WO2015008741A1

WO2015008741A1 - Polarizing plate and liquid crystal display device

Info

Publication number: WO2015008741A1
Application number: PCT/JP2014/068756
Authority: WO
Inventors: 直輝高橋
Original assignee: コニカミノルタ株式会社
Priority date: 2013-07-17
Filing date: 2014-07-15
Publication date: 2015-01-22
Also published as: KR20150140747A; KR101748065B1; JPWO2015008741A1; JP6330807B2; TW201510562A; TWI544227B

Abstract

　A polarizing plate (3) in which the total thickness of a first protective film (11) and a polarizing film (12) is 50 μm or less. A second protective film (13) contains a cellulose ester and a retardation-lowering agent. The retardation-lowering agent contains a sugar ester obtained by esterifying, with an aliphatic acyl group, all or some of OH groups in a compound (A) having at least one furanose or pyranose structure or in a compound (B) in which two to twelve furanose structures and/or pyranose structures are bonded. The sugar ester is contained at a proportion of at least 70% of the total mass of the retardation-lowering agent. In the second protective film (13), Ro is 0 to 10 nm and Rt is -10 to +10 nm.

Description

Polarizing plate and liquid crystal display device

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 are also 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.

Also, 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 with a 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.

Japanese Patent Laid-Open No. 2003-12859 (refer to Claim 1, Table 1, etc.) Japanese Patent No. 5162358 (refer to Claim 1, Table 2, etc.)

Conventionally, in a polarizing plate using a zero retardation film to which an ethylenic polymer or polyester polyol is added, the polarization function does not deteriorate in the usage environment. However, in recent years, it has been found that when the polarizing plate is thinned in accordance with the demand for thinning of a liquid crystal display device such as a mobile phone, the polarizing function is deteriorated in the polarizing plate using a conventional zero retardation film. This is considered to be due to the following reasons.

In order to reduce the thickness of the polarizing plate, it is necessary to reduce the thickness of the protective film (also referred to as a first protective film) on the surface side of the polarizer (the side opposite to the liquid crystal layer with respect to the polarizer). When a cellulose ester film is used as the first protective film, the cellulose ester film has high moisture permeability. Therefore, if the cellulose ester film is thinned, moisture easily passes through the cellulose ester film and reaches the polarizer, and includes PVA. The polarizer is easily deteriorated by the moisture.

Moreover, when the zero phase difference film to which the above-described ethylenic polymer or polyester polyol is added is used as a protective film (also referred to as a second protective film) on the back surface side (liquid crystal layer side) of the polarizer, The acid generated during the synthesis of the polyester polyol destroys the cross-linking of the PVA contained in the polarizer. For this reason, the thinning of the first protective film makes it easier for the polarizer, which is easily deteriorated by moisture passing therethrough, to become more and more deteriorated due to breakage of the crosslinking by the acid, resulting in deterioration of the polarizing function of the polarizing plate. To do.

In addition, the polarizing plate can be thinned by thinning the polarizer itself, but even in this case, the resistance of the polarizer itself is weakened, and the polarizer is easily deteriorated by moisture and acid. Similarly, the polarizing function of the polarizing plate deteriorates.

The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a polarizing plate capable of suppressing deterioration of the polarization function even if the polarizer and the protective film on the surface side are thinned, and the polarizing plate. And a liquid crystal display device provided with the same.

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

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 and the polarizing film is 50 μm 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,
The sugar ester is contained in a proportion of 70% 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,
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 said structure, in the thin structure whose sum total of a 1st protective film, a polarizing film, and thickness is 50 micrometers or less, the specific saccharide | sugar in the retardation reducing agent contained in a 2nd protective film (zero retardation film) By appropriately setting the ester content, deterioration of the polarization function can be suppressed.

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 this 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 polarizing film 12 is obtained, for example, by dyeing a PVA film with a dichroic dye and stretching it at a high magnification. 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 thickness is 50 μm or less. And the 2nd 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. This sugar ester is contained in a proportion of 70% or more with respect to the total mass of the retardation reducing agent. 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).

Here, in the case of ethylenic polymers and polyester polyols generally used as a retardation reducing agent, an acid is inevitably generated during the synthesis and remains slightly in the additive. In some cases, crosslinking of PVA contained in the polarizing film 12 laminated with the film is broken by an acid. On the other hand, since no acid remains after the synthesis of the sugar ester, if it is contained in a proportion of 70% or more of the total mass of the retardation reducing agent, even if the ethylenic polymer or polyester polyol is contained in the second protective film 13. Even if contained, it can suppress that the bridge | crosslinking of PVA contained in the polarizing film 12 is destroyed by an acid.

Thereby, in order to make the polarizing plate 3 thin, the total thickness of the first protective film 11 and the polarizing film 12 is set to 50 μm or less, and the polarizing film 12 is likely to be deteriorated by moisture that passes through the first protective film 11. Even so, it can be suppressed that the deterioration is further promoted by the component (acid generated during synthesis) contained in the second protective film 13. Therefore, even when the polarizing plate 3 is thinned, deterioration of the polarization function can be suppressed. In particular, when the total thickness of the first protective film 11 and the polarizing film 12 is as thin as 45 μm or less, the above-described configuration that suppresses the deterioration of the polarization function 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.

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 a furanose structure or a pyranose structure are bonded with an aliphatic acyl group. desirable. In this case, the retardation Ro in the in-plane direction can be reliably reduced, and for example, Ro ≦ 1 nm can be reliably realized.

The sugar ester is more preferably a compound in which all or part of the OH group 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 this case, the retardation Ro in the in-plane direction and the retardation Rt in the thickness direction can be reliably reduced. For example, Ro ≦ 1 nm and Rt ≦ 3 nm can be reliably realized.

Such a polarizing plate 3 of this embodiment is suitable for the liquid crystal display device 1, and among them, the zero phase difference is realized by the second protective film 13, so that the liquid crystal display device 1 driven in the IPS mode is used. Is preferred.

Hereinafter, details of the present embodiment will be described. In the following, the protective film on the liquid crystal cell side (second protective film) in the polarizing plate on the viewing side with respect to the liquid crystal cell will be described as an example. The configuration of the second protective film is the same as that of the liquid crystal cell. Of course, this can also be applied to the protective film on the opposite side (first protective film). In addition, when it is not necessary to distinguish a 2nd protective film and a 1st protective film clearly, these are collectively called a protective film collectively.

[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 following compounds, 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.

Also, 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, undecyl 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 preferable alicyclic monocarboxylic acids include cyclopentane carboxylic acid, cyclohexane carboxylic acid, cyclooctane carboxylic acid, and derivatives thereof.

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

In addition to the esterified compounds (A) and (B), an oligosaccharide esterified compound can be applied as a compound in which 3 to 12 furanose structures or pyranose structures are bonded.

Oligosaccharide is 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 production 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.

Hereinafter, specific examples of the sugar ester compound of the present embodiment will be given, but the present invention is not limited thereto.

The second protective film of the polarizing plate contains the above-mentioned sugar ester compound in an amount of 1 to 35% by mass, particularly 5 to 30% by mass in order to suppress 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 / 044433 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- (AG-) _n AB 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. More preferably, it has 1-20 carbon atoms, and particularly preferably has 1-12 carbon atoms. 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. More preferably, it has 1-20 carbon atoms, and particularly preferably has 1-12 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, 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.

Polyester polycondensation is performed by conventional methods. 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.

The conventional molecular weight adjustment 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.

The polyester of this embodiment is preferably contained in an amount of 1 to 40% by mass with respect to the cellulose ester. Further, it is preferable to contain 2 to 30% by mass. In particular, the content is preferably 3 to 15% by mass.

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. In the case of the same degree of substitution, birefringence decreases when the number of carbon atoms is large. 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.

Further, the retardation value can be appropriately controlled by the kind of the acyl group of the cellulose ester and the substitution degree of the acyl group to the pyranose ring of the cellulose resin skeleton.

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

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 method for measuring the substitution degree of the 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, and the mechanical strength of the resulting film is strong. Furthermore, 70,000-200000 are preferably used.

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 used 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 cottoned 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 also preferable that the synthesized cellulose ester is purified to remove low molecular weight components, and components that are not acetylated or have a low acetylation degree are removed by filtration.

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

In addition, cellulose ester is also affected by trace metal components in cellulose ester. 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, and more preferably in the range of 0 to 20 ppm. 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).

(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. Moreover, these plasticizers may have a function as the above-mentioned retardation reducing agent.

The polyhydric alcohol ester plasticizer is a compound represented by the above 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 ester 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 ester 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 a divalent or higher, preferably a divalent to 20valent polyvalent carboxylic acid and an alcohol. The aliphatic polyvalent carboxylic acid is preferably divalent to 20-valent, and in the case of an aromatic polyvalent carboxylic acid or alicyclic polyvalent carboxylic acid, it is preferably trivalent 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.)

Preferred examples of the polyvalent carboxylic acid include the following, but the present invention is not limited to these. 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.

The alcohol used for the polyvalent carboxylic acid ester compound is not particularly limited, and known alcohols 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. More preferably, it has 1 to 20 carbon atoms, and particularly preferably 1 to 10 carbon atoms. 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 polyvalent carboxylic 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 straight-chain or side-chain fatty acid having 1 to 32 carbon atoms can be preferably used. More preferably, it has 1 to 20 carbon atoms, and particularly preferably 1 to 10 carbon atoms.

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 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.

The molecular weight of the polyvalent carboxylic acid ester compound is not particularly limited, but is preferably in the range of 300 to 1000, and more preferably in the range of 350 to 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 polycarboxylic acid ester may be one kind or a mixture of two or more kinds.

The acid value of the polyvalent carboxylic 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
(Wherein 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-1,3-propanediol (3,3-dimethylolheptane), 3-methyl-1, 5-pentanediol 1,6-hexanediol, 2,2,4-trimethyl 1,3-pentanediol, 2-ethyl 1 There are 3-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, alkylene glycols having 2 to 12 carbon atoms are particularly preferable because of excellent compatibility with cellulose esters.

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. These glycols include 1 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 number average molecular weight of the polyester plasticizer is 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.

Hereinafter, a synthesis example of an aromatic terminal ester plasticizer that can be used in the present embodiment will be 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 the monohydric alcohol was refluxed, 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 of 1.33 × 10 ⁴ Pa to finally 4 × 10 ² Pa or less at 200 to 230 ° C., and then filtered to obtain 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. 1 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

Hereinafter, specific compounds of the aromatic terminal ester plasticizer that can be used in the present embodiment will be shown, but the present invention is not limited thereto.

(UV absorber)
The polarizing plate protective film of this embodiment can also contain an 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, and the like, 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.

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 Group, aryloxy group, alkylthio group, arylthio group, mono- or dialkylamino group, acylamino group or 5- to 6-membered heterocyclic group, 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.

Specific examples of the benzotriazole-based ultraviolet absorber are given below, but the present 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- Mixture of 4-hydroxy-5- (5-chloro-2H-benzotriazol-2-yl) phenyl] propionate (TINUVIN109)

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

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 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 an ultraviolet absorber.

The polarizing plate protective film of the present embodiment preferably contains two or more ultraviolet absorbers.

Also, as the ultraviolet absorber, a polymeric ultraviolet absorber can also be preferably used, and in particular, a polymer type ultraviolet 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, the operating conditions, etc., but when the dry film thickness of the polarizing plate protective film is 10 to 200 μm, the amount used is 0.5 to the polarizing plate protective film. Is preferably 10 to 10% by mass, and more preferably 0.6 to 4% by mass.

(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 size 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. A preferable amount of the cellulose ester is 1 to 10 parts by mass, and more preferably 3 to 5 parts by mass with respect to 100 parts by mass of the solvent.

In this 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 for performing 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. The concentration that achieves both of these is preferably 10 to 35% by mass, and more preferably 15 to 25% by 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.

The poor solvent used is not particularly limited, but for example, methanol, ethanol, n-butanol, cyclohexane, cyclohexanone, etc. are preferably used. The dope preferably contains 0.01 to 2% by mass of water. 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.

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 the 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 preferred 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, the cellulose ester solution is filtered using an appropriate filter medium such as filter paper. As the filter medium, it is preferable that the absolute filtration accuracy is small in order to remove insoluble matters and the like, but there is a problem that the filter medium is likely to be clogged if the absolute filtration accuracy is too small. For this reason, a filter medium with an absolute filtration accuracy of 0.008 mm or less is preferable, a filter medium with 0.001 to 0.008 mm is more preferable, and a filter medium with 0.003 to 0.006 mm is more 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 leaks, 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, still more preferably 50 pieces / cm ² or less, still more preferably 0 to 10 pieces / cm ² . 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.

It is preferable that the filtration pressure is small. 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 process is −50 ° C. to less than the boiling point of the solvent, and a higher temperature is preferable because the web can be dried faster. However, if the temperature is too high, the web may foam or become flat. May deteriorate. The support temperature is preferably 0 to 40 ° C, more preferably 5 to 30 ° C. Alternatively, it is also a preferable method that the web is gelled by cooling and peeled from the drum in a state containing a large amount of residual solvent.

The method for controlling the temperature of the metal support is not particularly limited, but 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. 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 The content is preferably 0 to 0.01% by mass or less.

In the film drying process, generally, a roll drying method (a method in which a plurality of rolls arranged at the top and bottom are alternately passed through the web for drying) or a tenter method for drying while transporting the web is employed.

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 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 from 50 to 140 ° C. in order to improve dimensional stability.

The thickness of the protective film is not particularly limited, but 10 to 200 μm is used. In particular, the film thickness is particularly preferably 10 to 100 μm. More preferably, it is 10 to 30 μm.

A protective film having a width of 1 to 4 m is used. Particularly, 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)
The protective film of the polarizing plate preferably has a retardation value Ro represented by the following formula of 0 to 10 nm and Rt of −10 to +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, it is more preferable that the retardation value Ro is in the range of 0 to 5 nm and Rt is 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.

The width retention or lateral stretching in the film forming step is preferably performed by a tenter, and 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 the measurement of θ1 can be performed 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%, 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, and the treatment of the polyvinyl alcohol resin film dyed with a dichroic dye 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 heat treatment is subjected to a heat treatment at a temperature in the range of 90 to 180 ° C. to produce a polarizing film having a thickness of more than 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 made of the resin layer having a thickness of 10 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. Of these, 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 performance and has few color spots, and is particularly preferably used for a large liquid crystal display device.

The polarizer obtained as described above is usually used as a polarizing plate with a protective film bonded to both sides or one side. Examples of the adhesive used 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, 2-ethylhexyl (meth) acrylate And polymers based on copolymers using two or more of these (meth) acrylic esters are preferably used. The pressure-sensitive adhesive usually has a polar monomer 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 the present embodiment can be incorporated into a fringe-field switching (FFS) mode type liquid crystal display device, and even in this case, the visibility is excellent and the viewing angle is expanded. A liquid crystal display device can be realized.

The protective film of the polarizing plate of this embodiment is the back side of the polarizing plate on the viewing side with respect to the liquid crystal cell among the two polarizing plates sandwiching the liquid crystal cell of the liquid crystal display device (the liquid crystal cell side with respect to the polarizer). However, it can also be applied to the protective film on the surface side of the polarizing plate (the side opposite to the liquid crystal cell with respect to the polarizer), or the polarizing plate on the backlight side with respect to the liquid crystal cell. It can also be applied to protective films on the front surface side (liquid crystal cell side with respect to the polarizer) and the back surface side (backlight side with respect to the polarizer).

<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 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 carrying out dehydration condensation reaction for 15 hours, and distilling off unreacted 1,2-propylene glycol under reduced pressure at 200 ° C. after completion of the 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 carried out by the polymerization method described in JP-A No. 2000-128911. That is, the following methyl acrylate (MMA) is introduced as a monomer into a flask equipped with a stirrer, a nitrogen gas inlet tube, a thermometer, an inlet and a reflux condenser, and nitrogen gas is introduced to replace the inside of the flask with nitrogen gas. An acrylic compound was obtained.

Then, after addition of thioglycerol, polymerization was performed 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 12 parts by weight Ester compound E1 4 parts by weight Matting agent: 12% ethanol dispersion of R812 (manufactured by Nippon Aerosil Co., Ltd.) 1.4 parts by weight Methylene chloride 430 parts by weight Ethanol 40 parts by weight Further, the additive component was put into a closed container and dissolved while stirring, and this was dissolved into 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.

[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 (1) was measured using an automatic birefringence meter KOBRA-WPR (Oji Scientific Instruments).

Specifically, the optical films 1 to 12 produced above were measured at three locations at a wavelength of 590 nm in a 23 ° C. and 55% RH environment at three locations, 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 to 12 produced as described above, polarizing plates 1 to 13 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. As a result, a polarizer 2 (coating polarizer) was obtained. The thickness of the polarizer 2 was adjusted to 3 μm.

(Preparation of polarizing plates 1 to 12)
Alkali saponification is performed on the other surface of the polarizer 1 using a KC2UA film (produced by Konica Minolta Co., Ltd.) having a thickness of 25 μm, which has been subjected to alkali saponification treatment on one surface of the polarizer 1, as a first protective film. The treated optical films 1 to 12 are bonded to each other as a second protective film and a 5% aqueous solution of polyvinyl alcohol as an adhesive, and then an adhesive layer is laminated on the optical film 1 to 12 side. ~ 12. The total thickness of the first protective film and the polarizer is 35 μm, which satisfies 50 μm or less (45 μm or less).

(Preparation of polarizing plate 13)
Alkali saponification is performed on the other surface of the polarizer 2 with a KC2UA film (produced by Konica Minolta Co., Ltd.) having a thickness of 25 μm that has been subjected to alkali saponification treatment on one surface of the polarizer 2 as a first protective film. The processed optical film 1 was used as a second protective film, and a polyvinyl alcohol 5% aqueous solution was bonded as an adhesive, and then an adhesive layer was laminated on the optical film 1 side to obtain a polarizing plate 13. The total thickness of the first protective film and the polarizer is 28 μm, which satisfies 50 μm or less (45 μm or less).

[Evaluation of image unevenness]
A liquid crystal display device including polarizing plates 1 to 13 was prepared and image unevenness was evaluated.

Specifically, iPad2 (manufactured by Apple) was prepared, the polarizing plate on the backlight side previously bonded was peeled off, and the polarizing plate produced as described above was bonded to the glass surface of the liquid crystal cell. A liquid crystal display device was prepared by bonding so that the absorption axis of the manufactured polarizing plate was in the same direction as the absorption axis of the polarizing plate bonded in advance.

The obtained liquid crystal display device was left in a chamber at 60 ° C. and 90% RH for 300 hours. Thereafter, the liquid crystal display device was taken out from the chamber, and the luminance uniformity (image unevenness) of the display screen was visually observed in a state where the liquid crystal display device was displayed in black at room temperature, and evaluated based on the following criteria. Note that the above-described image unevenness is synonymous with luminance unevenness due to light leakage during black display. In the following evaluation, ○ or ◎ is preferable.
(Evaluation criteria)
A: Image unevenness was hardly recognized.
○: When very careful, image unevenness is slightly observed, but there is no problem in actual use.
X: Image unevenness is recognized and there is a problem in actual use.

Table 3 shows the results of evaluation of image unevenness and the correspondence between the examples of the present invention and comparative examples.

From Table 3, in the liquid crystal display device using the polarizing plates 10 to 12, the evaluation result of the image unevenness is x. In the polarizing plates 10 to 12, the sugar ester contained in the protective film (zero retardation film) of the polarizing plate is less than 70% with respect to the total mass of the retardation reducing agent, and other retardation reducing agents (esters) This is probably because the deterioration of the polarizer due to the acid generated during the synthesis of the compounds E1 and E2 and the acrylic additive A1) cannot be suppressed, or the effect of suppressing the deterioration is small.

In other words, the deterioration of the polarizer is as follows: (1) the total thickness of the first protective film and the polarizer is reduced to 50 μm or less, so that moisture easily passes through the first protective film; (2) Crosslinking of PVA of the polarizer is destroyed by the acid, but when the sugar ester contained in the retardation reducing agent is small (there are many other retardation reducing agents) Since the destruction of (2) cannot be suppressed, the deterioration of the polarizer due to (1) is further promoted by (2). As a result of the deterioration of the polarizer in this way, light leakage is considered to occur during black display.

On the other hand, in the liquid crystal display device using the polarizing plates 1 to 8, the evaluation result of the image unevenness is good. This is because, in the polarizing plates 1 to 8, the sugar ester contained in the protective film of the polarizing plate is as large as 70% or more with respect to the total mass of the retardation reducing agent, and the destruction of (2) can be suppressed. Conceivable. That is, even when the total thickness of the first protective film and the polarizer is reduced to 50 μm or less, the deterioration of the polarizer due to the above (1) can be suppressed from being further promoted by the above (2). Therefore, even when the thickness is reduced, it is considered that as a result, the polarizers 10 to 12 are hardly deteriorated.

Further, from the results shown in Table 2, since the optical films 1 to 3 and 6 to 8 can suppress Ro to 1 nm or less, the sugar ester as a retardation reducing agent has two furanose structures or pyranose structures. If the OH group of the above compound is esterified with an aliphatic alkyl group, it can be said that there is an effect of reducing Ro. Further, in the optical films 1 and 6 to 8, since Rt can be suppressed to 3.0 nm or less, the sugar ester as an additive is a compound having two furanose or pyranose structures (here, sucrose). If the OH group is esterified with an acetyl group, it can be said that there is an effect of further reducing Rt.

In addition, in the liquid crystal display device using the polarizing plate 9, the result of evaluation of image unevenness is good, but the Rt of the optical film 9 used for the polarizing plate 9 exceeds 10 nm (see Table 2). It cannot be said that a zero retardation film has been realized. This is because the sugar ester contained in the retardation reducing agent of the optical film 9 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 the liquid crystal display device of the present 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 and the polarizing film is 50 μm 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,
The sugar ester is contained in a proportion of 70% 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 from −10 nm to +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 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 claim 1, wherein the total thickness of the first protective film and the polarizing film is 45 μm or less.

5. 5. The polarizing plate as described in any one of 1 to 4 above, wherein the thickness of the second protective film is 30 μm or less.

6). The polarizing plate according to any one of 1 to 5,
A liquid crystal display device comprising: a liquid crystal cell adhered to the pressure-sensitive adhesive layer of the polarizing plate.

7. 7. The liquid crystal display device as described in 6 above, which is driven in an IPS mode.

The polarizing plate of the present invention can be used particularly for 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

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 and the polarizing film is 50 μm 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,
The sugar ester is contained in a proportion of 70% 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 from −10 nm to +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 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 and the polarizing film is 45 μm or less.
The polarizing plate according to claim 1, wherein the second protective film has a thickness of 30 μm or less.
A polarizing plate according to any one of claims 1 to 5,
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 6, wherein the liquid crystal display device is driven in an IPS mode.