SHOE INSOLE

SEMELLE INTERIEURE D'ARTICLE CHAUSSANT

English Abstract

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ABSTRACT OF THE DISCLOSURE
A shoe insole having superior cushioning and
comfort, good resistance to buckling, and excellent
retention of cushioning properties after wear. The
insole consists of three layers:
(a) a bottom layer having compressive strength
of at least 0.3 kg/cm2 at 40% strain,
(b) an intermediate lays having less
compressive strength at 40% strain than the bottom layer,
and
(c) a top layer constructed of fabric.
The three layers are laminated together and shaped to fit
inside of an article of footwear.

Claims

The embodiments of the invention in which an exclus-
ive property or privilege is claimed are defined as
follows
1. An insole for disposition in an article of
footwear to provide cushioning and comfort to the
user consisting of:
(a) a bottom layer constructed of flexible foam
having a compressive strength of at least
0.3 kg/cm2 at 40 percent strain, a com-
pressive set of less than 20% and a sub-
stantially uniform thickness,
(b) an intermediate layer constructed of
flexible foam having a compressive strength
at 40 percent strain less than that of said
bottom layer, a compressive set of less
than 20% and a substantially uniform
thickness, and
(c) a top layer constructed of fabric, said
layers laminated together and shaped to fit
inside of an article of footwear to provide
cushioning and comfort to the user without
substantial permanent deformation of any of
said layers to the user's foot.
2. The insole of claim 1 wherein said bottom
layer has compressive strength between 0.6 and 1.2
kg/cm2 and said intermediate layer has compressive
strength between 0.2 and 0.7 kg/cm2.
3. The insole of claim 1 wherein the bottom
layer is from 1.2 to 1.8 mm thick, the intermediate
layer is from 1.2 to 1.8 mm thick and the top layer
is 0.2 to 0.4 mm thick.

4. The insole of claim 3 wherein the bottom
layer is 1.5 mm thick, has a compressive strength at
40% strain of 0.8 kg/cm2 and a compression set of
less than 10%; the intermediate layer is 1.5 mm
thick, has a compressive strength at 40% strain of
0.5 kg/cm2 and a compression set of less than 10%;
and the top layer is 0.3 mm thick.
5. The insole of claim 4 wherein the bottom
and intermediate layers are each made of sulfur-
vulcanized styrene-butadiene open cell foam and the
top layer is made of cotton-acetate cloth.

Description

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SHOE INSOLE
The present invention relates to a shoe insole
that may be inserted into an article of footwear. The
inventive insole provides superior cushioning and comfort
and has good resistance to buckling and excellent
retention of its cushioning properties after wear. The
inventive insole is surprisingly simple to manufacture.
Hying (US. Patent No. 4,055,699) discloses a
four-layer insole that is intended primarily to provide
insulation to the bottom of the foot. ~Isuing's insole is
more difficult to make than that of the present
invention.
Scholl (US. Patent No. 3,253,061) discloses a
single layer insole. While relatively simple to make,
Scholl's insole lacks the comfort and cushioning of the
present invention.
SUMMARY OF THE INVENTION
The present invention comprises an insole for
disposition in a article of footwear consisting of:
(a) a bottom layer constructed ox flexible
foam having a compressive strength of at least 0.3 kg/cm2
at 40 percent strain,

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(b) an intermediate layer constructed of
flexible foam having a compressive strength at 40 percent
strain, less than that of said bottom layer, and
(c) a top layer constructed of fabric,
said layers laminated together and shaped to
fit inside of an article of footwear.
BRIEF DESCRIPTION OF THE DRAWINGS
inure 1 is a top view of an insole in accord
dance with the invention.
Figure 2 is a sectional view of the insole of
figure 1 taken along section 2-2.
DETAILED DESCRIPTION OF THE INVENTION
As illustrated in figure 1, the insole 10 of
the invention may have the general outline of a human
foot. The insole has three layers that are laminated
together.
Bottom layer 11 is constructed of flexible foam
having a compressive strength of at least 0.3 kg/cm2 at
40 percent strain. That is, a compressive force of at
least 0.3 kg/cm2 is required to reduce the thickness of
the layer by 40 percent of its unstressed thickness.
Preferably layer 11 has compressive strength at 40
percent strain between 0.3 and 1.3 kg/cm2, more prefer-
ably 0.6 to 1.2 kg/cm2. Layer 11 is preferably from 1.2
to 1.8 mm thick. Preferably layer 11 has less than 50
percent (more preferably less than 20 percent) compress
soon set.
Compression set is determined as followed. The
initial thickness of the foam is measured without any
stress applied. Then a compressive force sufficient to
reduce the thickness of the foam by 50 percent it
,.

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applied. With this force applied, the material is
maintained in an oven at 70C for 23 hours. The material
it removed from the oven and the force is released. The
thickness of the unstressed material is then measured and
subtracted from the initial thickness. This gives the
loss in thickness, or set. The compression set is 100
multiplied by the ratio of the loss in thickness to the
initial thickness.
Intermediate layer 12 is constructed of
flexible foam having a compressive strength less than
that of the bottom layer at 40 percent strain.
Preferably intermediate layer 12 has compressive strength
at 40 percent strain in the range of 0.2 to 1.1 kg/cm2,
more preferably 0.2 to 0.7 kg/cm2. Layer 12 is
preferably from 1.2 to 1.8 mm thick. Layer 12 preferably
has compressive set less than 50 percent (more preferably
less than 20 percent).
Layers 11 and 12 may be made of flexible foamed
materials such as rubber latex, urethane, polyvinyl
chloride, styrene-butadiene latex, polyolefin, or any
other flexible foamed material having the required
compressive strengths. The preferred material is sulfur-
vulcanized, styrene-butadlene latex, open-celled foam
containing 2 to 80 weight percent filler and pigment,
more preferably 40 to 60 percent. The foam may also
contain fragrance and odor controlling ingredients.
Top layer 14 is fabric such as a twill weave of
cotton and acetate. Other woven and non woven fabrics
such as cotton, polyester, nylon, and various fiber
blends may be used. Top layer 14 may have thickness of
0.2 to 0.4 mm.
Layers 11, 12, and 14 are laminated together
and shaped to fit inside of an article of footwear, such
as a shoe or boot. The preferred shape for an insole for
the right foot is shown in figure 1. An insole for the

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left foot would lo a mirror image of the insole of figure
1.
The insole may have perforations 15, i.e. small
vertical holes. These holes are about 1 mm in diameter
spaced about 6 mm apart. The holes preferable pass
through all three layers. It is preferable to perforate
the entire insole. For simplicity only a small portion
of the insole is shown perforated in Figure 1. Menu-
lecture of the invention insoles may be performed by
foaming and laminating techniques known in the art, see
example, So Patent Nos. 4,257,176 and 4,185,402,
incorporated herein by reference. The desired
compressive properties may be attained by varying various
manufacturing properties such as density, amount of
filler etc.
EXAMPLE OF THE PRESENT INVENTION
An insole is accordance with figure 1 is
constructed as follows:
Tom Layer 11
Thickness: 1.5 mm
Density: 15 loft (0.24 my
Compressive strength
at 40~ strain: 0.8 kg/cm2
Material: sulfur-vulcanized,
styrene-butadiene,
open-cell foam
Compression set: Less than 10
percent

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Intermediate Layer 12
Thickness: 1.5 mm
Density: 12 lb/ft3 (0.19 g/cm3)
Compressive strength
at 408 strain: 0.5 kg/cm2
Material: sulfur-vulcanized,
styrene-butadiene,
opan-cell foam
Compression set: Issue than 10
percent
Top Layer 14
Thickness: 0.3 mm
Material: cotton-acetate
cloth
Comparative Prior-Art Example
A two-layer insole that has been sold in the
United States for a number of years has the following
properties.
Thickness: 3 mm
Density: 12 lb/ft3 (0.19 ~/cm3)
Compressive strength
at 40~ strain: 0.5 kg/cm2
Material: styrene-butadiene,
open-cell foam
Compression set: Less than 10
percent
Top Layer
Thickness: 0.3 mm
Material: cotton-acetate
cloth
The cushioning capacities of the two insoles were

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compared by measuring the thickness of the insole as it
was loaded with increasing weight from O to 2.5 kg/cm2,
the approximate force of a men standing on one heel. A
plot of the applied force versus thickness was drawn for
each insole. The area under the curve is a measure of
the cushioning capacity. The three-layer insole of the
invention provided 15 percent better cushioning than the
prior art two-layer insole. Upon wear the insoles of the
above examples lose some cushioning properties; but the
insole of the invention retains cushioning better than
that of prior art. At the end of a 15 day wear test the
insole of the invention provided 42 percent more
cushioning than the prior art two-layer insole. Further-
more, the insole of the present invention feels soft and
comfortable against the foot, despite its greater
cushioning ability.