Note: Descriptions are shown in the official language in which they were submitted.
97~7~
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
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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
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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
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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
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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.
