CONTAINER PROVIDED WITH A BASE WITH BULGING BEAMS

Abstract

Container (1) made from plastic material, provided with a body and a base (3) which extends from a lower end of the body, the base (3) including: a peripheral resting surface (5) which defines a flat annular deposition line (6) for the container (1); —a concave dome (9) which extends from the deposition line (6) to the central zone (7); a series of moulded beams (10) in the dome (9) which each radiate from the central zone (7) towards the resting surface (5), each beam (10) including a pair of radial grooves (11) which are moulded in the dome (9) and are separated by a radial rib which projects from the bases (12) of the grooves (11).

Description

The invention relates to the manufacture of containers, particularly bottles or jars, obtained by blow molding or stretch blow molding from blanks made of plastic material, such as polyethylene terephthalate (PET).

The manufacture by blow molding of a container consists ordinarily in introducing a blank (a preform or an intermediary container obtained by pre-blow molding of a preform) previously heated to a temperature higher than the glass transition temperature of the material into a mold having the impression of the container, and in injecting a pressurized fluid (particularly a gas such as air) into the blank. The blow molding can be completed by a prior stretching of the blank by means of a sliding rod.

The molecular double orientation or bi-orientation (axial and radial, respectively parallel and perpendicular to the general axis of the container) that the material undergoes during the blow molding imparts a certain structural rigidity to the container.

The reduction, dictated by the market, of the amount of material used for the manufacture of the containers, however, leads manufacturers to resort to manufacturing or shape tweaks to stiffen their containers, the double orientation proving to be insufficient. Consequently, two containers having equal weight do not necessarily have the same mechanical performance (stability, stiffness).

A well-known method for increasing the stiffness of a container is heat-setting, which consists of heating the wall of the mold to increase by thermal means the level of crystallinity of the material. This method, illustrated by the French patent FR 2 649 035 (Sidel) and its U.S. equivalent U.S. Pat. No. 5,145,632, is used particularly for HR (initials of the English term “heat resistant,” or heat-resistant) applications, in which the container is hot-filled.

Because of its cost and rate reduction that it imposes, however, this type of method could not be widespread for ordinary applications of the plain water type. For these applications, the structural stiffness of the base depends essentially on its shape. It is known to stiffen the base by means of radial beams, see, for example, the French patent FR 2 753 435 (Sidel). This base maintains its mechanical stability without turning over as long as the conditions of volume and/or of pressure in the container are normal and for a sufficient mass of material (on the order of 8 to 10 g for a container with a capacity of 0.5 liter). A reduction of the material mass (less than 8 g for a container with a capacity of 0.5 liter) causes a reduction in the performance of this type of container. The risk is heightened, during palletizing, of seeing some containers on the first level of the pallet collapse under the weight of the upper levels.

In order to stiffen the side wall of the container and thus in order to compensate partially for the reduction of material weight, it is known to inject, at the end of filling and before capping, a drop of a liquefied inert gas (particularly nitrogen), which, during the vaporization of the gas, puts the space under the neck (located between the liquid and the cap) under pressure (the relative pressure being on the order of 0.5 to 0.7 bar). However, this technique has the unwanted corollary of increasing the stresses that are exerted on the base (less than 2 g of material being reserved for it) and therefore proportionately increasing the risk that it be deformed in an uncontrolled manner, to the detriment of the stability of the container.

The objectives targeted, contradictory for some (and nevertheless preferably combined), are the following:

• • to lighten the container;
  • to enhance its mechanical performance;
  • to maintain or enhance its blowability (i.e., its ability to be shaped by blow molding) to make possible a blow molding at low pressure (less than or equal to about 20 bars);
  • to give the container a base that offers a good resistance to uncontrolled deformations (in particular on overturning), in particular under high internal pressure;
  • to give the container a base that gives it a good stability, particularly when the container is located on the first level of a pallet.

For this purpose, a container made of plastic material, provided with a body and with a base that extends from a lower end of the body, is proposed, the base comprising:

• • a peripheral seating surface that defines a flat annular setting line for the container;
  • a concave dome that extends from the setting line to a central zone;
  • a series of beams formed of recesses in the dome and that each radiate from the central zone to the seating surface, each beam comprising a pair of radial grooves that are formed of recesses in the dome and are separated by a radial rib that extends projecting from the bottoms of the grooves.

Provided with such a base, this container offers an excellent resistance to deformations caused by the pressure of the contents, possibly doubled by an axial compression due to palletizing.

Various additional characteristics can be provided, alone or in combination:

• • the rib is defined laterally by sides forming dropped edges;
  • the grooves of the pairs of grooves exhibit in cross-section a V-shaped profile;
  • the radial rib exhibits in cross-section a U-shaped profile;
  • the radial rib has a width L, measured crosswise, and a height H, such that their ratio L/H is between 0.5 and 2;
  • each beam extends to just beyond the seating surface, the setting line of which it interrupts;
  • the container comprises a pair of secondary ribs that extend projecting from an outer radial end of the beam;
  • the container further comprises a series of valleys formed of recesses in the dome, and which each extend between two beams, each valley radiating from the central zone to just beyond the seating surface.

Other objects and advantages of the invention will be brought out in the description of an embodiment, made below with reference to the accompanying drawings in which:

FIG. 1 is a perspective view from below of a container, in this case a bottle;

FIG. 2 is a perspective view from below, on an expanded scale, of the base of the container of FIG. 1, according to another orientation;

FIG. 3 is a bottom view of the base in FIG. 2;

FIG. 4 is a partial section of the base in FIG. 3, along the cutting plane IV-IV;

FIGS. 5 and 6 are perspective views, from above and according to two different orientations, of the base in FIG. 2, with details on an expanded scale in insets.

Shown in FIG. 1 is a container 1, in this case a bottle, made by stretch blow molding from a preform made of thermoplastic material, for example made of PET (polyethylene terephthalate).

Below, a non-flat zone is said to be concave when its center of curvature is located outside of the container, i.e., when it has a hollow directed toward the outside of the container 1. Conversely, a non-flat zone is said to be convex when the hollow of the zone is directed toward the inside of the container 1.

The container 1 comprises a side wall or body 2, generally cylindrical in shape and which extends along a main axis X of the container 1. The container 1 comprises a base 3, which extends from a lower end of the body 2. At an opposite upper end, the container further comprises a neck 4, provided with a rim.

After it is filled with liquid or pasty contents, the container 1 is closed in an airtight manner by means of an added cap, attached to the neck 4 by screwing.

The small amount of material allowed for the manufacture of the container 1 makes it vulnerable to the crushing forces sustained during its handling and its packaging (particularly during its palletizing). Of course, the body 2 has the advantage of being corrugated, as in the example illustrated in FIG. 1, but this structure does not impart sufficient strength to the container 1.

Between the cap and the contents remains a volume, referred to as under-neck volume, into which a gas can be injected that makes it possible to keep the entire container 1 under pressure, so as to stiffen the body 2 and thus to enhance the mechanical strength of the container 1 when it is handled. This gas is, for example, nitrogen, and its injection can be performed in liquid form by depositing a drop after the filling and just before the capping.

This technique effectively stiffens the body 2 but increases the mechanical stresses to which the base 3 is subjected, so that it is consequently necessary to reinforce it.

The base 3 comprises a peripheral seating surface 5 in the form of an annular bulge that extends approximately axially in the extension of the body 2.

The seating surface 5 defines an annular, flat setting line 6 that is interrupted locally (as we will see below), which forms the lower end of the container 1 and makes it possible for it to be set, standing up, on a flat surface. The setting line 6 does not, in practice, have a zero width (measured radially), but its width is small given its radius. For better visibility, the setting line 6 is shaded gray in FIG. 2.

The base 3 furthermore comprises a central zone 7 that is raised relative to the setting line 6. In the example illustrated, this central zone 7 can appear in the form of a portion of a sphere and can comprise at its center, in the X axis of the container 1, a button 8 derived from the injection of the preform from which the container 1 was formed.

The base 3 further comprises a concave dome 9 that extends from the setting line 6 to the central zone 7. This dome 9 has the general function of stiffening the base 3. The sole presence of the dome 9, however, is not enough to impart to the base 3 the necessary mechanical resistance to the deformations sustained under increased hydrostatic pressure from the pressure of the gas that is optionally present in the under-neck volume.

This is why the base 3 is provided with a series of beams 10 that are shaped in relief in the dome 9 and that radiate from the central zone 7 to the seating surface 5. The beams 10 number at least three. In the example illustrated, the beams 10 specifically number three but this number could be higher.

More specifically, each beam 10 comprises a pair of radial grooves 11 formed of recesses in the dome 9. Each groove 11 ends toward the inside of the container by a bottom 12 (preferably rounded), and is defined laterally by an outer side 13 and an inner side 14 that come together at the bottom and form an angle A between them. According to an embodiment that is illustrated in the figures, and more particularly in FIG. 4, the angle A is not zero: each groove 11 tapers toward the outside of the container 1 and thus has, in cross-section, a V shape, benefiting the blowability of the base 3 (i.e., its ability to be formed by blow molding with a good impression-taking). The angle A is preferably between 5° and 20°.

The grooves 11 are separated by a rib 15 that extends radially from an inner end 16 in the area of the central zone 7 to an outer end 17.

The rib 15 forms a bulge that protrudes from the bottoms 12 of the grooves 11, which ends by an end face 18. Thus, the beam 10 exhibits in cross-section (FIG. 4) a profile that is roughly in the shape of an M (or else in the shape of a W depending on the direction of observation of the container 1).

The rib 15 is defined laterally by the inner sides 14 of the grooves 11. According to an embodiment, the inner sides 14 form dropped edges (approximately parallel to one another) for the rib 15 that thus exhibits in cross-section a U-shaped profile, which benefits the structural stiffness of the beam 10 and more particularly its resistance to the stresses of bending and buckling.

As illustrated in FIG. 4, the rib 15 has a width, measured crosswise, marked L, and a height (measured between the bottom 12 of the grooves 11 and the end face 18), marked H, such that their ratio L/H is between 0.5 and 2. According to an advantageous embodiment, the ratio L/H is on the order of 1.4.

The height H of the rib 15 can be approximately constant over the entire length (measured radially) of the beam 10. On the other hand, its width L can vary, as in the example illustrated in FIG. 3 where the width L decreases (slightly) from the inner end 16 to the outer end 17.

According to an embodiment that is illustrated in the figures, the end face 18 extends, at least inside the perimeter defined by the setting line 6, in the extension of the dome 9 (i.e., the rib 15 is flush with the dome 9 without going beyond it). In other words, inside the perimeter defined by the setting line 6, the height H of the rib 15 is approximately equal to the depth of the grooves 11.

According to an embodiment that is illustrated in the figures, and more particularly visible in FIGS. 2 and 5, each beam 10 extends radially to beyond the seating surface 5, thus interrupting the setting line 6. Each beam 10 thus exhibits a central section 10A, which extends radially from its inner end 16 up to the right of the setting line 6, and a peripheral section 10B that extends the central section 10A from the right of the setting line 6 to the outer end 17. As is seen in FIG. 2, when seen from the outside of the container 1, the central section 10A is concave, while the peripheral section 10B is convex.

As is also seen in FIGS. 2 and 5, the depth of the grooves 11 is not constant over the entire length of the beam 10. This depth is essentially constant in the central section 10A, where it is approximately equal to the height H of the rib 15, while it is relatively greater in the area of the seating surface 5.

The particular structure, described above, of the beams 10, makes it possible to reinforce the dome 9. More specifically, the M-shaped (or W-shaped) structure of each beam 10 makes it particularly resistant to the bending stresses due to the pressure of the contents, as well as to the buckling stresses due to the axial compression of the palletized container 1 and to the lateral movements of the container 1 during various manipulations of the pallet.

It is, however, possible to further stiffen the base 3, thanks to a series of valleys 19 formed of recesses in the dome 9 and interposed between the beams 10.

As is seen in FIGS. 2 and 4, each valley 19 extends between two beams 10, radiating from the central zone 7 to beyond the seating surface 5, thus interrupting the setting line 6.

Each valley 19 is defined laterally by a pair of sides 20 that, as illustrated in FIG. 7, define between them an angle B of between 40° and 60°, which makes possible the stiffness of the base 3 without affecting its blowability.

While opening up under the effect of an axial compression (i.e., when the angle B increases), the valleys 19 tend to make the grooves 11 close back (i.e., to make the angle A decrease), which, on the one hand, stiffens the beams 10 and, on the other hand, makes it possible to absorb the distortions in the setting line 6 and thus to maintain its surface evenness.

To avoid ugly wrinkles around the outer ends 17 of the beams 10, the container 1 can be provided, for each beam 10, with a pair of secondary ribs 21 that extend projecting from the outer end 17. In the example illustrated, the secondary grooves 21 extend approximately at a right angle from the beam 10 in the manner of a T, along load lines found when the container 1 is put under axial compression.

Claims

1. Container (1) made of plastic material, provided with a body (2) and with a base (3) that extends from a lower end of the body (2), the base (3) comprising:

a peripheral seating surface (5) that defines a flat annular setting line (6) for the container (1);

a concave dome (9) that extends from the setting line (6) to a central zone (7);

a series of beams (10) formed of recesses in the dome (9) and which each radiate from the central zone (7) to the seating surface (5);

wherein each beam (10) comprises a pair of radial grooves (11) that are formed of recesses in the dome (9) and are separated by a radial rib (15) that extends projecting from the bottoms (12) of the grooves (11).

2. Container (1) according to claim 1, wherein the rib (15) is defined laterally by sides (14) that form dropped edges.

3. Container (1) according to claim 1, wherein the grooves (11) of the pairs of grooves exhibit in cross-section a V-shaped profile.

4. Container (1) according to claim 1, wherein the radial rib (15) exhibits in cross-section a U-shaped profile.

5. Container (1) according to claim 1, wherein the radial rib (15) exhibits a width L, measured crosswise, and a height H, such that their ratio L/H is between 0.5 and 2.

6. Container (1) according to claim 1, wherein each beam (10) extends to beyond the seating surface (5), the setting line (6) of which it interrupts.

7. Container (1) according to claim 6, further comprising a pair of secondary ribs (21) that extend projecting from an outer radial end (17) of the beam (10).

8. Container (1) according to claim 1, further comprising a series of valleys (19) formed of recesses in the dome (9), and which each extend between two beams (10), each valley (19) radiating from the central zone (7) to beyond the seating surface (5).

9. Container (1) according to claim 2, wherein the grooves (11) of the pairs of grooves exhibit in cross-section a V-shaped profile.