DE2120397A1 - Removal of static charges from plastic film - Google Patents

Abstract

Rolled film or woven thermoplastic sheet material is passed in a continuous belt below an enamelled wire at high voltage, e.g. 2 - 8 kV at 50 - 2000 Hz, and earthed rollers so that a continuous silent discharge of the electrostatic charges built up during prodn. takes place. The method is superior to the corona technique in that the surface of the material is not damaged.

Description

concerning:

"Method and Apparatus for Eliminating; the Static Electricity of Plastic Films" .

The invention relates to a method and an apparatus, that (which) is intended to reduce the electrostatic surface charge of films, foils or fabrics thermoplastic polymers that are used during their processing and when they are wound into rolls or when they are unwound occurs to be eliminated completely.

To remove the static electricity that remains between the surfaces of fabrics made of synthetic polymers, various chemical and physical means and methods have been proposed. the physical methods are generally based on the principle of ionization of the air in the vicinity of the places where

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the material is electrically charged, so that a large numbers of positive and negative charges are created in the space that the "ionizer" of the electrically charged substance separates. In practice this has led to the creation of two types of devices: Those that rely on electrostatic induction and consist of rows of grounded metal tips, and those in which the air either through radioactive substances or through the application of an increased voltage ionized on metal tips, creating an ionizing electric field.

In addition, there exist numerous devices which rely on ionizing fields of high intensity lead to electrical light discharges. These work on the surface of the polymer films and create active centers there, which play the role of chain initiators for the formation of graft polymers can play in order to initiate the polymerization of various monomers or to create a microporosity on plastic surfaces, which increases the adhesion of these surfaces various substances or their affinity for printing inks and other dyes is improved.

However, there is still no known simple and inexpensive device, which effectively and quickly dissipates the electrostatic charge and, in contrast to known devices, in which the corona effect is used, does not attack the surface of the substances to be treated itself. task the invention is therefore the development of a method and a convenient to use and safety regulations corresponding devices with the help of which one can quantitatively eliminate the electrical charge, in particular when winding and peeling off films, foils or fabrics

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from thermoplastic polymers, as well as in the manufacture of metallized plastic films, such as those used for manufacture used by capacitors occurs.

The inventive method consists in that in the vicinity of the material to be treated with the help of at least a coated wire held under high tension, placed parallel to the substrate and above the grounded wire Conductors are provided, causing a silent electrical discharge.

Under 'coated or lacquered wire' here is anything to understand wire-shaped part made of a conductive material, the surface of which is covered with a thin layer of a dielectric substance is coated - for example, lacquered copper wire - which causes the at each point between the wire under tension and the material to be treated occurring current discharge (courant d'effluve) im desired senses can be influenced.

Any metal with good electrical conductivity, such as copper, iron, a metal alloy, etc., can be used as the material for the thread provided that the wire to be produced therefrom has a sufficiently smooth surface and its mechanical strength is so great that it does not sag and vibrate over the surface to be treated can be stretched. In practice, one chooses the diameter of the wire as small as it is with regard to the subject in question Material and the mechanical stress to which it is subjected. The diameter can therefore are generally between 0.01 and 1 mm.

The coating material, i.e. the varnish, is used among known ones mineral and / or organic dielectric materials

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'OFUaiMAL iNSPECTED

selected. Plastic lacquers or, if necessary, with the usual Coatings with added fillers, e.g., polyesters, polyurethanes, epoxy resins, polyamide resins, polyimide resins, etc., are general well suited. The thickness of the top coat depends on the insulating materials applied and the diameter of the Wire and is usually on the order of 0.01 to 0.1 mm.

The tension under which the wire is held is an alternating voltage, the amplitude of which depends on the diameter of the wire used. The smaller the diameter of the wire, the smaller the amplitude. The value in practice fluctuates between 2,000 and 8,000 volts. The voltage must have a frequency higher than the usual network frequency. The frequency can practically be between 50 and 2,000 Hz without an upper one Really set the limit.

The distance between the wire and the plastic film to be treated is generally between 1 and 10 mm, however, depends largely on the intensity of the current discharge and the speed at which the film is peeled off will.

As already mentioned, according to the invention in the vicinity of the Wire earth conductor provided and arranged over this at such a distance that the majority of the Field lines close again without passing through the surface of the plastic film to be unloaded.

The implementation of the method according to the invention is extraordinary simple: it is enough between the film to be treated, which is continuously peeled off, and the one below

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A wire that is under voltage and located close to an earthing system maintains a regular discharge process to keep its easily controllable strength (amplitude) on the one hand large enough to allow the quantitative discharge of the film, on the other hand small enough so that the surface of the film is not damaged. The peeling speed of the plastic film depends of course on the frequency of the high voltage applied to the wire; it can for example be between 0.5 and 4- m / sec if the frequency is between 50 and 700 Hz lies and can reach at least 5 m / sec at a frequency of the order of 1 500 Hz. The length of the under The wire under tension preferably corresponds to the width of the material to be discharged. Otherwise it can be useful to arrange several coated wires parallel to each other over the material, which is a special Embodiment of the invention represents. According to another embodiment, two or more wires be arranged on different sides of the material to be unloaded, either facing each other or not.

The invention is explained in more detail with reference to the drawing, in which one embodiment of the device according to the invention and the method is shown in perspective.

The electrostatically charged plastic film 1 becomes continuously pulled through under the enamelled wire 2> over the two grounded wires running parallel to this Metal rods 3 are arranged, which are called "close holes" serve .. The wire 2 is connected to a resistor 4 via a High-voltage generator 5 connected to an alternating voltage gives away. When the device is put into operation, the

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ORfGJNAL INSPECTED

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Tension increased, except for the entire length of the wire a completely regular discharge, which is only visible in total darkness, occurs, which then occurs throughout the entire period Peeling of the film is kept constant.

A convenient means of determination well known to those skilled in the art the efficiency with which the electrostatic charge is removed consists in that the good, e.g. the film, after the treatment, dusted with a powdered mixture of red lead and sulfur (H. Bertein, Eevue generale d'Electricite, pp. 461 to 474 (1960)). An insufficient one Discharge is then shown by the fact that red lead grains at the negatively charged points of the surface and Sulfur powder adhere to the positively charged points, while no powder whatsoever is attached to a volatile discharge remain.

The method according to the invention and the associated device have been successfully used for the treatment of films made of polypropylene, made of polycarbonate with a thickness of 2 / µm and more and of metallized polyterephthalate filings in one Strength from 2.5 to 6yunt applied * It was applied continuously worked, being a single thin, old one being a filler containing polyurethane varnish coated copper wire at a distance of about 6 mm over the continuously peeled film was stretched. At a voltage of 4,500 V. and at frequencies from 100 to 7OO Bz the entire electrostatic charge of the films at a continuous take-off speed of 1 to 4 m / sec.

PATENT CLAIMS:

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Claims (8)

PATENT CLAIMS Λ 1)) Procedure for eliminating the electrostatic charge on the surface of continuously moving, web-shaped material, such as films, foils or fabrics made of thermoplastic materials Polymers, characterized in that one near the surface of the goods a silent electrical discharge with the help of at least one under high voltage held, conductive enamelled wire generated in a plane parallel to the surface to be treated is arranged and above which grounded conductors are arranged. 2) Method according to claim 1, characterized in that one with a high voltage of 2,000 to 8,000 V and operates at a frequency of 50 to 2,000 Hz. 3) Device for performing the method according to claim 1 or 2 with a transport device for the Web-shaped material to be treated, characterized by at least one electrically conductive, coated with lacquer Wire (2) arranged parallel to a surface of the web-shaped material (1) and connected to an alternating high-voltage generator (5) is connected and by parallel to the wire (2) and with respect to the goods (1) above this arranged conductors (3) 4) Device according to claim 3 *, characterized in that over the item to be treated (1) only a coated wire (2) and the grounded conductor (3) are arranged. 109847/1230 ORiGiNAL INSPECTED 5) Device according to claim 3 »characterized in that above and below the to be treated Well (1) at approximately the same distance from this one coated wire (2) is arranged. 6) Device according to one of claims 3 to 5 _S, characterized in that the wire (2) consists of a metal or a metal alloy and has a diameter of 0.01 to 1 mm. 7) Device according to one of claims 3 to 6, characterized in that the coating of the Wire (2) made of a dielectric, inorganic or organic material, in particular made of a plastic varnish an optionally filled high polymer ", 8) Device according to one of claims 3 to 7 »thereby characterized in that the distance between the wire (2) and the item to be treated (1) is 1 Ms 10 mm, in such a way that the regular silent discharge does not penetrate the thermoplastic material " 72XX1V 109847/12