JP3026901B2 - LCD panel - Google Patents

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 using electro-optical characteristics of a liquid crystal, and more particularly to a technique for enlarging a viewing angle of a 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 their large screens and large capacities. The operation mode of a liquid crystal display panel currently generally put into practical use is a twisted nematic (TN) type in which liquid crystal molecules exhibit a twisted alignment state of 90 ° between two glass substrates, 180 ° to 2 °.
There is a super twisted nematic (STN) type exhibiting 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 are uniformly and unidirectionally aligned at a certain pretilt angle with respect to the glass substrate at the glass substrate interface, and exhibit a state of being twisted by 90 ° between the upper and lower glass substrates. In such a 90 ° twist alignment state, generally, an alignment film made of a polyimide thin film formed on a glass substrate is rubbed in one direction using a rayon cloth or the like, and is arranged so that the direction is orthogonal between the upper and lower substrates. It is obtained by doing.

As shown in FIG. 6, when a voltage is applied to the TN type liquid crystal panel, the liquid crystal molecules which have been twisted by 90 ° begin to respond at a threshold voltage or higher, the twisted alignment state is released, and the liquid crystal molecules become splay alignment state. Means that the molecular long axis rises with respect to the glass substrate plane. When observing liquid crystal molecules while changing the azimuth angle Ψ at a position inclined by θ with respect to the substrate normal (Z axis), the direction 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 azimuthal direction, and the amount of birefringence (Δn) which is a product of the thickness (d) of the liquid crystal layer.
d) changes. Therefore, a polarizing plate is arranged so that the absorption axis is orthogonal to the rubbing direction on the outer surfaces of the upper and lower glass substrates, and when light is incident from the −Z-axis direction, the transmission intensity of the light varies with the change in the azimuthal direction, and the viewing angle is reduced. Asymmetry occurs. This asymmetry of the viewing angle is particularly problematic in the case of halftone display, and causes a reduction in display quality such as an extremely low contrast ratio depending on the viewing angle direction, or inversion of the displayed image. For this reason, in TN type liquid crystal display panels, efforts to increase the viewing angle have been actively made in recent years. As an example, a method of expanding a viewing angle by dividing a pixel of a TN type liquid crystal display panel into two regions having different alignment states (for example,
Takatori, Ke Sumiyoshi, Wai Hirai, S Kaneko: Japan Display '92, p.591, p.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 processing twice in order to divide the orientation region of one pixel into two, which complicates the process steps. Other methods have been proposed to further simplify the process and increase the viewing angle (Wy Toko, T.
Sugima, K. Kato, Y. Imla, S. Kobayashi: S.I.D. 93 Digest, 622 pages,
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 the liquid crystal molecules without performing a rubbing process, thereby increasing the viewing angle.

[0005]

In the above method, in order to perform switching by the polarization rotation effect of light, a chiral agent is added to a nematic liquid crystal to rotate liquid crystal molecules by 90 ° between upper and lower substrates, and the chiral nematic liquid crystal is added. 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 a polarizer is arranged on the substrate surface of this liquid crystal display panel so that the absorption axes thereof are orthogonal to each other and a voltage of a rectangular wave is applied, the liquid crystal molecules are in a splay alignment state above the threshold voltage, so that the initial alignment state is different. Disclination lines occur between the areas. When viewed from an oblique direction due to the occurrence of the disclination line, the viewing angle is increased, but the disclination line becomes a bright line, causing light leakage, and a sufficient contrast ratio cannot be obtained. There is also a problem that the drive voltage is increased due to disclination.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a liquid crystal display panel which solves the above-mentioned problems of the conventional technique of widening the viewing angle and which can increase the viewing angle and prevent a decrease in contrast ratio due to disclination lines. .

[0007]

According to a first aspect of the present invention, there is provided 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 negative dielectric anisotropy. The liquid crystal layer is provided on the inner surfaces of the pair of substrates.
Alignment film having vertical alignment action which is not rubbed
In contact with, the spontaneous spiral axis of the chiral nematic phase is substantially perpendicular to the surface of the substrate, and in a voltage applied state or a voltage non-applied state smaller than a threshold voltage, the liquid crystal molecules of the liquid crystal layer have a long molecular axis. The liquid crystal molecules exhibit an alignment state perpendicular or inclined perpendicular to the interface of the substrate, and in a voltage applied state equal to or higher than the threshold voltage , the liquid crystal molecules change their twist alignment state.
Exhibited, inclination direction different regions of the molecular long axis of the liquid crystal molecules is a liquid crystal display panel, characterized in that multiple occurrences.

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

[0009]

According to the first aspect of the present invention, the liquid crystal molecules take a vertical alignment state or a slightly inclined vertical alignment state at the interface between the upper and lower substrates, and the direction of the molecular long axis (hereinafter referred to as a director) is twisted between the upper and lower substrates. It is oriented in a state. In this state, the liquid crystal exhibits a uniform alignment state. When a polarizing plate is arranged on the substrate surface so that its absorption axis is orthogonal, the light that has entered as linearly polarized light propagates in the liquid crystal layer as linearly polarized light, is almost cut off by the polarizing plate on the emission side, and is sufficiently shielded. Is obtained. In a state where a voltage equal to or higher than the threshold voltage is applied, the liquid crystal molecules in the vertical alignment or the tilted vertical alignment have a director direction perpendicular to the electric field vector depending on the electric field strength. It becomes a bent alignment state. In this state, light incident as linearly polarized light is transmitted as elliptically polarized light due to the birefringence of the liquid crystal layer, and is emitted. Although the director direction is uniform in a small area (hereinafter, the area having the same director direction is referred to as a domain), since the domains are oriented in an arbitrary direction, a plurality of domains having different director directions are used. Will occur. When viewed from an oblique direction, the generation 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 one substrate interface, and are horizontally aligned at the other substrate interface, so that the liquid crystal molecules are continuously twisted between the upper and lower substrates. 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 the 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 is changed to an elliptically polarized state due to a birefringence effect due to a change in the director in the domain, and is transmitted through the output side polarizing plate. Above the threshold voltage, the liquid crystal molecules are deformed in accordance with the electric field strength so that the director direction becomes parallel to the electric field vector, and under sufficient electric field strength, the director becomes completely parallel to the electric field vector, and the 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 polarization plane, it is shielded by the output side polarizing plate. Therefore, since a plurality of domains having different director directions are generated, the contrast ratio is improved by expanding the viewing angle and reducing the retardation by eliminating the dependence of the retardation in the oblique direction on the angle.

[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 the 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, 9 is a polarizing plate and 10 is a reflecting plate. The manufacturing method will be described below.

An upper glass substrate 1 containing indium tin oxide (ITO) having a sheet resistance of 30 Ω / □ is patterned by photolithography to obtain 64 striped segment electrodes 2. Using the same method, 64 common electrodes 4 are formed on the lower glass substrate 3. 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 ° is formed by a printing method. As a material of 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, a plastic spacer 7 (for example, Micropearl: Sekisui Fine Co., Ltd.) is 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 printed and formed around 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 adhered 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: Merck Japan K.K.), a right-twisted chiral substance (eg, R-1011: Merck) is added, and the value of the spontaneous twist pitch p with respect to the cell gap d is 0 ≦.
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 an isotropic state and injected between the glass substrates 1 and 3 by a vacuum injection method. At this time, the glass substrates 1 and 3 also have a nematic phase-isotropic phase transition temperature (N
(Point I) or higher. 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.

A polarizing plate 9 is attached to the surfaces of the glass substrates 1 and 3 of the liquid crystal display panel manufactured as described above so that their absorption axes are orthogonal to each other. Light enters from the lower glass substrate 3 and is observed from above the upper glass substrate 1. In an applied voltage state equal to or lower than the threshold voltage, the liquid crystal molecules are in a vertical alignment state vertically or slightly inclined 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, so that a light-shielding state is obtained on the surface of the output polarizing plate.

FIG. 2 shows the liquid crystal display panel of this embodiment at 1/6.
FIG. 4 is a perspective view illustrating a microscopic alignment state in a pixel at an ON voltage when driven at 4 Duty. Reference numeral 13 in FIG. 2 represents a molecular long axis (director) of the liquid crystal molecule. Regions (domains) where the directors at the glass substrate interface are different
A plurality of 5, 16, and 17 disclination lines 18 occurred because the direction of the director was different between the domains. In a normal liquid crystal display panel, since a polyimide thin film is rubbed, only one domain in which the direction of a director is the same is seen in a pixel. In the case of the present embodiment, the rubbing treatment was not performed on the polyimide thin film, so that the liquid crystal molecules were oriented in an amorphous state due to the intermolecular force with the polyimide thin film, and the tilt direction was not defined. Is considered to have occurred. In each domain, the liquid crystal molecules exhibit a twisted state between the upper and lower glass substrates according to the set value of d / p. In the case of the present embodiment, since d / p is set to 0.25, the liquid crystal molecules are oriented with the director direction twisted by 90 ° between the upper and lower glass substrates. In this case, the 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 generation of a plurality of domains eliminates the anisotropy of the retardation in the viewing angle direction. Therefore, the viewing angle does not depend on the transmitted light intensity, and as a result, the viewing angle is enlarged.

FIG. 3 shows an applied voltage-relative transmittance characteristic (hereinafter referred to as a VT characteristic) 20 of the liquid crystal display panel of this embodiment. As a comparative example, a TN type multi-domain system (Y-
Toko, T. Sugiyama, K. Kato, Y. Imla, S. Kobayashi: S.I.D. 93 Digest, 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 according to 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 the steepness of the VT characteristic is also obtained. On the other hand, in the comparative example, although the state is a normally white state, if the voltage is equal to or higher than the threshold voltage, light leakage occurs due to generation of a disclination line, and a sufficient light shielding state cannot be obtained. For this reason, the steepness is also deteriorated.
In this embodiment as well, a disclination line occurs at a threshold voltage or higher, but the relative transmittance does not significantly change 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 a halftone voltage at which the relative transmittance at a front view angle is 50%. Each shows a region where the contrast ratio is 10. In this example, it was confirmed that the viewing angle was wider than that of the comparative example due to the generation of a plurality of domains and the improvement in steepness.

Further, when a reflection type display was performed by providing a reflection plate 10 on one side of the polarizing plate 9, 1/64 Duty
In the multiplex drive, a display with a high contrast and a wide viewing angle of 40 degrees or more in each of the upper, lower, left, and right directions with a front contrast ratio of 30: 1 or more and a contrast ratio of 10: 1 or more was achieved. In the present configuration, display is performed by the birefringence effect of light, so that greater retardation improves steepness. In this embodiment, the retardation (Δn × d) is set to 0.912 μm. When the retardation is 1 μm or more, coloring occurs because the transmittance of light propagating through the liquid crystal layer varies depending on the wavelength. When the retardation is 0.45 μm or less, sharpness sufficient for performing multiplex driving cannot be obtained, and Not preferred. Therefore, the retardation is 0.45 μm <Δn ×
The range of d <1 μm is practically preferable. It is sufficiently possible to apply this configuration to an active matrix panel. Further, a plastic substrate such as polyethersulfone can be used instead of the glass substrate. (Example 2) A polyimide thin film (for example, RN-779: Nissan Chemical) having a horizontal alignment effect on one of two plastic substrates with ITO (for example, polyarylate substrate: manufactured by Teijin Limited) in the same manner as in Example 1. Co., Ltd.)
A silane coupling having a vertical orientation (for example, ODS-E: manufactured by Chisso Petrochemical Co., Ltd.) is applied to the other substrate, and each is baked on a hot plate at 130 ° C. for 10 minutes. Thereafter, spacers having a particle size of 6 μm are dispersed on one of the plastic substrates 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 so that d / p becomes 0.25 is injected at a temperature equal to or higher than the NI point, gradually cooled, sealed, and then cooled. Obtain a substrate liquid crystal display panel. Next, polarizing plates are arranged on the upper and lower plastic substrates so that their absorption axes are orthogonal to each other, and light is incident from one of the substrates.

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 exhibits a vertical state and a horizontal state at the upper and lower substrate interfaces, respectively, and is in a continuous and twisted alignment state between the substrates. There are regions (domains) 24, 25, 26, and 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 state due to the birefringence effect in each domain, and transmits through the polarizing plate on the emission 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 at the threshold voltage or higher 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 less the polarization rotation of light passing through the liquid crystal layer, and the light propagates as linearly polarized light, so that light leakage is reduced and high contrast display is possible. The generation of a plurality of domains also has the effect of a wide viewing angle. Further, similarly to the first embodiment, the retardation on display is preferably 0.45 μm <Δnxd <1 μm.
In this embodiment, it is set to 0.804.

Further, in this embodiment, when a reflection 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 by the spacer is hardly affected, and the display quality is good. Is confirmed to be obtained. Further, since it is not necessary to perform rubbing, it is possible to prevent a decrease in yield due to rubbing, and there is a great effect in shortening the manufacturing process.

Although the plastic substrate of the present invention uses polyarylate as the plastic substrate in the above embodiment, 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 performing a rubbing process, and realizes a high contrast by twisting liquid crystal molecules in a twisted vertical alignment or a twisted hybrid alignment, and a wide viewing angle by multi-domain. However, it has a very large effect on shortening the manufacturing process, improving the yield, and further improving the display quality.

[Brief description of the 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 illustrating a microscopic alignment state in a pixel according to the first embodiment of the present invention.

FIG. 3 is a graph showing VT characteristics of Example 1 of the present invention.

FIG. 4 is a diagram illustrating viewing angle characteristics according to the first embodiment of the present invention.

FIG. 5 is a perspective view showing a microscopic alignment state in a pixel according to a second embodiment of the present invention.

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

[Explanation of symbols]

 DESCRIPTION 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 Polarizer 10 Reflector

Continuation of the front page (56) References JP-A-6-95120 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02F 1/1337

Claims (6)

(57) [Claims] 1. 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 negative dielectric anisotropy, and the liquid crystal layer is
Unrubbed vertical alignment on the inner surfaces of a pair of substrates
In contact with an alignment film having an effect, the spontaneous spiral axis of the chiral nematic phase is substantially perpendicular to the surface of the substrate, and in a voltage applied state or a voltage non-applied state smaller than a threshold voltage, liquid crystal molecules of the liquid crystal layer Presents an alignment state in which the major axis of the molecule is perpendicular or inclined perpendicular to the interface of the substrate, and when a voltage equal to or higher than the threshold voltage is applied , the liquid crystal
A liquid crystal display panel in which a plurality of liquid crystal molecules exhibit a twist alignment state, and a plurality of regions in which the liquid crystal molecules have different inclination directions of the molecular long axis are generated. 2. In a liquid crystal display panel having a liquid crystal layer sandwiched between a pair of substrates, the liquid crystal layer is a chiral nematic phase having a positive dielectric anisotropy, and a molecular long axis of liquid crystal molecules of the liquid crystal layer is provided. However, with a pretilt angle of horizontal or several degrees with respect to the interface of one of the substrates, there are a plurality of regions in which the major axis of the liquid crystal molecules are microscopically oriented in a uniform direction,
And the liquid crystal molecule long axis is vertically or obliquely vertically aligned with respect to the interface of the other opposing substrate, the liquid crystal molecules exhibit a twisted alignment state between the pair of substrates, and the liquid crystal molecule long axis is aligned between the regions. A liquid crystal display panel having a plurality of disclination lines in directions different from each other and near 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) between the liquid crystal layers are 0 <d / p <.
The liquid crystal display panel according to claim 1, wherein a relationship of 0.5 is satisfied. 4. The product of the refractive index anisotropy (Δn) of liquid crystal molecules and the thickness (d) of the liquid crystal layer is 0.45 μm <Δn × d <
4. The method according to claim 1, wherein the thickness is 1 μm.
Liquid crystal display panel as described. 5. A first polarizing plate and a reflecting plate are provided on a surface of one substrate opposite to a surface in contact with the liquid crystal layer, and a surface of the other substrate opposite to a surface in contact with the liquid crystal layer. Are 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 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.