JP2011237511A - Polarizing plate protective film and polarizing plate using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polarizing plate protective film improving the contrast of a liquid crystal display device and a polarizing plate using the same.SOLUTION: A polarizing plate protective film contains polyester or polycarbonate which has isosorbide as a diol component, and cellulose ester.

Description

  The present invention relates to a polarizing plate protective film used for a display device such as a liquid crystal display device and a polarizing plate using the same, and more particularly to a polarizing plate protective film for improving contrast and a polarizing plate using the same.

  With the recent increase in environmental awareness, there is a growing movement to actively utilize polymers derived from plant-derived materials. Various plant-derived polymers that can be used for the optical film are exemplified, and among them, cellulose ester and isosorbide polymer, which are particularly excellent in heat resistance, are attracting attention.

  An isosorbide-based polymer is preferable as an optical film as seen in, for example, Patent Document 1. However, when an isosorbide-based polymer, particularly a polycarbonate containing isosorbide as a diol component, is used for the polarizing plate protective film, it does not sufficiently contribute to the contrast of the liquid crystal display device.

  Cellulose ester, on the other hand, has been well known as the most suitable polymer for a polarizing plate protective film. The surface is made hydrophilic by alkali saponification treatment, bonded with polyvinyl alcohol, a polarizer, and a water-based adhesive, and then dried as a whole. It is customary to produce a polarizing plate. At this time, the speed of the saponification reaction and the speed of drying are advantageous because the cellulose ester having a low substitution degree, which is more hydrophilic, is advantageous, and therefore, the total substitution degree is preferably set low. However, in that case, it becomes more difficult to control the saponification reaction, and unevenness of the saponification treatment tends to occur in the surface. Further, the unevenness of the saponification treatment causes a slight unevenness of the shrinkage rate when the polarizing plate is dried, so that there is a problem that the axial accuracy uniformity of the polarizing plate is lowered and the contrast of the liquid crystal display device is lowered.

JP 2009-079191 A

  The objective of this invention is providing the polarizing plate protective film which raises the contrast of a liquid crystal display device, and a polarizing plate using the same.

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

  1. A polarizing plate protective film comprising polyester or polycarbonate containing isosorbide as a diol component, and cellulose ester.

  2. 2. The polarizing plate protective film according to 1 above, wherein the total degree of substitution of the cellulose ester is in the range of 1.5 to 2.5.

  3. 3. The polarizing plate protective film as described in 1 or 2 above, wherein the polyester or polycarbonate containing the isosorbide as a diol component has a weight average molecular weight of 30,000 or less.

  4). The polarizing plate protective film of any one of said 1-3 is laminated | stacked on at least one surface of a polarizer as a protective film, The polarizing plate characterized by the above-mentioned.

  According to the present invention, it was possible to provide a polarizing plate protective film that increases the contrast of a liquid crystal display device and a polarizing plate using the same.

  Hereinafter, embodiments for carrying out the present invention will be described in detail.

  As a result of intensive studies in view of the above problems, the present inventor has obtained a polarizing plate protective film containing a polyester or polycarbonate having isosorbide as a diol component and a cellulose ester, and a polarizing plate using the polarizing plate protective film. It has been found that the contrast can be increased and the present invention has been achieved.

  The inventor considered as follows about the mechanism by which the polarizing plate protective film of the present invention and the polarizing plate using the protective film increase the contrast of the liquid crystal display device.

  The isosorbide-based polymer has an ether bond, and the cellulose ester has a hydrogen bond due to a hydroxyl group, and each of them is basically amorphous but has a slight crystallinity. It is thought that by blending both polymers, the crystallinity can be inhibited by intermingling with each other. Therefore, it was estimated that the microscopic non-uniformity was eliminated and the random structure could be maintained. This mechanism is thought to be due to the fact that the mutual hydrogen bonding is different between ether and hydroxyl.

  When both the above polymers are blended, in the case of a film mainly composed of cellulose ester, the saponification reaction rate becomes uniform, unevenness in in-plane shrinkage is eliminated, and the optical axis accuracy of the polarizing plate is improved. In the case of mainly an isosorbide polymer, crystallization is inhibited and weak light leakage under crossed nicols can be prevented, so that the contrast of the liquid crystal display device can be improved. In other words, the present invention achieves an improvement in contrast that cannot be achieved by each polymer alone by blending.

  The present invention will be described in detail below.

[Polyester or polycarbonate containing isosorbide as diol]
Isosorbide is a diol compound obtained by transferring starch, and a polycarbonate can be obtained by polycondensing this with dimethyl carbonate or diphenyl carbonate. Moreover, polyester is obtained by reaction with dicarboxylic acid, and these reactions are achieved using a known polycarbonate reaction or polyester reaction. Examples of dicarboxylic acids used for polyesterification include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, phthalic acid, o-phthalic acid, isophthalic acid, m- Examples include phthalic acid, terephthalic acid, and p-phthalic acid. Since polycarbonate can be regarded as polyester by carbonation for convenience, carbonic acid can also be mentioned as the dicarboxylic acid used for the above-mentioned polyesterification. In the present invention, carbonic acid, oxalic acid, succinic acid, and adipic acid are particularly preferable. A combination of two or more dicarboxylic acids and a combination of diols other than isosorbide, that is, a copolymer may be prepared.

  The resin used in the present invention may be copolymerized with aliphatic diols or aromatic bisphenols as long as the characteristics are not impaired.

  Specifically, linear diols such as ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, cyclohexanediol, cyclohexanedimethanol, etc. Among these, 1,3-propanediol, 1,4-butanediol, hexanediol, and cyclohexanedimethanol are preferable.

  As aromatic bisphenols, 2,2-bis (4-hydroxyphenyl) propane (commonly known as “bisphenol A”), 1,1-bis (4-hydroxyphenyl) cyclohexane, 1,1-bis (4-hydroxyphenyl) -3,3,5-trimethylcyclohexane, 4,4 '-(m-phenylenediisopropylidene) diphenol, 9,9-bis (4-hydroxy-3-methylphenyl) fluorene, 2,2-bis (4 -Hydroxy-3-methylphenyl) propane, 2,2-bis (4-hydroxyphenyl) -4-methylpentane, 1,1-bis (4-hydroxyphenyl) decane, 1,3-bis {2- (4 -Hydroxyphenyl) propyl} benzene and the like.

  Means for obtaining polycarbonate are described in JP-A-2009-079191, polyester is described in JP-T-2002-512280, and copolymer is described in JP-A-2006-028441.

  The polyester or polycarbonate having isosorbide as a diol of the present invention preferably has a weight average molecular weight of 3,000 to 30,000. This range is the most compatible range with respect to the cellulose ester, and does not cause fine phase separation by the polymer blend, and further contributes to contrast. On the other hand, when the molecular weight is less than 3000, the film strength may be lowered, which is not preferable. More preferably, it is 5000 or more and 30,000 or less.

  The weight average molecular weight of polyester or polycarbonate having isosorbide as a diol can be measured by a known method using high performance liquid chromatography or the like.

[Cellulose ester]
In the cellulose ester, the acyl group may be an aliphatic acyl group or an aromatic acyl group. In the case of an aliphatic acyl group, it may be linear or branched and may further have a substituent. The portion that is not substituted with an acyl group usually exists as a hydroxyl group. These can be synthesized by known methods.

  However, it is preferable to use a lower fatty acid ester of cellulose from the viewpoint of optical properties. In the present invention, the lower fatty acid in the lower fatty acid ester of cellulose means a fatty acid having 5 or less carbon atoms. For example, cellulose acetate, cellulose propionate, cellulose butyrate, cellulose pivalate and the like are preferable lower cellulose esters of cellulose. It is mentioned as a thing.

  For example, the cellulose ester may be obtained by substituting the hydroxyl group of the raw material cellulose with an acetic anhydride, propionic anhydride and / or butyric anhydride in the usual manner with an acetyl group, a propionyl group and / or a butyl group within the range described below. It is obtained with. The method for synthesizing such a cellulose ester is not particularly limited. For example, the cellulose ester can be synthesized with reference to the method described in JP-A-10-45804 or JP-A-6-501040. Or the cellulose ester of Unexamined-Japanese-Patent No. 2005-281645 can be used.

  The cellulose ester of the present invention preferably has a total substitution degree in the range of 1.5 to 2.5. This range is the most compatible range for polyesters or polycarbonates with isosorbide as a diol, does not cause fine phase separation due to the polymer blend, is less susceptible to unevenness during saponification, and further contributes to contrast It is. The degree of substitution of acyl groups such as acetyl, propionyl and butyl groups can be measured according to ASTM-D817-96.

  The cellulose ester raw material cellulose 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 preferred. A cotton linter is preferably used from the viewpoint of peelability during film formation. The cellulose ester made from these can be mixed suitably or can be used independently.

  The mixing ratio of polyester or polycarbonate and cellulose ester having isosorbide as a diol is not particularly limited as long as it is in a compatible range, but from the viewpoint of imparting surface hydrophilicity by saponification treatment and uniformity of saponification treatment, cellulose It is preferable that the ester occupies a majority, and it is more preferable that the cellulose ester is 60 to 95% by mass. In the case of mixing, the respective resins can be mixed by melting or dissolving at the time of preparing the dope.

[Plasticizer]
It is preferable to add a compound known as a plasticizer to the polarizing plate protective film of the present invention from the viewpoint of improving the film, such as improving mechanical properties, imparting flexibility, imparting water absorption resistance, and reducing moisture permeability. .

  There is no particular limitation on the plasticizer used in the present invention, but a functional group capable of interacting with cellulose derivatives or other additives by hydrogen bonding or the like so as not to cause haze or bleed out or volatilize from the film. It preferably has a group.

  Examples of such functional groups include hydroxyl groups, ether groups, carbonyl groups, ester groups, carboxylic acid residues, amino groups, imino groups, amide groups, imide groups, cyano groups, nitro groups, sulfonyl groups, sulfonic acid residues, Examples thereof include a phosphonyl group and a phosphonic acid residue, and a carbonyl group, an ester group and a phosphonyl group are preferred.

  Examples of such plasticizers include phosphate ester plasticizers, phthalate ester plasticizers, trimellitic acid ester plasticizers, pyromellitic acid plasticizers, polyhydric alcohol ester plasticizers, glycolate plasticizers. Agents, citric acid ester plasticizers, fatty acid ester plasticizers, carboxylic acid ester plasticizers, polyester plasticizers and the like can be preferably used, but polyhydric alcohol ester plasticizers, polyester plasticizers are particularly preferable. Citrate ester plasticizers, phthalate ester plasticizers, non-phosphate ester plasticizers such as acrylic plasticizers such as polymethyl methacrylate having a molecular weight of 1,000 to 100,000 or a copolymer thereof. The polyhydric alcohol ester is composed of an ester of a dihydric or higher aliphatic polyhydric alcohol and a monocarboxylic acid, and preferably has an aromatic ring or a cycloalkyl ring in the molecule.

[Ultraviolet absorber]
The polarizing plate protective film of the present invention preferably contains an ultraviolet absorber, and examples of the ultraviolet absorber used include benzotriazole-based, 2-hydroxybenzophenone-based or salicylic acid phenyl ester-based ones. For example, 2- (5-methyl-2-hydroxyphenyl) benzotriazole, 2- [2-hydroxy-3,5-bis (α, α-dimethylbenzyl) phenyl] -2H-benzotriazole, 2- (3 Triazoles such as 5-di-t-butyl-2-hydroxyphenyl) benzotriazole, 2-hydroxy-4-methoxybenzophenone, 2-hydroxy-4-octoxybenzophenone, 2,2′-dihydroxy-4-methoxybenzophenone And benzophenones.

  Here, among the ultraviolet absorbers, an ultraviolet absorber having a molecular weight of 400 or more is not easily volatilized at a high boiling point and is not easily scattered during high-temperature molding, so that even a relatively small amount is effective.

[Retardation adjuster]
The polarizing plate protective film of the present invention is derived from a polarizing plate protective film and a liquid crystal layer by adding a retardation adjusting agent in the film or forming an alignment film to provide a liquid crystal layer in order to improve the liquid crystal display quality. Optical compensation ability can be imparted by combining retardation. In particular, the retardation adjusting agent can be expected to have the effect of coloring the film and reducing haze in that it can impart a desired retardation without excessive stretching.

  The compound to be added to adjust the retardation may be an aromatic compound having two or more aromatic rings as described in EP 911,656 A2, which is used as a retardation adjusting agent. preferable. For example, the following rod-shaped compounds are mentioned. 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, a 1,3,5-triazine ring is particularly preferred.

<Bar compound>
The polarizing plate protective film of the present invention preferably contains a rod-like compound having a maximum absorption wavelength (λmax) of the ultraviolet absorption spectrum of the solution shorter than 250 nm.

  From the viewpoint of the function of the retardation increasing agent, the rod-like compound preferably has at least one aromatic ring, and more preferably has at least two aromatic rings. The rod-like compound preferably has a linear molecular structure. The linear molecular structure means that the molecular structure of the rod-like compound is linear in the most thermodynamically stable structure. The most thermodynamically stable structure can be obtained by crystal structure analysis or molecular orbital calculation.

(Matting agent)
The polarizing plate protective film of the present invention preferably contains a matting agent as a slipping agent for preventing blocking of the film.

  As the matting agent, examples of inorganic compounds include silicon dioxide, titanium dioxide, aluminum oxide, zirconium oxide, calcium carbonate, calcium carbonate, talc, clay, tin oxide, indium oxide, zinc oxide, ITO, antimony oxide or a composite thereof. Mention may be made of oxides, calcined kaolin, calcined calcium silicate, hydrated calcium silicate, aluminum silicate, magnesium silicate and calcium phosphate. Fine particles containing silicon are preferred from the viewpoint of low turbidity, and silicon dioxide or silicone is particularly preferred.

  The average primary particle size of the matting agent is preferably 5 nm to 1 μm, and more preferably 5 to 50 nm. These are mainly contained as primary particles or secondary aggregates having an average particle size of 0.05 to 1 μm, preferably 0.05 to 0.3 μm. The content of these matting agents in the polarizing plate protective film of the present invention is preferably 0.05 to 10% by mass, particularly preferably 0.1 to 1% by mass.

[Other additives]
The polarizing plate protective film of the present invention further includes a dye, an anti-coloring agent, a crystal nucleating agent, a slip agent, a stabilizer, an anti-blocking agent, a peeling aid, a fluorescent brightening agent, a viscosity modifier, an antifoaming agent, and a transparent An agent, an antistatic agent, a pH adjusting agent or the like may be added.

  Various additives may be added batchwise to the liquid dope before film formation, or an additive solution may be separately prepared and added inline.

[Production method of polarizing plate protective film]
The polarizing plate protective film of the present invention can be produced by a known method such as a melt casting film forming method or a solution casting film forming method.

<Solution casting film forming method>
(Organic solvent)
An organic solvent useful for forming a dope when a polarizing plate protective film is produced by a solution casting method is not limited as long as it dissolves an isosorbide ester compound, a resin comprising a cellulose ester, and other additives at the same time. Can be used.

  For example, as a chlorine organic solvent, methylene chloride, as a non-chlorine organic solvent, methyl acetate, ethyl acetate, amyl acetate, acetone, tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane, cyclohexanone, ethyl formate, 2,2,2-trifluoroethanol, 2,2,3,3-hexafluoro-1-propanol, 1,3-difluoro-2-propanol, 1,1,1,3,3,3-hexafluoro- Examples include 2-methyl-2-propanol, 1,1,1,3,3,3-hexafluoro-2-propanol, 2,2,3,3,3-pentafluoro-1-propanol, and nitroethane. Methylene chloride, methyl acetate, ethyl acetate and acetone can be preferably used.

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

  In particular, a dope composition in which at least 15 to 45% by mass of the resin is dissolved in a solvent containing methylene chloride and a linear or branched aliphatic alcohol having 1 to 4 carbon atoms is preferable.

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

(Solution casting method)
In the solution casting method, a step of preparing a dope by dissolving a resin and an additive in a solvent, a step of casting the dope on a belt-like or drum-like metal support, and a step of drying the cast dope as a web , A step of peeling from the metal support, a step of stretching or maintaining the width, a step of further drying, and a step of winding up the finished film.

  The concentration of the resin in the dope is preferably higher because the drying load after casting on the metal support can be reduced. However, if the concentration of the resin is too high, the load during filtration increases and the filtration accuracy is poor. Become. As a density | concentration which makes these compatible, 10-35 mass% is preferable, More preferably, it is 15-25 mass%.

  The metal support in the casting (casting) step preferably has a mirror-finished surface, and a stainless steel belt or a drum whose surface is plated with a casting is preferably used as the metal support.

  The cast width can be 1 to 4 m. The surface temperature of the metal support in the casting step is set to −50 ° C. to a temperature at which the solvent boils and does not foam. A higher temperature is preferred because the web can be dried faster, but if it is too high, the web may foam or the flatness may deteriorate.

  The preferable support temperature is appropriately determined at 0 to 100 ° C, and more preferably 5 to 30 ° C. Alternatively, it is also a preferable method that the web is gelled by cooling and peeled from the drum in a state containing a large amount of residual solvent.

  The method for controlling the temperature of the metal support is not particularly limited, and there are a method of blowing hot air or cold air, and a method of contacting hot water with the back side of the metal support. It is preferable to use warm water because heat transfer is performed efficiently, so that the time until the temperature of the metal support becomes constant is short.

  When using warm air, considering the temperature drop of the web due to the latent heat of vaporization of the solvent, while using warm air above the boiling point of the solvent, there may be cases where wind at a temperature higher than the target temperature is used while preventing foaming. .

  In particular, it is preferable to perform drying efficiently by changing the temperature of the support and the temperature of the drying air during the period from casting to peeling.

  In order for the polarizing plate protective film to exhibit good planarity, the residual solvent amount when peeling the web from the metal support is preferably 10 to 150% by mass, more preferably 20 to 40% by mass or 60 to 130% by mass. %, Particularly preferably 20 to 30% by mass or 70 to 120% by mass.

  The amount of residual solvent is defined by the following formula.

Residual solvent amount (% by mass) = {(MN) / N} × 100
Note that M is the mass of a sample collected during or after the production of the web or film, and N is the mass after heating M at 115 ° C. for 1 hour.

  In the drying process of the polarizing plate protective film or resin, the web is preferably peeled off from the metal support and further dried to make the residual solvent amount 1% by mass or less, more preferably 0.1% by mass or less. And particularly preferably 0 to 0.01% by mass or less.

  In the film drying step, generally, a roll drying method (a method in which webs are alternately passed through a plurality of rolls arranged above and below) and a method in which the web is dried while being conveyed by a tenter method are employed.

(Stretching process)
The polarizing plate protective film of the present invention is preferably subjected to stretching treatment for adjusting the retardation.

  In the stretching step, the polarizing plate protective film can be sequentially or simultaneously stretched in the longitudinal direction (MD direction) and the width direction (TD direction). The draw ratios in the biaxial directions perpendicular to each other are preferably finally in the range of 1.0 to 3.0 times in the MD direction and 1.07 to 3.0 times in the TD direction.

  For example, a method in which peripheral speed differences are applied to a plurality of rolls and a roll peripheral speed difference is used to stretch in the MD direction, both ends of the web are fixed with clips and pins, and the distance between the clips and pins is increased in the traveling direction. And a method of stretching in the MD direction, a method of stretching in the transverse direction and stretching in the TD direction, a method of stretching in the MD / TD direction simultaneously and stretching in both the MD / TD directions, and the like.

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

  The film transport tension in the film forming process such as in the tenter depends on the temperature, but is preferably 120 N / m to 200 N / m, more preferably 140 N / m to 200 N / m per film width. 140 N / m to 160 N / m is most preferable.

  The temperature during stretching is (Tg-30) to (Tg + 100) ° C., more preferably (Tg-20) to (Tg + 80) ° C., and more preferably (Tg-5), where Tg is the glass transition temperature of the polarizing plate protective film. ) To (Tg + 20) ° C.

  The Tg of the polarizing plate protective film can be controlled by the type of material constituting the film and the ratio of the constituting materials. In the application of the present invention, the Tg when the film is dried is preferably 110 ° C. or higher, more preferably 120 ° C. or higher.

  Accordingly, the glass transition temperature is preferably 190 ° C. or lower, more preferably 170 ° C. or lower. At this time, the Tg of the film can be determined by the method described in JIS K7121.

  It is preferable that the temperature during stretching is 150 ° C. or more and the stretching ratio is 1.15 times or more because the surface is appropriately roughened. Roughening the film surface is preferable because it improves not only the slipperiness but also the surface processability, particularly the adhesion of the hard coat layer. The arithmetic average roughness Ra is preferably 2.0 nm to 4.0 nm, more preferably 2.5 nm to 3.5 nm.

<Melting method>
The melt film forming method refers to heating and melting a composition containing an additive such as a resin and a plasticizer to a temperature showing fluidity, and then casting the melt containing the fluid resin.

  More specifically, the heat 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 molding methods, the melt extrusion method is preferable from the viewpoint of mechanical strength and surface accuracy. It is preferable that a plurality of raw materials used for melt extrusion are usually kneaded in advance and pelletized.

  Pelletization may be performed by a known method. For example, a dry resin, a plasticizer, and other additives are supplied to an extruder with a feeder, kneaded using a single or twin screw extruder, and extruded from a die into a strand. Can be done by water cooling or air cooling and cutting.

  The additives may be mixed before being supplied to the extruder, or may be supplied by individual feeders.

  A small amount of additives such as particles and antioxidants are preferably mixed in advance in order to mix uniformly.

  The extruder is preferably processed at as low a temperature as possible so as to be able to be pelletized so that the shear force is suppressed and the resin does not deteriorate (decrease in molecular weight, coloring, gel formation, etc.). For example, in the case of a twin screw extruder, it is preferable to rotate in the same direction using a deep groove type screw. From the uniformity of kneading, the meshing type is preferable.

  A film is formed using the pellets obtained as described above. Of course, the raw material powder can be directly fed to the extruder by a feeder without being pelletized to form a film as it is.

  Using a single or twin screw extruder, the pellets are melted at a temperature of about 200 to 300 ° C., filtered through a leaf disk filter, etc. to remove foreign matter, and then formed into a film from a T die. The film is nipped by a cooling roll and an elastic touch roll, and solidified on the cooling roll.

  When introducing from the supply hopper to the extruder, it is preferable to prevent oxidative decomposition or the like under vacuum, reduced pressure, or inert gas atmosphere.

  The extrusion flow rate is preferably performed stably by introducing a gear pump or the like. Further, a stainless fiber sintered filter is preferably used as a filter used for removing foreign substances.

  The stainless steel fiber sintered filter is a united stainless steel fiber body that is intricately intertwined and compressed, and the contact points are sintered and integrated. The density of the fiber is changed depending on the thickness of the fiber and the amount of compression, and the filtration accuracy is improved. Can be adjusted.

  Additives such as plasticizers and particles may be mixed with the resin in advance, or may be kneaded in the middle of the extruder. In order to add uniformly, it is preferable to use a mixing apparatus such as a static mixer.

  The film temperature on the touch roll side when the film is nipped between the cooling roll and the elastic touch roll is preferably Tg or more and Tg + 110 ° C. or less of the film. A well-known roll can be used for the roll which has the elastic body surface used for such a purpose.

  The elastic touch roll is also called a pinching rotator. As the elastic touch roll, a touch roll disclosed in registered patent 3194904, registered patent 3422798, Japanese Patent Laid-Open No. 2002-36332, Japanese Patent Laid-Open No. 2002-36333, or the like can be preferably used. These can also use what is marketed.

  When peeling the film from the cooling roll, it is preferable to control the tension to prevent deformation of the film.

  Moreover, it is preferable that the film obtained as described above is stretched by the stretching operation after passing through the step of contacting the cooling roll.

  Prior to winding, the ends may be slit and cut to the width of the product, and knurling (embossing) may be applied to both ends to prevent sticking or scratching during winding. The knurling method can process a metal ring having an uneven pattern on its side surface by heating or pressing. In addition, since the film has deform | transformed and cannot use as a product normally, the holding | grip part of the clip of both ends of a film is cut out and reused.

<Saponification treatment>
The polarizing plate protective film of the present invention is preferably saponified before being attached to the polarizer. In particular, when the cellulose ester is 50% or more, it is easy to obtain improved adhesion by saponification treatment.

  The saponification treatment step comprises steps such as alkali treatment, neutralization, water washing and drying. In the alkali treatment step, the polarizing plate protective film is immersed in a sodium hydroxide or potassium hydroxide aqueous solution bath having a concentration of 0.1N to 2N. The temperature of the bath is 10 to 70 ° C., preferably 40 to 60 ° C., and the immersion time is 10 seconds to 5 minutes. In the neutralization step, an acid aqueous solution bath using 0.01 to 1% acetic acid or the like is used. The washing process is immersed in a water bath. After water droplets adhering to the surface are squeezed, they are dried in a drying process. The drying temperature is preferably 40 to 120 ° C.

  High-temperature alkali treatment is preferred for rapid saponification treatment, but in this case, it is difficult to obtain in-plane uniformity of the saponification treatment. When the degree of saponification is not uniform in the plane, a slight difference in shrinkage / expansion rate occurs, and stress unevenness occurs due to heat at the time of bonding or after bonding. Therefore, microscopic in-plane axial accuracy uniformity is lowered, and the contrast as a liquid crystal display device is likely to be lowered. The polarizing plate protective film of the present invention is less likely to cause stress unevenness even with high-temperature alkali treatment.

<Polarizing plate>
In the polarizing plate of the present invention, a polarizing plate protective film is laminated as a protective film on at least one surface of the polarizer.

  The polarizing plate of the present invention can be produced by a general method.

  It is preferable that an adhesive layer is provided on the back surface side of the protective film for polarizing plate of the present invention and laminated on at least one surface of a polarizer produced by immersion and stretching in an iodine solution.

  The polarizing plate protective film of the present invention may be used on the other surface, or another polarizing plate protective film may be used. For example, a commercially available cellulose ester film (for example, Konica Minoltack KC8UX, KC4UX, KC5UX, KC8UY, KC4UY, KC12UR, KC8UCR-3, KC8UCR-4, KC8UCR-5, KC8UE, KC4R-4, KC4FR-3, KC4FR-3, KC4FR-3, KC4FR-3, KC4FR-3, KC4FR-3, -1, KC8UY-HA, KC8UX-RHA, manufactured by Konica Minolta Opto Co., Ltd.) and the like are preferably used.

  A polarizer, which is a main component of a polarizing plate, is an element that allows only light of a plane of polarization in a certain direction to pass. A typical polarizer currently known is a polyvinyl alcohol-based polarizing film, which is polyvinyl alcohol. There are one in which iodine is dyed on a system film and one in which dichroic dye is dyed.

  For the polarizer, a polyvinyl alcohol aqueous solution is formed into a film and dyed by uniaxial stretching or dyed or uniaxially stretched and then preferably subjected to a durability treatment with a boron compound.

As the pressure-sensitive adhesive used in the pressure-sensitive adhesive layer, a pressure-sensitive adhesive having a storage elastic modulus at 25 ° C. in the range of 1.0 × 10 ⁴ Pa to 1.0 × 10 ⁹ Pa in at least a part of the pressure-sensitive adhesive layer is used. Preferably, a curable pressure-sensitive adhesive that forms a high molecular weight body or a crosslinked structure by various chemical reactions after the pressure-sensitive adhesive is applied and bonded is suitably used.

  Specific examples include, for example, urethane adhesives, epoxy adhesives, aqueous polymer-isocyanate adhesives, curable adhesives such as thermosetting acrylic adhesives, moisture-curing urethane adhesives, polyether methacrylate types, Examples include anaerobic pressure-sensitive adhesives such as ester-based methacrylate type and oxidized polyether methacrylate, cyanoacrylate-based instantaneous pressure-sensitive adhesives, and acrylate-peroxide-based two-component instantaneous pressure-sensitive adhesives.

  The pressure-sensitive adhesive may be a one-component type or a type that is used by mixing two or more components before use.

  The pressure-sensitive adhesive may be a solvent system using an organic solvent as a medium, or an aqueous system such as an emulsion type, a colloidal dispersion type, or an aqueous solution type that is a medium containing water as a main component. It may be a solvent type. The density | concentration of the said adhesive liquid should just be suitably determined with the film thickness after adhesion, the coating method, the coating conditions, etc., and is 0.1-50 mass% normally.

<Liquid crystal display device>
By incorporating the polarizing plate bonded with the polarizing plate protective film of the present invention into a liquid crystal display device, various liquid crystal display devices with excellent visibility can be produced. Especially, large liquid crystal display devices, digital signage, etc. It is preferably used for a liquid crystal display device for outdoor use. The polarizing plate bonded with the polarizing plate protective film of the present invention is bonded to the liquid crystal cell via the adhesive layer or the like.

  The polarizing plate to which the polarizing plate protective film of the present invention is bonded is reflective type, transmissive type, transflective type LCD or TN type, STN type, OCB type, HAN type, VA type (PVA type, MVA type), IPS type ( It is preferably used in LCDs of various drive systems such as FFS system).

  In particular, in a large-screen display device having a screen size of 30 or more, especially 30 to 54, there is no white spot at the periphery of the screen, and the effect is maintained for a long time.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto. In addition, although the display of "part" or "%" is used in an Example, unless otherwise indicated, "part by mass" or "mass%" is represented.

<< Preparation of isosorbide polymer >>
The isosorbide polymer according to the present invention is a polyester or polycarbonate having isosorbide as a diol component, and is obtained by condensation polymerization of isosorbide and dicarboxylic acid or carbonic acid. Each polymer was prepared by referring to Example 1 of JP-A-2009-079191 for the synthesis method of polycarbonate and Example 1 of JP-A-2007-65484 for the synthesis method of polyester. In addition, the temperature, the amount of the polymerization initiator, and the like were appropriately adjusted so that a polymer having a desired molecular weight was obtained.

  The contents of isosorbide polymers 1 to 10 prepared in Table 1 are shown as combinations of isosorbide and dicarboxylic acid or carbonic acid, and the weight average molecular weight of the obtained polymer.

The weight average molecular weight was measured by gel permeation chromatography. The conditions are as follows.
Solvent: Methylene chloride column: Shodex K806, K805, K803 (used by connecting 3 products manufactured by Showa Denko KK)
Column temperature: 25 ° C
Sample concentration: 0.1% by mass
Detector: RI Model 504 (manufactured by GL Sciences)
Pump: L6000 (manufactured by Hitachi, Ltd.)
Flow rate: 1.0ml / min
Calibration curve: Standard polystyrene STK standard polystyrene (manufactured by Tosoh Corp.) Mw = 100000-500 calibration curves with 13 samples were used. The 13 samples were approximately equally spaced.

<< Preparation of cellulose ester >>
The degree of substitution of the cellulose ester according to the present invention can be adjusted by a known method. In the examples, the total degree of substitution was changed with an acetyl group and a propionyl group. Hereinafter, the acetyl group substitution degree and the propionyl group substitution degree are abbreviated as DSac and DSpr, respectively. The total degree of substitution is the sum of DSac and DSpr.

<< Production of polarizing plate protective film >>
By the following method, the polarizing plate protective film 1 was prepared by the solution casting film forming method, and the polarizing plate protective film 17 was prepared by the melt film forming method, respectively.

<Preparation of polarizing plate protective film 1>
The materials of the following dope composition 1 were sequentially put into a sealed container, the temperature in the container was raised from 20 ° C. to 80 ° C., and the mixture was stirred for 3 hours while maintaining the temperature at 80 ° C. Dissolved completely. The silicon oxide fine particles were added dispersed in a solution of a solvent to be added in advance and a small amount of cellulose ester. This dope was filtered using a filter paper (Azumi filter paper No. 244, manufactured by Azumi Filter Paper Co., Ltd.), and the following dope composition 1 was obtained.

<Dope composition 1>
Cellulose ester (acetyl substitution degree 1.92, propionyl substitution degree 0.74)
100 parts by mass Silicon oxide fine particles 0.2 parts by mass (Aerosil R972V, manufactured by Nippon Aerosil Co., Ltd.)
Tinuvin 928 (manufactured by Ciba Japan Co., Ltd.) 1 part by mass Methylene chloride 300 parts by mass Ethanol 40 parts by mass Butanol 5 parts by mass Next, the obtained dope composition 1 was stainless steel through a casting die kept at a temperature of 35 ° C. The web was formed by casting on a support made of a steel endless belt and having a temperature of 35 ° C. Next, the web was dried on the support, and the web was peeled from the support with a peeling roll when the residual solvent amount of the web reached 80% by mass.

  The web after peeling is transported while being dried with 90 ° C drying air in a transport drying process using a plurality of rolls arranged on the top and bottom, and then grips both ends of the web with a tenter and then stretches in the width direction at a temperature of 130 ° C. It extended | stretched so that it might become 1.5 times before. After stretching with a tenter, the web was dried with a drying air at a temperature of 135 ° C. in a transport drying process using a plurality of rolls arranged vertically.

  After heat-treating for 15 minutes in an atmosphere with an atmosphere substitution rate of 15 (times / hour) in the drying process, the film is cooled to room temperature and wound up to protect a long polarizing plate having a width of 1.5 m, a film thickness of 40 μm, and a length of 4000 m. Film 1 was produced. Further, the film was wound by applying a knurling process with a width of 1 cm and an average height of 10 μm at both ends.

<Preparation of polarizing plate protective film 17>
A film 17 was produced by melt casting with the following composition.

<Composition of polarizing plate protective film 17>
Isosorbide-based polymer 8 100 parts by mass Irganox 1010 (manufactured by Ciba Japan Co., Ltd.) 0.5 parts by mass ADK STAB PEP-36 (manufactured by ADEKA Co., Ltd.) 0.1 part by mass Sumilizer GS (manufactured by Sumitomo Chemical Co., Ltd.) 0 .2 parts by mass Silica particles (R972V manufactured by Nippon Aerosil Co., Ltd.) 0.1 parts by mass The above isosorbide polymer 8 was dried at 70 ° C. under reduced pressure for 3 hours and cooled to room temperature, and then each additive was mixed. This mixture was melt-kneaded with a twin-screw extruder having a co-rotating meshing screw, extruded into a strand, cooled through water, and cut into a pellet.

  The obtained pellets were again dried at 90 ° C. and formed into a film using a production apparatus using an elastic touch roll. In a nitrogen atmosphere, it was melted at 240 ° C., extruded from the casting die onto the first cooling roll, and molded by pressing the film between the first cooling roll and the touch roll.

  The heat bolt was adjusted so that the gap width of the casting die was 0.5 mm within 30 mm from the end in the width direction of the film and 1 mm at other locations. As a touch roll, 80 degreeC water was poured as cooling water in the inside.

  On the peripheral surface of the first cooling roller from the position where the resin extruded from the casting die contacts the first cooling roll to the position at the upstream end in the first cooling roll rotation direction of the nip between the first cooling roll and the touch roll. The length along was set to 20 mm.

  Thereafter, the touch roll was separated from the first cooling roll, and the temperature T of the melted part immediately before being sandwiched in the nip between the first cooling roll and the touch roll was measured. The temperature T of the melted part immediately before being squeezed by the nip between the first cooling roll and the touch roll is 1 mm upstream from the nip upstream end P2, and a thermometer (HA-200E manufactured by Anritsu Keiki Co., Ltd.). ). As a result of the measurement, the temperature T was 235 ° C.

  The linear pressure with respect to the 1st cooling roll of a touch roll was 50 N / cm. Thereafter, using the roll peripheral speed difference, the film is stretched 1.7 times at 175 ° C. in the conveying direction, further introduced into the tenter, stretched 2.1 times at 160 ° C. in the width direction, and then 1% in the width direction. Cool to 30 ° C while relaxing, then release from the clip, clip the clip gripping part, apply a 20mm width and 25μm height knurling to both ends of the film, take-up tension 220N / m, taper with 40% taper Rolled up.

  The winding core had an inner diameter of 152 mm, an outer diameter of 165 to 180 mm, and a length of 1550 mm. A polarizing plate protective film 17 having a film thickness of 40 μm and a winding length of 3500 m was produced.

<Preparation of other polarizing plate protective film>
In the production of the polarizing plate protective film 1 by the above-described solution casting film forming method, the cellulose ester (DSac: 1.92, DSpr: 0.74, total substitution degree 2.66) was replaced with the isosorbide polymer shown in Table 2. It replaced with the combination of cellulose ester and made the polarizing plate protective films 2-8 and 11-14 similarly to the polarizing plate protective film 1. FIG. Similarly, in the production of the polarizing plate protective film 17 by the melt film forming method, the isosorbide-based polymer 8 is replaced with the combination of the isosorbide-based polymer and the cellulose ester shown in Table 2 in the same manner as the polarizing plate protective film 17, and polarized light is obtained. Plate protective films 9, 10 and 15, 16 were prepared. In addition, the mass blending ratio of the isosorbide polymer (IS) and the cellulose ester (CE) is shown in the table as (IS / CE). The total amount is the same. In Table 2, the solution casting film formation method is abbreviated as solution, the melt film formation method is melting, and the weight average molecular weight is abbreviated as Mw. Furthermore, the polarizing plate protective film was abbreviated as a protective film.

<Preparation of polarizing plate>
Polarizing plates 1 to 17 were produced according to the following using the polarizing plate protective films 1 to 17.

  A polyvinyl alcohol film having a thickness of 120 μm was uniaxially stretched (temperature: 110 ° C., stretch ratio: 5 times). This was immersed in an aqueous solution consisting of 0.075 g of iodine, 5 g of potassium iodide and 100 g of water for 60 seconds, and then immersed in an aqueous solution of 68 ° C. consisting of 6 g of potassium iodide, 7.5 g of boric acid and 100 g of water. This was washed with water and dried to obtain a polarizer.

Next, according to the following steps 1 to 4, the polarizer, the polarizing plate protective films 1 to 17, and the back side, Konica Minolta Op Co., Ltd. Konica Minolta Tack KC8UY was bonded as a polarizing plate protective film, respectively 1-17 A polarizing plate was produced. In attaching the polarizing plate protective film to the polarizer, each polarizing plate protective film was preliminarily saponified.
(Saponification treatment)
After soaking in an alkaline bath, it was washed with water in a water bath (water temperature 25 ° C.) and dried with hot air at 90 ° C. Alkaline bath: 2N potassium hydroxide aqueous solution, temperature 70 ° C., immersion time 20 seconds.

  Step 1: The polarizer was immersed in a polyvinyl alcohol adhesive tank having a solid content of 2% by mass for 1 to 2 seconds.

  Step 2: The excess adhesive adhered to the polarizer in Step 1 was gently wiped off, placed on the polarizing plate protective film of the present invention, and further placed on the back side with a cellulose ester film Konica Minoltack KC8UY. .

Step 3: Step polarizer and a polarizing plate protective film was laminated with a 2 and the back-side cellulose ester film Konica Minolta TAC KC8UY pressure 20-30 N / cm ^2, the conveyance speed was pasted at approximately 2m / min.

  Process 4: The sample which bonded the polarizer produced in the process 3, the polarizing plate protective film, and the back side cellulose-ester film Konica Minolta Tack KC8UY in the 80 degreeC dryer for 2 minutes is dried, and polarizing plate protective film 1- Polarizing plates 1 to 17 corresponding to 17 were prepared.

<Production of liquid crystal display device>
A liquid crystal panel for front contrast measurement was produced as follows, and the characteristics as a liquid crystal display device were evaluated.

  The polarizing plates on both sides of the SONY 40-type display KLV-40V2500 previously bonded were peeled off, and the 17 types of polarizing plates prepared above were respectively bonded to both surfaces of the glass surface of the liquid crystal cell.

  At that time, the direction of bonding of the polarizing plate is such that the surface of the surface-modified resin film of the present invention is on the liquid crystal cell side and the absorption axis in the same direction as the polarizing plate previously bonded. The liquid crystal display devices 1 to 17 corresponding to the polarizing plates 1 to 17 were produced.

  This liquid crystal display device was evaluated for front contrast as a characteristic representative of contrast.

<Evaluation>
(Front contrast of liquid crystal display device)
In an environment of 23 ° C. and 55% RH, the backlight of this liquid crystal display was turned on and left as it was for 30 minutes, and then measurement was performed. For measurement, EZ-Contrast 160D manufactured by ELDIM was used to measure the front luminance of white display and black display with a liquid crystal TV, and the ratio was defined as the front contrast. The measurement results were ranked as follows according to the value of the front contrast.
A: Front contrast ratio = 700: 1 or more O: Front contrast ratio = 500: 1 or more and less than 700: 1 Δ: Front contrast ratio = 300: 1 or more and less than 500: 1 X: Front contrast ratio = less than 300: 1 The results are shown in Table 2. In Table 2, the liquid crystal display device number is abbreviated as display device number, and the front contrast is abbreviated as contrast.

  As is apparent from the results shown in Table 2, it is understood that the front contrast of the liquid crystal display device is good when the polarizing plate prepared from the polarizing plate protective film of the present invention is used.

Claims (4)

  A polarizing plate protective film comprising polyester or polycarbonate containing isosorbide as a diol component, and cellulose ester.   The polarizing plate protective film according to claim 1, wherein the total degree of substitution of the cellulose ester is in the range of 1.5 to 2.5.   3. The polarizing plate protective film according to claim 1, wherein the polyester or polycarbonate containing the isosorbide as a diol component has a weight average molecular weight of 30,000 or less.   The polarizing plate protective film of any one of Claims 1-3 was laminated | stacked as a protective film on the at least one surface of the polarizer, The polarizing plate characterized by the above-mentioned.