JPS6116605B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a non-glare Fresnel lens in which the surface of the groove wall facing the center of the Fresnel lens is made into a light-scattering surface to prevent glare.

Fresnel lenses are used in a wide variety of fields because they can be mass-produced as large-area, thin lenses by pressing. One specific example where Fresnel lenses are used is in overhead projectors (hereinafter referred to as OHPs). In other words, in OHP, in order to use the light from the light source effectively, a large-diameter Fresnel lens is used to collect the light, and a transparent document to be projected is placed on the document placement surface near the Fresnel lens surface, so that the light is focused and narrowed. By arranging an imaging lens in the bent optical path, the projected image of the transparent original can be focused on the screen. The OHP user (lecturer) is located near the OHP and provides explanations while looking at the manuscript on the OHP and sometimes writing on the manuscript placed on the mounting surface. One drawback of OHP is that unnecessary light (rays not directed toward the imaging lens) reflected or refracted from the wall of the condensing Fresnel lens is extremely dazzling to the user.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for manufacturing a Fresnel lens in which unnecessary light is not generated due to reflection or refraction on groove walls.

The present invention is achieved by making the groove wall facing the center of the Fresnel lens a light-scattering rough surface,
Specifically, the groove wall that does not face the center of the press mold for manufacturing Fresnel lenses (the wall facing the groove wall facing the center of the Fresnel lens) is roughened, and this press mold This is achieved by hot-pressing a heat-softening transparent resin plate. A method for roughening one groove wall of the press mold will be described in detail later.

The present invention will be explained in detail below using the drawings.

Figure 1 shows an example of an OHP optical system. In FIG. 1, 1 is the outer wall of the OHP main body, 2 is a light source, and 3 and 4 are Fresnel lenses. Two Fresnel lenses are usually stacked one on top of the other to improve light concentration. 5 is a transparent original, 6 is an imaging lens, 7 is a reflection mirror, and 8 is a screen. Unnecessary light that is not used for projection is reflected or refracted from the groove walls of the Fresnel lens, as shown by arrows 9 and 10, and this reaches the user's eyes, causing a sensation of glare.

FIG. 2 is a diagram showing the principle of the generation of reflected light or refracted light from the groove walls of a Fresnel lens. In the figure, 13 is a substantially vertical groove wall facing the center of the lens. A light ray 14 obliquely incident on the back surface of the lens from the light source is first refracted at the back surface 11 of the lens and reaches the groove wall 12. After being refracted here, the light ray reaches the groove wall 13 where it is partially reflected (indicated by 16) and partially refracted (indicated by 15). Both light rays 15 and 16 travel at an angle that allows them to enter the eyes of the OHP user, causing glare.
When the eye is located in the traveling direction of the light ray 15, reflected light corresponding to 16 travels toward the eye from the groove wall on the reflective side with respect to the center of the lens. The light rays 17 incident on another path do not reach the groove wall 13 and proceed in a direction that does not cause glare. Generally, most of the light from the light source enters the groove wall of the lens from directions 14 and 17. Therefore, if the surface of the groove wall 13 is roughened and made light scattering, the light 1
4 is scattered by this surface, so the amount of light reaching the user's eyes is drastically reduced, reducing glare.

3 to 5 are explanatory diagrams of another method of manufacturing a Fresnel lens.

As shown in FIG. 3, a thin layer 19 of photoresist is first provided on the entire surface of the press mold 18, then a photomask 20 is placed over the entire surface of the press mold 18, and ultraviolet rays are uniformly irradiated. The pattern of the photomask is chosen so that resist remains only on the groove walls 22 not facing the center of the press mold. That is, if the photoresist is of negative type, a photomask is used in which the region corresponding to the groove wall facing the center of the press mold is opaque, as shown in FIG. After uniform UV exposure, the photoresist is developed, leaving the resist only on the groove walls 22 not facing the center of the press die, as shown in FIG. Next, the surface of the press is etched with an etchant that dissolves the metal constituting the press mold, and the resist is removed. As shown in FIG.
Only the groove walls 23 are etched, and a roughened groove wall 23 is obtained. A desired Fresnel lens can be obtained by hot-pressing a transparent thermoplastic resin plate 24 using the press mold thus obtained as shown in FIG.

Example 1 A nickel press type photoresist (positive type AZ-1350 manufactured by Shipley. Co., Ltd.) was coated with a thickness of about 1
Apply evenly with micron.

A separately prepared photomask (a pattern in which the groove walls that do not face the center of the press mold are black so that they are not exposed) is layered with resist, and the entire surface is uniformly irradiated with ultraviolet rays, followed by 0.5% water. It was developed with an aqueous sodium oxide solution. The trench wall facing the center was exposed. Next, the exposed nickel surface was roughened by etching with 1N nitric acid. Finally, the remaining resist was dissolved and removed with acetone, and then a new press mold was obtained in the same manner as in Example 1. Using this press mold, an acrylic resin plate was similarly hot pressed to obtain a Fresnel lens with almost no glare.

[Brief explanation of the drawing]

Fig. 1 is a side view schematically showing the optical system of a general overhead projector, and Fig. 2 is a partially enlarged cross-sectional view of a Fresnel lens to explain the principle of reflection and refraction of light by the Fresnel lens. ,
3 to 6 are cross-sectional views of a Fresnel lens press for explaining embodiments of the present invention, 18...
...Press mold, 19...Photoresist, 24...
...Transparent heat-softening resin board.

Claims (1)

[Claims] 1. (i) uniformly applying a photoresist to a press mold for a Fresnel lens; (ii) exposing and exposing the photoresist layer so that the resist remains only on the groove walls that do not face the center; (iii) etching and roughening the exposed groove walls facing the center; (iv) removing the remaining resist; and (v) molding the heat-softening resin in the press mold thus obtained. A method for manufacturing a Fresnel lens, characterized by hot pressing a plate.