JP2021120763A - Projection screen and image display system - Google Patents

Abstract

To provide a projection screen including a layer containing liquid crystal, by which an image can be viewed more easily with a wider viewing angle, and an image display system.SOLUTION: A projection screen 10 includes a pair of transparent conductive layers 11 and a light control layer 12 held between the pair of transparent conductive layers 11 and including a front surface 12F and a rear surface 12R. The light control layer 12 includes a polymer network 12a with a three-dimensional mesh shape including a plurality of domains 12c, and a liquid crystal molecule 12b existing in the domains 12c. The light control layer 12 changes between a first state of scattering light and a second state of transmitting light when the voltage to be applied to the light control layer 12 through the pair of transparent conductive layers 11 is changed. In the first state, the light entering from the rear surface 12R is scattered and the scattering light is emitted from the front surface 12F. When the light control layer 12 is in the first state, the light control layer 12 has a haze of 95% or more.SELECTED DRAWING: Figure 1

Description

The present invention relates to a projection screen and an image display system including the projection screen.

As a system for displaying an image on a screen by a projector or the like, a transmissive image display system and a reflective image display system are known. The image display system includes a housing, a projector, and a screen, a projection television in which the projector is located in the housing and the screen is located on the wall surface of the housing, and the projector and the screen are individually moved. Includes a display system that allows it. Among these, lenticular sheets and lens sheets such as Fresnel lens sheets are known as screens used in projection televisions.

For such a lens sheet, a light diffusion sheet in which fine particles having a refractive index different from that of the resin are dispersed in the resin is adopted. The light diffusing sheet forms an image of the light projected from the projector on one surface of the light diffusing sheet and emits it within a predetermined range (see, for example, Patent Document 1).

Instead of a screen using a lens sheet, a screen capable of switching between a transmissive state, in other words, a transparent state, and a scattered state, in other words, an opaque state is used, and light is emitted when the screen is in a scattered state. A transparent image display system that projects and displays an image is also known. With such an image display system, the screen can be made transparent when the image is not projected on the screen. As such a screen, a screen capable of switching between a transmission state and a scattering state by a liquid crystal layer is known.

As a screen that switches between a transmissive state and a scattered state by a liquid crystal layer, a screen having a liquid crystal layer formed of a polymer dispersed liquid crystal (PDLC) in which a liquid crystal is dispersed in a polymer is also known. (See, for example, Patent Document 2). The polymer-dispersed liquid crystal has a large number of isolated voids in the polymer layer, and the liquid crystal molecules are located in each of the voids dispersed in the polymer layer (see, for example, Patent Document 3).

In this screen, the difference between the refractive index of the liquid crystal and the refractive index of the polymer is used to switch between the transmission state and the scattering state. In this screen, the form of the screen having no alignment film for aligning the liquid crystal molecules is the normal type, and the form of the screen having the alignment film is the reverse type. In the normal type, the liquid crystal layer is in a transmissive state by applying an electric field to the liquid crystal layer, and the liquid crystal layer is in a scattered state by not applying an electric field to the liquid crystal layer. On the other hand, in the reverse type, the liquid crystal layer is in a transmissive state by not applying an electric field to the liquid crystal layer, and the liquid crystal layer is in a scattered state by applying an electric field to the liquid crystal layer.

Japanese Unexamined Patent Publication No. 2003-195422 Japanese Unexamined Patent Publication No. 10-363317 Japanese Unexamined Patent Publication No. 2013-76956

By the way, in the screen, when the surface to be observed by the observer is the surface, the vertical surface orthogonal to the surface is set as the reference surface, and the vertical surface including the line of sight of the observer is set as the observation surface, the reference surface and the observation surface are set. The angle formed by and is the viewing angle. For example, when the observer is observing the screen from the normal direction of the surface, the viewing angle is 0 °.

In the screen provided in the transmissive image display system, the image that the observer can see changes by changing the position where the observer observes the screen. In order to suppress this, it is preferable that the range on which the observer can visually recognize the image is wide on the side opposite to the side where the projector is located with respect to the screen. Even in an image display system that employs a screen including a layer containing a liquid crystal described above, it is required to make it easier to visually recognize an image with a wider viewing angle.

An object of the present invention is to provide a projection screen including a layer containing a liquid crystal, a projection screen that makes it possible to easily see an image in a wider viewing angle, and an image display system.

The projection screen for solving the above problems includes a pair of transparent conductive layers and a dimming layer sandwiched between the pair of transparent conductive layers and including a front surface and a back surface, and the dimming layers are plural. The magnitude of the voltage applied to the dimming layer through the pair of transparent conductive layers, which includes a polymer network having a three-dimensional network having the above domains and liquid crystal molecules located in the domains. By changing, it changes between the first state of scattering light and the second state of transmitting light, and in the first state, the light incident from the back surface is diffused and the scattered light is emitted from the front surface. do. When the dimming layer is in the first state, the haze of the dimming layer is 95% or more.

An image display system for solving the above problems includes a projection screen having a sheet shape including a front surface and a back surface and having a dimming layer, a projector that projects light onto the back surface of the projection screen, and the dimming. It is an image display system including a voltage application unit that applies a voltage to a layer, and a control unit that controls driving of the projector and driving of the voltage application unit. The projection screen is the projection screen, and in the thickness direction of the projection screen, the front surface of the projection screen, the front surface of the dimming layer, the back surface of the dimming layer, and the projection screen. The back surfaces are arranged in this order, and the control unit projects light onto the back surface of the projection screen with the projector in a state where the dimming layer is in the first state of the voltage application unit. The screen is made to emit scattered light from the surface of the projection screen.

According to the above configuration, the liquid crystal molecules are located in the polymer network stretched over the entire dimming layer. Therefore, in the plane of the dimming layer, the scattering of light by the polymer network and the scattering of light by the liquid crystal molecules are less likely to occur, and the scattered light is likely to be emitted from the entire surface of the dimming layer. As described above, since the scattered light emitted from the surface of the dimming layer is less likely to be biased, the amount of light emitted toward the observer is less likely to be reduced even if the viewing angle with respect to the projection screen is changed. As a result, the projection screen makes it easier to see the image in a wider viewing angle. Further, when the haze when the light control layer is in the first state is 95% or more, the viewing angle of the projection screen is likely to be widened.

In the projection screen, the average value of the domain diameter of the polymer network is preferably 0.1 μm or more and 3 μm or less.

According to the above configuration, since the light contained in the wavelength region of visible light is scattered to the same extent regardless of the wavelength, the light having white color can be emitted as scattered light, and the domain diameter is large. Compared with a configuration larger than 3 μm, it is possible to suppress the scattering angle of scattered light from becoming smaller.

In the projection screen, when the dimming layer is in the first state, the total light transmittance of the dimming layer is preferably 50% or more.

According to the above configuration, in the dimming layer having a domain diameter of 0.1 μm or more and 3 μm or less, the viewing angle of the projection screen is likely to be widened by including the total light transmittance within the above range.

In the projection screen, the thickness of the dimming layer is preferably 5 μm or more and 50 μm or less.

According to the above configuration, when the thickness of the dimming layer is 5 μm or more, the light incident on the dimming layer from the back surface of the dimming layer is adjusted until it is emitted from the surface of the dimming layer. It is scattered to the extent that the variation in brightness within the surface of the light layer is suppressed. Further, when the thickness of the dimming layer is 50 μm or less, it is possible to suppress the amount of light transmitted through the dimming layer from the back surface to the front surface of the dimming layer to be reduced, which is visually recognized by the observer. The low brightness of the image is suppressed.

In the projection screen, the density of the domains in the dimming layer is preferably 2 × 10 ⁷ / mm ³ or more and 2 × 10 ¹² / mm ³ or less.

According to the above configuration, when the density of the domains is 2 × 10 ⁷ / mm ³ or more, the light incident on the dimming layer from the back surface of the dimming layer is easily scattered in the dimming layer. As a result, the variation in brightness within the surface of the dimming layer is suppressed. Further, when the domain density is 2 × 10 ¹² / mm ³ or less, it is possible to suppress that the amount of light transmitted from the back surface to the front surface of the dimming layer is reduced because the domain density is too high. As a result, the brightness of the image visually recognized by the observer is suppressed from being lowered.

In the projection screen, the projection screen includes a front surface and a back surface, and in the thickness direction of the projection screen, the front surface of the projection screen, the front surface of the dimming layer, the back surface of the dimming layer, and the back surface of the dimming layer. , The back surface of the projection screen is arranged in this order. The vertical plane orthogonal to the surface of the projection screen is the visual field reference plane, the vertical plane including the direction in which the observer visually recognizes the projection screen is the observation plane, and the visual field reference plane and the observation plane are formed. When the angle is the viewing angle and the observer sees the projection screen from one side with respect to the viewing reference plane, the viewing angle is a negative value and the observer sees the projection screen from the other side with respect to the viewing reference plane. When the projection screen is visually recognized, the viewing angle is a positive value, the horizontal plane orthogonal to the back surface of the projection screen is the projection reference plane, and the plane including the direction in which the projector projects light onto the back surface of the projection screen. Is the projection plane, the angle formed by the projection reference plane and the projection plane is the projection angle, and the brightness of the surface of the projection screen is standardized by the brightness when the viewing angle is 5 °. The brightness is the standardized brightness. When the projection angle is 0 °, the projection screen has a half-value angle of the standardized luminance at the viewing angle of ± 22 ° and a 1/3 angle of the normalized luminance of ± 30.5 °. It is preferable that the configuration is as follows.

According to the above configuration, it is possible to prevent the brightness on the surface of the projection screen from becoming lower as the viewing angle changes, as compared with the configuration in which the absolute values of the half-value angle and the 1/3 angle are smaller.

In the image display system, the projection screen further includes a pair of alignment layers, one of the alignment layers being located between the surface and the transparent conductive layer, and the other. The alignment layer is located between the back surface and the transparent conductive layer, the voltage application unit applies an AC voltage to the dimming layer, and the control unit uses the period of the frame in the projector and the voltage. It is preferable to control the drive of the projector and the drive of the voltage application unit so that the cycles of the AC voltage in the application unit are different from each other.

According to the above configuration, since the period of the AC voltage and the period of the frame are different from each other, the moment when the AC voltage becomes 0V while the light corresponding to one frame is projected is at different timings for each frame. It includes being. Therefore, it is possible to prevent the image quality from being lowered as compared with the configuration in which the period of the AC voltage and the period of the frame are equal to each other.

According to the present invention, it is possible to make it easier to visually recognize an image with a wider viewing angle on a projection screen including a layer containing a liquid crystal.

The cross-sectional view which shows the cross-sectional structure in the 1st example of the projection screen in one Embodiment which embodies the projection screen. The cross-sectional view which shows the cross-sectional structure in the 2nd example of a projection screen. The block diagram which shows the schematic structure of the image system in one Embodiment which embodied the image display system. The block diagram which shows the schematic structure of the voltage application part provided in an image display system. A perspective view for explaining a viewing angle with respect to a projection screen. The perspective view for demonstrating the projection angle of a projector. A timing chart for explaining how to drive an image display system. A graph explaining the operation of an image display system. The graph which shows the Y stimulus value when the projection angle is -15 ° in Example 1 and Comparative Example 1. The graph which shows the Y stimulus value when the projection angle is −30 ° in Example 1 and Comparative Example 1. The graph which shows the Y stimulation value when the projection angle is −45 ° in Example 1 and Comparative Example 1. The graph which shows the Y stimulus value when the projection angle is −60 ° in Example 1 and Comparative Example 1. The graph which shows the normalized luminance when the projection angle is 0 ° in Example 1 and Comparative Example 1. The graph which shows the normalized luminance when the projection angle is −15 ° in Example 1 and Comparative Example 1. The graph which shows the normalized luminance when the projection angle is −30 ° in Example 1 and Comparative Example 1. The graph which shows the normalized luminance when the projection angle is −45 ° in Example 1 and Comparative Example 1. The graph which shows the normalized luminance when the projection angle is −60 ° in Example 1 and Comparative Example 1.

An embodiment in which the projection screen and the image display system are embodied will be described with reference to FIGS. 1 to 17. In the following, the configuration of the projection screen, the material for forming the projection screen, the configuration of the image display system, the driving method of the image display system, the operation of the projection screen, and the examples will be described in order.

[Projection screen configuration]
The configuration of the projection screen will be described with reference to FIGS. 1 and 2. Hereinafter, the first example and the second example in the configuration of the projection screen will be described. In addition, in FIG. 1 and FIG. 2, the sizes of the polymer network and the liquid crystal molecules contained in the dimming layer are exaggerated for convenience of illustration.

[First example]
As shown in FIG. 1, the projection screen 10 includes a pair of transparent conductive layers 11 and a dimming layer 12. The dimming layer 12 is sandwiched between a pair of transparent conductive layers 11 and includes a front surface 12F and a back surface 12R. The dimming layer 12 includes a polymer network 12a and a liquid crystal molecule 12b, the polymer network 12a has a three-dimensional network having a plurality of domains 12c connected to each other, and the liquid crystal molecule 12b is a polymer network 12a. It is located within the domain 12c. Each domain 12c is a void partitioned by a network of polymer networks 12a. The dimming layer 12 is formed of a polymer network liquid crystal (PNLC).

The state of the dimming layer 12 changes between the first state of scattering light and the second state of transmitting light by changing the magnitude of the voltage applied to the dimming layer 12. The dimming layer 12 scatters the light incident from the back surface 12R in the first state, and emits the scattered light from the front surface 12F.

In the projection screen 10 of the first example, since the dimming layer 12 is formed of PNLC, the liquid crystal molecules 12b are located in the polymer network 12a stretched over the entire dimming layer 12. Therefore, in the plane of the dimming layer 12, the scattering of light by the polymer network 12a and the scattering of light by the liquid crystal molecules 12b are unlikely to occur, and the scattered light is emitted from the entire surface 12F of the dimming layer 12. Easy to be done. As described above, since the scattered light emitted from the surface 12F of the dimming layer 12 is less likely to be biased, the amount of light emitted toward the observer becomes small even if the viewing angle with respect to the projection screen 10 changes. Hateful. As a result, according to the projection screen 10, the image can be easily visually recognized in a wider viewing angle.

For example, when no voltage is applied to the dimming layer 12, the state of the dimming layer 12 is the first state. When no voltage is applied to the dimming layer 12, the plurality of liquid crystal molecules 12b are irregularly arranged in the domain 12c in which each liquid crystal molecule 12b is located. As a result, it becomes difficult for light to pass through the dimming layer 12 from the front surface 12F toward the back surface 12R and from the back surface 12R toward the front surface 12F. As a result, the haze value in the dimming layer 12 becomes larger than when a voltage is applied to the dimming layer 12.

On the other hand, when a voltage of a predetermined magnitude is applied to the dimming layer 12, the dimming layer 12 is in the second state. When a voltage is applied to the dimming layer 12, in at least a part of the plurality of liquid crystal molecules 12b, the extending direction of the liquid crystal molecules 12b, that is, the longitudinal direction, intersects the front surface 12F and the back surface 12R in one direction, for example, the front surface. The liquid crystal molecules 12b are arranged along the normal direction of 12F and the back surface 12R. As a result, light can easily pass through the dimming layer 12 from the front surface 12F toward the back surface 12R and from the back surface 12R toward the front surface 12F. As a result, the haze value in the dimming layer 12 becomes smaller than when no voltage is applied to the dimming layer 12.

As described above, when the voltage is not applied to the dimming layer 12, the haze value of the dimming layer 12 is relatively large, and when the voltage is applied to the dimming layer 12, the dimming layer 12 is used. The dimming layer 12 having a relatively small haze value is the normal type dimming layer 12.

The haze value that the dimming layer 12 can take may be only the first value corresponding to the first state and the second value corresponding to the second state, and the dimming layer 12 may have only a second value. The configuration may be such that an intermediate value sandwiched between the maximum value and the minimum value in haze can be taken depending on the magnitude of the applied voltage. Further, when the dimming layer 12 has a configuration capable of taking at least one intermediate value, this intermediate value may be a haze value corresponding to the first state in the dimming layer 12. , The haze value corresponding to the second state may be used.

On the front surface 12F of the dimming layer 12 and the back surface 12R of the dimming layer 12, the maximum length in the region occupied by each domain 12c included in the polymer network 12a is the domain diameter D of the domain 12c. The maximum length in the region occupied by each domain 12c is the length of the straight line having the longest length among the straight lines passing through the center of gravity of the domain 12c. The average value of the domain diameter D is, for example, 0.1 μm or more and 3 μm or less, preferably 0.2 μm or more and 2 μm or less, and more preferably about 1 μm.

Since the dimming layer 12 tends to include the domain 12c in which the size of the domain 12c is substantially equal to the wavelength of visible light when the average value of the domain diameter D is 0.1 μm or more and 3 μm or less, it is included in the wavelength region of visible light. Light is scattered to about the same extent regardless of wavelength. Therefore, light having white color can be emitted as scattered light. Further, as compared with the configuration in which the domain diameter D is larger than 3 μm, it is possible to suppress the scattering angle of the light scattered by the polymer network 12a from becoming smaller. Further, when the average value of the domain diameter D is 1 μm or less, for example, 200 nm or more and 800 nm or less, the light component scattered in the traveling direction of light does not become too large with respect to the light component scattered in other directions. The variation in brightness on the surface of the dimming layer 12 can be further suppressed.

In the dimming layer 12, the mode of the domain diameter D is preferably included in the range of 0.1 μm or more and 3 μm or less. Further, it is preferable that both the minimum value and the maximum value of the domain diameter D are contained in 0.1 μm or more and 3 μm or less.

In the polymer network 12a, the number of domains 12c partitioned by the polymer network 12a per unit volume is the domain density, which is the density of the domains 12c in the dimming layer 12. The domain density is preferably 2 × 10 ⁷ / mm ³ or more and 2 × 10 ¹² / mm ³ or less. The domain density of the polymer network 12a can be counted in an image captured by a scanning electron microscope of the cross-sectional structure of the dimming layer 12.

When the domain density is 2 × 10 ⁷ / mm ³ or more, the light incident on the dimming layer 12 from the back surface 12R of the dimming layer 12 is likely to be multiple-scattered in the dimming layer 12. In-plane brightness variation on the surface 12F of the dimming layer 12 can be suppressed. When the domain density is 2 × 10 ¹² pieces / mm ³ or less, it is possible to suppress that the amount of light transmitted from the back surface 12R to the front surface 12F of the dimming layer 12 becomes small because the domain density is too high. As a result, the brightness of the image visually recognized by the observer is suppressed from being lowered.

In PNLC, the magnitude of the AC voltage for driving the liquid crystal molecule 12b depends on the characteristics in the structure of the polymer network 12a. More specifically, the magnitude of the AC voltage for driving the liquid crystal molecule 12b depends on the size of the domain 12c, the shape of the domain 12c, that is, the shape of the mesh partitioning the domain 12c, the thickness of the polymer network 12a, and the like. Depends on. Further, the magnitude of the AC voltage for driving the liquid crystal molecules 12b is set so that the desired light transmission and scattering in the dimming layer 12 are realized.

In order to realize sufficient light transmission and scattering as the projection screen 10 in the range where the effective value of the AC voltage is 100 V or less, it is preferable that the size is appropriate and uniform in the plurality of domains 12c. , It is preferable that the shapes of the domains 12c are also equal to each other.

In this respect, as described above, the average value of the domain diameter D is preferably 0.1 μm or more and 3 μm or less. If the average value of the domain diameter D is 0.1 μm or more and 3 μm or less and the domain density is 2 × 10 ⁷ / mm ³ or more and 2 × 10 ¹² / mm ³ , the size between the domains 12c is large. The mesh-like polymer network 12a in which the variation in the density is suppressed makes it possible to achieve both transmission and scattering of light in the first state.

The thickness T of the dimming layer 12 is preferably 5 μm or more and 50 μm or less, and more preferably 10 μm or more and 25 μm or less. When the thickness T of the dimming layer 12 is 5 μm or more, the light incident on the dimming layer 12 from the back surface 12R of the dimming layer 12 is emitted from the front surface 12F of the dimming layer 12. The light is scattered to the extent that the variation in brightness within the surface of the surface 12F of the dimming layer 12 is suppressed. When the thickness of the dimming layer 12 is 50 μm or less, it is possible to suppress that the amount of light transmitted through the dimming layer 12 decreases from the back surface 12R of the dimming layer 12 toward the front surface 12F, and by extension, the observer. It is possible to suppress the decrease in brightness of the image visually recognized by.

When the dimming layer 12 is in the first state, the total light transmittance of the dimming layer 12 is preferably 50% or more, and the haze of the dimming layer is preferably 95% or more. The total light transmittance of the dimming layer 12 is more preferably 73% or more. When the total light transmittance and haze of the dimming layer 12 having the domain diameter D of 0.1 μm or more and 3 μm or less are included in the above values, the viewing angle of the projection screen 10 can be easily widened.

The total light transmittance of each layer can be measured by a method conforming to JIS K 7361-1 (ISO 13468-1). In addition, the haze of each layer can be measured by a method conforming to JIS K 7136 (ISO 14782).

The transparent conductive layer 11 transmits light and applies a voltage to the dimming layer 12. One transparent conductive layer 11 is located on the front surface 12F and one on the back surface 12R of the dimming layer 12. Of the two transparent conductive layers 11, the transparent conductive layer 11 located on the front surface 12F of the dimming layer 12 is the first transparent conductive layer 11a, and the transparent conductive layer 11 located on the back surface 12R of the dimming layer 12 is the second. The transparent conductive layer 11b.

The total light transmittance of the transparent conductive layer 11 is preferably higher than the total light transmittance of the light control layer 12 when the light control layer 12 is in the second state. As a result, it is possible to prevent the total light transmittance of the projection screen 10 from becoming lower than the total light transmittance of the dimming layer 12.

The projection screen 10 further includes a pair of transparent base materials 13, and the pair of transparent base materials 13 sandwich a pair of transparent conductive layers 11 in the thickness direction of the projection screen 10. The pair of transparent base materials 13 is composed of a first transparent base material 13a and a second transparent base material 13b, and the first transparent base material 13a is in contact with the surface 12F of the dimming layer 12 in the first transparent conductive layer 11a. The second transparent base material 13b is located on the surface opposite to the surface, and the second transparent base material 13b is located on the surface of the second transparent conductive layer 11b opposite to the surface in contact with the back surface 12R of the dimming layer 12. The first transparent base material 13a and the first transparent conductive layer 11a form the first conductive film 14a, and the second transparent base material 13b and the second transparent conductive layer 11b form the second conductive film 14b. The pair of transparent base materials 13 have light transmittance, and the material for forming each transparent base material 13 may be various resins.

The total light transmittance of the transparent base material 13 is preferably higher than the total light transmittance of the light control layer 12 when the light control layer 12 is in the second state. As a result, it is possible to prevent the total light transmittance of the projection screen 10 from becoming lower than the total light transmittance of the dimming layer 12. The thickness of the transparent base material 13 is preferably 50 μm or more and 200 μm or less.

It is also possible to use a flexible resin film as the transparent base material 13. Since the transparent base material 13 has flexibility, the projection screen 10 also has flexibility. Such a projection screen 10 can be applied to a member including a curved surface shape in addition to being laminated on a flat member such as glass, and the projection screen 10 can be stored in a wound state. As described above, the flexible projection screen 10 increases the degree of freedom in handling.

In the first transparent base material 13a, the surface of the light control layer 12 opposite to the surface in contact with the surface 12F is the surface 10F of the projection screen 10, and in the second transparent base material 13b, the light control layer 12 The surface opposite to the surface in contact with the back surface 12R of the projection screen 10 is the back surface 10R of the projection screen 10. In the thickness direction of the projection screen 10, the front surface 10F of the projection screen 10, the front surface 12F of the dimming layer 12, the back surface 12R of the dimming layer 12, and the back surface 10R of the projection screen 10 are arranged in the order described.

[Second example]
As shown in FIG. 2, the projection screen 20 further includes a pair of alignment layers 21 in addition to a pair of transparent conductive layers 11, a dimming layer 12, and a pair of transparent base materials 13. Of the pair of alignment layers 21, one alignment layer 21 is a first alignment layer 21a located between the surface 12F of the dimming layer 12 and the first transparent conductive layer 11a, and the other alignment layer 21 is It is a second orientation layer 21b located between the back surface 12R of the dimming layer 12 and the second transparent conductive layer 11b.

Each alignment layer 21 is a vertical alignment film, and each liquid crystal molecule 12b is oriented so that the extending direction of the liquid crystal molecules 12b is along the normal direction of the plane on which the alignment layer 21 spreads. Therefore, when no voltage is applied to the dimming layer 12, the dimming layer 12 is in the second state. When no voltage is applied to the dimming layer 12, the plurality of liquid crystal molecules 12b have a plane method in which the orientation layer 21 extends in the extending direction of each liquid crystal molecule 12b in the domain 12c in which each liquid crystal molecule 12b is located. They are arranged along the line direction, that is, along the normal direction of the front surface 12F and the back surface 12R of the dimming layer 12.

As a result, light can easily pass through the dimming layer 12 from the front surface 12F toward the back surface 12R and from the back surface 12R toward the front surface 12F. As a result, the haze value in the dimming layer 12 becomes smaller than when a voltage is applied to the dimming layer 12.

On the other hand, when a voltage is applied to the dimming layer 12, the state of the dimming layer 12 is the first state. When a voltage is applied to the dimming layer 12, the plurality of liquid crystal molecules 12b are irregularly arranged in the domain 12c in which each liquid crystal molecule 12b is located. As a result, it becomes difficult for light to pass through the dimming layer 12 from the front surface 12F toward the back surface 12R and from the back surface 12R toward the front surface 12F. As a result, the haze value in the dimming layer 12 becomes larger than when no voltage is applied to the dimming layer 12.

As described above, when the voltage is applied to the dimming layer 12, the haze value of the dimming layer 12 is relatively large, and when the voltage is not applied to the dimming layer 12, the dimming layer 12 is used. The dimming layer 12 having a relatively small haze value is a reverse type dimming layer. As described above, the reverse type dimming layer 12 is embodied by the dimming layer 12 and the pair of alignment layers 21 sandwiching the dimming layer 12.

In the first transparent base material 13a, the surface of the light control layer 12 opposite to the surface in contact with the surface 12F is the surface 20F of the projection screen 20, and in the second transparent base material 13b, the light control layer 12 The surface opposite to the surface in contact with the back surface 12R of the projection screen 20 is the back surface 20R of the projection screen 20.

Also in the projection screen 20 of the second example, it is preferable that the domain diameter D and the domain density of the projection screen 10 of the first example are applied, and the thickness T of the dimming layer 12, the total light transmittance, and the haze are determined. It is preferred to be applied.

In addition to the above-mentioned Patent Documents 2 and 3, in Patent Document 4 (Japanese Patent Laid-Open No. 6-82748), it is possible to switch between a transmission state and a scattering state instead of a screen using a lens sheet. A technique has been proposed in which a screen is used and when the screen is in a scattered state, light is projected onto the screen to display an image.

According to this technique, it is possible to reduce the feeling of spatial oppression when the screen is not in use by making the screen transparent when no light is projected on the screen. As an example of such a screen, a screen capable of switching between a transmissive state and a scattered state by a liquid crystal layer has been proposed.

In order to control the viewing angle characteristics required for the projection screen, in the design of the light diffusion sheet in the screen using the lens sheet, the material of the fine particles, the shape of the fine particles, the particle size, the distribution of the particle size, the fine particles and the dispersed resin The difference in refractive index from and the amount of dispersion and the amount of dispersion are taken into consideration. The particle size of the fine particles is generally 10 μm or less.

The half-value angle, in other words, the α angle, is used as an index for widening the viewing angle by suppressing the decrease in the brightness of the image visually recognized when the viewpoint is changed. The α angle includes an αH angle which is an angle in the horizontal direction and an αV angle which is an angle in the vertical direction. The light diffusing sheet assists the diffusing characteristic at an angle among these angles that is difficult to control by the characteristic of the lens sheet. Assuming that the illuminance of the light projected on the surface of the screen is constant, the half-value angle and the front luminance, that is, the luminance when the viewing angle is 0 ° are generally inversely proportional to each other. Therefore, if the half-value angle is increased, the front brightness, in other words, the overall brightness of the screen is reduced. Therefore, it is very difficult to balance both of them at a high level.

The target value of the α angle is appropriately set according to the size of the screen displayed on the projection screen, the range in which the observer is located, and the projection conditions by the projector such as the projection distance and the projection angle. For example, when the range of the α angle is set to an appropriate range in the viewing angle and the viewing angle is set to −45 ° or more and 45 ° or less, the target value of the α angle is 45 ° or more.

In general, it is more important to increase the αV angle than to increase the αH angle. As the diffusion characteristics of the projection screen, not only half-value angles but also 1/3 angle, 1/10 angle, and 1/20 angle may be reported. The 1/3 angle is also called the β angle, the 1/10 angle is also called the γ angle, and the 1/20 angle is also called the δ angle.

The techniques exemplified in Patent Documents 2, 3 and 4 change the state in which the liquid crystal layer scatters light by switching between a state in which a voltage is applied to the liquid crystal layer and a state in which no voltage is applied. It is an alternative to the light diffusion layer having a structure in which the particles are dispersed. All of these techniques are proposals for an image display system suitable for switching between projecting light when the screen is in a scattered state and not projecting light when the screen is in a transmissive state. However, neither document considers the viewing angle characteristics of the screen and the suitability for projecting high-definition and high-resolution images.

[Projection screen forming material]
The forming material of each layer constituting the projection screen will be described.

[Dimming layer]
As described above, the dimming layer 12 includes the polymer network 12a and a plurality of liquid crystal molecules 12b located in the domain 12c of the polymer network 12a. The polymer network 12a is a polymer fiber. The resin constituting the polymer network 12a may be either a thermosetting resin or an ultraviolet curable resin.

Further, in the light control layer 12, the material for forming the polymer network 12a preferably contains a monomer having a polar group and a bifunctional monomer. The monomer having a polar group and the bifunctional monomer can be polymerized together with the above-mentioned resin by applying heat or by irradiating with ultraviolet rays. As the monomer having a polar group, a monomer having at least one polar group selected from the group composed of a hydroxy group, a carboxy group, and a phosphoric acid group can be used.

As the liquid crystal molecule 12b, any one of a liquid crystal molecule constituting a nematic liquid crystal, a liquid crystal molecule constituting a smectic liquid crystal, and a liquid crystal molecule constituting a cholesteric liquid crystal can be used.

When the resin constituting the polymer network 12a is an ultraviolet curable resin, the dimming layer 12 can be manufactured by the following manufacturing method. First, a liquid crystal composition containing the liquid crystal molecules 12b and the photopolymerizable compound is sealed between the pair of transparent conductive layers 11. Next, with respect to the enclosed liquid crystal composition, for example, from the side opposite to the liquid crystal composition with respect to the first transparent conductive layer 11a and from the side opposite to the liquid crystal composition with respect to the second transparent conductive layer 11b. Irradiate with ultraviolet rays. As a result, the photopolymerizable compound is photopolymerized to change the photopolymerizable compound into a polymer, and a polymer network 12a having innumerable fine domains 12c is formed by photopolymerization and cross-linking.

If the method is to simultaneously irradiate light from both sides of the enclosed liquid crystal composition, it is possible to suppress variations in the polymerization rate of the photopolymerizable compound in the thickness direction of the polymer network 12a. As a result, it is possible to suppress variations in the size of the domain 12c and variations in the shape of the domain 12c in both the surface direction of the transparent conductive layer 11 and the thickness direction of the dimming layer 12.

The method for manufacturing the dimming layer 12 is described in Japanese Patent No. 4387931 by Kyusyu Nanotec Optical Co., Ltd. Also when manufacturing the dimming layer 12 of the present embodiment, a method based on the manufacturing method described in this patent document can be adopted. As described above, this production method is effective in producing a polymer network 12a in which the size and shape of the domain 12c are controlled.

[Transparent conductive layer]
Each transparent conductive layer 11 may be a conductive film having light transmittance. As the material for forming the transparent conductive layer 11, a metal oxide having light transmittance and conductivity can be used. As the metal oxide, indium tin oxide (ITO), tin oxide (SnO ₂ ), zinc oxide (ZnO) and the like can be used.

Further, as the material for forming the transparent conductive layer 11, a conductive polymer which is a polymer having light transmittance and conductivity can be used. As the conductive polymer, it is preferable to use a polymer containing a π-conjugated conductive polymer and a polyanion. Examples of such a conductive polymer include PEDOT: PSS (polyethylene dioxythiophene).

When the material for forming the transparent conductive layer 11 is ITO, when the light transmitted through the dimming layer 12 is incident on the transparent conductive layer 11, it depends on the crystal structure of the transparent conductive layer 11 in the transparent conductive layer 11. The scattered and reflected light occurs. Therefore, the light incident on the transparent conductive layer 11 from the dimming layer 12 includes a light component scattered backward, that is, a light component scattered toward the back surface 12R of the dimming layer 12. Further, among the light incident on the transparent conductive layer 11 from the dimming layer 12, the light component scattered forward, that is, the light component scattered toward the side opposite to the dimming layer 12 with respect to the transparent conductive layer 11. Then, there is a tendency that the degree to which the color of the light component becomes white increases due to the color mixture of light having different colors.

On the other hand, when the material for forming the transparent conductive layer 11 is PEDOT: PSS, the amount of light components scattered backward is smaller than when the material for forming the transparent conductive layer 11 is ITO, and the light component is scattered forward. It is recognized that the scattered light components increase the contrast in the images displayed on the projection screens 10 and 20.

The contrast is the ratio of the light brightness to the dark brightness on the surfaces 10F and 20F, which are the screen surfaces of the projection screens 10 and 20, in the state where the light is projected on the projection screens 10 and 20. The bright brightness is the maximum value of the brightness on the surfaces 10F and 20F, and the dark brightness is the minimum value of the brightness on the surfaces 10F and 20F.

Further, in order to increase the contrast on the surfaces 10F and 20F of the projection screens 10 and 20, not only the brightness on the surfaces 10F and 20F is increased but also the dark brightness on the surfaces 10F and 20F is decreased. , 20 is adopted as a configuration. In order to reduce the dark brightness on the surfaces 10F and 20F, the brightness of the color on the surfaces 10F and 20F may be lowered, or the light scattered on the projection screens 10 and 20 may have a predetermined color other than white. The projection screens 10 and 20 may be configured.

[Transparent substrate]
As the transparent base material 13, a resin film having light transmittance can be used. As the material for forming the resin film, for example, polyethylene terephthalate, polyethylene, polycarbonate and the like can be used.

[Orientation layer]
As the material for forming the alignment layer 21, for example, a resin that is cured by irradiation with heat or a resin that is cured by irradiation with ionizing radiation such as ultraviolet rays and electron beams can be used. Examples of such a resin include a thermosetting resin, an ultraviolet curable resin, and an electron beam curable resin. Among these, an ultraviolet curable resin is preferable as a material for forming an alignment layer.

Examples of the ultraviolet curable resin include a resin containing at least one of a polymerizable oligomer or monomer having an acryloyl group, a polymerizable oligomer or monomer having a vinyl group, and a photopolymerization initiator. The ultraviolet curable resin may contain additives other than the photopolymerization initiator.

Examples of the polymerizable oligomer or monomer having an acryloyl group include urethane acrylate, epoxy acrylate, polyester acrylate, polyether acrylate, and melamine acrylate. Polymerizable oligomers or monomers having a vinyl group include acrylic acid, acrylamide, acrylonitrile, styrene and the like.

The alignment layer 21 may have fine irregularities on the surface opposite to the surface in contact with the transparent conductive layer 11. The fine irregularities of the alignment layer 21 allow the liquid crystal molecules 12b located in the alignment layer 21 to be oriented in a predetermined direction.

The liquid crystals used in each of Patent Documents 2, 3 and 4 are as follows. In Patent Documents 2 and 3, the PDLC described above is adopted, and the PDLC has a property that the contrast and color of the image displayed on the screen differ depending on the dependence on the viewing angle, that is, the viewing direction and viewing angle of the projection screen. Is said to be large.

Further, in Patent Document 4, a mixture prepared by mixing a thermosetting resin or a photocurable resin with a nematic liquid crystal, microbeads, a curing agent, and a photopolymerization initiator is adopted. The thermosetting resin is an epoxy resin or the like, and the photocurable resin is an acrylic resin, an epoxy resin, an en-thiol resin or the like. Further, in the same document, a mixture in which the encapsulated liquid crystal is dispersed in the above-mentioned resin, polyvinyl alcohol resin, emulsion resin such as acrylic or urethane, is adopted.

[Image display system configuration]
The configuration of the image display system will be described with reference to FIGS. 3 to 6.
As shown in FIG. 3, the image display system 30 includes projection screens 10 and 20, a projector 31, a voltage application unit 32, and a control unit 33. The projection screens 10 and 20 have a sheet shape including front surfaces 10F and 20F and back surfaces 10R and 20R, and also include a dimming layer 12. The projector 31 projects light L on the back surfaces 10R and 20R of the projection screens 10 and 20. The voltage application unit 32 applies an AC voltage to the dimming layer 12.

The control unit 33 controls the drive of the projector 31 and the drive of the voltage application unit 32. The control unit 33 causes the projector 31 to project light L onto the back surfaces 10R and 20R of the projection screens 10 and 20 with the light control layer 12 in the first state of the voltage application unit 32, thereby causing the projection screen 10 and 20R to project light L. Scattered light is emitted from the surfaces 10F and 20F of the projection screens 10 and 20 to 20.

The projection screens 10 and 20 are rear projection type screens, and the side opposite to the projector 31 with respect to the projection screens 10 and 20 is the observation side of the projection screens 10 and 20. The observer OB of the projection screens 10 and 20 observes the scattered light emitted from the surfaces 10F and 20F of the projection screens 10 and 20.

The control unit 33 is electrically connected to the projector 31 and the voltage application unit 32. A control signal for controlling the drive of the projector 31 and the voltage application unit 32 is generated, and the generated control signal is output to each of the projector 31 and the voltage application unit 32 at a predetermined timing.

The projector 31 starts and ends the projection of the light L toward the projection screens 10 and 20 by inputting the control signal output by the control unit 33. The projector 31 projects light L toward the projection screens 10 and 20 by a predetermined number of frames per unit time. The number of frames of the projector 31 is, for example, 30 fps (frame per second) or more and 1000 fps or less.

The voltage application unit 32 starts and ends the application of the AC voltage to the dimming layer 12 by inputting the control signal output by the control unit 33. The frequency of the AC voltage applied by the voltage application unit 32 is, for example, 50 Hz or more and 200 Hz or less, and the frequency of the AC voltage is set to a frequency different from the frequency of the frame. The AC voltage applied by the voltage application unit 32 is, for example, 0.1 V or more and 100 V or less.

When the image display system 30 includes a projection screen 10 including a normal type dimming layer 12, the control unit 33 causes the projector 31 to not apply a voltage to the dimming layer 12 to the voltage applying unit 32. Light is projected toward the back surface 10R of the projection screen 10. As a result, the light is incident on the dimming layer 12 in the first state, so that an image due to scattered light is displayed on the surface 10F of the projection screen 10.

On the other hand, when the image display system 30 includes a projection screen 20 including a reverse type dimming layer 12, the control unit 33 causes the voltage applying unit 32 to apply a voltage to the dimming layer 12. , The state of the dimming layer 12 is changed from the second state to the first state. After that, the control unit 33 causes the projector 31 to project light toward the back surface 20R of the projection screen 20. As a result, since the light is incident on the dimming layer 12 in the first state, an image due to scattered light is displayed on the surface 20F of the projection screen 20.

Note that FIG. 4 is a block diagram showing an example of the voltage application unit 32.
As shown in FIG. 4, the voltage application unit 32 includes a switch 41, a modulation unit 42, and an AC power supply 43. As described above, the AC power supply 43 applies an AC voltage to the pair of transparent conductive layers 11 sandwiching the dimming layer 12 at a predetermined frequency of, for example, 50 Hz or more and 200 Hz or less. When the switch 41 is on, the AC voltage output by the AC power supply 43 is applied to the transparent conductive layer 11, and when the switch 41 is off, the AC voltage output by the AC power supply 43 is transparent conductive. Not applied to layer 11.

The control unit 33 controls the drive of the voltage application unit 32 by electrically connecting to the switch 41 and the modulation unit 42 in the voltage application unit 32.

As shown in FIG. 5, the vertical planes orthogonal to the surfaces 10F and 20F of the projection screens 10 and 20 are the visual field reference planes BLs. The vertical surface including the direction in which the observer OB visually recognizes the projection screens 10 and 20 is the observation surface Pob. The angle formed by the visual field reference plane BLs and the observation plane Pob is the visual field angle θva. When the observer OB visually recognizes the projection screens 10 and 20 from one side with respect to the visual field reference plane BLs, the viewing angle θva is a negative value, and the observer OB views the projection screens 10 and 20 from the other side with respect to the visual field reference plane BLs. When visually recognized, the viewing angle θva is a positive value. On the surfaces 10F and 20F of the projection screens 10 and 20, the luminance standardized by the luminance when the viewing angle θva is 5 ° is the normalized luminance. Each vertical plane is a plane extending along the vertical VD.

As shown in FIG. 6, the horizontal plane orthogonal to the back surfaces 10R and 20R of the projection screens 10 and 20 is the projection reference plane BLp. The plane including the direction in which the projector 31 projects light onto the back surfaces 10R and 20R of the projection screens 10 and 20 is the projection surface Ppro. The angle formed by the projection reference plane BLp and the projection plane Ppro is the projection angle θpro. The projection angle θpro when projecting light from above the projection reference plane BLp in the vertical direction VD is a positive value, and the projection angle θpro when projecting light from below the projection reference plane BLp in the vertical direction VD is a positive value. Is a negative value.

[How to drive the image display system]
The driving method of the image display system 30 will be described with reference to FIG. 7.
As described above, when projecting light onto the projection screen 10 of the first example, the voltage application unit 32 does not apply an AC voltage to the dimming layer 12, while projecting light onto the projection screen 20 of the second example. , The voltage application unit 32 applies an AC voltage to the light control layer 12.

In the image display system 30, the control unit 33 controls the drive of the projector 31 and the drive of the voltage application unit 32 so that the cycle of the frame in the projector 31 and the period of the AC voltage in the voltage application unit 32 are different from each other. ing.

Here, as shown in FIG. 7, since the voltage application unit 32 applies an AC voltage to the dimming layer 12, the instantaneous value of the AC voltage applied by the voltage application unit 32 to the dimming layer 12 includes 0V. .. That is, the period during which the voltage applying unit 32 applies the AC voltage to the dimming layer 12 includes the moment when the voltage applying unit 32 does not apply the voltage to the dimming layer 12. When the instantaneous value of the AC voltage applied by the voltage applying unit 32 is 0, the state of the dimming layer 12 is the second state. Therefore, the light projected by the projector 31 onto the projection screen 20 is emitted from the surface 20F of the projection screen 20 by passing through the projection screen 20 with almost no scattering on the projection screen 20.

Therefore, only light having substantially the same area as the area occupied by the projector 31 on the plane orthogonal to the optical axis of the light projected toward the projection screen 20 is emitted to the observation side of the projection screen 20. As a result, only a part of the surface 20F of the projection screen 20 is in a state of increased brightness.

As described above, since the frequency of the AC voltage, that is, the voltage cycle C1 which is the cycle of the AC voltage is 200 Hz or less, the moment when the instantaneous value of the AC voltage is 0 V is 2.5 mm in the most frequent case. Occurs once every second. Since the number of frames of the projector 31, that is, the frame period C2, which is the period of the frames, is 30 fps or more and 1000 fps or less, the frames are projected onto the projection screen 20 at a frequency of once every 1 millisecond at the highest frequency. NS.

When the voltage period C1 and the frame period C2 are equal to each other, a moment when the AC voltage is 0V occurs at the same timing for each frame while the light corresponding to one frame is projected. Therefore, an image having a different color and vividness from the image to be visually recognized by the observer OB may be projected on the surface 20F of the projection screen 20 at the same timing for each frame. On the other hand, when the voltage period C1 and the frame period C2 are different from each other, the moment when the AC voltage becomes 0V while the light corresponding to one frame is projected is a timing different from each other for each frame. Is included. Therefore, it is possible to prevent the image quality from being lowered as compared with the configuration in which the voltage period C1 and the frame period C2 are equal to each other.

Even if the image display system 30 includes the projection screen 10 of the first example, when an AC voltage is applied to bring the dimming layer 12 into the first state, the voltage cycle C1 is the same as the above-described configuration. And the frame period C2 are preferably different from each other, whereby the same effect as the above-described configuration can be obtained.

[Action of projection screen]
The operation of the projection screen 10 will be described with reference to FIG.
FIG. 8 is a graph showing an example of optical characteristics in the projection screen 10 of the first example. In FIG. 8, while the optical characteristics of the projection screen 10 of the first example are shown by solid lines, the projection screen of the reference example is a projection screen including a dimming layer formed from PDLC, which is a conventional dimming layer. The optical characteristics in are shown by the alternate long and short dash line. Further, in the graph shown in FIG. 8, the vertical axis is the intensity of transmitted light on the surface of each projection screen, and is a relative standardized by the intensity of transmitted light when the viewing angle θva is 0 °. The intensity of transmitted light.

As shown in FIG. 8, in the projection screen 10 of the first example, the half-value angle, in other words, the α angle is ± 45 °. If the range of the α angle, in other words, 1/2 or more of the brightness when the projection screen is visually recognized from the front is set to the allowable range as the screen brightness, 90 ° is the field of view in the projection screen 10 of the first example. It can be said that the angle θva is an appropriate range.

On the other hand, in the projection screen of the reference example, the half-value angle is ± 20 °, and 40 ° can be said to be an appropriate range in the viewing angle θva. In the projection screen of the reference example, the viewpoint of the observer OB moves with respect to the projection screen even if the brightness when the viewing angle θva is 0 ° is about the same as that of the projection screen 10 of the first example. The accompanying decrease in brightness is more remarkable than that of the projection screen 10 of the first example.

[Example]
Examples will be described with reference to FIGS. 9 to 17.
As the projection screen of Example 1, a projection screen having a dimming layer, a pair of transparent conductive layers, and a pair of transparent substrates having the following configurations was prepared. The dimming layer was formed by PNLC, had a thickness of 20 μm, an average domain diameter of 1 μm, and a domain density of 1.0 × 10 ⁹ / mm ³ . The pair of transparent conductive layers were each formed of ITO and had a thickness of 50 nm. Each pair of transparent substrates was formed from PET and had a thickness of 50 μm.

As the projection screen of Comparative Example 1, a projection screen having a dimming layer, a pair of transparent conductive layers, and a pair of transparent substrates having the following configurations was prepared. The dimming layer was formed by PDLC and had a thickness of 20 μm. The pair of transparent conductive layers were each formed of ITO and had a thickness of 50 nm. Each pair of transparent substrates was formed from PET and had a thickness of 188 μm.

The total light transmittance and haze were measured for each of the projection screen of Example 1 and the projection screen of Comparative Example 1. In each test example, the state in which the AC voltage is not applied to the dimming layer is set as the first state, the AC voltage is applied to the dimming layer, and the total light transmittance of the dimming layer is high. The highest state was set as the second state, and the total light transmittance and haze in each state were measured.

A haze meter (NDH-7000SP, manufactured by Nippon Denshoku Kogyo Co., Ltd.) was used for measuring the total light transmittance and haze. The total light transmittance was measured by a method conforming to JIS K 7361-1 (ISO 13468-1), and the haze was measured by a method conforming to JIS K 7136 (ISO 14782). Further, the projection angle θpro of the light source when measuring the total light transmittance and the haze was set to 0 °, and the viewing angle θva was set to 0 °.

In addition, the Y stimulation value was measured for each of the projection screen of Example 1 and the projection screen of Comparative Example 1. A scattering distribution measurement system (IS-SA, manufactured by Radiant Vision Systems) was used for measuring the Y stimulation value, and a white LED (PFBR-150SW, manufactured by CCS Co., Ltd.) was used as a light source. The Y stimulation value was measured by a method conforming to JIS Z 8722. Further, the projection angle of the light source when measuring the Y stimulation value was set to −60 ° or more and 0 ° or less, and the viewing angle θva was set to −80 ° or more and 80 ° or less.

[Measurement result]
[Total light transmittance and haze]
In the projection screen of Example 1, it was found that the total light transmittance in the first state was 73% and the haze was 98%, and the total light transmittance in the second state was 83% and the haze. Was found to be 12%. In the projection screen of Comparative Example 1, it was found that the total light transmittance in the first state was 78% and the haze was 94%, and the total light transmittance in the second state was 79% and the haze. Was found to be 11%.

[Y stimulation value]
[measured value]
The measurement results of the Y stimulation value were as shown in FIGS. 9 to 12.
As shown in FIG. 9, when the projection angle θpro is −15 °, the Y stimulation value of Comparative Example 1 is equal to or greater than the Y stimulation value of Example 1 in the range of the viewing angle θva of −20 ° or more and 20 ° or less. Was recognized as. On the other hand, in the range where the viewing angle θva is -80 ° or more and less than -20 °, and is larger than 20 ° and 80 ° or less, the Y stimulus value of Example 1 is larger than the Y stimulus value of Comparative Example 1. Was recognized.

On the other hand, as shown in FIG. 10, when the projection angle θpro is −30 °, the Y stimulation value of Example 1 is the Y stimulus value of Comparative Example 1 in the range of the viewing angle θva of −80 ° or more and 80 ° or less. It was found that it was larger than the Y stimulation value of.

Further, as shown in FIG. 11, when the projection angle θpro is −45 °, and further, as shown in FIG. 12, the viewing angle θva is −80 ° even when the projection angle θpro is −60 °. It was found that the Y stimulus value of Example 1 was larger than the Y stimulus value of Comparative Example 1 in the range of 80 ° or less.

As described above, according to the projection screen of Example 1, when the projection angle θpro is in the range of -60 ° or more and -30 ° or less, the projection screen of Comparative Example 1 is used regardless of the size of the viewing angle θva. It was also found that the brightness on the surface of the projection screen was high.

In the image display system, the larger the absolute value of the projection angle θpro, the shorter the distance between the back surface of the projection screen and the projector. Therefore, an image display system having a projector having a large absolute value of the projection angle θpro is preferable in that the size of the space occupied by the image display system can be reduced as compared with a configuration in which the absolute value of the projection angle θpro is small. As described above, according to the projection screen of Example 1, the brightness on the surface is increased as compared with the projection screen of Comparative Example 1 in the range where the projection angle θpro is −60 ° or more and −30 ° or less. Therefore, according to the projection screen of the first embodiment, the brightness of the front surface can be increased while shortening the distance between the back surface and the projector.

[Standardized brightness]
The measurement results of the standardized luminance are as shown in FIGS. 13 to 17.
As described above, in the brightness of the surface of the projection screen, the brightness standardized by the brightness when the viewing angle θva is 5 ° is the normalized brightness. In this example, the Y stimulation value was used as the surface brightness.

As shown in FIG. 13, when the projection angle θpro is 0 °, the standardized luminance of Example 1 is higher than the normalized luminance of Comparative Example 1 in the range of the viewing angle θva of −80 ° or more and 80 ° or less. It was found to be large.

Further, when the projection angle θpro is −15 ° as shown in FIG. 14, when the projection angle θpro is −30 ° as shown in FIG. 15, the projection angle θpro is −45 ° as shown in FIG. In any case, it was found that the standardized brightness of Example 1 was larger than the standardized brightness of Comparative Example 1 in the range where the viewing angle θva was −80 ° or more and 80 ° or less.

On the other hand, as shown in FIG. 17, when the projection angle θpro is −60 ° and the viewing angle θva is in the range of −50 ° or more and 50 ° or less, the normalized brightness of Example 1 is the standardized brightness of Comparative Example 1. It was confirmed that the brightness was higher than the standardized brightness of. On the other hand, in the range where the viewing angle θva is -80 ° or more and less than -50 ° and the viewing angle θva is larger than 50 ° and 80 ° or less, the standardized brightness of Comparative Example 1 is higher than the standardized brightness of Example 1. Was also found to be large.

As described above, according to the projection screen of Example 1, it is recognized that the change in brightness on the surface of the projection screen is suppressed with the change of the viewing angle θva as compared with the projection screen of Comparative Example 1. rice field.

[Half-value angle and 1/3 angle]
The half-value angle and the 1/3 angle in the normalized luminance when the projection angle θpro is 0 ° are as shown in FIG.
As shown in FIG. 13, in the projection screen of Example 1, it was confirmed that the half-value angle was ± 22 ° and the 1/3 angle was ± 30.5 °. In other words, at the viewing angle θva, the range where the surface brightness is 1/2 or more of the normalized brightness is the range of -22 ° or more and 22 ° or less, and the surface brightness is 1/3 or more of the normalized brightness. It was found that a certain range was -30.5 ° or more and 30.5 ° or less.

On the other hand, in the projection screen of Comparative Example 1, it was confirmed that the half-value angle was ± 11 ° and the 1/3 angle was ± 14.5 °. In other words, at the viewing angle θva, the range in which the surface brightness is 1/2 or more of the normalized brightness is the range of -11 ° or more and 11 ° or less, and the surface brightness is 1/3 or more of the normalized brightness. It was found that a certain range was -14.5 ° or more and 14.5 ° or less.

Further, in the projection screen of Example 1, the difference between the half-value angle and the 1/3 angle is 8.5 ° in each of the positive range and the negative viewing angle range, and in the projection screen of Comparative Example 1, the difference is 8.5 °. It was found that the difference between the half-value angle and the 1/3 angle was 3.5 ° in each of the positive and negative viewing angles.

As described above, according to the projection screen of Example 1, it is recognized that the brightness on the surface of the projection screen is suppressed to be lowered with the change of the viewing angle θva as compared with the projection screen of Comparative Example 1. rice field.

As described above, according to one embodiment of the projection screen and the image display system, the effects listed below can be obtained.
(1) The liquid crystal molecules 12b are located in the polymer network 12a stretched over the entire dimming layer 12. Therefore, in the plane of the dimming layer 12, the scattering of light by the polymer network 12a and the scattering of light by the liquid crystal molecules 12b are unlikely to occur, and the scattered light is emitted from the entire surface 12F of the dimming layer 12. Easy to be done. In this way, since the scattered light emitted from the surface 12F of the dimming layer 12 is unlikely to be biased, even if the viewing angle θva with respect to the projection screens 10 and 20 changes, the light emitted toward the observer OB The amount of light does not easily decrease. As a result, according to the projection screens 10 and 20, the image can be easily visually recognized with a wider viewing angle θva.

(2) Since the light contained in the wavelength region of visible light is scattered to the same extent regardless of the wavelength, light having white color can be emitted as scattered light, and the domain diameter D is from 3 μm. It is possible to suppress the scattering angle of scattered light from becoming smaller than that of a large configuration.

(3) In the dimming layer 12 having a domain diameter D of 0.1 μm or more and 3 μm or less, the viewing angles θva of the projection screens 10 and 20 are likely to widen because the total light transmittance and the haze are included in the above ranges, respectively. Become.

(4) When the thickness T of the dimming layer 12 is 5 μm or more, the light incident on the dimming layer 12 from the back surface 12R of the dimming layer 12 is emitted from the front surface 12F of the dimming layer 12. In the meantime, the light is scattered to the extent that the variation in brightness within the surface 12F of the dimming layer 12 is suppressed. Further, when the thickness T of the dimming layer 12 is 50 μm or less, it is possible to suppress that the amount of light transmitted through the dimming layer 12 decreases from the back surface 12R of the dimming layer 12 toward the front surface 12F, which in turn suppresses the decrease in the amount of light transmitted through the dimming layer 12. , It is possible to suppress the decrease in brightness of the image visually recognized by the observer OB.

(5) When the density of the domain 12c is 2 × 10 ⁷ / mm ³ or more, the light incident on the dimming layer 12 from the back surface 12R of the dimming layer 12 is easily scattered in the dimming layer 12. As a result, variation in brightness within the surface 12F of the dimming layer 12 can be suppressed. Further, since the density of the domain 12c is 2 × 10 ¹² pieces / mm ³ or less, the density of the domain 12c is too high, so that the amount of light transmitted from the back surface 12R of the dimming layer 12 toward the front surface 12F is small. As a result, the brightness of the image visually recognized by the observer OB is suppressed from being lowered.

(6) Compared with a configuration in which the absolute values of the half-value angle and the 1/3 angle are smaller, it is possible to suppress the decrease in brightness on the surfaces 10F and 20F of the projection screens 10 and 20 as the viewing angle changes.

(7) Since the voltage period C1 and the frame period C2 are different from each other, the moment when the AC voltage becomes 0V while the light corresponding to one frame is projected includes the timings different from each other for each frame. Is done. Therefore, it is possible to prevent the image quality from being lowered as compared with the configuration in which the voltage period C1 and the frame period C2 are equal to each other.

The above-described embodiment can be appropriately modified and implemented as follows.
-At least one of the frequency of the AC voltage applied by the voltage application unit 32 and the number of frames in the projector 31 may be changeable values. In other words, the image display system 30 may have at least one of a configuration for changing the frequency of the AC voltage and a configuration for changing the number of frames. Even with such a configuration, if the frequency of the AC voltage and the frequency of the frame are different from each other, the same effect as (7) described above can be obtained.

A layer for adjusting the refractive index or an antireflection layer may be formed on the back surfaces 10R and 20R of the projection screens 10 and 20. As a result, it is possible to suppress the reflection of the light projected from the projector 31 on the projection screens 10 and 20, that is, the scattering to the rear. As a result, the light projected on the projection screens 10 and 20 can be effectively used, and the observer can visually recognize the image without the ghost image.

-The difference in the refractive index of each layer provided in the projection screens 10 and 20 and the state of the surface of each layer may be appropriately changed so as to suppress unnecessary reflection at the interface of each layer.

The light control layer 12 may contain a dye having a predetermined color and which does not interfere with the movement of the liquid crystal molecules 12b according to the magnitude of the AC voltage applied to the light control layer 12. According to such a configuration, the dimming layer 12 can have a predetermined color.

-The projection screens 10 and 20 can also be used as a reflective screen. In this case, the side where the projector 31 is located with respect to the projection screens 10 and 20 is the observation side of the projection screens 10 and 20. In the reflection type screen, it is necessary to apply a process to increase the reflectance of the light incident on the projection screen on the surface of the projection screen opposite to the side on which the projector is located. For example, it is preferable to form a reflective layer on a surface opposite to the side on which the projector is located.

[Advantages of PNLC]
The projection screen having a dimming layer formed of PNLC has the following advantages.
Compared to a light diffusing sheet with fixed light diffusing characteristics, the projection screen can electrically switch between a transmitted state and a scattered state, and the haze value can also be switched between multiple values. Is possible. Therefore, it is possible to change the viewing angle characteristics of the projection screen, and to instantly change the scattering property of the projection screen to the illuminance of the external environment, the brightness of the light, and the scattering property according to the image quality. This allows the observer to visually recognize the image in a suitable state. Further, according to the projection screen, it is possible to lower the drive voltage required for switching between the transmission state and the scattering state as compared with the configuration having a dimming layer formed of another liquid crystal.

Since the PNLC has a polymer network, the light projected by the projector is efficiently scattered forward according to the polymer network in which the domain diameter and the direction in which the domain is arranged are controlled. As a result, the loss of light projected by the projector and the light component scattered backward, which causes a ghost image, are suppressed, and the brightness of the image visually recognized by the observer can be increased.

In PNLC, when the liquid crystal molecule and the polymer network are phase-separated in the process of forming the PNLC, almost no unreacted component is generated, and the polymer network and the liquid crystal molecule are clearly separated with high purity. Further, when forming the PNLC, it is possible to realize an ideal orientation state without performing a process of orienting the pretilt angle by rubbing the transparent conductive layer, and the liquid crystal molecules are divided into domains by the polymer network. Orients almost uniformly to.

The domain diameter of the PNLC is preferably about 1 μm, which does not cause Rayleigh scattering, which is selective scattering depending on the wavelength, and is at least a visible light region wavelength, which is a wide wavelength range including a range of 400 nm or more and 780 nm or less. Scattering occurs efficiently. The diameter of the fine particles contained in the light diffusion sheet is approximately 2 μm or more and 10 μm or less, and the diameter of the droplets dispersed in PDLC is approximately several μm.

For the following reasons, it can be said that PNLC has an optimum structure for exhibiting suitable optical characteristics as a projection screen as compared with polymer-dispersed capsules (NCAP: Nematic curvilinear aligned Phase) and PDLC. That is, in PNLC, since the domain diameter and the network structure are optically uniform in PNLC, the domain diameter varies, so that scattering does not occur uniformly in the plane of PNLC, and Since the density of the liquid crystal layer varies, it is possible to prevent the scattering from occurring uniformly in the plane of the PNLC.

In NCAP and PDLC, the light components emitted from these include a large amount of reflection components at the interface of capsules and droplets in the liquid crystal layer. Since such capsules and droplets affect the intensity of the light component scattered forward from the liquid crystal layer as compared with the polymer network contained in PNLC, the intensity of the light component tends to vary in the plane of the liquid crystal layer.

[Target of projection screen]
-The projection screens 10 and 20 are projection televisions that project images from projectors equipped with various optical engines such as a liquid crystal display (LCD) and DMD (Digital Micro-mirror Device) (registered trademark of Texas Instruments). Can be applied to. The projection screens 10 and 20 can be applied to both a transmissive projection television and a reflective projection television. The transmissive type is also referred to as a projection type, a back projection type, a rear type, or the like, and the reflective type is also referred to as a front type or the like.

The projection screens 10 and 20 include a high-definition and high-resolution projector 31 having full HD (1920 × 1080), 4K (3840 × 2160), 8K (7680 × 4320), or a large number of pixels above these. It is preferably applied to the image display system 30.

-The projection screens 10 and 20 can also be used as partitions having functions such as curtains, blinds, and shoji screens. According to the projection screens 10 and 20, the state in which the projection screens 10 and 20 are used can be changed as follows.

(A) When the dimming layer 12 is in the second state, the inside of the space partitioned by the projection screens 10 and 20 can be visually recognized via the projection screens 10 and 20 (B). The space partitioned by the projection screens 10 and 20 is concealed from the outside by the dimming layer 12 in the first state. (C) Light is emitted from the projector 31 when the dimming layer 12 is in the first state. Projecting and displaying an image

Therefore, by applying these projection screens 10 and 20 to, for example, a show window, the eye-catching effect of the show window can be enhanced.

10, 20 ... Projection screen, 10F, 12F, 20F ... Front surface, 10R, 12R, 20R ... Back surface, 11 ... Transparent conductive layer, 11a ... First transparent conductive layer, 11b ... Second transparent conductive layer, 12 ... Dimming layer , 12a ... Polymer network, 12b ... Liquid crystal molecules, 12c ... Domain, 13 ... Transparent substrate, 13a ... First transparent substrate, 13b ... Second transparent substrate, 14a ... First conductive film, 14b ... Second conductive film , 21 ... Alignment layer, 21a ... First alignment layer, 21b ... Second alignment layer, 30 ... Image display system, 31 ... Projector, 32 ... Voltage application unit, 33 ... Control unit, 41 ... Switch, 42 ... Modulation unit, 43 ... AC power supply, BLp ... Projection reference plane, BLs ... Field reference plane, Pob ... Observation plane, Ppro ... Projection plane, θpro ... Projection angle, θva ... Viewing angle.

Claims (8)

A pair of transparent conductive layers and
It is sandwiched between the pair of transparent conductive layers and includes a dimming layer including a front surface and a back surface.
The light control layer contains a polymer network having a three-dimensional network having a plurality of domains and liquid crystal molecules located in the domains, and is applied to the light control layer via the pair of transparent conductive layers. By changing the magnitude of the voltage to be applied, the light is scattered between the first state of scattering light and the second state of transmitting light, and in the first state, the light incident from the back surface is diffused. Scattered light is emitted from the surface
When the dimming layer is in the first state,
A projection screen in which the haze of the dimming layer is 95% or more. The projection screen according to claim 1, wherein the average value in the domain diameter of the polymer network is 0.1 μm or more and 3 μm or less. When the dimming layer is in the first state,
The projection screen according to claim 1 or 2, wherein the total light transmittance of the dimming layer is 50% or more. The projection screen according to any one of claims 1 to 3, wherein the dimming layer has a thickness of 5 μm or more and 50 μm or less. The projection screen according to any one of claims 1 to 4, wherein in the dimming layer, the density of the domains is 2 × 10 ⁷ / mm ³ or more and 2 × 10 ¹² / mm ^{3 or less.} The projection screen includes a front surface and a back surface.
In the thickness direction of the projection screen, the front surface of the projection screen, the front surface of the dimming layer, the back surface of the dimming layer, and the back surface of the projection screen are arranged in this order.
The vertical plane orthogonal to the surface of the projection screen is the visual field reference plane.
The vertical surface including the direction in which the observer sees the projection screen is the observation surface.
The angle formed by the viewing reference surface and the observation surface is the viewing angle.
When the observer visually recognizes the projection screen from one side with respect to the visual field reference plane, the viewing angle is a negative value, and when the observer visually recognizes the projection screen from the other side with respect to the visual field reference plane. The viewing angle is a positive value and
The horizontal plane orthogonal to the back surface of the projection screen is the projection reference plane.
The plane including the direction in which the projector projects light onto the back surface of the projection screen is the projection surface.
The angle formed by the projection reference plane and the projection plane is the projection angle.
In the brightness of the surface of the projection screen, the brightness standardized by the brightness when the viewing angle is 5 ° is the normalized brightness.
When the projection angle is 0 °, the projection screen has a half-value angle of the standardized luminance at the viewing angle of ± 22 ° and a 1/3 angle of the normalized luminance of ± 30.5 °. The projection screen according to any one of claims 1 to 5, which is configured as described above. A projection screen having a sheet shape including a front surface and a back surface and having a dimming layer,
A projector that projects light onto the back surface of the projection screen,
A voltage application unit that applies a voltage to the dimming layer and
An image display system including a control unit that controls driving of the projector and driving of the voltage application unit.
The projection screen is the projection screen according to any one of claims 1 to 6.
In the thickness direction of the projection screen, the front surface of the projection screen, the front surface of the dimming layer, the back surface of the dimming layer, and the back surface of the projection screen are arranged in this order.
The control unit causes the projection screen to display light by projecting light onto the back surface of the projection screen with the light control layer in the first state of the voltage applying unit. An image display system that emits scattered light from the surface. The projection screen further comprises a pair of alignment layers.
Of the pair of alignment layers, one alignment layer is located between the front surface of the dimming layer and the transparent conductive layer, and the other alignment layer is the back surface of the dimming layer and the transparent layer. Located between the conductive layer
The voltage application unit applies an AC voltage to the dimming layer to apply an AC voltage.
The seventh aspect of claim 7, wherein the control unit controls the drive of the projector and the drive of the voltage application unit so that the period of the frame in the projector and the period of the AC voltage in the voltage application unit are different from each other. Image display system.

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