Method and apparatus for manufacturing waterproof footwear with attached compressible lining
A method and apparatus for making a lined waterproof footwear product, and footwear product formed therefrom, are provided. A last, having an exterior surface configured to correspond to the size and shape of the interior surface of the footwear product, is covered with a microcellular lining material. An injection mold comprises shells having a pre-determined configuration to mold an upper portion that attaches to the lining during the molding process. In the finished footwear product, the molded upper portion has a molded foot portion that extends around the wearer's foot and an upwardly-extending molded portion that covers a part of the lining while leaving another part of the lining uncovered.
1. A method for making an injection molded waterproof boot comprising a molded upper portion and a compressible lining material attached thereto whereby the compressible lining material becomes attached to the molded upper portion during injection molding of the upper portion, the method comprising:
(a) providing a last having an exterior surface which corresponds to an interior surface of the boot;
(b) covering at least a portion of the exterior surface of the last with a compressible microcellular lining material which compresses under pressure, the lining material having a foot portion adapted to cover a wearer's foot, and a leg portion adapted to extend up a part of the wearer's leg, with a widened area for receiving the wearer's calf;
(c) providing an upper mold configured for injection of a flowable injection material into an injection cavity to form the upper portion wherein the upper mold comprises first and second shells, each said shell having a pre-determined configuration, wherein
the upper mold is designed to form the molded upper portion in a desired shape such that, in the boot, the molded upper portion has a molded foot portion adapted to extend completely around the wearer's foot and to cover the foot portion of the lining, and an upwardly-extending molded portion adapted to extend upward from the molded foot portion and to cover a part of the leg portion of the lining while leaving another part of the leg portion of the lining uncovered; and
the pre-determined configuration of each said shell is designed to account for a dynamic non-uniform compression of the lining material during the injection molding, the pre-determined configuration of the shells designed to form:
(i) prior to the injection molding, a pre-injection cavity between the shells and the lining material covered last when the lining material covered last is located in the mold between the first and second shells, and with the shells in a closed position for injection molding; and
(ii) when the lining material covered last is located in the mold with the shells in a closed position and the injection material is being injected, a dynamically formed injection cavity between the shells and the lining material covered last wherein the configuration of the injection cavity is dynamically formed by pressure applied during the injection of the injection material which causes the lining material to compress and thereby reconfigure the pre-injection cavity to form the injection cavity;
(d) locating the lining material covered last between the first and second shells, closing the first and second shells in position for injection molding, the pre-injection cavity formed between the shells and the lining material covered last, and closing a sole shell containing a boot sole onto the ends of the first and second shells in line with the bottom of the lining material;
(e) injecting the flowable injection material into the pre-injection cavity between the shells and the lining material covered last to form and fill the injection cavity with injection material;
(f) hardening the injected injection material, whereby the hardened injection material attaches to the lining material and the boot sole, the hardened injection material forming the molded upper portion, wherein the molded upper portion, the attached lining material, and the attached boot sole together form the boot;
(g) opening the mold to expose the boot; and
(h) removing the boot from the last.
2. The method according to claim 1 wherein the boot is a winter boot.
3. The method according to claim 1 wherein the boot is a rain boot.
4. The method according to claim 1 wherein the step of injecting the flowable injection material comprises injecting the flowable injection material through an injection port on the upper mold.
5. The method according to claim 1 wherein the step of injecting the flowable injection material comprises injecting the flowable injection material through an injection port on the upper mold and not through the sole shell.
6. The method according to claim 1 wherein the step of injecting the flowable injection material consists of injecting the flowable injection material through the upper mold.