JP2009053583A - Anisotropic scattering element, polarizing plate, and liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an anisotropic scattering element excellent in productivity, having scattering anisotropy of polarized light and a function of improving luminance, and to provide a polarizing plate and a liquid crystal display device using the above element. <P>SOLUTION: The anisotropy scattering element includes optically isotropic domains having an aspect ratio of 2 to 100, dispersed and arranged in a supporting medium, wherein the domain contains particles having an aspect ratio of 1 to less than 10. The aspect ratio is defined by aspect ratio=(major diameter)/(minor diameter). The major diameter means the absolute maximum length of the domain or the particle, while the minor diameter means the shortest distance of two straight lines that are parallel to the absolute maximum length and interposes a projected image of the domain. <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 to 100 are dispersed and arranged in an optically isotropic support medium, wherein the support medium and the domains are phase-separated from each other An anisotropic scattering element comprising: a different cellulose ester that produces a polymer, wherein the domain includes particles having an aspect ratio of 1 or more and less than 10.

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 described in 1 above A polarizing plate characterized by.
3. 3. The polarizing plate according to 2 above, wherein the absorption axis of the absorptive polarizer is parallel to the major axis direction of the 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 cellulose ester which is a support medium for forming a film, and the domain contained therein.

<< Supporting media and domains >>
In the present invention, the support medium is for forming a polymer film for supporting the domain, and mainly contains cellulose ester. Here, a main component means what occupies 50 mass% or more as a component of a film.

  The domain of the present invention means an individual region existing in the above-mentioned support medium and phase-separated from the support medium. The domain contains particles, and the particles are present randomly.

  The domain and support medium of the present invention are optically isotropic. Here, being optically isotropic means that the refractive index of each part is substantially constant and continuous, and the variation of each part of the refractive index is less than 0.01. 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.

  The polymer forming the domain of the present invention is a cellulose ester, which is a different cellulose ester that causes phase separation from the cellulose ester as the support medium.

  In the present invention, the domain containing particles can be dispersed in the support medium by causing phase separation.

  Whether the cellulose ester of the support medium and the cellulose ester of the domain cause phase separation from each other cannot be uniquely defined from the structure of the cellulose ester. For example, there is a relationship that causes phase separation depending on the degree of substitution of the acyl group, the type of the acyl group, and the like, but the relationship can be finally confirmed by actually testing.

  The test can be as follows. First, a particle, for example, 10 g of titanium oxide is sufficiently kneaded with 10 g of cellulose ester forming a domain by a biaxial kneader, dissolved in 200 g of methylene chloride, and subjected to an ultrasonic disperser to prepare a domain particle dispersion. .

  Next, 60 g of cellulose ester that forms a support medium is dissolved in this particle dispersion, and after applying to an ultrasonic disperser, it is cast on a glass plate to a dry film thickness of 80 μm, and dried to prepare a test film.

  By observing this test film with an electron microscope, it can be confirmed that the domains containing the particles are phase-separated in the support medium.

  When phase separation occurs, it is observed that particles are dispersed in the domain. If no phase separation has occurred, the particles are present throughout the test film.

  When the same test was conducted without containing particles in the cellulose ester forming the domain, the refractive index was very close to that of the cellulose ester forming the support medium. It is extremely difficult to confirm that it has occurred.

  In other words, the present invention is that what has been thought to be a uniform film by easily mixing uniformly with cellulose esters so far, there is actually a state in which phase separation occurs. He found.

  And in this invention, the property which produces the phase separation was utilized for dispersion | distribution of particle | grains.

  Since both the domain and the polymer forming the support medium are cellulose esters, phase separation occurs, but other physical properties are similar, so the dispersion stability of the particles is high, and the haze of the film increases due to stretching Is also small.

  As described above, phase separation occurs not only in a solution system but also in a melt system in which cellulose ester is dissolved by heat.

  In melt film formation in which cellulose ester is dissolved by heat, the cellulose ester is heated and kneaded above the softening point, but when phase separation occurs, it does not become uniform even when kneaded above the softening point. If the particles contain particles, the state of phase separation can be confirmed.

  When no particles are contained, the refractive indexes are very close to each other as in the solution system, and it is difficult to confirm the phase separation state.

  The polymer forming the domain of the present invention may have birefringence. However, by stretching the film at a sufficiently high stretching temperature when the domain is produced, the stress in the film is reduced and the isotropic domain is formed. can do.

  Examples of the particles having an aspect ratio of 1 or more and less than 10 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. Preferably less than 10 particles.

  The particles of the present invention are commercially available, for example, as titanium oxide TTO 51A, 51C, 55A, 55C (Ishihara Sangyo Co., Ltd.) or Titania sol Queen Titanic (Catalytic Chemical Industry 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 long axis diameter / short axis diameter of the particles and domains 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).

  Image extraction is performed on the captured image, and it is confirmed that there are 300 or more images on the screen after image extraction. If the extraction is not sufficient, the detection level is manually adjusted so that 300 or more images are detected and extracted. Make adjustments.

  For each piece of image data extracted in this way, the major axis diameter / minor axis diameter can be measured as an average value, and the number average aspect ratio can be calculated.

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

  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” are preferable.

  The above phosphorus compounds are, for example, “Sumilizer GP” from Sumitomo Chemical Co., Ltd., “ADK STAB PEP-24G”, “ADK STAB PEP-36” and “ADK STAB 3010” from ADEKA Co., Ltd., Ciba Specialty Chemicals Co., Ltd. Those commercially available from the company as “IRGAFOS P-EPQ”, API Corporation, and “GSY-P101” from Sakai Chemical Industry Co., Ltd. are preferred.

  The hindered amine compound is preferably commercially available from Ciba Specialty Chemicals Co., Ltd. under the trade names “Tinuvin 144” and “Tinvin 770”, and from ADEKA Co., Ltd. under the name “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 compounds are preferably those commercially available from Sumitomo Chemical Co., Ltd. under the trade names of “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 according to the process used when recycled, but is generally in the range of 0.05 to 20% by mass relative to the resin that is the main raw material of the film. Is added.

  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 (Made by ADEKA) etc. are mentioned.

  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.

<< Method for producing anisotropic scattering element >>
The anisotropic scattering element of the present invention can be produced by either the solution casting method or the melt casting method. Here, the case of the solution casting method will be described as a representative.

1) Kneading Step of Particles to Cellulose Ester Forming Domains Particles such as titanium oxide are kneaded with cellulose ester forming domains by a biaxial kneader. The mass ratio of cellulose ester to particles is 10:90 to 90:10. Preferably it is 30: 70-70: 30. Other plasticizers may be added.

  A commercially available kneading machine can be used, for example, a product made by HAAKE can be used.

  The kneading temperature is 130 to 230 ° C. depending on the cellulose ester forming the domain.

2) Dissolution Step This is a step of forming the dope which is the final solution for dissolving the kneaded product and the support medium in a solvent for casting the solution to produce a film.

  First, the kneaded product is dissolved in a solvent for casting a solution, such as methylene chloride. After confirming that it is almost dissolved, further dispersion is ensured with an ultrasonic disperser.

  The cellulose ester which is a support medium is melt | dissolved in this dispersion. Dissolution is carried out at normal pressure, at a temperature lower than the boiling point of the main solvent, at a pressure higher than the boiling point of the main solvent, disclosed in JP-A-9-95544, JP-A-9-95557, or JP-A-9 Various dissolution methods such as a method using a cooling dissolution method as described in JP-A-95538 and a method using a high pressure as described in JP-A No. 11-21379 can be used. A method in which pressure is applied is preferable.

  Here, it is preferable to mix all the additives necessary for the optical film.

3) 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.

4) 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.

5) 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, peeling is difficult, or conversely, if it is peeled off after being dried sufficiently on the metal support, a part of the web will be halfway 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.

6) Drying and stretching step After peeling, the web is transferred using a drying device that alternately passes the web through rolls 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.

  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.

  The stretching may be online or offline, but online is preferred.

  FIG. 6 is an electron micrograph (5000 magnifications) before stretching in which the domain precursor of the present invention is dispersed in a support medium.

  The supporting medium is cellulose acetate propionate (acetyl group substitution degree 1.90, propionyl substitution degree 0.66), and the domain precursor is cellulose acetate propionate (acetyl group substitution degree 0.07, propionyl substitution degree 2.65). Are kneaded with titanium oxide particles (average particle size 40 μm, aspect ratio 1.2).

  Titanium oxide particles are kneaded with cellulose acetate propionate forming a domain, then dissolved in methylene chloride, cellulose acetate propionate as a supporting medium is further dissolved therein, and dispersed and cast.

  Methylene chloride dissolves the cellulose ester constituting both the support medium and the domain, but in the electron micrograph, it is observed that the particles are contained only in the cellulose acetate propionate of the previously kneaded domain. be able to.

FIG. 7 shows the film of FIG. The change in the shape of the domain can be clearly observed.
<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 (so-called Rayleigh scattering region) with respect to the light source wavelength, the same 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 surface 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
<< Preparation of anisotropic scattering element sample 1 >>
<Preparation of domain precursor kneaded material>
Cellulose acetate butyrate (acetyl substitution degree 1.05, butyryl group substitution degree 1.78, manufactured by Sigma-Aldrich) 7 parts by mass, titanium oxide particles TT051C (aspect ratio less than 2, average particle size 0.02 μm, manufactured by Ishihara Sangyo Co., Ltd.) 7 Mass parts, IRGANOX 1010 (manufactured by Ciba Specialty Chemicals), GSY-P101 (manufactured by Sakai Chemical Industry Co., Ltd.), Sumilizer GS (manufactured by Sumitomo Chemical Co., Ltd.), 0.3 mass% of cellulose ester, respectively And kneaded at 180 ° C. and 75 rpm for 15 minutes to obtain pellets 1.

<Preparation of dope solution>
The pellet produced above was dissolved in a mixed liquid of 192 parts by mass of methylene chloride and 8 parts by mass of ethanol, and finally dispersed for 30 minutes by an ultrasonic disperser. Into this dispersion, 60 parts by mass of cellulose acetate propionate (acetyl substitution degree 1.90, propionyl substitution degree 0.66 manufactured by Eastman Chemical Co., Ltd.) was added while stirring, and completely dissolved while heating under pressure. A dope solution was prepared.

<Film formation>
The dope solution was sufficiently mixed with an in-line mixer (Toray static type in-pipe mixer Hi-Mixer, SWJ), and then uniformly cast on a stainless steel band support having a width of 2 m by a belt casting apparatus.

  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.

  Maintaining the longitudinal (MD) stretch ratio to be 3.0 times by applying tension at the time of peeling, then holding the width at both ends of the web for several seconds at the tenter, and holding the width after relaxing the tension in the width direction Was further released for 30 minutes in a drying zone set at 110 ° C. for drying, and the residual solvent was reduced to 0.1 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 >>
In the production of the anisotropic scattering element 1, 7 parts by mass of cellulose acetate butyrate (acetyl substitution degree 1.05, butyryl group substitution degree 1.78, manufactured by Sigma-Aldrich) and titanium oxide particles TT051C (average particle diameter 0. 03 μm Ishihara Sangyo Co., Ltd.) 7 parts by mass cellulose acetate propionate (acetyl substitution degree 0.07, propionyl group substitution degree 2.65, Sigma Aldrich) 7 parts by mass, and titanium oxide particles MT-100HD (Aspect ratio less than 2 Average particle diameter 0.015 μm, manufactured by Teica Co., Ltd.) 7 parts by mass was used to produce pellets 2 and anisotropic scattering element samples 2 were produced.
<< Preparation of anisotropic scattering element sample 3 >>
14 parts by mass of the same pellet 2 used for the production of the anisotropic scattering element 2, 120 parts by mass of cellulose acetate propionate (acetyl substitution degree 1.90, propionyl substitution degree 0.66 manufactured by Eastman Chemical Co.) IRGANOX 1010 (manufactured by Ciba Specialty Chemicals), GSY-P101 (manufactured by Sakai Chemical Industry Co., Ltd.), and Sumilizer GS (manufactured by Sumitomo Chemical Co., Ltd.) were each used in an amount of 0.3% by mass with respect to the whole cellulose ester, It melt | dissolved at 250 degreeC and formed into a film using the twin-screw extrusion film forming machine (made by Technobel).

  In film formation, the extending | stretching process to MD direction was performed by letting a cooling roll and an elastic touch roll pass.

  An anisotropic scattering element sample 3 having a winding length of 1500 m having a width of 1.5 m, a knurling having a width of 1 cm at the end and a height of 8 μm was produced.

  Sample 4 was prepared while adjusting the draw ratio in the preparation for preparation of anisotropic scattering sample 1. Sample 5 was prepared while adjusting the draw ratio in the preparation for preparation of anisotropic scattering sample 2. Samples 6 and 7 were prepared while adjusting the draw ratio in the preparation for preparation of anisotropic scattering sample 3.

  For comparison, an anisotropic scattering element (Comparative 1) described in Example 30 of Japanese Patent No. 3090890 was used. At that time, the stretching ratio was adjusted to 3 times, and the film thickness after stretching was adjusted to 20 μm.

[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 element and 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. Using the anisotropic scattering element and KC8UCR that have been subjected to alkali saponification treatment on one side of this polarizer, KC8UCR on the other side, and a fully saponified polyvinyl alcohol 5% aqueous solution in combination as shown in Table 1 as an adhesive Each was pasted.

<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.

  For comparison 1, evaluation was performed by inserting between a sample (reference comparison) with KC8UCR on both sides and the diffusion plate 2.

  About the produced polarizing plate, the relative brightness | luminance which set the brightness | luminance of the sample (standard comparison) whose both surfaces are KC8UCR to 1 was represented with 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.

For 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 (reference sample) 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. .

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. It is the photograph before extending | stretching which disperse | distributed the domain precursor of this invention to the support medium. It is the photograph which extended | stretched the state of FIG. 6 3 times in MD direction.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Support medium 2 Domain precursor which caused phase separation 3 Domain 4 Anisotropic scattering element 5 Cellulose ester phase carrying particles in domain 6 Particles in domain A Stretching treatment

Claims (4)

An anisotropic scattering element in which domains having an optically isotropic aspect ratio of 2 to 100 are dispersed and arranged in an optically isotropic support medium, wherein the support medium and the domains are phase-separated from each other An anisotropic scattering element comprising: a different cellulose ester that produces a polymer, wherein the domain includes particles having an aspect ratio of 1 or more and less than 10.
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 it, wherein one of the two polarizing plate protective films is the anisotropic scattering element according to claim 1. A polarizing plate characterized by that.   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.