JP2005300711A - Screen and rear projector device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a screen in which contrast is improved by comparatively surely eliminating the effect of outdoor daylight, thereby decreasing the black level of an image, and to provide a rear projector using the screen. <P>SOLUTION: The screen 10, on which images are displayed by the emission of image light from back, includes: a selective transmission filter 2 which has the properties of highly transmitting light of specific wavelength region which corresponds to image light, and the properties of highly reflecting the light of visible wavelength region excepting at least the specific wavelength region; and a circular polarizer plate 3 disposed in front of the selective transmission filter 2. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a screen for displaying an image by irradiation of image light from the back and a rear projector device.

  In recent years, overhead projectors and slide projectors have been widely used as methods for presenting materials by a speaker in a conference or the like. In general households, video projectors and moving picture film projectors using liquid crystals are becoming popular. In these projector projection methods, light output from a light source is modulated by, for example, a transmissive liquid crystal panel to form image light, and the image light is emitted through an optical system such as a lens and projected onto a screen. To do.

  For example, a projector device (light source) capable of forming a color image on a screen separates light emitted from the light source into red (R), green (G), and blue (B) colors, and passes a predetermined optical path. An illumination optical system that converges the light beam, a liquid crystal panel (light valve) that optically modulates the RGB light beams separated by the illumination optical system, and a light combining unit that combines the RGB light beams light-modulated by the liquid crystal panel. The color image synthesized by the light synthesizing unit is enlarged and projected on the screen by the projection lens.

  Recently, a projector device has been developed that uses a narrow-band three-primary-color light source as a light source, and spatially modulates the luminous flux of each RGB color using a grating light valve (GLV) instead of a liquid crystal panel. Yes.

  In the projector apparatus described above, a projector screen is used to view a projected image. The projector screen is roughly divided into a front projector screen for irradiating projection light from a projector on the front side of the screen and viewing the reflected light on the screen, and a projection light from the projector on the back side of the screen through a mirror. There is a rear projector screen in which the light transmitted through the screen is viewed from the front side of the screen. In either method, the image displayed on the screen is required to have high contrast.

  However, in the conventional rear projector screen, outside light such as indoor lighting and sunlight from a window is taken into the projector device, and the outside light is reflected inside the device and returns to the rear projector screen again. As a result, the black level of the image displayed on the screen increases, causing a decrease in contrast.

  To solve this problem, as shown in FIG. 9, in the configuration in which the Fresnel lens 81, the lenticular lens 85, and the diffusion film 84 are sequentially provided from the back side, the light is absorbed by the non-condensing portion on the diffusion film 84 side of the lenticular lens 85. A screen 80 that suppresses reflection of external light by providing a light shielding layer 86 made of black stripes is known.

  In addition, a rear projector device has been proposed in which the screen has a two-layer structure of a diffusion plate and a circularly polarizing plate (see, for example, Patent Document 1). As a result, external light incident through the screen is reflected by the mirror inside the device and re-enters the screen, but is absorbed by the circularly polarizing plate and prevents transmission through the screen, so it is possible to suppress a decrease in contrast. It is.

JP-A-6-160794

  However, even in the screen shown in FIG. 9, since there is external light that enters the rear projector device from between the light shielding layers 86 made of black stripes, the light is reflected again out of the screen 80, thereby The black level increased and the contrast deteriorated.

The inventors actually measured the degree of reflection of external light in a commercially available rear projector apparatus using the screen 80, and the phenomenon was confirmed. That is, when the rear projector apparatus was installed with the power turned off as shown in FIG. 10, the luminance at the center of the screen was measured with a fluorescent lamp, it was 0.727 [cd / m ² ]. On the other hand, when a black cloth is attached between the Fresnel lens 81 and the lenticular lens 85 (position A in FIG. 9) of the screen 80 and the reflection from the inside of the projector apparatus is cut, the measurement is 0.412 [cd / m ^2]. It was confirmed that the luminance was reduced by 43%. The ambient light illuminance at the center of the screen was 216 [lux].

  Even if the screen shown in Patent Document 1 is used, the rear projector device has a space in which the optical system is housed, and external light that has once entered the device is reflected several times in the internal space. Since it sometimes goes outside, there was light that passed through the circularly polarizing plate and came out of the screen. That is, as shown in FIG. 11, as a characteristic of the circularly polarizing plate 93, the odd-numbered reflected light is absorbed by the circularly polarizing plate 93 because the polarization direction is reversed, passes again, and goes out of the rear projector device 900. However, since the polarization direction of the even-numbered reflected light returns to the original, it passes through the circularly polarizing plate 93 and goes out of the apparatus. As a result, it has been difficult to completely suppress the reduction in the contrast of the image.

  The present invention has been made in view of the above problems in the prior art, and more reliably eliminates the influence of external light to lower the black level of the image and improve the contrast, and a rear projector using the screen. An object is to provide an apparatus.

  The present invention provided to solve the above-mentioned problems is a screen that displays an image by irradiating image light from the back, has a high transmission characteristic with respect to light in a specific wavelength region corresponding to the image light, and at least A screen comprising: a selectively transmissive film having high reflection characteristics with respect to light in a visible wavelength region excluding the specific wavelength region; and a circularly polarizing plate disposed in front of the selectively transmissive film.

  In the present invention, external light incident on the front surface of the screen becomes circularly polarized light by passing through the circularly polarizing plate and enters the selective transmission film. Since the selective transmission film reflects light in the visible wavelength region excluding the specific wavelength region, the external light that has become circularly polarized light is almost reflected by the selective reflection film. Since circularly polarized light is reflected, the polarization state is reversed, so that external light reflected by the selective transmission film cannot be transmitted through the circularly polarizing plate and is absorbed. Therefore, on the screen of the present invention, it is possible to display a high-contrast image that is very little influenced by outside light.

Here, the selective transmission film can be constituted by an optical multilayer film in which a high refractive index layer and a low refractive index layer having a lower refractive index are alternately laminated. For the high refractive index layer, for example, niobium oxide (Nb ₂ O ₅ ), titanium oxide (TiO ₂ ), tantalum oxide (Ta ₂ O ₅ ), or the like is used, and for the low refractive index layer, for example, silicon oxide ( SiO ₂ ), magnesium fluoride (MgF ₂ ) or the like is used.

  The specific wavelength region preferably includes a red light wavelength region, a green light wavelength region, and a blue light wavelength region.

It is preferable to provide a Fresnel lens that makes the projected image light substantially parallel and enter the selective transmission film, and it is preferable to provide a diffusion layer that diffuses the image light on the front surface of the circularly polarizing plate. The diffusion layer preferably has an anisotropic diffusion characteristic in which the vertical diffusion angle is smaller than the horizontal diffusion angle.
Moreover, it is good to provide a lenticular lens between the said diffused layer and a circularly-polarizing plate, and it is further better to provide a black stripe in positions other than the condensing part by the lens part by the side of the diffused layer of the said lenticular lens.

  The present invention provided to solve the above-mentioned problems is a light source that projects image light, a reflection mirror that reflects the projection light from the light source, and the reflected light of the reflection mirror is projected from the back side. A rear projector apparatus comprising the screen according to any one of?

  According to the present invention, part of the external light incident on the screen is absorbed by the circularly polarizing plate, and most of the external light is reflected once by the selective transmission filter even if it passes through the circularly polarizing plate. Since the light is absorbed and does not come out of the screen, the influence of external light can be more reliably eliminated, the black level of the image can be reduced, and the contrast can be improved.

A screen according to a first embodiment of the present invention will be described below.
FIG. 1 is a diagram showing a configuration of a screen according to the present invention, and is a cross-sectional view seen from above the screen.
The screen 10 has a configuration in which a Fresnel lens 1, a selective transmission filter 2, a circularly polarizing plate 3, and a diffusion film 4 are provided in order from the back side (light source side).

  The Fresnel lens 1 converts image light projected from a light source into parallel light and enters the selective transmission filter 2, and may be a conventionally known screen for a rear projector.

  The selective transmission filter 2 has high transmission characteristics with respect to light in a specific wavelength region corresponding to image light from a light source, and has high reflection characteristics with respect to light in a visible wavelength region excluding at least the specific wavelength region It is.

  Such a selective transmission filter 2 is designed as a well-known Fabry-Perot filter. For example, as shown in FIG. 2, a high refractive index layer H and a low refractive index layer having a lower refractive index are formed on a substrate 2a. It is composed of an optical multilayer film in which L is alternately laminated, and has a structure in which a spacer layer 2b is sandwiched between reflecting mirrors 2c and 2d.

  The substrate 2a is used to form an optical multilayer film, and the material is not particularly limited, but is preferably transparent. As the substrate material, for example, a polymer material such as polyethylene terephthalate (PET), polycarbonate (PC), polyolefin (PO), polyethylene sulfide (PES), glass, or the like can be used. A hard coat layer (HC) for improving the substrate strength may be formed on the substrate 2a.

In such a selective transmission filter 2, the spacer layer 2b has an optical film thickness ND with a refractive index of N and a film thickness of D, with the following formula ND = ( n ± 1/2) λ (1)
Or ND = nλ (2)
It is good to form so as to satisfy. However, in Formula (1) and (2), n is a natural number.

  For example, when the image light is narrow band three primary color wavelength band light having a wavelength of 457 nm (blue), 532 nm (green), and 642 nm (red), the optical film thickness of the spacer layer 2b satisfying all the above conditions for these three wavelengths. An example of ND is ND = 1.06 μm. In this case, ND = 1.06 μm satisfies the condition of formula (1) at approximately 2.5 times λ = 457 nm, and satisfies the condition of expression (2) at approximately twice for λ = 532 nm. For λ = 642 nm, the condition of the formula (1) is satisfied by about 1.5 times. That is, high transmittance is shown in the three primary color wavelength regions. Although equation (2) is a high-order λ film, it goes without saying that the λ film is also a kind of λ / 2 film.

In the selective transmission filter 2, the high refractive index layer H includes a high refractive index material having a refractive index of 1.5 or more, preferably 2.0 to 2.7, such as niobium oxide (Nb ₂ O ₅ ), tantalum oxide. (Ta ₂ O ₅ ), titanium oxide (TiO ₂ ) or the like is used, and the low refractive index layer L has a refractive index of less than 1.5, preferably 1.3 to 1.5, for example, Silicon dioxide (SiO ₂ ), magnesium fluoride (MgF ₂ ) or the like is used. Such a high refractive index layer H and low refractive index layer L can be formed by a dry process such as a vapor deposition method or a sputtering method.

FIG. 3 shows the layer structure shown in FIG. 2, in which the high refractive index layer is an Nb ₂ O ₅ layer, the low refractive index layer is an SiO ₂ layer, and the layer thickness is 48 nm (Nb ₂ O ₅ layer) in order from the substrate 2a side. 79 nm (SiO ₂ layer), 48 nm (Nb ₂ O ₅ layer), 131 nm (SiO ₂ layer), 47 nm (Nb ₂ O ₅ layer), 739 nm (SiO ₂ layer), 47 nm (Nb ₂ O ₅ layer), 114 nm The transmission characteristics of the selective transmission filter 2 in the case of (SiO ₂ layer) and 48 nm (Nb ₂ O ₅ layer) are shown. As shown in this figure, this selective transmission filter 2 exhibits a high transmittance of more than 90% in the wavelength regions of wavelengths 457 nm (blue), 532 nm (green), and 642 nm (red), so that luminance is increased in these wavelength regions. It is suitable for a light source having a peak.

  The circularly polarizing plate 3 transmits either right circularly polarized light or left circularly polarized light, and absorbs circularly polarized light in a direction opposite to the transmitted circularly polarized light. For example, a linearly polarizing plate and birefringent light are used. It is only necessary that a retardation plate having a retardation of 1/4 wavelength is laminated. This circularly polarizing plate 3 is formed by crossing the optical axis of the retardation plate at an angle of 45 ° or 135 ° with respect to the transmission axis of the linearly polarizing plate, and depending on the angle, either right circularly polarized light or left circularly polarized light is formed. It is decided whether to absorb.

  The linear polarizing plate is not particularly limited. For example, a film made of a hydrophilic polymer material such as polyvinyl alcohol is dyed with a dichroic dye or iodine and stretched about 2 to 10 times in an aqueous boric acid solution. A polarizer is mentioned. Moreover, you may use what is obtained by aligning the liquid crystal and liquid crystal polymer containing a dichroic dye. There are no limitations on the liquid crystal or liquid crystal polymer, and nematic, smectic, cholesteric, discotic, and these positive and negative materials are used.

  In addition, as the retardation plate, a birefringent film having a retardation retardation of 1/4 wavelength of the visible light wavelength and a wideband 1/4 wavelength plate having a wide retardation of 1/4 wavelength in the visible light amount region is used. Good. This broadband quarter-wave plate can be realized by a combination of birefringent films having different retardation values. Examples of the retardation film include those obtained by stretching and orienting a polymer film. Although there is no limitation in particular in the polymer film used for a phase-difference film, what is optically transparent and has few orientation irregularities is used suitably. Examples thereof include polycarbonate, polyacrylate, polysulfone, polyolefin, polyethylene terephthalate, polyethylene naphthalate, norbornene, acrylic, polystyrene, and cellulose. Alternatively, a liquid crystal composition may be coated or impregnated on a polymer film.

  The diffusion film 4 is provided so as to scatter image light transmitted through the selective transmission filter 2 and the circularly polarizing plate 3 to widen the visual field and visually recognize a natural image. Such a diffusion film 4 is not particularly limited, and a conventionally known film such as a diffusion plate having an uneven surface, a bead arrangement layer, or a film on which a microlens array is formed can be used. .

An example in which the screen 10 having the above configuration is applied to a rear projector apparatus is shown in FIG.
Rear projector apparatus 100 includes a light source (optical engine) 11 that projects an image light, projection light from a light source 11 (the projector light) and the reflection mirror 12 for reflecting the L _P, reflected light L _R of the reflection mirror 12 is the rear side It projected from, and a screen 10 having the above structure is emitted to a viewer side as the image light L _i.

  The light source 11 may be any light source as long as it is used as a light source of a normal rear projector device. The light source 11 uses light including wavelength regions of the three primary colors of red (R), green (G), and blue (B). It is preferable to project light. In addition, since the wavelength region transmitted through the selective transmission filter 2 should be as narrow as possible, a light source having a characteristic that the half-value width of the luminance peak is narrow is particularly preferable. For example, a projector provided with a projector liquid crystal display device (LCD, SXRD), GLV, cathode ray tube (CRT), or LED and an illumination optical system corresponding to the LED.

Reflecting mirror 12 reflects the projector light L _P is the image light, which is projected on the screen 10 may be of a conventionally known in the rear projector.

In the rear projector device 100, the screen 10 includes the combination of the selective transmission filter 2 and the circularly polarizing plate 3, so that the following effects can be obtained with respect to the external light _Lo incident on the screen 10.

First, when external light L _o (for example, randomly polarized natural light) passes through the diffusion film 4 and enters the circularly polarizing plate 3, it is first polarized and separated by the linearly polarizing plate, one of which is absorbed and the other is transmitted through the retardation plate. To do. At this point, about half of the outside light is absorbed. Next, the remaining half of the linearly polarized light that has been transmitted is converted into one of right circularly polarized light and left circularly polarized light, for example, right circularly polarized light, by the phase difference plate.

  Next, the right circularly polarized light emitted from the circularly polarizing plate 3 enters the selective transmission filter 2, and the right circularly polarized light is transmitted and reflected according to the transmission / reflection characteristics of the selective transmission filter 2. That is, light in a wavelength region in which the selective transmission filter 2 has high transmission characteristics (light in a specific wavelength region corresponding to image light from the light source 11, for example, light in the RGB primary color wavelength region) is transmitted, and excludes this specific wavelength region The light in the visible wavelength region is reflected.

  Of the right circularly polarized light, the light reflected by the selective transmission filter 2 has a phase inverted by 180 ° and is reflected as left circularly polarized light in the opposite direction to the incident right circularly polarized light. For this reason, the right circularly polarized light (that is, left circularly polarized light) reflected by the selective transmission filter 2 is converted again into linearly polarized light parallel to the absorption axis of the linearly polarizing plate by the retardation plate of the circularly polarizing plate 3 and linearly polarized light. It will be absorbed by the board. That is, external light that passes through the circularly polarizing plate 3 and is reflected once by the selective transmission filter 2 is always absorbed by the circularly polarizing plate 3 and does not come out of the screen 10.

  Further, a part of the external light incident on the screen 10 passes through the circularly polarizing plate 3 and the selective transmission filter 2 and the Fresnel lens 1 and enters the rear projector device 100, but the ratio is the circularly polarizing plate 3 and the selection. It is suppressed to a greater extent than when the transmission filter 2 is not provided. As an example, the case where the screen 10 having the selective transmission filter 2 having the characteristics shown in FIG. 3 is applied to the rear projector device 100 and the case where the light of the fluorescent lamp as the indoor illumination is incident on the screen 10 as external light has been verified. The result of FIG. 5 was obtained.

  FIG. 5 shows the luminance distribution of the light from the fluorescent lamp. A curve A in the figure is a result of measuring the light of the fluorescent lamp itself, and a curve B in the figure passes through the screen 10 and the projector device 100. It is the result of measuring the light incident on the inside. Here, when the peak intensities of the curve A and the curve B are compared, the light transmission of the fluorescent lamp is considerably suppressed by passing through the screen 10 according to the present invention, and is completely suppressed depending on the wavelength region ( 0% in peak intensity ratio). In addition, the peak intensity ratio was suppressed to 28% even at the peak position P where the intensity was maximum.

On the other hand, the projector light L _P is the image light from the light source 11 is projected on the back side of the screen 10 via the reflection mirror 12, is incident on the selective transmission filter 2 into a parallel light by the Fresnel lens 1 . Next, since the selective transmission filter 2 is designed so that its transmission characteristics are optimal with respect to the light source 11, the incident image light is transmitted with high transmittance, and further passes through the circularly polarizing plate 3 and the diffusion film 4. and it is emitted from the screen 10 to reach the observer side as the image light L _i.
The external light L _O entering from the viewer side is hardly reflected off the screen 10 due to the effect of the screen 10 according to the present invention as described above. Therefore, it is possible to obtain an image with a higher contrast than the conventional rear projector apparatus.

  Instead of the diffusion film 4, the diffusion angle as shown in FIG. 6 is wide in the horizontal direction (the horizontal direction of the screen) and narrow in the vertical direction (the vertical direction of the screen), for example, an elliptical diffusion characteristic of FWHM 80 ° × 10 ° ( A diffusion film 4a having anisotropic diffusion characteristics) may be used. As a result, it is possible to provide an image with a wide viewing angle with a simpler screen configuration than the conventional one, together with the improvement in contrast.

Next, FIG. 7 shows a second embodiment of the screen according to the present invention.
The screen 20 has a configuration in which a lenticular lens 5 is provided between the circularly polarizing plate 3 and the diffusion film 4 in the screen 10 in FIG.
Thereby, the diffusion angle of the image light emitted from the screen 20 to the viewer side can be wide in the horizontal direction (the horizontal direction of the screen) and can have a narrow anisotropy in the vertical direction (the vertical direction of the screen). Is applied to a rear projector device, it is possible to provide a wide viewing angle image together with the improvement of the contrast.

Next, a third embodiment of the screen according to the present invention is shown in FIG.
The screen 30 has a configuration in which the light shielding layer 6 made of black stripes is provided at a position other than the light condensing portion by the lens portion on the diffusion film 4 layer side of the lenticular lens 5 in the screen 20 of FIG.
Since the reflection of external light can be suppressed by the light shielding layer 6, if this screen 30 is applied to the rear projector device, an image with higher contrast can be obtained in combination with the effect of the present invention.

It is sectional drawing which shows the structure of 1st Embodiment of the screen which concerns on this invention. 3 is a cross-sectional view showing a configuration example of a selective transmission filter 2. FIG. It is a figure which shows the transmission characteristic of the selective transmission filter of FIG. It is sectional drawing which shows the structure of the rear projector apparatus which concerns on this invention. It is a figure which shows the external light transmission suppression effect by the screen of this invention. It is a figure which shows the mode of the elliptical diffusion of the diffusion film 4a. It is sectional drawing which shows the structure of 2nd Embodiment of the screen which concerns on this invention. It is sectional drawing which shows the structure of 3rd Embodiment of the screen which concerns on this invention. It is sectional drawing which shows the structure of the conventional screen. It is a figure which shows the arrangement | positioning relationship between the conventional rear projector apparatus and a fluorescent lamp. It is a figure which shows the characteristic of a circularly-polarizing plate.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,81 ... Fresnel lens, 2 ... Selective transmission filter, 2a ... Substrate, 2b ... Spacer layer, 2c, 2d ... Reflector, 3,93 ... Circularly polarizing plate, 4, 4a ... Diffusing film, 5,85 ... Lenticular lens , 6,86 ... light shielding layer, 10,20,30,80 ... screen, 11 ... light source, 12 ... reflecting mirror, 100,800,900 ... rear projector device, L p _... projector light, L R _... reflected light, L _i : Image light,

Claims (10)

In the screen that displays the image by irradiation of image light from the back,
A selective transmission film having high transmission characteristics with respect to light in a specific wavelength region corresponding to the image light, and having high reflection characteristics with respect to light in a visible wavelength region excluding at least the specific wavelength region;
A screen comprising: a circularly polarizing plate disposed in front of the selectively permeable membrane.   The screen according to claim 1, wherein the selective transmission film includes an optical multilayer film in which a high refractive index layer and a low refractive index layer having a lower refractive index are alternately stacked.   The screen according to claim 2, wherein the high refractive index layer is made of niobium oxide, titanium oxide, or tantalum oxide, and the low refractive index layer is made of silicon oxide or magnesium fluoride.   The screen according to claim 1, wherein the specific wavelength region includes a wavelength region of red light, a wavelength region of green light, and a wavelength region of blue light.   The screen according to claim 1, further comprising: a Fresnel lens that makes the projected image light substantially parallel light and enters the selective transmission film.   The screen according to claim 1, further comprising a diffusion layer that scatters image light transmitted through the circularly polarizing plate.   The screen according to claim 6, wherein the diffusion layer has anisotropic diffusion characteristics in which a vertical diffusion angle is smaller than a horizontal diffusion angle.   The screen according to claim 6, further comprising a lenticular lens between the diffusion layer and the circularly polarizing plate.   The lenticular lens has a lens part on the circularly polarizing plate side, and a stripe-shaped light absorption layer is formed on the opposite side of the sheet surface at a position other than the light condensing part by the lens part. The screen according to claim 8. A light source that projects image light, a reflection mirror that reflects projection light from the light source, and a screen according to any one of claims 1 to 9, wherein the reflected light of the reflection mirror is projected from the back side. A rear projector device characterized by the above.

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