JP5993328B2 - Cellulose acylate film, polarizing plate and liquid crystal display device - Google Patents

Description

  The present invention relates to a cellulose acylate film, a polarizing plate using the same, and a liquid crystal display device. In particular, the present invention relates to a cellulose acylate film that can be preferably used as an optical film such as a polarizing plate protective film or a retardation film.

Conventionally, cellulose acylate films have been used for applications such as protective films for polarizing plates.
Patent Document 1 describes that a predetermined polycondensation ester compound is blended in a cellulose ester film in an amount of 35% by mass or more based on the cellulose ester to eliminate light unevenness.
Patent Document 2 discloses a film in which a predetermined polycondensation ester is blended with a cellulose ester film. It is also described that such a film can achieve the desired Re and Rth.

 By the way, in recent years, there is an increasing demand for thinning the liquid crystal display device. Therefore, it is beneficial if the polarizing plate, which is a component part of the liquid crystal display device, can be thinned.

JP 2012-063748 A JP 2011-105924 A

Here, as a method of thinning the polarizing plate, it is conceivable to thin the cellulose ester film used as a protective film for the polarizing plate. However, when the film is thinned, it becomes difficult to obtain predetermined optical characteristics. For example, with the technique described in Patent Document 1, it is difficult to develop retardation while reducing the film thickness.
Further, it has been found that the cellulose ester film having a certain degree of retardation as described in Patent Document 2 causes condensation unevenness due to condensation during transportation and storage. This point will be described in more detail. Usually, a liquid crystal cell or a liquid crystal display device to which a polarizing plate including a cellulose acylate film is bonded is enclosed in an antistatic bag and transported or stored. FIG. 1 is a schematic cross-sectional view showing a state of a polarizing plate 2 when a liquid crystal display device is placed in an antistatic bag 1.
The polarizing plate 2 usually has a polarizer 3 and a polarizing plate protective film provided on both sides. One of the polarizing plate protective films is, for example, a cellulose ester film 4 and the other is, for example, a retardation film or another protective film 5. Here, the dew condensation water 6 may accumulate between the antistatic bag 1 and the polarizing plate 2 during the transportation and storage. Since the condensed water usually accumulates partially, a portion where the condensed water is accumulated and a portion where the condensed water is not accumulated are generated on the surface of the polarizing plate 2. If it does so, distortion 7.7 will arise in the polarizing plate 2 corresponding between the part which condensed water accumulated, and the part which does not accumulate. And when this inventor examined, it turned out that this distortion influences an optical characteristic.
The present invention is intended to solve such problems, and is to provide a thin cellulose ester film that can exhibit a desired retardation and is less likely to cause condensation unevenness. Objective.

  Based on the above-mentioned problems, the inventors of the present application have conducted intensive studies. The present inventors have found that a high retardation can be exhibited even with a thin film while suppressing the present invention and completed the present invention.

Specifically, the above problem has been solved by the following means <1>, preferably from <2> to <11>.
<1> cellulose acylate having a total acyl substitution degree of 2.60 to 2.95;
Including at least one polycondensation ester containing an aromatic dicarboxylic acid residue and an aliphatic diol residue, in an amount of 35 to 100 parts by mass with respect to 100 parts by mass of cellulose acylate;
The ratio of residues containing aromatics to all dicarboxylic acid residues in the polycondensed ester is 40 to 100 mol%,
A cellulose acylate film having a thickness of 20 to 80 μm and satisfying the following (formula 1) and (formula 2).
(Formula 1) 30 ≦ Re (550) ≦ 100 nm
(Formula 2) 90 ≦ Rth (550) ≦ 170 nm
(However, Re (550) represents in-plane retardation (nm) at a wavelength of 550 nm, and Rth (550) represents retardation in the film thickness direction (nm) at a wavelength of 550 nm.)
<2> The equilibrium water content change by Karl Fischer method at 25 ° C. and 80% relative humidity of the film before and after immersing the cellulose acylate film in pure water at 40 ° C. for 16 hours is 1.0% by mass or less. > The cellulose acylate film described.
<3> The cellulose acylate according to <1> or <2>, wherein the dimensional change rate before and after the cellulose acylate film is allowed to stand for 24 hours in an environment of 60 ° C. and 90% relative humidity is ± 0.5% or less. the film.
<4> The cellulose acylate film according to any one of <1> to <3>, wherein a half-width of a peak having the largest tan δ value in dynamic viscoelasticity measurement is within 90 ° C.
<5> The cellulose acylate film according to any one of <1> to <4>, wherein a ratio of terephthalic acid residues to all dicarboxylic acid residues in the polycondensed ester is 40 mol% or more.
<6> The cellulose acylate film according to any one of <1> to <5>, wherein the film thickness is 30 to 60 μm.
<7> The cellulose acylate film according to any one of <1> to <6>, which is for a VA mode liquid crystal display device.
<8> A polarizing plate having the cellulose acylate film according to any one of <1> to <7>, a polarizing film, and a protective film.
<9> The polarizing plate according to <8>, wherein the protective film has a moisture permeability of 40 g and 90% relative humidity for 24 hours of 100 g / m ² or less.
<10> A liquid crystal display device having the polarizing plate according to <8> or <9>.
<11> Cellulose acylate having a total acyl substitution degree of 2.60 to 2.95, and at least one polycondensed ester containing an aromatic dicarboxylic acid residue and an aliphatic diol residue, based on 100 parts by mass of cellulose acylate 35 to 100 parts by mass of a cellulose acylate film having a residue ratio of 40 to 100 mol% with respect to all dicarboxylic acid residues in the polycondensed ester is 1.1 in the direction perpendicular to the transport direction. A method for producing a cellulose acylate film having a thickness of 20 to 80 μm, comprising stretching at a magnification of ˜2.0 times and further setting the temperature of the film drying zone after stretching to 30 to 90 ° C.

  According to the present invention, it is possible to provide a cellulose ester film having a thin thickness and capable of exhibiting a desired retardation and hardly causing condensation unevenness.

It is the cross-sectional schematic which shows the state which dew condensation produces | generates in a polarizing plate when transporting and storing a liquid crystal display device. It is a schematic sectional drawing of an example of the liquid crystal display device of this invention.

  Hereinafter, the contents of the present invention will be described in detail. In the present specification, “to” is used to mean that the numerical values described before and after it are included as a lower limit value and an upper limit value.

The cellulose acylate film of the present invention comprises a cellulose acylate having a total acyl substitution degree of 2.60 to 2.95 and at least one polycondensed ester containing an aromatic dicarboxylic acid residue and an aliphatic diol residue. The ratio of residues containing aromatics to all dicarboxylic acid residues in the polycondensation ester is 40 to 100 mol%, and the film thickness is 20 to 80 μm. Yes, the following (Formula 1) and (Formula 2) are satisfied.
(Formula 1) 30 ≦ Re (550) ≦ 100 nm
(Formula 2) 90 ≦ Rth (550) ≦ 170 nm
(However, Re (550) represents in-plane retardation (nm) at a wavelength of 550 nm, and Rth (550) represents retardation in the film thickness direction (nm) at a wavelength of 590 nm.)

 In the cellulose acylate film of the present invention, the equilibrium water content change by the Karl Fischer method at 25 ° C. and 80% relative humidity of the film before and after immersing the film in pure water at 40 ° C. for 16 hours is 1.0% by mass or less. It is preferable. When the equilibrium moisture content change of the film is large, a difference in shrinkage occurs between the region containing water and the region not containing water, and stress is generated. This stress causes unevenness in optical characteristics when viewed from the front (display performance from the front when incorporated in a liquid crystal display device). The change in equilibrium moisture content of the film can be further 0.8% by mass or less, more preferably 0.7% by mass or less, and particularly 0.5% by mass or less. As means for reducing the change in the equilibrium moisture content of the film as described above, the polycondensation ester and the blending amount thereof, the draw ratio at the time of production, the draw temperature, and the drying temperature after the drawing can be adjusted.

The cellulose acylate film of the present invention preferably has a dimensional change rate of ± 0.5% or less before and after being left for 24 hours in an environment of 60 ° C. and 90% relative humidity. When the rate of dimensional change of the film is large, a polarizing plate containing the film is incorporated into a liquid crystal display device, and then, when a wet heat test is performed, distortion occurs due to a local dimensional difference, and the phase difference axis shifts. . In the present invention, the dimensional change rate can be reduced by adjusting the polycondensed ester and the blending amount thereof, the draw ratio during production, the draw temperature, and the drying temperature after drawing.
In particular, in the present invention, even a stretched film is highly significant in that the dimensional change rate can be reduced.

  Details of the present invention will be described below.

<Cellulose acylate>
The cellulose acylate film used in the present invention contains cellulose acylate having a total acyl substitution degree of 2.60 to 2.95.
Examples of the film material contained in the cellulose acylate film of the present invention include cellulose esters, and ester substitution obtained by introducing a functional group biologically or chemically from the cellulose acylate and other cellulose as raw materials. Examples thereof include compounds having a cellulose skeleton. In addition, it is preferable that the cellulose acylate film of this invention contains the said cellulose acylate as a main component. Here, “as the main component” indicates a polymer when it is composed of a single polymer, and when it is composed of a plurality of polymers, the polymer having the highest mass fraction among the constituent polymers. It shows that.

  The cellulose acylate is an ester of cellulose and carboxylic acid, and the carboxylic acid is more preferably a fatty acid having 2 to 22 carbon atoms, and cellulose acylate being a lower fatty acid having 2 to 4 carbon atoms. Most preferred.

(Cellulose acylate raw material)
Cellulose acylate raw material cellulose used in the present invention includes cotton linter and wood pulp (hardwood pulp, softwood pulp), etc., and any cellulose acylate obtained from any raw material cellulose can be used. May be. Detailed descriptions of these raw material celluloses can be found in, for example, “Plastic Materials Course (17) Fibrous Resin” (Marusawa, Uda, Nikkan Kogyo Shimbun, published in 1970) and Invention Association Publication Technical Report 2001-1745 ( 7 to 8) can be used, and the cellulose acylate film of the present invention is not particularly limited.

(Degree of substitution of cellulose acylate)
Next, the cellulose acylate suitable for the present invention produced from the above-mentioned cellulose will be described.

  The cellulose acylate used in the present invention is one in which the hydroxyl group of cellulose is acylated, and the substituent can be any acetyl group having 2 carbon atoms to 22 carbon atoms. In the present invention, there is no particular limitation on the measurement of the degree of substitution of cellulose with a hydroxyl group in cellulose acylate, but the degree of binding of acetic acid and / or a fatty acid having 3 to 22 carbon atoms substituted with a hydroxyl group of cellulose is measured and calculated. The degree of substitution can be obtained. As a measuring method, it can carry out according to ASTM D-817-91.

In the cellulose acylate used in the present invention, the total acyl substitution degree of the cellulose acylate is 2.60 to 2.95, preferably 2.70 to 2.95, more preferably 2.75 to 2.93. 2.80 to 2.90 are more preferable.
If the total acyl substitution degree of the cellulose acylate used in the present invention is within the above preferred range, it is more preferable in terms of optical properties and humidity stability of the optical properties, and if it is 2.95 or less, a viewpoint that can further reduce haze. To preferred.

  Among the acetic acid substituted for the hydroxyl group of cellulose and / or the fatty acid having 3 to 22 carbon atoms, the acyl group having 2 to 22 carbon atoms may be an aliphatic group or an aryl group, and is not particularly limited. A mixture of They are, for example, alkyl carbonyl esters, alkenyl carbonyl esters, aromatic carbonyl esters, or aromatic alkyl carbonyl esters of cellulose, each of which may further have a substituted group. These preferred acyl groups include acetyl, propionyl, butanoyl, heptanoyl, hexanoyl, octanoyl, decanoyl, dodecanoyl, tridecanoyl, tetradecanoyl, hexadecanoyl, octadecanoyl I-butanoyl group, t-butanoyl group, cyclohexanecarbonyl group, oleoyl group, benzoyl group, naphthylcarbonyl group, cinnamoyl group and the like. Among these, acetyl group, propionyl group, butanoyl group, dodecanoyl group, octadecanoyl group, t-butanoyl group, oleoyl group, benzoyl group, naphthylcarbonyl group, cinnamoyl group and the like are preferable, and acetyl group, propionyl group, butanoyl group are preferable. Groups are more preferred. Further preferred groups are an acetyl group and propionyl, and the most preferred group is an acetyl group (when the cellulose acylate is cellulose acetate).

  The degree of polymerization of the cellulose acylate preferably used in the present invention is preferably 180 to 700 in terms of viscosity average degree of polymerization. In cellulose acetate, 180 to 550 is more preferable, 180 to 400 is more preferable, and 180 to 350. Is particularly preferred. If the degree of polymerization is not more than the upper limit, the viscosity of the cellulose acylate dope solution does not become too high, and a film can be easily produced by casting. If the degree of polymerization is equal to or greater than the lower limit, it is preferable because there is no inconvenience such as a decrease in strength of the produced film. The viscosity average degree of polymerization can be measured by Uda et al.'S intrinsic viscosity method {Kazuo Uda, Hideo Saito, "Journal of the Textile Society," Vol. 18, No. 1, pages 105-120 (1962)}. This method is also described in detail in JP-A-9-95538.

  The molecular weight distribution of cellulose acylate preferably used in the present invention is evaluated by gel permeation chromatography, and its polydispersity index Mw / Mn (Mw is a mass average molecular weight, Mn is a number average molecular weight) is small, and the molecular weight A narrow distribution is preferred. The specific value of Mw / Mn is preferably 1.0 to 4.0, more preferably 2.0 to 4.0, and most preferably 2.3 to 3.4. preferable.

<Polycondensed ester>
The cellulose acylate film of the present invention contains at least one polycondensation ester containing an aromatic dicarboxylic acid residue and an aliphatic diol residue in a ratio of 35 to 100 parts by mass with respect to 100 parts by mass of the cellulose acylate, The ratio of residues containing aromatics to all dicarboxylic acid residues in the polycondensed ester is 40 to 100 mol%.

  Content of the polycondensation ester in the cellulose acylate film of the present invention is 35 to 100 parts by mass, preferably 35 to 95 parts by mass, and 38 to 80 parts by mass with respect to 100 parts by mass of cellulose acylate. It is more preferable, and it is still more preferable that it is 38-50 mass parts.

The residue ratio containing the aromatic to the aromatic dicarboxylic acid residue determined by the formula below is 40 mol% to 100 mol%, preferably 45 to 90 mol%, more preferably 45 to 85 mol%. By setting the aromatic dicarboxylic acid residue ratio to 40 mol% or more, a cellulose acylate film exhibiting sufficient optical anisotropy can be obtained. Moreover, if it is 100 mol% or less, it is excellent in compatibility with a cellulose acylate, and it can make it difficult to produce a bleed-out at the time of film formation of a cellulose acylate film and at the time of heat-stretching.
The ratio of residues containing aromatics in the present invention is defined as follows.
Aromatic residue ratio (mol%) = [aromatic dicarboxylic acid residue (mol) / (aromatic dicarboxylic acid residue (mol) + aliphatic dicarboxylic acid residue (mol))] × 100
The polycondensed ester according to the present invention is obtained by mixing, for example, an aromatic dicarboxylic acid and an aliphatic diol.
The aromatic dicarboxylic acid residue preferably includes an aromatic dicarboxylic acid residue and an aliphatic dicarboxylic acid residue having an average carbon number of 4.0 to 5.0.

  The average carbon number of the aliphatic diol residue is a value calculated by multiplying the constituent carbon number by the composition ratio (molar fraction) of the aliphatic diol residue. For example, when it consists of 50 mol% of ethylene glycol residues and 50 mol% of 1,2-propanediol residues, the average carbon number is 2.5.

The number average molecular weight of the polycondensed ester is preferably 800 to 2500, more preferably 900 to 1800, and still more preferably 900 to 1250. If the number average molecular weight of the polycondensed ester is 800 or more, the volatility is low, and film failure and process contamination due to volatilization under high temperature conditions during stretching of the film of the present invention are less likely to occur. Moreover, if it is 2500 or less, compatibility with a cellulose acylate will become high and it will become difficult to produce the bleed-out at the time of film forming and at the time of heat-stretching.
The number average molecular weight of the polycondensed ester can be measured by a usual method using GPC (Gel Permeation Chromatography).
For example, the temperature of the columns (TSKgel Super HZM-H, TSKgel Super HZ4000 and TSKgel Super HZ2000 manufactured by Tosoh Corporation) is 40 ° C., THF is used as an eluent, the flow rate is 0.35 ml / min, detection is RI, The injection volume was 10 μl, the sample concentration was 1 g / l, and polystyrene was used as the standard sample.

(Aromatic dicarboxylic acid residue)
The aromatic dicarboxylic acid residue is contained in a polycondensed ester obtained from an aliphatic diol and a dicarboxylic acid containing an aromatic dicarboxylic acid.
In the present specification, a residue is a partial structure of a polycondensed ester and represents a partial structure having the characteristics of a monomer forming the polycondensed ester. For example, the dicarboxylic acid residue formed from dicarboxylic acid HOOC-R-COOH is -OC-R-CO-.

Examples of the aromatic dicarboxylic acid used in the present invention include phthalic acid, terephthalic acid, isophthalic acid, 1,5-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, 1,8-naphthalenedicarboxylic acid, and 2,8-naphthalene. Examples thereof include dicarboxylic acid and 2,6-naphthalenedicarboxylic acid.
In the polycondensed ester, an aromatic dicarboxylic acid residue is formed by the aromatic dicarboxylic acid used for mixing.
The aromatic dicarboxylic acid residue preferably has an average carbon number of 8.0 to 12.0, more preferably 8.0 to 10.0, and still more preferably 8.0. If it is this range, since it is excellent in compatibility with a cellulose ester and it is hard to produce a bleed-out also at the time of film forming of a cellulose acylate film and heat drawing, it is preferable. Moreover, since it can be set as the cellulose acylate film which can fully express the anisotropy suitable for using for an optical compensation film as an optical use, it is preferable.
Specifically, the aromatic dicarboxylic acid residue preferably includes at least one of a phthalic acid residue, a terephthalic acid residue, and an isophthalic acid residue, more preferably a phthalic acid residue or a terephthalic acid residue. It contains at least one, and more preferably contains a terephthalic acid residue.
That is, by using terephthalic acid as the aromatic dicarboxylic acid for mixing in the formation of the polycondensed ester, it is more compatible with cellulose acylate and bleeds out during the formation of the cellulose acylate film and during heat stretching. It can be set as the cellulose acylate film which is hard to produce. Moreover, aromatic dicarboxylic acid may be used alone or in combination of two or more. When two types are used, it is preferable to use phthalic acid and terephthalic acid.
By using together two kinds of aromatic dicarboxylic acids of phthalic acid and terephthalic acid, the polycondensation ester at normal temperature can be softened, which is preferable in terms of easy handling.
The content of the terephthalic acid residue in the dicarboxylic acid residue of the polycondensed ester is preferably 40 mol% or more, more preferably 40 mol% to 90 mol%, still more preferably 45 mol% to 80 mol%. .
By setting the terephthalic acid residue ratio to 40 mol% or more, a cellulose acylate film exhibiting sufficient optical anisotropy can be obtained. Moreover, if it is 95 mol% or less, it is excellent in compatibility with a cellulose acylate, and it can make it hard to produce a bleed-out also at the time of film formation of a cellulose acylate film and the time of heat-stretching.

(Aliphatic dicarboxylic acid residue)
The polycondensation ester may have an aliphatic dicarboxylic acid residue together with an aromatic dicarboxylic acid residue.
The average carbon number of the aliphatic dicarboxylic acid residue is a value calculated by multiplying the constituent carbon number by the composition ratio (molar fraction) of the aliphatic dicarboxylic acid residue.
The average carbon number of the aliphatic diol residue is a value calculated by multiplying the constituent carbon number by the composition ratio (molar fraction) of the aliphatic diol residue. For example, when it consists of 50 mol% of ethylene glycol residues and 50 mol% of 1,2-propanediol residues, the average carbon number is 2.5.
The aliphatic dicarboxylic acid residue is contained in a polycondensed ester obtained from a diol and a dicarboxylic acid containing an aliphatic dicarboxylic acid.
In the present specification, a residue is a partial structure of a polycondensed ester and represents a partial structure having the characteristics of a monomer forming the polycondensed ester. For example, the dicarboxylic acid residue formed from dicarboxylic acid HOOC-R-COOH is -OC-R-CO-.
Examples of the aliphatic dicarboxylic acid preferably used in the present invention include oxalic acid, malonic acid, succinic acid, maleic acid, fumaric acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, and dodecanedicarboxylic acid. Examples include acid or 1,4-cyclohexanedicarboxylic acid.
In the polycondensed ester, an aliphatic dicarboxylic acid residue is formed from the aliphatic dicarboxylic acid used for mixing.
The aliphatic dicarboxylic acid residue preferably has an average carbon number of 4.0 to 5.0, more preferably 4.0 to 4.9, and preferably 4.0 to 4.8. Further preferred. If it is this range, since it is excellent in compatibility with a cellulose acylate and it is hard to produce a bleed-out also at the time of film forming of a cellulose acylate film and heat drawing, it is preferable.
Specifically, it preferably includes a succinic acid residue, and when two types are used, it preferably includes a succinic acid residue and an adipic acid residue.
That is, one or two or more aliphatic dicarboxylic acids may be used for mixing in the formation of the polycondensed ester. When two types are used, it is preferable to use succinic acid and adipic acid.
By using two types of aliphatic dicarboxylic acids, succinic acid and adipic acid, the average carbon number of the diol residue can be reduced, which is preferable in terms of compatibility with cellulose acylate.
In addition, when the average carbon number of the aliphatic dicarboxylic acid residue is less than 4.0, the synthesis becomes difficult, so it cannot be used.

(Aliphatic diol)
The aliphatic diol residue is contained in a polycondensed ester obtained from an aliphatic diol and an aromatic dicarboxylic acid.
In the present specification, a residue is a partial structure of a polycondensed ester and represents a partial structure having the characteristics of a monomer forming the polycondensed ester. For example, the dicarboxylic acid residue formed from the diol HO—R—OH is —O—R—O—.
The polycondensed ester preferably contains an aliphatic diol residue having an average carbon number of 2.0 or more and 3.0 or less, more preferably an average carbon number of 2.0 or more and 2.8 or less. Is an aliphatic diol residue having an average carbon number of 2.0 or more and 2.5 or less. By setting the average number of carbon atoms of the aliphatic diol residue to 3.0 or less, compatibility with cellulose acylate can be improved, bleed-out is less likely to occur, and heating loss of the compound is reduced. In addition, it is difficult for a sheet-like failure to occur due to process contamination during drying of the cellulose acetate web. Further, when the average carbon number of the aliphatic diol residue is 2.0 or more, synthesis is facilitated.
Examples of the aliphatic diol used in the present invention include alkyl diols and alicyclic diols, such as ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 2-methyl-1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 2,2-dimethyl-1,3-propanediol (neopentyl glycol), 2,2-diethyl-1,3-propanediol (3,3-dimethylolpentane), 2-n-butyl-2-ethyl-1,3-propanediol (3,3-dimethylolheptane), 3- Methyl-1,5-pentanediol, 1,6-hexanediol, 2,2,4-trimethyl-1,3-pentanediol, 2-ethyl -1,3-hexanediol, 2-methyl-1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,12-octadecanediol, diethylene glycol, etc., and these are together with ethylene glycol It is preferable to use it as a 1 type, or 2 or more types of mixture.

The preferred aliphatic diol is at least one of ethylene glycol, 1,2-propanediol, and 1,3-propanediol, and particularly preferably at least one of ethylene glycol and 1,2-propanediol. . When two types are used, it is preferable to use ethylene glycol and 1,2-propanediol.
In the polycondensed ester, a diol residue is formed by the diol used for mixing.
The diol residue preferably includes at least one of an ethylene glycol residue, a 1,2-propanediol residue, and a 1,3-propanediol residue, and an ethylene glycol residue or a 1,2-propanediol residue It is more preferable that
Of the aliphatic diol residues, the ethylene glycol residue is preferably 20 mol% to 100 mol%, and more preferably 50 mol% to 100 mol%.

(Sealing)
Both ends of the polycondensed ester may be sealed or unsealed.
When both ends are sealed, it is preferable to react with a monocarboxylic acid for sealing. At this time, both ends of the polycondensed ester are monocarboxylic acid residues. In the present specification, a residue is a partial structure of a polycondensed ester and represents a partial structure having the characteristics of a monomer forming the polycondensed ester. For example, the monocarboxylic acid residue formed from monocarboxylic acid R—COOH is R—CO—. An aliphatic monocarboxylic acid residue is preferred, the monocarboxylic acid residue is more preferably an aliphatic monocarboxylic acid residue having 2 to 22 carbon atoms, and an aliphatic monocarboxylic acid residue having 2 to 3 carbon atoms is more preferred. It is more preferably a group, particularly preferably an aliphatic monocarboxylic acid residue having 2 carbon atoms.
When the number of carbon atoms of the monocarboxylic acid residue at both ends of the polycondensed ester is 3 or less, the volatility is lowered, the weight loss due to heating of the polycondensed ester does not increase, and process contamination and surface failure occur. Can be reduced.
That is, the monocarboxylic acid used for sealing is preferably an aliphatic monocarboxylic acid. More preferably, the monocarboxylic acid is an aliphatic monocarboxylic acid having 2 to 22 carbon atoms, more preferably an aliphatic monocarboxylic acid having 2 to 3 carbon atoms, and an aliphatic monocarboxylic acid residue having 2 carbon atoms. Particularly preferred is a group.
For example, acetic acid, propionic acid, butanoic acid, benzoic acid and derivatives thereof are preferable, acetic acid or propionic acid is more preferable, and acetic acid is most preferable.
Two or more monocarboxylic acids used for sealing may be mixed.
Both ends of the polycondensed ester are preferably sealed with acetic acid or propionic acid, and most preferably both ends become acetyl ester residues (sometimes referred to as acetyl residues) by acetic acid sealing.
When both ends are sealed, the cellulose acylate film can be obtained in which the state at normal temperature is unlikely to be in a solid form, the handling becomes good, and the humidity stability and polarizing plate durability are excellent.

  Although the specific example of the polycondensation ester concerning this invention is described in the following table | surfaces, it is not limited to these.

表中、単位は質量％である。ＴＰＡはテレフタル酸、ＰＡはフタル酸、ＳＡはコハク酸、ＡＡはアジピン酸、ＰＧは１，２−プロピレングリコール、ＥＧはエチレングリコール、Ａｃはアセチル基を表す。

In the table, the unit is mass%. TPA represents terephthalic acid, PA represents phthalic acid, SA represents succinic acid, AA represents adipic acid, PG represents 1,2-propylene glycol, EG represents ethylene glycol, and Ac represents an acetyl group.

When the solubility parameter (SP value (HOY method)) of the polycondensed ester described in the table is calculated, for example, P-3 is 22.3 (MPa) ^1/2 , and P-15 is 22.1 (MPa) ^1/2. P-41 was 22.2 (MPa) ^1/2 , which was close to 22.0 which is the SP value of cellulose acylate having an acetyl substitution degree of 2.81 and a number average molecular weight of 88,000.

The synthesis of the polycondensed ester is carried out by a conventional method such as a hot melt condensation method by a polyesterification reaction or transesterification reaction between a diol and a dicarboxylic acid, or an interfacial condensation method between an acid chloride of these acids and a glycol. Can also be easily synthesized.
In addition, the polycondensed ester according to the present invention is described in detail in Koichi Murai, “Plasticizer Theory and Application” (Kokai Shobo Co., Ltd., first edition issued on March 1, 1973). In addition, Japanese Patent Laid-Open Nos. 05-155809, 05-155810, Japanese Patent Laid-Open Nos. 05-97073, 2006-259494, 07-330670, 2006-342227, 2007-003679. The materials described in each publication can also be used. The contents described in these publications are incorporated herein.

The content of the raw material aliphatic diol, dicarboxylic acid ester, or diol ester contained in the polycondensed ester in the cellulose acylate film is preferably less than 1% by mass, and more preferably less than 0.5% by mass. Examples of the dicarboxylic acid ester include dimethyl phthalate, di (hydroxyethyl) phthalate, dimethyl terephthalate, di (hydroxyethyl) terephthalate, di (hydroxyethyl) adipate, and di (hydroxyethyl) succinate. Examples of the diol ester include ethylene diacetate and propylene diacetate.
The kind and ratio of each of the dicarboxylic acid residue, diol residue, and monocarboxylic acid residue contained in the polycondensation ester used in the present invention can be measured by a usual method using H-NMR. . Usually, deuterated chloroform can be used as a solvent.
For measurement of the hydroxyl value of the polycondensed ester, the acetic anhydride method described in Japanese Industrial Standard JIS K3342 (discontinued) can be applied. When the polycondensation ester is a polyester polyol, the hydroxyl value is preferably 55 or more and 220 or less, and more preferably 100 or more and 140 or less.

<Retardation adjuster>
The cellulose acylate film of the present invention may further contain a retardation adjusting agent.
The retardation adjusting agent is not particularly limited. For example, a triazine compound described in paragraphs 0022 to 0057 of JP-A-2003-344655, a rod-shaped compound described in paragraphs 0011 to 0032 of JP-A-2002-363343, JP-A-2005-134848, paragraphs 0056 to 0093 and JP-A 2007-119737, paragraphs 0031 to 0080, paragraphs 0256 of JP-A 2010-215879, paragraphs of JP-A 2011-69857 0026 to 0036, paragraphs 0024 to 0078 of JP 2012-208173 A, paragraphs 0022 to 0042 of JP 2012-189664 A, paragraphs 0023 to 0061 of JP 2012-123292 A, JP 2011-002633 A. Paragraph 00 of 5-0055, include compounds described in paragraphs 0023 to 0037, etc. of JP 2011-076031.
Two or more types of retardation adjusting agents can be used in combination.

  The addition amount of the retardation adjusting agent is preferably 0.1% or more and 30% or less, more preferably 0.3% or more and 20% or less, and further preferably 0.5% or more and 10% or less with respect to the cellulose ester in mass ratio. .

<Other additives>
In addition to the above, other additives may be added to the cellulose acylate film of the present invention within a range not departing from the gist of the present invention. Specifically, matting agents, release accelerators, ultraviolet absorbers described in JP-A-2006-28279, JP-A-3-199201, JP-A-5-194789, JP-A-5-271471, JP-A-6-107854. (For example, antioxidants, peroxide decomposers, radical inhibitors, metal deactivators, acid scavengers, amines) and the like described in each of the above publications.

<Method for producing cellulose acylate film>
The method for producing a cellulose acylate film having a thickness of 20 to 80 μm according to the present invention comprises cellulose acylate having a total acyl substitution degree of 2.60 to 2.95, an aromatic dicarboxylic acid residue and an aliphatic diol residue. At least one polycondensation ester is contained in an amount of 35 to 100 parts by mass with respect to 100 parts by mass of cellulose acylate, and the ratio of residues containing aromatics to all dicarboxylic acid residues in the polycondensation ester is 40 to 100 mol%. The cellulose acylate film is stretched at a magnification of 1.1 to 2.0 times in the direction perpendicular to the transport direction, and the temperature of the film drying zone after stretching is set to 30 to 90 ° C.

The film of the present invention can be preferably produced by a solvent cast method. In the solvent cast method, a film is produced using a solution (dope) in which cellulose ester is dissolved in an organic solvent.
Next, the organic solvent in which the cellulose ester of the present invention is dissolved will be described.
In the present invention, any of a chlorinated solvent containing a chlorinated organic solvent as a main solvent and a non-chlorinated solvent not containing a chlorinated organic solvent can be used as the organic solvent. Two or more organic solvents may be mixed and used.

  In preparing the cellulose ester solution of the present invention, a chlorinated organic solvent is preferably used as the main solvent. In the present invention, the type of the chlorinated organic solvent is not particularly limited as long as the object can be achieved within a range in which the cellulose ester can be dissolved, cast, and formed into a film. These chlorinated organic solvents are preferably dichloromethane and chloroform. Particularly preferred is dichloromethane. In addition, there is no particular problem in mixing an organic solvent other than the chlorinated organic solvent. In that case, it is necessary to use at least 50% by mass of dichloromethane in the total amount of the organic solvent. Other organic solvents used in combination with the chlorinated organic solvent in the present invention will be described below. That is, as another preferable organic solvent, a solvent selected from esters, ketones, ethers, alcohols, hydrocarbons and the like having 3 to 12 carbon atoms is preferable. The ester, ketone, ether and alcohol may have a cyclic structure. A compound having two or more functional groups of esters, ketones and ethers (that is, —O—, —CO— and —COO—) can also be used as a solvent. For example, other functional groups such as alcoholic hydroxyl groups can be used. You may have group simultaneously. In the case of a solvent having two or more types of functional groups, the number of carbon atoms may be within the specified range of the compound having any functional group.

  Examples of the esters having 3 to 12 carbon atoms include ethyl formate, propyl formate, pentyl formate, methyl acetate, ethyl acetate and pentyl acetate. Examples of ketones having 3 to 12 carbon atoms include acetone, methyl ethyl ketone, diethyl ketone, diisobutyl ketone, cyclopentanone, cyclohexanone, and methylcyclohexanone. Examples of the ether having 3 to 12 carbon atoms include diisopropyl ether, dimethoxymethane, dimethoxyethane, 1,4-dioxane, 1,3-dioxolane, tetrahydrofuran, anisole and phenetole. Examples of the organic solvent having two or more kinds of functional groups include 2-ethoxyethyl acetate, 2-methoxyethanol and 2-butoxyethanol.

In addition, the alcohol used in combination with the chlorinated organic solvent may be linear, branched or cyclic, and is preferably a saturated aliphatic hydrocarbon. The hydroxyl group of the alcohol may be any of primary to tertiary. Examples of the alcohol include methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, t-butanol, 1-pentanol, 2-methyl-2-butanol and cyclohexanol. As the alcohol, fluorine-based alcohol is also used. Examples thereof include 2-fluoroethanol, 2,2,2-trifluoroethanol, 2,2,3,3-tetrafluoro-1-propanol and the like. Further, the hydrocarbon may be linear, branched or cyclic. Either aromatic hydrocarbons or aliphatic hydrocarbons can be used. The aliphatic hydrocarbon may be saturated or unsaturated. Examples of hydrocarbons include cyclohexane, hexane, benzene, toluene and xylene.
As other solvents, for example, the solvents described in JP-A-2007-140497 can be used.

A cellulose ester solution can be prepared by a general method comprising treatment at a temperature of 0 ° C. or higher (ordinary temperature or high temperature). The solution can be prepared by using a dope preparation method and apparatus in a normal solvent cast method. In the case of a general method, halogenated hydrocarbon (especially dichloromethane) and alcohol (especially methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, t-butanol, 1) -Pentanol, 2-methyl-2-butanol and cyclohexanol) are preferably used.
The amount of the cellulose ester is adjusted so as to be contained in the obtained solution by 10 to 40% by mass. The amount of cellulose ester is more preferably 10 to 30% by mass. Arbitrary additives described later may be added to the organic solvent (main solvent).
The solution can be prepared by stirring the cellulose ester and the organic solvent at room temperature (0 to 40 ° C.). The high concentration solution may be stirred under pressure and heating conditions. Specifically, the cellulose ester and the organic solvent are placed in a pressure vessel and sealed, and stirred while heating to a temperature not lower than the boiling point of the solvent at normal temperature and in a range where the solvent does not boil. Moreover, it can also pressurize and heat after stirring at normal temperature, or can stir under pressurization and heating conditions after stirring at normal temperature.
The heating temperature is usually 40 ° C. or higher, preferably 60 to 200 ° C., more preferably 80 to 120 ° C., and particularly preferably 90 to 115 ° C.

Each component may be coarsely mixed in advance and then placed in a container. Moreover, you may put into a container sequentially. The container needs to be configured so that it can be stirred. The container can be pressurized by injecting an inert gas such as nitrogen gas. Moreover, you may utilize the raise of the vapor pressure of the solvent by heating. Or after sealing a container, you may add each component under pressure.
When heating, it is preferable to heat from the outside of the container. For example, a jacket type heating device can be used. The entire container can also be heated by providing a plate heater outside the container and piping to circulate the liquid.
It is preferable to provide a stirring blade inside the container and stir using this. The stirring blade preferably has a length that reaches the vicinity of the wall of the container. A scraping blade is preferably provided at the end of the stirring blade in order to renew the liquid film on the vessel wall.
Instruments such as a pressure gauge and a thermometer may be installed in the container. Each component is dissolved in a solvent in the container. The prepared dope is taken out of the container after cooling, or taken out and then cooled using a heat exchanger or the like.
Alternatively, two or more different solutions may be prepared in separate containers, and then the solutions may be mixed to prepare the dope. Each solution can also be added in-line to the dope prepared first.

<< Casting >>
A cellulose acetate film is produced from the prepared cellulose ester solution (dope) by a solvent cast method. It is preferable to add the compound having at least two aromatic rings to the dope.
The dope can be cast on a drum or band and the solvent evaporated to form a film. It is preferable to adjust the concentration of the dope before casting so that the solid content is 5 to 40%. The surface of the drum or band is preferably finished in a mirror state. The dope is preferably cast on a drum or band having a surface temperature of 30 ° C. or lower, and particularly preferably a metal support temperature of −10 ° C. to 20 ° C. Further, JP 2000-301555, JP 2000-301558, JP 07-032391, JP 03-193316, JP 05-086212, JP 62-037113, JP 02-276607. The methods described in JP-A Nos. 55-014201, 02-111511, and 02-208650 can be used in the present invention.

<< Dry >>
The dope drying on the metal support involved in the production of the cellulose acetate film is generally performed by applying hot air from the surface side of the metal support (drum or band), that is, the surface of the web on the metal support, drum Alternatively, a method of applying hot air from the back side of the band, a liquid whose temperature is controlled is brought into contact with the back side opposite to the band or drum dope casting surface, and the drum or band is heated by heat transfer to control the surface temperature. Although there is a heat method, the back surface liquid heat transfer method is preferable. The surface temperature of the metal support before casting may be any number as long as it is not higher than the boiling point of the solvent used for the dope. However, in order to promote drying and to lose fluidity on the metal support, the temperature should be set to 1 to 10 ° C. lower than the boiling point of the lowest boiling solvent. Is preferred. Note that this is not the case when the casting dope is cooled and peeled off without drying.
The Re value and Rth value of the cellulose acetate film can also be adjusted by adjusting the temperature on the metal support on which the dope film is cast, the temperature of the drying air applied to the dope film cast on the metal support, and the air volume. Can be adjusted. In particular, the Rth value is greatly affected by the drying conditions on the metal support. Increasing the temperature of the metal support, or increasing the temperature of the drying air applied to the dope film, or increasing the air volume of the drying air, that is, increasing the amount of heat applied to the dope film decreases the Rth value. Rth is increased by reducing. In particular, the drying of the first half part immediately after casting and before peeling off greatly affects the Rth value.

  Regarding the drying method in the solvent cast method, U.S. Pat. Nos. 45-4554, 49-5614, JP-A-60-176834, JP-A-60-203430, and JP-A-62-115035. Drying on the band or drum can be performed by blowing air or an inert gas such as nitrogen.

  The obtained film can be peeled off from the drum or band and further dried with high-temperature air whose temperature is successively changed from 100 to 160 ° C. to evaporate the residual solvent. The above method is described in Japanese Patent Publication No. 5-17844. According to this method, it is possible to shorten the time from casting to stripping. In order to carry out this method, it is necessary for the dope to gel at the surface temperature of the drum or band during casting.

In the solution casting method of the present invention, when casting a dope, it can be formed into a film using two or more kinds of dopes.
As a method using two or more kinds of dopes, simultaneous lamination co-casting or sequential lamination co-casting can also be performed. Furthermore, you may combine both casting. When performing simultaneous lamination and co-casting, a casting die to which a feed block is attached may be used, or a multi-manifold casting die may be used. It is preferable that at least one of the thickness of the layer on the air surface side and the thickness of the layer on the support side is 0.5% to 30% of the thickness of the entire film of the film composed of multiple layers by co-casting.
When performing simultaneous lamination co-casting, it is preferable that the high-viscosity dope is wrapped with the low-viscosity dope when the dope is cast from the die slit to the support. The solid content concentration of the outer layer dope is preferably equal to or less than the solid content concentration of the inner layer dope, more preferably 1% by mass or more, and more preferably 3% by mass or more. More preferably it is. Further, it is preferable that the composition ratio of the dope alcohol in contact with the outside world is equal to or greater than the composition ratio of the inner dope alcohol. The alcohol addition amount of the outer layer dope is preferably 1.0 to 6.0 times, more preferably 1.0 to 4.0 times, and more preferably 1.0 to 3.0 times that of the inner layer. It is particularly preferred that
Also, using two casting ports, the film formed on the support by the first casting port is peeled off, and the second casting is performed on the side that was in contact with the support surface to produce a film. You can also For example, the method described in Japanese Patent Publication No. 44-20235 can be mentioned.

  As the cellulose acylate solution to be cast, the same solution may be used, or different cellulose acylate solutions may be used. In order to give a function to a plurality of cellulose acylate layers, a cellulose acylate solution corresponding to the function may be extruded from each casting port. Furthermore, the cellulose acylate solution of the present invention can be cast simultaneously with other functional layers (for example, an adhesive layer, a dye layer, an antistatic layer, an antihalation layer, an ultraviolet absorbing layer, a polarizing layer, etc.).

  In the conventional single-layer solution, it is necessary to extrude a cellulose acylate solution having a high concentration and a high viscosity in order to obtain a necessary film thickness. In such a case, the stability of the cellulose acylate solution is poor and solid matter is generated, which often causes problems due to defects or poor flatness. As a solution to this problem, by casting a plurality of cellulose ester solutions from a plurality of casting ports, it is possible to extrude a highly viscous solution onto the support at the same time. Not only can a film be produced, but also the use of a concentrated cellulose acylate solution can achieve a reduction in drying load and increase the production speed of the film.

<< Extension >>
In the cellulose acylate film of the present invention, the retardation can be adjusted by a stretching treatment. For example, JP-A-62-115035, JP-A-4-152125, JP-A-4-284111, and JP-A-4-298310 can be used for positively stretching in the width direction (perpendicular to the conveying direction). And JP-A-11-48271. The stretching of the film can be carried out at room temperature or under heating conditions. The temperature during stretching is preferably 100 to 200 ° C, more preferably 120 ° C to 180 ° C, and further preferably 130 to 160 ° C.

The film may be stretched uniaxially only in the transport direction (TD) or in the width direction (MD, the direction orthogonal to the transport direction) or simultaneously or sequentially biaxially stretch, but it is preferable to stretch more in the TD direction. Stretching in the MD direction is preferably 1.0 to 1.3, and stretching in the TD direction is preferably 1.1 to 2.0 times, more preferably 1.15 to 1.9 times, and 1.15 to 1 .8 times is more preferable.
The stretching process may be performed in the middle of the film forming process, or the original fabric that has been formed and wound may be stretched.
When stretching is performed in the middle of the film forming process, stretching may be performed in a state including the residual solvent amount, and the residual solvent amount = (residual volatile matter mass / heat-treated film mass) × 100% is 0.05. It can be preferably stretched at -50%.
In the case of stretching the film that has been formed and wound, it is preferable to stretch the film in the width direction 1.1 to 2.0 times in a state where the residual solvent amount is 0 to 5%.

Further, the cellulose acylate film of the present invention may be biaxially stretched. Biaxial stretching includes simultaneous biaxial stretching and sequential biaxial stretching, but sequential biaxial stretching is preferred from the viewpoint of continuous production, and after casting the dope, the film is peeled off from the band or drum, After stretching in the width direction, the film is stretched in the longitudinal direction, or stretched in the longitudinal direction and then stretched in the width direction.
In order to relieve residual strain in stretching, reduce dimensional change, and to reduce variations in the width direction of the in-plane slow axis, it is preferable to provide a relaxation step after transverse stretching. In the relaxation step, it is preferable to adjust the width of the film after relaxation to a range of 100 to 70% (relaxation rate of 0 to 30%) with respect to the width of the film before relaxation. The temperature in the relaxation step is preferably an apparent glass transition temperature Tg-50 to Tg + 50 ° C. of the film. In normal stretching, in the relaxation rate zone after passing through this maximum widening rate, the time until it passes through the tenter zone is shorter than 1 minute.
Here, the apparent Tg of the film in the stretching process is that the film containing the residual solvent is enclosed in an aluminum pan, and the temperature is increased from 25 ° C. to 200 ° C. at 20 ° C./min with a differential scanning calorimeter (DSC). Tg was determined by obtaining an endothermic curve.

<< Dry after stretching >>
In this invention, it is preferable to dry after extending | stretching, It is preferable that the temperature of the film drying zone after extending | stretching shall be 100 degrees C or less, It is more preferable that it is 30 to 90 degreeC, More preferably, it is 50 to 80 degreeC More preferably, it is 60 degreeC-80 degreeC, Most preferably, it is 65 degreeC-75 degreeC.
When the stretching process is performed during the film forming process, the film can be dried while being conveyed.
In this invention, since there are many compounding quantities of polycondensation ester, it becomes easy to soften at the time of drying. Since the film of the present invention is produced by being conveyed in the MD direction, if the drying temperature is too high, the film is stretched in the MD direction and residual distortion occurs in the film. As a result, the dimensional change in the MD direction when wet heat is applied increases. In particular, since the film of the present invention is stretched, the dimensional change tends to be large. With such a film, if the drying temperature is too high, the dimensional change exceeds ± 0.5%, and display unevenness tends to occur when the display device is exposed to a moist heat environment.
The film containing a large amount of the polycondensed ester of the present invention dries the solvent faster than a film having a low content. Although it is only an estimate, there is a possibility that the solvent is easily removed from the film during drying due to the progress of plasticization by the polycondensed ester. Moreover, since the thickness of the film of this invention is as thin as 20-80 micrometers, drying is quick.
For this reason, a dimensional change can be effectively suppressed by making the temperature of the drying zone after extending | stretching low. That is, by setting the temperature of the drying zone to 90 ° C. or lower, the solvent is volatilized, but softening of the cellulose acylate can be suppressed. As a result, the dimensional change can be more effectively suppressed.

The drying time is not particularly limited, but is preferably 5 minutes to 40 minutes.
By selecting the optimal post-stretching drying temperature, the residual stress of the cellulose acylate film produced is relaxed, and the dimensional change, optical property change, and slow axis orientation change at high temperature and high temperature and high humidity are reduced. can do.

<< Heat treatment >>
In the case where the raw film that has been formed and wound is stretched, the stretched film may be manufactured through a process of further heat treatment. By passing through the heat treatment step, the residual stress of the produced cellulose acetate film is relaxed, and the dimensional change, optical property change, and slow axis orientation change under high temperature and high temperature and high humidity are reduced, which is preferable. Although the temperature at the time of a heating does not have a restriction | limiting in particular, 100 to 200 degreeC is preferable.

<< Heating steam treatment >>
In addition, the stretched film may be manufactured through a process of spraying water vapor heated to 100 ° C. or higher. By passing through this water vapor spraying process, the residual stress of the cellulose acetate film to be produced is relaxed, and the dimensional change, optical property change, and slow axis orientation change under high temperature and high temperature and high humidity become small. Therefore, it is preferable. The temperature of the water vapor is not particularly limited as long as it is 100 ° C. or higher, but considering the heat resistance of the film, the temperature of the water vapor is 200 ° C. or lower.

  These steps from casting to post-drying may be performed in an air atmosphere or an inert gas atmosphere such as nitrogen gas. The winder used for producing the cellulose acetate film of the present invention may be a commonly used winder such as a constant tension method, a constant torque method, a taper tension method, a program tension control method with a constant internal stress. Can be rolled up.

<Performances of cellulose acylate film>
The film of the present invention may be a single layer film or may have a laminated structure of two or more layers, but is preferably a single layer film.

<< Film thickness >>
The film of the present invention has a thickness of 20 to 80 μm. By using such a thin film, a thin polarizing plate and a thin liquid crystal display device can be obtained. The film thickness of the film of the present invention is preferably 20 to 75 μm, and more preferably 30 to 60 μm.

<< Film width >>
The film of the present invention preferably has a film width of 1000 mm or more, more preferably 1500 mm or more, and particularly preferably 1800 mm or more.

<< Half Width of Peak with Largest Tantan Value in Dynamic Viscoelasticity Measurement >>
In the film of the present invention, the half width of the peak having the largest tan δ value in the dynamic viscoelasticity measurement is preferably within 90 ° C, and more preferably within 80 ° C. The half width of the peak with the largest tan δ value in the dynamic viscoelasticity measurement is an index indicating the compatibility of cellulose acylate and other additives, and this value is within 80 ° C. so that the compatibility is excellent. As a result, the haze of the film can be reduced.

<< Haze >>
The film of the present invention preferably has an internal haze of 2% or less, more preferably 1% or less, and still more preferably 0.01 to 0.5%.

<< Photoelastic coefficient >>
The photoelastic coefficient of the film of the present invention is preferably 50 × 10 ⁻¹³ cm ² / dyne or less in order to reduce the color change with time of the liquid crystal display device.
As a specific measurement method, a tensile stress is applied to the long axis direction of a film sample 10 mm × 100 mm, the retardation at that time is measured with an ellipsometer (M150, JASCO Corporation), and the retardation for the stress is measured. The photoelastic coefficient is calculated from the amount of change.

<< Retardation >>
The Re (550) of the film of the present invention preferably satisfies the following (formula 1) and satisfies (formula 1 ′).
Moreover, as Rth (550) of the film of this invention, it is preferable to satisfy | fill (Formula 2) and to satisfy | fill (Formula 2 ').
Re and Rth can be measured using KOBRA 21ADH (manufactured by Oji Scientific Instruments).
(Formula 1) 30 ≦ Re (550) ≦ 100 nm
(Formula 1 ′) 30 ≦ Re (550) ≦ 80 nm
(Formula 2) 90 ≦ Rth (550) ≦ 170 nm
(Formula 2 ′) 93 ≦ Rth (550) ≦ 150 nm

  In this specification, Re (λ) and Rth (λ) represent in-plane retardation and retardation in the thickness direction at the wavelength λ, respectively. In the present specification, the wavelength λ is 550 nm unless otherwise specified. Re (λ) is measured by making light having a wavelength of λ nm incident in the normal direction of the film in KOBRA 21ADH (manufactured by Oji Scientific Instruments). Rth (λ) is Re (λ), with the in-plane slow axis (determined by KOBRA 21ADH) as the tilt axis (rotary axis) (in the absence of the slow axis, any direction in the film plane) Is measured in 6 points from the inclined direction in 10 degree steps from the normal direction to 50 degrees on one side with respect to the normal direction of the film. KOBRA 21ADH calculates based on the retardation value, the assumed average refractive index, and the input film thickness value. The retardation value is measured from any two directions with the slow axis as the tilt axis (rotation axis) (in the absence of the slow axis, the arbitrary direction in the film plane is the rotation axis), and the value Rth can also be calculated from the following formula (A) and formula (B) based on the assumed average refractive index and the input film thickness value. Here, as the assumed value of the average refractive index, values in the polymer handbook (John Wiley & Sons, Inc.) and catalogs of various optical films can be used. Those whose average refractive index is not known can be measured with an Abbe refractometer. The average refractive index values of main optical films are exemplified below: cellulose acylate (1.48), cycloolefin polymer (1.52), polycarbonate (1.59), polymethyl methacrylate (1.49), Polystyrene (1.59). The KOBRA 21ADH calculates nx, ny, and nz by inputting the assumed value of the average refractive index and the film thickness. Nz = (nx−nz) / (nx−ny) is further calculated from the calculated nx, ny, and nz.

Here, Re (θ) represents a retardation value in a direction inclined by an angle θ from the normal direction, nx, ny, and nz represent refractive indexes in respective principal axis directions of the refractive index ellipsoid, and d represents a film. Represents thickness.
Rth = ((nx + ny) / 2−nz) × d Formula (B)
At this time, an average refractive index n is required as a parameter, and a value measured by an Abbe refractometer (“Abbe refractometer 2-T” manufactured by Atago Co., Ltd.) was used.

<Polarizing plate>
The cellulose acylate film of the present invention functions as a retardation film, but is preferably incorporated as a protective film for a polarizing plate.
That is, the polarizing plate of the present invention includes a polarizer and at least one cellulose acylate film of the present invention on at least one side of the polarizer. Hereinafter, the polarizing plate of the present invention will be described.

Like the film of the present invention, the polarizing plate of the present invention is not only a polarizing plate in the form of a film piece cut into a size that can be incorporated into a liquid crystal display device as it is, but also in a long form by continuous production. The polarizing plate of the aspect (for example, aspects with roll length 2500m or more, 3900m or more) wound up in roll shape is also contained. In order to use for a large-screen liquid crystal display device, the width of the polarizing plate is preferably 1470 mm or more as described above.
In the polarizing plate of this invention, it is preferable that the film thickness of a polarizer is 3-20 micrometers, and it is more preferable that it is 5-20 micrometers.

In the polarizing plate of the present invention, at least one side of the polarizing plate protective film includes the film of the present invention, and a known cellulose acylate film can be used as the other polarizing plate protective film. The thickness of the other polarizing plate protective film is preferably 10 to 70 μm, and more preferably 20 to 65 μm.
In the present invention, it is also preferable to use a protective film having a moisture permeability of 100 g / m ² or less at 40 ° C. and 90% relative humidity for 24 hours for one of the protective films of the polarizing plate. By using such a film, it is possible to obtain a polarizing plate having a small change in elastic modulus and a small warpage. It is more preferable that the low moisture permeability protective film has a moisture permeability of 0.1 to 100 g / m ² at 40 ° C. and 90% relative humidity for 24 hours. In the case where a polarizing plate using such a low moisture permeability protective film is incorporated in a liquid crystal display device, it is preferable to provide a low moisture permeability protective film on the viewer side.

  Examples of the low moisture permeability protective film include polyester film, cycloolefin film, polycarbonate film, polyolefin film, polyacryl film, and mixed resin film of acrylic resin and cellulose ester resin.

As a polyester film, a polyethylene terephthalate film and a polyethylene naphthalate film are preferable. As a cycloolefin film, it is a norbornene-type film and the cycloolefin film of Unexamined-Japanese-Patent No. 2010-78700 can use it preferably. Commercially available products include Zeonoa, Zeonex (manufactured by Nippon Zeon Co., Ltd.), and APEL (manufactured by Mitsui Chemicals, Inc.).

As the polycarbonate film, commercially available products include Pure Ace, Pure Ace WR (manufactured by Teijin Chemicals Ltd.), and Elmec (manufactured by Kaneka Corp.). Examples of the polyolefin film include a polyethylene film, a polypropylene film, and a polymethylpentene film. An example of the polyacryl film is a polymethyl methacrylate film.

These can be produced by known methods.

Furthermore, the total thickness of the polarizing plate of the present invention is preferably 40 to 130 μm, more preferably 50 to 120 μm, and particularly preferably 65 to 100 μm. The total thickness here is intended to include an adhesive layer for bonding the polarizing plate protective film in addition to the polarizing plate and the polarizing plate protective film bonded to both sides of the polarizer.
The specific configuration of the polarizing plate of the present invention is not particularly limited, and a known configuration can be employed. For example, the configuration described in FIG. 6 of JP-A-2008-262161 can be employed.

<Liquid crystal display device>
The liquid crystal display device of the present invention includes at least one polarizing plate of the present invention. Since the liquid crystal display device of the present invention includes the polarizing plate of the present invention including the film of the present invention, the contrast in the front direction and the color change in the viewing angle direction are remarkably improved.
In the liquid crystal display device of the present invention, the glass constituting the liquid crystal cell preferably has a thickness of 50 to 500 μm. By using such glass, the thickness of the liquid crystal display device can be reduced.
The liquid crystal display device of the present invention is a liquid crystal display device having a liquid crystal cell and a pair of polarizing plates disposed on both sides of the liquid crystal cell, wherein at least one of the polarizing plates is the polarizing plate of the present invention. A VA, IPS, or OCB mode liquid crystal display device is preferable, and a VA mode liquid crystal display device is more preferable.
The specific configuration of the liquid crystal display device of the present invention is not particularly limited, and a known configuration can be adopted. For example, an example having the configuration shown in FIG. 2 can be adopted. Further, the configuration described in FIG. 2 of JP-A-2008-262161 can also be preferably employed.

  The present invention will be described more specifically with reference to the following examples. The materials, amounts used, ratios, processing details, processing procedures, and the like shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention is not limited to the specific examples shown below.

<Film formation of cellulose acetate film>
Using the cellulose acetate dope A shown below, a film was formed by a solution casting method and used for each example and comparative example.

Cellulose acetate dope A
――――――――――――――――――――――――――――――――――――――
Cellulose acetate: acetyl group substitution degree listed in the table below 100 parts by weight Polycondensation ester: A type listed in the table below was added in the amount listed in the table below. Retardation regulator: A- listed in the table below Dichloromethane 406 parts by mass Methanol 61 parts by mass with any of 1 to A-9 listed in the table below (unit: mass%) ---------- ―――――――――――――――――――

  The polycondensed ester was synthesized according to the description in JP-A No. 05-155809. That is, the dicarboxylic acid and diol described in the following table were used, and the ends were sealed with the groups described in the following table.

表中、単位は質量％である。ＴＰＡはテレフタル酸、ＰＡはフタル酸、ＡＡはアジピン酸、ＳＡはコハク酸、ＰＧは１，２−プロピレングリコール、ＥＧはエチレングリコール、Ａｃはアセチル基を表す。

In the table, the unit is mass%. TPA represents terephthalic acid, PA represents phthalic acid, AA represents adipic acid, SA represents succinic acid, PG represents 1,2-propylene glycol, EG represents ethylene glycol, and Ac represents an acetyl group.

  Retardation adjusting agents are disclosed in JP2010-215879A, JP2011-69857A, JP2012-208173A, JP2012-189664A, JP2012-123292A, JP10-123292A, respectively. The compounds were synthesized according to the methods described in JP2011-002633A and JP2011-076031A. The structures of the retardation adjusting agents A-1 to A-9 are described below (A-8 and A-9 are commercial products of Tokyo Chemical Industry Co., Ltd.).

  Cellulose acylate dope A has a matting agent (AEROSIL R972, manufactured by Nippon Aerosil Co., Ltd., secondary average particle size of 1.0 μm or less) as 0.13 parts by mass with respect to 100 parts by mass of cellulose acylate. The matting agent dispersion was mixed and stirred.

Solution casting in a single layer The dope having the above composition is put into a mixing tank, stirred to dissolve each component, and then filtered through a filter paper having an average pore size of 34 μm and a sintered metal filter having an average pore size of 10 μm to obtain cellulose acylate. A dope was prepared. The dope was cast with a band casting machine. The band was made of SUS.
The film surface temperature of the film in the stretching zone dried in the tenter device using a tenter device that transports the film peeled off from the band by clipping both ends of the web with a clip is the temperature (stretching temperature) listed in the table. While applying hot air, the film was stretched with a tenter in the transverse direction (direction perpendicular to the conveying direction) at the stretching ratios shown in the following table. Thereafter, the film was transferred from the tenter conveyance to the roll conveyance, and further dried at the film surface temperature (drying temperature) described in the following table and wound up. The film thickness at this time is shown in the following table.

<Evaluation>
<< Moisture content change by water contact test >>
The processed film was cut into 3 cm square and immersed in water at 40 ° C. for 16 hours. After dipping, the film was taken out, wiped off the water on the surface, and then conditioned for 3 hours in an environment of 25 ° C. and 80% relative humidity. Thereafter, the film was placed in a sealed container, and the water content was measured with a Karl Fischer moisture measuring device (AQ-2100, manufactured by Hiranuma Sangyo Co., Ltd.). The moisture content of the film in the initial state was measured by the same method after cutting the processed film into 3 cm squares, adjusting the humidity for 3 hours in an environment of 25 ° C. and 80% relative humidity. The absolute value of the difference between the moisture content after the water treatment and the moisture content in the initial state was defined as the moisture content change (unit: mass%). The results are shown in the following table.

<< Dimension change rate >>
The film of the present invention more preferably satisfies the following formula (7) in the direction of film conveyance and the direction orthogonal thereto at a dimensional change rate of about 24 hours at 60 ° C. and 90% relative humidity.
−0.5% ≦ {(L′−L0) / L0} × 100 ≦ 0.5% (7)
The L0 represents the film length after conditioning for 2 hours or more in an atmosphere of 25 ° C. and a relative humidity of 60%, and L ′ is 24 hours at 60 ° C. and 90% relative humidity, and further conditioned for 2 hours. Represents film length.

<< Calculation of half width of tan δ value by dynamic viscoelasticity measurement >>
Sample the film before stretching, cut the sample into 20 mm (width direction) x 5 mm (conveyance direction), and use DVA-225 manufactured by IT Measurement Control Co., Ltd., and set strain to 0.1% increase in tension mode The temperature was raised from 25 ° C. to 200 ° C. at a rate of 5 ° C./min, and the peak (peak corresponding to relaxation of the main chain of the polymer) temperature (T1) at which the tan δ value was the largest was determined. After creating the temperature vstan δ plot, a value (half value) that is half the value of the tan δ peak was calculated, and a temperature (T2) that was half value on the lower temperature side than the tan δ peak temperature was obtained. The half width was calculated from the following equation.
(Half width) = (T1-T2) × 2

<< Haze >>
The haze was measured using a turbidimeter (NDH2000, Nippon Denshoku Industries Co., Ltd.) for a film that was allowed to stand for 24 hours in an environment of 23 ° C. and a relative humidity of 55%.

  In the said table | surface, the addition amount of polycondensation ester is shown with the quantity (unit: mass part) with respect to 100 mass parts of cellulose acetate.

  As is clear from the above results, the thickness of the comparative example 1 could not be reduced, and the comparative examples 2, 3, and 7 could not achieve the predetermined retardation. In Comparative Examples 4 to 6, the moisture content change and the dimensional change were large. In Comparative Example 8, the predetermined retardation could not be achieved, and the dimensional change was large.

In addition, the polarizing plate 17-20 used the film shown in the following table | surface as a protective film.
PMMA: Polymethylmethacrylate film 40 μm (moisture permeability 80 g / m ² / day)
PET: Polyethylene terephthalate film 40 μm (moisture permeability 15 g / m ² / day)
COP: cycloolefin film 40 μm: ZEONOR film ZF14-040 manufactured by Nippon Zeon Co., Ltd. (moisture permeability 1 g / m ² / day)

<< Measurement of moisture permeability of protective film >>
The moisture permeability of the protective film was measured by a method (40 ° C. and 90% RH) specified by a moisture permeability test method (cup method) of JISZ0208 moisture-proof packaging material.

<Preparation of polarizing plate>
With reference to the description in paragraphs 0165 to 0175 of JP2012-103657A, the device was produced as follows.
A polyvinyl alcohol film having a thickness of 60 μm was swollen with water at 35 ° C. and immersed in an aqueous solution consisting of 0.075 g of iodine, 5 g of potassium iodide and 100 g of water, then 3 g of potassium iodide and 7. It was immersed in a 45 ° C. aqueous solution consisting of 5 g and 100 g of water and uniaxially stretched (temperature 55 ° C., stretch ratio 5 times). This was washed with water and dried to obtain a polarizer.

Subsequently, a polarizer, the cellulose acylate film, and TD60UL (manufactured by FUJIFILM Corporation) were bonded together according to the following steps 1 to 5 to produce a polarizing plate.
Step 1: Soaked in a 2 mol / L sodium hydroxide solution at 60 ° C. for 90 seconds, then washed with water and dried to obtain a cellulose acetate film saponified on the side to be bonded to the polarizer.
Process 2: The said polarizer was immersed in the polyvinyl alcohol adhesive tank of 2 mass% of solid content for 1-2 seconds.
Step 3: Excess adhesive adhered to the polarizer in Step 2 was lightly wiped off, and this was placed on the cellulose ester film treated in Step 1.
Process 4: The cellulose ester film laminated | stacked at the process 3, the polarizer, and the back side cellulose-ester film were bonded by the pressure of 20-30 N / cm <2>, and the conveyance speed about 2 m / min.
Step 5: A sample obtained by bonding the polarizer, the cellulose ester film, and TD60UL prepared in Step 4 in a drier at 70 ° C. was dried for 2 minutes, and polarizing plates corresponding to the cellulose ester films were prepared.

 Films other than the cellulose ester film were bonded to the polarizer as follows.

 A film with an adhesive obtained by applying the following ultraviolet (UV) curable adhesive on the film to a thickness of 5 μm using a micro gravure coater (gravure roll: # 300, rotational speed 140% / line speed). It was. Then, this was bonded together with the cellulose ester film with the roll machine to the polarizer immersed in the said polyvinyl alcohol adhesive agent.

 Electron beams were irradiated from both sides of the bonded film to obtain a polarizing plate having films on both sides of the polarizer. The line speed was 20 m / min, the acceleration voltage was 250 kV, and the irradiation dose was 20 kGy.

<< UV curing adhesive >>
An ultraviolet curable adhesive was prepared by blending 100 parts by mass of 2-hydroxyethyl acrylate and 11 parts by mass of ditrimethylolpropane tetraacrylate (manufactured by Sartomer Japan, trade name SR355).

<Production of liquid crystal display device>
A polarizing plate and a retardation plate on the front and back sides of a VA mode liquid crystal TV (UN46ES7000F, manufactured by Samsung) were peeled off and used as a liquid crystal cell. A polarizing plate described in Table 5 was bonded to a VA liquid crystal cell using an adhesive to produce a liquid crystal display device. At this time, they were bonded so that the absorption axes of the upper and lower polarizing plates were orthogonal to each other. The black luminance in the front direction was measured using a measuring device (EZ-Contrast XL88, manufactured by ELDIM) during black display in a dark room. In any liquid crystal display device, the black luminance in the front direction was 0.05 cd / m ² .

<Evaluation of liquid crystal display device>
<< Water contact unevenness >>
Each produced polarizing plate was cut out to 10 cm x 10 cm, and was bonded together to the VA mode liquid crystal display device. With the prepared liquid crystal display lying on its side, a 1 cm × 8 cm Bencot (manufactured by Asahi Kasei Co., Ltd.) was placed at 45 ° with respect to the absorption axis of the polarizing plate at the center of the viewing-side polarizing plate surface. Using a micropipette, 200 μl of pure water was dropped on the bencott, and the polarizing plate was immediately covered with Saran Wrap (registered trademark) (manufactured by Asahi Kasei Home Products), and the periphery was attached and sealed with Kapton tape (manufactured by Nitto Denko Corporation). . In this state, the panel was turned on and allowed to stand for 16 hours. Thereafter, the PET film was removed, the water on the film surface was wiped off, and after lighting for 24 hours, the panel was observed from the front direction when displaying black in a dark room to observe the presence or absence of unevenness.
Furthermore, the black luminance of the water contact portion and its peripheral portion was measured using a measuring device (EZ-Contrast XL88, manufactured by ELDIM) during black display in a dark room.
A: The difference in light leakage between the water contact portion and its periphery is 0.01 cd / m ² or less (not visually recognized at all).
B: The difference in light leakage between the water contact portion and its periphery is 0.01 to 0.05 cd / m ² or less (almost visually invisible).
C: The difference in light leakage between the water contact portion and its periphery is 0.05 to 0.1 cd / m ² (slightly visible but difficult to see)
D: The difference in light leakage between the water contact portion and its periphery is 0.1 cd / m ² or more (clearly visible)
Based on the above results, the practical levels were A and B.

<< Display performance after wet heat test >>
The liquid crystal display device mounted with each of the polarizing plates was left to stand in an environment of 60 ° C. and 90% for 1 day, then taken out, observed in a black display state at 23 ° C. and 55% environment, and screen uniformity when observed from the front. Evaluated.
A: Light leakage is hardly visually recognized. B: Light leakage is slightly visually recognized on a part of the screen.
C: Many light leaks were visually recognized.

<Evaluation of oblique light leakage>
The prepared liquid crystal display device mounted with each polarizing plate was lit in a dark room, observed in a black display state, and light leakage when observed from a polar angle of 60 degrees and an azimuth angle of 45 degrees was observed according to the following criteria.
A: Almost no light leakage is visually recognized B: Some light leakage is visually recognized C: Remarkable light leakage is visually recognized

DESCRIPTION OF SYMBOLS 1 Antistatic bag 2 Polarizing plate 3 Polarizer 4 Cellulose acylate film 5 Phase difference film 6 Condensation water 7 Distortion 22 Protective film 12 Viewing side polarizer 15 Phase difference film 13 Liquid crystal layer 14 Phase difference film 11 Backlight side polarizer 21 Protective film

Claims (6)

Cellulose acylate having a total acyl substitution degree of 2.60 to 2.95, and at least one polycondensed ester containing an aromatic dicarboxylic acid residue and an aliphatic diol residue, A cellulose acylate film containing 100 parts by mass and having a residue ratio of 40 to 100 mol% with respect to all dicarboxylic acid residues in the polycondensed ester is 1.1 to 2. A method for producing a cellulose acylate film having a thickness of 20 to 80 μm, comprising stretching at a magnification of 0 times and further setting the temperature of the film drying zone after stretching to 30 to 90 ° C. The equilibrium water content change by the Karl Fischer method at 25 ° C and 80% relative humidity of the film before and after immersing the cellulose acylate film in pure water at 40 ° C for 16 hours is 1.0 mass% or less. A method for producing a cellulose acylate film. The method for producing a cellulose acylate film according to claim 1 or 2, wherein a rate of dimensional change before and after the cellulose acylate film is allowed to stand for 24 hours in an environment of 60 ° C and 90% relative humidity is ± 0.5% or less. The method for producing a cellulose acylate film according to any one of claims 1 to 3, wherein a half-width of a peak having the largest tan δ value in dynamic viscoelasticity measurement is within 90 ° C. The manufacturing method of the cellulose acylate film of any one of Claims 1-4 whose ratio of the terephthalic acid residue with respect to all the dicarboxylic acid residues in the said polycondensation ester is 40 mol% or more. The method for producing a cellulose acylate film according to claim 1, wherein the film thickness is 30 to 60 μm.

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