JP3814368B2 - Cast film manufacturing method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a cast film by casting a dope obtained by dissolving a polymer material in a solvent from a die lip onto a support. More specifically, the present invention relates to a method for producing a cast film that suppresses the occurrence of streaky spots on the film surface and is excellent in surface smoothness and thickness uniformity.
[0002]
[Prior art]
In the solution casting method, a solution in which a polymer material is dissolved in a solvent (hereinafter referred to as a dope) is completely removed from foreign matters such as dust and bubbles, then extruded from a die, cast onto a support, dried and peeled off. This is a method for obtaining a film. Films produced by this method are used for various optoelectronic applications because they are superior in optical transparency and thickness uniformity and have less foreign matter than films obtained by melt extrusion.
[0003]
Conventionally, in this method, the dope gradually accumulates or adheres to the tip of the lip in the vicinity of the lip tip away from the dope at the start of discharge from the die or during the production of the film during the process of changing the discharge amount. There is a problem that the material is dried to become a gel-like material and fixed, and this causes a streaky defect by contacting the liquid film in the casting direction.
[0004]
As a means for solving these problems, for example, Japanese Patent Laid-Open No. 8-25381 is disclosed. According to this method, a method for producing a cast film is proposed in which a dope having a specific solution viscosity is extruded from a die composed of a lip having a flat edge with a tip parallel to a metal support. . However, even in this method, there remains a problem that the vertical stripes in the casting direction cannot be completely eliminated.
[0005]
[Problems to be solved by the invention]
The object of the present invention is to prevent generation of streaks in the casting direction of a liquid film cast on a support when producing a polymer material film by a solution casting method, and is excellent in surface smoothness and thickness uniformity. Another object is to provide a method for producing a cast film.
[0006]
[Means for Solving the Problems]
That is, the present invention is a method for producing a cast film by removing a solvent after casting a dope obtained by dissolving a polymer material in a solvent on a support from a die lip to form a liquid film.
(A) A lip side surface uses a die lip in which at least one inclined surface is formed at an angle of 20 to 80 ° with respect to the land portion, and a solvent discharge nozzle is installed on at least one of the inclined surfaces.
(B) A cast film manufacturing method characterized in that a solvent is cast from a solvent discharge nozzle while flowing along the inclined surface so that the discharge range covers the entire lip width and flowing to the lip tip.
[0007]
In the present invention, a polymer material such as aromatic polycarbonate is used. The aromatic polycarbonate used in the present invention refers to a polymer obtained by reacting an aromatic dihydroxy compound with a compound capable of forming a carbonic acid bond such as phosgene or diphenyl carbonate.
[0008]
Specific examples of the aromatic dihydroxy compound include the following compounds. That is, bis (hydroxy) such as 1,1-bis (4-hydroxy-t-butylphenyl) propane, 2,2-bis (4-hydroxyphenyl) propane, 2,2-bis (4-hydroxybromophenyl) propane, etc. Aryl) alkanes, 1,1-bis (4-hydroxyphenyl) cyclopentane, bis (hydroxyaryl) cycloalkanes such as 1,1-bis (4-hydroxyphenyl) cyclohexane, 4,4′-dihydroxydiphenyl ether, Dihydroxyaryl ethers such as 4,4-dihydroxy-3,3'-dimethylphenyl ether, dihydroxyaryl sulfides such as 4,4'-dihydroxydiphenyl sulfide and 4,4'-dihydroxy-3,3'-dimethylphenyl sulfide 4,4'-Dihydr Dihydroxymethyl sulfoxides such as xydiphenyl sulfoxide, 4,4'-dihydroxy-3,3'-dimethylphenyl sulfoxide, 4,4'-dihydroxydiphenyl sulfone, 4,4'-dihydroxy-3,3'-dimethyl And dihydroxyaryl sulfones such as phenyl sulfone.
[0009]
Of these, 2,2-bis (4-hydroxyphenyl) propane (bisphenol-A) is particularly preferably used. These aromatic dihydroxy compounds can be used alone or in combination.
[0010]
In general, it is also possible to use a polyester carbonate containing a terephthalic acid and / or isophthalic acid component. By using such a structural unit as a part of the structural component of the polycarbonate composed of bisphenol-A, the properties of the polycarbonate, such as heat resistance and solubility, can be improved. Such a copolymer can also be used in the present invention.
[0011]
The molecular weight of the aromatic polycarbonate is such that the viscosity average molecular weight determined from viscosity measurement at 20 ° C. in a methylene chloride solution having a concentration of 0.5 g / dl is 10,000 to 200,000, preferably 20,000 to 120,000. Ranges are used.
[0012]
As the solvent, methylene chloride, 1,3-dioxolane and the like are used.
[0013]
The dope used in the present invention is prepared by dissolving a polymer material such as an aromatic polycarbonate in a solvent mainly composed of methylene chloride or 1,3-dioxolane. The concentration of the polymer material in the dope is about 5 to 30% by weight.
[0014]
The dope is cast using a die lip to form a liquid film on a support such as a steel belt, a drum, or a support film (generally a biaxially oriented film of polyester). In particular, the method of the present invention is effective when a steel belt is used as the support.
[0015]
For removing the solvent, the cast film is usually dried on a support by a dryer. Drying can be carried out by a known method. Immediately after casting, it is preferable that the liquid film is uniformly dried so as not to be disturbed as much as possible, and after the latter half is solidified, it is preferably dried by blowing hot air.
[0016]
The present invention is characterized in that a specific die lip is used in the solution casting method.
[0017]
Hereinafter, the present invention will be described in detail with reference to the drawings.
1 and 2, 1 is a die lip, 2 is a lip side surface, 3 is a land portion, 4 is a lip tip surface, 5 is a gelled product, 6 is a solvent discharge nozzle, 7 is a solvent flow, 8 is a dope discharge port, 9 is a liquid film and 10 is a support.
[0018]
In FIG. 1, the solvent discharge nozzle 6 is disposed on the inclined surface of the lip side surface 2, and the tip of this nozzle is close to the lip side surface 2. A solvent is fed into the nozzle from a fixed amount supply pump (not shown) whose flow rate can be adjusted, and the solvent discharged from the nozzle first flows down along the inclined surface of the lip side surface 2 as shown by an arrow 7, Go around the tip. At this time, the angle, the edge R, and the like are not particularly limited, but a larger R is more effective because the solution is easier to turn to the tip surface.
[0019]
The solvent that has entered the lip tip surface 4 moves in the direction of the dope discharge port 8 due to the inclination of the tip while being held by the surface tension, reaches the dope gelled material 5 adhering to the vicinity thereof, Swell or dissolve. Eventually, the gelled product 5 leaves the position where it adheres due to the inclination of the tip surface 4 and the effect of the solvent, and is taken away from the die lip together with the cast liquid film 9.
[0020]
The present invention may be carried out continuously during film formation, or may be carried out when a gelled product is generated and a streak defect is generated.
[0021]
The gelled product is removed by releasing the solvent from the solvent discharge nozzle 6. In that case, since the film surface may be disturbed by the solvent, it is preferable to adjust the amount of the solvent released to an appropriate amount after the lip tip surface 4 is cleaned. If the amount of release is excessive, it will hinder processing such as peeling and transporting in the subsequent steps, so that the amount is preferably limited appropriately. The amount varies depending on the viscosity of the dope to be discharged, the viscosity, the thickness of the liquid film, and the like.
[0022]
As for the form of the nozzle, the solvent discharge range must cover the entire lip width, but streaky defects due to gelled products etc. are locally generated, so it is divided into several nozzles. It is preferable to control independently.
[0023]
In FIG. 1, the angle between the lip side surface 2 and the land portion 3 is about 60 °, and the entire die is tilted. The solvent discharge nozzle 6 is attached in the direction of travel of the support 10.
[0024]
On the other hand, in FIG. 2, the die body is not inclined, but the lip side surface 2 forms a two-step inclined portion. In this case, it is preferable that the tip of the solvent discharge nozzle 6 is attached on an extension line of the first step inclined surface. The nozzle is shown only on one side, but in the case of FIG. 2, it can be installed on either or both of the lip side surfaces 2.
[0025]
【The invention's effect】
According to the present invention, even when a dope gel-like substance that causes streaks adheres to the tip of the die lip, it can be removed by a very short process after changing the conditions during the film forming operation after the start of discharge. It is possible to efficiently produce a cast film that is free of streaks and excellent in thickness uniformity.
[Brief description of the drawings]
FIG. 1 illustrates an example of the present invention.
FIG. 2 illustrates another example of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Die lip 2 Lip side surface 3 Land part 4 Lip front end surface 5 Gelled product 6 Solvent discharge nozzle 7 Flow of solvent 8 Dope discharge port 9 Liquid film 10 Support body

Claims (1)

In a method for producing a cast film by removing a solvent after casting a dope obtained by dissolving a polymer material in a solvent on a support from a die lip to form a liquid film,
(A) A lip side surface uses a die lip in which at least one inclined surface is formed at an angle of 20 to 80 ° with respect to the land portion, and a solvent discharge nozzle is installed on at least one of the inclined surfaces.
(B) A method for producing a cast film, wherein the solvent is cast while flowing along the inclined surface so that the discharge range covers the entire lip width from the solvent discharge nozzle to the lip tip.

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