Patent Publication Number: US-2022221780-A1

Title: Projection screen

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a national phase of International Application No. PCT/CN2020/090757, filed on May 18, 2020, which claims priority to and the benefit of CN 201910463752.4, filed on May 30, 2019. The disclosures of the above applications are incorporated herein by reference. 
    
    
     FIELD 
     The present disclosure relates to the field of projection, and particularly to a projection screen. 
     BACKGROUND 
     The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. 
     A projection screen generally includes a diffusion layer, a substrate, and a reflection layer, which are successively stacked. The diffusion layer is provided towards viewers. Two kinds of light, projection and ambient light, are reflected to human eyes through the projection screen. The ambient light, as stray light, increases a minimum brightness of an image, thus reducing a contrast in an image displayed by projection. One solution is to selectively reflect the ambient light but the projection light. Namely, the projection light should be reflected while the reflection of the ambient light should be reduced as much as possible. Brightness gain is another important parameter for a projection system. Currently, an implementation method for increasing the brightness gain is to provide a micro-structural reflection on the projection screen such that the projection light focuses on emission at a certain angle as much as possible, so as to increase an image brightness in a range of orientation angle. Disadvantages for this method is that a visible angle of the projection screen is relatively small, rendering a non-uniform brightness problem in a vertical viewing angle. 
     SUMMARY 
     This section provides a general summary of the disclosure and is not a comprehensive disclosure of its full scope or all of its features. 
     An objective of the present application is to provide a projection screen, so as to solve a technical problem of a relatively small visible angle and a non-consistent brightness of the projection screen. 
     A projection screen is provided according to the present application. The projection screen includes: a substrate including a first substrate surface, wherein the first substrate surface includes a first area and a second area adjacent to the first area, the first area is provided with a plurality of first wire grid bodies extending along a first direction, and the second area is provided with a plurality of second wire grid bodies extending along the first direction; 
     each of the plurality of first wire grid bodies includes a first contact surface connected with the substrate, and a first surface, wherein a first angle is formed between the first contact surface and the first surface, and the first angles reduces gradually along a direction from the first area to the second area; and 
     each of the plurality of second wire grid bodies includes a second contact surface connected with the substrate, and a third surface, wherein a third angle is formed between the second contact surface and the third surface, and the third angles increases gradually along the direction from the first area to the second area. 
     Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       DRAWINGS 
       In order to describe embodiments of the present application or technical solutions in existing technology more clearly, appended drawings required to use in descriptions of embodiments or the existing technology will be described briefly below. Apparently, the appended drawings described below are only some embodiments of the present application, and a person skilled in the art can also obtain further drawings according to these drawings without creative efforts. 
       In order that the disclosure may be well understood, there will now be described various forms thereof, given by way of example, reference being made to the accompanying drawings, in which: 
         FIG. 1  is a structure schematic diagram of a relative position between a projection screen and a projector according to some embodiments of the present application; 
         FIG. 2  is a lateral structure schematic diagram of the projection screen shown in  FIG. 1 ; 
         FIG. 3  is a structure schematic diagram of a first wire grid structure in 
         FIG. 2 ; 
         FIG. 4  is a structure schematic diagram of a first wire grid structure and a second wire grid structure according to a first embodiment of the present application; 
         FIG. 5  is a schematic diagram of changes of a first angle and a third angle according to a first embodiment of the present application; 
         FIG. 6  is a schematic diagram of a size of a first wire grid body; 
         FIG. 7  is a structure schematic diagram of a first wire grid structure and a second wire grid structure according to a second embodiment of the present application; 
         FIG. 8  is a structure schematic diagram of a first wire grid structure and a second wire grid structure according to a third embodiment of the present application; 
         FIG. 9  is a structure schematic of a curved projection screen according to a fifth embodiment of the present application; 
         FIG. 10  is a structure schematic diagram of a nine-point uniformity applied in a brightness representation method of a projection screen according to the present application; and 
         FIG. 11  is a brightness changing curve of a nine-point uniformity at different positions of the projection screen. 
     
    
    
     The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
     DETAILED DESCRIPTION 
     The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features. 
     Technical solutions in embodiments of the present application will be described clearly and completely in combination with the appended drawings in embodiments of the present application. Apparently, the described embodiments are only some of embodiments of the present application, while not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by a person skilled in the art without creative efforts fall in a scope protected by the present application. 
     Referring to  FIG. 1  to  FIG. 4 , a projection screen  100  is provided according to the present application, which is used to reflect projection light from a projector  200 . The projection screen  100  is located in a first plane P 1 , and the projector is located in a second plane P 2  perpendicular to the first plane P 1 . It is noted that the projector  200  is located in front of the first plane such that the projection light can irradiate into the projection screen. It can be located in the second plane vertical to the first plane or not. The projection light is light of the projector  200  which carries image information. 
     An extension direction of an intersecting line between the first plane P 1  and the second plane P 2  is defined as a first direction L 1 , and a direction perpendicular to the first direction L 1  in the first plane L 1  is defined as a second direction L 2 . 
     Referring to  FIG. 2 , the projection screen  100  includes a substrate  10 , a diffusion layer  60  and a reflection layer  90 . The diffusion layer  60  is located at a side of the substrate  10  facing the projector  200 , and the reflection layer  90  is located at a side of the substrate  20  away from the projector  200 . Viewers will be located at a side close to the diffusion layer  60  of the projection screen, and the side corresponding to the reflection layer  90  is a side away from the viewer. 
     In the present application, a diffusion angle of the diffusion layer  60  is 5° to 30°. Organic resin particles in epoxy series, acrylic acid series or silicone series, or other inorganic scattering material may be used as material of the diffusion layer  60 . 
     Material of the substrate  10  includes organic materials such as PET, PC, PVC and PMMA. A thickness of the substrate  10  ranges from 1 mm to 10 mm. 
     The reflection layer  90  includes reflective material and is used to reflect the projection light. In an implementation, the reflection layer  90  further includes absorbing material or diffusion material, to further strengthen a light absorption effect and a light diffusion effect of the reflection layer. The reflective material includes metallic reflection material such as an aluminum sheet, aluminum powder and silver powder. The absorbing material includes organic pigments and inorganic pigments. The organic pigments include AZO and so on, and the inorganic pigments include carbon black, graphite, metallic oxide and so on. Organic resin particles in epoxy series, acrylic acid series or silicone series, or other inorganic scattering material may be used as the diffusion material. A reflectivity of the reflection layer  90  is 30% to 60%, in some embodiments, the reflectivity of the reflection layer  90  is 40% to 50%. In the reflection layer  90  of the present application, by reducing a percentage of the reflection material to reduce the reflectivity of the projection screen, the reflection to the ambient light is effectively reduced, thereby increasing a contrast of the projection screen. In addition, in the reflection layer  90  of the present application, by adding absorbing material to increase absorption to the ambient light, the contrast of the projection screen is further increased. In the reflection layer  90  of the present application, by adding a diffusion medium to increase an emergence angle of the projection light, the visible angle of the projection screen is further increased. 
     Specifically, in the present application, the projection light is diffused multiple times on the projection screen  100 . Firstly, the projection light is diffused through the diffusion layer  60 , and this diffusion is an ellipse or a circle diffusion with Gaussian 20° to 60° in a longitudinal direction, and Gaussian 5° to 20° in a longitudinal direction. Then the projection light is reflected and diffused simultaneously on the reflection layer  90 , and this diffusion is a Gaussian or Lamber scatter with a diffusion angle 10° to 30°. Finally, the projection light returns to the diffusion layer  60 , to further be diffused and then emitted. In this way, finally a horizontal field angle of the projection screen  100  is greater than 45°, and a longitudinal field angle is greater than 20°. A surface microstructure may also be applied to the diffusion layer  60  for performing a surface diffusion. The diffusion layer  60  control the scattering angle of light by the surface microstructure. A specific process includes fixing the surface microstructure on the substrate  10  by hot padding or UV glue. 
     It is known from the above description that in the projection screen  100  of the present application, the visible angle of the projection screen  100  is increased by the diffusion layer  60  and the reflection layer  90 , an anti-ambient light capability is further increased, and a better contrast can be obtained. However, when the projector is placed in front of the projection screen, the projection light of the projector is incident on a bottom surface of the projection screen  100  approximately vertically, and thus the incident light has a smaller incident angle. The projection light incident on a top of the projection screen has a larger incident angle. In this case, the emitted projection light has a larger reflection angle, such that a majority of projection light emitted from the top of the projection screen is far away from a viewing position of the viewer. Although the diffusion layer can diffuse a part of the projection light to the viewing position of the viewer, a majority of projection light is still wasted, such that the projection screen  100  has a relatively low brightness and an inconsistent bright uniformity. 
     Referring to  FIG. 3  to  FIG. 4 , to solve this problem, the projection screen  100  according to an embodiment of the present application further includes a first wire grid structure  20  provided on a surface of the substrate. The substrate  10  includes a first substrate surface  101  away from the projector  200 . The first substrate surface  101  includes a first area  101   a  and a second area  101   b  adjacent to the first area  101   a . The first area is provided with multiple first wire grid bodies extending along a first direction. Each first wire grid body  201  includes a first contact surface  201   c  connected with the substrate, and a first surface  201   a . There is a first angle θ 1  between the first surface  201   a  and the first contact surface  201   c . Multiple first angles θ 1  reduces gradually along a direction from the first area  101   a  to the second area  101   b . It should be noted that in an embodiment, the substrate  10  and the first wire grid structure  20  are formed integrally. That is to say, the first wire grid body  201  is formed on the first substrate surface  101  of the substrate  10  by transfer. 
     In the present application, compared with a traditional projection screen, the first wire grid body  201  is added on the first substrate surface  101  of the substrate  10 . The first wire grid body  201  is located on the first area  101   a  of the first substrate surface  101  of the substrate  10 , i.e., the first wire grid structure  20  is located at an area below the center of the projection screen  10 . The projection light emitted from the projector  200  is incident on the first area of the projection screen. In this case, an incident angle corresponding to the projection light is smaller. Several first wire grid bodies  201  are provided on the first area  101   a , and there is the first angle θ 1  between the first surface  201   a  of the first wire grid body  201  and the first substrate surface  101 . The incident angle of the projection light on the first surface  201   a  is increased by the first angle θ 1 , and a reflection angle of the projection light can be correspondingly increased. Thus, the projection light can be reflected to a higher position, such that the projection light is emitted from a position close to the center of the projection screen and the projection light can enter into a viewer sight as much as possible. With the projection light moving from the bottom to the position close to the center of the projection screen  10 , the incident angle of the projection light is larger and larger, and the reflection angle of the projection light is larger and larger as well. The projection light may be emitted above the projection screen  100 , and cannot enter into viewer eyes. The first angles θ 1  in the present application are reduced gradually along the direction from the first area  101   a  to the second area  101   b , i.e., extending upwardly from the bottom of the projection screen  100 . The first surface  201   a  is closer and closer to the first substrate surface  101 , which will reduce the incident angle of the projection light and correspondingly reduce the reflection angle of the projection light. The projection light will be emitted from the position close the center of the projection screen, such that the projection light may enter into the viewer sight as much as possible. 
     Each first wire grid body  201  further includes a second surface  201   b . There is a second angle θ 2  between the second surface  201   b  and the first contact surface  201   c . The second angle θ 2  is greater than a first threshold. Specifically, in the case that a thickness of the first wire grid body  201  and the first angle θ 1  are determined, an extending trend of the second surface  201   b  is opposite to that of the incident projection light in order to reduce an interference of the second surface  201   b  to the projection light as much as possible. If the second angle θ 2  is relatively smaller, an area of the second surface  201   b  is relatively larger, more incident projection light will be incident on the second surface  201   b . The incident projection light will be reflected by the second surface  201   b  to a lower position, which is hard to enter into the viewer eyes. This part of projection light cannot contribute to the image light on the projection screen, rendering a loss of projection light. Therefore, the second angle θ 2  needs to be greater than the first threshold in order to avoid the projection being incident on the second surface  201   b  as much as possible. 
     An angle between a normal direction of the projection screen  100  and the incident projection light is defined as A, and an angle between the projection light reflected by the projection screen  100  and the normal direction of the projection screen  100  is defined as B. In order to avoid the projection light being incident on the second surface  201   b , it is necessary to set the first threshold to be 90°-B, i.e., θ 2 &gt; 90 °-B. In the case that the thickness of the first wire grid body  201  and the first angle θ 1  is determined, if θ 2 &lt; 90 °-B, the second surface  201   b  is close to the first substrate surface  101 . In this case, the area of the second surface is larger, and more incident projection light is incident on the second surface  201   b . This part of light is reflected to a lower position by the second surface  201   b , which thus is difficult to provide the image light of the projection screen. Therefore, more projection light loss is caused, and a defect in the non-uniform brightness distribution at the viewer side is brought. When the second angle θ 2  between the second surface  201   b  and the first contact surface  201   c  is greater than the first threshold, a majority of the incident projection light will be incident on the first surface  201   a  and be reflected on the first surface  201   a.    
     Referring back to  FIG. 4 , the second area of the projection screen  100  is provided with multiple second wire grid bodies extending along the first direction. Each second wire grid body  401  includes a second contact surface  401   c  connected with the substrate and a third surface  401   a . There is a third angle θ 3  between the third surface  401   a  and the second contact surface  401   c . Multiple third angles θ 3  increase gradually in the direction from the first area  101   a  to the second area  101   b . It is noted that in an embodiment, the substrate  10  and the second wire grid structure  40  are formed integrally. That is, the second wire grid structure  400  is formed on the first substrate surface  101  of the substrate  10  by transfer. 
     In the present application, compared with a traditional projection screen  100 , the second wire grid body  401  is added on the substrate  10  of the projection screen  100 . The second wire grid body  401  is provided on the second area  101   b.    
     It can be known from the above description that the incident projection light includes the projection light incident on the first area  101   a  and the projection light incident on the second area  101   b . An incident angle of the projection light incident on the second area  101   b  is greater than that of the projection light incident on the first area  101   a . When the incident angle of the projection light is greater than a preset threshold, the incident projection light will enter to the second wire grid body  401  of the second wire grid structure  40 . That is, the incident projection light will be reflected by the third surface  401   a  of the second wire grid body  401 . Moreover, since the extending trend of the third surface  401   a  of the second wire grid body  401  is opposite to an incident direction of the projection light, the projection light will be incident on the third surface  401   a  in that case that the third angle θ 3  is not large. Since the second wire grid body  401  is located in a higher position of the projection screen  100 , the incident angle of the incident projection light on the third surface  401   a  will be larger. Therefore, a reflection angle will be larger correspondingly. However, the first substrate surface  101  of the present application is provided with multiple second wire grid bodies  401 . There is the third angle θ 3  between the third surface  401   a  and the second contact surface  401   c  of the second wire grid body  401 . The incident angle of the projection light incident on the third surface  401   a  is reduces due to the third angle θ 3 , thus reducing the reflection angle of the projection light correspondingly. Therefore, the projection light may be reflected to a lower position and will be emitted from a position close to the center of the projection screen  100 , and thus more projection light may enter into the viewer sight. 
     With the projection light moving from the center of the projection screen  100  to the top of the projection screen  100 , the incident angle of the projection light is larger and larger, and a reflection angle of the projection light is larger and larger as well. The projection light may be emitted above the projection screen  100 , and cannot enter into viewer eyes. The third angles θ 3  in the present application are increased gradually along the direction from the center of the projection screen  100  to the top of the projection screen  100 , i.e., extending upwardly from the center of the projection screen  100 . The third surface  401   a  is farther and farther away from the first substrate surface  101 , which will reduces the incident angle of the projection light, and correspondingly reduce the reflection angle of the projection light. The projection light will be emitted from a position close the center of the projection screen, and more projection light may enter into the viewer sight. 
     It is noted that, in the present application, illustration is made to the projection light when the projector located at the bottom of the projection screen. In an embodiment, the projector may be arranged at the top of the projection screen (a hoisted projector). In this case, wire grid structures of the projection screen may have an opposite angle change as above, which will not be repeated here. 
     Therefore, in the present application, by gradually reducing the first angle θ 1  between the first surface  201   a  and the first contact surface  201   c  along the direction from the first area  101   a  to the second area  101   b , both of the projection light at the bottom of the projection screen and that in the position below the center of the projection screen can be reflected to a position close to the center of the projection screen. That is, the projection light at the bottom of the projection screen and the projection light in the position below the center of the projection screen can converge to the center of the projection screen. Thus, approximately identical light enters into viewer eyes, increasing the brightness gain of the projection screen. 
     In the present application, by gradually increasing the third angle θ 3  between the third surface  401   a  and the second contact surface  401   c  along the direction from the first area  101   a  to the second area  101   b , both of the projection light at the top of the projection screen and that in a position above the center of the projection screen can be reflected to the position close to the center of the projection screen  100 . That is, the projection light at the top of the projection screen and the projection light in the position above the center of the projection screen can converge to the center of the projection screen  100 . Thus, approximately identical light enters into viewer eyes, increasing the brightness gain of the projection screen  100 . 
     Therefore, in the present application, the projection light is reflected to the position close to the center of the projection screen  100  as much as possible, so as to increase the brightness of a center area of the projection screen as much as possible, thus increasing the brightness gain of the projection screen. 
     Each second wire grid body  401  further includes a fourth surface  401   b . There is a fourth angle θ 4  between the fourth surface  401   b  and the second contact surface  401   c . The fourth angle θ 4  is greater than a second threshold. Specifically, in the case that a thickness of the second wire grid body  410  and the third angle θ 3  are determined, if the fourth angle θ 4  is too small and an area of the fourth surface  401   b  is relatively large, more projection light is incident on the fourth surface  401   b , and the incident projection light is reflected to a higher position by the fourth surface  401   b . Thus, the reflected projection light cannot enter into viewer eyes, which will result into a loss of the projection light. Therefore, in order to avoid too much projection light being incident on the fourth surface  401   b , the fourth angle θ 4  between the fourth surface  401   b  and the second contact surface  401   c  is required to be greater than the second threshold. 
     In this embodiment, in order to avoid the projection light being incident on the fourth surface  401   b , the second threshold needs to be set as 90°-A, i.e., θ 4 &gt;90°-A. Therefore, when the fourth angle θ 4  between the fourth surface  401   b  and the second contact surface  401   c  is greater than the second threshold, a majority of incident projection light is incident and reflected on the third surface  401   a.    
     In the present application, a boundary between the first area  101   a  and the second area  101   b , i.e., a segment in which the first wire grid structure  20  and the second wire grid structure  40  are provided, is determined by the following equation. Here, the first angle θ 1  satisfies the following equation (1), and the third angle θ 3  satisfies the following equation (2). 
     
       
         
           
             
               
                 
                   
                     θ 
                     1 
                   
                   = 
                   
                     
                       B 
                       - 
                       A 
                     
                     2 
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
             
               
                 
                   
                     θ 
                     3 
                   
                   = 
                   
                     
                       A 
                       - 
                       B 
                     
                     2 
                   
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
           
         
       
     
     When A=B, θ 1 =θ 3 . The projected incident light will transit from the first wire grid structure  20  to the second wire grid structure  40 , i.e., from the first surface  201   a  to the third surface  401   a.    
     Referring to  FIG. 5 , in a specific implementation, in a direction (the second direction) perpendicular to the projection screen, the boundary between the first area  101   a  and the second area  101   b  is located at 0.3 m away from the bottom. That is, the first wire grid structure  10  transits to the second wire grid structure  40 , at 0.3 m above the bottom. Moreover, the first angle θ 1  changes from an initial 20° to 0°, at 0.3 m above the bottom. In this case, A=B. The projected incident light will transit from the first wire grid structure  20  to the second wire grid structure  40 , and the projected incident light will be incident on the third surface  410   a . The third angle θ 3  ranges from 0° to 20°. 
     In this embodiment, the first wire grid structure  20  and the second wire grid structure  40  are provided between the substrate  10  and the reflection layer  90 . 
     In this embodiment, the reflection layer  90  may cover the first wire grid structure  20  or the second wire grid structure  40  by spraying, screen printing, and printing, etc. A thickness of the reflection layer  90  is controlled to be 10 micron to 3 millimeter. In some embodiments, spraying enables the reflection layer  90  to profile-followed attach to the surface of the first wire grid structure  20  or the second wire grid structure  40  well. Although there is a defect such as disbonding due to the environment, the optical properties such as reflection and absorbing of the projection screen  100  are not influenced since the defects takes place outwardly. The reflection layer  90  of the present application does not use a process such as magnetron sputtering or evaporation coating, such that a manufacturing speed is greatly increased and a cost is reduced greatly. 
     The first wire grid structure  20  and/or the second wire grid structure  40  is transparent or gray. The substrate  10  is transparent or gray. A color combination for the first wire grid structure  20  and/or the second wire grid structure  40 , and the substrate  10  is as follows. 
     A first color combination includes: a gray substrate  10 , and a gray first wire grid structure  20  and/or a gray second wire grid structure  40 . 
     A second color combination includes: a transparent substrate  10 , and a transparent first wire grid structure  20  and/or a transparent second wire grid structure  40 . 
     A third one color combination includes: a transparent substrate  10 , and a gray first wire grid structure  20  and/or a gray second wire grid structure  40 . 
     A fourth color combination includes: a gray substrate  10 , and a transparent first wire grid structure  20  and/or a transparent second wire grid structure  40 . 
     In the above color combination of the gray substrate  10 , and the gray first wire grid structure  20  and/or the gray second wire grid structure  40 , the ambient light may be further absorbed when the ambient light is relatively bright, so as to increase the contrast of the projection screen. 
     The substrate  10  is made by extrusion. The gray substrate  101  may be made by doping black absorbing material particles to the transparent substrate material. The black material particles includes organic pigments such as AZO and inorganic pigments such as carbon black, graphite, metallic oxide. If the first wire grid structure  20  and/or the second wire grid structure  40  is made by hot padding, the first wire grid structure  20  and/or the second wire grid structure  40  has the same color. If the first wire grid structure  20  and/or the second wire grid structure  40  is made by UV glue transfer printing, the black absorbing material, such as organic pigments (AZO and so on) and inorganic pigments (such as carbon black, graphite, metallic oxide, and so on), needs to be doped in the mixing process of the UV glue. 
     Referring to  FIG. 6 , a thickness h for the first wire grid structure  20  and/or the second wire grid structure  40  is 5 μm-100 μm. Specifically, a size p of each first wire grid body  201  of the first wire grid structure  20  and a thickness h of the first wire grid structure  20  satisfy an equation (3) below. 
     
       
         
           
             
               
                 
                   p 
                   = 
                   
                     h 
                     * 
                     
                       ( 
                       
                         
                           1 
                           
                             tan 
                             ⁢ 
                             
                               θ 
                               1 
                             
                           
                         
                         + 
                         
                           1 
                           
                             tan 
                             ⁢ 
                             
                               θ 
                               2 
                             
                           
                         
                       
                       ) 
                     
                   
                 
               
               
                 
                   ( 
                   3 
                   ) 
                 
               
             
           
         
       
     
     The size p of the first wire grid body  201  can be obtained as 20 μm to 300 μm by the above equation (3). In addition, if the size p of the first wire grid body  201  is fixed to be 100 μm, inverse computation may be performed to obtain the thickness of the first wire grid structure  20  to be 0-35 μm. 
     Similarly, a size p of each second wire grid body  401  of the second wire grid structure  40  and a thickness h of the second wire grid body  401  also satisfy the above equation. Similarly, the size p of the second wire grid body  401  can be obtained as 20 μm to 300 μm. Similarly, if the size p of the second wire grid body  401  is 100 μm, inverse computation may be performed to obtain the thickness of the second wire grid body  401  to be 0-35 μm. 
     Referring to  FIG. 7 , in a second embodiment of the present application, the first wire grid structure  20  and the second wire grid structure  40  are provided between the substrate  10  and the diffusion layer  60 . 
     The substrate  10  includes a second substrate surface  102  towards the projector  200 , and the second substrate surface  102  includes a third area  101   a  and a fourth area  102   b  connected with the third area  102   a . The third area  102   a  is horizontally connected with a second plane P 2 . The second wire grid structure  40  is provided on the third area  102   a  and extends along the first direction of the projection screen  100 . The second wire grid structure  40  includes successively connected multiple second wire grid bodies  401 . Each second wire grid body  401  has a thickness direction perpendicular to the first direction of the projection screen  100 . Each second wire grid body  401  includes a second contact surface  401   c  and a third surface  401   a . The second contact surface  401   c  contacts to the second substrate surface  102 . There is a third angle θ 3  between the third surface  401   a  and the second contact surface  401   c . The third angle θ 3  faces the third area  102   a . Multiple third angles reduce gradually along a direction from the third area  102   a  to the fourth area  102   b.    
     Similarly, it can be known from the description of the first embodiment that, when the multiple third angles θ 3  reduce gradually along the direction from the third area  102   a  to the fourth area  102   b , the third surface  401   a  is more and more close to the second substrate surface  102 , thus reducing the incident angle of the projection light. Correspondingly, the reflection angle of the projection light will be smaller, and the projection light will emit from a position closer to the center of the projection screen  100 . Therefore, more projection light can enter into the viewer sight. 
     The first wire grid structure  20  is provided on the fourth area  102   b  and extends along the first direction of the projection screen  100 . The first wire grid structure  20  includes successively connected multiple first wire grid bodies  201 . Each first wire grid body  201  has a thick direction perpendicular to the first direction of the projection screen  10 . Each first wire grid body  201  includes a first contact surface  201   c  and a first surface  201   a . The first contact surface  201   c  contacts with the second substrate surface  102 . There is a first angle θ 1  between the first surface  201   a  and the first contact surface  201   c . The first angle θ 1  faces the fourth area  102   b . Multiple first angles θ 1  increase gradually along the direction from the third area  102   a  to the fourth area  102   b.    
     Similarly, it can be known from the description of the first embodiment that, when the multiple first angles θ 1  increase gradually along the direction from the third area  102   a  to the fourth area  102   b , the first surface  201   a  is farther and farther away from the second substrate surface  102 , thus reducing the incident angle of the projection light. Correspondingly, the reflection angle of the projection light will be reduced as well, and the projection light will emit from a position closer to the center of the projection screen  100 . Therefore, more projection light can enter into the viewer sight. 
     In this embodiment, the first wire grid structure  20  and/or the second wire grid structure  40  is transparent or gray. The substrate  10  is transparent, black or gray. A color combination of the first wire grid structure  20  and/or the second wire grid structure  40 , and the substrate  10  is as follows. 
     A first color combination includes: a black substrate  10 , and a transparent first wire grid structure  20  and/or a transparent second wire grid structure  40 . 
     A second color combination includes: a gray substrate  10 , and a transparent first wire grid structure  20  and/or a transparent second wire grid structure  40 . 
     A third color combination includes: a transparent substrate  10 , and a transparent first wire grid structure  20  and/or a transparent second wire grid structure  40 . 
     A fourth color combination includes: a black substrate  10 , and a gray first wire grid structure  20  and/or a gray second wire grid structure  40 . 
     A fifth color combination includes: a gray substrate  10 , and a gray first wire grid structure  20  and/or a gray second wire grid structure  40 . 
     A sixth color combination includes: a transparent substrate  10 , and a gray first wire grid structure  20  and/or a gray second wire grid structure  40 . 
     In this embodiment, since the projection light firstly enters into the first wire grid structure  20  and/or the second wire grid structure  40  and then enters into the substrate  10 , the substrate  10  may be black or transparent. A black substrate  10  can further absorb the transmitted light. A transparent substrate  10  enables the transmitted light to emit from a back of the projection screen  100  directly. Therefore, the contrast of the projection screen  100  will not be influenced. 
     Referring to  FIG. 8 , a third embodiment of the present application differs from the first and the second embodiments in that there are two groups of the first wire grid structures  20 . One group of first wire grid structures is provided on the first area  101   a , and the other group of first wire grid structures  20  is provided on the fourth area  102   b . A specific arrangement is identical with those in the first embodiment and the second embodiment. There are two groups of second wire grid structures  40 . One group of second wire grid structures  40  is provide on the second area  101   b , and the other group of second wire grid structures  40  is provided on the third area  201   a . A specific arrangement for this is identical to those in the first embodiment and the second embodiment. 
     In this embodiment, a group of first wire grid structures  20  and a group of second wire grid structures  40  are provided between the substrate  10  and the reflection layer  90 . The other group of first wire grid structures  20  and the other group of second wire grid structures  40  are provided between the substrate  10  and the diffusion layer  60 . Therefore, in this embodiment, a combined effect of the first embodiment and the second embodiment may be obtained. Regardless of the projection light incident on the bottom of the projection screen  100  or on the top of the projection screen  100 , the projection screen  100  can emit the projection light from a position close to the center of the projection screen  100 , and more projection light may enter into the viewer sight. 
     Referring to  FIG. 9 , in a fourth embodiment of the present application, the projection screen  100  may be a curved screen with an arc shape. A bending direction of the projection screen  100  faces the projector  200  and the viewer. The center of the projection screen  100  is located in the viewer sight. Therefore, regardless of the shape of the projection screen  100 , light reflected through the curved projection screen  100  with the arc shape may enter into the viewer sight, further increasing the brightness uniformity of the projection screen  100 . 
     For the above embodiment, a simulation experiment is as follows. 
     Referring to  FIG. 10 , in order to represent the brightness uniformity of a screen, a representation method for the screen brightness uniformity is introduced in the present application. In the representation method, a nine-point uniformity may be used. Nine points distribute uniformly in half of the screen, and a brightness is L (n, n=1, 2, . . . , 9). The brightness uniformity is expressed by a ratio between a minimum brightness and a center brightness, which is expressed by an equation (4) below. 
     
       
         
           
             
               
                 
                   
                     9 
                     ⁢ 
                     
                       - 
                     
                     ⁢ 
                     point 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     uniformity 
                   
                   = 
                   
                     
                       min 
                       ⁢ 
                       
                         L 
                         ⁡ 
                         
                           ( 
                           n 
                           ) 
                         
                       
                     
                     
                       L 
                       ⁡ 
                       
                         ( 
                         2 
                         ) 
                       
                     
                   
                 
               
               
                 
                   ( 
                   4 
                   ) 
                 
               
             
           
         
       
     
     As recited above, the first wire grid structure  20  and the second wire grid structure  40  is used to reflect the projection light to a field of view of the viewer. An intersecting position of the reflected projection light is an intersection point of the projection screen  100 . A position of the intersection point will influence the brightness uniformity of the projection screen  100 . By an optical simulation, it can be determined that the projection brightness uniformity is almost irrelevant with a distance from the focus point to the projection screen  100 . However, when the position of the intersecting point changes along the direction perpendicular to the screen, a change of the nine-point uniformity can be shown in  FIG. 11  by the optical simulation. In the optical simulation, three angles of view are considered, which includes an angle of view sitting front and facing the true center of the screen, an angle of view having a constant viewing height and horizontal deviation 30° from the center position, and an angle of view standing at the true center of the screen. By comprehensive simulation for these angles of view, the brightness uniformity of the screen is above 70%, and the brightness uniformity is better. 
     In conclusion, in the present application, by gradually reducing the first angles between the first surface and the first contact surface along the direction from the first area to the second area, both of the projection light at the bottom of the projection screen and that at a position below the center of the projection screen can be reflected to a position close to the center of the projection screen. That is to say, the projection light at the bottom of the projection screen and the projection light at a position below the center of the projection screen can converge to the center of the projection screen. In this way, approximately identical light can be enter into viewer&#39;s eyes, increasing the visible angle of the projection screen and increasing a brightness uniformity of the projection screen. 
     The above embodiments are only preferable embodiments of the present application, and of course cannot limit the scope of the present application. A person skilled in the art can understand and realize all or part of the process of the above embodiments, and equivalent variations made according to claims of the present application still fall into the scope covered by the present application. 
     Unless otherwise expressly indicated herein, all numerical values indicating mechanical/thermal properties, compositional percentages, dimensions and/or tolerances, or other characteristics are to be understood as modified by the word “about” or “approximately” in describing the scope of the present disclosure. This modification is desired for various reasons including industrial practice, material, manufacturing, and assembly tolerances, and testing capability. 
     As used herein, the phrase at least one of A, B, and C should be construed to mean a logical (A OR B OR C), using a non-exclusive logical OR, and should not be construed to mean “at least one of A, at least one of B, and at least one of C.” 
     The description of the disclosure is merely exemplary in nature and, thus, variations that do not depart from the substance of the disclosure are intended to be within the scope of the disclosure. Such variations are not to be regarded as a departure from the spirit and scope of the disclosure.