JP2924114B2 - Method for producing thermoplastic polymer sheet - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a thermoplastic polymer sheet. More specifically, the present invention relates to a method for producing a thermoplastic polymer sheet having a small unevenness in sheet thickness in the longitudinal direction.

[Prior art] A thermoplastic polymer sheet is a base sheet of a magnetic recording material,
It is used as various industrial materials such as photographic base sheets and capacitor dielectric materials.
A high degree of dimensional accuracy is required for the thickness of the sheet, especially for the sheet thickness in the longitudinal direction.

Conventionally, when a molten thermoplastic polymer is extruded into a sheet on a moving cooling body and molded, if a discharge electrode to which a high voltage is applied is installed above the polymer sheet, the cooling body of the polymer sheet is electrostatically cooled. Can improve the degree of adhesion to
It is known that a good molding state can be obtained. (JP-A-49-55759) In this method, in order to obtain a good molding state,
The position of the discharge electrode is an important condition.

Particularly, the position of the discharge electrode in the longitudinal direction of the polymer is important, and there is disclosed a method in which the movement of the discharge electrode can be easily set while maintaining a constant distance from the moving cooling body. (JP-A-57-811
6).

Also disclosed is a method for adjusting the position to an optimum position at which good formability can be obtained in a shorter time, and it is shown that the speed can be increased by automatically controlling the quantified position of the maximum current value. (Japanese Unexamined Patent Publication No.
120028).

Regarding the position of the discharge electrode and the thickness unevenness of the sheet in the longitudinal direction, a method of measuring the sheet thickness after molding, performing frequency analysis and calculation, and controlling the position to minimize the thickness unevenness is disclosed. (JP-A-63-62723).

[Problems to be Solved by the Invention] However, in the study of the present inventors, it has been found that in the method of the related art, unevenness in the thickness of the sheet in the longitudinal direction is not sufficiently reduced.

That is, although the position at the maximum current value disclosed in Japanese Patent Application Laid-Open No. Sho 60-120028 is high in speed, it is excellent in preventing air entrapment between the molten polymer sheet and the moving cooling body, but the thickness unevenness in the longitudinal direction is minimal. do not become. Also, JP-A-63-6271
The method disclosed in No. 3 requires a long time for analysis and calculation, and there is a time lag for a non-stationarily fluctuating thickness, so that the method cannot be sufficiently controlled.

It is an object of the present invention to overcome the disadvantages of the prior art and to a method for producing a sheet with a small thickness variation in the longitudinal direction.

[Means for Solving the Problems] The present invention relates to a method in which a molten thermoplastic polymer is extruded from a die into a sheet and extruded onto a moving cooling body, and an electrostatic charge is applied by a discharge electrode provided above the polymer sheet, In the method for producing a thermoplastic polymer sheet which is tightly adhered to the moving cooling body, a film vibration of the molten polymer sheet between the die and the moving cooling body is detected, and the discharge is performed so that the amplitude of the film vibration is minimized. The present invention relates to a method for producing a thermoplastic polymer sheet, wherein an electrode is moved while maintaining a constant distance from a surface of a moving cooling body, and the discharge electrode is controlled to an optimum position.

The thermoplastic polymer in the present invention is a well-known polymer that can be molded as a sheet of polyolefins such as polyethylene and polypropylene, polyesters, polyamides, polyimides, polystyrenes and polyvinyls, and copolymers and mixtures thereof. It may contain other additives such as an antistatic agent, a weathering agent, a lubricant composed of organic particles and inorganic particles, and the like.

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

In the present invention, a known apparatus and method are used for imparting an electrostatic charge to the molten polymer by a discharge electrode.

 Hereinafter, the present invention will be described in detail with reference to the drawings.

In FIG. 1, a polymer sheet 2 melt-extruded from a die 1 contacts a moving cooling body 3 (in this case, a cooling roller).
It is cooled, solidified, and continuously sent to a post-processing step via a separation roller 11. 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 moving cooling body 3.

The discharge electrode 4 is connected to the cooling body 3 by a motor 6 and gears 7 and 8.
It can move so that the distance from the surface is constant.

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

Using the device configured as described above, the method of the present invention is performed 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 so that an appropriate potential gradient is generated between the electrodes and the polymer sheet 2 does not cause dielectric breakdown.

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 and controls the circumferential position of the electrode so that the amplitude of the vibration is minimized.
That is, the amplitude at the initial position and the amplitude at the position displaced by the minute distance are compared, and the discharge electrode is moved in a direction in which a smaller amplitude can be obtained. The membrane vibration is
Variations in the ground line at the point where the sheet and the moving cooling body first contact each other cause the relative speed of the sheet and the moving cooling body to fluctuate, resulting in uneven thickness in the longitudinal direction of the formed sheet. Depending on the circumferential position of the discharge electrode, the electrostatic force for controlling the film vibration changes, and as described above, there is an optimum position for minimizing the film vibration. It decreases and improves (see Fig. 3).

For the control, feedback control may be always performed, or, more practically, a method of setting an optimum position when the sheet forming conditions (thickness, speed, etc.) are changed.

In the present invention, it is important how to accurately measure the film vibration amplitude of the molten polymer sheet. As the film vibration measuring device 9, a known laser Doppler vibrometer, light reflection vibrometer, or the like can be used. .

EXAMPLES Hereinafter, the present invention will be described 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 was 300 μm, the sheet width was 1600 mm, the surface speed of the cooling roller was 50 m / min, and the interval between the die and the cooling roller was 40 m / m. The discharge electrode was a SUS wire having a diameter of 0.2 mm, the distance from the surface of the cooling body was set to 8 mm, and the applied voltage was set to 6 kv, and constant voltage control was performed.

For the film vibration measurement, a light reflection type vibrometer utilizing a change in the amount of reflected light was used.

The electrode position l and the membrane vibration amplitude R shown in FIGS.
As a result, when l = 55 mm, the membrane vibration amplitude R was a minimum of 820 μm.

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

Comparative Example 1 The film vibration amplitude R was 1220 μ when l = 50 mm under the same apparatus and conditions as in the example.

At this time, the thickness unevenness of the formed sheet in the longitudinal direction was 12.4 μm in a total length of 2 m.

Comparative Example 2 Similarly, when l = 60 mm, the membrane vibration amplitude R was 1040 μm.
And the thickness unevenness was 9.8 μm.

[Effects of the Invention] As described above, according to the manufacturing method of the present invention, the unevenness in the thickness of the obtained sheet in the longitudinal direction can be significantly reduced.

[Brief description of the drawings]

FIG. 1 is a schematic view of an apparatus for performing a manufacturing method according to the present invention. FIG. 2 is a schematic view of the vicinity of a base of the film manufacturing apparatus. FIG. 3 is a diagram showing the relationship between the electrode position and the membrane vibration, and the relationship between the electrode position and the thickness unevenness. DESCRIPTION OF SYMBOLS 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 meter 10 ... Analysis / control device 11 ... Pull-off roller

Claims (1)

(57) [Claims] 1. A molten thermoplastic polymer is formed into a sheet from a die and extruded onto a moving cooling body, and an electrostatic charge is applied by a discharge electrode provided above the polymer sheet to solidify and adhere to the moving cooling body. In the method for producing a thermoplastic polymer sheet, a film vibration of a molten polymer sheet between a die and a moving cooling body is detected, and the discharge electrode is moved in contact with a moving cooling body surface so that the amplitude of the film vibration is minimized. A method for manufacturing a thermoplastic polymer sheet, wherein the discharge electrode is controlled to an optimum position by moving the discharge electrode while keeping the distance constant.