Sports boot

The sports boot has a plastic shell (1) and an inner boot (8), the shell having at least one zone (12) which is less rigid than the less of the shell. The less rigid zone is a relatively flexible zone located on the side of the shell corresponding to the outside and/or inside of the foot, so as to face the metatarsophalangeal joint of the foot.

FIELD OF THE INVENTION 
The present invention relates to a sports boot, in particular a boot for 
gliding sports such as ski or skate boot, having a plastic shell and an 
inner boot, said shell having at least one zone which is less rigid than 
the rest of the shell. 
PRIOR ART 
Ever since plastic ski boots, comprising a relatively rigid shell which 
provides good support for the foot, appeared on the market it has been 
common for skiers with wide feet to experience pain at the 
metatarsophalangeal joint, on the outside of the foot, this pain being due 
to compression of this zone by the shell of the boot. In order to 
alleviate this pain, special equipment has been developed to expand the 
shell by deformation in the sensitive zone. Yet to this day, in spite of 
the perfection of dual injection and the developments made by specialist 
manufacturers, no practical solution has been found for this problem. 
It is admittedly true that Patent FR 2 077 184 proposed, for the first 
time, the manufacture, by dual injection, of a ski boot shell which has 
different degrees of flexibility in various regions of the upper, but the 
abovementioned problem has not been solved specifically and 
satisfactorily. This shell has a relatively flexible main part on which 
extra thicknesses of more rigid material are formed and relatively hard 
engagement zones are provided facing the metatarsophalangeal joint. 
The technique of dual injection, that is to say successive injections into 
the same mold, is also used to manufacture the boot described in Patent FR 
2 671 947. 
Lastly, U.S. Pat. No. 5,888,228 and International Model DM/037 399 describe 
a ski boot shell having zones with different rigidity, the most rigid 
parts forming a kind of triangulated rigid frame whose purpose is to 
optimize the transmission of forces between the leg and the binding. This 
frame extends into the metatarsophalangeal region. 
SUMMARY OF THE INVENTION 
The object of the present invention is to provide a simple solution to the 
problem of pain being experienced at the metatarsophalangeal joint. In 
fact, if the population of individuals who have a given shoe size is 
considered, the width of the metatarsophalangeal joint will vary, as will 
its position relative to the heel. 
The boot according to the invention is one wherein the less rigid zone is a 
relatively flexible zone on the side of the shell corresponding to the 
outside and/or inside of the foot, so as to face the metatarsophalangeal 
joint. 
This zone may be small, but it must be flexible enough to deform readily 
sideways under the force exerted by the metatarsophalangeal joint, but 
without exerting painful pressure on this zone. 
This less rigid zone is preferably obtained by injecting a flexible plastic 
into said zone, using a dual injection process. 
The shell may, of course, have some other zones with lower rigidity.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The ski boot represented in FIG. 1 consists of a shell 1, referred to as a 
variable-volume shell and intended to surround the foot and the ankle, and 
a cuff 2 which is articulated to the shell 1 at a point 3 located in the 
malleolar region, this cuff 2 being intended to surround the lower leg. 
According to a well-known design, this boot is provided with two 
tightening buckles 4 and 5 for tightening the shell 1, and two buckles 6 
and 7 for tightening the cuff 2. A comfort inner boot 8 is also shown. 
As can be seen in FIG. 2, the shell 1 is made of two layers of plastic 1a 
and 1b which are combined by a dual injection or multi-injection process, 
or alternatively by adhesive bonding or another equivalent process. The 
plastics used are preferably polyurethane. The layer 1a, located on the 
inside the shell, is made of a plastic whose elasticity is substantially 
greater than the elasticity of the outer part 1b, which includes the sole 
9 and the upper flap 10 of the shell which is made exclusively of the 
harder plastic. 
On the outside of the boot, the outer part 1b of the shell has a cutout 11 
which is positioned so as to surround a zone of the shell located facing 
the metatarsophalangeal joint of the foot. This cutout 11 delimits a zone 
12 in which only the less rigid plastic 1a is found. The flexibility of 
the plastic 1a is such that the zone 12 can deform slightly under the 
pressure of the metatarsophalangeal joint of the foot, so as to 
substantially reduce the pressure on this joint, and consequently prevent 
the onset of pain at this location. 
The plastic of the layer 1b has a hardness of between 58 and 60 shD, for 
example 62 shD, while the layer 1a has a hardness of between 45 shD and 55 
shD, for example 54 shD. 
The extent of the zone 12 may vary to some degree, but this extent should 
not be too great so as not to compromise the overall rigidity of the front 
end of the shell. 
Although the shell has been represented only with the cutout 11, it could 
have other zones of the same type with a view to lightening the shell as 
envisaged in the prior art. 
In a second embodiment of the invention, the shell 1 is made of a single 
layer of plastic, and has a cutout 11 similar to that in the first 
embodiment described above. This cutout delimits a zone in which a plastic 
element 13 is found which is less rigid than the rest of the shell, said 
element 13 being fixed to the comfort inner boot 8 itself, rather than to 
the shell 1, as in the first embodiment. The flexibility of this less 
rigid plastic element 13 also allows a slight deformation under the 
pressure of the metatarsophalangeal joint. Further, leaktightness of the 
shell 1 is ensured when tightening the boot on the foot. 
Various types of stacks of flexible and rigid materials may be envisaged, 
and in particular the flexible material could be provided only in the zone 
12. For example, the flexible material could lie in continuation of the 
rigid material, or even outside it. 
Other materials, for example textile materials or elastomers, could also be 
provided in the zone 12. 
In addition, the less rigid plastic element 13 may surround the inner boot 
8 at least partially. 
The embodiments described were presented by way of example, and the 
application of the invention is not limited to ski boots: the principle of 
the invention may equally well be applied to other boots, for example 
skate boots, which have a relatively rigid shell that creates problems 
similar to those encountered with ski boots.