CONTENANT ANTI-BOMBAGE

ANTI-BULGING CONTAINER

Abrégé français

Cette invention concerne un récipient anti-bombement (1) comprenant une paroi latérale (2) et un fond (3). La section du fond (3) prise dans un plan passant par l'axe de symétrie verticale (A) du récipient présente une concavité raccordéeà la paroi latérale (2) et suivie d'au moins deux gradins (6, 6') et d'un dôme. Chaque gradin (6, 6') comporte une partie rectiligne (5, 5') formant un angle (2', 2) avec un plan perpendiculaire à l'axe de de symétrie verticale du récipient, suivie d'une courbe concavité à courbure prononcée vers le bas. Le dôme (8) présente une faible concavité.

Abrégé anglais

The present invention is an anti-bulging container (1) comprising a side wall (2) and a base (3). In a cross section in a
plane comprising the container's central vertical axis (A), the base (3) comprises a concave outwards curved section (4) connected
to a side wall (2) followed by at least two stairs (6, 6') and a dome (8). Each stair (6, 6') consists of a straight part (5', 5) forming
an angle (2', 2) with a plane perpendicular to the container's central vertical axis, followed by a sharp concave outward curve. The
dome (8) consists of a smooth concave outward curve.

Revendications

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A container (1) of thermoplastic material comprising a side wall (2) and
a base (3), said base comprising in a cross section in a plane
comprising the container's vertical axis (A), a concave inwards curved
section (4) connected to the side wall (2), at least two successive
stairs, each stair consisting of a first and second straight part (5,5') formingan angle (.alpha.1, .alpha.2) with a plane (B) perpendicular to said axis (A), followed
by a first and second sharp concave outwards curve (6,6'), and a dome (8)
consisting of a smooth concave outwards curve, said base (3) being
symmetrical about said axis (A).
2. A container according to claim 1 which has a larger dimension in a
cross section in a plane perpendicular to the container's central vertical
axis of less then about 10cm.

3. A container according to claim 1 which has a circular cross section in a
plane perpendicular to the container's central vertical axis.

4. A container according to claim 1 comprising only two stairs.

5. A container according to claim 1 where .alpha.1 is equal to .alpha.2.

6. A container according to claim 1 wherein the first straight part (5) which isclosest to the periphery of the container is longer than the second straight
part (5') which is closest to the center of the container.
7. A container according to claim 1 where the radius of the first sharp concave
outwards curve (6) which is closest to the periphery of the container is larger
than the radius of the second sharp concave outwards curve (6') which is
closest to the center of the container.

Description

-~093/Z4377 ~371~ PCT/U5~3/04580




ANTI BULGING CONTAINER




Field o~ the invention : .

The present invention relates to a:container of thermoplastic
material for containing li~uids. The container is designed
so as to resist bulging. ~ .
:

Back~round of the invention ..

~t is well known in the art to use thermoplastic materials to
manufacture containers:for liquids. Some of the liquids to
be contalned by such containers, for instance bleach-
;containing compositions, create internal pressure which
builds up with time. In such cases, the containers are
progressively subjected to deformation due to the internal
pressure build-up, especially at their base. This phenomenon
is o~ten referred to as "bul~ing". This phenomenon is -' -
especially acute in warm countries where the containers may
be exposed to particularly elevated temperatur~s. In some
instances, bulging can be so severe so as to induce a base
deformation which is such that the container can no longer



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stay in upright position. For instance in supermarkets, the
containers may fall of the shelves.
:
Anti-bulging containers have been disclosed in the art, for
instance in DE 16 07 895, DE 21 11 534, EP 0 002 082 and our
co-pending European Application EP 91202524. These
references disclose containers having a central dome, where
the dome is connected to the side walls of the container by
pieces of thermoplastic material of various shapes.
It is therefore an obiect of the present invention to provide
a container of thermoplastic material for containing liquids
with improved resistance to bu~ging.

It is also an object of the present invention to provide a
solution to bulging which is particularly applicable to
containers of smaller size.

The problem of bulging can to some extent be addressed by
increasing the quantity of thermoplastic material used, so as
to manufacture a container with thick walls. However, this
solutiorl is quite objectionable from an environmental point
of view as well as from an ea5e of manufacturing viewpoint.
It is therefore an another object of the present invention ~to
provide a~ anti-bulging container of thermoplastic material
having walls of minimum thickness.


Summarv of the invention

The present invention is a container (1) of thermoplastic
material comprising a side wall ~2) and a base ~3), said base
comprising, in a cross section in a plane comprising the
container's vertical aXis ~A), a concave inwards curved
section (4) connected to the side wall (2), at least two
successive stairs, each stair consisting of a straight part


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(5,5l) forming an angle (~l,a2) with a plane (B)
perpendicular to said axis (A), followed by a sharp concav~e
outwards curve (6,6'~, and a dome (8) consisting of a smooth
concave outwards curve. The base (3) of the container (1) is
symmetrical about said axis (A).

,

Detailed description of the invention

The container according to the invention is made af a
thermoplastic material. Such materials have been extensively
described in the art and include vinyl chloride based resins,
polymers and copolymers derived from olefins, acrylic
polymers and copoly~ers, polyethylene, polypropylene, -.
polystyrene, polyethylene terephthalate, polyethylene
~erephthalate glycol, or mixtures thereof. The container can :-
be made by single or multi layer extrusion of such materials.
It can also be made out of recycled thermoplastic materials. ;~
A preferred thermoplastic material for use herein is
polyethylene. ~ .

The cross section of the container according to the present
invention, and/or its base, in a plane perpendicular to the -.-
con~ainer's vertical axis (A~, can be square or rectangular,
ovoid or circular. Furthermore, the base (3) of the.
container according to the present invention is symmetrical
about said axis (Aj. In a preferred embodiment of the J, '
invention, said cross section is circular. . The present
invention is particularly suitable for containers of rather
small size, i.e. where the container's largest dimension in
said cross sectio~ is less than lOcm. - -

The following description refers to fig 1 which represents
the lower part of the container in a cross section in a plane
comprising the container's central vertical axis (A). Fig 2


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represents a scale up of the lower part of the container, on
one side of (A).

The container (l) according to the present invention
comprises a side wall (2) and a base (3~. The base (3) which
is the gist of the present invention is connected to the s~de
wall (2). The base (3) comprises a curved section (4),
~ollowed by at least two stairs (5/6,5'/6') and a dome (8).

The curved section (4) is connected at one extremity to the
side wall(2)j and at the other extremity to at least two
successive stairs. The curve of said curved section (4) is
concave inwards, i.e. the interior of said curve faces the
inside of the container.

Each stair comprises a straiyht part (5,5') followed by a
sharp curve (6,6'). The straight parts (5,5') can be of same
dimensions, but in a preferred embodiment, the straight part
which is the closest to the periphery of the container is
longer than straight part which is~closest to the center of
thP container. Each straight part (5,5') forms an angle
(al,~2) with a plane (B) perpendicular to the container's
vertical.central axis (A). According to the present
inverltion, al and a2 can be different, but in a preferred
~mbodiment of the invention ~1 and ~2 are the same. Each
straight part (5,5') is connected to a sharp cuxve (6,6').
By sharp curv~, it is meant herein a curve who's radius is
smaller than the radius of the curved section (4). said
sharp curves (6,6') are concavP outwards, i.e. the interior
of each sharp curve (6,6') faces the outside of the
container. The radius of the sharp curves ~6,6') can be -:
identical, bu~ in a preferred embodiment, the radius of the
sharp curve which is closest to the periphery of the
container is larger than the radiu~ of the sharp curve which
is closes~ to the ~enter of the container. In a preferred



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embodiment of the present invention, the base (3) only
comprise two stairs.

The sharp curve of the stair which is closest to the center
of the container is connected to a dome (8). The dome (8)
~onsists of a smooth curve. Said smooth curve is concave ~
outwards, i~e. the interior of said curve faces the outside ~.
of the container. By smooth curve, it is meant herein a
curve who's radius is larger than the radius of both curved
sections (6,6'). .
:
The present invention ls further illustrated by the following
example.


ExamPle
::
cy~indrical container according to the present invention is.-
madP out of polyethylene. It has a diameter of 90mm. The .:
radius of the curved section (4j is 5.5mm. The length of the; -
straight part ~5) measured along plane (B) is 11.5 mm. The -~
radius of the sharp curve (6~ is 3~m. The length of the --
straight part (5'~ measured along pla-ne (B) is 4.65mm. The
radius of the sharp curve (6') is 2mm. Finally, the radius
of the dome is 9Omm. The thickness of the thermoplastic
material used for this embodiment is 1.5mm throughout the
container.




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