GB2316344A

GB2316344A - Coating of webs

Info

Publication number: GB2316344A
Application number: GB9617558A
Authority: GB
Inventors: Derek Boyden
Original assignee: ATC MANUFACTURING Ltd
Current assignee: ATC MANUFACTURING Ltd
Priority date: 1996-08-21
Filing date: 1996-08-21
Publication date: 1998-02-25
Also published as: GB9617558D0

Abstract

A method and apparatus are disclosed in which a double layer web of material comprising layers 12 and 13 is pulled past a flexible blade 18 under tension in order to coat the web with silicone. The blade flexes and forces the coating between the spaces of the fabric making up the web to provide a thin coating. Both sides of the web may be coated in this manner. The web is used in the manufacture of vehicle air bags.

Description

COATING OF WEBS The present invention relates to a web coating apparatus and to a method of coating a web. The invention is particularly applicable to the coating of webs that are to be used in the production of air bags for vehicles.

In the known method of coating an air bag a continuous length of material to be made up into the air bag is passed partially around a roller, as shown in the side view in Figure 1. A doctor knife 10 of steel is located adjacent to the periphery of the roller 11 and across the roller in order to control the thickness of coating that is applied from a dam 12 of coating material.

Figures 2 and 3 are a plan and a side cross-sectional view respectively of the length of material that is to be used to form the air bags. The length of material is of double thickness with the two layers 12 and 13 being sealed together as shown at 14 in the regions where they are to define the individual air bags and with the layers of material being separate between those sealed portions.

After both sides of the material have been coated the web is separated at locations between the sealed portions in order to provide the individual air bags.

As the coating material is expensive it is desirable to minimise the thickness being applied to the fabric whilst ensuring that the fabric is going to remain air tight when coated. Attempts have been made to reduce the thickness of the coating by reducing the distance of the knife from the adjacent point of the roller or to urge the knife more firmly towards the roller. However, as the knife pushes against the roller through the layers 12 and 13, the web is placed in great tension in order to pull it through that narrow gap. Indeed, the tension in the layers has been so great that the web tends to stretch in the direction in which it is pulled through the gap. In order to cope with that stretching it has been proposed to make the seals 14 in an oval shape with the minor axis extending in the direction of the tension such that the pulling and stretching of the webs pulls the oval out to make the seals 14 generally circular. However, clearly such tensions on the material are not desirable and undue stresses are placed on the fibres that comprise the layers.

The force exerted by the knife blade is also disadvantageous as the upper layer 12, facing away from the roller, will be pushed by the knife blade to stretch over the lower layer and bunch up at the downstream side of the seal 14 thereby forming a crease and creating an uncoated region or damaging the seal at that location or both.

Accordingly there is a limit to the thickness of silicone rubber that can be applied by this known method.

At present that limit is thought to be in the region of 40 to 50 gsm.

After one layer 12 has been coated, the other layer 13 is then coated. Then the individual bags are cut out by laser and everted to locate the coated layer on the inside.

It is an object of the present invention to attempt to alleviate some of the above described disadvantages.

According to one aspect of the present invention a web coating apparatus comprises a coating blade and tensioning means arranged to exert a tension on a web of material such that the web is urged into contact with the blade with power means being provided arranged to cause a web of material to move past the blade.

The blade may be flexible and may be arranged to flex as a result of tension in a web by, for instance, between 20 and 50 from the line taken from a fixed part of the blade that is restrained from flexing and that degree of flexure may be in the region of 3.50. The blade may be arranged to be fixed in position at a location spaced from the part of the blade that is arranged to be contacted by a web of material, for instance by being clamped between two parts that extend in the direction across the web of material.

The blade may include a forward edge and a rearward surface which a web of material is arranged to travel past and cooperate with. The blade may include a rearward edge spaced from the forward edge with which a web of material is arranged to cooperate.

According to a further aspect of the present invention a method of coating a web of material comprises urging the web into contact with a coating blade by exerting tension along a length of the web in the region of the blade and causing movement of the web past the blade such that a dam of liquid on the upstream side of the blade supplies liquid that is spread over the web by the blade as the web passes beneath the blade to coat the web.

The web may comprise a single layer of plain woven material. Alternatively, the web may comprise a plurality of layers and, in a particularly preferred embodiment the web comprises two layers. The two layers of the web may be separate from each other over at least part of their co-extent and preferably the majority of their co-extent.

The method may comprise coating first one side and then the other side of the web.

The web may comprise a fibrous web and the coating that is applied may be such that the majority of the coating is located between adjacent fibres, beneath the plane defined by the outermost extent of the fibres at that side of the layer. The coating that is applied to the outwardly facing surface of the web may be a non planar coating. A part of the outwardly facing surface of the coating may be located inwardly with respect to the depth of the web from the plane defined by the outermost extent of the adjacent fibres.

The method may comprise causing the blade to flex as a result of the tension in the web and the method may comprise causing the blade to flex by between 20 and 50 from a line taken from a fixed point of the blade and the part of the blade cooperating with the web and that degree of flexure may be in the region of 3.50.

The flexure or the orientation of the blade may allow the blade to have a trailing angle with respect to the direction of travel of the web. Thus the wiping action is exerted so as to push the coating into the fibres rather than the attacking angle of the blade shown in Figure 1 that scrapes a layer of the web.

The method may comprise causing the upwardly facing surface of material located between an upstream surface of the blade extending away from the web and a portion of the web extending upstream from that part of the blade by an included angle in the region of 90" or less than 900 or in the region of 700.

The method may comprise the web first contacting an upstream edge of the blade and then passing beneath an extent of the blade adjacent to the web and then being pulled away from a downstream edge of the blade with the upstream and downstream edges being spaced from each other.

The method may comprise applying a silicone coating to the web of less than 40 gsm or less than 30 gsm or in the region of the 25 gsm.

The present invention also includes a method of coating a web of two layers when using an apparatus as herein described as well as a web of two layers that has been coated by a method or apparatus as herein referred to.

The present invention includes any combination of the herein referred to features or limitations.

The invention may be carried into practice in various ways but one embodiment will now be described, by way of example, and with reference to the accompanying drawings, in which: Figure 4 is a schematic side view of an apparatus used to coat the layers 12 and 13 shown in Figures 2 and 3, and Figure 5 is a schematic enlarged sectional view of the coated fibres of one of the layers.

As shown in Figure 4 the layers 12 and 13 are supplied over a guide roller 15 to an anvil 16 and then to a further guide roller 17. A blade 18 is arranged between the anvil 16 and the roller 17 so as to deflect the layers from a straight path between those parts and to exert a downwards pressure on the layers. That downwards pressure is not resisted by the blade pressing against an article: rather the tension in the layers causes the upper layer to be pushed against the blade.

A dam 19 of silicone rubber is provided on the layers at the upstream side of the blade and across the width of the layers to ensure an adequate supply of coating material.

In contrast to the blade 10 shown in Figure 1, the blade 18 extends perpendicularly to the direction of travel of the layers at the point where the layers pass the blade. Furthermore, the blade 18, instead of having an edge of material having an included angle in excess of 90 , and in the region of 110 from the upwardly facing surface of the blade has the advancing layers, as shown in Figure 1, the blade 18 has an included angle in the region of 900 or less or in the region of 700 with the blade 18 having a significant horizontal extent in the direction of travel of the layers. That horizontal extent may be more than 5 mm or more than 10 mm or in the region of 15 mm.

In operation, the plastic blade, which is held firmly between the mounting blade 19 and a clamp plate 20, will flex slightly from its clamped portion towards its free edge in the direction of travel of the web as a result of the tension of the web. That flexure from the clamped portion may be in the region of 20 or 50 or in the region of 3.5 .

Accordingly, the blade has three operating regions comprising the initial front edge that restricts the amount of coating that can pass beneath the blade, the flat surface that assists in applying an even coating to the web and assists in the penetration of the coating in between the fibres and an exit edge that further urges the coating down to ensure that the resulting web is sealed by the coating. The exact effect of the different parts of the blade is not fully understood and each part may have varying degrees of effect either on restricting the depth of the coating being applied or in assisting in urging the coating down between the fibres. However, as the web is being pulled past the blade, and as the blade flexes slightly, it is thought that there will be a greater force urging the web towards engagement with the front edge of the blade than the corresponding force that urges them both into contact with the downstream edge of the blade thereby assisting in ensuring that a reduced depth of coating is allowed past the front edge of the blade.

The tension in the web of material is in the region of 0.7kg/cm. That compares with a tension of the web in Figure 1 in which the tension may be in the region of 0.2 - 0.3 kg/cm.

The hardness of the plastic or silicone rubber blade is preferably between 85 and 95 on the Shore Hardness test and preferably of the order of 90.

Figure 5 shows a much enlarged view of the outermost fibres 21 of one of the layers. The coating 22 applied by conventional machines such as that shown in Figure 1, is illustrated by a chain line 23. The coating 24 applied by the blade shown in Figure 4 is shown by a solid line.

That coating may be of minimal depth over the upper surface of the fibres or may in fact not have any depth there at all leaving the upper surface of the fibres exposed. However, the coating extends into the gap between the fibres and indeed the outwardly facing surface of the coating may be at lesser depth than the plane defined by the outermost edges of the fibres. It will be appreciated that a small continuous layer of coating may extend over the fibres and over the gaps between the fibres as well as the coating extending partially down between adjacent fibres but such a layer would be of less depth than that illustrated by the chain line 23.

Coating according to the present invention may apply a layer of less than 40 gsm or less than 35 gsm or in the region of 25 gsm.

The length of the lower edge of the blade in the extent of the direction of travel of the web may be less than 15 mm or less than 10 mm or in the region of 5 mm.

The plastic blade has a lower coefficient of friction than the steel blade shown in Figure 1. Accordingly, coating is less likely to stick to the plastic blade. If a steel blade was used that had a greater coefficient of friction then a greater depth of coating would be pulled into the space between the blade and the layer being coated thereby resulting in a thicker coating being applied to the web.

The blade may be a plastics blade. The blade may have a Shore hardness of between 85 and 95 and the hardness may be in the region of 90.

The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings), may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

1. A web coating apparatus comprising a coating blade and tensioning means arranged to exert a tension on a web of material such that the web is urged into contact with the blade with power means being provided arranged to cause a web of material to move past the blade.

2. Apparatus as claimed in Claim 1 in which the blade is flexible.

3. Apparatus as claimed in Claim 2 in which the blade is arranged to flex as a result of tension in the web.

4. Apparatus as claimed in Claim 2 or 3 in which the blade is arranged to flex between 2" and 50 from the line taken from a fixed part of the blade that is restrained from flexing.

5. Apparatus as claimed in Claim 4 in which the blade is arranged to flex in the region of 3.5 from the line.

6. Apparatus as claimed in any preceding claim in which the blade is arranged to be fixed in position at a location spaced from the part of the blade that is arranged to be contacted by a web of material.

7. Apparatus as claimed in Claim 6 in which the blade is arranged to be fixed in position by being clamped between two parts that extend in the direction across the web of material.

8. Apparatus as claimed in any preceding claim in which the blade includes a forward edge and a rearward surface which a web of material is arranged to travel past and cooperate with.

9. Apparatus as claimed in Claim 8 in which the blade includes a rearward edge spaced from the forward edge with which a web of material is arranged to cooperate.

10. Apparatus as claimed in any preceding claim in which the blade comprises a plastic blade.

11. Apparatus as claimed in Claim 10 in which the Shore Hardness of the blade is in the region of between 85 and 95.

12. Web coating apparatus substantially as herein described with reference to, and as shown in any of Figures 2 to 5 of the accompanying drawings.

13. A method of coating a web of material comprising urging the web into contact with a coating blade by exerting tension along a length of the web in the region of the blade and causing movement of the web past the blade such that a dam of liquid on the upstream side of the blade supplies liquid that is spread over the web by the blade as the web passes beneath the blade to coat the web.

14. A method as claimed in Claim 13 comprising urging a web comprising a single layer of plain woven material into contact with the coating blade.

15. A method as claimed in Claim 13 comprising urging a web comprising a plurality of layers into contact with the coating blade.

16. A method as claimed in Claim 15 comprising moving a web comprising two layers into contact with a coating blade.

17. A method as claimed in Claim 16 comprising the two layers being separate from each other over at least part of their co-extent.

18. Apparatus as claimed in Claim 17 comprising maintaining the two layers separate from each other along the majority of their co-extent.

19. A method as claimed in any of Claims 13 to 18 comprising coating first one side and then the other side of the web.

20. A method as claimed in any of Claims 13 to 19 comprising coating a fibrous web of material such that the majority of the coating is located between adjacent fibres, beneath the plane defined by the outermost extent of the fibres at that side of the layer.

21. A method as claimed in Claim 20 comprising coating the web with a non planar coating.

22. A method as claimed in any of Claims 13 to 21 in which a part of the outwardly facing surface of the coating is located inwardly with respect to the depth of the web from the plane defined by the outermost extent of adjacent fibres of a fibrous web.

23. A method as claimed in any of Claims 13 to 21 comprising causing the blade to flex as a result of the tension in the web.

24. A method as claimed in Claim 23 comprising causing the blade to flex by between 20 and 5 from a line taken from a fixed point of the blade and the part of the blade cooperating with the web.

25. A method as claimed in Claim 24 in which the degree of flexure is in the region of 3.5 .

26. A method as claimed in any of Claims 12 to 25 in which the orientation of the blade allows the blade to have a trailing angle with respect to the direction of travel of the web.

27. A method as claimed in Claim 25 in which the trailing angle with respect to the direction of travel of the web allows the blade to exert a wiping action so as to push the coating into the fibres.

28. A method as claimed in any of Claims 13 to 27 comprising causing the upwardly facing surface of material located between an upstream surface of the blade extending away from the web and a portion of the web extending upstream from that part of the blade by an included angle in the region of 900.

29. A method as claimed in any of Claims 13 to 27 comprising causing the upwardly facing surface of material located between an upstream surface of the blade extending away from the web and a portion of the web extending upstream from that part of the blade by an included angle of less than 900.

30. A method as claimed in Claim 29 comprising making that included angle in the region of 70".

31. A method as claimed in any of Claims 13 to 30 comprising the web first contacting an upstream edge of the blade and then passing beneath an extent of the blade adjacent to the web and then being pulled from a downstream edge of the blade with the upstream and downstream edges being spaced from each other.

32. A method as claimed in any of Claims 13 to 31 comprising applying a silicone coating to the web of less than 40 gsm.

33. A method as claimed in Claim 32 comprising applying the coating to the web of less than 30 gsm.

34. A method as claimed in Claim 33 comprising applying the coating to the web in the region of 25 gsm.

35. A method as claimed in any of Claims 13 to 34 comprising exerting a tension in the web in the region of 0.7 kg/cm.

36. A method of coating a web of material substantially as herein described with reference to, and as shown in any of Figures 2 to 5 of the accompanying drawings.

37. A method of coating a web of material as claimed in any of Claims 13 to 35 when using web coating apparatus as claimed in any of Claims 1 to 12.