JP4184187B2 - Projection screen - Google Patents

Description

  The present invention relates to a projection screen used for projection by a projector, for example.

2. Description of the Related Art Conventionally, a projection system for projecting light from a projector onto a projection screen and projecting an image or the like is used for business use or home use.
A projection screen used in such a projection system usually has a transparent or translucent porous fine particle held in a transparent medium and a reflective material disposed behind the transparent fine particle. 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 was a problem of being.
In order to solve such problems, a projection screen (see Patent Document 1) that suppresses reflection of external light or the like using cholesteric liquid crystal has been proposed. However, since the surface of the cholesteric liquid crystal is a mirror surface, since the projected light is specularly reflected, it has not been put into practical use.

  As another method, Patent Document 2 discloses a projection screen that uses a diffusive multilayer reflective polarizer or the like as a reflective polarization element. In addition to preventing reflection of light, the reflection of the reflected light is imparted by interfacial reflection of materials having different refractive indexes constituting the multilayer reflective polarizing material or by a diffusing element provided separately from the multilayer reflective polarizing material. Things are listed. Further, the projection screen uses a cholesteric reflective polarizing material as a reflective polarizing element, and the reflective polarizing element and the diffusing element are used in combination. In addition, there is also described that the light is not reflected, and a scattering effect is given to the reflected light by a diffusing element provided separately from the cholesteric reflective polarizing material.

However, the former described in Patent Document 2 is based on a linear polarization element such as a multilayer reflective polarizing material (such as DBEF manufactured by 3M), and is incorporated in a projection system or the like. When used, it is necessary to match the plane of polarization with a projector such as a liquid crystal projector that emits linearly polarized light. If the planes of polarization do not match, good image display cannot be realized. There was a problem.
Moreover, in the latter thing described in the said patent document 2, although circularly polarizing elements, such as a cholesteric reflective polarizing material, are used as a reflective polarizing element, the spreading | diffusion provided in the observer side of the reflective polarizing element Since the element imparts a scattering effect to the reflected light, the polarization separation function provided by the reflective polarizing element is impaired, and there is a problem that the visibility of the image cannot be sufficiently improved.

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

  Furthermore, in the above document, there is no description regarding the reflection bandwidth, and when the outside light is non-polarized light, the light is reflected to an extra wavelength, and the visibility of the image cannot be sufficiently improved. There was a problem.

JP-A-5-107660 Special Table 2002-540445

  From the above, it is desired to provide a projection screen that can be used in a bright environment and has high brightness.

  The present invention has a base material, a selective reflection function that is formed on the base material and selectively reflects light of a specific polarization component, and a diffuse reflection function that diffuses and reflects light of the specific polarization component. Each of the reflection bands having a reflection intensity of 50% or more with respect to the intensity of the peak wavelength of the reflection intensity distribution having a plurality of peak wavelengths in the visible light region of the polarization selective reflection layer. A projection screen characterized in that the total width is 200 nm or less.

  According to the present invention, light having a wavelength other than the respective reflection bandwidths of the polarization selective reflection layer is absorbed by the polarization selective reflection layer without being substantially reflected. Therefore, by setting the total reflection bandwidth within a predetermined range, the influence of external light can be reduced even in the presence of external light or the like, and a projection screen with high contrast can be obtained. be able to. In addition, the selective reflection function of the polarization selective reflection layer absorbs light other than a specific polarization component and further reduces the influence of external light by half. Therefore, a projection screen with high color purity can be obtained.

  In addition, since the polarization selective reflection layer has the diffuse reflection function, it is possible to efficiently diffuse and reflect incident light, and it can be used as a projection screen. Furthermore, according to the present invention, it is possible to visually recognize an image without forming surface irregularities (matte shape) such as a glare-preventing layer, so that a clear image quality without roughness can be obtained. Possible projection screens.

  In the said invention, the said polarization selective reflection layer may have two peak wavelengths in the intensity distribution of the reflected light in visible region. In this case, for example, a polarization selective reflection layer in which a layer having the reflection band in the red and green wavelength regions and a layer having the reflection band in the blue wavelength region are stacked can be used. This is because a projection screen preferable in terms of cost can be obtained.

  The present invention also provides a base material, a selective reflection function which is formed on the base material and selectively reflects light of a specific polarization component, and diffuse reflection which diffuses and reflects the light of the specific polarization component. A polarization selective reflection layer having a function, and having a reflection intensity of 50% or more with respect to the intensity of the peak wavelength of the intensity distribution of the reflected light having a plurality of peak wavelengths in the visible light region of the polarization selective reflection layer. Provided is a projection screen characterized in that each of the reflection bandwidths is 75 nm or less.

According to the present invention, since each reflection bandwidth of the selective reflection layer is equal to or less than the above value, the color purity of light reflected by the projection screen is high, and high quality with good color reproducibility. Projection screen. In addition, the selective reflection function of the polarization selective reflection layer can reduce the influence of external light and the like, and can provide a high-quality projection screen with high contrast even in a bright environment.
In addition, since the polarization selective reflection layer has the diffuse reflection function, it is possible to efficiently diffuse and reflect incident light, and it can be used as a projection screen. Furthermore, according to the present invention, it is possible to visually recognize an image without forming surface irregularities (matte shape) such as a glare-preventing layer, so that a clear image quality without roughness can be obtained. Possible projection screens.

  In the above invention, the specific polarization component may be right circularly polarized light or left circularly polarized light. As a result, only light of a specific polarization component (for example, right circularly polarized light) is selectively reflected, so that only about 50% of ambient light such as external light or illumination light having no polarization characteristics is reflected by the polarization selective reflection layer. Can be. 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.

  In the above invention, the light of the specific polarization component may be one linearly polarized light. In this case, the light of a specific polarization component reflected by the polarization selective reflection layer is P-polarized light or S-polarized light, and only light of a specific polarization component (for example, P-polarized light) is selected by the polarization separation characteristic of the polarization selective reflection layer. Therefore, ambient light having no polarization characteristics, such as ambient light and illumination light, can be reflected by the polarization selective reflection layer only by about 50%. For this reason, even when the brightness of the bright display portion such as white display is the same, the brightness of the dark display portion such as black display can be substantially halved and the contrast of the image can be approximately doubled. At this time, 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. In addition, since the light of a specific polarization component is one of linearly 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.

  Here, in the above invention, the polarization selective reflection layer may be a layer having the selective reflection layer having the selective reflection function and the diffusion layer having the diffuse reflection function. This is because, by making the layer having the selective reflection function and the layer having the diffuse reflection function independent, it is possible to easily control the respective characteristics.

  In the invention, the polarization selective reflection layer may be a layer having the selective reflection function and the diffuse reflection function in one layer. This is because the selective reflection function and the diffuse reflection function can be achieved with one layer, and a projection screen that is preferable in terms of manufacturing efficiency and cost can be obtained.

  At this time, it is preferable that the polarization selective reflection layer has a cholesteric liquid crystal structure. This is because the cholesteric liquid crystal structure allows the projected light to be diffused without impairing the polarization dispersion function, thereby providing a projection screen with excellent image visibility. In addition, by polarizing the light projected from the projector into a predetermined circularly polarized light, the projected light can be efficiently reflected, and the external light can be reflected by the specific wavelength reflectivity and circular polarization of the cholesteric liquid crystal. This is because the influence of light reflection can be prevented, so that a projection screen with high brightness can be obtained even in a bright environment.

  In any one of the inventions described above, the polarization selective reflection layer has a selective reflection center wavelength of 430 nm to 460 nm, 540 nm to 570 nm, and 580 nm to 540 nm with respect to a case where light is perpendicularly incident on the polarization selective reflection layer. It is preferable to selectively reflect light existing in the range of 620 nm. This is because, for example, light in the wavelength range of the three primary colors irradiated from a liquid crystal projector or the like can be reflected, and a projection screen capable of good color display can be obtained.

According to the present invention, light having a wavelength other than the respective reflection bandwidths of the polarization selective reflection layer is absorbed by the polarization selective reflection layer without being substantially reflected. Therefore, by setting the total reflection bandwidth within a predetermined range, the influence of external light can be reduced even in the presence of external light or the like, and a projection screen with high contrast can be obtained. be able to. In addition, the selective reflection function of the polarization selective reflection layer absorbs light other than a specific polarization component, and can further reduce the influence of outside light by half. A projection screen with high color purity can be obtained.
In addition, since the polarization selective reflection layer has the diffuse reflection function, it is possible to efficiently diffuse and reflect incident light, and it can be used as a projection screen. Furthermore, according to the present invention, it is possible to visually recognize an image without forming surface irregularities (matte shape) such as a glare-preventing layer, so that a clear image quality without roughness can be obtained. Possible projection screens.

  Hereinafter, the projection screen of the present invention will be described in detail.

  The projection screen of the present invention has two modes depending on the reflection intensity of the polarization selective reflection layer. As a first aspect, a base material, a selective reflection function that is formed on the base material and selectively reflects light of a specific polarization component, and diffuses and reflects the light of the specific polarization component A polarization selective reflection layer having a diffuse reflection function, and having a reflection intensity distribution having a plurality of peak wavelengths in the visible light region of the polarization selective reflection layer, the reflection intensity of 50% or more with respect to the intensity of the peak wavelength. The total of the reflection bandwidths is 200 nm or less. As a second aspect, a base material, a selective reflection function that is formed on the base material and selectively reflects light of a specific polarization component, and diffuses and reflects the light of the specific polarization component. A reflection layer that has a diffuse reflection function, and reflects the intensity distribution of reflected light having a plurality of peak wavelengths in the visible light region of the polarization selection reflection layer with respect to the intensity of the peak wavelength of 50% or more. Each of the reflection bandwidths having intensities is 75 nm or less.

  In any embodiment, the projection screen has a base material 1 and a polarization selective reflection layer 2 formed on the base material 1 and is projected from the projector 3, for example, as shown in FIG. It diffuses and reflects light.

In any of the above aspects, the polarization selective reflection layer has a selective reflection function that selectively reflects light of a specific polarization component, and a diffuse reflection function that diffuses and reflects light of the specific polarization component. Have According to the present invention, from the selective reflection function of the polarization selective reflection layer, light other than a specific polarization component is absorbed, and the influence of external light can be halved. However, a projection screen with high contrast and high color purity can be obtained. In addition, the diffuse reflection function of the polarization selective reflection layer allows incident light to be efficiently diffusely reflected and used as a projection screen. Furthermore, according to the present invention, it is possible to visually recognize an image without forming surface irregularities (matte shape) such as a glare prevention layer, so that a clear image quality without roughness can be obtained. Can be a projection screen.
Hereinafter, each aspect will be described in detail.

A. First Aspect First, a first aspect of the projection screen of the present invention will be described. According to a first aspect of the projection screen of the present invention, there is provided a base material, a selective reflection function that is formed on the base material and selectively reflects light of a specific polarization component, and diffuses the light of the specific polarization component. And a polarization selective reflection layer having a diffuse reflection function of reflecting, and the reflection intensity distribution having a plurality of peak wavelengths in the visible light region of the polarization selective reflection layer is 50% or more with respect to the intensity of the peak wavelength. The total of the reflection bandwidths having a reflection intensity of 200 nm or less is 200 nm or less.

According to this aspect, when light is incident on the polarization selective reflection layer, the light incident on the polarization selective reflection layer is absorbed without being substantially reflected in a region other than the reflection band. Here, in general, the visible light region is 380 nm to 780 nm and its width is 400 nm, but the total of the reflection bandwidths in this embodiment is 200 nm or less. Accordingly, external light incident on the polarization selective reflection layer can be absorbed without being substantially reflected by more than half, and the polarization selective reflection layer has a selective reflection function as described above. Thus, the influence of external light can be further reduced. As a result, even in a bright environment where external light, illumination light, or the like exists, it is possible to obtain a projection screen with high contrast without being affected by such light.
Hereinafter, the projection screen of this aspect will be described for each configuration.

1. Polarization selective reflection layer First, the polarization selective reflection layer used in the projection screen of this aspect will be described. The polarization selective reflection layer used in this embodiment is formed on a base material to be described later, and selectively reflects light of a specific polarization component, and diffuses and reflects the light of the specific polarization component. And a reflection intensity distribution having a plurality of peak wavelengths in the visible light region of the polarization selective reflection layer, and having a reflection intensity of 50% or more with respect to the intensity of the peak wavelength. The total of the reflection bandwidths is 200 nm or less.

  The polarization selective reflection layer used in the projection screen of this aspect has a plurality of peak wavelengths (a, b, and c) in the reflection intensity distribution in the visible light region of the polarization selective reflection layer, for example, as shown in FIG. Is. Here, the peak wavelength in this embodiment means a wavelength at which the polarization selective reflection layer reflects incident light to the maximum.

The reflection bandwidth is a width of a wavelength having a reflection intensity of 50% or more with respect to the reflection intensity of the peak wavelength, and the polarization selective reflection layer used in this embodiment has this reflection bandwidth (for example, FIG. The total of Δλ _a , Δλ _b , and Δλ _c ) shown in 3 is 200 nm or less.

  In this embodiment, the total reflection bandwidth Δλ is preferably 200 nm or less, particularly 195 nm or less, particularly 180 or less. This is because it is possible to obtain a projection screen with less color influence and higher color purity.

  The reflection intensity can be measured with a general reflection intensity measuring device. Specifically, it can be measured by UV3100PC (manufactured by Shimadzu Corporation), goniophotometer (manufactured by Apex), or the like, and the reflection bandwidth can be calculated from a graph or the like of the measured value.

  Here, the light of the specific polarization component reflected by the polarization selective reflection layer may be one of linearly polarized light, right circularly polarized light, or left circularly polarized light. It is preferable to use left circularly polarized light.

The linearly polarized light can be divided into two polarization states and has two directions orthogonal to each other. Therefore, the direction of the linearly polarized light diffusely reflected by the polarization selective reflection layer is changed to the linearly polarized light of the projector that emits the linearly polarized light. By matching with the direction, the image can be displayed brightly.
Here, as a layer that diffuses and reflects one linearly polarized light as the light of such a specific polarization component, for example, a multilayer reflective polarizing material having a diffusibility formed by materials having different refractive indexes (manufactured by 3M) DBEF).

  In addition, when the light of the specific polarization component reflected by the polarization selective reflection layer is right circularly polarized light or left circularly polarized light, the non-polarized light incident along the helical axis in the polarization selective reflection layer is The light is separated into two polarization states (right circularly polarized light and left circularly polarized light), one is transmitted and the rest is reflected. This phenomenon is known as circular dichroism. For example, when a spiral direction in a 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. .

That is, for example, as shown in FIG. 2, unpolarized light (right circularly polarized light 11R and left circularly polarized light 11L within the selective reflection wavelength region, right circularly polarized light 12R outside the selective reflection wavelength region, and the like, which is incident from the viewer side of the projection screen. The left circularly polarized light 12L) has one circularly polarized component (for example, selective reflection) belonging to the range of the reflection 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 11R in the wavelength range is reflected as reflected light 13, and other light (for example, left circular polarized light 11L in the selective reflection wavelength range, right circular polarized light 12R and left circular polarized light 12L outside the selective reflection wavelength range) is transmitted. .

  Therefore, in this embodiment, the polarization selective reflection layer is a layer that reflects a specific wavelength of polarized light on the same side as the light emitted from a projector or the like, so that the projected light can be efficiently reflected, and the brightness The projection screen can be made high.

  Furthermore, when the light of a specific polarization component diffusely reflected by the polarization selective reflection layer is right circularly polarized light or left circularly polarized light, when the projector (liquid crystal projector, etc.) emits linearly polarized light, linearly polarized light By using a retardation plate for converting the light into circularly polarized light, there is also an advantage that a projection screen can be used regardless of the direction of linearly polarized light.

Examples of such a substance exhibiting circular dichroism include a liquid crystal compound having cholesteric liquid crystallinity. A liquid crystal compound exhibiting cholesteric liquid crystallinity has a helical structure in which the director of the liquid crystal molecules rotates continuously in the thickness direction of the layer as the physical molecular arrangement of the liquid crystal molecules. Based on the physical molecular arrangement, the light beam has a polarization separation characteristic that separates a circularly polarized light component in one direction and a circularly polarized light component in the opposite direction.
The reflection intensity peak (maximum optical rotation light scattering) of the liquid crystal compound having cholesteric liquid crystallinity occurs at the wavelength λ ₀ of the following formula (1), and the reflection bandwidth Δλ at this time is expressed by the following formula (2). Is done.
λ ₀ = nav · p (1)
Δλ = Δn · p (2)

  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), nav is the average refractive index in a plane perpendicular to the helical axis, and Δn is the birefringence value is there.

  Here, since the peak wavelength is proportional to the helical pitch length p of the liquid crystal compound having a cholesteric liquid crystal structure, as shown in the above formula (1), the polarization selective reflection layer has a plurality of reflection intensities. In order to have a peak wavelength, a plurality of types of liquid crystal compounds having a cholesteric liquid crystal structure are used in combination. In addition, since the reflection band Δλ is determined by the birefringence value Δn and the helical pitch length p as shown in Expression (2), in the present embodiment, the birefringence value Δn and the helical pitch are determined. By selecting a liquid crystal compound having a cholesteric liquid crystal structure with an appropriate length p and average refractive index nav, and appropriately combining these liquid crystal compounds, the total reflection bandwidth Δλ may be within a predetermined value. It can be done. Note that the birefringence value Δn of a liquid crystal compound having a cholesteric liquid crystal structure is usually about 0.1 to 0.3.

  Here, in this aspect, the polarization selective reflection layer has a plurality of the peak wavelengths with respect to the reflection intensity in the visible light region, and the total of the reflection bandwidths is not more than the above value, and the projector or the like. As long as it is possible to reflect light having a wavelength irradiated from the light source, the peak wavelength value of the polarization selective reflection layer is not particularly limited. For example, as shown in FIG. It may have three peak wavelengths (indicated by a, b, and c in the figure) by combining three kinds of substances having, and for example, substances having different peak wavelengths as shown in FIG. 2 may be combined to indicate two peak wavelengths (indicated by d and e in the figure).

  The polarization selective reflection layer used in this embodiment preferably has red (R), green (G), and blue (B) peak wavelengths, for example, red (R) and green (G). When the wavelength range is included in one reflection bandwidth, a substance having these wavelengths and a substance having a blue (B) wavelength may be used, and two peak wavelengths may be used. In particular, it is preferable to use materials having respective peak wavelengths of red (R), blue (B), and green (G) and to have three peak wavelengths. This is because the light normally emitted from the projector consists of red (R), blue (B), and green (G), and color display is realized by these three primary colors.

  In this aspect, although it depends on the type of the projector specifically as the above wavelength, blue (B) 430 nm to 460 nm, green (G) 540 nm to 570 nm, red (R) 580 nm to 620 nm It is preferable to selectively reflect the wavelength. This is because a color screen can be displayed even if there is a difference in wavelength depending on the design of the apparatus, the type of light source, and the like, and a projection screen capable of expressing good white can be obtained. For such a polarization selective reflection layer having a plurality of peak wavelengths, for example, when a layer made of a liquid crystal compound having a cholesteric liquid crystal structure is used, a layer having a cholesteric liquid crystal structure having each helical pitch length is laminated. Can be configured. In addition, in the polarization selective reflection layer in the case of having the above two peak wavelengths, for example, a polarization selective reflection layer can be formed by forming a layer composed of two types of cholesteric liquid crystals, which is preferable in terms of manufacturing efficiency and cost. Can be.

  Moreover, it is preferable that the polarization selective reflection layer (each layer in the case where the polarization selective reflection layer is composed of a plurality of layers) has a thickness that reflects 100% of specific polarized light. The reflectance with respect to the polarized light of the polarization selective reflection layer usually depends on the film thickness of the polarization selective reflection layer, and is 100% with respect to light of a specific polarization component that is selectively reflected (for example, right circularly polarized light). This is because the image light cannot be efficiently reflected when the reflectivity is less than that. For example, when a layer made of a liquid crystal compound having a cholesteric liquid crystal structure is used, the film thickness is usually preferably 4 to 8 pitches in order to make the reflectance 100%, specifically, Although it depends on the type of material of the polarization selective reflection layer and the wavelength of the specific polarization, it is usually 1 μm to 10 μm. If it is thinner than the above film thickness, the reflectance will be low, making it difficult to reproduce the image projected on the projection screen with good brightness, and if it is thicker than the above film thickness, it will be difficult to control the cholesteric liquid crystal structure. This is because unevenness may occur.

Here, the polarization selective reflection layer used in this aspect has a selective reflection function that selectively reflects light of a specific polarization component and a diffuse reflection function that diffuses and reflects light of the specific polarization component. A polarization selective reflection layer. Here, the polarized light selective reflection layer of this aspect may be a layer having the selective reflection layer having the selective reflection function and the diffusion layer having the diffuse reflection function. It may be a layer having a selective reflection function and the diffuse reflection function.
Hereinafter, each case will be described separately.
a. When the polarization selective reflection layer is a layer having the selective reflection layer having the selective reflection function and the diffusion layer having the diffuse reflection function First, the polarization selective reflection layer is a selective reflection layer having the selective reflection function The case of a layer having a diffusion layer having the diffuse reflection function will be described. When the polarized light selective reflection layer has the selective reflection layer and the diffusion layer, the layer having the selective reflection function and the layer having the diffuse reflection function are formed independently of each other. Thereby, it can be said that it is preferable at the point which can control each characteristic easily. Hereinafter, each layer will be described.

(I) Selective Reflection Layer The selective reflection layer in this aspect has a selective reflection function that selectively reflects the light of the specific polarization component described above, and the reflection bandwidth described above falls within the above range. If it is a thing, it will not specifically limit. Examples of such a selective reflection layer include those that perform specular reflection and those that have a cholesteric liquid crystal structure in a planar alignment state. Particularly, the above-described multilayer reflective polarizing material (DBEF manufactured by 3M), cholesteric Examples thereof include a layer made of a liquid crystal compound having a liquid crystal structure. By using such a layer as the selective reflection layer, polarization separation characteristics can be obtained and the reflection bandwidth can be obtained, so that a specific polarization component of the light projected from the projector can be obtained. This is because only the light can be reflected. Here, the selective reflection layer used in this embodiment is preferably a layer made of a liquid crystal compound having a cholesteric liquid crystal structure among the above. This is because it is possible to easily realize the reflection bandwidth by selecting and combining liquid crystal compounds having a cholesteric liquid crystal structure in which the birefringence value Δn, the helical pitch length p, and the average refractive index nav are appropriate. Because it becomes. The layer made of a liquid crystal compound having such a cholesteric liquid crystal structure will be described in “b. When the polarization selective reflection layer is a layer having a selective reflection function and a diffuse reflection function in one layer” described later. Since it can be formed by a method of forming a layer made of a liquid crystal compound having a general cholesteric liquid crystal structure using the same material as the layer, detailed description thereof is omitted here.

(Ii) Diffusion layer Next, the diffusion layer will be described. The diffusion layer used in this aspect has a diffusion function of diffusing the light reflected by the selective reflection layer. Usually, such a diffusion layer is provided on the observation side of the selective reflection layer in order to diffuse the light reflected by the selective reflection layer and emit it to the viewer side of the projection screen. Thereby, the light reflected by the selective reflection layer can be diffused, and the projection screen can be used even in a bright environment, has high brightness, and has excellent visibility.

  Specifically, examples of the diffusion layer include a bulk diffusion material, a surface diffusion material, a holographic diffusion material, and any combination of these diffusion materials. Specific examples of the bulk diffusing material include particles arranged in a transparent medium. Furthermore, examples of the surface diffusing material include a structural surface, a fine structure surface, and a roughened surface. The diffusion achieved by the diffusing material may be random or ordered, or it may be partially ordered.

b. When the polarization selective reflection layer is a layer having a selective reflection function and a diffuse reflection function in one layer Next, the polarization selective reflection layer is in the one layer with the selective reflection function and the diffuse reflection. A case where the layer has a function will be described. When the polarization selective reflection layer has the two functions described above, it is not necessary to form a diffusion layer or the like as described above, so that the manufacturing efficiency can be improved and the cost and the like can be improved. Therefore, a preferable projection screen can be obtained.

Such a polarized light selective reflection layer is not particularly limited as long as it has the selective reflection function and the diffuse reflection function in one layer. A layer made of a liquid crystal compound having a function and having a cholesteric liquid crystal structure is preferable.
In the case of a normal cholesteric liquid crystal structure, the surface is in a specular state, and the projected light is reflected only in a certain direction, so that it is difficult to use as a projection screen. Since the layer made of the liquid crystal compound having the structure has the diffuse reflection function, it can be used as a projection screen. Such a diffuse reflection function is obtained when, for example, as shown in FIG. 5, there is a variation in the direction of the helical axis L of the block structure 30 of the liquid crystal compound having a cholesteric liquid crystal property constituting the polarization selective reflection layer 2. Can do.

  Here, in a normal cholesteric liquid crystal structure, there are only spiral axes in the same direction as the normal of the substrate plane, and since these spiral axes are aligned and aligned, the incident light is in a certain direction. It will be reflected. On the other hand, in the polarization selective reflection layer having variations in the direction of the helical axis L, the light having a specific wavelength incident on the polarization selective reflection layer is not limited to a certain direction depending on the direction of the helical axis L, for example, FIG. As shown in FIG. 4, since the light is reflected in various directions, the incident light is scattered and reflected.

  As a method for forming such a polarization selective reflection layer having a variation in the direction of the helical axis, for example, a substrate that will be described later is generally not oriented in a certain direction, or a polarization selective reflection layer is generally used. Examples thereof include a method for adjusting the amount of the leveling agent used and a method for adding a non-liquid crystal polymerizable compound in the polarization selective reflection layer. These methods may be used in combination. As a result, the alignment in the cholesteric liquid crystal structure is disturbed, and incident light can be scattered and reflected.

  Here, as the material of the polarization selective reflection layer described above, chiral nematic liquid crystal or cholesteric liquid crystal can be used, and any material having cholesteric liquid crystallinity is not particularly limited. A polymerizable liquid crystal material having a polymerizable functional group at the terminal is preferable. This is because an optically stable projection screen can be obtained after curing. In addition, when the polymerizable liquid crystal material exhibits nematic regularity or smectic regularity, a polymerizable chiral agent may be used. Hereinafter, the material used for the polarization selective reflection layer of this embodiment and the method for forming the polarization selective reflection layer will be described.

(1) Polymerizable liquid crystal material As an example of the polymerizable liquid crystal material having such a polymerizable functional group, for example, compound (I) represented by the following general formula (1) can be given. As the compound (I), it is also possible to use a mixture of two compounds included in the general formula (1). Furthermore, it may be composed of the compound (I) and the compound (II) represented by the following general formulas (2) to (12).
As the compound (I), two kinds of compounds included in the general formula (1) can be mixed and used.

In the general formula (1) representing the compound (I), R ¹ and R ² each represent hydrogen or a methyl group, but R ¹ and R ² are both hydrogen due to the wide temperature range showing the liquid crystal phase. preferable. 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, a and b which show the chain length of the (meth) acryloyloxy group of the molecular chain both ends of compound (I), and the alkylene group which is a spacer with an aromatic ring are respectively arbitrary integers in the range of 2-12. Although it can take, it is preferable that it is the range of 4-10, and it is more preferable that it is the range of 6-9. The compound of the general formula (1) in which a = b = 0 is poor in stability, is susceptible to hydrolysis, and 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 preferred because the temperature range showing liquid crystallinity is narrow.
In the example described above, an example of a polymerizable liquid crystal monomer has been described, but in this embodiment, a polymerizable liquid crystal oligomer, a polymerizable liquid crystal polymer, or the like can be used. As such a polymerizable liquid crystal oligomer and a polymerizable liquid crystal polymer, those conventionally proposed can be appropriately selected and used.

(2) Chiral agent In this embodiment, a chiral nematic liquid crystal having a cholesteric liquid crystal property in which a chiral agent is added to a nematic liquid crystal can also be suitably used.
The chiral agent used in this embodiment is a low molecular compound having an optically active site and means a compound having a molecular weight of 1500 or less. The chiral agent is mainly used for the purpose of inducing a helical pitch in the positive uniaxial nematic regularity expressed by the polymerizable liquid crystal material as shown in, for example, the compound (I) or the compound (II) used as necessary. . As long as this object is achieved, the polymerizable liquid crystal material, for example, the compound (I) or a mixture of the compound (I) and the compound (II) is compatible with each other in a solution state or a molten state, and the above nematic regularity is obtained. As long as the desired helical pitch can be induced in the polymerizable liquid crystal material without impairing the liquid crystallinity of the polymerizable liquid crystal material, the kind of the low-molecular compound as a chiral agent shown below is not particularly limited. It is preferable to have a polymerizable functional group in order to obtain an optical element having good heat resistance. It is essential that the chiral agent used for inducing a helical pitch in the liquid crystal has at least some chirality in the molecule. Accordingly, the chiral agent that can be used in this embodiment 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, a chiral sulfoxide, and the like. Alternatively, compounds having axial asymmetry such as cumulene and binaphthol can be exemplified. More specifically, commercially available chiral nematic liquid crystal, for example, S-811 manufactured by Merck Co., etc. may be mentioned.

  However, depending on the properties of the selected chiral agent, the nematic regularity destruction and orientation formed by the polymerizable liquid crystal material as exemplified by compound (I) or a mixture of compound (I) and compound (II) Or when the compound is non-polymerizable, the curability of the liquid crystalline composition may be lowered and the reliability of the cured film may be lowered. Furthermore, the use of a large amount of a chiral agent having an optically active site causes an increase in the cost of the composition. Accordingly, when a circularly polarized light controlling optical element having a short pitch cholesteric liquid crystal property is produced, a helical pitch is induced in the chiral agent having an optically active portion to be contained in the polymerizable liquid crystal material used in this embodiment. It is preferable to select a chiral agent having a large effect, specifically, a low molecular compound (III) having axial asymmetry in the molecule as represented by the general formula (13), (14), or (15) Is preferred.

In the general formula (13) or (14) representing the chiral agent (III), R ⁴ represents hydrogen or a methyl group. Y is any one of formulas (i) to (xxiv) shown above, and among them, any one of formulas (i), (ii), (iii), (v), and (vii) It is preferable that Moreover, d and e which show the chain length of an alkylene group can take arbitrary integers in the range of 2-12 individually, but it is preferable that it is the range of 4-10, and is the range of 6-9. Is more preferable. The compound of general formula (13) or (14) in which the value of d or e is 0 or 1 lacks stability, is susceptible to hydrolysis, and has high crystallinity. On the other hand, a compound having a d or e value of 13 or more has a low melting point (Tm). These compounds are less compatible with the compound (I) exhibiting liquid crystallinity or with the mixture of the compound (I) and the compound (II), and may cause phase separation depending on the concentration.

The amount of the chiral agent blended in the polymerizable liquid crystal material of this embodiment is determined in consideration of the helical pitch inducing ability and the cholesteric property of the finally obtained circularly polarized light controlling optical element. Specifically, although it varies greatly depending on the polymerizable liquid crystal material to be used, 0.01 to 60 parts by weight, preferably 0.1 to 40 parts by weight, more preferably 100 parts by weight of the total amount of the polymerizable liquid crystal material. Is selected in the range of 0.5 to 30 parts by weight, most preferably 1 to 20 parts by weight. When the amount is less than the above range, the polymerizable liquid crystal material may not be provided with sufficient cholesteric properties. When the amount exceeds the above range, the orientation of the molecule is hindered and adversely affected when cured by actinic radiation. There is a risk of affecting.
In this embodiment, it is not essential that such a chiral agent has polymerizability. However, in consideration of the thermal stability and the like of the obtained optical functional layer, it is preferable to use a polymerizable chiral agent that can be polymerized with the above-described polymerizable liquid crystal material and fix the cholesteric liquid crystal properties.

(3) Others In addition to the polymerizable liquid crystal material and the chiral agent, the polarization selective reflection layer used in this embodiment is generally a photopolymerization initiator, a sensitizer, a leveling agent, etc., if necessary. A material used for such a polarization selective reflection layer may be appropriately used.

  Examples of the photopolymerization initiator used in this embodiment include benzyl (also referred to as bibenzoyl), benzoin isobutyl ether, benzoin isopropyl ether, benzophenone, benzoyl benzoic acid, benzoyl methyl benzoate, and 4-benzoyl-4'-methyl diphenyl sulfide. Benzylmethyl ketal, dimethylaminomethyl benzoate, 2-n-butoxyethyl-4-dimethylaminobenzoate, isoamyl p-dimethylaminobenzoate, 3,3′-dimethyl-4-methoxybenzophenone, methylobenzoyl formate, 2 -Methyl-1- (4- (methylthio) phenyl) -2-morpholinopropan-1-one, 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) -butan-1-one, -(4- 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-propoxythioxanthone And so on. In addition to the photopolymerization initiator, it is also possible to add a sensitizer as long as the purpose of this embodiment is not impaired.

Here, the addition amount of the photopolymerization initiator used in this embodiment is 0.01 to 20% by weight, preferably 0.1 to 10% by weight, more preferably 0.5 to 5% by weight. Is preferred.
In this aspect, as described above, variations in the direction of the helical axis may be introduced into the liquid crystal compound that constitutes the polarization selective reflection layer using these materials. For example, by adding a large amount of a surfactant, the orientation of the cholesteric liquid crystal surface may be disturbed, and the above-described variation in the direction of the helical axis may be introduced, and a large amount of photopolymerization initiator may be added. It may be a method of introducing the above-mentioned variation by adding to the short-chain molecular chain of the cholesteric liquid crystal. In this case, the photopolymerization initiator after completion of the reaction also serves as an impurity that disturbs the orientation of the cholesteric liquid crystal in the cholesteric liquid crystal.

  Moreover, the dispersion | variation in the direction of the said helical axis may be introduce | transduced by adding the polymeric compound which does not have liquid crystal aligning property. This is because by adding a polymerizable compound having no liquid crystal orientation, the orientation of the cholesteric liquid crystal is disturbed and the helical axis of the liquid crystal compound is inclined. Further, by adding fine particles, the orientation of the cholesteric liquid crystal may be disturbed to introduce the variation in the direction of the helical axis. In this embodiment, a combination of the above methods may be used. In addition, the types and amounts of these additives are appropriately selected depending on the purpose and the like.

(4) Formation of polarization selective reflection layer In this embodiment, the composition for mixing each of the above materials is applied on a substrate described later, and oriented and cured to obtain the polarization selective reflection layer. it can.
As a method of applying the composition on the substrate, the composition obtained by mixing the above materials may be applied as it is, but from the viewpoint of adjusting the viscosity and orientation, it is used by dissolving in an organic solvent. Is preferred. In this case, the solvent used is not particularly limited as long as it does not erode the base material described later. For example, acetone, 3-methoxybutyl acetate, diglyme, cyclohexanone, tetrahydrofuran, toluene, xylene, chlorobenzene , Methylene chloride, methyl ethyl ketone, and the like can be used. In this case, the composition is usually diluted to 5% to 50% by weight, particularly 10% to 30% by weight.

  In addition, as a method for applying the composition, a generally used method can be used. For example, a roll coating method, a gravure coating method, a bar coating method, a slide coating method, a die coating method, a slit coating method. It can be carried out by a method, a dipping method or the like. When the substrate is a plastic film, roll-to-roll film coating may be used.

  Subsequently, the composition is held at a predetermined temperature at which the cholesteric liquid crystal structure is expressed, and the composition is oriented. In addition, the cholesteric liquid crystal structure of the polarization selective reflection layer to be finally obtained in this embodiment is not a planar alignment state but an alignment state having variations in the direction of the helical axis, but even in this case, an alignment treatment is necessary. It becomes. That is, an alignment process that aligns the directors of the liquid crystal molecules with a cholesteric liquid crystal structure in a certain direction on the substrate is not required, but an alignment process that forms a spiral axis in multiple directions in the cholesteric liquid crystal structure. Is necessary.

  The alignment treatment can be performed by maintaining the above composition at a predetermined temperature at which the cholesteric liquid crystal structure develops. As a result, the cholesteric liquid crystal exhibits a liquid crystal phase, and the liquid crystal molecules themselves are self-assembled to produce a liquid crystal. A helical structure is formed, in which molecular directors are continuously rotated in the layer thickness direction. The cholesteric liquid crystal structure expressed in such a liquid crystal phase state can be fixed by curing the cholesteric liquid crystal by a method as described later.

  In addition, when the solvent is contained in the liquid crystalline composition apply | coated on the base material, 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.

Next, the cholesteric liquid crystal layer that has been aligned in the above-described alignment treatment step is cured by the curing treatment step to fix the cholesteric liquid crystal structure that is 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, and (3) radiation. 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 crystal composition which is a material of a cholesteric liquid crystal layer. In this method, the liquid crystal polymer is applied to the substrate in a state of being dissolved in a solvent such as an organic solvent. In this case, the solidification with cholesteric liquid crystallinity can be achieved by simply removing the solvent by drying treatment. A 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 in which liquid crystal molecules in the liquid crystalline composition are thermally polymerized by heating to cure the cholesteric liquid crystal layer. 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 of heating the cholesteric liquid crystal layer formed on the substrate 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 or between the hot plate. A method can be used in which a slight air layer is provided and held so as to be 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.

  The heating temperature generally requires a high temperature of 100 ° C. or higher, but is preferably about 150 ° C. due to the heat resistance of the substrate. However, if a film specialized in heat resistance is used as the material of the substrate, 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 as described above. 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.

  By performing the above-described series of steps (coating step, alignment step and curing step), a projection screen having a polarization selective reflection layer composed of a single cholesteric liquid crystal layer can be produced. By repeating the above-described series of steps according to the number of peak wavelengths, a projection screen including a polarization selective reflection layer composed of a plurality of cholesteric liquid crystal layers can be manufactured. Here, when a polarization selective reflection layer is further coated on the polarization selective reflection layer having light diffusivity, the orientation state of the lower layer is continued, so there is no need to provide a layer for controlling the orientation in between. However, you may form other layers, such as an easily bonding layer, for example.

2. Next, the base material used for the projection screen of this aspect will be described. The base material used for the projection screen of this aspect is not particularly limited as long as the above-described polarization selective reflection layer can be formed. In this aspect, light of a wavelength in the visible light region is absorbed. It is preferable that it absorbs light within a range of 400 nm to 700 nm. Thereby, when light having a wavelength other than the specific wavelength reflected by the polarization selective reflection layer is incident, reflection can be prevented and a projection screen with high brightness can be obtained.

  As the base material that absorbs the wavelength in the visible light region, for example, a plastic film or the like in which a black pigment is kneaded can be used. Further, a light absorption layer may be formed on a transparent plastic film or the like, and this light absorption layer may be formed on the side where the polarization selective reflection layer is formed. Further, it may be formed on the opposite side.

  Further, in this embodiment, as described above, the base material may be a material with little surface orientation in order to introduce the variation in the direction of the helical axis in the polarization selective reflection layer. As a material with less surface orientation, for example, a plastic film that has not been stretched or a material that has not been rubbed can be used. Usually, the polarization selective reflection layer is formed on a plastic film or the like that has been stretched or rubbed so as to have good regularity, but in this embodiment, it is stretched or rubbed. By forming the polarization selective reflection layer on a non-base material, the liquid crystal on the surface of the base material is not regularly aligned, and thus it is possible to introduce variations in the helical axis in the polarization selective reflection layer. Because it becomes.

  The material used for the substrate is not particularly limited, and examples thereof include a plastic film, metal, paper, and glass. Examples of the plastic film include polycarbonate polymers, polyester polymers such as polyarylate and polyethylene terephthalate, polyimide polymers, polysulfone polymers, polyethersulfone polymers, polystyrene polymers, polyethylene and polypropylene. A film made of a thermoplastic polymer such as a polyolefin polymer, a polyvinyl alcohol polymer, a cellulose acetate polymer, a polyvinyl chloride polymer, or a polymethyl methacrylate polymer can be used.

  Further, the film thickness of the base material used in this embodiment is appropriately selected depending on the use and type of the projection screen. For example, when the projection screen is used in a roll-up manner, it is usually 15 μm to 300 μm. In particular, the thickness may be 25 μm to 100 μm. In addition, the film thickness of the base material is not particularly limited when the film is not used in a roll-up type and does not require flexibility such as a panel type.

  Moreover, in order to improve the adhesiveness with the said polarization selective reflection layer, the base material used for this aspect may have processed the surface by corona treatment, UV washing | cleaning, etc., for example.

  Furthermore, a plastic film or the like on which an easy-adhesion layer is formed may be used. For example, PET film A4100 with an easy-adhesion layer (trade name, manufactured by Toyobo Co., Ltd.) and easy-adhesion materials AC-X, AC-L, AC-W (Trade name, manufactured by Panac) may be used.

3. Projection Screen Next, the projection screen of this aspect will be described. The projection screen of this aspect is not particularly limited as long as the polarization selective reflection layer is formed on the base material. For example, as shown in FIG. The property improvement layer 4 may be formed, and the polarization selective reflection layer 2 may be formed on the adhesion improvement layer 4. Further, as described above, the polarization selective reflection layer can be obtained by laminating a layer made of a liquid crystal compound having a plurality of cholesteric liquid crystal structures, for example, in accordance with the number of peak wavelengths of the target reflection intensity. For example, as shown in FIG. 6, a red polarized light selective reflection layer (2R), a green polarized light selective reflection layer (2G), a blue polarized light selective reflection layer (2B), etc. may be used. May be provided.

  According to this aspect, since the polarization selective reflection layer has the above-described selective reflectivity, it selectively reflects only light of a specific polarization component (for example, right-handed circularly polarized light). It is possible to reflect only about 50% of ambient light such as by the polarization selective reflection layer. Further, as described above, since the total reflection bandwidth is set to half or less of the visible light region, the influence of external light can be further reduced to half or less. Therefore, 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 reduced to improve the contrast of the image. 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.

  In addition, the polarization selective reflection layer has the above diffuse reflectivity due to, for example, the variation of the direction of the helical axis L of the liquid crystal compound included in the cholesteric liquid crystal structure, so that the image light is not specularly reflected but diffusely reflected. This makes it easier to view the video. At this time, when the selectively reflected light is diffused due to, for example, structural nonuniformity of the cholesteric liquid crystal structure, the polarization selective reflection layer emits light of a specific polarization component (for example, within the selective reflection wavelength region). While reflecting other diffused light (for example, left circularly polarized light within the selective reflection wavelength region, right circularly polarized light and left circularly polarized light outside the selective reflection wavelength region) without diffusing. Can do. For this reason, the above-mentioned “depolarization” problem does not occur with respect to ambient light and image light transmitted through the polarization selective reflection layer, and image visibility is maintained while maintaining the original polarization separation function of the polarization selective reflection layer. Can be improved.

  As described above, according to this aspect, by setting the reflection bandwidth of the polarization selective reflection layer within a predetermined range, the influence of ambient light such as external light and illumination light can be suppressed, and the contrast of the image can be increased. The image can be displayed clearly even under bright ambient light.

In this embodiment, it is preferable to form the adhesion improving layer, and this adhesion improving layer is provided in order to improve the adhesion between the substrate and the polarization selective reflection layer. There are no particular limitations on the type and material of such an adhesion improving layer, and for example, an acrylic or epoxy material can be used.
Further, if necessary, a scratch prevention layer, a low reflection layer, an ultraviolet ray prevention layer, or the like may be provided.

  Further, in this aspect, the device that emits an image on the projection screen is not particularly limited as long as it can project an image on the projection screen with light shading. It may be like a projector that forms an image by disposing a film or the like. In this embodiment, it is preferable to use a self-luminous type projector such as a CRT type, a light valve type projector such as a liquid crystal type or a DLP type, and it is particularly preferable to polarize emitted light into circularly polarized light. For example, in the case of a liquid crystal projector, by passing through a phase difference plate that converts linearly polarized light to be converted into circularly polarized light, it is possible to convert it into circularly polarized light with almost no light loss. In this case, the retardation plate used preferably has a quarter wavelength, and specifically, it is preferable to use a plate having a wavelength of 137.5 nm in accordance with the highest visibility of 550 nm. Furthermore, since it is applied to all wavelengths of emitted RGB, it is particularly preferable that it is a broadband quarter wavelength phase difference plate. In addition, a single retardation plate by controlling the birefringence of the material, or a combination of a 1/4 wavelength retardation plate and a 1/2 wavelength retardation plate may be used. Here, the retardation plate may be incorporated in the projector, or may be externally attached to the injection port.

  In addition, since the CRT type and DLP type projectors are not controlled in polarization, it is preferable that the CRT type and DLP type projectors be linearly polarized via an optical element and a phase difference plate be disposed. In this case, the light quantity of the projector itself is halved, but it is possible to obtain a contrast improvement effect.

  Moreover, in this aspect, it is preferable that the indoor illumination or outside light in which the projection screen is used is circularly polarized light opposite to the circularly polarized light reflected by the projection screen. Thereby, even when external light, illumination, or the like is incident on the projection screen, the projection screen is almost absorbed without reflecting the light, so that the brightness can be high even in a bright environment. Because. At this time, as a method for controlling the illumination and external light, an absorption type circularly polarizing plate, a reflective type circularly polarizing plate using a circularly polarized light separating layer, a linearly polarized light separating layer, or the like can be used.

B. Second Aspect Next, a second aspect of the projection screen of the present invention will be described. The second aspect of the projection screen of the present invention is a substrate, a selective reflection function that is formed on the substrate and selectively reflects light of a specific polarization component, and diffuses the light of the specific polarization component. And 50% of the intensity of the reflected light having a plurality of peak wavelengths in the visible light region of the polarized light selective reflection layer with respect to the intensity of the peak wavelength. Each of the reflection bandwidths having the above reflection intensity is 75 nm or less.

  The light incident on the polarization selective reflection layer used in this aspect is absorbed without being reflected by light having a wavelength other than the reflection band, and substantially only the light having the wavelength in the reflection band is reflected. The Rukoto. Therefore, by setting the reflection bandwidth within a predetermined range, the color purity of reflected light can be increased, and a projection screen with good color reproducibility can be obtained. In addition, even in the presence of external light, the selective reflection of the polarization selective reflection layer absorbs light having a wavelength other than the reflection band without being substantially reflected. The projection screen with high contrast can be obtained even in a bright environment.

  Hereinafter, the polarization selective reflection layer used in the projection screen of this embodiment and the projection screen of this embodiment will be described. In addition, about the base material used for this aspect, since it is the same as that used in the 1st aspect mentioned above, description here is abbreviate | omitted.

1. Polarization selective reflection layer First, the polarization selective reflection layer used in this embodiment will be described. The polarization selective reflection layer used in this embodiment is formed on the base material and selectively reflects light of a specific polarization component and diffuses and reflects the light of the specific polarization component. A reflection reflection function having a reflection intensity of 50% or more with respect to the intensity of the peak wavelength of the reflection intensity distribution having a plurality of peak wavelengths in the visible light region of the polarization selective reflection layer. Each of the bandwidths is 75 nm or less.

For example, as shown in FIG. 3, the polarization selective reflection layer used in the projection screen of this aspect has a plurality of peak wavelengths (a, b, and c in the figure) in the reflection intensity distribution in the visible light region of the polarization selective reflection layer. The reflection bandwidths at these peak wavelengths (indicated by Δλ _a , Δλ _b , and Δλ _c in the figure) are each equal to or less than a predetermined value. The reflection intensity is measured by the same method as in the first aspect described above.
Here, specifically, the value of each of the reflection bandwidths is preferably 75 nm or less, and more preferably in the range of 40 nm to 65 nm. Thereby, the purity of each color reflected by the polarization selective reflection layer can be increased, and by combining these liquid crystal compounds, a projection screen with good color reproducibility can be obtained.

Further, the light of the specific polarization component reflected by the polarization selective reflection layer may be one of linearly polarized light, right circularly polarized light or left circularly polarized light. A circularly polarized circle is preferred.
By making the light of a specific polarization component reflected by the polarization selective reflection layer into right circularly polarized light or left circularly polarized light, it is possible to easily set a reflection band by using a layer made of a liquid crystal compound having a cholesteric liquid crystal structure, for example. This is because it can be selected.
For example, when a layer made of a liquid crystal compound having a cholesteric liquid crystal structure is used for the polarization selective reflection layer, the reflection bandwidth Δλ is equal to the cholesteric constituting the polarization selective reflection layer, as shown in the above-described equation (2). Since the liquid crystal compound having a liquid crystal structure is determined by the birefringence value Δn and the helical pitch length p, the liquid crystal compound having a cholesteric liquid crystal structure in which the birefringence value Δn and the helical pitch length p are appropriate. By selecting, the value of the reflection bandwidth can be made equal to or less than a predetermined value.

  Here, also in this aspect, the polarization selective reflection layer has two or more of the peak wavelengths with respect to the reflection intensity in the visible light region, and the respective reflection bandwidths are not more than the above values, The peak wavelength value and the like are not particularly limited as long as light having a wavelength irradiated from a light source such as a projector can be reflected. For example, the number of the polarization selective reflection layers may be two, but in this embodiment, in particular, those having three peak wavelengths of red (R), blue (B), and green (G), respectively. Preferably there is. This is because the light normally emitted from the projector consists of red (R), blue (B), and green (G), and color display is realized by these three primary colors.

  In this embodiment, the above wavelengths are specifically wavelengths of 430 nm to 460 nm for blue (B), 540 nm to 570 nm for green (G), and 580 nm to 620 nm for red (R), depending on the type of projector. It is preferable that the light is selectively reflected. This is because a color screen can be displayed even if there is a difference in wavelength depending on the design of the apparatus, the type of light source, and the like, and a projection screen capable of expressing good white can be obtained. Such a polarization selective reflection layer having a plurality of peak wavelengths can be configured, for example, by laminating layers having a cholesteric liquid crystal structure having each helical pitch length. The polarization selection wavelength used in this embodiment may have four or more peak wavelengths.

  Also in this aspect, it is preferable that the polarization selective reflection layer (each layer in the case where the polarization selective reflection layer is composed of a plurality of layers) has a thickness that reflects 100% of specific polarized light. The reflectance of the polarization selective reflection layer with respect to the polarization depends on the thickness of the polarization selective reflection layer, and is less than 100% with respect to light of a specific polarization component (for example, right circularly polarized light) that is selectively reflected. This is because the image light cannot be efficiently reflected when the reflectance is. In order to set the reflectance to 100%, for example, when a layer made of a liquid crystal compound having the cholesteric liquid crystal structure is used for the polarization selective reflection layer, the film thickness is preferably 4 to 8 pitches. Specifically, although it depends on the type of material of the polarization selective reflection layer and the wavelength of specific polarization, it is usually 1 μm to 10 μm. If it is thinner than the above film thickness, the reflectance will be low, making it difficult to reproduce the image projected on the projection screen with good brightness, and if it is thicker than the above film thickness, it will be difficult to control the cholesteric liquid crystal structure. This is because unevenness may occur.

Here, the polarization selective reflection layer used in this aspect has a selective reflection function that selectively reflects light of a specific polarization component and a diffuse reflection function that diffuses and reflects light of the specific polarization component. Is. Here, the polarization selective reflection layer of this aspect may also be a layer having the selective reflection layer having the selective reflection function and the diffusion layer having the diffuse reflection function, and in one layer, A layer having the selective reflection function and the diffuse reflection function may be used.
Note that the selective reflection layer and diffusion layer used in the polarization selective reflection layer used in this embodiment, or the material and formation method of the polarization selective reflection layer having the above two functions are the same as those in the first embodiment described above. Since there is, explanation here is omitted.
When the polarization selective reflection layer is a layer having the selective reflection function and the diffuse reflection function in one layer, the liquid crystal compound having the cholesteric liquid crystal structure is also specified in this embodiment. For example, as shown in FIG. 5, the polarization axis of the helical axis L of the block structure 30 of the liquid crystal compound having cholesteric liquid crystal properties constituting the polarization selective reflection layer 2 is reflected. It is preferable that the direction has variation.

2. Projection Screen Next, the projection screen of this aspect will be described. The projection screen of this aspect is not particularly limited as long as the polarized light selective reflection layer is formed on the base material. As in the first aspect, for example, as shown in FIG. Alternatively, the adhesion improving layer 4 may be formed on the substrate 1, and the polarization selective reflection layer 2 may be formed on the adhesion improving layer 4. Further, as described above, the polarization selective reflection layer can be obtained by laminating a layer made of a liquid crystal compound having a plurality of cholesteric liquid crystal structures, for example, in accordance with the number of peak wavelengths of the target reflection intensity. For example, as shown in FIG. 6, a red polarized light selective reflection layer (2R), a green polarized light selective reflection layer (2G), a blue polarized light selective reflection layer (2B), etc. may be used. May be provided.

  According to this aspect, since the polarization selective reflection layer has selective reflectivity that selectively reflects only light of a specific polarization component (for example, right circularly polarized light), ambient light such as outside light or illumination light that does not have polarization characteristics. Can be made to reflect only about 50% 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 approximately 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.

  Further, as described above, since the reflection bandwidth is less than or equal to the predetermined value, the color purity of the reflected light can be increased, and a projection screen with high color reproducibility can be obtained. is there.

  Still further, for example, the direction of the helical axis L of the liquid crystal compound included in the cholesteric liquid crystal structure varies, so that the polarization selective reflection layer has diffuse reflectivity, and the image light is diffused instead of specularly reflected. Reflected and the image becomes easy to see. At this time, for example, when the selectively reflected light is diffused due to the structural non-uniformity of the cholesteric liquid crystal structure, light of a specific polarization component (for example, right circularly polarized light in the selective reflection wavelength region) is emitted. While reflecting while diffusing, other light (for example, left circularly polarized light within the selective reflection wavelength region, right circularly polarized light and left circularly polarized light outside the selective reflection wavelength region) can be transmitted without being diffused. For this reason, the above-mentioned “depolarization” problem does not occur with respect to ambient light and image light transmitted through the polarization selective reflection layer, and image visibility is maintained while maintaining the original polarization separation function of the polarization selective reflection layer. Can be improved.

  As described above, according to the present aspect, by setting each reflection bandwidth of the polarization selective reflection layer within a predetermined range, the color purity is high, and the influence of ambient light such as external light and illumination light is small. It is possible to provide a projection screen that can display an image clearly even under a high environment and bright ambient light.

  Here, also in the projection screen of this aspect, similarly to the first aspect described above, an adhesion improving layer or the like may be formed. A layer, an ultraviolet ray prevention layer or the like may be provided. In addition, about these layers, since the thing similar to the 1st aspect mentioned above can be used, description here is abbreviate | omitted.

  Further, since the apparatus and the like for emitting an image on the projection screen are the same as those in the first aspect described above, description thereof is omitted here.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has substantially the same configuration as the technical idea described in the claims of the present invention, and any device that exhibits the same function and effect is the present invention. It is included in the technical scope of the invention.

  Hereinafter, the present invention will be specifically described with reference to examples.

  [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.
As the nematic liquid crystal, a liquid crystal containing the compound represented by the above chemical formula (12) was used.
Further, as the polymerizable chiral agent, the compound represented by the above chemical formula (15) 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 subjected to a bar coating method on a base material (Lumirror / AC-X, manufactured by Panac) on which an easy-adhesion layer is formed on a 200 mm □ black PET film. It applied by.
Next, the film was heated in an oven at 80 ° C. for 90 seconds to perform alignment treatment (drying treatment) to obtain a cholesteric liquid crystal layer from which the solvent was removed.
Thereafter, the cholesteric liquid crystal layer was irradiated with 365 nm ultraviolet light at 50 mW / cm ² for 1 minute to cure the cholesteric liquid crystal layer, thereby obtaining a first partial selective reflection layer having a selective reflection center wavelength at 440 nm. .

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

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

  As described above, as the polarization selective reflection layer, the first partial selective reflection layer that selectively reflects light in the blue (B) wavelength region (light having a selective reflection center wavelength at 440 nm), and green (G) A second partial selective reflection layer that selectively reflects light in the wavelength range (light having a selective reflection center wavelength at 550 nm) and light in the red (R) wavelength range (light having a selective reflection center wavelength at 600 nm). A projection screen was obtained in which a third partially selective reflection layer that selectively reflects () was laminated in order from the substrate side. The thickness of the first partial selective reflection layer was 3 μm, the thickness of the second partial selective reflection layer was 4 μm, and the thickness of the third partial selective reflection layer was 5 μm. 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.

  At this time, the reflection bandwidth of each color of the polarization selective reflection layer was 55 nm, 65 nm, and 75 nm, respectively, and the total of these was 195 nm.

[Comparative Example 1]
A projection screen was formed in the same manner as in Example 1 except that a stretched black PET film (Lumirror, manufactured by Panac Co., Ltd.) was used as the substrate and no variation in the direction of the helical axis was introduced. At this time, the polarization selective reflection layer was planarly aligned on the surface and had specular reflection. The cholesteric liquid crystal structure of each partial selective reflection layer of the polarization selective reflection layer of the projection screen thus obtained was in a planar alignment state.

[Comparative Example 2]
A film made of cholesteric liquid crystal of six layers was laminated while shifting the center wavelength of each layer by the same film forming method as in the example, and a projection screen was formed so that the reflection bandwidth was 400 nm to 650 nm.

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

The projection screen was installed perpendicular to the floor. In addition, the projector was arranged at a position approximately 2.5 m away from the projection screen in a direction perpendicular to the projection screen (a direction parallel to the floor).
In this state, image light (a still image with white and black areas) was projected onto the projection screen by the projector, and the contrast of the image was measured. Specifically, the luminance of each of the white and black images at the center of the projection screen is measured with a luminance meter (luminance meter BM-8, manufactured by Topcon Corporation), and the ratio is determined as the contrast (contrast = brightness of the white image). ÷ Intensity of black image).

  Table 1 below shows the contrast for each projection screen according to the example, comparative example 1, and comparative example 2.

  Each projection screen was visually observed. In this case, in the projection screen according to Comparative Example 1, reflection of light occurred specularly, and the image was difficult to view and could not be measured.

It is explanatory drawing which shows an example of the projection screen of this invention. It is explanatory drawing for demonstrating the optical function of the polarization selective reflection layer of this invention. It is explanatory drawing for demonstrating the reflection bandwidth of the polarization selective reflection layer of this invention. It is explanatory drawing for demonstrating the reflection bandwidth of the polarization selective reflection layer of this invention. It is explanatory drawing for demonstrating the optical function of the polarization selective reflection layer of this invention. It is a schematic sectional drawing which shows an example of the projection screen of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Base material 2 ... Polarization selective reflection layer

Claims (9)

  Polarization selective reflection having a base material, a selective reflection function that is formed on the base material and selectively reflects light of a specific polarization component, and a diffuse reflection function that diffuses and reflects light of the specific polarization component A reflection intensity distribution having a plurality of peak wavelengths in the visible light region of the polarization selective reflection layer, and a total of each reflection bandwidth having a reflection intensity of 50% or more with respect to the intensity of the peak wavelength A projection screen characterized by being 200 nm or less. The projection screen according to claim 1, wherein the polarization selective reflection layer has two peak wavelengths in an intensity distribution of reflected light in a visible light region. Polarization selective reflection having a base material, a selective reflection function that is formed on the base material and selectively reflects light of a specific polarization component, and a diffuse reflection function that diffuses and reflects light of the specific polarization component And a reflection bandwidth having a reflection intensity of 50% or more with respect to the intensity of the peak wavelength of the intensity distribution of the reflected light having a plurality of peak wavelengths in the visible light region of the polarization selective reflection layer, respectively. The projection screen according to claim 1, wherein the projection screen is 75 nm or less. 4. The projection screen according to claim 1, wherein the specific polarization component is right circular polarization or left circular polarization. 5. 4. The projection screen according to claim 1, wherein the light having the specific polarization component is one linearly polarized light. 5. The said polarization selective reflection layer is a layer which has the selective reflection layer which has the said selective reflection function, and the diffusion layer which has the said diffuse reflection function, The claim in any one of Claim 1-5 characterized by the above-mentioned. The projection screen according to the item. 6. The projection according to claim 1, wherein the polarization selective reflection layer has the selective reflection function and the diffuse reflection function in one layer. screen. The projection screen according to claim 7, wherein the polarization selective reflection layer has a cholesteric liquid crystal structure. The polarization selective reflection layer is a light having a selective reflection center wavelength in a range of 430 nm to 460 nm, 540 nm to 570 nm, and 580 nm to 620 nm with reference to a case where light is incident perpendicularly to the polarization selective reflection layer. The projection screen according to claim 1, wherein the projection screen is selectively reflected.

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