JP2005148489A - Projection system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a projection system capable of sharply displaying video even in the presence of bright environmental light and keeping color balance. <P>SOLUTION: The projection system 20 is equipped with a projection screen 10 having a polarized light selective reflecting layer 11 having a cholesteric liquid crystal structure selectively reflecting light of a specified polarized light component and a projector 121 which projects unpolarized video light on the projection screen 10. The projector 121 is equipped with a light source 50, condenser lenses 51 and 53, a color filter 52 arranged between the condenser lenses 51 and 53, a reflection part 60 including a plurality of micromirrors 60a to 60i arranged on a semiconductor, and a projection lens 54; and a light/dark ratio is increased by controlling the light/dark state of the light by varying tilts of the micromirrors 60a to 60i to improve the contrast, and the polarized light selective reflecting layer 11 holds the polarized state of the unpolarized video light. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a projection system that displays video by projecting video light onto a projection screen by a projector, and more particularly, to a projection system with excellent visibility that can display video clearly.

  As a conventional projection system, an image light projected by a projector is projected on a projection screen, and an observer observes the reflected light as an image.

  As a projection screen used in such a conventional projection system, a white paper material or a cloth material, or a plastic film coated with an ink that scatters white light is generally used. Further, as a higher quality projection screen, a screen that includes a scattering layer in which beads, pearls and the like are kneaded, and the scattering state of image light is controlled by this scattering layer is commercially available.

  By the way, in recent years, the demand for home use such as a home theater has increased with the miniaturization of the projector main body and the price reduction, and the projection system is often used in general homes. In this case, the projection system is often installed in a living space at home, but such a place is usually designed to easily receive ambient light such as outside light and illumination light. For this reason, a projection screen used in a projection system for home use is desired to be able to realize a good video display even under bright ambient light.

  However, in the above-described conventional projection screen, ambient light such as outside light and illumination light is reflected in the same manner as image light, so that it is difficult to realize a good image display under bright ambient light. There is a problem.

  Specifically, in the conventional projection system, the shade of the image is created by the difference in intensity of the projection light (image light) from the projector projected onto the projection screen. For example, a white picture is projected on a black background. In such a case, the portion where the projection light hits the projection screen is white and the other portion is black, and the shade of the image is created by such a difference in brightness between black and white. In this case, in order to realize a good video display, it is necessary to make the white display portion brighter and the black display portion darker to increase the contrast difference.

  However, since the above-described conventional projection screen reflects ambient light such as external light and illumination light without distinction from image light, both the white display portion and the black display portion become bright, and the brightness of black and white is increased. The difference in height will be small. For this reason, with the conventional projection screen described above, it is difficult to realize a good image display unless the influence of ambient light such as outside light or illumination light is suppressed by using a means or environment for darkening the room. There is a problem that.

  Under such a background, conventionally, a projection screen capable of realizing a good image display even under bright ambient light has been studied, for example, using a hologram or using a polarization separation layer. A thing etc. are proposed (refer patent documents 1 and 2).

  However, among the conventional projection screens described above, the projection screen using a hologram can control the scattering effect to make the white display portion brighter, and can display a relatively good image under bright ambient light. Although it can be realized, the hologram has a wavelength selectivity, but does not have a polarization selectivity, and there is a problem that an image can be clearly displayed only within a certain limit. Further, a projection screen using a hologram has a problem that it is difficult to enlarge the screen due to a manufacturing problem. Furthermore, a projection screen using a hologram has a problem that there is no polarization selectivity.

  On the other hand, in the projection screen using the polarization separation layer, it is possible to make the white display portion brighter while making the black display portion darker. The video can be displayed clearly.

  Specifically, in the above-mentioned Patent Document 1, a cholesteric liquid crystal that reflects light of each color of red, green, and blue (right circularly polarized light or left circularly polarized light) included in video light is used, and the circularly polarized light separation function of the cholesteric liquid crystal is used. Describes a projection screen that does not reflect approximately half of the ambient light.

  However, in the projection screen described in Patent Document 1, since the cholesteric liquid crystal is in the planar alignment state, when light is reflected by such a cholesteric liquid crystal, the reflection of light becomes specular reflection, and the light is reflected. It is difficult to visually recognize as an image. That is, in order to visually recognize light as an image, the reflected light needs to have a scattering effect. However, the projection screen described in Patent Document 1 does not consider this point at all.

On the other hand, the above-mentioned Patent Document 2 is a projection screen that uses a diffusive multilayer reflective polarizer as a reflective polarization element, and reflects a part of ambient light by a polarization separation function such as a multilayer reflective polarizer. It is described that the scattering effect is given to the reflected light by the interface reflection of the materials having different refractive indexes constituting the multilayer reflective polarizing material or the diffusion element provided separately from the multilayer reflective polarizing material. Has been.
Further, Patent Document 2 discloses a projection screen using a cholesteric reflective polarizing material or the like as a reflective polarizing element, and using the reflective polarizing element and a diffusing element in combination, polarization of a cholesteric reflective polarizing material or the like. There is a description that a part of the ambient light is not reflected by the separation function and a scattering effect is given to the reflected light by a diffusion element provided separately from the cholesteric reflective polarizing material.

  That is, in the projection screen using the polarization separation layer (organic film) described in the above-mentioned Patent Document 2, light of a specific polarization component is emitted in consideration of the polarization state of image light and ambient light projected from the projector. It is trying to improve the visibility of an image by diffuse reflection (giving a scattering effect to reflected light).

  Here, the projection system using the projection screen described in Patent Document 2 uses a projector (for example, a liquid crystal projector) that controls the polarization state of the image light to light of a specific polarization component. In a liquid crystal projector, the polarization state of image light is controlled by providing a retardation plate or the like inside or outside the liquid crystal projector.

However, in a projection system using a projector that controls the polarization state of image light, for example, when image light is incident on the polarization separation layer at an angle, a characteristic (phase difference action) unique to the polarization separation layer, which is an organic film. : Details will be described later), the polarization state of the image light is distorted. As a result, the reflection efficiency of the image light becomes non-uniform in the polarization separation layer.
For this reason, in the above-described projection system, for example, light having wavelength ranges indicating blue (B), green (G), and red (R), which are the three primary colors of light, is reflected with a balanced reflection intensity. It is assumed that the balance of the color maintained by the above will be lost.

Therefore, when constructing a projection system using a projection screen provided with a polarization separation layer (organic film), in order to prevent the visibility (particularly color balance) of the image from being deteriorated, Although it is necessary to apply a projector that takes into account the phase difference effect of the polarization separation layer, in the projection system using the projection screen described in Patent Document 2 described above, the projector that takes into account the phase difference effect of the polarization separation layer. Is not applied.
JP-A-5-107660 JP 2002-540445 A

  An object of the present invention is to provide a projection system that can clearly display an image even under bright ambient light and can maintain a color balance.

  In order to solve the above problems, the invention of claim 1 includes a projection screen including a polarization selective reflection layer that selectively reflects light of a specific polarization component, and the projection screen includes both linear polarization components. And a projector that projects light and / or light including both circularly polarized components as image light.

  According to a second aspect of the present invention, in the projection system according to the first aspect, the polarization selective reflection layer has at least two partial selective reflection layers, and the image light is obliquely projected onto the projection screen. In the projection system, the image light is maintained in a polarization state in each of the partial selective reflection layers.

  According to a third aspect of the present invention, in the projection system according to the first or second aspect, the projector uses light including both linearly polarized components and / or light including both circularly polarized components as light source light. A light source generated as follows, a two-dimensional array, a reflection portion including a plurality of micromirrors that reflect the light source light, and the light source light reflected by the micromirrors is projected. And a projection lens for projecting onto a screen.

  According to a fourth aspect of the present invention, in the projection system according to the first or second aspect, the projector includes a liquid crystal projector and a depolarizer disposed in the vicinity of the exit of the liquid crystal projector. Is a projection system characterized by

  A fifth aspect of the present invention is the projection system according to the first or second aspect, wherein the projector is a front projection type CRT.

  The invention of claim 6 is the projection system according to any one of claims 1 to 5, wherein the light of the specific polarization component is right circularly polarized light or left circularly polarized light. Projection system.

  The invention of claim 7 is the projection system according to any one of claims 1 to 5, wherein the light of the specific polarization component is one linearly polarized light. It is.

  The invention according to claim 8 is the projection system according to any one of claims 1 to 7, wherein the polarization selective reflection layer includes a polarization reflection layer that reflects light of the specific polarization component; The projection system is characterized by comprising a diffusing element that diffuses the light reflected by the polarizing reflection layer.

  The invention of claim 9 is the projection system according to any one of claims 1 to 7, wherein the polarization selective reflection layer itself has diffusibility. is there.

  According to a tenth aspect of the present invention, in the projection system according to the ninth aspect, the polarization selective reflection layer has a cholesteric liquid crystal structure, and is selectively reflected by a structural nonuniformity of the cholesteric liquid crystal structure. A projection system characterized by diffusing light.

  The invention of claim 11 is the projection system according to claim 10, wherein the cholesteric liquid crystal structure includes a plurality of spiral structure regions having different spiral axis directions.

  A twelfth aspect of the present invention is the projection system according to any one of the first to eleventh aspects, wherein the polarization selective reflection layer is light in a specific wavelength range that covers only a part of the visible light range. Is a projection system characterized by selectively reflecting.

  A thirteenth aspect of the present invention is the projection system according to any one of the first to twelfth aspects, wherein the polarization selective reflection layer has a case where light is incident perpendicularly to the polarization selective reflection layer. A projection system characterized by selectively reflecting light having a selective reflection center wavelength in a range of 430 to 460 nm, 540 to 570 nm, and 580 to 620 nm on the basis of a reference.

  The projection system of the present invention includes (1) a projection screen having a polarization selective reflection layer that selectively reflects light of a specific polarization component, light containing both linear polarization components, and / or both circular polarizations. Since it includes a projector that projects component-containing light as image light, the image light has little effect even if it receives a phase difference effect that is a characteristic property of the polarization separation layer that is an organic film. Reflected with a substantially uniform reflection efficiency at a position (for example, a central portion, an end portion, particularly, each partial selective reflection layer in the case of a laminated structure), and as a result, blue (B ), Green (G), and light having a wavelength range indicating red (R) can be reflected with a balanced reflection intensity, and the color balance can be maintained.

(2) Since the polarization selective reflection layer has at least two or more partially selective reflection layers, image light (light including both linearly polarized components and / or both) from the projector to the projection screen. When the image light is projected obliquely, the image light is maintained in its polarization state in each partial selective reflection layer, and as a result, is reflected almost uniformly at every position of each partial selective reflection layer. The image light can be reflected efficiently.

(3) The projector is arranged two-dimensionally with the light source, and changes the inclination of the light source light generated from the light source (light including both linearly polarized components and / or both circularly polarized components). And a projection lens for projecting light source light reflected by the micromirror onto the projection screen, the projector includes a plurality of micromirrors ( A so-called DLP (Digital Light Processing: registered trademark of Texas Instruments (TI)) projector having a reflection part (DMD: Digital Micro-mirror Device) including a micro-mirror, When projecting onto a projection screen, the amount of light passing through the projection lens is changed by changing the tilt of the micromirrors (so-called mirror switching), so And controls the corresponding strike), for example, in a projection screen, it is possible to contrast in the black to prevent lowered.
Specifically, in this projector, when the light is darkened, the tilt of the micromirror is changed so that the light source light reflected by the micromirror does not pass through the projection lens, and the light is also brightened. First, the inclination of the micromirror is changed so that the light source light reflected by the micromirror passes through the projection lens.

(4) Since the projector includes a liquid crystal projector and a depolarizer disposed in the vicinity of the exit of the liquid crystal projector, the image light emitted from the liquid crystal projector is not substantially changed in its optical axis. The light including both linearly polarized components and / or the light including both circularly polarized components can be projected onto the projection screen.

(5) Since the projector is a forward projection type CRT, a projection system can be constructed using a so-called three-tube projector.

(6) Since light of a specific polarization component is right circular polarization or left circular polarization, only light of a specific polarization component (for example, right circular polarization) is selectively reflected by the polarization separation characteristic of the polarization selective reflection layer. Therefore, it is possible to reflect only about 50% of ambient light such as outside light and illumination light having no polarization characteristics by the polarization selective reflection layer.
For this reason, even when the brightness of the bright display portion such as white display is the same, the brightness of the dark display portion such as black display can be substantially halved and the contrast of the image can be approximately doubled.

(7) Since the light of a specific polarization component is one linearly polarized light, linearly polarized light out of video light (for example, including right circularly polarized light, left circularly polarized light, P polarized light, and S polarized light) projected from the projector By matching the polarization separation characteristics of the polarization selective reflection layer in the direction of (P-polarized light, S-polarized light), an image can be displayed brightly.
Specifically, since the light of the specific polarization component is P-polarization or S-polarization, only the light of the specific polarization component (for example, P-polarization) is selectively reflected by the polarization separation characteristic of the polarization selective reflection layer. Therefore, it is possible to reflect only about 50% of ambient light such as external light and illumination light having no polarization characteristics by the polarization selective reflection layer.
For this reason, even when the brightness of the bright display portion such as white display is the same, the brightness of the dark display portion such as black display can be substantially halved and the contrast of the image can be approximately doubled.

(8) Since the polarization selective reflection layer is composed of a polarization reflection layer that reflects light of a specific polarization component and a diffusion element that diffuses light reflected by the polarization reflection layer, the polarization separation characteristic and the diffusion characteristic are independent. Therefore, it is possible to easily control each characteristic.

(9) Since the polarization selective reflection layer itself has diffusivity, a strong reflection intensity can be obtained because the polarization state of incident light is not disturbed.
On the other hand, when the diffusing element is provided on the viewer side of the reflective polarizing element, light is transmitted through the diffusing element before entering the reflective polarizing element, and the polarization state is disturbed. (This is called "biased"). For this reason, the original polarization separation function of the reflective polarizing element is impaired, and the visibility of the image cannot be sufficiently improved.

(10) The polarization selective reflection layer has a cholesteric liquid crystal structure and diffuses light of a specific polarization component due to the structural non-uniformity of the cholesteric liquid crystal structure, so there is no need to provide a diffusing element on the observation side.
Specifically, when the diffusing element is provided on the viewer side of the reflective polarizing element, the above-described “depolarization” problem occurs. Here, there are two types of light that pass through the diffusing element: ambient light (external light, etc.) and image light. When the polarization state of the ambient light is disturbed by the diffusing element, The light to be transmitted is converted into a component reflected by the reflective polarizing element by depolarization, and is reflected by the reflective polarizing element as unnecessary light.
In addition, when the polarization state of the image light is disturbed by the diffusing element, the light that should be reflected by the reflective polarizing element is converted to a component that is not reflected by the reflective polarizing element due to the depolarization. The element is transparent. Due to these two phenomena, the original polarization separation function is impaired, and the visibility of the image cannot be sufficiently improved.

(11) Since the cholesteric liquid crystal structure includes a plurality of spiral structure regions having different spiral axis directions, the above-described “depolarization” problem is caused with respect to ambient light and image light transmitted through the polarization selective reflection layer. Therefore, the visibility of the image can be improved while maintaining the original polarization separation function of the polarization selective reflection layer.
Specifically, in the polarization selective reflection layer, the cholesteric liquid crystal structure has structural non-uniformity, for example, the direction of the helical axis of the helical structure region included in the cholesteric liquid crystal structure varies. The image light is diffusely reflected, not specularly reflected, and the image is easy to visually recognize. At this time, the polarization selective reflection layer diffuses the selectively reflected light due to the structural non-uniformity of the cholesteric liquid crystal structure. This light can be transmitted without being diffused.

(12) Since the polarization selective reflection layer selectively reflects light in a specific wavelength range that covers only a part of the visible light range, the influence of ambient light such as outside light and illumination light is further suppressed. Therefore, the contrast of the video can be increased and the visibility of the video can be further improved.

(13) The polarization selective reflection layer selectively reflects light having a selective reflection center wavelength in the range of 430 to 460 nm, 540 to 570 nm, and 580 to 620 nm with reference to the case where light is incident vertically. Therefore, the reflection band of the projection screen can be made to correspond to the wavelength range of the image light.
Specifically, a projector that projects image light on a projection screen realizes color display with light in the wavelength ranges of red (R), green (G), and blue (B), which are the three primary colors of light. For example, light having a selective reflection center wavelength in the range of 430 to 460 nm, 540 to 570 nm, and 580 to 620 nm is projected on the basis of the case where light enters the projection screen vertically.

  Non-polarized video light is projected from a projector (for example, DLP projector) onto a projection screen with a polarization selective reflection layer for the purpose of displaying images clearly even under bright ambient light and maintaining color balance. It was realized by doing. Hereinafter, “non-polarized light” refers to light including both linearly polarized components (right circularly polarized light and left circularly polarized light) and / or light including both circularly polarized components (P polarized light and S polarized light).

Embodiments of the present invention will be described below with reference to the drawings.
Projection screen First, FIG. 1, a description will be given of the basic structure of the projection screen used in a projection system according to an embodiment of the present invention.

As shown in FIG. 1, the projection screen 10 reflects video light projected from the viewer side (upper side of the drawing) and displays an image, and selectively reflects light of a specific polarization component. A polarization selective reflection layer 11 that is an organic film having a cholesteric liquid crystal structure, and a support substrate 12 that supports the polarization selective reflection layer 11.
The details of the projection system that does not use the projection screen 10 will be described later.

  Among them, the polarization selective reflection layer 11 is made of a liquid crystalline composition exhibiting cholesteric regularity, and the director of the liquid crystal molecules is continuously rotated in the thickness direction of the layer as the physical molecular arrangement of the liquid crystal molecules. It has a spiral structure.

  The polarization selective reflection layer 11 has a polarization separation characteristic for separating a circularly polarized light component in one direction and a circularly polarized light component in the opposite direction based on the physical molecular arrangement of the liquid crystal molecules. ing. That is, in the polarization selective reflection layer 11, non-polarized light incident along the spiral axis is separated into two polarized light (right circularly polarized light and left circularly polarized light), one of which is transmitted and the remaining is reflected. Is done. This phenomenon is known as circular dichroism, and when a spiral direction in the spiral structure of liquid crystal molecules is appropriately selected, a circularly polarized component having the same optical rotation direction as this spiral direction is selectively reflected.

In this case, the maximum optical rotation light scattering occurs at the wavelength λ ₀ of the following equation (1).
λ ₀ = nav · p (1)
Here, p is the helical pitch length in the helical structure of the liquid crystal molecules (the length per pitch of the molecular helix of the liquid crystal molecules), and nav is the average refractive index in a plane perpendicular to the helical axis.

Further, the wavelength bandwidth Δλ of the reflected light at this time is expressed by the following equation (2). Here, Δn is a birefringence value.
Δλ = Δn · p (2)

That is, in FIG. 1, unpolarized light incident from the viewer side of the projection screen 10 (right circularly polarized light 31R and left circularly polarized light 31L within the selective reflection wavelength region, right circularly polarized light 32R and left circularly polarized light outside the selective reflection wavelength region). 32L) is one circularly polarized light component (for example, within the selective reflection wavelength region) belonging to the range of the wavelength bandwidth Δλ centered on the selective reflection center wavelength λ ₀ (selective reflection wavelength region) according to the polarization separation characteristic as described above. Right circularly polarized light 31R) is reflected as reflected light 33, and other light (for example, left circularly polarized light 31L within the selective reflection wavelength region, right circularly polarized light 32R and left circularly polarized light 32L outside the selective reflection wavelength region) is transmitted.

  Note that such a cholesteric liquid crystal structure of the polarization selective reflection layer 11 includes a plurality of spiral structure regions 30 having different directions of the spiral axis L, as shown in FIG. The light that is selectively reflected (reflected light 33) is diffused by such structural nonuniformity of the cholesteric liquid crystal structure. Here, the state in which the cholesteric liquid crystal structure has structural inhomogeneity refers to a state in which the direction of the helical axis L of the helical structure region 30 included in the cholesteric liquid crystal structure varies, as well as a nematic layer surface (die of liquid crystal molecules). A state in which at least a part of the surface of the same XY direction in the XY direction is not parallel to the surface of the polarization selective reflection layer 11 (when a cross-sectional TEM photograph of the dyed cholesteric liquid crystal structure film is taken, a gray pattern A state in which a continuous curve of the appearing layers is not parallel to the substrate surface), or a state in which fine particles of cholesteric liquid crystal are dispersed as a pigment. Further, the “diffusion” caused by the structural non-uniformity of the cholesteric liquid crystal structure is expanded to such an extent that the observer can recognize the reflected light (image light) reflected by the projection screen 10 as an image. Or to scatter.

  On the other hand, a general cholesteric liquid crystal structure is in a planar alignment state, and as shown in FIG. 2B, the direction of the helical axis L of each helical structure region 30 included in the cholesteric liquid crystal structure is all layers. The light that is selectively reflected (reflected light 36) is specularly reflected.

The helical structure region 30 included in the cholesteric liquid crystal structure of the polarization selective reflection layer 11 selectively selects light in a specific wavelength range that covers only a part of the visible light range (for example, a wavelength range of 400 to 700 nm). It is preferable to have a specific helical pitch length to reflect.
More specifically, the cholesteric liquid crystal structure of the polarization selective reflection layer 11 is non-reflective so as to selectively reflect only light in a wavelength range corresponding to the wavelength range of image light projected by a projector such as a liquid crystal projector. It is preferable to have at least two or more different helical pitch lengths (described later).

FIG. 3 is a diagram illustrating chromatic dispersion of image light projected from the projector. The horizontal axis represents wavelength (λ) and the vertical axis represents intensity (I).
In general, the projector realizes color display with light in the wavelength ranges of red (R), green (G), and blue (B), which are the three primary colors of light. In addition, 430 to 460 nm, 540 to 570 nm, and 580 to 620 nm used as wavelength ranges of red (R), green (G), and blue (B) are color filters used for a display that expresses white by the three primary colors of light. This is a general wavelength range for light sources and light sources.
Here, each color of red (R), green (G), and blue (B) has a specific wavelength (for example, blue (B) is 460 nm, green (G) is 550 nm, red (R), as illustrated. Is represented as a bright line having a peak at 600 nm.
However, such a bright line has a certain width, and since there is a difference in wavelength depending on the design of the apparatus and the type of light source, it is preferable that each color has a wavelength bandwidth of 30 to 40 nm. In addition, when the wavelength range of each color of red (R), green (G), and blue (B) is set outside the above-described range, white cannot be expressed, and white is yellowish white Or reddish white.

Next, the laminated structure of the polarization selective reflection layer 11 will be described.
When the cholesteric liquid crystal structure of the polarization selective reflection layer 11 has two or more types of helical pitch lengths that are discontinuously different, the polarization selective reflection layer 11 has at least two or more partially selective reflection layers with different helical pitch lengths. Can be configured by laminating each other.
Each of the partial selective reflection layers exists, for example, in a range of selective reflection center wavelengths of 430 to 460 nm, 540 to 570 nm, and 580 to 620 nm on the basis of the case where light is perpendicularly incident on the polarization selective reflection layer 11. The helical pitch length of the cholesteric liquid crystal structure may be determined so as to selectively reflect the light (the three primary colors of light).

FIG. 4 is a diagram illustrating the reflection band of the polarization selective reflection layer 11 when the wavelength ranges of the three primary colors of light are independent. The horizontal axis represents wavelength (λ) and the vertical axis represents reflectance (R).
FIG. 5 is a schematic sectional view showing a modification of the projection screen shown in FIG.
When the wavelength ranges of red (R), green (G), and blue (B), which are the three primary colors of light, are expressed as mutually selective selective wavelength ranges, the cholesteric liquid crystal structure of the polarization selective reflection layer 11 is It is preferable to have three types of helical pitch lengths that are discontinuously different, so that the reflection band of the polarization selective reflection layer 11 is red (R), green (G), and blue (B) as illustrated. Each can correspond to a wavelength range.
As shown in the figure, the projection screen 10 includes, for example, a polarization selective reflection layer 11 having a cholesteric liquid crystal structure that selectively reflects light of a specific polarization component, and a support base 12 that supports the polarization selective reflection layer 11. I have.

  Specifically, as shown in the drawing, the polarization selective reflection layer 11 selects the partial selective reflection layer 11a that selectively reflects light in the blue (B) wavelength region and the light in the green (G) wavelength region. And a partial selective reflection layer 11c that selectively reflects light in the red (R) wavelength region, and a partial selective reflection from the observation side to the support substrate 12 side. The layer 11c, the partial selective reflection layer 11b, and the partial selective reflection layer 11a are laminated in this order. In addition, the order of stacking the partial selective reflection layers 11a, 11b, and 11c is not necessarily limited to this, and an arbitrary order can be appropriately taken.

  In FIG. 5, each of the partial selective reflection layers 11a, 11b, and 11c emits light of a specific polarization component (for example, right-handed circularly polarized light) in the same manner as the polarization selective reflection layer 11 shown in FIGS. It has a cholesteric liquid crystal structure that selectively reflects and has a cholesteric liquid crystal structure that diffuses selectively reflected light due to its structural non-uniformity.

The thickness of the polarization selective reflection layer 11 (or each of the partial selective reflection layers 11a, 11b, and 11c constituting the polarization selective reflection layer 11) reflects substantially 100% of light in a specific polarization state that is selectively reflected. It is preferable to set the size to such a degree that the reflectance is saturated. This is because video light cannot be efficiently reflected if the reflectance is less than 100% with respect to light of a specific polarization component that is selectively reflected (for example, right circularly polarized light).
Note that the reflectance of the polarization selective reflection layer 11 (or the partial selective reflection layers 11a, 11b, and 11c constituting the polarization selective reflection layer 11) directly depends on the number of helical pitches, but the helical pitch length is If it is fixed, it indirectly depends on the thickness of the polarization selective reflection layer 11.
Specifically, in order to obtain a reflectance of 100%, it is said that about 4 to 8 pitches are necessary. For example, although it depends on the type of material of the liquid crystalline composition and the selective reflection wavelength region, for example, red (R ), Partially selective reflecting layers 11a, 11b, and 11c for reflecting light in one of the wavelength ranges of green (G) and blue (B), a thickness of about 1 to 10 μm is required.
On the other hand, the thicknesses of the partial selective reflection layers 11a, 11b, and 11c are not as good as they are thick. If they are too thick, it becomes difficult to control the orientation, unevenness, etc. Since the degree of light absorption increases, the above-mentioned range is appropriate.

Next, the property (phase difference action) peculiar to the polarization selective reflection layer 11 which is an organic film will be described.
FIG. 6 is a conceptual diagram for explaining the phase difference effect by the polarization selective reflection layer 11.
As described above, the polarization selective reflection layer 11 has a cholesteric liquid crystal structure, and this cholesteric liquid crystal structure is regarded as a bulk (herein, an internal region defined by the size of cholesteric liquid crystal molecules). Furthermore, in consideration of the point that the refractive index differs in the direction along the optical axis (X-axis, Y-axis, Z-axis in the figure) (having so-called refractive index anisotropy) in the inner region, the bulk has a disc shape. (See (a) in the figure).
For example, when the XY plane including the origin O is used as a reference, the cross-sectional shape of the disk-shaped region is a circle (complete circle) A as illustrated. Therefore, the diameter of this circle A can be expressed as nx (= ny) using the refractive index (n) of cholesteric liquid crystal molecules. Note that x and y are unit vectors on the X and Y axes.
Similarly, the cross-sectional shape of the disk-shaped region is an ellipse B reduced in the Z-axis direction when the YZ plane is used as a reference (see (a) in the figure), and the length of the long axis is ny and short. When the length of the axis is nz, ny (= nx)> nz. Note that z is a unit vector on the Z axis.

Here, when light of a specific polarization component (for example, right circularly polarized light) is incident on the bulk, the light of the specific polarization component is regarded as a vector passing through the origin O, and this vector is further defined as a normal line. It is possible to determine whether or not a phase difference effect occurs by considering a cross-sectional shape with reference to the plane (including the origin O).
Specifically, when the light 31A having a specific polarization component is perpendicularly incident on the bulk, the above-described cross-sectional shape is a circle A (see (b) in the figure). In this case, nx = ny, and nz that coincides with the vector direction of the light 31A is not involved, so that it does not receive a phase difference effect. Accordingly, the light 31A passes through this bulk while maintaining its polarization state.

On the other hand, when the light 31A having a specific polarization component is incident obliquely on the bulk, the above-described cross-sectional shape is an ellipse C (see (c) in the figure). In this case, the length of the major axis of the ellipse C is ny, and the length of the minor axis is nx ′. As a result, nx ′ <ny. Note that x ′ is a unit vector on the x ′ axis.
Thus, in the situation where the cross-sectional shape is an ellipse, the light 31A is affected by nz that coincides with the vector direction of the light 31A, and a phase difference action occurs. Therefore, the polarization state of the light 31A is distorted, for example, becomes elliptically polarized light.

Therefore, when light 31A of a specific polarization component is incident on the polarization selective reflection layer 11 having a cholesteric liquid crystal structure, the polarization state of the light 31A is determined by the position of the polarization selective reflection layer 11 (particularly, the polarization selective reflection layer). 11 has a laminated structure, it differs depending on the positions of the central selective portion and the edge portion of the partial selective reflection layers 11a, 11b, and 11c), and as a result, the reflection efficiency is also the position of the polarization selective reflection layer 11. Due to the unevenness.
The light 31A is affected by the phase difference effect as it passes through the bulk. For this reason, in the partial selective reflection layer 11a most laminated | stacked on the support base material 12 side, compared with the partial selective reflection layers 11b and 11c, the light 31A in which the polarization state was more distorted will be reflected. Therefore, in the polarization selective reflection layer 11 having a laminated structure, the reflection efficiency decreases as the partial selective reflection layer laminated on the support base material 12 side.

  For this reason, in the polarization selective reflection layer 11 that is the organic film described above, for example, light having wavelength ranges indicating the three primary colors of light, blue (B), green (G), and red (R), is balanced. The case where the balance of the color maintained by reflecting with a good reflection intensity is lost is assumed.

Therefore, in order to prevent the visibility on the projection screen 10 from being deteriorated (here, the color balance is lost), it is necessary to consider the polarization state of the light incident on the polarization selective reflection layer 11.
In the projection system 20 (see FIGS. 14 and 15) using the projection screen 10 according to the present embodiment, polarization selective reflection is achieved by applying a projector (such as a DLP projector) that can project non-polarized image light. The color balance was not disturbed by the influence of the phase difference effect of the layer 11.

  Next, the support base 12 will be described.

  The support base 12 is for supporting the polarization selective reflection layer 11 and can be formed using a material such as a plastic film, metal, paper, cloth, or glass.

  Here, the support substrate 12 preferably includes a light absorption layer that absorbs light in the visible light range.

  Specifically, for example, as shown in FIG. 7, the support base 12 (12A) may be formed using a plastic film (for example, a black PET film in which carbon is mixed) in which a black pigment is kneaded. . In this case, the entire support substrate 12 becomes a light absorption layer (light absorption substrate). Thereby, light that should not be reflected as reflected light 33 among unpolarized light incident from the viewer side of the projection screen 10 (left circularly polarized light 31L within the selective reflection wavelength region, right circularly polarized light outside the selective reflection wavelength region). 32R and left circularly polarized light 32L) and light incident from the back side of the projection screen 10 are absorbed to generate reflected light caused by ambient light such as external light and illumination light, and stray light caused by image light. It can be effectively prevented.

  In addition to the embodiment of the support substrate 12 (12A) shown in FIG. 7, as shown in FIGS. 8 and 9, on the surface on either side of the transparent support film 14 such as a plastic film, The support substrate 12 (12B, 12C) may be formed by forming the light absorption layer 15 made of a black pigment or the like.

  The thickness of the support base 12 is preferably 15 to 300 μm, more preferably 25 to 100 μm, considering that it can be wound up. On the other hand, when the support substrate 12 does not necessarily require flexibility as in the case of being used as a panel, the thickness can be increased without limitation.

  The plastic film used as the material for the support substrate 12 and the support film 14 includes polycarbonate polymers, polyester polymers such as polyethylene terephthalate, polyimide polymers, polysulfone polymers, and polyethersulfone polymers. Molecule, polystyrene polymer, polyolefin polymer such as polyethylene and polypropylene, polyvinyl alcohol polymer, cellulose acetate polymer, polyvinyl chloride polymer, polyacrylate polymer, polymethyl methacrylate polymer, etc. A film made of a thermoplastic polymer or the like can be used. In addition, the material of the support base material 12 and the support film 14 is not limited to this, Materials, such as a metal, a paper material, a cloth material, glass, can also be used.

  In addition, when laminating the polarization selective reflection layer 11 on the support substrate 12, as described later, it is common to apply an alignment treatment and a curing treatment after applying a liquid crystalline composition exhibiting cholesteric regularity. It is.

  In this case, since it is necessary to control the cholesteric liquid crystal structure of the polarization selective reflection layer 11 so as not to be in the planar alignment state, the support substrate 12 has an alignment ability on the surface on which the liquid crystalline composition is applied. It is preferable to use those not used.

  However, even if the material on the surface of the support substrate 12 on which the liquid crystalline composition is applied has an orientation ability on the surface, such as a stretched film, the support substrate 12 By subjecting the surface of the stretched film to surface treatment, or controlling the material of the liquid crystalline composition and the process conditions for aligning the liquid crystalline composition, the cholesteric liquid crystal structure of the polarization selective reflection layer 11 is planar aligned. It is possible to control so as not to be in a state.

  Further, when the surface of the support substrate 12 on which the liquid crystalline composition is applied has orientation ability, as shown in FIG. 10, the polarization selective reflection layer 11 and the support substrate 12 (12A ) Between the cholesteric liquid crystal structure of the polarization selective reflection layer 11 and the intermediate layer 13 in the cholesteric liquid crystal structure of the polarization selective reflection layer 11. It is also possible for the director of the liquid crystal molecules in the vicinity of the interface to face in a plurality of directions. In addition, when providing intermediate | middle layers 13, such as an easily bonding layer, the adhesiveness between the polarization selective reflection layer 11 and the support base material 12 can also be improved. In addition, as such an intermediate | middle layer 13, what is necessary is just to be able to acquire high adhesiveness with respect to both the material of the polarization selective reflection layer 11, and the material of the support base material 12, and the thing marketed generally is used. be able to. Specific examples include PET film A4100 with an easy-adhesion layer manufactured by Toyobo Co., Ltd., and easy-adhesive materials AC-X, AC-L, and AC-W manufactured by Panac. The intermediate layer 13 can also be used as a light absorbing layer that incorporates a black pigment or the like and absorbs light in the visible light region, like the support base 12 (12A) shown in FIG.

  Here, when the surface of the support substrate 12 does not have the alignment ability and the adhesion between the polarization selective reflection layer 11 and the support substrate 12 is sufficiently high, the intermediate layer 13 is necessarily provided. There is no. Moreover, as a method for improving the adhesiveness between the polarization selective reflection layer 11 and the support substrate 12, process methods such as corona treatment and UV cleaning can be used.

  In the projection screen 10 according to the present embodiment, as shown in FIG. 11, the support substrate 12 is provided on the opposite side of the support substrate 12 from the surface on which the polarization selective reflection layer 11 is provided. You may make it provide the light reflection layer 16 which reflects the light which injects into. As a result, when the support base 12 includes the light absorption layer in the manner as shown in FIGS. 7 to 9, the support base 12 receives ambient light such as external light and illumination light incident from the back side of the projection screen 10. Before reaching the material 12 (particularly, the light absorption layer contained therein), it can be effectively reflected, and the heat generation of the support base 12 can be effectively suppressed. As the light reflection layer 16, it is preferable to use a white scattering layer (paper material, white film, paint film, etc.), a metal plate, an aluminum powder film, or the like.

  Further, as shown in FIG. 11, the polarization selective reflection is performed on the surface of the support substrate 12 opposite to the surface on which the polarization selective reflection layer 11 is provided (the back side of the light reflection layer 16 in FIG. 11). You may make it provide the adhesion layer 17 for affixing the support base material 12 in which the layer 11 was provided to an external member. As a result, the projection screen 10 can be attached to an external member such as a whiteboard or a wall as needed during use. In addition, as the adhesive layer 17, it is preferable that the support base material 12 provided with the polarization selective reflection layer 11 can be detachably attached to an external member, and a re-peeling adhesive film (manufactured by Panac Corporation). It is preferable to use a weak adhesive film such as Moreover, it is preferable to affix the peeling film 18 on the surface of the adhesion layer 17 for the purpose of protecting the adhesion layer 17 when not in use.

  Furthermore, as shown in FIG. 11, a functional holding layer 19 may be provided on the surface of the polarization selective reflection layer 11 on the viewer side. As the functional retention layer 19, various types can be used. For example, a hard coat layer (HC layer), an antiglare layer (AG layer), an antireflection layer (AR layer), an ultraviolet absorption layer (UV absorption) Layer) and an antistatic layer (AS layer).

  Here, the hard coat layer (HC layer) is a layer for protecting the surface of the projection screen 10 to prevent scratches and dirt. The antiglare layer (AG layer) is a layer for preventing glare of the projection screen 10 and the like. The antireflection layer (AR layer) is a layer for suppressing reflection of light on the surface of the projection screen 10. The ultraviolet absorbing layer (UV absorbing layer) is a layer for absorbing an ultraviolet component that causes the liquid crystalline composition to change to yellow among the light incident on the projection screen 10. The antistatic layer (AS layer) is a layer for removing static electricity generated in the projection screen 10. When the functional holding layer 19 is used as an antistatic layer, the functional holding layer 19 does not necessarily have to be provided on the surface of the polarization selective reflection layer 11 on the viewer side. It may be provided on the back side surface, or the support base 12 itself may be provided with a function of removing static electricity by kneading carbon particles or the like into the support base 12.

Next, a case where the above-described projection screen 10 is applied to the projection system according to the present embodiment will be described.
FIG. 12 is a conceptual diagram of a projection system using the projection screen 10.
The projection system 20 includes a projection screen 10 and a projector 121 that projects image light on the projection screen 10. The projector 121 is disposed, for example, on the observation side of the projection screen 10 and projects unpolarized image light onto the projection screen 10 (details will be described later).
As described above, the projection screen 10 has polarization separation property, wavelength selectivity property, and scattering property by the polarization selective reflection layer 11, and suppresses the influence of ambient light (external light, illumination light, etc.) and contrast of the image. On the other hand, when light of a specific polarization component obliquely enters the polarization selective reflection layer 11, the reflection efficiency of the polarization selective reflection layer 11 becomes non-uniform due to the phase difference effect.

For this reason, in the projection system 20, in order to improve the visibility of the image (here, in particular, maintaining the color balance), it is necessary to project non-polarized image light from the projector 121 onto the projection screen 10. In addition, the contrast can be improved by controlling the light and dark state with high accuracy.
Specifically, the non-polarized video light projected from the projector 121 does not change its polarization state even when it receives a phase difference effect from the polarization selective reflection layer 11, and therefore the polarization selective reflection layer 11. (In particular, in the case of a laminated structure, the reflection efficiency can be made substantially uniform at any position of each of the partial selective reflection layers 11a, 11b, and 11c).

Therefore, the polarization selective reflection layer 11 transmits light having a wavelength range indicating the three primary colors of light, blue (B), green (G), and red (R), at any position of each partial selective reflection layer 11a, 11b, 11c. , The non-polarized image light projected from the projector 121 can be reflected without changing the wavelength dispersion (see FIG. 3) of the light intensity. Can do.
For this reason, according to the projection system 20, the light intensity of the projected non-polarized image light becomes the reflection intensity of the image light reflected by the projection screen 10, and as a result, the color balance is maintained, Can reproduce the hue.

Here, the projector 121 applied to the projection system 20 in the present embodiment will be described.
The projector 121 includes a light source 50, condenser lenses 51 and 53, a color filter 52 disposed between the condenser lenses 51 and 53, and a semiconductor (not shown) (for example, as shown in FIG. A reflection part (DMD: Digital Micro-mirror Device) 60 including a plurality of micromirrors (Micro-mirror) arranged on a CMOS semiconductor) and a projection lens 54 are provided.
The light source 50 is, for example, a xenon lamp, and generates non-polarized white light (light source light) with an excellent balance of R, G, and B, which are the three primary colors of light.
The condenser lens 51 is a lens for condensing the light source light generated by the light source 50 on the color filter 52. The color filter 52 is a color disk that can be rotated at a high speed by a rotation mechanism (not shown), and imparts colors such as R, G, and B to the light source light. The condenser lens 53 is a lens for condensing the light transmitted through the color filter 52 on the reflection unit 60.

Here, the reflection unit 60 will be described.
FIG. 13 is a conceptual diagram showing the operation of the micromirror included in the reflection unit 60 of the projector 121.
The reflection unit 60 is an optical semiconductor called a so-called DMD (Digital Micro-mirror Device), and is a micromirror disposed on a CMOS semiconductor (not shown) by a number corresponding to pixels (for example, 480 to 1.31 million). 60a-i (see (a) in the figure). That is, each of the micromirrors 60a to 60i serves as a pixel and constitutes an image displayed on the projection screen 10.
The micromirrors 60a to 60i can change the inclination (± 12 degrees) independently of each other. For example, the digital control (ON: +12 degrees, OFF: -12 degrees) can be performed at a high speed of several thousand times / second. The inclination is switched (see (b) in the figure).

The light reflected by the micromirror having an inclination of +12 degrees passes through the projection lens 54 and is projected as image light (non-polarized light) on the projection screen 10 (see FIG. 9). For this reason, the area on the projection screen 10 corresponding to the micromirror (tilt: +12 degrees) is displayed brightly (white).
On the other hand, since the light reflected by the micromirror having an inclination of −12 degrees is absorbed by a light absorption plate (not shown), the region on the projection screen 10 corresponding to the micromirror (inclination: 12 degrees) is dark. (Black) is displayed.

Accordingly, the reflection unit 60 controls the brightness / darkness state of the non-polarized image light projected from the projector 121 by adjusting the number of ON / OFF times (that is, the number of times of tilt switching) by digital control. Compared with a liquid crystal projector that controls the light / dark state of light by the movement of liquid crystal molecules accompanying an electric field, the light / dark state can be controlled with higher accuracy.
As a result, the contrast on the image on the projection screen 10 is improved and the polarization state of the image light is maintained, so that the color balance can be maintained.

  According to the projection system 20, the reflection efficiency of the projection screen 10 is prevented from becoming non-uniform due to the phase difference effect, and the image is clearly displayed even under bright ambient light, and the visibility (here, , Color balance, contrast).

The projector 121 is not limited to the above-described DLP projector as long as it can project non-polarized image light onto the projection screen 10. For example, the projector 121 may be a front projection type CRT (so-called three-tube projector), An appropriate projector such as a liquid crystal projector in which a depolarizer is disposed in the vicinity can be used.
Here, when a depolarizer is disposed in the vicinity of the exit of the liquid crystal projector, the image light emitted from the liquid crystal projector (polarized light) is not changed without substantially changing its optical axis. As a result, unpolarized video light can be projected onto the projection screen 10. The depolarizer is an element for making polarized light non-polarized. For example, the depolarizer is made of an optical crystal, and is made of a single sheet type having a wide transmission band, an optical crystal and synthetic quartz, and transmits transmitted light. There are two types that go straight.

As a basic structure of the projection screen 10, as shown in FIG. 2 (a), a polarization selective reflection layer having a cholesteric liquid crystal structure in which the direction of the helical axis L varies within the layer (that is, not in the planar alignment state). 11 has been described in detail as an example, but the present invention is not limited to this, and any layer having an appropriate structure may be applied as long as it is a layer that diffusely reflects light of a specific polarization component. Specific examples are given below.
(1) A polarized light reflecting layer for reflecting a specific polarized light component (for example, a mirror reflecting one or a cholesteric liquid crystal structure in a planar alignment state (FIG. 2 (b))) and reflected by this polarized light reflecting layer And a diffusion element that diffuses the emitted light. Thereby, since the polarization separation characteristic and the diffusion characteristic can be made independent, for example, each characteristic can be easily controlled.
The diffusing element may be, for example, a bulk diffusing material, a surface diffusing material, a holographic diffusing material, or any combination of these diffusing materials. The bulk diffusing material may be, for example, particles disposed in a transparent medium. The surface diffusing material may be, for example, a structural surface, a fine structure surface, a roughened surface, or the like. The diffusion provided by the diffusing material may be random, ordered, or partially ordered.

(2) It may be a layer that diffusely reflects linearly polarized light as light of a specific polarization component. Here, since linearly polarized light can be divided into two polarization states and has two directions orthogonal to each other, the non-polarized image light is projected from the projector 121 described above, so that the phase difference effect of this layer is obtained. The color balance can be maintained without disturbing the polarization state.
In addition, as a layer that diffusely reflects linearly polarized light as light of a specific polarization component, for example, there is a diffusive multilayer reflective polarizing material (such as DBEF manufactured by 3M) formed of materials having different refractive indexes. .

  Since linearly polarized light can be expressed by combining so-called P-polarized light (component parallel to the incident surface) and S-polarized light (component perpendicular to the incident surface), a layer that diffusely reflects this linearly polarized light Even when only light of a specific polarization component (for example, P-polarized light or S-polarized light) is diffusely reflected, this layer is projected in the same manner as the polarization selective reflection layer 11 described above by projecting non-polarized image light. The reflection efficiency can be made substantially uniform, and the color balance can be maintained.

  Next, a method for manufacturing the projection screen 10 as described above will be described.

  First, the support base material 12 on which the polarization selective reflection layer 11 is laminated is prepared. If necessary, an intermediate layer 13 such as an easy adhesion layer is laminated on the surface of the support base 12 on the side where the polarization selective reflection layer 11 is provided. At this time, the surface of the support substrate 12 on which the liquid crystalline composition is applied (or the surface when the intermediate layer 13 is present) is made to have no orientation ability.

  Next, after applying a liquid crystalline composition exhibiting cholesteric regularity on the support substrate 12 thus prepared, the polarization selective reflection layer 11 is laminated (fixed) by performing an alignment treatment and a curing treatment. )

  Hereinafter, details of each process (application process, alignment process process, and curing process process) for laminating (adhering) the polarization selective reflection layer 11 will be described.

(Coating process)
In the coating step, a cholesteric liquid crystal layer is formed by coating a liquid crystalline composition exhibiting cholesteric regularity on the support substrate 12. At this time, any existing method can be used as a method of applying the liquid crystalline composition. Specifically, a roll coating method, a gravure coating method, a bar coating method, a slide coating method, a die coating method, a slit coating method, a dipping method, or the like can be used. Moreover, when using a plastic film as the support base material 12, film coating by a so-called roll-to-roll system can be used.

  In addition, as a liquid crystalline composition apply | coated on the support base material 12, the chiral nematic liquid crystal and cholesteric liquid crystal which show cholesteric regularity can be used. Such a material is not particularly limited as long as it is a liquid crystal material capable of forming a cholesteric liquid crystal structure, and in particular, a polymerizable liquid crystal material having a polymerizable functional group at both ends of the molecule. It is preferable for obtaining the polarization selective reflection layer 11 which is optically stable after curing.

  Hereinafter, the case where a chiral nematic liquid crystal is used as the liquid crystalline composition will be described as an example. The chiral nematic liquid crystal is a mixture of a polymerizable liquid crystal material exhibiting nematic regularity and a chiral agent. Here, the chiral agent is for controlling the helical pitch length of the polymerizable liquid crystal material exhibiting nematic regularity so that the liquid crystalline composition exhibits cholesteric regularity as a whole. Moreover, a polymerization initiator and a suitable additive are added to such a liquid crystalline composition.

  Examples of polymerizable liquid crystal materials exhibiting nematic regularity include, for example, compounds represented by the following general formula (1) and compounds represented by the following formulas (2-i) to (2-xi). Can be mentioned. These compounds can be used alone or in combination.

  In the general formula (1), R1 and R2 each represent hydrogen or a methyl group, but it is preferable that both R1 and R2 are hydrogen because of the wide temperature range showing the liquid crystal phase. X may be hydrogen, chlorine, bromine, iodine, an alkyl group having 1 to 4 carbon atoms, a methoxy group, a cyano group, or a nitro group, but is preferably a chlorine or methyl group. Moreover, in the said General formula (1), a and b which show the chain length of the alkylene group which is a spacer of the (meth) acryloyloxy group and aromatic ring of both ends of a molecular chain are arbitrary in the range of 2-12, respectively. Although it can take an integer, it is preferably in the range of 4 to 10, and more preferably in the range of 6 to 9. The compound of the general formula (1) in which a = b = 0 is poor in stability, easily subjected to hydrolysis, and the compound itself has high crystallinity. In addition, the compound of the general formula (1) in which a and b are each 13 or more has a low isotropic transition temperature (TI). For this reason, both of these compounds are not preferable because the temperature range in which the liquid crystal phase is exhibited is narrow.

  In the above, examples of polymerizable liquid crystal monomers have been described as polymerizable liquid crystal materials exhibiting nematic regularity, but not limited thereto, polymerizable liquid crystal oligomers, polymerizable liquid crystal polymers, liquid crystal polymers, etc. It is also possible to use it. Such a polymerizable liquid crystal oligomer, polymerizable liquid crystal polymer and liquid crystal polymer can be appropriately selected from those conventionally proposed.

  On the other hand, a chiral agent is a low molecular compound having an optically active site, and is mainly a compound having a molecular weight of 1500 or less. The chiral agent is mainly used for the purpose of inducing a helical structure in the positive uniaxial nematic regularity expressed by the polymerizable liquid crystal material exhibiting nematic regularity. As long as this purpose is achieved, it is compatible with a polymerizable liquid crystal material exhibiting nematic regularity in a solution state or a molten state, without impairing the liquid crystal property of the polymerizable liquid crystal material exhibiting nematic regularity, The kind of the low molecular compound as the chiral agent is not particularly limited as long as it can induce a desired helical structure.

  In addition, the chiral agent used for inducing a helical structure in the liquid crystal in this way needs to have at least some chirality in the molecule. Accordingly, the chiral agent used here includes, for example, a compound having one or more asymmetric carbons, a compound having an asymmetric point on a heteroatom such as a chiral amine or chiral sulfoxide, or a cumulene. And compounds having an optically active moiety having axial asymmetry such as binaphthol. More specifically, a commercially available chiral nematic liquid crystal (for example, chiral dopant liquid crystal S-811 (manufactured by Merck)) can be mentioned.

  However, depending on the properties of the selected chiral agent, the nematic regularity formed by the polymerizable liquid crystal material exhibiting nematic regularity, the orientation deterioration, or the liquid crystallinity when the chiral agent is non-polymerizable. There exists a possibility of causing the fall of the sclerosis | hardenability of a composition, and the fall of the reliability of the film after hardening. Furthermore, the use of a large amount of a chiral agent having an optically active site leads to an increase in the cost of the liquid crystal composition. Therefore, when a polarization selective reflection layer having a cholesteric regularity with a short helical pitch length is formed, a chiral agent having an optically active site to be contained in the liquid crystalline composition has a large effect of inducing a helical structure. It is preferable to select an agent. Specifically, it is preferable to use a low molecular compound having axial asymmetry in the molecule as represented by the following general formula (3), (4) or (5). .

  In the general formula (3) or (4), R4 represents hydrogen or a methyl group. Y is any one of formulas (i) to (xxiv) shown above, and among them, any one of formulas (i), (ii), (iii), (v), and (vii) Preferably there is. Moreover, although c and d which show the chain length of an alkylene group can each take arbitrary integers in the range of 2-12, it is preferable that it is the range of 4-10, and is the range of 6-9. Is more preferable. The compound of the above general formula (3) or (4) in which the value of c or d is 0 or 1 lacks stability, is susceptible to hydrolysis, and has high crystallinity. On the other hand, a compound having a value of c or d of 13 or more has a low melting point (Tm). In these compounds, compatibility with a polymerizable liquid crystal material exhibiting nematic regularity is lowered, and phase separation or the like may occur depending on the concentration.

  In addition, such a chiral agent does not need to have polymerizability in particular. However, when the chiral agent has polymerizability, it is polymerized with a polymerizable liquid crystal material exhibiting nematic regularity, and the cholesteric regularity is stably fixed, so in terms of thermal stability, etc. Highly preferred. In particular, it is preferable to have a polymerizable functional group at both ends of the molecule in order to obtain the polarization selective reflection layer 11 having good heat resistance.

  The amount of the chiral agent contained in the liquid crystal composition is determined in consideration of the ability to induce a helical structure, the cholesteric liquid crystal structure of the polarization selective reflection layer 11 finally obtained, and the like. Specifically, although it varies greatly depending on the material of the liquid crystal composition used, 0.01 to 60 parts by weight, preferably 0.1 to 40 parts by weight, per 100 parts by weight of the total amount of the liquid crystal composition. More preferably, it is selected in the range of 0.5 to 30 parts by weight, most preferably 1 to 20 parts by weight. When the content of the chiral agent is less than the above range, sufficient cholesteric regularity may not be imparted to the liquid crystal composition. When the content exceeds the above range, the alignment of the liquid crystal molecules is inhibited. There is a risk of adverse effects when cured by actinic radiation.

  The liquid crystalline composition can be applied as it is on the support substrate 12, but it is dissolved in an appropriate solvent such as an organic solvent for the purpose of adjusting the viscosity to a coating apparatus or obtaining a good alignment state. An ink may be used.

  Such a solvent is not particularly limited as long as it can dissolve the polymerizable liquid crystal material as described above, but is preferably one that does not erode the support substrate 12. Specific examples include acetone, 3-methoxybutyl acetate, diglyme, cyclohexanone, tetrahydrofuran, toluene, xylene, chlorobenzene, methylene chloride, methyl ethyl ketone, and the like. The degree of dilution of the polymerizable liquid crystal material is not particularly limited, but it is 5 to 50%, more preferably 10 in view of the fact that the liquid crystal itself is a material with low solubility and high viscosity. It is preferable to dilute to about 30%.

(Orientation process)
In the coating step described above, after applying the liquid crystalline composition on the support substrate 12 and forming the cholesteric liquid crystal layer, in the alignment treatment step, the cholesteric liquid crystal layer is maintained at a predetermined temperature at which the cholesteric liquid crystal structure is expressed, The liquid crystal molecules in the cholesteric liquid crystal layer are aligned.

  In addition, the cholesteric liquid crystal structure of the polarization selective reflection layer 11 to be finally obtained in the present embodiment is not in the planar alignment state, but as shown in FIG. Although the orientation is dispersed in the layers, the orientation treatment is necessary even in this case. That is, an alignment process that aligns the directors of liquid crystal molecules having a cholesteric liquid crystal structure in a certain direction on the support substrate 12 is not required, but an alignment process that forms a plurality of helical structure regions 30 in the cholesteric liquid crystal structure. Is necessary.

  Here, when the cholesteric liquid crystal layer formed on the support substrate 12 is maintained at a predetermined temperature at which the cholesteric liquid crystal structure is developed, the cholesteric liquid crystal layer exhibits a liquid crystal phase, and the liquid crystal molecules are self-assembled by the self-integrating action of the liquid crystal molecules themselves. The spiral structure is formed by continuously rotating the director in the thickness direction of the layer. And the cholesteric liquid crystal structure expressed in such a liquid crystal phase can be fixed by curing the cholesteric liquid crystal layer by a method as described later.

  In addition, when the solvent is contained in the liquid crystalline composition apply | coated on the support base material 12, such an alignment process process is normally performed with the drying process for removing a solvent. In order to remove the solvent, a drying temperature of 40 to 120 ° C., preferably 60 to 100 ° C. is suitable. The drying time (heating time) exhibits a cholesteric liquid crystal structure, and the solvent is substantially removed. For example, it is preferably 15 to 600 seconds, and more preferably 30 to 180 seconds. In addition, when it turns out that an orientation state is inadequate after drying, it is good to extend a heating time suitably. In addition, when using the vacuum drying method in such a drying process, it is preferable to perform a separate heat treatment for the alignment process.

(Curing process)
After aligning the liquid crystal molecules in the cholesteric liquid crystal layer in the alignment treatment step described above, in the curing treatment step, the cholesteric liquid crystal layer is cured to fix the cholesteric liquid crystal structure expressed in the liquid crystal phase.

  Here, as a method used in the curing treatment step, (1) a method of drying a solvent in the liquid crystalline composition, (2) a method of polymerizing liquid crystal molecules in the liquid crystalline composition by heating, (3) radiation A method of polymerizing liquid crystal molecules in the liquid crystalline composition by irradiation of (4) and (4) a method combining these methods can be used.

  Among these, the method (1) is a method suitable when a liquid crystal polymer is used as a polymerizable liquid crystal material exhibiting nematic regularity contained in a liquid crystalline composition that is a material of a cholesteric liquid crystal layer. In this method, the liquid crystal polymer is applied to the support substrate 12 in a state dissolved in a solvent such as an organic solvent. In this case, the cholesteric regularity is obtained simply by removing the solvent by a drying process. A solidified cholesteric liquid crystal layer is formed. In addition, about the kind of solvent, drying conditions, etc., what was described in the apply | coating process and orientation process mentioned above can be used.

  The method (2) is a method of curing the cholesteric liquid crystal layer by thermally polymerizing liquid crystal molecules in the liquid crystal composition by heating. In this method, the bonding state of the liquid crystal molecules changes depending on the heating (firing) temperature. Therefore, if there is temperature unevenness in the plane of the cholesteric liquid crystal layer during heating, physical properties such as film hardness and optical characteristics are uneven. Here, in order to keep the film hardness distribution within ± 10%, the heating temperature distribution is also preferably within ± 5%, and more preferably within ± 2%.

  The method for heating the cholesteric liquid crystal layer formed on the support substrate 12 is not particularly limited as long as the uniformity of the heating temperature can be obtained, and it can be held in close contact with the hot plate, It is possible to use a method in which a slight air layer is provided between them and held parallel to the hot plate. Further, it may be a method in which the entire specific space such as an oven is heated or passed through the apparatus. In the case of using a film coater or the like, it is preferable to lengthen the drying zone so that a sufficient heating time can be taken.

  In general, a heating temperature of 100 ° C. or higher is required as the heating temperature, but it is preferably about 150 ° C. due to the heat resistance of the support base 12. However, if a film or the like specialized for heat resistance is used as the material of the support substrate 12, heating at a high temperature of 150 ° C. or higher is also possible.

  The method (3) is a method of curing the cholesteric liquid crystal layer by photopolymerizing liquid crystal molecules in the liquid crystalline composition by irradiation with radiation. In this method, an electron beam, ultraviolet rays, or the like can be appropriately used as radiation according to conditions. Usually, ultraviolet rays are preferably used from the viewpoint of easiness of the apparatus, and the wavelength is 250 to 400 nm. Here, when ultraviolet rays are used, it is preferable that a photopolymerization initiator is added to the liquid crystalline composition.

  Examples of the photopolymerization initiator added to the liquid crystal composition include benzyl (also referred to as bibenzoyl), benzoin isobutyl ether, benzoin isopropyl ether, benzophenone, benzoyl benzoic acid, methyl benzoyl benzoate, 4-benzoyl-4'- Methyldiphenyl sulfide, benzylmethyl ketal, dimethylaminomethylbenzoate, 2-n-butoxyethyl-4-dimethylaminobenzoate, isoamyl p-dimethylaminobenzoate, 3,3′-dimethyl-4-methoxybenzophenone, methylobenzoylpho Mate, 2-methyl-1- (4- (methylthio) phenyl) -2-morpholinopropan-1-one, 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) -butane-1- ON, 1- ( -Dodecylphenyl) -2-hydroxy-2-methylpropan-1-one, 1-hydroxycyclohexyl phenyl ketone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, 1- (4-isopropylphenyl) 2-hydroxy-2-methylpropan-1-one, 2-chlorothioxanthone, 2,4-diethylthioxanthone, 2,4-diisopropylthioxanthone, 2,4-dimethylthioxanthone, isopropylthioxanthone, 1-chloro-4-propoxy Examples include thioxanthone. In addition to the photopolymerization initiator, it is also possible to add a sensitizer as long as the object of the present invention is not impaired.

  In addition, the addition amount of the photopolymerization initiator added to the liquid crystalline composition is 0.01 to 20% by weight, preferably 0.1 to 10% by weight, more preferably 0.5 to 5% by weight. Preferably there is.

  The projection screen 10 including the polarization selective reflection layer 11 made of a single cholesteric liquid crystal layer can be manufactured by performing the above-described series of steps (coating step, alignment step and curing step). By repeating the above-described series of steps, it is possible to manufacture the projection screen 10 including the polarization selective reflection layer 11 composed of a plurality of cholesteric liquid crystal layers.

  In this case, if the lower cholesteric liquid crystal layer is formed and fixed, the same method can be used when applying the liquid crystalline composition of the second and subsequent cholesteric liquid crystal layers. In this case, the cholesteric liquid crystal structure (alignment state) of the upper cholesteric liquid crystal layer is a continuation of the cholesteric liquid crystal structure (alignment state) of the lower cholesteric liquid crystal layer, for alignment control between stacked cholesteric liquid crystal layers. There is no need to provide a layer. However, if necessary, an intermediate layer such as an easy adhesion layer may be provided between the cholesteric liquid crystal layers to be laminated. Since the conditions and materials used for the coating process, the alignment process process, and the curing process process when forming the second and subsequent cholesteric liquid crystal layers are as described above, the description thereof is omitted here.

  Thus, according to the present embodiment, in the projection system 20, the projection screen 10 includes the polarization selective reflection layer 11 having a cholesteric liquid crystal structure that selectively reflects light of a specific polarization component, and is included in the cholesteric liquid crystal structure. Due to structural non-uniformity of the cholesteric liquid crystal structure due to variations in the direction of the helical axis L of the helical structure region 30 to be diffused, the selectively reflected light is diffused. Even when the polarized image light is projected to receive the phase difference effect of the polarization selective reflection layer 11, which is an organic film, the polarization state of the image light is maintained, and the reflection efficiency in the polarization selection reflection layer 11 is maintained. Can be maintained in a uniform color balance, and the amount of light passing through the projection lens 54 can be adjusted by the inclination of the micromirrors 60a to 60i. By varying depending controls the brightness state of light with high accuracy, thereby improving the contrast.

  At this time, the polarization selective reflection layer 11 selectively reflects only light of a specific polarization component (for example, right circularly polarized light) due to the polarization separation characteristic of the cholesteric liquid crystal structure. Thus, it is possible to reflect only about 50% of the ambient light such as by the polarization selective reflection layer 11. For this reason, even when the brightness of the bright display portion such as white display is the same, the brightness of the dark display portion such as black display can be substantially halved and the contrast of the image can be approximately doubled.

  Further, in the polarization selective reflection layer 11, the cholesteric liquid crystal structure has structural non-uniformity, and the direction of the helical axis L of the helical structure region 30 included in the cholesteric liquid crystal structure varies. Is diffusely reflected rather than specularly reflected, making it easier to visually recognize the image. At this time, the polarization selective reflection layer 11 diffuses the selectively reflected light due to the structural nonuniformity of the cholesteric liquid crystal structure, so that light of a specific polarization component (for example, a right circle in the selective reflection wavelength region). While diffusing the polarized light 31R), other light (for example, the left circularly polarized light 31L within the selective reflection wavelength region, the right circularly polarized light 32R and the left circularly polarized light 32L outside the selective reflection wavelength region) is transmitted without being diffused. be able to. For this reason, the above-described “depolarization” problem does not occur with respect to ambient light and image light transmitted through the polarization selective reflection layer 11, while maintaining the original polarization separation function of the polarization selective reflection layer 11. Visibility can be improved.

  As described above, according to the projection screen 10 used in the projection system 20 of the present embodiment, the influence of ambient light such as external light and illumination light is suppressed by the polarization separation characteristic of the cholesteric liquid crystal structure, and the contrast of the image is increased. On the other hand, the structural non-uniformity of the cholesteric liquid crystal structure can give a scattering effect to the reflected light of the image light without reducing the visibility of the image, and display the image clearly even under bright ambient light Can do.

  Further, according to the projection screen 10 used in the projection system 20 of the present embodiment, the polarization selective reflection layer 11 selectively reflects light in a specific wavelength region that covers only a part of the visible light region. Therefore, the influence of ambient light such as external light and illumination light can be further suppressed to increase the contrast of the image, and the visibility of the image can be further improved.

Projection system

Next, a projection system using the projection screen 10 according to the above-described embodiment will be described.
FIG. 14 is a schematic diagram illustrating an example of a projection system including the projection screen 10.
FIG. 15 is a schematic diagram showing another example of the projection system including the projection screen 10.

  As shown in FIG. 14, the projection system 20 includes a projection screen 10, a projector 121 that projects image light on the projection screen 10, an illumination light source 23, a polarizing film 24, an illumination light source installation unit 25, and the like. I have. The projector 121 uses a DLP (digital light processing) projector as described above.

In general, the projector 121 realizes color display with light in the wavelength ranges of red (R), green (G), and blue (B), which are the three primary colors of light. For example, light is projected onto the projection screen 10. With reference to the case of vertical incidence, light having a selective reflection center wavelength in the range of 430 to 460 nm, 540 to 570 nm, and 580 to 620 nm is projected.
For this reason, it is preferable that the projection screen 10 selectively reflects only light in a wavelength range corresponding to the wavelength range of the image light projected by the projector 121. Thereby, reflection of light in the visible light range that is out of the above-described wavelength range among ambient light such as external light and illumination light can be prevented, and the contrast of the image can be increased.

  The projection system 20 normally includes an illumination light source 23 installed in an illumination light source installation unit 25 such as an indoor ceiling, and illuminates an observation space where the projection screen 10 is installed.

  Here, as shown in FIG. 14, when the illumination light source 23 is arranged so that the illumination light emitted from the illumination light source 23 is directly irradiated onto the projection screen 10, the projection is performed from the illumination light source 23. It is preferable that the illumination light 34 emitted toward the screen 10 mainly includes light having a polarization component different from the polarization component of light selectively reflected by the projection screen 10 (for example, left circularly polarized light). Thereby, it is possible to effectively prevent the illumination light from being reflected by the polarization selective reflection layer 11 of the projection screen 10 and to increase the contrast of the image.

  The polarization state of the illumination light 34 emitted from the illumination light source 23 can be controlled by providing a polarizing film 24 that transmits left circularly polarized light in the vicinity of the illumination light source 23. Here, as the polarizing film 24, an absorption-type circularly polarizing plate or a polarizing separation plate (reflection-type circularly polarizing plate) can be used. As the polarization separation plate, a circular polarization separation plate using a cholesteric liquid crystal layer or a retardation plate for converting linearly polarized light into circularly polarized light on the output side of the linearly polarized light separation plate is used. it can. Note that such a polarization separation plate is preferable in the sense that the loss of light amount is smaller than that of the absorption-type circularly polarizing plate.

In the projection system 20 shown in FIG. 14, the illumination light emitted from the illumination light source 23 is directly irradiated onto the projection screen 10, but not limited to this, as shown in FIG. The illumination light source 23 is installed in the illumination light source installation unit 26, and the illumination light 35 emitted from the illumination light source 23 is indirectly irradiated onto the projection screen 10 as illumination light 35 'through the illumination light reflector 27 such as the ceiling. It can be applied in the same way to the above.
However, in this case, since the polarization state of the circularly polarized light is reversed when the light is reflected by the illumination light reflector 27, the illumination light 35 emitted from the illumination light source 23 toward the illumination light reflector is as shown in FIG. Similarly to the case shown in FIG. 5, by arranging a polarizing film 24 ′ that transmits right circularly polarized light, light having the same polarization component as that of light selectively reflected by the projection screen 10 (for example, right circularly polarized light). ) Is mainly included. In addition, as polarizing film 24 ', the thing similar to the polarizing film 24 mentioned above can be used.
Thereby, the illumination light 35 ′ whose polarization state is reversed by the illumination light reflector 27 is mainly composed of light having a polarization component different from the polarization component of the light selectively reflected by the projection screen 10 (for example, left circularly polarized light). Accordingly, it is possible to effectively prevent the illumination light 35 ′ from being reflected by the polarization selective reflection layer 11 of the projection screen 10 and increase the contrast of the image.

  Further, in the projection system 20 according to this embodiment in which the projection screen 10 and the projector 121 are combined, non-polarized image light is projected from the projector 121, so that the reflection efficiency in the polarization selective reflection layer 11 is made substantially uniform. Thus, the color balance can be maintained, and the contrast state of the image light is controlled with high accuracy by the reflection unit 60, so that the contrast can be improved.

  Next, the embodiment described above will be specifically described.

(Concrete example)
A first cholesteric compound having a selective reflection center wavelength at 440 nm is prepared by dissolving a monomer mixed liquid crystal in which a chiral agent (5.3 wt%) is added to a main agent (94.7 wt%) composed of an ultraviolet curable nematic liquid crystal and dissolved in cyclohexanone. A liquid crystal solution was prepared.

  Note that a liquid crystal containing a compound represented by the above chemical formula (2-xi) was used as the nematic liquid crystal.

  As the polymerizable chiral agent, the compound represented by the above chemical formula (5) was used.

  Further, 5% by weight of a photopolymerization initiator (Ciba Specialty Chemicals) was added to the first cholesteric liquid crystal solution.

  Then, the first cholesteric liquid crystal solution prepared as described above is placed on a support substrate (Lumirror / AC-X, manufactured by Panac Corporation) having an easy-adhesion layer formed on a 200 × 200 mm black PET film. The coating method was applied.

  Next, the film was heated in an oven at 80 ° C. for 90 seconds to perform alignment treatment (drying treatment) to obtain a cholesteric liquid crystal layer from which the solvent was removed.

Thereafter, the cholesteric liquid crystal layer was irradiated with ultraviolet light of 365 nm at 50 mW / cm ² for 1 minute to cure the cholesteric liquid crystal layer, thereby obtaining a first partial selective reflection layer having a selective reflection center wavelength at 440 nm. .

  Similarly, the second cholesteric liquid crystal solution was directly applied on the first partially selective reflection layer, and an alignment treatment (drying treatment) and a curing treatment were performed. As a result, a second partial selective reflection layer having a selective reflection center wavelength at 550 nm was obtained. The second cholesteric liquid crystal solution is prepared by the same method as the first cholesteric liquid crystal solution, and the selective reflection center wavelength is set to 550 nm by controlling the mixing ratio of the nematic liquid crystal and the chiral agent. To have.

  Similarly, the third cholesteric liquid crystal solution was directly applied onto the second partially selective reflection layer, and subjected to alignment treatment (drying treatment) and curing treatment. As a result, a third partial selective reflection layer having a selective reflection center wavelength at 600 nm was obtained. The third cholesteric liquid crystal solution is prepared by the same method as the first cholesteric liquid crystal solution, and the selective reflection center wavelength is set to 600 nm by controlling the mixing ratio of the nematic liquid crystal and the chiral agent. To have.

  As described above, as the polarization selective reflection layer, the first partial selective reflection layer that selectively reflects light in the blue (B) wavelength region (light having a selective reflection center wavelength at 440 nm), and green (G) A second partial selective reflection layer that selectively reflects light in the wavelength range (light having a selective reflection center wavelength at 550 nm) and light in the red (R) wavelength range (light having a selective reflection center wavelength at 600 nm). A projection screen was obtained, in which a third partially selective reflection layer that selectively reflects) was laminated in order from the support substrate side. This projection screen is used in projection systems 1 and 4 described later. The thickness of the first partial selective reflection layer was 3 μm, the thickness of the second partial selective reflection layer was 4 μm, and the thickness of the third partial selective reflection layer was 5 μm. The cholesteric liquid crystal structure of each partial selective reflection layer of the polarization selective reflection layer of the projection screen thus obtained was not in the planar alignment state.

  Next, the projection system 1 was prepared. This projection system 1 is a system that combines the above-described projection screen and a DLP projector (ELP820, luminance: 2500 lumen, manufactured by Epson) that projects non-polarized light.

(Comparative example)
A projection system 2 was prepared. This projection system 2 is a system in which a projection screen in which partially selective reflection layers having a cholesteric liquid crystal structure in a planar alignment state are stacked on each other and a projector (DLP projector) used in the projection system 1 are combined.
A projection system 3 was prepared. The projection system 3 is a system in which a commercially available mat screen and a projector (DLP projector) used in the projection system 1 are combined.

A projection system 4 was prepared. This projection system 4 is a system that combines the projection screen used in the projection system 1 and a liquid crystal projector (LVP-XD350, luminance: 2500 lumen, manufactured by Mitsubishi Electric) that projects polarized light whose polarization state is controlled.
A projection system 5 was prepared. The projection system 5 is a system in which the projection screen (planar alignment state screen) used in the projection system 2 and the projector (liquid crystal projector) used in the projection system 4 are combined.
A projection system 6 was prepared. The projection system 6 is a system in which the projection screen (mat screen) used in the projection system 3 and the projector (liquid crystal projector) used in the projection system 4 are combined.

  In addition, the indoor lighting in which the projection systems 1 to 6 are installed is performed by a fluorescent lamp (one that emits non-polarized light) installed on the ceiling, and the projection systems 1 to 6 are at an angle of about 50 degrees from the ceiling. The projection screen is used in such a manner that illumination light is irradiated. At this time, the brightness just below the projection screen was 200 lux (lx) as measured by an illuminometer (digital illuminometer 510-02, manufactured by Yokogawa M & C).

  The projection screen was installed perpendicular to the floor. Further, in the projection systems 1 to 6, the projector is disposed at a position approximately 2.5 m away from the projection screen in a direction perpendicular to the projection screen (a direction parallel to the floor).

  In this state, image light (a still image having white and black areas) was projected from the projector onto the projection screen, and the projection systems 1 to 6 were visually observed from the front. Specifically, a change in color (change in color balance) and contrast (based on a black and white pattern) between the central portion and the outer periphery of the projection screen during full white display were observed.

(Evaluation results)
As a result, the projection system 2 could not visually recognize the image at the center and the outer periphery of the projection screen, and could not evaluate the contrast. Furthermore, in the projection system 3, the central portion and the outer peripheral portion of the projection screen were white and had no change in color, but the contrast was poor.
On the other hand, in the projection system 1, the central portion and the outer peripheral portion of the projection screen are white and have no change in color (the color balance is maintained), and the contrast is good.
Here, in the projection systems 1 to 3, since the same projector (DLP projector) is used, it was confirmed that the projection screen used in the projection system 1 obtains high contrast.

Further, in the projection system 5, images cannot be visually recognized at both the central portion and the outer peripheral portion of the projection screen, and the contrast cannot be evaluated. Furthermore, in the projection system 6, the central portion and the outer peripheral portion of the projection screen were white and had no change in color, but the contrast was poor.
On the other hand, in the projection system 4, the contrast was good, but the central portion of the projection screen was white and the outer peripheral portion was yellowish white, and the color changed (the color balance was lost).
Here, in the projection systems 4 to 6, since the same projector (liquid crystal projector) is used, it was confirmed that the projection screen used in the projection system 4 obtains a high contrast.

  Further, as a result of comparing the projection system 1 in which the color balance is maintained with the projection system 4 in which the color balance is lost, the projector (DLP projector) used in the projection system 1 is incorporated into the projection system. It was confirmed that the function of the projection screen was fully extracted and the visibility of the image (particularly, maintaining the color balance) was improved.

1 is a schematic sectional view showing a basic structure of a projection screen used in a projection system according to one embodiment of the present invention. The schematic diagram for demonstrating the orientation state and optical function of the polarization selective reflection layer of the projection screen shown in FIG. The figure which shows the wavelength dispersion of the image light projected from a projector. The figure which shows the reflection zone | band of the polarization selective reflection layer 11 in case the wavelength range of the three primary colors of light is independent. FIG. 6 is a schematic cross-sectional view showing a modification of the projection screen shown in FIG. 1. The conceptual diagram for demonstrating the phase difference effect | action by the polarization selective reflection layer. FIG. 10 is a schematic cross-sectional view showing another modification of the projection screen shown in FIG. 1. FIG. 10 is a schematic cross-sectional view showing still another modification of the projection screen shown in FIG. 1. FIG. 10 is a schematic cross-sectional view showing still another modification of the projection screen shown in FIG. 1. FIG. 10 is a schematic cross-sectional view showing still another modification of the projection screen shown in FIG. 1. FIG. 10 is a schematic cross-sectional view showing still another modification of the projection screen shown in FIG. 1. 1 is a conceptual diagram of a projection system 20 using a projection screen 10. FIG. The conceptual diagram which shows operation | movement of the micromirror contained in the reflection part 60 of the projector 121. FIG. 1 is a schematic diagram showing an example of a projection system including a projection screen according to one embodiment of the present invention. Schematic which shows the other example of the projection system provided with the projection screen which concerns on one Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Projection screen 11 Polarization selective reflection layer 11a, 11b, 11c Partial selection reflection layer 12, 12A, 12B, 12C Support base material 13 Intermediate layer 14 Support film 15 Light absorption layer 16 Light reflection layer 17 Adhesive layer 18 Peeling film 20 Projection system 23 Illumination light source 24, 24 'Polarizing film 25, 26 Illumination light source installation part 27 Illumination light reflector 30 Helical structure region 31R Right circular polarization within the selective reflection wavelength region 31L Left circular polarization within the selective reflection wavelength region 32R Right outside the selective reflection wavelength region Circularly polarized light 32L Left circularly polarized light outside the selective reflection wavelength region 33 Reflected light 34, 35, 35 'Illuminated light 50 Light source 51, 53 Condenser lens 52 Color filter 54 Projection lens 60 Reflector 60a to i Micro mirror 121 Projector

Claims (13)

A projection screen having a polarization selective reflection layer that selectively reflects light of a specific polarization component;
A projector that projects light including both linearly polarized components and / or light including both circularly polarized components on the projection screen as image light;
Projection system equipped with. The projection system according to claim 1, wherein
The polarization selective reflection layer has at least two partial selective reflection layers,
When the image light is projected obliquely on the projection screen, the image light is maintained in its polarization state in each of the partial selective reflection layers,
Projection system characterized by. The projection system according to claim 1 or 2,
The projector is
A light source that generates light including both linearly polarized components and / or light including both circularly polarized components as light source light;
A two-dimensional array that changes its inclination and includes a plurality of micromirrors that reflect the light source light; and
A projection lens for projecting the light source light reflected by the micromirror onto the projection screen;
Projection system equipped with. The projection system according to claim 1 or 2,
The projector comprises a liquid crystal projector and a depolarizer disposed in the vicinity of the exit of the liquid crystal projector;
Projection system characterized by. The projection system according to claim 1 or 2,
The projector is a front projection CRT;
Projection system characterized by. The projection system according to any one of claims 1 to 5,
The light of the specific polarization component is right circularly polarized light or left circularly polarized light,
Projection system characterized by. The projection system according to any one of claims 1 to 5,
The light of the specific polarization component is one linearly polarized light;
Projection system characterized by. The projection system according to any one of claims 1 to 7,
The polarization selective reflection layer includes a polarization reflection layer that reflects light of the specific polarization component, and a diffusing element that diffuses light reflected by the polarization reflection layer,
Projection system characterized by. The projection system according to any one of claims 1 to 7,
The polarization selective reflection layer itself has diffusibility,
Projection system characterized by. The projection system according to claim 9, wherein
The polarization selective reflection layer has a cholesteric liquid crystal structure, and diffuses selectively reflected light due to structural non-uniformity of the cholesteric liquid crystal structure.
Projection system characterized by. The projection system according to claim 10, wherein
The cholesteric liquid crystal structure includes a plurality of spiral structure regions having different spiral axis directions;
Projection system characterized by. The projection system according to any one of claims 1 to 11,
The polarization selective reflection layer selectively reflects light in a specific wavelength range covering only a part of the visible light range;
Projection system characterized by. The projection system according to any one of claims 1 to 12,
The polarization selective reflection layer emits light having a selective reflection center wavelength in a range of 430 to 460 nm, 540 to 570 nm, and 580 to 620 nm with reference to a case where light is incident perpendicularly to the polarization selective reflection layer. Selective reflection,
Projection system characterized by.

Images