JP2012047862A - Polarizer protective film, rolled polarizing plate, and liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polarizer protective film in which unevenness of a polarizer between a winding core and an outer winding layer of a rolled polarizer plate is suppressed, which is excellent in adhesion with the polarizer even when under a weak saponification condition, and excellent in rework processability of the polarizer plate, when manufacturing the rolled polarizer plate, and which has excellent display stability when used in a liquid crystal display device; and to provide the rolled polarizer plate and the liquid crystal display device.SOLUTION: The polarizer protective film contains an acrylic resin (A), and a cellulose ester resin (B), and satisfies all of specific requisites.

Description

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

  The demand for liquid crystal display devices is expanding in applications such as liquid crystal televisions and personal computer liquid crystal displays. Usually, a liquid crystal display device is composed of a liquid crystal cell in which a transparent electrode, a liquid crystal layer, a color filter, etc. are sandwiched between glass plates, and two polarizing plates provided on both sides thereof. In this configuration, a polarizer (also referred to as a polarizing film or a polarizing film) is sandwiched between two optical films (polarizer protective film). As the polarizer protective film, a cellulose ester film such as cellulose triacetate is usually used.

  One reason why cellulose ester films have been used as polarizer protective films has been that cellulose ester films are relatively excellent in optical isotropy. In addition, since cellulose ester films have moderate moisture permeability and hydrophilicity, water sizing is generally used for polyvinyl alcohol films that are generally used as polarizers when saponification treatment is performed with an alkaline solution. The reason is that they can be bonded together.

  When using a resin other than cellulose ester, in order to obtain sufficient adhesion to the polarizer, it is necessary to bond with a sticky adhesive, a factor that impairs physical stability and optical stability. Because it becomes. In particular, in recent years, it has been studied to provide a polarizer protective film with a function as a retardation film that also has an optical compensation function. In such a case, higher optical stability is required. .

  On the other hand, with the recent advancement of technology, the enlargement of the liquid crystal display device is accelerated, and the use of the liquid crystal display device is diversified. For example, it can be used as a large display installed on a street or in a store, or used as an advertising display in a public place using a display device called digital signage.

  In such an application, since it is assumed that it is used outdoors, fluctuation of the optical value due to moisture absorption of the polarizer protective film becomes a problem, and particularly when the polarizer protective film is used as a retardation film, it has a high optical value. Stability is required. However, it is difficult to obtain sufficient optical stability with a cellulose ester film such as a cellulose triacetate film that has been used conventionally. In order to impart moisture resistance, a large amount of hydrophobic plasticizer must be added. As a result, there were problems that the mechanical strength of the film was lowered and the adhesion to the polarizing plate was lowered.

  On the other hand, as a low hygroscopic optical film material, polymethyl methacrylate resin (hereinafter abbreviated as “PMMA”), which is a representative of acrylic resin, is excellent in optical stability and excellent in transparency and dimensional stability. Therefore, it was used suitably for an optical film.

  However, the acrylic resin film is fragile and brittle when compared with a cellulose ester film and the like, and is difficult to handle. In particular, it is difficult to stably produce an optical film for a large liquid crystal display device. It was. In addition, since the adhesiveness to the polarizer is lower than that of the cellulose ester film, a sticky adhesive is still necessary, which may impair the optical stability inherent in the acrylic resin. .

  In order to solve the above problems, an optical film has been proposed that blends a cellulose ester resin and an acrylic resin, has low hygroscopicity, excellent optical stability, and significantly improves brittleness without impairing transparency. (Patent Document 1).

  By the way, in recent years, as described in Patent Document 2, as a manufacturing method of an optical display device, a strip-shaped sheet-shaped polarizing plate product having a polarizer protective film is directly cut into a desired size by being wound, A method has been proposed in which the cut sheet-like product is bonded to an optical display device.

  Although the above-described method can improve the manufacturing yield of the optical display device, the following problems are newly revealed.

  The optical film proposed in Patent Document 1 is characterized by high moisture resistance but low moisture permeability compared to conventional cellulose ester films. For this reason, in the method of manufacturing an optical display device proposed in Patent Document 2, when a polarizing plate wound in a roll shape using the above film as a polarizer protective film is used in an optical display device, the roll polarizing plate is wound. There is a difference in the amount of moisture removed during the manufacture of the polarizing plate between the vicinity of the core and the outside of the winding (the side far from the winding core), and the polarizing plate near the core of the roll-shaped polarizing plate has a high water content. In an optical display device manufactured using a polarizing plate, the performance of the polarizer is deteriorated, and unevenness that appears whitish when the liquid crystal display device is viewed from the front and obliquely becomes a problem. In addition, the polarizing plate near the winding core has a polarizer and a polarizer when the separated film is peeled and removed immediately before the product cut into a predetermined size from the polarizing plate roll is bonded to a liquid crystal cell or other optical member. There was also a problem that the adhesiveness to the protective film was weak and the polarizer and the polarizer protective film were peeled off.

  In the conventional method of manufacturing an optical display device, a sheet-shaped product is manufactured once from a polarizing plate roll and transported to a panel processing manufacturer, and then bonded to the optical display device. Since the water was removed, the above problem did not occur.

  Furthermore, since the film proposed in Patent Document 1 blends an acrylic resin with a cellulose ester resin, the adhesion of the acrylic resin is not improved even when subjected to a saponification treatment. It was also revealed that under the saponification conditions, the adhesion to the polarizer was weak.

  For this reason, a polarizing plate roll using the above film as a polarizer protective film needs to be saponified under strong conditions. On the other hand, when saponified under strong conditions, the film brittleness deteriorates, and the polarizing plate roll From the above, it was found that the polarizing plate breaks when the polarizing plate is cut to a predetermined size for bonding to the optical display device or when the polarizing plate once bonded to the optical display device is reworked.

  In order to solve the above two problems, by increasing the ratio of the cellulose ester resin in the film proposed in Patent Document 1, the moisture permeability is improved, and the adhesion with the polarizer is improved even in normal saponification treatment. Although the improvement of the cellulose ester resin ratio was improved, the adhesion between the polarizer and the polarizer protective film was improved, but on the other hand, the fluctuation of the optical value due to moisture absorption became a problem, and it was used for liquid crystal display devices. The viewing angle changed and the color changed.

  For this reason, it has been very difficult to achieve both the optical stability of the film and the adhesion with the polarizer.

International Publication No. 2009/047924 Japanese Patent No. 4307510

  The present invention has been made in view of the above problems and situations, and the problem to be solved is that, when manufacturing a polarizing plate roll, the unevenness of the polarizer near the roll core and outside the roll is suppressed and weak. A polarizer protective film having excellent display stability even when used in a liquid crystal display device. Is to provide. Moreover, it is providing the roll-shaped polarizing plate and liquid crystal display device with which the said polarizer protective film was provided.

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

1. A polarizer protective film comprising an acrylic resin (A) and a cellulose ester resin (B), wherein the polarizer protective film satisfies all of the following requirements (1) to (4).
(1) When the masses of the acrylic resin (A) and the cellulose ester resin (B) are Am and Bm, respectively, the mass ratio (Am / Bm) is in the range of 50/50 to 95/5.
(2) The acrylic resin (A) has a weight average molecular weight (Mw) in the range of 5000 to 1000000.
(3) The acrylic resin (A) is represented by the following general formula (1).
Formula _{(1) :-( X) l -} (Y) m - (Z) n -
(However, X represents a copolymerizable monomer unit, Y represents a monomer unit copolymerizable with X, Z represents a monomer unit copolymerizable with either X or Z, and Y and Z are the respective units. (In the structure, it has a hydroxyl group, a carboxyl group, an amino group, or an amide group. L, m, and n are mass fractions, and l + m + n = 100.)
(4) When 23 ≦ {(m + n) / (l + m + n)} × 100 ≦ 60, the mass Am of the acrylic resin (A) satisfies the following relationship.

21 ≦ Am × {(m + n) / (l + m + n)} ≦ 60
2. The cellulose ester resin (B) has an acyl group average substitution degree in the range of 2.0 to 3.0, and a weight average molecular weight (Mw) in the range of 30,000 to 300,000. The polarizer protective film of item 1.

  3. Y and Z are monomers derived from 2-hydroxyethyl methacrylate, 2-hydroxyethyl acrylate, methacrylic acid, acrylic acid, N, N-dimethylacrylamide, N, N-dimethylmethacrylamide, or N-vinylpyrrolidone, respectively. 3. The polarizer protective film according to item 1 or 2, which is a unit.

  4). The polarizer protective film according to any one of Items 1 to 3 is provided on at least one surface of a polarizer obtained by staining a polyvinyl alcohol resin film with iodine or a dichroic dye. A roll-shaped polarizing plate, wherein the polarizing plate is wound in a roll shape in the longitudinal direction.

  5. A liquid crystal display device produced by bonding the roll-shaped polarizing plate of item 4 to a liquid crystal panel and cutting with a laser.

  In producing the polarizing plate roll by the above means of the present invention, the unevenness of the polarizer at the roll core and outside the roll is suppressed, and excellent adhesion to the polarizer even under weak saponification conditions, An object of the present invention is to provide a polarizer protective film having excellent reworkability of a polarizing plate and having excellent display stability even when used in a liquid crystal display device. Moreover, it is providing the roll-shaped polarizing plate and liquid crystal display device with which the said polarizer protective film was provided.

Cross-sectional schematic diagram showing an example of the layer structure of a roll-shaped polarizing plate or a sheet-shaped polarizing plate Cross-sectional schematic diagram showing a part of the rolled-up polarizing plate in an enlarged state

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 all of the following requirements (1) to (4): To do.
(1) When the masses of the acrylic resin (A) and the cellulose ester resin (B) are Am and Bm, respectively, the mass ratio (Am / Bm) is in the range of 50/50 to 95/5.
(2) The acrylic resin (A) has a weight average molecular weight (Mw) in the range of 5000 to 1000000.
(3) The acrylic resin (A) is represented by the following general formula (1).
Formula _{(1) :-( X) l -} (Y) m - (Z) n -
(However, X represents a copolymerizable monomer unit, Y represents a monomer unit copolymerizable with X, Z represents a monomer unit copolymerizable with either X or Z, and Y and Z are the respective units. (In the structure, it has a hydroxyl group, a carboxyl group, an amino group, or an amide group. L, m, and n are mass fractions, and l + m + n = 100.)
(4) When 23 ≦ {(m + n) / (l + m + n)} × 100 ≦ 60, the mass Am of the acrylic resin (A) satisfies the following relationship.

21 ≦ Am × {(m + n) / (l + m + n)} ≦ 60
The above features are technical features common to the inventions according to claims 1 to 5.

  As an embodiment of the present invention, the cellulose ester resin (B) has an acyl group average substitution degree in the range of 2.0 to 3.0 and a weight average molecular weight (Mw) from the viewpoint of manifesting the effects of the present invention. ) Is preferably in the range of 30,000 to 300,000. Furthermore, Y and Z are derived from 2-hydroxyethyl methacrylate, 2-hydroxyethyl acrylate, methacrylic acid, acrylic acid, N, N-dimethylacrylamide, N, N-dimethylmethacrylamide, or N-vinylpyrrolidone, respectively. It is preferable that the monomer unit.

  The polarizer protective film of the present invention is a roll-shaped polarizing plate in an embodiment in which the polarizer protective film is provided on at least one surface of a polarizer obtained by staining a polyvinyl alcohol resin film with iodine or a dichroic dye. Can be suitably used. Moreover, it can use suitably for the liquid crystal display device manufactured by bonding the said roll-shaped polarizing plate to a liquid crystal panel, and cut | disconnecting with a laser.

  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.

<Acrylic resin (A)>
The polarizer protective film of the present invention contains an acrylic resin (A) and a cellulose ester resin (B).

Moreover, all the following requirements (1) to (4) are satisfied.
(1) When the masses of the acrylic resin (A) and the cellulose ester resin (B) are Am and Bm, respectively, the mass ratio (Am / Bm) is in the range of 50/50 to 95/5.
(2) The acrylic resin (A) has a weight average molecular weight Mw in the range of 5,000 to 1,000,000.
(3) The acrylic resin (A) is represented by the following general formula (1).
Formula _{(1) :-( X) l -} (Y) m - (Z) n -
(However, X represents a copolymerizable monomer unit, Y represents a monomer unit copolymerizable with X, Z represents a monomer unit copolymerizable with either X or Z, and Y and Z are the respective units. (In the structure, it has a hydroxyl group, a carboxyl group, an amino group, or an amide group. L, m, and n represent mass fractions, and l + m + n = 100.)
(4) When 23 ≦ {(m + n) / (l + m + n)} × 100 ≦ 60, the mass Am of the acrylic resin (A) satisfies the following relationship.

21 ≦ Am × {(m + n) / (l + m + n)} ≦ 60
In the present invention, the effects of the above-described invention can be exhibited by selecting a monomer and adjusting the degree of polymerization, which will be described later, so as to satisfy all the above requirements (1) to (4).

  In the general formula (1), X represents a copolymerizable monomer unit, and examples of the monomer include an acrylic monomer, a methacrylic monomer, an olefin, acrylonitrile, styrene, vinyl acetate, and the like. International Publication No. 2009/047924 And monomers described in JP-A-2009-1744, JP-A-2009-179731, and the like.

  In the present invention, X is particularly preferably a methacrylic monomer such as methyl methacrylate.

  Y represents a monomer unit copolymerizable with X, Z represents a monomer unit copolymerizable with either X or Z, and Y and Z are a hydroxyl group, a carboxyl group, an amino group, Or it needs to have an amide group.

  As preferred monomers according to the monomer units represented by Y and Z, 2-hydroxyethyl methacrylate (2-HEMA), 2-hydroxyethyl acrylate (2-HEA), methacrylic acid (MA), acrylic acid (AA), N, N-dimethylacrylamide (DMAA), N, N-dimethylmethacrylamide (DMMA), N-vinylpyrrolidone (N-VP), and the like can be given.

  Also, acrylamide, N-methylacrylamide, N-butylacrylamide, N, N-diethylacrylamide, acryloylmorpholine, N-hydroxyethylacrylamide, acryloylpyrrolidine, acryloylpiperidine, methacrylamide, N-methylmethacrylamide, N-butylmethacrylamide N, N-diethylmethacrylamide, methacryloylmorpholine, N-hydroxyethylmethacrylamide, methacryloylpyrrolidine, methacryloylpiperidine, N-vinylformamide, N-vinylacetamide and the like.

  Commercially available monomers can be used as they are.

  In the general formula (1), l, m, and n represent mass fractions, and l + m + n = 100, and preferably 30 ≦ l ≦ 80 and 10 ≦ m ≦ 80. Further, m is appropriately selected depending on the properties of the monomer, but preferably 20 ≦ m ≦ 70.

  In the present invention, when 23 ≦ {(m + n) / (l + m + n)} × 100 ≦ 60, the mass Am of the acrylic resin (A) needs to be adjusted so as to satisfy the following relationship.

21 ≦ Am × {(m + n) / (l + m + n)} ≦ 60
When the above relationship is satisfied, the moisture permeability of the produced film and the adhesion between the polarizer and the polarizer protective film are greatly improved. When the polarizing plate roll is formed, the roll core and the unwinding polarizer Thus, a polarizing plate that is excellent in adhesion to a polarizer even under weak saponification conditions and that does not break during rework processing of the polarizing plate from a liquid crystal display device can be produced. Furthermore, it is possible to provide a polarizer protective film that improves moisture permeability but, on the other hand, has a small fluctuation of the retardation value with respect to the environmental humidity and, when used in a liquid crystal display device, has little fluctuation in viewing angle and change in color. Can do.

  On the other hand, when the above relationship is not satisfied, the moisture permeability of the manufactured film and the adhesion between the polarizer and the polarizer protective film are insufficient, and a product cut into a predetermined size from the polarizing plate roll is used as a liquid crystal cell or other optical In the method of manufacturing an optical display device by a method of directly bonding to a member, when the separate film is peeled and removed, a defect occurs in which the polarizer and the polarizer protective film are peeled off.

  In the acrylic resin according to the present invention, at least one of the monomer units X, Y, and Z needs to be an acrylic monomer or a methacrylic monomer.

  The acrylic resin (A) according to the present invention preferably has a weight average molecular weight (Mw) in the range of 5,000 to 1,000,000 from the viewpoint of compatibility with the cellulose ester resin (B) and improvement in brittleness.

  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.

  As the method for producing the acrylic resin (A) in the present invention, any known method such as suspension polymerization, emulsion polymerization, bulk polymerization, or solution polymerization may be used. 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.

<Cellulose ester resin (B)>
In the present invention, the average acyl group substitution degree of the cellulose ester resin (B) is in the range of 2.0 to 3.0, particularly from the viewpoint of transparency when improved in brittleness or compatible with the acrylic resin (A). The substitution degree of the acyl group having 3 to 7 carbon atoms 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. Is preferred.

  In the present application, the “acyl group average substitution degree” is the number of acylated hydroxyl groups (hydroxyl groups) among the three hydroxyl groups (hydroxyl groups) of anhydroglucose (per basic unit) constituting cellulose. It means an average value and indicates a value in the range of 0-3.

  Moreover, it is preferable that the weight average molecular weight (Mw) of cellulose-ester resin (B) exists in the range of 30000-300000.

  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, but a propionyl group is particularly preferably used. .

  As for the acyl substitution degree of the cellulose ester resin (B) according to the present invention, the total substitution degree (T) 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 it is 3.0, there is no problem, but 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 preferably 1.3 or less. .

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

  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 preferably in the range of 35,000 to 300,000 from the viewpoints of compatibility with the acrylic resin (A) and improvement in brittleness. In the present invention, two or more kinds of cellulose resins can be mixed and used.

  The weight average molecular weight of the cellulose ester resin according to the present invention can be measured by the GPC.

<Mixing of acrylic resin (A) and cellulose ester resin (B)>
In the present invention, when the masses of the acrylic resin (A) and the cellulose ester resin (B) are Am and Bm, respectively, the mass ratio (Am / Bm) is in the range of 50/50 to 95/5. Cost.

  That is, 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 at a mass ratio of 95: 5 to 50:50.

  When the acrylic resin (A) is more than 95: 5 in the mass ratio of the acrylic resin (A) and the cellulose ester resin (B), the moisture permeability by the cellulose ester resin (B) and the adhesion improving effect with the polarizer are improved. On the other hand, when the acrylic resin is less than 50:50, the optical stability when used in a liquid crystal display device is reduced, and the viewing angle varies and the color changes. .

  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 is 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 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.

<Other additive resins>
When the resin other than the acrylic resin (A) and the cellulose ester resin (B) is used for the polarizer protective film of the present invention, the addition amount is adjusted within a range not impairing the function of the polarizer protective film of the present invention. It is preferable.

  As a preferred resin, a low molecular acrylic resin obtained by polymerizing an ethylenically unsaturated monomer described in paragraphs (0072) to (0123) of JP 2010-32655 A (weight average molecular weight Mw of 500 or more and 30000 or less) Polymer).

  Most preferably, Mw is 2000-30000. If it is 1000 or less, a problem occurs in bleed-out, and if it exceeds 30000, the transparency deteriorates.

  Moreover, the vinyl polymer which has an amide bond of Nippon Shokubai Co., Ltd. can also be used. For example, polyvinylpyrrolidone K-30, K-85, and K-90 can also be used.

  The low molecular acrylic resin according to the present invention and the vinyl polymer having an amide bond are 0 to 15% by mass, preferably 0 to 10% by mass, based on the total mass of the polarizer protective film.

<Acrylic particles>
The polarizer protective film of the present invention may contain the acrylic particles described in Patent Document 1.

  As an example of a commercial item of such a multilayer structure acrylic granular composite, for example, “Metablene W-341” manufactured by Mitsubishi Rayon Co., “Kaneace” manufactured by Kaneka Chemical Co., Ltd., “Paralloid” manufactured by Kureha Chemical Co., Ltd., Examples include "Acryloid" manufactured by Rohm and Haas, "Staffroid" manufactured by Gantz Kasei Kogyo, Chemisnow MR-2G, MS-300X (manufactured by Soken Chemical Co., Ltd.), and "Parapet SA" manufactured by Kuraray. These can be used alone or in combination of two or more.

  In the polarizer protective film of the present invention, it is preferable to contain 0 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. Is more preferable.

<Other additives>
The polarizer protective film of the present invention is provided with a retardation control agent for controlling retardation, a plasticizer for imparting processability to the film, an antioxidant for preventing deterioration of the film, and an ultraviolet absorbing function. It is preferable to contain additives such as ultraviolet absorbers that perform and fine particles (matting agents) that impart slipperiness to the film.

<Polyester polyol of glycol and dibasic acid>
The polyester polyol that can be used in the present invention includes a dehydration condensation reaction between a glycol having an average carbon number of 2 to 3.5 and a dibasic acid having an average carbon number of 4 to 5.5, or the glycol. It is preferable to be produced by a conventional method by addition of a dibasic anhydride having an average carbon number of 4 to 5.5 and a dehydration condensation reaction.

<Polyester of aromatic dicarboxylic acid and alkylene glycol>
As the retardation control agent according to the present invention, an aromatic terminal polyester represented by the following general formula (I) can be used.

General formula (I) B- (GA) n-GB
(In the formula, B is a benzene monocarboxylic acid residue, G is an alkylene glycol residue having 2 to 12 carbon atoms, an aryl glycol residue having 6 to 12 carbon atoms, or an oxyalkylene glycol residue having 4 to 12 carbon atoms, A represents an alkylene dicarboxylic acid residue having 4 to 12 carbon atoms or an aryl dicarboxylic acid residue having 6 to 12 carbon atoms, and n represents an integer of 1 or more.)
In the general formula (I), a benzene monocarboxylic acid residue represented by B and an alkylene glycol residue, oxyalkylene glycol residue or aryl glycol residue represented by G, an alkylene dicarboxylic acid residue or aryl dicarboxylic group represented by A It is composed of an acid residue and can be obtained by a reaction similar to that of ordinary polyester.

  Specific examples of the aromatic terminal polyester according to the present invention include paragraphs (0183) to (0186) of JP-A 2010-32655.

  The content of the aromatic terminal polyester according to the present invention is preferably 0 to 20% by mass, and particularly preferably 1 to 11% by mass in the polarizer protective film.

<Polyhydric ester compound>
The polarizer protective film of the present invention can contain a polyhydric alcohol ester compound.

  Examples of the polyhydric alcohol ester compounds include paragraphs (0218) to (0170) of JP 2010-32655 A.

<Sugar ester compound>
As the sugar ester compound according to the present invention, it is possible to use a sugar ester compound having at least one pyranose structure or at least one furanose structure and having all or part of the OH groups of the structure esterified. preferable.

  Examples of the sugar ester compound used in the present invention include glucose, galactose, mannose, fructose, xylose, arabinose, lactose, sucrose, cellobiose, cellotriose, maltotriose, raffinose, etc. What has is preferable. An example is sucrose.

  The sugar ester compound used in the present invention is one in which a part or all of hydroxyl groups (hydroxyl groups) of the sugar compound are esterified or a mixture thereof.

  Specific examples of the sugar ester compound according to the present invention include paragraphs (0060) to (0070) of JP-A 2010-32655.

<Other additives>
In the polarizer protective film of the present invention, a plasticizer, a retardation control agent, an antioxidant, an ultraviolet absorber, matte particles and the like can be used in combination.

  Examples of the plasticizer include phthalate ester, fatty acid ester, trimellitic ester, phosphate ester, polyester, and epoxy.

  For phosphate ester plasticizers, triphenyl phosphate, tricresyl phosphate, cresyl diphenyl phosphate, octyl diphenyl phosphate, diphenyl biphenyl phosphate, trioctyl phosphate, tributyl phosphate, etc. For phthalate ester plasticizers, diethyl phthalate, dimethoxy Ethyl phthalate, dimethyl phthalate, dioctyl phthalate, dibutyl phthalate, di-2-ethylhexyl phthalate and the like can be used.

  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 10000, but preferably in the range of 600 to 3000, the plasticizing effect is large.

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

  The plasticizer is preferably added in an amount of 0.5 to 30 parts by mass with respect to 100 parts by mass of the composition containing an acrylic resin. If the added amount of the plasticizer exceeds 30 parts by mass, the surface becomes sticky, which is not preferable for practical use. These plasticizers may be used alone or in combination of two or more.

<Other phase difference control agents>
Other than the above phase difference controlling agent according to the present invention, those containing bisphenol A in the molecule are preferable. A compound in which ethylene oxide or propylene oxide is added to both ends of bisphenol A can be used.

  For example, BP series such as New Pole BP-2P, BP-3P, BP-23P, BP-5P, BPE-20 (F), BPE-20NK, BPE-20T, BPE-40, BPE-60, BPE-100, There are BPE series (manufactured by Sanyo Chemical Co., Ltd.) such as BPE-180, and BPX series (manufactured by Adeka Co., Ltd.) such as Adeka polyether BPX-11, BPX-33, BPX-55.

  Diallyl bisphenol A, dimethallyl bisphenol A, tetrabromobisphenol A with bisphenol A substituted with bromine, oligomers and polymers obtained by polymerizing this, bisphenol A bis (diphenyl phosphate) substituted with diphenyl phosphate, etc. Can be used.

  Polycarbonate obtained by polymerizing bisphenol A, polyarylate obtained by polymerizing bisphenol A with a dibasic acid such as terephthalic acid, and an epoxy oligomer or polymer polymerized with an epoxy-containing monomer can also be used.

  Modiper CL130D or L440-G obtained by graft polymerization of bisphenol A and styrene, styrene acrylic, or the like can also be used.

  Those having a triazine structure are also preferred. The compounds described in JP 2001-166144 A can be used.

<Antioxidant>
In this invention, what is generally known can be used as an antioxidant. In particular, lactone, sulfur, phenol, double bond, hindered amine, and phosphorus compounds can be preferably used.

  For example, those including those commercially available from BASF Japan under the trade names of “IrgafosXP40” and “IrgafosXP60” are preferable.

  The phenolic compound preferably has a 2,6-dialkylphenol structure. For example, BASF Japan Ltd., “Irganox 1076”, “Irganox 1010”, and ADEKA “ADEKA STAB AO-50” are trade names. What is marketed is preferable.

  The phosphorous compounds are, for example, from Sumitomo Chemical Co., Ltd., “Sumilizer GP”, ADEKA Co., Ltd., “ADK STAB PEP-24G”, “ADK STAB PEP-36”, “ADK STAB 3010”, BASF Japan Co., Ltd. IRGAFOS P-EPQ ", commercially available from Sakai Chemical Industry Co., Ltd. under the trade name" GSY-P101 "is preferred.

  As the hindered amine compound, for example, those commercially available from BASF Japan Ltd. under the trade names “Tinuvin 144” and “Tinvin 770” and ADEKA Co., Ltd. under the name “ADK STAB LA-52” are preferable.

  As the sulfur compound, for example, those commercially available from Sumitomo Chemical Co., Ltd. under the trade names of “Sumilizer TPL-R” and “Sumilizer TP-D” are preferable.

  The above-mentioned double bond compounds are preferably those commercially available from Sumitomo Chemical Co., Ltd. under the trade names of “Sumilizer GM” and “Sumilizer GS”.

  Furthermore, it is possible to contain a compound having an epoxy group as described in US Pat. No. 4,137,201 as an acid scavenger.

  The amount of these antioxidants and the like to be appropriately added is determined in accordance with the process at the time of recycling, but generally 0.05 to 20% by mass, preferably with respect to the resin as the main raw material of the film Is added in the range of 0.1 to 1% by mass.

  These antioxidants can obtain a synergistic effect by using several different types of compounds in combination rather than using only one kind. For example, the combined use of lactone, phosphorus, phenol and double bond compounds is preferred.

<Colorant>
In the present invention, it is preferable to use a colorant. The term “colorant” means a dye or a pigment. In the present invention, the colorant means an effect that makes the color tone of a liquid crystal screen a blue tone, a yellow index adjustment, or a haze reduction.

  Various dyes and pigments can be used as the colorant, but anthraquinone dyes, azo dyes, phthalocyanine pigments and the like are effective.

<Ultraviolet absorber>
Although the ultraviolet absorber used in the present invention is not particularly limited, for example, oxybenzophenone compounds, benzotriazole compounds, salicylic acid ester compounds, benzophenone compounds, cyanoacrylate compounds, triazine compounds, nickel complex compounds, inorganic powders Examples include the body. It is good also as a polymer type ultraviolet absorber.

<Matting agent>
In the present invention, it is preferable to add a matting agent in order to impart film slipperiness.

  The matting agent used in the present invention may be either an inorganic compound or an organic compound as long as it does not impair the transparency of the resulting film and has heat resistance during melting. These matting agents can be used alone or in combination of two or more.

  By using particles having different particle sizes and shapes (for example, acicular and spherical), both transparency and slipperiness can be made highly compatible.

  Among these, silicon dioxide is particularly preferably used since it has a refractive index close to that of cellulose ester and is excellent in transparency (haze).

  Specific examples of silicon dioxide include Aerosil 200V, Aerosil R972V, Aerosil R972, R974, R812, 200, 300, R202, OX50, TT600, NAX50 (manufactured by Nippon Aerosil Co., Ltd.), Sea Hoster KEP-10, Sea Hoster KEP- 30, Seahoster KEP-50 (manufactured by Nippon Shokubai Co., Ltd.), Silo Hovic 100 (manufactured by Fuji Silysia), nip seal E220A (manufactured by Nippon Silica Industry), Admafine SO (manufactured by Admatechs), etc. Goods etc. can be preferably used.

  The shape of the particles can be used without particular limitation, such as indefinite shape, needle shape, flat shape, spherical shape, etc. However, the use of spherical particles is particularly preferable because the transparency of the resulting film can be improved.

  When the particle size is close to the wavelength of visible light, light is scattered and the transparency is deteriorated. Therefore, the particle size is preferably smaller than the wavelength of visible light, and more preferably ½ or less of the wavelength of visible light. . If the size of the particles is too small, the slipperiness may not be improved, so the range of 80 nm to 180 nm is particularly preferable.

  The particle size means the size of the aggregate when the particle is an aggregate of primary particles. Moreover, when a particle is not spherical, it means the diameter of a circle corresponding to the projected area.

<Viscosity reducing agent>
In the present invention, a hydrogen bonding solvent can be added for the purpose of reducing the melt viscosity.

  The hydrogen bonding solvent is J.I. N. As described in Israel Ativili, “Intermolecular Forces and Surface Forces” (Takeshi Kondo, Hiroyuki Oshima, Maglow Hill Publishing, 1991) and electrically negative atoms (oxygen, nitrogen, fluorine, chlorine) An organic solvent capable of producing a hydrogen atom-mediated “bond” between a hydrogen atom covalently bonded to an electronegative atom, ie, a bond having a large bond moment and containing hydrogen, such as O—H (Oxygen hydrogen bond), N—H (nitrogen hydrogen bond), and organic solvent that can arrange adjacent molecules by including F—H (fluorine hydrogen bond).

  These have the ability to form stronger hydrogen bonds with cellulose than intermolecular hydrogen bonds of cellulose resin. In the melt casting method performed in the present invention, the glass transition temperature of the cellulose resin used alone is higher than that. The melt temperature of the cellulose resin composition can be lowered by the addition of a hydrogen bonding solvent, or the melt viscosity of the cellulose resin composition containing the hydrogen bonding solvent can be lowered at the same melting temperature than the cellulose resin. .

(Physical properties of polarizer protective film)
Hereinafter, the characteristic about the physical property etc. of the polarizer protective film of this invention is demonstrated.

<transparency>
A haze value (turbidity) is used as an index for judging the transparency of the polarizer protective film of the present invention.

  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.

  Moreover, it is preferable that the total light transmittance is 90% or more, More preferably, it is 93% or more. Moreover, as a realistic upper limit, it is about 99%.

  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. Can prevent the haze value from increasing by reducing the difference in refractive index between the resin (acrylic resin (A) and cellulose ester resin (B)) and acrylic particles.

  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.

<Retardation>
For the retardation, a 35 mm × 35 mm sample was cut out from the prepared polarizer protective film, conditioned at 25 ° C. and 55% RH for 2 hours, and at an automatic birefringence meter (KOBRA WR, Oji Scientific Co., Ltd.) in the vertical direction at 590 nm. Ro and Rt at each wavelength were calculated from the values measured from the above and the extrapolated values of the retardation values measured in the same manner while tilting the film surface.

The polarizer protective film of the present invention has an in-plane retardation value Ro (590) defined by the following formula (I) in the range of 0 to 100 nm, and a thickness direction defined by the following formula (II). It is preferable to adjust so that the retardation value Rt (590) of -100 is in the range of -100 to 100 nm.
Formula (I): Ro (590) = (nx−ny) × d (nm)
Formula (II): Rt (590) = {(nx + ny) / 2−nz} × d (nm)
[In the above formula, Ro (590) represents the in-plane retardation value in the film at a measurement wavelength of 590 nm, and Rt (590) represents the retardation value in the thickness direction in the film at 590 nm.

D represents the thickness (nm) of the polarizer protective film, nx represents the maximum refractive index in the plane of the film at 590 nm, and is also referred to as the refractive index in the slow axis direction. ny represents the refractive index in the direction perpendicular to the slow axis in the film plane at 590 nm, and nz represents the refractive index of the film in the thickness direction at 590 nm. ]
The in-plane retardation value Ro (590) is preferably in the range of 0 to 250 nm.

  On the other hand, the retardation value Rt (590) in the thickness direction is preferably in the range of −50 to 50 nm.

  The desired retardation is adjusted by adjusting the ratio of each resin within the range of 95: 5 to 50:50 mass ratio of acrylic resin and cellulose ester resin. This is done by adjusting the amount to be added.

  Furthermore, by adjusting and controlling the stretching temperature (combination of the temperatures of the respective sections), the magnification, the stretching speed, the stretching order, the residual solvent amount of the film when stretching, and the like according to the composition of the film. The retardation value can be set to a desired value.

  By adjusting the retardation to such a range, the viewing angle of the liquid crystal display device using the film of the present invention can be widened and the front contrast can be improved.

Front contrast = (brightness of white display measured from normal direction of display device) / (brightness of black display measured from normal direction of display device)
The viewing angle is an angle at which a certain level of contrast can be maintained when the viewing direction of the liquid crystal display device is tilted from the normal direction.

  The uniformity in the slow axis direction is also important, and the angle is preferably −5 to + 5 ° with respect to the film width direction, more preferably in the range of −1 to + 1 °, and particularly −0. It is preferably in the range of 5 to + 0.5 °, particularly preferably in the range of −0.1 to + 0.1 °. These variations can be achieved by optimizing the stretching conditions.

  In the polarizer protective film of the present invention, it is preferable that the height from the top of the adjacent mountain to the bottom of the valley is 300 nm or more and there is no streak continuous in the longitudinal direction with an inclination of 300 nm / mm or more.

  The shape of the streak was measured using a surface roughness meter. Specifically, using a Mitutoyo SV-3100S4, a stylus (diamond needle) having a tip shape of a cone of 60 ° and a tip curvature radius of 2 μm was used. The film is scanned in the width direction of the film at a measurement speed of 1.0 mm / sec while applying a load of 0.75 mN, and a cross-sectional curve is measured with a Z-axis (thickness direction) resolution of 0.001 μm.

  From this curve, the streak height reads the vertical distance (H) from the top of the mountain to the bottom of the valley. The slope of the streak is obtained by reading the horizontal distance (L) from the top of the mountain to the bottom of the valley and dividing the vertical distance (H) by the horizontal distance (L).

  Moreover, it is preferable that the thickness of the polarizer protective film of this invention is 20 micrometers or more and 150 micrometers or less. More preferably, it is 30 μm or more and 80 μm or less.

  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.

<Method for producing polarizer protective film>
The polarizer protective film of the present invention can be preferably used regardless of whether it is a film produced by a solution casting method or a film produced by a melt casting method.

  In the solution casting method, the production of the polarizer protective film of the present invention involves the step of preparing the dope by dissolving the acrylic resin (A), the cellulose ester resin (B) and the additive in a solvent, and the dope is shifted infinitely. The process of casting on an endless metal support, the process of drying the cast dope as a web, the process of peeling from the metal support, the process of stretching or maintaining the width, the process of further drying, the process of winding up the finished film Is done.

(Dope preparation process)
The concentration of the acrylic resin (A) and the cellulose ester resin (B) in the dope is preferably higher because the drying load after casting on the metal support can be reduced, but the acrylic resin (A) and the cellulose ester resin ( If the concentration of B) is too high, the load during filtration increases and the filtration accuracy deteriorates. As a density | concentration which makes these compatible, 10-35 mass% is preferable, More preferably, it is 15-25 mass%.

  The solvent used in the dope may be used alone or in combination of two or more, but it is possible to produce a mixture of good and poor solvents of acrylic resin (A) and cellulose ester resin (B). From the viewpoint of efficiency, it is preferable from the viewpoint of solubility of the acrylic resin (A) and the cellulose ester resin (B) that there are more good solvents.

  The preferable range of the mixing ratio of the good solvent and the poor solvent is 70 to 98% by mass for the good solvent and 2 to 30% by mass for the poor solvent. With a good solvent and a poor solvent, what melt | dissolves the acrylic resin (A) and cellulose-ester resin (B) to be used independently is defined as a good solvent, and the thing which swells independently or does not melt | dissolve is defined as a poor solvent. Therefore, the good solvent and the poor solvent vary depending on the total acyl substitution degree of the acrylic resin (A) and the cellulose ester resin (B).

  Although the good solvent used for this invention is not specifically limited, Organic halogen compounds, such as a methylene chloride, dioxolanes, acetone, methyl acetate, methyl acetoacetate, etc. are mentioned. Particularly preferred is methylene chloride or methyl acetate.

  Moreover, although the poor solvent used for this invention is not specifically limited, For example, methanol, ethanol, n-butanol, cyclohexane, cyclohexanone, etc. are used preferably. Moreover, it is preferable that 0.01-2 mass% of water contains in dope.

  Moreover, the solvent used for melt | dissolution of an acrylic resin (A) and a cellulose-ester resin (B) collect | recovers the solvent removed from the film by drying at the film formation process, and uses this again.

  The recovered solvent may contain trace amounts of additives such as plasticizers, UV absorbers, polymers, monomer components, etc. added to the acrylic resin (A) and the cellulose ester resin (B). Even if it is contained, it can be preferably reused, and if necessary, it can be purified and reused.

  As a method for dissolving the acrylic resin (A) and the cellulose ester resin (B) when preparing the dope described above, a general method can be used. When heating and pressurization are combined, it is possible to heat above the boiling point at normal pressure.

  It is preferable to stir and dissolve while heating at a temperature that is equal to or higher than the boiling point of the solvent at normal pressure and that the solvent does not boil under pressure, in order to prevent the generation of massive undissolved materials called gels and mamacos.

  Moreover, after mixing an acrylic resin (A) and cellulose-ester resin (B) with a poor solvent and making it wet or swell, the method of adding a good solvent and melt | dissolving is also used preferably.

  The pressurization may be performed by a method of injecting an inert gas such as nitrogen gas or a method of increasing the vapor pressure of the solvent by heating. Heating is preferably performed from the outside. For example, a jacket type is preferable because temperature control is easy.

  A higher heating temperature with the addition of a solvent is preferable from the viewpoint of solubility of the acrylic resin (A) and the cellulose ester resin (B). However, if the heating temperature is too high, the required pressure increases and the productivity is increased. Becomes worse.

  A preferable heating temperature is 45 to 120 ° C, more preferably 60 to 110 ° C, and still more preferably 70 ° C to 105 ° C. The pressure is adjusted so that the solvent does not boil at the set temperature.

  A cooling dissolution method is also preferably used, whereby the acrylic resin (A) and the cellulose ester resin (B) can be dissolved in a solvent such as methyl acetate.

  Next, the acrylic resin (A) and the cellulose ester resin (B) solution are filtered using an appropriate filter medium such as filter paper. As the filter medium, it is preferable that the absolute filtration accuracy is small in order to remove insoluble matters and the like, but there is a problem that the filter medium is likely to be clogged if the absolute filtration accuracy is too small.

  For this reason, a filter medium with an absolute filtration accuracy of 0.008 mm or less is preferable, a filter medium with 0.001 to 0.008 mm is more preferable, and a filter medium with 0.003 to 0.006 mm is still more preferable.

  There are no particular restrictions on the material of the filter medium, and ordinary filter media can be used. However, plastic filter media such as polypropylene and Teflon (registered trademark), and metal filter media such as stainless steel do not drop off fibers. preferable.

  It is preferable to remove and reduce impurities, particularly bright spot foreign matter, contained in the raw acrylic resin (A) and cellulose ester resin (B) by filtration.

A bright spot foreign material is placed with two polarizing plates placed in a crossed Nicol state, a polarizer protective film or the like is placed between them, light is applied from one polarizing plate, and observation is performed from the other polarizing plate. It is a point (foreign matter) where light from the opposite side appears to leak, and the number of bright spots having a diameter of 0.01 mm or more is preferably 200 / cm ² or less.

More preferably, it is 100 pieces / cm < ² > or less, More preferably, it is 50 pieces / m < ² > or less, More preferably, it is 0-10 pieces / cm < ² > or less. Further, it is preferable that the number of bright spots of 0.01 mm or less is small.

  The dope can be filtered by a normal method, but the method of filtering while heating at a temperature not lower than the boiling point of the solvent at normal pressure and in a range where the solvent does not boil under pressure is the filtration pressure before and after filtration. The increase in the difference (referred to as differential pressure) is small and preferable.

  A preferred temperature is 45 to 120 ° C, more preferably 45 to 70 ° C, and still more preferably 45 to 55 ° C.

  A smaller filtration pressure is preferred. The filtration pressure is preferably 1.6 MPa or less, more preferably 1.2 MPa or less, and further preferably 1.0 MPa or less.

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

  The cast width can be 1 to 4 m. The surface temperature of the metal support in the casting step is −50 ° C. to a temperature lower than the boiling point of the solvent, and a higher temperature is preferable because the web can be dried faster. May deteriorate.

  A preferable support temperature is 0 to 55 ° C, and more preferably 25 to 50 ° C. Alternatively, it is also a preferable method that the web is gelled by cooling and peeled from the drum in a state containing a large amount of residual solvent.

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

  The peeling tension when peeling the film from the support is preferably 300 N / m or less.

  In order for the produced film to exhibit good flatness, the residual solvent amount when peeling the web from the metal support is preferably 10 to 150% by mass, more preferably 20 to 40% by mass or 60 to 130% by mass. Especially preferably, it is 20-30 mass% or 70-120 mass%.

  In the present invention, the amount of residual solvent is defined by the following formula.

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

  In the drying step, the web is peeled off from the metal support, further dried, and the residual solvent amount is preferably 1% by mass or less, more preferably 0.1% by mass or less, and particularly preferably 0. It is -0.01 mass% or less.

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

  The means for drying the web is not particularly limited, and can be generally performed with hot air, infrared rays, a heating roll, microwave, or the like, but it is preferably performed with hot air in terms of simplicity.

  The drying temperature in the web drying step is preferably increased stepwise from 40 to 200 ° C.

(Co-casting process)
When producing a laminated structure film, a method of casting a plurality of acrylic resin (A) and cellulose ester resin (B) blend solutions of two or more layers on a smooth belt or drum as a metal support is preferable.

  When casting a blend solution of a plurality of acrylic resins (A) and cellulose ester resins (B), acrylic resins (A) and cellulose ester resins from a plurality of casting openings provided at intervals in the traveling direction of the metal support. (B) A film may be produced while casting and laminating each of the blend solutions (sequential layering), or two or more casting openings are provided in one die, and acrylic resin (A), cellulose ester The resin (B) blend solution may be cast at the same time to produce a multilayer structure film (simultaneous multilayering). Examples of the method for preparing the successive multilayers include the methods described in JP-B-60-27562, JP-A-61-210413, JP-A-61-158414, JP-A-1-122419, and the like. It is done. Examples of the method for producing the simultaneous multilayer include the methods described in JP-A-61-94724, JP-A-61-158413, JP-A-6-134933, and the like.

  Although the film thickness of a manufacturing film is not specifically limited, 10-200 micrometers is used. In particular, the film thickness is particularly preferably 10 to 100 μm. More preferably, it is 20-60 micrometers.

  The cellulose ester film according to the present invention is formed to have a width of 1 to 4 m, particularly preferably 1.4 to 4 m, and particularly preferably 1.9 to 3 m. If it exceeds 4 m, conveyance becomes difficult.

(Stretching process)
In order to give the following desired retardation values Ro and Rt to the acrylic and cellulose blend film, the acrylic and cellulose blend film may have the configuration of the present invention, and the refractive index may be controlled by controlling the transport tension and stretching operation. preferable.

  For example, the retardation value can be changed by lowering or increasing the tension in the longitudinal direction.

  Moreover, it is preferable to carry out biaxial stretching or uniaxial stretching sequentially or simultaneously with respect to the longitudinal direction (film forming direction) of the film and the direction orthogonal to the longitudinal direction of the film, that is, the width direction.

  In the present invention, it is preferable that the film obtained as described above is stretched 1.01 to 3.0 times in at least one direction after passing through the step of contacting the cooling roll. Stretching can improve surface quality, such as streaking, and adjust retardation.

  As a stretching method, a known roll stretching machine, a tenter or the like can be used. For example, a method in which a difference in peripheral speed is applied to a plurality of rolls, and the roll peripheral speed difference is used to stretch in the longitudinal direction, the both ends of the web are fixed with clips and pins, and the interval between the clips and pins is increased in the traveling direction. And a method of stretching in the vertical direction, a method of stretching in the horizontal direction and stretching in the horizontal direction, a method of stretching in the vertical and horizontal directions and stretching in both the vertical and horizontal directions. Of course, these methods may be used in combination.

  In the case of the so-called tenter method, driving the clip portion by the linear drive method is preferable because smooth stretching can be performed and the risk of breakage and the like can be reduced.

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

  It is preferable that the draw ratios in the biaxial directions perpendicular to each other are finally in the range of 0.8 to 1.5 times in the casting direction and 1.1 to 2.5 times in the width direction. It is preferable to carry out in the range of 0.8 to 1.0 times in the direction and 1.2 to 2.0 times in the width direction.

  The stretching temperature is preferably 120 ° C. to 200 ° C., more preferably 150 ° C. to 200 ° C., and more preferably 150 ° C. to 190 ° C. or less.

  The residual solvent in the film is preferably 20 to 0%, more preferably 15 to 0%.

  Specifically, it is preferable that the residual solvent is stretched by 11% at 155 ° C., or the residual solvent is stretched by 2% at 155 ° C. Alternatively, it is preferable that the residual solvent is stretched at 11% at 160 ° C, or the residual solvent is stretched at less than 1% at 160 ° C.

  The stretching is preferably performed under a uniform temperature distribution controlled in the width direction. The temperature is preferably within ± 2 ° C, more preferably within ± 1 ° C, and particularly preferably within ± 0.5 ° C.

  In the stretching step, known heat setting conditions, cooling, and relaxation treatment may be performed, and adjustment may be made as appropriate so as to have characteristics required for the intended film.

  For the purpose of reducing the retardation of the polarizer protective film produced by the above method and reducing the dimensional change rate, the film may be contracted in the longitudinal direction or the lateral direction.

  In order to shrink in the longitudinal direction, for example, there is a method in which the film is shrunk by temporarily clipping out the width stretching and relaxing in the longitudinal direction, or by gradually narrowing the interval between adjacent clips of the transverse stretching machine.

  The latter method can be performed by using a general simultaneous biaxial stretching machine and driving the clip portions in the longitudinal direction by, for example, a pantograph method or a linear drive method to smoothly and gradually narrow the clip portion. it can. You may combine with extending | stretching of arbitrary directions (diagonal direction) as needed. The dimensional change rate of the polarizer protective film can be reduced by shrinking 0.5% to 10% in both the longitudinal direction and the width direction.

  Stretching can be performed, for example, sequentially or simultaneously in the longitudinal direction of the polarizer protective film and the direction orthogonal to the longitudinal direction of the polarizer protective film, that is, the width direction.

  By stretching in the biaxial directions perpendicular to each other, the film thickness variation of the obtained polarizer protective film can be reduced. If the film thickness variation of the polarizer protective film is too large, the retardation will be uneven, and unevenness such as coloring may be a problem when used in a liquid crystal display.

  The film thickness variation of the polarizer protective film is preferably ± 3%, and more preferably ± 1%.

  The slow axis or the fast axis of the retardation film of the present invention is present in the film plane, and θ1 is preferably −1 ° or more and + 1 ° or less, assuming that the angle formed with the film forming direction is θ1. More preferably, it is 5 ° or more and + 0.5 ° or less, and more preferably −0.1 ° or more and + 0.1 ° or less.

  This θ1 can be defined as an orientation angle, and θ1 can be measured using an automatic birefringence meter KOBRA-21ADH (Oji Scientific Instruments). Each of θ1 satisfying the above relationship can contribute to obtaining high luminance in a display image, suppressing or preventing light leakage, and contributing to obtaining faithful color reproduction in a color liquid crystal display device.

  In the in-plane retardation value (Ro) and retardation value (Rt) in the thickness direction of the retardation film of the present invention, when used as a polarizer protective film, the in-plane retardation value (Ro) is 30 to 100 nm. And the retardation value (Rt) in the thickness direction needs to be in the range of 100 to 300 nm, but the in-plane retardation value (Ro) is in the range of 35 to 65 nm, and The retardation value (Rt) in the thickness direction is preferably in the range of 100 to 180 nm.

  Further, the variation of Rt and the width of the distribution are preferably less than ± 50%, preferably less than ± 30%, and preferably less than ± 20%. Further, it is preferably less than ± 15%, preferably less than ± 10%, preferably less than ± 5%, particularly preferably less than ± 1%. Most preferably, there is no variation in Rt.

  The retardation values Ro and Rt can be obtained by the following equations.

Ro = (nx−ny) × d
Rt = ((nx + ny) / 2−nz) × d
Here, d is the film thickness (nm), nx is the maximum refractive index in the plane of the film (also referred to as the refractive index in the slow axis direction), and ny is in the direction perpendicular to the slow axis in the film plane. The refractive index, nz, is the refractive index of the film in the thickness direction.

  The retardation values Ro and Rt can be measured using an automatic birefringence meter. For example, it can be obtained at a wavelength of 590 nm using KOBRA-21ADH (Oji Scientific Instruments) under an environment of 23 ° C. and 55% RH.

  It is known that the physical properties of the film vary greatly depending on the stretching temperature. This tendency is prominent around the glass transition temperature (Tg) of the film.

  As a result of the study by the present inventors, it was found that the adhesiveness between the retardation film and the polarizer is the best when the stretching temperature is Tg to Tg + 20 (° C.) of the resin. On the other hand, it was found that if the film was stretched at a temperature higher than Tg, the expression of retardation (retardation) was insufficient. It is better to stretch the phase difference at a temperature lower than Tg. However, if the stretching temperature is too low, it becomes difficult to stretch, so that the film becomes cloudy or breaks during stretching. As the film, stretching is preferably performed at Tg-20 to Tg (° C.).

  For this reason, the range of the stretching temperature that achieves both polarizer adhesion and retardation development is extremely narrow, and unless the Tg is the same, the desired performance cannot be obtained, but it is found that the performance is not stable due to the pinpoint. It was.

  As a result of studying to solve this problem, the retardation film has a three-layer structure, and the glass transition temperature (Tgs) of the surface layer (hereinafter sometimes referred to as skin layer) and the inner layer (hereinafter referred to as “skin layer”). It was found that when the glass transition temperature (Tgc) of the core layer (which may be a core layer) is adjusted so as to satisfy the relationship of the following relational expression (1), the film can be stretched at a temperature at which both polarizer adhesion and phase difference are compatible.

Relational expression (1): Tgc-30 (° C.) ≦ Tgs (° C.) ≦ Tgc-10 (° C.)
Moreover, it is preferable that it is 30-60 (%), and, as for a draw ratio, it is more preferable that it is 35-50 (%). Increasing the value improves the adhesion of the polarizer and the phase difference is good, but if the stretch ratio is too large, the film becomes cloudy or breaks during stretching.

  Examples of the method of changing the glass transition temperature include a method of changing the substitution degree of the cellulose ester and a method of adding an additive such as a plasticizer or a resin. In the method of changing the substitution degree of the cellulose ester, light scattering at the interface of the laminated layers, generation of bright spot foreign matters when recycled, and the like are preferable.

  When two or more types of resins are mixed, if the glass transition temperatures of the two resins are different, there are two or more glass transition temperatures for each resin. When melted, the glass transition temperature peculiar to each resin disappears and becomes one glass transition temperature, which becomes the glass transition temperature of the compatible resin.

  The glass transition temperature was measured according to JIS K7121 (1987) by using a differential scanning calorimeter (DSC-7 model manufactured by Perkin Elmer) at a heating rate of 20 ° C./min.

(Subsequent steps)
After stretching, after slitting the edge of the polarizer protective film to a product width with a slitter and cutting it off, both ends of the polarizer protective film are subjected to knurling (embossing processing) with a knurling device consisting of an embossing ring and a back roll. By applying to the film and winding it with a winder, sticking in the polarizer protective film (original winding) and generation of scratches are prevented. The knurling method can process a metal ring having an uneven pattern on its side surface by heating or pressing.

  In addition, you may reuse the both ends of the polarizer protective film cut out by the slitter as a raw material.

  Next, the winding process of the polarizer protective film is performed by protecting the polarizer while keeping the shortest distance between the outer peripheral surface of the cylindrically wound polarizer protective film and the outer peripheral surface of the movable transport roll immediately before this constant. The film is taken up on a take-up roll. In addition, a means such as a static elimination blower for removing or reducing the surface potential of the polarizer protective film is provided in front of the winding roll.

  The winder related to the production of the polarizer protective film of the present invention may be a commonly used winder such as a constant tension method, a constant torque method, a taper tension method, a program tension control method with a constant internal stress, etc. It can be wound up by the method. In addition, it is preferable that the initial winding tension at the time of winding of a polarizer protective film is 90.2-300.8 N / m.

  In the step of winding the polarizer protective film in the method of the present invention, the polarizer protective film is preferably wound under environmental conditions of a temperature of 20 to 30 ° C. and a humidity of 20 to 60% RH. If the temperature in the winding process is in the range of 20 to 30 ° C., there will be no wrinkles and there will be no deterioration of the polarizer protective film winding quality. Moreover, if the humidity in the winding process of the polarizer protective film is 20 to 60% RH, the deterioration of the polarizer protective film winding quality due to moisture absorption is reduced, the winding quality is excellent, there is no sticking failure, and the transportability is deteriorated. Nor.

  The winding core for winding the polarizer protective film in a roll shape may be of any material as long as it is a cylindrical core, but is preferably a hollow plastic core. The plastic material may be any heat-resistant plastic that can withstand the heat treatment temperature, and examples thereof include phenol resins, xylene resins, melamine resins, polyester resins, and epoxy resins.

  Moreover, the thermosetting resin reinforced with fillers, such as glass fiber, is preferable. For example, a hollow plastic core: a wound core made of FRP having an outer diameter of 6 inches (hereinafter, 1 inch is 2.54 cm) and an inner diameter of 5 inches is used.

  In the production of the polarizer protective film of the present invention, the roll length is preferably 10 to 5000 m, more preferably 50 to 4500 m, considering productivity and transportability.

  As the width of the polarizer protective film at this time, a width suitable for the width of the polarizer and the production line can be selected, but it is 0.5 to 4.0 m, preferably 1.0 to 3.0 m. It is preferable to manufacture a polarizer protective film and wind it up into a roll.

  A haze value (turbidity) is used as an index for judging the transparency of the polarizer protective film in the present invention. 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 0.5% or less, and 0.35% or less. More preferably.

  The polarizer protective film of the present invention preferably has a total light transmittance of 90% or more, more preferably 92% or more. 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.

  In addition, the polarizer protective film of the present invention has an elongation at break in at least one direction of 30% or more, more preferably 50% or more in the measurement based on JIS-K7127-1999. In the present invention, the elongation at break is used as a measure of brittleness. Other measures of brittleness are known, such as tear strength and ease of cracking by bending, but the higher the tear strength, the better the thickness, and the thinner the thickness, the better the polarizer protection. Since the influence of the film thickness is large, the elongation at break which is not affected by the film thickness is used as an index in the present invention. 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.

  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

  In addition, as for the polarizer protective film of this invention, it is preferable that the film width after extending | stretching is 1900 mm or more.

  Moreover, after peeling off after casting and drying and winding up in roll shape, functional thin films, such as a hard-coat layer and an antireflection layer, may be provided. Until processing or shipment, packaging is usually performed in order to protect the product from dirt, static electricity, and the like.

  The packaging material is not particularly limited as long as the above purpose can be achieved, but a material that does not hinder volatilization of the residual solvent from the film is preferable. Specific examples include polyethylene, polyester, polypropylene, nylon, polystyrene, paper, various non-woven fabrics, and the like. Those in which the fibers are mesh cloth are more preferably used.

<Roll-shaped polarizing plate and single-wafer-shaped polarizing plate>
The polarizer protective film of the present invention can be used for polarizing plates in various modes, and the polarizer is formed on at least one surface of a polarizer obtained by staining a polyvinyl alcohol resin film with iodine or a dichroic dye. It is preferable to use for the roll-shaped polarizing plate of the aspect provided with the protective film.

  In the present application, a polarizing plate manufactured in a rolled state is referred to as a “roll-shaped polarizing plate”, and a piece cut from the polarizing plate is referred to as a “single-sheet polarizing plate”. .

  The polarizing plate according to the present invention can be produced by a general method. The polarizer side of the polarizer protective film of the present invention is preferably bonded to at least one surface of a polarizer prepared by alkali saponification treatment and immersion-drawn in an iodine solution using a completely saponified polyvinyl alcohol aqueous solution. .

  Even if the said cellulose-ester film is used for the other surface, another polarizer protective film can also be bonded.

  For example, commercially available cellulose ester films (for example, Konica Minoltack KC8UX, KC5UX, KC8UCR3, KC8UCR4, KC8UCR5, KC8UY, KC4UY, KC4UE, KC8UE, KC8UY-HA, KC8UX-RWA, KC8UX-RHA, KC8UX-RHA, KC8UX KC4UXW-RHA-NC, manufactured by Konica Minolta Opto, Inc.) is also preferably used.

  In addition to the antiglare layer or the clear hard coat layer, the polarizer protective film used on the surface side of the liquid crystal display device preferably has an antireflection layer, an antistatic layer, an antifouling layer, and a backcoat layer.

  In addition, the "polarizer" which is the main component of the polarizing plate is an element that passes only light having a polarization plane in a certain direction, and a typical polarizer currently known is a polyvinyl alcohol polarizing film, There are one in which iodine is dyed on a polyvinyl alcohol film and one in which a 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. The film thickness of the polarizer is preferably 5 to 30 μm, particularly preferably 10 to 20 μm.

  Further, the ethylene unit content described in JP-A-2003-248123, JP-A-2003-342322, etc. is 1 to 4 mol%, the degree of polymerization is 2000 to 4000, and the degree of saponification is 99.0 to 99.99 mol%. Ethylene-modified polyvinyl alcohol is also preferably used.

  Among them, an ethylene-modified polyvinyl alcohol film having a hot water cutting temperature of 66 to 73 ° C. is preferably used.

  A polarizer using this ethylene-modified polyvinyl alcohol film is excellent in polarization performance and durability, and has few color spots, and is particularly preferably used for a large-sized liquid crystal display device.

  The polarizer obtained as described above is usually used as a polarizing plate with a protective film bonded to both sides or one side. Examples of the adhesive used for pasting include a PVA-based adhesive and a urethane-based adhesive. Among them, a PVA-based adhesive is preferably used.

  Hereinafter, the roll-shaped polarizing plate or the sheet-shaped polarizing plate according to the present invention will be described in more detail with reference to the drawings as appropriate.

  FIG. 1 is a schematic cross-sectional view showing an example of a layer configuration of a roll-shaped polarizing plate or a sheet-shaped polarizing plate.

  In the example shown in FIG. 1, a polarizer protective film 2 made of a transparent resin film is bonded to one side of a polarizer 1, and a polarizer protective film 3 is bonded to the other side of the polarizer 1. The outside pressure-sensitive adhesive layer 6 is provided on the polarizing plate 7. Then, a peelable protective film 4 is bonded to the surface of the polarizer protective film 2, and a separate film 5 is bonded to the surface of the outer pressure-sensitive adhesive layer 6, so that a roll-shaped polarizing plate or a sheet-shaped polarizing plate 8 is bonded. Is configured.

  FIG. 1 shows an example in which the pressure-sensitive adhesive layer provided on the other surface side of the polarizer 1 is a single layer. For example, the polarizer protective film 3 may be a polarizer protective film with a retardation function, In addition, two or more polarizer protective films 3 having a retardation function may be laminated to form a broadband circularly polarizing plate. In that case, the retardation films may be bonded via an adhesive layer. Therefore, the pressure-sensitive adhesive layer has two or more layers. Even in such a case, the separate film 5 is bonded to the surface of the outermost pressure-sensitive adhesive layer 6.

  In the roll-shaped polarizing plate or the sheet-shaped polarizing plate 8, the protective film 4 outside the polarizer protective film 2 and the separate film 5 outside the polarizer protective film 3 are used when the sheet-shaped polarizing plate 8 is inspected. It is provided for the purpose of protecting the polarizing plate 7 and the pressure-sensitive adhesive layer 6 when the leaf-shaped polarizing plate 8 is transported or stored.

  That is, the protect film 4 is provided for the purpose of protecting the surface of the polarizing plate 7 and is on the side opposite to the surface where the polarizing plate 7 is bonded to the liquid crystal cell. The protective film 4 is peeled off after the polarizing plate 7 is bonded to the liquid crystal cell.

  Moreover, the separate film 5 is provided on it for the purpose of covering the adhesive layer 6, and this adhesive layer 6 becomes the surface side which bonds the sheet-like polarizing plate 8 to a liquid crystal cell or another optical member. . And the separate film 5 provided on it is peeled and removed immediately before bonding to a liquid crystal cell or another optical member.

  The protective film 4 is usually composed of a transparent base resin film provided with an adhesive layer on the surface. Moreover, the separate film 5 is normally comprised with the transparent resin film in which the mold release process was performed, and the mold release process surface is bonded together to the adhesive layer 6. FIG. As the resin film constituting the protect film 4 and the separate film 5, for example, a film made of polyester such as polyethylene terephthalate or polyethylene naphthalate can be used.

  In the present invention, when the polarizing plate on which the protective film 4 and the separate film 5 are respectively bonded is wound up in a roll shape, the protective film 4 is shown in a schematic cross-sectional view in FIG. Is wound so that the inner side is the inner side and the separate film 5 is the outer side.

<Laser cutting>
When manufacturing the liquid crystal display device by bonding the roll-shaped polarizing plate to a liquid crystal panel and cutting with a laser, examples of the laser used include CO ₂ laser, YAG laser, and UV laser. The CO ₂ laser is preferable because it has high applicability in the thickness range and does not cause cracks or chipping.

  In the laser irradiation, the output and speed are not limited, and the laser irradiation may be performed by single irradiation or multiple irradiation. The output of the laser irradiation is, for example, 10 to 800 W, preferably 100 to 350 W when cutting with one irradiation, and preferably 50 to 200 W when cutting with two irradiations.

<Liquid crystal display device>
By incorporating the polarizing plate bonded with the polarizer protective film of the present invention into a liquid crystal display device, it is possible to produce various liquid crystal display devices with excellent visibility, but particularly large liquid crystal display devices, digital signage, etc. It is preferably used for a liquid crystal display device for outdoor use. The polarizing plate of 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 VA type screen of 30 type or more, particularly 30 type to 54 type, there is no white spot in the periphery of the screen and the effect is maintained for a long time.

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

Example 1
(Synthesis of acrylic copolymers A1 to A36)
In a glass flask equipped with a stirrer, two dropping funnels, a gas introduction tube and a thermometer, 40 g of a mixture of monomers X, Y and Z having the types and ratios shown in Table 1, 2 g of mercaptopropionic acid as a chain transfer agent, and 30 g of toluene was charged and the temperature was raised to 90 ° C. Thereafter, from one dropping funnel, 60 g of a mixture of monomers X, Y, and Z having the types and ratios shown in Table 1 was dropped over 3 hours, and at the same time dissolved in 14 g of toluene from the other funnel. 0.4 g of ronitrile was added dropwise over 3 hours. Thereafter, 0.6 g of azobisisobutyronitrile dissolved in 56 g of toluene was added dropwise over 2 hours, and the reaction was further continued for 2 hours to obtain polymer X. The obtained polymer X was solid at room temperature. Next, polymers X having different molecular weights were prepared by changing the addition amount of the chain transfer agent mercaptopropionic acid and the addition rate of azobisisobutyronitrile. The weight average molecular weight of the polymer X is shown in Table 1 by the following measurement method.

(Weight average molecular weight)
The weight average molecular weight of the polymer was determined by GPC polystyrene conversion described above. In addition, the monomer composition of acrylic copolymers A1 to A36 according to the present invention is shown in Table 1. The meanings of the abbreviations indicating the monomers described in Table 1 are as follows.
AA: ACMO acrylic acid: acryloylmorpholine DMAA: N, N-dimethylacrylamide DMMA: N, N-dimethylmethacrylamide GLM: glycerol monomethacrylate HEA: 2-hydroxyethyl acrylate HEMA: 2-hydroxyethyl methacrylate HPMA: 2-hydroxypropyl Methacrylate MA: Methacrylic acid MAA: Methyl acrylate MMA: Methyl methacrylate PS: Styrene N-VP: N-Vinylpyrrolidone

  The cellulose ester resin (B) according to the present invention is shown in Table 2.

The additive C is shown below.
C1: Aromatic terminal ester plasticizer Illustrative compound (14)
C2: Sugar ester compound exemplified compound (3)
C3: Polyhydric alcohol ester exemplary compound (16)
C4: Triazine compound shown below

(Preparation of dope solution)
Acrylic resin (A) A8 95 parts by mass Cellulose ester resin (B) B2 5 parts by mass Silicon oxide fine particles (Aerosil R972V (produced by Nippon Aerosil Co., Ltd.))
0.1 parts by mass Methylene chloride 300 parts by mass Ethanol 40 parts by mass (Preparation of optical film 1)
The dope solution was prepared with Finemet NF manufactured by Nippon Seisen Co., Ltd., then filtered, and uniformly cast onto 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 peeled cellulose ester web was evaporated at 35 ° C., slit to 1.6 m width, and then dried at a drying temperature of 135 ° C. while stretching 1.1 times in the width direction with a tenter. At this time, the residual solvent amount when starting stretching with a tenter was 10%. After stretching with a tenter and relaxing at 130 ° C for 5 minutes, drying was completed while transporting the drying zone at 120 ° C and 130 ° C with a number of rolls, slitting to a width of 1.5 m, and 10 mm wide at both ends of the film. A knurling process having a thickness of 5 μm was performed, and the film was wound around a core having an inner diameter of 6 inches with an initial tension of 220 N / m and a final tension of 110 N / m. The draw ratio in the MD direction calculated from the rotational speed of the stainless steel band support and the operating speed of the tenter was 1.01. The residual solvent amounts of the films listed in Table 2 were 0.1%, the film thickness was 40 μm, and the number of turns was 4000 m.

  Next, optical films 2 to 79 were produced in the same manner as the optical film 1, except that the types of acrylic resin, cellulose ester resin, addition amount, additive type, and addition amount were changed as shown in Tables 4 and 6. did.

Example 2
A polarizing plate having a layer structure shown in FIG. 1 was produced in a roll form using the produced polarizer protective film. FIG. 1 is a schematic cross-sectional view showing an example of a layer structure of a polarizing plate roll or a polarizing plate product to be manufactured. Moreover, the cross-sectional schematic diagram which expands a part and shows the state which winds up a polarizing plate roll was shown in FIG.

  As the protect film 5, a commercially available product “AS3-304” manufactured by Fujimori Industry Co., Ltd. was used. ("" Is the product name). The protective film 5 is obtained by forming an acrylic pressure-sensitive adhesive layer on the surface of a polyethylene terephthalate film having a thickness of 38 μm.

  A potassium hydroxide aqueous solution having a concentration of 1.5 mol / l at 45 ° C. is attached to one surface of a polarizer 1 made of polyvinyl alcohol to which iodine is adsorbed and oriented with a thickness of 23 μm via an adhesive made of an aqueous solution of a polyvinyl alcohol resin. The film was treated for 30 seconds, washed with water, and then dried at 100 ° C. for 10 minutes. Similarly, the other surface was treated in an aqueous 1.5 mol / l potassium hydroxide solution at 45 ° C. for 30 seconds via an adhesive composed of an aqueous solution of polyvinyl alcohol resin, washed with water, and then washed at 100 ° C. for 10 seconds. The polarizer protective film 3 (optical film 1) having a thickness of 40 μm which was dried for 5 minutes was bonded to the surface of the polarizer protective film 3 having a thickness of 38 μm. A sheet-like pressure-sensitive adhesive in which an acrylic pressure-sensitive adhesive layer 6 having a thickness of 25 μm is formed on a separate film 7 made of reethylene terephthalate is pasted on the pressure-sensitive adhesive layer 6 side. The protective film 5 was bonded to produce a polarizing plate roll 8 having the layer structure shown in Fig. 2. At this time, the transmission axis of the polarizer and the slow axis of the polarizer protective film 3 were parallel to each other. Bonding was performed.

  Subsequently, the polarizing plate roll 8 was produced similarly except having changed the kind of polarizer protective film 3 and the saponification process conditions of the polarizer protective film 3 as shown in Table 4.

  In addition, as a comparative example, a polarizing plate is similarly formed except that the optical film described in Example 1 of International Publication No. 2009/047924 is used instead of the polarizer protective film 3 and the saponification treatment conditions are changed as shown in Table 3. Roll 8 was produced.

(Evaluation of polarizing plate roll)
A part of the polarizing plate was cut out from the winding core and unwinding of the obtained polarizing plate roll, and evaluated by the following methods. The results of evaluation are shown in Tables 4-7. In addition, about the cutout part of a polarizing plate, it cut out as follows.
A: Less than 1000 m from the core part B: 1000 m or more and less than 2000 m from the core part C: 2000 m or more from the core part (Adhesion evaluation)
The polarizing plate cut out from the polarizing plate roll was measured by hand to determine whether it could be peeled off.

Evaluation criteria for adhesion:
◯: Bonded and cannot be peeled by hand Δ: Only the end portion is peeled off, and the member is destroyed when peeled further. ×: Can be easily peeled by hand.

(Evaluation of unevenness at the winding core and unwinding of the polarizing plate roll)
The polarizing plate previously peeled off from Sony 30-inch liquid crystal television KDL-32S1000, which is a vertical alignment type liquid crystal display device, is peeled off, and the polarizing plate cut out from the polarizing plate roll of the embodiment of the present invention is polarized in the polarization direction. A liquid crystal panel was prepared, and a plurality of (10 persons) evaluators visually observed unevenness that looked whitish when viewed from the front and oblique directions. Tables 4 and 6 show the cutout portion of the polarizing plate and the type of each film constituting the polarizing plate.

Evaluation criteria for unevenness of polarizing plate:
○: Unevenness is not seen at all Δ: Unevenness is slightly recognized, but it can be used as a product ×: Unevenness is recognized by many evaluators (5 or more).

(Evaluation of polarizing plate rework processing from liquid crystal display devices)
A glass panel used for a liquid crystal display device is prepared by pasting together a polarizing plate cut out from the polarizing plate roll of the embodiment of the present invention, and for the rework process, the pasted polarizing plate is again peeled off, It was confirmed whether it was able to peel. In addition, the part of B used the cutout part of a polarizing plate, and the kind of each film which comprises a polarizing plate was shown to Table 4 and 6. FIG.

Peel evaluation criteria:
○: Cracks or breakage in polarizing plate, can be peeled off from glass plate without peeling between polarizer and polarizer protective film Δ: Cracks or part of film is broken in polarizing plate, partly polarizer And peeling between the polarizer and the polarizer protective film x: Cracks in the polarizing plate, or destruction of the polarizing plate, and peeling between the polarizer and the polarizer protective film occurs.

(Viewing angle fluctuation)
For the evaluation of viewing angle characteristics, the transmitted light amount during black display and white display was measured using EZ-contrast manufactured by ELDIM. The viewing angle was evaluated by calculating contrast = (transmitted light amount during white display) / (transmitted light amount during black display).

  The durability of the viewing angle function was evaluated by measuring the viewing angle characteristics before and after 500 h treatment at 60 ° C. and 90% RH, and observing the change in angle indicating the viewing angle of contrast 10. In addition, the part of B used the cutout part of a polarizing plate, and the kind of each film which comprises a polarizing plate was shown to Table 4 and 6. FIG.

Evaluation criteria:
○: No change in up / down / left / right Δ: Change in viewing angle of 2 ° or more and less than 5 ° in either up / down / left / right direction ×: Change in viewing angle of 5 ° or more in either up / down / left / right direction

(Change in color)
The produced liquid crystal display device 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 similarly observed, and the presence or absence of a color change was visually confirmed by a plurality (10 persons) of evaluators. In addition, the part of B used the cutout part of a polarizing plate, and the kind of each film which comprises a polarizing plate was shown to Table 4 and 6. FIG.

Evaluation criteria:
○: No color change △: Color change may be slightly recognized, but a level that can be used as a product ×: Many evaluators (5 or more) recognize that the color change is large. Shown in Tables 4-7.

  From the results shown in Tables 4 to 7, when producing a polarizing plate roll, the unevenness of the polarizer on the roll core and the outside of the roll is suppressed, and the adhesiveness to the polarizer is maintained even under weak saponification conditions. Provided a polarizer protective film that has excellent display stability even when used in a liquid crystal display device. can do. Moreover, the roll-shaped polarizing plate and liquid crystal display device provided with the said polarizer protective film can be provided.

1 Polarizer 2 Polarizer Protective Film 1
3 Polarizer protective film 2
4 Protective film 5 Separate film 6 Adhesive layer 7 Polarizing plate 8 Roll-shaped polarizing plate roll or sheet-shaped polarizing plate

Claims (5)

A polarizer protective film comprising an acrylic resin (A) and a cellulose ester resin (B), wherein the polarizer protective film satisfies all of the following requirements (1) to (4).
(1) When the masses of the acrylic resin (A) and the cellulose ester resin (B) are Am and Bm, respectively, the mass ratio (Am / Bm) is in the range of 50/50 to 95/5.
(2) The acrylic resin (A) has a weight average molecular weight (Mw) in the range of 5000 to 1000000.
(3) The acrylic resin (A) is represented by the following general formula (1).
Formula _{(1) :-( X) l -} (Y) m - (Z) n -
(However, X represents a copolymerizable monomer unit, Y represents a monomer unit copolymerizable with X, Z represents a monomer unit copolymerizable with either X or Z, and Y and Z are the respective units. (In the structure, it has a hydroxyl group, a carboxyl group, an amino group, or an amide group. L, m, and n are mass fractions, and l + m + n = 100.)
(4) When 23 ≦ {(m + n) / (l + m + n)} × 100 ≦ 60, the mass Am of the acrylic resin (A) satisfies the following relationship.
21 ≦ Am × {(m + n) / (l + m + n)} ≦ 60   The acyl group average substitution degree of the cellulose ester resin (B) is in the range of 2.0 to 3.0, and the weight average molecular weight (Mw) is in the range of 30000 to 300000. The polarizer protective film of 1.   Y and Z are monomers derived from 2-hydroxyethyl methacrylate, 2-hydroxyethyl acrylate, methacrylic acid, acrylic acid, N, N-dimethylacrylamide, N, N-dimethylmethacrylamide, or N-vinylpyrrolidone, respectively. The polarizer protective film according to claim 1, wherein the polarizer protective film is a unit.   Polarized light provided with the polarizer protective film according to any one of claims 1 to 3 on at least one surface of a polarizer obtained by dyeing a polyvinyl alcohol resin film with iodine or a dichroic dye. A roll-shaped polarizing plate, wherein the plate is wound in a roll shape in the longitudinal direction.   A liquid crystal display device produced by bonding the roll-shaped polarizing plate according to claim 4 to a liquid crystal panel and cutting with a laser.

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