JP4903376B2 - Screen and image projection system - Google Patents

Description

  The present invention relates to a screen for projecting a light image from a high-luminance CRT, a liquid crystal projector, or the like, and an image projection system having the screen.

An image projection system such as a projection apparatus that projects an optical image using a high-luminance CRT, a liquid crystal projector, or the like can easily display a high-definition image on a large screen. It is widely used as a communication tool. The screen used here has a structure in which a white material or a reflective film is coated on the surface to improve light utilization efficiency, or beads are spread on the surface to improve visibility for multiple observers by light diffusion. The invention has been devised (see, for example, Patent Document 1). Alternatively, there is one in which a directional reflection structure such as a lenticular lens is provided on the screen surface so that a plurality of observers can efficiently display an image (for example, see Patent Document 2).
Japanese Patent Laid-Open No. 11-52107 (pages 4, 5 and 1) Japanese Patent Laid-Open No. 2002-169224 (page 3, FIG. 1)

  However, conventional screens made of diffusing materials such as beads can achieve a wide viewing angle, but the screen is dark due to low gain, while screens using lenticular lenses have high directivity and a bright screen with high gain. Although obtained, there was a problem that the viewing angle was narrowed. Therefore, an object of the present invention is to provide a projector screen having a wide viewing angle characteristic while maintaining a directivity and maintaining a bright screen.

  In the projector screen of the present invention, a plurality of fine layered structures or columnar structures are arranged in a plane, and the central region of the layered structure or columnar structure is formed with a higher refractive index than the outer peripheral region surrounding the layered structure or columnar structure. Using a directional light diffusion layer having a function of guiding light in the direction or a layered lens sheet or a columnar lens sheet as a directional diffusion sheet, the orientation direction of the layered structure or the columnar structure is the optical axis direction of the optical image from the projector, Alternatively, the optical axis direction and the direction symmetric with respect to the normal on the screen surface are substantially coincident with each other so that the projected light image is within the scattering incident angle range of the lens sheet. A projector screen that combines both the directivity of the lens sheet and the high viewing angle characteristics of the light diffusing particles by dispersing the light diffusing particles Can be present, it was possible to solve the above problems.

  According to the present invention, it is possible to provide a thin and lightweight screen having good viewing angle characteristics and luminance characteristics, so that not only the display quality of the projection system using the same can be improved, but also the projection system can be reduced in size and weight. It has the effect.

  In addition, the screen of the present invention not only has a high gain for the projected image, but also has a small reduction in visibility due to external light, so that a large-screen image with good visibility can be obtained even in a bright room under an illumination environment. It has the effect that the presentation environment in meetings and education can be made bright and favorable.

The screen of the present invention uses a directional light diffusion layer that scatters light incident at a specific angle range and transmits light incident at other angles, and uses light diffusing particles dispersed in the directional light diffusion layer. I have. The specific angle range of the directional light diffusing layer substantially coincides with the optical axis direction in which the optical image is projected, or a direction symmetric with respect to the optical axis direction and a perpendicular on the screen surface.

  Here, the directional light diffusion layer is configured by a layered lens having a function of guiding light in the thickness direction, and the layered lens includes a first region having a low refractive index formed continuously in the thickness direction, The second region having a higher refractive index than the first region continuously formed in the thickness direction has a layered structure formed alternately. Alternatively, the directional light diffusion layer is composed of a columnar lens layer having a function of guiding light in the thickness direction, and this columnar lens layer is formed by continuously forming a region having a higher refractive index than the surrounding region in the thickness direction. A plurality of columnar structures are provided in the plane.

  The light diffusing particles have an average particle size smaller than the layer thickness of the layered structure or the average diameter of the columnar structure. For example, translucent particles having an average particle diameter of 60 nm to 20 μm were used as the light diffusing particles.

  Further, a polarizing sheet is provided on the side opposite to the light projection side with respect to the directional light diffusion layer. In addition, a light reflection layer was provided on the side opposite to the light projection side with respect to the directional light diffusion layer. In addition, a black stripe that is a periodic absorption stripe is provided on the surface of the directional light diffusion layer. Further, the light diffusion layer is provided on the image projection side of the directional light diffusion layer.

  The image projection system of the present invention includes the screen having any one of the above-described configurations and an optical image projector that projects an optical image on the screen.

The screen of the present invention includes a directional light diffusion layer that scatters light incident at a specific angle range and transmits light incident at other angles, and light diffusion particles dispersed in the directional light diffusion layer. ing. The specific angle range of the directional light diffusing layer substantially coincides with the optical axis direction in which the optical image is projected, or a direction symmetric with respect to the optical axis direction and a perpendicular on the screen surface.

  The directional light diffusing layer 1 includes a plurality of fine layered structures 9 arranged in a plane, and the central region of these layered structures 9 is formed with a higher refractive index than the outer peripheral region surrounding the layered structure 9, and light is transmitted in the thickness direction. It has a function to guide. Alternatively, the directional light diffusing layer 1 has a plurality of fine columnar structures 9 arranged in a plane, and the central region of these columnar structures 9 is formed with a higher refractive index than the outer peripheral region surrounding the columnar structures 9, and the thickness direction It has a function to guide light to. These layered structures constitute layered lenses, and the columnar structures constitute columnar lenses. When the directional light diffusion layer 1 is composed of a layered lens, it is desirable that the layer stacking direction is horizontal or vertical with respect to the screen. In addition, light diffusion particles 10 are dispersed inside the directional light diffusion layer 1.

  FIG. 8 is a schematic plan view showing the arrangement of layered lenses or columnar lenses. FIG. 8A shows an example in which layered lenses are arranged with the longitudinal direction facing up and down, and these layered lenses have a structure in which a high refractive index layer 13 is surrounded by a low refractive index layer 14. FIG. 8B shows an example in which columnar lenses are arranged in a plane, and these columnar lenses have a structure in which a high refractive index region 13 is surrounded by a low refractive index region 14. These layered lenses and columnar lenses are not necessarily arranged regularly, and may be arranged irregularly.

  The optical axis direction of the layered lens or the columnar lens is referred to as the orientation direction. In the example shown in FIG. 1, the orientation direction of the layered lens or the columnar lens substantially coincides with the direction of the optical axis 6 of the optical image projected from the projector 5. That is, the layered lenses or the columnar lenses are arranged in a tilted downward direction on the viewpoint side in the plane of the directional light diffusion layer 1.

  The directional light diffusion layer 1 is a thin film layer having a film thickness of about 1 μm to 20 μm, and is oriented on the transparent support base 2. Further, instead of the directional light diffusion layer 1, a layered lens sheet or a columnar lens sheet having a layer thickness of about 20 μm to 2 mm may be disposed on the transparent support substrate. In these layered lens sheets or columnar lens sheets, a plurality of fine layered structures or columnar structures 9 are arranged in the plane, and the central region of these layered structures or columnar structures 9 has a refractive index compared to the outer peripheral region surrounding them. It is formed high and has a function of guiding light in the thickness direction.

As the directional light diffusion layer, the directional diffusion layer and the directional diffusion sheet are distinguished from each other according to the layer thickness. Specifically, a layer having a thickness of approximately 1 to 20 μm is referred to as a directional diffusion layer, and a layer having a thickness of approximately 20 μm to 2 mm is referred to as a directional diffusion sheet. In addition, in the following, for the sake of simplicity, the layered lens sheet and the columnar lens sheet will be represented by the same expression as a lens sheet unless particularly distinguished.

  The lens sheet is a graded index type layered lens or columnar lens whose refractive index continuously increases toward the center, or a two-layer structure in which the refractive index of the central portion is higher than the refractive index of the outer peripheral region surrounding it. The step index type layered lens or columnar lens is a film structure in which a plurality of step index type layered lenses or columnar lenses are arranged in a plane.

  Further, as shown in FIG. 3, the support base material 4 may be disposed or bonded to the outside of the light reflection layer 3. Thus, by disposing the support base 4 on the outside of the light reflection layer 3, the light reflection layer 3 can be protected from external mechanical force, humidity, and the like, and deterioration of the light reflectance can be prevented. When used as a front screen, unlike the support substrate 2, the support substrate 4 does not need to be made of a transparent material because it does not need to transmit light.

  5 and 6 schematically show the enlarged structure of the screen of this embodiment and the state of light incident thereon. The layered structure or columnar structure 9 constituting the lens sheet is composed of a high refractive index region 13 at the center and a low refractive index region 14 formed so as to surround it. In the drawing, for the sake of simplicity, the high refractive index region 13 and the low refractive index region 14 are drawn so as to have a clear boundary. However, in the case of a graded index columnar lens, the high refractive index region 13 and the low refractive index region are shown. There is no clear boundary with the region 14. In the case of a layered lens, such a difference in refractive index does not exist in the direction perpendicular to the paper surface of FIGS. The center axis of the layered lens or the columnar lens, that is, the optical axis can be produced with an arbitrary inclination of about 0 to 70 degrees with respect to the film surface normal.

  For example, the lens sheet is manufactured by irradiating a liquid reaction layer made of two or more kinds of photopolymerizable compounds having different refractive indexes mixed with light diffusing particles with ultraviolet rays through a photomask subjected to gradation processing. The refractive index distribution state is controlled by the difference in the photopolymerization rate of the photopolymerizable compound depending on the light irradiation intensity.

  The light diffusing particles have a particle size sufficiently smaller than the width of the layered lens or the diameter of the columnar lens. If this is not done, not only the lens function of the layered lens or columnar lens is impaired, but also the photopolymerization reaction cannot be carried out effectively. Typically, the particle size of the light diffusing particles is desirably 1/5 or less of the width of the layered lens or the diameter of the columnar lens.

  In addition, the inclination of the optical axis of the layered lens or the columnar lens can be controlled by adjusting the angle of the irradiated ultraviolet rays. At this time, the photopolymerizable compound can be applied directly on the support substrate by spin coating or dipping and cured to obtain a directional diffusion layer, and applied to the reaction stage or reaction roll and cured. If it peels afterward, a directional diffusion sheet can be obtained.

  In FIG. 5, an example of an optical path of light incident on the lens sheet from the outside is indicated by arrows 15 and 16. The light projected on the projector screen is incident on the columnar lens with various incident angles distributed within the spread angle of the projected light image. In the case of a step index type lens sheet, as indicated by the optical path 15 and the optical path 16 in FIG. 5, the light incident on the high refractive index region 13 is further refracted toward the normal side of the lens sheet incident surface according to Snell's law. To do. The light incident on the high refractive index region 13 enters the boundary surface with the low refractive index region 14, but when the incident angle to the boundary surface is larger than the critical angle, the incident light is totally reflected. Thus, the incident light is repeatedly reflected at the boundary surface between the high refractive index region 13 and the low refractive index region 14 and guided downward, reflected by the light reflecting layer 3 and again guided upward. The light is emitted from the incident surface of the lens sheet.

  At this time, the emission position and direction of light from the lens sheet are determined by the sheet thickness of the lens sheet, the incident angle and the incident position of light on the high refractive index region 13. The optical path 15 and the optical path 16 in FIG. 5 have the same incident angle but different incident positions, and therefore have different exit angles when guided through the interior and emitted again to the surface. Since the projected image from the projector enters various incident positions at various incident angles, the projected image is subjected to the same action as if it was scattered with the scattering angle being the surface. The scattering angle is determined by the refractive index difference or refractive index gradient between the high refractive index region 13 and the low refractive index region 14, the thickness of the sheet, and the lens diameter of the columnar lens. That is, the larger the refractive index difference or the refractive index gradient of the lens sheet, the larger the scattering angle. Furthermore, the haze value increases as the thickness of the lens sheet increases, as the lens radius decreases, and as the number density of columnar lenses in the sheet surface increases. Further, when the incident angle of light exceeds a specific angle, the incident light passes straight without being scattered. The incident angle range in which the incident light is scattered is referred to as the scattering incident angle, and the incident angle range in which the incident light travels straight through is referred to as the linear transmission angle. If light is incident at a scattering incident angle and there is no light reflection layer 4, the light is scattered and emitted when transmitted through the sheet.

  In the projector screen of the present invention, a lens sheet having a columnar lens diameter of 1 μm to 500 μm and a lens height (lens sheet thickness) of 1 μm to 2 mm can be used. However, considering the production yield, light utilization efficiency, ease of handling, etc., the lens diameter is preferably 5 μm to 100 μm, and the lens height when used as a sheet is preferably 20 μm to 200 μm. In addition, a columnar lens having a refractive index difference of 0.01 to 0.05 can be used. Moreover, the inclination angle with respect to the vertical line standing on the sheet surface of the columnar lens can be an arbitrary angle of about 0 to 70 degrees. When used as a directional diffusion layer, the layer thickness can be reduced to about 1 to 20 μm.

  On the other hand, FIG. 6 demonstrates the case where the incident angle to a lens sheet is a linear transmission angle. Since the configuration is the same as that in FIG. The incident light 17 is incident on the incident surface of the lens sheet at a large incident angle that is greater than or equal to the scattering incident angle. In this case, the light incident on the high refractive index region 13 is refracted and enters the sheet and reaches the boundary with the low refractive index region 14, but since the incident angle on the boundary is small, the light is not totally reflected and is low. The refractive index region 14 is entered. The light that has entered the low-refractive index region 14 enters the high-refractive index region 13 again, and then is reflected by the light reflecting layer 3 formed on the support base 4 and exits from the incident surface of the lens sheet. At this time, when the incident angle of the light reflected by the light reflecting layer 3 is within the range of the scattering incident angle, the light emitted from the incident surface is scattered. Further, when the incident angle of the light reflected by the light reflecting layer 3 is within the range of the linear transmission angle, the light emitted from the incident surface is regularly reflected without being scattered. Further, if the light reflecting layer 3 is not provided, the incident light 16 is transmitted almost linearly.

  On the other hand, in both cases of FIG. 5 and FIG. 6, when the light incident on the lens sheet enters the light diffusion particle 10, the light is diffused. That is, the light diffusing particles 10 act to spread incident light by diffusing incident light. As the light diffusing particles, particles having an average particle diameter of 60 nm to 20 μm and having a refractive index different from the refractive index of the material constituting the lens sheet are used. As the particle shape of the light diffusing particles, an indeterminate shape, a rod shape, or a spherical bead can be used. In particular, the spherical beads produced by the sol-gel method are well controlled in particle size and can select materials having various refractive indexes, so that the screen characteristics can be easily controlled.

  Further, by making the light diffusing particles 10 transparent, light loss due to absorption of the light diffusing particles can be prevented, and a projector image can be displayed efficiently. Further, the light diffusing particles are not necessarily transparent, and may be translucent particles. Even if the material itself is transparent, if the surface has irregularities or porous particles, the particles become translucent particles rather than transparent particles. Even if such translucent particles are used, there is little decrease in light utilization efficiency.

  As described above, since the lens sheet used in the present invention has excellent directivity, it is possible to obtain a clear image with high brightness in the viewing direction in which light is scattered and reflected. On the other hand, in the lens sheet orientation in which light is not scattered and reflected, the brightness of the projected image is drastically lowered and visibility is deteriorated. The light diffusing particles compensate for such a low viewing angle characteristic caused by the high directivity of the lens sheet, and have the effect of widening the viewing angle.

  Returning to the description of FIG. In FIG. 1, the projection image from the projector 5 is projected with the spread indicated by the light rays 7 and 8 around the optical axis 6. A screen in which the scattering incident angle of the lens sheet 1 is within the range of the spread of the projected image is selected and used in the screen of the present invention. By doing so, the projected light image is transmitted through the transparent support base material 2, and then follows the same optical path as shown in FIG. Therefore, a bright projection image with a wide viewing angle is observed for a person observing the screen from the viewpoint 11.

  FIG. 2 shows another configuration relating to the projector screen of the present invention. This configuration is different from the configuration shown in FIG. 1 in that the orientation direction of the columnar lens is substantially coincident with the direction of the optical axis of the projection light image and the direction symmetrical to the perpendicular on the screen surface. In this case, after the projection light image passes through the transparent support substrate 2, it follows the same optical path as shown in FIG. 6 within the lens sheet 1, and the light reflected by the light reflection layer 3 has a scattering incident angle. Therefore, it is uniformly scattered on the front surface. In the configuration shown in FIG. 2, the light scattering by the lens sheet occurs only on the surface portion, so the directivity of the scattered light is high, and the projected image can be made clearer than the configuration shown in FIG. Suitable for projecting high-resolution images.

  FIG. 3 shows another configuration relating to the projector screen of the present invention. In the configuration of FIG. 3, the support base 4 is arranged outside the light reflection layer 3 in the configuration shown in FIG. 2. With such a structure, it is possible to prevent the light reflection layer 3 from being damaged by protecting it from an external mechanical force.

1 and 2, by using a metal film having a thickness of about 200 nm or more as the light reflecting layer 3 in the structure of FIG. 3, the reflectance of the light reflecting layer 3 is improved, and as a result, the light utilization efficiency is increased. However, when the intensity of the light image from the projector is strong, the glare of the image increases and the natural feeling of the display image may be impaired. Therefore, the image quality is remarkably improved by reducing the reflectance of the light reflecting layer 3 used in FIG. 3 to 5 to 30% and simultaneously using a light-absorbing support substrate, for example, the black support substrate 4. Such a low-reflectivity light reflecting layer 3 is formed by forming a high refractive index layer such as TiO ₂ or ZrO ₂ on the support base 4 or the lens sheet, or by using these materials and a low refractive index layer such as SiO _2. It can be easily realized by forming an optical multilayer film in combination. Moreover, you may form metal thin films, such as Ag with a film thickness of about 10-20 nm, the compound of Ag, Pd, and Al. Even when the reflectance of the light reflection layer 3 is larger than 30%, the use of the light-absorbing support base 4 is effective in improving the image quality.

  Further, when the intensity of the projected light image from the projector is relatively weak and the projected image has little glare, instead of forming the light reflecting layer 3, a metal supporting base material whose mirror surface is processed is used as a supporting base. It may be used as the material 4.

  Another configuration relating to the present invention is shown in FIG. In the screen shown here, the lens sheet 1 is bonded to one side of the transparent substrate 2. The orientation direction of the lens sheet 1 is substantially coincident with the optical axis 6 of the optical image from the projector 5. Note that the viewpoint 11 of the observer with this configuration is on the opposite side of the projector 5 across the screen. Such a screen is called a rear screen. Thus, the projector screen of the present invention can be used not only as a front screen but also as a rear screen.

  In the configuration shown in FIG. 4, the light image projected from the projector 5 is incident on the lens sheet 1 within the range of the scattering angle, and is emitted with a specific scattering angle when exiting from the lens sheet 1. This scattering occurs with the same action as shown in FIGS. Therefore, the projection image can be observed from the viewpoint 11 with a wide viewing angle.

  On the other hand, in addition to the image from the projector 5, since the light from the object incident at a linear transmission angle is transmitted without being scattered by the screen of the present invention and enters the viewpoint 11, the observer projects from the projector 5. You can directly observe not only images but also objects behind the screen. Such usage is performed with a head-up display for the purpose of projection onto a window glass of a vehicle such as an automobile. In this case, the haze value by the light diffusing particles 10 is preferably a low value of about 20% or less.

  In any of the configurations shown in FIGS. 1 to 4, a sharper image can be projected by forming black stripes having the same pitch as the pixel pitch of the projected image on the surface of the lens sheet. . This black stripe can be easily formed by printing a binder in which a black dye such as a light-absorbing dye or a black pigment such as carbon is mixed. The surface on which the black stripe is formed may be formed on any surface of the lens sheet, but is formed on the surface opposite to the viewpoint 11 on the front screen and on the same side as the viewpoint 11 on the rear screen. Is preferred.

  As the black stripe, a so-called louver in which a layered stripe pattern in which a light-absorbing pigment or a dye is mixed in a direction perpendicular to the surface of a transparent acrylic plate may be used. Carbon powder is usually used as the light absorbing pigment. This louver acts as a black stripe sheet in which black areas and transparent areas are alternately laminated in the in-plane direction. Even if the pitch of the black stripe is several to several tens of times larger than the pixel pitch, the visibility is improved as compared with the case where there is no black stripe.

  1 to 4, when the image modulation element of the projector 5 uses a polarizing element such as a liquid crystal element, a polarizing sheet is provided on the surface of the support base 2 on the viewpoint 11 side. By pasting, the contrast of the projected image can be improved. In the case of such a polarized projector, the projection light image is light polarized in a specific direction. Therefore, if the polarization axis of the polarizing sheet is aligned with the polarization direction of the projected light image, the light loss of the projected image from the polarizing projector is small, while the polarizing sheet accounts for half of the external light incident on the screen from the viewpoint 9 side. This is because the contrast is improved due to absorption. However, when a color image is projected by a polarization projector, this effect is significant only when the polarization directions of the RGB images are the same.

  On the other hand, when observing an image from a specular reflection area where the intensity of the projected light from the projector 5 is high, moire fringes occur due to the reflected light being reflected multiple times inside the screen, or hot spots that are bright spot areas on the surface. Spots may occur. In order to prevent these, a light diffusion layer 18 is formed on the surface of the lens sheet 1 on the viewpoint 11 side as shown in FIG. As a result, light returning to the inside of the screen due to regular reflection from the surface of the lens sheet 1 can be reduced, and as a result, generation of moire fringes and hot spots is eliminated even in a regular reflection region where the intensity of the projected light image is strong. We were able to.

  As the light diffusion layer 18, a concavo-convex structure may be directly formed on the surface of the lens sheet 1, or a light diffusion film may be disposed or bonded to the viewpoint side surface of the lens sheet 1.

  1 to 3, when the viewpoint side surface of the screen is the support base material 2, the light diffusion layer 18 must be formed on the viewpoint side surface of the support base material 2. The formation method may form a concavo-convex structure directly on the viewpoint side surface of the support base material 2, or may arrange or join the light diffusion film on the viewpoint side surface of the support base material 2.

  As another method for forming the light diffusion layer 18, there is an antiglare structure in which a fine uneven structure is directly formed on the surface of the lens sheet 1. This concavo-convex structure is formed on a processing stage having a corresponding concavo-convex structure by applying ultraviolet rays to a liquid reaction layer composed of two or more kinds of photopolymerizable compounds having different refractive indexes through a photomask subjected to gradation processing. It is possible to produce the lens sheet 1 by controlling the refractive index distribution state by irradiating and controlling the photopolymerization rate of the photopolymerizable compound depending on the light irradiation intensity. Alternatively, only the surface of the high refractive index region may be slightly etched by immersing the lens sheet in a solvent or treating the lens sheet surface with a solvent. The haze value of the light diffusion layer 18 can be arbitrarily controlled by changing the roughness, fine shape, and formation density of the unevenness.

  In addition, as shown in FIG. 9, when the sheet | seat thickness of a directional light-diffusion sheet is thick enough, the support base material 2 is not necessarily required. Thus, when there is no support base material 2, it is possible to make the screen thickness substantially the same as the thickness of the directional diffusion sheet, and it is possible to wind it up or store it when folded.

  Further, the positional relationship between the position of the projector and the screen differs depending on the projection environment. FIG. 7 schematically shows the relationship. 7A, the projector 5 is disposed below the screen 100. In FIG. 7B, the projector 5 is disposed at the same height as the screen 100. In FIG. 7C, the projector 5 is disposed on the screen. 100 is disposed above 100. The arrangements shown in FIGS. 7A, 7B, and 7C are referred to as a lower position, a center position, and an upper position, respectively. In the description of the configuration shown in FIGS. 1 to 4, the case of the lower position is used. The projector screen of the present invention can be applied to any of the above-mentioned arrangements, and the important thing is that the orientation direction of the columnar lens in the lens sheet is approximately the same as the optical axis direction of the projection image. Alternatively, the optical axis direction and the direction symmetric with respect to the normal on the screen surface are generally coincident with each other. Further, the incident angle of the projected light image is set within the range of the scattering incident angle of the lens sheet used in the projector screen.

  The orientation direction of the lens sheet of the screen used in the arrangement shown in FIG. 7C can be the same direction as shown in FIGS. However, in the case of the rear screen of FIG. 4, it is necessary that the orientation direction of the columnar lens is approximately coincident with the optical axis direction and a direction symmetric with respect to the perpendicular on the screen surface. Further, the orientation direction of the lens sheet of the screen used in the arrangement shown in FIG. 7B is a direction perpendicular to the surface of the lens sheet.

  FIG. 10 shows the light transmission characteristics of the lens sheet used in the present invention. The lens sheet is not mixed with light diffusing particles. In FIG. 10, the incident angle of light to the lens sheet is represented on the horizontal axis, and the light transmission intensity for each incident angle is represented on the vertical axis. In the drawing, a characteristic curve 20 of the lens sheet when the orientation direction is 0 degrees and a characteristic curve 21 of the lens sheet when the orientation direction is α degrees are shown. However, the measurement was performed in the atmosphere.

  In the case of the characteristic curve 20, it can be seen that the light intensity of the lens sheet is almost zero at an angle ± β. When the incident angle is in the range of -β to β, light is scattered and transmitted, and when the absolute value of the incident angle is β or more, the light is transmitted without being scattered. That is, when used in transmission, the scattering angle is within the range of the incident angle of −β to β, and the other angle range is the linear transmission angle. Here, for convenience, β is called a scattering incident angle. When light diffusing particles are mixed in the lens sheet, the transmittance does not become zero even at the incident angle β because of the light diffused by the light diffusing particles.

  On the other hand, the characteristic curve 21 when the alignment direction of the columnar lens is tilted by α degrees is shifted to a position where the range of the scattering incident angle is shifted by α degrees as compared with the case where the alignment direction is 0 degrees. At that time, the angle width of the scattering incident angle hardly changes, and the range of the scattering incident angle shifts within the range of α−β to α + β. Accordingly, in FIG. 10, light incident at an angle α is scattered during transmission, but light incident at an angle −α is linearly transmitted without being scattered. Therefore, by illuminating the optical axis of the optical image from the projector with an inclination of α with respect to the screen, a bright image with a wide viewing angle can be obtained by setting the spread angle of the projected image to ± β.

  The above corresponds to the characteristics when the projector screen of the present invention is used in transmission (rear screen).

  Next, the case where the projector screen of the present invention is used for reflection (front screen) will be described with reference to FIG. First, consider the case of the characteristic curve 20 having an orientation direction of 0 degrees. At this time, the projection light incident from the projector at an angle of β to −β is reflected and scattered by the light reflection layer of the projector screen. However, if γ is an angle larger than β, the light incident at the incident angle γ is regularly reflected and is not scattered. For this reason, external light incident at an incident angle β or more does not affect the projected image, so that a projected image with good image quality can be obtained.

  Next, consider the case of the characteristic curve 21 using a lens sheet whose orientation direction is inclined by α. First, the light image projected from the projector in the incident angle range of incident angles α−β to α + β is scattered and reflected. The light projected from the projector in the incident angle range of -α-β to -α + β is reflected by the light reflecting layer and follows the same optical path as the light in the incident angle range of α-β to α + β on the surface. It is scattered and emitted. That is, there are two angular ranges scattered by the screen as described above. On the other hand, light incident at an angle other than the two scattering incident angles is scattered by the light scattering layer, but is reflected linearly by the lens sheet. Therefore, since the external light incident at an angle other than the two scattering incident angles has little influence on the projection image, a projection image with good image quality can be obtained.

  The value of β can be controlled to an arbitrary value of about 10 to 45 degrees by adjusting the sheet thickness of the columnar lens sheet, the diameter of the columnar lens, or the difference in refractive index of the columnar lens.

  Although the case where the support base material was used has been shown in each of the above configurations, it is not always necessary to use the support base material when the thickness of the lens sheet is as thick as 0.1 to 2 mm. Specific examples relating to the illumination device of the present invention will be specifically described below with reference to the drawings.

(Specific example 1)
A projector screen having the configuration shown in FIG. 1 was produced, and when the incident angle of the projected image was changed in the orientation direction of the lens sheet while a white image was projected on the screen, the change in luminance at the front of the screen was examined. . The spread angle of this white image was ± 2 degrees.

A lens sheet having a columnar lens diameter of 20 μm and a sheet thickness of 70 μm was used. The maximum refractive index difference between the high-refractive index region and the low-refractive index region is 0.02, and two types of graded index types made at 0 degrees and 15 degrees as the orientation directions were used. An alloy of Ag and Pd was formed on the back surface of the lens sheet by vacuum deposition of about 19 nm to form a light reflecting layer having a reflectance of 34%. A lens sheet attached to an acrylic plate having a thickness of 2 mm was used as a sample. In this lens sheet, titania spherical beads having an average particle diameter of 400 nm were mixed as light diffusing particles at a surface density of about 500 particles / mm ² .

  A white image for measurement was irradiated while changing the angle of incidence on the sample, and at that time, the reflected light intensity in the front direction perpendicular to the sample was measured. At this time, the result of the same measurement with the white calibration plate was used as a reference, and the measurement result with the white calibration plate was defined as gain 1.

  The measurement results are shown in FIG. It can be seen that the result 22 in the case where the orientation direction of the lens sheet is 0 degree has the maximum luminance at the incident angle of 0 degree and the viewing angle of 20 to 30 degrees. At this time, the gain at an incident angle of zero reached 3.6. This value is about 8% lower than when no light diffusing particles are mixed. Further, when the orientation direction of the lens sheet is 15 degrees, there are luminance peaks at incident angles of 15 degrees and -15 degrees. However, of the two peaks, the 15 degree peak has a value about four times larger than the -15 degree peak. The 15 degree peak gain was the same as curve 22. The 15 degree peak corresponds to the case shown in FIG. 1, and the -15 degree peak corresponds to the case shown in FIG. The reason why the peak at −15 degrees is weak is that the directivity of the scattered light is larger in this case, so that the amount of light incident on the measuring instrument placed in front is weaker.

  From the above results, it has been found that the projector screen of the present invention can realize a high-brightness image that is hardly affected by external light because it efficiently scatters and reflects only the projection light from the projector direction. However, when the light incident angle is 20 degrees or more, the gain sharply decreases. However, the gain increases to about 0.3 even at 45 degrees by mixing light diffusing particles, and the projection image can be observed.

(Specific example 2)
A projector screen having the configuration shown in FIG. 3 was produced, and the reflected light intensity from the screen was examined by changing the angle of the measuring instrument while projecting a white image from the front. The spread angle of this white image was ± 2 degrees. As in the case of the specific example 1, the result of the same measurement using a white calibration plate was defined as gain 1.

A lens sheet having a columnar lens diameter of 50 μm and a sheet thickness of 90 μm was used. The maximum refractive index difference between the high refractive index region and the low refractive index region was 0.02, and a graded index type having an inclination angle of 0 degree was used. As the light reflecting layer, a layer having a reflectance of about 90% by vacuum-depositing Ag on a polyethylene film was used. In addition, in the lens sheet, titania beads having average particle diameters of 400 nm and 1500 nm, respectively, were mixed at an area density of 1200 / mm ² to obtain Sample 2 and Sample 3, respectively. What stuck this columnar lens sheet on the acrylic board of thickness 2mm was used as a sample.

  The measurement results are shown in FIGS. FIG. 11 shows the result for sample 2, and FIG. 12 shows the result for sample 3. Both results show that light is diffusely reflected with a good gain up to about ± 80 degrees. Further, it has been found that the gain in the high viewing angle region increases as the diameter of the titania bead that is the light diffusion particle increases, but the gain in the vicinity of zero degrees decreases accordingly. In other words, it was found that if the mixture concentration on the lens sheet is the same, the directivity decreases as the particle size of the light diffusing particles increases, but an image can be projected at a wide angle.

(Specific example 3)
The same configuration as that used in Example 2, using those scattering the incident angle of 20 degrees as a lens sheet, ITO (Indium-Tin-Oxide ) of 800nm as a light diffusion particles obtained by mixing 1200 / mm ² Beads Samples were prepared, and the characteristics were examined in the same manner as in Example 2.

  FIG. 14 shows the result. It can be seen that the position of the gain peak has shifted to a position of 20 degrees. Further, the gain characteristic has an intermediate value between FIG. 12 and FIG. Even if the material is changed, the refractive indexes of ITO and titania are almost the same, so it can be seen that the light diffusing particles contribute the same degree to the screen luminance characteristics.

(Specific example 4)
A sample having a configuration similar to that used in specific example 2 and using titania beads as light diffusing particles and changing the average particle size from 20 nm to 20 μm was prepared, and the measurement angle was 30 degrees as in specific example 2. Gain measurement was performed. In addition, the mixing density of the titania beads was taken at two levels of 800 and 1200, and the results are shown in 24 and 25 of FIG. 15, respectively.

  As is clear from FIG. 15, it was found that regardless of the mixing density, the gain started to increase when the average particle diameter of the ITO beads was about 60 nm, and the light diffusion suddenly increased when the average particle diameter exceeded 1 μm. The light diffusion characteristics began to saturate from the vicinity where the average particle diameter exceeded 10 μm.

  From the above results, it was found that as the average particle size of the light diffusing particles becomes larger and as the mixing concentration becomes higher, the light diffusing property becomes larger, and as a result, the viewing angle property becomes better.

  Samples with light diffusion particles of 20 μm were not stable by photocuring, and the samples could be stably prepared by mixing light diffusion particles having an average particle size of about 10 μm or less. .

It is sectional drawing which shows the screen of this invention typically. It is sectional drawing which shows the screen of this invention typically. It is sectional drawing which shows the screen of this invention typically. It is sectional drawing which shows the screen of this invention typically. It is an expanded sectional view explaining the screen of this invention. It is an expanded sectional view explaining the screen of this invention. It is explanatory drawing which shows arrangement | positioning of a projector and a screen. It is a top view which shows typically lens arrangement | positioning of the screen of this invention. It is sectional drawing which shows the screen of this invention typically. It is a graph showing the characteristic of the columnar lens sheet used by this invention. It is a graph which shows the gain characteristic of the screen of this invention. It is a graph which shows the gain characteristic of the screen of this invention. It is a graph which shows the gain characteristic of the screen of this invention. It is a graph which shows the gain characteristic of the screen of this invention. It is a graph which shows the gain characteristic of the screen of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Directional diffusion sheet 2 Support base material 3 Light reflection layer 4 Support base material 5 Projector 9 Layered structure or columnar structure 10 Light diffusion particle 11 View point 13 High refractive index area 14 Low refractive index area 100 Screen

Claims (11)

In the screen that displays the projected light image,
A high-refractive index region and a low-refractive index region surrounding the high-refractive index region are continuously formed across the front and back surfaces, and scatters light incident at a specific angle range and transmits light incident at other angles. A screen comprising a light-transmitting directional light diffusion layer and light diffusion particles dispersed in each of the high refractive index region and the low refractive index region. The directional light diffusion layer has a layered structure in which the high refractive index regions and the low refractive index regions are alternately arranged in the plane of the layer, and the orientation direction of the layered structure is the directional light diffusion. The screen according to claim 1, wherein the screen is inclined with respect to the normal of the surface of the layer. The directional light diffusion layer has a plurality of columnar structures composed of the high refractive index regions, and the alignment direction of the columnar structures is inclined with respect to the normal of the surface of the directional light diffusion layer. The screen according to claim 1. The light diffusing particles is screen according to claim 2, characterized in that it has a small average particle diameter as compared with the thickness of the layered structure.   The screen according to claim 3, wherein the light diffusing particles have an average particle size smaller than an average diameter of the columnar structure. The light diffusing particles is screen according to claim 4 or 5, wherein the average particle size of the translucent particles 60Nm～20myuemu. The screen according to claim 6 , wherein a polarizing sheet is provided on the side opposite to the light projection side with respect to the directional light diffusion layer. The screen according to claim 7 , wherein a light reflection layer is provided on a side opposite to the light projection side with respect to the directional light diffusion layer. On the surface of the directional light-diffusing layer, a projector screen according to any one of claims 1 to 8, characterized in that black stripes are periodic absorption fringes are arranged. Screen according to any one of claims 1 to 9, characterized in that the light diffusing layer on the image projection side of the directional light-diffusing layer is provided. Image projection system comprising: the screen according to any one of claims 1-10, and a light image projector for projecting a light image on the screen.

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