JP2002221611A - Prism sheet for projection image display device, sheet type optical element, method for manufacturing sheet type optical element and projection image display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the length from front to rear in a projection image display device and to increase the projection magnification while increasing uniformity of the luminance and sharpness of the screen. SOLUTION: The prism sheet is formed by densely arranging many thin prisms 3 each composed of a first inclined face 1 and a second inclined face 2. The angle 2 of the second inclined face is controlled to totally reflect the light transmitting through the first inclined face 1 and to allow the light to emit. The angle θ1 between the first inclined face 1 and the second inclined face 2 is <=45 deg.. A flat top face 5 is formed to connect the top edge of the first inclined face 1 and the top edge of the second inclined face 2. The angle of the top face 5 is controlled not to inhibit the light entering the first face 1 of the adjacent prism 3 and totally reflected by the second inclined face 2, and the angle is gradually varied over the prism parts 3 according to the incident angle of light. The prisms 3 have a function of a light diffusing layer or a tint layer, or a light diffusing layer or a tint layer is unitedly laminated in the exit side of the prisms 3. In the prisms 3 in the region near the optical axis A, the angles formed by the first and second inclined faces 1, 2 to the plane perpendicular to the optical axis A decrease to almost 0 in the prisms nearer to the optical axis A.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a projection image display apparatus for displaying an image by a projection system, and more particularly to a prism sheet which is a sheet-like optical member used for improving image quality in such an apparatus. It is about.

[0002]

2. Description of the Related Art A projection-type image display device (hereinafter, referred to as a projection image display device) has been put to practical use for displaying a large-screen image. Previously, such a projection image display device used to project an image by using three CRTs of RGB, and thus had a problem that the image was unclear or was not clearly projected. However, recently, a liquid crystal projection system, which irradiates light from a light source to a liquid crystal panel for creating an image and projects it with an optical system, has been put into practical use. Despite the large screen, a clear, high-definition, high-luminance image is Is becoming available. In addition, a plasma display, which displays an image by causing a phosphor to emit light by ultraviolet light emitted from xenon in a plasma state, has already been put to practical use as a thin, large-screen image display device such as a wall-mounted television.

[0003] In such a projection image display device, electronics and liquid crystal control techniques are fundamental in a portion for producing an image source such as a liquid crystal panel. Technology is the basis. What is required of an image projection system is that a clear, bright, high-luminance image without unevenness can be obtained even on a larger screen.

[0004] Further, it is still required to make the device thinner, that is, to reduce the depth of the device. However, increasing the screen size and reducing the thickness are inconsistent demands in some aspects in optical technology. That is, to enlarge the screen, it is necessary to increase the magnification of projection. However, in order to increase the projection magnification while sufficiently increasing the brightness uniformity and sharpness of the screen, the optical path length tends to be long. As the optical path length increases, the depth of the device increases.
There is also a method of reducing the depth by increasing the number of times of folding with a reflecting mirror, but if the number of reflecting mirrors is increased, the problem of flare at the interface increases, and adjustment during assembly tends to be troublesome.

[0005]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and it is possible to reduce the depth of a projection image display device while maintaining the uniformity and brightness of the screen. Provided is a prism sheet that can increase the projection magnification while sufficiently increasing the height. Further, the present invention provides a method for manufacturing such a prism sheet and a projection image display device using such a prism sheet.

[0006]

In order to solve the above-mentioned problems, the invention according to claim 1 of the present application is an elongated object formed by a first slope and a second slope and extending in a specific direction. A prism sheet for a projection image display device, which is formed by arranging a large number of prism portions and arranging the sheets into a sheet shape, wherein the angle of the second slope is a total reflection of light transmitted through the first slope. And the light is emitted at an angle, and the angle formed by the first slope and the second slope is 45 degrees or less. Further, in order to solve the above problem, the invention according to claim 2 is configured such that, in the configuration of claim 1, the leading edge of the first slope and the leading edge of the second slope are not in contact with each other,
The distal end surface is formed so as to connect the two, and has a configuration equivalent to cutting the top of a triangle. In order to solve the above-mentioned problem, in the invention according to claim 3, in the configuration according to claim 2, the angle of the front end surface is incident on the first inclined surface of another adjacent prism portion, and The angle is set so as not to block the light totally reflected on the slope. Further, in order to solve the above problem, the invention according to claim 4 is based on claim 3.
In the above configuration, the angle of the front end surface is gradually changed in each prism portion according to the incident angle of light. According to a fifth aspect of the present invention, in the configuration according to any one of the first to fourth aspects, a specific direction in which each of the prism portions extends is a concentric circumference coaxial with the optical axis. It has a configuration that the directions are parallel to each other in an upward direction or a plane perpendicular to the optical axis. In order to solve the above-mentioned problem, the invention according to claim 6 is
The configuration according to any one of claims 1 to 5, wherein the plurality of prism portions are a light diffusion layer and / or a taint layer, or a light diffusion layer and / or a taint layer on an emission side of the plurality of prism portions. Are integrally laminated. According to a seventh aspect of the present invention, in order to solve the above problem, in the configuration of the sixth aspect, the light diffusion layer and / or the taint layer laminated on the emission side of the prism portion constitute a lenticular lens. There is a configuration that there is. In order to solve the above-mentioned problem, the invention according to claim 8 is an elongated prism formed by a first slope and a second slope and extending in a circumferential direction concentric with the optical axis. A projection sheet for a projection image display device in a sheet shape by arranging a large number of parts, wherein the first slope is located closer to the optical axis, and the second slope is located farther from the optical axis. Is located,
The peripheral prism portion, which is a prism portion located far away from the optical axis, has an angle of its second slope, which is an angle for totally reflecting light that has passed through the first slope and entered. Further, the peripheral prism portion has an angle formed by the first slope and the second slope of 45 degrees or less, and sets an angle formed by the first slope with respect to a plane perpendicular to the optical axis to the first angle. When the angle formed with respect to the plane perpendicular to the optical axis is the second angle, the first second angle is the optical axis in the central prism portion, which is the prism portion located inside the peripheral prism. Has a configuration in which it gradually approaches 0 as it approaches. According to a ninth aspect of the present invention, there is provided a prism which is constituted by a first slope and a second slope, and which is elongated in a circumferential direction concentric with the optical axis. A sheet optical element in the form of a sheet by arranging a large number of parts, wherein the angle formed by the first slope with respect to a plane perpendicular to the optical axis is a first angle, and the surface is perpendicular to the optical axis. When the angle formed with respect to the second angle is defined as the second angle, the first and second angles are asymptotic to 0 as approaching the optical axis in the central prism portion, which is each prism portion located inside the peripheral prism. Having a configuration. Further, in order to solve the above-mentioned problem, the invention according to claim 10 is to press a predetermined mold against a base material which is a base plate-shaped member made of a predetermined thermoplastic resin and to heat and press a predetermined surface shape. A method for manufacturing a sheet-shaped optical element, wherein the heating and pressing are performed while the mold is pressed against the substrate in a vacuum. Further, in order to solve the above problem, the invention according to claim 11 includes a projection source for producing an image to be projected, a screen placed on a projection surface,
A reflection optical element placed on an optical path for projecting an image formed by a projection source onto a screen, the reflection optical element having a predetermined angle with respect to the optical axis. It is a sheet-shaped optical element in which a number of prism parts are packed and arranged, and the inclined surface of each prism part reflects light from the projection source to reach the screen, and external light incident through the screen is It is configured to prevent returning to.

[0007]

Embodiments of the present invention (hereinafter, embodiments) will be described below. First, an embodiment of the invention of a prism sheet for a projection image display device (hereinafter simply referred to as a prism sheet) will be described. Figure 1
1 is a schematic cross-sectional view of a prism sheet according to a first embodiment. As shown in FIG. 1, the prism sheet has a first slope 1
And a plurality of elongated prism portions 3 each of which is constituted by the first and second inclined surfaces 2 and extends in a specific direction. The prism sheet is entirely made of resin, and is manufactured by a hot pressing method as described later. As shown in FIG. 1, the prism sheet has a cross-sectional shape in which one side is flat and the other side has a triangular wave shape including a first slope 1 and a second slope 2. In this embodiment, the optical axis A of the optical system on which the prism sheet is disposed is coaxial with the center axis of the prism sheet. The first slope 1 is located closer to the optical axis A, and the second slope 2 is located farther from the optical axis A.

FIG. 2 is a schematic perspective view for explaining the extending direction of each prism portion 3 of the prism sheet shown in FIG. There are two patterns in the extending direction of each prism portion 3 of the prism sheet. One is Figure 2 (1)
As shown in FIG. 3, each prism portion 3 extends in a direction on a concentric circumference coaxial with the optical axis A. In this pattern, each prism section 3 has a circular shape having a different diameter by a predetermined length. This predetermined distance is the pitch of each prism section 3 and corresponds to, for example, the distance between the vertices shown in FIG. As shown in FIG. 2B, the second pattern is a pattern in which the prism portions 3 extend in directions parallel to each other in a plane perpendicular to the plane in which the optical axes A and A 'extend. Accordingly, each prism section 3 has a linearly long shape. In this case, there are a case where the optical axis A intersects the prism sheet perpendicularly and a case where the optical axis A ′ obliquely intersects the prism sheet.

A major feature of the prism sheet shown in FIGS. 1 and 2 is that the angle of the second slope 2 is an angle at which the light that has passed through the first slope 1 and entered has been totally reflected. The angle formed by the first slope 1 and the second slope 2 (hereinafter, referred to as an angle)
Referred to as a vertex angle, indicated by theta ₁ in FIG. 1) is a point which is 45 degrees or less. Hereinafter, the technical significance of this point will be described with reference to FIGS. FIG. 3 and FIG.
FIG. 3 is a diagram for explaining the technical significance of the prism sheet shown in FIG. 2 and FIG. 3 illustrates a case where luminance correction is performed using a conventional Fresnel lens, and FIG. 4 illustrates a case where luminance correction is performed using the prism sheet of the embodiment.

The prism sheet according to the present embodiment is mainly used for luminance correction for making the luminance on the projection surface uniform. According to the projection method, the brightness increases in the central portion near the optical axis A, but decreases in the peripheral portion far from the optical axis A, resulting in a dark image. Therefore, it is necessary to improve the brightness of the peripheral part by collecting the light of the peripheral part which spreads away from the optical axis A by bending it toward the optical axis A.

Conventionally, Fresnel lenses are often used for such luminance correction. FIGS. 3A and 3B are diagrams schematically showing luminance correction using such a Fresnel lens. FIG. 3A shows a configuration in which light enters from the Fresnel side, and FIG. 3B shows a configuration in which light enters from the flat surface side. It is of a configuration that causes FIGS. 3A and 3B show an example in which a normal convex lens is used. As shown in FIGS. 3 (1) and 3 (2), when performing the brightness correction, the light that spreads outward away from the optical axis A is turned back from the optical axis A by the Fresnel lens, and the brightness decrease in the peripheral portion of the projection surface is reduced. Preventing.

Here, an optical axis A of light incident on a Fresnel lens or a prism sheet from a projection source such as an optical engine.
The spread angle for, hereinafter referred to as angle of view, will be indicated by the theta ₂ in FIG. As described above, the need to reduce the depth of the device has made it necessary to shorten the optical path length.
Therefore, angle theta ₂ tends to increase. Fig. 3 (1)
When large light L ₁ of the field angle as shown in (2) is incident,
Although some light L ₂ to correctly exit, the ratio of the light L _3, which would reflected by the surface of the Fresnel Fresnel lens becomes large. As a result, the light use efficiency is reduced, and the purpose of improving the brightness around the projection plane cannot be sufficiently achieved.

From the viewpoint of light use efficiency, FIG.
As shown in (2), a configuration in which light is incident from a flat surface is efficient. However, when it is arranged together with a lenticular lens or the like in order to improve the brightness at the periphery of the projection surface, it cannot be integrated in the case of flat surface incidence, and it is likely to be a two-piece configuration such as a Fresnel lens and a lenticular lens. In this case, problems such as flare at the interface and troublesome handling may occur. In the past, the configuration of a single sheet of light incident from the Fresnel side as shown in FIG. 3A was also studied, but as described above, there was a drawback that the light use efficiency was poor.

The configuration of the present embodiment has technical significance for solving such a problem. In other words, the present invention has a technical significance that the luminance at the periphery of the projection plane can be sufficiently improved even when the angle of view increases. More specifically, as shown in FIG. 4, in the present embodiment, light incident on the first slope 1 is transmitted through the first slope 1 and totally reflected on the second slope 2. ing. Thereafter, the light passes through the flat surface (emission surface) 4 and reaches the projection surface. For this reason, even if the angle of view increases, there is no light loss, and the luminance at the periphery of the projection plane can be sufficiently improved.

As can be seen by comparing FIGS. 3 and 4, the prism sheet of this embodiment utilizes the non-lens surface of the Fresnel lens, and totally reflects light at the non-lens surface. By doing so, even light with a large angle of view can be used sufficiently to increase the brightness on the projection surface. However, as will be described later, the prism sheet in the present invention is not necessarily limited to a lens functioning as a whole, and is not called a Fresnel lens but a prism sheet.

Next, a description will be given technical significance of that apex angle theta ₁ is turned 45 degrees or less. Figure 5 is a diagram illustrating the technical significance of the point where the apex angle theta ₁ is turned 45 degrees or less.

A typical example of a sheet-like optical element having a triangular cross section as shown in FIG. 1 is a Fresnel lens. In the Fresnel lens, as can be seen from the example shown in FIG. 3 and the like, the magnitude of the apex angle is as large as 60 degrees or 70 degrees. This is obtained by dividing a curved surface forming a lens function into a sheet shape, and has a background that the curvature of the original curved surface is not so large. Fresnel lenses are often
It is manufactured by molding with a mold, and the mold is manufactured by cutting with a cutting tool. However, in the case of a Fresnel lens having a small apex angle, the cutting edge of the cutting tool becomes an acute angle, and cutting becomes difficult. As described above, a Fresnel lens having a small apex angle does not have to be used, and is difficult to manufacture.

However, when the technical idea of utilizing the total reflection surface on the non-lens surface as in the present embodiment is adopted, it has been found by examination of the inventor that the performance cannot be sufficiently exhibited if the apex angle is large. Was. That is, FIG.
As shown in (1), the apex angle theta ₁ is large, light incident on the first slope 1 does not reach the second inclined surface 2, or worse missing from it the flat surface 4, a flat surface 4 The amount of light that is reflected internally and passes through to the outside increases. When such light increases, it becomes difficult to sufficiently improve the brightness around the projection surface.

Meanwhile, as shown in FIG. 5 (2), the apex angle theta ₁
Is small, much of the light incident from the first slope 1 is totally reflected by the second slope 2 and exits from the flat surface 4. For this reason, the effect of improving the brightness at the periphery of the projection plane can be sufficiently obtained. The extent to which the apex angle θ ₁ should be reduced depends on the angle of view θ ₂ , but in general, if the apex angle θ ₁ is 45 degrees or less, such an effect can be sufficiently obtained. The configuration in which the light incident from the first slope 1 is totally reflected by the second slope 2 and the apex angle θ ₁ is 45 degrees or less is applicable to all the prism units 3. You don't have to. For example, in order to increase the amount of light reaching the periphery of the projection surface, only the three prism units located in the periphery may correspond.

Next, a prism sheet according to a second embodiment of the present invention will be described. FIG. 6 is a schematic sectional view of a prism sheet according to the second embodiment. The prism sheet of the second embodiment differs from the first embodiment in the tip shape of each prism section 3. That is, as shown in FIG. 6, in the second embodiment, the leading edge of the first slope 1 and the leading edge of the second slope 2 are not in contact with each other, and the leading faces are connected so as to connect them. Is formed. That is, each prism portion 3 has a cross-sectional shape corresponding to cutting the top of the triangle.

The configuration of the second embodiment has the following technical significance. FIG. 7 is a diagram for explaining the technical significance of the prism sheet of the second embodiment shown in FIG. FIG. 7A corresponds to the prism sheet of the first embodiment. In the case of the configuration of the first embodiment, a prism unit 3 adjacent to a certain prism unit 3 inside (on the side closer to the optical axis A) the prism unit 3
However, there is a problem that light is blocked. FIG. 7A shows this situation. As shown in FIG. 7 (1), the distal end portion of a prism unit 3 (inner prism portion 3) shields the light L ₄ that has traveled in order to enter the prism portion 3 of the outer (outer prism part 3) Would. This light L ₄ is incident on the tip of the inner prism portion 3, is totally reflected by the second inclined surface 2 and emerges from the flat surface 4 as described above, but is totally reflected by the outer prism portion 3. , The inner position on the projection plane is reached. Then, the outer prism portion 3 further receives light L ₅ incident on the outer prism portion 3.
, And the prism portion 3 also blocks light incident on a further outer prism portion (not shown). Therefore, in the example shown in FIG. 7A, light tends to be gathered relatively inward.

On the other hand, in the second embodiment, as shown in FIG. 7 (2), because it is shaped tip of each prism portion 3 is cut, the light L ₄ incident on the prism portion 3 adjacent to the outer ', L ₅ ' is less likely to be shielded. For this reason, compared with the configuration shown in FIG. 7A, the amount of light that is turned outward and goes toward the projection surface increases, and the effect of improving the luminance at the periphery of the projection surface can be further enhanced.

When the end of each prism portion 3 is cut as in the second embodiment, the manufacture and handling of the prism sheet are facilitated, and the durability is improved. That is, each prism portion 3 is in the form of a simple triangular as shown in FIG. 1, further when the apex angle theta ₁ is of sharp that 45 degrees or less, the bytes to make a mold for a prism sheet manufacturing The blade also has a pointed tip, which causes problems such as easy breakage. Also, when carrying the manufactured prism sheet, the tip of each prism section 3 is easily chipped,
There are complications, such as the need for special considerations when carrying or attaching to a video display device. In addition, since the possibility that the tip of the prism portion 3 is chipped and replacement is required increases, a problem easily occurs in terms of durability. On the other hand, according to the configuration of the present embodiment, the apex angle θ ₁ formed by the first slope 1 and the second slope 2 is made as small as 45 degrees or less, and the angle of the tip of the prism portion 3 (with respect to the tip face 5). Each slope 1,
2) can be set to a wide angle of 45 degrees or more. Accordingly, there is no problem as described above, and the prism sheet is easy to manufacture and handle, and has high durability.

Next, the prism sheet of the third embodiment will be described.
explain about. FIG. 8 shows a prism system according to the third embodiment.
FIG. This third embodiment is based on the basic
Is the same as the second embodiment, except that
Special measures have been taken for the angle of the tip surface 5. Immediately
In addition, the tip of the first slope 1 and the tip of the second slope 2 are connected.
The angle of the distal end face 5 is determined according to the distance from the optical axis A.
In the rhythm part 3, it gradually changes. Gradual change putter
In this embodiment, the tip surface 5 and the
The angle formed by the optical axis A (hereinafter referred to as the tip surface angle, θ in FIG. 8)
₃₁, Θ₃₂, Θ₃₃), But goes away from the optical axis A
So that it gets bigger.

FIG. 9 is a diagram for explaining the technical significance of the prism sheet of the third embodiment shown in FIG. In FIG. 9, for the sake of simplicity, it is assumed that light for displaying an image is the same as light from a point light source. It's actually a bit more complicated, but it's essentially the same. FIG.
(1) As shown, when the same tip surface angle theta ₃ at each prism portion 3, or loss of light occurs, the effect of luminance improvement in the projection plane peripheral portion tends to occur a problem that the lowered. That is,
The prism portion 3 is located close to the optical axis A, when the arises that light L ₆ reaching the front end surface 5 is loss would be reflected back. Further, the prism unit 3 is located farther from the optical axis A, will light L ₇ to be incident on the outside of the prism portion 3 is shielded by the front of the prism portion 3, the effect of luminance improvement in the projection plane peripheral portion Will be reduced.
On the other hand, as shown in FIG. 9 (2), the distal end surface angle theta ₃ is the optical axis A
When the distance is gradually increased so that the distance from the projection unit increases, the effect of preventing the incident light from entering the outer prism unit 3 from being blocked in each prism unit 3 is optimized, so that light loss occurs and the brightness at the periphery of the projection surface is improved. The effect is not reduced.

Next, a prism sheet according to a fourth embodiment of the present invention will be described. FIG. 10 is a schematic sectional view of a prism sheet according to the fourth embodiment. In the prism sheet of the fourth embodiment, a light diffusion function is provided on the prism sheet itself, or a taint layer for enhancing color (contrast) is provided. Specifically, FIG.
In the case of 0 (1), each prism portion 3 is also used as a light diffusion layer and a taint layer. Such a prism sheet can be manufactured by molding a resin in which a diffusing material is uniformly dispersed. For example, a material obtained by dispersing a diffusing material and a tinting material having different refractive indexes in methacrylic resin can be used.

In the example shown in FIG. 10B, the light diffusing layer 61 and the taint layer 6
2 are integrally laminated. As described later, such a prism sheet is obtained by laminating a plate material for each prism portion 3, a plate material for the diffusion layer 61, and a plate material for the taint layer 62, pressing a mold, and hot pressing. Can be manufactured. The prism sheet having the above configuration may be manufactured by performing hot pressing using one multilayer member in which a layer for the diffusion layer 61 and a layer for the taint layer 62 are stacked in advance.

The taint layer 62 may form a lenticular lens. For example, irregularities are provided so that the exit surface of the taint layer 62 becomes a lenticular lens. Such irregularities can be similarly manufactured by a hot pressing method described later. By doing so, it is possible to improve the brightness by collecting light that is about to spread in the vertical direction, or to improve the viewing characteristics by expanding the light in the horizontal direction. This can be achieved by a sheet-shaped optical member.

If a sheet-like optical member such as a prism sheet, a diffusion plate, or a taint plate is separately provided, problems such as double images and flare may occur due to the influence at the interface. However, according to the prism sheet of the fourth embodiment,
Since there is no need to separately provide a diffusion plate or a taint plate, such a problem is suppressed. In the present embodiment, the thickness of the diffusion layer 61 is increased to some extent,
It is not very suitable for the special case where a thin diffusion layer of about 0 μm is required, but it is very advantageous in the case of a general-purpose product that is not so.

As a configuration for enhancing the contrast, a configuration using a lenticular lens has conventionally been adopted in many cases. A lenticular lens is a lens made by arranging a large number of cylindrical lenses into a sheet, and is used to increase the efficiency by collecting light that spreads in the vertical direction and widen the viewing angle by spreading the light in the horizontal direction. . Recently, a part that does not transmit light is provided in the lenticular lens to enhance the contrast, and the purpose is mainly performed in some cases.

Also in the prism sheets of the first to third embodiments, it is possible to enhance the contrast by combining with the lenticular lens. However, also in this case, since the optical element has a configuration of two optical elements, the problem of flare or double image at the interface may occur. As shown in FIG. 10B, the taint layer 6
Such a problem can be eliminated by laminating 2 integrally. In this case, the light diffusion layer 61 and the taint layer 62 may be reversed. Further, each prism portion 3 may be used only for the taint layer which is also used only for the light diffusion layer, or only the light diffusion layer 61 may be laminated on the emission side of each prism portion 3,
Only the taint layer 62 may be laminated.

Next, a fifth embodiment of the present invention will be described. FIG. 11 is a diagram illustrating a configuration of a prism sheet according to the fifth embodiment. In the fifth embodiment,
In the case of a prism sheet including the center of a concentric circle, a so-called “navel is seen” phenomenon is suppressed. "The navel is visible" means that when an image is projected using a Fresnel lens or the prism sheet of the first embodiment described above, in which each prism portion 3 extends on a concentric circle, Only an abnormal phenomenon that appears to shine like a small round spot or dot.

The phenomenon that “the navel is visible” (hereinafter, the navel-visible phenomenon) is caused by the angle of the slope of the central prism portion 3. FIG. 11 is a diagram illustrating this point, and is a diagram illustrating a cause of the occurrence of the navel appearance phenomenon. Fresnel lens and prism sheet of each embodiment
A small surface (small inclined surface) that is oblique to the optical axis A is provided in a segment shape. By optimizing the angle of the small slope in accordance with the positional relationship from the optical axis A, a desired lens function or the like is obtained.

Here, similarly, the slope near the optical axis A is referred to as the first slope.
One slope 1 and the far side slope are second slopes 2.
Then, the first slope 1 forms with respect to a plane perpendicular to the optical axis A.
Angle is the first angle θ₄And the plane perpendicular to the optical axis A
Is the second angle θ₅And Set the convex lens
In the case of a Fresnel lens or the like converted into a
As shown in (1), the first and second angles θ₄, Θ₅Is the optical axis
In many cases, it does not approach 0 on A. In FIG. 11 (1)
Is the first angle θ₄Only changes are shown, but the second
Angle θ ₅Is not asymptotically close to 0 on the optical axis A. This
, The angle θ on the optical axis A₄, Θ₅Is asymptotic to 0
Otherwise, the navel appears easily.

On the other hand, the prism sheet of the present embodiment has the first and second angles θ ₄ and θ ₄ so that the navel appearance phenomenon can be prevented.
₅ is gradually approached to 0 on the optical axis A. More specifically, the above-described configuration in which the angle of the second slope is an angle at which light that has passed through the first slope and entered and totally reflected and emitted is applied to the entire surface of the prism sheet. It does not mean that it is only the periphery. The inner portion (closer to the optical axis A) of the peripheral portion has a concave lens configuration. That is, in the central portion at a certain distance from the optical axis A, each prism portion 3 has a configuration in which the concave lens is converted into a sheet shape. In the present embodiment, the first and second angles θ ₄ and θ ₅ gradually approach 0 as approaching the optical axis A. Therefore, unnatural refraction of light at the center point (that is, a point on the optical axis A) is extremely small, and there is no navel appearance phenomenon.

The configuration in which such a navel appearance phenomenon is prevented is also effective when employing a configuration for improving the brightness around the projection plane as in the first to third embodiments.
It is generally effective for a sheet-like optical element in which a large number of prism parts 3 are packed and arranged. Therefore, the present invention is not limited to the prism sheet of each of the above embodiments, and can be applied to prism sheets having other configurations and Fresnel lenses in general.

The term "prism sheet"
The usage of the term “Fresnel lens” will be described briefly. "Prism sheet" is also "Fresnel lens"
The same applies to a sheet-like optical element in which a large number of prism portions 3 are packed and arranged. However, while the “Fresnel lens” has one lens action as a whole, the “prism sheet” does not matter whether it has a lens action. A lens function may or may not be provided, or a lens function may be provided in a specific prism unit 3 or a specific group of prism units 3. Therefore, the "prism sheet"
Is a concept including “Fresnel lens”.

Next, a prism sheet according to a sixth embodiment of the present invention will be described. FIG. 12 is a diagram illustrating a configuration of a prism sheet according to the sixth embodiment. The feature of the prism sheet of this embodiment is that the optical axis A does not coincide with the center axis C of the prism sheet. That is, as shown in FIG. 12, although the optical axis A crosses the prism sheet at the center of the prism sheet,
The direction of the optical axis A does not match the direction of the central axis C of the prism sheet. Such a configuration is often possible when trying to make the entire projection video display device compact. For example, there is a case in which a prism sheet is arranged in front of a screen.

In the case of the embodiment shown in FIG.
The slope on which the light enters (first slope 1) and the slope on which the incident light is totally reflected (second slope 2) may not be axially symmetric. That is, as shown in FIG. 12, each prism portion 3 is a linear shape that is long in the horizontal direction, the lower surface always corresponds to the first inclined surface 1, and the upper surface is always the second inclined surface 2. In some cases. Note that the first slope 1 and / or the second slope 2 (or both) may be arc-shaped in cross section (that is, spherical or cylindrical). Further, there may be a curved surface that is not spherical, such as an aspheric lens. With such a configuration, the effect of improving the luminance at the periphery of the projection plane can be obtained. For example, when the brightness of the upper portion on the projection surface is low, the angle of the second slope 2 and the like are appropriately selected so that the effect of total reflection can be increased in the prism unit 3 located on the upper side.

Next, an embodiment of the invention of a method for manufacturing a sheet-like optical element will be described. This description also serves as a description of the method for manufacturing the prism sheet of each of the above embodiments.
FIG. 13 is a schematic front sectional view of a sheet-like optical element manufacturing apparatus used in the method for manufacturing a sheet-like optical element of the present embodiment. The method of this embodiment employs a method called hot pressing. Hot pressing is a method of manufacturing a sheet-shaped optical element using a thermoplastic resin, and heats and presses a base plate-shaped member (hereinafter, a base material) made of a predetermined thermoplastic resin to obtain a predetermined optical element. This is a method for producing a sheet-shaped optical element having a surface shape.

A major feature of the method of this embodiment is that the hot pressing is performed in a vacuum. More specifically, the apparatus shown in FIG. 13 has a vacuum chamber 82 provided with a vacuum pump 81, a pair of hot plates 83 and 84 provided in the vacuum chamber 82, and a pattern to be transferred to the base material 87 having a surface. , And a pressing source (not shown) for pressing one of the hot plates 83 toward the other hot plate 84 to press the base 87. Hot platen 83,
Reference numeral 84 is heated to a predetermined temperature by a heater (not shown). As the heater, a heater using steam or a heater using Joule heat is used.

A case where a sheet-like optical element is manufactured using the apparatus shown in FIG. 13 will be described. As shown in FIG. 13, a base material 87 is sandwiched between a pair of molds 85 and 86, and a pair of hot plates 83 and 84
Place between Then, the heater is operated to heat the hot platen to a predetermined temperature, and in this state, a pressing source (not shown) is operated to press one hot platen 83 toward the other hot platen 84,
The substrate 87 is pressed. At this time, the vacuum pump 81 is operated in advance, and the inside of the vacuum chamber 82 is set to a predetermined vacuum pressure.

The substrate 87 is softened by heating, and the patterns of the molds 85 and 86 are transferred to the surface of the substrate 87 by pressing. This makes the product. The heating and pressurization are maintained for a predetermined time, and after cooling, the pair of hot plates 83 and 84 are separated from each other, and the inside of the vacuum chamber 82 is returned to the atmosphere to take out the product. In the case of a prism sheet as shown in FIG. 1, the flat surface 4 is a mirror surface, and therefore, a mold 86 for transferring the flat surface is used.
Is to make a mirror surface. However, the emission surface is a flat surface 4
Instead, a lenticular lens surface or the like may be used.
In this case, the shape of the mold 86 is appropriately selected so as to obtain such a surface.

An important point in the above manufacturing method is that the base material 8
In the heating and pressurizing step 7, since the atmosphere is a vacuum atmosphere, the gas in the base material 87 can be efficiently removed. If the heating and pressurization is performed under the atmospheric pressure instead of the vacuum atmosphere, the gas easily accumulates inside, and bubbles and the like are easily generated. If the air bubbles and the like remain, the patterns of the molds 85 and 86 are not correctly transferred to the base material 87, and there is a high possibility that the pattern will be defective. It is conceivable to provide gas vent holes in the molds 85 and 86 in order to improve the gas escape. However, there is a problem that the pattern of the gas vent holes is transferred to the base material 87. Further, a method may be adopted in which irregularities are provided on the base material 87 so that air can easily escape during heating, but the irregularities may remain in the product. On the other hand, when heating and pressurizing in a vacuum as in the present embodiment,
Since there is no residual bubbles or the like, and since there is no need to provide vent holes in the molds 85 and 86 or to provide irregularities in the base material 87, it is possible to manufacture a high-quality sheet-shaped optical element.

More specific conditions for the above manufacturing method will be described below. The base material 87 is made of methacryl (MM
A) A resin plate or an acrylic / styrene copolymer (MS) resin plate can be used. The thickness is about 1 to 3 mm. MMA
When a resin plate is used, the heating temperature is 150 ° C. to 190 ° C.
° C, pressurization is 40-60 kgf / cm ² (392-58
8N). In the case of MS resin plate, the heating temperature is 1
20 ° C to 170 ° C, pressurization is 35 to 55 Kgf / cm ²
(343-539N). In any case, the vacuum pressure is 650 mHg (8.67 · 10 ⁴ Pa) or less. For example, it is 600 mmHg (8 · 10 ⁴ Pa) or 500 mmHg (667 · 10 ⁴ Pa). In addition, as a cushion material, Ichikawa Kaori Co., Ltd. thickness 1mm
AACP cushion paper, KG353AR cushion paper, MMA resin plate or MS resin plate having a thickness of about 2 to 3 mm can be used. It should be noted that the prism sheet of each embodiment described above is not limited to being manufactured by the manufacturing method of this embodiment.

Next, an embodiment of the invention of a projection video display device will be described. FIG. 14 is a schematic side sectional view of an embodiment of the invention of the projection video display device. The apparatus shown in FIG. 14 includes a projection source 91 for producing an image to be projected, a screen 92 placed on a projection surface, and a reflecting optical element placed on an optical path for projecting an image produced by the projection source 91 onto the screen 92. And a housing 94 and the like accommodating them.

The projection source 91 employs a configuration in which an image is formed by a liquid crystal panel and the image is irradiated with light from a light source. An image is projected on the screen 92 by light transmitted through the liquid crystal panel or reflected by the liquid crystal panel. DMD (Digital M) that creates images by electrically controlling minute metal mirrors
icromirror Device) can also be used. still,
The projection source 91 contains therein a lens system that projects a created image on a screen 92. Such a projection source 9
1 is sometimes called an optical engine.

A major feature of the apparatus according to the present embodiment is that, as the reflection optical element 93, a sheet-like one in which prism parts 95 are packed and arranged is used. The reflection optical element 93 can be manufactured by a hot pressing method as in the case of the prism sheet described above. A major feature of the present embodiment is that the inclined surface of each prism portion 95 of the reflecting optical element 93 reflects light from the projection source 91 to reach the screen 92 and the screen 9.
2 is to prevent external light incident through the screen 2 from returning to the screen 92.

More specifically, referring to FIG. 14, the reflecting optical element 93 is composed of a flat surface 96 forming a predetermined angle with respect to the optical axis A, and a prism surface 97 opposite to the flat surface 96. Sheet. And the prism surface 97
It is the surface of the prism portion 95 that is arranged in a large number. One inclined surface 951 of each prism portion 95 is
The angle is such that the light from 1 is reflected and reaches the screen 92 uniformly. This angle may be the same for each prism part 95, but is often not the same. It is preferable that the one slope 951 has an angle at which the light from the projection source 91 is totally reflected.

The other slope 952 of each prism part 95 is
External light incident through the screen 92 is
It is something that does not return to. The function of the other slope of each prism section 95 will be described with reference to FIG. FIG. 15 is a sectional view of each prism portion 95 shown in FIG.
It is a figure explaining the function of the other slope 952 of.

FIG. 15A shows a conventional simple plane mirror.
It shows the situation when using. Simple plane mirror
In the case, external light incident through the screen 92 (in FIG.
To L ₀Is reflected on the plane mirror and returns to the screen 92.
It may be. This makes it difficult to see the video
Or the image quality may be degraded. one
On the other hand, in the configuration of the present embodiment, as shown in FIG.
External light incident through the screen 92 is
Reflected on the surface 952, one of the slopes of the adjacent prism portion 95
Do not transmit through the surface 951 and enter the reflecting optical element 93.
While being attenuated in the housing 94. Because of this,
Light does not return to screen 92. Because of this,
Effectively makes the image difficult to see and the image quality deteriorates
Has been prevented.

The angle of one inclined surface 951 and the other inclined surface 952 of each prism portion 95 is determined by the angle at which the light from the projection source 91 is reflected and reaches the screen 92, and the angle from the screen 92. External light is optimized from the viewpoint of what angle is most incident. Note that the prism portions 95 may extend on concentric circles as in the above-described embodiments, or may extend linearly in parallel with each other.
Further, as disclosed in Japanese Patent No. 2742780, each prism portion 3 may be formed in a pyramidal shape (a triangular pyramid, a quadrangular pyramid, or the like).

[0053]

As described above, according to the first aspect of the present invention, the angle of the second slope is the angle at which the light that has entered through the first slope is totally reflected and emitted. And the angle between the first slope and the second slope is 4
Since the angle is not more than 5 degrees, even when the angle of view becomes large, it is possible to sufficiently achieve an improvement in luminance around the projection plane. For this reason,
This is extremely suitable for a projection video display device that requires a small depth despite the large screen. According to the second aspect of the present invention, in addition to the above-described effects, since the end of each prism portion corresponds to a cut shape, a highly durable prism sheet which is easy to manufacture and handle is provided. . According to the third aspect of the present invention, in addition to the above-described effects, the angle of the tip surface of each prism portion is incident on the first slope of another adjacent prism portion and totally reflected on the second slope. Since the angle is set so as not to block light, the effect of improving the luminance at the periphery of the projection plane can be further enhanced. According to the fourth aspect of the present invention,
In addition to the above effects, the angle of the front end surface is gradually changed in each prism portion according to the incident angle of light, so that the effect of improving the luminance at the periphery of the projection surface can be further enhanced, and the light use efficiency is also improved. It does not drop. According to the invention of claim 6, in addition to the above effects, the prism sheet can have a light diffusion function and a color enhancement function. According to the seventh aspect of the invention, in addition to the same effects as those of the first aspect, the "navel appearance phenomenon" can be prevented. Further, according to the invention of claim 8, there is provided a sheet-like optical element in which the “navel appearance phenomenon” is prevented. According to the ninth aspect of the present invention, since heating and pressurization is performed in a vacuum, there is no residual bubbles or the like, and there is no need to provide a gas vent hole in the mold or provide irregularities in the substrate. Therefore, a high-quality sheet-shaped optical element can be manufactured. According to the tenth aspect of the present invention, since the outside light is prevented from returning to the screen, the image is difficult to see,
The image quality does not deteriorate.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a prism sheet according to a first embodiment.

FIG. 2 is a schematic perspective view illustrating a direction in which each prism section 3 of the prism sheet shown in FIG. 1 extends.

FIG. 3 is a diagram for explaining the technical significance of the prism sheet shown in FIGS. 1 and 2, and is a diagram for explaining a case where luminance correction is performed using a conventional Fresnel lens.

FIG. 4 is a diagram for explaining the technical significance of the prism sheet shown in FIGS. 1 and 2, and is a diagram for explaining a case where luminance correction is performed using the prism sheet of the embodiment.

FIG. 5 is a diagram for explaining the technical significance of the fact that the apex angle θ ₁ is 45 degrees or less.

FIG. 6 is a schematic sectional view of a prism sheet according to a second embodiment.

FIG. 7 is a diagram for explaining the technical significance of the prism sheet of the second embodiment shown in FIG.

FIG. 8 is a schematic sectional view of a prism sheet according to a third embodiment.

FIG. 9 is a diagram for explaining the technical significance of the prism sheet of the third embodiment shown in FIG.

FIG. 10 is a schematic sectional view of a prism sheet according to a fourth embodiment.

FIG. 11 is a diagram illustrating a configuration of a prism sheet according to a fifth embodiment.

FIG. 12 is a diagram illustrating a configuration of a prism sheet according to a sixth embodiment.

FIG. 13 is a schematic front sectional view of a sheet-shaped optical element manufacturing apparatus used in the sheet-shaped optical element manufacturing method of the embodiment.

FIG. 14 is a schematic side sectional view of an embodiment of the projection video display device according to the present invention.

FIG. 15 is a view for explaining the function of the other slope of each prism section 3 shown in FIG. 14;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 1st inclined surface 2 2nd inclined surface 3 prism part 4 flat surface 5 front-end surface 61 light diffusion layer 62 taint layer 81 vacuum pump 82 vacuum chamber 83 heating plate 84 heating plate 85 type 86 type 87 base material 91 projection source 92 screen 93 Optical element for reflection

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G03B 21/00 G03B 21/00 E H04N 5/74 H04N 5/74 A

Claims (11)

[Claims] 1. A prism for a projection image display device, comprising a plurality of elongated prism portions, each of which is constituted by a first slope and a second slope, and which extends in a specific direction, are packed and arranged. In the sheet, the angle of the second slope is an angle for totally reflecting and entering the light that has passed through the first slope and entered, and further, the first slope and the second slope. A prism sheet for a projection image display device, wherein the angle formed by the inclined surface is 45 degrees or less. 2. A front edge of the first slope and a front edge of the second slope are not in contact with each other, and a front face is formed so as to connect them, and a top of a triangle is cut. 2. The prism sheet for a projection image display device according to claim 1, wherein the prism sheet has a shape corresponding to the shape of the prism sheet. 3. An angle of the front end surface is set to an angle which does not block light which is incident on a first inclined surface of another adjacent prism portion and totally reflected on a second inclined surface. The prism sheet for a projection image display device according to claim 2. 4. The prism sheet for a projection image display device according to claim 3, wherein the angle of the front end surface is gradually changed in each prism portion according to the incident angle of light. 5. A specific direction in which each of the prism portions extends is a direction on a concentric circumference coaxial with the optical axis or a direction parallel to each other in a plane perpendicular to the optical axis. The prism sheet for a projection image display device according to claim 1. 6. The multiplicity of prism portions are light diffusion layers and / or taint layers, or the light diffusion layers and / or taint layers are integrally laminated on the emission side of the multiplicity of prism portions. The prism sheet for a projection image display device according to any one of claims 1 to 5, wherein: 7. The prism sheet for a projection image display device according to claim 6, wherein the light diffusion layer and / or the taint layer laminated on the emission side of the prism portion constitute a lenticular lens. 8. A sheet-like shape formed by arranging a large number of elongated prism portions which are constituted by a first slope and a second slope and extend in a circumferential direction concentric with the optical axis. A prism sheet for a projection image display device, wherein the first slope is located on a side closer to an optical axis, the second slope is located on a side farther from the optical axis, and a periphery far from the optical axis. The peripheral prism portion, which is a prism portion located at the angle of the second slope, is an angle that totally reflects the light that has passed through the first slope and entered, and further, the peripheral prism portion, The angle formed by the first slope and the second slope is 45 degrees or less, and the angle formed by the first slope with respect to a plane perpendicular to the optical axis is a first angle, and the angle formed by the optical axis is When the angle formed with respect to the vertical plane is the second angle, the periphery A prism portion located inside the rhythm in the central prism portion, the first second angle projection image display device prism sheet characterized by being asymptotic to 0 toward the optical axis. 9. A sheet shape formed by arranging a large number of elongated prism portions formed of a first slope and a second slope and extending in a circumferential direction concentric with the optical axis. A sheet-like optical element, wherein an angle formed by the first slope with respect to a plane perpendicular to the optical axis is a first angle, and an angle formed with respect to a plane perpendicular to the optical axis is a second angle. At this time, in the central portion of the prism portion at a certain distance from the optical axis, the first and second angles become 0 as approaching the optical axis.
A sheet-like optical element characterized by being asymptotic to: 10. A sheet-shaped optical element for manufacturing a sheet-shaped optical element having a predetermined surface shape by pressing a predetermined mold onto a substrate, which is a base plate-like member made of a predetermined thermoplastic resin, and applying heat and pressure. The method for producing a sheet-shaped optical element, wherein the heating and pressing are performed while the mold is pressed against the substrate in a vacuum. 11. A projection image comprising a projection source for producing an image to be projected, a screen placed on a projection surface, and a reflecting optical element placed on an optical path for projecting an image produced by the projection source onto the screen. In the display device, the reflecting optical element is a sheet-shaped optical element in which a number of prism parts are packed and arranged on a surface forming a predetermined angle with respect to the optical axis, and the slope of each prism part is: A projection image display device, which reflects light from a projection source to reach a screen and prevents external light incident through the screen from returning to the screen.