JP6330808B2 - Polarizing plate and liquid crystal display device - Google Patents

Description

  The present invention relates to a polarizing plate and a liquid crystal display device including the polarizing plate.

  With the high performance and high quality of liquid crystal display devices, various demands have been made for polarizing plate protective films used for polarizing plates.

  As a polarizing plate protective film for a general liquid crystal display device, a film made of cellulose ester is mainly used. Cellulose ester films are generally formed by a solution casting film forming method from the viewpoint of ensuring flatness, etc., but with this film forming method, the refractive index in the thickness direction is lower than the refractive index in the film plane. Tend.

  Therefore, Patent Document 1 proposes a cellulose ester film in which retardation in the thickness direction is reduced by adding an ethylenic polymer. Patent Document 2 proposes a cellulose ester film in which the retardation in the in-plane direction and the thickness direction is reduced by adding polyester polyol.

  The polarizing plate of the liquid crystal display device is configured by sandwiching a polarizer between two protective films. The polarizer is obtained, for example, by dyeing a PVA (polyvinyl alcohol) film with a dichroic dye and stretching the film at a high magnification.

  In an IPS (In-plain switching) mode type liquid crystal display device, a liquid crystal display device with reduced retardation is used rather than a polarizing plate using a polarizer that provides a retardation as a protective film on the liquid crystal layer side. The polarizing plate that has been used can improve the display performance (viewing angle, color, gradation) of the liquid crystal display. In this respect, the cellulose ester film of Patent Document 1 or 2 with reduced retardation is suitable as a protective film for a polarizing plate of an IPS mode type liquid crystal display device. In addition, below, the cellulose-ester film with which retardation was reduced is also called a zero phase difference film.

JP 2003-12859 A (refer to claim 1, Table 1 etc.) Japanese Patent No. 5162358 (refer to Claim 1, Table 2, etc.)

  By the way, if the moisture permeability of the protective film on the surface side (opposite to the liquid crystal layer) is high with respect to the polarizer, moisture in the air passes through the protective film and reaches the polarizer, and the polarizer is deteriorated. . As a result, the polarizing function of the polarizing plate deteriorates, and in the liquid crystal display device, light leakage occurs during black display, resulting in luminance unevenness (image unevenness). For this reason, it is desirable that the moisture permeability of the protective film on the surface side of the polarizer is low. The low moisture-permeable protective film can be realized by using, for example, an acrylic resin or a PET (polyethylene terephthalate) resin. In the IPS mode type liquid crystal display device, it is desirable to use the above-described conventional zero retardation film as a protective film on the back side (liquid crystal layer side) of the polarizer from the viewpoint of improving display performance.

  On the other hand, in recent years, with the demand for thinning of liquid crystal display devices, thinning of polarizing plates has been demanded. Thinning of the polarizing plate can be achieved by thinning each layer (low moisture-permeable protective film, polarizer, zero retardation film) of the polarizing plate.

  However, when each layer of the polarizing plate is thinned, the mechanical strength of each layer is lowered, and the mechanical strength of the entire polarizing plate is lowered. In particular, when the protective film having low moisture permeability is thinned, the flexibility is remarkably reduced, so that the mechanical strength of the entire polarizing plate is easily lowered. As a result, when performing the rework work after bonding the polarizing plate to the liquid crystal cell, the polarizing plate may be broken even if the tensile tension is weak, and the handling property of the polarizing plate is deteriorated. Note that the rework operation refers to an operation in which, when the bonding of the polarizing plate to the liquid crystal cell fails, the polarizing plate is peeled off and bonded to the liquid crystal cell again.

  The present invention has been made in view of the above-mentioned problems, and its purpose is to form a polarizing plate as a whole even if the low moisture-permeable protective film, polarizer, and zero retardation film are made thin. An object of the present invention is to provide a polarizing plate capable of improving the handleability by suppressing the decrease in mechanical strength of the liquid crystal display and a liquid crystal display device including the polarizing plate.

  The above object of the present invention is achieved by the following configurations.

A polarizing plate according to one aspect of the present invention is a polarizing plate in which a first protective film, a polarizing film as a polarizer, a second protective film, and an adhesive layer are laminated in this order,
The total thickness of the first protective film, the polarizing film, and the second protective film is 90 μm or less,
The moisture permeability of the first protective film is 400 g / m ² · 24 hr or less,
The second protective film contains a cellulose ester and a retardation reducing agent,
The retardation reducing agent is an OH group in a compound (A) having one furanose structure or pyranose structure, or in a compound (B) in which at least one furanose structure or pyranose structure is bonded to 2 to 12 inclusive. Including sugar esters all or partly esterified with aliphatic acyl groups,
In the second protective film,
Ro represented by the following formula (i) is 0 nm or more and 10 nm or less,
Rt represented by the following formula (ii) is -10 nm or more and +10 nm or less.
Formula (i) Ro = (nx−ny) × d
Formula (ii) Rt = {(nx + ny) / 2−nz} × d
(In the formula, Ro is the retardation value in the in-plane direction of the film, Rt is the retardation value in the thickness direction of the film, nx is the refractive index in the slow axis direction in the film plane, ny is the fast axis direction in the film plane) Refractive index, nz is the refractive index in the thickness direction of the film (refractive index is measured at a wavelength of 590 nm in an environment of 23 ° C. and 55% RH), and d is the thickness (nm) of the film.

  According to the above configuration, even when the total thickness of the polarizing plate is thinned by setting the total thickness of the first protective film having low moisture permeability, the polarizing film, and the second protective film realizing zero retardation to 90 μm or less. The second protective film contains the sugar ester having the above-described chemical structure as the retardation reducing agent, so that the entire polarizing plate has a mechanical strength as compared with the configuration in which the zero retardation is realized by the other retardation reducing agent. It is possible to suppress the decrease. As a result, breakage of the polarizing plate during reworking work can be suppressed, and its handling property can be improved.

  In addition, in this invention, a retardation reducing agent means the compound which has the effect | action which reduces the retardation value (Rt) of the thickness direction when it adds to a protective film compared with the case where it is not added. The retardation reducing agent preferably has a function of reducing the retardation value (Rt) in the thickness direction by 0.01 nm or more in terms of 80 μm when A mass% is added, compared to the case where it is not added. Used.

1 is a cross-sectional view illustrating a schematic configuration of a liquid crystal display device according to an embodiment of the present invention.

  An embodiment of the present invention will be described below with reference to the drawings. In the present specification, when the numerical range is expressed as A to B, the numerical value range includes the values of the lower limit A and the upper limit B. The present invention is not limited to the following contents.

  FIG. 1 is a cross-sectional view showing a schematic configuration of a liquid crystal display device 1 of the present embodiment. The liquid crystal display device 1 is configured by sandwiching a liquid crystal cell 2 between two polarizing plates 3 and 4 and is driven in an IPS mode. The liquid crystal cell 2 is configured by sandwiching a liquid crystal layer between two transparent substrates.

  The polarizing plate 3 includes a first protective film 11 on the front surface side (viewing side, opposite to the liquid crystal cell), a polarizing film 12 as a polarizer (polarizing film), and a second film on the back surface side (liquid crystal cell side). The protective film 13 and the pressure-sensitive adhesive layer 14 are laminated in this order. The pressure-sensitive adhesive layer 14 is bonded to the liquid crystal cell 2, whereby the polarizing plate 3 is located on the surface side of the liquid crystal cell 2. In addition, the polarizing plate 3 may further have functional layers such as a hard coat layer, an antiglare layer, and an antireflection layer on the side opposite to the polarizing film 12 with respect to the first protective film 11.

  The polarizing plate 4 is configured by laminating an adhesive layer 21, a protective film 22, a polarizing film 23, and a protective film 24 in this order. The pressure-sensitive adhesive layer 21 is bonded to the liquid crystal cell 2, whereby the polarizing plate 4 is located on the back side (backlight side) of the liquid crystal cell 2.

  The pressure-sensitive adhesive layer 21, the protective film 22, the polarizing film 23, and the protective film 24 of the polarizing plate 4 are the pressure-sensitive adhesive layer 14, the second protective film 13, the polarizing film 12, and the first protective film 11 of the polarizing plate 3, respectively. Therefore, in the following, the polarizing plate 3 will be described as an example, and the details thereof will be described, and the detailed description of the polarizing plate 4 will be omitted.

In the present embodiment, in the polarizing plate 3, the total thickness of the first protective film 11, the polarizing film 12, and the second protective film 13 is 90 μm or less. At this time, the moisture permeability (water vapor permeability) of the first protective film 11 is 400 g / m ² · 24 hr or less. The moisture permeability is determined as a value of moisture permeability (g / m ² · 24 hr) for 24 hours per 1 m ² under the condition of 40 ° C. and 90% RH by the method described in JIS Z 0208.

  The polarizing film 12 is obtained, for example, by dyeing a PVA film with a dichroic dye and stretching it at a high magnification, and the thickness thereof is 15 μm or less.

The second protective film 13 contains a cellulose ester and a retardation reducing agent. The retardation reducing agent is an OH group in the compound (A) having one furanose structure or pyranose structure, or in a compound (B) in which at least one furanose structure or pyranose structure is bonded to 2 to 12 inclusive. Including a sugar ester obtained by esterifying all or a part of the compound with an aliphatic acyl group. In the second protective film 13, Ro represented by the following formula (i) is 0 nm or more and 10 nm or less, and Rt represented by the following formula (ii) is −10 nm or more and +10 nm or less.
Formula (i) Ro = (nx−ny) × d
Formula (ii) Rt = {(nx + ny) / 2−nz} × d
(In the formula, Ro is the retardation value in the in-plane direction of the film, Rt is the retardation value in the thickness direction of the film, nx is the refractive index in the slow axis direction in the film plane, ny is the fast axis direction in the film plane) Refractive index, nz is the refractive index in the thickness direction of the film (refractive index is measured at a wavelength of 590 nm in an environment of 23 ° C. and 55% RH), and d is the thickness (nm) of the film.

  Note that when the expressions (i) and (ii) are satisfied at the same time, the generated phase difference is almost zero, so this phase difference is also referred to as a zero phase difference. By including the retardation reducing agent in the second protective film 13, the second protective film 13 can be made to function as a film that realizes a zero retardation (zero retardation film).

Since the first protective film 11 has a low water vapor transmission rate of 400 g / m ² · 24 hr or less, the polarizing film 12 can be prevented from being deteriorated by moisture that passes through the first protective film 11. However, when the protective film having low moisture permeability is thinned, the flexibility is lowered, and the mechanical strength of the entire polarizing plate 3 is easily lowered. In addition, the mechanical strength of the polarizing film 12 itself tends to decrease due to the thinning.

  On the other hand, the second protective film 13 contains a cellulose ester and a retardation reducing agent, and the retardation reducing agent contains a sugar ester having the above-described chemical structure. When the second protective film 13 contains the sugar ester, a zero phase difference can be realized both in the in-plane direction and in the thickness direction.

  Here, the sugar ester described above as the retardation reducing agent has a furanose structure or a pyranose structure, unlike the ethylenic polymer and polyester polyol as the retardation control agent. doing. For this reason, said sugar ester has a strong interaction with a cellulose ester. Therefore, even if the thickness of the second protective film 13 containing the sugar ester and the cellulose ester is reduced, the mechanical strength of the second protective film 13 can be suppressed from decreasing.

  Therefore, even when the total thickness of the first protective film 11, the polarizing film 12, and the second protective film 13 is 90 μm or less and the entire polarizing plate 3 is thinned, the mechanical strength tends to decrease due to the thinning. Since the first protective film 11 and the polarizing film 12 are supported by the second protective film 13, the mechanical strength of the polarizing plate 3 as a whole can be suppressed from decreasing. As a result, it is possible to suppress the breakage of the polarizing plate 3 during the reworking operation (operation to peel off the polarizing plate 3 attached to the liquid crystal cell 2) and to improve the handling property.

  In particular, in the case of a further thin configuration in which the total thickness of the first protective film 11, the polarizing film 12, and the second protective film 13 is 80 μm or less, the mechanical properties of the entire polarizing plate 3 due to the thinning of each layer. Due to the decrease in strength, the polarizing plate 3 is more easily broken during the reworking operation, so that the above-described configuration becomes more effective. In addition, when the thickness of the polarizing film 12 is as thin as 15 μm or less, the mechanical strength of the entire polarizing plate 3 is more likely to be lowered due to the thinning of each layer, and thus the above-described configuration is very effective. From the viewpoint of reducing the thickness of the polarizing plate 3, the thickness of the second protective film 13 is desirably 30 μm or less.

  Thus, focusing on the chemical structure (similarity of the chemical structure with the cellulose ester) of the sugar ester for realizing the zero retardation, contained in the second protective film 13, the entire polarizing plate 3 By utilizing as a means for suppressing a decrease in mechanical strength when thinning, it is possible to suppress breakage of the polarizing plate 3 and improve its handling property.

  From the viewpoint of surely reducing the retardation Ro in the in-plane direction and the retardation Rt in the thickness direction, the sugar ester is an OH in the compound (B) in which at least one of the furanose structure or the pyranose structure is bonded to 12 or less. A compound in which all or part of the group is esterified with an aliphatic acyl group is desirable. More preferably, the sugar ester is a compound in which all or part of the OH groups in the compound (B) in which at least one of the furanose structure or the pyranose structure is bonded is esterified with an acetyl group. Examples of such sugar esters include acetyl sucrose.

  In addition, since the first protective film 11 on the surface side of the polarizing plate 3 has low moisture permeability and can suppress deterioration of the polarizing film 12 due to moisture, when the polarizing plate 3 is applied to the liquid crystal display device 1, Luminance unevenness (image unevenness) can be suppressed by suppressing light leakage during display. Furthermore, since the second protective film 13 is composed of a zero retardation film, a decrease in mechanical strength when the polarizing plate 3 is thinned can be suppressed. Therefore, the polarizing plate 3 described above is an IPS mode type. And suitable for the thin liquid crystal display device 1.

The first protective film 11 may contain any resin as long as the moisture permeability is 400 g / m ² · 24 hr or less. Examples of such a low moisture permeability resin include polyethylene terephthalate (PET) resin, acrylic resin, and cyclic polyolefin resin (COP). Incidentally, the moisture permeability of the PET resin is 40 g / m ² · 24 hr, the moisture permeability of the acrylic resin is 100 g / m ² · 24 hr, and the moisture permeability of the COP is 0.1 g / m ² · 24 hr. . In addition, the preferable range of the water vapor transmission rate of the 1st protective film 11 is 100 g / m < ² > * 24hr or less.

  Details of this embodiment will be described below. In the following description, when it is not necessary to clearly distinguish the second protective film on the liquid crystal cell side and the first protective film on the viewing side with respect to the polarizing film, these are simply protected together. It is called a film.

[Second protective film]
[Compound having furanose structure or pyranose structure]
The 2nd protective film of a polarizing plate contains a cellulose ester and a retardation reducing agent as mentioned above. The retardation reducing agent includes an OH group in the compound (A) having one furanose structure or pyranose structure, or two or more and 12 or less furanose structures or pyranose structures bonded to each other. In which all or a part of the compound is esterified with an aliphatic acyl group (hereinafter, these compounds are also referred to as sugar esters or sugar ester compounds).

  Examples of the preferred compound (A) and compound (B) include the compounds shown below, but the present invention is not limited to these.

  Examples of the compound (A) include glucose, galactose, mannose, fructose, xylose, arabinose and the like. The compound (A) also includes maltitol obtained by reducing maltose with hydrogenation at high pressure.

  Examples of the compound (B) include lactose, sucrose, cellobiose, maltose, cellotriose, maltotriose, raffinose, kestose and the like. Of these compounds (A) and (B), those having both a furanose structure and a pyranose structure are particularly preferred. An example is sucrose.

  There is no restriction | limiting in particular as monocarboxylic acid used when synthesize | combining a sugar ester compound, Well-known aliphatic monocarboxylic acid, alicyclic monocarboxylic acid, etc. can be used. The carboxylic acid used may be one type or a mixture of two or more types.

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

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

  Details of the method for producing these compounds are described in, for example, JP-A-8-245678.

  In addition to the esterified compounds of the above compounds (A) and (B), an oligosaccharide esterified compound can be applied as a compound in which 3 to 12 at least one of a furanose structure or a pyranose structure is bonded.

  Oligosaccharides are produced by causing an enzyme such as amylase to act on starch, sucrose or the like. Examples of the oligosaccharide applicable to this embodiment include maltooligosaccharide, isomaltooligosaccharide, fructooligosaccharide, galactooligosaccharide, and xylooligosaccharide. Oligosaccharides can also be acetylated in the same manner as compounds (A) and (B).

  Next, an example of a production example of a sugar ester compound is shown. Acetic anhydride (200 ml) was added dropwise to a solution obtained by adding pyridine (100 ml) to glucose (29.8 g, 166 mmol), and allowed to react for 24 hours. Thereafter, the solution was concentrated by evaporation and poured into ice water. After standing for 1 hour, the mixture was filtered through a glass filter to separate the solid and water. The solid on the glass filter was dissolved in chloroform and separated with cold water until it became neutral. The organic layer was separated and dried over anhydrous sodium sulfate. After removing anhydrous sodium sulfate by filtration, chloroform was removed by evaporation and further dried under reduced pressure to obtain glycolose pentaacetate (58.8 g, 150 mmol, 90.9%). In addition, the above-mentioned monocarboxylic acid can be used instead of the acetic anhydride.

  Although the specific example of the sugar ester compound of this embodiment is given to the following, this invention is not limited to this.

  The second protective film of the polarizing plate contains the above sugar ester compound in the film in an amount of 1 to 35% by mass, particularly 5 to 30% by mass in order to suppress the deterioration of the polarization function and stabilize the display quality. Is preferred. Within this range, it is preferable that the excellent effects of the present invention are exhibited and there is no bleeding out during storage of the raw material. Further, a sugar ester compound in which all OH groups are esterified and a sugar ester compound in which one or more OH groups remain may be used in combination. Examples thereof include a mixture of sucrose octaacetate, sucrose heptaacetate, and sucrose hexaacetate. The mixing ratio is not particularly limited. For example, 30:30:30, 40:30:30, 40:50:10, 50:30:20, 60:30:10, 80:10:10, 90: 7: 3, 95: 5: 0, and the like. These may be controlled by adjusting the reaction time or the amount of monocarboxylic acid added to react with the sugar during esterification of the sugar, or may be mixed.

[Acrylic polymer]
The second protective film may contain an acrylic polymer having a weight average molecular weight of 500 or more and 30000 or less as a retardation reducing agent. As such an acrylic polymer, those described in paragraphs 0059 to 0093 of International Publication WO08 / 044463 are preferably used.

〔polyester〕
(Polyester represented by formula (B1) or (B2))
The second protective film may contain a polyester represented by the following general formula (B1) or (B2) as a retardation reducing agent. This is from divalent alcohol G having 2 to 12 carbon atoms and dibasic acid having 2 to 12 carbon atoms, monocarboxylic acid B ₁ having 1 to 12 carbon atoms, or B ₂ being a monoalcohol having 1 to 12 carbon atoms There is a polyester obtained.

General formula (B1)
B _1- (GA-) _m GB ₁
(In the formula, B ₁ represents a monocarboxylic acid having 1 to 12 carbon atoms, G represents a divalent alcohol having 2 to 12 carbon atoms, and A represents a dibasic acid having 2 to 12 carbon atoms. B ₁ , G and A do not contain an aromatic ring, and m represents the number of repetitions.

General formula (B2)
B _2- (A-G-) _n A-B ₂
(In the formula, B ₂ represents a monoalcohol having 1 to 12 carbon atoms, G represents a divalent alcohol having 2 to 12 carbon atoms, and A represents a dibasic acid having 2 to 12 carbon atoms. B ₂ , (G and A do not contain an aromatic ring. N represents the number of repetitions.)

The monocarboxylic acids represented by B _1, not particularly limited, and may be known aliphatic monocarboxylic acid, alicyclic monocarboxylic acid.

  Examples of preferred monocarboxylic acids include the following, but the present invention is not limited thereto.

  As the aliphatic monocarboxylic acid, a fatty acid having a straight chain or a side chain having 1 to 32 carbon atoms can be preferably used. It is more preferable that it is C1-C20, and it is especially preferable that it is C1-C12. When acetic acid is contained, the compatibility with the cellulose ester is increased, and it is also preferable to use a mixture of acetic acid and another monocarboxylic acid.

  Preferred aliphatic monocarboxylic acids include, for example, formic acid, acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, 2-ethyl-hexanecarboxylic acid, undecylic acid, laurin Saturated fatty acids such as acid, tridecylic acid, myristic acid, pentadecylic acid, palmitic acid, heptadecylic acid, stearic acid, nonadecanoic acid, arachidic acid, behenic acid, lignoceric acid, serotic acid, heptacosanoic acid, montanic acid, melicic acid, and laccelic acid And unsaturated fatty acids such as undecylenic acid, oleic acid, sorbic acid, linoleic acid, linolenic acid and arachidonic acid.

The monoalcohol component represented by B ₂ is not particularly limited, and known alcohols can be used. For example, an aliphatic saturated alcohol or aliphatic unsaturated alcohol having a straight chain or a side chain having 1 to 32 carbon atoms can be preferably used. The number of carbon atoms is more preferably 1 to 20, and particularly preferably 1 to 12 carbon atoms.

  Examples of the divalent alcohol component represented by G include the following, but the present invention is not limited thereto. For example, ethylene glycol, diethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,2-butylene glycol, 1,3-butylene glycol, 1,4-butylene glycol, 1,5-pentanediol, , 6-hexanediol, 1,5-pentylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, etc., among which ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol 1,2-butylene glycol, 1,3-butylene glycol, 1,4-butylene glycol, 1,6-hexanediol, diethylene glycol and triethylene glycol are preferred, and 1,3-propylene glycol, , 4-butylene glycol 1,6-hexanediol, are used preferably diethylene glycol.

  The dibasic acid (dicarboxylic acid) component represented by A is preferably an aliphatic dibasic acid or an alicyclic dibasic acid. Examples of the aliphatic dibasic acid include malonic acid, succinic acid, glutaric acid, Adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedicarboxylic acid, dodecanedicarboxylic acid, etc., especially aliphatic dicarboxylic acids having 4 to 12 carbon atoms, at least one selected from these To do. That is, two or more dibasic acids may be used in combination.

  m and n represent the number of repetitions and are preferably 1 or more and 170 or less.

  The weight average molecular weight of the polyester is preferably 20000 or less, and more preferably 10,000 or less. In particular, polyesters having a weight average molecular weight of 500 to 10,000 are preferable because they have good compatibility with cellulose esters and are less likely to evaporate or volatilize during film formation.

  Polycondensation of polyester is performed by a conventional method. For example, a direct reaction of the above dibasic acid and glycol, the above dibasic acid or an alkyl ester thereof, for example, a polyesterification reaction or transesterification reaction between a dibasic acid methyl ester and a glycol, or a hot melt condensation method, Alternatively, it can be easily synthesized by any method of dehydrohalogenation reaction between acid chloride of these acids and glycol, but polyester having a weight average molecular weight not so large is preferably by direct reaction. Polyester having a high distribution on the low molecular weight side has very good compatibility with the cellulose ester, and after forming the film, a polarizing plate protective film having low moisture permeability and excellent transparency can be obtained.

  As a method for adjusting the molecular weight, a conventional method can be used without any particular limitation. For example, depending on the polymerization conditions, in the method of blocking the molecular ends with a monovalent acid (monocarboxylic acid) or monovalent alcohol (monoalcohol), by controlling the amount of these monovalent compounds added, The molecular weight can be adjusted. In this case, a monovalent acid is preferable from the viewpoint of the stability of the polymer.

  For example, examples of the monovalent acid include acetic acid, propionic acid, butyric acid, etc., but the monovalent acid is not distilled out of the system during the polycondensation reaction, but is stopped and the monovalent acid is removed from the reaction system. Those which are easily distilled off when the acid is removed from the system are selected, but these may be mixed and used. In the case of direct reaction, the weight average molecular weight can also be adjusted by measuring the timing at which the reaction is stopped by the amount of water distilled off during the reaction. In addition, it can be adjusted by biasing the number of moles of glycol or dibasic acid to be charged or by controlling the reaction temperature.

  It is preferable to contain 1-40 mass% of polyester of this embodiment with respect to a cellulose ester. Furthermore, it is preferable to contain 2-30 mass%. It is preferable to contain 3-15 mass% especially.

  These compounds can be contained in an amount of 0.1 to 20% by mass in the second protective film of the polarizing plate.

  By using a film to which the acrylic polymer or polyester is added, a polarizing plate with little deterioration due to high temperature and high humidity can be obtained. Further, by using this polarizing plate, an IPS mode liquid crystal display device can be obtained in which the contrast and viewing angle stability are maintained for a long time and the surface flatness is excellent.

[Cellulose ester]
The cellulose ester used for the second protective film of the polarizing plate is not particularly limited, but the cellulose ester is a carboxylic acid ester having about 2 to 22 carbon atoms, and may be an aromatic carboxylic acid ester. A lower fatty acid ester is preferred.

  The lower fatty acid in the lower fatty acid ester of cellulose means a fatty acid having 6 or less carbon atoms. The acyl group bonded to the hydroxyl group may be linear or branched or may form a ring. Furthermore, another substituent may be substituted. When the degree of substitution is the same, birefringence decreases when the number of carbon atoms is large, and therefore, the number of carbon atoms is preferably selected from acyl groups having 2 to 6 carbon atoms. The cellulose ester preferably has 2 to 4 carbon atoms, more preferably 2 to 3 carbon atoms.

  The cellulose ester may be an acyl group derived from a mixed acid, and particularly preferably an acyl group having 2 and 3 carbon atoms or 2 and 4 carbon atoms. The cellulose ester used in the present embodiment includes cellulose mixed fatty acid in which propionate group or butyrate group is bonded in addition to acetyl group such as cellulose acetate propionate, cellulose acetate butyrate, or cellulose acetate propionate butyrate Esters can be used. The butyryl group that forms butyrate may be linear or branched. Cellulose esters preferably used in this embodiment are cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, and cellulose acetate phthalate.

  The retardation value can be appropriately controlled depending on the type of acyl group of the cellulose ester and the degree of substitution of the acyl group with the pyranose ring of the cellulose resin skeleton.

  Preferred cellulose esters in the present embodiment are those that simultaneously satisfy the following formulas (1) and (2).

Formula (1): 2.0 <= X + Y <= 3.0
Formula (2): 0 ≦ Y ≦ 2.0
In the formula, X is the degree of substitution of the acetyl group, and Y is the degree of substitution of the propionyl group or butyryl group. Those satisfying the above two formulas are suitable for producing a polarizing plate protective film exhibiting excellent optical properties.

  Of these, triacetyl cellulose and cellulose acetate propionate are particularly preferably used. In cellulose acetate propionate, 1.0 ≦ X ≦ 2.5, preferably 0.1 ≦ Y ≦ 1.5, and 2.0 ≦ X + Y ≦ 3.0. The measuring method of the substitution degree of an acyl group can be measured according to ASTM-D817-96.

  If the substitution degree of the acyl group is too low, there will be more unreacted parts with respect to the hydroxyl groups of the pyranose ring that constitutes the skeleton of the cellulose resin, and a large amount of the hydroxyl groups will remain, so that the humidity change of the retardation and the polarizing plate protective film As a result, the ability to protect the polarizer may decrease, which is not preferable.

  The number average molecular weight of the cellulose ester used in the present embodiment is preferably in the range of 60,000 to 300,000 because the mechanical strength of the resulting film is strong. Furthermore, the thing of 70000-200000 is used preferably.

The number average molecular weight of cellulose ester can be measured under the following conditions by high performance liquid chromatography.
Solvent: Acetone Column: MPW × 1 (manufactured by Tosoh Corporation)
Sample concentration: 0.2 (mass / volume)%
Flow rate: 1.0 ml / min Sample injection volume: 300 μl
Standard sample: Standard polystyrene Temperature: 23 ° C

  The cellulose as a raw material for the cellulose ester is not particularly limited, and examples thereof include cotton linter, wood pulp, and kenaf. Moreover, the cellulose ester obtained from them can be mixed and used in arbitrary ratios, respectively.

Cellulose esters use an organic acid such as acetic acid or an organic solvent such as methylene chloride when the acylating agent of the cellulose raw material is an acid anhydride (acetic anhydride, propionic anhydride, or butyric anhydride). The reaction is carried out using a novel protic catalyst. When the acylating agent is acid chloride (CH ₃ COCl, C ₂ H ₅ COCl, C ₃ H ₇ COCl), the reaction is carried out using a basic compound such as an amine as a catalyst. Specifically, it can be synthesized with reference to the method described in JP-A-10-45804.

  In the cellulose ester, the average substitution degree of the acyl group at the 6-position of the glucose unit is preferably 0.5 to 0.9.

  Unlike the 2nd and 3rd positions, the 6th position of the glucose unit constituting the cellulose ester has a highly reactive primary hydroxyl group. This primary hydroxyl group preferentially forms sulfate ester in the process of producing cellulose ester catalyzed by sulfuric acid. Therefore, by increasing the amount of catalytic sulfuric acid in the esterification reaction of cellulose, the average substitution degree at the 2nd and 3rd positions of the glucose unit can be increased as compared with the normal cellulose ester. Furthermore, if the cellulose is tritylated as necessary, the hydroxyl group at the 6-position of the glucose unit can be selectively protected. Therefore, the trityl group protects the hydroxyl group at the 6-position, and after esterification, the trityl group (protection) The average substitution degree at the 2nd and 3rd positions can be increased from the 6th position of the glucose unit. Specifically, a cellulose ester produced by the method described in JP-A No. 2005-281645 can also be preferably used.

  In the case of acetylcellulose, it is necessary to extend the time for the acetylation reaction in order to increase the acetylation rate. However, if the reaction time is too long, the decomposition proceeds at the same time, and the polymer chain is broken and the acetyl group is decomposed, resulting in undesirable results. Therefore, it is necessary to set the reaction time within a certain range in order to increase the degree of acetylation and suppress decomposition to some extent. It is not appropriate to define the reaction time because the reaction conditions are various and greatly change depending on the reaction apparatus, equipment and other conditions. As the decomposition of the polymer progresses, the molecular weight distribution becomes wider. Therefore, in the case of cellulose ester, the degree of decomposition can be defined by the value of weight average molecular weight (Mw) / number average molecular weight (Mn) that is usually used. That is, in the process of acetylation of cellulose triacetate, the weight average molecular weight is one index of the degree of reaction for allowing the acetylation reaction to be carried out for a sufficient time for acetylation without being too long and causing excessive decomposition. The value of (Mw) / number average molecular weight (Mn) can be used.

  An example of a method for producing a cellulose ester is shown below: 100 parts by mass of a flocculent linter as a cellulose raw material was crushed, 40 parts by mass of acetic acid was added, and pretreatment activation was performed at 36 ° C. for 20 minutes. Thereafter, 8 parts by mass of sulfuric acid, 260 parts by mass of acetic anhydride and 350 parts by mass of acetic acid were added, and esterification was performed at 36 ° C. for 120 minutes. After neutralization with 11 parts by mass of a 24% magnesium acetate aqueous solution, saponification aging was carried out at 63 ° C. for 35 minutes to obtain acetylcellulose. This was stirred for 160 minutes at room temperature using a 10-fold acetic acid aqueous solution (acetic acid: water = 1: 1 (mass ratio)), then filtered and dried to obtain purified acetylcellulose having an acetyl substitution degree of 2.75. . This acetylcellulose had Mn of 92000, Mw of 156000, and Mw / Mn of 1.7. Similarly, cellulose esters having different degrees of substitution and Mw / Mn ratios can be synthesized by adjusting the esterification conditions (temperature, time, stirring) and hydrolysis conditions of the cellulose ester. The Mw / Mn ratio of the cellulose ester is preferably 1.4 to 5.0.

  In addition, it is preferable to purify the synthesized cellulose ester to remove low molecular weight components and to remove unacetylated or low acetylated components by filtration.

  In the case of mixed acid cellulose ester, it can be obtained by the method described in JP-A-10-45804.

  Cellulose esters are also affected by trace metal components in cellulose esters. These are considered to be related to water used in the manufacturing process, but it is preferable that there are few components that can become insoluble nuclei, and metal ions such as iron, calcium, and magnesium contain organic acidic groups. Insoluble matter may be formed by salt formation with a possible polymer degradation product, etc., and it is preferable that the amount is small. The iron (Fe) component is preferably 1 ppm or less. As for the calcium (Ca) component, it is easy to form a coordination compound, that is, a complex with an acidic component such as carboxylic acid or sulfonic acid, and many ligands. Starch, turbidity).

  The calcium (Ca) component is 60 ppm or less, preferably 0 to 30 ppm. The magnesium (Mg) component is preferably in the range of 0 to 70 ppm, particularly preferably 0 to 20 ppm, since too much will cause insoluble matter. Metal components such as iron (Fe) content, calcium (Ca) content, magnesium (Mg) content, etc. are pre-processed by completely digesting cellulose ester with micro digest wet cracking equipment (sulfuric acid decomposition) and alkali melting. After being performed, it can be analyzed using ICP-AES (Inductively Coupled Plasma Atomic Emission Spectrometer).

[First protective film]
Next, the first protective film on the surface side of the polarizing plate will be described.

[Polyester resin]
As the first protective film of the polarizing plate, a film made of a polyester resin (polyester film) can be used. As the polyester, polyethylene terephthalate (PET) or polyethylene naphthalate (PEN) can be used, but other copolymer components may be included. These resins are excellent in transparency and excellent in thermal and mechanical properties, and the retardation can be easily controlled by stretching. In particular, PET is the most suitable material because it has a large intrinsic birefringence and relatively large retardation can be obtained relatively easily even if the film is thin.

  It is preferable that the polyester film has a retardation (in-plane direction) of 3000 to 30000 nm. When the retardation is less than 3000 nm, when a polyester film is used as a polarizing plate protective film and applied to a liquid crystal display device, it exhibits a strong interference color when observed from an oblique direction (color unevenness occurs) and ensures good visibility. Can not do it. A preferable lower limit value of retardation is 4500 nm, a more preferable value is 5000 nm, a still more preferable value is 6000 nm, a further preferable value is 8000 nm, and a further preferable lower limit value is 10,000 nm.

  On the other hand, the upper limit of retardation is 30000 nm. Even if a polyester film having a retardation of more than that is used, not only a further improvement effect of visibility is not obtained, but also the thickness of the film is considerably increased, and the handling property as an industrial material is reduced. Absent.

  In addition, said retardation can also be calculated | required by measuring the refractive index and thickness of a biaxial direction, and can also be calculated | required using commercially available automatic birefringence measuring apparatuses, such as KOBRA-21ADH (Oji Scientific Instruments). it can.

  The ratio (Ro / Rt) between the retardation Ro in the in-plane direction and the thickness direction retardation Rt of the polyester film is preferably 0.200 or more, more preferably 0.500 or more, and further preferably 0.600 or more. As the ratio (Ro / Rt) is larger, the birefringence effect is more isotropic, and color unevenness due to the observation angle is less likely to occur. The ratio (Ro / Rt) is 2.0 for a perfect uniaxial (uniaxial symmetry) film. However, as the film approaches a perfect uniaxial (uniaxial symmetry) film, the mechanical strength in the direction orthogonal to the orientation direction decreases significantly.

  On the other hand, the ratio (Ro / Rt) of the polyester film is preferably 1.2 or less, more preferably 1.0 or less. In order to completely suppress the occurrence of color unevenness due to the observation angle, the ratio (Ro / Rt) does not need to be 2.0, and 1.2 or less is sufficient. Even if the ratio (Ro / Rt) is 1.0 or less, it is possible to satisfy the viewing angle characteristics (180 degrees left and right, about 120 degrees up and down) required for the liquid crystal display device.

  In order to control the retardation of the film within the specific range described above, the stretching ratio, stretching temperature, and film thickness at the time of film formation may be appropriately set. For example, the higher the draw ratio, the lower the drawing temperature, and the thicker the film, the higher the retardation. Conversely, the lower the stretching ratio, the higher the stretching temperature, and the thinner the film, the lower the retardation.

〔acrylic resin〕
An acrylic resin can also be used as the resin constituting the first protective film of the polarizing plate.

  The acrylic resin may be a polymer mainly composed of alkyl methacrylate, may be a single polymer of alkyl methacrylate, or 50% by weight or more of alkyl methacrylate and a single amount other than alkyl methacrylate. It may be a copolymer of 50% by weight or less. In the polymer mainly composed of alkyl methacrylate, the alkyl methacrylate is preferably 70% by weight or more, more preferably 80% by weight or more, and still more preferably 90% by weight, based on the total of 100% by weight of all monomers. In addition, the alkyl methacrylate is 99% by weight or less. As the alkyl methacrylate, those having 1 to 4 carbon atoms of the alkyl group are usually used, and among them, methyl methacrylate is preferably used.

  The monomer other than alkyl methacrylate may be a monofunctional monomer having one polymerizable carbon-carbon double bond in the molecule, or two or more polymerizable carbons in the molecule. -Although the polyfunctional monomer which has a carbon double bond may be sufficient, a monofunctional monomer is used preferably here. Examples thereof include alkyl acrylates such as methyl acrylate and ethyl acrylate, styrene monomers such as styrene and alkyl styrene, and unsaturated nitriles such as acrylonitrile and methacrylonitrile. When using alkyl acrylate as a copolymerization component, the carbon number is 1-8 normally.

[Alicyclic olefin polymer resin]
As the resin constituting the first protective film of the polarizing plate, an alicyclic olefin polymer resin (COP) can also be used.

  Examples of alicyclic olefin polymer resins include cyclic olefin random multi-component copolymers described in JP-A No. 05-310845, hydrogenated polymers described in JP-A No. 05-97978, and JP-A No. 11 And thermoplastic dicyclopentadiene-based ring-opening polymers and hydrogenated products thereof described in JP-A-124429.

  The alicyclic olefin polymer resin will be described more specifically. The alicyclic olefin polymer resin is a polymer having an alicyclic structure such as a saturated alicyclic hydrocarbon (cycloalkane) structure or an unsaturated alicyclic hydrocarbon (cycloalkene) structure. The number of carbon atoms constituting the alicyclic structure is not particularly limited, but is usually 4 to 30, preferably 5 to 20, more preferably 5 to 15 in the mechanical strength, The properties of heat resistance and film formability are highly balanced and suitable.

  The proportion of the repeating unit containing the alicyclic structure in the alicyclic olefin polymer-based resin may be appropriately selected, but is preferably 55% by weight or more, more preferably 70% by weight or more, and particularly preferably 90%. % By weight or more. It is preferable for the ratio of the above repeating units to be in this range since the transparency and heat resistance of the film are improved.

  Examples of the alicyclic olefin polymer resins include norbornene resins, monocyclic olefin resins, cyclic conjugated diene resins, vinyl alicyclic hydrocarbon resins, and hydrides thereof. Among these, norbornene-based resins can be suitably used because of their good transparency and moldability.

  Examples of the norbornene-based resin include a ring-opening polymer of a monomer having a norbornene structure, a ring-opening copolymer of a monomer having a norbornene structure and another monomer, a hydride thereof, and a norbornene structure. And an addition copolymer of a monomer having a norbornene structure and an addition copolymer of another monomer or a hydride thereof. Among these, a ring-opening (co) polymer hydride of a monomer having a norbornene structure is particularly preferable from the viewpoints of transparency, moldability, heat resistance, low hygroscopicity, dimensional stability, and lightness. It can be used suitably.

  Monomers having a norbornene structure include bicyclo [2.2.1] hept-2-ene (common name: norbornene), tricyclo [4.3.0.12,5] deca-3,7-diene ( Common name: dicyclopentadiene), 7,8-benzotricyclo [4.3.12,5] dec-3-ene (common name: methanotetrahydrofluorene), tetracyclo [4.4.0.12, 5.17,10] dodec-3-ene (common name: tetracyclododecene), and derivatives of these compounds (for example, those having a substituent in the ring). Here, examples of the substituent include an alkyl group, an alkylene group, and a polar group. Moreover, these substituents may be the same or different and a plurality may be bonded to the ring. Monomers having a norbornene structure can be used singly or in combination of two or more.

  Examples of the polar group include a hetero atom or an atomic group having a hetero atom. Examples of the hetero atom include an oxygen atom, a nitrogen atom, a sulfur atom, a silicon atom, and a halogen atom. Specific examples of the polar group include a carboxyl group, a carbonyloxycarbonyl group, an epoxy group, a hydroxyl group, an oxy group, an ester group, a silanol group, a silyl group, an amino group, a nitrile group, and a sulfone group.

  Other monomers capable of ring-opening copolymerization with monomers having a norbornene structure include monocyclic olefins such as cyclohexene, cycloheptene, and cyclooctene and derivatives thereof; and cyclic such as cyclohexadiene and cycloheptadiene. And conjugated dienes and derivatives thereof.

  A ring-opening polymer of a monomer having a norbornene structure and a ring-opening copolymer of a monomer having a norbornene structure and another monomer copolymerizable with the monomer have a known ring-opening polymerization catalyst. It can be obtained by (co) polymerization in the presence.

  Examples of other monomers capable of addition copolymerization with a monomer having a norbornene structure include ethylene, propylene, and α-olefins having 2 to 20 carbon atoms such as 1-butene and derivatives thereof; cyclobutene and cyclopentene. And cycloolefins such as cyclohexene and derivatives thereof; and non-conjugated dienes such as 1,4-hexadiene, 4-methyl-1,4-hexadiene, and 5-methyl-1,4-hexadiene. These monomers can be used alone or in combination of two or more. Among these, α-olefin is preferable and ethylene is more preferable.

  An addition polymer of a monomer having a norbornene structure and an addition copolymer of a monomer having a norbornene structure with another monomer copolymerizable with a monomer having a norbornene structure are prepared in the presence of a known addition polymerization catalyst. It can be obtained by polymerization.

  A hydrogenated product of a ring-opening polymer of a monomer having a norbornene structure, a hydrogenated product of a ring-opening copolymer of a monomer having a norbornene structure and another monomer capable of ring-opening copolymerization thereof, Hydrogenated products of addition polymers of monomers having a norbornene structure, and hydrogenated products of addition copolymers of monomers having a norbornene structure and other monomers copolymerizable therewith It can be obtained by adding a known hydrogenation catalyst containing a transition metal such as nickel or palladium to the polymer solution and hydrogenating carbon-carbon unsaturated bonds, preferably 90% or more.

  Among norbornene-based resins, as a repeating unit, X: bicyclo [3.3.0] octane-2,4-diyl-ethylene structure and Y: tricyclo [4.3.0.12,5] decane-7, 9-diyl-ethylene structure, the content of these repeating units is 90% by weight or more with respect to the entire repeating unit of the norbornene-based resin, and the content ratio of X and the content ratio of Y It is preferable that the ratio is 100: 0 to 40:60 by weight ratio of X: Y. By using such a resin, it is possible to obtain a film having no dimensional change over a long period of time and having excellent optical property stability.

(Plasticizer)
The protective film of a polarizing plate can contain a plasticizer as needed. The plasticizer is not particularly limited, but is preferably a polycarboxylic acid ester plasticizer, a glycolate plasticizer, a phthalate ester plasticizer, a fatty acid ester plasticizer, a polyhydric alcohol ester plasticizer, or a polyester plasticizer. Agent, acrylic plasticizer and the like. Of these, when two or more plasticizers are used, at least one plasticizer is preferably a polyhydric alcohol ester plasticizer. In addition, these plasticizers may act as a retardation reducing agent.

  The polyhydric alcohol ester plasticizer is a compound represented by the aforementioned general formula (3).

  The glycolate plasticizer is not particularly limited, but alkylphthalylalkyl glycolates can be preferably used. Examples of alkyl phthalyl alkyl glycolates include methyl phthalyl methyl glycolate, ethyl phthalyl ethyl glycolate, propyl phthalyl propyl glycolate, butyl phthalyl butyl glycolate, octyl phthalyl octyl glycolate, methyl phthalyl Ethyl glycolate, ethyl phthalyl methyl glycolate, ethyl phthalyl propyl glycolate, methyl phthalyl butyl glycolate, ethyl phthalyl butyl glycolate, butyl phthalyl methyl glycolate, butyl phthalyl ethyl glycolate, propyl phthalyl butyl Glycolate, butyl phthalyl propyl glycolate, methyl phthalyl octyl glycolate, ethyl phthalyl octyl glycolate, octyl phthalyl methyl glycolate, octyl phthalate Ethyl glycolate, and the like.

  Examples of the phthalate ester plasticizer include diethyl phthalate, dimethoxyethyl phthalate, dimethyl phthalate, dioctyl phthalate, dibutyl phthalate, di-2-ethylhexyl phthalate, dioctyl phthalate, dicyclohexyl phthalate, and dicyclohexyl terephthalate.

  Examples of the citrate plasticizer include acetyl trimethyl citrate, acetyl triethyl citrate, and acetyl tributyl citrate.

  Examples of the fatty acid ester plasticizer include butyl oleate, methylacetyl ricinoleate, dibutyl sebacate and the like.

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

  The polyvalent carboxylic acid ester compound is composed of an ester of divalent or higher, preferably divalent to 20 valent polyvalent carboxylic acid and alcohol. The aliphatic polyvalent carboxylic acid is preferably 2 to 20 valent, and in the case of an aromatic polyvalent carboxylic acid or an alicyclic polyvalent carboxylic acid, it is preferably 3 to 20 valent.

  The polyvalent carboxylic acid is represented by the following general formula (21).

Formula (21)
R ₂ (COOH) _m (OH) _n
(However, R ₂ is an (m + n) -valent organic group, m is a positive integer of 2 or more, n is an integer of 0 or more, a COOH group is a carboxyl group, and an OH group is an alcoholic or phenolic hydroxyl group.)

  Examples of preferred polyvalent carboxylic acids include the following, but the present invention is not limited thereto. Trivalent or higher aromatic polyvalent carboxylic acids such as trimellitic acid, trimesic acid, pyromellitic acid or derivatives thereof, succinic acid, adipic acid, azelaic acid, sebacic acid, oxalic acid, fumaric acid, maleic acid, tetrahydrophthal An aliphatic polyvalent carboxylic acid such as an acid, an oxypolyvalent carboxylic acid such as tartaric acid, tartronic acid, malic acid and citric acid can be preferably used. In particular, it is preferable to use an oxypolycarboxylic acid from the viewpoint of improving retention.

  There is no restriction | limiting in particular as alcohol used for a polyhydric carboxylic acid ester compound, Well-known alcohol and phenols can be used. For example, an aliphatic saturated alcohol or aliphatic unsaturated alcohol having a straight chain or a side chain having 1 to 32 carbon atoms can be preferably used. It is more preferable that it is C1-C20, and it is especially preferable that it is C1-C10. In addition, alicyclic alcohols such as cyclopentanol and cyclohexanol or derivatives thereof, aromatic alcohols such as benzyl alcohol and cinnamyl alcohol, or derivatives thereof can also be preferably used.

  When an oxypolycarboxylic acid is used as the polycarboxylic acid, the alcoholic or phenolic hydroxyl group of the oxypolycarboxylic acid may be esterified with a monocarboxylic acid. Examples of preferred monocarboxylic acids include the following, but the present invention is not limited thereto.

  As the aliphatic monocarboxylic acid, a fatty acid having a straight chain or a side chain having 1 to 32 carbon atoms can be preferably used. It is more preferable that it is C1-C20, and it is especially preferable that it is C1-C10.

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

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

  Examples of preferred aromatic monocarboxylic acids include those in which an alkyl group is introduced into the benzene ring of benzoic acid such as benzoic acid and toluic acid, and two or more benzene rings such as biphenyl carboxylic acid, naphthalene carboxylic acid, and tetralin carboxylic acid. And aromatic monocarboxylic acids possessed by them, or derivatives thereof. Particularly preferred are acetic acid, propionic acid, and benzoic acid.

  Although there is no restriction | limiting in particular in the molecular weight of a polyhydric carboxylic acid ester compound, It is preferable that it is the range of molecular weight 300-1000, and it is still more preferable that it is the range of 350-750. The larger one is preferable in terms of improving the retention, and the smaller one is preferable in terms of moisture permeability and compatibility with the cellulose ester.

  The alcohol used for the polyvalent carboxylic acid ester may be one kind or a mixture of two or more kinds.

  The acid value of the polycarboxylic acid ester compound is preferably 1 mgKOH / g or less, and more preferably 0.2 mgKOH / g or less. By setting the acid value within the above range, retardation fluctuations are also suppressed, which is preferable.

(Acid value)
The acid value means the number of milligrams of potassium hydroxide necessary for neutralizing the acid (carboxyl group present in the sample) contained in 1 g of the sample. The acid value is measured according to JIS K0070.

  Examples of particularly preferred polyvalent carboxylic acid ester compounds are shown below, but the present invention is not limited thereto. For example, triethyl citrate, tributyl citrate, acetyl triethyl citrate (ATEC), acetyl tributyl citrate (ATBC), benzoyl tributyl citrate, acetyl triphenyl citrate, acetyl tribenzyl citrate, dibutyl tartrate, diacetyl dibutyl tartrate, Examples include tributyl trimellitic acid and tetrabutyl pyromellitic acid.

  The polyester plasticizer is not particularly limited, and a polyester plasticizer having an aromatic ring or a cycloalkyl ring in the molecule can be used. Although it does not specifically limit as a polyester plasticizer, For example, the aromatic terminal ester plasticizer represented by following General formula (22) can be used.

General formula (22)
B- (GA) _n -GB
(In the formula, B is a benzene monocarboxylic acid residue, G is an alkylene glycol residue having 2 to 12 carbon atoms, an aryl glycol residue having 6 to 12 carbon atoms, or an oxyalkylene glycol residue having 4 to 12 carbon atoms, A represents an alkylene dicarboxylic acid residue having 4 to 12 carbon atoms or an aryl dicarboxylic acid residue having 6 to 12 carbon atoms, and n represents an integer of 1 or more.)

  The compound represented by the general formula (22) includes a benzene monocarboxylic acid residue represented by B, an alkylene glycol residue, an oxyalkylene glycol residue or an aryl glycol residue represented by G, and an alkylene dicarboxylic acid represented by A. It is composed of a residue or an aryl dicarboxylic acid residue, and can be obtained by the same reaction as a normal polyester plasticizer.

  Examples of the benzene monocarboxylic acid component of the polyester plasticizer include benzoic acid, para-tert-butylbenzoic acid, orthotoluic acid, metatoluic acid, p-toluic acid, dimethylbenzoic acid, ethylbenzoic acid, normal propylbenzoic acid, and aminobenzoic acid. And acetoxybenzoic acid and the like, and these can be used as one kind or a mixture of two or more kinds, respectively.

  Examples of the alkylene glycol component having 2 to 12 carbon atoms of the polyester plasticizer include ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 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 (neopentyl glycol), 2,2 -Diethyl-1,3-propanediol (3,3-dimethylolpentane), 2-n-butyl-2-ethyl-1,3propanediol (3,3-dimethylolheptane), 3-methyl-1, 5-pentanediol 1,6-hexanediol, 2,2,4-trimethyl 1,3-pentanediol, 2-ethyl 1, -Hexanediol, 2-methyl 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,12-octadecanediol, etc., and these glycols are one kind or two kinds or more Used as a mixture. In particular, an alkylene glycol having 2 to 12 carbon atoms is particularly preferable because of excellent compatibility with a cellulose ester.

  In addition, examples of the oxyalkylene glycol component having 4 to 12 carbon atoms of the aromatic terminal ester include diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, and tripropylene glycol. It can be used as a seed or a mixture of two or more.

  Examples of the alkylene dicarboxylic acid component having 4 to 12 carbon atoms of the aromatic terminal ester include succinic acid, maleic acid, fumaric acid, glutaric acid, adipic acid, azelaic acid, sebacic acid, and dodecanedicarboxylic acid. These are used as one kind or a mixture of two or more kinds. Examples of the arylene dicarboxylic acid component having 6 to 12 carbon atoms include phthalic acid, terephthalic acid, isophthalic acid, 1,5 naphthalene dicarboxylic acid, and 1,4 naphthalene dicarboxylic acid.

  The polyester plasticizer has a number average molecular weight of preferably 300 to 1500, more preferably 400 to 1000. The acid value is 0.5 mgKOH / g or less, the hydroxyl value is 25 mgKOH / g or less, more preferably the acid value is 0.3 mgKOH / g or less, and the hydroxyl value is 15 mgKOH / g or less.

  Hereafter, the synthesis example of the aromatic terminal ester plasticizer which can be used by this embodiment is shown.

<Sample No. 1 (Aromatic terminal ester sample)>
A reaction vessel was charged with 410 parts of phthalic acid, 610 parts of benzoic acid, 737 parts of dipropylene glycol, and 0.40 part of tetraisopropyl titanate as a catalyst. While refluxing the monohydric alcohol, heating was continued at 130 to 250 ° C. until the acid value became 2 or less, and water produced was continuously removed. Next, the distillate is removed under reduced pressure at 200 to 230 ° C. under a reduced pressure of 1.33 × 10 ⁴ Pa to 4 × 10 ² Pa or less, and then filtered to remove an aromatic terminal ester plastic having the following properties An agent was obtained.
Viscosity (25 ° C., mPa · s); 43400
Acid value: 0.2

<Sample No. 2 (Aromatic terminal ester sample)>
Sample No. 1 was used except that 410 parts of phthalic acid, 610 parts of benzoic acid, 341 parts of ethylene glycol, and 0.35 part of tetraisopropyl titanate as a catalyst were used in the reaction vessel. In the same manner as in No. 1, an aromatic terminal ester having the following properties was obtained.
Viscosity (25 ° C., mPa · s); 31000
Acid value: 0.1

<Sample No. 3 (Aromatic terminal ester sample)>
Sample No. 1 was used except that 410 parts of phthalic acid, 610 parts of benzoic acid, 418 parts of 1,2-propanediol, and 0.35 part of tetraisopropyl titanate as the catalyst were used in the reaction vessel. In the same manner as in No. 1, an aromatic terminal ester having the following properties was obtained.
Viscosity (25 ° C., mPa · s); 38000
Acid value: 0.05

<Sample No. 4 (Aromatic terminal ester sample)>
Sample No. 4 was used except that 410 parts of phthalic acid, 610 parts of benzoic acid, 418 parts of 1,3-propanediol, and 0.35 part of tetraisopropyl titanate as a catalyst were used in the reaction vessel. In the same manner as in No. 1, an aromatic terminal ester having the following properties was obtained.
Viscosity (25 ° C., mPa · s); 37000
Acid value: 0.05

  Although the specific compound of the aromatic terminal ester plasticizer which can be used by this embodiment below is shown, this invention is not limited to this.

(UV absorber)
The protective film of a polarizing plate can also contain a ultraviolet absorber. The ultraviolet absorber is intended to improve durability by absorbing ultraviolet rays of 400 nm or less, and in particular, the transmittance at a wavelength of 370 nm is preferably 10% or less, more preferably 5% or less, and further Preferably it is 2% or less.

  The ultraviolet absorber to be used is not particularly limited, and examples thereof include oxybenzophenone compounds, benzotriazole compounds, salicylic acid ester compounds, benzophenone compounds, cyanoacrylate compounds, triazine compounds, nickel complex compounds, inorganic powders, and the like. Can be mentioned.

  For example, 5-chloro-2- (3,5-di-sec-butyl-2-hydroxylphenyl) -2H-benzotriazole, (2-2H-benzotriazol-2-yl) -6- (linear and side Chain dodecyl) -4-methylphenol, 2-hydroxy-4-benzyloxybenzophenone, 2,4-benzyloxybenzophenone, etc., and tinuvin 109, tinuvin 171, tinuvin 234, tinuvin 326, tinuvin 327, tinuvin 328, etc. These are commercially available products manufactured by Ciba Specialty Chemicals and can be preferably used.

  More preferably used ultraviolet absorbers are benzotriazole ultraviolet absorbers, benzophenone ultraviolet absorbers, and triazine ultraviolet absorbers, and particularly preferably benzotriazole ultraviolet absorbers and benzophenone ultraviolet absorbers.

  For example, as the benzotriazole ultraviolet absorber, a compound represented by the following general formula (b) can be used.

式中、Ｒ_１、Ｒ_２、Ｒ_３、Ｒ_４およびＲ_５は同一でも異なってもよく、水素原子、ハロゲン原子、ニトロ基、ヒドロキシル基、アルキル基、アルケニル基、アリール基、アルコキシル基、アシルオキシ基、アリールオキシ基、アルキルチオ基、アリールチオ基、モノもしくはジアルキルアミノ基、アシルアミノ基または５〜６員の複素環基を表し、Ｒ_４とＲ_５は閉環して５〜６員の炭素環を形成してもよい。また、上記記載のこれらの基は、任意の置換基を有していてよい。

In the formula, R ₁ , R ₂ , R ₃ , R ₄ and R ₅ may be the same or different, and are a hydrogen atom, halogen atom, nitro group, hydroxyl group, alkyl group, alkenyl group, aryl group, alkoxyl group, acyloxy Represents a group, aryloxy group, alkylthio group, arylthio group, mono- or dialkylamino group, acylamino group or 5- to 6-membered heterocyclic group, and R ₄ and R ₅ are closed to form a 5- to 6-membered carbocycle May be. Moreover, these groups described above may have an arbitrary substituent.

  Although the specific example of a benzotriazole type ultraviolet absorber is given to the following, this invention is not limited to these.

UV-1: 2- (2'-hydroxy-5'-methylphenyl) benzotriazole UV-2: 2- (2'-hydroxy-3 ', 5'-di-tert-butylphenyl) benzotriazole UV-3 : 2- (2'-hydroxy-3'-tert-butyl-5'-methylphenyl) benzotriazole UV-4: 2- (2'-hydroxy-3 ', 5'-di-tert-butylphenyl)- 5-Chlorobenzotriazole UV-5: 2- (2'-hydroxy-3 '-(3 ", 4", 5 ", 6" -tetrahydrophthalimidomethyl) -5'-methylphenyl) benzotriazole UV-6: 2,2-methylenebis (4- (1,1,3,3-tetramethylbutyl) -6- (2H-benzotriazol-2-yl) phenol)
UV-7: 2- (2'-hydroxy-3'-tert-butyl-5'-methylphenyl) -5-chlorobenzotriazole UV-8: 2- (2H-benzotriazol-2-yl) -6 (Linear and side chain dodecyl) -4-methylphenol (TINUVIN171)
UV-9: Octyl-3- [3-tert-butyl-4-hydroxy-5- (chloro-2H-benzotriazol-2-yl) phenyl] propionate and 2-ethylhexyl-3- [3-tert-butyl- 4-Hydroxy-5- (5-chloro-2H-benzotriazol-2-yl) phenyl] propionate mixture (TINUVIN 109)

  Furthermore, as the benzophenone ultraviolet absorber, a compound represented by the following general formula (c) is preferably used.

式中、Ｙは水素原子、ハロゲン原子、アルキル基、アルケニル基、アルコキシル基、またはフェニル基を表し、これらのアルキル基、アルケニル基及びフェニル基は置換基を有していてもよい。Ａは水素原子、アルキル基、アルケニル基、フェニル基、シクロアルキル基、アルキルカルボニル基、アルキルスルホニル基または−ＣＯ（ＮＨ）ｎ−１−Ｄ基を表し、Ｄはアルキル基、アルケニル基または置換基を有していてもよいフェニル基を表す。ｍ及びｎは１または２を表す。

In the formula, Y represents a hydrogen atom, a halogen atom, an alkyl group, an alkenyl group, an alkoxyl group, or a phenyl group, and these alkyl group, alkenyl group, and phenyl group may have a substituent. A represents a hydrogen atom, an alkyl group, an alkenyl group, a phenyl group, a cycloalkyl group, an alkylcarbonyl group, an alkylsulfonyl group or a —CO (NH) n-1-D group, and D represents an alkyl group, an alkenyl group or a substituent. Represents a phenyl group which may have m and n represent 1 or 2.

  In the above, the alkyl group represents, for example, a linear or branched aliphatic group having up to 24 carbon atoms, the alkoxyl group represents, for example, an alkoxyl group having up to 18 carbon atoms, and the alkenyl group has, for example, carbon number An alkenyl group up to 16 represents an allyl group, a 2-butenyl group, or the like. In addition, as substituents to alkyl groups, alkenyl groups, and phenyl groups, halogen atoms such as chlorine atoms, bromine atoms, fluorine atoms, etc., hydroxyl groups, phenyl groups (this phenyl group is substituted with alkyl groups or halogen atoms, etc.) May be used).

  Specific examples of the benzophenone-based ultraviolet absorber represented by the general formula (c) are shown below, but the present invention is not limited thereto.

UV-10: 2,4-dihydroxybenzophenone UV-11: 2,2'-dihydroxy-4-methoxybenzophenone UV-12: 2-hydroxy-4-methoxy-5-sulfobenzophenone UV-13: Bis (2-methoxy -4-hydroxy-5-benzoylphenylmethane)

  In addition, a discotic compound such as a compound having a 1,3,5 triazine ring is also preferably used as the ultraviolet absorber.

  It is preferable that the polarizing plate protective film of this embodiment contains 2 or more types of ultraviolet absorbers.

  As the UV absorber, a polymer UV absorber can be preferably used, and in particular, a polymer type UV absorber described in JP-A-6-148430 is preferably used.

  The method for adding the UV absorber is to add the UV absorber to the dope after dissolving the UV absorber in an alcohol such as methanol, ethanol or butanol, an organic solvent such as methylene chloride, methyl acetate, acetone or dioxolane, or a mixed solvent thereof. Or you may add directly in dope composition. For an inorganic powder that does not dissolve in an organic solvent, a dissolver or a sand mill is used in the organic solvent and cellulose ester to disperse and then added to the dope.

  The amount of the UV absorber used is not uniform depending on the type of UV absorber, usage conditions, etc., but when the dry film thickness of the polarizing plate protective film is 10 to 200 μm, it is 0.5 with respect to the polarizing plate protective film. -10 mass% is preferable, and 0.6-4 mass% is still more preferable.

(Fine particles)
The protective film for the polarizing plate preferably contains fine particles. As fine particles, examples of inorganic compounds include silicon dioxide, titanium dioxide, aluminum oxide, zirconium oxide, calcium carbonate, talc, clay, calcined kaolin, calcined calcium silicate, hydrated calcium silicate, aluminum silicate, magnesium silicate. And calcium phosphate. Fine particles containing silicon are preferable in terms of low turbidity, and silicon dioxide is particularly preferable.

  The average primary particle diameter of the fine particles is preferably 5 to 400 nm, and more preferably 10 to 300 nm. These may be mainly contained as secondary aggregates having a particle size of 0.05 to 0.3 μm, and may be contained as primary particles without being aggregated if the particles have an average particle size of 100 to 400 nm. preferable. The content of these fine particles in the polarizing plate protective film is preferably 0.01 to 1% by mass, particularly preferably 0.05 to 0.5% by mass. In the case of a polarizing plate protective film having a multilayer structure by the co-casting method, it is preferable to contain fine particles of this addition amount on the surface.

  Silicon dioxide fine particles are commercially available, for example, under the trade names Aerosil R972, R972V, R974, R812, 200, 200V, 300, R202, OX50, TT600 (above, Nippon Aerosil Co., Ltd.). Can do.

  Zirconium oxide fine particles are commercially available, for example, under the trade names Aerosil R976 and R811 (manufactured by Nippon Aerosil Co., Ltd.), and can be used.

  Examples of the polymer include silicone resin, fluororesin, and acrylic resin. Silicone resins are preferable, and those having a three-dimensional network structure are particularly preferable. For example, Tospearl 103, 105, 108, 120, 145, 3120, and 240 (above, manufactured by Toshiba Silicone Co., Ltd.) It is commercially available under the trade name and can be used.

  Among these, Aerosil 200V and Aerosil R972V are particularly preferably used because they have a large effect of reducing the friction coefficient while keeping the turbidity of the polarizing plate protective film low. In the polarizing plate protective film of this embodiment, it is preferable that the dynamic friction coefficient of at least one surface is 0.2 to 1.0.

  Various additives may be batch-added to a dope that is a cellulose ester-containing solution before film formation, or an additive solution may be separately prepared and added in-line. In particular, it is preferable to add a part or all of the fine particles in-line in order to reduce the load on the filter medium.

  When the additive solution is added in-line, it is preferable to dissolve a small amount of cellulose ester in order to improve mixing with the dope. The amount of the cellulose ester is preferably 1 to 10 parts by mass, more preferably 3 to 5 parts by mass with respect to 100 parts by mass of the solvent.

  In the present embodiment, for example, an in-line mixer such as a static mixer (manufactured by Toray Engineering Co., Ltd.) or SWJ (Toray Static In-Pipe Mixer Hi-Mixer) is preferably used to perform in-line addition and mixing.

(Method for producing protective film)
Next, the manufacturing method of the protective film of a polarizing plate is demonstrated.

  The protective film may be a film produced by a solution casting method or a film produced by a melt casting method, and both can be preferably used.

  The production of the protective film involves preparing a dope by dissolving cellulose ester and additives in a solvent, casting the dope on an endless metal support that moves indefinitely, drying the cast dope as a web It is performed by a step, a step of peeling from a metal support, a step of stretching or maintaining the width, a step of further drying, and a step of winding up the finished film.

  The process for preparing the dope will be described. The concentration of cellulose ester in the dope is preferably higher because the drying load after casting on the metal support can be reduced. However, if the concentration of cellulose ester is too high, the load during filtration increases and the filtration accuracy is poor. Become. As a density | concentration which makes these compatible, 10-35 mass% is preferable, More preferably, it is 15-25 mass%.

  The solvent used in the dope may be used alone or in combination of two or more, but it is preferable to use a mixture of a good solvent and a poor solvent of cellulose ester in terms of production efficiency, and there are many good solvents. This is preferable from the viewpoint of the solubility of the cellulose ester. The preferable range of the mixing ratio of the good solvent and the poor solvent is 70 to 98% by mass for the good solvent and 2 to 30% by mass for the poor solvent. With a good solvent and a poor solvent, what dissolve | melts the cellulose ester to be used independently is defined as a good solvent, and what poorly swells or does not melt | dissolve is defined as a poor solvent. Therefore, depending on the average acetylation degree (acetyl group substitution degree) of the cellulose ester, the good solvent and the poor solvent change. For example, when acetone is used as the solvent, the cellulose ester acetate ester (acetyl group substitution degree 2.4), cellulose Acetate propionate is a good solvent, and cellulose acetate (acetyl group substitution degree 2.8) is a poor solvent.

  The good solvent used is not particularly limited, and examples thereof include organic halogen compounds such as methylene chloride, dioxolanes, acetone, methyl acetate, and methyl acetoacetate. Particularly preferred is methylene chloride or methyl acetate.

  Moreover, although the poor solvent used is not specifically limited, For example, methanol, ethanol, n-butanol, cyclohexane, cyclohexanone, etc. are used preferably. Moreover, it is preferable that 0.01-2 mass% of water contains in dope. Moreover, the solvent used for melt | dissolution of a cellulose ester collect | recovers the solvent removed from the film by drying at the film-forming process, and uses this again. The recovery solvent may contain trace amounts of additives added to the cellulose ester, such as plasticizers, UV absorbers, polymers, monomer components, etc., but even if these are included, they are preferably reused. Can be purified and reused if necessary.

  A general method can be used as a method of dissolving the cellulose ester when preparing the dope described above. When heating and pressurization are combined, it is possible to heat above the boiling point at normal pressure. It is preferable to stir and dissolve while heating at a temperature that is equal to or higher than the boiling point of the solvent at normal pressure and that the solvent does not boil under pressure, in order to prevent the generation of massive undissolved materials called gels and mamacos. Moreover, after mixing a cellulose ester with a poor solvent and making it wet or swell, the method of adding a good solvent and melt | dissolving is also used preferably.

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

  The heating temperature with the addition of a solvent is preferably higher from the viewpoint of the solubility of the cellulose ester, but if the heating temperature is too high, the required pressure increases and the productivity deteriorates. A preferable heating temperature is 45 to 120 ° C, more preferably 60 to 110 ° C, and still more preferably 70 ° C to 105 ° C. The pressure is adjusted so that the solvent does not boil at the set temperature.

  Alternatively, a cooling dissolution method is also preferably used, whereby the cellulose ester can be dissolved in a solvent such as methyl acetate.

  Next, this cellulose ester solution is filtered using a suitable filter medium such as filter paper. As the filter medium, it is preferable that the absolute filtration accuracy is small in order to remove insoluble matters and the like, but there is a problem that the filter medium is likely to be clogged if the absolute filtration accuracy is too small. For this reason, a filtering medium having an absolute filtration accuracy of 0.008 mm or less is preferable, a filtering medium having a 0.001 to 0.008 mm is more preferable, and a filtering medium having a 0.003 to 0.006 mm is further preferable.

  The material of the filter medium is not particularly limited, and a normal filter medium can be used. However, a plastic filter medium such as polypropylene or Teflon (registered trademark) or a metal filter medium such as stainless steel is used as the fiber. It is preferable because there is no dropout. It is preferable to remove and reduce impurities, particularly bright spot foreign matter, contained in the raw material cellulose ester by filtration.

A bright spot foreign material is placed in a crossed Nicols state with two polarizing plates, a polarizing plate protective film is placed between them, light is applied from the side of one polarizing plate, and observed from the side of the other polarizing plate. It is a point (foreign matter) that light from the opposite side sometimes appears to leak, and the number of bright spots having a diameter of 0.01 mm or more is preferably 200 / cm ² or less. More preferably, it is 100 pieces / cm < ² > or less, More preferably, it is 50 pieces / cm < ² > or less, More preferably, it is 0-10 pieces / cm < ² > or less. Further, it is preferable that the number of bright spots having a diameter of 0.01 mm or less is small.

  The dope can be filtered by a normal method, but the method of filtering while heating at a temperature not lower than the boiling point of the solvent at normal pressure and in a range where the solvent does not boil under pressure is the filtration pressure before and after filtration. The increase in the difference (referred to as differential pressure) is small and preferable. A preferred temperature is 45 to 120 ° C, more preferably 45 to 70 ° C, and still more preferably 45 to 55 ° C.

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

  Here, the dope casting will be described. The metal support in the casting (casting) step preferably has a mirror-finished surface. As the metal support, a stainless steel belt or a drum whose surface is plated with a casting is preferably used. The cast width can be 1 to 4 m.

  The surface temperature of the metal support in the casting step is −50 ° C. to a temperature lower than the boiling point of the solvent, and a higher temperature is preferable because the web drying rate can be increased. However, if the temperature is too high, the web foams or is flat. May deteriorate. A preferable support body temperature is 0-40 degreeC, and 5-30 degreeC is still more preferable. Alternatively, it is also a preferable method that the web is gelled by cooling and peeled from the drum in a state containing a large amount of residual solvent.

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

In order for the protective film to exhibit good flatness, the residual solvent amount when peeling the web from the metal support is preferably 10 to 150% by mass, more preferably 10 to 40% by mass or 60 to 130% by mass. Yes, particularly preferably 10 to 30% by mass or 70 to 120% by mass. Here, the amount of residual solvent is defined by the following formula.
Residual solvent amount (% by mass) = {(MN) / N} × 100
Note that M is the mass of a sample collected at any time during or after the production of the web or film, and N is the mass after heating a mass of M at 115 ° C. for 1 hour.

  Further, in the drying step of the protective film, the web is peeled off from the metal support, and further dried, and the residual solvent amount is preferably 1% by mass or less, more preferably 0.1% by mass or less, particularly Preferably it is 0-0.01 mass% or less.

  In the film drying process, generally, a roll drying method (a method in which a plurality of rolls arranged on the upper and lower sides are alternately passed through and dried) or a method of drying while transporting the web by a tenter method is adopted.

  In order to produce a protective film, immediately after peeling from the metal support, the web is stretched in the conveying direction (longitudinal direction) where the amount of residual solvent of the web is large, and further, the width is obtained by a tenter method in which both ends of the web are gripped by clips or the like. It is particularly preferable to perform stretching in the direction (lateral direction).

  In order to stretch in the longitudinal direction immediately after peeling, peeling is preferably performed at a peeling tension of 210 N / m or more, particularly preferably 220 to 300 N / m.

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

  The drying temperature in the web drying step is preferably increased stepwise from 40 to 200 ° C, and more preferably in the range of 50 to 140 ° C in order to improve dimensional stability.

  Although the film thickness of a protective film is not specifically limited, 10-200 micrometers is used. In particular, the film thickness is particularly preferably 10 to 100 μm. More preferably, it is 10-40 micrometers.

  A protective film having a width of 1 to 4 m is used. In particular, those having a width of 1.4 to 4 m are preferably used, and particularly preferably 1.6 to 3 m. If it exceeds 4 m, conveyance becomes difficult.

(Stretching operation, refractive index control)
As for the protective film of a polarizing plate, it is preferable that the retardation value Ro represented by a following formula is 0-10 nm, and Rt is -10-10 + 10 nm.
Formula (i): Ro = (nx−ny) × d
Formula (ii): Rt = ((nx + ny) / 2−nz) × d
(In the formula, Ro is the retardation value in the film plane, Rt is the retardation value in the film thickness direction, nx is the refractive index in the slow axis direction in the film plane, ny is the refractive index in the fast axis direction in the film plane, and nz is (The refractive index in the thickness direction of the film, d represents the thickness (nm) of the film.)

  The refractive index can be obtained at a measurement wavelength of 590 nm in an environment of 23 ° C. and 55% RH using, for example, KOBRA-21ADH (Oji Scientific Instruments).

  Further, the retardation value Ro is preferably in the range of 0 to 5 nm, and Rt is preferably in the range of −10 to 10 nm in order to enhance the effect of the present invention.

  In order to obtain the retardation values Ro and Rt, it is preferable that the polarizing plate protective film has the configuration of the present invention, and further the refractive index is controlled by a stretching operation.

  For example, the film can be stretched sequentially or simultaneously in the longitudinal direction (film forming direction) of the film and the direction orthogonal to the longitudinal direction of the film, that is, the width direction.

  The draw ratios in the biaxial directions perpendicular to each other are preferably in the range of 1.0 to 2.0 times in the casting direction and 1.01 to 2.5 times in the width direction, respectively. It is preferable to carry out in the range of 1.01 to 1.5 times in the direction and 1.05 to 2.0 times in the width direction.

  There is no particular limitation on the method of stretching the web. For example, a method in which a difference in peripheral speed is applied to a plurality of rolls, and the roll peripheral speed difference is used to stretch in the longitudinal direction, the both ends of the web are fixed with clips and pins, and the interval between the clips and pins is increased in the traveling direction. And a method of stretching in the vertical direction, a method of stretching in the horizontal direction and stretching in the horizontal direction, a method of stretching in the vertical and horizontal directions and stretching in both the vertical and horizontal directions, and the like. Of course, these methods may be used in combination. In the case of the so-called tenter method, driving the clip portion by the linear drive method is preferable because smooth stretching can be performed and the risk of breakage and the like can be reduced.

  It is preferable to carry out the width maintenance or lateral stretching in the film forming step by a tenter, and it may be a pin tenter or a clip tenter.

  When the slow axis or the fast axis of the protective film exists in the film plane and the angle formed with the film forming direction is θ1, θ1 is preferably −1 ° or more and + 1 ° or less, and −0.5 ° or more. It is more preferable that the angle is + 0.5 ° or less. This θ1 can be defined as an orientation angle, and θ1 can be measured using an automatic birefringence meter KOBRA-21ADH (Oji Scientific Instruments). Each of θ1 satisfying the above relationship can contribute to obtaining high luminance in a display image, suppressing or preventing light leakage, and contributing to obtaining faithful color reproduction in a color liquid crystal display device.

(Physical properties)
The protective film preferably has a breaking elongation of 10 to 80%, and more preferably 20 to 50%.

  The visible light transmittance of the protective film is preferably 90% or more, and more preferably 93% or more.

  The haze of the protective film is preferably less than 1%, particularly preferably 0 to 0.1%.

(Polarizer)
The polarizing plate of this embodiment is formed by laminating a first protective film on the front side, a polarizing film as a polarizer, a second protective film on the back side, and an adhesive layer in this order. The liquid crystal display device to be described later is configured by attaching a polarizing plate to at least one surface of the liquid crystal cell so that the adhesive layer side is the liquid crystal cell side.

  The polarizing plate can be produced by a general method. The second protective film is preferably bonded to at least one surface of a polarizer prepared by subjecting the polarizer side of the second protective film to an alkali saponification treatment and immersion drawing in an iodine solution using a completely saponified polyvinyl alcohol aqueous solution. On the other surface of the polarizer, the same structure as the second protective film may be bonded as the first protective film, or another polarizing plate protective film may be bonded. As another polarizing plate protective film, a commercially available cellulose ester film (for example, Konica Minoltack KC8UX, KC4UX, KC5UX, KC8UY, KC4UY, KC12UR, KC8UCR-3, KC8UCR-4, KC8UCR-5, KC4FR-1, KC8UY- HA, KC8UX-RHA, manufactured by Konica Minolta Opto Co., Ltd.) are also preferably used.

  A polarizer, which is a main component of a polarizing plate, is an element that allows only light of a plane of polarization in a certain direction to pass. A typical polarizer currently known is a polyvinyl alcohol-based polarizing film, which is polyvinyl alcohol. There are one in which iodine is dyed on a system film and one in which dichroic dye is dyed. For the polarizer, a polyvinyl alcohol aqueous solution is formed into a film and dyed by uniaxial stretching or dyed or uniaxially stretched and then preferably subjected to a durability treatment with a boron compound. The film thickness of the polarizer is preferably 5 to 30 μm, particularly preferably 10 to 20 μm.

  For example, in JP-A-2003-240958, a step of dyeing a polyvinyl alcohol resin film with an aqueous solution containing a dichroic dye, the polyvinyl alcohol resin film dyed with a dichroic dye is treated with an aqueous boric acid solution. In a method for producing a polarizing film in which a dichroic dye is adsorbed and oriented on the polyvinyl alcohol resin film through a step and a step of uniaxially stretching the polyvinyl alcohol resin film, the treatment is performed with an aqueous solution containing the dichroic dye. The polyvinyl alcohol resin film before being subjected to heat treatment at a temperature in the range of 90 to 180 ° C. to produce a polarizing film having a film thickness exceeding 10 μm and less than 20 μm. It is also a preferable method to produce a thin polarizing film.

  Further, for example, in Japanese Patent No. 4751481, a laminated body in which a polyvinyl alcohol resin layer in which a dichroic substance is oriented is formed on an amorphous ester thermoplastic resin base material is formed by aerial auxiliary stretching and boric acid water. A polarizing film composed of the above resin layer having a thickness of 15 μm or less (so-called coating type polarizer) is manufactured by stretching in a two-stage stretching process consisting of stretching. Producing a film is also a preferred method.

  Further, the ethylene unit content described in JP-A-2003-248123, JP-A-2003-342322, etc. is 1 to 4 mol%, the degree of polymerization is 2000 to 4000, and the degree of saponification is 99.0 to 99.99 mol%. Ethylene-modified polyvinyl alcohol is also preferably used. Among them, an ethylene-modified polyvinyl alcohol film having a hot water cutting temperature of 66 to 73 ° C. is preferably used. The difference in hot water cutting temperature between two points 5 cm away in the TD direction of the film is more preferably 1 ° C. or less in order to reduce color spots, and two points separated 1 cm in the TD direction of the film. In order to reduce color spots, it is more preferable that the difference in the hot water cutting temperature is 0.5 ° C. or less.

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

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

  In addition, as the pressure-sensitive adhesive that forms the pressure-sensitive adhesive layer used when the polarizing plate is bonded to the liquid crystal cell, those using base polymers such as acrylic ester, methacrylic ester, butyl rubber, and silicone are used. it can. Although not particularly limited, based on (meth) acrylate esters such as butyl (meth) acrylate, ethyl (meth) acrylate, isooctyl (meth) acrylate, and 2-ethylhexyl (meth) acrylate And polymers based on copolymers using two or more of these (meth) acrylic esters are preferably used. In the pressure-sensitive adhesive, a polar monomer is usually copolymerized in these base polymers. Examples of the polar monomer include (meth) acrylic acid, 2-hydroxyethyl (meth) acrylate, (meth) acrylic acid 2 Examples thereof include monomers having a carboxyl group, a hydroxyl group, an amino group, an epoxy group, and the like, such as -hydroxypropyl, (meth) acrylamide, N, N-dimethylaminoethyl (meth) acrylate, and glycidyl (meth) acrylate. The pressure-sensitive adhesive usually contains one or more crosslinking agents in addition to the base polymer. Examples of the crosslinking agent include divalent or polyvalent metal salts that form a carboxylic acid metal salt with a carboxyl group, and polyisocyanate compounds that form an amide bond with a carboxyl group.

  The thickness of the pressure-sensitive adhesive layer can be about 3 to 50 μm. When forming an adhesive layer in a polarizing plate, you may perform surface treatments, such as a corona treatment, on the protective film surface of a polarizing plate. Moreover, when forming an adhesive layer, it is normal to cover the surface of an adhesive layer with a peeling film.

(Liquid crystal display device)
The liquid crystal display device of the present embodiment is configured by laminating the above polarizing plate and a liquid crystal cell. At this time, the polarizing plate and the liquid crystal cell are bonded by the pressure-sensitive adhesive layer of the polarizing plate. The liquid crystal cell has a liquid crystal layer sandwiched between transparent substrates, and is driven in an IPS (In Plane Switching) mode.

  Thus, by incorporating the polarizing plate of the present embodiment into an IPS mode type liquid crystal display device, a liquid crystal display device having excellent visibility and an increased viewing angle can be realized. Further, the polarizing plate of this embodiment can be incorporated into a fringe-field switching (FFS) mode type liquid crystal display device, and in this case, the visibility is excellent and the viewing angle is expanded. A liquid crystal display device can be realized.

<Example>
EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto. In addition, although the display of "part" or "%" is used in an Example, unless otherwise indicated, "part by mass" or "mass%" is represented.

[Materials used for optical films]
(Cellulose acylate)
Cellulose acylate: Cellulose triacetate (TAC) having a number average molecular weight of 70,000 having an acetyl group substitution degree of 2.80

(Retardation lowering agent)
<Sugar ester>
Using the sugars shown in Table 1 below, sugar esters were synthesized by changing the type and number of substituents of the aliphatic alkyl group (AL) and aromatic alkyl group (AR).

  In the table, “(number of substituents of AL + number of substituents of AR) / total number of OH groups” refers to the number of aliphatic alkyl groups (AL) and aromatic alkyl groups (AR) relative to the total number of OH groups that are substituents of the sugar ester. ) Represents the total number of substituents. For example, “5/8” indicates that 5 out of 8 substituents are substituents of AL and / or AR. Further, for example, when a sugar ester having a ratio of 5/8 and a sugar ester having a ratio of 6/8 are mixed at a ratio of 50:50, it is expressed as “5.5 / 8”.

<Ester compound>
<< Ester compound E1 >>
251 g of 1,2-propylene glycol, 278 g of phthalic anhydride, 91 g of adipic acid, 610 g of benzoic acid, 0.191 g of tetraisopropyl titanate as an esterification catalyst, 2 L four-neck equipped with a thermometer, stirrer, and slow cooling tube The flask is charged and gradually heated with stirring until it reaches 230 ° C. in a nitrogen stream. The ester compound E1 was obtained by making it dehydrate-condense for 15 hours, and depressurizingly distilling unreacted 1, 2- propylene glycol at 200 degreeC after completion | finish of reaction. The acid value was 0.10 and the number average molecular weight was 450.

<< Ester compound E2 >>
A polyester of adipic acid / ethylene glycol (average polymerization degree 2000) was used.

<Acrylic additive A1>
Bulk polymerization was performed by the polymerization method described in JP-A No. 2000-128911. That is, methyl acrylate (MMA) was charged as a monomer to a flask equipped with a stirrer, nitrogen gas inlet tube, thermometer, inlet and reflux condenser, nitrogen gas was introduced to replace the inside of the flask with nitrogen gas, An acrylic compound was obtained.

  Then, after addition of thioglycerol, polymerization was carried out for 4 hours, the contents were returned to room temperature, and 20 parts by mass of a 5% by mass benzoquinone tetrahydrofuran solution was added thereto to terminate the polymerization. The contents were transferred to an evaporator, and tetrahydrofuran, residual monomer and residual thioglycerol were removed under reduced pressure at 80 ° C. to obtain an acrylic additive A1 having a weight average molecular weight of 1000 measured using GPC.

[Preparation of optical film 1]
(Preparation of main dope 1)
A main dope having the following composition was prepared. First, methylene chloride and ethanol were added to the pressure dissolution tank. Cellulose ester A was added to a pressurized dissolution tank containing a solvent while stirring, and this was heated and completely dissolved while stirring.
Cellulose acylate 100 parts by weight Sugar ester T1 15 parts by weight Matting agent: R812 12% ethanol dispersion (manufactured by Nippon Aerosil Co., Ltd.) 1.4 parts by weight Methylene chloride 430 parts by weight Ethanol 40 parts by weight The solution was put into a sealed container and dissolved while stirring, and this was dissolved in Azumi filter paper No. 1 manufactured by Azumi Filter Paper Co., Ltd. The main dope 1 was prepared by filtration using 244.

(Formation of optical film 1)
The prepared main dope 1 was uniformly cast on a stainless steel band support at a temperature of 22 ° C. and a width of 1.8 m using a belt casting apparatus. With the stainless steel band support, the solvent was evaporated until the residual solvent amount became 20%, and the dope film (web) was peeled from the stainless steel band support with a peeling tension of 162 N / m.

  Next, the peeled web was evaporated at 35 ° C., and the solvent was slit to a width of 1.6 m. Thereafter, using a tenter stretching machine, the width of the peeled web (TD direction) was 1 with respect to the original width at a temperature of 160 ° C. . 1-fold stretching. At this time, the residual solvent amount when starting stretching by the tenter was 4% by mass.

  Then, drying was completed while transporting the drying zone of 120 ° C. and 140 ° C. with a large number of rollers, slitting to 1.3 m width, and knurling with a width of 10 mm and a height of 2.5 μm on both ends of the film, The film was wound around a core to produce an optical film 1. The film thickness was 20 μm and the winding length was 5000 m.

[Preparation of optical films 2 to 12]
Optical films 2 to 12 were produced in the same manner as the optical film 1 except that the types and ratios of additives contained in the main dope were changed as shown in Table 2.

[Preparation of optical film 13]
Two types are available: pellet 1 in which 45% acrylic rubber particles are blended in a 98/2 weight ratio copolymer of methyl methacrylate / methyl acrylate, and pellet 2 in which 15% acrylic rubber particles are blended. did. Pellet 1 and pellet 2 are put into an extruder at a ratio of 0.5: 0.5 and kneaded, and the molten film extruded from the T-die is sandwiched between two cooling rolls set at 45 ° C. The film was taken off while cooling to prepare an acrylic resin film having a thickness of 40 μm. This acrylic resin film is referred to as an optical film 13. The moisture permeability of the optical film 14 was 98 g / m ² · 24 hr.

[Production of Optical Film 14]
(Production of polyester A)
When the temperature of the esterification reactor was raised to 200 ° C., 86.4 parts by mass of terephthalic acid and 64.6 parts by mass of ethylene glycol were charged and 0.017 parts by mass of antimony trioxide as a catalyst while stirring. 0.064 parts by mass of magnesium acetate tetrahydrate and 0.16 parts by mass of triethylamine were charged. Subsequently, the pressure was raised and the esterification reaction was performed under the conditions of a gauge pressure of 0.34 MPa and 240 ° C., and then the esterification reaction vessel was returned to normal pressure, and 0.014 parts by mass of phosphoric acid was added. Furthermore, it heated up to 260 degreeC over 15 minutes, and 0.012 mass part of trimethyl phosphate was added. Then, after 15 minutes, dispersion treatment was performed with a high-pressure disperser, and after 15 minutes, the obtained esterification reaction product was transferred to a polycondensation reaction can and subjected to polycondensation reaction at 280 ° C. under reduced pressure.

  After completion of the polycondensation reaction, it is filtered through a NASRON filter with a 95% cut diameter of 5 μm, extruded into a strand from a nozzle, and cooled and solidified using cooling water that has been filtered (pore diameter: 1 μm or less) in advance. And cut into pellets. The obtained polyethylene terephthalate resin (A) had an intrinsic viscosity of 0.62 dl / g and contained substantially no inert particles and internally precipitated particles. (Hereafter, abbreviated as PET (A).)

(Production of polyester B)
10 parts by weight of a dried UV absorber (2,2 ′-(1,4-phenylene) bis (4H-3,1-benzoxazinon-4-one), PET (A) containing no particles (inherent viscosity Was 0.62 dl / g) and 90 parts by mass were mixed, and a polyethylene terephthalate resin (B) containing an ultraviolet absorber was obtained using a kneading extruder (hereinafter abbreviated as PET (B)).

(Adjustment of adhesive modification coating solution)
A transesterification reaction and a polycondensation reaction are carried out by a conventional method, and as a dicarboxylic acid component (based on the whole dicarboxylic acid component) 46 mol% terephthalic acid, 46 mol% isophthalic acid and 8 mol% sodium 5-sulfonatoisophthalate, A water-dispersible sulfonic acid metal base-containing copolymer polyester resin having a composition of 50 mol% ethylene glycol and 50 mol% neopentyl glycol as a glycol component (based on the entire glycol component) was prepared.

  Next, 51.4 parts by mass of water, 38 parts by mass of isopropyl alcohol, 5 parts by mass of n-butyl cellosolve, 0.06 parts by mass of nonionic surfactant were mixed and then heated and stirred. After adding 5 parts by mass of a water-dispersible sulfonic acid metal base-containing copolymer polyester resin and continuing to stir until the resin is no longer agglomerated, the resin water dispersion is cooled to room temperature to obtain a solid content concentration of 5.0% by mass. A uniform water-dispersible copolymerized polyester resin liquid was obtained. Furthermore, after dispersing 3 parts by mass of aggregated silica particles (Silicia 310, manufactured by Fuji Silysia Co., Ltd.) in 50 parts by mass of water, 99.46 parts by mass of the water-dispersible copolyester resin liquid was mixed with 0.54 parts by mass of the aqueous dispersion was added, and 20 parts by mass of water was added with stirring to obtain an adhesive modified coating solution.

  After drying 90 parts by mass of PET (A) resin pellets containing no particles as a raw material for the base film intermediate layer and 10 parts by mass of PET (B) resin pellets containing an ultraviolet absorber at 135 ° C. for 6 hours under reduced pressure (1 Torr) , And supplied to the extruder 2 (for the intermediate layer II layer). Also, the PET (A) was dried by an ordinary method and supplied to the extruder 1 (for the outer layer I layer and the outer layer III), and dissolved at 285 ° C. . After filtering these two kinds of polymers with a filter medium made of a sintered stainless steel (nominal filtration accuracy of 10 μm particles 95% cut), laminating them in a two-kind / three-layer confluence block, and extruding them into a sheet form from a die, The film was wound around a casting drum having a surface temperature of 30 ° C. using an electrostatic application casting method, and then cooled and solidified to produce an unstretched film. At this time, the discharge amount of each extruder was adjusted so that the thickness ratio of the I layer, the II layer, and the III layer was 10:80:10.

Next, after applying the adhesive property-modifying coating solution on the both sides of this unstretched PET film by a reverse roll method so that the coating amount after drying was 0.08 g / m ² , the coating was dried at 80 ° C. for 20 seconds. .

The unstretched film on which this coating layer was formed was guided to a tenter stretching machine, and the film was guided to a hot air zone at a temperature of 125 ° C. while being gripped by a clip, and stretched 4.0 times in the width direction. Next, while maintaining the width stretched in the width direction, the film was treated at a temperature of 225 ° C. for 30 seconds, and further subjected to a relaxation treatment of 3% in the width direction to obtain a uniaxially oriented PET film having a film thickness of about 60 μm. Let the PET film be the optical film 14. The moisture permeability of the optical film 14 was 36 g / m ² · 24 hr.

[Measurement of Ro and Rt]
For each of the optical films 1 to 12, the retardation value (Ro) in the in-plane direction defined by the following formula (i) and the following formula (ii) at a measurement wavelength of 590 nm in an environment of a temperature of 23 ° C. and a relative humidity of 55%. The retardation value (Rt) in the thickness direction defined by) was measured using an automatic birefringence meter KOBRA-WPR (Oji Scientific Instruments).

Specifically, three-dimensional refractive index measurements were performed on the optical films 1 to 12 produced above at 10 locations at a wavelength of 590 nm in an environment of 23 ° C. and 55% RH, and the average of the refractive indexes nx, ny, and nz. After obtaining the values, the retardation value Ro in the in-plane direction and the retardation value Rt in the thickness direction were calculated according to the following formula. The measurement results are also shown in Table 2.
Formula (i): Ro = (nx−ny) × d (nm)
Formula (ii): Rt = {(nx + ny) / 2−nz} × d (nm)
[In Formula (i) and Formula (ii), nx represents the refractive index in the direction x in which the refractive index is maximum in the in-plane direction of the film. ny represents the refractive index in the direction y orthogonal to the direction x in the in-plane direction of the film. nz represents the refractive index in the thickness direction z of the film. ]

[Preparation of polarizing plate]
Using the optical films 1-14 produced above, polarizing plates 1-22 were produced as follows.

(Preparation of polarizer 1)
A 30 μm thick polyvinyl alcohol film having an average polymerization degree of 2400 and a saponification degree of 99.9 mol% was immersed in warm water at 30 ° C. for 60 seconds to swell. Next, the obtained film was immersed in an aqueous solution of 0.3% iodine / potassium iodide (mass ratio = 0.5 / 8) and dyed while being stretched up to 3.5 times. Thereafter, the obtained film was stretched in a boric acid ester aqueous solution at 65 ° C. so that the total stretching ratio was 6 times. Thereafter, the obtained film was dried in an oven at 40 ° C. for 3 minutes to obtain a polarizer 1 having a thickness of 10 μm.

(Preparation of polarizer 2)
A polarizer described in Example 1 of Japanese Patent No. 4751481 was prepared as a polarizer 2. That is, a laminate in which a polyvinyl alcohol resin layer in which a dichroic substance is oriented is formed on an amorphous PET resin substrate is stretched in a two-stage stretching process consisting of air-assisted stretching and boric acid-water stretching. Thus, a polarizer 2 (coated on an amorphous PET resin substrate) was obtained. The thickness of the polarizer 2 was adjusted to 3 μm.

(Preparation of active energy ray-curable adhesive liquid (cationic polymerization type))
Each of the following components was mixed and then defoamed to prepare an active energy ray-curable adhesive solution. Triarylsulfonium hexafluorophosphate was blended as a 50% propylene carbonate solution, and the solid content of triarylsulfonium hexafluorophosphate was shown below.
3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate
45 parts by mass Epolide GT-301 (Daicel Chemical Industries alicyclic epoxy resin)
40 parts by mass 1,4-butanediol diglycidyl ether 15 parts by mass Triarylsulfonium hexafluorophosphate 2.3 parts by mass 9,10-dibutoxyanthracene 0.1 parts by mass 1,4-diethoxynaphthalene 2.0 parts by mass

(Preparation of polarizing plate 1)
The polarizing plate 1 was produced by the following method. First, as the first protective film, the optical film 13 prepared above was prepared, and the prepared active energy ray-curable adhesive solution was used as a microgravure coater (gravure roller: # 300, rotational speed 140% / line speed). ) To form an active energy ray-curable adhesive layer a.

  Next, the active energy ray-curable adhesive layer b is formed by coating the prepared optical film 1 with the prepared active energy ray-curable adhesive liquid to a thickness of 5 μm, as described above. did.

  Between the active energy ray-curable adhesive layers a and b, the produced polarizer 1 is disposed and bonded by a roller machine, and the optical film 13 / active energy ray-curable adhesive layer a / polarizer / A laminate in which the active energy ray-curable adhesive layer b / optical film 1 was laminated was obtained. In that case, it bonded by the roller machine so that the slow axis of an optical film and the absorption axis of a polarizer might mutually become orthogonal. And the polarizing plate 1 was produced by irradiating an electron beam from the both surfaces side of this laminated body. The line speed was 20 m / min, the acceleration voltage was 250 kV, and the irradiation dose was 20 kGy.

(Preparation of polarizing plates 2 to 22)
Polarizers 2 to 22 were produced in the same manner as described above except that the optical film and the polarizer used were changed to the combinations shown in Table 3.

[Measurement of tensile strength at break and evaluation of handling properties]
Under a 23 ° C. and 55% RH environment, a tensile tester (Tensilon; manufactured by A & C Co., Ltd.) was used to measure the breaking stress (MPa) in the absorption axis direction of the produced polarizing plate. The product multiplied by the thickness of the plate was calculated as the tensile strength at break (N). And the handling property at the time of the rework operation | work of the polarizing plates 1-21 was evaluated based on the following evaluation criteria. Table 3 also shows the results of the evaluation of the tensile strength at break and the handling properties of the polarizing plates 1 to 21. In addition, that the breaking point tension is T (N) means that the polarizing plate is broken only when the tension applied to the polarizing plate becomes T (N).
(Evaluation criteria)
A: Tensile strength at break is 70 N or more (even if the reworking conditions are changed, the polarizing plate can be peeled off without remaining)
○: Tension at break is 60 N or more (the polarizing plate can be peeled off without any residue during the rework operation).
Δ: Tensile strength at break is less than 60 N (the polarizing plate may be broken during reworking, and the polarizing plate may remain on the panel side).
X: Tensile strength at break is less than 50 N (the polarizing plate is broken during most rework operations, and the polarizing plate remains on the panel side).

  From Table 3, in the polarizing plates 1-18, the breaking point tension | tensile_strength is 60 N or more. This is because, in the polarizing plates 1 to 18, the second protective film contains a sugar ester substituted with an aliphatic acyl group as a retardation reducing agent for realizing a zero phase difference. Even if the protective film is made thinner, the mechanical strength of the second protective film can be ensured by the interaction between the sugar ester and the cellulose ester, and the first protection with low moisture permeability made of acrylic resin or PET resin. Even when the entire polarizing plate is thinned so that the total thickness of the film, the polarizer, and the second protective film is 90 μm or less, the mechanical strength is likely to be lowered due to the thinning, and the polarizing film This is probably because the child is supported by the second protective film and the mechanical strength of the polarizing plate as a whole can be prevented from decreasing. Accordingly, during the rework operation, the polarizing plate is hardly broken (because the polarizing plate cannot be broken unless a strong tension of 60 N or more is applied to the polarizing plate), and the handling property is improved.

  In particular, in the polarizing plates 1 to 11, even when the entire polarizing plate is thinned so that the total thickness of the first protective film, the polarizer, and the second protective film is 80 μm or less, the breaking point tension is 60 N or more. The effect of preventing breakage of the polarizing plate (improving handling properties) is obtained. Among them, in the polarizing plates 1 to 4 and 7 to 11, the tensile strength at break 80N or more is secured, and the effect of improving the handling property is surely obtained.

  From the above, it can be said that the sugar ester used as a retardation reducing agent is very effective in preventing breakage when the entire polarizing plate is thinned. In particular, in the polarizing plates 1 to 18, the thickness of the polarizer is 15 μm or less. However, even when the entire polarizing plate is thinned using such a thin polarizer, the second protective film has the above sugar content. By including an ester, it is possible to suppress a decrease in mechanical strength due to a reduction in the thickness of the entire polarizing plate, and to secure a breaking point tension of 60 N or more.

  On the other hand, in the polarizing plates 20 to 22, the breaking point tension is less than 60N. This is because, in the polarizing plates 20 to 22, the second protective film does not contain a sugar ester as a retardation reducing agent (from the fact that a zero retardation is realized by a retardation reducing agent other than a sugar ester. ), When the second protective film is thinned, its mechanical strength cannot be ensured, and therefore it is impossible to suppress the decrease in mechanical strength when the entire polarizing plate is thinned. It is done. For this reason, at the time of a rework operation, the polarizing plate is easily broken (the polarizing plate is broken even if the tension applied to the polarizing plate is weak as less than 60 N), and handling properties are deteriorated.

  In addition, about the polarizing plate 19, although the breaking point tension | tensile_strength is 60 N or more, Rt of the 2nd protective film (optical film 10) of the polarizing plate 19 is 10 nm or more, and the zero phase difference film is implement | achieved. Absent. This is because the sugar ester contained in the retardation reducing agent of the optical film 10 is obtained by esterifying the OH group of a compound having a furanose structure or a pyranose structure with an aromatic alkyl group, and the effect of bringing Rt close to zero is small. it is conceivable that.

  The polarizing plate and liquid crystal display device of this embodiment described above can be expressed as follows.

1. A polarizing plate in which a first protective film, a polarizing film as a polarizer, a second protective film, and an adhesive layer are laminated in this order,
The total thickness of the first protective film, the polarizing film, and the second protective film is 90 μm or less,
The moisture permeability of the first protective film is 400 g / m ² · 24 hr or less,
The second protective film contains a cellulose ester and a retardation reducing agent,
The retardation reducing agent is an OH group in a compound (A) having one furanose structure or pyranose structure, or in a compound (B) in which at least one furanose structure or pyranose structure is bonded to 2 to 12 inclusive. Including sugar esters all or partly esterified with aliphatic acyl groups,
In the second protective film,
Ro represented by the following formula (i) is 0 nm or more and 10 nm or less,
A polarizing plate, wherein Rt represented by the following formula (ii) is -10 nm or more and +10 nm or less.
Formula (i) Ro = (nx−ny) × d
Formula (ii) Rt = {(nx + ny) / 2−nz} × d
(In the formula, Ro is the retardation value in the in-plane direction of the film, Rt is the retardation value in the thickness direction of the film, nx is the refractive index in the slow axis direction in the film plane, ny is the fast axis direction in the film plane) Refractive index, nz is the refractive index in the thickness direction of the film (refractive index is measured at a wavelength of 590 nm in an environment of 23 ° C. and 55% RH), and d is the thickness (nm) of the film.

  2. The sugar ester is a compound obtained by esterifying all or part of the OH group in the compound (B) in which 2 or more and 12 or less of at least one of the furanose structure or the pyranose structure are bonded with an aliphatic acyl group. 2. The polarizing plate as described in 1 above, which is characterized by the following.

  3. The sugar ester is a compound obtained by esterifying all or part of the OH groups in the compound (B) in which at least one of at least one of a furanose structure or a pyranose structure is bonded with an acetyl group. 2. The polarizing plate according to 2.

  4). 4. The polarizing plate according to any one of 1 to 3, wherein a total thickness of the first protective film, the polarizing film, and the second protective film is 80 μm or less.

  5. 5. The polarizing plate according to any one of 1 to 4, wherein the polarizing film has a thickness of 15 μm or less.

  6). 6. The polarizing plate according to any one of 1 to 5, wherein the second protective film has a thickness of 30 μm or less.

7). The polarizing plate according to any one of 1 to 6,
A liquid crystal display device comprising: a liquid crystal cell adhered to the pressure-sensitive adhesive layer of the polarizing plate.

  8). 8. The liquid crystal display device as described in 7 above, which is driven in an IPS mode.

  The polarizing plate of the present invention is particularly applicable to a liquid crystal display device driven in the IPS mode.

DESCRIPTION OF SYMBOLS 1 Liquid crystal display device 2 Liquid crystal cell 3 Polarizing plate 11 1st protective film 12 Polarizing film 13 2nd protective film 14 Adhesive layer

Claims (8)

A polarizing plate in which a first protective film, a polarizing film as a polarizer, a second protective film, and an adhesive layer are laminated in this order,
The total thickness of the first protective film, the polarizing film, and the second protective film is 90 μm or less,
The moisture permeability of the first protective film is 400 g / m ² · 24 hr or less under the condition of 40 ° C. and 90% RH ,
The second protective film contains a cellulose ester and a retardation reducing agent,
The retardation reducing agent is an OH group in a compound (A) having one furanose structure or pyranose structure, or in a compound (B) in which at least one furanose structure or pyranose structure is bonded to 2 to 12 inclusive. Including sugar esters all or partly esterified with aliphatic acyl groups,
The sugar ester is contained at a ratio of 19/22 or more with respect to the total mass of the retardation reducing agent,
In the second protective film,
Ro represented by the following formula (i) is 0 nm or more and 10 nm or less,
A polarizing plate, wherein Rt represented by the following formula (ii) is -10 nm or more and +10 nm or less.
Formula (i) Ro = (nx−ny) × d
Formula (ii) Rt = {(nx + ny) / 2−nz} × d
(In the formula, Ro is the retardation value in the in-plane direction of the film, Rt is the retardation value in the thickness direction of the film, nx is the refractive index in the slow axis direction in the film plane, ny is the fast axis direction in the film plane) Refractive index, nz is the refractive index in the thickness direction of the film (refractive index is measured at a wavelength of 590 nm in an environment of 23 ° C. and 55% RH), and d is the thickness (nm) of the film.   The sugar ester is a compound obtained by esterifying all or part of the OH group in the compound (B) in which 2 or more and 12 or less of at least one of the furanose structure or the pyranose structure are bonded with an aliphatic acyl group. The polarizing plate according to claim 1.   The sugar ester is a compound obtained by esterifying all or a part of OH groups in a compound (B) in which at least one of a furanose structure or a pyranose structure is bonded to each other with an acetyl group. Or the polarizing plate of 2.   The polarizing plate according to claim 1, wherein the total thickness of the first protective film, the polarizing film, and the second protective film is 80 μm or less.   The polarizing plate according to claim 1, wherein the polarizing film has a thickness of 15 μm or less.   The polarizing plate according to claim 1, wherein a thickness of the second protective film is 30 μm or less. A polarizing plate according to any one of claims 1 to 6,
A liquid crystal display device comprising: a liquid crystal cell adhered to the pressure-sensitive adhesive layer of the polarizing plate.   The liquid crystal display device according to claim 7, wherein the liquid crystal display device is driven in an IPS mode.

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