JP4640065B2 - Manufacturing method of polarizing plate protective film, polarizing plate and liquid crystal display device - Google Patents

Description

  The present invention relates to a polarizing plate protective film, a production method thereof, a polarizing plate and a liquid crystal display device.

  A polarizing plate protective film is used for the purpose of protecting the polarizer. This polarizing plate protective film is a polarizing plate having a structure in which both surfaces of a polarizer are sandwiched. Conventionally, the display quality of a liquid crystal display device has been improved by using an optical compensation film having a retardation film attached thereto as a viewing angle compensation film. In recent years, the function of a retardation film has been fused with a polarizing plate protective film, and the role of the protective film has become multifunctional and the number of members can be reduced.

  On the other hand, viewing angle compensation is improving in the display quality of liquid crystal display devices, and discotic liquid crystal films are placed on the upper and lower surfaces of twisted nematic (TN) type liquid crystal cells to improve the viewing angle characteristics of liquid crystal cells. It is disclosed that it can be performed (for example, refer patent document 1).

  A technique for improving the viewing angle by improving the liquid crystal mode is a liquid crystal using a vertical alignment (VA) type liquid crystal cell in which a liquid crystal compound is aligned substantially vertically when no voltage is applied and is aligned substantially horizontally when a voltage is applied. A display device is disclosed (for example, see Patent Document 2). The VA type liquid crystal is characterized by having a wide viewing angle and a high speed response as compared with the conventional TN type liquid crystal display device. However, the VA type liquid crystal still needs improvement as compared with the CRT.

  The VA liquid crystal display device performs black display by a liquid crystal layer that is substantially vertically aligned and a pair of polarizing plates that are opposed to each other through the liquid crystal layer and arranged in a crossed Nicols state. When this is observed from the surface normal direction, a good black display is obtained. However, when observed from a direction inclined from the display surface normal (hereinafter referred to as “oblique viewing angle direction”), light leakage occurs and black display occurs. The quality of

  This light leakage in the oblique viewing angle direction causes birefringence when the vertically aligned liquid crystal layer is observed from the oblique viewing angle direction, and the transmission axes of the pair of polarizing plates arranged in the crossed Nicols state are in the oblique viewing angle direction. When observed from the above, it is caused by deviation from the relationship orthogonal to each other.

  With regard to a method for compensating the display quality of the viewing angle from these optical viewpoints, for example, Patent Document 3 discloses a design value of a compensation film in an MVA liquid crystal display device which is a multi-domain divided VA type. However, in Patent Document 3, the disclosure of a liquid crystal display device using a polarizing plate provided with an optical compensation film produced using a specific resin, and the polarizing plate protective film itself functions as an optical compensation film in viewing angle compensation. There is no disclosure of a liquid crystal display device including a polarizing plate having an integral protective film having both of the above. In recent years, development of a liquid crystal display device including a polarizing plate with improved display quality and excellent productivity has been desired in response to an increase in demand for a liquid crystal display device for TV mainly for moving images.

  On the other hand, the polarizer of the polarizing plate is obtained by adsorbing and stretching iodine or the like on a polymer film. That is, a solution called H ink containing a dichroic substance (iodine) is wet-adsorbed on a polyvinyl alcohol film, and then the film is uniaxially stretched to orient the dichroic substance in one direction. It is.

  As a protective film for the polarizing plate, cellulose triacetate is used among cellulose resins, particularly cellulose acetate.

  Generally, a polarizing plate protective film composed of a cellulose resin is physically used for protecting the polarizing plate. However, since the film production method is a film production method by a solution casting method using a halogen-based solvent, the cost required for solvent recovery has been a very heavy burden. For this reason, a variety of solvents other than halogen-based solvents were tested, but there was no substitute with satisfactory solubility. In addition to the alternative solvent, a new dissolution method such as a cooling method has been tried (see, for example, Patent Document 4), but industrial realization is difficult and further investigation is required.

  Conventionally, when a film is produced using a cellulose resin as a material for a polarizing plate protective film, there is a so-called solution casting method in which a solution in which the resin is dissolved in a solvent is cast, and then the solvent is evaporated and dried. Has been done. In the solution casting method, the solvent remaining inside the film must be removed, so that the capital investment and production cost for the production line such as the drying line, the drying energy, and the recovery and regeneration device for the evaporated solvent become enormous. Therefore, reducing them is an important issue.

  Therefore, if there is no solvent to be evaporated and dried at the time of film formation, it can be expected that the problems of the solution casting method can be avoided.

In order to improve this point, a film forming method by a melt casting method has been proposed (see Patent Document 5). However, production of a polarizing plate protective film by the melt casting method is difficult and has not yet been put into practical use. In particular, it was found that deterioration of the film surface property due to lip adhesion contamination at the extruded portion, breakage of the slitting portion during stretching or the like are likely to occur, and these improvements are necessary.
Japanese Patent Laid-Open No. 7-191217 JP-A-2-176625 JP 2003-262869 A Japanese Patent Laid-Open No. 10-95861 JP 2000-352620 A

  An object of the present invention is a polarizing plate protective film that is manufactured by a melt casting method that does not use a solvent during film formation, has little lip adhesion contamination of an extruder, and has little breakage at the slitting part during and after hot stretching. And a manufacturing method thereof, a polarizing plate using the polarizing plate protective film, and a liquid crystal display device with improved display quality using the polarizing plate.

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

(1) The total substitution degree of acyl groups is 2.5 to 2.9, the content of alkaline earth metal is 1 to 50 ppm, and the content of residual sulfuric acid (as the content of sulfur element) is 0.1 to 45 ppm. A film-forming material containing cellulose resin, 0.01% by mass or more and 5% by mass or less of a hindered amine compound or a hindered phenol compound and a plasticizer is heated and melted and extruded, and then the film obtained by cooling is heated again. A method for producing a polarizing plate protective film, characterized by cooling after hot stretching.

(2) The alkaline earth metal content of the cellulose resin is 1 to 30 ppm, the residual sulfuric acid content (as the content of sulfur element) is 0.1 to 30 ppm, and the free acid content is 1 to 70 ppm. The manufacturing method of the polarizing plate protective film as described in said (1) characterized by the above-mentioned.

(3) The in-plane retardation Ro of the polarizing plate protective film is 30 to 200 nm, and the retardation Rt in the thickness direction is 70 to 400 nm. The polarizing plate protection according to the above (1) or (2) A method for producing a film.

(4) The polarizing plate protective film manufactured by the method for manufacturing a polarizing plate protective film according to any one of (1) to (3) is used for at least one surface of a polarizer. Polarizer.

(5) A liquid crystal display device using the polarizing plate according to (4).

  According to the present invention, a polarizing plate protective film produced by a melt casting method that does not use a solvent at the time of film formation, has little lip adhesion contamination of the extruder, and has little breakage at the slitting part at the time of heat stretching and after heat stretching, A manufacturing method, a polarizing plate using the polarizing plate protective film, and a liquid crystal display device with improved display quality using the polarizing plate can be provided.

  The present invention was made in order to investigate a method for forming a film by thermally melting a cellulose resin. The film is formed into a film by melting and casting at an optimum temperature, and a polarizing plate protective film is provided. In addition, an optically characteristic polarizing plate protective film (retardation film) can be provided by the stretching process, and a liquid crystal display device with improved display quality has been obtained by using this as a polarizing plate. .

  As a result of earnest research, the present inventor has melt cast using a melt obtained by heating and melting a film-forming material containing 0.01 to 5% by mass of a hindered amine compound or a hindered phenol compound, a plasticizer and a cellulose resin. The cellulose resin has a total acyl group substitution degree of 2.5 to 2.9 and an alkaline earth metal content (total content of Ca and Mg) of 1. It is manufactured by a melt casting method that does not use a solvent during film formation by a polarizing plate protective film having a residual sulfuric acid content (as a content of sulfur element) of 0.1 to 45 ppm. It has been found that a polarizing plate protective film is obtained with a little breakage at the slitting part at the time of hot drawing and after hot drawing.

  Hereinafter, the present invention will be described in detail, but the present invention is not limited thereto.

[Melt casting method]
The polarizing plate protective film of the present invention is a cellulose resin film formed by melt casting. That is, the film is produced by heating and melting the film constituent material without using the solvent used for the solution casting, and using the melt.

  More specifically, the heating and melting molding method can be classified into a melt extrusion molding method, a press molding method, an inflation method, an injection molding method, a blow molding method, a stretch molding method, and the like. Among these, in order to obtain a polarizing plate protective film having excellent mechanical strength and surface accuracy, the melt extrusion method is excellent.

  Here, the film forming material is heated to exhibit its fluidity, and then extruded and formed on a drum or an endless belt is included in the melt casting method of the present invention as a melt casting film forming method.

  Film formation by the melt casting method is remarkably different from the solution casting method. When there is a volatile component in the material to be cast, the flatness and transparency of the film are ensured to utilize the function as a film or polarizing plate protective film. From the point of view, it is not preferable. This is because transparency deteriorates when volatile components are mixed into the formed film, and when a film is formed by extrusion from a die-slit, the film surface becomes a factor that causes streak into the film surface and induces deterioration in flatness. There are things to do. Therefore, when a film constituent material is formed into a film, it is not preferable that a component that volatilizes exists in a region lower than the melting temperature for film formation from the viewpoint of avoiding generation of a volatile component during heating and melting.

  Examples of the volatile component include moisture absorbed by any of the film constituent materials, oxygen or nitrogen gas mixed therein, or a solvent mixed before the material is purchased or synthesized, and is evaporated by heating. , Volatilization by sublimation or decomposition. The solvent here is different from the solvent for adjusting the resin as a solution as a solution casting, and is contained in a trace amount in the film constituting material. Therefore, selection of the film constituent material is important in avoiding the generation of volatile components.

  It is preferable that the film constituent material used for the melt casting of the present invention removes volatile components represented by the moisture and the solvent before film formation or during heating. A method by drying can be applied to this removal method, and a method such as a heating method, a reduced pressure method, or a heated reduced pressure method can be used. Drying may be performed in air or in an atmosphere in which an inert gas such as nitrogen or argon is selected as the inert gas. These inert gases preferably have a low content of water or oxygen, and preferably do not substantially contain them. When these known drying methods are performed, it is preferable in terms of film quality to be performed in a temperature range where the film constituting material does not decompose. For example, the moisture or solvent remaining after removal in the drying step is preferably 5% by mass or less, more preferably 1% by mass or less, based on the total mass of the film constituent materials. .

  In particular, the moisture content of the cellulose resin is preferably less than 3% by mass. These characteristic values can be measured by ASTM-D817-96. It is preferable that the cellulose resin is used as 0.1 to 1000 ppm by further reducing the moisture by heat treatment.

  The film constituent material can reduce the generation of volatile components by drying before film formation, and the resin alone or at least one mixture or compatible material other than the resin among the resin and the film constituent material. It can be divided and dried. A preferable drying temperature is preferably 80 ° C. or higher and Tg or lower of the material to be dried. Including the viewpoint of avoiding fusion between materials, the drying temperature is more preferably 100 to (Tg-5) ° C, and still more preferably 110 to (Tg-20) ° C. A preferable drying time is 0.5 to 24 hours, more preferably 1 to 18 hours, and further preferably 1.5 to 12 hours. Below these ranges, the removal rate of volatile components may be low, or drying may take too long, and when Tg is present in the material to be dried, heating to a drying temperature higher than Tg will cause the material to be removed. May be difficult to handle due to fusion. Drying is preferably performed at 1 atm or less, and particularly preferably performed while reducing the pressure from vacuum to 1/2 atm. Drying is preferably performed while appropriately stirring the material such as resin, and the fluidized bed system in which drying air or dry nitrogen is fed from the lower part in the drying container can perform necessary drying in a shorter time. This is preferable because it is possible.

  The drying process may be separated into two or more stages. For example, the material may be formed using a material that has been subjected to storage of the material in the preliminary drying process and drying immediately before film formation to immediately before a week. .

[Cellulose resin]
The cellulose resin used in the present invention is preferably a cellulose ester in which a hydroxyl group at positions 2, 3, and 6 of cellulose and an aliphatic carboxylic acid or an aromatic carboxylic acid are ester-bonded.

  When the hydrogen atom of the hydroxyl group of cellulose is a fatty acid ester with an aliphatic acyl group, the aliphatic acyl group has 2 to 20 carbon atoms, specifically acetyl, propionyl, butyryl, isobutyryl, valeryl, pivaloyl, hexanoyl , Octanoyl, lauroyl, stearoyl and the like.

  In the present invention, the aliphatic acyl group is meant to include those further having a substituent. When the aromatic ring is a benzene ring in the above-described aromatic acyl group, the substituent of the benzene ring Are exemplified.

  Further, when the esterified substituent of the cellulose resin is an aromatic ring, the number of substituents substituted on the aromatic ring is 0 or 1 to 5, preferably 1 to 3, particularly preferably. Is one or two. Further, when the number of substituents substituted on the aromatic ring is 2 or more, they may be the same or different from each other, but they may be linked together to form a condensed polycyclic compound (for example, naphthalene, indene, indane, phenanthrene, quinoline). , Isoquinoline, chromene, chroman, phthalazine, acridine, indole, indoline, etc.).

In the aromatic acyl group, when the aromatic ring is a benzene ring, examples of the substituent of the benzene ring include halogen atom, cyano, alkyl group, alkoxy group, aryl group, aryloxy group, acyl group, carbonamido group, sulfone. Amido group, ureido group, aralkyl group, nitro, alkoxycarbonyl group, aryloxycarbonyl group, aralkyloxycarbonyl group, carbamoyl group, sulfamoyl group, acyloxy group, alkenyl group, alkynyl group, alkylsulfonyl group, arylsulfonyl group, alkyloxy Sulfonyl group, aryloxysulfonyl group, alkylsulfonyloxy group and aryloxysulfonyl group, -S-R, -NH-CO-OR, -PH-R, -P (-R) ₂ , -PH-O-R, -P (-R) (-O-R), -P ( _{O-R) 2, -PH (} = O) -R-P (= O) (- R) 2, -PH (= O) -O-R, -P (= O) (- R) (- O -R), -P (= O) (-O-R) ₂ , -O-PH (= O) -R, -O-P (= O) (-R) _2- O-PH (= O) —O—R, —O—P (═O) (— R) (— O—R), —O—P (═O) (— O—R) ₂ , —NH—PH (═O) —R , —NH—P (═O) (— R) (— O—R), —NH—P (═O) (— O—R) ₂ , —SiH ₂ —R, —SiH (—R) ₂ , _{-Si (-R) 3, -O-} SiH 2 -R, include -O-SiH (-R) ₂ and -O-Si (-R) _3. R is an aliphatic group, an aromatic group or a heterocyclic group. The number of substituents is preferably 1 to 5, more preferably 1 to 4, further preferably 1 to 3, and most preferably 1 or 2. As the substituent, a halogen atom, cyano, alkyl group, alkoxy group, aryl group, aryloxy group, acyl group, carbonamido group, sulfonamido group and ureido group are preferable, halogen atom, cyano, alkyl group, alkoxy group, An aryloxy group, an acyl group and a carbonamido group are more preferred, a halogen atom, cyano, an alkyl group, an alkoxy group and an aryloxy group are more preferred, and a halogen atom, an alkyl group and an alkoxy group are most preferred.

  The halogen atom includes a fluorine atom, a chlorine atom, a bromine atom and an iodine atom. The alkyl group may have a cyclic structure or a branch. The number of carbon atoms in the alkyl group is preferably 1-20, more preferably 1-12, still more preferably 1-6, and most preferably 1-4. Examples of the alkyl group include methyl, ethyl, propyl, isopropyl, butyl, t-butyl, hexyl, cyclohexyl, octyl and 2-ethylhexyl. The alkoxy group may have a cyclic structure or a branch. The number of carbon atoms in the alkoxy group is preferably 1-20, more preferably 1-12, still more preferably 1-6, and most preferably 1-4. The alkoxy group may be further substituted with another alkoxy group. Examples of the alkoxy group include methoxy, ethoxy, 2-methoxyethoxy, 2-methoxy-2-ethoxyethoxy, butyloxy, hexyloxy and octyloxy.

  The number of carbon atoms of the aryl group is preferably 6-20, and more preferably 6-12. Examples of the aryl group include phenyl and naphthyl. The aryloxy group preferably has 6 to 20 carbon atoms, more preferably 6 to 12 carbon atoms. Examples of the aryloxy group include phenoxy and naphthoxy. The number of carbon atoms in the acyl group is preferably 1-20, and more preferably 1-12. Examples of the acyl group include formyl, acetyl and benzoyl. The number of carbon atoms of the carbonamide group is preferably 1-20, and more preferably 1-12. Examples of the carbonamido group include acetamide and benzamide. The number of carbon atoms in the sulfonamide group is preferably 1-20, and more preferably 1-12. Examples of the sulfonamide group include methanesulfonamide, benzenesulfonamide, and p-toluenesulfonamide. The number of carbon atoms in the ureido group is preferably 1-20, and more preferably 1-12. Examples of ureido groups include (unsubstituted) ureido.

  The number of carbon atoms in the aralkyl group is preferably 7-20, and more preferably 7-12. Examples of the aralkyl group include benzyl, phenethyl and naphthylmethyl. The number of carbon atoms in the alkoxycarbonyl group is preferably 1-20, and more preferably 2-12. Examples of the alkoxycarbonyl group include methoxycarbonyl. The aryloxycarbonyl group preferably has 7 to 20 carbon atoms, and more preferably 7 to 12 carbon atoms. Examples of the aryloxycarbonyl group include phenoxycarbonyl. The number of carbon atoms in the aralkyloxycarbonyl group is preferably 8-20, and more preferably 8-12. Examples of the aralkyloxycarbonyl group include benzyloxycarbonyl. The number of carbon atoms of the carbamoyl group is preferably 1-20, and more preferably 1-12. Examples of the carbamoyl group include (unsubstituted) carbamoyl and N-methylcarbamoyl. The number of carbon atoms in the sulfamoyl group is preferably 20 or less, and more preferably 12 or less. Examples of the sulfamoyl group include (unsubstituted) sulfamoyl and N-methylsulfamoyl. The number of carbon atoms in the acyloxy group is preferably 1-20, and more preferably 2-12. Examples of the acyloxy group include acetoxy and benzoyloxy.

  The alkenyl group has preferably 2 to 20 carbon atoms, and more preferably 2 to 12 carbon atoms. Examples of alkenyl groups include vinyl, allyl and isopropenyl. The number of carbon atoms in the alkynyl group is preferably 2-20, and more preferably 2-12. Examples of alkynyl groups include thienyl. The number of carbon atoms in the alkylsulfonyl group is preferably 1-20, and more preferably 1-12. The number of carbon atoms of the arylsulfonyl group is preferably 6-20, and more preferably 6-12. The alkyloxysulfonyl group preferably has 1 to 20 carbon atoms, more preferably 1 to 12 carbon atoms. The number of carbon atoms of the aryloxysulfonyl group is preferably 6-20, and more preferably 6-12. The number of carbon atoms in the alkylsulfonyloxy group is preferably 1-20, and more preferably 1-12. The number of carbon atoms of the aryloxysulfonyl group is preferably 6-20, and more preferably 6-12.

  The cellulose resin used in the present invention is preferably at least one selected from cellulose acetate, cellulose propionate, cellulose butyrate, cellulose acetate propionate, cellulose acetate butyrate, cellulose acetate phthalate, and cellulose phthalate.

  Among these, particularly preferable cellulose resins include cellulose acetate, cellulose propionate, cellulose butyrate, cellulose acetate propionate, and cellulose acetate butyrate.

  The total substitution degree of the acyl group of the cellulose resin used in the present invention is 2.5 to 2.9. If it is less than 2.5, the phase difference tends to fluctuate with time and environmental conditions, and if it exceeds 2.9, it tends to break due to thermal stretching. Preferably, the substitution degree of the acetyl group is 1.5 to 2.5, and the total substitution degree of the acyl group having 3 or more carbon atoms is 0.1 to 1.2, more preferably the substitution degree of the acetyl group is 1.5. It is preferable that the total substitution degree of the acyl group having ˜2.0 and 3 or more carbon atoms is 0.6˜0.9. More preferably, an acyl group having 3 to 22 carbon atoms is within the above range of substitution degree, and particularly preferably an acyl group having 3 to 22 carbon atoms is a propionyl group having 3 carbon atoms or a butyryl group having 4 carbon atoms. Is in the above range.

  Such a cellulose resin is obtained, for example, by substituting the acetyl group, propionyl group and / or butyl group within the above-mentioned range by a conventional method using acetic anhydride, propionic anhydride and / or butyric anhydride for the hydroxyl group of cellulose. can get. The method for synthesizing such a cellulose ester is not particularly limited, and for example, it can be synthesized with reference to the method described in JP-A-10-45804 or JP-A-6-501040.

  The degree of substitution of acyl groups such as acetyl, propionyl and butyl groups can be measured according to ASTM-D817-96.

  The raw material cellulose of the cellulose resin used in the present invention may be wood pulp or cotton linter, and the wood pulp may be softwood or hardwood, but softwood is more preferable. A cotton linter is preferably used from the viewpoint of peelability during film formation. Cellulose resins made from these can be used in appropriate mixture or independently. In particular, it is preferable to use a mixture of cellulose resins having different degrees of substitution.

(Alkaline earth metal content)
The alkaline earth metal content of the cellulose resin used in the present invention is in the range of 1 to 50 ppm. If it exceeds 50 ppm, lip adhesion stains increase or breakage tends to occur at the slitting part during or after hot stretching. Even if it is less than 1 ppm, it tends to break, but the reason is not well understood. In order to make it less than 1 ppm, since the burden of a washing | cleaning process becomes large too much, it is unpreferable also in that point. Furthermore, the range of 1-30 ppm is preferable. The alkaline earth metal as used herein refers to the total content of Ca and Mg, and can be measured using an X-ray photoelectron spectrometer (XPS).

(Residual sulfuric acid content)
The residual sulfuric acid content in the cellulose resin used in the present invention is in the range of 0.1 to 45 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, the deposits on the die lip during heat melting increase, such being undesirable. Moreover, since it becomes easy to fracture | rupture at the time of slitting at the time of hot drawing or after hot drawing, it is not preferable. A smaller amount is preferable, but if it is less than 0.1, it is not preferable because the burden of the washing step of the cellulose resin becomes too large. This is not well understood, although an increase in the number of washings may affect the resin. Furthermore, the range of 0.1-30 ppm is preferable. The residual sulfuric acid content can be measured according to ASTM-D817-96.

(Free acid content)
The free acid content in the cellulose resin used in the present invention is preferably 1 to 500 ppm. The free acid here is a carboxylic acid component constituting the cellulose ester, and in the case of cellulose acetate, acetic acid, in the case of cellulose acetate propionate, acetic acid or propionic acid, in the case of cellulose acetate butyrate, acetic acid or This is butyric acid, which is contained in the resin without being bound to cellulose. If the free acid content exceeds 500 ppm, deposits on the die lip increase and the web is liable to break. It is difficult to make the free acid content less than 1 ppm by washing. Furthermore, it is preferable that it is the range of 1-100 ppm, and also it becomes difficult to fracture | rupture. A range of 1 to 70 ppm is particularly preferable. The free acid content can be measured according to ASTM-D817-96.

  By washing the synthesized cellulose ester more sufficiently than when used in the solution casting method, the amount of alkaline earth metal and the residual sulfuric acid content can be within the above ranges, and the melt casting method When a film is produced by the above, adhesion to the lip portion is reduced, and a film having excellent flatness is obtained, and a film having good dimensional change, mechanical strength, transparency, moisture resistance, Rt value, and Ro value is obtained. be able to.

  The intrinsic viscosity of the cellulose resin is preferably 1.5 to 1.75 dl / g, and more preferably 1.53 to 1.63.

  The water content of the cellulose ester is preferably from 0.01 to 2.0% by mass, and more preferably from 0.01 to 1.5% by mass, from the viewpoint of obtaining high transparency of the obtained film. These characteristic values can be measured by ASTM-D817-96. The method for synthesizing such a cellulose ester is not particularly limited, and for example, it can be synthesized by the method described in JP-A-10-45804.

  The cellulose resin used in the present invention preferably has a small amount of bright spot foreign matter when formed into a film. A bright spot foreign material is an arrangement in which two polarizing plates are arranged orthogonally (crossed Nicols), a cellulose ester film is arranged between them, and the retardation phase of the polarizing plate protective film is placed on the transmission axis of the polarizing plate on one light source side. When the axes are located in parallel, it means that light leaks when observed at a position perpendicular to the outer surface of the other polarizing plate. At this time, the polarizing plate used for the evaluation is desirably composed of a protective film having no bright spot foreign matter, and a polarizing plate using a glass plate for protecting the polarizer is preferably used. The bright spot foreign matter is considered to be one of the reasons that the esterification part of the hydroxyl group contained in the cellulose resin is unreacted, and using a cellulose resin with few bright spot foreign substances and filtering the heated and melted cellulose resin Can be removed and reduced. Moreover, the number of bright spot foreign matter per unit area decreases as the film thickness decreases, and the bright spot foreign matter tends to decrease as the content of the cellulose resin contained in the film decreases.

As for the number of luminescent spots, the number of luminescent spots per unit area of 250 mm ² having a size of 5 to 50 μm recognized in the polarization crossed Nicol state is 300 or less and luminescent spots of 50 μm or more when the film is observed. The number is preferably zero. More preferably, the number of bright spots of 5 to 50 μm is 200 or less.

  When there are many bright spots, the image on the liquid crystal display is seriously adversely affected. In the present invention, since the protective film for polarizing plate itself functions as a retardation film, the presence of the bright spot is a factor of disorder of birefringence, which is not preferable in that an adverse effect on an image becomes large.

  In the case where the bright spot foreign matter is removed by filtration and the film forming process of melt casting is continuously performed, it is preferable for the cellulose resin at the time of heating and melting to contain a stabilizer in order to prevent deterioration of the resin.

  The melt casting method including the process of filtering bright spot foreign matters by heat melting is a bright casting method from the viewpoint of lowering the heat melting temperature when a plasticizer and cellulose resin composition to be described later is used, compared to a system in which no plasticizer is added. This is a preferable method from the viewpoint of improving the removal efficiency of point foreign matters and avoiding thermal decomposition. Moreover, what mixed the ultraviolet absorber and microparticles | fine-particles suitably as another additive mentioned later can also be filtered similarly.

  As the filter medium, conventionally known materials such as glass fiber, heat-resistant resin, and carbon fiber are preferably used, and ceramics, metals, and the like are particularly preferably used. The absolute filtration accuracy is preferably 50 μm or less, more preferably 30 μm or less, still more preferably 10 μm or less, and even more preferably 5 μm or less. These can be used in combination as appropriate. The filter medium can be either a surface type or a depth type, but the depth type is preferably used because it is relatively less clogged.

  In another embodiment, before the film constituent material is melted by heating, at least in the cellulose resin of the constituent material, at least one of the late stage of synthesis of the material and the step of obtaining a precipitate, Similarly, the bright spot foreign matter can be removed through the filtration step.

  The above-mentioned method of filtering the molten resin is more efficient when it is filtered with a solution because the melt has a high viscosity.

  In addition, once the cellulose resin is dissolved in a solvent, the cellulose resin solution is uniformly mixed with the hindered amine compound or hindered phenol compound used in the present invention, or further with a plasticizer, an ultraviolet absorber, fine particles, and other additives. It is preferable to obtain a solid material by filtering the cellulose resin solution and then drying the solvent. By using this, a melt containing a cellulose resin can be obtained. As the solvent, a good solvent used in a solution casting method such as methylene chloride, methyl acetate or dioxolane can be used, and a poor solvent such as methanol, ethanol or butanol may be used at the same time.

  Moreover, in order to set it as the said solution state, it can also pass through the process cooled to -20 degrees C or less in the process of melt | dissolving this constituent material in the solvent. When adding any one or more of stabilizers, plasticizers, and other additives to the cellulose resin, there is no particular limitation in the process of synthesizing the cellulose resin used in the present invention, but by the latter stage of the resin synthesis process Filter at least once in order to filter out bright spot foreign matter and insoluble matter, then add other additives, remove the solids by solvent removal or acid precipitation and dry, You may obtain the film structure material which mixed powder, when pelletizing.

  Uniform mixing of constituent materials other than cellulose resin with the resin before melting can contribute to imparting uniform meltability when heated and melted.

  When adding the stabilizer added to a cellulose resin, a plasticizer, and the said other additives, it is preferable that the total quantity including them is 1-30 mass% with respect to the mass of a cellulose resin.

  The polarizing plate protective film of the present invention may be appropriately selected from polymer materials and oligomers other than cellulose resin and mixed. The polymer material or oligomer is preferably one having excellent compatibility with the cellulose ester, and the transmittance when formed into a film is preferably 80% or more, more preferably 90% or more, and further preferably 92% or more. By mixing at least one polymer material or oligomer other than the cellulose resin, viscosity control during heat melting and film physical properties after film processing can be improved.

  In the present invention, it is necessary to add a hindered amine compound or a hindered phenol compound before or when the cellulose resin is heated and melted. The addition amount is preferably 0.01 to 5% by mass.

  The polarizing plate protective film of the present invention preferably further contains a stabilizer, an acid scavenger, a peroxide decomposer, a radical scavenger, a metal deactivator, amines and the like. These are described in JP-A-3-199201, JP-A-5-197373, JP-A-5-194789, JP-A-5-271471, JP-A-6-107854, and the like.

  On the other hand, when the film constituent material is heated and melted, the decomposition reaction becomes remarkable, and this decomposition reaction may be colored or deteriorated. Moreover, generation | occurrence | production of the unfavorable volatile component may be accompanied by a decomposition reaction.

  The film constituent material can be stored as one or more kinds of pellets for the purpose of avoiding material alteration and hygroscopicity, and a melt can be produced using this. Pelletization can improve the mixability or compatibility of the film constituent materials when melted, and contributes to obtaining optical uniformity of the film.

  The polarizing plate protective film of the present invention preferably has a haze value of less than 3%, more preferably less than 1%, still more preferably less than 0.3%, and particularly preferably less than 0.1%. .

[Hindered phenol compounds]
The hindered phenol compounds used in the present invention include 2,6-dialkylphenol derivative compounds such as those described in columns 12 to 14 of US Pat. No. 4,839,405. . Such a compound includes a compound represented by the following general formula (1).

  In the formula, R1, R2 and R3 represent further substituted or unsubstituted alkyl substituents. Specific examples of hindered phenol compounds include n-octadecyl 3- (3,5-di-t-butyl-4-hydroxyphenyl) -propionate, n-octadecyl 3- (3,5-di-t-butyl- 4-hydroxyphenyl) -acetate, n-octadecyl 3,5-di-tert-butyl-4-hydroxybenzoate, n-hexyl 3,5-di-tert-butyl-4-hydroxyphenylbenzoate, n-dodecyl 3, 5-di-t-butyl-4-hydroxyphenylbenzoate, neo-dodecyl 3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate, dodecyl β (3,5-di-t-butyl- 4-hydroxyphenyl) propionate, ethyl α- (4-hydroxy-3,5-di-t-butylphenyl) isobutyrate, octade Sil α- (4-hydroxy-3,5-di-t-butylphenyl) isobutyrate, octadecyl α- (4-hydroxy-3,5-di-t-butyl-4-hydroxyphenyl) propionate, 2- (n -Octylthio) ethyl 3,5-di-t-butyl-4-hydroxy-benzoate, 2- (n-octylthio) ethyl 3,5-di-t-butyl-4-hydroxy-phenylacetate, 2- (n- Octadecylthio) ethyl 3,5-di-t-butyl-4-hydroxyphenyl acetate, 2- (n-octadecylthio) ethyl 3,5-di-t-butyl-4-hydroxy-benzoate, 2- (2- Hydroxyethylthio) ethyl 3,5-di-t-butyl-4-hydroxybenzoate, diethyl glycol bis- (3,5-di-t-butyl-4) -Hydroxy-phenyl) propionate, 2- (n-octadecylthio) ethyl 3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate, stearamide N, N-bis- [ethylene 3- (3 5-di-t-butyl-4-hydroxyphenyl) propionate], n-butylimino N, N-bis- [ethylene 3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], 2- (2-stearoyloxyethylthio) ethyl 3,5-di-tert-butyl-4-hydroxybenzoate, 2- (2-stearoyloxyethylthio) ethyl 7- (3-methyl-5-tert-butyl-4- Hydroxyphenyl) heptanoate, 1,2-propylene glycol bis- [3- (3,5-di-tert-butyl-4-hydroxyl Nyl) propionate], ethylene glycol bis- [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], neopentyl glycol bis- [3- (3,5-di-t-butyl-) 4-hydroxyphenyl) propionate], ethylene glycol bis- (3,5-di-t-butyl-4-hydroxyphenyl acetate), glycerin-1-n-octadecanoate-2,3-bis- (3 5-di-t-butyl-4-hydroxyphenyl acetate), pentaerythritol-tetrakis- [3- (3 ′, 5′-di-t-butyl-4′-hydroxyphenyl) propionate], 1,1,1 -Trimethylolethane-tris- [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate], sorbite Ruhexa- [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate], 2-hydroxyethyl 7- (3-methyl-5-tert-butyl-4-hydroxyphenyl) propionate, 2- Stearoyloxyethyl 7- (3-methyl-5-t-butyl-4-hydroxyphenyl) heptanoate, 1,6-n-hexanediol-bis [(3 ', 5'-di-t-butyl-4-hydroxy Phenyl) propionate], pentaerythritol-tetrakis (3,5-di-t-butyl-4-hydroxyhydrocinnamate). Hindered phenol compounds of the type described above are commercially available, for example, from Ciba Specialty Chemicals under the trade names “Irganox 1076” and “Irganox 1010”.

[Hindered amine compounds]
Examples of the hindered amine compound (HALS) used in the present invention include, for example, columns 5 to 11 of U.S. Pat. No. 4,619,956 and columns 3 to 5 of U.S. Pat. No. 4,839,405. 2,2,6,6-tetraalkylpiperidine compounds, or their acid addition salts or complexes of them with metal compounds. Such a compound includes a compound represented by the following general formula (3).

  In the formula, R1 and R2 are H or a substituent. Specific examples of hindered amine compounds include 4-hydroxy-2,2,6,6-tetramethylpiperidine, 1-allyl-4-hydroxy-2,2,6,6-tetramethylpiperidine, 1-benzyl-4- Hydroxy-2,2,6,6-tetramethylpiperidine, 1- (4-t-butyl-2-butenyl) -4-hydroxy-2,2,6,6-tetramethylpiperidine, 4-stearoyloxy-2 , 2,6,6-tetramethylpiperidine, 1-ethyl-4-salicyloyloxy-2,2,6,6-tetramethylpiperidine, 4-methacryloyloxy-1,2,2,6,6-penta Methylpiperidine, 1,2,2,6,6-pentamethylpiperidin-4-yl-β (3,5-di-t-butyl-4-hydroxyphenyl) -propionate, 1-ben L-2,2,6,6-tetramethyl-4-piperidinylmaleate, (di-2,2,6,6-tetramethylpiperidin-4-yl) -adipate, (di-2 , 2,6,6-tetramethylpiperidin-4-yl) -sebacate, (di-1,2,3,6-tetramethyl-2,6-diethyl-piperidin-4-yl) -sebacate, (di- 1-allyl-2,2,6,6-tetramethyl-piperidin-4-yl) -phthalate, 1-acetyl-2,2,6,6-tetramethylpiperidin-4-yl-acetate, trimellitic acid-tri -(2,2,6,6-tetramethylpiperidin-4-yl) ester, 1-acryloyl-4-benzyloxy-2,2,6,6-tetramethylpiperidine, dibutyl-malonic acid-di- (1 , 2,2,6,6-pentamethyl-piperidin-4-yl) -ester, dibenzyl-malonic acid-di- (1,2,3,6-tetramethyl-2,6-diethyl-piperidin-4-yl) Ester, dimethyl-bis- (2,2,6,6-tetramethylpiperidin-4-oxy) -silane, tris- (1-propyl-2,2,6,6-tetramethylpiperidin-4-yl) -Phosphite, tris- (1-propyl-2,2,6,6-tetramethylpiperidin-4-yl) -phosphate, N, N'-bis- (2,2,6,6-tetramethylpiperidine- 4-yl) -hexamethylene-1,6-diamine, N, N′-bis- (2,2,6,6-tetramethylpiperidin-4-yl) -hexamethylene-1,6-diacetamide, 1 -Acetyl-4- N-cyclohexylacetamide) -2,2,6,6-tetramethyl-piperidine, 4-benzylamino-2,2,6,6-tetramethylpiperidine, N, N'-bis- (2,2,6, 6-tetramethylpiperidin-4-yl) -N, N'-dibutyl-adipamide, N, N'-bis- (2,2,6,6-tetramethylpiperidin-4-yl) -N, N'- Dicyclohexyl- (2-hydroxypropylene), N, N′-bis- (2,2,6,6-tetramethylpiperidin-4-yl) -p-xylylene-diamine, 4- (bis-2-hydroxyethyl) -Amino-1,2,2,6,6-pentamethylpiperidine, 4-methacrylamide-1,2,2,6,6-pentamethylpiperidine, α-cyano-β-methyl-β- [N- ( 2, 2, 6, 6 Tetramethylpiperidin-4-yl)] - amino - acrylic acid methyl ester. Examples of preferred hindered amine compounds include, but are not limited to, the following HALS-1 and HALS-2.

  It is preferable to contain at least one of the above compounds, and the content is preferably 0.01 to 5% by mass, more preferably 0.01 to 3% by mass, and still more preferably based on the mass of the cellulose resin. Is 0.01-0.8 mass%.

  When the content of the compound is less than the above range, the cellulose resin is likely to be thermally decomposed. When the content is more than the range of the addition amount, transparency as a polarizing plate protective film is lowered from the viewpoint of compatibility with the resin. And is not preferable because the film becomes brittle.

  In the present invention, the acid scavenger useful as a compound used for stabilizing the film constituting material at the time of heat melting is preferably an epoxy compound described in US Pat. No. 4,137,201. For example, metal epoxy compounds (eg, vinyl chloride) such as diglycidyl ethers of various polyglycols, especially polyglycols derived by condensation of about 8-40 moles of ethylene oxide per mole of polyglycol, diglycidyl ethers of glycerol, etc. Conventionally used in polymer compositions and with vinyl chloride polymer compositions), epoxidized ether condensation products, diglycidyl ether of bisphenol A (ie, 4,4'-dihydroxydiphenyldimethylmethane), epoxy Unsaturated fatty acid esters (especially esters of fatty acids having 2 to 22 carbon atoms and alkyls having about 2 to 4 carbon atoms such as butyl epoxy stearate), and various epoxidation lengths Chain fatty acid triglycerides etc. Epoxidized vegetable oils such as epoxidized soybean oil and other unsaturated natural oils (these are sometimes referred to as epoxidized natural glycerides or unsaturated fatty acids, these fatty acids generally contain 12 to 22 carbon atoms Is included). Particularly preferred are commercially available epoxy group-containing epoxide resin compounds EPON 815c and other epoxidized ether oligomer condensation products represented by the following general formula (2).

  In formula, n is an integer of 0-12. Other acid scavengers that can be used include those described in paragraphs 87 to 105 of JP-A-5-194788.

  The content of the acid scavenger is preferably 0.001 to 5% by mass, and more preferably 0.01 to 0.8% by mass.

[Plasticizer]
In the polarizing plate protective film of the present invention, a plasticizer is contained for improving mechanical properties, imparting flexibility, imparting water absorption resistance, reducing moisture permeability, and the like.

  Further, in the melt casting method performed in the present invention, the plasticity of the film constituent material is lower than that of the cellulose resin alone by the purpose of lowering the melting temperature of the film constituent material by the addition of a plasticizer, rather than the glass transition temperature of the cellulose resin alone used. The purpose which can reduce the melt viscosity of the film constituent material containing the agent is included.

  Here, the melting temperature of the film constituting material means a temperature at which the material is heated and fluidity is developed.

  If the cellulose resin alone is lower than the glass transition temperature, the fluidity for forming a film is not exhibited. However, at the glass transition temperature or higher, the resin has a reduced elastic modulus or viscosity due to heat absorption, and exhibits fluidity. In order to lower the melting temperature of the film constituent material, it is preferable for the plasticizer to be added to have a melting point or glass transition temperature lower than the glass transition temperature of the cellulose resin in order to satisfy the above object.

  The cellulose resin film used in the present invention contains at least one plasticizer.

  The plasticizer to be added is not particularly limited, but a plasticizer having low volatility is preferable. Moreover, it is preferable to contain 2 or more types of plasticizers. By containing two or more kinds of plasticizers, the plasticizer can be reduced. The reason is not clear, but it seems that elution is suppressed by the ability to reduce the amount added per type and the interaction between the two plasticizers and the cellulose ester. Also, an effect of lowering the melting temperature can be expected.

  The plasticizer is not particularly limited, and polyhydric alcohol ester plasticizers, phthalic acid esters, citrate esters, fatty acid esters, polyesters, polyurethanes, glycolate plasticizers, phosphate ester plasticizers, and the like are preferably used. Of these, at least one of them is preferably a polyhydric alcohol ester plasticizer.

  The polyhydric alcohol ester plasticizer is a plasticizer comprising an ester of a dihydric or higher aliphatic polyhydric alcohol and a monocarboxylic acid, and preferably has an aromatic ring or a cycloalkyl ring in the molecule. Preferably it is a 2-20 valent aliphatic polyhydric alcohol ester.

  The polyhydric alcohol used in the present invention is represented by the following general formula (1).

Formula (1) R _1- (OH) _n
However, R ₁ represents an n-valent organic group, n represents a positive integer of 2 or more, and the OH group represents an alcoholic and / or phenolic hydroxyl group.

  Examples of preferred polyhydric alcohols include the following, but the present invention is not limited to these. Adonitol, arabitol, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, polypropylene glycol, 1,2-propanediol, 1,3-propanediol, dipropylene glycol, tripropylene glycol, 1,2-butane Diol, 1,3-butanediol, 1,4-butanediol, dibutylene glycol, 1,2,4-butanetriol, 1,5-pentanediol, 1,6-hexanediol, hexanetriol, galactitol, mannitol , 3-methylpentane-1,3,5-triol, pinacol, sorbitol, trimethylolpropane, trimethylolethane, xylitol and the like. In particular, triethylene glycol, tetraethylene glycol, dipropylene glycol, tripropylene glycol, sorbitol, trimethylolpropane, and xylitol are preferable. The polyhydric alcohol preferably has 4 or more carbon atoms, more preferably 5 to 60, and particularly preferably 6 to 30.

  There is no restriction | limiting in particular as monocarboxylic acid used for the polyhydric alcohol ester of this invention, Well-known aliphatic monocarboxylic acid, alicyclic monocarboxylic acid, aromatic monocarboxylic acid, etc. can be used. Use of an alicyclic monocarboxylic acid or aromatic monocarboxylic acid is preferred in terms of improving moisture permeability and retention.

  Examples of preferred monocarboxylic acids include the following, but the present invention is not limited thereto.

  As the aliphatic monocarboxylic acid, a fatty acid having a straight chain or side chain having 1 to 32 carbon atoms can be preferably used. The number of carbon atoms is more preferably 1-20, and particularly preferably 1-10. When acetic acid is contained, the compatibility with the cellulose ester is increased, and it is also preferable to use a mixture of acetic acid and another monocarboxylic acid.

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

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

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

  Although there is no restriction | limiting in particular in the molecular weight of a polyhydric alcohol ester, It is preferable that it is 300-5000, 300-1500 is more preferable, It is more preferable that it is 350-750. A higher molecular weight is preferred because it is less likely to volatilize, and a smaller one is preferred in terms of moisture permeability and compatibility with cellulose ester.

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

  Below, the specific compound of a polyhydric alcohol ester is illustrated.

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

  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.

  Examples of the citrate plasticizer include acetyl trimethyl citrate, acetyl triethyl citrate, and acetyl tributyl citrate.

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

  Examples of the phosphoric ester plasticizer include triphenyl phosphate, tricresyl phosphate, cresyl diphenyl phosphate, octyl diphenyl phosphate, diphenyl biphenyl phosphate, trioctyl phosphate, tributyl phosphate, and non-volatile phosphorus described in JP-A-6-501040. An acid ester is mentioned, for example, arylene bis (diaryl phosphate) ester etc. are mentioned. It is preferable that the ratio of phosphate plasticizers such as triphenyl phosphate is less than 40% of the total plasticizer, and it is particularly preferable that the ratio is not substantially contained. “Substantially not containing” means that the content of the phosphoric ester plasticizer is less than 1% by mass, preferably 0.1% by mass, particularly preferably not added. As described above, when a phosphate ester plasticizer is included, the base material is likely to be deformed when the hard coat layer is formed, which is not preferable.

  The total content of the plasticizer in the cellulose ester film is preferably 5 to 30% by mass, more preferably 6 to 20% by mass, and particularly preferably 8 to 15% by mass with respect to the total solid content. The contents of the two kinds of plasticizers are each at least 1% by mass, preferably 2% by mass or more.

  The polyhydric alcohol ester plasticizer is preferably contained in an amount of 1 to 20% by mass, particularly preferably 3 to 15% by mass. If the amount is too small, deterioration of flatness is recognized, and if it is too large, bleeding out tends to occur. The ratio of the polyhydric alcohol ester plasticizer to the other plasticizer is preferably in the range of 1: 4 to 4: 1, more preferably 1: 3 to 3: 1. If the total content of the plasticizer is too much or too little, the film tends to be deformed and is not preferable.

  Further, a polymer obtained by polymerizing an ethylenically unsaturated monomer having a weight average molecular weight of 500 to 10,000 described in JP-A-2003-12859, an acrylic polymer, an acrylic polymer having an aromatic ring in the side chain, or a cyclohexyl group An acrylic polymer or the like having in the side chain is also preferably used.

  The addition amount of these compounds is preferably 0.5% by mass or more to less than 20% by mass, more preferably 1% by mass or more to 20% by mass, with respect to the resin in which the plasticizer constitutes the film. It is in the range of less than.

  When the volatile component is due to the thermal decomposition of the plasticizer, the thermal decomposition temperature Td (1.0) of the plasticizer is defined as the temperature when decreased by 1.0% by mass, and the melting temperature (Tm) of the film constituent material Higher than that. This is because, in particular, the plasticizer is added to the cellulose resin in a larger amount than other film constituent materials and has a great influence on the quality. The thermal decomposition temperature Td (1.0) can be measured with a commercially available differential thermogravimetric analysis (TG-DTA) apparatus.

[Other additives]
The polarizing plate protective film of the present invention preferably contains the following additives.

(UV absorber)
The ultraviolet absorber is excellent in the ability to absorb ultraviolet rays having a wavelength of 370 nm or less from the viewpoint of preventing deterioration of the polarizer and the display device with respect to ultraviolet rays, and has little absorption of visible light having a wavelength of 400 nm or more from the viewpoint of liquid crystal display properties. Those are preferred. Examples of the ultraviolet absorber used in the present invention include oxybenzophenone compounds, benzotriazole compounds, salicylic acid ester compounds, benzophenone compounds, cyanoacrylate compounds, nickel complex compounds, triazine compounds, and the like. A benzophenone compound, a benzotriazole compound with little coloring, and a triazine compound are preferable. Moreover, you may use the ultraviolet absorber of Unexamined-Japanese-Patent No. 10-182621 and 8-337574, and the polymeric ultraviolet absorber of Unexamined-Japanese-Patent No. 6-148430.

  Specific examples of the benzotriazole ultraviolet absorber include 2- (2′-hydroxy-5′-methylphenyl) benzotriazole, 2- (2′-hydroxy-3 ′, 5′-di-tert-butylphenyl) benzo Triazole, 2- (2'-hydroxy-3'-tert-butyl-5'-methylphenyl) benzotriazole, 2- (2'-hydroxy-3 ', 5'-di-tert-butylphenyl) -5 Chlorobenzotriazole, 2- (2′-hydroxy-3 ′-(3 ″, 4 ″, 5 ″, 6 ″ -tetrahydrophthalimidomethyl) -5′-methylphenyl) benzotriazole, 2,2-methylenebis (4- (1,1,3,3-tetramethylbutyl) -6- (2H-benzotriazol-2-yl) phenol), 2- (2'-hydroxy- '-Tert-butyl-5'-methylphenyl) -5-chlorobenzotriazole, 2- (2H-benzotriazol-2-yl) -6- (straight and side chain dodecyl) -4-methylphenol, octyl- 3- [3-tert-butyl-4-hydroxy-5- (chloro-2H-benzotriazol-2-yl) phenyl] propionate and 2-ethylhexyl-3- [3-tert-butyl-4-hydroxy-5 A mixture of (5-chloro-2H-benzotriazol-2-yl) phenyl] propionate can be mentioned, but is not limited thereto.

  As commercially available products, TINUVIN 109, TINUVIN 171 and TINUVIN 326 (all manufactured by Ciba Specialty Chemicals) can also be used.

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

  In the present invention, the ultraviolet absorber is preferably added in an amount of 0.1 to 20% by mass, more preferably 0.5 to 10% by mass, and further preferably 1 to 5% by mass. Two or more of these may be used in combination.

(Fine particles)
The polarizing plate protective film of the present invention can be added with fine particles in order to impart sliding properties, optical and mechanical functions. Examples of the fine particles include fine particles of an inorganic compound or fine particles of an organic compound.

  The shape of the fine particles is preferably a spherical shape, a rod shape, a needle shape, a layer shape, a flat shape or the like. Examples of the fine particles include oxidation of metals such as silicon dioxide, titanium dioxide, aluminum oxide, zirconium oxide, calcium carbonate, kaolin, talc, calcined calcium silicate, hydrated calcium silicate, aluminum silicate, magnesium silicate, and calcium phosphate. Inorganic fine particles such as materials, phosphates, silicates, carbonates and crosslinked polymer fine particles. Among these, silicon dioxide is preferable because it can reduce the haze of the film. These fine particles are preferably surface-treated with an organic substance because the haze of the film can be reduced.

  The surface treatment is preferably performed with halosilanes, alkoxysilanes, silazane, siloxane, or the like. The larger the average particle size of the fine particles, the greater the sliding effect, and the smaller the average particle size, the better the transparency. The average primary particle size of the fine particles is in the range of 0.01 to 1.0 μm. The average particle diameter of primary particles of preferable fine particles is preferably 5 to 50 nm, and more preferably 7 to 14 nm. These fine particles are preferably used for generating irregularities of 0.01 to 1.0 μm on the surface of the cellulose ester film. The content of fine particles in the cellulose ester is preferably 0.005 to 10% by mass with respect to the cellulose ester.

  Examples of the fine particles of silicon dioxide include Aerosil 200, 200V, 300, R972, R972V, R974, R202, R812, OX50, TT600 manufactured by Nippon Aerosil Co., Ltd., preferably Aerosil 200V, R972. , R972V, R974, R202, R812. Two or more kinds of these fine particles may be used in combination.

  When using 2 or more types together, it can mix and use in arbitrary ratios. Fine particles having different average particle sizes and materials, for example, Aerosil 200V and R972V can be used in a mass ratio of 0.1: 99.9 to 99.9: 0.1.

  These fine particles are preferably added by kneading. In another embodiment, fine particles dispersed in a solvent in advance and cellulose ester and / or plasticizer and / or ultraviolet absorber are mixed and dispersed, and then a solid is obtained by volatilizing or precipitating the solvent. It is preferable to use in the production process of the melt from the viewpoint that the fine particles can be uniformly dispersed in the cellulose resin.

  The fine particles can also be added to improve the mechanical, electrical and optical properties of the film.

  Moreover, the polarizing plate protective film of this invention can contain the additive for adjusting retardation. As the compound to be added for adjusting the retardation, an aromatic compound having two or more aromatic rings as described in the specification of European Patent 911,656A2 may be used as a retardation control agent. it can. Two or more aromatic compounds may be used in combination. The aromatic ring of the aromatic compound includes an aromatic heterocyclic ring in addition to the aromatic hydrocarbon ring. Particularly preferred is an aromatic heterocycle, and the aromatic heterocycle is generally an unsaturated heterocycle. Of these, compounds having a 1,3,5-triazine ring are particularly preferred.

  The polarizing plate protective film of the present invention can be provided with an optically anisotropic layer formed of liquid crystal or polyimide, etc., and optimal optical compensation can be achieved by combining the polarizing plate protective film and these optically anisotropic layers. It can also be done.

[Production method of polarizing plate protective film]
Although the manufacturing method of the polarizing plate protective film of this invention is demonstrated in detail below, this invention is not limited to this. In this, the longitudinal direction refers to the direction (longitudinal direction) in which the film is formed and conveyed, and the lateral direction (lateral direction) refers to the direction perpendicular to the film formed and conveyed direction.

  A raw material cellulose resin or a mixture of materials constituting a film is formed into pellets, dried with hot air or vacuum, then melt extruded using a melt obtained by heating and melting, and extruded from a T die into a sheet. Then, the film is brought into close contact with a cooling drum by an electrostatic application method or the like, and solidified by cooling to obtain a film. The temperature of the cooling drum is preferably maintained at 90 to 150 ° C.

  The film peeled from the above-mentioned cooling drum is heated again through one or a plurality of roll groups and / or a heating device such as an infrared heater, and cooled after being stretched in one or more stages in the longitudinal direction. preferable. At this time, when the glass transition temperature of the film of the present invention is defined as Tg, the film is heated within the range of (Tg-30) to (Tg + 100) ° C., more preferably (Tg-20) to (Tg + 80) ° C. It is preferable to stretch in the hand direction. It is preferable to perform transverse stretching within the temperature range of (Tg-20) to (Tg + 20) ° C. and then heat-set. In the case of transverse stretching, it is preferable to perform transverse stretching while sequentially raising the temperature difference in the range of 1 to 50 ° C. in a stretching region divided into two or more, because the thickness and optical distribution in the width direction can be reduced.

  It is also preferable to perform relaxation treatment after the stretching step.

  The Tg of the film can be controlled by the material type constituting the film and the ratio of the constituting materials. In the application of the present invention, the Tg of the film is preferably 120 ° C. or higher, and more preferably 135 ° C. or higher. This is because when the polarizing plate protective film of the present invention is used in a liquid crystal display device, if the Tg of the film is lower than the above, the temperature of the operating environment and the influence of the heat of the backlight cause the molecules fixed inside the film. The orientation state is affected, and there is a high possibility that the retardation value and the dimensional stability and shape as a film are greatly changed. On the other hand, if the Tg of the film is too high, it is difficult to produce because it is close to the decomposition temperature of the film constituting material, and the presence of a volatile component or coloring may occur due to the decomposition of the material itself used for forming a film. Therefore, 250 degrees C or less is preferable. At this time, the Tg of the film can be determined by the method described in JIS K7121.

  The polarizing plate protective film according to the present invention preferably performs refractive index control by a stretching operation in order to combine the functions of the retardation film. Hereinafter, the stretching method will be described.

  In the production of the polarizing plate protective film of the present invention, by stretching 0.8 to 2.0 times in one direction of the cellulose resin and 1.01 to 2.5 times in the direction perpendicular to the film plane, Ro and It can be controlled within the range of Rt. Stretching may be performed in multiple steps by changing the stretching ratio and temperature, or may be simultaneously performed in the biaxial direction. In the present invention, the in-plane retardation Ro is preferably 30 to 200 nm and the retardation Rt in the thickness direction is preferably 70 to 400 nm.

  For example, the film can be stretched sequentially or simultaneously in the longitudinal direction of the film and the direction perpendicular to the longitudinal direction of the film, that is, the width direction.

  At this time, if the stretching ratio in at least one direction is too small, a sufficient phase difference cannot be obtained, and if it is too large, stretching becomes difficult and breakage may occur.

  Further, stretching in biaxial directions perpendicular to each other is an effective method for bringing the refractive indexes nx, ny, and nz of the film defined below within the scope of the present invention.

Ro = (nx−ny) × d
Rt = {(nx + ny) / 2−nz} × d
(In the formula, Ro is the retardation value in the film plane, Rt is the retardation value in the film thickness direction, nx is the refractive index in the slow axis direction in the film plane, ny is the refractive index in the fast axis direction in the film plane, (nz represents the refractive index in the thickness direction of the film, and d represents the thickness of the film.)
For example, when stretching in the direction of melting and casting, if the shrinkage in the width direction is too large, the value of nz becomes too large. In this case, it can be improved by suppressing the width shrinkage of the film or stretching in the width direction. When stretching in the width direction, the refractive index may be distributed with a width. This is sometimes seen when the tenter method is used, but it is a phenomenon that occurs when the film is stretched in the width direction, causing contraction force at the center of the film and the end being fixed. It is thought to be called a phenomenon. Even in this case, by stretching in the casting direction, the bowing phenomenon can be suppressed, and the distribution of width retardation can be reduced.

  Furthermore, the film thickness fluctuation | variation of the film obtained can be reduced by extending | stretching in the biaxial direction orthogonal to each other. If the film thickness variation of the film is too large, the retardation will be uneven, and unevenness such as coloring may be a problem when used in a liquid crystal display.

  The film thickness variation of the cellulose ester film support is preferably within a range of ± 3%, further ± 1%, and more preferably ± 0.1%. For the purposes as described above, the method of stretching in the biaxial directions perpendicular to each other is effective, and the stretching ratio in the biaxial directions perpendicular to each other is finally 1.0 to 2.0 times in the casting direction. The width direction is preferably 1.01 to 2.5 times, the casting direction is 1.01 to 1.5 times, and the width direction is 1.2 to 2.0 times. It is more preferable for obtaining the retardation value of the present invention. The stretching temperature is preferably 80 to 200 ° C, more preferably 90 to 180 ° C.

  When the polarizer bonded to the polarizing plate protective film of the present invention has an absorption axis in the longitudinal direction, the transmission axis of the polarizer matches in the width direction. The polarizing plate protective film of the present invention preferably has a slow axis in the longitudinal direction or the width direction, and more preferably has a slow axis in the width direction.

  When a cellulose resin that obtains positive birefringence with respect to stress is used, the slow axis of the film can be imparted in the width direction by stretching in the width direction from the above-described configuration. In this case, in the present invention, in order to improve display quality, it is preferable that the slow axis of the film is in the width direction. In order to obtain the retardation value of the present invention, (stretch ratio in the width direction)> It is necessary to satisfy (the draw ratio in the casting direction). Further, it is desirable that the in-plane retardation Ro and the retardation Rt in the thickness direction hardly change even if there are environmental fluctuations such as temperature and humidity. Specifically, it is preferable that both Ro and Rt have a change rate of 1 nm / ° C. or less and a change rate of 2 nm /% RH or less.

  There is no particular limitation on the method of stretching the web. For example, a method in which a difference in peripheral speed is applied to a plurality of rolls, and the roll peripheral speed difference is used to stretch in the longitudinal direction, the both ends of the web are fixed with clips and pins, and the interval between the clips and pins is increased in the traveling direction. And a method of stretching in the vertical direction, a method of stretching in the horizontal direction and stretching in the horizontal direction, a method of stretching in the vertical and horizontal directions simultaneously, stretching in the horizontal direction and simultaneously contracting in the vertical direction, and the like. Of course, these methods may be used in combination. In the case of the so-called tenter method, driving the clip portion by the linear drive method is preferable because smooth stretching can be performed and the risk of breakage and the like can be reduced.

  These width maintenance or lateral stretching in the film forming step is preferably performed by a tenter, and may be a pin tenter or a clip tenter.

  As for the thickness of the polarizing plate protective film of this invention, 10-500 micrometers is preferable. In particular, it is preferably 20 μm or more, more preferably 35 μm or more. Moreover, 150 micrometers or less, Furthermore, 120 micrometers or less are preferable. Particularly preferred is 25 to 90 μm. If the polarizing plate protective film is thicker than the above-mentioned region, the polarizing plate after polarizing plate processing becomes too thick, so that it is not suitable for a thin and lightweight purpose in a liquid crystal display used for a notebook computer or a mobile electronic device. On the other hand, if the thickness is smaller than the above region, it is difficult to develop retardation as a retardation film, and the moisture permeability of the film is increased, so that the ability to protect the polarizer from humidity is reduced.

  In the solution casting method, when the film thickness is increased, the drying load is remarkably increased. However, in the present invention, since a drying step is not required, a film having a large film thickness can be produced with high productivity. Therefore, there is an advantage that it is easier than ever to increase the thickness of the film in accordance with the purpose of providing a necessary phase difference or reducing moisture permeability.

  The width of the polarizing plate protective film of the present invention is preferably 1 to 4 m, and particularly preferably 1.4 to 4 m. The winding length is preferably 500 to 5000 m, more preferably 1000 to 5000 m. Both ends of the width are wound with a knurling height of 0 to 25% of the film thickness.

  The cellulose ester film of the present invention preferably has a free volume radius determined by the positron annihilation lifetime method of 0.25 to 0.35 nm. It is particularly preferable that the free volume radius determined by the positron annihilation lifetime method is 0.25 to 0.31 nm and the half width is 0.04 to 0.1 nm.

  The free volume radius in this invention represents the space | gap part which is not occupied by the cellulose resin molecular chain. This can be measured using the positron annihilation lifetime method. Specifically, by measuring the time from the incidence of positrons to the sample until annihilation, non-destructively observing information on the vacancies, the size of the free volume, the number concentration, etc. from the annihilation lifetime You can ask.

<Measurement of free volume radius by positron annihilation lifetime method>
The positron annihilation lifetime and relative intensity are measured under the following measurement conditions.

(Measurement condition)
Positron beam source: 22 NaCl (strength 1.85 MBq)
Gamma ray detector: Plastic scintillator + photomultiplier tube Time resolution: 290ps
Measurement temperature: 23 ° C
Total count: 1 million counts Sample size: 20 slices cut to 20 mm × 15 mm are stacked to a thickness of about 2 mm. The sample is vacuum dried for 24 hours before measurement.

Irradiation area: About 10mmφ
Time per channel: 23.3ps / ch
According to the above measurement conditions, positron annihilation lifetime measurement is performed, and three-component analysis is performed by the nonlinear least square method. I1 + I2 + I3 = 100%). From the average annihilation lifetime τ3 having the longest lifetime, the free volume radius R3 (nm) was determined using the following formula. It is considered that τ3 corresponds to positron annihilation in the vacancies, and that the larger the τ3, the larger the vacancy size.

τ3 = (1/2) [1- {R3 / (R3 + 0.166)} + (1 / 2π) sin {2πR3 / (R3 + 0.166)}] − 1
Here, 0.166 (nm) corresponds to the thickness of the electron layer leached from the hole wall.

  The above measurement is repeated twice, and the average value and the half width are obtained from the peak and peak shape obtained from the relative strength and the void radius.

  The positron annihilation lifetime method is described in, for example, MATERIAL STAGE vol. 4, no. 5 2004 p21-25, Toray Research Center THE TRC NEWS No. 80 (Jul. 2002) p20-22, “Bunseki, 1988, pp. 11-20”, “Evaluation of free volume of polymer by positron annihilation method” can be referred to. .

  The particularly preferred free volume radius of the cellulose ester film according to the present invention is 0.25 to 0.31 nm, and the half width is 0.04 to 0.100 nm. The free volume radius of the film of the present invention is preferably distributed in the range of 0.20 nm to 0.40 nm, and the peak value of the free volume radius is preferably 0.25 to 0.31 nm. The full width at half maximum is preferably 0.040 to 0.095 nm, more preferably 0.045 to 0.090 nm, and still more preferably 0.050 to 0.085 nm.

  The method for setting the free volume radius of the cellulose ester film within a predetermined range is not particularly limited, but these can be controlled by the following method.

  The cellulose ester film is a cellulose ester film produced by a melt casting method using a heated melt, further at 105 to 170 ° C., preferably at an atmosphere substitution rate of 12 times / hour or more, more preferably 12 to 45 times. A cellulose ester film having a predetermined free volume radius can be obtained by heat treatment while being conveyed in an atmosphere of / hour. The treatment time is preferably 1 to 60 minutes.

The atmosphere replacement rate is defined as follows. When the atmosphere capacity of the heat treatment chamber is V (m ³ ) and the fresh air flow rate is FA (m ³ / hr), the atmosphere of the heat treatment chamber per unit time determined by the following formula is Fresh-air. Is the number of replacements by. Fresh air is not a wind that is circulated and reused among the air blown into the heat treatment chamber, and it is a fresh air that does not contain volatile components such as plasticizers and additives, or has been removed. I mean.

Atmosphere replacement rate = FA / V (times / hour)
Further, when the temperature exceeds 155 ° C., the effect of the present invention is hardly obtained, and even if the temperature is lower than 105 ° C., the effect of the present invention is hardly obtained. The treatment temperature is more preferably 120 to 160 ° C.

  In the melt casting method, a solvent is not used during film formation as in the solution casting method, and the additive used is not easily volatilized, so the atmosphere substitution rate may be low. However, the treatment is preferably performed in an atmosphere in which the atmosphere replacement rate is maintained at an atmosphere replacement rate of 12 times / hour or more in the processing section. By controlling the atmosphere substitution rate, the volatilized components are reduced from reattaching to the film. However, if the substitution rate is increased more than necessary, the cost increases, which is not preferable. If it exceeds 45 times, the flatness may be deteriorated due to flapping of the web in the heat treatment step. The treatment time under these conditions is preferably 1 minute to 1 hour.

  Further, in the heat treatment step, pressure treatment in the thickness direction can also control the free volume radius to a more preferable range. A preferable pressure is 0.5 to 10 kPa.

  When the angle formed between the slow axis or the fast axis of the polarizing plate protective film of the present invention and the film forming direction is θ1, θ1 is preferably −1 to + 1 °, and −0.5 to + 0.5 °. More preferably, it is particularly preferably −0.1 to + 0.1 °.

  This θ1 can be defined as an orientation angle, and θ1 can be measured using an automatic birefringence meter KOBRA-21ADH (Oji Scientific Instruments).

  Each of θ1 satisfying the above relationship can contribute to obtaining high luminance in a display image, suppressing or preventing light leakage, and contributing to obtaining faithful color reproduction in a color liquid crystal display device.

The photoelastic coefficient of the polarizing plate protective film of the present invention is preferably −10 ⁻¹³ Pa ⁻¹ to 10 ⁻¹³ Pa ⁻¹ , particularly 1 × 10 ⁻¹³ Pa ⁻¹ to 1 × 10 ⁻⁹ Pa ^−1. It is preferable that

  When the polarizing plate protective film of the present invention is used in a multi-domain VA mode, the polarizing plate protective film is disposed in the above region with the fast axis of the polarizing plate protective film as θ1. For example, when the polarizing plate and the liquid crystal display device are in the MVA mode, the configuration shown in FIG. 1 can be taken.

  The in-plane retardation (Ro) distribution of the cellulose ester film is preferably adjusted to 5% or less, more preferably 2% or less, and particularly preferably 1.5% or less. Moreover, although it is preferable to adjust the retardation (Rt) distribution of the thickness direction of a film to 10% or less, More preferably, it is 2% or less, Especially preferably, it is 1.5% or less.

  The numerical value of the retardation distribution is expressed by a variation coefficient (CV) of the retardation obtained by measuring the retardation at 1 cm intervals in the width direction of the obtained film. About the measurement method of the numerical value of the retardation and its distribution, for example, the in-plane retardation and the thickness direction retardation are obtained by the standard deviation by the (n-1) method, the coefficient of variation (CV) shown below is obtained, and the index And

Coefficient of variation (CV) = standard deviation / retardation average value In the polarizing plate protective film of the present invention, it is preferable that the distribution variation of the retardation value is small, and a polarizing plate comprising the polarizing plate protective film of the present invention in a liquid crystal display device. When used, the retardation distribution variation is preferably small from the viewpoint of preventing color unevenness and the like.

The polarizing plate protective film of the present invention may have a retardation value wavelength dispersibility, and when used in the same manner as described above for a liquid crystal display element, the wavelength dispersibility is appropriately selected in order to improve display quality. be able to. Here, similarly to the measured value Ro of the retardation film of the present invention at 590 nm, the in-plane retardation at ₄₅₀ nm R ₄₅₀ and the in-plane retardation at ₆₅₀ nm are defined as R ₆₅₀ .

In the present invention, when the display device is used for MVA described later, the wavelength dispersion in the in-plane retardation of the polarizing plate protective film of the present invention is preferably 0.7 <(R ₄₅₀ / R ₀ ) <1.0, 1.0 <(R ₆₅₀ / R ₀ ) <1.5. More preferably, 0.7 <(R ₄₅₀ / R ₀ ) <0.95, 1.01 <(R ₆₅₀ / R ₀ ) <1.2, and particularly preferably 0.8 <(R ₄₅₀ / R _0. ) <0.93, 1.02 <(R ₆₅₀ / R ₀ ) <1.1 can be selected in order to exert an effective effect on display color reproducibility.

  The polarizing plate protective film of the present invention is adjusted to a retardation value suitable for improving the display quality of a VA mode or TN mode liquid crystal cell. Of these, the VA mode is particularly preferably used for the MVA mode divided into the above multi-domains. At this time, Ro which is in-plane retardation is 30 to 200 nm, and Rt which is retardation in the thickness direction is required to be 70 to 400 nm.

  The above-mentioned in-plane retardation is based on the case of observing from the normal direction of the display surface when the two polarizing plates are arranged in crossed Nicols and the liquid crystal cell is arranged between the polarizing plates, for example, in the configuration of FIG. Thus, when observed from an oblique direction with respect to the normal direction of the display surface, light leakage caused by the deviation of the polarizing plate from the crossed Nicol state is mainly compensated. The retardation in the thickness direction mainly compensates for the birefringence of the liquid crystal cell similarly observed when viewed from an oblique direction when the liquid crystal cell is in a black display state in the TN mode or VA mode, particularly in the MVA mode. . By combining both of these behaviors, Ro and Rt can be optically compensated within the scope of the present invention. In the present invention, Ro and Rt can be adjusted with respect to the retardation of the liquid crystal cell itself.

  In the liquid crystal display device, when two polarizing plates of the present invention are arranged above and below the liquid crystal cell, Rt of the films 2a and 2b in the figure satisfies the above range and the total value of both of Rt is 140. It is preferable to set it to -500 nm. At this time, Ro and Rt of 2a and 2b may be the same or different. Preferably, Ro is 30 to 200 nm, Rt is 70 to 400 nm, particularly preferably Ro is 35 to 65 nm, and Rt is 90 to 180 nm, and the structure shown in FIG. 1 is applied to the MVA mode liquid crystal cell. The Rt / Ro ratio is preferably 2-6.

  When using the polarizing plate including the polarizing plate protective film of the present invention for a liquid crystal display device, it is preferable that the polarizing plate on at least one surface is the polarizing plate of the present invention, and that both surfaces are the polarizing plates of the present invention. preferable. When only one polarizing plate is the polarizing plate of the present invention, a polarizing plate using a conventional polarizing plate protective film can be used on the other surface. As the polarizing plate protective film, a cellulose ester film having preferably Ro of 0 to 4 nm, Rt of 20 to 60 nm, and a thickness of 35 to 85 nm is used. This cellulose ester film is used for 2b of FIG. 1, and the polarizing plate protective film of this invention is used for 2a. Alternatively, 2b may be a polarizing plate protective film of the present invention, and 2a may be a conventional polarizing plate protective film. At this time, Ro of the polarizing plate protective film of the present invention is set to 30 to 200 m, and Rt is set to 70 to 400 nm, which can contribute to improvement of display quality and is also preferable in terms of film production.

  In addition, as a conventional polarizing plate protective film, Konica Minoltack KC8UX, KC4UX, KC5UX, KC8UY, KC4UY, KC8UCR-3, KC8UCR-4, KC8UCR-5, KC12UR, KC8UX-H, KC8UY-HA, HC8X Konica Minolta Opto Co., Ltd.) is used. Moreover, the polarizing plate protective film of this invention can be preferably used not only for 2a or 2b or both but also for 1a and 1b.

  In the polarizing plate of the present invention, another functional layer may be disposed on the polarizing plate protective film used on the surface opposite to the retardation film as viewed from the polarizer, in order to improve the quality of the display device. Is possible.

  For example, it may be affixed to a film containing a known functional layer as a constituent for display in order to prevent reflection, anti-glare, scratch resistance, dust adhesion prevention, brightness improvement, or the polarizing plate surface of the present invention. It is not limited to.

  In general, a retardation film is required to obtain stable optical characteristics that the fluctuation of Ro or Rt is small as the above-mentioned retardation value. In particular, in a liquid crystal display device in a birefringence mode, these fluctuations may cause image unevenness.

  The long polarizing plate protective film produced by the method according to the solution casting method may vary depending on the volatilization of the amount of the organic solvent remaining in a very small amount in the film. This long polarizing plate protective film is manufactured, stored and transported in the state of a long roll (roll), and processed into a polarizing plate by a polarizing plate manufacturer or the like. Thus, the more you go into the roll, the slower the volatility in the presence of residual solvent. For this reason, a small amount of residual solvent concentration difference occurs from both ends to the center in the winding direction and in the width direction, and these may trigger the change and fluctuation of the retardation value over time. It was.

  On the other hand, since the long polarizing plate protective film of the present invention is produced by the melt casting method, unlike the solution casting method, there is no solvent for volatilization, and thus it is excellent in that there is little fluctuation. Technology. The present invention is excellent in that a long polarizing plate protective film can be obtained by continuously stretching a film produced by melt casting.

  Since the long polarizing plate protective film of the present invention by the melt casting method is mainly composed of a cellulose resin, it can be saponified. Therefore, it can be bonded with a polyvinyl alcohol polarizer and an aqueous adhesive. Since the conventional polarizing plate processing method can be applied and roll-to-roll bonding is possible, it is excellent that a long roll polarizing plate is obtained.

  These excellent effects can be exhibited particularly in a long scroll of 100 m or more, and a further remarkable effect can be obtained by increasing the length to 1500 m, 2500 m, and 5000 m.

  In the polarizing plate protective film of the present invention, the roll length is 100 to 5000 m, preferably 500 to 4500 m, considering productivity and transportability. The width of the film at this time depends on the width of the polarizer and the production line. A suitable width can be selected, and it may be manufactured in a width of 1 to 4.0 m, preferably 1.4 to 3.0 m and wound into a roll to be used for polarizing plate processing. A film having a width larger than that may be manufactured and wound after being rolled, and may be cut into a roll having a desired width, or may be wound while being slitted, or may be used for polarizing plate processing.

  In producing the polarizing plate protective film of the present invention, before and / or after stretching, an antistatic layer, a hard coat layer, a slippery layer, an adhesive layer, a gas barrier layer, a moisture proof layer, an antiglare layer, a barrier layer, a liquid crystal or a polyimide A functional layer such as an optically anisotropic layer may be applied. At this time, various surface treatments such as corona discharge treatment, plasma treatment, chemical treatment with alkali, etc. can be applied as necessary.

  A cellulose ester film having a laminated structure can also be produced by coextruding compositions containing cellulose resins having different additive concentrations such as the plasticizer, ultraviolet absorber, and matting agent. For example, a cellulose ester film having a structure of skin layer / core layer / skin layer can be produced. For example, fine particles such as a matting agent can be contained in the skin layer in a large amount or only in the skin layer. The plasticizer and the ultraviolet absorber can be contained in the core layer more than the skin layer, and may be contained only in the core layer. In addition, the type of plasticizer and ultraviolet absorber can be changed between the core layer and the skin layer. For example, the skin layer contains a low-volatile plasticizer and / or an ultraviolet absorber, and the core layer has excellent plasticity. It is also possible to add a plasticizer or an ultraviolet absorber excellent in ultraviolet absorption. The glass transition temperature of the skin layer and the core layer may be different, and the glass transition temperature of the core layer can be made lower than the glass transition temperature of the skin layer. Also, the viscosity of the melt containing the cellulose ester during melt casting may be different between the skin layer and the core layer, and the viscosity of the skin layer> the viscosity of the core layer or the viscosity of the core layer ≧ the viscosity of the skin layer may be used.

  The polarizing plate protective film of the present invention has a dimensional stability of ± 0.5% when measured at 80 ° C. and 90% RH, based on the dimensions of the film left at 23 ° C. and 55% RH for 24 hours. Is preferably less than ± 0.2%, more preferably less than ± 0.1%.

  The production method of the polarizing plate of the present invention is not particularly limited, and can be produced by a general method. The obtained polarizing plate protective film was treated with an alkali, and a polyvinyl alcohol film was immersed and drawn in an iodine solution. Can be pasted together. This method is preferable in that the polarizing plate protective film of the present invention can be directly bonded to the polarizer on at least one side.

  Further, instead of the alkali treatment, easy-adhesion processing as described in JP-A-6-94915 and JP-A-6-118232 may be applied to perform polarizing plate processing.

  The polarizing plate is composed of a polarizer and a protective film for protecting both surfaces of the polarizer, and can further be constructed by laminating a protective film on one surface of the polarizing plate and a separate film on the opposite surface. The protective film and the separate film are used for the purpose of protecting the polarizing plate when the polarizing plate is shipped or transported. In this case, the protect film is bonded for the purpose of protecting the surface of the polarizing plate, and is used on the side opposite to the surface where the polarizing plate is bonded to the liquid crystal plate. The separate film is used for the purpose of covering the adhesive layer.

<Liquid crystal display device>
A liquid crystal display device composed of a polarizing plate including the polarizing plate protective film of the present invention is used for developing a higher display quality than a normal polarizing plate. In particular, the effect of the present invention can be further exerted when used in a multi-domain liquid crystal display device, more preferably in a multi-domain liquid crystal display device by a birefringence mode.

  Multi-domaining is also suitable for improving the symmetry of image display, and various methods have been reported "Okita, Yamauchi: Liquid Crystal, 6 (3), 303 (2002)". The liquid crystal display cell is also shown in “Yamada, Yamahara: Liquid Crystal, 7 (2), 184 (2003)”, but is not limited thereto.

  The polarizing plate of the present invention includes an MVA (Multi-domain Vertical Alignment) mode represented by a vertical alignment mode, in particular, an MVA mode divided into four, a known PVA (Patterned Vertical Alignment) mode and an electrode multi-domained by an electrode arrangement. It can be effectively used in a CPA (Continuous Pinwheel Alignment) mode in which arrangement and chiral ability are fused. In addition, a proposal of an optically biaxial film in the adaptation to the OCB (Optical Compensated Bend) mode has been disclosed, and “T. Miyashita, T. Uchida: J. SID, 3 (1), 29 ( 1995) ”, the effect of the present invention can be exhibited in the display quality by the polarizing plate of the present invention. If the effect of this invention can be expressed by using the polarizing plate of this invention, arrangement | positioning of a liquid crystal mode and a polarizing plate will not be limited.

  The display quality of the display cell is preferably symmetrical with respect to human observation. Therefore, when the display cell is a liquid crystal display cell, it is possible to multiplex domains by giving priority to the symmetry on the observation side. A known method can be used to divide the domain, and can be determined in consideration of the properties of a known liquid crystal mode by a two-part dividing method, more preferably a four-part dividing method.

  Liquid crystal display devices are also being applied to color display and video display devices, and display quality in the present invention is improved by contrast and improved resistance to polarizing plates, making it possible to display faithful moving images with less fatigue. It becomes.

  In the liquid crystal display device of the present invention, the polarizing plate including the polarizing plate protective film of the present invention is disposed on only one surface of the liquid crystal cell or on both surfaces. At this time, it can contribute to the improvement of display quality by using so that the polarizing plate protective film of this invention contained in a polarizing plate may become a liquid crystal cell side. In FIG. 1, the films 2a and 2b face the liquid crystal cell of the liquid crystal display device.

  In such a configuration, the presence of the polarizing plate protective film of the present invention can optically compensate the liquid crystal cell. When the polarizing plate of the present invention is used in a liquid crystal display device, at least one polarizing plate in the liquid crystal display device may be the polarizing plate of the present invention. By using the polarizing plate of the present invention, a liquid crystal display device with improved display quality and excellent viewing angle characteristics can be provided.

  EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. In addition, the following "part" represents a "mass part".

  First, the measurement method and materials used will be described.

(Retardation Ro, Rt)
Using a film that was allowed to stand for 24 hours in an environment of 23 ° C. and 55% RH, the retardation of the film at a wavelength of 590 nm was measured with an automatic birefringence meter KOBRA-21ADH (manufactured by Oji Scientific Instruments). Asked. The average refractive index and film thickness d of the film constituent material measured with an Abbe refractometer were inputted, and the values of in-plane retardation (Ro) and thickness direction retardation (Rt) were obtained. Further, the values of the three-dimensional refractive indexes nx, ny, and nz are calculated by the above device.

Formula (1) Ro = (nx−ny) × d
Formula (2) Rt = {(nx + ny) / 2−nz} × d
(Where nx is the refractive index in the slow axis direction in the film plane, ny is the refractive index in the fast axis direction in the film plane, nz is the refractive index in the thickness direction of the film, and d is Represents the thickness of the film.)
(Haze)
It measured using the haze meter (1001DP type, Nippon Denshoku Industries Co., Ltd. product).

(Tg)
The sample was cut into a round shape, 10 mg was enclosed in an aluminum sample pan, and vacuum-dried for 24 hours or more. Then, it heated up in nitrogen gas atmosphere from room temperature to 300 degreeC by differential scanning calorimetry (DSC) (DSC8230 type | mold made from Rigaku Corporation) at 10 degree-C / min, and measured glass transition temperature (Tg). Tg was obtained by taking the temperature at which the DSC curve begins to deviate from the baseline.

(Material)
<Cellulose resin>
Cellulose resin 1: substitution degree of acetyl group is 1.75, substitution degree of propionyl group is 0.80, alkaline earth metal content is 6 ppm, residual sulfuric acid content (as sulfur element) is 16 ppm, free acid content is Cellulose acetate propionate with 20 ppm and intrinsic viscosity of 1.54 Cellulose resin 2: Degree of substitution of acetyl group 1.92, degree of substitution of propionyl group 0.76, alkaline earth metal content 15 ppm, residual sulfuric acid Cellulose acetate propionate with a content (as elemental sulfur) of 20 ppm, a free acid content of 8 ppm, and an intrinsic viscosity of 1.61 Cellulose resin 3: Degree of substitution of acetyl group is 1.94, degree of substitution of propionyl group 0.63, alkaline earth metal content 8 ppm, residual sulfuric acid content (as elemental sulfur) 25 ppm, free acid content Cellulose acetate propionate having an intrinsic viscosity of 1.54 and cellulose resin 4: Cellulose resin 4: acetyl group substitution degree 2.11, propionyl group substitution degree 0.70, alkaline earth metal content 30 ppm, residual Cellulose acetate propionate having a sulfuric acid content (as elemental sulfur) of 45 ppm, a free acid content of 110 ppm, and an intrinsic viscosity of 1.73 Cellulose resin 5: Acetyl group substitution degree of 1.92, propionyl group substitution degree Cellulose acetate propionate having an alkaline earth metal content of 6 ppm, a residual sulfuric acid content (as elemental sulfur) of 12 ppm, a free acid content of 20 ppm, and an intrinsic viscosity of 1.59. Substitution degree of acetyl group is 2.10, substitution degree of propionyl group is 0.82, alkaline earth gold Cellulose acetate propionate having a genus content of 105 ppm, a residual sulfuric acid content (as a sulfur element) of 80 ppm, a free acid content of 510 ppm, and an intrinsic viscosity of 1.61 Cellulose resin 7: Degree of substitution of acetyl groups is 1. 60, cellulose acetate having a propionyl group substitution degree of 0.82, an alkaline earth metal content of 100 ppm, a residual sulfuric acid content (as a sulfur element) of 70 ppm, a free acid content of 200 ppm, and an intrinsic viscosity of 1.5 Propionate cellulose resin 8: Degree of substitution of acetyl group 1.75, degree of substitution of propionyl group 0.80, alkaline earth metal content 55 ppm, residual sulfuric acid content (as sulfur element) 60 ppm, free acid Cellulose acetate propionate with a content of 110 ppm and an intrinsic viscosity of 1.57 Resin 9: Substitution degree of acetyl group is 2.0, substitution degree of butyryl group is 0.70, alkaline earth metal content is 3 ppm, residual sulfuric acid content (as sulfur element) is 1 ppm, free acid content is 20 ppm Cellulose acetate butyrate having an intrinsic viscosity of 1.6 Cellulose resin 10: acetyl group substitution degree 1.9, butyryl group substitution degree 0.9, alkaline earth metal content 6 ppm, residual sulfuric acid content Cellulose acetate butyrate with 12 ppm (as elemental sulfur), free acid content of 20 ppm, and intrinsic viscosity of 1.5 <Plasticizer>
Plasticizer 1: 10 parts by mass of trimethylolpropane tribenzoate Plasticizer 2: 10 parts by mass of triphenyl phosphate <Additives>
Additive 1: IRGANOX 1010 (Ciba Specialty Chemicals)
0.2 parts by mass Additive 2: Epoxidized tall oil (acid scavenger) 0.2 parts by mass Additive 3: HALS-1 0.2 parts by mass Example 1
(Preparation of polarizing plate protective films 1 to 17)
The cellulose resin was heat-treated at 120 ° C. for 1 hour in dry air and allowed to cool to room temperature in dry air. With respect to 90 parts by mass of the dried cellulose resin, the plasticizers and additives other than the cellulose resin are added in the composition shown in Table 1 and mixed with a Henschel mixer, and then heated using an extruder to produce pellets. Allowed to cool.

  After drying this pellet at 120 ° C., using an extruder, it is heated and melted at the melting temperature shown in Table 1, extruded from a T-die, and the roll temperature is obtained via a take-up roll at 158 ° C. The film was stretched 1.1 times in the direction, followed by 1.4 times in the width direction using a tenter, and then relaxed, and the ears at both ends of the width were removed by slitting while cooling. ), A knurling having a height of 10 μm and a width of 1.5 cm was provided at both ends, and wound to obtain a polarizing plate protective film 1 having a roll thickness of 80 μm, Ro of 50 nm, and Rt of 130 nm.

  The composition was changed to the composition shown in Table 1, and the polarizing plate protective films 2 to 17 were obtained in the same manner by controlling the stretching. The polarizing plate protective films 2 to 14 and 14 to 17 had Ro of 45 to 55 nm and Rt of 125 to 135 nm.

(Evaluation)
About the produced polarizing plate protective film, the lip | stick part adhesion, the fracture | rupture condition, and the luminescent point were evaluated as follows.

<Lip attachment>
After film formation of 30000 m, the adhesion state of the melt to the lip portion of the T-type die was observed and evaluated according to the following criteria.

◎: Adherence of the melt to the lip is not recognized. ○: Adherence of the melt to the lip is very slight but there is no problem. △: Adherence of the melt to the lip is slightly observed. Weak streaks are observed in the film formed ×: adhesion of the melt to the lip is recognized, and streaks are observed in the formed film
Further, the film formation was continued, and during the film formation for one week, the breaking condition of the film was observed from the thermal stretching to the slitter part, and evaluated according to the following criteria.

○: The film did not break from the hot stretching to the slitter part. Δ: The film broke 1-2 times from the hot stretching to the slitter part. X: The film was broken three or more times from the hot stretching to the slitter part. The results are shown in Table 1.

  It turns out that the polarizing plate protective film of this invention is excellent in the lip part adhesion and the fracture | rupture condition compared with a comparative example.

(Preparation of polarizing plate)
Next, the prepared polarizing plate protective films 1 to 17 and a commercially available KC8UY (80 μm TAC film manufactured by Konica Minolta) were subjected to the following alkali saponification treatment to prepare polarizing plates 1 to 17, respectively.

<Alkali saponification treatment>
Saponification process 2 mol / L NaOH 50 ° C. 90 seconds Water washing process Water 30 ° C. 45 seconds Neutralization process 10% HCl 30 ° C. 45 seconds Water washing process Water 30 ° C. 45 seconds After saponification treatment, water washing, neutralization and water washing are performed in this order. And then dried at 80 ° C.

<Production of polarizer>
A 120 μm-thick long roll polyvinyl alcohol film was immersed in 100 parts by mass of an aqueous solution containing 1 part by mass of iodine and 4 parts by mass of boric acid, and stretched in the transport direction 6 times at 50 ° C. to produce a polarizer.

  The prepared polarizing plate protective film (used as a retardation film) on the liquid crystal cell side of the polarizer, KC8UY as the protective film on the surface opposite to the liquid crystal cell, and the alkali saponified surface is 5% by mass of the fully saponified polyvinyl alcohol. An aqueous solution was used as an adhesive to bond from both sides, and a polarizing plate having protective films bonded to both sides was prepared.

(Production of VA liquid crystal display device)
The polarizing plate bonded to the Fujitsu 15-inch liquid crystal display VL-1530S is peeled off, and the transmission axes of the above-prepared polarizing plates 1 to 17 are pasted in the same direction as the transmission axis of the bonded polarizing plate. The VA type liquid crystal display devices 1 to 17 were produced respectively. Two polarizing plates were prepared in the same manner, and one was used for each of the observation side and the backlight side of the liquid crystal cell as shown in FIG. It bonded so that the polarizing plate protective film (retardation film) bonded by each polarizing plate might be arrange | positioned at the liquid crystal cell side.

(Evaluation)
About the produced VA type | mold liquid crystal display device, the viewing angle and the moving image were evaluated as follows.

<Viewing angle>
Viewing angle evaluation measured the liquid crystal panel which bonded the polarizing plate obtained above using ELZIM EZ-contrast. The measuring method evaluated the range of the inclination angle from the normal direction with respect to the panel surface in which the contrast ratio at the time of white display and black display of a liquid crystal panel is 10 or more. When the normal is 0 °, the viewing angle region becomes wider as the tilt angle increases.

  The evaluation panel was evaluated according to the following criteria, with the contrast value in an oblique 45 ° azimuth when the horizontal direction was 0 °.

A: The inclination angle from the normal direction to the panel surface is 80 ° or more. ○: The inclination angle from the normal direction to the panel surface is 70 ° or more and less than 80 °. X: The inclination from the normal direction to the panel surface. Table 2 shows the evaluation results where the angle was less than 70 °.

  Table 2 shows that the liquid crystal display device using the polarizing plate of the present invention is a liquid crystal display device having an excellent viewing angle.

It is a schematic diagram which shows the structure of the display apparatus of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1a Protective film 1b Protective film 2a Phase difference film 2b Phase difference film 5a, 5b Polarizer 3a, 3b Film slow axis direction 4a, 4b Polarizer transmission axis direction 6a, 6b Polarizer 7 Liquid crystal cell 9 Liquid crystal display device

Claims (5)

A cellulose resin having a total substitution degree of acyl groups of 2.5 to 2.9, an alkaline earth metal content of 1 to 50 ppm, and a residual sulfuric acid content (as a content of sulfur element) of 0.1 to 45 ppm, After heat-melting and extruding a film-forming material containing 0.01% by mass or more and 5% by mass or less of a hindered amine compound or a hindered phenol compound and a plasticizer, the film obtained by cooling is heated again and hot stretched The manufacturing method of the polarizing plate protective film characterized by cooling. The alkaline earth metal content of the cellulose resin is 1 to 30 ppm, the residual sulfuric acid content (as the sulfur element content) is 0.1 to 30 ppm, and the free acid content is 1 to 70 ppm. The manufacturing method of the polarizing plate protective film of Claim 1. The in-plane retardation Ro of the said polarizing plate protective film is 30-200 nm, and the retardation Rt of the thickness direction is 70-400 nm, The manufacturing method of the polarizing plate protective film of Claim 1 or 2 characterized by the above-mentioned. The polarizing plate protective film manufactured by the manufacturing method of the polarizing plate protective film of any one of Claims 1-3 is used for at least one surface of a polarizer, The polarizing plate characterized by the above-mentioned. A liquid crystal display device using the polarizing plate according to claim 4.

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