Patent Publication Number: US-11656502-B2

Title: Vertical alignment liquid crystal display module comprising an image color switch film having an average transmittance of a visible light spectrum for short and long wavelengths of the visible light

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority benefit of U.S. provisional application Ser. No. 63/177,942, filed on Apr. 21, 2021, and Taiwan application serial no. 110145813, filed on Dec. 8, 2021. The entirety of each of the above-mentioned patent applications is hereby incorporated by reference herein and made a part of this specification. 
    
    
     BACKGROUND 
     Technology Field 
     The disclosure relates to a display module, and particularly to a vertical alignment liquid crystal display module. 
     Description of Related Art 
     When LCD displays are operating, although in wide viewing angle technologies, such as vertical alignment (VA) or in-plane switching (IPS), materials such as compensation films or retardation films are used to compensate for color shifts caused by large viewing angles, it cannot be perfectly compensated due to the different exit angles of the signals. The color at the large viewing angle has been partially corrected with the compensation films or the retardation films, but there are still different degrees of color signal errors. With twisted nematic (TN) and VA technology, there are the most serious color signal errors. 
     From the perspective of the red, green, and blue color stability at each viewing angle of a display, even if the VA display technology is added with a compensation film, it can still be found that there may be serious color shift when the viewing angle is greater than 45 degrees, that is, there may be the problem of greenish and whitening, especially when the image is in a skin color. As a result, many brand manufacturers are reluctant to apply the VA technology to their high-end products. 
     However, the VA technology still has the advantages of high contrast and strong color rendering at a center viewing angle. Therefore, how to improve the problem of the color shift of a VA liquid crystal display at a large viewing angle deserves research and development. 
     SUMMARY 
     The disclosure provides a vertical alignment liquid crystal display module, which can effectively improve the problem of color shift at a large viewing angle. 
     An embodiment of the disclosure provides a vertical alignment liquid crystal display module including a vertical alignment liquid crystal display panel and an image color switch film. The image color switch film is disposed on the vertical alignment liquid crystal display panel. The image color switch film has a following optical characteristic in various viewing angle directions having included angles of 60 degrees to 75 degrees with respect to a normal of the image color switch film: an average transmittance of a visible light transmission spectrum of the image color switch film at an end of short wavelength is less than an average transmittance of the visible light transmittance spectrum of the image color witch film at an end of long wavelength. 
     In the vertical alignment liquid crystal display module of the embodiments of the disclosure, at a large viewing angle, the configuration of the image color switch film allows the average transmittance of the visible light transmission spectrum at the end of short wavelength to be less than the average transmittance of the visible light transmission spectrum at the end of long wavelength, so when the viewing angle is large, the problem of greenish white images or blueish white images can be effectively improved, thereby improving the color accuracy of skin color images. That is, the vertical alignment liquid crystal display module of the embodiments of the disclosure can effectively improve the problem of color shift at a large viewing angle. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1 A  is a schematic cross-sectional view of a vertical alignment liquid crystal display module according to an embodiment of the disclosure. 
         FIG.  1 B  is a schematic front view of the pixels of the vertical alignment liquid crystal display panel in  FIG.  1 A . 
         FIG.  1 C  is a three-dimensional layered view of the vertical alignment liquid crystal display module of  FIG.  1 A . 
         FIG.  1 D  is a three-dimensional schematic diagram of parallel polarized light and vertical polarized light of the vertical alignment liquid crystal display module of  FIG.  1 C . 
         FIG.  2    illustrates the optical simulation transmittance spectrum of an image color switch film  300  when the viewing angle is 75 degrees according to two embodiments of the disclosure. 
         FIG.  3 A ,  FIG.  3 B , and  FIG.  3 C  each illustrate the component ratios of blue, green, and red light emitted from the vertical alignment liquid crystal display panel and the component ratios of the blue, green, and red light further penetrating the image color switch film. 
         FIG.  4    is a schematic cross-sectional view of a vertical alignment liquid crystal display module according to another embodiment of the disclosure. 
         FIG.  5    is a schematic cross-sectional view of a vertical alignment liquid crystal display module according to yet another embodiment of the disclosure. 
         FIG.  6 A  and  FIG.  6 B  illustrate the reflectance spectra and transmittance spectra of the image color switch film when the viewing angle is 60 degrees according to three embodiments of the disclosure. 
         FIG.  7    is a broken line diagram illustrating the component ratios of the red light, the green light, and the blue light in a variety of different viewing angles when the image color switch film is not added to the 4-domain vertical alignment liquid crystal display panel. 
         FIG.  8    illustrates the reflectance spectra of the image color switch film and the light-transmitting substrate in the vertical alignment liquid crystal display module of  FIG.  4    at various viewing angles. 
         FIG.  9    is a schematic cross-sectional view of a vertical alignment liquid crystal display module according to still another embodiment of the disclosure. 
         FIG.  10    is a schematic cross-sectional view of a vertical alignment liquid crystal display module according to another embodiment of the disclosure. 
         FIG.  11 A  is a schematic cross-sectional view of a vertical alignment liquid crystal display module according to yet another embodiment of the disclosure. 
         FIG.  11 B  is a three-dimensional layered view of the vertical alignment liquid crystal display module of  FIG.  11 A . 
         FIG.  12    is a three-dimensional layered view of a vertical alignment liquid crystal display module according to still another embodiment of the disclosure. 
         FIG.  13    is a schematic cross-sectional view of a vertical alignment liquid crystal display module according to another embodiment of the disclosure. 
         FIG.  14    is a schematic cross-sectional view of a vertical alignment liquid crystal display module according to yet another embodiment of the disclosure. 
         FIG.  15    illustrates actual spectra of the vertical alignment liquid crystal display module of a control group, the embodiment of  FIG.  1 A , and the embodiment of  FIG.  5    when the red sub-pixels, the green sub-pixels, and the blue sub-pixels are all lit at a viewing angle of 60 degrees. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
       FIG.  1 A  is a schematic cross-sectional view of a vertical alignment liquid crystal display module according to an embodiment of the disclosure.  FIG.  1 B  is a schematic front view of the pixels of the vertical alignment liquid crystal display panel in  FIG.  1 A .  FIG.  1 C  is a three-dimensional layered view of the vertical alignment liquid crystal display module of  FIG.  1 A . Referring to  FIG.  1 A ,  FIG.  1 B , and  FIG.  1 C , a vertical alignment liquid crystal display module  100  of the embodiment includes a vertical alignment liquid crystal display panel (VA-LCD panel)  200  and an image color switch film  300 . In the embodiment, for example, the VA-LCD panel  200  is a multi-domain vertical alignment liquid crystal display panel (MVA-LCD panel). In  FIG.  1 B , an 8-domain vertical alignment liquid crystal display panel is taken as an example. Each sub-pixel  210  has eight alignment domains  212  of the liquid crystal molecules, and for example, the tilting directions of the liquid crystal molecules in the eight alignment domains  212  are four directions. For example, the four directions are approximately 45 degrees between the pixel alignment direction (i.e., the horizontal direction and the vertical direction). Moreover, adjacent one red sub-pixel  210 R, one green sub-pixel  210 G, and one blue sub-pixel  210 B can form one pixel. In another embodiment, the multi-domain vertical alignment liquid crystal display panel may also be a 4-domain vertical alignment liquid crystal display panel, and each sub-pixel  210  has four alignment domains  212  of the liquid crystal molecules. For example, the tilting directions of the liquid crystal molecules in the four alignment domains  212  are 4 directions. 
     The image color switch film  300  is disposed on the VA-LCD panel  200 .  FIG.  2    illustrates the optical simulation transmittance spectrum of the image color switch film  300  when the viewing angle is 75 degrees according to two embodiments of the disclosure. Referring to  FIG.  1 A ,  FIG.  1 B , and  FIG.  2   , the image color switch film  300  can adjust the original hue and frequency spectrum at various viewing angles and has the following optical characteristic for the VA-LCD panel  200  at a large viewing angle. Specifically, the image color switch film  300  has the following optical characteristic in various viewing angle directions having included angles of 60 degrees to 75 degrees with respect to the normal of the image color switch film  300 ; that is to say, the included angle is between the viewing angle direction and the normal of the image color switch film  300 . The average transmittance of the visible light transmission spectrum of the image color switch film  300  at an end E 1  of short wavelength is less than the average transmittance of the visible light transmission spectrum at an end E 2  of long wavelength. In the embodiment, the average transmittance of the visible light transmittance spectrum of the image color switch film  300  at the end E 1  of short wavelength refers to the average transmittance corresponding to the wavelengths ranging from 300 nm to 495 nm, and the average transmittance of the visible light transmittance spectrum of the image color switch film  300  at the end E 2  of long wavelength refers to the average transmittance corresponding to the wavelengths ranging from 570 nm to 750 nm. In  FIG.  2   , the dashed transmittance spectrum curve and the solid transmittance spectrum curve belong to two different embodiments. 
     In the vertical alignment liquid crystal display module  100  of the embodiment, at a large viewing angle, the configuration of the image color switch film  300  allows the average transmittance of the visible light transmission spectrum at the end E 1  of short wavelength to be less than the average transmittance of the visible light transmission spectrum at the end E 2  of long wavelength, that is allows more red light and yellow light to pass through and to refrain some blue light and green light from passing through, so when the viewing angle is large, the problem of greenish white images or blueish white images can be effectively improved, thereby improving the color accuracy of skin color images. That is, the vertical alignment liquid crystal display module  100  of the embodiment can effectively improve the problem of color shift at a large viewing angle. Moreover, the vertical alignment liquid crystal display technology still has the advantages of high contrast and strong color rendering at a center viewing angle. The embodiment can improve the color shift at a large viewing angle and retain the high contrast characteristics of the vertical alignment liquid crystal display technology, which can surpass the IPS technology and become the display technology with the superior effect of color rendering. 
     Specifically, please refer to  FIG.  3 A ,  FIG.  3 B , and  FIG.  3 C .  FIG.  3 A ,  FIG.  3 B , and  FIG.  3 C  each illustrate the component ratios of blue, green, and red light emitted from the vertical alignment liquid crystal display panel and the component ratios of the blue, green, and red light further penetrating the image color switch film. The fold line corresponding to the “original VA” in  FIG.  3 A  refers to the data of the light emitted from the VA-LCD panel  200 , and the fold line corresponding to the “with the added image color switch film” refers to the data of the light emitted from the VA-LCD panel  200  and then further penetrating the image color switch film  300 . According to  FIG.  3 A  to  FIG.  3 C , the image color switch film  300  can greatly increase the component ratio of the red light in the image light, slightly increase the component ratio of the green light, and effectively suppress the component ratio of the blue light, so the problem of the greenish white or blueish white images when the viewing angle is large can be effectively improved, and then the color accuracy of the skin color images can be improved. In the embodiment, the component ratios of blue light, green light, and red light refer to the ratio of the areas of blue light, green light, and red light under the spectrum curve. 
     In one embodiment, the image color switch film  300  has the optical characteristic in various viewing angle directions having included angles of 45 degrees to 75 degrees with respect to the normal of the image color switch film  300 . In one embodiment, the image color switch film  300  has the optical characteristic in various viewing angle directions having included angles of 30 degrees to 75 degrees with respect to the normal of the image color switch film  300 . In one embodiment, the image color switch film  300  has the optical characteristic in various viewing angle directions having included angles of 60 degrees to 90 degrees with respect to the normal of the image color switch film  300 . 
     In one embodiment, the optical characteristic further include that the transmittance of the visible light transmission spectrum increases first and then decreases from the end E 1  of short wavelength to the end E 2  of long wavelength. However, in other embodiments, the optical characteristic further include that the transmittance of the visible light transmission spectrum increases from the end E 1  of short wavelength to the end E 2  of long wavelength. 
     Referring to  FIG.  1 A  again, the image color switch film  300  includes at least one layer of interference film, and by the principle of film interference, light (i.e., red light, green light, and blue light) with different wavelengths is reflected and passes through the image color switch film  300 . In the embodiment, the at least one interference film includes a first light-transmitting film  310  and a second light-transmitting film  320 . The second light-transmitting film  320  is stacked with the first light-transmitting film  310 , and the refractive index of the first light-transmitting film  310  is less than the refractive index of the second light-transmitting film  320 . In one embodiment, the refractive index of the first light-transmitting film  310  is 1.6 or less, and the refractive index of the second light-transmitting film  320  is 1.8 to 2.4. In the embodiment, the vertical alignment liquid crystal display module  100  further includes a polarizing plate  110  disposed between the image color switch film  300  and the VA-LCD panel  200 . Moreover, in the embodiment, the second light-transmitting film  320  is disposed between the first light-transmitting film  310  and the polarizing plate  110 , and the refractive index of the first light-transmitting film  310  is 1.66 or less, for example. Moreover, the vertical alignment liquid crystal display module  100  may further include a polarizing plate  120 , and the VA-LCD panel  200  is disposed between the polarizing plate  110  and the polarizing plate  120 . 
     In the embodiment, for example, the material of the first light-transmitting film  310  is silicon dioxide (SiO2), magnesium fluoride (MgF2), or a coating material with a low refractive index. The material of the second light-transmitting film  320  may be a transparent ceramic material with a high refractive index, such as titanium dioxide, niobium pentoxide (Nb2O5), or indium tin oxide (ITO). 
     In the embodiment, the polarizing plate  110  includes a first transparent substrate  112 , a second transparent substrate  114 , a polarizing layer  116 , and a phase difference compensation film  118 . The first transparent substrate  112  is disposed between the image color switch film  300  and the VA-LCD panel  200 , and the second transparent substrate  114  is disposed between the first transparent substrate  112  and the VA-LCD panel  200 . The polarizing layer  116  is disposed between the first transparent substrate  112  and the second transparent substrate  114 , and the phase difference compensation film  118  is disposed between the first transparent substrate  112  and the second transparent substrate  114 . In the embodiment, the phase difference compensation film  118  is disposed between the polarizing layer  116  and the second transparent substrate  114 . In another embodiment, the phase difference compensation film  118  and the second transparent substrate  114  may be integrated, that is, the second transparent substrate  114  is a phase difference compensation film without an additional phase difference compensation film  118  disposed on the polarizing plate  110 . Specifically, the second transparent substrate  114  can turn into a phase difference compensation film through a stretching process. Alternatively, a liquid crystal layer (i.e., a phase difference compensation film  118 ) may be coated on the second transparent substrate  114 . Alternatively, a liquid crystal layer may be coated on the stretched second transparent substrate  114 , that is, the second transparent substrate  114  and the phase difference compensation film  118  both have the function of phase difference compensation. The phase difference compensation film  118  and the stretched second transparent substrate  114  may have birefringence or multi-refraction, that is, have different refractive indexes in different directions. Accordingly, the phase difference of the image light at the large viewing angle emitted from the VA-LCD panel  200  can be compensated, so that the image quality for the large viewing angle can be improved. The phase difference compensation film  118  can adopt various techniques well known to those with ordinary knowledge in the art, which is not repeated herein. 
     Moreover, the polarizing plate  120  may be a general polarizing plate, which may include two transparent substrates and a polarizing layer disposed between the two transparent substrates. A backlight module  400  commonly used in liquid crystal displays may be disposed under the polarizing plate  120 , which is well known to those with ordinary knowledge in the art and is not repeated herein. Moreover, the image color switch film  300  is not limited to only include the first light-transmitting film  310  and the second light-transmitting film  320 . In another embodiment, the image color switch film  300  may include three or more light-transmitting films with alternately stacked high and low refractive indexes. The disclosure is not limited thereto. Alternatively, in another embodiment, the image color switch film  300  may be a single light-transmitting film with a refractive index ranging from 1.35 to 2.5, and in one embodiment, it ranges from 1.5 to 2.5, for example. 
     In the embodiment, for example, the material of the first transparent substrate  112  and the second transparent substrate  114  is polyester (PET), tri-acetyl cellulose (TAC), polymethyl methacrylate (PMMA), or other plastic substrates, and the material of the polarizing layer  116  is polyvinyl alcohol (PVA), for example, but the disclosure is not limited thereto. 
       FIG.  1 D  is a three-dimensional schematic diagram of parallel polarized light and vertical polarized light of the vertical alignment liquid crystal display module of  FIG.  1 C . Referring to  FIG.  1 C  and  FIG.  1 D , in the embodiment, a transmission axis X 1  of the polarizing plate  110  is parallel to the short side direction of the VA-LCD panel  200 , a transmission axis X 2  of the polarizing plate  120  is parallel to the long side direction of the VA-LCD panel  200 , for example, and the transmission axis X 1  and the transmission axis X 2  are perpendicular to each other (as shown in  FIG.  1 C ). If the transmission axis X 1  of the polarizing plate  110  is perpendicular to the long side direction of the VA-LCD panel  200  (the long side direction is parallel to the desktop direction, for example), at the large viewing angle in the horizontal direction of the vertical alignment liquid crystal display module  100 , vertically polarized light can be observed. If viewed from a plane PLN formed by incident light  50  and reflected light  52  from the backlight module  400 , only the polarized light (i.e., the vertically polarized light) corresponding to the transmission axis X 1  of polarizing plate  110  and with a polarization direction PS perpendicular to the plane PLN can pass through. Therefore, in the interference design, the parameters (e.g., film thickness, refractive index, and the like) of the image color switch film  300  can be designed according to vertical polarized light, that is, tailored specifically for vertical polarized light to adjust its spectrum in the manner, so that it has the optical characteristic. Part of the incident light  50  passes through the polarizing plate  120 , the VA-LCD panel  200 , the polarizing plate  110 , and the image color switch film  300  and becomes transmitted light  54 , and part of the incident light  50  is reflected into the reflected light  52  by the image color switch film  300 . However, in another embodiment, the image color switch film  300  is located on the polarizing plate  120 . If its transmission axis X 2  is parallel to the short side direction of the VA-LCD panel  200  (this short side direction is perpendicular to the desktop), after the incident light  50  is incident to the VA-LCD panel  200  from the backlight module  400 , the reflected light  52  is generated after the incident light  50  hits the image color switch film  300 . The incident light  50  and the reflected light  52  form the plane PLN, most of the polarized light with the polarization direction PS perpendicular to the plane PLN can pass through the transmission axis X 2 , and the image color switch film  300  is also designed with the vertical polarization direction PS. Conversely, if the direction of the transmission axis X 2  is parallel to the long side direction of the VA-LCD panel  200  and the image color switch film  300  is located on the polarizing plate  120 , similarly, in the image adjustment of the horizontal large viewing angle, the image color switch film  300  is designed with the parallel polarization direction PP (where the parallel polarization direction PP is parallel to the plane PLN, and the polarization direction PP is parallel to the plane PLN of the polarized light called parallel polarized light). Generally speaking, when the parameters of the image color switch film  300  are designed based on vertical polarized light, it facilitates the design, and a small quantity of layers can be used to achieve the good optical characteristic described. 
       FIG.  4    is a schematic cross-sectional view of a vertical alignment liquid crystal display module according to another embodiment of the disclosure. A vertical alignment liquid crystal display module  100   a  of the embodiment is similar to the vertical alignment liquid crystal display module  100  of  FIG.  1 A . The difference between the two is that in the vertical alignment liquid crystal display module  100  of  FIG.  1 A , the first light-transmitting film  310  and the second light-transmitting film  320  are formed on the polarizing plate  110 . However, in the vertical alignment liquid crystal display module  100   a  of the embodiment, the first light-transmitting film  310  and the second light-transmitting film  320  of the image color switch film  300  are first formed on the light-transmitting substrate  330 , and then the light-transmitting substrate  330  is further attached to the polarizing plate  110  through an adhesive  340 . 
       FIG.  5    is a schematic cross-sectional view of a vertical alignment liquid crystal display module according to yet another embodiment of the disclosure. Referring to  FIG.  5   , the vertical alignment liquid crystal display module  100   b  of the embodiment is similar to the vertical alignment liquid crystal display module  100  of  FIG.  1 A , and the differences between the two are as follows. In the vertical alignment liquid crystal display module  100  of  FIG.  1 A , the image color switch film  300  is disposed outside the polarizing plate  110 . However, in the vertical alignment liquid crystal display module  100   b  of the embodiment, the image color switch film  300  may be integrated into the inside of the polarizing plate  110 . Specifically, in the embodiment, the image color switch film  300  is disposed between the first transparent substrate  112  and the VA-LCD panel  200 , the second transparent substrate  114  is disposed between the image color switch film  300  and the VA-LCD panel  200 , the polarizing layer  116  is disposed between the image color switch film  300  and the second transparent substrate  114 , and the phase difference compensation film  118  is disposed between the polarizing layer  116  and the second transparent substrate  114 . 
     In the embodiment, the order of the first light-transmitting film  310  and the second light-transmitting film  320  of the image color switch film  300  can be reversed, and the first light-transmitting film  310  may be under the second light-transmitting film  320 , or the second light-transmitting film  320  may be under the first light-transmitting film  310 . 
     The refractive index of the first light-transmitting film  310  is 1.6 or less, and the refractive index of the second light-transmitting film  320  is 1.8 to 2.5. In the embodiment, the refractive index of the first transparent substrate  112  is 1.7 or less. 
     In the embodiment, the vertical alignment liquid crystal display module  100   b  further includes a surface treatment layer  119 , and the first transparent substrate  112  is disposed between the surface treatment layer  119  and the image color switch film  300 . For example, the refractive index of the surface treatment layer  119  is less than 1.5. For example, the surface treatment layer  119  is an anti-glare layer, an anti-reflection layer, or a hard-coating layer. 
     Moreover, the same as those in the embodiment of  FIG.  1 A , the phase difference compensation film  118  and the second transparent substrate  114  may be integrated, that is, the second transparent substrate  114  is a phase difference compensation film, without an additional phase difference compensation film  118  disposed on the polarizing plate  110 . 
     In the embodiment, for example, the transmission axis X 1  of the polarizing layer  116  is parallel to the short side direction of the VA-LCD panel  200  (i.e., the direction into the paper surface of  FIG.  5   ), so when the eyes of the user look at the vertical alignment liquid crystal display module  100   b  at a large viewing angle in the horizontal direction, vertically polarized light may be seen. If the incident light  50  and the reflected light  52  at a large viewing angle are regarded as the plane PLN (referring to  FIG.  1 D ), the transmission axis X 1  of the polarizing plate  110  of the vertical alignment liquid crystal display module  100   b  is controlled to be parallel to the short side direction of the vertical alignment liquid crystal display module  100   b , and in the incident light  50 , only most of the polarized light with the polarization direction PS parallel to the short side direction can pass through the VA-LCD panel  200 , so the image color switch film  300  can be designed according to the direction of the transmission axis X 1  of the polarizing plate  110  to achieve the optical characteristic. However, in other embodiments, the transmission axis X 1  of the polarizing layer  116  may also be parallel to the long side direction of the VA-LCD panel  200 . 
       FIG.  6 A  and  FIG.  6 B  illustrate the reflectance spectra and transmittance spectra of the image color switch film when the viewing angle is 60 degrees according to three embodiments of the disclosure. In  FIG.  6 A  and  FIG.  6 B , the curve corresponding to “H=60-70 nm/L=130-140 nm” means that the thickness of the second light-transmitting film  320  of the image color switch film ranges from 60 nm to 70 nm, the thickness of the first light-transmitting film  310  is the spectrum data of 130 nm to 140 nm, and the meaning of the other curves can be analogically reasoned. Moreover, for example, in  FIG.  6 A  and  FIG.  6 B , the refractive index of the second light-transmitting film  320  is 1.8 to 2.4, and the refractive index of the first light-transmitting film  310  is 1.6 to 1.3, for example. The design goal of the image color switch film is to look at the transmittance spectrum of general white light. In the design of the image color switch film, the average transmittance of light with a wavelength of 600 to 800 nm may be greater than the average transmittance of light with a wavelength of 400 to 600 nm to form a tendency of low transmittance for short wavelengths and high transmittance for long wavelengths. 
       FIG.  7    is a broken line diagram illustrating the component ratios of the red light, the green light, and the blue light in a variety of different viewing angles when the image color switch film is not added to the 4-domain vertical alignment liquid crystal display panel. In the embodiment, the component ratios of the blue light, the green light, and the red light refer to the ratios of the areas of the blue light, the green light, and the red light under the spectrum curve.  FIG.  8    illustrates the reflectance spectra of the image color switch film  300  and the light-transmitting substrate  330  in the vertical alignment liquid crystal display module of  FIG.  4    at various viewing angles. Referring to  FIG.  4   ,  FIG.  7   , and  FIG.  8   , the image color switch film of the embodiment of the disclosure utilizes constructive interference reflection spectrum to design “the relative peak of the reflectance moves towards the upper left of  FIG.  8    as the viewing angle increases” as the main design focus. When observing the spectrum distribution of each viewing angle of the vertical alignment liquid crystal display panel, it is found that the ratio of red light in the 4-domain vertical alignment liquid crystal display panel rapidly decreases along with the increase of viewing angle, while the ratio of the green light and the ratio of the blue light increase, and similar problems happen to the 8-domain vertical alignment liquid crystal display panel. 
     In the image color switch film, the reflection effect of the constructive interference of the thin film (single layer or multi-layer, each film thickness ranging from about 10 to 750 nm) is used, the blue light or part of the green light is reflected at a large viewing angle and enters the inside of the liquid crystal display panel from the polarizing plate, so that the spectrum observed by the observer and the relative energy of the red light is higher than that of the original liquid crystal display panel with no image color switch film. Therefore, the ratio of the red light at the large viewing angle is adjusted to be close to the center viewing angle to confirm that the image quality of the large viewing angle is similar to the image quality of the center viewing angle. 
     In terms of design, for a preferred embodiment of the reflectance spectrum design, it is preferred that the relative peak area can move to the upper left (the blue light direction) as the viewing angle increases. When the peak of the blue band of the reflectance spectrum increases with the viewing angle, the reflectance spectrum can be designed to move to the upper left. The purpose is when the observer moves from the center viewing angle to the large viewing angle, since the blue light and green light reduction ratio is gradually increased, the image color switch film is allowed to be designed to also gradually improve the “ability to reduce the blue light” (or ability to increase the energy ratio of the red light and the yellow light), to be used on a vertical alignment liquid crystal display panel, and to reversely adjust the energy ratio of the red light, the green light, and the blue light at the large viewing angle. 
     To ensure that the interference effect can occur, if a single-layer film is taken as an example, the thickness of the formed film is d, the refractive index is n, and the viewing angle is θ, then n·d·cos θ=¼·m·λ, where m is an odd number, λ is the wavelength of light, the specific definition of θ is the angle between the line from the position of the eyes of the user to the center of the light-emitting surface of the vertical alignment liquid crystal display module and the normal of the vertical alignment liquid crystal display module. 
     In the embodiment of  FIG.  8   , the refractive index of the second light-transmitting film  320  is 2 to 2.4, for example, and the refractive index of the first light-transmitting film  310  is 1.3 to 1.5, for example. 
       FIG.  9    is a schematic cross-sectional view of a vertical alignment liquid crystal display module according to still another embodiment of the disclosure. Referring to  FIG.  9   , a vertical alignment liquid crystal display module  100   c  of the embodiment is similar to the vertical alignment liquid crystal display module  100   b  of  FIG.  5   , and the difference between the two is as follows. In the embodiment, the image color switch film  300  is disposed between the polarizing layer  116  and the second transparent substrate  114 . 
       FIG.  10    is a schematic cross-sectional view of a vertical alignment liquid crystal display module according to another embodiment of the disclosure. Referring to  FIG.  10   , a vertical alignment liquid crystal display module  100   d  of the embodiment is similar to the vertical alignment liquid crystal display module  100   b  of  FIG.  5   , and the differences between the two are as follows. In the embodiment, the image color switch film  300  is disposed between the second transparent substrate  114  and the VA-LCD panel  200 , that is, between the polarizing plate  110  and the VA-LCD panel  200 , and the image color switch film  300  is disposed above the VA-LCD panel  200 . 
       FIG.  11 A  is a schematic cross-sectional view of a vertical alignment liquid crystal display module according to yet another embodiment of the disclosure, and  FIG.  11 B  is a three-dimensional layered view of the vertical alignment liquid crystal display module of  FIG.  11 A . Referring to  FIG.  11 A  and  FIG.  11 B , a vertical alignment liquid crystal display module  100   e  of the embodiment is similar to the vertical alignment liquid crystal display module  100  of  FIG.  1 A  and  FIG.  1 C , and the differences between the two are as follows. In the vertical alignment liquid crystal display module  100   e  of the embodiment, the image color switch film  300  is disposed under the VA-LCD panel  200 , and the polarizing plate  120  is disposed between the image color switch film  300  and the VA-LCD panel  200 , but in other embodiments, the image color switch film  300  may also be disposed between the polarizing plate  120  and the VA-LCD panel  200 . 
     In the embodiment, the polarizing plate  120  includes a third transparent substrate  122 , a fourth transparent substrate  124 , and a polarizing layer  126 . The third transparent substrate  122  is disposed under the VA-LCD panel  200 , and the third transparent substrate  122  is disposed between the VA-LCD panel  200  and the fourth transparent substrate  124 . The polarizing layer  126  is disposed between the third transparent substrate  122  and the fourth transparent substrate  124 . The optional materials for the third transparent substrate  122  and the fourth transparent substrate  124  can be selected from the materials for the first transparent substrate  112  and the second transparent substrate  114 , and the optional materials for the polarizing layer  126  can be selected from the materials for the polarizing layer  116 . 
     In the embodiment, the transmission axis X 2  of the polarizing plate  120  (i.e., the transmission axis of the polarizing layer  126 ) is parallel to the short side direction of the VA-LCD panel  200 , so for light at a large viewing angle in the horizontal direction, the polarizing plate  120  allows the vertical polarized light from the image color switch film  300  to pass through and blocks the parallel polarized light from the image color switch film  300 . Therefore, the parameters of the image color switch film  300  can be set according to the vertically polarized light to achieve the optical characteristic. When the incident light  50  enters the polarizing plate  120  from the backlight module  400 , if the incident light  50  and the reflected light  52  are regarded as the plane PLN (as shown in  FIG.  1 D ), in the incident light  50 , most of the polarized light with the polarization direction PS perpendicular to the plane PLN can pass through the polarizing plate  120  while the polarized light with the polarization direction PP parallel to the plane PLN is absorbed by the polarizing plate  120 . Therefore, the image color switch film  300  can be designed according to the vertical polarized light relative to the plane PLN, and a small quantity of film layers can be used to achieve the optical characteristic. Moreover, by disposing the image color switch film  300  under the VA-LCD panel  200 , the visual taste of the vertical alignment liquid crystal display module  100   e  can be enhanced. This is because when the vertical alignment liquid crystal display module  100   e  does not emit light, the image color switch film  300  disposed on the lower layer may be less likely to reflect the ambient light from the outside, and the screen that the user sees may appear fairly dark black, thereby improving the visual taste. 
       FIG.  12    is a three-dimensional layered view of a vertical alignment liquid crystal display module according to still another embodiment of the disclosure. Referring to  FIG.  12   , a vertical alignment liquid crystal display module  100   f  of the embodiment is similar to the vertical alignment liquid crystal display module  100   e  of  FIG.  11 A  and  FIG.  11 B , and the differences between the two are as follows. In the vertical alignment liquid crystal display module  100   e  of  FIG.  11 A  and  FIG.  11 B , the transmission axis X 1  of the polarizing plate  110  is parallel to the long side direction of the VA-LCD panel  200 , and the transmission axis X 2  of the polarizing plate  120  is parallel to the short side direction of the VA-LCD panel  200 . What differs is that in the vertical alignment liquid crystal display module  100   f  of the embodiment, the transmission axis X 1  of the polarizing plate  110  is parallel to the short side direction of the VA-LCD panel  200 , and the transmission axis X 2  of the polarizing plate  120  is parallel to the long side direction of the VA-LCD panel  200 . Accordingly, at this time, the direction of the transmission axis X 2  of the polarizing plate  120  is parallel to the long side direction of the VA-LCD panel  200  (the long side direction is the horizontal direction). If the incident light  50  and the reflected light  52  are regarded as the plane PLN (as shown in  FIG.  1 D ), in the incident light  50 , most of the polarized light with the polarization direction PP parallel to the plane PLN can pass through the polarizing plate  120 , while the polarized light with the polarization direction PS perpendicular to the plane PLN is absorbed, so the image color switch film  300  can be designed according to the parallel polarized light relative to the plane PLN to achieve the optical characteristic. 
       FIG.  13    is a schematic cross-sectional view of a vertical alignment liquid crystal display module according to another embodiment of the disclosure. Referring to  FIG.  13   , the vertical alignment liquid crystal display module  100   g  of the embodiment is similar to the vertical alignment liquid crystal display module  100   e  of  FIG.  11 A , and the difference between the two is as follows. In the vertical alignment liquid crystal display module  100   g  of the embodiment, the image color switch film  300  is disposed between the third transparent substrate  122  and the fourth transparent substrate  124 . In  FIG.  13   , the image color switch film  300  is disposed on the polarizing layer  126  and the fourth transparent substrate  124  as an exemplary illustration. However, in other embodiments, the image color switch film  300  may also be disposed between the third transparent substrate  122  and the polarizing layer  126 . In the embodiment, the transmission axis X 2  of the polarizing layer  126  is parallel to the short side direction of the VA-LCD panel  200  (i.e., the direction into the paper surface of  FIG.  13   ), and the transmission axis X 1  of the polarizing plate  110  is parallel to the long side direction of the VA-LCD panel  200  (i.e., the direction parallel to the paper surface of  FIG.  13   ). However, in other embodiments, the transmission axis X 2  of the polarizing layer  126  may be parallel to the long side direction of the VA-LCD panel  200 , and the transmission axis X 1  of the polarizing plate  110  is parallel to the short side direction of the VA-LCD panel  200 . Moreover, in the embodiment, the third transparent substrate  122  may also be a phase difference compensation film. 
       FIG.  14    is a schematic cross-sectional view of a vertical alignment liquid crystal display module according to yet another embodiment of the disclosure. Referring to  FIG.  14   , a vertical alignment liquid crystal display module  100   h  of the embodiment is similar to the vertical alignment liquid crystal display module  100   g  of  FIG.  13   , and the difference between the two is as follows. In the vertical alignment liquid crystal display module  100   h  of the embodiment, a polarizing plate  120   h  further includes a phase difference compensation film  128  disposed between the third transparent substrate  122  and the polarizing layer  126 . The function and the material of the phase difference compensation film  128  are the same as the function and the material of the phase difference compensation film  118 , which may not be repeated herein. 
       FIG.  15    illustrates actual spectra of the vertical alignment liquid crystal display module of a control group, the embodiment of  FIG.  1 A , and the embodiment of  FIG.  5    when the red sub-pixels, the green sub-pixels, and the blue sub-pixels are all lit at a viewing angle of 60 degrees. In  FIG.  15   , the curve of the control group represents the vertical alignment liquid crystal display module without the image color switch film of the embodiment of the disclosure. According to  FIG.  15   , it is obvious that the spectrum intensity of the red light (the long wavelength part) of the vertical alignment liquid crystal display module  100  in the embodiment of  FIG.  1 A  and the spectrum intensity of the red light of the vertical alignment liquid crystal display module  100   b  in the embodiment of  FIG.  5    are significantly greater than the spectrum intensity of the red light of the control group, and this means that when the viewing angle is 60 degrees, the energy ratios of the red light and the yellow light of skin color are both increased (where the yellow light band refers to the wavelength ranging from about 570 nm to 590 nm), which effectively improves the color quality of images at large viewing angles. 
     In summary, in the vertical alignment liquid crystal display module of the embodiments of the disclosure, at a large viewing angle, the configuration of the image color switch film allows the average transmittance of the visible light transmission spectrum at the end of short wavelength to be less than the average transmittance of the visible light transmission spectrum at the end of long wavelength, that is allows more red light and yellow light to pass through and to refrain blue light and green light from passing through, so when the viewing angle is large, the problem of greenish white images or blueish white images can be effectively improved, thereby improving the color accuracy of skin color images. That is, the vertical alignment liquid crystal display module of the embodiments of the disclosure can effectively improve the problem of color shift at a large viewing angle. Moreover, the vertical alignment liquid crystal display technology still has the advantages of high contrast and strong color rendering at a center viewing angle. The embodiments of the disclosure can improve the color shift at a large viewing angle and retain the high contrast characteristics of the vertical alignment liquid crystal display technology, which can surpass the IPS technology and become the display technology with the superior effect of color rendering.