JP2006189817A - Projection screen and projection system equipped with the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a projection screen excellent in visibility, displaying images clearly under bright environment light, and capable of effectively preventing reflection of a projector light source. <P>SOLUTION: The projection screen 10 has a selectivity reflective layer 11 which selectively reflects specific light and a diffractive layer 50 disposed on the front face side of the selectivity reflective layer 11. Light incident from the front face side of the diffractive layer 50 at a specific incident angle or light incident from the back face side of the diffractive layer 50 at a specific incident angle after reflection by the selectivity reflective layer 11 is diffracted in the diffractive layer 50 to control the output direction of image light reflected by the selectivity reflective layer 11 and output to the front face side of the diffractive layer 50. At least one of the selectivity reflective layer 11 and the diffractive layer 50 has light diffusing property. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a projection system for projecting image light onto a projection screen by a projector to display an image, and in particular, to clearly display an image under bright ambient light and to reflect a projector light source (projector light source). The present invention relates to a projection screen excellent in visibility and capable of effectively preventing the projection and a projection system including the projection screen.

  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 and uses a polarization separation layer (see Patent Documents 1 and 2). ) Has been proposed.
JP-A-5-107660 Special Table 2002-540445

  In the projection screen using the conventional polarization separation layer described above, the white display portion can be brightened while the black display portion can be darkened, and the image can be clearly displayed under bright ambient light. Can do.

  Specifically, for example, in Patent Document 1 described above, 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 circularly polarized light separation of cholesteric liquid crystal is performed. A projection screen is described that prevents approximately half of the ambient light from being reflected by function.

  Patent Document 2 discloses a projection screen that uses a diffusive multilayer reflective polarizing material as a reflective polarizing element, and reflects a part of ambient light by a polarization separation function such as a multilayer reflective polarizing material. 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.

  However, in the projection screen described in Patent Document 1, the image light reflected by the polarization separation layer becomes specular reflection light, which causes a problem that the visibility of the image is lowered. In addition, since the emission direction of the image light reflected by the polarization separation layer is equal to the emission direction of the interface reflected light of the projector light source, the projector light source is reflected on the projection screen, and the image visibility is improved. There is also a problem that it falls.

  Moreover, in the projection screen described in the above-mentioned Patent Document 2, although the light reflected by the reflective polarizing element is given a scattering effect by a diffusing element or the like, reflection of the projector light source can be prevented. Since part of the reflected light, which is light, is mixed with the image light reflected by the reflective polarizing element, there is a problem in that the contrast of the image is lowered and the visibility of the image is deteriorated.

  The present invention has been made under such a background, and can display an image clearly under bright ambient light and can effectively prevent reflection of a projector light source, and has excellent visibility. An object is to provide a projection screen and a projection system including the projection screen.

  As a first solution, the present invention provides a selective reflection layer that selectively reflects specific light in a projection screen that reflects projected image light to display an image, and a front side of the selective reflection layer. The light is incident at a specific incident angle from the front side of the diffraction layer, or is incident at the specific incident angle from the back side of the diffraction layer after being reflected by the selective reflection layer. A diffraction layer that controls the emission direction of the image light reflected by the selective reflection layer and emitted to the front side of the diffraction layer, and at least one of the selective reflection layer and the diffraction layer One of them provides a projection screen characterized by having a diffusibility for diffusing light.

  In the first solving means described above, the diffraction layer diffracts light incident at a specific incident angle from the front side of the diffraction layer in a direction substantially perpendicular to the projection screen, and the selective reflection layer It is preferable to make it enter into. The diffractive layer diffracts light incident at a specific incident angle from the front side of the diffractive layer in a direction deviated by a predetermined angle from a substantially vertical direction with respect to the projection screen to form the selective reflection layer. It is preferable to make it enter. Further, the diffraction layer diffracts light incident at a specific incident angle from the back side of the diffraction layer after being reflected by the selective reflection layer in a direction substantially perpendicular to the projection screen, It is preferable to emit light to the front side.

  In the first solving means described above, the diffraction layer preferably has diffusion anisotropy.

  Furthermore, in the first solving means described above, it is preferable that the diffraction layer selectively diffracts light in a specific wavelength region included in the visible light region.

  Furthermore, in the first solving means described above, it is preferable that the diffraction layer is composed of a transmission volume hologram.

  Furthermore, in the first solving means described above, it is preferable that the selective reflection layer is a polarization selective reflection layer that selectively reflects light of a specific polarization component. Here, the selective reflection layer preferably has a cholesteric liquid crystal structure. In this case, it is preferable that the selective reflection layer has the diffusibility due to the structural nonuniformity of the cholesteric liquid crystal structure.

  Furthermore, in the first solving means described above, it is preferable that the selective reflection layer selectively reflects light in a specific wavelength range included in the visible light range.

  Furthermore, in the first solving means described above, it is preferable to further include a support base material that supports the selective reflection layer and the diffraction layer. Here, the support base material is a light absorption base material including a light absorption layer that absorbs light in a visible light region, and the support base material may be disposed on the back side of the selective reflection layer. . The support substrate may be a transparent substrate that transmits light in the visible light range.

  As a second solution, the present invention projects image light on the projection screen at an incident angle at which diffraction occurs in the projection screen according to the first solution described above and the diffraction layer of the projection screen. A projection system is provided that includes the projector.

  In the second solution described above, it is preferable that the selective reflection layer of the projection screen selectively reflects only light in a wavelength range corresponding to the wavelength range of image light projected by the projector. . Moreover, it is preferable that the diffraction layer of the projection screen selectively diffracts only light in a wavelength region corresponding to the wavelength region of the image light projected by the projector.

  Further, in the second solving means described above, the projection screen and the projection so that the image light projected by the projector is reflected by the selective reflection layer after being diffracted by the diffraction layer of the projection screen. When the projector is arranged, the image light projected onto the projection screen by the projector mainly includes light having a polarization component different from the polarization component of light selectively reflected by the projection screen. It is preferable. In addition, the projection screen and the projection screen so that the image light projected by the projector is transmitted without being diffracted by the diffraction layer of the projection screen, reflected by the selective reflection layer, and diffracted by the diffraction layer. When the projector is arranged, the image light projected on the projection screen by the projector has the same polarization component as the polarization component of light selectively reflected by the projection screen. It is preferable to contain mainly.

  According to the present invention, the diffractive layer is arranged on the front side of the selective reflection layer that selectively reflects specific light, and is incident on the front side of the diffractive layer at a specific incident angle or reflected by the selective reflection layer. By diffracting light incident at a specific incident angle from the back side of the diffraction layer later, the emission direction of the image light reflected by the selective reflection layer and emitted to the front side of the diffraction layer is controlled. For this reason, it is possible to make the emission direction of the image light reflected by the selective reflection layer different from the emission direction of the interface reflected light of the projector light source, effectively preventing the projector light source from being reflected. Can be sufficiently improved.

  Specifically, for example, a transmissive volume hologram that diffracts light incident from a specific direction in a direction centered on a direction different from the specific direction is used as the diffraction layer disposed on the front side of the selective reflection layer. By doing so, the light is diffracted when light is incident at an incident angle satisfying the diffraction condition of the diffraction layer (an angle satisfying the Bragg diffraction condition of the transmission-type volume hologram). At this time, in the diffraction layer, the image light reflected by the selective reflection layer is diffracted and its emission direction is controlled, while the interface reflected light of the projector light source is reflected in the regular reflection direction when viewed from the incident direction. Therefore, the image light reflected by the selective reflection layer and the interface reflected light of the projector light source can be separated to effectively prevent the projector light source from being reflected.

  Here, in the diffraction layer arranged on the front side of the selective reflection layer, (1) light incident at a specific incident angle from the front side of the diffraction layer is diffracted by the diffraction layer and then reflected by the selective reflection layer. (2) Light incident from the front side of the diffraction layer is transmitted without being diffracted by the diffraction layer, and is reflected by the selective reflection layer and then incident at a specific incident angle from the back side of the diffraction layer. There are two cases of diffracting at.

  Among these, in the case of (1) above, it is preferable that light incident at a specific incident angle from the front side of the diffraction layer is diffracted in a direction substantially perpendicular to the projection screen and incident on the selective reflection layer. As a result, the light reflected by the selective reflection layer passes through the diffraction layer and is emitted in a direction substantially perpendicular to the projection screen, and is reflected in the direction of regular reflection when viewed from the incident direction. It is possible to effectively prevent overlapping with the interface reflected light. Here, when light incident on the diffraction layer from a specific direction is diffracted by the diffraction layer in a direction substantially perpendicular to the projection screen, a part of the light reflected by the selective reflection layer is diffracted. It is retrorefracted by the layer and returns to the incident direction. The presence of such retro-diffracted light reduces the brightness of light emitted in a direction substantially perpendicular to the projection screen, but is useful for expanding the viewing angle of the image light in the incident direction. . That is, the diffraction efficiency of a diffraction layer made of a transmission type volume hologram or the like usually takes an arbitrary value that is not 100%. Accordingly, by appropriately adjusting the value of such diffraction efficiency, The brightness of the light emitted to can be adjusted. In addition, since the retroreflection as described above occurs when the angle of the light reflected by the selective reflection layer and re-entering the diffraction layer is an angle at which the retroreflection occurs, the selective reflection layer or the diffraction layer has diffusibility. In the case where the diffusion range includes an angle where retro-diffraction occurs, the viewing angle of the image light can be expanded in the incident direction in the same manner, and thereby substantially perpendicular to the projection screen. The brightness of the light emitted in the direction can be adjusted.

  In the case of (1) above, light incident at a specific incident angle from the front side of the diffraction layer is diffracted in a direction deviated by a predetermined angle from a substantially vertical direction with respect to the projection screen, and selectively reflected. It may be incident on the layer. In this case, since the light reflected by the selective reflection layer can be prevented from being retrorefracted by the diffraction layer, the brightness of the light emitted in a direction substantially perpendicular to the projection screen can be improved. it can.

  On the other hand, in the case of (2) above, the light incident at a specific incident angle from the back side of the diffraction layer after being reflected by the selective reflection layer is diffracted in a direction substantially perpendicular to the projection screen, It is good to emit to the front side. As a result, the light reflected by the selective reflection layer passes through the diffraction layer and is emitted in a direction substantially perpendicular to the projection screen, and is reflected in the direction of regular reflection when viewed from the incident direction. It is possible to effectively prevent overlapping with the interface reflected light.

  In the present invention, the selective reflection layer may be a polarization selective reflection layer having a cholesteric liquid crystal structure that selectively reflects light of a specific polarization component. According to such a polarization selective reflection layer, only light of a specific polarization component (for example, right circularly polarized light) is selectively reflected by the polarization separation characteristics of the cholesteric liquid crystal structure or the like. Only about 50% of ambient light such as light is reflected 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. At this time, when the projected image light enters the polarization selective reflection layer, the incident light is light having the same polarization component as that of the light selectively reflected by the polarization selective reflection layer (for example, right If circularly polarized light is mainly included, the projected image light can be reflected almost 100% by the polarization selective reflection layer, and the image light can be efficiently reflected. Here, when light is diffracted by the diffraction layer, the polarization state of the light (for example, the direction of circularly polarized light) is reversed. Therefore, if the image light projected from the projector is in the case of (1) above, It is preferable to mainly include light having a polarization component different from the polarization component of light selectively reflected by the polarization selective reflection layer (for example, left circularly polarized light). It is preferable to mainly include light having the same polarization component as that of the selectively reflected light (for example, right circularly polarized light).

  Further, according to the present invention, at least one of the diffraction layer and the selective reflection layer has a diffusibility for diffusing light, so that it is reflected by the selective reflection layer and emitted to the front side of the diffraction layer. The image light can be diffuse reflected light instead of specular reflection light, and the visibility of the image can be improved.

  Here, when the diffraction layer has diffusibility, anisotropy (diffusion anisotropy) may be given to the diffusivity. Thereby, for example, the viewing angle can be freely set while maintaining the gain in such a manner that light is diffused with a wider viewing angle in one direction and with a narrower viewing angle in the other direction. .

  On the other hand, when the selective reflection layer has diffusivity, the selective reflection layer is a cholesteric liquid crystal if it is a polarization selective reflection layer having a cholesteric liquid crystal structure that selectively reflects light of a specific polarization component. Structural nonuniformity is imparted to the cholesteric liquid crystal structure, for example, by providing variation in the direction of the helical axis of the helical structure region included in the structure. In this case, since the light selectively reflected by the polarization selective reflection layer becomes diffuse reflection light, it is easy to visually recognize an image. 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. For this reason, there is no problem of polarization state disturbance (depolarization) with respect to ambient light and video light transmitted through the polarization selective reflection layer, and the visibility of the image is maintained while maintaining the original polarization separation function of the polarization selective reflection layer. Can be improved.

  When the diffractive layer has diffusivity, the selective reflection layer does not necessarily have diffusivity. In this case, if the selective reflection layer is a polarization selective reflection layer having a cholesteric liquid crystal structure that selectively reflects light of a specific polarization component, the direction of the helical axis of the helical structure region included in the cholesteric liquid crystal structure To provide structural uniformity to the cholesteric liquid crystal structure. In this case, the light selectively reflected by the polarization selective reflection layer becomes specular reflection light, but is finally diffused by the diffraction layer, so that the visibility of the image is kept good.

  Furthermore, according to the present invention, at least one of the selective reflection layer and the diffraction layer selectively reflects or diffracts light in a specific wavelength region included in the visible light region, so that external light or The contrast of the image can be increased by further suppressing the influence of ambient light such as illumination light, and the visibility of the image can be further improved.

  That is, a projector that projects image light on a projection screen generally 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. The 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 the light is vertically incident on the projection screen. For this reason, in the projection screen, by selectively reflecting only the light in the wavelength range corresponding to the wavelength range of the image light projected by the projector, the above-mentioned environmental light such as external light and illumination light is the above-mentioned. Thus, reflection of light in the visible light range that is out of the wavelength range is prevented, and the contrast of the image can be increased.

  Furthermore, according to the present invention, from the front side of the projection screen, by using a light absorption substrate including a light absorption layer that absorbs light in the visible light region as a support substrate that supports the selective reflection layer and the diffraction layer. Of incident light, light that should not be reflected as reflected light, or light incident from the back side of the projection screen is absorbed and reflected in ambient light such as external light or illumination light, or image light It is possible to effectively prevent the occurrence of stray light. In addition, as the support substrate that supports the selective reflection layer and the diffraction layer, it is also possible to use a transparent substrate that transmits light in the visible light range. In this case, the entire projection screen is transparent, Application range (application such as pasting on a window glass and usually used as a window on which the opposite side can be seen).

  Furthermore, according to the present invention, by controlling the polarization state of the image light projected on the projection screen by the projector, the contrast of the image can be increased while suppressing the influence of stray light caused by the image light, The visibility of the video can be further improved.

  That is, in the case of (1) above, the image light projected on the projection screen by the projector mainly includes light having a polarization component different from the polarization component of the light selectively reflected by the projection screen. On the other hand, in the case of (2) above, by mainly including light having the same polarization component as that of the light selectively reflected by the polarization selective reflection layer (for example, right circularly polarized light), It is possible to effectively prevent the generation of stray light caused by light having a polarization component different from the polarization component of light selectively reflected by the selective reflection layer of the projection screen (for example, left circularly polarized light) and increase the contrast of the image. it can.

BEST MODE FOR CARRYING OUT THE INVENTION

  Embodiments of the present invention will be described below with reference to the drawings.

Projection Screen First, a projection screen according to an embodiment of the present invention will be described with reference to FIG.

  As shown in FIG. 1, the projection screen 10 according to the present embodiment reflects an image light projected at an incident angle α from the observer side (upper side of the drawing) and displays an image. The polarization selective reflection layer 11 having a cholesteric liquid crystal structure that selectively reflects the light of the polarized light component and the front surface side of the polarization selective reflection layer 11, and the light incident from a specific direction is different from the specific direction A diffraction layer 50 made of a transmission type volume hologram that diffracts in a direction centered on the direction, and a support substrate 12 that supports the polarization selective reflection layer 11 and the diffraction layer 50 are provided.

  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 orthogonal 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 (selective reflection wavelength region) of the wavelength bandwidth Δλ centered on the selective reflection center wavelength λ ₀ 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. In FIG. 1, the illustrated content at the left portion of the projection screen 10 (illustrated content at the broken portion of the diffraction layer 50) indicates the behavior of light when the diffraction layer 50 is not provided.

  When the polarization selective reflection layer 11 has a diffusibility for diffusing light, the cholesteric liquid crystal structure of the polarization selective reflection layer 11 has a spiral axis L direction as shown in FIG. Can include a plurality of spiral structure regions 30 different from each other and diffuse the selectively reflected light (reflected light 33) due to the structural non-uniformity 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 rectifier is the same in the XY direction) is not parallel to the surface of the polarization selective reflection layer 11 (when the cross-sectional TEM photograph of the dyed cholesteric liquid crystal structure film is taken, it is 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. The “diffusion” caused by the structural non-uniformity of the cholesteric liquid crystal structure is expanded to such an extent that the reflected light (image light) reflected by the projection screen 10 can be recognized as an image by the observer. Or to scatter.

  In addition, such a cholesteric liquid crystal structure of the polarization selective reflection layer 11 has a planar alignment state as shown in FIG. 2B if the polarization selective reflection layer 11 does not have a diffusibility for diffusing light. It may be. In this case, the directions of the helical axes L of the respective helical structure regions 30 included in the cholesteric liquid crystal structure all extend uniformly in parallel with the thickness direction of the layers, and the selectively reflected light (reflected light 36) is Specular reflection.

  The spiral structure region 30 included in the cholesteric liquid crystal structure of the polarization selective reflection layer 11 selectively reflects 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). Thus, it is preferable to have a specific helical pitch length. 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 types of helical pitch lengths that are continuously different. 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. The spiral pitch of the cholesteric liquid crystal structure so as to selectively reflect light having a selective reflection center wavelength in the range of 430 to 460 nm, 540 to 570 nm, and 580 to 620 nm on the basis of the case where light is incident vertically. The length should be determined.

  In addition, 430-460 nm, 540-570 nm, and 580-620 nm used as a wavelength range 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) is represented as a bright line having a peak at a specific wavelength (for example, green (G) is typically 550 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.

  Here, when the wavelength ranges of red (R), green (G), and blue (B) are expressed as selective reflection wavelength ranges that are independent from each other, the cholesteric liquid crystal structure of the polarization selective reflection layer 11 is discontinuous. It is preferable to have three different helical pitch lengths. On the other hand, the red (R) and green (G) wavelength ranges may be included in the wavelength bandwidth of the selective reflection wavelength range with one helical pitch length. In this case, the cholesteric liquid crystal structure is discontinuous. It is preferable to have two different helical pitch lengths.

  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 is a partial selection of at least two or more layers having different helical pitch lengths. It can be configured by stacking reflective layers on each other. Specifically, as shown in FIG. 3, a partial selective reflection layer 11a that selectively reflects light in the blue (B) wavelength region and a portion that selectively reflects light in the green (G) wavelength region. The selective reflection layer 11b and the partial selective reflection layer 11c that selectively reflects light in the red (R) wavelength region may be stacked in order from the support base 12 side. 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. 3, each of the partial selective reflection layers 11a, 11b, and 11c, like the polarization selective reflection layer 11 shown in FIG. 1, selectively reflects light of a specific polarization component (for example, right-handed circularly polarized light). It becomes a liquid crystal structure.

  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). 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 fixed indirectly depending on the thickness of the polarization selective reflection layer 11 (or the partial selective reflection layers 11a, 11b, and 11c constituting 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.

  The cholesteric liquid crystal structure of the polarization selective reflection layer 11 has an optical characteristic that the selective reflection wavelength region shifts to the short wavelength side (so-called “blue shift”) when light is incident obliquely. It is preferable to appropriately adjust the helical pitch length of the cholesteric liquid crystal structure in accordance with the incident angle α of the image light projected on the projection screen 10 with respect to the projection screen 10.

  Next, returning to FIG. 1, the diffraction layer 50 will be described.

  As shown in FIG. 1, the diffractive layer 50 disposed on the front side of the polarization selective reflection layer 11 diffracts light incident from a specific direction in a direction centered on a direction different from the specific direction. It consists of a volume hologram.

  Here, in the diffraction layer 50, an angle at which the incident angle α of the image light (for example, left circularly polarized light 31L) incident from the front side of the diffraction layer 50 satisfies the diffraction conditions of the diffraction layer 50 (the Bragg of the transmission volume hologram). When the angle satisfies the diffraction condition, as shown in FIG. 7, the image light (for example, left circularly polarized light 31 </ b> L) is diffracted and enters the polarization selective reflection layer 11 as diffracted light 37. Then, the diffracted light 37 incident on the polarization selective reflection layer 11 in this way is reflected by the polarization selective reflection layer 11 and then passes through the diffraction layer 50, and the reflected light 38 (the polarization selective reflection layer 11 has diffusibility). In this case, the light is emitted as diffuse light) to the front side of the diffraction layer 50. When light is diffracted by the diffraction layer 50, the polarization state of the light (for example, the direction of circular polarization) is reversed, so that the light selectively reflected by the polarization selective reflection layer 11 is right circular polarization. In this case, the image light incident from the front side of the diffraction layer 50 is preferably left circularly polarized light 31L.

  On the other hand, when the incident angle α of the image light (for example, the right circularly polarized light 31R) incident from the front side of the diffraction layer 50 does not satisfy the diffraction condition of the diffraction layer 50, the image light (for example, the right circularly polarized light 31R) is diffracted. Without being transmitted, and enters the polarization selective reflection layer 11. In this case, as shown in FIG. 10, the incident angle β of the reflected light 39 (light incident from the back side of the diffractive layer 50) that has been transmitted through the diffractive layer 50 and then reflected by the polarization selective reflection layer 11 is If the angle satisfies the diffraction condition (the angle satisfying the Bragg diffraction condition of the transmission volume hologram), the reflected light 39 is diffracted and emitted as the diffracted light 40 to the front side of the diffraction layer 50. When light is not diffracted by the diffractive layer 50, the polarization state of light (for example, the direction of circularly polarized light) is not reversed, and thus the light selectively reflected by the polarization selective reflection layer 11 is right circularly polarized light. In this case, the image light incident from the front side of the diffraction layer 50 is preferably right circularly polarized light 31R.

  As described above, the emission direction of the image light reflected by the polarization selective reflection layer 11 and emitted to the front side of the diffraction layer 50 is controlled, for example, reflected light toward the observer positioned substantially in front of the projection screen 10. 38 or diffracted light 40 can be emitted. Thereby, the image light (reflected light 38 or diffracted light 40) reflected by the polarization selective reflection layer 11 and emitted to the front side, and the projector light source (projector light source) reflected in the direction of regular reflection as viewed from the incident direction. ) Can be effectively prevented from being reflected from the projector light source.

  The diffraction layer 50 may have a diffusibility for diffusing light. In this case, regardless of whether or not the polarization selective reflection layer 11 has diffusibility, the image light reflected by the polarization selective reflection layer 11 and emitted to the front side of the diffraction layer 50 is specular reflection light. Therefore, the visibility of the image can be improved. In addition, when the diffraction layer 50 has diffusibility, you may give anisotropy (diffusion anisotropy) to the diffusivity. Thereby, for example, light is diffused with a wider viewing angle in one direction (for example, the left-right direction of the projection screen 10), and diffused with a narrower viewing angle in the other direction (for example, the vertical direction of the projection screen 10). In this manner, the viewing angle can be freely set while maintaining the gain.

  Here, as a method of producing the diffractive diffraction layer 50, there is a method of photographing a transmission volume hologram in an arrangement as shown in FIG. That is, as shown in FIG. 4, the transmission / scattering plate 62 is arranged substantially in parallel with an interval so as to face the hologram photosensitive material 61 made of a photopolymer or the like, and then the predetermined wavelength from the back side of the transmission / scattering plate 62. The scattered light 64 is generated on the transmission side of the transmission / scattering plate 62. Then, the scattered light 64 generated in this way is incident on the hologram photosensitive material 61 as object light, and the scattered light 64 that is object light and the parallel light 65 that is reference light are caused to interfere with each other, whereby the hologram photosensitive material 61 is obtained. A transmission volume hologram is recorded on top. Note that the hologram photosensitive material 61 on which the transmission volume hologram is recorded in this manner finally becomes the diffractive diffraction layer 50.

  In general, the hologram photosensitive material 61 is supported on a support base material, and a material such as a plastic film or glass can be used as the support base material. However, when the image light contains only a specific polarization component, the base material of the hologram photosensitive material 61 is preferably a base material with little birefringence, such as a TAC film, a norbornene heat-resistant transparent resin, or a cycloolefin polymer.

  Moreover, as a method for producing the diffraction layer 50 having diffusion anisotropy, a method of photographing a transmission type volume hologram in an arrangement as shown in FIGS. That is, as shown in FIGS. 22 and 23, the transmission / scattering plates 62 are arranged substantially in parallel with an interval so as to face the hologram photosensitive material 61 made of a photopolymer or the like. Then, by setting the horizontal or vertical length of the transmission / scattering plate 62 to a value different from that of the hologram photosensitive material, diffusion anisotropy can be generated. At this time, a dotted line portion in FIGS. 22 and 23 becomes a diffusion region. Therefore, for example, if a transmission scattering plate that is long in the horizontal direction is used, the horizontal diffusion angle can be made wider than the vertical diffusion angle. Also, the diffusion angle can be adjusted by the distance between the transmission scattering plate 62 and the hologram photosensitive material 61. In this way, the diffusion anisotropy can be arbitrarily set by changing the size and position of the hologram photosensitive material and the transmission scattering plate. In general use of the projection screen 10, the diffusion anisotropy is more horizontal than vertical. It is preferable to have a wide diffusion angle.

  On the other hand, as a method for producing the diffractive layer 50 having no diffusibility, there is a method of photographing a transmission type volume hologram in an arrangement as shown in FIG. That is, as shown in FIG. 5, the parallel light 66 is incident as the object light substantially perpendicularly on the hologram photosensitive material 61 made of a photopolymer or the like, and the parallel light 67 is incident as the reference light. And a parallel light 67 which is the reference light are caused to interfere with each other to record a transmission type volume hologram on the hologram photosensitive material 61. In addition, the hologram photosensitive material 61 on which the transmission type volume hologram is recorded in this manner finally becomes the diffraction layer 50 having no diffusibility.

  Moreover, it is preferable that the diffraction layer 50 selectively diffracts light in a specific wavelength region included in a visible light region (for example, a wavelength region of 400 to 700 nm). Specifically, for example, as shown in FIG. 6, the diffraction layer 50 may have a characteristic of efficiently diffracting light in the entire visible light region (for example, a wavelength region of 400 to 700 nm). In addition to this, a visible light region (for example, a wavelength region of 400 to 700 nm) is selected so that only light in a wavelength region corresponding to the wavelength region of image light projected by a projector such as a liquid crystal projector is selectively diffracted. ) That selectively diffracts light in a specific wavelength range (for example, light in the red (R), green (G), and blue (B) wavelength ranges) that covers only a part of You may make it have.

  Here, in the projection screen 10, it is preferable that at least one of the selective reflection layer 11 and the diffraction layer 50 has a diffusibility for diffusing light.

  As a 1st aspect in this case, as shown in FIG. 7, while the polarization selective reflection layer 11 has a diffusivity, the diffraction layer 50 does not have a diffusibility. In this case, as shown in FIG. 7, the image light (for example, left circularly polarized light 31 </ b> L) incident from the front side of the diffraction layer 50 at the incident angle α is diffracted by the diffraction layer 50 and selected as the diffracted light 37. The light enters the reflective layer 11. The diffracted light 37 incident on the polarization selective reflection layer 11 in this way is diffused and reflected by the polarization selective reflection layer 11, then passes through the diffraction layer 50, and is reflected from the interface reflected light 44 of the projector light source. The light (diffuse light) 38 is emitted to the front side of the diffraction layer 50. As described above, in the first aspect, although the diffraction layer 50 does not have diffusibility, the polarization selective reflection layer 11 has diffusibility, and thus the visibility of the image is ensured by this diffusivity. A wide viewing angle can be obtained.

  As a 2nd aspect, as shown in FIG. 8, while the polarization selective reflection layer 11 does not have diffusibility, the aspect in which the diffraction layer 50 has diffusivity is mentioned. In this case, as shown in FIG. 8, image light (for example, left circularly polarized light 31L) incident at an incident angle α from the front side of the diffraction layer 50 is diffracted and diffused by the diffraction layer 50, and is diffracted light (diffusion). Light) 37 'enters the polarization selective reflection layer 11. The diffracted light (diffused light) 37 ′ thus incident on the polarization selective reflection layer 11 is specularly reflected by the polarization selective reflection layer 11, then passes through the diffraction layer 50, and is interface reflected light 44 of the projector light source. The reflected light (diffused light) 38 ′ separated from the light is emitted to the front side of the diffraction layer 50. As described above, in the second aspect, although the polarization selective reflection layer 11 does not have diffusibility, the diffraction layer 50 has diffusibility, so that the image visibility is ensured by this diffusivity. A wide viewing angle can be obtained.

  As a 3rd aspect, as shown in FIG. 9, the aspect which both the polarization selective reflection layer 11 and the diffraction layer 50 have a diffusivity is mentioned. In this case, as shown in FIG. 9, image light (for example, left circularly polarized light 31L) incident at an incident angle α from the front side of the diffraction layer 50 is diffracted and diffused by the diffraction layer 50, and diffracted light (diffusion) Light) 37 'enters the polarization selective reflection layer 11. The diffracted light (diffused light) 37 ′ thus incident on the polarization selective reflection layer 11 is diffusely reflected by the polarization selective reflection layer 11, then passes through the diffraction layer 50, and is interface reflected light 44 of the projector light source. As a reflected light (diffused light) 38 ″ separated from the light, it is emitted to the front side of the diffraction layer 50. Thus, in the third aspect, both the polarization selective reflection layer 11 and the diffraction layer 50 are diffusive. Therefore, the visibility of the image can be secured by these diffusivities, and a wider viewing angle can be obtained.

  In any of the first to third aspects described above, the light incident at an incident angle α from the front side of the diffraction layer 50 is diffracted by the diffraction layer 50 in the case shown in FIGS. In addition to the case where the light is reflected by the selective reflection layer 11, the case shown in FIG. 10 (light incident from the front side of the diffraction layer 50 is transmitted without being diffracted by the diffraction layer 50). The same applies to the case where the light is reflected from the back side of the diffractive layer 50 at an incident angle β and is diffracted by the diffractive layer 50.

  7 to 9, the image light (for example, left circularly polarized light 31L) incident at the incident angle α from the front side of the diffraction layer 50 is diffracted in a direction substantially perpendicular to the projection screen 10. It is good to make it enter into the polarization selective reflection layer 11. As a result, the image light (reflected light 38, 38 ′, 38 ″) reflected by the polarization selective reflection layer 11 passes through the diffraction layer 50 and is emitted in a direction substantially perpendicular to the projection screen 10. It is possible to effectively prevent overlapping with the interface reflected light 44 of the projector light source that is reflected in the direction of specular reflection as viewed from the incident direction. 11 is diffracted in a direction substantially perpendicular to the projection screen 10 by the diffraction layer 50, the image light reflected by the polarization selective reflection layer 11 as shown in FIG. Is not only emitted as reflected light 41 in a direction substantially perpendicular to the projection screen 10, but part of it is recursively diffracted by the diffraction layer 50 and returned to the incident direction as recursive diffracted light 42. like The presence of the return-diffracted light 42 reduces the brightness of the light emitted in a direction substantially perpendicular to the projection screen 10, but is useful for expanding the viewing angle of the image light in the incident direction. That is, the diffraction efficiency of the diffractive layer 50 made of a transmission-type volume hologram usually takes an arbitrary value that is not 100%. Therefore, by appropriately adjusting the value of the diffraction efficiency, the diffraction layer 50 is substantially perpendicular to the projection screen 10. The brightness of the light emitted in the direction can be adjusted.Retro diffraction as described above is such that the angle of the light reflected by the polarization selective reflection layer 11 and reentering the diffraction layer 50 is the retro diffraction. Similarly, when the polarization selective reflection layer 11 or the diffraction layer 50 has diffusibility and the diffusion range includes an angle at which retro-diffraction occurs, similarly, Enter viewing angle The brightness of the light emitted in a direction substantially perpendicular to the projection screen 10 can be adjusted thereby, particularly when the diffraction layer 50 has diffusion anisotropy. Since the viewing angle can be freely set as described above, more complicated viewing angle control including the angle at which retro-diffraction occurs within the diffusion range can be performed.

  In the case shown in FIGS. 7 to 9, as shown in FIG. 12, the image light (for example, left circularly polarized light 31L) incident at the incident angle α from the front side of the diffraction layer 50 is applied to the projection screen 10. The light may be diffracted in a direction deviated by a predetermined angle from the substantially vertical direction and incident on the polarization selective reflection layer 11 with the incident angle as the predetermined angle. For example, the predetermined angle can be set to an angle that can prevent the light reflected by the polarization selective reflection layer 11 from being retrorefracted by the diffraction layer 50. In this case, the light reflected by the polarization selective reflection layer 11 can be prevented from being retrorefracted by the diffraction layer 50, so that the brightness of the light emitted in a direction substantially perpendicular to the projection screen 10 is improved. be able to.

  On the other hand, in the case shown in FIG. 10, image light (for example, right circularly polarized light 31 </ b> R) incident on the incident angle β from the back side of the diffractive layer 50 after being reflected by the polarization selective reflection layer 11 is approximately applied to the projection screen 10. It is preferable to diffract in the vertical direction and output to the front side of the diffraction layer 50. As a result, the light reflected by the polarization selective reflection layer 11 passes through the diffraction layer 50 and is emitted in a direction substantially perpendicular to the projection screen 10, and is reflected in the direction of regular reflection as viewed from the incident direction. It is possible to effectively prevent overlapping with the interface reflected light 44 of the projector light source.

  Next, returning to FIG. 1, the support base 12 will be described.

  The support substrate 12 is for supporting the polarization selective reflection layer 11 and the diffraction layer 50, and can be formed using a material such as a plastic film, metal, paper material, cloth material, 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. 13, the support substrate 12 (12A) is formed using a plastic film in which a black pigment is kneaded, for example, black lumirror (colored PET film manufactured by Toray Industries, Inc.). Good. 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 FIG. 13, the illustrated content at the broken portion of the diffraction layer 50 of the projection screen 10 indicates the behavior of light when the diffraction layer 50 is not provided.

  In addition to the embodiment of the support substrate 12 (12A) shown in FIG. 13, as shown in FIGS. 14 and 15, 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 support base 12 may be a transparent base that transmits light in the visible light range. In this case, unlike the support substrate 12 (12A, 12B, 12C) as the light absorbing substrate, it is impossible to prevent the occurrence of reflected light due to environmental light, stray light due to image light, and the like. However, since the entire projection screen 10 becomes transparent, it can be applied to various application ranges. Specifically, for example, a projection screen 10 whose supporting base material 12 is a transparent base material is pasted on a window glass, and is usually used as a window on which the opposite side can be seen. It is possible to realize a good video display without any reflection. That is, such a projection screen 10 can be used with high design such as being installed in a show window, and an effective eye-catching effect can be produced by setting the viewing angle according to the situation. . For this reason, the disadvantages of the conventional information tool using a projector, which could not be seen in a bright environment, can be solved and used effectively in applications such as advertising boards, information bulletin boards, and guide boards. In addition, although the thing with few hazes is preferable as a transparent base material mentioned above, Arbitrary materials, such as an acryl, glass, vinyl chloride, can be used if it is a material which permeate | transmits light. Moreover, the transparent base material mentioned above does not necessarily need to transmit the light of the whole visible light range, and may absorb the light of the specific wavelength of a visible light range. That is, the transparent base material mentioned above does not necessarily need to be colorless, and may be colored. Specifically, for example, a colored and transparent plastic plate or glass plate such as brown, blue, or orange used for a partition or a window can be used.

  Here, when the support substrate 12 is a transparent substrate, it is not always necessary to dispose the support substrate 12 on the back side of the polarization selective reflection layer 11 as in the projection screen 10 shown in FIG. The support substrate 12 is disposed between the diffraction layer 50 and the polarization selective reflection layer 11 as in the projection screen 10-1 shown in FIG. 16, or the diffraction layer 50 as in the projection screen 10-2 shown in FIG. You may arrange | position the support base material 12 to the front side. In this case, as the material used for the support base material 12, a material having no birefringence is used because it is necessary to exhibit the polarization separation function of the polarization selective reflection layer 11 without disturbing the polarization of the image light. It is preferable.

  In addition, the thickness of the support substrate 12 as the light absorbing substrate or the transparent substrate as described above is preferably 15 to 300 μm, more preferably 25 to 100 μm in consideration of enabling winding. . 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, if the polarization selective reflection layer 11 is to have diffusibility, it is necessary to control the cholesteric liquid crystal structure so as not to be in the planar alignment state. It is preferable to use a surface that does not have orientation ability on the surface to be formed.

  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. 18, 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 kneads a black pigment or the like and absorbs light in the visible light region, similarly to the support base 12 (12A) shown in FIG.

  Here, when the surface of the support substrate 12 does not have the orientation ability and the adhesion between the polarization selective reflection layer 11 and the support substrate 12 is sufficiently high, the intermediate layer 13 is not necessarily provided. There is no need to provide it. 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 addition, in the projection screen 10 according to the present embodiment, as shown in FIG. 19, the support base material 12 is provided on the surface of the support base material 12 opposite to the surface on the side where the polarization selective reflection layer 11 is provided. A light reflecting layer 16 that reflects light incident on the light 12 may be provided. As a result, when the support base 12 includes a light absorption layer in the manner as shown in FIGS. 13 to 15, the ambient light such as external light and illumination light incident from the back side of the projection screen 10 is supported by the support base 12. 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. 19, 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. 19). 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.

  Further, as shown in FIG. 19, a functional retaining layer 19 may be provided on the front surface of the diffraction layer 50 disposed on the front surface of the polarization selective reflection layer 11. 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 retaining layer 19 is used as an antistatic layer, the functional retaining layer 19 is not necessarily provided on the front surface of the diffraction layer 50 disposed on the front surface side of the polarization selective reflection layer 11. The support substrate 12 may be provided on the back surface, and the support substrate 12 itself is provided with a function of removing static electricity by kneading carbon particles or the like into the support substrate 12. May be.

  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, if the polarization selective reflection layer 11 is to have diffusibility, 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). 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, but from the viewpoint that an optically stable polarization selective reflection layer 11 can be obtained after curing. A polymerizable liquid crystal material having a polymerizable functional group at both ends is particularly preferable.

  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. In addition, a photopolymerization initiator and an appropriate 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), R ¹ and R ² each represent hydrogen or a methyl group, but both R ¹ and R ² are preferably 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 is degraded, the orientation is lowered, or the liquid crystallinity is deteriorated 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 is a chiral agent having 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), R ⁴ 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 has the direction of the spiral axis L of the plurality of spiral structure regions 30 in the layer as shown in FIG. There are a case where the alignment state is dispersed and a case where the planar alignment state is as shown in FIG. 2B. In either case, the alignment treatment is required. That is, in the former, an alignment process that forms a plurality of helical structure regions 30 in the cholesteric liquid crystal structure is necessary, and in the latter, an alignment process that forms a plurality of helical structure regions 30 in the cholesteric liquid crystal structure. In addition, an alignment process is required to align the directors of liquid crystal molecules having a cholesteric liquid crystal structure in a certain direction on the support substrate 12.

  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. If the polarization selective reflection layer 11 is not diffusive, the directors of liquid crystal molecules having a cholesteric liquid crystal structure are aligned on the support substrate 12 in a certain direction. 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 polarization selective reflection layer 11 composed of a single cholesteric liquid crystal layer is laminated (fixed) on the support base 12 by performing the above-described series of steps (coating step, alignment step and curing step). However, by repeating the series of steps described above, the polarization selective reflection layer 11 composed of a plurality of cholesteric liquid crystal layers can be laminated (fixed) on the support base 12. Thereby, for example, as shown in FIG. 3, a partial selective reflection layer 11a that selectively reflects light in the blue (B) wavelength region and a portion that selectively reflects light in the green (G) wavelength region. The polarization selective reflection layer 11 is obtained in which the selective reflection layer 11b and the partial selective reflection layer 11c that selectively reflects light in the red (R) wavelength region are sequentially laminated from the support base 12 side.

  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, after laminating (adhering) the polarization selective reflection layer 11 on the support substrate 12, the transmission selective volume hologram photographed by the method shown in FIG. 4 or FIG. The diffraction layer 50 is bonded. Thereby, it is possible to manufacture the projection screen 10 in which the polarization selective reflection layer 11 and the diffraction layer 50 are sequentially laminated in this order from the support base 12 side.

  In the above description, the case where the polarization selective reflection layer 11 composed of a single layer or a plurality of cholesteric liquid crystal layers is laminated (fixed) on the support substrate 12 has been described as an example. The polarization selective reflection layer 11 composed of a single layer or a plurality of cholesteric liquid crystal layers is performed on the diffraction layer 50 composed of a mold volume hologram by performing the above-described series of steps (coating step, alignment step and curing step). It may be laminated (fixed). In this case, depending on the material of the diffraction layer 50, it is not necessary to provide an intermediate layer such as an easy-adhesion layer, and the interlayer interface in the projection screen 10 can be reduced. It is possible to avoid the problem of deterioration of the visibility of the generated video.

  As described above, according to the present embodiment, the diffractive layer 50 is disposed on the front side of the polarization selective reflection layer 11 having a cholesteric liquid crystal structure that selectively reflects light of a specific polarization component, and the front side of the diffractive layer 50. Image light (for example, left-circularly polarized light 31L) incident at a specific incident angle α or image light (for example, right-circular circle) incident at a specific incident angle β from the back side of the diffraction layer 50 after being reflected by the polarization selective reflection layer 11 By diffracting the polarized light 31 </ b> R), the emission direction of the image light (reflected light 38, 38 ′, 38 ″ or diffracted light 40) reflected by the polarization selective reflection layer 11 and emitted to the front side of the diffraction layer 50 is controlled. For this reason, the emission direction of the image light (reflected light 38, 38 ', 38 "or diffracted light 40) reflected by the polarization selective reflection layer 11 and the output of the interface reflected light 44 of the projector light source. It is possible to make the direction different Thus, it is possible to effectively prevent the projector light source from being reflected and sufficiently improve the visibility of the image.

  Specifically, a transmission volume hologram that diffracts light incident from a specific direction in a direction centered on a direction different from the specific direction as the diffraction layer 50 disposed on the front side of the polarization selective reflection layer 11 Therefore, the light is diffracted when the light is incident at an incident angle satisfying the diffraction condition of the diffraction layer 50 (an angle satisfying the Bragg diffraction condition of the transmission volume hologram). At this time, the diffraction layer 50 diffracts the image light reflected by the polarization selective reflection layer 11 to control the emission direction, while the interface reflected light 44 of the projector light source is specularly reflected when viewed from the incident direction. Since the light is reflected in the direction, the image light (reflected light 38, 38 ', 38 "or diffracted light 40) reflected by the polarization selective reflection layer 11 and emitted to the front side and the interface reflected light 44 of the projector light source are generated. By separating, it is possible to effectively prevent the projector light source from being reflected.

  Further, according to the present embodiment, the polarization selective reflection layer 11 selectively reflects only light of a specific polarization component (for example, right circularly polarized light) by the polarization separation characteristic of the cholesteric liquid crystal structure. Only about 50% of ambient light such as external light or illumination light is reflected 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. At this time, when the projected image light enters the polarization selective reflection layer 11, the incident light is light having the same polarization component as the polarization component of the light selectively reflected by the polarization selective reflection layer 11 ( For example, if the light beam includes mainly right circularly polarized light, the projected image light can be reflected almost 100% by the polarization selective reflection layer 11, and the image light can be efficiently reflected. Here, when the light is diffracted by the diffraction layer 50, the polarization state of the light (for example, the direction of the circularly polarized light) is reversed, so that the projected image light is a case as shown in FIGS. If present, it is preferable to mainly include light having a polarization component different from the polarization component of light selectively reflected by the polarization selective reflection layer 11 (for example, left circularly polarized light 31L). It is preferable to mainly include light having the same polarization component as that of the light selectively reflected by the polarization selective reflection layer 11 (for example, right circularly polarized light 31R).

  Furthermore, according to the present embodiment, since at least one of the polarization selective reflection layer 11 and the diffraction layer 50 has a diffusibility for diffusing light, it is reflected by the polarization selective reflection layer 11 to be a diffraction layer. The image light emitted to the front side of 50 can be diffuse reflection light instead of specular reflection light, and the visibility of the image can be improved.

  At this time, in order to make the polarization selective reflection layer 11 have diffusibility, for example, the direction of the helical axis L of the helical structure region 30 included in the cholesteric liquid crystal structure is varied, and thus the structure of the cholesteric liquid crystal structure is obtained. It is sufficient to bring about non-uniformity. In this case, the light that is selectively reflected by the polarization selective reflection layer 11 becomes diffusely reflected light, which makes it easy to visually recognize an 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 problem of polarization state disturbance (depolarization) as described above does not occur with respect to ambient light and video light transmitted through the polarization selective reflection layer 11, and the original polarization separation function of the polarization selective reflection layer 11 is maintained. Meanwhile, the visibility of the image can be improved.

  In addition, when the diffraction layer 50 has diffusivity, the polarization selective reflection layer 11 does not necessarily have diffusivity. In this case, the direction of the helical axis L of the helical structure region 30 included in the cholesteric liquid crystal structure of the polarization selective reflection layer 11 is aligned, and structural uniformity is given to the cholesteric liquid crystal structure. In this case, the light selectively reflected by the polarization selective reflection layer 11 becomes specular reflection light, but is finally diffused by the diffraction layer 50, so that the visibility of the image is kept good.

  Furthermore, according to the present embodiment, the polarization selective reflection layer 11 selectively reflects light in a specific wavelength range covering only a part of the visible light range, or the diffraction layer 50 is in the visible light range. Because it selectively diffracts light in a specific wavelength range, it is possible to further suppress the influence of ambient light such as external light and illumination light, and to increase the contrast of the image, further improving the visibility of the image. Can be improved.

  Furthermore, according to the present embodiment, since the diffraction layer 50 made of a transmission type volume hologram has diffusion anisotropy, retro-diffraction property, etc., the viewing angle and gain can be freely controlled.

Projection System The projection screen 10 described above can be used by being incorporated in a projection system 20 having a projector 21 as shown in FIG.

  As shown in FIG. 20, the projection system 20 includes a projection screen 10 and a projector 21 that projects image light on the projection screen 10.

  Here, the incident angle α of the image light projected from the projector 21 with respect to the projection screen 10 is the polarization selection after the light incident from the front side of the diffraction layer 50 is diffracted by the diffraction layer 50 on the projection screen 10. When the light is reflected by the reflective layer 11, the angle is preferably an angle satisfying the diffraction condition of the diffraction layer 50 (an angle satisfying the Bragg diffraction condition of the transmission volume hologram). On the other hand, in the projection screen 10, light incident from the front side of the diffraction layer 50 is transmitted without being diffracted by the diffraction layer 50, reflected by the polarization selective reflection layer 11, and then incident from the back side of the diffraction layer 50. When the light is diffracted by the diffraction layer 50, the incident angle α of the image light projected from the projector 21 onto the projection screen 10 is an angle satisfying the diffraction condition of the diffraction layer 50 (the Bragg of the transmission type volume hologram). The angle satisfying the diffraction condition of (1) must not be satisfied. However, since the light reflected by the polarization selective reflection layer 11 must be diffracted by the diffraction layer 50, the incident angle β (see FIG. 10) of the reflected light incident from the back side of the diffraction layer 50 is An angle satisfying the diffraction condition (an angle satisfying the Bragg diffraction condition of the transmission volume hologram) is preferable.

  In the projection system 20 illustrated in FIG. 20, a CRT, a liquid crystal projector, a DLP (digital light processing) projector, or the like can be used as the projector 21, but is not particularly limited. However, the image light projected onto the projection screen 10 by the projector 21 is the polarization of light selectively reflected by the projection screen 10 in accordance with the diffraction pattern of the image light at the diffraction layer 50 as described above. It is preferable to mainly include either light of a polarization component different from the component (for example, left circular polarization) or light of the same polarization component (for example, right circular polarization).

  Here, when a liquid crystal projector is used as the projector 21, in many cases, substantially linearly polarized light is emitted from the operation principle. In such a case, linearly polarized light can be converted into circularly polarized light without loss of light quantity by emitting the image light emitted from the projector 21 via the phase difference plate 22 or the like.

  In addition, as the phase difference plate 22, a plate having a quarter wavelength phase difference is preferably used, and specifically, a plate having a phase difference of 137.5 nm in accordance with 550 nm having the highest visibility is ideal. . In addition, a broadband quarter-wave retardation plate is more preferable in the sense that it can be applied to light emitted in all the wavelength regions of red (R), green (G), and blue (B). Furthermore, a single retardation plate obtained by controlling the birefringence of the material, or a combination of a quarter wavelength retardation plate and a half wavelength retardation plate can be used.

  As shown in FIG. 20, such a retardation plate 22 may be incorporated in the projector 21 in addition to being externally attached to the exit of the projector 21.

  When a CRT or DLP projector is used as the projector 21, the light emitted from the projector 21 is non-polarized light. Therefore, when the circularly polarized light is emitted, a linearly polarizing plate and a phase difference are used. It is necessary to arrange a circularly polarizing plate made of a plate. In this case, the light quantity of the projector 21 itself is halved, but it is effective to generate stray light caused by light having a polarization component different from the polarization component of the light selectively reflected by the polarization selective reflection layer 11 of the projection screen 10. Therefore, the contrast of the image can be increased.

  Here, the projector 21 generally 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. The 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 is incident vertically. 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 21. 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. 20, 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 34 from being reflected by the polarization selective reflection layer 11 of the projection screen 10 and increase the contrast of the image. The light incident at an incident angle corresponding to the diffraction angle of the diffraction layer 50 of the projection screen 10 in the illumination light 34 is inverted in its polarization state when diffracted by the diffraction layer 50, and the polarization selective reflection layer 11. Although reflected, such light is negligible when viewed from the whole illumination light 34, and as a whole, the contrast of the image can be improved satisfactorily.

  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. 20, the illumination light 34 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 other illumination light source installation unit 26, and the illumination light 35 emitted from the illumination light source 23 is indirectly reflected on the projection screen 10 as illumination light 35 'via the illumination light reflector 27 such as the ceiling. The same applies to the case of irradiation. However, in this case, when the light is reflected by the illumination light reflector 27, the polarization state of the circularly polarized light is reversed. Therefore, 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 inverted 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. In this case as well, light incident at an incident angle corresponding to the diffraction angle of the diffraction layer 50 of the projection screen 10 among the illumination light 35 ′ is inverted in its polarization state when diffracted by the diffraction layer 50, and polarization selection is performed. Although reflected by the reflective layer 11, such light is negligible when viewed from the whole illumination light 35 ', and as a whole, the contrast of the image can be improved satisfactorily.

  Next, specific examples of the above-described embodiment will be described.

Example 1
A first cholesteric compound having a selective reflection center wavelength at 450 nm is prepared by dissolving a monomer mixed liquid crystal in which a chiral agent (6.0 wt%) is added to a main agent (94.0 wt%) composed of an ultraviolet curable nematic liquid crystal in cyclohexanone. A liquid crystal solution was prepared.

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

  The first cholesteric liquid crystal solution prepared as described above is a supporting base material (Lumirror / AC-X, manufactured by Panac Co., Ltd.) having an easy-adhesion layer formed on a 200 mm □ (200 mm × 200 mm) black PET film. It was applied by the bar coating method.

  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.

After that, the cholesteric liquid crystal layer is irradiated with ultraviolet rays of 365 nm at 50 mW / cm ² for 1 minute in a nitrogen atmosphere to cure the cholesteric liquid crystal layer, thereby partially selective reflection of the first layer having a selective reflection center wavelength at 450 nm. A layer was obtained.

  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, the first partial selective reflection layer that selectively reflects light in the blue (B) wavelength region (light having a selective reflection center wavelength at 450 nm) and light in the green (G) wavelength region (550 nm). 2nd partial selective reflection layer that selectively reflects light having a selective reflection center wavelength and light in the red (R) wavelength region (light having a selective reflection center wavelength at 600 nm) is selectively reflected. A polarization selective reflection layer (also referred to as a CLC screen) was obtained in which the third partial selective reflection layer was laminated in order from the support substrate side. 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. In addition, the cholesteric liquid crystal structure of each partial selective reflection layer of the polarization selective reflection layer of the projection screen obtained in this way was not in the planar alignment state but showed nonuniformity. Such a polarization selective reflection layer has a diffusion angle of ± 40 ° when right circularly polarized light is incident due to its structural nonuniformity.

  On the other hand, the diffraction layer was prepared by preparing a film having a volume hologram layer made of a photosensitive material and recording a transmission volume hologram on the volume hologram layer of the film.

（式中、Ｒ^５は水素原子またはメチル基、Ｒ^６はｐ−ビフェニリルメチリレン基またはフルオレニリデン基、Ａはエチレン基またはプロピレン基を示し、ｍ、ｎは各々１以上であり、ｍ＋ｎは２．０〜８．０の範囲の数である。） Specifically, the film thickness after drying a photosensitive material of the following composition ink on Lumirror T60 (manufactured by Toray Industries Inc., trade name of untreated PET film) as a supporting substrate having a thickness of 50 μm is 13 μm. And then drying to form a volume hologram layer, and laminating SP-PET03-BU (manufactured by Tocello, trade name of surface-peeled PET film) as release paper, and Lumirror T60 / volume hologram layer A film made of / SP-PET was prepared.
Composition: 70 parts by mass of polymethyl methacrylate resin (molecular weight 200,000) R ⁵ = H, R ⁶ = p-biphenylmethylylene group, m = n = 1 in the following general formula (6)
150 parts by mass-3,9-diethyl-3'-carboxymethyl-2,2'-thiacarbocyanine,
0.6 parts by mass of iodine salt 6 parts by mass of diphenyliodonium-trifluoromethanesulfonate 80 parts by mass of 1,6-hexanediol diglycidyl ether 390 parts by mass of solvent (n-butanol: methyl isobutyl ketone = 1: 1)

Wherein R ⁵ is a hydrogen atom or a methyl group, R ⁶ is a p-biphenylylmethylylene group or a fluorenylidene group, A is an ethylene group or a propylene group, m and n are each 1 or more, and m + n is 2 A number in the range of .0 to 8.0.)

A laser beam having a wavelength of 514 nm is used for the volume hologram layer of the produced film, and two substantially parallel lights as reference light and object light are incident at an incident angle of 30 ° and 0 °, respectively, in the arrangement shown in FIG. A transmission volume hologram was recorded by being incident and heated at 100 ° C. for 10 minutes. Thereafter, using a high pressure mercury lamp, exposure was performed at 3000 mJ / cm ² (in terms of 365 nm) to fix the hologram. The transmission volume hologram produced in this way does not have diffusibility.

  Example 1 A polarizing selective reflection layer and a diffraction layer (transmission volume hologram) from which release paper was peeled off were prepared in a size of 200 mm × 200 mm, and bonded to both surfaces of the same size glass. Obtained a projection screen. A substrate-less adhesive film (manufactured by Panac Company) was used for pasting.

  The projection screen according to Example 1 corresponds to the case shown in FIG. 7 (when the image light is diffracted and reflected by the polarization selective reflection layer after being diffracted in the vertical direction by the diffraction layer). Since the image light is incident on the selective reflection layer substantially perpendicularly, the wavelength regions of the partial selective reflection layers of the polarization selective reflection layer have selective reflection center wavelengths at 450 nm, 550 nm, and 600 nm, respectively.

(Example 2)
The polarization selective reflection layer of Example 2 was produced using a support base material having an orientation ability on the surface. Except for this point, the polarization selective reflection layer of this example was produced in the same manner as the polarization selective reflection layer of Example 1. In addition, the cholesteric liquid crystal structure of each partial selective reflection layer of the polarization selective reflection layer of the projection screen according to Example 2 obtained in this manner was planar alignment.

  The diffraction layer of Example 2 was manufactured using the method shown in FIG. Specifically, ground glass having a roughness of 1000 and a size of 500 mm × 500 mm was used as the transmission type diffusion plate. The transmissive diffusion plate was arranged so as to face a volume hologram layer having a size of 300 × 300 mm and spaced apart by 430 mm, and scattered light as object light was incident to produce a diffraction layer. Except for these points, the diffraction layer (transmission type volume hologram) of this example was produced in the same manner as the diffraction layer of Example 1. The produced diffraction layer (transmission type volume hologram) was incident at 30 ° and diffracted at 0 °, and had a diffusion angle of ± 30 ° at the center.

  The polarization selective reflection layer and the diffraction layer (transmission type volume hologram) prepared as described above were bonded to both surfaces of the glass, respectively, to obtain a projection screen according to Example 2. A substrate-less adhesive film (manufactured by Panac Company) was used for pasting.

  The projection screen according to Example 2 corresponds to the case shown in FIG. 8 (when the image light is reflected by the polarization selective reflection layer after being diffracted and diffused in the substantially vertical direction by the diffraction layer). Since the image light is incident on the polarization selective reflection layer substantially perpendicularly, the wavelength regions of the partial selective reflection layers of the polarization selective reflection layer have selective reflection center wavelengths at 450 nm, 550 nm, and 600 nm, respectively.

(Example 3)
The polarization selective reflection layer of Example 1 and the diffraction layer of Example 2 were bonded to both surfaces of glass, respectively, to obtain a projection screen according to Example 3. A substrate-less adhesive film (manufactured by Panac Company) was used for pasting. The projection screen according to Example 3 corresponds to the case shown in FIG. 9 (when the image light is diffracted and reflected by the polarization selective reflection layer after being diffracted and diffused in the vertical direction by the diffraction layer). Since the image light is incident on the polarization selective reflection layer substantially perpendicularly, the wavelength regions of the partial selective reflection layers of the polarization selective reflection layer have selective reflection center wavelengths at 450 nm, 550 nm, and 600 nm, respectively. .

Example 4
The diffraction layer (transmission type volume hologram) of Example 4 was produced in the same manner as the diffraction layer of Example 1. However, in the projection screen of the present example, the diffraction layer (transmission type volume hologram) was bonded to the glass with the front and back opposite to Example 1. Moreover, the polarization selective reflection layer of Example 4 was produced by the same method as the polarization selective reflection layer of Example 1, except that the ratio of the main agent composed of nematic liquid crystal and the chiral agent was changed. In the projection screen according to the fourth embodiment, the image light is transmitted through the diffraction layer without being diffracted (FIG. 10), diffusely reflected by the polarization selective reflection layer, and then incident on the diffraction layer and diffracted again. .

  Therefore, since the image light is incident on the polarization selective reflection layer at an angle, the selective reflection wavelength region of the polarization selective reflection layer is apparently shifted to the short wavelength side. For this reason, in the projection screen according to the present embodiment, the wavelength range (selective reflection center wavelength) of each partial selective reflection layer of the polarization selective reflection layer is projected by the projector in relation to such a shift amount. The wavelength is set longer than the wavelength range of the image light. Specifically, the wavelength ranges of the partial selective reflection layers of this embodiment have selective reflection center wavelengths at 510 nm, 640 nm, and 700 nm, respectively, which are not included in the wavelength range of the image light projected by the projector. I did it. Such adjustment of the selective reflection center wavelength of each partial selective reflection layer is performed by changing the ratio of the main agent and the chiral agent made of nematic liquid crystal during the production of each partial selective reflection layer. For example, when the selective reflection center wavelength of the partial selective reflection layer is set to 510 nm, it is realized by setting the main agent made of nematic liquid crystal to 94.7% by weight and the chiral agent added to the main agent to 5.3% by weight. Can be done.

(Example 5)
The diffraction layer (transmission type volume hologram) of Example 5 was produced in the same manner as the diffraction layer of Example 2. However, in the projection screen in the present example, the diffraction layer (transmission type volume hologram) was bonded to the glass with the front and back sides of Example 2 reversed. The polarization selective reflection layer of Example 5 was produced in the same manner as the polarization selective reflection layer of Example 2 except that the ratio of the main agent composed of nematic liquid crystal to the chiral agent was changed. In the projection screen according to the fifth embodiment, the image light passes through the diffraction layer without being diffracted (FIG. 10), is reflected by the polarization selective reflection layer, and then enters the diffraction layer again to be diffracted and diffused. The

  Therefore, since the image light is incident on the polarization selective reflection layer at an angle, the selective reflection wavelength region of the polarization selective reflection layer is apparently shifted to the short wavelength side. Therefore, similarly to Example 4, the wavelength ranges of the partial selective reflection layers of this example are selectively reflected at 510 nm, 640 nm, and 700 nm, respectively, which are not included in the wavelength range of the image light projected by the projector. It has a central wavelength.

(Example 6)
The diffraction layer (transmission type volume hologram) of Example 6 was produced in the same manner as the diffraction layer of Example 3. However, in the projection screen of the present example, the diffraction layer (transmission type volume hologram) was bonded to the glass with the front and back sides of Example 3 reversed. Moreover, the polarization selective reflection layer of Example 6 was produced by the same method as the polarization selective reflection layer of Example 3 except that the ratio of the main agent composed of nematic liquid crystal and the chiral agent was changed. In the projection screen according to the sixth embodiment, the image light is transmitted through the diffraction layer without being diffracted (FIG. 10), diffusely reflected by the polarization selective reflection layer, and then incident on the diffraction layer again to be diffracted and diffused. Is done.

  Therefore, since the image light is incident on the polarization selective reflection layer at an angle, the selective reflection wavelength region of the polarization selective reflection layer is apparently shifted to the short wavelength side. Therefore, similarly to Example 4 and Example 5, the wavelength range of each partial selective reflection layer of this example is not included in the wavelength range of the image light projected by the projector, 510 nm, 640 nm, 700 nm. Each has a selective reflection center wavelength.

(Example 7)
The diffractive layer (transmission volume hologram) of Example 7 is obtained by transmitting two substantially parallel lights as reference light and object light shown in FIG. 5 at incident angles of 30 ° and 0 °, respectively. Was recorded and produced. Except for this point, the diffraction layer of this example was fabricated in the same manner as the diffraction layer of Example 1. The produced diffraction layer (transmission-type volume hologram) is 30 ° incident and 5 ° diffracted, and has no diffusion angle. Moreover, the polarization selective reflection layer of Example 7 was produced by the same method as the polarization selective reflection layer of Example 1. The polarization selective reflection layer and the diffraction layer (transmission type volume hologram) thus prepared were bonded to both sides of the glass to obtain a projection screen according to Example 7. A substrate-less adhesive film (manufactured by Panac Company) was used for pasting.

  In the projection screen according to Example 7, the image light is diffracted by the diffraction layer and enters the polarization selective reflection layer at an incident angle of approximately 5 ° (FIG. 12). Thereafter, the image light is diffusely reflected by the polarization selective reflection layer. Since the incident angle of the image light to the polarization selective reflection layer is sufficiently small, the wavelength range of the polarization selective reflection layer is 450 nm, 550 nm, and 600 nm included in the wavelength range of the image light projected by the projector. Each had a selective reflection center wavelength.

(Example 8)
The diffraction layer (transmission type volume hologram) of Example 8 was produced by tilting the transmission diffusion plate by 5 ° with respect to the volume hologram layer and separating it by 100 mm in the arrangement shown in FIG. Except for this point, the diffraction layer of this example was produced in the same manner as the diffraction layer of Example 2. The produced diffraction layer (transmission volume hologram) was incident at 30 ° and diffracted at 5 °, and had diffusibility. Moreover, the polarization selective reflection layer of Example 8 was produced by the same method as the polarization selective reflection layer of Example 2. The polarization selective reflection layer and the diffraction layer (transmission type volume hologram) thus prepared were bonded to both surfaces of the glass to obtain a projection screen according to Example 8. A substrate-less adhesive film (manufactured by Panac Company) was used for pasting.

  In the projection screen according to Example 8, the image light is diffracted by the diffraction layer and diffused so that the incident angle with respect to the polarization selective reflection layer is in a range centered on 5 °. Thereafter, the image light is reflected by the polarization selective reflection layer. Since the incident angle of the image light to the polarization selective reflection layer is sufficiently small, the wavelength range of the polarization selective reflection layer is 450 nm, 550 nm, and 600 nm included in the wavelength range of the image light projected by the projector. Each had a selective reflection center wavelength.

Example 9
The polarization selective reflection layer of Example 1 and the diffraction layer of Example 8 were bonded to both surfaces of glass, respectively, to obtain a projection screen according to Example 9. A substrate-less adhesive film (manufactured by Panac Company) was used for pasting.

  In the projection screen according to Example 9, the image light is diffracted by the diffraction layer and diffused so that the incident angle with respect to the polarization selective reflection layer is in a range centered on 5 °. Thereafter, the image light is diffusely reflected by the polarization selective reflection layer. Since the incident angle of the image light to the polarization selective reflection layer is sufficiently small, the wavelength range of the polarization selective reflection layer is 450 nm, 550 nm, and 600 nm included in the wavelength range of the image light projected by the projector. Each had a selective reflection center wavelength.

(Comparative Example 1)
Using a black PET film (Lumirror, manufactured by Panac Co., Ltd.), which is a stretched film, as a supporting substrate, a polarization selective reflection layer was produced in the same manner as in Example 1, and this was used as a projection screen according to Comparative Example 1. That is, the projection screen of Comparative Example 1 does not have a diffraction layer. In addition, the cholesteric liquid crystal structure of each partial selective reflection layer of the polarization selective reflection layer of the projection screen obtained in this way was not in the planar alignment state but showed nonuniformity. Such a polarization selective reflection layer has a diffusion angle of ± 40 ° when right circularly polarized light is incident due to its structural nonuniformity. In the projection screen according to Comparative Example 1, the image light is incident substantially perpendicularly to the polarization selective reflection layer, and accordingly, the wavelength range of each partial selective reflection layer of the polarization selective reflection layer is 450 nm, The selective reflection center wavelengths are assumed to be 550 nm and 600 nm, respectively.

(Comparative Example 2)
A polarization selective reflection layer was produced by the same method as in Comparative Example 1 described above, except that a polarizing selective reflection layer was prepared after imparting orientation ability to the surface of the support substrate, and this was used as a projection screen according to Comparative Example 2. It was. That is, the projection screen of Comparative Example 2 does not have a diffraction layer. The cholesteric liquid crystal structure of each partial selective reflection layer of the polarization selective reflection layer of the projection screen according to Comparative Example 2 obtained in this way was in a planar alignment state. In the projection screen according to Comparative Example 2, the image light is incident substantially perpendicularly to the polarization selective reflection layer, and accordingly, the wavelength range of each partial selective reflection layer of the polarization selective reflection layer is 450 nm, The selective reflection center wavelengths are assumed to be 550 nm and 600 nm, respectively.

(Comparative Example 3)
As a commercially available projection screen, a projection screen (manufactured by OS Co., Ltd.) in which a scattering layer containing beads was formed on the surface of a cloth material was prepared.

(Evaluation results)
The image light emitted from the projector was projected on the projection screens according to Examples 1 to 9 and Comparative Examples 1 to 3, and the contrast was measured. As a projector, a DLP projector (manufactured by Plus) was used.

  Here, a circularly polarizing plate was disposed at the exit of the projector so that the emitted image light was circularly polarized.

  The projection screen was installed perpendicular to the floor. Regarding Examples 1 to 3 and Examples 7 to 9, the incident angle of the image light incident from the front side matches the diffraction angle of the transmission type volume hologram (diffraction layer) of the projection screen, that is, the projection of the image light. The projector was arranged so that the image light was incident from an oblique direction of about 30 ° with respect to the projection screen so that the incident angle on the screen was 30 °. On the other hand, in Examples 4 to 6, the incident angle of the image light incident from the front side is reflected by the polarization selective reflection layer so that it does not match the diffraction angle of the transmission type volume hologram (diffraction layer) of the projection screen. The projector was arranged so that the incident angle of the image light incident on the transmission volume hologram (diffraction layer) from the back side matched the diffraction angle of the transmission volume hologram (diffraction layer). For Comparative Examples 1 to 3, the projector was arranged so that the image light was incident on the projection screen substantially perpendicularly.

  In this state, image light (a still image with white and black areas) was projected onto the projection screen by the projector, and the contrast of the image was measured. Specifically, the luminance of each of the white and black images at the center of the projection screen is measured with a luminance meter (luminance meter BM-8, manufactured by Topcon Corporation), and the ratio is determined as the contrast (contrast = brightness of the white image). ÷ Intensity of black image).

  Table 1 below shows the contrast measured for each projection screen according to Examples 1 to 9 and Comparative Examples 1 to 3.

Further, each projection screen was visually observed. In this case, the projection screen according to Comparative Example 2 had a mirror reflection of light, and the image was difficult to view and could not be measured. In each of the projection screens of Examples 1 to 9 and Comparative Examples 1 and 3, images could be viewed well, but the contrast of the projection screens according to Examples 1 to 9 and Comparative Example 1 was high due to polarization separation. Compared with the projection screen according to Comparative Example 3, the contrast was improved and was improved by about 7 to 12 times. In addition, when Examples 1 to 3 and Examples 7 to 9 are compared, since no recursive diffraction occurs in Examples 7 to 9, compared with Examples 1 to 3, the direction from a direction perpendicular to the projection screen is smaller. Contrast improved.

  In addition, the contrast is measured at a position where there is no reflection of the projector light source, but in reality, the projection screens according to Comparative Examples 1 and 2 also cause interface reflection of the projector light source in the reflection direction of the image light, Visibility is reduced. Further, in the projection screen according to Comparative Example 3, such interface reflection is diffused over the entire surface of the projection screen, causing a reduction in contrast. On the other hand, in the projection screens according to the first to ninth embodiments, the image light and the interface reflected light of the projector light source are separated by the action of diffraction, and do not enter the image light, thereby improving the visibility of the image. It could be confirmed.

1 is a schematic sectional view showing a projection screen according to an 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. FIG. 6 is a schematic cross-sectional view showing a modification of the projection screen shown in FIG. 1. Schematic for demonstrating the production method of the diffraction layer which has the diffusivity contained in the projection screen shown in FIG. Schematic for demonstrating the preparation methods of the diffraction layer which does not have the diffusibility contained in the projection screen shown in FIG. The figure which shows the diffraction characteristic (relationship between a wavelength and diffraction efficiency) of the diffraction layer of the projection screen shown in FIG. FIG. 2 is a schematic cross-sectional view showing a combination example of a polarization selective reflection layer and a diffraction layer in the projection screen shown in FIG. 1. FIG. 6 is a schematic cross-sectional view showing another example of combination of the polarization selective reflection layer and the diffraction layer in the projection screen shown in FIG. 1. FIG. 5 is a schematic cross-sectional view showing still another example of a combination of a polarization selective reflection layer and a diffraction layer in the projection screen shown in FIG. 1. FIG. 2 is a schematic sectional view for explaining an example of light diffraction in the diffraction layer of the projection screen shown in FIG. 1. FIG. 3 is a schematic cross-sectional view for explaining another example of light diffraction in the diffraction layer of the projection screen shown in FIG. 1. FIG. 6 is a schematic cross-sectional view for explaining still another diffraction example of light in the diffraction layer of the projection screen shown in FIG. 1. 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. 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. Schematic which shows an example of the projection system provided with the projection screen which concerns on one embodiment of this invention. Schematic which shows the other example of the projection system provided with the projection screen which concerns on one embodiment of this invention. The schematic perspective view for demonstrating the production method of the diffraction layer which has the diffusion anisotropy contained in the projection screen shown in FIG. FIG. 2 is a schematic top view for explaining a method for producing a diffraction layer having diffusion anisotropy included in the projection screen shown in FIG. 1.

Explanation of symbols

10, 10-1, 10-2 Projection screen 11 Polarization selective reflection layers 11a, 11b, 11c Partial selective reflection layers 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 Release film 19 Functional holding layer 20 Projection system 21 Projector 22 Retardation plate 23 Illumination light source 24, 24 'Polarization film 25, 26 Illumination light source installation part 27 Illumination light reflector 30 Spiral structure region 31R In selective reflection wavelength region Right circularly polarized light 31L Left circularly polarized light 32R within the selective reflection wavelength region Right circularly polarized light 32L outside the selective reflection wavelength region Left circularly polarized light 33 outside the selective reflection wavelength region Reflected light (diffuse light)
34, 35, 35 'Illumination light 36 Reflected light (specular reflection light)
37 Diffracted light 37 ', 37 "Diffracted light (diffused light)
38, 38 ', 38 "Reflected light (diffuse light)
39 Reflected light (Specular reflection light)
40 Diffracted light (diffuse light)
41, 43 Reflected light 42 Retro-refracted light 44 Interface reflected light 50 Diffraction layer 61 Hologram photosensitive material 62 Transmission scattering plate 63 Illumination light 64 Object light (scattered light)
65 Reference beam (parallel beam)
66 Object light (parallel light)
67 Reference light (parallel light)
L Spiral axes α, α ', β Incident angle

Claims (19)

In the projection screen that reflects the projected image light and displays the image,
A selective reflection layer that selectively reflects specific light; and
A diffractive layer disposed on the front side of the selective reflection layer, the light incident at a specific incident angle from the front side of the diffractive layer or specified from the back side of the diffractive layer after being reflected by the selective reflection layer Diffracting the light incident at an incident angle of, and a diffraction layer that controls the emission direction of the image light reflected by the selective reflection layer and emitted to the front side of the diffraction layer,
A projection screen, wherein at least one of the selective reflection layer and the diffraction layer has a diffusibility for diffusing light.   The diffractive layer diffracts light incident at a specific incident angle from the front side of the diffractive layer in a substantially vertical direction with respect to the projection screen and makes the light enter the selective reflection layer. 2. The projection screen according to 1.   The diffractive layer diffracts light incident at a specific incident angle from the front side of the diffractive layer in a direction deviated by a predetermined angle from a substantially vertical direction with respect to the projection screen, and enters the selective reflection layer. The projection screen according to claim 1, wherein:   The diffractive layer diffracts light incident at a specific incident angle from the back side of the diffractive layer after being reflected by the selective reflection layer in a substantially vertical direction with respect to the projection screen, so that the front side of the diffractive layer The projection screen according to claim 1, wherein the projection screen is made to emit light.   The projection screen according to claim 1, wherein the diffraction layer has diffusion anisotropy.   The projection screen according to claim 1, wherein the diffraction layer selectively diffracts light in a specific wavelength range included in a visible light range.   The projection screen according to claim 1, wherein the diffraction layer is made of a transmission volume hologram.   The projection screen according to claim 1, wherein the selective reflection layer is a polarization selective reflection layer that selectively reflects light of a specific polarization component.   The projection screen according to claim 8, wherein the selective reflection layer has a cholesteric liquid crystal structure.   The projection screen according to claim 9, wherein the selective reflection layer has the diffusibility due to structural nonuniformity of the cholesteric liquid crystal structure.   The projection screen according to claim 1, wherein the selective reflection layer selectively reflects light in a specific wavelength range included in a visible light range.   The projection screen according to claim 1, further comprising a support base material that supports the selective reflection layer and the diffraction layer.   The support base material is a light absorption base material including a light absorption layer that absorbs light in a visible light range, and the support base material is disposed on the back side of the selective reflection layer. The projection screen according to claim 12.   The projection screen according to claim 12, wherein the support substrate is a transparent substrate that transmits light in a visible light range. A projection screen according to any one of claims 1 to 14,
A projection system, comprising: a projector that projects image light on the projection screen at an incident angle at which diffraction occurs in the diffraction layer of the projection screen.   The projection system according to claim 15, wherein the selective reflection layer of the projection screen selectively reflects only light in a wavelength range corresponding to a wavelength range of image light projected by the projector. .   The projection according to claim 15 or 16, wherein the diffraction layer of the projection screen selectively diffracts only light in a wavelength range corresponding to a wavelength range of image light projected by the projector. system. The projection screen and the projector are arranged so that the image light projected by the projector is reflected by the selective reflection layer after being diffracted by the diffraction layer of the projection screen,
The image light projected on the projection screen by the projector mainly includes light having a polarization component different from the polarization component of light selectively reflected by the selective reflection layer of the projection screen. The projection system according to any one of claims 15 to 17. The projection screen and the projection so that the image light projected by the projector is transmitted without being diffracted by the diffraction layer of the projection screen, reflected by the selective reflection layer, and diffracted by the diffraction layer. Machine is arranged,
The image light projected onto the projection screen by the projector mainly includes light having the same polarization component as the polarization component of light selectively reflected by the selective reflection layer of the projection screen. The projection system according to any one of claims 15 to 17.

Images