JP2002258047A - Method of manufacturing optical film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture an optical film by which the light usage efficiency of a polarizing board is enhanced and which is provided with polarization selectivity for selectively scattering polarization. SOLUTION: A coating liquid 42 where a liquid crystal compound is distributed in a water-soluble high molecular compound, is flow-cast on a supporting body 45 by a flow-casting die 44 and, then, dried so as to form a coating film 47. The coating film 47 is ripped from the supporting body 45, an electric field impressing device 49 impresses an electric field being 5 kV/cm and the liquid crystal compound is oriented. Then it is irradiated with ultraviolet rays by an immobilization processor 50 so as to immobilize the orientation of the liquid crystal compound. An adhering device 53 adheres a web 52 on the coating film 47 to obtain the optical film. Polarization selectivity is imparted to the optical film since the orientation of the liquid crystal compound is immobilized and, then, the film is suitably utilized for a scattered light type polarizing board.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an optical film, and more particularly to a method for manufacturing an optical film having polarization selectivity suitably used for a liquid crystal display device or the like.

[0002]

2. Description of the Related Art Natural light such as sunlight and light from ordinary artificial light sources such as lamps are unpolarized (randomly polarized light). However, polarized light (for example, linearly polarized light,
Components such as circularly polarized light and elliptically polarized light).
The extracted polarized light can be used for various optical devices. A liquid crystal display device that is widely used at present is a device that displays an image using the property of polarized light. The polarizing plate in a broad sense includes a linear polarizing plate, a circular polarizing plate, and an elliptically polarizing plate. However, a polarizing plate in a narrow sense usually means a linear polarizing plate and is the most basic polarizing plate. In this specification,
Unless otherwise specified, the polarizing plate means a linear polarizing plate.

As a linear polarizing plate, a light-absorbing polarizing plate made of a polyvinyl alcohol film is generally used. The polyvinyl alcohol-based polarizing plate is manufactured by stretching a polyvinyl alcohol-based film and adsorbing iodine or a dichroic dye. At this time, the transmission axis (polarization axis) of the polarizing plate corresponds to a direction perpendicular to the stretching direction of the film. The light-absorbing polarizing plate transmits only a polarized light component parallel to the polarization axis and absorbs a polarized light component in a direction perpendicular to the polarized light component. Therefore, the light use efficiency is theoretically 50% or less, and is actually a lower value.

In order to improve the light use efficiency of the polarizing plate,
It has been proposed to use a light-scattering polarizing plate instead of or in addition to the light-absorbing polarizing plate.
The light-scattering polarizing plate also transmits only the polarized light component parallel to the polarization axis, similarly to the light-absorbing polarizing plate. However, in the light-scattering type polarizing plate, the polarization component in the direction orthogonal to the polarization axis is scattered forward or backward without absorbing, thereby improving the light use efficiency of the polarizing plate. Light utilization efficiency improvement methods using light-scattering polarizing plates include:
Several approaches have been proposed.

First, there is an improvement method by depolarizing the forward scattered light. In the light-scattering type polarizing plate, the polarization component in the direction orthogonal to the polarization axis is scattered forward or backward. Of these, the forward scattered light is depolarized, and the polarization direction of the forward scattered light is rotated from the polarization direction of the incident light, so that the polarization component of the light scattering polarizer in the polarization axis direction is larger than that of the incident light. In a light-scattering polarizer, when many particles exist in the thickness direction, the degree of depolarization increases due to multiple scattering. As described above, when the scattering polarizer is used, the light use efficiency is improved by depolarizing the forward scattered light as compared with the case where only the light absorbing polarizer is used.

Next, there is an improvement method accompanying depolarization of the backscattered light. Back-scattered light of the polarization component in the direction orthogonal to the polarization axis of the light-scattering polarizing plate is depolarized when back-scattered. The backscattered light is reflected by the metal reflector disposed on the back of the backlight, which is the light source, and reenters the light scattering polarizer. Here, the re-incident light is depolarized when it is backscattered, and a polarization component parallel to the polarization axis of the scattering polarizer is generated, and this polarization component transmits through the scattering polarizer. As described above, the light use efficiency can be improved by repeating back scattering by the light scattering polarizer and reflection by the metal reflector.

[0007] There is also a method of improving the polarization direction of the backscattered light. When linearly polarized light enters the optical system in which the λ / 4 plate and the metal reflection plate are arranged at 45 ° to the slow axis of the λ / 4 plate, the reflected light is rotated by 90 ° with respect to the incident light. Will come back. Between the light scattering type polarizing plate and the metal reflecting plate arranged on the back of the backlight, the polarization axis of the light scattering type polarizing plate and the slow axis of the λ / 4 plate are 45 °.
The same effect as described above can be obtained by arranging them so that

The distribution of the direction of polarization of the light scattered backward by the light-scattering polarizing plate is large in the direction orthogonal to the polarization axis of the light-scattering polarizing plate. The backscattered light passes through the λ / 4 plate, is reflected by the metal reflector, and is again incident on the light-scattering polarizer in the polarization direction distribution parallel to the polarization axis of the light-scattering polarizer. The polarization component parallel to the polarization axis passes through the light-scattering polarizing plate. Thus, by arranging the λ / 4 plate between the light scattering type polarizing plate and the metal reflecting plate, the light use efficiency can be improved.

For a light-scattering type polarizing plate, see JP-A-8-7
Nos. 6114, 9-274108, 9-2
No. 97204, Japanese Patent Application Laid-Open No. 11-502036,
No. 11-509014 and U.S. Pat.
No. 20, No. 5,825,543 and No. 5,867,316.

[0010]

Among the conventional light-scattering type polarizing plates, Japanese Patent Application Laid-Open Nos. 8-76114 and 9-2741.
No. 08, Japanese Translation of PCT International Publication No. 11-502036,
-509014 and U.S. Pat.
No. 5,825,543, and No. 5,867,316, the light-scattering polarizing plate is manufactured by stretching a polymer film in the same manner as the light-absorbing polarizing plate. In the production method by stretching the polymer film, stretching unevenness in the plane of the film is likely to occur, and it is difficult to obtain uniform scattering characteristics over a large area. Moreover, the non-uniformity of the in-plane scattering characteristics of the light-scattering polarizing plate as described above leads to unevenness of the in-plane luminance of the liquid crystal display device.

Also, OA Aphonin et al. (Liq
uid Crystals, 395, vol.
According to 993), in a film in which droplets of a nematic liquid crystal are dispersed in a continuous phase made of a polymer, stretching the film is most effective as a means for orienting the liquid crystal in a uniaxial direction. However, the present inventor has found that there is still a problem that scattering of a polarized light component in a direction orthogonal to the polarization axis is still weak with the above method alone.

An object of the present invention is to provide a method for manufacturing an optical film having polarization selectivity in order to improve the light use efficiency of a polarizing plate and to easily control the scattering characteristics.

[0013]

According to the present invention, there is provided a method for producing an optical film, comprising: applying or casting a liquid composition containing a liquid crystal compound on a transparent film support; and applying an electric field to the liquid crystal compound. In one direction. In addition, it is preferable to include a drying and stretching step after the step of applying or casting the composition liquid. Further, it is preferable that the composition liquid contains a continuous phase containing at least one water-soluble polymer compound and a dispersed phase containing at least one liquid crystalline compound. further,
It is preferable to use the optical film obtained by the above-mentioned method for producing an optical film as a light-scattering polarizing plate or a light-absorbing polarizing plate.

According to a sixth aspect of the present invention, in the method for producing an optical film, a film having a phase separation structure comprising a continuous phase containing at least one water-soluble polymer compound and a dispersed phase containing at least one liquid crystalline compound is applied. Or, it is formed by drying after casting, and an electric field is applied in one direction parallel to the film surface,
The liquid crystal compound is oriented in one direction, and after this orientation, the orientation of the liquid crystal compound is fixed. As in the method for manufacturing an optical film according to claim 7, a film formed by coating or casting and then drying is stretched in one direction, and an electric field in the same direction as the stretching is applied to the film. By applying, the liquid crystal compound is aligned in one direction, and after this alignment,
The orientation of the liquid crystal compound may be fixed.

The strength of the applied electric field is 5 to 50 kV.
/ Cm. If the electric field is weak, a sufficient orientation effect cannot be obtained, and if it exceeds 50 kV / cm, dielectric breakdown may occur, which is not preferable from the viewpoint of safety in the manufacturing process.

As a method of fixing the arrangement of the liquid crystal compounds, it is preferable to cross-link the liquid crystal compounds by radiating ultraviolet rays and performing radical polymerization. As a cross-linking method, there is thermal polymerization in addition to radical polymerization. However, when thermal polymerization is used, the arrangement of the aligned liquid crystal compounds is disturbed by an electric field, which is not preferable. This is because when the temperature is increased, the liquid crystal compound changes from a nematic layer to an isotropic layer.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below, but the present invention is not limited to these embodiments. Further, terms used in the following description indicate preferred examples of the present invention, and do not indicate the meaning or technical scope of the terms of the present invention.

FIG. 1 is a schematic sectional view showing the basic structure of a light-scattering type polarizing plate of the present invention. In the light-scattering polarizing plate 10 shown in FIG. 1, a polarization selection layer 12 is provided on a web 11, and is separated into a continuous phase 13 and a dispersed phase 14. The dispersed phase 13 is made of an optically anisotropic compound having birefringence, and the two refractive indices n1 and n2 of the dispersed phase differ depending on the properties of the optically anisotropic compound used or the degree of orientation in the dispersed phase. In order for the light-scattering polarizing plate to function as a polarization-selective optical film, one of n1 and n2 needs to have a value substantially equal to the refractive index of the continuous phase, that is, less than 0.05. N1 at which the refractive indices are substantially equal
Alternatively, the direction of n2 corresponds to the transmission axis of the polarization selection layer.

The refractive index (n1) in the axial direction including the plane of polarization of the polarized light at which the total light transmittance of the polarization selection layer of the dispersed phase becomes the maximum, and the refractive index in the axial direction including the plane of polarization of the polarized light at which the total light transmittance becomes the minimum. Birefringence (| n1-n) which is the absolute value of the difference from the refractive index (n2)
2 |) is preferably 0.05 to 1.0, more preferably 0.10 to 1.0, and most preferably 0.15 to 1.0.
The continuous phase may have a birefringence of less than 0.05, and the difference in refractive index between the optically anisotropic compound and either n1 or n2 is less than 0.05, preferably less than 0.01, and more preferably less than 0.01. What is necessary is just less than 0.001. By the relationship between the refractive index of the continuous phase and the dispersed phase satisfies the above relationship,
The optical film functions as a polarization-selective optical film. The direction in which the refractive indices of the continuous phase and the dispersed phase are substantially equal, that is, less than 0.05, corresponds to the transmission axis of the polarization selective layer.

[Web] The web for holding a film having polarization selectivity to form a light-scattering polarizing plate is not particularly limited as long as it is transparent. Those having a light transmittance of 80% or more are preferable, and those having optical isotropy when viewed from the front are preferable. Therefore, the web is preferably made of a material having a small intrinsic birefringence. Such materials include ZEONEX, ZEONOR (manufactured by ZEON CORPORATION),
Commercial products such as ARTON (manufactured by JSR Corporation) and Fujitac (triacetyl cellulose manufactured by Fuji Photo Film Co., Ltd.) can be used. Furthermore, even for a material having a large intrinsic birefringence such as polycarbonate, polyester, polyarylate, polysulfone, and polyethersulfone, conditions such as solution casting and melt extrusion, as well as longitudinal and transverse stretching conditions are appropriately set. Can be obtained. When a protective film for protecting a polarizing layer of a polarizing plate is used as a web, triacetyl cellulose is particularly preferred. The thickness of the web is preferably from 10 to 500 μm, particularly preferably from 40 to 200 μm.

[0021] An undercoat layer may be provided on the web in order to impart adhesion to an adjacent layer. The material for forming such an undercoat layer is not particularly limited. For example, on triacetyl cellulose, gelatin, poly (meth) acrylate resin and its substitute, styrene-butadiene resin and the like are used. Further, a surface treatment such as a chemical treatment, a mechanical treatment, a corona treatment, and a glow discharge treatment may be performed.

[Continuous Phase] In the present invention, the water-soluble polymer compound contained in the continuous phase of the film having polarization selectivity only needs to be optically isotropic in the polarization selection layer. There is no particular limitation. Here, the optical isotropy means that the birefringence is less than 0.05. That is, the optically anisotropic compound can also be used as an optically isotropic compound if it is isotropic in the polarization selection layer. In addition, since most of the liquid crystal compounds used for the dispersed phase are soluble in an organic solvent, in order to obtain a phase-separated structure only by coating, a coating liquid in which liquid crystals are dispersed in an aqueous phase containing a water-soluble polymer compound is used. Just use it. In addition, since the use of water as a solvent has little effect on the environment, a water-soluble polymer compound is particularly preferable. Since the continuous phase is preferably not affected by an external environment such as temperature and humidity, a polymer having a crosslinked structure is preferable. The continuous phase is 5 to 95% by weight of the polarization selective layer, preferably 20 to 90% by weight, more preferably 50 to 8% by weight.
0% by weight.

As the water-soluble polymer compound, gelatin,
Examples include agarose, cellulose, polyvinyl alcohol and derivatives thereof, or polyacrylic acid, polygalacturonic acid, polyalginic acid and salts thereof. Also, from the viewpoint of dispersion stability and liquid crystal orientation during stretching,
Polyvinyl alcohol or modified polyvinyl alcohol is most preferred.

In order to make the water-soluble polymer compound into a continuous phase and the liquid crystal compound into a dispersed phase, a liquid crystal compound or an organic solvent solution of the liquid crystal compound is added to an aqueous polymer solution and irradiated with ultrasonic waves. Alternatively, any of known methods such as high-speed stirring can be used. In order to reduce the load of solvent drying, the concentration of the aqueous solution of the polymer compound is preferably 10% or more. It is preferable that the liquid crystal compound is added in a liquid state without being diluted with an organic solvent. As the dispersed particle size of the liquid crystalline compound, the average particle size is preferably 1000 nm or less, and particularly preferably 400 nm or less.

[Dispersed Phase] As the liquid crystalline compound contained in the dispersed phase of the film having polarization selectivity in the present invention, rod-shaped liquid crystalline molecules are preferably used. As the rod-like liquid crystal molecules, azomethines, azoxys, cyanobiphenyls, cyanophenyl esters, benzoates,
Preference is given to cyclohexanecarboxylic acid phenyl esters, cyanophenylcyclohexanes, cyano-substituted phenylpyrimidines, phenyldioxanes, tolanes and alkenylcyclohexylbenzonitrile. The rod-like liquid crystal molecules also include metal complexes. For rod-like liquid crystal molecules, see Quarterly Chemistry Review Vol. 22, Chapters 4, 7, and 11 of the Chemical Society of Japan (1994), edited by The Chemical Society of Japan, and the Liquid Crystal Device Handbook, edited by the 142nd Committee of the Japan Society for the Promotion of Science There is a description in Chapter 3.

The intrinsic birefringence of the rod-like liquid crystal molecules is preferably 0.10 or more. The rod-like liquid crystal molecules preferably have a polymerizable group. As the polymerizable group, an unsaturated polymerizable group, an epoxy group or an aziridinyl group is preferable,
Unsaturated polymerizable groups are more preferred, and ethylenically unsaturated polymerizable groups are most preferred. The rod-like liquid crystal molecules preferably have a molecular structure that is substantially symmetric with respect to the minor axis direction. For that purpose, it is preferable that the rod-shaped liquid crystal structure has polymerizable groups at both ends. The disperse phase accounts for 5 to 95% by weight, preferably 10 to 80% by weight, more preferably 20 to 50% by weight of the polarization selective layer.

[Surfactant] A surfactant may be added to reduce the dispersed particle size of the liquid crystal compound and to impart dispersion stability. The surfactant is not particularly limited, and is nonionic, ionic (anion, cation, betaine)
Either can be used. As nonionic surfactants,
Polyoxyethylene, polyoxypropylene, polyoxybutylene, a surfactant having a nonionic hydrophilic group of polyglycidyl and sorbitan, specifically, polyoxyethylene alkyl ether, polyoxyethylene alkyl phenyl ether, polyoxyethylene Ethylene-polyoxypropylene glycol, polyhydric alcohol fatty acid partial ester, polyoxyethylene polyhydric alcohol fatty acid partial ester, polyoxyethylene fatty acid ester, polyglycerin fatty acid ester, fatty acid diethanolamide, triethanolamine fatty acid partial ester can be exemplified. .

The anionic surfactants include carboxylate, sulfate, sulfonate and phosphate ester salts. Representative examples are fatty acid salt, alkylbenzene sulfonate, alkylnaphthalene sulfonate,
Alkyl sulfonate, α-olefin sulfonate, dialkyl sulfosuccinate, α-sulfonated fatty acid salt, N-methyl-N-oleyltaurine, petroleum sulfonate, alkyl sulfate, sulfated oil, polyoxyethylene alkyl Ether sulfate, polyoxyethylene alkyl phenyl ether sulfate, polyoxyethylene styrenated phenyl ether sulfate, alkyl phosphate, polyoxyethylene alkyl ether phosphate,
And naphthalene sulfonate formaldehyde condensate.

As the cationic surfactant, an amine salt,
Examples thereof include quaternary ammonium salts, pyridum salts, and the like. Primary to tertiary fatty amine salts, quaternary ammonium salts (tetraalkylammonium salts, trialkylbenzylammonium salts, alkylpyridium salts, alkylimidazolium salts, and the like) ). Examples of the amphoteric surfactant include carboxybetaine and sulfobetaine, and N-trialkyl-N-carboxymethylammonium betaine and N-trialkyl-N
-Sulfoalkylene ammonium betaine and the like.

[0030] These surfactants are described in Application of Surfactants (Koshobo, Takao Karimei, published September 1, 1980). In the present invention, a preferred surfactant is not particularly limited in its use amount, and any surfactant may be used as long as desired surfactant properties can be obtained. In addition, the addition amount of these surfactants is 0.00 0.001 g of the liquid crystal of the dispersed phase.
1 to 1 g is preferable, and 0.01 to 0.1 g is particularly preferable.

A liquid in which a liquid crystalline compound is dispersed in a continuous phase composed of a water-soluble polymer is subjected to a dip coating method, an air knife coating method, an extrusion method, a slide bead method, a curtain coating method, a roller coating method, a wire coating method. It can be applied on a support by a bar coating method, a gravure coating method, or the like. Further, a plurality of layers may be simultaneously coated on the support by an extrusion method, a slide bead method, a curtain coating method, or the like.

[Production Method] FIG. 2 shows a production line for an optical film having a polarization selective film according to the present invention. In a disperser 41, a liquid 42 in which a liquid crystalline compound is dispersed in a solution of a water-soluble polymer compound is applied to a coating die 4
4 is applied by a pump 43 to a support roll 45 which is conveyed in an endless shape on a backup roll 46 for application. Subsequently, the film is sent to a drying device 48, and after the coating film 47 obtained by evaporating the solvent is separated from the support 45, the liquid crystal compound in the film is oriented in one direction by an electric field applying device 49, and the polarization selectivity is improved. After the application, the orientation of the liquid crystal compound is fixed by the fixing treatment device 50. Subsequently, the coating film 47 is
The web 52 is bonded by a bonding device 53 and wound into a roll by a winder 51 to obtain a light-scattering polarizing plate. The bonding device 53 has a mechanism for applying the glue to the web 52, pressing the coating film 47 to bond the adhesive, and then drying with hot air. The electric field applying device 49 includes a DC high voltage power supply 54, a conductive backup roll 56 provided with an insulating coating layer 55, and a conductive backup roll 57. The DC high voltage is supplied to the backup roll 56, and the backup roll 57 is grounded. Is done.

As the support 45, an endless support such as a band or a drum, or a web-like support is used. When a web is used as the support, a liquid in which a liquid crystalline compound is dispersed in a continuous phase composed of a water-soluble polymer is applied onto the web, and then a unidirectional electric field is applied as it is, thereby obtaining a liquid crystalline compound. After imparting polarization selectivity by orienting, a light-scattering polarizing plate is obtained. Alternatively, it may be laminated on another web or transferred to another web to form a light-scattering polarizing plate.

As the drying device 48, a device for blowing hot air having a low solvent concentration, a device for irradiating infrared rays, or any other known device can be used. Examples of the shape of the dispersion plate for uniformly blowing the warm air having a low concentration of the solvent to the membrane surface include a perforated plate, a slit plate, and a nozzle plate. Heat sources for the method of irradiating infrared rays include heat generated by electric resistance, high-temperature fluids such as water vapor and oil, and the like.

When the solvent is volatilized to some extent from the coating film 47 shown in FIG. 4 and the coating film 47 has a self-holding property, the coating film 47 is peeled off from the support 45 and the coating film in contact with the support 45 is removed. By volatilizing the solvent from the surface of the film 47,
The problem that the liquid crystal compound having a large dispersed particle size gathers on the film surface where the solvent is volatilized and the distribution of the dispersed particle size of the liquid crystal compound in the film thickness direction is widened is solved, and there is an effect of increasing the degree of orientation of the liquid crystal compound.

The application of an electric field to the coating film 47 in the electric field applying device 49 differs depending on whether the anisotropy (Δε) of the dielectric constant of the liquid crystalline compound is positive or negative. When the anisotropy (Δε) is positive, the solvent is volatilized from a liquid in which a liquid crystalline compound is dispersed in a continuous phase made of a water-soluble polymer, and the solvent is volatilized. A method of applying an electric field in the same direction is preferred. Specifically, a high DC voltage is applied to the conductive backup roll 57 for transporting the film by the DC high voltage power supply 54, and the adjacent conductive backup roll is grounded, so that the direction is the same as the traveling direction of the film. Thus, a uniform electric field can be applied near the film surface. In order to avoid a short circuit or spark discharge, the surface of the conductive backup roll 56 to which a high DC voltage is applied is preferably formed with an insulating coating layer 55 of an insulating material such as ceramics such as alumina. Further, as a method of electrically connecting the backup roll and the DC high-voltage power supply, a ball bearing may be used as a bearing, and the conductive box storing the bearing may be connected to the DC high-voltage power supply. As a method for applying an electric field parallel to the plane of the membrane and in the same direction as the traveling direction of the membrane for a longer time, a conductive backup roll connected to a DC high voltage, and a conductive backup roll grounded, May be arranged alternately in the direction of travel.

When the anisotropy Δε of the dielectric constant of the liquid crystal compound is negative, the liquid crystal compound is parallel to the surface of the film obtained by volatilizing the solvent from the liquid in which the liquid crystal compound is dispersed in the continuous phase composed of the water-soluble polymer. And a method in which an electric field is applied in a direction perpendicular to the traveling direction of the film. Specifically, a plurality of rod-shaped or plate-shaped conductive materials are arranged as electrodes in parallel with the film traveling direction and close to the film surface, and a DC high voltage is applied to one electrode, and the other is applied to the other electrode. The electrode may be grounded. In order to avoid a short circuit or spark discharge, the surface of the backup roll to which a high DC voltage is applied is preferably coated with an insulating material such as ceramic such as alumina.

The strength of the electric field applied to the film in which the liquid crystalline compound is dispersed is preferably 5 kV / cm or more.
More preferably, it is 10 kV / cm or more. However, the upper limit is 50 kV / cm from the viewpoint of change in characteristics of the coating film 47 and safety in a manufacturing process.

In the fixing device 50 for fixing the liquid crystal compounds, the liquid crystal compounds having a crosslinkable functional group at the terminal are crosslinked. Examples of the crosslinkable functional group include a double bond group. As a method of cross-linking, there is a method in which a liquid crystal compound is radically polymerized by irradiating an ultraviolet ray to a coating film and radicals generated from an initiator contained in the coating film. Ultraviolet light can be easily generated by a mercury lamp or a metal halide lamp.

FIG. 3 shows another embodiment of a production line for an optical film having the polarization selective film according to the present invention. The same devices as those in FIG. 2 are denoted by the same reference numerals. The coating film 47 obtained by evaporating the solvent is first stretched in one direction by a stretching device 58. This stretching orients the liquid crystalline compound in one direction, and imparts a certain degree of polarization selectivity. Thereafter, when an electric field is applied by the electric field applying device 49, the liquid crystal compound in the film is further oriented in one direction, and stronger polarization selectivity is provided. After this,
The orientation of the liquid crystal compound is fixed by the fixing device 50. Subsequently, the coating film 47 is bonded to the web 52 by the bonding device 53 and wound into a roll by the winder 51. In the optical film formed in the present embodiment, since the coating film 47 is stretched before the application of the electric field and the fixing treatment, an optical film in which the liquid crystal compound is more appropriately oriented can be obtained.

As a method of continuously stretching the film in which the liquid crystalline compound is dispersed, there is a method using a nip roll, a method in which both ends of the film are clipped and the film is stretched in the width direction of the film, but is not necessarily limited thereto. Not done. In the method using the nip roll, the film is wound around the nip roller and nipped without slipping, these two rolls are driven by a motor, and the rotation speed of the two rolls is relatively changed, so that the film is moved in the transport direction of the film. Stretch.

When the water-soluble polymer, which is the continuous phase of the film, is swollen with a solvent, for example, water, and stretched, the degree of orientation of the liquid crystal compound in the dispersed phase can be further increased by stretching. As a method of swelling the film with a solvent, there is a method of applying a solvent to the film surface by a wire bar coating method or the like, or a method of spraying the solvent on the film surface, but is not necessarily limited thereto.

In order to facilitate the stretching step, a compound for lowering the glass transition temperature of the compound in the continuous phase may be added. When using a water-soluble polymer compound,
As pointed out by them, glycerin is particularly preferred as a plasticizer, but is not limited thereto.

FIG. 4 shows the most basic configuration of a liquid crystal display device. The general liquid crystal display device 15 has an edge light type backlight light source 21 on the rearmost surface as a light source. This light source is a backlight light source 21 in order from the back.
And a light guide plate 23 for emitting the light to the surface. Among the liquid crystal display devices, there is a type using a direct backlight without using a light guide plate, but any type of the light scattering type polarizing plate of the present invention is effective.

Above the light source is a liquid crystal cell 26 sandwiched between two conventional light-absorbing polarizing plates 24 and 25, thereby having an image display function. The light emitted from the light source is at least 50%
Since the light is absorbed, this configuration theoretically cannot provide a light use efficiency of 50% or more.

FIG. 5 is a schematic sectional view of a liquid crystal display device having a light-scattering polarizing plate formed from the optical film of the present invention. The same members as those in FIG. 4 are denoted by the same reference numerals. The light-scattering polarizing plate 31 of the present invention selectively transmits polarized light in the same direction as the transmission axis of the light-absorbing polarizing plate 24, and depolarizes a part of polarized light orthogonal to the polarizing plate transmission axis by forward scattering. The polarization plane is aligned in the transmission axis direction. Thereby, the light use efficiency is improved. That is,
Part of the light returns to the light source side due to back scattering, is depolarized by the light guide plate or the like, is reflected by the reflection plate, returns to the light scattering type polarizing plate 31, and is reused, further improving the use efficiency. .

The light-scattering polarizing plate 31 using the polarization-selective optical film of the present invention is usually used by laminating it with the light-absorbing polarizing plate 24. Laminated so that the transmission axis of the light-scattering polarizing plate and the transmission axis of the light-absorbing polarizing plate are substantially parallel,
This laminate is used as a backlight-side polarizing plate of a liquid crystal cell,
In addition, the polarization selective layer of the polarizing plate is disposed facing the backlight. In addition, a metal reflector is disposed on the back surface of the backlight.

It is preferable to further arrange a λ / 4 plate (not shown) between the backlight and the laminate of the light scattering type polarizing plate and the light absorbing type polarizing plate. Here, by arranging the transmission axis of the light scattering type polarizing plate and the light absorbing type polarizing plate and the slow axis of the λ / 4 plate substantially at 45 °,
The light scattering efficiency can be increased by the backscattered polarization rotation type.

By using a polarization-selective optical film or a light-scattering polarizing plate in a liquid crystal display device, the light use efficiency is increased, and as a result, the brightness of the display can be increased. In order to increase the luminance, the transmittance Tmax on the polarization plane where the total light transmittance is maximized is 75%.
As described above, the transmittance Tmin at the minimum polarization plane is preferably 60% or less, and Tmax is 80% or more and Tm
It is more preferable that in is 50% or less.

In the above embodiment, the light-scattering type polarizing plate has been described. In addition, the light-absorbing type polarizing plate can also orient the liquid crystal compound in one direction by applying an electric field. The manufacturing method of the present invention may be applied similarly to the light scattering type polarizing plate. In the case of a polarizing plate that absorbs light, the liquid crystal compound itself may absorb visible light (that is, may be a dye), or may be mixed with a dye arranged in the same direction as the aligned liquid crystal compound. Examples of the compound having a liquid crystal property as a dye include a lyotropic (Liotropic) liquid crystal. As described above, the present invention can be used as long as the manufacturing method is a method of applying or casting a composition liquid containing a liquid crystal compound.

[0051]

EXAMPLES The present invention will be described in detail with reference to the following examples, but the present invention is not limited to these examples.

[Preparation of Coating Solution for Light-Scattering Polarizing Plate] Using an ultrasonic disperser (UH-600, manufactured by SMT Corporation), the liquid temperature was 15 ° C., the ultrasonic output was 600 W, and the processing time was 20 minutes. Under conditions of 6 minutes, 66.5 g of a nematic liquid crystal compound having a crosslinkable group at both ends in 1000 g of a 20 wt% aqueous solution of polyvinyl alcohol (PVA205, manufactured by Kuraray Co., Ltd.).
And Irgacure 907 (JSR
0.6 g was dispersed. The average particle size of the nematic liquid crystal compound dispersed in the coating solution for the light-scattering polarizing plate was measured using a laser scattering particle size meter (model: LPA3000).
/ 3100, manufactured by Otsuka Electronics Co., Ltd.), the average particle size was 250 nm.

Example 1 A light-scattering type polarizing plate was produced by the production line shown in FIG. 100 μm thick,
Using polyethylene terephthalate (manufactured by Fuji Photo Film Co., Ltd.) having a width of 18 cm as a support 45, 0.5 m / m
The light-scattering polarizing plate coating solution 42 was applied to a thickness of 250 μm on a support 45 using an extrusion-type coating die 44. Subsequently, after the coating film 47 was formed by the drying device 48 which blows hot air at 50 ° C., the coating film 47 separated from the support 45 was applied with an electric field of 5 kV / cm for 1.2 seconds by the electric field applying device 49. 8J /
After irradiating with ultraviolet rays of ² cm ² , a 5 wt% aqueous solution of polyvinyl alcohol (PVA117, manufactured by Kuraray Co., Ltd.) was used as a sizing agent and attached to a web 52 of 100 μm thick triacetyl cellulose (manufactured by Fuji Photo Film Co., Ltd.). The resultant was dried at 120 ° C. to prepare a light-scattering polarizing plate of Example 1. Subsequently, an experiment was performed under the same conditions in which the electric field applied by the application device 49 was set to 10, 15 kV / cm.

Example 2 A light-scattering type polarizing plate was produced by the production line shown in FIG. 100 μm thick,
Using polyethylene terephthalate (manufactured by Fuji Photo Film Co., Ltd.) having a width of 18 cm as a support 45, 0.5 m / m
The substrate was conveyed at a speed of in, and the coating liquid for a light-scattering polarizing plate was applied on a support 45 with a thickness of 250 μm using an extrusion die as a coating die 44. Subsequently, the coating film 47 was formed by a drying device 48 in which hot air of 50 ° C. blows, and then the coating film 47 peeled off from the support 45 was stretched by a stretching processing device 58 in the traveling direction of the coating film 47. The stretching ratio was 1.5 times. Subsequently, an electric field of 20 kV / cm was applied by the electric field applying device 49 for 1.2 seconds. After irradiating the coating film 47 with ultraviolet rays of 8 J / cm ² by the fixing treatment device 50, polyvinyl alcohol (PVA11)
7, a 5 wt% aqueous solution of Kuraray Co., Ltd.)
A 100 μm-thick triacetyl cellulose (manufactured by Fuji Photo Film Co., Ltd.) was attached to the web 52 and
It dried at ℃ and produced the light-scattering type polarizing plate used as Example 2. Subsequently, an experiment was performed under the same conditions in which the electric field applied by the application device 49 was set to 30 kV / cm.

Comparative Example 1 A light-scattering type polarizing plate was prepared using the production line shown in FIG. No electric field was applied by the electric field applying device 49 in the line. Thickness 1
Polyethylene terephthalate (manufactured by Fuji Photo Film Co., Ltd.) having a width of 18 μm and a width of 18 cm was used as the support 45.
It was conveyed at a speed of 0.5 m / min, and the above-mentioned light scattering type polarizing plate coating liquid 42 was coated on a support 45 with a thickness of 250 μm using an extrusion die as a coating die 44. Subsequently, the coating film 47 was formed by a drying device 48 in which warm air of 50 ° C. blows, and then separated from the support 45. After irradiating the coating film 47 with 8 J / cm ² ultraviolet rays by the fixing treatment device 50, the ultraviolet rays were applied and bonded to the web 52 under the same conditions as in Example 1, and dried at 120 ° C. to obtain Comparative Example 1. A scattering type polarizing plate was prepared.

Comparative Example 2 A light-scattering type polarizing plate was prepared using the production line shown in FIG. No electric field was applied by the electric field applying device 49 in the line. The steps from the application of the light scattering type polarizing plate coating liquid 42 to the stretching of the coating film 47 were performed under the same conditions as in Example 2. Subsequently, the coating film 47
Under the same conditions as in Example 2, UV irradiation and lamination with the web 52 were performed to produce a light-scattering polarizing plate as Comparative Example 2.

[Evaluation of Optical Performance of Light-Scattering Polarizing Plate] The light transmittance (total light transmittance) of the light-scattering polarizing plate thus prepared was measured using a haze meter MODEL 1001DP (manufactured by Nippon Denshoku Industries Co., Ltd.). It was measured. The measurement is performed by inserting a polarizer between the light source and the film, and the transmittance of the polarizer and that of the light-scattering polarizing plate (the axis orthogonal to the stretching direction) are made the same, and the parallel transmittance and the orthogonality are set. Were evaluated as orthogonal transmittance. When there is polarization selectivity, the parallel type has a higher transmittance than the orthogonal type. The degree of polarization was determined from the obtained parallel transmittance and orthogonal transmittance. The degree of polarization is obtained by multiplying the square root of a value obtained by dividing (parallel transmittance-orthogonal transmittance) by (parallel transmittance + orthogonal transmittance) by 100. Table 1 collectively shows the optical performance evaluations of the light-scattering polarizing plates of the examples and the comparative examples.

[0058]

[Table 1]

From Example 1, by applying an electric field to the film, the parallel transmittance of the light-scattering polarizing plate was increased, the orthogonal transmittance was reduced, and the degree of orientation of the liquid crystalline compound could be increased.
It can be seen that the polarization selection performance was improved. In addition, Example 2 shows that the degree of orientation of the liquid crystal compound can be further increased by applying an electric field to the stretched film.

[0060]

According to the present invention, a step of coating or casting a liquid composition containing a liquid crystal compound on a transparent film support, and a step of applying an electric field to orient the liquid crystal compound in one direction. Therefore, an optical film having a large polarization selectivity can be easily manufactured. Further, by using this optical film, the light use efficiency of the polarizing plate is significantly improved.

[Brief description of the drawings]

FIG. 1 is a sectional view of a main part of a light-scattering type polarizing plate constituted by using an optical film according to the present invention.

FIG. 2 is a diagram showing a production line for an optical film according to the present invention.

FIG. 3 is a view showing another embodiment of the production line for the optical film according to the present invention.

FIG. 4 is a sectional view of a main part of a conventional liquid crystal display device.

FIG. 5 is a sectional view of a main part of a liquid crystal display device constituted by using the optical film according to the present invention.

[Explanation of symbols]

 11,52 Web 12 Polarization Selective Layer 13 Continuous Phase 14 Disperse Phase 21 Backlight Light Source 22 Reflector 23 Light Guide 24,25 Light Absorbing Polarizer 26 Liquid Crystal Cell 31 Light Scattering Polarizer 41 Disperser 42 Coating Solution 43 Pump 44 Coating die 45 Support 46 Coating backup roll 47 Coating film 48 Drying device 49 Electric field applying device 50 Fixing device 51 Winding device 53 Bonding device 54 DC high voltage power supply 55 Insulating coating layer 56, 57 Conductive backup roll 58 Stretching equipment

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H049 BA02 BA25 BA42 BA44 BB44 BB46 BB49 BC03 BC06 BC09 BC22 2H091 FA08X FA08Z FA11X FA11Z FA31Z FA41Z FB02 FC01 FC07 FC29 LA12 LA30 4F006 AA02 AA35 AA36 A04 AB06 AB06 AB04

Claims (9)

[The claims] 1. A method comprising: coating or casting a liquid composition containing a liquid crystal compound on a transparent film support; and applying an electric field to orient the liquid crystal compound in one direction. Method for producing an optical film. 2. The method for producing an optical film according to claim 1, further comprising a drying and stretching step after the step of applying or casting the composition liquid. 3. The optical device according to claim 1, wherein the composition liquid includes a continuous phase containing at least one water-soluble polymer compound and a dispersed phase containing at least one liquid crystalline compound. Film manufacturing method. 4. An optical film obtained by the method for producing an optical film according to any one of claims 1 to 3,
A method for producing an optical film used as a light-scattering polarizing plate. 5. An optical film obtained by the method for producing an optical film according to any one of claims 1 to 3,
A method for producing an optical film used as a light-absorbing polarizing plate. 6. A film having a phase separation structure composed of a continuous phase containing at least one water-soluble polymer compound and a dispersed phase containing at least one liquid crystalline compound, is formed by drying after coating or casting, A method for producing an optical film, characterized by applying a unidirectional electric field parallel to the film surface to orient the liquid crystal compound in one direction and fixing the orientation of the liquid crystal compound after the alignment. 7. A film having a phase separation structure composed of a continuous phase containing at least one water-soluble polymer compound and a dispersed phase containing at least one liquid crystalline compound, is formed by drying after coating or casting, This film is stretched in one direction, and an electric field in the same direction as the stretching is applied to the film to orient the liquid crystal compound in one direction, and after this alignment, the orientation of the liquid crystal compound is fixed. A method for producing an optical film. 8. The strength of the applied electric field is 5 to 50 k.
The method for producing an optical film according to any one of claims 1 to 7, wherein V / cm is V / cm. 9. The method according to claim 1, wherein the method of fixing the arrangement of the liquid crystal compounds is a method of irradiating ultraviolet rays to crosslink the liquid crystal compounds by radical polymerization. A method for producing the optical film described in the above.