JP2005242102A - Liquid crystal display element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display element in which no lowering of image quality occurs even when a high-luminance backlight is used. <P>SOLUTION: The liquid crystal display element comprises: a pair of polarizing plates; one or more optical retardation films; two electrode substrates each having an electrode layer on its one surface; and a liquid crystal layer interposed between the two electrode substrates so that the electrode layers are opposite to each other, and switches between light and dark by controlling light transmission and absorption with application or removal of a voltage. The liquid crystal display element has a portion of the other surface, of the electrode substrate having no electrode layer, being not in contact with the polarizing plate or the optical retardation film and/or a side face of the electrode substrate, covered with a material with a thermal conductivity B (W/mK), and when thermal conductivity of the substrate is represented by A (W/mK), a relation of the thermal conductivities satisfies an inequality A>B. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a liquid crystal display (LCD), particularly a liquid crystal display LCD which is a transmissive or transflective LCD requiring a backlight, a liquid crystal display LCD for notebook computers, a mobile terminal LCD, and a mobile phone LCD. It relates to an element.

Currently, as a liquid crystal display element, it is thin, light, good in image quality, and low in power consumption, so it is used for mobile phone displays, small and medium mobile electronic device displays, personal computer displays, and liquid crystal TV displays. It has been. As the liquid crystal drive system, TN (twisted nematic) and STN (super twisted nematic) systems accounted for the majority, but the display screen was viewed from the upper and lower angles and / or the left and right angles. In addition to obtaining the brightness and contrast of the case, VA (vertical alignment) and IPS (in-plane switching) systems are spreading on the market. Under such circumstances, in order to make it as bright as possible, the luminance of the backlight has been improved, and at present, a very bright luminance has been realized (Patent Document 1). However, since the luminance is increased, the thermal load applied to the panel of the liquid crystal display element becomes large, and the expansion due to heat of the electrode substrate sandwiching the liquid crystal layer between the two electrode substrates having the electrode layer on one surface of the substrate, Shrinkage cannot be ignored. As a result, an internal stress is generated due to a temperature gradient in the substrate of the liquid crystal display element, and a phase difference is generated in the substrate, resulting in light leakage on the screen of the liquid crystal display device, which greatly reduces image quality. Problem has occurred.
JP-A-9-218407

  An object of the present invention is to provide a liquid crystal display element that does not deteriorate image quality even when a backlight having high luminance is used.

  As a result of earnestly examining the liquid crystal display element in order to solve the above-mentioned problems, the present inventor has reduced the temperature distribution in the plane of the liquid crystal display element and suppressed the generation of internal stress in a substrate made of glass or plastic. Thus, it has been found that the occurrence of a phase difference from the electrode substrate can be suppressed. And we focus on keeping the temperature distribution in the surface of the substrate with electrodes (hereinafter sometimes referred to as electrode substrate) almost uniform, and provide liquid crystal display elements that are less likely to degrade image quality when the liquid crystal display device is lit continuously Has been successful.

That is, the present invention can be achieved by the following [1] to [3].
[1] A liquid crystal layer is sandwiched between a pair of polarizing plates, one or more retardation films, and two electrode substrates having an electrode layer on one surface of the substrate so that the electrode layers face each other, A liquid crystal display element capable of adjusting light transmission and absorption by applying or removing voltage to switch between a bright state and a dark state, and the thermal conductivity of the substrate is A (W / m · K) At this time, the other surface of the electrode substrate that does not have an electrode layer, the surface portion not in contact with the polarizing plate or the retardation film, and / or the side surface of the electrode substrate has a thermal conductivity B (W / m · K). A liquid crystal display element which is covered with a certain material and has a relationship of thermal conductivity satisfying A> B.
[2] The liquid crystal display element according to [1], wherein a surface portion not in contact with the polarizing plate or the retardation film and / or a side surface of the electrode substrate is coated with a material containing a polymer.
[3] The liquid crystal display element according to the above [2], wherein a surface portion that is not in contact with the polarizing plate or the retardation film and / or a side surface of the electrode substrate is covered with a heat insulating material.

  According to the present invention, it is possible to provide a liquid crystal display element that eliminates the generation of a phase difference of the substrate and causes almost no deterioration in image quality when the liquid crystal display device is continuously lit, and further improves the display quality of the liquid crystal display element Have

[Liquid crystal display element]
The liquid crystal display element in the present invention is composed of a pair of polarizing plates, one or more retardation films, and two substrates and a liquid crystal layer arranged to face each other. The optical axes of the two polarizing plates are arranged so as to be orthogonal to each other. In the electrode substrate, a transparent electrode made of ITO (indium tin oxide) is formed on the surface of a substrate (translucent substrate) made of glass or plastic as a base, and an alignment film is provided thereon. . The retardation film is formed of a stretched film made of a polymer film. As the liquid crystal layer, a material in which a main material is nematic liquid crystal having positive or negative dielectric anisotropy and a chiral material is added thereto can be used. As an alignment method of the liquid crystal display element, for example, an STN (super twisted nematic) method, a TN (twisted nematic) method, a VA (vertical alignment) method, an IPS (in-plane switching) method, an OCB (optically compensated bend) method. The present invention can be used in any of them. In particular, among them, a VA (vertical alignment) method with low black luminance and high contrast can be suitably used in the present invention. In addition, the liquid crystal display element may be a reflective liquid crystal display element, a transmissive liquid crystal display element, a transflective liquid crystal display element, or the like, and the present invention can be used in any of them. Among these, a transmissive and transflective liquid crystal display element using a backlight can give a good effect in the present invention.

  The present invention provides a substrate having electrodes in a liquid crystal display element, where the thermal conductivity of the substrate is A (W / m · K), and the electrode substrate surface or the side surface of the electrode substrate has a thermal conductivity B (W / W m · K), and the thermal conductivity relationship is A> B. This is the other surface that does not have the electrode layer of the electrode substrate in which the liquid crystal display element of the present invention is sandwiched between the liquid crystal layers of the liquid crystal display element, and is not in contact with the polarizing plate or the retardation film The surface portion and / or the side surface of the electrode substrate is covered with a material made of thermal conductivity B, and the substrate portion other than the electrode of the electrode substrate is made of a material made of thermal conductivity A and is thermally conductive. The rate A indicates a configuration that is greater than the thermal conductivity B. Generally, this electrode substrate is made of glass, and the thickness is about 0.2 to 1.0 mm for one sheet and 0.4 to 2.0 mm for two sheets. On the surface of the electrode substrate on which an image is displayed, one or more retardation films or polarizing plates are installed via an adhesive and are not exposed to air. However, the side surface of the substrate is usually not processed at all, and the current state is that the glass surface is in direct contact with air.

  Therefore, when a certain amount of heat is constantly given, the surface sandwiched between the retardation film and the polarizing plate (surface corresponding to the image display portion of the electrode substrate) and the surface where the glass surface is exposed (electrode substrate) In this case, since there is a difference in the amount of heat released, there is temperature unevenness (temperature distribution) in the entire surface of the glass substrate. Here, since the glass expands and contracts in volume due to a difference in temperature, this temperature unevenness directly causes stress strain generated in the plane of the glass. The stress strain indicates that a force is constantly applied to the glass, and therefore a phase difference is generated inside the glass. When a polarizer having a phase difference is placed between the polarizing plates arranged in crossed Nicols and having a black state, the polarization state of light transmitted between the polarizing plates is It changes, and light is transmitted through the polarizing plate arranged in crossed Nicols. When this phenomenon occurs in a glass substrate of a liquid crystal display element, it appears as a result of a reduction in image quality. In other words, in a liquid crystal display element, heat radiation from the side surface of the electrode substrate is large. Therefore, in the configuration of the current liquid crystal display element, when heat radiation from the backlight or the electronic substrate occurs, the image quality is increased with the passage of time. Decreases with the stress and strain generated. In order to suppress this, it is necessary to suppress the temperature distribution in the surface of the electrode substrate by implementing the state of the electrode substrate covered with the retardation film and the polarizing plate also on the side surface of the substrate. At this time, the thermal conductivity of the substrate is generally glass, and is 0.6 to 1.1 (W / m · K). On the other hand, the thermal conductivity of the laminate of the retardation film and the polarizing plate installed via the adhesive is about 0.2 (W / m · K), and the thermal conductivity with respect to the surface of the glass substrate. The material with low is installed, and it has the structure which suppresses the diffusion of heat. However, the side surface of the electrode substrate is in a state where the glass substrate surface is exposed, and the heat diffusion is larger than the surface on which the polarizing plate is installed, causing a temperature distribution in the glass surface. Cause. Therefore, the surface of the electrode substrate is not exposed to the air, that is, in the electrode substrate of the liquid crystal display element, when the thermal conductivity of the substrate is A (W / m · K), The side surface is covered with a material having thermal conductivity B (W / m · K), and the relationship of thermal conductivity is A> B, preferably AB> 0.1 (W / m · K), more preferably Is preferably A−B> 0.2 (W / m · K), so that excessive heat radiation from the side surface can be suppressed, so that deterioration in image quality can be suppressed.

  As a method for suppressing contact of the electrode substrate (mainly the side surface of the electrode substrate) with air (sometimes referred to as a sealing method), for example, a retardation film and a polarizing plate using an adhesive, and an image display surface of the electrode substrate Similarly, it is considered preferable to cover all surfaces of the electrode substrate and seal the electrode substrate surface. However, on the side surface of the electrode substrate, since the shape of the portion in contact with air is small, the sealing method in which the retardation film and the polarizing plate are used with an adhesive is difficult to process, and sufficient exposure suppression is performed. May be difficult. On the other hand, it is considered that sealing (coating) with a material containing a polymer, for example, a polymer resin itself is simple from the viewpoint of processing. Examples of the polymer resin include a thermoplastic polymer, a curable resin, and the like. However, if the polymer resin does not have an excessive thermal conductivity, it has adhesion to a glass substrate. Any one can be used as long as it is possible. Further, from the viewpoint of workability, a resin that is liquid when sealing and is cured through a crosslinking reaction or the like after being left standing or by applying external excitation energy is preferable. Any resin that is used for adhesives and glues may be used as a material that cures after being left standing. In addition, a crosslinkable curable resin is a resin that is cured through a crosslinking reaction or the like by external excitation energy. Cross-linked resins and the like can be mentioned, but any of them may be used.

  Typical examples of the actinic radiation curable resin include ultraviolet curable resins. Examples thereof include ultraviolet curable polyester acrylate resins, ultraviolet curable acrylic urethane resins, ultraviolet curable methacrylate resins, and ultraviolet curable resins. Type polyester acrylate resin and ultraviolet curable polyol acrylate resin. In particular, UV curable polyol acrylate resins are preferable, such as trimethylolpropane triacrylate, ditrimethylolpropane tetraacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, dipentaerythritol pentaacrylate, dipentaerythritol hexaacrylate, alkyl-modified diester. Photopolymerizable monomer oligomers such as pentaerythritol pentaerythritol are preferred. These polyol acrylate resins have advantages such as high crosslinkability and high curability, high hardness, small cure shrinkage, low odor and low toxicity, and relatively high safety.

  Examples of the electron beam curable resin preferably include those having an acrylate-based functional group, such as a relatively low molecular weight polyester resin, polyether resin, acrylic resin, epoxy resin, urethane resin, alkyd resin, spiroacetal resin. , Polybutadiene resin, polythiol polyene resin and the like.

Examples of the thermosetting resin include, for example, an epoxy resin, a phenoxy resin, a phenoxy ether resin, a phenoxy ester resin, an acrylic resin, a melamine resin, a phenol resin, and a urethane resin, or a mixture thereof. Among these, an epoxy resin, a phenoxy resin, a phenoxy ether resin, and a phenoxy ester resin-containing composition are preferable.
The thickness of the portion covered with the polymer material is, for example, 50 μm to 10 mm.

Further, as another embodiment of the present invention, the same effect can be expected even when a heat insulating material such as foamed polystyrene or sponge is installed with an adhesive as a sealing method for the portion of the electrode substrate exposed to the air. Therefore, materials corresponding to these can be preferably used.
The thickness of the heat insulating material is, for example, 50 μm to 10 mm.

Furthermore, as another embodiment of the present invention, a material in which an adhesive such as a commercially available vinyl tape, gum tape, cellophane tape, and mending tape and a thermoplastic polymer film are integrated is used as a liquid crystal display element. Since the effect of suppressing heat dissipation from the side surface of the glass substrate can be obtained by using the electrode substrate of the electrode substrate exposed to air, a tape combining any thermoplastic polymer film and an adhesive is used as the sealing material. You may use.
The thickness of the tape is, for example, 50 to 500 μm.

  In the present invention, the electrode substrate surface of the liquid crystal display element is configured such that the surface and side surfaces of the electrode substrate are not exposed to the air, thereby suppressing uneven heat dissipation from a part from the electrode substrate, and the stress generated in the electrode substrate. Distortion or the phase difference generated thereby can be suppressed, and the display quality can be kept high.

Examples of the present invention are shown below, but the present invention is not limited to these examples.
The thermal conductivity was measured by a heat flow meter method (based on JIS-A1412, ASTM-C518, ISO8301), and measured using Eihiro Seiki Co., Ltd. thermal conductivity measuring device HC-110.

[Creation of liquid crystal cell]
1% by weight of octadecyldimethylammonium chloride (coupling agent) was added to a 3% by weight aqueous solution of polyvinyl alcohol. This was spin-coated on a glass substrate (55 mm × 46 mm × 0.6 mm) with an ITO electrode, heat-treated at 160 ° C., and then rubbed to form a vertical alignment film. The rubbing treatment was performed so that the two glass substrates were in opposite directions. Two glass substrates were faced to each other so that the cell gap (d) was 5.5 μm. A liquid crystal compound (Δn: 0.05) mainly composed of ester and ethane was injected into the cell gap to prepare a vertical alignment liquid crystal cell (VA cell). The product of Δn and d was 275 nm.

[Creation of liquid crystal display element]
Two sheets of the VA cell were arranged using an adhesive so that the retardation film sandwiched the cell. Furthermore, a polarizing plate was disposed on both sides using a pressure sensitive adhesive in crossed nicols, thereby producing a liquid crystal display element. A voltage was applied to the liquid crystal display element with a 55 Hz short wave, and the liquid crystal display element was driven with a black display of 2V.

[Evaluation of liquid crystal display elements]
A backlight having a surface luminance of 200 cd / m ² was installed on one side of the liquid crystal display element, and continuous lighting was performed for 30 minutes. At that time, the display screen was black, and the uniformity of the in-plane black state in the liquid crystal display element immediately after lighting was compared with the state after 30 minutes. Evaluation is good if the display quality of the liquid crystal display element does not change. Good: Judged as ◯, unable to maintain the black state, and the brightness of part of the display area or specific area increased. Deterioration: judged as x.

[Example 1]
A liquid crystal display element having a VA cell prepared by the above method was used. Retardation film of electrode substrate of liquid crystal display element, side part not covered with polarizing plate, two-component curable epoxy resin adhesive, Konishi Bond “Bond Quick 5” (synthetic resin (100%) epoxy resin , Polyol, and tertiary amine as a composition) were applied and cured, and the portion of the liquid crystal display element in contact with air on the electrode substrate was covered with a thickness of about 1 mm. At this time, the thermal conductivity of the epoxy resin was 0.2 (W / m · K). On the other hand, the thermal conductivity of the glass substrate is 0.6 (W / m · K), which satisfies the relationship of thermal conductivity A> B in the claims. Thereafter, the liquid crystal display element was driven, and a backlight was installed in a state where black display was performed, and the liquid crystal display element was evaluated. Before and after continuous lighting of the backlight, the display quality of the liquid crystal display element in the black state did not change, and good display quality was maintained.

[Example 2]
A liquid crystal display element having a VA cell equivalent to that in Example 1 was used. The side surface part of the electrode substrate of the liquid crystal display element is completely covered with the adhesive vinyl tape for electrical insulation and VINI-TAPE (Toyo Chemical Co., Ltd.) on the side part not covered with the polarizing plate. Affixed and sealed in the state. At this time, the thermal conductivity of the vinyl tape was 0.3 (W / m · K). On the other hand, the thermal conductivity of the glass substrate is 0.6 (W / m · K), which satisfies the relationship of thermal conductivity A> B. Here, the liquid crystal display element was driven and the backlight was installed in a state where black display was performed, and the liquid crystal display element was evaluated. Before and after continuous lighting of the backlight, the display quality of the liquid crystal display element in the black state did not change, and good display quality was maintained.

[Comparative Example 1]
A liquid crystal display element having a VA cell equivalent to that in Example 1 was used. The liquid crystal display element was not processed at all except that a retardation film and a polarizing plate were installed on the electrode substrate. At this time, the liquid crystal display element was driven, and a backlight was installed in a state where black display was performed, and the liquid crystal display element was evaluated. Immediately after the backlight is lit, the black display quality of the liquid crystal display element was good, but after 30 minutes of continuous lighting, oval luminance dropouts were observed at the four corners of the liquid crystal display element to maintain the display quality. I couldn't.

[Comparative Example 2]
A liquid crystal display element having a VA cell equivalent to that in Example 1 was used. A graphite sheet and Matsushita Electronic Parts Co., Ltd. were placed with an adhesive on the side surface portion of the electrode substrate of the liquid crystal display element that was not covered with the retardation film and polarizing plate. At this time, the surface direction thermal conductivity of the graphite sheet (thickness 0.5 mm) was 300 (W / m · K), and the thickness direction thermal conductivity 15 (W / m · K). On the other hand, the thermal conductivity of the glass substrate is 0.6 (W / m · K), and the relationship of thermal conductivity A <B described in the claims is established. Here, the liquid crystal display element was driven and the backlight was installed in a state where black display was performed, and the liquid crystal display element was evaluated. Immediately after the backlight is turned on, the black display quality of the liquid crystal display element was good, but after 30 minutes of continuous lighting, a lack of brightness was observed in a part of the liquid crystal display element, and the display quality could not be maintained. It was.

  The present invention relates to a liquid crystal display (LCD), particularly a liquid crystal display LCD which is a transmissive or transflective LCD requiring a backlight, a liquid crystal display LCD for notebook computers, a mobile terminal LCD, and a mobile phone LCD. Useful for devices.

Claims (3)

  A liquid crystal layer is sandwiched between a pair of polarizing plates, one or more retardation films, and two electrode substrates having an electrode layer on one surface of the substrate so that the electrode layers face each other. Alternatively, a liquid crystal display element capable of adjusting light transmission and absorption by switching and switching between a bright state and a dark state, and when the thermal conductivity of the substrate is A (W / m · K), It is the other surface which does not have the electrode layer of an electrode substrate, and is the material whose surface part which is not in contact with a polarizing plate or retardation film, and / or the side surface of this electrode substrate is thermal conductivity B (W / m * K). A liquid crystal display element which is covered and has a relationship of thermal conductivity satisfying A> B.   The liquid crystal display element according to claim 1, wherein a surface portion not in contact with the polarizing plate or the retardation film and / or a side surface of the electrode substrate is coated with a material containing a polymer. The liquid crystal display element according to claim 2, wherein a surface portion that is not in contact with the polarizing plate or the retardation film and / or a side surface of the electrode substrate is covered with a heat insulating material.