GB2199515A

GB2199515A - Bar coating apparatus

Info

Publication number: GB2199515A
Application number: GB08700278A
Authority: GB
Inventors: John Victor Shepherd
Original assignee: Esselte Letraset Ltd
Current assignee: Esselte Letraset Ltd
Priority date: 1987-01-07
Filing date: 1987-01-07
Publication date: 1988-07-13
Also published as: GB8700278D0

Abstract

Simple bar coating apparatus is described. A sheet of material (3) to be coated is laid on a coating bed and the bar (1) is traversed across it. A bead of liquid between the bar and the sheet to be coated is moved across the sheet so that the liquid deposits as a coating. In accordance with the invention, at the same time as the bar is moved across the sheet, it is rotated about its axis but at a peripheral rotational speed less than that of its translational speed across the coating bed. Various mechanisms may be employed to cause the relatively slow rotation, which is preferably 1 to 35% of the translational speed. <IMAGE>

Description

BAR COATING APPARATUS This invention relates to bar coating apparatus.

There are many ways of applying coatings to sheets of material. One approach is that of so-called bar coating, where a bar is drawn across a sheet, with a bead of liquid to be coated on the sheet positioned between the sheet itself and the leading convex surface of the bar.

As the bar is moved across the sheet, the bead is moved with it, leaving a layer of material from the bead coated on the sheet, and this process continues until the bead is entirely exhausted.

Evenness of coating and ease of operation can be materially improved by the use of a bar which does not have a plain cylindrical surface, but rather a corrugated surface. A particular construction which has found widespread adoption is that of a wire wound bar, a so-called Meyer bar. Such bars are widely used for coating application.

During the application of a coating, the bar may be held stationary or it may be rolled across the surface to be coated in the fashion of a rolling pin. If it is held stationary, there is a danger that any contamination which might block one of the corrugations leads to a light, undercoated streak in the coated product. This can be avoided by the rotating or rolling method, but this in turn tends to deposit a series of strips or bands extending transversely to the axis of the bar which do not even out, particularly if the coating composition is fairly viscous.

If, when hand coating, a streak appears due to blockage and the bar is then turned, there tends to be a line of thicker deposition which has occured when the turning of the bar took place.

We have now found that it is possible, even using simple hand operated apparatus, to provide coatings of improved uniformity using a bar coating method by so arranging the bar that as it is drawn across the surface to be coated, it is slowly rotated at a peripheral speed less then that of its translational speed across the surface.

Working in this way, the danger of streaking due to build up or blockage for corrugations is reduced, as any blockage is simply moved round, away from the active coating slot, but in addition the coating is even, rather than tending to be in a set of parallel lines of lower concentration and higher concentration.

Numerous mechanical systems may be devised to enable the bar to be turned slowly as it is drawn across the surface to be coated. Preferably the speed of traverse across the surface to be coated and the rotational speed of the bar are in fixed relationship to one another, and this is preferably achieved by having a mechanical link between a member such as a friction wheel engaging the surface to be coated or of a coating bed on which it is supported and the bar itself.

The motive power to turn the bar and to take it across the surface to be coated may be manual, in which case a surface engaging means acts to transmit motion to the bar, or it may be e.g. electrical. For example an electric motor may be provided to drive the bar in rotation as well as simultaneously driving an assembly consisting of bar, motor and e.g. liquid reservoir across the surface to be coated.

In a further alternative, the surface to be coated may be mounted on a suitable platform, and a bar caused to traverse across the platform with rotation but with the rotation being generated by the interaction between something attached to the bar, e.g. a large pinion wheel, and a rack mounted away from the plane of the sheet to be coated.

The peripheral speed of rotation of the bar is preferably 1% to 35% of the translational speed of the bar but can be a higher percentage for low viscosity coatings, e.g. less than 5 poise. The translational speed may vary widely, e.g. 5 to 1000 cm/minute.

The sense of rotation of the bar should be such as to feed the coating composition into the nip, i.e. the peripheral rotation where the bar contacts the material to be coated should be opposite to the direction to the movement of the bar.

The bar should, in any practical embodiment of apparatus according to the invention, be easily removable from the remainder of the apparatus to enable it to be cleaned of coating composition after it has been used.

The invention is illustrated by way of example with reference to the accompanying drawings, in which: Figure 1 shows a simple form of bar coating apparatus in accordance with the invention, in perspective view, Figure 2 shows a motorized system, likewise in perspective view, and Figure 3 shows a non-motorised system.

Referring to Figure 1, this shows coating apparatus consisting of a coating bar 1 and a rotating drive unit 2. The apparatus is designed for use for coating a sheet of paper 3 which is laid on a surface 4.

The coating apparatus itself consists of a standard Meyer bar 1 which is connected via a push-on connection to a drive dog 10 mounted on a block 11. Drive dog 10 has a shaft connected to a toothed wheel 12, the shaft passing through the block 11. Toothed wheel 12 is a spur gear meshing with a further spur gear 13 which is fixedly mounted co-axially with a larger diameter spur gear 14.

This in turn engages with a small spur gear 15 which is mounted fixedly with respect to a drive wheel 16. prive wheel 16 engages the surface 4 and as drive 16 is rotated, the spur gears 15, 14, 13 and 12 constitute a reduction gear train. If the rotation of the drive wheel 16 is caused by moving the whole of the block 11 with its associated gears and with one end of the Meyer bar along, the Meyer bar is slowly rotated. Movement along is conveniently effected using a handle 18 on block 11.

In use of the apparatus, a bead of material to be coated is placed across the sheet of paper 3 and the Meyer bar 1 located adjacent and parallel to the bead. The bar is then drawn toward the bead with both hands, one holding the handle 18 and the other loosely holding the end 17 of the Meyer bar. The end 17 is held loosely in order to enable it to rotate as the assembly of block 11 and bar 1 is moved across the sheet 3 to leave a coated patch 20.

Figure 2 shows a motorised system. A casing 30 houses batteries (which help weight the system down), ballast and an electric motor. The motor drives a spur gear 31 at each end of the casing. Gear 31 which on the one hand meshes with a spur gear/sprocket wheel 32 which drives, via a chain 33, two drive wheels 34 at each end, and on the other hand, via a spur gear/sprocket 36, turns the Meyer bar 37. As the unit moves across a sheet of paper 3, it deposits a coating 20. Meyer bar 37 is demountable for cleaning.

Figure 3 shows a simple mechanical system. Surface 4 is a raised table of width slightly less than the length of a Meyer bar 40. On the end of bar 40 is a pinion 41 which engages in a rack 42. If the bar 40 is drawn to the left as seen in Figure 3, it rotates on a sheet 3 at much less than its translational speed across the sheet, and deposits a coating 20 as illustrated. The rack and pinion teeth do not mesh tightly to enable variation in the vertical position of the bar relative to the rack.

Claims

1. Bar coating apparatus consisting of a coating bed adapted to receive a sheet of material to be coated, a coating bar adapted to be moved across the bed in contact with a sheet of material located thereon and means acting in conjunction with the coating bed and adapted to rotate the coating bar about its axis such that the peripheral speed of the surface of the coating bar is lower than the translational speed of the bar across the coating bed.

2. Apparatus according to claim 1 and including means providing a fixed relationship between the peripheral turning speed of the bar and the translational speed of the bar across the bed.

3. Apparatus according to claim 2 and including a friction wheel adapted to engage the surface of the coating bed and rotate as the bar is moved across the surface and mechanically linked to the bar to rotate the bar as it moves across the coating bed.

4. Apparatus according to claim 2 and including an electric motor, means connecting the bar to the electric motor to rotate the bar when the electric motor is actuated and means connected to the electric motor and engaging the coating bed to drive the assembly including the electric motor across the coating bed.

5. Apparatus according to claim 2 and including a pinion wheel mounted substantially coaxially relative to the coating bar and a rack set away from the plane of the coating bed and engaging the pinion wheel.

6. Apparatus according to any of claims 1 to 5 wherein the peripheral speed of rotation of the bar is 1 to 35% of the translational speed of the bar across the bed.

7. Apparatus according to any one of the preceding claims and including means for traversing the bar at a translational speed of 5 to 1000 centimetres per minute.

8. Apparatus according to any one of the preceding claims and including means for detaching the coating bar from the remainder of the apparatus to enable it to be cleaned.

9. Bar -coating apparatus substantially as hereinbefore described with reference to any one of Figures 1 to 3 of the accompanying drawings.