WO2006094834A1

WO2006094834A1 - Method and apparatus for directly coating a substrate with a hot flowable viscous adhesive

Info

Publication number: WO2006094834A1
Application number: PCT/EP2006/002294
Authority: WO
Inventors: Alan Ryan; Gerald Ryan
Original assignee: Ryco Book Protection Services Limited
Priority date: 2005-03-11
Filing date: 2006-03-10
Publication date: 2006-09-14
Also published as: WO2006094835A1; EP1861209A1

Abstract

A method and apparatus for applying a coating of a hot flowable adhesive to one surface of a thin flexible substrate. The adhesive is heated to above the degradation temperature of the substrate, so as to coat the substrate. The adhesive is applied while the opposite surface of the substrate is in intimate contact with a heat sink, the heat sink being cooled to a temperature substantially below the degradation temperature such that heat is conducted away from the substrate so that the substrate does not reach its degradation temperature and is consequently undamaged.

Description

Method and Apparatus for Directly Coating a Substrate with a Hot Flowable Viscous Adhesive

This invention relates to a method and apparatus for coating a thin flexible substrate with a hot flowable viscous adhesive. The invention is particularly, but not exclusively, applicable to coating a hot-melt adhesive onto a thin sheet of PVC to be used as a veneer (also known as a PVC foil) in the manufacture of items of furniture such as kitchen doors, drawer fronts, pelmets and the like.

Current methods in the manufacture of MDF-based kitchen furniture and fittings generally comprise the following steps:

1. Manufacturers purchase sheets of MDF and machine them to the shape required (e.g. doors, panels, etc. ) .

2. The MDF doors or panels are sprayed with a two- pack heat activated adhesive. This is a time- consuming process, since the components react on contact forming a sticky surface which requires several hours to properly dry. It is also prone to quality control issues, since the MDF may not be sprayed evenly, e.g. due to bad workmanship. If an area of the MDF, particularly at an edge, is uncoated, then the veneer is likely to come away from the substrate within a short period of use. 3. A thin flexible PVC material is purchased, with different patterns for different wood effects. The PVC is not coated with adhesive. The PVC is in rolls approximately 1.5m in width and 150-25Om in length, and has a thickness of about 300- 450 microns.

4. The PVC is pulled off a roll in sheets of 3m length onto a special press, and laid on top of the MDF doors that have been sprayed with adhesive. The press then produces a vacuum and heats the assembly up to 120⁰C, which activates the adhesive on the MDF doors and allows the PVC to stick and form a permanent bond.

In the above procedure, the MDF is sprayed with the adhesive, set aside for drying of several hours, and the PVC bonded to it. This is particularly time- consuming and costly. There are important reasons why the industry has had to use this process rather than some faster adhesive application process.

One of the main limitations is the need for an adhesive that will meet certain safety standards. A furniture panel mounted above a cooker must be stable at quite high temperatures. British Standard BS 6222 Part 3 (and equivalent standards in other systems) specifies that veneer or foil coated panels must be able to withstand elevated temperatures over a period of time without exhibiting reduced adhesion between the foil and the panel. One therefore needs an adhesive that sets solid at temperatures below about 70-90 degrees centigrade. Two pack adhesives which react to form a solid adhesive at room temperature are therefore particularly useful because the components may be liquid at room temperature before meeting, at which point the reaction occurs.

Meltable adhesives, such as are used in hot flow processes, must have a melting point above the test temperatures. Such adhesives are typically extremely viscous at lower temperatures and need to be heated to 200 degrees or so to allow them to be used in liquid application processes. Such adhesives cannot be readily sprayed because of the high temperatures involved. Hot melt application processes are unsuitable for typical furniture panels because of the need to coat irregular surfaces, corners, routed features, protrusions, and the like.

A better solution would be to coat the PVC with the adhesive, which would then allow the direct application of the PVC to the MDF without the spraying and handling involved in coating the MDF.

The normal application of an adhesive to PVC is through use of a release-liner system. However, it is difficult to find a satisfactory adhesive that can be applied with a release liner technique at a temperature below that at which PVC foil will degrade. In any event, use of this method results in greater effort (in applying and subsequently removing the liner) , and greater cost due to the extra materials involved. Directly coating the PVC with the adhesive (e.g. using a hot melt technique) faces the problem that the hot- melt adhesive is very viscous and must be heated to about 205-210⁰C for it to be liquefied sufficiently for application. If PVC comes into contact with a substance at this temperature, the PVC instantly begins to shrivel up and melt (e.g. like a foil-coated plastic snack packet - such as a packet of potato crisps or chips - placed in an oven or on a fire) .

Accordingly, the invention provides a method of applying a coating of a hot flowable adhesive to one surface of a thin flexible substrate, the adhesive being above the degradation temperature of the substrate, wherein the adhesive is applied while the opposite surface of the substrate is in intimate contact with a heat sink cooled to a temperature substantially below the degradation temperature such that heat is conducted sufficiently rapidly away from the substrate that the latter does not reach its degradation temperature.

By "degradation temperature" we mean the substrate temperature above which the character or quality of the substrate would significantly deteriorate. This is about 150⁰C for the thin flexible PVC sheeting typically used in furniture manufacture as described above and used in the preferred embodiment.

Preferably the substrate is conveyed past the heat sink as a continuous length from a supply roll to a take-up roll, and the adhesive is applied to the substrate as it passes the heat sink.

Most preferably the heat sink comprises at least one cooled roller around which the substrate passes.

The invention further provides a method of veneering an item of furniture, comprising the steps of coating a thin flexible substrate with a hot melt adhesive by the method specified above, drying the adhesive, applying the substrate to the item of furniture, and applying heat and pressure to the substrate to activate the adhesive and cause the substrate to conform to and bond to the item.

A difficulty in extruding a viscous substance such as a hot melt adhesive of this kind, is the difficulty in ensuring an even coating weight on the substrate as it moves past the mouth of the slot die.

The invention further provides a slot die for coating a substrate with a viscous substance, the die comprising top and bottom elongated substantially parallel die members separated by a gap defining an adhesive exit slot between longitudinal forward edges of the die members, wherein the forward edge of the bottom die member extends beyond the forward edge of the top die member to form a narrow ledge on the bottom die member, whereby in use a viscous substance extruded from the slot beyond the forward edge of the top die member is received on the ledge before being picked up by a substrate moving past the forward edge of the bottom die member.

In general, use of a wide extrusion slot die means that it is harder to control the coating weight of the substance to be applied. The ledge created between the forward edges of the die members allows for a more even coating weight of the adhesive to be applied, and can be altered depending on how far the forward edge of the bottom die extends beyond the forward edge of the top

While the invention relates to the configuration of the slot dye, the corresponding method and apparatus of application associated with the use of the slot dye is also described.

Preferably said gap between the top and bottom die members is defined by a shim which also prevents exit of the adhesive from between longitudinal rear edges of the die members.

The invention further provides a slot die for coating a substrate with a hot flowable viscous adhesive, the die comprising top and bottom elongated substantially parallel die members separated by a shim, the shim defining an adhesive exit slot between longitudinal forward edges of the die members and preventing exit of the adhesive from between longitudinal rear edges of the die members, wherein the shim comprises a flat elongated back portion and a pair of flat arms extending forwardly from each end of the back portion to define an elongated generally U-shaped flat planar body which confines the adhesive on three sides and is open towards the adhesive exit slot, wherein the inside edges of the arms diverge away from the back portion such that the distance between the free ends of the arms is greater than the distance between the points at which the arms meet the forward edge of the back portion, whereby the length of the exit slot is greater than the length of the forward edge of the back portion between the arms .

Use of conventional shims in extrusion slot dies can prevent the even spread of the coating substance to the ends of the die. The shim in the present application has tapered arms edges, which allow for an even flow of the substance to be applied along the whole length of the slot die. In preferred embodiments the arms taper to a point at the forward corner of the die.

In another independent aspect of the invention there is provided a method of applying a coating of a hot flowable adhesive to a first surface of a thin flexible substrate, comprising the steps of: applying the adhesive, at a temperature suitable to allow extrusion thereof from a die, onto a front surface of an intermediate carrier sheet; allowing the adhesive to cool by an amount less than that which would bring the adhesive below the minimum temperature required for it to bond to the substrate; and contacting the adhesive on the front surface of the intermediate carrier sheet with a bonding surface of said thin flexible substrate while said adhesive is still above said minimum bonding temperature whereby said adhesive bonds to said bonding surface of said substrate; thereby resulting in the adhesive being cooled and bonded to the substrate permitting later removal of the intermediate carrier sheet.

In this aspect of the invention, the intermediate carrier sheet is employed to receive and transport a thin layer of adhesive suitable for application to the substrate, while the adhesive cools from an extrusion temperature (which may be too hot for the substrate, i.e. above the degradation temperature) to a lower temperature which is still sufficiently hot to allow the adhesive to properly bond with the substrate.

Thus, it has been recognised that while extrusion temperatures for hot melt adhesives may be too hot to allow their application to sensitive foils, an intermediate carrier can be employed to transfer the adhesive once a small amount of cooling has occurred, without adversely affecting the bonding of the adhesive to the substrate.

Preferably, the adhesive is applied to the front surface of the intermediate carrier sheet while the opposed back surface of the intermediate carrier sheet is in intimate contact with a primary heat sink.

Preferably, the step of contacting the adhesive with the substrate occurs while the intermediate carrier sheet is in intimate contact with the primary heat sink.

Preferably, the intermediate carrier sheet is conveyed past the primary heat sink as a substantially continuous length, and the adhesive is applied to the intermediate carrier sheet as the intermediate carrier sheet passes the primary heat sink, prior to the point of contact of the adhesive with the substrate.

Preferably, the substrate is provided as a substantially continuous length which is introduced into contact with the adhesive on the substantially continuous length of intermediate carrier sheet.

Preferably, the non-bonding surface of the substrate is in intimate contact with a secondary heat sink as the substrate is contacted with the adhesive to thereby conduct heat away from the substrate.

Preferably, the substrate is pre-cooled prior to contact with the adhesive.

Preferably, the pre-cooling occurs by conveying the substrate past an upstream auxiliary heat sink upstream of the point of contact of the substrate with the adhesive.

Alternatively, the pre-cooling may occur by subjecting the substrate to cooled air. Preferably, the coated substrate is wound onto itself on a substrate winding roller once the adhesive has cooled below its activation temperature.

Preferably, the intermediate carrier sheet is separated from contact with the adhesive once the adhesive has cooled below its activation temperature.

Preferably, the intermediate carrier sheet is wound onto itself on a liner winding roller once the intermediate carrier sheet is separated from the adhesive .

Preferably, the substrate, adhesive and intermediate carrier sheet are conveyed past a downstream auxiliary heat sink to accelerate the cooling of the adhesive.

Preferably, the downstream auxiliary heat sink is provided downstream of the point of contact of the substrate and the adhesive and upstream of the point of separation of the adhesive and the intermediate carrier sheet.

Preferably, the invention also provides an apparatus for applying a coating of a hot flowable adhesive to one surface of a thin flexible substrate, the apparatus comprising a supply roller for supplying a length of said substrate a take-up roller for receiving said length of substrate, and an adhesive application station intermediate said supply roller and take up roller, wherein said adhesive application station comprises an adhesive applicator and a heat sink, the adhesive applicator being adapted and controlled to apply an adhesive to the substrate at a temperature greater than the degradation temperature of the substrate, and the heat sink being positioned to make intimate contact with the substrate as it passes the adhesive applicator whereby heat is conducted sufficiently rapidly away from the substrate that the latter does not reach its degradation temperature.

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

Fig. 1 is a schematic side view of a first apparatus for coating a thin flexible substrate with a hot-melt adhesive;

Fig. 2 is an exploded view of a slot die used in the apparatus of Fig. 1;

Fig. 3 is a top view of the slot die of Fig. 2, omitting the top die member;

Fig. 4 is a cross-section through the slot die taken on the line IV-IV of Fig. 3;

Fig. 5 is an enlarged view of the adhesive exit slot of the slot die of Fig. 2; and

Fig. 6 is a schematic side view of a second apparatus for coating a thin flexible substrate with a hot-melt adhesive. Referring initially to Fig. 1 of the drawings, the apparatus comprises PVC supply and take-up rolls 10 and 12 respectively, rotatable about substantially parallel axes. Initially the roll 10 is full and the roll 12 is empty. The PVC on the full roll 10 is a continuous flexible sheet 150-25Om long, and is about 1.5m wide and, depending on the application, 300-450 microns thick. At this stage it is not coated with adhesive. In use the PVC sheet 20 is conveyed continuously from the supply roll 10 to the take-up roll 12 along a path defined by guide rollers 14 and refrigerated rollers 16, 18.

Solid adhesive to be applied to the PVC sheet 20 is added to a melt tank 22 where the adhesive is heated to melt it to form a viscous liquid. In this embodiment the adhesive is a polyamide adhesive and is heated to a temperature of approximately 205⁰C, which reduces the viscosity of the molten adhesive to allow it to be pumped into and extruded from a die. The hot viscous adhesive is pumped along a supply line 24 to an adhesive applicator 26 including a slot die 28, Figs. 2-5, where the adhesive 30 (Fig. 5) is applied as a thin coating 32 continuously across the width of the moving PVC sheet 20. The speed of the PVC sheet is typically 10-50 meters/min and the adhesive applied with a coating weight in the range 40-75g per square meter. The slot die 28 is heated to about 200⁰C to maintain the temperature of the adhesive prior to application to the PVC, and is biased against the moving PVC sheet with a pressure of about 3 bar. At the point at which the adhesive is applied to the exposed surface of the thin PVC sheet 20, the opposite surface of the sheet is in intimate contact with the refrigerated roller 16. The roller 16 is a hollow steel cylinder which contains 401trs of water and antifreeze at -5⁰C, the roller 16 being maintained at this temperature by continuously pumping chilled water through it via standard rotary bearings. The roller 16 therefore acts as a relatively massive heat sink for the thin PVC sheet 20, so that the heat of the adhesive 30 and die 28 is rapidly conducted away from the PVC sheet by the roller. The pressure of the slot die 28 on the sheet 20 ensures that the PVC is in uniform intimate contact with the roller 16 across its full width.

As a result, the PVC sheet 20 (which is already cold since it was brought into contact with the roller 16 prior to reaching the die 28) does not have time to reach its degradation temperature before the PVC has moved away from the heated die 28 and the adhesive coating 32 has cooled to below the degradation temperature. In this embodiment a second refrigerated roller 18 is placed immediately downstream of the roller 16. The roller 18 is constructed and cooled the same as the roller 16. The roller 18 continues to cool the adhesive and ensure that the temperature of the PVC does not rise above the degradation temperature. The outer surface of the roller 16 may be covered with a thin layer of rubber to allow a certain amount of give when applying the adhesive. If desired the PVC sheet can be pre-cooled by a third refrigerated roller (not shown) located upstream of the roller 16.

By the time the PVC sheet 20 has left the chilled rollers 16, 18 the adhesive coating is dry and so the coated PVC can be directly wound into the take-up roll 12 for storage for further use, without requiring a release liner.

If necessary, by swapping the now full take-up roll 12 with the empty supply roll 10, the adhesive-coated PVC sheet 20 can be passed a second time through the apparatus to increase the thickness of the adhesive coating. This might be necessary where the desired final thickness of adhesive, if applied in one pass at a given speed of the PVC sheet 20, would be too thick for sufficiently rapid cooling by the heat sinks 16, 18 to avoid degradation of the PVC sheet.

The adhesive-coated PVC sheet (or other veneer material) is now cut from the roll 12 in appropriate- sized lengths for application to MDF furniture panels such as doors, drawer fronts, etc. This is done using a conventional press, the PVC being laid on top of the furniture panel, adhesive side down. The press then produces a vacuum and heats the assembly up to 120⁰C, which re-activates the adhesive on the PVC and allows the PVC to conform to and adhere to the MDF panel and form a permanent bond.

Referring now to Figs. 2-5, the slot die 28 comprises top and bottom elongated substantially parallel die members 40, 42 respectively. The die members 40, 42 are separated by a shim 44, the three components 40, 42, 44 being secured tightly together by bolts, not shown (the bolt holes 46 are shown in Fig. 3, but are not otherwise seen in the drawings) . The die members 40, 42 are made of high tensile stainless steel while the shim 44 is made of brass or Teflon.

The shim can be advantageously made to precisely the right thickness by applying layer upon layer of thin

Teflon tape and cutting the tape to shape, such that as layers are added the thickness is increased incrementally. Such a shim can have its thickness adjusted by adding or removing layers to adjust the characteristics of the slot die if necessary.

By maintaining the die members 40, 42 slightly spaced apart with the shim 44, a slot 48 is defined between the longitudinal forward edges 50, 52 of the die members 40, 42. However, the forward edge 52 of the bottom die member 42 extends beyond the forward edge 50 of the top die member 40 to form a narrow ledge 54 on the bottom die member 42 projecting forwardly of the upper die member 40.

A highly elongated oval trough 56 is set into and extends along the length of the upper surface of the bottom die member 42, and one or more adhesive entrance ports 58 (only one shown) communicate with the trough 56 from the rear of the die member 42. In use, adhesive is pumped into the trough 56 via the port(s) 58 for distribution along the length of the die. The shim 44 comprises a flat elongated back portion 44A and a pair of flat arms 44B extending forwardly from each end of the back portion to define an elongated generally U-shaped flat planar body which confines the adhesive on three sides and is open towards the slot 48. Thus the shim 44 prevents the exit of adhesive 30 from the ends and between the longitudinal rear edges of the die members 40, 42 and ensures that the adhesive exits only through the front slot 48. The inside edges 44C of the arms 44B diverge away from the back portion 44A at about 45° such that the distance between the free ends of the arms is greater than the distance between the points at which the arms meet the forward edge of the back portion. Thus the length of the exit slot 48 is greater than the length of the forward edge of the back portion 44A between the arms 44B, allowing the slot 48 to extend substantially the full length of the die members 40, 42.

The length of the die members 40, 42 is approximately 1.5m (i.e. about the same as the width of the PVC sheet 20) and the depth of the adhesive exit slot 48, as determined by the thickness of the shim 44, ranges from 0.25mm to 2mm depending on the viscosity of the adhesive used. For example, a slot depth of lmm would typically be needed for an adhesive having a viscosity of 44,000 millipascals. The width of the ledge 54, i.e. the amount by which the edge 52 projects beyond the edge 50, is about 0.25mm. In use the viscous adhesive extruded from the slot 48 beyond the forward edge 50 of the top die member 40 is received on the ledge 54 where it is picked up by the PVC sheet 20 moving past the forward edge 52 of the bottom die member 42. In order to minimise the area of die 28 in contact or near to the PVC sheet 20 the forward edges 50, 52 of the top and bottom die members 40, 42 project forwardly slightly relative to the main body of the die members .

The weight of the adhesive coating 32 on the PVC sheet 20 depends upon the adhesive viscosity, the shim thickness, the rate of pumping the adhesive 30 to the slot die 28, and the speed of travel of the PVC sheet 20. The latter two variables, as well as the temperature of the adhesive and die, can be set by an operator control panel 34. The depth of the slot 48 can be set by using a shim 44 of the desired thickness.

The apparatus can be used to coat other thin flexible sheet material with other hot-melt adhesives. In all cases, however, the relevant parameters are selected so that the particular sheet material being coated does not reach its degradation temperature before the sheet material has moved away from the heated die and the adhesive has cooled to below the degradation temperature.

For certain thin PVC foils (e.g. ~ 200 micron thickness) , the direct application of the adhesive to the foil as described in the above embodiment results in degradation of the foil due to lesser structural integrity. Consequently, another method of application of the adhesive must be used. In this embodiment, an intermediate carrier sheet is employed to transfer hot- melt adhesive onto the PVC foil substrate.

While transfer coating methods are well-known in the area of pressure-sensitive adhesives, they are not conventionally used with the temperature-sensitive adhesives required in certain applications (e.g. where the adhesive must maintain its adhesion up to a threshold temperature such as in kitchen furniture) .

In this embodiment, as can be seen from Fig. 6, a new coating apparatus is employed. The apparatus comprises intermediate carrier sheet supply and take-up rolls 80 and 82 respectively, and PVC foil supply and take-up rolls 84 and 86 respectively. Initially, the supply rolls 80 and 84 are full, and the take-up rolls 82 and 86 are empty.

A length of intermediate carrier sheet 88 is conveyed continuously from the intermediate carrier sheet supply roll 80 to the intermediate carrier sheet take-up roll 82, along a path defined by guide rollers 14 and refrigerated rollers 92 and 94. In this embodiment, the intermediate carrier sheet comprises silicone paper, but it will be understood that other intermediate carrier sheet materials may be employed, for example filmic liners such as PET and PT.

A sheet of PVC foil 90 is conveyed continuously from the PVC supply roll 84 to the PVC take-up roll 86, along a path defined by guide rollers 14 and refrigerated rollers 94 and 96. This embodiment is particularly directed towards the coating of thin PVC foils (e.g. -100-300 micron thick), but it will be understood that foils of other thickness may similarly be used.

The adhesive is applied to the intermediate carrier sheet 88 using an adhesive applicator 26 including a slot die 28 as described previously. The adhesive is heated to such a temperature that the adhesive viscosity is reduced, so that the adhesive can be extruded through the slot die 28 and onto the intermediate carrier sheet. As the adhesive is applied to the intermediate carrier sheet, the opposite surface of the intermediate carrier sheet is in intimate contact with the refrigerated roller 92 which is maintained (in this embodiment) at a constant temperature of e.g. -2 to +4 degrees Celsius. The refrigerated roller acts as a heat sink to draw heat away from the adhesive, in a controlled manner, so that the adhesive drops below the degradation temperature of the foil (or sufficiently close above that temperature so that the specific heat capacity of the foil and the environment will prevent the foil from degrading on contact) .

The adhesive is evenly applied to the intermediate carrier sheet, and heat is conducted away from the adhesive through the refrigerated roller 92. The adhesive does not bond with the intermediate carrier sheet 88, as the intermediate carrier sheet is made from a suitably inert material, e.g. silicon paper in the present embodiment. The adhesive on the intermediate carrier sheet 88 is then brought into intimate contact with the PVC foil 90. In this embodiment, the PVC foil is conveyed in intimate contact with the refrigerated roller 96 prior to contact with the adhesive. The intermediate carrier sheet 88, adhesive, and PVC foil 90 are then sandwiched between the respective refrigerated rollers 92,96.

Either of the refrigerated rollers can be unrefrigerated provided that the temperature of the adhesive remains within the desired parameters, and the system designer has a reasonable amount of freedom in tailoring the system to the speeds, adhesives, foils and ambient termperatures of any given situation.

In the illustrated embodiment, however, the PVC foil 90 is pre-cooled through intimate contact with the refrigerated roller 96. Through the cooling effect of the two refrigerated rollers 92,96 the PVC foil is prevented from reaching its degradation temperature when the PVC foil comes into contact with the hot adhesive. However, the adhesive is maintained above a minimum bonding temperature e.g. 120 degrees Celsius that allows the adhesive to bond to the surface of the PVC foil.

As the skilled person will appreciate, the minimum bonding temperature can be generally equated with the activation temperature of the adhesive, but successful bonding is dependent not only on temperature but also on contact time and contact pressure. An adhesive with an activation temperature of 120 degrees Celsius might only generate a successful bond with the substrate when pressure is applied for a few minutes; such an adhesive will preferably be kept above a higher temperature so that bonding can occur effectively instantaneously due to the action of the rollers.

The sandwich of intermediate carrier sheet 88, adhesive, and PVC foil 90 is carried along a common path and conveyed past the further refrigerated roller 94. In this embodiment, the roller 94 cools the adhesive sufficiently so that it is below the activation/bonding temperature for the adhesive, though again this can be achieved through alternative cooling means such as through natural ambient cooling, blasting with cold air or even spraying with water.

At this point, the paths of the intermediate carrier sheet 88 and the PVC foil 90 diverge, the intermediate carrier sheet 88 being wound on to the intermediate carrier sheet take-up roll 82 and the PVC foil 90 being wound onto the PVC foil take-up roll 86. Due to the bond between the adhesive and the PVC foil, the adhesive is lifted off the front surface of the intermediate carrier sheet 88, and is wound onto the PVC foil take-up roller 86 with the PVC foil 90.

As the adhesive is, by now, cooled below its bonding temperature, the adhesive and PVC foil 90 can be stored in roll form without the adhesive sticking to the non- bonded surface of the PVC foil 90. In another embodiment of this invention, the intermediate carrier sheet need not be separated from the adhesive, and may be stored on the PVC take-up roll 86 for later removal.

It will be understood that further refrigerated rollers may be employed to pre-cool the PVC foil 90, or to conduct heat away from the intermediate carrier sheet 88, adhesive, PVC foil 90 sandwich.

The roll of coated PVC foil 90 can be removed, and the foil cut to appropriate-sized lengths for use in application to materials to be covered, as described

The invention is not limited to the embodiment described herein which may be modified or varied without departing from the scope of the invention.

Claims

1. A method of applying a coating of a hot flowable adhesive to one surface of a thin flexible substrate, the adhesive being above the degradation temperature of the substrate, wherein the adhesive is applied while the opposite surface of the substrate is in intimate contact with a primary heat sink cooled to a temperature substantially below the degradation temperature such that heat is conducted sufficiently^' rapidly away from the substrate that the latter does not reach its degradation temperature.

2. The method of claim 1, wherein the substrate is conveyed past the primary heat sink as a continuous length, and the adhesive is applied to the substrate as it passes the primary heat sink.

3. The method of claim 2, wherein the substrate is conveyed past a downstream auxiliary heat downstream of the primary heat sink, so that the temperature of the substrate is maintained below the degradation temperature of the substrate.

4. The method of claim 2 or 3, wherein the substrate is conveyed past an upstream auxiliary heat sink upstream of the primary heat sink, to pre-cool the substrate prior to the application of the adhesive.

5. The method of any one of claims 1-4, wherein the or each heat sink comprises a cooled roller over which the substrate passes.

6. The method of claim 5, wherein at least one cooled roller is coated with rubber.

7. The method of claim 5 or 6, wherein the cooled roller is maintained at a temperature within the range of -15' ⁰C to +5⁰C.

8. The method of any preceding claim, further comprising the step of applying one or more additional coatings of adhesive to the substrate in order to increase overall coating thickness.

9. The method of claim 8, wherein the applied adhesive is allowed to cool and harden between consecutive applications .

10. The method of any preceding claim, wherein the thin flexible substrate is PVC.

11. The method of any preceding claim, wherein the adhesive is a Polyamide/EVA/Polyurethane or known polymer adhesive.

12. The method of any preceding claim, wherein the degradation temperature is in the region of 130-210°C.

13. The method of any preceding claim, wherein the temperature of the adhesive when applied is in the region of 160-220°C.

14. The method of any preceding claim, wherein the substrate is a continuous flexible sheet at least 1.3m to 2m wide.

15. The method of any preceding claim, wherein the adhesive is applied to the substrate as the substrate moves at a speed of from 5m to 100m per minute.

16. The method of claim 15, wherein the speed is constant.

17. The method of any preceding claim, wherein the adhesive is applied to the substrate so that the eventual coating weight of the adhesive on the substrate is in the region of 40-15Og per metre squared.

18. The method of any preceding claim, wherein the adhesive is applied by pumping through a slot die positioned to sandwich the substrate between the slot die and the primary heat sink.

19. The method of claim 18, wherein the slot die is heated to a temperature in the range of 160-220⁰C.

20. A method of veneering an item of furniture, comprising the steps of coating a thin flexible substrate with a hot melt adhesive by a method as claimed in any preceding claim, drying the adhesive, applying the substrate to the item of furniture, and applying heat and pressure to the substrate to activate the adhesive and cause the substrate to conform to and bond to the item.

21. The method of claim 20, wherein the substrate is cut into a length suitable for the item of furniture to be coated.

22. The method of claim 20 or 21, wherein the adhesive is heated to a temperature of 120⁰C in a vacuum to activate the adhesive.

23. An apparatus for applying a coating of a hot flowable adhesive to one surface of a thin flexible substrate, the apparatus comprising a supply roller for supplying a length of said substrate a take-up roller for receiving said length of substrate, and an adhesive application station intermediate said supply roller and take up roller, wherein said adhesive application station comprises an adhesive applicator and a heat sink, the adhesive applicator being adapted and controlled to apply an adhesive to the substrate at a temperature greater than the degradation temperature of the substrate, and the heat sink being positioned to make intimate contact with the substrate as it passes the adhesive applicator whereby heat is conducted sufficiently rapidly away from the substrate that the latter does not reach its degradation temperature.

24. A slot die for coating a substrate with a hot flowable viscous adhesive, the die comprising top and bottom elongated substantially parallel die members separated by a shim, the shim defining an adhesive exit slot between longitudinal forward edges of the die members and preventing exit of the adhesive from between longitudinal rear edges of the die members, wherein the forward edge of the bottom die member extends beyond the forward edge of the top die member to form a narrow ledge on the bottom die member, whereby in use a viscous adhesive extruded from the slot beyond the forward edge of the top die member is received on the ledge before being picked up by a substrate moving past the forward edge of the bottom die member.

25. The slot die of claim 24, wherein the substrate is coated with a constant coating weight of adhesive, said coating weight being determined at least in part by the distance that the forward edge of the bottom die member extends beyond the forward edge of the top die member.

26. The slot die of any one of claims 24 to 25, wherein the gap between the top and bottom die members is defined by a shim which also prevents exit of the adhesive from between longitudinal rear edges of the die members.

27. The slot die of claim 26, wherein the slot die members are made of high tensile stainless steel.

28. The slot die of claim 27, wherein the shim is made of teflon or other heat resistant materials.

29. The slot die of claim 28, wherein the shim is built up from teflon tape layers adhered on top of one another .

30. The slot die of any one of claims 24-29, wherein the slot die is heated, in use, to a temperature in the range of 160-220°C.

31. A slot die for extruding a viscous substance, the die comprising top and bottom elongated substantially parallel die members separated by a shim, the shim defining an exit slot between longitudinal forward edges of the die members and preventing exit of the adhesive from between longitudinal rear edges of the die members, wherein the shim comprises a flat elongated back portion and a pair of flat arms extending forwardly from each end of the back portion to define an elongated generally U-shaped flat planar body which confines the substance on three sides and is open towards the adhesive exit slot, wherein the inside edges of the arms diverge away from the back portion such that the distance between the free ends of the arms is greater than the distance between the points at which the arms meet the forward edge of the back portion, whereby the length of the exit slot is greater than the length of the forward edge of the back portion between the arms .

32. The slot die of claim 31, wherein the shim arms taper forward to a point at the respective forward corners of the die.

33. The slot die of claim 31 or 32, wherein said die is an extrusion die adapted for extruding a hot melt adhesive .

34. The slot die of any one of claims 31-33, wherein the forward edge of the bottom die member extends beyond the forward edge of the top die member to form a narrow ledge on the bottom die member, whereby in use a viscous adhesive extruded from the slot beyond the forward edge of the top die member is received on the ledge before being picked up by a substrate moving past the forward edge of the bottom die member.

35. The slot die of any one of claims 31-34, wherein the shim comprises a plurality of layers of a tape of a heat resistant material one on top of another, whereby the shim thickness may be increased incrementally by adding further layers of said tape.