JP2003175522A - Method for producing cellulose acetate film and cellulose acetate film, polarizing plate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To adjust a friction force between a cellulose acetate film and a roller in a solvent casting process. <P>SOLUTION: A dope 14 of a dissolved cellulose acetate is casted from a casting die 15 onto a band 16 and dried to a film 17. To a side edge of the film 17 whose fringe is trimmed beforehand, a knurling is conducted with a stamp roller 22 in a roller conveying step. A depth of the knurling can be adjusted according to a thickness of the film 17. After further drying and cooling thereafter, a merchandise knurling is conducted. The side edge of the film where the previous knurling remains is cut off before uprolling the film. In this way the friction force between the film 17 and the roller can be adjusted to enhance conveyance stability while allowing no remainder of the previous knurling on the product. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a cellulose acetate film, and more particularly to a method for producing a cellulose acetate film used as an optical film such as a polarizing plate protective film.

[0002]

2. Description of the Related Art Cellulose acetate film has a low birefringence, transparency, moderate moisture permeability, high mechanical strength, and good dimensional stability against humidity and temperature changes. It is widely used as an optical material such as a film. Such a cellulose acetate film is manufactured by a solution film-forming method. This method is a drum which is an endless endless support after a polymer such as cellulose acetate is doped with a solvent by appropriately adding various additives. Alternatively, it is cast on a band, peeled off when it has self-supporting property, and dried to obtain a product film. Drying after peeling is generally performed by hot air drying while being conveyed by rolls. The continuously produced film is usually wound on a cylindrical winding core made of resin, metal, wood, cardboard, etc., with a length of several hundreds to several thousands depending on the application and facility capacity. The product is packaged as appropriate. Among them, during the roll conveyance after peeling from the endless support, if the friction between the roll and the film is insufficient, a slip phenomenon occurs, and the minute irregularities of the roll scratch the film and reduce the product value. Sometimes.
Most of the rolls in the drying zone are
This is because it does not have a function of independently driving, and simply rotates with the conveyance of the film by using the frictional force generated between the film and the conveyed film as the driving force. In order to prevent this, it is necessary to increase the frictional force between the roll and the film. Conventionally, a method of increasing the tension in the transport direction during roll transport has been adopted as the method. Further, there is a method of making the material and the surface state of the roll have a high frictional force so that the film exhibits an appropriate frictional force.

[0003]

However, the method of increasing the tension in the transport direction during roll transport is as follows.
The elongation of the film in the machine direction occurs remarkably especially in a high temperature environment, and there is a drawback that the performance of the film, particularly optical isotropy and dimensional stability are affected. Further, by increasing the surface friction force, the film may be wrinkled on the roll surface, and the film may be wrinkled. This problem becomes more remarkable as the film thickness becomes thinner, and it is necessary to adjust the frictional force between the roll and the film at any time. The surface material of the roll and the method of surface treatment are equipment-friendly,
There is a problem in terms of the flexibility of the friction force adjustment method.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a method for producing a cellulose acetate film in which scratches and wrinkles are less likely to occur, a cellulose acetate film, and a polarizing plate.

[0005]

In order to achieve the above object, the method for producing a cellulose acetate film by the solution casting method of the present invention comprises a step of drying the film peeled from the endless support while transporting the film, It is characterized in that knurling due to unevenness is applied to at least one side end portion of the film. The knurling is preferably performed immediately after the tenter drying when a tenter drying zone is provided in the manufacturing process. Further, it is effective in the roll conveying step, and most preferably after drying in the tenter drying zone and before introduction into the roll drying zone. Here, the knurling means that the film side end portion is subjected to a process generally called knurling embossing by using a marking roll. The finished product is generally knurled for the purpose of stabilizing the winding. Knurling in the roll conveying step of the present invention, it is also possible to knurling of the finished product, generally the knurling position of the finished product, the film width, etc. are strictly defined, roll drying zone,
In particular, it is not preferable to use the knurling performed before the solvent content is too low as the knurling of the finished product, because the knurling position may fluctuate due to minute fluctuations in the subsequent drying conditions. Therefore, after drying,
It is preferably not included in the finished product and cut out prior to the final winding step.

Even if it is provided on only one side of the film, it is effective to increase the thickness of the knurling. However, even if the thickness of the knurling is reduced, unevenness is provided on both sides of the film so that scratches can be prevented. preferable. Further, the manufacturing method of the present invention is characterized in that the thickness of the knurling can be arbitrarily set, and by optimizing this thickness,
According to the thickness and rigidity of the film, it is possible to prevent scratches and suppress the generation of wrinkles.

The knurling in the present invention is applied by plastic deformation of the film, and if the film rigidity at the time of applying the knurling is small, the knurling becomes weak,
The effect does not improve. Therefore, the knurling in the present invention should be applied at a stage where the film has a certain degree of rigidity, that is, in a state where the solvent content is low to some extent. On the other hand, when knurling is applied after the solvent content becomes extremely low, it is necessary to increase the length of the drying process or decrease the transport speed in the drying process in the drying process before knurling. It is disadvantageous in terms of cost. Therefore, the solvent content of the film when knurling is preferably 30% by weight or less, more preferably 10 to 30% by weight, and most preferably 10% by weight.
~ 25% by weight.

The knurling in the present invention prevents scratches while securing the frictional force between the non-driving roll and the film. Therefore, it is preferable that the number of the non-driving rolls before the knurling is small, and it is most preferable that the number is not at all. Further, considering the solvent content rate, productivity, and facility cost as described above, knurling may be performed before the final drying step, that is, when there is at least one non-driving roll after knurling. preferable.
The knurling in the present invention can also be applied to a co-casting method, a sequential casting method, etc. of a solution casting method which is a manufacturing method of various films having a laminated structure, a polarizing plate and the like. Further, depending on the film forming process, the tenter drying zone may not be provided, which is also effective.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The film in the solution casting method of the present invention can be produced from a dope using various known solvents. When cellulose acetate is used as the raw material polymer of the film, halogenated hydrocarbons such as methylene chloride, alcohols, esters, ethers and the like can be used alone or in combination as a solvent. The present invention also includes the case where a film is formed using these solvents.

The dissolved dope is generally filtered to remove foreign substances and undissolved raw materials. For the filtration, it is possible to use various known filter materials such as filter paper, filter cloth, non-woven fabric, metal mesh, sintered metal filter, and perforated plate. By filtering, foreign substances, undissolved substances, and the like in the dope can be removed, and the deterioration of film performance, damage, and defects due to these can be reduced or removed.

Further, the solubility can be further improved by heating the once-dissolved dope. For heating, there are a method of heating while stirring in a stationary tank, and a method of heating while transferring the dope by using various heat exchangers such as a multitubular type and a jacket pipe with a static mixer. Also,
It is also possible to provide a cooling step after the heating step and pressurize the inside of the apparatus to heat it to a temperature above the boiling point of the dope. By performing these heat treatments, undissolved substances that could not be completely dissolved can be completely or practically dissolved to a level that can be ignored, reducing the amount of foreign substances in the product film and reducing the filtration load. Can be achieved.

Further, known additives can be added to the dope. Examples of the additive include, but are not limited to, an ultraviolet absorber, a dispersant, and a plasticizer. It is also possible to add silica, kaolin, talc, etc. as other additives in the dope. After the dope is prepared, these additives can be mixed in-line by using a mixer or the like, or can be mixed at the same time when the dope is prepared.

FIG. 1 shows a typical example of a solution film-forming process in which the present invention is carried out. The ultraviolet absorbent solution and the fine particle dispersion liquid were mixed in-line from the supply pumps 10 and 11 using the static mixer 12, and this mixed liquid was further mixed in-line with the dope base material 13 to obtain a dope 14. The dope 14 is cast from the casting die 15 onto the band 16 which is an endless support, and the solvent is gradually volatilized by drying with hot air, so that the dope becomes self-supporting. Film 1 here
7 is stripped from the band 16 and conveyed while being in contact with the four driving rolls 18, and introduced into the tenter drying zone 19. In the tenter drying zone 19, the film 17 is bitten by a tenter clip installed on a tenter track (not shown) to hold both ears and dry while applying tension. Immediately after the film 17 leaves the tenter drying zone 19, both ears of the deformed film 17 held by the tenter clips are cut and removed by a cutting machine 20,
After passing through one drive roll 21, knurling (hereinafter referred to as process knurling) is performed on the film 17 by the marking roll 22.
On the side edge of. After the process knurling, the surface temperature of the film 17 is raised to a maximum of 130 ° C. while being conveyed by the roll 24 in the roll drying zone 23, and further dried, and then cooled to room temperature in the cooling zone 25, and then knurled by the marking roll 26 (Hereinafter referred to as product knurling). At this time, the engaging force of the marking roll is adjusted so that the average value of the thickness of the product knurling becomes the target value. Immediately after the product knurling, the process knurling is cut and removed by the edge cutting device 27 and wound on the winding core 28.

FIG. 2 is an explanatory view of process knurling. As shown in the drawing, the engraving roll 22 having a diameter of 100 mm provided with the knurling projection pattern 40
Two pairs were installed by sandwiching the two from above and below, and the film 17 was conveyed by a drive roll (not shown) to provide the knurling 41. Knurling protrusion pattern 4
0 can take various forms as long as it can provide sufficient knurling 41 to adjust the frictional force between the film 17 and the roll. The marking roll 22 may be installed at one side end of the film, but it may be installed at both side ends. The thickness average value of the knurling 41 is 314 mm for one rotation of the marking roll using a digital linear gauge DG-933 and gauge stand ST-022 manufactured by Ono Sokki Co., Ltd.
The film length corresponding to is divided into 20 equal parts, the thickness of each central part of the equally divided knurling portion is measured to obtain an average value, and the average film thickness value of the film 17 in the non-knurling portion is subtracted from this average value. Ask. It is possible to change the knurling thickness average depending on the conditions such as the transport speed, the film thickness of the film 17, the rigidity, and the like. The thickness of the knurling can be adjusted by adjusting the engaging force of the pair of marking rolls. Specifically, a method of placing a weight and applying a load,
Known methods such as a method of pressing with air pressure / water pressure / hydraulic pressure or a method of mechanically pressing with a spring can be used without limitation.

Regarding the measurement of the solvent content (unit: weight%) of the film 17 during the process knurling, in the present invention,
The weight of X-gram in a closed container before drying was removed, and Y-gram was removed by removing the lid of the closed container for 90 minutes in a dryer at 115 ° C., then closed again, cooled to room temperature, and opened once again. Immediately after that, the lid was re-covered again, and the weight after drying, Z gram, was taken as the total weight of the closed container and the lid, and the calculation formula (X-
Y) / (X−Z) × 100.

The presence or absence of scratches on the film 17 is visually inspected as follows, but is not limited to this. In the present invention, at the time of winding, the film surrounding the winding is darkened and the film of the slide projector is illuminated with the film 17, and if there is a scratch, the position can be seen as shining and thus can be confirmed and evaluated with extremely high accuracy. it can. If scratches are found, the scratched surface is confirmed by sampling the part and confirming the scratched part.
The contact surface or non-contact surface for the band can be specified.

[0017]

EXAMPLES The present invention will be specifically described below with reference to examples, but the contents of the present invention are not limited thereto. The preparation of the raw material dope 14 is similar to that of the example and the comparative example, so that this will be described first, and the film production and the results will be described later. (Preparation of Dope Base Material 13) Cellulose triacetate (oxidation degree 60.9%) 89.3% by weight Triphenyl phosphate 7.1% by weight Biphenyldiphenylphosphate 3.6% by weight Based on a solid content of 100 parts by weight. A mixed solvent consisting of 85% by weight of dichloromethane and 15% by weight of methanol is appropriately added, and the mixture is stirred to form a dope substrate 1
3 was prepared. The solid content concentration of the dope substrate 13 is 18.5.
% By weight. The dope substrate 13 was filtered through a filter paper (# 63) 34a manufactured by Toyo Roshi Kaisha, Ltd., and then a sintered metal filter (06N manufactured by Nippon Seisen Co., Ltd., nominal pore diameter 10) was used.
μm) 34b and then a sintered metal filter (12N manufactured by Nippon Seisen Co., Ltd., nominal pore diameter 40 μm) 34c.

(Preparation of Ultraviolet Absorber Solution) 2 (2′-Hydroxy-3 ′, 5′-di-tert-butylphenyl) -5-chlorobenzotriazole 5.33 wt% 2 (2′-hydroxy-3) ', 5'-Di-tert-amyl phenyl) benzotriazole 10.67% by weight Cellulose acetate (oxidation degree 60.8%) 3.57% by weight Triphenylphosphate 0.29% by weight Biphenyldiphenylphosphate 0.14 A UV absorber solution consisting of wt% methylene chloride 68.00 wt% methanol 12.00 wt% was prepared, and filtered once with an Astropore 10 μm filter manufactured by Fuji Photo Film Co., Ltd.

(Preparation of Fine Particle Dispersion) Silica (Aerosil R 972 manufactured by Nippon Aerosil Co., Ltd.) 2.00% by weight Cellulose acetate (degree of substitution 2.8) 2.00% by weight Triphenyl phosphate 0.16% by weight A dispersion liquid containing 0.08% by weight of biphenyldiphenylphosphate, 81.40% by weight of methylene chloride and 14.36% by weight of methanol was prepared and dispersed with an attritor so that the volume average particle diameter was 0.5 μm. Here, as the volume average particle diameter, a value measured by a particle size distribution measuring apparatus LA920 manufactured by Horiba Ltd. was used. This dispersion was filtered twice with an Astropore 10 μm filter manufactured by Fuji Photo Film Co., Ltd. to obtain a fine particle dispersion.

The ultraviolet absorbent solution and the fine particle dispersion were mixed in-line by using the static mixer 12, and this was further mixed in-line with the dope base material 13 to obtain the raw material dope 14. Here, the amount of the ultraviolet absorbent solution added is such that the product of the value of the amount of the ultraviolet absorbent based on the solid content in the dope expressed in weight% and the value of the thickness of the finished film expressed in μm is 83.2. It was adjusted. The addition amount of the fine particle dispersion is 0.13, which is the weight ratio of silica in the fine particle dispersion with respect to the weight of the completed film 17.
Adjusted so that

[Example 1] The dope 14 was formed into a film by a solution film-forming process as shown in FIG. The dope 14 is cast from a casting die 15 onto a band 16 as an endless support whose rotation speed is set to 50 m / min so that the film thickness of the product film is 80 μm, and dried by hot air until it has self-supporting property. And peeled off as film 17. The film 17 was introduced into a tenter drying zone 19 after passing through four driving rolls 18 and dried while applying tension while holding both ears. Immediately after the film 17 exits the tenter drying zone 19, both ears of the deformed film 17 held by the tenter clips are cut and removed, and one driving roll 21 is interposed, and then process knurling is performed by the engraving roll 22. . Process knurling is engraved roll 2 with a diameter of 100 mm
Two pieces of the film No. 2 were placed on each side of the film with one pair sandwiching the film, and the film was conveyed and applied to both side ends. When sampling was performed here and the solvent content rate of the film 17 was measured, it was 28% by weight. After that, the film was further dried by heating the surface temperature of the film 17 to a maximum of 130 ° C. in the roll drying zone 23. The tension in the roll drying zone 23 is 50-
It was 100 N / m. After cooling to room temperature in the cooling zone 25, product knurling was performed with a pair of marking rolls 26 on each side. At this time, the biting force of the engraving roll was adjusted so that the average value of the thickness of the product knurling was 10 μm. Immediately after the product knurling, both edge parts were cut and removed by the edge cutting device 27 so that the product film width became 1340 mm, and the product film was wound on the FRP winding core 28 having an outer diameter of 168 mm. The side edge after cutting was sampled, and the average value of the thickness of the process knurling was measured and found to be 4 μm. The winding tension is 22 at the start of winding.
It was 0 N / m and 140 N / m at the end of winding. The number of non-driving rolls installed from the ear cutting and removing process before the process knurling to the winding process was 350. At the time of winding, the film 17 surface was irradiated with light from a slide projector and visually inspected for scratches, but neither the contact surface nor the contact surface of the band 16 was scratched and wrinkles were not generated.

[Embodiment 2] Rotation speed of band 16 is 30 m
/ Min, and the roll drying zone tension is 50 to 70
The same procedure as in Example 1 was carried out except that N / m was set. When wound, the band 16 was visually inspected for scratches.
There were no scratches on the contact surface and the non-contact surface, and no wrinkles were generated.

[Example 3] Instead of installing the marking roll 22, a marking roll was used on the contact surface side of the band 16 of the film 17, and a flat roll having no knurling projection pattern on the non-contact surface side was used. As a pair, the same procedure as in Example 1 was performed except that one pair was installed at each end of the film. The presence of scratches was visually inspected during winding. Scratches were not found on the contact surface of the band 16, but were found on the non-contact surface. No wrinkles were observed.

[Embodiment 4] Process was carried out in the same manner as in Embodiment 3 except that the engagement force of the marking roll 22 was adjusted so that the average value of the knurling thickness was 8 μm. When wound, the presence or absence of scratches was visually inspected, but there was no scratch on the contact surface or the non-contact surface of the band 16, and no wrinkle was generated.

[Example 5] An example in which the marking roll 22 is installed on the contact surface side of the band 16 at one side end of the film 17 and on the non-contact surface side at the other side end The same procedure as in 3 was performed. When wound, the presence or absence of scratches was visually inspected, but there was no scratch on the contact surface or the non-contact surface of the band 16, and no wrinkle was generated.

[Embodiment 6] Process knurling is applied to film 1
Example 7 was performed in the same manner as in Example 1 except that only one side end of No. 7 was applied. The wound was visually inspected for scratches, but there was no scratch on the contact surface or the non-contact surface of the band 16,
There were no wrinkles.

[Embodiment 7] The film thickness of the finished film is 40 μm.
The same procedure as in Example 1 was performed except that the raw material dope 14 was cast so as to give m. The wound was visually inspected for scratches, and no wrinkles were found on the contact surface and the non-contact surface of the band 16, but wrinkles were observed.

[Embodiment 8] Process was carried out in the same manner as in Embodiment 7 except that the meshing force of the marking roll 22 was adjusted so that the average value of the knurling thickness was 2 μm. When the tape was wound up, it was visually inspected for scratches, but there were no scratches on the contact surface or the non-contact surface of the band 16 and no wrinkles were formed.

Example 9 Example 1 was repeated except that the drying conditions on the band 16 and in the tenter drying zone 19 were changed.
It carried out similarly to. The solvent content of the portion to which the process knurling was applied was 36% by weight, and the average thickness of the process knurling was 1 μm or less. When the wound was visually inspected for scratches, the scratches were not found on the non-contact surface of the band 16, but were found on the contact surface. No wrinkles were observed.

Comparative Example 1 Process was carried out in the same manner as in Example 1 except that no knurling was applied. When wound was visually inspected for scratches, the contact surface of the band 16
Scratches were also found on the non-contact surface. No wrinkles were found.

Comparative Example 2 The rotation speed of the band 16 is 30
The same procedure as in Comparative Example 1 was carried out except that m / min was set. When wound, the presence of scratches was visually inspected, but no wrinkles were found, but wrinkles were found.

[Comparative Example 3] The same procedure as in Comparative Example 2 was carried out except that the tension in the roll drying zone 23 was adjusted to 50 to 70 N / m. When wound, the presence or absence of scratches was visually inspected, and scratches were found on both the contact surface and the non-contact surface of the band 16. No wrinkles were observed.

[0033]

As described above, by imparting process knurling in the solution film-forming method of the present invention, the tension at the time of conveyance is increased, and the film is scratched without taking any facility measures such as processing the roll surface. The film can be transported and manufactured while preventing wrinkles.

[Brief description of drawings]

FIG. 1 is a process diagram of a solution film-forming method embodying the present invention.

FIG. 2 is an explanatory diagram of a knurling step in which the present invention is implemented.

[Explanation of symbols]

13 Dope base material 14 Dope 15 Casting die 16 bands 17 films 18 drive roll 19 tenter drying zone 21 drive roll 22 engraved roll 23 roll drying zone 24 rolls 25 cooling zones 26 engraving roll 27 ear cutting device 41 Knurling

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) // B29K 1:00 B29K 1:00 B29L 7:00 B29L 7:00 C08L 1:12 C08L 1:12 F Terms (reference) 2H049 BA02 BB13 BB33 BC09 BC22 3F104 AA03 DA29 KA11 4F071 AA09 AH16 BA02 BB02 BC01 BC08 4F205 AA01J AC05 AG01 AH73 GA07 GB02 GC07 GE22 GF24 GN08 GN30 GW23

Claims (9)

[Claims] 1. A method for producing a cellulose acetate film by a solution film-forming method, wherein a film peeled from an endless support is dried while being conveyed by rolls, and knurling is imparted to at least one side end of the film. Solution casting method characterized by the above. 2. The method for producing a cellulose acetate film according to claim 1, wherein the knurling is cut and removed after film drying and before winding. 3. The method for producing cellulose acetate according to claim 1, wherein the unevenness of the knurling is formed on both surfaces of the film. 4. The thickness of the knurling is adjusted according to the thickness of the film to be manufactured.
4. The method for producing a cellulose acetate film according to any one of 3 to 3. 5. The method for producing a cellulose acetate film according to claim 1, wherein the solvent content of the film when imparting the knurling is 30% by weight or less. 6. The method for producing a cellulose acetate film according to claim 1, wherein there is no non-driven roll before applying the knurling. 7. The method according to claim 1, wherein there is one or more non-driving rolls after the knurling is applied.
The method for producing a cellulose acetate film according to any one of 1. 8. A cellulose acetate film produced by using the production method according to any one of claims 1 to 7. 9. A polarizing plate comprising the cellulose acetate film according to claim 8 attached to at least one surface.