Container having a bottom with a corrugated internal seat portion

Container (1) of plastic material, comprising a body (5) and a bottom (6), the bottom (6) having an annular outer seat (8) defining a principal seating plane (9) for the container (1), and a deformable membrane (10) that extends radially inside the annular outer seat (8) and is arranged to be able to adopt two configurations:

The invention relates to the manufacture of containers, such as bottles or jars, obtained by blowing or stretch-blowing preforms made of thermoplastic material.

Conventional stretch-blowing induces a bi-orientation of the material (axial and radial) that gives good structural rigidity to the final container. However, the bi-orientation induces in the material residual stresses that, during hot filling (particularly with a liquid having a temperature above the glass transition temperature of the material), are released, causing a deformation of the container that could make it unfit for sale.

In order to minimize the deformations of the container during the retraction of the liquid accompanying its cooling after hot filling, it is known either to provide the body of the container with deformable panels that, during the cooling of the liquid, flex under the effect of the retraction, or to convey to the bottom the ability of the container to be deformed (or to be forcibly deformed).

The U.S. Pat. No. 7,451,886 (AMCOR) and international application WO 2009/050346 (SIDEL) both illustrate the technique of the deformable bottom: under the effect of the low pressure accompanying the retraction of the liquid, the bottom rises up towards the interior of the container.

The deformable bottom technique has, compared to the deformable panels technique, the advantage of minimizing the deformations of the body, particularly to the benefit of the aesthetic aspect of the container.

However, when the low pressure is too strong (for example when the fill temperature is high), the deformations of the bottom are insufficient to compensate for the variation in volume of the container, and the body is frequently undesirably (and uncontrollably) deformed as a result.

In order to increase the displacement of the bottom, it is known (see document WO 2006/068511, CO2PAC) to design the bottom so that it can adopt two positions separated from each other, to wit, a deployed position in which the bottom extends protruding to the exterior of the container, and a retracted position in which the bottom extends towards the interior of the container. The deployed position is adopted by the bottom before the container is filled, while the retracted position is adopted after the filling, in order to accompany the retraction of the liquid due to its cooling.

However, this technique assumes the return of the bottom from its deployed position to its retracted position. In order for this return to occur spontaneously, it is understandable that the low pressure in the container must be strong. Otherwise, the return does not occur, resulting in deformations on the body.

In order to avoid this situation, the document CO2PAC provides for forcing the changeover of the bottom from its deployed position to its retracted position by means of a tool by which pressure is applied on the bottom towards the interior of the container (seeFIGS. 12ato12d). This solution therefore assumes that such a tool be inserted in the manufacturing chain, at the expense of simplicity and rate of production.

Moreover, a container whose bottom comprises an annular structure provided with sequential formations (called teeth) is known from the document WO 2010/078341. This annular structure is supposed to form an articulation and uniformly distribute the stresses resulting from a cooling vacuum. However, in this design, the formation of the teeth (diamond-shaped) poses problems of blowability of the bottom, and in practice, it is necessary to use high blowing pressures to obtain the desired structure.

The invention therefore seeks to propose a container having a bottom that can be easily deformed (in particular without the need to use tools), and which has good blowability.

To that end, a container of plastic material is proposed, comprising a body and a bottom, the bottom having an annular outer seat defining a principal seating plane for the container, and a deformable membrane that extends radially inside the annular outer seat and is arranged to be able to adopt two configurations:a retracted configuration, in which the membrane extends axially above the principal seating plane;a deployed configuration, in which the membrane comprises an annular inner seat in the form of an annular bead projecting towards the exterior of the container, which extends axially beneath the principal seating plane and defines a secondary seating plane,
the bottom further comprising a series of hollow reserves in the annular inner seat, which form local discontinuities of the secondary seating plane.

Configured in this way, the bottom has an increased deformability under the effect of low pressure in the filled container, while enabling easy transport of the empty container resting on the inner seat, and still having good blowability.

Preferably, the inner seat comprises an internal section and a truncated cone-shaped external section, joined at the inner seat, and the hollow reserves form a junction between the internal and external sections through the inner seat.

Each hollow reserve extends, for example, over an angular extension J such that:

3602⁢n-10≤J≤3602⁢nwhere n is the number of reserves on the bottom, and J is the angular extension of each reserve expressed in degrees.

According to one embodiment, each hollow reserve extends over an angular extension substantially equal to an angular extension of a section of arc of the inner seat situated between two successive hollow reserves.

Preferably, each hollow reserve extends radially over an extension greater than the width of the inner seat.

Advantageously, each hollow reserve extends radially over an extension of between one-seventh and one-third of the diameter of the inner seat.

For example, each hollow reserve is in the shape of a horse saddle and has a double curvature.

Represented in the figures is a container1—in this instance, a bottle—produced by the stretch-blowing of a preform made of thermoplastic material such as PET (polyethylene terephthalate), previously heated to a temperature above the glass transition temperature of the material.

Said container1is preferably of the heat-resistant (HR) type; in this case, it can be manufactured by stretch-blowing in a mold whose wall is heated so as to increase the rate of crystallinity of the material by calorific input.

Said container1comprises, at an upper end, a threaded neck2, provided with a mouth3. In the extension of the neck2, the container1comprises in its upper part a shoulder4extended by a lateral wall or body5, which has an overall shape that is symmetrical in revolution around principal axis X of the container1.

The container1further comprises a bottom6that is extended at a lower end of the container1in the extension of the body5.

The body5is, in a lower part, substantially cylindrical and is extended downwards to a lower end7where it joins the bottom6.

The bottom6comprises, in the axial extension of the junction7, an external seat8in the form of an annular bead, which defines a principal seating plane9for the container1, by which said container can be placed flat on a flat surface such as a table.

The bottom6further comprises a membrane10that is extended radially from the external seat8towards the axis X of the container1, to a central region11of the bottom6, comprising successively, radially from the exterior towards the interior, a substantially flat annular central section12that is perpendicular to the axis X, then, at the center of the bottom6in the extension of the section12, a pin13protruding axially towards the interior of the container1.

The membrane10is deformable, being arranged to be able to adopt two configurations:a deployed configuration, represented by solid lines in the figures, in which the membrane10is extended at least in part beyond (or below, when the container is oriented neck upwards) the principal seating plane9—in other words, projecting towards the exterior of the container1,a retracted configuration, represented by broken lines in the cross-section ofFIG. 5, in which the membrane10is extended axially below (or above, when the container is oriented neck upwards) the principal seating plane9—in other words, projecting towards the interior of the container1, thus forming an arch substantially in the shape of a truncated cone.

The container1is formed in the deployed configuration of the membrane10. In this position, the membrane10comprises an annular bead projecting towards the exterior of the container, forming an annular inner seat14, which extends axially beyond (or below) the principal seating plane9and defines a secondary seating plane15by which the container can be placed flat on a flat surface (particularly on a conveyor belt when exiting the mold). The diameter of the secondary seating plane (shown by broken lines inFIG. 3) is indicated as A, and the distance measured axially between the principal seating plane9and the secondary seating plane15(FIG. 5) is indicated as B.

The outer seat8is internally bordered by an annular step16that extends axially over a small height, followed by an annular return17that, in the deployed position of the membrane10, extends radially in a plane substantially perpendicular to the axis X.

As can be clearly seen inFIG. 5, the membrane10comprises:an external truncated cone-shaped section18, which extends radially inward from the return17, and axially outwards (i.e., downwards) to the inner seat14;an internal section19, also truncated cone-shaped, which extends radially outwards from the annular central section12, and axially outwards (i.e., downwards) to the inner seat14, which thus forms a connection fillet between the outer section18and the inner section19, the concavity turned upwards.

The inner seat14thus forms the most protruding part (i.e., the lowest) of the membrane10.

As can be clearly seen in the figures, particularly inFIGS. 2 and 3, the bottom6comprises a series of hollow reserves20formed in the inner seat14.

The reserves20extend radially astride the inner seat14, and form a junction between the outer section18and the inner section19of the membrane10through the seat14.

The principal function of the hollow reserves20is to allow a progressive, flexible return of the membrane10from its deployed configuration (adopted upon completion of the forming in the mold, and preserved during any transport of the container1, then during the filling thereof), to its retracted configuration (adopted under the effect of a low pressure in the container1accompanying the cooling of the contents after capping).

Each reserve20has the overall shape of a horse saddle, and consequently has a double curvature, to wit:viewed from the side, a first curvature with concavity oriented downwards, having a radius denoted as C (seen at the center inFIG. 4),in radial cross-section, a second curvature with concavity oriented upwards, having a radius denoted as D (seen at the left inFIG. 5),

The hollow reserves20thus form undulations in the inner seat14, which generate local discontinuities of the secondary seating plane15. The secondary seating plane15is consequently formed from a discrete series of sections21of coplanar arcs at the end of the inner seat14, which extend between the hollow reserves20and whose radius of curvature is denoted as E (FIG. 5, at the right), which is consequently the radius of curvature of the inner seat14at the secondary seating plane15. Furthermore, F denotes the width of the inner seat14, i.e., the width (measured radially at the sections21of arc) of the junction between the outer section18and the inner section19of the membrane10, where the radius of curvature is constant and equal to E.

G denotes the depth, measured axially, of each hollow reserve20(i.e., the distance, measured axially, from the bottom of each reserve20to the secondary seating plane15).

Each reserve20comprises a central zone22, the contour of which, viewed from below in the axial direction (FIG. 3), is diamond-shaped, and which has the double curvature mentioned below. The junction of said central zone22with the adjacent sections of arc21is accomplished by means of connection fillets23with concavity oriented upwards, and whose radius of curvature, denoted as H, is comparable to the radius C (in absolute value). The junction of the central zone22with the outer and inner sections18,19of the membrane10is accomplished by means of connection fillets24with concavity oriented upwards, and whose radius of curvature, denoted as I, is comparable to the radii C and D, while slightly less in absolute value.

J denotes the angular extension of each reserve20and K denotes the angular extension of the sections of arc21, both measured in the secondary seating plane15around the axis X.

The number n of reserves20is preferably between 3 and 7, and the angular extension J (expressed in degrees) preferably verifies the following inequality:

According to an embodiment illustrated inFIG. 3, the angular extension J of the reserves20is comparable to the angular extension K of the sections of arc21. The angular extensions J, K are preferably substantially equal. In the illustrated embodiment, where the bottom6comprises five hollow reserves20(n=5) distributed uniformly over the perimeter of the inner seat14, the angular extensions J and K are approximately 35°.

Furthermore, L denotes the radial extension of the hollow reserves20. Said extension L is greater than the width F of the seat (and preferably even greater than or equal to three times the width F of the seat); moreover, the extension L is preferably between one-seventh and one-fourth of the diameter A of the inner seat14. In the embodiment illustrated inFIG. 3, L is approximately equal to one-sixth of the diameter A.

It will be noted that the lines visible in the figures are intended to better suggest the contour of the reserves20(and more particularly the central zones22and connection fillets23,24that frame them), but do not in any way indicate that there is a discontinuity between these different zones22,23,24. The presence of sharp edges would result in promoting the appearance of cracks during the return of the membrane by introducing strong local variations of the curvature of the material in the vicinity of the inner seat. This problem is avoided as a result of the hollow reserves20whose variations of curvature are progressive, which further improves the blowability of the container.

FIG. 5shows that the displacement of the membrane10in its return from its deployed configuration (shown in solid lines) to its retracted configuration (in broken lines), measured at the inner seat, is relatively large. More specifically, said displacement, denoted M, is substantially equal to twice the distance B between the two seating planes9,15, or preferably twice the sum of the distance B and the height, denoted N, of the step16. Said large displacement M is allowed by the configuration of the membrane10, and more particularly the progressivity of its return induced by the shape and dimensions of the hollow reserves20.

Said large displacement makes it possible to avoid as much as possible the occurrence of deformations on the body5accompanying the decrease of internal volume of the container1due to the cooling of the liquid and of the air present in the headspace (defined as the space between the liquid and the cap closing the container1).

To manufacture the container1that has just been described, the stretch-blowing technique in a mold will preferably be used, said mold comprising a sidewall defining a lower opening and a mold bottom that is movable with respect to the wall of the mold between:a lower position, adopted at the beginning of the blowing, in which the mold bottom is separated downwards from the opening, andan upper position, adopted at the end of blowing, in which the mold bottom blocks the opening and pushes up the material of the bottom6of the container1.

This technique, called boxing, makes it possible to increase the stretching rate of the bottom, to the benefit of its mechanical rigidity, and also to facilitate the imprinting of the membrane10, particularly at the hollow reserves20.