Polarizing plate, manufacturing method of polarizing plate and display device

Abstract

The objective of this invention is to provide a polarizing plate that suppresses color unevenness and contrast deviation caused by water content, a method for manufacturing the polarizing plate, and a display device. The solution is as follows: The polarizing plate of this invention is a polarizing plate sequentially comprising a first optical film, a polarizing element, and a second optical film. The first optical film contains polyester, and the second optical film contains polyester (I), polyester (II), and acetylated cellulose with an acetyl substitution degree in the range of 2.30 to 2.80.

Description

Technical Field

[0001] This invention relates to a polarizing plate, a method for manufacturing a polarizing plate, and a display device. More specifically, it relates to a polarizing plate that suppresses color unevenness and contrast deviation caused by moisture content. Prior Technology

[0002] In recent years, the operating environment for monitors (display devices) has become increasingly demanding. Furthermore, the need for larger monitors and improved display quality has driven up the demands on monitors. Consequently, the demand for polarizing plates used in display devices has also increased.

[0003] Typically, polarizing plates have a protective film or other functional film to protect the polarizing element or the polarizing plate itself.

[0004] Patent Document 1 discloses a liquid crystal display device with cellulose ester polarizing plate protective films A and B. However, when this liquid crystal display device is stored and used in a high humidity environment, or taken out of a high humidity environment and used immediately, uneven color occurs due to moisture. Furthermore, there is a problem with the contrast of the displayed image from this liquid crystal display device. [Previous Technical Documents] [Patent Literature]

[0005] [Patent Document 1] Korean Patent Publication No. 10-2017-0081024 Summary of the Invention

[0006] [The problem that the invention aims to solve]

[0007] The present invention is made in view of the above-mentioned problems / situations, and its solution is to provide a polarizing plate that suppresses color unevenness and contrast deviation caused by water content, a method for manufacturing the polarizing plate, and a display device. [Methods used to solve problems]

[0008] In order to solve the above-mentioned problems, the inventors investigated the causes of the problems and found that in a polarizing plate having a first optical film, a polarizing element and a second optical film in sequence, by making the first optical film contain polyester, the second optical film contain a specific polyester, and acetylated cellulose with an acetyl group substitution degree in the range of 2.30 to 2.80, the uneven color and contrast deviation caused by water content can be suppressed, thus completing the present invention. That is, the above-mentioned problems of the present invention are solved by the following means.

[0009] 1. A polarizing plate, comprising a first optical film, a polarizing element, and a second optical film sequentially thereof, characterized in that: The aforementioned first optical film contains polyester. The aforementioned second optical film contains a polyester represented by general formula (I), a polyester represented by general formula (II), and acetylated cellulose with a degree of acetyl substitution in the range of 2.30 to 2.80; General formula (I): T-(DP) nD General formula (II): T-(DP) nDT (In the aforementioned general formulas (I) and (II), T represents phenylcarboxylic acid residues, respectively; D represents an alkanediol residue with 2 to 12 carbon atoms, an aryldiol residue with 6 to 12 carbon atoms, or an oxyalkanediol residue with 4 to 12 carbon atoms, respectively. P represents alkane dicarboxylic acid residues with 4 to 12 carbon atoms, or aromatic dicarboxylic acid residues with 6 to 12 carbon atoms; n represents an integer greater than or equal to 1.

[0010] 2. The polarizing plate as described in item 1, wherein the content of polyester represented by the aforementioned general formula (II) is in the range of 70% to 90% by mass relative to the total mass of polyester represented by the aforementioned general formula (I) and polyester represented by the aforementioned general formula (II).

[0011] 3. The polarizing plate as described in item 1, wherein the polyester contained in the aforementioned first optical film is polyethylene terephthalate.

[0012] 4. The polarizing plate of item 1, wherein the aforementioned second optical film further contains an ester represented by the following general formula (III); General formula (III): TD.

[0013] 5. The polarizing plate as described in item 1, wherein the width of the aforementioned second optical film is in the range of 2.2 to 3.0 m.

[0014] 6. A method for manufacturing a polarizing plate, characterized in that the polarizing plate is manufactured as described in any one of items 1 to 5.

[0015] 7. A display device, characterized in that it comprises a polarizing plate as described in any one of claims 1 to 5, and The aforementioned second optical film system is disposed on the liquid crystal cell side. [Effects of the Invention]

[0016] By means of the present invention, a polarizing plate, a method for manufacturing a polarizing plate, and a display device can be provided that suppresses color unevenness and contrast deviation caused by water content.

[0017] While the mechanism of action or manifestation of the effects of this invention is not clear, it is speculated as follows.

[0018] The polarizing plate of the present invention is preferably included in a display device. In a display device equipped with the polarizing plate of the present invention, the first optical film is disposed on the outer side of the second optical film. Here, "outer side" refers to a position in the display device that is closer to the outside air. The second optical film is disposed on the liquid crystal cell that is closer to the first optical film.

[0019] In prior art, display devices stored in high humidity environments, when displaying monochrome images, often fail to produce uniform monochrome images, resulting in color unevenness. While the cause of this color unevenness is not fully understood, one possible reason is the in-plane non-uniformity of the phase difference value within the retardation film.

[0020] Acetyl cellulose films are commonly used as phase retardation membranes. However, in high humidity environments, water molecules readily coordinate with the hydrophilic groups (carbonyl and hydroxyl groups) of acetyl cellulose molecules, causing the phase difference value to fluctuate. Therefore, when a display device using an acetyl cellulose film as a phase retardation membrane is stored in a high humidity environment, its performance as a phase retardation membrane will degrade.

[0021] Large-scale display devices often incorporate large-area acetyl cellulose films. In high-humidity environments, due to their large size, the acetyl cellulose film cannot absorb moisture uniformly across its entire surface; the degree of moisture absorption is uneven throughout the surface. Consequently, the phase difference of the acetyl cellulose film becomes non-uniform across the entire surface, resulting in color inhomogeneity. In such display devices, if displaying monochrome images, color unevenness can be considered to occur.

[0022] Therefore, in display devices, it can be considered that by reducing the amount of water reaching the acetocellulose film, color unevenness caused by water content can be suppressed. Furthermore, it can be considered that even if water reaches the acetocellulose film, color unevenness caused by water content can be suppressed by preventing water molecules from co-locating to the carbonyl or hydroxyl groups of the acetocellulose molecules.

[0023] The first optical film contains polyester. Polyester has a higher proportion of hydrophobic sites in its chemical structure. Therefore, the first optical film does not readily absorb moisture, thus inhibiting moisture from entering the display device. Furthermore, it reduces the amount of water reaching the second optical film.

[0024] The second optical film contains acetylated cellulose with a degree of acetyl substitution ranging from 2.30 to 2.80. Furthermore, the second optical film contains polyesters represented by the above general formulas (I) and (II) as additives. In this specification, the polyesters represented by general formulas (I) and (II) are also referred to as "polyester (I)" and "polyester (II)" respectively.

[0025] Polyester (I) is composed of a monocarboxylic acid (T) and a glycol (D) at both ends. That is, unreacted hydroxyl groups are present at one end of polyester (I). This structure will be referred to below as "one-sided end-capped". On the other hand, polyester (II) is composed of monocarboxylic acids (T) at both ends. That is, unreacted carboxyl or hydroxyl groups are absent at both ends of polyester (II). This structure will be referred to below as "two-sided end-capped".

[0026] Polyesters (I) and (II) are composed of monocarboxylic acid (T), diol (D), and dicarboxylic acid (P). In the monocarboxylic acid (T), diol (D), and dicarboxylic acid (P) of this invention, the sites other than the carboxyl and hydroxyl groups exhibit hydrophobicity. Therefore, polyesters (I) and (II) are hydrophobic compounds. By adding hydrophobic compounds to acetylcellulose films, the overall hydrophobicity of the film is increased, making it less prone to moisture absorption.

[0027] The single-ended polyester (I) has a hydroxyl group at one end, which acts as a hydrophilic group. This hydroxyl group interacts with water molecules entering the film. Before interacting with the carbonyl or hydroxyl groups of the acetylated cellulose molecules, the water molecules interact with the hydroxyl group of the polyester (I), thus inhibiting the interaction between the acetylated cellulose molecules and water molecules. This suppresses fluctuations in the phase difference of the film.

[0028] From the perspective of improving the hydrophobicity of the film, it is preferable to add polyester (II) to both ends. However, even with the addition of polyester (II), it is difficult to completely prevent moisture from entering the film. Therefore, by also adding polyester (I), even if moisture enters the film, the interaction between water molecules and acetylated cellulose can be suppressed. In other words, by using polyester (I) and (II) in combination, the phase difference of the film caused by the interaction between water molecules and acetylated cellulose can be sufficiently suppressed. As a result, it can be considered that color unevenness caused by water content can be suppressed.

[0029] Furthermore, by adding polyesters (I) and (II), the intermolecular distance of acetylcellulose increases, and the intermolecular forces weaken. In other words, a plastic effect is produced. Therefore, in the manufacturing step of the second optical film, the entire film can be stretched uniformly, and the fast or slow axis of the film becomes uniform. As a result, it can be considered that deviations in in-plane contrast can be suppressed. Moreover, polyester (I) also produces a sufficient plastic effect, but polyester (II) produces an even higher plastic effect. By using polyesters (I) and (II) in combination, a high plastic effect can be considered to be obtained.

[0030] In other words, from the perspective of improving the hydrophobicity and plasticity of the film, it is considered better to add only polyester (II). However, by combining polyester (I), the variation in the phase difference of the film can be effectively suppressed. As a result, it can be considered that color unevenness and contrast deviation caused by water content can be suppressed, and the visual recognition in the display device can be further improved. Simple Explanation of the Diagram

[0031] [Figure 1] Cross-sectional view of the basic layer structure of a polarizing plate. [Figure 2] is a schematic diagram showing an example of the configuration of a display device. [Figure 3] Explanation of the measurement points in the evaluation of the deviation of the comparison. Implementation

[0032] The polarizing plate of the present invention is a polarizing plate having a first optical film, a polarizing element and a second optical film in sequence. The first optical film contains polyester, and the second optical film contains polyester represented by the above general formula (I), polyester represented by the above general formula (II), and acetylated cellulose with a degree of substitution of acetyl groups in the range of 2.30 to 2.80. This feature is a technical feature common to or corresponding to the following embodiments.

[0033] As an embodiment of the present invention, from the viewpoint of improving the hydrophobicity of the second optical film and suppressing color unevenness, the content of polyester represented by the aforementioned general formula (II) is preferably in the range of 70 to 90% by mass relative to the total mass of the polyester represented by the aforementioned general formula (I) and the polyester represented by the aforementioned general formula (II).

[0034] As an embodiment of the present invention, from the viewpoint of reducing the moisture reaching the second optical film and suppressing color unevenness, the polyester contained in the aforementioned first optical film is preferably polyethylene terephthalate.

[0035] As an embodiment of the present invention, from the viewpoint of preventing water molecules from coordinating with the hydrophilic group of acetylated cellulose molecules and suppressing uneven color, the aforementioned second optical film preferably further contains an ester represented by the above general formula (III).

[0036] As an embodiment of the present invention, the width of the aforementioned second optical film is preferably in the range of 2.2 to 3.0 m, which can achieve a high level of uniformity in extension and productivity while suppressing contrast deviation.

[0037] The method for manufacturing a polarizing plate according to the present invention is characterized by manufacturing the aforementioned polarizing plate.

[0038] The display device of the present invention is characterized by having the aforementioned polarizing plate, and the aforementioned second optical film system being disposed on the side of the liquid crystal cell.

[0039] The present invention and its constituent elements are described in detail below, as well as the forms and embodiments for implementing the present invention. Furthermore, in this case, "~" is used to indicate the lower and upper limits of the values ​​recorded before and after it.

[0040] 1. Overview of Polarizing Plates The polarizing plate of the present invention is a polarizing plate having a first optical film, a polarizing element and a second optical film in sequence. The first optical film contains polyester, and the second optical film contains polyester represented by the following general formula (I), polyester represented by the following general formula (II), and acetylated cellulose with a degree of substitution of acetyl in the range of 2.30 to 2.80.

[0041] General formula (I): T-(DP) nD General formula (II): T-(DP) nDT

[0042] (In the aforementioned general formulas (I) and (II), T represents phenylcarboxylic acid residues, respectively.) D represents an alkanediol residue with 2 to 12 carbon atoms, an aromatic diol residue with 6 to 12 carbon atoms, or an oxyalkanediol residue with 4 to 12 carbon atoms, respectively. P represents an alkyl dicarboxylic acid residue with 4 to 12 carbon atoms, or an aromatic dicarboxylic acid residue with 6 to 12 carbon atoms.

[0043] Figure 1 is a cross-sectional view of the basic layer structure of a polarizing plate. The polarizing plate 1 sequentially comprises a first optical film 2, a polarizing element 4, and a second optical film 5. The polarizing plate 1 may also have any additional layers as needed. For example, other layers may be present between the first optical film 2 and the polarizing element 4. Furthermore, other layers may be present between the polarizing element 4 and the second optical film 5.

[0044] The first optical film, the second optical film, and the polarizing element constituting the polarizing plate of the present invention will be described below. The polarizing plate of the present invention may also have other known functional layers.

[0045] 2. First optical film The first optical film of this invention contains polyester. Furthermore, the polyester referred to here is the polyester resin used as a raw material for the film. The first optical film may also contain known additives such as ultraviolet absorbers, as needed.

[0046] The first optical film of this invention can be a single-layer structure or a multi-layer structure. It is particularly preferred to be a multi-layer structure with three or more layers, and the middle layer contains an ultraviolet absorber.

[0047] From the viewpoint of adhesion to polarizing elements, the first optical film preferably has an easy-bond layer on at least one side. The easy-bond layer is preferably composed of at least one of polyester resin, polyurethane resin, or polyacrylic resin as its main component. Here, "main component" refers to a component that accounts for 50% or more by mass of the solid components constituting the easy-bond layer.

[0048] (1) Polyester Polyester, as a raw material resin, has excellent transparency, as well as excellent thermal and mechanical properties. Furthermore, the hysteresis value of polyester can be easily controlled through stretching processing.

[0049] Polyesters, particularly polyethylene terephthalate (PET) and polyethylene naphthalate (PAN), are preferred. Both PET and PAN have inherently high birefringence, making it relatively easy to obtain high hysteresis values ​​even in thin films. PAN, in particular, shows a significant effect.

[0050] Polyesters are obtained by condensing any dicarboxylic acid with a diol. Examples of dicarboxylic acids include terephthalic acid, isophthalic acid, phthalic acid, 2,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, diphenylcarboxylic acid, diphenoxyethanedicarboxylic acid, diphenylcarboxylic acid, anthracenedicarboxylic acid, 1,3-cyclopentanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, hexahydroterephthalic acid, hexahydroisophthalic acid, malonic acid, dimethylmalonic acid, succinic acid, 3,3-diethylsuccinic acid, glutaric acid, 2,2-dimethylglutaric acid, adipic acid, 2-methyl adipic acid, trimethyl adipic acid, pimelic acid, azelaic acid, dimeric acid, sebacic acid, octanoic acid, and dodecanoic acid.

[0051] Examples of glycols include ethylene glycol, propylene glycol, hexamethylene glycol, neopentyl glycol, 1,2-cyclohexanediethanol, 1,4-cyclohexanediethanol, decamethylethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 2,2-bis(4-hydroxyphenyl)propane, and bis(4-hydroxyphenyl)benzene. The dicarboxylic acid component and the diol component may each contain one or more of them.

[0052] The resulting polyester may include, for example, polyethylene terephthalate (PET), polyethylene terephthalate, polyethylene terephthalate, and polyethylene naphthalate (PEN). Polyethylene terephthalate or polyethylene naphthalate is particularly preferred, and polyethylene terephthalate is even more preferred.

[0053] Polyesters may also contain other copolymer components. From the viewpoint of mechanical strength, the proportion of copolymer components is preferably 3 mol% or less, more preferably 2 mol% or less, and even more preferably 1.5 mol% or less.

[0054] (2) Ultraviolet absorbers The first optical film preferably contains an ultraviolet absorber. By containing an ultraviolet absorber, the display device can be protected from ultraviolet radiation, resulting in excellent weather resistance. In particular, it can protect the alignment film of the liquid crystal cell from ultraviolet radiation.

[0055] Ultraviolet absorbers, such as cyclic imine esters, benzotriazoles, benzophenones, salicylates, cyanoacrylates, and triazines, are examples of such absorbers.

[0056] Cyclic imine esters are ultraviolet absorbers, such as 2,2'-(1,4-phenyl)bis(4H-3,1-benzoxazinone-4-one), 2-methyl-3,1-benzoxazinone-4-one, 2-butyl-3,1-benzoxazinone-4-one, 2-phenyl-3,1-benzoxazinone-4-one, etc.

[0057] Benzotriazole is a type of ultraviolet (UV) absorber, such as 5-chloro-2-(3,5-di-sec-butyl-2-hydroxyphenyl)-2H-benzotriazole. Other benzotriazole UV absorbers include (2-2H-benzotriazole-2-yl)-6-(linear and side-chain dodecyl)-4-methylphenol. Commercially available benzotriazole UV absorbers include the TINUVIN (registered trademark) series, such as "TINUVIN (registered trademark) 109, 171, 234, 326, 327, 328, 928" (all manufactured by BASF).

[0058] Benzophenone is a type of ultraviolet absorber, such as 2-hydroxy-4-benzyloxybenzophenone, 2,4-benzyloxybenzophenone, 2,2'-dihydroxy-4-methoxybenzophenone, 2-hydroxy-4-methoxy-5-sulfobenzophenone, and bis(2-methoxy-4-hydroxy-5-benzylphenylmethane).

[0059] Salicylic acid esters are ultraviolet absorbers, such as phenyl salicylate and p-tert-butyl salicylate. Cyanoacrylates are ultraviolet absorbers, such as 2'-ethylhexyl-2-cyano-3,3-diphenyl acrylate and ethyl-2-cyano-3-(3',4'-methylenedioxyphenyl)-acrylate.

[0060] Triazine-based ultraviolet absorbers, such as 2-(2'-hydroxy-4'-hexyloxyphenyl)-4,6-diphenyltriazine, are examples. Commercially available triazine-based ultraviolet absorbers include, for example, "TINUVIN (registered trademark) 477" (manufactured by BASF).

[0061] Among them, cyclic imine ester-based ultraviolet absorbers or benzotriazole-based ultraviolet absorbers are preferred.

[0062] The content of the ultraviolet absorber, relative to the total mass of the polyester, is preferably in the range of 0.1% to 10% by mass. Sufficient weather resistance of the film can be obtained by setting the content at 0.1% by mass or more. Sufficient transparency of the film can be obtained by setting the content at 10% by mass or less. More preferably, the content of the ultraviolet absorber, relative to the total mass of the polyester, is in the range of 0.5% to 10% by mass, and even more preferably in the range of 1.5% to 5% by mass.

[0063] (3) Manufacturing method of the first optical film The first optical film can be manufactured using known methods. Specifically, firstly, polyester is melted and extruded into a sheet. Then, the unaligned polyester film is stretched longitudinally at a temperature above its glass transition temperature using a speed difference in rollers. Afterward, the polyester film is stretched transversely using a tenter frame, subjected to heat treatment, and relaxed as needed. This yields a stretched polyester film (the first optical film). The stretched polyester film can be a uniaxially stretched film or a biaxially stretched film.

[0064] The manufacturing conditions for obtaining the polyester film can be appropriately set according to known methods. For example, the longitudinal stretching temperature and the transverse stretching temperature are, for example, in the range of 80~130°C, preferably in the range of 90~120°C. The longitudinal stretching ratio is, for example, in the range of 1.0~3.5 times, preferably in the range of 1.0 times~3.0 times. Furthermore, the transverse stretching ratio is, for example, in the range of 2.5~6.0 times, preferably in the range of 3.0~5.5 times.

[0065] Hysteresis can be controlled by appropriately setting the stretch ratio, stretching temperature, or film thickness. For example, the higher the difference between the stretch ratios of longitudinal and transverse stretching, the lower the stretching temperature, and the thicker the film, the easier it is for the hysteresis value to increase. Conversely, the lower the difference between the stretch ratios of longitudinal and transverse stretching, the higher the stretching temperature, and the thinner the film, the easier it is for the hysteresis value to decrease.

[0066] Furthermore, the higher the elongation temperature and the lower the total elongation, the easier it is to reduce the ratio of hysteresis to thickness hysteresis (Ro / Rth). Conversely, the lower the elongation temperature and the higher the total elongation, the easier it is to increase the ratio of hysteresis to thickness hysteresis (Ro / Rth). Details regarding hysteresis will be discussed later. The heat treatment temperature is, for example, in the range of 140~240℃, preferably in the range of 170~240℃.

[0067] The relaxation treatment temperature is, for example, in the range of 100~230℃, preferably in the range of 110~210℃, and more preferably in the range of 120~180℃. Furthermore, the relaxation amount is, for example, in the range of 0.1~20%, preferably in the range of 1~10%, and more preferably in the range of 2~5%. The relaxation treatment temperature and relaxation amount are preferably set such that the heat shrinkage rate of the polyester film after relaxation treatment at 150℃ is less than 2%.

[0068] In both uniaxial and biaxial extension processes, heat treatment or further extension can be performed after lateral extension. This helps to mitigate deformation of the alignment principal axis, such as bowing. The maximum deformation of the alignment principal axis in the extension direction caused by bowing is preferably within 30˚, more preferably within 15˚, and even more preferably within 8˚. By ensuring that the maximum deformation of the alignment principal axis is within 30˚, the optical characteristics among the leaflets can be made uniform during the subsequent fabrication of the polarizing plate.

[0069] Here, "alignment principal axis" refers to the direction of molecular alignment at any point on the extended polyester film. Furthermore, the deformation of the alignment principal axis relative to the extension direction refers to the angular difference between the alignment principal axis and the extension direction. More specifically, its maximum value refers to the maximum value in the direction perpendicular to the length direction. The alignment principal axis can be measured, for example, using a phase retardation film and optical material inspection device "RETS" (manufactured by Otsuka Electronics Co., Ltd.), or a molecular alignment meter "MOA" (manufactured by Oji Measurement & Testing Co., Ltd.).

[0070] From the perspective of suppressing variations in hysteresis values, a smaller film thickness unevenness is preferable. However, when aiming to impart a difference in hysteresis values ​​to achieve a low longitudinal elongation ratio, the longitudinal thickness unevenness tends to increase. The longitudinal thickness unevenness is very high within a certain range of elongation ratios. Therefore, it is preferable to set the film-forming conditions so that the longitudinal thickness unevenness falls outside this specific range. Hereinafter, longitudinal thickness unevenness will be referred to simply as "thickness unevenness".

[0071] The thickness unevenness is preferably below 5.0%, more preferably below 4.5%, even more preferably below 4.0%, and best of all below 3.0%.

[0072] Thickness unevenness can be measured by any means. For example, a continuous tape sample (3m in length) in the flow direction of the film can be taken. Then, using a commercially available measuring instrument, the thickness is measured at 100 points at 1cm intervals, and the maximum (d max), minimum (d min), and average (d) thickness are obtained. The thickness unevenness [%] can be calculated using the following formula. Commercially available measuring instruments include, for example, the electronic micrometer "Millitron 1240" (manufactured by Seiko EM Co., Ltd.). (Formula) Thickness unevenness [%] = ((d max - d min) / d) × 100

[0073] The thickness of the extended polyester film is not particularly limited. For example, the thickness is in the range of 15 to 300 μm, preferably in the range of 30 to 200 μm, and even more preferably in the range of 60 to 80 μm. By being within the above range, both thin-film properties and visual legibility can be taken into account.

[0074] The method for incorporating ultraviolet absorbers can be a known one. For example, a masterbatch can be prepared by pre-mixing the dried ultraviolet absorber with polyester raw materials using a compounding extruder. Then, methods for mixing specific masterbatches with polyester raw materials during film production can be listed. Furthermore, the term "masterbatch" here refers to that obtained by high-concentration blending and compounding of the added ultraviolet absorber. By using masterbatch, the amount of ultraviolet absorber added can be accurately adjusted.

[0075] From the perspective of ensuring uniform dispersion of the UV absorber, the content of the UV absorber is preferably in the range of 5% to 30% by mass relative to the total mass of the masterbatch. The masterbatch is preferably produced using a compounding extruder. The extrusion temperature is set above the melting point of the polyester raw material and below 290°C, preferably within the range of 1 to 15 minutes. By keeping the extrusion temperature below 290°C, the reduction of the UV absorber can be suppressed, and the decrease in the viscosity of the masterbatch can also be suppressed. Furthermore, by extruding for more than 1 minute, the UV absorber can be uniformly dispersed. Stabilizers, color modifiers, antistatic agents, etc., can also be added to the masterbatch as needed.

[0076] A multilayer film with three or more layers containing ultraviolet absorbers can be manufactured by the following method. For the outer layer, polyester granules are fed separately to a known melt-layer extruder. For the intermediate layer, a masterbatch containing ultraviolet absorbers is mixed with polyester granules in a specific ratio, dried, and then fed to a known melt-layer extruder. The mixture is extruded through a slit die into a sheet shape, cooled and solidified on a casting roll to obtain an unstretched film. That is, two or more extruders and a three-layer manifold or confluence block (e.g., a confluence block with a square confluence section) are used. Then, the film layers constituting the two outer layers and the film layer constituting the intermediate layer are laminated, and three-layer sheets are extruded from the interface tube and cooled and solidified on a casting roll.

[0077] From the perspective of removing foreign matter contained in polyester raw materials, high-precision filtration is preferable during melt extrusion. The filter media used for high-precision filtration preferably has a particle size (initial filtration efficiency 95%) of 15 μm or less. By ensuring the filter media has a particle size of 15 μm or less, foreign matter larger than 20 μm can be effectively removed.

[0078] Easy-adhesive layers can be formed using the following methods. The coating liquid used to form the easy-adhesive layer is preferably an aqueous coating liquid containing at least one of a water-soluble or water-dispersible copolymer polyester resin, acrylic resin, and polyurethane resin. Such coating liquids can be referenced, for example, Japanese Patent Nos. 3567927, 3589232, 3589233, 3900191, and 4150982.

[0079] The easy-adhesive layer can be obtained by applying a coating liquid to one or both sides of a uniaxially stretched film in the longitudinal direction, drying it at 100-150°C, and then further stretching it in the transverse direction. The final coating amount of the easy-adhesive layer is preferably in the range of 0.05-0.20 g / m². By using a coating amount of 0.05 g / m² or more, sufficient adhesion to polarizing components can be obtained. By using a coating amount of 0.20 g / m² or less, sufficient anti-blocking properties can be obtained. When the easy-adhesive layer is applied to both sides of the polyester film, the coating amounts of the easy-adhesive layer on both sides can be the same or different. The coating amount of the easy-adhesive layer on each side can be set within the above-mentioned range.

[0080] From the perspective of slip resistance, the easy-bonding layer preferably contains particles. The average particle size of these microparticles is preferably 2 μm or less. By ensuring the average particle size is 2 μm or less, the particles are less likely to detach from the easy-bonding layer. Examples of particles include inorganic particles such as titanium dioxide, barium sulfate, calcium carbonate, calcium sulfate, silicon dioxide, alumina, talc, kaolin, clay, calcium phosphate, mica, hydropyrite, zirconium oxide, tungsten oxide, lithium fluoride, and calcium fluoride. Other particles include organic particles such as styrene-based, acrylic-based, melamine-based, benzoguanamine-based, and polysiloxane-based particles. These can be a single type or two or more types.

[0081] The method for applying the coating liquid can be any known method. Examples of coating methods include, for instance, reverse roller coating, gravure coating, coincidence coating, roller brush coating, spray coating, air knife coating, wire rod coating, and tube doctor blade coating. One of these methods can be used alone, or two or more can be used in combination.

[0082] The average particle size of the above particles can be determined by the following method. The particles were photographed using a scanning electron microscope (SEM). The maximum diameter (distance between two furthest points) of 300-500 particles was measured at magnifications ranging from 2 to 5 mm, with the smallest particle being the smallest. The arithmetic mean of these diameters was taken as the average particle size.

[0083] (4) Physical properties of the first optical film (4.1) Hysteresis value The hysteresis values ​​Ro and Rth of the first optical film are defined by the following formulas. Equation (i) Ro=(n xn y)×d Formula (ii) Rth={(n x+ny) / 2-nz}×d (In equations (i) and (ii) above, nx represents the refractive index in the in-plane direction of the thin film, in the direction of maximum refractive index x. ny represents the refractive index in the in-plane direction of the thin film, in the direction of refractive index y, which is perpendicular to the direction x. nz represents the refractive index in the thickness direction z of the thin film. d[nm] represents the thickness of the thin film).

[0084] The in-plane hysteresis value Ro of the first optical film for light with a wavelength of 589 nm at 23°C and 55% RH is preferably in the range of 3000~30000 nm. By having Ro above 3000 nm, interference colors (rainbow patterns depending on the viewing angle) when observing the first optical film from an oblique angle can be reduced, resulting in good visual discernibility. Furthermore, by having Ro below 30000 nm, the film thickness can be reduced. Ro is preferably above 5000 nm, more preferably above 8000 nm, and even more preferably above 10000 nm.

[0085] The hysteresis ratio (Ro / Rth) is preferably in the range of 0.2 to 1.2, more preferably in the range of 0.5 to 1.0, and even more preferably in the range of 0.6 to 1.0. By keeping the ratio within these ranges, rainbow patterns that occur depending on the viewing angle of the film can be reduced. Furthermore, the hysteresis values ​​Ro and Rth can be controlled by the type of polyester or the stretching conditions during film manufacturing.

[0086] The hysteresis values ​​Ro and Rth for light with a wavelength of 589 nm can be measured using an automatic birefringence meter at an environment of 23°C and 55%RH. Examples of automatic birefringence meters include the "Axo Scan (Axo Scan Mueller Matrix Polarimeter)" (manufactured by Axomatrix).

[0087] (4.2) Thickness The thickness of the first optical film is preferably 5 μm or more, more preferably 10 μm or more, even more preferably 15 μm or more, and particularly preferably 20 μm or more. A thickness of 5 μm or more provides good water resistance and mechanical strength. Furthermore, the thickness of the first optical film is preferably 300 μm or less, more preferably 200 μm or less, even more preferably 100 μm or less, and particularly preferably 40 μm or less. A thickness of 100 μm or less balances thinness and visual clarity.

[0088] (5) Other functional layers The extended polyester film may have functional layers with various properties on at least one side. Examples of such functional layers include, for instance, a hard coating layer, an anti-glare layer, an anti-reflective layer, a low-reflection layer, a low-reflection anti-glare layer, an anti-reflective anti-glare layer, an antistatic layer, a polysiloxane layer, an adhesive layer, an anti-fouling layer, a fingerprint-resistant layer, a water-repellent layer, and a blue light filtering layer. This can further improve the appearance of uneven color when viewed from an oblique angle. Preferably, the functional layer is an anti-glare layer, an anti-reflective layer, a low-reflection layer, a low-reflection anti-glare layer, or an anti-reflective anti-glare layer.

[0089] When setting various functional layers, it is preferable to set an easy-bond layer on the surface of the extended polyester film. In this case, from the viewpoint of suppressing interference caused by reflected light, the refractive index of the easy-bond layer is preferably adjusted to be close to the geometric mean of the refractive indices of the functional layers and the extended polyester film. The refractive index of the easy-bond layer can be adjusted using known methods. For example, since the adhesive resin of the easy-bond layer contains titanium, zirconium, or other metals, the refractive index can be easily adjusted.

[0090] The coating liquid used to form the easy-adhesive layer preferably contains at least a water-soluble or water-dispersible copolymer polyester, acrylic resin, or polyurethane. Examples of coating liquids include water-soluble or water-dispersible copolymer polyester solutions, acrylic resin solutions, and polyurethane solutions described in Japanese Patent Publication No. 6-81714, Japanese Patent Publication No. 3200929, Japanese Patent Publication No. 3632044, Japanese Patent Publication No. 4547644, Japanese Patent Publication No. 4770971, Japanese Patent Publication No. 3567927, Japanese Patent Publication No. 3589232, Japanese Patent Publication No. 3589233, Japanese Patent Publication No. 3900191, and Japanese Patent Publication No. 4150982.

[0091] 3. Second optical film The second optical film of the present invention contains polyester (I), polyester (II), and acetylated cellulose with a degree of acetyl substitution in the range of 2.30 to 2.80.

[0092] (1) Polyester additives The second optical film of the present invention contains polyester (I) and (II). Hereinafter, polyester (I) and (II) will also be referred to together as "polyester additive". By containing polyester additive, the second optical film can suppress color unevenness and contrast deviation caused by water content in the polarizing plate.

[0093] (1.1) Structure of polyester additives Polyesters (I) and (II) are represented by the following general formulas (I) and (II). General formula (I): T-(DP) nD General formula (II): T-(DP) nDT

[0094] In general formulas (I) and (II), T represents a phenylcarboxylic acid residue, respectively. D represents an alkanediol residue with 2 to 12 carbon atoms, an aromatic diol residue with 6 to 12 carbon atoms, or an oxyalkanediol residue with 4 to 12 carbon atoms, respectively. P represents an alkyl dicarboxylic acid residue with 4 to 12 carbon atoms, or an aromatic dicarboxylic acid residue with 6 to 12 carbon atoms. n represents an integer greater than or equal to 1.

[0095] In the repeating structure of general formula (I), all n Ds and Ps can be of the same structure or can be of different structures. In the repeating structure of general formula (II), all n Ds and Ps can be of the same structure or can be of different structures. In general formula (I), the D in the repeating structure and the D at the end can have the same structure or different structures. In general formula (II), the D in the repeating structure and the D at the end can have the same structure or different structures. In general formula (II), the T at both ends can be of the same structure or different structures.

[0096] In general formula (I), T, D, and P can have the same or different structures as in general formula (II). Similarly, in general formula (I), n can have the same or different values ​​as in general formula (II). However, the structure of polyester (I) is preferably the same as that of polyester (II) except for the end (T) on one side. By making the structures of polyester (I) and polyester (II) similar, their compatibility is improved, and the effects of this invention can be significantly achieved.

[0097] In this invention, the term "residue" in phenylcarboxylic acid residue, alkyldiol residue, aromatic diol residue, oxyalkyldiol residue, alkyldicarboxylic acid residue, and aromatic dicarboxylic acid residue refers to the structure of the remaining part in the molecular formula, excluding the lost hydroxyl or hydrogen atom, for example, by forming an ester from phenylcarboxylic acid, alkyldiol, etc. That is, when a monocarboxylic acid is represented by "R-COOH", the monocarboxylic acid residue is represented by "R-CO-". When a dicarboxylic acid is represented by "HOOC-R-COOH", the dicarboxylic acid residue is represented by "-OC-R-CO-". When a diol is represented by "HO-R-OH", the diol residue is represented by "-ORO-" or "-OR-OH".

[0098] T represents the phenylcarboxylic acid residue. Examples of phenylcarboxylic acids include o-toluic acid, m-toluic acid, p-toluic acid, benzoic acid, p-tert-butylbenzoic acid, dimethylbenzoic acid, ethylbenzoic acid, n-propylbenzoic acid, aminobenzoic acid, and acetoxybenzoic acid. Toluic acid is particularly preferred among these. These may contain only one type or two or more types.

[0099] D represents an alkanediol residue with 2 to 12 carbon atoms, an aromatic diol residue with 6 to 12 carbon atoms, or an oxyalkanediol residue with 4 to 12 carbon atoms, respectively.

[0100] Alkanediols with 2 to 12 carbon atoms include, for example, ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,2-propanediol, 2-methyl-1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 2,2-dimethyl-1,3-propanediol (neopentanediol), and 2,2-diethyl-1,3-propanediol (3,3... 2-(3,3-dihydroxymethylpentane), 2-n-butyl-2-ethyl-1,3-propanediol (3,3-dihydroxymethylheptane), 3-methyl-1,5-pentanediol, 1,6-hexanediol, 2,2,4-trimethyl-1,3-pentanediol, 2-ethyl-1,3-hexanediol, 2-methyl-1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,12-octadecanediol, etc. Propylene glycol or neopentanediol is particularly preferred. These may contain only one type or two or more types.

[0101] Aryl glycols with 6 to 12 carbon atoms include 1,2-dihydroxybenzene (catechol), 1,3-dihydroxybenzene (resorcinol), and 1,4-dihydroxybenzene (hydroquinone). These may contain only one type or two or more types.

[0102] Oxyalkyl glycols with 4 to 12 carbon atoms include diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, and tripropylene glycol. Among these, diethylene glycol, triethylene glycol, or dipropylene glycol are particularly preferred. These may contain only one type or two or more types.

[0103] P represents an alkyl dicarboxylic acid residue with 4 to 12 carbon atoms, or an aromatic dicarboxylic acid residue with 6 to 12 carbon atoms.

[0104] Alkyl dicarboxylic acids with 4 to 12 carbon atoms include succinic acid, maleic acid, fumaric acid, glutaric acid, adipic acid, azelaic acid, sebacic acid, and dodecanedicarboxylic acid. These may contain only one type or two or more types.

[0105] Aromadicarboxylic acids with 6 to 12 carbon atoms include phthalic acid, terephthalic acid, isophthalic acid, 1,5-naphthalenedicarboxylic acid, and 1,4-naphthalenedicarboxylic acid. Phthalic acid is particularly preferred. These may contain only one type or two or more types.

[0106] n represents the number of repetitions. Ideally, n should be in the range of 1 to 170.

[0107] The number average molecular weight of polyester is preferably below 20,000, and more preferably below 10,000. In particular, polyester additives with a number average molecular weight in the range of 400 to 10,000 exhibit good compatibility with acetylated cellulose. Furthermore, polyester additives with a number average molecular weight in the range of 400 to 10,000 are less likely to cause evaporation or volatilization during film formation. The number average molecular weight of polyester can be determined by gel permeation chromatography (GPC). For low molecular weight compounds that cannot be determined by GPC, the number average molecular weight is calculated from the structural formula.

[0108] The preferred acid value of the polyester is below 0.5 mg KOH / g, and more preferably below 0.3 mg KOH / g. The preferred hydroxyl value of the polyester is below 25 mg KOH / g, and more preferably below 15 mg KOH / g.

[0109] "Acid value" refers to the number of mg of potassium hydroxide required to neutralize the acid contained in 1g of the sample. "Hydroxy value" refers to the number of mg of potassium hydroxide required to neutralize the acetic acid bonded to the hydroxyl group (hydroxyl group) when 1g of the sample is acetylated. Acid value and hydroxyl value can be determined according to JIS K0070.

[0110] Specific examples of polyester (II) are shown below. However, the invention is not limited thereto. Furthermore, polyester (I) and the ester (III) described later preferably have the same structure as T, D and P in polyester (II) described below.

[0111]

[0112]

[0113]

[0114]

[0115] (1.2) Synthesis method of polyester additives Polycondensation of polyesters is not particularly limited and well-known methods can be used. For example, the direct reaction of dicarboxylic acids with diols can be cited. Also, the polyesterification reaction of dicarboxylic acids or their alkyl esters (e.g., methyl esters) with diols, or the hot melt condensation method via transesterification, can be cited. Other examples include the dehydrohalogenation reaction of acid chlorides of dicarboxylic acids with diols.

[0116] Polyesters with a relatively low number-average molecular weight are better synthesized via direct reaction. Polyesters with a higher distribution on the low molecular weight side exhibit very high compatibility with acetylated cellulose. Furthermore, the resulting second optical film has low moisture permeability and excellent transparency.

[0117] There are no particular restrictions on the method for adjusting the molecular weight; well-known methods can be used. For example, when the ends of a molecule are capped with a monocarboxylic acid, the molecular weight can be adjusted by controlling the amount of monocarboxylic acid added. Furthermore, by controlling the amount of monocarboxylic acid added, one-sided or two-sided capping can be selected.

[0118] From this perspective, monocarboxylic acids are preferably those that are not distilled off the system during the polymerization condensation reaction, but are easily distilled off when the reaction is stopped and removed from the system. Alternatively, monocarboxylic acids that are not easily distilled off the system during the polymerization condensation reaction can be mixed with monocarboxylic acids that are easily distilled off when the reaction is stopped and removed from the system.

[0119] In the case of a direct reaction, the number-average molecular weight can be adjusted by calculating the timing of stopping the reaction based on the amount of water distilled off from the polymerization condensation reaction. Alternatively, the number-average molecular weight can be adjusted by shifting the molar number of the introduced dicarboxylic acid or diol. Furthermore, the number-average molecular weight can also be adjusted by controlling the reaction temperature.

[0120] As an example, this paper shows a method for synthesizing compound A by simply capping the end of a molecule with a monocarboxylic acid.

[0121]

[0122] (Synthesis of Intermediate 1) Dissolve the following components in ethyl acetate. 228.0 parts by weight of propylene glycol 121.0 parts by weight of triethylamine While keeping the temperature of the reaction solution below 50°C, the following components are added. 101.5 parts by weight of terephthalic acid chloride

[0123] After the addition was complete, the reaction solution was stirred at room temperature for 5 hours. Water was added to the reaction solution and stirred to remove the aqueous layer. The organic layer was further washed with water four times. The solvent of the organic layer was distilled off under reduced pressure to obtain intermediate 1 (127 parts by mass, yield 90%).

[0124] (Synthesis of compound P11) Dissolve the following components in toluene. Intermediate 1 71.5 parts by weight 30.0 parts by weight of triethylamine While keeping the temperature of the reaction solution below 50°C, the following components are added. p-Toluene chloride 19.3 parts by weight

[0125] After the addition was complete, the reaction solution was stirred at room temperature for 5 hours. Water was added to the reaction solution and stirred to remove the aqueous layer. The organic layer was further washed twice with a 5% sodium carbonate aqueous solution. After washing the organic layer with saturated brine, it was concentrated under reduced pressure. The resulting residue was purified by silica gel column chromatography to give compound A (37.5 parts by mass, yield 75%).

[0126] (1.3) Content of polyester additives The total content of polyester additives, relative to the total mass of the second optical film, is preferably in the range of 1 to 40% by mass, more preferably in the range of 2 to 30% by mass, and even more preferably in the range of 3 to 15% by mass.

[0127] The content of polyester (II) is preferably in the range of 70% to 90% by mass relative to the total mass of polyester (I) and polyester (II). By being within this range, uneven color caused by water content can be better suppressed.

[0128] (1.4) Low molecular weight esters The second optical film of the present invention preferably contains an ester (III). The ester (III) is represented by the following general formula (III).

[0129] General formula (III): TD Furthermore, T and D in general formula (III) are synonyms with T and D in general formulas (I) and (II) above.

[0130] The structure of polyester (III) is preferably the same as that of polyester (I) except for the repeating structure. By making the structures of polyester (I) and polyester (III) similar, their compatibility is improved, and the effects of the present invention can be significantly obtained.

[0131] The content of ester (III) is preferably in the range of 0.1 to 10% by mass, more preferably in the range of 0.2 to 8% by mass, and even more preferably in the range of 0.3 to 5% by mass, relative to the total mass of the second optical film.

[0132] The relationship between polyester (I), polyester (II) and ester (III) is as follows. Water resistance: Ester (III) < Polyester (I) < Polyester (II) Plasticity: Ester (III) < Polyester (I) < Polyester (II) Ease of movement: Polyester (II) < Polyester (I) < Ester (III)

[0133] The higher the proportion of hydrophobic to hydrophilic regions within the molecule of these compounds, the more hydrophobic the molecule exhibits and the higher its water resistance. Thin films containing compounds with high water resistance are less prone to water absorption, and their phase difference is less likely to change.

[0134] The larger the molecular weight of these compounds, the greater their plasticity. By containing compounds with high plasticity, thin films can be stretched uniformly, making the fast or slow axis of the film uniform.

[0135] The smaller the molecular weight of these compounds, the easier they are to move freely within the film. By including the film with a hydrophilic and easily mobile compound, water molecules will first coordinate with the compound, preventing them from coordinating with the hydrophilic groups of the acetylated cellulose molecules. In other words, by further containing ester (III), it is possible to further prevent water molecules from coordinating with the hydrophilic groups of acetylated cellulose molecules, thereby further suppressing the changes in the phase difference of the film.

[0136] (2) Acetyl cellulose Cellulose is a linear polymer composed of β-glucose linked by β-1,4-glycosidic bonds. Furthermore, cellulose esters are cellulose products obtained by replacing some or all of the hydrogen atoms in the hydroxyl groups (-OH) at positions 2, 3, and 6 of a glucose unit with acetyl groups. Cellulose esters with acetyl groups are called "acetylated cellulose".

[0137] The degree of substitution of the acetyl cellulose in this invention is in the range of 2.30 to 2.80. Preferably, the degree of substitution is in the range of 2.40 to 2.70. By having the degree of substitution within the above range, the desired phase difference value can be obtained.

[0138] (Degree of substitution of acetyl) The degree of acetyl substitution indicates the average number of acetyl groups per glucose unit. In other words, it indicates how many hydrogen atoms among the hydrogen atoms of the hydroxyl groups at positions 2, 3, and 6 in one glucose unit are substituted with acetyl groups. Therefore, the maximum degree of substitution of acetyl is 3.0, which means that all hydrogen atoms of the hydroxyl groups at positions 2, 3, and 6 are replaced by acetyl groups.

[0139] Acetyl groups can be substituted at the 2, 3, and 6 positions of a glucose unit on an average basis, or they can be substituted in a distributed manner. The degree of substitution of acetyl groups can be determined using the method specified in ASTM-D817-96.

[0140] From the viewpoint of obtaining the desired optical properties, acetocellulose with different degrees of substitution can be mixed. There are no particular restrictions on the mixing ratio of acetocellulose with different degrees of substitution.

[0141] From the viewpoint of mechanical strength, the number average molecular weight (Mn) of acetylated cellulose is preferably in the range of 2×10⁴ to 3×10⁵, more preferably in the range of 2×10⁴ to 1.2×10⁵, and even more preferably in the range of 4×10⁴ to 8×10⁴.

[0142] From the viewpoint of mechanical strength, the weight-average molecular weight (Mw) of acetylated cellulose is preferably in the range of 2×10⁴ to 1×10⁶, more preferably in the range of 2×10⁴ to 1.2×10⁵, and even more preferably in the range of 4×10⁴ to 8×10⁴. The number-average molecular weight (Mn) and weight-average molecular weight (Mw) of acetylated cellulose can be determined by the following methods.

[0143] <Gel Permeation Chromatography> Solvent: dichloromethane Tube string: Shodex K806, K805, K803G (or above, manufactured by Showa Denko Co., Ltd.) Connect 3 tubes for use. Column temperature: 25℃ Sample concentration: 0.1% by mass Detector: RI Model 504 (manufactured by GL Sciences) Pump: L6000 (Made by Hitachi, Ltd.) Flow rate: 1.0 mL / min Calibration curves: Calibration curves were obtained using 13 samples of standard polystyrene (STK standard polystyrene, manufactured by Tosoh Corporation) with a Mw range of 500 to 2,800,000. It is preferable that the 13 samples be used at approximately equal intervals.

[0144] Acetyl cellulose can be synthesized using known methods.

[0145] The raw material for acetylated cellulose is not particularly limited, and examples include cotton lint, wood pulp, and kenaf. The raw material cellulose, acetic acid, acetic anhydride, and a catalyst (such as sulfuric acid) are mixed to esterify the cellulose. The reaction continues until a cellulose triester is produced. In the triester, all three hydrogen atoms of the three hydroxyl groups in one glucose unit are replaced by acetylated groups.

[0146] Next, by hydrolyzing the cellulose triester, acetylated cellulose with the desired degree of acetylation is obtained. Afterwards, through steps such as filtration, precipitation, washing, dehydration, and drying, acetylated cellulose is finally obtained. Specifically, the method described in Japanese Patent Application Publication No. 10-45804 can be used for synthesis.

[0147] Commercially available acetylated cellulose products include "LM80, L20, L30, L40, L50" ​​(manufactured by Daicel) and "Ca398-3, Ca398-6, Ca398-10, Ca398-30, Ca394-60S" (manufactured by Eastman Chemical).

[0148] (3) Other additives The second optical film may further contain additives as needed. Examples of additives include sugar esters, acrylic polymers, plasticizers, and microparticles. Furthermore, the second optical film may also contain the aforementioned ultraviolet absorbers.

[0149] (3.1) Glycoesters The second optical film, by containing sugar esters, can adjust the phase difference of the film.

[0150] As a sugar ester, examples include compounds obtained by esterifying all or part of the hydroxyl groups (-OH) of a compound (A) having a furanose or pyranose structure with an aliphatic acetyl group. As a sugar ester, examples include compounds obtained by esterifying all or part of the hydroxyl groups (-OH) of a compound (B) obtained by bonding at least one of the furanose or pyranose structures in the range of 2 to 12 with an aliphatic acetyl group.

[0151] Examples of preferred compounds (A) and (B) may be listed below, but the invention is not limited to these.

[0152] Compound (A) may include, for example, glucose, galactose, mannose, fructose, xylose, arabinose, etc. Furthermore, compound (A) may also include maltitol, obtained by hydrogenating and reducing maltose under high pressure. Compound (B), for example, lactose, sucrose, cellodisaccharide, maltose, cellotrisaccharide, maltotrisaccharide, raffinose, fructotris, etc. Among these, compounds preferably possess both furanose and pyranose structures. Examples of compounds possessing both furanose and pyranose structures include sucrose.

[0153] The monocarboxylic acid used in the synthesis of sugar esters is not particularly limited; well-known aliphatic monocarboxylic acids and alicyclic monocarboxylic acids can be listed. The monocarboxylic acid can be a single type or a mixture of two or more types.

[0154] Aliphatic monocarboxylic acids, such as saturated fatty acids including acetic acid, propionic acid, butyric acid, isobutyric acid, valeric acid, hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, decanoic acid, 2-ethylhexanecarboxylic acid, undecanoic acid, lauric acid, tridecanoic acid, myristic acid, pentadecanoic acid, palmitic acid, heptadecanoic acid, stearic acid, nonadecanoic acid, icosanoic acid, icosanoic acid, icosanoic acid, heptadecanoic acid, limonic acid, triadecanoic acid, and tridodecanoic acid; and unsaturated fatty acids including undecenoic acid, oleic acid, sorbic acid, linolenic acid, linolenic acid, arachidonic acid, and octenic acid.

[0155] Alicyclic monocarboxylic acids, such as cyclopentanecarboxylic acid, cyclohexanecarboxylic acid, cyclooctanecarboxylic acid, or derivatives thereof, can be listed.

[0156] For example, the method for synthesizing these compounds can be found in Japanese Patent Application Publication No. 8-245678.

[0157] As a sugar ester, esterified compounds of oligosaccharides obtained by linking at least one of the furanose or pyranose structures in the range of 3 to 12 can also be used.

[0158] Oligosaccharides are produced by the action of enzymes such as amylase on starch, sucrose, etc. Examples of oligosaccharides include maltodextrin, isomaltodextrin, fructodextrin, galactodextrin, and xylooligosaccharides. Oligosaccharides can also be acetylated using the same method as compounds (A) and (B) mentioned above.

[0159] An example of the synthesis of a glucose ester is shown. A solution was prepared by adding pyridine (100 mL) to glucose (29.8 g, 166 mmol). Acetic anhydride (200 mL) was added dropwise to this solution, and the reaction was allowed to proceed for 24 hours. The solution was then concentrated by evaporation, and the concentrate was placed in ice water. After standing for 1 hour, the concentrate was filtered through a glass filter to separate the solid from the water. The solid on the glass filter was dissolved in chloroform, and the mixture was separated by cold water until the solution became neutral. After separating the organic layer, it was dried over anhydrous sodium sulfate. Anhydrous sodium sulfate was removed from the organic layer by filtration, and chloroform was removed by evaporation. The remaining reaction products were then further dried under reduced pressure to obtain glucose pentaacetate (58.8 g, 150 mmol, 90.9%). Furthermore, the aforementioned monocarboxylic acid can be used to replace the acetic anhydride.

[0160] Specific examples of sugar ester compounds applicable to the present invention are provided, but the present invention is not limited thereto.

[0161]

[0162]

[0163]

[0164]

[0165]

[0166] The content of sugar esters, relative to the total mass of the second optical film, is preferably in the range of 1 to 35% by mass, and more preferably in the range of 5 to 30% by mass. Within this range, the degradation of the polarization function of the polarizing plate can be suppressed, and the display quality of the display device can be stabilized. Furthermore, even if the original film of the second optical film is stored in a laminated, roller-like state, bleed-out is less likely to occur.

[0167] Sugar esters obtained by esterifying all OH groups can also be used in combination with sugar esters that retain one or more OH groups. Examples of combined sugar esters include mixtures of sucrose octaacetate, sucrose heptaacetate, and sucrose hexaacetate. The mixing ratio is not particularly limited; examples include combinations such as 30:30:30, 40:30:30, 40:50:10, 50:30:20, 60:30:10, 80:10:10, 90:7:3, and 95:5:0. The mixing ratio can be controlled by adjusting the reaction time during sugar esterification or the amount of monocarboxylic acid added to react with the sugar.

[0168] (3.2) Acrylic polymer The second protective film, by containing an acrylic polymer, can adjust the phase difference value of the film. The number average molecular weight of the acrylic polymer is preferably in the range of 500 to 30,000. Such acrylic polymer can be referred to paragraphs

[0059] to

[0093] of International Publication No. 2008 / 044463.

[0169] (3.3) Plasticizers The second optical film, by containing a plasticizer, allows for uniform stretching throughout the entire film system, resulting in a uniform fast or slow axis. Consequently, in display devices, in-plane contrast deviations can be suppressed. Furthermore, the second optical film, by containing a plasticizer, allows for adjustment of the phase difference value.

[0170] Plasticizers are not particularly limited, but examples include polycarboxylic acid ester plasticizers, glycol ester plasticizers, phthalate ester plasticizers, fatty acid ester plasticizers, polyol ester plasticizers, polyester plasticizers, acrylic plasticizers, etc.

[0171] Glycol ester plasticizers are not particularly limited, but alkyl phthalate alkyl glycolates are preferred. Examples of alkyl phthalate alkyl glycolates include methyl phthalate methyl glycolate, ethyl phthalate ethyl glycolate, propyl phthalate propyl glycolate, butyl phthalate butyl glycolate, octyl phthalate octyl glycolate, methyl phthalate ethyl glycolate, ethyl phthalate methyl glycolate, ethyl phthalate propyl glycolate, and methyl phthalate ethyl glycolate. Dimethyl phthalate, ethyl phthalate, butyl phthalate, butyl phthalate methyl glycolate, butyl phthalate ethyl glycolate, propyl phthalate, butyl phthalate propyl glycolate, methyl phthalate octyl glycolate, ethyl phthalate octyl glycolate, octyl phthalate methyl glycolate, octyl phthalate ethyl glycolate, etc.

[0172] Phthalate esters are plasticizers, such as diethyl phthalate, dimethoxyethyl phthalate, dimethyl phthalate, dioctyl phthalate, dibutyl phthalate, di-2-ethylhexyl phthalate, dioctyl phthalate, dicyclohexyl phthalate, and dicyclohexyl terephthalate.

[0173] Citrate ester plasticizers include, for example, trimethyl acetyl citrate, triethyl acetyl citrate, and tributyl acetyl citrate.

[0174] Fatty acid ester plasticizers include, for example, butyl oleate, methyl ricinoleate, and dibutyl sebacate.

[0175] Phosphate ester plasticizers include, for example, triphenyl phosphate, tricresyl phosphate, cresyl diphenyl phosphate, octyl diphenyl phosphate, diphenyl biphenyl phosphate, trioctyl phosphate, and tributyl phosphate.

[0176] (3.3.1) Polycarboxylic acid ester plasticizers Polycarboxylic acid esters may include esters of polycarboxylic acids and alcohols with 2 or more members, preferably in the range of 2 to 20 members. Furthermore, the number of members in aliphatic polycarboxylic acids is preferably in the range of 2 to 20 members, and in aromatic and alicyclic polycarboxylic acids, it is preferably in the range of 3 to 20 members.

[0177] Polycarboxylic acid systems are represented by the following general formula (IV).

[0178] General formula (IV): R 2(COOH) m(OH) n In the above general formula (IV), R 2 represents an organic group with a (m+n) valence, m represents a positive integer greater than 2, n represents an integer greater than 0, COOH group represents a carboxyl group, and OH group represents an alcoholic or phenolic hydroxyl group.

[0179] Polycarboxylic acids are not particularly limited, and examples include aromatic polycarboxylic acids or their derivatives with 3 or more members (e.g., trimellitic acid, pyromellitic acid, benzopyrenic acid), aliphatic polycarboxylic acids (e.g., succinic acid, adipic acid, azelaic acid, sebacic acid, oxalic acid, fumaric acid, maleic acid, tetrahydrophthalic acid), and oxy polycarboxylic acids (e.g., tartaric acid, hydroxymalonic acid, malic acid, citric acid). Among these, oxy polycarboxylic acids are particularly preferred from the perspective of improved retention.

[0180] In high-temperature and high-humidity environments, additives such as plasticizers are prone to precipitate or volatilize outside the film, resulting in a decrease in film mass. In this invention, "retention" refers to the property of inhibiting additive precipitation or volatilization outside the film, allowing the additives to remain within the film. Specifically, the mass of a sample is measured after being placed at 23°C and 55%RH for one day. Next, the mass of the sample is measured after being placed at 80°C and 90%RH for two weeks, and then further measured after being placed at 23°C and 55%RH for one day. The rate of change in mass of these samples is calculated and used as a measure of retention. The smaller the rate of change in mass, the higher the retention.

[0181] Alcohols are not particularly limited, and well-known alcohols or phenols may be listed. Examples of alcohols include straight-chain or aliphatic saturated or unsaturated alcohols with side chains in the range of 1 to 32 carbon atoms. The number of carbon atoms is preferably in the range of 1 to 20, and more preferably in the range of 1 to 10. Furthermore, examples of alcohols include alicyclic alcohols (cyclopentanol, cyclohexanol, etc.) or their derivatives, aromatic alcohols (benzyl alcohol, cinnamic acid, etc.) or their derivatives, etc. Alcohols can be used alone or in combination of two or more.

[0182] When using an oxy-based polycarboxylic acid as the polycarboxylic acid, the alcoholic or phenolic hydroxyl group of the oxy-based polycarboxylic acid can be esterified using a monocarboxylic acid. Monocarboxylic acids are not particularly limited; examples include the following.

[0183] Aliphatic monocarboxylic acids, such as straight-chain or side-chain fatty acids with 1 to 32 carbon atoms. The number of carbon atoms is preferably in the range of 1 to 20, and more preferably in the range of 1 to 10.

[0184] Aliphatic monocarboxylic acids, such as saturated fatty acids (acetic acid, propionic acid, butyric acid, valeric acid, hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, decanoic acid, 2-ethylhexanecarboxylic acid, undecanoic acid, lauric acid, tridecanoic acid, myristic acid, pentadecanoic acid, palmitic acid, heptadecanoic acid, stearic acid, nonadecanoic acid, icosanoic acid, icosanoic acid, icosanoic acid, heptadecanoic acid, linoleic acid, triadecanoic acid, tridodecanoic acid, etc.), and unsaturated fatty acids (undecenoic acid, oleic acid, sorbic acid, linolenic acid, linolenic acid, arachidonic acid, etc.).

[0185] Alicyclic monocarboxylic acids, such as cyclopentanecarboxylic acid, cyclohexanecarboxylic acid, cyclooctanecarboxylic acid, or derivatives thereof, can be listed.

[0186] Aromatic monocarboxylic acids, for example, include benzoic acid, benzoic acid with an alkyl group introduced into the benzene ring (such as toluene), aromatic monocarboxylic acids having two or more benzene rings (such as biphenylcarboxylic acid, naphtholic acid, tetrahydronaphtholic acid), or derivatives thereof. Among them, monocarboxylic acids are particularly preferred, such as acetic acid, propionic acid, or benzoic acid.

[0187] The molecular weight of the polycarboxylic acid ester is not particularly limited, but is preferably in the range of 300 to 1000, and more preferably in the range of 350 to 750. From the viewpoint of improved retention, a larger molecular weight is preferred, while from the viewpoint of moisture permeability and compatibility with acetylated cellulose, a smaller molecular weight is preferred.

[0188] The acid value of polycarboxylic acid esters is preferably below 1 mg KOH / g, and more preferably below 0.2 mg KOH / g. By maintaining the acid value within this range, environmental changes in hysteresis values ​​can be suppressed.

[0189] Examples of polycarboxylic acid esters are shown below, but the present invention is not limited thereto. Examples of polycarboxylic acid esters include triethyl citrate, tributyl citrate, acetylated triethyl citrate (abbreviated as ATEC), acetylated tributyl citrate (abbreviated as ATBC), benzyl tributyl citrate, acetylated triphenyl citrate, acetylated tribenzyl citrate, dibutyl tartrate, diacetylated dibutyl tartrate, tributyl trimellitate, and tetrabutyl benzoyltetraacetate.

[0190] (3.4) Microparticles The second protective film, by containing microparticles, can improve the lubricity of the film surface. Furthermore, when the films are stacked together, damage can be suppressed, or the films can adhere more closely to each other. In this invention, "microparticles" refers to particles with an average particle size in the range of 5 to 400 nm.

[0191] Microparticles can be inorganic or organic. Inorganic microparticles include, for example, silicon dioxide, titanium dioxide, aluminum oxide, zirconium oxide, calcium carbonate, talc, clay, and calcined kaolin. Other examples of inorganic microparticles include calcined calcium silicate, hydrated calcium silicate, aluminum silicate, magnesium silicate, and calcium phosphate. From the viewpoint of reducing turbidity, inorganic microparticles preferably contain silicon, with silicon dioxide being particularly preferred.

[0192] Silicon dioxide microparticles can also be used in commercially available products. Examples of commercially available products include "Aerosil (registered trademark) R972, R972V, R974, R812, 200, 200V, 300, R202, OX50, TT600" (all manufactured by Aerosil (Japan) Co., Ltd.).

[0193] Zirconia microparticles can also be used in commercially available products. Examples of commercially available products include "Aerosil (registered trademark) R976 and R811" (both manufactured by Aerosil (Japan) Co., Ltd.).

[0194] Polymers constituting organic microparticles include, for example, polysiloxane resins, fluoropolymers, and acrylic resins. Polysiloxane resins are particularly preferred, especially those with a three-dimensional network structure. Commercially available polysiloxane microparticles may also be used. Examples of commercially available products include "Tospearl (registered trademark) 103, 105, 108, 120, 145, 3120, and 240" (all manufactured by Toshiba Polysiloxane Co., Ltd.).

[0195] The microparticles are preferably "Aerosil (registered trademark) 200V" or "Aerosil (registered trademark) R972V". By containing these microparticles, the turbidity of the second optical film can be maintained at a low level, while the coefficient of friction is sufficiently reduced. The coefficient of kinetic friction of at least one side of the second optical film is preferably in the range of 0.2 to 1.0.

[0196] The average particle size of the primary particles is preferably in the range of 10 to 300 nm. The particles can also be contained in the form of secondary aggregates in the range of 0.05 to 0.3 μm in size. Particles with an average particle size in the range of 100 to 400 nm are preferably contained in the form of primary particles without aggregation.

[0197] The content of microparticles is preferably in the range of 0.01 to 1% by mass, and more preferably in the range of 0.05 to 0.5% by mass, relative to the total mass of the second optical film.

[0198] (4) Manufacturing method of the second optical film The manufacturing method of the second optical film can be either solution casting or melt casting. Solution casting is preferred.

[0199] The solution casting method for manufacturing thin films includes steps of modulating a dopant, casting the dopant onto a metal support, drying the web, and peeling the thin film off the metal support. Furthermore, the solution casting method for manufacturing thin films includes steps of extending or maintaining the width of the peeled film, further drying the film, and winding the completed film.

[0200] (4.1) Steps for modulating dopants In the process of preparing the dopant, acetylated cellulose and additives are dissolved in a solvent to prepare the dopant. A higher concentration of acetylated cellulose in the dopant is preferable as it reduces the drying load after casting on the metal support. Furthermore, by ensuring the concentration of acetylated cellulose is not too high, the pressure load during filtration can be suppressed, resulting in good filtration accuracy. From these perspectives, the content of acetylated cellulose relative to the total mass of the dopant is preferably in the range of 10-35% by mass, and more preferably in the range of 15-25% by mass.

[0201] The solvent used for preparing the dopant can be a single type or two or more. However, from a production efficiency perspective, it is preferable to mix a good solvent and a poor solvent for acetal cellulose, and from the perspective of acetal cellulose solubility, a higher proportion of good solvent is better. The mixing ratio of good solvent to poor solvent is preferably in the range of 70-98% by mass for good solvent and 2-30% by mass for poor solvent. Furthermore, a solvent that dissolves acetal cellulose on its own is defined as a "good solvent," while a solvent that swells or does not dissolve when used alone is defined as a "poor solvent."

[0202] Good solvents are not particularly limited, and examples include organohalogen compounds (such as dichloromethane), dioxolanes, acetone, methyl acetate, and methyl acetoacetate. Dichloromethane or methyl acetate are particularly preferred. Poor solvents are not particularly limited, and examples include methanol, ethanol, n-butanol, cyclohexane, and cyclohexanone.

[0203] The dopant preferably contains water in the range of 0.01 to 2% by mass. Regarding the solvent used for dissolving acetylated cellulose, the solvent removed from the film after drying can also be recovered and reused. The recovered solvent sometimes contains trace amounts of additives (e.g., plasticizers, UV absorbers, polymers, monomer components, etc.). Even if the recovered solvent contains additives, it can still be reused. The recovered solvent can also be purified and reused as needed.

[0204] The method for dissolving acetylated cellulose in the preparation of dopants can be a known method. For example, by combining heating and pressurization, the dopant can be heated to above its boiling point at atmospheric pressure. If the solvent is heated at a temperature above its boiling point at atmospheric pressure, and within the range where the solvent does not boil under pressure, while simultaneously stirring to dissolve the acetylated cellulose, the formation of lumps of undissolved material (gels or lumps) can be prevented. Furthermore, after wetting or swelling the acetylated cellulose with a poor solvent, a good solvent can be added to further dissolve it.

[0205] Pressurization methods include introducing inert gases such as nitrogen into the dissolving container, and increasing the vapor pressure of the solvent by heating. Heating is preferably performed externally, such as in a jacketed container, because temperature control is easier.

[0206] From the perspective of acetylated cellulose solubility, a higher heating temperature is preferable. Furthermore, by keeping the heating temperature moderate, pressure load can be suppressed, resulting in good productivity. From these perspectives, the heating temperature is preferably in the range of 45~120°C, more preferably in the range of 60~110°C, and even more preferably in the range of 70°C~105°C. The pressure is adjusted so that the solvent will not boil at the set temperature.

[0207] Other methods for dissolving acetylated cellulose include the cooling dissolution method. This method allows acetylated cellulose to be dissolved in solvents such as methyl acetate.

[0208] The acetylated cellulose solution is filtered using a suitable filter medium, such as filter paper. From the viewpoint of removing insoluble matter, the filter medium preferably has a low absolute filtration precision. Furthermore, by ensuring that the absolute filtration precision is not too low, clogging of the filter medium can be suppressed. From this perspective, the absolute filtration precision of the filter medium is preferably below 0.008 mm, more preferably in the range of 0.001 to 0.008 mm, and even more preferably in the range of 0.003 to 0.006 mm.

[0209] The material of the filter media is not particularly limited; any known filter media can be used. From the perspective of preventing fiber shedding, filter media made of plastic (polypropylene, Teflon (registered trademark) etc.) or metal (stainless steel, etc.) are preferred. Filtration can remove or reduce impurities, especially fine particles, contained in the acetylated cellulose raw material.

[0210] Two polarizing plates are arranged in an orthogonal Nikkor configuration, with a second optical film placed between them. Light is then shone from the side of one polarizing plate, and observation is performed from the side of the other polarizing plate. Points visible due to light leakage from the opposite side are called "bright spots." The number of bright spots with a diameter of 0.01 mm or more is preferably 200 or less / cm², more preferably 100 or less / cm². The number of bright spots with a diameter of 0.01 mm or more is even more preferably 50 or less / cm², and particularly preferably in the range of 0 to 10 / cm². Furthermore, a lower number of bright spots with a diameter of 0.01 mm or less is also preferred.

[0211] The dopant can be filtered using known methods. A particularly preferred method is to heat the solvent while filtering at a temperature above its boiling point under normal pressure, but within a range where the solvent does not boil under pressure. This method results in a smaller increase in the pressure difference before and after filtration. The heating temperature is preferably in the range of 45–120°C, more preferably in the range of 45–70°C, and even more preferably in the range of 45–55°C.

[0212] A lower filtration pressure is preferred. The preferred filtration pressure is below 1.6 MPa, more preferably below 1.2 MPa, and even more preferably below 1.0 MPa.

[0213] Various additives can be added in batches or in-line addition using separately prepared additive solutions. Especially when adding microparticles as dopants, it is preferable to add a portion or all of the amount in-line to reduce the load of microparticles on the filter material.

[0214] When adding the additive solution along the line, from the viewpoint of miscibility with the dopant, it is preferable to pre-dissolve a small amount of acetylated cellulose in the additive solution. The amount of acetylated cellulose added is preferably in the range of 1 to 10% by mass, and more preferably in the range of 3 to 5% by mass, relative to the total mass of the solvent.

[0215] Adding and mixing along the line can be done using, for example, a static mixer or an in-line mixer. Static mixers include those manufactured by Toray Engineering. In-line mixers include Toray's Hi-Mixer SWJ (a static in-line mixer manufactured by Toray Engineering).

[0216] (4.2) Step of casting dopant onto metal support In the step of casting the dopant onto a metal support, the dopant is cast onto an infinitely moving annular metal support. The metal support used in the casting (casting) step is preferably mirror-finished. The metal support is preferably a stainless steel strip, or a roller whose surface has been plated using casting. The casting width is preferably in the range of 1 to 4 meters.

[0217] (4.3) Steps for drying the wire mesh In the step of drying the web, the dopant cast on the metal support is dried as a web. The surface temperature of the metal support is preferably above -50°C, but not exceeding the boiling point of the solvent. A higher surface temperature accelerates the drying speed of the mesh. Furthermore, by preventing excessively high surface temperatures, blistering of the mesh can be prevented, resulting in good film planarity. From this perspective, the surface temperature is preferably in the range of 0~40°C, and more preferably in the range of 5~30°C. Alternatively, the mesh can be gelled by cooling the metal support, allowing the film to be peeled off from the roller while still containing a significant amount of residual solvent.

[0218] Methods for controlling the temperature of the metal support are not particularly limited; for example, methods such as blowing warm or cold air can be cited. Another example is contacting the back side of the metal support with warm water. Using warm water, because heat transfer is efficient, shortens the time it takes for the metal support to reach a certain temperature. When using warm air, air at a temperature higher than the target temperature of the metal support can also be used.

[0219] (4.4) Step of peeling the film off the metal support From the viewpoint of achieving good planarity of the film, the residual solvent content when the film (mesh) is peeled off from the metal support is preferably in the range of 10 to 150% by mass. More preferably, the residual solvent content is in the range of 10 to 40% by mass or 60 to 130% by mass, and even more preferably, in the range of 10 to 30% by mass or 70 to 120% by mass. Here, the residual solvent content is defined by the following formula.

[0220] Residual solvent content [mass%] = {(MN) / N} × 100 In the formula, M is the mass of the mesh or film sample. N is the mass of the mesh or film sample after heating at 115°C for 1 hour. Furthermore, the mesh or film sample can be taken at any point during or after manufacturing.

[0221] (4.5) Step of stretching or maintaining the width of the peeled film. In the step of stretching or maintaining the width of the peeled film, the film with a high residual solvent content immediately after peeling is stretched or its width maintained. It is preferably used in a tenter frame where the film is stretched in the transport direction (longitudinal direction) and then held at both ends by clips or similar means. Alternatively, it can be stretched simultaneously in both the transport direction (longitudinal direction) and the width direction (transverse direction).

[0222] When extending in the longitudinal direction, the peeling tension is preferably above 210 N / m, and more preferably in the range of 220~300 N / m.

[0223] By extending the process, the refractive index of the thin film can be controlled, as well as the hysteresis values ​​Ro and Rth.

[0224] The final elongation ratio is preferably in the range of 1.0 to 2.0 times in the conveying direction, and more preferably in the range of 1.01 to 1.5 times. The final elongation ratio is preferably in the range of 1.01 to 2.5 times in the width direction, and more preferably in the range of 1.05 to 2.0 times.

[0225] The method of stretching the film is not particularly limited. For example, a stretching method may include imparting a difference in circumferential speed to multiple rollers, and using this difference in roller circumferential speed to stretch the film in the longitudinal direction. Another stretching method may include fixing both ends of the film with clamps or pins, increasing the spacing between the clamps or pins in the conveying direction, and thus stretching the film in the longitudinal direction. Similarly, a method may include increasing the spacing between the clamps or pins in the width direction, and thus stretching the film in the transverse direction. Likewise, a method may include increasing the spacing between the clamps or pins in both the conveying and width directions simultaneously, and thus stretching the film in both the longitudinal and transverse directions.

[0226] These stretching methods can also be used in combination. Furthermore, in the case of a tenter frame, if the clamping fabric section is driven linearly, the stretching can be carried out smoothly, reducing the risk of film breakage.

[0227] Maintaining such width or extending it laterally is better done using a tenter machine, which can be either a pin tenter or a clip tenter.

[0228] When the fast or slow axis of the thin film exists within the film surface, and the angle formed with the conveying direction is set as θ1, θ1 is preferably within the range of -0.5 to +0.5˚, more preferably within the range of -0.3 to +0.3˚, and even more preferably within the range of -0.2 to +0.2˚. This θ1 can be defined as the alignment angle. θ1 can be measured using an automatic birefringence meter "KOBRA-21ADH" (Oji Measurement Instrument). By having θ1 within the above range, high brightness can be obtained in the displayed image. Furthermore, light leakage can be suppressed or prevented, and colors can be faithfully reproduced in color liquid crystal display devices.

[0229] (4.6) Step of further drying the film The step of further drying the film involves further drying the peeled film. Drying can be performed after stretching or simultaneously. The residual solvent content of the dried film is preferably less than 1% by mass, more preferably less than 0.1% by mass, and even more preferably less than 0.01% by mass.

[0230] The drying method is not particularly limited; for example, a roller drying method in which the film is alternately passed through multiple rollers arranged above and below for drying can be listed. Alternatively, the film can be dried while being stretched using the aforementioned tenter frame method.

[0231] The method of drying the film is not particularly limited; examples include hot air, infrared radiation, heated rollers, and microwaves. From a simple point of view, hot air is the preferred drying method.

[0232] The drying temperature is preferably increased in stages within the range of 40 to 200°C. From the viewpoint of dimensional stability, the drying temperature is more preferably within the range of 50 to 140°C.

[0233] (4.7) Steps for winding the finished film The finished film is preferably stored, for example, by being rolled into a roller.

[0234] (5) Physical properties of the second optical film (5.1) Hysteresis value The hysteresis value Ro is preferably in the range of 30 to 90 nm. The hysteresis value Rth is preferably in the range of 100 to 200 nm. By having the hysteresis value within the above range, light leakage can be suppressed when viewing a liquid crystal display device equipped with the polarizing plate of the present invention from an oblique direction.

[0235] (5.2) Thickness The thickness of the thin film is preferably in the range of 10~200μm, more preferably in the range of 10~60μm, and even more preferably in the range of 10~40μm.

[0236] (5.3) Width The width of the film is preferably in the range of 1 to 4 m, more preferably in the range of 1.3 to 4 m, and even more preferably in the range of 2.2 to 3.0 m. By having a width in the range of 2.2 to 3.0 m, it is possible to achieve a high level of uniformity in stretching and productivity.

[0237] 4.Polarizer In this invention, a "polarizing element" refers to a component that allows light with a polarization plane in a specific direction to pass through, and also includes a layer containing such a component. Examples of polarizing elements include polyvinyl alcohol (PVA) polarizing films. Among PVA polarizing films, there are those dyed with iodine and those dyed with dichroic dyes.

[0238] One method for manufacturing polarizing components is to prepare a film using an aqueous solution of polyvinyl alcohol, uniaxially stretch the resulting film, and then dye it. Alternatively, uniaxial stretching can be performed after dyeing, followed by a durability treatment with boron compounds or the like.

[0239] The thickness of the polarizing element is preferably in the range of 2~30μm, and more preferably in the range of 2~20μm.

[0240] Examples of polyvinyl alcohol (PVA) include ethylene-modified PVA as described in Japanese Patent Application Publication Nos. 2003-248123 and 2003-342322. This ethylene-modified PVA has an ethylene unit content in the range of 1-4 moles, a degree of polymerization in the range of 2000-4000, and a degree of saponification in the range of 99.0-99.99 moles. Particularly preferred are ethylene-modified PVA with a hot water cut-off temperature in the range of 66-73°C. The polarizing film of this ethylene-modified PVA exhibits excellent polarization performance and durability, with minimal color inconsistency, making it particularly suitable for use in large-scale liquid crystal display devices.

[0241] 5. Manufacturing method of polarizing plate The polarizing plate of the present invention can be manufactured by conventional methods. The surface of the first protective film of the present invention facing the polarizer is appropriately treated, then extended by immersion in an iodine solution. The film is then bonded to at least one side of the manufactured polarizer using a UV-curing adhesive or a water-based adhesive, as described later. The second protective film is similarly bonded to the other side of the polarizer.

[0242] The preferred bonding direction with the polarizer is, for example, bonding in a manner in which the absorption axis of the polarizer is perpendicular to the slow axis of each protective film.

[0243] (1) UV-curing adhesive The polarizing plate of the present invention is preferably manufactured by bonding the aforementioned optical film and polarizing element together using an ultraviolet-curing adhesive. By using an ultraviolet-curing adhesive, a polarizing plate with high strength and excellent planarity, even when thin, can be obtained.

[0244] (1.1) Composition of UV-curing adhesives UV-curable adhesive compositions for polarizing plates can include photoradical polymers that utilize photoradical polymerization and photocationic polymers that utilize photocationic polymerization. Furthermore, UV-curable adhesive compositions for polarizing plates can include hybrid compositions that utilize both photoradical polymerization and photocationic polymerization.

[0245] Photoradical polymerizable compositions, such as those described in Japanese Patent Application Publication No. 2008-009329, are examples. These compositions contain, in specific proportions, radical polymerizable compounds containing polar groups such as hydroxyl and carboxyl groups, and radical polymerizable compounds without polar groups.

[0246] The free radical polymerizable compound contained in the photoradical polymerization composition is preferably a compound having an ethylene unsaturated bond capable of free radical polymerization. Examples of compounds having an ethylene unsaturated bond capable of free radical polymerization include compounds having a (meth)acrylic group. Examples of compounds having a (meth)acrylic group include N-substituted (meth)acrylamide compounds and (meth)acrylate compounds.

[0247] Furthermore, (meth)acrylyl means acrylyl or methacrylyl, and (meth)acrylate means acrylate or methacrylate. Also, (meth)acrylamine means acrylamine or methacrylamine.

[0248] Photocationically cationic polymerizable compositions, such as those disclosed in Japanese Patent Application Publication No. 2011-028234, are examples. These compositions contain (α) a cationic polymerizable compound, (β) a photocationically cationic polymerization initiator, (γ) a photosensitizer exhibiting significant absorption of light with wavelengths longer than 380 nm, and (δ) a naphthalene-based photosensitizing aid. Cationic polymerizable compounds, such as epoxides and oxobutanes, are examples. UV-curing adhesives are not limited to these and may be used from known sources.

[0249] (2) Manufacturing method of polarizing plate After pretreatment of the optical film and polarizing element, a UV-curable adhesive is applied. Then, the optical film and polarizing element are bonded together through the UV-curable adhesive. Finally, the UV-curable adhesive is allowed to cure.

[0250] (2.1) Pre-processing steps In the pretreatment step, an easy-bonding treatment is performed on the bonding surface between the optical film and the polarizing element. Easy-bonding treatments include corona treatment and plasma treatment.

[0251] (2.2) Coating Steps In the coating step, the aforementioned UV-curing adhesive is applied to at least one of the bonding surfaces of the optical film and the polarizing element. When directly applying the UV-curing adhesive to the surface of the optical film or the polarizing element, the coating method is not limited. Examples of coating methods include doctor blades, wire rods, die coaters, corner roller coaters, gravure coaters, etc., and various wet coating methods can be used. Furthermore, after applying the UV-curing adhesive between the optical film and the polarizing element, pressure can be applied using rollers or the like to evenly spread the UV-curing adhesive.

[0252] (2.3) Bonding Steps In the bonding step, when a UV-curable adhesive is applied to the surface of the polarizer in the previous coating step, an optical film is laminated on top of the UV-curable adhesive. When a UV-curable adhesive is applied to the surface of the optical film, the polarizer is laminated on top of the UV-curable adhesive.

[0253] When casting an ultraviolet-curable adhesive between an optical film and a polarizing element, the optical film and the polarizing element are laminated in this state. Typically, in this state, pressure is applied by clamping the optical film sides with pressure rollers or similar materials. The pressure rollers can be made of materials such as metal or rubber. The pressure rollers on both sides can be made of the same material or different materials.

[0254] (2.4) Hardening steps In the curing step, the applied UV-curable adhesive is irradiated with ultraviolet light. Then, the UV-curable adhesive is cured, and the laminated optical film is bonded to the polarizer through the UV-curable adhesive. In this invention, the light-transmitting optical film is laminated on both sides of the polarizer using UV-curable adhesives. Preferably, in this state, UV irradiation is used to cure the UV-curable adhesives on both sides simultaneously.

[0255] The conditions for ultraviolet (UV) irradiation are not particularly limited as long as they allow the UV-curable adhesive to cure. The cumulative UV irradiation intensity is preferably in the range of 50-1500 mJ / cm², and more preferably in the range of 100-500 mJ / cm². From the viewpoint of improving yield, it is preferable that UV irradiation is applied from the side of the second optical film.

[0256] When manufacturing polarizing plates on a continuous production line, the linear speed is preferably in the range of 1~500 m / min, more preferably in the range of 5~300 m / min, and even more preferably in the range of 10~100 m / min. A linear speed of 1 m / min or higher ensures productivity. Furthermore, it suppresses damage to the optical film, resulting in polarizing plates with excellent durability. A linear speed of 500 m / min or lower allows for sufficient curing of the UV-curable adhesive. This results in an adhesive layer with the target hardness and excellent adhesion. Moreover, the linear speed is preferably adjusted to take into account the curing time of the adhesive.

[0257] 6. Display device The display device of the present invention is characterized by having the aforementioned polarizing plate, and the aforementioned second optical film being disposed on the liquid crystal cell side. By having the aforementioned polarizing plate, color unevenness and contrast deviation caused by water content can be suppressed.

[0258] The polarizing plate of this invention can be used in liquid crystal display devices with various driving methods, such as STN, TN, OCB, HAN, VA (MVA, PVA), IPS, and OCB. It is particularly preferred for use in IPS type liquid crystal display devices.

[0259] In liquid crystal display devices, two polarizing plates are typically used: one for the visual recognition side and one for the backlight side. The polarizing plate of this invention can be used as both polarizing plates or as a single-sided polarizing plate. For example, the bonding direction of the polarizing plates in an IPS-type liquid crystal display device can be found in Japanese Patent Application Publication No. 2005-234431.

[0260] The liquid crystal cell of the present invention includes a liquid crystal layer and a pair of substrates that hold the liquid crystal layer. From the viewpoint of thinning and lightening the display device, the pair of substrates are preferably glass substrates with a thickness in the range of 0.3 to 0.7 mm.

[0261] Figure 2 is a schematic cross-sectional view showing an example of the configuration of a display device (100) in which the polarizing plates (101A and 101B) of the present invention are arranged on both sides of a liquid crystal cell (101C).

[0262] In Figure 2, a liquid crystal cell (101C) is formed by sandwiching two sides of a liquid crystal layer (107) with glass substrates (108A and 108B) serving as transparent substrates. Polarizing plates (101A and 101B) are disposed on the respective surfaces of the glass substrates (108A and 108B) with an adhesive layer (106) in between, thereby forming a display device (100).

[0263] In the polarizing plates (101A and 101B), the first optical film system is bonded to positions 102A and 102B, and the second optical film system is bonded to positions 105A and 105B. The optical films are bonded to the polarizing elements (104A and 104B) respectively using ultraviolet-curing adhesives (103A~103D).

[0264] A liquid crystal cell (101C) is located on both sides of a liquid crystal material and includes an alignment film, a transparent electrode, and a glass substrate (108A and 108B). The glass substrate can be made of materials such as soda lime glass or silicate glass. Silicate glass is particularly preferred, and more specifically, silica glass or borosilicate glass is even more preferred.

[0265] The glass constituting the glass substrate is preferably alkali-free glass that is substantially free of alkali components. Specifically, the alkali content in the glass substrate is preferably below 1000 ppm. More preferably, it is below 500 ppm, and even more preferably below 300 ppm. By using alkali-free glass that is substantially free of alkali components, glass turbidity caused by cation substitution on the surface of the optical film can be suppressed. This suppresses the decrease in density on the surface of the optical film and prevents damage to the glass substrate.

[0266] Glass substrates can be manufactured using known methods such as float glass, drop glass, and overflow drop glass. Among these methods, the overflow drop glass is particularly preferred because the surface of the glass substrate does not come into contact with the forming component during the forming process, thus minimizing the risk of damage to the surface of the resulting glass substrate.

[0267] Glass substrates can also be commercially available. Examples of commercially available glass substrates include "AN100" (500μm thick, manufactured by Asahi Glass), "EAGLE XG(r) Slim" (300μm, 400μm, etc. thick, manufactured by Corning), and glass substrates (thickness range of 100~200μm, manufactured by Nippon Electric Glass).

[0268] As shown in Figure 2, the polarizing plates (101A, 101B) and the liquid crystal cell (101C) are bonded together through an adhesive layer (106). The adhesive layer can be formed using double-sided tape, UV-curable adhesive, or similar materials. Examples of double-sided tapes include substrate-free tape "MO-3005C" (25μm thick, manufactured by Lintec Corporation). The bonding method is not particularly limited and can be any known method.

[0269] In addition to the effects of this invention, the liquid crystal display device of this invention also exhibits excellent interlayer adhesion, excellent resistance to fading, and excellent resistance to oval unevenness in the displayed image. By using the polarizing plate of this invention, especially for large screens of 30 inches or more, a liquid crystal display device with excellent visual clarity, thin film, and lightweight design can be obtained. [Example]

[0270] The following examples illustrate the present invention, but the invention is not limited thereto. Furthermore, in the examples, the terms "parts" or "%" are used, which, unless otherwise specified, represent "parts by mass" or "% by mass". Furthermore, in the following embodiments, unless otherwise specified, the operation is carried out at room temperature (25°C).

[0271] 1. Production of polarizing plates (1) Fabrication of the first optical film The first optical film (optical film No. 1~2) is made according to the following method.

[0272] (1.1) Fabrication of optical film 1 (1.1.1) Synthesis of Polyester A Heat the esterification reactor to 200°C and add the following components. 86,400 parts by weight of terephthalic acid 64,600 parts by weight of ethylene glycol

[0273] While stirring the mixture, the catalyst described above was added to the esterification reactor. Then, a pressurized esterification reaction was carried out at a pressure of 0.34 MPa and a temperature of 240°C. 0.017 parts by weight of antimony trioxide Magnesium acetate tetrahydrate 0.064 parts by weight 0.160 parts by weight of triethylamine

[0274] Next, the esterification reactor was brought back to atmospheric pressure, and the following components were added. 0.014 parts by weight of phosphoric acid Further, the reactants are heated to 260°C over 15 minutes, and the following components are added to the esterification reactor. Trimethyl phosphate 0.012 parts by weight

[0275] After 15 minutes, the reactants were dispersed using a high-pressure disperser. After another 15 minutes, the reactants were transferred to a polymerization condensation reactor and subjected to a polymerization condensation reaction at 280°C under reduced pressure.

[0276] After the polymerization condensation reaction, the reaction product was filtered using a Naslon (registered trademark) NF-05S filter (95% cutoff diameter: 5μm, manufactured by Nippon Seiki Co., Ltd.). The reaction product was extruded into strips through a nozzle. Then, the reaction product was cooled and solidified using pre-filtered cooling water (pore size: 1μm or less), and cut into granules. The resulting polyester A (polyethylene terephthalate: PET) had an intrinsic viscosity of 0.62 dL / g. Furthermore, the polyester substantially does not contain inactive particles or internally precipitated particles.

[0277] (1.1.2) Modulation of Polyester B The dried ultraviolet absorber is mixed with the above-mentioned polyester A in the following ratio, and a compounding extruder is used to obtain polyester B containing the ultraviolet absorber.

[0278] Ultraviolet absorber (2,2'-(1,4-epenylphenyl)bis(4H-3,1-benzoxazinone-4-one) 10 portions by weight Polyester A 90 parts by weight

[0279] (1.1.3) Preparation of Adhesion Modified Coating Solution Using the following components, a copolymer polyester resin containing a water-dispersible sulfonate metal base is prepared by transesterification and polycondensation reactions using known methods.

[0280] Regarding the dicarboxylic acid component, it is blended in the following proportions relative to the total dicarboxylic acid component. 46 mol% terephthalic acid 46 mol% of isophthalic acid Sodium 5-sulfonatoisophthalate (8 moles) Regarding the diol component, it is blended in the following proportions relative to the total diol component. 50 moles of ethylene glycol Neopentyl glycol 50 mol%

[0281] Next, mix the following ingredients. 51.40 parts by weight of water 38.00 parts by weight of isopropanol n-Butylceroxose 5.00 parts by weight 0.06 parts by weight of nonionic surfactant

[0282] The mixture was then heated and stirred, and at the point when it reached 77°C, the following components were added. Stirring continued until the resin clumps disappeared, and the resin dispersion was cooled to room temperature to obtain a uniform aqueous copolymer polyester resin solution with a solid content of 5.0% by mass. 5.00 parts by weight of the above copolymerized polyester resin

[0283] Disperse the following components to prepare an aqueous dispersion of silicon dioxide particles. Condensed silica particles "Sylysia 310" (manufactured by Fuji SILYSIA Co., Ltd.) 3.00 parts by weight 50.00 parts by weight of water

[0284] Mix the following ingredients. 99.46 parts by weight of the above-mentioned water-dispersible copolymerized polyester resin solution 0.54 parts by weight of aqueous dispersion of silicon dioxide particles While stirring the mixture, the following components are added to obtain an adhesion-modified coating solution. 20.00 parts by weight of water

[0285] (1.1.4) Formation of optical film 1 The following polyester granules were dried under reduced pressure at 135°C and 133.3 Pa (1 Torr) for 6 hours and then fed into extruder 2 (for intermediate layer II). They were then melted at 285°C. Polyester A 90 parts by weight Polyester B 10 parts by weight

[0286] The synthesized polyester A was dried by conventional methods and fed to extruder 1 (for outer layer I and outer layer III) and melted at 285°C.

[0287] The molten polyester was filtered separately using stainless steel sintered filter media (nominal filtration accuracy 10μm particle rejection 95%). Then, it was laminated using two types of three-layer confluence blocks and extruded into sheets through an interface tube. Next, using an electrostatic casting method, the extruded polyester was wound onto casting rollers with a surface temperature of 30°C and cooled to solidify. This yielded an unstretched polyester film (PET film). Furthermore, the output of each extruder was adjusted so that the thickness ratio of layer I, layer II, and layer III was 10:80:10.

[0288] Next, the aforementioned adhesion-modifying coating solution is applied to both sides of the unstretched polyester film using a reverse roller method, resulting in a coating weight of 0.08 g / m² after drying. The coating solution is then dried at 80°C for 20 seconds.

[0289] An unstretched polyester film is guided to a tenter frame, and while holding the ends of the film with clamping cloth, it is stretched 4.0 times in width in a hot air zone at 125°C. Next, the film is treated at 225°C for 30 seconds while maintaining and holding the width-direction stretch. Further, the film is relaxed by 3% in the width direction. This yields a uniaxially aligned optical film 1 with a thickness of 50 μm.

[0290] (1.2) Fabrication of optical film 2 In the fabrication of optical film 1, triacetyl cellulose (TAC) was used to replace polyester, and optical film 2 was otherwise obtained by the same method.

[0291] (2) Fabrication of the second optical film The second optical film (optical film No. 3~17) is manufactured according to the following method.

[0292] (2.1) Fabrication of optical film 3 First, the details of the acetyl cellulose and polyester additives used in the production of the second optical film are described below.

[0293] (Acetyl cellulose) Acetyl cellulose 1 (AC1): Acetyl substitution degree 2.50 Acetyl cellulose 2 (AC2): Acetyl substitution degree 2.20 Acetyl cellulose 3 (AC3): Acetyl substitution degree 2.40 Acetyl cellulose 4 (AC4): Acetyl substitution degree 2.60 Acetyl cellulose 5 (AC5): Acetyl substitution degree 2.70 Acetyl cellulose 6 (AC6): Acetyl substitution degree 2.90

[0294] (additive) The structural formula of the additive is shown below. For compounds P11 and P21, the value of n is 1; for compounds P12 and P22, the value of n is 2.

[0295]

[0296] (2.1.1) Synthesis of Additives (2.1.1.1) Synthesis of compound P11 The reaction formula for synthesizing compound P11 from terephthalic acid chloride is shown below.

[0297]

[0298] (Synthesis of Intermediate 1) Dissolve the following components in ethyl acetate. 228.0 parts by weight of propylene glycol 121.0 parts by weight of triethylamine Keep the temperature of the reaction solution below 50°C, and add the following components. 101.5 parts by weight of terephthalic acid chloride

[0299] After the addition was complete, the reaction solution was stirred at room temperature for 5 hours. Water was added to the reaction solution and stirred to remove the aqueous layer. The organic layer was further washed with water four times. The solvent of the organic layer was distilled off under reduced pressure to obtain 127 parts by mass of intermediate 1 (yield 90%).

[0300] (Synthesis of compound P11) Dissolve the following components in toluene. Intermediate 1 71.5 parts by weight 30.0 parts by weight of triethylamine Keep the temperature of the reaction solution below 50°C, and add the following components. p-Toluene chloride 19.3 parts by weight

[0301] After the addition was complete, the reaction solution was stirred at room temperature for 5 hours. Water was added to the reaction solution and stirred to remove the aqueous layer. The organic layer was further washed twice with a 5% sodium carbonate aqueous solution. After washing the organic layer with saturated brine, it was concentrated under reduced pressure. The resulting residue was purified by silica gel column chromatography to give 37.5 parts by mass of compound P11 (75% yield).

[0302] (2.1.1.2) Synthesis of compound P21 In the synthesis of compound P11, the amount of p-toluene chloride added was changed to 38.6 parts by mass, otherwise compound P21 was obtained by the same method.

[0303] (2.1.1.3) Synthesis of compound P31 Dissolve the following components in ethyl acetate. 228.0 parts by weight of propylene glycol 121.0 parts by weight of triethylamine Keep the temperature of the reaction solution below 50°C, and add the following components. p-Toluene chloride 19.3 parts by weight

[0304] After the addition was complete, the reaction solution was stirred at room temperature for 5 hours. Water was added to the reaction solution and stirred to remove the aqueous layer. The organic layer was further washed with water four times. The solvent of the organic layer was distilled off under reduced pressure to give compound P31 (yield 90%).

[0305] (2.1.2) Modulation of dopants <Microparticle Dispersion> The following components were mixed in a dissolver for 50 minutes and then dispersed using a Manton-Gaulin homogenizer to obtain a microparticle dispersion. Microparticle "Aerosil (registered trademark) R812" (manufactured by Aerosil Japan Co., Ltd.) 11.0 parts by weight 89.0 parts by weight of ethanol

[0306] <Microparticle Additive Solution> Acetyl cellulose with a degree of substitution of 2.40 was added to a dissolving tank containing dichloromethane and heated until completely dissolved. The solution was then filtered using Anji Filter Paper No. 244 (Anji Filter Paper Co., Ltd.). While thoroughly stirring the filtered acetylated cellulose solution, the aforementioned microparticle dispersion was slowly added. The mixture was then dispersed using an atritor to achieve a specific particle size for the secondary particles. The resulting dispersion was filtered using a Fine Met NF (Nippon Seiki Co., Ltd.) to prepare the microparticle additive solution. 99.0 parts by weight of dichloromethane Acetyl cellulose 4.0 parts by weight 11.0 parts by weight of microparticle dispersion

[0307] Next, the main dopant solution with the following composition was prepared.

[0308] First, dichloromethane and ethanol are added to a pressurized dissolution tank. Acetyl cellulose with a degree of substitution of 2.40 is added to the pressurized dissolution tank containing the solvent while stirring. The solution is heated and stirred until completely dissolved. Two additives are then added to the solution and dissolved. The solution is filtered using Anji Filter Paper No. 244 (Anji Filter Paper Co., Ltd.) to prepare the main dopant solution.

[0309] Composition of the primary dopant solution 300.0 parts by weight of dichloromethane 30.0 parts by weight of ethanol 100.0 parts by weight of acetylated cellulose Compound P11 5.0 parts by weight Compound P21 5.0 parts by weight

[0310] Two parts by mass of microparticle additive solution were added to 100.0 parts by mass of the main dopant solution and thoroughly mixed using a wire mixer (Toray Hi-Mixer, SWJ) (manufactured by Toray Engineering Co., Ltd.). Furthermore, the content of compound P11 in the dopant solution was 5% by mass relative to the mass of acetylated cellulose. The same applies to compound P21, whose content was also 5% by mass relative to the mass of acetylated cellulose.

[0311] (2.1.3) Formation of optical film 3 The modified dopant was uniformly cast onto a stainless steel strip at a temperature of 22°C and a width of 2m using a tape casting apparatus. The solvent in the film was allowed to evaporate until the residual solvent content was less than 100%. Then, the film was peeled off from the stainless steel strip at a peel tension of 160 N / m.

[0312] Next, the peeled film is evaporated at 35°C and then cut. The film is then stretched 1.6 times its original width in the width direction (TD direction) at 160°C using a tenter frame. The residual solvent content of the film at the start of the tenter frame stretching is 3-15% by mass.

[0313] Subsequently, the film was simultaneously dried using multiple rollers in drying zones at 120°C and 140°C. The film was cut into 2.5m wide pieces, and knurling with a width of 10mm and a height of 2.5μm was applied to both ends of the film. Then, the film was wound onto a core to obtain an optical film 3 with a thickness of 40μm and a roll length of 3900m.

[0314] (2.2) Fabrication of optical films 4~17 In the fabrication of optical film 3, the type of resin, as well as the type and content of additives, were changed as recorded in Table I. Otherwise, optical films 4 to 17 were obtained using the same method. Furthermore, the thickness of optical films 4 to 17 was 40 μm.

[0315] (3) Fabrication of polarizing components A 60 μm thick strip of polyvinyl alcohol (PVA) film was prepared. While continuously conveying the film through guide rollers, it was immersed in a dyeing bath (30°C) containing iodine and potassium iodide for dyeing treatment, followed by a 2.5-fold stretching treatment. Subsequently, the film underwent a total 5-fold stretching and crosslinking treatment in an acidic bath (60°C) containing boric acid and potassium iodide. The resulting 12 μm thick iodine-PVA polarizing film was dried in a dryer at 50°C for 30 minutes. A polarizing element with a moisture content of 4.9% was then obtained.

[0316] (4) Production of polarizing plates (4.1) Fabrication of polarizing plate 1 The polarizing plate 1 is fabricated by bonding optical film 1 (first optical film), optical film 3 (second optical film) and polarizing element together.

[0317] (4.1.1) Preparation of water-based adhesives Mix the following ingredients to prepare a water-based adhesive. 100.0 parts by weight of pure water Carboxyl-modified polyvinyl alcohol "Kuraray Poval (registered trademark) KL318" (manufactured by Kuraray Co., Ltd.) 3.0 parts by weight Water-soluble polyamide epoxy resin "Sumirez (registered trademark) Resin 650" (30% solids concentration aqueous solution, manufactured by Sumitomo Chemical Chemtex Co., Ltd.) 1.5 parts by weight

[0318] (4.1.2) Pretreatment before the second optical film The optical film 3 was immersed in a saponification solution (10% by mass sodium hydroxide aqueous solution at 60°C) for 30 seconds. Then, the optical film 3 was immersed in a water bath for 5 seconds. This process was repeated twice. Afterward, the optical film 3 was rinsed with water for 5 seconds and then dried. The drying conditions were 70°C for 2 minutes.

[0319] Next, the optical film 3 was immersed in water at 30°C for 10 seconds to perform a swelling treatment. After that, the optical film 3 was dried at 40°C for 53 seconds.

[0320] (4.1.3) Bonding of optical film and polarizing element The surfaces of optical films 1 and 3 that are bonded to the polarizer are subjected to corona treatment. Then, the aforementioned water-based adhesive is applied to the surfaces bonded to the polarizer, and the optical films are bonded to both sides of the polarizer. Immediately afterwards, the laminated material is dried for 5 minutes in a hot air circulating dryer set to 80°C to obtain polarizer 1.

[0321] (4.2) Fabrication of polarizing plates 2~16 When manufacturing polarizing plate 1, the types of the first and second optical films are changed to those recorded in Table I and Table II. Otherwise, polarizing plates 2 to 16 are obtained by the same method.

[0322] Tables I and II show the composition of the obtained polarizing plates. Furthermore, the "-" in Table II indicates that the ingredient is not present. The "degree of substitution" in the table indicates the degree of acetyl substitution. The content of each additive in Table II represents the proportion of the additive relative to the mass of acetylated cellulose. Therefore, in the case of Example 2, for example, when converted to a proportion relative to the total mass of polyester (I) and polyester (II), the content of polyester (II) is 80% by mass.

[0323]

[0324]

[0325] 2. Evaluation (Manufacturing of a liquid crystal display device) Using the polarizing plates 1 to 16 prepared above, liquid crystal display devices 1 to 16 are manufactured according to the following method. In the obtained liquid crystal display devices, the deviation of in-plane contrast and water resistance (color unevenness caused by water content) are evaluated.

[0326] Two glass substrates with a thickness of 0.5 mm are prepared, along with an IPS-type liquid crystal cell containing a liquid crystal layer disposed between them. Then, the polarizing plates 1-16 prepared above are bonded together via an adhesive layer, with the second optical film serving as the liquid crystal cell side, to obtain liquid crystal display devices 1-16. The bonding is performed with the absorption axis of the polarizer on the visual recognition side (101A shown in FIG. 2) perpendicular to the absorption axis of the polarizer on the backlight side (101B shown in FIG. 2).

[0327] (1) Uneven color due to water content (water resistance) The resulting liquid crystal display device is placed horizontally on a table or similar surface. "Bemcot (registered trademark)" (manufactured by Asahi Kasei Corporation) is placed on a portion of the liquid crystal display device, and the Bemcot (registered trademark) is moistened. The Bemcot (registered trademark) is then coated with a 100μm thick polyester (PET) film to prevent it from drying out.

[0328] A black signal was input to the LCD device via PC, the LCD device was powered on, and left for 24 hours. The room temperature was set to 23°C and the panel temperature to 38°C. After 24 hours, the Bemcot (registered trademark) was removed. One minute later, the L* of the portion of the LCD device with the Bemcot (registered trademark) was used as the L* of the water-immersed portion, and the luminance was measured using an image colorimeter "EZ Contrast" (manufactured by ELDIM). The L* of the portion of the LCD device without the Bemcot (registered trademark) was used as the L* of the non-immersed portion, and the EZ contrast was measured. The L* change rate was then calculated using the following formula. L * rate of change = (L * of water-soaked portion) / (L * of non-soaked portion)

[0329] The measurements conducted using EZ as a comparison were performed with the liquid crystal display device showing black in color mode. The water immersion conditions were as follows: the liquid crystal display device was powered on and left to stand for 24 hours with Bemcot (registered trademark) fully immersed in water attached. In the L*a*b* color space, L represents lightness.

[0330] The rate of change of L* is evaluated based on the following criteria. A value of B or higher (A and B) is considered practically sound. AA:L * The rate of change is below 1.05. A:L * The rate of change is greater than 1.05 and less than 1.30. B:L * The rate of change is greater than 1.30 and less than 1.55. The C:L* rate of change exceeds 1.55.

[0331] Furthermore, in evaluations AA and A, no color unevenness caused by the change in L* between the water-impregnated and non-impregnated areas was observed. In evaluation B, slight color unevenness caused by the change in L* between the water-impregnated and non-impregnated areas was observed, but it was not a practical problem. In evaluation C, color unevenness caused by the change in L* between the water-impregnated and non-impregnated areas was observed, which posed a practical problem. In particular, when the L* change rate exceeded 1.80, strong color unevenness was observed.

[0332] (2) Bias in comparison The backlight of the obtained liquid crystal display device was continuously lit for 1 hour at 23°C and 55%RH, and the front contrast was measured. The front contrast measurement was performed according to the following procedure.

[0333] i) The frontal luminance of the display screen when the liquid crystal display device displays white was measured using the "EZ-Contrast160D" (manufactured by ELDIM). Here, "frontal luminance" refers to the luminance measured along the normal direction of the display screen. The frontal luminance of the display screen when the liquid crystal display device displays black was measured using the same method.

[0334] ii) The ratio of the frontal brightness of the display screen when displaying white to the frontal brightness of the display screen when displaying black is used as the frontal contrast. Frontal contrast = (frontal luminance when displaying white) / (frontal luminance when displaying black)

[0335] On the display screen of the liquid crystal display device, the frontal contrast of 9 points was measured. The 9 points on the display screen, as shown in Figure 3, are the center point of the display device and 8 other points. Four of the other 8 points are points on the diagonals of the display device. The distance from the four corners (A-D) of the display device to each point is 1 / 10 of the length of the diagonal. The remaining 4 points are points on lines that bisect the display device vertically and horizontally, respectively. These bisecting lines pass through the midpoints (E-H) of the four sides of the display device. The distance from the midpoints (E-H) of the four sides of the display device to each point is 1 / 10 of the length of the bisecting lines.

[0336] Calculate the average value of the 9 positive comparisons. Also, among the 9 positive comparisons, the maximum value of the positive comparison with the largest difference from the average value is determined. Then, calculate the deviation [%] of the positive comparison using the following formula.

[0337] Deviation in positive comparison [%] ={(Maximum value of positive comparison) - (Average value of positive comparison)} / (Average value of positive comparison) × 100

[0338] The deviation from the positive comparison is evaluated based on the following benchmarks. A score of B or above (AA~B) is considered to be practically problem-free. AA: The deviation for positive comparison was less than 1%. A: The deviation of positive comparison is more than 1% but less than 5%. B: The deviation of the positive comparison is more than 5% but less than 10%. C: The deviation in positive comparison is more than 10%.

[0339] Furthermore, in evaluation AA, no unevenness caused by the bias of direct comparison is observed. In evaluation A, a small unevenness caused by the bias of direct comparison is observed, but it poses no practical problem. In evaluation B, a slight unevenness caused by the bias of direct comparison is observed, but it poses no practical problem. In evaluation C, a large unevenness caused by the bias of direct comparison is observed, which poses a practical problem.

[0340] The evaluation results are shown in Table III. Furthermore, the "-" in the table indicates that light leakage has occurred and cannot be measured.

[0341]

[0342] As can be seen from the embodiments and comparative examples, the polarizing plate of the present invention can suppress color unevenness and contrast deviation caused by water content, thereby improving the visual recognition of the display device.

[0343] As can be seen from Examples 1, 2, 11 and 12, by making the content of polyester (II) in the range of 70 to 90% by mass relative to the total mass of polyester (I) and polyester (II), color unevenness can be more effectively suppressed.

[0344] As can be seen from Examples 1 and 3, by further containing polyester (III), color unevenness can be further suppressed.

[0345] As can be seen from Examples 1 and 8-10, by making the width of the second optical film within the range of 2.2 to 3.0 μm, the contrast deviation can be further suppressed.

[0346] 1:Polarizing plate 2: First optical film 4:Polarizer 5: Second optical film 100: Display device 101A, 101B: Polarizing plates 101C: Liquid Crystal Cell 102A, 102B: First optical film 103A, 103B, 103C, 103D: Continuing layers 104A, 104B: Polarizing components 105A, 105B: Second optical film 106: Adhesive layer 107: Liquid Crystal Layer 108A, 108B: Glass substrate

Claims

1. A polarizing plate comprising, sequentially having a first optical film, a polarizing element, and a second optical film, characterized in that the first optical film contains a polyester, and the second optical film contains a polyester represented by the following general formula (I), a polyester represented by the following general formula (II), and acetylated cellulose with a degree of substitution of acetyl groups in the range of 2.30 to 2.80; General formula (I): T-(DP)nD General formula (II): T-(DP)nDT (In the aforementioned general formulas (I) and (II), T represents a phenylcarboxylic acid residue; D represents an alkanediol residue with 2 to 12 carbon atoms, an aromatic diol residue with 6 to 12 carbon atoms, or an oxyalkanediol residue with 4 to 12 carbon atoms; P represents an alkanedicarboxylic acid residue with 4 to 12 carbon atoms, or an aromatic dicarboxylic acid residue with 6 to 12 carbon atoms; n represents an integer greater than or equal to 1).

2. The polarizing plate of claim 1, wherein the content of polyester represented by the aforementioned general formula (II) is in the range of 70 to 90% by mass relative to the total mass of polyester represented by the aforementioned general formula (I) and polyester represented by the aforementioned general formula (II).

3. The polarizing plate of claim 1, wherein the polyester contained in the aforementioned first optical film is polyethylene terephthalate.

4. The polarizing plate of claim 1, wherein the aforementioned second optical film further contains an ester represented by the following general formula (III); General formula (III): TD (in the aforementioned general formula (III), T represents a phenylcarboxylic acid residue; D represents an alkanediol residue having 2 to 12 carbon atoms, an aryldiol residue having 6 to 12 carbon atoms, or an oxyalkanediol residue having 4 to 12 carbon atoms).

5. The polarizing plate of claim 1, wherein the width of the aforementioned second optical film is in the range of 2.2 to 3.0 m.

6. A method for manufacturing a polarizing plate, characterized in that the polarizing plate is manufactured as described in any one of claims 1 to 5.

7. A display device, characterized in that it comprises a polarizing plate as described in any one of claims 1 to 5, and the aforementioned second optical film system is disposed on the side of the liquid crystal cell.

Images