JP3363049B2 - Pre-coated metal plate with excellent pressure mark resistance - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a precoated metal sheet, and more particularly, to a pressure-resistant mark which can be suitably used for household electric equipment, indoor or outdoor equipment, and the like. The present invention relates to a precoated metal sheet having excellent properties. 2. Description of the Related Art Metal plates used for home electric appliances and indoor or outdoor equipment are usually coated on both sides in order to improve decorativeness (aesthetics) and corrosion resistance. Used. In recent years, this coating process has been increasingly diversified and upscaled.For example, when used in refrigerators, washing machines, microwave ovens, etc., a high gloss appearance is required,
On the other hand, when used for audio-visual equipment and the like, it is required that the paint be applied so as to have an aesthetic appearance corresponding to each application, such as a required appearance with reduced gloss. The surface of the metal plate requiring an aesthetic appearance as described above is called a decorative surface, while the surface on the back side is called a non-decorative surface, and anticorrosion is required rather than aesthetic appearance. [0003] Such a coating treatment method is based on a post-coating method in which a metal plate is press-formed by a final product maker and then painted in response to a request from the final product maker aiming at pollution prevention, cost reduction, improvement of a workplace environment, and the like. ,
The pre-coat method is being switched to pre-painting on the metal sheet supply side such as a steel mill, and then press-molding it on the end product manufacturer side. The painted metal plate supplied by the latter precoat method is a precoated metal plate. [0004] The precoating method includes a method of coating with a metal band and a method of forming a cut plate (short metal plate) after cutting the metal band and then coating. In the former method, a fixed tension is applied to the painted metal plate and the coil is wound into a coil, and in the latter method, the metal band is cut into metal cut plates, and then the coating is performed. It is to be packed and stored. However, the conventional precoated metal plate has a problem that a pressure mark is generated. That is, in the above-mentioned pre-coating method, when coating with a metal band, the coated pre-coated metal plate is wound into a coil under a given tension as described above. Large pressure is applied to the surface of the film (the film formed on the metal plate surface by painting), and therefore, the non-painted surface (the surface of the film painted on the non-decorated surface)
Are transferred to the decorative painted surface (the surface of the film coated on the decorative surface), causing a phenomenon that the gloss of the decorative painted surface changes. This phenomenon is called a pressure mark. In the case of coating with a cut plate, prepainted metal plates after coating are stacked and packed / stored as described above. At this time, a pressure mark is generated in a portion where the weight of the metal plate is locally concentrated. [0006] The pre-coated metal plate on which the above-mentioned pressure mark has been generated is impaired in its original beautiful gloss, and therefore, its commercial value is significantly reduced. Therefore,
The occurrence of such a pressure mark is a very serious problem, and it is a reality that a solution to it is eagerly sought. [0007] As one of measures to prevent the generation of such pressure marks, a protective film having a thickness of about 60 µm is attached to the painted surface of the precoated metal plate after coating (at the time of coil winding or stacking). A method for preventing the occurrence of a pressure mark has also been proposed. However, in such a method, there is a problem that the cost is increased by using the protective film, and a great deal of labor is required to remove the protective film after performing press molding on the user side such as a home appliance manufacturer. Although it cannot be said that this is a measure for preventing the occurrence of a pressure mark, a method of restoring the original gloss by heating after the generation of the pressure mark is also known as a method of erasing the once generated pressure mark. In particular, it is adopted by users such as home appliance manufacturers. This method utilizes the principle that the original gloss can be restored by lightly heating the coating on which the pressure mark has been generated. However, this method has another problem that the addition of the heating step causes a decrease in productivity and an increase in cost. In the precoated metal plate, so-called blocking may occur in which the front and back surfaces of the wound coil or the stacked metal plate are in close contact. Since the upper and lower plates are in close contact with each other in the pre-coated metal plate in which the glocking occurs, a problem arises when a great deal of work is required to peel off the plate, and it is also important that such blocking does not occur in the pre-coated metal plate. . SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to solve the above-mentioned problems pointed out in the prior art and to provide protection. Providing a precoated metal sheet with excellent pressure mark resistance that can effectively suppress the occurrence of pressure marks due to coil winding and stacking after painting without increasing the cost and increase in the number of steps due to the use of film Is to do. [0011] The precoated metal plate of the present invention which has solved the above-mentioned problems is a metal plate having a decorative coating on one side and a non- decorative coating on the other side. The center line average roughness Ra of the decorative film on the precoated metal sheet having
(Μm) and the center line average roughness Ra (μm) of the non-decorative surface coating film
The absolute value of the difference between the two is | △ Ra | (μm), and the absolute value of the difference between the glass transition temperature Tg (° C.) of the decorative coating film and the glass transition temperature Tg (° C.) of the non-decorative coating film is | △. When Tg | (° C.), these have the gist in that they satisfy the following equations (1) and (2), respectively. 0.03 ≦ | △ Ra | ≦ 0.6 (1) 5 ≦ | △ Tg | ≦ 42 (2) The pressure mark is wound up after painting as described above. Alternatively, during stacking, the unevenness of the non-decorative painted surface of the precoated metal plate is transferred to the decorative painted surface to occur, and the gloss of the decorative painted surface changes. Therefore, as a method of preventing the occurrence of the pressure mark, the unevenness of the coating film on the front surface (painted surface) and the back surface (non-painted surface) of the pre-coated metal plate is made closer to the coating film on the non-painted painted surface. It was thought that it was effective to have sex. As a result of further research from this point of view, the present inventors have adjusted the surface roughness of the coating film on the front and back surfaces of the precoated metal plate, and have also been able to adjust the coating film on the decorative surface and the non-decorative surface. It has been found that adjusting the hardness of the film, particularly the difference in glass transition temperature, to a certain range can effectively prevent the occurrence of pressure marks. Hereinafter, the contents of the present invention will be described in detail mainly on these points. The surface roughness of a paint film is governed by the particle size, content and dispersity of the pigment contained in the paint film, the leveling property of the paint, the shrinkage state of the resin when cured, and the like. Is the largest. Therefore, the surface roughness of the coating film can be adjusted by changing the type of the pigment or the compounding material. Further, the glass transition temperature Tg of the coating film is governed by the composition and molecular weight of the resin serving as the vehicle component of the coating film, the functional group, the crosslinking agent, and the like. Therefore, by appropriately selecting the type of the resin and the blending amount of the crosslinking agent, the glass transition temperature Tg of the coating film on the decorative coating surface and the coating film on the non-cosmetic coating can be adjusted. In view of the fact that the pressure mark is caused by the transfer of the unevenness of the non-decorative painted surface on the back side to the decorative painted surface as described above, the surface roughness of the decorative painted surface and the non-decorative painted surface is considered. It is thought that if the correlation between the coating and the coating hardness (especially the glass transition temperature) is properly adjusted, the occurrence of pressure marks due to the transfer can be suppressed. We have studied quantitatively the effect of roughness and glass transition temperature on pressure marks. There are two types of changes in the glossiness of the decorative painted surface due to the occurrence of the pressure mark. When the decorative painted surface is smooth and prefers a high gloss, the change in the glossiness of the decorative painted surface is not smooth. For applications where irregularities on the decorative painted surface are transferred and roughened to reduce the surface gloss, and also to form fine irregularities on the decorative painted surface and prefer matte surfaces such as matt skin, The matte skin is smoothed and becomes a glossy surface. In other words, the pressure mark does not necessarily mean that the surface is roughened, but may cause a problem that the roughened satin surface is smoothed. This causes a problem in the change of glossiness. Therefore, it was considered effective to reduce the absolute value of the roughness of both painted surfaces in order to suppress the gloss change of the painted surface due to the transfer of the non-painted painted surface. The pressure mark is generated by transferring the unevenness of the non-decorative painted surface to the decorative painted surface as described above. It was considered effective to make the coating film hardness higher than the coating film hardness. In the precoated metal sheet according to the present invention,
The glossiness of the coating on the decorative side (decorative side coating) changes greatly depending on the pressure mark, and the surface roughness of the coating on the decorative side and the coating on the non-decorative side (non-decorative side coating) The greater the difference, the greater the change in gloss tends to be.
On the other hand, since the problem on the user side using the coated metal plate is a change in gloss generated on the surface coating film, the present invention uses a decorative coating film and a non-cosmetic film that can make the gloss change less noticeable. The difference in the surface roughness of the surface coating was specified. The difference between the center line average roughness Ra and the difference between the glass transition temperature Tg of the decorative coating film and the non-decorative coating film has an influence on the resistance to pressure marks. When the difference between the center line average roughnesses is 0, no pressure mark is generated, but the blocking resistance is significantly reduced. The degree of pressure mark generation is related to the surface roughness of the decorative and non-decorative coatings, but the presence or absence of pressure marks is affected by the difference in coating hardness between the decorative and non-decorative coatings. The hardness of the coating is determined by the glass transition temperature Tg of the coating. Normally, there is a relationship of hardness of a decorative coating film <hardness of a non-decorative coating film, but the glass transition temperature Tg of the non-decorative coating film
Is too high compared to the glass transition temperature Tg of the decorative coating film, the unevenness of the non-decorative coating film is transferred to the decorative coating film. However, conversely, when the difference between the glass transition temperatures Tg is small, that is, when the glass transition temperature Tg of the non-decorative surface coating is close to the glass transition temperature Tg of the non-decorative surface coating, the non-decorative surface coating becomes The cushion effect is exhibited, and the pressure mark is less likely to occur. As described above, when the coil is wound or the cut sheet is laminated after coating, the unevenness of the non-painted painted surface of the pre-coated metal plate is transferred to the decorative painted surface as described above. This is a phenomenon in which the gloss changes. Therefore, the difference in surface roughness (irregularity) between the decorative coating film and the non-decorative coating film of the pre-coated metal plate is reduced, and the non-decorative coating film having a higher surface hardness than the decorative coating film has a cushioning property. Various researches were conducted with the idea that giving them would be effective in preventing the occurrence of pressure marks. As a result, by adjusting the surface roughness of the decorative surface coating film and the non-decorative surface coating film of the precoated metal plate and the difference between the glass transition temperatures Tg of both the coating films within predetermined ranges, the generation of the pressure mark is effectively achieved. It was found that it could be prevented. Based on these findings, the inventors studied in detail the conditions under which pressure marks can be effectively prevented, and found that the center line average roughness Ra (μm) of the decorative coating film and the non-decorative coating film were determined. Center line average roughness Ra
(Μm) is the absolute value of |） Ra | (μm), and the absolute value of the difference between the glass transition temperature Tg (° C.) of the decorative coating film and the glass transition temperature Tg (° C.) of the non-decorative coating film To | △ Tg |
(° C.), if the center line average roughness Ra and the glass transition temperature Tg are adjusted so that they satisfy the following formulas (1) and (2), respectively, the pressure during winding or laminating is adjusted. The inventors have found that the occurrence of marks can be suppressed as much as possible, and have completed the present invention. 0.03 ≦ | △ Ra | ≦ 0.6 (1) 5 ≦ | △ Tg | ≦ 42 (2) The center line average roughness Ra and the glass transition temperature Tg, which are the calculation criteria of the above equation, are as follows. Is a value measured by the following method. (Center line average roughness Ra) The center line average roughness was measured with a surface roughness profile measuring device [manufactured by Tokyo Seimitsu Co., Ltd.]. The measurement conditions at this time are as follows. Measurement length: 25.4 mm Cut-off: 0.8 mm (glass transition temperature Tg) Heat flux type differential calorimeter “SSC5
200 DSC 220 "[trade name: manufactured by Seiko Electronics Industry Co., Ltd.] under the following conditions. Sample amount: about 10 mg Heating rate: 10 ° C./min Heating range: −50 to 200 ° C. Standard substance: Alumina Sample container: made of aluminum, sealed atmosphere: nitrogen gas, 30 ml / min Cooling medium: liquid nitrogen Next, the reason for limiting the numerical range in each of the above equations will be described. First, if the value of | △ Ra | exceeds 0.6 (μm), the roughness difference between the two coated surfaces increases, and even if the action of the coating film is improved by adjusting the glass transition temperature Tg, It is inevitable that irregularities on the non-decorative painted surface will be transferred to the decorative painted surface at the time of coil winding and lamination of the cut plate later, and as a result, it becomes impossible to prevent the generation of pressure marks. When the value of | △ Ra | is less than 0.03 (μm), the effect of pressure mark resistance can be obtained, but the surface roughness of the decorative surface coating film and the non-decorative surface coating film are almost the same. Therefore, the decorative coating film and the non-decorative coating film are blocked during coil winding or lamination of the cut plate after coating, and the surface appearance after peeling is poor. The surface roughness of the decorative coating film and the non-decorative coating film varies depending on the concentration of the pigment in the coating film, and the surface roughness (gloss) varies depending on the user's request. Line average roughness Ra
Is about 0.1 to 0.7 μm. On the other hand, if the value of | ΔTg | exceeds 42 (° C.), the cushion effect of the non-decorative surface coating film cannot be sufficiently obtained, and even if the value of | ΔRa | is appropriately adjusted. Pressure marks cannot be prevented from occurring. Also | △
When the value of Tg | is smaller than 5 (° C.), the effect of pressure mark resistance can be obtained, but the surface hardness of both coating films is almost the same. The surface coating film and the non-decorative surface coating film are blocked, and the appearance after peeling is poor. It is necessary that the precoated metal sheet has good scratch resistance and workability as required properties. To improve both of these properties, the glass transition temperature Tg of the decorative coating film is generally required. It is about 20 to 40 ° C. In addition, painting on non-decorative surfaces is generally called a service coat, and coating performance is not required as much as on decorative surfaces.
Therefore, the glass transition temperature Tg of the non-decorative surface coating film is suitably about 40 to 70 ° C. Thus, according to the present invention, it is possible to improve the characteristics itself of the decorative coating film and the non-decorative coating film to enhance the resistance to pressure marks, and it is not necessary to use a protective film or the like as in the prior art. In addition, it is not necessary to perform a heat treatment or the like in the middle of the processing, and it is possible to avoid the problem of quality deterioration due to the pressure mark. The metal sheet used in the present invention is not particularly limited. In addition to the most common cold-rolled steel sheet, hot-dip galvanized steel sheet, electro-galvanized steel sheet, galvannealed steel sheet, copper-plated steel sheet, tin The present invention can be applied to all kinds of plated steel sheets such as plated steel sheets, alloy steel sheets such as stainless steel, and non-ferrous metal sheets such as aluminum sheets and copper sheets. From the viewpoint of improving the adhesion between the coating film and the original plate, it is also effective to perform a chemical conversion treatment such as a phosphate treatment or a chromate treatment. There is no particular limitation on the paint used for the precoat coating, and all known precoat paints such as polyester paints, epoxy paints, polyamide paints, and polyurethane paints can be appropriately selected and used. Hereinafter, the present invention will be described in detail with reference to examples. However, the following examples do not limit the present invention, and all changes and implementations without departing from the spirit of the preceding and the following are possible. It falls within the technical scope of the invention. EXAMPLE As a base material for a precoated metal sheet used in the present example, a thickness: 0.6 mm and a zinc adhesion amount: 45 g / m
^Two hot-dip galvanized steel sheets were used. First, after the steel sheet is subjected to chromate treatment (Cr adhesion amount: 40 g / m ² ), assuming a decorative surface coating, a polyester coating is used for both the primer coat and the top coat, and a melamine resin is used as a curing agent in the coating of the top coat. Was added. As a matting agent, silica having a particle size of 3 to 5 μm is 0 to 10% by weight.
Coating with 2 coats and 2 bake (2 coats and 2 baking) coatings with different surface roughness (center line average roughness Ra) and glass transition temperature Tg of 25 ° C (corresponding to a decorative surface coating) ) Was prepared. At this time, the above-mentioned polyester-based paint (without adding a matting agent) was used, and the amount of the melamine-based resin was changed so that the glass transition temperature of the coating film was 35 ° C., 50 ° C.
A precoated steel sheet at 70 ° C. was prepared. Further, while changing the base resin in the polyester-based paint, the particle size: 3
Pre-coated steel sheets having various surface roughness and glass transition temperature Tg of coating film were prepared by adding 0 to 10% by weight of silica of ５5 μm. The one to which these decorative coatings are applied is referred to as a painted plate A (decorative surface). On the other hand, assuming a non-painted surface, a polyester paint containing a certain amount of a coloring pigment and a rust-preventive pigment is applied to the same hot-dip galvanized steel sheet (that has been subjected to chromate treatment) as described above. To obtain a coated plate B. At this time, by changing the kind of the base resin, the amount of the melamine resin (curing agent) added in the polyester-based paint, or the amount of the matting agent having a particle size of 3 to 5 μm, the non-decorative surface coating is performed. Film surface roughness and glass transition temperature T
g was varied. Next, the obtained painted plate A and painted plate B were
A paint film assuming a decorative paint surface (decorative paint film) and a paint film assuming a non-decorative paint surface (non-decorative paint film) are overlapped so as to be in contact with each other. Temperature: 40 ° C., pressure: 100 kg / cm A heat press test was performed under the conditions of ² for 24 hours in a pressurized state. After this test, the coated plate A and the coated plate B were peeled off, and a coating film (a coating film equivalent to a decorative surface) was visually observed on the coated plate A to check whether or not a pressure mark was generated. ：: No pressure mark was generated (pass) ×: Pressure mark was generated (failed) At the same time, the presence / absence of the occurrence of a glocking phenomenon was also examined. Those that did not peel off were evaluated as having gloking (x: failed), and those that peeled off easily were evaluated as no blocking (good: pass). Table 1 shows the results. [Table 1] As is clear from Table 1, those satisfying the requirements specified in the present invention (Experiments Nos. 1 to 11)
In each case, no generation of a pressure mark was observed, and no blocking phenomenon was observed. In contrast, Comparative Examples lacking any of the requirements specified in the present invention (Nos. 12 to 16)
It can be seen that pressure marks are generated and that a blocking phenomenon appears. The precoated metal sheet of the present invention is constituted as described above, and can be obtained by adjusting the composition of the coating film. After such adjustment is made, the adjustment can be made steady. Pre-coated metal plate can be manufactured under certain conditions, so that cost and labor are increased as in the case of using a conventional protective film, and there is no need to perform heat treatment during the processing process, which leads to cost increase and productivity It can be manufactured without lowering, and even if it is pressed during coil winding after coating or stacking of cutting boards, pressure mark does not occur and it has excellent pressure mark resistance, so the original Beautiful luster can be maintained. Therefore, in the fields of household electric appliances and indoor or outdoor equipment, there is no need for troublesome measures such as a measure for restoring the glossiness by heating the coating film, and the effect can be obtained with good economical efficiency.

Continuation of front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C23C 30/00

Claims (1)

(1) A precoated metal sheet having a decorative coating on one side of a metal plate and a non-decorative coating on the other side of the metal plate. The absolute value of the difference between the average roughness Ra (μm) and the center line average roughness Ra (μm) of the non-decorative surface coating film is |
ΔRa | (μm), and the glass transition temperature Tg (° C.) of the decorative coating film and the glass transition temperature Tg of the non-decorative coating film
When the absolute value of the difference in (° C.) is | △ Tg | (° C.), these satisfy the following expressions (1) and (2), respectively. Board. 0.03 ≦ | △ Ra | ≦ 0.6 (1) 5 ≦ | △ Tg | ≦ 42 (2)