food cans then drying the resin to set. CONSTITUTION:An aq. soln. of the resin consisting of a copolymer of ethylene or propylene of 60-250 acid values and about 32,000-47,000 peak mol.wts. and acrylic acid or methacrylic acid is coated on the inside surfaces of food cans at the amt. of coating of 20-280mg/dm<2> dry film weights, after which it is dried to set. The resin used in this method consists of the copolymer of ethylene or propylene and acrylic acid or methacrylic acid, wherein these monomers are constituted at the ratios of about 70-90wt% the former and about 30-10wt% the latter and are copolymerized by known polymn. methods for these monomers per se, for example, a pressure polymn. method.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of coating the inner surface of food cans, and more particularly to a method of coating the inner surface of food cans using a water-based paint for food cans that has excellent adhesion, process resistance, and corrosion resistance.

Traditionally, the lid and can body of two-piece cans, the lid and can body, and the bottom and can body of three-piece cans are tightly wrapped, which can scratch the already applied inner surface coating and cause rust. Is it the cause of sterilization or sterilization using heated steam? &Due to the rapid cooling treatment using cooling water, defects such as rust and black discoloration on the wound portion were pointed out.

In addition, as paints have recently become increasingly water-based, improvements in adhesion, processing resistance, and corrosion resistance of water-based paints for the inside of cans are urgently desired.

As a result of research into water-based paints for the inner surfaces of food cans in order to solve the rudder problem, the present inventors have completed the present invention, which is capable of forming a coating film with excellent corrosion resistance, adhesion, and processing resistance. .

That is, the present invention has an acid value of 60 to 250 and a peak molecular weight of about 52,000 to about 47. n [Relating to a food can inner surface coating method characterized by applying an aqueous solution of a resin made of a copolymer of ethylene or propylene and acrylic acid or methacrylic acid to the inner surface of the food can, and then drying and curing it. be.

The resin used in the present invention is composed of a copolymer of ethylene or propylene and acrylic acid or methacrylic acid, and the ratio of these single stitches is usually about 7 to 90 weight for the former and about 30 to 10 weight for the latter. It is composed of stitches and is copolymerized by polymerization methods known per se, such as pressure polymerization. The molecular weight and weight of the copolymer are approximately 32.5% at peak molecular weight determined by Körpermuesch chromatography (GPO).
El 11 [1 to about 47. The range of n n n is preferable, and the resin acid value range of 60 to 250 is suitable.

If the acid value is less than 60, the resin will not be easily soluble in water unless a large amount of hydrophilic organic solvent is added, and the frozen acid value will be 250.
? If it exceeds the limit, the processing resistance of the resin coating will drop sharply, so neither is suitable.

The resin having the above-mentioned properties is made water-soluble by adding ammonia water, an amine (for example, dimethylethanolamine), etc., and then used.

In addition, when a small amount (for example, 5 to 20 parts of the amount of water) of a hydrophilic solvent such as isobrobyl alcohol is used for water solubilization, the dissolution of the resin is promoted.

In the present invention, it is possible to obtain excellent coating film performance by using an aqueous solution of the above resin alone, but in some cases other aqueous resins such as aqueous amine resin, aqueous polyester resin, water-solubilized modified epoxy One or more selected from resins, water-based phenolic resins, water-based acrylic resins, etc. can be used in combination with the above resins. Also-
If desired, the aqueous solution of the resin may be subjected to the method of the present invention by adding known paint compounding agents such as pigments, dispersants, coating surface conditioners, hardeners, and curing accelerators.

In the present invention, an aqueous solution of the above-mentioned resin can be applied to the inner surface of a food can in an arbitrary amount as a paint for the inner surface of a food can, but it is preferable to apply an amount in the range of 20 to 180 μ/a in terms of dry coating weight. It is applied by a known method such as spray coating, roll coating, or flow coating, and then dried and cured. In this case, it may be applied once (single coat) within the above application amount range, or it may be applied in two coats (for example, base coat and top coat, in which case the top coat is the base coat). There is no problem even if the paint is of a different type. Furthermore, it is also possible to apply an aqueous solution of the above resin as a base coat and another type of food can paint as a top coat.

- Dry material 'II as above: 20 η/dt at 4 weight
r? Below, some areas may not be painted,
Alternatively, an extremely thin coating may occur, resulting in a decrease in corrosion resistance (1). Also, 1
80■/dn-? For J″J and -F, forced drying or baking of the coating film sometimes causes visual appearance of bubbling, creating craters and pinholes, and reducing adhesion and process resistance.

The present invention can be applied to all can-making materials such as aluminum, tinplate, and chin-free steel. The coating is applied to various parts of the inner surface of the can, such as the can body, can lid, can bottom, and cap. Furthermore, it can also be applied to the outer surface of the can if desired.

Embodiments of the present invention will be explained in detail with reference to Examples and Comparative Examples under nitrogen. In this work, ``part'' and ``kita'' mean weight part and weight section, respectively.

A. Production of copolymer resin liquid Production example 1 A monomer composition of 87.1 parts of ethylene and 12.9 parts of acrylic acid was copolymerized by a low-pressure polymerization method, and GPCIC
, l Nirbeek molecular sound approx. 4 n, n n n, acid value 10
0 copolymer resin? -I got it. 1 nO part of this resin, 29 parts of ammonia water, 6 parts of dimeric ethanolamine, 16 parts of deionized water, 550 parts of deionized water, 1 part of deionized water. and isopropyl alcohol 50
A small amount of the mixture was added to the mixed solution while stirring well to make it soluble in water, yielding a pale yellow translucent liquid.

Production Example 2 Powder 100 of a copolymer resin (peak molecular weight approximately 43.n O% acid value 155) obtained in the same manner as Production Example 1 and consisting of a monomer composition of 80 parts of ethylene and 20 parts of acrylic acid.
29qb was added to a mixture of 7.5 parts of aqueous ammonia, 25 parts of dimethylethanolamine, 350 parts of deionized water, and 50 parts of isopropyl alcohol while stirring well to dissolve it in water, resulting in a slightly yellow, translucent color. A liquid was obtained.

Production Example 3 89.2 parts of ethylene obtained in the same manner as Production Example 1,
A 6-copolymer resin consisting of a monomer composition of 10.8 parts of methacrylic acid (P), molecular weight approximately 36.n, 11 pieces of O, 7
A small amount of powdered ino part of No. 29 was added to a mixture of 4 parts of aqueous ammonia, 11 parts of dimethylethanolamine, 350 parts of deionized water, and 50 parts of isopropyl alcohol while stirring well to make it water-soluble and give a slightly yellow color. A translucent liquid was obtained.

Add 20 parts of this solution to a modified epoxy resin water-based paint, manufactured by Mobil Chemical Co., trade name 7Bw1oO, solid content 21%)
8n parts were mixed to prepare a resin liquid.

B. Preparation of Paint Paint 1 25F of deionized water was added to 100 volts of the resin liquid prepared in Production Example 1 to make a paint with a solid content of 20 cm.

The viscosity was 53 seconds at Ford Cup A4 (20° C., hereinafter the same). This is called paint 1.

Coating 2 A coating 1 with a solid content of 20% was prepared in the same manner as the Fi% coating 1 except that the resin liquid prepared in Production Example 2 was used. The viscosity was 54 seconds. This is called paint 2.

For the resins other than J21 using the resin liquid of Production Example 3, the formulation was the same as that of Paint 1 to produce a paint with a solid content of 20%. The viscosity was 52 seconds. This is referred to as paint 30 Paint 1a Water-soluble epoxy resin (
Manufactured by Ciba Geigy, trade name: Araldite XD823) 3
Mix 0 parts and 1.7? ,. Let this 'n be painted j% i a.

Paint 4 For comparison, a modified epoxy resin shield-based water-based paint (manufactured by Mobil Chemical Co., Ltd., 7Bw1no)'ff was used, and this was designated as paint 4.

C9 Test (1) Method ■ Painting Using a Nordson airless sprayer, tinplate method squeeze ironing can total rotation speed 2,300 r, p.

Each paint was applied to the inner surface under the coating conditions shown in Table 1 while rotating at m.m. The coating weight (ie, converted to dry coating weight) was measured at any time using a strand gauge manufactured by Strand Electronics, and the amount of spray discharged was adjusted to maintain a predetermined coating amount.

After painting, place it upright and set it at room temperature for 5 seconds,
Then, baking was performed for 4 minutes in a baking oven at 205° C. to obtain a test specimen.

Regarding Paint 1, in addition to a single coat (Example 1), a 2-coat/2-bake method was adopted, and Paint 1 was used as an undercoat with a dry film weight of 5011v/(
After coating to a thickness of 1 m' and baking at 205° C. for 4 minutes, a modified epoxy resin water-based 9-paint (78W100) that was baked under the same conditions as the undercoat was added (Example 2).

■ Adhesion test The specimen was immersed in boiling deionized water for 30 minutes, then taken out and immediately cooled in water to reach a substrate pressure on the coating surface5.
Use a knife to cut 4 holes in the grooves of the listener's corner, and press adhesive tape onto the holes. The tape is then quickly scratched off. At this time, the peeling of the paint film on the goblin area was investigated, and a score of 10 (full score) was given for no peeling, and a score of 0 was given for all of the paint film to be peeled off. Scored accordingly.

This test was conducted separately for six test specimens, and the scores were arithmetic averaged to express the results. The results are shown in Table-2.

■ Fabrication resistance test pieces were made. The coated surface is the front side, and the back side of the specimen is KO, 5.
A 4 m thick aluminum plate was inserted and bent 10-180 degrees, and a 3 kg weight was dropped vertically from a height of 5 ncnT onto the bent part to complete the bend. The sample was then immersed in boiling deionized water for 3 minutes, taken out, and immediately cooled with pressure water. The sample was examined for peeling of the coating film at the bent portion and scored according to the scoring method (2).

This test was conducted separately on six painted specimens, and the scores were arithmetic averaged to express the results. The results are shown in Table-2.

■ Corrosion resistance test Tin plate manufacturing method Paint was applied to the inner surface of a squeezed can using the coating method (■) and baked to prepare a test specimen.

550 with a 90° angle on the outer surface of the center part of the can body of the test specimen
Drop the weight from step 2 and make a dent! This was mixed with a salt/citric acid aqueous solution (Nac 0.1
%, citric acid 0.6%) for 1 hour.

Subsequently, the sample was immersed in the same aqueous solution and left at 50° C. for 24 hours. Thereafter, the above-mentioned common salt/citric acid aqueous solution is newly prepared, and the test specimen is immersed in it at 20° C. for 72 hours. Next, check the copper sulfate/hydrochloric acid aqueous solution (after sulfurization, peeling and blackening of the paint film).

A score of 1n (full score) was given for no blackening, and a score of 0 was given for a blackening of about 5 widths in the dented area, and scores were given according to the degree of blackening.

This test was conducted separately on four test specimens, and the scores were arithmetic averaged to represent the success M. The results are shown in Table 2.

Claims (1)

[Claims] 1. An acid value of 6n to 250 and a peak molecular weight of about 32.n
n O ~ about 47. [1] A method for coating the inner surface of a food can, which comprises applying an aqueous solution of a resin made of a copolymer of ethylene or propylene and acrylic acid or methacrylic acid to the inner surface of the whole food can, followed by drying and curing. 2. Dry the aqueous solution of the resin in a film type J120-180W
/ dW? A method for coating the inner surface of a food can according to claim 1, wherein the coating amount is as follows.