JPS5813637B2 - Electrodeposition coating method for airtight metal vessels - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for electrocoating the inner surface of a hermetic metal container.

More specifically, in a method of filling the inside of a hermetic metal container with a water-soluble paint and applying electricity between an electrode disposed inside the container and the container to paint the inner surface of the container, the surface area of the electrode,
An electrodeposition coating method in which the coating thickness formed on the inner surface of a container can be formed uniformly over the entire surface to be coated with a predetermined thickness by providing an electrode that satisfies specific conditions regarding the placement position. Regarding.

A typical conventional electrodeposition coating method involves moving a workpiece suspended by a hanger on a conveyor into an electrodeposition tank filled with a water-soluble paint, immersing the workpiece, and applying electricity to coat the workpiece.

In this type of conventional coating method, conditions such as the placement position of the electrode are considered depending on the shape of the workpiece to be immersed in the electrodeposition bath, but generally speaking, the electrode position and other conditions are Under the conditions that the surface area ratio (hereinafter referred to as pole ratio) is approximately 7, and the separation distance between the electrode and the surface to be coated of the workpiece (hereinafter referred to as pole distance) is approximately 130 mm or more, approximately 2
Apply electricity for ~3 minutes, which results in a film thickness of 15~25μ.
A dry coating film was obtained.

However, when attempting to electrodeposit the inner surface of a nearly hermetic metal container such as a fuel tank for an internal combustion engine, the metal container used as the workpiece is small and airtight, so it is difficult to use the electrodeposition bath as described above. Even if the coating method used is used, it is difficult to fully satisfy the above conditions.

In other words, if a single electrode is inserted into the workpiece by inserting it through the opening that is the fuel injection port due to the shape of the container, the distance between the electrodes will be significantly different between the vicinity of the opening and the inner surface deep inside the workpiece. This poses the problem that a thick coating film is formed on the inner surface near the opening and a thin coating film is formed on the inner surface inside, resulting in variations in the thickness of the coating film.

In view of the above-mentioned problems, the present inventors have created the present invention in order to effectively solve the problems.

An object of the present invention is to fill a water-soluble paint in a sealed metal container in which an electrode is disposed, and to apply electricity between the electrode and the metal container to paint the inner surface of the metal container. In the electrodeposition coating method, the ratio of the surface area of the electrode to the surface area of the surface to be coated of the metal container is 20.
To provide a method for electrocoating a hermetically sealed metal container, in which the electrodes are arranged so that the distance between the electrode and the surface to be coated is 0 or less, and the distance between the electrode and the surface to be coated is within the range of 30 to 30. be.

Therefore, an object of the present invention is to provide electrodes in the workpiece whose electrode ratio and inter-electrode distance satisfy predetermined conditions, so that even if the workpiece to be electrodeposited is small and has airtightness, it can be shortened. It is possible to uniformly form a coating film of extremely optimum thickness over the entire surface of the workpiece by applying electricity for a certain amount of time.

A preferred embodiment of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 is a schematic diagram of the coating apparatus, and FIG. 2 is a graph showing experimental results.

A water-soluble paint 3 is injected into an airtight metal container 1 through an opening 2 for fuel injection.

Further, an electrode 4 is inserted from the opening 2 into the paint stored in the container.
is inserted and placed.

The base of the electrode 4 is covered with an insulator 5, and one end thereof is connected to one terminal of a rectifier 6a of a DC power source 6.

The other terminal of the rectifier 6a is connected to the metal container 1, so that the container itself acts as the other pole, and the electrode 4 and the container 1 are connected to each other.
A voltage is applied between them, and electricity is supplied.

When electricity is applied, paint molecules in an ionized state move toward the inner surface of the container, and electrodeposition occurs on the inner surface 1a to form a coating film.

FIG. 2 shows the relationship between the pole ratio, the distance between poles, and the film thickness based on experimental results, with the horizontal axis representing the distance between poles and the vertical axis representing the film thickness.

Graph ■ shows the pole ratio of about 1, graph ■ shows the pole ratio of about 1, and graph ■ shows the film thickness at each distance between poles when the pole ratio is about 201 and electricity is applied for 10 seconds at a voltage of 250 V. This is what is shown.

In graph ■, when the distance between the poles is 40 mm or less and over 100 mm, it is out of the optimum film thickness range (15 to 25μ), and in graph ■, when the distance between poles is 50 mm or less, it is out of the optimum film thickness range. Under these conditions, it is technically difficult to uniformly form a coating film with an optimum thickness over the entire coating surface of the container using a single electrode inserted through the opening 2 of the container.

However, in contrast to graphs (2) and (2), graph (2) shows the feature that the film thickness is optimal over a wide range of distance between electrodes of about 30 to 200 mm.

According to the above experimental results, when the pole ratio is above and the distance between poles is 30mm or less, the thickness of the dry paint film becomes 25μ or more, and in extreme cases, general collapse of the paint film occurs, especially gasoline resistance. Adversely affects impact resistance and adhesion.

On the other hand, even if the pole ratio is 1/1 or more, the distance between poles is 200
If the thickness is more than mm, the thickness of the dried coating film obtained per unit time will be less than a few microns, which will have an adverse effect on corrosion resistance.

Therefore, in the present invention, the pole ratio is set to 200 or less, and the distance between poles (shortest straight line distance) is set to about 30 to 200 mm, thereby forming a stable dry coating film with a thickness of 15 to 25 μm on the entire painted surface of the inner surface of the container. Is possible.

Examples thereof will be described below.

Example 1 A rod-shaped anode electrode with a surface area of about 565.2 mm was placed inside a metal container with an internal capacity of 2600 cc and an inner surface area of about 119200 mm^, and after being filled with paint, electricity was applied for 10 seconds at a voltage of 250 cm.

After that, the remaining paint inside is discharged and heated in an atmosphere of 180℃ for about 30 minutes.
Baking was carried out for 0 minutes, and a stable dry coating film with a film thickness of 15 to 25 μm was obtained.

At this time, the pole ratio is 211' and the distance between poles is approximately 30 to 150 m.
It was m.

Example 2 A rod-shaped anode electrode with a surface area of about 659.4 mm was inserted into a metal container with an internal capacity of 6,650 cc and an inner surface area of about 252,000 mm, filled with paint, and then energized at a voltage of 250 V for 10 seconds.

Thereafter, the remaining paint inside was discharged, and baking was carried out for about 30 minutes in an atmosphere of 180°C to obtain a stable dry coating film with a film thickness of 15 to 25 μm.

At this time, the pole ratio is shoulder to shoulder, and the distance between poles is approximately 30 to 200 mm.
Met.

As is clear from the above description, according to the present invention, when a single electrode is arranged inside a hermetically sealed metal container and the inner surface of the container is electrodeposited, the surface area of the electrode is smaller than the surface area of the surface to be coated. By providing the electrodes so that the ratio and the distance between the electrodes and the inner surface satisfy certain conditions, it is possible to achieve the optimum film thickness over the entire surface of the container with a short application time of about 10 to 30 seconds. It exhibits the effect of being able to uniformly form a dry coating film having .

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory diagram of the coating method according to the present invention, and FIG. 2 is a graph showing experimental results. In the drawing, 1 is a workpiece which is a metal container, 3 is a water-soluble paint, 4 is an electrode, and 6 is a power source.

Claims (1)

[Claims] 1. A water-soluble paint is filled in a sealed metal container of a predetermined shape forming a fuel tank of a vehicle in which an electrode is disposed, and an electric current is applied between the electrode and the metal container to coat the inner surface of the metal container. In the electrodeposition coating method, the surface area ratio of the electrode to the surface area of the surface to be coated of the metal container is 200 or less, and the distance between the electrode and the surface to be coated is 30 to 200 mm. A method for electrodeposition coating a hermetic metal container, characterized in that the electrodes are arranged so as to be within a range.