JP2012108252A - Liquid crystal display element and manufacturing method for the same - Google Patents

Abstract

A liquid crystal display element using a high-contrast polymer ferroelectric liquid crystal and a method for manufacturing the same are obtained.
A first substrate and a second substrate facing each other, and a first alignment film and a second alignment film formed on each facing surface of the first substrate and the second substrate, respectively, and subjected to an alignment treatment by a rubbing method, The liquid crystal material including a polymer ferroelectric liquid crystal is sealed between the first substrate on which the first alignment film is formed and the second substrate on which the second alignment film is formed. And a rubbing direction of the first substrate and the second substrate is not parallel. With respect to the first substrate and the second substrate, the respective rubbing axes are provided in opposite directions of the twist of the liquid crystal and are line symmetric.
[Selection] Figure 1

Description

  The present invention relates to a liquid crystal display element using a polymer ferroelectric liquid crystal as a liquid crystal material and a method for manufacturing the same.

  In recent years, liquid crystal display elements have been put into practical use and widely used as light-weight, thin, and low-power-consumption video display elements. It is no exaggeration to say that almost all general liquid crystal display elements in practical use are liquid crystal display elements using nematic liquid crystals.

  A liquid crystal display element using nematic liquid crystal is formed on two substrates facing each other, transparent electrodes formed on opposite surfaces of the respective substrates, and transparent electrodes on the respective substrates. And a liquid crystal layer made of nematic liquid crystal injected between the substrates.

  TN (Twisted Nematic), ECB (Electrically Controlled Birefringence), STN (Super Twisted Nematic), IPS (In-Plane Switching) and VA (Virtual Alignment LCD) However, a liquid crystal display element using a nematic liquid crystal can perform continuous tone display, but does not have bistability (memory property) in principle.

  In addition, a liquid crystal display element using a nematic liquid crystal has high alignment uniformity, so that high contrast can be realized. In order to align the nematic liquid crystal, an alignment film that has been subjected to an alignment treatment by a rubbing method, that is, a rubbing method can be applied. On the other hand, a liquid crystal display element using nematic liquid crystal can realize a response speed applicable to a home television (moving video response), but considering the principle of nematic liquid crystal, it has a high response speed of less than 1 ms. It is not easy to respond to the change.

  Accordingly, in order to improve the response speed of the liquid crystal display element, a surface stabilized liquid crystal display (SS-FLC) mode liquid crystal display element using a low molecular ferroelectric liquid crystal instead of a nematic liquid crystal is proposed. Has been. An SS-FLC mode liquid crystal display element using a low molecular ferroelectric liquid crystal has a structure in which the nematic liquid crystal in the liquid crystal layer is replaced with a low molecular ferroelectric liquid crystal.

  The SS-FLC mode liquid crystal display element using low-molecular ferroelectric liquid crystal can improve the response speed compared with the liquid crystal display element using nematic liquid crystal, but has bistability in principle. It is not possible to simply perform continuous tone display. In order to perform continuous gradation display in an SS-FLC mode liquid crystal display element using low molecular ferroelectric liquid crystal, it is necessary to apply techniques such as area gradation, domain gradation, and frame gradation (for example, There is a problem that the structure becomes complicated and the cost becomes high.

  In addition, the SS-FLC mode liquid crystal display element using low molecular ferroelectric liquid crystal has a lower layer stability than the liquid crystal display element using nematic liquid crystal because the low molecular ferroelectric liquid crystal has a layer structure. To do. In addition, it is difficult to obtain uniform alignment, and the contrast is lowered as compared with a liquid crystal display element using nematic liquid crystal. In order to align the low-molecular ferroelectric liquid crystal, an alignment film that has been subjected to an alignment treatment by a rubbing method, that is, a rubbing method can be applied.

  Also, an HV (Half-V) mode or V mode liquid crystal display element that performs continuous tone display at the expense of bistability of an SS-FLC mode liquid crystal display element using a low-molecular ferroelectric liquid crystal. Has been proposed (see, for example, Patent Document 2). The HV mode and V mode liquid crystal display elements using the low-molecular ferroelectric liquid crystal aim at a high-speed response version of the liquid crystal display element using the nematic liquid crystal.

  The HV mode and V mode liquid crystal display elements using low-molecular ferroelectric liquid crystal can improve the response speed as compared with the liquid crystal display elements using nematic liquid crystal. In addition, HV mode and V mode liquid crystal display elements using low-molecular ferroelectric liquid crystal perform continuous tone display at the expense of bistability.

  In addition, the HV mode and V mode liquid crystal display elements using low molecular ferroelectric liquid crystal have a layered structure of the low molecular ferroelectric liquid crystal, so that the alignment stability is stable compared to the liquid crystal display element using nematic liquid crystal. Sex is reduced. In addition, it is difficult to obtain uniform alignment, and the contrast is lowered as compared with a liquid crystal display element using nematic liquid crystal. In order to align the low-molecular ferroelectric liquid crystal, an alignment film that has been subjected to an alignment treatment by a rubbing method, that is, a rubbing method can be applied.

  In order to improve the alignment stability of SS-FLC mode liquid crystal display elements using low-molecular ferroelectric liquid crystals, SS-FLC mode liquid crystal display elements using polymer ferroelectric liquid crystals have been proposed. (For example, see Patent Documents 3 to 7).

  An SS-FLC mode liquid crystal display element using a polymer ferroelectric liquid crystal is composed of two substrates facing each other, transparent electrodes formed on opposing surfaces of each substrate, and a high-potential injected between the substrates. A liquid crystal layer formed of molecular ferroelectric liquid crystal. Here, the liquid crystal layer is subjected to an alignment treatment by a shearing method (displacement method) in which a polymer ferroelectric liquid crystal is aligned by applying a shear stress to the substrate while applying a voltage between the substrates.

  The SS-FLC mode liquid crystal display element using polymer ferroelectric liquid crystal can achieve the same response speed as the liquid crystal display element using nematic liquid crystal, but has a large molecular weight and high viscosity. The response speed is slower than that of a liquid crystal display element using a conductive liquid crystal. In addition, an SS-FLC mode liquid crystal display element using a polymer ferroelectric liquid crystal has bistability in principle, and therefore cannot simply perform continuous gradation display, but performs continuous gradation display. It is necessary to apply the above-described techniques such as area gradation, domain gradation, and frame gradation. In this case, there is a problem that the structure becomes complicated and the cost becomes high.

  In addition, the SS-FLC mode liquid crystal display element using the polymer ferroelectric liquid crystal has a lower alignment stability than the liquid crystal display element using the nematic liquid crystal because the polymer ferroelectric liquid crystal has a layer structure. However, since the molecular weight is large, the alignment stability is higher than that of a liquid crystal display device using a low molecular ferroelectric liquid crystal. Further, since the polymer ferroelectric liquid crystal has a layer structure and it is difficult to obtain uniform alignment, it is not possible to obtain contrast as high as that of a liquid crystal display element using nematic liquid crystal. In addition, since the molecular weight is large, it is difficult to obtain uniform alignment by the rubbing method, and the alignment treatment is performed by a shearing method (slip method) having a complicated process.

  In addition, the above-described conventional liquid crystal display element using nematic liquid crystal, liquid crystal display element using low molecular ferroelectric liquid crystal (SS-FLC mode, HV mode, V mode), and polymer ferroelectric liquid crystal are used. Any of the liquid crystal display elements (SS-FLC (shearing method)) has a continuous gradation memory property that maintains (memory) the gradation state when the voltage is turned off while performing continuous gradation display. I don't have it.

  The relationship (potential curve) between the orientation angle (the orientation angle changes with voltage application) and the potential in a liquid crystal display element capable of continuous tone display (for example, nematic liquid crystal, HV mode, V mode) It is strongly influenced by the orientation treatment by the rubbing method.

  In an SS-FLC mode liquid crystal display element using a low-molecular ferroelectric liquid crystal or a polymer ferroelectric liquid crystal having bistability, liquid crystal molecules move to a bistable position when a voltage is applied. Based on the relationship between the orientation angle and the potential in SS-FLC mode using low-molecular ferroelectric liquid crystal or polymer ferroelectric liquid crystal, the principle of conventional liquid crystal display elements is to memorize the gradation state with intermediate gradation. I can't.

  For this reason, the conventional liquid crystal display element has a problem that, when the voltage is turned off while performing continuous gradation display, the continuous gradation memory property that retains (memory) the gradation state cannot be realized. there were. Therefore, it has been proposed to realize continuous tone memory performance by applying domain tones (see, for example, Non-Patent Document 1).

  In view of such a point, the applicant of the present invention is capable of continuous gradation display while having display characteristics equivalent to those of a liquid crystal display element using a nematic liquid crystal that has been widely used, and is capable of continuous display. A liquid crystal display element capable of realizing gradation memory properties has already been proposed. This includes a polymer ferroelectric liquid crystal as a liquid crystal material sealed between both opposing substrates.

Japanese Patent Laid-Open No. Sho 62-131225 JP 2004-86116 A JP-A-56-107216 JP-A-2-240192 JP-A-2-271326 Japanese Patent Laid-Open No. 3-42622 JP-A-6-281966

Hideo Fujikake et al, “Polymer-Stabilized Ferroelectric Liquid Crystal Devices with Grayscale Memory”, Jpn. J. et al. Appl. Phys, Vol. 36, pp. 6449-6454, 1997

  However, a ferroelectric liquid crystal composed of a polymer ferroelectric liquid crystal as a liquid crystal material sealed between both opposing substrates has a contrast of liquid crystal molecules as compared with a TN or IPS liquid crystal panel. Inferior.

  Further, since the ferroelectric liquid crystal has a layer structure, it is difficult to align the liquid crystal molecules in one direction, and it is difficult to obtain uniform alignment. For this reason, there is much light leakage during black display, and it is difficult to improve contrast.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to obtain a liquid crystal display element using a high-contrast polymer ferroelectric liquid crystal and a method for manufacturing the same.

  The liquid crystal display element according to the present invention includes a first substrate and a second substrate facing each other, a first alignment film formed on each of the opposing surfaces of the first substrate and the second substrate, and subjected to an alignment treatment by a rubbing method, A liquid crystal material containing a polymer ferroelectric liquid crystal is enclosed between a second alignment film, the first substrate on which the first alignment film is formed, and the second substrate on which the second alignment film is formed. The rubbing directions of the first substrate and the second substrate are not parallel to each other.

  In the method for manufacturing a liquid crystal display element according to the present invention, the first alignment film and the second alignment film that are aligned by the rubbing method are respectively formed on the opposing surfaces of the first substrate and the second substrate facing each other. A liquid crystal material containing a polymer ferroelectric liquid crystal is sealed between the alignment film forming step and the first substrate on which the first alignment film is formed and the second substrate on which the second alignment film is formed. And a liquid crystal layer forming step of forming a liquid crystal layer, wherein the rubbing directions of the first substrate and the second substrate are not parallel.

  According to the present invention, the rubbing directions of the first substrate and the second substrate are not parallel but cross rubbing, so that the twist is eliminated and the contrast is improved.

It is sectional drawing which shows the structure of the liquid crystal display element which concerns on Embodiment 1 of this invention. It is explanatory drawing at the time of forming the 1st orientation film 5 and the 2nd orientation film 6 by giving an upper and lower board | substrate an angle and carrying out cross rubbing. It is explanatory drawing when the twist in a Twist state is eliminated by carrying out cross rubbing, it will be in a Uniform state, and a contrast will rise. It is a figure which shows the experimental result of a rubbing angle and contrast.

  Hereinafter, preferred embodiments of a liquid crystal display device according to the present invention will be described with reference to the drawings.

Embodiment 1 FIG.
1 is a cross-sectional view showing a configuration of a liquid crystal display element according to Embodiment 1 of the present invention.
In FIG. 1, this liquid crystal display element includes a first substrate 1, a second substrate 2, a first transparent electrode 3, a second transparent electrode 4, a first alignment film 5, a second alignment film 6, a liquid crystal layer 7, and a sealing material. 8 is provided.

  The first substrate 1 and the second substrate 2 facing each other are each a glass substrate, and the liquid crystal layer 7 is made of a liquid crystal material containing a polymer ferroelectric liquid crystal between the first substrate 1 and the second substrate 2. It is enclosed and formed. Here, the liquid crystal material is a polymer ferroelectric liquid crystal or a mixture of a polymer ferroelectric liquid crystal and a low molecular liquid crystal. Light from a backlight (not shown) that is provided on the opposite side of the first substrate 1 from the liquid crystal layer 7 and functions as a light source is incident on the first substrate 1.

  The first transparent electrode 3 is formed on the surface of the first substrate 1 that faces the second substrate 2. The second transparent electrode 4 is formed on the surface of the second substrate 2 facing the first substrate 1. The first transparent electrode 3 and the second transparent electrode 4 constitute a pixel electrode and a counter electrode, respectively, and generate an electric field in the vertical direction with respect to the first substrate 1 and the second substrate 2.

  The first alignment film 5 is formed on the first transparent electrode 3 of the first substrate 1 and is subjected to an alignment process by a rubbing method. The second alignment film 6 is formed on the second transparent electrode 4 of the second substrate 2 and is subjected to an alignment process by a rubbing method.

Next, a manufacturing procedure of the liquid crystal display element according to the first embodiment of the present invention will be described.
First, the first transparent electrode 3 and the TFT (Thin Film Transistor, not shown) are formed on the first substrate 1 using a sputtering method or the like. In addition, a color filter (not shown) is attached to the second substrate 2 and the second transparent electrode 4 is formed on the color filter.

  Subsequently, after the first substrate 1 and the second substrate 2 are washed, polyimide is used as an alignment film on the first transparent electrode 3 and the TFT of the first substrate 1 and on the second transparent electrode 4 of the second substrate 2. (RN1199A: manufactured by Nissan Chemical Industries, Ltd.) is applied. This polyimide was spin-coated on a substrate with a transparent electrode to a thickness of 1000 mm.

  Next, pre-bake treatment and main cure treatment are performed on the first substrate 1 and the second substrate 2 coated with polyimide, and then firing is performed in a nitrogen atmosphere or an air atmosphere at a firing temperature ranging from 230 ° C. to 350 ° C. for 30 minutes. Then, an alignment process is performed by a rubbing method, and the first and second alignment films 5 and 6 are formed by cross-rubbing the upper and lower substrates with an angle as shown in FIG.

  As a result, as shown in FIG. 3, the twist in the Twist state is eliminated by performing the cross rubbing, the Uniform state is obtained, and the contrast is increased.

  Subsequently, after cleaning the first substrate 1 and the second substrate 2, a sealing material is applied to the periphery of the first substrate 1, and the first substrate 1 and the second substrate 2 are bonded together. Next, a liquid crystal material in which a high-molecular ferroelectric liquid crystal represented by the following chemical formula and a low-molecular liquid crystal are mixed is injected and sealed between the bonded first substrate 1 and second substrate 2. Then, the liquid crystal layer 7 is formed through an annealing process. Here, the reason why the high-molecular ferroelectric liquid crystal and the low-molecular liquid crystal are mixed is to reduce the viscosity of the liquid crystal material to improve the response speed and widen the operable temperature range. At this time, the liquid crystal material may be only a polymer ferroelectric liquid crystal.

  Instead of injecting a liquid crystal material between the first substrate 1 and the second substrate 2 that are bonded, a first sealant 8 is applied before the first substrate 1 and the second substrate 2 are bonded. A liquid crystal material may be dropped on one substrate 1. The liquid crystal filling time can be shortened by dropping the liquid crystal material.

  Subsequently, the liquid crystal display element on which the liquid crystal layer 7 is formed is subjected to an aging treatment (electric field application treatment) in which a voltage of AC 75 V is applied and the frequency is 62.5 Hz and the ISO temperature is rapidly cooled to room temperature. Is oriented in any bistable position. At this time, the temperature gradient is set to 10 ° C./min. Thus, by performing the electric field application process based on a predetermined temperature drop gradient, a special alignment process for the polymer ferroelectric liquid crystal becomes unnecessary.

  As described above, in the SS-FLC mode liquid crystal display element using the conventional polymer ferroelectric liquid crystal, during the aging, a high stress is applied to the liquid crystal display element by applying a shear stress while applying a voltage. Although a complicated process of aligning the dielectric liquid crystal is necessary, the liquid crystal display element according to Embodiment 1 of the present invention does not need this.

  A polarizing plate was attached to the panel thus produced, and the contrast was measured. The contrast is given by the brightness when displaying white / the brightness when displaying black.

  Table 1 and FIG. 4 show the experimental results of the rubbing angle and contrast. From this experimental result, it is understood that the contrast becomes approximately 100 or more when the rubbing angle of the upper substrate is in the range of 0 ° to 7 °, which is favorable. At this time, the rubbing axis of the lower substrate is axisymmetric to the upper substrate in the direction opposite to the twist of the liquid crystal, and the rubbing angle is in the range of 0 ° to −7 °. In Table 1, B represents black, W represents white, and CR represents contrast (W / B).

  As described above, rubbing is performed on the upper and lower substrates at different angles to bring the spontaneous polarization into a uniform state that matches the entire upper and lower substrates, thereby widening the viewing angle without problems such as unevenness and defects, and significantly increasing the contrast. I can do it.

  DESCRIPTION OF SYMBOLS 1 1st board | substrate, 2nd board | substrate, 3rd 1st transparent electrode, 4th 2nd transparent electrode, 5 1st alignment film, 6 2nd alignment film, 7 Liquid crystal layer, 8 Seal material.

Claims (10)

A first substrate and a second substrate facing each other;
A first alignment film and a second alignment film, which are formed on the opposing surfaces of the first substrate and the second substrate, respectively, and subjected to alignment treatment by a rubbing method;
A liquid crystal formed by sealing a liquid crystal material including a polymer ferroelectric liquid crystal between the first substrate on which the first alignment film is formed and the second substrate on which the second alignment film is formed. With layers,
The liquid crystal display element, wherein the rubbing directions of the first substrate and the second substrate are not parallel. The liquid crystal display element according to claim 1,
A liquid crystal display element, wherein the rubbing axes of the first substrate and the second substrate are provided in directions opposite to the twist of the liquid crystal. The liquid crystal display element according to claim 1 or 2,
A liquid crystal display element, wherein the rubbing axes are axisymmetric with respect to the first substrate and the second substrate. The liquid crystal display element according to any one of claims 1 to 3,
The liquid crystal display element, wherein the liquid crystal material is only the polymer ferroelectric liquid crystal. The liquid crystal display element according to any one of claims 1 to 3,
The liquid crystal display element, wherein the liquid crystal material is a mixture of the polymer ferroelectric liquid crystal and a low molecular liquid crystal. An alignment film forming step of forming a first alignment film and a second alignment film, each of which is aligned by a rubbing method, on each facing surface of the first substrate and the second substrate facing each other;
A liquid crystal material including a polymer ferroelectric liquid crystal is sealed between the first substrate on which the first alignment film is formed and the second substrate on which the second alignment film is formed to form a liquid crystal layer. A liquid crystal layer forming step,
The method for manufacturing a liquid crystal display element, wherein the rubbing directions of the first substrate and the second substrate are not parallel. In the manufacturing method of the liquid crystal display element of Claim 6,
A method for manufacturing a liquid crystal display element, characterized in that the rubbing axes of the first substrate and the second substrate are provided in directions opposite to the twist of the liquid crystal. In the manufacturing method of the liquid crystal display element of Claim 6 or 7,
A method of manufacturing a liquid crystal display element, wherein the rubbing axes are axisymmetric with respect to the first substrate and the second substrate. In the manufacturing method of the liquid crystal display element of any one of Claim 6-8,
The method of manufacturing a liquid crystal display element, wherein the liquid crystal material is only the polymer ferroelectric liquid crystal. In the manufacturing method of the liquid crystal display element of any one of Claim 6-8,
The method for producing a liquid crystal display element, wherein the liquid crystal material is a mixture of the high-molecular ferroelectric liquid crystal and the low-molecular liquid crystal.

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