JP4377771B2 - Projection screen and projection system including the same - Google Patents

Description

  The present invention relates to a projection system for projecting image light onto a projection screen by a projector and displaying the image, and in particular, includes a projection screen excellent in visibility capable of clearly displaying an image and the same. It relates to 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.

  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. In addition, a projection screen using a hologram has a problem that it is difficult to increase the screen size due to manufacturing problems.

  On the other hand, in the projection screen using the polarization separation layer, the white display portion can be brightened while the black display portion can be made darker, which is brighter than that using the hologram as described above. Images can be clearly displayed under light.

  Regarding the projection screen using such a polarization separation layer, the present inventor previously provided a polarization selective reflection layer having a cholesteric liquid crystal structure, and reduces the visibility of the image due to the structural nonuniformity of the cholesteric liquid crystal structure. Japanese Patent Application No. 2003-165687 proposes a projection screen that can give a scattering effect to reflected light of image light without any problem.

  The present invention is an improvement over the invention described in Japanese Patent Application No. 2003-165687, and minimizes the influence of a phase difference that occurs when light is incident obliquely on a polarization selective reflection layer having a cholesteric liquid crystal structure. It is an object of the present invention to provide a projection screen excellent in visibility capable of clearly displaying an image and a projection system including the projection screen.

  According to the present invention, as a first solution, in a projection screen that reflects projected image light and displays an image, a layered portion having refractive index anisotropy that selectively reflects light of a specific polarization component is provided. A polarization selective reflection layer having a repetitive structure stacked in a thickness direction, wherein the repetitive structure of the polarization selective reflection layer has a repetitive optical pitch length on the side of the polarization selective reflection layer on which image light is projected. The projection screen is characterized in that it is longer on the side farther away than.

  In the first solving means described above, the light of the specific polarization component is preferably right circularly polarized light or left circularly polarized light. The light of the specific polarization component may be one linearly polarized light.

  In the first solving means described above, it is preferable that a diffusion element that diffuses light reflected by the polarization selective reflection layer is further provided, or that the polarization selective reflection layer itself has diffusibility.

Further, in the first solving means described above, each of the partial selective reflection layers of the polarization selective reflection layer has a cholesteric liquid crystal structure as the repeating structure, and the helical axis of the helical structure region included in the cholesteric liquid crystal structure. It is preferable to diffuse the selectively reflected light by the variation in direction . In this case, 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, the polarization selective reflection layer selectively selects light in the red (R), green (G), and blue (B) wavelength ranges covering a part of the visible light range. It is preferable to reflect.

  Furthermore, in the first solving means described above, the polarization selective reflection layer has a repetitive structure in which layered portions having refractive index anisotropy that selectively reflect light of a specific polarization component are stacked in the thickness direction. And having at least two or more partially selective reflection layers stacked on each other, and the repeating structure of each of the partially selective reflection layers has a repeated optical pitch length so as to selectively reflect light in different wavelength ranges. The partial selective reflection is different from each other so that the repeated optical pitch length is longer in partial selective reflection on the side farther than the partial selective reflection layer on the side where image light is projected in the polarization selective reflection layer. The layers are preferably laminated in order. In this case, each of the partial selective reflection layers of the polarization selective reflection layer has a cholesteric liquid crystal structure as the repeating structure, and light that is selectively reflected by the structural nonuniformity of the cholesteric liquid crystal structure. It is preferable to diffuse. Moreover, it is preferable that the cholesteric liquid crystal structure of each partial selective reflection layer of the polarization selective reflection layer includes a plurality of spiral structure regions having different spiral axis directions. Here, it is preferable that an intermediate layer having easy adhesion or barrier property is provided between adjacent partial selective reflection layers of the polarized light selective reflection layer.

Furthermore, in the first solving means described above, it is preferable to further include a support substrate that supports the polarization selective reflection layer, and is disposed on the side of the layered portion having a long repeated optical pitch length. . The support substrate may be an absorption substrate including a light absorption layer that absorbs light in the visible light region, or a transparent substrate that transmits at least part of light in the visible light region. Also good.
Furthermore, in the first solving means described above, a functional holding layer including at least one layer selected from the group consisting of a hard coat layer, an antiglare layer, an antireflection layer, an ultraviolet absorption layer and an antistatic layer is further provided. It is preferable to provide. Here, when the functional retention layer is an antiglare layer, the antiglare layer is preferably composed of an isotropic layer having an irregular uneven shape, for example, a TAC having a mat surface. A film may be used. An uneven shape may be formed on the surface of the polarized light selective reflection layer on which video light is projected, and the anti-glare function may be imparted to the polarized light selective reflection layer by the uneven shape.

Furthermore, in the first solving means described above, it is preferable that the polarization selective reflection layer is made of a polymerizable liquid crystal material after solidification .

  The present invention provides, as a second solution means, a projection system comprising the projection screen according to the first solution means described above and a projector that projects image light on the projection screen. .

  According to the present invention, the polarization selective reflection layer has a repeating structure in which layered portions having refractive index anisotropy that selectively reflect light of a specific polarization component are stacked in the thickness direction, and this The repeated optical pitch length of the repeated structure is made longer on the side farther from the side on which the image light is projected in the polarization selective reflection layer. Here, when light is obliquely incident on the polarization selective reflection layer having such a repetitive structure, a phase difference occurs. For example, circularly polarized light is converted into elliptically polarized light. Then, the reflectance of selective reflection due to the repetitive structure is lowered, which causes a loss of light. In the present invention, as described above, a layered portion having a short repeated optical pitch length that can obtain a reflectance of almost 100% even on a thin film is disposed on the observation side as compared with a layered portion having a long repeated optical pitch length. Therefore, the light reflection efficiency as a whole is minimized by minimizing the influence of the phase difference that occurs in proportion to the thickness of the repetitive structure (the influence of the part closer to the observation side on the part far from the observation side). As a result, the video can be clearly displayed.

  Further, according to the present invention, since the polarization selective reflection layer selectively reflects only light of a specific polarization component (for example, right circularly polarized light), it polarizes ambient light such as outside light and illumination light that does not have polarization characteristics. Only about 50% of the selective reflection layer can be reflected. 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 100% by the polarization selective reflection layer, and the image light can be reflected efficiently.

  Furthermore, according to the present invention, the polarization selective reflection layer has a cholesteric liquid crystal structure as a repeating structure, and the cholesteric liquid crystal structure has structural non-uniformity (for example, a spiral structure region included in the cholesteric liquid crystal structure). If the direction of the spiral axis varies), the image light is diffusely reflected, not specularly reflected, and the image is easily visible. 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, the environmental light and image light transmitted through the polarization selective reflection layer do not cause the so-called depolarization problem that the polarization state is disturbed, while maintaining the original polarization separation function of the polarization selective reflection layer. Visibility can be improved.

  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 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 11 having a cholesteric liquid crystal structure (repetitive 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 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 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), 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 allows the observer to recognize the reflected light (image light) reflected by the projection screen 10 as an image. To spread or scatter 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, in the polarization selective reflection layer 11 ′, each spiral structure region 30 included in the cholesteric liquid crystal structure. The directions of the helical axis L all extend uniformly in parallel with the layer thickness direction, and the selectively reflected light (reflected light 36) is specularly reflected.

  In the present embodiment, the helical structure region 30 included in the cholesteric liquid crystal structure of the polarization selective reflection layer 11 is continuously different from the helical pitch length or discontinuously so as to cover a wide wavelength range. There are at least two types of helical pitch lengths, and the helical pitch lengths are used to minimize the influence of the phase difference that occurs when light is incident obliquely on the polarization selective reflection layer 11 having a cholesteric liquid crystal structure. In addition, the polarization selective reflection layer 11 is longer on the side farther from the side on which the image light is projected.

  Here, the spiral structure region included in the cholesteric liquid crystal structure of the polarization selective reflection layer 11 selectively reflects 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). 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. 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.

  Note that the thickness of the polarization selective reflection layer 11 having the cholesteric liquid crystal structure as described above is such that it reflects approximately 100% of light in a specific polarization state that is selectively reflected (the degree to which the reflectance is saturated). It is preferable that This is because video light cannot be efficiently reflected if the reflectance is less than 100% with respect to light of a specific polarization component that is selectively reflected (for example, right circularly polarized light). Note that the reflectance of the polarization selective reflection layer 11 directly depends on the number of helical pitches, but indirectly depends on the thickness of the polarization selective reflection layer 11 if the helical pitch length is fixed. ing.

  By the way, the polarization selective reflection layer 11 as described above, when the cholesteric liquid crystal structure has two or more types of helical pitch lengths that are discontinuously different, has at least two or more partial selective reflections having different helical pitch lengths. It can also be configured by stacking layers on each other. Specifically, as shown in FIG. 3, a partial selective reflection layer 11a that selectively reflects light in the red (R) 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 blue (B) wavelength range may be sequentially laminated in this order from the support base material 12 side. Here, the helical pitch length of each of the partial selective reflection layers 11a, 11b, and 11c becomes longer in order from the side on which the image light is projected in the polarized light selective reflection layer 11. In this case, the thickness of each of the partial selective reflection layers 11a, 11b, and 11c increases in order from the side on which the image light is projected in the polarization selective reflection layer 11. This is because when the light of a specific polarization state that is selectively reflected is reflected by approximately 100%, the minimum necessary thickness of each of the partial selective reflection layers 11a, 11b, and 11c increases as the helical pitch length increases. Because it becomes.

  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. It has a cholesteric liquid crystal structure that selectively reflects and has a cholesteric liquid crystal structure that diffuses selectively reflected light due to its structural non-uniformity.

  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. Thereby, 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 prevent generation of reflected light caused by ambient light such as outside light and illumination light, and stray light caused by image light. can do.

  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 polarization selective reflection layer 11 (or the partial selective reflection layers 11a, 11b, 11c constituting the polarization selective reflection layer 11) on the support base 12 so that the cholesteric liquid crystal structure is not in the planar alignment state. Therefore, it is preferable to use a support substrate 12 that does not have 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 in a planar alignment state.

  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. At this time, the surface of the support base 12 on the side on which the liquid crystalline composition is applied should not have alignment ability.

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

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

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

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

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

上記一般式（１）において、Ｒ^１及びＲ^２はそれぞれ水素又はメチル基を示すが、液晶相を示す温度範囲の広さからＲ^１及びＲ^２はともに水素であることが好ましい。Ｘは水素、塩素、臭素、ヨウ素、炭素数１〜４のアルキル基、メトキシ基、シアノ基、ニトロ基のいずれであっても差し支えないが、塩素又はメチル基であることが好ましい。また、上記一般式（１）において、分子鎖両端の（メタ）アクリロイロキシ基と芳香環とのスペーサーであるアルキレン基の鎖長を示すａ及びｂ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。ａ＝ｂ＝０である一般式（１）の化合物は、安定性に乏しく、加水分解を受けやすい上に、化合物自体の結晶性が高い。また、ａ及びｂがそれぞれ１３以上である一般式（１）の化合物は、アイソトロピック転移温度（ＴＩ）が低い。この理由から、これらの化合物はどちらも液晶相を示す温度範囲が狭く好ましくない。 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.

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. Accordingly, 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. You may make it ink.

  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, in this curing treatment step, it is preferable to use a method of curing the cholesteric liquid crystal layer by photopolymerizing liquid crystal molecules in the liquid crystalline composition by irradiation with radiation. In particular, in this embodiment, since it is necessary to change the helical pitch length in the cholesteric liquid crystal layer with respect to the thickness direction of the layer, the cholesteric liquid crystal layer is cured while appropriately controlling the helical pitch length in the cholesteric liquid crystal layer. It is preferable. Specifically, for example, by using a method as described in JP-A No. 14-286935, a cholesteric liquid crystal layer in a semi-cured state is obtained by evaporating the solvent in the liquid crystalline composition applied to the support base 12. After forming, it is preferable that the cholesteric liquid crystal layer is irradiated with radiation in an air atmosphere to cure the cholesteric liquid crystal layer over time. When a liquid crystal composition in which non-crosslinkable liquid crystal molecules are mixed in a polymerizable liquid crystal material is used, by using the method described in US Pat. No. 5,691,789, cholesteric It is also possible to change the helical pitch length in the liquid crystal layer with respect to the thickness direction of the layer.

  By performing the above-described series of steps (coating step, alignment step and curing step), the polarization selective reflection layer 11 having a long helical pitch on the side farther from the side on which the image light is projected is formed. The projection screen 10 provided can be manufactured.

  In addition to the above-described manufacturing method, by repeating the series of steps described above for a plurality of cholesteric liquid crystal layers, that is, while controlling the selective reflection center wavelength of the liquid crystalline composition exhibiting cholesteric regularity to be applied, By sequentially laminating a plurality of cholesteric liquid crystal layers having different helical pitch lengths on the support base 12, the partial selective reflection on the side farther from the partial selective reflection layer on the side on which the image light is projected can be achieved. You may make it manufacture the projection screen 10 provided with the polarization selective reflection layer 11 in which each partial selective reflection layer 11a, 11b, 11c was laminated | stacked in order so that the helical pitch length might become long. Specifically, 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 red (R) wavelength region, and a green (B) wavelength region. The partial selective reflection layer 11b that selectively reflects light and the partial selective reflection layer 11c that selectively reflects light in the blue (B) wavelength range are sequentially stacked in this order from the support substrate 12 side. The projection screen 10 may be manufactured.

  At this time, 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.

  Further, in the curing process for curing the cholesteric liquid crystal layer of each layer, the cholesteric liquid crystal layer is cured by a normal method without changing the helical pitch length in the layer thickness direction in the cholesteric liquid crystal layer. What is necessary is just to fix the cholesteric liquid crystal structure expressed in the state. The method used in such a curing treatment step includes (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 ) A method of polymerizing liquid crystal molecules in the liquid crystalline composition by irradiation with radiation, and (4) a method combining these methods can be used.

  Thus, according to the present embodiment, in the cholesteric liquid crystal structure of the polarization selective reflection layer 11 as shown in FIG. 1, the helical pitch length is larger than that of the polarization selective reflection layer 11 on which the image light is projected. If the polarization selective reflection layer 11 is composed of a plurality of partial selective reflection layers 11a, 11b, and 11c as shown in FIG. 3, the polarization selective reflection is performed. The partial selective reflection layers 11 a, 11 b, and 11 c are stacked so that the spiral pitch length is increased in order from the image light projecting side of the layer 11. In other words, a portion of a cholesteric liquid crystal structure with a short helical pitch length (layered portion) (a portion that selectively reflects light in the wavelength range of green (G) or blue (B)) that can obtain a reflectance of almost 100% even with a thin film The reflective layers 11b and 11c are closer to the observation side than the portion (layered portion) of the cholesteric liquid crystal structure having a long helical pitch length (partial selective reflective layer 11a that selectively reflects light in the red (R) wavelength region). It is arranged. For this reason, the reflection of light as a whole is minimized by minimizing the influence of the phase difference that occurs in proportion to the thickness of the cholesteric liquid crystal structure (the influence of the portion closer to the observation side on the portion far from the observation side). Efficiency can be improved, and as a result, a video can be displayed clearly.

  In addition, according to the present embodiment, the polarization selective reflection layer 11 (or each partial selective reflection layer 11a, 11b, 11c constituting the polarization selective reflection layer 11) has a specific polarization due to the polarization separation characteristic of the cholesteric liquid crystal structure. Since only the component light (for example, right-handed circularly polarized light) is selectively reflected, ambient light having no polarization characteristics, such as ambient light and illumination light, is selected by the polarization selective reflection layer 11 (or each partial selection constituting the polarization selective reflection layer 11). The reflection layers 11a, 11b, 11c) can be made to reflect only about 50%. 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, the projected image light is the same as the polarization component of the light selectively reflected by the polarization selective reflection layer 11 (or the partial selective reflection layers 11a, 11b, and 11c constituting the polarization selective reflection layer 11). If the light component of the polarization component (for example, right circularly polarized light) is mainly included, the projected image light is selectively reflected by the polarization selective reflection layer 11 (or the partial selective reflection layers 11a, 11b, and 11c constituting the polarization selective reflection layer 11). ) Can reflect almost 100%, and image light can be reflected efficiently.

  Furthermore, according to the present embodiment, the cholesteric liquid crystal structure of the polarization selective reflection layer 11 (or each partial selective reflection layer 11a, 11b, 11c constituting the polarization selective reflection layer 11) has structural nonuniformity. Since the direction of the spiral axis L of the spiral structure region 30 included in the cholesteric liquid crystal structure varies, the image light is diffusely reflected, not specularly reflected, and the image can be easily viewed. At this time, the polarization selective reflection layer 11 (or each partial selective reflection layer 11a, 11b, 11c constituting the polarization selective reflection layer 11) is selectively reflected due to the structural non-uniformity of the cholesteric liquid crystal structure. Since light is diffused, it reflects while diffusing light of a specific polarization component (for example, the right circularly polarized light 31R within the selective reflection wavelength region), while other light (for example, the left circularly polarized light 31L within the selective reflection wavelength region, selective reflection). The right circularly polarized light 32R and the left circularly polarized light 32L) outside the wavelength region can be transmitted without being diffused. For this reason, the polarization state of the ambient light and the image light transmitted through the polarization selective reflection layer 11 (or the partial selective reflection layers 11a, 11b, and 11c constituting the polarization selective reflection layer 11) is disturbed. Thus, the visibility of the image can be improved while maintaining the original polarization separation function of the polarization selective reflection layer 11.

  In the above-described embodiment, in the polarization selective reflection layer 11 shown in FIG. 3, the wavelength bands of red (R), green (G), and blue (B) are three selective reflection wavelength bands that are independent of each other. The case where each of these three selective reflection wavelength regions is expressed by each of the corresponding partial selective reflection layers of the three partial selective reflection layers 11a, 11b, and 11c has been described as an example. , Red (R), green (G), and blue (B) when at least two wavelength regions are continuously connected, the polarization selective reflection layer 11 is formed of two partial selective reflection layers. It is also possible to configure by. Here, taking as an example a case where the wavelength range of red (R) and green (G) is included in one selective reflection wavelength range, the polarization selective reflection layer 11 is configured as shown in FIG. ) And green (G) wavelength selective reflection layer 11d selectively, and blue (B) wavelength selective reflection layer 11c selectively reflective in this order. They are laminated in order from the support base 12 side. Even in this case, since the partial selective reflection layer 11c having a short helical pitch length is arranged on the observation side as compared with the partial selective reflection layer 11d having a long helical pitch length, it is generated in proportion to the thickness of the cholesteric liquid crystal structure. The influence of the phase difference (the influence of the portion closer to the observation side on the portion farther from the observation side) can be minimized.

  As described in the above-described embodiment, the polarization selective reflection layer 11 (or each partial selective reflection layer 11a, 11b, 11c constituting the polarization selective reflection layer 11) has structural non-uniformity. A material having a cholesteric liquid crystal structure is most preferably used. However, the present invention is not limited to this, and the following polarization selective reflection layer can also be used.

  In other words, in the above-described embodiment, right circularly polarized light or left circularly polarized light is selectively reflected as the polarization selective reflection layer 11 (or each partial selective reflection layer 11a, 11b, 11c constituting the polarization selective reflection layer 11). A layer having a refractive index anisotropy that selectively reflects light of a specific polarization component is repeatedly stacked in the thickness direction with a predetermined optical pitch length. As long as it has a structure, you may use what has a structure which selectively reflects one linearly polarized light like linearly polarizing elements, such as a multilayer reflective polarizing material. The repeating structure may be a laminate of a layered portion having a refractive index anisotropy and a layered portion having a different refractive index anisotropy (for example, isotropic). Here, the layered portion having refractive index anisotropy corresponds to the nematic layer portion in the case of the cholesteric liquid crystal structure. The repeated optical pitch length is a physical quantity having an optical meaning with respect to interference and wavelength, and corresponds to the helical pitch length in the case of a cholesteric liquid crystal structure. Specifically, it can be expressed as (repeated optical pitch length) = (spiral pitch length) × (refractive index).

  Further, in the above-described embodiment, the polarization selective reflection layer 11 (or the partial selective reflection layers 11a, 11b, and 11c constituting the polarization selective reflection layer 11) is caused by the structural non-uniformity of the cholesteric liquid crystal structure. However, as long as the visibility of the image is ensured, the cholesteric liquid crystal structure is in a planar alignment state so that the selectively reflected light is specularly reflected. You may use anything.

  Furthermore, in the above-described embodiment, the polarization selective reflection layer 11 (or each partial selective reflection layer 11a, 11b, 11c constituting the polarization selective reflection layer 11) itself has diffusibility, but this is not limitative. Alternatively, a diffusing element that diffuses the light reflected by the polarization selective reflection layer 11 may be provided separately from the polarization selective reflection layer 11.

  Furthermore, in the above-described embodiment, it is preferable to use a support substrate 12 that does not have alignment ability on the surface on which the liquid crystalline composition is applied. When the surface on the side on which the composition is applied has orientation ability, as shown in FIG. 5, the partial selective reflection layer 11 a and the support group on the support base material 12 side in the polarization selective reflection layer 11. By providing an intermediate layer 13 such as an easy-adhesion layer between the material 12, the orientation state of the cholesteric liquid crystal structure of the polarization selective reflection layer 11 (or each of the partial selective reflection layers 11 a, 11 b, 11 c constituting the same) is controlled. However, the director of the liquid crystal molecules in the vicinity of the interface with the intermediate layer 13 in the cholesteric liquid crystal structure of the polarization selective reflection layer 11 may be directed 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 absorption layer that kneads a black pigment or the like and absorbs light in the visible light region, like the supporting base material. In addition, when the polarization selective reflection layer 11 has a plurality of partial selective reflection layers 11a, 11b, and 11c laminated on each other, the polarization selective reflection layer 11 is laminated on the support substrate 12 as shown in FIG. An intermediate layer 13 such as easy adhesion may be provided between adjacent partial selective reflection layers of the partial selective reflection layers 11a, 11b, and 11c.

  Furthermore, in the above-described embodiment, a functional holding layer 19 may be provided on the observation side surface of the projection screen 10 (polarization selective reflection layer 11) as shown in FIG. 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 the projection screen 10 from being roughened. 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. In the case where the functional holding layer 19 is used as an antistatic layer, the functional holding layer 19 is not necessarily provided on the observation side surface of the projection screen 10, and is not provided on the back side of the support base 12. The support substrate 12 itself may be provided with a function of removing static electricity by kneading carbon particles or the like into the support substrate 12.

  The functional holding layer 19 used as an antiglare layer plays a role of preventing a phenomenon in which the space in which the viewer is present is reflected on the surface of the projection screen 10, and is important for viewing images well. It is. In this case, as the antiglare layer, a transparent layer having a concavo-convex shape on the surface is preferably used, thereby effectively preventing a mirror-like image from being formed due to interface reflection on the projection screen 10 surface. can do. In addition, as a method for forming such a transparent layer, for example, a sandblast method, a surface shape transfer at the time of mold formation, a chemical treatment, or other various methods such as a transparent resin or glass surface. A method of shaping the uneven shape can be used. Here, the concavo-convex shape formed on the surface of the transparent layer may be irregular or regular. In this case, in order not to impair the polarization separation function of the polarization selective reflection layer 11, the antiglare layer is preferably a layer having an isotropic refractive index. As a material for the antiglare layer, for example, glass, acrylic resin, polyester resin, or the like can be used, and a TAC (triacetyl cellulose) film having a mat surface can also be used.

  In addition, when providing the anti-glare function to the projection screen 10, as shown to Fig.6 (a), in addition to implement | achieving an anti-glare layer by the functional holding layer 19 separate from the polarization selective reflection layer 11, As shown in FIG. 6B, an uneven shape (see reference numeral 11e) is formed on the observation-side surface of the polarization selective reflection layer 11 (the surface of the partial selective reflection layer 11c positioned closest to the observation side). Thus, the anti-glare function may be imparted to the polarization selective reflection layer 11 itself.

  Furthermore, in the above-described embodiment, the case where the support base 12 of the projection screen 10 is an absorption base including a light absorption layer that absorbs light in the visible light range has been described as an example. Not limited to this, the support substrate 12 may be a transparent substrate that transmits at least part of light in the visible light range. In this case, the advantage of increasing the contrast of the video is lost, but the transparency of the projection screen 10 when the video is not displayed is high, so that the background can be seen through clearly and installed in a show window. It can be used with high design. In addition, an effective eye-catching effect can be produced by switching 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 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 partitions or windows can be used.

  Further, in the above-described embodiment, in the projection screen 10, between the polarization selective reflection layer 11 and the support base 12, or among the partial selective reflection layers 11 a, 11 b, 11 c constituting the polarization selective reflection layer 11. An intermediate layer (easily adhesive layer) 13 having easy adhesion can be provided between the adjacent partially selective reflection layers as described above. The intermediate layer 13 has a function in addition to easy adhesion. (Or in lieu of easy adhesion). The barrier property referred to here means that when a polarization selective reflection layer is directly laminated on a support substrate, or when another partial selective reflection layer is directly laminated on one partial selective reflection layer, It refers to a function of preventing a constituent part from moving (penetrating) into an upper layer and an upper layer constituent part from moving (penetrating) into a lower layer. When a substance moves between the upper layer and the lower layer, the original optical function (wavelength selectivity, polarization selectivity, diffusibility, etc.) of the polarization selective reflection layer (or partial selective reflection layer) constituting the upper layer or the lower layer However, it can be prevented by using an intermediate layer (barrier layer) having a barrier property as described above. Specifically, for example, in the case of laminating another partially selective reflective layer on one partially selective reflective layer by applying a liquid crystalline composition having cholesteric regularity, the type and process conditions of the liquid crystalline composition In some cases, the nematic liquid crystal component contained in the liquid crystalline composition for forming the upper partial selective reflection layer penetrates into the lower partial selective reflection layer, and changes (increases) the helical pitch length of the lower partial selective reflection layer. It can be letting you. However, even in this case, if a barrier layer is provided between the lower partial selective reflection layer and the upper partial selective reflection layer, such movement (penetration) of the nematic liquid crystal component is eliminated, and the partial selective reflection layer is eliminated. These optical functions (wavelength selectivity, polarization selectivity, diffusivity, etc.) can be maintained well.

  Examples of such a barrier layer include modified acrylate, urethane acrylate, polyester acrylate, and epoxy resin. These may be monofunctional or polyfunctional, and there are types of monomers and oligomers. Specifically, ethoxylated trimethylolpropane triacrylate, propoxylated glyceryl triacrylate, pentaerythritol tetraacrylate, ditrimethylolpropane tetraacrylate, dipentaerythritol hydroxypentaacrylate, ethoxylated pentaerythritol tetraacrylate, pentaacrylate ester, pentaerythritol Triacrylate, trimethylolpropane triacrylate, trimethylolpropane PO-modified triacrylate, isocyanuric acid EO-modified triacrylate, trimethylolpropane EO-modified triacrylate, dipentaerythritol penta- and hexaacrylate, urethane adduct, aliphatic polyamine epoxy Resin, polyaminoamide epoxy resin Aromatic diamine epoxy resin, alicyclic diamine epoxy resin, phenol resin epoxy resin, amino resin epoxy resin, mercaptan compound epoxy resin, dicyandiamide epoxy resin, Lewis acid complex compound epoxy resin, etc. Can do.

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

  As shown in FIG. 7, 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. 7, 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)
Prepare a first cholesteric liquid crystal solution having a selective reflection center wavelength at 600 nm by dissolving a monomer-mixed liquid crystal in which a chiral agent (3 wt%) is added to a main agent (97 wt%) composed of an ultraviolet curable nematic liquid crystal in cyclohexanone. did.

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

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

  Furthermore, 5 wt% of an acetophenone photopolymerization initiator manufactured by Ciba Specialty Chemicals was added to the first cholesteric liquid crystal solution.

  And the 1st cholesteric liquid crystal solution adjusted as mentioned above was apply | coated by the bar-coat method on a 200 mm □ black acrylic board.

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

Thereafter, the cholesteric liquid crystal layer was irradiated with 365 nm ultraviolet light at 10 mW / cm ² for 1 minute to cure the cholesteric liquid crystal layer, thereby obtaining a first partial selective reflection layer having a selective reflection center wavelength at 600 nm. .

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

  Similarly, the third cholesteric liquid crystal solution was directly applied onto the second partially selective reflection layer, and subjected to alignment treatment (drying treatment) and curing treatment. As a result, a third partial selective reflection layer having a selective reflection center wavelength at 450 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 450 nm by controlling the mixing ratio of the nematic liquid crystal and the chiral agent. To have.

  As described above, as the polarization selective reflection layer, the first partial selective reflection layer that selectively reflects light in the red (R) wavelength region (light having a selective reflection center wavelength at 600 nm), and the green (G) A second partial selective reflection layer that selectively reflects light in the wavelength range (light having a selective reflection center wavelength at 550 nm) and light in the blue (B) wavelength range (light having a selective reflection center wavelength at 450 nm). A projection screen was obtained in which the third partial selective reflection layer that selectively reflects () was sequentially laminated in this order from the support substrate side. The thickness of the first partial selective reflection layer was 5 μm, the thickness of the second partial selective reflection layer was 4 μm, and the thickness of the third partial selective reflection layer was 3 μm. The cholesteric liquid crystal structure of each partial selective reflection layer of the polarization selective reflection layer of the projection screen thus obtained was not in the planar alignment state.

(Comparative example)
Except for changing the order in which the first cholesteric liquid crystal solution, the second cholesteric liquid crystal solution, and the third cholesteric liquid crystal solution are applied, a polarization selective reflection layer is manufactured by the same method as the above-described example, A first partially selective reflection layer that selectively reflects light in the blue (B) wavelength range (light having a selective reflection center wavelength at 450 nm) and light in the green (G) wavelength range (selective reflection at 550 nm). A second partial selective reflection layer that selectively reflects light having a central wavelength) and three layers that selectively reflect light in the red (R) wavelength region (light having a selective reflection central wavelength at 600 nm). A projection screen was obtained in which the partial selective reflection layer of the eyes was laminated in this order from the support substrate side.

(Evaluation results)
The image light emitted from the projector was projected on each projection screen according to the example and the comparative example, and the contrast was measured. A liquid crystal projector (ELP-52, manufactured by Epson Corporation) was used as the projector.

  Here, a circularly polarizing plate was disposed at the exit of the projector so that the emitted image light was circularly polarized. In addition, the indoor lighting where the projector and the projection screen are installed is performed by a fluorescent lamp installed on the ceiling (which emits non-polarized light) and is illuminated on the projection screen at an angle of about 50 degrees from the ceiling. They were placed in such a relationship that they were irradiated with light. At this time, the brightness just below the projection screen was 200 lux (lx) as measured by an illuminometer (digital illuminometer 510-02, manufactured by Yokogawa M & C).

  The projection screen was installed perpendicular to the floor. In addition, the projector was arranged at a position approximately 2.5 m away from the projection screen in a direction perpendicular to the projection screen (a direction parallel to the floor).

  In this state, image light (a still image 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 contrast (contrast = brightness of white images). ÷ Intensity of black image).

また、各投影スクリーンを目視により観察したが、この場合、実施例及び比較例の各投影スクリーンでは良好に映像を視認することができた。 Table 1 below shows the contrast of each projection screen according to the example and the comparative example. As shown in the following Table 1, sufficient contrast was obtained with each projection screen according to the example and the comparative example.

Moreover, although each projection screen was observed visually, in this case, each projection screen of the example and the comparative example was able to visually recognize images satisfactorily.

  It should be noted that the position where the incident light of the image light is oblique (in the plane of the screen plane) in a state in which the image light (white and black checkered image) is projected on each projection screen according to the example and the comparative example by the projector. When the image was visually observed at a position of 15 ° or more with the normal direction being 0 °, the projection screen according to the example displayed a brighter image than the projection screen according to the comparative example.

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 sectional view showing a modification 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. Schematic which shows an example of the projection system provided with the projection screen which concerns on one embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Projection screen 11 Polarization selective reflection layer 11a, 11b, 11c, 11d Partial selective reflection layer 12 Support base material 13 Intermediate | middle layer 19 Functional maintenance layer 20 Projection system 21 Projector 22 Retardation plate 30 Helical structure area 31R In selective reflection wavelength range 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

Claims (22)

In the projection screen that reflects the projected image light and displays the image,
A polarization selective reflection layer having a repetitive structure in which layered portions having refractive index anisotropy that selectively reflect light of a specific polarization component are stacked in the thickness direction;
The projection screen characterized in that the repeating optical pitch length of the polarization selective reflection layer is longer on a side farther from the side on which image light is projected in the polarization selective reflection layer.   The projection screen according to claim 1, wherein the light of the specific polarization component is right circularly polarized light or left circularly polarized light.   The projection screen according to claim 1, wherein the light having the specific polarization component is one linearly polarized light.   The projection screen according to claim 1, further comprising a diffusing element that diffuses light reflected by the polarization selective reflection layer.   The projection screen according to claim 1, wherein the polarization selective reflection layer itself has diffusibility.   6. The polarization selective reflection layer has a cholesteric liquid crystal structure as the repeating structure, and diffuses selectively reflected light due to structural nonuniformity of the cholesteric liquid crystal structure. Projection screen described in.   The projection screen according to claim 6, wherein the cholesteric liquid crystal structure of the polarization selective reflection layer includes a plurality of spiral structure regions having different spiral axis directions.   2. The polarization selective reflection layer selectively reflects light in a wavelength range of red (R), green (G), and blue (B) that covers a part of a visible light range. The projection screen as described in any one of thru | or 7. The polarization selective reflection layer has a repetitive structure in which layered portions having refractive index anisotropy that selectively reflect light of a specific polarization component are stacked in the thickness direction, and at least two or more layers stacked on each other Having a partially selective reflective layer;
The repetitive structures of the partial selective reflection layers have different repetitive optical pitch lengths so as to selectively reflect light in different wavelength ranges, and portions of the polarization selective reflection layer on the side on which image light is projected The partial selective reflection layers are stacked in order so that the repeated optical pitch length is longer in partial selective reflection on the side farther from the selective reflection layer. Projection screen. Each of the partial selective reflection layers of the polarization selective reflection layer has a cholesteric liquid crystal structure as the repeating structure, and is selectively reflected when the direction of the helical axis of the helical structure region included in the cholesteric liquid crystal structure varies. The projection screen according to claim 9, wherein the projection screen diffuses light.   The projection screen according to claim 10, wherein the cholesteric liquid crystal structure of each of the partial selective reflection layers of the polarization selective reflection layer includes a plurality of spiral structure regions having different spiral axis directions. The projection screen according to claim 9, wherein an intermediate layer having easy adhesion is provided between adjacent partial selective reflection layers of the polarization selective reflection layer. .   The projection screen according to claim 9, wherein an intermediate layer having a barrier property is provided between adjacent partial selective reflection layers of the polarization selective reflection layer.   14. The support substrate for supporting the polarization selective reflection layer, further comprising a support substrate disposed on the side of a layered portion having a long repeated optical pitch length. The projection screen according to one item.   The projection screen according to claim 14, wherein the support substrate is an absorption substrate including a light absorption layer that absorbs light in a visible light range.   The projection screen according to claim 14, wherein the support substrate is a transparent substrate that transmits at least part of light in a visible light region.   The functional holding layer including at least one layer selected from the group consisting of a hard coat layer, an antiglare layer, an antireflection layer, an ultraviolet absorbing layer, and an antistatic layer is further provided. The projection screen according to claim 16.   The projection screen according to claim 17, wherein the functional holding layer is an antiglare layer, and the antiglare layer is composed of a layer having an irregular uneven shape and an isotropic refractive index.   The projection screen according to claim 18, wherein the antiglare layer is a TAC film having a matte surface.   2. An uneven shape is formed on a surface of the polarization selective reflection layer on which video light is projected, and the anti-glare function is imparted to the polarization selective reflection layer by the uneven shape. The projection screen as described in any one of thru | or 16. 21. The projection screen according to claim 1, wherein the polarization selective reflection layer is made of a polymerizable liquid crystal material after solidification . A projection screen according to any one of claims 1 to 21,
A projection system comprising: a projector that projects image light on the projection screen.

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