A seam tape for waterproof fabrics includes a thermoplastic adhesive layer and bonded to a waterproof film layer. Thermoplastic adhesive layer is preferably a polyamide adhesive having a melt index of at least about 200-400 and a melting temperature less than about 150xc2x0 C. The waterproof film layer is a high strength thermoplastic material preferably a polyester such as polyethylene terephthalate. The waterproof film layer should have a thickness of from about 0.25 mils up to about 2 mils. This tape can be applied at higher temperatures than prior seam tapes without damaging the waterproof layer. Thus application speeds can be increased and costs reduced. Further this eliminates any need to post treat crossover seams.

Waterproof fabric articles such as clothing, tents and like are formed from sections of laminated fabric which are sewn together along seams. In order to prevent water from seeping into the waterproof article it is necessary to form a watertight seal at all seams.
The seams in waterproof articles are generally not only sewn, but are also covered with a waterproof seam tape. These seam tapes generally include a thermoplastic adhesive layer laminated to a waterproof layer. The adhesive adheres to the interior side of the seam and plugs any holes created by the stitching. The waterproof layer prevents the stitching from penetrating the seam tape.
The waterproof layer can be a variety of different materials. For example, Reaney U.S. Pat. No. 5,162,149 discloses a carrier layer formed from a thermoplastic layer bonded to a polytetrafluoroethylene (PTFE) layer. Most commercially available seam tapes use a polyurethane layer. The polyurethane layer may optionally be covered with a nylon tricot layer for appearance purposes.
One such seam tape formally sold by Electro Seal Corporation used a polyamide adhesive layer having a high melt index bonded to a 2 mil thick polyurethane layer.
When these seam tapes are applied they are generally heated by applying extremely hot air in the neighborhood of 600-800xc2x0 C. to very quickly melt the thermoplastic adhesive. The goal is for the adhesive to soak into the back side of the fabric creating physical adhesion. The product then cools quickly.
The product disclosed in the Reaney patent is particularly expensive and may be relatively rigid. The polyurethane backed seam tapes are used extensively in the industry but have several disadvantages.
When the seam tape is heated and pressure is applied the stitching can force its way through the polyurethane layer. Once it breaks through the polyurethane layer the seam tape loses its waterproof character and the seam in effect fails. To overcome this problem, a thicker layer of polyurethane has been used, and in some applications exceeds 4 mils. This presents an additional problem because the thicker polyurethane layer is too stiff.
Crossover seams present a further problem. A crossover seam refers to the area where two seams meet either as a xe2x80x9cTxe2x80x9d or xe2x80x9cXxe2x80x9d junction. Crossover seams generally require special attention. In order to provide a water tight seam at cross overs prior art seam tapes had to be reheated at the crossover after application. This significantly increased expenses. Further, tapes with a polyurethane waterproof layer can be destroyed by this reheating. The stitching in the seams punctures even a thicker polyurethane layer. This is particularly a problem with crossover seams of PTFE based waterproof materials such as Gortex brand fabric. This is less of a problem with crossover seams of polyurethane waterproof fabric because they generally do not require the second heating.
The present invention is premised on the realization that a drastically improved seam tape is formed from a layer of polyamide thermoplastic adhesive having a high melt index adhered to a thin layer of polyester or a layer of PTFE. Preferably the adhesive layer is a polyamide adhesive having a melt index of at least about 400 at 175xc2x0 C. and 2,160 gms, a melt viscosity at 200xc2x0 C. of 2,500-5,000 cps and a molecular weight of 10,000-15,000.
The polyester layer when used is a high molecular weight (greater than 10,000) linear saturated polyester preferably polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate or polylcyclohexane-1,4 dimethylene terephthalate having a thickness of less than 2 mils, generally from about 0.25 to about 1 mils in thickness. A fabric layer such as nylon tricot, polyester tricot or polycotton tricot can be bonded to the polyester layer again for appearance and comfort.
The seam tape of the present invention can be applied very quickly to a seam because the particular adhesive melts very quickly and the polyester layer or the PTFE layer retains its strength and is not punctured. Further, once the seam tape is applied, the adhesive sets very quickly providing great strength which reduces the likelihood of failure of the seam. Because of its strength at higher temperatures, even a very thin polyester layer prevents the stitching from penetrating the seam tape during application. This provides an excellent barrier layer which is very difficult to inadvertently penetrate.
Other objects and advantages of the present invention will be further appreciated in light of the following detailed description and drawings in which: