JPH0784260A - Liquid crystal display panel - Google Patents

Abstract

PURPOSE:To provide the liquid crystal display panel which is produced without executing a rubbing treatment and realizes a higher contrast and wider visual field angle. CONSTITUTION:A liquid crystal layer clamped between a pair of substrates is a chiral nematic phase having negative dielectric anisotropy and molecular major axes 13 of liquid crystal molecules exhibit a twisted perpendicular orientation state between a pair of the substrates. Plural regions 14, 15, 16, 17 where the liquid crystal molecular major axes are oriented in a uniform direction exist microscopically and the directions of the liquid crystal molecular major axes 13 exist differently between the respective regions in the state of applying the voltage above the threshold voltage to the liquid crystal. In addition, the liquid crystal molecules exhibit a twisted orientation state between a pair of the substrates within the regions.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display panel for displaying an image by utilizing the electro-optical characteristics of liquid crystal, and more particularly to a technique for enlarging a viewing angle of the liquid crystal display panel and aligning liquid crystal molecules.

[0002]

2. Description of the Related Art In recent years, liquid crystal display panels utilizing the electro-optical characteristics of liquid crystals have been actively applied to OA equipment due to the increase in screen size and capacity. As an operation mode of a liquid crystal display panel that is currently put into practical use, a twisted nematic (TN) type in which liquid crystal molecules are twisted by 90 ° between two glass substrates, 180 ° to 2 °
There is a super twisted nematic (STN) type that exhibits a twisted orientation state of 70 °. The TN type is mainly used for an active matrix type liquid crystal display panel, and the STN type is used for a simple matrix type liquid crystal display panel.
The operation modes will be described below with reference to the drawings.

TN used for an active matrix type liquid crystal display panel or a small size liquid crystal display panel
In the case of the mold, the liquid crystal molecules at the interface of the glass substrate are uniformly oriented in one direction with a certain pretilt angle with respect to the glass substrate, and are twisted by 90 ° between the upper and lower glass substrates. In such a 90 ° twisted alignment state, generally, an alignment film made of a polyimide thin film formed on a glass substrate is rubbed in one direction by using rayon cloth or the like, and arranged so that the directions are orthogonal to each other between the upper and lower substrates. It is obtained by doing.

When a voltage is applied to the TN type liquid crystal panel as shown in FIG. 6, the liquid crystal molecules twisted by 90 ° start to respond at a threshold voltage or more, and the twisted alignment state is released to a splay alignment state. Becomes a state in which the long axis of the molecule stands up with respect to the glass substrate plane. When the liquid crystal molecules are observed while changing the azimuth angle Ψ at a position inclined by θ with respect to the substrate normal (Z axis), the orientation of the long axis of the liquid crystal molecules is not uniform in the azimuth direction. Therefore, the apparent refractive index anisotropy (Δn) of the liquid crystal molecules changes depending on the azimuth direction, and the birefringence amount (Δn) that is the product of the liquid crystal layer thickness (d) and
d) changes. Therefore, when polarizing plates are arranged on the outer surfaces of the upper and lower glass substrates so that the absorption axis is orthogonal to the rubbing direction and light is incident from the −Z-axis direction, the light transmission intensity varies with the change in the azimuth direction, and the viewing angle Asymmetry occurs. This asymmetry of the viewing angle becomes a problem particularly in the case of the halftone display, which causes the deterioration of the display quality such as the contrast ratio being extremely lowered depending on the viewing angle direction or the display image being inverted. Therefore, in the TN type liquid crystal display panel, in recent years, efforts have been actively made to expand the viewing angle. As an example, a method of dividing a pixel of a TN type liquid crystal display panel into two regions having different alignment states to increase the viewing angle (for example,
Takatori, Ke Sumiyoshi, Wai Hirai, S. Kaneko: Japan Display '92, p. 591, 19
1992; K. Takatori, K. Sumiyoshi, Y. Hirai, S. Kaneko: JA
PAN DISPLAY '92, PP.591, (1992)) has been proposed.
In this method, it is necessary to perform exposure and rubbing twice in order to divide the alignment region of one pixel into two, which complicates the process steps. Another method has been proposed that further simplifies the process and widens the viewing angle.
Sugiama, K. Kato, Wai Yimra, S. Kobayashi: SID 93 digest, p. 622,
1993; Y. Toko, T. Sugiyama, K. Katoh, Y. Iimura, SK
obayashi: SID 93 DIGEST, PP.622, (1993)). In this method, a large number of regions having different alignment states are formed by randomly aligning liquid crystal molecules without performing a rubbing treatment, thereby expanding the viewing angle.

[0005]

In the above method, a chiral nematic liquid crystal is added by adding a chiral agent to the nematic liquid crystal in order to rotate the liquid crystal molecules 90 ° between the upper and lower substrates in order to perform switching by the polarization rotation effect of light. age,
The spontaneous spiral pitch (p) is set so that d / p = 0.25 with respect to the thickness (d) of the liquid crystal layer. When polarizing plates are arranged on the substrate surface of this liquid crystal display panel so that their absorption axes are orthogonal to each other and a rectangular wave voltage is applied, liquid crystal molecules are in a splay alignment state at a threshold voltage or higher, and thus the initial alignment state is different. Disclination lines occur between areas. When viewed from an oblique direction due to the occurrence of the disclination line, the viewing angle is expanded, but the disclination line becomes a bright line to cause light leakage, and a sufficient contrast ratio cannot be obtained. There is also a problem that the driving voltage becomes high due to disclination.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems of the conventional technique of enlarging the viewing angle and to provide a liquid crystal display panel capable of enlarging the viewing angle and preventing the reduction of the contrast ratio due to the disclination line. .

[0007]

According to a first aspect of the present invention, there is provided a liquid crystal display panel in which a liquid crystal is sandwiched between a pair of substrates.
The liquid crystal layer is a chiral nematic phase having a negative dielectric anisotropy, the spontaneous helical axis of the chiral nematic phase is substantially perpendicular to the substrate interface, and in a voltage applied state or no voltage applied state smaller than the threshold voltage, The liquid crystal molecules have an alignment state in which the major axis of the liquid crystal is perpendicular or inclined to the interface of the substrate, and when a voltage higher than the threshold voltage is applied, a plurality of regions having different major axis directions of the liquid crystal molecules are generated. .

In a second aspect of the present invention, in a liquid crystal display panel in which liquid crystal is sandwiched between a pair of substrates, the liquid crystal layer is a chiral nematic phase having positive dielectric anisotropy, and the molecular length of liquid crystal molecules is long. The other substrate has a plurality of regions in which the major axis of the liquid crystal molecule is aligned in a microscopically uniform direction with the pretilt angle of the horizontal direction or several degrees with respect to the interface of one substrate, and facing each other. The liquid crystal molecules are vertically or tilted vertically to the interface, the liquid crystal molecule major axis directions are different between the respective regions, and the liquid crystal molecules exhibit a twisted alignment state between the pair of substrates in the regions. It has a plurality of disclination lines in the vicinity and in the liquid crystal layer.

[0009]

In the first aspect of the present invention, the liquid crystal molecules are vertically or slightly inclined at the interface between the upper and lower substrates, and the major axis of the molecule (hereinafter referred to as director) is twisted between the upper and lower substrates. Oriented in the state. In this state, the liquid crystal exhibits a uniform alignment state. When a polarizing plate is placed on the surface of the substrate so that its absorption axes are orthogonal to each other, the light incident as linearly polarized light propagates through the liquid crystal layer as linearly polarized light, and is almost cut off by the polarizing plate on the output side. Is obtained. When a voltage higher than the threshold voltage is applied, the liquid crystal molecules in the vertical alignment or the tilted vertical alignment have the director direction perpendicular to the electric field vector depending on the electric field strength. The bent alignment state is obtained. In this state, due to the birefringence of the liquid crystal layer, the light incident as linearly polarized light becomes elliptically polarized light, propagates and is emitted. By the way, the director direction is uniform in a small area (hereinafter, the area in which the director directions are the same is called a domain), but since the domains are oriented in arbitrary directions, domains with different director directions are different. Will occur. When viewed from an oblique direction, the appearance of a plurality of domains eliminates the dependence of the transmitted light intensity on the viewing angle, thereby increasing the viewing angle and improving the contrast ratio.

In the second aspect of the present invention, the liquid crystal molecules are vertically aligned at the interface of one substrate and horizontally aligned at the interface of the other substrate, so that the upper and lower substrates are continuously twisted. Since the director direction of the horizontally aligned liquid crystal molecules is arbitrary, a plurality of domains having different director directions are generated. Polarizing plates are arranged on the upper and lower substrate surfaces of this liquid crystal display panel so that their absorption axes are orthogonal to each other. When no voltage is applied or when the voltage is equal to or lower than the threshold voltage, the incident linearly polarized light becomes an elliptically polarized state due to the birefringence effect due to the director change in the domain and is transmitted through the emission side polarizing plate. Above the threshold voltage, the liquid crystal molecules are deformed so that the director direction becomes parallel to the electric field vector according to the electric field strength, and under sufficient electric field strength, the director becomes completely parallel to the electric field vector, and Refraction amount (hereinafter referred to as retardation)
Takes a value close to 0. In this case, since the incident linearly polarized light propagates in the liquid crystal layer without rotating the plane of polarization, it is shielded by the outgoing side polarizing plate. Therefore, since a plurality of domains having different director directions are generated, the contrast ratio is improved by widening the viewing angle and decreasing the retardation by eliminating the angle dependence of the retardation in the oblique direction.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. (Embodiment 1) FIG. 1 is a schematic sectional view showing an embodiment of a liquid crystal display panel of the present invention. In FIG. 1, 1 is an upper glass substrate, 2 is a segment electrode, 3 is a lower glass substrate, 4 is a common electrode, 5 is a polyimide thin film, 6 is a chiral nematic liquid crystal layer, 7 is a spacer, 8 is a sealing material, Reference numeral 9 is a polarizing plate, and 10 is a reflecting plate. The manufacturing method will be described below.

The upper glass substrate 1 having indium tin oxide (ITO) having a sheet resistance value of 30 Ω / □ is patterned by photolithography to obtain 64 striped segment electrodes 2. 64 common electrodes 4 are formed on the lower glass substrate 3 by using the same method. The segment electrode 2 and the common electrode 4 are arranged so as to be orthogonal to each other. On such glass substrates 1 and 3, a polyimide thin film 5 having a thickness of 800 Å is formed by a printing method. As a material for the polyimide thin film 5, for example, SE-7511L (manufactured by Nissan Chemical Industries, Ltd.)
Is used. The polyimide thin film 5 has a function of vertically aligning liquid crystal molecules on the glass substrate surface.

Next, spherical spacers 7 made of plastic (for example, Micropearl: Sekisui Fine Co., Ltd.) are uniformly dispersed on the lower glass substrate 3 or the polyimide thin film 5. The spherical diameter of the spacer is 6 μm. Further, a thermosetting sealing material 8 (for example, Struct Bond: manufactured by Mitsui Toatsu Chemicals, Inc.) is formed by printing on the periphery of the upper glass substrate 1 by providing a liquid crystal injection port, and the segment electrode 2 and the common electrode 4 are formed. The upper and lower glass substrates 1 and 3 are laminated so as to be orthogonal to each other, and the sealing material 8 is completely cured at a predetermined temperature.

Next, a nematic liquid crystal having a negative dielectric anisotropy having a refractive index anisotropy of 0.152 (for example, MLC-20).
09: manufactured by Merck Japan Co., Ltd., a right-handed chiral substance (for example, R-1011: manufactured by Merck) is added, and the value of the spontaneous twist pitch p is 0 ≦ with respect to the cell gap d.
The density is adjusted so that d / p <0.5 (or 0 <d / p <0.5). In this embodiment, a right-handed chiral substance is added so that the d / p value becomes 0.25. The chiral nematic liquid crystal 6 produced under such conditions is heated to be an isotropic state, and is injected between the glass substrates 1 and 3 by a vacuum injection method. At this time, the glass substrates 1 and 3 also have the nematic phase-isotropic phase transition temperature (N
It is heated to a temperature above the point I). After the chiral nematic liquid crystal 6 is completely filled, the liquid crystal display panel is gradually cooled and the liquid crystal injection port is sealed with a sealing resin.

Now, the polarizing plates 9 are attached to the surfaces of the glass substrates 1 and 3 of the liquid crystal display panel thus manufactured so that their absorption axes are orthogonal to each other. Light is incident from the lower glass substrate 3 and observed from above the upper glass substrate 1. In the applied voltage state below the threshold voltage, the liquid crystal molecules are vertically or slightly vertically aligned between the upper and lower substrates. At this time, since the retardation is almost 0, the incident linearly polarized light propagates in the liquid crystal layer without changing the polarization state, and thus the light-shielding state is obtained on the exit polarizing plate surface.

FIG. 2 shows the liquid crystal display panel of this embodiment in 1 / 6th.
It is a perspective view showing a microscopic alignment state in a pixel at an ON voltage when driven by 4 Duty. Reference numeral 13 in FIG. 2 represents the molecular long axis (director) of the liquid crystal molecule. Areas (domains) 14 and 1 with different directors at the glass substrate interface
There were a plurality of 5, 16, and 17, and the disclination line 18 generated due to the different directions of the directors among the domains was observed. In a normal liquid crystal display panel, since the polyimide thin film is rubbed, only one domain in which the direction of the director is the same can be seen in the pixel. In the case of the present embodiment, since the polyimide thin film is not subjected to rubbing treatment, the liquid crystal molecules are oriented in an amorphous state by the intermolecular force with the polyimide thin film, and the tilt direction is not defined, so that a plurality of domains are formed. Is considered to have occurred. In each domain, the liquid crystal molecules are twisted between the upper and lower glass substrates according to the set value of d / p. In the case of this embodiment, since d / p is set to 0.25, the liquid crystal molecules are oriented with their director directions twisted by 90 ° between the upper and lower glass substrates. In this case, incident light is emitted in an elliptically polarized state due to the birefringence effect of the liquid crystal layer.

When the liquid crystal display panel in this state is viewed from an oblique direction, the anisotropy of retardation in the viewing angle direction disappears due to the generation of a plurality of domains. Therefore, the transmitted light intensity does not depend on the viewing angle, and as a result, the viewing angle is expanded.

FIG. 3 shows an applied voltage-relative transmittance characteristic (hereinafter referred to as VT characteristic) 20 of the liquid crystal display panel of this embodiment. As a comparative example, TN type multi-domain method (Y
Toko, T. Sugiyama, K. Kato, Wai Yimra, S. Kobayashi: S. ID 93 digest, p. 622, 1993; Y. Toko, T. Sugiyama, K. Ka.
toh, Y.Iimura, S.Kobayashi: SID 93 DIGEST, PP.622, (199
The VT characteristic 21 of the liquid crystal display panel by 3)) is shown. In the present embodiment, the state is a normally black state, a sufficient light-shielding state is obtained below the threshold voltage, and steepness of the VT characteristic is obtained. On the other hand, in the comparative example, the state is normally white, but above the threshold voltage, light leakage occurs due to the occurrence of disclination lines, and a sufficient light shielding state cannot be obtained. Therefore, the steepness is deteriorated.
In the present embodiment as well, the disclination line is generated above the threshold voltage, but the relative transmittance does not change significantly due to the disclination line.

FIG. 4 shows the measurement of the viewing angle 22 of the present embodiment and the viewing angle 23 of the comparative example at the halftone voltage at which the relative transmittance at the front viewing angle is 50%. The respective regions have a contrast ratio of 10. In this example, it was confirmed that the viewing angle was wider than that of the comparative example due to the occurrence of a plurality of domains and the improvement in steepness.

Further, when a reflection plate 10 is provided on the polarizing plate 9 on one side to perform a reflection type display, 1/64 Duty
In the multiplex drive of (1), a high-contrast and wide-viewing display was achieved in which the viewing angle ensuring a front contrast ratio of 30: 1 or more and a contrast ratio of 10: 1 or more was 40 ° or more in each of the upper, lower, left, and right directions. In this configuration, since the display is performed by the birefringence effect of light, the steepness is improved as the retardation is increased. In this embodiment, the retardation (Δn × d) is set to 0.912 μm. If the retardation is 1 μm or more, the transmittance of light propagating through the liquid crystal layer varies depending on the wavelength, and coloring occurs. If the retardation is 0.45 μm or less, the steepness sufficient for multiplex driving cannot be obtained, and the display is Not preferable. Therefore, the retardation is 0.45 μm <Δn ×
A range of d <1 μm is practically preferable. It is sufficiently possible to apply this configuration to an active matrix type panel. A plastic substrate such as polyethersulfone can be used instead of the glass substrate. (Example 2) In the same manner as in Example 1, one of two plastic substrates with ITO (for example, polyarylate substrate: manufactured by Teijin Limited) has a polyimide thin film having a horizontal alignment action (for example, RN-779: Nissan Kagaku). (Made by corporation)
A silane coupling having vertical alignment (for example, ODS-E: manufactured by Chisso Petrochemical Co., Ltd.) is applied to the other substrate, and each substrate is baked on a hot plate at 130 ° C. for 10 minutes. After that, spacers having a particle size of 6 μm are dispersed on one plastic substrate so that the distribution density is about 200 per square mm, and the two plastic substrates are bonded with a sealant. A chiral nematic liquid crystal having a positive dielectric anisotropy (Δn = 0.134) adjusted to have d / p of 0.25 is injected at a temperature of NI point or higher, and is slowly cooled and sealed to obtain a plastic. A substrate liquid crystal display panel is obtained. Next, polarizing plates are arranged on the surfaces of the upper and lower plastic substrates so that their absorption axes are orthogonal to each other, and light is incident from one substrate side.

FIG. 5 is a perspective view showing an alignment state of liquid crystal molecules in a pixel when no voltage is applied in this embodiment. The director 13 presents a vertical state and a horizontal state at the upper and lower substrate interfaces, respectively, and has a continuous and twisted alignment state between the substrates. There are regions (domains) 24, 25, 26, 27 in which the director directions of the horizontally aligned liquid crystal molecules are different, and a disclination line 28 is generated between the domains. In this state, the linearly polarized light becomes an elliptically polarized light state in each domain due to the birefringence effect and is transmitted through the polarizing plate on the output side.

Next, by applying a voltage, the director of the liquid crystal molecules is displaced so as to be parallel to the electric field vector. The threshold voltage depends on d / p, and the threshold voltage tends to increase as d / p increases.

In the case of the structure of this embodiment, the retardation above the threshold voltage is smaller than that of the TN type multi-domain liquid crystal panel described in the first embodiment. Therefore, for the same applied voltage, the smaller the retardation value, the smaller the polarization rotation of the light passing through the liquid crystal layer, and the linearly polarized light is transmitted, so that the light leakage is reduced and high contrast display is possible. In addition, the generation of a plurality of domains also has an effect of wide viewing angle. Further, as in Example 1, the display retardation is preferably 0.45 μm <Δn × d <1 μm,
In this embodiment, it is set to 0.804.

Furthermore, in the present embodiment, when a reflecting plate is provided on the surface of one of the polarizing plates to form a liquid crystal display panel of a reflection type, the deterioration of the display quality due to the spacers has almost no effect and the good display quality is obtained. Was confirmed to get. In addition, since it is not necessary to perform rubbing, it is possible to prevent a decrease in yield due to rubbing, and it is also very effective in shortening the manufacturing process.

Although the plastic substrate of the present invention uses polyarylate as the plastic substrate in the above embodiments, other materials such as polyether sulfone and polycarbonate may be used.

[0026]

As is apparent from the above description,
The liquid crystal display panel of the present invention can be manufactured without rubbing treatment, and achieves high contrast by twisting liquid crystal molecules in a vertical alignment or twist hybrid alignment and wide viewing angle by multi-domain. However, it has a very great effect on shortening the manufacturing process, improving the yield, and further improving the display quality.

[Brief description of drawings]

FIG. 1 is a sectional view of a liquid crystal display panel according to a first embodiment of the present invention.

FIG. 2 is a perspective view showing a microscopic alignment state in a pixel according to the first embodiment of the present invention.

FIG. 3 is a graph showing a V-T characteristic of Example 1 of the present invention.

FIG. 4 is a diagram showing viewing angle characteristics in Example 1 of the present invention.

FIG. 5 is a perspective view showing a microscopic alignment state in a pixel of Example 2 of the present invention.

FIG. 6 is a perspective view of a TN type liquid crystal display panel in a voltage applied state.

[Explanation of symbols]

 1 Upper Glass Substrate 2 Segment Electrode 3 Lower Glass Substrate 4 Common Electrode 5 Polyimide Thin Film 6 Chiral Nematic Liquid Crystal Layer 7 Spacer 8 Sealing Material 9 Polarizing Plate 10 Reflecting Plate

Claims (6)

[Claims] 1. A liquid crystal display panel comprising a liquid crystal layer sandwiched between a pair of substrates, wherein the liquid crystal layer is a chiral nematic phase having negative dielectric anisotropy, and the spontaneous spiral axis of the chiral nematic phase is the Alignment in which the liquid crystal molecules of the liquid crystal layer are substantially perpendicular to the surface of the substrate and in which a voltage smaller than a threshold voltage is applied or no voltage is applied to the liquid crystal molecules. A liquid crystal display panel, which exhibits a state and in which a plurality of regions having different tilt directions of the molecular long axes of the liquid crystal molecules are generated when a voltage equal to or higher than the threshold voltage is applied. 2. A liquid crystal display panel having a liquid crystal layer sandwiched between a pair of substrates, wherein the liquid crystal layer is a chiral nematic phase having a positive dielectric anisotropy, and the molecular long axis of liquid crystal molecules of the liquid crystal layer. However, there is a plurality of regions in which the liquid crystal molecule major axis is aligned in a microscopically uniform direction with a pretilt angle of horizontal or several degrees with respect to the interface of one of the substrates,
And the liquid crystal molecule long axis is vertically or inclined vertically aligned with respect to the interface of the other opposite substrate, the liquid crystal molecules exhibit a twisted alignment state between the pair of substrates, and the liquid crystal molecule long axis of the region between the regions. A liquid crystal display panel, which is present in different directions and has a plurality of disclination lines in the vicinity of the substrate interface and in the liquid crystal layer. 3. The spontaneous spiral pitch (p) of the chiral nematic phase and the interlayer distance (d) of the liquid crystal layer are 0 <d / p <
The liquid crystal display panel according to claim 1 or 2, wherein the relationship of 0.5 is satisfied. 4. The product of the refractive index anisotropy (Δn) of liquid crystal molecules and the liquid crystal layer thickness (d) is 0.45 μm <Δn × d <
The thickness is 1 μm.
The liquid crystal display panel described. 5. A first polarizing plate and a reflector are provided on the surface of one substrate opposite to the surface in contact with the liquid crystal layer, and the side opposite to the surface of the other substrate in contact with the liquid crystal layer. Is provided with a second polarizing plate, and the first and second polarizing plates are
The liquid crystal display panel according to any one of claims 1 to 4, wherein the absorption axes are arranged so as to be orthogonal to each other. 6. The liquid crystal display panel according to claim 1, wherein at least one of the pair of substrates is a plastic substrate.