GB2053084A

GB2053084A - Joining plastics sheet material

Info

Publication number: GB2053084A
Application number: GB7922379A
Authority: GB
Original assignee: MASSEY SPORTS Ltd
Current assignee: MASSEY SPORTS Ltd
Priority date: 1979-06-27
Filing date: 1979-06-27
Publication date: 1981-02-04

Abstract

A waterproof seam is formed between a piece of fabric coated with a thin layer of plastics and a piece of the same or a different plastics sheet material with a radio- frequency welding machine. The overlapping pieces of sheet material are inserted between electrodes (1, 2) of the welding machine and one of the electrodes (1) has an elongate surface (9) which is pressed in parallel disposition onto the overlapping pieces whilst a uniform radio- frequency field is applied along the length of the elongate electrode surface (9). This procedure may be utilised in the manufacture of waterproof clothing, and the electrode with the elongate surface may be detachably mounted by means of a dovetail groove (6) and projection (7) so as to be readily interchangeable with other electrodes (1) having elongate surfaces (9) of different dimensions. Plastics coated sheets (10), (11) may be provided on the working surfaces of the electrodes (1), (2). <IMAGE>

Description

SPECIFICATION Joining plastics sheet material This invention relates to the joining of plastics sheet material particularly although not exclusively for use in the manufacture of waterproof clothing.

Plastics sheet material comprising a fabric coated with a thin layer of plastics, such as is described for example in co-pending Application No. 40583/78 may be particularly suitable for use in the manufacture of waterproof clothing having regard to the possible lightness, flexibility and porosity of same. However, such material is difficult to join with waterproof seams since conventional seamsealing techniques involving the application of heat to the seams to fuse same may burn through the thin plastics coating.

An object of the present invention is to overcome or at least minimise this problem.

According to one aspect of the invention therefore there is provided a method of forming a waterproof seam between at least two pieces of plastics sheet material, at least one such piece being formed from a fabric coated with a thin layer of plastics, wherein the said pieces are introduced in superimposed relationship between electrodes of a radio-frequency welding machine, at least one such electrode having an elongate surface which is pressed onto the overlapping pieces in parallel relationship therewith, and a radio-frequency field which is of a uniform nature throughout said elongate electrode surface is applied between the electrodes to effect heating of the plastics of said pieces thereby to weld same together.

With this procedure it has been possible to achieve a secure, waterproof seam even with plastics coated fabric in which the plastics constitutes only a thin, insubstantial layer.

The method may be applied to the manufacture of waterproof or protective clothing in the form of jackets, coats, trousers, or for any other suitable purpose. The method may involve the formation of a seam between only two pieces of plastics sheet material each of which comprises plastics coated fabric, although the invention is not intended to be restricted to this arrangement and the method may be applied to the formation of a seam between more than two pieces of plastics coated fabric or to one piece of plastics coated fabric with one piece of material formed wholly from plastics sheeting or to any other suitable combination of materials.

According to a second aspect of the present invention there is provided apparatus for use in performing the above method comprising a radio-frequency welding machine having electrodes between which superimposed sheets of plastics material can be introduced, one electrode comprising a table on which said sheets can be supported and the other electrode comprising a metal member having an elongate surface which extends parallel to said table and can be pressed towards same, and radio-frequency generating circuitry connected to said electrodes to generate a radio-frequency field therebetween which is of a uniform nature throughout said elongate surface and is capable of welding said sheets together.

Preferably the said metal member is detachable so that it can be interchanged with other electrodes having elongate surfaces of different dimensions to suit different welding requirements. In order to facilitate such interchange the metal member may be detachably connectable with an electrode support head of the machine via interengagement of co-operable guide configurations on the member and the head. With this arrangement, interchange of metal members can be readly effected but at the same time it can be ensured that a desired positioning of the metal member, particularly with regard to the parallel disposition of the elongate surface relative to the table, can be attained easily and conveniently. Said guide configurations conveniently may comprise a dovetail projection and groove.

The invention will now be described further by way of example only and with reference to the accompanying drawings in which:~ Figure 1 is a diagrammatic perspective view of one form of apparatus in accordance with the invention; and Figure 2 is a front view of an article of clothing manufactured utilising the method of the invention.

The apparatus comprises an r.f. welding machine having an upper electrode assembly 1 positioned above a horizontal metal table surface 2 which constitutes a lower electrode arrangement.

The upper electrode assembly 1 comprises an electrode 3 in the form of a metal bar fixed in a holder 4 which is detachably connected to a block 5 which is mounted on the machine (in a manner not shown) so as to be movable vertically. The block 5 has a dovetail groove 6 therein and a correspondingly shaped projection 7 is provided on the back of the holder 4. The projection 7 fits securely yet horizontally slidably within the groove 6 and the projection 7 can be fixed in position in the groove 6 against such sliding by means of a screw 8 extending through the holder 4.

The holder 4 and electrode 3 can be detached from the machine as and when required by releasing the screw 8 and sliding the projection 7 along and out of the groove 6. The holder 4 and electrode 3 (or a different interchangeable holder and electrode) are fitted to the machine by sliding the projection 7 into and along the groove 6 and then tightening the screw 8 and it will be appreciated that the projection 7 and groove 6 act to ensure that the holder 4 and electrode 3 when fitted adopt accurately a predetermined angular disposition relative to the block 5 (and hence to the table surface 2) without requiring complicated adjustments to be made. In such predetermined disposition, the bottom surface 9 of the electrode 3, which is a flat narrow rectangular surface say 2mm wide and up to 60cm long, is accurately parallel to the table surface 2.

The electrode 3 has wrapped around same a sheet 10 of thin relatively flexible plastics coated board. A sheet 11 of the same material is secured in position beneath the electrode 3 over the table surface 2.

The machine also incorporates appropriate circuitry (not shown) to generate an r.f. field between the electrode 3 and the table surface 2 capable of effecting dielectic heating and hence welding of suitable plastics materials disposed therebetween. The circuitry is adjusted so that the field is of a uniform nature throughout the entire length of the electrode surface 9.

The machine further incorporates a suitable power operated mechanism (not shown) for moving the electrode assembly 1 vertically downwardly towards the table surface 2 with the lower surface 9 of the electrode 3 maintained parallel to the table surface 2 throughout the movement thereby to enable a uniform pressure to be applied throughout the entire length of the electrode surface 9 to a workpiece placed on the table surface 2 under the electrode 3. The pressure may be of the order of say 2000 Ibs/sq. ins.

The welding machine so far described may be used in the manufacture of an article of waterproof or protective clothing of the kind shown in Fig. 2. The article is formed from sheets of a plastics coated fabric of the kind described for example in co-pending Application No. 40583/78. Thus the article may be formed from sheets of a material comprising a weft knit fabric of continuous filament polyester yarns with a 0.075mm thick coating of an aromatic polyurethane.The sheets are cut and stitched together and the stitched seams are then sealed to render same waterproof by welding the joined sheets together in the vicinity of the stitching by insertion of superimposed portions of the sheets between the electrodes 1, 2 of the welding machine and then generating the r.f. field for an appropriate period of time whilst pressure is applied to said portions in the manner described above.

The dimensions of the lower surface 9 of the electrode 3 (particularly the length thereof) are selected as by interchange of electrodes as described above in accordance with the size and shape of the seams to be welded.

During welding, the sheets 10, 11 define barrier layers which trap heat between the electrodes without otherwise interfering with the welding operation. The plastics coating applied to the board of the sheeting 10, 11 is such as to ensure that a smooth surface is presented to the workpiece which smooth surface is not effected by the heat produced and can readily separate from the workpiece after welding.

The article of clothing is formed from a single sheet 12 of the aforesaid plastics coated material making up the back and sleeves thereof, two further sheets 13 of the said material making up front panels, and two further smaller front sheets 14 of the said material utilised to make two front pockets (as shown in exaggerated sectional view at the left of Fig. 2).

The sheet 12 is stitched and welded to itself and to the other sheets 13, 14 at two arm seams 15, two front seams 16 and two side seams 17. The sheets 14 are stitched (but not welded) to the sheets 13 at bottom seams 18 and also along inner edge seams 19 which latter seams also act to fix a zip fastener.

For each pocket there is a flap which is formed from a band 20 formed wholly from plastics particularly thin pvc sheeting. Each band 20 is held in position by fixing an upper long edge thereof within a fold 21 of the respective sheet 13 by a stitched and welded seam 22 and also by incorporation of the ends of the band 20 in the respective seams 17, 19.

With the embodiment described above an attractive well-sealed reliably waterproof article of clothing can be manufactured in simple, convenient and inexpensive manner. In particular, despite the problems involved in joining sheet material formed from fabric with only a thin plastics coating, with the procedure described it is possible to achieve extremely low failure rates in the welding of the sheet material. Also, with the described procedure, no appreciable problems arise with regard to the welding of the pvc flaps 20 to the polyurethane coated sheet material.

Also the use as pocket flaps of bands which may be of different material (and possible also different colour) from the adjacent portions of the garment, and the fixing of same at the top and also the end edges thereof, give rise to a particularly attractive yet functional and well protected pocket arrangement, and indeed such an arrangement may constitute a further independent aspect of the present invention.

It is of course to be understood that the invention is not intended to be restricted to the details of the above embodiment which are described by way of example only.

Claims

1. A method of forming a waterproof seam between at least two pieces of plastics sheet material, at least one such piece being formed from a fabric coated with a thin layer of plastics, wherein the said pieces are intro duced in superimposed relationship between electrodes of a radio-frequency welding machine, at least one such electrode having an elongate surface which is pressed onto the overlapping pieces in parallel relationship therewith, and a radio-frequency field which is of a uniform nature throughout said elongate electrode surface is applied between the electrodes to effect heating of the plastics of said pices thereby to weld same together.

2. A method according to claim 1, applied to the manufacture of an article of waterproof clothing wherein sheets of fabric coated with a thin layer of plastics are cut then secured together with stitched seams, and said stitched seams are formed into waterproof seams as aforesaid.

3. A method according to claim 2, wherein said article of waterproof clothing is a jacket, and said sheets of plastics coated fabric comprise: a single sheet making up a back and two sleeves of the jacket, two further sheets making up front panels of the jacket, and two further smaller front sheets making up two front pockets of the jacket.

4. A method according to claim 3, wherein each pocket has a flap formed from a band which is fixed in position along an upper long edge thereof and also at opposite ends thereof.

5. A method according to claim 4, wherein each said flap is formed wholly from a plastics sheeting material.

6. A method according to claim 5, wherein the plastics material of said flaps is different from the plastics material which coats said fabric.

7. Pieces of plastics sheet material when joined with a waterproof seam according to the method of claim 1.

8. An article of waterproof clothing when formed by the method of any one of claims 2 to 6.

9. Apparatus for use in performing the method of claim 1, comprising a radio-frequency welding machine having electrodes between which superimposed sheets of plastics material can be introduced, one electrode comprising a table on which said sheets can be supported and the other electrode comprising a metal member having an elongate surface which extends parallel to said table and can be pressed towards same, and radiofrequency generating circuitry connected to said electrodes to generate a radio-frequency field therebetween which is of a uniform nature throughout said elongate surface and is capable of welding said sheets together.

10. Apparatus according to claim 9, wherein said metal member is detachable and interchangeable with other electrodes having elongate surfaces of different dimensions to suit different welding requirements.

11. Apparatus according to claim 10, wherein the metal member is detachably connectable with an electrode support head of the machine via interengagement of co-operable guide configurations on the member and on the head.

12. Apparatus according to claim 11, wherein said guide configurations comprise a dovetail projection and groove, the projection being slidable along the groove parallel to the table.

13. Apparatus according to claim 12, wherein a screw is provided for fixing the projection in position within the groove.

14. Apparatus according to any one of claims 9 to 13, further including sheets of plastics coated board applied respectively over the metal member and the table.

15. Apparatus according to any one of claims 9 to 13, when used in the method of any one of claims 1 to 6.

16. A method according to claim 2, substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

17. An article of clothing according to claim 8, substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

18. Apparatus according to claim 9, substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.