JPH0970919A - Inhibition of corrosion on edge surface of precoated steel sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to inhibit the corrosion of the edge surface of a precoated steel sheet and prevent a metallic luster from being generated, and at the same time, perform a high-quality coating at a low cost and with high manufacturing efficiency. SOLUTION: A UV(ultraviolet beam)-curable paint is applied to the edge surface part of a precoated steel sheet, and its paint film is cured by irradiation with a UV beam. In addition, the best-suited UV-curable paint is such that it contains 2wt.% or less of coloring pigment.

Description

Detailed Description of the Invention

[0001]

The present invention relates to home appliances, furniture,
The present invention relates to a method of using a precoated steel plate as an outer plate of a building material, an automobile part, or the like, and protecting the end surface of the precoated steel plate when subjected to shearing.

[0002]

2. Description of the Related Art Conventionally, for home electric appliances, furniture, building materials, automobile parts and the like, post-coating has been performed in which cold-rolled steel sheets or surface-treated steel sheets are formed and coated after shearing. But,
In recent years, steel manufacturers have been increasing the proportion of pre-coated steel sheets that have already been coated on cold-rolled steel sheets or surface-treated steel sheets for the purpose of omitting the coating process at the final product manufacturers. A drawback of using precoated steel sheets as outer plates is that after the precoated steel sheets are formed and sheared, the sheared end faces become unpainted and unplated iron surface, so corrosion such as rust occurs on these end faces. In addition, it is also possible that the end face is exposed to a metallic glossy surface different from the coating color of the steel plate surface. Therefore, when the end surface of the precoated steel sheet is visible from the outside in the final product, the metallic luster and rust on the end surface deteriorate the quality of the final product.

In order to solve this problem, in the prior art, the product is designed so that the end of the precoated steel sheet is folded inside the product so that the end face cannot be seen. Further, due to a design problem, when it is necessary to have a structure in which the end face can be seen on the outside of the product, a general organic solvent-based room temperature curable paint or thermosetting paint is applied to the end. However, in addition to the environmental problems of organic solvents, room-temperature curable coatings require 2
It takes more than 4 hours, which is inefficient in the process of manufacturing products. Since the thermosetting coating material needs to be heated at about 150 ° C. or higher in order to cure the coating film in a short time, it is necessary to provide equipment such as a heating furnace, resulting in high equipment cost.

Further, when the above-mentioned end face coating is applied to the pre-coated steel sheet, in order to maintain the beauty of the pre-coated surface (outer plate of the final product), it is required that the pre-coated coated surface does not wrap around. It In order to prevent the paint from wrapping around on the pre-coated surface, a technique was used in which a masking tape was applied to the non-painted part and the end face was painted from above, and the masking tape was peeled off after the coating film hardened. In many cases, an organic resin-based masking tape will swell in many cases, and it is necessary to select a tape material. Such a tape resistant to an organic solvent is expensive and costly.

[0005]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object thereof is to prevent corrosion of the end face portion of a precoated steel sheet and prevent metallic luster, and at the same time, at low cost and high cost. It is to provide a method that enables efficient and high-quality painting.

[0006]

[Means for Solving the Problems] In order to cure a coating film in a short time without applying heat, in the case of a solvent-based paint, it takes time or heat to remove the solvent. If the amount is reduced, the viscosity of the paint increases and the paintability deteriorates. Therefore, even if there is no solvent, keep low viscosity,
A paint that only needs to cure the resin can be cured in a short time.

To achieve the above object, the method of the present invention comprises:
It is characterized in that a UV paint is applied to the end face portion of the precoated steel sheet and this film thickness is cured by UV irradiation. The U
To the V paint, it is preferable to add a coloring pigment in an amount of 2% by weight or less in order to prevent metallic luster on the end surface.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, UV rays are applied to an end face exposed by shearing a precoated steel sheet or the like.
Apply hardened paint. The UV curable coating has a low viscosity even without a solvent, and if it is a clear resin having a high ultraviolet transmittance, it can be cured in a few seconds, which improves the efficiency in the product manufacturing process. Further, since the UV lamp, which is a light source of ultraviolet rays, needs to irradiate only the end surface of the coated steel plate, the cost is lower than that of a large heating furnace. Since it does not use organic solvents, it is good for the environment. Examples of the clear resin used as the UV curable coating material include acrylic resins such as acrylate, epoxy acrylate, urethane acrylate and polyester acrylate.

To prevent the metallic luster of the end face, a color pigment is added. When the UV curable coating material is colored, the UV transmittance decreases, and it takes time to cure. However, the precoated steel plate is usually a thin plate of 2 mm or less, and it is not necessary to apply a dark color to paint the end face portion thereof. Therefore, if the amount of the pigment added when coloring is set to a small amount of 2% by weight or less, the curing time can be shortened and the metallic luster can be eliminated. As a color pigment, carbon black for black, titanium oxide for white, phthalocyanine blue for blue, and the like are used for paints. In addition, a blue-based phthalocyanine-based dye, a black aniline black, and a red-based azo dye may be added to the paint for coloring.
The coating method of the UV curable coating material may be a commonly used coating method, and a coating method suitable for the application and environment of the product, such as spray coating or brush coating, can be freely selected.

Next, the UV curable coating material applied to the end faces is irradiated with ultraviolet rays to cure the coating film. Here, when the UV-curable coating is colored, the transmittance of ultraviolet rays decreases as the amount of pigment and dye added increases, so the balance between the color of the coating after curing and the coating curing time on the coating work surface. In consideration of the above, it is necessary to determine the addition amount of the pigment and the dye. As an example, FIG. 1 is a graph showing the relationship between the addition amount and the curing time when black carbon is added as a pigment to a certain UV curable coating material.

The method of irradiating with ultraviolet rays is to irradiate the entire edge with a commercially available ultraviolet lamp, or in consideration of prevention of deterioration of the precoat coating film by ultraviolet rays, an edge surface portion coated with a UV curing coating using an ultraviolet spot irradiation device You can freely choose to irradiate only. The irradiation time of ultraviolet rays will be appropriately adjusted depending on the addition amount of the coloring pigment or dye added to the UV curable coating, but under normal conditions, an irradiation time of up to about 20 seconds is sufficient. After the coating film has been cured by ultraviolet irradiation, when a masking tape is attached, the masking tape is peeled off, and when the masking tape is not attached, the external component is completed in the cured state.

[0012]

Example First, a sample was prepared by shearing a precoated steel sheet in which chromate treatment, primer coating, and topcoat were sequentially laminated on a steel sheet to a size of 100 mm × 50 mm. Next, a UV curable coating having the composition shown in Table 1 was prepared, and a 30 μm-thick brush coating was applied to the sheared end face of the precoated steel sheet. UV paint A urethane acrylate resin was used as the hard paint. An organic resin-based masking tape was attached to a part of the sheared portion. Then, the coated surface was irradiated with ultraviolet rays for 20 seconds using an ultraviolet irradiation device.

Next, for each sample, the presence or absence of metallic luster on the end face and the corrosion resistance were evaluated by the method according to JIS-Z0228 method. The corrosion resistance was evaluated according to the following criteria. ◯: No rust generation was observed. Δ: Slight rust generation was observed. X: Large amount of rust generation. Table 1 shows the evaluation results. As is clear from this table, the sample coated with the sheared end face by the method of the present invention has excellent corrosion resistance, and the metallic luster of the end face part disappears only by adding 2% or less by weight of the pigment to the paint. Further, it is also possible to use an organic resin masking tape which could not be used conventionally.

[0014]

[Table 1]

[0015]

As described above, the present invention is an end surface anticorrosion method for coating the end surface of a precoated steel sheet with a UV curable coating material that does not use an organic solvent. This makes it possible to cure for a short time without using a heating furnace to cure the coating film, and it is possible to simplify the process of end face coating. Moreover, since no organic solvent is used, it is environmentally friendly. Since it is possible to use masking tape made of organic resin, it is possible to protect the end surface of precoated steel sheet in an environment friendly, low cost and highly efficient manner.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a relationship between a pigment addition amount and a curing time when coloring a paint according to the present invention.

Claims (3)

[Claims] 1. A method for preventing corrosion of an end surface of a precoated steel sheet, which comprises applying a UV curable coating to the end surface portion of the precoated steel sheet and curing the coating film by UV irradiation. 2. The method for preventing corrosion of an end surface of a precoated steel sheet according to claim 1, wherein a color pigment is added to the UV curable coating material. 3. The method for preventing corrosion of an end surface of a precoated steel sheet according to claim 2, which contains a coloring pigment in an amount of 2% by weight or less.