JP2003175521A - Method for solvent casting film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent surface defect of a film in a method for solvent casting a film. <P>SOLUTION: A dope of a dissolved cellulose acetate or the like is casted from a casting die onto a band. The dope is dried to get self-sustainable on the band 12. Within 10 seconds from stripping off, a drying air 29 is supplied from an air supplier 28 to a surface of a film 14 on a side stripped off from the band 12. On this step, carrier rollers are arranged to touch the surface of the film 14 on the side stripped off from the band 12. The concentration of a solvent gas in the drying air 29 is maintained to 30 vol.% or lower. The solvent gas evaporated is kept from condensing and getting adsorbed on the film 14 so that the surface defect on the film 14 is prevented. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for solution-forming a film used as a photographic film support, a protective film for a polarizing plate or the like.

[0002]

2. Description of the Related Art Cellulose acylate films, especially cellulose acetate films, have low birefringence, transparency,
Since it has appropriate moisture permeability, high mechanical strength, and low humidity and temperature dependence of dimensional stability, it is widely used as a support for optical materials such as a polarizing plate protective film. Such a cellulose acylate film is produced by a solution film-forming method, which is a method in which a polymer is made into a dope and then the dope is cast from a casting die to an endless support and dried to form a film. Is what you get. A solvent having a low boiling point such as methylene chloride is mainly used as a solvent in many cases. For this reason, if the drying speed of the film is increased to increase productivity, the vaporized solvent tends to have a high concentration in the vicinity of the film and easily condense, and this is attached to the film surface, which easily causes surface defects of the film. As a result, the yield was reduced.

By the way, in Japanese Patent Laid-Open No. 5-185445, in the solution casting method, when the film is peeled from an endless support such as a drum or band, the organic solvent content of the film is 68% by weight or more. The drying air temperature was 30 to 80 during the transportation time from the peeling point for at least 20 seconds.
It is described that the temperature is set to ° C. In this way, by blowing dry air from the peeling point within a certain period of time, destabilization of conveyance due to the film being a soft film, sagging, flapping are prevented, and surface defects such as scratches, knicks, and wrinkles occur. Can be suppressed.

[0004]

However, the solution casting method described in the above publication is for the case where the solvent content is 68% by weight or more, and is intended to eliminate the instability of transport due to the buffy coat. It is a thing. In the case of a film having such a high solvent content, since a large amount of solvent is originally contained in the film, even if some volatile solvent aggregates and adheres to the film surface, it is difficult for the film to be clearly deformed. Therefore, in the film in the soft film state, the above-mentioned surface defects of the film do not occur. On the other hand, in the case of performing solution film formation by reducing the solvent content rate at the time of peeling, adhesion of the aggregating component of the solvent to the film surface has been a problem.

The present invention is intended to solve the above problems, and an object of the present invention is to provide a solution film-forming method capable of suppressing the occurrence of planar defects due to the aggregating component of a solvent.

[0006]

In order to achieve the above object, in the present invention, a polymer is dissolved in a solvent to prepare a dope, which is cast on an endless support by a casting die and dried with a dry air. In the method for producing a film by drying with radiant heating, the film is peeled off from the endless support, and at least the surface side in contact with the endless support is supplied with air within 10 seconds. It is configured. The solvent content of the film at the time of peeling from the endless support was 60.
It is preferably less than or equal to weight%.

After peeling the film from the endless support, the solvent abruptly volatilizes from the peeled surface, and the concentration becomes high in the vicinity of the film to easily condense. In order to prevent this from adhering to the film surface, the air supply is performed at least on the surface in contact with the endless support, preferably on the non-contact surface. The solvent gas concentration of the supply air is preferably 30% by volume or less. The solvent gas concentration at this time is measured by a general analytical instrument typified by gas chromatography.

Further, in the above method for producing a film,
In order to suppress the curl of both ears of the film, it is preferable to bring the transport roll into contact with the surface in contact with the endless support within 10 seconds after peeling the film from the endless support.

The polymer is preferably cellulose acylate, and the cellulose acylate is preferably cellulose acetate having a substitution degree of 2.6 or more.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The film of the present invention is not particularly limited as long as it is formed by a solution casting method.
Particularly preferred is cellulose acylate used for the protective film of the polarizing plate. As the cellulose acylate, various ester cellulose acylates can be used. Most preferably, the cellulose acetate has a substitution degree of 2.6 or more.

The film produced by the solution casting method of the present invention is
It can be produced from a dope using various known solvents. When cellulose acylate is used as the raw material polymer for the film, halogenated hydrocarbons such as methylene chloride (dichloromethane), esters, ethers, alcohols, etc. can be used alone or in combination. 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, various known filter materials such as filter paper, filter cloth, non-woven fabric, metal mesh, sintered metal, perforated plate and the like can be used. By filtering, foreign substances, undissolved substances and the like in the dope can be removed, and the performance deterioration, damage and defects of the product film due to these can be reduced or removed.

It is also possible to further improve the solubility 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 carrying out these heat treatments, minute undissolved substances that have not been completely dissolved can be completely or practically dissolved to such an extent that they can be ignored.
Foreign substances on the product film can be reduced, and the load of filtration can be reduced.

Further, known additives can be added to the dope. Examples of the additive include a plasticizer and an ultraviolet absorber, and triphenyl phosphate may be added as a component that becomes a solid after drying.
When film-forming the cellulose acetate by the solution film-forming method, a plasticizer such as triphenyl phosphate as a component that solidifies after drying, other additives, and various cellulose derivatives may be added if necessary. it can. Other additives such as silica, kaolin,
It is also possible to add talc or the like. These additives can be mixed at the same time when the dope is prepared, or can be mixed in-line by using a static mixer or the like when the dope is prepared and then transferred.

FIG. 1 shows a typical example of the solution film-forming process according to the present invention. The dope 10 is cast from a casting die 11 onto a band 12 as an endless support, and a solvent is gradually volatilized in a drying chamber 13 in which the band 12 is placed, so that a film is formed and self-supporting property is obtained. become.
Here, the film 14 is peeled off from the band 12, conveyed while being in contact with the plurality of rolls 15 to 18, and introduced into the tenter drying chamber 19. In the tenter drying chamber 19, the film 14 is conveyed while being bitten by a tenter clip 21 (see FIG. 2) installed on the tenter track 20. Then, it is sent to the roll drying chambers 23 and 24 through the guide roll 22,
The film 14 is dried while passing through a large number of rolls 25 in the drying chambers 23 and 24 to further reduce the contained solvent. Next, the winding device 26 winds the film 14 around the winding shaft 27. Among the solution film forming methods, there is a tenter drying step 1
The present invention is not limited to the configuration of FIG.

Next, from the band 12 to the tenter drying chamber 19
The film transport process up to is shown in FIG. Film 1
After peeling 4 from the band 12, the 1st-4th roll 1
It is sent into the tenter drying chamber 19 while being in contact with 5 to 18. Here, the tenter clip 21 is bitten into the tenter clip 21 to hold both ends of the film 14 and apply tension to further dry the film.

The first roll 15 and the fourth roll 18 are disposed below the film 14 and support the film 14. The second roll 16 and the third roll 17 are arranged above the film 14 and come into contact with the band peeling surface of the film 14. Each of these rolls is rotated by a driving device (not shown) to have the same peripheral speed as the film feeding speed. As described above, by bringing the rolls 15 to 18 into contact with each other from different surfaces, it is possible to obtain an effect of suppressing curling that occurs at both side end portions of the film 14 being conveyed.

An air supply device 28 is arranged above the film 14 in the vicinity of the peeling position of the film 14. The air supply device 28 is provided with a slit-shaped air supply port 28a that is long in the width direction of the film 14, and blows dry air 29 sent from a blower (not shown) from the air supply port 28a to the band peeling surface of the film 14. Send to. In addition,
The air supply port 28a is not limited to the one shown in the drawing, and may be any air supply that supplies a necessary and sufficient amount to the entire width of the film 14. Further, it is more preferable that the dry air 29 is sent to both sides of the film 14, and in this case, a similar air supply device 28 is arranged below the film 14. Such air supply needs to be performed within 10 seconds after peeling from the band 12, and even if it is performed thereafter, the effect is small.

FIG. 3 shows another embodiment in which the position of the transport roll is changed, and the same components as those shown in FIG. 2 are designated by the same reference numerals. In FIG. 3, instead of the second roll 16 in FIG.
The third roll 17 is brought into contact with the band peeling surface of the film 14 only. Although illustration is omitted, each roll may be arranged below the film 14 so that each roll supports only the surface not in contact with the band 12. Further, the number of rolls may be changed appropriately.

In the present invention, the solvent content (unit: weight%) of the film at the time of peeling is X grams as the weight of the film sample, and Y grams as the film sample after drying for 1 hour in a 115 ° C. high temperature air bath. When the weight of
The calculation formula (X−Y) / X × 100 is used, but the present invention is not limited to this.

[0021]

EXAMPLES The present invention will be specifically described below with reference to examples, but the contents of the present invention are not limited thereto.

Example 1 Cellulose triacetate (substitution degree 2.8) 89.3% by weight triphenyl phosphate 7.1% by weight Biphenidiphenyl phosphate 3.6% by weight With respect to 100 parts by weight of solid content, silica. A fine particle dispersion was appropriately added, and further, a mixed solvent of 92% by weight of dichloromethane and 8% by weight of methanol was appropriately added, and dissolved by stirring to prepare a dope. The solid content concentration of the dope was 19.2%.
This dope was formed into a film by a solution film forming process as shown in FIG. The dope 10 was cast from a casting die 11 onto a band 12 as an endless support, dried on the band 12 until the dope 10 had self-supporting property, and peeled off as a film 14. The solvent content at the time of peeling was 38% by weight.
After being stripped from the band 12, the film 14 is brought into contact with the second roll 16 and the third roll 17 on the release surface of the band 12 of the film, and the first roll 15 and the fourth roll 1
2 is conveyed by the roll shown in FIG. 2 which is arranged and supported on the lower side of the film.
Dry air 29 at ℃ 1 per minute for 1.5m wide film
It was fed by 0 cubic meter, and introduced into the tenter drying chamber 19 5 seconds after the peeling from the band. The solvent gas concentration of the dry air 29 was 0% by volume. In the carrying step before the introduction of the tenter drying chamber 19, the curl of the film edge was small and it was very good. After tenter drying, roll drying chamber 23, 24
It was further dried in and wound by the winding device 26. The winding film had a film thickness of 79 μm and a width of 1.33 m, and was visually inspected for a length of 50 m.
No deformation was observed.

Example 2 Cellulose triacetate (substitution degree 2.8) 89.3% by weight triphenyl phosphate 7.1% by weight Biphenyldiphenylphosphate 3.6% by weight With respect to 100 parts by weight of a solid content, silica is used. A fine particle dispersion was appropriately added, and a mixed solvent of 87% by weight of dichloromethane and 13% by weight of methanol was appropriately added and dissolved by stirring to prepare a dope. This dope 10 is cast into a band 1 by a casting die 11.
Band 1 cast onto 2 and until the dope is self-supporting
2 and dried as a film 14. The solvent content at the time of peeling was 40% by weight. After peeling off the film 14 from the band 12, the first roll 15, the second roll 40 and the fourth roll 18 are arranged below the film to support the film 14 as shown in FIG.
7 is conveyed while being brought into contact with a roll arranged so as to be in contact with the peeling surface of the band 12, and dried, and a dry wind 29 of 100 ° C. is applied from above to the film 14 having a width of 1.5 m on the second roll 40. 12 cubic meters per minute, band 12
It was introduced into the tenter drying chamber 19 3 seconds after the peeling. The solvent gas concentration of the dry air 29 was 17% by volume.
Film 14 in the transport process before introducing the tenter drying chamber 19
Was very good with less curl at the edges. After the tenter drying, it was further dried in the roll drying chambers 23 and 24, and wound by the winding device 26. The winding film had a film thickness of 79 μm and a width of 1.33 m, and when visually inspecting a length of 50 m, no deformation of the film was observed.

[Comparative Example 1] The same operation as in Example 1 was carried out except that the drying air 29 was not sent from above the carrying roll 16. The film thickness of the winding film is 79 μm, and the width is 1.
When the length was 33 m and the length of 3 m was visually inspected, deformation of the film was confirmed at four places.

[0025]

As described above, in the solution casting method of the present invention, the air supply step before the tenter drying is introduced within 10 seconds after peeling the film from the endless support. Therefore, after peeling from the belt, it was possible to prevent the volatile solvent from becoming a high concentration in the vicinity of the film. As a result, it becomes possible to prevent the surface defects of the film caused by the volatile solvent condensing and adhering to the film surface, thereby increasing the production yield of the film. Furthermore, after peeling from the belt support 10
When the roll is arranged so as to come into contact with the support contact surface of the film within seconds, the effect can be remarkably exhibited. Further, this effect was observed even when the solvent content of the film was as low as 60% by weight or less.

[Brief description of drawings]

FIG. 1 is a schematic view showing a solution film-forming step in which a solution film-forming method of the present invention is carried out.

FIG. 2 is a schematic diagram of a film transporting process from the band peeling unit to the tenter drying chamber introducing unit in which the present invention is carried out.

FIG. 3 is a schematic diagram of a film transporting process from the band peeling unit to the tenter drying chamber introducing unit, which is another embodiment of the present invention.

[Explanation of symbols]

10 dope 12 bands 14 films 15-18 rolls 19 tenter drying room 28 Air supply device 28a Air supply port 29 Air supply

Claims (5)

[Claims] 1. A polymer is dissolved in a solvent to prepare a dope, which is cast on an endless support and continuously peeled off.
In the method for producing a film by drying, the solvent content of the film peeled from the endless support is 60% by weight.
After peeling the film from the endless support at the following times:
A solution casting method comprising supplying air to at least the film surface side which is in contact with the endless support within 0 seconds. 2. A method of producing a film by dissolving a polymer in a solvent to prepare a dope, casting the dope on an endless support, peeling the dope, and then drying the film to peel the film from the endless support. Within 10 seconds, a roll is brought into contact with the film surface in contact with the endless support, and air is supplied to at least the film surface side in contact with the endless support. 3. The manufacturing method according to claim 1, wherein the solvent gas concentration of the supply air is 30% by volume or less. 4. The production method according to claim 1, wherein the polymer is cellulose acylate. 5. The method according to claim 4, wherein the cellulose acylate is cellulose acetate having a substitution degree of 2.6 or more.