JPS604750B2 - Coating method for welded joints of metal containers - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a manufacturing technology for metal container bodies, and more particularly to a continuous protective coating method for welded lap joints or butt joints of metal containers.

Generally, in the manufacture of metal containers, the joints of the containers are often joined together by welding, and an appropriate band-shaped protective coating is applied to the joints to improve airtightness, aesthetic appearance, and corrosion resistance.

In particular, when welding is performed by peeling off the anti-rust coating on pre-painted rough metal parts to be welded, the welded part is often rapidly damaged when compared to other parts. Since severe rusting and corrosion phenomena are observed, it is necessary to apply a particularly strong band-shaped coating. By the way, methods using paints such as solution enamel or lacquer paint are generally being explored as such band-like coating methods, but the surface tension of the coating liquid causes an extreme liquid film to form on the iron end portion of the seam weld. This will eventually lead to exposure of this acute area, resulting in insufficient protective coverage.

Separately, there is a known method of applying dry powder paint to the weld seam in a band shape using electrostatic powder coating and heat-fusing it to prevent the exposure of the sharp edge, but this method requires expensive special electrostatic coating equipment. The economic burden is extremely heavy.

However, it is possible to apply such a powder coating by suspending it in a liquid such as water, which has increased viscosity by dissolving highly viscous gums, but the suspension stability is insufficient and it is not suitable for industrial use. It is difficult to achieve continuous and uniform coating, and there are also side effects such as reduced corrosion resistance due to the use of gums.

In contrast to these methods, the present invention involves dispersing polyamide powder completely stably in a poor solvent for the polyamide whose specific gravity is adjusted to be approximately equal to the specific gravity of the powder, and then dispersing the dispersion liquid thus obtained. Industrially, it is possible to uniformly coat the powder continuously over a long period of time using economical coating equipment, then dry the solvent, and then melt the powder sufficiently to form a protective coating with a uniform thickness. The present invention provides a method for coating a welded joint portion of a metal container.

Here, the above-mentioned "polyamide powder" is a strong thermoplastic resin material that adheres well to metal materials, has sufficient corrosion resistance, and has excellent mechanical processability, such as 6-, 66 -, 6/10-, 11-, or 1
2-polyamide, and their copolymers and modified products; for example, polyamides containing these polyamide powders as a main ingredient and containing a small amount of conventional additives such as titanium oxide, etc. This does not preclude the use of so-called powder coatings.

As for the particle size of this polyamide powder, a particle size of 1 to 100 mm gives good results, but a particle size of 1 to 60 mm is particularly desirable.

In addition, the above-mentioned "poor solvents" which are other components refer to those that do not substantially dissolve the above-mentioned polyamide powder at room temperature, such as hydrocarbons such as hexane and toluene; ethers such as ethyl ether; ethyl acetate. esters such as;
Examples include ketones such as methyl ethyl ketone; alcohols such as ethyl alcohol and glycol; halogenated hydrocarbons such as trichloroethylene; and mixtures thereof.

Therefore, in order to adjust the specific gravity of the poor solvent over a wide range so that it is almost equal to the specific gravity of the polyamide powder, it is convenient to use a mixed solvent, and in particular, use a mixed solvent with a high specific gravity of halogenated hydrocarbons. It is recommended that

The dispersion thus prepared, consisting essentially of geometric polyamide and its poor solvent, is obtained as a long-term stable dispersion.

This dispersion can be coated on a metal container by conventional coating methods such as spraying, extrusion, and roll cornering.

Next, this coating film is dried at around room temperature to remove most of the solvent, and then heated and melted to a temperature in the range of 120 to 350 oo, resulting in a uniform coating with excellent corrosion resistance.

In some cases, it is an effective method to further improve corrosion resistance by subjecting the joint to a suitable primer treatment prior to carrying out the method of the present invention.

However, since the coating dispersion liquid in the method of the present invention is a stable dispersion, it is possible to industrially apply a uniform and stable strip-like coating to the welded joints of a large number of metal containers continuously. As a result, it is possible to obtain a protective coating having a sufficient and uniform thickness and excellent corrosion resistance.

Next, the present invention will be explained in more detail with reference to Examples.

Hereinafter, all parts mean parts by weight unless otherwise specified.

Example 1 Nippon Rilsan ■ has a particle size of 2 to 60 F, and a specific gravity of 1.
049, 42 parts of polyamide 11 powder, was mixed with a mixed solvent of dioxane Satoshibe and trichloroethylene 5.2 parts (
Specific gravity = 1.04), where it was dispersed while worshiping the lanterns,
A dispersion liquid was obtained which exhibited a completely uniform dispersion state and remained the same even after 10 days.

The dispersion thus obtained was sprayed onto each welded joint part of a large number of metal containers using a spray gun (caliber 0.5 side).
Continuously apply a strip of about 100A to the skin using ground pressure, then allow the solvent to dry, then apply 260A to the skin.
qo for 1 minute.

As a result, a uniform and highly rutted protective coating was applied. Furthermore, good coating results were obtained that showed sufficient corrosion resistance and passed the 180° bending test. In addition,
When using only dioxane (specific gravity = 1.034) as the sole solvent, a dispersion was prepared in the same manner, and a phenomenon was observed in which the dispersion separated into two layers within a few minutes after preparation, and the powder settled in the lower layer. The results showed that it was difficult to apply uniformly by spraying, etc.

Example 2 The mottled areas of "Amiran CM-83 Group" (polyamide copolymer powder manufactured by Toray ■: particle size = 1 to 80 mm, specific gravity = 1.08) were treated with 85.5 parts of dioxane.

Mixed solvent with 14.5 parts of leuthylene (specific gravity = 1.08
), a uniform dispersion liquid with good dispersion state was obtained. Next, the dispersion liquid was prepared with a diameter of 0.
Using 5 spray guns, continuously apply approximately 120 sprays to the welded parts of a large number of metal containers at a pressure of 10 k9/ground in approximately 1 gun.
It was applied in a band to the thickness of the mountain.

This coating was then air-dried and then heated at 160qC for 2 hours.
The mixture was melted by heating for a minute. As a result, a uniform and smooth coating film was obtained, and a good protective coating was obtained which had sufficient corrosion resistance and passed the 1800 bending test. In parallel with this, when a dispersion liquid was similarly prepared using only dioxane as the solvent, the result was that the dispersion separated into two layers within just a few minutes after preparation, making uniform coating difficult.

Claims (1)

[Claims] 1. A dispersion obtained by dispersing polyamide powder in a poor solvent with a specific gravity substantially equal to that of the polyamide is applied to the welded joint of a metal container, then dried, and then the powder is melted to form a uniform layer. characterized by forming a film,
A method of coating welded joints in metal welders.