Patent Application
20070289874
The following provides an explanation of preferred embodiments of the present invention with reference to the drawings.
By repeating this procedure, the anodic oxidized porous alumina having a tapered Shape can be obtained. The number of times the procedure is repeated is preferably two or more, more preferably 3 or more, and most preferably 5 or more. Increasing the number of times the procedure is repeated makes it possible to obtain a smoother tapered shape. Pores having various tap shapes can be formed by adjusting the duration of anodic oxidation and the duration of pore diameter enlargement treatment, thereby making it possible to design the optimum change in refractive index according to the period and pore depth.
In the present invention, oxalic acid, sulfuric acid, phosphoric acid, and the like can be used for the electrolyte of anodic oxidation. Among these, oxalic acid and sulfuric acid are preferable for obtaining a pore period of 50 to 400 nm to be able to prevent reflection in the visible light range.
In the case of using oxalic acid for the electrolyte, the concentration of the electrolyte is preferably 0.7 M or less. If the concentration is higher than 0.7 M, the current value becomes excessively high which may result in roughening of the surface. On the other band, when the concentration is too low, the speed of anodic oxidation decrease, so the concentration of the electrolyte is preferably 0.01 to 0.6 M.
The temperature of the electrolyte is preferably 60° C. or lower, and more preferably 45° C. or lower. If the temperature of the electrolyte is higher than 60° C., the phenomenon referred to as “scorching” occurs, which may damage the structure or melt the surface, and cause a disturbance in the regularity. On the other hand, when the temperature of the electrolyte is too low, the speed of anodic oxidation decreases, so the temperature of the electrolyte is preferably 10° C. or higher.
In addition, porous alumina having highly regular pores having a period of about 100 mn can be obtained by carrying out anodic oxidation when the formation voltage is 30 to 60 V, preferably 35 to 45 V, and more preferably 39 to 41 V. If the formation voltage is above or below this range, regularity tends to decrease, and pores having pore diameter and pore period larger than the wavelength of visible light may be obtained.
In the case of using sulfuric acid for the electrolyte, the concentration of the electrolyte is preferably 0.7 M or less. If the concentration is higher than 0.7 M, the current value becomes excessively large, so the surface may become coarsely. On the other hand, when the concentration of the electrolyte is too low, the speed of anodic oxidation decreases, so the concentration of the electrolyte is preferably 0.2 to 0.6 M.
The temperature of the electrolyte is preferably 30° C. or lower, and more preferably 20 C. or lower. If the temperature of the electrolyte is higher than 30° C., the phenomenon preferred to as “scorching” occurs, which may damage the structure or melt the surface, and cause a disturbance in the regularity. On the other hand, when the temperature of the electrolyte is too low, the speed of anodic oxidation decreases, so the temperature of the electrolyte is preferably 0° C. or higher,
Highly regular pores having a period of about 63 nm can be obtained by can out anodic oxidation when the formation voltage is 20 to 30 V, preferably 23 to 28 V, and more preferably 24 to 26 V. If the formation voltage is above or below this range, regularity tends to decrease, and pores having pore diameter and pore period larger than the wavelength of visible light may be obtained.
In the case of using phosphoric acid for the electrolyte, highly regular pores having a period of about 300 nm can be obtained by caring out anodic oxidation when the formation voltage is preferably 185 to 210 V, more preferably 190 to 200 V, and further more preferably 194 to 196 V.
A non-reflective structure having projections on the surface thereof can be obtained by using the anodic oxidized porous alumina having a tapered shape formed in this manner as a mold, transferring the structure to polymer molding material 1 (by, for example, transferring by filling a polymer into a mold) as shown in
In the case of using the anodic oxidized porous alumina having tapered pores for the mold, in addition to a method which uses the anodic oxidized porous alumina directly, a novel mold of the same shape, namely a stamper for producing an anti-reflective film, can be obtained from a material such as metal by using the anodic oxidized porous alumina as a mold as shown in
In the present invention, as shown in
In the present invention, as shown in
The following provides a more detailed explanation of the present invention based on examples thereof.
Anodic oxidation was carried out on an aluminum sheet of 99.990% purity for 50 seconds at a temperature of an electrolyte of 17° C., formation voltage of 40 V, and using 0.3 M oxalic acid for the electrolyte. Subsequently, pore diameter enlargement treatment was carried out by immersing for 5 minutes in 2% by weight phosphoric acid at 30° C. This procedure was repeated five times to obtain anodic oxidized porous alumina having tapered pores having a period of 100 nm, pore diameter opening of 80 nm, bottom of 25 nm, and pore depth of 300 nm.
After filling the pores with methyl methacrylate monomer containing benzoyl peroxide of 5% by weight as a polymerization initiator, the monomer was polymerized by irradiating with ultraviolet light. Following polymerization, the polymer layer was separated from the mold to obtain polymethyl methacrylate resin having an arrangement of projections on the surface thereof. As a result of measuring the reflectance of the resulting polymer film, reflectance was confirmed to have decreased.
Anodic oxidation was carried out on an aluminum sheet similar to that of Example 1 for 6 seconds at a temperature of an electrolyte of 17° C., formation voltage of 25 V and using 0.3 M sulfuric acid for the electrolyte. Subsequently, pore diameter enlargement treatment was carried out by immersing for 3 minutes in 10% by weight phosphoric acid at 30° C. After repeating this procedure five times, anodic oxidation was carried out for an additional 6 seconds to obtain anodic oxidized porous alumina having tapered pores having a period of 63 nm, pore diameter opening of 55 nm, bottom of 20 nm, and pore depth of 170 nm. Subsequently, reflectance was confirmed to have decreased as a result of trusferring the structure to a polymethyl metbacrylate resin in the same manner as Example 1.
After carrying out anodic oxidation on an aluminum sheet in the same manner as Example 1 for 2 hours at a temperature of an electrolyte of 17° C., formation voltage of 40 V and using 0.3 M oxalic acid for the electrolyte, the porous alumina layer was selectively dissolved and removed by a mixed solution of phosphoric acid and chromic acid. Subsequently, anodic oxidation and pore diameter enlargement treatment were repeated under the same conditions as Example 1 to obtain anodic oxidized porous alumina having tapered pores in which the pores were arranged with high regularity. Subsequently, reflectance was confirmed to have decreased as a result of tansferring the structure to a polymethyl methacrylate resin using the same procedure as Example 1.
Reflectance was confirmed to have decreased by forming anodic oxidized porous alumina having tapered pores using the same method as Example 1, followed by transferring to a polycarbonate resin using the porous alumina as a mold.
After forming anodic oxidized porous alumina having tapered pores using the same method as Example 1, polymethyl methacrylate was filled into the anodic oxidized porous alumina to obtain a negative mold of the porous alumina. Subsequently, a treatment was carried out on the surface of the polymethyl methacrylate to provide electrical conductivity followed by filling with nickel by plating. The polymethacrylate negative mold was then dissolved and removed to obtain a nickel positive mold having the same structure as the anodic oxidized porous alumina serving as the master mold. The nickel positive mold was then pressed onto heated polymethyl methacrylate to obtain a low-reflective film having an arrangement of projections on the surface thereof.
A mold having projections arranged at a period of 200 nm was pressed onto an aluminum sheet to obtain an arrangement of depressions corresponding to the projections in the surface of the aluminum sheet. Subsequently, anodic oxidation, at a formation voltage of 80 V and using 0.05 M oxalic acid for the electrolyte, and pore diameter enlargement treatment, were repeated five times to obtain the anodic oxidized porous alumina having tapered pores having a period of 200 nm, pore opening of 160 nm, bottom of 50 nm and pore depth of 500 nm. Subsequently, reflectance was confirmed to have decreased as a result of transferring the structure to polymethyl methacrylate resin using the same procedure as Example 1.
The present invention can be applied to all applications requiring the formation of an anti-reflective film, and is particularly suitable for various information equipment display devices requiring improved visibility.
While preferred embodiments of the invention have been described and illustrated above, it should be understood that these are exemplary of the invention and are not to be considered as Limiting. Additions, omissions, substitutions, and other modifications can be made without departing from the spirit or scope of the present invention- Accordingly, the invention is not to be considered as being limited by the foregoing description, and is only limited by the scope of the appended claims.
