Stabilized honeycomb shoe sole, particularly for athletic shoes

In a shoe sole, in particular for athletic shoes, that is assembled at least from an outsole and a cushioning midsole, where the midsole has recesses extending essentially perpendicular to the plane of the sole, to improve the comfort of such a shoe and to increase the dimensional stability of the sole parts, the midsole is formed of a first midsole element (1a) consisting of a compact thermoplastic material and a second midsole element (2a) consisting of a foamed plastic material. Recesses (3) are distributed at least predominantly over the entire first midsole element (1a) made of compact thermoplastic material and are closed on a side facing away from the second midsole element (2a). Additionally, the second midsole element (2a) is injected onto the first midsole element (1a) closing open ends of the recesses and optionally, partially penetrating the recesses and/or encapsulating stabilizing inserts disposed in the arch area of the first midsole element.

BACKGROUND OF THE INVENTION 
The present invention relates to a shoe sole, in particular for athletic 
shoes, that has an outsole and a cushioning midsole, and parts of the 
midsole comprise recesses or cells that extend essentially perpendicular 
to the plane of the sole. 
Such a shoe sole is known from German Utility Model 89 01 235 and its 
corresponding U.S. Pat. No. 5,084,987. In this known shoe sole, honeycomb 
cells or recesses, that extend perpendicular to the plane of the sole, are 
placed only in the central area under the heel bone or heel bone and ball 
of the foot to achieve there, on the one hand, good damping, but on the 
other hand, also to achieve high resiliency, and the entire midsole 
consists of foamed plastic. Similarly, U.S. Pat. No. 4,245,406 shows an 
athletic shoe in which the entire midsole is formed of a foamed plastic 
material, and a honeycomb-like structure of hollow regions and ridges is 
created in the region extending rearwardly of the metatarsal area. 
Furthermore, from U.S. Pat. No. 4,449,307 and U.K. Patent 510,426, outsoles 
are known which are formed of a compact, i.e., unfoamed, plastic or rubber 
material in which arrangements of ridges and recesses are formed at the 
upper surface thereof to increase the flexibility of the outsole. In shoes 
with these soles, the insole or footbed sits directly on the outsole 
without any cushioning midsole being provided. Likewise, in German Utility 
Model No. 87 14 058, a sole is formed of a compact, i.e., unfoamed, gum 
rubber material in which arrangements of lamellae-like ridges form air 
chambers that are open toward the tread surface of the sole but are closed 
by the tread layer that is applied to the bottom of the sole. The top of 
the sole is closed and in one embodiment, a footbed of a foamed material 
is applied thereon which has channels which enable the air chambers to 
"breath" through the footbed. 
SUMMARY OF THE INVENTION 
The object of the present invention is further to improve the comfort of an 
athletic shoe with a shoe sole of the above-mentioned type by extending 
the ability to obtain the good damping with simultaneous high resilience 
achievable in the initially mentioned known shoe sole, preferably only 
under the heel bone, to other areas of the shoe. 
Further, another object is to improve the dimensional stability of the sole 
parts to be able to maintain tighter tolerances in production without 
increased expense. 
These objects are achieved, according to preferred embodiments of the 
invention, in that the midsole is formed of a first midsole element 
consisting of a compact thermoplastic material and of a second midsole 
element consisting of a foamed plastic. A honeycomb-like array of cells or 
recesses are distributed at least predominantly over the entire first 
midsole element and these recesses are closed on a side facing away from 
the second midsole element, which is injected onto the first midsole 
element. 
These objects are further achieved by a preferred process in which the 
midsole, having the first midsole element formed of a compact 
thermoplastic material and the second midsole formed of the foamed plastic 
material, is produced in the following process steps: 
the first midsole element is injection molded with recesses extending 
essentially over the whole area thereof which are closed on one side; 
the finished first midsole element is inserted into a mold with a large 
mold cavity, with the sole side on which the recesses are closed lying on 
top, and liquid plastic is injected into the space remaining in the mold 
and foamed to form the second midsole element. 
To achieve good adhesion between the first and the second midsole element, 
according to a further development of the invention, the foamed plastic of 
the second midsole element extends partially into the recesses of the 
first midsole element, preferably about 1 mm to 3 mm, by a suitable dosing 
of the plastic injected into the mold. 
As a material for the first midsole element, a polyamide or polyurethane 
with a specific weight of 0.9 g/cm.sup.3 to 1.1 g/cm.sup.3 is provided, 
but for the second midsole element, foamed polyurethane with a specific 
weight of 0.3 g/cm.sup.3 to 0.8 g/cm.sup.3 is utilized. 
The cells or recesses of the honeycomb structure formed in the first 
midsole part can be of a variety of different cross-sectional shapes; for 
example, circular, elliptical, triangular, rectangular, hexagonal or cross 
sections shaped like other geometric figures may be used. The recesses 
should have smaller cross sections and/or thicker walls in areas which 
experience higher loads than in areas which are subjected to lower loads. 
To stabilize the midsole in the joint (arch) area, in the first midsole 
element, there are provided two or more rod-shaped or tubular stabilizers 
consisting of hard, preferably springy, plastic. These stabilizers are 
inserted into the first midsole element before injection of the second 
midsole element onto the first midsole element, preferably in the area of 
the ankle, near the lateral and medial sides and essentially parallel to 
them. When the second midsole element is injected, these stabilizers are 
encapsulated by the foamed plastic material. 
According to a first embodiment, the first midsole element is placed 
beneath the second midsole element and is produced integrally together 
with the outsole. The outsole consists of wear-resistant plastic or rubber 
in areas that are subjected to high loads in use, but in areas that 
experience lower loads, the outsole is left open. 
According to a second embodiment, the first midsole element is placed above 
the second midsole element, and the first midsole element does not extend 
over the entire surface of the second midsole element, but leaves open, in 
the toe area, a section encompassing an area that is at least about 1 cm 
to 2 cm wide and that is filled by foamed plastic of the second midsole 
element. On the other hand, the second midsole element does not extend 
over the entire surface of the first midsole element, but leaves open, in 
the heel area, a section of about 3 cm to 5 cm that is filled out, between 
the first midsole element and the outsole, with a compact plastic that may 
be the same as the material of the first midsole element or rubber. 
The advantages achieved with the invention are especially related to the 
fact that, with the air chambers formed in the first midsole element, the 
damping and the resilience in various areas of the sole can be selected 
individually. This is achieved, in particular, by using a plastic with a 
varying amount of foaming agent in various areas of the second midsole 
element. 
Further, the compact, i.e., unfoamed, thermoplastic material used for the 
first midsole element makes possible a greater dimensional stability of 
the midsole. Thus, the finished sole has a greater dimensional stability, 
overall. The dimensional stability becomes greater the larger the amount 
of compact plastic as compared to the foamed plastic, because a compact 
plastic part can be poured or injected much more exactly than a foamed 
plastic part. 
In particular, the hardness of the second midsole element consisting of 
foamed plastic varies quite considerably with its thickness. In sole areas 
with thicker walls of the foamed second midsole element, a higher degree 
of foaming is achieved, and thus a lower Shore hardness, than in sole 
areas in which the wall thickness of the foamed second midsole element is 
less. The less the wall thickness of an element consisting of foamed 
plastic, the higher also is the material density. Consequently, it is 
extremely difficult to inject foamed midsole elements or parts of them 
with close tolerances. Therefore, the lower the amount of the foamed 
second midsole element as compared to the entire midsole, the more the 
dimensional stability of the midsole according to the invention can be 
increased and the lower the expense will be. 
Finally, because of the fact that the second midsole element contributes 
considerably to the pressure distribution between the recesses of the 
first midsole element and the foot of the wearer, another advantage is 
achieved in that biomechanical functions can be supported by adjusting, in 
any way, the thicknesses of the second midsole element in various areas. 
The higher weight caused, basically, by the compact plastic used for the 
first midsole element is compensated for, very largely, by the recesses 
that are, preferably, distributed over the entire first midsole element. 
The embodiment according to the second alternative, in which the first 
midsole element is placed above the second midsole element and the first 
midsole element does not extend over the entire surface of the second 
midsole element, but leaves a section open in the toe area that is filled 
by foamed plastic of the second midsole element has, in particular, the 
advantage that, for the first midsole element, a single mold suffices for 
several main and intermediate sizes of the shoe to be produced. That is, 
depending on the shoe size, the toe area with foamed plastic of the second 
midsole element can be made larger or smaller. This means that, with the 
injection mold for shoe size 8, for example, midsoles for shoe sizes 81/2, 
9 and 91/2 can also be produced. The size difference is compensated for by 
modifying the mold for the lower second midsole element to be produced of 
foamed plastic. The costs for the molds are thus reduced overall. 
By the additional measure according to which the second midsole element 
does not extend over the entire surface of the first midsole element but 
leaves open a section in the heel area that is filled with compact plastic 
of the first midsole element or with elasticity-increasing rubber up to 
the outsole, the advantage is achieved that the amount of foamed plastic, 
which is more susceptible to bacteria, of the second midsole element is 
not increased, or at least not considerably increased, despite the 
extension at the tip of the foot, inasmuch as compensation is made at the 
heel. Further, the precision of the fit of the entire sole is increased, 
since the lower surface of the first midsole element made of compact 
plastic, which extends in the heel area to the outsole or to the inserted 
rubber layer, reduces the lower surface of the second, foamed midsole 
element. 
With respect to the production process, the advantages achieved include, in 
particular, the fact that the desired air chambers are produced in a 
simple way. 
These and other objects, features and advantages of the present invention 
will become apparent from the following detailed description of preferred 
embodiments of the invention when viewed in conjunction with the 
accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In the top view of FIG. 1, a top side of a first midsole element, 1a (FIG. 
2), 1b (FIG. 3) is shown. This first midsole element is formed of a 
compact, i.e., unfoamed, thermoplastic material, with a honeycomb-like 
array of cells or recesses 3 being distributed over essentially the entire 
sole area (these cells or recesses are only partially shown for 
illustrative simplicity). Furthermore, rod-shaped or tubular stabilizers 
7, that are made of a hard, preferably springy plastic, are placed under 
the area of the ankle and are inserted in grooves that are left open 
during production of first midsole element 1a, 1b. Basically, more than 
the two stabilizers 7 shown diagrammatically can be provided, and 
optionally, other stabilizers are placed closely adjacent to 
diagrammatically shown stabilizers 7, running essentially parallel to 
them. Stabilizers 7 increase the torsion resistance of midsole 1a, 2a 
(FIG. 2), 1b, 2b (FIG. 3). As a material for stabilizers 7, compact 
polyurethane, polyamide, or polyethylene is suitable. 
The cells or recesses 3 of the honeycomb structure formed in the first 
midsole element 1 can be a variety of different cross-sectional shapes; 
for example, in addition to circular recesses 3, elliptical, triangular, 
rectangular, hexagonanl (3a, 3b, 3c, and 3d, respectively in FIGS. 1A to 
1D) or cross sections shaped like other geometric figures may be used. The 
recesses should have smaller cross sections and/or thicker walls in areas 
which experience higher loads than in which are subjected to lower loads, 
and by way of example, FIG. 2A shows a portion of a first midsole element 
1 having walls 10 of differing thickness and recesses 3 of different cross 
section. 
The sectional view of FIG. 2, taken along line II--II of FIG. 1, shows 
first midsole element 1a with recesses 3, as well as a second midsole 
element 2a injected on the top side of the first midsole element and 
consisting of a foamed plastic material. Additionally, an outsole 4 is 
shown that has been injected onto the lower side of the first midsole 
element 1a in highly loaded areas 5. Outsole 4 is made of a wear-resistant 
plastic or rubber, which is left open in areas 6 which experience lower 
loads in use. This outsole 4 is simultaneously used as a closure for the 
lower end of recesses 3 while, in the areas that are not covered by the 
outsole, recesses 3 are, preferably, closed by partitions 8 that are 
inserted within them. 
With reference to FIG. 3, a section of another embodiment is shown. In this 
embodiment, a first midsole element 1b with recesses 3 has a second 
midsole element 2b that has been injected onto the underside of midsole 
element 1b. Midsole element 2b is a layer of foamed plastic, and an 
outsole 4 made of wear-resistant plastic is injected onto the lower side 
of the midsole element 2b. Additionally, second midsole element 2b does 
not extend rearwardly across the full heel area, and an 
elasticity-increasing rubber layer 11 is inserted in the heel area between 
the first midsole element 1b and the outsole 4. 
As can clearly be seen in FIGS. 2 and 3, some foamed plastic 9 penetrates 
into recesses 3 during injection of second midsole element 2a, 2b. The 
diagrammatic representation makes clear that, because of the varying 
volumes of recesses 3 along the extent of first midsole element 1a, 1b, 
the air remaining within the recesses 3 is more or less compressed 
depending on the degree of penetration of the foam and the volume of the 
recesses. As a result, by selecting the length of walls 10 that define the 
recesses 3, the damping and the resilience of midsole 1a, 2a; 1b, 2b, in 
different areas of the sole can be selected individually, without having 
to work with varying amounts of foaming agent in forming the second 
midsole element 2a, 2b. 
Also, when recesses 3 extend, in particular for weight reasons, preferably 
over the entire area of first midsole element 1a, 1b, a modified 
embodiment can also be advantageous in which, in any case, the perimetric 
edge areas of first midsole element 1a, 1b are not provided with recesses 
3. In the joint (arch) area, the inside (medial) or outside (lateral) edge 
areas without recesses 3 could be kept, basically, wider than in the other 
sole areas, to optionally enable stabilizers 7 to be dispensed with. That 
is, the wider, solid border portions of the compact plastic material of 
the first midsole layer can function, themselves, as stabilizers. 
Outsole 4 is provided, depending on the specific use of the shoe, in 
particular for an athletic shoe, with the usual cleats, ridges, bumps or 
other gripping elements which increase surefootedness. Diagrammatic 
representation of these gripping elements, which are known in the art, has 
been dispensed with for the sake of clarity of the representation. 
The areas of first midsole element 1a, according to FIG. 2, that are not 
covered by outsole 4 can be provided with convex, i.e., inward-pointed, 
arches, to further reduce the sole weight. Partitions 8, provided in 
recesses 3, constitute a blocking layer against penetration of foreign 
matter into midsole 1a, 2a and are, preferably, set back about 1 mm to 2 
mm relative to the side of first midsole element la that adjoins the 
outsole 5.