JPH10282315A - Optical diffusing plate and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical diffusing plate which is excellent in the diffusion effect, small in transmission loss, and excellent in the reduction effect of reflection of the external light. SOLUTION: Fine irregularity to refract and diffuse the light is provided on a surface 10 which is the incident side of the light, and a light absorption layer 12 is provided along the fine irregularity shape. The external light incident from an emitting surface 11 which is the observation side passes through the light absorption layer in the long path during the total reflection at the irregular surface provided on the incident surface 10, and is large attenuated to remarkably reduce the reflection of the external light. If the optical diffusing plate is used as a transmission type screen, the transmission efficiency is excellent and the excellent characteristic in contract can be realized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light diffusing plate suitable for a transmission screen and a method for manufacturing the same.

[0002]

2. Description of the Related Art In recent years, light diffusing plates for distributing and distributing sharply directional incident light over a wider angle range have been used as screens for rear projection televisions and front plates for liquid crystal display devices to improve the visibility of the devices. Used for

A light diffusing plate is provided with fine irregularities on the surface of the light transmitting plate on the incident side or the emitting side, and diffuses light by refraction on the irregular surface. In general, beads having different refractive indices are dispersed and light is diffused by a refraction function at the interface between the beads and the base material.

Among them, the method of providing fine irregularities on the surface on the emission side and the method of dispersing beads inside have a limit in the diffusion function that can be obtained, and it is intended to obtain a wide viewing angle by a large diffusion action. In this case, a method of providing fine irregularities on the surface on the incident side is effective.

FIG. 8 is a ray tracing diagram showing the diffusion effect of fine irregularities provided on the incident side. The incident light has extremely sharp directivity and is incident on the light transmitting plate 1 as a substantially parallel light flux. The incident light beam is refracted in accordance with the angle between the fine irregularities and the light beam, and is also refracted on the exit surface and diffused as shown.

As described above, the use of the light diffusion plate having the fine irregularities on the incident side makes it possible to diffuse the incident light efficiently over a wide range.

[0007]

As described above, the light diffusing plate provided with the fine irregularities on the incident side has an excellent diffusion function for the light incident from the incident surface side, but the exit surface on the observation side. There is a problem that the reflectance is large with respect to external light incident from the light source.

The greatest reason for the increase in the reflectance with respect to the incidence of external light from the observation side is the existence of the total reflection component. Ninth
The figure shows the situation.

FIG. 9 is a cross-sectional view showing a ray trajectory when external light is incident on the diffuser plate having fine irregularities on the incident side from the emission surface radiation direction.

As the material of the diffusion plate, PMMA, which is the most common transparent resin, is used. The refractive index of PMMA is about 1.5, and the total reflection condition is about 42 °. That is, light incident on the interface between PMMA and air from the PMMA side is totally reflected when the angle between the light beam and the normal to the interface is 42 ° or more.

Most of the light rays that have been totally reflected once repeat total reflection one to three times, and return to the observation side.

With respect to a tilt angle of 42 °, which is a condition of total reflection, the divergence angle of a light beam incident from the incident side is about 15 °. Will be totally reflected. When used as a transmissive screen, it is necessary to have a diffusivity of 30 ° or more at a half-diffusion angle (an angle at which the luminance becomes half of the front direction), and it is necessary to generate a totally reflected light beam. Specifically, there is an actual measurement example in which a diffuser plate having a diffusion half-value angle of about 30 ° has an external light reflectance of about 25% on the incident-side uneven surface.

As described above, when the reflectance is high with respect to the incidence of external light from the observation side, for example, when an image is to be used as a transmissive screen of a rear projection television, the contrast of the displayed image is increased in a bright environment. This is a significant impairment factor.

As a method of reducing such reflection, it is common to form the light diffusion plate from a material having a certain level of light absorption.

According to this configuration, while the projected light passes through the light absorbing portion once, the reflected light incident from the observation side and reflected on the incident surface reciprocates through the light absorbing portion, so that the projected light is attenuated. The contrast can be improved by attenuating by the square of the ratio.

However, if the reflection is sufficiently reduced by such a conventional method, the attenuation of the projection light is large and the image becomes extremely dark. For example, in order to attenuate the external light reflectance of about 25% on the incident side uneven surface in the above-described example to about 5%, which is close to the normal reflectance of 4% at a refractive index of 1.5,
The transmittance must be raised to the square root of 1/5, about 0.44 times.

[0017]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention forms a fine uneven shape for refracting and diffusing a light beam on one surface on which light is incident, and substantially conforms to the fine uneven shape. The light absorbing layer is arranged as described above.

According to the present invention, it is possible to greatly reduce the reflection of external light with a small loss of projection light, and to provide an efficient transmission screen with excellent contrast.

[0019]

DETAILED DESCRIPTION OF THE INVENTION The invention according to claim 1 has a fine uneven shape for refracting and diffusing a light beam on one surface on which light is incident, and the other surface on the observation side is substantially flat. The light absorbing layer is formed substantially along the fine irregularities, and external light totally reflected by the irregularities can be effectively absorbed.

According to a second aspect of the present invention, there is provided a step of forming a plate-shaped light-transmitting substrate having a light-absorbing layer on one surface, and the light-transmitting substrate having a light-absorbing layer on the surface. Hot pressing so that fine irregularities are formed on the surface, and one surface has a fine irregular shape, and the other surface is almost flat, almost along the fine irregularities. A light diffusion plate having a light absorption layer can be easily manufactured. And a light diffusion plate having a light absorbing layer that has fine irregularities on one surface and is substantially flat on the other surface and substantially along the minute irregularities can be easily manufactured.

According to a third aspect of the present invention, there is provided a method of forming a transparent substrate having fine irregularities on one surface and a substantially flat surface on the other surface, and light absorbing from the transparent substrate having the fine irregularities. Impregnating the conductive material with a light diffusing plate having a light absorbing layer such that one surface has fine irregularities and the other surface is substantially flat, and substantially conforms to the fine irregularities. Can be easily manufactured.

According to a fourth aspect of the present invention, the light absorbing material and the transparent material are independently melted, and are simultaneously supplied to one die and extruded to have a light absorbing layer on one surface layer. The other part is formed by a step of forming a transparent substantially flat two-layer substrate, and a first roll-shaped mold having an uneven surface and a second roll mold having a smooth surface. A surface having a light-absorbing layer on a surface layer portion of the two-layer substrate by sandwiching and sending out the two-layer substrate such that the formed surface and the first roll-shaped mold having an uneven shape on the surface are in contact with each other. Forming a fine irregular shape on the surface, the one surface having a fine irregular shape, the other surface being substantially flat, and a light having a light absorbing layer substantially along the fine irregularities. Diffuser can be easily manufactured.

According to a fifth aspect of the present invention, there is provided a method of forming a transparent substrate having fine irregularities on one surface and a substantially flat surface on the other surface, and forming the transparent substrate on the surface of the transparent substrate having the fine irregularities. Laminating a light-absorbing film so as to substantially conform to the irregularities. One of the surfaces has a fine irregularity shape and the other surface is substantially flat, and the light is substantially along the fine irregularities. A light diffusion plate having an absorption layer can be easily manufactured.

According to a sixth aspect of the present invention, there is provided a method of forming a substantially flat transparent substrate by melting a transparent material, supplying the molten material to a die, and extruding the transparent material. By sandwiching and sending out the transparent substrate and the light-absorbing film by a second roll mold having a smooth surface so that the light-absorbing film is in contact with the first roll-shaped mold having an irregular shape on the surface. Heat laminating step, wherein one surface has fine irregularities and the other surface is almost flat, and the light diffusing plate having a light absorbing layer almost along the fine irregularities can be easily formed. Can be manufactured.

According to a seventh aspect of the present invention, there is provided a method of forming a transparent substrate having fine irregularities on one surface and a substantially flat surface on the other side, and a step of masking the substantially flat surface of the transparent substrate. Immersing the transparent substrate having fine irregularities on one surface and masking the other surface in a tank filled with a liquid light absorbing material, and immersing the transparent substrate in a tank filled with the liquid light absorbing material A step of lifting the transparent substrate, which facilitates the formation of a light diffusion plate having a light absorbing layer such that one surface has fine irregularities and the other surface is substantially flat, and substantially conforms to the fine irregularities. Can be manufactured.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. (Embodiment 1) FIG. 1 is a perspective view showing an embodiment of the first aspect of the present invention.

The surface 10 on the incident side of the light diffusion plate 1 is formed with fine irregularities, and a light absorbing layer 12 in which a light absorbing material is dispersed in PMMA is provided substantially along the irregularities. The base material layer 13 is a transparent PM having almost no light absorption.
Formed by MA. The emission surface 11 on the observation side is a smooth plane. Although the optimum value of the thickness of the light absorbing layer depends on the uneven shape, the light absorbing layer is thinned to a range within which the totally reflected light exists along the uneven surface as shown in FIG. The light-absorbing material concentration of the light-absorbing layer is set so that light passing through the length of the light-absorbing layer is absorbed by about 30% and the transmittance becomes 70%.

The diffusing plate 1 is formed such that its cross section taken on any plane including the normal line of the surface is substantially equivalent.
That is, the uneven shape is formed isotropically, and the diffusion effect described later is also isotropic. FIG. 2 is a cross-sectional view taken along the arbitrary plane.

In this configuration, when the projection light having a substantially parallel luminous flux enters the incidence surface 10, the projection light is refracted by the uneven shape, and is emitted from the emission surface 11 and diffuses along a locus as shown in FIG. . In this case, the length of the projected light passing through the light absorbing layer is substantially equal to the thickness of the light absorbing layer defined in the normal direction of the uneven surface. Therefore, the projected light is attenuated about 0.7 times as compared with the case where the light absorbing layer is not provided.

On the other hand, external light incident from the light exit surface 11 is shown in FIG.
Part of the trajectory indicated by 0 repeats total reflection on the uneven surface and returns to the observation side. At this time, the total reflected light passes through the portion of the light absorbing layer provided along the uneven surface while repeating the total reflection. As a result, the length of the total reflection light passing through the light absorption layer is much larger than the thickness of the light diffusion layer defined by the normal direction of the uneven surface, and is 4 to 5 times. At this time, the absorption effect of the light absorbing layer having a certain concentration is determined by the length of the light passing through the light absorbing layer, and the transmittance is considered to decrease in proportion to the power of the length passing through the light absorbing layer. The total reflection of external light can be reduced from 0.24 times to 0.17 times the transmittance of the projected light from the fourth power to the fifth power of about 0.7 as compared with the case where there is no absorption layer.

In the conventional method in which the entire structure is made of a light absorbing material, the external light reflection can be reduced much more efficiently than when the total reflection component of the external light can be reduced only by the square of the transmittance. You can do it. For example, in the above-described example, in the conventional method, in order to reduce external light reflection to 1/5 of the transparent state, the transmittance of the projection light needs to be reduced to 0.44 times which is the square root of 1/5. On the other hand, according to the method of the present invention, it is sufficient that the ratio is 1/4 to the 5th root, 0.67 to 0.72 times, and the efficiency is improved to 1.5 times or more.

In the above description, an isotropic diffusion effect is obtained by making the uneven shape isotropic, but anisotropic diffusion having a different diffusion effect depending on the direction is also realized by making the unevenness, for example, a rugby ball-like anisotropic shape. You may do it. In an extreme case, it is also possible to diffuse in only one direction like a lenticular lens array.

Although the exit surface on the observation side is a smooth plane, if it is desired to reduce so-called "reflection" due to regular reflection, it is effective to apply a gentle matting process. However, in this case, a diffuse reflection component also occurs in the reflection of the external light on the emission surface, and the contrast is reduced.

Although PMMA, which is excellent in transparency, dyeability and workability, is used as the material, the material can be freely selected as long as it can be processed into fine irregularities with a two-layer structure of light absorption and transparency. For example, it is possible to use a PET film in which glass is used for a transparent base material and a dyeing treatment is applied to a light absorbing layer.

Further, the transmittance of a light beam passing through the light absorbing layer by the length of the thickness is set to be about 70%.
A higher transmittance can be set when importance is placed on efficiency, and a lower transmittance can be set when importance is placed on contrast. It is self-evident that the object of the present invention of reducing the external light reflection by setting the transmittance to the fourth power to the fifth power is set regardless of the transmittance.

Further, it is possible to apply a surface treatment such as antireflection, antistatic, surface hardening, etc. to the incident side surface or the outgoing side surface, and those effects are obvious to those skilled in the art.

(Embodiment 2) FIG. 3 is a process diagram showing a process of the invention according to claim 2.

(A) A light absorbing layer 12 is provided on the surface layer on one side, and a base material layer 13 is formed of a transparent flat light transmitting two-layer substrate.
It is formed of a thermoplastic material such as MMA.

(B) The surface of the light-transmitting substrate on which the light absorbing layer 12 is formed by heating the mold 21 having fine irregularities on the surface and the mold 22 on the plane to a temperature higher than the softening point of the thermoplastic resin. Hot pressing so that the uneven shape is transferred to the surface.

(C) After taking out, it is cooled. According to such a method, a light diffusion plate having fine irregularities on one surface and having a light absorbing layer along the irregularities can be easily obtained.

(Embodiment 3) FIG. 4 is a process chart showing a process of the invention according to claim 3.

(A) The transparent substrate 3 having fine irregularities on one surface 10 is formed by means such as hot pressing, extrusion molding, or casting.

(B) In a tank filled with the dye 4, the surface 10 on which the fine irregularities are formed is set so as to be in contact with the dye 4, and the surface is impregnated with the dye.

(C) At the stage when a predetermined light absorbing layer is formed on the surface layer of the uneven surface, the transparent substrate 3 is pulled up, and the peripheral part where the light absorbing layer is also formed on the side surface is cut.

According to such a method, a light diffusion plate having fine irregularities on one surface and having a light absorbing layer along the irregularities can be easily obtained.

(Embodiment 4) FIG. 5 is a process chart showing the steps of the invention according to claim 4.

In FIG. 5, reference numeral 5 denotes a two-layer extruder, in which two kinds of materials are independently melted, supplied to one die and extruded to form a two-layer substrate in which two kinds of materials are laminated in layers. it can.

(A) A light-absorbing material and a transparent material are supplied to the two-layer extruder 5, and a light-absorbing layer 12 is provided on one surface of the extruder 5. A layer substrate is formed.

(B) The above 2 which has been extruded and is in a softened state
The layer substrate is sandwiched between a roll-shaped mold 61 having an uneven surface and a roll-shaped mold 62 having a smooth surface.
The concave and convex shape is transferred to the surface on which No. 2 is formed.

According to such a method, a light diffusion plate having fine irregularities on one surface and having a light absorbing layer along the irregularities can be easily obtained.

(Embodiment 5) FIG. 6 is a process chart showing the steps of the invention according to claim 5.

(A) The transparent substrate 3 having fine irregularities on one surface 10 is formed by means such as hot pressing, extrusion molding, or casting.

(B) The light-absorbing film 6 is bonded to the surface 10 having the irregularities. (C) Pneumatic treatment is performed so that the light-absorbing film 6 conforms to the irregularities.

According to such a method, a light diffusing plate having fine irregularities on one surface and having a light absorbing layer along the irregularities can be easily obtained.

(Embodiment 6) FIG. 7 is a process chart showing a process of the invention according to claim 6.

(A) A flat transparent substrate 9 is formed by the extruder 7. (B) The light absorbing film 6 is supplied along one surface of the transparent substrate 9.

(C) Roll-shaped mold 81 having fine irregularities
At the same time, the light absorbing film 6 and the transparent substrate 9 are heat-laminated by a roll-shaped mold 82 having a smooth surface, and at the same time, the uneven surface is formed on the surface on which the light absorbing film is laminated.

According to such a method, a light diffusion plate having fine irregularities on one surface and having a light absorbing layer along the irregularities can be easily obtained.

(Embodiment 7) FIG. 8 is a process chart showing a process of the invention according to claim 7.

(A) The transparent substrate 3 having fine irregularities is formed on one surface 10 by means such as hot pressing, extrusion molding, or casting, and the surface other than the surface 10 having fine irregularities is masked with a masking film 16. Masking by

(B) Immerse the transparent substrate 3 in the tank filled with the liquid light-absorbing material 17 except for the irregular surface.

(C) The masked transparent substrate 3 immersed in the liquid light-absorbing material is pulled up at a predetermined speed, and the liquid light-absorbing material is deposited on the surface with a substantially uniform thickness.

(D) After the amount of the attached liquid light absorbing material is dried, the masking film 16 is peeled off.

According to such a method, a light diffusion plate having fine irregularities on one surface and having a light absorbing layer along the irregularities can be easily obtained.

[0065]

As described above, according to the present invention, one surface on which light is incident has fine irregularities for refracting and diffusing light, and the other surface on the observation side is almost flat. By forming the light absorbing layer substantially along the fine irregularities, it becomes possible to provide a light diffusion plate in which external light reflection is greatly reduced while minimizing the light loss of the projection light, and the light use efficiency is high and the contrast is high. This makes it possible to realize an excellent rear projection screen.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an embodiment of the invention described in claim 1;

FIG. 2 is a sectional view showing the embodiment of the invention described in claim 1;

FIG. 3 is a process chart showing an embodiment of the invention described in claim 2;

FIG. 4 is a process chart showing an embodiment of the invention described in claim 3;

FIG. 5 is a process chart showing an embodiment of the invention described in claim 4.

FIG. 6 is a process chart showing an embodiment of the invention described in claim 5;

FIG. 7 is a process chart showing an embodiment of the invention described in claim 6;

FIG. 8 is a process chart showing an embodiment of the invention described in claim 7;

FIG. 9 is a diagram showing a diffusion effect of a diffusion plate having fine irregularities on the incident side.

FIG. 10 is a diagram showing a locus of external light reflection of a diffuser plate having fine irregularities on an incident side.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Light diffusing plate 10 Incident surface 11 Outgoing surface 12 Light absorbing layer 13 Base material layer made of transparent material 21 Mold having fine unevenness 22 Mold having smooth flat surface 3 Transparent substrate having fine unevenness on surface 4 Dyeing material Reference Signs List 5 2-layer extruder 51 Roll-shaped mold having fine uneven surface 52 Roll-shaped mold having smooth surface 6 Light-absorbing film 7 Extruder 71 Roll-shaped mold having fine uneven surface 72 Roll having smooth surface Mold 8 Plate-shaped transparent substrate 9 Masking film 17 Liquid light absorbing material

Claims (7)

[Claims] 1. One surface on which light is incident has fine irregularities for refracting and diffusing light rays, and the other surface on the observation side is substantially flat, and the light is substantially aligned with the fine irregularities. A light diffusion plate having an absorption layer formed thereon. 2. A step of forming a flat light-transmitting substrate having a light-absorbing layer on a surface layer on one surface, and forming fine irregularities on the light-transmitting substrate on a surface having a light-absorbing layer on the surface layer. Heat-pressing so that the light-transmitting member has a light-absorbing layer that has fine irregularities on one surface and is substantially flat on the other surface, and substantially conforms to the fine irregularities. A method for manufacturing a light diffusing plate, characterized by being formed. 3. A step of forming a transparent substrate having fine irregularities on one surface and a substantially flat other surface, and a step of impregnating a light-absorbing material from the surface of the transparent substrate having fine irregularities. Forming a light-transmitting member having a light-absorbing layer that has fine irregularities on one surface and is substantially flat on the other surface and substantially conforms to the fine irregularities. Plate manufacturing method. 4. A light-absorbing material and a transparent material are each independently melted and simultaneously supplied to one die and extruded to have a light-absorbing layer on one surface surface portion, and the other portion is transparent. A step of forming a substantially flat two-layer substrate, and a first roll-shaped mold having an uneven surface and a second roll mold having a smooth surface, on the surface on which the light absorbing layer is formed and on the surface. By sandwiching and sending out the two-layer substrate so as to be in contact with the first roll-shaped mold having an uneven shape,
Shaping the surface of the two-layer substrate having a light-absorbing layer on the surface thereof with a fine unevenness, wherein one surface has a fine unevenness and the other surface is substantially flat. Forming a light-transmitting member having a light-absorbing layer substantially along the line. 5. A step of forming a transparent substrate having fine irregularities on one surface and a substantially flat surface on the other side, and forming a light on the surface of the transparent substrate having the fine irregularities substantially along the fine irregularities. Laminating an absorptive film to form a light-transmitting member having a light-absorbing layer that has fine irregularities on one surface and is substantially flat on the other surface, and that is substantially along the fine irregularities. A method of manufacturing a light diffusing plate. 6. A step of forming a substantially flat transparent substrate by melting a transparent material, supplying the molten material to a die, and extruding the transparent material, a first roll-shaped mold having an uneven surface, and a second smooth die having a smooth surface. Thermally laminating the transparent substrate and the light-absorbing film by a roll mold by sandwiching and sending the transparent substrate and the light-absorbing film so that the light-absorbing film is in contact with the first roll-shaped mold having an uneven shape on the surface. A light diffusing plate characterized by forming a light transmissive member having a fine unevenness on one surface and a substantially flat other surface, and having a light absorbing layer substantially along the fine unevenness. Manufacturing method. 7. A step of forming a transparent substrate having fine irregularities on one surface and a substantially flat surface on the other side, a step of masking the substantially flat surface of the transparent substrate, A step of immersing the transparent substrate having the other surface masked with irregularities in a tank filled with a liquid light absorbing material, and a step of pulling up the transparent substrate immersed in the tank filled with the liquid light absorbing material, A step of drying the liquid light-absorbing material attached to the surface of the raised transparent substrate, and a step of removing the mask, wherein one surface has fine irregularities and the other surface is substantially flat. And forming a light-transmitting member having a light-absorbing layer substantially along the fine irregularities.