JP2007030384A - Clear coat stainless steel plate preventing interference pattern - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a clear coat stainless steel plate having a fine surface preventing an interference pattern even if the clear coating film is thin. <P>SOLUTION: A clear coating film 2 having a multi-layered constitution of a lower layer 2d and a upper layer 2u is provided on a stainless steel plate the surface of which is smoothed by BA finishing, mirror polishing and the like. Light intensities of reflective lights L<SB>1</SB>, L<SB>2</SB>proceeding on the same direction from the surfaces of the stainless steel plate 1 and the clear coat film 2 are diminished by setting a refractive index of the clear coat film of the upper layer 2u lower than that of the clear coating film of the lower layer 2d so that a interference pattern caused by the interference of light is prevented. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a clear-coated stainless steel sheet used for exterior materials, interior materials, cover materials, etc. utilizing a glossy surface unique to stainless steel.

Stainless steel sheet has a beautiful surface in addition to corrosion resistance and durability, so it is used in a wide range of fields such as interior building materials, exterior building materials, vehicle outer plates, kitchen equipment, and home appliances. However, it is a drawback of stainless steel sheets that fingerprint marks adhere during handling and remain easily. It is also a drawback that it is easy to get wrinkled and noticeable during processing or construction.
A stainless steel plate is also used in which an oxide film is formed on a mirror-finished stainless steel plate and various colors are developed depending on the thickness of the oxide film. Fingerprints and wrinkles are particularly noticeable on the colored stainless steel plate.

  Therefore, in applications such as housings, interior materials, and cover materials for home appliances where the appearance is important, careful attention is paid to maintaining a beautiful surface state until the construction is completed, and a protective film is also applied. Means. Cover the stainless steel plate with a clear coating of polyester resin, polymer polyester resin, acrylic resin, acrylic silicone resin, epoxy resin, urethane resin, fluororesin, etc. Is also adopted.

A clear-coated stainless steel plate that has improved fingerprint resistance and reduced visibility of the attached fingerprint by a clear coating film is provided as a pre-coated steel plate that is processed into a product shape by press molding or the like. Clear coated stainless steel sheet can be processed into a product shape without the need to apply processing oil because lubrication is imparted by a clear coating, but a clear coating that is thicker than necessary tends to cause galling and enamel hair during mold forming. The appearance of the processed product is degraded. Defects such as galling and enamel hair greatly reduce the commercial value of colored stainless steel sheets.
A thin coating film is effective for improving the workability. However, when the coating film is thinned, an interference pattern is generated and the appearance is impaired. It is also a drawback of thinning that the strength of the coating film itself decreases as the film thickness decreases and it becomes easy to peel off.

The present applicant has clarified that when a clear coating film is formed discontinuously on the surface of a stainless steel plate, the occurrence of an interference pattern is suppressed, and a clear coated stainless steel plate with excellent fingerprint resistance and lubricity can be obtained ( Patent Documents 1 to 3).
Japanese Patent Publication No.7-37105 Japanese Patent No. 2512397 JP 2004-143494 A

  A discontinuous clear coating film is formed by applying a paint having a relatively high viscosity. The discontinuous coating is effective in preventing the occurrence of interference patterns, but mottled patterns appear due to the uneven thickness of the coating, or galling or enamel hair occurs during press molding, bending, etc. May occur in paint film. Moreover, since the surface of the underlying stainless steel plate is exposed through the discontinuous coating film, rust may occur from the fingerprint attached to the substrate surface as time elapses even though it is difficult to see the attached fingerprint at the initial stage. The adhesion of contaminants other than fingerprints may also be a starting point for rust and crevice corrosion.

  The interference pattern seen in the clear-coated stainless steel sheet is caused by an optical path difference generated between the reflected light from the surface of the transparent coating and the reflected light that is transmitted through the transparent film and reflected by the surface of the base steel. In order to prevent the appearance of interference patterns, it is conceivable to reduce the intensity of specular reflection light by completely flattening the clear coating, matting the clear coating, or roughening the coating original plate (stainless steel plate).

The completely flattened clear coating eliminates the undulation of the clear coating, which is one of the causes of color development in various colors, and aims to make the interference color monochromatic. However, as a practical problem, it is difficult to completely flatten the clear coating film, and it is industrially impossible to control the film thickness to the extent that no light interference occurs, that is, nanometer order.
In the clear coating film in which the matting agent is dispersed, the diffuse reflection of the transmitted light is promoted by the matting agent particles, and the intensity of the specular reflection light is weakened. However, the clear coating film has a color tone unique to the matting agent. Is easily disturbed. The roughening of the original plate is contrary to the use of the metallic luster that is an advantage of the stainless steel plate, and there is a limit to the suppression of the interference pattern when the roughening is performed so as not to impair the glossy surface.

If an attempt is made to suppress the expression of interference patterns by promoting diffuse reflection in the clear coating film, the original beautiful surface of the clear coated stainless steel sheet is likely to be damaged. Therefore, the present inventors investigated and examined various methods for suppressing the light interference effect by reducing the amount of reflected light from the clear coating surface in addition to the reflected light from the stainless steel plate surface. As a result, it was found that the refractive index of the clear coating has a great influence on the appearance of interference patterns.
The present invention is based on this knowledge, lowering the refractive index of the clear coating surface layer to increase the amount of light incident on the clear coating, while reducing the amount of reflected light from the clear coating surface, An object of the present invention is to provide a clear-coated stainless steel sheet that weakens the interference effect of light and suppresses the expression of interference patterns.

The clear-coated stainless steel plate of the present invention uses a stainless steel plate having a metallic gloss surface as an original plate, and a plurality of clear coating films are laminated on the stainless steel plate surface. The clear coating film which becomes the outermost layer has a lower refractive index than the clear coating film on the stainless steel plate side.
For example, when forming a clear coating with a two-layer structure consisting of a lower clear coating and an upper clear coating, acrylic, polyester, urethane, polyolefin, fluorine, epoxy, silicone, acrylic silicone, acetic acid The lower and upper clear films are formed by a combination of vinyl and chloroprene organic resins. It is preferable that the refractive index of the upper clear coating film is 1.50 or less and a difference of 0.02 or more is given to the refractive index of the upper clear coating film.

The generation mechanism of the interference pattern seen in the clear coated stainless steel sheet can be explained as follows.
When light is applied to a clear-coated stainless steel plate provided with a clear coating 2 on the surface of the stainless steel plate 1, light L ₁ that passes through the clear coating 2 and reflects on the surface of the stainless steel plate 1 is reflected on the surface of the clear coating 2 the incident light L _in the light L ₂ which is separated (FIG. 1). An optical path difference of ΔL (= 2t sin θ, θ: incident angle of the incident angle, t: film thickness of the clear coating film) occurs between the reflected lights L ₁ and L ₂ , and the stronger the optical path difference ΔL is, the closer to the light wavelength λ. Interference color occurs. The optical path difference ΔL close to the wavelength of light means that when the optical path difference ΔL = nλ, n is a small integer and the clear coating film 2 is thin. In the thin clear coating 2, the undulation of the film thickness becomes relatively large, the influence of the undulation on the optical path difference ΔL is emphasized, and as a result, interference patterns having various color tones are generated.

Assuming the mechanism of generating interference patterns, it is considered effective to reduce the amount of reflected light L ₁ and L ₂ , but the dispersion of matting agent and the roughening of the stainless steel plate 1 are clear coating as described above. It is not preferable for the original surface properties of the stainless steel plate. So, in this invention, the clear coating film 2 is made into a multilayer structure, and the refractive index of the surface side clear coating film is lowered compared with the clear coating film on the stainless steel plate side. For example, in a clear-coated stainless steel sheet (FIG. 2) in which the clear coating 2 has a two-layer structure of a lower layer 2d and an upper layer 2u (FIG. 2), the refractive index r _u of the upper clear coating 2u is higher than the refractive index r _d of the lower clear coating 2d. Is adjusted low.

Low refractive index r _u, the proportion of the incident light L _in is transmitted to the clear coating film 2 is large, which means that the small proportion of reflected as reflected light L ₂ at the surface of the clear coating film 2. Further, upper layer coating 2u / by irregularities in the lower coat layer 2d interface 3, diffuse reflection L ₃ at the interface 3 of the incident light L _in transmitted to the upper layer clearcoats 2u, reflected light L ₁ from the stainless steel plate 1 surface The diffuse reflection L _{4 at} the interface 3 is promoted when is diffused to the outside. The diffuse reflections L ₃ and L ₄ reduce the amount of reflected light L ₁ + L ₂ diffused to the outside. Therefore, compared with the single-layer clear coating film 2 (FIG. 1), both the reflected lights L ₁ and L ₂ become weak, and the interference pattern is suppressed.

Embodiment

  In the clear-coated stainless steel plate of the present invention, a stainless steel plate that has been BA-finished or mirror-polished is used as a coating original plate in order to utilize the surface properties with metallic luster. BA finishes and mirror polishing materials are materials with extremely small surface roughness and high specular reflection light compared to No.4, hairline, No.2DR, etc. In some cases, interference patterns tend to appear. For this reason, the effect of suppressing the interference action of light by the multilayering of the clear coating becomes remarkable. Quantitatively speaking, it is effective to form a clear coating on a stainless steel plate having a gloss mirror surface of 400 or more at 60 degrees. In addition, a stainless steel plate in which an interference color is developed by forming a transparent or translucent oxide film to such an extent that the metallic luster is not impaired can be used as the coating original plate.

The stainless steel sheet is subjected to pre-coating treatments such as degreasing, pickling, and surface adjustment in accordance with a conventional method, and then the coating film adhesion is improved by providing a chemical film by chromate treatment or chromium-free treatment as necessary. A plurality of types of clear paint is applied to the stainless steel plate, and the process of heating and drying is repeated to form a clear coating film having a multilayer structure with a small refractive index on the surface layer side.
For the clear paint, a combination selected from the following table is used in consideration of the weather resistance, coating film hardness, bending workability, transparency, etc. in addition to the refractive index.

  The lower clear coating film is formed from a coating material such as polymer polyester / melamine (No. 6), FEVE / isocyanate (No. 4), etc., which has good bending workability. In order to protect the surface of the stainless steel plate, it is preferably formed with a film thickness of 2 μm or more. However, when the film thickness exceeds 10 μm, defects such as galling and enamel hair tend to occur during processing. An antirust pigment, a coloring pigment, a metallic pigment, etc. can also be mix | blended with a lower clear coating film to such an extent that transparency is not impaired.

  The upper clear coating film has a lower refractive index than the lower clear coating film, and is made of paint such as FEVE / melamine (No. 2) or silica sol-added acrylic / isocyanate (No. 3) when coating hardness is required. Be filmed. The refractive index of the upper clear coating film is preferably 1.5 or less, and a difference of 0.02 or more is preferably given to the refractive index of the upper clear coating film. While the refractive index is 1.5 or less, the amount of light transmitted to the upper clear coating increases, while the effect of reducing the amount of light reflected by the clear coating is observed. Further, by appropriately managing the difference in refractive index between the upper layer and the lower layer, diffuse reflection at the interface is promoted, and the amount of regular reflection on the stainless steel plate surface is reduced. When the thickness of the upper clear coating film is 2 μm or more, the interference pattern resulting from the thinning of the clear coating film can be suppressed almost completely, but even if it exceeds 5 μm, an effect commensurate with the thick film cannot be obtained. The upper clear coating film is also effective in eliminating undulation that tends to occur in the lower clear coating film.

A SUS340 stainless steel plate with BA finish was used as the original coating. This stainless steel plate had a surface roughness Ra: 180 mm and a 60 ° specular gloss of 530 according to the measuring method specified in JIS K5600.
A chromium-based chemical conversion treatment solution is applied with a bar coater to a coated original plate that has been surface-cleaned through degreasing, water washing, surface conditioning, and drying steps, and dried at 100 ° C., so that the total Cr equivalent coating amount: 40 mg / m ² chromate A film was formed.
Subsequently, the clear paint of Table 1 was apply | coated and the lower layer and the upper layer clear coating film were formed by heating at 215-250 degreeC for 30 to 60 second. The film thickness of both the lower layer and the upper layer clear coating film was set to 5 μm, and the 2-coat 2-bake method was adopted.

The appearance of the obtained clear painted stainless steel sheet was investigated by the following test.
[Appearance test 1]
Visual observation of the surface of the coating film under sunlight, x indicates a test piece in which a remarkable interference pattern was observed, Δ indicates a suppression effect but still detects an interference pattern, and the interference pattern is suppressed and hardly detected The test piece was evaluated as ○, and the interference pattern generation was subjected to sensory evaluation.
[Appearance test 2]
The surface of the test piece was irradiated with a three-wavelength fluorescent lamp in which the interference pattern was most likely to occur, and the presence or absence of the interference pattern was examined by visual observation based on the same criteria as in the appearance test 1.

As seen in the test results in Table 2, in Test Nos. 1 to 9 provided with a clear coating film having a lower refractive index in the upper layer than in the lower layer, almost no interference pattern was observed in both appearance tests 1 and 2. . On the other hand, in Test Nos. 11 to 13 in which a clear coating film having a higher refractive index than the lower layer was provided, there was no effect of suppressing the interference pattern, and in particular, in the appearance test 2, a clear interference pattern was observed. Even in test No. 10 in which the lower and upper clear films were formed with the same paint, an interference pattern was generated.
In addition, a remarkable interference pattern was observed in the clear coated stainless steel plate provided with the clear coating film as a single layer. Although the interference pattern tended to weaken as the clear coating became thicker, the interference pattern was still observed even when the film thickness was 15 μm or more.

  As explained above, the clear coating film formed on the surface of the stainless steel plate has a multilayer structure, and when the surface side clear coating film has a low refractive index compared to the stainless steel plate side, the expression of the interference pattern is suppressed, A clear-coated stainless steel sheet utilizing the original metallic luster of a stainless steel sheet can be obtained. This clear-coated stainless steel sheet is a material that is useful in a wide range of fields, such as exterior materials, interior materials, exterior materials, and vehicle exterior plates that utilize beautiful surfaces.

Illustration of interference pattern appearing on clear painted stainless steel sheet Explanatory drawing that interference pattern is suppressed by clear coating film of multilayer structure

Explanation of symbols

1: Stainless steel plate 2: Clear coating film 2d: lower clearcoats 2u: upper clearcoats 3: the interface L _in the lower layer clear coating film / upper clearcoats: incident light L _1, L _2: the reflected light L _3, L ₄ : Diffuse reflection ΔL: Optical path difference t: Clear coating film thickness θ: Recess angle of incident angle

Claims (3)

  An interference pattern characterized in that multiple layers of clear coating are laminated on a stainless steel plate with a metallic glossy surface, and the refractive index of the clear coating is high on the stainless steel plate side and low on the surface layer side. Suppressed clear painted stainless steel sheet.   The clear coating has a two-layer structure of a lower clear coating and an upper clear coating, the refractive index of the upper clear coating is 1.50 or less, and the refractive index difference between the upper clear coating and the lower clear coating is 0. The clear-coated stainless steel sheet according to claim 1, which is 02 or more.   The clear-coated stainless steel sheet according to claim 1 or 2, wherein the stainless steel sheet has a 60-degree metallic luster of 400 or more.

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