Note: Descriptions are shown in the official language in which they were submitted.
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OUTSOLES FOR ESD TYPE PROTECTIVE FOOTWEAR AND METHODS
FOR MANUFACTURING THE SAME
FIELD OF THE INVENTION
The present invention relates to outsoles for footwear,
which prevent - electrostatic discharges (ESD) from
persons wearing the footwear to devices being handled,
and to methods for manufacturing such outsoles.
BACKGROUND OF THE INVENTION
Static electricity discharges from a person to an
electrostatic sensitive device or material being
handled, e.g. an integrated circuit or an electronic
device, is often sufficient to damage the device. For
example, it has been found that factory workers can
generate electrostatic potentials in excess of 20,000
volts simply by walking on a factory floor. The
friction between the sole of the footwear and the floor
material causes a high voltage potential to develop on
the worker. If the worker comes into close proximity to
an electrostatic sensitive device, the charged worker
can cause a discharge to the device and consequently
damage it.
Various means have been attempted to provide
electrostatic protection. The first such device is a
dissipative strap which is placed around the user's
ankle or in the shoe and which remains in contact with
the heel, see e.g. US 5,653,047. When the user
generates an electrostatic potential by walking on a
floor, the charge is substantially neutralized. Some of
the problems with this device include user's failure to
properly attach the device and failure of electrical
component due to irregular walking, since the grounding
device may not work properly until the heel comes into
sufficient contact with the floor.
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A second type of device is a static dissipative shoe.
Typically, these shoes fall in the electrostatic
discharge range of 106 to 109 ohms/sq. The outsole of
such shoe has chemical substances blended with the
plastic material of the outsole to create a static
dissipative resistance. Such shoe may have a limited
use due to the relatively high resistance and further
the chemical substance may limit the useful life of the
device.
To overcome the above drawbacks US 5,653,047 discloses
a shoe comprising conductive plugs which are located in
the toe region of the outsole of the shoe, and which
protrude slightly above the upper surface of the
outsole and below the lower surface of the outsole in
order to provide stable contact with both the ground
and a conductive layer on the inside of the shoe.
SUMMARY OF THE INVENTION
Problems and drawbacks associated with the shoe of US
5,653,047 may include (i) complex and expensive
manufacture, (ii) risk of occurrence of gaps or pockets
between the conductive plugs and the outsole, in which
dirt and moisture may be collected, (iii)
inconveniences when using the shoe if the conductive
plugs protrude too much and/or unreliable electric
contact if the conductive plugs protrude too little,
(iv) risk of unreliable operation after some time's use
due to wearing down of the conductive plugs, and (v) a
complicated structure at the upper end of the
conductive plugs.
A main object of the present invention is therefore to
provide an outsole for a footwear, which prevents
electrostatic discharges (ESD) from a person wearing
the footwear to a device being handled, and by which
the above problems and drawbacks of the prior art can
be_avoided or at least alleviated.
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A further object of the invention*is to provide such an
outsole, which has an improved reliability and
resistance against wear and tear.
A still further object of the invention is to provide a
method for manufacturing an outsole for a footwear,
which prevents damaging of devices caused by
electrostatic discharges, and which fulfils the above
objects.
These objects, among others, are attained by outsoles
and manufacturing methods as claimed in the appended
patent claims.
The invention will be described in greater detail below
with reference to the illustrative embodiments shown by
way of example in the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 illustrates a shoe having an outsole in
accordance with an embodiment of the present invention.
Fig. 2 is a cross sectional view of the shoe according
to Fig. 1.
Fig. 3 is an enlarged part of Fig. 2.
Figs. 4-6 are each a cross sectional view of a shoe
having an outsole in accordance with an alternative
embodiment of the invention.
Similar devices, parts, and details are denoted by
similar reference numerals throughout the drawings.
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DETAILED DESCRIPTION OF EMBODIMENTS
Figs. 1 and 2 show a shoe or footwear having an outsole
in accordance with an embodiment of the invention. The
shoe has an upper part 1 which is open at an upper end
portion thereof and, if desired, can be provided with a
protective cap (not explicitly shown) of conventional
.type. Reference numeral 2 indicates the outsole, and
reference numeral 3 indicates an insole made of a
comfort-improving material.
The outsole 2 comprises, according to the invention, an
electrically conductive connection from an upper
surface 2a of the outsole to a lower surface 2b of the
outsole in the form of a plurality of electrically
conductive fibers 4. The electrically conductive fibers
may be of carbon, of a metal, of an electrically
conductive polymer material, or of virtually any other
kind of electrically conductive material.
The electrically conductive fibers 4 are preferably
molded integrally in a hardenable flexible, material 5,
e.g. polyurethane material, of the outsole 2, so that
the electrically conductive fibers 4 maintain the
relative positions they adopt in connection with the
molding process. Hereby, the electrically conductive
fibers 4 are embedded in a hardenable binder, which at
surrounds at least portions of the electrically
conductive fibers 4, and, in a hardened state, fixates
the electrically conductive fibers 4 in their positions
relative one another.
According to the embodiment of Figs. 1-3, the
electrically conductive fibers 4 are arranged randomly
in relation to one another in a non-woven condition, so
that they do not form an arranged fibrous structure
like a woven fabric or equivalent. The electrically
conductive fibers 4 are preferably distributed directly
in the mold in a random pattern.
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The electrically conductive fibers 4 may be present
throughout the entire outsole 2 or a major portion
thereof, or they may be present at one or several
separate lateral portions of the outsole 2. The length
of the electrically conductive fibers 4 may be longer
than a thickness of the outsole 2 of the shoe.
Preferably, the electrically conductive fibers 4
provide a plurality of electrically conductive paths
from the upper surface 2a of the outsole 2 to the lower
surface 2b of the outsole 2. Hereby, a more reliable
low-resistivity electric connection is obtained.
With reference next to Fig. 4, which is a cross
sectional view of a shoe, a further embodiment of the
invention will be described. Here, each of the
electrically conductive fibers 4 is fixated to the
insole 3 (or to the upper surface 2a of the outsole 2
or to any other layer in contact with the outsole 2) at
a respective end thereof and the length of the
electrically conductive fibers 4 are longer than the
thickness of the outsole 2 of the shoe. The
electrically conductive fibers 4 are arranged so that
they each extend from the upper surface 2a of the
outsole 2 to the lower surface 2b of the outsole 2 to
thereby provide for multiple electric paths through the
outsole.
In Fig. 4 the electrically conductive fibers 4 are
distributed evenly throughout the outsole to obtain a
hair bristle brush like appearance of the electrically
conductive fibers 4 even though the electrically
conductive fibers 4 are embedded in the flexible
material 5 of the outsole 2.
In Fig. 5 a similar embodiment is illustrated. Here,
the electrically conductive fibers 4 are present at
several separate lateral portions of the outsole 2.
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In order to produce a manageable product made of such
randomly oriented fibers the electrically conductive
fibers 4 can be felted together. Felting means that the
electrically conductive fibers 4 become hooked together
and attached to one another in a non-woven condition.
Such a felted or tangled layer can, even if it is thin,
be handled as a unit during the procedure of
manufacturing the outsole 2. Other methods of holding
the fibers together which facilitate their handling can
also be used.
In Fig. 6 an embodiment of the invention, which makes
use of such felted layers in non-woven condition, is
illustrated. The embodiment comprises a plurality of
felted layers 4, wherein each layer comprises
electrically conductive fibrous material that provide
an electrically conductive connection from the upper
surface 2a of the outsole 2 to the lower surface of the
outsole 2b. The felted layers 4 are preferably arranged
substantially vertically in the outsole 2 at multiple
lateral locations of the outsole. Alternatively, only
one felted layer comprising electrically conductive
fibrous material is provided in the outsole 2.
Yet alternatively, or additionally, the plurality of
electrically conductive fibers may include one or
several woven layers of electrically conductive fibers
in the outsole, possibly arranged vertically in the
outsole.
Each of the felted or woven layers may be provided as a
double, triple, or multilayer.
In an alternative embodiment the plurality of
electrically conductive fibers may be stitched or
knitted into a fiber based system, matrix, or layer
made e. g. of a polymer material, which is then in turn
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molded integrally in the hardenable flexible material
of the outsole.
The electrically conductive fibers 4 may comprise
fibers of a linear density of fiber mass of between
about 0.5 and about 5 denier, and/or fibers of
different linear densities of fiber mass. The
electrically conductive fibers 4 may be provided in
lengths of between about 20 mm and about 100 mm.
The above outsole provides an excellent ESD protection
function. A footwear with the above outsole will
prevent electrostatic discharges from a person wearing
the footwear to a device being handled. Further, the
footwear reduces the risk for a person wearing the
footwear of getting an electric shock due to an
electrostatic discharge.
Besides, it has been noted that the resistance against
wear and tear is strongly enhanced by the presence of
fibers at the lower surface of the outsole.
Further, the outsole of the above kind may be provided
with a flexible anti-nail protective layer arranged in
between the insole 3 and the outsole 2 or within the
outsole 2 as being described in our pending US patent
application published under No. US-2006-0265909-A1.
The various embodiments of the outsole described above
may be combined to form yet further embodiments of the
invention. In particular, the plurality of electrically
conductive fibers may be present in a plurality of the
described structures or systems depicted above.
Further, the embodiments may be manufactured in a
plurality of manners according to the invention.
According to one method an outsole 2 for a shoe, which
prevents damage caused by electrostatic discharges, is
manufactured by (i) arranging or attaching electrically
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conductive fibers 4 at the under side of an insole 3 of
the shoe, which in turn is attached to an upper part 1
of the shoe, and (ii) molding flexible material 5 to
the insole 3 and optionally, to the upper part 1 to
thereby fixate the electrically conductive fibers 4 in
the flexible material 5 and thus form the outsole 2.
Naturally, the electrically conductive fibers 4 have to
extend through the entire outsole 2 to provide for an
electrically conductive connection through the outsole.
The electrically conductive fibers 4 may be arranged in
any manner disclosed in the present description.
According to another slightly different method an
outsole for a shoe, which prevents damage caused by
electrostatic discharges, is manufactured by (i)
arranging or attaching electrically conductive fibers
at the under side of an upper part of the shoe, which
is closed at a lower end portion thereof, and (ii)
molding flexible material to the upper part of the shoe
to thereby fixate the electrically conductive fibers in
the flexible material and thus form the outsole 2.
According to yet another method an outsole for a shoe,
which prevents damage caused by electrostatic
discharges, is manufactured by (i) arranging
electrically conductive fibers in a mold, and (ii)
molding the outsole by feeding flexible material to the
mold and harden the flexible material to thereby fixate
the electrically conductive fibers in the flexible
material of the outsole. The electrically conductive
fibers are molded so that an electrically conductive
connection from an upper surface of the outsole to a
lower surface of the outsole is obtained. Preferably,
electrically conductive fibers are protruding from the
upper and the lower surfaces of the outsole. The
outsole can in a later stage be attached to an upper
part of a shoe, thus forming an entire shoe, which
prevents electrostatic discharges from a person wearing
the footwear to a device being handled.
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It shall be appreciated that the term outsole as used
in the present text covers outsoles of the type
described above as well as any type of sole having a
combined outsole and insole.
