WO2003039870A1

WO2003039870A1 - Lamination process and apparatus

Info

Publication number: WO2003039870A1
Application number: PCT/GB2002/005001
Authority: WO
Inventors: John Davies
Original assignee: Caligen Foam Limited; Viktor Achter Limited
Priority date: 2001-11-09
Filing date: 2002-11-06
Publication date: 2003-05-15
Also published as: GB0126937D0

Abstract

A method of laminating a fusible visual sheet material (5) to a substrate (8) is disclosed. The method comprises heating the surface of the fusible sheet material (5) by impingement thereon of a high velocity hot gas stream to render the surface tacky. The substrate (8) is brought into contact with the tacky surface to bond the fusible sheet material (5) and the substrate (8) together.

Description

LAMINATION PROCESS AND APPARATUS

This invention relates to the bonding of sheet materials and is particularly, but not exclusively applicable to the bonding of foamed plastics sheet material to fabric or other sheet material to form a laminated structure.

Many modern fabrics consist of a woven or other textile fabric bonded to a layer of foamed plastics material, typically polyurethane foam, to form a foam/fabric composite. Such composite materials have improved drape and feel together with improved thermal insulation and other practical benefits.

One process for bonding such sheet materials to one another is by a flame lamination process in which the surface of the foam is heated by direct impingement thereon of a flame from a gas burner sufficient to bring about melting of the foam surface to a tacky condition in which it is brought into contact with the fabric or other sheet material to which it is to be bonded. This flame impingement technique produces generally satisfactory results, but requires very precise control to avoid excessive melting of the foam surface and the burner has to be in close proximity to the foam surface to be effective. Excessive melting also causes foam vapours to leave the heating zone as partially or uncombusted fumes which can result in gradual blockage of the burner due to foam vapours condensing on the burner body.

To maintain uniformity of processing it is necessary in such direct flame lamination techniques to ensure the flame does not lift or blow-off from the burner and this requires a relatively low gas exit velocity, typically of the order of 0.8 to 1.6 m/sec for propane gas. Such low velocity open flame burners therefore require to operate in close proximity to the sheet materials being laminated to achieve uniform heating and the burner is consequently susceptible to contamination by vaporised foam products which condense on the burner forming solid deposits which can cause blocking of the flame ports of the burner. This in turn produces flame defects which can cause unacceptable visual lines or marks on the finished laminate. According to the present invention there is provided a method of laminating a fusible sheet material to a substrate comprising heating the surface of the fusible sheet material by impingement thereon of a high velocity hot gas stream to render the surface tacky, and bringing the substrate into contact with said tacky surface whereby to bond the fusible sheet material and substrate together. The term "high velocity" is used herein to refer to a velocity of at least twice the flame velocity of an open flame burner for any given fuel and processing speed.

Preferably said fusible sheet material comprises a foamed plastics material and said substrate comprises a textile fabric. The foamed plastics material is preferably flexible polyurethane foam.

Preferably said hot gas stream is generated by combusting a gaseous fuel and directing the resultant hot gases on to the surface of said fusible sheet material. Alternatively said hot gas stream may be generated by electrically or otherwise heating a pressurised gas.

Where the gas stream is derived from combustion of a gaseous fuel, said fuel may comprise a hydrocarbon gas such as propane. Preferably the temperature of the gas stream is in the region of 750-1000°C. Tests using a propane gas burner delivering a hot gas stream at a velocity of 3 to 10 m/sec and a temperature of 900°C have produced improved bond strength between a polyurethane foam sheet and a textile fabric, with similar burn-off to that effected using known flame lamination techniques.

Advantageously the hot gas stream is generated by burning a mixture of atmospheric air and fuel gas in stoichiometric proportions with added oxygen rich gas to generate excess oxygen in the hot gas stream. Preferably the mixture has at least 5% more oxygen than required to produce stoichiometric combustion. Preferably the fuel gas mixture contains up to 25% excess oxygen. Preferably also the oxygen is pure oxygen. Preferably a secondary combustion or reaction zone is created between the source of said hot gas stream and the surface of the fusible sheet material, in which zone oxidation of vapours and impurities generated through melting of said surface takes place. Advantageously the source of said hot gas stream and said surface are separated by a distance of at least 30mm to define said zone. This allows recirculation patterns to establish adjacent to the hot gas stream to facilitate entrainment of said foam vapours and particulate matter into the hot gas stream.

In test bonding of polyurethane foam to fabric in which such a secondary reaction zone is created, reduced contaminant or "smoke" emission has been recorded and bond strength maintained with less burn-off of foam compared with known flame lamination techniques.

The invention also provides apparatus for laminating a fusible sheet material to a substrate, the apparatus comprising means for generating a high velocity hot gas stream, means for directing same on to the surface of the fusible sheet material to render said surface tacky and means for bringing said tacky surface into contact with said substrate to bond same together.

Preferably said means for generating said hot gas stream comprises a fuel gas burner having a combustion chamber and a discharge outlet through which a hot gas stream generated by combustion of fuel gas within the combustion chamber is directed on to the surface of said fusible sheet material.

Preferably said gas stream has a temperature in the region of 750- 1000°C.

Preferably said fuel gas is oxygen rich, that is to say it contains at least 5% more oxygen than required to effect stoichiometric combustion.

Preferably a secondary combustion or reaction zone is provided between an outlet from said means for generating said hot gas stream and the surface of said fusible sheet material. Advantageously said zone is defined by control of the spacing between said outlet and said surface, which spacing is preferably at least 30 mm.

Preferably said means for generating said hot gas stream is of elongated form adapted to extend transversely of said fusible sheet material and having walls formed from a high conductivity refractory material such as silicon carbide.

Preferably the outer surfaces of said walls are exposed to said reaction zone and maintained during operation at a temperature in excess of 300°C.

The invention also provides a laminated product comprising fusible sheet material bonded to a substrate by the method or using the apparatus aforesaid.

An embodiment of the invention will now be described, by way of example only, with reference to the accompanying diagrammatic drawings, in which: -

Fig. 1 is a pictorial view of one form of apparatus for bonding flexible polyurethane foam to a textile fabric; and

Fig. 2 is an enlarged vertical cross-section through part of the apparatus shown in Fig. 1.

Referring to the drawings, the apparatus is adapted to bond a sheet of polyurethane foam 5 drawn from a supply roll 6 over a guide roller 7 to a sheet of textile fabric 8 drawn from a supply roll 9 over a guide roller 10. The sheets 5 and 8 are fed into a nip formed between contra-rotating pressure rollers 11 and 12 in which region heat is applied to the surface of the foam by a heating device 13 such that the foam surface becomes tacky and adheres to the fabric 8 in the nip between the rollers 11 and 12 to produce a composite laminated fabric/foam sheet 14 which is wound on a take-up roll 15. The tension applied to the polyurethane foam sheet 5 and textile fabric 8 may be altered by adjustment of the respective guide rollers 7 and 10. The pressure applied to the foam and fabric sheet in the nip between the rollers 11 and 12 may be varied by bodily movement of one roller towards or away from the other. These adjustments are effected by known means not shown in the drawings. The speed of movement of the sheet materials through the nip between the rollers 11 and 12 is controlled by the speed of rotation of the take-up roll 15 which may be varied in a known manner.

The heating device 13 is shown in greater detail in Fig. 2 and comprises an elongated gas burner having a body portion 19 incorporating a mixing chamber 20 into which fuel gas and air may be supplied for delivery to a flame port 21. A pair of shroud members 22 are detachably mounted on the body portion 19 and define an elongated combustion chamber 23 in which the gaseous fuel/air mixture supplied through the flame port 21 is ignited by electrodes 24. At their outer ends the shroud members 22 define an outlet 25 in the form of an elongated slot through which hot gases generated by combustion of the fuel within the combustion chamber 23 are discharged from the burner into contact with the surface of the sheet 5 of polyurethane foam ahead of the nip 30 between the rollers 11 and 12.

The combustion process within the combustion chamber 23 is controlled such that the hot gases discharged through the outlet 25 have a relatively high velocity of around 1.6m/sec. or above in the case of propane gas. These hot gases thus impinge on the surface of the foam 5 and heat the foam to a temperature above its melting point thereby rendering the surface of the foam tacky just prior to entry into the nip 30. The pressure applied to the foam and fabric sheets as they are brought together in the nip 30 thus results in bonding of the foam to the fabric to produce a laminated sheet 14 which is withdrawn and wound on the take-up roll 15.

The construction of the burner 13 is such that the combustion process is contained within the combustion chamber 23 and only hot gases resulting from the combustion process discharge from the outlet 25 into contact with the foam sheet 5. There is therefore no contact between the flames generated by the combustion process and the surface of the foam, the flames being confined within the combustion chamber 23. This differs significantly from conventional flame lamination techniques in which low velocity flames generated by combustion of a gaseous fuel make direct contact with the surface of the foam. Melting of the foam surface by means of hot gases at relatively high velocity has been found to produce the same level of bond strength between the foam and the fabric with less burn-off of foam. Alternatively a stronger bond can be attained with similar foam burn-off to known flame lamination techniques.

These benefits may be attained using a conventional gaseous fuel such as natural gas or propane mixed with air in approximately stoichiometric proportions so as to effect substantially complete combustion of the fuel mixture within the combustion chamber 23. Additional benefits are attained by addition of an oxygen rich gas to the air gas mixture to give relatively higher concentrations of residual oxygen in the hot gas stream than otherwise obtainable with air-gas flames.

In the course of the lamination process melting of the surface of the foam results in the emission of vapours at the zone between the burner outlet and the nip between the rollers 11 and 12. Such vapours contaminate the surrounding atmosphere and can condense on the surface of conventional burners causing reduced efficiency and ultimately blocking. By use of an oxygen rich fuel mixture, the hot gases emitted from the outlet 25 contain unburnt oxygen which reacts with the vapours released from the foam resulting in oxidation and hence reduction in harmful releases into the surrounding atmosphere. Since the hot gases discharge from the burner at high velocity, the burner may be positioned further from the foam surface than in the case of conventional flame lamination, thus creating between the burner 13 and the nip 30 a secondary combustion or reaction zone in which eddy currents are created as indicated by the arrows 'E' in Fig. 2 and in which oxidation of foam vapours and contaminant particles may take place. This can be seen as a reduction in "smoke" generated at the region of the nip 30 compared with use of a fuel gas which is not oxygen rich and compared with conventional flame lamination techniques. Preferably the distance between the burner outlet and the surface of the foam is at least 30mm and generally in the region of 35-75mm.

The addition of oxygen ensures more intense and faster combustion of the fuel gas, relatively higher hot gas exit temperatures and the benefit of high concentration of residual oxygen in the hot gas stream. This high residual oxygen concentration promotes exothermic reaction in a secondary combustion zone between the foam and burner face with foam vapours that are entrained into the hot gas stream thus assisting in maintaining high gas temperatures and effectively incinerating fumes that would otherwise remain uncombusted. Preferably the added oxygen is pure oxygen or is derived from an oxygen rich gas.

The shrouds 22 of the burner 13 are preferably formed from a refractory material having a relatively high thermal conductivity, that is to say thermal conductivity in excess of around 15W/mC. A suitable material is silicon carbide. Such high thermal conductivity materials rapidly reach equilibrium temperatures on the internal face of the combustion chamber so that the apparatus reaches working temperature rapidly thus avoiding inconsistency in the foam/fabric bonding process. In addition since the outer surfaces of the shroud members 22 rapidly reach a high temperature, condensation of foam vapours on the shroud surface is reduced thus reducing the need for stoppages to remove contaminant deposits. A further benefit deriving from constructing the burner using a high thermal conductivity material is that heat is radiated on to the surface of the fabric 8 as it approaches the nip 30 whereby to pre-heat the fabric and facilitate bonding to the foam 5.

A cooling jacket (not shown) is preferably provided on the chamber 19 to remove conducted heat and avoid expansion and bowing or bending of the burner 13. In practical applications the apparatus may be of considerable width giving rise to possible bending of the burner which, if not controlled, can produce variable bonding across the width of the bonded foam/fabric laminate.

In one example a 4mm thick sheet of polyester polyurethane foam 2 metres wide having a density of 30Kg/m³ and 40 cells per linear inch was bonded to a 1mm thick woven polyester fabric of the same width. A burner of similar width having combustion chamber shrouds of silicon carbide with a thermal conductivity of 16W/mC was positioned with the outlet of the burner approximately 34mm from the surface of the foam adjacent the nip between two pressure rollers. The burner was supplied with a 10% oxygen rich gaseous fuel mixture supplied at a pressure of 10 millibars which was combusted within the burner to release a hot gas stream containing unburnt oxygen into the reaction zone defined between the burner outlet and the adjacent portions of the sheets of foam and fabric travelling round the pressure rollers. The burner was inclined to the surface of the foam at an angle of 58° and the hot gases impinged on the foam surface at a velocity of around 3 metres per second. The foam and fabric sheets were moved through the apparatus at a velocity of 25 metres per minute.

The laminated foam/fabric sheet thus produced was found to have a bond strength equivalent to that produced by flame lamination of similar materials, but with less burn-off of the polyurethane foam, thereby reducing wastage of foam and contamination through vaporisation of the foam surface during lamination. The process was run repeatedly without visible evidence of any deposition of materials on the surface of the burner and without requiring stoppage for cleaning purposes.

Various modifications may be made without departing from the invention. For example the velocity of discharge of hot gases on to the surface of the foam may be varied dependent on foam thickness, composition, speed of travel and fuel gas employed. Typically the minimum flame velocity using different fuel gases would be as follows:-

Natural gas 1.2 metres/second

Propane 1.6 metres/second

Hydrogen 9.6 metres/second

Town Gas 4.0 metres/second

these figures representing approximately twice the flame velocities employed in direct flame impingement lamination processes.

The distance of the burner or other hot gas generator from the surface of the foam may also be varied to control foam burn-off, impurity oxidation, preheating of the fabric and other factors. It should also be appreciated that while in the embodiment a fuel gas burner is employed to produce hot gases for impingement on the foam surface, other means of generating a hot gas stream may be employed. For example a nitrogen/oxygen mixture or other suitable gas may be heated electrically or by other means.

It should also be appreciated that while the invention has been described primarily with reference to the bonding of polyurethane foam to woven fabric, other fusible sheet materials including rigid or other flexible foamed plastics materials, may be bonded to other types of fabric or other substrates. In its wider aspects the invention may be used to bond any sheet material capable of melting by impingement thereon of a hot gas stream to a wide range of other sheet materials. The invention could also be applied to the production of multilayer laminations by employment of a plurality of burners or other hot gas generators of the same or different kinds at successive stages in a lamination process.

Whilst endeavouring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon.

Claims

1. A method of laminating a fusible sheet material to a substrate comprising heating the surface of the fusible sheet material by impingement thereon of a high velocity hot gas stream to render the surface tacky, and bringing the substrate into contact with said tacky surface whereby to bond the fusible sheet material and substrate together.

2. A method according to claim 1 wherein said fusible sheet material comprises a foamed plastics material and said substrate comprises a textile fabric.

3. A method according to claim 2 wherein the foamed plastics material is a flexible polyurethane foam.

4. A method according to claim 1, 2 or 3 wherein said hot gas stream is generated by combusting a gaseous fuel and directing the resultant hot gases on to the surface of said fusible sheet material.

5. A method according to claim 4 wherein said fuel comprises a hydrocarbon gas.

6. A method according to claim 5 wherein the hydrocarbon gas is selected from propane, natural gas, hydrogen and town gas.

7. A method according to any of claims 4 to 6 wherein the hot gas stream is generated by burning a mixture of atmospheric air and fuel gas in stoichiometric proportions with added oxygen rich gas to generate excess oxygen in the hot gas stream.

8. A method according to claim 7 wherein the mixture has at least 5% more oxygen than required to produce stoichiometric combustion.

9. A method according to claims 7 or 8 wherein the fuel gas mixture contains up to 25% excess oxygen.

10. A method according to claim 1, 2 or 3 wherein said hot gas stream is generated by electrically or otherwise heating a pressurised gas.

11. A method according to any preceding claim wherein a reaction zone is created between the source of said hot gas stream and the surface of the fusible sheet material, in which zone oxidation of vapours and impurities generated through melting of said sur ace takes place.

12. A method according to claim 11 wherein the source of said hot gas stream and said surface are separated by a distance of at least 30 mm to define said zone.

13. A method according to any preceding claim wherein the temperature of the gas stream is in the region of 750-1000°C.

14. A method according to any preceding claim wherein the velocity of the hot gas stream is between about 1 and about 10 m/sec.

15. Apparatus for laminating a fusible sheet material to substrate, the apparatus comprising means for generating a high velocity hot gas stream, means for directing same on to the surface of the fusible sheet material to render said surface tacky and means for bringing said tacky surface into contact with said substrate to bond same together.

16. Apparatus according to claim 15 wherein said means for generating said hot gas stream comprises a fuel gas burner having a combustion chamber and discharge outlet through which a hot gas stream generated by combustion of fuel gas within the combustion chamber is directed on to the surface of said fusible sheet material.

17. Apparatus according to claims 14, 15 or 16 wherein said fuel gas contains at least 5% more oxygen than required to effect stoichiometric combustion.

18. Apparatus according to any of claims 15 to 17 wherein a reaction zone is provided between an outlet from said means for generating said hot gas stream and the surface of said fusible sheet material.

19. Apparatus according to claim 18 wherein said zone is defined by control of the spacing between said outlet and said surface.

20. Apparatus according to claim 19 wherein said spacing is at least 30 mm.

21. Apparatus according to any of claims 15 to 20 wherein said means for generating said hot gas stream is of elongated form adapted to extend transversely of said fusible sheet material and having walls formed from a high conductivity refractory material such as silicon carbide.

22. Apparatus according to claim 21 wherein the outer surfaces of said walls are exposed to said reaction zone and maintained drying operation at a temperature in excess of 300°C.

23. Apparatus according to claims 14, 15 or 16 wherein said gas stream has a temperature in the region of 750-1000°C.

24. A method substantially as herein described with reference to the accompanying drawings.

25. Apparatus substantially as herein described with reference to the accompanying drawings.

26. Any novel subject matter or combination including novel subject matter disclosed herein, whether or not within the scope of or relating to the same invention as any of the preceding claims.