Patent Publication Number: US-2005141091-A1

Title: Reflex-type screen

Description:
This patent application claims priority from a Japanese patent application No. 2003-430942 filed on Dec. 25, 2003, and Japanese patent application No.2004-170495 filed on Jun. 8, 2004, the contents of which are incorporated herein by reference.  
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a reflex-type screen that reflects polarized light. More particularly, the invention relates to the reflex-type screen for reflecting back a polarized image projected by an optical engine.  
      2. Description of the Related Art  
      Conventionally, there is provided a reflex-type screen including a polarization plate and a surface diffusion layer which are stacked in an order on an rolled aluminum film reflecting layer via an adhesive layers. In this reflex-type screen, on the surface of the aluminum film reflecting layer, microscopic liner unevenness is formed, which is called hairline and extends in a direction. The conventional reflex-type screen diffuses and reflects the light by the hairline, thereby improving the view angle of the screen.  
      The hairline is the surface unevenness, which is generated by rolling, and the diffusion performances of horizontal direction and vertical direction on the screen are different from each other due to the hairline.  
      In addition, the art of adding a light diffusion ink layer in which a diffusing agent is doped to a light reflecting ink layer is known, in order to improve the diffusion performance of the screen. (Japanese Patent No. 2,953,289)  
      However, the hair line on the aluminum film reflecting layer is inevitably generated when the aluminum film is formed by rolling, so it is difficult to control the shape of the hair line as desired. Therefore, it is difficult to improve the diffusion performance of the screen by improving the diffusion performance of the aluminum film reflecting layer. In addition, because the art of adding a light diffusion ink layer increases the number of the layers of the screen, there is a problem that the production cost is expensive.  
      Therefore, it is an object of the present invention to provide a reflex-type screen, which are capable of overcoming the above drawbacks accompanying the conventional art. The above and other objects can be achieved by combinations described in the independent claims. The dependent claims define further advantageous and exemplary combinations of the present invention.  
     SUMMARY OF THE INVENTION  
      To achieve such objects, according to the first aspect of the present invention, a reflex-type screen for reflecting polarized light comprises a reflecting layer for reflecting back incident light, a lower adhesive layer including adhesive material, a polarization plate for transmitting polarized light, an upper adhesive layer including adhesive material; and a surface diffusion layer with a diffusing agent included inside for diffusing and transmitting apart of incident light and for diffusing and reflecting the other part of the incident light in its surface and said reflecting layer, said lower adhesive layer, said polarization plate, said upper adhesive layer and said surface diffusion layer are stacked in this order from opposite side of a light source, and said upper adhesive layer includes a diffusion agent dispersedly  
      According to the second aspect of the present invention, a reflex-type screen for reflecting polarized light comprises a reflecting layer for reflecting back incident light, a lower adhesive layer including adhesive material, a polarization plate for transmitting polarized light, an upper adhesive layer including adhesive material; and a surface diffusion layer with a diffusing agent included inside dispersedly, for diffusing and transmitting one part of incident light and also diffusing and reflecting the other part of the incident light in its surface and said reflecting layer, said lower adhesive layer, said polarization plate, said upper adhesive layer and said surface diffusion layer are stacked in this order from opposite side of a light source; and said upper adhesive layer includes a diffusion agent dispersedly.  
      In the second aspect of the present invention, said lower adhesive layer may include said diffusing agent dispersedly.  
      In both of the first aspect and the second aspect of the present invention, at least one of said upper adhesive layer and said lower adhesive layer may include a light absorption agent dispersedly and absorb a part of transmitted light.  
      In both of the first aspect and the second aspect of the present invention, the reflex-type screen may further comprise an absorber layer between the surface diffusion layer and the upper adhesive layer, for absorbing a part of transmitted light.  
      Alternatively, the reflex-type screen may further comprise an absorber layer between the upper adhesive layer and the polarization plate, for absorbing a part of transmitted light.  
      Alternatively, the reflex-type screen may further comprise an absorber layer between the polarization plate and the lower adhesive layer, for absorbing a part of transmitted light.  
      Alternatively, the reflex-type screen may further comprise an absorber layer between the lower adhesive layer and the reflecting layer, for absorbing a part of transmitted light.  
      In both of first aspect and the second aspect of the present invention, the reflecting layer may include unevenness which diffuses light, and the reflex-type screen may further comprise an increase reflecting layer between the lower adhesive layer and the reflecting layer, including a silver thin film layer of which height is lower than that of the unevenness.  
      Alternatively, the reflex-type screen may further comprise an increase reflecting layer between the lower adhesive layer and the reflecting layer, including a dielectric multiple film which has a low refractive index film and a high refractive index film of which refractive index is higher than that of the low refractive index film, and the low refractive index film and the high refractive index film are stacked alternately, and wherein an equation λ/4=n 1 d 1 =n 2 d 2  is satisfied where a film thickness of the low refractive index film is d 1 , a film thickness of the high refractive index film is d 2 , a refractive index of the low refractive index film is n 1 , a refractive index of the high refractive index film is n 2 , and a wavelength of green light (550 nm) is λ.  
      The summary of the invention does not necessarily describe all necessary features of the present invention. The present invention may also be a sub-combination of the features described above. The above and other features and advantages of the present invention will become more apparent from the following description of the embodiments taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a cross-section drawing showing a first embodiment of the reflex-type screen  10 .  
       FIG. 2  is a cross-section drawing showing a second embodiment of the reflex-type screen  10 .  
       FIG. 3  is a cross-section drawing showing a third embodiment of the reflex-type screen  10 .  
       FIG. 4  is a cross-section drawings showing a forth embodiment of the reflex-type screen  10 .  
       FIG. 5  is a cross-section drawing showing a fifth embodiment of the reflex-type screen  10 .  
       FIG. 6  is a cross-section drawing showing a sixth embodiment of the reflex-type screen  10 .  
       FIG. 7  is a cross-section drawing showing a seventh embodiment of the reflex-type screen  10 .  
       FIG. 8  is a cross-section drawing showing an eighth embodiment of the reflex-type screen  10 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      The invention will now be described based on the preferred embodiments, which do not intend to limit the scope of the present invention, but exemplify the invention. All of the features and the combinations thereof described in the embodiment are not necessarily essential to the invention.  
       FIGS. 1-3  are cross-section drawings showing basic configuration of the layers with respect to a reflex-type screen  10 . The reflex-type screen  10  includes an aluminum film reflecting layer  20 , a lower adhesive layer  18 , a polarization plate  16 , an upper adhesive layer  14 , and a surface diffusion layer  12  in this order from opposite side of a light source. The aluminum film reflecting layer  20  reflects incident light. The lower adhesive layer  18  and the upper adhesive layer  14  are made of adhesive agent. The polarization plate  16  transmits polarized light. The surface diffusion layer  12  including diffusing agent  30  diffuses and transmits one part of the incident light and also diffuses and reflects another part of the incident light on its surface.  
      In a first embodiment shown in  FIG. 1 , the upper adhesive layer  14  dispersedly includes a diffusing agent  30  internally. Alternatively, in a second embodiment shown in  FIG. 2 , in place of upper adhesive layer  14 , the lower adhesive layer  18  may include the diffusing agent dispersedly. Accordingly, the reflex-type screen  10  can display wide view angle images without making the number of the layers increase in comparison with conventional reflex-type screen.  
      As a more preferable configuration, like a third embodiment shown in  FIG. 3 , both of the upper adhesive layer  14  and the lower adhesive layer  18  include the diffusing agent  30  dispersedly. Accordingly, the diffusing agent  30  can be added to both the adhesive layer  14  and  18  so that the diffusing agent  30  is shared in the adhesive layer  14  and the adhesive layer  18 . Thus, the quantity of the diffusing agent  30  added to the upper adhesive layer  14  or the quantity of the diffusion agent  30  added to the lower adhesive layer  18  can be limited to a threshold, above which if the diffusing agent  30  is added, a poor appearance e.g. a streak is generated by cohesion. In other words, it is possible to give a desired diffusion performance to the reflex-type screen  10  without a poor appearance e.g. a streak, by adding the diffusing agent  30  to both the upper adhesive layer  14  and the lower adhesive layer  18 .  
      In addition, the lower adhesive layer  18  has a content of the diffusing agent  30  so that the polarized light axis of the polarized light, which passes through the lower adhesive layer  18 , does not change. On the other hand, the content of diffusing agent  30  of the upper adhesive layer  14  is higher than that of the lower adhesive layer  18 . Thus, a wide view angle can be acquired without decreasing the transmittance of the polarized image projected by a projector.  
      For example, the surface diffusion layer  12  is a transparent resin film including the diffusing agent  30 . As a resin film, TAC (tri-cellulose acetate), polypropylene, vinyl chloride, acryl, or a polycarbonate into which the diffusing agent  30  is kneaded, can be employed. For example, the thickness of the surface diffusion layer  12  is about 80 μm. In addition, the surface of the surface diffusion layer  12  is given the surface hardness and anti-glare effect by the anti-glare processing such as embossed processing or coating processing. In this embodiment, the anti-glare coating agent such as an acrylic binder doped with silica filler is coated to the TAC into which the diffusing agent  30  is kneaded, so as to produce the surface diffusion layer  12 . In addition, in this embodiment, the haze value of the surface diffusion layer  12  is about  60 .  
      A pressure sensitive type acrylic adhesive agent is employed as the upper adhesive layer  14  and lower adhesive layer  18 . As an adhesive agent, a high transparent adhesive agent, for example an acrylic adhesive agent or a urethane adhesive agent or polyester adhesive agent, can be employed. The thickness of each of the upper adhesive layer  14  and the lower adhesive layer  18  is preferably about 30 μm.  
      A dye polarization plate can be employed as the polarization plate  16 . As the polarization plate, the polarization degree is preferably equal to or greater than 90%. In this embodiment, an iodic polarization plate is used, of which polarization degree is 95% and, thickness is 120 μm. The polarization plate  16  gives a facility of polarization screen to reflex-type screen  10 . In other words, the reflex-type screen  10  cuts off about half of the outside light and transmits about 100% of the polarized light from the projector. Thus, the contrast under condition of a bright room can be improved.  
      An aluminum film, of which the thickness is equal to or less than 0.15 mm and which is made of ingot or slab by a roller, is employed as the aluminum film reflecting layer  20 . Specifically, a soft aluminum film 0.007 mm thick is employed. In addition, aluminum film reflecting layer  20  improves processability (affix processability) by attaching the aluminum film reflecting layer  20  to a base material  22  at the opposite side of the light source. A flexible resin film, e.g., a PET film 50 μm thick, is used as the base material  22 .  
      The diffusing agent  30  is added to at least one of the upper adhesive layer  14  and the lower adhesive layer  18  and is also added to the surface diffusion layer  12 . In this embodiment, as the diffusing agent  30 , a high transparent filler having spherical shape or indeterminate shape, made of silicone, styrene, or acryl can be used. Specifically, spherical silicone beads with 5 μm of the average particle size are employed.  
      The upper adhesive layer  14  and the lower adhesive layer  18  in which the diffusing agent  30  is dispersed are formed as follows. At first, the transparent diffusing agent  30  such as silicone, silica, styrene or acryl and diluents are kneaded with a transparent adhesive agent such as acrylic adhesive agent so as to produce the diffusion adhesive agent. This diffusion adhesive agent is coated on the surface of the aluminum film reflecting layer  20  and polarization plate  16  using a coating process such as a comma method.  
      The diffusion performance of the refracting screen  10  is improved and the view angle becomes wider by adding the diffusing agent  30  to at least one of the surface diffusion layer  12 , the upper adhesive layer  14 , and the lower adhesive layer  14 . However, since improvement of the diffusion performance decreases the peak gain, it is preferable that each proper quantities of the diffusing agent  30  is experimentally determined in accordance with both the view angle and peak characteristic which required for the reflex-type screen  10 . In addition, there is an upper limitation on processing of the quantity of the addition of the diffusion agent  30  added to both the upper adhesive layer  14  and the lower adhesive layer  18 . For example, the addition of the diffusing agent  30  is limited to about 1.5 weight percent when the weight percent of the acrylic adhesive agent (base agent) is 100. If the quantity of the addition is over the limitation, the processability, i.e. the coat processability decreases.  
      In addition, the quantity of each of the diffusing agent  30  added to the surface diffusion layer  12 , the upper adhesive layer  14  and the lower adhesive layer  18  should be within a threshold. If the diffusing agent  30  is added over the threshold, a poor appearance e.g. a streak will be generated by cohesion. The quantity of the addition can be determined by the haze value of each layer of the upper adhesive layer  14  and the lower adhesive layer  18 , respectively. For example, it is experimentally verified that the poor appearance, e.g. a streak, by cohesion of the diffusing agent  30  is not generated when the haze vales of each of the upper adhesive layer  14  and the lower adhesive layer  18  is less than 80, more preferably, when it is equal to or less than 70.  
      In addition, the haze value of each of the surface diffusion layer  12 , the upper adhesive layer  14  and the lower adhesive layer  18  is not necessarily equal to one another like the examples as described below. In other words, any combination of the addition of the diffusing agent  30  to the surface diffusion layer  12 , the upper adhesive layer  14  and the lower adhesive layer  18  can be used unless poor appearance, e.g. a streak, by cohesion of the diffusing agent  30  is not generated in each of the layers. It is obvious that the diffusion performance of the reflex-type screen  10  is improved when the combination of the quantity of the addition with respect to the surface diffusion layer  12 , the upper adhesive layer  14  and the lower adhesive layer  18  is any combination.  
      The relationship among the particle size of the diffusing agent  30 , the diffusion performance of the surface diffusion layer  12 , the diffusion performance of the upper adhesive layer  14 , and the diffusion performance of the lower adhesive layer  18  will be described as below. When the refractive index of each of the diffusing agent  30 , the binder of the surface diffusion layer  12 , the binder of the upper adhesive layer  14 , and when the binder of the lower adhesive layer  18  is adjusted to the same value, and when the weight percent of each additions is constant, the smaller the particle size of the diffusing agent  30  is, the larger the diffusion performance of each of the surface diffusion layer  12 , the upper adhesive layer  14  and the lower adhesive layer  18  becomes. In other words, the haze value of each of the surface diffusion layer  12 , the upper adhesive layer  14  and the lower adhesive layer  18  increases, thereby, the diffusion performance of the reflex-type screen  10  is improved. The range of the average particle size is from 1 to 20 μm, preferably about 5 μm. As the particle size becomes larger, the coating processability of each of the upper adhesive layer  14  and the lower adhesive layer  18  decreases. Since thickness of each of the upper adhesive layer  14  and the lower adhesive layer  18  is about from 25 to 35 μm, and since the thickness of the surface diffusion layer  12  is about 80 μm, for example, it is necessary that the particle size of the diffusing agent  30  is adequately less than the thickness.  
      On the other hand, the relationship among the refractive index of the diffusing agent  30 , the diffusion performance of the surface diffusion layer  12 , the diffusion performance of the upper adhesive layer  14 , and the diffusion performance of the lower adhesive layer  18  will be described as below. When the particle size of the diffusing agent  30  is constant and when the weight percent of each of the addition is constant, the larger the difference of the refractive index between the diffusing agent  30  and the binder of the surface diffusion layer  12 , or the difference of the refractive index between the diffusing agent  30  and the binder of the upper adhesive layer  14 , or the difference of the refractive index between the diffusing agent  30  and the binder of the lower adhesive layer  18  is, the larger the diffusion performance of each of the surface diffusion layer  12 , the upper adhesive layer  14  and the lower adhesive layer  18  becomes larger becomes. In other words, the haze value of each layers become high, thereby, the diffusion performance of the reflex-type screen  10  is improved. In addition, the refractive index of the diffusing agent  30  is about from 1.4 to 1.6. For example, the refractive index of the silicone filler that is used as the diffusing agent  30  is 1.42 and the refractive index of the acryl adhesive agent that is used as the binder is from 1.47 to 1.49.  
       FIGS. 4-8  show additional embodiments in which the optical function layers are added to improve the optical properties of the reflex-type screen  10 .  FIGS. 4-7  show embodiments, in which an absorber layer  40  is added to absorb a part of the light transmitted through a part of the layers configuring the reflex-type screen  10 .  FIG. 8  shows an embodiment, in which the increasing reflecting layer  50  is added to improve the reflectivity of the aluminum film reflecting layer  20 . Here, the embodiments in  FIGS. 4-8  show embodiments in which both the upper adhesive layer  14  and the lower adhesive layer  18  include diffusing agent  30 , an embodiment of the present invention is not limited to these embodiments, i.e. either the upper adhesive layer  14  or the lower adhesive layer  18  may include the diffusing agent  30 .  
      The reflex-type screen  10  shown in  FIG. 4  includes an absorber layer  40  between aluminum film reflecting layer  20  and the lower adhesive layer  18 .The absorber layer  40  includes a light absorption agent, which is made of black dye or black pigment, with adhesive agent or glue, and the absorber layer  40  is provided on the surface of the aluminum film reflecting layer  20  by coating processing. It is preferable that the black pigment is used as the light absorption agent because the black pigment is superior to the black dye with respect to the light stability. The absorber layer  40  has a visible light transmittance about from 50% to 80%. The absorber layer  40  absorbs outside light such as the light of lamps, or stray light such as the multiple reflection light reflected in the screen, the refore, the absorber layer  40  can improve the contrast of an image in visual sense. The principle according to which the absorber layer  40  improves the contrast in visual sense will be described herein after.  
      The absorber layer  40  absorbs not only outside light and stray light but also white image and black image projected directly from the projector so that the absorbed light intensity is equal to the intensity of (100-transmittance (%))%. In this case, humans feel that the contrast of the image increases because of the characteristic of their eyes. For example, if the brightness of the white image is 50, the brightness of black image is 5, and the transmittance of the absorber layer  40  is 50%, after the light of the images transmit the absorber layer  40 , then the brightness of the white image becomes 50 and the brightness of the black image becomes 5. Here, it is known that the quantity of the human sense can be expressed in logarithm function corresponding to physical quantity. This is known as Weber-Fechner Rule, it is S (sense quantity)=Log P (physical quantity)+C. Here, if C is assumed to be zero and the physical quantities described above are substituted, and if the physical quantities are 100 (the white image) and 10 (the black image), the sense quantities are derived to be 1 (the black image) and 2 (white image). Therefore, the contrast in sense quantity is expressed 2:1. On the other hand, if the physical quantities are 50 (the white image) and 5 (the black image), the sense quantities are derived to be 1.7 (black image) and 0.7 (white image). In this case, the contrast in sense quantity is expressed 1.7:0.7=2.4:1. In other words, the image, of which contrast in sense quantity, is expressed 2:1 is improved to 2.4:1 because of the function of the absorber layer  40 .  
      The absorber layer  40  may be placed between the polarization plate  16  and the lower adhesive layer  18  as shown in  FIG. 5 . The absorber layer  40  may be placed between the upper adhesive layer  14  and the polarization plate  16  as shown in  FIG. 6 . Alternatively, the absorber layer  40  may be placed between the surface diffusion layer  12  and the upper adhesive layer  14  as shown in  FIG. 7 . Whenever the absorber layer  40  is placed in any place as shown in  FIGS. 5-7 , the same effects can be produced.  
      Alternatively, instead of placing the absorber layer  40  shown in  FIGS. 4-7 , the light absorption agent may be dispersed at least one part of upper adhesive layer  14  and the lower adhesive layer  18 , so that the absorption agent absorbs a part of the transmitted light. In this case, it is preferable that the light absorption agent is added to the upper adhesive layer  14  or the lower adhesive layer  18  so that the visible light transmittances of the upper adhesive layer  14  or the visible light transmittances of the lower adhesive layer  18  is about from 50% to 80%. As described above, the light absorption agent is dispersed at least one of upper adhesive layer  14  and the lower adhesive layer  18 , to absorb a part of the light transmitting, thereby the same effect as the absorber layer  40  shown in  FIGS. 4-7 , i.e., the effect of improving the contrast of the reflex-type screen  10  in visible sense, can be obtained.  
       FIG. 8  is a cross-section drawing showing an eighth embodiment of the reflex-type screen  10 . In this embodiment, the reflex-type screen  10  further includes an increase reflecting layer  50  between the aluminum film reflecting layer  20  and the lower adhesive layer  18 , of which thickness is thinner than the height of the unevenness on the aluminum film reflecting layer  20  generated like hairline. The increase reflecting layer  50  increases the reflectivity without disturbing the light diffusion effect of the unevenness generated like hairline on the aluminum film reflecting layer  20 . The increase reflecting layer  50  is for example, silver thin film layer. For production method of the silver thin film layer, the silver thin film having about 1000 Å thickness is formed in sputter method or evaporation method on the aluminum film reflecting layer  20 . The reflectivity of silver is about 10% higher than that of aluminum. An experimental result shows that the screen gain of the reflex-type screen  10  was improved by about 20%. A transparent resin including urethane may coat the surface of the silver thin film. By this, air exposure and corrosion of the silver thin film can be prevented.  
      In addition, the increase reflecting layer  50  may be a dielectric multiple film. The dielectric multiple film includes a low refractive index film and a high refractive index film of which refractive index is higher than the low refractive index film and they are stacked alternately. The equation λ/4=n 1 d 1 =n 2 d 2  is satisfied, where the film thickness of low refractive index film is d1, the film thickness of high refractive index film is d2, the refractive index of the low refractive index film is n1, the refractive index of the high refractive index film is n2, and the wavelength of green light (550 nm) is λ. Thus, the reflectivity of the image can be increased, and mainly the green light at the center of the wavelength area of the image can be increased. The dielectric films are stacked, for example, by sputter methods on the surface of the aluminum film reflecting layer  20 . The layer configuration of the dielectric multiple films has for example, the low refractive index film, the high refractive index film, the low refractive index film, and the high refractive index film in this order. MgF 2  (magnesium fluoride) is an example of the low refractive index film, of which refractive index is 1.38 and CeO 2  (cerium oxide) is an example of the high refractive index film, of which refractive index is 2.2. The film thickness d1 of MgF 2  as an example of the low refractive index film and the film thickness d2 of CeO 2  as an example of the high refractive index film are expressed as follows according to the conditional equation described above. 
 
 d   1 (MgF 2 )=550/4/1.38=99.6 nm 
 
 d   2 (CeO 2 )=550/4/2.2=62.5 nm 
 
      In addition, it is possible to obtain an increase reflecting layer having smaller dependency on the incident angle by controlling the film thickness of each layers on the basis of the value of the film thickness which satisfies the conditional expression described above, i.e., the increase reflecting layer having less color drift due to the incident angle can be obtained. According to experiments, when such a dielectric multiple films is placed as the increase reflecting layer  50 , the reflectivity of the reflex-type screen  10  is improved by about 10%.  
      As is apparent from the above-mentioned description, according to the present embodiment, the reflex-type screen  10  for displaying a wide angle image and a bright image can be realized in low cost.  
      Although the present invention has been described by way of exemplary embodiments, it should be understood that those skilled in the art might make many changes and substitutions without departing from the spirit and the scope of the present invention which is defined only by the appended claims.