Retardation film, polarizing plate, and liquid crystal display device

Abstract

The invention provides a phase difference film capable of suppressing contrast unevenness in a liquid crystal display device just taken out from a high-humidity environment, and a polarizing plate and a liquid crystal display device provided with the phase difference film. The phase difference film according to the present invention has a first layer, a second layer, and a third layer in this order, each of the first layer, the second layer, and the third layer contains an acetyl cellulose and fine particles, the degree of substitution of acetyl groups in the acetyl cellulose contained in the second layer is in the range of 2.0-2.6, the second layer further contains a polyester having hydroxyl groups at both ends, and the third layer contains a polyester having hydroxyl groups at both ends. The content (mass%) of the fine particles in the second layer is greater than the content (mass%) of the fine particles in the first layer and the third layer.

Description

Technical Field

[0001] The present invention relates to a retardation film, a polarizing plate, and a liquid crystal display device. More specifically, the present invention relates to a retardation film capable of suppressing contrast unevenness in a liquid crystal display device immediately after being taken out from a high-humidity environment, and a polarizing plate and a liquid crystal display device including the retardation film. Background Art

[0002] In a cellulose acetate film having a laminated structure, a technique of adding a matting agent mostly in the surface layer or only in the surface layer is known (see Patent Document 1).

[0003] However, such a cellulose acetate film causes uneven contrast immediately after being taken out from a high-humidity environment, and thus may cause problems in inspections after transportation or the like.

[0004] Prior Art Documents

[0005] Patent Documents

[0006] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2011-162769 Summary of the Invention

[0007] The present invention has been made in view of the above circumstances. The problem to be solved by the present invention is to provide a retardation film capable of suppressing contrast unevenness in a liquid crystal display device immediately after being taken out from a high-humidity environment, and a polarizing plate and a liquid crystal display device including the retardation film.

[0008] In order to solve the above problems, the present inventors studied the causes of the above problems and the like. As a result, the present inventors found that: in a retardation film having a first layer, a second layer, and a third layer in this order, by making the first layer, the second layer, and the third layer all contain acetyl cellulose and fine particles, the degree of substitution of the acetyl group of the acetyl cellulose contained in the second layer is in the range of 2.0 to 2.6, the second layer further contains a polyester having hydroxyl groups at both ends, and the content rate [mass%] of the fine particles in the second layer is greater than the content rate [mass%] of the fine particles in the first layer and the third layer, the above problems can be solved, and thus the present invention has been completed.

[0009] That is, the above problems related to the present invention are solved by the following method.

[0010] 1. A retardation film, characterized in that it has a first layer, a second layer, and a third layer in this order,

[0011] the above first layer, the above second layer, and the above third layer all contain acetyl cellulose and fine particles,

[0012] the degree of substitution of the acetyl group of the acetyl cellulose contained in the above second layer is in the range of 2.0 to 2.6,

[0013] The second layer further contains a polyester having hydroxyl groups at both ends,

[0014] The content rate [mass %] of the fine particles in the second layer is larger than the content rates [mass %] of the fine particles in the first layer and the third layer.

[0015] 2. The phase difference film according to item 1, wherein the content rate [mass %] of the fine particles in the second layer is within a range of 2 to 5 times the average content rate [mass %] of the fine particles in the first layer and the third layer.

[0016] 3. The phase difference film according to item 1, wherein the fine particles are silica fine particles.

[0017] 4. A polarizing plate comprising the retardation film according to any one of items 1 to 3.

[0018] 5. A liquid crystal display device comprising the retardation film according to any one of items 1 to 3.

[0019] According to the above method of the present invention, it is possible to provide a retardation film capable of suppressing contrast unevenness in a liquid crystal display device immediately after being taken out of a high humidity environment, and a polarizing plate and a liquid crystal display device including the retardation film.

[0020] The mechanism of expression and action of the effect of the present invention is not clear, but is presumed as follows.

[0021] In a high humidity environment, water enters the interior of the phase difference film, and the water coordinates with the hydrophilic group of acetyl cellulose, thereby reducing the phase difference value of that part. It is believed that the contrast unevenness occurs in the liquid crystal display device just taken out of the high humidity environment. It should be noted that in the present invention, "high humidity environment" refers to an environment with a relative humidity of 75% RH or more.

[0022] The phase difference film of the present invention has the first layer, the second layer and the third layer in sequence, and the content of microparticles in the second layer is larger than that in the first layer and the third layer. Since the phase difference film contains both acetylcellulose and microparticles, the phase difference value is not easily affected by water. It is speculated that this is because the microparticles form hydrogen bonds with the hydrophilic group of the acetylcellulose, so that it is difficult for water to interact with the acetylcellulose. On the other hand, if the content of microparticles near the surface of the phase difference film is excessively increased, the slippage of the surface of the phase difference film becomes too high, which may cause problems such as winding deviation. The present invention can increase the content of microparticles in the second layer on the basis of adjusting the content of microparticles in the first and third layers with emphasis on slippage. As a result, the present invention can maintain the slippage in a good range and suppress the phase difference value from being affected by water. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a cross-sectional view of an embodiment of a retardation film.

[0024] Figure 2 It is a cross-sectional view of an embodiment of a liquid crystal display device.

[0025] Symbol Explanation

[0026] 10 First optical film

[0027] 20 Second optical film (retardation film)

[0028] 21 First layer

[0029] 22 Second layer

[0030] 23 Third layer

[0031] 30 Polarizer

[0032] 50 First polarizing plate

[0033] 60 Liquid crystal cell

[0034] 70 Second polarizing plate

[0035] 100 Liquid crystal panel

[0036] 200 Backlight

[0037] 500 Liquid crystal display device Detailed Embodiment

[0038] The retardation film of the present invention is characterized in that it sequentially has a first layer, a second layer, and a third layer. The above-mentioned first layer, the above-mentioned second layer, and the above-mentioned third layer all contain cellulose acetate and fine particles. The degree of substitution of the acetyl group of the cellulose acetate contained in the above-mentioned second layer is in the range of 2.0 to 2.6. The above-mentioned second layer further contains a polyester having hydroxyl groups at both ends. The content rate [mass%] of the fine particles in the above-mentioned second layer is greater than the content rate [mass%] of the fine particles in the above-mentioned first layer and the above-mentioned third layer.

[0039] This feature is a common or corresponding technical feature in the following embodiments.

[0040] The content rate [mass%] of the fine particles in the above-mentioned second layer is preferably in the range of 2 to 5 times the average content rate [mass%] of the fine particles in the above-mentioned first layer and the above-mentioned third layer. By being 2 times or more, the slidability is maintained in a good range, and the influence of water on the retardation value is further suppressed. By being 5 times or less, the haze is not too high, and it is not easy to reduce the contrast of the liquid crystal display device.

[0041] The fine particles are preferably silica fine particles. Since the refractive index of silica fine particles is close to that of acetylcellulose, the generation of haze can be suppressed by using silica fine particles.

[0042] The polarizing plate and liquid crystal display device of the present invention include the retardation film of the present invention.

[0043] Hereinafter, the present invention will be described in detail. In the present application, a numerical range described using "to" means that the numerical values ​​described before and after the range are included as the lower limit and the upper limit.

[0044] [1. Retardation film]

[0045] The phase difference film of the present invention has a first layer, a second layer and a third layer in sequence. The first layer, the second layer and the third layer all contain acetyl cellulose and microparticles. The degree of substitution of the acetyl group of the acetyl cellulose contained in the second layer is in the range of 2.0 to 2.6. The second layer further contains a polyester having hydroxyl groups at both ends. The content rate [mass %] of the microparticles in the second layer is greater than the content rate [mass %] of the microparticles in the first layer and the third layer.

[0046] Hereinafter, the first layer and the third layer are also referred to as "surface layers", and the second layer is also referred to as "core layer".

[0047] Figure 1 This is a cross-sectional view of one embodiment of a phase difference film.

[0048] Figure 1 The phase difference film 20 shown has a first layer 21, a second layer 22, and a third layer 23 in sequence. The thickness of the first layer 21 and the third layer 23 is, for example, in the range of 1 to 10 μm, respectively. The thickness of the second layer 22 is, for example, in the range of 5 to 50 μm. From the viewpoint of suppressing the influence of water on the phase difference value, the second layer 22 is preferably thicker than the first layer 21 and the third layer 23, respectively, and preferably thicker than the total thickness of the first layer 21 and the third layer 23. The overall thickness of the phase difference film 20 is, for example, in the range of 10 to 200 μm, preferably in the range of 10 to 60 μm, and more preferably in the range of 10 to 40 μm.

[0049] The width of the retardation film 20 is preferably in the range of 1 to 4 m, more preferably in the range of 1.3 to 4 m, and more preferably in the range of 2.2 to 3 m. By setting the width in the range of 2.2 to 3 m, both uniformity of stretching and productivity can be achieved at a high level.

[0050] The retardation film 20 may further include layers other than the first layer 21 , the second layer 22 , and the third layer 23 . Even in this case, it is preferred that the first layer 21 and the third layer 23 are the outermost layers on both sides of the retardation film 20 .

[0051] [1-2. Second layer]

[0052] The second layer contains acetyl cellulose having a degree of substitution of acetyl groups within a range of 2.0 to 2.6, fine particles, and a polyester having hydroxyl groups at both ends, and the second layer may contain other components.

[0053] (Acetyl Cellulose)

[0054] Acetyl cellulose is cellulose in which part or all of the hydrogen atoms in the hydroxyl groups (-OH) at the 2nd, 3rd and 6th positions in one glucose unit are replaced by acetyl groups. By setting the degree of substitution of acetyl groups in the acetyl cellulose contained in the second layer to be within the range of 2.0 to 2.6, it is easy to obtain a desired retardation value.

[0055] The degree of substitution of acetyl groups indicates the average number of acetyl groups per glucose unit. Specifically, the degree of substitution of acetyl groups indicates how many hydrogen atoms of the hydroxyl groups at positions 2, 3, and 6 in one glucose unit are replaced by acetyl groups. Therefore, the maximum value of the degree of substitution of acetyl groups is 3.0. When the degree of substitution of acetyl groups is 3.0, all the hydrogen atoms of the hydroxyl groups at positions 2, 3, and 6 are replaced by acetyl groups.

[0056] The acetyl group may be substituted evenly at the 2-position, 3-position, and 6-position in one glucose unit, or may be substituted in a distributed manner.

[0057] The degree of substitution of acetyl groups can be determined by the method specified in ASTM-D817-96.

[0058] From the viewpoint of obtaining desired optical properties, acetyl celluloses having different degrees of substitution may be mixed and used. The mixing ratio of acetyl celluloses having different degrees of substitution is not particularly limited.

[0059] From the viewpoint of mechanical strength, the number average molecular weight (Mn) of acetyl cellulose is preferably 2×10 4 ~3×10 5 In the range of 2×10 4 ~1.2×10 5 In the range of 4×10 4 ~8×10 4 within the range.

[0060] From the viewpoint of mechanical strength, the weight average molecular weight (Mw) of acetyl cellulose is preferably 2×10 4 ~1×10 6 In the range of 2×10 4 ~1.2×10 5 In the range of 4×10 4 ~8×10 4 within the range.

[0061] The number average molecular weight (Mn) and weight average molecular weight (Mw) of acetyl cellulose can be measured using gel permeation chromatography (GPC) under the following conditions.

[0062] Solvent: dichloromethane

[0063] Column: Connect three Shodex K806, K805 and K803G (all manufactured by Showa Denko K.K.)

[0064] Column temperature: 25°C.

[0065] Sample concentration: 0.1 mass%

[0066] Detector: RI Model 504 (manufactured by GLScience)

[0067] Pump: L6000 (manufactured by Hitachi, Ltd.)

[0068] Flow rate: 1.0mL / min

[0069] Calibration curve: A calibration curve based on 13 samples of standard polystyrene STK standard polystyrene (manufactured by TOSOH Corporation) with Mw=500 to 2800000 is used. The 13 samples are preferably used at substantially equal intervals.

[0070] Acetyl cellulose can be synthesized, for example, according to the following steps. There are no particular restrictions on the raw cellulose of acetyl cellulose, and examples thereof include cotton linters, wood pulp, and kenaf. The raw cellulose, acetic acid, acetic anhydride, and a catalyst (sulfuric acid, etc.) are mixed to esterify the cellulose. The reaction is carried out until triesters of cellulose are formed. In the triesters, the hydrogen atoms of the three hydroxyl groups in one glucose unit are all replaced by acetyl groups. Next, acetyl cellulose having a desired degree of acetyl substitution can be obtained by hydrolyzing the triesters of cellulose. Then, after filtering, precipitation, washing with water, dehydrating, and drying, acetyl cellulose is finally obtained. Specifically, the synthesis can be carried out with reference to the method described in Japanese Patent Gazette No. 10-45804.

[0071] Examples of commercially available products of acetyl cellulose include “LM80, L20, L30, L40, and L50” (all manufactured by Daicel Corporation), and “Ca398-3, Ca398-6, Ca398-10, Ca398-30, and Ca394-60S” (all manufactured by Eastman Chemical Corporation).

[0072] The content of acetyl cellulose in the second layer is, for example, in the range of 60 to 95% by mass.

[0073] (Polyester having hydroxyl groups at both ends)

[0074] The second layer contains a polyester having hydroxyl groups at both ends. The parts of the polyester other than the carboxyl group and the hydroxyl group show relative hydrophobicity. Therefore, for polyester, even if there are hydroxyl groups at both ends, the molecule as a whole shows hydrophobicity. By containing such a polyester, the degree of hydrophobicity of the phase difference film is improved. Therefore, the phase difference film is not easy to obtain moisture by containing polyester. In addition, the hydroxyl groups at both ends of the polyester react with the water molecules entering the phase difference film. Before the water molecules react with the hydrophilic groups of acetyl cellulose, they react with the hydroxyl groups at both ends of the polyester, thereby inhibiting the coordination of water with the hydrophilic groups of acetyl cellulose. Thus, the change in the phase difference value of the phase difference film can be suppressed, and then the uneven contrast in the liquid crystal display device just taken out of a high humidity environment can be suppressed.

[0075] The polyester having hydroxyl groups at both ends preferably has a structure represented by the following general formula (I).

[0076] General formula (I)

[0077]

[0078] In the formula, B represents a linear or branched alkylene group or a cycloalkylene group having 2 to 6 carbon atoms. A represents an aromatic ring having 6 to 14 carbon atoms. n represents a natural number of 1 or more.

[0079] The polyester having a structure represented by the general formula (I) can be obtained from an aromatic dicarboxylic acid and a linear or branched alkylene glycol or cycloalkylene glycol having 2 to 6 carbon atoms. Both ends of the polyester are capped with a monocarboxylic acid.

[0080] Examples of the aromatic dicarboxylic acid having 8 to 16 carbon atoms include phthalic acid, isophthalic acid, terephthalic acid, 1,5-naphthalene dicarboxylic acid, 1,4-naphthalene dicarboxylic acid, 1,8-naphthalene dicarboxylic acid, 2,3-naphthalene dicarboxylic acid, 2,6-naphthalene dicarboxylic acid, 2,8-naphthalene dicarboxylic acid, 2,2'-biphenyl dicarboxylic acid, 4,4'-biphenyl dicarboxylic acid, etc. Among them, 2,6-naphthalene dicarboxylic acid or 4,4'-biphenyl dicarboxylic acid is preferred.

[0081] Examples of the linear or branched alkylene glycol or cycloalkylene glycol having 2 to 6 carbon atoms include ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,2-butylene glycol, 1,3-butylene glycol, 2-methyl-1,3-propylene glycol, 1,4-butylene glycol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, 1,6-hexanediol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, etc. Among them, ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, or 1,3-butylene glycol is preferred.

[0082] Among them, in order to obtain the effects of the present invention, it is preferred that A is a naphthalene ring or a biphenyl ring which may have a substituent. Here, the substituent refers to an alkyl group, an alkenyl group or an alkoxy group having 1 to 6 carbon atoms.

[0083] It is preferable that n is in the range of 1-170.

[0084] The number average molecular weight of the polyester is preferably 20,000 or less, more preferably 10,000 or less. For polyesters in the range of number average molecular weight of 400 to 10,000, the compatibility with acetyl cellulose is good. In addition, polyesters in the range of number average molecular weight of 400 to 10,000 are not easy to evaporate or volatilize during the film-making process, so they are preferred. The number average molecular weight of the polyester can be measured by gel permeation chromatography (GPC). For low molecular weight compounds that cannot be measured by GPC, they can be calculated based on the structural formula.

[0085] The polyester of the present invention can be synthesized by a hot melt polymerization method based on a polyesterification reaction or an ester exchange reaction between the above-mentioned dicarboxylic acid and diol, or an interfacial condensation method between the above-mentioned dicarboxylic acid chloride and diols.

[0086] The polyester having a structure represented by the general formula (I) is exemplified below.

[0087]

[0088]

[0089] The content of the polyester having hydroxyl groups at both ends in the second layer is preferably in the range of 1 to 20% by mass, more preferably in the range of 5 to 15% by mass, relative to the content of the acetoacetate in the second layer.

[0090] (particle)

[0091] In the second layer, the fine particles form hydrogen bonds with the hydrophilic group of the acetyl cellulose, thereby suppressing the interaction between water and the acetyl cellulose. Thus, the second layer of the retardation film containing fine particles is not easily affected by water.

[0092] In the present invention, "fine particles" refer to particles having an average primary particle diameter of 5 to 400 nm. The fine particles may be inorganic fine particles or organic fine particles.

[0093] Examples of the inorganic fine particles include those containing silicon dioxide (SiO 2 ), titanium dioxide, aluminum oxide (Al 2 O 3), zirconium oxide, calcium carbonate, talc, clay, sintered kaolin, sintered calcium silicate, hydrated calcium silicate, aluminum silicate, magnesium silicate, calcium phosphate and the like. The inorganic particles are preferably silica particles. Since the refractive index of silica particles is close to that of acetylcellulose, the generation of haze can be suppressed by making the inorganic particles silica particles.

[0094] Examples of commercially available silica fine particles include AEROSIL (registered trademark) R972, R972V, R974, R812, 200, 200V, 300, R202, OX50, and TT600 (all manufactured by Nippon AEROSIL Co., Ltd.).

[0095] Examples of commercially available zirconium oxide fine particles include AEROSIL (registered trademark) R976 and R811 (each manufactured by Nippon AEROSIL Co., Ltd.).

[0096] Examples of the organic fine particles include fine particles containing silicone resin, fluororesin, acrylic resin, etc. Among them, the organic fine particles are preferably fine particles containing silicone resin, and particularly preferably fine particles containing silicone resin having a three-dimensional network structure.

[0097] Examples of commercially available silicone resin fine particles include Tospearl (registered trademark) 103, 105, 108, 120, 145, 3120, and 240 (all manufactured by Toshiba Silicone Corporation).

[0098] The average particle size of the primary particles of the microparticles is preferably in the range of 10 to 300 nm. The microparticles may also be included in the phase difference film as secondary agglomerates with a particle size in the range of 50 to 300 nm. Particles with an average particle size in the range of 100 to 400 nm are preferably not agglomerated but contained as primary particles.

[0099] The content of the fine particles in the second layer is preferably in the range of 0.01 to 5.0 mass %, more preferably in the range of 0.5 to 2.5 mass %, and even more preferably in the range of 0.7 to 2.0 mass %, relative to the total mass of the second layer.

[0100] (Other ingredients)

[0101] In addition to the above ingredients, the second layer may contain sugar esters, acrylic polymers, plasticizers, and the like.

[0102] [1-2. Layer 1 and Layer 3]

[0103] The first layer and the third layer contain acetyl cellulose and fine particles. The first layer and the third layer may contain other components. The compositions of the first layer and the third layer may be the same or different.

[0104] (Acetyl Cellulose)

[0105] The acetyl cellulose contained in the first layer and the third layer may be the same as or different from the acetyl cellulose contained in the second layer. The acetyl cellulose contained in the first layer and the third layer may be the same as or different from each other.

[0106] The degree of substitution of the acetyl cellulose contained in the first layer and the third layer is not particularly limited, but is preferably within the range of 2.0 to 2.6. This makes it easy to obtain a desired retardation value.

[0107] The content of acetyl cellulose in the first layer and the third layer is, for example, in the range of 60 to 95% by mass.

[0108] The content of the polyester having hydroxyl groups at both ends in the first layer is preferably in the range of 1 to 20% by mass, more preferably in the range of 5 to 15% by mass, relative to the content of the acetoacetate in the first layer.

[0109] The content of the polyester having hydroxyl groups at both ends in the third layer is preferably in the range of 1 to 20% by mass, more preferably in the range of 5 to 15% by mass, relative to the content of the acetoacetate in the third layer.

[0110] Other details about acetyl cellulose are as described above.

[0111] (particle)

[0112] By making the first layer and the second layer contain fine particles, the surface slip of the phase difference film is improved. In addition, by making the first layer and the second layer contain fine particles, when the phase difference films are overlapped, damage can be suppressed or the phase difference films can be closely adhered to each other.

[0113] The type of microparticles contained in the first layer and the third layer may be the same as or different from the type of microparticles contained in the second layer. The type of microparticles contained in the first layer and the third layer may be the same as or different from each other. It should be noted that the microparticles contained in the first layer and the third layer are preferably silica particles.

[0114] The degree of substitution of the acetyl cellulose contained in the first layer and the third layer is not particularly limited, but is preferably within the range of 2.0 to 2.6. This makes it easy to obtain a desired retardation value.

[0115] The content of the fine particles in the first layer is preferably in the range of 0.01 to 5.0 mass %, more preferably in the range of 0.05 to 1.0 mass %, and even more preferably in the range of 0.1 to 0.5 mass %, relative to the total mass of the first layer.

[0116] The content of the fine particles in the third layer is preferably in the range of 0.01 to 5.0 mass %, more preferably in the range of 0.05 to 1.0 mass %, and even more preferably in the range of 0.1 to 0.5 mass %, relative to the total mass of the third layer.

[0117] Other details about the microparticles are as described above.

[0118] (Polyester)

[0119] The first layer and the third layer may contain polyester. The polyester contained in the first layer and the third layer may be a polyester having hydroxyl groups at both terminals or may not be a polyester having hydroxyl groups at both terminals.

[0120] The types of polyesters contained in the first layer and the third layer may be the same or different. It should be noted that, like the polyester contained in the second layer, the polyesters contained in the first layer and the third layer are preferably polyesters having hydroxyl groups at both ends. In addition, the polyester is preferably a polyester having a structure represented by the above general formula (I).

[0121] By making the first layer and the third layer contain polyester having hydroxyl groups at both ends, the coordination of water and the hydrophilic group of acetyl cellulose can be suppressed in each of the first layer to the third layer. As a result, the fluctuation of the phase difference value of the phase difference film can be further suppressed, and the uneven contrast in the liquid crystal display device just taken out from a high humidity environment can be further suppressed.

[0122] The content of the polyester in the first layer is preferably in the range of 1 to 20% by mass, more preferably in the range of 5 to 15% by mass, relative to the content of the acetoacetate in the first layer.

[0123] The content of the polyester in the third layer is preferably in the range of 1 to 20% by mass, more preferably in the range of 5 to 15% by mass, relative to the content of the acetoacetate in the third layer.

[0124] (Other ingredients)

[0125] In addition to the above ingredients, the first layer and the third layer may contain sugar esters, acrylic polymers, plasticizers, and the like.

[0126] [1-3. Relationship of the content rate of fine particles]

[0127] In the phase difference film of the present invention, it is characterized in that the content rate [mass %] of the particles in the second layer is greater than the content rate [mass %] of the particles in the first layer and the third layer. When the content rate of particles in the first layer and the third layer is different, the content rate of particles in the second layer is greater than the content rate of particles in any one of the first layer and the third layer. Therefore, the present invention can increase the content rate of particles in the second layer on the basis of adjusting the content rate of particles in the first layer and the third layer by paying attention to the slip property. As a result, the present invention can maintain the slip property in a good range and suppress the phase difference value from being affected by water.

[0128] The content of the particles in the second layer is preferably in the range of 2 to 5 times the average content of the particles in the first and third layers. By being 2 times or more, the slip property can be maintained in a good range and the influence of water on the phase difference value can be further suppressed. By being 5 times or less, the haze will not be too high and the contrast of the liquid crystal display device will not be easily reduced.

[0129] [1-4. Phase difference value of phase difference film]

[0130] The retardation value Ro in the in-plane direction and the retardation value Rt in the thickness direction of the retardation film are defined by the following formulae, respectively.

[0131] Formula (i) Ro=(n x -n y )×d

[0132] Formula (ii) Rt={(n x +n y ) / 2-n z}×d

[0133] In the above formulas (i) and (ii), n x It represents the refractive index in the direction x where the refractive index is the largest in the film's in-plane direction. y It represents the refractive index in the direction y that is perpendicular to the direction x in the film's in-plane direction. z It represents the refractive index in the thickness direction z of the film. d[nm] represents the thickness of the retardation film.

[0134] The Ro of the retardation film when measured at 23°C and 55% RH with light of a wavelength of 589 nm is preferably in the range of 30 to 90 nm. The Rt of the retardation film when measured at 23°C and 55% RH with light of a wavelength of 589 nm is preferably in the range of 100 to 200 nm. By making Ro and Rt within the above range, light leakage when observing a liquid crystal display device having the retardation film of the present invention from an oblique direction is reduced.

[0135] Ro and Rt can be controlled by the composition of the retardation film, the stretching conditions during the production of the retardation film, and the like.

[0136] Ro and Rt can be measured using an automatic birefringence meter. Examples of the automatic birefringence meter include "Axo Scan (Axo Scan Mueller Matrix Polarimeter)" (manufactured by Axometrics).

[0137] [1-5. Method for producing phase difference film]

[0138] The method for producing the phase difference film may be a solution casting method or a melt casting method, among which the solution casting method is preferred.

[0139] The method for producing a film by the solution casting method includes, for example, the following steps.

[0140] (1) Process of preparing coatings for each layer

[0141] (2) Step of casting each layer of coating on a metal support

[0142] (3) Process of drying base film

[0143] (4) Step of peeling the film from the metal support

[0144] (5) Process of stretching or maintaining the width of the film

[0145] (6) Step of further drying the film

[0146] (7) Film winding process

[0147] (1) Process of preparing coatings for each layer

[0148] In this process, the required materials such as acetyl cellulose are dissolved or dispersed in a solvent to prepare the coating of each layer. The higher the content of acetyl cellulose in the coating, the less the drying load after casting on the metal support, and thus it is preferred. In addition, by not making the content of acetyl cellulose too high, the pressure load during filtration can be suppressed, and good filtration accuracy can be obtained. From these viewpoints, the content of acetyl cellulose in the coating is preferably in the range of 10 to 35 mass %, more preferably in the range of 15 to 25 mass %, relative to the total mass of the coating.

[0149] The solvent used in the preparation of the coating may be a single type or two or more types. From the viewpoint of production efficiency, it is preferred to mix a good solvent and a poor solvent for acetyl cellulose, and from the viewpoint of the solubility of acetyl cellulose, it is preferred to have more good solvent. Regarding the mixing ratio of the good solvent to the poor solvent, the good solvent is preferably in the range of 70 to 98% by mass, and the poor solvent is preferably in the range of 2 to 30% by mass. A solvent that dissolves acetyl cellulose alone is defined as a "good solvent", and a solvent that swells or does not dissolve when alone is defined as a "poor solvent".

[0150] As good solvent, there is no particular limitation, for example, organic halides (dichloromethane, etc.), dioxolanes, acetone, methyl acetate, methyl acetoacetate, etc. can be cited. Among them, dichloromethane or methyl acetate is preferred. As poor solvent, there is no particular limitation, for example, methanol, ethanol, n-butanol, cyclohexane, cyclohexanone, etc. can be cited.

[0151] The method for dissolving acetylcellulose when preparing the coating can be a known method. For example, when the heating method and the pressurizing method are combined, the coating can be heated above the boiling point under normal pressure. If the acetylcellulose is dissolved while the solvent is heated at a temperature above the boiling point under normal pressure and within a range where the solvent does not boil under pressure, the generation of blocky undissolved matter (gel or agglomerate) can be prevented. In addition, after the acetylcellulose is mixed with a poor solvent to make it wet or swell, a good solvent can be further added to dissolve it.

[0152] The pressurization method includes a method of pressurizing an inert gas such as nitrogen into the dissolution container, a method of increasing the vapor pressure of the solvent by heating, etc. Heating is preferably performed from the outside, and a jacketed device is preferred because temperature control is easy.

[0153] From the viewpoint of the solubility of acetyl cellulose, it is preferred that the heating temperature is high. In addition, by not making the heating temperature too high, the pressure load can be suppressed, and good productivity can be obtained. From these viewpoints, the heating temperature is preferably in the range of 45 to 120° C., more preferably in the range of 60 to 110° C., and more preferably in the range of 70 to 105° C. The pressure is adjusted so that the solvent does not boil at the set temperature.

[0154] As a method for dissolving acetyl cellulose, a cooling dissolution method can also be mentioned. By the cooling dissolution method, acetyl cellulose can be dissolved in a solvent such as methyl acetate.

[0155] It is also possible to use appropriate filter materials such as filter paper to filter the coating. From the viewpoint of removing insolubles, the absolute filtration accuracy of the filter material is smaller and more preferred. In addition, by not excessively reducing the absolute accuracy, the clogging of the filter material can be suppressed.

[0156] The coating can be prepared, for example, using a static mixer, an in-line mixer, etc. As a static mixer, a static mixer manufactured by Toray Engineering Co., Ltd. can be cited. As an in-line mixer, a Toray static in-line mixer (Hi-Mixer SWJ, manufactured by Toray Engineering Co., Ltd.) can be cited.

[0157] (2) Step of casting each layer of coating on a metal support

[0158] In this process, each layer of coating is cast on a continuously moving annular metal support. The method of casting each layer of coating is not particularly limited, and for example, a known co-casting method can be used. The metal support in the casting process is preferably a metal support with a mirror-finished surface. The metal support is preferably a stainless steel belt or a drum with a surface plated by a casting. The width of the casting is preferably in the range of 1 to 4 m, for example.

[0159] (3) Process of drying base film

[0160] In this process, the coating cast on the metal support is dried to form a base film. The surface temperature of the metal support is preferably above -50°C and less than the boiling point of the solvent. The higher the surface temperature, the faster the drying speed of the base film. In addition, by not making the surface temperature too high, the foaming of the base film can be prevented and good flatness of the film can be obtained. From these viewpoints, the surface temperature is preferably in the range of 0 to 40°C, more preferably in the range of 5 to 30°C. In addition, the base film can be gelled by cooling the metal support, and the film can be peeled off from the drum in a state containing a large amount of residual solvent.

[0161] As a method for controlling the temperature of the metal support, there is no particular limitation, and for example, a method of blowing warm air or cold air can be cited. In addition, a method of contacting warm water with the back side of the metal support can also be cited. Since the method using warm water can effectively transfer heat, the time for the temperature of the metal support to reach a certain value can be shortened. When using warm air, a wind with a temperature higher than the target temperature of the metal support can be used.

[0162] (4) Step of peeling the film from the metal support

[0163] In this process, the dried film is peeled off from the metal support. From the viewpoint of obtaining good planarity of the film, the residual solvent amount when peeling the film (base film) from the metal support is preferably in the range of 10 to 150 mass %. The residual solvent amount is more preferably in the range of 10 to 40 mass %, and more preferably in the range of 10 to 30 mass %. Here, the residual solvent amount is defined by the following formula.

[0164] Residual solvent amount [mass %] = {(M-N) / N} × 100

[0165] Wherein, M is the mass of the base film or film at any time, and N is the mass of the base film or film after heating at 115° C. for 1 hour.

[0166] (5) Process of stretching or maintaining the width of the film

[0167] In this process, the film with a large amount of residual solvent just after peeling is stretched or maintained in width. It is preferably stretched in the conveying direction (longitudinal direction), and further a tentering method is used in which both ends of the film are clamped with clamps. In addition, it is also possible to stretch in the conveying direction (longitudinal direction) and the width direction (transverse direction) at the same time.

[0168] In the longitudinal stretching, the peel tension is preferably 210 N / m or more, more preferably in the range of 220 to 300 N / m.

[0169] Through the stretching process, the refractive index of the film can be controlled, and the phase difference values ​​Ro and Rt can be controlled.

[0170] The final stretch ratio in the transport direction is preferably in the range of 1.0 to 2.0 times, more preferably in the range of 1.01 to 1.5 times. The final stretch ratio in the width direction is preferably in the range of 1.01 to 2.5 times, more preferably in the range of 1.05 to 2.0 times.

[0171] There is no particular restriction on the method of stretching the film. For example, as a stretching method, a method of applying a peripheral speed difference to a plurality of rollers and utilizing the roller peripheral speed difference to stretch the film in the longitudinal direction can be cited. As a stretching method, a method of fixing the two ends of the film with a clamp or a pin, expanding the interval between the clamp or the pin along the conveying direction, and stretching the film in the longitudinal direction can be cited. Similarly, a method of expanding the interval between the clamp or the pin along the width direction and stretching the film in the transverse direction can be cited. Similarly, a method of simultaneously expanding the interval between the clamp or the pin along the conveying direction and the width direction and stretching the film in both the longitudinal and transverse directions can be cited.

[0172] These stretching methods may also be used in combination. In addition, in the case of the tentering method, if the clamp portion is driven by a linear drive method, it can be stretched smoothly, and the risk of film breakage can be reduced.

[0173] The width retention or transverse stretching is preferably performed by a tentering method, which may be pin tentering or clip tentering.

[0174] If the fast axis or slow axis of the film exists in the film surface and the angle formed with the conveying direction is θ1, θ1 is preferably in the range of -0.5 to +0.5°, more preferably in the range of -0.3 to +0.3°, and more preferably in the range of -0.2 to +0.2°. This θ1 can be defined as an orientation angle. θ1 can be measured using an automatic birefringent meter "KOBRA-21ADH" (Prince Measuring Instruments). By making θ1 within the above range, high brightness can be obtained in the displayed image. In addition, light leakage can be suppressed or prevented, and colors can be faithfully reproduced in a color liquid crystal display device.

[0175] (6) Step of further drying the film

[0176] In this step, the peeled film is further dried. Drying can be performed after stretching or simultaneously. The residual solvent content of the dried film is preferably 1% by mass or less, more preferably 0.1% by mass or less, and more preferably 0.01% by mass or less.

[0177] The drying method is not particularly limited, and examples thereof include a roll drying method in which the film is dried by passing through a plurality of rolls alternately arranged vertically. Alternatively, the film may be dried while being stretched by the tentering method described above.

[0178] The method of drying the film is not particularly limited, and examples thereof include hot air, infrared rays, a heating roll, and microwaves. From the viewpoint of simplicity, the drying method is preferably hot air.

[0179] The drying temperature is preferably increased stepwise within a range of 40 to 200° C. From the viewpoint of dimensional stability, the drying temperature is more preferably within a range of 50 to 140° C.

[0180] (7) Film winding process

[0181] In this step, the processed film is wound into, for example, a roll.

[0182] [2. Polarizing plate and liquid crystal display device]

[0183] The polarizing plate and the liquid crystal display device of the present invention are characterized by comprising the above-mentioned retardation film of the present invention.

[0184] Figure 2 This is a cross-sectional view of one embodiment of a liquid crystal display device.

[0185] Figure 2 The liquid crystal display device 500 shown includes a liquid crystal panel 100 and a backlight 200. The liquid crystal panel 100 includes a first polarizing plate 50, a liquid crystal cell 60, and a second polarizing plate 70 in this order.

[0186] The first polarizing plate 50 is a polarizing plate located on the visible side, which is the opposite side to the backlight 200 side, in the liquid crystal display device 500. The second polarizing plate 70 is a polarizing plate located on the backlight 200 side in the liquid crystal display device 500.

[0187] The first polarizer 50 and the second polarizer 70 respectively include a first optical film 10, a polarizer 30, and a second optical film 20 in this order. In the first polarizer 50 and the second polarizer 70, the first optical film 10 is located on the side farther from the liquid crystal cell 60 than the second optical film 20. In the first polarizer 50 and the second polarizer 70, the second optical film 20 is located on the side closer to the liquid crystal cell 60 than the first optical film 10.

[0188] In the first polarizing plate 50 and the second polarizing plate 70, the phase difference film of the present invention can be used as the second optical film 20. Similarly, in the liquid crystal display device 500, the phase difference film of the present invention can be used as the second optical film 20. It should be noted that in the liquid crystal display device 500, as long as at least one of the second optical film 20 of the first polarizing plate 50 and the second optical film 20 of the second polarizing plate 70 is the phase difference film of the present invention, both of them do not need to be the phase difference film of the present invention.

[0189] The first optical film 10 is an optical film that functions as a protective film, a retardation film, and the like in the first polarizing plate 50 and the second polarizing plate 70. The first optical film 10 contains, for example, polyester, an ultraviolet absorber, and the like.

[0190] Polyester is preferably polyethylene terephthalate or polyethylene naphthalate. Polyethylene terephthalate and polyethylene naphthalate have large intrinsic birefringence, and it is relatively easy to obtain a high phase difference value even if the film is thinned. In particular, polyethylene naphthalate has a significant effect.

[0191] The ultraviolet absorber protects the liquid crystal display device 500 (especially the alignment film of the liquid crystal unit 60) from ultraviolet rays, thereby improving the durability of the liquid crystal display device 500. Examples of the ultraviolet absorber include cyclic iminoester ultraviolet absorbers, benzotriazole ultraviolet absorbers, benzophenone ultraviolet absorbers, salicylate ultraviolet absorbers, cyanoacrylate ultraviolet absorbers, and triazine ultraviolet absorbers. Among them, the ultraviolet absorber is preferably a cyclic iminoester ultraviolet absorber or a benzotriazole ultraviolet absorber. The content of the ultraviolet absorber is preferably in the range of 0.1 to 10% by mass relative to the total mass of the polyester.

[0192] The phase difference value Ro of the first optical film 10 in the in-plane direction relative to the light of wavelength 589nm under 23℃ and 55%RH environment is preferably within the range of 3000 to 30000nm. By making Ro above 3000nm, the interference color (the rainbow spot caused by the observation angle) when observing the first optical film 10 from an oblique direction can be reduced, and good visibility can be obtained. In addition, by making Ro below 30000nm, the thickness of the first optical film 10 can be reduced. Ro is preferably above 5000nm, more preferably above 8000nm, and more preferably above 10000nm.

[0193] The phase difference ratio (Ro / Rt) of the first optical film 10 is preferably in the range of 0.2 to 1.2, more preferably in the range of 0.5 to 1.0, and more preferably in the range of 0.6 to 1.0. By making the phase difference ratio (Ro / Rt) in the above range, the rainbow spots caused by the observation angle of the first optical film 10 can be reduced. The phase difference values ​​Ro and Rt can be controlled by the type of polyester, the stretching conditions during film production, etc.

[0194] The thickness of the first optical film 10 is preferably 5 μm or more, more preferably 10 μm or more, more preferably 15 μm or more, and particularly preferably 20 μm or more. By making the thickness of the first optical film 10 5 μm or more, the first optical film 10 can obtain good water resistance and mechanical strength. The thickness of the first optical film 10 is preferably 300 μm or less, more preferably 200 μm or less, more preferably 100 μm or less, and particularly preferably 40 μm or less. By making the thickness of the first optical film 10 100 μm or less, the first optical film 10 can have both thin film properties and visibility.

[0195] The polarizer 30 is an element that transmits only light with a fixed polarization plane. As the polarizer, for example, a polyvinyl alcohol-based polarizing film can be cited. The polyvinyl alcohol-based polarizing film includes a polarizing film obtained by dyeing a polyvinyl alcohol-based film with iodine and a polarizing film obtained by dyeing a dichroic dye.

[0196] The polarizer 30 can be produced by forming a film from a polyvinyl alcohol aqueous solution, uniaxially stretching the obtained film, and dyeing it. Alternatively, the film may be uniaxially stretched after dyeing and subjected to durability treatment with a boron compound or the like.

[0197] As polyvinyl alcohol, ethylene-modified polyvinyl alcohol described in Japanese Patent Application Publication No. 2003-248123, Japanese Patent Application Publication No. 2003-342322, etc. can be cited. In the ethylene-modified polyvinyl alcohol, the content of ethylene units is in the range of 1 to 4 mol%, the degree of polymerization is in the range of 2000 to 4000, and the degree of saponification is in the range of 99.0 to 99.99 mol%. Polyvinyl alcohol is preferably ethylene-modified polyvinyl alcohol having a hot water cutoff temperature in the range of 66 to 73° C. The polarizer 30 containing the ethylene-modified polyvinyl alcohol has excellent polarization performance and durability, less color unevenness, and is particularly preferably used in a large liquid crystal display device 500.

[0198] The thickness of the polarizer 30 is preferably in the range of 2 to 30 μm, more preferably in the range of 2 to 20 μm.

[0199] The first polarizing plate 50 and the second polarizing plate 70 may further include an adhesive layer (not shown) between the first optical film 10 and the polarizer 30 and between the polarizer 30 and the second optical film 20. The adhesive layer contains a cured product of an adhesive.

[0200] The first polarizer 50 and the second polarizer 70 can be made using a general method for polarizers. The first polarizer 50 and the second polarizer 70 can be made, for example, according to the following steps. The polarizer 30 is stretched. The polarizer 30 is immersed in an iodine solution. The first optical film 10 and the second optical film 20 are respectively subjected to a surface treatment on one side of the surface bonded to the polarizer 30. The surface treated surface of the first optical film 10 is bonded to at least one surface of the polarizer 30 using an adhesive. The surface treated surface of the second optical film 20 is bonded to the other surface of the polarizer 30 using an adhesive. The bonding is preferably performed in a direction in which the absorption axis of the polarizer 30 is orthogonal to the slow axis of the first optical film 10 and the second optical film 20. The adhesive is preferably an ultraviolet curing adhesive.

[0201] The liquid crystal cell 60 is not particularly limited and may be a general liquid crystal cell. The liquid crystal cell 60 has a layer structure of, for example, glass substrate / color filter / transparent electrode / alignment film / liquid crystal layer / alignment film / transparent electrode / TFT (Thin Film Transistor) / glass substrate in order from the first polarizer 50 side.

[0202] The first polarizer 50, the liquid crystal unit 60 and the second polarizer 70 may also be bonded via an adhesive layer (not shown). The adhesive layer is a layer formed, for example, using a double-sided tape, an ultraviolet curing adhesive, etc. As the double-sided tape, for example, a substrate-free tape "MO-3005C" (thickness 25 μm, manufactured by Lintech Co., Ltd.) can be cited. There is no particular limitation on the bonding method, and a known method can be used.

[0203] The backlight 200 is not particularly limited, and may be a general backlight. For example, the backlight 200 may be an LED backlight using a light emitting diode (LED).

[0204] The driving mode of the liquid crystal display device 500 of the present invention can be TN (twisted nematic) mode, STN (super twisted nematic) mode, IPS (in-plane switching) mode, OCB (optically compensated birefringence) mode, VA (vertical alignment) mode, HAN (hybrid alignment nematic) mode, etc. VA mode includes MVA (multi-domain vertical alignment) mode and PVA (patterned vertical alignment) mode. The phase difference film 20 of the present invention is particularly suitable for use in a VA mode liquid crystal display device 500.

[0205] Example

[0206] The present invention is specifically described below with reference to examples, but the present invention is not limited thereto. In the following examples, unless otherwise specified, the operation is carried out at room temperature (25° C.). In the following examples, unless otherwise specified, “%” and “parts” respectively mean “mass %” and “mass parts”.

[0207] [Production of Phase Difference Film (Second Optical Film)]

[0208] As the acetyl cellulose used in the preparation of the retardation film, acetyl cellulose having an acetyl group substitution degree of 1.8, 2.4, or 2.8 was used.

[0209] The polyester used in the preparation of the phase difference film is a polyester having hydroxyl groups at both ends and a polyester blocked at both ends. As the polyester having hydroxyl groups at both ends, a polyester obtained by reacting terephthalic acid, 2,6-naphthalene dicarboxylic acid and propylene glycol in a ratio of 1:1:3 is used. The molecular weight of the polyester having hydroxyl groups at both ends is 556. As the polyester blocked at both ends, a polyester obtained by reacting terephthalic acid, propylene glycol and benzoic acid in a ratio of 1:2:2 is used. The molecular weight of the polyester blocked at both ends is 490.

[0210] As fine particles used in the preparation of the retardation film, silica fine particles (AEROSIL R812, manufactured by Nippon AEROSIL Co., Ltd.) were used.

[0211] The following components were stirred and mixed in a mixer-dissolver for 50 minutes, and then dispersed in a high-pressure emulsifier (Manton-Gaulin) to prepare a fine particle dispersion (fine particle concentration: 11 mass %).

[0212] Microparticles: 11.0 parts by mass

[0213] Ethanol: 89.0 parts by mass

[0214] The following components were fully mixed in an in-line mixer (Toray static in-line mixer, Hi-Mixer SWJ, manufactured by Toray Engineering Co., Ltd.) to prepare a surface layer coating.

[0215] Dichloromethane: 300.0 parts by mass

[0216] Ethanol: 30.0 parts by mass

[0217] Acetyl cellulose (substitution degree: 2.4): 79.7 parts by mass

[0218] Polyester (both ends: hydroxyl groups): 19.9 parts by mass

[0219] Microparticle dispersion (microparticle concentration: 11 mass %): 3.6 parts by mass

[0220] The following components were fully mixed in an in-line mixer (Toray static in-line mixer, Hi-Mixer SWJ, manufactured by Toray Engineering Co., Ltd.) to prepare a core layer coating material.

[0221] Dichloromethane: 300.0 parts by mass

[0222] Ethanol: 30.0 parts by mass

[0223] Acetyl cellulose (substitution degree: 2.4): 79.5 parts by mass

[0224] Polyester (both ends: hydroxyl groups): 19.9 parts by mass

[0225] Microparticle dispersion (microparticle concentration: 11 mass %): 5.5 parts by mass

[0226] The coating for the surface layer, the coating for the core layer, and the coating for the surface layer are overlapped in this order, and the multi-layer co-casting is performed simultaneously. The coating for the core layer forms the second layer, and the coating for the surface layers on both sides thereof form the first layer and the third layer, respectively. Here, the casting amount of each coating is adjusted so that the thickness of the second layer after stretching is 30 μm, and the thickness of the first layer and the third layer are 3 μm, respectively. The solvent of the cast base film is evaporated on the casting belt until the residual solvent amount is about 30 mass%.

[0227] The film having a residual solvent content of about 30% by mass was peeled off from the casting belt, and the peeled film was stretched 35% in the width direction by a tenter while blowing hot air at 140°C.

[0228] Next, the film was transferred from the tenter conveyance to the roll conveyance, and the film was further dried at 120° C. Then, the film was wound up.

[0229] The retardation film of Example 1 was produced through the above operation.

[0230] In the preparation of the phase difference film of Example 1, the composition of each coating was appropriately changed so that the composition of the prepared phase difference film was as described in Table I and Table II, and the phase difference films of Examples 2 to 4 and Comparative Examples 1 to 5 were prepared in the same manner. In the "Both Ends" column of Table I and Table II, "OH" means that a polyester having hydroxyl groups at both ends is used. "End-capped" means that a polyester with both ends blocked is used.

[0231] [Table 1]

[0232] Table I

[0233]

[0234] [Table 2]

[0235] Table II

[0236]

[0237] The ratio (X / Y) of the content X [mass %] of the fine particles in the second layer to the average content Y [mass %] of the fine particles in the first and third layers in each retardation film is shown in Table III. The retardation of each retardation film is shown in Table III.

[0238] [Production of polarizing film]

[0239] Iodine was adsorbed on the stretched polyvinyl alcohol film to make a polarizer.

[0240] The phase difference film is subjected to the following saponification treatment. Prepare a 1.5 mol / L sodium hydroxide aqueous solution and keep it warm at 55°C. Prepare a 0.005 mol / L dilute sulfuric acid aqueous solution and keep it warm at 35°C. Immerse the phase difference film in the above sodium hydroxide aqueous solution for 2 minutes, and then immerse it in water to fully rinse the sodium hydroxide aqueous solution. Next, immerse it in the above dilute sulfuric acid aqueous solution for 1 minute, and then immerse it in water to fully rinse the dilute sulfuric acid aqueous solution. Next, fully dry the phase difference film at 120°C.

[0241] Next, the saponified phase difference film was attached to one side of the polarizer as the second optical film using a polyvinyl alcohol-based adhesive, and the transmission axis of the polarizer and the slow axis of the phase difference film were arranged in parallel.

[0242] A commercially available triacylated cellulose film (FUJITAC TD80UF, manufactured by Fujifilm Corporation) was subjected to the same saponification treatment as above.

[0243] Next, a saponified commercially available triacylated cellulose film was attached to the polarizer opposite to the retardation film attachment side using a polyvinyl alcohol adhesive. The transmission axis of the polarizer was arranged orthogonal to the slow axis of the first optical film (commercially available triacylated cellulose film).

[0244] Next, the laminate of the phase difference film, the polarizer, and the commercially available triacylated cellulose film was dried at 70° C. for 10 minutes or more. By the above operation, a polarizing plate was produced.

[0245] [Manufacturing of Liquid Crystal Display Device]

[0246] A 40-inch liquid crystal display (BRAVIA X1) made by SONY is prepared. Then, the two polarizing plates installed on both sides of the liquid crystal cell of the liquid crystal display are peeled off. Then, the polarizing plates made are respectively installed on both sides of the visible side and the backlight side of the liquid crystal cell to make a liquid crystal display device. At this time, in the polarizing plate configured on the visible side relative to the liquid crystal cell, the polarizing plate on the visible side is installed in a manner that the second optical film of the polarizer is located on the liquid crystal cell side and the first optical film is located on the visible side. In addition, in the polarizing plate configured on the backlight side relative to the liquid crystal cell, the polarizing plate on the backlight side is installed in a manner that the second optical film of the polarizer is located on the liquid crystal cell side and the first optical film is located on the backlight side.

[0247] [evaluate]

[0248] The liquid crystal display device prepared as above was stored at 23°C and 95% RH for 48 hours. The backlight of the stored liquid crystal display device was continuously turned on for 1 hour in an environment of 23°C and 55% RH, and then the front contrast ratio was measured. It should be noted that the front contrast ratio was measured according to the following steps.

[0249] (i) The front brightness of the display screen when the liquid crystal display device displays white (brightness measured from the normal direction of the display screen) was measured using EZ-Contrast 160D manufactured by ELDIM Co. Similarly, the front brightness of the display screen when the liquid crystal display device displays black was measured.

[0250] (ii) The ratio (B / A) of the front luminance B of the display screen when white is displayed to the front luminance A of the display screen when black is displayed is defined as the front contrast ratio.

[0251] As described above, the front contrast ratios of arbitrary 10 points on the display screen of the liquid crystal display device were measured.

[0252] The average contrast value was evaluated based on the average value of the 10-point front contrast values ​​obtained according to the following criteria. The evaluation results are shown in Table III.

[0253] A: The average front contrast ratio is above 6000.

[0254] B: The average value of the front contrast is 5500 or more and less than 6000.

[0255] C: The average value of the front contrast is 5000 or more and less than 5500.

[0256] D: The average front contrast ratio is less than 5000.

[0257] Furthermore, the maximum value of the front contrast having the largest difference from the average value among the obtained 10 points of front contrast was calculated. Then, the deviation (%) of the front contrast was calculated according to the following formula.

[0258] Deviation of front contrast (%) = {(maximum value of front contrast) - (average value of front contrast)} / (average value of front contrast) × 100

[0259] The contrast unevenness was evaluated based on the deviation of the front contrast according to the following criteria. The evaluation results are shown in Table III.

[0260] A: The deviation of the front contrast is less than 1%, and there is no unevenness.

[0261] B: The variation in front contrast is 1% or more and less than 5%, and the unevenness is small.

[0262] C: The variation in front contrast is 5% or more and less than 10%, and there is slight unevenness.

[0263] D: The variation in front contrast is 10% or more, and the unevenness is large.

[0264] [Table 3]

[0265] Table III

[0266]

[0267] In Comparative Example 4, the phase difference values ​​Ro and Rt did not reach the required level. In Comparative Example 5, when the phase difference film was wound, the slip property of the surface layer was too high, and winding deviation occurred.

[0268] From the above results, it was confirmed that the retardation film of the present invention can suppress uneven contrast in a liquid crystal display device immediately after being taken out from a high humidity environment.

Claims

1. A phase difference film, characterized in that: There are layer 1, layer 2 and layer 3 in sequence, The first layer, the second layer and the third layer all contain acetyl cellulose and microparticles. The degree of substitution of the acetyl group of the acetyl cellulose contained in the second layer is within the range of 2.0 to 2.6, The second layer further contains a polyester having hydroxyl groups at both ends, The content rate of the fine particles in the second layer is greater than the content rates of the fine particles in the first layer and the third layer, and the unit of the content rate is mass %.

2. The phase difference film according to claim 1, characterized in that: The content of the fine particles in the second layer is in the range of 2 to 5 times the average content of the fine particles in the first layer and the third layer, and the units of the content and the average content are mass %.

3. The phase difference film according to claim 1, characterized in that: The microparticles are silicon dioxide microparticles.

4. A polarizing plate, characterized in that: A phase difference film according to any one of claims 1 to 3 is provided.

5. A liquid crystal display device, characterized in that: A phase difference film according to any one of claims 1 to 3 is provided.

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