JPH11221833A - Manufacture of cellulose ester film and cellulose ester optical film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a film at a high productivity rate without deteriorating the flatness of the film by casting a cellulose ester solution to the surface of a rotating cooling drum, then scraping a coagulated coat from the surface and drying the coagulated coat while conveying the coat with the help of a tenter moving at a specific peripheral velocity in such a manner that both ends, in the width direction, of the coagulated coat are grasped by the tenter. SOLUTION: A cellulose ester composition solution is extruded to the surface of a rotating cooling drum 3 with the help of a casting die 2 of a casting part 1 and is dried and cooled while being moved and further, is coagulated until the dried film can be stably released. This cast film 4 is released from the drum 3 at a release position which is set beforehand and this film 7 is sent to a roller conveying zone 6 and further, is conveyed by conveying bus rollers 8a, 8b, 8c... while being held thereby. During conveying the film 7, it is dried by a drying blast, and is conveyed in such a state that the both ends of the film 7 in the width direction are held by a tenter 10 moving at a velocity 1.105-1.200 times the peripheral velocity of the drum 3 in a tenter conveyance zone 9. In addition, a solvent is blown off by the drying blast from a blow-off duct 11 and the film thus processed is taken up as an article of manufacture.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a cellulose ester film particularly suitable for optical applications.

[0002]

2. Description of the Related Art In recent years, thin transparent plastic films have recently been used as protective films for polarizing plates, optical compensation films such as retardation films,
There is an increasing demand for optical materials such as plastic substrates, photographic supports or moving image cells and optical filters, and OHP films. In particular, liquid crystal displays have recently been improved in image display quality and are now offered as lightweight and portable.
It has been widely used as an image display device for personal computers, word processors, portable terminal devices, televisions, and even digital still cameras and movie cameras. Is required. Since the quality of the polarizing plate is required to be improved in accordance with the improvement of the quality of the image display of the liquid crystal display, the transparent plastic film used as the protective film of the polarizing plate is also required to be of high quality. .

Optical films such as protective films for polarizing plates are required to have high transparency, low optical anisotropy, high flatness, easy surface treatment, and high durability in order to maintain high resolution and contrast display quality. Properties (dimensional stability, moisture and heat resistance, water resistance), no foreign substances in the film and on the surface, no scratches or scratches on the surface (scratch resistance), moderate film rigidity (handling) It is necessary to have various excellent characteristics such as appropriate water permeability.

[0004] As the plastic film having the above-mentioned preferable characteristics, a film made of cellulose ester, norbornene resin, acrylic resin, polyarylate resin, polycarbonate resin and the like is known. From the viewpoint, cellulose esters are mainly used. In particular, cellulose esters such as cellulose triacetate are most commonly used for optical applications because when they are used as a film-forming material, a film showing extremely high transparency and low optical anisotropy can be easily obtained. ing.

[0005] As a method for producing a film from these plastic materials (film-forming method), various film-forming techniques such as a solution film-forming method, a melt film-forming method and a rolling method are known.
In order to obtain a film having good flatness and low optical anisotropy, a solution casting method is particularly suitable. In the solution casting method, a raw material plastic material is dissolved in a solvent, and a solution obtained by adding various additives such as a plasticizer, an ultraviolet absorber, a deterioration inhibitor, a slipping agent, and a peeling accelerator as needed ( Dope) is cast on a surface of a temporary support made of a metal endless belt (endless band) or a rotating drum by a dope supply means (die), and dried to an appropriate level on the support to coagulate. This method comprises removing the coagulated film from the temporary support, passing the coagulated film through a drying device by various transporting means, and completely removing the solvent from the coagulated film.

In this solution casting method, it is strongly desired to increase the dope casting speed and the film winding speed at least to increase the productivity of the film. However, increasing the casting speed tends to hinder the production process and tends to cause quality defects in the obtained film. For example, a metal band (metal belt) as a temporary support
In the band method using, there is a limit to the film peeling speed. On the other hand, in the cooling casting method using a drum, when the dope is extruded from the casting die at a high speed and the casting speed is increased, when the dope is extruded onto the drum surface, surface defects, particularly irregularities called sharkskin, occur. There is a problem that the surface is likely to be generated on the surface and the irregularities on the dope surface remain on the surface of the finally obtained film. Therefore, the problem of planar defects occurring on the surface of the doped layer is a constraint on increasing the casting speed.

As a method for preventing the generation of sharkskin, Japanese Patent Application Publication No. 94-2498 proposes enlarging the tip of the lip of a casting die. JP-B-62-43846 proposes a method of simultaneously extruding a low-viscosity solution from a die so as to cover a high-viscosity solution by co-casting. However, any of these methods requires a new capital investment for their implementation, and there is a problem in industrially adopting them.

Japanese Patent Application Laid-Open No. 4-298310 discloses a tenter draw ratio (Ax100 / B, A: tenter speed, B: band speed) for the purpose of stably peeling the cellulose acetate coagulated film from the band in the band method. Is described in the range of 100.5 to 110.0%.

[0009]

SUMMARY OF THE INVENTION Accordingly, the present invention provides an improved method for producing a cellulose ester film using a solution casting method, which provides high productivity but without reducing the flatness of the resulting film. It is an object of the present invention to provide a method for producing a cellulose ester film.

[0010]

Means for Solving the Problems As a result of repeated studies aimed at solving the above-mentioned problems, the present inventors have found that using a cooling drum casting method makes it possible to obtain a cast cellulose ester coagulated film in comparison with a band method. Has been found to be possible in a state where the residual ratio of the solvent is high. The present inventor has further studied this new finding, and as a result, it has become possible to stably peel off the cellulose ester coagulation film in such a state where the solvent residual ratio is high. The draw ratio can be increased, and the winding speed of the finally obtained cellulose ester film can be increased without changing the dope casting speed. It has been found that it is possible to produce a cellulose ester film with high productivity without causing it.

Accordingly, the present invention provides a process of continuously casting a cellulose ester solution on the surface of a rotating cooling drum, and coagulating the cellulose ester solution on the surface of the cooling drum while rotating the cooling drum. Forming an ester coagulation film, removing the cellulose ester coagulation film from the cooling drum, and holding the cellulose ester coagulation film at both ends in the width direction in a direction perpendicular to the rotation axis of the cooling drum. There is provided a method for producing a cellulose ester film, comprising a step of drying while being transported using a tenter that moves at a speed of 1.105 to 1.200 times the peripheral speed of the cooling drum. The present invention also resides in a cellulose ester optical film produced by the above method.

Hereinafter, preferred embodiments of the method for producing a cellulose ester film and the cellulose ester optical film of the present invention will be described. (1) The moving speed of the tenter is 1.1 of the peripheral speed of the cooling drum.
The method for producing a cellulose ester film described above, wherein the speed is in the range of 10 to 1.150 times. (2) The method for producing a cellulose ester film described above, wherein the surface temperature of the cooling drum is in the range of -20C to 5C. (3) The method for producing a cellulose ester film described above, wherein the cellulose ester solution comprises a film forming component containing a cellulose ester and a plasticizer, and the concentration of the film forming component in the solution is in the range of 15 to 25% by weight.

(4) The solvent of the cellulose ester solution is
The above method for producing a cellulose ester film, which is a mixed solvent comprising 80 to 92% by weight of methylene chloride and 8 to 20% by weight of a lower alcohol. (5) The method for producing a cellulose ester film described above, wherein the cellulose ester is cellulose triacetate.

(6) Front retardation is 0 to 10n
m, a cellulose ester optical film produced by the above-mentioned method for producing a cellulose ester film. (7) A cellulose ester optical film produced by the above-described method for producing a cellulose ester film, wherein the thickness of the film is in the range of 50 to 110 µm and the retardation in the thickness direction is in the range of 20 to 50 nm.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a method for producing a cellulose ester film of the present invention will be described in detail. Examples of the cellulose ester of the raw material resin used in the present invention include lower fatty acid esters of cellulose such as cellulose triacetate, cellulose acetate propionate, and cellulose acetate butyrate. Particularly preferred is cellulose triacetate.

First, these raw materials are dissolved in an appropriate organic solvent to prepare a solution (dope) of the cellulose ester composition. Examples of the organic solvent include halogenated hydrocarbons (methylene chloride and the like), lower alcohols (alcohols having 6 or less carbon atoms such as methanol, ethanol and butanol), esters (methyl formate, methyl acetate and the like), ethers (Dioxane, dioxolan, diethyl ether, etc.). In the solution of the cellulose ester composition, there are known various plasticizers such as triphenyl phosphate, phosphate plasticizers such as biphenyldiphenyl phosphate, phthalate plasticizers such as diethyl phthalate, and polyester polyurethane elastomer. Is preferably added. Further, if necessary, various known additives such as an ultraviolet absorber, a deterioration inhibitor, a slipping agent, and a peeling accelerator may be added.

The concentration of the resin composition (a component constituting a film as a solid after drying) in the solution of the cellulose ester composition is preferably in the range of 15 to 25% by weight. If the content is less than 15% by weight, the amount of the volatile solvent component is too large, the drying load increases, and the critical casting speed tends to decrease. On the other hand, if it exceeds 25% by weight, the viscosity of the solution is increased, so that the fluidity is apt to decrease, and the appearance of the film is liable to be impaired such as occurrence of a streak. As the solvent, a solvent mixture containing methylene chloride as a main component, particularly a mixed solvent of methylene chloride and a lower alcohol (a mixed solvent of 80 to 92% by weight of the former and 8 to 20% by weight of the latter, optionally further May be added).

The preparation of the cellulose ester composition solution comprises:
The raw resin or the like may be stirred and mixed in a solvent by a well-known method to dissolve the resin, or the raw resin or the like may be temporarily swelled with a solvent by a cooling dissolution method, and then the swollen mixture is cooled to -10 ° C
It is also possible to use a method of cooling below and then heating to 0 ° C. or higher to dissolve.

Next, the solution (dope) of the cellulose ester composition was cast using an apparatus as shown in FIG.
By coagulating and finally drying, a cellulose ester film is produced.

In the production apparatus shown in FIG. 1, a solution (dope) of the cellulose ester composition is first extruded in a casting section 1 by a casting die 2 onto the surface of a rotating cooling drum 3. This drum 3 is usually -20 ° C
It is used in a state of being cooled to a temperature in the range of ５5 ° C. Further, the dope may be at room temperature, or may be heated to a temperature in the range of-. The dope cast on the surface of the cooling drum 3 is dried and cooled while moving by the rotating drum 3, and solidifies to a state where stable peeling is possible. The solidified casting film (coagulated film) 4 is then peeled off from the cooling drum 3 at a preset peeling position 5 and sent to the roller transport zone 6. The film 7 peeled off in the roller transport zone 6 is dried by the drying air while being held and transported by the transport pass rollers 8a, 8b, 8c,..., And most of the solvent is removed from both surfaces. Next, in the tenter transport zone 9, while the film 7 is held and transported in a state where both ends are bitten by the tenter 10, the solvent is completely removed from both surfaces by the drying air from the numerous blow-out ducts 11 and dried. It becomes a film. The dried film 7 is then wound up by a suitable winding means (not shown) to obtain a desired cellulose ester film.

In the present invention, the tenter draw ratio in the above step is in the range of 110.5 to 120.0% (preferably 111 to 115%). Here, the tenter draw ratio is a ratio of the tenter speed (the speed of the tenter moving in a direction perpendicular to the rotation axis of the cooling drum) and the drum speed (the peripheral speed of the cooling drum) expressed by the following equation. is there.

Tenter draw ratio (%) = 100 × A / B A: Tenter speed B: Drum speed That is, the tenter speed A is set to 1.
105 to 1.200 times (preferably 1.11 to 1.15)
Times).

In the present invention, the coagulated film peeled off from the cooling drum is stretched mainly between the peeling position 6 on the drum and the biting by the tenter 11 in the tenter transport zone 10. , Which corresponds to this stretching ratio. When the stretching ratio is larger than 120.0%, the optical properties of the film such as front retardation (Re) are affected, which is not preferable.

In the present invention, the tenter speed A is equivalent to the film winding speed, and the drum speed B is equivalent to the dope casting speed. Accordingly, by increasing the film winding speed in the range of 10.5 to 20.0% from the dope casting speed, the product film can be wound at a higher speed even if the casting speed is the same as the conventional one. As a result, the productivity of the film can be increased.

The drum speed B (the peripheral speed of the cooling drum)
It is usually preferable that the thickness be in the range of 30 to 80 m / min from the viewpoint of flatness such as prevention of sharkskin.

The thickness of the cellulose ester film thus obtained varies depending on the use of the film and the like, but is generally in the range of 20 to 500 μm, preferably in the range of 50 to 125 μm.

In order to obtain a cellulose ester film suitable for optical applications, a front retardation (R
e) is preferably in the range of 0 to 10 nm, and the retardation (Rth) in the thickness direction is 5 mm.
When it is in the range of 0 to 110 μm, it is preferably in the range of 20 to 50 nm.

The construction itself of the production apparatus which can be used for producing the cellulose ester film of the present invention is described in detail in JP-A-5-185445.
Further, the manufacturing apparatus which can be used in the present invention is not limited to the apparatus shown in FIG. 1, but is an apparatus having a casting section provided with a cooling drum and a drying section provided with a conveying means by a tenter. Any manufacturing apparatus may be used. For example, the dope may be cast by a co-casting method having a plurality of casting ports, and in this case, a film having a multilayer structure can be simultaneously formed.

Further, as described in the above-mentioned published technical report No. 94-2498, the tip of the lip of the casting die may be enlarged, or the above-mentioned Japanese Patent Publication No. Sho 62-43 may be used.
As described in JP-A-846, a low-viscosity dope may be simultaneously extruded from a die by wrapping a high-viscosity dope by co-casting. Can be more effectively prevented, and the productivity can be further improved.

[0030]

EXAMPLES [Example 1] A solution (dope) of a cellulose triacetate composition was prepared by stirring and mixing each component so as to have the following composition. Cellulose triacetate (acetation degree 60.8%) 100 parts by weight Triphenyl phosphate 12 parts by weight Methylene chloride 305 parts by weight Methanol 60 parts by weight 1-butanol 10 parts by weight

With the dope kept at 34 ° C., a metal drum (cooling drum rotating at a peripheral speed of 45 m / min) cooled to −5 ° C. from a casting die using an apparatus as shown in FIG. ) To form a casting film. After cooling and drying the cast film on the surface of the rotating cooling drum for 11 seconds to form a coagulated film, the coagulated film was peeled off from the drum, and then the tenter speed was 50 m / min (that is, the tenter draw ratio was 112%). In), the coagulated film was dried while being sequentially conveyed by a roller and a tenter to produce a cellulose ester film (thickness: 80 μm) according to the present invention.

[Comparative Example 1] In Example 1, the tenter speed was 46.8 m / min (tenter draw ratio: 104%).
A conventional cellulose ester film (thickness: 80 μm) was produced in the same manner as in Example 1 except that the thickness was changed to.

Comparative Example 2 A cellulose ester film (thickness) for comparison was prepared in the same manner as in Example 1 except that the drum speed was changed to 48 m / min (tenter draw ratio: 104%). : 80 μm).

[Evaluation of Cellulose Ester Film] With respect to each of the obtained cellulose ester films, the state of sharkskin generation was examined by visually observing the film surface. The flatness of the film was determined by the following AA to CC (C
C: unusable). AA: Sharkskin did not occur. BB: Some sharkskin was generated. CC: Sharkskin was noticeably generated. In addition, the retardation (Re) in the front direction and the retardation (Rth) in the thickness direction of each cellulose ester film were measured. The results obtained are summarized in Table 1.

[0035]

[Table 1] Table 1 フ ィ ル ム Film tenter Drum peripheral speed Retardation Shark draw ratio (tenter speed) Front Thickness direction Skin generation ──────────────────────────────────── Example 1 1.12 45 m / min 6.8 nm 46 nm AA (50 m / min)比較 Comparative Example 1 1.04 45 m / min 6.2 nm 42 nm AA (46.8 m / min) Comparative Example 2 1.04 48 m / min 6.1 nm 43 nm BB (50 m / min) ─────── ─────────────────────────────

As is clear from the results shown in Table 1, the cellulose ester film produced according to the method of the present invention (Example 1) is compared with the film produced according to the conventional method (Comparative Example 1). The tenter draw ratio is high (the dope casting speed is the same, the film winding speed is high), and despite the increased productivity, shark skin does not occur and excellent flatness is achieved. It had good optical properties with low retardation. On the other hand, in the cellulose film film (Comparative Example 2) manufactured by simultaneously increasing the drum speed and the tenter speed without increasing the tenter draw ratio, shark skin was generated and the flatness was impaired.

[0037]

According to the present invention, when a cellulose ester film is manufactured, a cooling drum is used in the step of manufacturing a coagulated film from a dope, so that even if the tenter draw ratio is higher than before, the flatness is reduced. , A cellulose film free from the occurrence of odor can be obtained. Therefore, while maintaining the excellent flatness of the cellulose ester film,
At the same time, productivity can be improved. Therefore, it is particularly advantageous particularly for the production of a cellulose film used as an optical film.

[Brief description of the drawings]

FIG. 1 is a schematic side view showing an example of a film manufacturing apparatus that can be used for carrying out the manufacturing method of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Casting part 2 Casting die 3 Cooling drum 4 Casting film (coagulated film) 5 Peeling position 6 Roller transport zone 7 Cellulose ester film 8a, 8b, 8c, 8d Pass roller 9 Tenter transport zone 10 Tenter 11 Outlet duct

Claims (8)

[Claims] 1. A step of continuously casting a cellulose ester solution on the surface of a rotating cooling drum, wherein the cellulose ester solution is solidified on the surface of the cooling drum while rotating the cooling drum to form a cellulose ester coagulated film. Forming, removing the cellulose ester coagulated film from the cooling drum, and surrounding the cooling drum in a direction perpendicular to the rotation axis of the cooling drum while gripping both ends in the width direction of the cellulose ester coagulated film. 1.105-speed
1. A method for producing a cellulose ester film, comprising a step of drying while being conveyed using a tenter that moves at a speed of 200 times. 2. The method for producing a cellulose ester film according to claim 1, wherein the moving speed of the tenter is in a range of 1.10 to 1.150 times the peripheral speed of the cooling drum. 3. The cooling drum has a surface temperature of -20 ° C. to 5 ° C.
The method for producing a cellulose ester film according to claim 1 or 2, wherein 4. The cellulose ester solution according to claim 1, wherein the cellulose ester solution comprises a film forming component containing a cellulose ester and a plasticizer, and the concentration of the film forming component in the solution is in the range of 15 to 25% by weight. The method for producing a cellulose ester film according to any one of the above items. 5. The method according to claim 1, wherein the solvent of the cellulose ester solution is 80%.
The method for producing a cellulose ester film according to any one of claims 1 to 4, wherein the mixed solvent is a mixed solvent consisting of methylene chloride in an amount of about 92% by weight and a lower alcohol in an amount of 8 to 20% by weight. 6. The method for producing a cellulose ester film according to claim 1, wherein the cellulose ester is cellulose triacetate. 7. A cellulose ester optical film produced by the method for producing a cellulose ester film according to any one of claims 1 to 6, wherein the front retardation is in the range of 0 to 10 nm. 8. When the thickness of the film is in the range of 50 to 110 μm, the retardation in the thickness direction is 20 to 50 n.
A cellulose ester optical film produced by the method for producing a cellulose ester film according to any one of claims 1 to 6, which is in the range of m.