GB2092266A

GB2092266A - Treater Roll

Info

Publication number: GB2092266A
Application number: GB8133274A
Authority: GB
Original assignee: El Paso Polyolefins Co
Current assignee: El Paso Polyolefins Co
Priority date: 1981-01-30
Filing date: 1981-11-04
Publication date: 1982-08-11
Also published as: DE3202766A1; ES8302371A1; IT8219307A0; JPS57139128A; GB2092266B; SE8200514L; IT1149480B; NO814380L; ES509193A0; FR2499324A1

Abstract

A roll used in apparatus for treating plastic film in a corona discharge employs two concentric, electrically conductive cylinders (1) and (4) with dielectric material filling the space (6) between the two concentric cylinders. <IMAGE>

Description

SPECIFICATION Treater Roll This invention relates to an improved backing drum or roll for supporting plastic film and its use during electrical treatment thereof, e.g., during corona discharge treatment of plastic films to improve adherence of inks, adhesives, etc. to the surface thereof.

The conventional backing drum or roll used in such treatments consists of an electrically conductive cylinder mounted on a concentric shaft and having a continuous coating of electrically insulating material on its outer surface which makes actual contact with the plastic film being carried thereby during said treatment.

However, none of the insulating coatings used for this purpose has proved entirely satisfactory since glass and refractory ceramics are very expensive and subject to cracking and spalling due to inherent brittleness while most of the polymeric coatings soon deteriorate in the corona discharge environment, especially due to the actions of heat and of ozone and other corrosive vapors generated in the discharge and due to the abrasiveness of the treated plastic film.

It is therefore, an object of the present invention to provide an improved treater roll, which can operate for significantly longer periods of time before the electrically insulating material needs to be replaced.

Another object of the invention is to provide an economical method of treating plastic film to improve the surface tension thereof.

The Invention The backing drum-or roll of the present invention is comprised of an electrically conductive outer cylinder for support of the plastic film, mounted on a central shaft an electrically conductive inner cylinder in concentric alignment with and spaced from said outer cylinder, and a dielectric layer positioned in the space between the inner and outer cylinders.

Brief Description of the Drawings Figure 1 is a cross sectional view of a suitable embodiment of a treater roll.

Figure 2 is a schematic diagram depicting the use of the treater roll in a corona discharge treatment of plastic film.

The invention will be described in greater detail with reference to the drawings.

In Figure 1, depicting one end section of the treater roll there is shown an electrically conductive inner cylinder 1, which is fabricated from any suitable metal which does not need to be corrosion resistant, since the cylinder will not be exposed to the corona discharge environment.

Because of low cost and low-weight, aluminum is a preferred material of construction this component. The thickness of the cylinder 1 can range from about 0.25 to about 1 inch. It is suitably mounted on the shaft portions 2 by means of the arrangement shown in Figure 1, although a variety of other mountings are also possible. In the depicted embodiment each end of the cylinder 1 is mounted, e.g., is shrink fitted, onto a cylindrical header 3 constructed from an electrically conductive metal, such as aluminum or any other metal that may have been used for cylinder 1. The headers 3 provide structural stability to the roller and true alignment to the central shafts, onto which the headers are mounted, advantageously by shrink fitting.

Spaced from the inner cylinder 1 there is located an outer cylinder 4, which is constructed from a corrosion resistant electrically conductive material such as stainless steel or from other suitable alloy steels. The thickness of the outer cylinder can range from about 0.250 to about 0.75 inches. The space 6 between the inner cylinder 1 and outer cylinder 4 is occupied as completely as possible by an electrically insulating material having sufficiently high dielectric constant and high dielectric strength to withstand the high potentials necessary during the discharge treatment. The distance between the inner and outer cylinder, which is the thickness of the dielectric material, is maintained between 0.030 and about 0.150 inches, preferably between about 0.080 and about 0.125 inches.

insulating end caps 7, anchored to the headers 3 by means of screws 8 (two shown of the eight used in the embodiment depicted in Figure 1) serve to protect the interior of the roller against the corrosive action of ozone and to support the central shaft without causing electrical shorts.

Teflon is a suitable material of construction for the end caps, however, many other insulating materials of sufficient structural strength may be used for this purpose with equal effectiveness.

The outer cylinder 4 is anchored at each end to insulating head caps 7 by means of screws 9 (one shown of eight used in the embodiment of Figure 1).

Referring back to the insulating in space 6, suitable materials therefor having the desired dielectric properties include epoxy, combinations of fibreglass with expoxy, Hypalon, Teflon, polyester, silicon rubber (raw or processed) silicate or ceramic particular materials. The dielectric constants of these insulation materials typically range from about 2.5 and about 5 and the dielectric strength from about 250 to about 500 volts/mil. The insulation can be achieved by a variety of techniques depending upon the nature of the dielectric material. For instance, powdery inorganic materials are poured into the space after assembly of the components of the treater roll. Similarly, viscous fluid materials can be poured or injected into the space after assembly.

Alternatively, prefabricated sleeves of the dielectric insulator can be pulled over the inner roll before installation of the outer cylinder.

Similarly, materials which have to be sprayed or painted onto a surface before curing, are applied to the entire outer surface of the inner cylinder.

Fibreglass reinforced epoxy coatings are advantageously applied by first winding glass filament around the inner cylinder and then spraying the epoxy material to fill the voids between the filaments.

Whichever technique is used to install insulating layer 6 air entrapment is the insulation should be avoided as much as possible, or problems with arcing will occur in those locations where insufficient quantity of dielectric material is present. Thus, care should be taken to avoid formation of air bubbles under sleeve coatings and in sprayed and painted coatings. A preferred method for installing the outer cylinder 4 onto the insulation coated inner cylinder is by shrink fitting method, thereby minimizing entrapment of air between the insulation and the outer cylinder. If the insulation composition is a hard material, such as epoxy or glass filled epoxy, it is of additional advantage to grind the surface of the insulation to a smooth finish after application to the inner cylinder.The surface of the outer cylinder 4, after assembly, is preferably ground to as smooth a finish as possible.

The use of the treater roll of Figure 1 in corona discharge treatment of plastic film is shown in Figure 2. The plastic film 10, guided by idler rolls 1 1 and 12, is passed over the treater roll which is grounded by a grounding conductor 13 attached to shaft 2. At 14 there is shown an electrode, which is electrically connected to a suitable high frequency, high voltage power source. The electrode is spaced from the treater roll and is positioned in parallel to the treater roll axis thereby establishing a uniform air gap between the electrode and the film passing over the roller.

The spacing is usually maintained below about 0.25 inches and preferably between about 0.02 and about 0.06 inches. The potential between the electrode and the treater roll should be maintained between about 3000 and about 30,000 volts and the treatment is typically carried at a frequency of from about 0.6 to about 25 KHz.

In a specific example of a treater roll essentially as depicted in Figures 1 and 2, the overall length of the roll was 65 inches, and the outside diameter 6.5 inches. The inner cylinder 1, which was fabricated from aluminium, has a wall thickness of 0.125 inches. The thickness of the insulation (fibreglass reinforced epoxy) completely filling space 6, was 0.100 inches and the thickness of the outer cylinder 4, which was fabricated from stainless steel, was 0.125 inches.

A variety of plastic film materials may be treated by the corona discharge treatment of this invention including polyolefins such as polyethylenes, polypropylenes, polybutene-1 and copolymers of two or more olefins having from 2 to 8 carbon atoms. Other film plastics include polystyrene, polyvinylchoride, vinylchloride copolymers, polyamides and others. It should be understood that the terms "plastic" and "polymer" used herein includes homopolymers, copolymers, terpolymers, block copolymers laminates and the like. The thickness of the film is generally maintained between about 0.2 to about 20 mils.

The advantages of the present invention are many. Incidents of burnouts and roll failures are significantly reduced and line speeds can be increased without causing any problems due to the required higher power requirements.

It should be understood that various modifications and variation may be made to the treater roll and the process as described without departing from the scope of this invention, which is defined in the appended claims.

Claims

1. In an apparatus for corona discharge treatment of plastic film a treater roll which comprises: an electrically conductive outer cylinder for support of the plastic film; mounted on a central shaft an electrically conductive inner cylinder in concentric alignment and spaced from said outer cylinder, and a dielectric material positiQ,ned in the space between the inner and outer cylinders.

2. The apparatus of claim 1, wherein the thickness of the dielectric material is between about 0.030 and about 0.150 inches.

3. The apparatus of claim 1, wherein the dielectric constant of the dielectric material is between 2.5 and about 5 and the dielectric strength is between about 250 and about 500 volts/mil.

4. The apparatus of claim 1, wherein the treater roll at each end is provided with insulating end caps.

5. In a process for producing plastic film of improved surface adherence to coating compositions by passing the film through a corona discharge the improvement which comprises establishing the corona discharge between an electrode and the grounded treater roll of claim 1.

6. Apparatus for corona discharge treatment of plastic film constructed and arranged to operate substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

7. A process for producing plastic film using the apparatus of any preceding claim and substantially as hereinbefore described with reference to the accompanying drawings.