JP2000122100A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal display element with an excellent alignment property. SOLUTION: The liquid crystal display element comprises a pair of substrates stuck together via stripe shaped partition members and liquid crystal with a smectic phase enclosed in a space on a straight line held between the substrates and the partition members. In this case, liquid crystal having >=3×10-6/K thermal expansion coefficient 501 of a smectic A phase layer of the liquid crystal in a direction normal to the layer is used.

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 used as a home, office and industrial information display terminal. In particular, the present invention relates to a liquid crystal display that holds a liquid crystal having a smectic phase in a liquid crystal panel frame to which a pair of substrates are bonded.

[0002]

2. Description of the Related Art Liquid crystal displays are widely used as display units for notebook computers because of their characteristics of low power consumption and space saving. In recent years, the size has increased,
It is expected that products with a size of 15 inches to 21 inches are being manufactured, and will gradually replace CRTs (Cathod Ray Tubes) used in desktop personal computers and televisions.

[0003] In addition to a type using a thin film transistor (TFT), a ferroelectric liquid crystal display (FLCD: Ferroelectric) using a chiral smectic C phase exhibiting ferroelectricity is used as a liquid crystal display.
Liquid Crystal Display) or anti-ferroelectric liquid crystal displays which use chiral smectic C _A phase exhibiting the antiferroelectric (AFLCD: Anti-Ferroelectric Liquid Cr
ystal Display). These are expected as next-generation liquid crystal displays, but the structure in which liquid crystal is sandwiched between a pair of glass substrates (liquid crystal panel frame) does not change in either liquid crystal display.

[0004] The distance between a pair of substrates is constant in a range of approximately 1 to 6 µm, but must be as uniform as possible.
For this purpose, a method of dispersing a spherical or rod-shaped substrate spacing support member called spacer beads between the substrates has been adopted.

[0005] The spacer beads are made of glass or resin, are dispersed in an appropriate solvent, and are applied and dried on a substrate. The coating and drying process is susceptible to static electricity and foreign matter. As a result, if the spacer beads are agglomerated or unevenly distributed, the spacing between the substrates becomes uneven and the display quality deteriorates. As the size of the liquid crystal panel increases, it becomes more difficult to spray the liquid crystal panel uniformly. In addition, since the spacer beads are only floating in the gap between the substrates, the spacing between the substrates is easily deformed and changed by an external pressure. However, such a problem also occurs that the spacer moves when the liquid crystal flows. . Still another problem exists on the display pixel because the position of the spacer cannot be controlled, and the display quality is degraded, such as white spots at that portion.

[0006] As a means for removing the disadvantages of the spacer bead dispersing method, there has been disclosed a technique in which a fine member is formed by photolithography to form a spacer, or further advanced, a pair of substrates is completely bonded through these. (For example, JP-A-63-50817, JP-B-2-36930, JP-A-4-255826, JP-A-7-84267, etc.).

According to these techniques, a spacing support member can be selectively formed in a non-pixel portion, and the uniformity of the substrate spacing is excellent. Since it is fixed on the substrate, it does not move, and the substrate can be washed, so that the yield at the time of cell production is extremely excellent. When completely adhered, the impact resistance of the panel is significantly improved,
It is suitable as a liquid crystal panel for ferroelectric liquid crystal and antiferroelectric liquid crystal in which the alignment layer is easily broken by impact.

In these liquid crystals, it is necessary not only to hold the liquid crystal in a panel having excellent impact resistance, but also to remove the zigzag defects peculiar to the layer structure of the smectic liquid crystal and to improve the alignment. (For example, JP-A-7-318912 and JP-A-8-87021). The reason is that it is necessary to move the liquid crystal molecules in the same direction as a whole in order to improve the orientation of these liquid crystals. The flow significantly improves the orientation. In order to flow, the liquid crystal must first be confined in a narrow and narrow space. In this state, the narrow space is cooled from one end (temperature gradient cooling). This process uses the effect that the liquid crystal molecules are dragged by volume contraction in the direction in which the temperature first decreases.

[0009]

[0005] Temperature gradient cooling is very effective in removing zigzag defects. But,
In our experiments, not all ferroelectric liquid crystals and antiferroelectric liquid crystals can dramatically remove zigzag defects, and some liquid crystals require a very steep and severe temperature gradient, In other liquid crystals, the effect was hardly recognized. Cells using such liquid crystals are:
Even when the temperature gradient cooling is not performed, zigzag defects and focal conics are intertwined with each other, and the alignment state is not good.

The present invention has been made in view of the above-mentioned circumstances, and an object thereof is to specify a coefficient of expansion of a liquid crystal layer in a normal direction and to specify a temperature range of a smectic A phase to obtain a good orientation. Is to provide a liquid crystal display device of the invention. In addition, it is an object of the present invention to provide a liquid crystal display device having a very good orientation by cooling with a temperature gradient.

[0011]

According to a first aspect of the present invention, a pair of substrates are adhered via a stripe-shaped partition member, and the pair of substrates are linearly sandwiched between the partition member and the substrate. A liquid crystal display device comprising a liquid crystal having a smectic phase in a space defined by the following formula.
A liquid crystal display element characterized in that the phase layer has a coefficient of thermal expansion in the layer normal direction of 3 × 10 ⁻⁶ / K or more.

According to a second aspect of the present invention, there is provided a liquid crystal display device, wherein the temperature range of the smectic A phase of the liquid crystal is 5 ° C. or more, and the liquid crystal has a chiral smectic C phase.

According to a third aspect of the present invention, there is provided a liquid crystal display device, wherein the temperature range of the smectic A phase of the liquid crystal is 15 ° C. or more, and the liquid crystal has a chiral smectic C _A phase.

According to a fourth aspect of the present invention, there is provided the liquid crystal display device, wherein the layer normal direction of the smectic phase is substantially parallel to the extension direction of the partition member.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
The thermal expansion coefficient of the liquid crystal is an important property because the temperature gradient cooling induces a flow in the liquid crystal by utilizing the drag due to the volume contraction. Even when cooling the entire panel uniformly, which is normally performed, strictly, there is a local temperature distribution, so that a local liquid crystal flow due to volume shrinkage should occur. Since the nematic phase has a flow property close to that of a liquid, the flow induced by volume shrinkage does not particularly affect the orientation. However, the smectic phase having a layer structure is
Since the movement of the liquid crystal between the layers in the normal direction of the layer is suppressed, the compound exhibits remarkable thermal expansion anisotropy unlike the nematic phase. It is considered that the liquid crystal flow induced by the volume shrinkage, particularly the flow in the direction normal to the layer, is smaller than the flow in the direction in the layer plane. The present inventors have found that the bending of the layer of the smectic phase induced by the flow in the direction of the layer normal is the cause of the zigzag defect, and that controlling the direction of this flow leads to the removal of the zigzag defect. According to this finding, the degree of thermal expansion in the layer normal direction is important. The degree of thermal expansion is what percentage of the length contracts, and is an amount determined by the coefficient of thermal expansion and the temperature range.

Therefore, the present inventors evaluated the thermal expansion of the smectic phase by a simple method and clarified the relationship with the orientation. The evaluation method will be described with reference to FIG.

The substrates 101 and 102 are made of an alignment film material HL.
1110 (manufactured by Hitachi Chemical) by spin coating
The resultant was baked at 80 ° C. for 1 hour to obtain alignment films 103 and 104. A photoresist MP is formed on the alignment film 103 of the substrate 101.
-S1400-25 (manufactured by Shipley Fur East) was applied by spin coating, and dried at 90 ° C for 30 minutes. After drying, the film was exposed using a photomask having a stripe pattern, developed for 30 seconds with a developer MP-Developer (manufactured by Shipley Far East), and baked at 150 ° C. for 1 hour.
As a result, a partition member 105 having a resist stripe pattern with a thickness of about 1.6 μm on the substrate 101 was obtained. Next, each of the substrates 101 and 102 was rubbed.
Rubbing was performed when the rubbing direction 307 (see FIG. 3) was parallel to the partition member 304 and when it was perpendicular to the partition member 304. The substrates 101 and 102 were bonded together and heated at 170 ° C. for 1 hour while applying a pressure of about 1 atm using a jig. As a result, a panel body in which the substrates 101 and 102 were completely bonded via the partition member 105 was obtained. The liquid crystal was heated to the isotropic phase temperature under a reduced pressure atmosphere, and the liquid crystal was sealed from the end of the panel body by utilizing the capillary phenomenon. Before the liquid crystal reached the entire surface of the panel, the temperature was lowered to suspend the encapsulation, and the encapsulation opening was sealed with epoxy adhesive. As a result, a panel body in which the liquid crystal was sealed in a linear space closed on one side was obtained.

FIG. 2 is an explanatory view of an apparatus used for measuring thermal expansion. Two types of panel bodies 201 were prepared: a panel body 301 for evaluating thermal expansion in a layer surface direction according to a rubbing direction and a panel body 302 for evaluating thermal expansion in a layer normal direction. The panel body 201 was sandwiched between surface heaters 202 with temperature controllers.
At this time, the meniscus 2 on the liquid crystal surface on the unclosed side
03 was captured by the CCD camera 204. While gradually heating with the surface heater, the movement amount of the meniscus 203 at each temperature was observed. The thermal expansion ratio and the thermal expansion coefficient were obtained from the obtained data. One example of the measurement results is shown in FIG. With respect to the temperature on the horizontal axis, the vertical axis represents the ratio of the length of the liquid crystal portion at each temperature to the initial length of the liquid crystal portion as a change in thermal expansion. Graph 4
01 indicates a change in thermal expansion in the layer normal direction, and a graph 402 indicates a change in thermal expansion in the layer surface direction. FIG. 5 shows the coefficient of thermal expansion calculated from the above. The vertical axis represents the coefficient of thermal expansion with respect to the temperature on the horizontal axis. Graph 501 shows the coefficient of thermal expansion in the layer normal direction,
The graph 502 shows the coefficient of thermal expansion in the layer surface direction.

The change in thermal expansion showed a large difference between the layer normal direction and the layer surface direction. In the liquid crystal to which the temperature gradient cooling was effective, the change in thermal expansion in the layer normal direction was about 0.03% or more from the smectic A phase temperature to room temperature, and the lower limit was found in the coefficient of thermal expansion. On the other hand, the thermal expansion change in the layer plane direction from the smectic A phase temperature to room temperature was as large as about 3%, but was not found to have any particular effect on the orientation.

The zigzag defect, which is a defect peculiar to the ferroelectric liquid crystal and the antiferroelectric liquid crystal, is a portion where the direction of bending of the smectic layer generated in the smectic C phase is alternately changed. The cause of the bending is the volume shrinkage of the liquid crystal due to the temperature drop, and when this occurs unevenly, it causes the generation of zigzag defects. The temperature gradient cooling utilizes the non-uniformity of volume shrinkage and the fact that the flow history generated by flowing the liquid crystal in the layer normal direction is reflected in the bending of the layer. Since the flow of the liquid crystal induced by the temperature gradient cooling is caused by the volume contraction of the liquid crystal in the layer normal direction, it is desirable that the thermal expansion change in the layer normal direction is large.

As a result of examining the thermal expansion of some liquid crystals, it was found that the chiral smectic C phase and the chiral smectic C _A phase had almost no thermal expansion in the layer normal direction. Even if thermal expansion was observed, it was found that the value was close to the thermal expansion of the glass substrate and was not effective. on the other hand,
The nematic phase has significantly higher fluidity and thermal expansion than the smectic phase, but does not have a layer structure, and thus plays a role of flow but does not play a central role in determining the direction of bending of the layer. In the liquid crystal having a chiral smectic C _A phase, a substance having a nematic phase has not been confirmed.

More important than these phases are:
It is a smectic A phase having a layer structure and a change in thermal expansion. Since the smectic A phase can be freely deformed as long as the layer interval is maintained, the layer is curved by the flow. If cooled in this state, the layer will break in a curved direction,
Therefore, the bending of the layers can be made uniform. Therefore, zigzag defects can be eliminated.

The change in volume shrinkage required to cause the flow to align the layers in the direction of the bend is approximately 0.0 in the normal direction of the layer.
Experiments have shown that 3% is sufficient. As described above, unless this amount of shrinkage is obtained in the smectic A phase instead of the nematic phase, chiral smectic C phase, or chiral smectic C _A phase, there is no effect of aligning the bending directions of the layers. At this time, the amount of shrinkage is determined by the temperature range of the same phase as the expansion coefficient of the smectic A phase. This is because shrinkage hardly occurs when the coefficient of expansion is small, and large shrinkage cannot be obtained when the temperature range of the phase is narrow.

From the results of the experiment, it was found that if the coefficient of thermal expansion in the layer normal direction was 3 × 10 ⁻⁶ / K or more, the liquid crystal could flow due to volume contraction. Further, it was found that the liquid crystal having a chiral smectic C phase requires a temperature range of the smectic A phase of 5 ° C. or more.

Since a liquid crystal having a chiral smectic C _A phase does not have a nematic phase, when a smectic A phase is precipitated from an isotropic phase, a layer structure is formed simultaneously while aligning the orientation of liquid crystal molecules. Therefore, unless the layer structure is adjusted in the smectic A phase, good orientation cannot be obtained. Therefore, it is considered that a liquid crystal having a chiral smectic C _A phase requires a wider temperature range of the smectic A phase than a liquid crystal having no chiral smectic C _A phase. This was also about 15 ° C. from the result of the experiment.

[0026] Depending on the liquid crystal, a chiral smectic C phase and chiral smectic C _A phase, there are those having both phases both by the liquid crystal phase used in display elements, the temperature range of smectic A phase is determined. That is, when the chiral smectic C phase is used, the temperature range of the smectic A phase must be 5 ° C. or more, and when the chiral smectic C _A phase is used, the temperature range of the smectic A phase must be 15 ° C. or more.

[0027]

<Example 1> Orientation film material HL on glass substrate
1110 was applied by spin coating and baked at 180 ° C. for 1 hour to obtain an alignment film. Photoresist MP-S1400-25 was applied on the alignment film of one substrate by spin coating, and dried at 90 ° C. for 30 minutes. After drying, the film was exposed using a photomask having a stripe pattern, developed with a developer MP-developer for 30 seconds, and baked at 150 ° C. for 1 hour. As a result, a partition member having a stripe pattern of a resist having a thickness of about 1.6 μm was formed on the alignment film. Next, the substrate was rubbed in parallel with the partition member. The substrates are bonded together and pressurized at about 1 atm using a jig.
Heated at 70 ° C. for 1 hour. As a result, a panel body in which the substrate was completely bonded via the partition member was obtained. The end of the panel body except the sealing port was sealed with epoxy resin. Enclosure of liquid crystal
After the inside of the panel body was evacuated, the sealing opening was closed with liquid crystal and the atmosphere was returned to normal pressure by heating to an isotropic phase temperature.

The encapsulated liquid crystal is Felix-SCE9 (manufactured by Hoechst) having a chiral smectic C phase. The liquid crystal has a coefficient of thermal expansion in the layer normal direction from the smectic A phase to room temperature of about 2 × 10 −5 / K, and the temperature range of the smectic A phase is 22 ° C. The orientation of the panel body after completion of the encapsulation had uniform zigzag defects, but the other portions had a uniform good orientation. When this panel body was heated to the isotropic phase temperature and cooled along the partition member from the end of the panel body (temperature gradient cooling), zigzag defects disappeared and uniform good orientation was obtained over the entire panel body. Was.

<Example 2> A panel body was prepared and liquid crystal was sealed in the same manner as in Example 1. The encapsulated liquid crystal is TM-C108 (manufactured by Chisso) having a chiral smectic C phase. The coefficient of thermal expansion of the liquid crystal in the layer normal direction from the smectic A phase to room temperature is about 1 × 10 −5 / K, and the temperature range of the smectic A phase is 54 ° C. The orientation of the panel body after completion of the encapsulation had uniform zigzag defects, but the other portions had a uniform good orientation. When this panel body was subjected to temperature gradient cooling, zigzag defects disappeared and uniform good orientation was obtained over the entire panel body.

Example 3 A panel was prepared and liquid crystal was sealed in the same manner as in Example 1. Encapsulated liquid crystal is a CS4000 with chiral smectic C _A phase (manufactured by Chisso). The coefficient of thermal expansion of the liquid crystal in the layer normal direction from the smectic A phase to room temperature is about 3 × 10 ⁻⁶ / K, and the temperature range of the smectic A phase is 17 ° C. The orientation of the panel body after completion of encapsulation had good zigzag defects, but the other portions had a substantially uniform good orientation. When this panel body was subjected to temperature gradient cooling, zigzag defects disappeared and uniform good orientation was obtained over the entire panel body.

[0031]

According to the present invention, the liquid crystal material satisfying the present invention is selected and sealed in the panel frame bonded by the partition member, so that the volume shrinkage of the liquid crystal layer in the normal direction of the liquid crystal due to the temperature drop becomes sufficiently large. The flow of liquid crystal sufficient to cause layer deformation is induced, and the bending direction of the smectic layer is determined. Furthermore, by applying the temperature gradient cooling, the bending direction of the smectic layer can be completely determined in one direction,
Zigzag defects can be completely removed.

On the other hand, the thermal expansion in the direction of the layer surface is orders of magnitude larger than that in the direction of the normal to the layer, but since the directions are different, there is almost no contribution to the bending of the layer. As the size increases, the amount of shrinkage increases, which tends to cause alignment disorder and liquid crystal cracking. This problem can be avoided by partitioning the inside of the panel body with a partition member as in the panel body of the present invention, thereby limiting the length in the layer plane direction and suppressing the amount of shrinkage, and restricting the liquid crystal movement in the layer plane direction. it can.

[0033]

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a panel body applied in the present invention.

FIG. 2 is an explanatory diagram of an apparatus used for evaluation of thermal expansion.

FIG. 3 is an explanatory view showing a difference between a panel body for evaluating thermal expansion in a layer normal direction and a layer plane direction.

FIG. 4 is a graph showing an example of evaluation results of thermal expansion.

FIG. 5 is a graph showing an example of calculating a coefficient of thermal expansion.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 101 ... Substrate 102 ... Substrate 103 ... Orientation film 104 ... Orientation film 201 ... Panel body 202 ... Surface heater 203 ... Liquid crystal meniscus 204 ... CCD camera 205 ... Partition member 301 ... Panel normal direction evaluation panel body 302 ... Layer direction evaluation Panel body 303 Substrate 304 Partition member 305 Smectic layer surface 306 Liquid crystal molecules 307 Rubbing direction 401 Thermal expansion change at each temperature (layer normal direction) 402 Thermal expansion change at each temperature (layer surface direction) 501 each Coefficient of thermal expansion at temperature (layer normal direction) 502 ... Coefficient of thermal expansion at each temperature (layer direction)

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Mayumi Iguchi 1-5-1, Taito, Taito-ku, Tokyo Toppan Printing Co., Ltd. F-term (reference) 2H088 FA02 FA10 FA20 GA04 MA20 2H089 HA02 HA10 KA02 LA09 NA05 NA14 NA25 NA31 QA15 RA13 2H090 HA14 JB02 KA14 LA02 MB01

Claims (4)

[Claims] 1. A liquid crystal display device comprising a pair of substrates bonded to each other via a stripe-shaped partition member and sealing a liquid crystal having a smectic phase in a linear space between the partition member and the substrate. A liquid crystal display device comprising a liquid crystal having a coefficient of thermal expansion of 3 × 10 ⁻⁶ / K or more in a layer normal direction of a liquid crystal smectic A phase layer. 2. The liquid crystal display device according to claim 1, wherein
A liquid crystal display device, wherein a liquid crystal having a smectic A phase temperature range of 5 ° C. or higher and having a chiral smectic C phase is used. 3. The liquid crystal display device according to claim 1, wherein
A liquid crystal display device, wherein a liquid crystal having a smectic A phase temperature range of 15 ° C. or higher and having a chiral smectic C _A phase is used. 4. The liquid crystal display device according to claim 1, wherein the direction of the layer normal of the smectic phase is substantially parallel to the extension direction of the partition member.