CA2097271A1 - Boot manufacturing process - Google Patents

Abstract

Abstract A process for the manufacture of waterproof footwear having a rubber upper and hard, molded outsole wherein the sole is directly molded to the rubber upper, thus producing a permanent, waterproof seal.

Description

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The invention is an impro~ed method for the manufacture of waterproof boots and shoes.

Waterproof footwear is typioally constru~ted from separately formed upper and outsole portions. This type of construction is preferrsd because it permits the upper and the sole to be made from different: materials. For example, the uppers of waterproof boots and sho~s are typically made from thin, pliable rubber) while the ~oles are usually thicker and are composed of unyielding yet flexible material such as hard rubber or plastic.

Owing to their different compositions or thicknesses, such separately formed uppers and outsoles are preferably cured under diferent conditions. This has usually been accomplished in the prior art by separately curing the soles and upper~ before bonding them together. Once cured, however, rubber or ~lastic out~oles and upper~ are not ea~ily joined. This may l~ad to ~eparation of the upper from the outsole, a serious flaw in a waterproof boot or shoe.

There have been several proce~ses described in the prior art which attempt to remedy this de~iciency.
However, none o~ these processes is completely successful. Most of these improvements describe methods of bonding pre-formed, uncured or partially cured, rubber outsoles to pre-formed uppers composed of various materials.

Bingham, U.S. Patent No. 3,035,291, discloses a process wherein the outsole is molded from rubber and is partially cured by vulcanization so that it will i'set"
(harden), thus allowing it to be easily removed from the mold. The sole iæ then bonded to a pre-cured uppar composed of layers of textile and rubber or plastic by first applying adhesi~e to the sole and the bottom of the -2- 20~271 upper, and then curing the entire boot in an oven. The setting and partial curing o~ the sole results in a weak bond, which must be strengthened by the addition of adhesive. Also, oven curing the entire boot a~ter bonding may cause the pre-cured upper to become overcured and brittle.

Saunders, U.S. Patent No. 927,287, daals with bonding a molded/ partially cured or uncured rubber outsole to an uncured rubber upper through the application of heat and pressure, thus bonding the sole and upper by vulcanization. This method elîminates the nee~ for adhesive. However, the molded sole must be set be~ore being bonded to the upper, thus reducing the strength of the bond.

Rosenbaum, U.S. Patent No. 3,085,294, describes a process wherein a thin, unmolded, uncured rubber outsole is pre-heated to a plastic state and bonded to an upper of leather, abric, plastic, etc. by applicatlon of heat and pressure. The sole i8 thu~ bonded to the UppQr by vulcanization. This method provides a stronger bond than the processes described above, where the sole is set or partially vulcanized before bonding to tha upper.
However, there are serious drawbacks. Firstly, pre-heating the sole may cause partial vulcanization, resulting in a weaker bond between sole and upper. Also, this process is limited to thin, unmolded outsoles which can be uniformly heated to a plastic state without appreciable ~urface vulcanization and which do not need to set before bonding. Accordingly, this process is unsuitable for use in the manufacture of most waterproof ~ootwear, which gensrally have thick, molded soles with slip-resistant treads.

An alternate method of securely bonding a rubber or plastic sole to an upper is to mold the sole directly _3_ 20~7271 onto the upper.

Rollmann, U.S. Patent No. 1,955,720, describes a process wherein a fabric or leather upper is positioned on a last and clamped to a mold corresponding to the shape of the sole. The mold contains a rubber mix which when heated to its vulcani~ation temperature expands to form a porous, sponge rubber intermediate sole. The pressure required -to bond the foam rubber sole to the upp~r is supplied by the force exerted by the expanding rubber foam on the bottom surface of the upper. While this process provides a superior bond between sole and upper it is limited to shoes with spcnge rubber soles, mainly slippers, and does not address the problems o~
joining a rubber upper to a rubber or plastic outsole.
Waterproof shoes and boots pre~erably have soles of hard, i.e., dense, rubber or plastic, which pre~rably contain no air pockets, and thereore, do not expand during curing.

The present invention overcomes the deficiencies of prior methods of bonding soles to uppers in waterproo~
footwear by providing a novel method for dir~ctly molding a hard rubber or plastic outsole onto a pre-cured rubber uppar.

Thus, according to the present invention, there is provided a process for the manufacture of waterproof ~ootwear having a molded outsole and rubber upper, comprising the ~teps of: building a rubber upper having toe, vamp) heel and bottom regions; curing the rubber upper; simultaneously molding the outsole ~rom a moldable polymeric material, bonding the sole to the bottom of the rubber upper by applying pressure, and curing the sole to a hardened state.

The bond between sole and upper produced by the ~4~ 2~7~71 presant process is less subject to separation than those described in the prior art because it is produced under pressure, and because the sole is molded directly onto the upper rather than being pre-set or pre-cured. The present process eliminates the need for separate molding, bonding and curing steps and is therefore more time efficient than methodæ for bonding pre-forme~ soles to pre-formed uppers. This process allows the outsola and upper to be cured under different conditions/ and eliminate~ the need for oven curing the assembled shoe, thus preventing the thin rubber upper from becoming brittle due to overcurin~.

Brief Description of the Drawings Figure 1 is a side elevation showing the upper, last and mold assembly prior to loading into tha molding machine.

Figure 2 is a side elevation showing the upper, last and mold assembly after loading into the molding machine.

Figure 3 is a side elevation showing the application of heat and pressure by the molding machine during the molding of the sole to the upper.

Description of the Preferred Embodiments The upper da.scribed in the present process is a conventional rubber upper 10 for a waterproof boot or shoe, having at least heel, toe, vamp and bottom regions.
The upper is preferably built on a last 12 from thin pleces of uncured, vulcani~able rubber. The pieces of tha upper are then bonded together and cured by vulcanization, which is preferably carried out by heating the upper in an autoclave. The inner surface of the upper is preferably provided with a layer of textile ~5- 2~7~71 fabric to enhance hoth the durability and the comort of the upper.

The finished upper is mounted in a molding machine 14 and the bottom of the upper is brought into contact with a heated mold 16 containing moldable polymeric material, preferably vulcanizable rubber, or pla~tic such as polyurethane or a thermoplastic. Pressure is applied to the bottom of the upper by the molding rnachine press 18. The pressure is preferably about 800 psi in order to forca the material forming the sole into intimate contact with all parts of the bottom surEace and edges o~ the upper. Simultaneously, through the application o~ heat, the material forming the outsole is cured. The cure cycle in the molding machine is preferably complete in no more than fifteen minutes, depending on the thickne~s and composition of the sole.

The finished ehoe i8 then removed from the molding machine. No further curing of the shoe is required.

Other embodiments of the invention will be readily apparent to a person skilled in the art, the scope of the invention being defined in the appended claims.

Claims (5)

1. A process for the manufacture of waterproof footwear having a hard, molded outsole and rubber upper, comprising the steps of:

building a rubber upper having toe, vamp, heel and bottom regions;
curing the rubber upper; and molding the outsole from a moldable polymeric material, bonding the outsole to the bottom of the cured rubber upper by application of at least about 800 psi pressure, and curing the outsole by application of heat, the molding, bonding and curing of the outsole to the cured rubber upper being carried out simultaneously.

2. The process of claim 1 wherein the molding, bonding and curing of the outsole is performed in a molding machine.

3. The process of claim 1 wherein the polymeric material is plastic.

4. The process of claim 3 wherein the plastic is selected from the group of polyurethane and thermoplastic.

5. The process of claim 1, wherein the polymeric material is rubber.