GB2174850A

GB2174850A - Device for the neutralisation of electrostatic charges on packaging material surfaces

Info

Publication number: GB2174850A
Application number: GB08610337A
Authority: GB
Inventors: Gunter Riess; Uto Bohme; Eckhardt Clauss
Original assignee: Nagema VEB
Current assignee: Nagema VEB
Priority date: 1985-05-07
Filing date: 1986-04-28
Publication date: 1986-11-12
Also published as: DE3607840C2; IT8647980A0; JPS61256596A; GB8610337D0; IT1191884B; DE3607840A1; DD237048A1

Abstract

A device for the neutralisation of electrostatic charges, for use in packaging machinery, where the polymer sheets used have a high surface resistance, so that considerable electrostatic charges have to be eliminated. The device comprises an ionisation electrode 6 supplied with a high voltage and having discharge points 14. The earthed counter-electrode 7 is embodied as a metal wire which has a diameter of 1 to 3 mm, and is arranged in the immediate vicinity of the web of packaging material 1 parallel to and on one side of the row of discharge points 14. The distance between the counter-electrode and the discharge points is 5-7 mm, the distance between the counter-electrode and the web of packaging material is 1-2 mm and the distance between the discharge points and the web of packaging material is 4-5 mm. The ionisation electrode comprises several windings of wire over an insulating sleeve on a high voltage metal bar, the ends of the windings extending to form the discharge points. <IMAGE>

Description

SPECIFICATION Device for the neutralisation of electrostatic charges on packaging material surfaces The invention relates to a device for the neutralisation of electrostatic charges. This device is used in particular in the construction of packaging machinery. The polymer sheets which are used there have a high surface resistance, so that considerable electrostatic charges have to be eliminated in connection with the separating and utilising operations required for technological reasons during the packing process.

A solution is known from DE-OS 27 21 370 in which electron emission devices which have capacitor bodies with spray points are used. An insulated conductor extends over the entire length through the capacitor body. The device is surrounded by an insulated casing which is embodied as the near earth. Openings for the spray points are recessed in the casing. Experiments have shown that this device must be assembled on both sides of the web of material in order to achieve a satisfactory effect. This can only be achieved in a few cases in the particular conditions of the construction of packaging machinery.

A device is proposed in DE-PS 959495 which has a metal wire as an electrode. This is surrounded by a slotted metal tube The slot points in the direction of the web of material. An auxiliary electrode is arranged in the vicinity of the web of material in order to accelerate the ion flow in the direction of the web of material. The auxiliary eletrode has the same potential as the web of material. This solution cannot be technically implemented, because the charge on the surface of the web of material fluctuates in polarity and magnitude. The auxiliary electrode has a constant potential, so that a continuous and definite discharge cannot be achieved.

A device is disclosed in DE-OS 2724118 which has points allocated to the spray points as the near earth.

Air is blown into this arrangement by a fan in the direction of the web of material.

This solution has the disadvantage that recom binations of ions occur, because the path from the place of origin to the place of effect is very long.

Furthermore the consumption of material is considerable and the space requirement is great.

All the solutions mentioned have the disadvantage that the small dimensions necessary for the conditions of packaging machinery construction cannot be achieved owing to the design. The proximity of metal parts cannot be avoided. As a result of these unfavourable space conditions no effective air ion isation is formed.

The device described in DE-OS 28 15 117 consists of an electrode which takes the form of a thin wire. A metallic bar is arranged parallel to the electrode as the earth. This solution can satisfy the requirements with respect to space occupied. However, this embo diment is sensitive to mechanical stresses. As a result of the direct application of high voltage there is no shockproof variant. Furthermore, the intensity of the generated ion flow is not sufficient to bring about an effective discharge of the surface of the packaging material.

The aim of the invention is to develop a device for the neutralisation of electrostatic charges which requires little space and operates reliably under the stated conditions.

The object underlying the invention is to develop a device which eliminates a strong and irregularly distributed charge on packaging material surfaces by effective air ionisation, even if the proximity of metal parts is unavoidable and the assembly conditions are restricted.

The object is solved in accordance with the invention in that the counter-electrode is embodied as a metal wire which has a diameter of 1 to 3 mm and is arranged in the immediate vicinity of the web of packaging material parallel to and on one side of the spray points. The distance between the metal wire and the web of packaging material is 1 to 2 mm and the distance between the spray points and the web of packaging material is 4 to 5 mm.

The solution in accordance with the invention has the advantage that the dimensions are very small.

The device can also be installed in the vicinity of metal parts, which in the case of ionisation devices of conventional design was not possible or greatly reduces the effect. The produced ionisation of the air is sufficient to definitely neutralise a packaging material which is electrostatically charged strongly and at differing polarity. Other advantages are the compact construction of the solution and the possibility of good integration directly in the area of critical active positions, preferably of packaging machinery. The embodiment is shock-proof. The invention will be explained in more detail below on the basis of an embodiment.The drawings have the following meaning: Figure 1 Assembly situation for the solution in accordance with the invention Figure2 Basic structure (longitudinal section) of the ionisator Figure 3 Cross-section (Section A-A) according to Fig. 2.

As can be seen from Figure 1, the web of packaging material 1 is fed through the two take-off rollers 2, 3 to the knife 4. The high electrostatic charges are particularly noticeable in a negative sense in this area, because difficulties are experienced in advancing the web of packaging material on the paper table 5. The device in accordance with the invention is therefore arranged at this critical position. It consists essentially of an ionisation bar 6 with spray points 14 and a counter-electrode 7 and is integrated into the paper table 5.

The ionisation bar 6 consists of a high voltage carrying metal tube 8, on which an insulating sleeve 9 is drawn. The windings 10 serving as spray electrodes are arranged on this. In the area of the windings 10 the insulating sleeve 9 is coated with a thin conductive layer 11. A graphite coating is particularly suitable. The high voltage cable 13 is attached at the clamping position 12. The ends of the windings run off at a tangent and take the form of spray points 14. The spray points 14 all point in the same direction. The distance between them is 10 -18 mm and the distance between the spray points 14 and the web of packaging material is 4 - 5 mm. The free point length is approximately 5 - 7 mm. This arrangement is surrounded by a plastic jacket 15 which leaves recesses 16 free for the spray points.

The cavities in this arrangement are lined with a casting resin 17. A near earth in the vicinity of the web of packaging material 1 is arranged as the counter-electrode 7. The counter-electrode 7 consists of a thin metal wire which has a thickness of 1 3 mm stretched parallel to the ionisation bar 6. The distance between the counter-electrode 7 and the web of packaging material 1 is 1 - 2 mm and the distance between the spray points 14 and the counter-electrode 7 is approximately 5 - 7 mm.

The mode of operation ofthe device in accordance with the invention is as follows: an alternating current voltage of 3.9 kV is applied to the high voltage cable 13. An electrical field in which ions are generated forms between the spray points 14 and the counter-electrode 7. As a result of the device in accordance with the invention electrostatic charges of + 10 to t 15 to kV/cm can be reduced to residual charges oft 0.15 to sporadically t 1.8 kV/cm. The take-off speed may be 100 m/min. No charge transfer occurs on the surface of the packaging material, even if low and high electrostatic charges of differing polarity alternate.

The alternation of charged and uncharged positions, referred to as streakiness, thus does not occur.

Claims

1. Device for the neutralisation of electrostatic charges on packaging material surfaces, consisting of a high voltage carrying metal tube which is covered with an insulating sleeve and has several windings of wire of which the ends run off at a tangent, point in one direction and take the form of spray points, whereby the cavities of this arrangement are lined with casting resin, the surface is covered with an insulating layer in which only the openings for the spray points are recessed and an earthed counter-electrode is arranged in the immediate vicinity of the spray points, characterised in that the counter-electrode (7) is embodied as a metal wire which has a diameter of 1 to 3 mm and is arranged in the immediate vicinity of the web of packaging material (1), parallel and on one side of the spray points (14).

2. Deviceforthe neutralisation of electrostatic charges on packaging material surfaces as claimed in Claim 1, characterised in that the distance between the counter-electrode (7) and the spray points (14) is 5-7 mm.

3. Device for the neutralisation of electrostatic charges on packaging material surfaces as claimed in Claim 1, characterised in that the distance between the counter-electrode (7) and the web of packaging material (1 ) is 1-2 mm.

4. Device for the neutralisation of electrostatic charges on packaging material surfaces as claimed in Claim 1, characterised in that the distance between the spray points (14) and the web of packaging material(l) is 4 - 5 mm.

5. A device for the neutralisation of electrostatic charges as claimed in claim 1, substantially as described herein with reference to and as illustrated by the accompanying drawings.