JP2008268417A - Anisotropic scattering element, polarizing plate and liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an anisotropic scattering element which is excellent in productivity, has polarization scattering anisotropy and has luminance improving function, and to provide a polarizing plate and a liquid crystal display device using the anisotropic scattering element. <P>SOLUTION: The anisotropic scattering element is made by dispersedly arranging domains 3 which are optically isotropic and have aspect ratio of ≥2 and ≤100 into a support medium, wherein the domains include particles having aspect ratio of ≥1 and <2. The aspect ratio is major axis diameter/minor axis diameter, the major axis diameter means the absolute maximum length of the domain and particle, and the minor axis diameter means the minimum distance between two straight lines when holding a projected image of the domain between the two straight lines parallel to the absolute maximum length. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention is a polarizing plate protective film having excellent productivity and having a polarization scattering anisotropy and a function of improving luminance, a polarizing plate using the same, and a liquid crystal display device.

  In recent years, in the field of liquid crystal display devices represented by liquid crystal televisions, improving the light extraction efficiency from the backlight is an important technical issue not only from the viewpoint of increasing luminance but also from the viewpoint of reducing power consumption. It has become.

  In that sense, the point is how efficiently the 50% (theoretical value) portion that is absorbed when light passes through the dichroic polarizing film can be used.

  In order to deal with such a problem, so-called brightness enhancement films having several light utilization efficiencies have been studied.

  For example, as disclosed in Patent Document 1, two layers having different refractive indexes are laminated and reflected using the principle of thin film interference, and there is an axis that is laminated but has no refractive index difference and transmits as it is. Examples thereof include a film that undergoes polarization separation and a polarization separation film that utilizes the circular dichroism of a cholestric liquid crystal as disclosed in Patent Document 2. However, these films have the disadvantages that the manufacturing difficulty is high and the productivity is low.

  Further, Patent Document 3 discloses a film having polarization scattering anisotropy comprising a dispersed phase of polymer particles in an optical continuous layer having birefringence.

  Although this technique is slightly less difficult to manufacture than the technique of Patent Document 1 or 2, it requires a technique with a high degree of difficulty in adjusting the refractive index.

  In addition, since the film surface is poorly smooth, it has the disadvantage that it is difficult to integrate with the dichroic polarizing film, and it can not meet the recent needs for reducing backlight side members in the field of liquid crystal display devices. Absent.

  As a technique related to a polarizing element having polarization scattering anisotropy having a relatively high productivity, for example, a needle-like inorganic particle having a large aspect ratio of 2 or more such as titanium oxide as disclosed in Patent Document 4 is UV-cured. A technique for dispersing in a resin is known.

  However, with this technique, the aggregation of titanium oxide particles having a large aspect ratio in the ultraviolet curable resin is not sufficiently improved, and a satisfactory brightness enhancement effect cannot be obtained.

In addition, some of these needle-like inorganic particles themselves were abnormally grown in the course of firing when the particles were produced, and some particles were fused together. As a result, there was a problem that the effect of improving luminance was not stable.
Japanese Patent No. 362215 JP 2003-227933 A JP 2000-506990 A Japanese Patent No. 3090890

  Accordingly, an object of the present invention is to provide an anisotropic scattering element having excellent productivity, polarization scattering anisotropy and brightness enhancement function, and further a polarizing plate and a liquid crystal display device using the same. is there.

The object of the present invention has been achieved by the following.
1. An anisotropic scattering element in which domains having an optically isotropic aspect ratio of 2 or more and 100 or less are dispersed and arranged in a support medium, wherein the domains include particles having an aspect ratio of 1 or more and less than 2. An anisotropic scattering element.

Aspect ratio = major axis diameter / minor axis diameter (where the major axis diameter means the absolute maximum length of each domain and particle, and the minor axis diameter is two straight lines parallel to the absolute maximum length, which are projected. (It means the shortest distance between two straight lines when the image of the domain is sandwiched.)
2. A polarizing plate comprising an absorptive polarizer and two polarizing plate protective films sandwiching the absorptive polarizer, wherein one of the two polarizing plate protective films is the anisotropic scattering element according to 1 above. A characteristic polarizing plate.
3. 3. The polarizing plate according to 2 above, wherein an absorption axis of the absorptive polarizer is parallel to a major axis direction of a domain of the anisotropic scattering element.
4). A liquid crystal display device comprising the anisotropic scattering element according to 1 above.

  According to the present invention, it is possible to use particles having a small aspect ratio, so that the productivity is excellent, the polarization scattering anisotropy, the anisotropic scattering element having the function of improving the brightness, and the polarizing plate using the same. In addition, a liquid crystal display device can be provided.

The present invention will be described in detail below.
<Anisotropic scattering element>
In the present invention, the anisotropic scattering element refers to a film having a polarization scattering anisotropy and a function of improving luminance. For example, a predetermined polarized light as disclosed in JP-T-11-509014 is used. It refers to a polymer film that can selectively transmit, selectively scatter other polarized light, and reuse the scattered light to improve luminance.

  And this polymer film consists of the polymer which is a support medium for forming a film, and the domainin contained therein.

《Support medium》
In the present invention, the support medium is for forming a polymer film for supporting a domain, and can be used as an optical film, such as a cycloolefin polymer, cellulose acylate, and olefin polymer. , Acrylic polymer, styrene polymer, polycarbonate polymer, and polyester polymer.

"domain"
The domain of the present invention means an individual region present in the aforementioned polymer film, which is isotropic and has a refractive index different from that of the support medium. The domain contains particles, and the particles are present randomly.

  Here, the different refractive index means that the difference in refractive index between the domain and the support is 0.02 or more.

  The domain of the present invention is substantially isotropic, and being substantially isotropic means that the refractive index of each part of the domain is substantially constant and continuous, and variation in each part of the refractive index is 0. It means less than .01. The variation in refractive index is preferably 0.005 or less, particularly preferably 0.001 or less.

  The domain according to the present invention has a shape with an aspect ratio of 2 to 100.

Aspect ratio = major axis diameter / minor axis diameter Here, the major axis diameter means the absolute maximum length of the domain, and the minor axis diameter is an image of the projected domain as two straight lines parallel to the absolute maximum length. This means the shortest distance between two straight lines.

  The domain of the present invention comprises a polymer for forming a domain and particles having an aspect ratio of 1 or more and less than 2 contained therein.

  Examples of the polymer forming the domain of the present invention include polyvinyl pyrrolidone, polyvinyl alcohol, cycloolefin polymer, cellulose acylate, olefin polymer, acrylic polymer, styrene polymer, polycarbonate polymer, and polyester polymer. Two or more of these may be used in combination.

  The polymer that forms the domain of the present invention is basically birefringent. However, by stretching the film at a sufficiently high stretching temperature when creating the domain, the stress in the film is alleviated. It can be a sex domain.

  Examples of the particles having an aspect ratio of 1 or more and less than 2 contained in the domain of the present invention include titanium oxide, calcium silicate, zinc oxide, aluminum oxide, zirconium oxide, antimony oxide, and silicon dioxide.

  Any aspect ratio of the particles contained in the domain of the present invention can be used originally. However, in the present invention, the aspect ratio generally considered to be small in luminance improvement is 1 or more. Even if it is less than 2 particle | grains, it has the characteristics that it can be used for a brightness improvement.

  The particles of the present invention are commercially available, for example, as titanium oxide TTO51C (Ishihara Sangyo Co., Ltd.) or titania sol Queen Titanic (Catalyst Chemical Industries Co., Ltd.).

  A high boiling point solvent, a surfactant or the like may be added to the domain in order to cause the particles to be stably present in the domain.

  The particles of the present invention may be surface treated with a surface modifier. As the surface treatment, various modifiers such as fatty acid-based, oil-based, surfactant-based, wax-based, silane coupling agent, carboxylic acid coupling agent, phosphoric acid-based coupling agent, and polymer system can be used.

  Treatment methods include coating methods that coat the surface with fatty acids, metal salts, surfactants, etc., topochemical methods that bind the coupling agent to the particle surface, and mechanochemical methods that add organic treatment agents in the particle grinding process. There are various methods such as a capsule method in which a monomer is polymerized or graft-polymerized on the particle surface and the particle surface is coated with a polymer. The modifier and treatment method vary depending on the type of support and domain, and can be appropriately handled.

  The major axis diameter / minor axis diameter of the domain in the film can be determined using image data observed with an electron microscope.

  For example, the produced film was photographed at a magnification of 20,000 with a transmission electron microscope, and the image was read in 300 dpi monochrome 256 gradation using a scanner Canon Scan FB 636U manufactured by Canon Inc. The read image was manufactured by Epson Direct Co., Ltd. Image processing software WinROOF ver3.60 (manufactured by Mitani Corp.) installed in Endeavor Pro720L (CPU; Athlon-1 GHz, memory: 512 MB).

  Perform domain image extraction on the captured image, confirm that there are more than 300 domains on the screen after domain image extraction, and if the extraction is not enough, manually adjust the detection level, Make adjustments to detect and extract domains.

  By measuring the major axis diameter / minor axis diameter as an average value for each domain of the image data extracted in this way, the aspect ratio of the average number of domains can be calculated.

  At this time, the shape of the domain does not necessarily reflect individual shapes of particles as shown in the following example.

  In the present invention, an aggregate composed of a plurality of constituent particles is regarded as one domain.

  The domain size of the present invention is preferably such that the major axis diameter of the domain is 400 to 10,000 nm and the minor axis diameter is 50 or more and less than 400 nm.

  The size of the particles of the present invention was 1 to 50 nm as an average particle diameter, and was calculated as the average value of the major axis diameter and the minor axis diameter in the domain size measurement method.

  The particle | grains of this invention are 1-99 volume% content with respect to a domain, Preferably it is 20-80 volume%. The volume% was expressed by converting the projected area by the transmission electron microscope into a volume (assuming a circle having the same area as the projected area and converted to the volume of a sphere having the radius).

  The particle dispersion method of the present invention can be broadly divided into two methods: a method using a disperser and a method using a kneader. The former is further divided into media distribution and medialess distribution. Examples of the media dispersion include a disperser such as a ball mill and a sand mill. Examples of the medialess dispersion include an ultrasonic type and a centrifugal type. In the present invention, either a disperser or a kneader may be used.

《Other additives》
<Plasticizer>
As the plasticizer used in the present invention, it is preferable to use a polyester plasticizer having a number average molecular weight of 300 or more and less than 2000 so as not to cause haze in the film, bleed out or volatilize from the film.

[Polyester plasticizer having a number average molecular weight of 300 to less than 2000]
The polyester plasticizer is not particularly limited, but a polyester plasticizer having an aromatic ring or a cycloalkyl ring in the molecule can be preferably used.

  For example, an aromatic terminal polyester plasticizer represented by the following general formula (1) is preferable.

General formula (1) B- (GA) n-GB
(In the formula, B is a benzene monocarboxylic acid residue, G is an alkylene glycol residue having 2 to 12 carbon atoms, an aryl glycol residue having 6 to 12 carbon atoms, or an oxyalkylene glycol residue having 4 to 12 carbon atoms, A represents an alkylene dicarboxylic acid residue having 4 to 12 carbon atoms or an aryl dicarboxylic acid residue having 6 to 12 carbon atoms, and n represents an integer of 1 or more.)
In the general formula (1), a benzene monocarboxylic acid residue represented by B and an alkylene glycol residue, oxyalkylene glycol residue or aryl glycol residue represented by G, an alkylene dicarboxylic acid residue or aryl dicarboxylic group represented by A It is composed of an acid residue.

  Examples of the benzene monocarboxylic acid component of the polyester plasticizer used in the present invention include benzoic acid, para-tert-butylbenzoic acid, orthotoluic acid, metatoluic acid, p-toluic acid, dimethylbenzoic acid, ethylbenzoic acid, and normalpropyl. There exist benzoic acid, aminobenzoic acid, acetoxybenzoic acid, etc., and these can be used as 1 type, or 2 or more types of mixtures, respectively.

  Examples of the alkylene glycol component having 2 to 12 carbon atoms of the polyester plasticizer of the present invention include ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,2-butanediol, and 1,3-butanediol. 1,2-propanediol, 2-methyl 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 2,2-dimethyl-1,3-propanediol (neopentyl glycol), 2,2-diethyl-1,3-propanediol (3,3-dimethylolpentane), 2-n-butyl-2-ethyl-1,3-propanediol (3,3-dimethylolheptane), 3-methyl -1,5-pentanediol 1,6-hexanediol, 2,2,4-trimethyl 1,3-pentanediol, 2-ethane 1,3-hexanediol, 2-methyl 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,12-octadecanediol, and the like. Used as a mixture of two or more.

  In particular, an alkylene glycol having 2 to 12 carbon atoms is preferable because of excellent compatibility with a cellulose derivative.

  Examples of the oxyalkylene glycol component having 4 to 12 carbon atoms of the polyester plasticizer of the present invention include diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, and tripropylene glycol. One kind or a mixture of two or more kinds can be used.

  Examples of the alkylene dicarboxylic acid component having 4 to 12 carbon atoms of the polyester plasticizer of the present invention include succinic acid, maleic acid, fumaric acid, glutaric acid, adipic acid, azelaic acid, sebacic acid, and dodecanedicarboxylic acid. These are each used as one or a mixture of two or more.

  Examples of the arylene dicarboxylic acid component having 6 to 12 carbon atoms include phthalic acid, terephthalic acid, isophthalic acid, 1,5 naphthalene dicarboxylic acid, and 1,4 naphthalene dicarboxylic acid.

  The polyester plasticizer used in the present invention has a number average molecular weight of preferably 300 to 1500, more preferably 400 to 1000.

  The acid value is preferably 0.5 mgKOH / g or less, the hydroxyl value is 25 mgKOH / g or less, more preferably the acid value is 0.3 mgKOH / g or less, and the hydroxyl value is 15 mgKOH / g or less.

  Polycondensation of the polyester plasticizer is performed by a conventional method. For example, a direct reaction of the above dibasic acid and glycol, the above dibasic acid or an alkyl ester thereof, for example, a polyesterification reaction or transesterification reaction between a dibasic acid methyl ester and a glycol, or a hot melt condensation method, Alternatively, it can be easily synthesized by any method of dehydrohalogenation reaction between acid chloride of these acids and glycol, but the polyester plasticizer of the present invention is preferably by direct reaction.

  A polyester plasticizer having a high distribution on the low molecular weight side has very good compatibility with a cellulose derivative, and after forming a film, a moisture permeability is small, and a cellulose derivative film rich in transparency can be obtained.

  A conventional method can be used as a method for adjusting the molecular weight without particular limitation. For example, depending on the polymerization conditions, the amount of these monovalent compounds can be controlled by a method of blocking the molecular ends with a monovalent acid or monovalent alcohol.

  In this case, a monovalent acid is preferable from the viewpoint of polymer stability. For example, acetic acid, propionic acid, butyric acid and the like can be mentioned, but during the polycondensation reaction, they are not distilled out of the system, but are stopped and such monovalent acids are removed out of the reaction system. Those that are easily removed are sometimes selected, but these may be mixed and used.

  In the case of direct reaction, the number average molecular weight can also be adjusted by measuring the timing at which the reaction is stopped by the amount of water distilled off during the reaction. In addition, it can be adjusted by biasing the number of moles of glycol or dibasic acid to be charged or by controlling the reaction temperature.

  The molecular weight of the polyester plasticizer of the present invention can be measured using the measurement method by GPC and the terminal group determination method (hydroxyl value).

  It is preferable to contain 1-40 mass% of the polyester plasticizer of this invention with respect to a cellulose derivative. It is preferable to contain 5-15 mass% especially.

  Specific examples of polyester plasticizers that can be preferably used in the present invention are given below.

[Other plasticizers]
In addition to the polyester plasticizer, other plasticizers can be used at the same time. For example, phosphate ester plasticizer, phthalate ester plasticizer, trimellitic acid ester plasticizer, pyromellitic acid plasticizer, polyhydric alcohol plasticizer, glycolate plasticizer, citrate ester plasticizer Fatty acid-terminated polyester plasticizers, carboxylic acid ester plasticizers, sugar plasticizers, acrylic polymers, and the like can be preferably used.

  In particular, in order to obtain the effects of the present invention, it is preferable to contain a polyhydric alcohol ester plasticizer, a sugar plasticizer, and an acrylic polymer.

[Polyhydric ester plasticizer]
The polyhydric alcohol ester is composed of an ester of a dihydric or higher aliphatic polyhydric alcohol and a monocarboxylic acid, and preferably has an aromatic ring or a cycloalkyl ring in the molecule.

  The polyhydric alcohol used in the present invention is represented by the following general formula (2).

Formula (2) R1- (OH) n
(However, R1 represents an n-valent organic group, and n represents a positive integer of 2 or more.)
Examples of preferred polyhydric alcohols include the following, but the present invention is not limited to these. Adonitol, arabitol, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, 1,2-propanediol, 1,3-propanediol, dipropylene glycol, tripropylene glycol, 1,2-butanediol, 1,3- Butanediol, 1,4-butanediol, dibutylene glycol, 1,2,4-butanetriol, 1,5-pentanediol, 1,6-hexanediol, hexanetriol, galactitol, mannitol, 3-methylpentane- Examples include 1,3,5-triol, pinacol, sorbitol, trimethylolpropane, trimethylolethane, xylitol, pentaerythritol, dipentaerythritol and the like. Of these, trimethylolpropane and pentaerythritol are preferable.

  There is no restriction | limiting in particular as monocarboxylic acid used for the polyhydric alcohol ester of this invention, Well-known aliphatic monocarboxylic acid, alicyclic monocarboxylic acid, aromatic monocarboxylic acid, etc. can be used.

  Use of an alicyclic monocarboxylic acid or aromatic monocarboxylic acid is preferable in terms of improving moisture permeability and retention. Examples of preferred monocarboxylic acids include the following, but the present invention is not limited thereto.

  As the aliphatic monocarboxylic acid, a fatty acid having a straight chain or a side chain having 1 to 32 carbon atoms can be preferably used. It is more preferable that it is C1-C20, and it is especially preferable that it is C1-C10.

  The use of acetic acid is preferred because the compatibility with the cellulose derivative is increased, and it is also preferred to use a mixture of acetic acid and another monocarboxylic acid.

  Preferred aliphatic monocarboxylic acids include acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, 2-ethyl-hexanecarboxylic acid, undecylic acid, lauric acid, tridecylic acid , Saturated fatty acids such as myristic acid, pentadecylic acid, palmitic acid, heptadecylic acid, stearic acid, nonadecanoic acid, arachidic acid, behenic acid, lignoceric acid, serotic acid, heptacosanoic acid, montanic acid, melicic acid, and laccelic acid, undecylenic acid, Examples thereof include unsaturated fatty acids such as oleic acid, sorbic acid, linoleic acid, linolenic acid and arachidonic acid.

  Examples of preferable alicyclic monocarboxylic acids include cyclopentanecarboxylic acid, cyclohexanecarboxylic acid, cyclooctanecarboxylic acid, and derivatives thereof.

  Examples of preferred aromatic monocarboxylic acids include those in which an alkyl group is introduced into the benzene ring of benzoic acid such as benzoic acid and toluic acid, and two or more benzene rings such as biphenyl carboxylic acid, naphthalene carboxylic acid, and tetralin carboxylic acid. Aromatic monocarboxylic acids possessed by them, or derivatives thereof. In particular, benzoic acid is preferred.

  The polyhydric alcohol ester preferably has a molecular weight in the range of 300-1500, and more preferably in the range of 350-750. A higher molecular weight is preferable because it is less likely to volatilize, and a lower molecular weight is preferable in terms of moisture permeability and compatibility with cellulose derivatives.

  The carboxylic acid used for the polyhydric alcohol ester may be one kind or a mixture of two or more kinds. Moreover, all the OH groups in the polyhydric alcohol may be esterified, or a part of the OH groups may be left as they are. The specific compound of a polyhydric alcohol ester is shown below.

  The content of the polyhydric alcohol ester according to the present invention is preferably 1 to 15% by mass, particularly preferably 3 to 10% by mass in the anisotropic scattering element.

[Sugar ester compound]
The anisotropic scattering element of the present invention may form a composition containing a sugar ester compound obtained by esterifying a hydroxyl group of a sugar compound in which 1 to 12 at least one structure selected from a furanose structure and a pyranose structure is bonded. preferable.

  Examples of the sugar compound of the present invention include glucose, galactose, mannose, fructose, xylose, arabinose, lactose, sucrose, cellobiose, cellotriose, maltotriose, raffinose, etc., particularly those having both a furanose structure and a pyranose structure. preferable.

  An example is sucrose.

  The sugar ester compound of the present invention is one in which part or all of the hydroxyl groups of the sugar compound are esterified or a mixture thereof.

  Specific compounds are shown below.

[Acrylic polymer]
The anisotropic scattering element of the present invention may further contain an acrylic polymer having a weight average molecular weight of 500 to 10,000. Preferably, the weight average molecular weight is 500 to 5,000.

  In addition to the above, the anisotropic scattering element after film formation is excellent in transparency, moisture permeability is extremely low, and exhibits excellent performance as a protective film for polarizing plates.

  In order to synthesize such a polymer, the following method is preferred.

  Such polymerization methods include a method using a peroxide polymerization initiator such as cumene peroxide and t-butyl hydroperoxide, a method using a polymerization initiator in a larger amount than normal polymerization, and a mercapto compound in addition to the polymerization initiator. And a method of using a chain transfer agent such as carbon tetrachloride, a method of using a polymerization terminator such as benzoquinone and dinitrobenzene in addition to the polymerization initiator, and further, Japanese Patent Application Laid-Open No. 2000-128911 or 2000-344823. Examples thereof include a compound having one thiol group and a secondary hydroxyl group, or a bulk polymerization method using a polymerization catalyst in which the compound and an organometallic compound are used in combination. In particular, the method described in the publication is preferable.

  The acrylic polymer of the present invention preferably contains 40% by mass or more of acrylic acid ester and methacrylic acid ester.

  Although the monomer as a monomer unit which comprises this polymer is mentioned below, it is not limited to this.

  Examples of the acrylate ester include methyl acrylate, ethyl acrylate, propyl acrylate (i-, n-), butyl acrylate (n-, i-, s-, t-), pentyl acrylate (n-, i-, s-), hexyl acrylate (n-, i-), heptyl acrylate (n-, i-), octyl acrylate (n-, i-), nonyl acrylate (n-, i-) , Myristyl acrylate (n-, i-), cyclohexyl acrylate, acrylic acid (2-ethylhexyl), benzyl acrylate, phenethyl acrylate, acrylic acid (ε-caprolactone), acrylic acid (2-hydroxyethyl), acrylic Acid (2-hydroxypropyl), acrylic acid (3-hydroxypropyl), acrylic acid (4-hydroxybutyl), acrylic acid (2-hydroxypropyl) Butyl), acrylic acid-p-hydroxymethylphenyl, acrylic acid-p- (2-hydroxyethyl) phenyl, etc .; a methacrylic acid ester in which the above acrylic acid ester is changed to a methacrylic acid ester; Acrylic acid, methacrylic acid, maleic anhydride, crotonic acid, itaconic acid and the like.

  Other ethylenically unsaturated monomers copolymerizable with acrylic acid esters and methacrylic acid esters: As vinyl esters, for example, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl valerate, vinyl pivalate, vinyl caproate, caprin Vinyl acetate, vinyl laurate, vinyl myristate, vinyl palmitate, vinyl stearate, vinyl cyclohexanecarboxylate, vinyl octylate, vinyl methacrylate, vinyl crotrate, vinyl sorbate, vinyl benzoate, vinyl cinnamate, etc. be able to.

  In the case of an acrylic acid or methacrylic acid ester monomer having a hydroxyl group, it is not a homopolymer but a constituent unit of a copolymer. In this case, it is preferable that the acrylic acid or methacrylic acid ester monomer unit having a hydroxyl group is contained in an acrylic polymer in an amount of 2 to 20% by mass.

  A polymer having a hydroxyl group in the side chain can also be preferably used. The monomer unit having a hydroxyl group is the same as the monomer described above, but acrylic acid or methacrylic acid ester is preferable. For example, acrylic acid (2-hydroxyethyl), acrylic acid (2-hydroxypropyl), acrylic acid (3 -Hydroxypropyl), acrylic acid (4-hydroxybutyl), acrylic acid (2-hydroxybutyl), acrylic acid-p-hydroxymethylphenyl, acrylic acid-p- (2-hydroxyethyl) phenyl, or these acrylic acids. The thing replaced by methacrylic acid can be mentioned, Preferably, it is acrylic acid-2-hydroxyethyl and methacrylic acid-2-hydroxyethyl.

  The acrylic acid ester or methacrylic acid ester monomer unit having a hydroxyl group in the polymer is preferably contained in the polymer in an amount of 2 to 20% by mass, more preferably 2 to 10% by mass.

  A polymer containing 2 to 20% by mass of the above-mentioned monomer unit having a hydroxyl group, of course, has excellent compatibility with cellulose derivatives, retention properties, dimensional stability, low moisture permeability, and polarization. It is particularly excellent in adhesiveness with a polarizer as a protective film for plates, and has the effect of improving the durability of the polarizing plate.

  Moreover, it is preferable to have a hydroxyl group at least at one terminal of the polymer main chain. The method of having a hydroxyl group at the end of the main chain is not particularly limited as long as it has a hydroxyl group at the end of the main chain, but radical polymerization having a hydroxyl group such as azobis (2-hydroxyethylbutyrate). A method of using an initiator, a method of using a chain transfer agent having a hydroxyl group such as 2-mercaptoethanol, a method of using a polymerization terminator having a hydroxyl group, a method of having a hydroxyl group at the terminal by living ion polymerization, A method of bulk polymerization using a compound having one thiol group and a secondary hydroxyl group as disclosed in JP-A No. 2000-128911 or 2000-344823, or a polymerization catalyst using the compound and an organometallic compound in combination The method described in the publication is particularly preferable.

  The polymer produced by the method related to the description in this publication is commercially available as Act Flow Series manufactured by Soken Chemical Co., Ltd., and can be preferably used.

  The polymer having a hydroxyl group at the terminal or the polymer having a hydroxyl group in a side chain has an effect of remarkably improving the compatibility and transparency of the polymer.

<Antioxidants, thermal degradation inhibitors>
In the present invention, conventionally known antioxidants and thermal deterioration inhibitors can be used. In particular, lactone, sulfur, phenol, double bond, hindered amine, and phosphorus compounds can be preferably used.

  For example, those including those commercially available from Ciba Specialty Chemicals under the trade names “IrgafosXP40” and “IrgafosXP60” are preferable.

  As the phenolic compound, those having a 2,6-dialkylphenol structure are preferable, for example, those commercially available under the trade names of Ciba Specialty Chemicals, Inc., “Irganox 1076” and “Irganox 1010”.

  Examples of the phosphorus compounds include Sumitizer GP from Sumitomo Chemical Co., Ltd., ADK STAB PEP-24G from Asahi Denka Kogyo Co., Ltd., “ADK STAB PEP-36” and “ADK STAB 3010”, Ciba Specialty. What is marketed by the chemical name "IRGAFOS P-EPQ", API Corporation, and Sakai Chemical Industry Co., Ltd. under the brand name "GSY-P101" is preferable.

  The hindered amine compound is preferably, for example, commercially available from Ciba Specialty Chemicals Co., Ltd. under the trade names “Tinvin 144” and “Tinvin 770”, and from Asahi Denka Kogyo Co., Ltd. as “ADK STAB LA-52”.

  As the sulfur compound, for example, those commercially available from Sumitomo Chemical Co., Ltd. under the trade names of “Sumilizer TPL-R” and “Sumilizer TP-D” are preferable.

  The above-mentioned double bond type compounds are preferably those commercially available from Sumitomo Chemical Co., Ltd. under the trade names “Sumilizer GM” and “Sumilizer GS”.

  Furthermore, it is possible to contain a compound having an epoxy group as described in US Pat. No. 4,137,201 as an acid scavenger.

  The amount of these antioxidants and the like to be added is determined appropriately in accordance with the process at the time of recycling and use. Added at.

  These antioxidants and thermal deterioration inhibitors can obtain a synergistic effect by using several different types of compounds in combination rather than using only one kind. For example, the combined use of lactone, phosphorus, phenol and double bond compounds is preferred.

<Retardation adjuster>
The anisotropic scattering element of the present invention may contain a compound for adjusting the retardation.

  The compound added to adjust the retardation can be an aromatic compound having two or more aromatic rings as described in EP 911,656A2.

  Two or more aromatic compounds may be used in combination. The aromatic ring of the aromatic compound includes an aromatic heterocyclic ring in addition to the aromatic hydrocarbon ring. An aromatic heterocyclic ring is particularly preferred, and the aromatic heterocyclic ring is generally an unsaturated heterocyclic ring. Of these, compounds having a 1,3,5-triazine ring are particularly preferred.

<Colorant>
In the present invention, it is preferable to use a colorant. The colorant means a dye or a pigment. In the present invention, the colorant means an effect of making the color tone of a liquid crystal screen blue, adjusting the yellow index, and reducing haze.

  Various dyes and pigments can be used as the colorant, but anthraquinone dyes, azo dyes, phthalocyanine pigments and the like are effective. Although the specific example of a preferable coloring agent is given to the following, it is not limited to these.

<Other additives>
The anisotropic scattering element of the present invention may contain an additive that can be added to a normal anisotropic scattering element in addition to the above compound.

  Examples of these additives include ultraviolet absorbers and fine particles.

  Although the ultraviolet absorber used in the present invention is not particularly limited, for example, oxybenzophenone compounds, benzotriazole compounds, salicylic acid ester compounds, benzophenone compounds, cyanoacrylate compounds, triazine compounds, nickel complex compounds, inorganic powders Examples include the body. It is good also as a polymer type ultraviolet absorber.

  As commercially available products, TINUVIN 171, TINUVIN 234, TINUVIN 360, TINUVIN 928 (all manufactured by Ciba Specialty Chemicals), “Sumisorb 250” (manufactured by Sumitomo Chemical), LA31 ( Asahi Denka Co., Ltd.).

  As fine particles used in the present invention, examples of inorganic compounds include silicon dioxide, titanium dioxide, aluminum oxide, zirconium oxide, calcium carbonate, calcium carbonate, talc, clay, calcined kaolin, calcined calcium silicate, and hydrated silicic acid. Mention may be made of calcium, aluminum silicate, magnesium silicate and calcium phosphate.

  Fine particles containing silicon are preferable in terms of low turbidity, and silicon dioxide is particularly preferable.

  The average primary particle size of the fine particles is preferably 5 to 50 nm, and more preferably 7 to 20 nm. These are preferably contained mainly as secondary aggregates having a particle size of 0.05 to 0.3 μm.

  The content of these fine particles in the anisotropic scattering element is preferably 0.05 to 1% by mass, particularly preferably 0.1 to 0.5% by mass. In the case of an anisotropic scattering element having a multilayer structure by the co-casting method, it is preferable to contain fine particles of this addition amount on the surface.

  Silicon dioxide fine particles are commercially available, for example, under the trade names Aerosil R972, R972V, R974, R812, 200, 200V, 300, R202, OX50, TT600, NAX50 (Nippon Aerosil Co., Ltd.). be able to.

  Zirconium oxide fine particles are commercially available, for example, under the trade names Aerosil R976 and R811 (manufactured by Nippon Aerosil Co., Ltd.) and can be used.

  Examples of the polymer include silicone resin, fluororesin, and acrylic resin. Silicone resins are preferable, and those having a three-dimensional network structure are particularly preferable. For example, Tospearl 103, 105, 108, 120, 145, 3120, and 240 (manufactured by Toshiba Silicone Co., Ltd.) It is marketed by name and can be used.

  Among these, Aerosil 200V and Aerosil R972V are particularly preferably used because they have a large effect of reducing the friction coefficient while keeping the turbidity of the anisotropic scattering element low.

《Domain creation method》
The domain of the present invention is a method in which a domain having an aspect ratio of 2 to 100 is prepared in advance and dispersed in a polymer as a support medium, and a domain intermediate before adjusting the aspect ratio (hereinafter referred to as a domain precursor). There is a method of adjusting the aspect ratio while producing an anisotropic scattering element by dispersing the precursor in a polymer as a support medium and then performing a process such as stretching, but the difficulty and reproducibility of domain shape production From the point of view, the latter is preferable.

<< Method for producing anisotropic scattering element >>
Hereinafter, the anisotropic scattering element according to the present invention can be produced by either a solution casting method or a melt casting method. Hereinafter, a production method using the solution casting method will be described.

1) Dissolution process In a dissolution vessel, the support medium and additives are dissolved in an organic solvent mainly composed of a good solvent for the support medium while stirring to form a dope, or the additive solution is mixed with the support medium solution. And forming a dope.

  For dissolution of the supporting medium, a method carried out at normal pressure, a method carried out below the boiling point of the main solvent, a method carried out under pressure above the boiling point of the main solvent, JP-A-9-95544, JP-A-9-95557, Alternatively, various dissolution methods such as a cooling method as described in JP-A-9-95538 and a high-pressure method as described in JP-A-11-21379 can be used. A method in which pressure is applied at a boiling point or higher is preferred.

  In the present invention, a dope is prepared by adding a dispersion of a domain precursor in this dissolution stage.

  The domain precursor dispersion is prepared by dissolving particles and a polymer in a solvent in advance, and adding a dispersing agent in some cases to perform a dispersion treatment.

  The concentration of the support medium in the dope is preferably 10 to 35% by mass. An additive is added to the dope during or after dissolution to dissolve and disperse, then filtered through a filter medium, defoamed, and sent to the next step with a liquid feed pump.

2) Casting process An endless metal belt, such as a stainless steel belt or a rotating metal drum, which feeds the dope through a liquid feed pump (for example, a pressurized metering gear pump) to a pressure die and transfers it indefinitely. This is a step of casting the dope from the pressure die slit to the upper casting position.

  A pressure die that can adjust the slit shape of the die base and facilitates uniform film thickness is preferred. The pressure die includes a coat hanger die and a T die, and any of them is preferably used. The surface of the metal support is a mirror surface.

  In order to increase the film forming speed, two or more pressure dies may be provided on the metal support, and the dope amount may be divided and stacked. Or it is also preferable to obtain the film of a laminated structure by the co-casting method which casts several dope simultaneously.

3) Solvent evaporation process The web (the state before the phase difference film is completed and still containing a lot of solvent) is heated on the metal support so that the web can be peeled from the metal support. This is the process of evaporating the solvent until

  In order to evaporate the solvent, there are a method of blowing air from the web side and / or a method of transferring heat from the back side of the metal support by a liquid, a method of transferring heat from the front and back by radiant heat, and the like. However, the drying efficiency is preferable.

  A method of combining them is also preferable. In the case of backside liquid heat transfer, it is preferable to heat at or below the boiling point of the main solvent of the organic solvent used in the dope or the organic solvent having the lowest boiling point.

4) Peeling process It is the process of peeling the web which the solvent evaporated on the metal support body in a peeling position. The peeled web is sent to the next process. It should be noted that if the residual solvent amount of the web at the time of peeling (the following formula) is too large, it is difficult to peel, or conversely, if it is peeled off after being sufficiently dried on the metal support, a part of the web is in the middle. It may come off.

  Here, there is a gel casting method (gel casting) as a method of increasing the film forming speed (the film forming speed can be increased by peeling while the residual solvent amount is as large as possible).

  For example, there are a method in which a poor solvent for the support medium is added to the dope and the gel is formed after casting the dope, a method in which the temperature of the metal support is lowered and the gel is formed.

  By gelling on the metal support and increasing the strength of the film at the time of peeling, the speed of film formation can be increased by speeding up the peeling.

  The amount of residual solvent during peeling of the web on the metal support is preferably within a range of 5 to 150% by mass depending on the strength of drying conditions, the length of the metal support, etc., but the amount of residual solvent is larger. In the case of peeling at a point in time, if the web is too soft, flatness at the time of peeling is easily lost, and slippage and vertical stripes due to peeling tension are likely to occur.

  In the present invention, the temperature at the peeling position on the metal support is preferably -50 to 40 ° C, more preferably 10 to 40 ° C, and most preferably 15 to 30 ° C.

  The residual solvent amount of the web at the peeling position is preferably 10 to 150% by mass, and more preferably 10 to 120% by mass.

  The amount of residual solvent can be represented by the following formula.

Residual solvent amount (% by mass) = {(MN) / N} × 100
Here, M is the mass of the web at an arbitrary point in time, and N is the mass when the mass M is dried at 110 ° C. for 3 hours.

5) Drying and stretching process After peeling, the web is transferred using a drying device that alternately passes the web through a roll arranged in the drying device and / or a tenter device that clips and transports both ends of the web with clips. To dry.

  In this invention, it is preferable to extend | stretch using a tenter apparatus as a method of extending | stretching 1.0 to 2.0 times with respect to the width direction between clips. More preferably, it is biaxially stretched in the longitudinal and transverse directions.

  In the present invention, it is effective to align domains having an aspect ratio of 2 to 100 in a specific direction by various methods.

  As a method for bringing the domain of the present invention into an oriented state in the support medium, for example, there is a method of stretching a polymer film in which the domain precursor is uniformly dispersed in the support medium in one direction.

  By adjusting the stretching conditions, the orientation of the domains can be adjusted and the aspect ratio can be adjusted simultaneously. In addition, by setting the stretching temperature to a sufficiently high temperature, for example, higher than the glass transition temperature of the support medium, the stress is relieved even when stretched, and the birefringence of the support medium can be reduced and isotropic. .

  Furthermore, in the stage where there is some fluidity before the film is completely solidified, for example, when a film is produced using a melt extrusion method, a method of increasing the film winding speed relative to the extrusion speed, The effect similar to stretching can be obtained by a method of solidifying after applying shear stress in one direction while maintaining the property.

  Further, when the domain has a magnetic field anisotropy or an electric field anisotropy, a method of solidifying in a supporting substrate while applying a magnetic field or an electric field in one direction can be used. It is also preferable to use these various methods in combination.

The stretching may be online or offline, but online is preferred.
<Evaluation of polarization scattering anisotropy of anisotropic scattering element>
The anisotropic scattering element of the present invention is characterized by having polarization scattering anisotropy. Here, having the polarization scattering anisotropy is defined as follows in the present invention.

  That is, when measuring the total amount of light transmitted through the anisotropic scattering element using linearly polarized incident light, the angle θ formed by the incident photoelectric field vibration axis and the film forming direction axis of the anisotropic scattering element Is changed in the plane of the anisotropic scattering element, and the ratio of the maximum value to the minimum value (maximum value / minimum value) of the total transmitted light amount is 1.2 or more, the anisotropic scattering The element is assumed to have polarization scattering anisotropy.

  In order to obtain this value, for example, using a haze meter such as NDH2000 manufactured by Nippon Denshoku Industries Co., Ltd., before the incident light hits the anisotropic scattering element to be measured, an iodine-containing PVA polarizing film or the like is used. Insert the light to linearly polarize the incident light, measure the total amount of transmitted light at each position while changing the rotation angle with the anisotropic scattering element being normal to the incident light, and determine the maximum and minimum values. This can be easily calculated.

The maximum value / minimum value ratio of the total amount of transmitted light by the above-described measurement method of the anisotropic scattering element having polarization scattering anisotropy in the present invention is 1.2 or more, and 1.5% is required for further enhancing the luminance improvement effect. It is preferable that it is above, and it is still more preferable that it is 2.0 or more.
<Orientation angle of anisotropic scattering element>
In the anisotropic scattering element having polarization scattering anisotropy according to the present invention, the average value of the absolute values (values that can be taken from 0 ° to 90 °) between the film forming direction and the major axis direction of each domain The orientation angle defined as follows is required to be a small value in order to increase the polarization scattering anisotropy.

  Here, as a specific method for obtaining the orientation angle, a transmission electron microscope was used to position the film slice in the film forming direction, and then the angles of the axis and 300 domains were measured. A method is adopted in which the sum of the numbers is averaged. In the present invention, the orientation angle of the domain of the anisotropic scattering element having the polarization scattering anisotropy is within 25 °, and in order to further enhance the luminance enhancement effect, it is preferably within 15 °, and within 5 °. It is particularly preferred that

  FIG. 1 is a schematic view of an anisotropic scattering element 4 including a domain 3 after the domain precursor 2 of the present invention is dispersed and the support medium 1 and the precursor are subjected to the stretching treatment A.

  FIG. 1 shows a state in which optically isotropic domains 3 are arranged in a substantially constant direction in the longitudinal direction of a film subjected to stretching treatment A (corresponding to a film forming direction or MD direction in the case of a roll film) on a support. Is shown.

  When the refractive index of the support medium 1 is n1 and the refractive index in the major axis direction of the domain 3 is n2 (the minor axis direction is also substantially equal), n1 <n2.

  Conventionally, the brightness enhancement film exhibits scattering anisotropy by aligning the refractive index n1 of the supporting medium with the refractive index in the minor axis direction of the domain and increasing the refractive index in the major axis direction of the domain.

However, in the present invention, even in the relationship of n1 <n2, if the short axis diameter of the domain is sufficiently short with respect to the light source wavelength (so-called Rayleigh scattering region), similar polarization scattering anisotropy can be expressed. I found out.
<Polarizing plate and liquid crystal display device>
The polarizing plate of the present invention will be described.

  The polarizing plate of the present invention can be produced by a general method. For example, after subjecting the anisotropic scattering element of the present invention to an alkali saponification treatment as a polarizing plate protective film, a triacetyl cellulose film is attached to one side of the polarizer and the other using a completely saponified polyvinyl alcohol aqueous solution. There is a way to match.

  The alkali saponification treatment refers to a treatment of immersing the anisotropic scattering element in a high-temperature strong alkaline solution in order to improve the wetness of the water-based adhesive and improve the adhesion.

  A conventionally well-known thing can be used as a polarizer used for the polarizing plate of this invention. For example, a film made of a hydrophilic polymer such as polyvinyl alcohol or ethylene-modified polyvinyl alcohol having an ethylene unit content of 1 to 4 mol%, a polymerization degree of 2000 to 4000, and a saponification degree of 99.0 to 99.99 mol%, A film stretched by treatment with a dichroic dye such as the above, or a film oriented by treating a plastic film such as vinyl chloride is used.

  The film thickness of the polarizer is preferably 5 to 30 μm. The polarizer thus obtained is bonded to an anisotropic scattering element.

  A commercially available cellulose ester film (KC8UX2M, KC4UX2M, KC5UN, KC4UY, KC8UY (all manufactured by Konica Minolta Opto)) can be used as the polarizing plate protective film on the other surface of the polarizer.

  In addition to the antiglare layer or the clear hard coat layer, the polarizing plate protective film used on the surface side of the display device preferably has an antireflection layer, an antistatic layer, and an antifouling layer.

  Further, at the time of producing the polarizing plate, it is preferable to perform bonding so that the in-plane slow axis of the anisotropic scattering element of the present invention and the transmission axis of the polarizer are parallel or orthogonal.

  The liquid crystal display device of the present invention can be produced by arranging and bonding the polarizing plate of the present invention obtained on the both sides of the liquid crystal cell. The anisotropic scattering element of the present invention is preferably used in liquid crystal display devices of various drive systems such as TN, VA, OCB, and HAN.

  Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto.

Example 1
<Production of anisotropic scattering element sample 1 having polarization scattering anisotropy>
<Preparation of domain precursor dispersion>
7 parts by mass of polyvinylpyrrolidone K90 (manufactured by Tokyo Chemical Industry Co., Ltd.) is dissolved in 8 parts by mass of ethanol, and 0.7 parts by mass of a titania-based composite oxide QUEEN TITANIC (with an aspect ratio of less than 2 and an average particle size of 7.5 nm) 0.2 parts by mass of Emulgen 404 (manufactured by Kao Corporation, HLB: 8.8) was added as a dispersant, and dispersed for 1 hour with an ultrasonic disperser to prepare a domain precursor dispersion.

<Preparation of dope solution>
76.9 parts by mass of cycloolefin polymer Arton (manufactured by JSR Co., Ltd.) was added to a pressurized dissolution tank containing 192 parts by mass of methylene chloride with stirring to completely dissolve the dope solution.

<Film formation>
While stirring the dope solution, the domain precursor dispersion was added, mixed well with an in-line mixer (Toray static type in-pipe mixer Hi-Mixer, SWJ), and then a stainless steel band with a width of 2 m was supported by a belt casting apparatus. It was cast evenly on the body.

  On the stainless steel band support, the solvent was evaporated until the residual solvent amount became 110% by mass, and the stainless steel band support was peeled off.

  A tension was applied during peeling to maintain the longitudinal (MD) stretch ratio at 3.0 times, and then the web was gripped at both ends of the tenter and stretched.

  After stretching, the width is maintained for several seconds, the tension in the width direction is relaxed, then the width is released, and further dried by transporting in a drying zone set at 110 ° C. for 30 minutes. Of 0.1% by mass or less.

By the above operation, an anisotropic scattering element sample 1 having a winding length of 3,000 m and a knurling having a width of 1.5 m, an end portion having a width of 1 cm and a height of 8 μm was produced.
<< Preparation of anisotropic scattering element sample 2 having polarization scattering anisotropy >>
In the production of the anisotropic scattering element 1, instead of Arton (manufactured by JSR Corporation), polyvinyl pyrrolidone K90 (manufactured by Tokyo Chemical Industry Co., Ltd.), polyvinyl pyrrolidone K90 (manufactured by Tokyo Chemical Industry Co., Ltd.), silicon Instead of 5 parts by mass of oil TSF4440 (manufactured by Nissho Sangyo Co., Ltd.) and 0.7 parts by mass of titania-based complex oxide QUEEN TITANIC (aspect ratio: less than 2, average particle size 7.5 nm, produced by Catalyst Chemicals Co., Ltd.) Anisotropic scattering element sample 2 was prepared using 0.7 part by mass of Al (OH) ₃ TTO51-C (aspect ratio: less than 2, stearic acid surface treatment average particle size 40 nm, manufactured by Ishihara Sangyo Co., Ltd.).
<< Preparation of anisotropic scattering element sample 3 having polarization scattering anisotropy >>
In the production of the anisotropic scattering element 1, instead of Arton (manufactured by JSR Co., Ltd.), acrylic resin Delvette ^™ (manufactured by Asahi Kasei Chemicals Co., Ltd.), polyvinylpyrrolidone K90 (manufactured by Tokyo Chemical Industry Co., Ltd.), cellulose Instead of 6 parts by mass of acetate propionate (Eastman Chemical Co., Ltd.) and 0.7 parts by mass of titania-based complex oxide QUEEN TITANIC (aspect ratio: less than 2 average particle size 7.5 nm, manufactured by Catalysts Chemical Co., Ltd.), An anisotropic scattering element sample 3 was prepared using 0.7 mass parts of titanium dioxide (aspect ratio: less than 2 average particle size 36 nm, manufactured by C-I Kasei Co., Ltd.).

  Samples 1 to 8 were prepared while adjusting the dispersion degree of the domain precursor, the draw ratio, and the residual solvent in the preparation of anisotropic scattering samples 1 to 3.

<Measurement of domain major axis diameter, minor axis diameter, and aspect ratio>
A thin section with a thickness of about several hundreds of nanometers is taken out near the surface of the manufactured anisotropic scattering element using a microtome, and this is photographed with a transmission electron microscope at a magnification of 20,000 times, and the image is scanned by a scanner manufactured by Canon Inc., CanonScan. Image processing software WinROOF ver3.60 (CPU: Athlon-1 GHz, memory: 512 MB) installed in Epson Direct's personal computer Endeavor Pro720L (CPU: Athlon-1 GHz, memory: 512 MB) was read using FB 636U with 300 dpi monochrome 256 gradations. (Mitani Corporation).

  Perform domain image extraction on the captured image, confirm that there are more than 300 domains on the screen after domain image extraction, and if the extraction is not enough, manually adjust the detection level, Make adjustments to detect and extract domains.

  For each domain of the image data extracted in this way, the major axis diameter / minor axis diameter was measured, and the average aspect ratio of the number of domains was calculated.

  The aspect ratio of the particles contained in the domain was also measured according to the above method.

[Confirmation of brightness improvement effect in anisotropic scattering element]
The brightness enhancement degree of the anisotropic scattering element of the present invention was measured using the brightness enhancement film evaluation system having the configuration shown in FIG.

  Measurement was performed under the same conditions with an anisotropic scattering element inserted with an integrating sphere with the anisotropic scattering element not inserted and the measurement light quantity set to 100%. In addition, the anisotropic scattering element was arrange | positioned so that the absorption axis of a polarizing plate and the orientation direction of a domain might become parallel, and measured.

The results are shown in Table 1.
Example 2
<Production of polarizing plate>
Using the anisotropic scattering elements 1, 3 and 7 and the cellulose ester film KC8UCR (manufactured by Konica Minolta Opto Co., Ltd.) prepared above, polarizing plates described in Table 1 were prepared.

  A 120 μm thick polyvinyl alcohol film was immersed in 100 kg of an aqueous solution containing 1 kg of iodine and 4 kg of boric acid and stretched 6 times at 50 ° C. to produce a polarizer. The above-mentioned anisotropic scattering elements 1, 3, 7 and KC8UCR subjected to alkali saponification treatment on one side of this polarizer, KC8UCR on the other side, 5% of fully saponified polyvinyl alcohol in combination with Table 1 Each aqueous solution was bonded as an adhesive.

<Alkali saponification treatment>
Saponification process 2N-NaOH 50 ° C 90 seconds
(If it is difficult to bond, 70 ° C 90 seconds)
Water washing step Water 30 ° C. 45 seconds Neutralization step 10% by mass HCl 30 ° C. 45 seconds Water washing step Water 30 ° C. 45 seconds Under the above conditions, the film sample is saponified, washed with water, neutralized, washed with water, and then dried at 80 ° C. went.

  About the produced polarizing plate, the relative brightness | luminance which set the brightness | luminance of the sample 9 (standard comparison) whose both surfaces are KC8UCR to 1 was represented on the following references | standards. The measurement of the brightness enhancement degree was in accordance with Example 1.

◎: Front luminance of 1.2 times or more ○: Front luminance of 1.1 times or more and less than 1.2 times Δ: Front luminance of 1.05 times or more and less than 1.1 times ×: Less than 1.05 times << Fabrication of VA liquid crystal display device >>
The polarizing plate on the backlight side of the 32-inch TV AQ-32AD5 manufactured by Sharp, which is a VA type liquid crystal display device, is peeled off, and the prepared polarizing plates are pasted on the glass surface of the liquid crystal cell (VA type). Thus, a liquid crystal display device was produced.

  At that time, KC8UCR was on the liquid crystal cell side, and the direction of bonding of the polarizing plate was such that the absorption axis was in the same direction as the polarizing plate bonded in advance.

<Evaluation of brightness of liquid crystal display device>
The front luminance of each manufactured liquid crystal display device was evaluated.

As the luminance, a value measured with a spectral radiance meter CS-1000 (manufactured by Konica Minolta Sensing Co., Ltd.) was defined as luminance (cd / m ² ). As a polarizing plate protective film instead of the anisotropic scattering element according to the present invention, a liquid crystal display device (sample 9) using a cellulose ester film KC8UX2MW (manufactured by Konica Minolta Opto Co., Ltd.) has a luminance of 1, and a liquid crystal display system The relative luminance was expressed by the following criteria.

◎: Front brightness of 1.2 times or more ○: Front brightness of 1.1 times or more and less than 1.2 times △: Front brightness of 1.05 times or more and less than 1.1 times ×: Less than 1.05 times Result Is shown in Table 1 below.

  From the results in Table 1, it can be seen that the VA type liquid crystal display device using the polarizing plate on which the polarizing plate protective film having polarization scattering anisotropy of the present invention is bonded exhibits an excellent brightness enhancement effect. .

Example 3
A polarizing plate was prepared in the same manner as in Example 1 except that the following ethylene-modified PVA film was used as the polarizing element instead of the polarizing element used in the polarizing plate of the present invention in Example 1, and the same evaluation as in Example 1 was performed. Thus, it was found that a polarizing plate having a high luminance improving effect can be produced.

<Polarizing element: Production of ethylene-modified PVA film>
100 parts by mass of ethylene-modified PVA having an ethylene unit content of 2.5 mol%, a saponification degree of 99.95 mol%, and a polymerization degree of 2400 is melt-kneaded and then dehydrated. After foaming, it was melt-extruded from a T die to a metal roll to form a film.

  The ethylene-modified PVA film obtained after drying and heat treatment had a thickness of 40 μm, and the average hot water cutting temperature of the film was 70 ° C.

  The ethylene-modified PVA film thus obtained was successively treated in the order of pre-swelling, dyeing, uniaxial stretching, fixing treatment, drying and heat treatment to produce a polarizing film.

  That is, the ethylene-modified PVA film is pre-swelled by immersing it in water at 30 ° C. for 60 seconds, and is immersed in a 35 ° C. aqueous solution having a boric acid concentration of 40 g / liter, an iodine concentration of 0.4 g / liter, and a potassium iodide concentration of 60 g / liter. Soaked for 2 minutes.

  Subsequently, it was uniaxially stretched 6 times in an aqueous solution at 55 ° C. with a boric acid concentration of 4%, and in an aqueous solution at 30 ° C. with a potassium iodide concentration of 60 g / liter, a boric acid concentration of 40 g / liter, and a zinc chloride concentration of 10 g / liter. For 5 minutes, and fixed.

  Thereafter, the ethylene-modified PVA film was taken out, dried with hot air at 40 ° C. under a constant length, and further subjected to heat treatment at 100 ° C. for 5 minutes to obtain a polarizer having a film thickness of 15 μm.

  The transmittance of the obtained polarizing film was 44.34%, the degree of polarization was 99.46%, and the dichroic ratio determined by calculation was 49.13. When the obtained polarizing film was placed at an angle of 10 degrees between two polarizing plates arranged in parallel to the stretching axis direction (0 degree), the central part and the end part of the polarizing film in the width direction. The difference in luminance was small, and the color spots were small and good.

It is a schematic diagram of the anisotropic scattering element containing the domain precursor and domain of this invention. It is an expansion schematic diagram of the domain precursor and domain of the present invention. It is a schematic diagram of the apparatus which verifies the brightness improvement effect of the anisotropic scattering element of this invention. It is a schematic diagram of the apparatus which verifies the brightness improvement effect of the polarizing plate which produced the anisotropic scattering element of this invention as a polarizing plate protective film. It is a schematic diagram of the apparatus which verifies the brightness improvement effect of the liquid crystal display device incorporating the polarizing plate using the anisotropic scattering element of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Support medium 2 Domain precursor 3 Domain 4 Anisotropic scattering element 5 Polymer phase which carries particle | grains in domain 6 Particle | grains in domain A Stretching process

Claims (4)

An anisotropic scattering element in which domains having an optically isotropic aspect ratio of 2 or more and 100 or less are dispersed and arranged in a support medium, wherein the domains include particles having an aspect ratio of 1 or more and less than 2. An anisotropic scattering element.
Aspect ratio = major axis diameter / minor axis diameter (where the major axis diameter means the absolute maximum length of each domain and particle, and the minor axis diameter is two straight lines parallel to the absolute maximum length, which are projected. (It means the shortest distance between two straight lines when the image of the domain is sandwiched.)   A polarizing plate comprising an absorptive polarizer and two polarizing plate protective films sandwiching the absorptive polarizer, wherein one of the two polarizing plate protective films is the anisotropic scattering element according to claim 1. A polarizing plate characterized by.   The polarizing plate according to claim 2, wherein an absorption axis of the absorptive polarizer is parallel to a major axis direction of a domain of the anisotropic scattering element.   A liquid crystal display device comprising the anisotropic scattering element according to claim 1.

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