JP2004271923A - Rear projection screen and image display device using same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve a problem that image disturbance called a speckle is caused when the effective screen size of an image source is small and the diameter D of a projection lens is small. <P>SOLUTION: A lenticular lens sheet has two layers of diffusing materials, and the absolute value of the difference in refractive index between the diffusing material on an image observation side (on the opposite side from the Fresnel lens sheet) and a base material is ≤0.03 and the mean particle size of the diffusing material is ≤10 μm. Or the lenticular lens sheet has two layers of diffusing materials, and the absolute value of the difference of the refractive index of the diffusing material on the Fresnel lens sheet side from that of a base material is ≥0.08 and the mean particle size of the diffusing material is ≤10 μm. Consequently, an image display device which hardly causes the speckle is obtained even when an image modulating element such as a reflection or a transmission liquid crystal panel and a display element equipped with a plurality of fine mirrors is used for an image source instead of a projection cathode-ray tube. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【００２４】
【表２】

【００２５】
【発明の効果】
本発明によれば、画像発生源に投写型ブラウン管に替わって反射型や透過型の液晶パネル、微小なミラーを複数備えた表示素子等の画像変調素子を用いてもスペックルの発生が少ない画像表示装置を得る事が出来る。
【図面の簡単な説明】
【図１】本発明による画像表示装置の一実施例を示す一部断面斜視図である。
【図２】図１に示す画像表示装置の背面投写型スクリーン３の構造を示す模式図である。
【図３】本発明による背面投写型スクリーン３の他の実施例の構造を示す模式図である。
【図４】本発明による背面投写型スクリーン３の他の実施例の構造を示す模式図である。
【図５】本発明による背面投写型スクリーン３の他の実施例の構造を示す模式図である。
【図６】本発明のレンチキュラーレンズ層を連続成形する方法を模式的に表した図である。
【図７】基材と拡散材の屈折率差の絶対値を横軸にスペックルのコントラストを縦軸にとった図である。
【図８】従来技術による画像表示装置の一部断面斜視図である。
【図９】従来技術による背面投写型スクリーンの構造を示す模式図である。
【符号の説明】
１…画像発生源、２…投写レンズ、３…背面投写型スクリーン、４…反射ミラー、５…筐体、６…フレネルレンズシート、７ａ、１１ａ、１２ｂ、１３ｃ…フレネルレンズ側拡散層、７ｂ、１１ｂ、１２ｃ、１３ｄ…画像観視側拡散層、８…ブラックストライプ、９…拡散材、１０…低屈折率差拡散材[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention provides an image display device including an image source, an optical component that enlarges and projects an image of the image source, and a rear projection screen that projects a projection image projected from the optical component. The present invention relates to a rear projection screen used for an image display device.
[0002]
[Prior art]
In recent years, image display devices that enlarge images displayed on a projection type cathode ray tube or liquid crystal display device as a small image source with a projection lens, etc., and project them on a rear projection screen It is spreading for use.
[0003]
Hereinafter, an image display device according to the related art will be described with reference to FIGS. 8 and 9. FIG. 8 is a partial cross-sectional perspective view of an image display device according to the prior art, and FIG. 9 is a schematic diagram showing the structure of a rear projection screen according to the prior art. 8, 51 is an image source, 52 is a projection lens for enlarging and projecting the image of the image source, 53 is a rear projection screen for projecting the image projected from the projection lens 52, and 54 is an image display A reflection mirror 55 provided to reduce the depth of the device is a housing for fixing these devices at predetermined positions. The image source 51 is composed of a projection type cathode ray tube, a liquid crystal display device or the like, and displays a small image. The projection lens 52 projects the image on the rear projection screen 53. Since the projection distance is generally long, a reflection mirror 54 is provided in the middle of the optical path to reduce the depth of the image display device.
[0004]
FIG. 9 is a schematic diagram showing the structure of a rear projection type screen 53 according to the related art. In the figure, 56 is a Fresnel lens sheet, 57 is a lenticular lens sheet, and 58 is a black stripe provided on the image viewing side of the lenticular lens sheet 57. The enlarged projection image (not shown) projected from the direction of the arrow a is converted into substantially parallel light or slightly inward light by the Fresnel lens sheet 56 and enters the lenticular lens sheet 57. The lenticular lens sheet 57 has a shape in which a plurality of lenticular lenses having a longitudinal direction in the screen screen vertical direction are arranged in the screen screen horizontal direction as shown in the figure, and serves to diffuse the image light in the screen screen horizontal direction. . A diffusing material 59 is kneaded in the lenticular lens sheet 57 and functions to diffuse the image light in the horizontal and vertical directions on the screen screen.
[0005]
In such a screen, image interference called speckle, which will be described in detail below, occurs. The measures against the speckle interference are described in, for example, Patent Document 1 or 2 below.
[0006]
[Patent Document 1] JP-A-7-168282 [Patent Document 2] JP-A-11-38512
[Problems to be solved by the invention]
Red, green, and blue projection CRTs having an effective screen size of about 5 to 7 inches have been used for the image source 51. However, in recent years, reflection-type or transmission-type liquid crystal panels, minute Image modulators such as display devices having a plurality of different mirrors have come to be used. Such an image modulating element has an effective screen size as small as about 1 inch, and its emitted light is closer to collimated light than a projection type cathode-ray tube. Therefore, the projection lens 52 is also small and has a high F value (the F value is the brightness of the lens). And is equal to the ratio f / D of the focal length f of the lens to the aperture D of the lens, and the high F value indicates that the aperture D of the lens is small if the focal length f is the same. If the light incident on the lens is close to the collimated light, the brightness can be secured even if the aperture D of the lens is small.) When the effective screen size of the image source 51 is small and the diameter D of the projection lens 52 is small, an image disturbance called speckle occurs.
[0008]
Speckle is generated by light scattered by minute diffusing elements located at spatially separated locations acting on one point behind and interfering with each other. In other words, light emitted from any one point on the image source 51 interferes through two points on the screen. Therefore, the smaller the image source 51 and the higher the surface density of the emitted light, the higher the height. The smaller the lens diameter D, the stronger the interference and the speckle contrast.
[0009]
In order to reduce the speckle, it is necessary to increase the effective screen size of the image source 51 or to increase the aperture D of the lens. However, this is contrary to the trend of using an image modulation element for the image source 51. Become. Therefore, measures have been taken to prevent light emitted from two points on the screen from interfering with each other, or to further diffuse the interfered light into white noise. Regarding the former measure, as disclosed in Patent Document 1, the lenticular lens sheet 57 constituting the rear projection screen 53 is not kneaded with the diffusing material 59, and is at least approximately three times the focal length of the lenticular lens. A diffusion layer is provided at a separated position, and the direction of a light beam incident on the diffusion material that causes speckle is increased by a lenticular lens to prevent interference. Although this method is very effective in removing the cause of speckles, it is necessary to provide a diffusion layer at a position separated by at least about three times the focal length of the lenticular lens. A new challenge has arisen.
[0010]
Regarding the latter measure, as disclosed in Patent Document 2 described above, the diffusion material 59 is not simply kneaded into the lenticular lens sheet 57 constituting the rear projection type screen 53, but a transparent intermediate layer 3 having a transparent intermediate layer is used. The layer structure is such that speckles generated in the first diffusion layer are hidden by the third diffusion layer. This method also has a problem that not only the resolution is deteriorated, but also that the diffusion performance on the viewing side is white due to external light and the contrast performance is deteriorated in a bright place.
[0011]
The present invention has been made in view of the above problems, and an object of the present invention is to provide a rear projection screen in which the occurrence of speckles is reduced while suppressing a decrease in resolution and contrast performance, and an image display apparatus using the same. Is to provide.
[0012]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, in the present invention, the lenticular lens sheet constituting the rear projection screen has two diffusion material layers, and the refractive index of the diffusion material located on the image viewing side (opposite to the Fresnel lens sheet). The absolute value of the difference between the refractive index of the diffusion layer and the base material of the diffusion layer was set to 0.03 or less, and the average particle size of the diffusion material was set to 10 μm or less.
[0013]
In order to further solve the above problem, in the present invention, the lenticular lens sheet constituting the rear projection type screen has two diffusion layers, and the refractive index of the diffusion material located on the image viewing side (the side opposite to the Fresnel lens sheet) is determined. The absolute value of the difference between the diffusion layer and the base material of the diffusion layer is set to 0.03 or less, and the average particle diameter of the diffusion material is set to 10 μm or less. The absolute value of the difference between the refractive index of the diffusion material of the layer and the refractive index of the base material of the diffusion layer was set to 0.08 or more, and the average particle size of the diffusion material was set to 10 μm or less.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings using examples.
[0015]
FIG. 1 is a partially sectional perspective view of an image display device according to the present invention. In FIG. 1, 1 is an image source, 2 is a projection lens for enlarging and projecting the image of the image source, 3 is a rear projection screen that projects the image projected from the projection lens, and 4 is an image display device. The reflection mirror 5 provided to reduce the depth of the device is a housing for fixing these devices at predetermined positions. The image source 1 includes a projection type cathode ray tube, a reflection type or transmission type liquid crystal panel, an image modulation element such as a display element having a plurality of minute mirrors, and the like, and displays a small image. The projection lens 2 projects the image on the rear projection screen 3, but since the projection distance is generally long, a reflection mirror 4 is provided in the middle of the optical path to reduce the depth of the image display device.
[0016]
FIG. 2 is a schematic diagram showing the structure of the rear projection type screen 3 according to the present invention. In the figure, 6 is a Fresnel lens sheet, 7 is a lenticular lens sheet, which is composed of two layers of different diffusing materials, 7a is a Fresnel lens side diffusion layer, 7b is an image viewing side diffusion layer, and 8 is the lenticular lens sheet 7 This is a black stripe provided on the image viewing side. The enlarged projection image (not shown) projected from the direction of the arrow b is converted into substantially parallel light or slightly inward light by the Fresnel lens sheet 6 and enters the lenticular lens sheet 7. As shown in the figure, the lenticular lens sheet 7 has a shape in which a plurality of lenticular lenses having the longitudinal direction in the screen screen vertical direction are arranged in the screen screen horizontal direction, and functions to diffuse the image light in the screen screen horizontal direction. . The lenticular lens sheet 7 is composed of two layers of different diffusing materials, and 7a is a Fresnel lens-side diffusing layer into which the diffusing material 9 is kneaded to diffuse the image light in the horizontal and vertical directions on the screen screen. do. Reference numeral 7b denotes an image viewing side diffusion layer into which a low refractive index difference diffusion material 10 is kneaded, and has a function of concealing speckles generated by the diffusion material 9 in the Fresnel lens side diffusion layer 7a. It is known that the concealing effect of the diffusing material is enhanced by reducing its average particle size. The inventors have experimentally found that the effect is particularly remarkable when the average particle size is set to 10 μm or less in the method of use as in the present invention. However, when the average particle size is reduced, there is a problem that white light is emitted by external light. Thus, the present inventors conducted an experiment by changing the refractive index of the base material and the diffusing material. As a result, if the difference in the refractive index between the base material and the diffusing material 10 is 0.03 or less, the problem that the light glows white due to external light has been a problem. It was found that it was easier than technology. As described above, the low refractive index difference diffusing material 10 of the present invention has an absolute value of a difference between the refractive index of the diffusing material and the substrate of 0.03 or less and an average particle diameter of the diffusing material of 10 μm or less. It is characterized by having such a configuration.
[0017]
FIG. 3 is a schematic view showing the structure of another embodiment of the rear projection screen 3 according to the present invention. In the figure, the same numbers as those in FIG. 2 represent the same parts. This embodiment differs from the embodiment of FIG. 2 in that the image-viewing-side diffusion layer 11b of the lenticular lens sheet 11 composed of two different layers of the diffusion material is colored. The coloring has the effect of further reducing the problem that the low-refractive-index-diffusion material 10 kneaded into the image-viewing-side diffusion layer 11b shines white due to external light. The Fresnel lens side diffusion layer 11a is the same component as 7a in FIG.
[0018]
FIG. 4 is a schematic diagram showing the structure of another embodiment of the rear projection type screen 3 according to the present invention. In the figure, the same numbers as those in FIG. 2 represent the same parts. This embodiment differs from the embodiment of FIG. 2 in that the lenticular lens sheet 12 is composed of three layers. 12a is a lenticular lens layer on the Fresnel lens side made of a transparent material that does not contain a diffusing material, and 12b is a Fresnel lens side diffusing layer into which a diffusing material 9 has been kneaded, and the image light is transmitted horizontally and vertically to the screen screen. It works to diffuse in the direction. Reference numeral 12c denotes an image viewing side diffusion layer into which a low refractive index difference diffusion material 10 is kneaded, and has a function of hiding speckles generated by the diffusion material 9 in the Fresnel lens side diffusion layer 12b. In FIG. 4, the image viewing side diffusion layer 12c is colored, and has an effect of reducing the problem that the low refractive index difference diffusion material 10 kneaded into the image viewing side diffusion layer 11b shines white due to external light. However, it goes without saying that the effects of the present invention can be maintained without coloring.
[0019]
FIG. 5 is a schematic view showing the structure of another embodiment of the rear projection screen 3 according to the present invention. In the figure, the same numbers as those in FIG. 4 represent the same parts. This embodiment is different from the embodiment of FIG. 4 in that the lenticular lens sheet 13 is formed of three layers different from the lenticular lens sheet 12 of the embodiment of FIG. A lenticular lens layer 13a on the Fresnel lens side is made of a transparent material that does not contain a diffusing material, and a base sheet 13b of the lenticular lens layer 13a is also made of a transparent material. Reference numeral 13c denotes a Fresnel lens-side diffusion layer into which the diffusion material 9 is kneaded, and serves to diffuse the image light in the horizontal and vertical directions on the screen screen. Reference numeral 13d denotes an image viewing-side diffusion layer into which the low-refractive index difference diffusion material 10 is kneaded, and has a function of hiding speckles generated by the diffusion material 9 in the Fresnel lens-side diffusion layer 13c. A black stripe 14 is formed at a predetermined position on the base sheet 13b of the lenticular lens layer 13a, and is adhered to the Fresnel lens side diffusion layer 13c with an adhesive 13e.
[0020]
The lenticular lens layer 13a, the base sheet 13b, and the black stripe 14 are usually manufactured as follows. FIG. 6 is a diagram schematically illustrating a method of continuously forming the lenticular lens layer. In the figure, 15a is an upper guide roller, 15b is a lower guide roller, and 13b is a base sheet that has been subjected to a surface treatment to improve the adhesiveness of the UV resin. The base sheet 13b moves downward from above while being pressed against the forming drum 17 around which the mold 16 is wound by the guide rollers 15a and 15b. The transparent UV resin is put into a position where the forming drum 17 around which the base sheet 13b and the mold 16 are wound starts to come into contact with each other, and the UV resin is irradiated by UV irradiation while the base sheet 13b and the forming drum 17 are in contact with each other. Harden. As a post-process, the black stripe 14 is formed at a predetermined position on the opposite side of the base sheet 13b from the lenticular lens by a photoresist method. The Fresnel lens-side diffusion layer 13c and the image viewing-side diffusion layer 13d may be separately manufactured and bonded, or two layers of different materials may be formed simultaneously.
[0021]
The embodiment of the rear projection type screen 3 according to the present invention has been described above with reference to FIGS. 2 to 5. However, the diffusing material 9 in FIGS. 2 to 5 is replaced with a diffusing material which generates less speckle as described below. The effect of the present invention becomes more remarkable by changing. FIG. 7 shows the results of an experiment conducted by the inventors, in which the average particle size of the diffusing material is used as a parameter, the absolute value of the refractive index difference between the substrate and the diffusing material is plotted on the horizontal axis, and the contrast of speckle is plotted on the vertical axis. FIG. The speckle contrast is determined by the Rear Projection Screens for Light Valve Projection System: Jill F. Goldenberg et al. 2: PP49-59, SPIE Vol. 3013 (1997). FIG. 7 shows that the speckle contrast decreases as the absolute value of the refractive index difference increases. However, when the average particle diameter of the diffusing material is about 30 μm, the contrast of the speckle does not decrease even if the absolute value of the refractive index difference is increased. In order to obtain the effect of the present invention, two conditions that the absolute value of the refractive index difference between the base material and the diffusion material is 0.08 or more and the average particle size of the diffusion material is 10 μm or less must be simultaneously realized. I understand. As described above, the diffusing material 9 of the present invention was configured such that the absolute value of the difference between the refractive index of the diffusing material and the substrate was 0.08 or more and the average particle size of the diffusing material was 10 μm or less. It has a special feature.
[0022]
For the selection of the materials of the base material and the diffusion material, for example, the combinations shown in Tables 1 and 2 may be selected.
[0023]
[Table 1]

[0024]
[Table 2]

[0025]
【The invention's effect】
According to the present invention, even if an image modulating element such as a reflective or transmissive liquid crystal panel or a display element having a plurality of micromirrors is used in place of a projection type cathode ray tube as an image source, an image in which generation of speckle is small is obtained. A display device can be obtained.
[Brief description of the drawings]
FIG. 1 is a partially sectional perspective view showing an embodiment of an image display device according to the present invention.
FIG. 2 is a schematic diagram showing a structure of a rear projection screen 3 of the image display device shown in FIG.
FIG. 3 is a schematic view showing the structure of another embodiment of the rear projection screen 3 according to the present invention.
FIG. 4 is a schematic view showing the structure of another embodiment of the rear projection type screen 3 according to the present invention.
FIG. 5 is a schematic diagram showing the structure of another embodiment of the rear projection screen 3 according to the present invention.
FIG. 6 is a diagram schematically illustrating a method of continuously forming a lenticular lens layer according to the present invention.
FIG. 7 is a diagram in which the abscissa represents the absolute value of the refractive index difference between the base material and the diffusing material, and the ordinate represents the speckle contrast.
FIG. 8 is a partial cross-sectional perspective view of an image display device according to the related art.
FIG. 9 is a schematic view showing a structure of a rear projection screen according to the related art.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Image generation source, 2 ... Projection lens, 3 ... Rear projection screen, 4 ... Reflection mirror, 5 ... Housing, 6 ... Fresnel lens sheet, 7a, 11a, 12b, 13c ... Fresnel lens side diffusion layer, 7b, 11b, 12c, 13d: image viewing side diffusion layer, 8: black stripe, 9: diffusion material, 10: low refractive index difference diffusion material

Claims (11)

An image source, an optical component for enlarging and projecting the image of the image source, and a rear projection screen that projects a projection image projected from the optical component,
The rear projection screen includes at least a Fresnel lens sheet disposed on the image source side and a lenticular lens sheet disposed on the image viewing side, and the lenticular lens sheet includes two diffusing materials. Including a diffusion layer,
Of the two diffusion layers, the absolute value of the difference between the refractive index of the diffusion material contained in the diffusion layer located on the image viewing side and the refractive index of the base material of the diffusion layer is 0.03 or less, and An image display device wherein the average particle size of the diffusion material is 10 μm or less. 2. The image display device according to claim 1, wherein the lenticular lens sheet has three layers, a layer located closest to the Fresnel lens is a lenticular lens layer made of a transparent material containing no diffusing material, and the remaining two layers are diffusion layers. The absolute value of the difference between the refractive index of the diffusion material of the diffusion layer located on the image viewing side and the refractive index of the base material of the diffusion layer is 0.03 or less, and the average particle size of the diffusion material Is smaller than 10 μm. 3. The image display device according to claim 2, wherein the lenticular lens layer is provided with a plurality of lenticular lenses that extend in a direction perpendicular to the screen and do not contain a diffusing material on a surface on a Fresnel lens side, and are opposite to the Fresnel lens. An image display device comprising: a black stripe provided at a predetermined position on a side surface; and a lenticular lens layer and a diffusion layer positioned on the Fresnel lens side bonded with an adhesive. 4. The image display device according to claim 1, wherein a base material of the diffusion layer located on the image viewing side is colored. 5. 5. The image display device according to claim 1, wherein an absolute value of a difference between a refractive index of a diffusion material of the diffusion layer located on the Fresnel lens side and a refractive index of a base material of the diffusion layer is 0. An image display device characterized in that it is not less than 08 and the average particle size of the diffusion material is 10 μm or less. A rear projection screen that projects a projection image projected from an optical component, the lenticular lens sheet including at least a Fresnel lens sheet disposed on an image source side and a lenticular lens sheet disposed on an image viewing side. The sheet includes two diffusion layers each containing a diffusion material,
Of the two diffusion layers, the absolute value of the difference between the refractive index of the diffusion material contained in the diffusion layer located on the image viewing side and the refractive index of the base material of the diffusion layer is 0.03 or less, and A rear projection screen, wherein the average particle size of the diffusing material is 10 μm or less. 7. The rear projection screen according to claim 6, wherein the lenticular lens sheet has three layers, the layer located closest to the Fresnel lens is a lenticular lens layer made of a transparent material not containing a diffusing material, and the remaining two layers are diffused. The absolute value of the difference between the refractive index of the diffusion material of the diffusion layer positioned on the image viewing side and the refractive index of the base material of the diffusion layer is 0.03 or less; A rear projection screen characterized in that the diameter is 10 μm or less. 8. The rear projection type screen according to claim 7, wherein the lenticular lens layer is provided with a plurality of lenticular lenses that extend in a direction perpendicular to the screen and do not contain a diffusing material, on a surface on a Fresnel lens side thereof. A rear projection screen comprising a black stripe provided at a predetermined position on an opposite surface, wherein the lenticular lens layer and a diffusion layer located on the Fresnel lens side are bonded with an adhesive material. 9. The rear projection type screen according to claim 6, wherein a base material of a diffusion layer located on the image viewing side is colored. 10. The rear projection screen according to claim 6, wherein the absolute value of the difference between the refractive index of the diffusion material of the diffusion layer located on the Fresnel lens side and the refractive index of the base material of the diffusion layer is different. A rear projection screen characterized in that it is not less than 0.08 and the average particle size of the diffusing material is not more than 10 μm. In a rear projection screen that projects the image of the image source projected from the optical component,
At least a Fresnel lens sheet arranged on the image generation source side and a lenticular lens sheet arranged on the image viewing side, wherein the lenticular lens sheet has first and second diffusion layers each containing a diffusing material Including
A rear projection screen, wherein the diffusion material contained in the first diffusion layer and the diffusion material contained in the second diffusion layer have different refractive indexes.

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