JP2013195903A - Liquid crystal display element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal display element having high display quality.SOLUTION: The liquid crystal display element comprises: a first substrate including a first electrode and subjected to alignment treatment; a second substrate including a second electrode, and subjected to alignment treatment; a liquid crystal layer to be twist-aligned, arranged between the first and the second substrates, and including a chiral agent. In the case where the liquid crystal layer does not contain the chiral agent, when a turning direction of twisting liquid crystal molecules is defined as a first turning direction, the chiral agent applies to the liquid crystal layer a turning performance toward a second turning direction opposite to the first turning direction. An electric field in a thickness direction of the liquid crystal layer can be generated by applying a voltage to the first electrode and the second electrode. At least one of the first substrate and the second substrate is provided with an electrode that can generate an electric field in a direction orthogonal to the thickness direction of the liquid crystal layer by applying a voltage. The alignment treatment and the addition of the chiral agent are performed so that liquid crystal molecules of the liquid crystal layer mutually transition between a focal conic alignment state and a reverse twist alignment state by a direction of applying an electric field to the liquid crystal layer.

Description

  The present invention relates to a liquid crystal display element, and more particularly to a liquid crystal display element containing an optically active substance (chiral agent) in a liquid crystal layer.

  The twist direction (first rotation direction) of the liquid crystal molecules determined by the combination of the alignment treatment direction and the pretilt angle of the pair of alignment films is opposite to the twist direction (second rotation direction) of the liquid crystal molecules induced by the chiral agent. For example, by applying a physical action to the liquid crystal layer so that the liquid crystal molecules are twisted in each direction (reverse twist arrangement state for the first turning direction, and for the second turning direction). A liquid crystal display element in which a spray twist arrangement state can be realized in a commutative manner is referred to as a reverse twisted nematic (RTN) type liquid crystal display element. The first turning direction is a turning direction in which liquid crystal molecules are twisted when no chiral agent is added to the liquid crystal layer.

  For example, Patent Document 1 describes a reverse twisted nematic liquid crystal display element. In the reverse twisted nematic liquid crystal display element described in Patent Document 1, the alignment state in which the liquid crystal molecules are twisted in the first turning direction is unstable. Although it is possible to obtain an alignment state that is twisted in the first rotation direction by applying a high voltage, the liquid crystal molecules transition to an alignment state that is twisted in the second rotation direction as time passes.

  While adding a chiral agent that rotates the liquid crystal molecules in the second rotation direction, the liquid crystal molecules are aligned in the first rotation direction by combining the alignment directions of the substrates, thereby increasing the strain in the liquid crystal layer and driving voltage. Patent Document 2 discloses an invention of a reverse twisted nematic liquid crystal element that can significantly reduce the above. However, in the invention described in Patent Document 2, the application of the voltage for changing from the arrangement state twisted in the second turning direction to the arrangement state twisted in the first turning direction is stopped, and after a few seconds, the original arrangement state Since the transition is made again to (the arrangement state twisted in the second turning direction), there is a problem that a high driving voltage is required when driving the liquid crystal element in the arrangement state twisting in the second turning direction.

  In a reverse twisted nematic liquid crystal display element, generally, liquid crystal molecules are arranged in an arrangement state in which the liquid crystal molecules are twisted in the first turning direction (reverse twist arrangement state) and in an arrangement state in which the liquid crystal molecules are twisted in the second turning direction (spray twist arrangement state). There is no big difference in the display state on the appearance, and there is a problem that it is difficult to obtain a high contrast ratio (difference in transmittance) even if bistability is given.

  A chiral agent that has an alignment treatment so that the angle formed between the upper and lower substrates in the rubbing direction is greater than 90 ° and less than 120 °, and the liquid crystal layer is twisted so as to be in the same direction as the angle formed in the rubbing direction. Patent Document 3 discloses an invention of a reverse twisted nematic liquid crystal display element characterized in that is added. The reverse twisted nematic liquid crystal display element described in Patent Document 3 is superior in sharpness at any temperature as compared with a normal twisted nematic liquid crystal display element. Further, due to the good sharpness, particularly in a simple matrix drive liquid crystal display element, it has a feature that it can be driven with high duty or has high contrast when driven with the same duty. Furthermore, the response at low temperature is faster than that of a normal twisted nematic liquid crystal display device, the transmittance during off-voltage does not decrease even in a high temperature environment, and a bright display can be realized. Advantages of both liquid crystal display elements using thin film transistors.

  The liquid crystal display element described in Patent Document 3 is very stable in the reverse twist alignment state and has superior electro-optical characteristics in that state than a normal twisted nematic liquid crystal display element. However, it is not an invention that positively utilizes the bistability of the reverse twist array state and the spray twist array state.

  Patent Document 4 discloses an invention of a reverse twisted nematic liquid crystal display element having a relatively low pretilt angle of 20 ° or more and 45 ° or less made by the present inventors. In this liquid crystal display element, when the chiral pitch is p and the thickness of the liquid crystal layer is d, a relatively small amount of chiral agent is added so that, for example, d / p is more than 0.04 and less than 0.25. ing.

  The liquid crystal display element described in Patent Document 4 is a liquid crystal display element with high display quality that realizes a high contrast ratio. However, it cannot be said that the contrast during frontal observation is high. This is an optical characteristic that is relatively preferable when used as a reflective display but is not preferable when used as a transmissive display.

Japanese Patent No. 2510150 JP 2007-293278 A JP 2010-186045 A JP 2011-203547 A

  An object of the present invention is to provide a liquid crystal display element with high display quality.

  According to one aspect of the present invention, a first substrate including a first electrode and subjected to an alignment treatment is disposed opposite to and parallel to the first substrate, and includes a second electrode and includes a second electrode subjected to an alignment treatment. And a liquid crystal layer that is disposed between the first substrate and the second substrate, includes a chiral agent, and is twist-aligned, and the liquid crystal layer does not include the chiral agent. When the swirl direction in which the liquid crystal molecules are twisted is the first swirl direction, the chiral agent gives the liquid crystal molecules in the liquid crystal layer a swirlability in the second swirl direction opposite to the first swirl direction, The liquid crystal layer can generate an electric field in the thickness direction of the liquid crystal layer by applying a voltage to the first electrode and the second electrode, and the first substrate, At least one of the second substrates is directly applied to the thickness direction of the liquid crystal layer by applying a voltage. An electrode capable of generating an electric field in a direction is formed, and an alignment treatment for the first substrate and the second substrate, and addition of a chiral agent to the liquid crystal layer are performed on the liquid crystal layer. There is provided a liquid crystal display element in which the liquid crystal molecules of the liquid crystal layer are changed to each other between a focal conic alignment state and a reverse twist alignment state depending on the direction of an applied electric field.

  According to the present invention, a liquid crystal display element with high display quality can be provided.

FIG. 1 is a flowchart illustrating a method for manufacturing a liquid crystal display device according to an embodiment. 2A and 2B are photographs showing a polarization microscope observation result of a display state of a plurality of manufactured liquid crystal display elements, and FIG. 2C is a schematic diagram showing a liquid crystal molecular arrangement of focal conic alignment. FIG. 3A shows a 0 ° -180 ° azimuth (left-right azimuth) for a liquid crystal display device (liquid crystal display device shown in FIG. 2B) manufactured under conditions where the pretilt angle is about 45 ° and d / p is 0.8. 3B is a graph showing the viewing angle dependency of the liquid crystal display element, and FIG. 3B shows a liquid crystal display device manufactured under the condition that the pretilt angle is about 45 ° and d / p is 0.8 (the liquid crystal display whose display state is shown in FIG. 2B). FIG. 3C is a graph showing the viewing angle-contrast characteristics of the liquid crystal display device according to the embodiment of the inventors' previous invention. FIG. 4 is a graph showing conditions that can realize the bistable state of the reverse twist arrangement state and the focal conic arrangement state. FIG. 5 is a schematic cross-sectional view in one pixel of the liquid crystal display device according to the embodiment. FIG. 6 is a schematic plan view showing a pattern of an ITO film formed on the upper transparent substrate 11a. FIG. 7 is a schematic plan view showing a pattern of an ITO film formed on the lower transparent substrate 11b. FIG. 8 is a schematic plan view showing a photomask used for etching the ITO film. FIG. 9 is a schematic plan view showing a part of a formation region of the lower alignment film 14b formed on the lower substrate 10b. FIG. 10 is a schematic plan view showing the structure of the liquid crystal display device according to the embodiment. 11A to 11C are external appearance photographs of the liquid crystal display device according to the example, and FIGS. 11D to 11F are schematic cross-sectional views showing the electric field direction when a voltage is applied between the electrodes.

  Hereinafter, the twisting force in the direction opposite to the direction in which the liquid crystal molecules tend to twist (the first turning direction) (the second turning direction) due to the orientation treatment (pretilt angle) applied to both the substrates sandwiching the liquid crystal layer ( Examples of twisted nematic liquid crystal display elements to which a chiral agent having chirality is added will be described.

  FIG. 1 is a flowchart illustrating a method for manufacturing a liquid crystal display device according to an embodiment. The inventors of the present application first prepared a plurality of liquid crystal display elements according to the flowchart shown in this figure, and preliminarily considered conditions for realizing good display.

  Two transparent substrates on which transparent electrodes, for example, ITO (indium tin oxide) electrodes are formed, are prepared (step S101). Here, a test cell having parallel plate type electrodes was used, and the two transparent substrates were washed and dried (step S102).

  An alignment film material is applied on the transparent substrate so as to cover the ITO electrode (step S103). The alignment film material was applied by spin coating. You may perform using flexographic printing or inkjet printing. In this example, the side chain density of the polyimide alignment film material that is usually used for forming the vertical alignment film is lowered and used as the alignment film material. This is because the side chain density can be controlled by giving an appropriate pretilt angle. The alignment film material was applied so that the alignment film had a thickness of 500 to 800 mm.

  Temporary baking (step S104) and main baking (step S105) of the transparent substrate coated with the alignment film material are performed. The main baking was performed by changing the baking temperature between 160 ° C and 200 ° C. Thus, an alignment film covering the ITO electrode was formed (steps S103 to S105).

  Next, a rubbing process (orientation process) is performed (step S106). The rubbing process is a process of rotating a cylindrical roll wound with a cloth at a high speed and rubbing on the alignment film, whereby the liquid crystal molecules in contact with the substrate can be aligned (aligned) in one direction. The rubbing treatment was performed under three conditions with the indentation amount being 0.4 mm, 0.8 mm, and 1.2 mm. The rubbing treatment was performed so that the twist angle of the liquid crystal display element was 70 ° or 90 °.

  Subsequently, in order to keep the thickness (inter-substrate distance) of the liquid crystal cell constant, a gap control material is sprayed on one transparent substrate surface by, for example, a dry spraying method (step S107). A plastic ball having a particle diameter of 4 μm was used as the gap control material, and the thickness of the liquid crystal cell was set to 4 μm.

  A sealant is printed on the other transparent substrate surface to form a main seal pattern (step S108). For example, a thermosetting sealing material containing glass fiber having a particle diameter of 4 μm is printed by a screen printing method. A sealing material can also be applied using a dispenser. Further, instead of thermosetting, a photo-curing sealing material or a light / heat combined curing type sealing material may be used.

  The transparent substrates are overlaid (step S109). Two transparent substrates are overlapped at a predetermined position to form a cell, and heat treatment is performed in a pressed state to cure the sealing material. For example, the sealing material is thermally cured using a hot press method. An empty cell is thus produced.

  For example, nematic liquid crystal is injected into the empty cell by vacuum injection (step S110). A chiral agent was added to the liquid crystal. As the chiral agent, CB15 or S-811 manufactured by Merck & Co., Inc. was used. The addition amount of the chiral agent was adjusted such that d / p was 0.5 to 1.2, for example, when the chiral pitch was p and the thickness (cell thickness) of the liquid crystal layer was d.

  The liquid crystal inlet is sealed with, for example, an ultraviolet (UV) curable end seal material (step S111), and the cell is heated to a temperature higher than the phase transition temperature of the liquid crystal in order to adjust the alignment of the liquid crystal molecules (step S112). Then, it breaks along the crack | wound attached to the transparent substrate with a scriber device, and divides it into individual cells.

  Chamfering (step S113) and cleaning (step S114) are performed on the subdivided cells.

  Finally, a polarizing plate is attached to the surface of the two transparent substrates opposite to the liquid crystal layer (step S115). The two polarizing plates were arranged in crossed Nicols so that the direction of the transmission axis was parallel to the rubbing direction. It can also be arranged so as to be orthogonal. A power source was connected between the ITO electrodes of both transparent substrates.

  FIG. 2A and FIG. 2B are photographs showing the results of observation with a polarizing microscope in the display state of the manufactured liquid crystal display elements. The photograph in FIG. 2A shows a display state when the liquid crystal display element manufactured under the condition that the pretilt angle is about 35 ° and d / p is 0.57, and the photograph in FIG. 2B has a pretilt angle of about 45 °. , That of a liquid crystal display device manufactured under conditions where d / p is 0.8 is shown.

  In FIG. 2A, a black portion (black display) is a region where a voltage is applied between the electrodes of both transparent substrates, and a white portion (white display) is a region where no voltage is applied. The same applies to FIG. 2B. FIG. 2B also shows an enlarged photograph of a white portion.

  The part that appears white appears to be a uniform white display by visual inspection, but a finely oriented pattern is observed when magnified and observed with a microscope. This is considered to be focal conic orientation.

  FIG. 2C shows an outline of the liquid crystal molecule alignment in the focal conic alignment. The focal conic orientation refers to an alignment state in which liquid crystal molecules have a spiral structure in the liquid crystal layer so that the spiral axis is parallel to the substrate (upper substrate and lower substrate) surface.

  On the other hand, in the portions shown in black in the photographs of FIGS. 2A and 2B, the liquid crystal molecules are in a reverse twist arrangement state in which the liquid crystal molecules are twisted in a direction that is easily twisted due to the pretilt angle of the upper and lower substrates against the twisting force imparted by the chiral agent. It is thought that it shows. Since the liquid crystal molecule located at the center of the liquid crystal layer in the thickness direction rises to some extent in the vertical direction, a black display may be obtained. In the liquid crystal cell fabrication conditions shown in the photograph of FIG. 2A and the liquid crystal cell fabrication conditions shown in the photograph of FIG. 2B, since the amount of the chiral agent added is relatively large, the strain inside the liquid crystal layer is large, It is inferred that the central molecule in the thickness direction is standing upright.

  The manufactured liquid crystal display element is in a focal conic alignment state in the initial state. When a voltage equal to or higher than the saturation voltage value of the electro-optic characteristic is applied between the ITO electrodes of both transparent substrates (a longitudinal electric field having a strength equal to or greater than the threshold value is generated), a transition to the reverse twist arrangement state occurs. From the photographs shown in FIGS. 2A and 2B, it can be seen that the manufactured liquid crystal display element performs display with a high contrast ratio even when viewed from the front.

  Note that the memory characteristics of white display (focal conic alignment state) and black display (reverse twist alignment state) are very stable, and microscopic changes in the alignment state of liquid crystal molecules were observed with a microscope. Stable for over half a year.

  FIG. 3A shows a 0 ° -180 ° azimuth (left-right azimuth) for a liquid crystal display device (liquid crystal display device shown in FIG. 2B) manufactured under conditions where the pretilt angle is about 45 ° and d / p is 0.8. ) Is a graph showing the transmittance viewing angle dependency. The horizontal axis of the graph represents the observation angle in the unit “°” when the front direction (substrate normal direction) is 0 °. The observation angle leaning to the right is shown as a positive angle, and the observation angle leaning to the left is shown as a negative angle. The vertical axis of the graph represents the transmittance in the unit “%”. A curve connecting diamonds (denoted as St) indicates the viewing angle dependency of the transmittance in the focal conic arrangement state. The curve connecting the squares (denoted as Ut) shows that in the reverse twist arrangement state.

  FIG. 3B shows an isocontrast curve of a liquid crystal display element (liquid crystal display element showing a display state in FIG. 2B) manufactured under conditions where the pretilt angle is about 45 ° and d / p is 0.8.

  As can be seen from FIG. 3B, a substantially symmetric isocontrast curve is obtained in all directions for the manufactured liquid crystal display element. Further, as shown in FIG. 3A, since the transmittance viewing angle dependence is almost symmetrical in both the focal conic arrangement state (white display) and the reverse twist arrangement state (black display), it is manufactured. It can be clearly seen that the liquid crystal display element has a symmetrical contrast characteristic. Thus, the produced liquid crystal display element is a liquid crystal display element excellent in viewing angle characteristics.

  For comparison, FIG. 3C shows viewing angle-contrast characteristics of a liquid crystal display device according to an embodiment of the inventors' previous invention. This drawing is the same drawing as that described in the drawing of FIG. 13 (FIG. 13A). As can be seen from FIG. 3C, in the liquid crystal display element according to the previous invention, the contrast ratio is asymmetrical. The liquid crystal display element preliminarily produced along the flow chart (FIG. 1) showing the manufacturing method of the liquid crystal display element according to the embodiment realizes the left-right symmetry of the contrast ratio as compared with the previous invention. The viewing angle characteristics are excellent. Further, from FIG. 3C, in the embodiment of the present invention, the contrast ratio at the time of frontal observation is slightly higher than 3, but from the graph shown in FIG. 3A, the front surface of the liquid crystal display element manufactured according to the manufacturing method according to the example is shown. The contrast ratio at the time of observation is calculated to be slightly less than 4. Thus, when viewed from the front, the viewing angle characteristic is also excellent in that display can be performed with a high contrast ratio. These features (high display quality) are also provided with liquid crystal display elements (described later) according to the embodiments.

  The inventor of the present application can realize the reverse twist alignment state and the focal conic alignment state interchangeably by giving a physical action to the liquid crystal layer, for example, and each alignment state of the liquid crystal molecules is stable. I have studied earnestly.

  FIG. 4 is a graph showing conditions that can realize the bistable state of the reverse twist arrangement state and the focal conic arrangement state. The horizontal axis of the graph indicates the pretilt angle in units of “°”, and the vertical axis indicates the amount of chiral agent added using d / p.

  In this figure, the focal conic arrangement state does not appear in the combination of the pretilt angle and d / p in the range below the curve connecting the diamonds. That is, if the amount of chiral agent added is too small, a spray twist arrangement state appears instead of a focal conic arrangement state.

  Further, in the combination of the pretilt angle and d / p in the range above the curve connecting the squares, the focal conic arrangement state is always obtained. That is, if the amount of chiral agent added is too large, the phase transition from the focal conic arrangement state to the reverse twist arrangement state cannot be performed.

  The curve slightly fluctuates depending on the anchoring strength of the interface and the elastic constant of the liquid crystal, but in the combination of the pretilt angle and d / p in the range between the two curves, the bistable state of the reverse twist alignment state and the focal conic alignment state A state is realized. The bistable state of the reverse twist arrangement state and the focal conic arrangement state is a special state that appears when the torsional force (chirality) of the chiral agent is controlled within a certain range.

  The circles indicate the pretilt angle (about 45 °) and d / p (0.8) of the liquid crystal display element whose display state is shown in FIG. 2B and whose viewing angle characteristics are shown in FIGS. 3A and 3B.

  From the results shown in this figure, it can be seen that the closer the pretilt angle is to the vertical, the easier it is to form a focal conic arrangement state even if the d / p value is low. According to experiments repeatedly conducted by the inventors of the present application, even if the pretilt angle is low, if the liquid crystal molecule alignment is made nearly vertical by voltage, the focal conic alignment state can be observed. On the other hand, the focal conic sequence state was not expressed unless the value of d / p was relatively high.

  The bistable state of the reverse twist alignment state and the focal conic alignment state is realized because the alignment process is such that a pretilt angle of 20 ° or more and 85 ° or less appears on both the upper and lower substrates sandwiching the liquid crystal layer. It can be said that the chiral agent is added to the liquid crystal layer in a range where d / p is 0.5 or more and 2 or less. In addition, when the orientation treatment is performed so that a pretilt angle of 35 ° or more and 55 ° or less appears on both the upper and lower substrates, a chiral agent is added in a range where d / p is 0.5 or more and 1.2 or less. In this case, it can be said that a bistable state of a reverse twist arrangement state and a focal conic arrangement state can be realized.

  Based on the above preliminary considerations, the inventors of the present application produced liquid crystal display elements according to the examples.

  FIG. 5 is a schematic cross-sectional view in one pixel of the liquid crystal display device according to the embodiment.

  The liquid crystal display device according to the embodiment includes an upper substrate 10a, a lower substrate 10b, and a twisted nematic liquid crystal layer 15 disposed between the substrates 10a and 10b.

  The upper substrate 10a includes an upper transparent substrate 11a, an upper solid electrode 12a formed on the upper transparent substrate 11a, and an upper alignment film 14a formed on the upper solid electrode 12a. The lower substrate 10b is formed on the lower transparent substrate 11b, the lower solid electrode 12b formed on the lower transparent substrate 11b, the insulating film 13 formed on the lower solid electrode 12b, and the insulating film 13. The lower alignment film 14b formed on the insulating film 13 so as to cover the first and second comb electrodes 12c and 12d and the first and second comb electrodes 12c and 12d is included.

  The upper and lower transparent substrates 11a and 11b are made of glass, for example. The upper and lower solid electrodes 12a and 12b and the first and second comb electrodes 12c and 12d are formed of a transparent conductive material such as ITO, for example. The first and second comb electrodes 12c and 12d are comb electrodes each having a plurality of comb portions. The comb-tooth portions of the first and second comb-tooth electrodes 12c and 12d are alternately arranged along the horizontal direction of the figure.

  The liquid crystal layer 15 is disposed between the upper alignment film 14a of the upper substrate 10a and the lower alignment film 14b of the lower substrate 10b.

  The upper and lower alignment films 14a and 14b are subjected to an alignment process by rubbing. The alignment treatment directions of the upper alignment film 14a and the lower alignment film 14b are orthogonal to each other when viewed from the normal direction of the upper and lower substrates 10a and 10b. When the rubbing direction of the upper alignment film 14a is the first direction and the rubbing direction of the lower alignment film 14b is the second direction, the second direction is the first direction when viewed from the normal direction of the upper substrate 10a. This is a direction that forms 90 ° in the clockwise direction with respect to the reference.

  A chiral agent is added to the liquid crystal material forming the liquid crystal layer 15. The alignment state of the liquid crystal molecules in the liquid crystal cell completed state (initial state) was a focal conic alignment.

  A power source 20 is electrically connected to the upper and lower solid electrodes 12a and 12b and the first and second comb electrodes 12c and 12d. A voltage can be applied to the electrodes 12a to 12d by the power source 20. For example, by applying an AC voltage equal to or higher than the threshold voltage between the solid electrodes 12a and 12b, the alignment state of the liquid crystal molecules can be transferred from the focal conic alignment to the reverse twist alignment.

  An upper polarizing plate 16a and a lower polarizing plate 16b are disposed on the surfaces of the upper substrate 10a and the lower substrate 10b opposite to the liquid crystal layer 15, respectively. Both polarizing plates 16a and 16b are arranged in a crossed Nicol manner so that the light transmission axis is parallel to the rubbing direction of the upper and lower substrates 10a and 10b. The liquid crystal display element according to the embodiment is a normally white type liquid crystal display element.

  With reference to FIGS. 6-10, the structure and manufacturing method of the liquid crystal display element by an Example are demonstrated in detail.

  FIG. 6 is a schematic plan view showing a pattern of an ITO film formed on the upper transparent substrate 11a. In the ITO film shown in this figure, for example, a pixel electrode (an electrode that forms the upper solid electrode 12a in each pixel) and an extraction electrode for the pixel electrode are formed.

The ITO film pattern is formed, for example, such that the ITO film extends in a stripe shape in the left-right direction in the figure. In this figure, the ITO films constituting the pixel electrodes are indicated by reference numerals 12A ₁ to 12A ₁₀ .

  The ITO film was patterned using a photolithography process after washing the glass substrate with ITO. Etching of ITO was performed by wet etching using ferric chloride. Patterning may be performed by irradiating a laser beam and removing the ITO film.

  FIG. 7 is a schematic plan view showing a pattern of an ITO film formed on the lower transparent substrate 11b. With the ITO film shown in this figure, for example, a pixel electrode (an electrode forming the lower solid electrode 12b in each pixel) and an extraction electrode for the pixel electrode are formed.

The ITO film pattern is formed, for example, such that the ITO film extends in a stripe shape in the vertical direction of the figure. In this figure, reference numerals 12B ₁ to 12B ₉ are attached to a part of the ITO film constituting the pixel electrode. In addition, the up-down direction of this figure and the left-right direction of FIG. 6 are directions orthogonal to each other.

  The ITO film can be patterned by the same method as the ITO film pattern forming method described with reference to FIG.

After patterning the ITO film, an insulating film 13 is formed on the lower transparent substrate 11b including the ITO film. The insulating film 13 is not formed on the extraction electrodes 12BT _{1 to} 12BT ₉ (terminal portion), for example. In this figure, the region where the insulating film 13 is not formed is hatched. The insulating film 13 can be formed by a method in which a resist is formed on the extraction electrode portion and the resist is removed by lift-off after forming the insulating film, or a method in which the extraction electrode portion is covered by a metal mask and formed by sputtering. . The insulating film 13 can be an organic insulating film or an inorganic insulating film such as SiO ₂ or SiN _x . You may form by those combination. In the example, a laminated film of an acrylic organic insulating film and SiO ₂ was used as the insulating film 13.

In the examples, a heat-resistant film (polyimide tape) was first attached to the extraction electrode portion and the like, and an organic insulating film was spin-coated (spun at 2000 rpm for 30 seconds) to a thickness of 1 μm. Next, the lower transparent substrate 11b on which the organic insulating film is spin-coated is baked at 220 ° C. for 1 hour in a clean oven, and then the lower transparent substrate 11b is heated to 80 ° C. with the heat-resistant film attached. A SiO ₂ film was formed to a thickness of 1000 mm by a sputtering method (AC discharge). The SiO ₂ film can also be formed using a vacuum deposition method, an ion beam method, a CVD method, or the like.

Here, when the heat-resistant film was peeled off, the organic insulating film and the SiO ₂ film were able to be removed at the location where the heat-resistant film was applied. Subsequently, in order to improve the insulation and transparency of the SiO ₂ film, the lower transparent substrate 11b was baked at 220 ° C. for 1 hour in a clean oven.

The formation of the SiO ₂ film is not essential, but the insulating property of the insulating film 13 can be improved by forming the SiO ₂ film. In addition, it is possible to improve the adhesion and patterning properties of the first and second comb electrodes 12c and 12d formed on the insulating film 13.

Instead of forming the organic insulating film, the insulating film 13 may be composed of only the SiO ₂ film. Since the SiO ₂ film tends to be porous, in this case, the thickness of the SiO ₂ film is desirably 4000 to 8000 mm. An inorganic insulating film 13 made of a laminate of a SiO ₂ film and a SiN _x film can also be used.

  An ITO film was formed on the insulating film 13. The ITO film was formed on the entire surface of the substrate by heating the lower transparent substrate 11b to 100 ° C. and sputtering (AC discharge). The film thickness was about 1200 mm. The ITO film can also be formed using a vacuum deposition method, an ion beam method, a CVD method, or the like. This ITO film was patterned by a photolithography process to form a first comb electrode 12c, a second comb electrode 12d, and extraction electrodes for these electrodes 12c and 12d.

  FIG. 8 is a schematic plan view showing a photomask used for etching the ITO film. The photomask includes a portion corresponding to the first comb electrode 12c, a portion corresponding to the second comb electrode 12d, a portion corresponding to the extraction electrode of the first comb electrode 12c, a portion corresponding to the extraction electrode of the second comb electrode 12d, and a lower solid. A portion corresponding to the extraction electrode of the electrode 12b is included. At the time of etching, an electrode is formed with an ITO film covered with each corresponding portion. In addition, the inventors of the present invention have electrode widths of 20 μm, 30 μm, and comb electrode portions of the comb-like electrode, and electrode intervals when the comb-tooth portions of the two comb-like electrodes are alternately arranged are 20 μm, 30 μm, 50 μm, 100 μm, The 1st comb-tooth electrode 12c and the 2nd comb-tooth electrode 12d were produced with the several electrode pattern set to 200 micrometers.

  Through the steps as described above, two substrates with electrodes were prepared (step S101 in FIG. 1). The two substrates with electrodes are washed and dried (step S102). In the case of water washing, pure water washing is performed. You may carry out using a detergent. It can be cleaned by either brush cleaning or spray cleaning. Then drain and drain. As a method other than water washing, UV washing and IR drying can be performed.

  On the two substrates with electrodes, an alignment film material was applied so as to cover the ITO electrodes (step S103). The alignment film material was applied by spin coating. You may perform using flexographic printing or inkjet printing. Normally, the side chain density of the polyimide alignment film material used for forming the vertical alignment film is lowered and used as the alignment film material. This is the same material as the alignment film material used for the liquid crystal display element produced for the preliminary consideration. The alignment film material was applied so that the alignment film had a thickness of 500 to 800 mm. Temporary baking (step S104) and main baking (step S105) of the substrate with electrodes coated with the alignment film material were performed. The main baking was performed in a clean oven at 180 ° C. for 1 hour. You may carry out at the temperature of 160 degreeC or more and 180 degrees C or less. Thus, an alignment film covering the ITO electrode was formed (steps S103 to S105).

  FIG. 9 is a schematic plan view showing a part of a formation region of the lower alignment film 14b formed on the lower substrate 10b. The lower alignment film 14b is formed, for example, in a region where the first and second comb electrodes 12c and 12d are arranged and pixels are defined. In this figure, only the upper left portion is shown as the formation region of the lower alignment film 14b, but the same applies to the other regions where the comb electrodes 12c and 12d are arranged.

  Next, a rubbing process (orientation process) was performed (step S106). In the rubbing process, the push amount is 0.8 mm, and a pretilt angle of 20 ° to 85 °, for example, 35 ° to 55 °, for example, 45 ° is developed in both the upper alignment film 14a and the lower alignment film 14b. Went so. Moreover, it implemented so that the twist angle of a liquid crystal display element might be set to 90 degrees.

  Note that the pretilt angle in this region is very difficult to measure, and the numerical value of 45 ° may include a considerable error. There may be a variation of about ± 15 ° to ± 30 ° due to a difference in measurement method and measurement accuracy.

  In order to set the cell thickness to 4 μm, a gap control material having a particle size of 4 μm was sprayed on one substrate surface (step S107). In order to set the cell thickness to 3 μm or more and 5 μm or less, it is possible to spray a gap control material having a particle size of 3 μm or more and 5 μm or less. A sealant was printed on the other substrate surface to form a main seal pattern (step S108). The two substrates were overlapped at a predetermined position (step S109), and the sealing material was cured.

  The two substrates are overlapped when the rubbing direction of the upper alignment film 14a is the first direction and the rubbing direction of the lower alignment film 14b is the second direction, the second direction is the normal line of the upper substrate 10a. When viewed from the direction (above), the first direction was used as a reference, and the direction was 90 ° clockwise.

  Nematic liquid crystal was injected by a vacuum injection method (step S110). As the liquid crystal material, a low refractive index anisotropic material having a refractive index anisotropy Δn of 0.067 was used. A chiral agent was added to the liquid crystal. CB15 manufactured by Merck & Co., Inc. was used as the chiral agent. The addition amount of the chiral agent was adjusted so that d / p was 0.8 (p = 5 μm) where p was the chiral pitch and d was the thickness of the liquid crystal layer. d / p is 0.5 or more and 2 or less, 35 when the alignment treatment is performed so that a pretilt angle of 20 ° or more and 85 ° or less is developed in the upper and lower alignment films 14a and 14b according to the pretilt angle, for example. When the orientation treatment is performed so that a pretilt angle of not less than 55 ° and not more than 55 ° is exhibited, it can be set in the range of 0.5 to 1.2.

  The liquid crystal injection port was sealed with an ultraviolet curing type end seal material (step S111), and the cell was heated to a temperature higher than the phase transition temperature of the liquid crystal in order to adjust the alignment of the liquid crystal molecules (step S112). Then, it broke along the crack | wound attached to the transparent substrate with the scriber apparatus, and subdivided into the individual cell. Chamfering (step S113) and cleaning (step S114) were performed on the subdivided cells.

  Finally, a polarizing plate was attached to the surface opposite to the liquid crystal layer of the two substrates (step S115). The two polarizing plates were arranged in crossed Nicols so that the direction of the transmission axis was parallel to the rubbing direction. It can also be arranged so as to be orthogonal. A power source was connected to the ITO electrodes (upper and lower solid electrodes 12a and 12b and first and second comb electrodes 12c and 12d) of both substrates.

FIG. 10 is a schematic plan view showing the structure of the liquid crystal display device according to the embodiment. FIG. 10 shows all the structures shown in FIGS. One pixel is defined by a horizontal electrode extending in the left-right direction and a vertical electrode extending in the vertical direction. In the figure, indicated by reference numeral of _12A 1 _{~12A 10} next electrode, shown in a part of the vertical electrodes are denoted by the sign of the _12B 1 _{~12B 9.} The arrows indicate pixels defined in a region where the horizontal electrode 12A ₉ and the vertical electrode 12B ₈ overlap when viewed from the substrate normal direction. Horizontal electrode 12A ₉ in the pixel corresponds to the upper solid electrode 12a of FIG. 5, the vertical electrode 12B ₈ corresponds to the lower solid electrode 12b.

  11A to 11C are external appearance photographs of the liquid crystal display device according to the example, and FIGS. 11D to 11F are schematic cross-sectional views showing the electric field direction when a voltage is applied between the electrodes. 11A to 11C show the case where the electrode width of the comb teeth of the first and second comb electrodes 12c and 12d is 20 μm, and the comb teeth of both the comb electrodes 12c and 12d are alternately arranged. 6 is a front view photograph of the region where the comb electrodes 12c and 12d are formed in a liquid crystal display device manufactured with an electrode spacing of 20 μm.

  FIG. 11A shows an appearance photograph of the liquid crystal display element in a completed state (initial state). In the initial state, the liquid crystal molecules are in a focal conic alignment state. Visually uniform white display was obtained.

  In this state, as shown in FIG. 11D, a voltage was applied between the upper solid electrode 12a and the lower solid electrode 12b. By applying a voltage to both electrodes 12a and 12b, a vertical electric field (electric field in the thickness direction of the liquid crystal layer) is generated in the liquid crystal layer.

  FIG. 11B is an appearance photograph after voltage is applied to the electrodes 12a and 12b. It can be seen that the whole has transitioned from the focal conic arrangement state to the reverse twist arrangement state. It can also be seen that a black display is obtained when viewed from the front. Further, conversely, it is confirmed that a vertical electric field is generated in the liquid crystal layer by applying a voltage to both electrodes 12a and 12b.

  Next, as shown in FIG. 11E, a voltage was applied to the lower solid electrode 12b, the first comb electrode 12c, and the second comb electrode 12d. By applying a voltage to the electrodes 12b, 12c, and 12d, a lateral electric field (an electric field in a direction perpendicular to the thickness direction of the liquid crystal layer, an electric field in the substrate plane) is generated in the liquid crystal layer. Note that a driving mode in which a liquid crystal layer is driven by applying a voltage to the electrodes 12b, 12c, and 12d to drive the liquid crystal display element is called an FFS mode (fringe field switching mode).

  FIG. 11C is an appearance photograph after driving the liquid crystal display element in the state shown in FIG. 11B in the FFS mode. It can be seen that the entire surface re-transitions to a state (focal conic arrangement state) similar to the initial state.

  The liquid crystal display element according to the embodiment is a liquid crystal display element capable of switching between a focal conic alignment state and a reverse twist alignment state. By applying a vertical electric field, the former can be changed to the latter. Moreover, the latter can be changed to the former by application of a transverse electric field. As a method of transitioning the reverse twist arrangement state to the focal conic arrangement state, driving in the IPS mode (in-plane switching mode) can be employed in addition to driving in the FFS mode.

  FIG. 11F shows the electric field direction generated in the IPS mode. When a voltage is applied to the first comb electrode 12c and the second comb electrode 12d, a lateral electric field is generated in the liquid crystal layer. A driving mode for driving a liquid crystal display element by generating a lateral electric field in the liquid crystal layer by applying a voltage to the first and second comb electrodes 12c and 12d is called an IPS mode.

  When a vertical electric field is applied to a liquid crystal layer in a focal conic alignment state in which liquid crystal molecules form a spiral in the in-plane direction, the liquid crystal molecules are 90 ° twisted due to the influence of the interface and located at the center in the thickness direction of the liquid crystal layer. Tilts vertically. Thus, it is considered that switching from the focal conic arrangement state to the reverse twist arrangement state is performed. In addition, it is considered that switching from the reverse twist alignment state to the focal conic alignment state is performed by disturbing the liquid crystal molecule alignment at the interface in the reverse twist alignment state by the addition of the lateral electric field.

  The liquid crystal display element according to the embodiment is a liquid crystal display element in which a focal conic alignment state and a reverse twist alignment state are shifted to each other depending on the direction of an applied electric field, and each state is stably maintained. Bistable display in a white display state and a black display state with high contrast can be easily realized. In particular, the black display is dark, and a clear display can be realized even when viewed from the front. Therefore, it can be suitably applied to any of a transmissive display, a translucent display, and a reflective display. In addition, the liquid crystal display element according to the embodiment is a liquid crystal display element having a symmetrical contrast ratio.

  In the liquid crystal display element according to the embodiment, for example, display utilizing memory property is possible.

  Pixels that are to be displayed in white are in a focal conic arrangement state, and pixels that are to be displayed in black are in a reverse twist arrangement state. A vertical electric field is applied to at least a pixel to be changed from white display to black display. A vertical electric field may be applied to a pixel for which black display is to be maintained. On the contrary, a horizontal electric field is applied to at least a pixel to be changed from black display to white display. A lateral electric field may be applied to a pixel for which white display is to be maintained.

The display can be rewritten, for example, for each line. As an example, in FIG. 10, one of the vertical electrode _12B 1 _{~12B 9,} for example, the vertical electrodes 12B _1, applies a rectangular wave of a degree that transition arrangement state does not occur (e.g. 150 Hz, about 5V). Along with this, the lateral electrode _12A 6 _{~12A 10} or the first and second comb electrodes, is applied to the longitudinal electrodes 12B ₁ voltage synchronized with or half cycle shifted square wave (e.g. 150 Hz, about 5V) is applied to.

In the pixel plus vertical electrode 12B waveform synchronized with waveforms added to _1, the display for a state of effectively voltage is not applied is not changed, the waveform and the half period shift made to the vertical electrodes 12B ₁ In the pixel to which the waveform is added, since a voltage of about 10 V is effectively applied, the voltage becomes equal to or higher than the saturation voltage and can be changed between white display and black display.

For example, a rectangular wave shifted by a half cycle is applied to the first and second comb electrodes and no voltage is applied to the horizontal electrodes 12A _{6 to} 12A ₁₀ to the pixels that are desired to be displayed in white. The pixel to be black display, a square wave shifted by a half period in the horizontal electrode 12A ₆ ~12A ₁₀ is applied, first, no voltage is applied to the second comb electrodes.

After the vertical electrodes 12B _1, also by applying a rectangular wave with respect to the longitudinal electrodes _12B 2 _{~12B 9,} by driving in the same manner, a matrix display can be performed. The rewritten display can be held semipermanently and can be compatible with a high contrast ratio.

  The liquid crystal display element according to the embodiment can be driven by a driving method using memory characteristics such as the above-described line-sequential rewriting method (line-sequential driving method). Ultra-low power consumption driving is possible that does not consume power except during display rewriting. Particularly when applied to a reflective display, the merit is great. Further, large-capacity dot matrix display can be performed by simple matrix display without using expensive TFTs or the like. That is, a large-capacity display can be performed at low cost.

  Furthermore, the liquid crystal display element according to the embodiment can be manufactured at low cost by the manufacturing method described with reference to FIGS. 1 and 6 to 10, for example. The manufacturing method is almost the same as the manufacturing method of a general twisted nematic liquid crystal display element except for the alignment film material, rubbing conditions (control of the amount of pressing), firing conditions of the alignment film, etc. There are few factors of cost increase compared with a display element.

    As mentioned above, although this invention was demonstrated along the Example, this invention is not limited to these.

  For example, in the embodiments, the polarizing plates are arranged in crossed Nicols to obtain a normally white display liquid crystal display element, but the polarizing plates may be arranged in parallel Nicols to form a normally black display liquid crystal display element. However, it would be easier to achieve a display with a high contrast ratio if it is normally white. In the case of normally white display, in order to obtain good black display, the angle formed by the transmission axis directions of the upper and lower polarizing plates 16a and 16b is preferably about 90 °.

  In the embodiment, the twist angle is 90 °, but other angles may be used. In that case, it is necessary to adjust the retardation value in the liquid crystal layer in order to increase the brightness in white display.

  Furthermore, in the embodiment, an electrode for generating a lateral electric field is formed only on the lower substrate 10b, but it can be formed not only on the lower substrate 10b but also on the upper substrate 10a. The electrode that generates the lateral electric field may be formed on at least one of the upper substrate 10a and the lower substrate 10b.

    It will be apparent to those skilled in the art that other various modifications, improvements, combinations, and the like are possible.

  It can be used for all liquid crystal display elements, for example, all liquid crystal display elements that perform simple matrix driving. Further, it can be used for a liquid crystal display element that requires low power consumption, wide viewing angle characteristics, low price, and the like.

  From the point of having memory properties, it can be preferably applied to reflective, transmissive, and projection displays, such as the display surface of information equipment (personal computer, portable information terminal, etc.) that does not require frequent rewriting, for example, with low power consumption. is there. Further, it can be used for information display surfaces of magnetically recorded or electrically recorded cards, toys for children, electronic paper, and the like.

  Furthermore, it can be used as a display for maintaining display even in the event of a power failure in the event of a disaster.

10a Upper substrate 10b Lower substrate 11a Upper transparent substrate 11b Lower transparent substrate 12a Upper solid electrode 12b Lower solid electrode 12c First comb electrode 12d Second comb electrode 13 Insulating film 14a Upper alignment film 14b Lower alignment film 15 Liquid crystal layer 16a Upper polarizing plate 16b Lower polarizing plate 20 Power supply

Claims (4)

A first substrate comprising a first electrode and subjected to orientation treatment;
A second substrate disposed in parallel and opposite to the first substrate, provided with a second electrode, and subjected to an orientation treatment;
A liquid crystal layer that is disposed between the first substrate and the second substrate, includes a chiral agent, and has a twist alignment;
In the case where the liquid crystal layer does not contain the chiral agent, when the turning direction in which the liquid crystal molecules are twisted is the first turning direction, the chiral agent is in the liquid crystal molecules of the liquid crystal layer opposite to the first turning direction. Giving the ability to turn in the second turning direction,
In the liquid crystal layer, it is possible to generate an electric field in the thickness direction of the liquid crystal layer by applying a voltage to the first electrode and the second electrode,
At least one of the first substrate and the second substrate is formed with an electrode capable of generating an electric field in a direction perpendicular to the thickness direction of the liquid crystal layer by applying a voltage,
The alignment treatment for the first substrate and the second substrate, and the addition of a chiral agent to the liquid crystal layer, the liquid crystal molecules of the liquid crystal layer are arranged in a focal conic arrangement depending on the direction of the electric field applied to the liquid crystal layer. A liquid crystal display element that is configured to transition between a state and a reverse twist arrangement state.   The first and second substrates are subjected to an alignment treatment so that a pretilt angle of 20 ° or more and 85 ° or less is expressed, where the chiral pitch is p and the thickness of the liquid crystal layer is d, d / p is The liquid crystal display element according to claim 1, wherein a chiral agent is added to the liquid crystal layer so as to be 0.5 or more and 2 or less.   In the liquid crystal layer, the first and second substrates are subjected to an alignment treatment so that a pretilt angle of 35 ° or more and 55 ° or less is developed, and d / p is 0.5 or more and 1.2 or less. The liquid crystal display element according to claim 2, wherein a chiral agent is added. The second substrate is
A transparent substrate;
The second electrode formed on the transparent substrate;
An insulating film formed on the second electrode;
First and second comb electrodes formed on the insulating film, wherein the comb teeth portions are alternately arranged; and
The liquid crystal display element according to claim 1, further comprising an alignment film formed on the insulating film so as to cover the first and second comb electrodes.