JPH06250003A - Production of fresnel lens - Google Patents

Abstract

PURPOSE:To provide a production method of Fresnel lens by which a light- absorbing layer can be accurately formed on the ineffective plane of the lens even when the prism pitch is small. CONSTITUTION:A Fresnel lens having several prisms 14 continuously formed on at least one surface of a transparent plate 12 is produced by this method. Each prism has an effective plane 16 with a specified angle and an ineffective plane 18 which does not substantially contribute to transmission of light. A light-absorbing layer 20 is formed on the ineffective plane. The production method includes steps of applying the light-absorbing layer 20 on the Fresnel lens with several prisms 14 formed, coating the Fresnel lens 10 with a photosensitive resist, exposing, and developing. In this method, the light-absorbing layer 20 is formed only on the ineffective plane 18 utilizing the difference of light quantity between on the effective plane 16 and the ineffective plane 18 when the resist is exposed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to various optical devices, and more particularly to a Fresnel lens used as a condenser lens of an audible head projector or a screen of a rear projection type display device.

[0002]

2. Description of the Related Art A Fresnel lens is one in which a plurality of prisms are continuously formed on at least one surface of a transparent plate, for example, in concentric circles, and have the same light-collecting characteristics as one convex lens, for example. Fresnel lenses are widely applied to optical devices because they can make the optical system thinner and lighter.

For example, in a rear projection display device using liquid crystal, image light spatially modulated by a liquid crystal panel is magnified and projected on a rear screen by a projection lens, and a viewer views the screen from the opposite side of the projection lens. To see. Such a transmissive screen generally has a structure in which a Fresnel lens, a diffusion plate, and a lenticular lens are stacked. Of these, the Fresnel lens consists of prisms arranged concentrically, and the divergent light projected from the projection lens is made to enter the diffuser plate as a light beam that is parallel to or converging with the optical axis. Is to determine. At this time, the viewing angles set are the same in both the horizontal and vertical directions, but generally the horizontal viewing angle needs to be wider than the vertical viewing angle.
Therefore, the lenticular lens is used to diffuse the light emitted from the diffuser plate again in the horizontal direction, thereby expanding the degree of diffusion in the horizontal direction.

In a Fresnel lens, for example, a plurality of prisms formed in a concentric shape each have two surfaces with different inclinations. Usually, one surface is formed with a predetermined inclination and is an effective surface that bends light in a predetermined direction,
The other surface is an ineffective surface that is formed substantially parallel to the optical axis and does not substantially contribute to the transmission of light. In the Fresnel lens, there is a problem that the light is reflected and refracted by the ineffective surface and travels toward the adjacent effective surface to become noise light.

Fresnel lenses are usually made by molding transparent plastic in a mold. Conventionally, in order to prevent noise light on the ineffective surface, it has been proposed to make the ineffective surface portion of the mold a minute rough surface, and thus use the ineffective surface as a rough surface to scatter light. Also, in order to prevent noise light on the ineffective surface, it is possible to absorb the noise light by roughening the ineffective surface into a satin-like texture by a method such as chemical treatment or sand blowing, and printing a black paint on it. Proposed.

[0006]

In order to prevent noise light on the ineffective surface, light is scattered by using the ineffective surface as a rough surface, and the scattered light becomes stray light, and a Fresnel lens is used in a display device. May cause a decrease in contrast. Further, although a mold having a rough invalid surface can be manufactured when the pitch of each prism is rough, if the pitch is made fine to improve the resolution, it becomes difficult to form such a invalid surface. Also, black paint can be printed on the ineffective surface when the pitch of each prism is sufficiently coarser than the alignment accuracy of the printing, but as with the case above, the pitch is finer for reasons such as improved resolution. If this happens, the alignment becomes difficult and it may not be possible to accurately print the black paint on the invalid surface.

An object of the present invention is to provide a manufacturing method of a Fresnel lens which can surely form a light absorbing layer on an ineffective surface even when the pitch of the prism is small.

[0008]

In the method of manufacturing a Fresnel lens according to the present invention, a plurality of prisms 14 are continuously formed on at least one surface of a transparent plate 12, and each prism is provided with an effective surface 16 having a predetermined inclination. And a non-effective surface 18 that does not substantially contribute to the transmission of light, and a light-absorbing layer or a light-shielding layer (hereinafter referred to as a light-absorbing layer) 20 is provided on the non-effective surface. Exposing the resist, including a step of applying a light absorption layer to the Fresnel lens having a plurality of prisms, a step of applying a photosensitive resist to the Fresnel lens having a plurality of prisms, and exposing and developing At this time, the light absorption layer is provided only on the ineffective surface by utilizing the difference in the light irradiation amount between the effective surface and the ineffective surface of each prism.

[0009]

In the above manufacturing method, the step of applying the light absorption layer can be performed simultaneously with the step of applying the resist. Alternatively, the step of applying the light absorbing layer can be performed before the step of applying the resist. Alternatively, the step of applying the light absorbing layer can be performed after the step of applying the resist. The light absorption layer is applied to the entire surface of the Fresnel lens, and the light absorption layer is provided only on the ineffective surface by utilizing the difference in the light irradiation amount between the effective surface and the ineffective surface of each prism when exposing the resist. That is, the light absorbing layer is not provided on the effective surface.

The simplest method of utilizing the difference in light irradiation amount between the effective surface and the ineffective surface is to use the difference in inclination angle between the effective surface and the ineffective surface. For example, the effective surface forms an angle of about 45 degrees or more with respect to the optical axis of the Fresnel lens, and the ineffective surface is substantially parallel to the optical axis of the Fresnel lens or 2 to 2.
It makes 3 angles. Therefore, when exposing the resist to ultraviolet rays in parallel with the optical axis of the Fresnel lens, the ultraviolet rays strongly strike the effective surface and hardly strike the ineffective surface. Therefore, when the resist is developed, the degree of development differs between the effective surface and the ineffective surface, so that the light absorbing layer can be provided only on the ineffective surface.

[0011]

8 and 9 show a Fresnel lens 10 according to the present invention, in which a plurality of prisms 14 are continuously formed on one surface of a transparent plate 12 in a concentric shape. Each prism 14 has an effective surface 16 provided with a predetermined inclination and an ineffective surface 18 that does not substantially contribute to the transmission of light. A light absorption layer 20 is provided on the ineffective surface 18. The light obliquely incident from the flat surface side of the Fresnel lens 10 is bent so as to be parallel to the optical axis of the Fresnel lens 10 as compared with the time of incidence, as indicated by an arrow L, and the effective surface 1
Emit from 6. A part of the light incident on the flat surface side of the Fresnel lens 10 reaches the ineffective surface 18, and if there is no light absorption layer 20, it is reflected by the ineffective surface 18 and is reflected by the effective surface 1 as indicated by an arrow N.
It is emitted from 6 and becomes noise light. In the present invention, since the light absorption layer 20 is provided, the light reaching the ineffective surface 18 is absorbed by the light absorption layer 20.
And the light absorbing layer 2 which is absorbed by the light and exits from the effective surface 16.
The light emitted from 0 is prevented or reduced.

FIG. 10 is a view showing a rear projection type display device as an application example of the Fresnel lens 10. This rear projection display device includes a light source 50, a liquid crystal panel 52, a projection lens 54, and a screen 56. LCD panel 5
The image light spatially modulated by 2 is enlarged and projected on the screen 56 by the projection lens 54. The screen 56 is the Fresnel lens 1 which is the subject of the present invention.
0, a diffusion plate 58, and a lenticular lens 60 are stacked. Of these, the Fresnel lens 10 determines the viewing angle in the left-right and up-down directions by causing the divergent light projected from the projection lens 54 to enter the diffusion plate 58 as a light beam that is parallel to or converges with the optical axis. At this time, the viewing angles set are the same in both the horizontal and vertical directions, but generally the horizontal viewing angle needs to be wider than the vertical viewing angle. Therefore, the lenticular lens 60 is used to diffuse the light emitted from the diffuser plate 58 again in the horizontal direction, thereby expanding the degree of diffusion in the horizontal direction.

FIG. 1 is a diagram showing a first embodiment of a method for manufacturing a Fresnel lens according to the present invention. At the time point shown in FIG. 1, a Fresnel lens 10 in which a plurality of prisms 14 are continuously formed by molding a transparent acrylic resin plate or the like with a mold not shown is prepared. This also applies to the subsequent examples. Each prism 14 has an effective surface 16 and an ineffective surface 18 as described above. In the present invention, such a Fresnel lens 10 is provided with a light absorbing layer only on the ineffective surface 18 by utilizing the difference in light irradiation amount between the effective surface 16 and the ineffective surface 18 of each prism when exposing the resist. It is characterized by being provided.

In FIG. 1, as shown in FIG.
After ultrasonically cleaning the Fresnel lens 10, a positive resist 30 containing a black paint is applied to the entire prism surface of the Fresnel lens 10 by a spinner. By appropriately selecting the rotation speeds of the resist solution and the spinner, for example, 1
After controlling the film thickness to ˜3 μm and applying the resist 30,
Pre-baking is performed at a predetermined temperature to dry the resist 30. Next, as shown in (B), the resist 30 is exposed. In this case, for example, the effective surface 16 forms an angle of approximately 45 degrees or more with respect to the optical axis of the Fresnel lens 10, and the ineffective surface 18 forms an angle of approximately parallel to 2-3 with respect to the optical axis of the Fresnel lens 10. ing. Therefore, the resist 3
When ultraviolet rays are applied parallel to the optical axis of the Fresnel lens 10 at the time of exposure 0, the ultraviolet rays hit the effective surface 16 strongly and the amount of light hitting the ineffective surface 18 is extremely small. That is, the same exposure as that through the mask is performed by utilizing the difference in the inclination angle between the effective surface 16 and the ineffective surface 18.

Then, the resist 30 is developed as shown in FIG. By controlling the irradiation amount of ultraviolet rays, the resist 30 on the effective surface 16 is dissolved in the developing solution, and the resist 30 on the ineffective surface is not dissolved in the developing solution and remains. The remaining resist 30 contains black paint,
As it is, it becomes the light absorption layer 20. Then, it is washed with pure water or the like. In this way, the light absorption layer 20 can be provided only on the ineffective surface 18.

FIG. 2 is a diagram showing a second embodiment of the present invention. In this embodiment, as shown in (A), the Fresnel lens 10 is ultrasonically cleaned and then the Fresnel lens 10 is cleaned.
Then, a negative resist 32 is applied by a spinner. By appropriately selecting the rotation speeds of the resist solution and the spinner, the film thickness is controlled to, for example, 1 μm, the resist 32 is applied, prebaked at a predetermined temperature, and the resist 32 is dried. Next, as shown in FIG.
2 is exposed. The negative resist 30 exhibits a cross-linking reaction when exposed to light, and is hardly soluble in a developing solution.

Also in this case, when the resist 32 is exposed to ultraviolet light in parallel with the optical axis of the Fresnel lens 10, the ultraviolet light strongly hits the effective surface 16 and the amount of light hitting the ineffective surface 18 is extremely small. Therefore, as shown in (C), when the resist 32 is developed, the resist 32 on the effective surface 16 remains without being dissolved in the developing solution, and the resist 32 on the ineffective surface 18 is dissolved in the developing solution. Then, it is washed with pure water or the like.

Next, as shown in (D), a black paint 34 in which black powder, pigment, etc. are mixed with an adhesive is applied by a spinner. By appropriately selecting the viscosity of the paint and the rotation speed of the spinner, the film thickness is controlled to, for example, 1 μm.
Then, as shown in (E), a resist swelling liquid is applied to swell the resist 32, and as shown in (F), the resist 32 is peeled off by spraying a resist stripping liquid. In this case, the resist 32 remaining on the effective surface 16 is peeled off together with the black paint 34, and the black paint 34 on the invalid surface 18 is not peeled off. In this way, the light absorption layer 20 can be provided only on the ineffective surface 18.

FIG. 3 is a diagram showing a third embodiment of the present invention. In this embodiment, as shown in (A), the Fresnel lens 10 is ultrasonically cleaned and then the Fresnel lens 10 is cleaned.
Then, the dye base material 36 is applied by a spinner. Since the acrylic resin or the like cannot be directly dyed, the dyeing base material 36 is applied first, and the dyeing base material 36 is made of, for example, gelatin, casein, glue, or the like. By appropriately selecting the viscosity of the dyeing base material 36 and the rotation speed of the spinner, the film thickness is controlled to, for example, 1 μm.

Next, a negative resist 32 is applied with a spinner to a film thickness of, for example, 1 μm. After coating, the resist 32 is prebaked at a predetermined temperature to dry the resist 32. Next, as shown in (C), the resist 32 is exposed. Also in this case, when ultraviolet rays are applied in parallel with the optical axis of the Fresnel lens 10 when exposing the resist 32, the ultraviolet rays hit the effective surface 16 strongly and the amount of light hitting the ineffective surface 18 is extremely small. Therefore, as shown in (D), when the resist 32 is developed, the resist 32 on the effective surface 16 is developed.
Of the resist 3 on the ineffective surface 18 remain without being dissolved in the developer.
2 dissolves in the developer. Then, it is washed with pure water or the like.

Here, the dye base material 36 on the ineffective surface 18
Is exposed. Then, as shown in (E), the black dye 38 is applied to the dye base material 36 to form the dye base material 3
Stain # 6. Then, as shown in (F), the resist 32 is stripped and washed, and as shown in (G),
The stainproofing agent 40 is applied so that the dyed base material 36 on the effective surface 16 is not dyed thereafter. In this way, the light absorption layer 20 can be provided only on the ineffective surface 18.

FIG. 4 is a diagram showing a fourth embodiment of the present invention. In this embodiment, as shown in (A), the Fresnel lens 10 is ultrasonically cleaned and then the Fresnel lens 10 is cleaned.
The black paint 40 is applied to the above by a spinner. Next, the positive resist 30 is applied by a spinner to a film thickness of, for example, 1 μm. After coating, the resist 32 is prebaked at a predetermined temperature to dry the resist 32. Next, as shown in (C), the resist 30 is exposed. Also in this case, when ultraviolet rays are applied in parallel with the optical axis of the Fresnel lens 10 during exposure of the resist 30, the ultraviolet rays hit the effective surface 16 strongly,
The amount of light striking the ineffective surface 18 is extremely small.

Then, as shown in FIG. 3D, when the resist 30 is developed, the resist 30 on the effective surface 16 is dissolved in the developing solution, and the black paint 40 thereunder is exposed. The resist 30 on the ineffective surface 18 remains without being dissolved in the developing solution. Therefore, as shown in (E), the black paint 40 on the effective surface 16 is removed with a solution that dissolves the black paint 40 and does not attack the resist 30. then,
As shown in (F), the resist 30 on the invalid surface 18
Is peeled off with a peeling liquid. In this way, the light absorption layer 20 can be provided only on the ineffective surface 18.

5 to 7 are views showing a fifth embodiment of the present invention. This embodiment shows an exposure apparatus after resist coating on the Fresnel lens 10. This example
It can be applied to the exposure process of each of the above embodiments.

The Fresnel lens 10 is supported by the rotary table 70, and the exposure device 72 is arranged obliquely with respect to the Fresnel lens 10 on the rotary table 70. The exposure device 72 includes an ultraviolet light source 74, a condenser lens 76, an emission lens 78, and a slit plate 80.
Including FIG. 6, the hatched portion in FIG. 6 indicates the irradiation area of the Fresnel lens 10 with ultraviolet rays. As shown in FIG. 6 and FIG. 7, the ultraviolet ray is obliquely applied to the portion corresponding to the radius of the Fresnel lens 10 from the outside in the radial direction, hits the ineffective surface 18 of the Fresnel lens 10 at an angle near vertical, and is effective. It is designed to strike the surface 16 at an angle close to parallel. Fresnel lens 10 is a turntable 7
Since it rotates on 0, the irradiation area rotates with respect to the rotary table 70 and covers the entire surface of the rotary table 70. By doing so, contrary to the above-described embodiments, the resist on the ineffective surface 18 is peeled off in the case of a positive type resist, and the resist on the effective surface 16 is peeled off in the case of a negative type resist. Become.

In the present invention, the refractive index of the light absorption layer 20 is preferably the same as or higher than the refractive index of the material of the Fresnel lens 10. When the refractive index of the light absorption layer 20 is the same as the refractive index of the material of the Fresnel lens 10, all the light hitting the ineffective surface 18 is incident on the light absorption layer 20, so that the light absorption effect is maximized. When the refractive index of the light absorption layer 20 is equal to or higher than the refractive index of the material of the Fresnel lens 10, total reflection of light that strikes the ineffective surface 18 is eliminated, and the proportion of light incident on the light absorption layer 20 increases. For example, the refractive index of acrylic resin used as the material of the Fresnel lens 10 is 1.49, and that of polycarbonate is 1.59. On the other hand, the resist is generally a phenolic resin, and its refractive index is 1.6 to
It is around 1.7. When using black paint or black dye, use Fresnel lens 1 with black powder or black pigment adhesive.
The refractive index can be adapted by using the same type of resin as the 0 material. In addition, in the present invention, the light absorption layer 20 can absorb the entire visible light, of course, but the light absorption layer 20 may absorb not only visible light but only a specific wavelength range. Further, the ineffective surface may be a mirror surface or a satin surface.

[0027]

As described above, according to the present invention,
Light enters the invalid surface of the Fresnel lens and is reflected by the invalid surface.
Noise light due to refraction can be significantly reduced, and in a display device or the like using a Fresnel lens, it is effective in reducing ghost images, and display quality can be improved.

[Brief description of drawings]

FIG. 1 is a diagram showing a manufacturing process of a first embodiment of the present invention.

FIG. 2 is a diagram showing a manufacturing process of a second embodiment of the present invention.

FIG. 3 is a diagram showing a manufacturing process of a third embodiment of the present invention.

FIG. 4 is a diagram showing a manufacturing process according to the fourth embodiment of the present invention.

FIG. 5 is a side view showing a fifth embodiment of the present invention.

FIG. 6 is a plan view of the table of FIG.

7 is a partially enlarged sectional view of FIG.

FIG. 8 is a plan view showing a Fresnel lens.

9 is an enlarged cross-sectional view of the Fresnel lens of FIG.

FIG. 10 is a diagram showing a display device using a Fresnel lens.

[Explanation of symbols]

 10 ... Fresnel lens 12 ... Transparent plate 14 ... Prism 16 ... Effective surface 18 ... Invalid surface

Front page continued (72) Inventor Toshihiro Suzuki, 1015 Kamiodanaka, Nakahara-ku, Kawasaki, Kanagawa, Fujitsu Limited (72) Inventor Takuya Yoshimi, 1015, Kamedota, Nakahara-ku, Kawasaki, Kanagawa Person Kunitaka Uejima 1015 Kamiodanaka, Nakahara-ku, Kawasaki City, Kanagawa Prefecture, Fujitsu Limited

Claims (6)

[Claims] 1. A plurality of prisms (14) are continuously formed on at least one surface of a transparent plate (12), and each prism substantially transmits light with an effective surface (16) provided with a predetermined inclination. A method of manufacturing a Fresnel lens having a non-contributing ineffective surface (18) and a light absorbing layer (20) provided on the ineffective surface, comprising: a Fresnel lens having a plurality of prisms; Comprising the steps of applying a layer, applying a photosensitive resist, exposing and developing,
A method of manufacturing a Fresnel lens, characterized in that a light absorption layer is provided only on an ineffective surface by utilizing a difference in light irradiation amount between an effective surface and an ineffective surface of each prism when exposing a resist. 2. A Fresnel lens in which the light absorbing layer or the light shielding layer on the ineffective surface of the Fresnel lens is formed of a light absorbing material or a light shielding material mixed in a resist, and a resist is applied to a Fresnel lens having a plurality of prisms and exposed. The method of manufacturing a Fresnel lens according to claim 1, wherein a light absorbing layer or a light shielding layer is formed on the ineffective surface in the developing step. 3. A fresnel lens having a plurality of prisms coated with a resist, exposed and developed, and then coated with a light absorbing layer or a light shielding layer, and then swelling and peeling the resist to form an ineffective surface. The method of manufacturing a Fresnel lens according to claim 1, wherein a light-absorbing layer light-shielding layer is formed on the surface. 4. A Fresnel lens having a plurality of prisms formed thereon is coated with a dye base material, then coated with a resist, exposed, developed, and dyed the dye base layer,
The Fresnel lens manufacturing method according to claim 1, wherein a light absorbing layer or a light shielding layer is formed on the ineffective surface in the step of removing the resist. 5. A Fresnel lens having a plurality of prisms formed thereon is coated with a light-absorbing material light-shielding material, and then a resist is applied, exposed, and developed, and the light-absorbing material or light-shielding material of the dissolved portion of the resist is applied. The method of manufacturing a Fresnel lens according to claim 1, wherein the light absorbing layer or the light shielding layer is formed on the ineffective surface by the steps of dissolving and washing and removing the remaining resist. 6. The method for manufacturing a Fresnel lens according to claim 1, wherein the refractive index of the light absorbing layer is equal to or higher than the refractive index of the Fresnel lens material.