WO2014029140A1 - 光学补偿结构及显示装置 - Google Patents

光学补偿结构及显示装置 Download PDF

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Publication number
WO2014029140A1
WO2014029140A1 PCT/CN2012/081096 CN2012081096W WO2014029140A1 WO 2014029140 A1 WO2014029140 A1 WO 2014029140A1 CN 2012081096 W CN2012081096 W CN 2012081096W WO 2014029140 A1 WO2014029140 A1 WO 2014029140A1
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front side
film
compensation structure
liquid crystal
back side
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French (fr)
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康志聪
海博
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TCL China Star Optoelectronics Technology Co Ltd
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Shenzhen China Star Optoelectronics Technology Co Ltd
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Priority to US13/702,583 priority Critical patent/US9011993B2/en
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    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
    • G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
    • G02F1/1333—Constructional arrangements; Manufacturing methods
    • G02F1/1335—Structural association of cells with optical devices, e.g. polarisers or reflectors
    • G02F1/13363—Birefringent elements, e.g. for optical compensation
    • G02F1/133634—Birefringent elements, e.g. for optical compensation the refractive index Nz perpendicular to the element surface being different from in-plane refractive indices Nx and Ny, e.g. biaxial or with normal optical axis
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B5/00—Optical elements other than lenses
    • G02B5/30—Polarising elements
    • G02B5/3025—Polarisers, i.e. arrangements capable of producing a definite output polarisation state from an unpolarised input state
    • G02B5/3033—Polarisers, i.e. arrangements capable of producing a definite output polarisation state from an unpolarised input state in the form of a thin sheet or foil, e.g. Polaroid
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
    • G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
    • G02F1/1333—Constructional arrangements; Manufacturing methods
    • G02F1/1335—Structural association of cells with optical devices, e.g. polarisers or reflectors
    • G02F1/133528—Polarisers

Definitions

  • the present invention relates to liquid crystal displays, and more particularly to an optical compensation structure and display device for a VA display mode.
  • the compensation by the wide viewing angle compensation film can effectively reduce the light leakage of the dark state picture, and can greatly improve the contrast of the picture within a certain viewing angle.
  • the compensation principle of the compensation film (or called the retardation film) is generally to correct the phase difference generated by the liquid crystal at different viewing angles, so that the birefringence properties of the liquid crystal molecules are compensated for symmetry. Different compensation modes are used for different liquid crystal display modes.
  • the compensation film used for large-size LCD TVs is mostly for VA display mode.
  • Konica's N-TAC was used in the early days, and later developed into OPOTES's Zeonor, Fujitsu.
  • the display device includes a VA (Vertical).
  • the Alignment, vertically aligning) the liquid crystal cell 300 and the optical compensation structure further include a front side polarizing plate 100 and a back side polarizing plate 200 disposed on both sides of the VA liquid crystal cell 300.
  • the front side polarizing plate setting 100 includes a front side polarizing unit 110 and a front side polarizing unit 110 on a side of a light emitting direction of the VA liquid crystal cell 300 (herein, a light direction is defined as a direction in which the backlight 400 is directed to the observer 500).
  • the first front side TAC film 120 is interposed with the VA liquid crystal cell 300.
  • the back side polarizing plate 200 includes a back side polarizing unit 220 and a back side biaxial film 210 disposed between the back side polarizing unit 220 and the VA liquid crystal cell 300, the back side biaxial film 210 having both a retardation film and protection The role of the membrane.
  • the viewing angle of a liquid crystal display device (such as a liquid crystal TV) (view Angle) is called the range of angle of view, including the horizontal view angle and the vertical view angle.
  • the horizontal view angle is based on the vertical normal of the liquid crystal cell, and is at a certain angle perpendicular to the left or right of the normal. The display image can still be seen normally, and this angle range is the horizontal viewing angle of the liquid crystal display device.
  • the horizontal normal of the liquid crystal cell is taken as the standard, the viewing angle of the upper and lower sides is called the vertical viewing angle.
  • the horizontal normal 300a of the VA liquid crystal cell is used as a reference to calibrate the direction.
  • the absorption axis 110a of the front side polarization unit 110 is parallel to the horizontal normal 300a
  • the slow axis 120a of the first front side TAC film 120 is perpendicular to the horizontal normal 300a
  • the back front side polarization unit 220 is The absorption axis 220a is perpendicular to the horizontal normal 300a
  • the slow axis 210a of the biaxial film 210 is perpendicular to the horizontal normal 300a.
  • the optical compensation structure described above includes a biaxial film (biaxial film 210) and is therefore also commonly referred to as a single layer biaxial film compensation structure.
  • the currently common solution is to replace the single-layer biaxial film compensation structure described above with a double-layer biaxial film compensation structure.
  • the original first front side TAC film 120 is replaced with a biaxial film, so that the front side polarizing plate 100 and the back side polarizing plate 200 are both biaxial.
  • the polarizing plate of the retardation film is replaced with a biaxial film, so that the front side polarizing plate 100 and the back side polarizing plate 200 are both biaxial.
  • the dark angle of these dark states is between the horizontal and vertical angles of view. Generally, the contrast and sharpness of the horizontal viewing angle have the greatest influence on the viewing effect, while the large viewing angle (close to the vertical viewing angle) has less influence on the viewer because it is not easily seen. It can be seen that the double-layer biaxial film compensation structure can improve the viewing effect. However, although the double-layer biaxial film compensation structure improves the display effect, the use of a double-layer biaxial film will increase the cost of the optical compensation structure, so that the display device thus prepared is at a disadvantage in the market competition.
  • the technical problem to be solved by the present invention is to provide an optical compensation structure and a display device in view of the defects in the prior art that the double-layer biaxial film compensation structure is used to solve the horizontal view dark state light leakage and the cost is increased.
  • an optical compensation structure comprising a front side polarizing plate and a back side polarizing plate respectively disposed on both sides of a VA liquid crystal cell;
  • the front side polarizing plate is disposed on a side of the light emitting direction of the VA liquid crystal cell, and includes a front side polarizing unit and a first front side TAC film disposed between the front side polarizing unit and the VA liquid crystal unit;
  • the absorption axis of the front side polarization unit is perpendicular to the horizontal normal of the VA liquid crystal cell;
  • the back side polarizing plate includes a back side polarizing unit and a biaxial film disposed between the back side polarizing unit and the VA liquid crystal cell; and an absorption axis of the back side polarizing unit is parallel to the horizontal normal.
  • the slow axis of the first front side TAC film is perpendicular to the absorption axis of the front side polarization unit.
  • the front side polarization unit includes a second front side TAC film and a front side disposed between the second front side TAC film and the first front side TAC film a PVA film; wherein a slow axis of the second front side TAC film is perpendicular to an absorption axis of the front side PVA film and a slow axis of the first front side TAC film.
  • the slow axis of the biaxial film is perpendicular to the absorption axis of the back side polarization unit.
  • the back side polarization unit includes a back side TAC film and a back side PVA film disposed between the back side TAC film and the biaxial film;
  • the slow axis of the back side TAC film is perpendicular to the absorption axis of the back side PVA film and to the slow axis of the biaxial film.
  • the in-plane retardation Ro of the biaxial film at a wavelength of 550 nm is 50.4 to 84 nm
  • the thickness direction retardation Rth-b at a wavelength of 550 nm is 168 to 280 nm.
  • the lower limit Y1 and the upper limit Y2 of the thickness direction retardation Rth-t of the first front side TAC film at a wavelength of 550 nm are respectively defined by the following formula:
  • the in-plane retardation Ro and the thickness direction retardation Rth-b are adjusted by changing the thickness and/or refractive index of the biaxial film.
  • a display device comprising a VA liquid crystal display unit and the optical compensation structure described above; wherein a front side polarizing plate of the optical compensation structure is disposed in a light emitting direction of the VA liquid crystal cell One side, a back side polarizing plate is disposed on the other side of the VA liquid crystal cell.
  • the VA liquid crystal cell is a multi-quadrant liquid crystal cell.
  • the present invention has the beneficial effects that in the optical compensation structure and the display device according to the embodiment of the present invention, the dark state can be leaked by deflecting the absorption axis of the front side polarization unit and the absorption axis of the back side polarization plate by 90 degrees.
  • the severe area shifts from a horizontal perspective to a vertical viewing angle, which improves the display compared to the existing single-layer biaxial film compensation structure.
  • the number of layers of the biaxial film is not increased, and only a single-layer biaxial film is used, which reduces the cost compared with the existing double-layered biaxial film compensation structure.
  • Figure 1 shows an exploded view of a display device of the prior art
  • FIG. 2 is a view showing a dark state light leakage distribution pattern of a prior art single-layer biaxial film compensation structure
  • FIG. 3 is a view showing a dark state light leakage distribution pattern of a prior art double-layered biaxial film compensation structure
  • FIG. 4 shows an exploded view of an optical compensation structure in accordance with an embodiment of the present invention
  • FIG. 5 shows an exploded view of the front side polarizing plate 100 exemplified in FIG. 4;
  • FIG. 6 shows an exploded view of the back side polarizing plate 200 exemplified in FIG. 4;
  • FIG. 7 shows a dark state light leakage profile of an optical compensation structure in accordance with an embodiment of the present invention
  • Figure 8 shows a curve of the amount of light leakage as a function of the delay value
  • Figure 9 shows a curve of the amount of light leakage as a function of the delay value
  • FIG. 10 is a diagram showing a dark state light leakage profile after an optical compensation structure according to an embodiment of the present invention is used in accordance with an embodiment of the present invention.
  • back side and front side are used in this application to refer to the nomenclature used for convenience of description, wherein the “back side” refers to being located between the liquid crystal cell and the backlight, “front side” “Side” refers to being located between the liquid crystal cell and the observer, or the other side of the liquid crystal cell relative to the backlight.
  • the direction of light is defined here as the direction in which the backlight is directed at the observer. It is to be understood that the various terms of the above are used for convenience of description and not limitation of the invention.
  • the front side polarizing plate 100 is disposed on the side of the light emitting direction of the VA liquid crystal cell 300 (herein, the light direction is defined as the direction in which the backlight 400 is directed to the observer 500), and includes a front side polarizing unit 110 and a front side polarizing unit 110.
  • the first front side TAC film 120 is interposed with the VA liquid crystal cell 300.
  • the back side polarizing plate 200 includes a back side polarizing unit 220 and a biaxial film 210 disposed between the back side polarizing unit 220 and the VA liquid crystal unit 300.
  • the slow axis 120a of the first front side TAC film 120 is perpendicular to the absorption axis of the front side polarization unit 110; the slow axis 210a of the biaxial film 210 is perpendicular to the absorption axis of the back side polarization unit 220.
  • the absorption axis 110a of the front side polarization unit 110 is perpendicular to the horizontal normal 300a of the VA liquid crystal cell 300;
  • the absorption axis 220a of the polarization unit 220 is parallel to the horizontal normal 300a.
  • the absorption axis 110a of the front side polarization unit 110 and the absorption axis 220a of the back side polarization unit 220 of the optical compensation structure according to the embodiment of the present invention are both deflected with respect to the single-layer biaxial film compensation structure of the prior art. 90°.
  • FIG. 5 shows an exploded view of the front side polarizing plate 100 illustrated in FIG. 4, the front side polarizing unit of the front side polarizing plate 100 including a second front side TAC film 111 and a second front side TAC a front side PVA film 112 between the film 111 and the first front side TAC film 120; wherein the absorption axis 112a of the front side PVA film 112 is perpendicular to the horizontal normal 300a, and the slow axis 111a and the front side of the second front side TAC film 111 The absorption axis 112a of the side PVA film 112 is perpendicular, and the slow axis 111a of the second front side TAC film 111 is parallel to the slow axis 120a of the first front side TAC film 120.
  • FIG. 6 shows an exploded view of the back side polarizing plate 200 exemplified in FIG. 4 including a back side TAC film 222 and a back side PVA disposed between the back side TAC film 222 and the biaxial film 210.
  • the absorption axis 221a of the back side PVA film 221 is parallel to the horizontal normal line 300a
  • the slow axis 222a of the back side TAC film 222 is parallel to the slow axis 210a of the biaxial film 210 and perpendicular to the absorption axis 221a of the back side PVA film 221. .
  • the optical compensation structure according to the embodiment of the present invention only needs to adopt a double-axis film (ie, the biaxial film 210) compared with the existing double-layer biaxial film compensation structure;
  • the absorption axis 110a of the front side polarization unit 110 and the absorption axis 220a of the back side polarization unit 220 are both deflected by 90° as compared with the layer biaxial film compensation structure.
  • the light leakage is serious.
  • the dark region where the light leakage is severe is close to the vertical vertical viewing angle, and the dark state leakage near the horizontal viewing angle is significantly reduced, so that Effectively improve the contrast and sharpness of the near horizontal viewing angle.
  • the cost is not improved.
  • the retardation value of the biaxial film 210 is further adjusted, or the retardation values of the first front side TAC film 120 and the biaxial film 210 are further adjusted at the same time.
  • the optical compensation structure includes the structure in FIGS. 4-6; the pretilt angle of the VA liquid crystal cell 300 is 85° to 89°, and the liquid crystal tilt angles in the four quadrants are 45°, 135°, 225°, respectively.
  • the phase difference LC of the liquid crystal ⁇ nd in the (324.3, 342.8) nm interval that is, the wavelength of 550 nm;
  • the light source uses blue-YAG (Yttrium Aluminum) Garnet) LED spectrum, the central brightness is defined as 100 nit, and the light source distribution is the Lambert distribution.
  • Biaxial in the figure Ro refers to the in-plane retardation Ro of the biaxial film 210
  • Biaxial Rth refers to the thickness direction retardation Rth-b of the biaxial film 210
  • TAC Rth refers to the thickness direction retardation Rth-t of the first front side TAC film 120.
  • the retardation values of the first front side TAC film 120 and the biaxial film 210 have a different influence on the dark state light leakage at different pretilt angles. That is, under different pretilt angles, the corresponding delay value range is the same when the dark state light leakage is minimum.
  • the thickness direction retardation Rth-b at a wavelength of 550 nm is 168 to 280 nm; the lower limit Y1 and the upper limit Y2 of the thickness direction of the first front side TAC film 120 at a wavelength of 550 nm are respectively passed by the formulas (1) and (2) )limited:
  • Nx and Ny are the in-plane refractive indices of the biaxial film 210, and Nz is the thickness refractive index.
  • FIG. 10 is a diagram showing a dark state light leakage distribution after an optical compensation structure according to an embodiment of the present invention, in accordance with an embodiment of the present invention, compared to the prior art single layer biaxial film compensation structure of FIG.
  • Dark state light leakage distribution map the dark state light leakage of the improved optical compensation structure is concentrated near the vertical viewing angle, the light leakage range is concentrated in a small viewing angle range, and the light leakage amount is significantly lower than that of the prior art single-layer biaxial film compensation structure.
  • the dark state leaks light is significantly lower than that of the prior art single-layer biaxial film compensation structure.
  • a VA mode liquid crystal display device includes a VA liquid crystal display unit and the above-described optical compensation structure, and some or all of the above-mentioned optical compensation structures are cited herein.
  • the front side polarizing plate 100 of the optical compensation structure is disposed on the side of the light outgoing direction of the VA liquid crystal cell 300
  • the back side polarizing plate 200 is disposed on the side of the light emitting direction of the back surface of the VA liquid crystal cell 300.
  • the VA liquid crystal cell 300 is a multi-quadrant liquid crystal cell, for example, a multi-quadrant liquid crystal cell composed of four quadrants.
  • TAC triacetate cellulose
  • PVA polyvinyl alcohol
  • biaxial film used in the present application may be any commercially available products of any type, here No longer listed in detail.
  • the optical compensation structure and the display device by absorbing the absorption axis 110a of the front side polarization unit 110 and the absorption axis 220a of the back side polarization unit 220 by 90 degrees, it is possible to The dark region with severe light leakage shifts from a horizontal viewing angle to a vertical viewing angle, which improves the display effect compared to the existing single-layer biaxial film compensation structure.
  • the number of layers of the biaxial film is not increased, and only a single-layer biaxial film is used, which reduces the cost compared with the existing double-layered biaxial film compensation structure.
  • an appropriate retardation value is set for the optical compensation structure and the display device described above, and the amount of light leakage is significantly reduced as compared with the conventional single-layer biaxial film compensation structure.

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Description

光学补偿结构及显示装置 技术领域
本发明涉及液晶显示，尤其涉及一种用于VA显示模式的光学补偿结构及显示装置。
背景技术
随着TFT-LCD的观察角度增大，画面的对比度不断降低，画面的清晰度下降。这是液晶层中液晶分子的双折射率随观察角度变化发生改变的结果，采用宽视角补偿膜进行补偿，可以有效降低暗态画面的漏光，在一定视角内能大幅度提高画面的对比度。补偿膜（或称为延迟膜）的补偿原理一般是将液晶在不同视角产生的相位差进行修正，让液晶分子的双折射性质得到对称性的补偿。针对不同的液晶显示模式，使用的补偿膜也不同，大尺寸液晶电视使用的补偿膜大多是针对VA显示模式，早期使用的有Konica公司的N-TAC，后来不断发展形成OPOTES公司的Zeonor，富士通的F-TAC系列，日东电工的X-plate等。
图1示出了现有技术中显示装置的爆炸图，如图1所示，该显示装置包括VA（Vertical Alignment，垂直排列）液晶单元300和光学补偿结构，该光学补偿结构进一步包括设置在VA液晶单元300两侧的正面侧偏振片100和背面侧偏振片200。其中，正面侧偏振片设置100在VA液晶单元300的出光方向（此处定义出光方向为背光源400指向观测者500的方向）一侧，包括正面侧偏振单元110和设置在正面侧偏振单元110与VA液晶单元300之间的第一正面侧TAC膜120。背面侧偏振片200包括背面侧偏振单元220和设置在背面侧偏振单元220与VA液晶单元300之间的背面侧双轴（Biaxial）膜210，该背面侧双轴膜210兼具延迟膜和保护膜的作用。
通常情况下将液晶显示装置（例如液晶电视）的可视角度（view angle）称为视角范围，包括水平可视角度和垂直可视角度两个指标，水平可视角度表示以液晶单元的垂直法线为准，在垂直于法线左或右方一定角度的位置上仍然能够正常的看见显示图像，这个角度范围就是液晶显示装置的水平可视角度。同理如果以液晶单元的水平法线为准，上下的可视角度就称为垂直可视角度。在本申请中为了描述方便，使用VA液晶单元的水平法线300a作为参照来标定方向。
在现有的光学补偿结构中，正面侧偏振单元110的吸收轴110a与水平法线300a平行，第一正面侧TAC膜120的慢轴120a与水平法线300a垂直；背正面侧偏振单元220的吸收轴220a与水平法线300a垂直，双轴膜210的慢轴210a与水平法线300a垂直。
上述光学补偿结构包括一层双轴膜（双轴膜210），因此通常也称之为单层双轴膜补偿结构。图2示出了单层双轴膜补偿结构的暗态漏光分布图，从图2可以看出单层双轴膜补偿结构的全视角暗态漏光分布，可知在phi=200-100，phi=1100-1600，phi=2000-2200，phi=3100-3300漏光严重，即接近水平位置的视角暗态漏光严重。然而，观众与液晶显示装置的相对位置决定了接近水平的视角更容易被观众看到，所以水平视角的对比度和清晰度对观看效果的影响最大。
为了解决上述问题，目前常用的解决方案是用双层双轴膜补偿结构来替换上述的单层双轴膜补偿结构。仍如图1所示，在双层双轴膜补偿结构中，采用双轴膜替换原有的第一正面侧TAC膜120，使得正面侧偏振片100和背面侧偏振片200均为带双轴延迟膜的偏振片。
图3示出了双层双轴膜补偿结构的暗态漏光分布图，从图3可以看出双层双轴膜补偿结构的全视角暗态漏光分布，可知在phi=300-600，phi=1200-1200，phi=2100-2100，phi=3000-3300漏光较为严重，这些暗态漏光严重的视角介于水平与垂直视角之间。通常水平视角的对比度和清晰度对观看效果的影响最大，而大视角（接近垂直视角）因为不容易被看到，对观众的影响较小。由此可以看出，采用双层双轴膜补偿结构可以提高观看效果。然而，双层双轴膜补偿结构虽然提高了显示效果，但是采用双层双轴膜将提高光学补偿结构的成本，使得由此制备的显示装置在市场竞争中处于劣势。
发明内容
本发明要解决的技术问题在于针对现有技术中采用双层双轴膜补偿结构解决水平视角暗态漏光而导致成本提高的缺陷，提供一种光学补偿结构以及显示装置。
本发明解决其技术问题所采用的技术方案是：依据本发明的一方面，提供了一种光学补偿结构，包括分别设置在VA液晶单元两侧的正面侧偏振片和背面侧偏振片；其中，
所述正面侧偏振片设置在所述VA液晶单元的出光方向一侧，包括正面侧偏振单元和设置在所述正面侧偏振单元与所述VA液晶单元之间的第一正面侧TAC膜；所述正面侧偏振单元的吸收轴与所述VA液晶单元的水平法线垂直；
所述背面侧偏振片包括背面侧偏振单元和设置在所述背面侧偏振单元与所述VA液晶单元之间的双轴膜；所述背面侧偏振单元的吸收轴与所述水平法线平行。
在依据本发明实施例的光学补偿结构中，所述第一正面侧TAC膜的慢轴与所述正面侧偏振单元的吸收轴垂直。
在依据本发明实施例的光学补偿结构中，所述正面侧偏振单元包括第二正面侧TAC膜和设置在所述第二正面侧TAC膜与所述第一正面侧TAC膜之间的正面侧PVA膜；其中，所述第二正面侧TAC膜的慢轴与所述正面侧PVA膜的吸收轴垂直、以及与所述第一正面侧TAC膜的慢轴平行。
在依据本发明实施例的光学补偿结构中，所述双轴膜的慢轴与所述背面侧偏振单元的吸收轴垂直。
在依据本发明实施例的光学补偿结构中，所述背面侧偏振单元包括背面侧TAC膜和设置在所述背面侧TAC膜与所述双轴膜之间的背面侧PVA膜；其中，所述背面侧TAC膜的慢轴与所述背面侧PVA膜的吸收轴垂直、以及与所述双轴膜的慢轴平行。
在依据本发明实施例的光学补偿结构中，所述双轴膜在波长550nm处的面内延迟Ro为50.4～84nm，在波长550nm处的厚度方向延迟Rth-b为168～280nm。
在依据本发明实施例的光学补偿结构中，所述第一正面侧TAC膜在波长550nm处的厚度方向延迟Rth-t的下限Y1和上限Y2分别通过以下公式限定：
Y1=0.00451×Rth-b2 - 2.7985×Rth-b + 444.44，
Y2=-0.0009256×Rth-b2 - 0.52686×Rth-b + 256.02。
在依据本发明实施例的光学补偿结构中，通过改变所述双轴膜的厚度和/或折射率来调节所述面内延迟Ro和所述厚度方向延迟Rth-b。
依据本发明的另一方面，还提供了一种显示装置，包括VA液晶显示单元和上述的光学补偿结构；其中，所述光学补偿结构的正面侧偏振片设置在所述VA液晶单元的出光方向一侧，背面侧偏振片设置在所述VA液晶单元的另一侧。
在依据本发明实施例的显示装置中，所述VA液晶单元是多象限的液晶单元。
本发明产生的有益效果是：在依据本发明实施例的光学补偿结构以及显示装置中，通过将正面侧偏振单元的吸收轴以及背面侧偏振片的吸收轴均偏转90°，可以将暗态漏光严重的区域从水平视角转移至垂直视角，较之现有的单层双轴膜补偿结构，提高了显示效果。与此同时，并没有增加双轴膜的层数，仅采用单层双轴膜，较之现有的双层双轴膜补偿结构，降低了成本。
附图说明
下面将结合附图及实施例对本发明作进一步说明，附图中：
图1示出了现有技术中显示装置的爆炸图；
图2示出了现有技术的单层双轴膜补偿结构的暗态漏光分布图；
图3示出了现有技术的双层双轴膜补偿结构的暗态漏光分布图；
图4示出了依据本发明实施例的光学补偿结构的爆炸图；
图5示出了图4中示例的正面侧偏振片100的爆炸图；
图6示出了图4中示例的背面侧偏振片200的爆炸图；
图7示出了依据本发明实施例的光学补偿结构的暗态漏光分布图；
图8示出了漏光量随延迟值的变化曲线；
图9示出了漏光量随延迟值的变化曲线；
图10示出了依据本发明实施例的光学补偿结构采用了依据本发明实施例的延迟值后的暗态漏光分布图。
具体实施方式
为了使本发明的目的、技术方案及优点更加清楚明白，以下结合附图及实施例，对本发明进行进一步详细说明。应当理解，此处所描述的具体实施例仅用以解释本发明，并不用于限定本发明。
在本申请中用到了术语“背面侧”和“正面侧”，其是为了描述方便所采用的方位名词，其中所述的“背面侧”指的是位于液晶单元和背光源之间，“正面侧”指的是位于液晶单元和观测者之间，或者是液晶单元相对背光源的另一侧。另外，此处定义出光方向为背光源指向观测者的方向。应当理解的是，以上所采用的各个术语仅仅是为了描述方便，并不是对发明的限制。
图4示出了依据本发明实施例的光学补偿结构，包括设置在VA液晶单元300两侧的正面侧偏振片100和背面侧偏振片200。其中，正面侧偏振片100设置在VA液晶单元300的出光方向（此处定义出光方向为背光源400指向观测者500的方向）一侧，包括正面侧偏振单元110和设置在正面侧偏振单元110与VA液晶单元300之间的第一正面侧TAC膜120。背面侧偏振片200包括背面侧偏振单元220和设置在背面侧偏振单元220与VA液晶单元300之间的双轴膜210。优选地，第一正面侧TAC膜120的慢轴120a与正面侧偏振单元110的吸收轴垂直；双轴膜210的慢轴210a与背面侧偏振单元220的吸收轴垂直。
不同于现有技术中的单层双轴膜补偿结构，在依据本发明实施例的光学补偿结构中，正面侧偏振单元110的吸收轴110a与VA液晶单元300的水平法线300a垂直；背面侧偏振单元220的吸收轴220a与水平法线300a平行。换句话说，相对于现有技术中的单层双轴膜补偿结构，依据本发明实施例的光学补偿结构的正面侧偏振单元110的吸收轴110a以及背面侧偏振单元220的吸收轴220a均偏转了90°。
具体而言，图5示出了图4中示例的正面侧偏振片100的爆炸图，该正面侧偏振片100的正面侧偏振单元包括第二正面侧TAC膜111和设置在第二正面侧TAC膜111与第一正面侧TAC膜120之间的正面侧PVA膜112；其中，正面侧PVA膜112的吸收轴112a与水平法线300a垂直，第二正面侧TAC膜111的慢轴111a与正面侧PVA膜112的吸收轴112a垂直，并且，第二正面侧TAC膜111的慢轴111a与第一正面侧TAC膜120的慢轴120a平行。
图6示出了图4中示例的背面侧偏振片200的爆炸图，该背面侧偏振单元220包括背面侧TAC膜222和设置在背面侧TAC膜222与双轴膜210之间的背面侧PVA膜221。其中，背面侧PVA膜221的吸收轴221a与水平法线300a平行，背面侧TAC膜222的慢轴222a与双轴膜210的慢轴210a平行，且与背面侧PVA膜221的吸收轴221a垂直。
从以上可以看出，依据本发明实施例的光学补偿结构与现有的双层双轴膜补偿结构相比，只需要采用一层双轴膜（即双轴膜210）；与现有的单层双轴膜补偿结构相比，正面侧偏振单元110的吸收轴110a以及背面侧偏振单元220的吸收轴220a均偏转了90°。图7示出了依据本发明实施例的该光学补偿结构的暗态漏光分布图，从图7可以看出单层双轴膜补偿结构的全视角暗态漏光分布，可知在phi=200-700，phi=1100-1300，phi=2300-2200，phi=2900-3100漏光严重。相比于图2中现有技术的单层双轴膜补偿结构的暗态漏光分布图，暗态漏光严重的区域已经接近上下垂直视角，而接近水平视角的暗态漏光明显降低，这样就可以有效的提高接近水平视角的对比度和清晰度。与此同时，因为只需要一层双轴膜，因此成本并没有提高。
为了保证漏光集中在上下垂直视角附近，并且漏光量和漏光范围要尽量小，进一步调节双轴膜210的延迟值，或者进一步同时调节第一正面侧TAC膜120和双轴膜210的延迟值。在模拟的过程中，光学补偿结构包括图4-6中的结构；VA液晶单元300的预倾角为85°到89°，在四个象限内的液晶倾角分别为45°、135°、225°以及315°，液晶的相位差LC △nd在（324.3,342.8）nm区间，即波长550nm处；光源使用蓝光-YAG（Yttrium Aluminum Garnet）LED光谱，中央亮度定义为100nit，光源分布为朗伯（Lambert）分布。
模拟结果例如如图8和9中的漏光量随延迟值的变化曲线所示，其中图8为LC △ND=324.3nm，预倾角为89°时，双轴膜210的面内延迟Ro和厚度方向延迟Rth-b、以及第一正面侧TAC膜120的厚度方向延迟Rth-t取不同值时的漏光量变化曲线；图9为LC △ND=342.8nm，预倾角为89°时，双轴膜210的面内延迟Ro和厚度方向延迟Rth-b、以及第一正面侧TAC膜120的厚度方向延迟Rth-t取不同值时的漏光量变化曲线。其中，图中的Biaxial Ro指代双轴膜210的面内延迟Ro，Biaxial Rth指代双轴膜210的厚度方向延迟Rth-b，TAC Rth指代第一正面侧TAC膜120的厚度方向延迟Rth-t。
在模拟中，我们发现不同预倾角下，第一正面侧TAC膜120和双轴膜210的延迟值对暗态漏光的影响趋势是一致的。即不同预倾角下，暗态漏光最小时对应的延迟值范围是一样的。根据模拟结果可以获得LC △ND在（324.3, 342.8）nm区间，预倾角在（850-890）区间，暗态漏光小于0.2nit（预倾角=890 时模拟出的暗态漏光值，非实测值）时对应的第一正面侧TAC膜120和双轴膜210的延迟值范围：双轴膜210在波长550nm处的面内延迟Ro为50.4～84nm，在波长550nm处的厚度方向延迟Rth-b为168～280nm；第一正面侧TAC膜120在波长550nm处的厚度方向延迟Rth-t的下限Y1和上限Y2分别通过公式（1）和（2）限定：
Y1=0.00451×Rth-b2 - 2.7985×Rth-b + 444.44， （1）
Y2=-0.0009256×Rth-b2 - 0.52686×Rth-b + 256.02 （2）。
已知的，双轴膜210的面内延迟Ro和厚度方向延迟Rth-b与其折射率和厚度d的关系满足公式（3）和（4）：
Ro=(Nx-Ny)×d （3）
Rth-b=[(Nx+Ny)/2-Nz]×d （4）
其中，Nx和Ny为双轴膜210的平面内折射率，Nz为厚度折射率。这样，我们可以通过以下三种方法来改变延迟值：改变厚度d来改变延迟值；在厚度d不变的情况下，改变折射率来改变延迟值；同时改变厚度d和折射率来调节延迟值。
图10示出了依据本发明实施例的光学补偿结构采用了依据本发明实施例的延迟值后的暗态漏光分布图，相比于图2中现有技术的单层双轴膜补偿结构的暗态漏光分布图，改善后光学补偿结构的暗态漏光集中在垂直视角附近，漏光范围集中在较小的视角范围内，且漏光量明显低于现有技术的单层双轴膜补偿结构造成的暗态漏光。
在依据本发明实施例的VA模式液晶显示装置包括VA液晶显示单元和上述光学补偿结构，此处部分或全部引用上述的光学补偿结构。其中，光学补偿结构的正面侧偏振片100设置在VA液晶单元300的出光方向一侧，背面侧偏振片200设置在VA液晶单元300背面出光方向的一侧。另外，VA液晶单元300是多象限的液晶单元，例如由4象限构成的多象限的液晶单元。
应当理解的是，本申请中使用的TAC（三醋酸纤维素）膜、PVA（聚乙烯醇）膜、双轴（Biaxial）膜可采用现有的市面上可售的任意型号的产品，此处不再详细列举。
从以上可以看出，在依据本发明实施例的光学补偿结构以及显示装置中，通过将正面侧偏振单元110的吸收轴110a以及背面侧偏振单元220的吸收轴220a均偏转了90°，可以将暗态漏光严重的区域从水平视角转移至垂直视角，较之现有的单层双轴膜补偿结构，提高了显示效果。与此同时，并没有增加双轴膜的层数，仅采用单层双轴膜，较之现有的双层双轴膜补偿结构，降低了成本。另外，针对上述光学补偿结构以及显示装置设置合适的延迟值，较之现有的单层双轴膜补偿结构，漏光量明显降低。

Claims (10)

  1. 一种光学补偿结构，其特征在于，包括分别设置在VA液晶单元两侧的正面侧偏振片和背面侧偏振片；其中，
    所述正面侧偏振片设置在所述VA液晶单元的出光方向一侧，包括正面侧偏振单元和设置在所述正面侧偏振单元与所述VA液晶单元之间的第一正面侧TAC膜；所述正面侧偏振单元的吸收轴与所述VA液晶单元的水平法线垂直；
    所述背面侧偏振片包括背面侧偏振单元和设置在所述背面侧偏振单元与所述VA液晶单元之间的双轴膜；所述背面侧偏振单元的吸收轴与所述水平法线平行。
  2. 根据权利要求1所述的光学补偿结构，其特征在于，所述第一正面侧TAC膜的慢轴与所述正面侧偏振单元的吸收轴垂直。
  3. 根据权利要求2所述的光学补偿结构，其特征在于，所述正面侧偏振单元包括第二正面侧TAC膜和设置在所述第二正面侧TAC膜与所述第一正面侧TAC膜之间的正面侧PVA膜；其中，所述第二正面侧TAC膜的慢轴与所述正面侧PVA膜的吸收轴垂直、以及与所述第一正面侧TAC膜的慢轴平行。
  4. 根据权利要求1所述的光学补偿结构，其特征在于，所述双轴膜的慢轴与所述背面侧偏振单元的吸收轴垂直。
  5. 根据权利要求4所述的光学补偿结构，其特征在于，所述背面侧偏振单元包括背面侧TAC膜和设置在所述背面侧TAC膜与所述双轴膜之间的背面侧PVA膜；其中，所述背面侧TAC膜的慢轴与所述背面侧PVA膜的吸收轴垂直、以及与所述双轴膜的慢轴平行。
  6. 根据权利要求1所述的光学补偿结构，其特征在于，所述双轴膜在波长550nm处的面内延迟Ro为50.4～84nm，在波长550nm处的厚度方向延迟Rth-b为168～280nm。
  7. 根据权利要求6所述的光学补偿结构，其特征在于，所述第一正面侧TAC膜在波长550nm处的厚度方向延迟Rth-t的下限Y1和上限Y2分别通过以下公式限定：
    Y1=0.00451×Rth-b2 - 2.7985×Rth-b + 444.44，
    Y2=-0.0009256×Rth-b2 - 0.52686×Rth-b + 256.02。
  8. 根据权利要求6所述的光学补偿结构，其特征在于，通过改变所述双轴膜的厚度和/或折射率来调节所述面内延迟Ro和所述厚度方向延迟Rth-b。
  9. 一种显示装置，其特征在于，包括VA液晶显示单元和权利要求1-8任一项所述的光学补偿结构；其中，所述光学补偿结构的正面侧偏振片设置在所述VA液晶单元的出光方向一侧，背面侧偏振片设置在所述VA液晶单元的另一侧。
  10. 根据权利要求9所述的显示装置，其特征在于，所述VA液晶单元是多象限的液晶单元。
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