US3419489A

US3419489A - Corona treating apparatus having an electrode with an adjustable width

Info

Publication number: US3419489A
Application number: US547287A
Authority: US
Inventors: Jr John T Delaney
Original assignee: Ethyl Corp
Current assignee: Ethyl Corp
Priority date: 1966-05-03
Filing date: 1966-05-03
Publication date: 1968-12-31
Anticipated expiration: 1985-12-31

Description

D 3 1968 J. T. DELANEY, JR 3,

CORONA TREATING APPARATUS HAVING AN ELECTRODE WITH AN ADJUSTABLE WIDTH Filed May 3. 1966 Sheet of 2 Dec. 31, 1968 J- T. DELANEY, JR 3,419,489

CORONA TREATING APPARATUS HAVING AN ELECTRODE WITH AN ADJUSTABLE WIDTH Filed May 5. 1966 Sheet 2 of 2 FIG.3

FIG. 2

FIG. 4

\ I i i l i i I l I i i i i United States Patent 3 419,489 CORONA TREATING APPARATUS HAVING AN ELECTRODE WITH AN ADJUSTABLE WIDTH John T. Delaney, Jr., Pattenburg, N.J., assignor to Ethyl Corporation, New York, N.Y., a corporation of Virginia Filed May 3, 1966, Ser. No. 547,287 6 Claims. (Cl. 204312) This invention relates to an apparatus for treating plastic materials that are in sheet or film form. More particularly, this invention relates to an adjustable length treater electrode assembly for use in an apparatus for treating plastic film by means of an electrical effect produced by the passage of electrical energy between two spaced-apart electrodes.

Untreated surfaces of certain plastic materials, e.g. polyethylene, cannot normally be satisfactorily imprinted with inks or adhesives using conventional techniques unless the surfaces are treated prior to application of the ink or adhesive. The preferred present day method of treating the surface of a plastic material to enhance its receptivity to printing inks or adhesives is to expose the surface to an electrical effect produced by the passage of electrical energy between spaced-apart electrodes. The most common treating apparatus utilizes a high frequency, high voltage discharge between the electrodes to produce a Corona or glow discharge. The apparatus commonly in use today includes a rotatable cylindrical electrode which is usually connected to the ground lead of the electrical power supply. The other lead from the electrical power supply is usually connected to a high voltage electrode which customarily has the form of a relatively narrow or knife edge longitudinal bar fixedly positioned parallel to and spaced a short distance from the rotating grounded electrode. An exemplary bar electrode is described in US. Patents 2,882,412 and 2,935,418.

The shape of the upper electrode has a great efiect upon the efiiciency with which the film surface is treated, upon the amount of power consumption in treating the film, and upon the maintenance required to keep a treating apparatus in operative condition. Most electrical treating apparatuses have the film in contact with the rotatable cylindrical electrode. It has been found that for most satisfactory service the grounded rotatable cylindrical electrode will be provided with a coating of a dielectric material on its cylindrical surface. Various thermoplastic materials have been used for the dielectric coating such as polyvinyl chloride, and the polyester film sold under the tradename Mylar. Also, these electrodes have been coated with glass by sintering directly onto the cylindrical surface. A preferred material in common use for forming the dielectric coating is Hypalon, a chlorosulfonated polyethylene.

A problem encountered in electrical treating of plastic film has been the damage caused to the dielectric coating on the large cylindrical electrode by arcing between the ends of the bar electrode and the rotating cylindrical electrode outside the area covered by the sheet of plastic material which is being treated on the rotating cylindrical electrode. When using a bar electrode that is wider than the film being treated, the electrical discharge between the bar and cylindrical electrode is more intense at the end portions of the cylindrical electrode which are not covered by the film being treated. Initially, the film receives sufficient treatment when the Hypalon covering on the cylindrical electrode is relatively new and still in good condition. However, when the heavy electrical discharge continues for some time at the end portions of the electrodes, the Hypalon covering on the ends of the cylindrical electrode undergoes a deterioration from the heavy electrical discharge and as a result loses its insulating properties.

This causes a further increase in the flow of electrical energy at the end portions of the electrodes which decreases the electrical treatment of the film. The flow of electrical energy to the ends of the electrodes continues to build up until arcing occurs, i.e. until substantially the entire flow of electrical energy occurs outside the area of the cylinder covered by the film being treated. Sometime the electrical resistance of the Hypalon fails suddenly and then all of the flow of electrical energy occurs in the end area of the electrodes outside of that covered by the film being treated. This is commonly known as burn-out and when it occurs the machine operator must shut down the treating line and have the Hypalon covering on the cylindrical electrode replaced. To minimize this damage, one alternative has been to cover the exposed area, i.e. that area on each end of the electrode which is not covered by the film being treated, of the cylindrical electrode with additional dielectric material such as plastic impregnated glass cloth, sheets of Mylar film, etc. The other altemative used in preventing this damage has been to change the high voltage bar electrode each time the width of film being run through the treater is changed. This is done in order to keep the high voltage or treater bar electrode of a length equal to or slightly less than the width of the film being run through the treating apparatus. Since the spacing between the high voltage bar electrode and the rotating grounded cylindrical electrode is critical, much time had to be spent in adjusting the new electrode when it was replaced. Additionally, the down time caused by changing and adjusting the bar electrode resulted in a substantial loss of production of film in those cases where the treating apparatus was used to treat the film as it Was produced by an extruder. Thus, there has been a need in the filmtreating art for an adjustable length electrode which could be readily adjusted to provide for effective treatment of a number of different width films on an electrical filmtreating apparatus without the necessity of replacing the high voltage electrode.

Therefore, it is an object of the present invention to provide an improved electrode assembly for a film-treating apparatus which electrode can be adjusted in length to accommodate a wide variety of plastic films having different widths.

Another object of the present invention is to provide an apparatus which employs an adjustable electrode which can be economically fabricated from readily available materials.

Still another object of the present invention is to provide an apparatus embodying an adjustable electrode assembly which will effectively treat plastic material without damaging portions of the treating apparatus.

These and other objects of the present invention are accomplished, in general, in an electrode assembly which includes a central tubular member that is provided with, at least on a part of its exterior surface, a plurality of substantially transverse ridges. An end tubular member is slidably mated with each end portion of the central tubular member, the end tubular members being provided with, at least on a part of their exterior surfaces, a plurality of substantially transverse ridges.

In one embodiment of the present invention, the ridges on the central tubular member are provided by helical threads which are formed in the exterior surface of the member. The ridges on the end tubular members are pro vided by a helical spring carried by each one of the end tubular members.

In another embodiment of the present invention, the ridges on the central tubular member are provided by a helical spring carried by this member and the ridges on the end tubular members are provided by helical threads formed in the exterior surface of each of the end members.

The foregoing and other objects of the present invention will become apparent from the following description taken in conjunction with the accompanying drawings wherein:

FIG. 1 is an elevational perspective view of a film-treating apparatus including the adjustable length electrode assembly of the present invention;

FIG. 2 is an elevational view of one embodiment for the adjustable length electrode assembly of the present invention, with portions broken away to more clearly show the construction;

FIG. 3 is a view along the line 3-3 of the electrode assembly shown in FIG. 2;

FIG. 4 is an elevational view of another embodiment of the adjustable length electrode assembly of the present invention, with portions broken away to more clearly show the construction; and

FIG. 5 is an elevational perspective view of a portion of a metal helix suitable for use in the construction of the adjustable length treater electrode assembly.

Referring now to FIG. 1, the apparatus for treating plastic film, designated generally by the numeral 10, is adapted to electrically treat a sheet of plastic material 11, which may be polyethylene, polypropylene, or any other plastic material which it is desired to treat in order to change the surface characteristics so as to improve the adhesion of inks, adhesives and the like to its surface. While reference is made to a sheet of film, the film may be in the form of a thin wall flattened tube as it is drawn from the nip rolls of a conventional tubular die blown film extrusion assembly. Also, the film may be fed from a preformed roll. The film passes over a rotatably mounted cylindrical electrode 12 which is carried on shafts 13-13, received in openings provided in spaced-apart support members 14-14. Electrical contact finger 15 presses on one end of shaft 13 and has connected thereto electrical lead 16 which in turn leads to the grounded side of an electrical power supply for energizing the treating appa ratus (not shown).

Preferably, the cylindrical rotatable electrode 12 is covered With a dielectric material such as polyvinyl chloride, the polyester film sold under the tradename Mylar, or Hypalon, a chlorosulfonated polyethylene or other suitable high dielectric material.

A top cross-support member 17 is attached to the upper ends of vertical support members 14 and extends therebetween. The adjustable length electrode assembly, designated generally by the numeral 18, is suspended from the top cross member 17 by means of threaded bolts 19-19 attached thereto. The electrical lead 20 is connected to one of the bolts 19 and in turn connected to the high voltage side of the power supply (not shown). If desired, the top cross-support member 17 may be made from a high dielectric material such as plastic, i.e. Plexiglas, Bakelite or other good electrical insulating plastic material, or optionally the bolts 1919 may be insulated by means of suitable insulating washers and sleeves (not shown) when it is desired to make top cross member 17 from metal or other conducting material.

Referring now to FIG. 2 of the drawings, one embodiment of the adjustable length electrode 18 of the present invention utilizes a central portion composed of a tubular member 21. This tubular member has a plurality of substantially transverse ridges 22 provided on the exterior surface thereof. While these ridges 22 may be formed by providing annular grooves in the exterior surface of central member 21, a more convenient way of preparing the ridges 22 is by providing a pattern of spiral ridges in the surface of the central member by threading the exterior surface of tube 21 with a common pipe threading apparatus. In such case the ridges 22 are helical in pattern and extend from one end of central member 21 to the other end thereof. It has been found that provision of uniformly spaced ridges 21, either in the form of annular rings or a helix, provide uniform distribution of the electrical discharge between the adjustable length electrode 18 and the rotatable cylindrical electrode 12. Projecting from the upper surface of central tubular member 21 are two mounting bolts 19-19. These bolts are attached to tubular member 21 by means of nuts 23 which are welded to the upper surface of central tubular member 21.

As can be seen more clearly in FIG. 3, each end of central tubular member 21 is provided with a slot 24 therein. A rectangular lug 25 is Welded to central tubular member 21 immediately adjacent to the slot 24 in each end thereof. Each lug has a threaded opening 26 therein which receives thumb screw 27. By means of the foregoing arrangement, the inside diameter of the portions of tubular member 21 can be changed to fixedly position the adjustable end tubular members 2828.

An end tubular member 28 is slidably received inside each end of central tubular member 21. By means of the lugs 2525 and thumb screw 27 in each end of tubular member 21, the end tubular members 28 can be locked in position with respect to a central tube 21. The outer end of each tubular member 29 has an arcuate shaped surface 29 which permits easy placement of a helical spring 30 carried by each end tubular member 28. One end of the spring 30 is clamped to the end of tube 28 by means of a clamp 31. The other end is attached by a similar clamp 31 to the end of central tubular member 21. Thus, as end tube 28 is slid in or out of central tube 21 the spring 30 contracts or expands to distribute itself uniformly over the surface of tube 28. By loosening thumb screw 27, tube 28 may be pushed into central tubular member 21 or extended therefrom a considerable distance. This provides a wide range of length adjustment for each end of central tubular member 21 whereby the electrode may be quickly changed to accommodate any width of film passing through an exemplary film-treating apparatus as depicted in FIG. 1. The

tubular sections

21 and 28 can be constructed of any suitable metal conductor such as aluminum or brass.

Referring now to FIG. 5, a perspective view of the metal helical spring 30 is depicted. In the form of the spring depicted, the cross-sectional shape of the helix or coil is in the form of a rectangle. In the preferred form of the helical spring 30, all of the coils are in face-to-faoe contact with each other when the spring is under no tension, i.e. a tension Spring is preferred as opposed to a compression spring which has its helical coils separated in a n-o-load position. While the particular form of the helical spring depicted in FIG. 5 utilizes a rectangular cross-sectional area, the invention is not limited to the use of any particular shape for the spring. Coil springs having a cylindrical cross-sectional area are also suitable for use in the adjustable electrode of the present invention. Other forms such as ellipsoidal, triangular, etc. may be used.

Referring now to FIG. 4, a second embodiment of the adjustable length treater electrode assembly of the present invention is depicted. This second embodiment is designated generally by the reference numeral 32. This form of the invention utilizes a central tubular portion 33 having a smooth exterior surface and with a diameter such that it is slidably received within the interior of end tubular members 34-34. The portion of the central tubular section 33 extending within the inner ends of the end tubular members 34 34 is covered by a helical spring 35. This spring may have a construction identical with that described previously for the helical spring 30. The ends of spring 35 are attached by clips 36 to the inner ends of the end tubular members 3434. The inner end of each end tubular member 34 is slotted and provided with lugs 25 in the same manner as shown in FIG. 3 of the drawing for the other embodiment of the adjustable length electrode. Thus, each end tube 34 can be fixedly positioned and locked to the central tubular member 33 to provide an adjustable length electrode of wide length variation. Each end of tubular member 34 is provided with a plurality of transverse ridges 37 similar to those provided in the central member 21 of the embodiment shown in FIG. 2. These ridges may be produced in similar fashion to those of the embodiment shown in FIG. 2, i.e. they may be made by providing annular grooves in the end members 34 or by threading each member throughout its length.

It is important that the outside diameter of the threaded members, whether they be end members or central members, be substantially equal to the outside diameter of the

helical spring

30 or 35 used in either embodiment of the invention. It is essential that the ridges or protuberances of the adjustable electrode, Whether they be provided by helical spring or by screw threads on a particular member be of the same outside diameter to provide a uniform outside diameter overall for the adjustable length electrode. This is necessary in order to maintain the same spacing of the adjustable electrode from the rotating electrode throughout the length of the two assemblies.

In one specific embodiment of the adjustable length electrode constructed in accordance with the present invention as shown in the embodiment depicted in FIG. 2 of the drawings, a drawn aluminum tubing having a length of 18 inches and an outside diameter of 2.250 inches and a Wall thickness of 0.18 inch was used for the central tubular section. This central section was threaded throughout its length on the exterior surface using a standard American pipe thread die which provided eleven threads per inch of length of the tube. The end tubular sections each had a length of 13 inches and were made from drawn aluminum tubing having an outside diameter of 1.875 inches with a wall thickness of 0.058. The helical springs utilized had one hundred turns in each coil. With the end tube members extended their practical maximum length, the overall length of the treating electrode was a maximum of 40 inches. With the end tubular members inserted as far into the central tube as permitted by the compression of the springs carried by the end members, the adjustable length electrode had a minimum length of 26% inches. Thus, using this embodiment of the adjustable length electrode of the present invention, one could treat film having a width of from 26% inches to 40 inches without removing the electrode from the treating apparatus. Additionally, the use of the present electrode avoids having to reset the spacing between the electrode and the lower roll as occurs when one uses a separate electrode for each width of film.

In another embodiment constructed similarly to that described heretofore, the lengths of the various members were proportionately increased but the same diameter tubing and thread size were used for the second embodiment. The helical springs utilized had four hundred and fifty turns in each coil. The second embodiment made according to the present invention had a maximum extendable length of 158 inches and a minimum length when the end sections were fully compressed of 96% inches. Thus, this form of the adjustable length electrode could treat any film having a width from 96% inches up to a maximum film width of 158 inches.

From the foregoing description of the invention, it will be obvious to persons skilled in the art to make modifications thereto. Other modifications are included in the scope and spirit of the present invention as defined by the appended claims.

What is claimed is:

1. In an apparatus for treating a polymeric film in a corona discharge, said apparatus comprising a first electrode and means for supporting the polymeric film adjacent said first electrode, said means including a second electrode and a dielectric material covering said second electrode, and means for supplying an electrical current to said electrode, the improvement wherein said first electrode comprises:

(a) a central tubular member being provided with, at least on a part of its exterior surface, a plurality of substantially transverse ridges; and

(b) at least one end tubular member slidably mated with at least one end portion of said central tubular member, said end tubular member being provided with, at least on a part of its exterior surface, a plurality of substantially transverse ridges.

2. In an apparatus for treating a polymeric film in a corona discharge, said apparatus comprising a first electrode and means for supporting the polymeric film adjacent said first electrode, said means including a second electrode and a dielectric material covering said second electrode, and means for supplying an electrical current to said electrodes, the improvement wherein said first electrode comprises:

(a) a central tubular member being provided with, at least on a part of its exterior surface, a plurality of substantially transverse ridges;

(b) an end tubular member slidably mated with each end portion of said central tubular member, said end tubular members being provided with, at least on a part of their exterior surfaces, a plurality of substantially transverse ridges.

3. In the apparatus of claim 2 wherein said ridges on said central tubular member are provided by helical threads formed in the exterior surface of said member, and said ridges on said end tubular members are provided by a helical spring carried by each of said end members.

4. In the apparatus of claim 2 wherein said ridges on said central tubular member are provided by a helical spring carried by said central tubular member, and said ridges on said end tubular members are provided by helical threads formed in the exterior surface of each of said end members.

5. In the apparatus of claim 2 wherein means is provided to fixedly position each of said end tubular members on said central tubular member.

6. In the apparatus of claim 2 wherein means is provided to mount said electrode in a fixed position relative to a second electrode.

References Cited UNITED STATES PATENTS 3,174,748 3/1965 Roberts et al. 271--8 3,291,711 12/1966 Moyer 204-l 3,294,971 12/1966 Von der Heide 25049.5

FOREIGN PATENTS 1,004,230 11/1951 France.

ROBERT K. MIHALEK, Primary Examiner.