JPH11943A - Method for producing thermoplastic resin film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a thermoplastic resin film, which can automatically adjust a discharge electrode to an appropriate range where a good molding state can be obtained in a short time, reduce material loss and improve productivity. SOLUTION: A molten thermoplastic resin is extruded from a die 1 onto a cooling rotary drum 3 to form a film.
An electrostatic charge is applied to the film 4 by the linear discharge electrode 2 provided in parallel with the rotation axis of the drum 3, and the film 4 is solidified while being transported in close contact with the drum 3. An electrode current measuring means for measuring a current flowing through the discharge electrode 2 when an electrostatic charge is applied to the film 4, a discharge electrode 2 and a cooling rotary drum 3
And an electrode position adjusting means for adjusting the position of the discharge electrode 2 while maintaining the distance from the surface. The AC component of the current signal obtained from the electrode current measuring means is frequency-analyzed, and the position of the discharge electrode 2 is adjusted by the electrode position adjusting means such that the value of the predetermined frequency component is equal to or less than the predetermined reference value. Do

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for producing a thermoplastic resin film. More specifically, the present invention relates to a method for producing a thermoplastic film having less unevenness in thickness and surface defects and excellent surface properties.

[0002]

2. Description of the Related Art As is well known, a thermoplastic resin film (also referred to as a sheet) is formed by forming a molten thermoplastic resin into a film from a slit-shaped die, extruding it onto a cooling drum, and then stretching. In this molding, a wire electrode, which is a discharge electrode to which a high voltage is applied, is provided at a predetermined position of information on the film on the cooling rotary drum. It is known that the degree of adhesion of the film to the cooling drum can be improved, and a good molding state can be obtained.

[0003] A minute current flows from the wire electrode to the cooling rotary roll side, and the thermoplastic resin is pressed against the cooling rotary roll by the electrostatic force generated at that time, and the air is caught between the film and the cooling rotary roll. Is prevented, the cooling efficiency is improved, and the moldability is improved.

By the way, in order to obtain the above-mentioned good molding state in this method, the position of the wire electrode is an important condition. In other words, of the positional relationship between the wire electrode and the surface of the cooling rotary drum, for the distance to the surface,
If this interval is too large, the potential gradient between the wire electrode and the cooling drum is reduced, and sufficient electric charge is not released from the wire electrode. Sufficient adhesion cannot be obtained. On the other hand,
If this interval is too narrow, the potential gradient becomes excessive, causing dielectric breakdown in the film, and causing defects such as pinholes.

[0005] In addition, the position of the rotating direction of the rotating drum for cooling the wire electrode, that is, the position of the film feeding direction,
When the film discharged from the cap is taken off on the surface of the cooling rotary drum that rotates at a predetermined speed in the state of natural fall, the radiation direction at the ground contact point where the film is grounded is set as a reference, and the wire electrode is installed upstream from this direction. However, before the film lands on the surface of the rotating drum for cooling in the state of natural fall, it is pressed against the rotating drum for cooling, so that the film is not stable and tends to vibrate or shake. Surface defects occur.

Conversely, if the film is installed downstream of the radiation direction, the cooling roll side of the film is already cooled and solidified to some extent at the point closest to the wire electrode where a large pressing force acts. Air is trapped in between, causing bubbles and surface defects.

Therefore, the optimum position of the wire electrode in the film feeding direction is at or immediately before the landing point on the surface of the cooling rotary drum in the state of natural fall without the action of external force such as electrostatic force of the film. In this case, stable landing and a good molding surface can be obtained by being installed at that position.

[0008]

However, this landing point is determined by the relationship between the plasticity of the discharged film and the rotation speed of the cooling rotary drum, and if there is a large change in the manufacturing conditions, the position of the discharge electrode is changed. There is a problem that the above-mentioned drawbacks and the like occur, and the adjustment takes time. Especially,
The change of the product brand is remarkable, and there has been a problem that it takes a lot of time to search for the optimum position of the discharge electrode.

On the other hand, Japanese Unexamined Patent Publication No. Sho 60-1200 discloses a conventionally proposed method for automatically positioning a wire electrode.
In the method of detecting the maximum value of the current flowing through the wire electrode as disclosed in Japanese Patent Publication No. 28-28, there is usually no inflection point in the current change, and it is inevitable that a spark discharge occurs during the detection. Further, in the method disclosed in Japanese Patent Application Laid-Open No. 4-83627, in which the current fluctuation width is adjusted to be the minimum, the position of the wire electrode is set to the normal current fluctuation width within an appropriate range that does not cause a defect or the like in the film. There is no minimum point and control is difficult.

The present invention has been made in order to solve the above-mentioned problems, and is capable of automatically adjusting a discharge electrode to a proper range position in which a good molding state can be obtained in a short time, which is an alternative to the above-mentioned prior art, and reduces material loss. It is an object of the present invention to provide a method for producing a thermoplastic resin film, which has a low productivity and improves productivity.

[0011]

SUMMARY OF THE INVENTION The method for producing a thermoplastic resin film of the present invention comprises the steps of: extruding a molten thermoplastic resin from a die onto a cooling rotary drum to form the film; In the method for producing a thermoplastic resin film, a static charge is applied to the film by a linear discharge electrode provided in parallel with the rotation axis, and the film is solidified while being transported in close contact with a cooling drum. An electrode current measuring means for measuring a current flowing through the discharge electrode when applying a voltage, and an electrode position adjusting means for adjusting the position of the discharge electrode while maintaining a distance between the discharge electrode and the surface of the cooling rotary drum, The frequency analysis is performed on the AC component of the current signal obtained from the electrode current measuring means, so that the value at the predetermined frequency component is equal to or less than the predetermined reference value, and the It is characterized by adjusting the position of the discharge electrode me.

In the present invention, the position of the discharge electrode is automatically adjusted by the position adjusting device based on the data while analyzing the frequency component of the current flowing through the detected discharge electrode. As for the method of adjusting the position, a method of temporarily changing the position of the discharge electrode by a predetermined amount by the position adjusting device and then adjusting until a constant change appears in the frequency component in the direction opposite to the change direction is preferable from the viewpoint of control stability. .

According to the present invention, the value of the current flowing through the discharge electrode is directly monitored at all times, whereby the position of the discharge electrode is automatically adjusted. It can be manufactured with low raw material loss and high productivity.

The thermoplastic resin in the present invention generally includes all resins that can be formed into a film (also called a sheet). Representative examples of these thermoplastic resins include polyesters such as polyethylene terephthalate and polyethylene naphthalate. Further, these copolymer mixtures may contain other additives and the like. Further, the film extruded from the die may be a single-layer film or a multilayer film in which the same or different resin layers are laminated in a plurality of layers.

The discharge electrode may be any one made of a linear conductive material, and usually a wire electrode made of a metal wire is used. Since a high DC voltage is normally applied to the discharge electrode, this current value is usually detected by a DC ammeter, but AC is used to adjust the position of the discharge electrode based on the result of analyzing the frequency component of the current value. There is no problem with the ammeter.

The apparatus for analyzing the frequency component of the current value may be a commercially available frequency analyzing apparatus. However, the position adjustment of the discharge electrode can be performed by using a commercially available personal computer and performing calculation using software capable of executing FFT. Can be calculated at a speed sufficient for

[0017]

FIG. 1 is an explanatory view of the structure of a film forming section of a thermoplastic resin film manufacturing apparatus for carrying out the method of the present invention. The film 4 made of the thermoplastic resin melt-extruded from the die 1 is cooled and solidified on the surface of the cooling drum 3. Here, the discharge electrode 2 is maintained at a high voltage by the high voltage generating mechanism 8, and as a result, a high charge is induced in the film 4, and the film 4 is brought into close contact with the cooling rotary drum 3, which is an opposite electrode. In this example, as shown by the arrow in the figure, a position adjustment (not shown) in which the position of the discharge electrode 2 can be moved while maintaining the axis of the discharge electrode 2 parallel to the cooling rotary drum 3 and maintaining the interval with the cooling rotary drum 3. A device is provided, on which the discharge electrode 2 is installed.

An ammeter 5 is connected to the discharge electrode 2 so that the current flowing through the discharge electrode can always be measured. The value of the current flowing through the discharge electrode measured by the ammeter 5 is input to the frequency component analysis device 6, and the output signal determines the position of the discharge electrode according to the signal of the controller 7 that moves the position adjustment device of the discharge electrode in a specific direction. Control is performed so as to maintain the distance from the cooling drum.

The control method will be described. As shown in FIG. 1, the film 4 extruded from the die 1 has a certain distance between the film 4 and the cooling rotary drum 3, and the film 4 is pressed on the cooling rotary drum 3 by the electrostatic force of the discharge electrode 2. Since the edge portion is open, it is in an unstable state. As described above, when the discharge electrode 2 is moved near the ground point between the film 4 and the cooling rotary drum 3, when the discharge electrode 2 is brought close to the film 4, the die 1 of the film 4 is cooled by the reaction force of the electrostatic force. When the vibration is started from the edge portion between the rotating drums 3 and further brought closer, the entire film between the die 1 and the cooling rotating drum 3 starts to vibrate, which causes uneven thickness and film defects. Further, the vibration of the film changes the distance between the film 4 and the discharge electrode 2, so that the electrostatic force changes and the discharge electrode 2
The value of the current flowing through varies also at the frequency of the vibration of the edge portion between the die 1 and the cooling rotary drum 3.

The discharge electrode 2 is moved with respect to the film 4 while keeping the distance from the cooling rotary drum 3, and a frequency component in which the current value fluctuates is detected by a frequency component analyzer 6. The position of the discharge electrode may be adjusted so as to be smaller than the size.

By utilizing this fact, the object can be achieved by moving the position of the discharge electrode to an appropriate range such that the film has no thickness unevenness or defects.

Hereinafter, an example in which a polyethylene terephthalate film is manufactured using the apparatus of this embodiment will be described. The polyethylene terephthalate resin is melted by being extruded from an extruder (not shown), and has a lip opening of 2 mm and 285 ° C.
Extruded from the die 1 set to a thickness of 100
A μm polyethylene terephthalate film 4 was formed. A voltage of 6.5 kV is applied to the discharge electrode 2, the distance to the surface of the cooling rotary drum 3 is set to move while maintaining 4 mm, and the position of the first discharge electrode 2 is set downstream of the landing point of the film 4. The position was set at a position where there was a defect due to air being trapped on the entire surface on the side, and adjustment control was started from this state. The movement of the discharge electrode 2 was performed at a low speed of 0.1 mm / sec. This was set by sufficiently considering the response time at which the edge portion of the film 4 starts vibrating due to the reaction force of the electrostatic force of the discharge electrode 2.

The film frequency analyzer is provided with a filter function to cut off the frequency components of the power supply and the frequency components caused by the eccentricity of the cooling rotary drum.

As the discharge electrode 2 was moved to the upstream side with respect to the traveling direction of the film, the movement of the discharge electrode 2 was stopped when the intensity of 10 Hz or less in the analysis result of the frequency analyzer increased to three times the initial state. .

It should be noted that the defect is always detected and the discharge electrode 2 is constantly detected.
Can be adjusted and controlled, but the delicate movement of the discharge electrode also affects the characteristics of the film 4 and creates defects such as unevenness in thickness. If not, the adjustment control is not performed. According to this example, adjustment man-hours at the time of brand change and the like are reduced by 40%.

[0026]

According to the present invention, the discharge electrode can be automatically and accurately adjusted to the optimum position range in a short time, thereby reducing the raw material loss and improving the productivity. Further, it is possible to stably obtain a film having excellent surface properties without a surface defect in a film as a product. As described above, the present invention greatly contributes to cost reduction, productivity improvement, quality improvement, and the like of the thermoplastic resin film.

[Brief description of the drawings]

FIG. 1 is a configuration of a film forming section of a thermoplastic resin film manufacturing apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Die 2 Discharge electrode 3 Rotating drum for cooling 4 Film 5 Ammeter 6 Frequency analyzer 7 Controller 8 High voltage generating mechanism

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[Procedure amendment]

[Submission date] July 15, 1997

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0002

[Correction method] Change

[Correction contents]

[0002]

2. Description of the Related Art As is well known, a thermoplastic resin film (also referred to as a sheet) is formed by forming a molten thermoplastic resin into a film from a slit-shaped die, extruding it onto a cooling drum, and then stretching. In this molding, a wire electrode, which is a discharge electrode to which a high voltage is applied, is provided at a predetermined position above the film on the cooling rotary drum, thereby forming an electrostatic capacitor. It is known that the degree of adhesion of the film to the cooling drum can be improved, and a good molding state can be obtained.

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0017

[Correction method] Change

[Correction contents]

[0017]

FIG. 1 is an explanatory view of the structure of a film forming section of a thermoplastic resin film manufacturing apparatus for carrying out the method of the present invention. The film 4 made of the thermoplastic resin melt-extruded from the die 1 is cooled and solidified on the surface of the cooling drum 3. Here, the discharge electrode 2 is maintained at a high voltage by the high voltage generating mechanism 8, and as a result, a high charge is induced in the film 4, and the film 4 is brought into close contact with the cooling rotary drum 3, which is an opposite electrode. In this example, while the discharge DENDEN electrode 2 to maintain the cooling drum 3 and axially parallel, and a position adjusting device (not shown) can move the position while maintaining the gap between the cooling drum is provided, in which Discharge electrodes 2 are provided.

Claims (1)

[Claims] When extruding a molten thermoplastic resin from a die onto a cooling rotary drum to form a film,
A method for producing a thermoplastic resin film in which a static charge is applied to a film by a linear discharge electrode provided in parallel with a rotation axis of a cooling drum, and the film is solidified while being closely contacted with the cooling drum and transferred. An electrode current measuring means for measuring a current flowing to a discharge electrode when applying an electrostatic charge to a film, and an electrode position adjustment for adjusting a position of the discharge electrode while maintaining a distance between the discharge electrode and the surface of the cooling drum. Means, an AC component of the current signal obtained from the electrode current measuring means is frequency-analyzed, and the discharge electrode is adjusted by the electrode position adjusting means so that the value of the predetermined frequency component is equal to or less than a predetermined reference value. The method for producing a thermoplastic resin film, wherein the position of the thermoplastic resin film is adjusted.