JPH0346297B2 - - Google Patents

Description

[Detailed description of the invention]

<Industrial Application Field> The present invention relates to a method for manufacturing a thermoplastic resin film by electrostatically pinning a thermoplastic resin melt-extruded into a film from a die onto a cooling drum to efficiently cool the thermoplastic resin. <Prior art and its problems> When manufacturing thermoplastic resin film, an electrostatic charge is applied to the molten film extruded from a die, and the film is electrostatically adhered to a grounded cooling drum to improve cooling efficiency. The so-called electrostatic pinning film forming technique is well known. By the way, in the conventional electrostatic pinning method, a molten film is run between a needle electrode or a wire electrode and a cooling drum serving as a counter electrode, and a high voltage is applied to the electrode. Electrostatic charges are deposited on a film in a certain molten state, but if the distance between the electrode wire (or needle electrode) and the film (or the distance between the electrode and the counter electrode) is not kept constant, the density of the deposited charges will decrease. This often results in mottling and unwanted or damaging discharges on the film. In the case of electric wire electrodes (hereinafter referred to as wires), the factor that makes such electrostatic pinning unstable is the vibration of the electric wire. For example, when the wire vibrates, periodic film thickness unevenness corresponding to the vibration period occurs in the product film, resulting in an unavoidable decrease in the yield of the product. In order to produce good products, it is necessary to prevent this wire vibration from occurring. The cause of this wire vibration is not clear, but it is generally thought to be caused by electrical force generated in the wire, surrounding mechanical vibrations, and external disturbances such as wind, and is associated with the speeding up and widening of recent film forming technology. Wire vibrations are becoming more common, and solving this problem is becoming more difficult. It is known that one way to solve this problem is to apply as high a tension as possible to the electrode wire, but in reality, if the tension is too high, there is a risk of the wire breaking, and if the wire breaks, it will cause a huge amount of damage such as a loss of operation stoppage. This will cause damage. Therefore, it is unavoidable to form a film in a low tension range without fear of wire breakage, but this low wire tension condition is extremely disadvantageous for wire vibration. Conventional thermoplastic resin film forming equipment fixes one end of a wire and applies tension to the other end with a spring, screw, weight, or cylinder using compressed air. There is no means to directly measure the tension applied to the wire. Therefore, the tension of the wire can be determined by the amount of extension of the spring mentioned above, the amount of tightening of the screw,
It will be controlled based on the weight of the weight, compressed air pressure, etc. However, in reality, the above-mentioned alternative properties cannot be said to be sufficient substitutes for the actual tension of the wire, and furthermore, there are variations in the alternative properties, so
If you try to maintain a high tension, unexpected tension may be applied and the wire may break. Also, avoid setting the tension too low to avoid wire breakage.
Even if you intend to set the tension to an appropriate level, the tension may be low, and wire vibration will occur. <Object of the invention> The object of the invention is to avoid wire breakage while
To provide a method for producing a thermoplastic resin film, in which the electrostatic pinning efficiency is increased by adjusting the tension of a wire under as high a tension as possible, and the thermoplastic resin melt-extruded from a die into a film is efficiently cooled. <Structure of the Invention> The present invention involves running a molten film made of a thermoplastic resin extruded from a die between an electrode made of a metal wire and a counter electrode made of a cooling drum, and applying a high voltage to the electrode. In the method for producing a thermoplastic resin film, the tension of the wire is measured and the tensile strength of the wire is determined to be 80 to 98% of the breaking strength of the wire. This is a method for producing a thermoplastic resin film characterized by adjusting the tension within a range. The present invention will be explained below. In the present invention, the thermoplastic resin forming the film includes all resins that can be formed into a film. Examples of these resins include polyvinyl chloride, polyvinylidene chloride, polypropylene, polyethylene, and polyethylene terephthalate. Next, an electrode consisting of a wire (for example, a needle electrode,
In this method, high-voltage static electricity is applied to a wire electrode, etc.), and a cooling drum that casts the film is used as a counter electrode (usually grounded) to bring the molten film into close contact with the static electricity. If a means for measuring wire tension is added, then almost any known electrostatic pinning device can be applied. A feature of the present invention is that the tension of the wire under high voltage is constantly measured during operation, and the actual tension is kept as high as possible within a predetermined range of the wire (tolerable range from the viewpoint of breakage). It must be adjusted and maintained with high precision. The tension adjustment of the wire is 80-98%, preferably 90-95% of the breaking strength of the wire. The method for applying tension to the wire is to fix one end of the wire, provide a tension adjustment means at the other end, and operate this means. A tension measuring means (tension meter) is provided between the wire support on the other end side and the tension applying adjustment means. As the tension measuring means, known means such as a spring (spring scale) or a strain gauge can be used. It is necessary to interpose an insulating member between the wire and the tension measuring means or the tension applying adjusting means to prevent the electricity applied to the wire from leaking. Further, as the tension applying and adjusting means, known means such as an air cylinder connected to an air pressure regulating valve, a spring that can adjust the amount of extension, and a weight that can increase or decrease the amount of weight can be used. The wire tension can be adjusted manually while checking the display on the tension measuring means. It is also possible to extract the tension as an electrical signal and automatically adjust the cylinder pressure (hydraulic pressure, air pressure, etc.) to adjust the wire tension. The wire tension can be adjusted manually or automatically in ways other than the above examples, and can be easily adjusted to within ±3% of the target value tension within the tension adjustment range described above.
High precision adjustment within 1% is also possible. Steel wire (piano wire) is often advantageously used as the material for the metal wire used as the electrode, but other conductive materials can also be used. In the present invention, the most important point is that the electrode wire maintained at a high tension can avoid vibration induction due to rotation and vibration of the film forming apparatus, and that this high tension can be easily adjusted. <Effects of the invention> a. Since the actual wire tension during film formation can be controlled with precision, it is possible to operate at a high tension close to the upper limit of allowable breaking strength, making it difficult for wire vibration to occur and preventing periodic thickness irregularities. The occurrence of defective products can be prevented. b Eliminates wire breakage due to excessive tension and associated loss of operation. <Examples> Examples of the present invention will be described below with reference to the drawings. FIG. 2 is a schematic side view of a thermoplastic resin film manufacturing apparatus. The film-like melt 40 melt-extruded from the die 10 is cooled and solidified on the surface of the cooling drum 30. During this film formation, the wire 20 is connected to a high voltage generator (not shown) to maintain a high voltage. As a result, a high charge is dielectrically deposited on the film 40, which is brought into close contact with the cooling drum serving as the counter electrode. In the present invention, the wire 20 is fixed at one end at a fixed end 26 as shown in FIG. 1, and the other end is connected to the tensioning adjustment device 24 through a wire support 28. A tension measurement means 22 is interposed between the other end of the wire and the tension adjustment device. The joint between the other end of the wire and the tension measuring means is electrically insulated. In the stretched state of the wire shown in Figure 1, when we investigated the variation in the actual tension when the tension was set using the conventional tension substitution characteristics, we found that it varied by up to ±15% of the target value when the tension substitution characteristics were the same. . On the other hand, when the wire was stretched paying attention to the indication on the tension meter, the variation in actual tension was accurately kept within ±1%.

[Table] From the above, electrostatic pinning enables stable film-forming work by precisely adjusting the tension of the wire, suppresses the occurrence of defective products due to wire vibration, and prevents unexpected breakage of the wire. It can be seen that this can be avoided and production efficiency and work efficiency can be improved.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing a state in which the wire of the present invention is stretched, and FIG. 2 is a schematic side view showing a film forming apparatus. In the drawing, 10 is a die,
20 is a wire, 22 is a tension measuring means, 24 is a tension adjustment device, 30 is a cooling drum, and 40 is a film.

Claims (1)

[Claims] 1 A molten film made of thermoplastic resin extruded from a die is run between an electrode made of a metal wire and a counter electrode made of a cooling drum, and charges are deposited on the film by applying a high voltage to the electrode. A method for producing a thermoplastic resin film in which the film is electrostatically brought into close contact with a cooling drum and cooled, wherein the tension of the wire is measured and the tension is adjusted within a range of 80 to 98% of the breaking strength of the wire. A method for producing a thermoplastic resin film characterized by: