WO2012002090A1 - Process for production of cellulose acetate film, cellulose acetate film, and polarizing plate and liquid crystal display device each equipped with the film - Google Patents

Abstract

Disclosed are: a process for producing a cellulose acetate film that has excellent haze and internal diffusion properties even when stretched at a high draw ratio and has high contrast when used in a polarizing plate or a liquid crystal display device; a cellulose acetate film; and a polarizing plate and a liquid crystal display device, each of which is equipped with the film. The process for producing a cellulose acetate film can produce a cellulose acetate film by a solution casting method using a dope comprising a solvent and a cellulose acetate having a degree of substitution by an acetyl group of 2.0-2.5, and is characterized in that the water content of the dope during casting is adjusted to 1.5 to 5 mass% inclusive, the dope is agitated at a temperature ranging from a temperature equal to or higher than the boiling point of the solvent at ambient pressure to a temperature higher by 50°C than the boiling point of the solvent at ambient pressure inclusive while shearing at a shear rate of 2×10³ to 2×10⁴ s^-1 and is subsequently formed into a film, and the film is stretched.

Description

Method for producing cellulose acetate film, cellulose acetate film, polarizing plate using the same, and liquid crystal display device

The present invention relates to a method for producing a cellulose acetate film, a cellulose acetate film, a polarizing plate using the same, and a liquid crystal display device.

In recent years, with the increase in size and definition of liquid crystal display devices, further widening of polarizing plates and improvement in display quality have been demanded.

Conventionally, a cellulose ester film has been used as a protective film for polarizing plates, but in order to achieve both wider width and display quality such as contrast, the conventional cellulose triacetate film (TAC film) is used as it is. There was a problem to do.

For example, if the cellulose triacetate film is stretched at a high magnification to widen the film, the additive bleeds out and a haze increase is observed, or the whitening of the film itself due to stretching increases internal scattering, resulting in a decrease in contrast and display quality. It was not excellent.

For this reason, it is conceivable to use a cellulose ester whose total acyl group that is easier to stretch has a low substitution degree (see Patent Documents 1 and 2). However, cellulose swell, which has a low degree of substitution, is inferior in solubility during dope preparation, and the presence of undissolved material adversely affects the quality of the film, and in particular causes internal scattering after stretching, and is not dissolved. In order to sufficiently dissolve the product, a treatment such as increasing the dissolution time is required, and the productivity is lowered. Furthermore, if filtration is performed with the undissolved material as it is, the life of the filter medium is shortened, and the work by exchanging the filter medium becomes a factor of cost increase.

Further, in Patent Document 3, in order to obtain a cellulose acylate film with improved haze and surface shape, a cellulose acylate having a total acyl group substitution degree of 2.1 to 2.7 is used, and a water content of 0. A technique for preparing a dope of 7% or less and defining the difference in SP value between the cellulose acylate and the solvent is disclosed. However, when a stretching process is performed at a high stretching ratio, haze increases and whitening of the film occurs. Increased internal scattering was observed, and there was still a problem with contrast and the like.

JP 2009-265598 A JP 2009-269944 A JP 2009-263619 A

Accordingly, an object of the present invention is to produce a cellulose acetate film, a cellulose acetate film, which has excellent haze and internal scattering even when stretched at a high magnification, and has high contrast when used in a polarizing plate, a liquid crystal display device, and the same. The polarizing plate and the liquid crystal display device used are provided.

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

1. A method for producing a cellulose acetate film by a solution casting method using at least a solvent and a dope containing cellulose acetate having a substitution degree of acetyl group of 2.0 to 2.5, wherein the water content during casting of the dope is 1 The dope is adjusted in the range of 5% by mass or more and 5% by mass or less, and the dope is at a temperature not lower than the boiling point at the normal pressure of the solvent and not higher than 50 ° C. above the boiling point at the normal pressure of the solvent. A method for producing a cellulose acetate film, comprising applying a shear force of 10 ³ s ⁻¹ to 2 × 10 ⁴ s ⁻¹ and stirring, casting the dope to form a film, and then stretching the dope.

2. 2. The method for producing a cellulose acetate film as described in 1 above, wherein the water content during casting of the dope is 2% by mass or more and 5% by mass or less.

3. 3. The method for producing a cellulose acetate film as described in 1 or 2 above, wherein the water content during casting of the dope is adjusted to the above range by adding water to the dope.

4. 4. The method for producing a cellulose acetate film according to any one of 1 to 3, wherein 0.745 ≦ D6 ≦ 0.95 is satisfied, where D6 is an acetyl substitution degree at the 6-position of the cellulose acetate. .

5. 5. The method for producing a cellulose acetate film according to any one of 1 to 4, wherein the stirring is performed with an in-line mixer or a disperser.

6. 6. The method for producing a cellulose acetate film according to any one of 1 to 5, wherein the stretching ratio is in the range of 140% to 180%, and the film width after stretching is 1900 mm to 2500 mm.

7. Any of 1 to 6 above, wherein the dope further contains a sugar ester compound having an average substitution degree of 5.0 to 7.0, or a phase difference adjusting agent represented by the following general formula (B): The method for producing a cellulose acetate film according to claim 1.

Formula (B) B- (GA) n-GB
(Wherein B is a hydroxy group or carboxylic acid residue, G is an alkylene glycol residue having 2 to 12 carbon atoms, an aryl glycol residue having 6 to 12 carbon atoms, or an oxyalkylene glycol residue having 4 to 12 carbon atoms) A represents an alkylene dicarboxylic acid residue having 4 to 12 carbon atoms or an aryl dicarboxylic acid residue having 6 to 12 carbon atoms, and n represents an integer of 1 or more.)
8). A cellulose acetate film produced by the method for producing a cellulose acetate film according to any one of 1 to 7.

9. 9. A polarizing plate, wherein the cellulose acetate film described in 8 is bonded to at least one surface of a polarizer.

10. 10. A liquid crystal display device, wherein the polarizing plate according to 9 is bonded to at least one surface of a liquid crystal cell.

ADVANTAGE OF THE INVENTION According to this invention, even if it extends | stretches at high magnification, it is excellent in a haze and internal scattering, and when used for a polarizing plate and a liquid crystal display device, the manufacturing method of a cellulose acetate film which is high contrast, a cellulose acetate film, and its use A polarizing plate and a liquid crystal display device can be provided.

It is the figure which showed typically an example of the solution casting method preferable for this invention. It is a flow which shows the manufacturing method of this invention using a disperser. It is a schematic diagram which shows the state which dripped glycerin on the slide glass. It is a schematic diagram which shows the state which put the sample film on glycerol. It is a schematic diagram which shows the state which dripped glycerin on the sample film. It is a schematic diagram which shows the state which put the cover glass on glycerol.

Hereinafter, modes for carrying out the present invention will be described in detail, but the present invention is not limited to these.

The method for producing a cellulose acetate film according to claim 1 of the present invention is a method for producing a cellulose acetate film by a solution casting method using at least a solvent and a dope containing cellulose acetate having an acetyl group substitution degree of 2.0 to 2.5. A method for producing, wherein the water content at the time of casting of the dope is adjusted to a range of 1.5% by mass or more and 5% by mass or less, and the dope is adjusted from the boiling point at the normal pressure of the solvent to the normal pressure of the solvent. And after stirring at a temperature not higher than the boiling point at 50 ° C. and a shear rate of 2 × 10 ³ s ⁻¹ to 2 × 10 ⁴ s ⁻¹ , casting the dope to form a film, The cellulose acetate film is characterized in that it is stretched, and with such a structure, it has excellent haze and internal scattering even when stretched at a high magnification, and has high contrast when used in polarizing plates and liquid crystal display devices. There is provided a method of manufacturing.

According to the study of the present inventor, the cellulose acetate having a low degree of substitution prepares a dope as compared with triacetyl cellulose (TAC) having a high degree of substitution or cellulose acetate propionate (CAP) which is a mixed fatty acid ester. The solubility of the resin at that time is unstable when the dope water content is the same as the dope in which TAC or CAP is dissolved, and undissolved substances are easily generated, and haze and internal scattering due to the undissolved substances are inferior. The dope moisture content is adjusted to 1.5 mass% or more and 5 mass% or less, and high shear is obtained at a temperature not lower than the boiling point at the normal pressure of the solvent used for the dope but not higher than the boiling point at the normal pressure of the solvent. Dissolving while stirring at a speed not only increases the solubility due to the influence of the hydrophilic group of cellulose acetate with a low degree of substitution, but also reduces the undissolved content, as well as loosening the molecular chains. It has been found that by increasing the amount of residual solvent retained during stretching, the stress burden on the film during stretching is reduced, and a cellulose acetate film excellent in haze and internal scattering can be produced while performing high magnification stretching. .

In the inventions according to claims 2 and 3, the water content of the dope is 2% by mass or more and 5% by mass or less, and is adjusted to the range of the water content by adding water to the dope.

Originally, additives such as cellulose acetate, solvent, plasticizer, etc., which are dope raw materials, contain moisture depending on the manufacturing process and humidity in the air, but the present invention adds to these moisture, and if necessary, by adding water The water content is adjusted.

As a result of intensive studies in view of the above problems, the present inventor sufficiently loosens cellulose acetate molecules with a low degree of substitution by adding water to adjust the moisture content, and further performs stirring at a high shear rate at a high temperature. Thus, it has been found that the undissolved material can be sufficiently dissolved, which is greatly different from the prior art in which it is better to reduce the moisture content of the dope as much as possible.

The present invention adjusts the moisture content of the dope at the time of casting to 1.5 mass% or more and 5 mass% or less, so that it is not necessary to strictly adjust the moisture content of cellulose acetate, additives such as plasticizers, and the solvent used. The moisture content of additives such as cellulose acetate and plasticizer is preferably adjusted to 5% by mass or less by passing through the drying step from the viewpoint of storage stability of the material, and more preferably 1% by mass or less. preferable. The water content of the solvent depends on the type of solvent used, but the water content is preferably 5% by mass or less, more preferably 0.2 to 1% by mass.

The water content is preferably adjusted by adding a predetermined amount of water in advance at the time of preparing the dope in terms of productivity. When batchwise, the specified amount of water is preferably added when adding the solvent.

The water content of the dope was measured by measuring 1 cm ³ of the solution using a Karl Fischer method with a moisture meter and a sample drying device (CA-03, VA-05, both Mitsubishi Chemical Corporation), and the amount of moisture contained in the dope. It is calculated by dividing (g) by the dope sample mass (g).

The invention according to claim 4 is characterized in that when the degree of acetyl substitution at the 6-position of the cellulose acetate is D6, 0.745 ≦ D6 ≦ 0.95, and hydrogen between cellulose acetate molecules By reducing the bonds, the molecular chains of cellulose are loosened, and in addition to the reduction of undissolved components during stirring, the retention of residual solvent during stretching is increased, reducing the stress burden on the film during stretching. It is.

The invention according to claim 5 is characterized in that the stirring is performed by an in-line mixer or a disperser described later.

The invention according to claim 6 is characterized in that the stretching ratio is in the range of 140% to 180%, and the film width after stretching is 1900 mm to 2500 mm, and in particular, widening is achieved by a high stretching ratio. It is.

The invention according to claim 7 is a sugar ester compound having an average substitution degree of 5.0 to 7.0, or an ester represented by the following general formula (B), from the viewpoint of suppressing an increase in haze due to high stretching. It is characterized by containing a compound.

The inventions according to claims 8, 9, and 10 include a cellulose acetate film having a low haze and low internal scattering produced by the method for producing a cellulose acetate film of the present invention, a polarizing plate having a high contrast, and a liquid crystal using the same. It is a display device.

First, each step of the solution casting method according to the present invention will be described.

FIG. 1 is a diagram schematically showing an example of a dope preparation step, a casting step, a solvent evaporation step, a peeling step, a drying and stretching step, and a winding step of a solution casting method preferable for the present invention.

In the dope preparation process, cellulose acetate, a plasticizer, additives and the like are dissolved and mixed in the main dissolution pot 1. If necessary, large agglomerates are removed from the matting agent charging pot 41 by the filter 44 with the liquid feed pump 43 and fed to the stock pot 42. Thereafter, the matting agent addition liquid is added from the stock pot 42 to the main dope dissolving pot 1. After that, the main dope solution is mixed in-line with the main dope solution via the conduit 16 through the stock tank 13 through the stock tank 13 after filtering the UV absorber prepared in the UV absorber charging pot 10 if necessary. Is done. The main dope solution is mixed in a mixer 21 which is an in-line mixer according to the present invention. Subsequently, it is filtered by the filter 3, defoamed by the stock tank 4, and guided to the die while being filtered.

Stirring at a shear rate according to the present invention is preferably performed in the main melting pot 1 or the mixer 21, and more preferably in the mixer 21. There is no restriction on the installation location of the mixer 21, and it is preferable to further provide the mixer 21 between the main dissolution vessel 1 and the filter 3 and perform stirring at a high shear rate in order to reduce the filtration load.

The mixer 21 is preferably a static mixer type in-line mixer. In-line mixers are commercially available as in-line mixers and static mixers. For example, a static mixer manufactured by Kenics (USA), a static mixing element SMV type manufactured by Sulger (Switzerland), a Shimazaki pipe mixer manufactured by Kodate Co., a Hi-Mixer manufactured by Toray Industries, and a static mixer manufactured by Noritake N10 etc. By adjusting the number of rotations using these, stirring can be performed in the range of a shear rate of 2 × 10 ³ s ⁻¹ to 2 × 10 ⁴ s ⁻¹ .

The shear rate can be calculated from the following formula based on the shape and size of the screw and cylinder and the screw rotation speed.

Formula γ = πDN / h
In the formula, γ is the shear rate, D is the outer diameter of the screw, N is the number of screw revolutions, and h is the tip clearance (interval between screws, etc.).

The temperature of the dope at the time of stirring with the mixer 21 is not less than the boiling point at a normal pressure of the solvent used for the dope and not more than 50 ° C. higher than the boiling point at the normal pressure of the solvent. When the solvent is mixed, the boiling point at normal pressure as the mixed solvent is obtained and set as the boiling point.

If it is less than the boiling point of the solvent, undissolved substances are likely to be generated, and if it exceeds 50 ° C., it boils and bubbles are mixed in the dope. The time required for stirring can be adjusted as appropriate, but it is preferably in the range of 5 seconds to 5 minutes from the viewpoint of performance and productivity. More preferably, it is in the range of 5 seconds to 1 minute.

FIG. 2 shows an example of the production method of the present invention using a disperser. In order to remove undissolved substances, a process of not only strengthening stirring and mixing but also retaining a certain amount in the middle is provided. It is preferable.

As a method for producing the dope, the dope being dissolved in the main dissolution vessel 1 as a dissolution vessel is fed to the disperser 50 and dispersed by the disperser 50, and then returned to the main dissolution vessel 1 again. And circulating the main dissolution vessel 1 is preferable because a sufficiently dissolved dope can be adjusted in a short time.

Cellulose acetate is mixed and swollen with a solvent in a dissolution vessel to form a dope. This dope still contains undissolved material. Thereafter, the dope passes through the dispersion step and returns to the melting pot again. The returned dope stays while being stirred in the melting pot and is again passed through the dispersion step. This circulation process is repeated until the undissolved material is sufficiently dissolved. In the circulation process, the dope can be continuously supplied to and passed through the disperser.

The maximum temperature when cellulose acetate is dissolved in the main dissolution vessel 1 is preferably 20 ° C. to 50 ° C. higher than the boiling point of the solvent. If it is less than 20 ° C., it takes a long time to dissolve, or if it exceeds 50 ° C., bubbles are easily generated due to boiling, which is not preferable.

In addition, the temperature of the dope in the step of stirring with the disperser 50 is performed from the boiling point of the solvent at a normal pressure to a temperature higher by 50 ° C. than the boiling point of the solvent at the normal pressure. If it is less than the boiling point of the solvent, undissolved substances are likely to be generated, and if it exceeds 50 ° C., it boils and bubbles are mixed in the dope.

The disperser 50 is preferably a medialess disperser. In particular, since a dope containing a low boiling point solvent is processed at a high temperature, a sealed type is preferable. As the sealed medialess disperser, for example, a continuous emulsification disperser manufactured by PRIMIX Co., Ltd. is used. TK / homomic line mill is particularly preferable. Moreover, the type which inserts an ultrasonic disperser in piping may be sufficient.

The shear rate of the disperser can also be calculated using the formula for determining the shear rate of the in-line mixer.

The step of preparing the dope will be further described. The concentration of the cellulose acetate in the dope is preferably higher because the drying load after casting on the metal support can be reduced. The load increases, and the filtration accuracy deteriorates. The concentration that achieves both of these is preferably 10 to 35% by mass, and more preferably 15 to 25% by mass.

The solvent used in the dope may be used alone or in combination of two or more, but it is preferable to use a mixture of a good solvent and a poor solvent of cellulose acetate in terms of production efficiency, and there are many good solvents. This is preferable from the viewpoint of solubility of cellulose acetate.

A preferable range of the mixing ratio of the good solvent and the poor solvent is 70 to 98% by mass for the good solvent and 2 to 30% by mass for the poor solvent. With a good solvent and a poor solvent, what dissolve | melts the cellulose acetate to be used independently is defined as a good solvent, and what does not swell or dissolve independently is defined as a poor solvent.

Therefore, good solvent and poor solvent change depending on the degree of acetyl group substitution of cellulose acetate.

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

The poor solvent used in the present invention is not particularly limited, but for example, methanol, ethanol, n-butanol, cyclohexane, cyclohexanone and the like are preferably used.

Further, as the solvent used for dissolving cellulose acetate, the solvent removed from the film by drying in the film forming process is recovered and reused.

The recovery solvent may contain trace amounts of additives added to cellulose acetate, such as plasticizers, UV absorbers, polymers, monomer components, etc., but these are preferably reused even if they are included. Can be purified and reused if necessary.

As a method for dissolving cellulose acetate in the main dissolution vessel 1 when preparing the dope described above, a general method can be used. When heating and pressurization are combined, it is possible to heat above the boiling point at normal pressure.

It is preferable to stir and dissolve while heating at a temperature that is higher than the boiling point of the solvent at normal pressure and that the solvent does not boil under pressure, in order to prevent the generation of massive undissolved material called gel or mamako. Specifically, it is preferable to stir and dissolve the dope at a temperature not lower than the boiling point at normal pressure of the solvent and not higher than 50 ° C. higher than the boiling point at normal pressure of the solvent.

Further, a method in which cellulose acetate is mixed with a poor solvent and wetted or swollen, and then a good solvent is added and dissolved is also preferably used.

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

The heating temperature with the addition of the solvent is preferably higher from the viewpoint of the solubility of cellulose acetate, but if the heating temperature is too high, the required pressure increases and the productivity deteriorates.

The preferred heating temperature is 45 to 120 ° C, more preferably 60 to 110 ° C, and still more preferably 70 ° C to 105 ° C. The pressure is adjusted so that the solvent does not boil at the set temperature.

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

Next, the cellulose acetate solution is filtered using a suitable filter medium such as filter paper. As the filter medium, it is preferable that the absolute filtration accuracy is small in order to remove insoluble matters and the like, but there is a problem that the filter medium is likely to be clogged if the absolute filtration accuracy is too small.

For this reason, a filter medium with an absolute filtration accuracy of 0.008 mm or less is preferable, a filter medium with 0.001 to 0.008 mm is more preferable, and a filter medium with 0.003 to 0.006 mm is still more preferable.

There are no particular restrictions on the material of the filter medium, and ordinary filter media can be used. However, plastic filter media such as polypropylene and Teflon (registered trademark), and metal filter media such as stainless steel do not drop off fibers. preferable.

It is preferable to remove and reduce impurities, particularly bright spot foreign matter, contained in the raw material cellulose acetate by filtration.

Bright spot foreign matter means that when two polarizing plates are placed in a crossed Nicol state, an optical film or the like is placed between them, light is applied from one polarizing plate side, and observation is performed from the other polarizing plate side. It is a point (foreign matter) where light from the opposite side appears to leak, and the number of bright spots having a diameter of 0.01 mm or more is preferably 200 / cm ² or less.

More preferably, it is 100 pieces / cm ² or less, still more preferably 50 pieces / m ² or less, still more preferably 0 to 10 pieces / cm ² . Further, it is preferable that the number of bright spots of 0.01 mm or less is small.

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

The preferred temperature is 45 to 120 ° C, more preferably 45 to 70 ° C, and still more preferably 45 to 55 ° C.

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

Next, the process after the casting process will be described.

In the casting process, in FIG. 1, an endless metal belt 31 such as a stainless steel belt or a rotating metal drum that feeds the dope to a pressure die 30 through a liquid feed pump (for example, a pressurized metering gear pump) in FIG. A dope is cast from a pressure die slit at a casting position on a metal support such as the like. A pressure die that can adjust the slit shape of the die base portion and can easily make the film thickness uniform is preferable. The pressure die includes a coat hanger die and a T die, and any of them is preferably used. The surface of the metal support is a mirror surface. In order to increase the film forming speed, two or more pressure dies may be provided on the metal support, and the dope amount may be divided and stacked. Or it is also preferable to obtain the film of a laminated structure by the co-casting method which casts several dope simultaneously.

The solvent evaporation step is a step in which the web (the dope is cast on the casting support and the formed dope film is called a web) is heated on the casting support to evaporate the solvent.

To evaporate the solvent, there are a method of blowing air from the web side, a method of transferring heat from the back side of the support by a liquid, a method of transferring heat from the front and back by radiant heat, etc., but the back side liquid heat transfer method has a drying efficiency. Well preferred. A method of combining them is also preferably used. The web on the support after casting is preferably dried on the support in an atmosphere of 40 to 100 ° C. In order to maintain the atmosphere at 40 to 100 ° C., it is preferable to apply hot air at this temperature to the upper surface of the web or heat by means such as infrared rays. From the viewpoint of surface quality, moisture permeability, and peelability, the web is preferably peeled from the support within 30 to 120 seconds.

The peeling step is a step of peeling the web where the solvent has evaporated on the metal support at the peeling position 33. The peeled web is sent to the next process. The temperature at the peeling position 33 on the metal support is preferably 10 to 40 ° C., more preferably 11 to 30 ° C.

The amount of residual solvent at the time of peeling of the web on the metal support at the time of peeling is preferably 50 to 120% by mass depending on the strength of drying conditions, the length of the metal support, and the like. If the web is peeled off at a time when the amount of residual solvent is larger, if the web is too soft, the flatness at the time of peeling will be lost, and slippage and vertical stripes are likely to occur due to the peeling tension. The amount of solvent is determined.

The amount of residual solvent in the web is defined by the following formula.

Residual solvent amount (%) = (mass before web heat treatment−mass after web heat treatment) / (mass after web heat treatment) × 100
Note that the heat treatment for measuring the residual solvent amount represents performing heat treatment at 115 ° C. for 1 hour.

The peeling tension at the time of peeling the metal support and the film is usually 196 to 245 N / m. However, if wrinkles easily occur at the time of peeling, it is preferable to peel with a tension of 190 N / m or less. It is preferable to peel at a minimum tension of ˜166.6 N / m, and then peel at a minimum tension of ˜137.2 N / m, and particularly preferable to peel at a minimum tension of ˜100 N / m.

In the present invention, the temperature at the peeling position on the metal support is preferably −50 to 40 ° C., more preferably 10 to 40 ° C., and most preferably 15 to 30 ° C.

In the drying and stretching step, after peeling, a drying device 35 that transports the web alternately through a plurality of rolls arranged in the drying device, or a tenter stretching device 34 that clips and transports both ends of the web with clips, Dry the web. Generally, the drying means blows hot air on both sides of the web, but there is also a means for heating by applying microwaves instead of the wind. Rapid drying tends to impair the flatness of the finished film. Drying at a high temperature is preferably performed from about 8% by mass or less of the residual solvent. Throughout, drying is generally performed at 40-250 ° C. In particular, drying at 40 to 160 ° C. is preferable. The stretching is preferably performed with a clip tenter, but a pin tenter can also be used.

In the present invention, stretching is preferably performed under the following conditions.
(1) 10 ° C. ≦ stretching temperature−tensile softening point of resin composition ≦ 100 ° C.
(2) 20% ≦ MD direction (casting direction) or TD direction (width direction) at least one draw ratio ≦ 100%
More preferably, 40% ≦ MD direction (casting direction) or TD direction (width direction) at least one draw ratio ≦ 80%
(3) 40% ≦ stretch ratio in MD direction + stretch ratio in TD direction ≦ 200%
Regarding the stretching conditions, if the stretching temperature is too low, the brittleness deteriorates. In this case, an unnecessarily stress is generated at the time of stretching, and the polymer molecules are excessively oriented, and this orientation is not preferable because it is easy to tear in the direction parallel to the stretching. An excessively high temperature is not preferable because entanglement of the polymer does not occur. In addition, when the temperature is too high, the polymer may flow or deteriorate.

When using a tenter apparatus for stretching, it is preferable to use an apparatus that can independently control the film gripping length (distance from the start of gripping to the end of gripping) by the left and right gripping means of the tenter. In the tenter process, it is also preferable to intentionally create sections having different temperatures in order to improve planarity.

The winding step is a step of winding the cellulose acetate film by the winder 37 after the residual solvent amount in the web is 2% by mass or less, and the residual solvent amount is 0.4% by mass or less. A film having good stability can be obtained. It is particularly preferable to wind up at 0.00 to 0.10% by mass.

As a winding method, a generally used one may be used, and there are a constant torque method, a constant tension method, a taper tension method, a program tension control method with a constant internal stress, etc., and these may be used properly.

The cellulose acetate film of the present invention is preferably a long film. Specifically, the cellulose acetate film is about 100 m to 5000 m, and is usually in the form of a roll. The width of the film is preferably 1300 to 4000 mm, more preferably 1900 mm to 2500 mm.

The film thickness of the cellulose acetate film of the present invention is not particularly limited, but when used for a polarizing plate protective film described later, it is preferably 20 to 200 μm, more preferably 25 to 100 μm, and 30 to 80 μm. It is particularly preferred.

<Cellulose acetate>
As the cellulose acetate film of the present invention, a film made of cellulose acetate having a degree of acetyl group substitution of 2.0 to 2.5 is used from the viewpoint of high retardation development due to stretching and enabling thinning. The preferred degree of acetyl group substitution is 2.2 to 2.48. The degree of acetyl substitution can be measured according to ASTM D-817-91.

Further, when the degree of acetyl substitution at the 6-position of cellulose acetate is D6, it is characterized by 0.745 ≦ D6 ≦ 0.95. A preferable range of D6 is 0.80 ≦ D6 ≦ 0.95. The 6-position acetyl substitution degree can be determined by NMR method.

The number average molecular weight (Mn) of the cellulose acetate according to the present invention is preferably in the range of 30000 to 300000, since the mechanical strength of the resulting film is strong. Further, those having 50000-200000 are preferably used.

The value of the ratio Mw / Mn of the weight average molecular weight (Mw) and the number average molecular weight (Mn) of cellulose acetate is preferably 1.4 to 3.0.

The mass average molecular weight Mw and number average molecular weight Mn of cellulose acetate were measured using gel permeation chromatography (GPC).

The measurement conditions are as follows.

Solvent: Methylene chloride Column: Shodex K806, K805, K803G (Used by connecting three Showa Denko Co., Ltd.)
Column temperature: 25 ° C
Sample concentration: 0.1% by mass
Detector: RI Model 504 (manufactured by GL Sciences)
Pump: L6000 (manufactured by Hitachi, Ltd.)
Flow rate: 1.0ml / min
Calibration curve: Standard polystyrene STK standard polystyrene (manufactured by Tosoh Corp.) Mw = 1000,000 to 500 13 calibration curves were used. Thirteen samples are used at approximately equal intervals.

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

The cellulose acetate according to the present invention can be produced by appropriately using known methods, and can be synthesized, for example, with reference to the method described in JP-A-10-45804.

An example of a method for producing cellulose acetate having a high degree of acetyl substitution at the 6-position according to the present invention (hereinafter referred to as 6-position highly acetylated cellulose acetate) is shown below.

[Production of 6-position highly acetylated cellulose acetate]
The method for producing a 6-position highly acetylated cellulose acetate having an acetyl group substitution degree of 2.0 to 2.5 according to the present invention is, for example, a total acetyl substitution degree of 1.0 to 2.5 (especially 1.5 to 1.5). To 2.5) partially acetyl-substituted cellulose acetate can be produced by treatment in a solvent containing at least acetic acid in the presence of an acid catalyst.

The 2-position acetyl substitution degree D2 of the partially acetyl-substituted cellulose acetate used as the raw material is, for example, 0.3 to 0.9, preferably 0.5 to 0.9, and the 3-position acetyl substitution degree D3 is, for example, 0. .3 to 0.9, preferably 0.5 to 0.9, and the acetyl substitution degree D6 at the 6-position is, for example, 0.3 or more and less than 0.9, preferably 0.5 to 0.8. The degree of acetyl substitution at each position can be determined by NMR method.

The average degree of polymerization of the partially acetyl-substituted cellulose acetate used as a raw material is, for example, about 20 to 500, preferably 81 to 500, more preferably 85 to 400, and particularly preferably about 90 to 250.

Examples of the acid catalyst used in the present invention include inorganic acids (such as mineral acids) such as hydrochloric acid, hydrobromic acid, perchloric acid, hypochlorous acid, chlorous acid, nitric acid, and sulfuric acid. Among these, hydrochloric acid, perchloric acid, hypochlorous acid, chlorous acid, and nitric acid are preferable. An acid catalyst can be used individually or in combination of 2 or more types.

The amount of the acid catalyst used is not particularly limited and can be appropriately selected in consideration of the reaction rate, reaction selectivity, cost, ease of post-treatment, etc. The content is about 0.1 to 50% by mass, preferably about 1 to 30% by mass, and more preferably about 1 to 20% by mass.

The reaction (treatment using an acid catalyst) is performed in a solvent containing at least acetic acid. As a solvent containing at least acetic acid, for example, acetic acid; a mixture of acetic acid and at least one organic solvent selected from the group consisting of halogen solvents, ketone solvents, ether solvents, ester solvents and amide solvents A solvent etc. are mentioned. Examples of the halogen solvent include methylene chloride, chloroform, carbon tetrachloride, tetrachloroethane, chlorobenzene and the like. Examples of the ketone solvent include acetone, methyl ethyl ketone, and cyclohexanone. Examples of the ether solvent include cyclic ethers such as tetrahydrofuran, 1,4-dioxane and dioxolane; chain ethers such as ethyl ether and isopropyl ether. Examples of the ester solvent include aliphatic carboxylic acid esters such as methyl acetate, ethyl acetate, and butyl acetate; aromatic carboxylic acid esters such as methyl benzoate and ethyl benzoate. Examples of the amide solvent include N, N-dimethylformamide, N, N-dimethylacetamide, N-methylpyrrolidone and the like.

In the present invention, among the above, a mixed solvent of acetic acid such as acetic acid / methylene chloride or acetic acid / chloroform and a halogen-based solvent; a mixed solvent of acetic acid and ketone-based solvent such as acetic acid / acetone or acetic acid / cyclohexanone, etc. A mixed solvent of acetic acid and at least one organic solvent selected from halogen solvents, ketone solvents, ether solvents, ester solvents and amide solvents is preferred. When a mixed solvent of acetic acid and another organic solvent is used, the ratio is, for example, the former / the latter (mass ratio) = 5/95 to 95/5, preferably 10/90 to 90/10, more preferably 20 / 80 to about 80/20.

Water is not particularly required in the reaction system, but a small amount may be used as necessary, for example, as a solvent for the acid catalyst. The amount of water is, for example, 0 to 10% by mass, preferably 0 to 5% by mass, and more preferably 0 to 1% by mass with respect to the reaction solvent (a solvent containing at least acetic acid).

The reaction temperature (treatment temperature using an acid catalyst) can be appropriately selected in consideration of the reaction rate and the selectivity of the reaction, but is preferably in the range of 0 to 100 ° C., particularly 20 to 60 ° C. If the temperature is too high, the degree of polymerization tends to decrease. On the other hand, if the temperature is too low, the reaction time becomes long and the productivity is low. The reaction time varies depending on the kind of partially acetyl-substituted cellulose acetate used as a raw material, the reaction temperature, the amount of acid catalyst used, etc., but is generally 0.5 to 24 hours, preferably 1 to 12 hours, more preferably 2 to 2 hours. About 8 hours. The treatment with an acid catalyst is usually performed at normal pressure, but may be performed under pressure or under reduced pressure. The treatment with an acid catalyst may be performed by any method such as a batch method, a semi-batch method, and a continuous method.

By the above treatment, the acetyl group of the partially acetyl-substituted cellulose acetate used as a raw material is moved to produce a 6-position highly acetylated cellulose acetate in which the 6-position hydroxyl group is selectively acetylated. In this case, 0.745 ≦ D6 ≦ 0.95. Moreover, according to the said method, the 6-position highly acetylated cellulose acetate with a narrow total substitution degree distribution is obtained. The total substitution degree distribution means a distribution state of the introduction positions of acetyl groups with respect to the cellulose main chain, and can be measured by an absorption band analysis of an infrared absorption spectrum. In addition, it is described in pages 219 to 221 of Hiroyuki Tadokoro, Polymer Structure (Chemical Doujin, 1976). The 6-position highly acetylated cellulose acetate having a narrow total substitution degree distribution has good solvent solubility and high uniformity of the reaction when subjected to a solution reaction. Therefore, even when a further derivative is produced, the optical properties are stable. A composition can be obtained. Moreover, since the solubility is good, the uniformity of the dope is high. Therefore, it is possible to obtain a film that suppresses optical foreign matters and has no uneven optical characteristics.

In addition, the free hydroxyl group of cellulose acetate may be acetylated by acetic acid in the system. Moreover, the polymerization degree of cellulose acetate falls with conditions.

After the treatment with the acid catalyst, the reaction product can be separated and purified by separation means such as filtration, concentration, extraction, crystallization, recrystallization, column chromatography and the like. For example, a base for neutralizing the acid catalyst is added to the reaction mixture after the treatment, if necessary, and stirred for an appropriate time, and then poured into a poor solvent to precipitate the product. The target 6-position highly acetylated cellulose acetate can be obtained by filtration, washing with an appropriate washing solution, and drying under reduced pressure, for example.

Examples of the base include nitrogen-containing heterocyclic compounds such as pyridine; tertiary amines such as triethylamine, and amines such as secondary amines such as diethylamine. The amount of the base used is, for example, 1 equivalent or more (1 to 20 equivalents), preferably about 1 to 5 equivalents, relative to the acid catalyst used. The temperature at which the base is added and stirred is, for example, 20 to 100 ° C., preferably 20 to 60 ° C. Examples of the poor solvent used for the precipitation operation include alcohols such as methanol, ethanol and isopropyl alcohol, hydrocarbons such as hexane and toluene, water, mixed solvents thereof, mixed solvents of these with other organic solvents, and the like. As the cleaning liquid, the solvents exemplified as the above poor solvent can be used.

The 6-position highly acetylated cellulose acetate thus obtained can be used as a film raw material as it is or after being further derivatized.

<Sugar ester compound, retardation adjusting agent>
The cellulose acetate film of the present invention preferably contains the following sugar ester compound or retardation adjusting agent in order to prevent performance deterioration due to high-magnification stretching.

<Sugar ester compound>
As the sugar ester compound, it is preferable to use a mixture of ester compounds in which at least one of the pyranose structure or furanose structure is 1 to 12, and a part of the OH group of the structure is esterified.

The ratio of esterification of an ester compound in which at least one of the pyranose structure or furanose structure is 1 to 12 and all or part of the OH groups of the structure is esterified is present in the pyranose structure or furanose structure. It is preferable that it is 70% or more of the OH group.

Examples of the sugar ester compound used in the present invention include the following, but the present invention is not limited to these.

Glucose, galactose, mannose, fructose, xylose or arabinose, lactose, sucrose, nystose, 1F-fructosyl nystose, stachyose, maltitol, lactitol, lactulose, cellobiose, maltose, cellotriose, maltotriose, raffinose or kestose .

Other examples include gentiobiose, gentiotriose, gentiotetraose, xylotriose, and galactosyl sucrose.

Among these compounds, compounds having both a pyranose structure and a furanose structure are particularly preferable.

For example, sucrose, kestose, nystose, 1F-fructosyl nystose, stachyose and the like are preferable, and sucrose is more preferable.

The monocarboxylic acid used for esterifying all or part of the OH group in the pyranose structure or furanose structure is not particularly limited, and is a known aliphatic monocarboxylic acid, alicyclic monocarboxylic acid, aromatic A monocarboxylic acid or the like can be used. The carboxylic acid used may be one type or a mixture of two or more types.

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

Examples of preferable alicyclic monocarboxylic acids include acetic acid, cyclopentanecarboxylic acid, cyclohexanecarboxylic acid, cyclooctanecarboxylic acid, and derivatives thereof.

Examples of preferred aromatic monocarboxylic acids include aromatic monocarboxylic acids having an alkyl group or alkoxy group introduced into the benzene ring of benzoic acid such as benzoic acid and toluic acid, cinnamic acid, benzylic acid, biphenylcarboxylic acid, and naphthalene. Examples thereof include aromatic monocarboxylic acids having two or more benzene rings such as carboxylic acid and tetralincarboxylic acid, or derivatives thereof. More specifically, xylyl acid, hemelic acid, mesitylene acid, prenylic acid, γ-isoduric acid, jurylic acid, mesitic acid, α-isoduric acid, cumic acid, α-toluic acid, hydroatropic acid, atropic acid, hydrocinnamic acid, salicylic acid, o-anisic acid, m-anisic acid, p-anisic acid Creosote acid, o-homosalicylic acid, m-homosalicylic acid, p-homosalicylic acid, o-pyro Technic acid, β-resorcylic acid, vanillic acid, isovanillic acid, veratromic acid, o-veratrumic acid, gallic acid, asaronic acid, mandelic acid, homoanisic acid, homovanillic acid, homoveratrumic acid, o-homoveratrumic acid, phthalonic acid, p- Although coumaric acid can be mentioned, benzoic acid and naphthylic acid are particularly preferable.

Oligosaccharide ester compounds can be applied as compounds having 1 to 12 at least one of the pyranose structure or furanose structure according to the present invention.

Oligosaccharides are produced by allowing an enzyme such as amylase to act on starch, sucrose, etc. Examples of oligosaccharides that can be applied to the present invention include maltooligosaccharides, isomaltooligosaccharides, fructooligosaccharides, galactooligosaccharides, and xylooligos. Sugar.

Moreover, the said sugar ester compound is a compound which condensed 1 or more and 12 or less of at least 1 sort (s) of the pyranose structure or furanose structure represented with the following general formula (A). R ₁₁ to R ₁₅ and R ₂₁ to R _{25 each} represents an acyl group having 2 to 22 carbon atoms or a hydrogen atom, m and n each represents an integer of 0 to 12, and m + n represents an integer of 1 to 12.

R ₁₁ to R ₁₅ and R ₂₁ to R ₂₅ are preferably a benzoyl group or a hydrogen atom. The benzoyl group may further have a substituent R ₂₆ , and examples thereof include an alkyl group, an alkenyl group, an alkoxyl group, and a phenyl group, and these alkyl group, alkenyl group, and phenyl group have a substituent. May be. Oligosaccharides can also be produced in the same manner as the ester compound according to the present invention.

Specific examples of the sugar ester compound according to the present invention will be given below, but the present invention is not limited thereto.

The average substitution degree of the sugar ester compound added to the cellulose acetate film of the present invention is preferably 5.0 to 7.0, and the range of the substitution degree is preferably 4 to 8. A particularly preferred range of the average substitution degree is 5.0 to 6.7. The substitution degree distribution may be adjusted to the desired substitution degree by adjusting the esterification reaction time or mixing compounds having different substitution degrees.

The average degree of substitution can be measured by spectroscopic techniques such as quantification of the obtained sugar ester compound by high-performance liquid chromatography (HPLC) or integral value of conventional ¹ H-NMR. .

The cellulose acetate film according to the present invention preferably contains a sugar ester compound in an amount of 0.5 to 30% by mass of the cellulose acetate film, and particularly preferably 2 to 15% by mass.

<Phase difference adjusting agent>
As the phase difference adjusting agent used in the present invention, an ester compound represented by the following general formula (B) can be preferably used.

Formula (B) B- (GA) n-GB
(Wherein B is a hydroxy group or carboxylic acid residue, G is an alkylene glycol residue having 2 to 12 carbon atoms, an aryl glycol residue having 6 to 12 carbon atoms, or an oxyalkylene glycol residue having 4 to 12 carbon atoms) A represents an alkylene dicarboxylic acid residue having 4 to 12 carbon atoms or an aryl dicarboxylic acid residue having 6 to 12 carbon atoms, and n represents an integer of 1 or more.)
In the general formula (B), a hydroxy group or carboxylic acid residue represented by B, an alkylene glycol residue or oxyalkylene glycol residue or aryl glycol residue represented by G, an alkylene dicarboxylic acid residue represented by A or It is composed of an aryl dicarboxylic acid residue and can be obtained by the same reaction as that of a normal ester compound.

Examples of the carboxylic acid component of the ester compound represented by the general formula (B) include acetic acid, propionic acid, butyric acid, benzoic acid, p-tert-butylbenzoic acid, orthotoluic acid, metatoluic acid, p-toluic acid, and dimethylbenzoic acid. , Ethyl benzoic acid, normal propyl benzoic acid, aminobenzoic acid, acetoxybenzoic acid, aliphatic acid and the like, and these can be used as one kind or a mixture of two or more kinds, respectively.

Examples of the alkylene glycol component having 2 to 12 carbon atoms of the ester compound represented by the general formula (B) include ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,2-butanediol, , 3-butanediol, 1,2-propanediol, 2-methyl 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 2,2-dimethyl-1,3-propanediol ( Neopentyl glycol), 2,2-diethyl-1,3-propanediol (3,3-dimethylolpentane), 2-n-butyl-2-ethyl-1,3-propanediol (3,3-dimethylolheptane) ), 3-methyl-1,5-pentanediol 1,6-hexanediol, 2,2,4-trimethyl 1,3-pentanedio And 2-ethyl 1,3-hexanediol, 2-methyl 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,12-octadecanediol, and the like. It is used as one kind or a mixture of two or more kinds.

Particularly, alkylene glycols having 2 to 12 carbon atoms are particularly preferable because of excellent compatibility with cellulose esters.

Examples of the oxyalkylene glycol component having 4 to 12 carbon atoms of the ester compound represented by the general formula (B) include diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, and tripropylene glycol. Yes, these glycols can be used as one or a mixture of two or more.

Examples of the alkylene dicarboxylic acid component having 4 to 12 carbon atoms of the ester compound represented by the general formula (B) include, for example, succinic acid, maleic acid, fumaric acid, glutaric acid, adipic acid, azelaic acid, sebacic acid, and dodecane. There exist dicarboxylic acid etc., and these are each used as a 1 type, or 2 or more types of mixture. Examples of the arylene dicarboxylic acid component having 6 to 12 carbon atoms include phthalic acid, terephthalic acid, isophthalic acid, 1,5 naphthalene dicarboxylic acid, and 1,4 naphthalene dicarboxylic acid.

The ester compound represented by the general formula (B) has a number average molecular weight of preferably 300 to 1500, more preferably 400 to 1000. The acid value is 0.5 mgKOH / g or less, the hydroxyl value is 25 mgKOH / g or less, more preferably the acid value is 0.3 mgKOH / g or less, and the hydroxyl value is 15 mgKOH / g or less.

Hereinafter, specific compounds of the ester compound represented by the general formula (B) that can be used in the present invention are shown, but the present invention is not limited thereto.

It is also preferable to use an aromatic compound having at least two aromatic rings as a phase difference adjusting agent. Two or more aromatic compounds may be used in combination as the aromatic compound. The aromatic ring of the aromatic compound includes an aromatic hetero ring in addition to the aromatic hydrocarbon ring. The aromatic hydrocarbon ring is particularly preferably a 6-membered ring (that is, a benzene ring). The aromatic heterocycle is generally an unsaturated heterocycle. The aromatic heterocycle is preferably a 5-membered ring, 6-membered ring or 7-membered ring, more preferably a 5-membered ring or 6-membered ring. Aromatic heterocycles generally have the most double bonds. As the hetero atom, a nitrogen atom, an oxygen atom and a sulfur atom are preferable, and a nitrogen atom is particularly preferable. Examples of aromatic heterocycles include furan ring, thiophene ring, pyrrole ring, oxazole ring, isoxazole ring, thiazole ring, isothiazole ring, imidazole ring, pyrazole ring, furazane ring, triazole ring, pyran ring, pyridine ring , Pyridazine ring, pyrimidine ring, pyrazine ring and 1,3,5-triazine ring. Details of these are described in JP-A No. 2004-109410, JP-A No. 2003-344655, JP-A No. 2000-275434, JP-A No. 2000-1111914, JP-A No. 12-275434, and the like.

The cellulose acetate film of the present invention preferably contains a retardation adjusting agent in an amount of 0.1 to 30% by mass, particularly 0.5 to 10% by mass of the cellulose acetate film.

<Other additives>
(Other plasticizers)
The cellulose acetate film according to the present invention can contain, in addition to the above additives, other plasticizers as necessary for obtaining the effects of the present invention.

The plasticizer is not particularly limited, but is preferably selected from glycolate plasticizers, phthalate plasticizers, fatty acid ester plasticizers and polyhydric alcohol ester plasticizers, ester plasticizers, acrylic plasticizers, and the like. Is done.

Of these, when two or more plasticizers are used, at least one is preferably a polyhydric alcohol ester plasticizer.

The polyhydric alcohol ester plasticizer is a plasticizer composed of an ester of a divalent or higher aliphatic polyhydric alcohol and a monocarboxylic acid, and preferably has an aromatic ring or a cycloalkyl ring in the molecule. A divalent to 20-valent aliphatic polyhydric alcohol ester is preferred.

The polyhydric alcohol preferably used in the present invention is represented by the following general formula (a).

Formula (a) R ₁₁ — (OH) _n
However, R ₁₁ represents an n-valent organic group, n represents a positive integer of 2 or more, and the OH group represents an alcoholic and / or phenolic hydroxyl group.

Examples of preferred polyhydric alcohols include the following, but the present invention is not limited to these.

Adonitol, arabitol, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, 1,2-propanediol, 1,3-propanediol, dipropylene glycol, tripropylene glycol, 1,2-butanediol, 1,3- Butanediol, 1,4-butanediol, dibutylene glycol, 1,2,4-butanetriol, 1,5-pentanediol, 1,6-hexanediol, hexanetriol, galactitol, mannitol, 3-methylpentane Examples include 1,3,5-triol, pinacol, sorbitol, trimethylolpropane, trimethylolethane, and xylitol.

In particular, triethylene glycol, tetraethylene glycol, dipropylene glycol, tripropylene glycol, sorbitol, trimethylolpropane, and xylitol are preferable.

There is no restriction | limiting in particular as monocarboxylic acid used for polyhydric alcohol ester, Well-known aliphatic monocarboxylic acid, alicyclic monocarboxylic acid, aromatic monocarboxylic acid, etc. can be used. Use of an alicyclic monocarboxylic acid or aromatic monocarboxylic acid is preferred in terms of improving moisture permeability and retention.

Preferred examples of the monocarboxylic acid include the following, but the present invention is not limited to this.

As the aliphatic monocarboxylic acid, a fatty acid having a straight chain or a side chain having 1 to 32 carbon atoms can be preferably used. The number of carbon atoms is more preferably 1-20, and particularly preferably 1-10. The inclusion of acetic acid is preferred because the compatibility with cellulose acetate increases, and it is also preferred to use a mixture of acetic acid and other monocarboxylic acids.

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

Examples of preferable alicyclic monocarboxylic acids include cyclopentane carboxylic acid, cyclohexane carboxylic acid, cyclooctane carboxylic acid, and derivatives thereof.

Examples of preferred aromatic monocarboxylic acids include those in which 1 to 3 alkoxy groups such as alkyl group, methoxy group or ethoxy group are introduced into the benzene ring of benzoic acid such as benzoic acid and toluic acid, biphenylcarboxylic acid, Examples thereof include aromatic monocarboxylic acids having two or more benzene rings such as naphthalenecarboxylic acid and tetralincarboxylic acid, or derivatives thereof. Benzoic acid is particularly preferable.

The molecular weight of the polyhydric alcohol ester is not particularly limited, but is preferably 300 to 1500, and more preferably 350 to 750. A higher molecular weight is preferred because it is less likely to volatilize, and a smaller one is preferred in terms of moisture permeability and compatibility with cellulose acetate.

The carboxylic acid used in the polyhydric alcohol ester may be one kind or a mixture of two or more kinds. Moreover, all the OH groups in the polyhydric alcohol may be esterified, or a part of the OH groups may be left as they are.

The glycolate plasticizer is not particularly limited, but alkylphthalylalkyl glycolates can be preferably used.

Examples of alkyl phthalyl alkyl glycolates include methyl phthalyl methyl glycolate, ethyl phthalyl ethyl glycolate, propyl phthalyl propyl glycolate, butyl phthalyl butyl glycolate, octyl phthalyl octyl glycolate, methyl phthalyl ethyl Glycolate, ethyl phthalyl methyl glycolate, ethyl phthalyl propyl glycolate, methyl phthalyl butyl glycolate, ethyl phthalyl butyl glycolate, butyl phthalyl methyl glycolate, butyl phthalyl ethyl glycolate, propyl phthalyl butyl glycol Butyl phthalyl propyl glycolate, methyl phthalyl octyl glycolate, ethyl phthalyl octyl glycolate, octyl phthalyl methyl glycolate, octyl phthalate Ethyl glycolate, and the like.

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

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

Examples of fatty acid ester plasticizers include butyl oleate, methylacetyl ricinoleate, and dibutyl sebacate.

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

(UV absorber)
The cellulose acetate film according to the present invention can also contain an ultraviolet absorber. The ultraviolet absorber is intended to improve durability by absorbing ultraviolet rays of 400 nm or less, and in particular, the transmittance at a wavelength of 370 nm is preferably 10% or less, more preferably 5% or less. is there.

Although the ultraviolet absorber used in the present invention is not particularly limited, for example, oxybenzophenone compounds, benzotriazole compounds, salicylic acid ester compounds, benzophenone compounds, cyanoacrylate compounds, triazine compounds, nickel complex compounds, inorganic powders Examples include the body.

The amount of the UV absorber used is not uniform depending on the type of UV absorber, usage conditions, etc., but when the dry thickness of the cellulose acetate film is 20 to 38 μm, it is 0.5 to 10 with respect to the cellulose acetate film. % By mass is preferable, and 0.6 to 4% by mass is more preferable.

(Antioxidant)
Antioxidants are also referred to as deterioration inhibitors. When a liquid crystal image display device or the like is placed in a high humidity and high temperature state, the cellulose acetate film may be deteriorated.

The antioxidant has a role of delaying or preventing the cellulose acetate film from being decomposed by, for example, the residual solvent amount of halogen in the cellulose acetate film or phosphoric acid of the phosphoric acid plasticizer. It is preferable to make it contain in a film.

As such an antioxidant, a hindered phenol compound is preferably used. For example, 2,6-di-t-butyl-p-cresol, pentaerythrityl-tetrakis [3- (3,5-di- -T-butyl-4-hydroxyphenyl) propionate], triethylene glycol-bis [3- (3-t-butyl-5-methyl-4-hydroxyphenyl) propionate], 1,6-hexanediol-bis [3 -(3,5-di-t-butyl-4-hydroxyphenyl) propionate], 2,4-bis- (n-octylthio) -6- (4-hydroxy-3,5-di-t-butylanilino)- 1,3,5-triazine, 2,2-thio-diethylenebis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], oct Decyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate, N, N'-hexamethylenebis (3,5-di-t-butyl-4-hydroxy-hydrocinnamamide) 1,3,5-trimethyl-2,4,6-tris (3,5-di-t-butyl-4-hydroxybenzyl) benzene, tris- (3,5-di-t-butyl-4-hydroxy Benzyl) -isocyanurate and the like.

In particular, 2,6-di-t-butyl-p-cresol, pentaerythrityl-tetrakis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], triethylene glycol-bis [3 -(3-tert-butyl-5-methyl-4-hydroxyphenyl) propionate] is preferred. Further, for example, hydrazine-based metal deactivators such as N, N′-bis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionyl] hydrazine and tris (2,4-di- A phosphorus processing stabilizer such as t-butylphenyl) phosphite may be used in combination.

The amount of these compounds to be added is preferably 1 ppm to 1.0%, more preferably 10 to 1000 ppm by weight with respect to cellulose acetate.

(Fine particles)
The cellulose acetate film according to the present invention preferably contains fine particles from the viewpoint of slipperiness and storage stability.

As fine particles, examples of inorganic compounds include silicon dioxide, titanium dioxide, aluminum oxide, zirconium oxide, calcium carbonate, calcium carbonate, talc, clay, calcined kaolin, calcined calcium silicate, hydrated calcium silicate, aluminum silicate, Examples thereof include magnesium silicate and calcium phosphate. When the fine particles contain silicon, turbidity is preferable, and silicon dioxide is particularly preferable.

Silicon dioxide that has been subjected to a hydrophobization treatment is preferable for achieving both slipperiness and haze. Of the four silanol groups, those in which two or more are substituted with a hydrophobic substituent are preferred, and those in which three or more are substituted are more preferred. The hydrophobic substituent is preferably a methyl group.

The primary particle diameter of silicon dioxide is preferably 20 nm or less, and more preferably 10 nm or less.

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

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

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

Among these, Aerosil 200V and Aerosil R972V are particularly preferable because they have a large effect of reducing the friction coefficient while keeping the haze of the cellulose acetate film low, and Aerosil R812 is most preferably used in the present invention. In the cellulose acetate film according to the present invention, the dynamic friction coefficient of at least one surface is preferably 0.2 to 1.0.

(Peeling aid)
In the present invention, it is also preferable to use a peeling aid in order to facilitate peeling of the web at the peeling point, and examples of preferred peeling aids used include yes citrate compounds such as polyvalent carboxylic acid esters. Esters include triethyl citrate, tributyl citrate, acetyl triethyl citrate (ATEC), acetyl tributyl citrate (ATBC), benzoyl tributyl citrate, acetyl triphenyl citrate, acetyl tribenzyl citrate, dibutyl tartrate, diacetyl dibutyl tartrate , Trimellitic acid tributyl, pyromellitic acid tetrabutyl and the like.

(dye)
A dye may be added to the cellulose acetate film according to the present invention for color adjustment. For example, a blue dye may be added to suppress the yellowness of the film. Preferred examples of the dye include anthraquinone dyes.

<Physical properties of cellulose acetate film>
(Retardation)
Although the cellulose acetate film of the present invention can have an optical compensation function as a retardation film, the retardation Ro defined by the formula (I) in the in-plane direction is used from the viewpoint of taking advantage of high retardation development property due to high stretching. It is preferably 30 nm or more, more preferably in the range of 30 to 200 nm, and particularly preferably in the range of 30 to 70 nm. The retardation Rth in the thickness direction defined by the formula (II) is preferably 70 nm or more, and more preferably in the range of 70 to 300 nm. Although there is no restriction | limiting in particular as an adjustment method of a phase difference, The method of adjusting with the said extending process is common.

Formula (I) Ro = (nx−ny) × d
Formula (II) Rth = {(nx + ny) / 2−nz} × d
(Where nx is the refractive index in the slow axis direction in the film plane, ny is the refractive index in the fast axis direction in the film plane, nz is the refractive index in the thickness direction of the film, and d is (The thickness of the film (nm).)
<Measurement of retardation Ro and Rth>
A 35 mm × 35 mm sample was cut out from the obtained film, conditioned at 25 ° C. and 55% RH for 2 hours, and measured with an automatic birefringence meter (KOBRA21DH, Oji Scientific Co., Ltd.) from the vertical direction at 546 nm and the film. It is calculated from the extrapolated value of the retardation value measured in the same manner while tilting the surface.

The moisture permeability of the cellulose acetate film of the present invention is preferably 300 to 1800 g / m ² · 24 h at 40 ° C. and 90% RH, more preferably 400 to 1500 g / m ² · 24 h, and 40 to 1300 g / m ² · 24 h. Particularly preferred. The moisture permeability can be measured according to the method described in JIS Z 0208.

The cellulose acetate film of the present invention has a breaking elongation of preferably 10 to 80%, more preferably 20 to 50%.

The visible light transmittance of the cellulose acetate film of the present invention is preferably 90% or more, and more preferably 93% or more.

The haze of the cellulose acetate film of the present invention is preferably less than 1%, particularly preferably 0 to 0.1%. Haze uses a haze meter (NDH2000 type, manufactured by Nippon Denshoku Industries Co., Ltd.) according to JIS K-7136 for one sample of a film sample that was conditioned for 24 hours in an air-conditioned room at 23 ° C. and 55% RH. To measure.

<Polarizing plate>
The cellulose acetate film of this invention can be used for a polarizing plate and a liquid crystal display device using the same.

The polarizing plate is characterized in that it is a polarizing plate in which the cellulose acetate film of the present invention is bonded to at least one surface of a polarizer. The liquid crystal display device of the present invention is characterized in that the polarizing plate according to the present invention is bonded to at least one liquid crystal cell surface via an adhesive layer.

The polarizing plate can be produced by a general method. The cellulose acetate film of the present invention is preferably bonded to at least one surface of a polarizer prepared by subjecting the polarizer side to alkali saponification treatment and immersion drawing in an iodine solution using a completely saponified polyvinyl alcohol aqueous solution.

Even if the cellulose acetate film is used on the other surface, it is also preferable to bond another film.

For example, commercially available cellulose ester films (for example, Konica Minoltack KC8UX, KC5UX, KC8UCR3, KC8UCR4, KC8UCR5, KC8UY, KC4UY, KC4UE, KC8UE, KC8UY-HA, KC8UX-RHA, KC8UX-RHA, KC8UX KC4UXW-RHA-NC, manufactured by Konica Minolta Opto Co., Ltd.) is preferably used.

The viewing side protective film of the polarizing plate used on the surface side of the display device preferably has an antireflection layer, an antistatic layer, an antifouling layer, and a backcoat layer in addition to the antiglare layer or the clear hard coat layer.

A polarizer, which is a main component of a polarizing plate, is an element that allows only light of a plane of polarization in a certain direction to pass. A typical polarizer currently known is a polyvinyl alcohol-based polarizing film, which is polyvinyl alcohol. There are one in which iodine is dyed on a system film and one in which dichroic dye is dyed.

The polarizer is formed by forming a polyvinyl alcohol aqueous solution into a film and dyeing the film by uniaxial stretching or dyeing or uniaxially stretching, and then performing a durability treatment with a boron compound. The film thickness of the polarizer is preferably 5 to 30 μm, particularly preferably 10 to 20 μm.

Further, the ethylene unit content described in JP-A-2003-248123, JP-A-2003-342322, etc. is 1 to 4 mol%, the degree of polymerization is 2000 to 4000, and the degree of saponification is 99.0 to 99.99 mol%. Ethylene-modified polyvinyl alcohol is also preferably used.

Among them, an ethylene-modified polyvinyl alcohol film having a hot water cutting temperature of 66 to 73 ° C. is preferably used.

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

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

<Liquid crystal display device>
By using the polarizing plate on which the cellulose acetate film of the present invention is bonded to a liquid crystal display device, the liquid crystal display device of the present invention having excellent visibility can be produced.

The cellulose acetate film of the present invention can be used for liquid crystal display devices of various drive systems such as STN, TN, OCB, HAN, VA (MVA, PVA), IPS, OCB. A VA (MVA, PVA) type liquid crystal display device is preferable.

In particular, even a large-screen liquid crystal display device having a 30-inch or larger screen can provide a liquid crystal display device with a wide viewing angle, excellent color visibility, and excellent visibility such as front contrast.

Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto.

Example 1
The sugar ester compounds and retardation adjusting agents used are shown in Table 1 below.

<Measurement of moisture content of dope>
The water content of the dope was measured by measuring 1 cm ³ of the solution using a Karl Fischer method with a moisture meter and a sample drying device (CA-03, VA-05, both Mitsubishi Chemical Corporation), and the amount of moisture contained in the dope. It was calculated by dividing (g) by the dope sample mass (g).

<Shear rate of in-line mixer in FIG. 1 and disperser in FIG. 2>
A Hi-Mixer manufactured by Toray Industries, Inc. was used as the in-line mixer, and a TK homomic line mill manufactured by Primix Co., Ltd. was used as the dispersing machine. When changing the shear rate, the screw rotation speed was changed.

The shear rate was calculated from the following formula from the screw, cylinder shape, size, and screw rotation speed.

Formula γ = πDN / h
In the formula, γ is the shear rate, D is the outer diameter of the screw, N is the number of screw revolutions, and h is the tip clearance (interval between screws, etc.).

<Production of Cellulose Acetate Film 101>
<Fine particle dispersion 1>
Fine particles (Aerosil R972V manufactured by Nippon Aerosil Co., Ltd.)
11 parts by mass Ethanol 89 parts by mass The above was stirred and mixed with a dissolver for 50 minutes, and then dispersed with Manton Gorin.

<Fine particle addition liquid 1>
The fine particle dispersion 1 was slowly added to the dissolution tank containing methylene chloride with sufficient stirring. Further, the particles were dispersed by an attritor so that the secondary particles had a predetermined particle size. This was filtered through Finemet NF manufactured by Nippon Seisen Co., Ltd. to prepare a fine particle additive solution 1.

Methylene chloride 99 parts by mass Fine particle dispersion 1 5 parts by mass A main dope solution having the following composition was prepared. First, water was added to the pressurized dissolution tank so that the water content of methylene chloride and ethanol and the dope solution at the time of casting were in the ratio specified in Table 1.

Cellulose acetate (acetyl substitution degree 2.45, 6-position acetyl substitution degree 0.80) was added to a pressure dissolution tank containing a solvent and water with stirring. This was heated and dissolved with stirring.

<Composition of main dope solution>
Methylene chloride 340 parts by mass Ethanol 64 parts by mass Water: Hydrolyzed cellulose acetate (acetyl substitution degree 2.45, 6-position acetyl substitution degree 0.80) so that the main dope liquid has a water content of 2.0% by mass 100 parts by mass Sugar ester compound: A-5 10 parts by mass Retardation adjusting agent: Ester compound represented by formula (B) / Exemplary compound B-5 4 parts by mass Particulate additive solution 1 1 part by mass The dope solution was prepared by adding to the dissolution vessel 1 and dissolving with stirring.

Next, the main dope solution was subjected to shearing at a shear rate of 10,000 s ⁻¹ at a temperature of 80 ° C. in the mixer 21 of FIG. 1 and stirred for 15 seconds. Thereafter, the main dope solution was Azumi filter paper No. 1 manufactured by Azumi Filter Paper Co., Ltd. Filtered using 244 and transferred the main dope solution to the stock tank.

Next, an endless belt casting apparatus was used to uniformly cast the dope solution on a stainless steel belt support at a temperature of 33 ° C. and a width of 1.75 m. The temperature of the stainless steel belt was controlled at 30 ° C.

On the stainless steel belt support, the solvent was evaporated until the residual solvent amount in the cast (cast) web became 75%, and then peeled off from the stainless steel belt support with a peeling tension of 130 N / m.

The peeled cellulose acetate film was stretched 55% in the width direction using a tenter while applying heat at 165 ° C. The residual solvent at the start of stretching was 10%.

Next, drying was terminated while the drying zone was conveyed by a number of rolls. The drying temperature was 130 ° C. and the transport tension was 100 N / m.

Next, the film was cut into a predetermined film width by a slitter, and then processed with an embossing device in the vicinity of the end of the film with an emboss height of 6 μm.

As described above, a cellulose acetate film 101 having a film width of 2.45 m and a dry film thickness of 40 μm was obtained.

The boiling point at normal pressure of the mixed solvent at the above ratio of methylene chloride and ethanol was 46 ° C.

<Production of Cellulose Acetate Films 102 to 146>
Cellulose acetate films 102 to 146 were produced in the same manner as the cellulose acetate film 101 except that the dope composition and production conditions were changed as shown in Tables 2 and 3.

Incidentally, at the level (109) using the disperser shown in FIG. 2, the main dope is returned to the main dissolving kettle once by a 30-second stirring time and then the main dope taken out from the main dissolving kettle 1 is filtered. And transferred to the stock tank.

In the table, CAP: Ac1.9 + Pr0.7 indicates cellulose acetate propionate having an acetyl group substitution degree of 1.9 and a propionyl group substitution degree of 0.7.

<Evaluation>
About each obtained cellulose acetate film, the retardation value, the presence or absence of an undissolved substance, and the internal haze were measured in the following manner.

(Measurement of retardation Ro and Rth)
A 35 mm × 35 mm sample was cut out from the obtained film, conditioned at 25 ° C. and 55% RH for 2 hours, and measured with an automatic birefringence meter (KOBRA21DH, Oji Scientific Co., Ltd.) from the vertical direction at 546 nm and the film. It calculated from the extrapolation value of the retardation value measured similarly, inclining a surface.

(Presence or absence of undissolved material)
When the obtained film is observed with a microscope MF-AT115-200 made by Mitutoyo at a magnification of 20 × and granular undissolved material is observed x, when transparent and particularly granular undissolved material is not observed ○ It was.

(Internal haze)
The prepared cellulose acetate film was conditioned for 5 hours or more in an environment of 23 ° C. and 55% RH, and then the internal haze value was evaluated by the following method.

<Internal haze measuring device>
Haze meter (turbidity meter) (model: NDH 2000, manufactured by Nippon Denshoku Co., Ltd.)
A 5V9W halogen bulb was used as the light source, and a silicon photocell (with a relative visibility filter) was used as the light receiving unit.

The cellulose acetate film of the present invention preferably has a value of 0.05 or less in the haze measurement of the film when a solvent having a refractive index of ± 0.05 is dropped onto the film with this apparatus. . The measurement was performed according to JIS K-7136.

Measure internal haze as follows. A description will be given with reference to FIGS.

First, the blank haze 1 of a measuring instrument other than a film is measured.
1. Drip a drop (0.05 ml) of glycerin on a cleaned glass slide. At this time, care is taken so that bubbles do not enter the droplet. Be sure to use glass that has been cleaned with a detergent because it may look dirty even if it looks clean. (See Figure 3)
2. Place the cover glass on top of it. Glycerin spreads without pressing the cover glass.
3. Set on a haze meter and measure blank haze 1.

Next, the haze 2 including the sample is measured by the following procedure.
4). Glycerol is dropped on the slide glass. (0.05ml) (See Fig. 3)
5). A sample film to be measured is placed thereon so that no air bubbles enter. (See Figure 4)
6). Glycerol is dropped on the sample film. (0.05 ml) (see FIG. 5)
7). Place the cover glass on top of it. (See Figure 6)
8). The laminate prepared as described above (from above, cover glass / glycerin / sample film / glycerin / slide glass) is set on a haze meter and haze 2 is measured.
9. (Haze 2) − (Haze 1) = (Internal haze of the cellulose acetate film of the present invention) is calculated.

All the above haze measurements were performed at 23 ° C. and 55% RH.

Moreover, the glass and glycerin used in the above measurement are as follows.

Glass: MICRO SLIDE GLASS S9213 MATUNAMI
Glycerin: Kanto Kagaku Deer Special Grade (Purity> 99.0%) Refractive index 1.47
<Production of polarizing plates 101 to 146>
A polyvinyl alcohol film having a thickness of 120 μm was uniaxially stretched (temperature: 110 ° C., stretch ratio: 5 times).

This was immersed in an aqueous solution consisting of 0.075 g of iodine, 5 g of potassium iodide and 100 g of water for 60 seconds, and then immersed in an aqueous solution of 68 ° C. consisting of 6 g of potassium iodide, 7.5 g of boric acid and 100 g of water. This was washed with water and dried to obtain a polarizer.

Next, according to the following steps 1 to 5, a polarizer and the cellulose acetate films 101 to 146 are bonded together with Konica Minolta Tack KC4UY (cellulose ester film manufactured by Konica Minolta Opto Co., Ltd.) on the back side, and polarizing plates 101 to 146 are attached. Produced.

Step 1: Cellulose acetate films 101 to 146 and Konica Minoltac KC8UY were soaked in a 2 mol / L sodium hydroxide solution at 60 ° C. for 90 seconds, then washed with water and dried to saponify the side to be bonded to the polarizer. Obtained.

Step 2: The polarizer was immersed in a polyvinyl alcohol adhesive tank having a solid content of 2% by mass for 1 to 2 seconds.

Step 3: Excess adhesive adhered to the polarizer in Step 2 was gently wiped off and placed on the cellulose acetate films 101 to 146 treated in Step 1.

Step 4: The cellulose acetate films 101 to 146 laminated in Step 3 were bonded to the polarizer and the back side Konica Minoltack KC8UY at a pressure of 20 to 30 N / cm ² and a conveying speed of about 2 m / min.

Step 5: A sample obtained by bonding the polarizer prepared in Step 4 with the cellulose acetate films 101 to 146 and Konica Minolta Tack KC8UY in a drier at 80 ° C. is dried for 2 minutes, and the cellulose acetate films 101 to 146 are respectively dried. Corresponding polarizing plates 101 to 146 were prepared.

<Production of liquid crystal display device>
A liquid crystal panel for viewing angle measurement was produced as follows, and the characteristics as a liquid crystal display device were evaluated.

The double-sided polarizing plates of Sony 40-type display BRAVIA X1 were peeled off, and the above-prepared polarizing plates 101 to 146 were each bonded to both surfaces of the glass surface of the liquid crystal cell.

At that time, the direction of bonding of the polarizing plate is absorbed so that the surfaces of the cellulose acetate films 101 to 146 of the present invention are on the liquid crystal cell side and in the same direction as the polarizing plate previously bonded. The liquid crystal display devices 101 to 146 corresponding to the polarizing plates 101 to 146 were respectively produced so that the axes were directed.

<Evaluation>
(Front contrast of liquid crystal display device)
The front contrast of each liquid crystal display device was measured. The front contrast was measured by a front contrast measuring device (EZ-contrast) manufactured by ELDIM, and the light quantity during white display and black display was measured. The measurement results were ranked according to superiority or inferiority according to the value of the front contrast as follows.
A: Front contrast ratio = 3000: 1 or more B: Front contrast ratio = 2999: 1 to 2000: 1
Δ: Front contrast ratio = 1999: 1 to 1000: 1
X: Front contrast ratio = 999: 1 or less (Evaluation of viewing angle)
The measurement was performed after the backlight of each liquid crystal display device was lit continuously for one week in an environment of 23 ° C. and 55% RH. For the measurement, EZ-Contrast 160D manufactured by ELDIM was used to measure the luminance in a direction tilted 60 degrees from the normal direction of the display screen of white display and black display on a liquid crystal display device, and the ratio (60 ° contrast) was observed in the field of view. It was a corner.

[Evaluation criteria for viewing angle]
A: 60 ° contrast is 100 or more ○: 60 ° contrast is 90 or more and less than 100 Δ: 60 ° contrast is 80 or more and less than 90 ×: 60 ° contrast is less than 80 Table 4 shows the evaluation results.

In the cellulose acetate film of the present invention, no undissolved material is observed, and even when the film is stretched at a high magnification and the film width is in the range of 1.9 to 2.5 m, there is no increase in haze and the cellulose acetate film for optical compensation is used. It was found to have a preferred retardation.

Further, when the contrast and viewing angle of the liquid crystal display device were evaluated, the liquid crystal display device equipped with the polarizing plate using the cellulose acetate film of the present invention had high contrast and visibility with a wide viewing angle because of low internal scattering. It was confirmed that the polarizing plate and the liquid crystal display device were excellent.

DESCRIPTION OF SYMBOLS 1 Main dissolution pot 3, 6, 12, 15 Filter 4, 13 Stock tank 5, 14 Liquid feed pump 8, 16 Pipe | tube 10 Ultraviolet absorber charging pot 20 Merge pipe 21 Mixer 30 Die 31 Metal support 32 Web 33 Peeling Position 34 Tenter device 35 Roll dryer 41 Particle charging vessel 42 Stock tank 43 Pump 44 Filter 50 Disperser

Claims (10)

1. A method for producing a cellulose acetate film by a solution casting method using at least a solvent and a dope containing cellulose acetate having a substitution degree of acetyl group of 2.0 to 2.5, wherein the water content during casting of the dope is 1 The dope is adjusted in the range of 5% by mass or more and 5% by mass or less, and the dope is at a temperature not lower than the boiling point at the normal pressure of the solvent and not higher than 50 ° C. above the boiling point at the normal pressure of the solvent. A method for producing a cellulose acetate film, comprising applying a shear force of 10 ³ s ⁻¹ to 2 × 10 ⁴ s ⁻¹ and stirring, casting the dope to form a film, and then stretching the dope.
2. 2. The method for producing a cellulose acetate film according to claim 1, wherein a moisture content during casting of the dope is 2% by mass or more and 5% by mass or less.
3. The method for producing a cellulose acetate film according to claim 1 or 2, wherein the water content at the time of casting of the dope is adjusted to the range by adding water to the dope.
4. The cellulose acetate film production according to any one of claims 1 to 3, wherein 0.76 ≤ D6 ≤ 0.95, where D6 is the degree of acetyl substitution at the 6-position of the cellulose acetate. Method.
5. The method for producing a cellulose acetate film according to any one of claims 1 to 4, wherein the stirring is performed with an in-line mixer or a disperser.
6. 6. The method for producing a cellulose acetate film according to claim 1, wherein the stretching ratio is in the range of 140% to 180%, and the film width after stretching is 1900 mm to 2500 mm. .
7. The dope further comprises a sugar ester compound having an average substitution degree of 5.0 to 7.0, or a phase difference adjusting agent represented by the following general formula (B). The manufacturing method of the cellulose acetate film of any one.
   Formula (B) B- (GA) n-GB
   (Wherein B is a hydroxy group or carboxylic acid residue, G is an alkylene glycol residue having 2 to 12 carbon atoms, an aryl glycol residue having 6 to 12 carbon atoms, or an oxyalkylene glycol residue having 4 to 12 carbon atoms) A represents an alkylene dicarboxylic acid residue having 4 to 12 carbon atoms or an aryl dicarboxylic acid residue having 6 to 12 carbon atoms, and n represents an integer of 1 or more.)
8. A cellulose acetate film produced by the method for producing a cellulose acetate film according to any one of claims 1 to 7.
9. A polarizing plate comprising the cellulose acetate film according to claim 8 bonded to at least one surface of a polarizer.
10. A liquid crystal display device comprising the polarizing plate according to claim 9 bonded to at least one surface of a liquid crystal cell.

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