JP2005107017A - Projection screen and projection system equipped therewith - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a projection screen excellent in visibility on which a video is vividly displayed even under bright ambient light and which improves the visibility of the video, and also to provide a projection system equipped with the projection screen. <P>SOLUTION: The projection screen 10-1 is equipped with a polarized light selective reflection layer 11-1 diffusing and reflecting the light of a prescribed polarized light component, and a supporting base material 12 or the like supporting the polarized light selective reflection layer 11-1. The polarized light selective reflection layer 11-1 has laminated structure where a partial selective reflection layer 11d diffusing and reflecting light (green (G) and red (R)) having different intensity peak wavelength by one layer and a partial selective reflection layer 11a diffusing and reflecting light having a wavelength region showing blue (B) are laminated together. <P>COPYRIGHT: (C)2005,JPO&NCIPI

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 difference.

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

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

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

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

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

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

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

  That is, in the projection screen using the polarization separation layer described in Patent Document 2, light of a specific polarization component is diffusely reflected (reflected) in consideration of the polarization state of image light and ambient light projected from the projector. By giving the light a scattering effect), the visibility of the image is being improved.

However, in the projection screen described in Patent Document 2, for example, the interface reflection that occurs on the surface of the polarization separation layer is not taken into account, so that, for example, the reflected light (interface reflected light) due to the interface reflection of the image light is observed by the observer. If observed, the light source light of the projector (projector or the like) is reflected, resulting in a problem that the visibility of the image on the projection screen is lowered.
In particular, when the polarization separation layer has a laminated structure, interface reflected light based on ambient light and image light is also generated at the interface between the laminated polarization separation layers.

Therefore, in the projection screen using the polarization separation layer, it is necessary to consider the amount of the interface reflected light in order to improve the visibility of the image. However, in the projection screen described in Patent Document 2, the interface reflection is performed. No consideration is given to the amount of light.
JP-A-5-107660 JP 2002-540445 A

  An object of the present invention is to provide a projection screen capable of clearly displaying an image even under bright ambient light and improving the visibility of the image, and a projection system including the projection screen.

  In order to solve the above-mentioned problems, the invention of claim 1 is a projection screen that displays video by diffusing and reflecting video light, which is light of a specific polarization component projected from the observation side, and is red and green. And a second partial selective reflection layer that diffusely reflects image light having a wavelength range indicating blue, and a second partial selective reflection layer that diffusely reflects image light having a wavelength range indicating blue. .

  According to a second aspect of the present invention, in the projection screen according to the first aspect, the image light having wavelength ranges indicating red, green, and blue is included in 580 to 620 nm, 540 to 570 nm, and 430 to 460 nm, respectively. It is the projection screen characterized.

  According to a third aspect of the present invention, in the projection screen according to the first or second aspect, a reflection wavelength region of the first partial selective reflection layer is 540 to 620 nm, and a reflection wavelength of the second partial selective reflection layer. The area is a projection screen characterized in that it is 430 to 460 nm.

  The invention of claim 4 is the projection screen according to any one of claims 1 to 3, wherein the light of the specific polarization component is right circularly polarized light or left circularly polarized light. Projection screen.

  The invention according to claim 5 is the projection screen according to any one of claims 1 to 3, wherein the light of the specific polarization component is one linearly polarized light. It is.

  A sixth aspect of the present invention is the projection screen according to any one of the first to fifth aspects, wherein the first partial selective reflection layer and the second partial selective reflection layer are formed of the specific polarization component. A projection screen comprising: a polarization reflection layer that reflects light; and a diffusion element that diffuses light reflected by the polarization reflection layer.

  The invention according to claim 7 is the projection screen according to any one of claims 1 to 5, wherein the first partial selective reflection layer and the second partial selective reflection layer are diffusible by themselves. It is a projection screen characterized by having.

  The invention of claim 8 is the projection screen according to any one of claims 1 to 7, wherein the first partial selective reflection layer and the second partial selective reflection layer have a cholesteric liquid crystal structure. A projection screen characterized by diffusing light of a specific polarization component due to structural non-uniformity of the cholesteric liquid crystal structure.

  A ninth aspect of the present invention is the projection screen according to the eighth aspect, wherein the cholesteric liquid crystal structure includes a plurality of spiral structure regions having different spiral axis directions.

  The invention of claim 10 is the projection screen according to any one of claims 1 to 9, wherein the first partial selective reflection layer is made of a material having a large birefringence value. It is a projection screen.

  The invention of claim 11 is the projection screen according to any one of claims 8 to 10, wherein the cholesteric liquid crystal structure of the first partial selective reflection layer has a helical pitch length continuous in the thickness direction. The projection screen is characterized by being different from each other.

  The invention of claim 12 is a projection system comprising: a projector that projects image light of at least three wavelength bands; and a projection screen that diffusely reflects light of a specific polarization component, the projection screen comprising: A first partial selective reflection layer that diffuses and reflects image light in at least two wavelength bands out of the image light, and image light in a wavelength band excluding at least the remaining image light in one wavelength band out of the image light. And a second partially selective reflection layer that diffusely reflects the projection system.

  A thirteenth aspect of the invention is the projection system according to the twelfth aspect, wherein the light of the specific polarization component is right circularly polarized light or left circularly polarized light.

  A fourteenth aspect of the invention is the projection system according to the twelfth aspect of the invention, wherein the light of the specific polarization component is one linearly polarized light.

The projection screen of the present invention (1) diffuses and reflects image light that is light of a specific polarization component projected from the observation side, and the projection screen that displays the image has an image having a wavelength range indicating red and green. Since it includes a first partial selective reflection layer that diffusely reflects light and a second partial selective reflection layer that diffusely reflects image light having a wavelength range indicating blue, the image light and the environment projected from the observation side When light is reflected at the interface of each partially selective reflection layer, the number of the interfaces themselves can be reduced by at least one. As a result, the amount of the reflected light from the interface is reduced, and the projection screen Visibility can be improved.
Specifically, the first partial selective reflection layer is a single layer having no interface, and can diffusely reflect green (G) and red (R) among the three primary colors of light.
Furthermore, since the first partial selective reflection layer diffusely reflects green (G) and red (R) in one layer, compared with the case of diffusely reflecting green (G) and red (R) in two layers, Since the film thickness can be reduced, so-called retardation effect can be reduced, and as a result, the reflection efficiency can be improved.

(2) Since the image light having the wavelength ranges indicating blue, green, and red is included in 430 to 460 nm, 540 to 570 nm, and 580 to 620 nm, respectively, the projector that projects the image light on the projection screen is Color display is realized by light in the wavelength range of blue (B), green (G), and red (R), which are the three primary colors of light. For example, based on the case where light is incident perpendicular to the projection screen. Thus, 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.

(3) The reflection wavelength range of the first partial selective reflection layer is 540 to 620 nm, and the reflection wavelength range of the second partial selective reflection layer is 430 to 460 nm. It can correspond to a wavelength range.
Specifically, according to the first partial selective reflection layer, light in the green (G) and red (R) wavelength regions can be diffusely reflected. Further, according to the second partial selective reflection layer, light in the blue (B) wavelength region can be diffusely reflected.

(4) Since light of a specific polarization component is right circular polarization or left circular polarization, only light of a specific polarization component (for example, right circular polarization) is selectively reflected by the polarization separation characteristic of the polarization selective reflection layer. Therefore, it is possible to reflect only about 50% of ambient light such as outside light and illumination light having no polarization characteristics by the polarization selective reflection layer.
For this reason, even when the brightness of the bright display portion such as white display is the same, the brightness of the dark display portion such as black display can be substantially halved and the contrast of the image can be approximately doubled. 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.
Even a projector (such as a liquid crystal projector) that emits linearly polarized light uses a projection screen regardless of the direction of linearly polarized light by using a phase difference plate for converting linearly polarized light into circularly polarized light. be able to.

(5) Since the light of a specific polarization component is one of linearly polarized light (P-polarized light or S-polarized light), the image can be displayed brightly by matching the direction of the linearly polarized light of the projector that emits the linearly polarized light. it can.
Specifically, since the light of the specific polarization component is P-polarization or S-polarization, only the light of the specific polarization component (for example, P-polarization) is selectively reflected by the polarization separation characteristic of the polarization selective reflection layer. Therefore, it is possible to reflect only about 50% of ambient light such as external light and illumination light having no polarization characteristics by the polarization selective reflection layer.
For this reason, even when the brightness of the bright display portion such as white display is the same, the brightness of the dark display portion such as black display can be substantially halved and the contrast of the image can be approximately doubled. 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, P-polarized light), the projected image is displayed. Light can be reflected almost 100% by the polarization selective reflection layer, and image light can be efficiently reflected.

(6) The first and second partial selective reflection layers include a polarization reflection layer that reflects light of a specific polarization component and a diffusion element that diffuses light reflected by the polarization reflection layer. The diffusion characteristics can be made independent and the respective characteristics can be easily controlled.

(7) Since the first and second partial selective reflection layers themselves have diffusibility, a strong reflection intensity is obtained because the polarization state of incident light is not disturbed.

(8) The first and second partial selective reflection layers have a cholesteric liquid crystal structure and diffuse light of a specific polarization component due to the structural nonuniformity of the cholesteric liquid crystal structure. There is no need to provide it.
Specifically, when a diffusing element is provided on the viewer side of the reflective polarizing element, light is transmitted through the diffusing element before entering the reflective polarizing element, and the polarization state is disturbed. (This is called "biased"). 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.

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

(10) Since the first partial selective reflection layer is made of a material having a large birefringence value Δn, the wavelength bandwidth Δλ in the selective reflection wavelength region can be increased (reason: p in the helical structure of liquid crystal molecules). When the helical pitch length is used, the relationship Δλ = Δn · p is established), and light in the wavelength ranges of green (G) and red (R) among the three primary colors of light can be diffusely reflected.

(11) Since the cholesteric liquid crystal structure of the first partial selective reflection layer has the helical pitch length p continuously different in the thickness direction, the wavelength bandwidth Δ of the selective reflection wavelength region based on the above-described relationship. λ can be increased.
Specifically, by continuously changing the concentration of the chiral agent that controls the helical pitch length p in the thickness direction, for example, the helical pitch length p on the observation side is made shorter or longer. By adjusting, it is possible to construct a cholesteric liquid crystal structure in which no interface is generated in the first partial selective reflection layer.
In addition, after applying a cholesteric liquid crystal solution to which a photopolymerization initiator has been added to a substrate to form an uncured liquid crystal layer, ultraviolet irradiation (the irradiation intensity here is in a state where a uniform helical pitch length p is maintained) The surface on the observation side of the liquid crystal layer is set to an air atmosphere having an oxygen concentration of 10% or more at normal pressure, while performing the irradiation intensity of about 1 to 10% compared to the irradiation intensity capable of curing the liquid crystal layer. By gradually reducing the oxygen partial pressure in the air atmosphere and heating the substrate, it is possible to manufacture a first partial selective reflection layer in which the helical pitch length p is continuously different in the thickness direction.

(12) The projection system includes a projector that projects image light of at least three wavelength bands, and a projection screen that diffusely reflects light of a specific polarization component, and the projection screen includes: A first partial selective reflection layer that diffuses and reflects image light in at least two wavelength bands; and a second partial selective reflection layer that diffuses and reflects image light in at least one remaining wavelength band of the image light. As a result, when image light or ambient light projected from the observation side is reflected at the interface of each partial selective reflection layer, the number of the interfaces themselves can be reduced by at least one. The amount of the interface reflected light can be reduced and the visibility of the projection screen can be improved.
In addition, since the projector for projecting image light is provided on the projection screen, the projection screen can be used by being incorporated in the projection system.
In the case where the projector projects image light in four wavelength bands (for example, image light obtained by adding one color such as cyan, magenta, etc. to red, green, and blue, which are the three primary colors of light). Two wavelength selective reflection layers may diffuse and reflect image light of two wavelength bands, and the first partial selective reflection layer may diffuse and reflect image light of three wavelength bands. One layer of the third partial selective reflection layer for diffusely reflecting image light in one wavelength band may be added.

(13) Since the light of the specific polarization component is right circular polarization or left circular polarization, only the light of the specific polarization component (for example, right circular polarization) is selectively reflected by the polarization separation characteristic of the polarization selective reflection layer. Therefore, it is possible to reflect only about 50% of ambient light such as outside light and illumination light having no polarization characteristics by the polarization selective reflection layer.

(14) Since the light of the specific polarization component is one of the linearly polarized light (P-polarized light or S-polarized light), the image can be displayed brightly by matching the direction of the linearly polarized light of the projector that emits the linearly polarized light. it can.

  In order to display images clearly even under bright ambient light, and to improve the visibility of images, video light in two wavelength ranges is projected on a projection screen that diffuses and reflects light of a specific polarization component. This is realized by including a first partially selective reflection layer that diffusely reflects (for example, green (G) and red (R)) having different intensity peak wavelengths.

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

Projection Screen First, the basic structure of 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 includes the basic structure of the projection screen 10-1 (see FIG. 13) according to the present embodiment. The projection screen 10 reflects an image light projected from the viewer side (upper side of the drawing) and displays an image, and has a cholesteric liquid crystal structure that selectively reflects light of a specific polarization component. A selective reflection layer 11 and a support base 12 that supports the polarization selective reflection layer 11 are provided.
The projection screen 10-1 has a partial selective reflection layer 11 d that diffuses and reflects light (green (G) and red (R)) having different intensity peak wavelengths in one layer, instead of the polarization selective reflection layer 11, and The polarization selective reflection layer 11-1 (see FIG. 13) in which the partial selective reflection layer 11a that diffusely reflects other light (blue (B)) is laminated is provided, which will be described in detail later. Further, details of the case where the projection screen 10 is not the basic structure will be described later.

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

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

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

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

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

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

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

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

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

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

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

  Specifically, as shown in the drawing, the polarization selective reflection layer 11 selects the partial selective reflection layer 11a that selectively reflects light in the blue (B) wavelength region and the light in the green (G) wavelength region. And a partial selective reflection layer 11c that selectively reflects light in the red (R) wavelength region, and a partial selective reflection from the observation side to the support substrate 12 side. The layer 11c, the partial selective reflection layer 11b, and the partial selective reflection layer 11a are laminated in this order.

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

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

  Next, the support base 12 will be described.

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

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

  Specifically, for example, as shown in FIG. 6, the support substrate 12 (12A) may be formed using a plastic film (for example, a black PET film in which carbon is mixed) with a black pigment. . In this case, the entire support substrate 12 becomes a light absorption layer (light absorption substrate). Thereby, light that should not be reflected as reflected light 33 among unpolarized light incident from the viewer side of the projection screen 10 (left circularly polarized light 31L within the selective reflection wavelength region, right circularly polarized light outside the selective reflection wavelength region). 32R and left circularly polarized light 32L) and light incident from the back side of the projection screen 10 are absorbed to generate reflected light caused by ambient light such as external light and illumination light, and stray light caused by image light. It can be effectively prevented.

  In addition to the aspect of the support substrate 12 (12A) shown in FIG. 6, as shown in FIGS. 7 and 8, on the surface on either side of the transparent support film 14 such as a plastic film, The support substrate 12 (12B, 12C) may be formed by forming the light absorption layer 15 made of a black pigment or the like.

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

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

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

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

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

  In addition, when the surface of the support substrate 12 on which the liquid crystalline composition is applied has orientation ability, as shown in FIG. 9, the polarization selective reflection layer 11 and the support substrate 12 (12A ) Between the cholesteric liquid crystal structure of the polarization selective reflection layer 11 and the intermediate layer 13 in the cholesteric liquid crystal structure of the polarization selective reflection layer 11. It is also possible for the director of the liquid crystal molecules in the vicinity of the interface to face in a plurality of directions. In addition, when providing intermediate | middle layers 13, such as an easily bonding layer, the adhesiveness between the polarization selective reflection layer 11 and the support base material 12 can also be improved. In addition, as such an intermediate | middle layer 13, what is necessary is just to be able to acquire high adhesiveness with respect to both the material of the polarization selective reflection layer 11, and the material of the support base material 12, and the thing marketed generally is used. be able to. Specific examples include PET film A4100 with an easy-adhesion layer manufactured by Toyobo Co., Ltd., and easy-adhesive materials AC-X, AC-L, and AC-W manufactured by Panac. The intermediate layer 13 can also be used as a light absorbing layer that incorporates a black pigment or the like and absorbs light in the visible light region, like the support base 12 (12A) shown in FIG.

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

  In the projection screen 10 according to the present embodiment, as shown in FIG. 10, the support substrate 12 is provided on the opposite side of the support substrate 12 from the surface on which the polarization selective reflection layer 11 is provided. You may make it provide the light reflection layer 16 which reflects the light which injects into. Accordingly, when the support base 12 includes the light absorption layer in the manner shown in FIGS. 6 to 8, the ambient light such as external light and illumination light incident from the back side of the projection screen 10 is supported by the support base 12. Before reaching the material 12 (particularly, the light absorption layer contained therein), it can be effectively reflected, and the heat generation of the support base 12 can be effectively suppressed. As the light reflection layer 16, it is preferable to use a white scattering layer (paper material, white film, paint film, etc.), a metal plate, an aluminum powder film, or the like.

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

  Furthermore, as shown in FIG. 10, a functional holding layer 19 may be provided on the surface of the polarization selective reflection layer 11 on the viewer side. As the functional retention layer 19, various types can be used. For example, a hard coat layer (HC layer), an antiglare layer (AG layer), an antireflection layer (AR layer), an ultraviolet absorption layer (UV absorption) Layer) and an antistatic layer (AS layer).

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

Next, a case where the above-described projection screen 10 is applied to a projection system will be described.
FIG. 11 is a conceptual diagram of a projection system using the projection screen 10. In addition, (a) in the figure shows a state in which the right circularly polarized light 31R in the selective reflection wavelength region indicating image light is diffusely reflected by the polarization selective reflection layer 11, and (b) in the figure is originally transmitted. A state in which ambient light to be reflected (including left circularly polarized light 31L within the selective reflection wavelength region, right circularly polarized light 32R outside the selective reflection wavelength region, and left circularly polarized light 32L outside the selective reflection wavelength region) is interface-reflected by the polarization selective reflection layer 11 Indicates.
The projection system includes a projection screen 10 and a projector 21 that projects image light on the projection screen 10. The projector 21 is disposed, for example, on the observation side (observer 50 side) of the projection screen 10, and projects the right circularly polarized light 31 </ b> R onto the projection screen 10.
The projection screen 10 is a projection screen including a polarization selective reflection layer 11 and a support base 12, and the polarization selection reflection layer 11 includes partial selective reflection layers 11 a, b, and c stacked on each other, The partial selective reflection layer 11c, the partial selective reflection layer 11b, and the partial selective reflection layer 11a are laminated in this order from the observation side to the support base 12 side.
As described above, the projection screen 10 has polarization separation property, wavelength selectivity property, and scattering property by the polarization selective reflection layer 11, and suppresses the influence of ambient light (external light, illumination light, etc.) and contrast of the image. Can be increased.

  In this projection system, right circularly polarized light 31 </ b> R that is image light to be reflected by the polarization selective reflection layer 11 is projected from the projector 21 onto the projection screen 10 as shown in FIG. Therefore, the right circularly polarized light 31 </ b> R is diffusely reflected inside the partial selective reflection layers 11 a, b, and c included in the polarization selective reflection layer 11 due to the polarization separation property, wavelength selectivity, and scattering property of the polarization selective reflection layer 11. Thus, the diffuse reflected light 33 is obtained.

Further, in the projection system, when used indoors or the like, as shown in (b) in the figure, the ambient light 31L, 32R, 32L that should not be reflected by the polarization selective reflection layer 11 is appropriately reflected on the projection screen 10. Is projected from the illumination light source 23 or the like.
The ambient lights 31L, 32R, and 32L are originally transmitted through the polarization selective reflection layer 11 due to the polarization separation property of the polarization selective reflection layer 11 and are incident on the support substrate 12, but when the light passes through the polarization selective reflection layer 11. The polarization state is somewhat disturbed, the interface E by the partial selective reflection layer 11c and the partial selective reflection layer 11b, the interface F by the partial selective reflection layer 11b and the partial selective reflection layer 11a, the partial selective reflection layer 11a and In some cases, the interface G is reflected at the interface G by the support base 12 and becomes interface reflected light 33B as shown in the figure.
The right circularly polarized light 31R described above is also somewhat disturbed in the polarization state when transmitted through the polarization selective reflection layer 11, and is reflected at the interfaces E, F, and G, respectively. The case where it becomes light is also assumed.

  Further, since the interface reflected light 31B is emitted to the observation side as shown in FIG. 4B, for example, the observer 50 observes not only the diffuse reflected light 33 but also the interface reflected light 31B. In some cases, the visibility of the video on the projection screen 10 may decrease.

  Therefore, in order to prevent the visibility on the projection screen 10 from being lowered, it is necessary to consider the amount of the interface reflected light 31B based on the ambient light 31L, 32R, 32L described above, and the projection screen 10- according to the present embodiment. In 1 (described later), instead of the polarization selective reflection layer 11, a polarization selective reflection layer 11-1 in which the interface itself is reduced by at least one is provided.

FIG. 12 is a diagram illustrating a reflection band of the polarization selective reflection layer 11-1 according to the present embodiment. The horizontal axis represents wavelength (λ) and the vertical axis represents reflectance (R).
FIG. 13 is a schematic sectional view showing the projection screen 10-1 according to the present embodiment.
When the wavelength band of green (G) and red (R) among the three primary colors of light is included in the wavelength bandwidth of the selective reflection wavelength band with one spiral pitch length, the cholesteric liquid crystal structure is discontinuously different. It is preferable to have two types of helical pitch lengths, so that the reflection band of the polarization selective reflection layer 11-1 can be set to a range corresponding to the wavelength range of blue (B), green (G) and It can be divided into ranges corresponding to the red (R) wavelength region (details will be described later).
Specifically, the polarization selective reflection layer 11-1 includes a partial selective reflection layer 11a that selectively reflects light in the blue (B) wavelength region, and green (G) and red (R), as illustrated. And a partial selective reflection layer 11d that selectively reflects light in the wavelength range of the partial selective reflection layer 11a, the partial selective reflection layer 11d, or the partial selective reflection layer from the observation side to the support base material 12 side. 11d and the partial selective reflection layer 11a are stacked in this order.

Here, the partial selective reflection layer 11d will be described in detail.
In the partial selective reflection layer 11d, for example, in order to selectively reflect light in the green (G) and red (R) wavelength regions, a birefringence value Δn (usually about 0.1: Formula (2) By adding a liquid crystalline composition (for example, Δn is about 0.3), the wavelength bandwidth Δλ centered on the selective reflection center wavelength λ ₀ can be increased. The layer can selectively reflect light in the green (G) and red (R) wavelength regions.

Here, the wavelength bandwidth (band) Δλ in the partial selective reflection layer 11d will be described. For comparison with the polarization selective reflection layer 11 described above, the band Δλ in the partial selective reflection layers 11b and 11c (see FIGS. 5 and 10) will also be described.
The partial selective reflection layer 11b is a layer that selectively reflects green (G) light. For example, when the selective reflection center wavelength λ ₀ is 550 nm,
p = λ ₀ /nav=550/1.55=355 nm
It becomes. In addition, nav is an average refractive index as described above, and generally has a value of 1.5 to 1.6.
Therefore, according to Equation (2), Δλ1 = Δn · p = 0.1 × 355 = 36 nm. Δn is a birefringence as described above, and is usually around 0.1.
On the other hand, in the case of a wide band, nav = 1.55 to 1.65 and Δn = 0.2 to 0.3. Therefore, according to equations (1) and (2),
p = 550 / 1.6 = 344 nm, Δλ2 = 0.2 × 344 = 69 nm
It becomes.

The partial selective reflection layer 11c is a layer that selectively reflects red (R) light. For example, when the selective reflection center wavelength λ ₀ is 600 nm, the calculation method described above
Δλ1 = 40 nm, Δλ2 = 76 nm
It becomes.

The partial selective reflection layer 11d is a layer that selectively reflects green (G) and red (R) light, and has a selective reflection center wavelength λ _{0 in} the range of 540 to 570 nm and 580 to 620 nm, respectively. For example, in the case of 540 to 620 (band: 80) nm, the green (G) and red (R) bands are calculated by the partial selective reflection layers 11a and 11b at both ends of the band, respectively. It is calculated by adding Δλ1 / 2. Therefore, Δλ = 36/2 + 80 + 40/2 = 118 nm.
In the case of 550 to 600 (band: 50) nm, the green (G) and red (R) bands are calculated as Δλ = 36/2 + 50 + 40/2 = 88 nm by the same calculation method. .
On the other hand, in the case of a wide band, the green (G) and red (R) bands are Δλ = 69/2 + 80 + 76/2 = 153 nm and Δλ = 69/2 + 50 + 76/2 = 123 nm, respectively, by the same calculation method. Become.

  Further, the film thickness of the partial selective reflection layer 11d that diffusely reflects green (G) and red (R) in one layer is the same as that of the partial selective reflection layer 11b that diffusely reflects green (G), and the red (R) is diffusely reflected. Since the film thickness can be made smaller than the thickness when the partial selective reflection layer 11c to be laminated is laminated, the so-called retardation effect can be reduced, and as a result, the reflection efficiency can be improved.

Next, a method for manufacturing the partial selective reflection layer 11d described above will be schematically described (for details, refer to Japanese Patent Application Laid-Open No. 2002-286935 already filed by the present applicant).
However, in order to apply this manufacturing method to this embodiment, in order to make the cholesteric liquid crystal structure of the partial selective reflection layer 11d into a liquid crystal structure having a diffusibility in which the planar alignment state is broken, an alignment film (partial selective reflection) is used. It is necessary not to use (having an orientation function for maintaining the horizontal state of the spiral structure region 30 included in the layer 11d).

  Specifically, a cholesteric liquid crystal solution to which a photopolymerization initiator is added is applied to an appropriate substrate having no alignment function described above to form an uncured liquid crystal layer, and then irradiated with ultraviolet rays (irradiation intensity here) The surface on the observation side of the liquid crystal layer is kept at normal pressure while the uniform helical pitch length p is maintained. An air atmosphere having an oxygen concentration of 10% or more, and further by gradually reducing the oxygen partial pressure in the air atmosphere and heating the substrate, the helical pitch length p continuously varies in the thickness direction, As a result, the partially selective reflection layer 11d in which no interface is generated can be manufactured.

  Specifically, by continuously changing the concentration of the chiral agent that controls the helical pitch length p in the thickness direction, for example, the helical pitch length p on the observation side becomes a shorter pitch or a longer pitch. Thus, a cholesteric liquid crystal structure in which no interface is generated in the partially selective reflection layer 11d can be constructed.

Next, the effect obtained by the lamination order of the partial selective reflection layers 11a and 11d in the polarization selective reflection layer 11-1 will be described.
Each of the three primary colors of light (red (R), green (G), and blue (B)) has a unique property. Hereinafter, blue (B) among the three primary colors of light will be described.
As described above, the polarization selective reflection layer 11-1 has a cholesteric liquid crystal structure, and the cholesteric liquid crystal structure includes a helical structure region 30 that is a liquid crystal molecule. A liquid crystal molecule is an organic compound and has a property of absorbing (or scattering) light having a wavelength region on the short wavelength side in the visible light region (for example, a wavelength region of 400 to 700 nm).
When the polarization selective reflection layer 11-1 is a layer polymerized by ultraviolet rays, the polarization selective reflection layer 11-1 after polymerization has a property of absorbing ultraviolet rays. Among the three primary colors, it has the property of easily absorbing blue (B) light that is closer to ultraviolet rays.

Here, among the three primary colors of light, the wavelength range of blue (B) is located on the short wavelength side compared to the wavelength ranges of other three primary colors, green (G) and red (R) (FIG. 3). reference).
Therefore, blue (B) of the three primary colors of light is the color that is most easily absorbed (or scattered) by the liquid crystal molecules. For example, the blue (B) is absorbed (or scattered) more than necessary by the liquid crystal molecules. As a result, the reflection efficiency and definition of blue (B) are reduced, and as a result, the visibility of the video is reduced.

  Here, when the partial selective reflection layer 11d is provided on the observation side of the partial selective reflection layer 11a (see FIG. 13), the blue (B) light is substantially transmitted through the partial selective reflection layer 11d. The liquid crystal molecules contained in the partial selective reflection layer 11d are absorbed (or scattered). Accordingly, the amount of light of blue (B) light has already decreased before reaching the partial selective reflection layer 11a, and as a result, the reflection efficiency of blue (B) light is reduced.

On the other hand, by arranging the partial selective reflection layer 11a that selectively reflects light in the blue (B) wavelength region on the outermost surface on the observation side (see FIG. 13), the blue (B) light There is no influence from the layer (absorption or scattering from liquid crystal molecules).
Therefore, in the polarization selective reflection layer 11-1, the partial selective reflection layers 11a and 11d are laminated in this order from the observation side to the support base 12 side in the order of the partial selective reflection layer 11a and the partial selective reflection layer 11d. The light reflection efficiency of B) can be increased, and the visibility of the image can be improved.

Next, green (G) among the three primary colors of light will be described.
FIG. 14 is a diagram showing a visibility curve. The horizontal axis represents wavelength (unit: nm), and the vertical axis represents specific luminous efficiency.
Visibility is a value indicating the sensitivity of eyes to light (sensitivity of feeling “brightness”), and differs depending on the wavelength (for example, the maximum is at a wavelength of 555 nm). The visibility curve relatively shows the visibility at other wavelengths with the wavelength 555 nm as a reference (specific luminous sensitivity = 1).
Here, as described above, the wavelength range of green (G) is 540 to 570 nm, and as shown in the figure, the specific luminous sensitivity of green (G) is that of red (R) and blue (B). Greater than specific visibility.
Accordingly, among the three primary colors of light, green (G) is the color that most feels “brightness” to the eye. For example, when the reflection efficiency of green (G) is low, the observer darkens the image. I feel it.

  Here, when the partial selective reflection layer 11a is provided on the observation side of the partial selective reflection layer 11d (see FIG. 13), the green (G) light is substantially transmitted through the partial selective reflection layer 11a. , Subjected to phase difference action. Specifically, circularly polarized light with good reflection efficiency (for example, right circularly polarized light) is distorted in its polarization state by receiving a phase difference effect, and becomes, for example, elliptically polarized light (for example, right elliptically polarized light). As a result, the reflection efficiency is lowered.

On the other hand, by disposing a partial selective reflection layer 11d that selectively reflects light in the green (G) and red (R) wavelength regions on the outermost surface on the observation side (see FIG. 13), the green (G) The light does not receive the phase difference effect from the partial selective reflection layer 11a.
In particular, in the partial selective reflection layer 11d, as described above, the spiral pitch length is continuously changed so that the concentration of the chiral agent is increased toward the observation side and the spiral pitch length is decreased toward the observation side. For example, since a layer that selectively reflects light in the green (G) wavelength region can be stacked on the observation side, the reflection efficiency of green (G) light can be further increased. it can.
Therefore, in the polarization selective reflection layer 11-1, the partial selective reflection layers 11a and 11d are laminated in this order from the observation side to the support base material 12 side in the order of the partial selective reflection layer 11d and the partial selective reflection layer 11a. The reflection efficiency of green (G) light having the highest visibility among the three primary colors can be increased, the brightness of the image can be improved, and the visibility can be improved.

Next, a case where the above-described projection screen 10-1 is applied to a projection system will be described.
FIG. 15 is a conceptual diagram of a projection system using the projection screen 10-1. Note that, in the projection screen 10-1 shown below, the same members as those of the projection screen 10 are denoted by the same reference numerals, and descriptions of overlapping portions such as functions are omitted as appropriate.
The projection system includes a projection screen 10-1 and a projector 21 that projects image light on the projection screen 10-1. For example, the projector 21 is disposed on the observation side (the observer 50 side) of the projection screen 10-1, and projects the right circularly polarized light 31R onto the projection screen 10-1.
The projection screen 10-1 is a projection screen provided with a polarization selective reflection layer 11-1 and a support substrate 12, and the polarization selective reflection layer 11-1 is partially laminated with the partial selective reflection layers 11a and 11d. For example, the partial selective reflection layer 11a and the partial selective reflection layer 11d are laminated in this order from the observation side to the support base 12 side (note that the lamination order may be reversed).

  In this projection system, as shown in (a) in the figure, right circularly polarized light 31R, which is image light to be reflected by the polarization selective reflection layer 11, is projected from the projector 21 onto the projection screen 10-1. Therefore, the right circularly polarized light 31 </ b> R is diffusely reflected inside the partial selective reflection layers 11 a and 11 d included in the polarization selective reflection layer 11, and becomes diffusely reflected light 33.

Further, in the projection system, when used indoors or the like, as shown in (b) in the figure, the ambient light 31L, 32R that should not be reflected by the polarization selective reflection layer 11-1 on the projection screen 10-1. 32L is projected from an appropriate illumination light source 23 or the like.
Here, since the partial selective reflection layer 11d can selectively reflect light in the green (G) and red (R) wavelength ranges in one layer, the polarization selective reflection layer 11-1 is polarized selective reflection. Compared to the layer 11, the number of interfaces per se is reduced.

Specifically, the polarization selective reflection layer 11 has three interfaces E, F, and G, but the polarization selective reflection layer 11-1 has two interfaces (partial selective reflection layer 11a and partial selection). There are only the interface H due to the reflective layer 11d and the interface I) due to the partially selective reflective layer 11d and the support substrate 12.
That is, the ambient light 31L, 32R, and 32L are reflected at the two interfaces H and I, respectively, as shown in the figure. Therefore, the interface reflected light 33B having a light amount reduced compared to the interface reflected light 33B on the projection screen 10. -1 will result.
The right circularly polarized light 31R described above is also somewhat disturbed in the polarization state when transmitted through the polarization selective reflection layer 11, and is reflected at the interfaces H and I, respectively, and becomes interface reflected light. However, the amount of interface reflected light can be reduced as compared with the projection screen 10.

Therefore, according to the projection screen 10-1, when the interface reflected light 31B-1 is emitted to the observation side, the observer 50 observes not only the diffuse reflected light 33 but also the interface reflected light 31B-1. However, since the light quantity of interface reflected light 31B-1 is reducing compared with the light quantity of interface reflected light 31B, it can prevent that the visibility of an image | video falls.
In the case where the projector 21 projects image light in four wavelength bands (for example, image light in which any one color such as cyan, magenta, etc. is added to red, green, and blue which are the three primary colors of light) The partial selective reflection layer 11a may diffusely reflect image light of two wavelength bands (here, blue, one added color), and the partial selective reflection layer 11d may reflect image light of three wavelength bands (here. Then, red, green, and one additional color) may be diffusely reflected, and further, a partial selective reflection layer (here, the added one) for diffusely reflecting the image light of one added wavelength band. One layer of color (not shown) may be added.

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

(2) It may be a layer that diffusely reflects linearly polarized light as light of a specific polarization component. Here, the linearly polarized light can be classified into two polarization states and has two directions orthogonal to each other. Therefore, the direction of the linearly polarized light of the projector that emits the linearly polarized light and the linearly polarized light that is diffusely reflected by this layer. By matching the direction, the image can be displayed brightly.
In addition, as a layer that diffusely reflects linearly polarized light as light of a specific polarization component, for example, there is a diffusive multilayer reflective polarizing material (such as DBEF manufactured by 3M) formed of materials having different refractive indexes. .

  Since linearly polarized light can be expressed by combining so-called P-polarized light (component parallel to the incident surface) and S-polarized light (component perpendicular to the incident surface), a layer that diffusely reflects this linearly polarized light If only the light of a specific polarization component (for example, P-polarized light or S-polarized light) is diffusely reflected, the contrast of the image can be increased as in the polarization selective reflection layer 11 described above, and the projected image If the light mainly includes P-polarized light or S-polarized light, the image light can be efficiently reflected.

  Next, a method for manufacturing the projection screen 10 including the basic structure of the present embodiment as described above will be described.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

  Therefore, the projection screen 10 includes the polarization selective reflection layer 11 having a cholesteric liquid crystal structure that selectively reflects light of a specific polarization component, and variation in the direction of the spiral axis L of the spiral structure region 30 included in the cholesteric liquid crystal structure. Due to the structural non-uniformity of the cholesteric liquid crystal structure due to the above, light that is selectively reflected is diffused.

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

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

  As described above, according to the projection screen 10-1 according to this embodiment including the projection screen 10 as a basic structure, the influence of ambient light such as external light and illumination light is suppressed by the polarization separation characteristic of the cholesteric liquid crystal structure. While enhancing the contrast of the image, the structural non-uniformity of the cholesteric liquid crystal structure can give a scattering effect to the reflected light of the image light without degrading the visibility of the image. Furthermore, in the laminated structure of the polarization selective reflection layer 11-1 that diffusely reflects light of a specific polarization component while displaying clearly, light (green (G) and red (R)) having different intensity peak wavelengths is 1 By including the partial selective reflection layer 11d that diffusely reflects in the layer, the number of interfaces in the polarization selective reflection layer 11-1 is reduced, and the amount of interface reflected light is reduced. It is possible to improve the visibility of the image.

  In addition, according to the present embodiment, the polarization selective reflection layer 11-1 selectively reflects light in a specific wavelength region that covers only a part of the visible light region. The contrast of the image can be increased by further suppressing the influence of ambient light such as light, and the visibility of the image can be further improved.

Projection system

Next, a projection system using the projection screen 10-1 according to the above-described embodiment will be described. As shown in FIG. 16, the projection screen 10-1 can be used by being incorporated in a projection system 20 including a projector 21.
FIG. 16 is a schematic diagram illustrating an example of a projection system including the projection screen 10-1.
FIG. 17 is a schematic diagram illustrating another example of the projection system including the projection screen 10-1.

As shown in FIG. 16, the projection system 20 includes a projection screen 10-1, a projector 21 that projects image light on the projection screen 10-1, a polarization conversion element 22, an illumination light source 23, and a polarizing film 24. And an illumination light source installation unit 25 and the like.
The projection screen 10-1 includes a polarization selective reflection layer 11-1 and a support base 12, and the polarization selective reflection layer 11-1 includes partial selective reflection layers 11a and 11d stacked on each other. For example, the partial selective reflection layer 11a and the partial selective reflection layer 11d are laminated in this order from the observation side to the support base 12 side.

  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 on the projection screen 10-1 by the projector 21 is light having the same polarization component as the light component selectively reflected by the projection screen 10-1 (for example, right circularly polarized light). It is preferable to contain mainly. At this time, the polarization conversion of the image light is performed by the polarization conversion element 22. For example, when the image light is converted into a circularly polarized light, a circularly polarizing plate is used.

  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, a phase difference plate can be used as the polarization conversion element 22. By emitting the image light emitted from the projector 21 via the phase difference plate 22 or the like, linearly polarized light can be converted into circularly polarized light without loss of light quantity.

  In addition, as the polarization conversion element (here, the phase difference plate) 22, one having a quarter wavelength phase difference is preferably used. Specifically, the phase difference of 137.5 nm is matched to 550 nm, which has the highest visibility. The one with 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 FIGS. 16 and 17, the phase difference plate 22 may be incorporated in the projector 21 in addition to being attached to the exit of the projector 21 as an external attachment.

  On the other hand, when a CRT or DLP projector is used as the projector 21, the light emitted from the projector 21 is non-polarized light. It is necessary to arrange a circularly polarizing plate made of a retardation plate. In this case, although the light quantity of the projector 21 itself is halved, it is 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 10-1 (for example, left circularly polarized light). It is possible to effectively prevent the occurrence of stray light and increase the contrast of the image. In addition, when linearly polarized light is used by the optical system inside the projector, only a retardation plate may be used without using a linearly polarizing plate.

  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. On the other hand, light having a selective reflection center wavelength in the range of 430 to 460 nm, 540 to 570 nm, and 580 to 620 nm is projected on the basis of the case where light is incident vertically. For this reason, in the projection screen 10-1, it is preferable to selectively reflect only light in a wavelength region corresponding to the wavelength region of the image light projected by the projector 21. Thereby, reflection of light in the visible light range that is out of the above-described wavelength range among ambient light such as external light and illumination light can be prevented, and the contrast of the image can be increased.

  In addition, the projection system 20 is normally provided with the illumination light source 23 installed in the illumination light source installation part 25, such as an indoor ceiling, and illuminates the observation space where the projection screen 10-1 is installed.

  Here, as shown in FIG. 16, when the illumination light source 23 is arranged so that the illumination light emitted from the illumination light source 23 is directly irradiated onto the projection screen 10-1, the illumination light source 23. So that the illumination light 34 emitted toward the projection screen 10-1 mainly includes light having a polarization component different from the polarization component of light selectively reflected by the projection screen 10-1 (for example, left circularly polarized light). It is preferable to do. Thereby, it is possible to effectively prevent the illumination light from being reflected by the polarization selective reflection layer 11 of the projection screen 10-1, thereby increasing the contrast of the image.

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

In the projection system 20 shown in FIG. 16, the illumination light emitted from the illumination light source 23 is directly irradiated onto the projection screen 10-1, but not limited thereto, as shown in FIG. The illumination light source 23 is installed in the illumination light source installation unit 26 other than the ceiling, and the illumination light 35 emitted from the illumination light source 23 passes on the projection screen 10-1 as illumination light 35 'via the illumination light reflector 27 such as the ceiling. The same applies to the case of indirect irradiation.
However, in this case, since the polarization state of the circularly polarized light is reversed when the light is reflected by the illumination light reflector 27, the illumination light 35 emitted from the illumination light source 23 toward the illumination light reflector is as shown in FIG. As in the case shown in FIG. 4, by arranging a polarizing film 24 ′ that transmits right circularly polarized light, light having the same polarization component as that of the light selectively reflected by the projection screen 10-1 (for example, right It is preferable to mainly include (circularly polarized light).
In addition, as polarizing film 24 ', the thing similar to the polarizing film 24 mentioned above can be used. Thereby, the illumination light 35 ′ whose polarization state is reversed by the illumination light reflector 27 is light having a polarization component different from the polarization component of the light selectively reflected by the projection screen 10-1 (for example, left circular polarization). Thus, it is possible to effectively prevent the illumination light 35 ′ from being reflected by the polarization selective reflection layer 11 of the projection screen 10-1, thereby increasing the contrast of the image.

  When the projection screen 10-1 according to the present embodiment is applied to the projection screen 20, the polarization selective reflection layer 11-1 that diffuses and reflects light of a specific polarization component has its intensity peak wavelength as described above. A partial selective reflection layer 11d that diffusely reflects light (green (G) and red (R)) in different layers and a partial selective reflection layer 11a that diffuses and reflects light having a wavelength range indicating blue (B). Since they have a structure in which they are stacked on each other, the number of interfaces in the polarization selective reflection layer 11-1 can be reduced. As a result, the interface reflected light 31B-1 based on ambient light and / or ambient light can be reduced. The light quantity of the interface reflection light based on this can be reduced, and the visibility of an image | video can be improved.

  Next, the embodiment described above will be specifically described.

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

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

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

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

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

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

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

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

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

  As described above, as the polarization selective reflection layer, the first partial selective reflection layer that selectively reflects light in the blue (B) wavelength region (light having a selective reflection center wavelength at 440 nm), and green (G) A second partial selective reflection layer that selectively reflects light in the wavelength range (light having a selective reflection center wavelength at 550 nm) and light in the red (R) wavelength range (light having a selective reflection center wavelength at 600 nm). ) Was selectively laminated with the third partial selective reflection layer in order from the support base material side to obtain a projection screen 2 as a comparative example (described later). The thickness of the first partial selective reflection layer was 3 μm, the thickness of the second partial selective reflection layer was 4 μm, and the thickness of the third partial selective reflection layer was 5 μm. The cholesteric liquid crystal structure of each partial selective reflection layer of the polarization selective reflection layer of the projection screen thus obtained was not in the planar alignment state.

A projection screen 1 was prepared. The projection screen 1 is a screen having a laminated structure composed of two layers, and in order from the support substrate side, a first partially selective reflection layer having a wide reflection wavelength band, and a wavelength range indicating blue (B) And a second partial selective reflection layer that selectively reflects light having a thickness. This second partial selective reflection layer corresponds to the first partial selective reflection layer on the projection screen 2 and is formed by the same manufacturing method.
The first partially selective reflection layer (cholesteric liquid crystal layer) on the projection screen 1 controls the mixing ratio of the nematic liquid crystal and the chiral agent by using a solution prepared by the same method as each cholesteric liquid crystal solution described above. By doing so, a selective reflection center wavelength was set at 560 nm.
Furthermore, the cholesteric liquid crystal layer is irradiated with 310 nm ultraviolet light at an irradiation intensity of 3 mW / cm ² for 3 minutes in the air (90 ° C.) to cure the cholesteric liquid crystal layer, thereby reflecting the reflection wavelength band to 520 to 650 nm. A first partially selective reflection layer having a thickness of 5 μm was obtained.

(Comparative example)
A projection screen 2 was prepared. As described above, the projection screen 2 is a screen having a cholesteric liquid crystal structure in which the planar alignment state is broken.
A projection screen 3 was prepared. As the projection screen 3, a commercially available mat screen was used.

(Evaluation results)
The contrast of each of the projection screens 1, 2, 3 was measured using a DLP projector.
A circularly polarizing plate was arranged at the exit of the projector so that the emitted light was circularly polarized. The projector was placed at a distance of about 2.5 m from each of the projection screens 1, 2, and 3. The projected image is displayed in full white so that the reflection of the projector light source can be easily confirmed. In addition, the evaluation of the visibility of the image on the entire screen was a still image with white and black areas.

  For indoor lighting, a fluorescent lamp (without polarization control) is used, and the fluorescent lamp is set so that the illumination light from the fluorescent lamp enters each projection screen 1, 2, 3 at an angle of about 50 degrees from the ceiling. Arranged. In this case, the brightness directly below each of the projection screens 1, 2, 3 was 200 lx (manufactured by Topcon).

In addition, each of the projection screens 1, 2 and 3 was arranged perpendicular to the floor, and the contrast of the front of the screen was measured using a luminance meter (Topcon luminance meter BM-8). The contrast is the luminance of the white display portion / the luminance of the black display portion.
As a result, in the projection screen 2, the brightness of black display was high due to scattering, and the contrast was 30. On the projection screen 3, the black display was whitened by the brightness of the external light, and the contrast was 4.
On the other hand, in the projection screen 1, since the scattering is small and the brightness of the black display is lowered, the contrast is 50, and the visibility of the image can be improved.

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

Explanation of symbols

DESCRIPTION OF SYMBOLS 10,10-1 Projection screen 11,11-1 Polarization selective reflection layer 11a, 11b, 11c, 11d Partial selective reflection layer 12, 12A, 12B, 12C Support base material 13 Intermediate | middle layer 14 Support film 15 Light absorption layer 16 Light reflection Layer 17 Adhesive layer 18 Release film 19 Functionality retaining layer 20 Projection system 21 Projector 22 Retardation plate 23 Illumination light source 24, 24 'Polarization film 25, 26 Illumination light source installation part 27 Illumination light reflector 30 Helical structure region 31R Selective reflection Right circularly polarized light within the wavelength region 31L Left circularly polarized light within the selective reflection wavelength region 32R Right circularly polarized light outside the selective reflection wavelength region 32L Left circularly polarized light outside the selective reflection wavelength region 33 Reflected light 34, 35, 35 ′ Illumination light

Claims (14)

A projection screen that diffuses and reflects image light, which is light of a specific polarization component projected from the observation side, and displays an image,
A first partial selective reflection layer that diffusely reflects image light having a wavelength range indicating red and green;
A second partial selective reflection layer that diffusely reflects image light having a wavelength range indicating blue;
Projection screen with. The projection screen according to claim 1,
Image light having wavelength ranges indicating red, green, and blue are included in 580 to 620 nm, 540 to 570 nm, and 430 to 460 nm, respectively.
Projection screen featuring. The projection screen according to claim 1 or 2,
The reflection wavelength region of the first partial selective reflection layer is 540 to 620 nm,
The reflection wavelength region of the second partial selective reflection layer is 430 to 460 nm,
Projection screen featuring. The projection screen according to any one of claims 1 to 3,
The light of the specific polarization component is right circularly polarized light or left circularly polarized light,
Projection screen featuring. The projection screen according to any one of claims 1 to 3,
The light of the specific polarization component is one linearly polarized light;
Projection screen featuring. The projection screen according to any one of claims 1 to 5,
The first partial selective reflection layer and the second partial selective reflection layer include a polarization reflection layer that reflects light of the specific polarization component, and a diffusion element that diffuses light reflected by the polarization reflection layer. ,
Projection screen featuring. The projection screen according to any one of claims 1 to 5,
The first partial selective reflection layer and the second partial selective reflection layer have diffusibility by themselves;
Projection screen featuring. The projection screen according to any one of claims 1 to 7,
The first partial selective reflection layer and the second partial selective reflection layer have a cholesteric liquid crystal structure, and diffuse light of a specific polarization component due to structural non-uniformity of the cholesteric liquid crystal structure;
Projection screen featuring. The projection screen according to claim 8.
The cholesteric liquid crystal structure includes a plurality of spiral structure regions having different spiral axis directions;
Projection screen featuring. The projection screen according to any one of claims 1 to 9,
The first partial selective reflection layer is made of a material having a large birefringence value;
Projection screen featuring. The projection screen according to any one of claims 8 to 10,
The cholesteric liquid crystal structure of the first partial selective reflection layer has a helical pitch length continuously different in the thickness direction;
Projection screen featuring. A projector that projects image light in at least three wavelength bands;
A projection screen that diffusely reflects light of a specific polarization component;
A projection system comprising:
The projection screen is
A first partial selective reflection layer that diffusely reflects image light in at least two wavelength bands of the image light;
A second partial selective reflection layer that diffusely reflects image light in at least one remaining wavelength band of the image light;
Including,
Projection system characterized by. The projection system according to claim 12, wherein
The light of the specific polarization component is right circularly polarized light or left circularly polarized light,
Projection system characterized by. The projection system according to claim 12, wherein
The light of the specific polarization component is one linearly polarized light;
Projection system characterized by.

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