JP2001100316A - Screen for projecting picture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a screen for projecting a picture constituted so that a speckle is hardly caused and a projecting picture with high resolution and high quality can be obtained. SOLUTION: This screen for projecting a picture is constituted so that the shape, the relative positional relation, the refractive index or the like of a light scattering body are changed timewise by light, an electric field, a magnetic field, heat, stress or the like and the scattering distribution and/or the phase of scattered waves are changed timewise in a light diffusion layer of the light scattering body.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention belongs to the field of image display technology, and more particularly to an image projection screen suitable as a screen for a projection television or a microfilm reader. The image projection screen of the present invention is particularly suitable for LCD (liquid crystal) projectors and D
It is suitably used for an image projection screen on which an optical image formed on a light valve having a pixel display portion arranged in a matrix, such as an MD (digital micromirror device) projector, is projected.

[0002]

2. Description of the Related Art Conventionally, in a rear projection type projection television, it is required to observe a projected image brightly in a wide angle range on an observation side. An anisotropic image projection screen is used in a visual field range which is narrower but is appropriately diffused. As such an image projection screen, a lenticular lens extending in the vertical direction is provided side by side on one or both surfaces of the sheet, and a light diffusing material is further contained in the light diffusing sheet thus provided with light diffusing properties. A lenticular lens sheet is generally used in which light is widely diffused in a horizontal direction by a lenticular lens and light is diffused to some extent in a vertical direction by a light diffusing material.

On the other hand, as a projection image source used in combination with an image projection screen, instead of a CRT, L
2. Description of the Related Art A projector using a device that performs display using a matrix pixel structure such as a CD or a DMD has become widespread. Such a projector is extremely preferable as an image light source for a display device of a computer such as a personal computer that often does not receive the influence of terrestrial magnetism and observes still images unlike a CTR projector. In an image projection screen using such an LCD or DMD as a projector, 40 to 6 pixels used in a projection television or the like are used.
In addition to those having a size of 0 inches, those having a relatively small area of about 14 to 40 inches, such as a personal computer monitor for observation from a relatively close position, require new performance.

That is, a phenomenon called "speckle" or scintillation, which occurs when a light diffusing material added to the inside of a lenticular lens interferes with projection light, and a phenomenon that the diffusing material glare (hereinafter referred to as "speckle"). Description), and in recent years the conventional VG
From A and SVGA, it is required to clearly resolve a pixel having a large number of pixels such as XGA and SXGA.

With respect to such required performance, in particular, LCD
The following solutions have been proposed for transmissive screens used in, for example, rear projection type projection televisions, as well as screens for projectors using a DMD or a DMD.

[0006] Regarding the above, JP-A-8-31386.
No. 5, U.S. Pat. No. 5,674,543, U.S. Pat. No. 3,712,707, and Japanese Patent Application Laid-Open No. Sho 55-12980, in which a light diffusing layer is divided or a concentration gradient of a light diffusing material is provided in the thickness direction. Accordingly, a method for reducing speckle has been proposed.

With respect to the above, Japanese Patent Laid-Open No. 55-1298
No. 0 discloses that the thickness of the diffusion layer is reduced to 100 μm or less in order to obtain a screen having a resolution higher than the resolution of the human eye (5 to 10 lines / mm).

[0008]

However, in the prior art as described above, all of the required performances described above cannot be satisfied. In particular, the reduction of speckles and the high resolution generally have a trade-off relationship. When the speckles are reduced, the resolution is reduced, and when the resolution is increased, the speckles are remarkable. For example, in Japanese Patent Application Laid-Open No. 8-313865, speckles are reduced by dividing the light diffusion layer and making the distance from the incident surface of the first light diffusion layer to the emission surface of the second light diffusion layer 1.5 mm or more. Although it can be reduced, when the number of pixels is high, such as XGA or SXGA, the resolution is reduced, and a high-resolution projected image cannot be provided. Also, Japanese Patent Application Laid-Open No. 55-129
When the thickness of the diffusion layer is 100 μm or less as disclosed in Japanese Patent Publication No. 80, a high-resolution projected image can be obtained, but speckles become remarkable and a high-quality projected image cannot be provided.

Also, Japanese Utility Model Publication No. 51-18772, US Pat. No. 3,650,608, US Pat.
Japanese Patent Application Publication No. 64-64 and the like have proposed a method in which one liquid crystal plate is used as a light diffusion layer, and the alignment is dynamically controlled using an electric field to cause dynamic scattering and remove speckle. However, in such a method, since the liquid crystal molecules are dynamically aligned using an electric field, a part of the polarization of the transmitted light is lost due to the anisotropy of the liquid crystal, and the intensity of the transmitted light is reduced.
There is a problem that the projected image becomes dark. In addition to this, a polarizing film may be attached to an image projection screen for the purpose of increasing the contrast of a projected image in a liquid crystal projector or the like. The problem is that the intensity of the transmitted light decreases due to the deviation of the polarized light transmission axis. further,
If only one liquid crystal plate is used as the light diffusing layer, changes in speckles and brightness are recognized, and there is also a problem that when viewing the projected image, discomfort is felt.

It is an object of the present invention to provide an image projection screen which can be used in combination with a liquid crystal projector or the like, in which speckles hardly occur and a high-resolution and high-quality projected image can be obtained. It is the purpose.

[0011]

SUMMARY OF THE INVENTION In view of such circumstances, the present inventors have changed the scattering distribution of the scattered waves of the light diffusion layer constituting the image projection screen with time, thereby obtaining the image projection screen. The inventors have found that speckle can be eliminated without lowering the resolution of the screen, and have arrived at the present invention. That is, the image projection screen of the present invention is an image projection screen on which an optical image is projected by projection light, and the scattering distribution and / or the phase of the scattered wave in the light diffusion layer constituting the image projection screen. It is characterized by being changed over time.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Generally, speckles generated on an image projection screen are such that incident light to be projected is completely coherent light such as laser light, or white lamp light such as xenon lamp. When the light is partially coherent, the scattered waves (coherent components) formed by the light scatterers included in the incident light when passing through the light diffusion layer are complicated and randomly interfere with each other. It is believed that. When light having partial coherence such as white lamp light is incident, speckles that are not so remarkable as laser light do not occur, but the coherency of incident light increases as the white light source approaches the point light source. The occurrence of noise becomes remarkable. Similarly, when the distance from the light source to the image projection screen is increased, or when the light from the light source is narrowed down to a narrow emission range, the coherence of the incident light is increased and speckles are significantly generated. .

Further, such a speckle is reduced as the scattering angle θ of the scattered wave in the light diffusion layer is increased, and the speckle is reduced by superposition of a scattered wave having a disturbed phase from a wide area. It has been known. As a method of reducing the speckle, a method of providing a gap between two light diffusion layers and a method of increasing a solid angle of incidence on an image projection screen can be cited. However, these methods significantly increase the resolution of an image. It was to decrease.

Therefore, in the present invention, by changing the scattering distribution and phase of the scattered waves formed by the light incident on the image projection screen passing through the light diffusion layer, the image projection screen is changed. This reduces or eliminates the occurrence of speckles without lowering the resolution.

In the present invention, changing the scattering distribution or phase of a scattered wave with time means, for example, that the scattered light is periodically shaken at a speed of 10 Hz or more, preferably 30 Hz or more, more preferably 50 Hz or more. As described above, the temporal change is performed at a speed that cannot be perceived by human eyes. In this way, by dynamically changing the scattering distribution and phase of the scattered waves formed by the light scatterers included in the light diffusion layer at a speed that cannot be detected by human eyes, specific static interference A pattern (speckle pattern) is not formed, and it is possible to reduce the glare when the observer observes the projected image. Furthermore, in order to further enhance the speckle reduction effect by dynamic change of scattered light, a light diffusion layer (hereinafter, referred to as a first light diffusion layer) that temporally changes the scattering distribution and phase of scattered waves. In addition, one or more light diffusion layers (hereinafter, referred to as a second light diffusion layer) are provided between the observer and the first light diffusion layer to make it more difficult to detect dynamic changes in scattered light. Is preferred.

FIG. 1 shows the configuration of an image projection screen in which one or more light diffusion layers are provided between the observer and the first light diffusion layer. In the figure, 1 is a first light diffusion layer, 2 is a second light diffusion layer, and 3 is a transparent resin layer. 1A shows a configuration in which a first light diffusion layer 1 and a second light diffusion layer 2 are separated from each other, and a gap is provided therebetween. (B) is the second light diffusion layer 2
The transparent resin layer 3 is formed on the observation side of (a), and (c) shows a structure in which the first light diffusion layer 1 and the second light diffusion layer are integrated via the transparent resin layer 3. (D) shows a structure in which the surface of the first light diffusion layer 1 has an uneven shape. In the present invention, the configuration of the image projection screen is not limited to these, and a lenticular lens, a Fresnel lens sheet, a polarizing film, and the like may be used in appropriate combination.

The light scatterer of the present invention is preferably an optically isotropic one having relatively no polarization selectivity.
As shown in FIGS. 2A to 2D, an elliptical shape, a spherical shape,
A variety of shapes such as an amoeba shape and a needle shape can be used. Further, a complex modulation structure like spinodal decomposition as shown in (e) and dispersed in a matrix may be used. These light scatterers may be dispersed by adding the light scatterer into the matrix of the light diffusion layer, or may be developed by utilizing the phase separation phenomenon of the incompatible system of the polymer blend during the polymerization of the matrix. It may be expressed by a crystallization phenomenon from a molten state.

If the size of the light scatterer is too small, the light scattering efficiency as an image projection screen is reduced.
It is necessary to make the light diffusion layer thicker than necessary or to contain a large amount of light scatterers, which causes a decrease in resolution. Conversely, if it is too large, the light scattering distribution is more biased toward the forward scattering side, so that good light diffusion characteristics Therefore, it is preferable to use an appropriate size. For example, when the light scatterer is spherical, the particle diameter is preferably about 0.2 to 50 μm, more preferably 1 to 20 μm, and further preferably 2 to 10 μm. In a device having a spinodal decomposition-like modulation structure, the diffusion efficiency can be increased even if the size is relatively small.

It is preferable that the size of the light scatterer is not so large with respect to the wavelength of light. This means that the correlation size of the light scatterer is a, the deformation of the light scatterer,
A change in shape or position due to movement, rotation, vibration, or the like is defined as ΔX. When there is no change in the refractive index, if ΔX <a, a part of the correlation between the light scatterers is maintained, and static light due to interference is obtained. This is because the scattering form will eventually remain, and although the glare is reduced, speckles tend not to be completely removed. Therefore, the size (a) of the light scatterer preferably satisfies the following expression (1), and more preferably the expression (2).

[0020]

(Equation 2)

(Equation 3) In the present invention, changes in the shape and position of the light scatterer (Δ
X) has a sufficient effect of reducing and removing speckles when it is about several μm. In addition, by using an optically isotropic light scatterer having relatively no polarization selectivity, even when a polarizing film is used in combination with an image projection screen, the light intensity is attenuated due to a shift in the polarization transmission axis. And a bright image can be obtained.

The refractive index of the light scattering medium is preferably 0.03 or more, more preferably 0.05 or more in the light diffusion layer having the sea-island structure from the viewpoint of the scattering efficiency. It is. The refractive index of the light scatterer can be set so as to have a refractive index distribution in the light diffusion layer. In addition, the thickness of the light diffusion layer and the distribution of the light scatterers can be appropriately set in consideration of the light diffusion characteristics as an image projection screen depending on the shape and concentration of the light scatterers.

In the present invention, in order to temporally change the scattering distribution and phase of the scattered wave by the light diffusion layer, the shape, relative positional relationship and refractive index of the light scatterer contained in the light diffusion layer must be changed. It can be performed by changing over time. Also, by changing the form of the light diffusion layer,
The shape of the light scatterer can be relatively changed. As described above, in order to change the shape, relative positional relationship, refractive index, and form of the light diffusion layer of the light scattering layer contained in the light diffusion layer with time, light, an electric field, and a magnetic field are applied to the light diffusion layer. ,
A scattering distribution changing means for continuously applying heat or stress over time or intermittently is provided, and the light, electric field, magnetic field, heat, stress, the shape of the light scatterer, the relative positional relationship and the like. The refractive index is changed with time.

As a method of changing the shape of the light scatterer by the scattering distribution changing means, for example, as shown in FIG. 3A, a light diffusion layer in which a polymer electrolyte gel is dispersed as a light scatterer is used. A method of inducing a shape change such as swelling, shrinking, bending, etc. in the polymer electrolyte gel by changing the applied voltage sandwiched between the transparent electrodes 4, a light scatterer formed by associating or binding of molecules having a large electric polarity. A method of rearranging light scatterers by applying an electric field to the dispersed light diffusion layer, as shown in FIG. 3B, a light diffusion layer in which light scatterers having a large magnetic polarity are dispersed. Magnetic coil 5
For example, a method of rearranging the light scatterers by applying a magnetic field using the method described above may be used, and a piezoelectric material may be used for the light scatterers.

In the case where heat is used as the scattering distribution changing means, for example, a crystalline polymer, an organic low molecular weight crystal, an inorganic crystal, a colloidal crystal having a low crystal transition temperature and a high rate of crystal change with temperature change as a light scattering body. For example, a method of causing a shape change by heat-induced crystal transition, a method of causing a shape change by heat swelling and shrinking by using a light scatterer composed of colloid particles or gel-like particles, and the like can be used. As the scattering distribution changing means using such heat, various generally used heat sources can be used, but it is preferable to use invisible light such as infrared light which does not impair the projected image. Further, as shown in FIG. 3C, the shape of the light scatterer can be changed by applying a mechanical vibration stress in the plane direction of the light diffusion layer.

When the shape of the light scatterer is changed by the scattering distribution changing means as described above, the thickness of the light diffusion layer is preferably set to about several tens μm to 100 μm.
In particular, when an electric field is applied, by forming a light diffusion layer having such a thickness, the distance between the electrodes is shortened, and a large electric field can be applied at a relatively low voltage. Body shape can be changed.

As a method of changing the relative positional relationship of the light scatterers as the scattering distribution changing means, there is a method of changing the relative positional relationship by translational movement, asymmetric rotation, scattering, vibration of the center of gravity, etc. of the light scatterers. Can be For example, by applying an electric field to a light-diffusing layer in which a charged colloid is dispersed as a light-scattering body, the colloid is propelled by an electric perturbation or diffused to change the relative positional relationship. A method of applying an electric field to a light diffusion layer in which light scatterers formed by associating or binding molecules having a large electric polarity are dispersed in a light diffusion layer in which light scatterers having a large magnetic polarity are dispersed A method of applying a magnetic field using a coil or the like may be used. As a method of utilizing heat as the scattering distribution changing means, for example, similarly to the method shown in FIG. 3A, a light diffusion layer is sandwiched between electrode plates using a transparent resistance film or the like. A method of causing the light scatterer to perform micro Brownian motion or macro Brownian motion by changing the temperature of
Methods of shrinking and deforming are exemplified. As the scattering distribution changing means using such heat, various generally used heat sources can be used, but it is preferable to use invisible light such as infrared light which does not impair the projected image.

As a method of changing the refractive index on the surface or inside of the light scatterer as the scattering distribution changing means, there are light scatterers formed by associating or binding molecules having a large electric or magnetic polarity as the light scatterer. A method of applying an electric field or a magnetic field to a light diffusion layer in which a light scatterer made of an organic nonlinear optical material, an inorganic nonlinear optical material, an electro-optical material, or the like that causes a change in the refractive index due to an electric field or a magnetic field is cited. Can be Here, the refractive index of the light scatterer is a complex refractive index (n ^* ) represented by the following equation (3) involved in the light diffusion phenomenon.

[0028]

(Equation 4) (Here, n ₁ is a real number term indicating a refractive index measured by a refractometer or the like, and n ₂ is a complex term indicating a term which contributes as a light absorption (loss) effect of a light scatterer during light scattering. j indicates a complex display.) The scattering distribution of the light scatterer is determined by the form of the refractive index distribution, and the phase of the scattered wave is obtained by changing n ₁ and n _{2 in} the equation (3). Changes. Similarly, the light scattering phenomenon is defined by refractive index fluctuation, and changing the refractive index distribution of the light scatterer has the same effect as changing the shape of the light scatterer.

When only the refractive index of the light scatterer changes, a large change in the refractive index is required. This is because it is possible to change the phase of the scattered wave by changing the refractive index, but the correlation of the refractive index distribution with respect to the interference of the scattered wave of the entire light scatterer does not change the shape and positional relationship of the light scatterer. This is because the correlation between the refractive index distributions is likely to be partially maintained. The fact that a certain correlation of the refractive index distribution is maintained in the light diffusion layer at a certain rate means that stationary static interference remains, and speckles may be generated. .

In the present invention, the material of the matrix or the light scatterer constituting the light diffusion layer is a liquid material,
Gels, rubbers, thermoplastic resins, and the like are preferred. By using such a material, light,
A small supply of external energy, such as an electric field, a magnetic field, heat, or stress, can change the shape and relative positional relationship of the light scatterer, and even without such energy supply, the light scatterer In some cases, it is possible to change the shape, relative positional relationship, and the like. In particular, such liquids, gels, rubbers, thermoplastic resins,
It is preferable that the average relaxation time of these molecular motions is short, and for example, the average molecular motion relaxation time evaluated by a quasi-elastic light scattering method or the like is preferably about 0.5 seconds or less, more preferably 0.1 second or less. Seconds or less, more preferably 2
0 second (corresponding to 50 Hz in frequency) or less. here,
As liquids, colloidal solutions, emulsions, polymer solutions,
Common liquids such as electrolytes, organic solvents, and water can be used. Further, as the gel-like substance, an organic or inorganic gel substance such as a chemically cross-linked gel and a physically cross-linked gel can be used, and among them, those having a sol-gel transition temperature lower than room temperature are preferable, The lower the sol-gel transition temperature, the better. Further, as the rubber-like material and the thermoplastic resin, those having a glass transition temperature lower than room temperature are preferable, and those having a glass transition temperature much lower than room temperature are more preferable.

[0031]

The image projection screen of the present invention has a light,
The shape, relative positional relationship, refractive index, etc. of the light scatterer are temporally changed by an electric field, a magnetic field, heat, stress, etc., and the scattering distribution and / or phase of the scattered wave of the light diffusion layer is temporally changed. Accordingly, it is possible to provide an image projection screen that hardly generates speckles and can obtain a high-resolution and high-quality projected image.

[0032]

[Brief description of the drawings]

[0033]

FIG. 1 is a schematic diagram showing a configuration of an image projection screen of the present invention.

[0034]

FIG. 2 is a schematic view showing a shape of a light scatterer used in the present invention.

[0035]

FIG. 3 is a schematic diagram showing a specific example of a scattering distribution changing means of the present invention.

[0036]

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 first light diffusion layer 2 second light diffusion layer 3 transparent resin layer 4 transparent electrode 5 magnetic coil

Claims (8)

[Claims] 1. An image projection screen on which an optical image is projected by projection light, wherein a scattering distribution and / or a phase of a scattered wave is temporally changed in a light diffusion layer constituting the image projection screen. An image projection screen, characterized in that: 2. The light diffusion layer is provided with a scattering distribution changing means for applying light, an electric field, a magnetic field, heat, and a stress, and the shape of a light scattering body included in the light diffusion layer is controlled by the scattering distribution changing means. 2. The screen according to claim 1, wherein at least one of the position and the refractive index is changed with time. 3. An image projection screen according to claim 2, wherein a means for applying a vibration stress in a plane direction of said light diffusion layer is used as said scattering distribution changing means. 4. A liquid material, wherein the matrix of the light diffusion layer is a liquid material,
The image projection screen according to any one of claims 1 to 3, wherein the screen is made of any one of a gel, a rubber, and a thermoplastic resin. 5. The image projection screen according to claim 2, wherein the light scatterer has a matrix made of one of a liquid material, a gel material, a rubber material, and a thermoplastic resin. 6. The image projection screen according to claim 4, wherein the relaxation time of the liquid material, the gel material, the rubber material, and the thermoplastic resin is 0.5 seconds or less. 7. The light scatterer has a correlation size of a,
3. The image projection screen according to claim 2, wherein the following expression (1) is satisfied when the movement or vibration distance of the scatterer is ΔX. (Equation 1) 8. At least a part of the light scatterer is a heat deformable material, a material having an electric polarity, a material having a magnetic polarity, a material having a non-linear optical effect, a material having an electro-optical effect, a piezoelectric material, a colloid. 3. An image projection screen according to claim 2, comprising at least one of colloidal crystals.