Note: Descriptions are shown in the official language in which they were submitted.
This inven-tion rel~tes to pro~e,tiye footwear in
cJeneral and specifi~ally -to an insulative micl~sole insert
moulda~le into the sole of such footwear.
BA~KGROUND OF TEIE INVENTION
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There have been several recent developments in the
protective footwear indus-try which have cc)ntributed greatly to
the rea.Lization of economies of manufac-ture and -to i~proved
pro-tection for the wearer. Canadian Patent No. 1,118~594
issued February 23, 1982 to Swenco Limited teaches a protective
:L~ mid-sole, desirably made from stainless sl::eel, w~ich can be
moulded into the footwear sole and which provides protection
over su~stantially the entire area of the sole, especially in
the arch, ball and toe regions~ Canadian Patent No. 1,120,710
issued March 30, 1982 to Swenco Limi-ted teaches a moulded plas-tic
heel Eiller which can be moulded into the footwear heel to re-
duce the amount of rubber or moulding compound required and
which can be securely a-t-tached to a pro-tec:~tive mid-sole or .shank
prior to sole mouldin~. The use of the he~el filler or the heel
filler-mid-sole/shank assembly has proven to be a s-tride forward
~0 in the manufacturing and protec-tion aspect:.s of this particular
industry.
There are, on the other hand, certain areas in which
further improvement is required. For example, a work boo-t or
shoe including a puncture-prooE metallic mid-sole as described
in the aforementioned patents could feel uncomfortably cold to
the wearer when used in an extremely cold environment. Also,
the foot o:E the wearer tends to persp.ire and such perspiration
i:E it soaks througl tiLe inne.r sole and reaches the metallic
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mid-sole could enhance -the cold feeling. Fur-thermore, such
perspiration and any other moisture en-tering the boot tends to
accelerate the wear of an inner sole in -the ball or toe regions.
If the boot becomes so worn that an inner hole develo~s to the
point where d.irect foot contact with the mid-sole, or indirect
contact therewith through moisture, occurs, the wearer runs a
risk of electrocution i.f the metallic mid--sole is contacted by
live electricity, for example ~y the exposed end of a live wire
stepped on by the wearer, which end penetrates and touches the
mid-sole. There is, therefore a need for improved pro-tective
footwear which offers better thermal and electrical insulation
properties than has heen available in the past.
In present methods used by stanclards organizations in
Nor-th ~merica and Europe, -tests for thermal and dielec-tric resis-
tance are carried out on new (unworn) foot.wear only. No allow~
ances are made for wear (either normal or excessive) o~ the
outsole bottom or the insole. Such tes-tin.g would obviously be
difficult. It is thus desirable, in the absence oE such
"~ccelerated" wear testing/ to an-ticipa-te the possible problems
resulting from such wear and therefore -to proyide thermal and
dielectric protection despite excessive wear.
With respect to thermal insulation it has been known
to provide die cut foam or moulded plastic inserts for placing
wi-thin the foot area of boots or shoes. Such inserts have the
disadvantaqes that: they tend to break down with wear; they
can actually increase the rate of perspiration, .reducing comfort;
-they reduce the volume of the .footwear intler.ior, thereby cramp-
incJ the foc~t; and they may not fit the boot or shoe perfectly,
perhaps leavin~ a cJap around the per.iphery which in the heel area
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c~uld be noticed by the wearer, leadiny t.o further di.scomfort.
SUMMARY OF T~IE INVENTION
. . _
The present invention provides a moulded plastic in-
sert or mid-sole, desirably formed from cellular polye-thylene,
polypropylene, or other suitable plastics having c~ood thermal
and dielectric proper-ties as per ASTM tes-t:rnethods C177 and
D149 respectively and which can in turn be moulded into the
sole of protective footwear thereby servir,g to increase both
the thermal and electrical insulative properties of the sole.
Particular advantages accrue when the insert is used
in conjunction or assembly with a metallic punc-ture-proof mid-
sole such as is described in the aforementioned patents. In
such an assernbly the insert member would be atop the me-tallic
mid-sole and would reduce the unwanted transmission oE heat
from the foot of the wearer to the exterior adjacent the sole.
ln addition, the i.nsert member would grea-t:ly reduce the possi-
b;.lity of electrical transmission from the ex-terior ~o the wear-
er's foot, even pxesupposing tha-t live electrical contac-t had
been made with the metallic mid-sole, that: the inner sole was
worn through and that there was mo:isture (perspiration) within
the boot or shoe. Static electricity prob~:Lems would also be
grea-tly reduced as there would be no grounding of the wearer's
body through his footwear~ Other advantages accrue to the
wearer, since even with worn footwear, considerable dielectric
pro-tection is a:Eforded if electrical contact is made wi-th other
than the feet, the path to ground bein~ .int:errupted at the
insula-tive mid-sole.
Thus, the present invention may be broadly de:Eined as
an :insulatlve m:id-sole rnouldable wittlin a sole of an article of
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footwear comprising a plate member conforming generally in
plan and elevation to the contours of the sole with toe, ball,
arch and heel portions, the member being formed from a plastics
material having suitable thermal insulati~n and dieLectric pro-
perties and serving to insulate the interior of the footwear
both thermally and electrically from the exterior thereof ad~
jacent the underside of -the sole.
In one particular embodiment the present invention
prov;des a mid-sole assembly mouldable within a sole of an
article of protective footwear comprising a metallic first mid-
sole member conforming generally in plan and elevation to the
contours of the sole with toe, ball, arch and heel portions and,
positioned above the first mid--sole member, an insulative second
mid~sole member having toe, ball~ arch and heel portions, the
second mid-sole member being formed from a plastics material
having suitable thermal insulation and dielectric properties and
serving to insulate the interior of the footwear both thermally
and electrically from the exterior thereof adjacent the under-
side of the sole.
2~ It ~hould be mentioned that the insulative mid~sole
of the present invention may be pre~assembled -to a puncture-
proof mid-sole and/or to a moulded heel filler, as described in
the aforementioned patents. Such pre-assembly could be by way
of a through aperture in the heel portion of the insulative
mid-sole which is adapted to be mated wit:h a corresponding pro-
jection on the upper surface of the heel filler. The puncture-
proof mid-sole would also have a -through aperture alignable
w.ith the aperture of the insul.ative mid-sole and matab].e w.ith
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the projection(s) on the heel filler. The insulative mid-sole
could be pre-assembled to the punc-ture-proof mid-sole by appro-
priate means, such as a plastic eyelet passing through the two
components at each end thereof, or a moul,led boss on the insul-
ative mid-sole "snapped" into small holes provided at the front
and back of a protective metallic plate.
Finally, the insulative mid-sole need not be of uniform
thickness -throughout. For example, its thickness could be re-
duced in the toe region where the material of the upper tends
to bunch, and becomes thicker, when the upper is secured to the
sole. Such bunching can be compensated for by reducing the
thickness of the insula-tive mid-sole .in the toe region so that
the overall thickness of the footwear sole is reasonably uniform
and the wearer is not faced with uncomfort.able constructions.
Also, the thickness of the insulative mid-sole can vary
from one area thereof to another to improve comfort or to facili-
tate better footwear manufacture, without detracting from the
in-tended purpose of the invention.
BRIEF DESCRI~TION OF THE DRAWINGS
Figure 1 sllows in perspective th.e .insulative mid-sole
of the present invention.
Figure 2 shows in perspective t.h.e insulative mid~sole
of the present invention in combination with a puncture--proof
mid-sole and a heel fill.er.
Figure 3 shows in perspective t.h.e insula-tive mid~sole
oE the presen-t inverltion secured -to a pun.c-ture~proof mid-sole.
Figure 4 shows a work boot in pa.rtial cross section,
incorporating thexein an assembly as sho~rl in Figure 2
Pg/~-~ - 5 -
DESCRIPTION OF THE PREE'ERRED EMBODIMENT
Before discussing the present invention in detail, it
is desirable to describe the environment: in which the invention
is useful and in that regard reference is made to Figure 4
which illustrates in par-tial cross-secl:i.on the sole portion of
a typical cor~mon work boo-t 10. Such a koot usually includes a
protective high carbor s-teel toe cap 12 covered in-teriorly and
exteriorly by leather layers 14 and 16 respec-tively. At the
` heel and ankle areas various layers of leather, constituting
portions of the outer boot 18, the inner boot 20 and the heel
reinforcemen-t 22 are shown in par-t. The inner sole 24 is
typically constructed of recons-ti-tuted leather or o-ther
"breathable" material.
The external sole 26 includes a heel portion 28, an arch
portion 30, a ball portion 32 and a toe Iportion 34. The heel
and ball por-tions may have corrugatiorls or other friction-
enhancing means on the underside thereoE. Typically the sole 26
is moulded of rubber, rubber compounds or plastics ma-terial
and such mould~ng rnay he hy injection, compression or the
recently developed injection/compression processes.
As described in the aforementioned Canadian patents, a
moulded plastics heel filler 36 is located wi-thin -the heel
portion 28 of the sole 26. Details of l_he heel filler are no-t
parti.cularly pert:inent to -the present invention,with the
exception -that. the heel fille:r can have at leas-t one projec-tion
52 ~F.igure 2) extenclin~3 upward]y from the upper surface -thereof~
Als.o :i.n accordance ~ith the aforemen-t:ioned Canadian pa-tents -the
sd /li~G -6
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sole 26 desirably contains a puncture-proof metall:ic mid-sole 38 which
provîdes protection to the wearer against sharp ob-jec-ts whi.ch ~ght pene-
trate the toe ball or arch portions 34, 32, 30 o:E the sole 2~. Again!
detail.s of the mid~sole 38 are not rcquired for the present invention with
tha exception that it can have aperture means (not shown) engagable with
the projec~ion~s) 52 of the heel filler 36 for se(~lring the mid-sole 38
to the heel fil:Ler 36 preferably prior to placement: thereof into the sole mould.
. The present invention will now be desc:ribed with particular ref-
erence to Figures.l to 4.
Figure 1 shows the most basic cx~mponerlt: of the present invention
that being an insulative mid-sole 40, being a plat:e me~ber haYing a periphery
42 that generally follc~ws but is approximately 15 ~m. inside the outline of
a boot sole and having a three-dimentional contour that generally confornLs
to the contours of the foo-twear last, closely sim~.lating the contours of the
hun~ul foot. Thus the plate member will have a slightly dished heel portion 44,
a somewhat downwardly curved arch portlon 46, a dished ball portion 48 ancl a
slightly upwardly inclined toe portion 50. The plate ~enber is desirably mould-
ed from a materi.al, such as cellular polyethylene, polypro~ylene or other
s~itcible plastic~s materic~. that has speciEic properties: (a) it will no-t
~0' break down at the temperatures at which the sole 2l~ is moulded; (b) it
exhibits a relatively high thernkal resistance; and (c~ it has good dielectric
properties, acting as an elec~trical insulator. It has been found that a thick-
ness for the plate member in the order -to 4 to 6 mm gives satisfactory in-
sulative properties without seriously affecting the flexibilit~ of -the boot
sole 26.
P~ 7 --
It has also been found thal the most desirable
material fox the plate member is ce]lular polyethylene~ th~t
material having all of the aEorement.ioned desired properties.
While it is preferable that the plate mernber be
moulded so as to have a three-dimensional contour as described,
it would also be possible to die cut the plate member from a
flat sheet of foamed polyethylene. Such a flat plate member
would be sufficiently flexible that .it would conform generall.y
to th~ sole contour of the lasted boot when the sole is moulded.
With reference to Figures 2 to 4, the preferred con-
figurations of the present invention, are illustrated. As
indicated previously the insulative mid-sole has particular
ad~Jantages when used in conjunction with a puncture-proof mid-
sole 38 such as is descrlbed in the aforementioned Canadian
patents. Such a mid-sole 38 conforms yenerally to the
~' peripheral contour of the sole 26 in the toe, ball and arch
areas and in the heel region has through aper-ture means (no-t
shown) which mate with one or more prc)jections 52 on the heel
filler 36. The mid-sole 38 is intendled to pro-tect the wearer's
foot agains-t sharp objec-ts wh.ich he m.i.ght step on and which,
absent t:he mid-sole 38, would penetrate the sole 26. In the
vulnerable arch area the mid-sole 38 would be provided with a
longitudinaLly extending downwardly p:rojecting rib (not shown)
which adds streng-th to the mid-sole and tends to de~lec-t the
point o~ a sharp object away from a perletrating path.
As shown in E`igure 2, a heel f.i.ller 36 is seen as being
connected to a protective mid~sole 38 by way of the projection
52. An insu:Lative mid-sole 40 :is positioned atop the protective
sd/~.f 8-
a~
mid-sole 38 and is secured as part of the overall asser~ly
by way of the projection 52 engaging a corresponding aperture
56. Figure 2 also clearly shows that over the major len~th of
the assembly, from the toe to adjacent the heel area, the edge
of the insulative mid-sole 40 is inset from the edge of the
protective mid-sole 38. This stepped effect permits the under-
turned edge (lasting margin) of the upper to have a zone ~here
it can ~e placed without adding to the thickness o~ the sole 26.
The lasting margin will be sealed to the s~le 26 by the rubber
of the sole 26. Also t if the mid-sole 40 does not lie completely
against the mid-sole 38; wh.ich is very likely to occur, the mould-
ing compound of the sole can penetrate the gap between the mid--
soles for addit.ional insulative and securi;ng effectv
When an assembly .such as that shown in Figure 2 is
moulded into the sole of a work boot or oth~er protective footwear,
as shown in Figure 4, several advantages are attained. From an
economic standpoint the insulative mid-sole 40 ac-ts as a filler,
there~y reducing subc;ta:ntially the amount of rubher material or
compound needed to mould the sole 26 since the mid-~ole ~0 wi:Ll
replace the material otherwise loca-ted abov,3 the mid-sole 38r
The cost o~ an insulated mid-sole 40 is considerably less than the
cost of the material it replaces and is considerably lighter in
wei.ght. Secondly the insulati.ve mid-sole 40 aids in -the.rmally
isolating and însula-ting the interior of the boot lO with respect
to the atmosphere, especially ex-terior to t.he sole 26. Thus when
workin~ in a cold envirol~nen-t there will be less heat -transmission
from the foot wi-thi.n th~ boot throuc3h to the ground through the
sole ~60 Lastly, the .i.nsulative mid-sole 4() has excellen-t
P~ _ g _
dielectric properties and serves to electrically insulate
the interior of the boot from the exteri.or below the sole 26.
Even if, under the wors-t conditions, there is electrical
contact with the metallic mid-sole 38 the wearer is protected
from electrical "contact with his foot by th.e insulative
mid-sole '10~ Electrical contact made by other than through
the footwear is less deleterious, since the path to ground is
interrupted at the mid-sole 40.
Figure 3 shows one manner in wh:i.ch an insulative mid-
sole 40 can be preassembled to a metall:ic mid-sole 38 In
this case the mid-sole 38 is initially :Eormecd with a through
hole adjacent each end as is the mid-so:Le 40. When the mid-
soles are brought together the respective holes will be in
alignment and they can be secured together by plaastic or other
non-metallic eyelets 54 or rivets crimped to the mid-soles
through the aligned holes~ IE a heel f:i.ller 36 is to be used
the two mid-soles would also be providerl with. appropriate aper-
~ures, 5uch as 56 (Figure 2) for :mating with corresponding pro-
Jection(s~ 52 on tha heel fil.ler. Also, since each eyelet it-
sel~ defines a throucJh opening 58, those openin~s 58 can beusecl in conjunction with locating pins :i.n th~ lasting machine
to properly position the mid~sole assembly prior -to sole moulding.
While not specifically illustral:ed in the drawings, it
would be possible to bond the insulative mid-sole 40 to ei.ther,
or both, of the insole or outsole, or the metallic pro-t~ctive
mid-so].e. To facili-tate suc.h bonding orle or bo-th surfaces of
the micl-sole 40 may be in-tegra].l.y covered with a sui-table
non-woven material insert moulded to the mid-sole at the time
pg/~ - 10 -
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of its manufac-ture. Since the preferrell material for the
mid-sole ~0 is polyethylene or polypropylene neither of
which can be bonded to differen-t substrltes by conventional
methods such conversion would be -very clesirable.
Another mechanism for connec-ting together the mid
soles 40 and 38 would involve the provision of depending
bosses (not shown) moulded to the underside of -the mid-sole
40 at each end thereof and receivable in correspondin~ aper-
tures at each end of the rnid-sole 38.
As a further alternative, the protectiye mid-sole 38
could be insert moulded into a sui-ta~le plastics material
to form an insulative mid-sole with the protecti`ve mid-sole
encapsulated therein. Such a constructiion would avoid the
necessity of any separate step to assem~le the two mid-soles
together in a mechanical way as described above.
The foregoing describes -the bes-t: modes of putting the
present invention i.nto effect as presen-t;ly known. I-t is under-
stoocl that variations in configura-tions de-tails or materials
may occur to a person skilled in the ar-t: without departing
from the spirit of the invention. Thus the pro-tection to be
afforded the presen-t inven-tion is to be determined from the
claims appended hereto.
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