Plastic ball

A plastic ball is disclosed, in particular a PVC air ball having a ball skin consisting of a skin base substance, in which a predetermined amount of stiffening material the hardness of which is greater than that of the skin base substance is added to the skin base substance.

BACKGROUND OF THE INVENTION 
1. Field of the Invention. The present invention relates to a plastic ball 
having a ball skin consisting of a skin base substance. 
2. Description of the prior Art. The known plastic balls have in general 
the problem that when their ball skin is cut or torn by a sharp object, 
the inner pressure and the possible exertion of load on the ball result in 
a widening of the cut so that, within a very short period of time, the 
tear widens and leads to the explosive bursting of the air ball. 
Plastic balls having a diameter within the range of 45 to 75 cm are acted 
on by the weight of a person for therapeutic and play purposes. If such a 
ball comes into contact with a sharp object, for instance if a child plays 
with the ball on a stone floor, this can lead to the skin of the ball 
being torn. Due to the inner air pressure of the ball and the additional 
load on the ball due to the weight of the body of the person, the tear or 
hole in the skin of the ball widens very rapidly, so that the air 
contained therein can escape and the ball collapses. The person sitting or 
lying on the ball thus drops suddenly onto the ground, possibly even on 
the sharp object, which may result in serious injuries. 
U.S. Pat. No. 4,169,594 discloses a ball which has two layers of different 
materials. In that case, an outer layer is formed of PVC and an inner 
layer of several different materials. The physical properties (for 
instance elasticity and hardness) of the inner layer can be controlled by 
the selection of these materials, the limit being established by the fact 
that the two layers remain attached to each other. A similar multi-layer 
ball is furthermore known from Federal Republic of Germany Utility Model 
69 18 355. 
The object of the present invention is therefore to provide a burst-proof 
plastic ball which does not suddenly collapse on itself in the event that 
the skin of the ball is torn, so that the danger of the person handling 
the ball being injured is reduced. 
SUMMARY OF THE INVENTION 
This object is achieved by a plastic ball having a ball skin consisting of 
a skin base substance in the manner that a predetermined amount of 
stiffening material the hardness of which is greater than that of the skin 
base substance is added to the skin base substance. 
The ball skin of the plastic ball of the invention, particularly a PVC air 
ball, preferably has greater resistance to tearing or continued tearing, 
especially in expanded, pumped, or inflated condition. The greater 
resistance to tearing has the result, on the one hand, that it is more 
difficult for a sharp object to tear the skin of the ball and, on the 
other hand, that a tear which has formed in the skin of the ball cannot 
suddenly widen, so that the air can escape only slowly from the air ball 
and the ball does not suddenly collapse. In the event that the tear in the 
skin of the ball caused by the sharp object is present in a region which 
is not of a greater hardness, the tear widens due to the internal air 
pressure or the load on the ball until it reaches one of the distributed 
regions of greater hardness. A greater force must then be applied in order 
to widen the tear further. This force can, in general, not be applied by 
the internal air pressure or the load on the air ball, particularly if a 
part of the air has already escaped from the ball. Accordingly, the 
tearing process comes to an end and the air can only escape slowly through 
the small crack which has thus been defined. The person using the ball 
thus has time to move away from the ball. A decrease in the danger of 
injury to the person using the ball is thus obtained in advantageous 
manner. 
Furthermore, the plastic ball of the present invention can be produced in 
advantageous manner, with little waste and thus at more favorable cost. 
The plastic ball of the invention, due to the added stiffening material, 
furthermore has the advantageous property that after the application of 
load on the ball (for instance, by the weight of a person), the ball 
temporarily has a substantially elliptical shape in cross section or a 
flattening, this being counteracted again after some time. Due to this 
substantially elliptical shape, the ball does not roll away, particularly 
upon the release of the load, but rather oscillates or swings around a 
stable position. This property is of advantage, in particular, in plastic 
balls which are used for therapeutic purposes, since the danger of injury 
in particular to the patients is thereby reduced. 
In a further preferred embodiment of the present invention, the stiffening 
material contains plastic, in particular acrylate or methacrylate, 
preferably alkyl acrylate or alkyl methacrylate, and with particular 
preference polymethyl methacrylate. In particular, the stiffening material 
advantageously contains a plastic which is compatible with the skin base 
substance. The stiffening material preferably enters into a bond with the 
skin base substance and can furthermore preferably be softened by a 
plasticizer present in the skin base substance. 
In another preferred embodiment of the present invention, the stiffening 
material is present a proportion by weight of the plastic ball total 
weight of 1 to 30%, in particular 5 to 20%, preferably 10 to 17%, and with 
particular preference about 15 % of the total weight of the ball. 
In one advantageous embodiment of the plastic ball of the invention, the 
stiffening material is in powder form and is preferably distributed 
substantially uniformly over the entire skin of the ball. Furthermore, the 
powdered stiffening material preferably has a particle size of a maximum 
dimension of 10 to 500 .mu.m, in particular 20 to 100 .mu.m, preferably 30 
to 70 .mu.m, and with particular preference 40 to 60 .mu.m. 
In another preferred embodiment, the plastic ball is an air ball of 
plasticized polyvinylchloride (PVC). 
In another advantageous embodiment of the plastic ball of the invention, 
the stiffening material contains a hard sheet, preferably of PVC. The hard 
sheet preferably has a thickness within the range of 0.1 to 1 mm, and in 
particular 0.2 to 0.5 mm, and with particular preference 0.3 to 0.4 mm. 
The hard sheet preferably contains a proportion of plasticizer of 1 to 30% 
by weight, in particular 2 to 8% by weight and preferably about 5% by 
weight. 
Furthermore, the surfaces formed by the stiffening material preferably have 
an irregular shape of dimensions within the range of 1 to 30 mm. The 
surfaces formed by the stiffening material account together for a 
percentage of 1 to 30% of the total surface of the ball. 
In another preferred embodiment of the plastic ball of the invention, the 
stiffening material contains a solid plastic.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
The ball skin 10 shown in FIG. 1 has a stiffening material in the form of a 
plurality of distributed regions 20 which have a greater hardness or 
resistance to tearing. These distributed regions or volumes 20 account for 
about 3% by weight of the total weight of the ball. The distributed 
regions 20 are of an irregular shape the maximum dimension of which is 
within the range of 1 to 20 mm, and they correspond as a whole to a 
proportion of the surface of 1 to 20% of the total surface of the ball in 
its inflated as well as non-inflated state. Furthermore, the distributed 
regions 20 can either be distributed over the entire surface of the ball 
skin 10 or only over a predetermined part of the entire surface. The large 
number of distributed regions 20 can contain or consist of pieces of hard 
sheet of PVC. These pieces of hard sheet have a thickness within the range 
of 0.1 to 1 mm, preferably 0.2 to 0.5 mm, and with particular preference 
0.3 to 0.4 mm. The hard sheet has a plasticizer percentage (of the PVC) of 
plasticizer substance (for instance dioctylphthalate (DOP), 
dinonylphthalate (DINP), dibutylphthalate (DIBP), benzylbutylphthalate 
(BBP), didodecylphthalate (DIDP), stabilizers, chlorinated polyolefins or 
nitrile rubber which lies within the range of 1 to 30%, preferably 2 to 8% 
and with particular preference about 3% of the PVC. The hard sheet can be 
of irregular shape with a dimension of 1 mm to 30 mm and can possibly 
contain a coloring component. It is produced by chopping hard sheeting 
web. 
The ball skin 10 furthermore has a greater wall thickness at the 
distributed regions or volumes 20 than at the other regions. In this way, 
also, the resistance to tearing of the ball skin 10 is advantageously 
increased in these regions. Plastic balls having a plurality of 
distributed regions 20 of greater hardness and a diameter of 45 to 75 cm 
are produced. The chopped pieces of hard sheet account for 2 to 5% or 2 to 
3% by weight of the total weight of the PVC. A preferred embodiment has a 
weight ratio of about 50-60 grams of hard-sheet pieces to 1600 grams of 
PVC, corresponding to about 3-4% by weight of the PVC. 
The embodiment of a ball skin 10 shown in FIG. 2 has a plurality of 
distributed regions 20 of greater hardness which, viewed in cross section, 
can be distributed over the entire thickness of the ball skin 10. The 
thickness of the ball skin 10 is from 0.5 to 3 mm. In particular, the 
distributed regions 20 can also constitute the entire thickness of the 
ball skin 10. The plastic ball, furthermore, has upward bulges 30, 30' and 
downward bulges 40, 40', 40" on the distributed regions 20. There is thus 
produced an undulated surface or profile by which the resistance to 
slipping is advantageously increased. 
In an embodiment not shown in the drawing, the ball can, in known manner, 
have one or more handles so that, for instance, a child can play with the 
ball by jumping around while seated on it. In the case of such a ball, the 
plurality of distributed regions 20 of greater hardness can be distributed 
in particular in the region opposite the handles, i.e. the region which 
preferably comes into contact with the ground. Thus, greater resistance to 
tearing or hardness in a lower region is obtained in order advantageously 
to assure less danger of bursting and thus of injury. The large number of 
distributed regions 20 of greater hardness can, in particular, however, 
also be distributed over the entire surface of the ball. 
The plastic ball of the invention has a ball skin 10 which is formed of a 
skin base substance to which a given amount of stiffening material is 
added. In advantageous further developments, this stiffening material is 
polymethyl methacrylate (PMMA) or polyester or ethylene vinyl acetate 
(EVA). The stiffening material, in particular PMMA, has a hardness which 
is greater than that of the skin base substance of the ball skin 10, for 
instance plasticized PVC or PVC provided with plasticizer. The ball skin 
substance 10 has, in particular, a hardness of 40 to 60 Shore. The PMMA is 
added before the gelation or hardening of the PVC mass or paste and 
distributes itself homogeneously therein. Accordingly, the PMMA is 
uniformly distributed in the ball skin 10 and results in a high, 
previously unobtained, resistance to tearing. 
In this embodiment, a tear remains limited, in particular, to the original 
tear by a sharp object and does not widen further at all. The surfaces of 
the torn ball skin 10 which border the tear have a rough surface, which 
surfaces are otherwise smooth, for instance, in the case of PVC without 
additives. This roughness results from the addition to the skin base 
substance of agents or materials for stiffening or hardening (for 
instance, PMMA) and is related to the high resistance to tearing. 
The surface of the ball skin 10 has, in the case of the addition of PMMA, 
due to the hygroscopic properties of PMMA, a large number of small bubbles 
which cause, in addition to the addition itself, a rough or dull surface 
of the ball. This roughness advantageously results in improved resistance 
to slipping and thus a more dependable handling of the ball. 
The addition of PMMA to the skin base substance, for instance plasticized 
PVC, furthermore has the result that, upon contact with the skin, the 
material has a more agreeable or warmer feel than plasticized PVC without 
addition of PMMA. 
The stiffening material enters, in particular, into a bond, for example in 
the form of coherence or adherence, with the skin base substance, this 
bond being produced, for instance, by Van-der-Walls, polarization or ionic 
forces. In particular, a gap-less bond is present between stiffening 
material and skin base substance, so that upon a tear of the ball skin, 
the stiffening material does not readily separate from the skin base 
substance. 
The stiffening material, for instance PMMA, is not "attacked" or softened 
or dissolved by plasticizers which are present in the skin base substance 
for the plasticizing or establishing of an elasticity of the skin base 
substance, so that the ball has resiliency or elasticity.