JPWO2015015538A1 - Polarizing plate protective film, polarizing plate and liquid crystal display device - Google Patents

Abstract

The objective of this invention is providing the polarizing plate protective film which can suppress deterioration of a polarizer when there are few dimensional changes by water content and it adhere | attached using water paste. The polarizing plate protective film of the present invention has a tensile modulus of elasticity of 3 GPa or more at 23 ° C. and 55% RH, and is conditioned at 23 ± 1 ° C. and 55% RH for 12 hours or more. When the film is immersed, the initial elongation rate of the film is 0.03 to 0.1% / min, and the film has an elongation of 0.4% or less after 30 minutes have passed after the film is immersed in water. , Polarizing plate protective film.

Description

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

  Currently, portable liquid crystal display devices such as smart phones and tablets are widely used. These liquid crystal display devices are required to be thin.

  A liquid crystal display device usually has a liquid crystal cell and a pair of polarizing plates sandwiching the liquid crystal cell. The polarizing plate may have a polarizer, a retardation film (F2 or F3) disposed on the liquid crystal cell side, and a protective film (F1 or F4) disposed on the opposite side of the liquid crystal cell.

  As the protective film (F1 or F4), a cellulose triacetate film (TAC) is used because it is transparent, has low birefringence, and can be easily adhered to a polarizer through water glue. However, since the cellulose triacetate film has high moisture permeability, when exposed to high humidity, the dimensional change of the polarizer is likely to occur due to moisture that has passed through the film. The dimensional change of the polarizer occurs when the polarizer contains water and expands under high humidity; and the water escapes and contracts under low humidity. Such a dimensional change of the polarizer tends to cause a bend of the panel (polarizing plate / liquid crystal cell / polarizing plate laminate); in particular, it becomes more prominent as the glass plate of the liquid crystal cell is thinner. Such a panel bend tends to cause display unevenness of the liquid crystal display device.

  Therefore, as a protective film having low moisture permeability, for example, a cyclic olefin resin film (for example, Patent Document 1), an acrylic resin film (for example, Patent Documents 2 and 3), a film containing an acrylic resin and a cellulose ester (for example, Patent Document 4 and 5) etc. are proposed.

JP 2004-258188 A JP 2007-63541 A JP 2012-180423 A JP 2011-253090 A JP 2009-299075 A

  By the way, a polarizing plate can be obtained by bonding a protective film and a polarizer through water paste, and then drying the resulting laminate. However, when the moisture permeability of the protective film is low, when the laminate is dried, the moisture of the water paste taken into the protective film is difficult to escape and the polarizer is liable to deteriorate. As a result, there is a problem that a red defect called reddish is likely to occur in the obtained polarizing plate.

  On the other hand, in order to reduce the dimensional change of the polarizer that causes panel bend, it is desired that the protective film has high mechanical strength and little dimensional change due to water content; in particular, small dimensional change due to water content.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a polarizing plate protective film that has little dimensional change due to water content and can suppress deterioration of a polarizer when bonded using water paste. And

[1] A film having a tensile modulus of elasticity of 3 GPa or higher at 23 ° C. and 55% RH, and after being conditioned in water at 23 ± 1 ° C. and 55% RH for 12 hours or more and then immersed in water at 23 ± 1 ° C. A polarizing plate protective film having an initial elongation rate of 0.03 to 0.1% / min and a film elongation of 0.4% or less after 30 minutes of immersion of the film in water.
[2] The polarizing plate protective film according to [1], including a (meth) acrylic resin.
[3] The polarizing plate protective film according to [2], wherein the water-octanol distribution coefficient of the (meth) acrylic resin is 1.2 or more.
[4] The polarizing plate protective film according to any one of [1] to [3], further comprising 5 to 25% by mass of a cellulose ester relative to the film.
[5] The polarizing plate protective film according to any one of [1] to [4], wherein the cellulose ester has a water-octanol distribution coefficient of 0 or more.
[6] The method according to any one of [1] to [5], comprising a (meth) acrylic resin having a water-octanol partition coefficient of 1.2 or more and a cellulose ester having a water-octanol partition coefficient of 0 or more. Polarizing plate protective film.
[7] The polarizing plate protective film according to any one of [1] to [6], wherein the polarizing plate protective film has a thickness of 10 to 50 μm.

[8] A polarizing plate comprising a polarizer and the polarizing plate protective film according to any one of [1] to [7].
[9] A first glass substrate and a second glass substrate having a thickness of 0.3 mm or more and less than 0.7 mm, and a liquid crystal layer disposed between the first glass substrate and the second glass substrate. Including a liquid crystal cell, a first polarizing plate disposed on the first glass substrate of the liquid crystal cell, and a second polarizing plate disposed on the second glass substrate of the liquid crystal cell, The first polarizing plate is a first polarizer, a protective film F1 disposed on a surface of the first polarizer opposite to the liquid crystal cell, and the liquid crystal cell of the first polarizer. A protective film F2 disposed on the surface on the side, the second polarizing plate is a second polarizer, and a protective film F3 disposed on the surface of the second polarizer on the liquid crystal cell side The protective film F4 disposed on the surface of the second polarizer opposite to the liquid crystal cell Seen, one or both of the protective film F1 and the protective film F4 is a polarizing plate protective film according to any one of [1] to [7], the liquid crystal display device.

  ADVANTAGE OF THE INVENTION According to this invention, the polarizing plate protective film which can suppress the deterioration of a polarizer when there are few dimensional changes by water content and it adhere | attached using water paste can be provided.

It is a figure which shows the relationship of the elongation amount of a film with respect to the elapsed time when a film is immersed in water. It is a schematic diagram which shows an example of the fundamental structure of a liquid crystal display device.

  As described above, when the laminate of the glass substrate and the polarizing plate is moved from the high temperature and high humidity condition to the high temperature and low humidity condition, warpage (panel bend) is likely to occur so that the glass substrate side becomes convex. In order to suppress such panel bends, it is effective that 1) the protective film has a mechanical strength that can withstand the shrinkage force of the polarizer; 2) the shrinkage force of the protective film is reduced.

  1) In order to increase the mechanical strength of the protective film, the protective film preferably has a high tensile elastic modulus. However, since the shrinkage force of the protective film is proportional to the product of the tensile elastic modulus, the dimensional change amount and the film thickness of the protective film, the higher the tensile elastic modulus of the protective film, the larger the shrinkage force of the protective film. Therefore, in order to reduce the shrinkage force of the protective film while increasing the tensile elastic modulus of the protective film, it is desired to reduce the amount of dimensional change due to water content of the protective film as much as possible.

  The amount of dimensional change due to the moisture content of the protective film depends on the moisture content rate (initial elongation rate) and the moisture content (elongation amount). FIG. 1 is a diagram showing the relationship between the film elongation and the immersion time when the film is immersed in water. In FIG. 1, the moisture content of the film corresponds to the initial film elongation rate; the moisture content of the film corresponds to the elongation of the film after a certain period of time.

  In order to reduce the dimensional change due to water content, it is preferable to reduce both the water content (elongation amount) and the water content rate (elongation rate) of the film. However, if the water content rate (elongation rate) is too small, it is difficult for water to escape from the film, and reddish (red defects) is likely to occur in a polarizing plate produced using water paste (see the downward arrow in FIG. 1).

  Therefore, in this invention, it is preferable to adjust the elongation rate and elongation amount of the film when the protective film is impregnated with water to a predetermined range as indicated by the hatched portion in FIG.

  Specifically, the protective film is preferably not more than 0.4%, more preferably not more than 0.35%, after 30 minutes of immersion in 23 ± 1 ° C. water. More preferably, it is 0.3% or less. When the elongation amount of the protective film is not more than a certain value, the moisture content of the film is small, so that the dimensional change amount of the film is small and panel bend is easily suppressed. The lower limit of the amount of elongation of the protective film can be about 0.2% in order to make it easy for water to escape.

  The protective film preferably has an initial elongation rate of 0.03-0.1% / min when immersed in water at 23 ± 1 ° C., and preferably 0.04-0.09% / min. More preferably, it is 0.04% / min or more and less than 0.08% / min. If the elongation rate of the protective film is below a certain level, the moisture content of the film is not too high, so that the dimensional change of the film can be reduced. On the other hand, when the elongation rate of the protective film is not less than a certain level, the moisture content of the film is not too small, so that water can be easily removed moderately, and redish can be hardly generated.

The elongation amount and elongation rate of the protective film can be measured by the following procedure.
1) Condition the protective film for 12 hours or more under the condition of 23 ± 1 ° C. and 55% RH.
2) The film equipped with the water immersion attachment is immersed in 23 ± 1 ° C. pure water using TMA / SS7100 manufactured by Hitachi High-Tech, and then taken out to measure the elongation of the film. The amount of elongation is measured in the MD direction of the film. Then, the “elongation (%)” of the film 30 minutes after the start of immersion is obtained. The MD direction is the film forming direction of the film and indicates the longitudinal direction of the film in the wound body; the TD direction is the direction orthogonal to the film forming direction of the film and indicates the width direction of the film.
3) The measured values obtained are plotted as abscissa: immersion time (minutes) and ordinate: film elongation (%) to obtain a curve. The slope of the obtained curve from the start of immersion to 2 minutes later (the slope of the elongation with respect to the immersion time) is defined as “elongation rate (% / min)”.

  When the protective film has an in-plane slow axis, the MD direction is preferably “the in-plane slow axis direction of the film” or “the direction perpendicular to the in-plane slow axis direction”; more preferably “in-plane slow axis direction”. It may be a “direction perpendicular to the slow axis direction”.

  The amount of elongation of the protective film is adjusted by the film composition; the elongation rate of the protective film can be adjusted by the film composition and surface treatment. In order to set the elongation and elongation rate of the protective film within the above ranges, a resin having a relatively high hydrophobicity and a resin having a relatively low hydrophobicity are combined; It is preferable to hydrophobize the film surface. Examples of combinations of resins with relatively high hydrophobicity and resins with relatively low hydrophobicity include combinations of (meth) acrylic resins and cellulose esters described later; urethane urea resins and polyester-polyurethane plastics described below. Combinations with agents are included.

  The tensile elastic modulus of the protective film at 23 ° C. and 55% RH is preferably 3 GPa or more, and more preferably 4 GPa or more. When the tensile elastic modulus of the protective film is a certain value or more, it can withstand the contraction force of the polarizer, so that panel bend is easily suppressed. The upper limit of the tensile elastic modulus of the protective film may be 10 GPa or less because handling becomes difficult. The tensile elastic modulus of the protective film at 23 ° C. and 55% RH is preferably substantially 3 GPa to 5 GPa.

The tensile elastic modulus of the protective film can be measured by the following method.
The protective film is cut into a size of 100 mm (MD direction) × 10 mm (TD direction) to obtain a sample film. In accordance with JIS K7127, this sample film is pulled in the MD direction using a Tensilon RTC-1225A manufactured by Orientec Co., Ltd., and the tensile elastic modulus in the MD direction is measured. The measurement is performed at 23 ° C. and 55% RH.

  The tensile elastic modulus of the protective film can be adjusted mainly by the film composition and production conditions. In order to increase the tensile elastic modulus of the protective film, it is preferable to increase the degree of orientation of the resin, for example, by stretching. It is also preferable to densify the resin by heat treatment.

1. Protective film The protective film of this invention contains a (meth) acrylic resin or urethane urea resin, and another resin or additive as needed.

(Meth) acrylic resin The (meth) acrylic resin can be a homopolymer of (meth) acrylic acid ester; or a copolymer of (meth) acrylic acid ester and another monomer copolymerizable therewith. Of these, a copolymer of (meth) acrylic acid ester and another monomer copolymerizable therewith is preferable because it is easy to adjust the hydrophobicity. In the present invention, (meth) acrylic acid ester refers to methacrylic acid ester or acrylic acid ester.

  The (meth) acrylic acid ester is preferably a (meth) acrylic acid alkyl ester, and more preferably methyl methacrylate.

  Examples of other monomers copolymerizable with methyl (meth) acrylate include (meth) acrylic acid esters other than methyl methacrylate; α, β-unsaturated acids such as acrylic acid and methacrylic acid; maleic acid, fumarate Divalent carboxylic acids containing unsaturated groups such as acid and itaconic acid; aromatic vinyl compounds such as styrene, α-methylstyrene and nucleus-substituted styrene; α, β-unsaturated nitriles such as acrylonitrile and methacrylonitrile; maleic anhydride Maleimide, N-substituted maleimide; glutaric anhydride and the like. The alkyl group in the acrylic acid alkyl ester and methacrylic acid alkyl ester may be cyclic or chain-like. These other monomers may be used alone or in combination of two or more.

  (Meth) acrylic acid esters other than methyl methacrylate are (meth) acrylic acid chain alkyl esters having 1 to 20 carbon atoms; alicyclic alkyl esters having 6 to 20 carbon atoms; or 6 carbon atoms. ~ 20 aryl esters and the like. Examples of the chain alkyl ester having 1 to 20 carbon atoms of (meth) acrylic acid include t-butyl methacrylate. Examples of the alicyclic alkyl ester of 6 to 20 carbon atoms of (meth) acrylic acid include tert-butylcyclohexyl methacrylate, adamantyl methacrylate, isobornyl methacrylate and the like. Examples of the aryl ester of (meth) acrylic acid having 6 to 20 carbon atoms include benzyl methacrylate and phenoxyethyl methacrylate.

  Especially, in order to make elongation amount and elongation rate of a protective film into the said range, it is preferable that another monomer contains a monomer with relatively high hydrophobicity.

  The monomer having relatively high hydrophobicity may be an aromatic ring-containing monomer or an alicyclic group-containing monomer. Examples of the aromatic ring-containing monomer include aromatic vinyl compounds such as styrene, α-methylstyrene, and nucleus-substituted styrene. Examples of the alicyclic group-containing monomer include methacrylic acid alkyl ester having a cyclic alkyl group. Of these, aromatic ring-containing monomers are preferable, and styrene is more preferable.

  Styrene includes atactic polystyrene, isotactic polystyrene, syndiotactic polystyrene, and the like depending on its stereoregularity, and can be appropriately selected according to hydrophobicity. Of these, syndiotactic polystyrene (SPS) having high heat resistance and hydrophobicity is more preferable.

  The content ratio of the structural unit derived from the monomer having a relatively high hydrophobicity with respect to all the structural units constituting the copolymer is preferably 20 to 90% by mass, although depending on the required hydrophobicity, 20 It is preferable that it is -80 mass%, and it is more preferable that it is 20-50 mass%. When the content ratio of the structural unit derived from the monomer having relatively high hydrophobicity is within the above range, the hydrophobicity of the (meth) acrylic resin can be easily increased appropriately.

  The content ratio of the structural unit derived from methyl methacrylate with respect to all the structural units constituting the copolymer is preferably 10 to 80% by mass, and more preferably 20 to 80% by mass.

  The weight average molecular weight (Mw) of the (meth) acrylic resin is preferably 10,000 to 2,000,000 in order to make the mechanical strength of the protective film equal to or higher than a certain level and ensure fluidity during film formation. More preferably, it is 10,000 to 1,000,000.

The weight average molecular weight (Mw) of the (meth) acrylic resin can be measured by gel permeation chromatography. The measurement conditions can be as follows.
Solvent: Methylene chloride Column: Three Shodex K806, K805, K803G (manufactured by Showa Denko KK) are connected and used.
Column temperature: 25 ° C
Sample concentration: 0.1% by mass
Detector: RI Model 504 (GL Science Co., Ltd.)
Pump: L6000 (manufactured by Hitachi, Ltd.)
Flow rate: 1.0 ml / min
Calibration curve: Standard polystyrene STK standard polystyrene (manufactured by Tosoh Corp.) Mw = 1.0 × 10 ^{6 to} 5.0 × 10 ² 13 calibration curves are used. The 13 samples are preferably selected at approximately equal intervals.

  The (meth) acrylic resin can be combined with a cellulose ester as described later from the viewpoint of adjusting the elongation rate of the protective film. In order to obtain good compatibility with the cellulose ester, the solubility parameter (SP value) of Fedors of the (meth) acrylic resin is preferably close to the SP value of the cellulose ester, and is 16.6 to 20.1. Is more preferable, and 17.7 to 18.6 is more preferable.

The SP value can be obtained by calculation using the Fedors parameter. The unit of SP value is the square root of the value obtained by dividing the cohesive energy density ΔE by the molar volume V, and “(cm ³ / cal) ^1/2 ” can be used. The parameters of Fedors are described in References: Basic Science of Coatings by Yuji Harada, Kashiwa Shoten (1977), p54-57.

  The (meth) acrylic resin preferably has appropriate hydrophobicity in order to make the elongation rate and elongation amount of the protective film within the above ranges. Therefore, the water-octanol distribution coefficient (Log P value) of the (meth) acrylic resin is preferably 1.2 or more, and more preferably 1.4 or more. If the LogP value of the (meth) acrylic resin is not less than a certain level, the elongation amount / elongation speed of the film is likely to be not more than a certain value. On the other hand, if the LogP value is too high, the amount of elongation and the elongation rate of the film may be too small, so that it may be 2.8 or less.

  In order to increase the LogP value of the (meth) acrylic resin, for example, the monomer constituting the (meth) acrylic resin contains a monomer having a relatively high hydrophobicity such as styrene; the hydrophobicity is relatively high What is necessary is just to raise the content rate of a monomer.

  The urethane urea resin may be a resin obtained by reacting the polyol (a), the polyamine (b), and the polyisocyanate (c).

  The polyol (a) preferably contains an alicyclic structure-containing polycarbonate polyol (a1) and an aromatic polyester polyol (a2).

  The alicyclic structure-containing polycarbonate polyol (a1) may be a compound obtained by reacting a carbonic ester or phosgene with an alicyclic structure-containing polyol. Examples of the carbonate include dimethyl carbonate and the like. Examples of the alicyclic structure-containing polyol include 1,2-cyclopentanediol, 1,4-cyclohexanediol, and the like. Specific examples of the alicyclic structure-containing polycarbonate polyol (a1) include UC-100 manufactured by Ube Industries, Ltd.

  The aromatic polyester polyol (a2) is a compound obtained by esterifying an alkylene diol and an aromatic dicarboxylic acid or a dialkyl ester compound thereof. Examples of the alkylene diol include ethylene glycol, 1,2-propylene glycol and the like. Examples of aromatic dicarboxylic acids include terephthalic acid, naphthalenedicarboxylic acid, and the like; examples of aromatic dicarboxylic acid dialkyl esters include dimethyl terephthalate, diethyl terephthalate, and the like.

  The ratio of the alicyclic structure-containing polycarbonate polyol (a1) to the aromatic polyester polyol (a2) in the polyol (a) is (a1) / (a2) = 90 because the resulting resin has appropriate hydrophobicity. It is preferable that it is / 10-60 / 40, and it is more preferable that it is 85 / 15-75 / 25. The content ratio of the structural unit derived from the polyol (a) in the urethane urea resin can be 40 to 80% by mass with respect to the total of the structural units of the polyol (a), the polyamine (b) and the polyisocyanate (c).

  Polyamine (b) is preferably an alicyclic structure-containing polyamine; examples include isophorone diamine, 4,4'-dicyclohexylmethane diamine, diaminocyclohexane and the like. The content ratio of the structural unit derived from the polyamine (b) in the urethane urea resin can be 1 to 20% by mass with respect to the total of the structural units of the polyol (a), the polyamine (b) and the polyisocyanate (c).

  Polyisocyanate (c) is preferably an alicyclic structure-containing polyisocyanate; examples include isophorone diisocyanate, 4,4′-dicyclohexylmethane diisocyanate, 2,4 or 2,6-methylcyclohexane diisocyanate. Etc. are included. The content ratio of the structural unit derived from polyisocyanate (c) in the urethane urea resin can be 15 to 50% by mass with respect to the total of the structural units of polyol (a), polyamine (b) and polyisocyanate (c).

  Urethane urea resin, for example, after reacting polyol (a) with polyisocyanate (c) to obtain a urethane prepolymer containing an isocyanate group at the molecular end; reacting the urethane prepolymer with polyamine (b) Can be obtained.

  Among these resins, (meth) acrylic resins are preferable because they have appropriate hydrophobicity and can easily adjust optical properties.

  The protective film of the present invention may further contain other resins and additives as necessary.

  The other resin preferably contains a cellulose ester because it can easily adjust the elongation amount and elongation rate of the film by combining with (meth) acrylic resin.

Cellulose ester Cellulose ester is a compound obtained by esterifying cellulose and at least one of aliphatic carboxylic acid and aromatic carboxylic acid. That is, the cellulose ester contains at least one of an aliphatic acyl group and an aromatic acyl group.

  The number of carbon atoms in the aliphatic acyl group is preferably 2 to 7, and more preferably 2 to 4. Examples of the aliphatic acyl group include acetyl group, propionyl group, butanoyl group and the like. The number of carbon atoms in the aromatic acyl group is preferably 6-24. Examples of the aromatic acyl group include a benzoyl group, a 4-phenyl-benzoyl group, a trimethylbenzoyl group, a thiophene group, and a naphthyl group, and preferably a benzoyl group.

  Among them, as will be described later, in order to increase the LogP value of the cellulose ester, the acyl group contained in the cellulose ester preferably contains an aromatic acyl group; the hydrophobicity (LogP value) of the cellulose ester is excessively high. It is more preferable to further include an aliphatic acyl group in order to prevent it from occurring. The content ratio of the aromatic acyl group in the acyl group contained in the cellulose ester can be about 5 to 25%, preferably about 10 to 20% with respect to the total of the acyl groups.

  Specific examples of cellulose esters include cellulose acetate propionate, cellulose acetate benzoate, cellulose acetate propionate benzoate, cellulose acetate biphenylate, cellulose acetate propionate biphenylate, etc. Cellulose acetate benzoate and the like are preferable.

  The total substitution degree of the acyl group of the cellulose ester is 2.0 or more, preferably 2.5 or more, more preferably 2.7 or more, and further preferably 2.8 or more. The upper limit of the total substitution degree of the acyl group can be set to 3, for example, preferably 2.95. In order to make the cellulose ester hydrophobic (increase the LogP value), for example, it is preferable to increase the total substitution degree of acyl groups.

  The substitution degree of the acyl group of cellulose ester can be measured by the method prescribed in ASTM-D817-96.

  The weight average molecular weight of the cellulose ester is preferably 50,000 to 500,000, more preferably 100,000 to 300,000, and 150,000 to 250,000 in order to obtain a certain level of mechanical strength. More preferably. The molecular weight distribution (weight average molecular weight Mw / number average molecular weight Mn) of the cellulose ester is preferably 1.0 to 4.5. The weight average molecular weight and molecular weight distribution of the cellulose ester can be measured by gel permeation chromatography (GPC) as described above.

  The cellulose ester preferably has an appropriate hydrophobicity in order to make the elongation rate and elongation amount of the protective film within the above ranges. Accordingly, the water-octanol partition coefficient (Log P value) of the cellulose ester is preferably 0 or more, more preferably 0.5 or more, and even more preferably 1.0 or more. If the LogP value of the cellulose ester is a certain level or more, for example, when combined with a (meth) acrylic resin, appropriate hydrophobicity is easily obtained. If the LogP value of the cellulose ester is too high, the compatibility with the (meth) acrylic resin may be lowered.

  In order to increase the LogP value of the cellulose ester, as described above, an aromatic acyl group may be contained; or the content ratio of the aromatic acyl group may be increased.

  The absolute value of the difference between the LogP value of the cellulose ester and the LogP value of the (meth) acrylic resin is preferably 8 or less, and more preferably 6 or less. When the difference in the LogP value is below a certain value, the cellulose ester and the (meth) acrylic resin are easily compatible with each other, and the effect of adding the cellulose ester is easily obtained.

  The content of the cellulose ester is preferably 5 to 25% by mass and more preferably 5 to 15% by mass with respect to the entire protective film. By setting the content of the cellulose ester to a certain level or more, it is easy to increase the elongation amount and elongation rate (particularly the elongation amount) of the protective film. By making the content of the cellulose ester not more than a certain value, it is possible to suppress the elongation amount of the protective film from becoming excessively high.

  Examples of the additive include a plasticizer, an ultraviolet absorber, a matting agent (fine particles), and the like.

  Examples of the plasticizer include polyester plasticizers, phthalate ester plasticizers, phosphate ester plasticizers, and acrylic plasticizers. These may be used alone or in combination of two or more.

  The polyester plasticizer includes a repeating unit derived from a condensate of dicarboxylic acid and diol.

  The dicarboxylic acid can be an aliphatic dicarboxylic acid, an alicyclic dicarboxylic acid or an aromatic dicarboxylic acid. The number of carbon atoms of the aliphatic dicarboxylic acid is preferably 4-20, more preferably 4-12. Examples of the aliphatic dicarboxylic acid include malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedicarboxylic acid, dodecanedicarboxylic acid and the like.

  The number of carbon atoms of the aromatic dicarboxylic acid is preferably 8 to 20, and more preferably 8 to 12. Examples of aromatic dicarboxylic acids include 1,2-benzenedicarboxylic acid (phthalic acid), 1,3-benzenedicarboxylic acid (isophthalic acid), 1,4-benzenedicarboxylic acid (terephthalic acid), 1,5-naphthalene Dicarboxylic acid, 1,4-xylidene dicarboxylic acid and the like are included, and 1,4-benzenedicarboxylic acid (terephthalic acid) is preferable.

  The number of carbon atoms of the alicyclic dicarboxylic acid is preferably 6 to 20, and more preferably 6 to 12. Examples of the alicyclic dicarboxylic acid include 1,3-cyclobutane dicarboxylic acid, 1,3-cyclopentane dicarboxylic acid, 1,4-cyclohexane dicarboxylic acid, 1,4-cyclohexane diacetic acid and the like.

  The dicarboxylic acid for obtaining the polyester compound may be one kind or two or more kinds. The dicarboxylic acid for obtaining the polyester compound preferably contains an aromatic dicarboxylic acid in order to increase the hydrophobicity of the transparent substrate layer or increase the compatibility with the cellulose ester. More preferably, both aliphatic dicarboxylic acids are included.

  The diol can be an aliphatic diol, an alkyl ether diol, an alicyclic diol or an aromatic diol.

  The carbon number of the aliphatic diol is preferably 2 to 20, more preferably 2 to 12. Examples of the aliphatic diol include ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,2-butanediol, 1,3-butanediol, 1,2-propanediol, and the like. The number of carbon atoms of the alkyl ether diol is preferably 4-20, more preferably 4-12. Examples of the alkyl ether diol include polytetramethylene ether glycol, polyethylene ether glycol and polypropylene ether glycol.

  The number of carbon atoms of the alicyclic diol is preferably 4 to 20, and more preferably 4 to 12. Examples of the alicyclic diol include 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol and the like.

  The number of carbon atoms of the aromatic diol is preferably 6-20, more preferably 6-12. Examples of aromatic diols include 1,2-dihydroxybenzene (catechol), 1,3-dihydroxybenzene (resorcinol), 1,4-dihydroxybenzene (hydroquinone), and the like. The diol for obtaining the polyester compound may be one kind or two or more kinds. The diol for obtaining the polyester compound preferably contains an aliphatic diol.

  Among them, the polyester compound containing a repeating unit derived from a condensate of an aliphatic diol and a dicarboxylic acid containing an aromatic dicarboxylic acid and an aliphatic dicarboxylic acid is preferable because the transparency of the film containing the polyester compound is good. ,preferable.

  The molecular terminal of the polyester compound may be sealed with a monocarboxylic acid or a monoalcohol as necessary.

  The monocarboxylic acid can be an aliphatic monocarboxylic acid, an alicyclic monocarboxylic acid or an aromatic monocarboxylic acid. The number of carbon atoms of the aliphatic monocarboxylic acid may preferably be 2-30, more preferably 2-4. Examples of the aliphatic carboxylic acid include acetic acid, propionic acid and the like. Examples of the alicyclic monocarboxylic acid include cyclohexyl monocarboxylic acid. Examples of aromatic monocarboxylic acids include benzoic acid, para-tert-butyl benzoic acid, orthotoluic acid, metatoluic acid, p-toluic acid, dimethyl benzoic acid, ethyl benzoic acid, normal propyl benzoic acid, aminobenzoic acid, acetoxybenzoic acid, Phenylacetic acid, 3-phenylpropionic acid and the like are included.

  The monoalcohol can be an aliphatic monoalcohol, an alicyclic monoalcohol, or an aromatic monoalcohol. The number of carbon atoms in the aliphatic monoalcohol is 1-30, preferably 1-3. Examples of the aliphatic monoalcohol include methanol, ethanol, propanol, isopropanol and the like. Examples of the alicyclic monoalcohol include cyclohexyl alcohol and the like. Examples of the aromatic monoalcohol include benzyl alcohol and 3-phenylpropanol.

Specific examples of the polyester compound include the following. In Table 1, TPA: terephthalic acid, PA: phthalic acid, SA: succinic acid, AA: adipic acid are shown.

  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, dicyclohexyl terephthalate and the like.

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

  The acrylic plasticizer can be a homopolymer or copolymer of a (meth) acrylic acid ester monomer that does not have an aromatic ring in the molecule. Among them, there is a copolymer of (meth) acrylic acid ester X having no aromatic ring and having a hydrophilic group and (meth) acrylic acid ester Y having no aromatic ring and having no hydrophilic group. preferable.

  Examples of the (meth) acrylic acid ester X having no aromatic ring and having a hydrophilic group include (meth) acrylic acid (2-hydroxyethyl), (meth) acrylic acid (2-hydroxypropyl), (meta ) Acrylic acid (3-hydroxypropyl), (meth) acrylic acid (4-hydroxybutyl), (meth) acrylic acid (2-hydroxybutyl) and the like.

  Examples of (meth) acrylic acid ester Y having no aromatic ring and no hydrophilic group include methyl acrylate, ethyl acrylate, propyl acrylate (i-, n-), butyl acrylate (n- , I-, s-, t-), pentyl acrylate (n-, i-, s-), hexyl acrylate (n-, i-), heptyl acrylate (n-, i-), octyl acrylate (N-, i-), nonyl acrylate (n-, i-), myristyl acrylate (n-, i-), acrylic acid (2-ethylhexyl) and the like are included.

  In the copolymer of (meth) acrylic acid ester Y and Y, the content ratio (molar ratio) of the structural unit derived from (meth) acrylic acid ester X and the structural unit derived from (meth) acrylic acid ester Y is X: Y. = 1: 1 to 1:99.

  The weight average molecular weight of the acrylic plasticizer is preferably 500-30000, and more preferably 500-10000. An acrylic plasticizer having a weight average molecular weight within the above range has good compatibility with a (meth) acrylic resin and the like, and is less likely to volatilize during film formation.

Polyester-urethane plasticizer Polyester-urethane plasticizer is preferably used as a plasticizer for urethane urea resin. The polyester-urethane plasticizer is a polyester-urethane obtained by a reaction between polyester and diisocyanate, and has a repeating unit represented by the following general formula (1).

In general formula (1), l represents an integer of 2 to 4; m represents an integer of 2 to 4; and n represents 1 to 100. R represents the structural unit shown below; the benzene ring in the structural unit shown below may further have a substituent such as an alkyl group.

  The polyester for obtaining the polyester-urethane plasticizer may be a polyester having hydroxyl groups at both ends, obtained by reacting glycol with a dibasic acid. Examples of glycols include ethylene glycol, 1,3-propanediol and 1,4-butanediol; examples of dibasic acids include succinic acid, glutaric acid and adipic acid. The degree of polymerization n of the polyester is preferably 1 to 100. The molecular weight of the polyester is preferably 1000-4500.

  Diisocyanates for obtaining polyester-urethane plasticizers include polymethylene isocyanates such as ethylene diisocyanate, trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, and p-phenylene diisocyanate. , Aromatic diisocyanates such as tolylene diisocyanate, p, p′-diphenylmethane diisocyanate, 1,5-naphthylene diisocyanate, m-xylylene diisocyanate, and the like. Among these, tolylene diisocyanate, m-xylylene diisocyanate, and tetramethylene diisocyanate are preferable because they have good compatibility with the cellulose ester after being made into a polyurethane.

  The weight average molecular weight of the polyester-urethane plasticizer is preferably 2000 to 50000, and more preferably 5000 to 15000.

  The total content of these plasticizers is preferably 0.5 to 30% by mass with respect to the total of the resin components as the main component (total of (meth) acrylic resin and urethane urea resin), More preferably, it is 20 mass%. When the content of the plasticizer is within the above range, the plasticizing effect is easily obtained without causing the film to bleed out.

  Examples of a preferable film composition for setting the amount of elongation / elongation speed of the protective film within the above range include 1) a combination of a (meth) acrylic resin having a Log P value of 1.2 or more and a cellulose ester; 2) ( A combination of a (meth) acrylic resin and a cellulose ester having a LogP value of 0 or more; and 3) a combination of a (meth) acrylic resin having a LogP value of 1.2 or more and a cellulose ester having a LogP value of 0 or more. Especially, since it is easy to adjust the elongation amount and elongation rate of the protective film to a preferable range, a combination of (3) a (meth) acrylic resin having a LogP value of 1.2 or more and a cellulose ester having a LogP value of 0 or more is preferable. .

Ultraviolet absorber The ultraviolet absorber may be a benzotriazole compound, a 2-hydroxybenzophenone compound, a salicylic acid phenyl ester compound, or the like. Examples thereof include 2- (5-methyl-2-hydroxyphenyl) benzotriazole, 2- [2-hydroxy-3,5-bis (α, α-dimethylbenzyl) phenyl] -2H-benzotriazole, 2 -Triazoles such as (3,5-di-t-butyl-2-hydroxyphenyl) benzotriazole, 2-hydroxy-4-methoxybenzophenone, 2-hydroxy-4-octoxybenzophenone, 2,2'-dihydroxy- Benzophenones such as 4-methoxybenzophenone are included.

  Of these, UV absorbers having a molecular weight of 400 or more are less likely to volatilize at a high boiling point and are difficult to disperse even during high-temperature molding. For this reason, it is preferable that the molecular weight of a ultraviolet absorber is 250-1000, and it is more preferable that it is 400-800. Examples of ultraviolet absorbers having a molecular weight of 400 or more include 2- [2-hydroxy-3,5-bis (α, α-dimethylbenzyl) phenyl] -2-benzotriazole and 2,2-methylenebis [4- ( 1,1,3,3-tetrabutyl) -6- (2H-benzotriazol-2-yl) phenol] and the like.

  The content of the ultraviolet light inhibitor is preferably 0.001% to 5% by mass in the protective film, and more preferably 0.1% to 3%.

Matting agent The matting agent can impart slipperiness to the protective film. The matting agent can be inorganic fine particles or organic fine particles.

  Examples of inorganic compounds constituting the inorganic fine particles include silicon dioxide, titanium dioxide, aluminum oxide, zirconium oxide, calcium carbonate, calcium carbonate, talc, clay, calcined kaolin, calcined calcium silicate, hydrated calcium silicate, silicic acid. Aluminum, magnesium silicate, calcium phosphate and the like are included. Of these, silicon dioxide is preferred because the increase in film haze is small.

  Examples of silicon dioxide include Aerosil 200V, Aerosil R972V, Aerosil R972, R974, R812, R202 (above Nippon Aerosil Co., Ltd.), Seahoster KEP-10, KEP-30, KEP-50 (above, Nippon Shokubai Co., Ltd.) Manufactured).

  The shape of the particles is not particularly limited, and may be indefinite, acicular, flat, spherical or the like. Especially, since the transparency of the transparent base material layer obtained is favorable, a spherical particle is preferable.

  When the particle size is close to the wavelength of visible light, light is scattered and transparency is lowered. Therefore, the particle size is preferably smaller than the wavelength of visible light, and more preferably ½ or less of the wavelength of visible light. . If the size of the particles is too small, the slipperiness may not be improved, so the range of 80 nm to 180 nm is preferable. The size of the particle means the size of the aggregate when the particle is an aggregate of primary particles. Moreover, when a particle is not spherical, it means the diameter of a circle corresponding to the projected area.

  The content of the matting agent can be about 0.05 to 1.0% by mass with respect to the total of the resin components as the main components (total of (meth) acrylic resin and urethane urea resin), preferably 0. .1 to 0.8 mass%.

  The protective film may be subjected to a surface treatment as necessary in order to easily adjust the elongation rate when immersed in water to the above range. For example, when the hydrophobicity of the base film is insufficient (for example, a (meth) acrylic resin film having a low LogP value), the surface of the film may be subjected to a hydrophobic treatment. The hydrophobizing treatment can be performed, for example, by subjecting the film surface to a corona treatment and then contacting with a modifier (eg, 3H-tetrafluoropropionic acid chloride) in the presence of a catalyst.

  The thickness of the protective film is preferably not more than a certain value in order to reduce the shrinkage force of the protecting film; it is preferably not less than a certain value in order to reduce the permeation of water. Therefore, the thickness of the protective film is preferably 10 to 80 μm, more preferably 10 to 70 μm, still more preferably 10 to 50 μm, and particularly preferably 10 to 40 μm.

  The protective film may be a single layer film or a laminated film. When the protective film is a laminated film, all layers constituting the protective film have the above-described composition (preferably a combination of a cellulose ester having a certain LogP value and a (meth) acrylic resin having a certain LogP value). Is preferred.

  On the protective film of the present invention, other functional layers such as an antireflection layer may be further laminated as necessary within the range not impairing the effects of the present invention.

Physical properties of protective film (haze)
The haze value of the protective film is preferably 3.0% or less, more preferably 2.0% or less, further preferably 1.0% or less, and 0.5% or less. Is particularly preferred. The haze of the protective film can be measured with a haze meter (turbidimeter) (model: NDH 2000, manufactured by Nippon Denshoku Co., Ltd.) in accordance with JIS K-7136.

(Retardation)
In the protective film, the in-plane retardation R ₀ measured under the conditions of a measurement wavelength of 590 nm and 23 ° C. and 55% RH preferably satisfies 0 ≦ R ₀ ≦ 20 nm, and satisfies ₀ nm ≦ R ₀ ≦ 10 nm. It is more preferable. The thickness direction retardation Rth of the protective film measured under conditions of a measurement wavelength of 590 nm and 23 ° C. and 55% RH preferably satisfies 0 nm ≦ Rth ≦ 80 nm, and more preferably satisfies 0 nm ≦ Rth ≦ 50 nm. . The protective film having such a retardation value is preferably used as a protective film (F1 or F4) for a liquid crystal display device, as will be described later. R ₀ and Rth can be adjusted depending on the composition of the film and stretching conditions.

Retardation _R0 and Rth are defined by the following equations, respectively.
Formula (I): R ₀ = (nx−ny) × d (nm)
Formula (II): Rth = {(nx + ny) / 2−nz} × d (nm)
(In formulas (I) and (II),
nx represents the refractive index in the slow axis direction x where the refractive index is maximum in the in-plane direction of the protective film; ny is the refraction in the direction y perpendicular to the slow axis direction x in the in-plane direction of the protective film. Nz represents the refractive index in the thickness direction z of the protective film; d (nm) represents the thickness of the protective film)

The retardations _R0 and Rth can be determined by the following method, for example.
1) Condition the protective film at 23 ° C. and 55% RH. The average refractive index of the optical compensation film after humidity adjustment is measured with an Abbe refractometer or the like.
The protective film after 2) humidity, measuring the _{R 0} when the light is incident in parallel to the measurement wavelength 590nm to normal of the film surface, KOBRA21DH, in Oji Scientific Corporation.
3) With KOBRA21ADH, the slow axis in the surface of the protective film is set as the tilt axis (rotation axis), and light having a measurement wavelength of 590 nm is obtained from the angle (incident angle (θ)) of θ with respect to the normal of the surface of the protective film. The retardation value R (θ) when incident is measured. The retardation value R (θ) can be measured at 6 points every 10 °, with θ ranging from 0 ° to 50 °. The in-plane slow axis of the protective film can be confirmed by KOBRA21ADH.
4) nx, ny, and nz are calculated by KOBRA21ADH from the measured R ₀ and R (θ) and the above-described average refractive index and film thickness, and Rth at a measurement wavelength of 590 nm is calculated. The measurement of retardation can be performed under conditions of 23 ° C. and 55% RH.

  The angle θ1 (orientation angle) formed by the in-plane slow axis of the protective film and the width direction of the film is preferably −1 ° to + 1 °, more preferably −0.5 ° to + 0.5 °. . The orientation angle θ1 of the protective film can be measured using an automatic birefringence meter KOBRA-WR (Oji Scientific Instruments).

  The protective film preferably has a total light transmittance of 80% or more, more preferably 90% or more, and still more preferably 93% or more.

  The protective film can be produced by a solution casting method or a melt casting method. Of these, the solution casting method is preferred because it is easy to obtain a film having high flatness and few streak-like failures.

  The production of the protective film of the present invention by the solution casting method includes 1) a step of obtaining a dope solution by dissolving each of the above components in a solvent, and 2) a step of casting the dope solution on an endless metal support, 3) It is preferable that the film-like product obtained by drying the cast dope solution is removed through a step of peeling from the metal support.

1) Dissolution Step Any organic solvent useful for preparing the dope solution can be used without limitation as long as it dissolves each of the above components such as a (meth) acrylic resin and a urethane urea resin.

  For example, the chlorinated organic solvent includes methylene chloride. Non-chlorine organic solvents include methyl acetate, ethyl acetate, amyl acetate, acetone, tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane, cyclohexanone, ethyl formate, 2,2,2-trifluoroethanol, 2, 2,3,3-hexafluoro-1-propanol, 1,3-difluoro-2-propanol, 1,1,1,3,3,3-hexafluoro-2-methyl-2-propanol, 1,1, Examples include 1,3,3,3-hexafluoro-2-propanol, 2,2,3,3,3-pentafluoro-1-propanol, and nitroethane. Of these, methylene chloride, methyl acetate, ethyl acetate, acetone and the like are preferable.

  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. By containing alcohol in the dope solution, the film-like material is gelled, and peeling from the metal support becomes easy.

  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. Of these, ethanol is preferred because of the stability of the dope, relatively low boiling point, and good drying properties.

  Dissolution of cellulose ester and the like includes a method performed at normal pressure, a method performed below the boiling point of the main solvent, a method performed under pressure above the boiling point of the main solvent, and a method performed under pressure above the boiling point of the main solvent. Is preferred.

  The concentration of cellulose ester or the like in the dope liquid can be in the range of 15 to 45% by mass in total. The dope solution is preferably further filtered in order to remove foreign substances in the dope solution.

2) Casting step The dope solution is fed to a pressure die through a liquid feed pump (for example, a pressurized metering gear pump). Then, the dope solution is cast from the slit of the pressure die to a casting position on an endless metal support (for example, a stainless belt or a rotating metal drum) that is transferred infinitely.

  A pressure die that can adjust the slit shape of the die base portion and can easily make the film thickness uniform is preferable. Examples of the pressure die include a coat hanger die and a T die, and any of them is preferably used. The surface of the metal support is a mirror surface. In order to increase the film forming speed, two or more pressure dies may be provided on the metal support, and the flow rate of the dope solution may be divided and stacked. Or you may obtain the film of a laminated structure by the co-casting method which casts several dope liquid simultaneously.

3) Solvent evaporation / peeling step The dope solution cast on the metal support is heated on the metal support to evaporate the solvent in the dope solution to obtain a film-like material.

  In order to evaporate the solvent, there are a method of blowing wind from the dope liquid surface side, a method of transferring heat from the back surface of the support by a liquid, a method of transferring heat from the front and back by radiant heat, etc. The drying efficiency is good and preferable. The dope solution on the metal support is preferably dried on the support in an atmosphere within the range of 40 to 100 ° C. In order to maintain the atmosphere in the range of 40 to 100 ° C., it is preferable to apply hot air at this temperature to the dope liquid surface on the metal support or to heat by means such as infrared rays.

  The film-like material obtained by evaporating the solvent on the metal support is peeled off at the peeling position. From the viewpoint of surface quality, moisture permeability, and peelability of the obtained film-like material, it is preferable to peel the film-like material from the metal support within 30 to 120 seconds after casting. The temperature at the peeling position on the metal support is preferably in the range of 10 to 40 ° C, more preferably in the range of 11 to 30 ° C.

  The amount of residual solvent of the film-like material on the metal support at the time of peeling can be set in the range of 50 to 120% by mass, for example.

The amount of residual solvent in the film is defined by the following formula.
Residual solvent amount (%) = (mass before heat treatment of film-like material−mass after heat treatment of film-like material) / (mass after heat treatment of film-like material) × 100
The heat treatment for measuring the residual solvent amount represents performing a heat treatment at 140 ° C. for 1 hour.

  The peeling tension when peeling the metal support and the film is usually in the range of 196 to 245 N / m. However, if wrinkles easily occur during peeling, peeling with a tension of 190 N / m or less is preferable. Further, it is more preferable to peel with a tension of 80 N / m or less.

  The peeled film-like material may be dried while being transported by a plurality of rollers disposed in the drying device as necessary. The drying is generally performed by applying hot air to both surfaces of the film-like material, but may be heated by applying microwaves instead of hot air. Throughout, the drying is generally carried out in the range of 40-250 ° C. It is particularly preferable to dry within the range of 40 to 200 ° C. When drying with a tenter stretching apparatus, the drying temperature is preferably in the range of 30 to 160 ° C, and more preferably in the range of 50 to 150 ° C.

  As described above, in order to increase the tensile elastic modulus of the protective film, it is preferable to stretch the film obtained in 3) above to orient the resin molecules. Therefore, you may further perform the process (stretching process) of extending | stretching the film obtained by said 3).

4) Stretching process Stretching of the obtained film may be performed in at least one of the width direction (TD direction), the transport direction (MD direction) or the oblique direction of the film. When stretching in both the width direction (TD direction) and the transport direction (MD direction) of the film, stretching in the width direction (TD direction) of the film and stretching in the transport direction (MD direction) may be performed sequentially. You may do it simultaneously.

  The draw ratio can be 1.01 to 3.0 times, preferably 1.1 to 2.0 times in each direction. When stretching in both the width direction (TD direction) and the transport direction (MD direction) of the film, it is finally 1.01 to 3.0 times, preferably 1.1 to 2.0 times in each direction. Is preferred.

  The stretching temperature is preferably Tg to (Tg + 50) ° C., more preferably Tg to (Tg + 40) ° C. Specifically, in the case of a (meth) acrylic resin / cellulose ester mixture, the stretching temperature can be about 100 to 190 ° C.

  In order to adjust the retardation of the film obtained after stretching or to reduce the dimensional change, the film obtained after stretching is shrunk in the transport direction (MD direction) or the width direction (TD direction) as necessary. May be. In order to shrink the film obtained after stretching in the transport direction (MD direction), for example, the clip gripped in the width direction may be released and relaxed in the transport direction.

5) Winding process The obtained protective film may be provided in a long shape or may be provided in a sheet form. The long protective film can usually be wound in a roll shape in the longitudinal direction (MD direction) to form a wound body.

  The length of the long protective film can be in the range of 100 to 10,000 m. The width of the long protective film may be in the range of 1 to 4 m, preferably in the range of 1.4 to 3 m.

2. Polarizing plate The polarizing plate of this invention contains a polarizer and the protective film arrange | positioned at the at least one surface.

About Polarizer The polarizer can be an iodine-based polarizing film or a dye-based polarizing film using a dichroic dye. The iodine-based polarizing film and the dye-based polarizing film may be generally a film obtained by uniaxially stretching a polyvinyl alcohol-based film and then dyeing with iodine or a dichroic dye; After the film is dyed with iodine or a dichroic dye, it may be a uniaxially stretched film (preferably a film further subjected to a durability treatment with a boron compound). The absorption axis of the polarizer is parallel to the stretching direction of the film.

  The polyvinyl alcohol film may be a film formed from a polyvinyl alcohol aqueous solution. The polyvinyl alcohol film is preferably an ethylene-modified polyvinyl alcohol film because it is excellent in polarizing performance and durability performance, and has few color spots.

  Examples of dichroic dyes include azo dyes, stilbene dyes, pyrazolone dyes, triphenylmethane dyes, quinoline dyes, oxazine dyes, thiazine dyes and anthraquinone dyes.

  The thickness of the polarizer is preferably 30 μm or less and more preferably in the range of 2 to 25 μm in order to reduce the contraction force of the polarizer.

About a protective film (F1 or F4) It is preferable that a protective film is a protective film of this invention. The protective film and the polarizer of the present invention are preferably laminated so that the MD direction of the protective film coincides with the absorption axis direction of the polarizer. This is because the contraction force of the polarizer is considered to have the largest absorption axis direction.

About retardation film (F2 or F3) The above-mentioned protective film may be further arrange | positioned on the surface on the opposite side to the surface where the above-mentioned protective film is arrange | positioned of a polarizer; May be.

  The retardation film is not particularly limited, and may be, for example, a cellulose ester film. Examples of the cellulose ester contained in the cellulose ester film include cellulose acetate, cellulose acetate propionate, and cellulose acetate propionate butyrate.

The cellulose ester preferably has a total acyl group substitution degree of 1.5 or more and 2.5 or less, and more preferably satisfies the following formulas (a) and (b).
Formula (a) 2.0 ≦ X + Y ≦ 2.5
Formula (b) 0 ≦ Y ≦ 1.5 (wherein X represents the degree of substitution of the acetyl group, and Y represents the degree of substitution of the propionyl group or butyryl group, or a mixture thereof)

  The retardation of the retardation film can be set according to the type of liquid crystal cell to be combined. For example, the in-plane retardation Ro (590) measured at a wavelength of 590 nm under 23 ° C. RH 55% of the retardation film is in the range of 30 to 150 nm, and the retardation Rth (590) in the thickness direction is 70 to 300 nm. Can be a range. A retardation film having a retardation in the above range is suitable as a retardation film such as a VA liquid crystal cell.

  The polarizing plate can be obtained through a step of bonding a polarizer and a protective film. Bonding of the protective film and the polarizer can be performed using a completely saponified polyvinyl alcohol adhesive (water paste) or an active energy ray-curable adhesive. For example, when water paste is used for bonding, a polarizer and a protective film are bonded together through water paste; the resulting laminate can be dried to obtain a polarizing plate.

  When the amount of the cellulose ester contained in the protective film is small, the protective film and the polarizer may not be sufficiently bonded with water glue. In that case, you may further form an easily bonding layer in the bonding surface with the polarizer of a protective film.

  The easy-adhesion layer can be formed by applying a resin composition containing a carboxyl group-containing urethane resin and a crosslinking agent, and then drying and curing. The urethane resin having a carboxyl group can be obtained, for example, by further copolymerizing a chain extender having a free carboxyl group in addition to a polyol and a polyisocyanate. Examples of the chain extender having a free carboxyl group include dihydroxycarboxylic acid, dihydroxysuccinic acid and the like. The cross-linking agent is preferably a polymer having a group capable of reacting with a carboxyl group; examples thereof include an acrylic polymer or a styrene / acrylic polymer having an oxazoline group.

  In the protective film contained in the polarizing plate of the present invention, both the amount of elongation and the elongation rate are adjusted to a certain level or more. Thereby, when drying the laminated body which bonded together the protective film and the polarizer through the water paste, the water | moisture content of the water paste taken in the protective film can be extracted moderately. Thereby, in order to remove the water | moisture content which remained in the protective film, when heating and drying, the reddish (red defect) of the polarizing plate which arises because a polarizer deteriorates can be suppressed.

3. Liquid Crystal Display Device The liquid crystal display device of the present invention includes a liquid crystal cell and a pair of polarizing plates that sandwich the liquid crystal cell. And at least one of a pair of polarizing plates can be used as the polarizing plate of the present invention.

  FIG. 2 is a schematic diagram illustrating an example of a basic configuration of the liquid crystal display device. As shown in FIG. 2, the liquid crystal display device 10 of the present invention includes a liquid crystal cell 30, a first polarizing plate 50 and a second polarizing plate 70 that sandwich the liquid crystal cell 30, and a backlight 90.

  The liquid crystal cell 30 has a pair of transparent substrates 31 and 33 and a liquid crystal layer 35 sandwiched between them.

  The transparent substrates 31 and 33 are preferably glass substrates. The thickness of the glass substrate is preferably not more than a certain value in order to reduce the thickness of the liquid crystal display device, etc., preferably 0.3 mm or more and less than 0.7 mm, and preferably 0.3 to 0.5 mm. More preferred.

  The display mode of the liquid crystal cell 30 may be various display modes such as STN, TN, OCB, HAN, VA (MVA, PVA), and IPS. For obtaining high contrast, the VA (MVA, PVA) mode is used. It is preferable that

  For example, in a VA liquid crystal cell, a pixel electrode for applying a voltage to liquid crystal molecules is disposed on one transparent substrate. The counter electrode may be disposed on the one transparent substrate (where the pixel electrode is disposed) or may be disposed on the other transparent substrate.

  The liquid crystal layer includes liquid crystal molecules having negative or positive dielectric anisotropy. The liquid crystal molecules are liquid crystal molecules when no voltage is applied (when an electric field is not generated between the pixel electrode and the counter electrode) due to the alignment regulating force of the alignment film provided on the liquid crystal layer side surface of the transparent substrate. Are oriented so that their long axes are substantially perpendicular to the surface of the transparent substrate.

  In the VA liquid crystal cell configured as described above, an electric field is generated between the pixel electrode and the counter electrode by applying an image signal (voltage) to the pixel electrode. Thereby, the liquid crystal molecules initially aligned perpendicularly to the surface of the transparent substrate are aligned so that the major axis thereof is in the horizontal direction with respect to the substrate surface. In this way, the liquid crystal layer is driven, and the image display is performed by changing the transmittance and reflectance of each sub-pixel.

  The first polarizing plate 50 can be disposed on the glass substrate 31 of the liquid crystal cell 30 via an adhesive layer (not shown). The first polarizing plate 50 includes a first polarizer 51, a protective film 53 (F1) disposed on the viewing side surface of the first polarizer 51, and a liquid crystal cell side of the first polarizer 51. And a protective film 55 (F2) disposed on the surface.

  The second polarizing plate 70 can be disposed on the glass substrate 33 of the liquid crystal cell 30 via an adhesive layer (not shown). The second polarizing plate 70 includes a second polarizer 71, a protective film 73 (F3) disposed on the liquid crystal cell side surface of the second polarizer 71, and the backlight side of the second polarizer 71. And a protective film 75 (F4) disposed on the surface.

  The thickness of the pressure-sensitive adhesive layer can be about 1 to 30 μm.

  And at least one or both of the 1st polarizing plate 50 and the 2nd polarizing plate 70 can be made into the polarizing plate of this invention. That is, at least one of the protective film 53 (F1) and the protective film 75 (F4) can be used as the protective film of the present invention. It is preferable that the MD direction of the protective film 53 (F1) and the absorption axis direction of the first polarizer 51 coincide. It is preferable that the MD direction of the protective film 75 (F4) coincides with the absorption axis direction of the second polarizer 71.

  As described above, in the protective film of the present invention, the amount of elongation and the elongation rate are adjusted to be constant or less. Thereby, although the protective film of the present invention has a high tensile elastic modulus, the dimensional change of the protective film (when changed from high temperature and high humidity to high temperature and low humidity) is small; While having strength, the shrinkage force due to water content is reduced. Thereby, the panel bend which is easy to occur when the glass substrate of the liquid crystal cell is thin can be suppressed.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto.

1. Material of protective film (1) Resin components A1 to A9: (Meth) acrylic resin shown in Table 2 below U1: Urethane urea resin synthesized by the following method (Synthesis of urethane urea resin U1)
1) Synthesis of aromatic polyester polyol (a2-1) In a four-necked flask having an internal volume of 3 liters equipped with a thermometer, a stirrer and a reflux condenser, 659.4 g of dimethyl 2,6-naphthalenedicarboxylate and terephthalic acid Dimethyl 58.3 g, 1,2-propylene glycol 684.8 g and zinc acetate dihydrate 0.084 g as an esterification catalyst were charged, and the temperature was increased stepwise until 210 ° C. with stirring under a nitrogen stream. And it was made to react for a total of 13 hours. After the reaction, unreacted 1,2-propylene glycol was removed under reduced pressure at 160 ° C., and the room temperature solid aromatic polyester polyol (a2-1) (acid value: 0.08, hydroxyl value: 213, number average molecular weight: 590).
2) Synthesis of urethane urea resin U1 Aliphatic cyclic structure-containing polycarbonate polyol (a1-1) (Ube) was added to a 5-liter four-necked flask equipped with a thermometer, a stirrer, an inert gas inlet, and a reflux condenser. UC-100 manufactured by Kosan Co., Ltd., 300 parts by mass of a hydroxyl value: 116.4 mg KOH / g) and 75 parts by mass of the synthesized aromatic polyester polyol (a2-1) were charged, and 4,4′-dicyclohexylmethane diisocyanate ( 238.0 parts by mass of c-1) and 330.1 parts by mass of toluene were added and reacted at 80 ° C. for 3 hours while suppressing heat generation. Thereby, a toluene solution of a urethane prepolymer having an isocyanate group at the molecular end was obtained.
Next, after mixing the toluene solution, 1235.6 parts by mass of N, N-dimethylformamide (b-1), 287.7 parts by mass of toluene, and 205.9 parts by mass of sec-butanol, The mixture was cooled to 0 ° C., mixed with 73.4 parts by mass of isophoronediamine, and reacted at 70 ° C. for 3 hours to obtain urethane urea resin U1 (weight average molecular weight: 147000, nonvolatile content: 25% by mass).

(2) Cellulose ester Cellulose ester A to I: Cellulose ester shown in Table 3 below

(3) Other additives Additive 1: Actflo-UT1001 (manufactured by Soken Chemical Co., Ltd., acrylic low molecular weight, terminal hydroxyl group)
Additive 2: Polyester-urethane plasticizer (polyester-urethane having an average molecular weight of 7300 obtained by reacting dihydroxy polyester consisting of adipic acid and ethylene glycol with an average molecular weight of 2125 and tolylene diisocyanate by a conventional method)
Plasticizer 1: ARUFON UP1170 (manufactured by Toagosei Co., Ltd., acrylic plasticizer, non-functional)
Plasticizer 2: Dioctyl phthalate (DOP)
UV absorber: ADK STAB LA31RG (manufactured by Adeka, ADK STAB 2,2′-methylenebis [6- (2H-benzotriazol-2-yl) -4- (1,1,3,3-tetramethylbutyl) phenol])

2. Production of protective film (Example 1)
The following components were mixed to prepare a dope.
(Composition of dope)
(Meth) acrylic resin A2: 95 parts by mass Additive 1 (Actoflo-UT1001): 5 parts by mass Methylene chloride: 213.9 parts by mass Ethanol: 67.6 parts by mass

  The obtained dope was uniformly cast on a stainless steel band support at a temperature of 30 ° C. and a width of 2 m using a belt casting apparatus. On the stainless steel band support, the solvent in the dope was evaporated until the residual solvent amount reached 70%. And the obtained film-like thing was peeled from the stainless steel band support body.

  Next, the peeled film-like material was further dried at 45 ° C., and then the obtained film was dried while being transported by a plurality of rollers through a drying zone at 110 ° C. and 140 ° C. to obtain a film having a thickness of 40 μm. .

  The surface of the obtained film was subjected to corona treatment under the condition of 100W. Thereafter, the corona-treated film was suspended in a separable flask, and pyridine (Wako Pure Chemicals) was added as a catalyst and 3H-tetrafluoropropionic acid chloride (Wako Pure Chemicals) was added as a modifier. The reaction was performed under reduced pressure for an hour. Thereby, the surface of the film was fluorinated to obtain a film 101.

(Example 2)
A film 102 having a thickness of 40 μm was obtained in the same manner as in Example 1 except that the film composition was changed to (meth) acrylic resin A6 / cellulose ester E = 90 parts by mass / 10 parts by mass.

(Example 3)
A film 103 having a thickness of 40 μm was obtained in the same manner as in Example 1 except that the film composition was changed to (meth) acrylic resin A1 / cellulose ester E = 90 parts by mass / 10 parts by mass.

(Comparative Example 1)
Except that the film composition was changed to general-purpose PMMA, pellets were obtained in the same manner as in Example 1, and then melt-extruded to obtain a film having a thickness of 40 μm. On this film, the following vinylidene chloride solution was applied so as to have a dry thickness of 5 μm to obtain a film 104.
(Vinylidene chloride solution)
Chlorine-containing polymer (Saran Resin R204 manufactured by Asahi Kasei Life & Living Co., Ltd.): 12 parts by mass Tetrahydrofuran: 63 parts by mass

(Comparative Example 2)
A film 105 having a thickness of 40 μm was obtained in the same manner as in Example 1 except that the film composition was changed to (meth) acrylic resin A1 / cellulose ester I = 90 parts by mass / 10 parts by mass.

(Comparative Example 3)
The film composition was changed to general-purpose PMMA / CAP482 (cellulose acetate propionate having an acetyl group substitution degree of 0.19, a propionyl group substitution degree of 2.56, and a total substitution degree of 2.75) = 65 parts by mass / 35 parts by mass Obtained a film 106 having a thickness of 40 μm in the same manner as in Example 1.

Example 4
The following components were mixed to prepare Dope 1.
(Dope 1)
Urethane urea resin U1: 100 parts by mass Additive 2 (polyester-polyurethane): 10 parts by mass Methyl ethyl ketone: 500 parts by mass

  The obtained dope 1 was uniformly cast on a stainless steel band support at a temperature of 30 ° C. and a width of 2 m using a belt casting apparatus. On the stainless steel band support, the solvent in the dope was evaporated until the residual solvent amount reached 70%. And the obtained film-like thing was peeled from the stainless steel band support body. The obtained film was dried at 45 ° C. and further dried at 110 ° C. and 140 ° C. to obtain a film 107 having a thickness of 40 μm.

(Example 5)
The film composition was 91.4 parts by mass of (meth) acrylic resin A3, 5 parts by mass of plasticizer 1 (ARUFON UP1170 manufactured by Toagosei Co., Ltd.), 2 parts by mass of plasticizer 2 (dioctyl phthalate), UV absorber ( A film 108 having a film thickness of 40 μm was obtained in the same manner as in Example 1 except that LA31RG manufactured by Adeka Corporation was changed to 1.6 parts by mass.

(Example 6)
A film 109 having a thickness of 40 μm was obtained in the same manner as in Example 1 except that the film composition was changed to (meth) acrylic resin A6 / cellulose ester A = 90 parts by mass / 10 parts by mass.

(Comparative Example 4)
As a cellulose triacetate film, 4UA (manufactured by Konica Minolta, film thickness of 40 μm) was prepared. A hard coat liquid 1 having the following composition described in JP-A No. 2008-158483 was applied to one side of this film so that the dry thickness was 5 μm to obtain a film 110.
(Hard coat solution 1)
PET-30 (a mixture of pentaerythritol triacrylate and pentaerythritol tetraacrylate [manufactured by Nippon Kayaku Co., Ltd.]): 40.0 g
DPHA (mixture of dipentaerythritol pentaacrylate and dipentaerythritol hexaacrylate [manufactured by Nippon Kayaku Co., Ltd.]): 10.0 g
Irgacure 184: 2.0g
SX-350 (crosslinked polystyrene particles, average particle size 3.5 μm, refractive index 1.60, manufactured by Soken Chemical Co., Ltd., 30% toluene dispersion): 2.0 g
Cross-linked acrylic-styrene particles (average particle size 3.5 μm, refractive index 1.55, manufactured by Soken Chemical Co., Ltd., 30% toluene dispersion): 13.0 g
FP-13 (fluorine surface modifier of the following formula): 0.06 g
Sol liquid a: 11.0 g
Toluene: 38.5g

(Example 7)
A film 111 having a film thickness of 40 μm was obtained in the same manner as in Example 1 except that the film composition was changed to (meth) acrylic resin A6 / cellulose ester E = 65 parts by mass / 35 parts by mass.

(Example 8)
A film obtained in the same manner as in Example 7 was stretched 1.7 times at a stretching temperature of 170 ° C., and then heat treated at 120 ° C. for 24 hours to obtain a film 112 having a thickness of 40 μm.

(Comparative Example 5)
A film 113 having a thickness of 40 μm was obtained in the same manner as in Comparative Example 1 except that the corona treatment and the application of the vinylidene chloride solution were not performed.

(Comparative Examples 6, 8-9)
Films 114 and 116 to 117 shown in Table 4 were prepared. In Table 4, 4UA is cellulose ester film 4UA (manufactured by Konica Minolta, film thickness 40 μm); COP is cyclic olefin resin film (manufactured by Nippon Zeon, film thickness 68 μm); PET is polyethylene terephthalate film (film thickness 100 μm) Indicates.

(Comparative Example 7)
A film 115 having a film thickness of 40 μm was obtained in the same manner as in Comparative Example 2 except that the film composition was changed to general-purpose PMMA / CAP482 = 70 parts by mass / 30 parts by mass.

(Examples 9 to 12, Comparative Example 10)
Films 118 to 122 having a thickness of 40 μm were obtained in the same manner as in Example 2 except that the content ratio of the cellulose ester was changed as shown in Table 5.

(Examples 13 to 19)
Except having changed the kind of cellulose ester as shown in Table 6, it carried out similarly to Example 2, and obtained the films 123-129 with a film thickness of 40 micrometers.

(Examples 20 to 25)
Except having changed the kind of (meth) acrylic resin as shown in Table 7, it carried out similarly to Example 13, and obtained the films 130-135 with a film thickness of 40 micrometers.

  The tensile elasticity modulus, elongation rate, and elongation amount of the obtained film were measured by the following methods.

(Tensile modulus)
The obtained film was cut into a size of 100 mm (MD direction) × 10 mm (TD direction) to obtain a sample film. In accordance with JIS K7127, the sample film was pulled in the MD direction using a Tensilon RTC-1225A manufactured by Orientec Co., Ltd., and the tensile elastic modulus in the MD direction was measured. The measurement was performed at 23 ° C. and 55% RH.

(Elongation amount / Elongation speed)
The obtained film (film thickness 40 μm) was conditioned for 12 hours or more under the condition of 23 ± 1 ° C. and 55% RH. Then, the film equipped with the water immersion attachment was immersed in 23 ± 1 ° C. pure water using TMA / SS7100 manufactured by Hitachi High-Tech, and taken out to measure the amount of elongation of the film. The elongation amount was measured in the MD direction of the film. And the "elongation amount (%)" of the film 30 minutes after the start of immersion was determined.

  The obtained measurement data was plotted with the immersion time (minutes) on the horizontal axis and the film elongation (%) on the vertical axis to obtain a curve. The slope of the obtained curve from the start of immersion until 2 minutes later (the slope of the elongation with respect to the immersion time) was calculated to determine “elongation rate (% / min)”.

Moreover, about some films, adhesiveness with a polarizer was evaluated.
(Adhesiveness)
First, a 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 at 50 ° C. to a stretching ratio of 6 times in the transport direction to prepare a polarizer having a thickness of 25 μm. .

1) Adhesiveness by saponification treatment The films obtained in Examples or Comparative Examples were subjected to alkali saponification treatment under the following conditions, and then washed with water, neutralized and washed with water.
Saponification step 2M-NaOH 50 ° C. 90 seconds Water washing step Water 30 ° C. 45 seconds Neutralization step 10% by mass HCl 30 ° C. 45 seconds Water washing step Water 30 ° C. 45 seconds The resulting film was dried at 80 ° C.

The film subjected to the alkali saponification treatment was bonded to one surface of the above prepared polarizer using a 5% aqueous solution of completely saponified polyvinyl alcohol as an adhesive, and then dried to obtain a laminate. The adhesive properties at the interface between the polarizing plate protective film and the polarizer when the polarizing plate protective film of the obtained laminate was peeled off in the 180 ° direction were measured and evaluated based on the following criteria.
○: The polarizing plate protective film tears and does not peel at the interface between the polarizing plate protective film and the polarizer. Δ: Some peeling is observed at the interface between the polarizing plate protective film and the polarizer. ×: The polarizing plate protective film and the polarizer. Peel at the interface with

2) Adhesiveness by easy-adhesive layer For 100 g of water-based urethane resin having a carboxyl group (Daiichi Kogyo Seiyaku, trade name: Superflex 210, solid content: 33%), a crosslinking agent (manufactured by Nippon Shokubai, trade name: (Epocross WS700, solid content: 25%) 20 g was added and stirred for 3 minutes to obtain an easy-adhesive composition.

  The obtained easy-adhesive composition was applied to the corona discharge treated surface of the film subjected to the corona discharge treatment by a bar coater (# 6). The obtained film was put into a hot air dryer (140 ° C.), and the easy-adhesive composition was dried for about 5 minutes to form an easy-adhesive layer (0.2 to 0.4 μm). And the obtained easily bonding layer and the said produced polarizer were bonded together through the completely saponified polyvinyl alcohol 5% aqueous solution, Then, it was made to dry and the laminated body was obtained. The adhesiveness of the obtained laminate was evaluated in the same manner as described above.

The evaluation results of Examples 1 to 8 and Comparative Examples 1 to 9 are shown in Table 4, the evaluation results of Examples 9 to 12 and Comparative Example 10 are shown in Table 5, and the evaluation results of Examples 13 to 19 are shown in Table 6. Table 7 shows the evaluation results of Examples 20 to 25.

  As shown in Tables 4 to 7, it can be seen that the films of Examples 1 to 25 have moderately low elongation amounts and elongation rates and moderately high tensile elastic moduli. On the other hand, it can be seen that Comparative Examples 1 to 10 cannot achieve an appropriate elongation amount, elongation rate, and tensile modulus.

  Specifically, it can be seen that the films of Comparative Examples 1 and 8 to 9 are conventional low-moisture permeable films; or films having a low-moisture permeable layer, and at least the elongation rate is too small. On the other hand, since the films of Comparative Examples 4, 6 and 10 include the cellulose ester film, it can be seen that at least the elongation rate is too large. Since Comparative Examples 3 and 7 contain a certain amount of cellulose ester having a low LogP value, it can be seen that the elongation rate is too high. It can be seen that the film of Comparative Example 5 has a low tensile modulus.

  And as Table 5 shows, it turns out that the amount of elongation and elongation rate of a film become so large that there is much content of the cellulose ester with comparatively high moisture permeability. As Table 6 shows, the higher the hydrophobicity of the cellulose ester is, the lower the affinity of the film with water is. As shown in Table 7, it can be seen that the higher the hydrophobicity of the (meth) acrylic resin, the lower the affinity of the film with water, and therefore the smaller the elongation amount / elongation speed of the film.

3. Production of Polarizing Plate (Example 26)
1) Preparation of polarizer A 120 μm-thick long roll polyvinyl alcohol film is 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 at 50 ° C. to a stretching ratio of 6 times in the transport direction. Thus, a polarizer having a thickness of 25 μm was obtained.

2) Preparation of retardation film RT1 The following components were stirred and mixed with a dissolver for 50 minutes, and then dispersed with Manton Gorin to obtain a fine particle dispersion 1.
(Fine particle dispersion 1)
Fine particles (Aerosil R812 manufactured by Nippon Aerosil Co., Ltd.): 11 parts by mass Ethanol: 89 parts by mass

Next, while sufficiently stirring in a dissolution tank containing methylene chloride, the obtained fine particle dispersion 1 was slowly added and further dispersed with an attritor so that the particle size of the secondary particles became a predetermined size. . The obtained solution was filtered with Finemet NF manufactured by Nippon Seisen Co., Ltd., and a fine particle additive solution 1 was obtained.
(Fine particle addition liquid 1)
Methylene chloride: 99 parts by mass Fine particle dispersion 1: 5 parts by mass

A main dope solution having the following composition was prepared. First, methylene chloride and ethanol were added to the pressure dissolution tank. Cellulose acetate having a acetyl group substitution degree of 2.00, a sugar ester compound, and a fine particle additive solution 1 were added to a pressure-dissolving tank containing a solvent while stirring, and the mixture was completely dissolved by stirring while heating. This was designated as Azumi Filter Paper No. manufactured by Azumi Filter Paper Co., Ltd. The main dope solution was prepared by filtration using 244. The above was put into a sealed main dissolution vessel 1 and dissolved with stirring to prepare a dope solution.
(Main dope solution)
Methylene chloride: 340 parts by mass Ethanol: 64 parts by mass Cellulose acetate (acetyl group substitution degree: 2.00): 100 parts by mass Sugar ester compound: benzyl saccharose with an average substitution degree of 5.5: 12 parts by mass Fine particle additive solution: 1: 1 mass Part

  After casting (casting) the above-mentioned dope solution on a stainless steel belt support, the solvent was evaporated until the residual solvent amount reached 75% to obtain a web. The obtained web was peeled off from the stainless belt support with a peeling tension of 130 N / m, and stretched 37% in the width direction using a tenter while applying heat at 170 ° C. The residual solvent of the web at the start of stretching was 15%.

  Next, drying was terminated while the drying zone was conveyed by a number of rolls. The drying temperature was 130 ° C. and the transport tension was 100 N / m. As described above, a retardation film RT1 having a dry film thickness of 25 μm was obtained.

Production of Polarizing Plate As shown below, the produced film was alkali saponified, then washed with water, neutralized and washed with water.
Saponification process 2M-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 Thereafter, the obtained polarizing plate protective film was dried at 80 ° C. It was. Similarly, the produced retardation film RT1 was also subjected to alkali saponification treatment.

  And the above-mentioned film 101 which carried out the alkali saponification process was bonded together to one surface of the produced said polarizer by using the completely saponified polyvinyl alcohol 5% aqueous solution as an adhesive agent. Similarly, an alkali saponified retardation film RT1 was bonded to the other surface of the polarizer using a 5% aqueous solution of completely saponified polyvinyl alcohol as an adhesive. The bonding was performed so that the transmission axis of the polarizer and the in-plane slow axis of the film 101 were parallel. The laminated laminate was dried at 60 ° C. to obtain a polarizing plate 201.

(Examples 27-50, Comparative Examples 11-20)
Polarizing plates 202 to 235 were obtained in the same manner as in Example 26 except that the type of the protective film was changed as shown in Tables 8 to 11.

Among these, as shown in Table 5, since the film 118 having a cellulose ester content of less than 5% has a small amount of cellulose that functions for saponification adhesion, even if it is subjected to alkali saponification treatment, it adheres with water paste. There wasn't. Therefore, for the film 118, an easy-adhesive composition having the following composition was prepared, and an easy-adhesive layer was formed.
(Preparation of easy-adhesive composition)
To 100 g of an aqueous urethane resin having a carboxyl group (Daiichi Kogyo Seiyaku, trade name: Superflex 210, solid content: 33%), a crosslinking agent (manufactured by Nippon Shokubai, trade name: Epocross WS700, solid content: 25%) ) 20 g was added and stirred for 3 minutes to obtain an easy-adhesive composition.

  The obtained easy-adhesive composition was applied to the corona discharge treated surface of the protective film subjected to the corona discharge treatment by a bar coater (# 6). Thereafter, the protective film was put into a hot air dryer (140 ° C.), and the applied easy-adhesive composition was dried for about 5 minutes to form an easy-adhesive layer (0.2 to 0.4 μm).

  And the obtained easily bonding layer and polarizer were bonded together through the water paste, and the polarizing plate 218 was obtained.

  The reddish of the obtained polarizing plate and the panel bend were evaluated by the following methods.

(Reddish)
The obtained polarizing plate was put in a thermo at 20 ° C. and 95% RH and stored for 200 hours. After the storage, the obtained polarizing plate was visually observed whether or not a red defect (reddish) due to deterioration of the polarizer occurred, and evaluated based on the following criteria.
◎: No red defect is observed on the polarizing plate ○: Red defect is slightly recognized on the polarizing plate, but there is almost no problem ×: Red defect is recognized on the polarizing plate

(Panel bend)
A glass plate (A4 size) having a thickness of 0.5 mm was prepared. On this glass plate, the produced polarizing plate was bonded through an adhesive to obtain a panel. The lamination was performed so that the retardation film of the polarizing plate was on the glass plate side. As the pressure-sensitive adhesive, a 25 μm thick double-sided tape (baseless tape MO-3005C) manufactured by Lintec Corporation was used.

The obtained panel was allowed to stand in a room temperature state of 23 ° C. and 55% for half a day, and then stored in a thermostat of 40 ° C. and 90% RH for 24 hours. Thereafter, the panel was taken out and placed in a 40 ° C. dry thermo and dried for 2 hours. The amount of warpage of the panel obtained after drying was measured immediately. The amount of warpage of the panel was measured by measuring the height from the horizontal plane at the four corners of the panel, and taking the average value thereof.
◎: Panel warpage is less than 1.0 mm ◎: Panel warpage is 1.0 mm or more and less than 2.0 mm ○: Panel warpage is 2.0 mm or more and less than 3.5 mm △: Panel warpage is 3 .5mm or more and less than 5.0mm x: Panel warpage is 5mm or more

The evaluation results of Examples 26 to 33 and Comparative Examples 11 to 19 are shown in Table 8, the evaluation results of Examples 34 to 37 and Comparative Example 20 are shown in Table 9, and the evaluation results of Examples 38 to 44 are shown in Table 10. Table 11 shows the evaluation results of Examples 45 to 50.

  As shown in Tables 8 to 11, it can be seen that neither the reddish nor the panel bend occurs in the polarizing plates of Examples 26 to 50. On the other hand, it can be seen that at least one of reddish or panel bend occurs in the polarizing plates of Comparative Examples 11 to 20.

  Specifically, it can be seen that the polarizing plates of Comparative Examples 11, 18 and 19 in which at least the elongation rate of the protective film is too small do not cause panel bend but produce reddish. On the other hand, it can be seen that the polarizing plates of Comparative Examples 12 to 14, 16 and 17 in which at least one of the elongation amount and the elongation rate of the protective film is too large do not cause reddish but produce panel bend. In the polarizing plate of Comparative Example 12, the LogP value of the cellulose ester was too high, the cellulose ester and polymethyl methacrylate were not sufficiently compatible, and the effect of improving the tensile modulus due to the addition of the cellulose ester was not obtained. Conceivable.

  Furthermore, as shown in Table 9, it can be seen that the reddish of the polarizing plate is easily reduced when the amount of elongation and the elongation rate of the film are moderately large. As shown in Tables 10 and 11, it can be seen that the panel bend is likely to be reduced when the elongation amount and elongation rate of the film are moderately small.

4). Production of liquid crystal display device (Example 51)
As a liquid crystal cell, a VA liquid crystal cell having two glass substrates having a thickness of 0.5 mm and a liquid crystal layer disposed therebetween was prepared. Then, the prepared polarizing plates 201 are bonded to both surfaces of the prepared liquid crystal cell via a 25 μm thick double-sided tape (baseless tape MO-3005C) manufactured by Lintec to obtain a liquid crystal display panel. It was. The bonding was performed such that the retardation film RT1 of the polarizing plate 201 was in contact with the liquid crystal cell.

  Then, after removing the liquid crystal display panel (polarizing plate / liquid crystal cell / laminate of polarizing plate) from the 40-inch display BRAVIA KLV-40J3000 (VA method) manufactured by SONY, the liquid crystal display panel prepared above is arranged, and the liquid crystal A display device 301 (1) was obtained. The attached liquid crystal display panel was set so that the slow axis of the retardation film RT1 and the slow axis of the polarizing plate previously attached were parallel.

  Liquid crystal display devices 301 (2) and 301 (3) were produced in the same manner except that the thickness of the two glass substrates constituting the liquid crystal cell was 0.2 mm and 0.7 mm, respectively.

(Examples 52 to 76, Comparative Examples 21 to 30)
Liquid crystal display devices 302 to 335 were obtained in the same manner as in Example 51 except that the polarizing plate 201 was sequentially changed to the polarizing plates 202 to 235.

  The bend unevenness of the obtained liquid crystal display device was measured by the following method.

(Bendmura)
The produced liquid crystal display device was left in an environment of 40 ° C. and 95% RH for 24 hours. Next, with the liquid crystal display device displaying black in a 40 ° C. dry environment, the difference between the luminance near the four vertices of the display screen and the luminance near the center of the display screen (image unevenness between the central portion and the peripheral portion) Was visually observed. And it evaluated based on the following reference | standard.
○: Image unevenness was not recognized ×: Image unevenness was recognized

The evaluation results of Examples 51 to 58 and Comparative Examples 21 to 29 are shown in Table 12, the evaluation results of Examples 59 to 62 and Comparative Example 30 are shown in Table 13, and the evaluation results of Examples 62 to 68 are shown in Table 14. Table 15 shows the evaluation results of Examples 69 to 74.

  As shown in Tables 12 to 15, when the thickness of the glass substrate is 0.5 mm, a liquid crystal display device using a polarizing plate having a panel bend evaluation result of Δ or x becomes a practical problem. In contrast to the occurrence of panel bend unevenness; no practically problematic bend unevenness was observed in any of the liquid crystal display devices using polarizing plates with panel bend evaluation results of ◯ or higher.

  Further, it has been found that even when the thickness of the glass substrate is 0.5 mm, even if the polarizing plate does not cause bend unevenness, the bend unevenness may occur when the glass substrate thickness is 0.2 mm. On the contrary, it has been found that even when the thickness of the glass substrate is 0.5 mm, the bend unevenness may not occur when the thickness of the glass substrate is 0.7 mm even when the polarizing plate generates the bend unevenness. From these things, it turned out that the protective film of this invention can suppress especially the bend nonuniformity especially when the thickness of a glass substrate is 0.3 mm or more and less than 0.7 mm.

  This application claims the priority based on Japanese Patent Application No. 2013-156705 of an application on July 29, 2013. The contents described in the application specification and the drawings are all incorporated herein.

  ADVANTAGE OF THE INVENTION According to this invention, even if the thickness of a polarizer is thin, the polarizing plate with little deterioration of a polarizer by the moisture which permeate | transmitted can be provided.

DESCRIPTION OF SYMBOLS 10 Liquid crystal display device 30 Liquid crystal cell 50 1st polarizing plate 51 1st polarizer 53 Protective film (F1)
55 Protective film (F2)
70 Second polarizing plate 71 Second polarizer 73 Protective film (F3)
75 Protective film (F4)
90 backlight

Claims (9)

The tensile elastic modulus at 23 ° C. and 55% RH is 3 GPa or more,
After humidity conditioning at 23 ± 1 ° C. and 55% RH for 12 hours or more, the initial elongation rate of the film when immersed in water at 23 ± 1 ° C. is 0.03 to 0.1% / min. And the polarizing plate protective film whose elongation amount of the film after immersion for 30 minutes after immersing a film in water is 0.4% or less.   The polarizing plate protective film of Claim 1 containing a (meth) acrylic resin.   The polarizing plate protective film according to claim 2, wherein a water-octanol distribution coefficient of the (meth) acrylic resin is 1.2 or more.   The polarizing plate protective film of Claim 1 which further contains 5-25 mass% cellulose ester with respect to the said film.   The polarizing plate protective film of Claim 4 whose water-octanol partition coefficient of the said cellulose ester is 0 or more.   The polarizing plate protective film according to claim 1, comprising a (meth) acrylic resin having a water-octanol distribution coefficient of 1.2 or more and a cellulose ester having a water-octanol distribution coefficient of 0 or more.   The polarizing plate protective film according to claim 1, wherein the polarizing plate protective film has a thickness of 10 to 50 μm.   A polarizing plate comprising a polarizer and the polarizing plate protective film according to claim 1. A liquid crystal cell comprising a first glass substrate and a second glass substrate having a thickness of 0.3 mm or more and less than 0.7 mm, and a liquid crystal layer disposed between the first glass substrate and the second glass substrate; ,
A first polarizing plate disposed on the first glass substrate of the liquid crystal cell;
Including a second polarizing plate disposed on the second glass substrate of the liquid crystal cell,
The first polarizing plate is a first polarizer, a protective film F1 disposed on a surface of the first polarizer opposite to the liquid crystal cell, and the liquid crystal cell of the first polarizer. Including a protective film F2 disposed on the side surface,
The second polarizing plate is opposite to the second polarizer, the protective film F3 disposed on the surface of the second polarizer on the liquid crystal cell side, and the liquid crystal cell of the second polarizer. Including a protective film F4 disposed on the side surface,
The liquid crystal display device in which one or both of the protective film F1 and the protective film F4 is the polarizing plate protective film according to claim 1.

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