JP2998811B2 - Transmissive screen and rear projection type image display device using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transmission screen and a rear projection type image display apparatus using the same.

[0002]

2. Description of the Related Art A rear surface of a rear projection television receiver or the like which enlarges an image displayed on a projection type cathode ray tube or a liquid crystal display device as a small image source by a projection lens and projects the image on a transmission screen from the rear side. In recent years, projection-type image display apparatuses have remarkably improved image quality and can enjoy powerful realism with a large screen.
It is becoming popular for business use.

In this rear projection type image display device, when a projection type cathode ray tube is used as an image generation source, the three primary colors of red, green, and blue have been conventionally compared with the cathode ray tube in order to sufficiently increase the brightness of the screen on the screen. 2. Description of the Related Art There is a configuration in which a projection lens is combined to synthesize an image of three primary colors on a screen.

In the rear projection type image display device having this configuration, a conventional image display device is disclosed in, for example, Japanese Patent Application Laid-Open No. 58-192.
As described in Japanese Patent Publication No. 022, a transmissive screen having a configuration in which a Fresnel lens sheet and a lenticular lens sheet in which fine particles that scatter light are dispersed and arranged therein is generally used.

FIG. 16 is a perspective view showing a transmission screen according to the prior art. In FIG. 1, reference numeral 1 denotes a transmissive screen, 2 denotes a Fresnel lens sheet disposed on the image generation source (CRT screen) side, and 3 denotes a lenticular lens sheet disposed on the image viewing side. 20, 30
Are the base materials of the Fresnel lens sheet 2 and the lenticular lens sheet 3, respectively, each of which is made of a transparent thermoplastic resin. Of these, in the base material 30 of the lenticular lens sheet 3, fine particles of a light diffusing material for diffusing light are dispersed. 21 and 22 are the Fresnel lens sheets 2,
The entrance surface 21 is a plane surface, and the exit surface 22 is a convex Fresnel lens surface.

Reference numeral 31 denotes an entrance surface of the lenticular lens sheet 3, which has a shape in which lenticular lenses having a longitudinal direction perpendicular to the screen screen are arranged in the horizontal direction of the screen screen. Reference numeral 32 denotes an exit surface of the lenticular lens sheet 3. A lenticular lens having a similar shape is arranged substantially opposite to the lenticular lens on the entrance surface 31, and a convex projection is provided between adjacent lenticular lenses. A light absorbing layer (black stripe) on the projection 33;
6 are stacked.

In the above conventional transmission screen,
The luminous flux emitted from each point of the display screen on each surface of the projection type cathode ray tube passes through a projection lens (neither is shown) and is incident on the incident surface 21 of the Fresnel lens sheet 2. At this time, the incident light beam is converted into a substantially parallel light beam by the Fresnel lens constituting the emission surface 22 of the Fresnel lens sheet 2 and is incident on the lenticular lens sheet 3.

The light rays incident on the lenticular lens sheet 3 are directed by the respective lenticular lenses constituting the incident surface 31 to the focal points near the respective lenticular lens surfaces on the exit surface 32, and diffuse from the focal points in the horizontal direction of the screen screen. Then, the light is emitted toward the image viewing side in a form of being diffused in the vertical direction of the screen screen by the fine particles serving as the light diffusing material dispersed in the base material 30.

FIG. 17 is a vertical sectional view showing a section of the lenticular lens sheet 3 used in the transmissive screen 1 shown in FIG. 16 in a direction perpendicular to the screen, at the center in the width direction of one lenticular lens constituting the light exit surface 32. It shows a cross section in the vertical direction of the screen. Also, FIG.
FIG. 17 is a horizontal cross-sectional view showing a cross section of the lenticular lens sheet 3 used in the transmissive screen 1 of FIG. 16 in a screen horizontal direction.

In FIGS. 17 and 18, fine particles as a light diffusing material are dispersed in the base material 30 of the lenticular lens sheet 3 as described above.
The incident light beam 14 enters the screen in the horizontal direction after being incident from the incident surface 31.
The light advances while diffusing in the vertical direction of the screen, and is emitted from the emission surface 32 to the image viewing side mainly in the vertical direction of the screen.

Therefore, if the amount of the light diffusing material is increased,
The light spreads over a wider angle range, spreading the directional characteristics,
The so-called viewing angle increases. Here, the light beam that has passed through the lenticular lens sheet 3 is diffused in the horizontal direction of the screen depending on the shape of the incident surface of the lenticular lens sheet 3, and is diffused in the vertical direction of the screen by the action of the light diffusing material. It should be added that

[0012]

In the above-mentioned conventional transmission screen, as shown in FIGS. 17 and 18, the base material 30 of the lenticular lens sheet 3 contains
As described above, the fine particles of the light diffusing material are dispersed, so that the incident light beam 14 enters the screen 31 while diffusing in the horizontal direction and the vertical direction of the screen after being incident from the incident surface 31, and the image is viewed from the exit surface 32. Light exits to the viewing side. If the amount of the light diffusing material is increased, light is diffused in a wider angle range, and the so-called viewing angle is increased. However, on the other hand, the following problems arise.

That is, as shown in FIGS. 17 and 18, the incident light beam 14 is diffused by the light diffusing material before reaching the focal point on the exit surface 32. As the amount of the material increases, the image at the focal point on the emission surface 32 becomes blurred, the focus characteristic is reduced, and the resolution is deteriorated. In order to increase the diffusion angle, it is effective to increase the refractive index of the light diffusing material or increase the amount of the light diffusing material. Reflection increases, resulting in reduced transmittance and reduced screen brightness.

By the way, in the conventional transmission screen 1, as described above, the lenticular lens sheet 3
Is a row of lenticular lenses whose longitudinal direction is the screen vertical direction, and the exit surface 32 of the lenticular lens sheet 3 in the cross section in the screen horizontal direction.
Is the focal plane of the lenticular lens on the entrance surface 31. Here, the focal plane of the lenticular lens is arranged in the horizontal direction of the screen at a pitch equal to the pitch of the lenticular lens on the entrance plane 31, and between the focal planes, a light opaque portion through which light hardly passes. Is formed. Therefore, the light non-transmissive portion is referred to as a convex protrusion 33, and the light absorbing layer 6 is provided on the surface on the image viewing side. The light absorbing layer 6 is generally called a “black stripe” because it looks like black straight lines perpendicular to the screen are arranged in parallel.

However, the provision of such a convex projection 33 and the light absorbing layer 6 cannot solve the above-mentioned problem caused by the light diffusing material, and further causes the following problem.

That is, since the projection type cathode ray tubes for red, green and blue are arranged in the horizontal direction with respect to the transmission type screen, red image light, green image light, The position of the focal point of the blue image light is also different on the emission surface 32 of the lenticular sheet 3 which is the focal plane of the lenticular lens, and the focal points of the red image light and the blue image light are shifted to the green image light. Are located side by side with the focal point between them. Therefore, of the light emitted from the emission surface 32, the red image light or the blue image light is emitted closer to the convex protrusion 33 than the green image light.

At this time, if the width of the light absorbing layer (black stripe) 6 is increased in order to reduce the reflectance of the lenticular lens sheet 3 with respect to external light incident from the image viewing side, the convex projections 33 are inevitably formed. Of the red image light or blue image light emitted from the emission surface 32 toward the convex protrusion 33, a part thereof is shielded at the edge of the convex protrusion 33. As a result, when viewed obliquely from the transmissive screen in the horizontal direction of the screen, the ratio of each image light changes. That is, the color balance of the three primary colors of red, green, and blue changes depending on the viewing position in the horizontal direction of the screen, and a so-called color shift occurs in which the image appears to change in color.

For example, consider a case in which white and black vertical stripe images are displayed on a transmission screen. The light collected by the lenticular lens on the entrance surface 31 is
As shown in FIG. 18, since the light is diffused by the light diffusing material, a part of the light does not reach the exit surface 32 of the lenticular sheet 3 which is the focal plane of the lenticular lens, and the adjacent convex protrusions The light reaches the portion 33 and is absorbed by the light absorbing layer 6, and as a result, the amount of light in the white portion of the image decreases. In addition, when the amount of the light diffusing material is increased, a part of the light reaches the adjacent exit surface 32 (light wraps around). In some cases, light may reach the emission surface 32 corresponding to the above, and in that case, the black portion of the image becomes bright. In this manner, the light amount decreases in the white portion of the image, and the black portion of the image becomes brighter due to wraparound, so that the contrast decreases.

It is an object of the present invention to solve the above-mentioned conventional problems and to provide a transmission type for a rear projection type image display apparatus which has good focus characteristics, screen brightness and contrast, and has little color shift. To provide a screen.

[0020]

In order to achieve the above object, in the transmission type screen of the present invention, lens elements are provided in the horizontal direction of the screen instead of the lenticular lens sheet conventionally used on the image viewing side. By using a lens sheet continuously arranged in the vertical direction, the directivity characteristics of the image light in the screen horizontal direction and the screen vertical direction are controlled. Further, in order to improve the contrast of the screen, in addition to the above-described configuration, the lens elements adjacent to each other that are formed on the incident surface side on the exit surface of the lens sheet.
Prevention at a position opposed to the joint portion of the child and the lens element, to form a convex protrusion of finite width, by providing a light absorbing layer thereon, by absorbing external light, the contrast reduction due to external light And a contrast improvement measure of performing the operation.

[0021]

In the rear projection type image display apparatus using the transmissive screen having the above-mentioned structure, light emitted from an image source such as a projection type cathode ray tube enters the screen via a projection lens, and the image source of the screen is generated. It passes substantially parallel light in the Fresnel lens sheet arranged on the side, which is disposed on the image viewing side of the screen lens
When the light is incident on the sheet and the diffusion of the light emitted from the sheet is divided into the diffusion in the horizontal direction of the screen and the diffusion in the vertical direction of the screen, the diffusion in the horizontal direction of the screen is controlled by the lens cross-sectional shape of the lens element in the horizontal direction of the screen. Directional diffusion of the lens
It is controlled by the lens cross-sectional shape of the element in the screen vertical direction. Therefore, the light diffusing material is not included in the lens element.
Light diffusion material
Not enough (or as much as the amount of light diffusing material can be reduced)
Good focusing characteristics. Also, depending on the lens cross-sectional shape
By appropriately performing such control, it is possible to minimize the occurrence of color shift. From the above, there is no need to mix a light diffusing material inside the sheet to diffuse the image light, and the image on the screen is not blurred,
Good focus characteristics are obtained, and image light is not scattered in the course of passing through the screen, so that the brightness and contrast characteristics of the screen on the screen are good.

Furthermore, a light absorbing layer (black stripe) can be provided on the convex projection on the exit surface of the lens sheet . In this case, extraneous light such as illumination light enters the exit surface of the transmission screen. Then, some of the incident light is absorbed in the light absorbing layer and is not reflected, so that the contrast when viewing the image in a bright place is further improved.

[0023]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a perspective view showing a transmission screen as a first embodiment of the present invention. In the figure, 1 is a transmission screen, 2 is a Fresnel lens sheet, and 4 is a micro lens sheet. The Fresnel lens sheet 2 and the micro lens sheet 4 are fixed to each other at ends (not shown). Reference numerals 20 and 40 denote base materials of the Fresnel lens sheet 2 and the micro lens sheet 4, respectively, each of which is made of a substantially transparent material. In this embodiment, no light diffusing material is used for any of the substrates 20 and 40 of the Fresnel lens sheet 2 and the micro lens sheet 4.

Reference numeral 21 denotes an entrance surface of the Fresnel lens sheet 2, which is a plane in this embodiment. Reference numeral 22 denotes an emission surface of the Fresnel lens sheet 2 for emitting image light, which is a convex Fresnel lens. Reference numeral 41 denotes an entrance surface of the microlens sheet 4, which has a shape in which microlens elements are continuously arranged in the horizontal and vertical directions of the screen. 42
Denotes an exit surface of the microlens sheet 4, and an entrance surface 41
Microlens elements are arranged substantially opposite to the microlens elements, and a convex protrusion 43 is formed at the boundary between the microlens elements adjacent to each other.
The light absorbing layer 6 is provided thereon.

Next, the functions of the Fresnel lens sheet 2 and the micro lens sheet 4 constituting the transmission screen 1 shown in FIG. 1 will be described. FIG. 2 is a sectional view showing a main part of a rear projection type image display device using the transmission type screen 1 shown in FIG. 1, and FIG.
FIG. 3 is a schematic development view when the projection optical system of the rear projection type image display device is developed on a horizontal plane.

2 and 3, reference numeral 1 denotes a transmissive screen, 7R, 7G, and 7B denote projection CRTs for red, green, and blue, respectively, and 8R, 8G, and 8B denote projection CRTs 7R, 7G, and 7B, respectively. Projection lens, 10
R, 10G, and 10B are projection light beams of red, green, and blue, respectively. Reference numeral 11 denotes a reflecting mirror for turning back the projected light beams 10R, 10G, and 10B. FIG. 3 is a development view in which the reflecting mirror is omitted.

Reference numeral 12 denotes a housing, 13R, 13G, 13
B Each projection lens 8R, 8G, 8B are optical axis, at a point S ₀ near the center of the transmissive screen 1, it intersects the optical axis intensive angle theta.

2 and 3, the projection light flux 10R,
10G and 10B are incident on the transmission screen 1 while spreading. Accordingly, in each pixel of the image on the transmissive screen 1, when viewing a specific color, the principal ray of each pixel is incident on the transmissive screen 1 in a direction in which the principal ray is radiated to the approximate center of the screen.

These projection light fluxes 10R, 10G, 10B
Is diffused in the screen horizontal direction and the screen vertical direction by the transmissive screen 1, for example, when frosted glass is used as the transmissive screen 1, the direction of the principal ray is the brightest direction for each pixel, For a viewer at a certain position, only a part of the image is bright and the surrounding area looks very dark.

In order to prevent this, in the transmission type screen 1 shown in FIG.
Indicates that the luminous flux of the image light incident on the entire surface of the incident surface 21 is red, green,
It has a function of converting the light into a parallel light flux for each blue color by the convex Fresnel lens on the emission surface 22 and making the light enter the microlens sheet 4, thereby improving the brightness distribution of the screen on the screen. . However, at this time, it should be noted that the incident angles of the red, green, and blue light rays on the microlens sheet 4 are different from each other in each pixel.

On the other hand, the micro lens sheet 4 has a function of diffusing the light flux of the image light emitted from the Fresnel lens sheet 2 in the horizontal direction and the vertical direction of the screen for each pixel, and emitting the light toward the image viewing side. ing.

The entrance surface 41 of the micro lens sheet 4 is
The microlens elements are continuously arranged in the screen horizontal direction and the screen vertical direction, and the diffusion of the image light in the screen horizontal direction depends on the horizontal cross-sectional shape of the microlens element (in the present embodiment, the center of curvature is on the image viewing side). The diffusion in the screen vertical direction is controlled by the vertical cross-sectional shape of the microlens element (in this embodiment, a shape having a center of curvature on the image viewing side).

The exit surface 4 of the microlens sheet 4
Reference numeral 2 denotes a microlens element disposed at a position facing the microlens element on the incident surface 41 described above. The diffusion in the vertical direction of the screen is controlled by the vertical cross-sectional shape of the microlens element (in this embodiment, the shape having the center of curvature on the image viewing side). .

By the way, as a lens shape for satisfactorily diffusing image light in the horizontal direction of the screen, a circular shape, a parabolic surface, an elliptical shape and the like are generally used. In particular, in recent years, many products adopt an elliptical shape. For example, in the lenticular lens sheet 3 shown in FIG. 16, the thickness direction is set to the major axis direction of the elliptical shape, and one of the two focal points of the elliptical shape is selected. Is located inside the base material 30 and the other focal point is located near the surface of the emission surface 32, and the elliptical eccentricity e
Is selected so as to have a value substantially corresponding to the reciprocal of the refractive index n of the substrate 30.

Therefore, also in this embodiment, an elliptical shape is adopted as the lens shape for diffusing the image light in the horizontal direction of the screen. As a further development, a strong aspherical shape such as a plastic lens may be used.

As described above, in this embodiment,
By controlling the diffusion of the image light in the horizontal and vertical directions of the screen by controlling the shape of the two lens surfaces,
Good diffusion characteristics can be obtained without using a light diffusing material as in the related art. Therefore, since the light diffusing material is not used, it is possible to prevent the deterioration of the focus characteristic, the decrease in the brightness of the screen, the occurrence of the color shift, and the deterioration of the contrast due to the light diffusing material, which are problems in the related art. Also, even if a light diffusing material is used in combination, the amount of the light diffusing material can be reduced, so that the focus characteristic is reduced, the screen brightness is reduced,
Occurrence of color shift and reduction in contrast can be suppressed within an allowable range.

Next, the structure and function of the microlens sheet 4 of the transmission screen 1 shown in FIG. 1 will be described in more detail. FIG. 4 is a horizontal cross section (BB cross section) of the microlens sheet 4 used in the transmission screen 1 of FIG.
FIG. 4 is a horizontal cross-sectional view showing a pair of microlens elements on an entrance surface 41 and an exit surface 42 in an enlarged manner. The incident surface 41 has a shape having a center of curvature on the image viewing side for the following reason.

In the rear projection type image display device, as shown in FIG. 3, the projection lens 8G for green is used.
13G is the optical axis 1 of the projection lens 8R for red.
It intersects the optical axis 13B of the projection lens 8B for 3R and blue at an optical axis concentration angle θ. Accordingly, in each pixel on the screen, the red, green, and blue principal rays enter at different angles, and when the projection light flux of each color is diffused in the horizontal direction by the transmissive screen 1, each pixel The direction of the principal ray is the brightest direction. Therefore, even if this is the case, depending on the viewing position in the horizontal direction of the screen, red,
The color balance of the three primary colors, green and blue, changes, and the so-called color shift of the image appears to change.

In order to reduce this color shift, in the transmission screen 1 shown in FIG. 1, the entrance surface 41 of the microlens sheet 4 has a shape having a center of curvature on the image viewing side as shown in FIG. By doing so, the directions of the principal rays of each color for each pixel are made substantially parallel.

On the other hand, the emission surface 4 of the microlens sheet 4
Reference numeral 2 denotes a shape having a center of curvature on the image generation source side, and the shape controls the diffusion characteristic of the emitted image light. Further, a convex protrusion 43 having a constant width is provided at a position facing the boundary between the microlens elements on the incident surface 41, and the light absorbing layer 6 is formed on the surface thereof to form illumination light or the like. The reduction in contrast due to external light is reduced.

FIG. 5 is a cross-sectional view (AA) of the microlens sheet 4 used in the transmissive screen 1 of FIG.
FIG. 4 is a vertical cross-sectional view showing a light-receiving surface 41 and a light-emitting surface 4.
2 is an enlarged view of a pair of microlens elements in FIG.

In this embodiment, in order to further reduce the decrease in contrast due to external light such as illumination light, the above-mentioned convex protrusion 43 having a constant width in the vertical direction of the screen is provided. 6 is formed. For this purpose, it is necessary to once condense the image light near the surface of the light exit surface 42. Therefore, the incident surface 41 has a shape having a center of curvature on the image viewing side.

Next, the diffusion in the vertical direction of the screen will be described. The spread in the screen vertical direction does not need to be as large as the spread in the screen horizontal direction. For this reason, in the present embodiment, the incident surface 4
Reference numeral ₁ denotes a lens shape having a center of curvature on the image viewing side, and the image light is once focused near the emission surface 42 (P _{1 in the} figure is focused) by the lens function (light collection function) of the incident surface 41. At this time, the relationship between the thickness t _{1 of the} microlens sheet base material 40 in the optical axis direction and the focal length f ₁ of the lens on the entrance surface 41 is set to be t ₁ <f _1, and the shape of the exit surface 42 the with lens shape (diverging function) having a center of curvature on the image viewing side, the focal length of the synthesis by both surfaces of the lens function long (figure P ₂ focus), and the diffusion of the screen vertical direction is small It controlled so that it might become. With such a configuration, the center of the lens surface on the image viewing side of the microlens is concave, and the microlens surface is unlikely to become an obstacle when forming the light absorbing layer 6.

FIG. 6 is a perspective view showing a transmission screen as a second embodiment of the present invention. In the figure, 1 is a transmission screen, 2 is a Fresnel lens sheet, and 4 is a micro lens sheet. The Fresnel lens sheet 2 and the micro lens sheet 4 are fixed to each other at ends (not shown). 20 and 40 are base materials of the Fresnel lens sheet 2 and the micro lens sheet 4, respectively.
Both are made of almost transparent materials. In this embodiment, no light diffusing material is used for any of the substrates 20 and 40 of the Fresnel lens sheet 2 and the micro lens sheet 4.

Reference numeral 21 denotes an incident surface of the Fresnel lens sheet 2, which is a flat surface in this embodiment. Reference numeral 22 denotes an emission surface of the Fresnel lens sheet 2 for emitting image light, which is a convex Fresnel lens. Reference numeral 41 denotes an entrance surface of the microlens sheet 4, which has a shape in which microlens elements are continuously arranged in the horizontal and vertical directions of the screen. Reference numeral 42 denotes an exit surface of the microlens sheet 4. The microlens elements are arranged substantially opposite to the microlens elements on the entrance surface 41, and a projecting portion is provided at a boundary between adjacent microlens elements. 43 are formed, and the light absorbing layer 6 is provided thereon.

FIG. 7 is a cross-sectional view (BB) of the microlens sheet 4 used in the transmissive screen 1 of FIG.
FIG. 3 is a horizontal cross-sectional view showing a light-receiving surface 41 and a light-emitting surface 4.
2 is an enlarged view of a pair of microlens elements in FIG.

In order to obtain the same effect as the embodiment of FIG.
The lens shape of the entrance surface 41 has a center of curvature on the viewing side, and the lens shape of the exit surface 42 has a center of curvature on the image source side.

FIG. 8 shows the transmission screen 1 shown in FIG.
Section of the microlens sheet 4 used for the vertical direction of the screen
FIG. 4 is a vertical cross-sectional view showing (AA cross section), which is an enlarged view of a pair of microlens elements on an entrance surface 41 and an exit surface 42.

In the present embodiment, similarly to the embodiment shown in FIG. 1, in order to further reduce the decrease in contrast due to external light such as illumination light, the above-mentioned convex projection 43 having a constant width is provided in the vertical direction of the screen. The light absorbing layer 6 is formed on the surface. For this purpose, it is necessary to temporarily condense the image light near the surface of the exit surface 42, and therefore, the incident surface 4
1 has a shape having a center of curvature on the image viewing side.

Next, the diffusion in the vertical direction of the screen will be described. The spread in the screen vertical direction does not need to be as large as the spread in the screen horizontal direction. For this reason, in the present embodiment, the incident surface 4
1 is a lens shape having a center of curvature on the image viewing side, and the sheet material 4
Condensing image light in 0 (Figure in P ₃ focus), and to diverge in the vicinity of the exit surface 42. At this time, the relationship between the thickness t _{2 of the} microlens sheet base material 40 in the optical axis direction and the focal length f ₂ of the lens on the incident surface 41 is set so that t ₂ > f _2. the by a lens shape with a center of curvature on the image source side (condensing action), and a composite focal length of the apparent double-sided lens long acting (figure P ₄ focus), and the vertical direction of the screen Was controlled so as to reduce diffusion.

With the above configuration, the formation of the microlens element can be performed more easily than in the embodiment shown in FIG. As described above, in the rear projection type image display apparatus, as shown in FIG. 3, in the horizontal direction of the screen, the optical axis 13G of the projection lens 8G for green is changed to the optical axis 13R of the projection lens 8R for red. , Blue optical axis 13B of projection lens 8B
And at an optical axis concentration angle θ, the red, green, and blue principal rays enter the pixels on the screen at different angles. Therefore, the red light condensed by the lens function of the entrance surface 41 of the microlens sheet 4,
The positions of the focal points of the green and blue image lights also differ from each other in the horizontal direction of the screen, and the focal points of the red and blue image lights are located side by side with the focal point of the green image light interposed therebetween.

On the other hand, in the vertical direction of the screen, the optical axis 13G of the projection lens 8G for green, the optical axis 13R of the projection lens 8R for red, and the optical axis 13B of the projection lens 8B for blue substantially coincide with each other. Therefore, the positions of the focal points of the red, green, and blue image lights condensed by the lens function of the incident surface 41 of the microlens sheet 4 also substantially match.

The entrance surface 4 of the microlens sheet 4
Due to the lens function of 1, the image light is considerably condensed in the direction perpendicular to the screen in the vicinity of the emission surface 42. Therefore, focusing on these points, an embodiment will be described in which a decrease in contrast due to external light such as illumination light is further reduced.

FIG. 9 is a perspective view showing a transmission screen as a third embodiment of the present invention, and FIG. 10 is a cross-sectional view (BB) of the microlens sheet 4 used in the transmission screen 1 of FIG. FIG. 11 is a vertical cross-sectional view showing a cross section (AA cross section) of the microlens sheet 4 used in the transmissive screen 1 in FIG.
It is.

That is, as described above, the red, green, and green light condensed by the lens function of the entrance surface 41 of the microlens sheet 4.
Although the positions of the focal points of the blue image lights are different from each other in the horizontal direction of the screen, but substantially coincide with each other in the vertical direction of the screen, furthermore, due to the lens action of the entrance surface 41 of the microlens sheet 4, the position near the exit surface 42 , since the image light is significantly condensing on the screen vertically, the width W ₂ of the convex protrusions 43 provided in the vertical direction of the screen shown in FIG. 11, FIG. 10
It can be larger than the width W ₁ of the convex protrusions 43 provided in the horizontal direction of the screen shown in.

Therefore, in the present embodiment, the width W ₂ of the projection 43 provided in the vertical direction of the screen is made larger than the width W ₁ of the projection 43 provided in the horizontal direction of the screen. The ratio of the light absorbing layer 6 laminated on the entire surface of the screen is increased to further reduce the decrease in contrast due to external light such as illumination light.

As described above, according to each of the embodiments, a transmissive screen having good directivity characteristics due to the lens shape of the microlens element and sufficiently reducing contrast deterioration due to external light such as illumination light can be obtained. realizable. However, on the other hand, when an image on the screen is viewed from a region outside the proper viewing range, so-called cutoff occurs in which light is not emitted in the video viewing direction. Hereinafter, this solution technique will be described with reference to FIG.

FIG. 12 is a vertical sectional view showing a vertical section of a microlens sheet 4 used in a transmission screen according to a fourth embodiment of the present invention.
And a plurality of pairs of microlens elements on the emission surface 42 are illustrated in an enlarged manner.

In the present embodiment, the microlens sheet 4 has a lens shape whose exit surface 42 has a center of curvature on the image source side, and the entrance surface lens area of the entrance surface 41 has a center of curvature on the image viewing side. The joint 45 between adjacent microlens elements has a lens shape having a center of curvature on the image generation source side (hereinafter, this area is referred to as a joint lens area). Further, on the emission surface of the image light facing the joint lens region, a convex protrusion 43 is provided in order to reduce the above-mentioned decrease in contrast to external light, and the light diffusion layer 6 is laminated on the surface. .

The light emitted from the Fresnel lens sheet (not shown) becomes almost parallel light and enters the incident surface 41 of the micro lens sheet 4 arranged on the image viewing side. At this time, the incident light beam 14a incident on the entrance surface lens area of the entrance surface 41
Is temporarily focused in the base material 40 by the lens function of the entrance surface lens, and a desired diffusion characteristic in the vertical direction of the screen is obtained by the lens function of the exit surface 42. On the other hand, the incident light beam 14b incident on the joint lens region on the incident surface 41 is incident on a region (lower side in the figure) different from the incident light beam 14a incident on the incident surface lens region on the exit surface 42 due to the diverging action. Have different directional characteristics (the diffusion angle is wider in this embodiment). Therefore, the diffusion characteristics actually obtained on the image viewing side are equal to the superposition of the above two types of light diffusion characteristics.

The cut-off described above can be reduced by controlling the diffusion characteristics of the incident light beam 14b incident on the joint lens region by the lens shape of the joint lens region of the incident surface 41 and the lens shape of the emission surface 42. Can be reduced.

The lens shape of the joint lens region is not limited to the lens shape of the present embodiment, but may be any shape as long as it has a diverging function similar to that of the present embodiment. It may be shaped. In addition, by further roughening the lens surface of the light exit surface 42, or by applying or dispersing a diffusing material to the lens surface of the light exit surface 42 or dispersing it in the vicinity of the lens surface, the above diffusion characteristics can be improved. Can be

Next, a technique for reducing color unevenness of a transmission screen will be described with reference to FIG. FIG. 13 shows the fifth embodiment of the present invention.
It is a perspective view which shows the transmission type screen as an Example of FIG. In the figure, 1 is a transmission screen, 2 is a Fresnel lens sheet, and 4 is a micro lens sheet. The Fresnel lens sheet 2 and the micro lens sheet 4 are fixed to each other at ends (not shown). In the figure, point a corresponds to the center of the screen, and point b corresponds to the periphery of the screen.

FIG. 14 is a horizontal sectional view showing a horizontal section of the microlens sheet 4 used in the transmission screen 1 of FIG. 13, and a solid line in FIG. BB section), and the broken line indicates a section (DD section) at point b at the periphery of the screen. Also, FIG.
FIG. 14 is a vertical cross-sectional view illustrating a cross section of the microlens sheet 4 used in the transmission screen 1 of FIG. 13 in a screen vertical direction.
In the figure, a solid line indicates a section (AA section) at a point a of the screen center, and a broken line indicates a section (CC section) at a point b around the screen.

In general, in a rear projection type image display apparatus, as described above, the Fresnel lens sheet 2 is arranged on the image source side of the transmissive screen 1, and red and green light incident on the entire incident surface of the Fresnel lens sheet 2. The light is converted by a Fresnel convex lens on the exit surface so that the light becomes substantially parallel for each blue color (see FIG. 3).

However, at this time, the angles of incidence of the red, green, and blue image light on the microlens sheet 4 are different (particularly, this tendency is remarkable in the peripheral portion of the screen), so that the emission direction of the image light is changed. When viewed from the front of the screen on the screen, the color balance changes between the center of the screen and the periphery of the screen. This is the cause of uneven color.

In this embodiment, in order to reduce the color unevenness, as shown in FIGS. 14 and 15, the optical axis of the entrance surface 41 and the exit surface 42 of the microlens element are located at the center of the screen and at the periphery of the screen. By shifting the light emitted from the microlens element toward the front of the screen. Specifically, the optical axis of the emission surface 42 is shifted to the outside of the screen with respect to the optical axis of the incident surface 41 in the peripheral portion of the screen. This shift amount (L _{H in} the horizontal direction, L _{V in} the vertical direction) needs to be increased as the image viewing position is closer, but since the above-described color shift increases, it is about 30% of the pitch of the microlenses. It is desirable to do.

In addition to the image quality improvement described above, as means for controlling the directivity of the image light of the rear projection type image display device in the screen vertical direction, the center of the Fresnel lens of the Fresnel lens sheet 2 is adjusted in the horizontal direction of the screen of the Fresnel lens sheet 2. And the light emitted from the transmissive screen 1 can be directed to the upper or lower side of the screen and further to the right or left side.

The above description has been made with respect to an optical system using three projection CRTs of monochromatic colors of red, green, and blue, and an image display device using the optical system. When the number of lines increases to 9 or the like, or when a liquid crystal element is used as a video source instead of a cathode ray tube, or when the video source is a color image such as a slide or movie film (combined in the middle of the optical system) It is needless to say that the present invention also includes an optical system for projecting an image with a single projection lens, and an image display apparatus using the optical system.

[0070]

As is apparent from the above description, according to the present invention, image light from an image source such as a projection type cathode-ray tube enters a transmission type screen through a projection lens, and is transmitted through the transmission type screen. When the light is emitted from the last microlens sheet without being diffused inside the substrate in each of the constituent lens sheets, the light is diffused in the horizontal direction and the vertical direction of the screen due to the shape of both surfaces of the microlens element. For this reason, the image on the exit surface is hardly blurred, and there is an effect that a good focus characteristic can be obtained.

Further, by making the cross-sectional shape in the horizontal direction of the screen on both sides of the microlens element an optimal shape, there is an effect that color shift is reduced and a good image can be obtained. Furthermore, when a light absorbing layer is provided on a light-impermeable portion on the light-emitting surface of the microlens sheet, where light hardly passes, light incident on the screen is diffused before reaching the light-emitting surface and is absorbed by the light-absorbing layer. In addition, since the light absorbing layer can reduce the reflection of external light such as illumination light, there is an effect that a good contrast can be obtained.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a transmission screen as a first embodiment of the present invention.

FIG. 2 is a sectional view showing a main part of a rear projection type image display device using the transmission type screen 1 shown in FIG.

FIG. 3 is a schematic development view when the projection optical system of the rear projection type image display device of FIG. 2 is developed on a horizontal plane.

4 is a horizontal cross-sectional view showing a cross section (BB cross section) of a microlens sheet 4 used in the transmission screen 1 of FIG. 1 in a screen horizontal direction.

FIG. 5 is a vertical cross-sectional view showing a cross section (AA cross section) of a microlens sheet 4 used in the transmission screen 1 of FIG. 1 in a screen vertical direction.

FIG. 6 is a perspective view showing a transmission screen as a second embodiment of the present invention.

7 is a horizontal cross-sectional view showing a horizontal cross section (BB cross section) of the microlens sheet 4 used in the transmission screen 1 of FIG.

8 is a vertical cross-sectional view showing a cross section (AA cross section) of a microlens sheet 4 used in the transmission screen 1 of FIG. 6 in a screen vertical direction.

FIG. 9 is a perspective view showing a transmission screen as a third embodiment of the present invention.

10 is a horizontal cross-sectional view showing a horizontal cross section (BB cross section) of the microlens sheet 4 used in the transmission screen 1 of FIG.

11 is a vertical cross-sectional view showing a cross section (AA cross section) of the microlens sheet 4 used in the transmissive screen 1 of FIG. 9 in a screen vertical direction.

FIG. 12 is a vertical cross-sectional view showing a cross section in a screen vertical direction of a microlens sheet 4 used for a transmission screen as a fourth embodiment of the present invention.

FIG. 13 is a perspective view showing a transmission screen as a fifth embodiment of the present invention.

14 is a horizontal cross-sectional view showing a horizontal cross section of a microlens sheet 4 used in the transmission screen 1 of FIG.

15 is a vertical cross-sectional view showing a cross section of a microlens sheet 4 used in the transmissive screen 1 of FIG. 13 in a screen vertical direction.

FIG. 16 is a perspective view showing a transmission screen according to the related art.

17 is a vertical cross-sectional view showing a cross section of the lenticular lens sheet 3 used in the transmissive screen 1 of FIG. 16 in a screen vertical direction.

FIG. 18 is a horizontal sectional view showing a horizontal section of the lenticular lens sheet 3 used in the transmission screen 1 of FIG.

[Explanation of symbols]

1 ... Transmissive screen, 2 ... Fresnel lens sheet, 3
... Lenticular lens sheet, 4 ... Micro lens sheet, 5 ... Light diffusing material, 6 ... Light absorbing layer, 20, 30, 40
... Base material 21, 31, 41 ... Incident surface, 22, 32, 42
... Outgoing surface, 33 ... Convex projection, 14 ... Incoming light beam, 7R,
7G, 7B: Projection type cathode ray tube, 8R, 8G, 8B: Projection lens, 9G: Bracket, 11: Reflector, 12: Housing, 10B, 10G, 10R: Projection light flux, 13R, 13
G, 13B ... optical axis.

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takahiko Yoshida 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Prefecture Inside the Media Research Laboratory, Hitachi, Ltd. (56) References JP-A-57-81254 (JP, A) JP-A-1-292323 (JP, A) JP-A-58-216235 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G03B 21/62

Claims (6)

(57) [Claims] The surface on the image viewing side forms a Fresnel lens.
The first lens sheet is placed on the image source side,
Lens cross-sectional shape in vertical direction and lens in horizontal direction
The cross-sectional shape has a center of curvature on the image viewing side and has a positive refractive power
Lens elements on at least one surface
And viewing the second lens sheet arranged in the horizontal direction
Side, and among the diffusion characteristics of the image light emitted from the second lens sheet to the image viewing side, the diffusion characteristic in the screen vertical direction is the lens cross-sectional shape in the screen vertical direction of the lens element. And a diffusion characteristic in a horizontal direction of the screen depends on a lens cross-sectional shape of the lens element in a horizontal direction of the screen. 2. The transmission screen according to claim 1, wherein the lens elements are arranged on a surface of the second lens sheet on the image viewing side. 3. The transmission screen according to claim 1, wherein the lens elements are arranged on at least a surface on the image viewing side of the second lens sheet, and the lens elements are arranged on the surface. A transmission screen, characterized in that the lens surface or the inside of the substrate near the lens surface is a scattering surface. 4. The transmissive screen according to claim 1, wherein a light diffusing material is mixed into a base material near a lens surface of the lens element arranged on the image viewing side. Type screen. 5. The transmissive screen according to claim 1, wherein a light diffusing material is provided on a lens surface of the lens element arranged on the image viewing side. 6. A rear projection type image display device using the transmission type screen according to claim 1.