JP2003231138A - Cellulose ester film and method for manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cellulose ester film excellent in optical characteristics and film strength as the protective film of a polarizing plate, and a method for manufacturing the same. <P>SOLUTION: The cellulose ester film is manufactured by casting a cellulose ester-containing solution on a metal support by a solution casting film forming method and peeling the formed film to fix or stretch the same in a lateral direction. When the feed speed of the metal support is set to A (m/min) and the feed speed of a taking-up part is set to B (m/min) in a process for drying the formed cellulose film until the residual amount of the solvent in the film becomes 1 mass % or less after peeling and taking up the dried film, B/A is set to 1.005-1.100. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a cellulose ester film useful for a liquid crystal image display device and a method for producing the cellulose ester film.

[0002]

2. Description of the Related Art A liquid crystal image display device (LCD) has a low voltage and a low power consumption, can be directly connected to an IC circuit, and can be thinned, so that it can be displayed on a word processor or a personal computer. Widely used as a device. By the way, the basic configuration of this liquid crystal image display device is one in which polarizing plates are provided on both sides of a liquid crystal cell, for example, and this polarizing plate allows only light having a polarization plane in a certain direction to pass. Therefore, in the liquid crystal display device, it plays an important role of visualizing a change in orientation of the liquid crystal display device due to an electric field. That is, the performance of the polarizing plate largely affects the performance of the liquid crystal display device.

The cellulose ester film used for this polarizing plate is used as a protective film for a polarizing plate on one or both sides of a polarizing film made of a polyvinyl alcohol film which is uniaxially stretched and dyed with iodine by saponifying the surface with alkali. A laminated polarizing plate is produced by using an adhesive such as polyvinyl alcohol. Cellulose ester film used for this polarizing plate has high transparency, high flatness, high durability (dimensional stability, wet heat resistance, water resistance) and low optical anisotropy in order to maintain high resolution and contrast display quality. It has excellent properties such as the following properties: transparency, no foreign matter in the film and on the surface, no scratches or scratches on the surface (scratch resistance), moderate film rigidity (handlability), and moderate water permeability. Is required.

The cellulose ester film used in the above-mentioned fields is manufactured by using a solution casting film forming method and apparatus like the film base of the silver halide photographic light-sensitive material which has been conventionally used.

As an example of a method for producing a cellulose triacetate film by a solution casting film forming method, for example,
It is carried out by the apparatus for manufacturing a cellulose triacetate film as shown in FIG. FIG. 1 is a schematic view showing an example of a solution casting film-forming cellulose ester film manufacturing apparatus. In FIG. 1, first, a cellulose ester is dissolved in a mixed solvent of a good solvent that dissolves it and a poor solvent that does not dissolve it, and various additives such as a plasticizer and an ultraviolet absorber are added to this solution as needed. To prepare a cellulose triacetate solution (hereinafter, also referred to as a dope), and the endless metal support 1 (for example, in the form of a belt or a drum, which has a mirror-finished surface, and which is a metal support or simply a support. A film F (also referred to as a web or a dope film) by casting from a die 2 on a substrate (sometimes referred to as a body), and adjusting the temperature and humidity from drying steps 3 and 4 provided above and below the metal support 1. After air is blown, cooling and constant drying are carried out, the film F is peeled off by the peeling roll 5, transferred by the roll 63, introduced into the roll drying device 6, and fed to the roll 63. Route the film F I, dry gas air 61 film F that has been introduced in the meantime
Is dried and wound as a cellulose triacetate film by the winding machine 72 of the winding section 7 to be manufactured.

Generally, in the drying step, a film as shown in FIG. 1 is generally passed through a number of rolls 63 in a zigzag manner, and a dry air is blown thereto. US Pat. No. 2,319,05
There is also a method of drying with infrared rays as described in No. 3 specification. Furthermore, instead of hanging the film directly on the roll,
A so-called air loop method has also been developed, in which air is blown and the film is floated by the wind pressure to move the film in a non-contact state with a hanging body (for example, Japanese Patent Laid-Open No. 55-135046).

On the other hand, film stretching is carried out for the purpose of improving the mechanical strength and the like of films of polyester, polypropylene, etc. As one of the stretching methods, both side edges of the film are fixed with clips or the like for 2 to 6 A tenter system in which double stretching is performed is known. As a method utilizing this tenter method, for example, Japanese Patent Application Laid-Open No. 59-211006 discloses a technique for producing a substrate of a liquid crystal display panel from a film of a phenoxy resin or the like, and this film includes a cellulose acetate film. It is also suggested therein that it can also be used. Also, Japanese Patent Laid-Open No. 4-284421
JP-A-62-115035 discloses a method for producing a cellulose triacetate film using a tenter drying device, and FIG. 2 shows a solution cast film-forming cellulose ester film having the above tenter drying device. An example of a manufacturing apparatus is shown.

In the same manner as the method shown in FIG. 1, the film F peeled off by the peeling roll 5 is a tenter dryer 8
The film is dried by holding the width by gripping both ends of the film with clips or by slightly stretching the width. After the drying is completed, a wound cellulose ester film is obtained.

When the cellulose ester film was produced by the above method, there were some problems. That is, after peeling the dope cast on the metal support, by stretching in the width direction with a tenter, the planarity is improved,
On the other hand, the orientation angle increases in the width direction. In general,
When the orientation angle is large, the degree of polarization of the polarizing plate is reduced, which causes a reduction in resolution and contrast.

Further, the polyvinyl alcohol film used for the polarizing plate has a high water absorption property and greatly shrinks when left under high humidity, and the protective film adhered to both sides peels off the adhered film if the mechanical strength is weak. It may cause trouble such as.

Further, since the liquid crystal display device can be made thin and compact, a notebook personal computer,
Application to car navigators, mobile phones, game consoles, etc. is progressing at an extremely rapid rate, and is becoming thinner and smaller. As a result, there has been a demand for further development of a thin film for the conventionally used cellulose ester film of liquid crystal image display devices. In the case of such a thin film, if a tenter is used to improve the flatness, the orientation angle is likely to be large, and similarly, there is a concern that the degree of polarization may be reduced. In addition, in the case of a thin film, since the strength of the film is weakened, the force for suppressing the shrinkage of the polyvinyl alcohol film due to moisture absorption is further weakened.

[0012]

The present invention has been made in view of the above problems, and an object thereof is to provide a cellulose ester film excellent in optical properties and film strength as a polarizing plate protective film and a method for producing the same. Is to provide.

[0013]

The above objects of the present invention have been achieved by the following constitutions.

1. A method of producing a cellulose ester film by casting a solution containing a cellulose ester on a metal support by a solution casting film forming method, peeling the film, fixing or stretching in the width direction, and peeling the film. To a residual solvent amount of 1% by mass or less of the film, and during the step of winding the film, the transport speed of the metal support is A (m
/ Min), the conveyance speed at the winding section is B (m / min)
And B / A is 1.005 to 1.100.

2. The method for producing a cellulose ester film according to the above item 1, wherein the residual solvent amount of the film when peeled from the metal support is 20% by mass or more and 150% by mass or less.

3. The method for producing a cellulose ester film as described in 1 or 2 above, wherein the film thickness is 20 to 60 μm.

4. A cellulose ester film produced by casting or peeling a solution containing a cellulose ester on a metal support by a solution casting film-forming method, and fixing or stretching the film in the width direction. Is dried to a residual solvent amount of 1% by mass or less, and the metal support is conveyed at a speed of A (m / mi) in the step during winding.
n), when the transport speed in the winding section is B (m / min), the cellulose ester film is produced under the condition that B / A is 1.005 to 1.100.

5. Item 5. The cellulose ester film according to Item 4, wherein the residual solvent amount of the film when peeled from the metal support is 20% by mass or more and 150% or less.

6. When the orientation angle θ in the transport direction is 0 degree, the orientation angle θ distribution in the width direction is 5 degrees or less, and the in-plane retardation value R0 is 2 to 5 nm. The cellulose ester film according to.

7. 6. The cellulose ester film as described in 4 or 5 above, which has a thickness of 20 to 60 μm.

8. When the orientation angle θ in the transport direction is 0 degree, the orientation angle θ distribution in the width direction is 5 degrees or less, and the in-plane retardation value R0 is 0.5 to 2 nm. The cellulose ester film according to any one of items 5 and 7.

The details of the present invention will be described below. In the invention according to claims 1 and 4, a cellulose ester film produced by casting or peeling a solution containing a cellulose ester on a metal support by a solution casting film forming method, and fixing or stretching the film in the width direction. Alternatively, in the manufacturing method thereof, after peeling, the residual solvent amount of the film is dried to 1% by mass or less, and in the process during winding, the transport speed of the metal support is A (m / min), winding. B / A is 1.005, where B (m / min) is the conveying speed at the take-up section.
The feature is that it is 1.100.

First, the method for producing the cellulose ester film of the present invention will be described. In the method for producing a cellulose ester film of the present invention, as the production steps, as shown in FIGS. 1 and 2, a step of casting a dope on a metal support and a drying on the metal support are mainly performed. It comprises a step, a peeling step of peeling the film from the metal support, and a step of drying the film.

In the support used in the present invention, it is preferable that the surface of an endless metal support which is transferred infinitely has a mirror surface. In the casting step, the dope is sent to a press die through a press type quantitative gear pump, and at the casting position, a metal support,
For example, a step of casting a dope from a pressure die onto a stainless belt or a rotating metal drum. Other casting methods include, for example, a doctor blade method for adjusting the film thickness of a cast dope film with a blade, or a method using a reverse roll coater for adjusting with a reverse rotating roll. It is preferable to use the pressure die from the viewpoint that the slit shape can be adjusted and the film thickness can be easily made uniform. Examples of the pressure die include a coat hanger die and a T die, and any of them is preferably used. Further, 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 to form a multilayer film. To adjust the film thickness, to obtain the desired thickness,
It can be carried out by appropriately adjusting the dope concentration, the amount of liquid fed by the pump, the slit gap of the die die, the extrusion pressure of the die, the speed of the metal support, and the like.

The drying step on the metal support is a step of heating the web (hereinafter referred to as a dope film after casting on the metal support to be a web) on the support to evaporate the solvent. . To evaporate the solvent, for example, a method of blowing heated air from the web side and the back side of the metal support, a method of transferring heat from the back surface of the support with a heated liquid, a method of transferring heat from the front and back by radiant heat, and the like can be mentioned. it can. Further, a method of appropriately selecting and combining them is also preferable. Also,
The thinner the web, the faster the drying. The temperature of the metal support may be the same throughout, or may be different depending on the position.

The peeling step is a step in which the organic solvent is evaporated on the metal support and the web is peeled before the metal support makes one round, and then the film is sent to the drying step. The position where the web is peeled from the metal support is called the peeling point,
A roll that assists peeling is called a peeling roll. Depending on the thickness of the web, if the amount of residual solvent in the web at the peeling point (the following formula) is too large, it may be difficult to peel, or conversely, if the web is sufficiently dried on the support and then peeled, the web May be partly peeled off.

In the invention according to claim 2 or 5, the web is preferably peeled off when the residual solvent amount measured by the method described below is 20 to 150% by mass, and more preferably 50 to 150% by mass. . When peeling less than 20% by mass, residual stress occurs in the cellulose ester film when the tension in the transport direction is increased for the purpose of increasing the mechanical strength of the cellulose ester film of the present invention,
Dimensional characteristics deteriorate. On the other hand, when it exceeds 150% by mass, peeling residue occurs, which is a cause of surface defects of the cellulose ester film, which is not preferable.

Further, as one of the methods for increasing the film forming speed by peeling while the amount of residual solvent is as large as possible, there is a gel casting method (gel casting) which can peel even if the amount of residual solvent is large. be able to.
The gel casting method includes a method in which a poor solvent for cellulose ester is added to the dope to cause gelation after the dope casting, or a method in which the temperature of the support is lowered to cause gelation.
There is also a method of adding a metal salt to the dope. By causing gelation on the support and strengthening the dope film, peeling can be accelerated and the film formation speed can be increased. When peeling when the amount of residual solvent is larger, if the film is too soft, the flatness at the time of peeling will be impaired, and peeling tension will easily cause cracks and vertical streaks, and the amount of residual solvent is determined in consideration of economic speed and quality. To be

The amount of residual solvent used in the present invention can be represented by the following formula. Residual solvent amount (mass%) = {(M−N) / N} × 100 Here, M is the mass of the film at an arbitrary time point, and N is the mass of M film when dried at 110 ° C. for 3 hours. is there.

In the film drying step, the film peeled from the support is further dried, and in the present invention, the residual solvent amount is set to 1% by mass or less, more preferably 0.5% by mass or less, whereby the dimensional stability is improved. It is preferable for obtaining a good film. In the film drying step, generally, a roll suspension method, a pin tenter method, or a clip tenter method is used to dry the film while conveying the film. In the present invention, it is preferable to dry while stretching in the width direction at a stretching ratio of 3% or more in the tenter system in order to improve dimensional stability, and more preferably, the stretching ratio is 3.0.
˜9.0%, and more preferably 3.0 to 6.0%.

In the present invention, it is particularly preferable to carry out width retention or stretching immediately after peeling from the support where the amount of residual solvent is large, because the effect of improving the dimensional stability is further exhibited.

In the drying step after peeling from the support, the film tends to shrink in the width direction due to the evaporation of the solvent. Further, the higher the temperature, the greater the shrinkage. It is preferable that the shrinkage is dried while being suppressed as much as possible in order to improve the flatness and dimensional stability of the finished film. From this point, for example, JP-A-62-46
It is preferable to use a so-called tenter system, which is a method of drying all or a part of the drying process as disclosed in Japanese Patent No. 625, while holding both ends of the width of the film with clips in the width direction.

In the present invention, the means for drying the film is not particularly limited, and for example, hot air, infrared rays, heating rolls, microwaves and the like can be used. From the viewpoint of simplicity, hot air is used. The method is preferred. The drying temperature is preferably in the range of 40 to 150 ° C in 3 to 5 stages, and the drying temperature is preferably gradually increased. Further, it is preferable to perform the drying temperature in the range of 80 to 140 ° C because of high dimensional stability. It is preferable for realizing the property.

The steps from casting to post-drying described above are
It may be in an air atmosphere or in an atmosphere of an inert gas such as nitrogen gas. Further, it goes without saying that the dry atmosphere is carried out in consideration of the explosion limit concentration of the solvent.

The winding machine for producing the cellulose ester film of the present invention may be a commonly used one, for example, constant tension method, constant torque method, taper tension method, program tension control with constant internal stress. It can be wound by a winding method such as a method.

In the present invention, after peeling, the residual solvent amount of the film is dried to 1% by mass or less, and in the process during winding, the transport speed of the metal support is A (m / min), the winding portion. When the transport speed at B is (m / min), B /
The feature is that A is 1.005 to 1.100.

Specifically, it can be determined by the transport speed (m / min) of the metal support forming the film shown in FIGS. 1 and 2 and the transport speed of the winder 72 of the winding section 7. . In the present invention, B / A is 1.005 to 1.
One of the features is 100, but preferably,
It is 1.005 to 1.080.

In the present invention, there is no particular limitation on the method for optimally adjusting the transporting device for the metal support or the winding section so that the B / A range defined above is satisfied, but the drying conditions in each step are not particularly limited. It is most effective to properly adjust the transport tension condition and the like.

The details of the cellulose ester film of the present invention will be described below. Cellulose ester used in the cellulose ester film of the present invention is obtained by reacting cellulose selected from linter pulp, wood pulp and kenaf pulp with acetic anhydride, propionic anhydride, or butyric anhydride by a conventional method. Cellulose triacetate, cellulose acetate propionate, cellulose acetate butyrate, and cellulose acetate propionate butyrate in which the degree of substitution of all acyl groups for the hydroxyl groups of cellulose is 2.5 to 3.0 are preferably used.

The substitution degree of the acetyl group of the cellulose ester according to the present invention is preferably at least 1.5 or more. The method for measuring the degree of substitution of the acyl group of the cellulose ester can be carried out according to ASTM D-817-91. The molecular weight of these cellulose esters is 70,000 to 300,0 as a number average molecular weight.
The range of 00 is preferable because the mechanical strength when formed into a film is strong, and more preferably 80,000 to 200,000. Usually, after a reaction such as washing with water, the cellulose ester becomes flaky and is used in that shape. The particle size is 0.05 as an average particle size.
The range of up to 2.0 mm is preferable from the viewpoint of accelerating the solubility.

The cellulose ester film contains a plasticizer such as phthalic acid ester or phosphoric acid ester, an ultraviolet absorber, an antioxidant, a matting agent, etc., so that the silver halide photographic light-sensitive material derived from the cellulose ester film can be obtained. This is preferable because the material and the performance of the liquid crystal image display device can be improved.

In the present invention, the plasticizer which can be contained in the cellulose ester film is not particularly limited, but examples of the phosphoric acid ester type include triphenyl phosphate, tricresyl phosphate, cresyl diphenyl phosphate and octyl. Diphenyl phosphate, diphenyl biphenyl phosphate, trioctyl phosphate, tributyl phosphate, etc., as phthalic acid ester type, diethyl phthalate, dimethoxyethyl phthalate, dimethyl phthalate, dioctyl phthalate, dibutyl phthalate, di-2-ethylhexyl phthalate, etc., glycolic acid ester type As, triacetin, tributyrin, butylphthalyl butyl glycolate, ethylphthalyl ethyl glycolate,
Methyl phthalyl ethyl glycolate, butyl phthalyl butyl glycolate, etc. can be mentioned. If desired, two or more plasticizers may be used in combination.

When used in the cellulose ester film of the present invention, the usage ratio of the phosphate ester type plasticizer is 50.
It is preferable that the content is at most% by mass because hydrolysis of the cellulose ester film is unlikely to occur and durability is excellent. It is more preferable that the ratio of the phosphoric acid ester-based plasticizer is small, and it is particularly preferable to use only the phthalic acid ester-based or glycolic acid ester-based plasticizer. The addition amount of the plasticizer to the cellulose ester is preferably 0.5 to 30% by mass, and particularly preferably 2 to 15% by mass.

Further, in the present invention, as the ultraviolet absorber which can be contained in the cellulose ester film, from the viewpoint of preventing the deterioration of the liquid crystal, it has an excellent absorbing ability for the ultraviolet light having a wavelength of 370 nm or less, and has a good liquid crystal display property. In view of the above point, a material that absorbs visible light having a wavelength of 400 nm or more as little as possible is preferably used. In particular, the transmittance at a wavelength of 370 nm needs to be 10% or less, preferably 5% or less, and more preferably 2% or less. In the present invention, as the ultraviolet absorber that can be used, for example,
Examples thereof include oxybenzophenone-based compounds, benzotriazole-based compounds, salicylate-based compounds, benzophenone-based compounds, cyanoacrylate-based compounds, nickel complex salt-based compounds, and the like, and benzotriazole-based compounds with little coloring are preferable. Examples of commercially available benzotriazole-based UV absorbers include, but are not limited to, TINUVIN 109, TINUVIN 171, TINUVIN 326, TINUVIN 327, and TINUVIN 328 manufactured by Ciba Specialty Chemicals. You may use 2 or more types of ultraviolet absorbers.

The ultraviolet absorber may be added to the dope after the ultraviolet absorber is dissolved in an organic solvent such as alcohol, methylene chloride, methyl acetate or dioxolane, or added directly to the dope composition. Good. For inorganic powders that are not soluble in an organic solvent, a dissolver or a sand mill is used in an organic solvent and a cellulose ester to disperse them and then added to the dope. In the present invention, the amount of the ultraviolet absorber used can be added in the range of 0.5 to 20% by mass with respect to the cellulose ester,
6-5.0 mass% is preferable, and especially preferable is 0.6-
It is 2.0 mass%.

In the present invention, it is preferable that the cellulose ester film contains a fine-particle matting agent. Examples of the fine-particle matting agent include silicon dioxide, titanium dioxide, aluminum oxide, zirconium oxide, calcium carbonate, It is preferable to contain inorganic fine particles such as kaolin, talc, calcined calcium silicate, hydrated calcium silicate, aluminum silicate, magnesium silicate, and calcium phosphate, or crosslinked polymer fine particles.
Of these, silicon dioxide is preferable because it can reduce the haze (devitrification) of the film. The secondary particles of fine particles preferably have an average particle diameter of 0.01 to 1.0 μm, and the content thereof is 0.0 with respect to the cellulose ester.
05-0.5 mass% is preferable. Particles such as silicon dioxide are often surface-treated with an organic substance, but such particles are preferable because they can reduce the haze of the film. Examples of preferable organic substances in the surface treatment include halosilanes, alkoxysilanes, silazanes,
Examples include siloxane. As for the average particle size of the fine particles, the larger the matte effect is and the smaller the average particle size is, the more excellent the transparency is. Therefore, the average particle size of the primary particles of the fine particles is preferably 5 to 50 nm, more preferably 7
Is about 20 nm. It is preferable that these fine particles usually exist as an aggregate in the cellulose ester film to form irregularities of 0.01 to 1.0 μm on the surface of the cellulose ester film. As the fine particles of silicon dioxide, for example, AERO manufactured by Nippon Aerosil Co., Ltd.
SIL 200, 200V, 300, R972, R97
2V, R974, R202, R812, OX50, TT
600 and the like can be mentioned, preferably AEROSI
L200V, R972, R972V, R974, R20
2, R812. Two or more kinds of these matting agents may be used in combination. When two or more kinds are used in combination, they can be mixed and used at an arbitrary ratio. In this case, a matting agent having different average particle diameters or materials, for example, AEROSIL 200V
And R972V in the same mass ratio of 0.1: 99.9 to 99.
It can be used in the range of 9 to 0.1.

Next, a method for preparing the cellulose ester dope in the present invention will be described. While stirring an organic solvent mainly composed of a good solvent for cellulose ester in a dissolution vessel, flaky cellulose ester is added and dissolved to form a dope. As the dissolution method, for example, a method performed at normal pressure, a method performed at a temperature not higher than the boiling point of the main solvent, a method performed while pressurizing at a temperature not lower than the boiling point of the main solvent, JP-A-9-95544 and 9-95557. Or the same 9-9
There are various melting methods such as a cooling melting method as described in JP-A-5538 and a high pressure method as described in JP-A-11-21379. The dissolved cellulose ester solution, so-called dope, is then filtered with a filter medium, defoamed, and sent to the next step by a pump. The concentration of cellulose ester in the dope is
Generally, it is 10 to 35 mass%, but preferably 15 to
It is 25 mass%. The polymer useful in the present invention can be added to the cellulose ester dope by adding the polymer after dissolving the polymer in an organic solvent in advance or directly adding it to the cellulose ester dope without any particular limitation. In this case, it is necessary to add it carefully so that the polymer does not become cloudy or phase-separated in the dope.

The good solvent that can be used in the present invention is an organic solvent having a good solubility in cellulose ester, and examples thereof include methyl acetate, ethyl acetate, amyl acetate, ethyl formate, acetone, cyclohexanone,
Methyl acetoacetate, tetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, 1,4
-Dioxane, 2,2,2-trifluoroethanol,
2,2,3,3-hexafluoro-1-propanol,
1,3-difluoro-2-propanol, 1,1,1,
3,3,3-hexafluoro-2-methyl-2-propanol, 1,1,1,3,3,3-hexafluoro-2
-Propanol, 2,2,3,3,3-pentafluoro-1-propanol, nitroethane, 2-pyrrolidone,
N-methyl-2-pyrrolidone, 1,3-dimethyl-2-
Examples thereof include imidazolidinone, methylene chloride, bromopropane, and the like, and particularly, methyl acetate, acetone, methylene chloride can be preferably used. However, it is preferable to use a non-chlorine organic solvent in view of recent environmental problems. Further, it is preferable to use a lower alcohol such as methanol, ethanol or butanol together with these organic solvents because the solubility of the cellulose ester in the organic solvent can be improved and the dope viscosity can be reduced. In particular,
Ethanol having a low boiling point and low toxicity is preferable. The organic solvent used in the dope according to the present invention is preferably used by mixing a good solvent and a poor solvent of cellulose ester in terms of production efficiency, and a preferable range of the mixing ratio of the good solvent and the poor solvent is a good solvent. Is 70 to 98% by mass, and the poor solvent is 2 to 30% by mass. The good solvent and poor solvent used in the present invention are defined as those in which the cellulose ester used alone is dissolved and those in which they are not dissolved alone are defined as poor solvents. The poor solvent used in the dope according to the present invention is not particularly limited, and examples thereof include methanol, ethanol, n-butanol, cyclohexane, acetone,
Cyclohexanone and the like can be preferably used. For the polymers useful in the present invention, it is preferable to use a good solvent for cellulose ester as the organic solvent. As described above, when a low molecular weight plasticizer is used, it can be added by a usual addition method. Even if it is added directly into the dope, it is dissolved in an organic solvent in advance and then poured into the dope. Good.

In the present invention, when the various additive solutions or dispersions as described above are added to the cellulose ester dope, they are transferred from the respective transfer systems, and when the transfer pipes merge, the respective addition elements are combined with the dope liquid. A method is also preferable in which the mixture is allowed to be liquid, and immediately after that, it is thoroughly mixed with an in-tube mixer.
For example, it is preferable to use an in-line mixer such as a static mixer SWJ (Toray static type in-tube mixer Hi-Mixer Toray Engineering). When an in-line mixer is used, it is also possible to apply the cellulose ester to a dope that is concentrated and dissolved under high pressure.

In the present invention, in the preparation of the cellulose ester dope, it is necessary to remove foreign matter, especially foreign matter which is easily recognized as an image in a liquid crystal image display device. When the cellulose ester film of the present invention is used as a protective film for a polarizing plate, it is no exaggeration to say that its quality is determined by this filtration accuracy.
It is preferable that the filter material used for filtration has a small absolute filtration accuracy, but if the absolute filtration accuracy is too small, clogging of the filter material easily occurs, and the filter material must be replaced frequently, which reduces productivity. There is a problem of making it. For this reason,
The filter medium used in the cellulose ester dope according to the present invention preferably has an absolute filtration accuracy of 0.008 mm or less, more preferably 0.001 to 0.008 mm, and more preferably 0.003 to 0.006 mm. More preferable. The material of the filter medium is not particularly limited, and a usual filter medium can be used. However, a filter medium made of plastic fiber such as polypropylene or Teflon (R) or a metal filter medium such as stainless fiber may not be dropped. None preferred. The filtration of the cellulose ester dope according to the present invention can be carried out by a usual method, but a method of filtering while heating under pressure at a temperature not lower than the boiling point of the solvent at normal pressure and the solvent does not boil, is filtered. A rise in the differential pressure before and after the material (hereinafter sometimes referred to as filtration pressure) is small, which is preferable. The preferred temperature range is 45 to 120 ° C, more preferably 45 to 70 ° C, and even more preferably 45 to 55 ° C. It is preferable that the filtration pressure is small. The filtration pressure is preferably 1.6 × 10 ⁶ Pa or less, more preferably 1.2 × 10 ⁶ Pa or less, and further preferably 1.0 × 10 ⁶ Pa or less.

If the raw material cellulose ester contains a cellulose ester having an acyl group which is not substituted or has a low degree of substitution, foreign matter failure (hereinafter also referred to as bright spot failure) may occur. A bright spot failure means that when a cellulose ester film is placed between two polarizing plates in a crossed state (crossed nicols), light is irradiated from one side, and the other side is observed with an optical microscope (50 times), normal cellulose is observed. In the case of an ester film, the light is blocked and you cannot see anything black, but if there is a foreign substance, the light leaks from it and appears as a spot-like appearance. The larger the diameter of the bright spot failure, the greater the actual damage in the case of a liquid crystal image display device, and the diameter is preferably 50 μm or less, more preferably 10 μm or less, and further preferably 8 μm or less. The diameter of the bright spot means the diameter of the bright spot which is approximated to a perfect circle and measured. The number of bright spot defects is practically no problem if the diameter is 400 pieces / cm ² or less, but preferably 300 pieces / cm ² or less.
It is more preferable that the number is 0 / cm ² or less. In order to reduce the number and size of such bright spot failures, it is necessary to sufficiently filter fine foreign matter. In addition, JP-A-200
As described in 0-137115, a method of re-adding a pulverized product of a cellulose ester film once formed into a dope as a raw material for cellulose ester and its additive is to reduce bright spot failure. Is a preferred method.

The thickness of the cellulose ester film is generally 20 to 200 μm. However, in the present invention, the thickness is 20 because the polarizing plate used for LCD and the like is required to be thin and lightweight. The thickness is preferably -60 μm, more preferably 30-60 μm, still more preferably 35-50 μm. When the thickness is less than 20 μm, the rigidity of the film is reduced, and thus problems such as wrinkles are likely to occur in the manufacturing process of the polarizing plate.
If the thickness exceeds 60 μm, the contribution to the thinning of the LCD is reduced, which is not preferable.

In the cellulose ester film of the invention according to claim 6, when the orientation angle θ in the transport direction is 0 degree,
The orientation angle θ distribution in the width direction is preferably 5 degrees or less, and the in-plane retardation value R0 is preferably 2 to 5 nm. Further, in the cellulose ester film of the invention according to claim 8, the orientation angle θ in the transport direction is Is 0 degree, the orientation angle θ distribution in the width direction is preferably 5 degrees or less, and the in-plane retardation value R0 is preferably 0.5 to 2 nm.

The orientation angle θ in the present invention is an angle (degree) formed by the film transport direction during film formation and Nx, and the in-plane retardation value R0 (nm) is expressed by the following equation.

R0 = (Nx−Ny) × d Nx: Refractive index in the x direction which is the maximum refractive index direction in the plane of the film Ny: Refraction in the y direction which is the direction in the plane perpendicular to the x direction Ratio d: Film thickness (nm) In the present invention, the distribution of the orientation angle θ in the width direction is preferably 5 degrees or less, more preferably 0.1 to 5
It is degree.

In the present invention, an ordinary refractometer can be used to measure the refractive index of the entire cellulose ester film. For example, after measuring the entire refractive index, an automatic birefringence meter KOBRA-21ADH (Oji Scientific Instruments Co., Ltd.)
Manufactured under the conditions of 23 ° C. and 55% RH at a wavelength of 590 nm, three-dimensional refractive index is measured, refractive indices Nx and Ny are calculated, and the film thickness is measured to obtain R.
The zero value and the orientation angle θ can be obtained.

Optical isotropy is one of the important qualities of a polarizing plate. This is greatly influenced by the cellulose ester film, which is an essential component. So far
A cellulose ester film having excellent optical isotropy has been used as a protective film. The optical isotropy is a quality that is affected by the retardation value R0 and the orientation angle θ, and a low R0 value is required to obtain excellent optical isotropy.

The cellulose ester film of the present invention comprises
It has excellent optical isotropy, is free from stains, and can be preferably used for liquid crystal display members. The liquid crystal display member referred to in the present invention is a member used in a liquid crystal display device, for example, a polarizing plate, a protective film for a polarizing plate, a retardation plate, a reflection plate, an optical compensation film, a viewing angle improving film, Examples thereof include antiglare film, antireflection film, antistatic film and the like. Among the above description, it is preferably used for a polarizing plate or a protective film for a polarizing plate.

[0059]

The present invention will be described in detail below with reference to examples, but the embodiments of the present invention are not limited thereto.

Example 1 << Preparation of Cellulose Ester Solution (Dope) >> 100 parts by mass of cellulose triacetate having a degree of acetyl substitution of 2.88 (number average molecular weight 150,000) 10 parts by mass of triphenyl phosphate 2 parts by mass of ethylphthalylethyl glycolate TINUVIN 326 (manufactured by Ciba Specialty Chemicals) 1 part by mass AEROSIL 200V (manufactured by Nippon Aerosil Co., Ltd.) 0.1 part by mass Methylene chloride 475 parts by mass Ethanol 25 parts by mass Each of the above compositions is sequentially charged into a closed container, and then added to a kettle. Internal temperature is 7
After the temperature was raised to 0 ° C., the mixture was stirred at 70 ° C. for 3 hours to completely dissolve each composition. After that, the stirring was stopped, the liquid temperature was lowered to 43 ° C. to prepare the dope, and the dope was immediately sent to the filtration step described below through the connected pipe, and the filtration flow rate of 300 L / M ²
-In some cases, the filtration pressure was 1.0 × 10 ⁶ Pa.

<< Preparation of Cellulose Acetate Films 1 to 8 >> The dope prepared above was cast and dried using a solution casting film-forming cellulose ester film producing apparatus having a tenter drying device shown in FIG. An acetate film was produced. However, the first described in FIG.
The thing except the 2nd roll dryer 6 was used.

The dope solution prepared above was cast on the support 1 made of a stainless belt through the die 2, the temperature of the stainless belt was controlled at 25 ° C., and 45 ° C. from the drying step 4 on the film F side. From the drying step 3 on the stainless belt side, the film is dried by applying a 40 ° C. air at 10 m / sec vertically to dry the film, and the residual solvent amount in the film is 70%. After evaporating the solvent to reach the mass%, peeling was performed with the peeling roll 5.

Next, the film is introduced into the tenter drying device 8 and the roll drying device 9 and dried at 105 ° C. while maintaining the width in the tenter drying device 8, and subsequently the film is arranged in a zigzag pattern. It is dried at 120 ° C. in 9 and wound up by the winder 72 of the winding section 7, and finally 2
After cooling to 0 ° C., a cellulose triacetate film 1 (also referred to as film sample 1) having a thickness of 80 μm was produced. The tension during the transport of the film was 196 N / width throughout the above steps.

Next, in the production of the above-mentioned film sample 1, film samples 2 to 8 were produced in the same manner except that the transport speed ratio B / A, the residual solvent amount at the time of peeling and the film thickness were changed. did.

In the preparation of Samples 2 to 8, the transport speed ratio B / A was adjusted by the transport speed A (m / m) of the metal support.
(in) was set under the same conditions for all the samples, and the transport speed B (m / min) of the winding section was appropriately adjusted. Further, the amount of residual solvent at the time of peeling was adjusted by changing the temperature and the amount of drying air of the metal support.

<< Evaluation of Cellulose Acetate Film >>
With respect to the film samples 1 to 8 which are cellulose acetate films produced as described above, the retardation value R0, the orientation angle θ, and the elastic modulus in the transport direction (MD direction) as the film strength were measured according to the following methods. went.

(Measurement of Retardation Value R0 and Orientation Angle θ) To measure the retardation value R0, an automatic subrefractometer K
Using OBRA-21ADH (manufactured by Oji Scientific Instruments),
Measured in an environment of 23 ° C. and 55% RH, and measured at 10 points in the width direction of the sample according to the method described above. The width when the maximum value of the retardation value R0 and the orientation angle θ in the transport direction are 0 degrees. The maximum value of the orientation angle θ in the hand direction was measured.
The average film thickness d was measured by a laser focus displacement meter LT-8010 manufactured by Keyence Corporation.

(Measurement of MD Modulus) Each of the above-prepared film samples was cut out in a width direction (TD direction) of 10 mm and in a transport direction (MD direction) of 200 mm, and was cut under an atmosphere of 23 ° C. and 55% relative humidity for 12 minutes. After performing time humidity control, using Orientec Tensilon (RTA-100),
Fix the upper and lower ends in the transport direction (MD direction) with chucks, set the distance between chucks to 100 mm, and pull speed 1
Pulling at 00 mm / min, elastic modulus in MD direction (N / m
m ² ) was measured. The larger the value, the higher the strength against tension.

Table 1 shows the results obtained as described above.

[0070]

[Table 1]

As is clear from Table 1, when the transport speed of the metal support defined by the present invention is A (m / min) and the transport speed at the winding section is B (m / min), B / The film sample produced with A of 1.005 to 1.100 is
It can be seen that the retardation value is small, the orientation angle distribution in the width direction is small, and the tensile strength in the MD direction is excellent as compared with the comparative example.

Example 2 << Preparation of Polarizing Plate >> Using the cellulose acetate films 1 to 8 prepared in Example 1, polarizing plates 1 to 8 were prepared according to the method described below.

100 g of an aqueous solution containing 1 g of iodine and 4 g of boric acid was used as a polyvinyl alcohol film having a thickness of 120 μm.
And was stretched 6 times at 50 ° C. to form a polarizing film. Each of the cellulose ester films subjected to the alkali saponification treatment described below was attached to both surfaces of this polarizing film using a 5% aqueous solution of completely saponified polyvinyl alcohol as an adhesive to prepare polarizing plates 1 to 8.

(Alkali saponification treatment) Step Treatment liquid Treatment temperature Treatment time Saponification step: 2 mol / L NaOH 50 ° C. 90 seconds Water washing step: Water 30 ° C. 45 seconds Neutralization step: 10 mass% HCl 30 ° C. 45 seconds Water washing step : Water 30 ° C. 45 seconds Saponification of each cellulose ester film under the above conditions,
Washing with water, neutralization, and washing with water were carried out in this order, followed by drying at 80 ° C.

<< Evaluation by Liquid Crystal Display Panel >> Commercial liquid crystal display panel (NEC color liquid crystal display Mu
ltiSync LCD1525J: Model name LA-15
The polarizing plates on both sides of (29HM) are carefully peeled off, and the polarizing plates 1 to 8 whose polarization directions are aligned are adhered to the liquid crystal display panels 1 to 8 to evaluate the visibility according to the following method. .

(Evaluation of Preservability of Polarizing Plates) The liquid crystal display panels 1 to 8 prepared above were stored for 1 week in an atmosphere of 40 ° C. and 80% relative humidity, and then the surface of each liquid crystal display panel was visually observed, The storability was evaluated according to the following criteria.

⊚: There is no change on the liquid crystal display panel surface at all, and there is no unevenness on the display screen. ◯: A slight film peeling is recognized on the liquid crystal display panel surface, but there is no effect on the display screen. Δ: Liquid crystal display panel. Film peeling was observed on the surface, and a slight effect was also shown on the display screen. ×: Clear film peeling was found on the liquid crystal display panel surface, and the effect was also shown on the display screen. As a result, all the comparative products had an evaluation rank of Δ or ×, but the liquid crystal display panels using the film sample of the present invention were all ◎ or ○, and the liquid crystal display panel was long under high humidity conditions. It was possible to confirm that the film was prevented from peeling off due to film shrinkage even after being stored for a period of time, and that the protective film was strong enough.

[0078]

According to the present invention, it is possible to provide a cellulose ester film useful for a liquid crystal display device having a small orientation angle distribution in the width direction and excellent film strength, and a method for producing the same.

[Brief description of drawings]

FIG. 1 is a schematic view showing an example of a solution casting film-forming cellulose ester film manufacturing apparatus that can be used in the present invention.

FIG. 2 is a schematic view showing an example of a solution casting film-forming cellulose ester film manufacturing apparatus having a tenter drying apparatus, which can be used in the present invention.

[Explanation of symbols]

F film (also called web) 1 metal support Two dies 3, 4 drying process 5 peeling roll 6, 9 roll dryer 7 Winding part 8 tenter dryer 61 Dry gas wind 63 rolls 72 Winder

Claims (8)

[Claims] 1. A method for producing a cellulose ester film, which is produced by casting or peeling a solution containing a cellulose ester on a metal support by a solution casting film forming method, and fixing or stretching the film in the width direction. , The film is peeled off, the film is dried to a residual solvent amount of 1% by mass or less, and the film is wound up.
min), and B / A is 1.005 to 1.100, where B (m / min) is the conveying speed in the winding section, and a method for producing a cellulose ester film. 2. The method for producing a cellulose ester film according to claim 1, wherein the residual solvent amount of the film when peeled from the metal support is 20% by mass or more and 150% by mass or less. 3. The method for producing a cellulose ester film according to claim 1, wherein the film thickness is 20 to 60 μm. 4. A cellulose ester film produced by fixing or stretching a film obtained by casting and peeling a solution containing a cellulose ester on a metal support by a solution casting film forming method in the width direction, and peeling the film. After that, the residual solvent amount of the film is dried to 1% by mass or less, and the transport speed of the metal support is A (m / min) in a step during winding.
When the conveying speed at the winding section is B (m / min),
A cellulose ester film produced under the condition that B / A is 1.005 to 1.100. 5. The cellulose ester film according to claim 4, wherein the residual solvent amount of the film when peeled from the metal support is 20% by mass or more and 150% by mass or less. 6. When the orientation angle θ in the transport direction is 0 degree,
6. The cellulose ester film according to claim 4, wherein the orientation angle θ distribution in the width direction is 5 degrees or less and the in-plane retardation value R0 is 2 to 5 nm. 7. The cellulose ester film according to claim 4, wherein the film thickness is 20 to 60 μm. 8. When the orientation angle θ in the transport direction is 0 degree,
The orientation angle θ distribution in the width direction is 5 degrees or less, and the in-plane retardation value R0 is 0.5 to 2 nm. 8. The cellulose according to claim 4, 5, or 7. Ester film.