JPH02173614A - Formation of oriented film of liquid crystal element - Google Patents

Abstract

PURPOSE:To easily form an oriented film having strong liquid crystal orienting power on a substrate without executing a rubbing treatment by bringing the soln. of a resin material which constitutes the oriented film into contact with the surface of the transparent electrode substrate and applying a shearing stress on the soln. of the resin material to fluidize and orient the material and drying the soln. CONSTITUTION:The soln. of the resin material which constitutes the oriented film is applied on a gravure plate 4 and a roller 3 is rotated backward to transfer the resin soln. from a gravure plate onto an offset plate 2. The roller 3 is then rotated forward to transfer the resin soln. from the offset plate 2 to the transparent electrode substrate 1. The resin material is fluidized and oriented while the substrate 1 is translationally moved to apply the shearing stress to the soln. of the resin material by applying a translational speed difference between the substrate 1 and the roller 3. After the substrate 1 surface is offset printed in such a manner, the substrate is imposed rapidly on a hot plate and is heated to evaporate the solvent and to form the oriented film.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a method for forming an alignment film on the surface of a transparent electrode substrate constituting a liquid crystal element.

(Prior Art) Liquid crystal elements are widely used as display devices for wristwatches, calculators, televisions, and the like. This liquid crystal element has a structure in which two transparent electric grid substrates are placed facing each other and held close to each other via a spacer to form a cell, and a liquid crystal material is injected into the inside of this cell. An alignment film that has been subjected to alignment treatment in one direction is provided on the opposite surface of the transparent electrode substrate in order to align liquid crystal molecules in one direction.

A conventional method for forming an alignment film is to obliquely deposit an inorganic substance such as SiO on the surface of a transparent electrode substrate. However, the oblique deposition method is capable of forming a uniform deposited film on a large substrate. It is difficult to obtain an alignment film with a low liquid crystal alignment force, and the cost is high, so it is not suitable as a mass production technique.

Therefore, the method for forming an alignment film is to apply a solution of a resin material such as polyimide that makes up the alignment film onto the surface of a transparent electrode substrate using a spin code method or an offset printing method, and after drying, apply a solution of a resin material such as polyimide to the surface of a transparent electrode substrate, and after drying, apply a solution of a resin material such as polyimide to the surface of a transparent electrode substrate. The method of rubbing is used as the most practical method. This rubbing process is applied to resin thin films formed by spin code methods or offset methods, which are not used as liquid crystals.

This is because it does not exhibit the effect of causing the -'r-+ orientation, and only becomes capable of orienting the liquid crystal molecules after the rubbing treatment.

The effect of this rubbing treatment has not been elucidated for a long time, but in recent years it has been reported that the rubbing treatment causes the polymer chains on the surface of the resin thin film to become oriented, thereby showing the effect of orienting the liquid crystal molecules. ing. In fact, it is well known that oriented polymers exhibit a strong liquid crystal alignment force.

However, in the rubbing process, the resin RH formed on the substrate
The following problems occur because the product is rubbed with a cloth, etc. That is, the static electricity generated by the rubbing process is discharged, thereby destroying the transparent electrode pattern, thin film transistor, etc. formed on the substrate surface, or deteriorating the characteristics.

Furthermore, since the rubbing process generates a large amount of dust, the dust may cause scratches on the surface or become trapped in the liquid crystal element.

(Problems to be Solved by the Invention) The present invention has been made to solve the above-mentioned problems, and it is possible to easily form an alignment film with a strong liquid crystal alignment force without performing a rubbing treatment, and it is transparent. It is an object of the present invention to provide a method that can avoid problems such as electrostatic damage to electrode patterns or thin film transistors and generation of dust.

[Structure of the Invention] (Means and Effects for Solving the Problems) The method for forming an alignment film for a liquid crystal element of the present invention includes steps for forming an alignment film for aligning liquid crystal molecules on the surface of a transparent electrode substrate constituting a liquid crystal element. , the surface of the transparent electrode substrate is brought into contact with a solution of a resin material constituting the alignment film, and a shear stress is applied to the solution of the resin material to fluidly orient the resin material, followed by drying. be.

In the present invention, the resin material constituting the alignment film is as follows:
Specifically, one type or a mixture of two or more types selected from the group of polyimide, polyamic acid, polyamide, polyester amide, polyamide amic acid, polyester, polyester imide, and polyether sulfone can be mentioned. Basically, anything can be used as long as it is soluble in the solvent. Dissolve these resins in a suitable solvent,
The viscosity of the solution is adjusted according to the thickness of the alignment film.

In the present invention, the following method can be mentioned as a specific means for fluidly orienting the resin material by applying abrasion stress to the solution of the resin material.

For example, in the offset printing method, a solution of a resin material is transferred from a gravure plate to an offset plate on the surface of a roller,
Furthermore, there is a method of providing a translational speed difference between the roller and the transparent electrode substrate when transferring from the offset plate to the transparent electrode substrate. For this purpose, a translation drive mechanism for the substrate is provided, or a drive mechanism is provided that makes the translation speed of the roller slower than the circumferential speed of the roller surface. With this method, the orientation of the alignment film can be controlled according to the translation speed difference.

Alternatively, there is a method in which a transparent electrode substrate is immersed in a resin solution, the substrate surface is made substantially perpendicular to the solution surface, and the substrate is pulled out of the solution in a certain direction. In this case, the optimum pulling speed varies depending on the type of resin, solvent, and viscosity, but it is generally desirable to be 8 to 50 cm/1 tH. This is because if the pulling rate is too fast, the uniformity of the film thickness will be impaired, while if the pulling rate is too slow, sufficient orientation will not be obtained. in this way,
The thickness and orientation of the alignment film can be controlled by adjusting the viscosity of the solution, the rate of pulling the substrate, etc.

Another method is to apply a solution of a resin material onto the surface of a transparent electrode substrate and spread the solution in a certain direction using a pressure plate. In this case, it is desirable to adjust the viscosity of the resin material solution to 1 poise or more, more preferably in the range of 5 to 5 poise. If the viscosity is less than 1 void, the fluidity of the solution of the resin material applied to the substrate surface is high, making it impossible to orient the polymer chains. On the other hand, if the viscosity is high, for example 100 voids or more, the resin material solution cannot be uniformly spread over the substrate surface even if a pressure plate is used, and problems such as streaks appearing in the direction of stress may occur. Polymer chains cannot be well oriented. In this method, the thickness and orientation of the alignment film can be controlled by controlling the viscosity of the solution and the like.

In addition to this, a method of attaching a stretched polymer film to the surface of the transparent electrode substrate may also be considered, but this method is not preferred because it is not possible to reduce the thickness of the film to about 3 mm or less. This is because if the thickness of the alignment film is thick, a large proportion of the signal voltage applied between the electrodes during use will be distributed to the alignment film and will not be effectively applied to the liquid crystal.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

Examples 1 to 20 and Comparative Examples 1 to 4 FIG. 1 is a schematic diagram of an offset printing press used to carry out the method of the present invention. In FIG. 1, between a substrate 1 and a gravure plate 4, an offset roller 3 having a diameter of 200 m+* and having an offset plate 2 attached thereto is arranged. The roller 3 is rotated at a rotational angular velocity ω (radian/second) by a roller rotation drive mechanism, and in conjunction with this, is translated at a translation speed of 100ω (am 2 /sec) by a roller translation drive mechanism. Further, unlike a normal offset printing machine, the substrate 1 is also translated by the substrate translation drive mechanism at a translation speed of v (am/sec) in the forward direction or in the reverse direction with respect to the traveling direction of the roller 3.

Using this offset printing machine, an alignment film is formed in the following manner. First, a resin solution is applied onto the gravure plate 4, and the roller 3 is rotated in reverse to transfer the resin solution from the gravure plate 4 to the offset plate 2. Next, the roller 3 is rotated forward to transfer the resin solution from the offset plate 2 to the substrate 1. At this time, the substrate 1 is translated at a translation speed of v (mm/sec) to provide a translation speed difference between the roller 3 and the substrate 1.

In this case, if the gap between the substrate 1 and the surface of the offset plate 2 is d, a shear rate gradient of v/d (1/sec) is created. d
is approximately 1 trm, so even at v-0, about 1 mm/sec, a shear rate group of 10' (1/sec) is created.

A solution of polyimide or polyamic acid in N-methylpyrrolidone adjusted to a predetermined concentration as shown in Table 1 was prepared by setting the rotational angular velocity of the roller and the translational velocity of the substrate to the values shown in Table 1, and applying the solution to the substrate as described above. After offset printing was performed on the film, it was immediately placed on a hot plate and heated to evaporate the solvent to obtain an alignment film having the film thickness shown in Table 1.

In addition, in Comparative Examples 1 to 4, the translation speed of the substrate was 0, and no shear stress was applied to the resin solution. Also, Comparative Example 2.
In No. 4, an alignment film was formed at a substrate translation speed of 0, and then a rubbing process was performed.

Furthermore, a cell is assembled using the substrate on which the alignment film is formed,
A liquid crystal device was fabricated by injecting twisted nematic liquid crystal. Regarding these liquid crystal elements, the number of alignment defects per 1 cm2 was investigated, and the alignment force of the alignment film was evaluated. The results are also listed in Table 1.

As is clear from Table 1, the alignment film formed by the method of the present invention exhibits a practically sufficient alignment force.

Implementation N2L22 As shown in FIG. 2, the substrate 11 is attached to the substrate support 12, and after being immersed in the solution 14 of the resin material contained in the container 13, the surface of the substrate 11 is made almost perpendicular to the surface of the solution 14. Then, the substrate support 12 and the substrate 11 were pulled out of the solution 14 in a certain direction and dried to form an alignment film.

Example 2I A polyimide/chibutyrolactone solution was used as the resin material solution, the viscosity of this solution was adjusted to 20 centipoise, and after immersing a substrate attached to a substrate support in this solution, the substrate surface was placed against the solution surface. 15cm/s almost vertically
I pulled up at a speed of in. After leaving it for 15 minutes, transfer it to a 100℃ oven to evaporate the solvent. ! A 1-thick alignment film was obtained.

It was confirmed that this alignment film showed good alignment force.

Example 22 A polyamic acid/N-methylpyrrolidone solution was used as a resin material solution, the viscosity of this solution was adjusted to 15 centivoise, and a substrate attached to a substrate support was immersed in this solution, and the substrate surface was placed on the solution surface. It was pulled up at a rate of 8 (to)/ml at a rate of approximately perpendicular to the surface.

The mixture was directly transferred to an oven at 150°C to evaporate the solvent. Furthermore, the substrate support was immersed in the solution again, and 30c
The substrate support was pulled up in the axial direction perpendicular to the liquid level at a speed of m/sin, left as it was for 30 minutes, and then the solvent was evaporated in an oven to obtain an alignment film with a thickness of 2p.

It was confirmed that this alignment film showed good alignment force.

Example 23.24 As shown in FIG.
After coating, the solution 22 was spread in a certain direction using a pressure plate 23, and then dried to form an alignment film.

Example 23 A polyimide/chibutyrolactone solution was used as a resin material solution, the viscosity of this solution was adjusted to 10 voids, and this solution was applied onto a substrate and then spread by a pressure plate. This was quickly transferred onto a hot plate at <100° C., and the solvent was evaporated to obtain an alignment film having a thickness of one line.

It was confirmed that this alignment film showed good alignment force.

Example 24 A polyamic acid/N-methylpyrrolidone solution was used as a resin material solution, the viscosity of this solution was adjusted to 5 voids, and this solution was applied onto a substrate placed on a hot plate at 100°C, and then processed. It was spread out with a pressure plate. This at 150℃
After curing for 1 hour, an alignment film having a thickness of 500 wafers was obtained.

It was confirmed that this alignment film showed good alignment force.

[Effects of the Invention] As detailed above, according to the method of the present invention, an alignment film with a strong liquid crystal alignment force can be easily formed without performing a rubbing treatment, and it is possible to easily form an alignment film with a strong liquid crystal alignment force without performing a rubbing process. Problems of destruction and generation of waste can be avoided, and its industrial value is extremely large.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram of an offset printing machine used to form an alignment film in an embodiment of the present invention, and FIG. 2 is an explanatory diagram showing a method for forming an alignment film in another embodiment of the present invention. , FIG. 3 is an explanatory view showing a method for forming an alignment film in still another embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Substrate, 2... Offset plate, 3... Offset roller 4... Gravure plate, 11... Substrate,
DESCRIPTION OF SYMBOLS 12... Substrate support body, 13... Container, 14... Solution of resin material, 21... Substrate, 22... Solution of resin material, 23... Pressure plate. Applicant's agent Patent attorney Takehiko Suzue

Claims (1)

[Claims] In forming an alignment film for aligning liquid crystal molecules on the surface of a transparent electrode substrate that makes up a liquid crystal element, a solution of a resin material that makes up the alignment film is brought into contact with the surface of the transparent electrode substrate, and the solution is mixed with the solution of the resin material. 1. A method for forming an alignment film for a liquid crystal element, which comprises applying stress to fluidize and orient a resin material and then drying it.