JPS6136991B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for forming an anticorrosion coating on a metal container. In particular, it relates to a method of forming the coating at processed parts such as joints where deterioration of the coating is most likely to occur in the container.

BACKGROUND OF THE INVENTION Conventionally, anticorrosion coatings have been applied to metal containers to protect them from the contents and the outside air.
Since this anti-corrosion coating is usually painted on the metal material, it often deteriorates during the manufacturing process. In particular, the joints are subject to severe processing, so their deterioration is significant. Generally, a band-shaped repair coating is formed on the deteriorated part of the anticorrosive coating using a solution paint such as enamel, lacquer, or paint, but this is not necessarily considered to be a sufficient anticorrosion coating when considering the corrosion resistance to the contents.

A conventional method for forming an anticorrosion coating is to apply a dry powder paint to a metal surface or its deteriorated part by electrostatic powder coating, and then heat and fuse it to form a metal container. A coating device is required and the economic burden is extremely large.

In addition, dry powder paint is suspended in a liquid such as water that has increased viscosity by dissolving highly viscous gums.
A method of painting is also considered, but its suspension stability is insufficient and it is difficult to achieve continuous and uniform coating on an industrial scale, and the use of gums has side effects such as a decrease in corrosion resistance.

Therefore, the present inventors have arrived at the present invention as a result of studying a method for forming an anticorrosion coating that does not have the above-mentioned drawbacks.

That is, in the present invention, a dispersion obtained by dispersing polyamide resin powder in a poor solvent having substantially the same specific gravity as the resin is applied to a metal container, dried, and then the resin powder is This is a method for forming an anticorrosive coating on a metal container, which is characterized by forming an anticorrosive coating by heating and melting.

According to the method of the present invention, a dispersion is obtained by uniformly and stably dispersing polyamide resin powder in a poor solvent, the polyamide resin powder being adjusted to have a specific gravity substantially equal to the specific gravity of the resin powder. can be applied industrially to metal containers continuously over a long period of time using ordinary economical coating equipment, and can form a highly corrosion-resistant protective film. It is particularly suitable for forming coatings on processed parts such as joints.

In the present invention, "polyamide resin powder" refers to
It is a tough thermoplastic resin that adheres well to metal materials and has sufficient corrosion resistance, chemical resistance, and various mechanical processability. For example 6-, 6, 6-, 6, 1
It refers to 0-, 11-, or 12-polyamide resins, copolymers or mixtures thereof, or modified products thereof. Furthermore, this does not preclude the use of so-called powder coatings which are mainly composed of these polyamide resins and contain small amounts of conventional additives such as titanium oxide.

As for the particle size of the polyamide resin powder used in the present invention, a particle size of 1 to 100 microns gives good results, and a particle size of 1 to 60 microns is particularly preferred.

The "poor solvent" used in the present invention refers to a solvent that does not substantially dissolve the polyamide resin powder at room temperature, such as hydrocarbons such as hexane and toluene, ethers such as ethyl ether, and ethyl acetate. Esters, ketones such as methyl ethyl ketone, halogenated hydrocarbons such as trichlorethylene, alcohols such as ethyl alcohol and glycol, and mixtures thereof can be used, and the specific gravity may be approximately equal to that of the polyamide resin powder. In order to adjust the specific gravity of the poor solvent over a wide range, it is convenient to use a mixed solvent, and it is particularly recommended to use a halogenated hydrocarbon with a high specific gravity. The thus prepared dispersion of polyamide resin powder of substantially equal specific gravity and its poor solvent is a uniform and stable dispersion for a long period of time.

However, since the dispersion liquid to be coated is a uniform and stable dispersion liquid, the method of the present invention can be applied continuously (it can also be done intermittently, but continuous is industrially preferable) and at high speed using ordinary economical coating methods. Moreover, since the dispersion method is not very complicated, the anticorrosion coating can be formed economically.

This dispersion can be applied to a metal container by spray coating, which is a common coating method. Next, the painted dispersion was dried at around room temperature to volatilize most of the solvent, and then heated at 120 to 350℃.
By heating and melting the material to a temperature within this range, a tough, uniform coating with excellent corrosion resistance can be obtained. In some cases, the coated portion may be subjected to a primer treatment prior to carrying out the present invention.

Since the coating dispersion is a uniform and stable dispersion, the coating dispersion of the present invention can be uniformly coated continuously on the inside and outside of a large number of metal containers, on areas where the protective coating has deteriorated such as areas with deteriorated surface protection or processed areas such as joints. It is possible to carry out stable repair coating industrially, and as a result, it is possible to obtain an anticorrosive coating with a sufficient and uniform thickness and excellent corrosion resistance.

EXAMPLES The present invention will be explained in more detail with reference to Examples below, but the present invention is not limited thereto. All the following parts are by weight unless otherwise specified.

Example 1 Nippon Rilsan Co., Ltd.'s particle size is 2 to 60μ and the specific gravity is
40 parts of polyamide powder of 1.04% dioxane and 98% of dioxane
When dispersed with good stirring in a mixed solvent (specific gravity = 1.04) of 2 parts of trichlorethylene and 2 parts of trichlorethylene, a dispersion liquid was obtained that exhibited a completely uniform dispersion state and remained in the same state even after 10 days. Ta. The dispersion thus obtained was sprayed onto the joints of multiple metal containers using a regular spray device (nozzle diameter: 0.508 mm).
Apply the coating continuously under a pressure of Kg/cm ² in a band approximately 10 mm wide and approximately 100 μ thick, and after drying the solvent at around room temperature,
When applied by heating and melting at 260°C, a uniform and tough anticorrosion coating was obtained that had sufficient corrosion resistance and could withstand a 180 degree bending test.

Comparative Example For comparison, a dispersion was prepared in the same manner as in Example 1 except that toluene (specific gravity = 0.868) was used as the sole solvent. Within a few minutes after preparation, the powder and solvent separated into two layers and the powder A phenomenon of sedimentation in the lower layer was observed, making it difficult to apply uniformly with a spray device.

Example 2 38 parts of "Amilan CM-833P" polyamide copolymer powder (particle size 1 to 80μ, specific gravity = 1.08) manufactured by Toray Industries, Inc. was mixed with a mixed solvent of 85.5 parts of dioxane and 14.5 parts of trichlorethylene (specific gravity = 1.08). When the mixture was dispersed with thorough stirring, a uniform dispersion liquid with a good dispersion state was obtained. The dispersion thus obtained was sprayed onto the processing parts of a large number of metal containers using a conventional spray device (nozzle diameter
0.508mm), the width is reduced continuously at a pressure of 4Kg/ ^cm2 .
It is painted in a strip shape of 10mm thick and about 100μ, and after drying the solvent in the vicinity at all times, it is melted and fused by heating at 220℃.It has sufficient corrosion resistance and can withstand a 180 degree bending test. A uniform and tough anti-corrosion coating was obtained.

Comparative Example 2 For comparison, a dispersion liquid was prepared in the same manner as in Example 2 except that dioxane (specific gravity = 1.034) was used as the sole solvent. Within a few minutes after preparation, the powder and solvent separated into two layers. Powder sedimentation to the lower layer was observed, making it difficult to apply using a spray device.

Example 3 The dispersion obtained in Example 1 was applied to the side seam of a metal container whose inner surface was coated with an anticorrosion coating (a container joined with a lock seam and soldered from the outside).
Using a spray device (nozzle diameter 0.508 mm), apply the coating to a width of about 10 mm and a thickness of about 100 μ at a pressure of 4 Kg/cm ^2. After the solvent has evaporated and dried, heat and melt at 260°C for about 22 seconds. Even after putting 4% acetic acid solution into the metal container in which the anti-corrosion repair coating had been applied and storing it at 30°C for 30 days, no changes such as rust were observed on the areas where the anti-corrosion repair coating had been applied.

Comparative Example 3 When a 4% acetic acid solution was added to the side seam of the same metal container used in Example 3 and a solution-type epoxy resin anticorrosion repair coating was applied and the container was stored at 30°C, the side seam was repaired in an average of 25 days. The processed parts were corroded and there was a hole.

Example 4 Using a spray device (nozzle diameter 5.08 mm), 4 kg of the dispersion obtained in Example 2 was applied to the top-bottom joint (joined by double wrapping) of a metal container whose inner surface was coated with an anticorrosion coating. Thickness approx. 100 at a pressure of / ^cm2
After applying it to μ and letting the solvent evaporate to dryness, it was heated to about 220°C.
Even after putting a dye solution with a pH of 1 to 2 in a metal container that was heated and melted for 20 seconds to form an anticorrosion repair coating and storing it at room temperature for 180 days, rusting etc. did not occur on the areas where the anticorrosion repair coating was applied. No change was observed.

Comparative Example 4 A dye solution with a pH of 1 to 2 was added to the same metal container used in Example 4, with a solution-type epoxy resin anti-corrosion repair coating applied to the top and bottom seams, and the treated part began to corrode at room temperature for 150 days. I was impressed by a part of it.

Claims (1)

[Scope of Claims] 1. A dispersion obtained by dispersing polyamide resin powder in a poor solvent for the polyamide resin having substantially the same specific gravity as the resin is applied to a metal container, dried,
A method for forming an anti-corrosion coating on a metal container, comprising: then heating and melting the resin powder to form an anti-corrosion coating. 2. The method for forming an anticorrosive film according to claim 1, wherein the dispersion is applied particularly to processed parts such as joints of metal containers.