JPS599225B2 - Protective coating formation method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of forming a protective coating of cured resin on the surface of an article.

Epoxy resin has traditionally been applied to the surfaces of electrical components such as capacitors and resistors to improve their physical and chemical resistance.
A protective coating is applied using a thermosetting resin such as an unsaturated polyester resin, and the methods for forming the protective coating include embedding using a mold (Poting) and encapsulation.
In addition to methods such as ulating), a dipping method that does not use a mold has been adopted.

The method of forming a protective coating using a mold has the advantage that the resulting product has a constant shape and can be applied to articles with complex shapes.
Although it is an advantageous method, it is inferior in workability, so the immersion method is also said to be an industrially advantageous method. The present invention provides an industrially advantageous method for forming a protective coating that overcomes the drawbacks of this dipping method. Conventionally, a thixotropic thermosetting resin has been used as a liquid resin composition in the dipping method, but when this highly thixotropic liquid resin composition is used, it is difficult to fully perform the protective function as a protective coating layer. Although it is possible to form a sufficiently thick coating, this results in so-called excessive quality, and from the perspective of saving resources, and because electric parts in particular are required to be compact and have a certain size, the coating layer may become irregular. I don't like it to be thick.

On the other hand, if this thixotropic property is weakened, depending on the shape of the target article, it may be possible to form a protective coating with an insufficient thickness to exert its protective function. For example, the surface of some types of capacitors is made up of both a resin film and a metal surface, so when they are immersed and pulled up, the amount of liquid resin that adheres to the metal surface is small. In some cases, virtually no adhesion occurs. Further, for example, in the case of a rectangular parallelepiped article, the amount of resin deposited on the edges or vertices is small, which deteriorates the quality of the final product. The present inventors conducted research to solve the above problem, and applied an ultraviolet curable liquid resin composition in advance to the parts of the article to which the curable liquid resin composition is difficult to adhere, and irradiated it with ultraviolet rays. The present invention has been achieved in which an ultraviolet curable liquid resin composition is cured to a degree that it becomes solid and can maintain its shape, and then a dipping method is performed.

By carrying out the method of the present invention, the characteristics of ultraviolet curable resins that cure in an extremely short time and the effect of preventing sagging during curing of liquid resin compositions due to the curing method that does not apply heat are effectively utilized. Therefore, a uniform protective coating can be formed without causing any hindrance to the work.

As the ultraviolet curable liquid resin composition used in the practice of the present invention, ultraviolet curable resin compositions such as those commonly used for paints or printing inks can be used, and ethylenically unsaturated double bonds The monomer and/or prepolymer having the above and a photopolymerization initiator are essential components, and known inorganic or organic gelling agents, flame retardants, colorants, and other fillers are added as appropriate depending on the purpose. You can also do that.

Generally, the thixotropic properties of this ultraviolet curable resin composition should be stronger than those of the liquid resin composition applied later. In the practice of the present invention, methods for applying the ultraviolet curable resin composition to the desired parts of the article include brush coating, spray coating, and methods such as applying the ultraviolet curable resin composition to the entire surface of the article by dipping and wiping off unnecessary parts. can be adopted, but
There are no particular restrictions. In carrying out the present invention, the curable liquid resin composition used in the subsequent process may be thermosetting or ultraviolet curable. It is also possible to adopt a method in which a thermal polymerization initiator is added to the same ultraviolet curable liquid resin composition as described above, irradiated with ultraviolet rays as a first step, and then heated. A thermal polymerization initiator can also be added to the ultraviolet curable liquid resin composition in the previous step. In order to facilitate understanding, the present invention will be specifically described below with reference to the drawings.

FIG. 1 is a perspective view showing a capacitor as an example of an article to which the present invention is applied, FIG. 2 is a sectional view taken along the line A-N in FIG. FIG. 2 is a sectional view taken along the line AN in FIG. 1, showing the state of resin adhesion according to the method of the present invention.

In FIG. 1, a part of the surface of a capacitor 1 is a polyester resin film surface 2, and a part is a metal vapor-deposited surface 3, to which conducting wires 5, 5' are connected.

When this capacitor 1 is immersed in a conventional thermosetting liquid resin composition and pulled up, as shown in FIG. Adhesion is not sufficient in some parts. In the method of the present invention, since the film 7 of ultraviolet curable resin is formed in advance on the metal deposition surface 3 and the edge portion 6, a uniform protective coating can be formed as a whole as shown in FIG. Although the figure shows an article having both a metal surface and a resin film, even if the surface is a uniform material, the amount of liquid resin composition adhered to the ridges or apex portions is small. It goes without saying that it is better to form a film of ultraviolet curable resin in advance.

Examples are shown below.

Example "Central part" refers to parts by weight. Example 1 About 1 m77 of the following ultraviolet curable resin composition was added to a capacitor as shown in Fig. 1 as shown in Fig. 3! The coating was applied to a thickness of 100 mL and cured by irradiating it with ultraviolet rays in a conventional manner.

Next, it was immersed in the following liquid resin composition (B) that is cured by ultraviolet rays and heat, and after being pulled up, it was irradiated with ultraviolet rays for about 5 seconds at a distance of 10 Cfn using a 2 kW high-pressure mercury lamp.
It was further heated in an oven at 105° C. for 30 minutes to obtain a completely cured protective coating. The thickness of this protective coating is almost uniform and approximately 2 ml.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing a capacitor as an example of an article to which the present invention is applied, FIG. 2 is a sectional view taken along the line A-N in FIG. FIG. 2 is a sectional view taken along the line A-X in FIG. 1, showing the state of resin adhesion according to the method of the present invention. Each symbol in the figure is as follows. 1...Capacitor, 2...Polyester resin film surface, 3...Metal vapor deposition surface, 4...Fabric edge, 5,
5t...Conducting wire, 6...Resin composition, 7.
...Film made of ultraviolet curable resin.

Claims (1)

[Claims] 1. In a method of forming a protective coating in which a curable liquid resin composition is applied to the surface of an article by a dipping method and then cured, the curable liquid resin composition does not easily adhere to parts of the article or has a sufficient thickness as a protective coating. An ultraviolet curable liquid resin composition is applied in advance to the parts of the article that are difficult to adhere to, irradiated with ultraviolet rays to stabilize at least the shape of the ultraviolet curable liquid resin composition, and then cured. A protective coating formation method in which the protective coating is immersed in a liquid resin composition and cured.