JP2000071315A - Production of polyester sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable high speed casting of a thin film for a condenser having electric insulating properties as important characteristics by stably and strongly holding electrostatic adhesion action at both ends of a sheet in a sheet casting method applying electrostatic charge to both ends of the sheet and closely bringing the other central part of the sheet into contact with a cooling roll by air pressure to solidify the same. SOLUTION: A polyester sheet is produced by extruding molten polyester into a sheet form from an orifice-shaped mouthpiece and applying electrostatic charge to both side ends of the formed sheet-like article and closely bringing the other central part of the sheet-like article into contact with a cooling roll by air pressure to solidify the same. In this case, the AC vol. resistivity of the polymer of both side end corresponding parts to which electrostatic charge is applied in the sheet-like article is 1×106-1×108 Ω.cm and that of the polymer of the other central part is 1×108-5×109 Ω.cm.

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 polyester sheet, and more particularly, to extruding a molten polyester into a sheet and cooling it by bringing it into close contact with a cooling roll by using both a gas pressing method and an electrostatic adhesion method. And a method for producing a thin sheet of polyester excellent in electrical insulation at a high speed.

[0002]

2. Description of the Related Art A method of casting a polyester sheet is a method in which an electrostatic charge is applied to the surface of a molten polymer sheet and the molten polymer sheet is brought into close contact with a cooling roll and solidified by the Coulomb force. Is generally adopted.

[0003] This electrostatic adhesion method is excellent in uniformity of thickness and can produce a sheet having few surface defects. However, when the casting speed is increased, a defective adhesion characteristic is generated. It is difficult to increase the charge density per area, and it is difficult to increase productivity.

In order to solve this problem, there have been proposed a method of increasing the discharge capability of the discharge electrode, a method of increasing the electric conductivity of the molten polymer to increase the density of electrostatic charges attached thereto, and the like. The method has a poor effect because the sheet is liable to cause electrical breakdown, and the method has a problem that the obtained film has a poor electrical insulation property and is not suitable for, for example, a film for a film capacitor. Therefore, as a solution to this, for example, Japanese Patent No. 2
No. 701540 is a composite film composed of a main layer and a sub-layer,
A method has been proposed in which the casting speed is increased by making the sublayer thinner than the main layer a polymer having high electric conductivity, but there is a problem that a portion having low electric insulation exists in the film.

As another casting method, British Patent No. 1310604 and JP-B-53-35587 are disclosed.
The sheet-like material extruded from the mouthpiece is brought into close contact with the cooling roll surface by pressing gas, and neck-in of the sheet-like material (a phenomenon in which the sheet width is reduced while the sheet-like material is taken up by the cooling roll) is caused by the sheet-like material. A method has been proposed in which an electrostatic charge is applied to both side edges to fix both sides of the sheet in close contact with the surface of the chill roll. The tightness of fixing does not reach the required level, the width narrows without being able to withstand the shrinkage stress of the neck-in, the seat width fluctuates significantly,
This causes troubles such as cutting in a post-process such as stretching performed after casting. Therefore, even in this method, it is difficult to cast a thin sheet at a high speed with a polymer having low electric conductivity at the time of melting.

[0006]

The inventors of the present invention have studied to solve such a problem. As a result, it has been found that the polymer at both ends of the sheet, which exerts the electrostatic adhesion force in the gas pressing method, has high electric conductivity. The inventors have found that such a problem can be overcome at once by maintaining the state, and arrived at the present invention. Generally, both side edges of the sheet are inferior in thickness uniformity and are cut off after the production of the sheet or after the production of the film and are not commercialized.

[0007]

That is, the present invention provides a solution
Press the molten polyester from the orifice-shaped base into a sheet
And apply static charge to both sides of the sheet,
The central part of the roller is tightly adhered to the cooling roll by gas pressure.
The method for producing a sheet according to
The AC volume resistance of the polymer corresponding to the both ends to which an electrostatic charge is added
Resistance rate 1 × 10⁶~ 1 × 10⁸Ω · cm and the other
The AC volume resistivity of the polymer at the center is 1 × 10⁸~ 5x
10⁹Ω · cm
A preferred embodiment of the present invention.
By increasing the temperature of the polymer corresponding to the side edge,
The AC volume resistivity at both ends is 1 × 10⁶~ 1 × 10⁸Ω
cm And the polymer corresponding to both ends of the film
AC volume resistivity is 1 × 10⁶~ 1 × 10⁸Ω · cm No po
The method includes substitution with a limer.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, the polyester is an aromatic polyester such as polyethylene terephthalate, polyethylene-2,6-naphthalate or the like, or an aromatic copolymer polyester such as ethylene terephthalate or ethylene-2,6-naphthalate as a main component. Polyester.

The orifice-shaped base is, for example, a T-die,
This is a base with a straight opening, such as a fish tail die.

In the present invention, the thickness of the sheet is 5 to 15
0 μm is suitable, but more preferably 5 to 100 μm.

In the present invention, the term "pressing gas" refers to pressing applied to a sheet or a sheet by dynamic pressure or static pressure of air or a gas mainly composed of air and including dry mist, and is an air knife or a static knife. It can be generated by a pressure chamber or the like. Among them, the static pressure chamber is preferable from the viewpoint of the uniformity of the thickness of the sheet.

The pressure of the gas is 1 in the case of an air knife.
By blowing a gas having a pressure of 00 to 2000 Pa, particularly air, from a nozzle, and 1 in a static pressure chamber.
It is preferable to carry out the reaction at an internal pressure of 0 to 500 Pa.
The length of the static pressure chamber in the sheet running direction depends on the casting speed, but is preferably 5 to 50 cm.

The electrostatic charge may be positive or negative. To apply an electrostatic charge, a high DC voltage is applied to a needle-like electrode or a parallel electrode in which a thin, short linear or blade-like electrode is placed parallel to the cooling roll (parallel to the axial direction) to cause corona discharge. Generate and add charge.

The portion corresponding to both side edges of the sheet to which an electrostatic charge is applied is preferably within a range of 30 mm from both side edges of the sheet. If it is closer to the center than this, it is not preferable because there is a problem that the cooling of the end portion on the sheet side becomes insufficient or the useful width of the product becomes narrow.

The measurement of the AC volume resistivity of the molten polymer in the present invention is preferably carried out using, for example, the apparatus shown in FIG. The measurement sample 1 uses a sheet having a thickness of about 150 μm. On the upper surface of the cylindrical lower electrode 2 having a diameter of 20 cm, 15
5.6cm in diameter and 0.2mm in thickness that can hold a parallel gap of 0μm
cm of the upper electrode 3, and the measurement sample is inserted so as to be in close contact with the electrode.

The lower electrode has a built-in power supply device 4 and a temperature detecting end 5. The variation in the surface temperature of the lower electrode on the measurement surface is within 1 ° C., and the temperature difference between the lower end and the detecting end is 8 ° C./min. Construct so as to be within 2 ° C. The detected temperature is measured by the reading thermometer 7. The whole of the electrode is placed in the heat insulation box 11.

The power supply 18 applies the generated voltage between the two electrodes via the standard resistor 9, and the power supply is a power supply that generates 100 V and 50 Hz. As for the current flowing through this circuit, the voltage generated across the standard resistor is read by an electron meter 10 having an internal impedance of 100 MΩ or more.

In the present invention, the AC volume resistivity of the sheet-like polymer is measured by measuring the temperature of the lower electrode at a rate of 8 ° C./min. Performed at a temperature, the AC volume resistivity Z is obtained from the following equation from the applied voltage E, current I, electrode area S, and electrode interval d.

[0019]

(Equation 1)

In the present invention, the AC volume resistivity is 1 × 10 ^{8 to} 5 × 10 ⁹ Ω · c at the center corresponding to the sheet to be manufactured.
m, the portion corresponding to both ends is 1 × 10 ⁶ to 1 × 10 ⁸ Ω · cm. The AC volume resistivity generally varies with the temperature of the polymer, and the higher the temperature, the lower the resistivity. Therefore, even if a single polymer is used, the resistivity of the corresponding portion can be reduced by increasing the polymer temperature at the portion corresponding to both side edges of the sheet. It is preferable that the polymer temperature at the portion corresponding to both side edges of the sheet is higher than the polymer temperature at the portion corresponding to the center of the sheet by 5 ° C or more, more preferably 10 ° C or more.

As another method for lowering the AC volume resistivity of the portions corresponding to both side ends, there is a method of replacing both ends with a polymer having a low AC volume resistivity. For example, the polymer is provided at a portion corresponding to both ends of an orifice of a base. For example. A polymer having a low AC volume resistivity can be produced by adding a specific second component. Examples of the second component include alkali metals, alkaline earth metals, and the like, and compounds thereof, and sulfonic acids having an ester-forming functional group such as tetrabutylphosphonium salt of 3,5-dicarboxybenzenesulfonic acid. A quaternary phosphonium salt, a polyester containing a metal compound selected from Zn, Mg, and Mn compounds and a phosphorus compound in a specific ratio in the process of polymer formation, and the like are conveniently used. For example, alkali metals, alkaline earth metals, and in these compounds, the amount of metal is 0.05 to 100 ppm (based on the polymer), Zn, M
g, the metal compound of the Mn compound is 10 to 50 as the metal amount.
0 ppm (based on the polymer), the ratio of the phosphorus compound to the metal compound is 1 to 5 mol, and 0.1% for the phosphonium salt.
It is preferred to use from the range of ~ 45 mmol% (based on the total acid component of the polymer).

The sheet cast according to the present invention is continuously guided to a biaxial stretching step, and can be stably and favorably stretched without troubles such as cutting.

[0023]

The present invention will be further described below with reference to examples.

Example 1 Contains a sodium compound and has an AC volume resistivity at 275 ° C. of 5 × 10 ⁸ Ω ·
cm of polyethylene terephthalate, orifice width 4
From a 40 mm base to a 35 μm thick sheet, temperature 27
Extruded at 5 ° C. However, the portions of the die corresponding to both side edges of the sheet were locally heated to a temperature of 305 ° C. The AC volume resistivity of the polymer at that temperature was 8 × 10 ⁷ Ω · cm.

The sheet is taken up by a cooling roll having a diameter of 700 mm, and a needle-shaped corona discharge electrode is installed at a portion corresponding to both side edges of the sheet near the roll contact point of the sheet, and a DC voltage of 8 Kv is applied to the sheet to cover the entire width of the sheet. Through the static pressure chamber, air pressure was applied at 200 Pa for casting. The sheet take-up speed was set to 50 m / min, and further increased to 70 m / min.

As a result, the electrostatic adhesion at both side edges of the sheet worked well at any speed, and a sheet having a uniform width could be stably produced.

[Comparative Example 1] Casting was performed in the same manner and under the same conditions as in Example 1 except that the temperature of the corresponding portions on both sides of the sheet-like material was the same as that of the central portion. As a result, at a sheet take-up speed of 50 m / min, poor electrostatic adhesion occurred 1 to 3 times per hour, resulting in a change in sheet width. At a take-off speed of 70 m / min, the normal electrostatic contact state was maintained for only several minutes to 10 minutes, and stable production was not possible.

Example 2 Using a die having an orifice width of 440 mm, polyethylene-2,6-naphthalate was extruded from the center of the die at a temperature of 290 ° C. into a sheet having a thickness of 35 μm. Polyethylene-2,6-naphthalate containing tetrabutylphosphonium salt of 5,5-dicarboxybenzenesulfonic acid was extruded at a temperature of 295 ° C. Extruded from the center of the orifice 2
The AC volume resistivity of the polymer at 95 ° C. is 9 × 10 ⁸
The polymer at 295 ° C. extruded from both ends of the Ω · cm orifice was 3 × 10 ⁷ Ω · cm.

Casting was carried out in the same manner and under the same conditions as in Example 1 except for the cap. As a result, at both the take-up speeds of 50 m / min and 70 m / min, the state of electrostatic adhesion at both side edges of the sheet was good, and even at a speed of 80 m / min, a sheet having a uniform width could be stably produced.

[Comparative Example 2] A method similar to that of Example 2 except that the composition and temperature of the polymer extruded from both ends of the orifice of the die were the same as the polymer extruded from the center of the orifice. , And cast under the conditions. As a result, the normal electrostatic adhesion state was maintained for only several minutes at the sheet take-up speed of 50 m / min, and the normal electrostatic adhesion state could not be maintained at the take-up speed of 70 m / min or more.

[0031]

According to the present invention, when a sheet is produced by applying an electrostatic charge to both side edges of a sheet-like material and solidifying and solidifying the other central portion with a cooling roll by pressing gas, the sheet is equivalent to both side edges. Since the AC volume resistivity of the polymer in the portion is kept low, the electrostatic adhesion action on both side edges of the sheet is stably and firmly maintained, and high-speed casting of a thin film for a capacitor or the like having an important characteristic of electric insulation and a thin film is possible.

[Brief description of the drawings]

FIG. 1 is a schematic view of an apparatus for measuring the volume resistivity of a molten polymer.

[Explanation of symbols]

 1: Polymer 2: Lower electrode 3: Upper electrode 4: Heating device 5: Temperature detection terminal 6: Ammeter 7: Reading thermometer 8: Power supply 9: Standard resistance 10: Electron meter 11: Insulation box

Claims (3)

[Claims] 1. Production of a sheet in which molten polyester is extruded from an orifice-shaped die into a sheet, and an electrostatic charge is applied to both side edges of the sheet, and the other central portion is tightly adhered to a cooling roll by gas pressure. In the method, the AC volume resistivity of the polymer corresponding to both side edges to which an electrostatic charge is added in the sheet-like material is 1 × 10 ⁶ to 1 × 10 ⁸ Ω · cm.
Wherein the other polymer at the center has an AC volume resistivity of 1 × 10 ^{8 to} 5 × 10 ⁹ Ω · cm. 2. The temperature of the polymer at a portion corresponding to both side edges of the film is made higher than the temperature of the polymer at the other central portion.
The method for producing a polyester sheet according to the above. 3. The method for producing a polyester sheet according to claim 1, wherein the polymer corresponding to both ends of the film is replaced with a polymer having an AC volume resistivity of 1 × 10 ⁶ to 1 × 10 ⁸ Ω · cm.