JP2006221069A - Screen and rear projector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a screen reducing a glare feeling (speckle) on an image plane, and also to provide a rear projector provided with the screen. <P>SOLUTION: The screen is provided with a Fresnel lens sheet 1 which emits light from a light source as substantially parallel light, and a lenticular sheet comprising: lenticular lenses 2 which allow substantially parallel light to be made incident and display images; and a light diffusing sheet 4. The light diffusing sheet 4 is formed by holding a polymer dispersion liquid crystal layer 41 where fine particles 41<SB>LC</SB>of liquid crystal are dispersed and fixed in a polymer matrix 41<SB>m</SB>, between two sheets of transparent substrates 42 having transparent conductive films 42e, and an AC voltage is applied to the transparent conductive films 42e. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a screen and a rear projector device that display an image by irradiating image light from the back using a lenticular sheet having a polymer-dispersed liquid crystal layer.

  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 capable of forming a color image on a screen separates light rays emitted from a light source into red (R), green (G), and blue (B) colors and converges them on a predetermined optical path. An illumination optical system, 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 a screen by a 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. This projector screen is roughly divided into a front projector screen for irradiating projection light from the front side of the screen and viewing the reflected light on the screen, and a projection light from the back side of the screen for transmission through the screen. There is a rear projector screen for viewing light from the front side of the screen. In either method, the image displayed on the screen is required to have high contrast.

  A recent rear projector screen has been proposed in which contrast is improved by forming a black stripe 3 corresponding to a non-condensing portion of the lenticular lens 2 as shown in FIG. 1 (for example, Patent Document 1). reference.).

  In addition, rear projector devices (rear projection systems) are popular as a display capable of easily displaying a large screen, mainly in the United States. Furthermore, as high-quality images such as DVDs, digital broadcasts, and high-definition broadcasts have recently entered the home, interest in large-screen displays has increased, and inexpensive rear projector devices tend to be desired in countries other than the United States.

Here, since a conventional rear projector apparatus using a CRT (cathode ray tube) has been the mainstream, there are two major problems described below, which have been an obstacle to popularization.
The first is the use of three CRTs with a long overall length, so the entire box is large, and there are problems with space such as large areas other than the screen and large depths. It was a hindrance to popularization in small places.
Second, even if the input energy is increased in CRT, the phenomenon of luminance saturation caused by the phosphor occurs, and the luminance cannot be increased. Therefore, the screen is dark, the luminance distribution is large, and the viewing angle dependency is large. Has become a hindrance to its spread.

  In recent years, with the advent of a new rear projector device (micro display type rear projector) that combines a micro lamp such as liquid crystal or MEMS (micro mechanical system) and a discharge lamp, the above problem has been gradually solved. It is a major factor to be reviewed.

JP 2003-131325 A

  However, as the brightness is increased by the micro display, the glare of the screen, which has not been a problem until now, so-called speckle becomes conspicuous, and the solution has become the most important matter of the rear projector device.

  SUMMARY An advantage of some aspects of the invention is that it provides a screen and a rear projector device that can reduce glare (speckle) on a screen.

  The present invention provided to solve the above problems includes a Fresnel lens sheet that emits light from a light source as substantially parallel light, a lenticular lens that displays the image when the substantially parallel light is incident thereon, and a light diffusing sheet. The light diffusing sheet is formed by sandwiching a polymer dispersed liquid crystal layer in which fine particles of liquid crystal are dispersed and fixed in a polymer matrix between two transparent substrates having a transparent conductive film. The screen is characterized in that an AC voltage is applied to the transparent conductive film (Claim 1).

Here, the frequency of the AC voltage is preferably 60 Hz or more.
The fine particles of the liquid crystal preferably contain a dichroic dye.

  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 to 3. (Claim 4)

According to the screen of the present invention, the liquid crystal alignment state in the polymer-dispersed liquid crystal layer can be changed by applying an alternating voltage, and the diffusion characteristics and transmission characteristics of the light diffusion sheet can be changed over time. Here, flickering of the superimposed display image can be eliminated by setting the frequency of the applied AC voltage to a frequency not perceived as flicker perception. Further, by including a dichroic dye, particularly a white dye, in the liquid crystal microparticles, it is possible to further control the light diffusion characteristics and the transmission characteristics, thereby realizing an easy-to-view display image.
According to the rear projector device of the present invention, the temporal change of the light intensity pattern caused by the light interference is superimposed and displayed due to the high-speed temporal change of the diffusion characteristic and transmission characteristic of the light diffusion sheet. The display image can be homogenized and glare (speckle) can be reduced.

A configuration of a screen used in a conventional rear projector apparatus is shown in FIG.
The screen 90 includes a Fresnel lens sheet 1, a lenticular lens 2, a black stripe 3, and a light diffusing sheet 9 that direct light projected from a projector light source perpendicularly to the screen and make the screen brightness uniform. And a lenticular sheet facing the person. Furthermore, there is a model with a front decorative board 5 that reduces surface reflection and enhances the sense of quality.

  In the lenticular sheet, in addition to the action of the lenticular lens 2 that normally directs the light from the projector light source toward the viewer, the action of reducing the external light by the black stripe 3, the light from the projector light source is a light diffusion sheet There are three actions of diffusing / imaging by 9.

Here, as the light diffusion sheet 9, generally, a glass or plastic fine powder having a refractive index different from that of the substrate material is applied on the substrate material or directly kneaded into the substrate material. However, the light diffusing sheet 9 interferes with the light emitted from the light diffusing sheet 9 to cause the intensity of the light on the screen, resulting in a glaring feeling and poor visibility.
The inventor has intensively studied to solve this problem, and has reached the present invention.

The screen according to the present invention will be described below.
FIG. 2 is a cross-sectional view showing the configuration of the screen according to the present invention.
As shown in FIG. 2A, the screen 10 is provided with a Fresnel lens sheet 1, a lenticular lens 2, a black stripe 3, a light diffusion plate sheet 4, and a front decorative plate 5 in this order from the back side (light source side). It is. The present invention is characterized in that a light diffusion sheet 4 capable of dynamically switching the diffusion state is provided in place of the light diffusion sheet 9 in the conventional screen. A combination of the lenticular lens 2, the black stripe 3, and the light diffusing plate sheet 4 is referred to as a lenticular sheet.

  The Fresnel lens sheet 1 converts image light projected from a light source into parallel light and enters the lenticular lens, and may be a conventionally known screen for a rear projector device.

  The lenticular lens 2 collects the parallel light emitted from the Fresnel lens sheet 1 and directs it toward the viewer without waste, and may be a conventionally known screen for a rear projector device.

  The black stripe 3 serves as a light shielding layer for obtaining a high contrast image.

As shown in FIG. 2B, the light diffusing sheet 4 includes a polymer-dispersed liquid crystal layer 41 in which liquid crystal microparticles 41 _LC are dispersed and fixed in a polymer matrix 41 _m , and the polymer-dispersed liquid crystal. It consists of two transparent substrates 42 having a transparent conductive film 42e sandwiching the layer 41, and an AC voltage is applied from the power source E to the transparent conductive film 42e.

The polymer-dispersed liquid crystal layer 41 is made of a so-called polymer-dispersed liquid crystal (PDLC) and uses a solution containing the polymer material and liquid crystal to encapsulate, polymerize, separate the thermal phase. The liquid crystal microparticles 41 _LC are dispersed and fixed in a matrix 41 _m made of a polymer material by a separation method, a solvent evaporation phase separation method, or the like.

The material constituting the polymer matrix 41 _m is not particularly limited as long as it is a transparent polymer material, but its refractive index substantially matches the refractive index corresponding to the ordinary ray of the liquid crystal constituting the microparticle 41 _LC . It is preferable. In view of suitability as such an optical material, an acrylic resin is preferable.

The shape of the liquid crystal microparticle 41 _LC is not particularly limited, such as a spherical shape, a droplet shape, or a rugby ball shape. The material (liquid crystal) constituting the fine particles 41 _LC of is not limited particularly as long as it can be used in the polymer dispersed liquid crystal material (PDLC). For example, a commonly used liquid crystal material such as nematic liquid crystal or cholesteric liquid crystal may be used. At this time, it is preferable to control Δn (index of refractive index anisotropy) by adjusting a substituent of the liquid crystal, a synthesis method, or the like so that diffusion characteristics and transmission characteristics suitable for the light diffusion sheet 4 can be obtained. The structural formulas of liquid crystal compounds that can be used in the present invention are exemplified below.

  When the thickness of the polymer-dispersed liquid crystal layer 41 is increased, the diffusibility is improved, the transparency is deteriorated and the effect of image formation is increased, but the response of the liquid crystal alignment is deteriorated, and the necessary applied voltage is increased. Such disadvantages also come out. It is preferable to be within a thickness range of 5 to 50 μm.

  The transparent substrate 42 is obtained by forming a transparent conductive film 42e on a transparent base substrate 42b. The base substrate 42b may be a transparent polymer film or glass, and the transparent conductive film 42e may be a thin film of indium tin oxide (ITO), for example.

FIG. 3 is a schematic diagram showing a state of the polymer dispersed liquid crystal layer 41 depending on whether or not an AC voltage is applied from the power source E to the transparent conductive film 42e.
If the power supply E in there the AC voltage applied to the transparent conductive film 42e (ON state, FIG. 3 (a)), when the applied AC voltage (effective voltage) is sufficiently large, the dielectric having the liquid crystal constituting the fine particles 41 _LC Due to the rate anisotropy, the liquid crystal is oriented in a direction perpendicular to the electric field generated between the two transparent conductive films 42e, and as a result, the polymer-dispersed liquid crystal layer 41 transmits light of all wavelengths of incident light. It becomes.

On the other hand, when no AC voltage is applied from the power source E to the transparent conductive film 42e (OFF state, FIG. 3B), the wall (polymer matrix 41 _m ) that is in contact with the liquid crystal forming the microparticle 41 _LC is constrained. The force acts dominantly, and the liquid crystal is randomly oriented and diffuses or reflects a part of the incident light.

In the present invention, by applying an alternating voltage to the transparent conductive film 42e from a power source E, the said alignment state of the liquid crystal constituting the fine particles _{41 LC} ON state (FIG. 3 (a)) OFF state (FIG. 3 ( It is possible to change the diffusion characteristics and transmission characteristics of the light diffusing sheet 4 over time by changing at a high speed with b)).

Further, in the present invention, it is only necessary that the diffusion characteristics and transmission characteristics of the light diffusion sheet 4 change with time. Therefore, the alignment state of the liquid crystal constituting the microparticle 41 _LC is not necessarily the ON state (FIG. 3A). ) And / or the OFF state (FIG. 3 (b)), and an intermediate state between the ON state (FIG. 3 (a)) and the OFF state (FIG. 3 (b)) is the center. The alignment of the liquid crystal may change slightly over time. This can be adjusted by the constituent material and thickness of the polymer-dispersed liquid crystal layer 41, the dispersion state of the microparticles 41 _LC , the application condition of the AC voltage (voltage value (for example, about 5 V as effective value), frequency), and the like.

  As described above, when the diffusion characteristics and transmission characteristics of the light diffusing sheet 4 change with time, innumerable different scattering patterns are generated corresponding to the change with time. As a result, the image projected from the back of the screen 10 also has different image formation patterns depending on the scattering patterns, and these image formation patterns are superimposed and displayed, so that the display image is homogenized, which is a conventional problem. The feeling of glare (speckle) is reduced.

Moreover, it is preferable that the frequency of an alternating voltage is 60 Hz or more. The frequency of the alternating voltage can be said to be the switching frequency of the alignment state of the liquid crystal. When this frequency is lower than 60 Hz, the flickering of the displayed image is recognized and the visibility is deteriorated. This is a report that requires a spatial frequency of 60 Hz or more in order not to feel flicker on a screen having a luminance of 150 to 200 cd / m ² (NHK Giken monthly report 18, 11, p.661-668; visual spatial frequency characteristics) ).

  In addition, it is preferable to include a dichroic dye in the liquid crystal microparticles because the control of the diffusion characteristics and transmission characteristics of the light diffusion sheet 4 becomes easier.

An example is shown in FIG. Here, the polymer dispersed liquid crystal layer is formed by dispersing and fixing the fine particles 41 _LCp composed of the liquid crystal LC and the dichroic dye p in the polymer matrix 41 _m .
When an AC voltage is applied from the power source E to the transparent conductive film 42e (ON state, FIG. 4 (a)), the liquid crystal constituting the microparticle 41 _LCp is two transparent conductive films as in FIG. 3 (a). The dichroic dye p is oriented in the same manner along the direction perpendicular to the electric field generated between 42e. As a result, the polymer-dispersed liquid crystal layer 41 is in a state of transmitting light of all wavelengths of incident light.

On the other hand, when no AC voltage is applied from the power source E to the transparent conductive film 42e (OFF state, FIG. 4 (b)), the liquid crystal constituting the microparticle 41 _LCp is randomly oriented as in FIG. 3 (b). Accordingly, the dichroic dye p is similarly randomly oriented. As a result, a part of incident light is diffused or reflected.

  As described above, even when the dichroic dye is included, it is possible to create a transmission and scattering state depending on whether or not an AC voltage is applied. Therefore, it is possible to change the diffusion characteristics and transmission characteristics of the light diffusion sheet 4 over time. It is possible to reduce the glare (speckle) which has been a problem in the past.

For example, the light diffusion sheet 4 in the screen of the present invention may be manufactured as follows. Here, an example by the polymerization phase separation method is shown.
(S11) A liquid crystal (nematic liquid crystal, for example, p-alkyle-p′-alkoxyazoxybenzene) is dissolved with a raw material (polymerizable monomer or oligomer) of the polymer matrix 41 _m to prepare a solution. Specifically, the raw material of the polymer matrix 41 _m and the liquid crystal are put into a container at a predetermined volume ratio, and are stirred and melted using a stirrer until uniform.

It is important that the raw material of the polymer matrix 41 _m has solubility in liquid crystals and durability. For example, an ultraviolet curable monomer that undergoes a cross-linking polymerization reaction upon irradiation with ultraviolet rays is preferable.
In addition, the mixing volume ratio of resin and liquid crystal is 50:50 as a standard, but in the mixing of resin and liquid crystal, the diffusibility increases as the mixing ratio of liquid crystal increases, and the permeability tends to deteriorate. The mixing ratio may be set based on the image performance.

(S12) The solution is applied with a uniform thickness on the transparent substrate 42 on which the transparent conductive film 42e is formed by a doctor blade method or the like.
(S13) The other transparent substrate 42 is placed on the coating film so that the transparent conductive film 42e is in contact with the coating film, and the two transparent substrates are sandwiched by the spacers via the spacer. The thickness of the polymer dispersed liquid crystal layer 4 may be adjusted by the spacer.
(S14) The ultraviolet curable monomer is photopolymerized by irradiating ultraviolet rays from either one of the transparent substrates 42. Irradiation with ultraviolet rays is preferably performed under the condition that the photopolymerization is necessary and sufficient, for example, 15 mW / cm ² and about 60 seconds. Thereby, the polymer dispersed liquid crystal layer 41 in which the liquid crystal microparticles 41 _LC are dispersed and fixed in the polymer matrix 41 _m is formed.
(S15) The electrode for applying a voltage from the power source E is attached to the transparent conductive film 42e of the transparent substrate 42 to complete the light diffusion sheet 4.

In the case of producing a light diffusion sheet having a polymer-dispersed liquid crystal layer in which fine particles 41 _LCp composed of liquid crystal LC and dichroic dye p are dispersed and fixed in polymer matrix 41 _m as shown in FIG. In step S11, the liquid crystal in which the dichroic dye is dissolved in advance is dissolved in the ultraviolet curable monomer. At this time, although the amount of the dichroic dye dissolved in the liquid crystal varies depending on the type of the liquid crystal, the effect of whitening at the time of light scattering (FIG. 4B) becomes larger when the dichroic dye is dissolved in a large amount.

Moreover, you may produce the light-diffusion sheet 4 in the screen of this invention as follows.
(S21) Similarly to step S11, a liquid crystal (nematic liquid crystal, for example, p-alkyle-p'-alkoxyazoxybenzene) is dissolved with an ultraviolet curable monomer that undergoes a cross-linking polymerization reaction by ultraviolet irradiation to prepare a solution. .
(S22) As the transparent substrate 42, a substrate in which a transparent conductive film 42e is formed on the flat surface side of the lenticular lens 2 is used, and the solution is applied thereon with a uniform thickness by a doctor blade method or the like.
(S23) The coating film is irradiated with ultraviolet rays to photopolymerize the ultraviolet curable monomer, and the polymer dispersed liquid crystal layer 4 is formed.
(S24) A transparent conductive film 42e is formed on the polymer dispersed liquid crystal layer 4 by sputtering or the like.
(S25) An electrode for applying a voltage from the power source E is attached to each transparent conductive film 42e to complete a light diffusion sheet. In this case, the front decorative plate 5 is assumed to be disposed.

  According to this manufacturing method, the base substrate 42b in the transparent substrate 42 can be omitted, so that light loss due to the optical interface can be reduced.

  The front decorative plate 5 has a protective layer for preventing scratches and a conventionally known antireflection film.

  Next, the rear projector apparatus according to the present invention will be described.

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 And the screen 10 having the above-described structure that emits the image light _Li to the observer side.

  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 apparatus 100, a projector light L _P is the image light from the light source 11, via the reflecting mirror 12 is projected on the back side of the screen 10, the lenticular lens into a parallel light by the Fresnel lens sheet 1 2 Is incident on. Next, the parallel light is condensed by the lenticular lens 2 and passes through the black stripe 3 without waste to enter the light diffusion sheet 4. Light incident at a light diffusion sheet 4 is diffused and reaches the viewer side as the image light L _i is transmitted through the front decorative plate 5.

  Here, since a predetermined alternating voltage is applied to the light diffusion sheet 4 and the diffusion characteristics change with time, the imaging patterns in a myriad of different scattering states corresponding to this change with time. When these image formation patterns are superimposed and displayed, the display image is homogenized and the glare (speckle) is reduced.

Examples of the present invention will be described below.
(1) Sample preparation conditions (S31) A solution was prepared by changing the following materials to a polymer raw material: liquid crystal in a weight ratio of 10:90 to 30:70 and making them compatible.
-Polymer raw material (monomer); Nippon Kayaku HX-620 (Caprolacton-modhified hydroxyl pivalic acid ester neopentyglycol diacrylate)
Polymerization initiator: Merck Darocure 1173 (2-hydroxy-2-methyl-1-phenylpropan-1-one)
・ Liquid crystal (nematic liquid crystal); pyridine derivatives of the following structural formula

(S32) The solution was applied to the transparent substrate 42 on which the transparent conductive film 42e was formed with a uniform thickness by a doctor blade method.
(S33) The other transparent substrate 42 is placed on the coating film so that the transparent conductive film 42e is in contact with the coating film, and the two transparent substrates 42 sandwich the coating film via the spacer. In addition, the space | interval of the transparent substrate 42 was 11 micrometers by the spacer.
(S34) The ultraviolet curable monomer was photopolymerized by irradiating ultraviolet rays of 100 mW / cm ² or less from the outside of one transparent substrate 42. As a result, the polymer dispersed liquid crystal layer 41 in which the liquid crystal microparticles 41 _LC are dispersed and fixed in the polymer matrix 41 _m is formed.
(S35) An electrode for applying a voltage from the power source E is attached to the transparent conductive film 42e of the transparent substrate 42 to complete the light diffusion sheet 4.
A screen shown in FIG. 2 was produced using this light diffusion sheet 4.

(2) Sample evaluation Using the above sample screen, an image using a liquid crystal display device for projector (SXRD) as a light source from the back of the screen in a state where an AC voltage having an effective voltage value of 5 V and a frequency of 60 Hz is applied to the polymer dispersed liquid crystal layer 4 Light was projected and observed from the front. For comparison, the conventional screen (comparison screen) shown in FIG. 1 was also observed.

  As a result, all sample screens were found to be less glaring than the comparison screen. When the polymer-dispersed liquid crystal layer 4 is driven with an alternating voltage of 60 Hz, there are at least 60 different liquid crystal patterns per second (more numbers including the transition state), and these are overlapped and observed. It will be. Here, the speckle contrast (intensity) C was estimated to be about 1/8 (less than 1/60 route) from the following formula, which was in good agreement with the sensitivity test result.

C = C ₀ / (n ^1/2 )
(Where n is the number of superimposed patterns, C _{0 is the} original speckle contrast)

It is sectional drawing which shows the structure of the conventional screen. It is sectional drawing which shows the structure of the screen which concerns on this invention. It is the schematic which shows the state of a polymer dispersion liquid crystal layer. It is the schematic which shows the state of the polymer dispersion liquid crystal layer containing a dichroic dye. It is sectional drawing which shows the structure of the rear projector apparatus which concerns on this invention.

Explanation of symbols

_{DESCRIPTION OF SYMBOLS} 1 ... Fresnel lens sheet, 2 ... Lenticular lens, 3 ... Black stripe, 4 ... Light diffusion sheet, 41 ... Polymer dispersion liquid crystal layer, 41 _LC , 41 _LCp ... Fine particles, 41 _m ... polymer matrix, 42 ... transparent substrate, 42b ... base substrate, 42e ... transparent conductive film, 5 ... front decorative plate, 10 ... screen, 11. ..Light source, 12 ... reflecting mirror, 100 ... rear projector device, E ... power source, LC ... liquid crystal, p ... dichroic dye

Claims (4)

In a screen comprising a Fresnel lens sheet that emits light from a light source as substantially parallel light, and a lenticular sheet that includes the lenticular lens that displays the image when the substantially parallel light is incident thereon, and a light diffusion sheet.
The light diffusion sheet is formed by sandwiching a polymer dispersed liquid crystal layer in which fine particles of liquid crystal are dispersed and fixed in a polymer matrix between two transparent substrates having a transparent conductive film. A screen to which an alternating voltage is applied.   The screen according to claim 1, wherein the frequency of the AC voltage is 60 Hz or more.   The screen according to claim 1, wherein the liquid crystal microparticles contain a dichroic dye. 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 3 in which the reflected light of the reflection mirror is projected from the back side. A rear projector device characterized by that.

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