JP2565704B2 - Film formation method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for forming an oriented polymer thin film on a substrate. The oriented polymer thin film is useful as an orientation film in a liquid crystal cell.

2. Description of the Related Art In liquid crystal switching devices such as liquid crystal display devices, liquid crystal shutters, liquid crystal light valves, and switching devices for optical information processing that utilize the electro-optical effect of liquid crystals, it is generally necessary to preferentially orient the liquid crystal molecules in one direction. Many studies have been made on the fact that this alignment treatment greatly affects the quality of these liquid crystal switching elements. The alignment state of the liquid crystal on the substrate surface is largely classified into a homogeneous alignment that is aligned parallel to the substrate surface and a homeotropic alignment that is aligned perpendicular to the substrate surface.

In actual light switching, an electric field or heat is applied to the liquid crystal aligned in this way to change the alignment state of the liquid crystal, and by utilizing changes in birefringence, light polarization, light scattering, etc.,
Turns the light on and off.

The following methods have been known as methods for aligning liquid crystal molecules.

An oblique deposition method of inorganic compounds such as SiO, SiO ₂ and Au.

A method in which a silane coupling agent is applied and the coating film is rubbed in one direction with a cotton cloth or the like.

A method of rubbing an organic polymer coating film such as nylon.

A method of rubbing a polyimide coating film. However, oblique deposition is a batch process, and it takes a long time to perform one batch process, resulting in poor productivity. Further, there is a difference in the alignment performance depending on the type of the liquid crystal used, and the selectivity of the liquid crystal is large.

The method of using a silane coupling agent is such that the orientation decreases or disappears due to heating at the time of manufacturing an element, for example, heating at the time of curing an adhesive for an outer peripheral seal for sealing a liquid crystal, or in a high-temperature environment. It may deteriorate with time when stored under.

Similarly, a polymer coating such as nylon also has poor heat resistance and orientation performance is degraded.

The method of rubbing the polyimide film has the following drawbacks, although the above-mentioned drawbacks are few.

(1) Since polyimide is generally insoluble and infusible,
A solution of the precursor polyamic acid is applied to the substrate and then heated to ring-close to form a polyimide. But,
At this time, a high temperature of 300 ° C. or higher is required, so that members constituting the element, for example, the substrate are significantly restricted. For example, glass and the like do not hinder, but plastic films and the like melt, deform, and decompose the substrate. Further, in a color liquid crystal display device provided with a color filter, a dye or a polymer binder constituting the filter is deteriorated. Further, in a substrate in which a thin film transistor or a diode array is formed on the substrate, the characteristics of the element will change.

(2) If the thickness is not at least several hundred Å, alignment defects will occur due to the non-uniformity of the coating film, so it is used at a thickness of several hundred Å or more. As a result, yellowing peculiar to polyimide occurs, and the transmittance decreases when the element is used in a transmissive manner, and the reflectance decreases when the element is a reflective type. Further, when used as a display element, the appearance is damaged due to coloring. Furthermore, because it is an insulator, you can remove the polyimide from the electrode lead-out part,
Alternatively, it is necessary to perform partial coating so that polyimide is not coated on the electrode portion, which complicates the process.

(3) Since the rubbing process is required, the number of processes is increased, and dust is generated from the cotton cloth or the like during rubbing, which reduces the yield.

Further, it is generally known that a Langmuir-Blodgett method is used to form a monomolecular film. According to this method, a thin film having a structural regularity regulated in a direction perpendicular to a substrate can be obtained. If this is further advanced to form a polymer monomolecular film by orienting the main chain in one direction, this thin film has regularity in the vertical direction and the plane direction of the film,
Various applications including the above-mentioned liquid crystal alignment film can be expected.

The present inventor has previously proposed, as a liquid crystal alignment treatment method, to form a monomolecular film of polyimide or a cumulative film of the polyimide by the Langmuir-Blodgett method (Japanese Patent Application No. 61-61).
-52114). This film exhibits uniaxial alignment in which the polymer main chain is aligned in the pulling direction of the substrate, and the liquid crystal is aligned in this main chain. This thin film is obtained when a hydrophilic substrate is used as the substrate, but the orientation direction of the polymer main chain is liable to change due to dust on the substrate or the accumulated film, the influence of the hydrophilicity of the substrate, etc., and a stable orientation is obtained. Was sometimes difficult to obtain.

OBJECT OF THE INVENTION The present invention aims to stably form an oriented polymer monomolecular film.

The film forming method of the present invention uses a hydrophobic substrate or a substrate subjected to a hydrophobization treatment as a substrate, and a polymer monomolecular film or monomolecular cumulative film on the substrate by using the Langmuir-Blodgett method. Is formed.

 Hereinafter, the present invention will be described in more detail.

The Langmuir-Blodgett method itself is already known, and when an amphiphilic polymer solution is developed on a subphase such as water, the polymer monolayer directs the hydrophilic part toward the subface. Orient. For example, when a long-chain alkylamine salt of polyamic acid as described below is used, the main chain is oriented toward the sub-face. A partition is provided on the sub-face surface to reduce the development area, and at a predetermined surface area, the substrate placed perpendicular to the sub-face is passed through the sub-face surface to move the substrate up and down, and the polymer monomolecular film is transferred to the substrate. .

When the substrate is hydrophilic, the polymer main chain is oriented and transferred in the pulling direction of the substrate. In this monomolecular film or its accumulated film, the polymer main chain is oriented, and it is used as an alignment film of liquid crystal as it is or after a post-treatment as described later if it is a polyamic acid or the like. However, when the substrate is hydrophilic, a stable oriented polymer film may not be obtained due to defects on the substrate.

In the present invention, it was found that by using a hydrophobic substrate or a substrate provided with hydrophobicity, the polymer main chain is oriented in the direction perpendicular to the pulling direction, and more stable orientation can be obtained.

As a hydrophobic substrate, the contact angle with water is 20 degrees or more,
More preferably, those of 30 degrees or more are used.

As the hydrophobic substrate, an inorganic substrate such as a glass plate subjected to a hydrophobic treatment, a silicone substrate subjected to a hydrophobic treatment, a glass substrate having a transparent conductive film subjected to a hydrophobic treatment, or an acrylic resin, Polyester, polyimide, polyether sulfone, polysulfone, polycarbonate, cellulose resin, polystyrene, phenol resin,
Examples include plastic plates such as urea resin and melamine resin, and hydrophobized substrates thereof.

The hydrophobic treatment method may be, for example, a silane coupling agent treatment, a titanium coupling agent treatment, an aluminum coupling agent treatment, a chromium coupling agent treatment, or the like. In addition, a hydrophobic treatment can be performed by vapor deposition or application of a resin solution. Further, in the case of a resin substrate, it can be carried out by surface graft polymerization, steam treatment method, monomer coating polymerization or the like.

The coupling agent treatment can be carried out by applying a coupling agent, washing and drying if necessary. The representative coupling agents are as follows.

Silane coupling agent _{H 2 N (CH 2) 2} NH (CH 2) 3 Si (OCH 3) 3 (CH 3) 3 SiNHSi (CH 3) 3 _{CH 3 Si (OCH 3) 3} CH 3 Si (OCH 2 CH 3) 3 ClCH 2 CH 2 CH 2 Si (OCH 3) 3 _{CH 3 SiCl 3 (CH 3)} 2 SiCl 2 (CH 3) 3 SiCl titanium coupling agent _{Ti (O-i-C 3} H 7) 4 Ti (O-n-C 4 H 9) 4 Ti [O-CH _{2 CH (C 2 H 5)} C 4 H 9 ] _{4 Ti (O-C 17 H} 35) 4 Ti (O-i-C 3 H 7) 2 [OCCH ₃ CHOCH _{3] 2} Ti (O-i-C _{As the} polymer forming the ₃ H ₇ ) (OCOC ₁₇ H ₃₅ ) ₃ monolayer, those having an amphipathic structure are used, and examples thereof include polyamic acid (polymide, polyetherimide, polyamideimide, polyesterimide). , Long-chain alkylamine salts of polyimide, precursors such as indoquinazolidione); long-chain alkyl long-chain alkylesters, long-chain alkylamides or long-chain alkyl of polyacrylic acid polymers such as polyacrylic acid or polymethacrylic acid. Ammonium salt; long-chain alkylamine salt of maleic anhydride copolymer hydrate; Such partial long chain fatty acid esters of vinyl alcohol are exemplified.

In particular, when used as a horizontal alignment film of liquid crystal, a long-chain alkylamine salt of polyamic acid is suitable. The long-chain alkylamine salt of polyamic acid is characterized in that a long-chain alkylamine is eliminated by post-treatment, so that a stable film is obtained and high heat resistance is obtained.

The long-chain alkylamine salt of polyamic acid is synthesized, for example, as follows. Further, after the monomolecular film or the accumulated film is formed, it is converted into a polyimide film by post-treatment. First, polyamic acid (3) synthesized from tetracarboxylic dianhydride (1) and diamine (2)
A long-chain alkylamine (4) is added to the solution of 1 to synthesize a polyamic acid alkylamine salt (5). This polyamic acid alkylamine salt is converted into polyimide (6) by cyclization with heat or acid anhydride.

Here, Ar ¹ and Ar ² are respectively a tetracarboxylic dianhydride and a linking group serving as a skeleton of a diamine, n is an integer of 1 or more, and R ¹ and R ² are a lower alkyl group or a hydrogen atom, R ³ represents a long-chain alkyl group.

Tetracarboxylic acids that can be used for the synthesis of polyamic acid alkylamine salts include pyromellitic dianhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride, 3,4,3 ′, and 4 ′. -Biphenyltetracarboxylic dianhydride, 2,3,2 ', 3'-biphenyltetracarboxylic dianhydride, bis (3,4-dicarboxyphenyl) methane dianhydride, bis (3,4-dicarboxy Phenyl) ether dianhydride, bis (3,4-dicarboxyphenyl) sulfone dianhydride, 2,2-bis (3,4-carboxyphenyl) propane dianhydride, 3,4,3 ', 4'- Benzophenone tetracarboxylic dianhydride, butane tetracarboxylic dianhydride,
1,2,5,6-naphthalene tetracarboxylic acid anhydride, thiophene-2,3,4,5-tetracarboxylic acid anhydride, perylene-
Examples thereof include 3,4,9,10-tetracarboxylic acid anhydride and ethylene tetracarboxylic acid anhydride.

As the diamine, metaphenylenediamine, paraphenylenediamine, 3,3′-diaminobiphenyl, 4,4 ′
-Cyanoamiobiphenyl, 4,4'-diaminobiphenyl, 3,3'-methylenedianiline, 4,4'-methylenedianiline, 4,4'-ethylenedianiline, 4,4'-isopropylidenedianiline, 3,3′-oxydianiline, 4,4 ′
-Oxydianiline, 3,4'-oxydianiline, 3,3 '
-Thiodianiline, 4,4'-thiodianiline, 3,3'-carbonyldianiline, 4,4'-carbonyldianiline,
3,3'-sulfonyldianiline, 4,4'-sulfondianiline, 1,4-naphthalenediamine, 1,5-naphthalenediamine, 2,2-bis (4-aminophenyl) propane, benzidine, 3,3 ′ -Dimethylbenzidine, 3,3′-dimethoxybenzidine, 2,4-bis (β-amino-tert-butyl) toluene, bis (4-β-amino-tert-butylphenyl) ether, 1,4-bis ( 2-methyl-4-aminepentyl) benzene, 1-isopropyl-2,4-phenylenediamine, m-xylylenediamine, p-xylylenediamine, di (4-aminocyclohexyl) methane, hexamethylenediamine, 2,2 Examples thereof include dimethyl propylene diamine and 1,4-diaminocyclohexane.

Tetracarboxylic acids and amines can be used alone or in combination of two or more.

The polymerization degree n is preferably an integer of 10 to 500. When the polymerization degree n is smaller than 10, the mechanical properties of the film and the adhesion to the substrate are reduced, and the alignment of liquid crystal molecules is inhibited due to elution into the liquid crystal. When n exceeds 500, the solubility of polyamic acid decreases.

As long-chain alkylamines, N, N-dimethyl-n-
Octylamine, N-methyl-n-octylamine, N,
N-dimethyl-n-decylamine, N-methyl-n-decylamine, n-decylamine, n-octylamine,
N, N-dimethyl-n-dodecylamine, N-methyl-n
-Dodecylamine, n-dodecylamine, N, N-dimethyl-n-tetradecylamine, N-tetradecylamine, N-methyltetradecylamine, N, N-dimethyl-
n-hexadecylamine, N-methyl-n-hexadecylamine, n-hexadecylamine, N, N-dimethyl-
n-octadecylamine, N-methyl-n-octadecylamine, n-octadecylamine, N, N-dimethylbehenylamine, arachidylamine, behenylamine, N,
N-dimethylbehenylamine and the like can be exemplified. In order to obtain a good Langmuir-Blodgett film and to realize excellent orientation, the long-chain alkyl group preferably has 8 to 25 carbon atoms, and more preferably 12 to 25 carbon atoms.

From the viewpoint of the film-forming property on the water surface and the alignment property with respect to the liquid crystal, the amount of the long-chain alkylamine used is preferably 0.5 to 4 equivalents based on the repeating unit of the polyamic acid.

As the solvent that can be used for producing the polyamic acid alkylamine acid, N, N-dimethylformamide, N, N
-Dimethylacetamide, N-methyl-2-pyrrolidone, dimethyl sulfoxide, tetramethylene sulfone,
Examples include cursol and phenol. Further, benzene or the like can be added to improve the solubility.

Since the polyamic acid alkylamine salt thus prepared is an amphipathic molecule having a hydrophobic alkyl group and a hydrophilic carboxylic acid amine salt in the molecule, Langmu
A monomolecular film can be formed by the Langmuir-Blodgett method developed by ir.

Next, the substrate is immersed in an acid anhydride such as acetic anhydride, propionic anhydride, butyric anhydride, or by heating to cause dehydration and ring closure and elimination of an amine having a long-chain alkyl group to form a polyimide (6). To do. At this time, heat ring closure is 200
A method using an acid anhydride is suitable because a high temperature of about ° C is required and the alignment performance is deteriorated. At this time, if a tertiary amine such as triethylamine or pyridine is added, the reaction is promoted. Further, a solvent can be added as required. It should be noted that the solvent cannot dissolve the polyamic acid. For ring closure with acid anhydride, a temperature of about 20 ° C to 60 ° C is sufficient,
For example, in the system of acetic anhydride-pyridine-benzene (1: 1: 3), the reaction is completed in several hours at room temperature and about one hour at 40 ° C., and the treatment can be performed at an extremely low temperature.

The polyimide monomolecular film thus obtained or a cumulative film thereof has a high heat resistance peculiar to polyimide because long-chain alkyl groups are eliminated after the film is formed. It is a film that shows no change and is suitable for use as an alignment film in a liquid crystal cell of a liquid crystal light switching element.

In order to use a polymer monomolecular film or a cumulative film formed by the method of the present invention as an alignment film of a liquid crystal cell, a substrate used for the liquid crystal cell, for example, a transparent conductive film is formed as described above. Hydrophobization treatment is performed on a substrate on which glass or plastic, a color filter is formed, a substrate on which a thin film transistor is formed, etc. to form a polymer cumulative (monomolecular) film, and then a spacer or the like is formed by a conventionally known method. Then, the liquid crystal may be injected into the space between the substrates by adhering to the opposing substrate. In this case, the alignment treatment on the counter substrate side does not necessarily have to be the polymer accumulation film (monomolecular film).

FIG. 1 is a cross-sectional view showing a constitutional example of a liquid crystal cell using the polymer film of the present invention, in which an upper substrate 11 and a lower substrate 21 are arranged so as to face each other, and a liquid crystal is sealed with a sealant 31. 33 is enclosed to form the liquid crystal cell 10. A transparent electrode 23 is provided on the surface of the lower substrate 21, and an alignment film 25 is further formed thereon. A transparent electrode 13 is provided on the opposite surface of the upper substrate 11, and an alignment film 15 is further formed on the transparent electrode 13.

The alignment films 15 and 25 are polymer monolayers or monolayers accumulated using the method of the present invention.

The polymer film according to the present invention has the ability to align liquid crystal molecules substantially horizontally (homodiously) with respect to the substrate. further,
Liquid crystal molecules can be removed from Langmuir® without rubbing.
It has the ability to preferentially orient uniaxially in the direction perpendicular to the pull-up direction of the substrate when it is manufactured by the blow jet method. For example, in the case of the twisted nematic mode which is widely used at present as a liquid crystal display element, the liquid crystal display element may be formed so that the pulling-up directions of the upper and lower substrates are orthogonal to each other.

The polymer alignment film of the present invention includes, for example, nematic liquid crystal (which may contain cholesteric liquid crystal), cholesteric liquid crystal, smectic liquid crystal A, smectic liquid crystal G ^* , smectic liquid crystal H ^* , and smectic liquid crystal C.
^* , Smectic liquid crystal C and the like can be aligned.

The liquid crystal operating modes that can be realized using the polymer film of the present invention include twisted nematic mode (TN), dynamic scattering mode (DSM), cholesteric nematic phase transition mode, electric field control birefringence mode, guest host mode, etc. Operating method using electro-optical effect of electric field or current control, scattering by heat, operating method using thermo-optical effect using refractive index change, scattering using both electric field and heat, electrothermo-optic controlling refractive index An operation method utilizing the effect can be exemplified, and in these display modes, a substrate on which a color filter is formed, a substrate on which a thin film transistor is formed, a metal-insulating film-metal (MI
It is also possible to use a substrate on which a non-linear element such as M) is formed. In these cases, since there is almost no heat history at the time of forming the alignment film, it is particularly effective without changing the performance and the operating characteristics.

The cumulative number of monomolecular layers in which the polymer film of the present invention functions as an alignment film for liquid crystal is preferably 1 to 500 times, more preferably 1 to 300 times, and further preferably 2 to 100 times. This is 2.5 Å ~ 6 Å depending on the material used, and the thickness of the polymer monolayer is 2.5 Å
It is equivalent to 750Å or 1800Å from 6 to 6Å.

When the film thickness is large, the uniaxial alignment of the liquid crystal tends to be disturbed, which is not preferable. Further, in the case of a coloring substance such as polyimide, coloring of the alignment film becomes large, which is not preferable.

Even if it is a monomolecular film or a cumulative layer of several layers, the orientation of the liquid crystal is very good, so compared with the film thickness (several hundred Å ~ 2000 Å) of polyimide film etc. by ordinary spin coating or printing method,
It can be made extremely thin. Therefore, it is possible to provide a liquid crystal switching element which is not colored and has a high transmittance when it is used in a transmission type and a high reflectance when used in a reflection type.

Further, when the polymer is thinned in this way, most of the drive voltage is applied to the liquid crystal layer even if the electrode lead-out portion 23a has the alignment film 25 which is an insulating film as shown in FIG. The productivity is extremely high because the step of partially coating the alignment film or the process of removing the alignment film of the electrode lead-out portion which has been conventionally performed can be omitted.

In the oblique deposition method of an inorganic substance such as SiO, the deposition angle and the deposited film thickness of a large-area substrate cannot be made uniform. Further, even with a polyimide alignment film formed by conventional coating and rubbing, it is difficult to obtain a uniform coating film over a large area, and it is also difficult to make the load during rubbing uniform over the entire area. Was an obstacle. On the other hand, the polymer alignment film according to the present invention can easily and uniformly process a large area, and is suitable for manufacturing a large area display device.

In addition, the alignment treatment method of the present invention does not require a rubbing process, so that the process is simplified and the yield is improved without the problem of dust generated during rubbing.

Furthermore, when a long-chain alkylamine salt monomolecular film of polyamic acid or this cumulative film is formed and the long-chain alkylamine is eliminated by post-treatment, it has high heat resistance,
Provide a highly reliable oriented polymer film that does not deteriorate the orientation even under the environment of high temperature storage, high temperature and high humidity storage, etc. It is suitable as an alignment film for liquid crystals because it has the property of sufficiently withstanding the heating during the production of the polymer alignment film, the outer peripheral seal and the like.

EFFECTS OF THE INVENTION According to the present invention, by using a hydrophobic substrate or a substrate that has been subjected to a hydrophobic treatment, the orientation of the polymer is more uniform than in the case of using a hydrophilic substrate, and the orientation of the polymer on the substrate or during accumulation is high. It is hardly affected by defects and good orientation can be obtained.

Further, the film obtained in the present invention is excellent in the alignment property of the liquid crystal since the polymer has a good alignment property, and has high productivity, and is suitable as a liquid crystal alignment film.

Example 1 1 mmol / L of polyamic acid synthesized from pyromellitic dianhydride and 4,4-diaminodiphenyl ether
Mixed solvent of N, N-dimethylacetamide and benzene (1:
1) To the solution, an N, N-dimethyl-n-hexadecylamine solution having the same concentration and the same solvent was added in an amount of twice equivalent to the repeating unit of the polyamic acid to prepare a polyamic acid alkylamine salt solution. . This solution was dropped onto ion-exchanged water, and a partition plate provided in the water tank
While maintaining the surface pressure of dyne / cm, a glass substrate having a hydrophobic surface on the water surface was vertically moved up and down to form a cumulative film of 10 layers on the upper substrate.

The hydrophobizing treatment was performed by immersing the glass substrate in a 1% toluene solution of trimethylchlorosilane for 5 hours, followed by washing and drying.

The polyamic acid cumulative film formed by this method is
From the measurement of the absorption of polarized UV, it was confirmed that the polymer main chain was oriented perpendicular to the pulling direction of the substrate.

Next, the substrate on which the cumulative film was formed was immersed in a mixed solution of acetic anhydride-pyridine-benzene (1: 1: 3) at 20 ° C for 6 hours to remove long-chain alkyl groups and complete imidization. did. Next, the substrate was washed with pure water and vacuum dried. It was also confirmed that the main chain of this polyimide cumulative film was oriented in a direction perpendicular to the pulling direction of the substrate.

Example 2 Epoxy adhesive containing spacer particles of 20 μm was printed on the outer periphery of the substrate obtained in Example 1 so that the counter substrate and the substrate in the same orientation treatment were antiparallel to each other. And pasted together. Next, from the voids formed in the adhesive layer, by the vacuum encapsulation method, the biphenyl liquid crystal E7 (nematic liquid crystal) manufactured by BDH and the BD
A mixture with a dichroic dye D37 manufactured by H. Co. (D37; 1.3%) was injected to prepare a guest-host type liquid crystal cell.

In this cell, it was confirmed that the liquid crystal was uniaxially oriented in the pulling direction of the substrate, and the state was uniform.

Calculated to evaluate the manufactured orientation, 550 nm and the absorbance on the polarization parallel to the substrate pulling direction in (absorption peak of the 2-color dye) (A), likewise perpendicular absorbance (ratio of A _⊥ (A _⊥ / A) When I did, it showed a high value of 6.0,
This value changed little in any area in the cell.

Example 3 As the polyamic acid, pyrrolimet dianhydride was added as p.
When the same procedure as in Example 1 and Example 2 was carried out except that a compound synthesized from phenylenediamine was used,
Similarly, the orientation was high.

Reference Example 2% N of the same polyamic acid as that used in Example 1
The methylpyrrolidone solution was applied onto a glass plate by spin coating and heat treated at 120 ° C for 30 minutes and 270 ° C for 1 hour. This substrate was rubbed in one direction with a cotton cloth for rubbing treatment.

Then, in the same manner as in Example 2, a cell was constructed so that the rubbing directions were antiparallel. For this cell, the ratio (A / A) of the absorbance (A) for polarized light parallel to the rubbing direction and the absorbance (A⊥) for polarized light that is also vertical.
⊥) was measured and calculated, and it was 6.0, which was the same orientation performance as that of this example.

This also indicates that the alignment film of the present invention has excellent alignment performance.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a configuration example of a liquid crystal cell using a polymer thin film formed by the present invention as an alignment film. 11 Upper substrate, 13, 23 Transparent electrode 15, 25 Alignment film, 21 Lower substrate

Claims (1)

(57) [Claims] 1. A hydrophobic substrate or a substrate subjected to a hydrophobizing treatment is used as a substrate, and a polymer monomolecular film or monomolecular cumulative film is formed on the substrate by the Langmuir-Blodgett method. A method for forming a film.