JPH1124076A - Method of forming liquid crystal alignment film - Google Patents

Abstract

(57) [Summary] [Problem] It is possible to suppress print sag, and as a result, it is possible to design with a small design tolerance and high accuracy.
An object of the present invention is to provide a method for forming a liquid crystal alignment film. In a method for forming a liquid crystal alignment film by a printing method using an alignment film coating solution obtained by mixing an alignment film material with a mixed solvent, the mixed solvent is preferably 2 or less.
-(2-ethoxyethoxy) ethanol is contained. In this case, the mixed solvent is a mixture of N-methyl-pyrrolidone, 2-butoxyethanol, and 2- (2-ethoxyethoxy) ethanol, and is coated with 2- (2-ethoxyethoxy) ethanol. More preferably, the concentration in the liquid is 10% by weight to 30% by weight.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for forming a liquid crystal alignment film by a printing method using an alignment film coating solution obtained by mixing an alignment film material with a mixed solvent.

[0002]

2. Description of the Related Art In manufacturing a liquid crystal cell which is a main component of a liquid crystal display, a transparent electrode, a liquid crystal alignment film, and the like are formed on two transparent substrates in a predetermined pattern. The liquid crystal alignment film is provided to control the alignment of the liquid crystal, and is generally formed by selectively applying an alignment film coating solution in which an alignment film material is mixed with a solvent onto a transparent substrate by a printing method. You.

[0003]

In such a method for forming a liquid crystal alignment film, an alignment film coating liquid is not applied according to a predetermined pattern determined when the liquid is applied to a transparent substrate.
A so-called print sagging phenomenon that runs off the pattern occurs. If the print sag is large, the design tolerance (design margin when the print sag is taken into consideration) must be increased, and the accuracy is reduced at the design stage. However, in the conventional method of forming a liquid crystal alignment film, printing sagging exceeding a desired degree occurs, and as a result, there is a problem that a design tolerance must be increased and accuracy is lowered in a design stage. For example, N-methyl-pyrrolidone, which is generally used for forming a liquid crystal alignment film, and 2
A case in which a liquid crystal alignment film is formed by a printing method using a coating liquid for an alignment film in which a polyimide precursor polyamic acid is dissolved as a material for an alignment film in a mixed solvent with butoxyethanol will be described. FIG. 3 shows the difference in the amount of print sag due to the difference in the concentration of the polyamic acid in this case.
The concentration of 2-butoxyethanol in the alignment film coating solution is 15
Weight% is fixed. As can be seen from FIG. 3, as the concentration of the alignment film material increases, the amount of print sag decreases, but still a print sag of about 1 mm is observed. In addition, even if printing sag can be suppressed by increasing the density, the amount of wasted alignment film material per printing increases by that much, and the cost increases.
In some cases, it may be difficult to control the film thickness to the conventional thickness. Therefore, it is difficult to say that increasing the density is an optimal method for suppressing print sag. further,
Since the degree of the print sag is affected by the compatibility of the alignment film coating solution and the printing original plate in addition to the concentration of the alignment film coating solution, it is not easy to suppress the print sag.

An object of the present invention is to provide a method for forming a liquid crystal alignment film capable of suppressing print sagging and consequently having a small design tolerance and a highly accurate design.

[0005]

Means for Solving the Problems To solve the above-mentioned problems, the invention according to claim 1 of the present invention provides a printing method using an alignment film coating solution obtained by mixing an alignment film material in a mixed solvent. In the method for forming a liquid crystal alignment film, the mixed solvent is 2- (2-ethoxyethoxy).
It is characterized by containing ethanol. According to the first aspect of the present invention, since the mixed solvent contains 2- (2-ethoxyethoxy) ethanol, print sag is suppressed, and a liquid crystal alignment film with high dimensional accuracy can be formed.

[0006] The invention described in claim 2 is the invention according to claim 1.
Wherein the mixed solvent is a mixture of N-methyl-pyrrolidone, 2-butoxyethanol and 2- (2-ethoxyethoxy) ethanol. According to a second aspect of the present invention, in the method for forming a liquid crystal alignment film according to the first aspect, the mixed solvent is 2- (2-ethoxyethoxy) in addition to N-methyl-pyrrolidone and 2-butoxyethanol. A) Since the solvent is a mixture of ethanol, a high-precision liquid crystal alignment film can be formed while suppressing print sagging, as in the first aspect of the present invention.

According to a third aspect of the present invention, in the method for forming a liquid crystal alignment film according to the second aspect, the coating liquid for the alignment film comprises 10% by weight of the 2- (2-ethoxyethoxy) ethanol. Preferably, it is contained in an amount of up to 30% by weight. If the content of 2- (2-ethoxyethoxy) ethanol in the coating solution for the alignment film is less than 10% by weight, print sagging cannot be effectively suppressed. The coatability is reduced, and it is desirable that the content be in the range of 10% by weight to 30% by weight. Claim 3
According to the invention described in the above, the 2- (2)
-Ethoxyethoxy) ethanol concentration from 10% by weight
Since it is 30% by weight, like the invention according to claim 2,
A highly accurate liquid crystal alignment film can be formed while suppressing print sag.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a method for forming a liquid crystal alignment film of the present invention will be described. The method for forming a liquid crystal alignment film of the present invention is a method of forming a liquid crystal alignment film by applying an alignment film coating solution obtained by mixing an alignment film material with a mixed solvent on a transparent substrate by a printing method.

The mixed solvent used here is 2- (2-
(Ethoxyethoxy) ethanol must be included. By containing the solvent, print sagging can be suppressed when the coating liquid for an alignment film is applied by a printing method.

The solvent to be mixed besides 2- (2-ethoxyethoxy) ethanol varies depending on the material of the alignment film, the printing method selected, and the like.
A solvent having the property of dissolving at least the alignment film material,
Mix with a solvent to improve coatability. As the solvent having the property of dissolving the alignment film material, the solvent selected depends on the alignment film material to be used. However, in the case of a polyimide alignment film, an amide solvent is most often used. -Pyrrolidone. Solvents with low surface tension are selected as solvents for improving coatability,
For example, 2-butoxyethanol (butyl cellosolve)
Is mentioned.

The alignment film material used in the present invention includes:
Any material that functions as a liquid crystal alignment film and can be formed by a printing method can be used, and examples thereof include various polyimide materials. In general, a polyimide-based material is hardly soluble or insoluble in a solvent when an imide structure is formed, and thus is dissolved in a mixed solvent in a polyamic acid state as a precursor thereof.

In the method for forming a liquid crystal alignment film according to the present invention, an alignment film material is mixed with a mixed solvent containing 2- (2-ethoxyethoxy) ethanol to prepare an alignment film coating solution. For example, N-methyl-pyrrolidone, 2
-Butoxyethanol, 2- (2-ethoxyethoxy)
A polyamic acid is dissolved in a mixed solvent of ethanol to prepare an alignment film coating solution. At this time, 2
The concentration of-(2-ethoxyethoxy) ethanol is preferably from 10% by weight to 30% by weight.
5% to 25% by weight is more preferred and about 20% by weight is optimal. If it is less than 10% by weight, print sagging cannot be effectively suppressed, and if it exceeds 30% by weight, the proportion of 2-butoxyethanol which relatively contributes to coatability decreases, resulting in uneven printing and blurring. This is because the resulting coatability may deteriorate during printing. The concentration of 2-butoxyethanol in the coating solution for the alignment film is 10% by weight to 20% by weight.
% By weight is good. When the amount is less than 10% by weight, the coatability is inferior, and blurring may occur at the time of application. This is because there are times when it cannot be suppressed. The concentration of the polyamic acid in the coating solution for the alignment film is about 5 to 15% by weight.

Next, a transparent electrode or the like is already formed on the alignment film coating solution prepared as described above using various printing methods usually used for forming a liquid crystal alignment film, such as letterpress printing and intaglio printing. On a transparent substrate. After the application, the solvent is removed and, if necessary, the mixture is heated to form a liquid crystal alignment film having a thickness of about 500 to 1500 angstroms.

The print sag of the liquid crystal alignment film formed by the above method can be obtained by measuring the amount of protrusion from the pattern designed in advance. When the mixed solvent contains 2- (2-ethoxyethoxy) ethanol, print sagging is suppressed by about several tens% as compared with the case where the mixed solvent does not contain 2- (2-ethoxyethoxy) ethanol.

As described above, in the method of forming a liquid crystal alignment film according to the present invention, in which a liquid crystal alignment film is formed by a printing method using an alignment film coating liquid obtained by mixing an alignment film material with a mixed solvent, Since the mixed solvent contains 2- (2-ethoxyethoxy) ethanol, a liquid crystal alignment film can be formed while suppressing print sag during coating,
As a result, a method for forming a liquid crystal alignment film having a small design tolerance and enabling a highly accurate design is provided.

When the mixed solvent is a mixture of N-methyl-pyrrolidone, 2-butoxyethanol and the above-mentioned 2- (2-ethoxyethoxy) ethanol, print sag can be similarly suppressed. . In this case, if the coating liquid for the alignment film contains 2- (2-ethoxyethoxy) ethanol at a concentration of 10% by weight to 30% by weight, print sag can be more effectively suppressed.

In the above embodiment, the alignment film coating solution in which polyamic acid is dissolved in a mixed solvent is applied. However, a polyimide soluble in a solvent is dissolved in the mixed solvent to prepare the alignment film coating solution. It may be prepared to form a liquid crystal alignment film. In addition, if necessary, the alignment film coating solution mixed with 2- (2-ethoxyethoxy) ethanol may contain N-methyl-
After mixing other components other than pyrrolidone and 2-butoxyethanol, the mixture may be applied to form a liquid crystal alignment film.

[0018]

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

1. Formation of Liquid Crystal Alignment Film (Examples 1 to 3)
Pyrrolidone (NMP), 2-butoxyethanol (B
E), 2- (2-ethoxyethoxy) ethanol (EE
E) and polyamic acid (PA) were mixed at a weight ratio shown in Table 1 to prepare an alignment film coating solution.

[Table 1] The prepared alignment film coating solution was applied by letterpress printing as follows. FIG. 1 shows a main configuration diagram of a printing machine used in the present embodiment. In FIG. 1, 1 is a printing machine, 2 is a squeegee, 3
Denotes a transfer plate, and 4 denotes a relief plate. One of the alignment film coating solutions prepared in Examples 1 to 3 was applied to the transfer plate 3, and an excess alignment film coating solution was removed using a squeegee 2. Next, the alignment film coating liquid was transferred from the transfer plate 3 to a relief plate 4 having a convex portion formed on the surface thereof in a predetermined pattern. And
The letterpress 4 is placed on the glass substrate L on which the ITO electrodes are formed.
Was transferred and coated with an alignment film coating solution. After the application, the solvent is removed by heating to cause a dehydration-condensation reaction of the polyamic acid.
Angstrom thickness was formed. (Comparative Example 1) PA (6% by weight), BE (15% by weight), NMP7 without 2- (2-ethoxyethoxy) ethanol
9% by weight was mixed to prepare an alignment film coating liquid. Using this alignment film coating liquid, a liquid crystal alignment film was formed in exactly the same manner as in Examples 1 to 3.

2. Evaluation of print sag The print sag amount of the liquid crystal alignment film formed above was measured, and the results are summarized in FIG. From FIG. 2, 2- (2-
It can be seen that when ethoxyethoxy) ethanol is included, the print sag amount is reduced by about several tens of percent as compared with the case where no ethoxyethoxy) ethanol is included. However, when the content of 2- (2-ethoxyethoxy) ethanol was 30%, the content of 2-butoxyethanol was relatively reduced, and printing unevenness sometimes occurred. The mixing ratio of the coating liquid for the alignment film is most preferable in the present embodiment.

[0021]

According to the invention described in the present invention, print sag can be suppressed by including 2- (2-ethoxyethoxy) ethanol in the coating solution for the alignment film, and as a result, the design tolerance is reduced. This is a method for forming a liquid crystal alignment film that is small and can be designed with high accuracy.

[Brief description of the drawings]

FIG. 1 is a diagram showing a main configuration diagram of a printing press used in the present embodiment.

FIG. 2 is a graph showing a difference in print sag amount due to a difference in concentration of 2- (2-ethoxyethoxy) ethanol in the present embodiment.

FIG. 3 is a graph showing a difference in print sag amount due to a difference in the concentration of an alignment film material in an alignment film coating solution using a conventional mixed solvent.

Claims (3)

[Claims] In a method for forming a liquid crystal alignment film by a printing method using an alignment film coating solution obtained by mixing an alignment film material in a mixed solvent, the mixed solvent is 2- (2- A method for forming a liquid crystal alignment film, characterized by containing (ethoxyethoxy) ethanol. 2. The liquid crystal according to claim 1, wherein the mixed solvent is a mixture of N-methyl-pyrrolidone, 2-butoxyethanol, and the 2- (2-ethoxyethoxy) ethanol. A method for forming an alignment film. 3. The liquid crystal alignment film according to claim 2, wherein the coating liquid for the alignment film contains the 2- (2-ethoxyethoxy) ethanol at a concentration of 10% by weight to 30% by weight. Formation method.