JP2002202529A - Liquid crystal display device and method of manufacturing for the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely implement transfer from spray orientation to bent orientation with a liquid crystal display device which makes display by subjecting the orientation state of the liquid crystal molecules in a liquid crystal cell to the orientation described above by impressing voltage above the threshold to the liquid crystal layer. SOLUTION: The liquid crystal display device having two substrates 102 facing each other and the liquid crystal layer 101 gasped between the substrates is specified to <=0.7 deg. in the difference between the absolute value of the pretilt angle of the liquid crystal molecules existing near the one substrate and the absolute value of the pretilt angle of the liquid crystal molecules existing near the other substrate. The region where the liquid crystal molecules having the molecular axis horizontal with respect to the substrate plane in the liquid crystal layer 101 are maldistributed more to one substrate side than the central part of the liquid crystal layer and the regions where the liquid crystal molecules are maldistributed more to the other substrate side than the central part of the liquid crystal layer are thereby regulated to exist approximately uniformly when the voltage below the threshold is impressed to the liquid crystal layer 101.

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 device used for a liquid crystal television, a liquid crystal monitor and the like.

[0002]

2. Description of the Related Art Conventionally, a TN type liquid crystal display device has been generally used as a liquid crystal display device. In addition, as a liquid crystal display device featuring high-speed response, an optical compensation bend mode (Optica
lly self-Compensated Bend mode; hereinafter, referred to as “OCB”. ) Type liquid crystal display devices are being studied. In addition, OC
For the B-type liquid crystal display device, refer to “IEICE Technical Report EDI98-144, p. 199”.

In this OCB type liquid crystal display device, a liquid crystal layer is sandwiched between substrates, and a transparent electrode is formed as a voltage applying means on the surface of the substrate on the liquid crystal layer side. Before the power is turned on, the alignment state of the liquid crystal is in a state called splay alignment. When the power of the device is turned on, a relatively large voltage is applied to the voltage applying means in a short time to change the orientation of the liquid crystal to a bend orientation state.
Displaying using this bend alignment state is a feature of the OCB type liquid crystal display device.

[0004]

However, in the conventional OCB type liquid crystal display device, the transition to the bend alignment state is not reliable, and the pixels in the splay alignment state remain, which causes the display of a bright spot defect or the like. There was a problem of becoming a defect.

[0005] It is an object of the present invention to provide a liquid crystal display device capable of reliably performing transition from splay alignment to bend alignment.

[0006]

According to the liquid crystal display device of the present invention, by applying a voltage to a liquid crystal layer sandwiched between two substrates, the alignment state of the liquid crystal layer is changed from splay alignment to bend alignment. Then, display is performed.

In such a liquid crystal display device, an initial alignment state in which no voltage is applied is a splay alignment in which liquid crystal molecules are arranged substantially horizontally (FIG. 2A). When a relatively high voltage is applied to the liquid crystal layer in this initial state, bend alignment occurs from a specific portion, and a bend transition nucleus is formed (FIG. 2).
D). However, in the region other than the region where the bend transition nuclei are generated, a portion where the liquid crystal molecules which are substantially horizontal with respect to the substrate plane are present on one substrate side due to the splay alignment (FIGS. 2B and 2C). . Such a state occurs on both of the two substrates. That is, as shown in FIG. 2, there are two states in which the portion where the liquid crystal molecules substantially horizontal to the plane of the substrate exists is unevenly distributed on one substrate side. Hereinafter, these two states are referred to as an up-spray state (FIG. 2B) and a down-spray state (FIG. 2C).

The present inventors have examined this splay alignment-bend alignment transition mechanism in more detail. When only one of the upspray state and the downspray state occurs preferentially, the state is stabilized. As a result, it has been found that the speed of transition from the stable state to the bend orientation becomes slow, and the certainty of the transition decreases.

In order to achieve the above object, a first liquid crystal display device of the present invention comprises two substrates facing each other and a liquid crystal layer sandwiched between the substrates, wherein the liquid crystal layer has a threshold value or more. A liquid crystal display device that performs display by applying a voltage of the liquid crystal layer to change the alignment state of liquid crystal molecules in the liquid crystal layer from splay alignment to bent alignment, and a voltage less than the threshold is applied to the liquid crystal layer. In the liquid crystal layer, a region in which liquid crystal molecules whose molecular axes are horizontal to the substrate plane are unevenly distributed on one substrate side from the center of the liquid crystal layer, and the other is located on the other side of the center of the liquid crystal layer. It is characterized in that the region unevenly distributed on the substrate side exists substantially evenly.

With such a configuration, in the process of transition from the splay alignment to the bend alignment, the state from the application of voltage to the transition to the upspray state or the downspray state (the state prior to the upspray state or the downspray state). ) Can be made relatively long. The state before the up-spray state or the down-spray state is relatively unstable. When bend transition nuclei are generated in such a state, the bend orientation rapidly grows. Therefore, according to the first liquid crystal display device, the transition to the bend alignment can be performed quickly and reliably.

In the first liquid crystal display device, when a voltage less than the threshold value is applied to the liquid crystal layer, the liquid crystal molecules whose molecular axis is horizontal to the plane of the substrate are applied to the liquid crystal layer. The area ratio (U: D) of the region (U) unevenly distributed on one substrate side from the center of the layer and the region (D) unevenly distributed on the other substrate side from the center of the liquid crystal layer is 40: It is preferable to be in the range of 60 to 60:40.

In order to achieve the above object, a second liquid crystal display device of the present invention comprises two substrates facing each other and a liquid crystal layer sandwiched between the substrates, wherein the liquid crystal layer has a threshold value or more. A liquid crystal display device that performs display by changing the alignment state of the liquid crystal molecules in the liquid crystal layer from the splay alignment to the vent alignment by applying a voltage of the pre-tilt angle of the liquid crystal molecules existing near one substrate. The absolute value,
The difference from the absolute value of the pretilt angle of the liquid crystal molecules existing near the other substrate is 0.7 degrees or less.

The difference between the pretilt angles of the two substrates is large (that is, the asymmetry of the pretilt angle is large).
Then, one of the up-spray state and the down-spray state is preferentially stabilized, and as a result, the certainty of the transfer is reduced. On the other hand, according to the second liquid crystal display device, by increasing the symmetry of the pretilt angle between the two substrates, it is possible to make the probabilities of the up-spray state and the down-spray state almost equal, As a result, in the process of shifting from the splay alignment to the bend alignment, the time for unstable alignment before the upspray state or the downspray state can be made relatively long, and the transition to the bend alignment is quickly and reliably performed. It is possible to do.

In the second liquid crystal display device, the absolute value of the pretilt angle of the liquid crystal molecules existing near one substrate and the absolute value of the pretilt angle of the liquid crystal molecules existing near the other substrate are both determined. Is also preferably 4 degrees or less.

According to a third aspect of the present invention, there is provided a liquid crystal display device comprising: two substrates facing each other; and a liquid crystal layer sandwiched between the substrates. A liquid crystal display device that performs display by applying the above voltage to change the alignment state of liquid crystal molecules in the liquid crystal layer from splay alignment to bent alignment, and performs a pretilt angle of liquid crystal molecules existing near one substrate. , And the absolute value of the pretilt angle of the liquid crystal molecules existing near the other substrate is 4 degrees or less.

Conventionally, it has been said that the larger the pretilt angle, the more likely the transition occurs. However, the present inventors have found that in consideration of mass productivity, variation in pretilt angle, and the like, transition is more likely to occur as the pretilt angle is relatively small. The present invention is based on such knowledge, and improves the symmetry of the pretilt angle between two substrates by setting the absolute value of the pretilt angle to 4 degrees or less. As a result, the transition to the bend alignment is achieved. Can be performed promptly and reliably.

Further, in the first to third liquid crystal display devices, it is preferable that a bend transition nucleus inducing means is formed on at least one of the substrates. As the bend transition nucleus inducing means, means for causing a part of the liquid crystal layer to be twisted can be used. The bend transition nucleus inducing means includes, for example, convex structures such as spherical structures and columnar structures, concave structures, electric field applying means for applying a lateral electric field to the liquid crystal layer, and asymmetric carbon atoms. An alignment film or the like can be used. Further, it is also possible to use a nonlinear element formed on the substrate as a means for inducing bend transition nuclei.

In addition, the first to third liquid crystal display devices include:
It is preferably an OCB type liquid crystal display device.

In order to achieve the above object, a first manufacturing method of the present invention comprises two substrates facing each other, and a liquid crystal layer sandwiched between the substrates, wherein the liquid crystal layer has a threshold value or more. A method for manufacturing a liquid crystal display device, in which display is performed by applying a voltage to change the alignment state of liquid crystal molecules in the liquid crystal layer from splay alignment to bent alignment, and performing rubbing on a surface of the substrate in contact with the liquid crystal layer. A rubbing density of 2 in the rubbing alignment treatment.
0000 mm ² or more.

According to such a manufacturing method, the liquid crystal display device of the present invention as described above can be manufactured.

[0021] In the first manufacturing method, it is preferable that the rubbing amount is 0.3 mm or more.

In order to achieve the above object, a second manufacturing method of the present invention comprises two substrates facing each other, and a liquid crystal layer sandwiched between the substrates, wherein the liquid crystal layer has a thickness not less than a threshold value. A method for producing a liquid crystal display device in which a voltage is applied to cause a liquid crystal molecule in the liquid crystal layer to transition from a splay alignment to a bent alignment to perform display, and the liquid crystal layer is aligned on a surface of the substrate in contact with the liquid crystal layer. Forming a film precursor and baking it to form an alignment film, wherein when the baking temperature in the forming process is changed by 20%, the pretilt of liquid crystal molecules in contact with the alignment film is increased. The alignment film is characterized in that the amount of change in the angle can be 0.5 degrees or less.

The liquid crystal display device of the present invention as described above can be manufactured by such a manufacturing method.

In order to achieve the above object, a third manufacturing method of the present invention comprises two substrates facing each other, and a liquid crystal layer sandwiched between the substrates, wherein the liquid crystal layer has a thickness not less than a threshold value. A method for producing a liquid crystal display device in which a voltage is applied to cause a display state by shifting an alignment state of liquid crystal molecules in the liquid crystal layer from a splay alignment to a bent alignment. In a state in which a voltage less than the threshold is applied to the layer, a region in the liquid crystal layer, in which liquid crystal molecules whose molecular axes are horizontal to the substrate plane are unevenly distributed on one substrate side from the center of the liquid crystal layer. An inspection step of evaluating an area ratio of the liquid crystal layer to a region unevenly distributed on the other substrate side from the center of the liquid crystal layer.
In the third manufacturing method, a liquid crystal display device in which the area ratios are substantially equal in the inspection step is accepted.

According to such a manufacturing method, the first liquid crystal display device of the present invention as described above can be manufactured more reliably.

In the first to third manufacturing methods, it is preferable that the liquid crystal display is an OCB type liquid crystal display.

[0027]

FIG. 1 is a sectional view showing an example of the structure of a liquid crystal display device according to the present invention. In this liquid crystal display device, two substrates 102 are arranged to face each other via a spacer, and a liquid crystal layer 101 is sandwiched between the substrates 102. Although not shown, a transparent electrode and an alignment film are formed on the surface of the substrate 102 on the liquid crystal layer 101 side, respectively. Also, on the surface of the substrate 102 opposite to the liquid crystal layer 101 side,
A polarizing plate 104, a phase compensating plate 103, and the like are appropriately arranged. Further, the liquid crystal display device includes a voltage applying unit for applying a voltage to the liquid crystal layer via the transparent electrode.

In the liquid crystal display device, in the initial state where no voltage is applied to the liquid crystal layer, the liquid crystal layer is in a splay alignment (see FIG. 2A). In the splay alignment, the tilt (tilt angle) of the liquid crystal molecules with respect to the substrate plane is small over the entire liquid crystal layer, and the molecular axes of the liquid crystal molecules are substantially horizontal to the substrate plane at the center of the liquid crystal layer. It is. That is, the portion where the liquid crystal molecules whose molecular axis is horizontal to the substrate plane exists at the center of the liquid crystal layer. In addition, the liquid crystal layer has a so-called parallel alignment having substantially no twisted structure over the entire liquid crystal layer, and the alignment of the liquid crystal is almost vertically symmetric.

When a voltage (for example, about 25 V) equal to or more than a threshold value is applied to the liquid crystal layer in the initial state in a direction perpendicular to the substrate plane, the alignment state of the liquid crystal layer is changed to bend alignment (see FIG. 2D). it can. FIG. 1 schematically shows the alignment state of liquid crystal molecules when the liquid crystal layer is in a bend alignment. In the bend alignment, the absolute value of the tilt angle of the liquid crystal molecules is small near the surfaces of both substrates, and the absolute value of the tilt angle of the liquid crystal molecules is large in the central portion of the liquid crystal layer, and is substantially perpendicular to the substrate plane. .

As described above, the liquid crystal display device performs display by changing the alignment state of the liquid crystal layer from the splay alignment to the bend alignment. An example of such a liquid crystal display device is an OCB type liquid crystal display device.

In the liquid crystal display device of the present embodiment, when a voltage lower than the threshold is applied to the liquid crystal layer, the above-described area in the up-spray state and the area in the down-spray state are substantially equal. Has been adjusted to exist. Specifically, when a voltage lower than the threshold value is applied to the liquid crystal layer, a region (U) in an up-spray state is obtained.
The area ratio (U: D) of the area to be in the down spray state (D) is, for example, 40:60 to 60:40, and preferably 45:55 to 55:45.

The area ratio can be measured as follows. 1V without bend transition
When a voltage of the order of magnitude is applied, the up-spray state and the down-spray state described above occur. When this is observed from a direction inclined from the front, particularly from a direction inclined in the rubbing direction, the two types of regions can be easily distinguished because they look different colors and brightness. Then, the area ratio can be obtained by calculating the area ratio of the two regions thus determined.

Furthermore, it is preferable that such an upspray area and a downspray area exist in each pixel. This also proves that the upspray state and the downspray state coexist if a disclination line is generated in the pixel under observation with a microscope under the same voltage application state as described above. Further, it is preferable that the area ratio of the region in the up-spray state and the region in the down-spray state in each pixel is within the above range.

In order to obtain such characteristics, in the liquid crystal display device of the present embodiment, it is desired that the absolute values of the pretilt angles of the two substrates are as equal as possible, that is, the symmetry of the pretilt angles is good. . This is because the better the symmetry of the pretilt angle, the more quickly and surely the bend transition can be realized at a low voltage. Specifically, the difference between the absolute value of the pretilt angle of the liquid crystal molecules present near one substrate and the absolute value of the pretilt angle of the liquid crystal molecules present near the other substrate is preferably 0.7 degrees or less,
More preferably, the angle is adjusted to 0.5 degrees or less. By setting the pretilt angle difference in the above range, it is possible to realize quick and reliable bend transition at a relatively low voltage (for example, 25 V or less). The lower limit of the difference between the absolute values of the pretilt angles is 0 degree or more.

The pretilt angle (θ) is defined as follows: the inclination of the molecular axis of the liquid crystal molecules with respect to the substrate plane is -90 ° ≦ θ ≦ 90 with respect to the state horizontal to the substrate plane (θ = 0 °).
This is an angle expressed in the range of °.

In the liquid crystal display device of the present embodiment, it is preferable that the variation of the pretilt angle in the same substrate is small for each of the two substrates. This is because the smaller the variation of the pretilt angle, the easier it is to improve the symmetry of the pretilt angle between the two substrates. For example, the variation amount of the pretilt angle in the same substrate is, for example, 0 to 0.7 degrees, preferably 0 to 0.5 degrees.

Further, in the liquid crystal display device of the present embodiment, the absolute value of the pretilt angle of the liquid crystal molecules existing near both substrates is set relatively small. This is because the smaller the absolute value of the pretilt angle is, the smaller the variation of the pretilt angle becomes, and as a result, it becomes easier to improve the symmetry of the pretilt angle between the two substrates. The absolute value of the pretilt angle is, for example, 4 degrees or less, preferably 3 degrees or less, and more preferably 2 degrees or less. The lower limit of the absolute value of the pretilt angle is not particularly limited, but is preferably 1 degree or more. If the temperature is less than 1 degree, bend transition may not easily occur.

In the liquid crystal display device according to the present embodiment, as a method for improving the symmetry of the pretilt angle, for example, the following method can be mentioned.

(First Method) The first method is to form an alignment film on the surface of the substrate which is in contact with the liquid crystal layer, and to reduce the variation in pretilt angle by selecting the type of the alignment film. . As described above, since the variation can be reduced as the pretilt angle is smaller, the absolute value of the pretilt angle of the liquid crystal molecules present at the interface with the alignment film can be controlled as small as possible. Preferably, a material is used. The preferred range of the pretilt angle is as described above.

For example, when a polyimide-based alignment film is used, the length of the side chain extending from the main chain of the polyimide is reduced, the density of the side chain is reduced, the imidization ratio of the polyimide is reduced, and the film hardness is increased. By such a method, the pretilt angle can be reduced. As for the length of the side chain, the total number of carbon atoms in the side chain is desirably 10 or less. As for the side chain density, polyimide having side chains (P
It is desirable that the ratio (P1 / P2) of the polyimide (P2) having no side chain to 1) be 1/3 or less. Further, the imidization ratio is desirably 90% or less, and the film hardness is desirably H or more in pencil hardness.

It is also effective to use, as the alignment film, a material capable of minimizing the variation of the pretilt angle with respect to the variation of the forming conditions. For example, in the case of a polyimide-based alignment film, the polyimide precursor is baked in the forming step, and the variation of the pretilt angle when the calcination temperature is changed by 20% may be 0.5 degrees or less. preferable. Similarly, the firing time is set to 20%.
It is preferable that the amount of change in the pretilt angle when changed is 0.5 degrees or less. Examples of the alignment film having such characteristics include, for example, a polyimide-based alignment film such as "SE7992 (trade name)" manufactured by Nissan Chemical Co., and "JALS1051 (trade name)" manufactured by Nippon Synthetic Rubber Co., Ltd. Can be

The second method is a method in which an alignment film is formed on the surface of the substrate in contact with the liquid crystal layer, and the conditions for forming the alignment film are adjusted to reduce the variation in the pretilt angle. For example, when a polyimide-based alignment film is used, the higher the firing temperature when firing the polyimide alignment film precursor, the more the variation in pretilt angle can be reduced. Similarly, the longer the firing time, the more the variation in pretilt angle can be reduced.

The third method is to reduce the variation in pretilt angle by performing a rubbing treatment on the surface of the substrate in contact with the liquid crystal layer and, when forming an alignment film, on the alignment film surface and adjusting the processing conditions. It is. As the strength of the rubbing process is increased, the pretilt angle can be reduced, and as a result, the variation in the pretilt angle can be reduced.

In the rubbing treatment, generally, the surface of the substrate (or alignment film) is fixed with a pile raised from the rubbing cloth by rotating a rotating roller around which the rubbing cloth is wound while approaching the substrate moving in a certain direction. This is performed by rubbing in the direction. In this case, the strength of the rubbing treatment can be evaluated, for example, by the rubbing density [mm ² ]. Here, the rubbing density R [m
m ² ] is expressed as follows: R = l × v × t = 2 (z × r) ^1/2 · 2πr × p / 60.2 (z × r) ^1/2 / s = 0.42zr ² p / s It is. Here, l is the contact distance [mm], v is the linear velocity [mm / s], t is the processing time [s], and z is the pushing amount [m].
m], r is the radius of the roller [mm], π is the pi, p is the number of rotations of the roller [rpm], s is the moving speed of the substrate [mm /
s]. The contact distance is defined as the length of the tip of the pile raised from the rubbing cloth in contact with the substrate, and the linear velocity is defined as the speed at which the tip of the pile raised from the rubbing cloth moves on the substrate. The pushing amount is defined as the difference between the length of the pile foot raised from the rubbing cloth and the distance from the base of the pile foot to the substrate.

In this method, the rubbing density is set to 20 in order to realize a good pretilt angle symmetry.
It is preferable that the thickness be 000 mm ² or more. By setting such a range, good bend transition characteristics can be achieved. Further, the upper limit of the rubbing density is not particularly limited, for example, 40,000 m
m ² or less. Further, a more preferable range of the rubbing density is 20,000 to 35000 mm ² .

In the rubbing treatment, the rubbing density is preferably adjusted by adjusting the amount of indentation. For example, when the number of rotations of the roller is 600, the moving speed of the substrate is 20 mm / s, and the radius of the roller is 75 mm, the pushing amount is preferably 0.3 mm or more, and more preferably 0.5 mm or more. preferable. The upper limit of the pushing amount is not particularly limited, but is, for example, 0.9 mm or less. If this value is exceeded, the problem that other scratches are likely to occur may occur. FIG. 3 is a graph showing an example of the relationship between the pushing amount and the pretilt angle when the rubbing process is performed under the above conditions.

There is also a factor that varies the pretilt during the manufacturing process. During the manufacturing process of a liquid crystal panel using an active matrix substrate, TF
An ionizer blower (static elimination gun) is generally installed to prevent electrostatic breakdown of the T element. Here, the charged substrate is discharged by blowing ionized air. As shown in FIG. 4B, the present inventor has found that when the ionizer blower 2402 is locally irradiated, the pretilt of the irradiated portion is locally reduced. Since it is extremely rare that the pretilt lowers at the same place in both substrates to be combined, such pretilt fluctuation causes pretilt asymmetry.

In order to prevent the pretilt fluctuation, it is sufficient to irradiate the whole surface of the ionizer blower instead of irradiating it locally. FIG. 4A is a conceptual diagram showing the structure. As described above, by using the ionizer blower 2403 having a plurality of injection ports to perform uniform irradiation from the upper surface of the substrate, the variation amount of the pretilt can be made uniform. Here, the ionizer blower is most needed when the substrate is lifted and separated from the stage. At this time, irradiation is performed from the upper surface of the substrate.

Further, in the liquid crystal display device of the present invention,
Preferably, at least one of the substrates has a bend transition nucleus inducing means. As shown in FIG. 5, when such a bend transition nucleus inducing means is provided, even if the absolute value of the absolute value of the pretilt angle of the liquid crystal molecules existing near both substrates is slightly large, it is quick and reliable at a relatively low voltage. Bend transition can be achieved. Therefore, when a bend transition nucleus inducing means is provided, the difference in the absolute value of the pretilt angle can be adjusted to preferably 1 degree or less, more preferably 0.8 degree or less. In addition, by intentionally making the specific substrate side asymmetric and forming a transition nucleus on the specific substrate side, it is possible to favorably transfer even asymmetric two degrees or less.

As means for inducing bend transfer nuclei, for example,
A convex structure formed on the substrate surface can be employed. FIG. 6 is a sectional view showing an example of a liquid crystal display device having such a convex structure. Near the region where the convex structure 210 is formed, the orientation of the liquid crystal molecules is different from the orientation of the surrounding liquid crystal region, and the liquid crystal layer forms a slight twist orientation in this region. The splay-to-bend transition can be rapidly progressed by applying a voltage to the portion where the twist orientation is formed, and a bend transition nucleus can be formed.

The shape of the convex structure 210 is not particularly limited. For example, a columnar structure such as a circular column, an elliptic column, a triangular column and a quadrangular column, and a cone-shaped structure such as a cone, a triangular pyramid and a quadrangular pyramid can be used. A body, a spherical structure and the like can be used.

Further, as long as the convex structure 210 can form a convex shape on the surface of the substrate 102 which is in contact with the liquid crystal layer 101, the location where the convex structure 210 is formed is not particularly limited. However,
As shown in FIG. 6, when the alignment film 106 is formed on the substrate, it is formed below the alignment film 106. For example, the convex structure 210 may be formed so as to be interposed between the substrate 102 and the electrode 105 as shown in FIG. 6 or may be formed so as to be interposed between the electrode and the alignment film. .

The size of the convex structure 210 is not particularly limited. For example, the ratio (h / T) of the height (h) of the convex structure 210 to the thickness (T) of the liquid crystal layer 101 is 0.3 to 1.0, preferably 0.8 to 1.0. Can be adjusted as follows. Specifically, the h is, for example, 2.5 to 5 μm, preferably 4 to 5 μm.
5 μm.

The number of the convex structures 210 is not particularly limited, either. One or more, preferably 1 to 100, is preferably present for each pixel.

With respect to the material for forming the convex structure 210,
There is no particular limitation, and various insulating materials can be used. Examples of such an insulating material include an acrylic photoresist. The use of a photoresist has an advantage that the etching process can be simplified.

The method of forming such a convex structure 210 is not particularly limited. For example, when a photoresist is used as a material for forming the convex structure, a method in which the photoresist is formed on a substrate and then patterned into a desired shape by photolithography can be employed. If the material for forming the convex structure is not a photoresist, a film of the material for forming the convex structure is formed on a substrate, a photoresist is applied thereon, and the photoresist is applied by photolithography. After patterning into a desired shape, a method of etching the convex structure forming material using this as a mask can be adopted. When a spherical structure is used as the convex structure, a method of dispersing particles having a desired shape in an appropriate resin and applying the dispersed resin on a substrate can also be adopted.

In addition, a concave structure may be used instead of the convex structure. The shape of the concave structure is not particularly limited, for example, a column having a columnar concave portion such as a cylinder, an elliptic column, a triangular column, and a square column, and a cone-shaped concave portion such as a cone, a triangular pyramid, and a square pyramid. And the like.

The size of the concave structure is not particularly limited. For example, the depth of the concave portion of the concave structure may be set in the same manner as the height of the convex portion of the convex structure. it can. Also, the location of the concave structure,
The number and forming material are the same as those of the convex structure. In addition, as a method for forming the concave structure, a method using a photolithography method as exemplified as the method for forming the convex structure can be employed.

Further, as the bend transition nucleus inducing means, a lateral electric field applying means can be adopted. FIG. 7 is a sectional view showing an example of a liquid crystal display device having such a lateral electric field applying means. In this liquid crystal display device, a pixel electrode 214 and a nonlinear element 212 electrically connected to the pixel electrode 214 are formed on one substrate 102. As the non-linear element 212, for example, a thin film transistor (TFT) can be used. Further, a gate line (not shown) for operating the nonlinear element 212 and a source line 213 for supplying an electric signal to the pixel electrode are formed on the substrate. In addition, FIG.
The pixel electrode 214, the nonlinear element 212,
FIG. 4 is a plan view illustrating an example of an arrangement of a gate line 215 and a source line 213.

In the liquid crystal display device having such a configuration, a convex portion is formed on the surface of the first substrate 208 due to the presence of the nonlinear element 212, and this is used as a bend transition nucleus inducing means, like the above-mentioned convex structure. Function. The ratio (h / T) of the height (h) of the projections formed on the surface of the active matrix substrate to the thickness (T) of the liquid crystal layer is as follows:
For example, it can be adjusted to be 0.02 to 0.2, preferably 0.1 to 0.2. Specifically, the h
Is, for example, 0.1-1 μm, preferably 0.5-1 μm
It is.

Further, by applying a voltage to the pixel electrode 214 and the source line 213, a horizontal electric field can be generated between the two. When such a lateral electric field is applied to the liquid crystal layer, a twisting effect is given to the liquid crystal molecules, and a bend transition nucleus can be formed in this portion.

For the liquid crystal display device having the structure shown in FIG. 7, for example, a bend transition can be generated by applying a voltage having a waveform as shown in FIG. Briefly describing this transition waveform, a +25 V, 1 second DC waveform is applied to an electrode (opposite electrode) formed on the other substrate (a substrate having no nonlinear element), a voltage of ± 7 V is applied to the source line, An AC rectangular waveform of 30 Hz (field frequency) and 50% duty is applied. At this time, a voltage of 7 V is applied to the pixel electrode. In addition, +15 V is applied to the gate line.

As a structure of the substrate provided with such a lateral electric field applying means, a structure as shown in FIG. 10 can be adopted. In this example, a capacitor electrode 216 is formed on one substrate 102, and an insulating film 217 is formed so as to cover the capacitor electrode 216. Then, the insulating film 217
The pixel electrode 214 is formed thereon. Pixel electrode 214
Are formed so as to overlap with the capacitance electrode 216. Further, the pixel electrode 214 has a slit in a portion overlapping with the capacitor electrode 216. Also, this substrate 20
7 and 8, a non-linear element connected to the pixel electrode 214, a gate line and a source line are formed. When such a structure is adopted, a transverse electric field is generated in the slit portion, whereby a plurality of twist orientations can be formed to generate a bend transition nucleus.

A bend transition can be generated in the liquid crystal display device having the structure shown in FIG. 10, for example, by applying a voltage having a waveform as shown in FIG. This transition waveform will be briefly described.
A DC waveform of 5 V and 1 second is applied, while an AC rectangular waveform of voltage ± 7 V, frequency 30 Hz (field frequency) and duty 50% is applied to the source line. At this time, a voltage of 7 V is applied to the pixel electrode. In addition, +15 V is applied to the gate line. Further, the same voltage as that of the counter electrode is applied to the capacitor electrode. Note that the capacitor electrode and the counter electrode may be structurally short-circuited. Also,
Immediately before applying such a transition waveform, it is desirable not to apply an electric field between the liquid crystal layer, that is, the pixel electrode and the counter electrode. In order to realize this, both the counter electrode and the source line may be set to 0V.

It is also possible to form an alignment film containing an asymmetric carbon atom on at least one of the substrates and use this as a means for inducing bend transition nuclei. When an alignment film having an asymmetric carbon atom is used, a twist effect is exerted on liquid crystal molecules existing near the asymmetric carbon atom, and a bend transition nucleus can be formed in this portion.

As such an alignment film, for example, a polymer compound having an asymmetric carbon atom can be used. In this case, the asymmetric carbon atom may be contained in the main chain or the side chain of the polymer compound. Further, the alignment film may be a mixture of a low molecular compound containing an asymmetric carbon atom and a high molecular compound.

The alignment film is preferably a polymer compound having an asymmetric carbon atom in the main chain, and particularly preferably a polyimide compound having an asymmetric carbon atom in the main chain. Such a polyimide-based compound can be represented, for example, by the following general formula [Chemical Formula 1] or [Chemical Formula 2].

[0068]

Embedded image

[0069]

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[0070] However, in the [formula 1] and [Formula 2], R is (n is an integer of 1 or more.) C _n H _{2n + 1} or its halogen substituents, for example, CH ₃ , CH
F ₂ and CF ₃ . X represents -COO-, -O-, -C =
C -, - is or -C = C-hydrogen or halogen substituents - CH _2.

Here, what is necessary is to have an asymmetric carbon, which tends to cause a twist alignment in the liquid crystal molecules. This facilitates the transfer. When the base of the side chain has an asymmetric carbon, the entire side chain has an effect of generating twisted orientation. Even if it is in the middle of the side chain or at the tip, it is effective to some degree. The highest effect is at the base of the side chain. Furthermore, the longer the length of the side chain is, the more effective it is. It is desirable that the total number of carbon atoms is 3 or more.

Compounds suitable as the alignment film include:
Specifically, the following compounds can be exemplified.

[0073]

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The method and conditions for forming such an alignment film are not particularly limited. For example, conditions can be selected so as to obtain the pretilt angle as described above. Also, the thickness of the alignment film is not particularly limited.
nm, preferably 70-100 nm.

According to the liquid crystal display device of this embodiment, as described above, by improving the symmetry of the pretilt angle, the upspray state and the downspray state when a voltage less than the threshold is applied to the liquid crystal display device. The existence ratios of the states are adjusted substantially equally. As a result, in this liquid crystal display device, in the process of applying a voltage equal to or higher than the threshold value to transition from the splay alignment to the bend alignment, the time required from the voltage application to the transition to the up spray state or the down spray state is relatively long. , For example, about 0.5 seconds. As described above, if the time until the transition to the up-spray state or the down-spray state is long, the time required for the unstable orientation before that becomes long. When a bend transition nucleus is generated in such a state, the bend orientation rapidly grows, so that the transition to the bend orientation can be quickly and reliably performed.

To provide such a liquid crystal display device,
In the manufacturing process, after manufacturing a liquid crystal display device, a voltage lower than a threshold is applied to the liquid crystal layer, and the area ratio between a region in an upspray state and a region in a downspray state in the liquid crystal layer is evaluated. The area ratio is substantially equal, preferably 40:60 to 60:40, and more preferably 45:60.
An inspection step may be performed so that the liquid crystal display device having a ratio of 55 to 55:45 is accepted. This inspection step can be performed by applying a voltage of, for example, about 1 V to the liquid crystal layer and observing the display surface in this state from a direction inclined from the front, particularly from a direction inclined in the rubbing direction. . In this case, the two types of regions can be easily distinguished because they look different colors and brightness.

[0077]

The present invention will be described below in more detail with reference to examples. However, the present invention is not limited by the following examples.

Example 1 A liquid crystal cell having the same structure as that of FIG. 1 was manufactured in the following manner. First, two glass substrates are prepared, and indium tin oxide (hereinafter referred to as “ITO”) is formed on each of them with a thickness of 200 nm, and is patterned by photolithography and etching to form an ITO electrode. Formed. afterwards,
On the substrate, a polyimide-based alignment film material ("RN7492 (trade name)" manufactured by Nissan Chemical Industries, Ltd.) is applied by a spin coating method so as to cover the ITO electrode, and this is applied at 180 ° C for 1 hour in a thermostat. By curing, an alignment film was formed.

Thereafter, the alignment film on the substrate was subjected to a rubbing treatment using a rubbing cloth made of rayon. The rubbing treatment uses a rotating roller wrapped with a rubbing cloth,
The rotation was performed while approaching the substrate moving in a certain direction, and the surface of the alignment film was rubbed in a certain direction with a pile raised from a rubbing cloth. The rubbing conditions were as follows: the number of rotations of the roller was 600, the moving speed of the substrate was 20 mm / s, the radius of the roller was 75 mm, and the pushing amount was 0.5 mm. That is, the rubbing density was 35000 mm ² .

The two substrates are arranged so as to face each other via a spacer (manufactured by Sekisui Fine Chemical Co., Ltd.), and the edges thereof are sealed with a sealing resin (“Stract Bond 352A (product name)” manufactured by Mitsui Toatsu Chemicals, Inc.). ) To produce a cell. In the cell, the substrate interval was 6.5 μm. In the cell, a liquid crystal (“MJ9” manufactured by Merck Japan Ltd.) was used.
6435 (trade name) ": refractive index anisotropy Δn = 0.13
8) was injected by a vacuum injection method to obtain a liquid crystal cell A.

In the above liquid crystal cell A, the pretilt angle of the liquid crystal molecules existing at the interface of the alignment film was measured, and it was found that the pretilt angle was 3 to 3.2 degrees on one substrate side and 3.2 to 3.2 degrees on the other substrate side.
It was 3.5 degrees. The pretilt angle was measured by a crystal rotation method.

A polarizing plate was stuck on both sides of the liquid crystal cell A, and a 20 V rectangular wave was applied between the electrodes of the liquid crystal cell A. The transition from the splay alignment to the bend alignment was observed. All electrode regions transitioned from splay alignment to bend alignment. Note that the polarizing plates were arranged such that the polarizing axes thereof make an angle of 45 degrees with the rubbing direction of the alignment film, and the directions of the polarizing axes were orthogonal to each other.

Further, when 1 V was applied between the electrodes of the liquid crystal cell 1A and the existence ratio of the region in the up-spray state and the region in the down-spray state was evaluated, it was confirmed that these two regions were present almost equally. did it. The evaluation was made by observing from the direction inclined by 30 ° in the rubbing direction from the front, and comparing the area ratios of domains that appeared in two different colors.

(Comparative Example 1) A liquid crystal cell R was produced in the same manner as described above, except that in the rubbing treatment applied to the alignment film, the indentation amount was 0.2 mm, and the moving speed of the substrate was 60 mm / s. That is, in this comparative example, the rubbing density was set to 4700 mm ² .

In the liquid crystal cell R, the pretilt angle of the liquid crystal molecules existing at the interface of the alignment film was measured to be 4 to 5 degrees on one substrate side and 5 to 6 degrees on the other substrate side.

Further, on both surfaces of the liquid crystal cell R, the first embodiment was used.
In the same manner as described above, a polarizing plate was bonded to each other, a 20 V rectangular wave was applied between the electrodes, and the transition from the splay alignment to the bend alignment was observed. No transition to bend orientation occurred.

[0087]

As described above, according to the liquid crystal display device of the present invention, the time during which the liquid crystal alignment becomes unstable during the transition from the splay alignment to the bend alignment can be made relatively long. As a result, the transition to the bend alignment can be performed quickly and reliably.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating an example of a liquid crystal display device of the present invention.

FIG. 2 is a schematic diagram for explaining a transition process of the liquid crystal display device of the present invention.

FIG. 3 is a diagram illustrating a relationship between a pushing amount and a pretilt angle during a rubbing process.

FIG. 4 is a schematic view showing the operation of an ionizer blower.

FIG. 5 is a diagram showing a relationship between asymmetry of a pretilt angle between both substrates and a voltage required for transition.

FIG. 6 is a sectional view showing another example of the liquid crystal display device of the present invention.

FIG. 7 is a sectional view showing still another example of the liquid crystal display device of the present invention.

8 is a plan view illustrating an arrangement of pixel electrodes and various wirings in the liquid crystal display device illustrated in FIG.

9 is a diagram showing an example of a transition waveform applied to the liquid crystal display device shown in FIG.

FIG. 10 is a sectional view showing still another example of the liquid crystal display device of the present invention.

11 is a diagram showing an example of a transition waveform applied to the liquid crystal display device shown in FIG.

[Explanation of symbols]

 Reference Signs List 101 liquid crystal 102 substrate 103 retardation plate 104 polarizing plate 105 transparent electrode 106 alignment film 210 convex structure 212 nonlinear element 213 source line 214 pixel electrode 215 gate line 216 capacitance electrode 217 insulating film

Continued on the front page (72) Inventor Yoshiki Tanaka 1006 Kazuma Kadoma, Kazuma, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. Inventor Junichi Kobayashi 1006 Kazuma Kadoma, Kadoma City, Osaka Prefecture F-term (reference) 2H088 GA02 HA03 JA10 JA12 KA14 LA06 MA04 MA18 2H090 HD14 KA07 KA18 MA03 MB01 MB14

Claims (28)

[Claims] 1. A liquid crystal display device comprising: two substrates opposed to each other; and a liquid crystal layer sandwiched between the substrates, and by applying a voltage equal to or greater than a threshold value to the liquid crystal layer, aligning liquid crystal molecules in the liquid crystal layer. A liquid crystal display device that performs display by shifting a state from a splay alignment to a vent alignment, and when a voltage less than the threshold is applied to the liquid crystal layer, a molecular axis of the liquid crystal layer with respect to the substrate plane. A region in which horizontal liquid crystal molecules are unevenly distributed on one substrate side from the central portion of the liquid crystal layer and a region unevenly distributed on the other substrate side than the central portion of the liquid crystal layer are substantially uniformly present. Liquid crystal display device. 2. When a voltage lower than the threshold value is applied to the liquid crystal layer, liquid crystal molecules whose molecular axis is horizontal to the plane of the substrate in the liquid crystal layer are closer to one side than the center of the liquid crystal layer. The area ratio (U: D) of the region (U) unevenly distributed on the substrate side and the region (D) unevenly distributed on the other substrate side from the center of the liquid crystal layer is in a range of 40:60 to 60:40. The liquid crystal display device according to claim 1. 3. The liquid crystal display device according to claim 1, wherein a bend transition nucleus inducing means is formed on at least one of the substrates. 4. The liquid crystal display according to claim 3, wherein the bend transition nucleus inducing means is a convex structure or a concave structure formed on the substrate. 5. The method according to claim 3, wherein the vent transition nucleus inducing means is an electric field applying means for applying a lateral electric field to the liquid crystal layer.
3. The liquid crystal display device according to 1. 6. The liquid crystal display device according to claim 3, wherein said bent transition nucleus inducing means is means for causing a part of said liquid crystal layer to be twisted. 7. An OCB type liquid crystal display device.
7. The liquid crystal display device according to any one of 6. 8. A liquid crystal display device comprising: two substrates facing each other; and a liquid crystal layer sandwiched between the substrates, and by applying a voltage equal to or more than a threshold to the liquid crystal layer, aligning liquid crystal molecules in the liquid crystal layer. A liquid crystal display device that performs display by shifting a state from a splay alignment to a bent alignment, and displays an absolute value of a pretilt angle of liquid crystal molecules existing near one substrate and a pretilt angle of liquid crystal molecules existing near the other substrate. Wherein the difference from the absolute value of is less than or equal to 0.7 degrees. 9. An absolute value of a pretilt angle of liquid crystal molecules existing near one substrate and an absolute value of a pretilt angle of liquid crystal molecules existing near the other substrate are each 4 degrees or less. 9. The liquid crystal display device according to 8. 10. The liquid crystal display device according to claim 8, wherein a bend transition nucleus inducing means is formed on at least one of the substrates. 11. The liquid crystal display device according to claim 10, wherein the bend transition nucleus inducing means is a convex structure or a concave structure formed on the substrate. 12. The liquid crystal display device according to claim 10, wherein said bent transition nucleus inducing means is an electric field applying means for applying a lateral electric field to said liquid crystal layer. 13. The method according to claim 1, wherein the bent transition nucleus inducing means is a means for causing a part of the liquid crystal layer to be twisted.
The liquid crystal display device according to 0. 14. An OCB type liquid crystal display device.
14. The liquid crystal display device according to any one of items 13 to 13. 15. A liquid crystal display device comprising: two substrates facing each other; and a liquid crystal layer sandwiched between the substrates, and by applying a voltage higher than a threshold value to the liquid crystal layer, aligning liquid crystal molecules in the liquid crystal layer. A liquid crystal display device that performs display by shifting a state from a splay alignment to a bent alignment, and an absolute value of a pretilt angle of liquid crystal molecules existing near one substrate,
A liquid crystal display device, wherein the absolute value of the pretilt angle of the liquid crystal molecules existing near the other substrate is 4 degrees or less. 16. The liquid crystal display device according to claim 15, wherein a bend transition nucleus inducing means is formed on at least one of the substrates. 17. The liquid crystal display device according to claim 16, wherein the bend transition nucleus inducing means is a convex structure or a concave structure formed on the substrate. 18. The liquid crystal display according to claim 16, wherein said bent transition nucleus inducing means is an electric field applying means for applying a lateral electric field to said liquid crystal layer. 19. The vent transition nucleus inducing means is means for causing a part of the liquid crystal layer to be twisted.
7. The liquid crystal display device according to 6. 20. An OCB type liquid crystal display device.
20. The liquid crystal display device according to any one of 5 to 19. 21. A liquid crystal display device comprising: two substrates facing each other; and a liquid crystal layer sandwiched between the substrates, and by applying a voltage higher than a threshold value to the liquid crystal layer, aligning liquid crystal molecules in the liquid crystal layer. A method for manufacturing a liquid crystal display device that performs display by shifting a state from a splay alignment to a vent alignment, and includes a step of performing a rubbing process on a surface of the substrate that is in contact with the liquid crystal layer, wherein a rubbing density of the rubbing alignment process is reduced. A method for manufacturing a liquid crystal display device, wherein the size is 20,000 mm ² or more. 22. A rubbing process in which the amount of indentation is 0.
22. The method for manufacturing a liquid crystal display device according to claim 21, which is not less than 3 mm. 23. The method according to claim 21, wherein the liquid crystal display device is an OCB type liquid crystal display device. 24. A liquid crystal display device comprising: two substrates facing each other; and a liquid crystal layer sandwiched between the substrates, and by applying a voltage higher than a threshold value to the liquid crystal layer, aligning liquid crystal molecules in the liquid crystal layer. A method for manufacturing a liquid crystal display device that performs display by shifting a state from a splay alignment to a vent alignment, wherein an alignment film precursor is formed on a surface of the substrate that is in contact with the liquid crystal layer, and baked to form an alignment film. Forming a film, wherein the alignment film has a baking temperature of 2 in the forming step.
A method for manufacturing a liquid crystal display device, characterized in that the liquid crystal display device is an alignment film capable of reducing the amount of change in the pretilt angle of liquid crystal molecules in contact with the alignment film to 0.5 degree or less when 0% is changed. 25. The method according to claim 24, wherein the liquid crystal display device is an OCB type liquid crystal display device. 26. A liquid crystal display device comprising: two substrates facing each other; and a liquid crystal layer sandwiched between the substrates, and by applying a voltage equal to or higher than a threshold value to the liquid crystal layer, aligning liquid crystal molecules in the liquid crystal layer. A method for manufacturing a liquid crystal display device for performing display by shifting a state from a splay alignment to a bent alignment, wherein after the liquid crystal display device is manufactured, a voltage less than the threshold is applied to the liquid crystal layer. In the layer, the liquid crystal molecules whose molecular axes are horizontal to the substrate plane are unevenly distributed on one substrate side from the center of the liquid crystal layer, and the liquid crystal molecules are unevenly distributed on the other substrate side than the center of the liquid crystal layer. A method for manufacturing a liquid crystal display device, comprising an inspection step of evaluating an area ratio with respect to a region to be formed. 27. A liquid crystal display device in which the area ratios are substantially equal in the inspection step.
3. The method for manufacturing a liquid crystal display device according to item 1. 28. The method according to claim 26, wherein the liquid crystal display device is an OCB type liquid crystal display device.