JP3788734B2 - Method for producing homeotropic alignment liquid crystal film and homeotropic alignment liquid crystal film - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a homeotropic alignment liquid crystal film. The present invention also relates to a homeotropic alignment liquid crystal film obtained by the production method, and further to an optical film. The homeotropic alignment liquid crystal film can be used alone or in combination with other films as an optical film such as a retardation film, a viewing angle compensation film, an optical compensation film, and an elliptically polarizing film.
[0002]
[Prior art]
Homeotropic alignment of a liquid crystal compound occurs when the molecular major axis of the liquid crystal phase is substantially perpendicular to the substrate forming a thin film (liquid crystal phase) on average. There are very few materials that spontaneously homeotropically align, and therefore vertical alignment agents are generally used to produce such alignment. As a liquid crystal compound that can be homeotropically aligned by a vertical alignment agent, for example, a nematic liquid crystal compound is known. An overview of the alignment technique of the liquid crystal compound is described in, for example, Chemical Review 44 (Surface Modification, Edited by The Chemical Society of Japan, pages 156 to 163).
[0003]
Various organic or inorganic alignment agents are known as vertical alignment agents capable of homeotropic alignment of the liquid crystal compound, but many of the commonly used alignment agents are designed to work effectively on a glass substrate. Has been.
[0004]
Examples of such conventional organic alignment agents include lecithin, silane surfactants, n-octadecyltriethoxysilane, titanate surfactants, pyridinium salt polymer surfactants, hexadecyltrimethylammonium halides, or And chromium complex. These organic alignment agents are dissolved in a suitable volatile solvent so that the active ingredient is very small (typically less than 1%) and then, for example, by spin coating or other well known coating methods. After coating on the substrate, the volatile solvent is evaporated to form a thin film of an organic alignment agent on the glass substrate. These organic alignment agents are characterized by having polar end groups thought to be attracted to the polar glass surface and nonpolar long-chain alkyl chains arranged perpendicular to the glass surface. A homeotropic alignment is generated in the liquid crystal compound on such a surface.
[0005]
In addition, as the inorganic alignment agent, for example, one obtained by depositing SiO _x or In ₂ O ₃ / SnO ₂ on a glass substrate at a vertical angle is known, and causes homeotropic alignment in the liquid crystal compound. In addition, polyimide films with alkyl side chains are also used as homeotropic alignment films for liquid crystal displays and the like.
[0006]
However, each of the above conventional alignment agents gives homeotropic alignment to the liquid crystal compound only on the glass substrate, and is not so much for alignment on a substrate made of a polymer material such as a plastic film or a plastic sheet. It does not work effectively. The surface of the substrate made of a polymeric material is presumed to have a poor affinity for the polar end groups of the conventional alignment agents and therefore generally exhibits no or only a slight homeotropic alignment. It remains to show the orientation. In addition, the formation of the alkyl side chain-attached polyimide film requires a heat treatment at a high temperature, but it can withstand the baking of the polyimide alignment film, and there are only a few transparent plastic films that can be used for optical applications.
[0007]
[Problems to be solved by the invention]
The present invention provides a method for producing a homeotropic alignment liquid crystal film capable of homeotropic alignment of a liquid crystal polymer on a substrate without using a vertical alignment film, and a homeotropic alignment liquid crystal obtained by the production method. The object is to provide a film. Furthermore, it aims at providing the optical film which has a homeotropic alignment liquid crystal film layer on a board | substrate without passing a vertical alignment film.
[0008]
[Means for solving problems]
As a result of intensive studies to solve the above problems, the present inventors have found that the object can be achieved by the following method, and have completed the present invention.
[0009]
That is, the present invention provides a general formula (a) as a monomer unit (a) containing a liquid crystalline fragment side chain on a substrate not provided with a vertical alignment film :
[Chemical 1C]
(Wherein R ¹ represents a hydrogen atom or a methyl group, a represents a positive integer of 1 to 6, X ¹ represents a —CO ₂ — group or —OCO— group, R ² represents a cyano group, and has 1 to 6 carbon atoms. An alkoxy group, a fluoro group, or an alkyl group having 1 to 6 carbon atoms, b and c each represent an integer of 1 or 2, and a monomer unit having a side chain having nematic liquid crystallinity ,
As the monomer unit (b) containing a non-liquid crystalline fragment side chain , the general formula (b):
[Chemical 2C]
(Wherein R ³ is a hydrogen atom or a methyl group, R ⁴ is an alkyl group having 7 to 22 carbon atoms, a fluoroalkyl group having 1 to 22 carbon atoms, or the general formula (c):
[Chemical 3C]
However, d is a positive integer from 1 to 6, R ⁵ represents an alkyl group having 1 to 6 carbon atoms. In a state where the liquid crystal polymer is homeotropically aligned in a liquid crystal state, and then the alignment state is maintained. The present invention relates to a method for producing a homeotropic alignment liquid crystal film, which is fixed.
[0010]
In the present invention, a vertical alignment film is obtained by using a side chain type liquid crystal polymer comprising a monomer unit (a) containing a liquid crystalline fragment side chain and a monomer unit (b) containing a non-liquid crystalline fragment side chain as the liquid crystal polymer. This realizes the homeotropic alignment of the liquid crystal polymer without using. The side chain type liquid crystal polymer is a monomer unit containing a non-liquid crystalline fragment side chain having an alkyl chain in addition to the monomer unit (a) containing a liquid crystalline fragment side chain of a normal side chain type liquid crystal polymer. (B), the monomer unit (b) containing a non-liquid crystalline fragment side chain allows the nematic liquid crystal phase to be expressed by a heat treatment, for example, without the use of a vertical alignment film, thereby producing a homeo It is presumed that the tropic orientation has been exhibited. Then, the homeotropic alignment liquid crystal film in which the heat is removed and vitrified to fix the homeotropic alignment liquid crystal polymer layer is manufactured.
[0011]
In the method for producing the homeotropic alignment liquid crystal film, the substrate may be made of various materials such as a polymer material, a glass substrate, and a metal. Polymeric materials are also used as plastic sheets or plastic films. There is no restriction | limiting in the kind of board | substrate used for the manufacturing method of this invention, A glass substrate, a polymer substance, and a metal can be especially used without a restriction | limiting, and a polymer substance can be used as a plastic sheet or a plastic film.
[0012]
The present invention also relates to a homeotropic alignment liquid crystal film obtained by the production method.
[0013]
Furthermore, the present invention relates to a monomer unit (a) containing a liquid crystalline fragment side chain on a substrate not provided with a vertical alignment film , wherein the general formula (a):
[Chemical 1D]
(Wherein R ¹ represents a hydrogen atom or a methyl group, a represents a positive integer of 1 to 6, X ¹ represents a —CO ₂ — group or —OCO— group, R ² represents a cyano group, and has 1 to 6 carbon atoms. An alkoxy group, a fluoro group, or an alkyl group having 1 to 6 carbon atoms, b and c each represent an integer of 1 or 2, and a monomer unit having a side chain having nematic liquid crystallinity ,
As the monomer unit (b) containing a non-liquid crystalline fragment side chain, the general formula (b):
[Chemical 2D]
(Wherein R ³ is a hydrogen atom or a methyl group, R ⁴ is an alkyl group having 7 to 22 carbon atoms, a fluoroalkyl group having 1 to 22 carbon atoms, or the general formula (c):
[Chemical 3D]
However, d is a positive integer from 1 to 6, R ⁵ represents an alkyl group having 1 to 6 carbon atoms. ), An optical film provided with a homeotropic alignment liquid crystal film layer in which a side chain type liquid crystal polymer containing a monomer unit having a linear side chain is homeotropically aligned.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
As the liquid crystal polymer capable of forming a homeotropic alignment liquid crystal layer in the present invention contains the following monomer units monomer unit containing a liquid crystalline fragment side chain (a) and containing the non-liquid crystalline fragment side chain (b) A side chain type liquid crystal polymer is used.
[0015]
The monomer unit (a) has a side chain having nematic liquid crystallinity, for example, the general formula (a):
[Chemical 1]
(Wherein R ¹ represents a hydrogen atom or a methyl group, a represents a positive integer of 1 to 6, X ¹ represents a —CO ₂ — group or —OCO— group, R ² represents a cyano group, and has 1 to 6 carbon atoms. An alkoxy group, a fluoro group, or an alkyl group having 1 to 6 carbon atoms, and b and c each represent an integer of 1 or 2.).
[0016]
The monomer unit (b) has a linear side chain. For example, the monomer unit (b) has the general formula (b):
[Chemical 2]
(Wherein R ³ is a hydrogen atom or a methyl group, R ⁴ is an alkyl group having 7 to 22 carbon atoms, a fluoroalkyl group having 1 to 22 carbon atoms, or the general formula (c):
[Chemical 3]
However, d is a positive integer from 1 to 6, R ⁵ represents an alkyl group having 1 to 6 carbon atoms. ) Monomer units.
[0017]
Further, the ratio of the monomer unit (a) to the monomer unit (b) is not particularly limited and varies depending on the type of the monomer unit. However, when the ratio of the monomer unit (b) is increased, the side chain type liquid crystal polymer is changed. Since the liquid crystal monodomain orientation is not exhibited, it is preferable that (b) / {(a) + (b)} = 0.01 to 0.8 (molar ratio). In particular, 0.1 to 0.5 is more preferable.
[0018]
The side chain type liquid crystal polymer preferably has a weight average molecular weight of 2,000 to 100,000. By adjusting the weight average molecular weight to such a range, performance as a liquid crystal polymer is exhibited. When the weight average molecular weight of the side chain type liquid crystal polymer is too small, the film forming property of the alignment layer tends to be poor. Therefore, the weight average molecular weight is more preferably 2.5000 or more. On the other hand, if the weight average molecular weight is excessive, the orientation as a liquid crystal tends to be poor and it becomes difficult to form a uniform alignment state. Therefore, the weight average molecular weight is more preferably 50,000 or less.
[0019]
The side chain liquid crystal polymer can be prepared by copolymerizing an acrylic monomer or a methacrylic monomer corresponding to the monomer unit (a) and the monomer unit (b). The monomers corresponding to the monomer unit (a) and the monomer unit (b) can be synthesized by a known method. The copolymer can be prepared, for example, according to a polymerization method such as a conventional acrylic monomer such as a radical polymerization method, a cationic polymerization method, and an anionic polymerization method. When applying the radical polymerization method, various polymerization initiators can be used. Among them, decomposition temperatures such as azobisisobutyronitrile and benzoyl peroxide are not high and are not low. Those are preferably used.
[0020]
The substrate to which the side chain type liquid crystal polymer is applied may be any shape of a glass substrate, a metal foil, a plastic sheet, or a plastic film. The thickness of the substrate is usually about 10 to 1000 μm.
[0021]
The plastic film is not particularly limited as long as it does not change with the orientation temperature. For example, polyester polymers such as polyethylene terephthalate and polyethylene naphthalate, cellulose polymers such as diacetyl cellulose and triacetyl cellulose, polycarbonate polymers, polymethyl Examples thereof include a film made of a transparent polymer such as an acrylic polymer such as methacrylate. Styrene polymers such as polystyrene and acrylonitrile / styrene copolymers, polyethylene, polypropylene, polyolefins having a cyclic or norbornene structure, olefin polymers such as ethylene / propylene copolymers, vinyl chloride polymers, nylon and aromatic polyamides, etc. Examples thereof include films made of transparent polymers such as amide polymers. Furthermore, imide polymers, sulfone polymers, polyether sulfone polymers, polyether ether ketone polymers, polyphenylene sulfide polymers, vinyl alcohol polymers, vinylidene chloride polymers, vinyl butyral polymers, arylate polymers, polyoxymethylene polymers Examples thereof include a film made of a transparent polymer such as a polymer, an epoxy-based polymer, and a blend of the aforementioned polymers. Among these, a plastic film having a high hydrogen bonding property is preferable.
[0022]
Moreover, as a metal film, the said film formed from aluminum etc. is mentioned, for example.
[0023]
As plastic films, polymers having a norbornene structure such as ZEONOR (trade name, manufactured by ZEON CORPORATION), ZEONEX (trade name, manufactured by ZEON CORPORATION), Arton (trade name, manufactured by JSR Corporation), etc. A plastic film made of a substance has excellent optical properties. Since these polymer substances (plastic films) have very little optical anisotropy, the aligned liquid crystal film layer of the side chain type liquid crystal polymer formed on the plastic film transfers the aligned liquid crystal film layer to another plastic film. Without being used, it can be used as an optical film for optical compensation of a liquid crystal display as a homeotropic alignment retardation film as it is. Further, regarding the aligned liquid crystal film layer of the side chain type liquid crystal polymer formed on a metal film such as a plastic film or an aluminum foil having optical anisotropy, the side chain type liquid crystal polymer is converted into an aligned liquid crystal film, and then norbornene is used. The film can be used for an optical film such as an optical compensation film by transferring directly or via an adhesive or adhesive onto a transparent plastic film having a small optical anisotropy such as a film having a structure or cellulose triacetate.
[0024]
Examples of the method of coating the side chain type liquid crystal polymer on the substrate include a solution coating method using a solution in which the side chain type liquid crystal polymer is dissolved in a solvent or a method of melting and applying the liquid crystal polymer. Of these, the method of coating the side chain type liquid crystal polymer solution on the support substrate by the solution coating method is preferable.
[0025]
The solvent used in preparing the solution varies depending on the side chain type liquid crystal polymer and the type of substrate, and cannot generally be said, but usually halogenated such as chloroform, dichloromethane, dichloroethane, tetrachloroethane, trichloroethylene, tetrachloroethylene, chlorobenzene, etc. Hydrocarbons, phenols such as phenol and parachlorophenol, aromatic hydrocarbons such as benzene, toluene, xylene, methoxybenzene, and 1,2-dimethoxybenzene, acetone, ethyl acetate, tert-butyl alcohol, Glycerin, ethylene glycol, triethylene glycol, ethylene bricol monomethyl ether, diethylene glycol dimethyl ether, ethyl cellosolve, butyl cellosolve, 2-pyrrolidone, N-methyl-2 Pyrrolidone, pyridine, triethylamine, tetrahydrofuran, dimethylformamide, dimethylacetamide, dimethyl sulfoxide, can be used acetonitrile, butyronitrile, carbon disulfide and the like. The concentration of the solution depends on the solubility of the side chain type liquid crystal polymer to be used and the film thickness of the final oriented liquid crystal film, but cannot be generally stated, but is usually 3 to 50% by weight, preferably 7 to 30%. It is in the range of wt%.
[0026]
The thickness of the homeotropically oriented liquid crystal film layer comprising the coated side chain type liquid crystal polymer is preferably about 1 to 10 μm. In particular, when it is necessary to precisely control the film thickness of the homeotropic alignment liquid crystal film, the film thickness is almost determined at the stage of coating on the substrate, so control of the solution concentration, the film thickness of the coating film, etc. Need to pay special attention.
[0027]
As a method for coating the side chain type liquid crystal polymer solution adjusted to a desired concentration using the above-mentioned solvent on the substrate, for example, a spin coating method, a bar coating method, or the like can be employed. After coating, the solvent is removed and a liquid crystal polymer layer is formed on the substrate. The conditions for removing the solvent are not particularly limited, as long as the solvent can be largely removed and the liquid crystal polymer layer does not flow or even flows down. Usually, the solvent is removed by drying at room temperature, drying in a drying oven, heating on a hot plate, or the like.
[0028]
Next, the side chain type liquid crystal polymer layer formed on the support substrate is brought into a liquid crystal state and homeotropically aligned. For example, heat treatment is performed so that the liquid crystal polymer is in the liquid crystal temperature range, and homeotropic alignment is performed in the liquid crystal state. The heat treatment can be performed by the same method as the above drying method. The heat treatment temperature varies depending on the side chain type liquid crystal polymer to be used and the type of the support substrate, and thus cannot be generally described, but is usually 60 to 300 ° C., preferably 70 to 200 ° C. The heat treatment time varies depending on the heat treatment temperature and the type of the side chain type liquid crystal polymer to be used and the substrate, but cannot be generally specified, but is usually selected in the range of 10 seconds to 2 hours, preferably 20 seconds to 30 minutes. If it is shorter than 10 seconds, homeotropic alignment formation may not proceed sufficiently.
[0029]
After the heat treatment is completed, a cooling operation is performed. As the cooling operation, the homeotropic alignment liquid crystal film after the heat treatment can be performed by taking it out from the heating atmosphere in the heat treatment operation to room temperature. Moreover, you may perform forced cooling, such as air cooling and water cooling. The alignment of the homeotropic alignment layer of the liquid crystal polymer is fixed by cooling to a temperature lower than the glass transition temperature of the liquid crystal polymer.
[0030]
In this way, a thin film of a side chain type liquid crystal polymer is produced, and a homeotropically oriented aligned liquid crystal film is obtained by fixing it while maintaining the alignment. The alignment liquid crystal layer has molecules aligned in the same direction. Therefore, it is well known that the alignment vector of this alignment liquid crystal layer can be frozen or stabilized and its anisotropic properties can be preserved. Such thin films have been confirmed for their optical properties and can be used in various applications. Is done. The alignment liquid crystal layer is a thin film having a uniaxial positive birefringence.
[0031]
The orientation of the homeotropic alignment liquid crystal layer obtained as described above can be quantified by measuring the optical phase difference of the liquid crystal layer at an angle inclined from normal incidence. In the case of homeotropic alignment liquid crystal films, this retardation value is symmetric with respect to normal incidence. Several methods can be used to measure the optical phase difference. For example, an automatic birefringence measuring device (manufactured by Oak) and a polarizing microscope (manufactured by Olympus) can be used. This homeotropic alignment liquid crystal film appears black between the crossed Nicol polarizers.
[0032]
The homeotropic alignment liquid crystal film thus obtained is used as an optical film. The oriented liquid crystal film may be peeled off from the substrate, or may be used as it is as an oriented liquid crystal layer formed on the substrate without being peeled off.
[0033]
【Example】
Examples of the present invention will be described below with reference to examples, but the present invention is not limited to the examples.
[0034]
Example 1
[Formula 4]
20 parts by weight of a side chain type liquid crystal polymer represented by the above chemical formula 4 (n = 18 in the formula, indicating the mol% of the monomer unit, and expressed as a block for convenience, weight average molecular weight 5000) A solution dissolved in 80 parts of dichloroethane was applied to a plastic film (20 μm) using a norbornene polymer (trade name: Zeonoa, manufactured by Nippon Zeon Co., Ltd.) as a polymer material by spin coating. Next, the liquid crystal polymer layer is homeotropically aligned by heating at 160 ° C. for 1 minute and then cooled to room temperature at a time, and the homeotropic alignment liquid crystal layer (2 μm) is fixed with vitrification while maintaining the alignment. A liquid crystal film was obtained.
[0035]
When the sample (homeotropic alignment liquid crystal film with a substrate) was crossed Nicol and the sample was observed from a direction perpendicular to the film surface, nothing was seen from the front. This confirmed homeotropic orientation. That is, it was found that no optical phase difference occurred. When this film was tilted and light was incident from an oblique direction and observed in the same manner with crossed Nicols, light transmission was observed.
[0036]
The optical retardation of the film was measured with an automatic birefringence measuring device. The measurement light was incident on the sample surface vertically or obliquely, and the homeotropic alignment was confirmed from the chart of the optical phase difference and the incident angle of the measurement light. In homeotropic alignment, the phase difference (front phase difference) in the direction perpendicular to the sample surface is almost zero. Regarding this sample, when the phase difference was measured obliquely in the slow axis direction of the liquid crystal layer, it was determined that the homeotropic alignment was obtained because the phase difference value increased as the incident angle of the measurement light increased. did it.
[0037]
Example 2
In Example 1, a homeotropic alignment liquid crystal film was produced in the same manner as in Example 1 except that a norbornene polymer (trade name: Zeonex, manufactured by Nippon Zeon Co., Ltd.) was used as the polymer material for the plastic film. Further, the homeotropic orientation of the sample was confirmed in the same manner as in Example 1.
[0038]
Example 3
In Example 1, a homeotropic alignment liquid crystal film was produced in the same manner as in Example 1 except that a norbornene-based polymer (trade name: Arton, manufactured by JSR Corporation) was used as the polymer material for the plastic film. Further, the homeotropic orientation of the sample was confirmed in the same manner as in Example 1.
[0039]
Example 4
In Example 1, a homeotropic alignment liquid crystal film was produced in the same manner as in Example 1 except that aluminum foil (15 μm) was used instead of the plastic film as the substrate. Next, the homeotropic alignment liquid crystal film was transferred to a cellulose triacetate film, separated from the substrate to obtain a sample, and the homeotropic alignment of the sample was confirmed in the same manner as in Example 1.
[0040]
Example 5
In Example 1, a homeotropic alignment liquid crystal film was produced in the same manner as in Example 1 except that a glass substrate (1 mm) was used instead of the plastic film as the substrate. Further, the homeotropic orientation of the sample was confirmed in the same manner as in Example 1.
[0041]
Comparative Example 1
[Chemical formula 5]
In Example 1, the same operation as Example 1 was performed except having used the side chain type liquid crystal polymer (weight average molecular weight 5000) shown by the said Chemical formula 5 as a formation material of a liquid-crystal layer. Further, the sample was evaluated in the same manner as in Example 1, but homeotropic alignment could not be confirmed. When observed from the front, it is cloudy, and the liquid crystal directors are present in all directions, and it is thought that the alignment of the liquid crystal is disturbed.

Claims (5)

As a monomer unit (a) containing a liquid crystalline fragment side chain on a substrate not provided with a vertical alignment film , the general formula (a):
(Wherein R ¹ represents a hydrogen atom or a methyl group, a represents a positive integer of 1 to 6, X ¹ represents a —CO ₂ — group or —OCO— group, R ² represents a cyano group, and has 1 to 6 carbon atoms. An alkoxy group, a fluoro group, or an alkyl group having 1 to 6 carbon atoms, b and c each represent an integer of 1 or 2, and a monomer unit having a side chain having nematic liquid crystallinity ,
As the monomer unit (b) containing a non-liquid crystalline fragment side chain , the general formula (b):
(Wherein R ³ is a hydrogen atom or a methyl group, R ⁴ is an alkyl group having 7 to 22 carbon atoms, a fluoroalkyl group having 1 to 22 carbon atoms, or the general formula (c):
However, d is a positive integer from 1 to 6, R ⁵ represents an alkyl group having 1 to 6 carbon atoms. In a state where the liquid crystal polymer is homeotropically aligned in a liquid crystal state, and then the alignment state is maintained. A method for producing a homeotropic alignment liquid crystal film, which is fixed.   2. The method for producing a homeotropic alignment liquid crystal film according to claim 1, wherein the material of the substrate is a polymer substance, glass or metal.   A homeotropic alignment liquid crystal film obtained by the production method according to claim 1. As a monomer unit (a) containing a liquid crystalline fragment side chain on a substrate not provided with a vertical alignment film , the general formula (a):
(Wherein R ¹ represents a hydrogen atom or a methyl group, a represents a positive integer of 1 to 6, X ¹ represents a —CO ₂ — group or —OCO— group, R ² represents a cyano group, and has 1 to 6 carbon atoms. An alkoxy group, a fluoro group, or an alkyl group having 1 to 6 carbon atoms, b and c each represent an integer of 1 or 2, and a monomer unit having a side chain having nematic liquid crystallinity ,
As the monomer unit (b) containing a non-liquid crystalline fragment side chain, the general formula (b):
(Wherein R ³ is a hydrogen atom or a methyl group, R ⁴ is an alkyl group having 7 to 22 carbon atoms, a fluoroalkyl group having 1 to 22 carbon atoms, or the general formula (c):
However, d is a positive integer from 1 to 6, R ⁵ represents an alkyl group having 1 to 6 carbon atoms. An optical film provided with a homeotropic alignment liquid crystal film layer in which a side chain type liquid crystal polymer containing a monomer unit having a linear side chain represented by formula (1) is homeotropically aligned. 5. The optical film according to claim 4, wherein the substrate is made of a polymer material, glass or metal .