GB2373744A

GB2373744A - Coating a flexible web with a metal

Info

Publication number: GB2373744A
Application number: GB0100389A
Authority: GB
Inventors: Simon David Bennet; Mark Richard Whitnall
Original assignee: Valmet General Ltd
Current assignee: Bobst Manchester Ltd
Priority date: 2001-01-06
Filing date: 2001-01-06
Publication date: 2002-10-02
Also published as: GB0100389D0

Abstract

In apparatus for coating a flexible web under vacuum, the web is fed from an unwind reel 2 to a rewind reel 3 via a process drum 4. The drum 4 is disposed adjacent evaporator means 6 comprising an intermetallic boat or boats 6 to each of which two elementary feeds in wire 6d, 6e or strip form are fed and evaporated in the boat or boats 6. The arrangement provides improved uniformity of coating with better control of wetting and evaporation rate, low power consumption and boat life. The coating material is preferably metallic.

Description

APPARATUS FOR AND A METHOD OF DEPOSITING A COATING ON A FLEXIBLE MOVING WEB The present invention relates to apparatus for and a method of depositing a coating on a flexible moving web.

The demand for higher speed vacuum web metallizers has led to various designs and modifications to optimize process performance parameters. The main factor behind such interest is the highly competitive market for metallizing which continuously pushes towards reductions in cost and improvements in quality. So far most of the work in this area has concentrated on improving line speed by increasing evaporation rate, improving deposition uniformity and reducing heat load on film. For this type of work, a fundamental understanding of the evaporation conditions using intermetallic resistance heated boats is necessary for the final performance of the metallizer. Prior art apparatus for web metallization comprises a row of evaporation boats disposed in the direction of web movement and spaced parallel to one another at equal distances. Patent DE 970 246 discloses apparatus to improve coating uniformity by having evaporators disposed in two or more parallel rows. The rows are offset with respect to each other in such a manner that if viewed from the side, the rows overlap and thus do not allow an evaporation gap to form. U. S. Patent No. 5242500 discloses a row of evaporators aligned with the

direction of web movement and equidistantly spaced from each other. The individual evaporators are offset with respect to one another. Although this arrangement improves coating uniformity, it is not satisfactory for high rate evaporation because of the requirement for a higher supply of energy for evaporating the wire and subsequent high heat load on film.

According to one aspect of the present invention, there is provided apparatus for coating a flexible moving web comprising a housing defining a chamber, means for evaporating coating material in the chamber, means for supplying a flexible web to be coated and means for receiving a coated web characterised in that the means for evaporating comprises at least one evaporation boat and means for feeding two elongate elements of coating material to the boat.

According to another aspect of the present invention there is provided a method of coating a flexible moving web including the steps of supplying the flexible web, feeding two wires of coating material to means for evaporating to evaporate material to be coated onto the web and means for receiving the flexible web coated with evaporated material.

In a preferred embodiment of the invention, the means for evaporating comprises a plurality of evaporator boats each having a dual element feed. The boats are arranged in a plurality of rows, advantageously two rows. The boats of each row are preferably equidistantly spaced and advantageously offset in relation to the boats of the next adjacent row.

There may be more than two element feeds to the or each boat. The element feeds may be wire feeds or strip feeds. In another embodiment the means for evaporating may comprise a single boat having a plurality of evaporator zones each having a two or more element feed (wire or strip). The evaporation zone provided by the boat or boats is disposed transversely to the direction of travel of the web. The or each boat is preferably made of an intermetallic ceramic. This comprises a mixture of ceramics at least one of which is electrically conductive. The means for supplying advantageously comprises an independently driven unwind reel and the means for receiving an independently driven rewind reel. An independently driven process drum is disposed between the two reels. The reels and drum may be operated to drive the web at various speeds under controlled tension.

In order that the invention may be more clearly understood, embodiments thereof will now be described, by way of example with reference to the accompanying drawings in which: Figure 1 is a diagrammatic side elevational view of coating apparatus according to the invention.

Figure 2 is a diagrammatic plan view of a modification of part of the apparatus of figure 1, and Figure 3 is a diagrammatic side elevational view, to a larger scale, of part of the apparatus of figure 1.

Referring to the drawings, the coating apparatus comprises a housing defining a vacuum chamber 1. A winding system for a flexible web to be coated is disposed inside the chamber. The system comprises independently driven unwind reel 2, rewind reel 3 and process drum 4.

Various pulleys guide the flexible web on its journey from unwind reel 2, over process drum 4 to rewind reel 3. These pulleys are referenced 11, 12,13, 14 and 15. The winding system is capable of moving the flexible web at a variety of speeds under controlled tension.

The winding system is conventional. Adjacent the process drum 4 is disposed means 6 for evaporating coating material. These means comprises an evaporator having an electrically heated evaporator boat 6c made of an intermetallic material although other materials could also be used. Intermetallic ceramic material is a mixture of ceramic materials and includes a component which is electrically conductive so that the mixture is partially electrically conductive. A two wire feed feeds coating material in wire form to the evaporator boat. In this particular embodiment, the two wires 6d and 6e are fed from opposite ends respectively of the boat by individual wire feeders 6a and 6b. However, the wires can be fed in side by side arrangement from dual wire feeders as shown in the modification illustrated in figure 2. In this modification the evaporator means comprise two rows of individual intermetallic evaporators 7 and 8. The evaporators comprise electrically heated boats made of intermetallic ceramic although

other materials can also be used. The evaporators in each row are equally spaced and those 7 in one row 1 are offset or displaced with respect to those 8 in the other row and also overlap slightly those in the other row. Each boat is arranged with its longitudinal axis in the direction of travel of the web.

In operation, wires of material to be coated such as aluminium, zinc or copper are fed to the boat or boats to produce continuous evaporation of the material. Meanwhile the flexible web of polymer or other suitable material is fed from the unwind reel 2 over the process drum and to the rewind reel 3 and is thereby coated with the coating material evaporated.

Having a dual wire feed to the or each boat creates two localized dense molten spots in the vicinity where the wires contact the cavity of the or each evaporator. This in turn increases the size of the molten pool which in turn increases the rate of evaporation. When the aluminium or other coating material begins to evaporate power consumption drops by approximately 30% due to current electric flowing through molten aluminium which has higher electrical conductivity than the ceramic material of the boat. Improved uniformity of coating across the width of the web can also be achieved together with better controllability of wetting and evaporation rate, lower power consumption and improved boat life and performance. Furthermore arcing and spitting can be reduced.

It will be appreciated that the above embodiments have been described by way of example only and that many variations are possible without departing from the scope of the invention. For example, wire feeders may be replaced by metal strip feeders. More than two feeders (wire or strip) may be used with each boat. Instead of a plurality of individual boats a single long ceramic electrically conductive trough may be used with a dual feed system in each evaporation zone along the boat. The lengthwise dimension of the boat is disposed transversely to the direction of travel of the web.

I

Claims

CLAIMS 1. Apparatus for coating a flexible moving web comprising a housing defining a chamber, means for evaporating coating material in the chamber, means for supplying a flexible web to be coated and means for receiving a coated web characterised in that the means for evaporating comprises at least one evaporation boat and means for feeding two elongate elements of coating material to the boat.
2. Apparatus as claimed in claim 1, in which the means for evaporating comprises a plurality of evaporator boats.
3. Apparatus as claimed in claim 2, in which each evaporator boat has a dual element feed.
4. Apparatus as claimed in claim 2 or 3, in which the boats are arranged in a plurality of rows.
5. Apparatus as claimed in claim 4, in which the boats are arranged in two rows.
6. Apparatus as claimed in any of claims 4 or 5, in which the boats in each row are equidistantly spaced.
7. Apparatus as claimed in any of claims 4 to 6, in which the boats in each row are offset in relation to the boats of the next adjacent row.
8. Apparatus as claimed in any of claims 2 to 7, in which there are more than two element feeds to each boat.
9. Apparatus as claimed in claim 1, in which the means for evaporating

comprises a single boat having a plurality of evaporator zones each having two or more element feeds.
10. Apparatus as claimed in any preceding claim, in which the element feeds are wire feeds.
11. Apparatus as claimed in any of claims 1 to 9, in which the element feeds are strip feeds.
12. Apparatus as claimed in any preceding claim, in which the evaporation zone provided by the boat or boats is disposed transversely to the direction of travel of the web.
13. Apparatus as claimed in any preceding claim, in which the or each boat is preferably made of an intermetallic ceramic.
14. Apparatus as claimed in any preceding claim, in which the means for supplying advantageously comprises an independently driven unwind reel and the means for receiving an independently driven rewind reel.
15. Apparatus as claimed in claim 14, in which an independently driven process drum is disposed between the two reels.
16. Apparatus for coating a flexible web substantially as hereinbefore described with reference to Figure 1 and 3 or to Figures 1 and 3 with the modification of Figure 2 of the accompanying drawings.
17. A method of coating a flexible moving web including the steps of supplying the flexible web, feeding two wires of coating material to means for evaporating to evaporate material to be coated onto the

web and means for receiving the flexible web coated with evaporated material.
18. A method as claimed in claim 17, in which two wires are fed to each of a plurality of evaporator boats.
19. A method as claimed in claim 17 or 18, in which the web travels transversely to the evaporation zone of the boats or boats.
20. A method as claimed in claim 17,18 or 19, in which the web is supplied from an independently driven unwind reel and received by an independently driven rewind reel.
21. A method as claimed in claim 17,18, 19 or 20, in which the web is supported on a process drum disposed adjacent the means for evaporating.
22. A method of coating a flexible web substantially as hereinbefore described with reference to Figure 1 and 3 or to Figures 1 and 3 with the modification of Figure 2 of the accompanying drawings.