JPWO2008018279A1 - Polarizing plate protective film, polarizing plate and liquid crystal display device using the same - Google Patents

Abstract

The present invention provides a polarizing plate protective film excellent in productivity and having a polarization scattering anisotropy and a brightness enhancement function, and further a polarizing plate and a liquid crystal display device using the same. This polarizing plate protective film is a polarizing plate protective film having polarization scattering anisotropy including an optical continuous phase composed of cellulose ester and a domain having an aspect ratio defined by the following formula (1) of 2 or more. The acetyl group substitution degree X and the propionyl group substitution degree Y of the cellulose ester satisfy the conditions specified by the following formulas (2) and (3), and the film forming direction of the polarizing plate protective film and each of The average value of the absolute value of the angle formed with the major axis direction of the domain is within 25 °. Formula (1) Aspect ratio = major axis diameter / minor axis diameter (the major axis diameter is the absolute maximum length of the domain, and the minor axis diameter is an image of the domain projected by two straight lines parallel to the absolute maximum length. Distance between two straight lines), formula (2) 2.3 ≦ X + Y ≦ 2.8, formula (3) 0.7 ≦ Y ≦ 2.3

Description

  The present invention relates to a polarizing plate protective film having polarization scattering anisotropy excellent in productivity, a polarizing plate using the same, and a liquid crystal display device.

  In recent years, in the field of liquid crystal display devices represented by liquid crystal televisions, 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 solve such a problem, so-called brightness enhancement films have been studied in order to enhance some light utilization efficiency. For example, as disclosed in Patent Document 1, a layer that has birefringence and a layer that does not have birefringence are stacked, and an axis that reflects using the principle of thin film interference by changing the refractive index, and And a film that separates polarized light by having an axis that does not have a difference in refractive index and transmits light as it is, and a polarized light separating film that utilizes the circular dichroism of 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. Further, Patent Document 3 discloses a film having polarization scattering anisotropy comprising a dispersed phase of polymer particles in an optical continuous phase having birefringence. Is used for polarization separation. Although this technique is slightly less difficult to manufacture than the technique of Patent Document 1 or Patent Document 2, both the birefringence and the refractive index must be adjusted. Required. In addition, since the smoothness of the film surface is poor, it has the disadvantage that it is difficult to integrate with the dichroic polarizing film, and 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, a technique with a high degree of difficulty is required in which both the birefringence and the refractive index have to be adjusted, in that a dispersed phase of polymer particles is contained in the phase to provide polarization scattering anisotropy. The difficulty remains.

  As information on a polarizing element having polarization scattering anisotropy with relatively high productivity, for example, needle-shaped scattering particles such as titanium oxide are oriented in a specific direction as disclosed in Patent Document 4, A technique for dispersing in a resin is known. In this technology, fine acicular particles having a refractive index different from that of the resin are dispersed in the UV curable resin, so that reflection occurs with respect to the polarization in the major axis direction of the particles, and polarization in the minor axis direction of the particles. In contrast, since the particles are sufficiently small with respect to the wavelength of the light beam to be not reflected by the Rayleigh scattering region, polarization scattering anisotropy is provided. 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.

On the other hand, it is very common to use a triacetyl cellulose film as a polarizing plate protective film, but in the simple combination category of the conventional cellulose ester and the above patent document group, it is not possible to form a domain with excellent dispersibility, It has been difficult to provide a polarizing plate protective film that has sufficient polarization scattering anisotropy and can exhibit a brightness enhancement function when used in a liquid crystal display device.
Japanese Patent No. 362215 JP 2003-227933 A JP 2000-506990 A Japanese Patent No. 3090890

  Accordingly, an object of the present invention is to provide a polarizing plate protective film having excellent productivity and polarization scattering anisotropy, and further a polarizing plate and a liquid crystal display device using the same.

  The above object of the present invention is achieved by the following configurations.

  1. A polarizing plate protective film having a polarization scattering anisotropy comprising an optical continuous phase comprising a cellulose ester and a domain having an aspect ratio defined by the following formula (1) of 2 or more, wherein the acetyl group of the cellulose ester The degree of substitution X and the degree of substitution Y of propionyl group satisfy the conditions specified by the following formulas (2) and (3), and the film forming direction of the polarizing plate protective film and the major axis direction of each domain An average value of absolute values of angles formed is within 25 °, and a polarizing plate protective film.

Formula (1)
Aspect ratio = major axis diameter / minor axis diameter (where the major axis diameter means the absolute maximum length in the domain, and the minor axis diameter is the projected domain with two straight lines parallel to the absolute maximum length. Means the distance between two straight lines when
Formula (2)
2.3 ≦ X + Y ≦ 2.8
Formula (3)
0.7 ≦ Y ≦ 2.3
2. The minimum value of the refractive index difference between the optical continuous phase and the domain is 0.25 or more, the major axis diameter of the domain is 400 nm or more and 10,000 nm or less, and the minor axis diameter is 50 nm or more and 390 nm or less. 2. The polarizing plate protective film according to 1 above, wherein

  3. 3. The polarizing plate protective film according to 1 or 2, wherein the domain is an inorganic compound that has been surface-treated with a surface modifier.

  4). 4. A polarizing plate integrated in the order of polarizing plate protective film / dichroic polarizing film / polarizing plate protective film B according to any one of 1 to 3, wherein the absorption axis of the dichroic polarizing film Is in the longitudinal direction of the polarizing plate protective 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 backlight side.

  The objective of this invention is providing the polarizing plate protective film which is excellent in productivity and has polarization scattering anisotropy, and also using this, and a liquid crystal display device.

It is a schematic diagram which shows an example 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 the figure which showed typically an example of the dope preparation process, casting process, and drying process of a solution casting film forming method. It is a block diagram which shows an example 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
64 Light diffusion plate 65 Light guide plate 66 Backlight 67 Liquid crystal display panel 68 Viewing side polarizing plate

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

  A film having polarization scattering anisotropy (hereinafter, also referred to as a brightness enhancement film) selectively transmits predetermined polarized light and other polarized light as disclosed in, for example, JP-T-11-509014. Can be selectively scattered, and when used in a liquid crystal display device, it means a film that can improve brightness by reusing scattered light.

  The polarizing plate protective film of the present invention has a polarization scattering anisotropy, and is a film that can improve luminance by being used in a liquid crystal display device. An optical continuous phase composed of a cellulose ester and the following formula ( 1) the domain having an optical anisotropy with an aspect ratio of 2 or more, and the acetyl group substitution degree X and propionyl group substitution degree Y of the cellulose ester are represented by the following formulas (2) and (2): The average value of the absolute value of the angle formed by the film forming direction of the polarizing plate protective film and the major axis direction of each domain is satisfied within the condition specified in (3) is 25 ° or less. .

Formula (1)
Aspect ratio = major axis diameter / minor axis diameter In the above formula (1), 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. It means the distance between two straight lines when sandwiching the domain image.

Formula (2)
2.3 ≦ X + Y ≦ 2.8
Formula (3)
0.7 ≦ Y ≦ 2.3
Furthermore, the minimum value of the refractive index difference between the optical continuous phase and the domain contained in the polarizing plate protective film is preferably 0.25 or more, and the major axis diameter of the domain is 400 nm to 10,000 nm, the minor axis is The diameter is preferably 50 nm to 390 nm, and the domain is preferably an inorganic compound that has been surface-treated with a surface modifier.

  Hereinafter, the present invention will be described in detail.

(Optical continuous phase / domain)
In the present invention, the optical continuous phase refers to a 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. Preferably, the variation in refractive index is 0.005 or less, particularly preferably 0.001 or less. Further, in the present invention, the domain means an individual region that exists in the same film as the above-described optical continuous phase and has a refractive index different from that of the optical continuous phase. The “different refractive index” in the present invention means that the difference between the refractive index at any axis of the domain and the refractive index of the optical continuous phase is 0.02 or more. The domain itself may or may not have a birefringence.

  The domain according to the present invention has an aspect ratio of 2 or more represented by the following formula (1).

Formula (1)
Aspect ratio = major axis diameter / minor axis diameter In the above formula (1), 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. It means the distance between two straight lines when sandwiching the domain image.

  The domain according to the present invention is a particle having an aspect ratio of 2 or more as defined by the above formula, and the aspect ratio is in the range of 3 to 100 in order to enhance the orientation of the domain as described later. Is more preferable, more preferably in the range of 5-50, particularly preferably in the range of 10-30.

  A domain having an aspect ratio of 2 or more is preferable because the orientation can be sufficiently enhanced, and as a result, the polarization scattering anisotropy described later is strong, and a sufficient brightness enhancement effect can be obtained.

  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 using a transmission electron microscope, and the image was taken using a Canon Scan FB 636U manufactured by Canon Inc., and 300 dpi (dpi in the present invention is about 2.54 cm). The image is read in monochrome 256 gradations, and the read image is image processing software WinROOF ver3 installed in Endeavor Pro720L (CPU: Athlon-1 GHz, memory: 512 MB), a personal computer manufactured by Epson Direct Corporation. 60 (Mitani Corporation). Perform domain image extraction on the captured image, confirm that there are more than 300 domains on the screen after domain image extraction, and if the extraction is not enough, manually adjust the detection level, Make adjustments to detect and extract domains. For each domain of the image data extracted in this way, the major axis diameter / minor axis diameter can be measured, and the average aspect ratio of the number of domains can be calculated. At this time, the shape of the domain does not necessarily reflect individual shapes of particles as shown in the following example. In the present invention, an aggregate composed of a plurality of constituent particles is regarded as one domain. In the case of an indefinite domain, the major axis has the absolute maximum length of the domain, converted into an ellipse having the same area as the domain projection area, and the minor axis is obtained according to the above definition.

  As the domain, for example, particles made of inorganic particles or organic compounds can be used.

Examples of the inorganic particles include TiO ₂ (rutile type, anatase type, or mixed crystals thereof), calcium silicate (wollastonite, zonotolite, etc.), potassium titanate, aluminum borate, basic magnesium sulfate, glass fiber, etc. Is mentioned.

  Examples of the particles made of an organic compound include polymer particles made of a silicone resin, a fluororesin, and an acrylic resin. In particular, silicone resins are preferable, and those having a three-dimensional network structure are preferable. Only one kind of these inorganic particles or polymer particles can be used as a domain, or a plurality of kinds can be used as a domain in the same film.

  In the present invention, the domain is preferably an inorganic compound that has been surface-treated with a surface modifier described later.

  The size of the domain is preferably such that the major axis diameter of the domain is 400 nm to 10000 nm and the minor axis diameter is 50 nm to 390 nm from the viewpoint of increasing the polarization scattering anisotropy.

  The refractive index of the domain is preferably in the range of 1.3 to 3.0. In addition, the minimum value of the difference in refractive index between the optical continuous phase and the domain is 0.02 or more, preferably 0.25 or more, and more preferably 0.5 or more in terms of increasing the polarization scattering anisotropy. preferable.

  In the polarizing plate protective film having polarization scattering anisotropy of the present invention, the domain is preferably contained in an amount of 0.1% by volume or more, and the preferred aspect of the content rate is in each case depending on the domain type and its size. Although it is different, in the case of a domain having a refractive index of 2.0 or more, the volume is preferably 5% by volume or less, and in the case of a grain domain having a refractive index of 1.3 to less than 2.0, the volume is made 20% by volume or less. preferable.

  The particles used as the domains according to 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.

  Treatment methods include coating methods in which the surface is coated with fatty acids, metal salts, surfactants, etc., topochemical methods in which a coupling agent is bonded to the particle surface, and mechano- nos that add organic treatment agents in the particle grinding process. There are various methods such as a chemical method and 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 with a coupling agent is generally preferred.

  There are two methods for dispersing the surface-treated particles in the cellulose ester-based resin: a method using a disperser and a method using a kneader.

  The former is further divided into media distribution and medialess distribution. Examples of the media dispersion include 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 one having a bead diameter of 0.1 mm or less because a domain having excellent dispersibility can be obtained while preventing breakage and reaggregation of particles.

(Polarized light scattering anisotropy)
The polarizing plate protective film of the present invention has a polarization scattering anisotropy. Here, having polarization scattering anisotropy is defined as follows in the present invention. That is, when measuring the total amount of light transmitted through 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 When the ratio of the maximum value and the minimum value of the total transmitted light amount (maximum value / minimum value) is 1.2 or more when changed in the plane of the polarizing plate protective film, the polarizing plate protective film is polarized Defined as having scattering anisotropy.

  In order to obtain this value, for example, using a haze meter such as NDH2000 manufactured by Nippon Denshoku Industries Co., Ltd., before the incident light hits the polarizing plate protective film to be measured, an iodine-containing polyvinyl alcohol polarizing film, etc. Insert the light to linearly polarize the incident light, measure the total transmitted light amount at each position while changing the rotation angle of the polarizing plate protective film with the incident light as a normal line, and determine the maximum and minimum values. This can be easily calculated. The maximum value / minimum value ratio of the total amount of transmitted light by the measurement 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.

  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 2 or more according to the present invention in a specific direction by various methods. As a method for orienting domains according to 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 particular, it is preferable to set the production conditions such that the film is stretched in the film forming direction because it is not necessary to provide a separate stretching step and the domains can be oriented by a simple method. Moreover, in the stage of producing a film, the use of high aspect ratio particles, or by adjusting the viscosity of the liquid containing the particles and the resin and the shape of the die, the method of increasing the shear stress applied to the high aspect ratio particles, The orientation in a specific direction can be increased. Furthermore, at the stage where there is some fluidity before completely solidifying as a film, for example, when producing a film using a melt extrusion method, a method of increasing the film winding speed relative to the extrusion speed, The effect similar to that of 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 brightness improvement effect is exhibited.

(Orientation angle)
Definition of the absolute value of the angle formed by the film forming direction and the major axis direction of each domain (a value that can be taken from 0 ° to 90 °) of the polarizing plate protective film having polarization scattering anisotropy of the present invention. However, the orientation angle 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, a transmission electron microscope is used to determine the position of the film slice in the film forming direction, and then the angle between this axis and each of the 300 domains is measured. A method is adopted in which the sum of the numbers is averaged. In the present invention, the orientation angle of the domain of the polarizing plate protective film having polarization scattering anisotropy is within 25 °, and is preferably within 15 ° in order to further enhance the luminance enhancement effect, within 5 °. It is particularly preferred that

(Dichroic polarizing film)
There is no limitation in particular with the dichroic polarizing film which concerns on this invention, A general dichroic polarizing film can be used. In general, a dichroic polarizing film is a dichroic polarizer sandwiched between two polarizing plate protective films, and light that is almost completely plane-polarized with half the intensity of incident light at the maximum. Through. Usually, the material particles constituting the dichroic polarizer have crystals or molecules oriented in the same direction. A dichroic polarizing film for a liquid crystal display device is typically obtained by coloring polyvinyl alcohol with iodine or a dichroic dye and stretching it uniaxially.

  FIG. 1 is a schematic diagram 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 an aspect ratio of 2 or more.

  In FIG. 1, in the optical continuous phase 1 mainly composed of cellulose ester, a state in which domains having an aspect ratio of 2 or more are arranged in a substantially constant direction in the longitudinal direction (film forming direction or MD direction) of the polarizing plate protective film. Show. 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 domain 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. However, the polarizing plate protective film having polarization scattering anisotropy of the present invention is not limited to the above refractive index relationship, for example, a relationship such as n2> n3> n1 and n3-n1 ≧ 0.5. However, if the short axis diameter of the domain is sufficiently short with respect to the light source wavelength (so-called Rayleigh scattering region), the same polarization scattering anisotropy can be expressed. In this case, 50 nm to 390 nm is preferable as a standard of the short axis diameter of the domain.

(Cellulose ester)
The optical continuous phase according to the present invention is characterized by comprising a cellulose ester.

  In particular, the cellulose ester used in the present invention is characterized in that it is cellulose acetate propionate in which the acetyl group substitution degree X and the propionyl group substitution degree Y satisfy the conditions defined by the following formulas (2) and (3). is there.

Formula (2)
2.3 ≦ X + Y ≦ 2.8
Formula (3)
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. Actually, even when the propionyl group substitution degree (Y) is Y <0.7 or Y> 2.3, the domain dispersibility is inferior. Apart from this, when Y> 2.3, there is also a problem that the adhesiveness with the dichroic polarizing film deteriorates.

  Although there is no limitation in particular as a cellulose which is a 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 (for example, acetic anhydride, propionic anhydride, butyric anhydride), an organic solvent such as acetic acid or an organic solvent such as methylene chloride 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 is 1 type of the cellulose ester 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 Then, 67 parts by mass of propionic acid was 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 the mixed 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 the mixed solution B was added and stirred for 17 hours. Furthermore, 333 mass parts of liquid mixture C and 730 mass parts of liquid mixture D were added, and it 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 the mixed solution E was added, and then dried at 70 ° C. for 3 hours under vacuum to obtain cellulose acetate propionate.

  As a result of calculating the substitution degree of the obtained cellulose ester 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 and 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, in order to increase the degree of acetylation and suppress degradation to some extent, it is necessary to set the reaction time within a certain range. 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 value of weight average molecular weight (Mw) / number average molecular weight (Mn) that is usually used. That is, in the process of acetylation of cellulose triacetate, the weight average is used as one indicator of the degree of reaction in order to allow the acetylation reaction to be carried out for a sufficient time for acetylation without being excessively decomposed. The value of molecular weight (Mw) / number average molecular weight (Mn) can be used.

  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 (hereinafter also referred to as GPC). 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).

(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. Examples of the chlorinated organic solvent include methylene chloride (methylene chloride), which is suitable for dissolving cellulose ester, 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. Although methylene chloride can be used for cellulose esters other than cellulose triacetate, 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 used in 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. After casting the dope on the metal support, the solvent starts to evaporate, and when the alcohol ratio increases, the dope film (web) gels, making the web strong and easy to peel off from the metal support. It can be used as a gelling solvent, and when these ratios are small, it also has a role of promoting 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 of its excellent dope stability, relatively low boiling point, and good drying properties. These organic solvents are referred to as poor solvents because they are not soluble in cellulose esters by themselves.

  In order to obtain good film surface quality, 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.

  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 polarizing plate protective film according to the present invention or the polarizing plate protective film B described later, a compound known as a so-called plasticizer is used to improve mechanical properties, impart flexibility, impart water resistance, reduce water vapor transmission rate, and adjust retardation. It is preferable to add for purposes such as, for example, phosphoric acid esters and carboxylic acid esters are preferably used.

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

  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 citric acid esters such as acetyltriethyl citrate. And acetyltributyl citrate. 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 the alkyl phthalyl alkyl glycolate include methyl phthalyl methyl glycolate, ethyl phthalyl ethyl glycolate, propyl phthalyl propyl glycolate, butyl phthalyl butyl glycolate, octyl phthalyl octyl glycolate, and 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 glycol Butyl phthalyl ethyl glycolate, propyl phthalyl butyl glycolate, butyl phthalyl propyl glycolate, methyl phthalyl octyl glycolate, ethyl phthalyl Examples include octyl glycolate, octyl phthalyl methyl glycolate, octyl phthalyl ethyl glycolate, etc., such as methyl phthalyl methyl glycolate, ethyl phthalyl ethyl glycolate, propyl phthalyl propyl glycolate, butyl phthalyl butyl glycol Rate, 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 (1).

General formula (1)
R _1- (OH) n
In the general formula (1), R ₁ represents an n-valent organic group, n represents a positive integer of 2 or more, and the OH group represents an alcoholic or phenolic hydroxyl group.

  The polyhydric alcohol ester plasticizer is a plasticizer comprising an ester of a divalent 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, and xylitol. 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 a 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 preferable alicyclic monocarboxylic acids include cyclopentanecarboxylic acid, cyclohexanecarboxylic acid, cyclooctanecarboxylic acid, and derivatives thereof.

  Examples of preferred aromatic monocarboxylic acids include those in which an alkyl group is introduced into the benzene ring of benzoic acid such as benzoic acid and toluic acid, and two or more benzene rings such as 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.

  Although the specific compound of the polyhydric alcohol ester plasticizer used for this invention is shown below, this invention is not limited to this.

  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.

  Furthermore, in this invention, it is preferable to use the aromatic terminal ester plasticizer represented by following General formula (2).

General formula (2)
B- (GA) n-GB
In the general formula (2), 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 having 4 to 12 carbon atoms. A glycol residue, 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 in accordance with JIS K0070 (1992).

  Hereinafter, the synthesis example of the aromatic terminal ester plasticizer used for this invention is shown.

<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 the 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., and then filtered to obtain an aromatic terminal ester having the following properties. Obtained.

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
Although the specific compound of the aromatic terminal ester plasticizer used for this invention below is shown, this invention is not limited to this.

The content of the aromatic terminal ester plasticizer used in the present invention is preferably 1 to 20% by mass, particularly preferably 3 to 11% by mass (ultraviolet absorber) in the cellulose ester film.
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, Polymer ultraviolet absorbers described in 2002-47357, 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 has an excellent ability to absorb ultraviolet rays having a wavelength of 370 nm or less, and from the viewpoint of liquid crystal display properties, it has little absorption of visible light having a wavelength of 400 nm or more 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 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 are 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 method of adding the UV absorber to the dope can be used without limitation as long as it dissolves the UV absorber in the dope, but in the present invention, the UV absorber is methylene chloride, methyl acetate, dioxolane or the like. Dope by dissolving in a good solvent for cellulose ester or mixed organic solvent of good solvent and poor solvent such as lower aliphatic alcohol (methanol, ethanol, propanol, butanol, etc.) and adding it to cellulose ester solution as UV absorber solution Is preferable. 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-tert-butyl-4-hydroxyphenyl) propionate, N, N′-hexamethylenebis (3,5-di-tert-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, fine particles can be contained in the polarizing plate protective film as a matting agent, which facilitates conveyance and winding.

  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. Examples of preferred silicon dioxide fine particles for the present invention include Aerosil R972, R972V, R974, R812, 200, 200V, 300, R202, OX50, and TT600 (manufactured by Nippon Aerosil Co., Ltd.) manufactured by Nippon Aerosil Co., Ltd. And commercially available products such as Aerosil 200V, R972, R972V, R974, R202, and 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. For example, Tospearl 103, 105, 108, 120, 145, 3120, and 240 (above, manufactured by Toshiba Silicone Co., Ltd.) I can list them.

  The silicon dioxide fine particles preferably have a primary average particle diameter 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, and further preferably 5 to 12 nm. A smaller average diameter of primary particles is preferable 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.

(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. Further, a surfactant, a peeling accelerator, an antistatic agent, a flame retardant, a lubricant, an oil agent and the like may be added.

[Film forming method]
The polarizing plate protective film of the present invention can be formed by either a solution casting film forming method or a melt extrusion film forming method. Hereinafter, details of the solution casting film forming method will be described as an example.

(Solution casting film forming method)
The polarizing plate protective film of the present invention is preferably formed by a solution casting film forming method. Here, the solution casting film forming method will be described with reference to FIG.

  FIG. 2 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 used 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 can cause fibers to fall off. Less preferred. 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. 2 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, 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. 2. A cellulose ester solution (sometimes referred to as a dope stock solution) and a domain-forming material solution are respectively transferred by liquid feed pumps 5 and 14 and 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 On the endless metal support 31 that sends the dope prepared up to the previous process to the die 30 and transfers it infinitely, for example, a stainless steel belt or a metal support 31 such as a rotating metal drum This is a step of casting the dope from the die 30 at the casting position. The surface of the metal support 31 is a mirror surface. A die 30 (for example, a pressure die) is preferable because the slit shape of the die portion can be adjusted and the film thickness can be easily made uniform. The die 30 includes a coat hanger die and a T die, and any of them is preferably used. 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 and 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 higher the drying speed of the solvent, which is preferable. However, if the temperature is too high, foaming may occur and the 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 peeling occurs while the amount of residual solvent 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 is likely to be lost, and a slip or vertical stripe due to the peeling tension is likely to occur, and the amount of residual solvent at the time of peeling is determined in consideration of 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 head space 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. 2, the roll drying device 35 is disposed after the tenter device 34, but is not limited to this configuration. 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 of 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 at the time of film production by TD or MD. It is possible to adopt a method of stretching in the direction, or a method of making a dope flow during casting and orienting the domain forming material along this flow. 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 orient the domain forming material.

(7) Stretching process (also called tenter process)
The polarizing plate protective film of the present invention can control polarization scattering anisotropy by adjusting birefringence by stretching or adjusting the orientation of domains. 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.

  In addition, since the polarizing plate protective film of the present invention has characteristics as a polarizing plate protective film composed of cellulose ester, it is used as a long film having a brightness enhancement function in the production process of a polarizing plate in a roll shape. Since the film can be delivered, the roll-shaped film 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 disposed with a polarizer sandwiched between the polarizing plate protective film having polarization scattering anisotropy of the present invention.

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

  In the present invention, cellulose ester films such as cellulose acetate propionate film and cellulose triacetate film (TAC film) (for example, Konica Minolta Op Co., Ltd. Konica Minolta Tack KC8UX2M, KC4UX, KC5UX, KC4UY, KC4UE, KC4FR- 1, KC4FR-2, KC8UY, KC12UR, KC8UY-HA, KC8UX-RHA, etc. are preferably used), cycloolefin polymer film, polycarbonate film, polyester film or polyacryl film are transparent, mechanical properties, optically anisotropic In particular, a cellulose ester film and a cycloolefin polymer film are preferable, and a polarizing plate is produced by roll-to-roll as described above. Therefore, a cellulose ester film having excellent saponification suitability is most preferable. 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 (also referred to as the maximum refractive index in the plane of the film and the refractive index in the slow axis direction) at 23 ° C. RH and 590 nm, and the refractive index ny (slow in the plane of the film). The refractive index in the direction perpendicular to the phase axis) and the refractive index nz (the 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 −15 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 5,000 to 30,000 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 aromatic in the molecule. Weight average molecular weight 5000 obtained by copolymerizing ethylenically unsaturated monomer Xb having no ring and having a hydrophilic group The upper 30000 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 to 500 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 one thiol group and a secondary hydroxyl group, or a bulk polymerization method using a polymerization catalyst in which the compound and an organometallic compound are used in combination. In particular, 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 represents a factor of 0.5 mol / L potassium hydroxide ethanol solution, D represents an acid value, and 28.05 represents 1/2 of 1 mol amount of potassium hydroxide 56.11.)
The above-mentioned polymer X and polymer Y are both excellent in compatibility with cellulose ester, excellent in productivity without evaporation and volatilization, good retention as a protective film for polarizing plates, low moisture permeability, and dimensional stability. Are better.

The content of the polymer X and the polymer Y in the cellulose ester film is preferably in a range satisfying the following formulas (III) and (IV). 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 (III)
5 ≦ Xg + Yg ≦ 35 (mass%)
Formula (IV)
0.05 ≦ Yg / (Xg + Yg) ≦ 0.4
A preferable range of the formula (III) 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 of 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 polarized light scattering anisotropy of the present invention that 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 also functions as an excellent brightness enhancement film in a liquid crystal display device.

  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 the surface on the backlight side of the 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.

  Although the polarizing plate of this invention can also be arrange | positioned also at the visual recognition side, it is preferable to arrange | position only at the backlight side of a liquid crystal panel from the point which avoids visual recognition obstruction based on backscattering.

  FIG. 3 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-2001-215497, JP-A-2001-305535, JP-A-2003-215585, JP-A-2004-29091, JP-A-2004-102119, and the like. Light is used effectively.

  In particular, the liquid crystal display device using the polarizing plate of the present invention has a size of 15 inches or more, and the present invention is effective for a thin liquid crystal display device having 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 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 display device of the present invention with excellent visibility and expanded viewing angle is produced. I can do it.

  The lateral electric field switching mode in the present invention includes a fringe-field switching (FFS) mode, 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 present 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 lower 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
<< Production of polarizing plate protective film having polarization scattering anisotropy >>
Table 1 shows the particles, plasticizer, and ultraviolet absorber used.

  100 parts by mass of the following dope solution is sufficiently mixed with an in-line mixer (Toray's static in-tube mixer Hi-Mixer, SWJ), and then uniformly fed to a stainless steel band support having a width of 2 m using a belt casting apparatus. Extended. 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. 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 Plasticizer (A 5.5 parts by mass Plasticizer (B) 5.5 parts by mass Ultraviolet absorber (A) 1.2 parts by mass Ultraviolet absorber (B) 0.8 parts by mass Particle (A) 2 parts by mass Next, dope (cellulose) The polarizing plate protection is the same as that of the polarizing plate protective film 101 except that the ester resin and the kind of particles are changed as shown in Table 2 and the longitudinal (MD) stretch ratio is changed as shown in Table 2. Films 102 to 124 were produced. Moreover, the polarizing plate protective film 125 was produced according to the polarizing plate protective film 101 except having used the ultraviolet curable resin described in the Example of patent 3090890 instead of the cellulose ester resin. 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.

  The acyl group substitution degree of the cellulose ester resin was measured according to the method prescribed in ASTM-D817-96.

  The major axis diameter, minor axis diameter, and aspect ratio of the domains in the film were measured according to the following measurement methods.

<Measurement of domain major axis diameter, minor axis diameter, aspect ratio, orientation angle>
A thin section having a thickness of about several hundreds of nanometers is taken out near the surface of the produced film using a microtome, and this is photographed at a magnification of 20,000 with a transmission electron microscope, and the image is scanned by Canon Scan FB 636U manufactured by Canon Inc. The image is read in 300 dpi monochrome 256 gradation, and the read image is image processing software WinROOF ver3.60 (Mitani Corporation) installed in Endeavor Pro720L (CPU: Athlon-1 GHz, memory: 512 MB), a personal computer manufactured by Epson Direct Co., Ltd. (Made by Co., Ltd.) 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, Adjustments were made to detect and extract domains. For each domain of the image data extracted in this way, the major axis diameter / minor axis diameter was measured, and the average aspect ratio of the number of domains was calculated. In addition, when the angle formed between the film forming direction of the polarizing plate protective film and the major axis direction of the domain is taken as the orientation angle, the average value of the absolute value of the orientation angle is determined using a transmission electron microscope. Then, the angles of this axis and 300 domains were measured, and the total of these was obtained by averaging the numbers.

<< Preparation of polarizing plate protective film B >>
(Preparation of polarizing plate protective film 201)
<Fine particle dispersion>
Fine particles (Aerosil R972V (produced by Nippon Aerosil Co., Ltd.)) 11 parts by weight Ethanol 89 parts by weight The above was stirred and mixed with a dissolver for 50 minutes, and then dispersed with Manton Gorin, a high-pressure disperser.

<Fine particle additive solution>
Cellulose ester A was added to a dissolution tank containing methylene chloride and heated to completely dissolve, and this was then added to Azumi filter paper No. 3 manufactured by Azumi Filter Paper Co., Ltd. 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 A (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 A main dope solution of composition 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 with 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 201 having a thickness of 40 μm and a winding length of 3000 m having a width of 1.5 m, an end portion having a width of 1 cm and a height of 8 μm was prepared.

<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 Plasticizer (A 5.5 parts by mass Plasticizer (B) 5.5 parts by mass UV absorber (A) 1.2 parts by mass UV absorber (B) 0.8 parts by mass (Preparation of polarizing plate protective film 202)
<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 to 500 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 mass Thioglycerol 5 parts by mass <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 weight Polymer X Table 4 amount Polymer Y Table 4 amount Silicon dioxide dispersion 1 10 parts by weight UV absorber (A) 1.2 parts by weight UV absorber (B) 0.8 parts by weight Methylene chloride, polymer X, and polymer Y were completely dissolved while stirring, and then silicon dioxide dispersion 1 was added and stirred and mixed to prepare dope addition liquid 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, the lateral tension is relaxed at 130 ° C to release the width retention, and then drying is completed while transporting the drying zone at 120 ° C and 130 ° C with many rolls, and slitting to a width of 1.5m. Both ends of the film were subjected to a knurling process having a width of 10 mm and a height of 7 μm, and wound on a 6-inch inner diameter core with an initial tension of 220 N / m and a final tension of 110 N / m to obtain a polarizing plate protective film 202 shown in Table 3. 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 described in Table 3 was 0.1%, the film thickness was 40 μm, and the winding length was 3000 m.

<Production of polarizing plate>
Polarizing plates 301 to 350 shown in Tables 5 and 6 were produced using the produced polarizing plate protective films 101 to 125 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, which have been subjected to alkali saponification treatment on both surfaces of the polarizing film, are combined with a combination of Tables 5 and 6, and a completely saponified polyvinyl alcohol 5% aqueous solution is combined. Each was bonded as an adhesive.

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

<< 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 325 are respectively made of glass of a liquid crystal cell (VA type). The liquid crystal display devices 301 to 325 were prepared by bonding to the surface.

  At that time, the polarizing plate protective film 201 as the polarizing plate protective film B 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 previously bonded polarizing plate. .

<< 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 326 to 350 are respectively liquid crystal. It stuck on the glass surface of a cell (IPS type), and produced the liquid crystal display devices 326-350.

  At that time, the polarizing plate protective film 202 as the polarizing plate protective film B 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 previously bonded polarizing plate. .

  Using the liquid crystal display devices 301 to 350 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 ). Polarizing plate protective film 115 disposed on the backlight side
The luminances of the liquid crystal display devices 315 and 340 using the above were set to 1, and the relative luminance in each liquid crystal display method was expressed by the following criteria.

◎: Front brightness of 1.2 times or more ○: Front brightness of 1.1 times or more and less than 1.2 times △: Front brightness of 1.05 times or more and less than 1.1 times ×: Less than 1.05 times Result Are shown in Tables 5 and 6 below.

  From the results of Tables 5 and 6, VA type liquid crystal display devices 301 to 314 and IPS type liquid crystal display devices 326 to 326 using the polarizing plate on which the polarizing plate protective film having polarization scattering anisotropy of the present invention was bonded. It can be seen that 339 shows an excellent luminance improvement effect.

Example 2
In place of the polarizing element used in the polarizing plates 301 to 314 and 326 to 339 of the present invention described in Example 1, a polarizing plate was prepared in the same manner except that the following ethylene-modified PVA film was used as the polarizing element. When the same evaluation as in Example 1 was carried out, it was found that a polarizing plate having a high luminance improvement effect could be produced.

<Polarizing element: Production of ethylene-modified PVA film>
100 parts by mass of ethylene-modified PVA having an ethylene unit content of 2.5 mol%, a saponification degree of 99.95 mol%, and a polymerization degree of 2400 is melt-kneaded and then dehydrated. After foaming, it was melt-extruded from a T die to a metal roll to form a film. The ethylene-modified PVA film obtained after drying and heat treatment had a thickness of 40 μm, and the average hot water cutting temperature of the film was 70 ° C.

  The ethylene-modified PVA film thus obtained was successively treated in the order of pre-swelling, dyeing, uniaxial stretching, fixing treatment, drying and heat treatment to produce a polarizing film. That is, the ethylene-modified PVA film is pre-swelled by immersing it in water at 30 ° C. for 60 seconds, and is immersed in a 35 ° C. aqueous solution having a boric acid concentration of 40 g / liter, an iodine concentration of 0.4 g / liter, and a potassium iodide concentration of 60 g / liter. Soaked for 2 minutes. Subsequently, it was uniaxially stretched 6 times in an aqueous solution at 55 ° C. with a boric acid concentration of 4%, and in an aqueous solution at 30 ° C. with a potassium iodide concentration of 60 g / liter, a boric acid concentration of 40 g / liter, and a zinc chloride concentration of 10 g / liter. For 5 minutes, and fixed. Thereafter, the ethylene-modified PVA film was taken out, dried with hot air at 40 ° C. under a constant length, and further subjected to heat treatment at 100 ° C. for 5 minutes to obtain a polarizing film having a film thickness of 15 μm.

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

Claims (5)

A polarizing plate protective film having a polarization scattering anisotropy comprising an optical continuous phase comprising a cellulose ester and a domain having an aspect ratio defined by the following formula (1) of 2 or more, wherein the acetyl group of the cellulose ester The degree of substitution X and the degree of substitution Y of propionyl group satisfy the conditions specified by the following formulas (2) and (3), and the film forming direction of the polarizing plate protective film and the major axis direction of each domain An average value of absolute values of angles formed is within 25 °, and a polarizing plate protective film.
Formula (1)
Aspect ratio = major axis diameter / minor axis diameter (where the major axis diameter means the absolute maximum length in the domain, and the minor axis diameter is the projected domain with two straight lines parallel to the absolute maximum length. Means the distance between two straight lines when
Formula (2)
2.3 ≦ X + Y ≦ 2.8
Formula (3)
0.7 ≦ Y ≦ 2.3   The minimum value of the refractive index difference between the optical continuous phase and the domain is 0.25 or more, the major axis diameter of the domain is 400 nm or more and 10,000 nm or less, and the minor axis diameter is 50 nm or more and 390 nm or less. The polarizing plate protective film according to claim 1, wherein the polarizing plate protective film is provided.   The polarizing plate protective film according to claim 1, wherein the domain is an inorganic compound that has been surface-treated with a surface modifier.   A polarizing plate integrated in the order of polarizing plate protective film / dichroic polarizing film / polarizing plate protective film B according to any one of claims 1 to 3, wherein the two colors A polarizing plate characterized in that the absorption axis of the polarizing film is in the longitudinal direction of the polarizing plate protective film.   The polarizing plate according to claim 4 is used, and the polarizing plate protective film according to any one of claims 1 to 3 is disposed on the backlight side. Liquid crystal display device.