JPH03291631A - Orientation control method for liquid crystal high polymer - Google Patents

Abstract

PURPOSE:To execute the control of an angle of torsion with high accuracy by orientating a liquid crystal high polymer on a first substrate, and thereafter, superposing other second substrate to which the orientation processing is performed. CONSTITUTION:A liquid crystal high polymer layer 3 is formed on a first substrate 1 to which such an orientation processing as a liquid crystal high polymer is oriented in one direction is performed. Subsequently, after the liquid crystal high polymer is oriented, a second substrate 4 which is subjected to orientation processing in the same way is superposed so that its orientation processing surface comes into contact closely with the liquid crystal high polymer layer 3. After this second substrate 4 is superposed, it is heated to a temperature at which the liquid crystal high polymer takes a liquid crystal phase, and by holding it for a prescribed time, molecules of the liquid crystal high polymer layer 3 which comes into contact with a second substrate 4 can be arranged in the orientation processing direction of a second substrate 4. That is, even if an angle of torsion has an in-plane distribution on a first substrate 1, a uniform angle of torsion is obtained completely by the orientation control of a second substrate 4. In such a way, a monodomain orientation in which the angle of torsion is controlled with high accuracy is obtained easily.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for controlling the alignment of liquid crystal polymers used in compensating plates for liquid crystal display elements, optical memory media, and the like.

(Prior art and problems to be solved by the invention) The alignment state of liquid crystals changes depending on external fields such as electric fields, magnetic fields, and shear forces, and by utilizing the accompanying changes in optical properties, various types of optoelectronics can be realized. used in the field.

Among these, liquid crystal polymers have higher viscosity in the liquid crystal state than low-molecular liquid crystals, so after being oriented in the liquid crystal state, the liquid crystal orientation state can be fixed by cooling to below the glass transition point. It has characteristics not found in low-molecular liquid crystals. Utilizing this, attempts are being made to apply it to optical electronics fields such as thermal writing optical memories and optical filters. In order to realize these, it is necessary to highly control the desired molecular orientation. For example, the color compensation plate for super twisted nematic (STN) type liquid crystal display elements, which is a type of optical filter, is S
It is inserted between the liquid crystal cell and the polarizing plate of a TN type liquid crystal display element, and it must function to return the light that has become elliptically polarized by the liquid crystal cell to linearly polarized light. , and can only be manifested by orienting it in a certain direction with a high degree of order and uniformity.

In the case of low-molecular liquid crystals, alignment control methods have almost been established, but in the case of liquid crystalline polymers, they have not been fully established.

As an example of controlling the orientation of liquid crystalline polymers, methods of applying an external force such as shear stress, and methods of applying an external field such as a magnetic field or electric field are known, but these methods do not allow orientation control over a large area. It cannot be said that it is possible or sufficient in terms of uniformity. If the method of injecting liquid crystal polymers into the gap between substrates that have been subjected to alignment treatment in the same way as for low-molecular liquid crystals is applied to liquid crystal polymers, the high viscosity of liquid crystal polymers will cause problems during injection. The liquid crystalline polymer is oriented along the flow, and if the desired orientation cannot be obtained or if the area becomes large, even injection becomes difficult.

The present inventors have discovered that good alignment can be achieved over a large area by coating a liquid crystalline polymer on an aligned substrate and heating it to the liquid crystal temperature with one side in contact with air. In this method, if the liquid crystalline polymer has a twisted structure, non-uniformity in thickness directly results in non-uniformity in twist angle. Furthermore, in the above-mentioned compensating plate for a liquid crystal display element, etc., it is required to control the thickness extremely precisely in order to control the twist angle.

The present invention has been made in view of the problems of the prior art as described above, and its purpose is to uniformly spread over a large area,
The present invention provides a method for controlling the orientation of a liquid crystalline polymer film in which the orientation is highly controlled.

(Means and effects for solving the problems) According to the present invention, a liquid crystal polymer layer is formed on a first substrate subjected to an alignment treatment that aligns liquid crystal polymers in one direction, Orientation control of a liquid crystalline polymer, which comprises aligning a liquid crystalline polymer and then superimposing a second substrate that has been similarly aligned so that its alignment treated surface comes into close contact with the liquid crystalline polymer layer. A method is provided.

Next, the present invention will be explained in detail using the drawings.

FIG. 1 schematically shows the procedure of the method for controlling the alignment of liquid crystalline polymers according to the present invention.

3-4- First, the alignment layer 2 is formed on a substrate such as glass or plastic. Orientation treatment methods include forming a polymer film of polyimide, polyetherimide, polyamideimide, polyesterimide, polyamide, polyester, polyvinyl alcohol, polyacrylonitrile, etc., and then rubbing it; organic metals such as alkoxysilane, organic titanate, etc. Examples include a method of rubbing a coating film of a compound or a heat-treated film thereof, a method of oblique vapor deposition of silicon oxide, etc. Orientation treatment is also possible by directly rubbing the plastic substrate.
In this case, the alignment layer 2 becomes unnecessary.

Next, a liquid crystal polymer layer 3 is formed by applying a liquid crystal polymer to the alignment-treated surface.

The liquid crystalline polymer that can be used in the present invention is a thermotropic liquid crystalline polymer, and its structure is not particularly limited, but for example, polyester, polyesteramide,
Main chain type liquid crystalline polymer made of polycarbonate, polyether, etc. and having a liquid crystalline residue in the main chain with the following structure: X"MAl-X"+
, -0-etc.-Ph-Ph-COO-Ph-, -Ph-N
=CH-Ph-etc.A'knee+CH,sff,-(-C8
,CH,Om? →CH2CH, O soup.

body CH.

-N=N-, * represents an asymmetric carbon atom, and n represents an integer from 0 to 18. 〉 Or a side chain type liquid crystal polymer such as a vinyl polymer or polysiloxane having a liquid crystal residue in the side chain and having the following structure: (However, R3 is an alkyl group, an alkoxy group, a halogen atom, a nitro group, or a cyano group. and n represents an integer from 0 to 18.). Liquid crystalline polymers may be used alone or in combination. It is also possible to introduce an optically active group into the liquid crystalline polymer or add an optically active compound.

As a coating method, a method is used in which the liquid crystalline polymer is directly coated at a temperature equal to or higher than the glass transition point at which it has fluidity, or a method in which the liquid crystalline polymer is dissolved in a solvent and coated or printed as a solution is used. The latter method is particularly preferably used in terms of uniformity of film thickness and ease of control. The solvent for the liquid crystalline polymer varies depending on the type of liquid crystalline polymer used, degree of polymerization, etc., but is usually selected from the following.

Chloroform, dichloroethane, tetrachloroethane,
Halogenated hydrocarbons such as trichlorethylene, tetrachlorethylene, and orthodichlorobenzene; phenolic solvents such as phenol, 0-chlorophenol, and cresol; aprotic polar solvents such as dimethylformamide, dimethylacetamide, and dimethylsulfoxide;
Ether solvents such as tetrahydrofuran and dioxane, and mixed solvents thereof.

The solution concentration varies depending on the coating method, the viscosity of the polymer, the desired film thickness, etc. Taking a compensation plate for a liquid crystal display element as an example, the required film thickness is 2 to 10 mm. Since it is about 2~
It is used in a range of 50% by weight2, preferably in a range of 5 to 30%. As the coating method, a spin code method, a roll coating method, a gravure coating method, a dipping method, a screen printing method, etc. are adopted. After coating the liquid crystalline polymer, the solvent is removed by drying, and the liquid crystalline polymer is aligned by heat treatment at a temperature at which the liquid crystalline polymer exhibits liquid crystallinity.

In this way, in the present invention, only one side of the liquid crystalline polymer layer is brought into contact with the alignment layer, and the other side is brought into contact with the outside air. On the other hand, if both sides are brought into contact with the alignment layer, sufficient alignment will not occur.

This is because liquid crystal polymers have a higher viscosity than low-molecular liquid crystals, so when they come into contact with the alignment layer, the fluidity at the interface of the alignment film is greatly reduced, making it difficult for molecules to rearrange. it is conceivable that. In the present invention, the alignment film interface is 1
Therefore, rearrangement easily occurs and uniform orientation tends to occur.

The temperature at which the liquid crystalline polymer is aligned needs to be higher than the glass transition point of the liquid crystalline polymer and lower than the transition temperature of the liquid crystalline polymer to an isotropic liquid.

The lower the viscosity of the polymer, the better, in order to aid the alignment by the surface activity of the alignment film, and therefore the higher the temperature, but if it is too high, this is not preferable as it will increase costs and worsen workability.

- The temperature within the shell is preferably in the range of 50°C to 300°C.

The liquid crystalline polymer film obtained as described above has excellent monodomain orientation, but since it is a coating method, thickness distribution is unavoidable, and the desired thickness is 0.5%. 5
It is difficult to obtain a surface accuracy of z or less. This value is sufficient for some applications, but in cases where the liquid crystal polymer has a twisted structure and the twist angle also needs to be controlled, such as in compensation plates for liquid crystal display elements, the film thickness distribution may be affected. This also results in a distribution of twist angles, which is undesirable. In order to introduce a twisted structure into the liquid crystalline polymer of the present invention, a liquid crystalline polymer exhibiting a cholesteric liquid crystal phase may be used. A liquid crystalline polymer exhibiting a cholesteric liquid crystal phase may be obtained by introducing an optically active group into a liquid crystalline polymer exhibiting a nematic phase as described above, or by adding an optically active substance to the liquid crystalline polymer exhibiting a nematic phase. In this case, the liquid crystalline polymer is aligned in the direction of the alignment treatment on the alignment film surface, and the twist angle corresponding to the natural pitch, that is, the natural pitch, is P in the thickness direction. , where d is the film thickness and ω is the twist angle, a twist angle of ω=360×d/P, (″) is formed.

In the present invention, after the liquid crystalline polymer is once aligned on a substrate, a second substrate 4 which has been subjected to another alignment treatment is superimposed as shown in FIG. It enables control.

The second substrate 4 is made of a light-transmitting material such as glass or plastic, and its surface in contact with the liquid crystal polymer layer 3 is subjected to alignment treatment to align the liquid crystal polymer almost horizontally and in one direction. The method described for the first substrate 1 can be used for the orientation treatment 6 on which the layer 5 is applied. The direction of the alignment treatment is set approximately equal to the desired alignment direction of the liquid crystal polymer in contact with the second substrate surface, which is determined by the desired ω.

After the second substrates 4 are superimposed, the molecules of the liquid crystalline polymer layer 3 in contact with the second substrate 4 are heated to a temperature at which the liquid crystalline polymer takes a liquid crystal phase and held for a certain period of time. can be aligned in the orientation treatment direction of the substrate 4. That is, even if the torsion angle has an in-plane distribution on the first substrate l, by controlling the orientation of the second substrate 4, a uniform torsion angle can be obtained over the entire surface. It is particularly preferable that ω and the angle formed by the orientation treatment direction of both substrates are approximately equal, or that the difference between the two is approximately an integral multiple of 180°. If the deviation from this condition becomes large, it becomes difficult to rearrange the liquid crystal molecules, and domain division is likely to occur. The allowable deviation angle is approximately 45° or less, preferably 30° or less, and particularly preferably 20" or less. In the present invention, the liquid crystal polymer is once in a state where only one side is in contact with the alignment film and is easily aligned. After the first alignment process is performed, interface regulation from both sides works under conditions where the movement required for rearrangement of the liquid crystal polymer is small, making it easy to obtain monodomain alignment with highly precise control of twist angle. The obtained orientation state is
It is extremely stable because it is maintained by rapid cooling below the glass transition temperature.

(Examples) Next, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to these Examples.

11-Example 1 Polyimide varnish PIQ manufactured by Hitachi Chemical was coated on a glass substrate to a thickness of about 1,000 mm using a spin code method, and then baked at 270° C. to form a polyimide film.

Next, the polyimide film was rubbed in one direction with a Tetron flocked cloth to perform a rubbing treatment.

A nematic liquid crystal polysiloxane liquid crystal polymer represented by the following formula (A) and a polysiloxane liquid crystal polymer having an optically active group represented by the following formula (B) were mixed in a mixed solvent of phenol/tetrachloroethane (weight ratio 50 :50) to a concentration of 25% by weight.

The ratio of polymers (A) and (8) was 3:l (weight ratio).

(Ch: Cholesteryl) 12- This solution was applied onto the above alignment film by a spin code method, and then dried at 70°C, and then heat-treated at 170°C for 30 minutes at which the polymer (A) exhibits a nematic phase. When this state was rapidly cooled to room temperature, a liquid crystalline polymer film with a fixed orientation of 4.6 μm in thickness was obtained, but the film thickness was 0.05 μm.
It has a distribution of about m, and the twist angle also has a pitch (7, 5
approximately 2° to the expected value of 220” (μm)
It had a distribution of degrees.

Next, a second glass substrate that had been subjected to the same orientation treatment was
Layer the alignment films in vacuum so that the rubbing direction makes an angle of 220° and the surface of the alignment film is in contact with the liquid crystal polymer.
Heat treatment was performed at ℃ for 30 minutes. After quenching to room temperature, the obtained orientation structure was observed and found to be a monodomain uniform orientation, the twist angle was 2200, and the helical axis was perpendicular to the substrate.

Retardation Δn-d was 0.82 μm.

Furthermore, it was confirmed that there was no distribution of twist angles in the 150 mm x 150 mm compensator plate, showing extremely excellent uniformity.

(Effects of the Invention) In the method for controlling the alignment of liquid crystalline polymers of the present invention, the liquid crystalline polymers are once subjected to a first alignment treatment in a state where only one side is in contact with an alignment film and easily aligned, and then the liquid crystalline polymers are aligned easily. Since interface regulation from both sides works under conditions where the movement required for polymer rearrangement is small, monodomain alignment with highly precisely controlled torsion angles can be easily obtained. Additionally, since the liquid crystalline polymer is sandwiched between the substrates, it is characterized by high reliability. Therefore, it can be advantageously used in optical electronics fields such as thermal writing optical memories and optical filters. In particular, the present invention is particularly useful as a method for producing a color compensating plate for a super twisted nematic (STN) type liquid crystal display element in that the twist angle can be highly controlled.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of the method for controlling the alignment of liquid crystalline polymers according to the present invention. 1... First substrate 2... Alignment treated layer 3... Liquid crystalline polymer 4... Second substrate 5... Alignment treated layer

Claims (2)

[Claims] (1) Forming a liquid crystal polymer layer on a first substrate that has been subjected to an alignment treatment that aligns the liquid crystal polymer in one direction,
Orientation control of a liquid crystalline polymer, which comprises aligning a liquid crystalline polymer and then superimposing a second substrate that has been subjected to a similar alignment treatment so that the alignment treated surface comes into close contact with the liquid crystalline polymer layer. Method. (2) The liquid crystal polymer exhibits a nematic or cholesteric phase, and the twist angle ω determined by its natural pitch P_0 and the film thickness d of the liquid crystal polymer layer is approximately equal to the angle formed by the orientation treatment direction of both substrates. or the difference between the two is approximately 18
2. The method for controlling the alignment of a liquid crystalline polymer according to claim 1, wherein the angle is an integral multiple of 0[deg.].