JPH0483627A - Manufacture of thermoplastic polymer sheet - Google Patents

Abstract

PURPOSE:To control a discharge electrode at an optimum position and to reduce a longitudinal thickness irregularity by detecting variation in a discharge current and moving the electrode while holding a distance to the surface of a moving cooler constant to minimize its variation width. CONSTITUTION:A polymer sheet 2 melted and extracted from a base 1 is brought into contact with a moving cooler 3, solidified, and continuously fed to a posttreating step through a peeling roller 11. A distance between a discharge electrode 4 and the surface of the cooler 3 is set to a suitable predetermined value so as to generate a suitable transfer gradient therebetween and not to generate an insulation breakdown at the sheet 2. A current variation width is monitored, its width variation is differentiated, and a position where its differential coefficient becomes '0' by a controller 10. The variation width at an initial position (arbitrary) is compared with that at a position when the electrode is displaced at an infinitesimal distance, and the electrode is moved in a direction for obtaining a smaller variation width.

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 extracting and molding a molten thermoplastic polymer into a sheet on a moving cooling body, a discharge electrode to which a high voltage is applied is installed above the polymer sheet, and the polymer sheet is electrostatically transferred to the cooling body. It is known that good molding conditions can be obtained by improving the degree of adhesion to
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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;
A method for easily setting the moving cooling body while keeping the distance to the moving cooling body constant is disclosed (Japanese Patent Laid-Open No. 57-8116).
.

Furthermore, it also discloses a method for adjusting to the optimum position that provides good formability in a short time, and it is shown that speeding up can be achieved by automatically controlling the quantified position of maximum current value ( JP-A-6O-120028
).

Regarding the position of the discharge electrode and the thickness of the sheet in the longitudinal direction,
A method is disclosed in which the sheet thickness after molding is measured, frequency analysis and calculations are performed, and the thickness is controlled to a position where unevenness is minimized (Japanese Patent Application Laid-Open No. 63-62723).

[Problems to be Solved by the Invention] However, studies conducted by the present inventors have revealed that the thickness irregularities 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, although it is excellent in preventing air from being trapped between the molten polymer sheet and the moving cooling body to increase speed, the longitudinal thickness unevenness is minimal. do not become. Also, Unexamined Japanese Patent Publication No. 6
The method disclosed in No. 3-62723 requires time for analysis and calculation, and cannot adequately control thickness fluctuations that fluctuate unsteadily due to a time lag.

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 producing a thermoplastic polymer sheet that is tightly solidified on the moving cooling body, discharge current fluctuations are detected and the distance between the discharge electrode and the surface of the moving cooling body is kept constant so that the width of the fluctuation is minimized. The present invention relates to a method for producing a thermoplastic polymer sheet, characterized in that the discharge electrode is controlled to an optimum position by moving the discharge electrode while maintaining the discharge electrode at an optimum position.

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, polyvinyls, etc., and copolymers and mixtures thereof. It may also contain other additives, such as antistatic agents, weathering agents, and lubricants made of organic or inorganic particles.

Further, the sheet extracted from the nozzle may be a single layer or a multi-layered sheet. In the present invention, a known apparatus method is used to impart an electrostatic charge to the molten polymer using a discharge electrode.

The present invention will be explained in detail below with reference to the drawings.

In FIG. 1, the polymer sheet 2 melt-extracted from the nozzle 1 is brought into contact with a moving cooling body 3 (in this case, a cooling roller), cooled and solidified, and is continuously transferred 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 moving cooling body.

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

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. Circumferential position (see Figure 2)
The relationship between the current flowing from the discharge electrode 4 to the cooling body 3 is the third
The relationship between the position of the discharge electrode in the circumferential direction and the thickness unevenness in the longitudinal direction of the sheet is shown in FIG.

In FIG. 3, the width indicated by R indicates the current fluctuation width measured by the ammeter 9. Also, l indicates the electrode position. In FIG. 3, region B corresponds to a region centered on the landing point of the polymer sheet 2 on the cooling roller 3, region C corresponds to the downstream side of the landing point, and region A corresponds to the upstream side of the landing point. In region C, the polymer sheet is solidified, the adhesion of the sheet is weak, and air is trapped between the sheet and the cooling body, so the current value is low and fluctuates widely, and the sheet thickness is uneven. not good. In region A, although the current value is high, the current fluctuation is large and the thickness unevenness is also large.

In region B, the current fluctuation is the smallest, especially in the region where the fluctuation width is the smallest and the thickness unevenness is also small.

Therefore, in order to position the discharge electrode as close to the position as possible, the current fluctuation range is monitored, the fluctuation range change is differentiated, and the position where the differential coefficient becomes 0 is controlled by the control device 10.

In other words, the current fluctuation width at the initial position (arbitrary) is compared with the current fluctuation width at a position where the discharge electrode is displaced by a small distance, and the discharge electrode is moved in the direction where the smaller fluctuation width is obtained. . The control may be performed by constant feedback control, or more practically, by setting the optimum position when the sheet forming conditions (thickness, speed, etc.) are changed.

[Example code] 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 was extruded from a die into a sheet. At this time, the sheet thickness was 100 μm, the sheet width was 720 mm, the surface speed of the cooling roller was 40 m/min, and the interval between the die and the cooling roller was 20 m/m. The discharge electrode has a diameter of 0.
Using a 2mm SUS wire, the distance from the cooling body surface is 8.
mm, the applied voltage was set to 6 KV, and constant voltage control was performed. When the relationship between the electrode position l, the current value A1, and the current fluctuation width I was investigated, the current fluctuation width R showed the minimum 0°08 mA when l=33 mm, so a sheet was formed with jl'=33 mm. At this time, the current value is 2. It was OmA.

The thickness unevenness in the longitudinal direction of the obtained sheet was 2 m in total length, and 2.
It was 1μ.

Comparative Example-1 A with exactly the same equipment conditions as in Example! = 30mm, the current value increased to 2.1mA, and the fluctuation range R also decreased to 0.
The current was increased to 20mA. The thickness unevenness in the longitudinal direction of the sheet obtained at this time was 4. It was Ott.

Comparative Example-2 Similarly, when /=36mm, the current value was 1°8mA
The fluctuation range was 0.12 mA.

The thickness unevenness of the sheet obtained at this time was 2.4 μm.

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

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an embodiment of an apparatus for carrying out the manufacturing method according to the present invention. FIG. 2 is a schematic diagram showing the base portion of FIG. 1, and is for showing the electrode position l. FIG. 3 is a diagram showing the relationship between electrode position, current value, and current fluctuation width, and FIG. 4 is a diagram showing the relationship between electrode position and thickness unevenness. 1 Nitrometal 2: Thermoplastic polymer sheet 3: Cooling roller 4: Discharge electrode 5: High voltage power supply 6: Motor 7: Gear gear ammeter control device/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, discharge current fluctuations are detected and the fluctuation width is minimized.
A method for producing a thermoplastic polymer sheet, comprising controlling the discharge electrode to an optimal position by moving the discharge electrode while maintaining a constant distance from the surface of the moving cooling body.