JP2002001745A - Manufacturing method for cast film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a stripe defect in the spreading direction which is generated on a film flow-cast on a metal supporting body from occurring when a plastic polymer film is manufactured by a solution casting method, and at the same time, manufacture the film which is excellent in surface smoothness and thickness uniformity at a favorable productivity. SOLUTION: On a flow-casting die 1, a manifold 2 and a slit 3 are formed. The distal end of the slit 3 is formed into a die lip 4. Under the flow-casting die 1, the endless ring-shape metal supporting body 5 is provided in a manner to be able to run. The die lip 4 is treated in such a manner that the surface roughness (Ra value) may become 0.1 μm or lower. The lip clearance d of the die lip 4 is formed in a manner to become 0.9 to 1.3 mm. A dope 6 is fed to the die 1, and is spread from the die lip 4 to the metal supporting body 5, and thus, the film 7 is manufactured. The dope 6 is adjusted in such a manner that the viscosity at 30 deg.C may be 450 to 650 poise.

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 film by a solution casting method, and more particularly to a method for producing a film cast on a metal support, which suppresses the occurrence of streak defects and has a smooth surface. And a method for producing a cast film having good thickness uniformity.

[0002]

2. Description of the Related Art In a solution casting method, a polymer solution obtained by dissolving a plastic polymer in a solvent (hereinafter referred to as a dope) is extruded from a casting die and cast on a metal support.
This is a method of obtaining a film by drying and peeling. Films produced by this solution casting method are more excellent in optical isotropy and thickness uniformity than films produced by the melt extrusion method,
Further, since there are few foreign substances, they are widely used in optoelectronic applications such as polarizing film protective films, retardation films, and transparent conductive films.

However, in such a solution casting method, when a dope is cast from a casting die to form a film on a metal support, the burrs are generated at a die lip portion of the casting die where the dope is discharged. However, there is a problem that streaks occur in the casting direction of the film due to the burrs.

Therefore, hitherto, it has been attempted to suppress streak defects by changing the shape of the die, the viscosity of the dope, the moving speed of the metal support, and the like. For example, JP-A-8-25381 discloses that the solution viscosity is 5 to 200 poise.
Is extruded from a die composed of a lip having a flat edge and a tip parallel to the metal support and cast, and the moving speed of the metal support is set to 0.
A method for producing a cast film that suppresses the occurrence of burrs at a rate of 5 to 10 m / min has been proposed.

[0005]

However, even if the film is cast by changing the shape of the die, the viscosity of the dope, the moving speed of the metal support, etc., the degree of the streak defect can be reduced in any case. It could not be erased. Also,
The method for producing a cast film proposed in Japanese Patent Application Laid-Open No. H8-25381 is disclosed in Japanese Patent Application Laid-Open No. H8-25381.
Since the speed was set to 0 m / min, the productivity was low, and streak defects could not be completely eliminated.

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems and, when producing a plastic polymer film by a solution casting method, prevents a stripe defect in a casting direction generated in a film cast on a metal support. It is an object of the present invention to provide a method for producing a cast film capable of producing a film having excellent surface smoothness and thickness uniformity with high productivity.

[0007]

The inventor of the present invention has studied diligently the cause of the above-described die burrs, and found that defects such as minute scratches and dents that occur during die fabrication or maintenance. It was found that scratches and the like generated during grinding by grinding stone were the cause. Further, the present inventors have conducted further intensive studies and have found that the generation of the burrs can be suppressed by reducing the surface roughness of the die lip to a predetermined value or less, thereby completing the present invention.

That is, the method for producing a cast film according to the present invention is a method for producing a film by casting a polymer solution obtained by dissolving a plastic polymer in a solvent from a casting die onto a metal support. The surface roughness (Ra value) of the part where the polymer solution comes into contact with the liquid is 0.1 μm or less.

In the method for producing a cast film of the present invention, the die lip has a surface roughness (Ra value) of 0.1 μm.
By doing the following, the occurrence of the burrs is suppressed, and as a result, the streak defect is improved to the extent that it is difficult to confirm it.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION In the method for producing a cast film of the present invention, the surface roughness (Ra value) of the portion of the die lip where the polymer solution comes into contact is 0.1 μm or less, preferably 0.08 μm or less. . When the surface roughness (Ra value) exceeds 0.1 μm, there is a possibility that burrs may occur. The surface roughness (Ra value) is measured by a known method using a stylus type surface roughness meter or the like.

The viscosity of the polymer solution is not particularly limited, but the viscosity at 30 ° C. is preferably from 450 to 650 poise, more preferably from 450 to 600 poise. By setting the viscosity in the above-described range, the streak defect can be further improved. The viscosity of the polymer solution is 4
If it is less than 50 poise, the discharge pressure cannot be secured when the discharge of the polymer solution from the die lip is started, and the polymer solution is not discharged simultaneously over the entire width of the die. For this reason,
The lower die lip tip will be soiled. Also, it becomes difficult to adjust the thickness in the width direction. On the other hand, if it exceeds 650 poise, the discharge pressure of the polymer solution becomes too large, and a shark skin-like surface defect is generated due to the shear force of the die lip tip and the discharged polymer solution.

The lip clearance of the die lip of the casting die is preferably 0.9 to 1.3 mm, and 1.0 to 1.2 mm.
5 mm is more preferable. By setting the lip clearance in the above-described range, the streak defect can be further improved. If the lip clearance is less than 0.9 mm, a streak-like defect may occur even if the tip of the lip is slowly deformed. Further, it is difficult to change the lip clearance in the width direction to adjust the thickness of the film in the width direction to make it uniform. If it exceeds 1.3 mm, the discharge pressure cannot be secured when the discharge of the polymer solution from the die lip is started, and the polymer solution is not discharged simultaneously over the entire width of the die. For this reason, the tip of the lower die lip is soiled. Also, it becomes difficult to adjust the thickness in the width direction.

It is preferable to combine the viscosity of the polymer solution with the lip clearance, that is, the viscosity of the plastic polymer solution at 30 ° C. is 450 to 650 poise, and the lip clearance of the casting die lip is 0.9 to 0.9. By setting the thickness to 1.3 mm, the streak defect can be further improved.

The finished thickness of the film obtained by casting is 35 to
65 μm is preferred, and 38 to 50 μm is more preferred.
If the completed thickness of the film is less than 35 μm, the polymer solution is not flattened (leveled) on the metal support, and streak-like defects become apparent. Also, 65μ
If it exceeds m, the drying load increases and the casting speed needs to be reduced, so that the productivity is reduced.

The plastic polymer used in the present invention is not particularly limited, but the method for producing a cast film according to the present invention is preferably used in producing a cellulose ester film. Typical examples of the cellulose ester include lower fatty acid esters of cellulose, for example, cellulose acetate, cellulose acetate butyrate, and cellulose acetate propionate. A lower fatty acid means a fatty acid having 6 or less carbon atoms. Among these, cellulose acetate is particularly preferred, and cellulose acetate includes cellulose triacetate (TA).
C) and cellulose diacetate (DAC).

A method for manufacturing a cast film according to the present invention will be described with reference to the drawings of a cast film manufacturing apparatus.

FIG. 1 is a partial schematic view of a cast film manufacturing apparatus. In FIG. 1, reference numeral 1 denotes a casting die, in which a manifold 2 and a slit 3 are formed, and a tip of the slit 3 is a die lip 4. An endless annular metal support 5 is provided below the casting die 1 so as to run freely. The die lip 4 is processed so that the surface roughness (Ra value) is 0.1 μm or less, and is formed such that the lip clearance d of the die lip 4 is 0.9 to 1.3 mm. ing.

In the casting apparatus as described above, the dope 6 is supplied to the casting die 1 and cast from the die lip 4 to the metal support 5 to form the film 7. At this time, the dope 6 has a viscosity of 450 to 650 at 30 ° C.
It has been adjusted to poise.

[0019]

EXAMPLES The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.

Example 1 100 parts by weight of cellulose triacetate 7 parts by weight of triphenyl phosphate 5 parts by weight of biphenyldiphenyl phosphate A solid having the above composition was dissolved in a solvent consisting of 92 parts by weight of methylene chloride and 8 parts by weight of methanol. Doped. The solid content concentration of the dope was adjusted to 17.5% by weight. Using such a dope, a film was formed by a cast film manufacturing apparatus shown in FIG.

After the dope is allowed to stand and deaerated, it is sent to the casting die 1 via a filter (not shown) by a liquid sending pump (not shown), and the metal support 5 running at 30 m / min. Was cast. The dope cast from the casting die 1 onto the metal support 5 is dried to a residual solvent amount of 22% by weight or less, and then stripped off from the metal support 5 to have a thickness of 40 to 4 mm.
A 5 μm film was obtained. The die lip clearance is
1.0 mm.

No streak defects were observed in the film on the metal support. In addition, when the thickness distribution of the obtained film in the casting direction, the thickness distribution in the direction perpendicular to the casting direction, and the appearance of the film were examined, no unevenness of the thickness was observed and the surface smoothness was good.

Example 2 The solid concentration in the dope was 19
Using the same cast film manufacturing apparatus and dope as in Example 1 except that the weight% was adjusted, casting was performed under the same conditions to form a film.

Almost no streak defects were observed in the film on the metal support. In addition, when the thickness distribution of the obtained film in the casting direction, the thickness distribution in the direction perpendicular to the casting direction, and the appearance of the film were examined, no unevenness of the thickness was observed and the surface smoothness was good.

Comparative Example 1 A film was cast by using the same casting film manufacturing apparatus and dope as in Example 1 above under the same conditions except that the die lip clearance was 1.6 mm.

Streak defects occurred in the casting direction of the film on the metal support. Also, the thickness distribution of the obtained film in the direction perpendicular to the casting direction was very uneven, and satisfactory quality was not obtained.

[Comparative Example 2] Using the same casting film manufacturing apparatus and dope as in Example 2 except that the roughness (Ra) of the liquid contact surface of the die lip was set to 0.5, the film was cast under the same conditions. The membrane was made.

Streak defects occurred in the casting direction of the film on the metal support. Also, the thickness distribution of the obtained film in the direction perpendicular to the casting direction was very uneven, and satisfactory quality was not obtained.

Comparative Example 3 A casting was performed under the same conditions using the same casting film manufacturing apparatus and dope as in Example 1 except that the die lip clearance was set to 0.7 mm, and a film was formed.

Streak defects occurred in the casting direction of the film on the metal support. Also, the thickness distribution of the obtained film in the direction perpendicular to the casting direction was very uneven, and satisfactory quality was not obtained.

Table 1 shows the results of Examples 1 and 2 and Comparative Examples 1 to 3.

[0032]

[Table 1]

The evaluation of the surface condition of the cast line is as follows. ：: Good ○: Within practical limit ×: Not practical

The surface roughness of the liquid contact surface of the die lip is determined by measuring the amount of deformation measured with a stylus-type surface roughness profile measuring device: Surfcom 550A (manufactured by Tokyo Seimitsu Co., Ltd.).
The yzing System SAS-2001 [Meishinki Machine Co., Ltd.] was used to calculate the Ra value.

[0035]

According to the present invention, a cast film having excellent surface smoothness and thickness uniformity can be produced with high productivity without generating streak defects in the casting direction from the die tip.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a casting die portion of a solution casting film forming apparatus for performing a method for producing a cast film of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Casting die 2 ... Manifold 3 ... Slit 4 ... Die lip 5 ... Metal support 6 ... Dope 7 ... Film d ... Lip clearance

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (Reference) C08L 1:10 C08L 1:10 F term (Reference) 2H049 BA06 BB33 BB49 BC09 BC22 4F071 AA09 AA88 AH12 AH19 BB02 BC01 BC12 BC16 4F205 AA00C AA01 AC05 AE09 AG01 AJ02 AM32 AR12 AR13 GA07 GB02 GC07 GE03 GF01 GF24 GN24

Claims (3)

[Claims] 1. A method for producing a film by casting a polymer solution obtained by dissolving a plastic polymer in a solvent from a casting die onto a metal support, wherein the surface of the die lip of the casting die is in contact with the polymer solution. A method for producing a cast film, wherein a thickness (Ra value) is 0.1 μm or less. 2. The method according to claim 1, wherein the viscosity of the polymer solution at 30 ° C. is 450 to 650 poise, and the lip clearance of the die lip is 0.9 to 1.3 mm. 3. The method for producing a cast film according to claim 1, wherein the plastic polymer is cellulose acetate, and the finished film thickness obtained by casting is 35 to 65 μm.