JP5810872B2 - Protective film for polarizing plate, method for producing the same, polarizing plate, and liquid crystal display device - Google Patents

Description

  The present invention relates to a protective film for a polarizing plate, a method for producing the same, a polarizing plate, and a liquid crystal display device. More specifically, the present invention relates to a light-diffusing polarizing plate protective film, a method for producing the same, a polarizing plate using the protective film, and a liquid crystal display device.

  A liquid crystal display device (hereinafter also referred to as “LCD”) includes a backlight unit, a liquid crystal cell, and a polarizing plate. The polarizing plate usually comprises a polarizing plate protective film (also referred to as “polarizing film protective film” or “polarizing plate protective film”) and a polarizer (also referred to as “polarizing film”). As the polarizer, a polyvinyl alcohol film dyed with iodine and stretched is often used, and both surfaces thereof are covered with a protective film for a polarizing plate. As a protective film for a polarizing plate, a cellulose acylate film having excellent moisture permeability and excellent adhesion to a polarizer is often used.

  In recent years, thinning and cost reduction have been advanced in the field of LCD. Since the liquid crystal display device is not a self-luminous display device, a light source such as a cold cathode tube (CCFL) or LED is provided on the back side of the liquid crystal cell (backlight side) or on the edge portion (edge light type) of the light guide plate. Is always placed. Since these light sources are generally linear light sources or point light sources, a light diffusion sheet or a light diffusion film (also referred to as a “diffusion sheet” or “diffusion film”) is used in order to form a uniform surface light source. . In addition, the light diffusing sheet has interference fringes such as moire caused by interference between a prism sheet often used as a member for imparting directivity to light and incident light, or interference between pixels in a liquid crystal cell and incident light. Can be suppressed.

  However, in recent years, with the trend toward thinning and cost reduction, the number of liquid crystal display device members has been reduced, and LCDs that do not use a light diffusion sheet have come out. Even when a light diffusing sheet is used, the distance between the light source and the light diffusing sheet is reduced due to the thinning of the LCD. Therefore, it is difficult to eliminate interference fringes such as moire only with the conventional light diffusing sheet. It is becoming. Therefore, as a substitute for the light diffusion sheet, a liquid crystal display device having a light diffusion property on the surface of the back side (backlight side) polarizing plate has been used.

  For example, Patent Document 1 proposes a light diffusing polarizing plate having a light diffusing layer having predetermined characteristics, which contains porous amorphous particles and spherical particles in a dispersed manner, and discloses that a light diffusing sheet can be omitted by this. ing. Patent Documents 2 and 3 propose the use of a light diffusion film containing translucent fine particles and crosslinkable fine particles as a protective film for a polarizing plate. However, according to this method, there are a problem that the fine particles fall off when the polarizing plate is formed, and a problem that it cannot be manufactured at a low cost.

  For these reasons, there has been a demand for a new film that does not lose fine particles and has both light diffusibility sufficient to eliminate moire fringes and suitability for a protective film for polarizing plates.

  Patent Document 4 discloses a light scattering sheet having a sea-island structure in which a dope composed of a plurality of resins is cast on a film as a support and phase-separated without using fine particles, and cellulose acylate and non-cellulose. A light scattering sheet prepared by applying a mixed solution of acylate on a support film is disclosed. When this light scattering sheet was used as a protective film for a polarizing plate, it was found that there was a problem that the polarizing plate turned red when left for a long time under low temperature and high humidity. It was also found that the structure in which the light diffusion layer having a sea-island structure is provided on the cellulose film by coating has a problem that the adhesion between the cellulose film and the light diffusion layer deteriorates in a high humidity environment.

  The polarizing plate is delivered to the display device manufacturer by any transportation means such as a car, a ship, and an airplane, but may be exposed to low temperature and high humidity during the transportation process. Therefore, a defect that turns red under low temperature and high humidity is a serious defect to be solved.

  It has not been conventionally known that such a problem occurs when the light diffusion sheet is used as a protective film for a polarizing plate. Therefore, the present inventors have conducted intensive studies to solve the red discoloration and adhesion of the polarizing plate under low temperature and high humidity. As a result, the reason why the polarizing plate using the scattering sheet of Patent Document 4 turns red under low temperature and high humidity is due to uneven moisture permeability in the film surface, and cellulose acylate is used. It was found that the problem can be solved by using a protective film for a polarizing plate formed by the conventional co-casting (also called laminated casting) method.

  Patent Document 5 is an example in which cellulose acylate is co-cast and a protective film for a polarizing plate having a large external haze is produced. A protective film for a polarizing plate having a low internal haze and a high external haze is prepared by incorporating a matting agent in the outermost layer and adjusting the stretching conditions. However, the light scattering ability of this film is extremely insufficient, and moiré fringes cannot be eliminated.

  In order to improve the light scattering performance, the fine particles to be contained in the outermost layer were changed to one having a large particle size and co-cast to produce a film. It has been found that there is a problem that film peeling occurs between the outermost layer and the inner layer.

  Thus, there is a demand for a protective film for a polarizing plate having a light diffusing function that can be converted into a polarizing plate without any problem through the same polarizing plate forming process as before, but still has a level suitable for practical use. The current situation does not exist.

JP 2000-75134 A JP 2010-277080 A JP 2010-164931 A JP 2002-250806 A JP 2011-132396 A

  The inventor of the present invention has been made in view of the above-mentioned problems and situations, and the problem to be solved is that when the polarizing plate is used, the problem of red discoloration does not occur even under low temperature and high humidity, and the moire does not peel off between layers. It is providing the protective film for polarizing plates which has a light-diffusion function sufficient for cancellation. Moreover, it is providing the manufacturing method of the protective film for polarizing plates, the polarizing plate provided with the protective film for polarizing plates, and a liquid crystal display device.

  As a result of studying the cause of the above problems and the like in order to solve the above problems, the present inventor has a three-layer structure of a protective film for a polarizing plate and combines two kinds of cellulose acylates satisfying a specific relationship. Thus, the present inventors have found that a protective film for a polarizing plate can be provided which does not cause a problem of red discoloration even under low temperature and high humidity, does not peel off between layers, and has a light diffusing function sufficient for eliminating moire.

That is, the said subject of this invention is solved by the following means.
1. A film having at least a three-layer structure that is adjacent in the order of layer A, layer B, and layer C, wherein the layer A, the layer B, and the layer C contain at least cellulose acylate and are contained in the layer B The cellulose acylate satisfies the following formula (1), and the layer C has a sea-island structure in which two types of cellulose acylate are mixed, and the two types of cellulose acylate constituting the layer C The mixing ratio value CE (I) / CE (II) of CE (I) and CE (II) is in the range of 60/40 to 95/5, and the propionyl substitution degree of CE (I) is Pr (I ), CE (II) where the substitution degree of acetyl group is Ac (II) and the substitution degree of propionyl is Pr (II), X and Y represented by the following formulas (2) and (3) are (I) Arithmetic average roughness R of the surface on the side of layer C satisfying X ≦ Y within a range of ≧ 0.5 The protective film for polarizing plates, wherein a is in the range of 0.05 to 2.0 μm.
Formula (1): ZB ≧ 2.0
(However, ZB represents the total acyl group substitution degree of the cellulose acylate contained in the layer B.)
Formula (2): X = 2 × Pr (II) + Ac (II)
Formula (3): Y = 0.7 × Pr (I) +1.7
2. 2. The protective film for polarizing plate according to item 1, wherein the average length RSm of the roughness curve element on the surface on the layer C side is in the range of 5 to 40 μm.
3. The internal haze value of the said protective film for polarizing plates exists in the range of 0.08-5.0, The protective film for polarizing plates of Claim 1 or 2 characterized by the above-mentioned.
4). The cellulose acylate contained in the layer A satisfies the following formula (4), wherein the polarizing plate protective film according to any one of the first to third aspects.
Formula (4): ZA ≧ 2.7
(However, ZA represents the total acyl group substitution degree of cellulose acylate contained in layer A.)
5. A method for producing a polarizing film-protecting film to produce a polarizing plate protective film as set forth in paragraph 1 to 4 any one of paragraphs, co-flow cast dope the layer A, layer B and layer C A method for producing a protective film for a polarizing plate, comprising a step of forming a web and a stretching step of stretching the web.
6). A polarizing plate comprising the protective film for a polarizing plate according to any one of items 1 to 4 .
7). A liquid crystal display device comprising the polarizing plate according to item 6 .

  By the above means of the present invention, a protective film for a polarizing plate having a light diffusing function sufficient for eliminating moire, without causing a problem of red discoloration even under low temperature and high humidity when formed into a polarizing plate, and its The manufacturing method of the protective film for polarizing plates can be provided. Furthermore, a polarizing plate and a display device provided with the polarizing plate protective film can be provided.

  The expression mechanism or action mechanism of the effect of the present invention is not clear, but is presumed as follows.

  A polarizing plate using a protective film for a polarizing plate having a light diffusing layer produced by a known method, or a polarizing plate when a light scattering sheet produced by a known method is diverted to a protective film for a polarizing plate has a low temperature. The reason why the color changes to red under a high humidity environment is considered to be due to unevenness in the ease of moisture removal from the surface of the protective film for polarizing plate. When making a cellulose film into a polarizing plate, a means of saponifying with an alkaline solution and bonding with a polyvinyl alcohol polarizer using water paste is often used. However, a light diffusion layer made of fine particles or the like, or cellulose ester and non-cellulose In the case of a protective film for a polarizing plate having a light-scattering layer with an ester sea-island structure, a difference in moisture permeability occurs in the concavo-convex portions of the light diffusion layer after saponification. , It is considered to cause red discoloration.

  In the present invention, films A and B are laminated adjacent to each other in this order, and the layer C is divided into two types of cellulose acylate resins CE (I ) And CE (II) to form irregularities due to the sea-island structure. Therefore, since no fine particles are used, fine particles do not fall off, and moire fringes can be eliminated by the unevenness formed by two types of cellulose resins. Furthermore, when producing a polarizing plate using this film, it is saponified with alkali in the same manner as a normal polarizing plate protective film, and then bonded to the polarizer, but the irregularities formed in the layer C of the present invention Since only consists of cellulose acylate, red discoloration hardly occurs in a low temperature and high humidity environment due to uneven moisture permeability. Furthermore, by being a laminated structure containing at least cellulose acylate, this unevenness in moisture permeability can be further reduced, and even a film with light scattering ability having an uneven structure on the surface can be used under low temperature and high humidity. It is considered that the red discoloration was effectively suppressed.

The figure which showed typically the co-casting process of the film forming method of the protective film for polarizing plates of this invention The figure which showed typically an example of dope preparation process, casting process, drying process, and extending process of the solution casting film forming method of the present invention The figure which showed the example of the structure of the conventional liquid crystal display device typically The figure which showed the example of the structure of the liquid crystal display device of this invention typically The figure which showed typically the layer structure of the protective film for polarizing plates of this invention Schematic of a front luminance measuring device according to the present invention

  The protective film for polarizing plate of the present invention is a film having at least a three-layer structure that is adjacent in the order of layer A, layer B, and layer C, wherein the layer A, the layer B, and the layer C are at least cellulose acid. The cellulose acylate contained in the layer B satisfies the formula (1), and the layer C has a sea-island structure in which two types of cellulose acylates are mixed, The arithmetic average roughness Ra of the C-side surface is in the range of 0.05 to 2.0 μm. This feature is a technical feature common to the inventions according to claims 1 to 8.

In addition, as an embodiment of the present invention, the value CE (I) / CE (II) of the mixing ratio of the two types of cellulose acylate CE (I) and CE (II) constituting the layer C is from 60/40 to Within the range of 95/5,
When the propionyl substitution degree of CE (I) is Pr (I), the acetyl group substitution degree of CE (II) is Ac (II), and the propionyl substitution degree is Pr (II),
When X and Y represented by the formula (2) and the formula (3) satisfy Pr ≦ I within the range of Pr (I) ≧ 0.5, the two resins are phase-separated to form a sea-island structure. Therefore, it is preferable.

  Moreover, it is preferable that the average length RSm of the surface roughness curve element on the layer C side is in the range of 5 to 40 μm because a light diffusion effect sufficient for eliminating moire fringes can be obtained.

  Moreover, it is preferable from a viewpoint of front luminance when it is set as the display apparatus that the internal haze value of the said protective film for polarizing plates exists in the range of 0.08-5.0.

  Moreover, it is preferable that the cellulose acylate contained in the layer A satisfies the following formula (4) because an effect of improving the peelability from the support (metal belt or metal drum) during film formation can be obtained.

  Moreover, as a manufacturing method of the protective film for polarizing plates of this invention, the process of co-casting the dope of the said layer A, the layer B, and the layer C and forming a web, Then, the extending process of extending | stretching this web. It is preferable to include a film having good adhesion between the three layers, and a bonding step is unnecessary, which is preferable in terms of production cost.

  The protective film for polarizing plates of the present invention can be suitably included in polarizing plates and liquid crystal display devices.

  Hereinafter, the present invention, its components, and modes and modes for carrying out the present invention will be described in detail. In addition, in this application, "-" is used in the meaning which includes the numerical value described before and behind that as a lower limit and an upper limit.

<Outline of protective film for polarizing plate of the present invention>
The protective film for polarizing plate of the present invention is a film having at least a three-layer structure that is adjacent in the order of layer A, layer B, and layer C, wherein the layer A, the layer B, and the layer C are at least cellulose acid. The cellulose acylate contained in the layer B satisfies the following formula (1), and the layer C has a sea-island structure in which two types of cellulose acylate are mixed, The arithmetic mean roughness Ra of the surface on the C side is in the range of 0.05 to 2.0 μm.

Formula (1): ZB ≧ 2.0
(However, ZB represents the total acyl group substitution degree of the cellulose acylate contained in the layer B)
Here, the layer A is a layer having a function of improving the peelability from the support (metal belt or metal drum) during film formation, and cellulose acylate having a high acyl group total substitution degree ZA is preferable. The layer B is a layer having both a function as a protective film for a polarizing plate and a function as a support (base) for the layers A and C, and is mainly composed of cellulose acylate. Layer C is a layer responsible for the light diffusion function, and is composed of two types of cellulose acylate CE (I) and CE (II).

  In this way, by making the polarizing plate protective film into a three-layer structure, it becomes possible to select a resin having physical properties for each purpose for the layer A, the layer B, and the layer C as compared with the case of a single-layer structure. A polarizing plate protective film having desirable characteristics can be obtained.

  That is, the layer A contains cellulose acetate having a total acyl group substitution degree ZA of 2.7 or more to improve the peelability from the support (metal belt or metal drum), and the layer B has total acyl group substitution. The rigidity as a protective film for polarizing plates can be maintained by containing cellulose acylate having a degree ZB of 2.0 or more. In addition, functions such as moisture permeability sufficient to protect the polarizer can be provided. Layer C contains a mixture of two types of cellulose acylates CE (I) and CE (II) having different types of acyl groups and / or different degrees of substitution, and the arithmetic average roughness of at least one surface of the film When Ra is in the range of 0.05 to 2.0 μm, the light diffusing function is expressed and the effect of eliminating moire fringes is obtained. Furthermore, the deterioration of the polarizer due to the different saponification easiness of the surface of the layer C can be solved by adopting a three-layer configuration.

  In order to impart light diffusibility to the protective film for polarizing plate of the present invention, the layer C contains two types of cellulose acylate resins to form a sea-island structure, and a continuous phase composed of cellulose acylate CE (I) (sea ) And a concavo-convex shape having a sea-island structure composed of a dispersed phase (island) composed of cellulose acylate CE (II).

  Even if two kinds of cellulose acylates are mixed, in a simple combination of cellulose acylates, the cellulose acylates are often compatible with each other and cannot have a light diffusion function. As a result of many studies, the present inventor has determined that CE (I) used as a main component and CE (II used as a subcomponent) as a combination of cellulose acylate CE (I) and cellulose acylate CE (II) to be blended. In the case where the acyl group substitution degree and the acyl substitution degree of both satisfy the relationship of the present invention, an uneven shape with a sea-island structure can be formed. With this uneven shape, moire fringes can be eliminated and sufficient light diffusibility can be imparted.

  The mixing ratio of the cellulose acylate CE (I) and the cellulose acylate CE (II) is determined by the ratio CE (I) / CE (II) of the cellulose acylate CE (I) and CE (II) being 60 / It is preferable to be within the range of 40 to 95/5. When in this range, the sea-island structure is effectively formed. That is, when CE (I) is less than 60% by mass, dope gelation is likely to occur, and a sea-island structure is not formed, and CE (II) that should form islands is a film dispersed. It is not preferable because it may be trapped or a uniform film cannot be produced. Further, when CE (I) exceeds 95% by mass, it becomes difficult to phase-separate into a clear shape, and a part of the interface becomes compatible, and sufficient light diffusibility and moire eliminating ability cannot be obtained. It is not preferable.

As a preferred embodiment of the present invention, the layer C constituting the polarizing plate protective film of the present invention is such that X and Y represented by the following formulas (2) and (3) are Pr (I) ≧ 0.5 In order to form the sea-island structure, X ≦ Y is preferable.
Formula (2): X = 2 × Pr (II) + Ac (II)
Formula (3): Y = 0.7 × Pr (I) +1.7
In order to form the sea, cellulose acylate CE (I) is preferably a soft resin, and cellulose acylate having a flexible substituent and cellulose acetate propionate are suitable. When the propionyl group substitution degree Pr (I) of CE (I) is 0, a sea-island structure is not formed, and it is preferable that Pr (I) ≧ 0.5.

  As the cellulose acylate CE (II) for forming an island, cellulose acylate which is easily intermolecularly or intermolecularly interacted is suitable. Cellulose acylate CE (II) may be any cellulose acylate regardless of the type of acyl group such as cellulose acetate, cellulose diacetate, cellulose triacetate, cellulose acetate propionate, and cellulose acetate butyrate. Among the components, the substitution degree of the acyl group and the substitution of the propionyl group such that X and Y represented by the formula (2) and the formula (3) satisfy Pr ≦ I within the range of Pr (I) ≧ 0.5. A cellulose acylate having a degree is preferable.

  In the present invention, the cellulose acylate CE (I) is a flexible cellulose acylate, and the cellulose acylate CE (II) is a cellulose acylate having a certain degree of rigidity, thereby forming a sea-island structure sufficient for a light diffusion function. It is considered possible.

  Further, by configuring the layer C as described above, the arithmetic average roughness Ra of one surface of the film is in the range of 0.05 to 2.0 μm, and can have a sufficient light diffusion function, Moreover, it becomes possible to make an internal haze value into a preferable value, and moire fringe elimination ability improves.

  FIG. 5 shows the layer structure of the polarizing plate protective film (14a in FIG. 4) of the present invention. A represents a layer A, B represents a layer B, and C represents a layer C. The layer A is composed of a single film having a three-layer structure in which a layer B is laminated on the layer A and a layer C is further laminated thereon. The layer C of C is a layer having a light diffusing function, which is composed of a resin (CE (II)) forming the island i and a resin (CE (I)) forming the sea s.

<Cellulose acylate used in the film of the present invention>
The cellulose acylate used in the layer A according to the present invention may have a total acyl group substitution degree ZA of 2.7 or more, and the acyl group only needs to contain either an acetyl group or a propionyl group. In addition, other acyl groups may include a butyryl group, a pentanate group, a hexanate group, and the like. Specifically, the cellulose acylate preferably used may be a mixed fatty acid ester such as cellulose acetate, cellulose diacetate, cellulose triacetate, cellulose propionate, cellulose acetate propionate, cellulose acetate butyrate, and cellulose acetate pentanate. Good.

  The cellulose acylate used in the layer B according to the present invention may have a total acyl group substitution degree ZB of 2.0 or more, and the acyl group may contain either an acetyl group or a propionyl group. Other acyl groups may include a butyryl group, a pentanate group, a hexanate group, and the like. Specifically, the cellulose acylate preferably used may be a mixed fatty acid ester such as cellulose acetate, cellulose diacetate, cellulose triacetate, cellulose propionate, cellulose acetate propionate, cellulose acetate butyrate, and cellulose acetate pentanate. Good.

As the cellulose acylate CE (I) and cellulose acylate CE (II) used for the layer C according to the present invention, as described above,
The substitution degree of propionyl group of cellulose acylate CE (I) is Pr (I),
Cellulose acylate CE (II) has an acetyl group substitution degree of Ac (II),
When the substitution degree of propionyl group of cellulose acylate CE (II) is Pr (II), X and Y represented by the following formulas (2) and (3) are such that Pr (I) ≧ 0.5 It is preferable to satisfy X ≦ Y within the range.

Formula (2): X = 2 × Pr (II) + Ac (II)
Formula (3): Y = 0.7 × Pr (I) +1.7
It is preferable that The portion not substituted with an acyl group is usually present as a hydroxy group.

  The measuring method of the said acyl group substitution degree can be measured according to ASTM-D817-96.

  Here, the acyl group substitution degree represents the total of the ratios of cellulose esterified at the 2nd, 3rd and 6th positions of the glucose repeating unit constituting the cellulose. Specifically, the substitution degree is 1 when the hydroxy groups (hydroxyl groups) at the 2-position, 3-position and 6-position of cellulose are esterified 100%. Therefore, when all of the 2nd, 3rd and 6th positions of the cellulose are 100% esterified, the degree of substitution is 3 at the maximum.

  Further, when the glass transition point Tg of cellulose acylate CE (I) (CE (I)) and the glass transition point Tg of cellulose acylate CE (II) (CE (II)) are used, the polarizing plate of the present invention. Since the protective film is preferably stretched at a temperature at which the stretching temperature T is Tg (CE (I)) <T <Tg (CE (II)) in the stretching step, the cellulose acylate CE (I), cellulose acylate The rate CE (II) is preferably selected such that Tg (CE (I)) <Tg (CE (II)).

(Measurement method of glass transition point (Tg))
The Tg of cellulose acylate can be measured by a differential scanning calorimetry method. Specifically, a differential scanning calorimeter EXSTADSC6000 (manufactured by SII Nano Technology) is used.

  As a measurement procedure, 10.0 to 12.0 mg of resin is precisely weighed to 0.01 mg, sealed in an aluminum pan, and set in a sample holder. The reference used an empty aluminum pan. As measurement conditions, the measurement temperature is 0 to 200 ° C., the temperature increase rate is 5 ° C./min, the temperature decrease rate is 10 ° C./min, and the heat-cool-heat control is performed, and the analysis is performed based on the data in the 2nd Heat. .

  Tg draws an extension line of the baseline before the rise of the first endothermic peak and a tangent line indicating the maximum inclination between the rising portion of the first endothermic peak and the peak apex, and the intersection is defined as Tg.

(Method for synthesizing cellulose acylate)
The cellulose acylate used in the present invention can be synthesized by a known method. Specifically, it can be synthesized with reference to methods described in JP-A-10-45804, JP-A-2009-161701, JP-A-2003-270442, and the like.

  Cellulose as a raw material of cellulose acylate is not particularly limited, and examples thereof include cotton linter, wood pulp (derived from coniferous tree, derived from broadleaf tree), kenaf and the like.

  Generally, cellulose is esterified by mixing cellulose as a raw material, a predetermined organic acid (such as acetic acid or propionic acid), an acid anhydride (such as acetic anhydride or propionic anhydride), and a catalyst (such as sulfuric acid). The reaction proceeds until the triester is formed. In the triester, the three hydroxy groups of the glucose unit are substituted with an acyl group of an organic acid. When two or more kinds of organic acids are used at the same time, a mixed ester type cellulose acylate such as cellulose acetate propionate or cellulose acetate butyrate can be produced. Next, cellulose acylate having a desired degree of acyl group substitution is synthesized by hydrolyzing the triester of cellulose. Thereafter, cellulose acylate can be obtained through steps such as filtration, precipitation, washing with water, dehydration, and drying.

  The mixed ester type cellulose acylate used in the present invention can be synthesized using an acid anhydride or acid chloride as an acylating agent. When the acylating agent is an acid anhydride, an organic acid (for example, acetic acid) or methylene chloride is used as a reaction solvent. As the catalyst, an acidic catalyst such as sulfuric acid is used. When the acylating agent is an acid chloride, a basic compound is used as a catalyst. In the most general synthetic method in the industry, cellulose acylate is obtained by esterifying cellulose with a mixed organic acid component containing an organic acid (acetic acid, propionic acid, butyric acid) corresponding to acetyl group and propionyl group or an acid anhydride thereof. Is synthesized.

  The amount of the acetylating agent, propionylating agent, and butyrylating agent used is adjusted so that the ester to be synthesized falls within the range of the substitution degree described above. The amount of the reaction solvent used is preferably 100 to 1000 parts by mass, more preferably 200 to 600 parts by mass with respect to 100 parts by mass of cellulose. It is preferable that the usage-amount of an acidic catalyst is 0.1-20 mass parts with respect to 100 mass parts of cellulose, More preferably, it is 0.4-10 mass parts.

  The reaction temperature is preferably 10 to 120 ° C, more preferably 20 to 80 ° C. Other acylating agents and esterifying agents (for example, sulfate esterifying agents) may be used in combination. Further, after completion of the acylation reaction, the degree of substitution may be adjusted by hydrolysis (saponification) as necessary. After completion of the reaction, the reaction mixture is separated using conventional means such as precipitation, washed and dried to obtain a mixed fatty acid ester of cellulose (for example, cellulose acetate propionate).

  As the cellulose acylate used in the present invention, either cellulose triacetate synthesized from cotton linter or cellulose triacetate synthesized from wood pulp can be used alone or in combination. It is preferable to use a large amount of cellulose acylate synthesized from a cotton linter that has good releasability from a belt or drum because of high production efficiency.

  The weight average molecular weight (Mw) of cellulose acylate is preferably 75,000 or more, and more preferably in the range of 75,000 to 400,000. The number average molecular weight (Mn) is preferably 60,000 to 240,000. If the number average molecular weight is within this range, the mechanical strength of the resulting film is increased, which is preferable. More preferably, cellulose acylate having a number average molecular weight of 70,000 to 200,000 is used.

  The measuring method of the weight average molecular weight (Mw) and number average molecular weight (Mn) of a cellulose acylate can be based on the following method.

(Molecular weight measurement method)
The weight average molecular weight (Mw) and the number average molecular weight (Mn) were 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 calibration curves were used. Thirteen samples are used at approximately equal intervals.

(Residual sulfuric acid content)
The residual sulfuric acid content in the cellulose acylate is preferably in the range of 0.1 to 45 mass ppm in terms of elemental sulfur. These are considered to be contained in the form of salts. If the residual sulfuric acid content exceeds 45 ppm by mass, there is a tendency to break during hot stretching or slitting after hot stretching. The residual sulfuric acid content is more preferably in the range of 1 to 30 mass ppm. The residual sulfuric acid content can be measured by a method prescribed in ASTM-D817-96.

(Free acid content)
Moreover, it is preferable that the free acid content in a cellulose acylate is 1-500 mass ppm. The above range is preferable because it is difficult to break as described above. In addition, it is preferable that free acid content is the range of 1-100 mass ppm, and also it becomes difficult to fracture | rupture. The range of 1-70 mass ppm is especially preferable. The free acid content can be measured by the method prescribed in ASTM-D817-96.

(Residue amount adjustment method)
By washing the synthesized cellulose acylate more sufficiently than when used in the solution casting method, the residual alkaline earth metal content, residual sulfuric acid content, and residual acid content are within the above ranges. And can be preferable.

(Bright spot foreign matter)
Moreover, it is preferable that a cellulose acylate has few bright spot foreign materials when it is made into a film. Bright spot foreign matter means that when two polarizing plates are placed in a crossed Nicol state, an optical film or the like is placed between them, light is applied from one polarizing plate side, and observation is performed from the other polarizing plate side. It means a point (foreign matter) where light from the opposite side appears to leak. The number of bright spots having a diameter of 0.01 mm or more is preferably 200 / cm ² or less, more preferably 100 / cm ² or less, and 50 / cm ² or less. Is more preferably 30 pieces / cm ² or less, particularly preferably 10 pieces / cm ² or less, and most preferably none.

Further, the bright spots having a diameter of 0.005 to 0.01 mm or less are also preferably 200 pieces / cm ² or less, more preferably 100 pieces / cm ² or less, and 50 pieces / cm ² or less. Is more preferably 30 pieces / cm ² or less, particularly preferably 10 pieces / cm ² or less, and most preferably none.

(Metal content)
Cellulose acylate is also affected by trace metal components in cellulose acylate. These trace metal components are thought to be related to the water used in the production process, but it is preferable that there are few components that can become insoluble nuclei, especially iron (Fe), calcium (Ca), magnesium. Metal ions such as (Mg) may form an insoluble matter by forming a salt with a polymer decomposition product or the like that may contain an organic acidic group, and it is preferable that the amount of the metal ion is small. In addition, the calcium (Ca) component easily forms a coordination compound (that is, a complex) with an acidic component such as a carboxylic acid or a sulfonic acid, and many ligands. Insoluble starch, turbidity) may be formed.

  Specifically, for the iron (Fe) component, the content in cellulose acylate is preferably 1 mass ppm or less. Moreover, about calcium (Ca) component, content in a cellulose acylate becomes like this. Preferably it is 60 mass ppm or less, More preferably, it is 0-30 mass ppm. Furthermore, regarding the magnesium (Mg) component, too much is also insoluble, so the content in the cellulose acylate is preferably 0 to 70 ppm by mass, and particularly preferably 0 to 20 ppm by mass. .

  It should be noted that the content of metal components such as the content of iron (Fe) component, the content of calcium (Ca) component, the content of magnesium (Mg) component, etc., is a micro digest wet cracking device ( After pretreatment with sulfuric acid decomposition (sulfuric acid decomposition) and alkali fusion, analysis can be performed using ICP-AES (inductively coupled plasma emission spectrometer).

<Additives>
Various additives can be added to the protective film for polarizing plates of the present invention as necessary.

[Plasticizer]
In the protective film for polarizing plates of this invention, it is also possible to use a plasticizer together in order to improve the fluidity and flexibility of the composition. Examples of the plasticizer include phthalate ester, fatty acid ester, trimellitic ester, phosphate ester, polyester, and epoxy.

  Of these, polyester and phthalate plasticizers are preferably used. Polyester plasticizers are superior in non-migration and extraction resistance compared to phthalate ester plasticizers such as dioctyl phthalate, but are slightly inferior in plasticizing effect and compatibility.

  Therefore, it can be applied to a wide range of uses by selecting or using these plasticizers according to the use.

(Polyester plasticizer)
The polyester plasticizer is a reaction product of a monovalent or tetravalent carboxylic acid and a monovalent or hexavalent alcohol, and is mainly obtained by reacting a divalent carboxylic acid with a glycol. . Representative divalent carboxylic acids include glutaric acid, itaconic acid, adipic acid, phthalic acid, azelaic acid, sebacic acid and the like.

  In particular, when adipic acid, phthalic acid or the like is used, those having excellent plasticizing properties can be obtained. Examples of the glycol include glycols such as ethylene, propylene, 1,3-butylene, 1,4-butylene, 1,6-hexamethylene, neopentylene, diethylene, triethylene, and dipropylene. These divalent carboxylic acids and glycols may be used alone or in combination.

  The ester plasticizer may be any of ester, oligoester, and polyester types, and the molecular weight is preferably in the range of 100 to 10,000, and preferably in the range of 600 to 3000, which has a large plasticizing effect.

  The viscosity of the plasticizer has a correlation with the molecular structure and molecular weight. In the case of an adipic acid plasticizer, the viscosity is preferably in the range of 200 to 5000 MPa · s (25 ° C.) in view of compatibility and plasticization efficiency. Furthermore, some polyester plasticizers may be used in combination.

  The plasticizer is preferably added in an amount of 0.5 to 30 parts by mass with respect to 100 parts by mass of the film according to the present invention. If the added amount of the plasticizer exceeds 30 parts by mass, the surface becomes sticky, which is not preferable for practical use.

(Polyhydric ester plasticizer)
The polyhydric alcohol ester plasticizer is an ester compound of a polyhydric alcohol represented by the following general formula (1).
Formula (1): R _1- (OH) _n
(Wherein R ₁ represents an n-valent organic group, and n represents a positive integer of 2 or more)
Preferred examples of the polyhydric alcohol include ethylene glycol, propylene glycol, trimethylolpropane, and pentaerythritol.

  As monocarboxylic acid used for polyhydric alcohol ester, well-known aliphatic monocarboxylic acid, alicyclic monocarboxylic acid, aromatic monocarboxylic acid, etc. can be used.

  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.

  Examples of preferred alicyclic monocarboxylic acids include cyclopentane carboxylic acid, cyclohexane carboxylic acid, cyclooctane carboxylic acid, or derivatives thereof.

  Examples of preferred aromatic monocarboxylic acids include those in which an alkyl group is introduced into the benzene ring of benzoic acid such as benzoic acid and toluic acid, and two or more benzene rings such as biphenylcarboxylic acid, naphthalenecarboxylic acid, and tetralincarboxylic acid. The aromatic monocarboxylic acid which has, or derivatives thereof can be mentioned. In particular, benzoic acid is preferred.

  The molecular weight of the polyhydric alcohol ester is preferably in the range of 300 to 1500, and more preferably in the range of 350 to 750. The carboxylic acid used for the polyhydric alcohol ester may be one kind or a mixture of two or more kinds. Moreover, all the hydroxyl groups (OH groups) in the polyhydric alcohol may be esterified, or a part of the hydroxyl groups may be left as they are.

  In addition, trimethylolpropane triacetate, pentaerythritol tetraacetate and the like are also preferably used. It is also preferable to use the ester compound (A) represented by the general formula (I) described in JP-A-2008-88292.

(Polycarboxylic acid ester plasticizer)
The polyvalent carboxylic acid ester compound is composed of an ester of divalent or higher, preferably divalent to 20 valent polyvalent carboxylic acid and alcohol. The aliphatic polyvalent carboxylic acid is preferably 2 to 20 valent, and in the case of an aromatic polyvalent carboxylic acid or an alicyclic polyvalent carboxylic acid, it is preferably 2 to 20 valent.

The polyvalent carboxylic acid is represented by the following general formula (2).
Formula (2): R ₂ (COOH) _m (OH) _n
(Wherein R ₂ is an (m + n) -valent organic group, m is a positive integer of 2 or more, n is an integer of 0 or more, a COOH group is a carboxy group, and an OH group is an alcoholic or phenolic hydroxy group)
Examples of preferable polyvalent carboxylic acids include the following. Divalent or higher polyvalent aromatic carboxylic acids or derivatives such as phthalic acid, terephthalic acid, isophthalic acid, trimellitic acid, trimesic acid, pyromellitic acid, succinic acid, adipic acid, azelaic acid, sebacic acid, oxalic acid Aliphatic polycarboxylic acids such as fumaric acid, maleic acid and tetrahydrophthalic acid, and oxypolycarboxylic acids such as tartaric acid, tartronic acid, malic acid and citric acid can be preferably used.

  Known alcohols and phenols can be used as the alcohol used in the polyvalent carboxylic acid ester compound that can be used in the present invention. For example, an aliphatic saturated alcohol 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. Further, cycloaliphatic alcohols such as cyclopentanol and cyclohexanol or derivatives thereof, aromatic alcohols such as benzyl alcohol and cinnamyl alcohol, or derivatives thereof can also be preferably used. Examples of phenol include phenol, paracresol, dimethyl Phenol etc. can be used individually or in combination of 2 or more types.

  It is also preferable to use the ester compound (B) represented by the general formula (II) described in JP-A-2008-88292.

  Although there is no restriction | limiting in particular in the molecular weight of a polyhydric carboxylic acid ester compound, It is preferable that it is the range of molecular weight 300-1000, and it is more preferable that it is the range of 350-750.

  The alcohol used for the polyvalent carboxylic acid ester may be one kind or a mixture of two or more kinds.

  The acid value of the polyvalent carboxylic acid ester compound is preferably 1 mgKOH / g or less, and more preferably 0.2 mgKOH / g or less.

  The acid value refers to the number of milligrams of potassium hydroxide necessary for neutralizing the acid (carboxy group present in the sample) contained in 1 g of the sample. The acid value is measured according to JIS K0070.

(Glycolate plasticizer)
The glycolate plasticizer is not particularly limited, but alkylphthalylalkyl glycolates can be preferably used. Examples of the alkyl phthalyl alkyl glycolates include methyl phthalyl methyl glycolate, ethyl phthalyl ethyl glycolate, propyl phthalyl propyl glycolate, butyl phthalyl butyl glycolate, octyl phthalyl octyl glycolate and the like.

(Phthalate ester plasticizer)
Examples of the phthalate ester plasticizer include diethyl phthalate, dimethoxyethyl phthalate, dimethyl phthalate, dioctyl phthalate, dibutyl phthalate, di-2-ethylhexyl phthalate, dioctyl phthalate, dicyclohexyl phthalate, and dicyclohexyl terephthalate.

(Citrate ester plasticizer)
Examples of the citrate plasticizer include acetyl trimethyl citrate, acetyl triethyl citrate, and acetyl tributyl citrate.

(Fatty acid ester plasticizer)
Examples of fatty acid ester plasticizers include butyl oleate, methylacetyl ricinoleate, and dibutyl sebacate.

(Phosphate ester plasticizer)
Examples of the phosphate ester plasticizer include triphenyl phosphate, tricresyl phosphate, cresyl diphenyl phosphate, octyl diphenyl phosphate, diphenyl biphenyl phosphate, trioctyl phosphate, tributyl phosphate and the like.

(Sugar ester compound plasticizer)
The protective film for polarizing plate of the present invention has at least one furanose structure or pyranose structure as a plasticizer, and all or part of OH groups in the compound having 1 to 12 furanose structures or pyranose structures bonded thereto. Esterified compounds (sometimes referred to as sugar ester compounds) can be included.

  Examples of preferable “compounds having at least one furanose structure or pyranose structure and having 1 to 12 furanose structures or pyranose structures bonded to each other” include JP-A Nos. 62-42996 and 10-237084. It is described in.

  When it is contained in the protective film for polarizing plate of the present invention, it is preferably contained in an amount of 0 to 35% by mass, particularly 5 to 30% by mass with respect to the cellulose acylate.

[Ultraviolet absorber]
It is also preferable that the protective film for polarizing plates of the present invention contains an ultraviolet absorber, and examples of the ultraviolet absorber used include benzotriazole-based, 2-hydroxybenzophenone-based or salicylic acid phenyl ester-based ones. For example, 2- (5-methyl-2-hydroxyphenyl) benzotriazole, 2- [2-hydroxy-3,5-bis (α, α-dimethylbenzyl) phenyl] -2H-benzotriazole, 2- (3 Triazoles such as 5-di-t-butyl-2-hydroxyphenyl) benzotriazole, 2-hydroxy-4-methoxybenzophenone, 2-hydroxy-4-octoxybenzophenone, 2,2'-dihydroxy-4-methoxybenzophenone And benzophenones.

  Here, among ultraviolet absorbers, ultraviolet absorbers having a molecular weight of 400 or more are less likely to volatilize at a high boiling point and are difficult to disperse even during high-temperature molding, so that the weather resistance is effectively improved with a relatively small amount of addition. be able to.

  Examples of the ultraviolet absorber having a molecular weight of 400 or more include 2- [2-hydroxy-3,5-bis (α, α-dimethylbenzyl) phenyl] -2-benzotriazole, 2,2-methylenebis [4- (1, 1,3,3-tetrabutyl) -6- (2H-benzotriazol-2-yl) phenol], bis (2,2,6,6-tetramethyl-4-piperidyl) sebacate, bis ( Hindered amines such as 1,2,2,6,6-pentamethyl-4-piperidyl) sebacate and 2- (3,5-di-t-butyl-4-hydroxybenzyl) -2-n-butylmalonic acid Bis (1,2,2,6,6-pentamethyl-4-piperidyl), 1- [2- [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionyloxy] ethyl L] -4- [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionyloxy] -2,2,6,6-tetramethylpiperidine and the like, hindered phenol and hindered amine Examples include hybrid systems having both structures, and these can be used alone or in combination of two or more. Among these, 2- [2-hydroxy-3,5-bis (α, α-dimethylbenzyl) phenyl] -2-benzotriazole and 2,2-methylenebis [4- (1,1,3,3- Tetrabutyl) -6- (2H-benzotriazol-2-yl) phenol] is particularly preferred.

[Fine particles]
In the protective film for polarizing plate of the present invention, if necessary, fine particles may be added after the treatment step of the cellulose acylate solution.

  Examples of the fine particles include silicon dioxide, titanium dioxide, aluminum oxide, zirconium oxide, calcium carbonate, calcium carbonate, talc, clay, calcined kaolin, calcined calcium silicate, hydrated calcium silicate, and aluminum silicate. And magnesium silicate and calcium phosphate. Further, fine particles of an organic compound can also be preferably used. Examples of organic compounds include polytetrafluoroethylene, cellulose acetate, polystyrene, polymethyl methacrylate, polypropyl methacrylate, polymethyl acrylate, polyethylene carbonate, acrylic styrene resin, silicone resin, polycarbonate resin, benzoguanamine resin, melamine resin Examples thereof include polyolefin-based powders, polyester-based resins, polyamide-based resins, polyimide-based resins, polyfluorinated ethylene-based resins, and pulverized and classified products of organic polymer compounds such as starch. Alternatively, a polymer compound synthesized by a suspension polymerization method, a polymer compound made spherical by a spray drying method or a dispersion method, or an inorganic compound can be used.

  Fine particles containing silicon are preferable in terms of low turbidity, and silicon dioxide is particularly preferable. The average primary particle diameter of the fine particles is preferably 5 to 400 nm, and more preferably 10 to 300 nm.

  These may be mainly contained as secondary aggregates having a particle size of 0.05 to 0.3 μm, and may be contained as primary particles without being aggregated if the particles have an average particle size of 100 to 400 nm. preferable.

  The content of these fine particles in the cellulose acylate is preferably 0.01 to 1% by mass, particularly preferably 0.05 to 0.5% by mass.

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

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

  Examples of the polymer include silicone resin, 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 (manufactured by Toshiba Silicone Co., Ltd.) It is marketed by name and can be used.

  Among these, Aerosil 200V and Aerosil R972V are particularly preferably used because they have a large effect of reducing the friction coefficient while keeping the turbidity of the retardation film low. In the protective film for polarizing plates of this invention, it is preferable that the dynamic friction coefficient of at least one surface is 0.2-1.0.

[Other additives]
Furthermore, various antioxidants can also be added to the protective film for polarizing plates of the present invention in order to improve the thermal decomposability and thermal coloring during molding. It is also possible to add an antistatic agent to give antistatic performance.

  For the protective film for polarizing plate of the present invention, a flame retardant acrylic resin composition containing a phosphorus flame retardant may be used.

  Phosphorus flame retardants used here include red phosphorus, triaryl phosphate ester, diaryl phosphate ester, monoaryl phosphate ester, aryl phosphonate compound, aryl phosphine oxide compound, condensed aryl phosphate ester, halogenated alkyl phosphorus. Examples thereof include one or a mixture of two or more selected from acid esters, halogen-containing condensed phosphate esters, halogen-containing condensed phosphonate esters, halogen-containing phosphite esters, and the like.

  Specific examples include triphenyl phosphate, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, phenylphosphonic acid, tris (β-chloroethyl) phosphate, tris (dichloropropyl). Examples thereof include phosphate and tris (tribromoneopentyl) phosphate.

  Furthermore, various antioxidants can also be added to the protective film for polarizing plates of the present invention in order to improve the thermal decomposability and thermal coloring during molding. It is also possible to add an antistatic agent to give antistatic performance.

  Various additives may be batch-added to a dope that is a resin-containing solution before film formation, or an additive solution may be separately prepared and added in-line. In particular, it is preferable to add a part or all of the fine particles in-line in order to reduce the load on the filter medium.

  When the additive solution is added in-line, it is preferable to dissolve a small amount of resin in order to improve mixing with the dope. A preferable amount of the resin is 1 to 10 parts by mass, and more preferably 3 to 5 parts by mass with respect to 100 parts by mass of the solvent.

  In order to perform in-line addition and mixing in the present invention, for example, an in-line mixer such as a static mixer (manufactured by Toray Engineering), SWJ (Toray static type in-tube mixer Hi-Mixer) or the like is preferably used.

(Acrylic copolymer)
The protective film for polarizing plates of the present invention can contain an acrylic polymer having a weight average molecular weight of 500 or more and 30000 or less. Above all, the weight obtained by copolymerizing ethylenically unsaturated monomer Xa having no aromatic ring and hydrophilic group in the molecule and ethylenically unsaturated monomer Xb having no aromatic ring and having a hydrophilic group in the molecule. Polymer X having an average molecular weight of 5,000 to 30,000, more preferably, an ethylenically unsaturated monomer Xa having no aromatic ring and a hydrophilic group in the molecule and an ethylenically unsaturated group having no aromatic ring and a hydrophilic group in the molecule. A weight average molecular weight of 500 to 3,000 obtained by polymerizing a polymer X having a weight average molecular weight of 5,000 to 30,000 obtained by copolymerization with a saturated monomer Xb and an ethylenically unsaturated monomer Ya having no aromatic ring. The polymer Y is preferably contained.

  It can add in the range of 1-30 mass% with respect to a cellulose acylate.

<The manufacturing method of the protective film for polarizing plates of this invention>
As a manufacturing method of the protective film for polarizing plates of this invention, the manufacturing method which includes the process of co-casting the dope of layer A, layer B, and layer C and forming a web, and then extending | stretching the said web. It is preferable that

That is, as a film forming method of the protective film for polarizing plate of the present invention,
(A) a step of dissolving a resin and an additive in an organic solvent to form a dope;
(B) a casting process in which the dope is cast on a support (metal belt or metal drum) to form a web;
(C) A drying step for drying the web, and (d) 1.03 to 1.2 times or less at a temperature at which the stretching temperature T satisfies Tg (CE (I)) <T <Tg (CE (II)). Stretching at a magnification,
It is preferable to use a production method having In the casting step for forming the web of (b) above, it is preferable to use a co-casting method described later.

  Hereinafter, although the example of the casting method of the protective film for polarizing plates of this invention is demonstrated, the solution casting by a co-casting method is preferable as a casting method.

  Although it does not specifically limit as a film forming method of the protective film for polarizing plates of this invention, The layer A, the layer B, and the layer C may each be formed into a film, may be bonded together, and it is a co-casting method. The three layers may be manufactured as a single unit. As the co-casting method, a simultaneous casting method in which three layers are cast at the same time to produce a three-layer laminated film can be employed. Further, it is also possible to employ a sequential casting method in which each layer is sequentially cast on a support (metal belt or metal drum) and three layers are stacked to form a single film. Either method may be employed in the present invention. A film produced by simultaneous and sequential co-casting can produce a film having good adhesion between three layers, and is advantageous in terms of production cost because a bonding step is unnecessary.

(Co-casting method)
In the co-casting method by simultaneous casting, as shown in FIG. 1, the three types of dopes of the layer A 122, the layer B 120, and the layer C 121 are cast together from a casting die 89 on a traveling support 85. Is done by. The co-casting method by sequential casting is performed by sequentially performing multilayer casting from a number of casting ports on the support 85. In this invention, it is preferable to cast by the co-casting method by simultaneous casting. Here, by adjusting the casting amount of each dope, the layer B can be made thickest, and the film thickness t2 of the layer A, the film thickness t1 of the layer B, and the film thickness t3 of the layer C can be arbitrarily controlled. At the same time, the three layers are cast and then cooled and gelled while volatilizing the solvent, and the web is peeled off. Next, the film can be obtained by drying with hot air until the residual solvent amount is about 10% by mass and then drying with hot air.

  In the co-casting method, a cellulose acylate film can be produced by a solvent cast method from two or more kinds of prepared cellulose acylate solutions (dope).

  The dope is cast on a support (metal belt or metal drum), and the solvent is evaporated to form a film. The concentration of the dope before casting is preferably adjusted so that the solid content is 18 to 35% by mass. The surface of the drum or belt is preferably finished in a mirror state. For casting and drying methods in the solvent casting method, U.S. Pat. No. 736892, JP-B Nos. 45-4554, 49-5614, JP-A-60-176834, No. 60-203430, and No. 62-1115035.

  The dope is preferably cast on a metal belt or a metal drum having a surface temperature of 10 ° C. or less. After casting, it is preferable to dry it by applying air for 2 seconds or more. The obtained film can be peeled off from a metal belt or a metal drum, and further dried with high-temperature air whose temperature is successively changed from 100 ° C. to 160 ° C. to evaporate the residual solvent. The above method is described in Japanese Patent Publication No. 5-17844. According to this method, it is possible to shorten the time from casting to stripping. In order to carry out this method, it is necessary for the dope to gel at the surface temperature of the metal belt or metal drum during casting.

  In the present invention, the obtained cellulose acylate solution (dope) is formed by casting the two or more kinds of cellulose acylate solutions on a smooth belt or drum as a support. There is no restriction | limiting in particular as a manufacturing method of the film of this invention other than the above, A well-known co-casting method can be used. For example, the film may be produced while casting and laminating a solution containing cellulose acylate from a plurality of casting ports provided at intervals in the traveling direction of the metal support. The methods described in JP-A Nos. 158414, 1-122419, and 11-198285 can be applied. Further, it may be formed into a film by casting a cellulose acylate solution from two casting ports. For example, JP-B-60-27562, JP-A-61-94724, JP-A-61-947245, It can be carried out by the methods described in JP-A Nos. 61-104813, 61-158413, and 6-134933. Further, a cellulose acylate film in which a flow of a high-viscosity cellulose acylate solution described in JP-A-56-162617 is wrapped with a low-viscosity cellulose acylate solution and the high- and low-viscosity cellulose acylate solutions are simultaneously extruded. A casting method may be used. Furthermore, it is also a preferable aspect that the outer solution described in JP-A-61-94724 and JP-A-61-94725 contains a larger amount of an alcohol component which is a poor solvent than the inner solution.

  Alternatively, by using two casting ports, the film cast on the metal support is peeled off by the first casting port, and the second casting is performed on the side in contact with the metal support surface. Further, a film may be prepared, for example, a method described in Japanese Patent Publication No. 44-20235. The cellulose acylate solutions to be cast may be the same solution or different cellulose acylate solutions, and are not particularly limited. In order to give a function to a plurality of cellulose acylate layers, a cellulose acylate solution corresponding to the function may be extruded from each casting port. As a method for producing the film of the present invention, it is preferred that the film formation is simultaneous or sequential multilayer casting film formation.

  In the case of co-casting, the inner and outer thicknesses are not particularly limited, but preferably the outer side is preferably 0.2 to 50% of the total film thickness, more preferably 2 to 30%. . Here, in the case of co-casting with three or more layers, the total thickness of the layer in contact with the metal support and the layer in contact with the air side is defined as the outer thickness.

  In the case of co-casting, a cellulose acylate film having a laminated structure can be produced by co-casting cellulose acylate solutions having different additive concentrations such as the above-mentioned plasticizer, ultraviolet absorber and matting agent. For example, a cellulose acylate film having a structure of layer A / layer B / layer C can be produced. For example, the matting agent can be contained in the layer A and the layer C, or in the layer A or the layer C only. More plasticizers and ultraviolet absorbers can be contained in layer B than layers A and C, and may be contained only in layer B. In addition, the types of plasticizer and ultraviolet absorber can be changed in layer B, layer A and layer C. For example, the layer A and layer C contain a low-volatile plasticizer and / or ultraviolet absorber, A plasticizer excellent in plasticity or an ultraviolet absorber excellent in ultraviolet absorption can also be added to B. Moreover, it is also a preferable aspect that a release agent is contained only in the layer A on the metal support side. It is also preferable to add more alcohol, which is a poor solvent, to layer A and layer C than to layer B in order to cool the metal support by the cooling drum method to gel the solution. The Tg of layer A, layer B and layer C may be different, and the Tg of layer B is preferably lower than the Tg of layers A and C. Further, the viscosity of the solution containing cellulose acylate during casting may be different between layer A, layer C and layer B, and the viscosity of layer A and layer C is preferably smaller than the viscosity of layer B. The viscosity of B may be smaller than the viscosity of layers A and C.

  In the present invention, the multi-layer cast dope is dried and peeled off from the support (metal belt or metal drum).

(Organic solvent)
The organic solvent useful for forming the dope when the protective film for polarizing plate of the present invention is produced by the solution casting method is not limited as long as it dissolves a plurality of polymers and other additives used at the same time. Can be used.

  For example, as the chlorinated organic solvent, methylene chloride, as the non-chlorinated organic solvent, 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- Examples include 2-methyl-2-propanol, 1,1,1,3,3,3-hexafluoro-2-propanol, 2,2,3,3,3-pentafluoro-1-propanol, and nitroethane. Methylene chloride, methyl acetate, ethyl acetate and acetone can be preferably used.

  In addition to the organic solvent, the dope preferably contains 1 to 40% by mass of a linear or branched aliphatic alcohol having 1 to 4 carbon atoms. When the proportion of alcohol in the dope increases, the web gels, and peeling from the metal support becomes easy, and when the proportion of alcohol is small, the role of promoting the dissolution of the polymer in non-chlorine organic solvent system is there.

  In particular, it is a dope composition in which at least 15 to 45 mass% in total of a sea polymer and an island polymer are dissolved in a solvent containing methylene chloride and a linear or branched aliphatic alcohol having 1 to 4 carbon atoms. It is preferable.

  Examples of the linear or branched aliphatic alcohol having 1 to 4 carbon atoms include methanol, ethanol, n-propanol, iso-propanol, n-butanol, sec-butanol, and tert-butanol. Ethanol is preferred because of the stability of these dopes, the relatively low boiling point, and good drying properties.

  Hereinafter, the preferable film forming method of the protective film for polarizing plates of this invention is demonstrated.

FIG. 2 is a diagram schematically showing an example of a dope preparation step, a casting step, and a drying step of a solution casting film forming method preferable for the present invention.
(1) Dissolution Step In this step, a dope is formed by dissolving a resin and other additives in an organic solvent mainly composed of a good solvent for the polymer to be used while stirring the resin and other additives.

  For dissolution of the resin, a method performed at normal pressure, a method performed below the boiling point of the main solvent, a method performed under pressure above the boiling point of the main solvent, JP-A-9-95544, JP-A-9-95557, or Various dissolution methods such as a method using a cooling dissolution method as described in JP-A-9-95538 and a method using a high pressure as described in JP-A-11-21379 can be used. A method in which pressure is applied as described above is preferable.

  After the resin and additives are dissolved, it is filtered through a filter medium, defoamed, and sent to the next step with a liquid feed pump. It is preferable to use a filter medium having a collected particle diameter of 0.5 to 5 μm and a drainage time of 10 to 25 sec / 100 ml.

  Thereafter, the dope solution is filtered by the main filter 3, and an ultraviolet absorber additive solution is added inline to the dope solution 16.

In many cases, the dope may contain about 10 to 50% by mass of the recycled material. The return material is a product obtained by finely pulverizing the optical film, which is generated when the optical film is formed, and is obtained by cutting off both sides of the film, or by using an optical film original that has been speculated out due to scratches, etc. .
(2) Casting process An endless support 31, such as a stainless steel belt or a rotating metal drum, which feeds the dope to the pressure die 30 through a liquid feed pump (for example, a pressurized metering gear pump) and transfers it infinitely. The dope is cast from the pressure die slit to the casting position on the metal support.

A pressure die that can adjust the slit shape of the die base portion and can easily make the film thickness uniform is preferable. Examples of the pressure die include a coat hanger die and a T die, and any of them is preferably used. The surface of the support is a mirror surface. In order to increase the film forming speed, two or more pressure dies may be provided on the support, and the dope amount may be divided and stacked. Or it is preferable to obtain the film of a laminated structure by the above-mentioned co-casting method which casts several dope simultaneously.
(3) Solvent evaporation step In this step, the web (the dope is cast on the casting support and the formed dope film is referred to as “web”) is heated on the support to evaporate the solvent.

  To evaporate the solvent, there are a method of blowing air from the web side and / or a method of transferring heat from the back side of the support by a liquid, a method of transferring heat from the front and back by radiant heat, and the like. High efficiency and preferable. A method of combining them is also preferably used.

In order to adjust the residual solvent amount at the time of peeling, the liquid temperature to be brought into contact with the back surface of the support in the solvent evaporation step, the contact time with the support, and the like may be appropriately adjusted.
(4) Peeling process It is the process of peeling the web which the solvent evaporated on the support body in a peeling position. The peeled web is sent to the next process.

  The temperature at the peeling position on the support is preferably 10 to 40 ° C, more preferably 11 to 30 ° C.

  In addition, it is preferable to peel in the range of 5-120 mass% about the residual solvent amount at the time of peeling of the web on the support body at the time of peeling depending on the strength of drying conditions, the length of the support body, and the like.

  The amount of residual solvent used in the present invention can be expressed by the following formula.

Residual solvent amount (% by mass) = {(MN) / N} × 100
Here, M is the mass of the web at an arbitrary point, and N is the mass when M is dried at 110 ° C. for 3 hours.
(5) Drying and stretching step After peeling, a drying device 35 that transports the web alternately through a plurality of rolls arranged in the drying device, and / or a tenter stretching device 34 that clips and transports both ends of the web with clips. Use to dry the web.

  Generally, the drying means blows hot air on both sides of the web, but there is also a means for heating by applying microwaves instead of the wind. Too rapid drying tends to impair the flatness of the finished film. Drying at a high temperature is preferably performed from about 8% by mass or less of the residual solvent. Throughout the drying is generally carried out at 40-250 ° C.

  When using a tenter stretching apparatus, it is preferable to use an apparatus that can independently control the film gripping length (distance from the start of gripping to the end of gripping) left and right by the left and right gripping means of the tenter. In the tenter process, it is also preferable to intentionally create sections having different temperatures in order to improve planarity.

  It is also preferable to provide a neutral zone between different temperature zones so that the zones do not interfere with each other.

  In addition, extending | stretching operation may be divided | segmented and implemented in multiple steps, and it is also preferable to implement biaxial stretching in a casting direction and a width direction. When biaxial stretching is performed, simultaneous biaxial stretching may be performed or may be performed stepwise.

  In this case, stepwise means that, for example, stretching in different stretching directions can be sequentially performed, stretching in the same direction is divided into multiple stages, and stretching in different directions is added to any one of the stages. Is also possible. That is, for example, the following stretching steps are possible.

-Stretch in the casting direction-Stretch in the width direction-Stretch in the casting direction-Stretch in the casting direction-Stretch in the width direction-Stretch in the width direction-Stretch in the casting direction-Stretch in the casting direction Simultaneous biaxial stretching includes stretching in one direction and contracting the other while relaxing the tension.

  It is preferable that the stretching ratio is stretched in the width direction, the longitudinal direction, particularly in the width direction at a ratio within 1.03 to 1.2 times in order to form the sea-island structure.

  In the stretching step, the protective film for polarizing plate of the present invention is preferably stretched at a temperature at which the stretching temperature T is Tg (CE (I)) <T <Tg (CE (II)). Therefore, among the resins forming the sea-island structure, the glass transition temperature of the resin constituting the island (cellulose acylate CE (II)) is higher than that of the resin constituting the sea (cellulose acylate CE (I)). is there.

  Specifically, the temperature when performing tenter stretching is preferably within 30 to 200 ° C, and more preferably within 100 to 200 ° C.

For temperature control during stretching, known means such as hot air or microwave can be used.
In the tenter process, it is preferable that the temperature distribution in the width direction of the atmosphere is small from the viewpoint of improving the uniformity of the film. The temperature distribution in the width direction in the tenter process is preferably within ± 5 ° C, and within ± 2 ° C. Is more preferable, and within ± 1 ° C. is most preferable.
(6) Winding step This is a step of winding the film as a film by the winder 37 after the residual solvent amount in the web is 2% by mass or less. The dimensional stability is achieved by setting the residual solvent amount to 0.4% by mass or less. A film having good properties can be obtained. It is particularly preferable to wind up at 0.00 to 0.10% by mass.

  As a winding method, a generally used method may be used. There are a constant torque method, a constant tension method, a taper tension method, a program tension control method with a constant internal stress, and the like.

  The average film thickness of the protective film for polarizing plate of the present invention is preferably in the range of 20 to 85 μm from the viewpoint of the function as a protective film for polarizing plate, curling of the polarizing plate, and the like.

  More preferably, it exists in the range of 20-45 micrometers. The film thickness was measured at an arbitrary 10 points in the film plane with a contact-type film thickness meter, and an average value was taken.

  The polarizing plate-protecting film of the present invention is preferably a long film. Specifically, the polarizing plate-protecting film has a thickness of about 100 m to 5000 m and is usually provided in a roll shape. Moreover, it is preferable that the width | variety of a film is 1.3-4m, and it is more preferable that it is 1.4-2m.

<Arithmetic mean roughness Ra>
As for the protective film for polarizing plates of this invention, arithmetic mean roughness Ra based on JISB0601-2001 in the at least one surface exists in the range of 0.05-2.0 micrometers. When the value of Ra is 0.05 μm or more, a sufficient scattering effect can be obtained and moire fringes can be eliminated. If Ra is 2.0 micrometers or less, it can suppress effectively that front luminance falls when it is set as a display apparatus. The arithmetic average roughness Ra is measured using a measuring instrument according to JIS B0601-2001, for example, Olympus 3D laser microscope LEXT OLS4000, Kosaka Laboratory, Surfcoder MODEL SE-3500, etc. Can be measured.

<Average length RSm of roughness curve element>
In the protective film for polarizing plate of the present invention, a light diffusion effect sufficient for eliminating moire fringes is obtained when the average length RSm of the surface roughness curve element on the layer C side is in the range of 5 to 40 μm. Therefore, it is preferable. The average length RSm of the roughness curve element is a measuring instrument according to JIS B0601-2001, for example, Olympus Corporation 3D laser microscope LEXT OLS4000, Kosaka Laboratory Co., Ltd., Surfcoder MODEL SE-3500. It can measure using.

<Haze value>
In the protective film for polarizing plate of the present invention, the total haze value of one film is in the range of 20 to 80%, and the internal haze value obtained by (total haze value) − (surface haze value) is 0. It is preferable that it exists in the range of 08 to 5%.

  When the total haze value is 20% or more, moire fringes can be eliminated, and when the total haze value is 80% or less, it is preferable in that it is possible to suppress a decrease in front luminance. A more preferable range of the total haze value is within 35 to 50%. The internal haze value is preferably in the range of 0.08 to 30% from the viewpoint of suppressing moire fringes and preventing reduction in front luminance. A more preferable range of the internal haze value is 0.08 to 5.0%.

  As these haze values, values measured according to JIS K7136 using, for example, a haze meter NDH2000 manufactured by Nippon Denshoku Industries Co., Ltd. can be used in an atmosphere of 23 ° C. and 55% RH.

  The total haze value is a haze value of one sheet of the present invention, and the internal haze value is a value obtained by subtracting the external haze value from the total haze value. As the internal haze value, a measurement value obtained by covering both surfaces of the film with glycerin having a refractive index of 1.47, sandwiching the two glass plates and measuring the same as the total haze value can be used. By doing in this way, the influence of the haze value (namely, external haze value) by the uneven | corrugated shape of a surface can be disregarded, and only the haze value inside a film can be measured.

<Polarizing plate>
A polarizing plate is mainly comprised by the protective film for two polarizing plates which protects both the front side and back side of a polarizer. The polarizing plate protective film of the present invention is used for at least one of the two polarizing plate protective films sandwiching the polarizer from both sides. Since the film of the present invention has not only a moire eliminating ability but also a protective film property, the manufacturing cost of the polarizing plate can be reduced. The polarizing plate of the present invention can be used as a polarizing plate on the backlight side of the image display device or a polarizing plate on the viewing side. When used for the backlight unit-side polarizing plate, the film of the present invention is disposed so that it is closest to the backlight. When used for the polarizing plate on the viewing side, the film of the present invention is disposed so as to be the outermost layer. When used as a polarizing plate on the viewing side, reflection of external light and the like can be prevented, and a polarizing plate that can improve contrast in an environment with external light (light room) can be obtained.

<Liquid crystal display device>
As an example of the configuration of a conventional liquid crystal display device, in the direct type, as shown in FIG. 3A, from the light source side, [light source 1a / diffusion plate 3a / light collecting sheet 4a (prism sheet etc.) / Upper diffusion Sheet 5a / liquid crystal panel 12a (polarizer 10a / protective film (retardation film, etc.) 9a / substrate 8a / liquid crystal cell 7a / protective film 11a)], which is mainly used for large LCDs such as televisions. It is. On the other hand, as shown in FIG. 3B, the side light type configuration is such that the light source 1a is composed of a light emitting light source 2a and a light guide plate 13a, and is mainly used for small LCDs for monitors and mobile applications. .

  The lower diffusion sheet is an optical sheet having strong light diffusibility mainly for reducing in-plane luminance unevenness of the backlight unit (BLU) 6a, and the condensing sheet transmits diffused light in the front direction of the liquid crystal display device (display device plane). The upper diffusion sheet is used to reduce the moire generated by a periodic structure such as a prism sheet that is a light condensing sheet or a pixel in a liquid crystal cell, and the lower diffusion sheet. This optical sheet is used to further reduce in-plane luminance unevenness that cannot be removed by the sheet.

  In the liquid crystal display device of the present invention, as shown in FIGS. 4A and 4B, light diffusibility is imparted to the protective film for polarizing plate of the lower polarizing plate instead of the upper diffusion sheet (film 14a). The same or higher performance as that of the upper diffusion sheet is exhibited. With such a configuration, moire fringes can be suppressed without lowering the front luminance. Furthermore, the protective film for polarizing plate of the present invention can be manufactured without requiring a coating process or a complicated process, and the cost of the entire liquid crystal display device can be reduced by adopting a configuration in which the upper diffusion sheet is removed in this way. it can.

  Liquid crystal cell display methods include twisted nematic (TN), super twisted nematic (STN), vertical alignment (VA), in-plane switching (IPS), and optically compensated bend cell (OCB) modes. It can be preferably used for a transmissive, reflective, or transflective liquid crystal display device.

  As a light-emitting light source (light emitter) used for the light source, CCFL (Cold Cathode Fluorescent Lamp), HCFL (Hot Cathode Fluorescent Lamp, hot cathode tube), LED (Light Emitting Diode, Light-Emitting Diode), OLED Organic light-emitting diode, organic light emitting diode [organic EL], inorganic EL, and the like can be preferably used.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto. In the examples, the display of “part” or “%” is used, but “part by mass” or “% by mass” is expressed unless otherwise specified.

  First, the evaluation method of the protective film for polarizing plate of the present invention will be described.

<Evaluation method>
(Interlayer adhesion)
Interlayer adhesion was evaluated for the purpose of evaluating film peeling between layers. The layer C side of the protective film for polarizing plate to be evaluated, produced by the method described below, was faced up and irradiated with light for 150 hours by a light resistance tester (I Super UV Tester, manufactured by Iwasaki Electric Co., Ltd.). Then, after adjusting the humidity for 24 hours under the conditions of a temperature of 23 ° C. and a relative humidity of 55%, the adhesion was evaluated by a cross cut test. Specifically, the evaluation area is 1 cm square, and the depth is slightly reached to the surface of the transparent plastic film, and a 1 mm square grid is cut into the surface of the cured film layer using a single blade razor blade. Apply a commercially available 25 mm wide cellophane tape, leaving one end of the tape across the slit, rubbing it with plastic or metal with a curved surface, and holding that end of the unattached tape by hand The ratio of the area where the cured film layer was peeled to the area of the tape applied from the score line was evaluated as follows. When the peeling area is 15% or more with respect to the evaluation area, it is at a low practical level.

A: Not peeled at all O: The peeling area was less than 15% with respect to the evaluation area. X: The peeling area was 15% or more with respect to the evaluation area (moire fringe elimination ability).
A video signal generator is used to input a signal to the liquid crystal display device to be evaluated, which is manufactured by the method described below, and the entire surface is displayed in gray with 128/256 gradations, and the screen is observed from various directions in a dark room. The presence or absence of moire was evaluated as follows.

◎: Moire is not observed ○: Moire can be seen only slightly depending on the direction when attention is paid.
X: Moire clearly observed (redness fluctuation under low temperature and high humidity)
About the liquid crystal display device to be evaluated, which was produced by the procedure described below, half was covered with a moisture-proof seed and left in a constant temperature and humidity chamber at 10 ° C. and 98% RH for 100 hours. Thereafter, the luminance Y and the hue u ′ are measured with a spectral radiance meter (CS-2000, manufactured by Konica Minolta) for each of the portion covered with the moisture-proof sheet and the portion not covered with the moisture-proof sheet, and the differences ΔY and Δu ′ are calculated. Asked. Each difference was judged according to the following criteria. This redness variation was used as an index of red discoloration.

A: 1 cd / m ² > ΔY and 0.0002> Δu ′
○: 5 cd / m ² >ΔY> 1 cd / m ² , 0.0005> Δu ′> 0.0002
X: ΔY ≧ 5 cd / m ² , Δu ′> 0.0005
(Evaluation of front brightness)
The light source of the liquid crystal display device to be evaluated, which was produced by the procedure described below, was turned on, installed so that the panel surface was perpendicular to the floor surface, and lit for 120 minutes in a 23 ° C. 55% RH environment. . Thereafter, the front luminance at the center of the monitor was measured in a dark room using a spectral radiance meter 8c (CS-2000, manufactured by Konica Minolta) (see FIG. 6). Here, 1c represents a liquid crystal display device of the present invention and a comparative example, and 8c represents a spectral radiance meter.

  Evaluation was performed with respect to the front luminance when a commercially available cellulose ester film 4UY (manufactured by Konica Minolta Opto Co., Ltd.) was used as the evaluation standard, and a 4UY polarizing plate produced by the same method was used for the rear polarizing plate. The ratio of the front luminance of the film was calculated and evaluated according to the following criteria.

A: 99% or more of the front luminance of 4UY ○: 90% or more of the front luminance of 4UY and less than 99% ×: Less than 90% of the front luminance of 4UY Next, a polarizing plate using the protective film for polarizing plate of the present invention A method for manufacturing a liquid crystal display device will be described.

<Preparation of polarizing plate>
(Preparation of retardation film F)
[Fine particle dispersion 1]
-Fine particles (Aerosil R972V manufactured by Nippon Aerosil Co., Ltd.) 11 parts by mass-Ethanol 89 parts by mass The above was stirred and mixed with a dissolver for 50 minutes, and then dispersed with Manton Gorin to prepare a fine particle dispersion 1.

[Fine particle addition liquid 1]
The fine particle dispersion 1 was slowly added to the dissolution tank containing methylene chloride with sufficient stirring. 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 1.

-Methylene chloride 99 mass parts-Fine particle dispersion 1 5 mass parts The dope liquid of the following composition was prepared. First, methylene chloride and ethanol were added to the pressure dissolution tank. Cellulose acetate was added to a pressurized dissolution tank containing a solvent while stirring. This was heated and stirred to dissolve completely, and this was dissolved in Azumi Filter Paper No. A dope solution was prepared by filtration using 244.

（ポリエステル化合物Ｐの合成）
窒素雰囲気下、テレフタル酸ジメチル４．８５ｇ、１，２−プロピレングリコール４．４ｇ、ｐ−トルイル酸６．８ｇ、テトライソプロピルチタネート１０ｍｇを混合し、１４０℃で２時間攪拌を行った後、更に２１０℃で１６時間攪拌を行った。次に、１７０℃まで降温し、未反応物の１，２−プロピレングリコールを減圧留去することにより、ポリエステルＰを得た。 [Composition of dope solution]
Methylene chloride 340 parts by mass Ethanol 64 parts by mass Resin (f) (cellulose acylate) 100 parts by mass Additive (3) (Structural formula 1 below) 10.0 parts by mass Polyester compound (compound P below) 2 .5 parts by mass / particulate additive solution 1 1 part by mass

(Synthesis of polyester compound P)
In a nitrogen atmosphere, 4.85 g of dimethyl terephthalate, 4.4 g of 1,2-propylene glycol, 6.8 g of p-toluic acid, and 10 mg of tetraisopropyl titanate were mixed and stirred at 140 ° C. for 2 hours. Stirring was carried out at ° C for 16 hours. Next, the temperature was lowered to 170 ° C., and unreacted 1,2-propylene glycol was distilled off under reduced pressure to obtain polyester P.

Acid value: 0.1
Number average molecular weight: 490
Dispersity: 1.4
Component content of molecular weight 300-1800: 90%
Hydroxy (hydroxyl) value: 0.1
Hydroxy group (hydroxyl group) content: 0.04%
The composition was put into a closed container and dissolved with stirring to prepare a dope solution. Next, an endless belt casting apparatus was used to uniformly cast the dope solution on a stainless steel belt support at a temperature of 33 ° C. and a width of 2000 mm. The temperature of the stainless steel belt was controlled at 30 ° C.

  On the stainless steel belt support, the solvent was evaporated until the residual solvent amount in the cast (cast) film was 75%, and then peeled off from the stainless steel belt support with a peeling tension of 130 N / m.

  Thereafter, the film is stretched using a tenter stretching apparatus, and then dried by being transported in a drying zone set at 130 ° C. for 30 minutes to have a film thickness of 40 μm having a width of 2 m, a width of 1 cm at an end, and a height of 8 μm. No. retardation film F was prepared and wound up at 5000 m.

  The retardation values Ro (590) and Rt (590) of the retardation film F were 20 nm and 110 nm, respectively.

(Preparation of polarizing plate)
A 120 μm thick polyvinyl alcohol film was uniaxially stretched (temperature: 110 ° C., stretch ratio: 5 times) to obtain a long roll film.

  This was immersed in an aqueous solution composed of 0.075 g of iodine, 5 g of potassium iodide and 100 g of water for 60 seconds, and then immersed in an aqueous solution of 68 ° C. composed of 6 g of potassium iodide, 7.5 g of boric acid and 100 g of water. This was washed with water and dried to obtain a long roll-shaped polarizer.

  Then, according to the following processes 1-5, the polarizing plate was produced by bonding the long roll-shaped polarizer, the protective film for polarizing plates to be evaluated, and the retardation film F on the back side with roll-to-roll.

  Step 1: The film was immersed in a 2 mol / L sodium hydroxide solution at 60 ° C. for 90 seconds, then washed with water and dried to obtain a protective film for polarizing plate to be evaluated in which the side to be bonded to the polarizer was saponified.

  Process 2: The said polarizer was immersed in the polyvinyl alcohol adhesive tank of 2 mass% of solid content for 1-2 seconds.

  Step 3: Excess adhesive adhered to the polarizer in Step 2 is gently wiped off, and this is placed on a layer A of polarizing plate protective films 1 to 16 to be described later subjected to saponification treatment in Step 1, and further An optical film F saponified in the same manner as in Step 1 was placed above.

Step 4: The polarizing plate protective film, the polarizer, and the retardation film F, which were laminated in Step 3, were bonded using water paste at a pressure of 20 to 30 N / cm ² and a conveyance speed of about 2 m / min.

  Step 5: A sample prepared by laminating the polarizer prepared in Step 4, the protective film for polarizing plate to be evaluated, and the retardation film F with a roll-to-roll in a dryer at 80 ° C. for 2 minutes, Produced.

  The produced polarizing plate had the layer A side of the protective film for polarizing plates to be evaluated according to the present invention adhered to the polarizer.

<Production of liquid crystal display device>
(Production of display device)
The rear side polarizing plate of a commercially available liquid crystal monitor (manufactured by Samsung, SyncMaster 743BM) was peeled off, and the polarizing plate prepared above was bonded instead. However, when bonding to the liquid crystal cell, the absorption axis of the polarizing plate faces in the same direction as the polarizing plate bonded in advance so that the retardation film F side of the polarizing plate is adjacent to the liquid crystal cell. Were pasted together. The backlight unit has a configuration of light guide plate / lower diffusion sheet / prism sheet / prism sheet in order from the light source side. In this way, a liquid crystal display device to be evaluated was produced.

  Next, production examples of the protective film for polarizing plate of the present invention and the protective film for polarizing plate for comparison will be described.

The additives used in the following examples and comparative examples are shown below.
Additive (1): MX-350 (cross-linked polymethylmethacrylate true spherical particles, average particle size 3.5 μm, manufactured by Soken Chemical Co., Ltd.)
Additive (2): Aerosil R972 (manufactured by Nippon Aerosil Co., Ltd.)
Additive (3): Structural formula 1
Additive (4): terephthalic acid / succinic acid / ethylene glycol / propylene glycol copolymer (polymerization ratio 10: 10: 11: 9)
Additive (5): Succinic acid / adipic acid / ethylene glycol copolymer (polymerization ratio 3: 2: 5)
Additive (6): UV absorber (manufactured by Tinuvin 928BASF)
Additive (7): Benzotriazole-based ultraviolet absorber (20/80 mass% mixture of TINUVIN326 / TINUVIN328, each manufactured by BASF Japan Ltd.)
The resins (a) to (j) used in the following examples and comparative examples are shown in Table 1.

まず、偏光板の低温高湿度下での赤色変色と層間密着、モアレ解消能を評価する目的で、以下の偏光板用保護フィルム１〜７を作製した。

First, the following protective films 1-7 for polarizing plates were produced for the purpose of evaluating red discoloration, interlayer adhesion, and moire eliminating ability of the polarizing plate under low temperature and high humidity.

(Comparative Example 1: Production of protective film 1 for polarizing plate)
<Dope for layer A>
[Dope composition for layer A]
Resin (c) (cellulose acylate) 100.0 parts by mass Triphenyl phosphate 8.0 parts by mass Biphenyl diphenyl phosphate 4.0 parts by mass Additive (7) 2.0 parts by mass Additive (2) 0.1 parts by mass, methylene chloride 365.5 parts by mass, methanol 54.6 parts by mass The above composition was put into a mixing tank, stirred to dissolve each component, and further heated to 90 ° C. for about 10 minutes. It filtered with the filter paper with an average hole diameter of 34 micrometers, and the sintered metal filter with an average hole diameter of 10 micrometers.

<Dope for layer B>
[Dope composition for layer B]
Resin (c) (cellulose acylate) 100.0 parts by mass Triphenyl phosphate 8.0 parts by mass Biphenyl diphenyl phosphate 4.0 parts by mass Additive (7) 2.0 parts by mass Methylene chloride 365.5 Mass part / Methanol 54.6 parts by mass The above composition was put into a mixing tank, stirred to dissolve each component, further heated to 90 ° C. for about 10 minutes, and then a filter paper having an average pore diameter of 34 μm and a calcined paper having an average pore diameter of 10 μm. It filtered with the metal filter.

<Dope for layer C>
[Dope composition for layer C]
Resin (c) (cellulose acylate) 100.0 parts by mass Triphenyl phosphate 8.0 parts by mass Biphenyl diphenyl phosphate 4.0 parts by mass Additive (7) 2.0 parts by mass Additive (1) 0.1 parts by mass, methylene chloride 365.5 parts by mass, methanol 54.6 parts by mass The above composition was put into a mixing tank, stirred to dissolve each component, and further heated to 90 ° C. for about 10 minutes. It filtered with the filter paper with an average hole diameter of 34 micrometers, and the sintered metal filter with an average hole diameter of 10 micrometers.

<Co-casting>
The dopes of the above layers A to C were co-cast simultaneously so that the film thickness after drying was 3 μm / 35 μm / 5 μm. Using the casting apparatus shown in FIG. 1, casting is performed so that the dope for layer A is mirror-finished and cooled to −10 ° C. on the metal belt side, and is cooled and gelled while volatilizing the solvent, and the web is peeled off. I took it. The film was dried with hot air at 100 ° C. until the residual solvent amount was 10% by mass, and then dried with hot air at 140 ° C. for 10 minutes to obtain a comparative protective film 1 for polarizing plate of Comparative Example 1.

<Physical properties of film>
When the surface on the layer C side of the protective film for polarizing plate of Comparative Example 1 was observed with a 3D laser microscope, irregularities derived from the fine particles were observed. The arithmetic average roughness Ra was 0.080 μm.

(Comparative Example 2: Production of protective film 2 for polarizing plate)
<Dope for layer C>
[Dope composition for layer C]
Resin (g) (cellulose acylate) 3 parts by weight Resin (d) (polymethyl methacrylate) 3 parts by weight Acetone 94 parts by weight <Layer B>
Coat film in which polyvinyl alcohol (Kuraray Co., Ltd., alkyl-modified PVA MP203) is coated on the surface of a triacetyl cellulose film (manufactured by Konica Minolta: KC4UY).

<Application>
After casting the dope for layer C on the layer B film, the layer C was left in an oven at 20 ° C. for 3 minutes to evaporate acetone to form a layer C having a thickness of 3 μm. A protective film 2 was obtained.

<Physical properties of film>
When the surface on the layer C side was observed with a 3D laser microscope, a sea-island structure was formed. The arithmetic average roughness Ra was 0.540 μm.

(Comparative Example 3: Production of protective film 3 for polarizing plate)
<Dope for layer B>
[Dope composition for layer B]
-Resin (h) (cellulose acylate) 100.0 parts by mass-Additive (4) 18.5 parts by mass-Methylene chloride 365.5 parts by mass-Methanol 54.6 parts by mass The above composition was put into a mixing tank. Each component was dissolved by stirring, and further heated to 90 ° C. for about 10 minutes, and then filtered through a filter paper having an average pore size of 34 μm and a sintered metal filter having an average pore size of 10 μm.

<Dope for layer C and layer A>
[Dope composition for layer C and layer A]
Resin (e) (cellulose acylate) 100.0 parts by mass Additive (4) 11.0 parts by mass Additive (2) 0.2 parts by mass Methylene chloride 365.5 parts by mass Methanol 54.6 Part by mass The above composition was put into a mixing tank, stirred to dissolve each component, further heated to 90 ° C. for about 10 minutes, and then filtered through a filter paper having an average pore size of 34 μm and a sintered metal filter having an average pore size of 10 μm.

<Co-casting>
The protective film 3 for a polarizing plate for comparison in Comparative Example 3 was prepared by co-casting the dope for layer B, the dope for layer C, and the dope for layer A so as to have a film thickness ratio of 57/1/1. Got.

<Extension>
The obtained web (film) was peeled off from the band, sandwiched between clips, and when the residual solvent amount relative to the mass of the entire film was 30 to 5%, it was 172 ° C. using a tenter under the conditions of fixed-end uniaxial stretching. The film was stretched 1.32 times in the direction (lateral direction) perpendicular to the film transport direction. Thereafter, the clip was removed from the film and dried at 130 ° C. for 20 minutes.

<Physical properties of film>
The obtained Comparative Example 3 film had a total Hz of 0.52 and an internal Hz of 0.02. When the surface on the layer C side was observed with a 3D laser microscope, slight irregularities derived from the fine particles were observed, and the arithmetic average roughness Ra was 0.020 μm.

(Example 1: Production of protective film 4 for polarizing plate)
<Dope for layer A>
[Dope composition for layer A]
Resin (g) (cellulose acylate) 100.0 parts by mass Additive (5) 7.0 parts by mass Methylene chloride 365.5 parts by mass Methanol 54.6 parts by mass The above composition was put into a mixing tank. Each component was dissolved by stirring, and further heated to 90 ° C. for about 10 minutes, and then filtered through a filter paper having an average pore size of 34 μm and a sintered metal filter having an average pore size of 10 μm.

<Dope for layer B>
[Dope composition for layer B]
Resin (g) (cellulose acylate) 100.0 parts by mass Additive (5) 7.0 parts by mass Methylene chloride 365.5 parts by mass Methanol 54.6 parts by mass The above composition was put into a mixing tank. Each component was dissolved by stirring, and further heated to 90 ° C. for about 10 minutes, and then filtered through a filter paper having an average pore size of 34 μm and a sintered metal filter having an average pore size of 10 μm.

<Dope for layer C>
[Dope composition for layer C]
Resin (a) (cellulose acylate) 75.0 parts by mass Resin (b) (cellulose acylate) 25.0 parts by mass Additive (5) 7.0 parts by mass Methylene chloride 365.5 parts by mass Methanol 54.6 parts by mass The above composition was put into a mixing tank, stirred to dissolve each component, further heated to 90 ° C. for about 10 minutes, and then a filter paper having an average pore size of 34 μm and a sintered metal filter having an average pore size of 10 μm. And filtered.

<Co-casting and stretching>
The dopes of the layers A to C are co-cast simultaneously so that the film thickness after drying is A / B / C is 3/35/5, and stretched in the transverse direction by 10% at 160 ° C. using a tenter, The protective film 4 for polarizing plates of the present invention of Example 1 was obtained.

<Physical properties of film>
When the surface on the layer C side of the obtained protective film for polarizing plate of Example 1 was observed with a 3D laser microscope, irregularities due to the sea-island structure were observed. The arithmetic average roughness Ra was 0.330 μm.

(Comparative Example 4: Production of protective film 5 for polarizing plate)
<Dope for layer A>
[Dope composition for layer A]
Resin (g) (cellulose acylate) 100.0 parts by mass Additive (5) 7.0 parts by mass Methylene chloride 365.5 parts by mass Methanol 54.6 parts by mass The above composition was put into a mixing tank. Each component was dissolved by stirring, and further heated to 90 ° C. for about 10 minutes, and then filtered through a filter paper having an average pore size of 34 μm and a sintered metal filter having an average pore size of 10 μm.

<Dope for layer B>
[Dope composition for layer B]
Resin (g) (cellulose acylate) 100.0 parts by mass Additive (5) 7.0 parts by mass Methylene chloride 365.5 parts by mass Methanol 54.6 parts by mass The above composition was put into a mixing tank. Each component was dissolved by stirring, and further heated to 90 ° C. for about 10 minutes, and then filtered through a filter paper having an average pore size of 34 μm and a sintered metal filter having an average pore size of 10 μm.

<Dope for layer C>
[Dope composition for layer C]
Resin (c) (cellulose acylate) 75.0 parts by mass Resin (b) (cellulose acylate) 25.0 parts by mass Additive (5) 7.0 parts by mass Methylene chloride 365.5 parts by mass Methanol 54.6 parts by mass The above composition was put into a mixing tank, stirred to dissolve each component, further heated to 90 ° C. for about 10 minutes, and then a filter paper having an average pore size of 34 μm and a sintered metal filter having an average pore size of 10 μm. And filtered.

<Co-casting and stretching>
The dopes of the layers A to C were co-cast simultaneously so that the film thickness after drying was A / B / C was 3/35/5, and stretched in the transverse direction by 10% at 180 ° C. using a tenter, A protective film 5 for polarizing plate for comparison in Comparative Example 4 was obtained.

<Physical properties of film>
When the surface on the layer C side of the obtained protective film for polarizing plate of Comparative Example 4 was observed with a 3D laser microscope, no unevenness was observed. The arithmetic average roughness Ra was 0.010 μm.

(Comparative Example 5: Production of protective film 6 for polarizing plate)
<Dope for layer A>
[Dope composition for layer A]
Resin (g) (cellulose acylate) 100.0 parts by mass Additive (5) 7.0 parts by mass Methylene chloride 365.5 parts by mass Methanol 54.6 parts by mass The above composition was put into a mixing tank. Each component was dissolved by stirring, and further heated to 90 ° C. for about 10 minutes, and then filtered through a filter paper having an average pore size of 34 μm and a sintered metal filter having an average pore size of 10 μm.

<Dope for layer B>
[Dope composition for layer B]
Resin (g) (cellulose acylate) 100.0 parts by mass Additive (5) 7.0 parts by mass Methylene chloride 365.5 parts by mass Methanol 54.6 parts by mass The above composition was put into a mixing tank. Each component was dissolved by stirring, and further heated to 90 ° C. for about 10 minutes, and then filtered through a filter paper having an average pore size of 34 μm and a sintered metal filter having an average pore size of 10 μm.

<Dope for layer C>
[Dope composition for layer C]
Resin (a) (cellulose acylate) 75.0 parts by mass Resin (f) (cellulose acylate) 25.0 parts by mass Additive (5) 7.0 parts by mass Methylene chloride 365.5 parts by mass Methanol 54.6 parts by mass The above composition was put into a mixing tank, stirred to dissolve each component, further heated to 90 ° C. for about 10 minutes, and then a filter paper having an average pore size of 34 μm and a sintered metal filter having an average pore size of 10 μm. And filtered.

<Co-casting and stretching>
The dopes of the layers A to C were co-cast simultaneously so that the film thickness after drying was A / B / C was 3/35/5, and stretched in the transverse direction by 5% at 160 ° C. using a tenter, A comparative protective film 6 for polarizing plate of Comparative Example 5 was obtained.

<Physical properties of film>
When the surface on the layer C side of the obtained protective film for polarizing plate of Comparative Example 5 was observed with a 3D laser microscope, irregularities due to the sea-island structure were observed. The arithmetic average roughness Ra was 0.040 μm.

(Comparative Example 6: Production of protective film 7 for polarizing plate)
<Dope for layer A>
[Dope composition for layer A]
Resin (g) (cellulose acylate) 100.0 parts by mass Additive (5) 7.0 parts by mass Methylene chloride 365.5 parts by mass Methanol 54.6 parts by mass The above composition was put into a mixing tank. Each component was dissolved by stirring, and further heated to 90 ° C. for about 10 minutes, and then filtered through a filter paper having an average pore size of 34 μm and a sintered metal filter having an average pore size of 10 μm.

<Dope for layer B>
[Dope composition for layer B]
Resin (g) (cellulose acylate) 100.0 parts by mass Additive (5) 7.0 parts by mass Methylene chloride 365.5 parts by mass Methanol 54.6 parts by mass The above composition was put into a mixing tank. Each component was dissolved by stirring, and further heated to 90 ° C. for about 10 minutes, and then filtered through a filter paper having an average pore size of 34 μm and a sintered metal filter having an average pore size of 10 μm.

<Dope for layer C>
[Dope composition for layer C]
Resin (d) (polymethyl methacrylate) 75.0 parts by mass Resin (f) (cellulose acylate) 25.0 parts by mass Methylene chloride 260.7 parts by mass Methanol 35.7 parts by mass The mixture was put into a mixing tank, stirred to dissolve each component, further heated to 90 ° C. for about 10 minutes, and then filtered through a filter paper having an average pore size of 34 μm and a sintered metal filter having an average pore size of 10 μm.

<Co-casting and stretching>
The dopes of the layers A to C are co-cast simultaneously so that the film thickness after drying is A / B / C is 3/35/5, and stretched in the transverse direction by 10% at 140 ° C. using a tenter, A protective film 7 for comparative polarizing plate 7 of Comparative Example 6 was obtained.

<Physical properties of film>
When the surface on the layer C side of the obtained protective film for polarizing plate of Comparative Example 6 was observed with a 3D laser microscope, irregularities due to the sea-island structure were observed. The arithmetic average roughness Ra was 0.500 μm.

比較例１では、微粒子を用いて層Ｃの凹凸を形成しているために、これを用いた偏光板は低温高湿環境下において赤色に変色してしまった。 A polarizing plate and a liquid crystal display device were prepared by the above-described methods using the protective films 1 to 7 for the polarizing plate produced as described above, and evaluated for redness fluctuation under low temperature and high humidity, interlayer adhesion, and moire fringe elimination ability. did. The results are shown in Table 2.

In Comparative Example 1, since the unevenness of the layer C was formed using fine particles, the polarizing plate using the layer C was changed to red in a low temperature and high humidity environment.

  In Comparative Example 2, since the scattering layer of layer C was provided by coating, the interlayer adhesion of the polarizing plate protective film was poor. Further, since the scattering layer contains a non-cellulose ester, the polarizing plate using the protective film for polarizing plate has undergone redness variation, that is, red discoloration in a low temperature and high humidity environment.

  In Comparative Example 3, although slight unevenness due to the fine particles was observed, the scattering ability was insufficient for eliminating moire. Also, the color was slightly changed to red under low temperature and high humidity due to the fine particles.

  In Comparative Example 4, the layer C of the protective film for a polarizing plate did not form a sea-island structure, so the moire eliminating ability was not obtained.

  In Comparative Example 5, although the layer C of the protective film for polarizing plate formed a sea-island structure, the arithmetic average roughness Ra was too small, so that sufficient moire eliminating ability was not obtained.

  In Comparative Example 6, since the layer C contains a non-cellulose ester, the moisture permeability was uneven, and the color changed to red under a low temperature and high humidity environment.

  From the above results, the protective film for polarizing plate of the present invention has superior performance in terms of red discoloration under low temperature and high humidity, interlayer adhesion, and moire fringe elimination ability, compared with the protective film for polarizing plate for comparison. I understand that

  Next, due to the difference in cellulose ester species and mixing ratio used in layer A, layer B, and layer C, the red color change and interlayer adhesion of the polarizing plate under low temperature and high humidity, the moire eliminating ability when used as a display device, and the front luminance. The following films 8 to 17 were prepared for the purpose of evaluation.

(Example 2: Production of protective film 8 for polarizing plate)
<Dope for layer A>
[Dope composition for layer A]
Resin (c) (cellulose acylate) 100.0 parts by mass Additive (5) 7.0 parts by mass Methylene chloride 365.5 parts by mass Methanol 54.6 parts by mass The above composition was charged into a mixing tank. Each component was dissolved by stirring, and further heated to 90 ° C. for about 10 minutes, and then filtered through a filter paper having an average pore size of 34 μm and a sintered metal filter having an average pore size of 10 μm.

<Dope for layer B>
[Dope composition for layer B]
Resin (b) (cellulose acylate) 100.0 parts by mass Additive (5) 7.0 parts by mass Methylene chloride 365.5 parts by mass Methanol 54.6 parts by mass The above composition was put into a mixing tank. Each component was dissolved by stirring, and further heated to 90 ° C. for about 10 minutes, and then filtered through a filter paper having an average pore size of 34 μm and a sintered metal filter having an average pore size of 10 μm.

<Dope for layer C>
[Dope composition for layer C]
Resin (i) (cellulose acylate) 60.0 parts by mass Resin (b) (cellulose acylate) 40.0 parts by mass Additive (5) 7.0 parts by mass Methylene chloride 365.5 parts by mass 54.6 parts by mass of methanol CE (I) is the resin (i), CE (II) is the resin (b), and the propionyl group substitution degree Pr (I) of CE (I) is (Y), and CE (II ) Of acetyl group substitution degree Ac (II) and propionyl group substitution degree Pr (II) × 2 (X) was X ≦ Y.
X = 2 × Pr (II) + Ac (II)
Y = 0.7 × Pr (I) +1.7
The above composition was put into a mixing tank, stirred to dissolve each component, further heated to 90 ° C. for about 10 minutes, and then filtered through a filter paper having an average pore size of 34 μm and a sintered metal filter having an average pore size of 10 μm.

<Co-casting and stretching>
The dopes of the layers A to C were co-cast simultaneously so that the film thickness after drying was A / B / C was 3/35/5, and stretched in the transverse direction by 10% at 180 ° C. using a tenter, The protective film 8 for polarizing plates of this invention of Example 2 was obtained.

<Physical properties of film>
When the surface on the layer C side of the obtained protective film for polarizing plate of Example 2 was observed with a 3D laser microscope, irregularities due to the sea-island structure were observed. The arithmetic average roughness Ra of the surface on the layer C side was 0.350 μm, and the average length RSm of the roughness curve element was 38.0 μm. The internal haze value was 2.00.

( Reference example : production of protective film 9 for polarizing plate)
<Dope for layer A>
It was prepared in the same way with the same composition as in Example 2.

<Dope for layer B>
It was prepared in the same way with the same composition as in Example 2.

<Dope for layer C>
It was prepared in the same manner as in Example 2 except that the resin (i) was 55 parts by mass and the resin (b) was 45 parts by mass.

CE (I) is resin (i), CE (II) is resin (b), and the propionyl substitution degree Pr (I) of CE (I) is (Y), and the acetyl substitution degree Ac of CE (II) is Ac. The relationship between (II) and the sum (X) of propionyl substitution degree Pr (II) × 2 was X ≦ Y.
X = 2 × Pr (II) + Ac (II)
Y = 0.7 × Pr (I) +1.7
<Co-casting and stretching>
The dopes of the layers A to C were co-cast simultaneously so that the film thickness after drying was A / B / C was 3/35/5, and stretched in the transverse direction by 10% at 180 ° C. using a tenter, The protective film 9 for polarizing plates of the reference example was obtained.

<Physical properties of film>
When the surface on the layer C side of the obtained protective film for polarizing plate of Example 3 was observed with a 3D laser microscope, irregularities due to the sea-island structure were observed. The arithmetic average roughness Ra of the surface on the layer C side was 0.480 μm, and the average length RSm of the roughness curve element was 42.0 μm. The internal haze value was 2.40.

(Example 4: Production of protective film 10 for polarizing plate)
<Dope for layer A>
It was prepared in the same way with the same composition as in Example 2.

<Dope for layer B>
It was prepared in the same way with the same composition as in Example 2.

<Dope for layer C>
It was prepared in the same manner as in Example 2 except that the resin (i) was 95 parts by mass and the resin (b) was 5 parts by mass.

CE (I) is the resin (i), CE (II) is the resin (b), and the CE (I) propionyl group substitution degree Pr (I) (Y) and CE (II) acetyl group substitution The relationship between the degree Ac (II) and the sum of propionyl group substitution degree Pr (II) × 2 (X) was X ≦ Y.
X = 2 × Pr (II) + Ac (II)
Y = 0.7 × Pr (I) +1.7
<Co-casting and stretching>
The dopes of the above layers A to C were simultaneously co-cast so that the film thickness A / B / C after drying was 3/35/5, and stretched in the transverse direction by 10% at 180 ° C. using a tenter. The protective film 10 for polarizing plates of Example 4 of the present invention was obtained.

<Physical properties of film>
When the surface on the layer C side of the obtained protective film for polarizing plate of Example 4 was observed with a 3D laser microscope, irregularities due to the sea-island structure were observed. The arithmetic average roughness Ra of the surface on the layer C side was 0.050 μm, and the average length RSm of the roughness curve element was 5.1 μm. The internal haze value was 0.08.

(Comparative Example 7: Production of protective film 11 for polarizing plate)
<Dope for layer A>
It was prepared in the same way with the same composition as in Example 2.

<Dope for layer B>
It was prepared in the same way with the same composition as in Example 2.

<Dope for layer C>
It was prepared in the same manner as in Example 2 except that the resin (i) was 97 parts by mass and the resin (b) was 3 parts by mass.

CE (I) is the resin (i), CE (II) is the resin (b), and the CE (I) propionyl group substitution degree Pr (I) (Y) and CE (II) acetyl group substitution The relationship between the degree Ac (II) and the sum of propionyl group substitution degree Pr (II) × 2 (X) was X ≦ Y.
X = 2 × Pr (II) + Ac (II)
Y = 0.7 × Pr (I) +1.7
<Co-casting and stretching>
The dopes of the layers A to C were co-cast simultaneously so that the film thickness after drying was A / B / C was 3/35/5, and stretched in the transverse direction by 10% at 180 ° C. using a tenter, A comparative polarizing plate protective film 11 of Comparative Example 7 was obtained.

<Physical properties of film>
When the surface on the layer C side of the obtained protective film for polarizing plate of Comparative Example 7 was observed with a 3D laser microscope, irregularities due to the sea-island structure were not observed. The arithmetic average roughness Ra of the surface on the layer C side was 0.003 μm, and the average length RSm of the roughness curve element was 2.0 μm. The internal haze value was 0.02.

(Comparative Example 8: Production of protective film 12 for polarizing plate)
<Dope for layer A>
It was prepared in the same way with the same composition as in Example 2.

<Dope for layer B>
It was prepared in the same way with the same composition as in Example 2.

<Dope for layer C>
It prepared like Example 2 except having replaced resin (i) and resin (b) with 70 mass parts of resin (i), and 30 mass parts of resin (j).

CE (I) is resin (i), CE (II) is resin (j), and CE (I) is composed of propionyl group substitution degree Pr (I), and CE (II) is substituted with acetyl group. The relationship between the degree Ac (II) and the sum of propionyl group substitution degree Pr (II) × 2 (X) was X> Y.
X = 2 × Pr (II) + Ac (II)
Y = 0.7 × Pr (I) +1.7
<Co-casting and stretching>
The dopes of the layers A to C were co-cast simultaneously so that the film thickness after drying was A / B / C was 3/35/5, and stretched in the transverse direction by 10% at 180 ° C. using a tenter, A protective film 12 for polarizing plate for comparison in Comparative Example 8 was obtained.

<Physical properties of film>
When the surface on the layer C side of the protective film for polarizing plate of Comparative Example 8 obtained was observed with a 3D laser microscope, the unevenness due to the sea-island structure was not observed. The arithmetic average roughness Ra of the surface on the layer C side was 0.004 μm, and the average length RSm of the roughness curve element was 2.1 μm. The internal haze value was 0.01.

(Example 5: Preparation of polarizing plate protective film 13) <Dope for layer A>
The same composition as in Example 2 was prepared in the same manner except that the additive was changed from (5) to (3).

<Dope for layer B>
The same composition as in Example 2 was prepared in the same manner except that the additive was changed from (5) to (3).

<Dope for layer C>
Instead of the resin (i) and the resin (b), the resin (a) is changed to 95 parts by mass, the resin (f) is changed to 5 parts by mass, and the additive is changed from (5) to (3). Prepared in the same manner as Example 2.

CE (I) is resin (a), CE (II) is resin (f), and CE (I) has propionyl group substitution degree Pr (I) (CE) and CE (II) acetyl group substitution The relationship between the degree Ac (II) and the sum of propionyl group substitution degree Pr (II) × 2 (X) was X ≦ Y.
X = 2 × Pr (II) + Ac (II)
Y = 0.7 × Pr (I) +1.7
<Co-casting and stretching>
The dopes of the layers A to C are co-cast simultaneously so that the film thickness after drying is A / B / C is 3/35/5, and stretched in the transverse direction by 10% at 160 ° C. using a tenter, The protective film 13 for polarizing plates of this invention of Example 5 was obtained.

<Physical properties of film>
When the surface of the protective film for polarizing plate of Example 5 obtained on the layer C side was observed with a 3D laser microscope, irregularities due to the sea-island structure were observed. The arithmetic average roughness Ra of the surface on the layer C side was 0.060 μm, and the average length RSm of the roughness curve element was 4.5 μm. The internal haze value was 0.08.

(Example 6: Production of protective film 14 for polarizing plate)
<Dope for layer A>
The same composition as in Example 5 was prepared in the same manner.

<Dope for layer B>
The same composition as in Example 5 was prepared in the same manner.

<Dope for layer C>
Example 5 except that 70 parts by mass of resin (i), 30 parts by mass of resin (b), 10 parts by mass of additive (3), and 2.3 parts by mass of additive (6) were added. Prepared in the same way.

CE (I) is the resin (i), CE (II) is the resin (b), and the CE (I) propionyl group substitution degree Pr (I) (Y) and CE (II) acetyl group substitution The relationship between the degree Ac (II) and the sum of propionyl group substitution degree Pr (II) × 2 (X) was X ≦ Y.
X = 2 × Pr (II) + Ac (II)
Y = 0.7 × Pr (I) +1.7
<Co-casting and stretching>
The dopes of the layers A to C are co-cast simultaneously so that the film thickness after drying is A / B / C is 3/35/5, and stretched in the transverse direction by 10% at 170 ° C. using a tenter, The protective film 14 for polarizing plates of the present invention of Example 6 was obtained.

<Physical properties of film>
When the surface of the protective film for polarizing plate of Example 6 obtained on the layer C side was observed with a 3D laser microscope, irregularities due to the sea-island structure were observed. The arithmetic average roughness Ra of the surface on the layer C side was 0.520 μm, and the average length RSm of the roughness curve element was 40.0 μm. The internal haze value was 5.20.

(Example 7: Production of protective film 15 for polarizing plate)
<Dope for layer A>
The same composition as in Example 6 was prepared in the same manner.

<Dope for layer B>
The same composition as in Example 6 was prepared in the same manner.

<Dope for layer C>
It was prepared in the same manner as in Example 5 except that the resin (i) was 80 parts by mass and the resin (b) was 20 parts by mass.

CE (I) is the resin (i), CE (II) is the resin (b), and the CE (I) propionyl group substitution degree Pr (I) (Y) and CE (II) acetyl group substitution The relationship between the degree Ac (II) and the sum of propionyl group substitution degree Pr (II) × 2 (X) was X ≦ Y.
X = 2 × Pr (II) + Ac (II)
Y = 0.7 × Pr (I) +1.7
<Co-casting and stretching>
The dopes of the layers A to C are co-cast simultaneously so that the film thickness after drying is A / B / C is 3/35/5, and stretched in the transverse direction by 10% at 170 ° C. using a tenter, A protective film 15 for polarizing plate of the present invention of Example 7 was obtained.

<Physical properties of film>
When the surface on the layer C side of the obtained protective film for polarizing plate of Example 7 was observed with a 3D laser microscope, irregularities due to the sea-island structure were observed. The arithmetic average roughness Ra of the surface on the layer C side was 0.260 μm, and the average length RSm of the roughness curve element was 10.5 μm. The internal haze value was 0.06.

(Example 8: Production of protective film 16 for polarizing plate)
<Dope for layer A>
The same composition as in Example 7 was prepared in the same manner except that the resin (b) (cellulose acylate) was used instead of the resin (c) (cellulose acylate).

<Dope for layer B>
It was prepared in the same way with the same composition as in Example 7.

<Dope for layer C>
It was prepared in the same manner as in Example 7 except that the resin (i) was 70 parts by mass and the resin (b) was 30 parts by mass.

CE (I) is the resin (i), CE (II) is the resin (b), and the CE (I) propionyl group substitution degree Pr (I) (Y) and CE (II) acetyl group substitution The relationship between the degree Ac (II) and the sum of propionyl group substitution degree Pr (II) × 2 (X) was X ≦ Y.
X = 2 × Pr (II) + Ac (II)
Y = 0.7 × Pr (I) +1.7
<Co-casting and stretching>
The dopes of the layers A to C are co-cast simultaneously so that the film thickness after drying is A / B / C is 3/35/5, and stretched in the transverse direction by 10% at 170 ° C. using a tenter, The protective film 16 for polarizing plates of this invention of Example 8 was obtained.

<Physical properties of film>
When the surface of the protective film for polarizing plate of Example 8 obtained on the layer C side was observed with a 3D laser microscope, irregularities due to the sea-island structure were observed. The arithmetic average roughness Ra of the surface on the layer C side was 0.120 μm, and the average length RSm of the roughness curve element was 21.0 μm. The internal haze value was 0.40.

(Example 9: Preparation of polarizing plate protective film 17) <Dope for layer A>
The same composition as in Example 8 was prepared in the same manner except that the resin (j) was used instead of the resin (b).

<Dope for layer B>
The same composition as in Example 8 was prepared in the same manner except that the resin (h) was used instead of the resin (b).

<Dope for layer C>
It was prepared in the same manner as in Example 8 except that the resin (a) was replaced by 60 parts by mass and the resin (b) was replaced by 40 parts by mass instead of the resin (i).

CE (I) is resin (a), CE (II) is resin (h), and CE (I) has propionyl group substitution degree Pr (I) (CE) and CE (II) acetyl group substitution The relationship between the degree Ac (II) and the sum of propionyl group substitution degree Pr (II) × 2 (X) was X ≦ Y.
X = 2 × Pr (II) + Ac (II)
Y = 0.7 × Pr (I) +1.7
<Co-casting and stretching>
The dopes of the layers A to C were co-cast simultaneously so that the film thickness after drying was A / B / C was 3/35/5, and stretched in the transverse direction by 10% at 180 ° C. using a tenter, The protective film 17 for polarizing plates of this invention of Example 9 was obtained.

<Physical properties of film>
When the surface on the layer C side of the obtained protective film for polarizing plate of Example 9 was observed with a 3D laser microscope, irregularities due to the sea-island structure were observed. The arithmetic average roughness Ra of the surface on the layer C side was 0.200 μm, and the average length RSm of the roughness curve element was 39.0 μm. The internal haze value was 1.40.

比較例７では、偏光板用保護フィルムの層ＣのＣＥ（Ｉ）とＣＥ（II）の比率が９７／３であるため海島構造を形成せず、表示装置にしたときのモアレ解消能が不十分であった。また、比較例８では、Ｃ層のＸとＹの関係が、Ｘ＞Ｙであったために、海島構造を形成せず、表示装置にしたときのモアレ解消能が不十分であった。 About the protective films 8-17 for polarizing plates produced as mentioned above, internal haze, low-temperature, high-humidity redness fluctuation, interlayer adhesion, moire fringe eliminating ability, and front luminance were evaluated. The results are shown in Table 3.

In Comparative Example 7, since the ratio of CE (I) and CE (II) of layer C of the protective film for polarizing plate is 97/3, the sea-island structure is not formed, and the moire eliminating ability when used as a display device is not good. It was enough. In Comparative Example 8, since the relationship between X and Y of the C layer was X> Y, the sea-island structure was not formed, and the moire eliminating ability when the display device was used was insufficient.

  On the other hand, it turns out that the protective film for polarizing plates of this invention, the polarizing plate provided with the same, and a display apparatus have the outstanding performance in any evaluation item.

70 Casting membrane 85 Support (metal belt or metal drum)
120 layer B dope 121 layer C dope 122 layer A dope 120a layer B
121a Layer C
122a Layer A
t1 Layer B thickness t2 Layer A thickness t3 Layer C thickness 1 Dissolution kettle 3, 6, 12, 15 Filter 1, 4, 13 Stock tank 5, 14 Feed pump 8, 16 Conduit 17 Three-way valve DESCRIPTION OF SYMBOLS 10 Ultraviolet absorber preparation pot 20 Merge pipe 21 Mixer 30 Die 31 Support body 32 Web 33 Peeling position 34 Tenter stretcher 35 Roll dryer 37 Winder 41 Particle preparation tank 42 Stock tank 43 Pump 44 Filter 1a Light source 2a Light emission Light source 3a Lower diffusion sheet (or diffusion plate)
4a Light collecting sheet (prism sheet, lens sheet)
5a Upper diffusion sheet 6a Backlight unit 7a Liquid crystal cell 8a Transparent substrate (glass, plastic)
9a Protective film (or retardation film)
10a Polarizer 11a Protective film 12a Liquid crystal panel 13a Light guide plate 14a Protective film for polarizing plate of the present invention (light diffusion film)
A layer A
B layer B
C layer C
s Sea i Island 1c Liquid crystal display device 8c Spectral radiance meter

Claims (7)

A film having at least a three-layer structure that is adjacent in the order of layer A, layer B, and layer C, wherein the layer A, the layer B, and the layer C contain at least cellulose acylate and are contained in the layer B The cellulose acylate satisfies the following formula (1), and the layer C has a sea-island structure in which two types of cellulose acylate are mixed, and the two types of cellulose acylate constituting the layer C The value of the mixing ratio of CE (I) and CE (II) CE (I) / CE (II) is in the range of 60/40 to 95/5, and the degree of propionyl group substitution of CE (I) is Pr ( When the substitution degree of acetyl group of I) and CE (II) is Ac (II) and the substitution degree of propionyl group is Pr (II), X and Y represented by the following formulas (2) and (3) are satisfies X ≦ Y within the Pr (I) ≧ 0.5, and the arithmetic mean of the layer C side of the surface Protective film for a polarizing plate, wherein the Ra is in the range of 0.05 to 2.0.
Formula (1): ZB ≧ 2.0
(However, ZB represents the total acyl group substitution degree of the cellulose acylate contained in the layer B.)
Formula (2): X = 2 × Pr (II) + Ac (II)
Formula (3): Y = 0.7 × Pr (I) +1.7 2. The protective film for polarizing plate according to claim 1, wherein an average length RSm of a roughness curve element on the surface of the layer C side is in a range of 5 to 40 μm. The protective film for polarizing plates according to claim 1 or 2, wherein an internal haze value of the protective film for polarizing plates is in a range of 0.08 to 5.0. The protective film for polarizing plates according to any one of claims 1 to 3 , wherein the cellulose acylate contained in the layer A satisfies the following formula (4).
Formula (4): ZA ≧ 2.7
(However, ZA represents the total acyl group substitution degree of cellulose acylate contained in layer A.) It is a manufacturing method of the polarizing film protective film which manufactures the protective film for polarizing plates as described in any one of Claims 1-4 , Comprising: Dope of the said layer A, the layer B, and the layer C is co-casting A method for producing a protective film for a polarizing plate, comprising a step of forming a web and a stretching step of stretching the web. A polarizing plate comprising the protective film for a polarizing plate according to any one of claims 1 to 4 . A liquid crystal display device comprising the polarizing plate according to claim 6 .

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