JPH09297309A - Production of liquid crystal oriented structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a process which eliminates the need for a rubbing treatment to be the cause for product defects, such as display defects and element destruction, and more rapidly and easily produces a liquid crystal oriented structure having pretilts. SOLUTION: A substrate 1 formed with a photosensitive high-polymer film 2 which induces the nature to orient liquid crystal molecules in an intra-surface direction parallel with a polarization direction 4 when the film absorbs polarized light having the wavelength within a prescribed wavelength region on its surface is first prepd. Next, the photosensitive high-polymer film 2 of the substrate 1 is irradiated with one kind of the polarized light having the wavelength within the prescribed wavelength region with diagonal incidence and by inclining the polarization direction 4 from the direction perpendicular to the incident surface, by which the light is absorbed in the photosensitive high-polymer film 2 and the oriented structure having the pretilts is formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a liquid crystal alignment structure having a pretilt which does not require rubbing.

[0002]

2. Description of the Related Art A liquid crystal display device used for a liquid crystal display or the like changes a specific molecular arrangement of liquid crystal to another different molecular arrangement by an external action such as an electric field and changes the optical characteristics between them. The change is used as a visual change for display. Generally, an alignment treatment is performed on the surface of a glass substrate holding liquid crystal in order to arrange liquid crystal molecules in a specific alignment state.

As a conventional alignment treatment, a so-called rubbing method has been adopted in which a glass substrate sandwiching a liquid crystal is unidirectionally rubbed with something like cotton cloth. In the case of rubbing treatment, static electricity is generated when the glass substrate is rubbed with something like cotton cloth.
This static electricity may cause dielectric breakdown of the alignment film of the substrate, defective alignment, or damage to the electrodes below the alignment film. This reduces the performance of the liquid crystal display device.

In addition, minute dust generated by rubbing may adhere to the substrate due to static electricity, and this dust may cause a display defect such as a gap defect of a liquid crystal cell or a black dot or a white dot.

In order to solve the problem associated with such rubbing treatment, a method of carrying out an alignment treatment without rubbing treatment has been proposed. For example, an alignment treatment method using an optical polarization memory film has been studied.

The alignment treatment method using the optical polarization storage film is
After forming the optical polarization storage film on the substrate surface, the liquid crystal alignment is formed by irradiating the optical polarization storage film with polarized light. It is possible to impart orientation to the liquid crystal molecules according to the polarization direction of the irradiation light to the optical polarization storage film irradiated with the polarized light.

By the way, when a voltage is applied to the liquid crystal cell to arrange the liquid crystal molecules in a predetermined direction, it is desired to give a directionality in which all the liquid crystal molecules start to tilt uniformly from a fixed direction. Usually, the alignment treatment is performed by rubbing so that the liquid crystal molecules are inclined in advance by a predetermined angle with respect to the substrate surface. That is, one end of the liquid crystal molecule is raised so that the long axis direction of the liquid crystal molecule at the substrate interface when a voltage is not applied to the liquid crystal cell forms an angle with the substrate surface. This state is called pretilt, and the angle of the liquid crystal molecules in the major axis direction with respect to the substrate surface is called pretilt angle.

The liquid crystal molecules having no pretilt do not have a uniform rising direction when a voltage is applied, and the tilt of the liquid crystal molecules may be reversed depending on the state and position of the applied voltage. Boundaries between groups of liquid crystal molecules having different rising directions may appear as line defects on the display screen.

In particular, innumerable defects described above are generated near the threshold voltage of the applied voltage, and the defect position moves around with the passage of time or changes in the applied voltage, so that the existence of the defect is easily visually recognized. At the same time, the occurrence of light scattering,
Since the contrast is also deteriorated, the display quality is remarkably deteriorated as a liquid crystal display element.

[0010]

In the previously proposed alignment treatment method using the optical polarization memory film as described above, the alignment direction imparted to the liquid crystal molecules is mainly in the in-plane direction of the substrate. Therefore, the pretilt which is important in the liquid crystal display device is not provided.

Japanese Patent Application No. 7-11 filed by the applicant of the present application
The specification of 1851 proposes a method in which a photosensitive polymer optical polarization storage film is irradiated with polarized light in the ultraviolet region to perform alignment treatment without rubbing.

In the method disclosed in the specification of Japanese Patent Application No. 7-111851, the alignment treatment is performed in the direction perpendicular to the polarization direction of the polarized light for irradiation. In this method, in order to impart a pretilt angle to the alignment film, it is necessary to irradiate the polarized light storage film with ultraviolet polarized light in two different directions.

For example, in the first irradiation of polarized light, the polarized light is irradiated to the optical polarization storage film from the normal direction of the substrate, so that the orientation in the direction parallel to the substrate surface and the direction perpendicular to the polarization direction is obtained. give. Then, in the next second irradiation, the pretilt alignment is given by irradiating the optical polarization storage film with polarized light from a direction oblique to the substrate surface. In this method, the alignment treatment in a desired direction having a pretilt cannot be performed unless the irradiation treatment is performed twice.

However, in such a method that requires two irradiation steps, the irradiation time is inevitably long, and the irradiation directions are different between the first irradiation and the second irradiation, so that the irradiation device must be reset. There is a problem that the tact (processing time required for one substrate) of the liquid crystal cell substrate manufacturing process cannot be increased due to time and the like. Further, there is a problem that the design and operation of the irradiation device are very complicated and cumbersome, and the manufacturing cost is naturally high.

An object of the present invention is to provide a method for easily manufacturing a liquid crystal alignment structure having a pretilt in a shorter time while eliminating a rubbing process which causes a product defect such as a display defect or an element destruction. is there.

[0016]

The method for producing a liquid crystal alignment structure according to the present invention has a wavelength within a predetermined wavelength region and when polarized light is absorbed, liquid crystal molecules are aligned in an in-plane direction parallel to the polarization direction. A step of preparing a substrate on the surface of which a photosensitive polymer film that gives rise to a property is formed, and one type of polarized light having a wavelength within the predetermined wavelength range is obliquely incident and the polarization direction is inclined from a direction perpendicular to the incident surface. A method of manufacturing a liquid crystal alignment structure, comprising: a light absorption step of irradiating the photosensitive polymer film on the substrate and absorbing the light by the photosensitive polymer film to form an alignment structure having a pretilt.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION As a result of experiments conducted by the inventor of the present invention, when various polyimide thin films as shown in FIG. 2 are irradiated with ultraviolet light polarized in the normal direction of the film, the film undergoes an alignment treatment. It was confirmed that the liquid crystal was uniformly aligned. Then, the orientation direction depends on the wavelength and the polarization direction of the ultraviolet light to be irradiated.

The results of the experiment will be described in more detail below. When the irradiation light (polarized light) had a wavelength λ of 230 to 260 nm, the liquid crystal was aligned parallel to the polarization direction. When the irradiation light (polarized light) had a wavelength λ of 300 to 340 nm, the liquid crystal was aligned at right angles to the polarization direction. When the irradiation light (polarized light) has a wavelength of λ = 260 to 300 nm, the orientation direction of the liquid crystal depends on the irradiation amount (illuminance × time), and in the beginning of the case where the irradiation amount is small, the liquid crystal molecules are aligned parallel to the polarization direction. The orientation direction changed little by little as the irradiation amount increased, and finally, the orientation became perpendicular to the polarization direction at a sufficient irradiation amount. It was found that the alignment treatment was not performed by the irradiation of the irradiation light having a wavelength of 340 nm or more.

The phenomenon described above is because the phenomena of and proceed at the same time, and as a result of comparing the reaction efficiency (speed) between the phenomenon of and, the phenomenon of is more efficient (the reaction speed is faster). , At the beginning of irradiation, it is oriented parallel to the polarization direction,
It is considered that the orientation direction changes as the light irradiation amount increases.

By utilizing this phenomenon, when the substrate is irradiated with polarized ultraviolet light only once from an oblique direction, it is aligned in a direction parallel to the polarization direction and at the same time a pretilt is imparted to the alignment of the liquid crystal. It could be confirmed.

Further, by utilizing this phenomenon together, it is possible to obtain a multi-domain structure by performing an alignment treatment such that the alignment direction is deviated by 90 degrees for each minute region of the substrate. In that case, the alignment direction can be easily changed by changing the bandpass filter for changing the light wavelength without changing the setting of the irradiation device.

A method of manufacturing a liquid crystal alignment structure according to the present invention will be described with reference to FIG. As shown in FIG. 1, a substrate 1 having a photosensitive polymer film 2 made of a polyimide thin film formed on the surface thereof.
Prepare The directions parallel to the surface of the substrate 1 and orthogonal to each other are the x direction and the y direction, and the direction perpendicular to the surface of the substrate 1 is z.
Direction. 4 at an angle of irradiation θ with respect to the surface of the substrate 1
The polarized light 3 having the polarization direction indicated by the arrow is irradiated and absorbed by the photosensitive polymer film 2. As a result, the photosensitive film is provided with an alignment structure having a pretilt angle p in the direction indicated by arrow 5. The polarization direction 4 and the alignment direction 5 are both in the xz plane.

Next, an example of actually manufacturing an alignment structure having a pretilt using the above method will be described below. Example 1 A polyimide solution (referred to as PI-A) having the molecular structure shown in FIG. 3 was applied on a glass substrate having a transparent electrode formed thereon by a spin coating method, followed by firing.
A polyimide thin film having a thickness of about 100 nm was formed.

Substrates were produced by irradiating this substrate with polarized ultraviolet light having a wavelength λ = 230 to 260 nm under various irradiation directions. The illuminance of the polarized light was 0.5 mW / cm ² (measured by model UV-MO2-UV25 manufactured by Oak Co., Ltd.), and the substrate was prepared by changing the irradiation time from 0 to a maximum of 1200 seconds. Then, the liquid crystal alignment of the substrates having different irradiation times was evaluated.

As a result, in the irradiation from the z-axis direction (θ = 90 °), when the irradiation time is 600 seconds or more (irradiation amount of 300 mJ), a uniform and clean alignment state almost equal to that of the rubbing method is obtained, and the alignment is performed. The direction was parallel to the polarization direction of the irradiation ultraviolet light with respect to the in-plane direction of the substrate.

Further, when the heat treatment was carried out at the time of light irradiation, the reaction efficiency was improved. Substrate temperature during light irradiation is 150 ° C
And the irradiation time is 300 seconds (irradiation amount 150 mJ)
As described above, an alignment state equivalent to the result of the above example was obtained.

Further, as shown in FIG. 1, when polarized ultraviolet light is irradiated onto the substrate 1 from an oblique direction, the irradiation angle θ is set under three conditions of 30 °, 45 ° and 60 °. Under the conditions, the alignment treatment was performed by changing the irradiation time.

As a result, when the irradiation angle θ is 30 °, 1
9 for irradiation time of 200 seconds or more and irradiation angle of 45 °
If the irradiation time is 00 seconds or more and the irradiation angle is 60 °, 70
When the irradiation time was 0 seconds or more, a good alignment state was exhibited. From this result, the irradiation time required to obtain a certain good alignment state is about 1 / time of the irradiation time in the case of obliquely irradiating or in the direction of normal (θ = 90 °).
It means that it becomes sin θ times, and in that case, the irradiation effect received by the polyimide thin film becomes equal.

When the pretilt angle p of the substrate of this example was measured by the crystal rotation method, when the irradiation angle θ = 30 °, it was p = 0.49 °, and the irradiation angle θ =
In the case of 45 °, p = 0.22 ° and the irradiation angle θ = 60
In the case of °, p = 0.14 °, and it was found that the irradiation angle θ of the polarized ultraviolet light and the pretilt angle p are correlated with each other.

Further, at normal incidence, the wavelength λ = 300 to 340
When irradiated with polarized ultraviolet light of nm, the irradiation time is 90
At 0 seconds or more, a uniform orientation similar to that of the rubbing method was obtained. The orientation direction was perpendicular to the polarization direction of the irradiation ultraviolet light with respect to the in-plane direction of the substrate. However, in this case, no pretilt was applied.

When the wavelength λ of the irradiation light was 340 nm or more, the liquid crystal was not aligned even after irradiation for a sufficient time. Example 2 A polyimide solution having a molecular structure shown in FIG. 4 (P
IB. ), The wavelength λ = 230-26
An experiment for manufacturing an oriented structure was conducted under 0 nm at exactly the same conditions as in Example 1.

PI-A and PI-B differ in the structure of the diamine portion of the polyimide. PI-A has a large polarity, and PI-B has a small polarity. Both structures of the acid anhydride part are the same.

As a result of the experiment with PI-B, the change of the orientation with respect to the dose was almost the same as that of PI-A in all cases. However, regarding the degree of orientation,
PI-B has a clear difference from PI-A, and when observed with a polarizing microscope, it shows a slightly rough alignment state,
It was inferior to the orientation state of PI-A.

However, in the case of PI-B, although there is a degree of difference from the case of PI-A, since the irradiation amount is almost the same and the best alignment state is obtained, this light irradiation method (irradiation light wavelength λ
= 230-260 nm), the structure of the acid anhydride part of the polyimide material is particularly important in the alignment treatment process,
It is presumed that it does not depend so much on the structure of the diamine moiety.

Further, the structure of the diamine portion gives a difference in the degree of the alignment state, and it can be presumed that when a diamine that increases the polarity of the polyimide is used, the alignment state of the liquid crystal becomes better.

Example 3 Using a polyimide solution (referred to as PI-C) having the molecular structure shown in FIG. 5, the wavelength λ =
An experiment for manufacturing an oriented structure was conducted under the same conditions as in Example 1 or 2 at 230 to 260 nm.

As a result, although there is a difference in the dose required to reach the best alignment state from the other examples, there is another process in which the alignment state becomes better as the dose increases. A tendency similar to that of the example was shown.

In Example 3, the best alignment state was achieved when the irradiation time was 1000 seconds or more, and the alignment state at that time was PI-.
It was almost the same as in the case of A. From the above results, as the photosensitive polymer film, when using a polyimide composed of acid anhydride moieties having different structures, although there is a difference in the irradiation time of polarized ultraviolet light, it is possible to obtain the same alignment effect across the whole I understand.

By selecting the wavelength of the irradiation polarized light, it is possible to control the alignment of the liquid crystal in the direction parallel to the polarization direction of the irradiation light with respect to the in-plane direction of the substrate. When forming an orientation parallel to the polarization direction, if the polarized light is irradiated in a polarization direction that is oblique to the substrate surface and that is tilted with respect to the normal to the incident surface, it will be pre-tilted by irradiation of one (1 type) polarized light. Orientation can be realized.

By utilizing the control of the alignment direction by selecting the irradiation wavelength, it is possible to form an alignment structure in which the alignment direction is deviated by 90 degrees for each minute region of the substrate. As a result, a multi-domain structure can be obtained.

In that case, a bandpass filter (not shown) for changing the light wavelength is arranged in the optical path of the polarized light 3 in FIG. Wavelength λ = 2 by selecting bandpass filter
Irradiation at 30 to 260 nm can align the liquid crystal in parallel with the polarization direction and impart a pretilt. Wavelength λ
= 300 to 340 nm, the liquid crystal is aligned at right angles to the polarization direction. When this is irradiated while switching the bandpass filter for each minute area on the substrate surface, the orientation directions t1 to t4 of the liquid crystal molecules formed in the adjacent domains 10 as shown in FIG. Different liquid crystal alignment structures can be formed.

If polarized light is incident through a mask having a checkerboard-shaped window region, the alignment structure shown in FIG. 6A can be formed by irradiating ultraviolet rays twice. FIG.
In the case of the structure (A), it is difficult to give a pretilt to half of the minute regions 10. To give a pretilt to the entire minute area, 2 wavelengths of light oriented parallel to the polarization direction are used.
The light may enter the photosensitive polymer film from one or more directions. Ultraviolet irradiation using the above mask can also be used.

FIG. 6B shows an example of an alignment pattern that can be realized when ultraviolet rays are irradiated from four directions. The orientation directions t11, t12, t13, and t14 all have a pretilt, and they are sequentially rotated 90 degrees in the in-plane direction of the substrate. The ultraviolet irradiation direction may be changed by rotating the optical system or the substrate.

The method of manufacturing the alignment structure described above can be applied to not only liquid crystal display elements but also optical retardation films and optical compensation films. Although the present invention has been described with reference to the embodiments, the present invention is not limited to these embodiments. For example, it will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.

[0045]

As described above, according to the present invention, the pretilt can be imparted without rubbing, so that the occurrence of display defects and element destruction associated with rubbing can be suppressed. Furthermore, by appropriately selecting the wavelength of the polarized light for irradiation, the liquid crystal can be controlled to be aligned in a direction parallel to or perpendicular to the polarization direction of the irradiated light. further,
Since the pretilt alignment can be realized by irradiating the substrate surface with the polarized light once from the oblique direction after selecting the wavelength, it is possible to easily manufacture the liquid crystal alignment structure having the pretilt in a shorter time and reduce the cost.

[Brief description of drawings]

FIG. 1 is a schematic perspective view showing light irradiation conditions in a method for manufacturing an alignment structure according to the present invention.

FIG. 2 is a diagram showing molecular structures of various polyimides that can be used in the method for producing an oriented structure according to the present invention.

FIG. 3 is a diagram showing a molecular structure of polyimide used in Examples.

FIG. 4 is a diagram showing a molecular structure of a polyimide used in another example.

FIG. 5 is a diagram showing a molecular structure of a polyimide used in yet another example.

FIG. 6 is a schematic perspective view showing an example of forming multi-domains formed on a substrate by using the method of the embodiment.

[Explanation of symbols]

 1 substrate 2 photosensitive polymer film 3 polarized light irradiation direction 4 polarized light direction 5 pretilt alignment direction 10 domain

Claims (5)

[Claims] 1. A substrate having a photosensitive polymer film formed on its surface, which has a property of aligning liquid crystal molecules in an in-plane direction parallel to the polarization direction when absorbing polarized light having a wavelength within a predetermined wavelength range. The step of preparing, and irradiating the photosensitive polymer film of the substrate with one kind of polarized light having a wavelength within the predetermined wavelength range obliquely incident and tilting the polarization direction from a direction perpendicular to the incident surface, A method for producing a liquid crystal alignment structure, comprising a light absorption step of forming an alignment structure having a pretilt by absorbing it in a polymer film. 2. The method for producing a liquid crystal alignment structure according to claim 1, wherein the photosensitive polymer film is polyimide. 3. The wavelength of the polarized light is from 230 nm to 26 nm.
The method for producing a liquid crystal alignment structure according to claim 1, wherein the range is 0 nm. 4. The method according to claim 1, further comprising the step of irradiating polarized light having a wavelength in the range of 300 to 340 nm.
A method for producing a liquid crystal alignment structure according to any one of 1. 5. The method for producing a liquid crystal alignment structure according to claim 1, further comprising the step of heating the substrate when the polarized light is irradiated.