JP4008417B2 - Broadband cholesteric liquid crystal film, manufacturing method thereof, circularly polarizing plate, linear polarizer, illumination device, and liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wide-band choresteric liquid crystal film which is made thin, has a wide reflection band and can be manufactured in a smaller number of manufacturing processes. <P>SOLUTION: The wide-band choresteric liquid crystal film is obtained by applying a liquid crystal mixture containing a polymerizable mesogene compound (a), a polymerizable chiral agent (b) and a photo-isomerization material (c) on a base material and subjecting the coating to UV polymerization, and it is characterised by having &ge;200 nm reflection band width. <P>COPYRIGHT: (C)2004,JPO&amp;NCIPI

Description

  The present invention relates to a broadband cholesteric liquid crystal film and a method for producing the same. The broadband cholesteric liquid crystal film of the present invention is useful as a circularly polarizing plate (reflection type polarizer). The present invention also relates to a linear polarizer, an illumination device, and a liquid crystal display device using the circularly polarizing plate. Furthermore, this invention relates to the polarizing element system using the said circularly-polarizing plate, and the viewing angle expansion liquid crystal display device using the said polarizing element system.

  In general, a liquid crystal display has a structure in which liquid crystal is injected between glass plates on which transparent electrodes are formed, and polarizers are arranged before and after the glass plate. A polarizer used in such a liquid crystal display is produced by adsorbing iodine, a dichroic dye, or the like on a polyvinyl alcohol film and stretching it in a certain direction. The polarizer itself thus produced absorbs light oscillating in one direction and passes only light oscillating in the other direction to produce linearly polarized light. For this reason, the efficiency of the polarizer cannot theoretically exceed 50%, which is the biggest factor for reducing the efficiency of the liquid crystal display. Also, due to this absorbed light, if the light source output is increased to a certain extent, the liquid crystal display device will display due to heat generated by the heat conversion of the absorbed light, or the polarizer will be destroyed, or the liquid crystal layer inside the cell will be affected by heat. It has caused adverse effects such as deterioration of quality.

  A cholesteric liquid crystal having a circularly polarized light separation function has a selective reflection characteristic that reflects only circularly polarized light whose wavelength is the spiral pitch of the liquid crystal, with the rotational direction of the spiral of the liquid crystal coincident with the circular polarization direction. By using this selective reflection characteristic, only specific circularly polarized light of natural light in a fixed wavelength band is transmitted and separated, and the rest is reflected and reused, whereby a highly efficient polarizing film can be manufactured. At this time, the transmitted circularly polarized light is converted into linearly polarized light by passing through the λ / 4 wavelength plate, and the direction of this linearly polarized light is aligned with the transmission direction of the absorbing polarizer used in the liquid crystal display, thereby achieving high transmittance. A liquid crystal display device can be obtained. That is, when a cholesteric liquid crystal film is used as a linear polarizer in combination with a λ / 4 wave plate, there is theoretically no light loss. Therefore, when a conventional absorption polarizer that absorbs 50% of light is used alone. In comparison, theoretically, the brightness can be improved by a factor of two.

However, the selective reflection characteristics of cholesteric liquid crystals are limited to a specific wavelength band, and it is difficult to cover the entire visible light range. The selective reflection wavelength region width Δλ of the cholesteric liquid crystal is
Δλ = 2λ · (ne−no) / (ne + no)
no: Refractive index of cholesteric liquid crystal molecules with respect to normal light ne: Refractive index of cholesteric liquid crystal molecules with respect to extraordinary light λ: Represented by the center wavelength of selective reflection, which depends on the molecular structure of the cholesteric liquid crystal itself. If ne-no is increased from the above formula, the selective reflection wavelength region width Δλ is widened, but ne-no is usually 0.3 or less. When this value is increased, other functions as liquid crystal (alignment characteristics, liquid crystal temperature, etc.) are insufficient and practical use is difficult. Therefore, in practice, the selective reflection wavelength region width Δλ is about 150 nm at the maximum. Many of the practically usable cholesteric liquid crystals were only about 30 to 100 nm.

The selective reflection center wavelength λ is
λ = (ne + no) P / 2
P: It is represented by the helical pitch length required for one rotation of the cholesteric liquid crystal. If the pitch is constant, it depends on the average refractive index and the pitch length of the liquid crystal molecules.

  Therefore, in order to cover the entire visible light region, a plurality of layers having different selective reflection center wavelengths are laminated, or the pitch length is continuously changed in the thickness direction to form an existence distribution of the selective reflection center wavelengths themselves. It was.

  For example, there is a method of continuously changing the pitch length in the thickness direction (see, for example, Patent Document 1, Patent Document 2, Patent Document 3, etc.). In this method, when the cholesteric liquid crystal composition is cured by ultraviolet exposure, the composition ratio of the liquid crystal compositions having different reaction rates is obtained by making a difference in the exposure intensity on the exposed surface side and the exit surface side and by making a difference in the polymerization rate. The change is provided in the thickness direction.

  The point of this method is to take a large difference in exposure intensity between the exposure surface side and the exit surface side. Therefore, in many cases of the above-mentioned prior art examples, a method of mixing an ultraviolet absorber with a liquid crystal composition, generating absorption in the thickness direction, and amplifying a difference in exposure amount due to an optical path length has been adopted. .

  However, the technique of continuously changing the pitch length as in Patent Document 1 requires a liquid crystal layer thickness of about 15 to 20 μm that is necessary for the function to be exhibited. Cost increase was inevitable due to the need for more. Further, the exposure time is required for about 1 to 60 minutes, and a long production line with an exposure line length of 10 to 600 m is required to obtain a line speed of 10 m / min. If the line speed is lowered, the line length can be reduced, but the production speed is inevitably lowered.

  As described in Patent Document 1, the cholesteric pitch is changed by a composition ratio change consisting of a mass transfer due to a difference in ultraviolet exposure intensity in the thickness direction for changing the pitch length in the thickness direction and a polymerization rate difference associated therewith. This is because it is difficult to form a rapid pitch change due to a theoretical problem to be controlled. In Patent Document 1, since the pitch length is different by about 100 nm between the short pitch side and the long pitch side, it is necessary to change the composition ratio greatly. To realize this, a considerable liquid crystal thickness, weak UV irradiation, and a long exposure time are required. is necessary.

  In Patent Document 3, the mobility of the substance whose pitch is changed is better than that of the material example used in Patent Document 1, so that film formation can be performed with an exposure amount of about 1 minute. However, even in this case, a thickness of 15 μm is required.

  In Patent Document 2, the temperature condition between the primary exposure and the secondary exposure is changed, and the time necessary for the composition ratio to change in the thickness direction is separately provided in a dark place. Also, about 10 to 30 minutes are necessary.

  In Patent Document 2 and Patent Document 3, the liquid crystal coating thickness is about 15 μm, and when compared with Patent Document 1 that requires about 20 μm, the liquid crystal layer has a pitch change due to a change in the composition ratio in the thickness direction. It can be seen that many cholesteric liquid crystal thicknesses and mass transfer times are required to cover the entire visible light range.

  Further, in Patent Document 4, at least three layers are necessary to cover the entire visible light region, and it is necessary when covering the long wavelength side to improve the viewing angle characteristics and taking countermeasures against oblique incident light. The number of stacked layers is 4 to 5 layers, and it is inevitable that the manufacturing process is complicated and the yield decreases due to an increase in the number of processes.

  By combining such a broadband circularly polarized light reflection plate with a phase difference plate, a diffused light source can be converted into parallel light. By using such a collimated light source and a diffusion plate, it is possible to construct a viewing angle expansion system for a liquid crystal display device.

  For example, as seen in Patent Document 5 and Patent Document 6, if a retardation plate that is controlled so that the phase difference value in the normal incidence direction and the phase difference value in the oblique incidence direction are specifically different is inserted between the polarizers, transmission is performed. The angle distribution of the light beam is restricted, and if an absorption polarizer is used, the light beam is transmitted only near the front and all the peripheral light beam is absorbed. If a circularly polarizing plate (reflection type polarizer) is used for this, light rays are transmitted only in the vicinity of the front surface and all peripheral light rays are reflected. If such a theory is used, it is possible to condense and collimate the light emitted from the backlight without causing an absorption loss.

A viewing angle widening system can be constructed by combining such a collimated backlight source and a diffuser plate with little backscattering and no depolarization. However, as described above, the conventional method of laminating a plurality of liquid crystal layers (Patent Document 4) has a problem of increasing the number of processes due to the multi-layer lamination, and the method of increasing the liquid crystal layer thickness as in Patent Document 1 and Patent Document 2 is used. Each has its own problem of high costs.
JP-A-6-281814 Japanese Patent No. 3272668 JP 11-248943 A JP-A-9-189811 Japanese Patent No. 2561483 Japanese Patent Laid-Open No. 10-321025

  SUMMARY OF THE INVENTION An object of the present invention is to provide a broadband cholesteric liquid crystal film that has a broadband reflection band, is thin, and can be manufactured with a small number of manufacturing steps, and a method for manufacturing the same.

  Another object of the present invention is to provide a circularly polarizing plate using the broadband cholesteric liquid crystal film, and further to provide a linear polarizer, an illumination device, and a liquid crystal display device using the circularly polarizing plate.

  Furthermore, an object of the present invention is to provide a polarizing element system using the circularly polarizing plate and to provide a viewing angle widening liquid crystal display device using the polarizing element system.

  As a result of intensive studies to solve the above problems, the present inventors have found that the above object can be achieved by the following broadband cholesteric liquid crystal film and a method for producing the same, and have completed the present invention. That is, the present invention is as follows.

The present invention is a single-layer cholesteric liquid crystal film obtained by applying a liquid crystal mixture containing a polymerizable mesogenic compound (a), a polymerizable chiral agent (b) and a stilbene (c) to a substrate and subjecting it to ultraviolet polymerization. And
The present invention relates to a broadband cholesteric liquid crystal film characterized by having a reflection bandwidth of 300 nm or more.

In the broadband cholesteric liquid crystal film, the pitch length of the cholesteric liquid crystal film is preferably continuously changed .

In the broadband cholesteric liquid crystal film, the liquid crystal mixture may contain a photopolymerization initiator (d) .

In the broadband cholesteric liquid crystal film, the polymerizable mesogenic compound (a) has one or more polymerizable functional groups, and the polymerizable chiral agent (b) has one or more polymerizable functional groups. Is preferred .

The present invention provides the broadband cholesteric liquid crystal film described above, wherein a liquid crystal mixture containing a polymerizable mesogenic compound (a), a polymerizable chiral agent (b) and a stilbene (c) is applied to a substrate and subjected to ultraviolet polymerization. Manufacturing method .

The present invention also relates to the following invention.
Circularly polarizing plate using the above broad band cholesteric liquid crystal film.

A linear polarizer obtained by laminating a λ / 4 plate on the circularly polarizing plate described above .

The linear polarizer as described above, obtained by laminating a cholesteric liquid crystal film, which is a circularly polarizing plate, on a λ / 4 plate so that the pitch length is continuously narrowed.

A linear polarizer obtained by adhering an absorptive polarizer to the transmission axis of the linear polarizer described above so that the direction of the transmission axis is aligned.

An illumination device comprising the circularly polarizing plate described above or the linear polarizer described above on a surface side of a surface light source having a reflective layer on a back surface side.

A liquid crystal display device comprising a liquid crystal cell on a light emitting side of the illumination device described above .

Between at least two reflective polarizers (a) in which the wavelength bands of selective reflection of polarized light overlap each other,
A retardation layer (b) having a front phase difference (normal direction) of substantially zero and a phase difference of λ / 8 or more with respect to incident light that is inclined by 30 ° or more with respect to the normal direction is disposed. A polarizing element system,
A polarizing element system, wherein the reflective polarizer (a) is the circularly polarizing plate described above .

The polarizing element system as described above , wherein the selective reflection wavelengths of at least two layers of the reflective polarizer (a) overlap each other in a wavelength range of 550 nm ± 10 nm.

The polarizing element system as described above , wherein the retardation layer (b) has a fixed planar orientation of a cholesteric liquid crystal phase having a selective reflection wavelength region other than the visible light region.

The polarizing element system as described above, wherein the retardation layer (b) has a homeotropic alignment state of a rod-like liquid crystal fixed.

The polarizing element system as described above, wherein the retardation layer (b) is one in which the nematic phase or columnar phase alignment state of the discotic liquid crystal is fixed.

The polarizing element system as described above, wherein the retardation layer (b) is a biaxially oriented polymer film.

The polarizing element system as described above, wherein the retardation layer (b) is an inorganic layered compound having negative uniaxiality and fixed in orientation so that the optical axis is in the normal direction of the surface.

A backlight system in which a diffused light source is converted into a parallel light using the polarizing element system described above ,
A liquid crystal cell through which the collimated light beam is transmitted;
A polarizing plate disposed on both sides of the liquid crystal cell;
A viewing angle widening film for diffusing transmitted light, disposed on the viewing side of the liquid crystal cell;
A liquid crystal display device with a wide viewing angle, characterized by containing at least.

A λ / 4 plate is arranged on the viewing side (liquid crystal cell side) of the polarizing element system described above, and the axial direction of linearly polarized light obtained by transmission and the transmission axis direction of the lower surface side (light source side) polarizing plate of the liquid crystal display device The viewing angle widening liquid crystal display device as described above , wherein the viewing angle expansion liquid crystal display device is arranged in alignment.

The viewing angle enlarging liquid crystal display device as described above , wherein a diffusion plate substantially free from backscattering and depolarization is used as the viewing angle enlarging film.

The viewing angle expansion liquid crystal display device according to any one of the above , wherein each layer is laminated using a translucent adhesive or pressure-sensitive adhesive.

The broadband cholesteric liquid crystal film of the present invention is obtained by ultraviolet polymerization of a polymerizable liquid crystal mixture, and the liquid crystal mixture contains stilbene (c) as a photoisomerization material. Such stilbene (c) realizes shortening of the ultraviolet irradiation time and thinning of the coating thickness.

Stilbene (c) has been reported to be able to reversibly control the selective reflection band of cholesteric liquid crystal by photoisomerization reaction, as described in the 1999 Proceedings of the Annual Meeting of the Japanese Liquid Crystal Society 66-69. . For example, azobenzene undergoes an isomerization reaction from a trans form to a cis form by irradiating ultraviolet rays around 365 nm, from a cis form to a trans form by visible light or heat near 440 nm. That is, it has been reported that when a substrate coated with a liquid crystal mixture containing stilbene (c) is irradiated with ultraviolet rays, the reflection band of the cholesteric liquid crystal shifts.

When stilbene (c) is added to the liquid crystal mixture and irradiation is performed so that the ultraviolet irradiation amount is distributed in the thickness direction, isomerization from trans to cis further proceeds on the ultraviolet irradiation side. On the other hand, isomerization from trans to cis hardly proceeds on the side opposite to the ultraviolet irradiation side. Therefore, a distribution difference relating to the trans-cis abundance ratio appears in the thickness direction, and it is possible to manufacture a broadband cholesteric liquid crystal film having a selective reflection wavelength region width covering the entire visible light region in a single layer. The broadband cholesteric liquid crystal film thus obtained functions as a broadband circularly polarized light reflector, has optical properties equivalent to those of Patent Documents 1 to 4 and the like, can reduce the thickness, and can further reduce the manufacturing process. Cost can be reduced by drastic reduction.

  That is, the broadband cholesteric liquid crystal film of the present invention can be thinned, and the amount of expensive liquid crystal material used can be reduced. Further, the entire thickness of the liquid crystal layer can be reduced, and the number of laminations can be reduced. As a result, the number of manufacturing processes can be reduced, and the cost can be reduced by improving the line speed.

The broadband cholesteric liquid crystal film of the present invention has a wide reflection bandwidth at a selective reflection wavelength of 300 nm or more, and has a broadband reflection bandwidth. Reflection bandwidth is more preferably at 400nm or more. The reflection bandwidth of 300 nm or more is preferably in the visible light region, particularly in the wavelength region of 400 to 800 nm.

  The reflection bandwidth is a reflection band having a reflectance that is half of the maximum reflectance when the reflection spectrum of the broadband cholesteric liquid crystal film is measured with a spectrophotometer (Otsuka Electronics Co., Ltd., instantaneous multi-photometry system MCPD-2000). It was.

The cholesteric liquid crystal film of the present invention is obtained by ultraviolet polymerization of a liquid crystal mixture containing a polymerizable mesogenic compound (a), a polymerizable chiral agent (b) and stilbene (c).

  As the polymerizable mesogenic compound (a), those having at least one polymerizable functional group and having a mesogenic group composed of a cyclic unit or the like are preferably used. Examples of the polymerizable functional group include an acryloyl group, a methacryloyl group, an epoxy group, and a vinyl ether group. Among these, an acryloyl group and a methacryloyl group are preferable. Further, by using a compound having two or more polymerizable functional groups, a crosslinked structure can be introduced to improve durability. Examples of the cyclic unit serving as a mesogenic group include biphenyl, phenylbenzoate, phenylcyclohexane, azoxybenzene, azomethine, azobenzene, phenylpyrimidine, diphenylacetylene, diphenylbenzoate, and bicyclohexane. Cyclohexylbenzene, terphenyl and the like. In addition, the terminal of these cyclic units may have substituents, such as a cyano group, an alkyl group, an alkoxy group, a halogen group, for example. The mesogenic group may be bonded via a spacer portion that imparts flexibility. Examples of the spacer portion include a polymethylene chain and a polyoxymethylene chain. The number of repeating structural units forming the spacer portion is appropriately determined depending on the chemical structure of the mesogenic portion, but the repeating unit of the polymethylene chain is 0 to 20, preferably 2 to 12, and the repeating unit of the polyoxymethylene chain is 0 to 0. 10, preferably 1-3.

  The polymerizable mesogenic compound (a) having one polymerizable functional group is, for example, a general formula of the following chemical formula 1:

(Wherein R ₁ represents a hydrogen atom or a methyl group, n represents an integer of 1 to 5).

  As specific examples of the polymerizable mesogenic compound (a) having one polymerizable functional group, for example,

The compound represented by these is mention | raise | lifted.

  Specific examples of the polymerizable mesogenic compound (a) having two polymerizable functional groups include, for example, LC242 manufactured by BASF.

  Examples of the polymerizable chiral agent (b) include LC756 manufactured by BASF.

  The amount of the polymerizable chiral agent (b) is preferably about 1 to 20 parts by weight, preferably 3 to 7 parts by weight based on 100 parts by weight of the total of the polymerizable mesogenic compound (a) and the polymerizable chiral agent (b). The part is more suitable. The helical twisting force (HTP) is controlled by the ratio of the polymerizable mesogenic compound (a) and the polymerizable chiral agent (b). By setting the ratio within the above range, the reflection band can be selected so that the reflection spectrum of the obtained cholesteric liquid crystal film can cover the entire visible range.

The amount of stilbene (c) added is not particularly limited, but is about 0.1 to 20 parts by weight with respect to 100 parts by weight of the total of the polymerizable mesogenic compound (a) and the polymerizable chiral agent (b). Preferably, 2 to 10 parts by weight is more preferable.

  Various photopolymerization initiators (d) can be used without particular limitation. Examples thereof include Irgacure 184, Irgacure 907, Irgacure 369, Irgacure 651 and the like manufactured by Ciba Specialty Chemicals. The blending amount of the photopolymerization initiator is preferably about 0.01 to 10 parts by weight with respect to 100 parts by weight of the total of the polymerizable mesogenic compound (a) and the polymerizable chiral agent (b), and 0.05 to 5 parts by weight. The part is more suitable. Depending on the photopolymerization initiator (d), ultraviolet irradiation conditions, and the amount of photoisomerizable material (c) added, it is not always necessary to add them. For example, when the polymerizable mesogenic compound (a) and the polymerizable chiral agent (b) have sufficiently high reaction rates such as a combination of those having two polymerizable functional groups, a photopolymerization initiator ( The addition of d) is not necessary.

In the present invention, a solution in which a liquid crystal mixture containing a polymerizable mesogenic compound (a), a polymerizable chiral agent (b), a stilbene (c), and, if necessary, a photopolymerization initiator (d) is dissolved in a solvent. Can be used as The solvent to be used is not particularly limited, but methyl ethyl ketone, cyclohexanone, cyclopentanone and the like are preferable. The concentration of the solution is usually about 3 to 50% by weight.

  The production of the cholesteric liquid crystal film of the present invention is carried out by applying the liquid crystal mixture to a substrate and performing ultraviolet polymerization.

  A conventionally known substrate can be used as the substrate. For example, a thin film made of polyimide, polyvinyl alcohol or the like is formed on a substrate, and this is rubbed with a rayon cloth or the like, an obliquely deposited film, a polymer having a photocrosslinking group such as cinnamate or azobenzene, or polyimide with polarized ultraviolet A photo-alignment film, a stretched film, or the like that has been irradiated with is used. In addition, it can also be oriented by magnetic field, electric field orientation, and shear stress manipulation.

  As the substrate, polyethylene terephthalate, triacetyl cellulose, norbornene resin, polyvinyl alcohol, polyimide, polyarylate, polycarbonate, a film made of plastic such as polysulfone or polyethersulfone, a glass plate, and a quartz sheet are used.

  After the liquid crystal mixture is applied to one substrate, the other substrate can be laminated. When the liquid crystal mixture is a solution, the solution is applied to one substrate and dried, and then the other substrate is laminated. The drying temperature for volatilizing the solvent may be a temperature not lower than the boiling point of the solvent. Usually, the temperature may be set in the range of about 80 to 160 ° C. according to the type of solvent.

  The coating thickness of the liquid crystal mixture (in the case of a solution, the coating thickness after solvent drying) is preferably about 1 to 20 μm, and more preferably about 2 to 10 μm. When the coating thickness is thinner than 1 μm, although the reflection bandwidth can be secured, the degree of polarization itself tends to decrease, which is not preferable. On the other hand, when the thickness is larger than 20 μm, the reflection bandwidth and the degree of polarization are not significantly improved, and the cost is simply increased.

Ultraviolet illuminance is preferably ^{0.1~30mW / cm 2, 1~20mW / cm} 2 is more preferable. Further, the irradiation time is preferably as short as 5 minutes or less. More preferably, it is 3 minutes or less, More preferably, it is 1 minute or less. In addition, if it heats from the direction opposite to the ultraviolet irradiation side, it is possible to broaden the band in a shorter time.

  The heating temperature at the time of irradiation with ultraviolet light or after irradiation may be higher than the liquid crystal temperature. Usually, 140 ° C. or lower is generally suitable. Specifically, about 60-140 degreeC is preferable and 80-120 degreeC is suitable. There is an effect of promoting the diffusion rate of the monomer component by heating. When the temperature is lower than 60 ° C., the diffusion rate of the polymerizable mesogenic compound (a) is very slow, and it takes a very long time to widen the band.

  The cholesteric liquid crystal film thus obtained may be used without being peeled from the substrate, or may be peeled from the substrate.

  The broadband cholesteric liquid crystal film of the present invention is used as a circularly polarizing plate. On the circularly polarizing plate, a λ / 4 plate can be laminated to form a linear polarizer. The cholesteric liquid crystal film which is a circularly polarizing plate is preferably laminated so that the pitch length is continuously narrowed with respect to the λ / 4 plate.

  As a λ / 4 plate, a birefringent film obtained by stretching a film made of an appropriate polymer such as polycarbonate, norbornene resin, polyvinyl alcohol, polystyrene, polymethyl methacrylate, polypropylene, other polyolefins, polyarylate, or polyamide. And an alignment film made of a liquid crystal material such as a liquid crystal polymer, and an alignment layer of a liquid crystal material supported by a film. The thickness of the λ / 4 wavelength plate is usually preferably from 0.5 to 200 μm, particularly preferably from 1 to 100 μm.

  A retardation plate that functions as a λ / 4 wavelength plate in a wide wavelength range such as a visible light region exhibits, for example, a retardation layer that functions as a λ / 4 wavelength plate and other retardation characteristics for light light having a wavelength of 550 nm. It can be obtained by a method of superposing a retardation layer, for example, a retardation layer functioning as a λ / 2 wavelength plate. Therefore, the retardation plate disposed between the polarizing plate and the brightness enhancement film may be composed of one or more retardation layers.

  An absorptive polarizer is attached to the transmission axis of the linear polarizer with its transmission axis direction aligned.

  The polarizer is not particularly limited, and various types can be used. Examples of the polarizer include hydrophilic polymer films such as polyvinyl alcohol film, partially formalized polyvinyl alcohol film, and ethylene / vinyl acetate copolymer partially saponified film, and two colors such as iodine and dichroic dye. Examples thereof include polyene-based oriented films such as those obtained by adsorbing volatile substances and uniaxially stretched, polyvinyl alcohol dehydrated products and polyvinyl chloride dehydrochlorinated products. Among these, a polarizer composed of a polyvinyl alcohol film and a dichroic material such as iodine is preferable. The thickness of these polarizers is not particularly limited, but is generally about 5 to 80 μm.

  A polarizer obtained by dyeing a polyvinyl alcohol film with iodine and uniaxially stretching it can be produced, for example, by dyeing polyvinyl alcohol in an aqueous solution of iodine and stretching it 3 to 7 times the original length. If necessary, it can be immersed in an aqueous solution of boric acid or potassium iodide. Further, if necessary, the polyvinyl alcohol film may be immersed in water and washed before dyeing. In addition to washing the polyvinyl alcohol film surface with dirt and anti-blocking agents by washing the polyvinyl alcohol film with water, it also has the effect of preventing unevenness such as uneven coloring by swelling the polyvinyl alcohol film. is there. Stretching may be performed after dyeing with iodine, may be performed while dyeing, or may be dyed with iodine after stretching. The film can be stretched in an aqueous solution of boric acid or potassium iodide or in a water bath.

  The polarizer is usually used as a polarizing plate with a transparent protective film provided on one side or both sides. The transparent protective film is preferably excellent in transparency, mechanical strength, thermal stability, moisture shielding property, isotropy and the like. Examples of transparent protective films include films made of transparent polymers such as polyester polymers such as polyethylene terephthalate and polyethylene naphthalate, cellulose polymers such as diacetyl cellulose and triacetyl cellulose, polycarbonate polymers, and acrylic polymers such as polymethyl methacrylate. Can be given. 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. In particular, those having a small optical birefringence are preferably used. From the viewpoint of the protective film of the polarizing plate, triacetyl cellulose, polycarbonate, acrylic polymer, cycloolefin resin, polyolefin having norbornene structure, and the like are preferable.

  Moreover, the polymer film described in JP-A-2001-343529 (WO01 / 37007), for example, (A) a thermoplastic resin having a substituted and / or unsubstituted imide group in the side chain, and (B) a substitution in the side chain And / or a resin composition containing an unsubstituted phenyl and a thermoplastic resin having a nitrile group. A specific example is a film of a resin composition containing an alternating copolymer composed of isobutylene and N-methylmaleimide and an acrylonitrile / styrene copolymer. As the film, a film made of a mixed extruded product of the resin composition or the like can be used.

  A transparent protective film that can be particularly preferably used in terms of polarization characteristics and durability is a triacetylcellulose film whose surface is saponified with an alkali or the like. Although the thickness of a transparent protective film can be determined suitably, generally it is about 10-500 micrometers from points, such as workability | operativity, such as intensity | strength and handleability, and thin layer property. 20-300 micrometers is especially preferable, and 30-200 micrometers is more preferable.

  Moreover, it is preferable that a transparent protective film has as little color as possible. Therefore, Rth = [(nx + ny) / 2−nz] · d (where nx and ny are the main refractive index in the plane of the film, nz is the refractive index in the film thickness direction, and d is the film thickness). A protective film having a retardation value in the film thickness direction of −90 nm to +75 nm is preferably used. By using a film having a thickness direction retardation value (Rth) of −90 nm to +75 nm, the coloring (optical coloring) of the polarizing plate caused by the protective film can be almost eliminated. The thickness direction retardation value (Rth) is more preferably −80 nm to +60 nm, and particularly preferably −70 nm to +45 nm.

  The transparent protective film may be a transparent protective film made of the same polymer material on the front and back, or may be a transparent protective film made of a different polymer material or the like.

  The surface of the transparent protective film to which the polarizer is not adhered may be subjected to a hard coat layer, an antireflection treatment, an antisticking treatment, or a treatment for diffusion or antiglare.

  The hard coat treatment is applied for the purpose of preventing scratches on the surface of the polarizing plate. For example, a transparent protective film with a cured film excellent in hardness, sliding properties, etc. by an appropriate ultraviolet curable resin such as acrylic or silicone is used. It can be formed by a method of adding to the surface of the film. The antireflection treatment is performed for the purpose of preventing reflection of external light on the surface of the polarizing plate, and can be achieved by forming an antireflection film or the like according to the conventional art. Further, the anti-sticking treatment is performed for the purpose of preventing adhesion with an adjacent layer.

  The anti-glare treatment is applied for the purpose of preventing the outside light from being reflected on the surface of the polarizing plate and obstructing the visibility of the light transmitted through the polarizing plate. For example, the surface is roughened by a sandblasting method or an embossing method. It can be formed by imparting a fine concavo-convex structure to the surface of the transparent protective film by an appropriate method such as a blending method of transparent fine particles. The fine particles to be included in the formation of the surface fine concavo-convex structure are, for example, conductive materials made of silica, alumina, titania, zirconia, tin oxide, indium oxide, cadmium oxide, antimony oxide or the like having an average particle size of 0.5 to 50 μm. In some cases, transparent fine particles such as inorganic fine particles, organic fine particles made of a crosslinked or uncrosslinked polymer, etc. are used. When forming a surface fine uneven structure, the amount of fine particles used is generally about 2 to 50 parts by weight, preferably 5 to 25 parts by weight, based on 100 parts by weight of the transparent resin forming the surface fine uneven structure. The antiglare layer may also serve as a diffusion layer (viewing angle expanding function or the like) for diffusing the light transmitted through the polarizing plate to expand the viewing angle.

  The antireflection layer, antisticking layer, diffusion layer, antiglare layer, and the like can be provided on the transparent protective film itself, or can be provided separately from the transparent protective layer as an optical layer.

  The linear polarizer described above can be provided with an adhesive layer for adhering to other members such as a liquid crystal cell. The pressure-sensitive adhesive forming the pressure-sensitive adhesive layer is not particularly limited. For example, an acrylic polymer, silicone-based polymer, polyester, polyurethane, polyamide, polyether, fluorine-based or rubber-based polymer is appropriately selected. Can be used. In particular, those having excellent optical transparency such as an acrylic pressure-sensitive adhesive, exhibiting appropriate wettability, cohesiveness, and adhesive pressure-sensitive adhesive properties, and being excellent in weather resistance, heat resistance and the like can be preferably used.

  In addition to the above, in terms of prevention of foaming and peeling phenomena due to moisture absorption, deterioration of optical properties and liquid crystal cell warpage due to differences in thermal expansion, etc., as well as formability of liquid crystal display devices with high quality and excellent durability An adhesive layer having a low moisture absorption rate and excellent heat resistance is preferred.

  The adhesive layer is, for example, natural or synthetic resins, in particular, tackifier resins, fillers or pigments made of glass fibers, glass beads, metal powders, other inorganic powders, colorants, antioxidants, etc. It may contain an additive to be added to the adhesive layer. Moreover, the adhesion layer etc. which contain microparticles | fine-particles and show light diffusibility may be sufficient.

  The attachment of the adhesive layer can be performed by an appropriate method. For example, a pressure sensitive adhesive solution of about 10 to 40% by weight in which a base polymer or a composition thereof is dissolved or dispersed in a solvent composed of a suitable solvent alone or a mixture such as toluene and ethyl acetate is prepared. A method of attaching it directly on the polarizer by an appropriate development method such as a casting method or a coating method, or a method of forming an adhesive layer on a separator according to the above and transferring it onto an optical element, etc. Can be given. The pressure-sensitive adhesive layer can also be provided as an overlapping layer of different compositions or types in each layer. The thickness of the pressure-sensitive adhesive layer can be appropriately determined according to the purpose of use and adhesive force, and is generally 1 to 500 μm, preferably 5 to 200 μm, particularly preferably 10 to 100 μm.

  On the exposed surface of the adhesive layer, a separator is temporarily attached and covered for the purpose of preventing contamination until it is put to practical use. Thereby, it can prevent contacting an adhesion layer in the usual handling state. As the separator, except for the above thickness conditions, for example, a suitable thin leaf body such as a plastic film, rubber sheet, paper, cloth, nonwoven fabric, net, foamed sheet or metal foil, or a laminate thereof, silicone type or Appropriate conventional ones such as those coated with an appropriate release agent such as long-chain alkyl, fluorine-based, or molybdenum sulfide can be used.

  In addition, each layer such as the adhesive layer absorbs ultraviolet rays by a method such as a method of treating with a UV absorber such as a salicylic acid ester compound, a benzophenol compound, a benzotriazole compound, a cyanoacrylate compound, or a nickel complex compound. It may be a thing with a performance.

  The linear polarizer of the present invention can be preferably used for forming various devices such as a liquid crystal display device. The liquid crystal display device can be formed according to the conventional method. That is, a liquid crystal display device is generally formed by appropriately assembling components such as a liquid crystal cell, an optical element, and an illumination system as necessary, and incorporating a drive circuit. However, the linear polarizer of the present invention is used. There is no limitation in particular except a point, and it can apply according to the former. As the liquid crystal cell, any type such as a TN type, an STN type, or a π type can be used.

  An appropriate liquid crystal display device such as a liquid crystal display device in which the linear polarizer is disposed on one side or both sides of the liquid crystal cell, or a backlight or a reflector used in an illumination system can be formed. In that case, the linear polarizer according to the present invention can be installed on one or both sides of the liquid crystal cell. When linear polarizers are provided on both sides, they may be the same or different. Further, when forming a liquid crystal display device, for example, a single layer or a suitable part such as a diffusing plate, an antiglare layer, an antireflection film, a protective plate, a prism array, a lens array sheet, a light diffusing plate, a backlight, etc. Two or more layers can be arranged.

  The circularly polarizing plate (reflection polarizer) using the cholesteric liquid crystal film has a front phase difference (normal line) between at least two layers of the reflection polarizers (a) in which the wavelength bands of selective reflection of polarized light overlap each other. (Direction) is almost zero, and is used in a polarizing element system in which a phase difference layer (b) having a phase difference of λ / 8 or more with respect to incident light incident at an angle of 30 ° or more with respect to the normal direction is arranged. In addition, the cholesteric liquid crystal film may have either the maximum pitch or the minimum pitch of the helical twisted molecular structure on the phase difference layer (b) side, but from the viewpoint of the viewing angle (good viewing angle, small coloring), If the reflective polarizer (a) is expressed as (maximum pitch / minimum pitch), it is preferable that the reflective polarizer (a) is arranged as follows: maximum pitch / minimum pitch / retardation layer (b) / maximum pitch / minimum pitch. Further, as shown in FIG. 6, when combining λ / 4 plates, it is preferable to arrange the reflective polarizer (a) so that the minimum pitch side is the λ / 4 plate side.

  The polarizing element system, that is, the cholesteric liquid crystal laminate having a broadband selective reflection function has a circular polarization reflection / transmission function in the front direction, and can be used as a broadband circular polarizing plate in a liquid crystal display device. In this case, it can be used as a circularly polarizing plate by being arranged on the light source side of a circularly polarized liquid crystal cell, for example, a transmissive VA mode liquid crystal cell having a multi-domain.

  The retardation layer (b) has a phase difference of approximately zero in the front direction and a phase difference of λ / 8 or more with respect to incident light at an angle of 30 ° from the normal direction. Since the front phase difference is intended to maintain vertically incident polarized light, it is desirable that the front phase difference be λ / 10 or less.

  For incident light from an oblique direction, it is determined as appropriate depending on the angle at which it is totally reflected so as to be efficiently polarized and converted. For example, in order to achieve total reflection at an angle of about 60 ° from the normal line, the phase difference when measured at 60 ° may be determined to be about λ / 2. However, since the polarization state of the transmitted light from the reflective polarizer (a) is also changed by the C-plate-like birefringence of the reflective polarizer itself, the measured light at the angle of the C plate that is normally inserted is measured. The phase difference may be a value smaller than λ / 2. Since the phase difference of the C plate increases monotonously as the incident light is tilted, λ / 8 or more with respect to incident light at an angle of 30 ° as a guide for causing effective total reflection when tilted at an angle of 30 ° or more. Just have it.

  The material of the retardation layer (b) is not particularly limited as long as it has the above optical characteristics. For example, a planar alignment state of a cholesteric liquid crystal having a selective reflection wavelength other than a visible light region (380 nm to 780 nm), a homeotropic alignment state of a rod-like liquid crystal, a columnar alignment or a nematic alignment of a discotic liquid crystal , A negative uniaxial crystal oriented in the plane, a biaxially oriented polymer film, and the like.

  In the present invention, the C plate in which the planar alignment state of the cholesteric liquid crystal having a selective reflection wavelength other than the visible light region (380 nm to 780 nm) is fixed is not colored in the visible light region as the selective reflection wavelength of the cholesteric liquid crystal. Is desirable. Therefore, it is necessary that the selectively reflected light is not in the visible region. The selective reflection is uniquely determined by the cholesteric chiral pitch and the refractive index of the liquid crystal. Although the value of the center wavelength of selective reflection may be in the near-infrared region, it is more desirable to be in the ultraviolet region of 350 nm or less because it is affected by the optical rotation and a slightly complicated phenomenon occurs. The formation of the cholesteric liquid crystal layer is performed in the same manner as the formation of the cholesteric layer in the above-described reflective polarizer.

  The C plate in which the homeotropic alignment state is fixed in the present invention is a liquid crystalline thermoplastic resin or liquid crystal monomer exhibiting nematic liquid crystal properties at high temperatures, and an ionizing radiation such as an electron beam or ultraviolet ray, as necessary, and an alignment aid. A polymerizable liquid crystal polymerized by heat or a mixture thereof is used. The liquid crystallinity may be either lyotropic or thermotropic, but is preferably a thermotropic liquid crystal from the viewpoint of ease of control and ease of formation of a monodomain. Homeotropic alignment is obtained, for example, by coating the birefringent material on a film on which a vertical alignment film (long-chain alkylsilane or the like) is formed, and expressing and fixing a liquid crystal state.

  As a C plate using discotic liquid crystal, a discotic liquid crystal material having a negative uniaxial property such as a phthalocyanine or triphenylene compound having an in-plane molecular spread as a liquid crystal material, a nematic phase or a columnar phase is used. It is expressed and fixed. Examples of the negative uniaxial inorganic layered compound are detailed in JP-A-6-82777.

  C plate using biaxial orientation of polymer film is a method of biaxially stretching a polymer film having positive refractive index anisotropy in a balanced manner, a method of pressing a thermoplastic resin, and cutting out from a parallel oriented crystal. It is obtained by a method.

  The layers may be stacked, but it is desirable to stack the layers using an adhesive or a pressure-sensitive adhesive from the viewpoint of workability and light utilization efficiency. In that case, the adhesive or pressure-sensitive adhesive is transparent, has no absorption in the visible light region, and the refractive index is preferably as close as possible to the refractive index of each layer from the viewpoint of suppressing surface reflection. From this viewpoint, for example, an acrylic pressure-sensitive adhesive can be preferably used. Each layer is separately formed into a monodomain in the form of an alignment film, etc., and sequentially laminated by a method such as transfer to a translucent substrate, an alignment film or the like for alignment without providing an adhesive layer, etc. It is also possible to form each layer as appropriate and form each layer directly in sequence.

  In each layer and (viscous) adhesive layer, particles are added to adjust the degree of diffusion as necessary to give isotropic scattering, UV absorbers, antioxidants, leveling during film formation A surfactant or the like can be appropriately added for the purpose of imparting property.

  The polarizing element (cholesteric liquid crystal laminate) of the present invention has a circularly polarized light reflection / transmission function, but can be used as a linear polarizer that converts transmitted light into linearly polarized light by combining it with a λ / 4 plate.

  The λ / 4 plate is not particularly limited, but is a general-purpose transparent resin film that generates a phase difference by stretching, such as polycarbonate, polyethylene terephthalate, polystyrene, polysulfone, polyvinyl alcohol, polymethyl methacrylate, or an ARTON film made by JSR. A norbornene-based resin film or the like is preferably used. Further, it is preferable to use a retardation plate that performs biaxial stretching and compensates for a change in retardation value due to an incident angle because the viewing angle characteristics can be improved. Further, a λ / 4 plate obtained by fixing a λ / 4 layer obtained by aligning liquid crystal, for example, other than the development of retardation due to stretching of the resin may be used. In this case, the thickness of the λ / 4 plate can be greatly reduced. The thickness of the λ / 4 wavelength plate is usually preferably from 0.5 to 200 μm, particularly preferably from 1 to 100 μm.

  The λ / 4 plate functions well only for a specific wavelength in a single layer made of a single material, but there is a problem that the function of the λ / 4 plate deteriorates for other wavelengths due to wavelength dispersion characteristics. Therefore, if the λ / 2 plate is laminated with a specified axial angle, it can be used as a broadband λ / 4 plate that functions in a practically acceptable range over the entire visible light range. In this case, each λ / 4 plate and λ / 2 plate may be made of the same material, or may be a combination of materials made of separate materials obtained in the same manner as the λ / 4 plate described above.

  For example, a λ / 4 plate (140 nm) is laminated on a broadband circularly polarizing plate, and the λ / 2 plate (270 nm) is arranged at 117.5 degrees with respect to this axial angle. In this case, the transmission polarization axis is 10 degrees with respect to the axis of the λ / 4 plate. Since the bonding angle varies depending on the phase difference value of each phase difference plate, the bonding angle is not limited to the above bonding angle.

  An absorptive polarizer is attached to the transmission axis of the linear polarizer with its transmission axis direction aligned.

(Arrangement of diffuse reflector)
It is desirable to dispose a diffuse reflector on the lower side of the light guide plate as the light source (on the side opposite to the liquid crystal cell arrangement surface). The main component of the light beam reflected by the collimating film is an oblique incident component, and is regularly reflected by the collimating film and returned to the backlight direction. Here, when the reflector on the back side has high regular reflectivity, the reflection angle is preserved, and the light cannot be emitted in the front direction and becomes lost light. Accordingly, it is desirable to dispose a diffuse reflector in order to increase the scattering reflection component in the front direction without preserving the reflection angle of the reflected return beam.

(Distribution plate arrangement)
It is also desirable to install an appropriate diffusion plate between the collimating film and the backlight source in the present invention. This is because the light reuse efficiency is increased by scattering the incident and reflected light rays in the vicinity of the backlight light guide and scattering a part thereof in the vertical incident direction.

  The diffusion plate used can be obtained by a method of embedding fine particles having different refractive indexes in a resin, in addition to a surface irregularity shape. This diffusion plate may be sandwiched between the collimating film and the backlight, or may be bonded to the collimating film.

  When the liquid crystal cell having the collimated film attached thereto is disposed close to the backlight, there is a risk that Newton's ring may occur in the gap between the film surface and the backlight, but the light guide plate side surface of the collimated film in the present invention The occurrence of Newton rings can be suppressed by disposing a diffuser plate having surface irregularities on the surface. Moreover, you may form the layer which served as the uneven | corrugated structure and the light-diffusion structure in the surface itself of the collimating film in this invention.

(Arrangement of viewing angle expansion film)
The viewing angle expansion in the liquid crystal display device of the present invention diffuses a light beam with good display characteristics near the front surface obtained from the liquid crystal display device combined with a parallel light backlight, and is uniform within the entire viewing angle. It is obtained by obtaining good display characteristics.

  The viewing angle widening film used here is a diffusion plate that does not substantially have backscattering. The diffusion plate can be provided as a diffusion adhesive material. The location is on the viewing side of the liquid crystal display device, but it can be used either above or below the polarizing plate. However, it is desirable to provide a layer as close to the cell as possible, such as between the polarizing plate and the liquid crystal cell, in order to prevent the deterioration of the contrast due to the influence of the blur of the pixel or the like or the slight remaining backscattering. In this case, a film that does not substantially eliminate polarized light is desirable. For example, a fine particle dispersion type diffusion plate as disclosed in JP-A Nos. 2000-347006 and 2000-347007 is preferably used.

  When the viewing angle widening film is located outside the polarizing plate, the collimated light beam is transmitted from the liquid crystal layer to the polarizing plate, so that in the case of the TN liquid crystal cell, it is not necessary to use a viewing angle compensating retardation plate. In the case of an STN liquid crystal cell, it is only necessary to use a retardation film in which only the front characteristics are well compensated. In this case, since the viewing angle widening film has an air surface, it is possible to adopt a type based on a refraction effect due to the surface shape.

  On the other hand, when a viewing angle widening film is inserted between the polarizing plate and the liquid crystal layer, it becomes a diffused light at the stage where it passes through the polarizing plate. In the case of a TN liquid crystal, it is necessary to compensate for the viewing angle characteristics of the polarizer itself. In this case, it is necessary to insert a retardation plate for compensating the viewing angle characteristics of the polarizer between the polarizer and the viewing angle widening film. In the case of STN liquid crystal, it is necessary to insert a phase difference plate for compensating the viewing angle characteristics of the polarizer in addition to the front phase difference compensation of STN liquid crystal.

  In the case of a viewing angle widening film having a regular structure inside, such as a conventional microlens array film or hologram film, a microlens included in a black matrix of a liquid crystal display device or a conventional parallel light conversion system of a backlight Moire was likely to occur due to interference with a fine structure such as an array / prism array / louver / micromirror array. However, the collimated film in the present invention has no regular structure in the plane, and there is no regular modulation of the emitted light, so there is no need to consider compatibility with the viewing angle widening film and the arrangement order. Accordingly, the viewing angle widening film is not particularly limited as long as it does not cause interference / moire with the pixel black matrix of the liquid crystal display device, and the options are wide.

  In the present invention, it is a light scattering plate as described in JP-A-2000-347006 and JP-A-2000-347007, which has substantially no backscattering as a viewing angle widening film and does not cancel polarization. A haze of 80% to 90% is preferably used. In addition, a hologram sheet, a microprism array, a microlens array, or the like can be used as long as it does not form interference / moire with the pixel black matrix of the liquid crystal display device even if it has a regular structure inside.

  Note that the liquid crystal display device is manufactured by appropriately using various optical layers and the like according to a conventional method.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated, this invention is not limited to these Examples.

Example 1
A mixture comprising 96 parts by weight of LC242 manufactured by BASF as the polymerizable mesogenic compound (a), 4 parts by weight of LC756 manufactured by BASF as the polymerizable chiral agent (b), and 5 parts by weight of stilbene as the photoisomerizable material (c). A methyl ethyl ketone solution (30 wt% solids content) was prepared. The solution was cast on a stretched polyethylene terephthalate substrate, dried at 100 ° C. for 2 minutes to remove the solvent, and the other polyethylene terephthalate substrate was laminated. Subsequently, ultraviolet irradiation at 5 mW / cm ² for 3 minutes and heating at 100 ° C. for 10 seconds were performed to obtain a target cholesteric liquid crystal film.

  One polyethylene terephthalate substrate was removed. The reflection spectrum of the cholesteric liquid crystal film (circularly polarizing plate) is shown in FIG. The circularly polarizing plate had good circularly polarized light separation characteristics (reflection band) in the range of 400 to 800 nm. The total thickness of the cholesteric liquid crystal layer (film) was 10 μm. The pitch length of the obtained cholesteric liquid crystal layer was 0.2 μm near the ultraviolet irradiation surface (1 μm lower layer from the ultraviolet irradiation surface) and 0.5 μm near the opposite surface (1 μm lower layer from the opposite surface). The pitch length was measured by a cross-sectional TEM photograph. In this way, a cholesteric liquid crystal film having a broad band so as to cover visible light could be produced as a single layer.

Example 2
The wide band cholesteric liquid crystal film (circularly polarizing plate) obtained in Example 1 is continuously narrowed with respect to the λ / 4 plate obtained by biaxially stretching a polycarbonate resin film (thickness 80 μm). In the direction, it bonded together with the acrylic adhesive material (thickness 25 micrometers). Further, an absorption polarizing plate TEG1465DU manufactured by Nitto Denko was bonded to this so that the transmission axis directions coincided to obtain a broadband polarizing plate.

  When this was used as the lower plate of the TFT-LCD and placed on a sidelight type backlight and the luminance improvement rate was measured, a luminance improvement of 1.3 times or more was obtained compared to the case of not using the product of the present invention. . The luminance was measured with a viewing angle measuring device EZ-CONTRAST manufactured by ELDIM. In addition, the optical characteristic (reflection spectrum) obtained the performance equivalent to the case where the film obtained by patent documents 1 thru | or 4 grade | etc., Is used.

Example 3
88.6 parts by weight of a photopolymerizable nematic liquid crystal monomer (LC242 manufactured by BASF), 11.4 parts by weight of a chiral agent (LC756 manufactured by BASF) and 5 parts by weight of a photopolymerization initiator (Irgacure 907, manufactured by Ciba Specialty Chemicals) A cyclopentanone solution (30 wt% solids content) of a mixture consisting of The solution was adjusted and blended so that the selective reflection wavelength was 350 nm. The above solution was coated on a polyethylene terephthalate substrate using a wire bar so that the thickness after drying was 4 μm, and the solvent was dried. Thereafter, the temperature was raised once to the isotropic transition temperature of the liquid crystal monomer, and then gradually cooled to form a layer having a uniform alignment state. The obtained layer was irradiated with ultraviolet rays to fix the alignment state to obtain a C plate layer (negative). When the retardation of the C plate was measured, the retardation value was 100 nm when measured with an inclination of 2 nm and 30 ° in the front direction with respect to light having a wavelength of 550 nm.

  On the other hand, two broadband cholesteric liquid crystal films (circular polarizing plate: reflective polarizer) obtained in Example 1 were prepared. The C plate layer was transferred onto the reflective polarizer layer using a translucent adhesive. Further, the same reflective polarizer layer was transferred and laminated on the upper part using the same translucent adhesive to obtain a polarizing element. A λ / 4 plate made of biaxially stretched polyethylene terephthalate was bonded to this, and the polarizing plate and the transmission axis were bonded to each other, and then bonded to a TFT liquid crystal display device, and placed on a dot printing type backlight. In this sample, a viewing angle compensation film was not used in the TFT liquid crystal display device, and a polarizing plate (SEG1425DU manufactured by Nitto Denko) was used alone for both the front and back of the liquid crystal cell. In addition, a normal TN cell was adopted inside the cell. Also, prism sheets were not used.

  A mat PET diffuse reflector is disposed on the lower surface of the backlight. The obtained collimating system collects light in the same manner as the prism condensing sheet, transmits circularly polarized light, and the thickness of the combination of two prism sheets and a reflective polarizer reaches 500 μm. It was extremely thin, about 1/20. The light collecting characteristic was about ± 50 degrees from the direction perpendicular to the screen.

Example 4
In Example 3 , a C plate having a retardation value of 120 nm when measured with an inclination of 30 ° was used, and an acrylic adhesive (thickness between the polarizing plate on the surface side of the liquid crystal display device and the liquid crystal cell was used. 30 μm, refractive index 1.47), except that a 92% light diffusion adhesive layer (thickness 25 μm) in which silica spherical particles (particle size 4 μm, blending part number 30% by weight) are dispersed is placed and bonded A sample was prepared in the same manner as in Example 4. In the sample, the condensing characteristic in the front direction was substantially narrowed to about ± 30 degrees. The obtained viewing angle widening liquid crystal display device did not cause gradation inversion within ± 60 degrees, and maintained good display characteristics in confirmation of viewing angle characteristics by gray scale display.

Comparative Example 1
A methyl ethyl ketone solution (30 wt% solid content) of a mixture comprising 96 parts by weight of the above-mentioned BASF LC242 as the polymerizable mesogenic compound (a) and 4 parts by weight of the BASF LC756 as the polymerizable chiral agent (b). Prepared. A cholesteric liquid crystal film was obtained in the same manner as in Example 1 except that the above solution was used. The reflection spectrum of the cholesteric liquid crystal film (circularly polarizing plate) is shown in FIG . The obtained circularly polarizing plate had good circularly polarized light separation characteristics in the range of 650 to 750 nm. The pitch length of the obtained cholesteric liquid crystal layer was 0.44 μm near the ultraviolet irradiation surface (1 μm lower layer from the ultraviolet irradiation surface) and 0.46 μm near the opposite surface (1 μm lower layer from the opposite surface). From FIG. 2 , it can be seen that the reflection band is narrower than that of Example 1.

Comparative Example 2
A 0.1 μm thick polyvinyl alcohol alignment film is formed on a triacetyl cellulose film, and after rubbing treatment, cholesteric liquid crystal polymers with selective reflection center wavelengths of 610 nm, 550 nm, and 450 nm are successively 3 layers each having a thickness of 2 μm. Formed and oriented. A λ / 4 plate obtained by biaxially stretching a polycarbonate resin film (thickness: 80 μm) was bonded to the cholesteric liquid crystal film to obtain a linear polarizer. A polarizing plate (TEG1465DU manufactured by Nitto Denko) was bonded to the linear polarizer so that the transmission axis directions coincided with each other to obtain a polarizing plate integrated polarizing element. This was used as a lower plate of the TET-LCD, placed on a sidelight type backlight, and the luminance improvement rate was measured. Compared with Example 1, the luminance was reduced by 30% or more.

2 is a reflection spectrum of a cholesteric liquid crystal film produced in Example 1. 2 is a reflection spectrum of a cholesteric liquid crystal film produced in Comparative Example 1 . 6 is a conceptual diagram of a broadband polarizing plate used in Example 2. FIG. FIG. 10 is a conceptual diagram of a viewing angle widening liquid crystal display device manufactured in Example 4 ;

Explanation of symbols

1: Absorption type polarizing plate 2: λ / 4 plate 3: Cholesteric liquid crystal film (circular polarizing plate), reflective polarizer (a)
4: Adhesive layer 5: Phase difference plate (b): C plate 6: Viewing angle widening film (diffusion adhesive)
30: Polarizing element A1: Linear polarizer A2: Linear polarizer in which an absorption polarizing plate is further laminated on A1: LC: Liquid crystal cell BL: Backlight D: Diffuse reflector

Claims (30)

A liquid crystal mixture containing a polymerizable mesogenic compound (a), a polymerizable chiral agent (b) and a stilbene (c) is applied to a substrate, and is a single-layer cholesteric liquid crystal film obtained by ultraviolet polymerization,
A broadband cholesteric liquid crystal film having a reflection bandwidth of 300 nm or more.   2. The broadband cholesteric liquid crystal film according to claim 1, wherein the pitch length of the cholesteric liquid crystal film changes continuously.   The broadband cholesteric liquid crystal film according to claim 1 or 2, wherein the liquid crystal mixture contains a photopolymerization initiator (d).   The polymerizable mesogenic compound (a) has one or more polymerizable functional groups, and the polymerizable chiral agent (b) has one or more polymerizable functional groups. The broadband cholesteric liquid crystal film according to any one of? The broadband cholesteric liquid crystal film according to any one of claims 1 to 4, wherein the liquid crystal mixture is applied to one base material, and then the other base material is laminated and subjected to ultraviolet polymerization. 6. The broadband cholesteric liquid crystal film according to claim 5, wherein the base material is the same base material. The broadband cholesteric liquid crystal film according to claim 1, wherein the substrate is a polyethylene terephthalate substrate. The addition amount of stilbene (c) is 0.1 to 20 parts by weight with respect to a total of 100 parts by weight of the polymerizable mesogenic compound (a) and the polymerizable chiral agent (b). The broadband cholesteric liquid crystal film according to any one of? The broadband cholesteric liquid crystal film according to claim 1, wherein the liquid crystal mixture has a thickness of 1 to 20 μm. Polymerizable mesogen compound (a), a polymerizable chiral agent A liquid-crystal mixture comprising (b) and stilbene (c), applied to a substrate, according to any one of claims 1 to 9, characterized in that the UV polymerization Manufacturing method of broadband cholesteric liquid crystal film. UV illuminance in UV polymerization is 0.1-30 mW / cm ² The method for producing a broadband cholesteric liquid crystal film according to claim 10. The method for producing a broadband cholesteric liquid crystal film according to claim 10 or 11, wherein the irradiation time in ultraviolet polymerization is 5 minutes or less. The method for producing a broadband cholesteric liquid crystal film according to any one of claims 10 to 12, wherein the heating temperature after irradiation or after irradiation is 60 to 140 ° C. Circularly polarizing plate using the broad band cholesteric liquid crystal film according to any one of claims 1-9. A linear polarizer obtained by laminating a λ / 4 plate on the circularly polarizing plate according to claim 14 . The linear polarizer according to claim 15, which is obtained by laminating a cholesteric liquid crystal film, which is a circularly polarizing plate, on a λ / 4 plate so that the pitch length is continuously narrowed. A linear polarizer obtained by adhering an absorptive polarizer to the transmission axis of the linear polarizer according to claim 15 or 16 so that the direction of the transmission axis is aligned. An illuminating device comprising the circularly polarizing plate according to claim 14 or the linear polarizer according to any one of claims 15 to 17 on a surface side of a surface light source having a reflective layer on a back surface side. A liquid crystal display device comprising a liquid crystal cell on a light emitting side of the illumination device according to claim 18 . Between at least two reflective polarizers (a) in which the wavelength bands of selective reflection of polarized light overlap each other,
A retardation layer (b) having a front phase difference (normal direction) of substantially zero and a phase difference of λ / 8 or more with respect to incident light that is inclined by 30 ° or more with respect to the normal direction is disposed. A polarizing element system,
The polarizing element system, wherein the reflective polarizer (a) is the circularly polarizing plate according to claim 14 . 21. The polarizing element system according to claim 20 , wherein the selective reflection wavelengths of at least two layers of the reflective polarizer (a) overlap each other in a wavelength range of 550 nm ± 10 nm. The polarizing element system according to claim 20 or 21 , wherein the retardation layer (b) has a fixed planar orientation of a cholesteric liquid crystal phase having a selective reflection wavelength region other than a visible light region. The polarizing element system according to claim 20 or 21, wherein the retardation layer (b) has a fixed homeotropic alignment state of the rod-like liquid crystal. The polarizing element system according to claim 20 or 21, wherein the retardation layer (b) is one in which a nematic phase or columnar phase alignment state of a discotic liquid crystal is fixed. The polarizing element system according to claim 20 or 21, wherein the retardation layer (b) is a biaxially oriented polymer film. The polarized light according to claim 20 or 21, wherein the retardation layer (b) is an inorganic layered compound having negative uniaxiality and is oriented and fixed so that the optical axis is in the normal direction of the surface. Element system. A backlight system that uses a polarizing element system according to any one of claims 20 to 26 to convert a diffused light source into parallel light;
A liquid crystal cell through which the collimated light beam is transmitted;
A polarizing plate disposed on both sides of the liquid crystal cell;
A viewing angle widening film for diffusing transmitted light, disposed on the viewing side of the liquid crystal cell;
A liquid crystal display device with a wide viewing angle, characterized by containing at least. A λ / 4 plate is disposed on the viewing side (liquid crystal cell side) of the polarizing element system according to any one of claims 20 to 26 , and the axial direction of linearly polarized light obtained by transmission and the lower surface side (light source side) of the liquid crystal display device 28. The viewing angle widening liquid crystal display device according to claim 27 , wherein the transmission axis directions of the polarizing plates are aligned. 29. A viewing angle widening liquid crystal display device according to claim 27 or 28, wherein a diffusion plate substantially free of backscattering and depolarization is used as the viewing angle widening film. The viewing angle expansion liquid crystal display device according to any one of claims 27 to 29 , wherein each layer is laminated using a translucent adhesive or pressure-sensitive adhesive.