Super-twisted nematic liquid crystal display

Abstract

The utility model relates to the technical field of liquid crystal displays, and discloses a super-twisted nematic liquid crystal display, which comprises a super-twisted nematic liquid crystal box, an upper polaroid and a lower polaroid, the phase difference delay value of the liquid crystal compensation film is matched with the super-twisted nematic liquid crystal box, the change value of the phase difference delay value of the liquid crystal compensation film before and after weather resistance tests of 95 DEG C * 500 h and 65 DEG C * 95% * 500 h is smaller than or equal to 3%, and the rotation angle of the liquid crystal compensation film ranges from 175 degrees to 280 degrees and is matched with the rotation angle of the super-twisted nematic liquid crystal box. The liquid crystal compensation film is compounded in the upper polaroid, the compensation value of the liquid crystal compensation film is decreased along with temperature rise, the temperature change of the liquid crystal compensation film is similar to that of a super-twisted nematic liquid crystal box, the compensation effect can be achieved at different temperatures, and the good optical effect is kept. Meanwhile, the liquid crystal compensation film is also of a twisted structure, and the birefringence effect of liquid crystals in the liquid crystal box is completely compensated.

Description

Technical Field

[0001] This utility model relates to the field of liquid crystal display technology, and in particular to a super-twisted nematic liquid crystal display. Background Technology

[0002] Compared to traditional twisted nematic liquid crystal displays (TN-LCDs), super-twisted nematic liquid crystal displays (STN-LCDs) have a larger twist angle, typically around 180°–270°. This large twist angle results in a very steep electro-optical response characteristic, which is precisely what high multiplexing is required for. For this reason, STN-LCDs offer superior image quality when used in large-scale displays with high levels of passive multiplexing. However, due to the birefringence effect of the STN liquid crystal (LC) layer, super-twisted nematic (STN) liquid crystal cells suffer from lag issues, which limits their application in color displays.

[0003] To address the latency issue in STN-LCD liquid crystal display cells and achieve the desired STN LCD display effect, existing technologies typically employ one or two compensation films (i.e., phase retardation films) for retardation compensation. These compensation films are uniformly stretched polymer films, such as polycarbonate films or cyclic olefin polymer films. While these compensation film layers significantly improve the optical behavior of (S)TN liquid crystal displays, they lack the necessary twisted structure and cannot fully compensate for the birefringence effect of the display.

[0004] Furthermore, because the physical properties of liquid crystal materials change with temperature, the threshold voltage and transmittance spectrum of LCDs will drift with temperature. The relationship between liquid crystal imaging and temperature is indirect. Temperature mainly affects the imaging effect of liquid crystals by influencing the physical and optical properties of the liquid crystal materials. Within a certain temperature range, the refractive index, optical anisotropy, and other optical properties of liquid crystals change with temperature, thus affecting the contrast and brightness of the liquid crystal image. As temperature changes, the threshold voltage and response time of the liquid crystal change, corresponding to different required torsional forces, resulting in different liquid crystal response speeds and thus changes in the display. The effect of temperature on the rotation speed of liquid crystal molecules affects the response time of the liquid crystal display. As the temperature increases, the rotation speed of liquid crystal molecules increases, and the response time of the liquid crystal display becomes shorter; as the temperature decreases, the rotation speed of liquid crystal molecules decreases, and the response time of the liquid crystal display becomes longer. In low-temperature environments, the viscosity of the liquid crystal increases, corresponding to an increase in the required torsional force, leading to a decrease in the liquid crystal response speed, and the display gradually fades as the temperature decreases. As temperature increases, the liquid crystal molecules become more disordered, reducing the contrast and brightness of the liquid crystal display and affecting its performance. Conversely, as temperature decreases, the contrast and brightness increase, but the color reproduction deteriorates. Higher temperatures also narrow the viewing angle, while lower temperatures widen it. The effects of temperature on liquid crystal molecule alignment are generally mitigated using temperature compensation techniques.

[0005] If the LCD display experiences temperature changes, the retardation value also changes, while the twist angle, twist direction, and dispersion do not change with temperature. This can lead to a decrease in the contrast and color of the LCD display at different operating temperatures. Utility Model Content

[0006] The purpose of this invention is to provide a super-twisted nematic liquid crystal display with better compensation effect, and to provide at least a beneficial option or create conditions for solving one or more technical problems existing in the prior art.

[0007] To achieve the above objectives, the present invention adopts the following technical solution.

[0008] A super-twisted nematic liquid crystal display includes a super-twisted nematic liquid crystal cell, an upper polarizer, and a lower polarizer, wherein the upper polarizer and the lower polarizer are respectively attached to the upper and lower surfaces of the super-twisted nematic liquid crystal cell; wherein a liquid crystal compensation film is laminated on the upper polarizer, the phase retardation value of the liquid crystal compensation film is matched with that of the super-twisted nematic liquid crystal cell, and the change in the phase retardation value of the liquid crystal compensation film before and after weathering tests at 95℃×500h and 65℃×95%×500h is ≤7%, the rotation angle of the liquid crystal compensation film is 175~280°, matching the rotation angle of the super-twisted nematic liquid crystal cell, and the optical axis of the liquid crystal compensation film is perpendicular to that of the super-twisted nematic liquid crystal cell.

[0009] More preferably, the substrate film of the liquid crystal compensation film is a cellulose triacetate film, a cyclic olefin polymer film, a polymethyl methacrylate film, or a polyethylene terephthalate film, and the liquid crystal material coated on the substrate film after tribo-alignment or photo-alignment is a cholesterol disk-shaped liquid crystal.

[0010] More preferably, the phase retardation value of the liquid crystal compensation film at a wavelength of 550nm is 200-1200nm.

[0011] More preferably, the angle between the optical axis of the liquid crystal compensation film and the absorption axis of the upper polarizer is 30~150°.

[0012] More preferably, the upper polarizer is composed of an upper protective film layer, a first polarizing element protective layer, a first adhesive layer, an upper polarizing element layer, a second adhesive layer, a second polarizing element protective layer, a first pressure-sensitive adhesive layer, a liquid crystal compensation film layer, a second pressure-sensitive adhesive layer, and a first release film layer, which are sequentially bonded from top to bottom; the lower polarizer is composed of a lower protective film layer, a third polarizing element protective layer, a second adhesive layer, a lower polarizing element layer, a fourth adhesive layer, a fourth polarizing element protective layer, a third pressure-sensitive adhesive layer, and a second release film layer, which are sequentially bonded from bottom to top.

[0013] More preferably, the thickness of each protective film layer is 38–100 µm, the thickness of each polarizing element protective layer is 18–85 µm, the thickness of each polarizing element layer is 8–35 µm, the thickness of each pressure-sensitive adhesive layer is 10–30 µm, and the thickness of each release film layer is 35–100 µm.

[0014] More preferably, the thickness of each protective film layer is 50-60µm, the thickness of each polarizing element protective layer is 40-85µm, the thickness of each polarizing element layer is 18-32µm, the thickness of each pressure-sensitive adhesive layer is 18-25µm, and the thickness of each release film layer is 38-55µm.

[0015] More preferably, the polarizing element protective layers are selected from cellulose triacetate film, cyclic olefin polymer film, polymethyl methacrylate film and polyethylene terephthalate film.

[0016] More preferably, each adhesive layer is a thermosetting adhesive layer or a UV-curing adhesive layer.

[0017] More preferably, each pressure-sensitive adhesive layer is a thermosetting pressure-sensitive adhesive layer or a UV-curing pressure-sensitive adhesive layer.

[0018] The technical solution provided by this utility model has at least the following technical effects or advantages.

[0019] The decrease in hysteresis of the super-twisted nematic liquid crystal cell with increasing temperature (and vice versa) is due to the decrease in birefringence of the low molecular weight liquid crystal material used in the cell. As the temperature approaches the clearing temperature (Tc), the temperature dependence of the liquid crystal material's birefringence increases, while above Tc, the birefringence (and corresponding changes in birefringence) is zero. This invention utilizes a liquid crystal compensation film in the upper polarizer whose composite compensation value decreases with increasing temperature. Similar to the temperature change of the super-twisted nematic liquid crystal cell, this film can achieve its compensation effect at different temperatures while maintaining excellent optical performance. Simultaneously, the liquid crystal compensation film also has a twisted structure, completely compensating for the birefringence effect of the liquid crystal within the cell.

[0020] This invention employs a liquid crystal layer method similar to that of STN liquid crystal displays, aligning its optical axis perpendicular to the optical axis of the liquid crystal cell, thus more successfully compensating for the undesirable color effects of STN liquid crystal displays. When the STN layer has the same absolute retardation value (∆n•d), the same dispersion (depending on the wavelength of ∆n), equal twist angles, and a twist direction opposite to that of the STN liquid crystal, optimized compensation for perpendicularly incident light can be achieved. These standards apply at all operating temperatures of the display, and the compensation value (retardation value) of its compensation film varies with temperature, consistent with the retardation amount of STN-LCD with temperature changes, meaning the same optical effect is maintained at different temperatures. This results in excellent optical performance at different temperatures, reduces the need for double-layer compensation film lamination, and lowers manufacturing costs.

[0021] Other beneficial effects of this invention will become more apparent in the following description or practice. Attached Figure Description

[0022] Figure 1 The diagram shown is a structural schematic of the super-twisted nematic liquid crystal display of this invention.

[0023] Figure 2 The diagram shown is a schematic of the upper polarizer.

[0024] Figure 3The diagram shown is a schematic of the structure of the lower polarizer.

[0025] Explanation of the reference numerals in the attached figures.

[0026] 1: Super-twisted nematic liquid crystal cell, 2: Upper polarizer, 3: Lower polarizer.

[0027] 201: Upper protective film layer; 202: First polarizing element protective layer; 203: First adhesive layer; 204: Upper polarizing element layer; 205: Second adhesive layer; 206: Second polarizing element protective layer; 207: First pressure-sensitive adhesive layer; 208: Liquid crystal compensation film layer; 209: Second pressure-sensitive adhesive layer; 210: First release film layer.

[0028] 301: Lower protective film layer, 302: Third polarizing element protective layer, 303: Second adhesive layer, 304: Lower polarizing element layer, 305: Fourth adhesive layer, 306: Fourth polarizing element protective layer, 307: Third pressure-sensitive adhesive layer, 308: Second release film layer. Detailed Implementation

[0029] The specific embodiments of this utility model will be further described below with reference to the accompanying drawings, making the technical solution and beneficial effects of this utility model clearer and more explicit. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this utility model, and should not be construed as limiting this utility model.

[0030] Additional aspects and advantages of this invention will become apparent in the description that follows, or may be learned by practice of this invention.

[0031] Reference Figure 1 As shown, a super-twisted nematic liquid crystal display includes a super-twisted nematic liquid crystal cell 1, an upper polarizer 2, and a lower polarizer 3, wherein the upper polarizer 2 and the lower polarizer 3 are respectively attached to the upper and lower surfaces of the super-twisted nematic liquid crystal cell 1.

[0032] Reference Figure 2 As shown, the upper polarizer 2 is composed of, from top to bottom, an upper protective film layer 201, a first polarizing element protective layer 202, a first adhesive layer 203, an upper polarizing element layer 204, a second adhesive layer 205, a second polarizing element protective layer 206, a first pressure-sensitive adhesive layer 207, a liquid crystal compensation film layer 208, a second pressure-sensitive adhesive layer 209, and a first release film layer 210. The second pressure-sensitive adhesive layer 209 is used to bond the upper polarizer 2 to the super-twisted nematic liquid crystal cell 1.

[0033] The first polarizing element protective layer 202 and the second polarizing element protective layer 206 are cellulose triacetate films, cyclic olefin polymer films, polymethyl methacrylate films, or polyethylene terephthalate films. The thickness of the first polarizing element protective layer 202 and the second polarizing element protective layer 206 is 18–85 µm, more preferably 40–85 µm. The thickness of the upper polarizing element layer 204 is 8–35 µm, more preferably 18–32 µm. Each polarizing element protective layer and the upper polarizing element layer 204 are bonded together with adhesive, which can be a thermosetting polyvinyl alcohol adhesive or a UV-curing adhesive.

[0034] The second polarizing element protective layer 206 and the liquid crystal compensation film layer 208 are composited through a first pressure-sensitive adhesive layer 207. The pressure-sensitive adhesive can be a thermosetting pressure-sensitive adhesive or a UV-curable pressure-sensitive adhesive.

[0035] The substrate of the liquid crystal compensation film 208 is a cellulose triacetate film, a cyclic olefin polymer film, a polymethyl methacrylate film, a polyethylene terephthalate film, etc. The substrate film is coated with liquid crystal material after being aligned by a triboelectric method or a photo-alignment method, and then cured by thermosetting or UV curing to obtain the phase retardation film. To control the rotation angle of the liquid crystal layer in the phase retardation film, the liquid crystal material is preferably a cholesteric disk-shaped liquid crystal. The compensation value of the liquid crystal compensation film is in the range of 200–1200 nm (wavelength below 550 nm), more preferably 300–1000 nm (wavelength below 550 nm). The phase retardation value of the liquid crystal compensation film is matched to the liquid crystal display.

[0036] The rotation angle of the super-twisted nematic liquid crystal cell 1 is typically 180 to 270° (-180 to -270°), and the rotation angle of the liquid crystal compensation film is 175 to 280°, which matches the rotation angle of the liquid crystal.

[0037] The phase difference (retardation) value of the liquid crystal compensation film changes by ≤3% before and after weathering tests at 95℃×500h and 65℃×95%×500h.

[0038] The angle between the optical axis of the liquid crystal compensation film 208 and the absorption axis of the upper polarizing element layer 204 is 30° to 150°, and more preferably 45° to 135°.

[0039] The thickness of the first pressure-sensitive adhesive layer 207 and the second pressure-sensitive adhesive layer 209 is 10–30 µm, more preferably 18–25 µm. The thickness of the upper protective film layer 201 is 38–100 µm, more preferably 50–60 µm. Using a thicker protective film layer can better avoid problems such as folding and indentation caused by thinner products during production.

[0040] The thickness of the first release film layer 210 is 35–100 µm, more preferably 38–55 µm. Using a thicker release film layer avoids problems such as folding, unevenness, and indentation that can occur when the product is thinner during production.

[0041] The upper polarizer 1 meets the requirements of weather resistance of 95℃×500h and 65℃×95%×500h.

[0042] Reference Figure 3 As shown, the lower polarizer 3 is composed of a lower protective film layer 301, a third polarizer element protective layer 302, a second adhesive layer 303, a lower polarizer element layer 304, a fourth adhesive layer 305, a fourth polarizer element protective layer 306, a third pressure-sensitive adhesive layer 307, and a second release film layer 308, which are sequentially bonded from bottom to top.

[0043] The substrates of the third polarizing element protective layer 302 and the fourth polarizing element protective layer 306 are cellulose triacetate film, cyclic olefin polymer film, polymethyl methacrylate film, or polyethylene terephthalate film. The thickness of each polarizing element protective layer is 18–85 µm, more preferably 40–85 µm. The thickness of the lower polarizing element layer 304 is 8–35 µm, more preferably 18–32 µm. The lower polarizing element layer 304 is bonded to the third polarizing element protective layer 302 and the fourth polarizing element protective layer 306 with adhesive, which can be a thermosetting polyvinyl alcohol adhesive or a UV-curing adhesive.

[0044] After the fourth polarizing element protective layer 306 is coated with the third pressure-sensitive adhesive layer 307, the second release film layer 308 is laminated on it. The third pressure-sensitive adhesive layer 307 can be a thermosetting pressure-sensitive adhesive or a UV-curing pressure-sensitive adhesive. The third pressure-sensitive adhesive layer 307 is mainly used for bonding with the super-twisted nematic liquid crystal cell 1.

[0045] It should also be noted that in the description of this utility model, directional terms such as "center", "horizontal", "longitudinal", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", and "counterclockwise" indicate the orientation and positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this utility model and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. They should not be construed as limiting the specific protection scope of this utility model.

[0046] In this utility model, unless otherwise explicitly specified and limited, the terms "assembly," "connection," and "joining" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can also refer to a mechanical connection; they can refer to a direct connection or a connection through an intermediate medium; or they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this utility model according to the specific circumstances.

[0047] In this utility model, unless otherwise specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "below," and "over" the second feature includes the first feature being directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Above," "below," and "under" the second feature includes the first feature being directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0048] Based on the above description of the structure and principle, those skilled in the art should understand that this utility model is not limited to the specific embodiments described above. Improvements and substitutions made using techniques known in the art based on this utility model all fall within the protection scope of this utility model, which should be defined by the claims and their equivalents. Parts not described in the specific embodiments are all prior art or common knowledge.

Claims

1. A super-twisted nematic liquid crystal display, comprising a super-twisted nematic liquid crystal cell, an upper polarizer, and a lower polarizer, wherein the upper polarizer and the lower polarizer are respectively attached to the upper surface and the lower surface of the super-twisted nematic liquid crystal cell; characterized in that, A liquid crystal compensation film is laminated on the upper polarizer. The phase retardation value of the liquid crystal compensation film matches the super-twisted nematic liquid crystal cell and decreases with increasing temperature. The phase retardation value of the liquid crystal compensation film changes by ≤7% before and after weathering tests at 95℃×500h and 65℃×95%×500h. The rotation angle of the liquid crystal compensation film is 175~280°, matching the rotation angle of the super-twisted nematic liquid crystal cell. The liquid crystal compensation film is perpendicular to the optical axis of the super-twisted nematic liquid crystal cell.

2. The super-twisted nematic liquid crystal display according to claim 1, characterized in that, The substrate film of the liquid crystal compensation film is a cellulose triacetate film, a cyclic olefin polymer film, a polymethyl methacrylate film, or a polyethylene terephthalate film. The liquid crystal material coated on the substrate film after being rubbed or photo-aligned is a cholesterol disk-shaped liquid crystal.

3. The super-twisted nematic liquid crystal display according to claim 1, characterized in that, The phase retardation value of the liquid crystal compensation film at a wavelength of 550nm is 200-1200nm.

4. A super-twisted nematic liquid crystal display according to claim 1, characterized in that, The angle between the optical axis of the liquid crystal compensation film and the absorption axis of the upper polarizer is 30~150°.

5. A super-twisted nematic liquid crystal display according to claim 1, characterized in that, The upper polarizer is composed of an upper protective film layer, a first polarizing element protective layer, a first adhesive layer, an upper polarizing element layer, a second adhesive layer, a second polarizing element protective layer, a first pressure-sensitive adhesive layer, a liquid crystal compensation film layer, a second pressure-sensitive adhesive layer, and a first release film layer, which are sequentially bonded from top to bottom. The lower polarizer is composed of a lower protective film layer, a third polarizing element protective layer, a second adhesive layer, a lower polarizing element layer, a fourth adhesive layer, a fourth polarizing element protective layer, a third pressure-sensitive adhesive layer, and a second release film layer, which are sequentially bonded from bottom to top.

6. A super-twisted nematic liquid crystal display according to claim 5, characterized in that, The thickness of the liquid crystal compensation film is 20–100 μm, and the thickness of the liquid crystal coating on the liquid crystal compensation film is 1–10 μm.

7. A super-twisted nematic liquid crystal display according to claim 5, characterized in that, The compensation value of the liquid crystal compensation film varies within a range of ≤7% at temperatures between 25 and 90°C.

8. A super-twisted nematic liquid crystal display according to claim 5, characterized in that, The thickness of the protective film layer is 38–100 µm, the thickness of the polarizing element protective layer is 18–85 µm, the thickness of the polarizing element layer is 8–35 µm, the thickness of the pressure-sensitive adhesive layer is 10–30 µm, and the thickness of the release film layer is 35–100 µm.

9. A super-twisted nematic liquid crystal display according to claim 5, characterized in that, The polarizing element protective layer is selected from cellulose triacetate film, cyclic olefin polymer film, polymethyl methacrylate film and polyethylene terephthalate film.

10. A super-twisted nematic liquid crystal display according to claim 5, characterized in that, The adhesive layer is a thermosetting adhesive layer or a UV-curing adhesive layer, and the pressure-sensitive adhesive layer is a thermosetting pressure-sensitive adhesive layer or a UV-curing pressure-sensitive adhesive layer.

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