JP3387955B2 - Alignment varnish for liquid crystal display devices - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aligning agent varnish for a liquid crystal display device, and more specifically, an alignment agent used for producing a liquid crystal display cell having a polymer type alignment film such as polyimide as an alignment film for controlling the alignment of liquid crystal. It is related to the agent varnish.

[0002]

2. Description of the Related Art Liquid crystal display devices are characterized by low voltage driving, low power consumption, thin display devices and the like, including watches, calculators,
It is used as various display devices for TVs, word processors, personal computers, etc., and its application is expanding more and more in the future. As technologies to support this, various technological developments such as cell substrates, spacers, light sources, driving technologies, liquid crystal materials, display systems, seal materials, color filters, electrode technologies, alignment films, etc. have been carried out. An excellent liquid crystal display device can be obtained only when these are completed in parallel at the same time. But,
At present, various problems still remain.

The electrical characteristics of the liquid crystal device have problems such as the occurrence of a burn-in phenomenon which is considered to be caused by the magnitude of the residual charge of the device, or the flicker of the screen and the deterioration of the contrast due to the decrease of the voltage holding ratio. is there. Also in the field of alignment film, the coating property of alignment film (occurrence of cissing, crater formation, pinhole formation, etc.), tilt angle size, tilt angle stability, alignment irregularity, and deterioration of display characteristics due to inclusion of foreign matter Etc., there are various problems.

Regarding the pinholes of the coating film, in the case of pinholes such as paints, the cause is that when there is dust on the coated surface, when there is water or oil in the air during spray coating, there are microscopic holes in the base. It is said that when the coating material is present, or when the coating material is applied extremely thickly, or when the coating material contains a solvent having a low boiling point, or when a by-product is generated during curing, it is likely to occur. However, air spray is not used at the time of forming the alignment film as in the case of coating, and the glass substrate is not perforated nor thickly coated like coating. In the case of a polyimide-based alignment film, water is generated as a by-product, but the fact that pinhole-like defects occur in the preliminary drying stage before the imidization reaction means that the defects are water during imidization. It is unlikely that this is due to the occurrence of.

In a liquid crystal display device using a polymer-based alignment film such as polyimide, a methacrylic acid ester-based polymer, an acrylic acid ester-based polymer, as an auxiliary component of the alignment film,
Alternatively, the inclusion of these copolymers reduces the residual charge of the liquid crystal display element, and although the mechanism is not clear, the occurrence of uneven threshold values around the foreign matter when the foreign matter is mixed in the liquid crystal display cell (foreign matter) Occurrence of unevenness in the threshold value in the periphery prevents unevenness in the display contrast in the periphery and lowers the display quality of the liquid crystal display element), and an excellent liquid crystal display element is obtained (Japanese Patent Application No. 4-360272). ).

However, if these ester-based polymers are simply contained, pinhole-like defects due to this component may occur. For such a pinhole-like defect, the above-described solution for preventing the occurrence of pinholes during painting cannot be applied. The present invention has been completed by further research based on these findings.

[0007]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a liquid crystal display device having a polymer type alignment film, which has electrical characteristics, unevenness in threshold when foreign matter is mixed in a cell, and alignment film. It is an object of the present invention to provide an aligning agent varnish for use in manufacturing a liquid crystal display element in which pinhole-like defects on the surface are improved.

[0008]

The present invention provides a varnish containing a polyimide-based alignment film material as a main component, and as an auxiliary component, an acrylic acid ester polymer, a methacrylic acid ester polymer, and a copolymer thereof. One or more selected from polymers is 10-10000 ppm, preferably 50-100.
A solvent that contains 0 ppm and dissolves the main component (hereinafter sometimes referred to as the first type solvent) and the auxiliary component, and has a boiling point of 10 ° C. or more higher than any other coexisting solvent. A varnish for a polyimide- based alignment film, containing a solvent that does not precipitate the main component (hereinafter, also referred to as a second type solvent).

As a result, the phenomenon of residual charge of a liquid crystal display device having a polymer type alignment film or the threshold unevenness occurring around the foreign substance when the foreign substance is mixed into the cell is improved, and the pinning property of the ester polymer is improved. Hole-like defects can also be improved. If the specific solvent is not used and the content of the ester-based polymer is out of the above range, small defects such as pinholes or spots may be present on the surface of the alignment film. Will be greatly damaged.

Homopolymers or copolymers of acrylic acid esters and methacrylic acid esters can be obtained by a usual polymerization method, and as a commercial product, there are "Polyflow" series ("Polyflow" is a trademark of Kyoeisha) and the like. In the present invention, these components are contained in an amount of 10-10000 ppm, but if the amount is less than 10 ppm, the effect is small.
If it exceeds ppm, the rubbing cloth may be contaminated or the tilt angle may be adversely affected.

On the other hand, the above-mentioned auxiliary component polymer is dissolved, and the boiling point is higher than that of other solvent by about 10 ° C. or more,
Examples of the solvent (second type solvent) that does not precipitate the polymer component forming the alignment film, which is the main component, include diethylene glycol-based solvents and ethylene glycol-based solvents. Specific examples of these include diethylene glycol-based diethylene glycol monoalkyl ethers having 1 or more carbon atoms in the alkyl chain, diethylene glycol dialkyl ethers having 2 or more carbon atoms in the alkyl chain, and 2 carbon atoms in the alkyl chain. One or more diethylene glycol monoalkyl ether acetates may be mentioned. Also, for ethylene glycol type,
Examples thereof include ethylene glycol monoalkyl ether having an alkyl chain having 4 or more carbon atoms, and ethylene glycol monoalkyl ether acetate having an alkyl chain having 2 or more carbon atoms. However, the upper limit of the alkyl chain length of these glycol-based compounds is set such that the boiling point of the solvent compound does not exceed 300 ° C. The reason is that if the boiling point exceeds 300 ° C., the solvent becomes difficult to dry, which is not preferable.

The difference between the boiling points of the other solvent and the second type solvent is set to at least plus about 10 ° C. because the effect of the second type solvent is small at plus 10 ° C. or less. Needless to say, a plurality of these solvents can be used. Speaking of an example of a polyimide-based aligning agent, a polyimide-based varnish is usually synthesized from a tetracarboxylic acid and a diamine in a polar organic solvent and used as a varnish for a polyamic acid solution. This varnish is applied, dried, baked (imidized) and then rubbed to be used as a polyimide alignment film. In addition, soluble polyimide is synthesized,
It may be used as a polyimide film by applying a polyimide solution varnish and solvent drying. As the solvent for these polyamic acid or soluble polyimide varnish, a polar solvent having a boiling point of about 200 ° C. or less can be mentioned, as described later.

The content of the polyamic acid or soluble polyimide in the varnish of the present invention is 0.1-20%, preferably about 1-10%. In these varnishes, if the content of the polymer-based alignment film material as the main component exceeds 20%, the viscosity of the varnish becomes too large, which is not preferable. On the other hand, if the content is less than 0.1%, on the contrary, the viscosity is too small and it is difficult to form an appropriate film thickness.

The reaction solvent for the polyamic acid is N,
N-dimethylformamide, N, N-diethylformamide, N, N-dimethylacetamide, N-methylpropionamide, dimethylsulfoxide, N-methyl-2
-A polar organic solvent (the above-mentioned first type solvent) such as pyrrolidone (hereinafter abbreviated as NMP) is used. The boiling points of these solvents are as follows. Solvent name (first type solvent) Boiling point (° C) N, N-dimethylformamide 153 N, N-diethylformamide 177 N, N-dimethylacetamide 166 N-methylpropionamide 148 dimethylsulfoxide 189 N-methyl-2-pyrrolidone 202 When these solvents are used as a varnish solvent for polyamic acid, the above-mentioned auxiliary component ester polymer is not dissolved, and pinhole-like defects are likely to occur. When using these solvents, rather than these solvents,
Generation of the pinhole-like defects by using together with a solvent having a boiling point higher by about 10 ° C., which dissolves the ester polymer and does not precipitate the dissolved polymer for alignment film in the varnish. Is prevented.

For example, when NMP is used as a reaction solvent for polyamic acid, since ethylene glycol monobutyl ether has a lower boiling point than NMP, the second aspect of the present invention is used.
However, when N, N-dimethylformamide is used as the reaction solvent, the boiling point of ethylene glycol monobutyl ether is about 10% lower than that of the first solvent.
Since the temperature is high, it will function as the second type solvent of the present invention.

The content of the second type solvent in the varnish of the present invention depends on the content of the polymer component forming the alignment film,
It is 2-50%, preferably 2-40%. When the content of the polymer component for forming the alignment film is small, it is possible even at 50% because there is no precipitation of the polymer component. . When the mixing ratio of the second type solvent is less than 2%, the effect of the invention is small, and when it exceeds 50%, the polymer component forming the alignment film is precipitated at room temperature or low temperature, or used. Depending on the two kinds of solvents, due to the heavy use of these solvents, the repellency may increase during the application of the varnish, and it may take a long time to dry or the drying temperature may increase. This is not preferable because it may cause harmful effects.

In the present invention, the solvent of the first kind and the solvent of the second kind are good solvents for the main component and the auxiliary component, respectively, but conversely, they are poor solvents for the auxiliary component and the main component. There are many things. Therefore, in the present invention, the mixing ratio of the first and second solvents must be determined in consideration of the contents of the main component and the auxiliary component, particularly the content of the main component.

When the content of the main component becomes large in the varnish of the present invention, it is desirable to appropriately increase the content of the auxiliary component.

[0019]

【Example】

Examples 1-7 and Comparative Examples 1-4 Pyromellitic acid was used as the tetracarboxylic acid component of the polyamic acid, and 1,1-bis ((4-aminophenoxy) phenyl) -4-n-propylcyclohexane was used as the diamine component. NMP as the first type solvent
Was used to synthesize a polyamic acid. After that, polymer concentration 7%, ethylene glycol monobutyl ether (boiling point 170 ° C) 50%, NMP (boiling point 202 ° C) 43%
The original varnish was adjusted so that To this varnish, the second type solvent and auxiliary components shown in Table 1 were added to adjust the concentration so that both components had the composition shown in Table 1. As an auxiliary component, a varnish containing a copolymer of methacrylic acid ester and acrylic acid ester (trade name "Polyflo" manufactured by Kyoeisha Co., Ltd.) was applied onto a glass substrate with a spinner (rotation speed 3000 rpm for 10 seconds). , Dry on a hot plate set at 50 ° C for 5 minutes, then add 100
The surface condition of the coating film obtained by drying at 60 ° C. for 60 minutes was compared and observed with the blank. In addition, in order to use it as an alignment film for a liquid crystal element, it is necessary to perform a pre-drying and then a baking treatment for an imidization reaction at a high temperature. Since the purpose is to see, the evaluation was performed by omitting the baking treatment at high temperature. In the original varnish, 50% of ethylene glycol monobutyl ether and 43% of NMP, which is the first type of solvent, are used, and these two types are equivalent to other solvents in the present application, but ethylene glycol monobutyl ether is ,
In this original composition, the first type of solvent (in this case NM
Since it has a lower boiling point than P), it does not correspond to the second type solvent. Ethylene glycol monobutyl ether can be the second type solvent when the first type solvent uses a solvent having a boiling point lower by about 10 ° C. than ethylene glycol monobutyl ether. In the original composition, NMP has the higher boiling point of the two types of solvent, so here, NMP is used.
A composition system using a solvent having a boiling point of about 10 ° C. or more is higher than the above.

[0020]

[Table 1]

Example 8 and Comparative Example 5 Using the varnishes used in Example 1 and Comparative Example 1, 1
A coating film is formed by a spinner on a substrate provided with 0 × 10 cm ² square ITO transparent electrodes, dried at 100 ° C. for 1 hour, and then baked at 220 ° C. for 1.5 hours to perform imidization. It was

Then, the surface of the substrate was rubbed with a roll around which a rubbing cloth made of velvet-like rayon was wound to perform orientation treatment. By the same operation, a glass substrate provided with 10 alignment films for each example was prepared, and the surface of the substrate was observed with the naked eye. As a result, a pinhole-like defect was found on the substrate prepared using the varnish of Example 1. Although not observed at all, many pinhole-like defects were observed on the glass substrate using the varnish of Comparative Example 1.

Each of the ten glass substrates is combined with two glass substrates to form five cell gaps of 6.5.
A μm 240 ° twisted STN cell was assembled. LIXON-4200 (manufactured by Chisso Corp.) containing a chiral agent S-811 (manufactured by Chisso Corp.) as a liquid crystal material was filled in this cell to prepare five liquid crystal elements. When a DC voltage of 5 V was applied to these liquid crystal elements and the on-off operation was repeated, an average of 5.2 circular display irregularities with a diameter of 1 mm or more was observed in the element produced using the varnish of Comparative Example 1. However, in the cells produced using the varnish of Example 1, the average display unevenness of 1 mm or more in diameter was 0.4. When the central portions of these circular display irregularities were observed with a microscope, foreign matter was confirmed in almost the central portion.

[0024]

By using the varnish for liquid crystal alignment film of the present invention, it is possible to suppress the occurrence of pinhole-like defects on the surface of the liquid crystal alignment film. Further, by using this alignment film, it is possible to improve the unevenness of the threshold value and the residual charge caused by the inclusion of foreign matter in the cell, and it is possible to manufacture a liquid crystal display element with improved display quality.

Claims (3)

(57) [Claims] 1. A varnish containing a polyimide-based alignment film material as a main component, comprising: (1) an auxiliary component comprising at least one of an acrylic acid ester and a methacrylic acid ester homopolymer and a copolymer (2) a main component. At least one solvent that dissolves the polyimide-based material of the component, and (3) the auxiliary component is dissolved, and the boiling point thereof is 300 ° C. or lower, which is 10 ° C. or higher higher than the boiling point of any other coexisting solvent, and the orientation A varnish for a liquid crystal alignment film, which comprises at least one solvent that does not precipitate a polyimide-based main component that forms a film, and whose auxiliary component content is 10-10000 ppm as a whole. 2. A solvent for dissolving an auxiliary component is a diethylene glycol monoalkyl ether having an alkyl chain having 1 or more carbon atoms, a diethylene glycol dialkyl ether having 2 or more alkyl chain carbon atoms in total, and an alkyl chain having 2 carbon atoms. Or more diethylene glycol monoalkyl ether acetate, at least one selected from ethylene glycol monoalkyl ether having 4 or more carbon atoms in the alkyl chain, and ethylene glycol monoalkyl ether acetate having 2 or more carbon atoms in the alkyl chain. The varnish for liquid crystal alignment film according to claim 1. 3. A liquid crystal display device produced by using the varnish for a liquid crystal alignment film according to claim 1 or 2 .