JP4066919B2 - Image display device and rear projection screen used therefor - Google Patents

Description

  The present invention relates to an image display device that enlarges and projects an image of an image generation source and displays the image on a rear projection screen, a rear projection screen used in the image display device, a Fresnel lens sheet, and a manufacturing method thereof.

  Image display devices that use a projection lens, etc., to enlarge the image displayed on a projection cathode-ray tube or a liquid crystal display device as a compact image source and project it onto a rear projection screen have recently seen remarkable improvements in image quality. It is spreading for use.

  In such an image display device, the depth of the image display device is reduced by using a reflection mirror that reflects an enlarged image from the projection lens and guides it to the rear projection screen. As a rear projection screen used for this, a Fresnel lens sheet for converting an enlarged projection image into substantially parallel light or light slightly inward, and a lenticular lens sheet for diffusing image light in the horizontal direction of the screen are usually used. For example, a configuration described in Patent Document 1 below is known as a rear projection screen for coping with further thinning of the image display device.

WO / 02/27399

  The problem of the present invention will be described with reference to FIGS. If the image display device has the same screen size, the thinner the depth, the more advantageous in terms of weight, cost, and installation space. A reflection mirror 54 is provided to reduce the depth of the video display device. As a means for further reducing the depth, there is a method of widening the projection lens 52. However, there is a limit to widening the angle of the lens. For example, when the aspect ratio is 16: 9 and the diagonal is 65 inches, if the projection distance is 700 mm or less, the image generation source 51 and the projection lens 52 interfere with the projection light. A shadow is formed on the rear projection screen 53. Therefore, if an attempt is made to reduce the thickness only by widening the projection lens 52, as shown in FIG. 8, when the aspect ratio is 16: 9 and the diagonal is 65 inches, the depth of the optical system is 400 mm (the depth of the image display device). 450 mm) is the limit. In FIG. 8, the center of the optical axis of the projection lens 52 and the center of the rear projection screen 53 coincide with each other and the optical axis and the screen are set to be vertical. By setting it in the vicinity, the image generation source 51 and the projection lens 52 do not interfere with the projection light even when the projection distance is 700 mm or less. 9 is a screen size having an aspect ratio of 16: 9 and a diagonal size of 65 inches as in FIG. 8, but the optical axis center of the projection lens 52 coincides with the lower end of the rear projection screen 53 and the projection distance is 500 mm. In this case, the depth of the optical system can be reduced to 300 mm (the depth of the image display device is 350 mm).

  As described above, by reducing the projection distance of the projection lens 52 and setting the center of the optical axis of the projection lens 52 in the vicinity of the lower end of the rear projection screen 53, the video display device can be made thinner. However, in this case, the following new problem occurs.

  In FIG. 9, since the screen size is 65 inches diagonal with an aspect ratio of 16: 9, assuming that the optical axis center of the projection lens 52 is the center of the lower end of the rear projection screen 53, the projection lens 52 to the rear projection screen 53 The screen incident angle of the image light incident on the upper left and right ends is 65.2 degrees. FIG. 10 is a diagram showing the relationship between the incident angle of light on the screen of a general exit surface Fresnel lens and the reflection loss. From the figure, it is understood that the reflection loss of the screen is as large as 36% when the light incident angle is 65.2 degrees. If the video display device is further reduced in thickness, this loss increases rapidly, resulting in a problem that the video display device becomes darker at the upper left and right ends of the screen.

  Further, in Patent Document 1, as a rear projection screen corresponding to a reduction in the thickness of an image display device, a refractive prism and a total reflection prism are alternately provided on a light incident surface of a Fresnel lens, and a light emitting surface is planar. It is disclosed that. However, since the configuration described in Patent Document 1 has a configuration in which a refractive prism is provided on the light incident surface of the Fresnel lens, the efficiency is lowered, and a mid-range image (a donut-shaped range on the screen) that is particularly important as an image. There is a problem that becomes darker.

  The present invention has been made in view of the problems as described above, and an object thereof is to provide a technique suitable for shortening the depth of a video display device. It is another object of the present invention to provide a technique suitable for shortening the depth of a video display device without greatly impairing the image quality (brightness) of the displayed video on the screen.

  In order to achieve the above object, according to the present invention, an incident angle to a Fresnel lens sheet of a projected image projected from an optical component is at least a predetermined angle on an image generation source side of a Fresnel lens sheet constituting a rear projection screen. A total reflection prism portion that emits incident light as an output light having a predetermined output angle by a total reflection phenomenon after the first refraction phenomenon is provided in a range that is greater than or equal to (for example, approximately 40 degrees). A refraction type prism portion that emits as a light beam having a predetermined emission angle by a second refraction phenomenon is provided in a range facing a portion where the total reflection type prism portion on the viewing side is not provided. is there.

  In the present invention, the region where the refractive prism portion is provided is a region where the light beam emitted from the total reflection prism portion overlaps at least one pitch of the refractive prism portion.

  Further, in the present invention, the total reflection surface of the total reflection prism portion provided on the image generation source side of the Fresnel lens sheet constituting the rear projection screen is concave on the image generation source side.

  In addition, the method for producing a Fresnel lens sheet according to the present invention includes forming a refractive prism portion and a total reflection prism portion by simultaneously subjecting a transparent substrate such as polymethyl methacrylate to a methyl methacrylate-styrene copolymer to thermal compression molding on both sides. It is formed. Alternatively, after forming the refractive prism portion on the image viewing side by thermal compression molding, the total reflection prism portion may be formed on the opposite side with an ultraviolet curable resin. Alternatively, a transparent base material on which a transparent ultraviolet curable resin layer having a total reflection prism portion is formed on the surface opposite to the surface on which the refractive prism portion is formed may be bonded and fixed with an adhesive layer.

  According to the present invention, the video display device can be thinned. In particular, it is possible to reduce the thickness of the image display device without greatly degrading the image quality of the image displayed on the screen, for example, the brightness.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a partial sectional perspective view of a video display device according to the present invention. The image generation source 1 is composed of 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 onto 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 in order to reduce the depth of the image display device. These elements are fixed at predetermined positions accommodated in the housing 5.

  FIG. 2 is a schematic diagram showing the structure of the rear projection screen 3 according to the present invention. An enlarged projection image (not shown) projected from the direction of the arrow b is converted into substantially parallel light or light slightly inward by the Fresnel lens sheet 6 and enters the lenticular lens sheet 7. The lenticular lens sheet 7 has a shape in which a plurality of lenticular lenses whose longitudinal direction is the vertical direction of the screen screen are arranged in the horizontal direction of the screen screen as shown in the figure, and functions to diffuse the image light in the horizontal direction of the screen screen. . A black stripe 8 extending in the vertical direction of the screen is formed on the exit surface of the lenticular lens sheet 7 and absorbs external light incident from the screen exit side. Further, a diffusing material 9 is kneaded into the lenticular lens sheet 7 and functions to diffuse the image light in the horizontal and vertical directions of the screen screen. The embodiment of the rear projection screen according to the present invention shown in FIG. 2 is an incident angle of the enlarged image light beam projected from the direction of the arrow b on the image generation source side surface of the Fresnel lens sheet to the Fresnel lens sheet. Is a total reflection type in which an incident light beam is emitted as a light beam having a predetermined emission angle by a total reflection phenomenon after the first refraction phenomenon in a range (first region) where at least a predetermined angle or more, for example, approximately 40 degrees or more. A prism unit 10 (first prism) is provided. Further, a range (second region) where a light ray of the projected image is incident at an angle less than the predetermined angle on the image generation side surface of the Fresnel lens sheet is defined as a flat surface portion where the total reflection prism portion is not provided. Furthermore, a refraction-type prism portion (second prism) that emits as a light beam having a predetermined emission angle by a second refraction phenomenon in a range facing the second region on the visual viewing side of the Fresnel lens sheet. 11 is provided. The total reflection prism unit 10 has a convexity (protrusions) toward the image generation source side, and the refraction type prism unit 11 has a convexity (protrusions) toward the image viewing side.

  The operation of the total reflection prism unit 10 will be described with reference to FIG. FIG. 3 is a longitudinal sectional view of the Fresnel lens sheet 6 according to the present invention shown in FIG. 2, and the position is near the left (right) upper end of the rear projection screen 3 of FIG. The arrow in the figure indicates the direction of the light beam. As shown in FIG. 3, a total reflection prism portion 10 is provided on the image generation source side of the Fresnel lens sheet 6, and the viewing side is planar. A light ray incident from the image generation source side is incident from the c-plane (incident surface) of the total reflection type prism unit 10, is totally reflected by the d-plane (total reflection surface), and then is emitted substantially horizontally to the viewing side. . FIG. 3 is a longitudinal sectional view of a portion where the viewing side is flat, but a refractive prism portion is provided in a range facing a portion where the total reflection prism portion is not provided. The boundary portion between the two is configured such that the light emitted from the total reflection type prism portion overlaps at least one pitch of the refraction type prism portion. The reason for this will be described with reference to FIG.

  FIG. 4 is a longitudinal sectional view of the Fresnel lens sheet 6 according to the present invention, which is a boundary portion where the total reflection prism portion 10 provided on the image generation source side is provided. As shown in FIG. 4, a total reflection prism portion 10 is provided in a region (second region) where the image light is incident at a predetermined incident angle (40 degrees) or less on the Fresnel lens sheet 6 image source side. A flat portion (flat portion) 12 is formed. If the incident angle of the projected image projected from the optical component on the image generation source side to the Fresnel lens sheet 6 is small, the total reflection prism unit 10 cannot be provided. Therefore, in the range where the incident angle of the projected image on the Fresnel lens sheet 6 is small, the image source side is flat and the refractive prism portion 11 is provided on the viewing side as a normal exit surface Fresnel lens. As described above, in the Fresnel lens sheet 6 according to the present invention, the image source side suddenly changes from a flat portion to a portion where the total reflection prism portion 10 is provided. Since the image source side and the viewing side of the Fresnel lens sheet 6 are molded by different molds, it is difficult to make the both sides completely coincide with each other due to the alignment and expansion and contraction due to the temperature difference. Therefore, even if the above-described image generation source side is changed from a flat portion to a portion provided with the total reflection type prism portion 10, a prevention means is required to prevent this change from appearing in the image. In the Fresnel lens sheet 6 according to the present invention shown in FIG. 4, the boundary portion is configured such that light rays emitted from the total reflection type prism portion overlap at least one pitch of the refraction type prism portion. That is, most of the area of the Fresnel lens sheet 6 facing the first area on the image viewing side is planar, but a part of the area on the image viewing side (the first area) (A portion facing the total reflection prism 10 located in the vicinity of the boundary between the flat region and the planar second region) is provided with a refractive prism 11 having one to several pitches, several tens pitches, or more. . That is, a part of the total reflection prism portion 10 and a part of the refractive prism 11 are overlapped in the thickness direction of the Fresnel lens sheet 6.

  After entering from the c-plane of the total reflection prism portion 10 and totally reflected by the d-plane, if the viewing side of the Fresnel lens sheet 6 is flat, it emits light as it is, but when entering the refraction-type prism portion 11, it enters as shown in the figure. The light is totally reflected by the refraction type prism unit 11 and emitted upward, and cannot be seen from the viewing side. Since these image lights cannot be seen from the viewer side, the images will be lost, but the image defect that the image light disappears and the black arc appears because the image source side of the Fresnel lens sheet 6 is shifted from the viewer side is Disappear. Further, even if the image is missing, the amount is only the amount of deviation on both sides, and since it is manufactured with higher accuracy than the original, it cannot be noticeably a large missing.

  Next, another embodiment of the present invention will be described with reference to FIGS. FIG. 5A is a longitudinal sectional view of a portion where the total reflection type prism portion 10 of one embodiment of the Fresnel lens sheet 6 according to the present invention is provided, and is the same as the portion shown in FIG. This is a portion where the incident angle to the Fresnel lens sheet 6 is large. In the figure, only the light beam passing portion is hatched. The same reference numerals and symbols as those in FIG. 4 denote the same parts and the same parts. In the portion where the incident angle to the Fresnel lens sheet 6 of the projected image in FIG. 4 is small, the light output from the Fresnel lens sheet 6 continued almost seamlessly, whereas the incident angle to the Fresnel lens sheet 6 in FIG. In a large portion, the light emitted from the Fresnel lens sheet 6 is completely divided into a light emitting portion and a non-light emitting portion. The presence of the light-free portion causes moiré between the lenticular lens sheet 7 of the rear projection screen 3 and the pixels of the image source, and some preventive means is required. FIG. 5B is a longitudinal sectional view of a portion where the total reflection prism portion 14 of another embodiment of the Fresnel lens sheet according to the present invention is provided. In the figure, only the light beam passing portion is hatched. In FIG. 5B, reference numeral 14 denotes a total reflection prism portion provided on the image source side of the Fresnel lens sheet 13. In the Fresnel lens sheet 13 according to the present invention shown in FIG. 5 (b), the light ray enters from the e-plane of the total reflection prism portion 14 and is totally reflected by the f-plane, but the f-plane is formed in a concave shape on the image generation source side. As a result, the reflected light spreads, and as a result, there is no break in the image light on the viewing side. As a result, moire does not occur between the total reflection prism portion 14 on the image source side and the lenticular lens sheet 7 of the rear projection screen 3 and the pixels of the image source.

  In general, the prism portion of the Fresnel lens sheet is molded using an ultraviolet curable resin. However, when the prism is provided on both sides like the Fresnel lens sheet of the present invention, the ultraviolet curable resin does not transmit ultraviolet rays. Therefore, only one side can be molded. Therefore, the Fresnel lens sheet of the present invention can be manufactured by carrying out the manufacturing method shown below.

  First, in the first manufacturing method, a transparent base material such as polymethyl methacrylate or a copolymer of methyl methacrylate-styrene is subjected to thermal compression molding on both sides simultaneously with two opposing molds of a refraction type prism part and a total reflection type prism part. . Since this method does not use an ultraviolet curable resin, a Fresnel lens sheet having prism portions on both sides of the present invention can also be easily manufactured.

  FIG. 6 is a diagram for explaining another embodiment of the method for producing a Fresnel lens sheet according to the present invention. A refractive prism 11 is molded on the transparent base material 15 constituting the Fresnel sheet 6. The total reflection prism 10 is molded on the transparent ultraviolet curable resin layer 16 adhered to the surface of the transparent substrate 15 where the refractive prism 11 is not formed. Specifically, after forming the refractive prism portion 11 on the image viewing side by heat compression molding a transparent base material 15 such as polymethyl methacrylate or methyl methacrylate-styrene copolymer, ultraviolet rays are formed on the opposite side. The total reflection prism portion 10 is formed of a cured resin. In the embodiment of FIG. 6, the ultraviolet curable resin adheres not only to the total reflection prism portion 10 but also to the flat surface portion to form the transparent ultraviolet curable resin layer 16.

  FIG. 7 is a view for explaining another embodiment of the method for producing a Fresnel lens sheet according to the present invention. A refractive prism portion 20 is formed on the first transparent ultraviolet curable resin layer 19 bonded to the first transparent substrate 18 constituting the Fresnel lens sheet 17. A second transparent ultraviolet curable resin layer 21 is provided on the surface of the first transparent substrate 18 where the refractive prism 20 is not formed, and a total reflection prism portion 22 is formed thereon. The second transparent ultraviolet curable resin layer 21 on which the total reflection type prism portion 22 is formed is formed on the second transparent base material 23 by an ultraviolet curable method, and then is adhered to the first transparent base material 18 by the adhesive layer 24. Bonded and fixed.

  For the first transparent base material 18 constituting the Fresnel lens sheet 17, for example, polymethyl methacrylate or a copolymer of methyl methacrylate-styrene can be used. Further, the second transparent base material 23 of the second transparent ultraviolet curable resin layer 21 on which the total reflection prism portion 22 is formed is made of polyethylene terephthalate subjected to a surface treatment that facilitates adhesion of the ultraviolet curable resin, and the adhesive layer 24. A highly transparent acrylic adhesive can be used. In the above description, the second transparent ultraviolet curable resin layer 21 in which the total reflection type prism portion 22 is formed is adhered by the adhesive layer 24, but the first transparent ultraviolet curable resin layer 19 in which the refractive prism portion 20 is formed is adhered. The effect is the same even if the layers 24 are bonded.

  According to the present invention, in order to reduce the depth of the video display device, the optical axis center of the projection lens is set near the lower end of the rear projection screen, and the screen incident angle of the video light incident on the left and right upper ends of the rear projection screen is Even if it becomes excessive, the reflection loss of the screen can be suppressed. Further, according to the present invention, it is possible to reduce the moire phenomenon that occurs in the Fresnel lens sheet. Thus, according to the present invention, it is possible to obtain a bright image display device up to the upper left and right ends of the screen.

1 is a partial cross-sectional perspective view showing an embodiment of a video display device according to the present invention. It is a schematic diagram which shows the structure of the rear projection type screen 3 of the video display apparatus shown in FIG. It is a longitudinal cross-sectional view of the Fresnel lens sheet 6 according to the present invention shown in FIG. It is a longitudinal cross-sectional view of the Fresnel lens sheet 6 by this invention, and is a boundary part in which the total reflection type prism part 11 provided in the image source side is provided. The longitudinal cross-sectional view of the boundary part in which the total reflection type prism part 11 of one Example of the Fresnel lens sheet 6 by this invention is provided, and the boundary in which the total reflection type prism part of the other Example of the Fresnel lens sheet by this invention is provided It is a longitudinal cross-sectional view of a part. It is a figure explaining one Example of the manufacturing method of the Fresnel lens sheet by this invention. It is a figure explaining the other Example of the manufacturing method of the Fresnel lens sheet by this invention. It is a figure which shows the limit of thickness reduction of the optical system by the wide angle of the projection lens. 6 is a diagram showing a reduction in the thickness of the optical system when the optical axis center of the projection lens 52 is set at the lower end center of the rear projection screen 53. FIG. It is the figure which showed the relationship between the light ray incident angle to the screen of a common output surface Fresnel lens, and reflection loss.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Image generation source, 2 ... Projection lens, 3 ... Rear projection type screen, 4 ... Reflection mirror, 5 ... Case, 6, 13, 17 ... Fresnel lens sheet, 7 ... Diffusion sheet, 10, 14, 22 ... All Reflective prism portion 11, 20,... Refractive prism portion, 12 ... Flat portion where total reflection prism portion on the image source side is not provided, 15, 18, 23 ... Transparent substrate, 16, 19, 21 ... Transparent UV curable resin layer, 24 ... adhesive layer

Claims (8)

In rear projection screens where images from image sources are projected,
A Fresnel lens sheet arranged at least on the image generation source side,
A diffusion sheet disposed on the image viewing side and diffusing image light on the image viewing side;
The Fresnel lens sheet reflects the incident light to the first region to the first region on the side of the image generation source of the Fresnel lens sheet where the light of the projected image is incident at a predetermined incident angle or more. Including a first prism that is convex on the image generation source side, including a total reflection surface that leads to the image viewing side of
The second region on the side of the image generation source where the light beam of the projection image is incident at a angle less than the predetermined incident angle is planar,
Video viewing for refracting and emitting a light beam incident on the second region and transmitted through the Fresnel lens sheet in a region facing the second region on the image viewing side of the Fresnel lens sheet A convex second prism is provided on the side,
The rear projection screen is characterized in that the second prism is not provided in a region facing the first region on the image viewing side surface of the Fresnel lens sheet . The rear projection screen according to claim 1,
Wherein the predetermined angle of incidence, rear projection screen you characterized by about 40 degrees. The rear projection screen according to claim 1,
The video-watching side of the Fresnel lens sheet, the back surface projection screen you wherein the first region facing the region is planar. The rear projection screen according to claim 3,
The first prism located in the vicinity of the boundary between the first region and the second region is opposed to a part of the region facing the first region on the image viewing side surface of the Fresnel lens sheet. as such, rear projection screen characterized in that said second prism is provided. A video source,
An optical component for enlarging and projecting the image of the image source;
A rear projection screen that projects a projected image projected from the optical component,
The rear projection screen includes a diffusing sheet for diffusing the image light into at least a video source side to the Fresnel lens sheet and the image viewing side,
A video source side surface of the Fresnel lens sheet,
The range where the incident angle is at least more than approximately 40 degrees to the Fresnel lens sheet of the incident light of the projection image projected from the optical component, given by the total reflection phenomenon of the incident light beam after the first refraction phenomenon the total reflection type prism portion be emitted as output light beam output angle provided, a video viewing side surface of the Fresnel lens sheet,
Wherein the region facing the portion not provided with the total reflection type prism portion, a refractive prism portion provided to emit a second refraction phenomenon as an outgoing light beam of a predetermined output angle,
The video display device is characterized in that the refractive prism portion is not provided in a range facing a portion where the total reflection prism portion is not provided . The video display device according to claim 5, wherein
The region where the refractive prism portion is provided is a region in which the light emitted from the total reflection prism portion overlaps at least one pitch or more of the refractive prism portion. The video display device according to claim 5, wherein
An image display device characterized in that a total reflection surface of a total reflection prism portion provided on the image generation source side of the Fresnel lens sheet is concave on the image generation source side. The rear projection screen according to claim 1, wherein
The region where the second prism on the image viewing side is provided is a region in which light emitted from the first prism on the image generation source side overlaps at least one pitch of the second prism. Rear projection type screen.

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