TWI637850B - Polarizing plate and liquid crystal display device - Google Patents

Abstract

The total thickness of the first protective film (11), polarizing film (12), and second protective film (13) of the polarizing plate (3) is 90 μm or less. The moisture permeability of the first protective film (11) is 400g / m ² . Below 24hr. Contained in the second protective film (13). There are cellulose esters and delay reducers. The retardation reducing agent includes a compound (A) having one furanose structure or pyranose structure, or at least one compound (B) bonded with two or more 12 or less furanose structures or pyranose structures All or a part of the OH group is a sugar ester esterified with an aliphatic acetyl group. Ro of the second protective film (13) is 0 nm or more and 10 nm or less, and Rt is -10 nm or more + 10 nm or less.

Description

Polarizing plate and liquid crystal display device

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

With the high performance of liquid crystal display devices. High quality, the polarizer protective film used in the polarizer also has various requirements.

In general, polarizing plate protective films for liquid crystal display devices mainly use films made of cellulose ester. The cellulose ester film is generally formed by a solution casting film forming method from the viewpoint of ensuring flatness, etc. However, in this film forming method, the refractive index in the thickness direction tends to be lower than the refractive index in the film surface.

Therefore, Patent Document 1 proposes a cellulose ester film that reduces the retardation in the thickness direction by adding an ethylene polymer. In addition, Patent Document 2 proposes a cellulose ester film that reduces the retardation in the in-plane direction and the thickness direction by adding polyester polyol.

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

In the IPS (In-plain switching) mode liquid crystal display device, the use of a polarizer that imparts a phase difference to the polarizer as a protective film on the liquid crystal layer side, and a polarizer that reduces the retardation can be used The display performance (angle of view, hue, tone) of the monitor is improved. At this point, the cellulose ester film of Patent Document 1 or 2 whose retardation is reduced is suitable for the protective film of the polarizing plate of the IPS mode liquid crystal display device. In addition, the cellulose ester film whose retardation is reduced is also referred to as a zero retardation film hereinafter.

[Previous Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open No. 2003-12859 (request item 1, table 1, etc. as a reference)

[Patent Document 2] Japanese Patent No. 5162358 (request item 1, table 2, etc. for reference)

However, if the protective film on the polarizer surface side (the opposite side of the liquid crystal layer) has a high moisture permeability, moisture in the air passes through the protective film to reach the polarizer, and the polarizer deteriorates. As a result, the polarizing function of the polarizing plate deteriorates, and in the liquid crystal display device, light leakage occurs during black display, resulting in uneven brightness (uneven image). Therefore, the moisture permeability of the protective film on the surface side of the polarizer is preferably low. The protective film with low moisture permeability can be realized by using, for example, acrylic resin or PET (polyethylene terephthalate) resin Now. In addition, in the IPS mode type liquid crystal display device, as the protective film on the back side (liquid crystal layer side) of the polarizer, it is preferable to use the above-mentioned conventional zero retardation film from the viewpoint of improvement in display performance.

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

However, thinning each layer of the polarizing plate decreases the mechanical strength of each layer, and the mechanical strength of the entire polarizing plate decreases. In particular, the thinning of the protective film with low moisture permeability significantly reduces the ductility, which tends to reduce the mechanical strength of the entire polarizing plate. As a result, when performing the secondary processing operation after attaching the polarizing plate to the liquid crystal cell, the polarizing plate may break even if the tensile tension is weak, and the operability of the polarizing plate is reduced. In addition, the secondary processing operation refers to the operation of peeling the polarizing plate and then attaching to the liquid crystal cell again when the polarizing plate fails to adhere to the liquid crystal cell.

The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a low-moisture protective film, polarizer, and zero retardation film constituting a polarizing plate that can reduce the mechanical strength of the entire polarizing plate and reduce A polarizing plate with improved operability and a liquid crystal display device provided with the polarizing plate.

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

The polarizing plate on one side 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 first protective film and the polarizing film and the second The total thickness of the protective film is 90 μm or less, and the moisture permeability of the first protective film is 400 g / m ² . 24 hrs or less, the second protective film contains cellulose ester and a retardation reducing agent, and the retardation reducing agent contains a compound (A) having a furanose structure or a pyranose structure, or 2 or more bonded to 12 or less Sugar esters in which all or part of the OH groups in at least one compound (B) of the furanose structure or pyranose structure are esterified with an aliphatic acetyl group, in the second protective film, the following formula ( i) The RO represented is 0 nm or more and 10 nm or less, and the Rt represented by the following formula (ii) is -10 nm or more + 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 direction of the slow phase axis in the film surface, and ny is the direction of the phase advance axis in the film surface. Refractive index, nz is the refractive index in the thickness direction of the film (refractive index is measured in an environment of 23 ° C. and 55% RH at a wavelength of 590 nm), and d is the thickness of the film (nm)).

According to the above configuration, the thickness of the first protective film with low moisture permeability, the polarizing film, and the second protective film with zero phase difference can be combined In the case where the thickness of the polarizing plate is reduced to 90 μm or less, the second protective film contains the sugar ester of the above-mentioned chemical structure as a retardation reducing agent, which can be suppressed compared to a configuration in which zero retardation is achieved by other retardation reducing agents The mechanical strength of the entire polarizing plate is reduced. As a result, it is possible to suppress the breakage of the polarizing plate during the secondary processing operation and improve the operability.

In addition, in the present invention, the retardation-reducing agent refers to a compound that has an effect of reducing the retardation value (Rt) in the thickness direction when it is added to the protective film as compared with the case where it is not added. Regarding the retardation reducing agent, when A mass% is added, compared with the case where it is not added, it is preferable to use a function that reduces the retardation value (Rt) in the thickness direction by 0.01 nm or more in terms of 80 μm.

1‧‧‧LCD display device

2‧‧‧Liquid crystal cell

3‧‧‧ Polarizer

11‧‧‧The first protective film

12‧‧‧ Polarized film

13‧‧‧Second protective film

14‧‧‧Adhesive layer

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

One embodiment of the present invention will be described below based on the drawings. In addition, in this specification, when the numerical range is expressed as A to B, the numerical range includes the values of the lower limit A and the upper limit B. In addition, the present invention is not limited to the following.

1 is a cross-sectional view of a schematic configuration of a liquid crystal display device 1 of this embodiment. The liquid crystal display device 1 is a liquid crystal cell 2 with two polarizing plates 3.4 Holder constitutes and drives in IPS mode. The liquid crystal cell 2 is composed of a liquid crystal layer sandwiched by two transparent substrates.

The polarizing plate 3 is a first protective film 11 that sequentially laminates the surface side (the side opposite to the viewing side and the liquid crystal cell), the polarizing film 12 as a polarizer (polarizing film), and the first side on the back side (liquid crystal cell side) 2. The protective film 13 and the adhesive layer 14 are formed. After the adhesive layer 14 is bonded to the liquid crystal cell 2, the polarizing plate 3 is located on the surface side of the liquid crystal cell 2. In addition, the polarizing plate 3 is a functional layer that may further have a hard coat layer, an anti-glare layer, an anti-reflection layer, etc. on the opposite side of the first protective film 11 and the polarizing film 12.

The polarizing plate 4 is formed by laminating the adhesive layer 21, the protective film 22, the polarizing film 23, and the protective film 24 in this order. After the adhesive layer 21 is connected to the liquid crystal cell 2, the polarizing plate 4 is located on the back side (backlight side) of the liquid crystal cell 2.

Moreover, the adhesive layer 21, the protective film 22, the polarizing film 23, and the protective film 24 of the polarizing plate 4 have the same structure as the adhesive layer 14, the second protective film 13, the polarizing film 12, and the first protective film 11 of the polarizing plate 3. Therefore, in the following, the polarizing plate 3 is taken as an example for detailed description, and the detailed description of the polarizing plate 4 is omitted.

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

The polarizing film 12 is, for example, a PVA film dyed with a dichroic dye and stretched at a high magnification, and its thickness is 15 μm or less.

The second protective film 13 contains cellulose ester and retardation reducing agent. The retardation reducing agent includes at least one compound (B) of compounds (A) having one furanose structure or pyranose structure, or two or more than 12 furanose structures or pyranose structures bonded to each other All or part of the OH groups in the sugar esters are esterified with an aliphatic acetyl group. In the second protective film 13, RO represented by the following formula (i) is 0 nm or more and 10 nm or less, and Rt represented by the following formula (ii) is -10 nm or more + 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 direction of the slow phase axis in the film surface, and ny is the direction of the phase advance axis in the film surface. Refractive index, nz is the refractive index in the thickness direction of the film (refractive index is measured in an environment of 23 ° C. and 55% RH at a wavelength of 590 nm), and d is the thickness of the film (nm)).

In addition, since the equations (i) and (ii) are satisfied at the same time, the generated phase difference is almost zero, which is also called zero phase difference. By including the retardation reducing agent in the second protective film 13, the second protective film 13 can be used as a film that achieves zero retardation (zero retardation film).

Because the first protective film 11 has a moisture permeability of 400 g / m ² . The low moisture permeability of 24 hr or less can suppress the deterioration of the polarizing film 12 caused by the moisture transmitted through the first protective film 11. However, when the protective film with low moisture permeability is thinner, the ductility is lowered, and the mechanical strength of the entire polarizing plate 3 is likely to be lowered. In addition, the polarizing film 12 itself is easily reduced in mechanical strength due to its thinness.

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

Here, the aforementioned sugar ester as a retardation reducing agent is different from the ethylene polymer or polyester polyol which is also used as a retardation controlling agent, and has a furanose structure or a pyranose structure, which is similar to a cellulose ester chemical structure. Therefore, the interaction between the above sugar ester and cellulose ester is strong. Therefore, even if the second protective film 13 containing the sugar ester and the cellulose ester is thinned, the mechanical strength of the second protective film 13 can be suppressed from decreasing.

Therefore, even if the total thickness of the first protective film 11, the polarizing film 12, and the second protective film 13 is 90 μm or less, the entire thickness of the polarizing plate 3 becomes thinner, and the first protective film 11 and the first protective film 11 that tend to reduce mechanical strength due to the thinning The polarizing film 12 is supported by the second protective film 13 to suppress the decrease in the mechanical strength of the entire polarizing plate 3. As a result, it is possible to suppress the breakage of the polarizing plate 3 during the secondary processing operation (the peeling operation performed by re-attaching the polarizing plate 3 adhered to the liquid crystal cell 2) to improve the operability.

In particular, the total thickness of the first protective film 11, the polarizing film 12 and the second protective film 13 becomes a thinner structure with a thickness of 80 μm or less, and the mechanical strength of the entire polarizing plate 3 is reduced due to the thinning of each layer, and secondary processing The breakage of the polarizing plate 3 during operation becomes more likely to occur, so the above configuration is more effective. In addition, the thickness of the polarizing film 12 is 15 μm or less In the case of a thin type, the reduction in the mechanical strength of the entire polarizing plate 3 due to the thinning of each layer is more likely to occur, so the above configuration becomes very effective. From the viewpoint of thinning the polarizing plate 3, the thickness of the second protective film 13 is preferably 30 μm or less.

The sugar ester contained in the second protective film 13 for achieving zero phase difference focuses on its chemical structure (similarity to the chemical structure of cellulose ester), and is used as a mechanism for suppressing the thinning of the entire polarizing plate 3 The means for reducing the strength can suppress the breakage of the polarizing plate 3 and improve the operability.

From the viewpoint that the retardation Ro in the in-plane direction and the retardation Rt in the thickness direction do become smaller, the aforementioned sugar ester is a compound (B) in which at least one of the furanose structure or the pyranose structure is bonded to two or more but less than 12 Compounds in which all or part of the OH groups are esterified with an aliphatic acyl group are preferred. In addition, the aforementioned sugar ester is preferably a compound in which all or a part of the OH groups in the compound (B) in which at least one furanose structure or pyranose structure is bonded via an acetyl group are esterified. Examples of such sugar esters include sucrose.

In addition, since the first protective film 11 on the surface side of the polarizing plate 3 has low moisture permeability, the deterioration of the polarizing film 12 due to moisture can be suppressed. When the polarizing plate 3 is used in the liquid crystal display device 1, black display can be suppressed. Light leakage to suppress uneven brightness (uneven image). Furthermore, since the second protective film 13 is composed of a zero retardation film and can suppress a decrease in mechanical strength when the polarizing plate 3 is thinned, the polarizing plate 3 is suitable for the IPS mode thin liquid crystal display device 1.

The first protective film 11 may contain a moisture permeability of 400g / m ² . Any resin below 24hr. Examples of such low moisture permeability resins include polyethylene terephthalate (PET) resin, acrylic resin, and cyclic polyolefin resin (COP). That is, the moisture permeability of PET resin is 40g / m ² . 24hr, the moisture permeability of acrylic resin is 100g / m ² . 24hr, COP permeability is 0.1g / m ² . 24hr. In addition, the preferable range of the moisture permeability of the first protective film 11 is 100 g / m ² . Below 24hr.

Hereinafter, this embodiment will be described in detail. In the following description, it is not necessary to clearly distinguish the relative polarizing film as the second protective film on the liquid crystal cell side and the first protective film on the viewing side.

[Second protective film] [Compound with furanose structure or pyranose structure]

The second protective film of the polarizing plate contains cellulose ester and retardation reducing agent as described above. The retardation reducing agent includes at least one compound (B) of compounds (A) having one furanose structure or pyranose structure, or at least one type of furanose structure or pyranose structure bonded to two or more and twelve or less (B) ) Compounds in which all or part of the OH groups are esterified with an aliphatic acyl group (hereinafter, these compounds are also referred to as sugar esters or sugar ester compounds).

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

Examples of the compound (A) include glucose, semi- Lactose, mannose, fructose, xylose, arabinose, etc. In addition, the compound (A) also contains maltitol obtained by reducing maltose after hydrogenation under high pressure.

In addition, examples of the compound (B) include lactose, sucrose, cellobiose, maltose, cellotriose, maltotriose, raffinose, and sucralose. Among these compounds (A) and (B), it is particularly preferable to have both a furanose structure and a pyranose structure. Examples include sucrose.

The monocarboxylic acid used when synthesizing the sugar ester compound is not particularly limited, and conventional aliphatic monocarboxylic acids, alicyclic monocarboxylic acids and the like can be used. The carboxylic acid used may be one kind or a mixture of two or more kinds.

Preferred aliphatic monocarboxylic acids, such as acetic acid, propionic acid, butyric acid, isobutyric acid, valeric acid, hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, capric acid, 2-ethyl-hexanecarboxylic acid, undecyl Acid, lauric acid, tridecyl acid, myristic acid, pentadecyl acid, palmitic acid, heptadecanoic acid, stearic acid, nonadecanoic acid, eicosanoic acid, behenic acid, tetracosanoic acid , Saturated fatty acids such as ascorbic acid, octacosanoic acid, octacosanoic acid, tricosanoic acid, and behenic acid, undecylenic acid, oleic acid, sorbic acid, linolenic acid, sublinseed oil Unsaturated fatty acids such as acids, arachidonic acid, octenoic acid, etc.

Examples of preferred alicyclic monocarboxylic acids include cyclopentanecarboxylic acid, cyclohexanecarboxylic acid, cyclooctanecarboxylic acid, or derivatives thereof.

The production methods of these compounds are described in detail in Japanese Patent Laid-Open No. 8-245678.

In addition to the esterification of the above compound (A) and compound (B) Compounds, esterified compounds of oligosaccharides can be used as at least one kind of compound in which 3 to 12 furanose structures or pyranose structures are bonded.

Oligosaccharide-based starch, sucrose, etc. are produced by the action of enzymes such as amylase. Examples of oligosaccharides applicable in the present embodiment include malto-oligosaccharides, isomalt-oligosaccharides, fructooligosaccharides, galactose oligosaccharides, and xylo-oligosaccharides. Oligosaccharides can also be acetylated in the same manner as the above-mentioned compound (A) and compound (B).

Next, an example of a production example of a sugar ester compound will be given. Anhydrous acetic acid (200 ml) was added dropwise to a solution of pyridine (100 ml) added to glucose (29.8 g, 166 mmol), and the reaction was carried out for 24 hours. After that, the solution was concentrated with an evaporator and poured into ice water. After standing for 1 hour, it was filtered with a glass filter to separate the solid and water, and the solid on the glass filter was dissolved in chloroform, and the liquid was separated with cold water until it became neutral. After separating the organic layer, it was dried over anhydrous sodium sulfate. After removing anhydrous sodium sulfate by filtration, chloroform was removed by an evaporator, and dried under reduced pressure to obtain glucose pentaacetate (58.8 g, 150 mmol, 90.9%). Furthermore, instead of the above-mentioned anhydrous acetic acid, the above-mentioned monocarboxylic acid may also be used.

Specific examples of the sugar ester compound of the present embodiment are given below, but the present invention is not limited to this.

In order to suppress the deterioration of the polarizing function and stabilize the display quality, the second protective film of the polarizing plate is preferably 1 to 35% by mass, especially 5 to 30% by mass of the sugar ester compound contained in the film. If within this range, present Now, the excellent effect of the present invention is better, and at the same time, there is no overflow in storage of raw materials. In addition, a sugar ester compound in which all OH groups are esterified and one or more sugar ester compounds in which OH groups remain may be used together. For example, sucrose octaacetate, sucrose heptaacetate, a mixture of sucrose hexaacetate, etc. Although 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 combination. These can be controlled by adjusting the reaction time at the time of esterification of the sugar or the amount of monocarboxylic acid reacted with the sugar or can be mixed separately.

[Acrylic polymer]

The second protective film may contain an acrylic polymer having a weight average molecular weight of 500 or more and 30,000 or less as a retardation reducing agent. For such an acrylic polymer, those described in paragraphs 0059 to 0093 of International Publication No. WO08 / 044463 are preferably used.

[Polyester] (Polyester represented by general 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 obtained from G 2 to 12 dihydric alcohol G and C 2 to 12 dibasic acid, C 1 to 12 monocarboxylic acid B ₁ or C 1 to 12 mono alcohol B ₂ Of polyester.

General formula (B1) B _1- (GA-) _m GB ₁

(In the formula, B ₁ is a monocarboxylic acid having 1 to 12 carbon atoms, G is a dihydric alcohol having 2 to 12 carbon atoms, and A is a dibasic acid having 2 to 12 carbon atoms. B ₁ , G, and A do not contain Aromatic ring. M is the number of repetitions).

General formula (B2) B _2- (AG-) _n AB ₂

(In the formula, B ₂ is a monoalcohol with 1 to 12 carbons, G is a dibasic alcohol with 2 to 12 carbons, and A is a dibasic acid with 2 to 12 carbons. B ₂ , G, and A do not contain aromatics Ring. N is the number of repetitions).

The monocarboxylic acid represented by B ₁ is not particularly limited, and conventional aliphatic monocarboxylic acids, alicyclic monocarboxylic acids, etc. can be used.

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

For the aliphatic monocarboxylic acid, a fatty acid having a straight chain or a side chain having 1 to 32 carbon atoms may be preferably used. The carbon number 1-20 is the best, and the carbon number 1-12 is particularly good. If it contains acetic acid, the compatibility with cellulose ester is increased, which is better. It is also better to use acetic acid in combination with other monocarboxylic acids.

Preferred aliphatic monocarboxylic acids include, for example, formic acid, acetic acid, propionic acid, butyric acid, valeric acid, hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, capric acid, 2-ethyl-hexane carboxylic acid, eleven Acid, lauric acid, tridecyl acid, myristic acid, pentadecyl acid, palmitic acid, heptadecanoic acid, stearic acid, nonadecanoic acid, eicosanoic acid, behenic acid, twenty-four Saturated fatty acids such as acid, ascorbic acid, octacosanoic acid, octacosanoic acid, tricosanoic acid, and behenic acid, undecylenic acid, oleic acid, sorbic acid, linoleic acid, and sub-Asia sesame oil Unsaturated fatty acids such as acids and arachidonic acid.

The monoalcohol component represented by B ₂ is not particularly limited, and conventional alcohols can be used. For example, an aliphatic saturated alcohol or an aliphatic unsaturated alcohol having a linear or side chain having 1 to 32 carbon atoms can be preferably used. The carbon number 1-20 is the best, and the carbon number 1-12 is particularly good.

The dihydric alcohol component represented by G may be, for example, the following, but the present invention is not limited to these. For example ethylene glycol, diethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 1,5- Pentanediol, 1,6-hexanediol, 1,5-pentanediol, diethylene glycol, triethylene glycol, tetraethylene glycol, etc. Among these, ethylene glycol, 1, 2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 1,6-hexanediol, diethylene glycol, triethyl The diol is preferably, further preferably 1,3-propanediol, 1,4-butanediol 1,6-hexanediol, and diethylene glycol.

The component of dibasic acid (dicarboxylic acid) represented by A is preferably aliphatic dibasic acid or alicyclic dibasic acid. For example, for aliphatic dibasic acid, malonic acid, succinic acid, glutaric acid are used , Adipic acid, pimelic acid, suberic acid, azalea acid, sebacic acid, undecane dicarboxylic acid, dodecane dicarboxylic acid, etc., in particular, the number of carbon atoms used as aliphatic dicarboxylic acid is 4 ~ 12 people, at least one of them selected. That is, two or more kinds of dibasic acids can be used in combination.

m and n are repetition numbers, preferably 1 or more and 170 or less.

The weight average molecular weight of the polyester is preferably 20,000 or less, and more preferably 10,000 or less. In particular, polyesters with a weight average molecular weight of 500 to 10000 have good compatibility with cellulose esters, and during film production, evaporation and volatilization are also Not easy to produce and better.

Polycondensation of polyester is carried out in the usual way. For example, by the direct reaction of the above dibasic acid with diol, the above dibasic acid or these alkyl esters, such as the polyesterification reaction or transesterification of the methyl ester of dibasic acid with diol It can be easily synthesized by any method of the hot melt condensation method or the dehydrohalogenation reaction of acid chlorides of these acids and diols, but polyesters with a weight average molecular weight not so large are preferably reacted directly. The compatibility of polyester and cellulose ester with high distribution on the low molecular weight side is very good. After the film is formed, a polarizing plate protective film with low moisture permeability and excellent transparency can be obtained.

The method for adjusting the molecular weight is not particularly limited, and conventional methods can be used. For example, depending on the polymerization conditions, in the method of blocking the molecular ends with a monobasic acid (monocarboxylic acid) or a monohydric alcohol (monool), the molecular weight can be adjusted by controlling the amount of such monovalent compounds added. In this case, the monobasic acid is preferable from the viewpoint of the stability of the polymer.

For example, as the monobasic acid, for example, acetic acid, propionic acid, butyric acid, etc., it is selected that the polycondensation reaction does not distill out of the system, and after the stop, when the monobasic acid is removed outside the system, it is easy to distill, But these can also be mixed. Moreover, in the case of a direct reaction, the weight average molecular weight can also be adjusted by measuring the timing of stopping the reaction due to the amount of water distilled off in the reaction. Others can also be adjusted by changing the mole number of added diol or dibasic acid, or by controlling the reaction temperature.

The polyester of the present embodiment preferably contains 1 to 40% by mass relative to cellulose ester. Furthermore, it is more preferable to contain 2 to 30% by mass. It is particularly preferable to contain 3 to 15% by mass.

These compounds may contain 0.1 to 20% by mass in the second protective film of the polarizing plate.

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

[Cellulose ester]

The cellulose ester used for the second protective film of the polarizing plate is not particularly limited. In terms of cellulose ester, it is a carboxylic acid ester having a carbon number of about 2 to 22, or an aromatic carboxylic acid ester, especially cellulose. Lower fatty acid esters are preferred.

The lower fatty acid in cellulose lower fatty acid ester means a fatty acid having 6 or less carbon atoms. The acetyl group bonded to the hydroxyl group may be linear or branched, and may form a ring. Furthermore, other substituents may be substituted. In the case of the same degree of substitution, since the aforementioned carbon number is large, the birefringence decreases. Therefore, the carbon number is preferably selected from acetyl groups having a carbon number of 2 to 6. The carbon number of the cellulose ester is preferably 2 to 4, and the carbon number is more preferably 2 to 3.

The aforementioned cellulose ester may also use an acetyl group derived from a mixed acid, and it is particularly preferred to use an acetyl group having a carbon number of 2 and 3, or a carbon number of 2 and 4. For the cellulose ester used in the present embodiment, cellulose acetate propionate, cellulose acetate butyrate, or cellulose acetate propionate butyl ester can be used in addition to propylene or butyl ester groups. Mixed fatty acid ester of cellulose. In addition, the butyl acetyl group forming the butyl ester may be linear or branched. In this embodiment, the cellulose esters suitable for use are cellulose acetate and ethyl acetate. Cellulose acid butyrate, cellulose acetate propionate, cellulose acetate phthalate.

Moreover, the retardation value can be suitably controlled by the kind of the aforementioned acetyl group of the cellulose ester and the degree of substitution of the acetyl group with respect to the pyranose ring of the cellulose resin skeleton.

In terms of preferable cellulose esters of the present embodiment, those satisfying the following formulas (1) and (2) are preferred.

Formula (1): 2.0 ≦ X + Y ≦ 3.0

Formula (2): 0 ≦ Y ≦ 2.0

In the formula, X is the degree of substitution of acetyl group, and Y is the degree of substitution of propyl group or butyl group. Those who meet the above formula 2 are suitable for manufacturing polarizing plate protective films with excellent optical characteristics.

Among them, it is particularly preferable to use triacetyl cellulose and cellulose acetate propionate. In cellulose acetate propionate, preferably 1.0 ≦ X ≦ 2.5, 0.1 ≦ Y ≦ 1.5, 2.0 ≦ X + Y ≦ 3.0. The method for measuring the degree of substitution of acetyl group can be determined according to ASTM-D817-96.

If the degree of substitution of the aforementioned acetyl group is too low, the unreacted part of the pyranose ring constituting the skeleton of the cellulose resin to the hydroxyl group increases, and because the hydroxyl group remains too much, there is a delayed humidity change or a polarizing plate protective film to protect polarized The situation where the child's ability is reduced is not good.

The cellulose ester used in this embodiment has a number average molecular weight in the range of 60,000 to 300,000, and the film obtained has a strong and strong mechanical strength. It is better to use 70,000 ~ 200,000.

The number average molecular weight of cellulose ester can be measured by high-speed liquid chromatography under the following conditions.

Solvent: acetone

Column: MPW × 1 (Tosoh Corporation)

Sample concentration: 0.2 (mass / volume)%

Flow rate: 1.0ml / min

Sample injection volume: 300μl

Standard sample: Standard polystyrene

Temperature: 23 ℃

Although the cellulose of the raw material of cellulose ester is not particularly limited, for example, cotton linters, wood pulp, hemp hibiscus, etc. may be mentioned. Furthermore, the cellulose esters obtained from them can be mixed and used in any ratio.

For cellulose esters, when the acetylating agent of the cellulose raw material is an anhydride (anhydrous acetic acid, anhydrous propionic acid, anhydrous butyric acid), use an organic solvent such as acetic acid-like organic acid or methane chloride and use a sulfuric acid-like protonic catalyst React. When the acetylating agent is an acid chloride (CH ₃ COCl, C ₂ H ₅ COCl, C ₃ H ₇ COCl), an amine-like basic compound is used as a catalyst for the reaction. Specifically, it can be synthesized by referring to the method described in Japanese Patent Laid-Open No. 10-45804.

In cellulose esters, the average substitution degree of the acetyl group at the 6th position of the glucose unit is preferably 0.5 to 0.9.

The 6th position of the glucose unit constituting the cellulose ester is different from the 2nd and 3rd positions and has a highly reactive primary hydroxyl group. This primary hydroxyl group preferentially forms sulfate esters in the production process of cellulose esters using sulfuric acid as a catalyst. because Therefore, in the esterification reaction of cellulose, by increasing the amount of catalyst sulfuric acid, the average substitution degree of the 2nd and 3rd positions of the glucose unit can be made higher than that of the 6th position compared to the general cellulose ester. Furthermore, if necessary, trimethylation of cellulose can selectively protect the hydroxyl group at the 6-position of the glucose unit. Therefore, after triphenylmethylation to protect the hydroxyl group at the 6-position and perform esterification, the When the group (protecting group) is detached, the average substitution degree of the 2 and 3 positions of the glucose unit is higher than that of the 6 position. Specifically, the cellulose ester produced by the method described in Japanese Patent Application Laid-Open No. 2005-281645 can also be suitably used.

In the case of acetyl cellulose, if the acetification rate is to be increased, it is necessary to extend the acetification reaction time. However, if the reaction time is too long, the decomposition proceeds at the same time, causing the polymer chain to be cut or the decomposition of acetylene, etc., which produces undesirable results. Therefore, in order to improve the degree of vinegarification and suppress decomposition to a certain extent, the reaction time needs to be set within a certain range. Due to various reaction conditions and large changes due to other conditions of the reaction device or equipment, it is not appropriate to limit the reaction time. As the decomposition of the polymer progresses, the molecular weight distribution gradually widens, so even in the case of cellulose ester, the degree of decomposition can be specified by the value of weight average molecular weight (Mw) / number average molecular weight (Mn) that is generally used. That is, the weight average molecular weight (Mw) / number, which is an indicator of the degree of reaction in which cellulose triacetate is esterified, but is not too long and decomposition is excessively progressed, and the esterification reaction is carried out for a sufficient period of time, can be used. The value of the average molecular weight (Mn).

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

In addition, the synthesized cellulose ester is preferably purified to remove low-molecular-weight components, and components that have not been vinegarized or have a low vinegarization degree are filtered and removed.

In addition, in the case of mixed acid cellulose ester, it can be obtained by the method described in Japanese Patent Laid-Open No. 10-45804.

In addition, cellulose esters are also affected by trace metal components in cellulose esters. These are considered to be related to the water used in the manufacturing process, but it is better to have fewer components that can be used as insoluble cores. Metal ions such as iron, calcium, and magnesium may form with polymer decomposed products that may contain organic acid groups. It is better to use less salt to form insolubles. The iron (Fe) component is preferably 1 ppm or less. Regarding calcium (Ca) components, it is easy to form coordination compounds, that is, complex compounds, with acidic components such as carboxylic acid or sulfonic acid, and many ligands, and a large amount of scum (insoluble precipitation, turbidity) derived from insoluble calcium is formed.

The calcium (Ca) component is 60 ppm or less, preferably 0 to 30 ppm. Regarding the magnesium (Mg) component, after all, too much will produce insoluble content, so It is preferably 0 ~ 70ppm, especially 0 ~ 20ppm. Metal components such as iron (Fe) content, calcium (Ca) content, magnesium (Mg) content, etc., make the completely dried cellulose ester pre-treated with MicRodigest wet decomposition device (sulfuric acid decomposition), alkali fusion After that, analysis was performed using ICP-AES (Inductively Coupled Plasma Luminescence Spectrometer).

[1st protective film]

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

[polyester resin]

For the first protective film of the polarizing plate, a film made of polyester resin (polyester film) can be used. For polyester, polyethylene terephthalate (PET) or polyethylene naphthalate (PEN) can be used, but it can also contain other copolymerized components. These resins have excellent transparency, as well as excellent thermal and mechanical properties, and can easily control the delay by extension processing. In particular, PET has a large inherent birefringence, and even if the thickness of the film is thin, it can easily obtain a large retardation, so it is the best material.

The polyester film preferably has a retardation (in-plane direction) of 3000 to 30000 nm. When the retardation is less than 3000 nm, the polyester film is used as a polarizing plate protective film for liquid crystal display devices. When viewed from an oblique direction, it exhibits a strong dry color (color unevenness), which cannot ensure good visibility. The preferred lower limit value of retardation is 4500 nm, the more preferred value is 5000 nm, the more preferred value is 6000 nm, the further preferred value is 8000 nm, and the more preferred lower limit value is 10000 nm.

On the other hand, the upper limit of retardation is 30000 nm. Even if a polyester film having a retardation of more than this is used, not only can no substantial improvement effect of visibility be obtained, but also the thickness of the film becomes quite thick, reducing the operability as an industrial material, which is not good.

In addition, the above-mentioned retardation can be obtained by measuring the refractive index and thickness in the two-axis direction, or using a commercially available automatic birefringence measuring device of KOBRA-21ADH (Oji Measuring Instruments Co., Ltd.).

The ratio of the in-plane retardation Ro of the polyester film to the thickness direction retardation Rt (Ro / Rt) is preferably 0.200 or more, more preferably 0.500 or more, and still more preferably 0.600 or more. The larger the above ratio (Ro / Rt), the more isotropic the birefringence effect becomes, and it becomes difficult to cause color unevenness depending on the viewing angle. On the other hand, in a completely uniaxial (1-axis symmetric) film, the above ratio (Ro / Rt) becomes 2.0. However, with the nearly complete uniaxial (1-axis symmetrical) film, the mechanical strength in the direction perpendicular to the alignment direction is significantly reduced.

On the other hand, the above ratio (Ro / Rt) of the polyester film is preferably 1.2 or less, and more preferably 1.0 or less. In order to completely suppress the occurrence of color unevenness due to the viewing angle, the above ratio (Ro / Rt) need not be 2.0, and it is sufficient to be 1.2 or less. In addition, even if the above ratio (Ro / Rt) is 1.0 or less, the viewing angle characteristics (180 degrees left and right and 120 degrees up and down) required by the liquid crystal display device can be sufficiently satisfied.

In order to control the retardation of the film within the above-mentioned specific range, it is sufficient to appropriately set the stretching magnification or stretching temperature during film formation, and the thickness of the film. For example, the higher the stretching ratio, the lower the stretching temperature, and the thicker the film thickness, the easier it is to obtain high retardation. Conversely, the lower the stretching magnification, the stretching temperature The higher the degree, the thinner the thickness of the film, and it becomes easier to obtain low delay.

[Acrylic]

For the resin constituting the first protective film of the polarizing plate, acrylic resin can also be used.

The acrylic resin may be a polymer mainly composed of alkyl methacrylate or a single polymer of alkyl methacrylate, or it may be other than 50% by weight of alkyl methacrylate and other than alkyl methacrylate Copolymers with monomers below 50% by weight. For polymers based on alkyl methacrylate, based on 100% by weight of all monomers, the alkyl methacrylate is preferably 70% by weight or more, more preferably 80% by weight or more, and more It is preferably 90% by weight or more, and the alkyl methacrylate is 99% by weight or less. As for the alkyl methacrylate, those whose alkyl group has 1 to 4 carbon atoms are generally used, and methyl methacrylate is preferably used.

In addition, the monomer other than the alkyl methacrylate may be a monofunctional monomer having one polymerizable carbon-carbon double bond in the molecule or a polyfunctional monomer having two or more polymerizable carbon-carbon double bonds in the molecule. It is suitable for monofunctional monomers. Examples thereof include methyl acrylate or ethyl acrylate alkyl acrylate, styrene or alkyl styrene styrene monomer, acrylonitrile or methacrylonitrile unsaturated nitrile. When an alkyl acrylate is used as a copolymerization component, the carbon number is usually 1 to 8.

[Alicyclic olefin polymer resin]

For the resin constituting the first protective film of the polarizing plate, grease can also be used Cyclic olefin polymer resin (COP).

Examples of alicyclic olefin polymer resins include cyclic olefin random multi-component copolymers described in Japanese Patent Laid-Open No. 05-310845, hydrogenated polymers described in Japanese Patent Laid-Open No. 05-97978, and Japanese Patent Laid-Open No. 11 -124429 Thermoplastic dicyclopentadiene ring-opening polymer and its hydride, etc.

The alicyclic olefin polymer-based resin will be described more specifically. The alicyclic olefin polymer resin is a polymer having an alicyclic structure like a saturated alicyclic hydrocarbon (cycloalkane) structure or an unsaturated alicyclic hydrocarbon (cycloolefin type) structure. The number of carbon atoms constituting the alicyclic structure, although not particularly limited, is generally in the range of 4 to 30, preferably 5 to 20, more preferably 5 to 15, mechanical strength, heat resistance, and film forming Sexual characteristics are highly balanced and good.

The ratio of the repeating unit composed of an alicyclic structure in the alicyclic olefin polymer-based resin may be appropriately selected, but is preferably 55 wt% or more, more preferably 70 wt% or more, and particularly preferably 90 wt% %the above. If the ratio of the above repeating units is within this range, the transparency and heat resistance of the film are improved, which is preferable.

Examples of alicyclic olefin polymer resins include norbornene resins, monocyclic cyclic olefin resins, cyclic conjugated diene resins, vinyl alicyclic hydrocarbon resins, and the like. Hydride and so on. Among these, norbornene-based resins have good transparency and moldability and are suitable for use.

As for the norbornene-based resin, for example, a ring-opening polymer having a monomer having a norbornene structure, or a ring-opening copolymer of a monomer having a norbornene structure and other monomers or their hydrides, having a Norbornene Addition polymers of structured monomers, addition copolymers of monomers with a norbornene structure and other monomers, or their hydrides, etc. Among these, the hydrogenated ring-opening (co) polymer of a monomer having a norbornene structure, from the viewpoints of transparency, moldability, heat resistance, low moisture absorption, dimensional stability, and lightness, etc. In view, it is particularly suitable for use.

Examples of monomers having a norbornene structure include bicyclo [2.2.1] hept-2-ene (common name: norbornene) and tricyclo [4.3.0.12,5] dec-3,7-diene (Common name: dicyclopentadiene), 7,8-benzotricyclo [4.3.0.12,5] dec-3-ene (common name: tetramethylenetetramine), tetracyclo [4.4.0.12,5.17 , 10] Dodec-3-ene (common name: tetracyclododecene), and derivatives of these compounds (for example, those having a substituent in the ring), etc. Here, as the substituent, for example, an alkyl group, an alkylene group, and a polar group are mentioned. In addition, these substituents may be the same or different and a plurality of bonds to the ring. The monomer having a norbornene structure may be used alone or in combination of two or more.

As for the kind of polar group, for example, a hetero atom or an atomic group having a hetero atom can be mentioned. Examples of heteroatoms include oxygen atoms, nitrogen atoms, sulfur atoms, silicon atoms, halogen atoms, and the like. Specific examples of the polar group include a carboxyl group, a carbonyloxycarbonyl group, an epoxy group, a hydroxyl group, an oxy group, an ester group, a silanol group, a silane group, an amine group, a nitrile group, and a sulfonyl group.

Other monomers that can be ring-opened and copolymerized with monomers having a norbornene structure include monocyclic olefins such as cyclohexene, cycloheptene, and cyclooctene, or derivatives thereof; and cyclohexane Cyclic conjugated dienes such as diene and cycloheptadiene or their derivatives; etc.

Ring-opening polymer with norbornene structure monomer and Ring-opening copolymers of other monomers copolymerizable with monomers having a norbornene structure can be obtained by subjecting the monomers to (co) polymerization in the presence of a conventional ring-opening polymerization catalyst.

Other monomers that can be copolymerized with monomers having a norbornene structure include, for example, ethylene, propylene, 1-butene, etc., C 2-20 α-olefins or derivatives thereof; Cycloolefins such as cyclobutene, cyclopentene, and cyclohexene or derivatives thereof; and 1,4-hexadiene, 4-methyl-1,4-hexadiene, and 5-methyl -1,4-Hexadiene and other non-conjugated dienes. These monomers can be used alone or in combination of two or more. Among these, α-olefin is preferable, and ethylene is more preferable.

The addition polymer of a monomer having a norbornene structure and the addition copolymer of other monomers copolymerizable with the monomer having a norbornene structure can be added by conventional addition polymerization It is obtained by polymerization in the presence of a medium.

Hydride of a ring-opening polymer of a monomer having a norbornene structure, a hydride of a ring-opening copolymer of a monomer having a norbornene structure and other monomers copolymerizable with the ring-opening copolymer thereof, having a norbornene structure The hydride of the addition polymer of the monomer and the addition copolymer of the monomer with the norbornene structure and other monomers copolymerizable with it can be obtained by the solution of these polymers, A conventional hydrogenation catalyst containing transition metals containing nickel, palladium, etc. is added, and the carbon-carbon unsaturated bond is preferably hydrogenated by 90% or more.

The norbornene-based resin has X: bicyclo [3.3.0] octane-2,4-diyl-ethylene structure and Y: tricyclo [4.3.0.12,5] decane-7,9-diyl- The ethylene structure is used as a repeating unit. The content of these repeating units is more than 90% by weight relative to the total repeating unit of the norbornene-based resin. 100: 0 ~ 40: 60 is better. By using such a resin, it is possible to obtain a film with no long-term dimensional change and excellent stability of optical characteristics.

(Plasticizer)

The protective film of the polarizing plate may contain a plasticizer as necessary. The plasticizer is not particularly limited, but it is preferably composed of polycarboxylic acid ester plasticizer, glycolate plasticizer, phthalate ester plasticizer, fatty acid ester plasticizer and polyol ester plasticizer, Ester plasticizer, acrylic plasticizer, etc. are selected. Among them, when two or more plasticizers are used, it is preferred that at least one of them is a polyol ester plasticizer. In addition, these plasticizers may also function as the retardation reducing agent.

The polyol ester plasticizer is a compound represented by the general formula (3).

Although the glycolate plasticizer is not particularly limited, alkyl phthalimide alkyl glycolates can be suitably used. For alkyl phthalimide alkyl glycolates, for example, methyl phthaloyl methyl glycolate, ethyl phthaloyl ethyl glycolate, propyl phthalate Methyl propyl glycolate, butyl phthaloyl butyl glycolate, octyl phthaloyl octyl glycolate, methyl phthalate ethyl glycolate , Ethyl phthalate methyl glycolate, ethyl phthalate propyl glycolate, methyl phthalate butyl glycolate, ethyl o Phthaloyl butyl glycolate, butyl phthaloyl methyl glycolate, butyl phthaloyl ethyl glycolate, propyl phthaloyl butyl ethanol Ester, butyl phthaloyl propyl glycolate, methyl phthaloyl octyl glycolate, ethyl phthaloyl octyl glycolate, octyl phthalate Formyl methyl glycolate, octyl phthalate ethyl glycolate, etc.

For phthalate plasticizers, such as diethyl phthalate, dimethoxyethyl phthalate, dimethyl phthalate, dioctyl phthalate, Dibutyl phthalate, di-2-ethylhexyl phthalate, dioctyl phthalate, dicyclohexyl phthalate, dicyclohexyl terephthalate, etc. .

For citrate-based plasticizers, for example, acetyl trimethyl citrate, acetyl triethyl citrate, acetyl tributyl citrate, and the like.

Examples of the fatty acid ester-based plasticizer include butyl oleate, glycol methyl oleate, and dibutyl sebacate.

Examples of phosphate ester plasticizers include triphenyl phosphate, tricresyl phosphate, cresyl diphenyl phosphate, octyl diphenyl phosphate, diphenyl biphenyl phosphate, and trioctyl. Phosphate, tributyl phosphate, etc.

The polycarboxylic acid ester compound is composed of an ester of a polyvalent carboxylic acid and an alcohol having a divalent or higher value, preferably a divalent to 20-valent value. The aliphatic polycarboxylic acid is preferably 2 to 20 valence, and the aromatic polycarboxylic acid or alicyclic polycarboxylic acid is preferably 3 to 20 valence.

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

General formula (21) R ₂ (COOH) _m (OH) _n

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

Examples of preferred polycarboxylic acids include the following, but the present invention is not limited to these. Trimellitic acid, trimesic acid, pyromellitic acid, trivalent or more aromatic polycarboxylic acids or derivatives thereof, succinic acid, adipic acid, azalea acid, sebacic acid, oxalic acid, rich Maleic acid, maleic acid, tetrahydrophthalic acid-like aliphatic polycarboxylic acid, tartaric acid, malonic acid, malic acid, citric acid-like oxidized polycarboxylic acid, etc. In particular, the use of oxidized polycarboxylic acids is preferable in terms of improvement in retention and the like.

The alcohol used for the polycarboxylic acid ester compound is not particularly limited, and conventional alcohols and phenols can be used. For example, an aliphatic saturated alcohol or an aliphatic unsaturated alcohol having a linear or side chain having 1 to 32 carbon atoms can be preferably used. The carbon number 1-20 is the best, and the carbon number 1-10 is particularly good. In addition, alicyclic alcohols such as cyclopentanol and cyclohexanol or derivatives thereof, aromatic alcohols such as benzyl alcohol and cinnamyl alcohol or derivatives thereof, etc. may also be suitably used.

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

As the aliphatic monocarboxylic acid, it is preferable to use a carbon number of 1 ~ 32 There are straight chain or side chain fatty acids. The carbon number 1-20 is the best, and the carbon number 1-10 is particularly good.

Preferred aliphatic monocarboxylic acids include, for example, acetic acid, propionic acid, butyric acid, valeric acid, hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, capric acid, 2-ethyl-hexanecarboxylic acid, undecylic acid , Lauric acid, tridecyl acid, myristic acid, pentadecyl acid, palmitic acid, heptadecanoic acid, stearic acid, nonadecanoic acid, eicosanoic acid, behenic acid, tetracosanoic acid, Saturated fatty acids such as ascorbic acid, hexacosanoic acid, octacosanoic acid, tricosanoic acid, and behenic acid, undecylenic acid, oleic acid, sorbic acid, linolenic acid, linolenic acid , Unsaturated fatty acids such as arachidonic acid, etc.

Examples of preferred alicyclic monocarboxylic acids include cyclopentanecarboxylic acid, cyclohexanecarboxylic acid, cyclooctanecarboxylic acid, or derivatives thereof.

Examples of preferred aromatic monocarboxylic acids include those in which the benzene ring of benzoic acid such as benzoic acid and toluic acid is introduced into an alkyl group, biphenylcarboxylic acid, naphthalenecarboxylic acid, tetrahydronaphthalenecarboxylic acid, etc. Aromatic monocarboxylic acids with more than one benzene ring, or their derivatives. Especially acetic acid, propionic acid and benzoic acid are preferred.

Although the molecular weight of the polycarboxylic acid ester compound is not particularly limited, the range of the molecular weight of 300 to 1000 is preferable, and the range of 350 to 750 is even more preferable. The greater the retention, the better, and the smaller the moisture permeability and the compatibility with cellulose esters.

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

The acid value of polycarboxylic acid ester compound is 1mgKOH / g or less Preferably, 0.2mgKOH / g is even better. Since the acid value is in the above range, the delayed environmental change is also suppressed, which is preferable.

(Acid value)

The acid value refers to the number of milligrams of potassium hydroxide necessary to neutralize 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 preferable polycarboxylic 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, Acetyltriphenyl citrate, acetotribenzyl citrate, dibutyl tartrate, dibutyl tartrate, tributyl trimellitate, tetrabutyl pyromellitic acid Wait.

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. As the polyester-based plasticizer, although not particularly limited, for example, an aromatic terminal ester-based plasticizer represented by the following general formula (22) can be used.

General formula (22) B- (GA) _n -GB

(In the formula, B is a benzene monocarboxylic acid residue, G is an alkylene glycol residue having 2 to 12 carbon atoms, or an aryl diol residue having 6 to 12 carbon atoms, or an alkylene oxide having 4 to 12 carbon atoms. Alcohol residue, A is a C4-12 alkylene dicarboxylic acid residue or carbon number 6 to 12 aryl dicarboxylic acid residues, n is an integer of 1 or more).

The compound represented by general formula (22) is composed of a benzene monocarboxylic acid residue represented by B and an alkylene glycol residue represented by G or an alkylene oxide residue or an aryldiol residue represented by A, The alkylene dicarboxylic acid residue or the aryl dicarboxylic acid residue can be obtained by reacting with a general polyester plasticizer.

The benzene monocarboxylic acid component of polyester plasticizers, such as benzoic acid, p-tert-butyl benzoic acid, o-toluic acid, m-toluic acid, p-toluic acid, dimethyl benzoic acid, ethyl benzoic acid, n Propyl benzoic acid, amino benzoic acid, acetoxybenzoic acid, etc., can be used as a mixture of one or two or more of them.

The polyester plasticizers have 2 to 12 carbon diol components, including ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, and 1,3-butane. Glycol, 1,2-propanediol, 2-methyl 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 2,2-dimethyl-1 , 3-propanediol (neopentyldiol), 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 1,3-hexanediol, 2-methyl 1,8-octanediol, 1,9-nonanediol, 1 , 10-decanediol, 1,12-octadecanediol, etc. These diols can be used in a mixture of one or more. In particular, C2-C12 alkanediols have excellent compatibility with cellulose esters, so they are particularly good.

In addition, the above-mentioned aromatic terminal ester has an alkylene oxide glycol component having 4 to 12 carbon atoms, for example, diethylene glycol, triethylene glycol, tetraethylene glycol, Dipropylene glycol, tripropylene glycol, etc. These diols can be used alone or in combination of two or more.

The alkyl terminal dicarboxylic acid components of the aromatic terminal esters having 4 to 12 carbon atoms include, for example, succinic acid, maleic acid, fumaric acid, glutaric acid, adipic acid, azalea acid, sebacic acid, and deca Dioxane dicarboxylic acids and the like are used as a mixture of one kind or two or more kinds. The aryl dicarboxylic acid components having 6 to 12 carbon atoms include phthalic acid, terephthalic acid, isophthalic acid, 1,5 naphthalene dicarboxylic acid, and 1,4 naphthalene dicarboxylic acid.

Polyester plasticizer. The number average molecular weight is preferably in the range of 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.

The following is a synthesis example of an aromatic terminal ester plasticizer that can be used in this embodiment.

<Sample No. 1 (Aromatic terminal ester sample)>

In the reaction vessel, add 410 parts of phthalic acid, 610 parts of benzoic acid, 737 parts of dipropylene glycol, and 0.40 parts of tetraisopropyl titanate as a catalyst at a time, and install a reflux condenser in a nitrogen stream under stirring. While refluxing the excess monohydric alcohol, continue heating at 130 to 250 ° C until the acid value is below 2, and the produced water is continuously removed. Next, the distillate was removed under reduced pressure of 200 to 230 ° C. and 1.33 × 10 ⁴ Pa to the final 4 × 10 ² Pa or less, and then filtered to obtain an aromatic terminal ester-based plasticizer having the following properties.

Viscosity (25 ℃, mPa · s); 43400

Acid value; 0.2

<Sample No. 2 (Aromatic terminal ester sample)>

In the reaction vessel, except that 410 parts of phthalic acid, 610 parts of benzoic acid, 341 parts of ethylene glycol, and 0.35 parts of tetraisopropyl titanate as a catalyst were used, it was completely the same as Sample No. 1. Aromatic terminal esters of the following properties.

Viscosity (25 ℃, mPa · s); 31000

Acid value; 0.1

<Sample No. 3 (Aromatic terminal ester sample)>

In the reaction vessel, except that 410 parts of phthalic acid, 610 parts of benzoic acid, 418 parts of 1,2-propanediol, and 0.35 parts of tetraisopropyl titanate as a catalyst were used, it was exactly the same as Sample No. 1. Groundly, an aromatic terminal ester having the following properties is obtained.

Viscosity (25 ℃, mPa · s); 38000

Acid value; 0.05

<Sample No. 4 (Aromatic terminal ester sample)>

In the reaction vessel, except for using 410 parts of phthalic acid, 610 parts of benzoic acid, 418 parts of 1,3-propanediol, and 0.35 parts of tetraisopropyl titanate as a catalyst, it is exactly the same as Sample No. Groundly, an aromatic terminal ester having the following properties is obtained.

Viscosity (25 ℃, mPa · s); 37000

Acid value; 0.05

The following are specific compounds of the aromatic terminal ester-based plasticizer that can be used in this embodiment, but the present invention is not limited thereto.

(UV absorber)

The protective film of the polarizing plate may also contain an ultraviolet absorber. UV absorption The purpose of the collector is to absorb ultraviolet rays below 400 nm to improve the durability. Especially, the transmittance at a wavelength of 370 nm is preferably 10% or less, more preferably 5% or less, and even more preferably 2% or less.

The ultraviolet absorber used is not particularly limited, and examples thereof include benzophenone-based compounds, benzotriazole-based compounds, salicylate-based compounds, benzophenone-based compounds, cyanoacrylate-based compounds, and triazine-based compounds. Compounds, nickel complex compounds, inorganic powders, etc.

For example, 5-chloro-2- (3,5-di-sec-butyl-2-hydroxyphenyl) -2H-benzotriazole, (2-2H-benzotriazol-2-yl) -6 -(Straight chain and side chain dodecyl) -4-methylphenol, 2-hydroxy-4-benzyloxybenzophenone, 2,4-benzyloxybenzophenone, etc. Tinuvin 109, Tinuvin 171, Tinuvin 234, Tinuvin 326, Tinuvin 327, Tinuvin 328 and other Tinuvin, all of which are commercially available from Ciba Specialty Chemicals Inc., are suitable for use.

The more suitable ultraviolet absorbers are benzotriazole-based ultraviolet absorbers, benzophenone-based ultraviolet absorbers, triazine-based ultraviolet absorbers, particularly preferably benzotriazole-based ultraviolet absorbers, benzophenone-based UV absorber.

For example, for the benzotriazole ultraviolet absorber, the 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 represent hydrogen atom, halogen atom, nitro group, hydroxyl group, alkyl group, alkenyl group, aryl group, alkoxy group, ethyl Acyloxy, aryloxy, alkylthio, arylthio, mono- or dialkylamino, acetylamino or 5-6 membered heterocyclic groups, R ₄ and R ₅ may be ring-closed Form a carbon ring of 5-6 members. In addition, the above-mentioned groups may have any substituents.

The following are specific examples of benzotriazole-based ultraviolet absorbers, but the present invention is not limited thereto.

UV-1: 2- (2 ' - hydroxy-5' - methylphenyl) benzotriazole

UV-2: 2- (2 ' - hydroxy-3', 5 '- bis -tert- butylphenyl) benzotriazole

UV-3: 2- (2 ' - hydroxy -3' -tert- butyl-5 '- methylphenyl) benzotriazole

UV-4: 2- (2 ' - hydroxy-3', 5 '- bis -tert- butylphenyl) -5-chlorobenzotriazole

UV-5: 2- (2 ' -Hydroxy-3 ' -(3 " , 4 " , 5 " , 6 " -Tetrahydroxylylenediimidylmethyl) -5 ' -methylphenyl) benzo Triazole

UV-6: 2,2-methylenebis (4- (1,1,3,3-tetramethylbutyl) -6- (2H-benzotriazol-2-yl) phenol)

UV-7: 2- (2 ' - hydroxy -3' -tert- butyl-5 '- methylphenyl) -5-chlorobenzotriazole

UV-8: 2- (2H-benzotriazol-2-yl) -6- (linear and side chain dodecyl) -4-methylphenol (TINUVIN171)

UV-9: octyl-3- [3-tert-butyl-4-hydroxy-5- (chloro-2H-benzotriazol-2-yl) phenyl] propionate and 2-ethylhexyl- 3- [3-tert-butyl-4-hydroxy-5- (5-chloro-2H-benzotriazol-2-yl) phenyl] propionate mixture (TINUVIN109)

Furthermore, for the benzophenone-based ultraviolet absorber, the compound represented by the following general formula (c) can be suitably used.

In the formula, Y is a hydrogen atom, a halogen atom, an alkyl group, an alkenyl group, an alkoxy group, or a phenyl group, and these alkyl groups, alkenyl groups, and phenyl groups may have a substituent. A It is 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 is an alkyl group, an alkenyl group or may have a substitution Phenyl. m and n are 1 or 2.

In the above, the alkyl group is, for example, a straight-chain or branched aliphatic group up to carbon number 24, the alkoxy group is, for example, an alkoxy group up to carbon number 18, and the alkenyl group is, for example, an alkenyl group up to carbon number 16. , Allyl, 2-butenyl and so on. Examples of the substituents of the alkyl group, alkenyl group, and phenyl group include a halogen atom such as a chlorine atom, a bromine atom, a fluorine atom, etc., a hydroxyl group, and a phenyl group (in this phenyl group, an alkyl group or a halogen atom may be substituted) )Wait.

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

UV-10: 2,4-dihydroxybenzophenone

UV-11: 2,2 '- dihydroxy-4-methoxy-benzophenone

UV-12: 2-hydroxy-4-methoxy-5-sulfobenzophenone

UV-13: bis (2-methoxy-4-hydroxy-5-benzylphenylmethane)

In addition, disc-shaped compounds such as compounds having 1,3,5 triazine rings are also suitable as ultraviolet absorbers.

The polarizing plate protective film of this embodiment preferably contains two or more kinds of ultraviolet absorbers.

In addition, as the ultraviolet absorber, a polymer ultraviolet absorber may also be suitably used, and in particular, a polymer type ultraviolet absorber described in Japanese Patent Laid-Open No. 6-148430 is preferably used.

The method of adding ultraviolet absorber can be used in alcohols such as methanol, ethanol, butanol or methane chloride, methyl acetate, acetone, dioxolane An organic solvent such as these or a mixed solvent thereof is dissolved in the ultraviolet absorber and then added to the dopant or directly added to the dopant composition. If the inorganic powder is insoluble in organic solvent, use a crusher or sand mixer in the organic solvent and cellulose ester, and add it to the dopant after dispersion.

The amount of UV absorber used varies depending on the type of UV absorber, use conditions, etc. However, when the dry film thickness of the polarizer protective film is 10 to 200 μm, it is better to be 0.5 to 10% by mass relative to the polarizer protective film, 0.6 ~ 4% by mass is even better.

(Fine particles)

The protective film of the polarizing plate preferably contains fine particles. In terms of fine particles, examples of inorganic compounds include silica, titania, alumina, zirconia, calcium carbonate, talc, clay, calcined kaolin, calcined calcium silicate, hydrated calcium silicate, aluminum silicate, Magnesium silicate and calcium phosphate. The fine particles are those containing silicon, and the turbidity becomes lower, especially silicon dioxide.

The average particle diameter of the primary particles of the microparticles is preferably 5 to 400 nm, and more preferably 10 to 300 nm. These may mainly contain secondary agglomerates with a particle size of 0.05 to 0.3 μm. If the particles have an average particle size of 100 to 400 nm, they may also be included as primary particles without aggregation. 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 multi-layer polarizing plate protective film produced by a co-casting method, the surface preferably contains fine particles in the added amount.

The fine particles of silicon dioxide, such as AeRosilR972, R972V, R974, R812, 200, 200V, 300, R202, OX50, The trade name of TT600 (above, manufactured by AeRosil Co., Ltd. in Japan) is commercially available for use.

The fine particles of zirconia are commercially available under the trade names of AeRosil R976 and R811 (above, manufactured by Japan AeRosil Co., Ltd.), for example.

Examples of the polymer include silicone resin, fluorine resin and acrylic resin. Silicone resin is preferred, especially those with a three-dimensional network structure, such as Tospearl 103, Tong 105, Tong 108, Tong 120, Tong 145, Tong 3120 and Tong 240 (above, Toshiba Silicone Co., Ltd.) The trade name is commercially available and can be used.

Among them, AeRosil200V and AeRosilR972V can maintain the low turbidity of the polarizer protective film and have a large effect of reducing the friction coefficient, so it is particularly suitable for use. In the polarizing plate protective film of this embodiment, the dynamic friction coefficient of at least one side is preferably 0.2 to 1.0.

Various additives can be added in batches in the dopant of the cellulose ester-containing solution before film formation, or another additive solution is prepared for continuous addition. Especially in order to reduce the load of particulates on the filter material, it is better to add a part or the whole amount continuously.

When the additive dissolving solution is continuously added, it is preferable to dissolve a small amount of cellulose ester in order to improve the miscibility with the dopant. The preferred amount of cellulose ester is 1 to 10 parts by mass relative to 100 parts by mass of the solvent, and more preferably 3 to 5 parts by mass.

In this embodiment, for continuous addition and mixing, for example, a static mixing tube (Toray Engineering Co., Co., Ltd.), SWJ (Toray static in-line mixer Hi-Mixer) and other pipeline mixers.

(Method of manufacturing protective film)

Next, the manufacturing method of the protective film of a polarizing plate is demonstrated.

The protective film may be a film manufactured by a solution casting method or a film manufactured by a melt casting method, and both may be suitably used.

The production of protective film, through the steps of preparing dopants after dissolving cellulose esters and additives in the solvent, the step of casting the dopants on the continuously moving metal support, making the cast dopants as The step of drying the mesh, the step of peeling from the metal support, the step of extending or maintaining the width, the step of drying, and the step of winding the completed film are carried out.

The steps for modulating the dopant are explained. The concentration of the cellulose ester in the dopant is preferably the one that can reduce the drying load after casting the metal support. However, if the concentration of the cellulose ester is too concentrated, the load during filtration is increased, which causes the filtration accuracy to change. difference. In terms of both these concentrations, it is preferably 10 to 35% by mass, and even more preferably 15 to 25% by mass.

Although the solvent used for the dopant can be used alone or in combination of two or more, a good solvent and a poor solvent in which cellulose ester is mixed are preferable in terms of production efficiency, and many of them are in the solubility of cellulose ester On the best. The preferred range of the mixing ratio of the good solvent and the poor solvent is that the good solvent is 70 to 98% by mass, and the poor solvent is 2 to 30% by mass. Good solvent and poor solvent mean that the cellulose ester used alone is defined as a good solvent, alone as Swelling or insoluble is defined as a poor solvent. Therefore, due to the average degree of cellulose esterification (degree of substitution of acetyl acetate), good solvents and poor solvents change. Acid cellulose becomes a good solvent, and cellulose acetate (acetyl substitution degree 2.8) becomes a poor solvent.

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

In addition, the poor solvent used is not particularly limited, and for example, methanol, ethanol, n-butanol, cyclohexane, cyclohexanone, etc. are preferably used. Moreover, it is preferable that the dopant contains 0.01 to 2% by mass of water. In addition, the solvent used for dissolving the cellulose ester is recovered by drying the solvent removed from the film in the film forming step, and it can be reused. The recovered solvent may also contain traces of additives added to the cellulose ester, such as plasticizers, ultraviolet absorbers, polymers, monomer components, etc., but containing them may also be suitable for reuse, and if necessary Reuse after refining.

For the method of dissolving the cellulose ester when preparing the dopant described above, a general method can be used. Combined heating and pressurization, it can be heated to above the boiling point of normal pressure. It is preferable to stir and dissolve while heating at a temperature above the boiling point of the solvent under normal pressure and the solvent does not boil under pressure to prevent the generation of colloids or massive undissolved substances called lumps. In addition, a method of mixing cellulose ester with a poor solvent to wet or swell it, and then adding a good solvent to dissolve it is also suitable.

The pressurization can be performed by a method of pressurizing an inert gas such as nitrogen gas or a method of heating to increase the vapor pressure of the solvent. The heating is preferably performed from the outside, for example, the sheath type is preferable because the temperature control is easy.

If the heating temperature of the added solvent is high, the solubility of cellulose ester is preferable. However, if the heating temperature is too high, the required pressure becomes high and the productivity becomes poor. The preferred heating temperature is 45 ~ 120 ° C, 60 ~ 110 ° C is better, 70 ° C ~ 105 ° C is even better. Also, the pressure is adjusted so that the solvent does not boil at the set temperature.

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

Next, the cellulose ester solution is filtered using an appropriate filter material such as filter paper. In terms of filter materials, in order to remove insolubles, the absolute filtration accuracy is preferably smaller, but if the absolute filtration accuracy is too small, there is a problem that the filter materials may become clogged. Therefore, a filter material with an absolute filtration accuracy of 0.008 mm or less is preferable, a filter material of 0.001 to 0.008 mm is better, and a filter material of 0.003 to 0.006 mm is even better.

The material of the filter material is not particularly limited, and general filter materials can be used, but a plastic filter material such as polypropylene or Teflon (registered trademark) or a metal filter material such as stainless steel is preferred because of no fiber shedding. . By filtering, the impurities contained in the cellulose ester of the raw material, especially the bright spots and foreign substances, are preferably removed and reduced.

Bright spot foreign body refers to the arrangement of two polarizers in the state of orthogonal polarizers, a polarizer protective film is placed between them, the light is irradiated from the side of the polarizer on one side, and can be seen from the side of the polarizer on the other side To the point (foreign matter) where light leaks from the opposite side, the number of bright spots with a diameter of 0.01 mm or more is preferably 200 / cm ² or less. More preferably 100 / cm ² or less, and then the best of 50 / cm ² or less, ² or less is good again 0 to 10 / cm. In addition, bright spots with a diameter of 0.01 mm or less are also preferable.

Although the filtering of the dopant can be carried out by a general method, the method of filtering while heating at a temperature above the boiling point of the solvent under normal pressure and under pressure, at a temperature within the range where the solvent does not boil, due to the filtering pressure before and after the filtering The difference (referred to as differential pressure) rise is small and preferably. The preferred temperature is 45 ~ 120 ℃, 45 ~ 70 ℃ is better, 45 ~ 55 ℃ is even better.

The filter pressure is preferably the smaller. The filter pressure is preferably below 1.6 MPa, better below 1.2 MPa, and even better below 1.0 MPa.

Here, the casting of the dopant will be explained. In the casting (casting) step, the surface of the metal support is preferably a mirror surface. For the metal support, it is better to use a stainless steel strip or a drum in which the surface is plated by casting. The width of the casting can be 1 ~ 4m.

The surface temperature of the metal support in the casting step is between -50 ° C and the temperature that does not reach the boiling point of the solvent. The higher the temperature, the faster the drying speed of the mesh, so it is better, but if it is too high, the mesh will foam, The situation where the flatness deteriorates. The better support temperature is 0 ~ 40 ℃, 5 ~ 30 ℃, even better. Alternatively, it is also a preferable method to peel from the drum in a state where the network is colloidized by cooling and contains a large amount of residual solvent.

Although the method of controlling the temperature of the metal support is not particularly limited, there are a method of blowing warm air or cold air or a method of bringing warm water into contact with the inside of the metal support. Since those who use warm water, heat transfer is carried out efficiently, so gold The time until the temperature of the support becomes constant is short and good. In the case of using warm air, there is a case where wind with a temperature higher than the intended temperature is used.

In order to make the protective film exhibit good flatness, the amount of residual solvent when peeling the mesh from the metal support is preferably 10 to 150% by mass, more preferably 10 to 40% by mass or 60 to 130% by mass, especially It is 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 (mass%) = {(M-N) / N} × 100

In addition, M is the mass of the sample taken at any time during or after the manufacture of the mesh or film, and N is the mass of the mass M after heating at 115 ° C for 1 hour.

In addition, in the drying step of the protective film, the web is peeled off from the metal support and then dried to make the amount of residual solvent 1% by mass or less, preferably 0.1% by mass or less, particularly preferably 0 to 0.01% %the following.

In the film drying step, a roll drying method (a method in which a plurality of rollers arranged above and below are staggered through a web to dry) or a method of drying while conveying the web by a tenter method is generally used.

In order to make a protective film, after peeling from the metal support, the amount of residual solvent in the mesh immediately extends to the conveying direction (long direction), and the ends of the mesh are held by a tensioner such as a spring fastener It is particularly preferable to extend in the width direction (lateral direction).

In order to extend in the long direction immediately after peeling, the peeling tension is preferably 210 N / m or more, and particularly preferably 220 to 300 N / m.

The method of drying the web is not particularly limited, and it can be generally performed by hot air, infrared rays, heating rollers, microwaves, etc., but it is preferably hot air for simplicity.

In the drying step of the mesh, the drying temperature is preferably increased stepwise from 40 to 200 ° C, and it is preferably performed in the range of 50 to 140 ° C because of the good dimensional stability.

Although the thickness of the protective film is not particularly limited, 10 to 200 μm can be used. In particular, the film thickness is particularly preferably 10 to 100 μm. Even better is 10-40 μm.

The protective film can be used with a width of 1 ~ 4m. In particular, those with a width of 1.4 ~ 4m should be used, especially 1.6 ~ 3m. If it exceeds 4m, transportation becomes difficult.

(Extended operation, refractive index control)

For the protective film of the polarizing plate, the retardation value Ro expressed by the following formula is 0 to 10 nm, and Rt is preferably -10 to +10 nm.

Formula (i): Ro = (nx-ny) × d

Formula (ii): Rt = ((nx + ny) / 2-nz) × d

(Where, 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 direction of the slow phase axis in the film surface, ny is the refractive index in the direction of the phase axis in the film surface, nz is The refractive index in the thickness direction of the film, d is the thickness of the film (nm)).

The above-mentioned refractive index can be obtained by using, for example, KOBRA-21ADH (Oji Measuring Instruments Co., Ltd.) at a measurement wavelength of 590 nm under an environment of 23 ° C. and 55% RH.

Furthermore, the retardation value Ro is in the range of 0 to 5 nm and Rt is in the range of -10 to 10 nm, which is more effective in improving the effect of the present invention.

In order to obtain the retardation values Ro and Rt, it is preferable to use a polarizer protective film as the configuration of the present invention, and to further control the refractive index by stretching.

For example, the film can be extended sequentially or simultaneously in the longitudinal direction of the film (film-forming direction) and the direction perpendicular to the in-plane of the film, that is, the relative width direction.

The extension magnifications in two mutually perpendicular directions are preferably 1.0 to 2.0 times in the casting direction and 1.01 to 2.5 times in the width direction, and 1.01 to 1.5 times in the casting direction and 1.05 to 2.0 times in the width direction. good.

The method of extending the mesh is not particularly limited. For example, the circumferential speed difference is set on a plurality of rollers, and the method of extending the circumferential speed difference between the rollers is used to fix the two ends of the mesh with spring fasteners or spikes, so that the interval between the spring fasteners or spikes The method of extending in the direction and extending in the long direction, the method of expanding in the horizontal direction and extending in the same direction, or the method of extending the length and width at the same time and extending in both directions of length and width, etc. Of course, these methods can be used in combination. In addition, in the case of the so-called tenter method, if the spring fastener portion is driven by a linear driving method, it can be smoothly extended, and the risk of breakage or the like can be reduced, which is preferable.

It is preferable that the width of the film-making step is maintained or the lateral extension is performed by the tenter, and it can also be a pin nail tenter or a spring fastener tenter.

Protect the late phase axis or advance phase axis of the film to exist the film surface Inside, the angle with the film forming direction is θ1 and θ1 is preferably -1 ° or more and + 1 ° or less, and more preferably -0.5 ° or more + 0.5 ° or less. This θ1 can be defined as the alignment angle, and the measurement of θ1 can be performed using an automatic birefringence meter KOBRA-21ADH (Oji measuring machine). θ1 conforms to each of the above-mentioned relationships to provide high brightness to the display screen, to suppress or prevent light leakage, and to obtain faithful color reproduction in the color liquid crystal display device.

(Physical properties)

Protective film, the elongation at break is preferably 10 ~ 80%, 20 ~ 50% is even better.

The visible light transmittance of the protective film is preferably over 90%, and even better than 93%.

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

(Polarizer)

The polarizing plate of this embodiment is formed by sequentially 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. The later-described liquid crystal display device is formed by attaching a polarizing plate to at least one surface of the liquid crystal cell so that the adhesive layer side becomes the liquid crystal cell side.

The polarizing plate can be manufactured by a general method. The saponification type polyvinyl alcohol is used to perform alkali saponification on the polarizer side of the second protective film, and immersing and extending at least one side of the polarizer produced in an iodine solution The aqueous solution is preferably laminated. On the other side 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. For other polarizer protective films, commercially available cellulose ester films (such as Konicaminolta tack KC8UX, KC4UX, KC5UX, KC8UY, KC4UY, KC12UR, KC8UCR-3, KC8UCR-4, KC8UCR-5, KC4FR-1, KC8UY-HA , KC8UX-RHA, above Konica Minolta Opto (share system) is also suitable for use.

The main component of the polarizer is a polarizer that transmits only light in a certain direction of the polarization plane. The representative polarizer is now known as a polyvinyl alcohol-based polarizing film. Those who dyed dichroic dyes. As the polarizer, a film made of an aqueous solution of polyvinyl alcohol and then uniaxially stretched and dyed, or uniaxially stretched after dyeing, preferably a boron compound for durability treatment is preferably used. The film thickness of the polarizer is preferably 5-30 μm, especially 10-20 μm.

For example, in Japanese Patent Laid-Open No. 2003-240958, in the step of dyeing a polyvinyl alcohol-based resin film with an aqueous solution containing a dichroic dye, the polyvinyl alcohol-based resin film dyed with a dichroic pigment is taken with an aqueous solution of boric acid In the method of processing and the step of uniaxially stretching the polyvinyl alcohol-based resin film to produce a polarizing film in which the polyvinyl alcohol-based resin film is adsorbed and oriented to a dichroic dye, the aqueous solution containing the dichroic dye The polyvinyl alcohol-based resin film before treatment is subjected to heat treatment at a temperature in the range of 90 to 180 ° C to produce a polarizing film with a film thickness exceeding 10 μm and less than 20 μm, but this method is also a preferred method for manufacturing a thin polarizing film .

Also, for example, in Japanese Patent No. 4551481, a film made of an amorphous ester-based thermoplastic resin substrate is oriented to a laminate of a polyvinyl alcohol-based resin layer with a dichroic substance, and is assisted in stretching with boric acid by air The two-step stretching step consisting of stretching is carried out to produce a polarizing film (so-called coating-type polarizer) composed of the above resin layer with a thickness of 15 μm or less, and this method is also a preferred method for manufacturing a thin polarizing film.

In addition, Japanese Patent Laid-Open No. 2003-248123, Japanese Patent Laid-Open No. 2003-342322, etc. described ethylene content of 1 to 4 mol%, polymerization degree 2000 to 4000, saponification degree 99.0 to 99.99 mol% ethylene modification Polyvinyl alcohol is also suitable for use. Among them, the ethylene modified polyvinyl alcohol film with hot water cut-off temperature of 66 ~ 73 ℃ is suitable for use. In addition, the difference in hot water cutoff temperature between two points 5 cm apart in the TD direction of the film is preferably below 1 ° C in reducing stains, and the difference in hot water cutoff temperature between two points 1 cm apart in the TD direction of the film is Below 0.5 ° C is even better in reducing color spots.

In addition to the excellent polarizing performance and durability, the polarizer using the ethylene-modified polyvinyl alcohol film has few color spots, and is particularly suitable for large-scale liquid crystal display devices.

The polarizers obtained as described above are generally used as polarizing plates by laminating protective films on both sides or one side thereof. Examples of the adhesive used when bonding the polarizer to the protective film include PVA-based adhesives and urethane-based adhesives. Among them, PVA-based adhesives are suitable for use.

In addition, it is used when attaching a polarizing plate to a liquid crystal cell For the adhesive of the adhesive layer, those using matrix polymers such as acrylate, methacrylate, butyl rubber, and silicone can be used. Although not particularly limited, it is preferable to use butyl (meth) acrylate, ethyl (meth) acrylate, isooctyl (meth) acrylate, 2-ethylhexyl (meth) acrylate as (methyl ) A polymer based on acrylate or a copolymer using two or more kinds of (meth) acrylates as a base. Adhesives are usually copolymerized with polar monomers in these matrix polymers. For the polar monomers, for example, (meth) acrylic acid, (meth) acrylic acid 2-hydroxyethyl ester, (meth) acrylic acid 2-hydroxyl Propyl ester, (meth) acrylamide, N, N-dimethylaminoethyl (meth) acrylate, epoxypropyl (meth) acrylate generally have carboxyl ester, hydroxyl, amine group, Epoxy and other monomers. Adhesives usually contain one or more crosslinking agents in addition to the matrix polymer. The crosslinking agent includes, for example, a divalent or polyvalent metal salt forming a carboxylic acid metal salt with a carboxyl group, and a polyisocyanate compound forming an amide bond with a carboxyl group.

The thickness of the adhesive layer can be about 3-50 μm. When an adhesive layer is formed on the polarizing plate, a surface treatment such as corona treatment may be applied to the surface of the protective film of the polarizing plate. In addition, when forming an adhesive layer, the surface of the adhesive layer is generally coated with a peeling film or the like in advance.

(Liquid crystal display device)

The liquid crystal display device of this embodiment is constituted by laminating the polarizing plate and the liquid crystal cell. At this time, the polarizing plate and the liquid crystal cell are adhered by the adhesive layer of the polarizing plate. The liquid crystal cell is formed by holding a liquid crystal layer on a transparent substrate, and Driven in IPS (In Plane Switching) mode.

In this way, by incorporating the polarizing plate of the present embodiment into an IPS mode type liquid crystal display device, a liquid crystal display device with excellent visibility and an enlarged viewing angle can be realized. Moreover, the polarizing plate of this embodiment can also be incorporated into a wide viewing angle technology (FFS: Fringe-Field Switching) mode type liquid crystal display device, and even in this case, a liquid crystal display with excellent visibility and an enlarged viewing angle can be realized Device.

<Example>

Hereinafter, the present invention will be specifically described with examples, but the present invention is not limited to these. In the examples, the expression "parts" or "%" is used, but it is not particularly limited to "parts by mass" or "mass%".

[Materials used for optical films] (Cellulose amide)

Cellulose Acetate: Cellulose Triacetate (TAC) with an average molecular weight of 70,000 and a degree of acetyl substitution of 2.80

(Delay reducer) <Sugar ester>

Using the sugars described in Table 1 below, the types and number of substituents of the aliphatic alkyl (AL) and aromatic alkyl (AR) groups were changed to synthesize the respective sugar esters.

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

<Ester compound> "Ester Compound E1"

Add 251 g of 1,2-propanediol, 278 g of anhydrous phthalic acid, 91 g of adipic acid, 610 g of benzoic acid, and 0.191 g of tetraisopropyl titanate as an esterification catalyst to a thermometer, stirrer, and slow cooling tube A 2L four-necked flask was gradually heated to 230 ° C with stirring in a nitrogen flow. A dehydration condensation reaction was carried out for 15 hours. After the reaction was completed, the unreacted 1,2-propanediol was distilled off under reduced pressure at 200 ° C to obtain an ester compound E1. The acid value is 0.10 and the number average molecular weight is 450.

"Ester Compound E2"

Adipic acid / ethylene glycol polyester polyol (average degree of polymerization 2000) was used.

<Acrylic additive A1>

Block polymerization is performed by the polymerization method described in Japanese Patent Laid-Open No. 2000-128911. That is, in a flask equipped with a stirrer, a nitrogen gas introduction tube, a thermometer, an inlet, and a reflux cooling tube, methacrylate (MMA) as a monomer is introduced, and after introducing nitrogen gas, the flask is replaced with nitrogen gas to obtain acrylic acid Department of compounds.

After the addition of thioglycerol, polymerization was performed for 4 hours to return the contents to room temperature, and 20 parts by mass of a benzoquinone 5 mass% tetrahydrofuran solution was added thereto to stop the polymerization. The contents were transferred to an evaporator, and tetrahydrofuran, residual monomers, and residual thioglycerol were removed under reduced pressure at 80 ° C to obtain Acrylic additive A1 having a weight average molecular weight of 1000 as measured by GPC.

[Fabrication of Optical Film 1] (Modulation of main dopant 1)

The main dopant of the following composition was prepared. First add methane chloride and ethanol to the pressurized dissolution storage tank. Cellulose ester A was put into the pressure-dissolving storage tank to which the solvent was added while stirring, and it was heated to completely dissolve while stirring.

Furthermore, the above additive component was put into a closed container, dissolved after stirring, and then it was filtered using Azumi filter paper No. 244 made of Azumi filter paper (strand) to prepare the main dopant 1.

(Filming of Optical Film 1)

The main dopant 1 prepared as described above was uniformly cast on a stainless steel belt support at a temperature of 22 ° C. and a width of 1.8 m at a temperature of 22 ° C. On the stainless steel belt support, the solvent was evaporated until the amount of residual solvent became 20%, and the dopant film (mesh) was peeled from the stainless steel belt support at a peeling tension of 162 N / m.

Next, the peeled web evaporated the solvent at 35 ° C and cut it to 1.6 m, and then, using a tenter stretching machine, stretched 1.1 times the width in the width direction (TD direction) at 160 ° C in the width direction (TD direction). At this time, the amount of residual solvent when the tenter began to stretch was 4% by mass.

After that, the drying area at 120 ° C and 140 ° C was dried by multiple rollers, cut into 1.3m, and subjected to a knurling process with a width of 10mm and a height of 2.5μm on both ends of the film, and then wound around the axis ， Fabricated optical film 1. The film thickness is 20 μm, and the winding length is 5000 m.

[Fabrication of optical film 2 ~ 12]

The types and ratios of additives contained in the main dopant are changed as in Table 2, and the optical films 2 to 12 are produced in the same manner as the optical film 1.

[Fabrication of Optical Film 13]

A copolymer prepared by blending a copolymer of methyl methacrylate / methyl acrylate with a weight ratio of 98/2 to 45% of acrylic rubber particles 1 and particles 2 to which acrylic rubber particles 15% are similarly blended. kind. Pellet 1 and pellet 2 were put into the extruder at a ratio of 0.5: 0.5 and kneaded. The molten film extruded from the T-die was pulled with two cooling rolls set at 45 ° C while being cooled, and a thickness of 40 μm was produced. Acrylic resin film. The acrylic resin film is used as the optical film 13. The moisture permeability of the optical film 14 is 98g / m ² . 24hr.

[Fabrication of Optical Film 14] (Production of polyester A)

The esterification reaction tank was heated, and when it reached 200 ° C, 86.4 parts by mass of terephthalic acid and 64.6 parts by mass of ethylene glycol were added, and 0.017 parts by mass of antimony trioxide as a catalyst and magnesium acetate 4 hydrate were added while stirring 0.064 parts by mass and 0.16 parts by mass of triethylamine. Next, the pressure was increased, and the pressure esterification reaction was carried out under the conditions of a gauge pressure of 0.34 MPa and 240 ° C., the esterification reaction tank was returned to normal pressure, and 0.014 parts by mass of phosphoric acid was added. Furthermore, it took 15 minutes, the temperature was raised to 260 ° C, and 0.012 parts by mass of trimethyl phosphate was added. Next, after 15 minutes, the dispersion treatment was performed in a high-pressure disperser, and after 15 minutes, the obtained esterification reaction product was sent to a polycondensation reaction tank, and the polycondensation reaction was performed under reduced pressure at 280 ° C.

After the polycondensation reaction is completed, it is filtered with a 95% Naslon filter with a particle size of 5 μm, extruded from the nozzle into a rope shape, and cooled with cooling water that has been pre-filtered (pore size: 1 μm or less) , Solidify, cut into granules. The inherent viscosity of the obtained polyethylene terephthalate resin (A) was 0.62 dl / g, and it did not substantially contain inactive particles and internally precipitated particles. (Hereinafter referred to as PET (A)).

(Production of polyester B)

10 parts by mass of dry ultraviolet absorbent (2,2 '-(1,4-phenylene) bis (4H-3,1-benzoxazinone-4-one), particle-free PET (A ) (Intrinsic viscosity is 0.62dl / g) 90 parts by mass, use mixing The extruder obtained polyethylene terephthalate resin (B) containing an ultraviolet absorber. (Hereinafter referred to as PET (B)).

(Adjustment of Adhesively Modified Coating Liquid)

The transesterification reaction and the polycondensation reaction are carried out in the usual way, and 46 mole% terephthalic acid, 46 mole% isophthalic acid and 5-sulfonic acid are prepared as the dicarboxylic acid component (relative to the entire dicarboxylic acid component). Copolymerization of an aqueous dispersible sulfonic acid metal base composed of 8 mol% sodium phthalate, 50 mol% ethylene glycol and 50 mol% neopentyl glycol as the diol component (total diol component) polyester resin.

Next, after mixing 51.4 parts by mass of water, 38 parts by mass of isopropyl alcohol, 5 parts by mass of n-butyl cellosolve, and 0.06 parts by mass of nonionic surfactant, the mixture was heated and stirred to reach 77 ° C, and the above aqueous dispersion was added 5 parts by mass of the copolymerized polyester resin of the sulfonic acid metal base, after continuous stirring until there is no resin solid, the resin aqueous dispersion is cooled to normal temperature to obtain a uniform water-dispersible copolymerization with a solid concentration of 5.0% by mass Ester resin liquid. Furthermore, after dispersing 3 parts by mass of aggregate silica particles (manufactured by Fuji-silysia Co., Ltd., SYLYSIA 310) in 50 parts by mass of water, SYLYSIA 310 was added to 99.46 parts by mass of the water-dispersible copolymerized polyester resin solution. 0.54 parts by mass of the aqueous dispersion, and 20 parts by mass of water were added while stirring to obtain an adhesively modified coating liquid.

As a raw material for the base film intermediate layer, 90 parts by mass of PET (A) resin particles without particles and 10 parts by mass of PET (B) resin particles containing ultraviolet absorbers were dried under reduced pressure at 135 ° C for 6 hours After (1 Torr), it is supplied to the extruder 2 (for the middle layer II layer), and the PET (A) is dried by a conventional method and then supplied to the extruder 1 (for the outer layer I layer and the outer layer III), at 285 Dissolve at ℃. The two kinds of polymers were filtered with a stainless steel sintered filter material (formal filtration accuracy of 10 μm particles 95% blocked), laminated in two kinds of three-layer confluence section, extruded into a flake shape from a nozzle, and then used In the electrostatic casting method, a casting drum with a surface temperature of 30 ° C is taken for cooling and solidification to produce an unstretched film. At this time, the discharge amount of each extruder was adjusted so that the thickness ratio of the I layer, the II layer, and the III layer was 10:80:10.

Next, by applying the reverse roll method to both sides of the unstretched PET film so that the coating amount after drying became 0.08 g / m ² , the adhesive modified coating liquid was applied, followed by drying at 80 ° C. for 20 seconds. .

The unstretched film forming the coating layer was introduced into a tenter stretching machine, and the end portion of the film was sandwiched by a spring fastener, while being introduced into a hot air area at a temperature of 125 ° C, and stretched 4.0 times in the width direction. Next, the width in the width direction was maintained, and the treatment was carried out at a temperature of 225 ° C for 30 seconds, and then a 3% relaxation treatment in the width direction to obtain a uniaxially oriented PET film with a film thickness of about 60 μm, using the PET film as an optical film 14. The moisture permeability of the optical film 14 is 36g / m ² . 24hr.

[Measurement of Ro and Rt]

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

Specifically, the optical films 1 to 12 prepared above were subjected to a three-dimensional refractive index measurement at 10 locations at a wavelength of 590 nm under an environment of 23 ° C. and 55% RH, and the average values of the refractive indexes nx, ny, and nz were obtained. Then, the retardation value Ro in the in-plane direction and the retardation value Rt in the thickness direction are calculated according to the following formula.结果 的 结果 如 表 2。 The results are shown in Table 2.

Formula (i): Ro = (nx-ny) × d (nm)

Formula (ii): Rt = {(nx + ny) / 2-nz} × d (nm) [In formulas (i) and (ii), nx is the direction in which the refractive index becomes the largest in the in-plane direction of the thin film Refractive index in x. ny is the refractive index in the direction y perpendicular to the aforementioned direction x in the in-plane direction of the film. nz is the refractive index in the thickness direction z of the film].

[Production of polarizer]

Using the optical films 1 to 14 produced above, polarizing plates 1 to 22 were produced as follows.

(Production of Polaron 1)

A polyvinyl alcohol film with a thickness of 30 μm and an average degree of polymerization of 2400 and a degree of saponification of 99.9 mol% was immersed in warm water at 30 ° C. for 60 seconds to swell. Next, the obtained thin film was immersed in an aqueous solution of 0.3% concentration of iodine / potassium iodide (mass ratio = 0.5 / 8), and dyed while extending 3.5 times. After that, make the obtained film in a 65 ° C borate aqueous solution at a full extension ratio It is extended by 6 times. After that, the obtained film was dried in an oven at 40 ° C. for 3 minutes to obtain polarizer 1 with a thickness of 10 μm.

(Production of Polaron 2)

As the polarizer 2, the polarizer described in Example 1 of Patent No. 4551481 is prepared. That is, on an amorphous PET resin substrate, a laminate of a polyvinyl alcohol-based resin layer having a dichroic substance on the film-forming layer is stretched in two steps consisting of air-assisted stretching and boric acid water stretching Stretching to obtain polaron 2 (applied on an amorphous PET resin substrate). The thickness of the polarizer 2 is adjusted to 3 μm.

(Preparation of active energy ray-curable adhesive liquid (cationic polymerization type))

After mixing the following components and defoaming, an active energy ray-curable adhesive liquid is prepared. In addition, triaryl alkane hexafluorophosphate is mixed with a 50% propylene carbonate solution. The following is the solid content of triaryl alkane hexafluorophosphate.

(Production of polarizer 1)

The polarizing plate 1 is produced in the following method. First, as the first protective film, the optical film 13 prepared above was prepared, and the active energy ray-curable adhesive solution prepared above was used in a micro gravure coater (gravure printing cylinder: # 300, rotation speed 140% / line speed) , Coated with a thickness of 5 μm to form an active energy ray-curable adhesive layer a.

Next, in the optical film 1 prepared above, the active energy ray-curable adhesive solution prepared above was applied in the same manner as above to a thickness of 5 μm to form an active energy ray-curable adhesive layer b.

Between the active energy ray-curable adhesive layers a and b, the above-prepared polarizer 1 is placed and bonded with a roller machine to obtain a laminated optical film 13 / active energy ray-curable adhesive layer a / polarized light Lamination of sub-active energy ray-curable adhesive layer b / optical film 1. At this time, the lamination is carried out in such a way that the retardation axis of the optical film and the absorption axis of the polarizer are perpendicular to each other. Then, electron beams are irradiated from both sides of the laminate to produce a polarizing plate 1. In addition, the linear velocity was 20 m / min, the acceleration voltage was 250 kV, and the irradiation dose was 20 kGy.

(Production of polarizing plates 2-22)

Polarizing plates 2 to 22 were produced in the same manner as described above except that the optical film and polarizer used were combined as shown in Table 3.

[Measurement of break point tension and evaluation of operability]

Using a tensile tester (Tensilon; manufactured by A & C Co., Ltd.) under a 23 ° C 55% RH environment, measure the breaking point stress (MPa) of the produced polarizing plate in the absorption axis direction, and multiply the breaking point stress by the thickness of the polarizing plate It is calculated as the breaking point tension (N). In addition, according to the following evaluation criteria, the operability of the polarizing plates 1 to 21 during the secondary processing operation is evaluated. The results of the evaluation of the break point tension and operability of polarizing plates 1 to 21 are shown in Table 3. In addition, the tension at the breaking point being T (N) means that the polarizing plate breaks only when the tension applied to the polarizing plate becomes T (N).

(Evaluation criteria)

◎: The tension at the breaking point is 70 N or more (even if the secondary processing operation conditions are changed, the polarizing plate is peeled off without leaving)

○: The tension at the breaking point is 60 N or more (the polarizing plate is peeled off without remaining during the secondary processing operation).

△: The tension at the breaking point is less than 60N (the polarizing plate may break during the secondary processing operation, and the polarizing plate may remain on the panel side).

×: The breaking point tension is less than 50N (the polarizing plate is broken in almost all secondary processing operations, and the polarizing plate remains on the panel side).

According to Table 3, in the polarizing plates 1 to 18, the breaking point tension becomes 60 N or more. This is because the polarizing plates 1 to 18 and the second protective film contain aliphatic acetyl substituted sugar esters as retardation reducing agents to achieve zero retardation. Even if the second protective film is made thinner, the sugar ester and cellulose Ester phase Interaction can ensure the mechanical strength of the second protective film, and it is considered that even if the total thickness of the first protective film, polarizer, and second protective film made of acrylic resin or PET resin with low moisture permeability is less than 90 μm When the whole polarizing plate is thinned, the first protective film and the polarizer, which are easily reduced in mechanical strength due to thinning, are supported by the second protective film, which can suppress the decrease in the mechanical strength of the entire polarizing plate. Therefore, during the secondary processing operation, the polarizing plate becomes hard to break (because the polarizing plate is not broken without applying strong tension of 60 N or more to the polarizing plate), and the operability becomes good.

In particular, in the case of polarizing plates 1 to 11, even if the total thickness of the first protective film, polarizer, and second protective film is 80 μm or less, the whole polarizing plate is made thinner by ensuring that the breaking point tension is 60 N or more. The effect of preventing the polarizing plate from breaking (operability improvement). Among them, the polarizing plates 1 to 4 and 7 to 11 ensure that the breaking point tension is more than 80N, and the effect of improving operability can be surely obtained.

From the above, it can be said that the above-mentioned sugar ester that can be used as a retardation reducing agent is very effective in preventing breakage when the entire polarizing plate is thinned. In particular, in polarizers 1 to 18, the thickness of the polarizer is 15 μm or less, but even if such a thin polarizer is used to make the entire polarizer thinner, the second protective film contains the above sugar ester, which can suppress the entire polarizer. The reduction in mechanical strength caused by the reduction in thickness ensures that the breaking point tension is above 60N.

In contrast, in the polarizing plates 20-22, the breaking point tension is less than 60N. It is considered that the polarizing plates 20 to 22 do not contain sugar esters as retardation reducing agents in the second protective film (a retardation reducing agent other than sugar esters achieves a zero retardation), and when the second protective film is made thinner, it cannot be ensured Its mechanical strength Degree, it is impossible to suppress the decrease in mechanical strength when the entire polarizing plate is thinned. Therefore, the polarizing plate becomes easily broken during the secondary processing operation (even if the polarizing plate is weakly tensioned to less than 60N, the polarizing plate is still broken), and the workability is reduced.

In addition, although the tension at the breaking point of the polarizing plate 19 is 60 N or more, the Rt of the second protective film (optical film 10) of the polarizing plate 19 is 10 nm or more, and a zero retardation film is not realized. It is considered that the sugar ester contained in the retardation reducing agent of the optical film 10 is one in which the OH group of the compound having a furanose structure or a pyranose structure is esterified with an aromatic alkyl group, and the effect of reducing Rt to zero is small.

The polarizing plate and 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 sequentially laminated, and the thicknesses of the first protective film, the polarizing film, and the second protective film The total is 90 μm or less, and the moisture permeability of the first protective film is 400 g / m ² . 24 hrs or less, the second protective film contains cellulose ester and a retardation reducing agent, and the retardation reducing agent contains a compound (A) having a furanose structure or a pyranose structure, or 2 or more bonded to 12 or less Sugar esters in which all or part of the OH groups in at least one compound (B) of the furanose structure or pyranose structure are esterified with an aliphatic acetyl group, in the second protective film, the following formula ( i) RO represented by 0 nm or more and 10 nm or less, Rt represented by the following formula (ii) is -10 nm or more + 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 direction of the slow phase axis in the film surface, and ny is the direction of the phase advance axis in the film surface. Refractive index, nz is the refractive index in the thickness direction of the film (refractive index is measured in an environment of 23 ° C. and 55% RH at a wavelength of 590 nm), and d is the thickness of the film (nm)).

2. The polarizing plate according to the above 1, wherein the sugar ester is all or part of the OH group in the compound (B) of at least one type of the furanose structure or the pyranose structure in which two or more than 12 are bonded A compound that is esterified with an aliphatic acyl group.

3. The polarizing plate as described in 1 or 2 above, wherein the sugar ester is formed by bonding all or part of the OH group in at least one compound (B) of two furanose structures or pyranose structures. Acetyl and esterified compounds.

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

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

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

7. A liquid crystal display device characterized by having the foregoing The polarizing plate described in any one of 1 to 6 and the liquid crystal cell adhered to the adhesive layer of the polarizing plate.

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

[Industrial Applicability]

The polarizing plate of the present invention can be particularly used in a liquid crystal display device driven in IPS mode.

Claims (10)

A polarizing plate comprising a first protective film, a polarizing film as a polarizer, a second protective film, and an adhesive layer adhering to a liquid crystal cell of a liquid crystal display device, the first protective film and the polarizing film The total thickness of the second protective film is 90 μm or less, and the moisture permeability of the first protective film is 400 g / m ² . 24 hrs or less, the second protective film contains cellulose ester and a retardation reducing agent, and the retardation reducing agent contains a compound (A) having a furanose structure or a pyranose structure, or 2 or more bonded to 12 or less Sugar esters in which all or part of the OH groups in at least one compound (B) of the furanose structure or pyranose structure are esterified with an aliphatic acetyl group, in the second protective film, the following formula ( i) RO represented by 0nm or more and 10nm or less, Rt represented by the following formula (ii) is -10nm or more + 10nm or less, formula (i) Ro = (nx-ny) × d formula (ii) Rt = { (nx + ny) / 2-nz} × d (where 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, and nx is the refractive index in the direction of the slow phase axis in the film surface , Ny is the refractive index in the direction of the phase-advancing axis in the film surface, nz is the refractive index in the thickness direction of the film (refractive index is measured in an environment of 23 ° C., 55% RH, and a wavelength of 590 nm), and d is the thickness of the film (nm)). The polarizing plate according to claim 1, wherein the sugar ester is all or part of the OH group in the compound (B) in which at least one furanose structure or at least one pyranose structure is bonded to two or more than 12 A compound esterified by an aliphatic acyl group. The polarizing plate according to claim 1, wherein the sugar ester is a compound (B) in which at least one kind of two furanose structures or pyranose structures is bonded to all or part of the OH group via an acetyl group And esterified compounds. The polarizing plate according to claim 1, wherein the total thickness of the first protective film, the polarizing film, and the second protective film is 80 μm or less. The polarizing plate according to claim 1, wherein the thickness of the polarizing film is 15 μm or less. The polarizing plate according to claim 1, wherein the thickness of the second protective film is 30 μm or less. A liquid crystal display device characterized by a polarizing plate described in any one of claims 1 to 6 and a liquid crystal cell adhered to the adhesive layer of the polarizing plate. The liquid crystal display device described in claim 7 is driven in the IPS mode. The liquid crystal display device according to claim 7, wherein the polarizing plate is located on the viewing side of the liquid crystal cell. The liquid crystal display device according to claim 7, wherein the polarizing plate is located on the backlight side of the liquid crystal cell.