U.S. patent number 3,724,105 [Application Number 05/125,889] was granted by the patent office on 1973-04-03 for footwear.
This patent grant is currently assigned to Monsanto Chemicals Limited. Invention is credited to Donald Weight.
United States Patent |
3,724,105 |
Weight |
April 3, 1973 |
FOOTWEAR
Abstract
Footwear, such as a boot or shoe, having an insole comprising an
extruded foamed resin sheet wherein the resin is an ethylene-vinyl
acetate copolymer or a blend thereof with polyethylene and has a
polymerized vinyl acetate content of 2-17 percent by weight. The
insole has a substantially uniform thickness, a substantially
closed cell structure, and a density of 17-40 pounds per cubic
foot. Preferably, the insole is treated with an electric discharge
prior to being bonded to the other components of the article of
footwear. The insole can be bonded to these other components by any
suitable means, preferably by the use of an adhesive.
Inventors: |
Weight; Donald (Chalfont Saint
Ciles, EN) |
Assignee: |
Monsanto Chemicals Limited
(London, EN)
|
Family
ID: |
26824062 |
Appl.
No.: |
05/125,889 |
Filed: |
March 18, 1971 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
793559 |
Jan 23, 1969 |
3624191 |
Nov 30, 1971 |
|
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Current U.S.
Class: |
36/44 |
Current CPC
Class: |
A43B
13/38 (20130101); B29C 59/10 (20130101); B29L
2031/507 (20130101); B29K 2105/046 (20130101); B29K
2023/06 (20130101) |
Current International
Class: |
A43B
13/38 (20060101); B29C 59/10 (20060101); B29C
59/00 (20060101); A43b 013/38 () |
Field of
Search: |
;36/43,44,32R |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Guest; Alfred R.
Parent Case Text
CROSS-REFERENCES TO RELATED APPLICATIONS
This is a division of application Ser. No. 793,559, filed Jan. 23,
1969, now U.S. Pat. No. 3,624,191 issued Nov. 30, 1971.
Claims
What is claimed is:
1. An improved insole comprising an extruded foamed resin sheet
having a substantially uniform thickness of 0.04-0.2 inch, a
substantially closed cell structure, and a density of 17-40 pounds
per cubic foot, the improvement which comprises an extruded foamed
resin sheet, wherein said resin is selected from the group
consisting of:
A. copolymers of ethylene and vinyl acetate, said vinyl acetate
comprising about 3 to about 15 per cent by weight of said
copolymer, and
B. blends of ethylene-vinyl acetate copolymers with polyethylene,
said vinyl acetate comprising about 3 to about 15 per cent by
weight of said blend, said ethylene vinyl acetate copolymer having
about 17 to about 45 percent vinyl acetate in the copolymer.
2. The insole of claim 2 wherein the polymerized vinyl acetate
content of the copolymer is 3- 5 percent by weight.
3. The insole of claim 1 wherein the thickness of the sheet is
0.05-0.1 inch.
4. The insole of claim 1 wherein at least 75 percent of the cells
have a diameter of 0.004-0.04 inch.
5. The insole of claim 1 wherein the density of the sheet is 22-30
pounds per cubic foot.
6. An insole of claim 1, wherein at least one side of said sheet
having an adhesive surface.
7. An insole of claim 1, wherein each side of said sheet having a
non-foamed skin less than 0.002 inch in thickness.
8. An insole of claim 1, wherein said sheet comprises a heelboard
in combination with a flexible forepart said flexible forepart
being coplanar with said heelboard.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to footwear and more particularly relates to
a novel insole comprising an extruded foamed resin sheet and to an
article of outer footwear, such as a boot or shoe, having such an
insole.
2. Description of the Prior Art
In the construction of outer footwear such as boots and shoes, the
upper is normally fastened to an assembly comprising an insole and
a heel board while the assembly is held on a last, a sole and heel
are then fastened to the underside of the assembly, and the parts
of the insole and heel board visible within the shoe are finally
covered by a lining or sock. The heel board is usually made of a
relatively rigid material such as fiberboard, but the insole needs
to be more flexible. The nature of the insole is indeed of extreme
importance in determining the comfort and life expectancy of the
shoe as a whole, since it serves to hold the upper to the sole and
also to cushion the foot of the wearer. As has been mentioned, the
insole needs to be flexible in the interests of comfort, but
another important requirement that generally militates against
flexibility is the need for good "recovery," i.e., ability of the
shoe to regain its original shape after being subjected to
deformation in use. Repeated flexure and impact when the shoe is in
use result in deformation of the shoe as a whole, and, unless a
shoe has the ability to recover overnight from the effects of being
worn for a day, it will give only a few months' wear before
generally deteriorating, becoming ill-fitting, uncomfortable, and
unattractive in appearance.
Hitherto, it has been usual to employ for the production of insoles
such materials as cardboard, paper pulp, leather pulp, leather, and
similar materials, usually treated with a resin in order to afford
some resistance to moisture. However, such materials suffer from
the very real disadvantage that they are not as flexible as is
desirable, and, even when treated with a resin, they absorb
moisture either from outside the shoe or from a perspiring foot.
When moist, they are readily deformed and have a tendency to
disintegrate or delaminate, thus admitting water through the edge
of the insole, which in turn leads to very rapid disintegration of
the structure of the shoe as a whole. Perspiration can also cause
some of these materials to rot. Some synthetic materials have been
tested as insoles but have been found to be defective either
because of insufficient flexibility or because of a tendency to
"spread," i.e., stretch so that the necessary shape retention is
not obtained. It can therefore be seen that the choice of an insole
material is not a simple matter and that the materials that have
hitherto been proposed fall well short of the ideal.
SUMMARY OF THE INVENTION
An object of the invention is to provide a novel insole having good
flexibility, resistance to moisture, and recovery.
Another object is to provide an article of footwear having such an
insole.
These and other objects are attained by (1) forming an insole
comprising an extruded foamed resin sheet having a substantially
uniform thickness of 0.04-0.2 inch, a substantially closed cell
structure, and a density of 17-40 pounds per cubic foot from a
resin which is an ethylene-vinyl acetate copolymer or a blend
thereof with polyethylene and which contains 2-17 percent by weight
of polymerized vinyl acetate, (2) bonding the insole to a
relatively rigid heel board to form an assembly, and (3) bonding
the other components of a shoe or the like to said assembly to form
an article of footwear.
DESCRIPTION OF THE DRAWINGS
FIG. 1 a perspective view of an insole assembly having a heelboard
according to the invention, and
FIG. 2 a section through a shoe incorporating the insole assembly
shown in FIG. 1.
The insole assembly consists of a heelboard 1 and a flexible
forepart 2, the flexible forepart and the lower surface of the
heelboard being composed of a sheet of foamed resin. In addition
the heelboard 1 comprises a shank board 3, for example of cellulose
fiber, skived to zero thickness at its forward end 4 and adhered to
the upper surface of the sheet of foamed resin.
The shoe illustrated in FIG. 2 comprises an insole assembly 5
having a heelboard 6, the lower surface 7 of which is composed of a
sheet of foamed resin which forms the forepart (8).
In constructing the shoe the outer edge 9 of the upper 10 is bent
around the heelboard 6 and adhesively bonded to its lower surface
7. The sole proper 11 is then adhesively attached to the insole
assembly 5 followed by the heel 12.
FIG. 3 is a section view through the insole sheet of foamed resin
showing the foamed interior 13 and the non-foamed exterior skin
layers (14).
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The following examples are given to illustrate the invention and
are not intended as a limitation thereof. Unless otherwise
specified, quantities mentioned are quantities by weight.
EXAMPLE I
Dry blend 98 parts of an ethylene-vinyl acetate (88:12) copolymer
resin in granular form with 2 parts of anhydrous calcium acetate,
and feed the resulting mixture into the hopper of a screw extruder
having a barrel with a nominal diameter of 1.5 inches. Inject
nitrogen under pressure into the molten mixture in the extruder
barrel, and extrude the resulting foamable composition at a
temperature of 130.degree. C. into the atmosphere through a slit
die having a length of 6 inches and a width of 0.025 inch. The
product is a soft foam strip having a thickness of 0.08 inch, a
density of 24 pounds per cubic foot, and a fine closed cell
structure.
Subject both sides of the sheet to the action of an alternating
electric discharge of 10,000 volts and 3 kilocycles per second by
passing the sheet between two electrodes spaced 0.15 inch apart,
each part of the sheet being exposed to the discharge for 0.1
second. Cut the sheet into pieces in the shape of insoles suitable
for ladies' casual shoes, and adhere each insole to a heel board
made of a cellulose fiberboard known as "shank board" by means of a
neoprene adhesive at 70.degree. C. for 5 seconds under pressure.
Then adhere the resulting assembly to a leather upper by means of a
neoprene adhesive applied at 70.degree. C. for 5 seconds, and
finally attach a rubber composition sole and heel to the assembly,
also by a neoprene adhesive.
The resulting shoe has a very flexible and comfortable sole. The
insole survives extended wearer trials without failure, whereas a
pulped leather insole in an otherwise identically constructed shoe
disintegrates after only a few months. The resistance to moisture
of the insole of the invention is excellent. The recovery ability
of the shoe of the invention is infinitely superior to that of the
control shoe, the latter being misshapen and ill-fitting after only
3 months whereas the shoe of the invention retains its good shape
and fit after 12 months of use.
Trials of other women's and children's shoes according to the
invention show no case of failure due to insole cracking, the
trials always being ended by failure of a different component of
the shoe.
EXAMPLE II
Repeat Example I except for substituting an ethylene-vinyl acetate
(96:4) copolymer for the ethylene-vinyl acetate (88:12) copolymer.
The resulting shoe is similarly flexible and comfortable and is
just as successful in passing wearer trials. The insole has the
additional advantage of reduced sensitivity to the effects of heat
during application of the neoprene adhesive, thus permitting the
use of slightly more severe bonding conditions if required.
The resin used in the practice of the invention preferably contains
from 3 or 7 to 15 percent by weight of polymerized vinyl acetate,
e.g., 3-5 percent or 10-13 percent by weight. As demonstrated in
the Examples, excellent results are obtained employing resins
containing, respectively, about 4 percent and about 12 percent by
weight of vinyl acetate. Preferably, the resin is an ethylene-vinyl
acetate copolymer, but it can be a blend of polyethylene with such
a copolymer. When it is a blend, the proportion of vinyl acetate in
the copolymer can, of course, be greater than 17 percent by weight,
e.g., up to 30 percent or even 45 percent by weight, sufficient
polyethylene being blended with the copolymer to reduce the vinyl
acetate content of the resin as a whole to a value within the
required range. The polyethylene can be of the "low-pressure" type
made using a chromium oxide or organometallic catalyst system, but
it is preferably a "high-pressure" polyethylene, e.g., a
polyethylene having a density of 0.90-0.94 grams per cc. Ethylene
and vinyl acetate are usually the only monomers polymerized into
the resin, but a small proportion not exceeding 3 or 5 percent by
weight of the total, of a third monomer such as propylene or methyl
methacrylate can be polymerized into the resin if desired.
The sheet has a substantially uniform thickness, i.e., the
thickness does not vary by more than 15 percent. Preferably, any
thickness variation is not greater than 5 percent. The type of
footwear being made determines the choice of insole thickness
ordinarily, thinner insoles usually being needed for children's and
ladies' shoes than for men's boots or shoes. Preferably, the
thickness is from 0.05 to 0.1 or 0.15 inch; very often 0.06-0.085
inch is particularly suitable.
The foamed sheet has a substantially closed cell structure, i.e.,
the majority, normally at least 90 percent, of the cells are
closed. Preferably the majority, and more preferably at least 75
percent, of the cells have a diameter of 0.004-0.04 inch, e.g.,
0.01-0.03 inch.
The density of the sheet is very often 20-40 pounds per cubic foot,
preferably 22-30 pounds per cubic foot; and a density at the lower
end of this range, e.g., about 24 pounds per cubic foot, is usually
most suitable. The sheet may have a non-foamed skin on each side,
but this is not usually thicker than about 0.002 inch.
The foamed sheet is an extruded one and is normally made by
extruding a foamable mixture of the resin and a suitable blowing
agent under pressure through a die into a zone of lower pressure
(usually the atmosphere) so that the expansion of the blowing agent
and foaming of the resin take place. Usually a slit die is used,
but it is also possible to employ an annular die to extrude a tube
of foamed resin that is later slit longitudinally and opened out
into a flat sheet. When a slit die is used, it can have a flared
outlet if desired, and a pair of rollers can be placed in front of
it so that the extruding sheet passes between them; such rollers
assist in the production of a smooth flat sheet free of thickness
variations and corrugations.
As indicated above, any suitable blowing agent can be used, but the
preferred blowing agents are those which are gases or vapors under
normally atmospheric conditions. Volatile liquids can also be used.
In many cases, the blowing agent is one that is normally gaseous
but which, while under pressure before extrusion, will be present
in solution in the molten or semi-molten resin. Exemplary of
volatile blowing agents that can be used are lower aliphatic
hydrocarbons such as ethane, propane, butane, pentane, etc.; lower
alkyl halides such as methyl chloride, trichloromethane,
1,2-dichlorotetrafluoroethane, etc.; and inorganic gases such as
carbon dioxide or nitrogen. Nitrogen and the lower aliphatic
hydrocarbons, especially butane or isobutylene, are preferred; and
a mixture of nitrogen and a lower aliphatic hydrocarbon is often
particularly useful. The blowing agent can also be a chemical
blowing agent, e.g., a bicarbonate such as sodium bicarbonate or
ammonium bicarbonate, or an organic nitrogen compound that yields
nitrogen on heating, such as dinitrosopentamethylenediamine or
barium azodicarboxylate. In the case of a liquid or readily
liquifiable blowing agent, 3-30 percent, especially 7-20 percent,
based on the weight of resin, is often a suitable proportion. When
the blowing agent is a permanent gas, it is more convenient to
consider relative volumes at standard temperature and pressure. For
example, the use of 0.5-5 parts, preferably 1-2 parts, by volume of
nitrogen at S.T.P. in conjunction with 1 part by volume of
polyethylene gives excellent results. The use of amounts of blowing
agent at the lower end of the above ranges often results in the
production of a thicker sheet.
The blowing agent is sometimes employed in conjunction with a
nucleating agent, which assists in the formation of a large number
of fine cells. A wide range of nucleating agents can be employed,
including finely-divided inert solids such as silica or alumina
(optionally in conjunction with zinc stearate), or small quantities
of a substance that decomposes at the extrusion temperature to give
a gas can be used. An example of the latter class of nucleating
agents is sodium bicarbonate, optionally in conjunction with a weak
acid such as tartaric or citric acid. Boric acid, calcium acetate,
calcium propionate, and calcium benzoate are also excellent
nucleating agents. A small proportion of the nucleating agent,
e.g., up to 5 percent by weight of the resin, is usually
effective.
The resin can also contain such additives as coloring agents,
antioxidants, stabilizers, lubricants, etc., if desired. For
example, it is often desirable to color the resin when it is to
form part of a sandal, the construction of which renders the edge
of the insole visible as the welt. A clay or other brown pigment is
very often suitable for this purpose.
According to a preferred feature of the invention, the sheet is
subjected to the action of an electric discharge. This has been
found not only to improve the adhesion of hot melt and other
adhesives to the insole, but also surprisingly to reduce
undesirable adhesion of the insole to any metal platen or press
foot employed in assembling the shoe. A voltage, preferably
alternating, above 3,000 volts, preferably 5,000-30,000 volts, is
usually suitable, especially one having a frequency of
1,000-100,000 cycles per second. It is preferably a corona
discharge but can be a spark or spray discharge. Preferably, both
sides of the sheet are treated, with the electrodes situated, e.g.,
0.005-0.2 inch away from the surfaces; and an application time of
0.003-1 second, especially 0.01-0.5 second, is generally
satisfactory.
The production of the articles of footwear can follow normal
practice, although it is necessary to ensure that the degree of
exposure to elevated temperatures, e.g., when using a hot melt
adhesive, is not sufficient to cause collapse of the foam
structure. This can generally be arranged where the necessary
bonding between insole and other components of the shoe is achieved
by means of a cold or hot melt adhesive or with a polyurethane or
neoprene adhesive, or even by injection molding of a plasticized
polyvinyl chloride sole and heel, provided that contact with
elevated temperatures is maintained for as short a time as
possible. It is, for instance, surprising that a polyamide or
polyester hot melt adhesive can be used at 240.degree. C. with an
insole material having a softening temperature of only 120.degree.
C. or even less, if the period of time for which the insole is
exposed to this temperature is not more than 5 seconds. Even better
results in this respect can be obtained if the resin of the insole
material contains a proportion of vinyl acetate at the lower end of
the range, e.g., 3-7 percent or 3-5 percent by weight. Any metal
platen or press foot maintained in contact with the insole during
the process should normally be at a temperature lower than the
softening point of the resin. Rubber vulcanizing is not generally a
suitable method because of the excessive temperature/time cycles
involved. Traditional methods such as stitching or nailing can, of
course, be employed.
The excellent flexibility of the insoles of the invention renders
them particularly useful as components of ladies' casual shoes and
children's footwear, but they can also be very well employed in,
e.g., men's shoes or boots, ladies' court shoes, ladies' fashion
boots, or sports footwear for either sex.
It is obvious that many variations can be made in the products and
processes set forth above without departing from the spirit and
scope of this invention.
* * * * *