GB2174929A

GB2174929A - Coating sheets

Info

Publication number: GB2174929A
Application number: GB08512021A
Authority: GB
Inventors: Ronald Edward Knight
Original assignee: Wallace Knight Ltd
Current assignee: Wallace Knight Ltd
Priority date: 1985-05-13
Filing date: 1985-05-13
Publication date: 1986-11-19
Also published as: EP0221128A1; AU5868986A; WO1986006655A1; GB8512021D0

Abstract

A layer of coating material (104) is applied to a rotating applicator roller (100) which deposits the layer on a substrate (112) like thin foils, laminates, paper and cardboard being moved passed it. The substrate (112) is forced against the rotating roller (100) by a stream of gas (A) delivered against the underside of the substrate (112).

Description

SPECIFICATION Apparatus and method for coating a substrate The present invention is concerned with an apparatus and a method for applying a coating material to a substrate.

Up until the present time, the coating of substrates has generally been carried out by passing the substrate to be coated between an applicator roller and a pressure roller as for example shown in Figures 1 and 2. Firstly, the applicator roller 10 has a layer of the coating material 20 deposited on its surface. This can be done in a variety of ways, for instance by transferring a coating material from a coating tray 11 via a pick up and a transfer roller 12 and 13 respectively to the applicator roller. The applicator roller and the pressure roller 14 rotate at identical peripheral speeds, and co-operate to drive the substrate 15 between them. The applicator roller deposits a layer of the coating material onto the surface of the substrate 21 as the substrate passes between the rollers.

The applicator roller is generally provided with a rubber layer 16 to ensure both that a constant pressure can be maintained on the substrate to produce an even layer of the coating material, and that the substrate is driven smoothly through the machine. However, when coating individual sheets of substrate, at the ends of and between individual sheets, the pressure roller comes into direct contact with the applicator roller and is therefore contaminated with the coating material. This coating material has to be removed to prevent it contaminating the underside of the following substrate sheet. This is generally done by placing doctor blades 17 around the path of the surface of the pressure roller. A drip tray 18 is also generally provided.However, this does not remove all the contamination, and so in the case of sensitive applications, a solvent bath is sometimes placed in the path of the surface of the pressure roller.

Thus there is a need for a coating machine capable of coating sheets of substrate on one side with a coating material without the problem of the coating material being applied to the other side.

Afurther problem present in previous coating methods is that when coating very thin substrates (typically paper of less than 220 gm/m2 and especially paper of less than 180 gm/m2), the sheets of substrate tend to cling to the applicator roller instead of passing cleanly through the machine. This makes the coating of such sheets very difficult if not impossible. To overcome this problem air knives 19 have been used with some success to strip the sheets from the roller. However such knives limit the size of the sheets which may be coated and also the speed at which the machine can work at.

According to one aspect of the present invention, there is provided an apparatus for applying a coating material to a surface of a substrate comprising means for applying a layer of the coating material to the surface of a rotating applicator roller, means for moving the substrate past the coated roller, and means for delivering a stream of gas to force the substrate against the coated roller.

According to a further aspect of the present invention, there is provided a method of applying a coating material to a surface of a substrate comprising the steps of: coating the surface of a rotating applicator roller with the coating material, moving the substrate past the coated roller, and delivering a stream of gas to force the substrate against the coated roller.

The present invention therefore provides a coating apparatus without the need for a pressure roller as used in the prior art. This is replaced by a stream of gas delivered onto a first surface of the substrate so as to force the second surface against the applicator roller.

In the present invention, the undersurface of the substrate is preferably supported so that its upper surface is out of contact, in the absence of the stream of gas, with the coated surface of the applicator roller. Thus, in the absence of a substrate between the support and the applicator roller, coating material will not be deposited from the applicator roller onto the support. Thus the problem of the pressure roller being coated with coating material is overcome.

In a further preferred aspect of the invention, the coated surface of the applicator roller is arranged to slide over the surface of the substrate, which is found to prevent the two surfaces from sticking together. This can be achieved in two possible ways.

Firstly, the applicator roller can be driven at a speed such that its coated surface has a different speed, either faster or slower, than that at which the substrate is moved past it. Alternatively, the applicator roller can be positioned at an angle relative to the direction in which the substrate is moved. This causes their respective surfaces to move in different directions where they contact one another, resulting in the two surfaces sliding across each other.

In the drawings: Figure lisa schematic sectional view of a prior art coating apparatus.

Figure 2 is a close-up sectional view of the prior art showing, in an exaggerated manner, the contact between the applicator roller and the pressure roller.

Figure 3 is a schematic sectional view of the coating apparatus of the present invention.

Figure 4 is a schematic plan view of one embodiment of the present invention.

As previously discussed, Figures 1 and 2 illustrate a coating apparatus of the prior art. This comprises an applicator roller and a pressure roller between which the substrate is fed and consequently coated.

This apparatus has several disadvantages as outlined above.

Turning to Figure 3, this shows a schematic sectional view of a coating apparatus according to one embodiment of the present invention. This provides an applicator roller 100 of circular crosssection rotatively mounted on driving means 102.

The applicator roller has a layer of coating material deposited on its surface via pick-up roller 106 and transfer roller 108. The coating material 104 is conveniently picked up by the pick up roller from a tray of coating material 110. The substrate 112 which is to be coated, is mounted on vacuum conveyors 114and passes beneath the applicator roller 100.

The vacuum conveyor is driven by vacuum rollers 116. A feed roller 118 is conveniently located before the applicator roller to drive the substrate past the applicator roller.

In order to force the substrate against the coated roller, a stream of gas, illustrated by arrow A, is delivered against the underside of the substrate, forcing it against the roller.

The stream of gas is conveniently supplied from a plenum chamber 122 which is in turn connected to a pressurised gas source such as a fan or air pump 120. The gas is then forced out of either a narrow slot or plurality of orifices 124 so as to be impinge on the undersurface of the substrate forcing its top surface against the roller 100, causing the coating material to be deposited on the moving substrate.

For the purposes of the present invention, any suitable gas may be used, but for economic reasons, air is preferred.

The plenum chamber 122 has atop surface wall 126 which forms a support on which the substrate 112 moves during the coating step. This wall has down turned edges 127,128to stop snagging of the substrate.

The distance between the wall 126 of the plenum chamber and the surface of the coating on the applicator roller is generally greater than the thickness of the uncoated substrate 112. This enables the applicator roller to slide over the substrate resulting in the sticking of the substrate to the applicator roller being greatly reduced.

The two surfaces can be caused to slide with respect to each other in two possible ways.

Firstly, the applicator roller can be driven at a speed such that its coated surface has a different speed, either faster or slower than that of the substrate. Alternatively, the applicator roller can be positioned so that it is skewed with respect to the direction in which the substrate is moved, as shown in Figure 4. This causes their respective surfaces to move in different directions where they contact one another, resulting in the two surfaces sliding with respect to each other. It is possible, in this embodiment, that the surface of the applicator roller can have a speed such that the component of the speed in the direction of the movement of the substrate is the same as the speed of the substrate itself. The sliding action will be provided by the component of the motion of the surface of the applicator roller perpendicular to the direction of the movement of the substrate.

As a consequence of the sliding action, the previous problems of thin substrates sticking to the applicator roller is removed, and substrates of below 220 gm/m2 and especially below 180 gm/m2 can be coated.

The stream of gas from the plenum chamber is conveniently delivered through the support wall 126 onto the undersurface of the substrate.

Up until the present time, it has been necessary to provide a layer of rubber 16 on the outer surface of the applicator roller 10 so as to apply a pressure on the substrate 15 between the rollers 10 and 14 as shown in Figures 1 and 2. However, in the present invention, there is no need to provide such a layer, as the means forcing the substrate against the roller 100 is the stream of gas. Thus the present applicator roller may be made of a more durable material such as steel. However, the applicator roller can be made of alternative suitable materials such as synthetic rubber.

In previous coating apparatus, so-called "analox" rollers have been used for rollers 106 or 108. Such a roller comprises a roller having a surface with a plurality of dimples in it. These rollers are capable of depositing a predetermined weight of coating material per unit area on a surface pressed against them.

However, it has not been possible, until the present time, to produce applicator rollers 100 from such a material, as the necessary deformation permitted by a rubber layer is not possible when using a metal surfaced roller.

The present invention also envisages that the applicator roller may have grooves cut into it or be threaded. The use of such recesses allows a controlled amount of coating material to be deposited on the substrate, therefore giving an improved finish.

The applicator roller 100 is movable relative to the support 126, so that different thicknesses of substrate can be fed through the apparatus of the present invention. Thus, the applicator roller and drive means, andlorthe plenum chamber are preferably mounted for vertical movement.

Various coatings might be used in connection with the present invention, such as clear coatings. These can be used to produce a varnish or gloss finish on packaging for such articles as record sleeves, cosmetic containers, and book covers. It is also possible to use either pigmented or adhesive coatings to produce a coated substrate having a coloured or adhesive finish respectively.

Preferred substrates which may be used in connection with the apparatus of the present invention are thin foils, plastics, laminates, paper and cardboard.

Claims

1. An apparatus for applying a coating material to a surface of a substrate comprising means for applying a layer of the coating material to the surface of a rotating applicator roller, means for moving the substrate past the roller, and means for delivering a stream of gas against the substrate to force it against the coated roller.

2. An apparatus according to claim 1, wherein the stream of gas is delivered from a plenum chamber connected to a supply of the gas.

3. An apparatus according to claim 2, wherein the supply of gas is a fan, an air pump or any pressurised source.

4. An apparatus according to any preceding claim, wherein the gas is air.

5. An apparatus according to any preceding claim, wherein the means delivering the stream of gas is a narrow slot or plurality of orifices.

6. An apparatus according to any preceding claim, wherein means are provided for supporting the undersurface of the substrate at a distance from the coated roller greater than the thickness of the substrate.

7. An apparatus according to claim 6, wherein the means for delivering the stream of gas extends through the support.

8. An apparatus according to claim 6 or claim 7, wherein dependent on claim 2, wherein the support forms at least a portion of a wall of the plenum chamber.

9. An apparatus according to any preceding claim, wherein the applicator roller is made from steel or synthetic rubber.

10. An apparatus according to any preceding claim wherein the applicator roller is an analox roller.

11. An apparatus according to any of claim 1 to 9, wherein the applicator roller has grooves cut into its surface.

12. An apparatus according to any of claim 1 to 9, wherein the applicator roller is a threaded roller.

13. An apparatus according to any preceding claims, wherein the applicator roller and support are movable relative to one another to accommodate different thicknesses of substrate.

14. An apparatus according to any preceding claim, wherein the coating is a clear coating.

15. An apparatus according to claim 14, wherein the coating is varnish or gloss.

16. An apparatus according to any of claims 1 to 13, wherein the coating is a pigmented coating.

17. An apparatus according to any preceding claim, wherein the substrate and the surface of the applicator roller are arranged to slide over one another.

18. An apparatus according to claim 17, wherein the applicator roller and the substrate are arranged to slide as a consequence of the means moving the substrate and the means driving the applicator roller being arranged so that the surface of the applicator roller moves at a different speed than the substrate.

19. An apparatus according to claim 17, wherein the applicator roller and the substrate are arranged to slide as a consequence of the applicator roller being skewed with respect to the direction in which the substrate is moved.

20. An apparatus according to any preceding claim, wherein the means for moving the substrate is a series of vacuum conveyors and vacuum rollers.

21. A method of applying a coating material to a surface of a substrate comprising the steps of: coating the surface of a rotating applicator roller with the coating material, moving the substrate past the coated roller, moving the substrate past the coated roller, and pressing the substrate against the coated roller, wherein said pressing means consists solely of means for delivering a stream of gas against the substrate.

21. A method of applying a coating material to a surface of a substrate comprising the steps of: coating the surface of a rotating applicator roller with the coating material, moving the substrate past the coated roller, and delivering a stream of gas to force the substrate against the coated roller.

22. A method according to claim 19, wherein the surface of the applicator roller slides over the substrate to prevent sticking between them.

23. A method according to claim 22, wherein the surface of the applicator roller has a different speed than the substrate to cause sliding between them.

24. A method according to claim 22, wherein the applicator roller is positioned with a skewed orientation with respect to the direction in which the substrate is moved to cause sliding between them.

25. A method according to any of claims 19 to 24, wherein the gas is air.

26. A method according to any of claim 19 to 25, further comprising the step of supporting the undersurface of the substrate at a distance from the coated roller greater than the thickness of the substrate.

27. A method according to any of claims 19 to 26, wherein the substrate is paper or cardboard.

28. An apparatus substantially as described herein with reference to Figure 3 of the accompanying drawings.

29. A method substantially as described herein with reference to Figure 3 of the accompanying drawings.

Amendments to claims filed on 13/2/86 Superseded claims Claims 1 and 21

1. An apparatus for applying a coating material to a surface of a substrate comprising means for applying a layer of the coating material to the surface of a rotating applicator roller, means for moving the substrate past the roller, and means for pressing the substrate against the coated roller, wherein said pressing means consists solely of means for delivering a stream of gas against the substrate.