JP2873822B2 - Liquid crystal display device and manufacturing method thereof - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a liquid crystal display device and a method for manufacturing the same.

[Background of the Invention]

Recently, liquid crystal display devices have been used in various application fields because of their advantages such as low power consumption, low manufacturing cost, light weight and thinness, and easy colorization. It is becoming possible.

A liquid crystal display device generally includes a pair of substrates having an alignment layer on an inner surface thereof and a liquid crystal composition layer formed between the substrates. Conventionally, a twist nematic type, a super twist type, a guest Host type,
Liquid crystal display devices of a birefringence control type, a phase transition type, a dynamic scattering type, a ferroelectric type and the like are known.

Among them, the twisted nematic type liquid crystal display device is configured by enclosing a liquid crystal composition layer made of nematic liquid crystal between a pair of substrates having an alignment layer on the inner surface, and the twist angle of liquid crystal molecules in the liquid crystal composition layer is , Usually 90 degrees. This twisted nematic type liquid crystal display device has advantages in that it is easy to manufacture and has a fast response. However, on the other hand, in general, the contrast ratio in high multiplex driving display is low, and the direction in which a person looks at the liquid crystal display surface ( (Gaze direction), there is a drawback that the practical fixable range where a practically sufficient contrast ratio and display quality can be obtained is narrow.

On the other hand, a super twist type liquid crystal display device is configured such that a liquid crystal composition layer composed of nematic liquid crystal is sealed between a pair of substrates having an alignment layer on the inner surface, and the twist angle of liquid crystal molecules in the liquid crystal composition layer is usually 180. The range is ~ 360 degrees. In order to drive a liquid crystal display having such a large twist angle stably, an alignment layer for giving a large alignment pretilt angle, usually 5 degrees or more, to liquid crystal molecules is required. The alignment pretilt angle refers to an angle formed between a director direction of liquid crystal molecules in contact with the surface of the alignment layer and a surface of the substrate having the alignment layer. Note that the director direction refers to a direction in which the major axes of the liquid crystal molecules are preferentially aligned.

According to such a super twist type liquid crystal display device, a high contrast ratio can be obtained, and a sufficiently wide practical fixable range can be obtained. From such a viewpoint, recently, a super-twist type liquid crystal display device has received particular attention.

[Problems to be solved by the invention]

The following techniques have been known as means for forming an alignment layer.

A rubbing method in which a coating made of polyimide or the like is provided on the surface of the substrate, and the coating is rubbed with a cloth or the like to impart alignment ability.

An oblique vapor deposition method in which a deposition material such as SiO is vapor-deposited on a substrate surface at an oblique angle to form a groove in a fixed direction on a substrate surface.

In the above means, the alignment layer can be easily formed. However, the alignment pretilt angle obtained by the alignment layer is as small as about 2 to 3 degrees, and therefore, a super twist type liquid crystal having sufficient performance for practical use It is difficult to configure a display device.

In the above means, a large alignment pretilt angle can be obtained, but it takes a considerably long time to form an alignment layer, and mass production is difficult, and therefore, productivity is low. Further, there is a problem that display quality is inferior because the thickness of the alignment layer or the deposition angle tends to be non-uniform.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its objects the following objects: (1) To provide a liquid crystal display device capable of obtaining a large alignment pretilt angle with a simple structure; It is an object of the present invention to provide a manufacturing method capable of manufacturing a liquid crystal display device capable of obtaining a large alignment pretilt angle.

[Means for solving the problem]

In order to achieve the above object, the liquid crystal display device of the present invention comprises:
In a liquid crystal display device having an alignment layer, the alignment layer is composed of a coating made of a polymer having a nonpolar atomic group in its main chain, and the nonpolar atomic group has a silicon number of 3 or more. It is a chain silyl group.

Here, the polymer is preferably a polyimide-based or polyamide-based polymer.

The method for producing a liquid crystal display device of the present invention comprises preparing a coating solution with a polyamic acid or polyamide having a non-polar atomic group in its main chain and a polar solvent, and applying the coating solution to a substrate for a liquid crystal display device. After coating, the coating film is dried and / or heat-treated in an atmosphere having a relative humidity of 55% or less to form a polyimide- or polyamide-based polymer film. Is applied to a substrate for a liquid crystal display device, and dried and / or heat-treated to form a polyimide or polyamide polymer film, and the polymer film is subjected to an alignment treatment to form an alignment layer. And a step of performing

In this production method, the nonpolar atomic group has 5 carbon atoms.
It is preferable that the nonpolar atomic group is an alkyl group or a perfluoroalkyl group, or that the nonpolar atomic group is a linear silyl group having 3 or more silicon atoms.

Further, in this production method, it is preferable to adjust the alignment pretilt angle of the liquid crystal molecules according to the size of the nonpolar atomic group in the main chain of the polyamic acid or polyamide, and the degree of the heat treatment and the alignment treatment.

[Action]

Since the alignment layer is constituted by a coating made of a polymer having a non-polar atomic group in its main chain, and the non-polar atomic group is a linear silyl group having 3 or more silicon atoms, the non-polar atom Due to the presence of the groups, the surface tension of the alignment layer is reduced, and a large alignment pretilt angle is obtained.

When the polymer is a polyimide-based or polyamide-based polymer, the orientation layer has excellent durability.

A polymer having a nonpolar atomic group in its main chain has low solubility in a solvent due to its nonpolarity, but it can be well dissolved in a polar solvent as a polyamic acid or polyamide having a large polar group. Thus, a coating solution can be prepared. Further, in an atmosphere having a relative humidity of 55% or less, the coating liquid is applied to a substrate for a liquid crystal display device, and dried and / or heat-treated to form a polyimide-based or polyamide-based polymer film. Since the polar group of the polyamic acid or polyamide changes to a group having a smaller polarity, the relative polarity of the polymer decreases, and the surface tension of the coating decreases. By applying, it is possible to form a uniform alignment layer from which a large alignment pretilt angle is obtained.

When the nonpolar atomic group has 5 or more carbon atoms, the surface tension of the alignment layer is surely reduced, and a large alignment pretilt angle is obtained.

Then, the size of the non-polar atomic group in the main chain of the polyamic acid or polyamide, the degree of the heat treatment and the degree of the orientation treatment are adjusted to adjust the magnitude of the orientation pretilt angle. An orientation pretilt angle is obtained.

[Specific configuration of the invention]

 Hereinafter, the present invention will be described specifically.

In the present invention, a liquid crystal display device is provided by using an alignment layer composed of a polymer film having a nonpolar atomic group composed of a linear silyl group having 3 or more silicon atoms in its main chain. Constitute.

Further, in the production method of the present invention, a coating solution is prepared from a polyamic acid or polyamide having a nonpolar atomic group in its main chain and a polar solvent, and the coating solution is prepared under an atmosphere having a relative humidity of 55% or less. The liquid is applied to a substrate for a liquid crystal display device, dried and / or heat-treated to form a polyimide or polyamide polymer film, and the polymer film is subjected to an alignment treatment to form an alignment layer. Form.

In the production method of the present invention, the `` non-polar atomic group ''
Even when a polar group portion is contained in an atomic group consisting only of a non-polar aliphatic or aromatic hydrocarbon or the like constituting a main chain in a polymer, or a polar group portion is partially contained, a large non-polar group is present before and after the polar group portion. An atomic group that is present and that is totally insoluble in polar solvents. Further, the main chain refers to a main chain forming a polymer skeleton in which a repeating unit is bonded by, for example, an imide bond, an amide bond, an ester bond, an ether bond, or the like in a polymer.

The nonpolar atomic group is preferably long as a whole, but may be partially branched. Further, the size of the nonpolar atomic group is preferably 5 or more in terms of carbon number in an aliphatic chain, and particularly preferably 5 or more and 20 or less. In the nonpolar atomic group, when the number of carbon atoms is 4 or more, the effect of sufficiently increasing the orientation pretilt angle is small. That is, by selecting a nonpolar atomic group having a large number of carbon atoms, the orientation pretilt angle can be increased. However, when the number of carbon atoms is 20 or more, the applicability of the coating solution is reduced, or the adhesion of the coating to the substrate is reduced.

As such a nonpolar atomic group, a group consisting of only a nonpolar group is preferable, but a group having a small polarity may be partially contained. Further, one or more nonpolar atomic groups may be provided for each repeating unit of the main chain, or may be provided for each of a plurality of repeating units. Practically, it is preferable that at least one nonpolar atomic group is present for every five repeating units. In addition, the nonpolar atomic group may be composed of only a single species, or may be composed of a combination of plural species.

 Specifically, the following nonpolar atomic groups are preferable.

(1) A linear alkyl group having 5 or more carbon atoms.

(2) A group in which part of a linear alkyl group having 5 or more carbon atoms is substituted by a nonpolar group or a group having a small polarity as described below.

(3) A linear alkyl group having 5 or more carbon atoms has
Groups with up to 20 branches.

(4) A group in which part or all of the hydrogen atoms of the above-mentioned alkyl groups have been substituted with fluorine atoms.

(5) A linear silyl group having 3 or more silicon atoms.

Specific examples of the nonpolar atomic group include those represented by the following structural formula.

The bonding position in the main chain of the nonpolar atomic group may be, for example, in the case of a polyimide-based polymer, any of dicarboxylic anhydride and diamine, which are monomers for constituting the polymer. . For example, in a polyamic acid which is a precursor of a polyimide-based polymer, the following structural formula (1)
As shown, the positions of R ² from the diamine and R ¹ from the dicarboxylic anhydride are possible.

Structural formula (1) (Wherein, R ¹ and R ² represent an aromatic group, an aliphatic group, or a cycloaliphatic group.) In order to obtain a film made of a polyimide or polyamide polymer having a nonpolar atomic group As a material,
Examples thereof include polyimide, polyimide amide, polyester imide, polyamide, polyester amide, and polyether amide having a nonpolar atomic group. Alternatively, a polyamic acid having a nonpolar atomic group, which is a precursor of polyimide, may be subjected to a heat treatment to form a polyimide. These polyimide-based or polyamide-based polymers may be modified by adding a cross-linking agent to increase the film strength, or may be added with a silane coupling agent or the like to increase the adhesive strength.

Having a non-polar atomic group, as a polyimide-based or polyamide-based polymer, the weight average molecular weight is, for example, 1,000
Those in the range of 55,000,000 can be used. As the basic skeleton of such a polyimide or polyamide polymer, an aromatic, aliphatic, or cycloaliphatic polymer can be used. Among these materials, an aromatic polyimide-based material and an aromatic polyamide-based material are particularly preferable because a polymer film having high heat resistance and high mechanical strength can be obtained.

In the production method of the present invention, a polyamic acid having a nonpolar atomic group is obtained by subjecting a dicarboxylic anhydride and a diamine to a condensation reaction, and it is necessary that at least one of the polyamic acids has a nonpolar atomic group. is there.

Specific examples of the diamine having a nonpolar atomic group include, for example, m-phenylenediamine, p-phenylenediamine, m-xylenediamine, p-xylenediamine, 4,
4'-diaminodiphenyl ether, 4,4'-diaminodiphenylmethane, 3,3'-dimethyl-4,4'-diaminodiphenylmethane, 3,3 ', 5,5'-tetramethyl-4,4'-
Diaminodiphenylmethane, 2,2'-bis (4-aminophenyl) propane, benzine, 4,4'-diaminodiphenylsulfide, 4,4'-diaminodiphenylsulfone, 1,5-diaminonaphthalene, 3,3'-dimethyl Benzidine, 3,3'-dimethoxypendidine, 2,4'-bis (β
-Amino-tert-butyne) toluene, bis (4-β-amino-tert-butylphenyl) ether, 1,4-bis (2-methyl-4-aminopentyl) benzene, 1,4-
Bis (4-aminophenoxy) benzene, bis ([gamma] -aminopropyl) tetramethyldisiloxane, 4,4'-diaminodiphenyltetramethyldisiloxane, and the like in which a nonpolar atomic group is linked to the main chain may be mentioned. it can.
Aromatic ones are particularly preferred from the viewpoint of heat resistance.

Specific examples of dicarboxylic anhydrides include, for example, pyromellitic anhydride, 2,3,6,7-naphthalenetetracarboxylic anhydride, and 3,3 ′, 4,4′-diphenyltetracarboxylic anhydride. 1,2,5,6-naphthalenetetracarboxylic anhydride, 2,2 ', 3,3'-diphenyltetracarboxylic anhydride, thiophene-2,3,4,5-tetracarboxylic anhydride, 2 , 2'-bis (3,4-biscarboxyphenyl) propane anhydride, perylene-3,4,9,10-tetracarboxylic anhydride, bis (3,4-dicarboxyphenyl) ether anhydride, 3 ', 4,4'-benzophenone tetracarboxylic anhydride, cyclobutane-1,2,3,4-tetracarboxylic anhydride, cyclopentane 1,2,3,4-tetracarboxylic anhydride, etc. Can be. Aromatic ones are particularly preferred from the viewpoint of heat resistance. Non-polar atomic groups may be linked to these main chains.

Further, as a polyamide-based polymer having a non-polar atomic group, for example, (Ar ¹ , Ar ² , Ar ³ : aryl group R ¹ , R ² , R ³ , R ⁴ : H, F, alkyl group, perfluoroalkyl group, alkoxy group R ⁵ , R ⁶ : H, F, alkyl group , A perfluoroalkyl group).

It is preferable that a polar functional group is introduced into the polyamide-based polymer having these nonpolar atomic groups in order to enhance solubility in a solvent when preparing a coating solution. Also,
It is preferable that the polarity of such a polar functional group is reduced by adding a cross-linking agent or the like to the coating solution and reacting with the additive in a heat treatment after forming the coating film.

The solvent used for preparing the coating solution needs to be capable of dissolving a polyamic acid or polyamide having a large nonpolar atomic group. Further, it is preferable that the material has low molecular weight and appropriate volatility. The use of a low molecular weight solvent allows the coating film to be dried quickly at a lower temperature, and efficiently forms a polymer film while preventing heat from disturbing the film surface. Can be. Further, it is more preferable that it has a low boiling point. By using a solvent having a low boiling point, a polymer film having excellent surface characteristics can be formed.

As a specific example of such a solvent, for example, N-methyl-2
-Pyrrolidone, dimethylacetamide, dimethylformamide, dimethylsulfoxide, N-methylcaprolactam, tetramethylurea, pyridine, dimethylsulfolane, hexamethylphosphoramide, butyrolactone and the like. These polar solvents may be used alone or in combination of two or more.
In addition, a solvent that does not dissolve the polyamic acid or polyamide having a nonpolar atomic group may be used by adding it to the polar solvent as long as the polyamic acid or polyamide can be dissolved. For example, by adding a low molecular weight solvent such as alcohols, ketones, ethers and esters, it is possible to lower the boiling point of the polar solvent or to improve the applicability to a substrate.

In the preparation of the coating solution, the concentration of the polyamic acid or polyamide having a nonpolar atomic group is usually 0.1 to 20.
% Range. When the concentration is too high, the coating properties are reduced, and when the concentration is too low, the coating strength is apt to be lowered.

The application method is not particularly limited, and various methods can be adopted. Specific examples include spin coating, dip coating, printing coating, roller coating, brush coating, and spray coating. The thickness of the coating film is 100 to 2,000 mm in thickness when dried, preferably 200 to 1000
Å is good.

In order to improve the uniformity of the surface of the coating film, it is preferable to leave the coating film in an undried state for a certain period of time after completion of the coating process.

Next, the coating film is dried if necessary, and further heated, the solvent is volatilized and removed, and the polyamic acid is imidized to form a polyimide polymer, or a polyamide polymer is formed, A coating made of the polymer is formed.

The drying process is performed as needed, and may be omitted. In the case of performing a drying treatment, conditions vary depending on the type of the solvent and cannot be unequivocally defined.

The heat treatment is a treatment necessary to remove residual solvent and to proceed an imidization reaction or a cross-linking reaction to polymerize. The heating temperature is, for example, 100 to 400 ° C., and the heating time is, for example, about tens of minutes to several hours. By appropriately selecting the heating temperature or the heating time, the magnitude of the orientation pretilt angle can be adjusted with a relatively large degree of freedom.

These coating, drying, and heat treatment steps must be performed in a low humidity atmosphere having a relative humidity of 55% or less. This is because the solubility of a polyamic acid or polyamide having a non-polar atomic group in a solvent is relatively low, and the polar solvent is hygroscopic. This is because agglomerates are formed in the film or the uniformity of the film surface is disturbed, so that a uniform liquid crystal alignment layer cannot be formed. The relative humidity is preferably less than 40%.

The coating film made of the polymer formed as described above is subjected to an alignment treatment by an appropriate means to form an alignment layer. The means for the alignment treatment is not particularly limited, and various methods can be adopted. Specifically, a rubbing treatment method in which the surface of the coating is rubbed in a certain direction with a cloth or the like, a method of spraying or flowing fine particles or fluid in a certain direction on the surface of the coating, a corona discharge treatment of the coating surface from a certain direction And other methods.

The size of the alignment pretilt angle obtained by the alignment layer formed as described above depends on the size of the nonpolar atomic group in the main chain of the polyimide or polyamide polymer, the degree of the heat treatment and the degree of the alignment treatment. Can be adjusted. That is, the magnitude of the orientation pretilt angle tends to increase as the number of carbon atoms in the nonpolar atomic group increases, as the heat treatment temperature increases, and as the orientation treatment is performed weaker. The coating made of the polymer formed as described above can also be used as a highly uniform vertical alignment layer unless an alignment treatment is performed.

The substrate for the liquid crystal display device is not particularly limited, and various substrates can be used. Specifically, soda glass, borosilicate glass, glass substrates such as quartz glass,
A plastic substrate such as uniaxially stretched polyethylene terephthalate, polyethersulfone, or polyvinyl alcohol, or a metal substrate such as aluminum or stainless steel can be used. Note that it is necessary to provide an electrode layer or a driving element for driving the liquid crystal on the surface of the substrate before forming the alignment layer.

The liquid crystal is not particularly limited, and a substance conventionally used in the art can be used. Specifically, for example, a nematic liquid crystal, a cholesteric liquid crystal, a smectic liquid crystal, a ferroelectric liquid crystal, or the like can be used.

〔Example〕

Hereinafter, examples of the present invention will be specifically described,
The present invention is not limited to these examples.

<Example 1> Concentration of polyamic acid having a nonpolar atomic group in the main chain obtained by condensation of pyromellitic anhydride with 1,8-bis (4-aminophenyl) -n-perfluorooctane A 2% N-methylpyrrolidone solution was prepared, and a coating film was formed on a substrate on which a transparent electrode pattern was formed by spin coating using this solution as a coating solution. Next, the solvent is evaporated and dried under an atmosphere having a humidity of 40% or less, and further,
Heat treatment was performed at 350 ° C. for 30 minutes to cause an imidization reaction, thereby obtaining a film of a polyimide-based polymer having a thickness of 600 °.

This coating was rubbed in a certain direction with a nylon flocking cloth to form an alignment layer.

A substrate on which the above-mentioned alignment layer is formed and a liquid crystal "ZLI-2293"
(Manufactured by Merck) and a pretilt angle was measured, which was a large value of 25 °.

In addition, a twist angle of 27
When a 0 ° liquid crystal display device was produced, it had uniform alignment characteristics and excellent display quality.

<Example 2> A 3% N-methylpyrrolidone solution of a polyetheramide resin having a nonpolar atomic group in the main chain represented by the following structural formula (A) was prepared, and this solution was used as a coating solution. Then, a coating film was formed on the substrate on which the transparent electrode pattern was formed by the spin coating method. Then, the solvent was evaporated and dried at room temperature in an atmosphere of 35% humidity, and further heat-treated at 150 ° C. for 1 hour to obtain a film of a polyetheramide polymer having a film thickness of 500 °.

This film was rubbed at a high density with a small contact pressure in a certain direction using a rayon flocking cloth to form an alignment layer.

A substrate on which the above-mentioned alignment layer is formed and a liquid crystal "ZLI-2293"
(Manufactured by Merck) and a pretilt angle was measured, which was a large value of 32 °.

In addition, a twist angle of 27
When a 0 ° liquid crystal display device was produced, it had uniform alignment characteristics and excellent display quality.

Structural formula (A) <Example 3> Polyamic acid "RN- having a non-polar atomic group in the main chain"
715 "(manufactured by Nissan Chemical Industries, Ltd.) in a mixed solvent of N-methylpyrrolidone and butylcellosolve (N-methylpyrrolidone:
Butylcellsolve = 4: 1) to prepare a coating solution having a concentration of 6%, and using this coating solution, an alignment layer was formed in the same manner as in Example 2. However, the heat treatment was performed at 240 ° C. for 1 hour, and the film thickness was 900 °.

A substrate on which the above-mentioned alignment layer is formed and a liquid crystal "ZLI-2293"
(Manufactured by Merck) and a pretilt angle was measured, which was a large value of 35 °.

In addition, a twist angle of 27
When a 0 ° liquid crystal display device was produced, it had uniform alignment characteristics and excellent display quality.

<Comparative Example 1> A coating solution having a concentration of 1.7% was prepared with an N-methylpyrrolidone solution of polyetheramide "HL-1100" (manufactured by Hitachi Chemical Co., Ltd.) having no nonpolar atomic group in its main chain. Using this coating solution, an alignment layer was formed in the same manner as in Example 2.

A substrate on which the above-mentioned alignment layer is formed and a liquid crystal "ZLI-2293"
(Manufactured by Merck) and a pretilt angle was measured and found to be as small as 2 °.

In addition, a twist angle of 27
When a 0 ° liquid crystal display device was manufactured, stripe-shaped domains were generated during driving, and sufficient display characteristics could not be obtained.

〔The invention's effect〕

According to the present invention, it is possible to form an alignment layer having a large alignment pretilt angle with a simple configuration.
Further, a liquid crystal display device having an alignment layer capable of obtaining a large alignment pretilt angle can be manufactured with high productivity.

In particular, when the number of carbon atoms of the nonpolar atomic group is 5 or more, it is possible to form an alignment layer that is uniform and has a large alignment pretilt angle.

When the nonpolar atomic group is composed of an alkyl group or a perfluoroalkyl group, the homogeneity of the alignment layer is further improved.

When the polymer is a polyimide-based or polyamide-based polymer, the durability of the alignment layer is improved.

The size of the non-polar atomic group in the main chain of the polyamic acid or polyamide, the degree of the heat treatment and the degree of the orientation treatment are adjusted to adjust the magnitude of the orientation pretilt angle, so that the desired orientation pretilt angle can be obtained with a considerably large degree of freedom. The resulting alignment layer can be formed.

As a result, according to the present invention, it is possible to obtain a liquid crystal display device having an alignment layer capable of obtaining a large alignment pretilt angle easily and in a mass production manner. In fact, a desired orientation pretilt angle can be obtained over a wide range from 5 to 90 degrees, and a super twist type liquid crystal display device having practically sufficient performance can be efficiently obtained.

Claims (7)

(57) [Claims] 1. A liquid crystal display device having an alignment layer, wherein the alignment layer is constituted by a coating made of a polymer having a nonpolar atomic group in its main chain, and wherein the nonpolar atomic group has a silicon number. Is a linear silyl group of 3 or more. 2. The method according to claim 1, wherein the polymer is a polyimide or polyamide polymer.
A liquid crystal display device according to the item. 3. A coating solution is prepared from a polyamic acid or polyamide having a non-polar atomic group in its main chain and a polar solvent, and the coating solution is subjected to a liquid crystal display device under an atmosphere having a relative humidity of 55% or less. Forming a polyimide- or polyamide-based polymer film by applying to a substrate for drying and / or heat treatment to form an alignment layer by further performing an alignment treatment on the polymer film. A method for manufacturing a liquid crystal display device, comprising: 4. The method according to claim 3, wherein the nonpolar atomic group has 5 or more carbon atoms. 5. The method for manufacturing a liquid crystal display device according to claim 3, wherein the nonpolar atomic group comprises an alkyl group or a perfluoroalkyl group. 6. The method according to claim 3, wherein the nonpolar atomic group is a linear silyl group having 3 or more silicon atoms.
13. The method for manufacturing a liquid crystal display device according to item 10. 7. The method according to claim 1, wherein the pretilt angle of the liquid crystal molecules is adjusted according to the size of the nonpolar atomic group in the main chain of the polyamic acid or the polyamide, and the degree of the heat treatment and the alignment treatment. 7. The method for manufacturing a liquid crystal display device according to any one of items 3 to 6.