1. Field of the Invention
This invention relates to a minutely working method of and apparatus for forming a minute working pattern on a surface, and precisely manufacturing a lens sheet optical element such as a lenticular lens or a Fresnel lens, an orifice plate for an ink jet head, etc.
2. Related Background Art
A transmission type screen used in a projection television set generally comprises a Fresnel lens sheet functioning to condense incident light and disposed on a light source side, and a lenticular lens sheet disposed on an observer side to diffuse the incident light in a horizontal direction. Also, a contrivance for heightening contrast as by forming a black light absorbing port is provided between lenticular lenses in the lenticular lens sheet.
In recent years, however, the higher minuteness of the quality of clear vision, high vision, etc. has been advanced, and high resolution has also been required in the transmission type screen as described above. Accordingly, higher minuteness is also required of the aforementioned lens sheet, and with the higher minuteness of this lens sheet, the distance between lenses is shortened, and a thin lens sheet element is desired in order to shorten the optical path thereof. However, with the higher minuteness, the delicate minute working shape of the lens sheet such as the uniformity of the thickness thereof greatly affects the quality of image.
Also, for an orifice plate for an ink jet head, liquid crystal polymer, polysulfone or the like excellent in oil resistance and heat resistance is generally used as an ink applying port with oil resistance and also heat resistance in a thermal ink jet printer taken into account. Further, a contrivance such as controlling the surface energy of resin film is provided to improve the detachability of ink liquid.
In recent years, however, the resolution of the ink jet printer has been more and more improved and in the above-mentioned orifice plate or an orifice formed on the plate, it has become required to form a very minute shape highly accurately.
As methods of manufacturing an optical element such as a lens sheet, a semiconductor element or an orifice plate there are known, for example, the following methods.
(1) An extrusion heat melting molding method of subjecting a T die to minute working, and forming a continuous minute pattern in a taking-over direction, as described in Japanese Patent Application Laid-open No. 5-127258 and Japanese Patent Application Laid-open No. 9-043732, and a method of forming and transferring a continuous minute pattern on a take-up roll itself at that time.
(2) A casting method called the cast method of applying a predetermined amount of resin soluble in an organic solvent or the like in a molten state or the precursor or ungulvanized material thereof itself in a dissolved state to the inner surface or the outer surface of a mold, subjecting it to a desolvent process, and further heat-treating it as required, and thereafter peeling it.
(3) A photopolymer method using active energy ray curing type resin comprising ultraviolet ray curing type resin, as described in Japanese Patent Application Laid-open No. 8-328264.
(4) A heating press method of again pressing and heating a primary worked article such as a sheet or film of transparent resin to thereby form a minute pattern.
(5) A method of protecting only a necessary portion such as a resin plate, and removing an unnecessary portion by a solvent such as an acid or alkali or physical energy such as a laser beam, as described in Japanese Patent Application Laid-open No. 10-076668.
However, to make an optical element of higher minuteness, thin wall and uniform film thickness or an orifice plate of a convex type rectangular parallelepiped required by the use of the above-described minutely working method, the following various problems are encountered.
In the extrusion heat melting molding method of item (1) above, a continuous pattern of the same shape can be formed in the taking-over direction of the film or sheet, but a pattern in the non-taking-over direction cannot be formed. Also, it is difficult take up the extruded film or sheet by a roll machine or the like and therefore, to produce film or a sheet continuously, a very long take-over line is required and as the result, the cost is increased. Further, the uneven shape is crushed when the film or sheet passes the pressing roll.
Also, in the casting method and the photopolymer method of items (2) and (3) above, liquid resin is used and therefore, to obtain a sheet or film of a uniform film thickness, there are difficult problems such as the control of the density of the solution, the adjustment of drying atmosphere, the control of the entrainment of air bubbles, the solvent processing cost in the drying step and the fine adjustment of the application intensity of the active energy such as ultraviolet rays, and as the result, the degree of freedom lacks remarkably.
Further, the heating press method of item (4) above is a technique of reworking a primary molded article and is generally often used, but the heating press machine is very bulky and expensive and therefore, as the result, what is manufactured by the heating press method becomes expensive. Also, when in the heating press method, a sheet of a large area of 50 inches or greater is to be pressed, it is very difficult to uniformly maintain the temperature distribution of the entire surface, and the sheet becomes warped or the lens shape formed by a partial difference in the degree of crystallization may partly differ.
Also, in the method of item (5) removing only the unnecessary portion, when for example, a convex minute pattern is to be formed, most of it is an unnecessary portion and is the object to be removed, and this is irrational in both of production and cost.