JP3441963B2 - Manufacturing method of liquid crystal element - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a liquid crystal device which can align a liquid crystal polymer in a short time and is excellent in mass productivity.

[0002]

BACKGROUND OF THE INVENTION Aligned liquid crystal polymer layers or liquid crystal elements provided with them on a supporting substrate are used in various fields of optoelectronics. Examples thereof include a retardation plate for compensating the retardation of a liquid crystal cell to suppress coloring and the like, and a circularly polarized light separating layer using a cholesteric liquid crystal as a liquid crystal polymer.

Conventionally, as a method of manufacturing the liquid crystal element,
A method has been known in which a liquid crystal polymer solution is applied on an alignment film, dried, and then heated to a temperature not lower than the glass transition temperature of the liquid crystal polymer and a temperature at which a liquid crystal phase is exhibited (Japanese Patent Laid-Open No. 3-932).
No. 1, No. 3-9325, No. 3-9325). However, the alignment takes a long time, and therefore, there is a problem that defects such as cissing are generated in the previously oriented portion while waiting for the orientation of the subsequent portion.

[0004]

DISCLOSURE OF THE INVENTION It is an object of the present invention to develop a manufacturing method capable of efficiently orienting a liquid crystal polymer, efficiently obtaining a liquid crystal element having few defects such as cissing and excellent in quality uniformity. To do.

[0005]

A solution means of the present invention, after drying it by coating a liquid crystal polymer solution on the orientation film in the liquid crystal polymer non-orientation state, high 50 ° C. or higher than the glass transition temperature of the liquid crystal polymer, and a liquid crystal phase The present invention provides a method for manufacturing a liquid crystal element, which comprises heating to a temperature at which

[0006]

According to the present invention, the liquid crystal polymer can be efficiently aligned in a short time, and a liquid crystal element having few defects such as cissing and excellent in quality uniformity can be efficiently obtained. This is due to the fact that the alignment state of the liquid crystal polymer at the time of drying greatly affects the time required for the subsequent heat alignment treatment.

That is, the inventors of the present invention have conducted extensive studies to overcome the above-mentioned problems, and have studied the structures and types and layer thicknesses of liquid crystal polymers, types and states of alignment films, electric fields and magnetic fields, etc. It was found that, even if the factors are unified, the conditions from the coating of the liquid crystal polymer solution to the heating alignment treatment give a great change in the alignment state of the liquid crystal polymer.

On the basis of the above findings, when the coating layer of the liquid crystal polymer solution was dried and observed for its alignment state with an optical microscope or an electron microscope, for example, the coating layer showed a glass transition temperature at which the liquid crystal polymer exhibited a liquid crystal phase. In the case of the one dried at a temperature close to it, a small domain-shaped orientation portion has already been formed, and it takes a long time to orient it in the monodomain state, and the heating orientation treatment causes an isotropic phase transition. It was clarified that it takes a long time to orient to a monodomain state even if the temperature is favorable for the orientation near the temperature.

In the present invention , it is possible to avoid the above-mentioned drying process in which the small domain-shaped alignment portion is formed by the non- alignment drying method, and thus it is possible to favorably align the mono-domain state in a short heat treatment. It is possible to efficiently obtain a liquid crystal element having excellent quality uniformity.

[0010]

Production method of the present invention embodiment of the Invention, after drying it by coating a liquid crystal polymer solution on the LCD polymer unoriented state on the orientation film, the glass transition temperature of the liquid crystal polymer 5
A liquid crystal element is obtained by heating to a temperature higher than 0 ° C. and exhibiting a liquid crystal phase.

The liquid crystal polymer may be, for example, a nematic type, a smectic type, a cholesteric type or a discotic type, depending on the desired liquid crystal element such as a polarizing layer, an optical rotatory layer, a retardation layer or a circularly polarized light separating layer. An appropriate thermotropic substance such as a mixed system can be used, and there is no particular limitation. Therefore, it is possible to use various types of liquid crystal polymers such as a main chain type or a side chain type, or a compound other than the liquid crystal polymer, for example, a compound containing a compound such as a chiral component.

The liquid crystal polymer is applied and developed as a solution with a solvent, but any suitable solvent capable of dissolving the liquid crystal polymer can be used, and there is no particular limitation. Incidentally, examples thereof include halogenated hydrocarbons such as chloroform, dichloroethane, trichloroethylene, tetrachloroethane, tetrachloroethylene, methylene chloride and orthodichlorobenzene.

Phenol and o-chlorophenol,
Mixed solvents of phenols such as cresol and the above-mentioned halogenated hydrocarbons, aprotic polar solvents such as dimethylformamide, dimethylacetamide and dimethylsulfoxide, ethers such as tetrahydrofuran and dioxane, other cyclohexanone and N-methylpyrrolidone, etc. Are also mentioned as examples of the solvent.

The concentration of the liquid crystal polymer solution may be appropriately determined depending on the coating method and viscosity. Generally, 90% by weight or less, especially 5 to 60% by weight, based on the solid content forming the liquid crystal polymer layer from the viewpoint of uniform coating property and drying efficiency.
In particular, the concentration is 10 to 40% by weight. When preparing the liquid crystal polymer solution, various additives such as stabilizers, plasticizers and metals can be blended as necessary.

The liquid crystal polymer solution is applied onto the alignment film. The liquid crystal polymer can be aligned by applying and developing it on the alignment film. As the alignment film, for example, a rubbing film of a polymer layer, an oblique vapor deposition film of SiO ₂ or the like, or an oriented film substrate made of a stretched film, a UV curable LCP, or the like can be used, and an appropriate one can be used. There is no limit. Therefore, any of the conventional alignment films known for low-molecular liquid crystals and liquid crystal polymers can be used.

Incidentally, examples of the polymer for forming the above-mentioned rubbing-treated film, stretched film, etc. are polyethylene, polypropylene, olefin polymers such as polyolefin having a norbornene structure and ethylene-propylene copolymer, polyethylene terephthalate and polyethylene naphthalate. Polyester polymers such as polybutylene terephthalate, cellulose polymers such as cellulose diacetate and cellulose triacetate, acrylic polymers such as polymethylmethacrylate, and amide polymers such as nylon and aromatic polyamide.

Further, imide polymers, polyamideimide polymers, polyetherimide polymers, sulfone polymers, polyethersulfone polymers, polyetheretherketone polymers, polyphenylene sulfide polymers, vinyl alcohol polymers, vinyl chloride polymers. Polymers such as vinylidene chloride-based polymers, vinyl butyral-based polymers, carbonate-based polymers, arylate-based polymers, polyoxymethylene-based polymers, and styrene-based polymers are also examples of the above-mentioned rubbing film or stretched film-forming polymer. .

From the viewpoint of the alignment efficiency of the liquid crystal polymer and the like, the alignment film is preferably a rubbing film of polyimide or polyvinyl alcohol, a rubbing film of a stretched film, or a stretched film. In the rubbing treatment film, the liquid crystal polymer can be oriented in the rubbing direction including the rubbing treatment film of the stretched film, and in the stretched film, the liquid crystal polymer can be oriented in the molecular orientation direction.

The above-mentioned alignment film is formed, for example, by coating a polymer solution on a supporting base material and coating the surface thereof with a cloth composed of cellulosic fibers such as cotton and rayon, polyester, synthetic fibers such as polyamide, or urethane or polyamide. A rubbing method such as a method of rubbing in a predetermined direction with a sponge or a method of obliquely vapor-depositing an alignment film forming material on a supporting base material has a thickness of 5 μm or less, preferably 0.001 to 1 μm.
It may be formed as a single-layer or multi-layer thin film having a thickness of m, particularly 0.01 to 0.5 μm. On the other hand, the stretched film can be used as a substrate that supports the liquid crystal polymer layer including the rubbing-treated product.

The rubbing-treated film may be formed by co-extruding a polymer for forming an alignment film and a polymer for forming a supporting substrate to form a laminated film having two or more layers, and subjecting it to a rubbing treatment. Can also be formed. The rubbing-treated film made of the above-mentioned polyimide may be, for example, a film obtained by applying polyamic acid or a derivative thereof on a supporting base material to make it a polyimide and then rubbing it.

As the supporting base material, an appropriate single-layer or multi-layer transparent base material such as a base material made of the above-mentioned polymer for forming an alignment film can be used. In particular, a substrate having excellent isotropy and having as little birefringence as possible, such as a cellulose triacetate film or a glass plate, can be preferably used from the viewpoint of the orientation of the liquid crystal polymer. The thickness of the supporting substrate is appropriately determined, but is generally 500 μm or less, preferably 5 to 200 μm, particularly 10 to 100 μm in view of light transmittance and strength.

On the other hand, the orientation film comprising the above-mentioned orientation film substrate is a single-layer or multi-layer film formed by an appropriate method such as casting method, extrusion method, coextrusion method of two layers or three layers or more. It can be obtained by a method of stretching treatment by an appropriate method such as uniaxial or biaxial. A uniaxially stretched film is preferable in terms of uniformity of molecular orientation. The oriented film substrate may be a non-stretched film that is molecularly oriented by crystallization. The thickness of the oriented film substrate can be the same as that of the supporting substrate described above.

The preferred alignment film has excellent alignment uniformity. Variations in the orientation of the orientation film may reduce the orientation of the liquid crystal polymer or cause variations in the orientation direction.

The coating of the liquid crystal polymer solution on the alignment film is performed by
For example, spin coating method, roll coating method, flow coating method, printing method, dip coating method, casting film forming method, bar coating method, gravure printing method, or the like can be used, and there is no particular limitation. At the time of coating, a method of superposing liquid crystal polymer layers in which liquid crystal polymers of the same kind or different kinds are repeatedly applied through an alignment film or after orientation treatment of the previous coating layer can be adopted.

The process of the coating layer of a liquid crystal polymer solution for orienting the liquid crystal polymer in the present invention, a coating layer of its after the liquid crystal polymer was dried so as not aligned,
50 ° C higher than the glass transition temperature of liquid crystal polymer,
Moreover, it is performed by heating to a temperature at which a liquid crystal phase is exhibited.

[0026] For example, therefore, while continuously coating a liquid crystal polymer solution on an alignment film, also take such continuous production method of the liquid crystal element, such as a method in which heat treatment by introducing the coating layer in a heating furnace or the like You can

In the present invention, the purpose is to obtain a liquid crystal polymer layer that is well aligned in a monodomain state by a heat treatment for a short time. From the point of that purpose, the liquid crystal polymer to be subjected to the heat alignment treatment is as much as possible. it is Ru advantageous der in the non-oriented state basis.

[0028] Drying in the is likely progressing the small domain shaped oriented portions in the vicinity of or above the glass transition temperature of the liquid crystal polymer is formed.

When the small domain-shaped oriented portion is formed, it is necessary to collapse the oriented portion into a monodomain state, and it takes a long heat treatment to collapse the oriented portion. The short time of the heat treatment, which is the object of the invention, is impaired.

Therefore, in the present invention, the liquid crystal polymer is dried so as not to be aligned in a small domain shape, that is, in a non-aligned state. Examples of such a drying treatment for preventing alignment include a method of drying at a temperature lower than the glass transition temperature of the liquid crystal polymer, especially at a temperature lower by 20 ° C. or more than the glass transition temperature.

A preferred drying method in which orientation is prevented is a method of drying at a temperature as low as possible, for example, a temperature lower than the glass transition temperature by 50 ° C. or more. Therefore, it is preferable to dry at a temperature such as room temperature when the glass transition temperature is 75 ° C. or higher, and at a cooling temperature which is lower than room temperature when the glass transition temperature is lower than 75 ° C.

At the time of drying, it is preferable that the drying atmosphere is in a state where the solvent content is small by a blowing method or the like from the viewpoint of efficiency or the like, and a reduced pressure atmosphere may be used. The drying treatment is preferably performed so that the amount of residual solvent in the coating layer is 20% or less, particularly 15% or less, and particularly 10% or less, from the viewpoint of short-time property of the subsequent heat orientation treatment. .

50 ° C. higher than the glass transition temperature of the liquid crystal polymer for the purpose of aligning the dried coating layer.
The heat treatment at a temperature higher than the above and exhibiting a liquid crystal phase is
Although it may be heated to an appropriate temperature within the range, it is preferable to set the temperature as high as possible below the isotropic phase transition temperature of the liquid crystal polymer from the viewpoint of improving the degree of orientation.

The orientation of the liquid crystal polymer is to fix the orientation state by orienting the liquid crystal polymer by heat treatment at a temperature exhibiting a liquid crystal phase and then cooling it to a glass state by cooling it below the glass transition temperature. Can be done by. For the cooling, an appropriate method such as a forced cooling method or a natural cooling method can be adopted.

In the above, in the present invention, the liquid crystal polymer layer is satisfactorily brought into a monodomain state by a method of cooling after a short time heating alignment treatment of usually 10 minutes or less, especially 5 minutes or less, especially 4 minutes or less. It is possible to obtain an oriented liquid crystal element of interest.

The thickness of the liquid crystal polymer layer formed on the alignment film can be appropriately determined according to the purpose of use. Generally, from the viewpoints of preventing alignment disorder and reduction of transmittance, and the desired optical function, the thickness is 100 μm or less, preferably 0.5 to 50 μm, and particularly 1 to 20 μm.

As described above, according to the manufacturing method of the present invention, based on various optical characteristics of the alignment layer of the liquid crystal polymer used, for example, various types of polarizing plates, optical rotatory plates, retardation plates, circularly polarized light separating plates, etc. The liquid crystal element can be obtained with high mass productivity. In that case, the alignment layer of the liquid crystal polymer provided on the supporting base material can be put to practical use as a liquid crystal element formed integrally with the supporting base material, or can be separated from the supporting base material to align the liquid crystal polymer. It can also be put to practical use as a liquid crystal element composed of the layer itself.

Therefore, the liquid crystal element according to the present invention may be composed only of a liquid crystal polymer layer such as a liquid crystal polymer oriented film, or may be composed of a liquid crystal polymer layer and a supporting substrate which are superposed and integrated.

[0039]

On the uniaxially oriented PET film of EXAMPLE 1 thickness 80 [mu] m, A chestnut <br/> Le-based thermotropic after 20 wt% tetrahydrofuran solution coating the at wire bar of a liquid crystal polymer, 20 ° C. large of
Blow air and dry until the amount of residual solvent reaches 7%.
After the drying treatment, it was put in a drying heater at 170 ° C., and after 3 minutes, it was taken out and allowed to cool at room temperature.

From the above, it was possible to obtain a liquid crystal element having a nematic liquid crystal layer having a thickness of 2 μm, which was well aligned in the monodomain state in the stretching direction of the PET film .

The liquid that has been dried in the above
The crystalline polymer layer shows no optical anisotropy and is non-oriented
It was a state.

The liquid crystal polymer used above is a glass transition material.
The transition temperature is 85 ° C and the isotropic phase transition temperature is 230 ° C.
It exhibits a nematic liquid crystal phase in the intermediate temperature range of
It Further, the above-mentioned alignment state is observed by an optical microscope and
It was confirmed by observing the cross section with a transmission electron microscope.

Comparative Example 1 On a cellulose triacetate film having a thickness of 80 μm, a thickness of
By providing a polyvinyl alcohol layer of about 0.1 μm,
Rubbed with emissions cloth 3 a coating layer of that in the 100 ° C. oven by applying a liquid polymer solution onto the rubbed
A liquid crystal element having a liquid crystal layer having a thickness of 2 μm was obtained in the same manner as in Example 1 except that the material was placed in a drying heater for 1 minute at 170 ° C. and dried for 3 minutes. In this case, the liquid crystal polymer was oriented in a small domain state in the drying treatment stage, and the obtained liquid crystal element had the nematic liquid crystal phase oriented in the rubbing direction to some extent, but as a whole, the liquid crystal polymer layer was about 200 μm. It was oriented in a multi-domain state of size.

Comparative Example 2 The coating layer of the liquid crystal polymer solution was placed in a dryer at 100 ° C. for 3 minutes to be dried, and then dried in a dryer / heater at 170 ° C. for 30 minutes.
A liquid crystal element having a liquid crystal layer having a thickness of 2 μm was obtained in the same manner as in Example 1 except that the liquid crystal element was placed for a while. In this case, the liquid crystal polymer was oriented in a small domain state in the drying treatment stage, and the obtained liquid crystal element had the nematic liquid crystal phase oriented in the stretching direction to some extent, but as a whole, the liquid crystal polymer layer had several layers.
It is oriented in mm-size multi-domain state,
Repelling of the liquid crystal polymer was observed here and there.

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-8-146416 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G02B 5/30

Claims (3)

(57) [Claims] 1. A liquid crystal polymer solution is applied onto an alignment film and dried to a non-aligned state of the liquid crystal polymer, and the dry coating layer is at least 50 ° C. higher than the glass transition temperature of the liquid crystal polymer and has a liquid crystal phase. A method for manufacturing a liquid crystal element, which comprises heating to a temperature at which 2. The production method according to claim 1, wherein the dry coating layer is dried to a dry state with a residual solvent amount of 20% or less by an air blowing method at a temperature lower than the glass transition temperature of the liquid crystal polymer by 20 ° C. or more. . 3. The method of claim 1 or 2, the manufacturing method alignment film comprising polyimide, polyvinyl alcohol or a stretched film rubbed film, or a stretched film.