JP2004272235A - Fresnel lens sheet and rear projection screen - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a Fresnel lens sheet and a rear projection screen which are used for a rear projection television and reduce ghosts. <P>SOLUTION: The Fresnel lens sheet comprises a Fresnel lens substrate and a Fresnel lens and the light-source side surface is of ≤200 μm in mean pitch and 3 to 15 μm in 10-point mean roughness. Further, included is the rear projection screen constituted by combining the Fresnel lens sheet and a lenticular lens sheet. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

  The present invention relates to a Fresnel lens sheet and a rear projection screen used in a rear projection television.

In a rear projection television, which is one of large-screen televisions, image light projected from a light source is reflected by a reflection mirror and forms an image on a screen. The screen basically has a three-piece structure including a Fresnel lens sheet, a lenticular lens sheet, and a front panel from the light source side.
Rear-projection screens used in rear-projection televisions usually combine a Fresnel lens sheet and a lenticular lens sheet.However, there are some images on the image due to reflection on the Fresnel lens sheet surface and stray light inside the Fresnel lens sheet. Has brought the disadvantages. For example, when the screen of the rear projection television is viewed from below at a short distance, the image at the top of the screen can be further enlarged and viewed at a slightly lower portion. Such a phenomenon in which multiple elephants are seen is generally called a ghost. It is thought that this cause appears when stray light inside the Fresnel lens sheet and light reflected on the light source side surface are reflected by the reflection mirror and re-enter. In recent years, the luminance of a light source has been increased in order to improve image luminance, and therefore, this ghost tends to be more emphasized.

  This phenomenon will be described with reference to the drawings (FIG. 1). In a rear projection screen in which a reflection mirror 2 is arranged on the back of the Fresnel lens sheet 1, incident light 3 from a light source enters the Fresnel lens sheet and exits to the observer side. At this time, light is partially reflected on the light source side surface 5 of the Fresnel lens sheet 1, is reflected again by the reflection mirror 2, and is emitted to the observer side to become ghost light 4b. The light 3 that has entered the Fresnel lens is partially reflected by the emission-side surface 6, and is reflected again by the light-source-side surface 5 and the reflection mirror 2 to be emitted as ghost lights 4 a and 4 c.

  In order to reduce such a ghost, a hairline is formed on the surface opposite to the Fresnel lens forming surface in a direction perpendicular to the longitudinal direction of the lenticular lens (see Patent Document 1). The surface has a uniform concavo-convex shape, and its haze value, half-value angle, 1/3 angle, and the like are defined in a certain range (see Patent Document 2). An anti-reflection film is formed on the surface opposite to the Fresnel lens forming surface. (See Patent Document 3) and the like.

  As in the prior art, the light source side surface of the Fresnel lens sheet is made uneven or antireflection treatment to diffuse or reduce stray light and surface reflection inside the screen, thereby reducing ghosting. However, the above prior art is not sufficiently effective for a rear projection television using a recent high-luminance light source.

JP-A-5-158153 JP-A-5-127257 Japanese Patent No. 3056571

  An object of the present invention is to provide a more effective and simple ghost reduction method than the above-mentioned conventional technology.

The present inventors have assiduously studied and found that ghosts can be effectively reduced by the following method. That is, the present invention provides a Fresnel lens sheet described in the following (1) to (4), a rear projection screen described in the following (5), a method for producing a Fresnel lens sheet described in the following (6), and a description in the following (7). And a method of manufacturing a rear projection type screen.
(1) A Fresnel lens sheet comprising a Fresnel lens substrate and a Fresnel lens, the light source side surface having an average pitch of 200 μm or less and a ten-point average roughness of 3 to 15 μm.
(2) The Fresnel lens substrate includes a layer composed of 100 parts by weight of a thermoplastic resin and 6 to 30 parts by weight of light diffusing fine particles having a refractive index satisfying the formula (1) and having an average particle diameter of 13 to 30 μm ( The Fresnel lens sheet according to 1).
0 ≦ | Np−Ns | <0.02 (1)
(Np is the refractive index of the thermoplastic resin, Ns is the refractive index of the light diffusing fine particles)
(3) The Fresnel lens according to any one of (1) and (2), wherein the Fresnel lens substrate is made of a thermoplastic resin obtained by molding using a metal roll having a ten-point average roughness of 6 to 15 μm on the surface. Sheet.
(4) The Fresnel lens sheet according to any one of (1) to (3), wherein the Fresnel lens substrate is made of a copolymer resin of methyl methacrylate and styrene.
(5) A rear projection screen combining the Fresnel lens sheet and the lenticular lens sheet according to any one of (1) to (4).
(6) A method for producing a Fresnel lens sheet, comprising forming a Fresnel lens substrate using a metal roll having a surface having a ten-point average roughness of 6 to 15 μm, and laminating a Fresnel lens to the Fresnel lens substrate.
(7) A Fresnel lens substrate is formed using a metal roll having a ten-point average roughness of 6 to 15 μm on the surface, and a Fresnel lens is bonded to the Fresnel lens substrate to produce a Fresnel lens sheet. A method for manufacturing a rear projection screen, comprising combining a lenticular lens sheet.

By using the Fresnel lens sheet and the rear projection screen of the present invention, stray light and surface reflection inside the screen can be effectively diffused, and ghosts generated thereby can be significantly reduced. Therefore, the rear projection television using the Fresnel lens sheet and the rear projection screen of the present invention can obtain a good image without ghost light.
Although the presently preferred embodiment of the present invention has been described, it is obvious to those skilled in the art that the present invention can be modified and improved without departing from the scope of the present invention described in the appended claims. It is about to do.

The Fresnel lens sheet of the present invention includes a Fresnel lens substrate and a Fresnel lens, and has a light source side surface with an average pitch of 200 μm or less and a ten-point average roughness of 3 to 15 μm.
FIG. 2 shows a ghost reduction mechanism according to the present invention. In a rear projection screen in which a reflection mirror 2 is disposed on the back of a Fresnel lens sheet 1, incident light 3 from a light source enters the Fresnel lens sheet 1 and is observed. Out to the user side. At this time, the incident light 3 is partially reflected by the light source side surface 5 of the Fresnel lens sheet 1, but the reflected light indicated by the dotted line does not travel in one direction because the light source side surface 5 has an uneven shape. Scatters in various directions. As a result, the ghost light is inconspicuous.
If the pitch of the light source side surface 5 of the Fresnel lens sheet is too large, an uneven pattern will be reflected on the screen, so that it is necessary to reduce the pitch appropriately. The height of the unevenness on the light source side surface needs to be appropriately high in order to effectively diffuse stray light and surface reflected light inside the Fresnel lens sheet. As a result of intensive studies by the inventors, it has been concluded that the average pitch is preferably 200 μm or less, and the ten-point average roughness representing the height of the unevenness is preferably 3 to 15 μm. Further, the average pitch is preferably 150 μm or less, and the ten-point average roughness is preferably 4 to 12 μm. If the average pitch is larger than 200 μm or the ten-point average roughness is smaller than 3 μm, these stray light and surface reflected light cannot be effectively diffused.

As a method of forming the irregularities on the light source side surface of the Fresnel lens sheet of the present invention, a method of adding light diffusing fine particles can be considered. That is, by using a Fresnel lens substrate comprising 100 parts by weight of a thermoplastic resin and 6 to 30 parts by weight of light diffusing fine particles having a refractive index satisfying the formula (1) and having an average particle size of 13 to 30 μm. Has a fine uneven shape on the light source side.
0 ≦ | Np−Ns | <0.02 (1)
(Np is the refractive index of the thermoplastic resin, Ns is the refractive index of the light diffusing fine particles)
The addition amount of the light diffusing fine particles is more preferably 9 to 20 parts by weight based on 100 parts by weight of the thermoplastic resin. If the added amount of the light diffusing fine particles is too low, sufficient roughness is not exhibited, and if the added amount of the light diffusing fine particles is too high, appearance defects such as stripes and sink marks due to the light diffusing fine particles occur.

  When light-diffusing fine particles are added to form a concavo-convex shape on the light source side surface of the Fresnel lens sheet, as the amount of light-diffusing fine particles increases, the ten-point average roughness increases, and the pitch decreases. Effective for reduction. However, when the refractive index of the light diffusing fine particles is significantly different from the refractive index of the thermoplastic resin as the base material, the haze value of the sheet increases significantly as the amount of addition increases. Therefore, when an attempt is made to obtain a surface state having a practical ghost reduction effect, the haze value becomes too high and sufficient luminance cannot be obtained. That is, by using light diffusing fine particles having a refractive index satisfying the formula (1), a sheet having a practical haze value can be obtained even when a large amount of light diffusing fine particles are added. If the average particle size of the light diffusing fine particles is too small, it is difficult to obtain a sufficient ten-point average roughness. On the other hand, when the average particle size of the light diffusing fine particles is too large, productivity is significantly impaired. Therefore, the average particle size of the light diffusing fine particles is preferably 13 to 30 μm. For example, a thermoplastic resin is a methyl methacrylate-styrene copolymer resin (a pellet having a weight average molecular weight of 150,000, obtained by copolymerizing a monomer mixture comprising 64% by weight of methyl methacrylate and 36% by weight of styrene, a refractive index of 1.53). ), It is preferable to use methyl methacrylate-styrene crosslinked fine particles (refractive index 1.53) and the like. When the thermoplastic resin is polymethyl methacrylate (PMMA) (refractive index 1.49), acrylic crosslinked fine particles (refractive index) are used. It is preferable to use a ratio of 1.49).

  Furthermore, by forming the Fresnel lens substrate into a multilayer structure having two or more layers made of a thermoplastic resin and adding light diffusing fine particles only to the light source side surface layer, an effective uneven shape can be formed with a smaller addition amount. Can be done. At this time, the effect can be obtained with a smaller amount of addition as the thickness of the light source side surface layer is smaller, but is not particularly limited.

  As another method of forming an uneven shape on the light source side surface of the Fresnel lens substrate, there is a method of shaping using a mold having an uneven shape. That is, this is a method in which extrusion molding of a thermoplastic resin is performed using a metal roll having an uneven surface, and an irregular shape is formed on the surface of the thermoplastic resin resin molded product, and is used as a Fresnel lens substrate. This is an effective method particularly at the time of extrusion molding, but is not limited to this. At this time, if the unevenness of the surface of the metal roll is too small, the unevenness of the surface of the Fresnel lens substrate does not become an effective shape, that is, the ten-point average roughness is not less than 3 μm and the average pitch is not more than 200 μm. If the surface of the metal roll has an excessively large unevenness, the thermoplastic resin in a molten state sticks to the metal roll, which significantly impairs productivity. As a result of intensive studies by the inventors, it has been concluded that the ten-point average roughness of the metal roll surface is preferably 6 to 15 μm and the average pitch is 100 to 300 μm. By using such a roll, a sheet having a ten-point average roughness of 3 to 15 μm and an average pitch of 200 μm or less can be obtained.

  In the present invention, a Fresnel lens substrate can be manufactured by forming a Fresnel lens substrate using a metal roll having a ten-point average roughness of 6 to 15 μm on the surface and laminating the Fresnel lens to the Fresnel lens substrate. . Since the surface on which the surface irregularities are formed is disposed on the light source side and the Fresnel lens is disposed on the observer side, the Fresnel lens is bonded to the surface opposite to the surface having the surface irregularities using a metal roll.

  In the present invention, a Fresnel lens substrate is formed using a metal roll having a ten-point average roughness of 6 to 15 μm on the surface, and a Fresnel lens is laminated to the Fresnel lens substrate to produce a Fresnel lens sheet. By combining a lenticular lens sheet with a lenticular lens sheet, a rear projection screen can be manufactured. The Fresnel lens is bonded to the surface on the opposite side to the surface on which the surface irregularities are formed using a metal roll.

  As the thermoplastic resin used for the Fresnel lens substrate constituting the Fresnel lens sheet of the present invention, methyl methacrylate, methacrylate, any copolymer resin selected from styrene, etc., include polycarbonate and the like, but are not particularly limited thereto. It is not something. Among them, a copolymer resin of methyl methacrylate and styrene is most preferable in terms of transparency, rigidity, water absorption, refractive index, and the like.

  The Fresnel lens is obtained by arranging lenses in concentric circles and arranging them, and has the same effect as a lens and can be made thinner. In general, a Fresnel lens used for a rear projection television has a thickness of about 100 μm. As the material, a UV curable resin, an electron beam curable resin, or the like is used.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the following Examples.
In Examples, a pellet having a weight average molecular weight of 150,000 and a refractive index of 1 obtained by copolymerizing a methyl methacrylate-styrene copolymer resin (64 wt% of methyl methacrylate and 36 wt% of styrene) as a thermoplastic resin was used. .53) was used.

The measuring instruments are Surfcom 554A (10-point average roughness Rz, average pitch Sm) manufactured by Tokyo Seimitsu Co., Ltd., and a haze meter COH-300A (Haze) manufactured by Nippon Denshoku Co., Ltd.
For the ghost evaluation, use a commercially available LCD rear-projection television, remove the Fresnel lens sheet used for the product, set the Fresnel lens sheet / sample of each example, project a test pattern image, and move the ghost to a predetermined distance. Was visually evaluated.
The notation of the ghost evaluation result was as follows.
◎: very good (large ghost reduction effect)
：: good (during ghost reduction effect)
Δ: Slightly inferior (small ghost reduction effect)
×: Inferior (no ghost reduction effect)

<Example 1>
Styrene-methyl methacrylate crosslinked light-diffusing fine particles (average particle size 18 μm, refractive index 1.53 (refractive index difference from methyl methacrylate-styrene copolymer resin 0.00) with 100 parts of methyl methacrylate-styrene copolymer resin) A first layer composed of 13 parts and a second layer composed of a methyl methacrylate-styrene copolymer resin were obtained as a multilayer sheet by coextrusion. At this time, the thickness of each layer was about 0.2 mm for the first layer and about 1.8 mm for the second layer. The haze, Rz, and Sm of the first layer of the multilayer sheet were measured. A Fresnel lens (using a UV-curable urethane-based resin, having a thickness of about 100 μm) was attached to the second layer of the multilayer sheet, combined with a lenticular lens sheet and mounted on a rear projection television, and the presence or absence of a ghost phenomenon was visually observed. . Table 1 shows the results.

<Example 2>
Styrene-methyl methacrylate crosslinked light-diffusing fine particles (average particle size 18 μm, refractive index 1.53 (refractive index difference from methyl methacrylate-styrene copolymer resin 0.00) with 100 parts of methyl methacrylate-styrene copolymer resin) A first layer composed of 6.6 parts added and a second layer composed of a methyl methacrylate-styrene copolymer resin were obtained as a multilayer sheet by coextrusion. At this time, the thickness of each layer was about 0.2 mm for the first layer and about 1.8 mm for the second layer. The haze, Rz, and Sm of the first layer of the multilayer sheet were measured. A Fresnel lens (using a UV-curable urethane-based resin, having a thickness of about 100 μm) was attached to the second layer of the multilayer sheet, and attached to a rear projection television in combination with a lenticular lens sheet, and the presence or absence of a ghost phenomenon was visually observed. . Table 1 shows the results.

<Example 3>
When a methyl methacrylate-styrene copolymer resin is obtained by extrusion molding, one of the polishing rolls is replaced with an embossed metal roll having an irregular shape with a surface of Rz 7 μm and an average pitch of 130 μm, and one surface has an irregular shape. A sheet (Fresnel lens substrate) was obtained. The haze, Rz and Sm of this sheet (Fresnel lens substrate) were measured. A Fresnel lens (using a UV-curable urethane-based resin, having a thickness of about 100 μm) was attached to this sheet (Fresnel lens substrate), and the sheet was mounted on a rear projection television in combination with a lenticular lens sheet, and the presence or absence of a ghost phenomenon was visually observed. Table 1 shows the results.

<Comparative Example 1>
Styrene-methyl methacrylate crosslinked light-diffusing fine particles (average particle size: 12 μm, refractive index: 1.55 (difference in refractive index from methyl methacrylate-styrene copolymer resin: 0.02) to 100 parts of methyl methacrylate-styrene copolymer resin) Was added to obtain a single layer sheet. The haze, Rz and Sm of this single layer sheet were measured. A Fresnel lens (using a UV-curable urethane-based resin, having a thickness of about 100 μm) was attached to this sheet, combined with a lenticular lens sheet and mounted on a rear projection television, and the presence or absence of a ghost phenomenon was visually observed. Table 1 shows the results.

<Comparative Example 2>
Styrene-methyl methacrylate crosslinked light-diffusing fine particles (average particle size: 12 μm, refractive index: 1.55 (refractive index difference from methyl methacrylate-styrene copolymer resin: 0.02)) were added to 100 parts of methyl methacrylate-styrene copolymer resin. A first layer composed of 4.5 parts and a second layer composed of a methyl methacrylate-styrene copolymer resin were obtained as a multilayer sheet by coextrusion. The thickness of each layer is the same as in Example 1. The haze, Rz, and Sm of the first layer of the multilayer sheet were measured. A Fresnel lens (using a UV-curable urethane-based resin, having a thickness of about 100 μm) was attached to the second layer of the multilayer sheet, and attached to a rear projection television in combination with a lenticular lens sheet, and the presence or absence of a ghost phenomenon was visually observed. . Table 1 shows the results.

<Comparative Example 3>
A single-layer sheet of only methyl methacrylate-styrene copolymer resin was obtained by extrusion molding. The haze, Rz and Sm of this single layer sheet were measured. A Fresnel lens (using a UV-curable urethane-based resin, having a thickness of about 100 μm) was attached to this sheet, combined with a lenticular lens sheet and mounted on a rear projection television, and the presence or absence of a ghost phenomenon was visually observed. Table 1 shows the results.

Ghosting mechanism Ghost reduction mechanism according to the present invention

Explanation of reference numerals

DESCRIPTION OF SYMBOLS 1 ... Fresnel lens sheet 2 ... Reflection mirror 3 ... Incident light from light source 4a-4c ... Ghost light 5 ... Fresnel lens sheet light source side surface 6 ... Fresnel lens sheet emission side surface

Claims (7)

A Fresnel lens sheet comprising a Fresnel lens substrate and a Fresnel lens, wherein the light source side surface has an average pitch of 200 μm or less and a ten-point average roughness of 3 to 15 μm. 2. A Fresnel lens substrate comprising a layer comprising 100 parts by weight of a thermoplastic resin and 6 to 30 parts by weight of light diffusing fine particles having a refractive index satisfying the formula (1) and having an average particle size of 13 to 30 [mu] m. Fresnel lens sheet.
0 ≦ | Np−Ns | <0.02 (1)
(Np is the refractive index of the thermoplastic resin, Ns is the refractive index of the light diffusing fine particles) The Fresnel lens sheet according to any one of claims 1 to 2, wherein the Fresnel lens substrate is made of a thermoplastic resin obtained by molding using a metal roll having a surface with a ten-point average roughness of 6 to 15 µm. The Fresnel lens sheet according to any one of claims 1 to 3, wherein the Fresnel lens substrate is made of a copolymer resin of methyl methacrylate and styrene. A rear projection screen comprising a combination of the Fresnel lens sheet according to claim 1 and a lenticular lens sheet. A method for manufacturing a Fresnel lens sheet, comprising: forming a Fresnel lens substrate using a metal roll having a surface having a ten-point average roughness of 6 to 15 μm, and bonding a Fresnel lens to the Fresnel lens substrate. A Fresnel lens substrate is formed using a metal roll having a ten-point average roughness of 6 to 15 μm on the surface, and a Fresnel lens sheet is laminated on the Fresnel lens substrate to produce a Fresnel lens sheet. And a method for manufacturing a rear projection screen.

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