JPH09201869A - Method and apparatus for manufacturing thermoplastic polymer sheet - Google Patents

Abstract

(57) Abstract: A thermoplastic polymer sheet having excellent thickness uniformity is obtained even when a polymer having a poor electrostatic application property is formed into a sheet. SOLUTION: A molten thermoplastic polymer sheet is discharged from a die in a sheet shape onto a moving cooling body, and an electrostatic charge is applied by a wire-shaped discharge electrode to bring the discharged sheet into close contact with the moving cooling body. In the method for producing a thermoplastic polymer sheet, when the melting specific resistance R at 280 ° C. of the thermoplastic polymer sheet is R ≧ 5 × 10 ⁸ (Ω · cm), the discharge electrode has a wire diameter φ. (M
m) and a wire tension F (N) of 2500φ ² ≧ F ≧ 1000φ ² (N) 1.0 ≧ φ ≧ 0.15 (mm) are used. , And equipment.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method and an apparatus for producing a thermoplastic polymer sheet. More specifically, the present invention relates to a method and an apparatus capable of producing a thermoplastic polymer sheet having excellent thickness uniformity even when a raw material having a poor electrostatic application property is used.

[0002]

2. Description of the Related Art In the production of thermoplastic polymer sheets,
The reason for deteriorating the thickness uniformity is that the sheet-like molten polymer is grounded on the moving cooling body and, when it is cooled and solidified, an entrained airflow is caught between the sheet and the cooling body, so It is thought that there is a change in the grounding point of the sheet and that the sheet vibrates between the die and the cooling body.

In the prior art, when an electrostatic charge is applied by a discharge electrode for casting, the discharge electrode is fixed at an appropriate position and the electrostatic charge is effectively applied to the sheet-like melt to form a sheet. It is intended to improve the thickness uniformity by suppressing entrainment of the accompanying air current generated between the moving cooling bodies, fluctuation of the grounding point of the sheet on the cooling body, and vibration of the sheet between the die and the cooling body (for example, Japanese Patent Publication 37-6142).

[0004]

However, in such a conventional technique, when a polymer having a high melt specific resistance value, which indicates the conductivity of the molten polymer sheet at the time of melting, that is, the adhesion between the sheet and the moving cooling body, is used. In addition, since the adhesion between the sheet and the moving cooling body is poor, the uneven thickness tends to be poor. In particular, when the wire diameter is made thin in order to increase the strength of the electric field generated from the discharge electrode, the breaking tension of the wire will be low, so the wire tension must be set low and the string vibration of the wire will occur. However, there is a problem in that the unevenness in thickness in the longitudinal direction of the sheet cannot be improved especially.

Therefore, an object of the present invention is to make it possible to obtain a thermoplastic polymer sheet having excellent thickness uniformity even when such a polymer having a poor electrostatic application property is formed into a sheet. It is in.

[0006]

In order to solve the above-mentioned problems, a method for producing a thermoplastic polymer sheet according to the present invention is a method in which a molten thermoplastic polymer sheet is discharged in a sheet form from a die onto a cooling body. Then, in the method for producing a thermoplastic polymer sheet in which an electrostatic charge is applied by a wire-shaped discharge electrode to bring a discharged sheet into close contact with a moving cooling body, a specific melting point value of the thermoplastic polymer sheet at 280 ° C. R
Is R ≧ 5 × 10 ⁸ (Ω · cm), the wire diameter φ (m
m), and a wire tension F (N) of 2500φ ² ≧ F ≧ 1000φ ² (N) 1.0 ≧ φ ≧ 0.15 (mm) is used.

Further, the apparatus for producing a thermoplastic polymer sheet according to the present invention discharges the molten thermoplastic polymer sheet in a sheet form from a die onto a cooling body, and discharges electrostatic charges by a wire-shaped discharge electrode. In a thermoplastic polymer sheet manufacturing apparatus for applying and adhering a discharged sheet to a moving cooling body, a melting specific resistance value R of the thermoplastic polymer sheet at 280 ° C. is R ≧ 5 × 10 ⁸ (Ω · cm), the wire used for the discharge electrode has a wire diameter φ (mm) and a wire tension F (N) of 2500φ ² ≧ F ≧ 1000φ ² (N) 1.0 ≧ φ ≧ 0.15 (mm ) Is satisfied.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, a thermoplastic polymer in a molten state is extruded from a die into a sheet shape and extruded onto a moving cooling body, and an electrostatic charge is applied by a discharge electrode made of a wire to bring the molten polymer into close contact. In a method for producing a thermoplastic polymer sheet which is solidified on a moving cooling body, a melting specific resistance value R showing an electrostatic application characteristic of the sheet in a molten state is 5 × 10 ^8.
Ω · cm or higher, and when the adhesion between the sheet and the moving cooling body is poor, the wire diameter φ is 0.15 mm or more and 1.0
The wire tension F is set to 1000φ ² (N) or more to minimize the string vibration of the wire while maintaining the electric field strength to be not more than mm, and the breaking tension is not reached 2500φ ²
(N) It is characterized in that the thickness uniformity of the sheet can be improved by setting the conditions below so that the wire will not be cut.

For example, as shown in FIG. 1, the molten thermoplastic polymer sheet 2 discharged from the die 1 is a moving cooling body 3 (a cooling drum in the illustrated example, but an endless belt for cooling or the like is also possible. Is discharged onto the moving cooling body 3 and is brought into close contact with the surface of the moving cooling body 3 to be cooled and solidified on the moving cooling body 3 to form an unstretched sheet 4. When discharged onto the moving cooling body 3, an electrostatic charge is applied to the thermoplastic polymer sheet 2 from the wire discharge electrode 5, thereby improving the adhesion on the moving cooling body 3 and stabilizing the landing point. Thus, the string vibration of the seat 2 between the base 1 and the moving cooling body 3 is suppressed.

In the present invention, the thermoplastic resin used generally includes all resins which can be formed into a film. As these resins, polyester represented by polyethylene terephthalate, polyethylene-2,6-naphthalate, etc., polyolefin, polyamide, polyphenylene sulfide, polyvinyl chloride, polyvinylidene chloride and the like can be used.

In the present invention, the melting resistance R at 280 ° C. is R ≧ 5 × 10 ⁸ (Ω · cm), which is relatively poor in electrostatic applicability. The melting specific resistance of such a polymer depends not only on the characteristics of the polymer itself but also on the conductive substance added to the polymer.

The diameter φ and the tension F of the wire used for the discharge electrode must satisfy 2500φ ² ≧ F ≧ 1000φ ² (N) 1.0 ≧ φ ≧ 0.15 (mm). As wire tension conditions,
More preferably, it is 2000φ ² ≧ F ≧ 1250φ ² (N). More preferably, the wire diameter is 0.3 ≧ φ ≧ 0.15 (mm). In the above range, wire breakage is likely to occur near the upper limit of the wire tension, and wire vibration is likely to occur near the lower limit, but by setting it within the above range, both wire breakage and wire vibration are suppressed.

By setting the wire diameter φ within the above range, a good electric field strength can be obtained, a desired electrostatic charge can be imparted to the sheet, and a good electrostatic applicability can be obtained.

In order to achieve such wire conditions, the wire material is preferably a metal having a high breaking tension such as rhenium or tungsten.

As an electrostatic application device for applying a high voltage between a discharge electrode made of a wire and a moving cooling body which is grounded, the molten polymer sheet is brought into close contact with the moving cooling body by electrostatic action. A conventionally known one can be applied.

The unstretched sheet cooled and molded on the moving cooling body may be used as it is, or may be uniaxially stretched or biaxially stretched at a predetermined ratio to obtain a film product.

[0017]

【Example】

Example 1 A resin composed of a linear polyester having an intrinsic viscosity of 0.7 and a melting specific resistance of 10 ⁹ Ω · cm was melted by an extruder at a set temperature of 285 ° C., and coarse foreign matters in the polymer were filtered by a filter having a filtration accuracy of 20 μm. After removing, lip gap 3mm
It was discharged from the die of (1) and brought into close contact with a moving cooling body (casting drum) having a surface temperature of 25 ° C. to form a sheet having a thickness of 300 μm. When the molten polymer was brought into close contact with the drum, the wire diameter of the discharge electrode to which a direct current voltage of 10 kV was applied was set to 0.15 mm, and the wire tension was set to 25 N. At this time, the difference between the maximum and minimum thickness unevenness in the longitudinal direction of the intermediate product was as good as 4 μm.

Example 2 The discharge electrode has a wire diameter of 0.2 mm and a wire tension of 7 mm.
The same procedure was performed as in Example 1 except that the setting was 5N. At this time, the difference between the maximum and minimum thickness unevenness in the longitudinal direction of the intermediate product is
It was 2.5 μm, which is an improvement over the case of Example 1.

Comparative Example 1 The discharge electrode has a wire diameter of 0.1 mm and a wire tension of 1
The same procedure was performed as in Example 1 except that the setting was 0N. At this time, the maximum and minimum difference in the thickness unevenness in the longitudinal direction of the intermediate product is
8 μm, which is worse than in Examples 1 and 2.

Comparative Example 2 The discharge electrode has a wire diameter of 0.2 mm and a wire tension of 3
The same procedure was performed as in Example 1 except that the setting was 0N. At this time, the maximum and minimum difference in the thickness unevenness in the longitudinal direction of the intermediate product is
It was 5 μm, which was worse than in Examples 1 and 2.

Comparative Example 3 The discharge electrode has a wire diameter of 0.2 mm and a wire tension of 1
The same procedure was performed as in Example 1 except that the setting was 10N. At this time, the difference between the maximum and minimum thickness unevenness in the longitudinal direction of the intermediate product at the beginning of film formation was as good as 2 μm, but deterioration of the wire progressed over time and wire breakage occurred.

Comparative Example 4 A resin having an intrinsic viscosity of 0.65 and a melting specific resistance of 10 ⁸ Ω · cm and having a good electrostatic application property was used, and the wire diameter of the discharge electrode was set to 0.
1 mm, wire tension set to 10 N, and 0.
Films were formed in the same manner as in Example 1 with respect to two types, which were set to 75 N at 2 mm. As a result, the difference between the maximum and minimum thickness unevenness in the longitudinal direction of the intermediate product was as good as 2 μm, while the latter was 4 μm. Low melting specific resistance,
It has been found that when a resin having a good electrostatic application property is used, it is greatly affected by the decrease in electric field strength due to the thin wire diameter.

[0023]

As described above, a resin sheet having a high melting specific resistance and poor electrostatic applicability is discharged onto a moving cooling body,
When carrying out a manufacturing method of applying electrostatic charge to the sheet by a wire-shaped discharge electrode and causing the sheet to adhere and solidify, by setting the wire diameter of the present invention in the range of the wire tension,
It is possible to suppress wire string vibration, stabilize the landing point of the sheet on the moving cooling body, obtain good electrostatic chargeability, and improve the thickness unevenness of the intermediate product in the longitudinal direction.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an apparatus for producing a thermoplastic polymer sheet according to an embodiment of the present invention.

[Explanation of symbols]

 1 Die 2 Melt Sheet 3 Moving Coolant 4 Forming Sheet 5 Discharge Electrode

Claims (2)

[Claims] 1. A thermoplastic polymer sheet in a molten state is discharged from a mouthpiece in a sheet shape onto a moving cooling body, and electrostatic charges are applied by a wire-shaped discharge electrode to bring the discharged sheet into close contact with the moving cooling body. In the method for producing a thermoplastic polymer sheet, the thermoplastic polymer sheet has a wire diameter as the discharge electrode when the melting specific resistance R at 280 ° C. is R ≧ 5 × 10 ⁸ (Ω · cm). φ (m
m) and a wire tension F (N) of 2500φ ² ≧ F ≧ 1000φ ² (N) 1.0 ≧ φ ≧ 0.15 (mm) are used. . 2. A thermoplastic polymer sheet in a molten state is discharged from a die in a sheet shape onto a moving cooling body, and an electrostatic charge is applied by a wire-shaped discharge electrode to bring the discharged sheet into close contact with the moving cooling body. In the apparatus for producing a thermoplastic polymer sheet, the wire used for the discharge electrode has a melting specific resistance value R of ≧ 5 × 10 ⁸ (Ω · cm) at 280 ° C. in the thermoplastic polymer sheet. A wire diameter φ (mm) and a wire tension F (N) of 2500φ ² ≧ F ≧ 1000φ ² (N) 1.0 ≧ φ ≧ 0.15 (mm) Manufacturing equipment.