JP2008076478A - Protective film for polarizing plate, and polarizing plate and liquid crystal display device using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a protective film for a polarizing plate, the film capable of improving optical characteristics, particularly luminance of a display as the protective film itself has polarization scattering anisotropy, and excellent in productivity and durability, and to provide a polarizing plate using the protective film for a polarizing plate, and a liquid crystal display device using the polarizing plate. <P>SOLUTION: The protective film for a polarizing plate contains an optical continuous phase comprising cellulose ester and acicular titanium oxide as domains, wherein the domains comprise acicular titanium oxide produced by hydrolyzing and condensing titanium alkoxide in an alcohol-water mixture solvent to obtain amorphous acicular titanium oxide and heat treating the amorphous acicular titanium oxide. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a polarizing plate protective film having polarization scattering anisotropy, a polarizing plate using the polarizing plate protective film, and a liquid crystal display device, and more particularly, providing a polarizing plate protective film with a luminance improving function, a luminance improving function and a polarizing plate protective function. The present invention relates to a polarizing plate provided with a film integrated with at least one surface, and a liquid crystal display device using the polarizing plate.

  In recent years, in the field of liquid crystal display devices represented by liquid crystal televisions, how efficiently the light energy from the backlight is used is important not only from the viewpoint of increasing luminance but also from the viewpoint of reducing power consumption. Has become a major technical issue. In that sense, the point is usually how efficiently a 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 by utilizing the principle of thin film interference, and an axis that is laminated but has no refractive index difference and transmits as it is. Examples thereof include a film that is polarized and separated by having it, and a polarization separation film that utilizes the circular dichroism of a cholesteric liquid crystal as disclosed in Patent Document 2. However, all of these films have drawbacks that the manufacturing difficulty is high and the productivity is low. Patent Document 3 discloses a film having polarized light scattering anisotropy comprising a dispersed phase of polymer particles in an optical continuous phase having birefringence. Although this technique is slightly less difficult to manufacture than the technique of Patent Document 1 or Patent Document 2 described above, a technique with a high degree of difficulty of adjusting the refractive index is still required. In addition, since the film surface is poorly smooth, it has the disadvantage that it is difficult to integrate with a dichroic polarizing film, which can meet the recent needs for reducing the number of backlight side members in the field of liquid crystal display devices. is not. Japanese Patent Application No. 2006-111680 discloses a technique in which the poor smoothness of Patent Document 3 is improved and a polarizing plate protective film function and a brightness enhancement function are integrated, but optical continuousness having birefringence is disclosed. As in Patent Document 3, there remains a demand for a highly difficult technique of adjusting the refractive index, in that a dispersed phase of polymer particles is included in the phase to provide polarization scattering anisotropy.

  As information on a polarizing element having polarization scattering anisotropy with relatively high productivity, a technique for dispersing scattering particles such as titanium oxide as disclosed in Patent Document 4 in a resin is known. However, as in the example of Patent Document 4, even if a method of dispersing the titanium oxide needle-like particles in the specific UV curable resin is re-examined, the particle aggregation is not sufficiently improved and the brightness enhancement effect as disclosed is obtained. I couldn't. In addition, Patent Document 4 has no description regarding a polymer resin as an optical continuous phase, and there is no description about the dispersibility of individual domains, which is considered to be one of the important problems in practical use. Furthermore, the polarizing plate laminated in the order of polarizing plate protective film / dichroic polarizing film / cellulose ester type polarizing plate protective film prepared using UV curable resin and scattering particles has a poor moisture permeability balance, and the humidity environment changes. Therefore, problems such as light leakage are likely to occur.

Patent Document 4 discloses a method for producing an anisotropic scattering element by dispersing and arranging scattering particles having an aspect ratio of 1 or more in support media having different refractive indexes. There was no mention of the method and the orientation method, and the minor axis diameter shown in the examples was 0.13 μm or more and less than 20 aspect ratio, which was insufficient for increasing the brightness.
Japanese Patent No. 362215 JP 2003-227933 A JP 2000-506990 A Japanese Patent No. 3090890

  Therefore, an object of the present invention is to provide a polarizing plate protective film that can improve the optical characteristics of the display, particularly the brightness, and has excellent productivity and durability, because the polarizing plate protective film itself has polarization scattering anisotropy. And providing a polarizing plate using the polarizing plate protective film and providing a liquid crystal display device using the polarizing plate.

  The inventors have found that the above object of the present invention can be achieved by the following configurations, and have completed the present invention.

  1. A polarizing plate protective film comprising an optically continuous phase composed of cellulose ester and acicular titanium oxide as domains, wherein the domains are obtained by hydrolysis and condensation of titanium alkoxide in alcohol and water mixed solvent. A polarizing plate protective film characterized by being acicular titanium oxide produced by heat-treating titanium.

  2. 2. The polarizing plate protective film as described in 1 above, wherein the acicular titanium oxide has an aspect ratio of 20 or more and a minor axis diameter of 150 nm or less.

  3. 2. The polarizing plate according to 1 above, wherein the average value of the angle formed by the major axis direction of each domain is within 25 ° when the film forming direction of the polarizing plate protective film is 0 ° Protective film.

  4). 4. A polarizing plate integrated in the order of a polarizing plate protective film according to any one of 1 to 3 / a dichroic polarizing film / polarizing plate protective film B utilizing a light absorption action by a dichroic substance. A polarizing plate, wherein the absorption axis of the dichroic polarizing film is in the longitudinal direction of the film.

  5. 5. A liquid crystal display device comprising the polarizing plate according to 4 and the polarizing plate protective film according to any one of 1 to 3 disposed on a light source side.

  According to the present invention, since the polarizing plate protective film itself has polarization scattering anisotropy, it is possible to improve the optical characteristics of the display, particularly the luminance, and to provide a polarizing plate protective film excellent in productivity and durability, and A polarizing plate using a polarizing plate protective film and a liquid crystal display device using the polarizing plate can be provided.

  The best mode for carrying out the present invention will be described in detail below, but the present invention is not limited thereto.

  The polarizing plate protective film of the present invention is a film having a polarization scattering anisotropy and a brightness enhancement function (also referred to as a brightness enhancement film), and as disclosed in JP-A-11-509014, it is optical. By forming a film in which the refractive index of the continuous phase and the refractive index on the transmission axis side of the domain having optical anisotropy are substantially equal, a predetermined polarized light is selectively transmitted and another polarized light is selected. It is a film that can be scattered and can improve brightness by reusing scattered light. However, in order to sufficiently improve the light utilization rate of the film having polarization scattering anisotropy, the optical continuous phase must be colorless and transparent and easily stretched. Although it is necessary that the difference in refractive index between the transmission axis side and the slow axis side of the domain having a directivity is large, selection of a material satisfying these requirements has been extremely difficult. Further, it has been newly found that the angle dependency of the luminance is reduced by the domain of the present invention in which the high aspect ratio and the short axis diameter are defined.

  The polarizing plate protective film of the present invention is a film having a polarization scattering anisotropy and a brightness enhancement function, and includes a polarizing scattering film containing an optical continuous phase composed of a cellulose ester and acicular titanium oxide as domains having optical anisotropy. An acicular titanium oxide produced by heat-treating amorphous acicular titanium oxide obtained by hydrolyzing and condensing a titanium alkoxide in a mixed solvent of alcohol and water. The acicular titanium oxide has an aspect ratio of 20 or more and a minor axis diameter of 150 nm or less.

  Furthermore, when the film forming direction of the polarizing plate protective film is 0 °, the polarizing plate protective film is preferably a polarizing plate protective film having an average value of absolute values of angles formed with the major axis direction of each domain within 25 °.

  Hereinafter, the present invention will be described in detail.

(Optical continuous phase)
In the present invention, the optical continuous phase refers to an optical phase in which the refractive index of each portion of the polymer film is substantially constant and continuous, and the variation in each portion 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 having optical anisotropy refers to a minute region having a difference in refractive index between the major axis direction of the domain and the minor axis direction perpendicular to the domain, and the difference in refractive index is preferably 0.01 or more.

  The optical continuous phase of the present invention is characterized by comprising a cellulose ester, and the cellulose ester referred to in the present invention is preferably a carboxylic acid ester having about 2 to 22 carbon atoms, particularly a lower fatty acid ester of cellulose. Preferably there is. The lower fatty acid in the lower fatty acid ester of cellulose means a fatty acid having 6 or less carbon atoms. For example, cellulose acetate, cellulose propionate, cellulose butyrate, cellulose acetate phthalate, etc. This refers to mixed fatty acid esters such as cellulose acetate propionate and cellulose acetate butyrate as described in U.S. Pat. No. 8,231,761, U.S. Pat. No. 2,319,052.

In particular, the cellulose ester used in the present invention is characterized by cellulose acetate propionate having an acetyl group substitution degree X and a propionyl group substitution degree Y satisfying the following formulas (1) and (2).
Formula (1) 2.3 <= X + Y <= 2.8
Formula (2) 0.7 <= Y <= 2.3
These acyl group substitution degrees can be measured according to the method prescribed in ASTM-D817-96.

  According to the study by the present inventors, surprisingly, the dispersibility of the domains in the film was extremely excellent by setting the total acyl group substitution degree (X + Y) and the propionyl group substitution degree (Y) within the above ranges. It was found to be something. The reason for this is not clear, but by adjusting the hydrophobic / hydrophilic balance of cellulose acetate propionate within a certain range, the cellulose acetate propionate has an affinity between the domain and the organic solvent during the film formation process. It is presumed that it may act as a dispersant that maximizes the viscosity. Therefore, even when the propionyl group substitution degree (Y) is Y <0.7, if Y> 2.3, the domain dispersibility is inferior. As another influence, when Y> 2.3, the dichroic polarizing film There is also a problem that the adhesiveness of the resin deteriorates.

  Although there is no limitation in particular as a cellulose of the raw material of the cellulose ester which concerns on this invention, Cotton linter, wood pulp, kenaf etc. can be mentioned. Moreover, the cellulose ester obtained from them can be used individually or in mixture in arbitrary ratios, respectively.

In the cellulose ester according to the present invention, when the acylating agent of the cellulose raw material is an acid anhydride (acetic anhydride, propionic anhydride, butyric anhydride), an organic solvent such as acetic acid or an organic solvent such as methylene chloride is used. The reaction is carried out using a protic catalyst such as sulfuric acid. When the acylating agent is acid chloride (CH ₃ COCl, C ₂ H ₅ COCl, C ₃ H ₇ COCl), the reaction is carried out using a basic compound such as an amine as a catalyst. Specifically, it can be synthesized by the method described in JP-A-10-45804. In the cellulose ester, the acyl group reacts with the hydroxyl group of the cellulose molecule. Cellulose molecules are composed of many glucose units linked, and there are three hydroxyl groups per glucose unit. The number of acyl groups derived from these three hydroxyl groups is called the degree of substitution. For example, cellulose triacetate has an acetyl group bonded to all three hydroxyl groups of the glucose unit.

  Although an example of the manufacturing method of the cellulose acetate propionate which concerns on this invention is shown below, this invention is not limited to this.

<Synthesis example of cellulose acetate propionate>
The compound was synthesized with reference to Example B of JP-T-6-501040.

  The following mixed liquids A to E were prepared.

A: Propionic acid: Concentrated sulfuric acid = 5: 3 (mass ratio)
B: Acetic acid: pure water = 3: 1 (mass ratio)
C: Acetic acid: pure water = 1: 1 (mass ratio)
D: Acetic acid: pure water: magnesium carbonate = 12: 11: 1 (mass ratio)
E: Aqueous solution in which 0.5 mol of potassium carbonate and 1.0 mol of citric acid are dissolved in 14.6 kg of pure water. In a reaction vessel equipped with a mechanical stirrer, 100 parts by mass of cellulose purified from cotton, 317 parts by mass of acetic acid And 67 parts by mass of propionic acid were added and stirred at 55 ° C. for 30 minutes. After the temperature of the reaction vessel was lowered to 30 ° C., 2.3 parts by mass of Solution A was added and stirred for 30 minutes. After cooling the temperature of the reaction vessel to −20 ° C., 100 parts by mass of acetic anhydride and 250 parts by mass of propionic anhydride were added and stirred for 1 hour. After raising the temperature of the reaction vessel to 10 ° C, 4.5 parts by mass of Solution A was added, and the temperature was raised to 60 ° C and stirred for 3 hours. Further, 533 parts by mass of Solution B was added and stirred for 17 hours. Further, 333 parts by mass of Solution C and 730 parts by mass of Solution D were added and stirred for 15 minutes. After filtering the insoluble matter, water was added while stirring the solution until the formation of the precipitate was completed, and the white precipitate thus formed was filtered. The obtained white solid was washed with pure water until the washing solution became neutral. To this wet product, 1.8 parts by mass of Solution E was added, and then dried under vacuum at 70 ° C. for 3 hours to obtain cellulose acetate propionate.

  When the substitution degree of the obtained cellulose ester was calculated based on ASTM-D817-96, the substitution degree with an acetyl group was 2.08, and the substitution degree with a propionyl group was 0.72. Moreover, when GPC was measured on the said conditions, Mn was 92000, Mw was 156000, and Mw / Mn was 1.7.

  The synthesized cellulose ester is preferably purified to remove low molecular weight components or to remove unacetylated components by filtration.

  The molecular weight of the cellulose ester used in the present invention is 50,000 to 350,000 in terms of weight average molecular weight (Mw). More preferable is 60000-300000, and 80000-250,000 is particularly preferable.

  In the case of acetylcellulose, it is necessary to extend the time for the acetylation reaction in order to increase the acetylation rate. However, if the reaction time is too long, the decomposition proceeds simultaneously, and the polymer chain is broken and the acetyl group is decomposed. Therefore, it is necessary to set the reaction time within a certain range in order to increase the degree of acetylation and suppress decomposition to some extent. It is not appropriate to define the reaction time because the reaction conditions vary and greatly vary depending on the reaction equipment, equipment and other conditions. As the decomposition of the polymer progresses, the molecular weight distribution becomes wider. Therefore, in the case of cellulose ester, the degree of decomposition can be defined by the commonly used weight average molecular weight (Mw) / number average molecular weight (Mn). That is, in the process of acetylation of cellulose triacetate, the weight average molecular weight (Mw) is used as one index of the degree of reaction for allowing the acetylation reaction to take place for a sufficient period of time without causing excessive decomposition due to being too long. ) / Number average molecular weight (Mn).

  In the cellulose ester used in the present invention, the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn), Mw / Mn is preferably 1.4 to 3.9 as described above, and more preferably. It is in the range of 1.6 to 3.5.

  The average molecular weight and molecular weight distribution of the cellulose ester can be measured by a known method using gel permeation chromatography. Using this, the number average molecular weight and the weight average molecular weight are measured.

  The measurement conditions are as follows.

<Gel permeation chromatography: molecular weight measurement by GPC>
The method for measuring the number average molecular weight by GPC was diluted with tetrahydrofuran so that the sample solid content concentration was 0.1%. Since the particles were included, the particles were removed using a filter, and the measurement was performed at a column temperature of 25 ° C. under the following conditions.

Column: Tosoh Corporation TSKgelG5000HXL-TSKgelG2000H XL
Eluent: THF (tetrahydrofuran)
Pump: L6000 (manufactured by Hitachi, Ltd.)
Flow rate: 1.0 ml / min
Detection: RI Model 504 (manufactured by GL Sciences)
Sample concentration: 0.8%
Standard sample / calibration curve: Standard polystyrene STK standard polystyrene (manufactured by Tosoh Corp.) Mw = 100000-500 calibration curves with 13 samples are used. It is preferable that the 13 samples are substantially equally spaced.

  Cellulose esters are also affected by trace metal components in cellulose esters. These are considered to be related to water used in the production process, but it is preferable that there are few components that can become insoluble nuclei, and metal ions such as iron, calcium, and magnesium contain organic acidic groups. Insoluble matter may be formed by salt formation with a polymer degradation product or the like that may be present, and it is preferable that the amount is small. The iron (Fe) component is preferably 1 ppm or less. About calcium (Ca) component, it is contained in a lot of ground water and river water, etc., and it becomes hard water, and it is unsuitable as drinking water. It easily forms a coordination compound, that is, a complex with a ligand, and forms scum (insoluble starch, turbidity) derived from many insoluble calcium.

  The calcium (Ca) component is 60 ppm or less, preferably 0 to 30 ppm. The magnesium (Mg) component is preferably in the range of 0 to 70 ppm, particularly preferably 0 to 20 ppm, since too much will cause insoluble matter. Metal components such as iron (Fe) content, calcium (Ca) content, magnesium (Mg) content, etc. are pre-processed by completely digesting cellulose ester with micro digest wet cracking equipment (sulfuric acid decomposition) and alkali melting. After performing, it can obtain | require by performing an analysis using ICP-AES (inductively coupled plasma emission spectroscopy analyzer).

(Acicular titanium oxide)
In the present invention, the domain means an individual region existing in the same film as the optical continuous phase and having a refractive index different from that of the optical continuous phase. Use as a domain.

The acicular titanium oxide according to the present invention has an aspect ratio of 20 or more and a minor axis diameter of 150 nm or less.
(Here, the aspect ratio is the value of the major axis diameter / minor axis diameter, the major axis diameter means the absolute maximum length in the domain, and the minor axis diameter is two straight lines parallel to the absolute maximum length. Means the distance between two straight lines when the projected domain image is sandwiched between them, provided that when the projected domain image is rectangular, the major axis diameter is the length of the long side and the minor axis diameter is Means the length of the short side.)
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. For each domain of the image data extracted in this way, the major axis diameter / minor axis diameter can be measured, and the average aspect ratio of the number of domains can be calculated. In the present invention, an aggregate composed of a plurality of constituent particles is regarded as one domain. In the case of an indefinite domain, the major axis has the absolute maximum length of the domain and is converted into an ellipse having the same area as the domain projection area, and then the minor axis is obtained according to the above definition.

  The aspect ratio of the acicular titanium oxide according to the present invention is preferably in the range of 20 to 100, more preferably in the range of 20 to 50 in the sense of enhancing the domain orientation as described later.

  In a domain having an aspect ratio of less than 20, the orientation is not sufficiently enhanced, and as a result, the polarization scattering anisotropy described later is weak, and a sufficient brightness enhancement effect cannot be obtained. The minor axis diameter is preferably 150 nm or less, and more preferably 100 nm or less. The lower limit is preferably 50 nm or more. When the minor axis diameter is less than 50 nm or more than 150 nm, the transmitted light anisotropy is deteriorated, and a sufficient brightness enhancement effect cannot be obtained.

  The acicular titanium oxide according to the present invention may be either a rutile type or an anatase type crystal, but a rutile type is preferable in that it has a high refractive index and a small photocatalytic activity.

  The above-mentioned acicular titanium oxide particles having a small minor axis diameter and a large aspect ratio according to the present invention are produced by heat-treating amorphous acicular titanium oxide obtained by hydrolyzing and condensing titanium alkoxide in a mixed solvent of alcohol and water. It is characterized by being. The acicular titanium oxide fine particles of the present invention are amorphous. For example, from the measurement of wide-angle X-ray diffraction, it can be seen that acicular titanium oxide fine particles before heat treatment are amorphous having no crystal structure because no diffraction peak is observed.

  The acicular titanium oxide fine particles of the present invention are made from titanium alkoxide.

Titanium alkoxide
General formula (1): Ti (OR) ₄
(Wherein R represents an alkyl group having 1 to 6 carbon atoms)
It is a compound represented by these. The alkyl group having 1 to 6 carbon atoms represented by R may be linear or branched, and is methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n -Pentyl, n-hexyl and the like are exemplified. Of these, alkyl having 1 to 4 carbon atoms such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl and the like are preferable. More preferably, R is ethyl, n-propyl, isopropyl, or n-butyl. Particularly preferably, R is ethyl, isopropyl or n-butyl.

  The alcohol contained in the solvent is an alcohol containing at least methanol. Specifically, it is a mixture of methanol and at least one alcohol selected from the group of alcohols having 2 or more carbon atoms. Examples of the alcohol having 2 or more carbon atoms include linear or branched alcohols having 2 to 10 carbon atoms. Examples of linear or branched alcohols having 2 to 10 carbon atoms include ethanol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, sec-butyl alcohol, tert-butyl alcohol, n-pentyl alcohol, n Examples include monohydric alcohols such as hexyl alcohol, heptyl alcohol, octyl alcohol, nonyl alcohol, and decanol, and polyhydric alcohols such as ethylene glycol, glycerin, 1,2-propanediol, and 1,3-propanediol. Preferably, C2-C4 alcohols, such as ethanol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, sec-butyl alcohol, ethylene glycol, are mentioned. The content of methanol in the alcohol contained in the solvent is 90% by volume or more, preferably 95% by volume or more, and more preferably 97% by volume or more with respect to the total volume of the alcohol.

  If the content of methanol is small, the production of needle-shaped fine particles decreases and the production of spherical fine particles increases, which is not preferable. In particular, when it is intended to selectively obtain acicular titanium oxide crystals, it is preferable to use only methanol as the solvent.

  Further, the solvent used in the present invention needs to contain a trace amount of water. The water content required in this reaction is, for example, about 0.0025 to 10 parts by mass, preferably about 0.01 to 8 parts by mass, more preferably 0.05 to 100 parts by mass of titanium alkoxide. 5 parts by mass, particularly preferably about 0.1 to 5 parts by mass. When the reaction is carried out under anhydrous conditions under an anhydrous alcohol solvent, the reaction usually proceeds little or very slowly. On the other hand, when the amount of water is too large, hydrolysis proceeds, but it is difficult to obtain desired acicular titanium oxide fine particles.

  The acicular titanium oxide fine particles of the present invention are produced by adding the above titanium alkoxide to the above solvent and causing the reaction. Specifically, white acicular titanium oxide fine particles are deposited by dropping liquid titanium alkoxide (I) into a solvent and stirring or ultrasonicating for a certain time. It is preferable to add titanium alkoxide (I) dropwise thereto while stirring or sonicating the solvent. The obtained acicular titanium oxide fine particles have a shape with a small minor axis diameter and a large aspect ratio because only the average major axis diameter grows with time while maintaining the average minor axis diameter almost constant. Depending on the reaction time, the aspect ratio can be controlled while the average minor axis diameter of the acicular titanium oxide fine particles is fixed, and the average minor axis diameter and the average major axis diameter are almost uniform, that is, the needle shape has a narrow particle size distribution. Titanium oxide fine particles can be obtained.

  After completion of the above reaction, the reaction mixture is centrifuged, and the obtained acicular titanium oxide fine particles are dried. The centrifugation conditions may be, for example, about 5000 to 20000 rpm and 5 minutes or more. Moreover, drying conditions should just be a grade which can remove said reaction solvent, and what is necessary is just to dry normally for about 1 to 12 hours at 60-100 degreeC under normal pressure or pressure reduction (0.001 MPa or less).

  Further, since the obtained acicular titanium oxide fine particles are amorphous, it is necessary to convert them into crystalline acicular titanium oxide fine particles by heat treatment. As heat treatment conditions, for example, amorphous needle-like titanium oxide fine particles can be heat-treated in air at about 450 to 550 ° C. for about 30 minutes to 2 hours to obtain metastable anatase type crystals. it can. A stable rutile crystal can be obtained by heat-treating the amorphous acicular titanium oxide fine particles in air at about 600 to 900 ° C. for about 1 to 12 hours. That is, the amorphous acicular titanium oxide fine particles obtained by the above reaction can be led to fine particles having different crystal structures by selecting the heat treatment conditions.

  The acicular titanium oxide particles used as the domain of the present invention are preferably subjected to various surface treatments for the purpose of improving the affinity with the cellulose ester resin and the organic solvent in the film production process.

  For particles that have been sufficiently dried to remove moisture, fatty acid-based, oil-based, surfactant-based, wax-based, silane coupling agent, titanate coupling agent, carboxylic acid-based coupling agent, phosphoric acid-based coupling agent, Various modifiers such as polymers can be used.

  In addition, a coating treatment with a metal oxide such as silica or alumina can be performed for the purpose of suppressing the photocatalytic activity.

  Treatment methods include a coating method that coats the surface with fatty acids, metal salts, surfactants, etc., a topochemical method that binds the coupling agent to the particle surface, and a mechanochemical that adds an organic treatment agent in the particle grinding process. There are various methods such as a method, 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 type of modifier used to treat the particle surface varies slightly depending on the combination of the particle type and the cellulose ester resin, but the coating treatment method using a fatty acid modifier or various silanes. A topochemical treatment method with a coupling agent is generally preferred.

  The method for dispersing the surface-treated particles in the cellulose ester resin is roughly divided into two methods, a method using a disperser and a method using a kneader.

  The former can be further divided into media distribution and medialess distribution. Examples of the media dispersion include those using a dispersing machine such as a ball mill, a sand mill, and a dyno mill, and examples of the medialess dispersion include an ultrasonic type, a centrifugal type, and a high pressure type. In the present invention, various mill dispersions or dispersions using a kneader are preferred. As a kneading method, using one or two rotor extruders, resin is introduced from the hopper, and when the viscosity drops to some extent, particles are introduced from the side to minimize damage to the particles. And kneadability can be improved. As a mill dispersion method, it is preferable to use a bead having a diameter of 0.1 mm or less because a domain having excellent dispersibility can be obtained while preventing breakage and reaggregation of particles.

  In the polarizing plate protective film having polarization scattering anisotropy and a function of improving luminance according to the present invention, the domain is preferably 0.1% by volume or more and 5% by volume or less.

  FIG. 1 is a schematic view of a polarizing plate protective film having polarization scattering anisotropy including an optical continuous phase mainly composed of cellulose ester according to the present invention and a domain having optical anisotropy.

  FIG. 1 shows a state in which an optical anisotropy domain is aligned in the longitudinal direction (film forming direction or MD direction) of the polarizing plate protective film in a substantially constant direction in the optical continuous phase 1 mainly composed of cellulose ester. Is shown. When the refractive index of the optical continuous phase (resin) is n1, the refractive index in the major axis direction of the domain is n2, and the refractive index in the minor axis direction of the domain is n3, when n1 = n3 and n2 <n3, The polarized light parallel to the minor axis direction is transmitted, and the polarized light parallel to the major axis direction is scattered. If the transmitted polarized light is parallel to the transmission axis of the light absorbing polarizer, the polarized light is transmitted through the polarizer.

(Polarized light scattering anisotropy)
The polarizing plate protective film of the present invention has a polarization scattering anisotropy. Here, having the polarization scattering anisotropy is defined as follows in the present invention. That is, when measuring the total transmitted light amount of the polarizing plate protective film using linearly polarized incident light, the angle θ formed by the incident photoelectric field vibration axis and the axis in the film forming direction of the polarizing plate protective film is the angle θ. When the ratio between the maximum value and the minimum value (maximum value / minimum value) of the total transmitted light amount is 1.2 or more when changing in the plane of the polarizing plate protective film, the polarizing plate protective film is polarized Suppose that it has scattering anisotropy.

  In order to obtain this value, for example, using a haze meter such as NDH2000 manufactured by Nippon Denshoku Industries Co., Ltd., an iodine-containing PVA polarizing film is inserted before the incident light hits the polarizing plate protective film to be measured. Then, the incident light is linearly polarized, and the amount of transmitted light at each position is measured while changing the rotation angle with the polarizing plate protective film being normal to the incident light, and the maximum value and the minimum value are obtained. Can be easily calculated. The maximum value / minimum value ratio of the total amount of transmitted light by the above-described measuring method of the polarizing plate protective film having polarization scattering anisotropy in the present invention is 1.2 or more, and 1.5 or more in order to further enhance the luminance improvement effect. It is preferable that it is 2.0, and it is still more preferable that it is 2.0 or more.

(Orientation method)
In the present invention, as a means for imparting polarization scattering anisotropy to the polarizing plate protective film, it is effective to orient the domains having an aspect ratio of 20 or more in a specific direction by various methods. As a method for orienting domains of the present invention, for example, in the case of a film in which domains are uniformly dispersed, there is a method of stretching the film in one direction. In addition, at the stage of film production, the use of high aspect ratio particles, or the method of increasing the shear stress applied to particles with high aspect ratio by devising the viscosity of the liquid containing the particles and the resin or the shape of the die, make it more specific. The orientation in the direction can be improved. 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.

  By providing polarization scattering anisotropy by such a method, the degree of polarization can be greatly improved. However, the polarizing plate on the backlight side with respect to the liquid crystal cell in the liquid crystal display is used as the polarizing plate of the present invention. By so doing, a so-called luminance improvement effect is exhibited.

  In the present invention, a method for increasing the shear stress applied to particles having a high aspect ratio, that is, a dope containing an optical continuous phase composed of a cellulose ester, an organic solvent, and acicular titanium oxide particles is applied from a die to a casting support. In the process of casting and drying the web (film) peeled off from the support, the dope is stretched by controlling the flow rate of the dope flowing through the die slit toward the exit side, and the amorphous particles are also formed. It can be oriented along the dope, which is preferable. Hereinafter, a specific method will be described.

  The dope flow rate (V) in the die inlet pipe, the dope flow rate (Vm) in the die manifold, and the speed ratio Rvm = Vm / V are preferably set to 0.5 ≦ Rvm ≦ 20.

  Here, the dope flow rates V and Vm are defined by the following equations.

V = Q / A
Q [m ³ / hr]: Dope volume flow rate A [m ² ]: Cross-sectional area of die inlet Vm = Q / Am
Q [m ³ / hr]: Dope volume flow rate Am [m ² ]: Cross-sectional area in the manifold When the Rvm is less than 0.5, the orientation of the amorphous particles cannot be sufficiently obtained, and even when the Rvm exceeds 20, Since the amorphous particles cannot follow the movement of the surrounding dope due to inertia, sufficient orientation cannot be obtained.

  From the above viewpoint, Rvm is preferably 0.5 ≦ Rvm ≦ 20, and more preferably 0.8 ≦ Rvm ≦ 10.

  Usually, in the dice, the flow path is widened when entering the manifold from the pipe, so that the flow velocity is reduced and the irregular particles tend to be directed in the direction perpendicular to the flowing direction. In the case of a die, particularly in the center of the width, the direction is slightly in the TD direction and the direction toward the end is slightly in the MD direction, and the desired MD orientation and width uniformity cannot be obtained. The inner wall in the thickness direction of the manifold is curvilinearly narrowed so that the Am of A is less than or equal to A, and the flow rate is within the above range, whereby the irregular particles are arranged in the MD direction with a high degree of orientation in the film. Therefore, the luminance improvement effect can be enhanced.

  Further, it is preferable that the time for the dope to pass through the die slit portion: t is 0.005 to 5 [sec].

Here, the dope passage time: t is defined by the following equation: t = Q / Sv
Q [m ³ / hr]: Dope volume flow rate Sv [m ³ ]: Die slit volume When t is less than 0.005, shearing on the slit wall surface is insufficient, and irregular particles cannot be oriented, and t is 5 Even if the average particle size exceeds 50 ° C., the orientation effect of the amorphous particles reaches a peak, and conversely, in order to apply such a long time shearing time, a film is formed at a low speed or a very long slit is required. In the former, productivity is significantly reduced. In the latter case, since the pressure of the die and the upstream liquid supply system becomes very high, a high-pressure liquid supply pump, a high pressure-resistant liquid supply pipe, and a die are required, which increases the equipment cost.

  From the above viewpoint, t is preferably 0.005 to 5 [sec], and more preferably 0.01 to 2.

  Thus, by controlling the passage time of the die slit, it is possible to enhance the orientation in the film of the amorphous particles that determine the brightness enhancement effect.

  The dope flow rate (Vu) at the upper end of the die slit, the dope flow rate (Vd) at the lower end of the slit, and the flow rate ratio Vs = Vd / Vu are preferably set to 1.1 ≦ Vs ≦ 20.0.

  By controlling the flow rate of the dope flowing through the slit so as to accelerate toward the exit side in this way, the dope is stretched and the amorphous particles can be oriented along the dope. If Vs is less than 1.1, the particles cannot be oriented, and if it exceeds 20, the amorphous particles cannot follow the movement of the surrounding dope due to inertia and cannot be oriented. Vs is preferably 1.1 ≦ Vs ≦ 20.0, and more preferably 1.5 ≦ Vs ≦ 15.0.

Further, it is preferable that the dope extrusion speed (V ₁ ) from the die lip, the moving speed (V ₂ ) of the support surface, and the speed ratio Rvs = V ₂ / V ₁ be 1.05 ≦ Rvs ≦ 20.

  When casting the dope from the die onto the casting support, the particles in the wet film can be oriented MD by stretching the casting film in this manner. The range of Rv is preferably 1.05 ≦ Rvs ≦ 20, and more preferably 1.1 ≦ Rvs ≦ 6.

  Within 30 seconds after the film is cast on the casting support, the web is dried under the conditions satisfying the following formula.

30 ≦ Z ≦ −5.3926T + 421.2
Z: Residual solvent amount [mass%] at an arbitrary time point on the web
Z = {(MN) / N} × 100
M: Mass at an arbitrary point of the web N: Mass when mass M was dried at 110 ° C. for 3 hours T: Film average temperature [° C.]
If Z is less than 30%, adhesion of irregularly shaped particles to the surface of the cast support occurs, web peelability deteriorates, and in the range exceeding −5.3926T + 421.2, the irregularly shaped particles The orientation will be low. This is presumably because the amorphous particles move due to Brownian motion, weak vibrations of the support, etc., before the wet film dries to a certain degree of hardness, and the orientation is relaxed.

(Orientation angle)
Therefore, the average 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 of the polarizing plate protective film having polarization scattering anisotropy according to the present invention. The orientation angle defined as a value is required to be a small value in order to increase the polarization scattering anisotropy. Here, as a specific method of obtaining the orientation angle, using a transmission electron microscope, after positioning the film slice in the film forming direction, measure each angle between this axis and about 300 domains, A method is adopted in which these totals are obtained by averaging the numbers. In the present invention, the orientation angle of the domain of the polarizing plate protective film having the polarization scattering anisotropy is within 25 °, and in order to further enhance the brightness enhancement effect, it is preferably within 15 °, preferably within 5 °. It is particularly preferred.

  As a method for producing a polarizing plate protective film containing these domains, a dispersion containing at least a domain and a resin for dispersing the domain is prepared in advance, and then the dispersion and the cellulose ester are mixed with a solvent. It can obtain by the manufacturing method of the polarizing plate protective film which casts a solution using dope prepared by. Similarly, a polarizing plate protective film can be obtained by a melt casting method.

(Organic solvent)
Organic solvents that dissolve cellulose esters and are useful for forming cellulose ester solutions or dopes include chlorinated organic solvents and non-chlorinated organic solvents. Methylene chloride (methylene chloride) can be mentioned as a chlorinated organic solvent, and it is suitable for dissolving cellulose esters, particularly cellulose triacetate. Due to recent environmental problems, the use of non-chlorine organic solvents has been studied. Examples of the non-chlorine organic solvent include methyl acetate, ethyl acetate, amyl acetate, acetone, tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane, cyclohexanone, ethyl formate, 2,2,2-trifluoroethanol, 2,2,3,3-hexafluoro-1-propanol, 1,3-difluoro-2-propanol, 1,1,1,3,3,3-hexafluoro-2-methyl-2-propanol, 1, Examples include 1,1,3,3,3-hexafluoro-2-propanol, 2,2,3,3,3-pentafluoro-1-propanol, nitroethane, and the like. When these organic solvents are used for cellulose triacetate, a dissolution method at room temperature can be used, but an insoluble material can be obtained by using a dissolution method such as a high-temperature dissolution method, a cooling dissolution method, or a high-pressure dissolution method. Can be reduced, which is preferable. For cellulose esters other than cellulose triacetate, methylene chloride can be used, but methyl acetate, ethyl acetate, and acetone are preferably used. Particularly preferred is methyl acetate. In the present invention, an organic solvent having good solubility with respect to the cellulose ester is referred to as a good solvent, and has a main effect on dissolution, and an organic solvent used in a large amount among them is a main (organic) solvent or a main ( Organic) solvent.

  The dope according to the present invention preferably contains 1 to 40% by mass of an alcohol having 1 to 4 carbon atoms in addition to the organic solvent. These are gelling solvents that make dope film (web) gel when the dope is cast on a metal support and the solvent starts to evaporate and the ratio of alcohol increases, making the web strong and easy to peel off from the metal support. When these ratios are small, there is also a role of promoting the dissolution of the cellulose ester of the non-chlorine organic solvent. Examples of the alcohol having 1 to 4 carbon atoms include methanol, ethanol, n-propanol, iso-propanol, n-butanol, sec-butanol, and tert-butanol. Of these, ethanol is preferred because it has excellent dope stability, has a relatively low boiling point, and has good drying properties. These organic solvents are called poor solvents because they are not soluble in cellulose esters alone.

  It is preferable that the concentration of the cellulose ester in the dope is adjusted to 15 to 30% by mass and the dope viscosity is adjusted to a range of 100 to 500 Pa · s in order to obtain good film surface quality.

  Additives added to the dope include plasticizers, ultraviolet absorbers, antioxidants, dyes, and fine particles. In the present invention, additives other than fine particles may be added during the preparation of the cellulose ester solution, or may be added during the preparation of the fine particle dispersion. It is preferable to add a plasticizer, an antioxidant, an ultraviolet absorber, or the like that imparts heat and moisture resistance to the polarizing plate used in the liquid crystal image display device. The additive will be described below.

(Plasticizer)
In the present invention, a compound known as a so-called plasticizer is added to the cellulose ester solution or dope for the purpose of improving mechanical properties, imparting flexibility, imparting water absorption resistance, reducing water vapor permeability, and adjusting retardation. For example, aromatic terminal esters, phosphate esters, and carboxylic acid esters are preferably used.

  Examples of phosphate esters include triphenyl phosphate, tricresyl phosphate, phenyl diphenyl phosphate, and the like.

  In the present invention, it is preferable to use an aromatic terminal ester plasticizer represented by the following general formula (2).

General formula (2) 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 (2), 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 and can be obtained by a reaction similar to that of a normal polyester plasticizer.

  Examples of the benzene monocarboxylic acid component of the aromatic terminal ester plasticizer used in the present invention include, for example, benzoic acid, para-tert-butylbenzoic acid, orthotoluic acid, metatoluic acid, p-toluic acid, dimethylbenzoic acid, ethylbenzoic acid, There are normal propyl benzoic acid, aminobenzoic acid, acetoxybenzoic acid and the like, and these can be used as one kind or a mixture of two or more kinds, respectively.

  Examples of the alkylene glycol component having 2 to 12 carbon atoms of the aromatic terminal ester plasticizer used in the present invention include ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,2-butanediol, , 3-butanediol, 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-ethyl 1,3 There are hexanediol, 2-methyl 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,12-octadecanediol, etc., and these glycols are one kind or a mixture of two or more kinds. Used as.

  Examples of the oxyalkylene glycol component having 4 to 12 carbon atoms of the aromatic terminal ester include diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, and tripropylene glycol. Or it can be used as a mixture of two or more.

  In addition, examples of the aryl glycol component having 6 to 12 carbon atoms of the aromatic terminal ester include hydroquinone, resorcin, bisphenol A, bisphenol F, bisphenol and the like, and these glycols are used as 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 aromatic terminal ester include succinic acid, maleic acid, fumaric acid, glutaric acid, adipic acid, azelaic acid, sebacic acid, and dodecanedicarboxylic acid. These are used as one kind or a mixture of two or more kinds. Examples of the aryl dicarboxylic acid component having 6 to 12 carbon atoms include phthalic acid, terephthalic acid, 1,5 naphthalene dicarboxylic acid, and 1,4 naphthalene dicarboxylic acid.

  The aromatic terminal ester plasticizer has a number average molecular weight of preferably 300 to 2000, more preferably 500 to 1500. 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.

<Acid value and hydroxyl value of aromatic terminal ester>
The acid value means the number of milligrams of potassium hydroxide necessary for neutralizing the acid (carboxyl group present at the molecular end) contained in 1 g of the sample. The acid value and hydroxyl value are measured according to JIS K0070 (1992).

  Hereinafter, although the synthesis example of the aromatic terminal ester plasticizer used for this invention is shown, this invention is not limited to this.

<Sample No. 1 (Aromatic terminal ester sample)>
Into a reaction vessel, 820 parts (5 moles) of phthalic acid, 608 parts (8 moles) of 1,2-propylene glycol, 610 parts (5 moles) of benzoic acid and 0.30 parts of tetraisopropyl titanate as a catalyst are charged all at once. While stirring in an air stream, a reflux condenser was attached to reflux excess monohydric alcohol, and heating was continued at 130 to 250 ° C. until the acid value became 2 or less, and water produced was continuously removed. Next, the distillate is removed under reduced pressure of 6.65 × 10 ³ Pa to 4 × 10 ² Pa or less at 200 to 230 ° C., followed by filtration to obtain an aromatic terminal ester having the following properties. It was.

Viscosity (25 ° C., mPa · s); 19815
Acid value: 0.4
<Sample No. 2 (Aromatic terminal ester sample)>
A sample was used except that 500 parts (3.5 moles) of adipic acid, 305 parts (2.5 moles) of benzoic acid, 583 parts (5.5 moles) of diethylene glycol, and 0.45 parts of tetraisopropyl titanate as a catalyst were used in the reaction vessel. No. In the same manner as in No. 1, an aromatic terminal ester having the following properties was obtained.

Viscosity (25 ° C., mPa · s); 90
Acid value: 0.05
<Sample No. 3 (Aromatic terminal ester sample)>
Sample No. except that 410 parts (2.5 moles) of phthalic acid, 610 parts (5 moles) of benzoic acid, 737 parts (5.5 moles) of dipropylene glycol and 0.40 parts of tetraisopropyl titanate as the catalyst were used in the reaction vessel. . In the same manner as in No. 1, an aromatic terminal ester plasticizer having the following properties was obtained.

Viscosity (25 ° C., mPa · s); 43400
Acid value: 0.2
Examples of carboxylic acid esters include phthalic acid esters and citric acid esters; phthalic acid esters such as dimethyl phthalate, diethyl phosphate, dioctyl phthalate and diethyl hexyl phthalate; and citrate esters such as acetyl triethyl citrate and acetyl citrate. Mention may be made of tributyl. Other examples include butyl oleate, methylacetyl ricinoleate, dibutyl sebacate, and triacetin. Alkylphthalylalkyl glycolates are also preferably used for this purpose. The alkyl in the alkylphthalylalkyl glycolate is an alkyl group having 1 to 8 carbon atoms. Examples of alkyl phthalyl alkyl glycolates include methyl phthalyl methyl glycolate, ethyl phthalyl ethyl glycolate, propyl phthalyl propyl glycolate, butyl phthalyl butyl glycolate, octyl phthalyl octyl glycolate, methyl phthalyl ethyl glycolate, Ethyl phthalyl methyl glycolate, ethyl phthalyl propyl glycolate, propyl phthalyl ethyl glycolate, methyl phthalyl propyl glycolate, methyl phthalyl butyl glycolate, ethyl phthalyl butyl glycolate, butyl phthalyl methyl glycolate, butyl Phthalyl ethyl glycolate, propyl phthalyl butyl glycolate, butyl phthalyl propyl glycolate, methyl phthalyl octyl glycolate, ethyl phthalyl octyl Collate, octyl phthalyl methyl glycolate, octyl phthalyl ethyl glycolate and the like can be mentioned, such as methyl phthalyl methyl glycolate, ethyl phthalyl ethyl glycolate, propyl phthalyl propyl glycolate, butyl phthalyl butyl glycolate, Octyl phthalyl octyl glycolate is preferably used. These alkyl phthalyl alkyl glycolates may be used in combination of two or more.

  Polyhydric alcohol esters are also preferably used.

  The polyhydric alcohol used in the present invention is represented by the following general formula (3).

Formula (3) R1- (OH) n
In the formula, R1 represents an n-valent organic group, n represents a positive integer of 2 or more, and an OH group represents an alcoholic and / or phenolic hydroxyl group.

  The polyhydric alcohol ester plasticizer is a plasticizer comprising 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. Preferably it is a 2-20 valent aliphatic polyhydric alcohol ester.

  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 and the like. In particular, triethylene glycol, tetraethylene glycol, dipropylene glycol, tripropylene glycol, sorbitol, trimethylolpropane, and xylitol are preferable.

  There is no restriction | limiting in particular as monocarboxylic acid used for polyhydric alcohol ester, 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 preferred 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 side chain having 1 to 32 carbon atoms can be preferably used. The number of carbon atoms is more preferably 1-20, and particularly preferably 1-10. When acetic acid is contained, the compatibility with the cellulose ester is increased, and it is also preferable 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-hexanoic 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, laccelic acid, undecylenic acid, olein Examples thereof include unsaturated fatty acids such as acid, sorbic acid, linoleic acid, linolenic acid, and arachidonic acid.

  Examples of preferred alicyclic monocarboxylic acids include cyclopentane carboxylic acid, cyclohexane carboxylic acid, cyclooctane carboxylic acid, or 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 biphenylcarboxylic acid, naphthalenecarboxylic acid, and tetralincarboxylic acid. The aromatic monocarboxylic acid which has, or those derivatives can be mentioned. Benzoic acid is particularly preferable.

  The molecular weight of the polyhydric alcohol ester is not particularly limited, but is preferably 300 to 1500, and more preferably 350 to 750. A higher molecular weight is preferred because it is less likely to volatilize, and a smaller one is preferred in terms of moisture permeability and compatibility with cellulose ester.

  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.

  It is preferable that these compounds are contained so that it may become 1-30 mass% with respect to a cellulose ester, Preferably it is 1-20 mass%. In order to suppress bleeding out during stretching and drying, a compound having a vapor pressure at 200 ° C. of 1400 Pa or less is preferable.

  These compounds may be added together with the cellulose ester or the solvent during the preparation of the cellulose ester solution, or may be added during or after the solution preparation.

  As other additives, polyesters and polyester ethers described in JP-A No. 2002-22956, urethane resins described in JP-A No. 2003-171499, rosins and rosin derivatives described in JP-A No. 2002-146044, epoxy resins, and ketone resins , Toluenesulfonamide resin, ester of polyhydric alcohol and carboxylic acid described in JP-A-2003-96236, compound described in general formula (1) of JP-A-2003-165868, polyester weight described in JP-A-2004-292696 Examples thereof include a coalescence or a polyurethane polymer. These additives can be contained in the dope or fine particle dispersion.

(UV absorber)
The polarizing plate protective film of the present invention can contain an ultraviolet absorber. Examples of ultraviolet absorbers that can be used include oxybenzophenone compounds, benzotriazole compounds, salicylic acid ester compounds, benzophenone compounds, cyanoacrylate compounds, nickel complex compounds, triazine compounds, and the like. A benzotriazole-based compound with little coloring is preferable. Further, ultraviolet absorbers described in JP-A-10-182621, JP-A-8-337574, JP-A-2001-72782, JP-A-6-148430, JP-A-2002-31715, JP-A-2002-169020, 2002-2002. Polymer ultraviolet absorbers described in 47357, 2002-363420, and 2003-113317 are also preferably used. As an ultraviolet absorber, from the viewpoint of preventing the deterioration of polarizers and liquid crystals, it is excellent in the ability to absorb ultraviolet rays having a wavelength of 370 nm or less, and from the viewpoint of liquid crystal display properties, the absorption of visible light having a wavelength of 400 nm or more is small. Is preferred.

  Specific examples of UV absorbers useful in the present invention include 2- (2′-hydroxy-5′-methylphenyl) benzotriazole, 2- (2′-hydroxy-3 ′, 5′-di-tert-butylphenyl). ) Benzotriazole, 2- (2′-hydroxy-3′-tert-butyl-5′-methylphenyl) benzotriazole, 2- (2′-hydroxy-3 ′, 5′-di-tert-butylphenyl)- 5-chlorobenzotriazole, 2- (2′-hydroxy-3 ′-(3 ″, 4 ″, 5 ″, 6 ″ -tetrahydrophthalimidomethyl) -5′-methylphenyl) benzotriazole, 2,2-methylenebis ( 4- (1,1,3,3-tetramethylbutyl) -6- (2H-benzotriazol-2-yl) phenol), 2- (2′-hydroxy-3′- ert-butyl-5′-methylphenyl) -5-chlorobenzotriazole, 2- (2H-benzotriazol-2-yl) -6- (linear and side chain dodecyl) -4-methylphenol, octyl-3- [3-tert-butyl-4-hydroxy-5- (chloro-2H-benzotriazol-2-yl) phenyl] propionate and 2-ethylhexyl-3- [3-tert-butyl-4-hydroxy-5- (5 -Chloro-2H-benzotriazol-2-yl) phenyl] propionate and the like can be mentioned, but not limited thereto. As commercially available products, TINUVIN 109, TINUVIN 171 and TINUVIN 326 (all manufactured by Ciba Specialty Chemicals) can be preferably used. An example of the polymeric ultraviolet absorber is a reactive ultraviolet absorber RUVA-93 manufactured by Otsuka Chemical Co., Ltd.

  Specific examples of the benzophenone compounds include 2,4-dihydroxybenzophenone, 2,2′-dihydroxy-4-methoxybenzophenone, 2-hydroxy-4-methoxy-5-sulfobenzophenone, bis (2-methoxy-4-hydroxy- 5-benzoylphenylmethane) and the like, but is not limited thereto.

  The ultraviolet absorber described above preferably used in the present invention is preferably a benzotriazole-based ultraviolet absorber or a benzophenone-based ultraviolet absorber, which has high transparency and is excellent in the effect of preventing the deterioration of the polarizing plate and the liquid crystal element, and unnecessary coloring. A benzotriazole-based ultraviolet absorber with a lower content is particularly preferably used.

  The ultraviolet absorber can be added to the dope without limitation as long as it dissolves the ultraviolet absorber in the dope. In the present invention, the ultraviolet absorber is cellulose such as methylene chloride, methyl acetate, dioxolane and the like. A dope by adding a good solvent for an ester or a mixed solvent of a good solvent and a poor solvent such as a lower aliphatic alcohol (methanol, ethanol, propanol, butanol, etc.) and adding it to a cellulose ester solution as an ultraviolet absorber solution. Is preferred. In this case, it is preferable to make the dope solvent composition and the solvent composition of the ultraviolet absorber solution the same or as close as possible. The content of the ultraviolet absorber is 0.01 to 5% by mass, particularly 0.5 to 3% by mass.

(Antioxidant)
As the antioxidant, hindered phenol compounds are preferably used. For example, 2,6-di-t-butyl-p-cresol, pentaerythrityl-tetrakis [3- (3,5-di-t- Butyl-4-hydroxyphenyl) propionate], triethylene glycol-bis [3- (3-tert-butyl-5-methyl-4-hydroxyphenyl) propionate], 1,6-hexanediol-bis [3- (3 , 5-di-t-butyl-4-hydroxyphenyl) propionate], 2,4-bis- (n-octylthio) -6- (4-hydroxy-3,5-di-t-butylanilino) -1,3 , 5-triazine, 2,2-thio-diethylenebis [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate], octadecyl-3 (3,5-di-t-butyl-4-hydroxyphenyl) propionate, N, N′-hexamethylenebis (3,5-di-t-butyl-4-hydroxy-hydrocinnamamide), 1,3 , 5-trimethyl-2,4,6-tris (3,5-di-t-butyl-4-hydroxybenzyl) benzene, tris- (3,5-di-t-butyl-4-hydroxybenzyl) -isocyanate Examples include nurate. In particular, 2,6-di-t-butyl-p-cresol, pentaerythrityl-tetrakis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], triethylene glycol-bis [3- (3-t-butyl-5-methyl-4-hydroxyphenyl) propionate] is preferred. Further, for example, hydrazine-based metal deactivators such as N, N′-bis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionyl] hydrazine and tris (2,4-di-t A phosphorus-based processing stabilizer such as -butylphenyl) phosphite may be used in combination. The amount of these compounds added is preferably 1 ppm to 1.0%, more preferably 10 to 1000 ppm in terms of mass ratio with respect to the cellulose ester.

(Matting agent)
In the present invention, in addition to the needle-like fine particles having birefringence as a preferred domain forming material, fine particles as a matting agent can be further contained in the polarizing plate protective film. Thereby, conveyance and winding can be facilitated.

  The particle size of the matting agent is preferably primary particles or secondary particles of 10 nm to 0.1 μm. A substantially spherical matting agent having a primary particle acicular ratio of 1.1 or less is preferably used.

  As the fine particles, those containing silicon are preferable, and silicon dioxide is particularly preferable. Preferred fine particles of silicon dioxide for the present invention include, for example, Aerosil R972, R972V, R974, R812, 200, 200V, 300, R202, OX50, TT600 (Nippon Aerosil Co., Ltd.) manufactured by Nippon Aerosil Co., Ltd. A commercially available product name can be mentioned, and Aerosil 200V, R972, R972V, R974, R202, R812 can be preferably used. Examples of polymer fine particles include silicone resin, fluorine resin, and acrylic resin. Silicone resins are preferable, and those having a three-dimensional network structure are particularly preferable. Examples include Tospearl 103, 105, 108, 120, 145, 3120, and 240 (manufactured by Toshiba Silicone Co., Ltd.). I can do it.

  The fine particles of silicon dioxide preferably have a primary average particle size of 20 nm or less and an apparent specific gravity of 70 g / L or more. The average diameter of the primary particles is more preferably 5 to 16 nm, further preferably 5 to 12 nm. A smaller primary particle average diameter is preferred because haze is low. The apparent specific gravity is preferably 90 to 200 g / L or more, and more preferably 100 to 200 g / L or more. Higher apparent specific gravity makes it possible to produce a high-concentration fine particle dispersion, which is preferable because no haze or aggregates are generated.

The addition amount of the matting agent in the present invention is preferably 0.01 to 1.0 g, more preferably 0.03 to 0.3 g, and still more preferably 0.08 to 0.16 g per 1 m ^{2 of} the polarizing plate protective film.

(Surfactant)
The dope or fine particle dispersion used in the present invention preferably contains a surfactant, and is not particularly limited to phosphoric acid, sulfonic acid, carboxylic acid, nonionic, cationic and the like. These are described in, for example, JP-A-61-243837. The addition amount of the surfactant is preferably 0.002 to 2% by mass and more preferably 0.01 to 1% by mass with respect to the cellulose ester. If the addition amount is less than 0.001% by mass, the effect of addition cannot be exhibited sufficiently, and if the addition amount exceeds 2% by mass, precipitation or insoluble matter may occur.

  Nonionic surfactants include surfactants having nonionic hydrophilic groups such as polyoxyethylene, polyoxypropylene, polyoxybutylene, polyglycidyl and sorbitan, and specifically include polyoxyethylene alkyl ethers, polyoxyethylene alkyl ethers, and polyoxyethylene alkyl ethers. Oxyethylene alkyl phenyl ether, polyoxyethylene-polyoxypropylene glycol, polyhydric alcohol fatty acid partial ester, polyoxyethylene polyhydric alcohol fatty acid partial ester, polyoxyethylene fatty acid ester, polyglycerin fatty acid ester, fatty acid diethanolamide, triethanolamine Examples include fatty acid partial esters.

  Examples of the anionic surfactant include carboxylate, sulfate, sulfonate, and phosphate ester salt. Representative examples include fatty acid salt, alkylbenzene sulfonate, alkyl naphthalene sulfonate, alkyl sulfonate, α-olefin sulfonate, dialkylsulfosuccinate, α-sulfonated fatty acid salt, N-methyl-N oleyl taurine, petroleum sulfonate, alkyl sulfate, sulfated oil, polyoxyethylene alkyl ether sulfate, Examples thereof include polyoxyethylene alkyl phenyl ether sulfate, polyoxyethylene styrenated phenyl ether sulfate, alkyl phosphate, polyoxyethylene alkyl ether phosphate, and naphthalene sulfonate formaldehyde condensate.

  Examples of cationic surfactants include amine salts, quaternary ammonium salts, pyridium salts, etc., and primary to tertiary fatty amine salts, quaternary ammonium salts (tetraalkyl ammonium salts, trialkylbenzyl ammonium salts, Alkyl pyridium salt, alkyl imidazolium salt, etc.). Examples of amphoteric surfactants include carboxybetaine and sulfobetaine, such as N-trialkyl-N-carboxymethylammonium betaine and N-trialkyl-N-sulfoalkyleneammonium betaine.

The fluorosurfactant is a surfactant having a fluorocarbon chain as a hydrophobic group. Examples of the fluorine-containing _{surfactant, C 8 F 17 CH 2 CH} 2 O- (CH 2 CH 2 O) 10 -OSO 3 Na, C 8 F 17 SO 2 N (C 3 H 7) (CH 2 CH 2 O _{) 16 -H, C 8 F 17} SO 2 N (C 3 H 7) CH 2 COOK, C 7 F 15 COONH 4, C 8 F 17 SO 2 N (C 3 H 7) (CH 2 CH 2 O) 4 _{- (CH 2) 4 -SO 3} Na, C 8 F 17 SO 2 N (C 3 H 7) (CH 2) 3 -N + (CH 3) 3 · I -, C 8 F 17 SO 2 N (C _{3 H 7) CH 2 CH 2} CH 2 N + (CH 3) 2 -CH 2 COO -, C 8 F 17 CH 2 CH 2 O (CH 2 CH 2 O) 16 -H, C 8 F 17 CH 2 CH ₂ O (CH ₂ ) ₃ —N ⁺ (CH ₃ ) ₃ .I ⁻ , H (CF ₂ ) ₈ —CH ₂ CH ₂ OCOCH ₂ CH (SO ₃ ) COOCH ₂ CH ₂ CH ₂ CH ₂ (CF ₂ ) _{8 -H, H (CF 2) 6} CH 2 _{CH 2 O (CH 2 CH 2} O) 16 -H, H (CF 2) 8 CH 2 CH 2 O (CH 2) 3 -N + (CH 3) 3 · I -, H (CF 2) 8 CH 2 _{CH 2 OCOCH 2 CH (SO 3} ) COOCH 2 H 2 CH 2 CH 2 C 8 F 17, C 9 F 17 -C 6 H 4 -SO 2 N (C 3 H 7) (CH 2 CH 2 O) 16 - H, C ₉ F ₁₇ —C ₆ H ₄ —CSO ₂ N (C ₃ H ₇ ) (CH ₂ ) ₃ —N ⁺ (CH ₃ ) ₃ · I ^−, etc. Absent.

(Peeling accelerator)
Furthermore, a peeling accelerator for reducing the load during peeling may be added to the dope. Of these, surfactants are effective, and phosphoric acid-based, sulfonic acid-based, carboxylic acid-based, nonionic-based, cationic-based and the like are not particularly limited thereto. These peeling accelerators are described in, for example, JP-A-61-243837. Japanese Patent Application Laid-Open No. 57-500833 discloses a polyethoxylated phosphate ester as a peeling accelerator. JP-A-61-69845 discloses that a mono- or di-phosphoric acid alkyl ester in which a non-esterified hydroxy group is in the form of a free acid can be rapidly removed by adding to the cellulose ester. JP-A-1-299847 discloses that the peeling load can be reduced by adding a phosphoric ester compound containing a non-esterified hydroxyl group and a propylene oxide chain and inorganic particles.

  Moreover, it is preferable that the compound represented by the following general formula (4) or (5) is contained.

Formula _{(4) (R 1 -B 1} -O) n1 -P (= O) - (OM 1) n2
Formula (5) R ₂ -B ₂ -X
In the formula, R ₁ and R ₂ are each a substituted or unsubstituted alkyl group, alkenyl group, aralkyl group or aryl group having 4 to 40 carbon atoms; M ₁ is an alkali metal, ammonia, or a lower alkyl amine. Yes; B ₁ and B ₂ are each a divalent linking group; X is a carboxylic acid or a salt thereof, a sulfonic acid or a salt thereof, or a sulfate ester or a salt thereof; n1 is 1 or 2; Yes; and n2 is 3-n1.

The cellulose acylate film contains at least one release agent represented by the formula (4) or (5). Hereinafter, these release agents will be described. Preferred examples of R ₁ and R ₂ include substituted and unsubstituted alkyl groups having 4 to 40 carbon atoms (for example, butyl, hexyl, octyl, 2-ethylhexyl, nonyl, dodecyl, hexadecyl, octadecyl, eicosanyl, docosanyl, myricyl). , Etc.), substituted with 4 to 40 carbon atoms, unsubstituted alkenyl groups (for example, 2-hexenyl, 9-decenyl, oleyl, etc.), substituted with 4 to 40 carbon atoms, unsubstituted aryl groups (for example, phenyl, Naphthyl, methylphenyl, dimethylphenyl, trimethylphenyl, ethylphenyl, propylphenyl, diisopropylphenyl, triisopropylphenyl, t-butylphenyl, di-t-butylphenyl, tri-t-butylphenyl, isopentylphenyl, octylphenyl, Isooctylphenyl, isononyl phen Nyl, diisononylphenyl, dodecylphenyl, isopentadecylphenyl).

  Of these, more preferred are alkyl as hexyl, octyl, 2-ethylhexyl, nonyl, dodecyl, hexadecyl, octadecyl, docosanyl, alkenyl as alkenyl, aryl as phenyl, naphthyl, trimethylphenyl, diisopropylphenyl, triisopropyl. Isopropylphenyl, di-t-butylphenyl, tri-t-butylphenyl, isooctylphenyl, isononylphenyl, diisononylphenyl, dodecylisopentadecylphenyl.

Next, the divalent linking group of B ₁ and B ₂ will be described. C1-10 alkylene, poly (degree of polymerization 1-50) oxyethylene, poly (degree of polymerization 1-50) oxypropylene, poly (degree of polymerization 1-50) oxyglycerin, and a mixture thereof. . Preferred linking groups among these are methylene, ethylene, propylene, butylene, poly (degree of polymerization 1-25) oxyethylene, poly (degree of polymerization 1-25) oxypropylene, and poly (degree of polymerization 1-15) oxyglycerin.

  X is carboxylic acid (or salt), sulfonic acid (or salt), sulfate ester (or salt), and particularly preferably sulfonic acid (or salt) or sulfate ester (or salt). Preferred salts are Na, K, ammonium, trimethylamine and triethanolamine. Specific examples of preferred compounds of the present invention are described below.

RZ-1 C ₈ H ₁₇ O—P (═O) — (OH) ₂
RZ-2 C ₁₂ H ₂₅ O—P (═O) — (OK) ₂
RZ-3 C ₁₂ H ₂₅ OCH ₂ CH ₂ O—P (═O) — (OK) ₂
RZ-4 C ₁₅ H ₃₁ (OCH ₂ CH ₂ ) ₅ O—P (═O) — (OK) _{2
RZ-5 {C 12 H 25} O (CH 2 CH 2 O) 5} 2 -P (= O) -OH
_{RZ-6 {C 18 H 35} (OCH 2 CH 2) 8 O} 2 -P (= O) -ONH 4
_{RZ-7 (t-C 4} H 9) 3 -C 6 H 2 -OCH 2 CH 2 O-P (= O) - (OK) 2
_{RZ-8 iso-C 9 H} 19 -C 6 H 4 -O- (CH 2 CH 2 O) 5 -P (= O) - (OK) (OH)
RZ-9 C ₁₂ H ₂₅ SO ₃ Na
RZ-10 C ₁₂ H ₂₅ OS ₃ Na
RZ-11 C ₁₇ H ₃₃ COOH
RZ-12 C ₁₇ H ₃₃ COOH · N (CH ₂ CH ₂ OH) _{3
RZ-13 iso-C 8 H} 17 -C 6 H 4 -O- (CH 2 CH 2 O) 3 - (CH 2) 2 SO 3 Na
_{RZ-14 (iso-C 9} H 19) 2 -C 6 H 3 -O- (CH 2 CH 2 O) 3 - (CH 2) 4 SO 3 Na
RZ-15 sodium triisopropyl naphthalene sulfonate RZ-16 sodium tri-t-butyl naphthalene sulfonate RZ-17 C ₁₇ H ₃₃ CON (CH ₃ ) CH ₂ CH ₂ SO ₃ Na
RZ-18 C ₁₂ H ₂₅ -C ₆ H ₄ SO ₃ .NH ₄
The amount of these compounds used is preferably 0.002 to 2% by mass in the dope. More preferably, it is 0.005-1 mass%, More preferably, it is 0.01-0.5 mass%. The addition method is not particularly limited, but it may be liquid or solid as it is and added together with other materials before dissolution, or may be added later to a cellulose ester solution prepared in advance. By containing these, it becomes easy to align the domains.

(Other additives)
In addition, thermal stabilizers such as inorganic fine particles such as kaolin, talc, diatomaceous earth, quartz, calcium carbonate, barium sulfate, titanium oxide, and alumina, and alkaline earth metal salts such as calcium and magnesium may be added. Furthermore, an antistatic agent, a flame retardant, a lubricant, an oil agent, etc. may be added.

[Casting method for casting]
The method for forming the polarizing plate protective film of the present invention may be either a solution casting film forming method or a melt casting film forming method. Here, the solution casting film forming method will be described with reference to FIG.

  FIG. 3 is a diagram showing an example of a process schematically showing a dope preparation process, a casting process, and a drying process of the solution casting film forming method according to the present invention.

(1) Cellulose ester solution preparation process In this invention, dope is prepared by mixing the domain formation material and cellulose ester which were prepared previously, and a solvent. Specifically, it is preferable to add and mix or disperse a part of the solvent and the domain forming material in the dissolution vessel, and then add and dissolve the remaining solvent and cellulose ester with stirring. Additives such as plasticizers can be added later or added to the dissolution vessel.

  Alternatively, an additive such as cellulose ester or a plasticizer may be added to the solvent in the dissolution vessel while stirring, and the domain forming material may be further added during dissolution of the cellulose ester. Alternatively, a solvent and an additive such as a cellulose ester and a plasticizer can be mixed to obtain a cellulose ester solution, and the domain-forming material mixed or dispersed in the solvent can be added thereto while stirring.

  The method for preparing the cellulose ester solution will be described in more detail.

  An additive such as cellulose ester and plasticizer is dissolved in an organic solvent mainly composed of a good solvent for the cellulose ester with stirring. For dissolution, a method performed at normal pressure, a method performed below the boiling point of the main solvent, a high-temperature dissolution method performed by pressurization above the boiling point of the main solvent, a cooling dissolution method performed by cooling and a high-pressure dissolution method performed at a considerably high pressure However, in the present invention, the high temperature dissolution method is preferably used.

  The cellulose ester solution obtained by mixing the domain-forming material, cellulose ester, and solvent in the dissolution vessel is dissolved in the cellulose ester and then sent to a filter by a pump and filtered.

  Filtration is preferably carried out using the cellulose ester solution with an appropriate filter medium such as filter paper for filter press. As the filter medium in the present invention, it is preferable that the absolute filtration accuracy is small in order to remove insoluble matter, etc., but if the absolute filtration accuracy is too small, there is a problem that the filter medium is likely to be clogged, and absolute filtration Filter media with an accuracy of 8 μm or less are preferred, filter media in the range of 1-8 μm are more preferred, and filter media in the range of 3-6 μm are even more preferred. Examples of filter paper include No. of Azumi Filter Paper Co., Ltd., a commercially available product. 244, 277, etc. can be mentioned and used preferably.

  There are no particular restrictions on the material of the filter medium for filtration, and ordinary filter media can be used. However, plastic filter media such as polypropylene and Teflon (registered trademark) and metal filter media such as stainless steel do not lose fibers. preferable. Filtration can be performed by a normal method, but the method of filtering while heating or keeping the temperature at a temperature in a range not lower than the boiling point of the organic solvent used under normal pressure and in a range where the organic solvent does not boil is a filter medium. The increase in differential pressure before and after (hereinafter sometimes referred to as filtration pressure) is small and preferable. The preferred temperature range depends on the organic solvent used, but is 45 to 120 ° C, more preferably 45 to 70 ° C, and still more preferably 45 to 55 ° C. The filtration pressure is preferably as small as possible, preferably 0.3 to 1.6 MPa, more preferably 0.3 to 1.2 MPa, and still more preferably 0.3 to 1.0 MPa.

  The dope thus obtained is stored in a stock tank, defoamed and then used for casting.

  As described above, it is preferable to prepare a dope by mixing a domain forming material and a cellulose ester solution in a dope pot. However, a part or all of the cellulose ester solution and the domain forming material may be mixed in-line. You can also. For example, FIG. 3 shows an example of the step of adding the domain forming material in-line. The domain-forming material solution mixed or dispersed in a suitable solvent is joined with a cellulose ester solution (or may be referred to as a dope stock solution) in a joining pipe 20. A filter is disposed immediately before the merging pipe 20, and for example, lump and large foreign matter generated from the path due to exchange of the filter medium can be removed from the domain forming material solution or the dope stock solution being fed. . Here, a metal filter having solvent resistance is preferably used. The filter medium is preferably a metal, particularly stainless steel, from the viewpoint of durability. From the viewpoint of clogging, it is preferable to have a porosity of 60 to 80%. Most preferably, the filtration is performed with a metal filter medium having an absolute filtration accuracy of 30 to 60 μm and a porosity of 60 to 80%, so that coarse foreign matters can be reliably removed over a long period of time. preferable. Examples of metal filter media having an absolute filtration accuracy of 30 to 60 μm and a porosity of 60 to 80% include, for example, NF-10, NF-12, and NF-13 of Fine pore NF series manufactured by Nippon Seisen Co., Ltd. Can be mentioned.

(2) In-line addition process When a dope is prepared by previously mixing a domain-forming material, a cellulose ester, and a solvent in a melting pot, it is usually unnecessary to add the domain-forming material in-line. However, if necessary, all or part of the domain forming material can be mixed in-line. The in-line addition process will be described with reference to FIG. 3. A cellulose ester solution (sometimes referred to as a dope stock solution) and a domain-forming material solution are transferred by liquid feed pumps 5 and 14, filtered by filters 6 and 15, 8 and 16 are transferred, and both liquids are merged by the merge pipe 20. Since the combined liquids are transported in layers in the conduit, they are difficult to mix as they are. Therefore, the two liquids are merged and then transferred to the next step while being sufficiently mixed by the mixer 21 such as an in-line mixer. As an in-line mixer that can be used in the present invention, for example, a static mixer SWJ (Toray static type in-pipe mixer Hi-Mixer, manufactured by Toray Engineering) is preferable.

  In the dope prepared by the step (2), the solid content concentration in the dope is preferably adjusted to 15% by mass or more, particularly preferably 18 to 30% by mass. If the solid content concentration in the dope is too high, the viscosity of the dope becomes too high, and a sharkskin or the like may occur during casting to deteriorate the film flatness. Therefore, it is preferably 30% by mass or less.

(3) Casting process An endless metal support 31, for example, a stainless steel belt or a rotating metal drum, in which the dope prepared up to the previous process is fed to the die 30 shown as an example in FIG. This is a step of casting the dope from the die 30 to the casting position on the metal support 31 or the like. The surface of the metal support 31 is a mirror surface. The die 30 can adjust the slit shape of the die portion, and can easily control the domain orientation and make the film thickness uniform. In order to increase the film forming speed, two or more dies may be provided on the metal support 31, and the dope amount may be divided to be stacked.

  The surface temperature of the metal support for casting is 10 to 55 ° C., the temperature of the dope is 25 to 60 ° C., and the temperature of the solution is preferably equal to or higher than the temperature of the support. More preferably, the temperature is set to a temperature of

  The higher the solution temperature and the support temperature, the faster the solvent can be dried. However, if the temperature is too high, foaming or flatness may be deteriorated.

  Although the more preferable range of the temperature of a support body is dependent on the organic solvent to be used, it is 20-55 degreeC, and the more preferable range of solution temperature is 35-45 degreeC.

(4) Solvent evaporation step Web 32 can be peeled from metal support 31 by heating web 32 (referred to as dope film after casting dope on metal support as web) 32 on metal support 31 This is a step of evaporating the solvent until. In order to evaporate the solvent, there are a method of blowing air from the web 32 side and / or a method of transferring heat from the back surface of the metal support 31 by a liquid, a method of transferring heat from the front and back by radiant heat, and the like. This method is preferable because of good drying efficiency. 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 step In this step, the web 32 having the solvent evaporated on the metal support 31 is peeled off at the peeling position 33. The peeled web 32 is sent to the next process. If the residual solvent amount of the web 32 (explained later) at the time of peeling is too large, peeling is difficult, or conversely, if the film is sufficiently dried on the metal support 31 and then peeled off, a part of the web 32 is halfway. May come off. In the present invention, when the thin web is peeled from the metal support, it is preferable to peel the thin web with a force within 170 N / m from the minimum tension that can be peeled as the peeling tension, in order to prevent the flatness from being deteriorated and hung. A force within 140 N / m is more preferred.

  There is a gel casting method (gel casting) as a method for increasing the film forming speed (the film forming speed can be increased because the film is peeled off while the residual solvent amount is as large as possible). For example, a poor solvent for the cellulose ester is added to the dope, and the dope is cast and then gelled, and the temperature of the metal support is lowered to gel. By gelling on the metal support 31 and increasing the strength of the film at the time of peeling, peeling can be accelerated and the film forming speed can be increased. The web 32 on the metal support 31 can be peeled in the range of 5 to 150% by mass depending on the strength of the condition, the length of the metal support 31, etc., but peels off when the amount of residual solvent is larger. In this case, if the web 32 is too soft, the flatness at the time of peeling tends to be lost, or a slip or vertical stripe due to the peeling tension is likely to occur, and the residual solvent amount at the time of peeling is determined in consideration of the economic speed and quality. Therefore, in the present invention, the temperature at the peeling position on the metal support 31 is 10 to 40 ° C., preferably 15 to 30 ° C., and the residual solvent amount of the web 32 at the peeling position is 10 to 120% by mass. It is preferable to do.

  In order to maintain good flatness of the polarizing plate protective film during production, the amount of residual solvent when peeling from the metal support is preferably 10 to 150% by mass, more preferably 70 to 150% by mass. More preferably, it is 100-130 mass%. The proportion of the good solvent contained in the residual solvent is preferably 50 to 90%, more preferably 60 to 90%, and particularly preferably 70 to 80%.

  In the present invention, the residual solvent amount can be expressed by the following formula.

Residual solvent amount (% by mass) = {(MN) / N} × 100
Here, M is a mass at an arbitrary time point of the web, and is a mass measured by the following gas chromatography. N is a mass when the M is dried at 110 ° C. for 3 hours. The measurement is performed by gas chromatography connected to a headspace sampler. In the present invention, gas chromatography 5890 type SERISII and headspace sampler HP7694 type manufactured by Hewlett-Packard Company were used and the measurement was performed under the following measurement conditions.

Headspace sampler heating conditions: 120 ° C, 20 minutes GC introduction temperature: 150 ° C
Temperature rise: 40 ° C, hold for 5 minutes → 100 ° C (8 ° C / min)
Column: J-W DB-WAX (inner diameter 0.32 mm, length 30 m).

(6) Drying step After peeling, generally, the web 32 is dried using a roll drying device 35 that alternately conveys the web 32 through a plurality of rolls and a tenter device 34 that grips and conveys both ends of the web 32. . In FIG. 3, the roll drying device 35 is arranged after the tenter device 34, but is not limited to this arrangement. As a drying means, hot air is generally blown on both sides of the web, but there is also a means for heating by applying a microwave instead of the wind. Too rapid drying tends to impair the flatness of the finished film. Throughout, the drying temperature is usually in the range of 40 to 250 ° C. The drying temperature, the amount of drying air, and the drying time differ depending on the solvent used, and the drying conditions may be appropriately selected according to the type and combination of the solvents used. 37 is winding of the completed polarizing plate protective film. In the step of drying the polarizing plate protective film, the residual solvent amount is preferably 0.5% by mass or less, more preferably 0.1% by mass or less.

  The polarizing plate protective film according to the present invention is formed into a film by a casting process after preparing a dope to which a domain forming material is added. As a method for orienting the added domain forming material, the film is formed by TD or A method of stretching in the MD direction or a method of making a dope flow during casting and orienting the domain forming material along the flow can be used. Further, the orientation of the domain forming material can be promoted by an electric field or a magnetic field. In particular, in the present invention, it is preferable to use a method of stretching at least in the MD direction in order to align the domain forming material.

(7) Stretching process (also called tenter process)
The polarizing plate protective film of the present invention can adjust birefringence by stretching. A film containing a solvent can be stretched during the production of the solution casting method, or a film in a state where the solvent is dried can be stretched. The stretching temperature is preferably performed at a glass transition temperature of the film of −20 ° C. to a temperature at which the film flows. Here, the glass transition temperature of the film can be measured by a known method. Stretching can be performed in the film forming direction or the width direction, but in the present invention, it is preferable to stretch at least in the longitudinal direction. By stretching, the ratio of domains oriented in the stretching direction can be increased.

  The stretching process will be described in more detail. The draw ratio at the time of producing the polarizing plate protective film of the present invention is 1.01 to 3 times, preferably 1.5 to 3 times, with respect to the film forming direction or the width direction. When stretching in the biaxial direction, the side to be stretched at a high magnification is 1.01 to 3 times, preferably 1.5 to 3 times, and the stretching ratio in the other direction is 0.8 to 1.5. The film can be stretched by a factor of preferably 0.9 to 1.2.

  Thereby, while being able to obtain preferably the polarizing plate protective film which has the polarization scattering anisotropy of this invention, the flatness favorable polarizing plate protective film can be obtained. It is preferable to perform the width maintenance or the transverse stretching in the film forming process by a tenter, and it may be a pin tenter or a clip tenter.

(8) Winding step This is a step of winding the web after drying as a film. By setting the amount of residual solvent to finish drying to 0.5% by mass or less, preferably 0.1% by mass or less, a film having good dimensional stability can be obtained. The winding method may be a commonly used winder, and there are methods for controlling the tension such as the constant torque method, constant tension method, taper tension method, and program tension control method with constant internal stress. That's fine.

  The film thickness of the polarizing plate protective film of the present invention varies depending on the purpose of use, but from the viewpoint of thinning the liquid crystal display device, the finished film is preferably in the range of 10 to 150 μm, more preferably in the range of 30 to 100 μm, particularly The range of 40-80 micrometers is preferable. If it is too thin, for example, the required strength as a protective film for a polarizing plate may not be obtained. If it is too thick, the advantage of thinning the film over the conventional polarizing plate protective film is lost. In adjusting the film thickness, it is preferable to control the dope concentration, the pumping amount, the slit gap of the die base, the extrusion pressure of the die, the speed of the metal support and the like so as to obtain a desired thickness. Further, as a means for making the film thickness uniform, it is preferable to use a film thickness detection means to feed back and adjust the programmed feedback information to each of the above devices.

  In the process from immediately after casting through the solution casting film forming method to drying, the atmosphere in the drying apparatus may be air, or may be performed in an inert gas atmosphere such as nitrogen gas or carbon dioxide gas. .

(Polarizing plate and liquid crystal display)
Next, the case where the polarizing plate protective film having polarization scattering anisotropy of the present invention is used for a liquid crystal display device will be described.

  The polarizing plate protective film having polarization scattering anisotropy of the present invention has an advantage that a conventional polarizing plate manufacturing process can be utilized because the resin constituting the polarizing plate protective film is a cellulose resin, and is particularly commonly used. The polarizing plate protective film according to the present invention can be directly bonded with a water-soluble adhesive material such as water glue to a light-absorbing polarizer utilizing a dichroic dye by stretching a polyvinyl alcohol derivative. Therefore, it is greatly superior in thinning and productivity.

  Moreover, since the polarizing plate protective film according to the present invention has characteristics as a polarizing plate protective film composed of cellulose ester, the production process of the polarizing plate in a roll shape as a long film having a brightness enhancement function Therefore, the roll-shaped film also has an advantage that it is not necessary to use a protective sheet for preventing scratches and dust adhesion.

  It is preferable that the polarizing plate of this invention takes the structure of the polarizer / polarizing plate protective film B using the polarizing plate protective film / dichroic polarizing film which has polarization scattering anisotropy.

  In the present invention, it is preferable that the polarizing plate protective film, the polarizer, and the polarizing plate protective film B having polarization scattering anisotropy are all long films, and for laminating each, roll-to-roll is performed. It is preferable.

  When used in a liquid crystal display device, it is preferable that a polarizing plate protective film having polarization scattering anisotropy is disposed on the most backlight side among polarizing plates in a transmissive liquid crystal display device.

  For the polarizing plate protective film having polarization scattering anisotropy, the polarizing plate protective film B positioned opposite to the polarizer may be a TAC film represented by a general cellulose acetate resin. The film B may be a polarizing plate protective film having a function of a viewing angle widening film or a retardation film. Moreover, when using as a polarizing plate, you may install the functional film or functional layer for improving display quality with respect to a contrast or a hue on the polarizing plate protective film B through an adhesion layer or an adhesive layer.

  The polarizing plate protective film B used for the polarizing plate of the present invention may be a cellulose ester film or a polarizing plate protective film other than the cellulose ester film. Further, the present invention, regardless of the properties of the polarizing plate protective film B, in the drying process of polarizing plate production using water paste or the like, the polarizing plate protective film of the present invention preferably has moisture permeability, In this case, there is an advantage that moisture contained in the production of the polarizing plate can be removed in the drying process.

Accordingly, in the present invention, the moisture permeability of the polarizing plate protective film having polarization scattering anisotropy of the present invention is preferably 50 g / m ² / day or more, and preferably 100 g / m ² / day or more. It is preferable at the point which reduces the drying load at the time of manufacture. On the other hand, the upper limit of the moisture permeability of the polarizing plate protective film having scattering anisotropy of the present invention is preferably 1500 g / m ² / day or less from the viewpoint of maintaining the polarizing ability of the polarizer, more preferably 1200 g / m ² / day or less.

  When the polarizing plate protective film is alkali saponified with an alkali solution, the wettability with respect to water is increased, which leads to adhesion with a polyvinyl alcohol-based paste represented by the aforementioned water paste. In the polarizing plate protective film of the present invention, at least one surface has a contact angle with water before saponification treatment of 60 ° or more and 80 ° or less, and a contact angle with water after saponification treatment of 15 ° or more and 40 ° or less. It is preferable.

  Examples of the polarizer preferably used for the polarizing plate of the present invention include a polyvinyl alcohol polarizing film, which includes a polyvinyl alcohol film dyed with iodine and a dichroic dye dyed. As the polyvinyl alcohol film, a modified polyvinyl alcohol film modified with ethylene is preferably used. For the polarizer, a polyvinyl alcohol aqueous solution is formed into a film and dyed by uniaxial stretching or dyed or uniaxially stretched and then preferably subjected to a durability treatment with a boron compound. The film thickness of the polarizer is 5 to 40 μm, preferably 5 to 30 μm, and particularly preferably 5 to 20 μm. One side of the polarizing plate protective film of the present invention is bonded to the surface of the polarizer to form a polarizing plate.

  Since the polarizer is stretched in a uniaxial direction (usually the longitudinal direction), when the polarizing plate is placed in a high-temperature and high-humidity environment, the stretching direction (usually the longitudinal direction) shrinks, and the direction orthogonal to the stretching (usually normal) Extends in the width direction). As the thickness of the polarizing plate protective film decreases, the expansion / contraction ratio of the polarizing plate increases, and in particular, the amount of contraction in the stretching direction of the polarizer increases. Usually, the stretching direction of the polarizer is bonded to the casting direction (MD direction) of the polarizing plate protective film. Therefore, when the polarizing plate protective film is thinned, it is particularly important to suppress the stretching rate in the casting direction. . Since the polarizing plate protective film of this invention is excellent in dimensional stability, it is used suitably as such a polarizing plate protective film.

  Next, the polarizing plate protective film B preferable in the present invention will be described.

  A preferred polarizing plate protective film B in the present invention is the other polarizing plate protective film that is disposed with a polarizer interposed between the polarizing plate protective film having polarization scattering anisotropy according to the present invention.

  The polarizing plate protective film B is not particularly limited. For example, a polyester film such as polyethylene terephthalate or polyethylene naphthalate, a polyethylene film, a polypropylene film, a polycycloolefin film, cellophane, a cellulose acetate film, a cellulose acetate butyrate film, Cellulose acetate phthalate film, cellulose acetate propionate film, cellulose triacetate, cellulose ester film such as cellulose nitrate or derivatives thereof, polyvinylidene chloride film, polyvinyl alcohol film, ethylene vinyl alcohol film, syndiotactic polystyrene series Film, polycarbonate film, cycloolefin Rimmer film (for example, ARTON (manufactured by JSR), ZEONEX, ZEONOR (manufactured by ZEON Corporation)), polymethylpentene film, polyetherketone film, polyethersulfone film, polysulfone film, polyetherketoneimide film, polyamide film And acrylic film or polyacrylate film.

  In the present invention, a cellulose ester film such as a cellulose acetate propionate film or a cellulose triacetate film (TAC film) (for example, Konica Minolta Op Co., Ltd. Konica Minolta Tack KC8UX2M, KC4UX, KC5UX, KC4UY, KC8UY, KC12UR, KC8UY-HA, KC8UX-RHA, etc. are preferably used), cycloolefin polymer film, polycarbonate film, polyester film or polyacryl film are preferable in terms of transparency, mechanical properties, and lack of optical anisotropy. An ester film and a cycloolefin polymer film are preferred. From the viewpoint of producing a polarizing plate by roll-to-roll as described above, a cellulose ester having excellent saponification suitability. A stealth film is most preferred. These resin films may be films formed by a melt casting method or a solution casting method.

  The polarizing plate protective film B used in the present invention preferably has a retardation value Ro defined by the following formula of 0 to 300 nm and a retardation value Rt of -600 to 600 nm. Further, a more preferable range is a range where the Ro value is 0 to 120 nm and an Rt value is −400 to 400 nm, and a particularly preferable range is a range where the Ro value is 0 to 100 nm and the Rt value is −300 to 300 nm.

Formula (i) Ro = (nx−ny) × d
Formula (ii) Rt = ((nx + ny) / 2−nz) × d
In the formula, nx, ny, and nz are the refractive index nx (maximum in-plane refractive index of the film, also referred to as the refractive index in the slow axis direction) at 23 ° C. RH and 590 nm, and ny (the slow axis in the film plane). ) (Refractive index in the direction perpendicular to), nz (refractive index of the film in the thickness direction), and d is the thickness (nm) of the film.

  When the polarizing plate protective film B used in the present invention is used as an optical compensation film of a VA liquid crystal display device having a VA mode liquid crystal cell, the Ro value is 20 to 150 nm and the Rt value is 70 to 400 nm. Is preferred. The Ro value is more preferably 30 to 100 nm. When two optical compensation films are used in the VA liquid crystal display device, the Rt value of the film is preferably 70 to 250 nm. When one optical compensation film is used for the VA liquid crystal display device, the Rt value of the film is preferably 150 to 400 nm.

  The polarizing plate protective film B used in the present invention is also suitable for a polarizing plate protective film used in a transverse electric field switching mode type (also referred to as IPS mode type) liquid crystal display device. The retardation values Ro and Rth are preferably in the range of 0 nm ≦ Ro ≦ 2 nm and −15 nm ≦ Rth ≦ 15 nm. More preferably, 0 nm ≦ Ro ≦ 0.5 nm and −5 nm ≦ Rth ≦ 5 nm.

  When the polarizing plate protective film B used in the present invention is used as a polarizing plate protective film used in a transverse electric field switching mode type (also referred to as IPS mode type) liquid crystal display device, the polarizing plate protective film B has a weight average molecular weight of 500. It is preferable to contain an acrylic polymer having a molecular weight of 30000 or less. Among them, an ethylenically unsaturated monomer Xa having no aromatic ring and a hydrophilic group in the molecule and an ethylenic group having no aromatic ring and a hydrophilic group in the molecule. Polymer X having a weight average molecular weight of 5000 or more and 30000 or less obtained by copolymerization with unsaturated monomer Xb, more preferably, ethylenically unsaturated monomer Xa having no aromatic ring and no hydrophilic group in the molecule and in the molecule Weight average molecular weight 500 obtained by copolymerization with ethylenically unsaturated monomer Xb having no aromatic ring and having a hydrophilic group 30000 and the following polymers X, preferably contains a weight average molecular weight of 500 to 3,000 of the polymer Y obtained by polymerization of ethylenic unsaturated monomer Ya not having an aromatic ring.

<Polymer X, Polymer Y>
The polymer X used in the present invention comprises an ethylenically unsaturated monomer Xa having no aromatic ring and a hydrophilic group in the molecule and an ethylenically unsaturated monomer Xb having no aromatic ring and having a hydrophilic group in the molecule. It is a polymer having a weight average molecular weight of 5,000 to 30,000 obtained by copolymerization.

  Preferably, Xa is an acrylic or methacrylic monomer that does not have an aromatic ring and a hydrophilic group in the molecule, and Xb is an acrylic or methacrylic monomer that does not have an aromatic ring in the molecule and has a hydrophilic group.

  The polymer X used in the present invention is represented by the following general formula (X).

Formula (X)
-(Xa) m- (Xb) n- (Xc) p-
More preferably, it is a polymer represented by the following general formula (X-1).

Formula (X-1)
_{- [CH 2 -C (-R 1} ) (- CO 2 R 2)] m- [CH 2 -C (-R 3) (- CO 2 R 4 -OH) -] n- [Xc] p-
(In the formula, R ₁ and R ₃ represent H or CH _3. R ₂ represents an alkyl group having 1 to 12 carbon atoms or a cycloalkyl group. R ₄ represents —CH ₂ —, —C ₂ H ₄ —. Or -C ₃ H _6- , Xc represents a monomer unit polymerizable to Xa and Xb, m, n and p represent molar composition ratios, provided that m ≠ 0, n ≠ 0, k ≠ 0. M + n + p = 100.)
Although the monomer as a monomer unit which comprises the polymer X used for this invention is mentioned below, it is not limited to this.

  In X, the hydrophilic group means a group having a hydroxyl group or an ethylene oxide chain.

  Examples of the ethylenically unsaturated monomer Xa having no aromatic ring and no hydrophilic group in the molecule include methyl acrylate, ethyl acrylate, propyl acrylate (i-, n-), and 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-), acrylic acid (2-ethylhexyl), acrylic acid (ε-caprolactone), acrylic acid (2-hydroxyethyl) ), Acrylic acid (2-ethoxyethyl), or the like, or those obtained by replacing the acrylic ester with a methacrylic ester. Among these, methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate, and propyl methacrylate (i-, n-) are preferable.

  The ethylenically unsaturated monomer Xb having no aromatic ring in the molecule and having a hydrophilic group is preferably acrylic acid or methacrylic acid ester as a monomer unit having a hydroxyl group. For example, acrylic acid (2-hydroxyethyl), List acrylic acid (2-hydroxypropyl), acrylic acid (3-hydroxypropyl), acrylic acid (4-hydroxybutyl), acrylic acid (2-hydroxybutyl), or those in which these acrylic acids are replaced by methacrylic acid. Preferred are acrylic acid (2-hydroxyethyl) and methacrylic acid (2-hydroxyethyl), acrylic acid (2-hydroxypropyl), and acrylic acid (3-hydroxypropyl).

  Xc is not particularly limited as long as it is an ethylenically unsaturated monomer other than Xa and Xb and copolymerizable, but preferably has no aromatic ring.

  The molar composition ratio m: n of Xa, Xb and Xc is preferably in the range of 99: 1 to 65:35, more preferably in the range of 95: 5 to 75:25. P of Xc is 0-10. Xc may be a plurality of monomer units.

  When the molar composition ratio of Xa is large, the compatibility with the cellulose ester is improved, but the retardation value Rth in the film thickness direction is increased. When the molar composition ratio of Xb is large, the compatibility is deteriorated, but the effect of reducing Rth is high. Further, if the molar composition ratio of Xb exceeds the above range, haze tends to occur during film formation, and it is preferable to optimize these and determine the molar composition ratio of Xa and Xb.

  As for the molecular weight of the polymer X, the weight average molecular weight is from 5,000 to 30,000, more preferably from 8,000 to 25,000.

  By setting the weight average molecular weight to 5,000 or more, it is preferable because the cellulose ester film has advantages such as less dimensional change under high temperature and high humidity and less curling as a polarizing plate protective film. When the weight average molecular weight is 30000 or less, the compatibility with the cellulose ester is further improved, and bleeding out under high temperature and high humidity, and further haze generation immediately after film formation is suppressed.

  The weight average molecular weight of the polymer X used in the present invention can be adjusted by a known molecular weight adjusting method. Examples of such a molecular weight adjusting method include a method of adding a chain transfer agent such as carbon tetrachloride, lauryl mercaptan, octyl thioglycolate, and the like. The polymerization temperature is usually room temperature to 130 ° C., preferably 50 ° C. to 100 ° C., and this temperature or the polymerization reaction time can be adjusted.

  The measuring method of a weight average molecular weight can be based on the following method.

(Weight average molecular weight measurement method)
The weight average molecular weight Mw was measured using gel permeation chromatography.

  The measurement conditions are as follows.

Solvent: Methylene chloride Column: Shodex K806, K805, K803G (Used by connecting three Showa Denko Co., Ltd.)
Column temperature: 25 ° C
Sample concentration: 0.1% by mass
Detector: RI Model 504 (manufactured by GL Sciences)
Pump: L6000 (manufactured by Hitachi, Ltd.)
Flow rate: 1.0ml / min
Calibration curve: Standard polystyrene STK standard polystyrene (manufactured by Tosoh Corp.) Mw = 100000-500 calibration curves with 13 samples were used. Thirteen samples are used at approximately equal intervals.

  The polymer Y used in the present invention is a polymer having a weight average molecular weight of 500 or more and 3000 or less obtained by polymerizing an ethylenically unsaturated monomer Ya having no aromatic ring. A weight average molecular weight of 500 or more is preferable because the residual monomer of the polymer is reduced. Moreover, it is preferable to set it as 3000 or less in order to maintain retardation value Rth fall performance. Ya is preferably an acrylic or methacrylic monomer having no aromatic ring.

  The polymer Y used in the present invention is represented by the following general formula (Y).

General formula (Y)
-(Ya) k- (Yb) q-
More preferably, it is a polymer represented by the following general formula (Y-1).

General formula (Y-1)
_{- [CH 2 -C (-R 5} ) (- CO 2 R 6)] k- [Yb] q-
(In the formula, R ₅ represents H or CH _3. R ₆ represents an alkyl group having 1 to 12 carbon atoms or a cycloalkyl group. Yb represents a monomer unit copolymerizable with Ya. K and q Represents a molar composition ratio, where k ≠ 0 and k + q = 100.)
Yb is not particularly limited as long as it is an ethylenically unsaturated monomer copolymerizable with Ya. Yb may be plural. k + q = 100, q is preferably 0-30.

  The ethylenically unsaturated monomer Ya constituting the polymer Y obtained by polymerizing an ethylenically unsaturated monomer having no aromatic ring is, for example, 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- Ethyl hexyl), acrylic acid (ε-caprolactone), acrylic acid (2-hydroxyethyl), acrylic acid (2-hydroxypropyl), acrylic acid (3-hydroxypropiyl) ), Acrylic acid (4-hydroxybutyl), acrylic acid (2-hydroxybutyl), methacrylic acid ester, the above acrylic acid ester changed to methacrylic acid ester; unsaturated acid, for example, acrylic acid, methacrylic acid , Maleic anhydride, crotonic acid, itaconic acid and the like.

  Yb is not particularly limited as long as it is an ethylenically unsaturated monomer copolymerizable with Ya. Examples of vinyl esters include vinyl acetate, vinyl propionate, vinyl butyrate, vinyl valerate, vinyl pivalate, and vinyl caproate. Vinyl caprate, vinyl laurate, vinyl myristate, vinyl palmitate, vinyl stearate, vinyl cyclohexanecarboxylate, vinyl octylate, vinyl methacrylate, vinyl crotonate, vinyl sorbate, vinyl cinnamate and the like are preferred. Yb may be plural.

  In order to synthesize the polymers X and Y, it is difficult to control the molecular weight in normal polymerization, and it is desirable to use a method that can align the molecular weight as much as possible by a method that does not increase the molecular weight so much. 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 using a chain transfer agent such as carbon tetrachloride, a method using a polymerization terminator such as benzoquinone and dinitrobenzene in addition to the polymerization initiator, and further disclosed in JP 2000-128911 or 2000-344823. Examples thereof include a compound having a single 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 polymer Y uses a compound having a thiol group and a secondary hydroxyl group in the molecule as a chain transfer agent. The polymerization method of use is preferred. In this case, the terminal of the polymer Y has a hydroxyl group and a thioether resulting from the polymerization catalyst and the chain transfer agent. The compatibility of Y and cellulose ester can be adjusted by this terminal residue.

  The hydroxyl values of the polymers X and Y are preferably 30 to 150 [mg KOH / g].

(Measurement method of hydroxyl value)
This measurement conforms to JIS K 0070 (1992). This hydroxyl value is defined as the number of mg of potassium hydroxide required to neutralize acetic acid bonded to a hydroxyl group when 1 g of a sample is acetylated. Specifically, sample Xg (about 1 g) is precisely weighed in a flask, and 20 ml of an acetylating reagent (a solution obtained by adding pyridine to 20 ml of acetic anhydride to 400 ml) is accurately added thereto. An air cooling tube is attached to the mouth of the flask and heated in a glycerin bath at 95-100 ° C. After 1 hour and 30 minutes, the mixture is cooled, 1 ml of purified water is added from an air condenser, and acetic anhydride is decomposed into acetic acid. Next, titration is performed with a 0.5 mol / L potassium hydroxide ethanol solution using a potentiometric titrator, and the inflection point of the obtained titration curve is set as the end point. Further, as a blank test, titration is performed without a sample, and an inflection point of the titration curve is obtained. The hydroxyl value is calculated by the following formula.

Hydroxyl value = {(BC) × f × 28.05 / X} + D
(Wherein B is the amount of 0.5 mol / L potassium hydroxide ethanol solution used in the blank test (ml), and C is the amount of 0.5 mol / L potassium hydroxide ethanol solution used in the titration (ml). F is a factor of 0.5 mol / L potassium hydroxide ethanol solution, D is an acid value, and 28.05 is 1/2 of 1 mol amount of potassium hydroxide 56.11)
All of the above-mentioned X polymer polymers Y have excellent compatibility with cellulose esters, excellent productivity without evaporation and volatilization, good retention as a protective film for polarizing plates, low moisture permeability, and excellent dimensional stability. ing.

The content of the polymer X and the polymer Y in the cellulose ester film is preferably in a range satisfying the following formulas (i) and (ii). When the content of the polymer X is Xg (mass% = the mass of the polymer X / the mass of the cellulose ester × 100) and the content of the polymer Y is Yg (mass%),
Formula (i) 5 ≦ Xg + Yg ≦ 35 (mass%)
Formula (ii) 0.05 ≦ Yg / (Xg + Yg) ≦ 0.4
A preferable range of the formula (i) is 10 to 25% by mass.

  If the total amount of the polymer X and the polymer Y is 5% by mass or more, the polymer X and the polymer Y sufficiently act to reduce the retardation value Rth. Moreover, if it is 35 mass% or less as a total amount, adhesiveness with a polyvinyl alcohol-type polarizer will be favorable.

  The polymer X and the polymer Y can be directly added and dissolved as a material constituting the dope liquid described later, or can be added to the dope liquid after being previously dissolved in an organic solvent for dissolving the cellulose ester.

  Hereinafter, the properties of the polarizing plate protective film having polarizing scattering anisotropy and the polarizing plate protective film B according to the present invention are summarized below.

(Transmissivity of polarizing plate protective film B)
High transmittance is demanded as a member of an LCD display device, and the 500 nm transmittance of the manufactured polarizing plate protective film B added by combining the above-mentioned additives is preferably 85 to 100%, and 90 to 100%. More preferably, 92 to 100% is most preferable. The 400 nm transmittance is preferably 40 to 100%, more preferably 50 to 100%, and most preferably 60 to 100%. Moreover, ultraviolet absorption performance may be calculated | required, In that case, 0 to 10% is preferable, as for 380 nm transmittance | permeability, 0 to 5% is still more preferable, and 0 to 3% is the most preferable.

(Thickness distribution in the width direction of the polarizing plate protective film)
The polarizing plate protective film of the present invention preferably has a thickness distribution R (%) in the width direction of 0 ≦ R (%) ≦ 5%, more preferably 0 ≦ R (%) ≦ 3%. Particularly preferably, 0 ≦ R (%) ≦ 1%.

(Haze value of polarizing plate protective film B)
The polarizing plate protective film B of the present invention preferably has a haze value of 2% or less, more preferably 1.5%, and most preferably 1% or less.

(Elastic modulus of polarizing plate protective film)
The elastic modulus is preferably in the range of 1.5 to 5 GPa, more preferably in the range of 1.8 to 4 GPa, and particularly preferably in the range of 1.9 to 3 GPa.

  Further, the stress at break is preferably in the range of 50 to 200 MPa, more preferably in the range of 70 to 150 MPa, and most preferably in the range of 80 to 100 MPa.

  The elongation at break at 23 ° C. and 55% RH is preferably in the range of 20 to 80%, more preferably in the range of 30 to 60%, and most preferably in the range of 40 to 50%. .

  Further, the hygroscopic expansion coefficient is preferably in the range of −1 to 1%, more preferably in the range of −0.5 to 0.5%, and most preferably 0 to 0.2% or less.

Further, the bright spot foreign matter is preferably 0 to 80 pieces / cm ² , more preferably 0 to 60 pieces / cm ² , and most preferably 0 to 30 pieces / cm ^2. .

(Center line average roughness of polarizing plate protective film (Ra))
When using a polarizing plate protective film as a member for LCD, high flatness is required to reduce light leakage of the film. The center line average roughness (Ra) is a numerical value defined in JIS B 0601, and examples of the measuring method include a stylus method or an optical method.

  As centerline average roughness (Ra) of the polarizing plate protective film of this invention, 20 nm or less is preferable, More preferably, it is 10 nm or less, Especially preferably, it is 4 nm or less.

<Polarizer>
The polarizing plate of the present invention and the liquid crystal display device of the present invention using the polarizing plate will be described.

  The polarizing plate can be produced by a general method. The polarizing plate protective film having polarization-scattering anisotropy of the present invention, which has been subjected to alkali saponification treatment, is a completely saponified polyvinyl alcohol aqueous solution on at least one surface of a polarizer prepared by immersing and stretching a polyvinyl alcohol film in an iodine solution. It is preferable to stick together. It is preferable to paste the polarizing plate protective film B on the other surface.

  The polarizing plate according to the present invention is a polarizing plate integrated in the order of a polarizing plate protective film having a polarization scattering anisotropy / dichroic polarizing film / polarizing plate protective film B according to the present invention. The absorption axis of the polarizing film is in the longitudinal direction of the polarizing plate protective film. With this configuration, the polarizing plate protective film of the present invention functions as an excellent brightness enhancement film.

  The polarizing plate can be constituted by further bonding a protective film on one surface of the polarizing plate and a separate film on the other surface. The protective film and the separate film are used for the purpose of protecting the polarizing plate at the time of shipping the polarizing plate and at the time of product inspection.

<Liquid crystal display device>
By using the polarizing plate of the present invention as a liquid crystal display device bonded to at least one surface of a liquid crystal cell, the luminance can be improved and the liquid crystal display device of the present invention excellent in visibility can be produced. The polarizing plate protective film of the present invention is a reflective, transmissive, transflective LCD or TN type, STN type, OCB type, HAN type, VA type (PVA type, MVA type), IPS type LCD etc. Are preferably used. In particular, a large-screen display device with a 30-inch screen or more has the effect that there is little unevenness in color and undulation, and eyes are not tired even during long-time viewing.

  The arrangement position of the polarizing plate in the liquid crystal display device is not particularly limited and can be arranged on the viewing side. However, the polarization on the light source side of the liquid crystal panel is avoided from the viewpoint of avoiding the visual hindrance based on the back scattering by the scattering polarizing plate. It is preferable to arrange as a plate.

  FIG. 4 shows a configuration example of a liquid crystal display device preferable for the present invention, but the present invention is not limited to this.

  The liquid crystal display device of the present invention includes a polarizing plate 60 (polarizing plate protective film 61 having polarization scattering anisotropy) adjacent to the light reflecting plate 64, the backlight 67, the light guide plate 65, and the light diffusing plate 66. / Configuration of dichroic polarizing film 62 / polarizing plate protective film B63 utilizing light absorption action by dichroic substance), liquid crystal display panel 68, and viewing side polarizing plate 69 are preferably stacked in this order.

  As a specific example of the light guide plate, a light source such as a light source such as a light source such as a linear light source such as a cathode tube (light-emitting diode) or an EL is disposed on the side surface of a transparent resin plate, and light transmitted through the plate to the resin plate. Can be emitted to one side of the plate by diffusion, reflection, diffraction, interference, or the like. When forming a laminated polarizing plate including a light guide plate, a prism array layer composed of a prism sheet or the like for controlling the light emission direction, a light diffusion plate for obtaining uniform light emission, and light emitted from a linear light source are guided. Auxiliary means such as a light source holder for guiding the light plate to the side surface of the light plate can be arranged in an appropriate combination by arranging one layer or two or more layers at predetermined positions such as the upper and lower surfaces and the side surface of the light guide plate.

  The backlight of the liquid crystal display device is preferably a direct backlight type. Specific examples of the direct backlight system include backlights described in JP-A No. 2001-215497, JP-A No. 2001-305535, JP-A No. 2003-215585, JP-A No. 2004-29091, JP-A No. 2004-102119, and the like. Is effectively used.

  In particular, the liquid crystal display device using the polarizing plate of the present invention is effective for a thin liquid crystal display device having a size of 15 inches or more and a large influence of heat in which the distance between the light source and the polarizing plate is shortened.

<Horizontal electric field switching mode type liquid crystal display device>
By incorporating a polarizing plate using the polarizing plate protective film B used in the present invention into a commercially available IPS (In Plane Switching) mode type liquid crystal display device, the liquid crystal of the present invention has excellent visibility and an increased viewing angle. A display device can be manufactured.

  The transverse electric field switching mode of the present invention includes a fringe-field switching (FFS) mode in the present invention, and the polarizing plate of the present invention can be incorporated in the same manner as the IPS mode, and has the same effect. The liquid crystal display device of the invention can be manufactured. The polarizing plate protective film B used in the present invention is preferably installed between the driving liquid crystal cell and the backlight side polarizing element.

  EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

Example 1
<< Synthesis of acicular titanium oxide particles A >>
In a 30 ° C. air atmosphere, ₂₀ ml of titanium isopropoxide [Ti (O-iPr) ₄ ] was added dropwise over a few minutes to a stirred mixture of 1000 ml of methanol and 0.1 ml of H ₂ O. Stirring continued for an additional minute. The resulting fine particles were separated and collected by a centrifugal separator and then dried under reduced pressure. By SEM observation, it was confirmed that the obtained titanium oxide fine particles were needle-shaped having an average minor axis diameter of 55 nm and an average major axis diameter of 1250 nm (aspect ratio 22.7). These particles were in an amorphous state, and it was confirmed by X-ray diffraction that the crystal system became a rutile type when heated at 800 ° C. for 1 hour. The acicular titanium oxide particles B to E of the present invention shown in Table 1 were similarly produced except for the reaction temperature.

<< Production of polarizing plate protective film having polarization scattering anisotropy >>
100 parts by mass of the following dope solution is thoroughly mixed with an in-line mixer (Toray static type in-pipe mixer Hi-Mixer, SWJ), then using a belt casting apparatus, using the die of FIG. It was cast uniformly on the support. At that time, it was performed under the casting conditions and drying conditions for accelerating the flow rate of the dope flowing through the die slit toward the outlet side, which is indicated by Condition-1 in Table 2. In the table, Rvm, t, Rvs, Z, and T are as defined in the section of the alignment method.

  Next, the solvent was evaporated on the stainless steel band support until the residual solvent amount became 110%, and the stainless steel band support was peeled off. The film was stretched so that the longitudinal (MD) stretch ratio was 1.2 times by applying tension at the time of peeling, and then the both ends of the web were gripped by a tenter, and the stretch ratio in the width (TD) direction was 1.1. It extended | stretched so that it might become double. The residual solvent at the start of stretching was 30%. After stretching, hold for several seconds while maintaining its width, release the width holding after relaxing the tension in the width direction, further carry for 30 minutes in the third drying zone set at 125 ° C., and perform drying, A polarizing plate protective film 101 which is a polarizing plate protective film according to the present invention having a width of 1.5 m, a thickness of 40 μm having a knurling of 1 cm in width and a height of 8 μm, and a winding length of 3000 m was produced.

<Composition of dope 101>
Methylene chloride 300 parts by weight Ethanol 40 parts by weight Cellulose ester (cellulose acetate propionate; acetyl group substitution degree 1.9, propionyl group substitution degree 0.7, total acyl group substitution degree 2.6) 100 parts by weight Trimethylolpropane tri Benzoate 5.5 parts by weight Aromatic terminal ester plasticizer Sample No. 1 5.5 parts by mass Tinuvin 109 (manufactured by Ciba Specialty Chemicals) 1.2 parts by mass Tinuvin 171 (manufactured by Ciba Specialty Chemicals) 0.8 parts by mass Acicular titanium oxide particles A 2 parts by mass Acicular oxidation Polarizing plate protective films 102 to 116 were produced in the same manner as the polarizing plate protective film 101 except that the type of titanium particles and the dope casting / drying conditions were changed as shown in Table 3. As comparative polarizing plate protective films 106 to 108, 114, titanium oxide particles (FTL-100, 200, 300 manufactured by Ishihara Sangyo Sangyo Co., Ltd.) outside the present invention described in Examples of Japanese Patent No. 3090890 were used. In addition, the conditions at the time of casting were changed suitably so that the final film thickness might be 40 micrometers similarly to the polarizing plate protective film 101.

<Evaluation>
The following evaluation was implemented about the obtained polarizing plate protective film.

(Measurement of orientation angle)
After positioning the film slice in the film forming direction using a transmission electron microscope, the angle formed by this axis and the major axis direction of each of the 300 domains was measured, and the absolute values of the angles were summed to obtain the number average. The orientation angle (°) of the domain was determined.

(Evaluation of polarization scattering anisotropy of film)
Using a haze meter (NDH2000 manufactured by Nippon Denshoku Industries Co., Ltd.), before the incident light hits the polarizing plate protective film to be measured, an iodine-containing PVA polarizing film is inserted to linearly polarize the incident light, The total amount of transmitted light at each position was measured while changing the rotation angle of the polarizing plate protective film with the incident light as a normal line. The evaluation was performed in a constant temperature and humidity chamber adjusted to 23 ° C. and 55% in order to keep the influence of heat the same. The ratio between the maximum value and the minimum value is shown in Table 3.

(Evaluation of film brightness angle dependency)
For the evaluation of the viewing angle characteristics, the transmitted light quantity at the time of white display was measured by changing the angle with EZ-contrast manufactured by ELDIM using the above sample, and the half-value luminance range was evaluated. The wider the half-value range, the smaller the angle dependency. The half-value range of each sample is shown in Table 3.

  From Table 3, it can be seen that the polarizing plate protective films 101 to 105, 109 to 113, 115 and 116 of the present invention are excellent in polarization scattering anisotropy and luminance angle dependency.

  Further, it was found that the dope casting / drying condition was that the condition-2 had a smaller orientation angle and the domain orientation was likely to be uniform.

<< Preparation of polarizing plate protective film B >>
(Preparation of polarizing plate protective film B201 for VA type liquid crystal)
<Fine particle dispersion>
Fine particles (Aerosil R972V (produced by Nippon Aerosil Co., Ltd.)) 11 parts by mass Ethanol 89 parts by mass The above was stirred and mixed with a dissolver for 50 minutes, and then dispersed with Manton Gorin.

<Fine particle additive solution>
The following cellulose ester was added to a dissolution tank containing methylene chloride, and heated to completely dissolve, then, this was added to Azumi Filter Paper No. Filtered using 244. While finely stirring the filtered cellulose ester solution, the fine particle dispersion was slowly added thereto. Further, the particles were dispersed by an attritor so that the secondary particles had a predetermined particle size. This was filtered through Finemet NF manufactured by Nippon Seisen Co., Ltd. to prepare a fine particle additive solution.

Methylene chloride 99 parts by weight Cellulose ester (cellulose acetate propionate; acetyl group substitution degree 1.6, propionyl group substitution degree 0.8, total acyl group substitution degree 2.4) 4 parts by weight Fine particle dispersion 11 parts by weight The following composition The main dope solution was prepared. First, methylene chloride and ethanol were added to the pressure dissolution tank. The cellulose ester was added to the pressure dissolution tank containing the solvent while stirring. This was heated and stirred to completely dissolve, and a plasticizer and an ultraviolet absorber were further added and dissolved. This was designated as Azumi Filter Paper No. The main dope solution was prepared by filtration using 244.

  In addition to adding 100 parts by mass of the main dope solution and 5 parts by mass of the fine particle additive solution, mix thoroughly with an in-line mixer (Toray static type in-pipe mixer Hi-Mixer, SWJ), and then use a belt casting device to It was cast uniformly on a 2 m stainless steel band support. On the stainless steel band support, the solvent was evaporated until the residual solvent amount became 110%, and the stainless steel band support was peeled off. When peeling, the film is stretched so that the longitudinal (MD) stretch ratio is 1.1 times, and then both ends of the web are held by a tenter, and the stretch ratio in the width (TD) direction is 1.3. It extended | stretched so that it might become double. After stretching, hold for several seconds while maintaining its width, release the width holding after relaxing the tension in the width direction, further carry for 30 minutes in the third drying zone set at 125 ° C., and perform drying, A polarizing plate protective film B201 having a width of 1.5 m, a width of 1 cm at the end, a film thickness of 40 μm having a knurling height of 8 μm, and a winding length of 3000 m was produced.

<Composition of dope 201>
Methylene chloride 390 parts by weight Ethanol 80 parts by weight Cellulose ester (cellulose acetate propionate; acetyl group substitution degree 1.6, propionyl group substitution degree 0.8, total acyl group substitution degree 2.4) 100 parts by weight Trimethylolpropane tri Benzoate 5.5 parts by weight Aromatic terminal ester plasticizer Sample No. 1 5.5 parts by mass Tinuvin 109 (manufactured by Ciba Specialty Chemicals) 1.2 parts by mass Tinuvin 171 (manufactured by Ciba Specialty Chemicals) 0.8 parts by mass (Preparation of polarizing plate protective film B202 for IPS type liquid crystal) )
<Synthesis of Polymer X>
A glass flask equipped with a stirrer, two dropping funnels, a gas introduction tube and a thermometer was charged with 40 g of the monomer Xa and Xb mixed solution of the types and ratios shown in Table 4, 2 g of mercaptopropionic acid as a chain transfer agent and 30 g of toluene. The temperature was raised to 90 ° C. Thereafter, 60 g of a mixture of monomers Xa and Xb having the types and ratios shown in Table 4 was dropped from one dropping funnel over 3 hours, and at the same time, azobisisobutyronitrile 0 dissolved in 14 g of toluene from the other funnel. .4 g was added dropwise over 3 hours. Thereafter, 0.6 g of azobisisobutyronitrile dissolved in 56 g of toluene was added dropwise over 2 hours, and the reaction was further continued for 2 hours to obtain polymer X. The obtained polymer X was solid at room temperature. The weight average molecular weight of the polymer X is shown in Table 4 by the following measurement method.

  In Table 4, MMA and HEA are abbreviations for the following compounds, respectively.

MMA: methyl methacrylate HEA: 2-hydroxyethyl acrylate (weight average molecular weight measurement)
The weight average molecular weight was measured using gel permeation chromatography.

  The measurement conditions are as follows.

Solvent: Methylene chloride Column: Shodex K806, K805, K803G (Used by connecting three Showa Denko Co., Ltd.)
Column temperature: 25 ° C
Sample concentration: 0.1% by mass
Detector: RI Model 504 (manufactured by GL Sciences)
Pump: L6000 (manufactured by Hitachi, Ltd.)
Flow rate: 1.0ml / min
Calibration curve: Standard polystyrene STK standard polystyrene (manufactured by Tosoh Corp.) Mw = 100000-500 calibration curves with 13 samples were used. Thirteen samples are used at approximately equal intervals.

<Synthesis of polymer Y>
Bulk polymerization was performed by the polymerization method described in JP-A No. 2000-128911. That is, the following methyl acrylate (MA) as monomer Ya was introduced into a flask equipped with a stirrer, nitrogen gas inlet tube, thermometer, inlet and reflux condenser, and nitrogen gas was introduced to replace the inside of the flask with nitrogen gas. The following thioglycerol was added with stirring. After the addition of thioglycerol, the temperature of the contents was appropriately changed and polymerization was performed for 4 hours. The contents were returned to room temperature, and 20 parts by mass of a 5% by weight benzoquinone tetrahydrofuran solution was added thereto to stop the polymerization. The contents were transferred to an evaporator, and tetrahydrofuran, residual monomer and residual thioglycerol were removed under reduced pressure at 80 ° C. to obtain polymer Y described in Table 4. The obtained polymer Y was liquid at room temperature. The weight average molecular weight of the polymer Y is shown in Table 4 by the above measurement method.

Methyl acrylate 100 parts by weight Thioglycerol 5 parts by weight

<Composition of dope 202>
(Silicon dioxide dispersion 1)
Aerosil 972V (manufactured by Nippon Aerosil Co., Ltd.) 12 parts by mass (average diameter of primary particles 16 nm, apparent specific gravity 90 g / liter)
88 parts by mass of ethanol or more was stirred and mixed with a dissolver for 30 minutes, and then dispersed with Manton Gorin. The liquid turbidity after dispersion was 200 ppm. 88 parts by mass of methylene chloride was added to the silicon dioxide dispersion while stirring, and the mixture was stirred and mixed for 30 minutes with a dissolver to prepare a silicon dioxide dispersion dilution 1.

(Dope additive solution 1)
Methylene chloride 50 parts by mass Polymer X Table 4 amount Polymer Y Table 4 amount Silicon dioxide dispersion 1 10 parts by mass Tinuvin 109 (manufactured by Ciba Specialty Chemicals Co., Ltd.) 1.2 parts by mass Tinuvin 171 (Ciba Specialty Chemicals Co., Ltd.) Manufactured) 0.8 parts by mass The methylene chloride, the polymer X, and the polymer Y were completely dissolved while stirring, and then the silicon dioxide dispersion 1 was added and mixed by stirring to prepare a dope additive solution 1.

(Preparation of dope 202)
Cellulose ester (cellulose triacetate synthesized from linter cotton, acetyl group substitution degree 2.92) 100 parts by mass Methylene chloride 380 parts by mass Ethanol 30 parts by mass Dope additive 1 The above preparation parts are put into a sealed container and heated. The solution was completely dissolved while stirring, and Azumi Filter Paper No. 24. The dope 202 was prepared by filtration.

  The dope solution was filtered with Finemet NF manufactured by Nippon Seisen Co., Ltd., and uniformly cast on a stainless steel band support at a temperature of 22 ° C. and a width of 2 m using a belt casting apparatus. With the stainless steel band support, the solvent was evaporated until the residual solvent amount became 105%, and the film was peeled from the stainless steel band support with a peeling tension of 162 N / m. The peeled cellulose ester web was evaporated at 35 ° C., slit to 1.6 m width, and then dried at a drying temperature of 135 ° C. while stretching 1.1 times in the width direction with a tenter. At this time, the residual solvent amount when starting stretching with a tenter was 10%. After stretching with a tenter and releasing the width retention by releasing the width tension at 130 ° C., the drying is finished while conveying the drying zone of 120 ° C. and 130 ° C. with a number of rolls, and slitting to a width of 1.5 m, A knurling process having a width of 10 mm and a height of 7 μm was applied to both ends of the film, and the film was wound around a core having an inner diameter of 6 inches with an initial tension of 220 N / m and a final tension of 110 N / m to obtain a polarizing plate protective film B202. The draw ratio in the MD direction calculated from the rotational speed of the stainless steel band support and the operating speed of the tenter was 1.1 times. The residual solvent amount of the polarizing plate protective film B202 was 0.1%, the film thickness was 40 μm, and the winding length was 3000 m.

<Production of polarizing plate>
Polarizing plates 301 to 332 shown in Table 5 were produced using the produced polarizing plate protective films 101 to 116 and polarizing plate protective films B201 and 202.

  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 form a polarizing film. The polarizing plate protective films 101 to 125 and the polarizing plate protective films B201 and 202 subjected to the alkali saponification treatment on both surfaces of the polarizing film are combined with each other as shown in Table 5 using a completely saponified polyvinyl alcohol 5% aqueous solution as an adhesive. Pasted together.

<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 Inside 10% by mass HCl 30 ° C 45 seconds Water washing step Water 30 ° C 45 seconds Under the above conditions, saponification, water washing, neutralization, water washing are performed in this order, and then drying is performed at 80 ° C. went.

<< Production of VA liquid crystal display device >>
The polarizing plate on the backlight side of the 32-inch TV AQ-32AD5 made by Sharp, which is a VA type liquid crystal display device, is peeled off, and the prepared polarizing plates 301 to 316 are each made of glass of a liquid crystal cell (VA type). The liquid crystal display devices 301 to 316 were prepared by bonding to the surface.

  At that time, the polarizing plate protective film B201 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 that had been bonded in advance.

<< IPS mode type liquid crystal display device >>
Using a 23-inch Toshiba liquid crystal television FACE 23LC100, which is an IPS mode type liquid crystal display device, the polarizing plate on the backlight side previously bonded is peeled off, and the produced polarizing plates 317 to 332 are respectively liquid crystals. It bonded on the glass surface of a cell (IPS type), and produced the liquid crystal display devices 317-332.

  At that time, the polarizing plate protective film B202 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 that had been bonded in advance.

  Using the liquid crystal display devices 301 to 332 produced as described above, the luminance was evaluated in the following manner.

<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 ). The luminances of the liquid crystal display devices 306 and 322 using the polarizing plate protective film 106 disposed on the backlight side are set to 1, respectively, and the relative luminance in each liquid crystal display method is represented 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 5 below.

  From the results shown in Table 5, the polarizing plate on which the polarizing plate protective film having the polarization scattering anisotropy of the present invention is bonded together in both the VA-type liquid crystal display device and the IPS-type liquid crystal display device shows an excellent brightness enhancement effect. I understand.

It is a schematic diagram of the polarizing plate protective film which has the polarization scattering anisotropy containing the optical continuous phase and domain which mainly have the cellulose ester which concerns on this invention. It is a schematic diagram which shows the dope flow path inside dice | dies. It is the figure which showed typically the dope preparation process of the solution casting film forming method concerning this invention, a casting process, and a drying process. It is the schematic which shows the structure of the liquid crystal display device preferable for this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,10 Melting pot 3,6,12,15 Filter 4,13 Stock tank 5,14 Liquid feed pump 8,16 Conduit 20 Junction pipe 21 Mixer 30 Die 31 Metal support 32 Web 33 Peeling position 34 Tenter device 35 Roll dryer 60 Polarizing plate 61 Polarizing plate protective film 62 Dichroic polarizer 63 Polarizing plate protective film B according to the present invention
64 Light reflector 65 Light guide plate 66 Light diffuser plate 67 Backlight 68 Liquid crystal cell 69 Viewing side polarizing plate

Claims (5)

A polarizing plate protective film comprising an optically continuous phase composed of cellulose ester and acicular titanium oxide as domains, wherein the domains are obtained by hydrolysis and condensation of titanium alkoxide in alcohol and water mixed solvent. A polarizing plate protective film characterized by being acicular titanium oxide produced by heat-treating titanium. The polarizing plate protective film according to claim 1, wherein the acicular titanium oxide has an aspect ratio of 20 or more and a minor axis diameter of 150 nm or less. 2. The polarized light according to claim 1, wherein the average value of the angle formed by the major axis direction of each domain is within 25 ° when the film forming direction of the polarizing plate protective film is 0 °. Board protection film. A polarizing plate integrated in the order of a polarizing plate protective film according to any one of claims 1 to 3 / a dichroic polarizing film / polarizing plate protective film B utilizing a light absorption action by a dichroic substance. A polarizing plate, wherein the absorption axis of the dichroic polarizing film is in the longitudinal direction of the film. A liquid crystal display device comprising the polarizing plate according to claim 4 and the polarizing plate protective film according to any one of claims 1 to 3 disposed on a light source side.

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