Note: Descriptions are shown in the official language in which they were submitted.
CA 022~7616 1998-12-29
METHOD FOR SEAMLESS CON~LK~ ON OF
MOLDED ELASTOMER PRODUCTS
FIELD OF THE INVENTION
The present invention relates generally to processes
for the manufacture of molded elastomeric products, and,
more particularly, to a process for the manufacture of a
elastomeric product in which there are a plurality of
layers having different characteristics, such as different
colors and/or durometers, which are bonded together
chemically as a result of the molding process so as to
obviate any possible delamination of the layers.
BACKGROUND OF THE INVENTION
The present invention is directed principally to flat-
molded and form-molded (e.g., dip-molded) elastomeric
CA 022~7616 1998-12-29
products, formed by the curing of fluid elastomer
materials, in which for reasons of functionality and/or
aesthetics it is important that different portions, areas,
sections or layers of the product be formed of elastomeric
materials having different durPmeters, colors, and/or other
material characteristics.
Notable examples of flat-molded products of this type
include shoe soles, in which it is desirable to have
certain areas with higher durometers for durability and
others with lower durometers for cushioning, and logos on
athletic clothing, in which it is important that different
areas of the article be formed in distinct, often bright
colors. Examples of form-molded products, in turn, include
gloves and boots, in which again it is often important for
certain areas of the product to be formed of materials
having different durometers, colors, or other
characteristics so as to er.hance the function or appearance
of the article; for example, it may be advantageous for one
section of a glove or boot to be very elastic and pliable
while another section is more rigid and puncture-resistant,
while yet another section may be specifically configured
for traction or cushioning.
In conventional practice, such articles have usually
been manufactured using injection molding or compression
molding processes. Conventional injection molding
processes are capable of using only one color/durometer of
material at a time: in products where two or more colors
are required, these must be silk-screened or otherwise
painted/coated onto the surface of the injection molded
part and thus tend to wear off quickly in use. Multi-
durometer and multi-color parts can also be created through
a compression molding process, which requires that each
part of a specific color or durometer be molded separately
CA 022~7616 1998-12-29
and then assembled using adhesives and pressure, but this
is a very labor-intensive and expensive technique and the
pieces often tend to delaminate or otherwise come apart in
use.
Another common problem with injection and compression
molding is the extreme cost which is inherent in making the
molds which are required for these processes (e.g., a
production mold can easily cost $50,000 US or more), which
makes, for example, seasonal style changes prohibitively
expensive. Furthermore, since the materials which are
traditionally used in these products and processes are
relatively non-elastic in nature, multiple molds are
required for different sizes of each product; for example,
in the case of shoe soles, separate, specific molds are
required for each size and width of foot.
In addition to the problems which have been discussed
above, yet another difficulty often develops in the case of
close-fitting molded elastomeric products, for example, the
waterprcof boots and gloves which are widely used in
athletic/sports activities such as scuba diving, snow/water
skiing, surfing/windsurfing, and so on. Waterproof boots
and gloves of this kind are conventionally constructed of
shaped rubber-cloth pieces which are sewn together, with
the seams then being coated with rubber/sealant to
waterproof them. Not only is this process inefficient and
labor-intensive, it is very common for the seams to stretch
during use, so that the article develops leaks and becomes
water logged. As a result, such boots/gloves tend to fill
and expand with water (especially under hard use), so that
they do not conform properly to the wearer's foot/hand; as
a stop-gap measure, such articles are often fitted with
zippers (which may create yet another source of leaks) in
an effort to allow the boot or glove to be donned/removed
CA 022~7616 1998-12-29
while remaining tightly contoured to the ankle or wrist.
Also, the seams and zipper can be quite uncomfortable and
abrasive to the user's foot.
A one-piece boot, glove or other molded article which
incorporates multiple characteristics (e.g., different
durometers and/or colors) in different sections or areas,
but without requiring the use of adhesives or seams, would
solve these problems. Prior art attempts at providing a
solution along these lines have not been feasible, however,
at least from a commercial standpoint. For example, the
following three U.S. patents disclose various waterproof,
resilient articles which are adapted to fit various parts
of a human body, but the processes which are taught therein
are not entirely satisfactory for use in connection with
the types of products which have been described above.
For example, U.S. Patent No. 2,666,208 (Funk)
discloses a process for manufacture of prosthetic
stockings. The stockings are formed of a sheer fabric base
which is coated on one side with alternate layers of
rubber-like and filler materials to render the stocking
opaque. Funk does not, however, disclose any commercially
feasible batch or continuous process for which is capable
of forming a seamless elastomeric product having different
material characteristics (e.g., different colors or
durometers) in various areas or sections.
U.S. Patent No. 3,633,216 (Schonboltz) discloses a
rubber surgical glove which is formed of a relatively thin
material so as to provide maximum tactile agility and ease
of manipulation. The glove has at least one finger portion
which is made with a double thickness to prevent punctures
and the passage of contamination therethrough. Schonboltz
does not disclose any process for bonding elastomers having
different colors, durometers, or other characteristics.
CA 022~7616 1998-12-29
--5--
U.S. Patent No. 4,133,624 (Heavner et al.) discloses a
molded glove having hand and wrist portions. The wrist
portion includes a plurality of longitudinal channels
around the circumference thereof, and also a plurality of
circumferential channels at the end opposite the hand
portion. The channels cross one another, and the thickness
of the glove along the channels is greater than the
thickness in adjacent areas; the purpose of the channels is
to provide the cuff with improved resistance against
rolling down while being worn, as compared with gloves
which have only longitudinal flutes/channels or beaded
cuffs. The reference does not disclose any process for
bonding elastomers having different colors, durometers or
other characteristics.
Other known prior art includes the following:
Canadian Patent No. 1,077,263 (Stockli) discloses a
boot for aquatic activities. A cellular elastomeric sock
is bonded to a non-cellular, in-situ vulcanized outsole
which includes a toe portion, a heel portion and foxing.
The sock may be covered with a fabric such as nylon.
Bonding of the outsole may be aided by applying a first
layer of neoprene cement, which penetrates and impregnates
the fabric, and a second layer of a natural rubber cement.
Vulcanizing of the outsole is carried out in a heated,
pressurized environment. Stockli does not disclose any
process in which elastomers having different colors,
durometers or other characteristics are permanently bonded
in the molding process itself.
French Patent No. 2,454,280 (Fritsch) discloses a
beach shoe which is made by dipping a hollow mold into
latex to produce an elastic, close-fitting shoe having
variable wall thickness. Greater wall thicknesses at the
sole and at the top, toe and heel areas are produced by
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using a mold having thicker walls those regions, so that
the greater local heat capacity of the mold in these areas
results in a greater build-up of gelled latex material.
Fritsch does not disclose any process for bonding
elastomers having different material characteristics.
CA 022~7616 1998-12-29
SIJMMARY OF THE INVENTION
The present invention has solved the problems cited
above, and is a process for manufacture of multi-
characteristic (typically multi-durometer and/or multi-
color) seamless elastomeric article formed by immersion
molding or flat molding. One example of an immersion
molded article is an aqua boot formed by dipping a heated
mold into a liquid solution of a resilient, curable
elastomer, such as a polyvinyl chloride plastisol. An
example of a flat-molded product, in turn, is an outer sole
for an athletic shoe which is formed by dispensing such an
elastomer solution into one or more cavities in a heated,
open-topped mold.
The invention thus in one aspect pertains to a method
for manufacture of a seamless, one-piece, elastomeric
article, such as a boot, having multiple material
characteristics (e.g., multi-durometer, multi-color,
elastic/inelastic and/or foamed/non-foamed sections), by
the sequential steps of (a) immersing a heated mold having
a shape corresponding to the interior of the article into a
heated solution of a latex-based elastomer having a first
material characteristic, so that a layer of the first
elastomer gels thereon, (b) withdrawing the mold which is
coated with the layer of the first elastomer, (c) partial
curing the layer of the first elastomer (e.g., by placing
the elastomer-coated mold in an oven for a predetermined
period of time), (d) immersing at least a portion of the
mold in a heated solution of a second latex-based elastomer
having a second material characteristic, so that a layer of
the second elastomer gels on at least a portion of the
layer of the first elastomer, (e) withdrawing the mold
which is coated with the layers of the first and second
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elastomers, and (f) fully curing the layers of the first
and second elastomers so that a permanent chemical bond
forms at the interface of the two layers. The mold and
coatings can be cured in an inverted position so as to
prevent drip/runs from forming on the distal end of the
article. Depending on the design of the article, one or
more additional layers of elastomer material may be used.
The correct thickness and height of the article can be
achieved by (a) immersing the mold in the first elastomer
up to the full design height of the article, (b) permitting
the layer of first elastomer to adhere to the mold to a
predetermined thickness, (c) removing the mold and
partially curing the first layer, (d) immersing the
elastomer coated mold into the second elastomer solution up
to a predetermined dip line which is at or below the full
design height of the article, (e) permitting the layer of
the second elastomer to adhere to the first layer to a
predetermined thicknes~, which in combination with the
thickness of the first layer gives that portion of the
article a total thickness which is approximately equal to a
design thickness, (f) withdrawing the mold from the second
elastomer solution, and (g) fully curing the layers of
first and second elastomer materials so that the permanent
chemical bond is formed between the two.
A thick sole or base can be formed on the article by
immersing the elastomer coated mold in a third elastomer
solution before the first two layers of elastomers are
fully cured. This third elastomer may be an open or closed
cell material and also forms a chemical bond with one or
both of the others. Alternatively, an outsole or other
outer/bottom layer manufactured as a flat-molded product
can be bonded to the article by laying this on the article
before the elastomer coating on the mold is completely
CA 022~7616 1998-12-29
cured; the flat-molded layer will then chemically bond to
the dip-molded layer when heated to an elevated
temperature.
In one embodiment, the mold is heated to a temperature
from about 300~ to about 450~F and is then immersed in the
first elastomer solution for a period of time from about 1
second to about 180 seconds. The mold and first elastomer
layer are then placed in an oven with an air temperature in
the range from about 190~ to about 700~F for a period of
time from about 10 seconds to about 5 minutes, prior to
immersing the mold and first elastomer coating in the
second elastomer solution and repeating the above steps.
Where there is to be a third layer, the mold and
elastomer coatings are subsequently immersed in the third
elastomer solution for a period of time from about 1 second
to about 240 seconds so as to form the third layer over the
first two layers or portions thereof. The mold and
elastomer coatings ca~ then be placed in an oven with air
temperatures ranging about 190~ to about 700~F for a period
from about 1 second to about 5 minutes to complete the cure
and the chemical bond between the layers. The mold and the
elastomer coatings can then be submerged in a room
temperature water bath after being removed from the curing
oven.
The elastomers used in the process of the present
invention include polyvinyl chloride plastisols, with
latex-based elastomer solutions being particularly suitable
for this purpose. Any suitable durometer may be used, with
durometers in the range from about 40 to about 120 being
typical.
A pattern (e.g., a tread pattern) can be
pressed/imprinted into a layer on the mold after the
CA 022~7616 1998-12-29
-10-
elastomer has been at least partially cured and while the
material is still soft.
A fabric layer can be placed over the mold and at
least a portion of the fabric can be immersed in the
elastomer solution together with the mold so that the
elastomer layer forms over the fabric layer, thereby
forming a lining in the article. The fabric and elastomer
are placed in an oven at an elevated temperature to
complete the curing process.
The invention also provides a process for
manufacturing a chemically-bonded, multi-characteristic,
flat-molded elastomer article, such as an outsole for an
athletic shoe, for example. The process comprises the
sequential steps of: (a) providing a mold having at least
one cavity formed in a face thereof which has a shape
corresponding to at least a portion of the article, (b)
heating the mold to an elevated temperature, preferably in
an infrared oven, (c) dispensing a first liquid, latex-
based elastomer solution having a first material
characteristic into the cavity, up to about the lip
thereof, (d) heating the mold and the first elastomer
solution to an elevated temperature so as to at least
partially cure the first elastomer solution in the mold,
(e) dispensing a second liquid, latex-based elastomer
solution having a second material characteristic into the
mold, so that a layer of the second elastomer solution
extends over at least a portion of the first elastomer
material in the cavity therein, (f) fully curing the layers
of the first and second elastomer materials so that a
permanent chemical bond forms at the interface of the two
layers, and (g) removing the article from the mold.
There may be a plurality of cavities in the face of
the flat mold which are separated by walls or dams in the
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mold, and each cavity may be filled separately with an
elastomer solution having a different material
characteristic. The layer of second elastomer material is
then dispensed over the top of two or more of these
cavities so as to bond all of the elastomeric layers
together in a single, seamless article.
In one embodiment, the flat mold may be pre-heated in
an infrared oven to a temperature between about room
temperature and about 300~F. After the first liquid
elastomer has been dispensed into the cavity, the mold may
be placed in an oven with an air temperature ranging from
about 190~ to 700~F, for a period of between 1 second and
5 minutes, until the first elastomer is at least partially
cured. After the second elastomer is dispensed into the
mold on top of the partially cured first elastomer, the
mold may be placed in the oven at the above temperatures
for sufficient time to allow the new layer to at least
partially cure over the first elastomer material.
Where there is to be a third elastomeric layer, the
first two layers are only partially cured and then the
third layer may be dispensed on top of the other elastomers
and placed in the oven at the aforementioned temperature
range for sufficient time to enable all layers to
completely cure and bond.
The layers bonded together can be comprised of both
open and close cell formulations, with the open cell
formulations providing the cushioning which is sought in
particular areas or sections of footwear.
CA 022~7616 1998-12-29
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 iS an elevational view of an exemplary high-top
watersports boot formed in accordance with the process of
the present invention;
FIG. 2 is an elevational view of an alternative,
low-top watersports shoe formed in accordance with the
process of the present invention;
FIG. 3 is an elevational view of a mold which can be
used in the process of the present invention to form the
footwear of FIGS. 1-2;
FIG. 4 is a schematic view illustrating the sequential
steps in the process of forming a boot or other article in
accordance with the present invention by dipping a heated
mold in a series of elastomer solutions, with partial
curing of the elastomers occurring between certain of the
immersion phases;
FIG. 5 is an elevational view of a cross-section taken
vertically through the mold of FIG. 3, showing this with an
exemplary elastomeric watersports boot being formed on the
exterior thereof, and with elastomer upper and lower soles
being molded onto the bottom of the boot;
FIG. 6 is a schematic view somewhat similar to FIG. 4,
illustrating the sequential steps in the process of forming
flat-molded articles in accordance with the present
invention, by dispensing liquid elastomers into walled
cavities in an open-faced mold, with partial curing of the
elastomers taking place between certain of the dispensing
phases;
FIG. 7 is a perspective view illustrating an exemplary
multi-cavity mold with walls or dams which separate the
cavities for the different liquid elastomers, but which
terminate below the upper lip of the mold in order to leave
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room for one or more additional layers of elastomer
solution to be poured over the top of the layers in the
separate cavities; and
FIG. 8 is a perspective view illustrating an exemplary
multi-characteristic, one-piece, seamless article
manufactured in the mold which is shown in FIG. 7, using
the process which is shown in FIG. 6.
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-14-
DETAILED DESCRIPTION
FIGS. 1-8 illustrate specific embodiments of the
invention which include both immersion molding (FIGS. 1-5)
and flat molding (FIGS. 6-8). In both cases the basic
process steps are similar, the main difference being that
in immersion molding the different layers of elastomeric
material are built up on the exterior of a male mold which
is dipped into the solution, whereas in flat molding the
elastomer materials are dispensed into the interior of a
female mold.
a. Immersion Molding
i. Process Steps
The immersion molding embodiment of the present
invention will be described herein with reference to an
exemplary boot for use in aquatic sports, such as those
which have been described above, although it will be
understood that the process steps are equally applicable to
the manufacture of other types of molded elastomeric
products having configurations which suit them for
formation over a male mold, such as "rubber" gloves, to
give just one example.
One of the several advantages of forming an immersion-
molded boot or similar product in accordance with the
present invention is that this eliminates the need for
seams to join separately molded pieces of the article,
thereby overcoming the disadvantages which exhibited by
conventional products having seams. For example, the
present invention permits construction of an elastomeric,
one-piece boot which conforms snugly to the foot yet which
CA 022~7616 1998-12-29
does not require a zipper to do so; moreover, the boot can
be molded so that in certain areas (as around the ankle,
for example) the elastomeric material is more elastic or
"stretchy" for ease of use, while in other areas (as in the
sole) the material is tougher and has a higher durometer
for superior wear and penetration resistance. Also, a
liner such as a neoprene coated fabric may be optionally
included.
Immersion molding of the boot or other product can be
carried out in a batch or continuous process by staged dips
of a heated mold to regulated depths into heated elastomer-
reducer solutions of the same or different formulations,
with intermediate, partial cure states (the term "partial
cure" as used herein means that a skin coat is formed on
top of the elastomer to a degree that the elastomer will
not run or mix with a new layer of liquid elastomer
deposited on the first) to provide chemically-bonded layers
having different specified properties.
Accordingly, as can be seen in FIG. 1, an exemplary
high top boot 2 constructed in accordance with the present
invention includes a throat portion 10, a body portion 12,
an uppersole portion 14, and a lower, walking sole portion
16, all of which are bonded together in the course of the
molding process. FIG. 2 illustrates a side view of a
similar shoe-type boot 20 having a somewhat lower throat
portion 22, body portion 24, upper sole portion 26, and
walking sole portion 28. FIG. 3, in turn, shows a
sectional view of the hollow metal mold 30 which is used to
form the inner part of both the boot in FIG. 1 and the boot
in FIG. 2. The contour, support and thickness of the
throat, body, and sole portions are created according to
the depth and time the mold is dipped into the elastomer
solution.
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-16-
The lmmersion molding process is illustrated
schematically in FIG. 4 in relation to the high top boot 2
of FIG. 1. As can be seen, the mold 30, which is
preferably a hollow metal (e.g., aluminum) body coated with
TeflonTM or a similar material, is heated in an infrared
oven 32 until the required temperature is reached
(typically, between 1 and 20 minutes).
The construction of the mold, the TeflonTM (or
similar) coating, and the use of an infrared oven all play
a part in enabling the process of the present invention to
achieve a very short cycle time during which the elastomer
materials are cured, as compared with conventional
processes. In the case of conventional molding process
using elastomer plastisols, the cure times typical range
from 15-20 minutes and upward. It has been found, however,
that such long cure times cause certain of the oils in the
plastisol material to "burn off", resulting in color
deterioration, durometer variations, and other problems in
the finished product. The present invention avoids these
problems by keeping cure cycle times down in the range of
about 3 minutes. In particular, it has been found that by
using a very dull (e.g., sandblasted) exterior finish on
aluminum molds (as opposed to a high "shine" finish), the
infrared energy doesn't reflect off the molds, and moreover
the TeflonTM (or equivalent) finish enables the mold to
first absorb heat very quickly and to then cool down very
quickly so as to rapidly heat quench into the material.
The heated mold is submerged by holding rod 31 in a
tank 34 of specified resilient elastomer solution 36
(which may be either undiluted or thinned as desired with a
thinner or reducer) up to the top of the throat portion 10
for a specified length of time (typically, in the range
from 1 to 180 seconds), so that the elastomer solution gels
CA 022~7616 1998-12-29
on the outside of the mold to form a coating having a
predetermined thickness. The mold 30, toyether with the
layer forming the throat portion 10 and body portion 12, is
then removed from the dip, inverted, and the elastomer
layer is allowed to partially cure on the heated mold
and/or in oven 32 (typically at an air temperature ranging
from 190~ to 700~F and typically from one second to five
minutes). Visible gases, which appear as smoke, are
released from the boot during cure. Curing has been
completed to a sufficient stage when the smoke has
continued for a certain time, which is determined by
experience. Satisfactory partial cure times are governed
by oven efficiency, formulations, temperatures, and other
relevant process parameters.
The mold is then turned back upright and dipped into
the second solution 37 (which can have the same or a
different formulation from that of the first solution 36),
this time up to the top of the upper sole portion and for a
further specified period of time (typically, from 1 to 240
seconds), thus creating a contour line between the body
portion 12 and the upper sole portion 14 of the boot. The
mold 30 is then withdrawn from the elastomer-reducer
solution 37, inverted, and placed in oven 32 to partially
cure the first and second coatings.
The lower, walking sole portion 16 is then formed by
removing the mold 30 from the oven, uprighting the mold,
and dipping the mold and into another elastomer formulation
39, up to the top of lower sole portion 16, so as to create
a thick, durable, penetration-resistant walking sole for
the boot (see process step (g) in FIG. 4). Alternatively,
the lower sole portion can be formed in a separate mold
(e.g., flat-molded) placed on upper sole 14, and bonded to
it by glue and/or heat.
CA 022~7616 1998-12-29
The first elastomer solution 36, second solution 37,
and third solution 39 can be different formulations to
provide their respective layers with different material
characteristics/properties which are suited to their
intended purposes. For instance, with respect to the
manufacture of the exemplary boot 2, the first solution 36
should provide a soft, resilient elastomer layer which can
be readily stretched so that the boot can be pulled on or
off a foot with ease. The second solution 37 can be
formulated to provide a more rigid, durable coating, for
good wear purposes. The third solution 39 can be
formulated to provide a coating which stands scuffing and
provides traction and long wear. It will be recognized,
however, that any suitable combination of formulations can
lS be used. Also, further dipping solutions may be included
in the process if desired.
After the respective dippings, the boot and mold 30
are inverted and placed in an oven (typically at an air
temperature ranging from 190~ to 700~F and typically from
one second to five minutes) until the elastomer layers are
completely cured. The boot 2 is then removed from the
oven 3 and is left on the mold 30 until it has cooled to
room temperature. Cooling can be accelerated by immersing
the mold 30 and the boot 2 in a water tank 38, as seen in
FIG. 4, step (k). Once peeled from the mold 30, the boot 2
is allowed to cure for a further twenty-four hours at room
temperature to ensure that final curing and full strength
are achieved.
FIG. 4, step (j), illustrates an optional intermediate
step that can be conducted to form a grid or tread pattern,
with or without a logo, on the sole portion 16 of the boot.
A female mold 40, which can have formed thereon in inverse
pattern a traction, tread or grid pattern, with or without
CA 022~7616 1998-12-29
-19-
a logo, is pressed against the bottom of sole portion while
it is still soft so as to imprint the pattern into sole
portion before dipping the boot in the water tank 28.
FIG. 5 illustrates a side section view of boot 2
5 formed on the mold 30. FIG. 5 illustrates readily the
different thicknesses of the various portions, for
instance, the lower sole portion 16 is thicker than the
upper sole portion 14. The body portion 12 is thinner yet,
and is formed of a stretchable, resilient grade of
elastomer to permit the boot to be pulled on or off the
foot. The upper sole portion is formed of a somewhat
higher durometer, more durable material to provide
cushioning support for the foot of the wearer, and may also
be formed in a contrasting color for added aesthetic
15 appeal. The lower sole portion 16, in turn, is formed of a
coating which provides traction and wear resistance.
FIG. 5 also illustrates a rim portion 42 which can be
formed at the top of the throat portion 10, by means of a
corresponding groove 44 formed in mold 30: the rim portion
serves to retard ripping of the throat portion when this is
pulled over a foot.
FIG. 6 illustrates a side section view of a boot which
is formed with an neoprene and nylon ankle sock portion 46,
with an elastomer upper sole portion 14 and an elastomer
25 lower sole 16. As with the process steps described above,
the ankle sock 46 is dipped in the elastomer solutions to
specified depths to form the upper and lower sole portions.
ii. Equipment and Materials
As was noted above, a male mold for use in a
continuous, staged dipping process in accordance with the
present invention is suitably formed of a heat conductive
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-20-
metal material, with cast aluminum being especially
suitable for this purpose. The mold can be formed to have
the shape of the finished article according to conventional
casting/forging technology, using plaster of paris or
sandcast molds, for example.
Hollow metal molds are generally preferable to solid-
core molds, since solid metal mandrels shaped in the form
of the article generally possess excessive heat capacity,
and as a result these hold the heat for too long a time for
dipping and partial curing to be conducted efficiently and
with short enough cycle times; use of lower temperatures
with solid molds tends to prolong the setting time of the
article beyond acceptable limits, and again heat transfer
and curing times tend to be excessive.
Hollow metal molds have been found generally superior
to ceramic molds as well, since the latter tend to be too
porous to provide satisfactory results: Gases tend to be
absorbed and contained in the ceramic mold and then, after
the mold has dipped in elastomer-reducer solution, these
gases escape into the elastomer layer forming undesirable
pores in the coating. Moreover, the heat in a ceramic mold
does not transfer satisfactorily and, as a consequence, a
partially cured boot was not readily obtained.
Suitable liquid elastomer plastisol materials for use
in each of the example processes described herein are
latex-based solutions available from QCM Company (930 S.
Central, Kent, Washington 98032, U.S.A.), with suitable
examples including QCM's batch nos. P7002, P6721, P6957,
P8109, P6940, P5963, P6027, P5608, P5957, P5029. The
process is not, however, restricted to these specific
formulations. The mixture is let stand for a period of 24
hours prior to use, to permit any undesirable entrained air
bubbles to escape from the solution.
CA 022~76l6 l998-l2-29
-21-
The infrared oven used in the below example is
preferably from 6 cubic feet to 1800 cubic feet and
typically maintains an air temperature of between 190~ and
700~F.
iii. Example Processes - Immersion Molding
A number of alternative processes and steps can be
utilized according to the principles of the present
invention in order to manufacture a given article which has
various desired custom features. The examples are
illustrative in order to demonstrate certain materials and
parameters that can be used with the immersion molding
process described above, and are not exhaustive. For
example, it will be recognized that the elastomer dip times
and the cure times are variable according to the elastomer-
reducer formulation that is used, the type of heat capacity
of the mold that is used, and the type and thickness of the
mclded article that is to be formed, and other process
2 0 parameters.
Example Process #1
For the formation of an exemplary aqua boot such as
that described above, a hollow aluminum mold of about 1/4
inch (1 cm) wall thickness in the shape of a human foot has
been found to work well under the following conditions.
The mold is heated in an infrared oven to between 190~
and 700~F for from 1 to 20 minutes. The mold is then
dipped in an upright manner into the first elastomer
solution, such as QCM No. 6957, which is tailored to
provide a tough, resilient waterproof article having
sufficient elasticity to be pulled on and off over a user's
foot. In preliminary experimentation, utilizing pure
CA 022~7616 1998-12-29
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elastomers without reducers, finished articles were found
to be impractical because they had little or no stretch.
The elastomer solution according to specifications can be
held in a bath tank at a temperature ranging from about
60~F to about 120~F.
Initially, the heated mold is dipped into the
elastomer solution (P6957) for typically between 1 and 180
seconds during which time the solution gels and accumulates
in a layer against the heated exterior surface of the mold;
since the rate of accumulation is proportional to the time
of immersion, the immersion time and mold temperature are
selected to produce a predetermined thickness for that
particular layer or area of the article. The mold and
elastomer coating are then raised or lifted out of the
solution, inverted, and allowed to partially cure due to
the heat contained in the mold. The mold is then moved to
the oven and curing continues until the desired degree of
partial cure is achieved.
Then, if a thicker section or a section with different
material characteristics (e.g., a different durometer or
color) is required, the mold together with the first
coating is dipped partially or completely into a second
solution, where it remains for a period of time sufficient
for a coating of the second elastomer to adhere to the
first layer, typically between 1 and 240 seconds depending
on the desired thickness. The mold with the second
elastomer solution coated thereon is then removed from the
second solution, inverted, and held in the oven with an air
temperature between 190~ and 700~F for a period of time
sufficient to at least partially cure the outer layer of
elastomer. The two-layered article may subsequently be
dipped into a third elastomer solution should yet another
characteristic be required in the article. The mold, which
CA 022~7616 1998-12-29
now has two layers of different elastomers adhered to at
least a portion of it, will remain in the third elastomer
solution for a period of time sufficient for a coating of
the third elastomer to adhere to the first and second
elastomers or portions thereof, typically between 1 second
and 5 minutes.
The depth that the mold is dipped to is governed by
the design of the article, as is the portion of the mold
which is dipped in each phase. For example, the final
elastomer solution may be an open cell material and may be
dipped long enough to provide a comparatively thick
coating. As was noted above, the thickness is determined
by the length of time in the dip and the heat of the mold.
If required, the article can be taken during some part of
its curing process, while the elastomer is still soft, and
placed against a mold to imprint the elastomer with some
suitable pattern; for example, the final layer, which forms
the bottom of the boot in this example, can be imprinted
with a textured surface pattern for enhanced traction.
Following curing, the mold and the elastomer article
molded thereon are removed from the oven and dipped in a
cooling tank containing water preferably held at between
about 50~F and about 90~F, to cool the mold and formed
article; the mold and the elastomer article are cooled
quickly and efficiently in this manner. The mold and the
elastomer article are then removed from the cooling tank
and the article is peeled off the mold.
Optionally, another section can be formed separately
and bonded to the main article, for example by placing a
separate flat molded elastomer article (which may be
constructed as described below) against the elastomer
covered mold before the outer elastomer layer theron is
fully cured. Together these are placed in the final cure
CA 022~7616 1998-12-29
-24-
oven where they will bond. Also optionally, a section can
be formed separately and bonded to the main article by
placing the separate flat molded article on the elastomer
covered mold after the elastomer has been removed from the
final cure oven but while it is still hot and before it has
been shocked by water.
Example Process #2
The hollow mold described in Example Process #1 above
is first fitted with a sock formed of neoprene coated nylon
fabric which is pulled over the mold. The mold and fabric
are then heated to between about 250~F and about 450~F for
a period of about 30 seconds to about 18 minutes.
The mold and the neoprene and nylon fabric are then
dipped into the elastomer bath up to a specified height for
a period of time sufficient to allow the elastomer to
adhere to the fabric. Three dips of typically between 1
and 180 seconds can be used, the first to provide an
initial sheer coating, the second to provide an
intermediate layer, and the third to provide an outer layer
(all of the same elastomer formulation), so that the
overall desired thickness of the coating can be achieved.
After the final dip, the mold and the elastomer coated
fabric are inverted and placed in an oven with an air
temperature of between about 190~ and about 700~F for a
period of between about 1 - 5 minutes to ensure bonding of
the various layers. Inversion prevents projecting runs and
drips from forming on the bottom of the article.
After the first layer of elastomer has at least
partially cured to form the upper layer of the article, the
mold, fabric and upper layer are dipped into a second
elastomer solution for a period of time sufficient to allow
the second formulation to adhere to the first or a portion
CA 022~7616 1998-12-29
thereof, typically between about 1 second and about 6
minutes. The depth to which the mold is dipped is governed
by the design of the article.
After the dip into the second elastomer formulation,
the mold, fabric and layered elastomers are inverted and
placed in an oven with an air temperature typically between
about 190~ and about 700~F for a period of time, typically
between about 1 second and about 5 minutes. The depth that
the mold is dipped to is again governed by the design of
the article. The final elastomer solution may be dipped
into up to three times (or more, in some embodiments), with
intervening cure periods in order to achieve the desired
thickness. The mold, fabric and layers of elastomers are
then placed in an oven for a period of time sufficient to
allow all layers of elastomers to completely cure,
typically from about 10 seconds to about 8 minutes.
If required, the article can be taken during some part
of its curing process, while the elastomer is still soft,
and placed against a mold so as to may imprint the
elastomer with some suitable pattern.
By using this process, it is possible to form an
article having a neoprene and nylon fabric inner liner and
one or more outer coatings of cured elastomer, according to
graded thicknesses, as illustrated in FIGS. 1 and 2.
Alternatively, by complete immersion(s) the neoprene and
nylon fabric can be coated entirely with elastomer.
b. Flat Molding
Flat goods with areas of distinctly different
characteristics can be achieved by creating ferrous or
non-ferrous open-face molds, typically milled or
cast/forged to a typical depth of between lmm and 50mm to
CA 022~7616 1998-12-29
-26-
form one or more distinct cavities. For the reasons
discussed above, the mold is most preferably formed of
matt-finish aluminum coated with TeflonTM.
The mold can be in the shape of any generally flat-
surfaced article, such as an athletic shoe sole or logo,for example. Where the product is to have one or more
features (e.g., raised letters in the example which is
shown) which are to be bonded to a common base or "backing"
layer, the mold has one or more walls or dams which
separate the cavities so that the different liquid
elastomers for the various features do not run together.
Depending on the design of the article, these dams may or
may not extend all the way to the lip of the mold.
FIG. 6 illustrates schematically a process for
producing a flat molded article 40 and 66 (FIG. 4) using a
TeflonTM-coated metal female mold 50, heated in an oven 52,
(step (m) in FIG 7) to a temperature range typically
between about 60~F (approximately room temperature) and
about 300~F. As with the process described above, the
molds are preferably heated in an infrared oven, with an
air temperature approximately ranging from about 190~ to
about 700~F. In the exemplary process which is described
below, the infrared ovens are shaped as a tube and are
preferably from about 6 to about 24 inches high, about 1 to
about 8 feet wide, and about 6 to about 100 feet long.
The heated mold travels from the oven to under a
liquid elastomer dispenser 74, (step (n) in FIG 7) which
dispenses elastomers 80, 81, 82, 83 having different
characteristics (e.g., different densities, durometers
and/or colours) into mold cavities 54, 56, 58, 60, up to
the level of the dams 70; as previously noted, durometers
of the cured elastomer materials typically range from about
40 to about 120, and suitable types of elastomer
CA 022~7616 1998-12-29
-27-
formulations are described above. The mold then moves to
oven 52, (step (p) FIG. 7) where the elastomers are partly
cured.
After partial curing, the mold next travels under
another liquid elastomer dispenser 78, (step (t) in FIG. 7)
where an elastomer solution 62 is dispensed from all of the
nozzles so that this flows over the top of the partially
cured elastomers 80, 81, 82, and 83 in the separate mold
cavities. This liquid elastomer 62 forms a continuous
layer which bonds to and joins the other elastomer sections
(80,81,82,83) and may or may not fill the mold 50 all the
way to its upper lip. The elastomer used to fill the
mold above the dams forms a chemical bond with each of the
different elastomer formulations which were initially laid
down within the cavities, and has the capacity to bond with
both open or closed cell elastomers.
The mold and elastomers then moved once again to oven
52, ~step (s) in FIG. 7) where the elastomers are at least
partially cured (should only two layers be required for the
finished article, then step (f) will be complete cure).
The third layer of the article is then formed by dispensing
another elastomer solution 64 (step (r) in FIG.7), which
may or may not be an open cell formulation (open cell
formulations provide the cushioning which is often sought
in footwear), from dispenser 76. Dispenser 76 dispenses
formulation 64 out of as many nozzles as are required. The
elastomer filled mold is then moved to oven 52 (step (q)
FIG 7), where all layers of elastomer are fully cured and
bonded.
AS the final step in the process, the mold and cured
elastomer article are moved through an air cooling chamber
68, (step (u) in FIG 7) before the finished article 66 is
removed from the mold (step (v) in FIG. 7).
CA 022~7616 1998-12-29
The disadvantages inherent in prior art injection
molding processes, which require a separate mold for each
size and width of the article (e.g., for each size and
width of shoe sole) can thus be overcome in the present
invention, by forming the upper or "backing" layer or
layers of an elastomer solution which exhibits a high
degree of elasticity. The elasticity will allow one mold
size to fit more than one size and width, since the elastic
backing layer(s) will "stretch" as necessary, while the
individual features/areas on the bottom of the sole or
other article can be formed with a higher durometer and
less elasticity to provide the product with satisfactory
performance and wear characteristics.
Furthermore, the problems with delamination
experienced in prior art processes are not possible with
this process, which allows partially cured liquid
elastomers to chemically bond into one, inseparable unit.
The process is also cost efficient, since it can be
employed in an automated process with high-volume hourly
output.
As will be apparent to those skilled in the art, in
light of the foregoing disclosure, many alterations and
modification are possible in the practice of this invention
without departing from the spirit or scope thereof.
Accordingly, the scope of the invention is to be construed
in accordance with the substance defined by the following
claims.
