JP2004233987A - Wide-band cholesteric liquid crystal film, its manufacturing method, circular polarizing plate, linear polarizer, illumination apparatus and liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wide-band cholesteric liquid crystal film having a wide reflection band and favorable durability. <P>SOLUTION: The wide-band cholesteric liquid crystal film 3 is obtained by applying a liquid crystal mixture containing a polymerizable mesogene compound (a), a polymerizable chiral agent (b) and a photopolymerization initiator (c) on an alignment base material and subjected to UV polymerization in an inert gas atmosphere. The film has ≥200 nm of reflection band width. <P>COPYRIGHT: (C)2004,JPO&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 using the circularly polarizing plate, a lighting device, and a liquid crystal display device.

  Generally, 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 plates. A polarizer used for such a liquid crystal display is manufactured by adsorbing iodine, a dichroic dye, or the like on a polyvinyl alcohol film and stretching the same in a certain direction. The polarizer thus manufactured per se absorbs light oscillating in one direction and passes only light oscillating in the other direction to produce linearly polarized light. Therefore, the efficiency of the polarizer cannot theoretically exceed 50%, which is the largest factor that lowers the efficiency of the liquid crystal display. Also, due to this absorbed light, if the output of the light source is increased to a certain degree or more, the liquid crystal display device will break down the polarizer due to the heat generated by the heat conversion of the absorbed light, or display the liquid crystal layer inside the cell due to the thermal effect. This has caused adverse effects such as deterioration of quality.

  A cholesteric liquid crystal having a function of separating circularly polarized light has a selective reflection characteristic in which the direction of rotation of the liquid crystal helix coincides with the direction of circular polarization, and reflects only circularly polarized light whose wavelength is the helical pitch of the liquid crystal. By using this selective reflection characteristic, only specific circularly polarized light of natural light in a certain 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 a λ / 4 wavelength plate, and the direction of the linearly polarized light is aligned with the transmission direction of the absorption 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 wavelength plate, there is theoretically no loss of light. Therefore, when a conventional absorption polarizer that absorbs 50% of light is used alone, In comparison, a two-fold improvement in brightness can be obtained in theory.

However, the selective reflection characteristic of the cholesteric liquid crystal is limited to only a specific wavelength band, and it has been difficult to cover the entire visible light range. The selective reflection wavelength range width △ λ of cholesteric liquid crystal is
Δλ = 2λ · (ne−no) / (ne + no)
no: Refractive index of cholesteric liquid crystal molecules to normal light ne: Refractive index of cholesteric liquid crystal molecules to extraordinary light λ: Expressed by the central wavelength of selective reflection and depends on the molecular structure of cholesteric liquid crystal itself. From the above equation, if the value of ne-no is increased, the width of the selective reflection wavelength region Δλ can be increased, but the value of ne-no is usually 0.3 or less. When this value is increased, other functions (alignment characteristics, liquid crystal temperature, etc.) of the liquid crystal become insufficient, and practical use has been difficult. Accordingly, in practice, the selective reflection wavelength region width Δλ is at most about 150 nm. Most of practically usable cholesteric liquid crystals have a thickness of 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 turn of the cholesteric liquid crystal, and if the pitch is constant, it depends on the average refractive index of the liquid crystal molecules and the pitch length.

  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 the existence distribution of the selective reflection center wavelength itself. Was.

  For example, there is a method of continuously changing the pitch length in the thickness direction (for example, refer to Patent Document 1, Patent Document 2, Patent Document 3, etc.). In this method, when the cholesteric liquid crystal composition is cured by ultraviolet light exposure, the difference in the exposure intensity between the exposed surface side and the outgoing surface side, and the difference in the polymerization rate, the composition ratio of the liquid crystal compositions with different reaction rates. 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 emission surface side. Therefore, in many cases of the above-mentioned prior art examples, a method of mixing an ultraviolet absorber into a liquid crystal composition, generating absorption in a thickness direction, and amplifying a difference in exposure amount due to an optical path length has been adopted. .

  However, the cholesteric liquid crystal film obtained by additional testing of the above-mentioned prior art has a phenomenon in which an ultraviolet absorber precipitates on the surface of the cholesteric liquid crystal film or a bonding interface with another layer during a durability test (heating test or humidification test). It was observed. This is because the UV absorber has a low molecular weight and migrates in the film during a long-term durability test, and is considered to be agglomerated. For general industrial materials, this level of surface precipitation was not recognized as an abnormal appearance, and even if it was deposited on the interface, it was not a problem that led to interface delamination. However, the cholesteric liquid crystal film used in the liquid crystal display device is located on the optical path of strong transmitted light, and when such a precipitate is generated, the precipitated particles are directly visually observed. Alternatively, optical problems such as a change in the light scattering distribution of the light source due to a haze at which a precipitate is generated have occurred.

If the cholesteric liquid crystal film is used in a room temperature environment, it is unlikely that this kind of precipitate is generated. However, when used in a liquid crystal display device, precipitation of an ultraviolet absorber is inevitable if the radiation heat from the light source of the backlight is strong and is exposed for a long period of time. Such precipitates are hard to be visually recognized if they are uniformly deposited on the surface, and are not easily recognized as defects. In some cases, the amount of deposition increased only in the region where the surface was uneven, and the region was visually recognized as in-plane unevenness. Moreover, the display luminance required for the liquid crystal display device in recent years exceeds 200 candela, and the light source side is exposed to a light irradiation intensity of about 10,000 candela. Due to this irradiation intensity, heat of about 40 to 60 ° C. is continuously applied to the light source side of the liquid crystal display device depending on the use environment temperature. For this reason, not only the heating reliability test but also the continuous lighting test mounted on the liquid crystal display device showed the deposition of the ultraviolet absorber. For example, when an ultraviolet polymer obtained from a cholesteric liquid crystal composition containing an ultraviolet absorber is put in an environment of 80 ° C. × 500 hours, 60 ° C., 90% RH × 500 hours, cloudiness, haze rise, and powder on the surface Body deposition was remarkably observed.
JP-A-6-281814 Japanese Patent No. 3272668 JP-A-11-248943

  An object of the present invention is to provide a broadband cholesteric liquid crystal film having a broadband reflection band and a method for manufacturing the same. Another object of the present invention is to provide a broadband cholesteric liquid crystal film having a broadband reflection band and excellent durability, and a method for producing 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, a lighting device, and a liquid crystal display using the circularly polarizing plate.

  The present inventors have conducted intensive studies to solve the above problems, and as a result, 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, in the present invention, a liquid crystal mixture containing a polymerizable mesogen compound (a), a polymerizable chiral agent (b) and a photopolymerization initiator (c) is applied on an alignment substrate, and the mixture is irradiated with an ultraviolet ray under an inert gas atmosphere. The present invention relates to a cholesteric liquid crystal film obtained by polymerization, which has a reflection bandwidth of 200 nm or more.

  The broadband cholesteric liquid crystal film of the present invention is obtained by polymerizing a polymerizable liquid crystal mixture with an ultraviolet ray, and has a reflection bandwidth of a selective reflection wavelength as wide as 200 nm or more, which is an unprecedented broadband reflection bandwidth. Have. The reflection bandwidth is preferably at least 300 nm, more preferably at least 400 nm. Further, it is preferable that the reflection bandwidth of 200 nm or more is provided in a visible light region, particularly in a wavelength region of 400 to 800 nm.

  The reflection bandwidth is obtained by measuring the reflection spectrum of a broadband cholesteric liquid crystal film with a spectrophotometer (manufactured by Otsuka Electronics Co., Ltd., instantaneous multi-photometry system MCPD-2000), and has a reflection band having half the maximum reflectance. And

  In the broadband cholesteric liquid crystal film, it is preferable that the pitch length of the cholesteric liquid crystal film is changed so as to be continuously narrowed from the ultraviolet radiation side.

  In the broadband cholesteric liquid crystal film, it is preferable that the polymerizable mesogen compound (a) has one polymerizable functional group and the polymerizable chiral agent (b) has two or more polymerizable functional groups.

  As disclosed in Broer et al., Nature, Vol. 378, pp. 467 (1995), a broadband cholesteric liquid crystal film in which a mesogenic compound having chirality is diffused and whose pitch continuously changes is obtained. On the other hand, in the present invention, a mesogen compound having one polymerizable functional group is diffused to obtain a broadband cholesteric liquid crystal having a continuously changing pitch, so that the order of changes in chiral pitch is reversed. That is, in the present invention, it is possible to obtain a broadband cholesteric liquid crystal film having a pitch change such that the pitch length continuously narrows from the ultraviolet irradiation side. Further, the pitch length is preferably changed so that the difference between the ultraviolet radiation side and the opposite side is at least 100 nm. The pitch length was read from a cross-sectional TEM image of the broadband cholesteric liquid crystal film.

  The obtained cholesteric liquid crystal film has a Grand Jean structure in which the pitch length changes so as to be continuously narrowed from one side. On the long pitch length side, it is preferable to have a spiral structure having a pitch length showing reflection in the infrared region continuously or discontinuously or a layer in which the spiral is substantially eliminated. In the above-mentioned broadband cholesteric liquid crystal film, the layer in which the helical structure having a long pitch length or the helical structure is almost eliminated may be a retardation layer having a retardation value of 50 to 450 nm optically with respect to incident light from the front. preferable. As described above, the cholesteric liquid crystal has a portion exhibiting selective reflection in the visible region (380 to 780 nm) and has a layer having a pitch completely different from the portion exhibiting selective reflection on the long pitch length side. ing. This layer is a retardation layer as an optical property, and its retardation value can be controlled between 50 and 450 nm. For example, when the retardation value is 100 to 160 nm, light in the visible light region passing through the cholesteric liquid crystal film shows linearly polarized light. On the other hand, when the phase difference value is 200 to 400 nm, it can be converted into a state of circularly polarized light having a rotation opposite to the state of circularly polarized light transmitted through the cholesteric liquid crystal. Thus, the polarization state of transmitted light can be freely controlled by the retardation value of the retardation layer of the broadband cholesteric liquid crystal film. Therefore, it can be easily used as a polarizing plate according to the mode of the liquid crystal display to be used.

  The liquid crystal mixture forming the broadband cholesteric liquid crystal film may not contain an ultraviolet absorber.

  The broadband cholesteric liquid crystal film of the present invention can have a broadband reflection bandwidth without using an ultraviolet absorber. Therefore, it is possible to suppress an increase in haze, a decrease in the transmittance of polarized light, and visualization of precipitated particles by using an ultraviolet absorber, and the durability under a heating / humidifying environment is good, and the reliability is excellent. .

In the broadband cholesteric liquid crystal film, the molar extinction coefficient of the polymerizable mesogen compound (a) is preferably from 50 to 500 dm ³ mol ⁻¹ cm ⁻¹ ＠ 365 nm. Those having the molar extinction coefficient have an ultraviolet absorbing ability. The molar extinction coefficient is more preferably from 100 to 250 dm ³ mol ^-1 cm ^-1 ＠ 365 nm. If the molar extinction coefficient is less than 50 dm ³ mol ^-1 cm ^-1 ＠ 365 nm, it is difficult to obtain a wide band without a sufficient difference in polymerization rate. On the other hand, if it is larger than 500 dm ³ mol ^-1 cm ^-1 ＠ 365 nm, the polymerization may not proceed completely and the curing may not be completed. The molar extinction coefficient is a value obtained by measuring a spectrophotometric spectrum of each material and measuring the obtained absorbance at 365 nm.

  As the polymerizable mesogen compound (a), the following general formula (1):

（但し、Ｒ₁ は水素原子またはメチル基を示す。ｎは１〜５の整数を表す。）で表される化合物が好適である。

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

  Further, the present invention provides a method for applying a liquid crystal mixture containing a polymerizable mesogen compound (a), a polymerizable chiral agent (b) and a photopolymerization initiator (c) on an alignment substrate, and then, under an inert gas atmosphere, A method for producing the broadband cholesteric liquid crystal film, which is characterized by performing ultraviolet polymerization. The broadband cholesteric liquid crystal film of the present invention can be produced by controlling the temperature, ultraviolet irradiance, and irradiation time of ultraviolet irradiation of the liquid crystal mixture applied on an alignment substrate in an inert gas atmosphere.

  The present invention also relates to a circularly polarizing plate using the broadband cholesteric liquid crystal film.

  The present invention also relates to a linear polarizer obtained by laminating a λ / 4 plate on the circularly polarizing plate. In the linear polarizer, the cholesteric liquid crystal film, which is a circularly polarizing plate, is preferably laminated on the λ / 4 plate so that the pitch length is continuously narrowed.

  The present invention also relates to a linear polarizer obtained by attaching an absorption polarizer to the transmission axis of the linear polarizer so that the transmission axis direction thereof is aligned.

  The λ / 4 plate used for the linear polarizer has the following formula: (nx−nz) / (nx−ny), where the in-plane main refractive index is nx and ny, and the main refractive index in the thickness direction is nz. It is preferable that the defined Nz coefficient satisfies -0.5 to -2.5.

  Further, the present invention relates to a lighting device comprising the above-mentioned circularly polarizing plate or linear polarizer on the front side of a surface light source having a reflective layer on the back side.

  Furthermore, the present invention relates to a liquid crystal display device having a liquid crystal cell on the light emission side of the lighting device.

  As the linear polarizer, the lighting device, and the liquid crystal display device, those in which all or a part of each forming layer is in close contact with an adhesive layer can be used.

  The broadband cholesteric liquid crystal film of the present invention is used as a circularly polarizing plate, and a linear polarizer can be obtained by combining a λ / 4 plate. Further, the reliability of the liquid crystal display device can be improved by combining an absorbing polarizer or the like.

  The cholesteric liquid crystal film of the present invention is obtained by applying a liquid crystal mixture containing a polymerizable mesogen compound (a), a polymerizable chiral agent (b) and a photopolymerization initiator (c) onto an alignment substrate, and then applying an inert gas atmosphere. It is obtained by UV polymerization below.

As the polymerizable mesogen compound (a), a compound having at least one polymerizable functional group and having a mesogen group composed of a cyclic unit or the like is preferably used. Examples of the polymerizable functional group include an acryloyl group, a methacryloyl group, an epoxy group, and a vinyl ether group, and among these, an acryloyl group and a methacryloyl group are preferable. As described above, the polymerizable mesogen compound (a) preferably has a molar extinction coefficient of 50 to 500 dm ³ mol ^-1 cm ^-1 ＠ 365 nm. As described above, as the polymerizable mesogen compound (a) having such a molar extinction coefficient, the following general formula (1):

（但し、Ｒ₁ は水素原子またはメチル基を示す。ｎは１〜５の整数を表す。）で表される化合物が好適である。

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

  Specific examples of the polymerizable mesogen compound (a) include, for example,

で表される化合物があげられる。

The compound represented by is mentioned.

  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 mesogen compound (a) and the polymerizable chiral agent (b). Parts are more preferred. The helical torsional force (HTP) is controlled by the ratio of the polymerizable mesogen 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 region.

  Various photopolymerization initiators (c) can be used without particular limitation. For example, Irgacure 184, Irgacure 907, Irgacure 369, Irgacure 651 and the like manufactured by Ciba Specialty Chemicals Inc. may be mentioned. The compounding amount of the photopolymerization initiator is preferably about 0.01 to 10 parts by weight, preferably 0.05 to 5 parts by weight, based on 100 parts by weight of the polymerizable mesogen compound (a) and the polymerizable chiral agent (b) in total. Parts are more preferred.

  Further, in the present invention, a solution in which a liquid crystal mixture containing a polymerizable mesogen compound (a), a polymerizable chiral agent (b) and a photopolymerization initiator (c) is dissolved in a solvent can be used. 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 on an alignment substrate and then polymerizing the mixture under an inert gas atmosphere.

  As the alignment base material, a conventionally known one can be used. For example, a thin film made of polyimide, polyvinyl alcohol, etc. is formed on a substrate and then rubbed with a rayon cloth or the like. A rubbing film, an oblique deposition film, a polymer having a photocrosslinking group such as cinnamate or azobenzene, or a polarized ultraviolet light A photo-alignment film, a stretched film, or the like irradiated with is used. In addition, the orientation can be performed by a magnetic field, an electric field orientation, and a shear stress operation.

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

  The liquid crystal mixture is transferred to an inert gas atmosphere after being applied to the alignment substrate. When the liquid crystal mixture is a solution, the solution is applied to an alignment substrate, dried, and then transferred to an inert gas atmosphere. 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 the solvent.

  The coating thickness of the liquid crystal mixture (in the case of a solution, the coating thickness after drying the solvent) is preferably about 5 to 20 μm, and more preferably about 7 to 12 μm. If the coating thickness is less than 5 μm, it may not be possible to form a helical pitch sufficient to cover a reflection bandwidth of 200 nm or more, and if the coating thickness is more than 20 μm, the alignment regulating force may not act sufficiently and may cause poor alignment. .

  The inert gas is not particularly limited as long as it does not affect the ultraviolet polymerization of the liquid crystal mixture. Examples of such an inert gas include nitrogen, argon, helium, neon, xenon, and krypton. Of these, nitrogen is the most versatile and preferred.

  Irradiation with ultraviolet light may be performed from either the alignment substrate side or the applied liquid crystal mixture side.

  As the polymerization temperature when irradiating ultraviolet rays, 140 ° C. or lower is generally suitable. Specifically, about 60 to 140 ° C. is preferable, and 80 to 120 ° C. is suitable. Heating has the effect of accelerating the diffusion rate of the monomer component. If the temperature is lower than 60 ° C., the diffusion rate of the polymerizable mesogen compound (a) is very slow, and it takes a very long time to broaden the band.

Ultraviolet illuminance is preferably ^{0.1~20mW / cm 2, 1~10mW / cm} 2 is more preferable. If the UV illuminance exceeds 20 mW / cm ² , the polymerization reaction rate becomes higher than the diffusion rate, and the band is not broadened. The irradiation time is as short as 5 minutes or less, preferably 3 minutes or less, and most preferably 1 minute or less.

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

  The broadband cholesteric liquid crystal film of the present invention is used as a circularly polarizing plate. A linear polarizer can be formed by laminating a λ / 4 plate on the circularly polarizing plate. The cholesteric liquid crystal film, which is a circularly polarizing plate, is preferably laminated on the λ / 4 plate so that the pitch length is continuously narrowed.

  The λ / 4 plate has an Nz coefficient defined by the formula: (nx−nz) / (nx−ny), where in-plane main refractive indices are nx and ny, and main refractive index in the thickness direction is nz. Those satisfying -0.5 to -2.5 are preferable.

  As the 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 or other polyolefin, 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, and 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 shows, for example, a retardation layer that functions as a λ / 4 wavelength plate with respect to light-color light having a wavelength of 550 nm and other retardation characteristics. It can be obtained by a method of superimposing 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 absorption type 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 a hydrophilic polymer film such as a polyvinyl alcohol-based film, a partially formalized polyvinyl alcohol-based film, an ethylene-vinyl acetate copolymer-based partially saponified film, and a dichromatic dye such as iodine or a dichroic dye. And uniaxially stretched by adsorbing a hydrophilic substance, or a polyene-based oriented film such as a dehydrated product of polyvinyl alcohol or a dehydrochlorinated product of polyvinyl chloride. Among these, a polarizer composed of a polyvinyl alcohol-based film and a dichroic substance 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-based film with iodine and uniaxially stretching can be produced, for example, by dyeing polyvinyl alcohol by immersing it in an aqueous solution of iodine, and stretching the film to 3 to 7 times its original length. If necessary, it can be immersed in an aqueous solution of boric acid or potassium iodide. Further, if necessary, the polyvinyl alcohol-based film may be immersed in water and washed with water before dyeing. By washing the polyvinyl alcohol-based film with water, dirt on the surface of the polyvinyl alcohol-based film and an anti-blocking agent can be washed, and by swelling the polyvinyl alcohol-based film, the effect of preventing unevenness such as uneven dyeing can be obtained. is there. Stretching may be performed after dyeing with iodine, may be performed while dyeing, or may be dyed with iodine after stretching. Stretching can be performed in an aqueous solution of boric acid or potassium iodide or in a water bath.

  The polarizer is usually provided with a transparent protective film on one or both sides and used as a polarizing plate. The transparent protective film preferably has excellent transparency, mechanical strength, thermal stability, moisture shielding property, isotropy and the like. Examples of the transparent protective film 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. Is raised. Styrene polymers such as polystyrene and acrylonitrile / styrene copolymer; polyethylene, polypropylene, polyolefins having a cyclic or norbornene structure; olefin polymers such as ethylene / propylene copolymer; vinyl chloride polymers; nylon and aromatic polyamides And a film made of a transparent polymer such as an amide-based polymer. Furthermore, imide-based polymers, sulfone-based polymers, polyethersulfone-based polymers, polyetheretherketone-based polymers, polyphenylene sulfide-based polymers, vinyl alcohol-based polymers, vinylidene chloride-based polymers, vinylbutyral-based polymers, arylate-based polymers, and polyoxymethylene-based polymers Films made of transparent polymers such as polymers, epoxy polymers and blends of the above polymers are also included. In particular, those having low optical birefringence are preferably used. From the viewpoint of a protective film for a polarizing plate, triacetyl cellulose, polycarbonate, an acrylic polymer, a cycloolefin resin, a polyolefin having a norbornene structure, and the like are preferable.

  Further, polymer films described in JP-A-2001-343529 (WO 01/37007), for example, (A) a thermoplastic resin having a substituted and / or unsubstituted imide group in the side chain, and (B) a thermoplastic resin having a side chain And / or an unsubstituted phenyl and a resin composition containing a thermoplastic resin having a nitrile group. A specific example is a film of a resin composition containing an alternating copolymer of isobutylene and N-methylmaleimide and an acrylonitrile / styrene copolymer. As the film, a film composed of a mixed extruded product of a resin composition or the like can be used.

  A transparent protective film that can be particularly preferably used in view of polarization characteristics and durability is a triacetyl cellulose film whose surface has been saponified with an alkali or the like. Although the thickness of the transparent protective film can be determined as appropriate, it is generally about 10 to 500 μm from the viewpoint of workability such as strength and handleability, and thin layer property. In particular, 20 to 300 μm is preferable, and 30 to 200 μm is more preferable.

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

  As the transparent protective film, a transparent protective film made of the same polymer material on both sides may be used, or a transparent protective film made of a different polymer material or the like may be used.

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

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

  The anti-glare treatment is performed for the purpose of preventing external light from being reflected on the surface of the polarizing plate and hindering the visibility of light transmitted through the polarizing plate, and is, for example, a roughening method using a sand blast method or an embossing method. The transparent protective film can be formed by giving a fine uneven structure to the surface of the transparent protective film by an appropriate method such as a method of mixing transparent fine particles or the like. As the fine particles to be contained in the formation of the surface fine uneven structure, for example, a conductive material composed of silica, alumina, titania, zirconia, tin oxide, indium oxide, cadmium oxide, antimony oxide and the like having an average particle size of 0.5 to 50 μm. Transparent fine particles such as inorganic fine particles that may be used and organic fine particles made of a crosslinked or uncrosslinked polymer or the like are used. When forming the fine surface unevenness structure, the amount of the fine particles to be used is generally about 2 to 50 parts by weight, preferably 5 to 25 parts by weight, per 100 parts by weight of the transparent resin forming the fine surface unevenness structure. The anti-glare layer may also serve as a diffusion layer (such as a viewing angle enlargement function) for diffusing light transmitted through the polarizing plate to increase the viewing angle and the like.

  The anti-reflection layer, anti-sticking layer, diffusion layer, anti-glare layer and the like can be provided on the transparent protective film itself, or can be provided as an optical layer separately from the transparent protective layer.

  The lamination of the linear polarizer, and further the lamination of various optical layers, can be performed by a method of sequentially laminating sequentially in a manufacturing process of a liquid crystal display device or the like. It is excellent in stability and assembling work, and has an advantage that a manufacturing process of a liquid crystal display device or the like can be improved. Appropriate bonding means such as an adhesive layer can be used for lamination. At the time of the bonding, the optical axes thereof can be set at an appropriate arrangement angle depending on the target retardation characteristic or the like.

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

  In addition to the above, prevention of foaming and peeling phenomena due to moisture absorption, reduction of optical characteristics due to thermal expansion difference and the like, prevention of warpage of the liquid crystal cell, and, in view of the formability of a liquid crystal display device having high quality and excellent durability, etc. An adhesive layer having low moisture absorption and excellent heat resistance is preferred.

  The adhesive layer is, for example, a natural or synthetic resin, in particular, a tackifier resin, or a filler, a pigment, a colorant, an antioxidant, or the like made of glass fiber, glass beads, metal powder, other inorganic powder, and the like. May be added to the pressure-sensitive adhesive layer. In addition, an adhesive layer containing fine particles and exhibiting light diffusibility may be used.

  The attachment of the adhesive layer can be performed by an appropriate method. As an example thereof, for example, an adhesive solution of about 10 to 40% by weight is prepared by dissolving or dispersing a base polymer or a composition thereof in a solvent composed of a single solvent or a mixture of appropriate solvents such as toluene and ethyl acetate, A method in which it is directly attached on the polarizer by an appropriate developing method such as a casting method or a coating method, or a method in which an adhesive layer is formed on a separator according to the above and transferred to an optical element. Is raised. The adhesive layer may be provided as a superimposed layer of different compositions or types of layers. The thickness of the pressure-sensitive adhesive layer can be appropriately determined depending on the purpose of use, adhesive strength, and the like, and is generally 1 to 500 µm, preferably 5 to 200 µm, particularly preferably 10 to 100 µm.

  A separator is temporarily attached to the exposed surface of the adhesive layer for the purpose of preventing contamination and the like until the adhesive layer is put to practical use and covered. This can prevent the adhesive layer from coming into contact with the adhesive layer in a normal handling state. Except for the above thickness conditions, the separator may be, for example, a plastic film, a rubber sheet, paper, cloth, a nonwoven fabric, a net, a foamed sheet or a metal foil, a suitable thin sheet such as a laminate thereof, or a silicone-based material as necessary. Appropriate conventional ones, such as those coated with an appropriate release agent such as a long-chain alkyl-based, fluorine-based, or molybdenum sulfide, may be used.

  Each layer such as an adhesive layer may be subjected to ultraviolet absorption by a method such as a method of treating with an ultraviolet absorber such as a salicylic acid ester compound, a benzophenol compound, a benzotriazole compound, a cyanoacrylate compound, or a nickel complex compound. It may have a function.

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

  Appropriate liquid crystal display devices such as a liquid crystal display device in which the linear polarizer is arranged on one or both sides of a liquid crystal cell, and a lighting system using a backlight or a reflector can be formed. In that case, the linear polarizer according to the present invention can be installed on one side 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 the liquid crystal display device, for example, a suitable component such as a diffusion plate, an anti-glare layer, an antireflection film, a protection plate, a prism array, a lens array sheet, a light diffusion plate, a backlight, etc. Two or more layers can be arranged.

  Hereinafter, the present invention will be described with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

  In each of the examples, the polymerizable mesogen compound (a) is represented by the following chemical formula 5,

で表される化合物を用いた。モル吸光係数は、２２０ｄｍ³ ｍｏｌ^-1ｃｍ^-1＠３６５ｎｍであった。また、重合性カイラル剤（ｂ）として、ＢＡＳＦ社製ＬＣ７５６を用いた。

The compound represented by was used. The molar extinction coefficient was 220 dm ³ mol ^-1 cm ^-1 ＠ 365 nm. Further, as the polymerizable chiral agent (b), LC756 manufactured by BASF was used.

Example 1
A mixture comprising 96 parts by weight of the polymerizable mesogen compound (a) of the above formula 5, 4 parts by weight of the polymerizable chiral agent (b), and 5 parts by weight of Irgacure 184 (manufactured by Ciba Specialty Chemicals) as a photopolymerization initiator (c). Was prepared (a 30 wt% solids content). The solution was cast on a stretched polyethylene terephthalate substrate and dried at 100 ° C. for 2 minutes to remove the solvent. Subsequently, while heating at 120 ° C. in a nitrogen atmosphere, ultraviolet irradiation was performed from the substrate side at 3 mW / cm ² for 5 minutes to obtain a target cholesteric liquid crystal film.

  FIG. 2 shows the reflection spectrum of the obtained cholesteric liquid crystal film (circularly polarizing plate). The circularly polarizing plate had good circularly polarized light separation characteristics (reflection band) in the range of 450 to 890 nm. The total thickness of the cholesteric liquid crystal layer (film) was about 9 μm. The pitch length of the obtained cholesteric liquid crystal layer was 0.54 μm near the ultraviolet irradiation surface (1 μm below the ultraviolet irradiation surface) and 0.27 μm near the opposite surface (1 μm below the opposite surface).

  The pitch length of the obtained circularly polarizing plate is continuously reduced with respect to the wide viewing angle λ / 4 plate (Nz coefficient = −1.2) obtained by biaxially stretching the polycarbonate resin film (thickness: 80 μm). In such a direction, they were bonded with an acrylic adhesive (thickness: 25 μm). Furthermore, an absorption type polarizing plate SEG1425DU manufactured by Nitto Denko was laminated with an adhesive to obtain a broadband polarizing plate.

Example 2
From 96 parts by weight of the polymerizable mesogen compound (a) of the above formula 5, 4 parts by weight of the polymerizable chiral agent (b), and 0.5 parts by weight of Irgacure 907 (manufactured by Ciba Specialty Chemicals) as a photopolymerization initiator (c). A cyclopentanone solution (30 wt% solids content) of the resulting mixture was prepared. The solution was cast on a stretched polyethylene terephthalate substrate and dried at 100 ° C. for 2 minutes to remove the solvent. Subsequently, while heating at 120 ° C. in a nitrogen atmosphere, ultraviolet irradiation was performed from the substrate side at 3 mW / cm ² for 5 minutes to obtain a target cholesteric liquid crystal film.

  FIG. 3 shows the reflection spectrum of the obtained cholesteric liquid crystal film (circularly polarizing plate). The obtained circularly polarizing plate had good circularly polarized light separation characteristics in the range of 510 to 970 nm. The total thickness of the cholesteric liquid crystal layer (film) was about 9 μm. Further, the pitch length of the obtained cholesteric liquid crystal layer was 0.57 μm near the ultraviolet irradiation surface (1 μm below the ultraviolet irradiation surface) and 0.31 μm near the opposite surface (1 μm below the opposite surface).

  The pitch length of the obtained circularly polarizing plate is continuously reduced with respect to the wide viewing angle λ / 4 plate (Nz coefficient = −1.2) obtained by biaxially stretching the polycarbonate resin film (thickness: 80 μm). In such a direction, they were bonded with an acrylic adhesive (thickness: 25 μm). Further, an absorption type polarizing plate TEG1465DU manufactured by Nitto Denko was laminated with an adhesive material to obtain a broadband polarizing plate.

Example 3
From 96 parts by weight of the polymerizable mesogen compound (a) of formula 5, 4 parts by weight of the polymerizable chiral agent (b), and 0.05 parts by weight of Irgacure 369 (manufactured by Ciba Specialty Chemicals) as a photopolymerization initiator (c). A cyclopentanone solution (30 wt% solids content) of the resulting mixture was prepared. The solution was cast on a stretched polyethylene terephthalate substrate and dried at 100 ° C. for 2 minutes to remove the solvent. Next, while heating at 120 ° C. in a nitrogen atmosphere, ultraviolet irradiation was performed from the substrate side at 11 mW / cm ² for 5 minutes to obtain a target cholesteric liquid crystal film.

  FIG. 4 shows the reflection spectrum of the obtained cholesteric liquid crystal film (circular polarizing plate). The obtained circularly polarizing plate had good circularly polarized light separation characteristics in the range of 520 to 920 nm. The total thickness of the cholesteric liquid crystal layer (film) was about 9 μm. Further, the pitch length of the obtained cholesteric liquid crystal layer was 0.56 μm near the ultraviolet irradiation surface (1 μm below the ultraviolet irradiation surface) and 0.31 μm near the opposite surface (1 μm below the opposite surface).

  The obtained circularly polarizing plate was laminated on a λ / 4 plate (NRF film made by Nitto Denko △ n = 140 nm, Nz coefficient = −1.2) in such a direction that the pitch length was continuously narrowed. A λ / 2 plate (NRZ film manufactured by Nitto Denko @ n = 270 nm, Nz coefficient = 0.5, viewing angle characteristic compensation type) was arranged at 117.5 degrees with respect to the axis angle. For the lamination, an acrylic adhesive material (thickness: 25 μm) was used. In this case, the transmission polarization axis is 10 degrees with respect to the axis of the λ / 4 plate, so that an absorption type polarizer SEG1425DU manufactured by Nitto Denko was similarly adhered in this direction to obtain a broadband polarization plate.

Comparative Example 1
A mixture comprising 96 parts by weight of the polymerizable mesogen compound (a) of the above formula 5, 4 parts by weight of the polymerizable chiral agent (b), and 5 parts by weight of Irgacure 184 (manufactured by Ciba Specialty Chemicals) as a photopolymerization initiator (c). Was prepared (a 30 wt% solids content). The solution was cast on a stretched polyethylene terephthalate substrate and dried at 100 ° C. for 2 minutes to remove the solvent. Subsequently, while heating at 80 ° C. in a nitrogen atmosphere, ultraviolet irradiation was performed from the substrate side at 50 mW / cm ² for 5 minutes to obtain a target cholesteric liquid crystal film.

  FIG. 5 shows the reflection spectrum of the obtained cholesteric liquid crystal film (circularly polarizing plate). The obtained circularly polarizing plate had good circularly polarized light separation characteristics in the range of 710 to 880 nm. The total thickness of the cholesteric liquid crystal layer (film) was about 9 μm. The pitch length of the obtained cholesteric liquid crystal layer was 0.52 μm near the ultraviolet irradiation surface (1 μm below the ultraviolet irradiation surface) and 0.52 μm near the opposite surface (1 μm below the opposite surface).

  The pitch length of the obtained circularly polarizing plate is continuously reduced with respect to the wide viewing angle λ / 4 plate (Nz coefficient = −1.2) obtained by biaxially stretching the polycarbonate resin film (thickness: 80 μm). In such a direction, they were bonded with an acrylic adhesive (thickness: 25 μm). Further, a polarizing plate was obtained by laminating an absorption polarizing plate SEG1425DU manufactured by Nitto Denko with an adhesive.

Comparative Example 2
A mixture comprising 96 parts by weight of the polymerizable mesogen compound (a) of the above formula 5, 4 parts by weight of the polymerizable chiral agent (b), and 5 parts by weight of Irgacure 184 (manufactured by Ciba Specialty Chemicals) as a photopolymerization initiator (c). Was prepared (a 30 wt% solids content). The solution was cast on a stretched polyethylene terephthalate substrate and dried at 100 ° C. for 2 minutes to remove the solvent. Next, while heating at 40 ° C. under a nitrogen atmosphere, ultraviolet irradiation was performed from the substrate side at 3 mW / cm ² for 5 minutes to obtain a target cholesteric liquid crystal film.

  FIG. 6 shows the reflection spectrum of the obtained cholesteric liquid crystal film (circularly polarizing plate). The obtained circularly polarizing plate had good circularly polarized light separation characteristics in the range of 720 to 870 nm. The total thickness of the cholesteric liquid crystal layer (film) was about 9 μm. The pitch length of the obtained cholesteric liquid crystal layer was 0.52 μm near the ultraviolet irradiation surface (1 μm below the ultraviolet irradiation surface) and 0.52 μm near the opposite surface (1 μm below the opposite surface).

  The pitch length of the obtained circularly polarizing plate is continuously reduced with respect to the wide viewing angle λ / 4 plate (Nz coefficient = −1.2) obtained by biaxially stretching the polycarbonate resin film (thickness: 80 μm). In such a direction, they were bonded with an acrylic adhesive (thickness: 25 μm). Further, a polarizing plate was obtained by laminating an absorption polarizing plate SEG1425DU manufactured by Nitto Denko with an adhesive.

Comparative Example 3
96 parts by weight of the polymerizable mesogen compound (a) represented by Chemical Formula 5, 4 parts by weight of the polymerizable chiral agent (b), 5 parts by weight of Irgacure 184 (manufactured by Ciba Specialty Chemicals) as a photopolymerization initiator (c), and Tinuvin 400 A cyclopentanone solution (30% by weight solids content) of a mixture consisting of 1 part by weight (UV absorber, manufactured by Ciba Specialty Chemical Co., Ltd.) was prepared. The solution was cast on a stretched polyethylene terephthalate substrate and dried at 100 ° C. for 2 minutes to remove the solvent. Subsequently, while heating at 80 ° C. in a nitrogen atmosphere, ultraviolet irradiation was performed from the substrate side at 50 mW / cm ² for 5 minutes to obtain a target cholesteric liquid crystal film.

  FIG. 7 shows the reflection spectrum of the obtained cholesteric liquid crystal film (circularly polarizing plate). The obtained circularly polarizing plate had good circularly polarized light separation characteristics in the range of 710 to 860 nm. The total thickness of the cholesteric liquid crystal layer (film) was about 9 μm. Further, the pitch length of the obtained cholesteric liquid crystal layer was 0.51 μm near the ultraviolet irradiation surface (1 μm below the ultraviolet irradiation surface) and 0.51 μm near the opposite surface (1 μm below the opposite surface).

  The pitch length of the obtained circularly polarizing plate is continuously reduced with respect to the wide viewing angle λ / 4 plate (Nz coefficient = −1.2) obtained by biaxially stretching the polycarbonate resin film (thickness: 80 μm). In such a direction, they were bonded with an acrylic adhesive (thickness: 25 μm). Further, a polarizing plate was obtained by laminating an absorption polarizing plate SEG1425DU manufactured by Nitto Denko with an adhesive.

  The following evaluations were performed on the (broadband) polarizing plates obtained in the examples and comparative examples. Table 1 shows the results.

(Brightness improvement rate)
The luminance when the (broadband) polarizing plate was mounted on a 15-inch TFT liquid crystal display device was measured by BM7 manufactured by TOPCON. The magnification of the increased luminance was calculated as compared to the luminance without the broadband cholesteric liquid crystal film.

(Viewing angle characteristics: color tone change)
The viewing angle characteristics were evaluated based on the following criteria by deriving Δxy using a viewing angle measuring device EZ-CONTRAST manufactured by ELDIM.
Δxy = ((x ₀ −x ₁ ) ² + (y ₀ −y ₁ ) ² ) ^0.5
Front chromaticity (x ₀ , y ₀ ), 60 ° chromaticity (x ₁ , y ₁ )
Good: Color tone change Δxy at a viewing angle of 60 ° is 0.04 or less.
Poor: color tone change Δxy at a viewing angle of 60 ° was 0.04 or more.

(durability)
After the broadband polarizing plate or the polarizing plate was put in an environment of 80 ° C., 60 ° C. and 90% RH for 500 hours, the presence or absence of a powdery substance deposited on the surface was visually determined. When a powdery substance is present, there is a problem as an optical application.

It is a conceptual diagram of the polarizing plate used for evaluation of Examples 1-3 and Comparative Examples 1-3. 3 is a reflection spectrum of the cholesteric liquid crystal film produced in Example 1. 5 is a reflection spectrum of the cholesteric liquid crystal film produced in Example 2. 9 is a reflection spectrum of the cholesteric liquid crystal film produced in Example 3. 5 is a reflection spectrum of a cholesteric liquid crystal film produced in Comparative Example 1. 9 is a reflection spectrum of a cholesteric liquid crystal film produced in Comparative Example 2. 9 is a reflection spectrum of a cholesteric liquid crystal film produced in Comparative Example 3.

Explanation of reference numerals

Reference Signs List 1 polarizing plate 2 λ / 4 plate 3 cholesteric liquid crystal film (circular polarizing plate)
4 Adhesive layer

Claims (14)

  A liquid crystal mixture containing a polymerizable mesogen compound (a), a polymerizable chiral agent (b) and a photopolymerization initiator (c) is applied on an alignment substrate, and is subjected to ultraviolet polymerization under an inert gas atmosphere. A broadband cholesteric liquid crystal film having a reflection bandwidth of 200 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 so as to continuously narrow from the ultraviolet radiation side.   3. The broadband cholesteric liquid crystal according to claim 1, wherein the polymerizable mesogen compound (a) has one polymerizable functional group, and the polymerizable chiral agent (b) has two or more polymerizable functional groups. the film.   4. The broadband cholesteric liquid crystal film according to claim 1, wherein the liquid crystal mixture does not contain an ultraviolet absorber. The broadband cholesteric liquid crystal film according to any one of claims 1 to 4, wherein the molar extinction coefficient of the polymerizable mesogen compound (a) is 50 to 500 dm ³ mol ^-1 cm ^-1 ＠ 365 nm. The polymerizable mesogen compound (a) has the following general formula (1):

(Wherein R ₁ represents a hydrogen atom or a methyl group; n represents an integer of 1 to 5). A broadband cholesteric according to any one of claims 1 to 5, wherein LCD film.   Applying a liquid crystal mixture containing a polymerizable mesogen compound (a), a polymerizable chiral agent (b) and a photopolymerization initiator (c) onto an alignment substrate, and then performing ultraviolet polymerization polymerization under an inert gas atmosphere. The method for producing a broadband cholesteric liquid crystal film according to any one of claims 1 to 6, wherein   A circularly polarizing plate using the broadband cholesteric liquid crystal film according to claim 1.   A linear polarizer obtained by laminating a λ / 4 plate on the circular polarizer according to claim 8.   The linear polarizer according to claim 9, 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 attaching an absorption type polarizer to the transmission axis of the linear polarizer according to claim 9 or 10 so that the transmission axis direction thereof is aligned.   When the λ / 4 plate has an in-plane principal refractive index of nx and ny and a thickness direction principal refractive index of nz, the Nz coefficient defined by the formula: (nx−nz) / (nx−ny) becomes The linear polarizer according to any one of claims 9 to 11, which satisfies -0.5 to -2.5.   An illumination device comprising a circular polarizer according to claim 8 or a linear polarizer according to any one of claims 9 to 12 on the front side of a surface light source having a reflective layer on the back side. A liquid crystal display device comprising a liquid crystal cell on the light emitting side of the lighting device according to claim 13.

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