JPH0477230A - Manufacture of themroplastic polymeric sheet - Google Patents

Abstract

PURPOSE:To remarkable reduce the unevenness of the longitudinal thickness of obtained sheet by a method wherein an electrical discharge electrode is regulated so as to take optimum position by shifting the electrical discharge electrode under the condition that the distance between the electrical discharge electrode and the surface of a moving cooling body is kept at constant so as to minimize the amplitude of the membrane vibration of molten polymeric sheet spanned between a mouthpiece and the moving cooling body. CONSTITUTION:Molten thermoplastic polymer is extruded in the form of sheet from a mouthpiece 1 onto a moving cooling body (cooling roller) 3 and applied by electrostatic charge with an electrical discharge electrode 4, which is installed above polymeric sheet 2, so as to be brought into close contact with the moving cooling body 3 in order to be solidified. In this case, the membrane vibration of the molten polymeric sheet 2 spanned between the mouthpiece 1 and the moving cooling body 3 is detected with a measuring device 9 so as to regulate the electrical discharge electrode for taking the optimum position, at which the amplitude of the membrane vibration becomes minimum, by shifting the electrical discharge electrode 4 under the condition that the distance between the electrical discharge electrode 4 and the surface of the moving cooling body 3 is kept at constant.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a method for manufacturing thermoplastic polymer sheets.

More specifically, the present invention relates to a method for producing a thermoplastic polymer sheet with small variations in sheet thickness in the longitudinal direction.

[Prior Art] Thermoplastic polymer sheets are used as materials for various industrial applications, such as base sheets for magnetic recording materials, base sheets for photographs, and dielectric materials for capacitors. A high degree of dimensional accuracy is required regarding the sheet thickness in the longitudinal direction.

Conventionally, when extruding and molding a molten thermoplastic polymer into a sheet onto a moving cooling body, a discharge electrode to which a high voltage is applied is installed above the polymer sheet. It is known that it is possible to improve the degree of adhesion to the material and obtain a good molding condition. (JP-A-49-557) In this method, the position of the discharge electrode is an important condition in order to obtain a good molding state.

In particular, the position of the discharge electrode in the longitudinal direction of the polymer is important, and a method has been disclosed in which the discharge electrode can be easily moved while maintaining a constant distance from the moving cooling body.

(Unexamined Japanese Patent Publication No. 57-8116).

It also discloses a method for adjusting to the optimal position where good moldability can be obtained in a shorter time, by automatically controlling the position to the quantified position of maximum current value.
It has been shown that speeding up can be measured (Japanese Patent Application Laid-open No. 60-1
20028).

Regarding the position of the discharge electrode and the uneven thickness of the sheet in the longitudinal direction,
A method is disclosed in which the thickness of the sheet after molding is measured, frequency analysis and calculations are performed, and control is performed to a position that minimizes thickness unevenness. (Unexamined Japanese Patent Publication No. 63-62723).

[Problems to be Solved by the Invention] However, studies conducted by the present inventors have revealed that the thickness unevenness in the longitudinal direction of the sheet cannot be sufficiently reduced by the method of the prior art.

That is, at the position of the maximum current value disclosed in JP-A-60-120028, in order to increase the speed, the molten polymer sheet and
Although it is excellent in preventing air from being trapped between the moving cooling bodies, it does not minimize longitudinal thickness unevenness. Also, Unexamined Japanese Patent Publication No. 6
The method disclosed in No. 3-62723 takes a long time to analyze and calculate, and there is a delay in dealing with thickness fluctuations that fluctuate unsteadily, so that it cannot be adequately controlled.

The object of the present invention is to overcome the drawbacks of the prior art and to provide a method for producing a sheet with small thickness variations in the longitudinal direction.

[Means for Solving the Problems] The present invention involves extruding a molten thermoplastic polymer into a sheet from a die onto a moving cooling body, applying an electrostatic charge using a discharge electrode installed above the polymer sheet, In the method for manufacturing a thermoplastic polymer sheet that is tightly solidified on the moving cooling body, the membrane vibration of the molten polymer sheet between the base and the moving cooling body is detected, and the discharge is controlled so that the amplitude of the membrane vibration is minimized. The present invention relates to a method for producing a thermoplastic polymer sheet, which comprises controlling the discharge electrode to an optimal position by moving the electrode while maintaining a constant distance from the surface of a moving cooling body.

The thermoplastic polymer in the present invention includes well-known polymers that can be molded into sheets such as polyolefins such as polyethylene and polypropylene, polyesters, polyamides, polyimides, polystyrenes, and polyvinyls, and copolymers and mixtures thereof. It may also contain other additives, such as antistatic agents, weathering agents, and lubricants made of organic particles or inorganic particles.

Further, the sheet extruded from the die may be a single layer or a multilayered sheet.

In the present invention, known devices and methods are used to impart an electrostatic charge to the molten polymer using a discharge electrode.

The present invention will be described in detail below using the drawings.

In FIG. 1, a polymer sheet 2 melted and extruded from a die 1 is brought into contact with a moving cooling body 3 (in this case, a cooling roller), cooled and solidified, and continues to a post-processing process via a separating roller 11. sent to A high voltage is applied to the discharge electrode 4 by a high voltage generator 5, and the discharge electrode 4 is maintained at a high potential with respect to the mobile cooling body 3.

The discharge electrode 4 is connected to the cooling body 3 by a motor 6 and a gear 7.8.
It can move at a constant distance from the surface.

The membrane vibration of the molten polymer sheet between the cap 1 and the moving cooling body 3 is monitored by a non-contact membrane vibration measuring device 9.

Using the apparatus configured as described above, the method of the present invention is carried out as follows.

First, the distance between the discharge electrode 4 and the surface of the cooling body 3 is set to an appropriate constant value such that an appropriate potential gradient occurs therebetween and no dielectric breakdown occurs in the polymer sheet 2.

Next, position control of the discharge electrode 4 in the circumferential direction of the cooling body 3 will be described.

As described above, the membrane vibration signal monitored by the membrane vibration measuring device 9 is input to the analysis/control device 10, which controls the circumferential position of the electrode so that the amplitude of vibration is minimized. That is, the amplitude at the initial position and the amplitude at a position displaced by a minute distance are compared, and the discharge electrode is moved in the direction in which a smaller amplitude is obtained. Membrane vibrations cause variations in the ground line at the initial contact point between the sheet and the moving cooling body, resulting in variations in the relative velocity of the sheet and the moving cooling body, resulting in longitudinal thickness unevenness of the formed sheet. . The electrostatic force that controls membrane vibration changes depending on the circumferential position of the discharge electrode, and as mentioned above, there is an optimal position that minimizes membrane vibration, and by controlling it to that minimum position, it is possible to eliminate uneven thickness in the longitudinal direction. Decrease/improve (see Figure 3).

Control may be constant feedback control, or
Furthermore, in practice, a method may be used in which the optimum position is set when the sheet molding conditions (thickness, speed, etc.) are changed.

In the present invention, how accurately it is important to measure the membrane vibration amplitude of a molten polymer sheet, the membrane vibration measuring device 9
For this, a known laser Doppler vibrometer, optical reflection vibrometer, etc. can be used.

[Example] Hereinafter, the present invention will be explained in more detail with reference to Examples.

Example 1 Using the apparatus shown in FIG. 1, molten polyethylene terephthalate extruded from a die into a sheet was molded. At this time, the sheet thickness is 300μ, the sheet width is 1600+nm,
The surface speed of the cooling roller was 50 m/min, and the distance between the cap and the cooling roller was 40 m/min.

And so. A SUS wire with a diameter of 0.2 mm was used as the discharge electrode, the distance from the cooling body surface was set to 8 mm, and the applied voltage was set to 6 kV to perform constant voltage control.

A light reflection type vibrometer that uses changes in the amount of reflected light was used to measure membrane vibration.

When we investigated the relationship between the electrode position l and the membrane vibration amplitude R shown in Figures 2 and 3, we found that l! = 55 mm, the membrane vibration amplitude R was the minimum of 820μ.

The thickness unevenness in the longitudinal direction of the sheet formed at this time is 2
It was 7.8μ in m.

Comparative Example 1 Using the same apparatus and conditions as in Example, and setting 7=50 mm, the membrane vibration amplitude R was 1220 μ.

The thickness unevenness in the longitudinal direction of the sheet molded at this time was 12.4 μ over a total length of 2 m.

Comparative Example 2 Similarly, when /=60 mm, the membrane vibration amplitude R was 10
The thickness was 40μ, and the thickness unevenness was 9.8μ.

[Effects of the Invention] As explained above, the manufacturing method of the present invention can significantly reduce the thickness unevenness in the longitudinal direction of the obtained sheet.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an apparatus for carrying out the manufacturing method according to the present invention. FIG. 2 is a schematic diagram of the vicinity of the base of the film manufacturing apparatus. FIG. 3 is a diagram showing the relationship between electrode position and membrane vibration, and between electrode position and thickness unevenness. 1, base 2, thermoplastic polymer sheet 3, cooling roller 4, discharge electrode 5, high voltage power supply 6, motor 7, gear 8, gear 9, membrane vibration measuring device 10, analysis/control device 11, separation roller

Claims (1)

[Claims] A thermoplastic polymer sheet in which a molten thermoplastic polymer is extruded in a sheet form from a die onto a moving cooling body, and an electrostatic charge is applied by a discharge electrode installed above the polymer sheet to solidify the thermoplastic polymer in close contact with the moving cooling body. In the manufacturing method, the membrane vibration of the molten polymer sheet between the cap and the moving cooling body is detected, and the distance between the discharge electrode and the moving cooling body surface is kept constant so that the amplitude of the membrane vibration is minimized. 1. A method for producing a thermoplastic polymer sheet, which comprises controlling the discharge electrode to an optimal position by moving the discharge electrode while moving the sheet.