CA2323546A1

CA2323546A1 - Ultrasonic seam bonding method and apparatus

Info

Publication number: CA2323546A1
Application number: CA002323546A
Authority: CA
Inventors: Robert Clark
Original assignee: Individual
Current assignee: Rosslyn Precision Ltd
Priority date: 1998-03-12
Filing date: 1999-03-12
Publication date: 1999-09-16
Also published as: EP1077802B1; GB9805176D0; US6521067B1; AU2741199A; EP1077802A1; DE69913125D1; ATE254994T1; WO1999046110A1; DE69913125T2

Abstract

This invention relates to an apparatus and method for joining fabric, particularly for joining separate pieces of layered fabric, by means of a waterproof seam in a single operation. The seam bonding apparatus comprises a hot-melt adhesive supply (20), a transducer (24) which supplies ultrasonic energy and a sonotrode (23) which directs the ultrasonic energy to an application point on the seam to be bonded. Adhesive, preferably molten nylon, is fed through a passage (25) in the sonotrode (23) via an exit aperture (28) at the end of the sonotrode to the application point. Local heat is applied to the other side of the seam at the application point, and the seam is then subjected to local cooling to form a permanent waterproof seam.

Description

2

3 This invention relates to an apparatus and method for

4 joining fabric, particularly for joining separate pieces of layered fabric, by means of a waterproof seam 6 in a single operation.

8 The apparatus and method of the invention allows 9 separate pieces of fabric (woven, non-woven or laminated) to be joined with a strong, flexible, 11 waterproof seam in a single operation.

13 Presently, many fabrics are sewn together with thread.
14 If waterproofing of the seams is required, this is achieved by applying a sealing tape. This is a non-16 porous adhesive tape which covers the seam completely, 17 and prevents moisture from passing through the gap 18 between the fabric pieces, through the needle holes or 19 along the threads. Making such a seam is a two-stage process, with the seam first being sewn, and then later 21 being waterproofed with sealing tape. Such a process 22 is time consuming and costly.

24 An alternative method of joining thin sheets of thermoplastic is by welding the sheets together. Such "A 02323546 2000-09-12 ' . ~ .. .. .. .... .. ..
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1 welds are formed by overlapping the sheets of material 2 and then fusing them by heating. This is done by using 3 heated rollers or knives, or by ultrasonic action, as is 4 disclosed by Canadian Patent Application No 2,056,812_ S
6 Adhesives may be used to join overlapping sheets of 7 material to form a seam, but the practice is uncommon, 8 due to problems in reliability, surface preparation, and 9 achieving uniform adhesive spread.
11 Overlapping welded or glued bonds are problematic for 12 laminated fabrics. When the seam is flexed, any loads are 13 transferred through the adjacent outer laminations of 14 each piece of fabric (see Fig 1). This results in an uneven stress distribution over the cross-section of the 16 fabric, which leads eventually to de-lamination. In the 17 case of laminated fabrics, better stress transfer would 18 be obtained by joining the fabric pieces end-to-end, with I9 adhesive, so that loads could be transferred evenly across the bond in contrast to the prior art. For 21 example, Canadian Patent Application No 2,056,812 22 discloses a method of joining sheets of a non-woven 23 fabric in an overlapping or face to face configuration 24 (see Figures 2 and 3 therein and page 2, lines 12-17 therein) applying a hot-melt adhesive through a glue 26 nozzle, passing the sheets over a patterned anvil roll 27 and heating the joint by means of an ultrasonic horn 28 which transmits mechanical vibrations to the sheets to be 29 joined. This method does not function well with fabrics other than very light, thin non-woven fabrics.

32 It is ar_ object of the present invention to provide an 33 apparatus and method for joining fabric in a single 34 operation, which is suitable for use with laminated fabrics, which promotes penetration of the fabric by AMENDED SHEET

1 the adhesive, and which allows a strong bond to be 2 made.

4 According to a first aspect of the invention there is provided a seam bonding apparatus comprising a hot-melt 6 adhesive supply means, an ultrasonic energy source and 7 a sonotrode adapted to direct ultrasonic energy to an 8 application point on the seam to be bonded, wherein the 9 sonotrode has therein a passage adapted to permit flow therethrough of adhesive from said hot-melt adhesive 11 supply means to said application point.

13 Preferably the apparatus further comprises a nozzle 14 communicating with said passage. Preferably said nozzle is adapted to be less than 5mm from the 16 application point, most preferably less than 2mm from 17 the application point.

19 According to a particular embodiment said nozzle is integral with said sonotrode. Preferably said passage 21 comprises a first axial portion. Preferably said 22 passage further comprises a substantially radial 23 portion communicating with said axial portion.

According to a further particular embodiment the 26 apparatus comprises a glue chamber adjacent to said 27 sonotrode. Preferably said passage and said nozzle 28 each communicate with said glue chamber. Preferably 29 said glue chamber has a parabolically shaped inner surface.

32 Preferably said hot-melt adhesive supply means 33 comprises a hot-melt adhesive tank and a pump.
34 Preferably the apparatus further comprises a heated delivery pump connecting said pump to the passage.

1 According to a second aspect of the invention there is 2 provided a method for producing a bond between members 3 of an article, said method comprising the steps of:
4 heating a hot-melt adhesive until it is molten, feeding said molten adhesive to an application 6 point in which said adhesive contacts said members, 7 applying ultrasound energy by means of a sonotrode 8 to said molten adhesive, and 9 allowing said molten adhesive to cool and thereby form a bond between said members.

12 Preferably mechanical vibrations are induced by the 13 ultrasound energy in said members to aid the formation 14 of the bond.
16 Preferably the molten adhesive is fed through a passage 17 in said sonotrode.

19 Preferably the molten adhesive is fed onto the application point through a nozzle positioned such that 21 there is a small gap between said members and said 22 nozzle. Preferably said gap is less than 5 mm, most 23 preferably less than 2 mm.

Preferably said members are positioned in an abutting 26 position, such that a butt bond is produced between 27 said members.

29 Preferably the method uses an apparatus according to the first aspect of the invention.

32 According to a third aspect of the invention there is 33 provided an article comprising a plurality of members 34 and having a bond produced between two of said members by the method according to the second aspect of the 36 invention.

1 The method and apparatus of the invention offer 2 significant advantages over the prior art. The method 3 poses little threat to the operator, and the following 4 effects of using ultrasound aid the formation of a good

5 bond:

6

7 a. Energy can be transmitted via the molten adhesive

8 to the seam. This energy can also be focused.

9 b. Ultrasound causes heating and softening of solid 11 polymer, such as the fabric fibres in contact with 12 the adhesive. Crystallisation of the molten 13 adhesive is also inhibited.

c. Ultrasound can cause cavitation in liquids. There 16 are two manifestations:

18 i. Cyclical expansion and contraction of 19 stationary voids. This causes pumping of the surrounding liquid, to form microstreams.

22 ii. Random formation of large voids which 23 subsequently implode, causing high pressure 24 transients.
26 These effects encourage separation of the fabric 27 fibres and active infiltration by the adhesive.

29 The fabric may be preheated to achieve a good bond with the holt-melt adhesive.

32 The process is particularly effective when used with 33 composite fabrics having between two and four layers 34 with a total thickness of 200-500 ~.m. With such fabrics the method can achieve seam sealing rates in 36 the range 2-8 m/min (0.033-0.33 m/s).

10 PCT/GB99/00758 1 Seam sealing according to the invention can be carried 2 out with composite fabrics whose outer layers are 3 commonly polyester, nylon, acrylic or polyester-cotton.
4 The composite fabrics may include semi-permeable membranes of polyamide or polyurethane.

7 It is possible to extrude the adhesive into a thread, 8 allowing it to be fed to the seam as a solid.
9 Different diameters of thread may be matched with different thicknesses of material, to be transported by

11 the same feed mechanism as the fabric.

12

13 Cooling may be by forced convection, using the cold

14 air-stream from a vortex tube. The hot air by-product of the tube may be used for preheating the fabric.

17 Peltier heat pump assemblies are available, rated at 18 tens of Watts. These may be attached to compression 19 plates, recessed to avoid contact with the adhesive, which remove heat from the fabric by conduction, and 21 from the melt by radiation and conduction via the 22 fabric.

24 An embodiment of the invention will now be described, by way of example only, with reference to the 26 accompanying figures, where:

28 Fig. 1 is a section through a prior art laminated 29 fabric seam;
31 Fig. 2 is a section through a laminated fabric seam 32 obtained by the apparatus and method of the invention;

34 Fig. 3 is a schematic view of the apparatus according to a first embodiment of the invention;

1 Fig. 4 is a schematic view of the apparatus according 2 to a second embodiment of the invention;

4 Fig. 5 is a schematic view of the apparatus according to a third embodiment of the invention;

7 Figs. 6 to 8 are sections through three alternative 8 embodiments of the apparatus shown in Fig. 3, showing 9 different sonotrode arrangements;
11 Fig. 9 is a side elevation of the sonotrode of the 12 apparatus of Fig. 7;

14 Fig. 10 is a section through a fourth alternative embodiment of the apparatus shown in Fig. 3;

17 Fig. 11 is a side elevation on an apparatus according 18 to a further embodiment of the invention, showing the 19 heating and cooling means;
21 Fig. 12 is a front elevation on line XII-XII of Fig.
22 11;

24 Fig. 13 is a plan view on the fabric support surface of the apparatus of Fig. 11;

27 Fig. 14 is a schematic view of the apparatus of Fig. 11 28 incorporating a video gap detection system; and Fig. 15 is a plan view on the fabric support surface of 31 the apparatus of Fig. 14.

33 Referring to Fig. 1 there is shown a seam 1 formed by 34 applying adhesive 7 between two laminated fabric sheets 2 and 3. When the joined sheets are subject to tension 36 in the direction of arrow 4, then there is a tendency 1 for laminations 5 and 6 to separate from the other 2 laminations.

4 Referring to Fig. 2 there is shown a seam 11 between two laminated fabric sheets 12 and 13. Adhesive 17 is 6 applied between the two sheets 13 such that each 7 lamination 15a, 15b, 15c of sheet 12 is bonded to a 8 respective lamination 16a, 16b, 16c of sheet 13. When 9 the joined sheets are subject to tension in the direction of arrow 14, then there is no tendency for 11 one lamination to separate from the other laminations 12 in the sheet.

14 Referring to Fig. 3, adhesive, in a molten state, is stored in a tank 20. When required, the adhesive is 16 pumped to the delivery apparatus 22 at an 17 electronically controlled rate by a polymer pump 21 or 18 similar pump. The delivery apparatus 22 consists of a 19 hollow sonotrode 23 attached to an ultrasonic transducer 24. The adhesive is further heated by the 21 ultrasound as it passes through a passage 25 in the 22 sonotrode, which is separated from the fabric 26 by a 23 small gap 27. This gap 27 is bridged by the adhesive 24 when a bead of adhesive (not shown) is formed at the nozzle 28, so that the seam in the fabric 26 is coupled 26 by the adhesive to the sonotrode 23. Ultrasound energy 27 is thus transferred to the material of the fabric 26 as 28 well as to the adhesive, so that there is local heating 29 and/or melting of the fabric 26 at the seam. This improves the bond between the fabric 26 and the 31 adhesive.

33 Referring to Fig 4, there is shown an alternative 34 method of feeding adhesive to the sonotrode 23.
Granules 120 of hot melt adhesive in the solid state 36 (for example stock nylon granules} are placed in a feed 1 hopper 121. A feed screw 122 feeds the granules along 2 the feed tube 123 to a small internal reservoir 124 3 within the sonotrode 23. The granules are heated 4 within the reservoir 124 and are then fed through the passage 25 to the fabric 26, in the same manner as 6 described with reference to ig 3.
F

8 Referring to Fig 5, there is shown a further 9 alternative method of feeding adhesive to the sonotrode 23. Nylon in thread form 220 is supplied on a bobbin 11 221 which is mounted on a support 222 so that it can 12 rotate freely. An electrically controlled push-pull 13 feed motor 223 feeds the thread along a pipe 224 to a 14 small internal passage 225 within the sonotrode 23.
The thread is heated within the passage 225 and is then 16 fed through the exit passage 25 to the fabric 26, in 17 the same manner as described with reference to Fig 3.

19 Fig 6 shows a detail of a sonotrode 23a having a reservoir 30 formed as a conical bore within a base 31 21 attached to the lower end of the sonotrode 23a. The 22 lower face 29 of the sonotrode 23a is conical. Glue is 23 introduced into the reservoir 30 through the entrance 24 32 by means of a pump (not shown), and air is bled along a passage 40 from lower face 29 of the sonotrode 26 out through the bleed hole 33 in the base 31 of the 27 sonotrode. A supplementary heater 34 aids heating of 28 the adhesive in the reservoir 30. A thermocouple 35 29 monitors the temperature in the reservoir 30. The glue is fed through nozzle 36. O-ring seals 39 allow 31 relative vibration movement between the sonotrode 23a 32 and the base 31. The inner surface of the reservoir 30 33 could be parabolic instead of conical, to focus the 34 ultrasound to the lower end of the reservoir 30 and the outlet nozzle 36.

1 In the arrangement of Fig. 6 a proportion of the 2 ultrasonic energy is absorbed by the glue inside the 3 reservoir 30, and does not leave the nozzle 36 to 4 excite the glue lying on the fabric 26.

6 Referring to Fig 7, there is shown a sonotrode 7 arrangement which overcomes this problem. Ultrasound 8 is transmitted down through the glue in the chamber, 9 via the modified sonotrode 50, which is shown in more 10 detail in Fig 9. The modified sonotrode comprises a 11 large diameter cylinder 51 at one end of which is a 12 small diameter cylinder 52, connected to the large 13 cylinder 51 by radiused chamfers 53. The end 54 of the 14 small diameter cylinder has a conical shape which acts as an exit nozzle for the glue, and has an axial 16 passage 55 bored therein, typically of 1 or 2 mm 17 diameter and extending as far as a radial passage 56 of 18 similar diameter with which it communicates.

The modified sonotrode 50, as shown in Fig 7, has two 21 o-rings 57 either side of the radial passage 56, which 22 limit the glue to a band surrounding the narrow stem 52 23 of the sonotrode. Glue is fed via entrance 58 through 24 passages 59 and 60 to a chamber 61 bounded by the sonotrode stem 52, the o-rings 57 and a cylindrical 26 bore in the base 31. The cylindrical bore may have a 27 sleeve lining 62.

29 It is possible to eliminate the o-rings, which tend to wear and fail in this arrangement. In this case the 31 axial glue passage can extend further along the 32 sonotrode, as shown in Fig. 3 to a radial passage 56' 33 in the main body 51 of the sonotrode. A rigid 34 connection 63 at the surface of the sonotrode connects the radial passage 56' to a heated glue supply pipe 64 36 which is flexible enough to accommodate the vibratory 1 movement of the sonotrode with respect to the pump 21.

3 Fig 8 shows an alternative nozzle arrangement to that 4 of Fig 7. The same reference signs are used to denote the same features as those in Fig 7. The nozzle 67 of 6 Fig 8 incorporates an extended sleeve member 62 which 7 covers the end of the sonotrode stem 52 and has an 8 axial passage 65 through which the glue exits. There 9 is a single o-ring 57 above the exit of the radial passage 56, so that the glue fills a small reservoir 11 66.

13 The arrangements of Figs 7 and 8 limit the dissipation 14 of ultrasound by reducing the volume of glue in contact with the sonotrode. The glue is prevented from 16 escaping upward from the radial passage 56 by the o-17 ring 57 between the nozzle interior and the sonotrode.

19 Fig 9 shows a side view of the sonotrode used in the nozzle of Fig 8. The sonotrode is longer than strictly 21 necessary, because it passes through the hot glue tank 22 in the base 31. Typically the length is about 200 mm, 23 the diameter of the upper portion 51 is about 30 to 40 24 mm and the diameter of the lower portion is about 7 to 10 mm. In the version shown schematically in Fig 3 the 26 tank is remote from the sonotrode and connected by a 27 heated pipe. The frequency used with the sonotrode of 28 Fig 9 was 20kHz, which is just audible. Preferably 29 higher frequencies are used, typically 30kHz or 40kHz.
This increased frequency reduces the wavelength of the 31 ultrasound in the sonotrode, so a shorter length will 32 be required.

34 Referring to Fig 10, there is shown a sonotrode arrangement which utilises a booster to amplify the 36 ultrasound energy at the point of application, and 1 which has a simplified arrangement for connecting the 2 adhesive supply hose to the sonotrode. Ultrasound is 3 generated by the transducer 24 and amplified by the 4 booster 71, whose cross-sectional area reduces in size away from the transducer. The booster is coupled by a 6 threaded connection 72 to the sonotrode 70. The 7 sonotrode comprises a large diameter cylinder 81, 8 typically 30 mm diameter and 20 mm long, at one end of 9 which is a small diameter cylinder 82, typically 12 mm diameter and 45 mm long, connected to the large 11 cylinder 81 by radiused chamfers 83. The end 84 of the 12 small diameter cylinder has a conical shape which acts 13 as an exit nozzle for the glue, and has an axial 14 passage 78 bored therein, typically of 1 mm diameter and extending as far as a radial passage 77 typically 16 of 2 mm diameter with which it communicates.

18 The small diameter cylinder 82 of the sonotrode 70, as 19 shown in Fig 10, has a yoke 73 arranged about it at the nodal point of the sonotrode, and sealed to the 21 sonotrode by two o-rings 74, typically of PTFE or other 22 suitable heat resistant material. The yoke 73 may be 23 of aluminium or brass or other suitable material. The 24 o-rings 74 are positioned either side of a circumferential grooved passage 79 in the yoke, which 26 communicates with the radial passage 77 in the 27 sonotrode and an entrance bore 75 in the yoke. The 28 seals 74 limit the glue to the grooved passage 79 29 surrounding the narrow stem 82 of the sonotrode. Glue is fed by means of heated hose 64 through connector 76 31 to the entrance bore 75 of the yoke 73, and then 32 through the radial and axial passages 77, 78 in the 33 sonotrode to the exit nozzle 85.

The apparatus may include handling and feed mechanisms 36 (not shown), similar to those of a conventional sewing 1 machine. The adhesive delivery/insonation device is 2 held stationery while the pieces of fabric to be joined 3 are passed below. Fabric handling and feed mechanisms 4 may maintain a fixed gap between the pieces as they pass below the bonding equipment. The two pieces of 6 fabric being joined are held stationary, relative to 7 one another, until the adhesive has cooled enough for 8 the seam to be mechanically stable. In one variation 9 of the invention the machine incorporates a flat-bed for making sheets of bonded fabric; in another 11 variation the machine has an arm, on which the adhesive 12 supply nozzle is mounted, in order to produce tubes 13 such as sleeves.

The cooling rate of the seam may be enhanced by using 16 one or more refrigeration devices. These are important 17 in rapidly cooling the joint after formation when the 18 fabric is processed at high speed.

Various cooling methods are possible. Vortex tubes can 21 produce a pressurised source of cold air, down to sub-22 zero temperatures. A by-product of their operation is 23 a stream of hot air, which may be used for fabric pre-24 heating. Solid-state refrigerating devices known as thermo-electric devices may also be used. These use 26 the Peltier effect and are capable of pumping from 27 milliwatts to hundreds of watts of heat. The 28 evaporation of water droplets sprayed into the hot seam 29 allows an excellent cooling rate, but the adhesives tend to absorb water. Presently, a therrno-electric 31 device is favoured as a cooling method.

33 To further aid adhesion, the fabric may be preheated, 34 for example by using an infra-red heater.
36 It is possible to incorporate the apparatus of the 1 invention in a hand-held device, which can be moved 2 like a MIG welding apparatus to form a seam between 3 pieces of fabric. This allows unrestricted movement in 4 three dimensions.
6 It is possible to mount the apparatus of the invention 7 on a robotic arm to allow automated seam-bonding on 8 three dimensional objects. One application for such a 9 system would be to bond the pieces of a shoe, held on a last.

12 One example of an apparatus according to the invention 13 which also incorporates heating and cooling means is 14 shown at Figs 11 to 13. A sonotrode 23 is mounted such that its height may be varied in the direction of Arrow 16 A, to allow for the joining of fabrics of different 17 thickness and to allow access to the nozzle. Hot melt 18 adhesive is supplied through the sonotrode in a manner 19 described above with reference to Figs 3 to 10. An infra red source 90 is mounted such that its position 21 can be varied (for example to position 90') in the 22 directions of arrows B, C and D to direct the infra red 23 energy to the most appropriate point on the fabric 24 support surface 91 so as to preheat the portions of fabric 26 as they move in the direction of arrow E
26 towards the sonotrode 23.

28 An electrically heated hot plate 92 directly beneath 29 the sonotrode heats the fabric at the point of application of the adhesive, to ensure that the 31 adhesive fully penetrates the fabric joint.
32 Immediately behind the hot plate 92 is a cooled plate 33 93 connected to a bottom side cooling assembly 34 comprising a Peltier device 94, a ribbed heat sink 95 and a fan 96. The hot plate 92 and cooled plate 93 36 project through a slot 97 in the fabric support surface 1 91. Between the slot 97 and the plates 92, 93 is 2 provided insulation 98 in the form of 3 polyetheretherketone (PEEK) or similar. The hot plate 4 92 and bottom side cooling assembly are secured to the 5 fabric support surface 91 by countersunk bolts 99.

7 In addition there is provided a top side cooling 8 assembly comprising a stainless steel roller 101, 9 mounted on a bearing 102 adapted to maximise heat 10 transfer between the roller 101 and the roller housing 11 103, a Pettier device 104 and a heat sink 105. The 12 assembly is supported on an insulating support arm 106 13 by fasteners 107, and the support arm 106 is held by a 14 main support 108 secured to the apparatus.
16 Typically the sonotrode comprises four cylindrical 17 sections, each connected by a radiused chamfer. The 18 upper section 23a is typically between 20 and 50 mm in 19 diameter and between 20 and 40 mm in length.
Subsequent sections 23b, 23c, 23d are between 5 and 10 21 mm smaller in diameter than the adjoining section 22 above, and are of a similar length. Typically the 23 lower section 23d, in which is provided the glue outlet 24 passage 55, is between 6 and 15 mm in diameter.
26 Figs 14 and 15 show how video detection may be used 27 with the apparatus of the invention to sense the gap 28 between the fabrics to be joined. A video camera 114 29 has a field of vision 112 on the fabric support surface 91. The information from the video camera is fed to a 31 programmed control unit 115 (DSP or PLC) which adjusts 32 the position and operation of the two steerable drive 33 rollers 113, which each guide one of the pieces of 34 fabric 26a, 26b to be joined. The control unit ensures that the edges of the fabric 26a, 26b pass through the 36 heated area 110 beneath the infra red source 90 and 1 that the edges are the correct distance apart when 2 passing through area lli beneath the sonotrode 23, at 3 the point of application of the adhesive. The adhesive 4 and fabric is then cooled as it passes beneath the cooling roller 101.

7 This technology is applicable in the clothing and 8 footwear industries, and has other textile-based 9 applications such as sailmaking, filter production and medical barrier products. Ultrasound-enhanced adhesive 11 bonding may have other applications, on substrates 12 which are difficult to join with conventional 13 adhesives.

Typically the sonotrodes are 7~/4 long. The vertical 16 glue passages 55 are typically 1 mm in diameter. The 17 radial or transverse passages 56 are typically 2 mm in 18 diameter. The sleeve 62 is of brass. The sonotrode 19 23, 50 may be made of steel, but more preferably of nickel copper alloy, which is stronger than steel and 21 has better high temperature properties. The transducer 22 may be any suitable transducer, such as Model No UST
23 640 manufactured by Herfurth.

Qlue Tests 27 The various nozzle arrangements have been tested with 28 adhesives. During these tests the adhesive was seen to 29 foam, and smoke at high ultrasound powers. In the nozzle of Fig 6 this occurred as soon as the ultrasound 31 was applied, but after prolonged exposure, at high 32 power, it continued once the power was switched off.
33 In the first case it would appear that the adhesive 34 absorbs the ultrasonic energy directly, and the delayed foaming is probably due to heating by the sonotrode.
36 The heating of the sonotrode seems partly due to the 1 rising glue temperature, and partly due to direct 2 ultrasonic heating of the sonotrode, or friction with 3 the o-rings. The rate of o-ring failure was quite 4 high, and the high temperatures attained could have degraded them (Viton is able to withstand temperatures 6 of over 200°C, but the sonotrode was reaching at least 7 300°C in places). The foaming appeared to occur inside 8 the sonotrode, without air being drawn up through the 9 aperture. Also, on cooling, many of the bubbles contracted until they were no longer visible. This 11 implies that the vapour forming the foam is a component 12 of the adhesive, or a gas dissolved in it.

14 The height of the nozzle above the fabric made a difference to the quality of the bead's penetration of 16 the fabric's surface. At a distance of more than 2 mm, 17 the bead cooled too much to penetrate the fabric. At 18 lower distances the end of the sonotrode was slightly 19 submerged in the bead lying on the fabric. This continued to heat the bead and kept it molten.

22 For the nozzle of Fig 8, ultrasound seemed to make no 23 difference to the bead until a hot glue foam poured out 24 of the nozzle, which bonded well to the fabric. This was then followed by flow which showed no signs of 26 ultrasonic action. The mechanism for this spasmodic 27 flow could have been gradual heating of the adhesive 28 close to the sonotrode end. The viscosity would have 29 decreased, and once foaming occurred the increased volume could have forced the contents out. This 31 behaviour may imply that the glue need only be super-32 heated to give a good bond and that the fabric need not 33 be exposed to the ultrasound.

When a monel (copper nickel alloy) sonotrode replaced a 36 steel sonotrode in the arrangement of Fig 7, the 1 apparatus gave comparable results, but the transducer 2 needed less power. The steel appeared to absorb 3 ultrasonic energy more than the monel. This may have 4 been work-hardening the metal, giving heat as a by-product, and leading to the eventual failure.

7 The adhesive appears not to transmit ultrasound very 8 well, absorbing most of the energy close to the point 9 of application. This explains why the adhesive foams immediately, when the ultrasound is applied to the 11 nozzle of Fig 7.

13 The beads formed by the nozzle of Fig 7 give superior 14 penetration of the fabric surface when compared to the others. The adhesive is hot when it emerges from the 16 nozzle. Also, the partial emersion of the sonotrode in 17 the adhesive, gives direct coupling between the 18 ultrasound and the adhesive on the fabric. This 19 supplies more heat.
21 The adhesive used is any suitable hot melt adhesive, 22 supplied in granular or thread form, and may be a stock 23 nylon such as Grilltex (R) Type D1299 made by EMS-24 American Grilon Inc.
26 The ultrasonic system of the invention has several 27 advantages over laser-based techniques. Ultrasound is 28 inherently safer than laser radiation, which is 29 especially hazardous to the eye. This is particularly important for a unit which is to be used in any 31 orientation on three-dimensional objects. The laser 32 system also requires adhesive of a controlled opacity, 33 so that it absorbs some energy while transmitting the 34 remainder to the substrate. The ultrasonic system is not influenced by the opacity of the adhesive, so 36 pigments can be added for aesthetic effect, if desired.

WO 99/46110 PCT/GB99100?58 Z These and other modifications and improvements can be 2 incorporated without departing from the scope of the 3 invention.

Claims

CLAIMS:

1. Seam bonding apparatus for forming a seam between fabric sheets, the apparatus comprising a hot-melt adhesive supply means, an ultrasonic energy source and a sonotrode adapted to direct ultrasonic energy to an application point on the seam to be bonded, wherein the sonotrode has therein a passage adapted to permit flow therethrough of adhesive from said hot-melt adhesive supply means through an exit aperture to said application point, characterized in that said fabric sheets have edges which are aligned in an end to end relationship.

2. Apparatus according to Claim 1, wherein said exit aperture comprises a nozzle communicating with said passage.

3. Apparatus according to Claim 1 or 2, wherein said passage comprises a first portion substantially parallel to the axis of the sonotrode.

4. Apparatus according to Claim 3, wherein said passage further comprises a second substantially radial portion communicating with said first portion.

5. Apparatus according to any preceding Claim, further comprising a glue chamber within or adjacent to said sonotrode.

6. Apparatus according to Claim 5, wherein said glue chamber has a parabolically shaped inner surface.

7. Apparatus according to any preceding Claim, wherein said hot-melt adhesive supply means comprises a hot-melt adhesive tank and a pump.

8. Apparatus according to any preceding Claim, wherein said hot-melt adhesive supply means further comprise a heated pipe connected to the sonotrode.

9. Apparatus according to any of Claims 1 to 6, wherein said hot-melt adhesive supply means comprises a hopper containing meltable adhesive in granular form and a feed means.

10. Apparatus according to any of Claims 1 to 6, wherein said hot-melt adhesive supply means comprises a reel of meltable adhesive in thread form and a thread feed motor.

11. Apparatus according to any preceding Claim, further comprising a fabric support surface adjacent to the exit aperture and fabric propulsion means adapted to propel the fabric in a drive direction.

12. Apparatus according to Claim 11, wherein the fabric support surface is provided with an electrically heatable plate adjacent to the exit aperture.

13. Apparatus according to Claim 11 or 12, wherein the fabric support surface is provided with an electrically cooled plate downstream of the exit aperture in said drive direction.

14. Apparatus according to any preceding Claim, wherein the sonotrode comprises a substantially cylindrical lower portion and wherein the exit aperture is centrally positioned at the lower end of the lower portion.

15. Method for producing a bond between edges of members of an article, said method comprising the steps of:
heating a hot-melt adhesive until it is molten;
feeding said molten adhesive to an application point in which said adhesive contacts said edges of members;
applying ultrasound energy by means of a sonotrode to said molten adhesive and said edges of members;
and allowing said molten adhesive to cool and thereby form a bond between said edges of members;
characterized in that said edges of members of an article are aligned in an end to end relationship.

16. Method according to Claim 15, whereby mechanical vibrations are induced by the ultrasound energy in said members to aid the formation of the bond.

17. Method according to Claim 15 or 16, whereby the molten adhesive is fed through a passage in said sonotrode.

18. Method according to any of Claims 15 to 17, whereby said members are subject to local heating at the said application point before applying said adhesive.

19. Method according to any of Claims 15 to 18, whereby said members are subject to local cooling in the area of the bond after applying said adhesive.

20. Method according to any of Claims 15 to 19, wherein said hot melt adhesive is nylon.

21. Method according to any of Claims 15 to 20, whereby the method uses an apparatus according to any of Claims 1 to 14.

22. Article comprises a plurality of members and having a butt bond produced between two of said members by the method according to any of Claims 15 to 21.

23. Method for producing a bond between edges of a member or members of an article, said method comprising the steps of:

aligning two edges of a member or members in an end to end relationship;

applying both molten adhesive and ultrasonic energy to said aligned edges of a member or members; and allowing said molten adhesive to cool and thereby form a bond between said edges of a member or members.

24. Method according to Claim 23, wherein said member or members of an article are laminates.

25. Article comprises a plurality of edges of a member or members joined by the method according to Claim 23 or Claim 24.