JP2009237002A - Light reflecting aluminum material - Google Patents

Abstract

The present invention provides a light-reflective aluminum material that is used for an inexpensive and highly reflective reflector, a building material that requires a design with high luster, an electronic device casing, and the like, and has excellent durability.
An aluminum substrate containing 99.5% by weight or more of Al, a transparent second coating layer formed on at least one surface thereof and having a film thickness of 500 to 3000 nm and a refractive index N2, and A transparent first coating layer formed on the two coating layers and having a film thickness of 1000 to 10000 nm and a refractive index N1, wherein N2 and N1 are 0.7 <N2 / N1 <1.3 Aluminum material.
[Selection] Figure 1

Description

  The present invention relates to a light-reflective aluminum material that is used for an inexpensive and highly reflective reflector, a building material that requires a highly lustrous design, an electronic device casing, and the like, and has excellent durability.

  Materials for automotive parts such as reflectors and wheels such as illuminators have a highly glossy reflecting surface on the surface from the viewpoint of regular reflection and design. In order to protect this reflecting surface, conventionally, an aluminum plate was used as a base material, and an anodized film was formed on this surface by anodizing treatment, or an organic coating film was formed on the same surface.

Furthermore, since the adhesion of an organic coating film may be inferior when directly coated on an aluminum plate, a method of coating after anodizing treatment (for example, see Patent Document 1) has been proposed. Also, since the production cost of anodizing treatment is high, a method of forming an inorganic film by applying a silicate-based inorganic paint on the surface of a substrate (see, for example, Patent Document 2) has been proposed.
JP 62-83497 A JP 7-21816 A

  However, when applying only the anodized film, it is necessary to increase the film thickness if priority is given to durability such as weather resistance and corrosion resistance, and to reduce the film thickness if priority is given to reflectivity. There was a problem that I could not. In the case of a thin film of about 1000 to 3000 nm, some visible light in the range of 380 to 780 nm in the range of 380 to 780 nm due to light interference is intensified and some cancels out with a period of about 50 nm. There is also a problem that a phenomenon occurs, light that is qualitatively different from the light source is reflected, and it is not suitable for use as a reflector. In the case where an organic resin is directly coated on an aluminum plate having good light reflectivity, there is a problem that adhesion is poor or light reflectivity is greatly reduced.

  Next, what coated the aluminum plate which gave the anodizing process described in patent document 1 is unclear about the reflectance of an aluminum base material, and the film thickness of a coating film. Furthermore, although this coating film is simply an acrylic melamine resin and has some weather resistance and corrosion resistance, in actual use, the coating film may be discolored over time due to sunlight or ultraviolet rays from a lamp, resulting in a decrease in reflectivity. Due to the lack of dirtiness, the reflection surface gradually became dirty over time, resulting in a problem in durability such as a decrease in reflectivity.

  In addition, in the case where an inorganic film is formed by applying a silicate-based inorganic paint on the surface of a substrate described in Patent Document 2, a film is formed when weather resistance and corrosion resistance are given priority as in the case of applying only an anodized film. When the thickness is increased and the reflectivity is prioritized, there is a problem that it is necessary to reduce the film thickness and it is impossible to achieve both durability and reflectivity.

Further, in Patent Document 2, although the durability is not sufficient, the film thickness is set to 2000 to 3000 nm in consideration of the balance with reflectivity (the middle of the film thickness range defined in claim 1 of the same document). In the same manner as when an anodized film is applied, light that is qualitatively different from the light source is reflected due to light interference, which is not suitable as a reflector.
As described above, there is a strong demand for a light-reflective aluminum material excellent in light reflectivity and durability.

  For these reasons, the present inventors use a specific highly reflective aluminum base material, and the film formed on the base material has a two-layer structure of the second film layer and the first film layer, and each film By setting the thickness and the refractive index within a specific range, it was found that durability and reflectivity can be highly compatible without reducing reflectivity, and the present invention has been completed.

  The present invention is the aluminum substrate containing 99.5% by weight or more of Al, and the transparent second coating layer having a film thickness of 500 to 3000 nm and a refractive index N2 formed on at least one surface thereof. And a transparent first film layer formed on the second film layer and having a film thickness of 1000 to 10000 nm and a refractive index N1, wherein N2 and N1 are 0.7 <N2 / N1 <1.3. A light-reflective aluminum material characterized in that it is present.

  The light reflecting aluminum according to claim 2, wherein the surface on which the second coating layer of the aluminum substrate is formed has a center line average roughness Ra of 0.1 μm or less and an unevenness average interval Sm of 10 μm or more. A material was used.

  The present invention is the organic resin film according to claim 3, wherein the first film layer is an organic resin film layer containing at least one selected from the group consisting of an acrylic resin, a silicon polyester resin, and a fluorine resin. The layer contains at least one of an ultraviolet absorber and colloidal silica having an average particle size of 200 nm or less, the content of the ultraviolet absorber is 0.1 to 10 parts by mass with respect to 100 parts by mass of the resin, and the average particle size is 200 nm. Content of the following colloidal silica was 0.1-20 mass parts with respect to 100 mass parts of resin.

  In the present invention, the second coating layer is an inorganic coating layer containing at least one selected from the group consisting of aluminum oxide, zirconium oxide, sodium silicate, potassium silicate, and colloidal silica.

  The light-reflective aluminum material according to the present invention is a regular reflective material excellent in durability such as weather resistance and corrosion resistance. It is suitably used as a housing material for recent digital home appliances.

A. Aluminum Base In the present invention, a high purity aluminum material having an Al content of 99.5% by weight or more is used as the aluminum base. When the Al content is less than 99.5% by weight, the absorption of visible light by impurities increases, so that even if a high degree of surface smoothness is achieved, the regular reflectance is poor.

  As parameters representing the degree of surface roughness of the aluminum substrate, centerline average roughness Ra and unevenness average interval Sm defined by JIS B 0601 are adopted. Ra needs to be 0.1 μm or less and Sm should be 10 μm or more. When Ra exceeds 0.1 μm or Sm is less than 10 μm, the diffuse reflectivity increases, and as a result, the regular reflectivity is inferior.

  Conventionally, as a parameter of surface roughness, only Ra is often used as an index. As a result of detailed studies by the present inventors, it has been found that Sm, which is a parameter representing the average interval between the irregularities on the surface, is also an important index. To make such a smooth surface with Ra and Sm as an index, reduce the roll surface roughness when cold rolling to product thickness, use a small rolling roll with a hemispherical contact area, etc. It is necessary to appropriately select bright rolling conditions. Since a coating layer having a two-layer structure, which will be described later, is formed on at least one surface of the aluminum substrate, at least the surface on which the coating layer is formed needs to have such a surface roughness surface.

B. Pretreatment Next, before forming the second film layer on the surface of the aluminum substrate, a degreasing treatment is performed as a pretreatment according to a conventional method. An oxide layer by natural oxidation is usually formed on the surface of the aluminum substrate. Such an oxide layer is often contaminated with residual rolling lubricating oil, foreign matter pushed in by rolling, and the like. Such residual lubricating oil and foreign matters are washed and removed with an alkaline degreasing agent. Further, when a strong alkaline degreasing agent is used, a cleaning deposit is often formed, and it is also necessary to remove this by post-treatment with an acid. In the present invention, specular reflectivity is very important, and therefore the degreasing conditions are appropriately selected within a range that does not reduce specular reflectivity.

C. Two-layer coating layer
C-1. It is an extremely difficult problem to satisfy both the refractive index and the film thickness of the light-reflective aluminum material with sufficient durability and reflectivity in the second coating layer and the first coating layer . This is because it is necessary to increase the film thickness in order to improve durability, and it is necessary to reduce the film thickness in order to improve or not reduce reflectivity. The inventors use an aluminum material having a specific purity, provide a two-layered coating layer composed of a second coating layer and a first coating layer, and the refractive index of the second coating layer and the first coating layer. By setting the film thickness in a specific range, this difficult problem has been solved.

  The first coating layer is a transparent durable coating, but when only the first coating layer having a film thickness in the range of 1000 to 10000 nm as defined in claim 1 is directly formed on the aluminum substrate, it is reflective. It has been found that not only the performance decreases but also the durability is inferior. Moreover, when only the 2nd film layer which has the film thickness in the range of 500-3000 nm prescribed | regulated to Claim 1 was formed directly on the aluminum base material, it became clear that it was inferior to durability.

  The inventors consider that the increase / decrease in reflectivity is related to the phase of reflected light, and by reducing the reflectivity by defining the refractive index ratio in both layers in relation to the film thickness with two coating layers. It has been found that can be significantly suppressed. And it discovered that the film thickness which can exhibit such a reflectance reduction inhibitory effect was in the range of the film thickness from which durability was acquired, and came to complete this invention simultaneously. The manifestation mechanism of the effect of suppressing the reflectance reduction has not been fully elucidated, but a second film layer is provided between the first film layer, which is a durable film, and an aluminum plate having a specific purity. By setting the refractive index ratio and the film thickness range to a specific range, durability can be ensured without reducing reflectivity.

Regarding the refractive index ratio in both coating layers for obtaining the above-described reflectance reduction suppressing effect, assuming that the refractive index of the first coating layer is N1 and the refractive index of the second coating layer is N2, 0.7 <N2 / N1 < 1.3. When N2 / N1 is less than 0.7 and exceeds 1.3, the difference in refractive index between the first film layer and the second film layer becomes large, and as a result, the influence of light interference in both film layers is increased. It turned out to be prominent. That is, among visible rays in the range of 380 to 780 nm, there is a phenomenon in which some of the visible light intensifies and some cancels out with a period of about several tens of nm, and light that is qualitatively different from the light source is reflected. Is done. As a result, not only the reflectance decreases as a whole, but also light reflection (wavelength selectivity of reflected light) that is qualitatively different from the light source based on interference action occurs, which is not suitable as a light reflecting material. By setting 0.7 <N2 / N1 <1.3, it is possible to suppress the wavelength selectivity of such reflected light while achieving the effect of reducing the reflectance.
The graph of FIG. 2 illustrates the wavelength dependence of the regular reflectance, and shows examples of Example 3 and Comparative Example 2 described later. In Example 3, the regular reflectance gradually decreases from the wavelength of 400 nm to the high wavelength side, and in Comparative Example 2, the regular reflectance decreases from the wavelength of 400 nm to the high wavelength side while undulating.

  Next, the film thickness of the second coating layer needs to be 500 to 3000 nm. When this film thickness is less than 500 nm, the effect of reducing the decrease in reflectivity achieved by providing the first coating layer is small and the reflectivity is decreased. Although the mechanism of manifesting the effect of suppressing the reduction in reflectance has not been fully elucidated, it has been found that the film thickness of the second coating layer appears only when the wavelength is not less than the wavelength of visible light. When this film thickness exceeds 3000 nm, the influence of light absorption inside the second coating layer is increased, and the reflectivity is lowered.

  Furthermore, the film thickness of the first coating layer needs to be 1000 to 10,000 nm. When this film thickness is less than 1000 nm, the role of the protective film is not sufficiently exhibited and the durability is inferior. In addition, the wavelength selectivity of the reflected light increases due to the relationship with the second coating layer, and light that is qualitatively different from the light source is reflected, which is not suitable as a reflector. When the film thickness exceeds 10,000 nm, the influence of light absorption by the first coating layer is increased, and the reflectivity is lowered.

C-2. Formation of the second coating layer After the pretreatment, a transparent second coating layer is formed on at least one surface of the aluminum substrate surface. The second coating layer is preferably an inorganic coating layer containing at least one selected from the group consisting of aluminum oxide, zirconium oxide, sodium silicate, potassium silicate, and colloidal silica.

  The second coating layer containing aluminum oxide is formed on the aluminum substrate by, for example, an anodizing process using a sulfuric acid bath according to a conventional method. Moreover, an alumina sol, a zirconia sol, etc. are apply | coated on an aluminum base material by the dip coating method, a doctor blade method, etc., The 2nd film layer containing an aluminum oxide and a zirconium oxide can be formed by heat-processing this. Further, by applying an aqueous solution of sodium silicate, potassium silicate, and colloidal silica on an aluminum base material and baking and curing it, these silicate-based second coating layers can be formed.

C-3. Formation of the first coating layer The first coating layer formed on the surface of the second coating layer is preferably an organic resin coating layer that is transparent and has weather resistance. It is a resin having high transparency and excellent weather resistance, and an organic resin film layer composed of at least one selected from the group consisting of acrylic resins, silicon polyester resins and fluorine resins. Is preferred. In a non-transparent organic resin film layer to which a color pigment or dye is added, reflectivity is reduced due to light absorption or diffuse reflection by the color pigment or dye in the film layer. Furthermore, in the organic resin film layer having no weather resistance, the film layer discolors with time during actual use, so that the reflectivity is lowered and the durability is inferior. The discoloration in this case includes yellowing due to deterioration of the coating layer and white turbidity due to decomposition of the resin component and roughening of the surface.

  When the first film layer is an organic resin film made of at least one selected from the group consisting of an acrylic resin, a silicon polyester resin and a fluorine resin, an ultraviolet absorber and an average are added to the organic resin film layer. You may contain at least any one of colloidal silica with a particle size of 200 nm or less.

  Ultraviolet rays are high energy rays, and the first and second films and the aluminum substrate are deteriorated by the ultraviolet rays. In order to prevent such deterioration due to ultraviolet rays, an ultraviolet absorber is contained in the first film to suppress the deterioration effect due to ultraviolet rays. When the ultraviolet absorber is contained, 0.1 to 10 parts by mass of the ultraviolet absorber is contained with respect to 100 parts by mass of the resin. When the ultraviolet absorber is less than 0.1 part by mass, the organic resin film layer is easily deteriorated with ultraviolet rays over time and easily yellowed, and the reflectivity is lowered and the durability is inferior. When the ultraviolet absorber exceeds 10 parts by mass, the absorption of light by the ultraviolet absorber becomes remarkable and the reflectivity is lowered. Although it does not specifically limit as a ultraviolet absorber, A benzotriazole type, a benzophenone type, a benzoate type etc. are used. In addition, the ultraviolet absorber is an additive type that is not incorporated in the form bonded to the resin skeleton just by being added to the resin, and a reactive type that is incorporated in the form bonded to the resin skeleton as a monomer during resin synthesis. Either can be used. The reactive type is more preferable because it exhibits stable performance.

  By imparting antifouling properties to the first coating layer, it is possible to reduce the deterioration of reflectivity over time due to dirt adhesion during actual use based on the difference in use environment, and it becomes possible to improve the reliability of durability. . Such imparting of antifouling property can be achieved by including colloidal silica in the first coating layer. Colloidal silica hardens the first coating film and reduces the burying of dirt in the first coating, and the adhering contaminants can be easily washed away with rainwater etc. due to the hydrophilicity of the first coating. Antifouling property is demonstrated.

  The average particle diameter of the colloidal silica to be contained is 200 nm or less. When the average particle diameter exceeds 200 nm, the average particle diameter exceeds the wavelength of visible light (380 to 780 nm), and the visible light is diffusely reflected or absorbed by colloidal silica. As a result, the transparency of the first film is lowered and the reflectivity is reduced.

  The amount of colloidal silica added is preferably 0.1 to 20 parts by mass with respect to 100 parts by mass of the resin. When the addition amount is less than 0.1 parts by mass with respect to 100 parts by mass of the resin, the addition amount is too small and the antifouling effect is insufficient. When the addition amount exceeds 20 parts by mass with respect to 100 parts by mass of the resin, the effect of improving the antifouling property due to the increase in the addition amount is small and uneconomical. Moreover, the viscosity increase of the coating material for 1st membrane | film | coat becomes remarkable, and problems, such as a coating property falling, generate | occur | produce.

Hereinafter, the present invention will be described in detail with reference to examples.
Examples 1-24 and Comparative Examples 1-10
As the aluminum substrate, an aluminum plate (material: JIS A1080, plate thickness 0.5 mm) whose surface was mirror-finished to have the surface roughness shown in Table 1 by conventional bright rolling was used. This aluminum plate was degreased and then a second coating layer was formed under the conditions shown in Table 1. Further, a first coating layer was further formed on the second coating layer under the conditions shown in Table 1.

Degreasing was performed using a commercially available aluminum degreasing agent. After degreasing, the second film layer was formed as follows. After the degreasing treatment, the aluminum oxide coating layer as the second coating layer was anodized with a sulfuric acid bath by a conventional method. A 15% by weight sulfuric acid aqueous solution is used as the electrolyte, and a sulfuric acid anodic oxide film having a predetermined thickness is formed under conditions of an electrolysis temperature of 15 ° C., a current density of 0.5 to 3 A / dm ² , and an electrolysis time of 1 to 10 minutes. did.

  The zirconium oxide coating layer as the second coating layer was formed by applying a zirconia sol by a dip coating method and heat treating at 300 ° C. after degreasing treatment. The silicate-based coating layers of sodium silicate, potassium silicate, and colloidal silica as the second coating layer are applied by applying respective aqueous solutions (concentration of 30 to 50% by weight) and baking and curing at 180 to 250 ° C. Formed.

  The first coating layer is coated with a paint (using naphtha as a solvent) made of any of resin, ultraviolet absorber, and colloidal silica with a roll coater under the conditions shown in Table 1, and PMT (maximum plate temperature) 200 It was formed by baking at ~ 300 ° C. The resin content in the coating solution was 20 to 40% by weight of the total solution amount.

  In Comparative Example 1, the second coating layer was not formed, and in Comparative Example 2, the first coating layer was not formed. In Comparative Example 9, titania sol was applied by a dip coating method and heat treated at 300 to 400 ° C. to form a second coating layer. In Comparative Example 10, the first coating layer was formed by applying titania sol on the second coating layer and heat-treating it.

  A cross-sectional view of the light-reflective aluminum material sample produced as described above is schematically shown in FIG. In FIG. 1, 1 is a first coating layer, 2 is a second coating layer, and 3 is an aluminum substrate.

  About the produced light reflective aluminum material sample, regular reflection property, durability, and antifouling property were evaluated by the following test method.

(Regular reflection)
For specular reflection, a spectrocolorimeter CM-2600d manufactured by Konica Minolta Co., Ltd. was used, and the SCI (wavelength 550 nm was received under the conditions of D65 light source -2 ° field of view as the measurement conditions and 8 ° received diffused light illumination as the optical conditions. Regular reflection light included) reflectance and SCE (regular reflection light removal) reflectance were measured and evaluated by regular reflectance (SCI-SCE). In addition, regular reflectance (SCI-SCE) made 60% or more the pass.

(durability)
Durability was evaluated by a salt spray test and an accelerated weathering test. The salt spray test was performed according to JISZ2371, and the accelerated weather resistance test was performed according to JISH4001. The test time was 1000 hours for all tests. The sample appearance after the salt spray test and after the accelerated weathering test was evaluated according to the following criteria.
○: No abnormality ○ △: Discoloration, corrosion, and swelling are slight and good △: Discoloration, corrosion, and swelling are available, but ×: Any of discoloration, corrosion, or swelling is large and cannot be used.
○, ○ △ and △ were accepted, and x was rejected.

(Anti-fouling property)
For antifouling properties, the appearance after the carbon contamination test was evaluated according to the following criteria. Here, in the carbon contamination test, a 5% carbon black aqueous solution is applied to one surface of a sample and dried at 80 ° C. for 2 hours. Thereafter, the coated surface was wiped with a soft cloth under running water, and the extent of carbon black stains remaining on the surface was visually evaluated. The evaluation criteria are as follows.
Y: No abnormality
○ △: Slightly left behind △: Slightly left behind ×: Greatly left behind ○ ○, ○ △ and △ were accepted, and x was rejected.

  The test results obtained are shown in Table 1.

  As is apparent from the results shown in Table 1, in Examples 1 to 18, specular reflection and durability resistance are good, and in Examples 19 to 24, in addition to specular reflection and durability, antifouling properties are also good. there were.

On the other hand, in Comparative Examples 1 to 10, either regular reflection or durability was inferior.
In Comparative Example 1, since the second coating layer was not formed, the regular reflectivity and durability were inferior.
In the comparative example 2, since the 1st membrane | film | coat layer was not formed, the salt spray test result was inferior among durability.
In Comparative Example 3, since the film thickness of the first film layer was too thick and the film thickness of the second film layer was too thin, the regular reflection property was inferior.
In Comparative Example 4, specular reflectivity was inferior because the surface roughness of the aluminum substrate was large.
In the comparative example 5, since the film thickness of the 2nd film layer was too thin, the regular reflection property was inferior.
In Comparative Example 6, specular reflectivity was inferior because the thickness of the second coating layer was too thick.
In Comparative Example 7, since the thickness of the first coating layer was too thin, the salt spray test result was inferior among the durability.
In Comparative Example 8, regular reflection was poor because the thickness of the first coating layer was too thick.
In Comparative Example 9, since N2 / N1 was too large, the reflected light was qualitatively different from the light source based on the interference action, and the regular reflection at 550 nm was inferior.
In Comparative Example 10, since N2 / N1 was too small, the reflected light was qualitatively different from the light source based on the interference action, and the regular reflection at 550 nm was inferior.
In Comparative Example 11, the regular reflectance was inferior because the purity of the aluminum base material was less than 99.5% by weight.
In Comparative Example 12, the specular reflectivity was inferior because it was a comparison with Example 3 and the thickness of the second coating layer was too thick.
In Comparative Example 13, since the second coating layer was not formed in comparison with Example 3, the specular reflection and durability were inferior.
In Comparative Example 14, since N2 / N1 was too large, the reflected light was qualitatively different from the light source based on the interference action, and the regular reflection at 550 nm was inferior.

  The film layer formed on the aluminum substrate of the specified purity has a two-layer structure consisting of the second film layer and the first film layer, and the thickness and refractive index of each film are set within a specific range, thereby providing good reflectivity. And can achieve durability.

FIG. 1 is a cross-sectional view of a light reflective aluminum material according to the present invention. FIG. 2 is a graph illustrating the wavelength dependence of regular reflectance.

Explanation of symbols

1 ... 1st film layer 2 ... 2nd film layer 3 ... Aluminum base

Claims (4)

  An aluminum base material containing 99.5% by weight or more of Al, a transparent second coating layer formed on at least one surface thereof and having a film thickness of 500 to 3000 nm and a refractive index N2, and the second coating layer And a transparent first coating layer having a thickness of 1000 to 10,000 nm and a refractive index N1, wherein N2 and N1 are 0.7 <N2 / N1 <1.3. Aluminum material.   The light-reflective aluminum material according to claim 1, wherein the surface of the aluminum substrate on which the second coating layer is formed has a center line average roughness Ra of 0.1 µm or less and an unevenness average interval Sm of 10 µm or more.   The first film layer is an organic resin film layer containing at least one selected from the group consisting of an acrylic resin, a silicon polyester resin, and a fluorine resin, and an ultraviolet absorber and a colloidal having an average particle size of 200 nm or less It contains at least one of silica, the ultraviolet absorber content is 0.1 to 10 parts by mass with respect to 100 parts by mass of the resin, and the content of colloidal silica having an average particle size of 200 nm or less is 100 parts by mass of the resin. The light-reflective aluminum material of Claim 1 or 2 which is 0.1-20 mass parts with respect to.   4. The inorganic coating layer according to claim 1, wherein the second coating layer is an inorganic coating layer containing at least one selected from the group consisting of aluminum oxide, zirconium oxide, sodium silicate, potassium silicate, and colloidal silica. The light reflective aluminum material according to one item.

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