JPS649186B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a mold for manufacturing a multifocal Fresnel lens used for a rear projection screen or the like.

In order to enable bright and uniform viewing of the screen, rear projection screens are generally provided with concentric Fresnel lenses that converge incident light from a light source onto a viewing position. However, such a concentric Fresnel lens converges light uniformly in the horizontal and vertical directions, which may cause problems when observing a screen or the like. FIGS. 1 and 2 are explanatory diagrams showing desirable transmission states of a screen equipped with such a Fresnel lens. That is, in the horizontal direction, the light from the light source L is expanded as much as possible by the Fresnel lens F of the screen S, as shown in Figure 1, and conversely, in the vertical direction, it is limited as shown in Figure 2. Ideally, it should be configured so that it spreads within a defined range.

From this point of view, a multifocal Fresnel lens with different focal lengths in the vertical and horizontal directions was developed in 1983.
This method is already known as Publication No. 144347 and Japanese Utility Model Application No. 124837/1983. However, the above invention does not disclose a specific method for manufacturing such a Fresnel lens. Such a multifocal Fresnel lens can be manufactured by cutting, but the cutting method is complicated, the productivity is low, and the cost is high.

In view of this situation, the present invention attempts to easily manufacture a mold for manufacturing a multifocal Fresnel lens by skillfully utilizing the shrinkage phenomenon caused by heating of a stretched thermoplastic synthetic resin. That is, the gist of the present invention is to form a lens surface by cutting a Fresnel lens into a thermoplastic synthetic resin plate manufactured with different stretching ratios in the vertical and horizontal directions, and then to A method for manufacturing a mold for a multifocal Fresnel lens, comprising heating a synthetic resin plate to form a multifocal Fresnel lens, and transferring the obtained multifocal Fresnel lens surface to produce a mold. .

The present invention will be explained below with reference to the drawing of the embodiment shown in FIG.

FIGS. 3A to 3F are explanatory diagrams showing the manufacturing process of the present invention, and the process will be explained in the following order. FIG. 3A shows a base plate 1A of a thermoplastic synthetic resin plate, and the material used is a thermoplastic synthetic resin such as acrylic resin, polycarbonate resin, or vinyl chloride resin. Figure 3B shows this original plate 1A in one axial direction 2
The stretched plate 1B is produced by heating and stretching, and is stretched only in the vertical direction without stretching in the horizontal direction. It is known that when such a stretched plate 1B is reheated, the stretched portion shrinks and returns to almost its original shape.
The stretched plate 1B of the present invention is not limited to such a uniaxially stretched plate 1B, but may be a biaxially stretched plate with different longitudinal and horizontal stretching ratios.

FIG. 3C shows a Fresnel lens plate 1C in which a concentric Fresnel lens surface is formed on the stretched plate 1B produced as described above. Formation of such a Fresnel lens surface is performed by cutting, but it can be performed in the same manner as when manufacturing a general Fresnel lens. FIG. 3D shows a multifocal Fresnel lens plate 1D obtained by heat-treating the Fresnel lens plate 1C described above. When heated again in this manner, the stretched portion of the Fresnel lens surface is shrunk as shown in FIG. In other words, if the stretching direction 2 of the uniaxially stretched sheet is the vertical direction H of the screen, the shape of the Fresnel lens does not change in the horizontal direction V, so the vertical direction H
In this case, the inclination of the lens is larger and a finer pitch elliptical Fresnel lens is created, resulting in a Fresnel lens whose focal length is shorter in the vertical direction as shown in the figure. Of course, even when a biaxially stretched plate with different stretching ratios in the vertical and horizontal directions is used, it can be shrunk by heating again to form a multifocal Fresnel lens surface.

Figures E and F explain the process of manufacturing a mold using the multifocal Fresnel lens plate 1D obtained as described above as a kind of matrix. The state in which a metal vapor deposition film 3 such as silver is formed is shown. Then, the metal vapor deposited film 3 is electroplated as a conductor to make it thicker, removed from the multifocal Fresnel lens plate 1D, and bonded to a base material to obtain a mold M as shown in FIG. 3F. This mold M is manufactured by a method called electroforming, but there is also a method of pouring a low-melting metal onto the multifocal Fresnel lens surface, solidifying it, removing it, and applying metal plating to the lens surface. can also be adopted.

When manufacturing a multifocal Fresnel lens using the mold M obtained as described above, this mold M
Therefore, it can be easily manufactured using a synthetic resin material such as the above-mentioned acrylic resin by a method such as a hot press method, an injection molding method, or a cast polymerization method. In addition, in the present invention, since the multifocal Fresnel lens plate 1D used as a matrix is manufactured by utilizing shrinkage caused by reheating during stretching, the stretching magnification is determined in accordance with the predetermined vertical and horizontal focal lengths. It's good to do that. Shrinking the Fresnel lens surface once cut in this way reduces the pitch of the lens, which is advantageous from the standpoint of preventing moiré, but generally the minimum pitch that can be cut into a mold by cutting is 0.1 mm. However, using the mold of the present invention has the advantage that the pitch of the Fresnel lens can be reduced.

Since the present invention has the configuration as described in detail above, it has the advantage that a mold for producing a multifocal Fresnel lens can be easily manufactured by skillfully utilizing the properties of thermoplastic synthetic resin.

[Brief explanation of drawings]

FIGS. 1 and 2 are explanatory diagrams showing a desirable transmission state of a screen equipped with a Fresnel lens, and FIGS. 3A to 3F are explanatory diagrams of the manufacturing process of the present invention. 1A... Original plate, 1B... Stretched plate, 1C... Fresnel lens plate, 1D... Multifocal Fresnel lens plate, 3... Metal vapor deposited film, M... Mold.

Claims (1)

[Claims] 1 A Fresnel lens is cut into a thermoplastic synthetic resin plate manufactured with different stretching ratios in the longitudinal and lateral directions to form a lens surface, and then this thermoplastic synthetic resin plate is heat-treated to form a multilayer film. 1. A method for manufacturing a mold for a multifocal Fresnel lens, which comprises forming a focal Fresnel lens and manufacturing a mold by transferring the obtained multifocal Fresnel lens surface.