JPS637135B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a method for producing a thermoplastic polymer sheet, and more specifically, a thermoplastic polymer sheet is extruded onto the surface of a moving cooling body and rapidly cooled and molded. The present invention relates to a method for producing a plastic polymer sheet.

[Prior art]

Conventional methods for producing thermoplastic polymer sheets include: (1) An electrode member charged to a high voltage is provided on the top surface of an electrically grounded cooling roller, static electricity is applied to the top surface of the sheet, and the sheet is cooled. Method for obtaining adhesion to the roll (hereinafter referred to as conventional example-1),
(2) A method of obtaining an adhesion effect by charging the cooling roller itself to a high voltage (hereinafter referred to as conventional example 2) is known.

However, in both conventional methods, when attempting to efficiently produce a polymer sheet by increasing the speed of the cooling roll, air is trapped between the sheet and the cooling roll, resulting in deterioration of the surface condition of the polymer sheet. get up. In the method of Conventional Example-1, this upper limit speed is 40 to 50 m/min. Also, conventional example-
Method 1 has problems due to the lifespan of the electrodes, electrode breakage, etc.Furthermore, since the electrodes are placed through the sheet, if there is a defect in the sheet, electrical discharge may occur from the electrodes to the roller, causing damage to the roller surface. Therefore, there are various problems in operation. Further, although Conventional Example 2 does not have the above-mentioned problems, the upper limit speed is 25 to 30 m/min, according to the studies of the present inventors, which is considerably inferior to Conventional Example 1.

Therefore, the present inventors conducted studies to find a method that does not have the above-mentioned problems and has a high upper limit speed, and found that the method of Conventional Example 2 has the following problems with the upper speed limit. found.

(1) A minute electrical discharge occurs between the cooling roller surface and the polymer sheet just before it comes into contact with the roller, resulting in a decrease in electrostatic adhesion.

(2) If the voltage is further increased, spark discharge occurs from the roller to the die from which the sheet is extruded, causing a significant decrease in adhesion and damage to the roller surface.

Therefore, the method of Conventional Example 2 had the problem that the voltage could not be increased until sufficient adhesion was obtained at high speed, and the upper limit of the speed remained low.

[Purpose of the invention]

An object of the present invention is to solve the problems of the above-mentioned conventional examples and to provide a method by which a polymer sheet can be produced stably at high speed.

[Structure of the invention]

In order to achieve the above object, the present invention consists of the following configuration. That is, the molten thermoplastic polymer is extruded from a die into a sheet onto a moving cooling body,
In the method for producing a polymer sheet in which a voltage is applied between the surface of the moving cooling body and the die to electrostatically solidify the material, the space on the side of the melt-extruded polymer sheet that is in contact with the moving cooling body; This is a method for producing a thermoplastic polymer sheet, characterized in that the vicinity of the contact between the polymer sheet and a moving cooling body is maintained in an atmosphere of a gas having higher electrical insulation properties than air.

Thermoplastic polymers in the present invention include 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 thereof; It may be a mixture and may contain other additives. Further, the molten sheet extruded from the die may be a single layer or a multilayered sheet.

The moving cooling body refers to cooling rollers, cooling belts, etc., and also includes composites thereof. In addition, if the surface of the cooling roller, cooling belt, etc. is coated with another layer, this is also included. In the device to which the present invention is applied, at least one of the base or the moving cooling body is electrically insulated from the earth (earth wire).

In addition, methods for insulating a mobile cooling body include insulating the mobile cooling body itself from the ground, as well as coating the mobile cooling body with a conductive layer via an insulating layer and insulating the conductive layer from the ground. In the latter case, the moving cooling body as the part to which the voltage is applied shall refer to its electrically conductive layer. Further, the conductive layer may be a layer made of metal or a layer made of semiconductor, and on the layer,
Furthermore, an insulating layer may be coated. In addition to insulating the cap itself from the ground, methods for insulating the cap also include providing a conductive layer on the part that comes into contact with the polymer inside the cap and insulating that conductive layer from the ground. In the latter case, the cap as the part to which the voltage is applied refers to the conductive layer.

The voltage applied between the surface of the movable cooling body and the cap may be either alternating current or direct current, but it is preferably a direct current with a voltage fluctuation rate of 1% or less, and is preferably negative on the movable cooling body side with respect to the cap.

The space on the side of the melt-extruded polymer sheet that is in contact with the moving cooling body, and the vicinity where the polymer sheet and the moving cooling body come into contact (hereinafter referred to as the "near the contact point") has higher insulating properties than air. Maintain a gas atmosphere, preferably a gas having an insulating property 1.3 times or more that of standard air. Insulation here means ASTM
Defined by dielectric breakdown voltage according to the method described in D2477. Typical gases that satisfy this condition are:
Contains sulfur hexafluoride and many halocarbons.

To maintain a gas atmosphere, (1) Cover the entire area near the contact point with a cover to isolate it from the outside air and replace the atmosphere with gas. (2) As shown in Figure 1, a gas flow is continuously supplied from a nozzle near the contact point. Such,
This can be achieved by any method.

Next, the present invention will be explained based on the drawings, but is not limited thereto. FIG. 1 shows a schematic diagram of an apparatus used in the method for producing a thermoplastic polymer sheet of the present invention. In FIG. 1, a polymer sheet 2 is melt-extruded from a die 1.
comes into contact with a moving cooling body (in this case, a cooling roller) 3, is cooled and solidified, and is continuously sent to a post-treatment step via a separating roller 4.

An insulating film 5 is provided on the surface of the cooling roller 3, and a conductive film 6 is further provided thereon. A voltage is applied between the conductive film 6 and the cap 1 by a power supply device 7. The insulating gas is continuously supplied from the cylinder 8 through the nozzle 9 to the vicinity of the contact point between the polymer sheet 2 and the moving cooling body 3.

〔Effect of the invention〕

In the present invention, by maintaining the vicinity of the point of contact between the polymer sheet and the moving cooling body in an atmosphere of gas having higher electrical insulation properties than air, the upper limit of the sheet production speed can be reduced.
We were able to significantly increase this compared to the conventional method.

〔Example〕

Hereinafter, one embodiment of the present invention will be described based on Examples.

Example 1 A sheet of polyethylene terephthalate was molded using the apparatus shown in FIG. The equipment conditions are a mouth width of 400 mm, a mouth slit width of 1 mm, a cooling roller diameter of 800 mm, a nozzle width of 400 mm, and the insulating gas is sulfur hexafluoride (dielectric breakdown voltage is 2.2 that of air).
times) was continuously supplied from the nozzle at a flow rate of 1/min. The voltage applied to the roller was increased each time poor adhesion of the sheets occurred while increasing the roller speed. At the same time, the roller potential fluctuations were monitored using an oscilloscope to check for the occurrence of minute discharges.

When a sheet was manufactured by the method described above,
No micro discharge occurs even when boosted to 30kV, 200μA
The speed at which the electric current stably flowed through the 350 mm wide sheet and the sheets started to cause poor adhesion was 90 m/min.

Comparative Example 1 A sheet was manufactured in the same manner as in Example 1 except that no gas was supplied. When the sheet was manufactured, micro discharge started to occur at 14 kV, and when the voltage was increased above 14 kV, the adhesion of the sheet decreased. At this time, the average is about 270μA
An average current of 330 mm in width flowed through the sheet, but due to the occurrence of minute discharges, current fluctuations of ±50 μA were observed. As a result, the speed at which poor adhesion of the sheets began could not be set higher than 30 m/min.

As is clear from the above examples, the method of the present invention allows the upper limit of sheet production speed to be significantly increased compared to the conventional method.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view of the apparatus used in the present invention. 1: Base, 2: Polymer sheet, 3: Moving cooling body, 4: Separation roller, 5: Insulating film, 6:
Conductive film, 7: Power supply device, 8: Insulating gas, 9:
nozzle.

Claims (1)

[Claims] 1. A method for producing a polymer sheet in which a molten thermoplastic polymer is extruded from a die into a sheet onto a moving cooling body, and a voltage is applied between the surface of the moving cooling body and the die to electrostatically solidify the polymer sheet. , the space on the side of the melt-extruded polymer sheet in contact with the moving cooling body, and the vicinity where the polymer sheet and the moving cooling body come into contact, is maintained in an atmosphere of gas having higher electrical insulation properties than air. A method for producing a thermoplastic polymer sheet.