JP2001228547A - Back projection type screen and back projection type display - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a back projection type screen which is great in a scintillation lessening effect by minimizing the side effects, such as the deterioration of resolving power and the degradation in efficiency, which arise if high diffusivity is imparted to a Fresnel lens sheet in order to sufficiently lessen the scintillation which occurs because of the sharp directivity of projected light with the conventional back projection type display using a liquid crystal panel. SOLUTION: Light diffusive particles 512 to be dispersed into a lenticular lens sheet 5 are formed to ellipsoidal bodies of revolutions. As a result, the concentration of rays near to foci when light having high directivity is made incident is relieved and the scintillation is lessened.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art In recent years, there has been an increasing need for large screens, mainly for TV receivers, and a rear projection display has attracted attention as a device suitable for large screen display. As a rear projection display, a CRT is generally used as an image source. However, a device using light modulation by a liquid crystal panel or the like has been developed, and it is expected that a lighter and more compact device will be realized. FIG. 6 schematically shows the basic configuration.

The light emitted from the lamp 1 is applied to a liquid crystal panel 2
The image formed by spatial modulation is enlarged and projected by the projection lens 3. In an actual device, it is general to use three liquid crystal panels to realize color display. In this case, light from the lamp 1 is converted into red, green, and blue components by a color separation optical system. It has a complicated structure such as being disassembled and transmitting through three liquid crystal panels, respectively, but these are omitted here.

[0004] Examples of the same type of device using spatial modulation include a device using a reflection type liquid crystal device as a modulating device, and a device using many fine mirrors whose angles can be varied.

[0005] As shown in the figure, light diverging from the center to the periphery and having extremely directivity is partially incident on the screen 4 installed on the image plane. The degree of the directivity is represented by the projection directivity angle θ, and the projection magnification M and the F-number F of the projection lens are used.

[0006]

(Equation 1)

Can be expressed as

By the way, in the case of an apparatus using a CRT as an image source, since a CRT of about 5 inches is used, the projection magnification M is about 10 on a 50 "class display, and the F number is for taking in diffused light from a phosphor. The projection directional angle θ is about 0.05 (about 3 °).

On the other hand, when an image modulation element such as a liquid crystal panel is used, an element of about 1 inch is used, and it is necessary to use illumination light having relatively high directivity due to the characteristics of the element. Is as large as about 3, the projection directional angle θ is as small as about 0.003 (about 0.2 °), and the directivity of the projection light incident on the screen is extremely strong.

The screen 4 functions to appropriately distribute such projection light to enable good image recognition.

[0011] Even if a simple diffuser is used for the screen 4, the minimum image observation is possible. However, since the projected light is divergently incident as described above, the peripheral portion has outward directivity, and when viewed from the front of the screen, the peripheral luminance becomes extremely dark compared to the central luminance, When viewed obliquely, the brightness of the screen becomes remarkably nonuniform, for example, the near end is bright and the far end is extremely dark.

In order to eliminate such non-uniformity, it is common to arrange a Fresnel lens sheet 41 on the projection side of the diffusion means.

The Fresnel lens sheet 41 functions to convert the projection light divergently incident on the screen 4 from the projection lens 3 into parallel light whose main directivity is substantially perpendicular to the screen surface.

In this way, if the main directional direction of light at each part of the screen is converted to a direction perpendicular to the screen surface and then diffused, the brightness becomes substantially uniform over the entire screen regardless of the observation direction. Can be realized.

Further, as the diffusing means, a lenticular lens sheet 42 is generally used instead of using a simple isotropic diffusing plate.

While good image recognition is required horizontally from various angles as an observation range, if good image recognition can be performed within a limited range of standing and sitting in the vertical direction, If the light is effectively distributed to the required area by anisotropic diffusion, a bright image can be provided as a whole. The lenticular lens sheet 42 realizes the anisotropic diffusion.

The lenticular lens sheet 42 has a lenticular lens array whose longitudinal direction is perpendicular to the plane of incidence, in which light diffusing particles having a refractive index slightly larger than the refractive index of the substrate are dispersed. The projection light converted into almost parallel light by the Fresnel lens sheet 41 is:
In the horizontal direction, the light is diffused in a relatively wide range by the synergistic action of the lenticular lens and the light diffusing particles, and in the vertical direction, it is diffused in a relatively narrow range only by the effect of the light diffusing particles. Diffusion is achieved.

The base material of the lenticular lens sheet 42 is usually PMMA (polymethyl methacrylate) having a refractive index of about 1.49 or MS resin (copolymer of styrene and methyl methacrylate) having a refractive index of about 1.52. , The light-diffusing particles have a refractive index of 0.02 to
True spherical beads made of MS resin or glass which is about 0.07 large are used.

Further, by providing a black stripe on the non-light-collecting portion of the exit surface of the lenticular lens sheet 42, it is possible to reduce contrast deterioration due to external light without losing projected light. This is a great advantage of using.

In the rear projection type display using the above-described light modulation element, a phenomenon called scintillation, which has not become apparent in a device using a CRT as an image source, has become a problem. This causes glare on the screen due to minute brightness, and is also called speckle.

The mechanism of the occurrence will be briefly described with reference to the drawings.

When spherical particles having a small difference in refractive index from the substrate exist in the substrate as described above, the spherical particles act as a lens having extremely small aberration and excellent imaging performance.

Assuming that the refractive index of the substrate is n1 and the refractive index of the spherical particles is n2, the focal length fb of the lens composed of the spherical particles is the difference between the particle diameter d of the spherical particles and the above-mentioned refractive index n2-n1.
= Approximately by Δn

[0024]

(Equation 2)

## EQU1 ##

Therefore, when parallel light is incident on the spherical particle portion, a point with extremely high brightness is generated at a focal position fb away from the spherical particle. FIG. 7 schematically shows the pattern.
In FIG. 7, reference numeral 40 denotes a spherical particle.

When the incident light is not perfectly parallel light but has directivity of ± θ ′, as shown in FIG. 7, the luminescent spot spreads in diameter d ′ in proportion to its directivity angle θ ′. Its diameter d '

[0028]

(Equation 3)

Is calculated as In the rear projection type display, the directional angle θ ′ is the angle of the directional angle θ of the projection light shown in the equation (1) in the base material,

[0030]

(Equation 4)

And substituting equation (4) into equation (3)

[0032]

(Equation 5)

Is obtained.

In the case of an apparatus using a CRT as an image source, the projection directional angle θ is relatively large as 0.05 (about 3 °) as described above, and d ′ / d is 0.
When it is about 5, the area of the bright spot has a diameter that is about half the diameter of the light diffusion particle.

On the other hand, when a modulation element such as a liquid crystal panel is used, the projection directional angle θ is 0.003 (about 0. 3).
2 ′), d ′ / d in the above Δn is about 0.03, and the area of the bright spot is 1/30 of the diameter of the light diffusion particle.
Focus on a range of diameters.

The area of this bright spot area is 1/200 or less as compared with the case of a device using a CRT as an image source, and the local illuminance becomes an extremely bright bright spot of 200 times or more, which causes image hindrance as scintillation. .

As a method of reducing such scintillation, Japanese Patent Laid-Open Publication No. Hei 8-313865 proposes that two diffusion elements be provided at a fixed distance.
In this case, in addition to using a general lenticular lens sheet as a diffusion element in which diffusion particles are dispersed therein, it is common to provide a diffusion element in a Fresnel lens sheet which is a basic element of a screen together with a lenticular lens sheet. It is a target.

In Japanese Patent Application Laid-Open Nos. 10-293361 and 10-293362, an appropriate diffusion characteristic to be imparted to a Fresnel lens sheet is defined by a haze value.

As described above, when the light diffusing particles are dispersed not only in the lenticular lens sheet but also in the Fresnel lens sheet, light enters the light diffusing particles dispersed in the lenticular lens sheet from various angles, and the incident directivity angle θ It becomes possible to reduce scintillation by increasing '.

[0040]

However, when the diffusing particles are dispersed in the Fresnel lens sheet as described above,
Side effects such as deterioration in resolution and efficiency are caused.

Degradation of the resolving power occurs when light diffused at one point of the Fresnel lens sheet spreads before reaching the lenticular lens sheet, and is diffused again by the lenticular lens sheet. It increases in proportion to the applied diffusion properties and the spacing between the two diffusion elements.

Further, the reduction in efficiency occurs because components absorbed and lost by the black stripes provided on the exit surface of the lenticular lens sheet increase due to diffusion in the Fresnel lens sheet, and diffusion in the Fresnel lens sheet is large. It becomes more noticeable.

Further, as another problem, in order to obtain a diffusion characteristic and a diffusion element interval required for reducing scintillation,
The Fresnel lens sheet requires a certain thickness or more, and there is a problem that it is difficult to reduce the thickness of the Fresnel lens sheet, which is effective in alleviating a ghost image generated by multiple reflection inside the Fresnel lens sheet.

An object of the present invention is to solve the above problems and to provide a rear projection screen in which the side effect due to diffusion in a Fresnel lens sheet is reduced while reducing scintillation. Also, by using such a rear projection screen, scintillation is slight,
It is another object of the present invention to provide a rear-projection display that has excellent resolution and transmission efficiency and does not cause a ghost image to be prominent.

[0045]

To achieve the above object, the present invention has the following arrangement.

The rear projection screen according to the first configuration of the present invention has at least a lenticular lens sheet and a Fresnel lens sheet, and each of the lenticular lens sheet and the Fresnel lens sheet has a refractive index different from that of the base material. % Of the light diffusing particles are dispersed, and the light diffusing particles dispersed in the lenticular lens sheet are spheroidal. According to such a configuration, since the light transmitted through the light diffusion particles dispersed in the lenticular lens sheet is less concentrated locally, the rear projection screen in which the scintillation is reduced while the diffusion in the Fresnel lens sheet is suppressed to be small. Can be realized.

Further, the rear projection type screen according to the second configuration of the present invention has at least a lenticular lens sheet and a Fresnel lens sheet, and the lenticular lens sheet and the Fresnel lens sheet each have a refractive index of a base material. Light diffusing particles having different refractive indices are dispersed, the light diffusing particles dispersed in the lenticular lens sheet have a higher refractive index than the base material, and the light diffusing particles dispersed in the Fresnel lens sheet are the light diffusing particles. It is characterized by having a lower refractive index than the substrate. According to such a configuration, the focal point of the light diffusing particles dispersed in each of them is kept away from the other diffusing element, so that it is possible to increase the substantial diffusing element interval by using a thin Fresnel lens sheet. A ghost image with a small rear projection screen can be realized while reducing scintillation.

Further, a rear projection type display according to the present invention has the above rear projection type screen.
According to this configuration, it is possible to realize a highly efficient rear-projection display with little image disturbance such as generation of scintillation and ghost images, excellent resolution, and the like.

[0049]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a rear projection type screen according to the present invention will be described with reference to the drawings.

(Embodiment 1) FIG. 1 is a horizontal sectional view showing an example of an embodiment of a rear projection type screen of the present invention.

The rear projection type screen shown in the figure is composed of a Fresnel lens sheet 41 and a lenticular lens sheet similarly to the general rear projection type screen shown in FIG. In order to make the structure more suitable for the rear projection display used, the laminated lenticular lens sheet 5 (Japanese Patent Application No.
No. 91889).

The Fresnel lens sheet 41 forms a concentric Fresnel lens on the projection side and the observation side on the projection side, and has the same function as one convex lens as a whole.
A, PC (polycarbonate), MS or the like is used as a base material, and is formed by a known technique such as a hot press method or a 2P (photopolymer) method, in which crosslinked polymer beads or glass beads having a different refractive index from the base material are formed. Are dispersed as spherical light diffusion particles 411.

The laminated lenticular lens sheet 5 has a lenticular lens film 5 on the surface of the diffusion sheet 52 on the projection side.
1 has a laminated structure in which the transparent adhesive layer 53 is bonded by a transparent adhesive layer 53.

The lenticular lens film 51 is made of PET
Lenticular lens 5 on one surface of a transparent film such as (polyethylene terephthalate) using an ultraviolet curable resin.
11 is formed, and a black stripe 512 made of a light absorbing material is formed in the light-impermeable region on the other surface.

The diffusion sheet 52 is made of a light-transmitting material such as acrylic or polycarbonate, and is obtained by two-layer extrusion of the light-transmitting material alone and a material obtained by mixing the light-transmitting material with the light-diffusing particles 521. The spheroidal light diffusion particles 521 are dispersed in the vicinity of the bonding surface with the transparent adhesive layer 53. The refractive index of the light diffusion particles 521 is set to be slightly larger than the refractive index of the light transmitting material.

In the above configuration, the spheroidal light diffusion particles 52
FIG. 2 schematically shows the ray trajectory when the parallel light is incident on 1. FIG. 2A shows light diffusion particles 5 with respect to the optical axis of the incident light.
FIG. 2B shows a case where the major axes of the light diffusing particles 521 are parallel to the major axis of the incident light.

As shown in the figure, in any case, the light incident on the spheroidal light diffusing particles 521 does not concentrate on one point unlike the case using the spherical light diffusing particles.
Scintillation caused by local concentration of light rays is reduced as compared with the case where spherical light diffusing particles are used.

As described above, since the scintillation in the parallel light incident state is reduced, it is possible to reduce the scintillation by using the Fresnel lens sheet 41 having a small diffusion, and it is possible to reduce the resolution which is a side effect due to the diffusion of the Fresnel portion. , And a reduction in efficiency can be reduced.

(Embodiment 2) FIG. 3 is a horizontal sectional view showing another embodiment of the rear projection type screen of the present invention.

The configuration of FIG. 3 is similar to the configuration of FIG. 1 and the functions of the Fresnel lens sheet 41 and the laminated lenticular lens sheet 5 are the same, but the Fresnel lens sheet 41
The difference is that the refractive index of the spherical light diffusing particles 412 dispersed inside is lower than that of the base material. Further, in FIG. 3, the light diffusion particles 522 dispersedly contained in the diffusion sheet 52 are spherical high refractive index light diffusion particles unlike FIG.

FIG. 4 schematically shows the ray trajectory when parallel light is incident on the light diffusing particles 412 having a refractive index lower than the refractive index of the substrate.

In the above setting, the light is divergently diffused, and the focal point is on the incident side of the light diffusing particles 412. It is equivalent to the case where it is arranged on the side.

The above is substantially equivalent to an increase in the distance between the diffusing elements disposed on the Fresnel lens sheet and the lenticular lens sheet, respectively. When ordinary light diffusing particles having a higher refractive index than the substrate are used. A greater scintillation reduction effect can be realized, and the same scintillation reduction effect can be realized by using a thinner Fresnel lens sheet.

As described above, according to the present invention, it is possible to reduce scintillation in a thin Fresnel lens sheet, which has been difficult in the past, and to realize a rear projection type screen effective for reducing ghost images.

(Embodiment 3) FIG. 5 is a perspective view schematically showing an embodiment of a rear projection type display according to the present invention, which is a perspective view so that the arrangement of main elements can be understood.

In FIG. 5, reference numeral 6 denotes an optical engine, in which a lamp serving as a light source, an illumination optical system, a color separation optical system, a liquid crystal panel, a color synthesizing optical system, and the like are appropriately arranged. To form an image by spatial modulation. The image is enlarged and projected by the projection lens 3.

The projection light bent by the mirror 7 forms an image on the screen 4, is diffused by the action of the screen 4, and can be observed as an image from various angles. These elements are arranged inside the cabinet 8 to prevent outside light from entering the apparatus.

The screen 4 uses the lenticular lens sheet described in the first embodiment shown in FIG. 1 and the Fresnel lens sheet described in the second embodiment shown in FIG. 3, and is equivalent to a conventional screen. It has a scintillation reduction function, and the thickness of the Fresnel lens sheet is small, and its diffusion action is small.

According to the configuration of the present invention, the diffusion in the Fresnel lens sheet can be minimized, and the deterioration of the resolution and the efficiency can be reduced, and the ghost image which becomes remarkable in proportion to the thickness of the Fresnel lens sheet can be reduced. It is possible to realize a rear-projection display with reduced resolution, minimal image disturbance such as scintillation and ghost images, and excellent resolution.

[0070]

As is apparent from the above description, according to the rear projection screen and the rear projection display of the present invention, it is possible to display an image having excellent resolution with little image disturbance such as scintillation and ghost images. realizable.

[Brief description of the drawings]

FIG. 1 is a partially enlarged horizontal sectional view showing a first embodiment of a rear projection screen according to the present invention.

FIG. 2 is a schematic diagram of a ray trajectory in a state where parallel light is incident on spheroidal light diffusing particles.

FIG. 3 is a partially enlarged horizontal sectional view showing a second embodiment of the rear projection type screen of the present invention.

FIG. 4 is a schematic diagram of a ray trajectory in a state where parallel light is incident on light diffusing particles having a lower refractive index than a base material.

FIG. 5 is a horizontal sectional view showing an embodiment of the rear projection display of the present invention.

FIG. 6 is a horizontal sectional view schematically showing a basic configuration of a general rear projection display.

FIG. 7 is a schematic diagram showing the generation of a bright spot when the projection light is incident on the light diffusion particles.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 lamp 2 liquid crystal panel 3 projection lens 4 screen 41 Fresnel lens sheet 411 spherical light diffusing particles 412 low refractive index light diffusing particles 42 lenticular lens sheet 5 laminated lenticular lens sheet 51 lenticular lens film 511 lenticular lens 512 black stripe 52 diffusion sheet 521 rotation Ellipsoidal light diffusing particles 522 High refractive index light diffusing particles 53 Transparent adhesive layer 6 Optical engine 7 Mirror 8 Cabinet

Claims (3)

[Claims] 1. A lenticular lens sheet and a Fresnel lens sheet, wherein the lenticular lens sheet and the Fresnel lens sheet each have dispersed therein light diffusing particles having a refractive index different from that of a base material. A rear projection screen, wherein the light diffusion particles dispersed in the lens sheet are spheroidal. 2. The lenticular lens sheet and the Fresnel lens sheet, wherein the lenticular lens sheet and the Fresnel lens sheet each have dispersed therein light diffusing particles having a refractive index different from that of a substrate. The light diffusion particles dispersed in the lens sheet have a higher refractive index than the substrate, and the light diffusion particles dispersed in the Fresnel lens sheet have a lower refractive index than the substrate. Projection screen. 3. A rear projection display comprising the rear projection screen according to claim 1.