JPS6023329B2 - Liquid crystal cell alignment treatment method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an alignment treatment method for a liquid crystal display device, specifically a dynamic scattering type display device using a liquid crystal having negative dielectric anisotropy, a guest host type color liquid crystal display device, and a method for aligning a liquid crystal display device. In a liquid crystal display device such as a color liquid crystal display device using an anisotropic liquid crystal due to the ECB effect, liquid crystal molecules are uniformly aligned in one direction perpendicular to the surface of the substrate that it touches or at an arbitrary angle from the perpendicular. The present invention relates to an alignment treatment method for treating the surface of a substrate.

Liquid crystal display devices are rapidly being put into practical use due to their characteristics of low voltage operation and low power consumption. Taking advantage of these characteristics, they are used in wristwatches, calculators, instrument panels, etc., but most of them are of the field effect type (TN). Although there is a strong demand for other operating systems and color display systems, these have drawbacks and have been problematic for practical use.

That is, one of the major obstacles was the lack of a good alignment display method for uniformly aligning liquid crystal molecules with negative dielectric anisotropy in one direction at an angle perpendicular to or close to perpendicular to the substrate surface. FIG. 1 explains a dynamic scattering type (abbreviated as DS type) display, in which a liquid crystal 6 is sandwiched between substrates 1 and 2, and the outer periphery is sealed with a sealing material 5. .

Electrodes 3 and 4 are formed inside the substrate, as shown in Figure 1a.
As shown in FIG. 2, when no fin pressure is applied, the liquid crystal molecules 6 are aligned perpendicular to the substrate surface. Figure 1b shows the state when an AC voltage is applied, and the liquid crystal 6a in the part sandwiched between the electrodes becomes in a turbulent state and violently changes its direction, scattering the incident light, so the part where the AC voltage is not applied. 7a, a pattern with high contrast can be obtained. Like this DS
In type display, it is required that the liquid crystal be aligned perpendicular to the substrate surface in the initial state. Figure 2 shows the guest host type (C
This explains the color display (abbreviated as H-type), in which a liquid crystal with negative dielectric anisotropy containing a small amount of dichroic dye 17 is sandwiched inside substrates 11 and 12, and the outer periphery is sealed. It is sealed with material 15. There is an electrode 1 inside the substrate.
3 and 14 are formed and when no voltage is applied, the liquid crystal molecules 16 are aligned perpendicularly to the substrate surface, and the dichroic dye 17 is also aligned perpendicularly accordingly. When an alternating current voltage is applied to this, the liquid crystal 16a in the part sandwiched between the electrodes becomes aligned nearly parallel to the substrate surface, as shown in FIG. Since the arrangement is close to parallel to the substrate surface, selective absorption occurs depending on the wavelength of light, resulting in color development. By the way, the degree of this selective absorption depends on the angle between the direction of the light and the dichroic dye, so in order to obtain uniform coloring, the liquid crystal and the dichroic dye must be
All the chromatic dyes must be oriented in the same direction and arranged parallel to the substrate surface. If the initial state is completely perpendicular to the substrate surface, the direction in which the liquid crystal molecules are deposited will not be determined when voltage is applied, resulting in color unevenness and an unsightly appearance. Therefore, in a GH type display cell, it is desirable that the liquid crystal be oriented slightly in one direction from perpendicular to the substrate surface in the initial state. FIG. 3 explains color display by the ECB effect, in which a liquid crystal 26 with negative dielectric anisotropy is sandwiched inside substrates 21 and 22, and the outer periphery is sealed with a sealing material 25. .

Electrodes 23 and 24 are formed inside the substrate, and a third
As shown in figure a, when no voltage is applied, liquid crystal molecules 2
6 are arranged substantially perpendicular to the substrate surface. When an alternating current voltage is applied, the portion of the liquid crystal 26a sandwiched between the electrodes moves vertically as shown in FIG. 3b. Color modulation of the light occurs in accordance with this tilt angle, making continuous multicolor display possible.
The initial orientation in this method is determined by the purpose of use, and an orientation treatment method is required that can obtain any angle from vertical orientation to orientation close to parallel orientation. In addition, in order for the direction of the liquid crystal molecules to be uniform when voltage is applied,
As in the case of GH-type display cells, it is desirable that the alignment be not completely vertical but tilted in one direction by a moderate angle from the vertical. As described above, liquid crystal molecules with negative dielectric anisotropy are in the initial state, that is, in the state where no voltage is applied,
These display devices require a processing method to orient the substrate perpendicularly or at an appropriate angle from perpendicular to the surface of the substrate. For this purpose, there have been known treatment methods such as coating the substrate with an organic treatment agent such as lecithin or organic silane, or combining a friction treatment such as rubbing with application of the organic treatment agent. However, organic treatment agents have the disadvantage of being sensitive to heat, so when a substrate treated with an organic treatment agent is framed in a cell, an inorganic seal using glass frit requires heating of about 500 qC to seal the outer periphery. Therefore, it was not possible to use it, and an organic sealing material had to be used. Therefore, the liquid crystal display device has poor moisture resistance and poor reliability in terms of service life. In addition, coating only with an organic treatment agent can only provide orientation perpendicular to the substrate surface, so DS
In addition to mold marking, the above-mentioned rubbing treatment and the like have been used in combination, but it has been difficult to obtain an initial orientation with any desired nuisance. On the other hand, in the TN-type liquid crystal cell currently in practical use, there is an alignment treatment method in which an inorganic material such as Si0 is diagonally deposited on the substrate surface. It is possible to form a cell using an inorganic seal on a substrate that has been subjected to alignment treatment, and it is widely used as a practical alignment treatment method for producing highly reliable liquid crystal cells.

The inorganic substance here is not limited to Si0, but also An,
Metals such as Ag, Cn, AI, Cr, Si02, Ce02
, MgF2, Mt. 203 and other dielectric materials may be used. FIG. 4 explains the orientation in this oblique evaporation method. When an inorganic substance is evaporated from a direction 36 forming an angle 6 with the normal 35 of the substrate 31, the evaporation material 32 is deposited obliquely toward the evaporation source.
It is believed that due to the effect of this shape, the liquid crystal molecules 33 are uniformly aligned at an angle a with the substrate 31. Here, the angle is the deposition angle, and the angle a is the tilt angle of the liquid crystal molecules.
In this oblique evaporation method, when the evaporation angle is less than about 70o, the tilt angle of the liquid crystal molecules is 00, that is, they are aligned parallel to the substrate surface, and when the evaporation angle is about 70o or more, the tilt angle of the liquid crystal molecules increases as the evaporation angle increases. It is known that there is a tendency towards However, no matter how much we change the deposition conditions using this method, the tilt angle of the liquid crystal molecules remains at 500.
There is a limit to the degree of alignment, and vertical or near-vertical alignment could not be obtained. The present invention solves all of the above-mentioned problems, and allows the tilt angle of liquid crystal molecules to be set to 90 degrees or any angle below 90 degrees, and can sufficiently withstand high temperatures during inorganic sealing. This provides an orientation processing method. In other words, the orientation treatment method of the present invention is to deposit an inorganic substance on a substrate repeatedly from two or more directions at a deposition angle of 7° or more from at least one of the directions, thereby creating a negative effect on the substrate surface. It vertically aligns dielectrically anisotropic liquid crystal molecules, makes the OAP effect effective, and is effective for unidirectional substrate surface treatment in the hybrid effect, and can also be used as an alignment treatment method for GH type display devices. The present invention provides an alignment processing method that fully satisfies the function of a display device. Hereinafter, the present invention will be explained based on examples.

FIG. 5 explains the orientation treatment method of the present invention using an example of vapor deposition from 20,000 directions. This indicates that the steps are repeated in sequence to perform vapor deposition two or more times.
The deposition direction is not limited to two directions, and the deposition angle may be from three or more directions. In either case, liquid crystal molecules 4
3 is oriented substantially perpendicularly to the substrate 41. This is considered to be because the deposited substance 42 is deposited almost vertically on the substrate, and due to the effect of this shape, the liquid crystal molecules 43 are also aligned almost vertically to the substrate surface. What is important in the present invention is that the deposition angle from at least one direction is 700 or more, and the deposition angle is 70 degrees.
Vertical alignment could not be obtained by the following vapor deposition alone. This is believed to be because when the deposition angle is less than 70 degrees, the substrate surface is uniformly and densely covered with the deposited material, making it impossible to obtain the structure shown in FIG. When deposited at a deposition angle of 70 degrees or more, it can be estimated from electron microscopy and film density measurements that the deposited material forms a film with many gaps.
It can be considered that diagonal and vertical deposition is occurring as shown in the figure and FIG. In the present invention, the parameters for controlling the tilt angle of vertical alignment include the difference in deposition amount from each direction, the difference in deposition angle, the difference in deposition rate, the difference in deposition material, and the deposition direction.

If all conditions are made equal, the vertical alignment of the tilt angle 900 can be obtained, and even if each condition is appropriately selected, the vertical alignment of the tilt angle 90o can also be obtained. The tilt angles when different conditions are provided will be described below.
Figure 6 shows that when the same material is deposited on a substrate 51 from two directions 56 and 57 at deposition angles a57 at deposition rates v56 and v57, the liquid crystal molecules are tilted in the direction 56 and the tilt angle a<
900 is shown.

The amount of evaporation from the direction 56 is t56, and the amount of evaporation from the direction 57 is t57, and when t56>[57, the orientation shown in FIG. 3 is obtained.

The deposition material is Si○, and the deposition angles are both 056 and 857.
Fig. 7 shows the experimental results in the case of dust deposition, and the tilt angle was varied from 900 to 6y. It is clear that a tilt angle smaller than 4 can be obtained by increasing the difference in the amount of vapor deposition. In addition, when the amount of vapor deposited at one time is large in repeated vapor deposition, the amount of vapor deposited in the final step has a large influence, and the liquid crystal molecules are crowded in the direction of the final vapor deposition. FIG. 8 shows the experimental results when vapor deposition was carried out repeatedly in the two directions with the same thickness and the final vapor deposition amount was set as tn.

This example also shows that the tilt angle of the liquid crystal molecules can be easily controlled. Although the data is omitted, similar results were obtained when simultaneous vapor deposition was performed from two or more directions under the same conditions at a vapor deposition angle of 700 or more, and finally vapor deposition was added from one direction at a vapor deposition angle of 700 or more. 70 when making a difference in the deposition angle
When 0S026<027, the arrangement shown in FIG. 9 is obtained, and the larger the difference in vapor deposition angle, the smaller the tilt angle of the liquid crystal molecules. This is in a so-called TN type display cell.
This is qualitatively consistent with the fact that when the deposition angle is obliquely deposited from one direction, the tilt angle of the liquid crystal molecules increases as the deposition angle increases. With this method, the amount of change in the tilt angle of the liquid crystal molecules is smaller than with other methods, but it is suitable for mass production because it has good repeatability. When providing a difference in the welding speed, if v stage>v57, the arrangement shown in FIG. 9 will be obtained, and the greater the difference in the welding speed, the smaller the tilt angle.

This also agrees with the fact that when performing oblique deposition from one direction in a TN type display cell, the tilt angle of the liquid crystal molecules decreases as the deposition rate increases. The case where a difference is provided in the vapor deposition direction will be explained using an example in which vapor deposition is performed from three directions.

FIG. 10 is a view seen from the vertical direction of the substrate surface, 91,
92 and 93 indicate the deposition direction, and the angle between them is 89,,8
It is 92,893. Assuming that all other deposition conditions are equal, when 091=092=89=120o, the liquid crystal molecules are aligned perpendicular to the substrate surface, for example, 09,>092=0
When the angle is 93, the liquid crystal molecules are oriented in contact with the 91 direction.
Although it was not possible to quantitatively measure these relationships due to the influence of other factors, we were able to confirm them qualitatively. In the same way, it is clear that the orientation of liquid crystal molecules can be controlled by appropriately determining the deposition direction in the case of two directions, or in the case of four or more directions. The method of changing the deposition material depending on the direction utilizes the fact that the interaction force with liquid crystal molecules differs depending on the material.

In FIG. 6, when a substance with a strong effect of horizontally aligning liquid crystal molecules is deposited from the direction 56, and a relatively weak substance is deposited from the direction 57, the liquid crystal molecules are oriented in the same direction as 56.
To date, Si○ is the most excellent material that has a strong effect of horizontally aligning liquid crystal molecules. As described above, according to the present invention, the angle of the liquid crystal molecules with negative dielectric anisotropy can be easily controlled to be perpendicular to the substrate surface or at an appropriate angle from the perpendicular. Since the distribution treatment layer according to the present invention is an inorganic substance, it does not deteriorate at high temperatures, and therefore, it is possible to produce a liquid crystal cell with an inorganic seal that is particularly reliable even when it is desired to improve moisture resistance, for example. Therefore, DS type display cell, GH type color display cell, ECB
This invention provides a major advance in the manufacture of liquid crystal display devices, including type color display cells, which require a so-called perpendicular orientation or a hybrid orientation that is a combination of parallel and perpendicular orientations.

[Brief explanation of drawings]

FIG. 1 is an orientation state diagram of a DS type display, where a represents an initial state, b represents a voltage applied state, and FIG. 2 is an orientation state diagram of a GH type display, where a represents an initial state, b represents a voltage applied state, Figure 3 is E
In the orientation state diagram of the CB type display, a represents the initial state and b represents the voltage applied state. FIG. 4 is an enlarged view showing the alignment state of liquid crystal molecules subjected to alignment treatment by conventional oblique vapor deposition, FIG. 5 is an enlarged view showing the alignment of liquid crystal molecules when subjected to the vapor deposition treatment of the present invention, and FIG. Explanatory diagrams showing other embodiments of the present invention, FIGS. 7, 8, and 9 are graphs showing the relationship between the vapor deposition amount ratio, the final vapor deposition amount, the vapor deposition speed ratio, and the tilt angle. FIG. 10 is an explanatory diagram showing the angles in the case of dust deposition from three directions according to the present invention. 31, 41, 51
...Substrate, 46, 47, 56, 57... Vapor deposition direction, 42... Deposit of vapor deposition material, 43, 53...
・・・・・・Liquid crystal molecules, 8・・・・・・Adhesion angle. Tsutomu 1 figure Tea figure 2 figure 3 figure 4 Tsutomu figure 5 figure 0 Atsushi figure 8 figure younger brother? Illustration of younger brother 10

Claims (1)

[Scope of Claims] 1. In a liquid crystal cell comprising a negative dielectric anisotropy liquid crystal sandwiched between two substrates each having an alignment layer on the surface, an inorganic substance is applied to the surface of the substrates in two or more directions. The alignment treatment layer is formed by sequentially repeating vapor deposition or ion plating, and the molecules of the negative dielectric anisotropy liquid crystal are aligned substantially perpendicular to the surface of the substrate when no voltage is applied. A method for aligning a liquid crystal cell, characterized by: 2. The method for aligning a liquid crystal cell according to claim 1, wherein the incident angle of the inorganic substance from at least one direction is 70° C. or more with respect to the normal to the substrate surface. 3. The method for aligning a liquid crystal cell according to claim 1 or 2, wherein the inorganic substance is SiO.