JP2005292423A - Polarized light selecting reflection sheet, projection screen provided with the same, and projection system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polarized light selecting reflection sheet, superior in visibility and capable of clearly displaying an image, even in bright environmental light by suppressing an undesirable diffusion effect (scattering effect) out of diffusion effects to be given to the reflected light of image light. <P>SOLUTION: The projection screen 10 is provided with a polarized light selecting reflection layer 11, having cholesteric liquid crystal structure for selectively reflecting light of a specific polarized light component and a support base material 12 for supporting the polarized light selecting reflecting layer 11. The cholesteric liquid crystal structure of the polarized light selecting reflecting layer 11 includes a plurality of spiral structure areas, in which the directions of screw axes L are respectively different and reflected light 33 is diffused by the structural irregularities of the cholesteric liquid crystal structure. The thickness (t) of the polarized light selecting reflecting layer 11 is set to a value so that transmissivity in the center wavelength of selective reflection of the polarized light selecting reflecting layer 11 is unsaturated. The transmissivity at the center wavelength of selective reflection of the polarized light selecting reflection layer 11 is preferably 3 to 35%. <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, a polarization selective reflection sheet excellent in visibility capable of displaying an image clearly and the same. The present invention relates to a projection screen and a projection system.

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

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

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

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

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

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

Under such a background, conventionally, a projection screen capable of realizing a good image display even under bright ambient light has been studied, for example, using a hologram or using a polarization separation layer. A thing etc. are proposed (refer patent documents 1 and 2).
JP-A-5-107660 JP 2002-540445 A

  However, among the conventional projection screens described above, the projection screen using a hologram can control the scattering effect to make the white display portion brighter, and can display a relatively good image under bright ambient light. Although it can be realized, the hologram has a wavelength selectivity, but does not have a polarization selectivity, and there is a problem that an image can be clearly displayed only within a certain limit. Further, a projection screen using a hologram has a problem that it is difficult to enlarge the screen due to a manufacturing problem.

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

  Specifically, 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.

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

  On the other hand, the above-mentioned Patent Document 2 is a projection screen that uses a diffusive multilayer reflective polarizer as a reflective polarization element, and reflects a part of ambient light by a polarization separation function such as a multilayer reflective polarizer. In addition, the reflection of the reflected light is described 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 diffusion effect is given to the reflected light by a diffusion element provided separately from the cholesteric reflective polarizing material.

  However, the former one described in Patent Document 2 is based on a linearly polarizing element such as a multilayer reflective polarizing material (such as DBEF manufactured by 3M), and is therefore incorporated in a projection system or the like. When used in a projector, it is necessary to match the plane of polarization with a projector such as a liquid crystal projector that emits linearly polarized light. If the planes of polarization do not match, a good image display cannot be realized. There is a problem.

  In the latter one described in Patent Document 2, a circularly polarizing element such as a cholesteric reflective polarizing material is used as the reflective polarizing element, but it is provided on the viewer side of the reflective polarizing element. Since the diffused element gives a diffused effect to the reflected light, the polarization separation function provided by the reflective polarizing element is impaired, and there is a problem that the visibility of the image cannot be sufficiently improved.

  In other words, since the diffusing element is provided on the viewer side of the reflective polarizing element, the light is transmitted through the diffusing element before entering the reflective polarizing element, and the polarization state is disturbed (which is Called "bias"). Here, there are two types of light that pass through the diffusing element: ambient light (external light, etc.) and image light. When the polarization state of the ambient light is disturbed by the diffusing element, The light to be transmitted is converted into a component reflected by the reflective polarizing element by depolarization, and is reflected by the reflective polarizing element as unnecessary light. In addition, when the polarization state of the image light is disturbed by the diffusing element, the light that should be reflected by the reflective polarizing element is converted to a component that is not reflected by the reflective polarizing element due to the depolarization. The element is transparent. Due to these two phenomena, the original polarization separation function is impaired, and the visibility of the image cannot be sufficiently improved.

  As described above, in the conventional projection screen described above, both the one using a hologram and the one using a polarization separation layer as described in Patent Documents 1 and 2 are constant under bright ambient light. Therefore, the video can be displayed clearly only at the limit, and the visibility of the video cannot be sufficiently improved.

  Under such a background, the applicant previously provided with a polarization selective reflection layer having a cholesteric liquid crystal structure, and the image non-uniformity of the cholesteric liquid crystal structure prevents the image light from being deteriorated. A projection screen that can give a diffused effect to reflected light has been proposed (Japanese Patent Application No. 2003-165687).

  The present invention has been made for the purpose of further improving such a projection screen, and suppresses an undesired diffusion effect (scattering effect) among the diffusion effects given to the reflected light of the image light. However, it is an object of the present invention to provide a polarization selective reflection sheet that can display an image clearly and has excellent visibility, and a projection screen and a projection system including the polarization selective reflection sheet.

  As a first solution, the present invention includes a polarization selective reflection layer that selectively reflects light of a specific polarization component, and includes a polarization selective reflection layer that diffuses reflected light by its own structure. There is provided a polarization selective reflection sheet characterized in that the thickness of the selective reflection layer is set to such a size that the transmittance at the selective reflection center wavelength of the polarization selective reflection layer becomes unsaturated.

  In the first solving means described above, it is preferable that the transmittance at the selective reflection center wavelength of the polarization selective reflection layer is 3 to 35%.

  In the first solving means described above, it is preferable that the polarization selective reflection layer has a cholesteric liquid crystal structure, and diffuses reflected light due to structural nonuniformity of the cholesteric liquid crystal structure. Here, it is preferable that the cholesteric liquid crystal structure of the polarization selective reflection layer includes a plurality of spiral structure regions having different spiral axis directions.

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

  In the first solving means described above, the polarization selective reflection layer is preferably made of a polymerizable liquid crystal material.

  As a second solution, the present invention provides a projection screen that reflects projected image light to display an image, and includes one or more polarization selective reflection sheets laminated on each other according to the first solution described above. And a support substrate that supports the one or more polarization selective reflection sheets.

  In the second solving means described above, it is preferable that the one or more polarization selective reflection sheets have different selective reflection center wavelengths. Here, the selective reflection center wavelengths of the respective polarization selective reflection sheets are based on the case where light is perpendicularly incident on the respective polarization selective reflection sheets, and the selective reflection center wavelengths are 430 to 460 nm, 540 to 570 nm, and It is preferably in the range of 580 to 620 nm.

  In the second solving means described above, the support base material preferably includes a light absorption layer that absorbs light in the visible light range.

  Furthermore, in the above-described second solving means, it is preferable that an intermediate layer that is provided between the polarization selective reflection layer and the support base material and enhances the adhesion between them is further provided.

  The present invention provides as a third solution means a projection system comprising the projection screen according to the second solution means described above and a projector for projecting image light onto the projection screen. .

  According to the present invention, in the polarization selective reflection sheet, the polarization selective reflection layer that selectively reflects light of a specific polarization component diffuses the reflected light by its own structure, and the polarization selection The thickness of the reflective layer is set such that the transmittance at the selective reflection center wavelength of the polarization selective reflection layer becomes unsaturated.

  At this time, the polarization selective reflection layer selectively reflects only light of a specific polarization component (for example, right-handed circularly polarized light) due to its polarization separation characteristic. Therefore, such a polarization selective reflection layer is provided as a polarization selective reflection sheet. When used in a projection screen, ambient light having no polarization characteristics, such as ambient light and illumination light, can be reflected by the polarization selective reflection layer only approximately half. 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, if the projected image light mainly includes 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), the projected image light is projected. The image light can be reflected almost entirely by the polarization selective reflection layer, and the image light can be reflected efficiently.

  Further, in the polarization selective reflection layer, the reflected light is diffused by its own structure (for example, a cholesteric liquid crystal structure having structural non-uniformity), so that the image light is diffusely reflected, not specularly reflected, The video is easier to see. At this time, since the polarization selective reflection layer diffuses the reflected light by its own structure, it reflects while diffusing the light of a specific polarization component, while allowing other light to pass through without being diffused. it can. For this reason, the above-mentioned “depolarization” problem does not occur with respect to ambient light and image light transmitted through the polarization selective reflection layer, and image visibility is maintained while maintaining the original polarization separation function of the polarization selective reflection layer. Can be improved. An example in which the cholesteric liquid crystal structure has structural non-uniformity includes a case where the direction of the helical axis of the helical structure region included in the cholesteric liquid crystal structure varies.

  Here, the most important thing in the present invention is that the thickness of the polarization selective reflection layer (a polarization selective reflection layer that selectively diffuses and reflects light of a specific polarization component by its own structure) as described above is set. In other words, the transmittance is selected so that the transmittance at the selective reflection center wavelength of the polarization selective reflection layer becomes unsaturated. Here, “transmittance is unsaturated” means that the transmission spectrum of light in a specific polarization state reflected by the polarization selective reflection layer is a saturated spectrum (minimum value of transmittance (at the selective reflection center wavelength). Value) reaches a lower limit and is not a spectrum having a transmittance of about 0% over a predetermined wavelength range, but an unsaturated spectrum (a Gaussian distribution shape in which the minimum value of the transmittance does not reach the lower limit). It means that the spectrum is inverted).

  In this regard, in the above Japanese Patent Application No. 2003-165687 filed earlier by the present applicant, focusing on the fact that the diffusion effect increases as the thickness of the polarization selective reflection layer increases, The thickness is not particularly limited, and conversely, it was desirable to have a sufficient thickness. However, after that, as a result of earnest research conducted by the present inventor, even a polarization selective reflection layer having a cholesteric liquid crystal structure having a structural nonuniformity, when the thickness is thick, an undesirable diffusion effect ( It was found that the difference in the interface refractive index and the scattering effect due to the impurities in the material) remarkably appeared, and the superiority of polarization separation was impaired, which hindered good visibility. On the other hand, even when the thickness of the polarization selective reflection layer is thin, light that should be selectively reflected is transmitted, so that the diffuse reflectance is lowered and the superiority of polarization separation is impaired. For this reason, in order to maintain high contrast, it is necessary to keep the brightness of image light projected from a projector such as a liquid crystal projector high.

  Based on such knowledge, according to the present invention, the thickness of the polarization selective reflection layer as described above (the polarization selective reflection layer that selectively diffuses and reflects light of a specific polarization component by its structure) Is set to such a size that the transmittance at the selective reflection center wavelength of the polarization selective reflection layer is unsaturated, while sufficiently ensuring the diffusion effect given to view the light as an image, It is possible to effectively suppress the diffusion effect (scattering effect) that becomes an obstacle to obtaining good visibility. For this reason, according to the present invention, it is possible to improve the contrast of the image, and to display the image clearly even under bright ambient light, thereby realizing good visibility.

  Here, the transmittance at the selective reflection center wavelength of the polarization selective reflection layer is preferably 3 to 35%. In this case, the light that should be selectively reflected is transmitted. The above-described effects can be effectively achieved while minimizing.

  Further, according to the present invention, the polarization selective reflection layer is configured to selectively reflect light in a specific wavelength range that covers only a part of the visible light range. In the projection screen provided as the polarization selective reflection sheet, the influence of ambient light such as outside light or illumination light can be further suppressed to increase the contrast of the image, 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.

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 including a polarization selective reflection layer (polarization selective reflection sheet) 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 from the observer side (the upper side of the drawing) and displays an image, and has a specific polarization component. A polarization selective reflection layer (polarization selective reflection sheet) 11 having a cholesteric liquid crystal structure that selectively reflects light (for example, right circularly polarized light) and a support base 12 that supports the polarization selective reflection layer 11 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 perpendicular to the helical axis.

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

Δλ = Δn · p (2)
That is, in FIG. 1, unpolarized light incident from the viewer side of the projection screen 10 (right circularly polarized light 31R and left circularly polarized light 31L within the selective reflection wavelength region, right circularly polarized light 32R and left circularly polarized light outside the selective reflection wavelength region). 32L) is one circularly polarized light component belonging to the range (selective reflection wavelength region) of the wavelength bandwidth Δλ centered on the selective reflection center wavelength λ ₀ in the polarization selective reflection layer 11 in accordance with the polarization separation characteristics as described above. (For example, the right circularly polarized light 31R within the selective reflection wavelength region) is reflected as the reflected light 33, and 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.

  Note that such a cholesteric liquid crystal structure of the polarization selective reflection layer 11 includes a plurality of spiral structure regions 30 having different directions of the spiral axis L, as shown in FIG. The light that is selectively reflected (reflected light 33) is diffused by such structural nonuniformity of the cholesteric liquid crystal structure. Here, the state in which the cholesteric liquid crystal structure has structural inhomogeneity refers to a state in which the direction of the helical axis L of the helical structure region 30 included in the cholesteric liquid crystal structure varies, as well as a nematic layer surface (die of liquid crystal molecules). A state in which at least a part of the surface of the 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). The “diffusion” caused by the structural non-uniformity of the cholesteric liquid crystal structure allows the observer to recognize the reflected light (image light) reflected by the projection screen 10 as an image. To expand to the extent.

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

  In the present embodiment, it is preferable that the thickness t of the polarization selective reflection layer 11 is set to a size such that the transmittance at the selective reflection center wavelength of the polarization selective reflection layer 11 is unsaturated. Here, “transmittance is unsaturated” means that the transmission spectrum of light in a specific polarization state reflected by the polarization selective reflection layer 11 is a saturated spectrum (minimum value of transmittance (at the selective reflection center wavelength). Value) reaches a lower limit and is not a spectrum having a transmittance of about 0% over a predetermined wavelength range, but an unsaturated spectrum (a Gaussian distribution shape in which the minimum value of the transmittance does not reach the lower limit). It means that the spectrum is inverted). The “transmittance” is a ratio of the transmitted light amount when the incident light amount of light in a specific polarization state reflected by the polarization selective reflection layer 11 is 100%, and “100% −transmittance−regular reflection”. "Rate" corresponds to the diffuse reflectance.

  More specifically, the transmittance at the selective reflection center wavelength of the polarization selective reflection layer 11 is preferably 3 to 35%. This is because when the thickness t of the polarization selective reflection layer 11 is thick and the transmittance is smaller than 3%, an undesirable diffusion effect (scattering effect) appears remarkably, the superiority of polarization separation is impaired, and good visibility. Because it will be an obstacle for them. Further, in this case, there are problems that it is difficult to control the orientation, unevenness occurs, and the degree of light absorption by the material itself increases. On the other hand, when the thickness t of the polarization selective reflection layer 11 is small and the transmittance is greater than 35%, light that should be selectively reflected is transmitted, so that the diffuse reflectance is lowered and the superiority of polarization separation is achieved. Will be damaged.

  Note that the transmittance (diffuse reflectance) of the polarization selective reflection layer 11 directly depends on the number of helical pitches. However, if the helical pitch length is fixed, the transmittance of the polarization selective reflection layer 11 is indirectly determined. It depends on the thickness t. Specifically, when a cholesteric liquid crystal is used for the polarization selective reflection layer 11, depending on the type of material of the liquid crystalline composition and the selective reflection wavelength range, in order to obtain a transmittance of 3 to 35%, About 4 to 12 pitches are required. For this reason, for example, when the selective reflection center wavelength of the polarization selective reflection layer 11 is 550 nm, the thickness t is about 1.4 to 4.2 μm.

  Here, the spiral structure region 30 included in the cholesteric liquid crystal structure of the polarization selective anti-sheet 11 selectively selects light in a specific wavelength region that covers only a part of the visible light region (for example, a wavelength region of 400 to 700 nm). It is preferable to have a specific helical pitch length so as to be reflected. 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. The red (R) and green (G) wavelength ranges may be included in the wavelength bandwidth of the selective reflection wavelength range with one spiral 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 emits light of a specific polarization component (for example, right-handed circularly polarized light) in the same manner as the polarization selective reflection layer 11 shown in FIGS. A cholesteric liquid crystal structure that selectively reflects and has a cholesteric liquid crystal structure that diffuses reflected light due to its structural non-uniformity. Here, the polarization components of the light selectively reflected by the partial selective reflection layers 11a, 11b, and 11c are the same. Further, the thickness t of each of the partial selective reflection layers 11a, 11b, and 11c is set to such a size that the transmittance at the selective reflection center wavelength of the partial selective reflection layers 11a, 11b, and 11c is unsaturated. Yes.

  In addition, in the polarization selective reflection layer 11 shown in FIG. 3, between the support base material 12 and the partial selective reflection layer 11a, between the partial selective reflection layer 11a and the partial selective reflection layer 11b, and between the partial selective reflection layer 11b and the partial. An intermediate layer such as an easy-adhesion layer may be provided between the selective reflection layer 11c, thereby controlling the alignment state of the cholesteric liquid crystal structures of the partial selective reflection layers 11a, 11b, and 11c, It becomes possible to improve the adhesion between the reflective layers 11a, 11b, and 11c.

  Next, the support base 12 will be described.

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

  Here, the support substrate 12 preferably includes a light absorption layer that absorbs light in the visible light range. Specifically, for example, the support base 12 is formed using an acrylic plate or a plastic film (for example, a black PET film kneaded with carbon) in which a black pigment is kneaded (in this case, the support base 12 Or a light absorption layer made of a black pigment or the like may be formed on the surface of either side of a transparent support film such as a plastic film. Accordingly, light that should not be reflected as reflected light among unpolarized light incident from the viewer side of the projection screen 10 (left circularly polarized light within the selective reflection wavelength region, right circularly polarized light outside the selective reflection wavelength region, and Left circularly polarized light) and light incident from the back side of the projection screen 10 are absorbed to effectively generate reflected light caused by ambient light such as outside light and illumination light, and stray light caused by image light. Can be prevented.

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

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

  In addition, when laminating the polarization selective reflection layer 11 (or the partial selective reflection layers 11a, 11b, and 11c constituting the polarization selective reflection layer 11) on the support substrate 12, the cholesteric regularity is set as described later. After applying the liquid crystal composition shown, it is common to perform an alignment treatment and a curing treatment.

  In this case, it is necessary to control the cholesteric liquid crystal structure 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) so as not to be in a planar alignment state. As the material 12, it is preferable to use a material having no alignment ability on the surface on which the liquid crystalline composition is applied. 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, and controlling the material of the liquid crystalline composition, the process conditions for aligning the liquid crystalline composition, etc., the polarization selective reflection layer 11 (or the polarization selective reflection layer 11). It is possible to control so that the cholesteric liquid crystal structure of each of the partial selective reflection layers 11a, 11b, and 11c) that constitutes is not a planar alignment state.

  Further, when the surface of the support substrate 12 on which the liquid crystalline composition is applied has orientation ability, the polarization selective reflection layer 11 (or the partial selective reflection layer constituting the polarization selective reflection layer 11). 11a) and the supporting substrate 12 are provided with an intermediate layer such as an easy-adhesion layer, whereby the polarization selective reflection layer 11 (or each of the partial selective reflection layers 11a, 11b, 11c constituting the polarization selective reflection layer 11). Liquid crystal near the interface with the intermediate layer in the cholesteric liquid crystal structure 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) by controlling the alignment state of the cholesteric liquid crystal structure. It is also possible for the molecular director to be oriented in multiple directions. In addition, when providing intermediate | middle layers, such as an easily bonding layer, improving the adhesiveness between the polarization selective reflection layer 11 (or the partial selective reflection layer 11a which comprises the polarization selective reflection layer 11) and the support base material 12 is improved. You can also. In addition, as such an intermediate | middle layer, 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 generally uses what is marketed. Can do. 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 can also be used as a light absorption layer that incorporates a black pigment or the like and absorbs light in the visible light range.

  Here, the surface of the support substrate 12 does not have the orientation ability, and the polarization selective reflection layer 11 (or the partial selective reflection layer 11a constituting the polarization selective reflection layer 11) and the support substrate 12 are not provided. When the adhesion is sufficiently high, it is not always necessary to provide an intermediate layer. 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.

  Next, a method for manufacturing the projection screen 10 including the polarization selective reflection layer (polarization selective reflection sheet) 11 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 such as an easy adhesion layer is laminated on the surface of the support base 12 on the side where the polarization selective reflection layer 11 is provided. At this time, the surface of the support substrate 12 on which the liquid crystalline composition is applied (or the surface when there is an intermediate layer) is made to have no orientation ability.

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

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

(Coating process)
In the coating step, a cholesteric liquid crystal layer is formed by coating a liquid crystalline composition exhibiting cholesteric regularity on the support substrate 12. At this time, any existing method can be used as a method of applying the liquid crystalline composition. Specifically, a roll coating method, a gravure coating method, a bar coating method, a slide coating method, a die coating method, a slit coating method, a dipping method, or the like can be used. Moreover, when using a plastic film as the support base material 12, film coating by a so-called roll-to-roll system can be used. At this time, the thickness of the cholesteric liquid crystal layer is set such that the transmittance at the selective reflection center wavelength of the cholesteric liquid crystal layer is 3 to 35%. Specifically, for example, when the selective reflection center wavelength of the cholesteric liquid crystal layer is 550 nm, the thickness is about 1.4 to 4.2 μm.

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

  Hereinafter, the case where a chiral nematic liquid crystal is used as the liquid crystalline composition will be described as an example. The chiral nematic liquid crystal is a mixture of a polymerizable liquid crystal material exhibiting nematic regularity and a chiral agent. Here, the chiral agent is for controlling the helical pitch length of the polymerizable liquid crystal material exhibiting nematic regularity so that the liquid crystalline composition exhibits cholesteric regularity as a whole. The selective reflection center wavelength caused by the molecular structure of the polymerizable liquid crystal material can be controlled by changing the chiral power by changing the type of the chiral agent or by changing the concentration of the chiral agent. Moreover, a polymerization initiator and a suitable additive are added to such a liquid crystalline composition.

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

In the general formula (1), 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 the molecular chain both ends 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.

上記一般式（３）又は（４）において、Ｒ^４は水素又はメチル基を示す。Ｙは上記に示す式（ｉ）〜（ｘｘｉｖ）の任意の一つであるが、中でも、式（ｉ）、（ｉｉ）、（ｉｉｉ）、（ｖ）及び（ｖｉｉ）のいずれか一つであることが好ましい。また、アルキレン基の鎖長を示すｃ及びｄは、それぞれ個別に２〜１２の範囲で任意の整数をとり得るが、４〜１０の範囲であることが好ましく、６〜９の範囲であることがさらに好ましい。ｃ又はｄの値が０又は１である上記一般式（３）又は（４）の化合物は、安定性に欠け、加水分解を受けやすく、結晶性も高い。一方、ｃ又はｄの値が１３以上である化合物は融点（Ｔｍ）が低い。これらの化合物では、ネマチック規則性を示す重合性の液晶材料との間の相溶性が低下し、濃度によっては相分離などが起きるおそれがある。 However, depending on the properties of the selected chiral agent, the nematic regularity formed by the polymerizable liquid crystal material exhibiting nematic regularity, the orientation deterioration, or the liquid crystallinity when the chiral agent is non-polymerizable. There exists a possibility of causing the fall of the sclerosis | hardenability of a composition, and the fall of the reliability of the film after hardening. Furthermore, the use of a large amount of a chiral agent having an optically active site leads to an increase in the cost of the liquid crystal composition. Therefore, when a polarization selective reflection layer having a cholesteric regularity with a short helical pitch length is formed, a chiral agent having an optically active site to be contained in the liquid crystalline composition has a large effect of inducing a helical structure. It is preferable to select an agent. Specifically, it is preferable to use a low molecular compound having axial asymmetry in the molecule as represented by the following general formula (3), (4) or (5). .

In the general formula (3) or (4), 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.

  Note that the cholesteric liquid crystal structure of the polarization selective reflection layer 11 to be finally obtained is not in the planar alignment state, and the direction of the spiral axis L of the plurality of spiral structure regions 30 is in the layer as shown in FIG. However, even in this case, the alignment treatment is necessary. That is, an alignment process that aligns the directors of liquid crystal molecules having a cholesteric liquid crystal structure in a certain direction on the support substrate 12 is not required, but an alignment process that forms a plurality of helical structure regions 30 in the cholesteric liquid crystal structure. Is necessary.

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

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

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

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

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

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

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

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

  The method (3) is a method of curing the cholesteric liquid crystal layer by photopolymerizing liquid crystal molecules in the liquid crystalline composition by irradiation with radiation. In this method, an electron beam, ultraviolet rays, or the like can be appropriately used as radiation according to conditions. Usually, ultraviolet rays are preferably used from the viewpoint of easiness of the apparatus, and the wavelength is 250 to 400 nm. In the case where the cholesteric liquid crystal layer is cured by ultraviolet rays, oxygen inhibits radicals and decreases the reactivity of liquid crystal molecules, so that an inert gas such as nitrogen or argon (oxygen concentration is 5% or less, and further 0 It is preferable to cure within 5% or less. 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.

  A projection screen 10 having a polarization selective reflection layer (polarization selective reflection sheet) 11 made of a single cholesteric liquid crystal layer is obtained by performing the above-described series of steps (application step, alignment treatment step, and curing treatment step). Although it can be manufactured, a polarization selective reflection layer (polarization selective reflection sheet) 11 composed of a plurality of cholesteric liquid crystal layers (partial selective reflection layers 11a, 11b, and 11c) is provided by repeating the series of steps described above. The projection screen 10 can be manufactured. Thus, for example, as shown in FIG. 3, as the polarization selective reflection layer 11, a partial selective reflection layer 11a that selectively reflects light in the blue (B) wavelength region, and light in the green (G) wavelength region. A projection screen 10 in which a partial selective reflection layer 11b that selectively reflects light and a partial selective reflection layer 11c that selectively reflects light in the red (R) wavelength region are sequentially laminated from the support base 12 side. It can be manufactured.

  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.

  In the above, the polarization selective reflection layer 11 constituting the projection screen 10 (or the partial selective reflection layers 11a, 11b, 11c constituting the polarization selective reflection layer 11) is peeled off from the support base 12 and the polarization selective reflection layer. 11 alone can be used as a polarization selective reflection sheet.

  As described above, according to the present embodiment, in the polarization selective reflection layer 11 that selectively diffuses and reflects light of a specific polarization component by its own structure, the thickness t is selected by the polarization selective reflection layer 11. In order to visually recognize light as an image on the projection screen 10 having such a polarization selective reflection layer 11 as a polarization selective reflection sheet, the size is set so that the transmittance at the reflection center wavelength becomes unsaturated. It is possible to effectively suppress the diffusion effect (scattering effect), which is an obstacle to obtaining good visibility, while sufficiently ensuring the diffusion effect given to the film. For this reason, according to the present invention, it is possible to improve the contrast of the image, and to display the image clearly even under bright ambient light, thereby realizing good visibility. In particular, by setting the transmittance at the selective reflection center wavelength of the polarization selective reflection layer 11 to be 3 to 35%, while minimizing the situation where light that should be selectively reflected is transmitted, The above-described effects can be effectively achieved.

  Further, according to the present embodiment, the polarization selective reflection layer 11 selectively reflects light in a specific wavelength range that covers only a part of the visible light range. In the projection screen 10 provided with the reflective layer 11 as a polarization selective reflection sheet, the influence of ambient light such as external light and illumination light can be further suppressed to increase the contrast of the image, and the visibility of the image can be further improved. it can.

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. 4, the projection system 20 includes a projection screen 10 and a projector 21 that projects image light on the projection screen 10.

  Among these, as the projector 21, a CRT, a liquid crystal projector, a DLP (digital light processing) projector, or the like can be used, but is not particularly limited. However, the image light projected onto the projection screen 10 by the projector 21 mainly includes light having the same polarization component as the light component selectively reflected by the projection screen 10 (for example, right circularly polarized light). preferable.

  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, what has a 1/4 wavelength phase difference is used preferably, and what specifically has a phase difference of 137.5 nm to 550 nm with 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. 4, such a phase difference 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 amount of light of the projector 21 itself is halved, but stray light caused by light having a polarization component different from the polarization component of light selectively reflected by the polarization selective reflection layer 11 of the projection screen 10 (for example, left circularly polarized light). It is possible to effectively prevent the occurrence of the above and increase the contrast of the image.

  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.

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

(Example)
Cholesteric having a selective reflection center wavelength at 550 nm by dissolving a monomer mixed liquid crystal in which a chiral agent (1.15% by weight) is added to a main agent (20% by weight with respect to the total amount of the solution) composed of an ultraviolet curable nematic liquid crystal in cyclohexanone. A liquid crystal solution was prepared.

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

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

  Furthermore, 1% by weight of a photopolymerization initiator manufactured by Ciba Specialty Chemicals was added to the first cholesteric liquid crystal solution.

  Then, the cholesteric liquid crystal solution prepared as described above was applied on a 10 cm square glass by a spin coating method.

  Next, vacuum drying was performed to obtain a cholesteric liquid crystal layer from which the solvent was removed.

Thereafter, the cholesteric liquid crystal layer was irradiated with ultraviolet rays of 365 nm at 20 mW / cm ² for 1 minute in an air atmosphere to cure the cholesteric liquid crystal layer. The cholesteric liquid crystal structure of the cholesteric liquid crystal layer thus cured was not in the planar alignment state.

  As described above, a projection screen was obtained in which a polarization selective reflection layer (polarization selective reflection sheet) having a selective reflection center wavelength at 550 nm was laminated on a raw glass. Note that the thickness of the polarization selective reflection layer of the projection screen thus obtained was 1.5 μm.

(Example 2)
A projection screen according to Example 2 was manufactured by the same method as in Example 1 except that the thickness of the polarization selective reflection layer of the finally obtained projection screen was 2.1 μm.

(Example 3)
A projection screen according to Example 3 was manufactured by the same method as in Example 1 except that the thickness of the polarization selective reflection layer of the finally obtained projection screen was 3.1 μm.

Example 4
A projection screen according to Example 4 was manufactured in the same manner as in Example 1 except that the thickness of the polarization selective reflection layer of the finally obtained projection screen was 4.1 μm.

(Comparative Example 1)
A projection screen according to Comparative Example 1 was manufactured in the same manner as in Example 1 except that the thickness of the polarization selective reflection layer of the finally obtained projection screen was 1.2 μm.

(Comparative Example 2)
A projection screen according to Comparative Example 2 was manufactured by the same method as in Example 1 except that the thickness of the polarization selective reflection layer of the finally obtained projection screen was 4.6 μm.

(Comparative Example 3)
A projection screen according to Comparative Example 3 was manufactured in the same manner as in Example 1 except that the thickness of the polarization selective reflection layer of the finally obtained projection screen was 6.5 μm.

(Comparative Example 4)
A projection screen according to Comparative Example 4 was manufactured in the same manner as in Example 1 except that the thickness of the polarization selective reflection layer of the finally obtained projection screen was 8.9 μm.

(Evaluation results)
The projection screens according to Examples 1 to 4 and Comparative Examples 1 to 4 were installed so as to be perpendicular to the floor in a dark room. The projector was placed at a position approximately 2 m away from the projection screen in a direction perpendicular to the projection screen (a direction parallel to the floor). Here, a liquid crystal projector (TLP-T621, manufactured by Toshiba Corporation) was used as the projector. In addition, a circularly polarizing plate was installed at the exit of the projector so that the emitted image light became circularly polarized light (circularly polarized light in the same direction as the circularly polarized light selectively reflected by each projection screen).

  In this state, image light (a still image with white and black areas) was projected onto each projection screen by the projector, and the images projected on each projection screen were visually observed.

  Further, the transmitted light amount of each projection screen is measured by a spectrophotometer (MPC-3100, manufactured by Shimadzu Corporation), and the transmittance (the ratio of the transmitted light amount when the incident light amount of circularly polarized light is set to 100%) based on the measurement result. )

  Furthermore, the contrast of the image projected on each projection screen was measured. Specifically, the luminance of each of the white and black images at the center of the projection screen is measured by a color luminance meter (CS-100A, manufactured by Konica Minolta Sensing Co., Ltd.), and the ratio is compared with the contrast (contrast = white image). Luminance ÷ Brightness of black image).

The results are shown in the following Table 1, FIG. 5 and FIG. In the following Table 1, in the item of “brightness”, “○” indicates that the image is observed brightly by visual evaluation, and “×” indicates that the image is observed darkly. In addition, in the item of “scattering”, in the visual evaluation, “◯” indicates that there is little scattering and the image visibility is good, and “X” indicates that there is much scattering and the image visibility is poor.

  As can be seen from Table 1 above, each of the projection screens according to Examples 1 to 4 is good in both the brightness of the video and the degree of scattering, and the video projected on each projection screen is good. I was able to see. On the other hand, in the projection screen according to Comparative Example 1, the intensity of the reflected light was weak and the visibility of the image light was low. In each of the projection screens according to Comparative Examples 2 to 4, although the intensity of the reflected light was strong, the degree of scattering was strong and the visibility of the image light was low.

  Further, as can be seen from FIG. 5, when the relationship between the thickness of the polarization selective reflection layer of each projection screen and the contrast in Examples 1 to 4 and Comparative Examples 1 to 4 is seen, the thickness is 1.5 μm (transmittance 35). %) And 4.1 μm (transmittance 3%), inflection points exist. The relationship between the thickness of the polarization selective reflection layer and the transmittance is as shown in FIG. 6. If the thickness of the polarization selective reflection layer becomes too thin, light that should be selectively reflected is transmitted. End up. Moreover, even if the thickness of the polarization selective reflection layer becomes too thick, the transmittance does not decrease as the thickness increases, and the state becomes saturated. Here, considering the contrast characteristics shown in FIG. 5 and the transmittance characteristics shown in FIG. 6, the thickness of the polarization selective reflection layer is a range between the two inflection points, that is, 1 It can be seen that it may be set between .5 μm (transmittance 35%) and 4.1 μm (transmittance 3%).

The schematic sectional drawing which shows the projection screen provided with the polarization selective reflection layer (polarization selective reflection sheet) which concerns on one embodiment of this 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 which shows an example of the projection system provided with the projection screen shown in FIG. The figure which shows the relationship between the thickness of the polarization selective reflection layer in the projection screen which concerns on Examples 1-4 and Comparative Examples 1-4, and contrast. The figure which shows the relationship between the thickness of the polarization | polarized-light selective reflection layer and the transmittance | permeability in the projection screen which concerns on Examples 1-4 and Comparative Examples 1-4.

Explanation of symbols

10 Projection screen 11 Polarization selective reflection layer (polarization selective reflection sheet)
11a, 11b, 11c Partial selective reflection layer 12 Support base material 20 Projection system 21 Projector 22 Phase difference plate 30 Spiral structure region 31R Right circularly polarized light 31L within the selective reflection wavelength region Left circularly polarized light 32R within the selective reflection wavelength region Outside the selective reflection wavelength region Right circularly polarized light 32L left circularly polarized light 33, 36 outside the selective reflection wavelength region

Claims (12)

A polarization selective reflection layer that selectively reflects light of a specific polarization component, comprising a polarization selective reflection layer that diffuses reflected light by its own structure;
The polarization selective reflection sheet, wherein the thickness of the polarization selective reflection layer is set to a size such that the transmittance at the selective reflection center wavelength of the polarization selective reflection layer is unsaturated.   The polarization selective reflection sheet according to claim 1, wherein a transmittance of the polarization selective reflection layer at the selective reflection center wavelength is 3 to 35%.   The polarization selective reflection sheet according to claim 1, wherein the polarization selective reflection layer has a cholesteric liquid crystal structure, and diffuses reflected light due to structural nonuniformity of the cholesteric liquid crystal structure.   The polarization selective reflection sheet according to claim 3, wherein the cholesteric liquid crystal structure of the polarization selective reflection layer includes a plurality of spiral structure regions having different spiral axis directions.   5. The polarization selection according to claim 1, wherein the polarization selective reflection layer selectively reflects light in a specific wavelength range that covers only a part of a visible light range. Reflective sheet.   The polarization selective reflection sheet according to any one of claims 1 to 5, wherein the polarization selective reflection layer is made of a polymerizable liquid crystal material. In the projection screen that reflects the projected image light and displays the image,
One or more polarization selective reflection sheets laminated to each other according to any one of claims 1 to 6,
A projection screen, comprising: a support base that supports the one or more polarization selective reflection sheets.   The projection screen according to claim 7, wherein the one or more polarization selective reflection sheets have different selective reflection center wavelengths.   The selective reflection center wavelength of each of the polarization selective reflection sheets is any one of the ranges of 430 to 460 nm, 540 to 570 nm, and 580 to 620 nm on the basis of the case where light enters the polarization selective reflection sheet perpendicularly. The polarization selective reflection sheet according to claim 8, wherein:   The projection screen according to claim 7, wherein the support base includes a light absorption layer that absorbs light in a visible light range.   11. The projection screen according to claim 7, further comprising an intermediate layer provided between the polarization selective reflection layer and the support base material and improving adhesion between the both. . A projection screen according to any one of claims 7 to 11,
A projection system comprising: a projector that projects image light on the projection screen.

Images