The present application relates to an improved joining tape for joining the edge of sheet material, a method of making such a tape and an improved method of joinin carpet or other sheet material. The invention also relates to an improved heating strip fo use in conjunction with a separate joining tape having heat softenable adhesive thereon In particular, although not exclusively, the application relates to improvements in joinin adjacent edge portions of carpet.

While the invention can be used for joining and separating a wide variety of form of sheet material including fabrics, wall surfacing materials and the like, the invention wil be described hereinafter in relation to the joining and separating of carpet material. Background of the Invention

It is well known to join adjacent abutting edges of carpets with a joining tap provided with a heat softenable adhesive. It is also known to supply heat to the joinin tape by passing electric current through an element such as a layer of metal foil provide in the tape.

Australian Patent No. 464878 describes such a joining tape which consists of layer of heat insulating material such as paper, a layer of metal foil, a joining medium and an upper layer of a ribbon of heat softenable adhesive composition. The joining medium may be filaments, threads, scrim, woven material or the like secured to the tape.

Australian Patent No. 529440 describes another such joining tape which consists of a layer of backing paper, such as crepe paper, a strip of metal foil overlying the paper, a layer of reinforcing filaments such as rayon, glass fibre or the like which extend substantially transversely of the tape and one or more beads of adhesive extending longitudinally of the tape overlying the filaments or fibers. The layers may be laminated together or sewn together by one or more lines of stitching.

A disadvantage of the above joining tapes is that their strength is not uniform in all directions along the plane of the tape. This is especially the case where reinforcing filaments extend substantially transversely of the tape or in the case of woven reinforcing materials with cross wefts. In practice, such filaments or wefts are spaced such that there may be two or three filaments/wefts per centimeter of the tape. Traffic along the carpet

join, such as a person walking on the join, causes the tape to flex and constant flexin causes weakening of the tape, such that the tape is prone to split lengthwise.

Further disadvantages are present in the prior art tapes where such tapes are sew together. The sewing operation is time consuming and the equipment costs are high Further, each line of stitching along the tape, results in a row of punctures creating a lin of weakness along the tape.

In Australian Patent No. 568068, the relatively high cost of including metal foil i the joining tape was overcome by producing a reusable heating strip provided with th metal foil and a separate joining tape which has the heat softenable adhesive thereon bu no metal foil in its construction. In use, the separate joining tape is placed above th heating strip and underneath abutting edges of two pieces of carpet. Electric current i caused to pass through the metal foil of the strip to effect heating of the strip to sufficient temperature to enable the separate joining tape to bond to the carpet.

After the bonding operation and the strip has been allowed to cool, the strip may be removed and used again. The heating strip comprises a backing of crepe or kraft paper to which one or two laterally spaced strips of metal foil are sewn using cotton or fiberglass thread. In the case of spaced foil strips being used, they are electrically shorted at one end by the use of an electrical shorting member so that the circuit can be completed at the other end of the heating strip. A difficulty with the above heating strip is that in use, moisture released by heating of the carpet wets the crepe paper backing and/or the stitching. This causes the backing and the stitching to deteriorate thereby reducing the useful life of the heating strip. Moisture trapped between the backing and the strip also causes corrosion on the side of the metal foil facing the strip. A further difficulty with the strip is that continual heating and reheating results in buckling of the metal foil in the strip. This may be caused by the foil having a greater coefficient of thermal expansion as compared to the relatively inextensible strip to which the foil is inextensibly secured by the stitching. It may be due to the continual uncontrolled rate of heating and cooling which the foil undergoes each time it is used or the uneven heat loss from the foil where parts contact the joining tape. It may be due to the combined effects of the above factors.

Irrespective of the cause, the buckling is undesirable as it results in uneven heatin of the separate joining tape and an unsatisfactory join in the carpet. Further, the fo strains against the relatively inextensible stitching producing lines of weakness along th seam lines. It is an object of the present invention to provide an improved joining tape whic has more uniform strength in all directions along the plane of the tape.

It is a further object of the present invention to provide a method of formin joining tape which overcomes the previous difficulties in making joining tape.

It is another object of the present invention to provide a heating strip whic minimizes buckling of metal foil in the strip.

It is yet another object of the present invention to provide a heating strip which i protected against deterioration due to moisture. Disclosure of the Invention

In accordance with a first aspect of the present invention, there is disclosed joining tape for joining the edges of sheet material in abutting relationship, the joinin tape including an elongated strip of metal foil, the metal foil having a thickness whereb an electric current passed through the foil causes heating thereof to a temperatur sufficient to enable a heat softenable adhesive provided on the tape to bond the tape to the edges of the sheet material, characterized in that the tape includes a further layer o reinforcing material which has substantially uniform strength in all directions extending along the plane of the layer.

In a preferred form of the invention, the reinforcing material is a matted or felted sheet comprised of intermixed fibers or filaments bonded together to form a sheet and by virtue of its construction has substantially uniform strength in all directions along the plane of the sheet. Preferably the fibers comprising the sheet are synthetic fibers. A most preferred reinforcing material is Typar (by Du Pont) made of polypropylene fibers. Typar is gossamer in appearance and has the ability to absorb the heat softening adhesive, thereby further increasing its strength.

A heavy grade of reinforcing material may be combined with a heat softenable adhesive to impart a degree of rigidity into the tape. Such a tape will have the advantage of reducing the likelihood of the carpet along the join being raised through use to form

a ridge.

A layer of backing material may also be provided to protect material underneat the joining tape, such as carpet underlay, from the effects of heat. Preferably the backin material comprises paper such as crepe kraft paper. In the preferred form of th invention, the paper and Typar are laminated to either side of the metal foil.

Aluminium foil is the preferred metal foil to be used in conjunction with th present invention. A further preferred feature is that the foil comprises two laterally spaced strips of foil, the spacing being up to 5 mm. The spaced strips may be permanently electrically connected at one end of a length of tape such that the circuit may be completed by attaching leads to each of the strips at a position along the foil spaced from said one end.

In accordance with a second aspect of the present invention, there is disclosed a method of forming the joining tape as described above, the method being characterized in that the metal foil, reinforcing material and backing material are held together by adhesive such that the tape is produced in laminated form.

The adhesive bonding together the layers of the laminated tape may be a thermoplastic adhesive. However, it is preferred that the thermoplastic adhesive has a higher melting temperature than the heat softenable adhesive used to bond the tape to the sheet material in order that the tape may be bonded to the sheet material at a temperature which does not result in disintegration of the laminated tape.

In accordance with a third aspect of the present invention, there is disclosed a heating strip for heating a joining tape having a heat softenable adhesive provided thereon, said heating strip including a strip of metal foil secured to a strip of backing material, the metal foil having a thickness whereby an electric current passed through the foil causes heating through a range of temperatures to soften the heat softenable adhesive, the heating strip characterized in that the foil is secured to the backing material by a bonding means which is extensible in the range of temperatures thereby minimizing constraint to thermal expansion of the metal foil.

Preferably, the bonding means comprises a synthetic rubber material or like material such as silicone rubber. Suitably the bonding means does not lose its bonding ability in the range of temperatures through which it is heated.

In a preferred form of the invention, one side of the strip of metal foil may al be covered with a layer of insulating material to control the rate heating and therefore t rate of thermal expansion/contraction. Therefore it is desirable that the bonding mea and the insulating material are of the same or similar material so that when heated, t bonding means has the same expansion and elasticity properties as the layer of insulatin material. It has been found that silicone rubber exhibits all the required propertie

Preferably, the strip of metal foil is secured along only one longitudinal edge thereof t the backing sheet and the layer of insulating material is provided on the side of the met foil opposite to that facing the backing material. In a most preferred form of th invention, the tape is in the form of two laterally spaced foil strips, each of the strip being secured to the backing material by a strip of bonding means disposed centrally o the backing strip. It is preferable that at one end of the heating strip, the foil strips ar permanently electrically connected.

It is also desirable that the layer of insulating material be water resistant. Silicon rubber also meets this objective.

The backing strip may also comprise water resistant material to protect the heatin strip form moisture released from surrounding carpet during heating. Alternatively, th backing strip may be backed by a layer of silicone rubber.

Preferably a dispenser is provided on which the heating tape can be wound into coil when not in use, a permanent electrical connection being made between the pair o foil strips at the outermost end of the heating strip. Thus the strip can be unwound to th desired length and electrical connection made to the unwound portion of the heating strip the tape remaining on the dispenser not being subject to the electrical heating.

In accordance with another aspect of the present invention, there is disclosed heating strip for heating a joining tape having heat softenable adhesive provided thereon, said heating strip including an elongated strip of metal foil having a thickness whereb an electric current passed through the foil causes heating to a temperature to soften the heat softenable adhesive, the heating strip characterized in that the metal foil is covered on one side with insulating material to control the rate of heating or cooling and therefore the rate of thermal expansion/contraction of the metal foil.

In accordance with a further aspect of the present invention, there is disclosed a

heating strip for heating a joining tape having a heat softenable adhesive provided thereon said heating strip including an elongate heating element secured to a strip of backin material, the element adapted to be heated to a temperature to soften the heat softenabl adhesive, the heating strip characterized in that the backing material is water resistant an a further layer of water resistant material is provided on the side of the element stri opposite to the backing material.

Preferably, the backing material is comprised of fiberglass such as mesh or tape. The layer of water resistant material may be silicone rubber.

The element may be metal foil through which an electric current is passed to hea the element. Alternatively, the element may constitute a flat braid of metal wires o filaments. In a further alternative, conductive plastic material may be used as the heating element. Brief Description of the Drawings

Fig. 1 is a plan view of a preferred joining tape in accordance with the first aspect of the present invention.

Fig. 2 is a schematic view of an apparatus used to perform the method in accordance with the second aspect of the present invention.

Fig. 3 is a sectional view of a heating strip constructed in accordance with the third aspect fourth and fifth aspects of the present invention. Fig. 4 is a sectional view of a second embodiment of the heating strip.

Fig. 4A is a sectional view of a third embodiment of the heating strip. Fig. 5 is a sectional view of a fourth embodiment of the heating strip. Fig. 6 is a plan schematic view of the heating strip of Fig. 5. Fig. 7 is a perspective view of the heating strip of any of figures 3 to 6 wound on a dispensing apparatus.

Fig. 8 is a perspective view of the heating strip in use. Description of the preferred Embodiments

As illustrated in Figure 1, the preferred joining tape 10 comprises a backing material 12 of crepe kraft paper. Two laterally spaced strips 14, 15 of metal foil are laminated to the paper 12 by a first layer of adhesive 16, preferably a thermoplastic adhesive. The strips of foil are spaced up to 5 mm apart. A strip of Typar 17 (made by

Du Pont) is then laminated to the foil 14, 15 either by virtue of adhesive at the out edges between the inner edges of the foil and which is not covered by the foil 14, 15 by a further layer of thermoplastic adhesive applied to the metal foil. The heat softenab adhesive which bonds the tape to the underside of the carpet is formed in longitudin 5 beads 18. The foil strips 14, 15 are permanently electrically connected at one end. (n shown).

In use, the joining tape 10 is placed under the abutting edges of the carpet piec to be joined (not shown). A source of electric potential is connected to the ends of th foil strips located at the opposite end of the joining tape at which they are permanentl 10 electrically connected. The consequent heating of the foil occurs at a temperatur sufficient to melt the heat softenable adhesive which enters the pores of the Typar and th carpet backing to thereby bond the Typar to the edges of the carpet pieces. The carp is then rolled along the join to ensure a strong bond.

In the schematic view of the process shown in figure 2, the backing paper 12, meta

15 foil strips 14, 15 and Typar 17 are drawn from rolls 20, 21 and 22 respectively. In th first step, the metal foil 14, 15 is caused to lay flat on the strip of backing paper 1 whereafter it is drawn into laminating machine 24. The laminating machine 24 dispense a layer of thermoplastic adhesive between the paper 12 and the foil strips 14, 15

Preferably, the adhesive is dispensed at a temperature of up to 350°C. The Typar stri

20 17 is then drawn into the laminating machine 24 and pressed onto the paper and foi laminate with a roller 25 so that it contacts the adhesive thereon. A layer of hea softenable thermoplastic adhesive is then applied in beaded form to the top surface of th

Typar 17. This application of adhesive may take place between 120°C and 175°C. Th laminated joining tape 10 is then passed through a cooling stage 27 and pinch roller 2

25 before being rolled up as the finished product 29.

Referring now to the embodiments of Figures 3 to 6, one form of the heating stri 30 as shown in Figure 3 comprises a strip of backing material 32 to which a pair of meta foil strips 33 are secured by a central bead of silicone rubber 34. Each of the foil strip 33 are coated on their upper and outer surface by a layer of silicone rubber 35. 0 The backing material 32 is preferably heat and water resistant such as fibreglas mesh or tape, Kevlar or a mesh or tape having a heavy grade filament of fibre glas

woven in. The edges of the backing strip 32 are selvedged or otherwise treated to preven fraying. The foil strips are spaced approximately 5 mm apart and the bead of silicon rubber bead 34 spans this distance to electrically insulate the strips and secure the inne edge of each strips 33 firmly to the backing material 32. The silicone rubber is preferabl 5 able to withstand temperatures up to 300 degrees centigrade.

The remainder of the underside of the metal foil strips 33 are not secured to th backing material 32. The upper surface of the metal foil strips are covered with a laye of silicone rubber 35, 1 to 5 mm in thickness. This covering of silicone rubber is als able to withstand high temperatures. The silicone rubber 35 may cover each of the foi 10 strips 33 independently or alternatively may be a single sheet covering both foil strips 33 as shown in Figures 5 and 6.

The undersurface of the metal foil strips 33 are left uncovered for contact with electrical connectors at a desired location along the length of the heating strip. The preferred manner of connection is to pinch the foil strips 33 together and make contact 15 with each foil strip with a respective connector.

The metal foil 33 may be made of aluminium, brass, bronze, steel, or any other suitable conductive alloy. As an alternative, a flat braid of conductive wires or filaments may be used. A further alternative is conductive plastic material.

Figure 4 illustrates another heat strip in which the underside of the backing material

20 32 is coated with a layer of silicone rubber 36. The metal foil strips 35 are secured to the backing sheet 32 and mutually insulated by a central bead 34 as before. Figure 4A is a variation of Figure 4 in which a layer of silicone rubber 38 with integral central bead 34 secures the metal foil strips 35 to the backing material 32.

A thermostat may be provided to control the heating of the heating strip. A 25 preferred form of thermostat is a "Bi Metal" probe which operates to switch off current to the foil when a predetermined temperature is achieved.

Figure 7 illustrates a dispenser 39 for the heating strip 30. The dispenser 39 allows the heating strip 30 to be wound up into a coil for easy storage. The dispenser has handle

40 and guide roller 41. 0 Figure 8 illustrates the dispenser 39 positioned at one end of a join 44 between two pieces of carpet 42, 43. A portion of the heating tape 30 has been unwound from the

dispenser 39 sufficient to extend the full length of the join 44. A separate joining tape having heat softenable adhesive (as described below) is placed above the heating strip 30. The end of the heating tape distant from the dispenser 39 has the associated ends of foil strips 33 electrically connected such that the circuit may be completed by applying the electric potential between the end of each of the strips adjacent the dispenser thus long carpet joins may be made without the requirement for long electrical leads.

The separate joining tape to be used in conjunction with the heating strip is made from Typar (made by Du pont) for uniform strength characteristics. The Typar strip is impregnated with the heat softenable adhesive. A heavy grade of Typar may be used to prevent "ridging" as previously discussed. A further advantage in the use of Typar is that it is water resistant and therefore does not deteriorate on shampooing or steam cleaning of the carpet.