Expansible yarns and threads, and products made using them
A precursor yarn or thread is made by passing a central element, e.g., a filament, a tow, or a flat member, through a bath of a binder, such as a low-temperature hot-melt adhesive, and aqueous urethane, or an acrylic material, with which is mixed a quantity of hard-shelled microspheres which expand when heated to a higher temperature. This is then covered by a sheath, e.g, of PVC, polyurethane, polyester, acrylic resin, polycarbonate, polypropylene, or polyethylene in a second bath. When this product is heated to a transition temperature which is characteristic of the microspheres chosen, the microspheres expand, swelling the sheath. Such a precursor could be woven into a fabric and then heated, so that as the yarn expands the fabric mesh becomes tighter, reducing its porosity. This would be useful as a yarn in making papermaker's felts.
1. A method for producing and using an expansible filamentary sheathed precursor, comprising the steps of:
passing a multifilamentary central member through a first bath comprising a quantity of heat-expansible microspheres in a liquid binder, such that the liquid binder penetrates between the filaments of the central member, such that the surface of said multifilamentary central member is coated by said heat-expansible microspheres, and such that the microspheres do not substantially penetrate between the filaments of the multifilamentary central member;
applying a sheath of thermoplastic material to the coated central member, by:
passing said multifilamentary central member coated by said heat-expansible microspheres through a quantity of a desired thermoplastic material having been heated to a temperature above the activation temperature of the microspheres so as to be melted, and immediately cooling the surface of the thermoplastic material, such that molten thermoplastic material is solidified over the coating of heat-expansible microspheres on the central member without expansion of the heat-expansible microspheres, thus forming an expansible sheathed precursor comprising a multifilamentary central member with a coating of expansible microspheres on the surface thereof, sheathed by the thermoplastic material;
employing the expansible sheathed precursor in fabrication of a product; and
exposing the fabricated product to heat, causing the sheath of thermoplastic material to soften and the expansible microspheres to expand, such that the expansible sheathed precursor expands, modifying the properties of the fabricated product in a desired manner.
2. The method of claim 1 , wherein the step of employing the sheathed precursor in manufacture of a product comprises the step of weaving a fabric using the sheathed precursor at least in part as the yarn used in weaving, whereby the porosity of the fabric is modified upon exposure to heat.
3. The method of claim 1 , wherein the step of employing the sheathed precursor in manufacture of a product comprises the step of employing the sheathed precursor as a thread employed in sewing a product together, whereby punctures formed upon sewing are sealed by expansion of the sheathed precursor upon exposure of the sewn product to heat.
4. The method of claim 1 , wherein the step of employing the sheathed precursor in manufacture of a product comprises the step of using the sheathed precursor as an decorative surface, woven, knit or embroidery yarn.
5. The method of claim 1 , wherein the step of employing the sheathed precursor in manufacture of a product comprises the step of coating the precursor yarns with a hardening resin and heating the yarns to cause the microspheres to expand while confined to a desired shape, so that the expanded yarns are secured in the desired position by the hardened resin.
6. The method of claim 5 , wherein the yarns having been coated with a hardening resin are confined to a desired shape during heating of the yarns and hardening of the resin by being wound over a mandrel, such that a product of desired cross-sectional shape is formed after the microspheres have expanded and the resin hardened.
7. The method of claim 5 , wherein the yarns having been coated with a hardening resin are confined to a desired shape during heating of the yarns and hardening of the resin by confined in a mold, such that a product of desired cross-sectional shape is formed after the microspheres have expanded and the resin hardened.
8. The method of claim 1 wherein the sheath of thermoplastic material is applied to the coated central member by passing the coated central member through a bath of molten thermoplastic material.
9. The method of claim 1 wherein the sheath of thermoplastic material is applied to the coated central member by extruding the thermoplastic material over the coated central member.
10. The method of claim 1 , wherein the thermoplastic material of said sheath is selected from the group consisting of PVC, polyurethane, polyester, acrylics, polycarbonate, polypropylene, and polyethylene.
11. The method of claim 1 , wherein said multifilamentary central member is selected from the group comprising spun and filamentary yarns, threads, ribbons, wires, and tows, of both metallic and non-metallic materials.
12. The method of claim 1 , wherein the microspheres are adhered to the filamentary central member using a binder selected from the group consisting of low-temperature hot-melt adhesives, aqueous urethane, and acrylics.
13. The method of claim 1 , wherein the microspheres are hard shelled generally spherical members formed of thermoplastic material filled with a material that expands substantially when heated to a transition temperature.