JPS6311969B2 - - 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, it 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]

Various methods are conventionally known for rapidly cooling and molding thermoplastic polymer sheets using the action of static electricity. For example, as shown in FIG. 1, a polymer sheet 3 melt-extruded from a die 1
When manufacturing a polymer sheet while bringing the molten polymer sheet 3 into contact with the moving cooling body 2 and solidifying it by cooling, the melted polymer sheet 3 is placed near the point where the molten polymer sheet 3 contacts the moving cooling body 2 and A method of manufacturing a polymer sheet by providing an electrode 5 on the side not in contact with the moving cooling body 2 and applying a voltage between the electrode 5 and the moving cooling body 2, as shown in FIG.
A method of manufacturing a polymer sheet 3 while applying a voltage between a base 1 and a moving cooling body 2, as shown in FIG. 3, an electrical insulating film 7 is provided on the surface of the moving cooling body 2,
On the other hand, an electrode 5 is provided on the surface of the film 7 before the molten polymer sheet 3 comes into contact with the polymer sheet 3 while applying a voltage between the electrode 5 and the moving cooling body 2.
There are known methods of manufacturing.

However, although such conventional methods improve production speed and sheet thickness unevenness compared to methods that do not utilize the effect of static electricity, they have the disadvantage that they are not sufficient.

[Purpose of the invention]

The present invention solves the drawbacks of the above-mentioned prior art,
The purpose of this invention is to provide a method by which sheets can be manufactured at high speed and stably.

[Structure of the Invention] The present invention provides a sheet manufacturing method in which a molten thermoplastic polymer is extruded onto a moving cooling body in the form of a sheet and cooled and solidified. , and a voltage E1 of 5 to 15 kV is applied between the electrode provided on the side of the polymer sheet not in contact with the moving cooling body and the moving cooling body, and a voltage _E1 is applied between the base and the moving cooling body. Voltage higher than ₁
E ₂ was applied to each, and the space on the side of the melt-extruded polymer sheet in contact with the moving cooling body, where the polymer sheet and the moving cooling body were in contact, was filled with a gas having higher electrical insulation than air. The present invention is characterized by a method for producing a thermoplastic polymer sheet that is maintained in an atmosphere.

Thermoplastic polymers in the present invention include 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. Further, the molten sheet extruded from the die may be a single layer or a multilayered sheet.

The device applied to the present invention includes a slit-shaped mouthpiece, a moving cooling body, and a molten sheet extruded from the mouthpiece near the point where it comes into contact with the moving cooling body, and on the side where the molten sheet does not come into contact with the moving cooling body. A well-known melt film forming apparatus equipped with an electrode is used to conduct electricity from air to the space on the side of the melt-extruded polymer sheet that is in contact with the moving cooling body, and in the vicinity of the area where the polymer sheet and the moving cooling body come into contact. It is equipped with a device that maintains a highly insulating gas atmosphere.

Note that the moving cooling body in this device includes a cooling roller, a cooling belt, etc., and also includes a composite body thereof.

Further, the electrode may be made of metal, carbon, or other conductive material, and its shape includes any shape such as wire, needle, knife, and band shape.

However, the device according to the present invention is a device in which at least one of the base or the moving cooling body is electrically insulated from the earth (ground) in the above device.

In addition, methods for insulating a mobile cooling body include insulating the mobile cooling body itself from the ground wire, as well as coating the mobile cooling body with a conductive layer via an insulating layer, and coating the conductive layer with the ground wire. In the case where the latter moving cooling body is covered with a conductive layer, the moving cooling body as a part to which a voltage is applied shall refer to that conductive layer. Further, the conductive layer may be a layer made of metal or a layer made of semiconductor, and the layer may be further covered with an insulating layer.

In the present invention, 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, preferably refers to the space where the melted polymer sheet is formed into a sheet. a polymer sheet surface that is extruded and contacts a moving cooling body;
A space sandwiched between the surfaces of the moving cooling body and having at least the width of the polymer sheet and separated by a plane perpendicular to the surface of the moving cooling body from a position at least 3 mm away from the contact point on the surface of the moving cooling body. It is desirable that the space be on the side of the contact point.

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 simply referred to as the "near the contact point") has a higher insulating property than air. gas atmosphere,
Preferably, it is necessary to maintain a gas atmosphere having an insulating property 1.2 times or more that of standard air. Insulation here is defined by dielectric breakdown voltage according to the method described in ASTM D 2477. Typical gases that satisfy this condition include sulfur hexafluoride and many halocarbons.

To maintain the above 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 4, a gas flow is continuously supplied from a nozzle near the contact point.
This can be achieved by any of the above methods.

In the above-mentioned apparatus, the present invention applies a voltage E ₁ of 5 to 15 kV between the electrode and the moving cooling body, and a voltage E higher than the voltage E ₁ between the base and the moving cooling body when manufacturing the sheet. ₂ is applied to each of the sheets, and the vicinity of the contact point between the sheet and the moving cooling body is maintained in a highly electrically insulating gas atmosphere to manufacture the sheet.

Next, the present invention will be explained based on the drawings, but the present invention is not limited thereto.

4 and 5 are cross-sectional views showing one embodiment of the present invention. In each figure, 1 is a base, 2 is a moving cooling body (cooling roller), 3 is a polymer sheet, and 4 is a separation roller. , 5 is an electrode, 6 is a power supply device, 7 is an electrically insulating film, 8 is a conductive film, 9 is a resistor, 10
is an insulating gas cylinder, 11 is a gas supply nozzle, 12
is an auxiliary power supply.

Referring to FIG. 4, the cap 1 is connected to a ground wire, and the electrode 5 is connected to the ground wire via a resistor 9. Furthermore, the mobile cooling body 2 is covered with a conductive film 8 via an insulating film 7, and the conductive film 8 is connected to one end of the power supply device 6 with a brush (not shown) connected to the ground wire at one end. connected via.

On the other hand, the polymer sheet 3 melt-extruded from the die 1 is transferred to a moving cooling body 2 coated with a conductive film 8.
The polymer sheet is cooled and solidified.

The insulating gas is supplied from the insulating gas cylinder 10 to the nozzle 1.
1 to the vicinity of the contact point.

Next, FIG. 5 will be explained. Figure 5 shows the fourth
An auxiliary power supply device 12 is connected in parallel to the resistor 9 shown in the figure, and the rest is the same as in FIG. 4. In FIG. 5, a voltage E ₁ is supplied from an auxiliary power supply device 12, and a voltage E ₂ is supplied from a power supply device 6, respectively.

In the present invention, the voltage fluctuation rate of E ₁ and E ₂ is ±
It is desirable that it be 1% or less, preferably ±0.5% or less.

Note that in both FIGS. 4 and 5, the case where the mobile cooling body 2 is covered with the conductive film 8 via the insulating film 7 has been described; When coated, the "moving cooling body" to which E ₁ and E ₂ are applied in the present invention is
It shall be read as "a conductive film coated on a moving cooling body."

The case where the mobile cooling body is coated with a conductive film has been described above, but the entire mobile cooling body is insulated from the ground wire, and E ₁ and E ₂ are applied between the mobile cooling body, the electrodes, and the cap. Alternatively, the base may be insulated from the ground wire and E ₁ and E ₂ may be applied. Furthermore, E ₁ and E ₂ may be applied by independent power supplies.

The voltages E ₁ and E ₂ to be applied may be either alternating current or direct current, but preferably they are direct current and both E ₁ and E ₂ are negative on the moving cooling body side. In addition, the voltage _E1 applied between the electrode 5 and the moving cooling body 2 is 5 to 15 kV.
(distance between electrode 5 and moving cooling body 2 is 3 to 15 mm). Further, it is desirable that the voltage _E2 applied between the cap 1 and the movable cooling body 2 is 8 to 60 kV (distance between the cap 1 and the movable cooling body 2 is 10 to 80 mm).

In order to increase the adhesion force due to electrostatic force, E ₁ ,
Although it is preferable to make both _E2 high, the voltage _E1 between the electrode 5 and the movable cooling body 2 makes the vicinity of the electrode 5 a kind of plasma state, and the micro discharge is stabilized between the movable cooling body 2 and the electrode 5. The condition must be such that it occurs. If E ₁ is less than 5 kV, micro discharges will not occur and there will be no adhesion effect, and if it exceeds 15 kV, spark discharge will occur, making it impossible to stably produce a polymer sheet.

On the other hand, the voltage E ₂ between the cap 1 and the moving cooling body 2
This causes a conductive current to flow between the base 1 and the moving cooling body 2 via the molten polymer sheet. In order to stabilize and increase the speed, it is preferable to increase the current, but if a micro discharge occurs between the moving cooling body 2 and the molten polymer sheet, the static generated between the sheet and the moving cooling body The electric field is destroyed and the adhesion effect is lost. If the voltage E ₂ is less than 8 kV, the adhesion effect due to electrostatic force will be small, and if it exceeds 36 kV under normal atmosphere, a micro discharge will occur between the molten polymer sheet and the moving cooling body 2 and the adhesion effect will be lost, but the contact point By keeping the surrounding area in an atmosphere of gas that is more electrically insulating than air, the micro-discharge inception voltage between the polymer sheet and the moving cooling body 2 can be increased to 60kV. Preferably, a high gas atmosphere is maintained.

Furthermore, under the conditions of the voltages E ₁ and E ₂ , currents flow between the moving cooling body 2 and the electrode 5 and between the moving cooling body 2 and the cap 1, respectively.
The resistance between the moving cooling body 2 and the electrode 5 is substantially equal to the thickness of the molten polymer sheet, whereas the resistance between the movable cooling body 2 and the base 1 is substantially equal to the longitudinal length of the molten polymer sheet. Due to the presence of the resistance, the majority of the current flows between the moving cooling body 2 and the electrode 5, and only a small amount of current flows between the base 1 and the moving cooling body 2. In other words, under the condition that E ₂ ≦E ₁ ,
The conduction current between the cap 1 and the moving cooling body 2 and the electric field formed on the surface of the moving cooling body are small, and compared to a system that does not add E ₂ , the effect is to produce a polymer sheet at high speed and stably. is small and almost negligible. By setting the condition E ₁ <E ₂ , the conduction current with the moving cooling body 2 can be increased to the extent that the effect of producing the polymer sheet extremely rapidly and stably occurs.

〔Effect of the invention〕

In the present invention, a voltage E ₁ of 5 to 15 kV is applied between the electrode and the moving cooling body, a voltage E ₂ higher than the voltage E ₁ is applied between the base and the moving cooling body, and the polymer sheet is connected to the moving cooling body. Since the vicinity of the contact point was maintained in an atmosphere of a gas having higher electrical insulation properties than air, an excellent effect could be obtained in that the sheet could be manufactured stably at high speed.

〔Example〕

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

Example 1 The intrinsic viscosity of orthochlorophenol solution at 25℃ is
After vacuum drying polyethylene terephthalate pellets with a diameter of 0.615 at 180°C, they were melted at 280°C in an extruder with a screw diameter of 90 mm, and then sent to the mouth of the device shown in Fig. 4 (slit width 1.0 mm) with a length of 400 cm. The mixture was extruded as a wide sheet, cooled and solidified using a moving cooling body (cooling roller), and then molded into a sheet.

The cooling roller has a diameter of 800φ and is cooled with 35°C cold water, and the surface is coated with alumina and then further coated with metal to give it a mirror finish, so the surface metal layer is coated with alumina. It is completely insulated from the previous cooling roller. The distance between this surface metal layer and the cap was 30 mm. In addition, the electrode was installed at a distance of 5 mm above the surface metal layer, and a wire electrode with a diameter of 0.25 mm was used, as shown in Figure 4.
Wired to ground via a 3MΩ variable resistor.

Then, the resistor and power supply were adjusted so that 8 kV was applied between the electrode and the metal layer provided on the cooling roller, and 12 kV was applied between the metal layer provided on the base and the cooling roller. However, a DC power supply was used as the power supply for applying voltage, and the negative terminal of the power supply was connected to a metal layer provided on the cooling roller.

When the speed of the cooling roller 2 was increased without supplying insulating gas from the insulating gas cylinder 10 through the nozzle 11, the speed at which poor sheet adhesion began to occur was 80 m/min. To further increase the speed, the voltage between the electrode and the metal layer on the cooling roller is increased.
When the voltage between the cap and the metal layer on the cooling roller was increased to 14kV while maintaining the voltage at 8kV, a micro discharge occurred between the surface of the cooling roller and the sheet before it came into contact with the cooling roller, causing the sheets to stick together. Something bad happened.

Therefore, when sulfur hexafluoride was supplied as an insulating gas from the supply nozzle at a flow rate of 1/min, the discharge stopped and the voltage between the electrode and the metal layer provided on the cooling roller was maintained at 8kV, and the cap and cooling roller were cooled. When the voltage between the metal layers on the roller was increased to 20kV, the speed at which poor adhesion began to occur was
It became 100m/min. At this time, the current flowing between the cap 1 and the cooling roller was 250 μA, and the current flowing between the electrode 5 and the cooling roller was 1.4 mA.

Comparative Example 1 A sheet was molded in the same manner as in Example 1 using the apparatus shown in FIG. The cooling roller was grounded and the electrode wiring was changed as shown in FIG. 1, but this was the same as in Example 1. In this method, when the DC voltage applied between the electrode and the cooling roller was set to 10 kV and the speed was increased, poor sheet adhesion began to occur at 50 m/min. At this time, the current flowing between the electrode and the cooling roller is 1.6
It was mA. When the voltage was further increased, a spark discharge occurred from the electrode to the cooling roller, and the speed could not be increased beyond that speed.

Comparative Example 2 A sheet was molded in the same manner as in Example 1 using the apparatus shown in FIG. DC voltage between cooling roller and base
When 15 kV was applied and the speed was increased, poor sheet adhesion occurred at 30 m/min, and even if the voltage was further increased, the poor adhesion did not improve and the speed could not be increased.

Comparative Example 3 Using the device shown in Fig. 5, the power supply device 6, variable resistor 9, and auxiliary power supply device 10 were adjusted, and 8 kV was applied between the electrode 5 and the cooling roller 2, and 8 kV was applied between the base 1 and the cooling roller 2. When a sheet was formed in the same manner as in Example 1 except that an insulating gas was supplied through the nozzle 11 at a rate of 1/min, the speed at which poor adhesion of the sheet began to occur was 45 m/min. that time,
The current flowing between base 1 and cooling roller 2 is 90μA
The current flowing between the electrode 5 and the cooling roller 2 was 1.4 mA.

Comparative Example 4 A sheet was molded in the same manner as in Example 1 using the apparatus shown in FIG. At that time, when a voltage of 8 kV was applied between the electrode 5 and the cooling roller 2 by the power supply device 6, the speed at which poor sheet adhesion started occurred was 40 kV.
m/min. At that time, the current flowing between the electrode 5 and the cooling roller 2 was 1.4 mA.

[Brief explanation of the drawing]

1, 2, and 3 are cross-sectional views showing an example in which the conventional sheet manufacturing method is applied, FIG. 4 is a cross-sectional view showing an example in which the sheet manufacturing method of the present invention is applied, and FIG. This figure is a sectional view showing an example in which the sheet manufacturing apparatus shown in FIG. 4 is partially improved. DESCRIPTION OF SYMBOLS 1: Base, 2: Moving cooling body, 3: Polymer sheet, 4: Separation roller, 5: Electrode, 6: Power supply device, 7: Electrical insulation film, 8: Conductive film, 9: Resistor, 10: Insulating gas cylinder, 11: Gas supply nozzle.

Claims (1)

[Claims] 1. In a method for manufacturing a sheet in which a molten thermoplastic polymer is extruded onto a moving cooling body in the form of a sheet and solidified by cooling, the polymer sheet is placed in the vicinity of the point where the polymer sheet contacts the moving cooling body, and A voltage E ₁ of 5 to 15 kV is applied between the electrode provided on the side that does not contact the moving cooling body and the moving cooling body, and a voltage E ₂ higher than voltage E 1 is applied between the base and the moving _cooling body. The space on the side of the melt-extruded polymer sheet in contact with the movable cooling body, where the polymer sheet and the movable cooling body contact each other, is maintained in an atmosphere of gas that has higher electrical insulation than air. A method for producing a thermoplastic polymer sheet, characterized in that: