JPH03119319A - Liquid crystal oriented film - Google Patents

Abstract

PURPOSE:To obtain a liq. crystal oriented film having superior liq. crystal orienting property, superior mechanical chemical and thermal durability and enabling remarkable reduction of film thickness by rubbing a thin film formed on a substrate by spin coating with a polymer contg. repeating untis of specified crotonic ester. CONSTITUTION:A thin film formed on a substrate by spin coating with a polymer contg. repeating units of crotonic ester represented by formula I is rubbed. In the formula I, R is 3-12C branched alkyl, 3-12C cycloalkyl, 2-6C substd. alkyl having a 3-14C cyclic substituent, 3-10C substd. cycloalkyl having a cyclic substituent or siloxane-contg. hydrocarbon. The resulting oriented film has a smooth surface free from defects such as pinholes and can highly orient a liq. crystal.

Description

Detailed Description of the Invention <Industrial Application Field> The present invention relates to a liquid crystal alignment film, and more specifically, a liquid crystal alignment film in which a thin film containing a crotonate ester polymer is aligned, and a monomolecular solid of the crotonate ester polymer. The present invention relates to a liquid crystal alignment film formed by stacking films on a substrate.

<Prior art> As a display method, the liquid crystal method uses little electrical energy and can display relatively fast responses, and is also capable of displaying from small to large areas.
Various developments have been made in recent years.

Conventionally, when manufacturing liquid crystal display devices, the key point is how to arrange the liquid crystal molecules regularly, and for this purpose, it is extremely important to impart orientation to the liquid crystal substrate, and various alignment treatment methods are known. ing.

As methods for orientation treatment of substrates, for example, solution coating, plasma treatment, rubbing, vapor deposition, and pulling coating are known (co-authored by Tadashi Matsumoto and Ichiro Tsunoda), "Latest Technology of Liquid Crystals - Physical Properties, Materials, and Applications". There is.

Of the methods mentioned above, the rubbing method is the most common, and in this method the substrate itself is rubbed in a certain direction with something like cloth or leather (rubbing), or a film of inorganic or organic material is applied to the surface of the substrate. This method utilizes the property that liquid crystal molecules are aligned parallel to the rubbing direction by this treatment. Currently, this method is commonly used at liquid crystal cell manufacturing sites, and generally involves coating the #M liquid crystal base with polyimide resin and then rubbing the film to control the arrangement of liquid crystal molecules. It is.

In the future, liquid crystal displays with higher contrast and faster response will be desired, but to achieve this, it is necessary to make the alignment film itself ultra-thin and control it on the ongest long order. It is also important to control the orientation more precisely. Polyimide resin is a very excellent material in terms of heat resistance, mechanical strength, and liquid crystal alignment, but when creating an alignment film, it is better to make the film as thin as possible. It is necessary to be able to perform spin cord coating, roll coating, dip coating, spray coating, gravure coating, etc. As an organic solvent for dissolving this resin, dimethylformamide, N-methyl-2
- Highly polar, high-boiling organic solvents such as pyrrolidone and dimethylacetamide, which are not preferred for forming thin films by coating.

Therefore, for these purposes, the current method of spin-coding or coating polyimide resin and then rubbing it to create an alignment film requires making the film even smaller and more uniform and free from defects. This method has the disadvantage that the desired orientation cannot be controlled by the rubbing method.

On the other hand, after forming a monomolecular film of a low-molecular compound having a hydrophilic group and a hydrophobic group on the water surface, pressure is applied to form a monomolecular solid film (LB' film, Langmuir-Prodgett film). A method of utilizing an ultra-thin film obtained by accumulating on a substrate, a method of similarly accumulating a polymerizable low-molecular compound and polymerizing an LB film (Japanese Patent Laid-Open No. 63-274451), etc. have been proposed.

However, low molecular weight LB films have poor compatibility with liquid crystals.

It is impractical due to insufficient chemical, thermal, and mechanical resistance, and polymerizable LB films have the drawback of shrinkage and film defects due to shrinkage during polymerization.

<Problem that the invention seeks to solve> The objects of the present invention are: 1. Excellent mechanical alignment of liquid crystals;

The object of the present invention is to provide a liquid crystal alignment film that has excellent chemical and thermal durability and can be made into an ultra-thin film.

<Means for Solving the Problems> According to the present invention, on the substrate, the following general formula (1) carbon number 3
A crotonic acid ester representing a substituted cycloalkyl group or a siloxane hydrocarbon group of ~1O, each of the above groups may contain a hetero atom or may be substituted with a halogen atom) A liquid crystal alignment film is provided, which is formed by rubbing a thin film formed from a polymer containing repeating units by a spin cord method to align it.

Further, according to the present invention, there is provided a liquid crystal alignment film formed by accumulating a monomolecular solid film (LB film) of the above polymer on a substrate.

The present invention will be explained in more detail below.

In the present invention, the following general formula (1) (wherein R is a branched alkyl group having 3 to 12 carbon atoms, a cycloalkyl group having 3 to 12 carbon atoms, or a carbon having a substituent having a ring structure having 3 to 14 carbon atoms) Substituted alkyl group of number 2 to 6,
A crotonate ester polymer containing a repeating unit of crotonate ester having a substituent having a ring structure is used. In the formula, R is a branched alkyl group having 3 to 12 carbon atoms, a cycloalkyl group having 3 to 12 carbon atoms, or a cycloalkyl group having 3 to 14 carbon atoms.
represents a substituted alkyl group having 2 to 6 carbon atoms having a substituent having a ring structure, a substituted cycloalkyl group having 3 to 10 carbon atoms having a substituent having the above ring structure, or a siloxane hydrocarbon.

The branched alkyl group, the cycloalkyl group, the substituted alkyl group, the substituted cycloalkyl group, and the siloxane hydrocarbon group include a nitrogen atom, an oxygen atom, a phosphorus atom,
It may contain a heteroatom such as a sulfur atom, or may be substituted with a halogen atom.

Polymers of crotonate esters having repeating units represented by the general formula (r) include 1, for example, isopropyl crotonate, tart-butyl crotonate, cyclohexyl crotonate, 5ac-butyl crotonate, and crotonate.
Crotonate ester having a hydrocarbon group such as 4-methyl-2-pentyl; (trimethylsilyl)crotonate,
Crotonic acid esters having a siloxane hydrocarbon group such as 3-tris(trimethylsiloxy)silylpropylcrotonate; 1-butoxy-2-propylcrotonate, 2-cyanoethylcrotonate, glycidylcrotonate, diethylphosphonomethylcrotonate , 2-methylthioethylcrotonate and other heteroatom-containing crotonic acid esters; perfluorooctylethylcrotonate, trifluoromethylcrotonate, pentafluoroethylcrotonate, hexafluoroisopropylcrotonate, 1-chloroisopropylcrotonate Homopolymers or copolymers of crotonic esters substituted with halogen atoms such as crotonic esters, or crotonic ester polymers obtained by copolymerizing crotonic esters with various copolymerizable monomers are preferably used. I can do it. To produce the crotonic acid ester polymer,
It can be obtained by polymerization or copolymerization using a normal anionic polymerization method. The reaction conditions for the polymerization or copolymerization are not particularly limited, but it is preferable to carry out the reaction at -100 to 100°C for 2 to 30 hours, and the resulting crotonic acid ester polymer The molecular weight of is preferably from 10ooO to 2,000,000.

Examples of the copolymerizable monomer include vinyl acetate, vinyl propionate, vinyl caproate, vinyl benzoate, styrene, α-methylstyrene, chloromethylstyrene, methyl vinyl ether, n-butyl ether,
Aliphatic or aromatic allyl esters, acrylic or methacrylic esters, acrylonitrile, vinyl chloride, vinylidene chloride, ethylene, butadiene, chloroprene,
Preferred examples include isoprene and inbutylene.

In addition, as a polymerization initiation catalyst, n-butyllithium, n-
Examples include sodium amyl, potassium n-octyl, sodium naphthalene, sodium anthracene, phenylmagnesium bromide, 5ec-butylmagnesium chloride, and triethylaluminum. The amount of the polymerization initiator used is preferably 10 parts by weight or less, more preferably 5 parts by weight or less, based on 100 parts by weight of the yK monomer.

The crotonic acid ester polymer used in the present invention preferably contains 60 mol% or more of the repeating unit of the crotonic acid ester represented by the general formula (I). If the repeating unit of crotonate ester in the polymer is less than 60 mol%, the rigid rod-like structure which is the original property of the crotonate ester polymer cannot be maintained, and spin cord or LB
It is difficult to form a uniform thin film by this method, and it may become thermally and chemically unstable, so it is not preferable.

In the present invention, in order to produce a liquid crystal alignment film having a thin film of a crotonic acid ester polymer, the crotonic acid ester polymer is formed into a thin film by a spin cord method, and the resulting thin film is subjected to a rubbing treatment. Specifically, for example, first, the crotonic acid ester polymer is dissolved in a transpirationable organic solvent to prepare a dilute solution of the crotonic acid ester. As the transpirationable organic solvent, general-purpose organic solvents such as chloroform, ethylene dichloride, benzene, toluene, 1,1.2-trichloro-1°2.2-
Trifluoroethane and the like can be mentioned. Further, the solution concentration of the crotonic acid ester polymer is preferably a solution containing 0.1 to 20 mg/mQ, particularly preferably 0.5 to 3IIIg/mQ of the crotonic acid ester polymer.
A solution of a crotonic acid ester polymer can be obtained by adjusting the concentration to a range of IIIQ. Next, the solution of the crotonic acid ester polymer is applied onto the liquid crystal substrate by a spin coating method, and the number of revolutions of the spin coater is adjusted to 1000 to 1,000 to form a thin film with a thickness of preferably 10 to 1,000.
Preferably, the spin code is 5000.

The film thickness also changes slightly depending on the working temperature, but under each of the above conditions, the desired ultra-thin polymer film is usually manufactured by spin-coding at a working temperature of about 10 to 35°C, and then It can be obtained by rubbing the substrate in a certain direction with cotton cloth, gauze, etc.

Further, in the present invention, as a method for producing a liquid crystal alignment film formed by accumulating a monomolecular solid film (LB film) of a crotonate ester polymer on a substrate, 1 for example, a crotonate ester polymer is mixed with water. A dilute solution of the crotonic acid ester polymer is prepared by dissolving it in a non-transpirationable organic solvent, and then the crotonic acid ester solution is spread on the clean water surface to form a gas film. Examples of the evaporative organic solvent include general-purpose organic solvents such as chloroform, ethylene dichloride, benzene, toluene, 1,1.2-trichloro-1,2,2-trifluoroethane, and crotonic acid ester. The polymer is made into a dilute solution of these organic solvents and spread gently on the water surface. When spreading on the water surface, it is necessary to pay attention to the concentration of the crotonic acid ester polymer solution and the type of solvent. The concentration of the developing solution is preferably 0.
．． The range is from 1 to 110 l1/IIIQ, particularly preferably from 0.1 to 3 mg/mQ. When spread on the water surface and evaporating the solvent, a gas film with a surface pressure of 1 mN/m or less is obtained in which each molecule does not interact with each other.
Regarding the gas film obtained as described above.

For example, apply pressure from the horizontal direction, preferably with a surface pressure of 3
It is maintained at ~30 mN/m to form a solid film state.

How much surface pressure to set depends on the type of crotonic acid ester polymer used. Obtain the surface pressure-area (FA) isotherm curve in advance, and find the sharp rising part of the FA curve that corresponds to the solid membrane. The surface pressure is preferably set at a surface pressure of 6. Next, a liquid crystal alignment film can be manufactured by depositing the obtained solid film on a substrate by a vertical dipping method or a horizontal deposition method.

In the present invention, various commonly used substrates can be used as the substrate for producing the crotonic acid ester polymer thin film or monomolecular solid film (LB film). For this purpose, it is necessary to use a conductive transparent substrate, and a substrate made of ordinary glass imparted with conductivity, such as an ITO (indium oxide) glass substrate or a NESA (tin oxide) glass substrate, is used.

In addition, substrates made of various transparent resins imparted with conductivity can also be used, but from the viewpoint of surface smoothness, scratch resistance, etc., conductive glass substrates are preferable.

<Effects of the Invention> Since the liquid crystal alignment substrate of the present invention uses a thin film of crotonic acid ester polymer, it has a smooth film surface without film defects such as pinholes, and has a high degree of orientation by rubbing. , or can be obtained by accumulating the LB film on the substrate,
It allows liquid crystal to be highly oriented and is extremely useful for various liquid crystal display devices.

<Examples> Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited by these.

Isopropyl polycrotonate (abbreviated as PiPCA) rotated by a spinner at 2500 times/min on a glass substrate with a conductive film made of indium oxide with a size of 25 x 25 m.
A chloroform solution (1 mg/mQ) of 1 mQ was spin-coded, the rotation was continued for 1 minute, and then the chloroform was sufficiently evaporated to form a thin film (film thickness: 230 mm) of PiPCA. The thin film creation conditions and film thickness are shown in Table 1. Using a primary rubbing device, the thin film obtained with a cotton cloth was rubbed 10 times in a fixed direction, and the substrate was subjected to alignment treatment to produce a substrate with liquid crystal alignment characteristics. Obtained.

Using the two obtained liquid crystal alignment substrates, a liquid crystal cell 10 shown in FIG. 1 was created. That is, on an ITO glass substrate consisting of a glass substrate 12 coated with an ITO film 11, a thin film 13 is accumulated and two liquid crystal alignment film substrates 14 of the present invention are stacked so that the alignment directions are perpendicular to each other, and a liquid crystal 15 ( 4'
-(4-cyanobiphenyl)4-(4'-hebutylbiphenyl)carboxylate) was sealed to create a twisted nematic alignment type liquid crystal cell 10, and then an electrode 16 was attached, and then visual observation using a polarizing plate was performed. by lol
Alternatively, we applied a voltage and examined the electrical response. As a result, it was found that the liquid crystal was sufficiently oriented and a liquid crystal display element prepared using a substrate having an alignment film of this crotonic acid ester polymer had extremely excellent responsiveness to electricity. Table 1 shows the conditions and film thickness.

Pt was prepared in the same manner as in Example 1, except that a 1 mg/mQ chloroform solution of poly(monobutyl crotonate) (hereinafter abbreviated as PtBCA) was used instead of PiPCA in Example 1.
A liquid crystal alignment substrate having a BCA spin code film (thickness: 280 mm) was prepared. Table 1 shows the thin film creation conditions and film thickness.
Shown below. Using the two obtained liquid crystal alignment substrates, Example 1
A liquid crystal cell 1o was prepared in the same manner as above, and the orientation and electrical response of the liquid crystal were examined. As a result, the alignment of the liquid crystal is good,
It was also found that the response to electrical stimulation was good.

In place of PiPCA in Example 1, poly(cyclohexyl crotonate) (Example 3) was substituted with poly(cyclohexyl crotonate).
-butyl) (Example 4), poly(4-methyl-2-pentyl crotonate) (Example 5), poly(perfluorooctylethyl crotonate) (Example 6), poly(4-methyl-2-pentyl crotonate) (Example 6), hexafluoroisopropyl) (Example 7
), poly(2-chloroisopropyl crotonate) (
Example 8), poly(1-butoxy-2-propyl crotonate) (Example 9), and poly(adamantyl crotonate) (Example 10) were used as Example 1 under the conditions shown in Table 1. A liquid crystal alignment film substrate 14 was prepared in the same manner, and a liquid crystal cell 10 was produced as a prototype to examine the liquid crystal alignment and electrical response. As a result, it was found that in all liquid crystal cells, the liquid crystal orientation was good and the responsiveness to electricity was also good. .

A Teflon trough with an internal area of 15 x 50 aJ and a depth of 2 cm was filled with pure water, and the room temperature was set at 20°C.

50μ of a chloroform solution of poly(isopropyl crotonate) (abbreviated as PiPCA) with a concentration of 0.5a+g/-
m was gently dropped onto the water surface to evaporate the solvent. Then, while sensing the surface pressure, a length 20 m was placed on the trough.
A cm Teflon barrier was moved in parallel at a speed of 5 m/sin to narrow the area.

The relationship between surface pressure and molecular occupied area (FA curve) was determined.

Figure 1 shows the FA curve of PiPCA. From this curve,
The accumulation of LB film shows a rapid rise at 5 to 30 N.
A surface pressure of /m was found to be suitable. Therefore, an LB film was formed with a surface pressure of 20 mN/m, and five layers were accumulated on an ITO glass substrate by a vertical dipping method to create a polymer alignment film on the substrate.

A liquid crystal cell was created using the two obtained liquid crystal alignment substrates. That is, in FIG. 1, a liquid crystal cell was prepared in the same manner as in Example 1 except that the LB film was used instead of the polymer thin film 13, and after attaching electrodes, a test was carried out by visual inspection using a polarizing plate. , the electrical response was investigated by applying a voltage. As a result, it was found that the liquid crystal was sufficiently oriented and that a liquid crystal display element created using a substrate with an alignment film of the obtained crotonic acid ester polymer had extremely excellent responsiveness to electricity. did. Table 2 shows the conditions and film thickness.

Poly(crotonic acid-111) instead of PiPCA in Example 11
0.5 of tert-butyl) (hereinafter abbreviated as PtBCA)
Example 11 except that mg/mQ chloroform solution was used.
Similarly, a PtBCA LB film (surface pressure 15 mN/m
) was used to create a liquid crystal cell using a liquid crystal alignment film substrate with five layers, and the alignment and electrical response of the liquid crystal were investigated. As a result, it was found that the alignment of the liquid crystal was good and the electrical response was also good.

Table 2 shows the conditions and film thickness.

In place of PiPCA in Example 11, poly(cyclohexyl crotonate) (Example 13) was used.
5ea-butyl) (Example 14), poly(4-methyl-2-pentyl crotonate) (Example 15), poly(4-methyl-2-pentyl crotonate) (Example 15),
perfluorooctylethyl crotonate) (Example 16)
), poly(hexafluoroisopropyl crotonate)
(Example 17), poly(2-chloroisopropyl crotonate) (Example 18), poly(1-butoxy-2-
A liquid crystal alignment film substrate was prepared in the same manner as in Example 11 using propyl crotonate (Example 19) and poly(adamantyl crotonate) (Example 20) under the conditions shown in Table 2, and a liquid crystal cell was prototyped. Then, the orientation of the liquid crystal and the electrical response were investigated. As a result, the liquid crystal orientation in the liquid crystal cell is good, and the responsiveness to electricity is -λ

[Brief explanation of drawings]

FIG. 1 is a perspective view of the liquid crystal cell prepared in Example 1. 10...Liquid crystal cell, 11...ITO film, 12...Glass substrate, 13...Polymer thin film, 14...Liquid crystal alignment film substrate, 15...Liquid crystal.

Claims (1)

[Claims] 1) On the substrate, there are the following general formula (I) ▲ mathematical formula, chemical formula, table, etc. ▼... (I) (wherein R is a branched alkyl group having 3 to 12 carbon atoms, A cycloalkyl group having 3 to 12 carbon atoms, a substituted alkyl group having 2 to 6 carbon atoms having a substituent having a ring structure having 3 to 14 carbon atoms,
Represents a substituted cycloalkyl group or siloxane-based hydrocarbon group having 3 to 10 carbon atoms having a substituent in the ring structure, each of the groups may contain a hetero atom, and is not substituted with a halogen atom. A liquid crystal alignment film obtained by aligning a thin film formed by a spin coating method of a polymer containing repeating units of crotonic acid ester represented by the following formula and subjecting it to rubbing treatment. 2) A liquid crystal alignment film formed by stacking a monomolecular solid film (LB film) of the polymer according to claim 1 on a substrate.