JP2004271924A - Rear projection screen and image display device using same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rear projection screen which reduces speckles by preventing resolution and contrast performance from decreasing and to provide an image display device using the same. <P>SOLUTION: The rear projection screen is equipped with a 1st sheet and a 2nd sheet which are arranged in the travel direction of image light. The 1st sheet includes a Fresnel sheet (6) having a Fresnel lens formed on its projection surface and the 2nd sheet has a lenticular lens (8) which is concave to an image source side and a diffusion sheet (7) which is arranged on an image observation side and contains a particulate light diffusing material. In this constitution, the speckles are reducible 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

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image display device in which an image of an image source is enlarged by a projection lens and projected on a screen, and a rear projection screen used for the image display device.
[0002]
[Prior art]
In a projection-type image display device, a reflection-type or transmission-type liquid crystal panel or an image modulation element such as a display element having a plurality of minute mirrors is used as a small image source instead of a projection-type CRT. Have been. The diameter of the projection lens for such an image modulation element is smaller than that of a projection lens for a projection type cathode-ray tube, and there is a problem that an image disturbance called speckle easily occurs due to a light diffusing material in a rear projection type screen. . Such a problem and its countermeasure are described in, for example, Patent Document 1 below.
[0003]
Further, the fact that the light emitted from the image modulation element is closer to collimated light (parallel light) than that of a projection type cathode-ray tube also causes the occurrence of speckles, and a countermeasure thereof is described in, for example, Patent Document 2 below. I have.
[0004]
[Patent Document 1] JP-A-7-168282 [Patent Document 2] JP-A-11-38512 [0005]
[Problems to be solved by the invention]
The speckles are generated when light scattered by minute diffusion elements located at a spatially separated location acts on one point behind and interferes 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.
[0006]
Therefore, in order to reduce speckle, it is necessary to increase the effective screen size of the image source or to increase the aperture D of the lens, but this goes against the trend of using an image modulation element as the image source. Become. Therefore, measures have been taken to prevent the light emitted from two points on the screen from interfering with each other, or to further diffuse the interfering light into white noise.
[0007]
Regarding the former measure, as disclosed in Patent Document 1, a lenticular lens sheet constituting a rear projection type screen is not kneaded with a diffusing material, and is positioned at least three times the focal length of the lenticular lens. Is provided with a diffusion layer. Thereby, the direction of the light beam incident on the diffusing material causing speckle is increased by the lenticular lens so as not to interfere. However, this countermeasure is very effective because it eliminates the cause of speckles. However, the diffusion layer must be provided at a position that is at least three times the focal length of the lenticular lens, resulting in a large resolution. There is a new problem of deterioration.
[0008]
Regarding the latter measure, as disclosed in Patent Document 2, instead of simply kneading a diffusing material into a lenticular lens sheet constituting a rear projection screen, a three-layer structure having a transparent intermediate layer is used. Thus, speckles generated in the first diffusion layer are hidden by the third diffusion layer. This countermeasure also has a problem that not only the resolution is deteriorated, but also the diffusion layer on the viewing side looks white due to external light, and the contrast performance in a bright place is deteriorated.
[0009]
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.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, according to the present invention, a lenticular lens of a lenticular lens sheet is formed into a lens shape which is conventionally convex on the image source side and is concave on the image source side, and is kneaded into the conventional lenticular lens sheet. The diffusing material, which was included, was provided on the viewing side of the lenticular lens without being kneaded into the lenticular lens.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings using examples.
[0012]
FIG. 1 is a partial sectional perspective view of a projection type image display device to which the present invention is applied. The image generation source 1 is composed of, for example, a reflection-type or transmission-type liquid crystal panel, or an image modulation element such as a display element having a plurality of minute mirrors. The image (image light modulated by the image modulation element) displayed on the image source 1 is enlarged by the projection lens 2, reflected by the reflection mirror 4, and projected from the rear of the rear projection screen 3. The image source 1, the projection lens 2, the rear projection screen 3, and the reflection mirror 4 are fixed at predetermined positions of a housing 5 and housed. 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.
[0013]
The image modulating element as described above 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. For this reason, the projection lens 2 used in the present embodiment is smaller and has a higher F value (the F value is a numerical value representing the brightness of the lens, and the focal length f of the lens and the focal length f of the lens are smaller than the projection lens for a projection type cathode-ray tube). Is equal to the ratio f / D of the aperture D. The high F value indicates that the aperture D of the lens is small if the focal length f is the same, and if the light incident on the lens is close to the collimated light, the lens is closed. The brightness can be secured even if the aperture D is small.).
[0014]
FIG. 2 is a schematic diagram showing the structure of the rear projection type screen 3 according to the present invention. The rear projection screen 3 includes a first sheet and a second sheet arranged along the traveling direction of image light (the direction of arrow b in FIG. 2). The first sheet includes a Fresnel lens sheet 6 in which a concentric Fresnel lens is formed on one of the light incident surface and the light exit surface (the light exit surface in the present embodiment). The second sheet has a plurality of lenticular lenses 8 which are concave toward the image generation source and extend in the vertical direction of the screen, and a diffusion sheet 7 which is a diffusion layer containing a particulate diffusion material for diffusing image light. And A plurality of concave lenticular lenses 8 are provided side by side in the horizontal direction of the screen. An enlarged projection image (not shown) projected from the direction of arrow b is converted into substantially parallel light or light slightly inward by the Fresnel lens sheet 6 and enters the diffusion sheet 7. These operations will be described with reference to FIG. FIG. 3 is a cross-sectional view of the rear projection screen 3 according to the present invention shown in FIG. 2 and is located near the center right end of the rear projection screen 3 of FIG. Arrows in the figure indicate the directions of light rays. A group of light rays incident from the lower left of the figure is changed in a substantially horizontal direction by the Fresnel lens sheet 6 and is incident on the concave lenticular lens 8 on the image source side. A group of light rays that have entered the concave lenticular lens 8 in a substantially horizontal direction on the image source side are diverged by the concave lenticular lens on the image source side, further diffused by the diffusion sheet 7, and then viewed on the viewing side (arrows). in the direction c).
[0015]
As described above, speckles are generated when light scattered by minute diffusion elements located at a spatially separated location acts on one point behind and interferes with each other. Is diffused by a concave lenticular lens on the image source side, so that even if there is a diffusing material, they hardly interfere with each other. This will be described with reference to FIGS. FIG. 4 is a view for explaining the operation of a lenticular lens having a convex shape on the image generating source side. Light rays incident from a Fresnel lens sheet (not shown) are once converged by a lenticular lens having a convex shape on the image generating source side. It is made to emanate after being made. Therefore, if the diffusing material is present in a range up to twice the focal length f, speckle is generated. As described in the related art, if the diffusing material is provided at a position separated by at least about three times the focal length of the lenticular lens, speckle does not occur, but there is a problem that the resolution is extremely deteriorated. FIG. 5 is a view for explaining the operation of the lenticular lens having a concave shape on the image generating source side according to the present invention. Light rays incident from a Fresnel lens sheet (not shown) have a concave lenticular lens on the image generating source side. Dissipated in. Therefore, even if the diffusing material is in the vicinity of the lenticular lens, generation of speckle is extremely small. As shown in the figure, if the diffusing material is separated by the focal length f of the lenticular lens, the same effect is obtained as if the diffusing material was separated by three times the focal length of the lenticular lens having a convex shape toward the image source. That is, in the present embodiment, the distance between the vertex of the concave lenticular lens 8 (the curved surface near the optical axis) and the light incident surface of the diffusion sheet 7 (the boundary surface between the lenticular lens 8 and the diffusion sheet 7) is The focal length f of the concave lenticular lens is substantially equal to the focal length f. As described above, in the present invention, since the lenticular lens and the diffusing material are at a short distance, the deterioration of the resolution is small.
[0016]
FIG. 6 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 is different from the embodiment of FIG. 2 in that the boundary between the concave lenticular lenses 9 on the image source side provided on the Fresnel lens sheet 6 side of the diffusion sheet 7 (hereinafter referred to as a ridge). Is provided with a black stripe 10. Hereinafter, the operation of the black stripe 10 will be described with reference to FIGS. FIG. 7 is a cross-sectional view of the diffusion sheet 7 according to the present invention shown in FIG. 2 and a lenticular lens 8 having a concave shape on the image source side provided on the Fresnel lens sheet (not shown) side of the diffusion sheet 7. . In the figure, arrows indicate external light. Part of the external light that enters from the viewing side repeats total reflection at the interface of the lenticular lens 8 having a concave shape toward the image generation source side as shown in the figure, and is condensed on the ridge d of the lenticular lens 8. This means that in the embodiment of FIG. 2, the presence of external light causes a disadvantage that the ridge of the lenticular lens 8 shines. FIG. 8 is a cross-sectional view of the diffusion sheet 7 according to the present invention shown in FIG. 6 and a lenticular lens 9 having a concave shape on the image source side provided on the Fresnel lens sheet (not shown) side of the diffusion sheet 7. . The difference from FIG. 7 is that a black stripe 10 is provided at the edge of the lenticular lens 9. Since the black stripe 10 repeats total reflection at the interface of the lenticular lens 9 and absorbs external light condensed on the ridge of the lenticular lens 9, the ridge of the lenticular lens 9 does not shine even when external light is present. However, since the black stripe 10 is on the light incident side of the lenticular lens, the aperture ratio of the lenticular lens is reduced. Therefore, when the present invention is carried out under the condition that there is no external light, it is better not to have the black stripe 10. Further, even when the black stripe 10 is provided, it is necessary to make its width as narrow as possible. In the current state of the art, the width is limited to about 0.01 mm, and is manufactured by screen printing or hot stamping using a matte black pigment-based foil.
[0017]
FIG. 9 is a schematic view 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. 6 represent the same parts. This embodiment is different from the embodiment of FIG. 6 in that the coloring sheet 11 is provided on the viewing side of the diffusion sheet 7 (the side opposite to the Fresnel lens sheet 6). The coloring sheet 11 has an effect of reducing a problem that the diffusion material kneaded in the diffusion sheet 7 shines white due to external light. As shown in FIG. 9, the coloring sheet 11 is preferably provided on the viewing side of the diffusion sheet 7. This is because, when the transmittance of the colored sheet 11 is η, external light that enters the diffusion material kneaded into the diffusion sheet 7 from the viewing side, is reflected by the diffusion material, and returns to the viewing side again is η ^2. This is because the effect of the colored sheet 11 is attenuated to be the best.
[0018]
FIG. 10 is a schematic diagram 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. 6 represent the same parts. This embodiment differs from the embodiment of FIG. 6 in that the diffusion sheet 12 is colored. As compared with the embodiment shown in FIG. 9, the coloring effect is lower, but there is an advantage that the number of parts is reduced.
[0019]
FIG. 11 is a schematic view 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. 6 represent the same parts. This embodiment is different from the embodiment of FIG. 6 in that an antireflection sheet 13 is provided on the viewing side of the diffusion sheet 7 (the side opposite to the Fresnel lens sheet 6). The antireflection sheet 13 is adhered to the diffusion sheet 7 with a colored adhesive 14. The anti-reflection sheet 13 is generally used to reduce the reflection of external light. However, by coloring the adhesive material 14 as in the present invention, the same coloring effect as in the embodiment shown in FIG. 9 can be obtained. Can be
[0020]
The embodiments of the present invention have been described with reference to FIGS. 2, 6, 9, 10, and 11. Hereinafter, their manufacturing method and material selection will be described. 12 and 13 are diagrams schematically showing a method of manufacturing the lenticular lens 9 having a concave shape on the image generation source side in sheet units according to the present invention. In FIG. 12, reference numeral 15 denotes a mold for a lenticular lens, which is usually formed by winding a thin plate such as brass around a processing drum (not shown) and processing it with a lathe (not shown). At this time, the tool bit (not shown) of the processing tool is made of an industrial diamond, but only a tip having a convex shape can be made. Therefore, as shown in the figure, the mold 15 has a concave shape, and only a convex lenticular lens can be formed as it is. Therefore, as shown in FIG. 12, a UV resin for a mold is poured onto a mold 15 and pressed by a glass plate 16, and further, UV is irradiated from above the glass plate 16 to solidify the UV resin and invert the mold 15. make.
[0021]
FIG. 13 is a diagram showing a method of forming a concave lenticular lens 9 on the image generation source side using the resin mold prepared as described above. In the figure, 17 is a resin mold, 7 is a diffusion sheet, and 16 is a glass plate. A transparent UV resin is flowed on the resin mold 17, the diffusion sheet 7, which has been subjected to a surface treatment to improve the adhesiveness of the UV resin, is placed thereon, and further pressed by the glass plate 16 to irradiate UV light from above the glass plate 16. UV resin is hardened and manufactured. The concave lenticular lens 9 on the image source side is adhered to the surface-treated diffusion sheet 7 to form one sheet. Thereafter, if necessary, a black stripe 10 is provided on the ridge of the lenticular lens 9 by screen printing or a hot stamp using a matte black pigment-based foil, or an antireflection sheet 13 is formed on the diffusion sheet 7 with a colored adhesive material 14. Or glue.
[0022]
FIG. 14 is a diagram schematically showing a method of continuously forming a lenticular lens by winding the resin mold 17 made in FIG. 12 around a forming drum 18. In the figure, 19a is an upper guide roller, 19b is a lower guide roller, and 20 is a base sheet that has been subjected to a surface treatment to improve the adhesiveness of the UV resin. The base sheet 20 moves downward from above while being pressed against the forming drum 18 around which the resin mold 17 is wound by the guide rollers 19a and 19b. The transparent UV resin is put into a position where the base sheet 20 and the forming drum 18 around which the resin mold 17 is wound start to come into contact, and is irradiated with UV while the base sheet 20 and the forming drum 18 are in contact to solidify the UV resin. . Further, as a post-process, the black stripes 10 can be continuously provided on the edges of the lenticular lens 9 by screen printing or hot stamping using a matte black pigment-based foil. Thereafter, the sheet is cut into a predetermined size and adhered to the diffusion sheet 7 with a transparent adhesive material. Further, the antireflection sheet 13 is adhered to the diffusion sheet 7 with a colored adhesive 14 as necessary.
[0023]
The concave lenticular lens 9 on the image generation source side of the present invention is made of a material having a large linear expansion coefficient due to moisture absorption, for example, a polymethyl methacrylate UV resin. Conversely, the diffusion sheet 7 is made of a material that absorbs less moisture than the lenticular lens 9, such as a copolymer of methyl methacrylate-styrene, polyethylene terephthalate, and polycarbonate. With this configuration, when the screen absorbs moisture, the diffusion sheet 7 and the lenticular lens 9 warp so as to have a convex shape toward the Fresnel lens sheet 6 side. The Fresnel lens sheet 6 and the lenticular lens 9 are kept in close contact.
[0024]
As described above, according to the present invention, it is possible to reduce the occurrence of speckles while suppressing deterioration in image resolution and / or contrast performance. This has the effect of enabling
[0025]
【The invention's effect】
According to the present invention, it is possible to display a high-quality image on a screen.
[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 cross-sectional view of the rear projection screen 3 according to the present invention shown in FIG.
FIG. 4 is a diagram illustrating the operation of a lenticular lens having a convex shape on the image generation source side.
FIG. 5 is a diagram illustrating the operation of a concave lenticular lens on the image generation source side according to the present invention.
FIG. 6 is a schematic diagram showing the structure of another embodiment of the rear projection screen 3 according to the present invention.
7 is a cross-sectional view of the diffusion sheet 7 and the concave lenticular lens 8 according to the present invention shown in FIG.
FIG. 8 is a cross-sectional view of the diffusion sheet 7 and the concave lenticular lens 9 according to the present invention shown in FIG.
FIG. 9 is a schematic view showing the structure of another embodiment of the rear projection screen 3 according to the present invention.
FIG. 10 is a schematic diagram showing the structure of another embodiment of the rear projection screen 3 according to the present invention.
FIG. 11 is a schematic view showing the structure of another embodiment of the rear projection type screen 3 according to the present invention.
FIG. 12 is a diagram schematically illustrating a method of manufacturing a resin mold for manufacturing a concave lenticular lens 9 on the image generation source side in sheet units according to the present invention.
FIG. 13 is a diagram schematically illustrating a method of manufacturing a lenticular lens 9 having a concave shape on the image generation source side in a sheet unit according to the present invention.
FIG. 14 is a diagram schematically illustrating a method of continuously forming a concave lenticular lens on the image generation source side according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Image source, 2 ... Projection lens, 3 ... Rear projection screen, 4 ... Reflection mirror, 5 ... Case, 6 ... Fresnel lens sheet, 7 ... Diffusion sheet, 8 ... Concave lenticular on the image source side Lens, 10: black stripe, 11: colored sheet, 13: anti-reflective sheet, 14: colored adhesive

Claims (15)

An image source, an optical component for enlarging and projecting the image of the image source, and a rear projection screen for projecting a projected image projected from the optical component, wherein the rear projection screen has at least an image generation source. A Fresnel lens sheet arranged on the source side, and a diffusion sheet arranged on the image viewing side and diffusing image light,
An image display device, wherein a plurality of lenticular lenses extending in the vertical direction on the screen with a concave shape on the image source side are formed on the Fresnel lens sheet side of the diffusion sheet. 2. The image display device according to claim 1, wherein a black stripe is provided at a boundary between the plurality of lenticular lenses. The image display device according to claim 1, wherein a coloring sheet is provided on an image viewing side of the diffusion sheet. The image display device according to claim 1, wherein the diffusion sheet is colored. 2. The image display device according to claim 1, wherein an antireflection sheet is adhered to the viewing side of the diffusion sheet using a colored adhesive. 2. The image display device according to claim 1, wherein the lenticular lens is made of a material having a large coefficient of linear expansion due to moisture absorption, and the diffusion sheet is made of a material having less moisture absorption than the lenticular lens. Image display device. 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 source side, and a diffusion sheet arranged on the image viewing side and diffusing image light,
A rear projection screen in which a plurality of lenticular lenses extending in the vertical direction of the screen with a concave shape on the image source side are formed on the Fresnel lens sheet side of the diffusion sheet, and are arranged side by side in the horizontal direction of the screen. . 8. The rear projection screen according to claim 7, wherein a black stripe is provided at a boundary between the plurality of lenticular lenses. 8. The rear projection screen according to claim 7, wherein a coloring sheet is provided on an image viewing side of the diffusion sheet. 8. The rear projection screen according to claim 7, wherein the diffusion sheet is colored. The rear projection type screen according to claim 7, wherein an antireflection sheet is adhered to the viewing side of the diffusion sheet using a colored adhesive. 8. The rear projection screen according to claim 7, wherein the lenticular lens is made of a material having a large linear expansion coefficient due to moisture absorption, and the diffusion sheet is made of a material having less moisture absorption than the lenticular lens. Type screen. In a rear projection screen that projects the image of the image source projected from the optical component,
A first sheet and a second sheet are arranged in this order along the traveling direction of the image light from the image source, and the first sheet has a Fresnel lens formed on at least one surface thereof, and The sheet No. 2 has a plurality of lenticular lenses formed on the light incident side thereof and formed in a concave shape on the image source side and extending in the vertical direction of the screen, and for diffusing the image light to the light emitting side. A rear projection screen, wherein a diffusion layer containing a diffusion material is provided. In the optical axis direction of the concave lenticular lens, the distance between the apex of the concave lenticular lens and the light incident surface of the diffusion layer is substantially equal to the focal length of the concave lenticular lens. The rear projection type screen according to claim 13. 14. The rear projection screen according to claim 13, wherein a light absorbing portion is provided at a boundary between the plurality of concave lenticular lenses.

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