JP2012198355A - Polarizer protective film, and polarizing plate and liquid crystal display device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polarizer protective film which has less haze, lower moisture permeability, and higher brittleness; and to provide a polarizing plate which reduces polarization unevenness and contrast unevenness, and a liquid crystal display device which has a wide viewing angle and prevents color change (color shift).SOLUTION: A polarizer protective film contains an acryl resin (A), a cellulose ester resin (B), and a carboxylic acid sugar ester compound (C), satisfying specific requirements.

Description

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

  In recent years, it has been demanded that the liquid crystal display device can cope with various usage environments such as an increase in size and use in digital signage.

  Conventionally, a cellulose ester film has been used in a liquid crystal display device, but when it is assumed to be used outdoors, moisture absorption deterioration of the film becomes a problem, and further improvement in moisture resistance is required. .

  In low-humidity materials, acrylic resins have been used suitably because of their high transparency. However, there has been a problem in that distortion is likely to occur during long-term use and the brittleness is poor. Although brittleness has been improved by mixing with cellulose ester, etc., mixing with cellulose ester with high molecular weight and acrylic has poor compatibility, so the solvent is difficult to dissolve during production compared to conventional cellulose ester, or peeling There is a problem that stress is sometimes applied and distortion occurs, and further, the adhesion to the polarizer is low, which is not sufficient for use as a polarizer protective film (see, for example, Patent Document 1).

Japanese Patent No. 3322406

  The present invention has been made in view of the above problems and situations, and a solution to that problem is to provide a polarizer protective film having low haze, low moisture permeability, and high brittleness. It is another object of the present invention to provide a polarizing plate with reduced polarization unevenness and contrast unevenness, and a liquid crystal display device having a wide viewing angle and no color change (color shift).

  The above-mentioned problem according to the present invention is solved by the following means.

1. A polarizer protective film containing an acrylic resin (A), a cellulose ester resin (B), and a carboxylic acid sugar ester compound (C), which satisfies the following requirements (1) to (4) A polarizer protective film.
(1) The acrylic resin (A) has a weight average molecular weight in the range of 80000 to 1000000.
(2) The cellulose ester resin (B) has an average acyl group substitution degree in the range of 2.0 to 3.0 and a weight average molecular weight in the range of 75,000 to 300,000.
(3) The mass ratio (A: B) of the acrylic resin (A) and the cellulose ester resin (B) is in the range of 95: 5 to 30:70.
(4) The carboxylic acid sugar ester compound (C) was formed by ester-linking a sugar hydroxyl group and a polybasic acid having 7 to 18 carbon atoms having two or more carboxyl groups in one molecule. It is a long-chain alkylcarboxylic acid sugar ester compound having one or more carboxyl groups in one molecule.

  2. 2. The polarizer protective film according to item 1, wherein the cellulose ester has an average acetyl group substitution degree in the range of 2.0 to 2.5.

  3. The polarizer protective film according to item 1 or 2, wherein a carboxylic acid sugar ester compound represented by the following general formula (1) is contained.

[In General Formula (1), R _{1 to} R ₈ represent a hydrogen atom, a substituted or unsubstituted alkylcarbonyl group, or a substituted or unsubstituted arylcarbonyl group, and R _{1 to} R ₈ are the same. Or different. ]
4). Under the measurement conditions of a temperature of 23 ° C., a relative humidity of 55% RH, and a measurement wavelength of 590 nm, the in-plane retardation value Ro defined by the following formula (I) is in the range of 0 to 10 nm, and the following formula (II) 4. The polarizer protective film according to claim 1, wherein the retardation value Rt in the thickness direction defined by is in a range of −15 to 15 nm.
Formula _{(I): Ro = (n} x -n y) × d (nm)
Formula (II): Rt = {(n _x + n _y ) / 2−n _z } × d (nm)
[In the above formula, Ro represents an in-plane retardation value in the polarizer protective film, and Rt represents a thickness direction retardation in the film. Further, d represents the thickness of the retardation film, n _x represents a refractive index of the maximum (slow axis direction) in the plane of the polarizer protective film. n _y represents a refractive index in the direction perpendicular to the slow axis in the polarizer protective film plane (fast axis direction), n _z represents the refractive index of the polarizer protective film in the thickness direction. The measurement conditions are the same as above. ]
5. A polarizer comprising the polarizer protective film according to any one of items 1 to 4 above.

  6). A liquid crystal display device comprising the polarizer protective film according to any one of items 1 to 4 above.

  By the above means of the present invention, a polarizer protective film having a low haze, low moisture permeability, and high brittleness can be provided. Furthermore, it is possible to provide a polarizing plate with reduced polarization unevenness and contrast unevenness, and a liquid crystal display device with a wide viewing angle and almost no color change (color shift).

  In the present invention, a carboxylic acid sugar ester compound having a specific substitution degree and further having one or more carboxyl groups and long chain alkyl groups in one molecule (hereinafter referred to as “long chain alkyl carboxylic acid sugar ester”). By using the “compound”, the disadvantages of the cellulose ester and the acrylic resin can be eliminated, the moisture permeability and brittleness can be improved, and a film having high adhesion to the polarizer can be obtained. Furthermore, the said effect can further be heightened by using together the carboxylic acid sugar ester compound represented by General formula (1).

  Although the mechanism of expression of the effect of the present invention has not been elucidated, the long-chain alkylcarboxylic acid sugar ester compound is a cellulose ester and a short-chain carboxylic acid sugar ester compound that acts as a plasticizer (for example, represented by the general formula (1) It is compatible with mixed resin formed by mixing cellulose ester resin and acrylic resin, and easy to remove solvents. It is considered that the thickness can be improved. That is, the long-chain alkyl carboxylic acid sugar ester compound has a skeleton similar to the above mixed resin as compared with the short-chain carboxylic acid ester compound, and has a long-chain alkyl group to improve compatibility and ease of solvent removal. It is thought that it has an action effect. Below 7 carbon atoms, it tends to bleed out and peel off easily. On the other hand, it is estimated that the compatibility is deteriorated above 18.

The figure which showed typically the dope preparation process, casting process, and drying process of the solution casting film forming method used for this invention. Schematic diagram showing a state in which glycerin is dropped on a slide glass Schematic diagram showing the state of a sample film placed on glycerin Schematic diagram showing the state in which glycerin is dropped on the sample film Schematic diagram showing a state where a cover glass is placed on glycerin

  The polarizer protective film of the present invention is an optical film containing an acrylic resin (A), a cellulose ester resin (B), and a carboxylic acid sugar ester compound (C), and the above requirements (1) to (4) It is characterized by satisfying. This feature is a technical feature common to the inventions according to claims 1 to 6.

  As an embodiment of the present invention, it is preferable that the average acetyl group substitution degree of the cellulose ester is in the range of 2.0 to 2.5 from the viewpoint of manifesting the effect of the present invention. Furthermore, it is preferable that the carboxylic acid sugar ester compound represented by the general formula (1) is contained.

  In the present invention, the in-plane retardation value Ro defined by the formula (I) is within the range of 0 to 10 nm under the measurement conditions of a temperature of 23 ° C., a relative humidity of 55% RH, and a measurement wavelength of 590 nm. The thickness direction retardation value Rt defined by the formula (II) is preferably in the range of -15 to 15 nm.

  The polarizer protective film of this invention can be used suitably for a polarizing plate and a liquid crystal display device.

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

(Long-chain alkyl group carboxylic acid sugar ester compound)
The polarizer protective film of the present invention is a polarizer protective film containing an acrylic resin (A), a cellulose ester resin (B), and a carboxylic acid sugar ester compound (C), and the carboxylic acid sugar ester compound (C ) And a hydroxyl group of sugar and a polybasic acid having 7 to 18 carbon atoms having two or more carboxyl groups in one molecule, and one or more carboxyl groups and a long-chain alkyl group in one molecule And a carboxylic acid sugar ester compound (also referred to as “long-chain alkyl group carboxylic acid sugar ester compound” in the present application).

  Here, “sugar” refers to hexose selected from glucose, fructose, galactose, mannose, or an isomer or derivative thereof, pentose selected from xylose, arabinose, an isomer or derivative thereof, tetrose selected from erythrose, threose, or the like Examples include isomers and derivatives. These sugars may be D-form or L-form. Among these, hexose is excellent in terms of hydrophilicity. Among hexoses, glucose is excellent as a hydrophilic group, and D-form is more excellent.

  In glucose (ring-closed state), the number of hydroxyl groups (hydroxyl groups) is five, and a maximum of five ester bonds can be performed. From the viewpoint of water solubility, it is preferable that three or less hydroxyl groups (hydroxyl groups) and a polybasic acid are ester-bonded, and one hydroxyl group (hydroxyl group) and a polybasic acid are more preferably ester-bonded.

  Glucose (ring-closed state) has 6 carbon atoms in its chemical structure, but the hydroxyl group (hydroxyl group) at the C6 position is preferred as the hydroxyl group (hydroxyl group) to be esterified with a polybasic acid. Since only the C6 position is a primary hydroxyl group (hydroxyl group), esterification of this part is preferable because the conformation of the bonded polybasic acid becomes diversified.

  The sugar may be a monosaccharide in which the above-mentioned constituent sugars are present alone or may be a polysaccharide in which two or more are ether-bonded. Among these, oligosaccharides having one monosaccharide constituting a sugar or 2-10 ether sugars constituting a sugar are excellent in that they have high water solubility and low viscosity. The number of constituent sugars in the sugar is preferably 1 to 5, more preferably 1 to 3, and particularly preferably 1 to 2.

  As the disaccharide, maltose, isomaltose, cellobiose, sucrose, laminaribiose, xylobiose, chitobiose, sophorose, gentiobiose, trehalose and the like can be suitably used. As the trisaccharide, maltotriose, isomaltotriose cellotriose, raffinose, xylotriose or the like can be preferably used.

  In general, “polybasic acid” refers to an acid having two or more protons that can be donated in one molecule of an acid, that is, a general term for acids having a basicity of 2 or more. It is necessary to have two or more carboxyl groups in the molecule.

  Examples of polybasic acids include dicarboxylic acids (dibasic acids) and tricarboxylic acids. Dicarboxylic acid is an organic compound having two carboxyl groups. The molecular formula of dicarboxylic acid can be written as HOOC-R-COOH (R is a divalent substituent derived from alkane, alkene, alkyne, etc.). Examples of the dicarboxylic acid include oxalic acid (carbon number 2), malonic acid (carbon number 3), succinic acid (carbon number 4), itaconic acid (carbon number 4), glutaric acid (carbon) as linear saturated dicarboxylic acid. 5), adipic acid (carbon number 6), pimelic acid (carbon number 7), suberic acid (carbon number 8), azelaic acid (carbon number 9), sebacic acid (carbon number 10), dodecanedioic acid (carbon number) 12), tetradecanedioic acid (14 carbon atoms), hexadecanedioic acid (16 carbon atoms), octadecanedioic acid (18 carbon atoms), dimer acid (36 carbon atoms), and saturated / unsaturated cyclic dicarboxylic acid Phthalic acid (carbon number 8), isophthalic acid (carbon number 8), terephthalic acid (carbon number 8), cyclohexanedicarboxylic acid (carbon number 8), and the like.

  Next, tricarboxylic acid is an organic compound having three carboxyl groups. Examples of the tricarboxylic acid include citric acid (2-hydroxypropanetricarboxylic acid (carbon number 6)), aconitic acid (2-carboxypropane-1-entrycarboxylic acid (carbon number 6)), and isocitric acid (1-hydroxypropane). -1,2,3-tricarboxylic acid (carbon number 6)), oxalosuccinic acid (1-oxopropane-1,2,3-tricarboxylic acid (carbon number 6)), 1,3,6-hexamethylenetricarboxylic acid , Trimesic acid (benzene-1,3,5-tricarboxylic acid (carbon number 9)) and the like.

  The structure of the carbon chain of the polybasic acid is not particularly limited and may be saturated or unsaturated, but it is preferable to use a saturated dibasic acid.

  In this embodiment, saccharides and polybasic acids are used as raw materials, and can be esterified by various methods. Esterification methods include dehydration condensation using enzymes such as lipase and protease, dehydration condensation using acid catalyst or alkali catalyst, polybasic acid carboxylic acid once methyl esterified, and transesterification And a method of esterifying with sugar.

The structure of the carboxylic acid sugar ester compound can be analyzed by a known method. For example, the chemical structure of the carboxylic acid sugar ester compound can be identified by measuring one-dimensional NMR ( ¹ H-NMR, ¹³ H-NMR) using high resolution NMR (ADVANCE400 400 MHz manufactured by BRUKER). Furthermore, the attribution of each spectrum can be determined by two-dimensional NMR using CH-COSY.

  When the carboxylic acid sugar ester compound functions as a plasticizer, the content of the carboxylic acid sugar ester compound is preferably 1 to 35% by mass with respect to the cellulose ester from the viewpoint of the effect as a plasticizer. It is more preferable that it is 1-20 mass%.

  On the other hand, when the carboxylic acid sugar ester compound functions as a release agent, the content of the carboxylic acid sugar ester compound is 0.01 to 1% by mass with respect to the base resin from the viewpoint of the effect as a release agent. Preferably there is.

(Carboxylic acid sugar ester compound represented by the general formula (1))
In the present invention, as the carboxylic acid sugar ester compound, in addition to the carboxylic acid sugar ester compound having the above-described carboxyl group and long-chain alkyl group, a carboxylic acid sugar ester compound represented by the following general formula (1) is contained. It is preferable that

[In General Formula (1), R _{1 to} R ₈ represent a hydrogen atom, a substituted or unsubstituted alkylcarbonyl group, or a substituted or unsubstituted arylcarbonyl group, and R _{1 to} R ₈ are the same. Or different. ]
In the present invention, the compound represented by the general formula (1) (hereinafter also referred to as a carboxylic acid sugar ester compound) has an average substitution degree of 3.0 to 6.0 and a substitution degree of 4 or less. It is preferable to contain 30-80 mass%.

In the present invention, the degree of substitution of the compound represented by the general formula (1) is the number of substituents other than hydrogen among the eight hydroxyl groups (hydroxyl groups) included in the general formula (1). It represents, that is, the number including groups other than hydrogen among R _{1 to} R _{8 in} the general formula (1). Therefore, when all of R _{1 to} R ₈ are substituted with a substituent other than hydrogen, the degree of substitution is 8.0, which is the maximum value, and when R _{1 to} R ₈ are all hydrogen atoms, 0.0 It becomes.

  As the degree of substitution of the general formula (1) in the present invention, it is appropriate to use the average degree of substitution, and the average degree of substitution is measured from the area ratio of the chart showing the degree of substitution distribution by high performance liquid chromatography by the following method. be able to.

  In the present invention, it is preferable that the carboxylic acid sugar ester compound has a higher degree of substitution in consideration of only the retardation development. However, in consideration of moisture resistance and internal haze, the average degree of substitution is slightly lower, and more than a certain level. It has been found that a mixture of low substitution components is preferred.

  The effect mechanism presumes that this is achieved by making the property of phase difference expression and compatibility with cellulose ester a mixture of compounds having similar structures.

  The average substitution degree is more preferably 4.0 or more, and the component having a substitution degree of 4 or less is preferably 35% by mass or more.

In General Formula (1), R _{1 to} R ₈ represent a hydrogen atom, a substituted or unsubstituted alkylcarbonyl group, or a substituted or unsubstituted arylcarbonyl group, and R _{1 to} R ₈ are the same. May be different.

  Examples of the sugar as a raw material for synthesizing the carboxylic acid sugar ester compound according to the present invention include the following, but the present invention is not limited thereto.

  Glucose, galactose, mannose, fructose, xylose or arabinose, lactose, sucrose, nystose, 1F-fructosyl nystose, stachyose, maltitol, lactitol, lactulose, cellobiose, maltose, cellotriose, maltotriose, raffinose or kestose .

  In addition, gentiobiose, gentiotriose, gentiotetraose, xylotriose, galactosyl sucrose, and the like are also included.

  As the monocarboxylic acid used in the synthesis of the carboxylic acid sugar ester compound according to the present invention, known aliphatic monocarboxylic acid, alicyclic monocarboxylic acid, aromatic monocarboxylic acid and the like can be used. The carboxylic acid used may be one kind or a mixture of two or more kinds.

  Examples of preferred aliphatic monocarboxylic acids include acetic acid, propionic acid, butyric acid, isobutyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, 2-ethyl-hexanecarboxylic acid, undecylic acid, Saturation of lauric acid, tridecylic acid, myristic acid, pentadecylic acid, palmitic acid, heptadecylic acid, stearic acid, nonadecanoic acid, arachidic acid, behenic acid, lignoceric acid, serotic acid, heptacosanoic acid, montanic acid, mellicic acid, and laxaric acid Examples thereof include unsaturated fatty acids such as fatty acids, undecylenic acid, oleic acid, sorbic acid, linoleic acid, linolenic acid, arachidonic acid and octenoic acid.

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

  Examples of preferable aromatic monocarboxylic acids include aromatic monocarboxylic acids having 1 to 5 alkyl groups or alkoxy groups introduced into the benzene ring of benzoic acid such as benzoic acid and toluic acid, cinnamic acid, benzylic acid, An aromatic monocarboxylic acid having two or more benzene rings such as biphenyl carboxylic acid, naphthalene carboxylic acid and tetralin carboxylic acid, or a derivative thereof can be mentioned, and benzoic acid is particularly preferable.

Some specific examples according to the present invention are shown below, but these are cases where R _{1 to} R ₈ are all the same substituent R, and the present invention is not limited thereto.

  The carboxylic acid sugar ester compound according to the present invention can be produced by reacting a sugar ester with an acylating agent (also referred to as an esterifying agent, for example, an acid halide of acetyl chloride, an anhydride such as acetic anhydride). The distribution of the degree of substitution is possible by adjusting the amount of acylating agent, the timing of addition, and the esterification reaction time, but it is possible to mix carboxylic acid sugar ester compounds of different degrees of substitution or purely isolated substitution. By mixing compounds of different degrees, it is possible to adjust components having a target average substitution degree and a substitution degree of 4 or less.

  (Synthesis Example: Synthesis Example of Compound According to the Present Invention)

  Four-headed Kolben equipped with a stirrer, a reflux condenser, a thermometer, and a nitrogen gas inlet tube were charged with 34.2 g (0.1 mol) of sucrose, 135.6 g (0.6 mol) of benzoic anhydride, 284. 8 g (3.6 mol) was charged, the temperature was raised while bubbling nitrogen gas through a nitrogen gas introduction tube with stirring, and an esterification reaction was carried out at 70 ° C. for 5 hours.

Next, the inside of the Kolben was depressurized to 4 × 10 ² Pa or less, and after excess pyridine was distilled off at 60 ° C., the inside of the Kolben was depressurized to 1.3 × 10 Pa or less and the temperature was raised to 120 ° C. Most of the acid and benzoic acid formed were distilled off. Then, 1 L of toluene and 300 g of a 0.5% by mass aqueous sodium carbonate solution were added, and the mixture was stirred at 50 ° C. for 30 minutes and then allowed to stand to separate a toluene layer. Finally, 100 g of water is added to the collected toluene layer, and after washing with water at room temperature for 30 minutes, the toluene layer is separated, and toluene is distilled off at 60 ° C. under reduced pressure (4 × 10 ² Pa or less). The carboxylic acid sugar ester compound 1 which is a mixture of A-1, A-2, A-3, A-4, A-5, etc. was obtained.

  When the obtained mixture was analyzed by high performance liquid chromatography-mass spectrometry (HPLC-MS), A-1 was 1.2% by mass, A-2 was 13.2% by mass, and A-3 was 14.2% by mass. %, A-4 was 35.4% by mass, A-5 and the like were 40.0% by mass. The average degree of substitution was 5.2.

  Similarly, 158.2 g (0.7 mol) of benzoic anhydride, 146.9 g (0.65 mol), and 124.3 g (0.55 mol) were reacted with an equimolar amount of pyridine. A sugar ester of such ingredients was obtained.

  Next, a part of the obtained mixture is purified by column chromatography using silica gel to obtain 100% pure A-1, A-2, A-3, A-4, A-5, etc., respectively. Obtained.

  A-5 or the like means a mixture of all components having a substitution degree of 4 or less, that is, compounds having substitution degrees of 4, 3, 2, 1. The average substitution degree was calculated with A-5 and the like being the substitution degree 4.

  In the present invention, the average degree of substitution was adjusted by adding in combination the sugar ester close to the desired degree of average substitution, isolated A-1 to A-5, and the like by the method prepared here.

<Measurement conditions for HPLC-MS>
1) LC section Device: JASCO CO., LTD. Column oven (JASCO CO-965), detector (JASCO UV-970-240 nm), pump (JASCO PU-980), degasser (JASCO DG-980-50)
Column: Inertsil ODS-3 Particle size 5 μm 4.6 × 250 mm (manufactured by GL Sciences Inc.)
Column temperature: 40 ° C
Flow rate: 1 ml / min
Mobile phase: THF (1% acetic acid): H ₂ O (50:50)
Injection volume: 3 μl
2) MS unit Device: LCQ DECA (manufactured by Thermo Quest)
Ionization method: Electrospray ionization (ESI) method Spray Voltage: 5 kV
Capillary temperature: 180 ° C
Vaporizer temperature: 450 ° C
(Resin constituting the polarizer protective film)
The polarizer protective film of the present invention is a polarizer protective film containing an acrylic resin (A) and a cellulose ester resin (B), and satisfies the following requirements (1) to (3): To do.
(1) The acrylic resin (A) has a weight average molecular weight in the range of 80000 to 1000000.
(2) The cellulose ester resin (B) has an average acyl group substitution degree in the range of 2.0 to 3.0 and a weight average molecular weight in the range of 75,000 to 300,000.
(3) The mass ratio (A: B) of the acrylic resin (A) and the cellulose ester resin (B) is in the range of 95: 5 to 30:70.

  Hereinafter, the resin constituting the polarizer protective film will be described in detail.

<Acrylic resin (A)>
The acrylic resin used in the present invention includes a methacrylic resin. Although it does not restrict | limit especially as resin, What consists of 50-99 mass% of methyl methacrylate units and 1-50 mass% of other monomer units copolymerizable with this is preferable.

  Other monomers that can be copolymerized include alkyl methacrylates having 2 to 18 carbon atoms, alkyl acrylates having 1 to 18 carbon atoms, acrylic acid, methacrylic acid, and the like. Unsaturated group-containing divalent carboxylic acids such as saturated acid, maleic acid, fumaric acid and itaconic acid, aromatic vinyl compounds such as styrene and α-methylstyrene, α, β-unsaturated nitriles such as acrylonitrile and methacrylonitrile, Maleic anhydride, maleimide, N-substituted maleimide, glutaric anhydride and the like can be mentioned, and these can be used alone or in combination of two or more monomers.

  Among these, methyl acrylate, ethyl acrylate, n-propyl acrylate, n-butyl acrylate, s-butyl acrylate, 2-ethylhexyl acrylate, and the like are preferable from the viewpoint of thermal decomposition resistance and fluidity of the copolymer. n-Butyl acrylate is particularly preferably used.

  The acrylic resin (A) used for the polarizer protective film of the present invention has a weight average molecular weight (particularly from the viewpoint of improving brittleness as an optical film and improving transparency when compatible with the cellulose ester resin (B)). Mw) needs to be in the range of 80000 to 1000000. In addition, it is preferable to be in the range of 100,000 to 600,000, and it is more preferable to be in the range of 150,000 to 400,000.

  When the weight average molecular weight (Mw) of the acrylic resin (A) is less than 80000, sufficient brittleness improvement cannot be obtained, and compatibility with the cellulose ester resin (B) deteriorates. Although the upper limit of the weight average molecular weight (Mw) of an acrylic resin (A) is not specifically limited, It is a preferable form that it shall be 1 million or less from a viewpoint on manufacture.

  The weight average molecular weight of the acrylic resin according to the present invention can be measured by gel permeation chromatography. The measurement conditions are as follows.

Solvent: Methylene chloride Column: Shodex K806, K805, K803G (Used by connecting three Showa Denko Co., Ltd.)
Column temperature: 25 ° C
Sample concentration: 0.1% by mass
Detector: RI Model 504 (manufactured by GL Sciences)
Pump: L6000 (manufactured by Hitachi, Ltd.)
Flow rate: 1.0ml / min
Calibration curve: Standard polystyrene STK standard polystyrene (manufactured by Tosoh Corp.) Mw = 2,800,000-500 calibration curves with 13 samples were used. The 13 samples are preferably used at approximately equal intervals.

  The methyl methacrylate monomer content in the acrylic resin according to the present invention can be measured with a gas chromatograph mass spectrometer. The measurement conditions are as follows.

Sample: Acrylic resin is dissolved in acetonitrile to prepare a 0.1% sample solution Sample volume: 1 μl
Equipment: HP 5890 Series II / HP 5971 MSD
Column: InertCAP for amines (0.32 mmid × 30 m) manufactured by GL Sciences
Inlet: 200 ° C
MSD: SIM m / z = 55,100
OVEN: 60 ° C. (4 min) → 15 (° C./min)→120° C.
In addition, the quantity of the methyl methacrylate monomer in the produced polarizer protective film of this invention can also be measured by the same method.

  There is no restriction | limiting in particular as a manufacturing method of the acrylic resin (A) in this invention, You may use any well-known methods, such as suspension polymerization, emulsion polymerization, block polymerization, or solution polymerization. Here, as a polymerization initiator, a normal peroxide type and an azo type can be used, and a redox type can also be used. Regarding the polymerization temperature, suspension or emulsion polymerization may be performed at 30 to 100 ° C, and bulk or solution polymerization may be performed at 80 to 160 ° C. In order to control the reduced viscosity of the obtained copolymer, polymerization can be carried out using alkyl mercaptan or the like as a chain transfer agent.

  A commercially available thing can also be used as an acrylic resin which concerns on this invention. For example, Delpet 60N, 80N (Asahi Kasei Chemicals Co., Ltd.), Dianal BR52, BR80, BR83, BR85, BR88 (Mitsubishi Rayon Co., Ltd.), KT75 (Denki Kagaku Kogyo Co., Ltd.) and the like can be mentioned. . Two or more acrylic resins can be used in combination.

<Cellulose ester resin (B)>
The cellulose ester resin (B) according to the present invention has an average acyl group substitution degree in the range of 2.0 to 3.0 and a weight average molecular weight in the range of 75,000 to 300,000.

  In addition, the glucose unit which comprises cellulose with a β-1,4-glycoside bond has free hydroxyl groups (hydroxyl groups) at the 2nd, 3rd and 6th positions. The cellulose ester according to the present invention is a polymer (polymer) obtained by esterifying some or all of these hydroxyl groups (hydroxyl groups) with an acyl group.

  “Acyl group substitution degree” represents the total of the ratios of esterification of hydroxyl groups (hydroxyl groups) at the 2nd, 3rd and 6th positions of glucose as a repeating unit. Specifically, the degree of substitution is 1 when each of the hydroxyl groups (hydroxyl groups) at the 2nd, 3rd and 6th positions of cellulose is 100% esterified. Therefore, when all of the 2nd, 3rd and 6th positions of cellulose are 100% esterified, the degree of substitution is 3 at the maximum.

  In the present application, the “average acyl group substitution degree” refers to an acyl group substitution degree in which the acyl group substitution degree of a plurality of glucose units constituting the cellulose ester is expressed as an average value per unit.

  In addition, the measuring method of acyl group substitution degree can be measured according to ASTM-D817-96.

  Examples of the acyl group include acetyl group, propionyl group, butanoyl group, heptanoyl group, hexanoyl group, octanoyl group, decanoyl group, dodecanoyl group, tridecanoyl group, tetradecanoyl group, hexadecanoyl group, octadecanoyl group, and isobutanoyl. Group, tert-butanoyl group, cyclohexanecarbonyl group, oleoyl group, benzoyl group, naphthylcarbonyl group, cinnamoyl group and the like.

  Among these, an acetyl group, a propionyl group, a butanoyl group, a dodecanoyl group, an octadecanoyl group, a tert-butanoyl group, an oleoyl group, a benzoyl group, a naphthylcarbonyl group, a cinnamoyl group, and the like are more preferable, and an acetyl group is particularly preferable. A propionyl group and a butanoyl group (when the acyl group has 2 to 4 carbon atoms), more preferably an acetyl group.

  The cellulose ester resin (B) according to the present invention has a substitution degree of acyl group of 2.0 to 3.0, carbon, particularly from the viewpoint of transparency when improved in brittleness or compatible with the acrylic resin (A). It is preferable that the substitution degree of the acyl group having 3 to 7 is 1.2 to 3.0, and the substitution degree of the acyl group having 3 to 7 carbon atoms is 2.0 to 3.0. That is, the cellulose ester resin according to the present invention is a cellulose ester resin substituted with an acyl group having 3 to 7 carbon atoms. Specifically, propionyl, butyryl and the like are preferably used, and a propionyl group is particularly preferable. Used.

  When the substitution degree of the acyl group of the cellulose ester resin (B) is less than 2.0, that is, when the residual degree of the hydroxyl groups (hydroxyl groups) at the 2,3,6-positions of the cellulose ester molecule is more than 1.0. However, when the acrylic resin (A) and the acrylic resin (B) are not sufficiently compatible with each other and used as an optical film, haze becomes a problem.

  Moreover, even if the substitution degree of the acyl group is 2.0 or more, if the substitution degree of the acyl group having 3 to 7 carbon atoms is less than 1.2, sufficient compatibility is not obtained or brittleness Will be reduced. For example, even when the substitution degree of the acyl group is 2.0 or more, the substitution degree of the acyl group having 2 carbon atoms, that is, the acetyl group is high, and the substitution degree of the acyl group having 3 to 7 carbon atoms is 1.2. If it is less than 1, the compatibility is lowered and the haze is increased. Further, even when the substitution degree of the acyl group is 2.0 or more, the substitution degree of the acyl group having 8 or more carbon atoms is high, and the substitution degree of the acyl group having 3 to 7 carbon atoms is less than 1.2. The brittleness deteriorates and desired characteristics cannot be obtained.

  The acyl substitution degree of the cellulose ester resin (B) according to the present invention is that the substitution degree is 2.0 to 3.0, and the substitution degree of the acyl group having 3 to 7 carbon atoms is 1.2 to 3.0. If there is no problem, it is preferable that the total substitution degree of acyl groups other than those having 3 to 7 carbon atoms, that is, acetyl groups or acyl groups having 8 or more carbon atoms is 1.3 or less.

  Further, the substitution degree of the acyl group of the cellulose ester resin (B) is more preferably in the range of 2.5 to 3.0.

  In the present invention, the acyl group may be an aliphatic acyl group or an aromatic acyl group. In the case of an aliphatic acyl group, it may be linear or branched and may further have a substituent. The number of carbon atoms of the acyl group in the present invention includes an acyl group substituent.

  When the said cellulose ester resin (B) has an aromatic acyl group as a substituent, it is preferable that the number of the substituents X substituted to an aromatic ring is 0-5. Also in this case, it is necessary to pay attention so that the substitution degree of the acyl group having 3 to 7 carbon atoms including the substituent is 1.2 to 3.0. For example, since the benzoyl group has 7 carbon atoms, when it has a substituent containing carbon, the benzoyl group has 8 or more carbon atoms and is not included in the acyl group having 3 to 7 carbon atoms. Become.

  Further, when the number of substituents substituted on the aromatic ring is 2 or more, they may be the same or different from each other, but they may be linked together to form a condensed polycyclic compound (for example, naphthalene, indene, indane, phenanthrene, quinoline). , Isoquinoline, chromene, chroman, phthalazine, acridine, indole, indoline, etc.).

  In the cellulose ester resin (B) as described above, having a structure having at least one kind of an aliphatic acyl group having 3 to 7 carbon atoms is used as a structure used for the cellulose resin according to the present invention.

  As for the substitution degree of the cellulose ester resin (B) according to the present invention, the substitution degree of the acyl group is 2.0 to 3.0, and the substitution degree of the acyl group having 3 to 7 carbon atoms is 1.2 to 3.0. is there.

  Moreover, it is a preferable structure that the sum total of the substitution degree of other than an acyl group having 3 to 7 carbon atoms, that is, an acetyl group and an acyl group having 8 or more carbon atoms is 1.3 or less.

  The cellulose ester resin (B) according to the present invention is preferably at least one selected from cellulose acetate propionate, cellulose acetate butyrate, cellulose acetate benzoate, cellulose propionate, and cellulose butyrate, Those having an acyl group having 3 or 4 carbon atoms as a substituent are preferred.

  Among these, cellulose ester resins that are particularly preferred are cellulose acetate propionate and cellulose propionate.

  The portion not substituted with an acyl group usually exists as a hydroxyl group (hydroxyl group). These can be synthesized by known methods.

  In addition, the substitution degree of an acetyl group and the substitution degree of other acyl groups are obtained by a method prescribed in ASTM-D817-96.

  The weight average molecular weight (Mw) of the cellulose ester resin according to the present invention is 75000 or more, particularly from the viewpoint of improving compatibility with the acrylic resin (A) and brittleness, and is preferably in the range of 75,000 to 300,000. More preferably, it is in the range of ˜240,000, particularly preferably in the range of 160000 to 240000. When the important average molecular weight (Mw) of the cellulose ester resin is less than 75,000, the effect of improving heat resistance and brittleness is not sufficient, and the effect of the present invention cannot be obtained. In the present invention, two or more kinds of cellulose resins can be mixed and used.

  In the polarizer protective film of the present invention, the acrylic resin (A) and the cellulose ester resin (B) are contained in a mass ratio of 95: 5 to 30:70, preferably 95: 5 to 50:50. More preferably, it is 90: 10-60: 40.

  If the mass ratio of the acrylic resin (A) and the cellulose ester resin (B) is more than 95: 5, the effect of the cellulose ester resin (B) cannot be sufficiently obtained, and the mass ratio is When the amount of acrylic resin is less than 30:70, the moisture resistance becomes insufficient.

  In the polarizer protective film of the present invention, the acrylic resin (A) and the cellulose ester resin (B) are preferably contained in a compatible state. The physical properties and quality required for an optical film are achieved by supplementing each other by dissolving different resins.

  Whether the acrylic resin (A) and the cellulose ester resin (B) are in a compatible state can be determined by, for example, the glass transition temperature Tg.

  For example, when the glass transition temperatures of the two resins are different, when the two resins are mixed, there are two or more glass transition temperatures of the mixture because there is a glass transition temperature of each resin. When they are compatible, the glass transition temperature specific to each resin disappears and becomes one glass transition temperature, which becomes the glass transition temperature of the compatible resin.

  In addition, the glass transition temperature here is the intermediate | middle calculated | required according to JISK7121 (1987), using the differential scanning calorimeter (DSC-7 type | mold by Perkin Elmer), measured with the temperature increase rate of 20 degree-C / min. The point glass transition temperature (Tmg).

  The acrylic resin (A) and the cellulose ester resin (B) are each preferably an amorphous resin, and either one may be a crystalline polymer or a partially crystalline polymer. In the present invention, the acrylic resin (A) and the cellulose ester resin (B) are preferably compatible with each other to become an amorphous resin.

  The weight average molecular weight (Mw) of the acrylic resin (A) and the weight average molecular weight (Mw) of the cellulose ester resin (B) and the degree of substitution in the polarizer protective film of the present invention are soluble in the solvents of both resins. It is obtained by measuring each after fractionation using the difference. When fractionating the resin, it is possible to extract and separate the soluble resin by adding a compatible resin in a solvent that is soluble only in either one. At this time, heating operation or reflux is performed. May be. A combination of these solvents may be combined in two or more steps to separate the resin. The dissolved resin and the resin remaining as an insoluble matter are filtered off, and the solution containing the extract can be separated by an operation of evaporating the solvent and drying. These fractionated resins can be identified by general structural analysis of polymers. When the polarizer protective film of the present invention contains a resin other than the acrylic resin (A) or the cellulose ester resin (B), it can be separated by the same method.

  If the weight average molecular weights (Mw) of the compatible resins are different, the high molecular weight substances are eluted earlier by gel permeation chromatography (GPC), and the lower molecular weight substances are eluted after a longer time. Therefore, it can be easily fractionated and the molecular weight can be measured.

  In addition, the molecular weight of the compatible resin is measured by GPC, and at the same time, the resin solution eluted every time is separated, the solvent is distilled off, and the dried resin is different by quantitatively analyzing the structure. By detecting the resin composition for each molecular weight fraction, it is possible to identify each compatible resin. By measuring the molecular weight distribution of each of the resins separated in advance based on the difference in solubility in a solvent by GPC, it is possible to detect each of the compatible resins.

  In the present invention, “containing acrylic resin (A) and cellulose ester resin (B) in a compatible state” means mixing each resin (polymer), resulting in a compatible state. This means that a state in which a precursor of acrylic resin such as monomer, dimer or oligomer is mixed with cellulose ester resin (B) and then polymerized by polymerization is not included. .

  For example, the process of obtaining a mixed resin by mixing a precursor of an acrylic resin such as a monomer, dimer, or oligomer with the cellulose ester resin (B) and then polymerizing it involves a complicated polymerization reaction. The resin is difficult to control the reaction, and it is difficult to adjust the molecular weight. In addition, when a resin is synthesized by such a method, graft polymerization, cross-linking reaction or cyclization reaction often occurs. In many cases, the resin is soluble in a solvent or cannot be melted by heating. Since it is difficult to elute the resin and measure the weight average molecular weight (Mw), it is difficult to control the physical properties and it cannot be used as a resin for stably producing an optical film.

  Unless the function as an optical film is impaired, the polarizer protective film of this invention may contain resin and additives other than an acrylic resin (A) and a cellulose-ester resin (B), and may be comprised.

  When the resin other than the acrylic resin (A) and the cellulose ester resin (B) is contained, even if the added resin is in a compatible state, it may be mixed without being dissolved.

  The total mass of the acrylic resin (A) and the cellulose ester resin (B) in the polarizer protective film of the present invention is preferably 55% by mass or more, more preferably 60% by mass or more of the polarizer protective film of the present invention. Especially preferably, it is 70 mass% or more.

  When using resins and additives other than the acrylic resin (A) and the cellulose ester resin (B), it is preferable to adjust the addition amount within a range that does not impair the function of the polarizer protective film of the present invention.

<Acrylic particles>
The polarizer protective film of the present invention preferably contains acrylic particles.

  The acrylic particle according to the present invention is an acrylic component present in a particle state (also referred to as an incompatible state) in an optical film containing the acrylic resin (A) and the cellulose ester resin (B) in a compatible state. To express.

  The acrylic particles may be obtained by, for example, collecting a predetermined amount of the produced optical film, dissolving it in a solvent, stirring, and sufficiently dissolving and dispersing the PTFE membrane filter having a pore diameter less than the average particle diameter of the acrylic particles. It is preferable that the weight of the insoluble matter filtered and collected is 90% by mass or more of the acrylic particles added to the optical film.

  The acrylic particles used in the present invention are not particularly limited, but are preferably acrylic particles having a layer structure of two or more layers, and particularly preferably the following multilayer structure acrylic granular composite.

  The multilayer structure acrylic granular composite is formed by laminating the innermost hard layer polymer, the cross-linked soft layer polymer exhibiting rubber elasticity, and the outermost hard layer polymer from the central portion toward the outer peripheral portion. This refers to a particulate acrylic polymer having a structure.

  That is, the multilayer structure acrylic granular composite is a multilayer structure acrylic granular composite comprising an innermost hard layer, a crosslinked soft layer, and an outermost hard layer from the central portion toward the outer peripheral portion. This three-layer core-shell multilayer acrylic granular composite is preferably used.

  Preferred embodiments of the multilayer structure acrylic granular composite used in the acrylic resin composition according to the present invention include the following. (A) Monomer comprising 80 to 98.9% by mass of methyl methacrylate, 1 to 20% by mass of alkyl acrylate having 1 to 8 carbon atoms of alkyl group, and 0.01 to 0.3% by mass of polyfunctional grafting agent An innermost hard layer polymer obtained by polymerizing a mixture of the body, (b) in the presence of the innermost hard layer polymer, an alkyl acrylate having an alkyl group of 4 to 8 carbon atoms of 75 to 98.5% by mass. A crosslinked soft layer polymer obtained by polymerizing a mixture of monomers comprising 0.01 to 5% by mass of a polyfunctional crosslinking agent and 0.5 to 5% by mass of a multifunctional grafting agent, (c) In the presence of a polymer composed of an inner hard layer and a crosslinked soft layer, a mixture of monomers consisting of 80 to 99% by weight of methyl methacrylate and 1 to 20% by weight of alkyl acrylate having 1 to 8 carbon atoms in the alkyl group. Outermost hard layer weight obtained by polymerizing And the obtained three-layer structure polymer is an innermost hard layer polymer (a) 5 to 40% by mass, a soft layer polymer (b) 30 to 60% by mass, and The outermost hard layer polymer (c) is composed of 20 to 50% by mass, has an insoluble part when fractionated with acetone, and an acrylic granular composite having a methyl ethyl ketone swelling degree of 1.5 to 4.0 at the insoluble part. .

  As disclosed in Japanese Patent Publication No. 60-17406 or Japanese Patent Publication No. 3-39095, not only the composition and particle size of each layer of the multilayer structure acrylic granular composite are defined, but also the multilayer structure acrylic granular composite. By setting the tensile modulus of the body and the degree of swelling of methyl ethyl ketone in the acetone-insoluble part within a specific range, it is possible to realize a further sufficient balance between impact resistance and stress whitening resistance.

  Here, the innermost hard layer polymer (a) constituting the multi-layer structure acrylic granular composite is 80 to 98.9% by mass of methyl methacrylate and 1 to 20% of alkyl acrylate having 1 to 8 carbon atoms in the alkyl group. % And a mixture of monomers consisting of 0.01 to 0.3% by mass of a polyfunctional grafting agent is preferred.

  Here, examples of the alkyl acrylate having 1 to 8 carbon atoms in the alkyl group include methyl acrylate, ethyl acrylate, n-propyl acrylate, n-butyl acrylate, s-butyl acrylate, 2-ethylhexyl acrylate, and the like. And n-butyl acrylate are preferably used.

  The ratio of the alkyl acrylate unit in the innermost hard layer polymer (a) is preferably 1 to 20% by mass.

  Examples of the polyfunctional grafting agent include polyfunctional monomers having different polymerizable functional groups, such as allyl esters of acrylic acid, methacrylic acid, maleic acid, and fumaric acid, and allyl methacrylate is preferably used. . The polyfunctional grafting agent is used to chemically bond the innermost hard layer polymer and the soft layer polymer, and the ratio used during the innermost hard layer polymerization is 0.01 to 0.3% by mass. .

  The crosslinked soft layer polymer (b) constituting the acrylic granular composite is an alkyl acrylate 75-98.5 having 1 to 8 carbon atoms in the presence of the innermost hard layer polymer (a). What is obtained by polymerizing a monomer mixture consisting of mass%, polyfunctional crosslinking agent 0.01 to 5 mass% and polyfunctional grafting agent 0.5 to 5 mass% is preferred.

  Here, as the alkyl acrylate having 4 to 8 carbon atoms in the alkyl group, n-butyl acrylate or 2-ethylhexyl acrylate is preferably used.

  In addition to these polymerizable monomers, it is possible to copolymerize 25% by mass or less of other monofunctional monomers capable of copolymerization.

  Examples of other monofunctional monomers that can be copolymerized include styrene and substituted styrene derivatives. As for the ratio of the alkyl acrylate having 4 to 8 carbon atoms in the alkyl group and styrene, the glass transition temperature of the polymer (b) decreases as the former increases, that is, the ratio can be softened.

  On the other hand, from the viewpoint of the transparency of the resin assembly, the refractive index of the soft layer polymer (b) at room temperature is set to the innermost hard layer polymer (a), the outermost hard layer polymer (c), and the hard heat. It is more advantageous to make it closer to the plastic acrylic resin, and the ratio between them is selected in consideration of these.

  As the polyfunctional grafting agent, those mentioned in the item of the innermost layer hard polymer (a) can be used. The polyfunctional grafting agent used here is used to chemically bond the soft layer polymer (b) and the outermost hard layer polymer (c), and the proportion used during the innermost hard layer polymerization is impact resistance. 0.5-5 mass% is preferable from a viewpoint of the property provision effect.

  As the polyfunctional crosslinking agent, generally known crosslinking agents such as divinyl compounds, diallyl compounds, diacrylic compounds, and dimethacrylic compounds can be used, and polyethylene glycol diacrylate (molecular weight 200 to 600) is preferably used.

  The polyfunctional cross-linking agent used here is used to generate a cross-linked structure at the time of polymerization of the soft layer (b) and develop an effect of imparting impact resistance. However, if the above-mentioned polyfunctional grafting agent is used during the polymerization of the soft layer, the polyfunctional crosslinking agent is not an essential component because the crosslinked structure of the soft layer (b) is generated to some extent. Is preferably 0.01 to 5% by mass from the viewpoint of imparting impact resistance.

  In the presence of the innermost hard layer polymer (a) and the soft layer polymer (b), the outermost hard layer polymer (c) constituting the multilayer structure acrylic granular composite is 80 to 99 mass% of methyl methacrylate. % And a mixture of monomers composed of 1 to 20% by mass of an alkyl acrylate having 1 to 8 carbon atoms in the alkyl group is preferable.

  Here, as the acrylic alkylate, those described above are used, and methyl acrylate and ethyl acrylate are preferably used. The ratio of the alkyl acrylate unit in the outermost hard layer (c) is preferably 1 to 20% by mass.

  Further, for the purpose of improving the compatibility with the acrylic resin (A) during the polymerization of the outermost hard layer (c), it is also possible to use an alkyl mercaptan or the like as a chain transfer agent in order to adjust the molecular weight.

  In particular, it is preferable to provide the outermost hard layer with a gradient such that the molecular weight gradually decreases from the inside toward the outside in order to improve the balance between elongation and impact resistance. As a specific method, the outermost hard layer is divided into two or more monomers to form the outermost hard layer, and the amount of chain transfer agent to be added each time is increased sequentially. It is possible to decrease the molecular weight of the polymer forming the layer from the inside to the outside of the multilayer structure acrylic granular composite.

  The molecular weight formed at this time can also be examined by polymerizing a mixture of monomers used each time under the same conditions and measuring the molecular weight of the resulting polymer.

  The particle diameter of the acrylic particles preferably used in the present invention is not particularly limited, but is preferably 10 to 1000 nm, more preferably 20 to 500 nm, and particularly 50 to 400 nm. Most preferred.

  In the acrylic granular composite that is a multilayer structure polymer preferably used in the present invention, the mass ratio of the core and the shell is not particularly limited, but when the entire multilayer structure polymer is 100 parts by mass, The core layer is preferably 50 to 90 parts by mass, and more preferably 60 to 80 parts by mass. In addition, the core layer here is an innermost hard layer.

  Examples of such commercially available multilayered acrylic granular composites include, for example, “Metablene” manufactured by Mitsubishi Rayon Co., “Kane Ace” manufactured by Kaneka Chemical Co., Ltd., “Paralloid” manufactured by Kureha Chemical Co., Ltd., Rohm and Haas "Acryloid" manufactured by KK, "Staffyroid" manufactured by Gantz Kasei Kogyo Co., Ltd., "Parapet SA" manufactured by Kuraray Co., Ltd., and the like can be used.

  In addition, specific examples of the acrylic particles that are graft copolymers that are preferably used as the acrylic particles preferably used in the present invention include unsaturated carboxylic acid ester monomers, unsaturated monomers in the presence of a rubbery polymer. Graft copolymer obtained by copolymerizing a mixture of a monomer comprising a saturated carboxylic acid monomer, an aromatic vinyl monomer, and, if necessary, other vinyl monomers copolymerizable therewith Is mentioned.

  There is no particular limitation on the rubbery polymer used for the acrylic particles as the graft copolymer, but diene rubber, acrylic rubber, ethylene rubber, and the like can be used. Specific examples include polybutadiene, styrene-butadiene copolymer, block copolymer of styrene-butadiene, acrylonitrile-butadiene copolymer, butyl acrylate-butadiene copolymer, polyisoprene, butadiene-methyl methacrylate copolymer, Butyl acrylate-methyl methacrylate copolymer, butadiene-ethyl acrylate copolymer, ethylene-propylene copolymer, ethylene-propylene-diene copolymer, ethylene-isoprene copolymer, and ethylene-methyl acrylate copolymer A polymer etc. are mentioned. These rubbery polymers can be used alone or in a mixture of two or more.

  In addition, when adding acrylic particles to the polarizer protective film of the present invention, the refractive index of the mixture of the acrylic resin (A) and the cellulose ester resin (B) is close to the refractive index of the acrylic particles. It is preferable in terms of obtaining a high film. Specifically, the refractive index difference between the acrylic particles and the acrylic resin (A) is preferably 0.05 or less, more preferably 0.02 or less, and particularly preferably 0.01 or less.

  In order to satisfy such a refractive index condition, a method of adjusting the monomer unit composition ratio of the acrylic resin (A) and / or the composition ratio of the rubbery polymer or monomer used in the acrylic particles The refractive index difference can be reduced by the method for preparing the optical film, and an optical film excellent in transparency can be obtained.

  The difference in refractive index referred to here means that the optical film according to the present invention is sufficiently dissolved in a solvent in which the acrylic resin (A) is soluble to obtain a cloudy solution, which is subjected to an operation such as centrifugation. The solvent was separated into a soluble part and an insoluble part, and the soluble part (acrylic resin (A)) and the insoluble part (acrylic particles) were purified, and then measured for the refractive index (23 ° C., measurement wavelength: 550 nm). Indicates the difference.

  There is no restriction | limiting in particular in the method of mix | blending an acrylic particle with an acrylic resin (A) in this invention, After blending an acrylic resin (A) and another arbitrary component previously, an acrylic particle is normally 200-350 degreeC. A method of uniformly kneading with a single or twin screw extruder while adding is preferably used.

  Further, a method in which a solution in which acrylic particles are dispersed in advance is added to and mixed with a solution (dope solution) in which acrylic resin (A) and cellulose ester resin (B) are dissolved, acrylic particles and other optional additives. A method such as in-line addition of a solution obtained by dissolving and mixing the above can be used.

  A commercially available thing can also be used as an acrylic particle concerning this invention. For example, Metabrene W-341 (manufactured by Mitsubishi Rayon Co., Ltd.), Chemisnow MR-2G, MS-300X (manufactured by Soken Chemical Co., Ltd.) and the like can be mentioned.

  In the polarizer protective film of the present invention, it is preferable to contain 0.5 to 30% by mass of acrylic particles with respect to the total mass of the resin constituting the film, and it is contained in the range of 1.0 to 15% by mass. More preferably.

<Other additives>
In the polarizer protective film of the present invention, a plasticizer can be used in combination in order to improve the fluidity and flexibility of the composition. Examples of the plasticizer include phthalate ester, fatty acid ester, trimellitic ester, phosphate ester, polyester, and epoxy.

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

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

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

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

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

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

  It is preferable to add 0.5-30 mass parts of plasticizers with respect to 100 mass parts of the polarizer protective film of the present invention. If the added amount of the plasticizer exceeds 30 parts by mass, the surface becomes sticky, which is not preferable for practical use.

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

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

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

  Furthermore, various antioxidants can also be added to the polarizer protective film of the present invention in order to improve the thermal decomposability and thermal colorability during molding. In addition, an antistatic agent can be added to impart antistatic performance to the polarizer protective film of the present invention.

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

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

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

  According to the polarizer protective film of the present invention, it is possible to simultaneously achieve improvements in low hygroscopicity, transparency, high heat resistance and brittleness that could not be achieved with conventional resin films.

  In the present invention, the brittleness index is determined based on the criterion of whether or not it is “an optical film in which ductile fracture does not occur”. By obtaining the polarizer protective film of the present invention, in which ductile fracture does not occur and brittleness is improved, when producing a polarizing plate for a large liquid crystal display device, no breakage or cracking occurs during production, It can be set as the optical film excellent in the handleability. Here, the ductile fracture is a fracture caused by applying a stress larger than the strength of a certain material, and is defined as a fracture accompanied by significant elongation or drawing of the material until the final fracture. The fracture surface is characterized by numerous indentations called dimples.

  In the present invention, whether or not it is “an optical film that does not cause ductile fracture” is evaluated based on the fact that no breakage or the like is observed even when a large stress is applied such that the film is folded in two. . Even if it is used as a polarizing plate protective film for a large-sized liquid crystal display device, if it is an optical film that does not cause ductile fracture even when such a large stress is applied, problems such as breakage during production Furthermore, even when the optical film is used after being peeled off after being pasted once, no breakage occurs and the optical film can be sufficiently reduced in thickness.

  In the present invention, the tension softening point is used as an index of heat resistance. In addition to the increasing size of liquid crystal display devices and the increasing brightness of backlight light sources, the use of digital signage and other outdoor applications demands higher brightness. However, if the tension softening point is 105 ° C. to 145 ° C., it can be determined that sufficient heat resistance is exhibited. In particular, it is more preferable to control at 110 to 130 ° C.

  As a specific measuring method of the temperature indicating the tension softening point of the optical film, for example, the optical film is cut out at 120 mm (length) × 10 mm (width) using a Tensilon tester (ORIENTEC, RTC-1225A). The temperature can be raised at a rate of 30 ° C./min while pulling with a tension of 10 N, and the temperature at the time when the pressure reaches 9 N is measured three times, and the average value can be obtained.

  From the viewpoint of heat resistance, the optical film preferably has a glass transition temperature (Tg) of 110 ° C. or higher. More preferably, it is 120 ° C. or higher. Especially preferably, it is 150 degreeC or more.

  In addition, the glass transition temperature here is the intermediate | middle calculated | required according to JISK7121 (1987), using the differential scanning calorimeter (DSC-7 type | mold by Perkin Elmer), measured with the temperature increase rate of 20 degree-C / min. Point glass transition temperature (Tmg).

  As an index for judging the transparency of the optical film in the present invention, haze value (turbidity) is used. In particular, liquid crystal display devices used outdoors are required to have sufficient brightness and high contrast even in a bright place. Therefore, the haze value is required to be 1.0% or less, and 0.5% or less. More preferably.

  According to the polarizer protective film of the present invention containing the acrylic resin (A) and the cellulose ester resin (B), high transparency can be obtained, but acrylic particles are used for the purpose of improving another physical property. In that case, an increase in haze value can be prevented by reducing the refractive index difference between the resin (acrylic resin (A) and cellulose ester resin (B)) and the acrylic particles.

  In addition, since the surface roughness also affects the haze value as the surface haze, it is also effective to suppress the particle size and addition amount of acrylic particles within the above ranges, and to reduce the surface roughness of the film contact portion during film formation. It is.

  In addition, the hygroscopicity of the optical film in the present invention is evaluated by dimensional change with respect to humidity change.

  The following method is used as an evaluation method of dimensional change with respect to humidity change.

  In the casting direction of the produced optical film, two marks (crosses) were attached and treated at 60 ° C. and 90% RH for 1000 hours, and the distance between the mark (cross) before and after treatment was measured with an optical microscope. Obtain the dimensional change rate (%). The dimensional change rate (%) is expressed by the following formula.

Dimensional change rate (%) = [(a1-a2) / a1] × 100
a1: Distance before heat treatment a2: Distance after heat treatment When an optical film is used as a protective film for a polarizing plate of a liquid crystal display device, unevenness or a change in retardation value occurs due to a dimensional change due to moisture absorption. This causes problems such as a decrease in contrast and uneven color. In particular, the above problem becomes significant when the polarizing plate protective film is used in a liquid crystal display device used outdoors. However, if the dimensional change rate (%) under the above conditions is less than 0.5%, it can be evaluated that the optical film exhibits sufficiently low hygroscopicity. Furthermore, it is preferable that it is less than 0.3%.

  In the polarizer protective film of the present invention, it is preferable that the defects in the film plane having a diameter of 5 μm or more are 1 piece / 10 cm square or less. More preferably, it is 0.5 piece / 10 cm square or less, more preferably 0.1 piece / 10 cm square or less.

  Here, the diameter of the defect indicates the diameter when the defect is circular, and when the defect is not circular, the range of the defect is determined by observing with a microscope by the following method, and the maximum diameter (diameter of circumscribed circle) is determined.

  The range of the defect is the size of the shadow when the defect is observed with the transmitted light of the differential interference microscope when the defect is a bubble or a foreign object. When the defect is a change in the surface shape, such as transfer of a roll flaw or an abrasion, the size is confirmed by observing the defect with the reflected light of a differential interference microscope.

  In addition, when observing with reflected light, if the size of the defect is unclear, aluminum or platinum is deposited on the surface for observation.

  In order to obtain a film having excellent quality expressed by such a defect frequency with high productivity, it is necessary to filter the polymer solution with high precision immediately before casting, to increase the cleanliness around the casting machine, It is effective to set drying conditions after rolling stepwise and to dry efficiently while suppressing foaming.

  When the number of defects is greater than 1/10 cm square, for example, when the film is tensioned during processing in a later process, the film may break with the defects as a starting point, and productivity may decrease. Moreover, when the diameter of a defect becomes 5 micrometers or more, it can confirm visually by polarizing plate observation etc., and when used as an optical member, a bright spot may arise.

  Moreover, even when it cannot visually confirm, when a hard-coat layer etc. are formed on the said film, a coating agent cannot be formed uniformly and may become a fault (coating omission). Here, the defect is a void in the film (foaming defect) generated due to the rapid evaporation of the solvent in the drying process of the solution casting, a foreign matter in the film forming stock solution, or a foreign matter mixed in the film forming. This refers to the foreign matter (foreign matter defect) in the film.

  Moreover, the polarizer protective film of the present invention preferably has a breaking elongation in at least one direction of 10% or more, more preferably 20% or more in the measurement based on JIS-K7127-1999.

  The upper limit of the elongation at break is not particularly limited, but is practically about 250%. In order to increase the elongation at break, it is effective to suppress defects in the film caused by foreign matter and foaming.

  The thickness of the polarizer protective film of the present invention is preferably 20 μm or more. More preferably, it is 30 μm or more.

  The upper limit of the thickness is not particularly limited, but in the case of forming a film by a solution casting method, the upper limit is about 250 μm from the viewpoint of applicability, foaming, solvent drying, and the like. In addition, the thickness of a film can be suitably selected according to a use.

  The polarizer protective film of the present invention preferably has a total light transmittance of 90% or more, more preferably 93% or more. Moreover, as a realistic upper limit, it is about 99%. In order to achieve excellent transparency expressed by such total light transmittance, it is necessary not to introduce additives and copolymerization components that absorb visible light, or to remove foreign substances in the polymer by high-precision filtration. It is effective to reduce the diffusion and absorption of light inside the film.

  Also, reduce the surface roughness of the film surface by reducing the surface roughness of the film contact part (cooling roll, calender roll, drum, belt, coating substrate in solution casting, transport roll, etc.) during film formation. It is also effective to reduce the diffusion and reflection of light on the film surface by reducing the refractive index of the acrylic resin.

  The polarizer protective film of the present invention can be particularly preferably used as a polarizing plate protective film for a large-sized liquid crystal display device or a liquid crystal display device for outdoor use as long as the physical properties as described above are satisfied.

  Such physical properties include the polarizer protective film of the present invention containing the acrylic resin (A) and the cellulose ester resin (B) in a mass ratio of 95: 5 to 30:70, and the weight of the acrylic resin (A). The average molecular weight Mw is 80000 or more, the substitution degree of the acyl group of the cellulose ester resin (B) is 2.00 to 3.00, and the substitution degree of the acyl group having 3 to 7 carbon atoms is 1.2 to 3. It can be obtained by making it an optical film characterized by having a weight average molecular weight (Mw) of 75000 or more.

<Formation of polarizer protective film>
Although the example of the film forming method of the polarizer protective film of this invention is demonstrated, this invention is not limited to this.

  As a method for forming the polarizer protective film of the present invention, production methods such as an inflation method, a T-die method, a calendar method, a cutting method, a casting method, an emulsion method, and a hot press method can be used. From the viewpoints of suppressing foreign matter defects and optical defects such as die lines, solution casting by casting is preferred.

(Organic solvent)
The organic solvent useful for forming the dope when the polarizer protective film of the present invention is produced by the solution casting method dissolves the acrylic resin (A), the cellulose ester resin (B), and other additives at the same time. Anything can be used without limitation.

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

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

  In particular, in a solvent containing methylene chloride and a linear or branched aliphatic alcohol having 1 to 4 carbon atoms, three types of acrylic resin (A), cellulose ester resin (B), and acrylic particles, A dope composition in which at least 15 to 45 mass% in total is dissolved is preferable.

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

  Hereinafter, the preferable film forming method of the polarizer protective film of the present invention will be described.

1) Dissolution step In an organic solution mainly composed of a good solvent for the acrylic resin (A) and the cellulose ester resin (B), the acrylic resin (A), the cellulose ester resin (B), and optionally acrylic particles, The step of dissolving other additives while stirring to form a dope, or the acrylic resin (A) or cellulose ester resin (B) solution, if necessary, may be mixed with an acrylic particle solution or other additive solution for main dissolution. This is a step of forming a dope that is a liquid.

  For dissolving the acrylic resin (A) and the cellulose ester resin (B), a method performed at normal pressure, a method performed below the boiling point of the main solvent, a method performed under pressure above the boiling point of the main solvent, JP-A-9-95544 Various melting methods such as a method of performing a cooling dissolution method as described in JP-A-9-95557 or JP-A-9-95538, a method of performing at a high pressure as described in JP-A-11-21379, and the like. Although it can be used, a method in which pressure is applied at a temperature equal to or higher than the boiling point of the main solvent is particularly preferable.

  The total amount of the acrylic resin (A) and the cellulose ester resin (B) in the dope is preferably in the range of 15 to 45% by mass. An additive is added to the dope during or after dissolution to dissolve and disperse, then filtered through a filter medium, defoamed, and sent to the next step with a liquid feed pump.

  It is preferable to use a filter medium having a collected particle diameter of 0.5 to 5 μm and a drainage time of 10 to 25 sec / 100 ml.

  In this method, the aggregate remaining at the time of particle dispersion and the aggregate generated when the main dope is added are aggregated by using a filter medium having a collected particle diameter of 0.5 to 5 μm and a drainage time of 10 to 25 sec / 100 ml. Can only be removed. In the main dope, the concentration of particles is sufficiently thinner than that of the additive solution, so that aggregates do not stick together at the time of filtration and the filtration pressure does not increase suddenly.

  FIG. 1 is a diagram schematically showing an example of a dope preparation step, a casting step, and a drying step of a solution casting film forming method preferable for the present invention.

  If necessary, large agglomerates are removed from the acrylic particle charging kettle 41 by the filter 44 and fed to the stock kettle 42. Thereafter, the acrylic particle additive solution is added from the stock kettle 42 to the main dope dissolving kettle 1.

  Thereafter, the main dope solution is filtered by the main filter 3, and an ultraviolet absorbent additive solution is added in-line from 16 to this.

  In many cases, the main dope may contain about 10 to 50% by mass of the recycled material. The return material may contain acrylic particles. In that case, it is preferable to control the addition amount of the acrylic particle addition liquid in accordance with the addition amount of the return material.

  The additive solution containing acrylic particles preferably contains 0.5 to 10% by mass of acrylic particles, more preferably 1 to 10% by mass, and 1 to 5% by mass. Most preferably.

  If it is in the said range, since an addition liquid is low-viscosity, it is easy to handle and it is easy to add to the main dope, it is preferable.

  The return material is a product obtained by finely pulverizing the optical film, which is generated when the optical film is formed, and is obtained by cutting off both sides of the film, or by using an optical film original that has been speculated out due to scratches, etc. .

  In addition, an acrylic resin, a cellulose ester resin, and, in some cases, acrylic particles kneaded into pellets can be preferably used.

2) Casting process An endless metal belt 31 such as a stainless steel belt or a rotating metal drum that feeds the dope to a pressure die 30 through a liquid feed pump (for example, a pressurized metering gear pump) and transfers it indefinitely. This is a step of casting a dope from a pressure die slit to a casting position on a metal support.

  A pressure die that can adjust the slit shape of the die base portion and can easily make the film thickness uniform is preferable. The pressure die includes 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 dope amount may be divided and stacked. Or it is also preferable to obtain the film of a laminated structure by the co-casting method which casts several dope simultaneously.

3) Solvent evaporation step In this step, the web (the dope is cast on the casting support and the formed dope film is called a web) is heated on the casting support to evaporate the solvent.

  To evaporate the solvent, there are a method of blowing air from the web side and / or a method of transferring heat from the back side of the support by a liquid, a method of transferring heat from the front and back by radiant heat, and the like. High efficiency and preferable. A method of combining them is also preferably used. The web on the support after casting is preferably dried on the support in an atmosphere of 40 to 100 ° C. In order to maintain the atmosphere at 40 to 100 ° C., it is preferable to apply hot air at this temperature to the upper surface of the web or to heat by means such as infrared rays.

  From the viewpoint of surface quality, moisture permeability, and peelability, it is preferable to peel the web from the support within 30 to 120 seconds.

4) Peeling process It is the process of peeling the web which the solvent evaporated on the metal support body in a peeling position. The peeled web is sent to the next process.

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

  In addition, it is preferable that the residual solvent amount at the time of peeling of the web on the metal support at the time of peeling is peeled in the range of 50 to 120% by mass depending on the strength of drying conditions, the length of the metal support, and the like. If the web is peeled off at a time when the amount of residual solvent is larger, if the web is too soft, the flatness at the time of peeling will be lost, and slippage and vertical stripes are likely to occur due to the peeling tension. The amount of solvent is determined.

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

Residual solvent amount (%) = (mass before web heat treatment−mass after web heat treatment) / (mass after web heat treatment) × 100
Note that the heat treatment for measuring the residual solvent amount represents performing heat treatment at 140 ° C. for 2 hours.

  The peeling tension at the time of peeling the metal support and the film is usually 196 to 245 N / m. However, when wrinkles easily occur at the time of peeling, it is preferable to peel with a tension of 190 N / m or less. It is preferable to peel at a minimum tension that can be peeled to 166.6 N / m, and then peel at a minimum tension to 137.2 N / m, and particularly preferably peel at a minimum tension to 100 N / m.

  In the present invention, the temperature at the peeling position on the metal support is preferably -50 to 40 ° C, more preferably 10 to 40 ° C, and most preferably 15 to 30 ° C.

5) Drying and stretching step After peeling, a drying device 35 that transports the web alternately through rolls arranged in the drying device and / or a tenter stretching device 34 that clips and transports both ends of the web with clips. And dry the web.

  Generally, the drying means blows hot air on both sides of the web, but there is also a means for heating by applying microwaves instead of the wind. Too rapid drying tends to impair the flatness of the finished film. Drying at a high temperature is preferably performed from about 8% by mass or less of the residual solvent. Throughout the drying is generally carried out at 40-250 ° C. It is particularly preferable to dry at 40 to 160 ° C.

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

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

  The stretching operation may be performed in multiple stages. For example, stretching may be performed mainly in the first half of the tenter process and the width may be maintained to relieve the stress of the film in the second half, or after sufficient preheating in the first half of the tenter process, the stretching operation may be performed in the second half. Also good. It is also preferable to perform biaxial stretching in the casting direction and the width direction. When biaxial stretching is performed, simultaneous biaxial stretching may be performed or may be performed stepwise.

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

-Stretch in the casting direction-Stretch in the width direction-Stretch in the casting direction-Stretch in the casting direction-Stretch in the width direction-Stretch in the width direction-Stretch in the casting direction-Stretch in the casting direction Simultaneous biaxial stretching includes stretching in one direction and contracting the other while relaxing the tension. The preferable draw ratio of simultaneous biaxial stretching can be taken in the range of x1.01 to x1.5 times in both the width direction and the longitudinal direction.

  When the tenter is used, the residual solvent amount of the web is preferably 20 to 100% by mass at the start of the tenter, and it is preferable to perform drying while applying the tenter until the residual solvent amount of the web becomes 10% by mass or less. More preferably, it is 5% by mass or less.

  The drying temperature when performing the tenter is preferably 30 to 160 ° C, more preferably 50 to 150 ° C, and most preferably 70 to 140 ° C.

  In the tenter process, it is preferable that the temperature distribution in the width direction of the atmosphere is small from the viewpoint of improving the uniformity of the film. The temperature distribution in the width direction in the tenter process is preferably within ± 5 ° C, and within ± 2 ° C Is more preferable, and within ± 1 ° C. is most preferable.

  It is preferable to further reduce the amount of residual solvent in the drying step after the tenter. The amount of residual solvent is preferably 5% or less, and more preferably 2% or less.

  80 to 160 degreeC is preferable and the drying temperature of the drying process after a tenter process has more preferable 90 to 140 degreeC. The drying temperature is preferably set lower in the first half of the drying step and higher in the second half.

  This drying temperature can be adjusted by the residual solvent and conveyance tension of the web. That is, when the residual solvent is large, the apparent Tg of the web is lowered. Therefore, it is preferable to suppress the elongation of the web by lowering the drying temperature.

  Alternatively, the residual solvent can be further reduced while the elongation of the web is suppressed by lowering the conveying tension using a tension cut roll and setting the drying temperature higher.

  When the web stretches greatly, a phase difference other than the design value developed in the tenter process appears on the finished optical film, which is not preferable.

  The methyl methacrylate monomer can be efficiently removed by the combination of the temperature, time, and draw ratio of the tenter process and the temperature and time of the drying process after the tenter process, and the film characteristics, particularly brittleness, can be improved.

  In the drying process after the tenter process, it is preferable to raise the temperature to some extent, but there are cases where the temperature cannot be increased because of the conveyance tension. In this case, since the film is conveyed while being gripped, the effect of removing the methyl methacrylate monomer and improving the brittleness can be obtained by setting the tenter process, which hardly takes tension in the conveying direction, to a high temperature.

  In the tenter process, if the film is stretched in the first half, the thickness of the web becomes thin at an early stage, so that the effects of removing methyl methacrylate monomer and improving brittleness may be easily obtained. However, since there is an influence of the residence time in the tenter process, it is necessary to appropriately select a combination of the temperature and the draw ratio.

  Moreover, it is preferable to perform a drying process at a temperature 20 degreeC or more higher than Tg of a web in either the tenter process and the drying process after a tenter process. By performing this processing step, brittleness can be greatly improved. Even if the methyl methacrylate monomer is removed by extending the time at a temperature lower than Tg + 20 ° C. of the web, the effect of improving brittleness is small.

  On the other hand, if the temperature is too high in the tenter process and the drying process after the tenter process, methyl methacrylate monomer is generated due to decomposition of the resin, which is not preferable.

6) Winding step This is a step of winding the optical film by the winder 37 after the residual solvent amount in the web is 2% by mass or less, and the dimensional stability is achieved by setting the residual solvent amount to 0.4% by mass or less. A film having good properties can be obtained. It is particularly preferable to wind up at 0.00 to 0.10% by mass.

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

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

  Although there is no restriction | limiting in particular in the film thickness of the polarizer protective film of this invention, When using for the polarizing plate protective film mentioned later, it is preferable that it is 20-200 micrometers, it is more preferable that it is 25-100 micrometers, and 30-80 micrometers. It is particularly preferred that

〔Polarizer〕
The polarizing plate of the present invention is a polarizing plate having at least a polyester film, a polarizer, and the polarizer protective film of the present invention as constituent elements.

  When using the polarizer protective film of this invention as a protective film for polarizing plates, a polarizing plate can be produced by a general method. It is preferable that an adhesive layer is provided on the back side of the optical film according to the present invention, and is bonded to at least one surface of a polarizer produced by immersing and stretching in an iodine solution.

  A polarizer, which is a main component of a polarizing plate, is an element that transmits only light having a plane of polarization in a certain direction. A typical polarizing film known at present is a polyvinyl alcohol polarizing film, which is a polyvinyl alcohol. There are one in which iodine is dyed on a system film and one in which dichroic dye is dyed.

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

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

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

  The pressure-sensitive adhesive may be a one-component type or a type in which two or more components are mixed before use.

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

[Liquid Crystal Display]
By incorporating the polarizing plate of the present invention into a liquid crystal display device, it is possible to produce various liquid crystal display devices with excellent visibility, and particularly for liquid crystal display devices for outdoor use such as large liquid crystal display devices and digital signage. Preferably used. The polarizing plate according to the present invention is bonded to a liquid crystal cell via the adhesive layer or the like.

  The polarizing plate according to the present invention is a reflective type, transmissive type, transflective LCD or TN type, STN type, OCB type, HAN type, VA type (PVA type, MVA type), IPS type (including FFS type), etc. It is preferably used in LCDs of various driving methods. In particular, in a large-screen display device having a screen size of 30 or more, especially 30 to 54, there is no white spot at the periphery of the screen, and the effect is maintained for a long time.

  In addition, there was little color unevenness, glare and wavy unevenness, and the eyes were not tired even during long-time viewing.

  EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

<Carboxylic acid sugar ester compound having a carboxyl group and a long-chain alkyl group>
Table 5 details the carboxylic acid sugar ester compounds having a carboxyl group and a long-chain alkyl group used in the examples.

[Synthesis of C-1 to C-7]
Glucose 0.2 mM and dodecanedioic acid (both manufactured by Wako Pure Chemical Co., Ltd.) 0.2 mM were dispersed in 150 ml of dehydrated acetone, and 6 g of lipase (Novozyme SP435) and 30 g of molecular sieve 3A were sequentially added to the mixture. The mixture was stirred for 48 hours to obtain a reaction product (monoester selectivity was 95%, glucose conversion was 70%).

  The obtained reaction product was dissolved in 2 L of dimethoxyethane, and a clear solution was obtained through a PTFE membrane filter (aperture 0.2 μm). This was concentrated under reduced pressure at 12 kPa (90 torr) to obtain a crude carboxylic acid sugar ester compound C-1. The crude carboxylic acid sugar ester compound C-1 was dissolved in n-propyl acetate at 120 ° C. and cooled and crystallized to obtain a carboxylic acid sugar ester compound C-1.

  In the synthesis of C-1, carboxylic acid sugar ester compounds C-2 to C-7 were obtained in the same manner except that the dibasic acids listed in Table 5 were used.

<Carboxylic acid sugar ester compound represented by Formula 1>
The carboxylic acid sugar ester compounds represented by the general formula 1 used in the examples are as shown in Tables 1 to 3.

<Acrylic resin (A)>
Table 6 describes acrylic resins A1 to A4 and BR85 used in the examples. The acrylic resins A1 to A4 were adjusted by a known method.
A1: Monomer mass ratio (MMA: MA = 98: 2), Mw 70000
A2: monomer mass ratio (MMA: MA = 97: 3), Mw 160000
A3: monomer mass ratio (MMA: MA = 97: 3), Mw550,000
A4: monomer mass ratio (MMA: MA = 97: 3), Mw 1100000
Dianar BR85 (Mitsubishi Rayon Co., Ltd., hereinafter referred to as BR85), Mw 280000
The ratio of the MMA unit in the molecule in the commercially available acrylic resin was 90% by mass or more and 99% by mass or less.

<Cellulose ester resin (B)>
In Table 7, it describes about the detail of cellulose-ester resin CE1-CE30 used for an Example.

  In the table, ac: acetyl group, pr: propionyl group, bt: butyryl group, pen: pentyl group, hep: heptyl group, bz: benzoyl group, oct: octyl group, ph: phenyl group.

<Production of polarizer protective film>
Each polarizer protective film was produced as follows.

<Preparation of acrylic fine particles (D1)>
A reactor with a reflux condenser with an internal volume of 60 liters was charged with 38.2 liters of ion-exchanged water and 111.6 g of sodium dioctylsulfosuccinate, and the temperature was raised to 75 ° C. under a nitrogen atmosphere while stirring at a rotational speed of 250 rpm. The effect of oxygen was virtually eliminated. Add 0.36 g of APS, and after stirring for 5 minutes, add a monomer mixture consisting of 1657 g of MMA, 21.6 g of BA, and 1.68 g of ALMA, and hold for another 20 minutes after detecting the exothermic peak. Polymerization of the innermost hard layer was completed.

  Next, 3.48 g of APS was added, and after stirring for 5 minutes, a monomer mixture consisting of 8105 g of BA, 31.9 g of PEGDA (200), and 264.0 g of ALMA was continuously added over 120 minutes. After completion of the addition, the mixture was further maintained for 120 minutes to complete the polymerization of the soft layer.

  Next, 1.32 g of APS was added, and after stirring for 5 minutes, a monomer mixture consisting of 2106 g of MMA and 201.6 g of BA was continuously added over 20 minutes, and held for another 20 minutes after the addition was completed. Polymerization of the outermost hard layer 1 was completed.

  Next, 1.32 g of APS was added, and after 5 minutes, a monomer mixture consisting of 3148 g of MMA, 201.6 g of BA, and 10.1 g of n-OM was continuously added over 20 minutes, and the addition was completed. Later held for another 20 minutes. Next, the temperature was raised to 95 ° C. and held for 60 minutes to complete the polymerization of the outermost hard layer 2.

  A small amount of the polymer latex thus obtained was collected, and the flat particle size was determined by the absorbance method, which was 0.10 μm. The remaining latex was put into a 3% by mass sodium sulfate warm aqueous solution, salted out and coagulated, and then dried after repeated dehydration and washing to obtain acrylic fine particles (D1) having a three-layer structure.

  The above abbreviations are the following materials.

MMA; methyl methacrylate MA; methyl acrylate BA; n-butyl acrylate ALMA; allyl methacrylate PEGDA; polyethylene glycol diacrylate (molecular weight 200)
n-OM; n-octyl mercaptan APS; ammonium persulfate (dope solution 1 composition)
Dianal BR85 (manufactured by Mitsubishi Rayon Co., Ltd.) 65 parts by mass Cellulose ester resin (acyl group substitution degree 2.75, acetyl group substitution degree 0.19,
Propionyl group substitution degree 2.56, Mw = 200000) 35 parts by mass Carboxylic acid sugar ester compound C-1 0.5 part by mass Compound of general formula (1) 1-1 5 parts by mass Acrylic particles (D1) 5 parts by mass Inorganic Fine particles (Aerosil R972V) 0.27 parts by mass Methylene chloride 256 parts by mass Ethanol 48 parts by mass The above composition was sufficiently dissolved while heating to prepare a dope solution 1.

  The produced dope solution was uniformly cast on a stainless steel band support at a temperature of 22 ° C. and a width of 2 m using a belt casting apparatus. With the stainless steel band support, the solvent was evaporated until the amount of residual solvent reached 100%, and peeling was performed from the stainless steel band support with a peeling tension of 162 N / m.

  The web of the peeled resin composition was evaporated at 35 ° C., slit to 1.5 m width, and then stretched by 1.30 times (30%) in the width direction with a tenter at a drying temperature of 140 ° C. Dried. At this time, the residual solvent amount when starting stretching with a tenter was 10%.

  After stretching with a tenter, relaxation was performed at 130 ° C. for 5 minutes, and then drying was completed while transporting a 120 ° C. drying zone with a number of rolls, slitting to a width of 1.5 m, and a width of 10 mm and a height of 5 μm at both ends of the film. A roll sample 101 of the polarizing plate protective film 101 having a thickness of 40 μm and a length of 5200 m was obtained by winding it around a core of 15.24 cm in inner diameter with an initial tension of 220 N / m and a final tension of 110 N / m.

  Thereafter, the materials were changed as shown in Tables 8 and 9, and polarizing plate protective films 102 to 152 were produced in the same manner as the polarizer protective film 101.

<Evaluation>
《Internal haze》
The prepared polarizer protective film was conditioned for 5 hours or more in an environment of 23 ° C. and 55% RH, and then the internal haze value was evaluated by the following method.

<Internal haze measuring device>
Haze meter (turbidity meter) (model: NDH 2000, manufactured by Nippon Denshoku Co., Ltd.)
A 5V9W halogen bulb was used as the light source, and a silicon photocell (with a relative visibility filter) was used as the light receiving unit.

  The polarizer protective film of the present invention has a value of 0.05 or less in the haze measurement of the film when a solvent having a refractive index of ± 0.05 is dropped on the film with this apparatus. preferable. The measurement was performed according to JIS K-7136.

  The internal haze measurement is performed as follows. This will be described with reference to FIGS.

First, the blank haze 1 of a measuring instrument other than a film is measured.
1. Drip a drop (0.05 ml) of glycerin on a cleaned glass slide. At this time, care is taken so that bubbles do not enter the droplet. Be sure to use glass that has been cleaned with a detergent because it may look dirty even if it looks clean. (See Figure 2)
2. Place the cover glass on top of it. Glycerin spreads without pressing the cover glass.
3. Set on a haze meter and measure blank haze 1.

Next, the haze 2 including the sample is measured by the following procedure.
4). Glycerin (0.05 ml) is dropped on a slide glass (see FIG. 2).
5. A sample film to be measured is placed thereon so that air bubbles do not enter (see FIG. 3).
6). Glycerin (0.05 ml) is dropped on the sample film (see FIG. 4).
7). A cover glass is placed thereon (see FIG. 5).
8). The laminate prepared as described above (from above, cover glass / glycerin / sample film / glycerin / slide glass) is set on a haze meter and haze 2 is measured.
9. (Haze 2) − (Haze 1) = (Internal haze of the polarizer protective film of the present invention) is calculated.

  All the above haze measurements were performed at 23 ° C. and 55% RH.

  Moreover, the glass and glycerin used by the said measurement are as follows.

Glass: MICRO SLIDE GLASS S9213 MATUNAMI
Glycerin: Kanto Kagaku Deer Special Grade (Purity> 99.0%) Refractive index 1.47
(Ductile fracture: brittleness evaluation)
The polarizer protective film is cut out at 100 mm (vertical) × 10 mm (width), folded in the center in the vertical direction once in a mountain fold, and in a valley fold, and this evaluation is measured three times. It was evaluated with. In addition, breaking of evaluation here represents having broken into two or more pieces.
○: Cannot be folded three times ×: Can be folded at least once out of three times (polarizer adhesion)
The produced polarizing plate is cut into a square of 5 cm × 5 cm, left in an atmosphere of 23 ° C. and 55% RH for 24 hours, and then peeled off from the corner at the interface between the polarizer and the polarizer protective film. This operation is performed with 100 polarizing plates for one type of sample, and the number of polarizing plates in which peeling is observed between the polarizer and the polarizer protective film is counted.
A: 0 to 2 sheets ○: 3 to 5 sheets Δ: 6 to 20 sheets ×: 21 sheets or more The polarizer adhesion is preferably at least the ○ level.

  The contents and evaluation results of the above polarizer protective films 101 to 152 are shown in Tables 8 and 9.

  As is apparent from the results shown in Tables 8 and 9, it can be seen that the polarizer protective film of the present invention is excellent in evaluation of internal haze, brittleness, and polarizer adhesion.

<Preparation of polarizing plates 201-253>
Each polarizing plate was produced as follows.

  A 120 μm-thick long roll polyvinyl alcohol film was immersed in 100 parts by mass of an aqueous solution containing 1 part by mass of iodine and 4 parts by mass of boric acid, and stretched 5 times in the transport direction at 50 ° C. to prepare a polarizer.

  Next, a polyvinyl alcohol-based adhesive was applied to both sides of the polarizer, and alkali saponification treatment was performed on one side of the polarizer with a 1.5N KOH solution under saponification conditions of 40 ° C. for 60 seconds. The obtained polarizer protective film 1 was laminated with KC6UY (Konica Minolta Opto Co., Ltd.) that had been subjected to the same saponification treatment on the other surface, and bonded together with a roll machine, and then dried at a drying process of 60 ° C. for 120 seconds. The polarizing plate 201 was produced.

  Hereinafter, the materials were changed as shown in Tables 10 and 11, and polarizing plates 202 to 253 were produced in the same manner as the polarizing plate 201.

<Production of liquid crystal display device>
Each of the produced polarizing plates was used to evaluate the display characteristics of the film according to the present invention. Using a Hitachi liquid crystal television Wooo W32-L7000, which is a horizontal electrolysis mode type liquid crystal display device, the polarizing plates on both sides that have been bonded in advance are peeled off, and the prepared polarizing plates are bonded to the glass surfaces of the liquid crystal cells, respectively. did.

  The prepared polarizing plates were bonded so that the absorption axis was oriented in the same direction as the polarizing plate that had been bonded in advance, thereby preparing each liquid crystal display device.

<Evaluation>
(Contrast unevenness)
The liquid crystal display device was stored at 23 ° C. and 95% RH for 48 hours. The stored liquid crystal display device was continuously lit for 1 hour in an environment of 23 ° C. and 55% RH, and then the front contrast was measured.

  The front contrast was measured by the following procedure.

  i) The front luminance (luminance measured from the normal direction of the display screen) when the liquid crystal display device displayed white was measured by EZ-Contrast 160D manufactured by ELDIM. Similarly, the front luminance of the display screen when the liquid crystal display device displayed black was measured.

  ii) The ratio of the front luminance of the display screen when white is displayed to the front luminance of the display screen when black is displayed is defined as the front contrast.

Front contrast = (Front brightness when displaying white) / (Front brightness when displaying black)
As described above, the front contrast at any 10 points on the display screen of the liquid crystal display device was measured. And the average value of the 10 front contrasts obtained was calculated | required. Furthermore, the maximum value of the front contrast that maximizes the difference from the average value was obtained from the 10 front contrasts obtained. Then, variation (%) in front contrast was obtained from the following equation.

Variation in front contrast (%) = {(maximum value of front contrast) − (average value of front contrast)} / (average value of front contrast) × 100
The evaluation of the front contrast variation was performed according to the following criteria.
◎: Front contrast variation is less than 1%, no unevenness ○: Front contrast variation is 1% or more and less than 5%, and variation is small Δ: Front contrast variation is 5% or more and less than 10% , Slightly uneven ×: Front contrast variation is 10% or more and unevenness is large (viewing angle fluctuation)
The following evaluation was performed using the liquid crystal display devices 301 to 353 produced as described above.

The viewing angle of the liquid crystal display device was measured using EZ-Contrast 160D manufactured by ELDIM in an environment of 23 ° C. and 55% RH. Subsequently, the polarizing plate treated at 60 ° C. and 90% RH for 1000 hours was measured in the same manner, and the viewing angle fluctuation was evaluated in four stages according to the following criteria.
◎: No viewing angle variation ○: Slight viewing angle variation is observed Δ: Viewing angle variation is observed ×: Viewing angle variation is large (color change: color shift)
Regarding the manufactured liquid crystal display devices 301 to 353, the display was displayed in black in an environment of 23 ° C. and 55% RH and observed from an oblique angle of 45 °. Subsequently, the polarizing plate treated at 60 ° C. and 90% RH for 1000 hours was observed in the same manner, and the color change was evaluated in four stages according to the following criteria.
：: No color change ○: Color change is slightly recognized Δ: Color change is recognized ×: Color change is large Tables 10 and 11 show the results of the above evaluation.

  As can be seen from the results shown in Tables 10 and 11, it can be seen that the liquid crystal display according to the polarizer film of the present invention is excellent in evaluation of contrast unevenness, viewing angle variation, and color change (color shift).

Example 2
<Evaluation>
Retardation values Ro and Rt of the prepared polarizer protective films 101 to 102 and 106 and KC4UA manufactured by Konica Minolta Opto Co., Ltd. were measured by the following methods.

<Measurement of retardation values Ro and Rt>
The average refractive index of the film sample was measured using an Abbe refractometer and a spectral light source. The thickness of the film was measured using a commercially available micrometer.

  Using an automatic birefringence meter KOBRA-21ADH (manufactured by Oji Scientific Instruments Co., Ltd.), the retardation of the film was measured at a wavelength of 590 nm in the same environment for 24 hours in an environment of 23 ° C. and 55% RH. . The above-mentioned average refractive index and film thickness were input into the following formula, and the in-plane retardation Ro and the thickness direction retardation Rt were determined.

Formula _{(I): Ro = (n} x -n y) × d
Formula (II): Rt = {(n _x + n _y ) / 2−n _z } × d
_{(Wherein, n x, n y, n} z is, 23 ℃ · 55% RH, the maximum in-plane refractive index of the refractive index _{n x} (film in 590 nm, also referred to as a slow axis direction of the refractive index.), n _y (refractive index in the direction perpendicular to the slow axis in the film plane), n _z (refractive index of the film in the thickness direction), and d is the film thickness (nm).
The above evaluation results were compared for the liquid crystal display devices 301 to 302, 306, and 353.

  The evaluation results are shown in Table 12.

  As can be seen from the results shown in Table 12, it can be seen that the liquid crystal display according to the polarizer film of the present invention is excellent in evaluation of contrast unevenness, viewing angle fluctuation, and color change (color shift).

DESCRIPTION OF SYMBOLS 1 Melting pot 3, 6, 12, 15 Filter 4, 13 Stock tank 5, 14 Liquid feed pump 8, 16 Conduit 10 Ultraviolet absorber charging pot 20 Merge pipe 21 Mixer 30 Die 31 Metal support 32 Web 33 Peeling position 34 Tenter device 35 Roll dryer 41 Particle charging vessel 42 Stock tank 43 Pump 44 Filter

Claims (6)

A polarizer protective film containing an acrylic resin (A), a cellulose ester resin (B), and a carboxylic acid sugar ester compound (C), which satisfies the following requirements (1) to (4) A polarizer protective film.
(1) The acrylic resin (A) has a weight average molecular weight in the range of 80000 to 1000000.
(2) The cellulose ester resin (B) has an average acyl group substitution degree in the range of 2.0 to 3.0 and a weight average molecular weight in the range of 75,000 to 300,000.
(3) The mass ratio (A: B) of the acrylic resin (A) and the cellulose ester resin (B) is in the range of 95: 5 to 30:70.
(4) The carboxylic acid sugar ester compound (C) was formed by ester-linking a sugar hydroxyl group and a polybasic acid having 7 to 18 carbon atoms having two or more carboxyl groups in one molecule. It is a long-chain alkylcarboxylic acid sugar ester compound having one or more carboxyl groups in one molecule.   2. The polarizer protective film according to claim 1, wherein an average acetyl group substitution degree of the cellulose ester is in a range of 2.0 to 2.5. The polarizer protective film according to claim 1 or 2, wherein a carboxylic acid sugar ester compound represented by the following general formula (1) is contained.

[In General Formula (1), R _{1 to} R ₈ represent a hydrogen atom, a substituted or unsubstituted alkylcarbonyl group, or a substituted or unsubstituted arylcarbonyl group, and R _{1 to} R ₈ are the same. Or different. ] Under the measurement conditions of a temperature of 23 ° C., a relative humidity of 55% RH, and a measurement wavelength of 590 nm, the in-plane retardation value Ro defined by the following formula (I) is in the range of 0 to 10 nm, and the following formula (II) 4. The polarizer protective film according to claim 1, wherein a retardation value Rt in a thickness direction defined by is in a range of −15 to 15 nm. 5.
Formula _{(I): Ro = (n} x -n y) × d (nm)
Formula (II): Rt = {(n _x + n _y ) / 2−n _z } × d (nm)
[In the above formula, Ro represents an in-plane retardation value in the polarizer protective film, and Rt represents a thickness direction retardation in the film. Further, d represents the thickness of the retardation film, n _x represents a refractive index of the maximum (slow axis direction) in the plane of the polarizer protective film. n _y represents a refractive index in the direction perpendicular to the slow axis in the polarizer protective film plane (fast axis direction), n _z represents the refractive index of the polarizer protective film in the thickness direction. The measurement conditions are the same as above. ]   A polarizing plate comprising the polarizer protective film according to any one of claims 1 to 4.   A liquid crystal display device comprising the polarizer protective film according to any one of claims 1 to 4.

Images