GB2171338A

GB2171338A - Bar coating apparatus

Info

Publication number: GB2171338A
Application number: GB08504760A
Authority: GB
Inventors: David Horton
Original assignee: Letraset International Ltd; Letraset Ltd
Current assignee: Letraset International Ltd; Letraset Ltd
Priority date: 1985-02-25
Filing date: 1985-02-25
Publication date: 1986-08-28
Also published as: GB8504760D0

Abstract

Bar coating apparatus includes a plurality of micrometers (10, 11, 12) spaced along a flexible bar (4). By adjusting the micrometers, the evenness of coating application may be improved. The flexibility of the bar (4) allows it to be matched to the actual conditions of coating. In particular the application of a thicker coating in the middle of a web than at its edges can be avoided. <IMAGE>

Description

SPECIFICATION Bar coating apparatus This invention relates to bar coating apparatus.

In order to coat liquids onto webs of material it is common practice to form an even coating by drawing a bar of metal, glass or the like across the surface of the web. In continuous coating processes, the bar is held stationary and the web moved past it and appropriate means are provided continuously to supply liquid to be coated onto the web to the upstream side of the bar/web nip. Swell known type of bar for this purpose consists of a metal core wound with metal wire and known as a Meyer bar.

For many coating applications, precise evenness of the applied coating, while clearly desirable, is not critical. However there are applications where coating thickness is of particular importance. For example in the graphic arts industry, use is made of colour coated films and these must be produced with a very high evenness of colour i.e. there should be no colour variation to the observer, even over a wide distance such as several tens of centimetres.

In order to produce such materials it has been conventional to use bar coaters and to use substantial diameter bars in order to try and keep the bar straight and so promote evenness of coating. Large diameter bars are expensive to manufacture and still do not always give satisfactory results.

We have now found that if instead of trying to make the bar stiffer e.g. by making it larger diameter an attempt is made to adjust a smaller diameter bar, much improved results may be obtained.

According to a first feature of the present invention there is provided bar coating apparatus comprising a cylindrical coating bar, an adjacent convex cylindrical surface forming a nip with the coating bar, means for feeding a web of material through the nip and means for providing on the upstream side of the nip and between the web and the bar a bead of liquid to be coated on the web, wherein the apparatus includes means supporting the bar and enabling the distance between the bar and the convex surface to be varied at a plurality of positions along the length of the bar.

Preferably the bar is relatively thin and flexible, most preferably within the range of 8 to 10 mm diameter. The preferred form of bar is a wire-wound Meyer bar.

Preferably the apparatus includes a relatively rigid bar-supporting member, a seating in a machine frame in which the bar supporting member may be set, means for adjusting the position of the barsupporting member relative to the seating, and means for adjusting the distance between the relatively inflexible bar supporting member and the bar itself at a plurality of locations along the length of the bar.

It has surprisingly been found that substantially improved results may be obtained using an arrangement of this type with as few as three spaced positions along the bar. At each of these spaced positions a support for the bar is provided together with an adjusting means enabling the distance of that support from the supporting member to be varied. Most conveniently, the supporting member takes the form of a saddle or shoe of appropriate material, preferably polytetrafluoroethylene, which is mounted on a screw thread adjuster. For ease of adjustment the preferred form of screw thread adjustment is a micrometer screw with appropriate graduations about a cylinder in order to enable the amount of adjustment to be precisely measured.The bar is rotationally fixed i.e. it does not rotate about its axis during use in order that any eccentricities do not give rise to coating unevenness.

A particular advantage of the apparatus of the present invention is that it can be used not only to produce very even coatings, but also to make coatings of intentional unevenness. Thus, for example, coating thickness may vary from one side of a coated web to the other, or from both sides towards a minimum or maximum in the web centre, in each case in a controllable or reproducible fashion. This is of value in producing e.g. graduated tone products for graphic arts purposes.

The invention is illustrated by way of example with reference to the accompanying drawing which shows in diagrammatic perspective view a simple bar coater apparatus according to the present invention for use in manufacturing tinted overlay films.

Referring to the drawing a film web to be coated with a coloured tint material and denoted 1 runs over a backing roller 2 and upwardly away from the roller in the direction of arrow 3. Set adjacent the surface of the web 1 remote from the backing roller are an inktray 13 and a Meyerbar4. The Meyerbaris 10 mm in diameter and is formed of a stainless steel core wound with stainless steel wire 0.2 to 0.7 mm thick, the wire thickness depending on the desired coating thickness.

The ends of the bar are held in two lateral brackets themselves held together by a cross member 14 of substantial cross section and formed of a material of high stiffness, for example of low carbon steel. This assembly is set in a machine frame 6 in which its position may be adjusted by means of two micrometer screw devices 7, 8 one set in each end.

The distance of portions of the Meyer bar from the cross member may be adjusted by means of three spaced micrometer screw gauge devices 10, 11, 12 each of which is mounted in the cross member and has a forwardly projecting extension the position of the end of which relative to the cross member may be adjusted by turning the micrometer screw in each case in standard fashion. On the end of the projection in each case is a polytetrafluoroethylene shoe 15 which has a concave face adapted to fit round half the circumference of the Meyer bar4 remote from the back-up roiler.

In use the ink tray 3 is filled with appropriate ink and the web is fed continuously through the nip. A bead of ink builds up between web 1 and Meyer bar 4 on the upstream side of the nip and some passes through the nip to form a coating on the web leaving the nip. The evenness of this coating may be adjusted by individually adjusting the three micrometers 10, 11, 12 mounted on the cross member 14.

The overall colour density may be adjusted by changing Meyer bar and/or by adjusting the two end micrometers 7 and 8 to bring the Meyer bar 4 closer to or remove it more distant from the back-up roller respectively.

Claims

1. Bar coating apparatus comprising a cylindrical coating bar, an adjacent convex cylindrical surface forming a nip with the coating bar, means for feeding a web of material through the nip and means for providing on the upstream side of the nip and between the web and the bar a bead of liquid to be coated on the web, wherein the apparatus includes means supporting the bar and enabling the distance between the bar and the convex surface to be varied at a plurality of positions along the length of the bar.

2. Bar coating apparatus according to claim 1 wherein the diameter of the bar is within the range of 8 to 10 mm.

3. Bar coating apparatus according to claim 1 or 2 wherein the bar is a wire-wound Meyer bar.

4. Bar coating apparatus according to any one of claims 1 to 3 wherein the apparatus includes a relatively inflexible bar-supporting member, a seating in a machine frame in which the bar-supporting member may be set, means for adjusting the position of the bar-supporting member relative to the seating, and means for adjusting the distance between the relatively inflexible bar-supporting member and the bar itself at a plurality of locations along the length of the bar.

5. Bar coating apparatus according to any one of claims 1 to 4 wherein there are three spaced supporting positions.

6. Bar coating apparatus according to any one of claims 1 to 5 wherein the bar is supported at each of the spaced positions in a saddle or shoe mounted on a screw thread adjuster.

7. Bar coating apparatus according to claim 6 wherein the screw thread adjuster is a micrometer screw.

8. Bar coating apparatus substantially as hereinbefore described with reference to the accompanying drawings.