EP4469359A1 - Container having a reinforced petaloid bottom and bottom of a mould for producing such a container - Google Patents

Abstract

The present invention relates to a container (1) made of plastic provided with a body (5) and with a bottom (6) extending from a lower end of the body (5), the bottom (6) comprising: - a peripheral heel (7) defining a bearing plane; - an arch (10) that extends from a central region (11) to the heel (7); - a series of main reinforcing grooves (13) that are formed as hollows in the arch (10) extending radially from the central region (11) to the heel (7) and subdividing the arch (10) into a series of angular sectors, each main groove (13) being laterally bordered, at its junction with each angular sector of the arch (10) that is adjacent thereto, by a reinforcing rib (14) that protrudes relative to said sector; the container being characterised in that the reinforcing ribs (14) bordering two adjacent main grooves (13) extend in the direction of the heel (7) and meet at the border with the heel (7) to form a hollow island (15), between two adjacent main grooves (13), having a substantially triangular or trapezoidal shape. The invention also relates to the bottom of a mould for producing such a container.

Description

DESCRIPTION

TITLE: Container having a reinforced petaloid-type bottom and mold bottom for the manufacture of such a container

Technical area

The present invention relates to the field of containers, in particular bottles or jars, manufactured by blow molding or stretch blow molding from blanks made of plastic material such as polyethylene terephthalate (PET).

State of the art

A container comprises, in a conventional manner, a body delimiting the general volume of the container, extended, at an upper end of the container, by a neck, through which the container is filled and emptied, and, at a lower end, by a bottom which close the container.

The bottom must be able to withstand, without noticeably deforming, at least the hydrostatic pressure of the column of liquid which surmounts it. There are many background shapes, depending on the applications involved. Thus, for carbonated applications (typically sodas), the bottoms are generally petaloid in shape, comprising alternating valleys, hemispherical in shape, and projecting feet, the ends of which form a seat for the container. Such a background is described in document FR2959214 in particular.

The document FR2959214 describes a container made of thermoplastic material obtained by blow molding or stretch blow molding from a blank, this container comprising a petaloid bottom provided with projecting feet, separated by hollow valleys which extend radially from a central zone of the bottom, each foot having two flanks which each laterally border a valley. Each foot is provided, on each of its flanks, with a cheek which projects laterally on the side of the valley.

The petaloid bottom appears as a relatively successful solution with good resistance to high internal pressures in the container (thanks to the hemispherical shape of the valleys). However, the petaloid base requires a large quantity of material (around 15 to 18 g for a 0.5 l container), as well as a relatively high blowing pressure, to ensure correct impression taking of the feet and valleys. However, these constraints appear to be justified by the relatively high price at which the products concerned are distributed.

However, petaloid bases cannot be suitable for applications of the still liquid type (typically table water), for which the blowing pressure and the quantity of material used are minimized (today of the order of 10 g for a container of 0.5 I). Furthermore, these petaloid bottoms have the disadvantage of being unstable on the conveyors of the production lines, the fall of a bottle with a petaloid bottom running the risk of causing the production line to stop.

A bottom provided with a simple concave vault is not able to withstand, without significant deformation, a low pressure, of the order of 1 bar, in the bottle. It has therefore been proposed to provide the bottom with radial ribs, intended to reinforce the bottom in order to allow it to better resist the deformations induced by the pressure.

However, it is becoming common, for certain applications of flat liquids sensitive to oxidation (in particular fruit juices, but also certain flat waters), to expel the air above the flat liquid and replace it with an inert gas (typically nitrogen). In practice, this operation is carried out by pouring a drop of liquefied inert gas onto the surface of the flat liquid, immediately preceding the sealing of the container. This operation, called inerting (nitrogenation in the case of nitrogen), induces an overpressure in the container. Even seemingly slight (up to 1 bar), this overpressure is enough to significantly increase the stresses exerted on the bottom.

Furthermore, the manufacture by blow molding of a container usually consists of introducing into a mold with the cavity of the container a blank (a preform or an intermediate container obtained by pre-blowing a preform) previously heated to a temperature higher than the glass transition temperature of the material, and injecting a fluid (in particular a gas such as air) under pressure into the blank. Blowing can be completed by prior stretching of the blank by means of a sliding rod. The double molecular orientation that the material undergoes during the blowing (axial and radial, respectively parallel and perpendicular to the general axis of the container) gives the container a certain structural rigidity.

But the reduction - dictated by the market - in the quantity of material used for the manufacture of the containers leads the manufacturers to resort to tricks of manufacture or shape to stiffen their containers, the bi-orientation proving insufficient. As a result, two containers of equal weight do not necessarily have the same mechanical performance (strength, rigidity).

A well-known process for increasing the rigidity of a container is "heat setting", which consists in heating the wall of the mold to increase the degree of crystallinity by thermal means as described in document FR2649035 in particular and which is usually employed for HR applications (initials of the English term "heat resistant"), in which the container is hot filled.

Said document FR2649035 describes a process in which a container is molded by stretch-blow molding from a polyethylene terephthalate (PET) preform. The body of the preform alone is heated to a temperature at which longitudinal stretching and transverse stretching do not induce stress in the material constituting the container. The preform is then transferred to a mould, the walls of which are heated and maintained at a temperature lower than that of the body of the preform, where it is stretched longitudinally and blown. Thus, the bidrawing rate involved to pass from the preform to the container is between 7 and 9.

But, because of its cost and the reduction in rate which it imposes, this type of process cannot be generalized to ordinary applications of the plain water type. For these applications, the structural rigidity of the bottom depends essentially on its shape.

In this respect, it is known to stiffen the bottom by means of radial grooves. This is the case in particular of documents FR2753435, FR2932458 and WO2011/157952.

The document FR2753435 describes a container, such as a bottle, made of plastic material, obtained by injection then stretching/blowing of a preform. The bottom of the container is provided with reinforcement grooves which open at the junction between the bottom and the wall or extend slightly on the wall. Said grooves have their other end at the extreme theoretical limit of the unstretched central part of the bottom of the container. In this way, the grooves have an optimum length without ever ending up in unstretched, and therefore amorphous, material, and the bottom has maximum resistance to creep and other stresses.

The bottom of this container retains its mechanical strength without turning over as long as the volume and/or pressure conditions in the container are normal. However, when these conditions are extreme, the bottom tends to sag, even overturning. Thus, when the container is stored in high heat, typically when it is stored on a pallet outdoors in full sun, the temperature of the contents can reach or exceed 50°C, and the increase in pressure induced by the expansion of the contents exceed the threshold beyond which the bottom turns. The container then becomes unstable, with a high risk of the entire pallet collapsing. Similarly, when the container is stored in a freezer at temperatures at which the contents freeze, the expansion induced by solidification causes the bottom to turn over, the container also becoming unstable.

The document FR2932458 describes a thermoplastic container having a body and a bottom comprising: a concave vault, a concave dome opening in the center of said vault, an annular zone surrounding the base of said vault and forming a flat base, shaped zones claws extending the bottom of the body radially and offset in external projection with respect to the vault, and radial grooves delimited between the zones in the form of claws, grooves whose bottom is formed by radial sections of the vault and which have a depth radially variable maximum in line with the annular zone forming a seat. Such a bottom is capable of withstanding without significant deformation the hydrostatic pressure due to the column of liquid increased by an overpressure not exceeding approximately 2×10 5 Pa.

Document WO2011/157952 is also known, which discloses a plastic container. Said container made of thermoplastic material, comprising a body extending between a neck and a bottom capable of withstanding without significant deformation a hydrostatic pressure due to the column of a liquid contained in said container, said column of liquid being increased by a pressure not exceeding 2x105 Pa, said bottom comprising main ribs in the form of grooves open outwards, of substantially radial extent passing through an annular zone forming a substantially flat seat by which said bottom can rest stably on a flat support, said main ribs rising on a wall connecting the bottom with the body of the container. The container has a shoulder forming a connecting zone between said connecting wall and said body of the container, and said main ribs rise beyond said shoulder.

It would theoretically be possible to form deep recessed reserves on the bottom (in particular a deep vault) capable of increasing the mechanical strength of the bottom. However, this shape trick, as effective as it is, requires both an additional material, incompatible with the aforementioned lightening requirements, and a high blowing pressure, incompatible with the energy saving requirements, which suppose on the contrary a reduction in the blowing pressure necessary for forming the container.

There is therefore a need for a container whose mechanical performance is improved with equivalent blowability (that is to say capacity of the container to be formed by blowing), whose optimized shape of the bottom gives it a good compromise between blowability and rigidity. , whose bottom offers good resistance to overturning, and which, under extreme conditions of pressure and/or internal volume, can remain stable and whose manufacturing rate is higher without the appearance of undulations on the seat.

Disclosure of Invention

One of the aims of the invention is therefore to remedy all or part of these drawbacks by proposing a plastic container and a mold base for the manufacture of such a container providing improved mechanical performance for blowing, the optimized shape of the bottom gives it a good compromise between blowability and rigidity, whose bottom offers good resistance to rollover, and which, under extreme conditions of pressure and/or internal volume, remains stable and whose manufacturing rate is faster raised without the appearance of undulations on the seat.

To this end, and in accordance with the invention, there is proposed a plastic container provided with a body and a bottom extending from a lower end of the body, the bottom comprising: a peripheral seat defining a support plane; a vault which extends from a central zone to the seat; a series of main reinforcing grooves which are recessed in the arch, extend radially from the central zone towards the seat and subdivide the arch into a series of angular sectors, each main groove being edged laterally, at its junction with each angular sector of the vault which is adjacent to it, by a reinforcing rib which projects in relation to said sector; said container being remarkable in that the reinforcing ribs bordering two adjacent main grooves extend in the direction of the seat and join together bordering the seat to form a hollow island, between the two adjacent main grooves, of substantially triangular or trapezoidal.

Provided with such a bottom structured in this way, the container offers better mechanical performance than conventional arches with an equal quantity of material, while offering good blowability. In addition, the container offers better resistance to overturning, remains stable under extreme conditions of pressure and/or internal volume, and allows a higher production rate without the appearance of undulations on the seat.

Various additional characteristics can be provided, alone or in combination: the reinforcing ribs have a cross section in the general shape of a U with a depth of between 0.5 mm and 3 mm; the reinforcing ribs have a width of between 1 and 8 mm; the main grooves have a radius between 1.5 mm and 6 mm; it has four to seven main grooves uniformly distributed angularly; the series of main reinforcement grooves formed hollow in the arch extend radially from the central zone towards the heel; the vault has two concentric regions, namely a central region and a peripheral region separated by a median axial setback which extends continuously around the central zone, that is to say that said setback is not interrupted perpendicular to the main grooves but extends to the bottom of these, so that the central region is raised with respect to the peripheral region; the interior surface of the median axial recess is between 50% and 80% of the interior surface of the vault; the inner surface of the median axial recess is substantially equal to 60% of the inner surface of the arch; the median axial offset has a height of between 1 and 4.5 mm the median axial offset has a height of 2.5 mm; the recess has an angle of between 0 and 45° with respect to the longitudinal axis X; the median axial offset intersects with the islands extending between the main reinforcing grooves; the median axial recess extends discontinuously while being interrupted at least in line with the islands.

Another object of the invention relates to a mold base for the manufacture of a container according to the invention from a plastic preform, said mold base being able to be mounted movably in a mold comprising two movable walls l relative to the other and intended to form the body of the container, said mobile mold bottom pushing the constituent plastic material of the container towards its opening, said mold bottom comprising at least a first annular part intended to form at least part of the heel, a second dome-shaped part intended to come into contact with an amorphous central zone of the preform to form the arch, said second part comprising a series of so-called main bosses extending radially from the central zone of the dome towards the first annular part and subdividing the dome into a series of angular sectors, intended to form the series of main reinforcement grooves which subdivide the vault into a series of angular sectors, each main boss being bordered laterally, at its junction with each sector angular of the dome which is adjacent to it, by a so-called reinforcing groove which extends hollow with respect to said sector and intended to form the reinforcing rib laterally bordering each main groove; said mold bottom being remarkable in that the reinforcing grooves bordering two adjacent main bosses extend in the direction of the first annular part and meet while bordering the first annular part to form a projecting island, between the two adjacent main bosses , of substantially triangular or trapezoidal shape. Such a mold base thus structured makes it possible to produce containers according to the invention at high speeds without the appearance of corrugation on the heel of the container, to produce containers offering better mechanical performance than conventional grooved bases for an equal amount of material. , while providing good blowability.

Various additional characteristics can be provided, alone or in combination: the reinforcing grooves have a cross section in the general shape of an inverted U with a height of between 0.5 mm and 3 mm; the reinforcing grooves have a width of between 1 and 8 mm; the main bosses have a radius between 1.5 mm and 6 mm;

It has four to seven main bosses evenly distributed angularly; the series of main bosses formed projecting from the dome extend radially from the central zone of the dome to the first annular part; the dome has two concentric regions, namely a central region and a peripheral region separated by a median axial recess which extends continuously around the central region, that is to say that said recess is not interrupted perpendicular to the main bosses so that the central region is lowered relative to the peripheral region; the inner surface of the median axial recess is between 50% and 80% of the inner surface of the dome; the inner surface of the median axial recess is substantially equal to 60% of the inner surface of the dome; the median axial recess has a depth of between 1 and 4.5 mm; the median axial recess has a depth of 2.5 mm; the recess has an angle of between 0 and 45° with respect to the longitudinal axis X; the median axial offset intersects with the islands extending between the main bosses; the recess extends discontinuously around the central region, being interrupted at the level of the projecting islands. Brief description of the drawings

Other advantages and characteristics will emerge better from the following description of several variant embodiments, given by way of non-limiting examples, of the container and the bottom of the mold for the manufacture of said container in accordance with the invention, with reference to the accompanying drawings in which: Figure 1 is a bottom perspective view of a plastic container according to the invention, Figure 2 is a perspective view, on an enlarged scale, of the bottom of the container according to the invention shown in Figure 1, Figure 3 is a bottom plan of the container according to the invention, Figure 4 is a radial sectional view, in perspective, of the bottom of the container according to the invention, Figure 5 is a view in radial section of the bottom of the container according to the invention, figure 6 is an exploded perspective view of a mould, including a mold bottom, for the manufacture of a container according to the invention, the figure is a side view of the mold base according to the invention, FIG. 8 is a top view of the mold base according to the invention, FIG. 9 is a perspective view of an alternative embodiment of the mold base according to the invention.

Embodiment of the invention

In the remainder of the description of the invention, the same reference numerals designate the same elements. The various views are not necessarily drawn to scale.

Referring to Figure 1, the container 1 according to the invention consists, in this case, of a bottle made by stretch blow molding from a preform of thermoplastic material, for example PET (polyethylene terephthalate).

Said container 1 comprises, at an upper end, a neck 2, provided with a rim 3. In the extension of the neck 2, in the direction of the lower end of the container 1, the latter comprises, in the usual way, in its part upper shoulder 4 flaring out in the opposite direction to the neck 2, this shoulder 4 being extended by a side wall or body 5, of generally cylindrical shape of revolution around a vertical longitudinal axis X, shown in broken lines, of the container 1.

The container 1 further comprises a bottom 6 which extends opposite the neck 2, from a lower end of the body 5. Said bottom 6 comprises a peripheral heel 7 in the form of an annular bead which extends substantially axially in the extension of the body 5. The heel 7 ends in a laying plane 8, also called seat, perpendicular to the longitudinal axis X of the container 1, said laying plane 8 defining the lower end of the container 1 and allowing the container 1 to be placed, vertically, on a flat surface.

DI is denoted the diameter of the laying plane 8, the term “diameter” covering not only the case (illustrated) where the container 1 (and therefore the bottom 6) has a circular contour, but also the case where the container 1 would be at polygonal contour (for example square), in which case the term “diameter” would designate the diameter of the circle in which this polygon would fit without thereby departing from the scope of the invention.

Towards the interior of the container 1, the heel 7 comprises a tapered annular flange 9 which extends towards the interior of the container 1 in the extension of the laying plane 8, the truncated cone formed by the flange 9 opening towards down (undercut) and having an apex angle of at least 70°. This flange 9 may have a height of between 1 mm and 3 mm, for example around 1.5 mm. Furthermore, said flange 9 may have a flat or convex outer wall whose radius of curvature is preferably between 5 mm and 30 mm.

Furthermore, the bottom 6 also comprises a concave vault 10, in the form of a substantially spherical cap with a concavity facing the outside of the container 1 in the absence of constraint, that is to say in the absence of contained in the container 1. The arch 10 extends from the heel 7, in the extension of the flange 9, to a central zone 11 of the bottom 6 forming a pin projecting towards the inside of the container 1, with in its center an amorphous pellet 12 which corresponds to the zone of injection of the material constituting the preform having served to produce the container and can fulfill a centering function during the forming, by blowing, of the container 1.

In addition, with reference to Figures 1 to 5, said bottom 6 comprises a series of main reinforcement grooves 13 formed hollow towards the inside of the container 1, which extend radially from the central zone 11 towards the heel 7 and subdivide the arch 10 into a series of angular sectors. These main reinforcement grooves 13 extend as far as cheek 9 of said heel 7. continued. The main grooves 13 are for example five in number (as in the example shown, which corresponds to a container with a capacity of 0.5 liters), but this number could be higher, in particular six in the case of a container with a capacity greater than or equal to 1 liter, or even seven in the case of a container with a capacity greater than or equal to 2.5 liters.

It is obvious that the main grooves 13 may be 4 in number, for example, for a container 1 of smaller capacity without departing from the scope of the invention.

Each main groove 13 is bordered laterally, at its junction with each angular sector of the vault 10 which is adjacent to it, by a reinforcing rib 14 which projects in relation to said angular sector. Said reinforcing ribs 14 border two adjacent main grooves 13, extend in the direction of the heel 7 and join together bordering said heel 7 to form a hollow island 15, between the two adjacent main grooves 13. Each hollow island 15 thus formed has a generally substantially triangular or trapezoidal shape. These reinforcing ribs 14 and the hollow islands 15 increase the rigidity of the bottom and make it possible to avoid the appearance of undulations at the level of the heel 7 during the manufacture of the container, including at high production rates.

Particularly advantageously, the outer surface of the islands 15 is grained. Indeed, the graining of the islands 15 makes it possible to slow down the material during stretch-blow molding, to increase the thickness of the wall of said islands 15 and ultimately to increase the rigidity of the latter.

Depending on the capacity of the container, the reinforcing ribs have a generally U-shaped cross-section with a depth of between 0.5 mm and 3 mm and a width of between 1 and 8 mm. As for the main grooves 13, the latter have a radius of between 1.5 mm and 6 mm. In order to further increase the rigidity of the bottom, with reference to FIGS. 1 to 5, the arch 10 advantageously has two concentric regions, namely an annular central region 16 surrounding the central zone 11 of the bottom 6, and an annular peripheral region 17 surrounding the central region 15, separated by a recess called recess 18 which extends axially over a predetermined height H. This recess 18 is substantially median with respect to the arch 10, that is to say that the central region 16 and the peripheral region 17 have substantially the same radial extension. Incidentally, said recess 18 may have an angle of between 0 and 45° with respect to the longitudinal axis X.

According to the invention, this recess 18 extends continuously, that is to say it is not interrupted in line with the main grooves 13 but extends to the bottom thereof.

According to an alternative embodiment of the container according to the invention, not shown in the figures, the recess 18 may extend discontinuously by being interrupted in line with the islands 15 for example.

Said axial recess 18 extends annularly around the central zone 11 . In the embodiment shown, where the container 1 is of substantially cylindrical shape of revolution around its longitudinal axis X, the recess 18 forms a ring with a circular outline, the diameter of which is denoted D2. In the variants already mentioned, where the container 1 would have a polygonal contour in cross section, the recess 18 would also have a polygonal contour, homothetic to the outer contour of the container 1. D2 would then designate the diameter of the circle in which the polygonal contour would fit. of the recess 18.

By the presence of the axial recess 18, the central region 16, although having a radius of curvature substantially identical to that of the peripheral region 17, is slightly raised relative to the latter, being offset towards the inside of the container. 1.

According to one embodiment, the diameter D2 of the recess 17 is between 50% and 80% of the diameter DI of the laying plane 8. In the example illustrated, the ratio D2/D1 is around 60%. As for the height H of the recess 18, it is substantially constant on its contour, being advantageously between 1 mm and 4.5 mm. For a container with a capacity of 1.5 liters; the height H of the recess 18 is rather between 1 and 3 mm, and for example approximately 2.5 mm.

The function of the recess 18 is to maintain the stability of the container 1 under conditions of extreme pressure and/or volume, in particular when an excess pressure prevails in the container 1 induced by an expansion of the contents and of the volume under the neck, due to example to an exposure of the container 1 (full) to the sun, or when the contents undergo an expansion induced by its solidification, due for example to the storage of the container 1 (full) in a freezer.

Under these conditions, the content exerts on the bottom 6 a pressure which tends to collapse it. The recess 18 however opposes the complete reversal of the bottom 6 by inducing a stiffening of the arch 10 in its middle region, and by limiting the deformation of the arch 10 so as to widen the heel 7 towards the center of the bottom 6. maximum, the bottom 6 actually undergoes a reversal but in a controlled manner, the central region 16 of the vault 10 then forming a secondary heel by which the container 1 can rest stably on a support surface.

If the diameter D2 of the recess 18 was too small (typically less than 50% of the diameter DI of the laying plane 8), the surface of the secondary heel formed by the central region 16 turned over would be too small and the container would be unstable. If, on the contrary, the diameter D2 of the recess 18 was too large (typically greater than −80% of the diameter DI of the laying plane 8), the risk of the bottom 6 turning over would be increased, the deformation of the arch 10 less well controlled, and this would result in instability of the container.

An axial (that is to say cylindrical) recess 18 extending over a relatively low height H offers a good compromise between control of the deformation of the bottom 6 as it has just been described, and good blowability. bottom 6.

The container 1 provided with this bottom 6 presents a good compromise between the mechanical performance (that is to say the capacity of the container 1 to resist deformations and, when these occur, to undergo them in a controlled manner) and the blowability (i.e. the capacity of the container 1 to be formed by blowing). With reference to FIGS. 6 to 8, a molding unit 19 according to the invention is described for the forming, from a blank, usually typically a preform, of a container, such as a bottle or a can, according to the invention.

Said molding unit 19, with reference to FIG. 6, comprises a mold 20 provided with a side wall 21 which defines a cavity 22 at the imprint of a part of the container. Said mold 20 further comprises a bottom 23 in the cavity of the bottom of the container, said mold 20 being made of metal, for example steel or aluminum (this term also covering aluminum alloys). The cavity 22, and ultimately the container 20, extends along a main axis X which defines a vertical direction. Any plane perpendicular to the main X axis is said to be horizontal. According to an embodiment illustrated in the drawings, the side wall 21 comprises two half-molds 20A, 20B each defining a half-cavity 24A, 24B of the body of the container and mounted in rotation with respect to each other around a common axis formed by a hinge, not shown in the figures, between an open position, in which the half-molds 20A, 20B are angularly separated from each other and the mold bottom 23 is lowered relative to the half -moulds 20A, 20B to allow the introduction of the blank and the evacuation of the container formed, and a closed position, in which the half-molds 20A, 20B are applied against each other and trap between them the mold bottom 23, as shown in Figures 6 to 8, to thereby form the cavity 22 and define the footprint of the container to be formed. Thus, said mold bottom 23 is able to be mounted movably in mold 20 comprising two walls movable relative to each other and intended to form the body of the container, said movable mold bottom 23 pushing back the constituent plastic from the container to its opening.

Said mold base 23 comprises a first annular part 24 intended to form at least partly the heel 7 of the container 1, a second dome-shaped part 25 intended to come into contact with an amorphous central zone of the preform to form the vault 10 of container 1.

Said second part 25 comprises a series of so-called main bosses 26 extending radially from the central zone of the dome 25 towards the first annular part 24 and subdividing the dome 25 into a series of angular sectors, intended to form the series of main grooves of reinforcement which subdivide the arch into a series of angular sectors, each main boss 26 being bordered laterally, at its junction with each angular sector of the dome 25 which is adjacent to it, by a so-called reinforcing groove 27 which extends hollow with respect to said sector and intended to form the reinforcing rib laterally bordering each main groove. In the embodiment shown in the figures, the series of main bosses 27 formed projecting from the dome 25 extend radially from the central zone of the dome 25 to the first annular part 24.

Furthermore, the reinforcing grooves 27 bordering two adjacent main bosses 26 extend in the direction of the first annular part 24 and join together bordering the first annular part 24 to form a projecting island 28, between the two adjacent main bosses 26 , of substantially triangular or trapezoidal shape. Said reinforcing grooves 27 have a cross section in the general shape of an inverted U.

Particularly advantageously, the surface of the projecting islands 28 is grained. Indeed, the graining of the projecting islands 28 makes it possible to slow down the material during stretch-blow molding, to increase the thickness of the wall of the islands 15 of the bottle and ultimately to increase the rigidity of the latter. Said graining of the projecting islands 28 may be obtained by any mechanical and/or chemical surface treatment well known to those skilled in the art.

Such a mold bottom 23 structured in this way makes it possible to produce containers according to the invention at high speeds without the appearance of corrugation on the heel of the container, to produce containers offering better mechanical performance than conventional grooved bottoms with a quantity of material equal, while offering good blowability.

The main bosses 26 are, for example, five in number (as in the example illustrated, which corresponds to a bottom of the mold for the manufacture of a container with a capacity of 0.5 liters), but this number could be greater, in particular by six in the case of a container with a capacity greater than or equal to 1 liter, or even seven in the case of a container with a capacity greater than or equal to 2.5 liters.

It is obvious that the main bosses 26 may be 4 in number, for example, for a container 1 of smaller capacity without departing from the scope of the invention. Depending on the capacity of the container to be manufactured, the reinforcing grooves 27 have a cross section in the general shape of an inverted U with a height of between 0.5 mm and 3 mm and a width of between 1 and 8 mm. As for the main bosses, these have a radius of between 1.5 mm and 6 mm.

In order to further increase the rigidity of the bottom of the container to be manufactured, the dome 25 of the bottom of the mold 23 has two concentric regions, namely a central region 29 and a peripheral region 30 separated by a median axial recess 31 which extends from continuously around the central region 29, that is to say that said recess 31 is not interrupted perpendicular to the main bosses 26 so that the central region 29 is lowered relative to the peripheral region 30.

This recess 31 is substantially median with respect to the arch 25, that is to say that the central region 29 and the peripheral region 30 have substantially the same radial extension. In addition, the median axial offset 30 intersects with the islands 28 extending between the main bosses 26.

According to the invention, this recess 31 extends continuously, that is to say it is not interrupted in line with the main bosses 26 but extends as far as the crest of the latter.

Said axial recess 31 extends annularly around the central region 29. In the embodiment shown, the recess 31 forms a ring with a circular outline; However, it is obvious that, for the manufacture of a container 1 having a polygonal contour in cross section, the recess 31 would also have a polygonal contour, homothetic to the outer contour of the container 1 to be manufactured.

By the presence of the axial recess 31, the central region 29, although having a radius of curvature substantially identical to that of the peripheral region 30, is slightly lowered relative to the latter. According to one embodiment, the diameter D2 of the recess 31 is between 50% and 80% of the diameter DI of the laying plane 8. In the example illustrated, the ratio D2/D1 is around 60%.

As for the depth of the recess 1, it is substantially constant on its contour, advantageously being between 1 and 4.5 mm. For a container with a capacity of 1.5 liters; the depth of the recess 31 is rather between 1 and 3 mm, and for example approximately 2.5 mm. Incidentally, said recess 31 may have an angle of between 0 and 45° with respect to the longitudinal axis X.

Furthermore, the interior surface of the median axial recess 31 is between 50% and 80% of the interior surface of the dome 25 and, preferably, said interior surface of the median axial recess 31 is substantially equal to 60% of the interior surface of the dome 25.

According to a last embodiment variant of the bottom of the mold according to the invention, with reference to FIG. 9, said bottom of the mold 23 comprises, in the same way as previously, a first annular part 24 intended to form at least in part the heel 7 of the container 1, a second dome-shaped part 25 intended to come into contact with an amorphous central zone of the preform to form the vault 10 of the container 1. Said second part 25 comprises a series of so-called main bosses 26 s extending radially from the central zone of the dome 25 towards the first annular part 24 and subdividing the dome 25 into a series of angular sectors, intended to form the series of main reinforcement grooves which subdivide the vault into a series of angular sectors, each main boss 26 being bordered laterally, at its junction with each angular sector of the dome 25 which is adjacent to it, by a so-called reinforcing groove 27 which extends hollow with respect to said sector and intended to form the reinforcing rib laterally bordering each main groove. In the embodiment shown in the figures, the series of main bosses 27 formed projecting from the dome 25 extend radially from the central zone of the dome 25 to the first annular part 24.

Furthermore, the reinforcing grooves 27 bordering two adjacent main bosses 26 extend in the direction of the first annular part 24 and join together bordering the first annular part 24 to form a projecting island 28, between the two adjacent main bosses 26 , of substantially triangular or trapezoidal shape. the said reinforcing grooves 27 have a cross section in the general shape of an inverted U.

In order to further increase the rigidity of the bottom of the container to be manufactured, the dome 25 of the bottom of the mold 23 has two concentric regions, namely a central region 29 and a peripheral region 30 separated by a median axial recess 31

The bottom of the mold 23 differs from that described above in that the setback 31 extends discontinuously around the central region 29, that is to say that said setback 31 is interrupted at the level of the projecting islands. 28.

It goes without saying that said recess 31 could also be interrupted at the level of the main bosses 26 without departing from the scope of the invention. Finally, it is quite obvious that the examples which have just been given are only particular illustrations in no way limiting as to the fields of application of the invention.

Claims

1. Plastic container (1) provided with a body (5) and a bottom (6) extending from a lower end of the body (5), the bottom (6) comprising: a heel (7) peripheral defining a support plane; an arch (10) which extends from a central zone (11) to the heel (7); a series of main reinforcement grooves (13) which are formed hollow in the arch (10), extend radially from the central zone (11) towards the heel (7) and subdivide the arch (10) into a series of angular sectors, each main groove (13) being bordered laterally, at its junction with each angular sector of the arch (10) which is adjacent to it, by a reinforcing rib (14) which projects in relation to said sector; characterized in that the reinforcing ribs (14) bordering two adjacent main grooves (13) extend in the direction of the heel (7) and come together bordering the heel (7) to form a hollow island (15), between the two main grooves (13) adjacent, of substantially triangular or trapezoidal shape. 2. Plastic container according to claim 1 characterized in that the reinforcing ribs (14) have a cross section in the general shape of a U with a depth of between 0.5 mm and 3 mm. 3. Plastic container according to any one of claims 1 or 2 characterized in that the reinforcing ribs (14) have a width of between 1 and 8 mm. 4. Plastic container according to any one of claims 1 to 3 characterized in that the main grooves (13) have a radius of between 1.5 mm and 6 mm. 5. Plastic container according to any one of claims 1 to 4 characterized in that it comprises four to seven main grooves (13) uniformly distributed angularly. 6. Plastic container according to any one of the preceding claims, characterized in that the series of main reinforcing grooves (13) formed hollow in the arch (10) extend radially from the central zone (11) to at least the heel (7). 7. Plastic container according to any one of the preceding claims, characterized in that the arch (10) has two concentric regions, namely a central region (16) and a peripheral region (17) separated by a recess (18) axial median which extends continuously around the central region (16), that is to say that said recess (18 is not interrupted perpendicularly to the main grooves (13) but extends to the bottom of these, so that the central region (16) is raised with respect to the peripheral region (17). 8. Plastic container according to claim 7 characterized in that the inner surface of the recess (18) median axial is between 50% and 80% of the inner surface of the arch (10). 9. Plastic container according to claim 8 characterized in that the inner surface of the recess (18) median axial is substantially equal to 60% of the inner surface of the arch (10). 10. Plastic container according to any one of claims 7 to 9 characterized in that the recess (18) median axial has a height of between 1 and 4.5 mm. 11. Plastic container according to claim 10 characterized in that the recess (18) median axial has a height of 2.5 mm. 12. Plastic container according to any one of claims 7 to 11 characterized in that the recess (18) has an angle of between 0 and 45° relative to the longitudinal axis X. 13. Plastic container according to any one of claims 7 to 12 characterized in that the recess (18) median axial intersects with the islands (15) extending between the main grooves (13) reinforcement. 14. Plastic container according to any one of claims 7 to 12 characterized in that the recess (18) median axial extends discontinuously being interrupted at least to the right of the islands (15). 15. Plastic container according to any one of claims 1 to 14 characterized in that the outer surface of the islands (15) is grained. 16. Mold base (23) for the manufacture of a container (1) according to any one of claims 1 to 15 from a plastic preform, said mold base (23) being adapted to be movably mounted in a mold (20) comprising two walls movable relative to each other and intended to form the body (5) of the container (1), said bottom mold (23) pushing the constituent plastic material of the container (1) towards its opening, said bottom (23) of the mold comprising at least a first annular part (24) intended to form at least in part the heel (7), a second dome-shaped part (25) intended to come into contact with an amorphous central zone (11) of the preform to form the arch (10), said second part (25) comprising a series of so-called main bosses (26 ) extending radially from the central zone of the dome (25) towards the first annular part (24) and subdividing the dome (25) into a series of angular sectors, intended to form the series of main reinforcing grooves (13) which subdivide the vault (10) into a series of angular sectors, each main boss (26) being bordered laterally, at its junction with each angular sector of the dome (25) which is adjacent to it, by a so-called reinforcing groove (27) which extends hollow with respect to said sector and intended to form the reinforcing rib (14) laterally bordering each main groove (13), characterized in that the reinforcing grooves (27) bordering two adjacent main bosses (26) extend in the direction of the first annular part (24) and come together bordering the first annular part (24) to form an island (28) projecting between the two main bosses (26) adjacent, of substantially triangular or trapezoidal shape. 17. Mold base according to claim 16 characterized in that the reinforcing grooves (27) have a cross section in the general shape of an inverted U with a height of between 0.5 mm and 3 mm. 18. Mold base according to any one of claims 16 or 17 characterized in that the reinforcing grooves (27) have a width of between 1 and 8 mm. 19. Mold base according to any one of claims 16 to 18 characterized in that the main bosses (26) have a radius of between 1.5 mm and 6 mm. 20. Mold base according to any one of claims 16 to 19 characterized in that it comprises four to seven main bosses (26) uniformly distributed angularly. 21. Mold base according to any one of claims 16 to 20, characterized in that the series of main bosses (26) formed projecting from the dome (25) extend radially from the central zone of the dome (25) to 'to the first annular part (24). 22. Mold base according to any one of claims 16 to 21 characterized in that the dome (25) has two concentric regions, namely a central region (29) and a peripheral region (30) separated by a recess (31 ) median axial which extends continuously around the central region (29), that is to say that said recess (31) is not interrupted perpendicular to the main bosses (26) so that the central region (29) is lowered relative to the peripheral region (30). 23. Mold base according to claim 22 characterized in that the inner surface of the recess (31) median axial is between 50% and 80% of the inner surface of the dome (25). 24. Mold base according to claim 23 characterized in that the inner surface of the recess (31) median axial is substantially equal to 60% of the inner surface of the dome (25). 25. Mold base according to any one of claims 22 to 24 characterized in that the recess (31) median axial has a depth of between 1 and 4.5 mm. 26. Mold base according to claim 25 characterized in that the recess (31) median axial has a depth of 2.5 mm. 27. Mold base according to any one of claims 22 to 26 characterized in that the recess (31) has an angle of between 0 and 45° relative to the longitudinal axis X. 28. Mold base according to any one of claims 22 to 27, characterized in that the median axial recess (31) intersects with the islands (28) extending between the main bosses (26). 29. Mold base according to any one of claims 22 to 27 characterized in that the median axial recess (31) extends discontinuously around the central region (29) being interrupted at the islands (28) projecting. 30. Mold base according to any one of claims 16 to 29 characterized in that the surface of the projecting islands (28) is grained.