JPS5855832B2 - How to cover the side seams of welded cans - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of coating iron parts for correcting defects on the side edges of a welded can.

The can body of a welded can is usually made by bending a steel plate cut into a rectangle into a cylindrical shape, overlapping the opposite sides of the rectangle to form four parts, and
It is made by welding the next four parts.

Therefore, even if anti-corrosion treated steel such as tin-free steel is used as the material for the can, corrosion may occur from the cut edges of the material or the welded metal. It is necessary to prevent this by some means.

As a means for preventing the above-mentioned corrosion, it is conventionally known to coat these four parts with a solution-type paint or a powder paint in which a film-forming substance is dissolved or dispersed in an organic solvent.

However, there is a level difference in the next four parts of the welded can due to the overlapping of the cut edges of the can material, and if you use solution-based paint or powder paint to coat this level difference completely, the coating will not work. This causes various defects in the film.

In other words, when solution-based paints are applied thickly, even with a film thickness of about 10 to 20 microns, bubbles are generated during heating during coating baking.
Further, the cut edge cannot be sufficiently covered due to the occurrence of deflection or flow.

Powder coatings also do not have sufficient film-forming properties for thick coatings of about 30 to 70 μm, and pinholes are likely to occur.

In addition, solution-based paints pose a risk of fire and environmental pollution due to the solvent, and special equipment is required to prevent them.

Powder coatings also require equipment to avoid the problem of environmental pollution due to dust, and also have the disadvantage that it is difficult to transport the powder at high speed and stably.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a method for completely covering the four steps of a welded can with a coating free of defects such as pinholes.

A further object of the present invention is to provide a method for simply and easily coating the four parts of a welded can without the risk of fire or environmental pollution.

In order to achieve the above purpose, the present inventors, as a result of research,
If the white part of the side of the welded can is coated with a coating film of slurry paint, the next part of the side of the welded can can be coated without sagging or defects such as bubbles, cissing, and cracks in the coating. It has been found that the film can be coated with a film thickness sufficient to completely cover the steps in the white area, and that the cut edge can also be completely corrected.

That is, the present invention provides a method for coating a white part of a welded can by drying and/or setting a slurry paint applied to the white part, and then applying a coating film of the dried and/or set slurry paint to the white part. This method is characterized by forming a coating film with a thickness of 10 to 100 μm by heating the material to a temperature higher than its melting point or softening point.

In this specification, slurry paint refers to 0.1 to 5.0
It means a paint in which a film-forming substance powdered to a particle size of μ is dispersed in a liquid medium in a suspension state.

In the present invention, any known slurry paint can be used.

Preferred examples of slurry coatings that can be used in the present invention include thermoplastic polyester resins, acrylic resins, polyolefin resins, polyvinyl chloride resins, polyamide resins, vinyl acetate resins, polyvinyl acecool resins, polyether resins, polycarbonate resins, and epoxy resins. resin,
0.1-50μ, preferably 0.2-20μ, more preferably 0.1-50μ, more preferably 0.1-50μ, more preferably 0.1-50μ, preferably 0.2-20μ, more preferably 0.1-50μ, more preferably 0.1-50μ, preferably 0.2-20μ, more preferably 0.1-50μ, more preferably 0.1-50μ, more preferably 0.1-50μ, more preferably 0.2-20μ, more preferably 0.1-50μ, more preferably 0.2-20μ, more preferably 0.1-50μ, more preferably 0.1-50μ, more preferably 0.1-50μ, more preferably 0.1-50μ, more preferably 0.2-20μ, more thermoplastic or thermosetting resins such as alkyd resins, polyurethane resins, epoxy ester resins, phenolic resins, amino resins, and silicone resins. 5~10μ
This is an aqueous slurry paint made by dispersing particles with a particle size of .

The water-based slurry paint contains a small amount of surfactant and.

Alternatively, it may contain a small amount of a water-soluble organic solvent.

The surfactant helps disperse the film-forming substance particles and improves the stability of the paint, and the organic solvent improves the wetting and film-forming properties of the paint.

However, in the present invention, organic liquids that do not dissolve the resin particles, such as aliphatic alcohols having 1 to 5 carbon atoms such as butanol and propatool, and 6 to 8 carbon atoms such as hexane, are used. Slurry coatings based on aliphatic hydrocarbons or ketones such as acetone can also be used.

The solid content concentration of the slurry paint used in the present invention is usually 5 to 70% by weight, preferably 10 to 50% by weight, and more preferably 20 to 40% by weight.

In the present invention, the above-mentioned slurry paint is applied to the white part of the welded can side surface to a thickness such that the final coating film has a thickness of 10 to 100μ, preferably 20 to 80μ, more preferably 30 to 70μ. , is set.

If the thickness of the coating film is 10 μm or less, there is a risk that the cut edge of the step will not be corrected and an exposed portion will be formed.

If the film thickness is 100 μm or more, bubbles are likely to occur and sagging is also likely to occur.

There are no particular restrictions on the method of applying the slurry paint to the white area on the side surface of the welded can, and any known method such as air spraying, airless spray roll coating, or the like can be used at any time.

The paint that has been applied and set on the surface of the object to be coated as described above is then dried if necessary, and then subjected to a film forming step.

When the coating film forming substance of the slurry paint used is a thermoplastic resin, the coating film forming process is carried out at a temperature higher than the melting point of the thermoplastic resin,
When the coating film-forming substance is a thermosetting resin, the coating is heated to a temperature equal to or higher than its softening point.

This heating temperature varies depending on the type of film-forming substance resin in the paint used; for example, in the case of a slurry paint whose film-forming substance is thermoplastic polyester resin, it is 100° to 5°C.
00°C, preferably 1200° to 350°C, more preferably 150° to 300°C.

As for the heating means for forming the coating film, any known heating means such as hot air oven heating, gas burner heating, infrared heating, or high frequency heating can be used as needed, and there are no particular limitations.

However, direct local heating with gas burners is advantageous.

The coating method of the present invention using a slurry coating for the white area on the side surface of a welded can is more effective than the coating method using a conventional solution-type coating or powder coating, since it does not cause problems such as bubbles, chips, pinholes, or cracks. In addition to being able to obtain a thick, defect-free and excellent coating film, which ensures that the next white area is completely covered with a defect-free coating film, it is also possible to apply the coating at high speed to the object being coated, and to prevent fires. There is no risk of danger or environmental pollution, therefore, there is no need for special exhaust combustion equipment, and it is possible to collect unused paint,
It has advantages such as easy wastewater treatment and the ability to obtain a thick coating film in one coat using solvent-based coating equipment.

The method of covering the sides and four parts of a welded can according to the present invention can be applied to any metal can, such as tinplate, tin-free steel (chrome-plated steel), black plate (untreated steel).
It can be applied to welded cans made of materials such as aluminum, steel sheets chemically treated with chromic acid or phosphoric acid, and galvanized steel sheets.

The present invention will be further explained below with reference to Examples.

Reference Example 1 (Manufacture of water slurry paint A) Maleic anhydride kraft polyethylene with a number average molecular weight of 55,000 and a melting point of 130°C is ground into a powder with an average particle size of 3 μm (maximum particle size of 10 μm), and this is poured into deionized water. A water slurry paint A was obtained by adding 0.1 part of a surfactant (sodium oleate) and forcibly dispersing the mixture.

The solids content was 48% and the particle size was 33 cps (25°C).

Reference Example 2 (Manufacture of water slurry paint B) A condensate of isophthalic acid and propylene glycol,
Polyester with a number average molecular weight of 62,000 and a melting point of 132°C is ground into a powder with an average particle size of 2μ (maximum particle size of 16μ), which is deionized together with 0°2 parts of a surfactant (Modern Law Monsanto Chemical Co., Ltd.). It was added to water and forcedly dispersed to obtain water slurry paint B.

The solids content was 40% and the particle size was 29 cps (25°C).

Reference Example 3 (Manufacture of solvent slurry paint C) Average molecular weight 53000. Nylon 12 resin with a melting point of 172°C was crushed to obtain a powder with an average particle size of 4 μm (maximum particle size of 18 μm), and dispersed in n-butyl alcohol to reduce the solid content to 35 μm.
% solvent slurry paint C was obtained.

Reference Example 4 (Production of solution-type paint) Epoxy resin (Epicor) which is a condensation product of bisphenol A and epichlorohydrin and has a number average molecular weight of 2900.
1007 manufactured by Shell Chemical Co., Ltd.) and 75 parts of butyl ether urea formaldehyde resin (Super Beckamine P-1
38 (manufactured by Inu Nippon Ink) was dissolved in a mixed solvent of 50 parts of methyl ethyl ketone and 50 parts of toluene to obtain a solution-type paint with a solid content of 25%.

Reference Example 5 (Manufacture of powder coating E) A condensate of isophthalic acid and propylene glycol,
Number average molecular weight 62000. A polyester having a melting point of 132° C. was ground to obtain a powder coating E having an average particle size of 15 μm (maximum particle size of 80 μm).

Example 1 A tin plate with a thickness of 0.26 mm was coated with epoxyphenol paint (the ratio of epoxy resin to phenol resin was 1:
1 mixture) was coated on the margins of the can body, except for the seam area, so that the film thickness after baking was 5 microns on the inner surface and 3 microns on the outer surface, and then dried in a hot air drying oven at 200°C for 10 minutes. The painted tin plate obtained by baking and hardening for a minute was used to make a body blank for a No. 4 can (blank length 238.33 mm, blank bite 122.22 m).
m) was cut into a cylindrical shape using a roll former, and the side ends were overlapped by 0.4 mm and welded to create a can body.

The seam portions of the inner and outer surfaces of the can body obtained by the above method were coated with an airless gun to a width of 10 mm and a dry coating thickness of 4 mm.
After spray painting the water slurry paint A of Reference Example 1 to a thickness of 0 to 60 microns, it was baked in a hot air drying oven at 180°C for 3 minutes to create an adhesive striped coating on the area adjacent to the seam. .

Then, the coating state of the above coating was observed, and the cut edge coverage was examined using a sulfuric acid steel solution.

Furthermore, the can body obtained by the above method was flanged by a conventional method, and then a 301 diameter tin lid, which was also obtained by a conventional method and had an epoxyphenol coating on the inner and outer surfaces, was double-sealed. Pack the samurai in empty cans.
A tin lid similar to the above 301 diameter was double-sealed, and retort treatment was performed at 121° C. for 90 minutes.

Packed cans (200 cans each) that have undergone the above retort treatment,
Open the can immediately after retorting and after storing it at 50℃ for 1 year.
The condition of the coating film on the joint part of the can body was observed.

The respective results are shown in Table 1 below.

Example 2 Water slurry paint B of Reference Example 2 was applied to the seam parts of the inner and outer surfaces of a tin can body obtained in the same manner as in Example 1 using an airless gun under the same conditions as in the Example. An adhesive striped coating was created on the can body adjacent to the seam.

In the same manner as in Example 1, the state of the coating film at the seam of the can body and the cut edge coverage were examined, and the state of the coating film was also observed immediately after retorting and after storing at 50° C. for 11 years after packing the samurai in water.

The respective results are shown in Table 1 below. Example 3 Solvent slurry paint C of Reference Example 3 was applied to the seam parts of the inner and outer surfaces of a tin can body obtained in the same manner as in Example 1 using an airless gun under the same conditions as in Example 1. , an adhesive striped coating was created on the portion adjacent to the can body seam.

In the same manner as in Example 1, the state of the coating film at the seam of the can body and the coverage of the cut edges were examined, and the state of the coating film was also observed after packing the boiled horsetails and observing them immediately after retorting and after storage at 50°C for one year. .

The respective results are shown in Table 1 below.

Example 4 A tin-free steel plate with a thickness of 0.26 mm was welded in the same manner as in Example 1, and the seams of the inner and outer surfaces of the resulting can body were welded using an airless gun.
Under the same conditions as above, the water slurry paint A of Reference Example 1 was applied to form an adhesive striped coating on the portion adjacent to the seam of the can body.

In the same manner as in Example 1, the state of the coating film at the seam of the can body and the coverage of the cut edges were examined, and the state of the coating film was also observed after packing the boiled horsetails and observing them immediately after retorting and after storage at 50°C for one year. .

The respective results are shown in Table 1 below.

Example 5 A black plate (untreated steel plate) with a thickness of 0.26 mm was welded in the same manner as in Example 1, and the joints on the inner and outer surfaces of the resulting can body were coated with the following: The water slurry paint A of Reference Example 1 was applied using an airless gun under the same conditions as in Example 1 to create an adhesive striped coating on the area adjacent to the can body splicing area.

In the same manner as in Example 1, the state of the coating film at the seam of the can body and the coverage of the cut edge were investigated, and the state of the coating film was further observed after boiling in water and after retorting and after storage at 50°C for one year. did.

The respective results are shown in Table 1 below.

Comparative Example 1 The solution-type paint of Reference Example 4 was applied to the seam portions of the inner and outer surfaces of a tin can body obtained in the same manner as in Example 1 using an airless gun under the same conditions as in Example 1. An adhesive striation coating was created on the can body adjacent to the seam.

In the same manner as in Example 1, the state of the coating film at the seam of the can body and the coverage of the cut edges were examined, and the state of the coating film was also observed after packing the boiled horsetails and observing them immediately after retorting and after storage at 50°C for one year. .

The respective results are shown in Table 1 below. Comparative Example 2 A tin can body obtained in the same manner as in Example 1 was coated with a powder coating gun on the seam part of the inner surface so that the width was 10 mm and the thickness of the dried coating was 30 to 50 microns. After applying the powder coating E of Reference Example 5, it was baked for 15 minutes in a hot air drying oven at 180°C to form an adhesive striped coating on the area adjacent to the seam.

As in Example 1, the state of the coating on the seam of the can body and the coverage of the cut edges were examined, and the state of the coating was further observed after packing the boiled horsetail and storing it immediately after retorting and at 50°C for one year. did.

The respective results are shown in Table 1 below.

Claims (1)

[Claims] 1. A method for covering four parts of a side seam of a welded can,
Applicable? A slurry paint is applied to the four parts, the applied paint is dried and/or set, and then the dried and/or set slurry paint is heated to a temperature higher than the melting point or softening point of the film-forming material of the slurry paint to form a film with a thickness of 10 to 10. A method characterized by forming a coating film of 100μ. 2 The film-forming substance of the slurry paint is a thermoplastic polyester resin, acrylic resin, polyolefin resin, polyvinyl chloride resin, polyamide resin, vinyl acetate resin, polyvinyl acecool resin, polyether resin, polycarbonate resin, epoxy resin, alkyd resin. 2. The method according to claim 1, wherein the resin is selected from at least one of the group consisting of polyurethane resin, epoxy ester resin, phenol resin, amino resin, and silicone resin. 3. The method according to claim 1 or 2, wherein the slurry paint is an aqueous slurry paint.