JP5955257B2 - Cellulose acetate film, polarizing plate and liquid crystal display device - Google Patents

Description

  The present invention relates to a cellulose acetate film, a polarizing plate using the same, and a liquid crystal display device. In particular, the present invention relates to a cellulose acetate 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 polyester plasticizer is blended in a cellulose resin composition in an amount of 3 to 50 parts by mass or more with respect to 100 parts by mass of the cellulose resin, thereby being excellent in moisture permeability.
Patent Document 2 describes that moisture resistance is excellent by blending a predetermined ester compound with a cellulose ester film.

WO2010 / 087219 pamphlet JP 2006-282987 A

Incidentally, in recent years, in order to reduce the cost of a liquid crystal display device, after assembling a liquid crystal cell, it is transported and the cell is assembled in a panel at another location. At this time, there was a case where dew condensation occurred during transportation or storage, and it turned out that display unevenness occurs in a part corresponding to the dewed part when the cell is turned on after being assembled into a panel. This point will be described in more detail. Usually, a liquid crystal cell 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 cell 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. In the portion where the condensed water is accumulated, the equilibrium moisture content increases, and after the lighting of the panel, distortion 7.7 caused by the difference in the equilibrium moisture content occurs between the portion where the condensed water is accumulated and the portion where the condensed water is not accumulated. . And when this inventor examined, it turned out that this distortion influences an optical characteristic. In addition, it was found that the phase difference also changed in the portion where the condensed water accumulated. Due to these effects, display unevenness from the front and oblique directions when incorporated in a liquid crystal display device occurs.
The present invention is intended to solve such problems, and is a cellulose ester film having a small thickness, and when incorporated in a liquid crystal display device, display unevenness from the front and oblique directions due to condensation is achieved. An object is to provide a cellulose acetate film which is not easily formed.

  As a result of intensive studies by the inventors of the present invention based on the above problems, the cellulose acetate having an acetyl substitution degree of 2.40 to 2.60 has a property of easily containing moisture, and further contains moisture once. In addition, there is a problem that it is easier to attract water. On the other hand, since the polycondensed ester is hydrophobic, it can be made hydrophobic when blended in the membrane. Furthermore, when the proportion of the polycondensed ester in the membrane is increased, the proportion of cellulose acetate in the membrane can be relatively reduced, and the equilibrium water content change can be further suppressed. However, when a large amount of polycondensed ester is blended, bleeding out of the polycondensed ester becomes a problem. Therefore, as a result of further investigation by the present inventor, 60 to 120 parts by mass of cellulose acetate having a degree of acetyl substitution of 2.40 to 2.60 and a predetermined polycondensation ester with respect to 100 parts by mass of cellulose acetate. As a result, it was found that the change in equilibrium moisture content can be suppressed to suppress display unevenness, and the problem of bleeding out can be solved, and the present invention has been completed.

Specifically, the above problem has been solved by the following means <1>, preferably from <2> to <7>.
<1> Aromatic dicarboxylic acid in dicarboxylic acid, having cellulose acetate having an acetyl substitution degree of 2.40 to 2.60, and a polycondensed ester containing an aromatic dicarboxylic acid residue and an aliphatic diol residue Is 40 mol% or more, the terminal of the polycondensation ester and the structure of the aliphatic diol satisfy the following formula (1) or (2), and the polycondensation ester is 60 to 120 parts by mass with respect to 100 parts by mass of the cellulose acetate. The equilibrium moisture content change before and after water treatment by the Karl Fischer method at 25 ° C. and 80% relative humidity of the film before and after being immersed in pure water at 40 ° C. for 16 hours is 0.8% by mass or less. Cellulose acetate film.
(1) end of the polycondensation ester is acetate, are sealed with at least one benzoic acid and toluic acid, the average carbon number of the aliphatic diol is 2 to 2.3.
(2) The terminal of the polycondensed ester is a hydroxyl group, and the average carbon number of the aliphatic diol is 2.4 to 2.8.
<2> The cellulose acetate film according to <1>, wherein a weight average molecular weight of the polycondensed ester is 1500 or less, and a ratio of components having a molecular weight of 400 or less in the polycondensed ester is less than 4% by mass.
<3> The cellulose acetate film according to <1> or <2>, wherein an increase in haze after heat treatment for 2 minutes at a film main chain relaxation temperature Tα is less than 0.40%.
<4> Cellulose acetate film comprising stretching a cellulose acetate film at a stretching temperature of less than 150 ° C., wherein the cellulose acetate film has an acetyl substitution degree of 2.40 to 2.60, and an aromatic dicarboxylic acid residue And a polycondensed ester containing an aliphatic diol residue, the ratio of the aromatic dicarboxylic acid in the dicarboxylic acid is 40 mol% or more, and the terminal of the polycondensed ester and the structure of the aliphatic diol are represented by the following formula (1): Alternatively, Karl Fischer at 25 ° C. and 80% relative humidity of the film satisfying (2) and containing 60 to 120 parts by mass of the polycondensed ester with respect to 100 parts by mass of the cellulose acetate and immersed in pure water at 40 ° C. for 16 hours. Cellulose characterized in that the change in equilibrium moisture content before and after water treatment by the method is 0.8% by mass or less Method for producing acetate film.
(1) end of the polycondensation ester is acetate, are sealed with at least one benzoic acid and toluic acid, the average carbon number of the aliphatic diol is 2 to 2.3.
(2) end of the polycondensation ester is a hydroxyl group, an average carbon number of the aliphatic diol is 2.4 to 2.8.
<5> A polarizing plate having the cellulose acetate film according to any one of <1> to <3> or the cellulose acetate film produced by the method according to <4>, and a polarizer.
<6> The protective film according to <5>, wherein the moisture permeability is less than 170 g / m ² · day, and the protective film is disposed on a surface opposite to the surface of the polarizer on the liquid crystal cell side. Polarizing plate.
<7> An optical display device comprising the polarizing plate according to <5> or <6>.

  According to the present invention, it has become possible to provide a cellulose acetate film that is less likely to cause display unevenness when incorporated in a liquid crystal display device and is less likely to cause bleed out.

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 acetate film of the present invention comprises a cellulose acetate having an acetyl substitution degree of 2.40 to 2.60 and a polycondensed ester containing an aromatic dicarboxylic acid residue and an aliphatic diol residue. The proportion of the aromatic dicarboxylic acid is 40 mol% or more, the terminal of the polycondensed ester and the structure of the aliphatic diol satisfy the following formula (1) or (2), and the polycondensed ester is added to 100 parts by mass of the cellulose acetate. 60 to 120 parts by mass, and the film before and after being immersed in pure water at 40 ° C. for 16 hours has an equilibrium water content change before and after water treatment by the Karl Fischer method at 25 ° C. and 80% relative humidity of 0.8% by mass or less. It is characterized by.
(1) end of the polycondensation ester is acetate, are sealed with at least one benzoic acid and toluic acid, the average carbon number of the aliphatic diol is 2 to 2.3.
(2) end of the polycondensation ester is a hydroxyl group, an average carbon number of the aliphatic diol is 2.4 to 2.8.

The cellulose acetate film of the present invention is a film in which one of the cellulose acetate and the polycondensed ester is a main component, and the total of the cellulose acetate and the polycondensed ester is usually 70% by mass of the cellulose acetate film of the present invention. It is preferable to occupy 80% by mass or more.
The cellulose acetate film of the present invention has an equilibrium water content change by the Karl Fischer method at 25 ° C. and 80% relative humidity before and after immersing the film in pure water at 40 ° C. for 16 hours is 0.8% by mass or less. 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 equilibrium water content change of the film is preferably 0.6% by mass or less, more preferably 0.5% by mass or less, and further preferably 0.4% by mass or less. As a means for reducing the change in the equilibrium moisture content of the film as described above, the polycondensed ester and its blending amount, the draw ratio during production, and the draw temperature can be adjusted.

  Details of the present invention will be described below.

<Cellulose acetate>
The cellulose acetate used in the present invention is not particularly defined as long as the degree of acetyl substitution is 2.40 to 2.60.
Examples of cellulose acetate as a raw material for cellulose acetate include cotton linter and wood pulp (hardwood pulp, softwood pulp). Cellulose acetate obtained from any raw material cellulose can be used, and in some cases, a mixture may be used. Detailed descriptions of these raw material celluloses can be found in, for example, Marusawa and Uda, “Plastic Materials Course (17) Fibrous Resin”, published by Nikkan Kogyo Shimbun (published in 1970), and the Japan Society of Invention and Innovation Technical Bulletin No. 2001. The cellulose described in No.-1745 (pages 7 to 8) can be used.

Glucose units having β-1,4 bonds constituting cellulose have free hydroxyl groups at the 2nd, 3rd and 6th positions. Cellulose acetate is a polymer obtained by esterifying some or all of these hydroxyl groups with acetyl groups. The degree of substitution means the ratio of cellulose esterified at each of the 2nd, 3rd and 6th positions, and the hydroxyl group is 100% esterified at each of the 2nd, 3rd and 6th positions. Has a substitution degree of 1, and when all of the hydroxyl groups at the 2-position, 3-position and 6-position are 100% esterified, the substitution degree is 3.
The total degree of acetyl substitution, that is, DS2 + DS3 + DS6 is 2.40 to 2.60, preferably 2.40 to 2.55, and more preferably 2.4 to 2.50. Here, DS2 is the substitution degree of the hydroxyl group at the 2-position of the glucose unit with the acetyl group, DS3 is the substitution degree of the hydroxyl group at the 3-position with the acetyl group, and DS6 is the substitution degree of the hydroxyl group at the 6-position with the acetyl group. .
The measurement of the degree of substitution of cellulose with a hydroxyl group is not particularly limited, but the degree of substitution can be obtained by measuring the degree of binding of acetic acid substituted with the hydroxyl group of cellulose. As a measuring method, it can carry out according to ASTM D-817-91.

  The degree of polymerization of cellulose acetate 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 preferable. Particularly preferred. If the degree of polymerization is not more than the upper limit, the viscosity of the cellulose acetate dope solution does not become too high, and it is preferable because the 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 acetate preferably used in the present invention is evaluated by gel permeation chromatography, and its polydispersity index Mw / Mn (Mw is mass average molecular weight, Mn is number average molecular weight) is small, and molecular weight distribution. Is preferably narrow. 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 polycondensation ester contained in the cellulose acetate film of the present invention contains an aromatic dicarboxylic acid residue and an aliphatic diol residue, contains 60 to 120 parts by mass with respect to 100 parts by mass of cellulose acetate, and is aromatic in the dicarboxylic acid. The ratio of dicarboxylic acid is 40 mol% or more, and the terminal of the polycondensation ester and the structure of the aliphatic diol satisfy the following formula (1) or (2).
(1) end of the polycondensation ester is acetate, are sealed with at least one benzoic acid and toluic acid, the average carbon number of the aliphatic diol is 2 to 2.3.
(2) end of the polycondensation ester is a hydroxyl group, an average carbon number of the aliphatic diol is 2.4 to 2.8.
When a large amount of polycondensation ester is contained in the cellulose acetate film as in the present invention, the ratio of the aromatic dicarboxylic acid residue in the dicarboxylic acid residue, the presence or absence of terminal end of the polycondensation ester, the carbon of the aliphatic diol Bleed out can be greatly suppressed by adjusting the chain length.

The polycondensed ester according to the present invention is obtained by mixing, for example, an aromatic dicarboxylic acid and an aliphatic diol.
The 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. Moreover, it is preferable that the aromatic dicarboxylic acid residue ratio represented below is 40 mol%-95 mol%.
Aromatic dicarboxylic acid residue ratio (mol%) = [aromatic dicarboxylic acid residue (mol) / (aromatic dicarboxylic acid residue (mol) + aliphatic dicarboxylic acid residue (mol))] × 100

  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 weight average molecular weight of the polycondensed ester is preferably 1500 or less, more preferably 1000 or less, and still more preferably 800 or less. Although there is no restriction | limiting in particular about a minimum, It is preferable that it exceeds 400. If the weight average molecular weight of the polycondensed ester is 1500 or less, the compatibility with cellulose acetate is increased, and bleeding out during film formation and heat stretching is less likely to occur.
The weight average molecular weight of the polycondensed ester can be measured by a known method, for example, by gel permeation chromatography.

  In the polycondensed ester, the ratio of the component having a molecular weight of 400 or less in the polycondensed ester is preferably less than 4% by mass, more preferably less than 3% by mass, and even more preferably less than 1% by mass. . By setting the ratio of the component having a molecular weight of 400 or less to less than 4% by mass, the component that volatilizes during the production of the film can be reduced, and the bleed-out during film formation can be more effectively suppressed.

The number average molecular weight of the polycondensed ester is preferably 600 to 2500, more preferably 700 to 1800, and still more preferably 700 to 1250. If the number average molecular weight of the polycondensed ester is 600 or more, the volatility becomes lower, and film failure or process contamination due to volatilization under high temperature conditions during stretching of the film of the present invention is less likely to occur. Moreover, if it is 2500 or less, compatibility with a cellulose acetate 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 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.

Content of the polycondensation ester in the cellulose acetate film of this invention is 60-120 mass parts with respect to 100 mass parts of cellulose acetate, It is preferable that it is 70-115 mass parts, and it is 80-110 mass parts. More preferable.
By setting the content to 60 parts by mass or more, the equilibrium water content can be suppressed, and by setting the content to 120 parts by mass or less, bleeding out can be suppressed.

(Aromatic dicarboxylic acid residue)
The aromatic dicarboxylic acid residue is contained in a polycondensed ester obtained from a 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-.
The aromatic dicarboxylic acid residue ratio in the dicarboxylic acid residue of the polycondensed ester used in the present invention is preferably 40 mol% to 95 mol%, more preferably 45 mol% to 70 mol%, and more preferably 50 mol% to 70 mol%. % Is more preferable.
By setting the aromatic dicarboxylic acid residue ratio to 40 mol% or more, a cellulose acetate film exhibiting more sufficient optical anisotropy can be obtained. Moreover, if it is 95 mol% or less, it is excellent in compatibility with a cellulose acetate, and it can make it difficult to produce a bleed-out also at the time of film forming of a cellulose acetate film and the time of heat-stretching.

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 acetate film and heat drawing, it is preferable. Moreover, since it can be set as the cellulose acetate 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. By using terephthalic acid, the change in the equilibrium water content of the cellulose acetate film of the present invention can be further reduced.
In other words, by using terephthalic acid as the aromatic dicarboxylic acid for mixing in the formation of the polycondensed ester, it is more compatible with cellulose acetate and causes bleed-out when the cellulose acetate film is formed and heated. It can be made a difficult cellulose acetate film. 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, preferably 10 mol% to 100 mol%, more preferably 40 mol% to 75 mol%, More preferably, it is 45 mol%-60 mol%. By setting the terephthalic acid residue ratio to 40 mol% or more, a cellulose acetate film exhibiting sufficient optical anisotropy (particularly Rth) can be obtained. Moreover, by setting it as 95 mol% or less, it is excellent in compatibility with a cellulose acetate, and it can make it more difficult to produce a bleed-out also at the time of film forming of a cellulose acetate 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 aliphatic dicarboxylic acid residue is contained in a polycondensed ester obtained from a diol and a dicarboxylic acid containing an aliphatic dicarboxylic acid.
The ratio of the aliphatic dicarboxylic acid residue in the dicarboxylic acid residue of the polycondensed ester used in the present invention is preferably 5 mol% to 60 mol%, more preferably 5 mol% to 55 mol%, and more preferably 20 mol% to 40 mol. % Is more preferable.
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. By setting it in this range, compatibility with cellulose acetate is excellent, and it is preferable because bleeding out is less likely to occur at the time of film formation and heat stretching of the cellulose acetate film.
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 aliphatic dicarboxylic acid residue can be reduced, and the compatibility with cellulose acetate can be further improved, which is preferable.
Further, it is preferable that the aliphatic dicarboxylic acid residue has an average carbon number of 4.0 or more because synthesis becomes easy.

(Aliphatic diol residue)
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 diol residue formed from the diol HO—R—OH is —O—R—O—.
The ratio of the aliphatic diol residue in the diol of the polycondensed ester used in the present invention is preferably 90 mol% or more.
The preferred average carbon number of the polycondensed ester varies depending on the structure of the terminal. Where the terminal of the polycondensation ester are sealed with at least one acid, benzoic acid and toluic acid, average carbon number includes an aliphatic diol residues of 2.0 to 2.3, preferably having an average carbon It is an aliphatic diol residue having a number of 2.0 or more and 2.2 or less, more preferably an average carbon number of 2.0 or more and 2.1 or less. By setting the average number of carbon atoms of the aliphatic diol residue to 2.3 or less, compatibility with cellulose acetate can be improved, bleedout is less likely to occur, and the heat loss of the compound is reduced. It is difficult to cause a surface failure that is considered to be caused by 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.
If end of the polycondensed ester is a hydroxyl group, include aliphatic diol residues average carbon number is 2.4 to 2.8, preferably an average carbon number of 2.4 or more 2.7 or less, more Preferably, it is an aliphatic diol residue having an average carbon number of 2.5 or more and 2.6 or less. By setting the average carbon number of the aliphatic diol residue to 2.4 to 2.8, compatibility with cellulose acetate can be improved, and bleeding out is less likely to occur. Moreover, the polycondensation ester can be softened, and as a result, the brittleness of the film can be improved.
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

(Sealing)
The terminal of the polycondensed ester is sealed with acetic acid, benzoic acid, toluic acid, or a hydroxyl group. Sealing may be performed at both ends of the polycondensed ester, or only one end. Note that toluic acid includes o-toluic acid, m-toluic acid, and p-toluic acid.
At this time, both ends of the polycondensed ester are hydroxyl groups or 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—.
By adjusting the structure of end-capping and the structure of the above-mentioned aliphatic diol, the compatibility with cellulose acetate is further improved, and the occurrence of bleed-out can be more effectively suppressed.

  Although the specific example of the polycondensation ester concerning this invention is described in the following Table 1, it is not limited to these.

表中、ＴＰＡはテレフタル酸、ＰＡはフタル酸、ＩＰＡはイソフタル酸、２，６-ＮＤＡは２，６−ナフタレンジカルボン酸、２，８-ＮＤＡは２，８−ナフタレンジカルボン酸、１，４-ＮＤＡは１，４−ナフタレンジカルボン酸、１，５-ＮＤＡは１，５−ナフタレンジカルボン酸、１，６-ＮＤＡは１，６−ナフタレンジカルボン酸、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、２−ｍ−１３ＰＧは２−メチル−１、３プロピレングリコール、１３ＰＧは１，３−プロピレングリコールを表す（以下、本明細書において同じ）。

In the table, TPA is terephthalic acid, PA is phthalic acid, IPA is isophthalic acid, 2,6-NDA is 2,6-naphthalenedicarboxylic acid, 2,8-NDA is 2,8-naphthalenedicarboxylic acid, 1,4- NDA is 1,4-naphthalenedicarboxylic acid, 1,5-NDA is 1,5-naphthalenedicarboxylic acid, 1,6-NDA is 1,6-naphthalenedicarboxylic acid, SA is succinic acid, AA is adipic acid, PG is 1,2-propylene glycol, EG represents ethylene glycol, 2-m-13PG represents 2-methyl-1,3 propylene glycol, and 13PG represents 1,3-propylene glycol (hereinafter the same in the present specification).

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 content of the raw material aliphatic diol, dicarboxylic acid ester, or diol ester contained in the polycondensed ester in the cellulose ester 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 acetate 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 to 30 parts by weight, more preferably 0.5 to 20 parts by weight, still more preferably 1 to 10 parts by weight, and 3 to 7 parts by weight with respect to 100 parts by weight of the cellulose ester. Part is particularly preferred.

<Other additives>
In addition to the above, other additives may be added to the cellulose acetate 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. Degradation inhibitors (eg, antioxidants, peroxide decomposers, radical inhibitors, metal deactivators, acid scavengers, amines) described in each of the above publications, sugar derivatives described in JP 2012-108349 A, etc. Is exemplified.

<Method for producing cellulose acetate film>
The method for producing a cellulose acetate film of the present invention includes stretching the cellulose acetate film at a stretching temperature of less than 150 ° C., and the cellulose acetate film has a degree of acetyl substitution of 2.40 to 2.60. And a polycondensed ester containing an aromatic dicarboxylic acid residue and an aliphatic diol residue, the polycondensed ester containing 60 to 120 parts by mass with respect to 100 parts by mass of the cellulose acetate, The film before and after immersion for 16 hours is characterized in that the change in equilibrium moisture content before and after water treatment by the Karl Fischer method at 25 ° C. and 80% relative humidity is 0.8 mass% or less.
The film of the present invention can be produced by a solvent cast method. In the solvent cast method, a film is produced using a solution (dope) in which cellulose acetate is dissolved in an organic solvent.
Next, the organic solvent in which the cellulose acetate 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 acetate 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 cellulose acetate can be dissolved, cast and film-formed. 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 acetate solution can be prepared by a general method comprising treating at a temperature of 40 ° C. or higher (room 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 cellulose acetate is adjusted so as to be contained in the obtained solution in an amount of 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 a 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 acetate 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 acetate solution to be cast, the same solution may be used, or different cellulose acetate solutions may be used. In order to give a function to a plurality of cellulose acetate layers, a cellulose acetate solution corresponding to the function may be pushed out from each casting port. Furthermore, the cellulose acetate 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 absorption layer, a polarizing layer, etc.).

  In the conventional single-layer liquid, it is necessary to extrude a cellulose acetate 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 acetate solution is poor and solid matter is generated, which often causes problems such as defects in the surface and 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 acetate solution can achieve a reduction in drying load and increase the production speed of the film.

<< Extension >>
The film of the present invention is preferably stretched. 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 stretching temperature is less than 150 ° C, preferably 140 ° C or less, and more preferably 132 ° C or less. In the present invention, stretching at such a low temperature is preferable because variation in retardation can be reduced. This is based on the fact that the cellulose acetate film of the present invention has a large amount of polycondensed ester, and therefore the film in the film forming process tends to be relatively soft. When trying to develop retardation by stretching a soft film, the retardation (particularly Rth) tends to vary. it can.
Although there is no restriction | limiting in particular about the minimum of extending | stretching temperature unless a fracture | rupture etc. are caused, For example, it can be 90 degreeC or more.
Note that the cellulose acetate film of the present invention may not require stretching, such as when retardation is not required. Further, even when retardation is required to be expressed, it can be expressed by blending a known retardation developer.

The stretching of the film may be uniaxial stretching only in the transport direction or width direction, or simultaneous or sequential biaxial stretching, but it is preferable to stretch more in the width direction. Stretching in the width direction is preferably 1 to 100% stretching, more preferably 10 to 70% stretching, and particularly preferably 15 to 35% stretching. Stretching in the conveying direction is preferably 1 to 10%, particularly preferably 2 to 5%.
In this invention, it is obtained by extending | stretching a cellulose acetate film, and it is preferable that this draw ratio is 1 to 100% in the direction (width direction) perpendicular | vertical with respect to a conveyance direction.
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 step, stretching may be performed in a state including the residual solvent amount, and the residual solvent amount = (mass of residual volatile matter / film mass after heat treatment) × 100% is the solvent 15 It is preferably at most 10 mass%, more preferably at most 10 mass%, further preferably at most 5 mass%, particularly preferably at most 1 mass%.
In the case of stretching the raw film that has been formed and wound, it is preferable to stretch 1 to 100% in the width direction with the residual solvent amount being 5% by mass, and more preferably 10 to 70%. Particularly preferably, the stretching is 20 to 60%.

The stretching process may be performed in the middle of the film forming process, and then the original film that has been formed and wound may be further stretched.
In the case of further stretching after winding the film stretched in the middle of the film forming process, the stretching in the middle of the film forming process may be performed in a state including the amount of residual solvent. Solvent amount = (residual volatile matter mass / film mass after heat treatment) × 100% is preferably stretched at 0.05 to 50%, and the stretch of the original film formed and wound up has a residual solvent amount of 0 It is preferable to stretch in the state of ˜5%, and the stretching in the width direction is preferably performed in the range of 1 to 100% based on the unstretched state, more preferably 10 to 70%, and particularly preferably 20 to 60% stretch.

The cellulose ester 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 reduce variation 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 >>
When the stretching process is performed during the film forming process, the film can be dried while being conveyed. It is preferable that drying temperature is 50 to 150 degreeC, More preferably, it is 50 to 120 degreeC, More preferably, it is 60 to 100 degreeC. The drying time is not particularly limited, but is preferably 10 to 40 minutes. By selecting the optimal post-stretching drying temperature, the residual stress of the cellulose acetate film produced 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. be able to.

<< 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, 50 to 120 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 preferably 140 ° 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.

<Performance of cellulose acetate 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 preferably has a film thickness of 40 to 80 μm, more preferably more than 45 μm and 80 μm or less, and even more preferably 50 to 70 μm. By setting it as such a range, the effect of this invention is exhibited more effectively.

<< 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.

<< Rth variation >>
The variation of Rth (590) of the film of the present invention, measured as follows, is preferably less than 2 nm, more preferably less than 1.5 nm, and more preferably less than 1 nm.
The width of the film processed to a total width of 1980 mm is set to 0 mm in the center in the width direction, cut out at intervals of ± 900 mm (100 mm intervals) in the width direction and ± 1000 mm (100 mm) in the longitudinal direction, and Re and Rth at each point are KOBRA 21ADH (Oji measurement) The standard deviation of Rth was calculated from all point data, and the value was defined as Rth variation.
If the longitudinal direction and the width direction are not clear, any direction may be defined as the longitudinal direction and the width direction.

<< Internal 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%.

<< Haze rise after heat treatment >>
It is preferable that the haze of the film before stretching and the change in haze (haze increase) after heat treatment at the main chain relaxation temperature Tα measured by dynamic viscoelasticity for 2 minutes is less than 0.40%. More preferably, it is less than 30%, and more preferably less than 0.20%. Since the film of the present invention hardly causes bleed-out of the polycondensed ester, such a low haze value after heat treatment can be achieved.
The main chain relaxation temperature Tα is the largest tan δ value when the temperature is raised from 25 ° C. to 200 ° C. at a set strain 0.1% temperature raising rate of 5 ° C./min in the tensile mode in dynamic viscoelasticity measurement. It refers to the temperature at the peak top when a peak (peak corresponding to relaxation of the main chain of the polymer) is measured.

<< 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.

<< Re, Rth >>
As Re (590) of the film of the present invention, 30 to 100 nm is preferable, 40 to 80 nm is more preferable, and 40 to 60 nm is more preferable.
Moreover, as Rth (590) of the film of this invention, 90-180 nm is preferable, 100-160 nm is more preferable, 110-140 nm is further more preferable.
Re and Rth can be measured using KOBRA 21ADH (manufactured by Oji Scientific Instruments).

<Retardation>
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 590 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 acetate 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 acetate 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 3-100 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 less than 170 g / m ² for one of the protective films of the polarizing plate. 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 60 to 130 μm, more preferably 70 to 120 μm, and particularly preferably 70 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>
<< Preparation of cellulose acetate >>
Using the cellulose acetate dope shown below, a film was formed by a solution casting method and used for each of Examples and Comparative Examples.

Cellulose acetate dope ――――――――――――――――――――――――――――――――――――――
Cellulose acetate: acetyl group substitution degree listed in the table below 100 parts by mass Polycondensation ester: Retardation adjusting agent H1: 3 parts by mass dichloromethane added 406 parts by mass of the types listed in the table below Methanol 61 parts by 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、Ｂｚはベンゾイル基を、ｐ−ｔｏｌはパラートルイル基を、ＯＨは水酸基を表す。

In the table, the unit is mass%. TPA is terephthalic acid, PA is phthalic acid, AA is adipic acid, SA is succinic acid, PG is 1,2-propylene glycol, EG is ethylene glycol, Ac is acetyl group, Bz is benzoyl group, p-tol is A paratoluyl group, OH represents a hydroxyl group.

Retardation adjusting agent H1

  In the cellulose acetate dope, the matting agent (AEROSIL R972, manufactured by Nippon Aerosil Co., Ltd., secondary average particle size of 1.0 μm or less) is 0.13 parts by mass with respect to 100 parts by mass of cellulose acetate. 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 and stirred to dissolve each component, followed by filtration 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. 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.

  Re and Rth of each film were measured using KOBRA 21ADH (manufactured by Oji Scientific Instruments). The measurement wavelength was 590 nm.

<Evaluation>
<< Measurement of equilibrium 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 equilibrium 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 equilibrium moisture content after water treatment and the equilibrium moisture content in the initial state was defined as the equilibrium moisture content change (unit: mass%).

<< Rth variation evaluation of film >>
The width of the film processed to a total width of 1980 mm is set to 0 mm in the center in the width direction, cut out at intervals of ± 900 mm (100 mm intervals) in the width direction and ± 1000 mm (100 mm) in the longitudinal direction, and Re and Rth at each point are KOBRA 21ADH (Oji measurement) The measurement was performed using a device (manufactured by K.K.). The standard deviation of Rth was calculated from all point data, and the value was defined as Rth variation. The value of Rth variation was divided into three stages, and the practical levels were defined as A, B, and C.
A: Rth variation less than 1 nm B: Rth variation from 1 nm to less than 2 nm C: Rth variation from 2 nm to less than 4 nm D: Rth variation of 4 nm or more

<< Measurement of haze rise by heat treatment >>
The film before stretching was collected, the sample was cut into 20 mm (width direction) × 5 mm (transport direction), and the main chain relaxation temperature Tα of the film was determined by dynamic viscoelasticity measurement. When DVA-225 manufactured by IT Measurement Control Co., Ltd. is used and the temperature is increased from 25 ° C. to 200 ° C. at a set strain 0.1% temperature increase rate of 5 ° C./min in the tensile mode, the tan δ value becomes the largest. The peak (peak corresponding to relaxation of the main chain of the polymer) was measured, and the temperature at the peak top was defined as Tα.
Next, the film before stretching was cut into a 10 cm square, and four sides were fixed to a SUS frame using a clip, and heated in a thermostatic bath until the film surface temperature reached Tg determined above. The haze value of the film after heating and the film before heating was measured, and the difference was defined as the haze increase value by heat treatment.

<< Bleed-out evaluation >>
The state of the stretched film sample was visually observed and divided into three stages as follows. A, B, and C were determined to have no practical problem.
A: There is no crying out of the additive in both the part holding the film with the tenter and the center part of the film.
B: Some additive crying is seen in the part holding the film with the tenter, but no crying is seen in the center of the film.
C: In addition to the part gripping the film with the tenter, the additive cries out in the film surface, but crys out in the area of 90% of the width of the film centered on the tenter. Is not seen.
D: In addition to the portion gripping the film with the tenter, crying is also observed in an area having a width of 90% of the central portion with respect to the film width gripped by the tenter.

表中、Ａｃはアセチル基を、Ｂｚはベンゾイル基を、ｐ−ｔｏｌはｐートルイル基を、ＯＨは水酸基を表す。

In the table, Ac represents an acetyl group, Bz represents a benzoyl group, p-tol represents a p-toluyl group, and OH represents a hydroxyl group.

  From the table, it can be seen that the film of the present invention has a low equilibrium moisture content and can suppress bleed out. Further, it can be seen that Rth variation and haze change after heat treatment are low.

<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.

Then, according to the following processes 1-5, the polarizer, the said cellulose acetate film, and TD60UL (made by Fuji Film Co., Ltd.) were bonded together, and the polarizing plate was produced.
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.
Step 4: Step 3 Cellulose ester film laminated with the polarizer and the pressure backside cellulose ester films 20-30 N / cm ^2, the conveyance speed was pasted at approximately 2m / 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.

In addition, the film shown in the following table was used as a protective film.
PMMA1: Polymethylmethacrylate film 20 μm (moisture permeability 200 g / m ² / day)
PMMA2: Polymethylmethacrylate film 25 μm (moisture permeability of 160 g / m ² / day)
PMMA3: 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 the method (40 ° C. and 90% relative humidity) defined by the moisture permeability test method (cup method) of JISZ0208 moisture-proof packaging material.

<Evaluation of liquid crystal display device>
<< Evaluation of front contact unevenness of liquid crystal display device >>
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. In the state where the produced liquid crystal display device was laid down sideways, 1 cm × 8 cm Bencot M-3II (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, Saran Wrap (registered trademark) and Bencott were removed, the water on the film surface was wiped off, and after lighting for 24 hours, the panel was observed from the front direction during black display 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.

<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: Based on the above results in which significant light leakage is visually recognized, A and B are practically used.

DESCRIPTION OF SYMBOLS 1 Antistatic bag 2 Polarizing plate 3 Polarizer 4 Cellulose acetate butyrate 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 (7)

A cellulose acetate having an acetyl substitution degree of 2.40 to 2.60 and a polycondensation ester containing an aromatic dicarboxylic acid residue and an aliphatic diol residue, and the ratio of the aromatic dicarboxylic acid in the dicarboxylic acid is 40 mol% or more, the terminal of the polycondensation ester and the structure of the aliphatic diol satisfy the following formula (1) or (2), and the polycondensation ester is contained in an amount of 60 to 120 parts by mass with respect to 100 parts by mass of the cellulose acetate. Cellulose acetate film characterized in that the change in equilibrium moisture content before and after water treatment by the Karl Fischer method at 25 ° C. and 80% relative humidity of the film before and after being immersed in pure water at 40 ° C. for 16 hours is 0.8% by mass or less. .
(1) end of the polycondensation ester is acetate, are sealed with at least one benzoic acid and toluic acid, the average carbon number of the aliphatic diol is 2 to 2.3.
(2) end of the polycondensation ester is a hydroxyl group, an average carbon number of the aliphatic diol is 2.4 to 2.8. The cellulose acetate film according to claim 1, wherein the weight average molecular weight of the polycondensed ester is 1500 or less, and a ratio of components having a molecular weight of 400 or less in the polycondensed ester is less than 4% by mass. The cellulose acetate film according to claim 1 or 2, wherein the amount of increase in haze after heat treatment at the film main chain relaxation temperature Tα for 2 minutes is less than 0.40%. Stretching the cellulose acetate film at a stretching temperature of less than 150 ° C., wherein the cellulose acetate film has a cellulose acetate having an acetyl substitution degree of 2.40 to 2.60, an aromatic dicarboxylic acid residue, and an aliphatic group. A polycondensation ester containing a diol residue, the ratio of the aromatic dicarboxylic acid in the dicarboxylic acid is 40 mol% or more, and the terminal of the polycondensation ester and the structure of the aliphatic diol are represented by the following formula (1) or (2 ), And the polycondensed ester contains 60 to 120 parts by mass with respect to 100 parts by mass of the cellulose acetate, and water by Karl Fischer method at 25 ° C. and 80% relative humidity before and after immersion in pure water at 40 ° C. for 16 hours. Cellulose acetate characterized by a change in equilibrium moisture content before and after treatment of 0.8% by mass or less Method of manufacturing over Tofirumu.
(1) end of the polycondensation ester is acetate, are sealed with at least one benzoic acid and toluic acid, the average carbon number of the aliphatic diol is 2 to 2.3.
(2) end of the polycondensation ester is a hydroxyl group, an average carbon number of the aliphatic diol is 2.4 to 2.8. And cellulose acetate Phil beam according to any one of claims 1 to 3, and a polarizer, a polarizing plate. The polarizing plate according to claim 5, comprising a protective film having a moisture permeability of less than 170 g / m ² · day, and the protective film is disposed on a surface opposite to a surface on the liquid crystal cell side of the polarizer. . An optical display device comprising the polarizing plate according to claim 5.

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