GB2346624A - Waterproofing of stitched articles - Google Patents

Abstract

In forming a seam for an article of footwear, clothing or other seamed article, a stitching thread 14 is provided with a coating which can be activated by heat or otherwise to seal punctures in sheet members 11,12 caused by needling to form the stitches. The coating may be a polyurethane dispersion with a foaming agent or may be a hot melt coating, e.g. of polyester, elastomer, nylon, polyolefin, EVA, polyvinylidene fluoride or polyurethane. Solvent borne systems of acrylic, nylon, epoxy, urethane, polychloroprene or natural rubber may also be used.

Description

WATERPROOFING OF STITCHED ARTICLES This invention relates to improvements in waterproofing of stitched articles, particularly seams used in assembling or making up articles such as footwear, waterproof clothing, sheets, tents and tarpaulins for example.

Securing of a seam by stitching involves puncturing a watertight membrane for passage of the stitching thread therethrough. Ordinarily, if no precautions are taken, the stitch punctures form a path for capillary seepage of water through the seam, so that the footwear, clothing or other cover will leak when exposed to heavy rain or standing water.

To obviate this, seams may be taped with adhesive tape, or particularly when thermoplastic materials are used, formed by heat welding, or for other materials, adhesive welding. It has been found however that in practice welded seams, particularly for use on footwear or heavy duty clothing are insufficiently durable to withstand prolonge wear so that such, e. g. footwear, rarely wears out as a result of other forms of wear (such as thinning of the soles) before the welded seam has begun to part.

It is thus desirable to provide a method and means whereby secure, preferably sewn or stitched seams, can be rendered substantially completely waterproof to provide both the necessary seam strength for a durable article of footwear, clothing, etc., and the desired degree of watertightness.

An object of the invention is accordingly to provide a method and means whereby this desirable result can be obtained.

According to a first aspect of the invention, there is provided means for use in forming a watertight stitched seam comprising a stitching thread consisting of a natural or synthetic yarn, characterised in that it further comprises a coating of a sealant composition which can be activated after stitching to seal stitching holes of the seam.

The coating may comprise a water-borne polyurethane dispersion, which preferably includes at least one foaming agent such as expandable thermoplastic micro spheres.

Alternatively other materials may be used for the main component of the coating such as an acrylic, EVA, epoxy, fluorocarbon, ionomer or polyamide plastics material.

The coating may be applied to the thread in the form of either 100% solids, aqueous or solvent-borne polymer systems for impregnation or coating of the thread or yarn. Acrylic, nylon epoxy, urethane, polychloroprene or natural rubber latex may be used as the basis for such systems.

Alternatively, the coating may be applied by hot melt or extrusion processes (e. g. to provide a sheath about a synthetic monofilament yarn core), and hot melt or extrusion grades of coating material, based on, for example, a polyester, an eiastomer, nylon, polyolefin, EVA, polyvinylidene fluoride, ionomer, or a thermoplastic potyurethane may be used.

In the case of thermoplastic application of the coating to the yarn, a foaming agent is preferably present in the composition, and this may for example be one or more of azodicarbonamide ; p-toluenesulfonyl hydrazide; 5-phenyltetrazole ; or sodium bicarbonate.

From another aspect, the present invention provides a method of forming a watertight stitched seam, characterised in that the stitches are formed using a yarn or thread comprising a coating of a sealant composition which can be activated after stitching to seal stitching holes of the seam.

Preferably the method is characterised by the further step of activating the sealant composition after stitching. This may be effected by application of heat to the stitching as for example by ironing with a hot iron, irradiation with infra red, or any other method where the composition can be heated to a temperature of 80 to 230 C.

The invention also provides a yarn or thread coated with the sealant composition and an article of footwear, waterproof clothing, sheet or cover including such a seam.

A preferred method of the invention, and a preferred seam made by the method and according to the invention will now be described with reference to the accompanying drawings, wherein: Figure 1 is a perspective view of a sample seam according to the invention; Figure 2 is an enlarged sectional view of a stitch in the seam, with proportions exaggerated for illustration ; Figure 3 is a cross-section of a sheathed monofilament yarn for use in the seam; and Figure 4 is a cross-section of a coated and impregnated twisted yarn or thread for use in the seam.

Referring to Figure 1, a seam is formed between two sheets 11,12 which are connected by stitches 13 formed by a thread or yarn 14 passed through and looped over and under the sheets 11, 12 in an overlap zone 15.

The thread or yarn 14 accords with Figure 3 or Figure 4, and may be a sheathed monofilament having a sheath 16 of a sealant composition, and a core 17 of a monofilament yarn which may be of any synthetic yarn forming material, such as polyamide, polyester or the like. Alternatively the thread or yarn 14 may, as in Figure 4, be a twisted yarn, of natural or synthetic fibres 18 impregnated with and embedded in a coating 19 of sealant composition.

When the seam is formed by inserting the stitches through the overlapped sheet ends, the sheets are perforated by the sewing needle at each pass of the thread. As suggested in Figure 2, there remains a channel for seepage or capillary leakage of water through the stitch holes 20.

In accordance with the invention, the sheath 18 or 19 of the thread 14 is softened, foamed or fused by application of heat after forming the seam, by application of a heated iron, infra red radiation or the like, to heat the sealant composition to a temperature in the range of 80 C to 230 C.

This heating of the sealant composition causes the composition to fill the stitch holes 20 by fusion or foaming so that the possibility of water seepage through is obviated. This is shown in somewhat exaggerated form in Figure 2.

A first example of sealant composition used in the invention by way of example comprises an aqueous dispersion of polyurethane, an unexpanded syntactic foaming filler, a blocked cross-link, a low friction agent, a low volatility solvent, and de-ionised water.

Proportions of the composition in one embodiment are: Composition p. p. w Aqueous Polyurethane dispersion 100 De-ionised water 50 Unexpanded syntactic foaming filler 4 Low volatility solvent 2 Blocked cross linker 5 Low friction 1 The polyurethane may be provided as an already reacted polyurethane composition, or as a polyurethane processor with a polyol and a polyisocyanate component to be added together in the dispersion to react.

The polyurethane provides a polymer binder to provide strength, retention of the appearance or finish of the thread, to ensure a desired water vapour transmission rate and enable bonding to polyurethane substrates, such as sole or upper material, to promote bonding and sealing of the yarn or thread.

The de-ionised water is effectively pure distille water with no dissolve acid, alkali or salt ions, and provides the degree of expansion or dilution required for economic application of the composition, and to attain desired thread drape properties.

The foaming filler provides for foaming of the polyurethane at 80 - 150 C, whilst the softened polymer wets and bonds to the stitched article.

The cross-linker serves to increase the modulus of the material after foaming of the coating to prevent creep of the yarn or thread, and the low friction agent facilitates sewing by allowing the coated thread to slip easily through stitching holes.

A second example of sealant composition used in the invention comprises: t Polyurethane dispersion-320 parts by weight Expancel 820 DU (TM)-80 p. p. w.

Foammaster 8034E (TM)-3.2 p. p. w.

Pigment dispersion-80 p. p. w.

The pigment dispersion comprises: Polyurethane dispersion-60 p. p. w.

Titanium dioxide-20 p. p. w.

The polyurethane dispersion used in both cases is an anionic dispersion with 35% solids, the polurethane being derived from reaction of polyoxyproplene glycol with meta-TMXDI and 2-methyl-1, 5-pentamethylene diamine.

The resulting sealant composition is applied to the thread using a die, and allowed to dry at temperatures below 80 C.

The thread coated with the sealant composition is used to stitch an article such as a shoe, or joining waterproof fabrics, and is then expanded using heating by infra red, dry steam, hot metal or a convection oven to a temperature in excess of 80 C. The use of dry steam is preferred.

The Expancel (TM) foaming additive may be used at between 3 to 20%, depending upon the required density.

Yarn or threads coated with a composition as set out above can be used to stitch seams between e.g. soles and uppers, or different upper parts in footwear, or between parts of water proff clothing, and thereafter substantially prevent leakage of water due to hydrostatic pressure or capillary action along the thread and through the stitch holes, as the composition tends to provide a seal between the yarn or thread and the material through which the stitch has been formed, particularly where the material is itself a polyurethane based material.

Alternative sealant compositions can be based upon other polymeric binders such as acrylic, EVA, epoxy, fluorocarbons, ionomers, and polyamide. These may be 100% solids aqueous or solvent-borne polymer systems for impregnation or coating of the thread or yarn, including urethane, acrylic, polyamide, epoxy, polychloroprene or natural rubber latex, or hot melt and extrusion compositions based on polyester elastomer, polyamide, polyurethane, EVA, polyvinylidene fluoride, ionom rs, or thermoplastic polyurethanes.

In the case of thermoplastic application of the sealant to the thread or yarn, the foaming agent may be one of the known foaming additives such as azodicarbonamide; p-toluenesulfonyl hydrazide ; 5-phenyltetrazole ; or sodium bicarbonate.

By use of the method and seam construction of the invention, it is possible to provide a stitched seam suitable for use in the manufacture of footwear, waterproof clothing, sheets, tarpaulins and tents which is watertight without capillary or other water leakage so that a durable watertight article is provided.

The seam of the invention may be combined with additional securement means such as adhesive, thermal welding or taping to provide additional security to the seam.

Claims (19)

1. CLAIMS 1. Means for use in forming a watertight stitched seam, comprising a stitching thread consisting of a natural or a synthetic yarn, characterised in that said yarn has a coating of a sealant composition which can be activated after stitching to seal stitching holes of the seam.
2. 2. Means according to claim 1, wherein said coating comprises a water borne polyurethane dispersion.
3. 3. Means according to claim 2, wherein the polyurethane dispersion inclues at least one foaming agent.
4. 4. Means according to claim 3 wherein the foaming agent comprises thermoplastic microspheres.
5. 5. Means according to claim 1 wherein a main component of the coating is any one of an acrylic, E. V. A, an epoxy, a fluorocarbon, an ionomer or a polyamide plastics material.
6. 6. Means according to any preceding claim wherein the coating is applied to the thread in the form of a 100% solids reactive soivent-borne polymer system effecting impregnation or coating the yarn.
7. 7. Means according to claim 6 wherein the solvent used is water based.
8. 8. Means according to any one of claims 1 to 5, wherein the coating is applied by a hot melt or extrusion process.
9. 9. Means according to claim 8 wherein the coating is provided as a sheath about a monofilament yarn core.
10. 10. Means according to claim 8 or 9, wherein the coating material is an extrudable or hot melt material based on one of a polyester, or elastomer, a polyamide, a polyolefin, EVA, polyvinylidene fluoride an ionomer or a thermoplastic urethane.
11. 11. Means according to any preceding claim wherein the coating inclues a foaming agent, between 3-20% by weight.
12. 12. Means according to claim 11 wherein the foaming agent is one or more of azodicarbonamide; P-toluenesulfonyl hydrazide ; 5 phenyttetrazole ; or sodium bicarbonate.
13. 13. A method of foaming a watertight stitched seam characterised in that the stitches are formed using a yarn or thread comprising a coating of a sealant composition which can be activated after stitching to seal stitching holes of the seam.
14. 14. A method according to claim 13 including the further step of activating the sealant composition after stitching.
15. 15. A method according to claim 14 wherein said activation is effected by applying heat to the stitching, to heat the coating to a temperature from 80 C to 230 C.
16. 16. A method according to claim 15, wherein the heat is applied by any one of ironing with a hot iron or irradiation with infra-red.
17. 17. A method according to claim 15 wherein the heat is applied using dry stream.
18. 18. An article of footwear, waterproof clothing or sheet or cover including a seam made by a method according to any one of claims 13 to 16.
19. 19. An article of footwear, waterproof clothing or sheet or cover including a seam made using means according to any one of claims 1 to 12.