EP2125533B1 - Plastic bottle with a champagne base and production method thereof - Google Patents

Description

The present invention relates to a bottle of the champagne bottom type, that is to say the bottom has a dome having an outwardly oriented concavity, which is intended in particular, but not exclusively, to contain a carbonated beverage . More particularly, the invention relates to a plastic bottle comprising a body extending longitudinally along a central axis from a neck to a lower end and having a predetermined thickness, and a bottom, said bottom comprising a connected skirt. at a lower end of the body and extending to a peripheral support zone on which the bottle rests in a vertical position, a continuously rounded concavity dome facing outward and extending from the peripheral support zone to a vertex located substantially on the central axis, and grooves having a bottom and extending radially between the skirt and the dome to define between them feet of the peripheral support zone. The grooves have a longitudinal bottom line extending on the bottom of said grooves in their direction of radial elongation.

Funds of this type are used for bottles containing carbonated beverages generating a high internal pressure. Indeed, the dome of these funds said "champagne" have a good ability to withstand the internal pressure by its geometric shape continuously rounded and soft, that is to say without marked relief likely to generate mechanical stress concentrations. Nevertheless, the connection of this dome with the skirt at the level of the peripheral support zone poses stability problems of the bottle, because under the effect of the internal pressure, the support zone can swell asymmetrically on an angular portion. This is the reason why it is known to provide peripheral grooves which define reinforced feet relative to a continuous annular support zone. However, in the prior art, these grooves have been tangentially connected to the dome, i.e. with an orientation of the bottom of the groove forming an almost flat angle with the tangent to the dome, or with a wide radius of curvature at the connection, in order not to create a zone of weakness in the dome and therefore to reduce its thickness compared to traditional champagne glass background. But the thickness of the dome still remained higher than that of the body of the bottle, and from its top to the support zone to also preserve the strength of the dome as a whole. Such domes provided with reinforcing grooves are known, for example documents FR-A-2,300,707 and WO-A-03/091117 .

Champagne bottoms have the disadvantage of having a relatively high weight due to the presence of a relatively thick dome to withstand a given internal pressure. However, there is a constant desire to reduce the weight of plastic bottles in order to limit the amount of raw material needed and to limit the impact of the packaging on the environment.

The present invention therefore aims to optimize the bottom of a bottle, either to withstand a higher pressure to constant weight, or to reduce the weight of a current bottom for a given drink.

For this purpose, the subject of the present invention is a bottle according to claim 1.

It appeared, especially during tests at 40 ° for 72 hours, that the bottles thus produced bore better internal pressure than comparable prior bottles. This especially with respect to similar bottles in terms of size and weight, which have a petaloid convex bottom. In addition, relative to these funds, the height of the grooves separating the feet is significantly reduced and the aesthetic appearance is improved.

These surprising results can be attributed to two factors. On the one hand, the bottom of the grooves connected at an angle to the dome can be used to transmit radial forces on the periphery of the skirt, which would limit the possibility of flattening the dome and avoid the dome turns sometimes noted. On the other hand, the side walls of the grooves form flanges substantially perpendicular to the dome and extending over the height of a lower portion thereof, which would create reinforcements similar to ribs.

Note however that to connect the grooves to the dome, we will favor a rounded profile with a non-zero radius of curvature, rather than a sharp angle. But such a radius of curvature will remain significantly lower than the characteristic dimensions of the bottom, including the radius of curvature of the rounded bottom line of the grooves. The directions of the bottom line and the tangent to the dome are then of course determined at the ends of the rounded connection profile.

The grooves open into a lower part of the dome delimited vertically, compared to a part top of the dome, by the outlet of the bottom of said grooves. According to a further feature of the invention, the annular lower portion of the dome has a thickness substantially equal to the predetermined thickness of the body, while the upper portion of the dome has a minimum thickness significantly greater than said predetermined thickness. This results in a weight saving thanks to the combined effect of grooves reinforcing this lower part of the dome.

The variation in thickness between the annular lower part and the upper part of the dome is of course not discontinuous, but with a certain progressivity. The thickness of the upper part may be substantially variable and in particular increasing towards the apex which corresponds to the point of injection of the preform. By cons, the thickness of the lower portion does not vary significantly, of the order of a few tens of percent, and reaches a value almost equal to the predetermined thickness at the feet of the support zone, unlike champagne funds of the prior art for which one seeks a significant thickness in this area of support to strengthen it.

• l'angle formé entre la direction du fond des rainures et la direction tangente au dôme au niveau du débouché est égal à 120 degrés ; en effet, un angle supérieur à 150 degrés ne devrait pas bloquer suffisamment la partie supérieure du dôme tandis qu'un angle inférieur à 90 degrés entraînerait une utilisation de matière plus importante sans améliorer la résistance à la pression ;
• la ligne de fond des rainures présente un profil courbe avec un rayon de courbure croissant depuis la jupe jusqu'au dôme ; de manière à former un angle plus prononcé au niveau du débouché dans le dôme qu'au niveau du débouché dans la jupe ;
• l'épaisseur minimale de la partie supérieure du dôme est égale à au moins deux fois l'épaisseur prédéterminée, et de préférence environ égale à trois fois ladite épaisseur prédéterminée ; ce qui permet de conférer la résistance suffisante à cette partie dans laquelle le plastique est moins étiré, mais sans toutefois alourdir excessivement le fond ;
• en dehors du sommet du dôme correspondant à un point d'injection de la matière plastique, l'épaisseur de la partie supérieure du dôme varie dans une plage d'une à trois fois l'épaisseur minimale, afin d'éviter l'accumulation de matière plastique inutile, notamment vers le sommet ;
• le sommet du dôme comporte un téton en creux de concavité orientée vers l'extérieur, ce qui favorise l'étalement de la préforme autour de l'axe central pour mieux répartir la matière plastique sur la partie supérieure du dôme ;
• la hauteur des rainures au niveau du débouché dans le dôme est comprise entre 30 et 60% de la hauteur du dôme mesurée sur sa face extérieure, et de préférence d'environ 40% ; ce qui permet un bon compromis entre l'économie de matière, la résistance à la pression et l'aspect esthétique ;
• la zone d'appui comprend des pieds présentant en section radiale un profil arrondi de rayon de courbure nettement inférieur au rayon de courbure minimal du dôme et s'étendant circonférentiellement sur une majeure partie de la périphérie de la zone d'appui ; le faible rayon de courbure des pieds augmentant leur résistance à la force d'appui sur un support et leur longueur circonférentielle cumulée répartissant cette force de contact.

In preferred embodiments of the invention, one or more of the following provisions are also used:

• the angle formed between the direction of the bottom of the grooves and the direction tangent to the dome at the outlet is equal to 120 degrees; indeed, an angle greater than 150 degrees should not sufficiently block the top of the dome while an angle less than 90 degrees would result in a greater material use without improving the resistance to pressure;
• the bottom line of the grooves has a curved profile with a radius of curvature increasing from the skirt to the dome; so as to form a more pronounced angle at the outlet in the dome than at the outlet in the skirt;
• the minimum thickness of the upper part of the dome is equal to at least twice the predetermined thickness, and preferably about three times said predetermined thickness; which makes it possible to confer sufficient resistance to this part in which the plastic is less stretched, but without, however, excessively increasing the bottom;
• outside the top of the dome corresponding to an injection point of the plastic, the thickness of the upper part of the dome varies in a range of one to three times the minimum thickness, in order to avoid the accumulation of useless plastic material, especially towards the summit;
• the top of the dome has a recessed pint of concavity oriented outwards, which promotes the spreading of the preform around the central axis to better distribute the plastic on the upper part of the dome;
• the height of the grooves at the outlet in the dome is between 30 and 60% of the height of the dome measured on its outer face, and preferably about 40%; which allows a good compromise between economy of material, resistance to pressure and aesthetic appearance;
• the bearing zone comprises feet having in radial section a rounded profile of radius of curvature substantially smaller than the minimum radius of curvature of the dome and extending circumferentially over a major part of the periphery of the support zone; the small radius of curvature of the feet increasing their resistance to the support force on a support and their cumulative circumferential length distributing this contact force.

• une préforme standard présentant un évidement intérieur cylindrique terminé par un hémisphère ;
• un moule de forme correspondant aux dimensions extérieures d'une bouteille telle que définie ci-dessus, et dans lequel on effectue une opération de thermo-soufflage de la préforme dans le moule avec une tige d'étirage en contact avec le fond de la préforme, et caractérisé en ce que l'on ajuste les paramètres de thermo-soufflage et d'avance de la tige d'étirage de manière à obtenir une épaisseur dans la partie annulaire inférieure du dôme sensiblement égale à l'épaisseur prédéterminée du corps de la bouteille et une épaisseur minimale de la partie supérieure du dôme nettement plus importante que ladite épaisseur prédéterminée.

A bottle as defined above can advantageously be produced according to a manufacturing process in which:

• a standard preform having a cylindrical inner recess terminated by a hemisphere;
• a mold of shape corresponding to the external dimensions of a bottle as defined above, and in which an operation of thermo-blow molding of the preform in the mold with a drawing rod in contact with the bottom of the preform is carried out , and characterized in that one adjusts the parameters of thermo-blow and advance of the drawing rod so as to obtain a thickness in the lower annular portion of the dome substantially equal to the predetermined thickness of the body of the bottle and a minimum thickness of the upper part of the dome significantly larger than said predetermined thickness.

Thanks to the use of standard preform and the increasing possibilities of setting parameters of thermo-blow, it is particularly easy to switch from a production of bottles according to the invention to a conventional production, or to manage these two types of production on a site, for example to produce a natural water declined with different degrees of fizzing.

• la figure 1 est une vue partielle de face d'une bouteille réalisée selon l'invention ;
• la figure 2 est une vue de dessous de la figure 1 ;
• la figure 3 est une vue en perspective de dessous de la figure 1 et,
• la figure 4 est une vue en coupe rapportée selon la ligne IV-IV de la figure 2.

Other features and advantages of the invention will become apparent from the following description, given by way of non-limiting example, with reference to the figures in which:

• the figure 1 is a partial front view of a bottle made according to the invention;
• the figure 2 is a view from below of the figure 1 ;
• the figure 3 is a perspective view from below of the figure 1 and,
• the figure 4 is a sectional view taken along line IV-IV of the figure 2 .

In the various figures, identical references designate identical or similar elements.

To the figure 1 , is partially shown a bottle for containing a carbonated beverage. This bottle comprises a body 1 which extends longitudinally along a central vertical axis Z between an upper end connected to a neck provided with a closure system, not shown, and a lower end 1b. The lower end of the body 1b corresponds to the height of the body from which its section decreases to form a bottom 2. The body 1 has a uniform circular section, but it could comprise reliefs or grooves and consequently a section that is not constant all the way up.

As we see best at the figure 4 , the body 1 is formed by a thin wall of plastic, such as for example a polyester and more particularly PET. The body 1 has a thickness e1 subsequently called "predetermined thickness", which is relatively reduced to save the plastic material. By way of example in the embodiment shown, the predetermined thickness is 0.4 mm, but it could vary substantially depending on the internal pressure and the dimensions of the bottle. For a bottle of carbonated water with a capacity ranging between 25 c1 and 2 liters, this thickness can vary between 0.3 and 0.5 mm. It's about a body of cylindrical section with a diameter of about 75 mm, but it could be an oval or polygonal section.

The bottom 2 comprises a skirt 3 connected to the lower end 1b tangentially thereto. The skirt 3 extends downwards to a peripheral support zone 5, visible at the figure 2 , on which the bottle is intended to rest in a vertical position. The outer diameter of the skirt 3 decreases from the lower end 1b to the bearing zone 5 so that it has a diameter of about 30% less than the diameter of the body 1. This decrease is here continuous and according to the profile of a curve, which favors its resistance to pressure.

The central portion of the bottom 2 comprises a dome 7 whose apex 7a is centered on the axis Z. This dome 7 has the overall shape of a hemisphere. However, the base 7b of the dome connected to the peripheral support zone 5, takes a shape a little more curved than an ideal sphere. In any case the dome 7 has a continuous rounded profile, except possibly in a region limited to the vertex 7a as explained below, and preferably with a symmetry of revolution about the Z axis. Indeed, discontinuities or marked changes of direction in the wall of the dome would not allow it to resist the deformations and transmit the pressure supported to the bearing zone 5.

Grooves 9 extend in a radial direction relative to the central axis Z between the skirt 3 and the dome 7, so that they define between them feet 11 of the peripheral support zone 5. In the embodiment shown, these grooves 9 are six in number, but their number could be odd and vary between three and a dozen.

As can be seen on the left half-view of the figure 4 , the skirt 3 and the dome 7 are connected together by the feet 11 of the peripheral support zone 5, which have a rounded profile of radii which are much greater than the thickness of the wall in this zone and well below the radii of the curvature of the dome. Thus, each foot 11 has a rounded radial profile of constant thickness. The rounded profile of the feet 11 has a small radius of curvature, much lower than the minimum radius of curvature of the dome, which allows them to resist without deformation at higher pressures than a flat bearing area.

It will be noted that the circumferential width of the grooves 9 is constant over their radial elongation and less than the circumferential width of the feet 11 arranged between them. The set of feet 11 extends circumferentially over a major part of the periphery of the bearing zone 5 on which the weight of the bottle rests.

The cross section of the grooves 9 has the shape of a V with a rounded bottom. Consequently, it is possible to define on these grooves a bottom 9a in the form of a line represented in broken lines at Figures 1 to 3 . On either side of this bottom line 9a extend side walls (9b, 9c) of the grooves. It would be the same with grooves having a profile "U".

The bottom of each groove 9 opens into the dome 7 at a zone 9d said outlet. This outlet 9d is defined as a zone, and not a point, since each groove 9 is connected to the dome 7 by a radius of curvature connection profile r , and not a sharp angle. This of course for the purpose of not creating stress concentrations. But it will be noted that this radius of curvature r is very small, especially with respect to the radius of curvature of the rounded bottom line 9a of the grooves or the dome 7, and more than ten times less than these radii. Thus, when considering the bottom 9 of a groove and the wall of the dome 7 in this outlet area 9d, these form an angle α between them, regardless of the radius of curvature of the connection.

More specifically, the direction D of the bottom line 9a of a groove 9 forms with the tangent to the dome T, oriented towards the central axis Z, a pronounced angle α at the outlet 9d, that is to say at the ends of the radius connecting profile r connecting these zones. By "pronounced angle" is meant an angle of at least a few tens of degrees greater than a closed angle and less than a flat angle. Preferably, this angle α is between 90 degrees and 150 degrees, and preferably about 120 degrees, as in the embodiment shown.

The set of outlets 9d of the groove funds defines a virtual line 7c, represented in broken lines on the Figures 2 to 3 . This line of separation 7c delimits the dome 7 in a lower portion 15 extending to the peripheral support zone 5, and an upper portion 16 extending from this line 7c to the top 7a of the dome. The lower part 15 therefore corresponds to an annular surface into which the grooves 9 open. It will be noted that the geometric characteristics indicated are defined with respect to the external surface of the base 2, since this external surface is defined precisely by a mold, while that the inner surface is obtained by deformation under the pressure of the hot air injected during the operation of thermo-blowing, and therefore more subject to variations in geometry.

It appears that this arrangement of the grooves 9 relative to the dome 7 improves the resistance to the internal pressure of the bottom 2. It would appear that, on the one hand, the bottom of each of the grooves 9 forms a rigid spacer extending up to the periphery of the skirt 3, which would block the dome 7 radially at the separation line 7c, and thus avoid flattening the upper part 16. Such a blocking could not be obtained with funds from groove tangentially connected to the dome, or by a large radius of curvature. On the other hand the side walls (9b, 9c) form flanges substantially perpendicular to the lower part 15 of the dome and large width from their connecting line, unlike wings that would widen in the case of connected grooves tangentially to the dome. This arrangement of the grooves 9 does not increase the weight of the bottom 2 relative to the front bottom having a thick dome, but increases the resistance to the internal pressure. The ratio of pressure resistance to bottom weight is thus increased.

However, the profile of the bottom lines 9a of the grooves is not necessarily rectilinear to play this role of spacer transmitting the forces. Indeed, as in the embodiment shown, it may be advantageous to provide that the bottom lines 9a of the grooves extend longitudinally along a curved line having a radius of curvature increasing from the skirt 3 to the dome 7, that is that is analogous to the form of a comma. This allows a more tangential connection of the grooves 9 at the top of the skirt 3 where the depth of the grooves decreases. While the profile of bottom lines 9a of the grooves is closer to a straight line at the dome 7.

In addition, this arrangement of the grooves 9 may advantageously be combined with a judiciously chosen local reduction in the thickness of the dome 7 to also obtain a reduction in the weight of the bottom 2. Indeed, as can be seen in FIG. figure 4 , the lower part 15 of the dome has a thickness e15, substantially constant, which is very much lower than the average thickness of the upper part 16 of the dome, and even the minimum thickness e2 of this upper part. Thus, in addition to increasing the strength, a reduction in bottom weight can be achieved. More particularly, the thickness e15 of the lower portion 15 of the dome is substantially constant and approximately equal to the predetermined thickness e1 of the body wall.

It should be noted, however, that it is not a question of making a sudden change in thickness in the form of a circular edge at the level of the separation line. It is therefore to be understood by the thickness e15 of the lower part 15 and the minimum thickness e2 of the upper part 16 of the dome a thickness measured a little away from the separating line 7c, as indicated on FIG. figure 4 by the references e15 and e2. Nevertheless, this thickness transition is sufficiently marked to be visible to the naked eye in the form of a variation of opacity of the dome 7.

Note that the thickness of the skirt 3, but also the feet 11 of the peripheral support zone 5 and the wall of the grooves 9, is also substantially constant and equal to the predetermined thickness e1 of the body. This provision, which can be observed by a transparency beyond the separation line 7c that is almost identical to the transparency of the body, allows a substantial gain in the weight of the bottom 2 for a given pressure resistance. This gain is sensitive when the thickness e15 of the lower part 15 is at least less than twice the minimum thickness e2 of the upper part 16. A good compromise is obtained in the embodiment shown with a thickness e15 of the lower part 15 is equal to one-third of the minimum thickness e2 of the upper part 16. Or in other words, when the minimum thickness e2 of the upper part 16 of the dome 7 is approximately equal to three times the predetermined thickness e1 of the body 1.

Of course, it is possible to reduce the weight of the bottom 2 by saving the material used to form the upper part 16 of the dome, and this by limiting the maximum thickness of the upper part of the dome with respect to its minimum thickness e2. By improving the stretching and spreading of the plastic material of the preform to obtain a variation of the maximum thickness with respect to the minimum thickness e2 in a ratio of not more than 3, the weight of the upper part 16 of the dome is highly optimized. For the maximum thickness, however, it is possible to exclude the region of the apex 7a of the dome, which generally corresponds to a point of injection of the plastic into the preform centered on the Z axis, since it is almost impossible to obtain a stretch of this area.

Those skilled in the art will understand that the higher the height h of the bottom of the grooves 9 at the outlets 9d, the lower the portion of the dome 15 is extended and therefore the greater the weight gain. Nevertheless, this height can not approach the height H of the dome, measured at its vertex 7a, under penalty of forming a flat connection angle α decreasing the effect of grooves blocking and the risk of problems with the pressure resistance of the grooves 9 themselves, especially at their side face (9b, 9c). Moreover, by increasing the height h of the bottom of the grooves, their visual impact is increased. A good compromise between these requirements can be obtained with a height h of the bottom of the grooves 9 at their outlet 9d between 30 and 60% of the height H of the dome 7, and preferably about 40% as in the mode of shown embodiment.

In order to obtain a good spread of the plastic material in the upper part 16 of the dome 7, there is provided at the top 7a of the dome a hollow stud 17, concavity oriented outwardly as the dome. When the plastic material of the heat-blown preform first comes into contact with this stud 17, it undergoes a first drawing more pronounced than if it met a perfectly hemispherical dome, because of the lower radius of curvature of this stud 17. The stud 17 forms a recess relative to the rounded overall profile of the dome 7, but it does not decrease the pressure resistance of the dome 7 as a whole since the thickness of material is still important in this central zone of low stretch.

The realization of the external geometrical shapes indicated above is easily obtained by the shape of the mold in which the bottle is thermo-blown. The question of obtaining the thicknesses indicated, and more particularly the thickness transition between the lower and upper parts (15, 16) of the dome, requires more know-how and tests of the skilled person. For example, it is known to use preforms with sensitive local thickness variations to obtain thicknesses determined in certain areas by the thermo-blown bottle. But the test campaigns carried out have shown that it is quite possible to obtain the optimum thicknesses by adjusting the parameters of the operation of thermo-blowing of the bottle, while using a perfectly standard preform, it is that is, in which the interior space of the preform has the shape of a cylinder terminated by a hemisphere. As a reminder, the operation of thermo-blowing mainly consists of preheating a preform, placing it in a mold with the shapes of the bottle and of dimensions much greater than the preform, injecting a hot gas at a temperature, a pressure and a determined flow, while accompanying or even assisting the expansion of the preform with a drawing rod in contact with the bottom of the preform. These operations are performed in a more or less complex sequence and providing for a more or less significant cooling of the mold. In addition, the adjustment of these parameters during testing and production can be done accurately through an increasingly sophisticated computer control. The fact of using a standard preform has the particular advantage of simplifying the implementation of the production of bottles according to the invention, and possibly the return to a production of other types of bottle. This also allows, in addition to the economies of scale on the purchase of preforms, a simpler management of the supply and stocks on a production site where are bottled different drinks more or less carbonated, and which therefore require bottles with different pressure strengths.

The embodiment described is in no way limiting, the given geometric indications may vary substantially depending on the volume and the section of the bottle, and depending on the nature of the drink. As such, he It should be noted that the bottle produced according to the invention can be perfectly suitable for non-gaseous liquids, such as for example flat water, which can be packaged under pressure and create a very high pressure wave on the bottom in case of drop of the bottle.

Claims (10)

1. A plastic bottle comprising a body (1) extending longitudinally on a central axis (Z) from a neck to a lower end (1b) and having a predetermined thickness (e1), and a "champagne" base (2), said base comprising a skirt (3) connected to the lower end of the body and extending to a peripheral bearing zone (5), a continuously rounded dome (7) with a concavity oriented outward and extending from the peripheral bearing zone to an apex (7a) situated substantially on the central axis (Z), and grooves (9) having a bottom and extending radially between the skirt and the dome, the grooves having a longitudinal bottom line (9a) extending over the bottom of said grooves in their direction of radial extension,
   characterized in that each of the grooves (9) is connected to the dome (7) via a radius of curvature that is very slight, and in that at its end adjacent to the outlet (9d) of the bottom of the grooves (9) opening into the dome (7), the bottom line (9a) of the grooves has a direction (D) forming a pronounced angle (α) with the direction (T) tangential to the dome (7) at the outlet (9d) of the bottom of said grooves (9) in the dome (7), said pronounced angle (α) being between 90 degrees and 150 degrees.
2. The bottle as claimed in the preceding claim, wherein the angle (α) formed between the direction (D) of the bottom of the grooves (9) and the direction (T) tangential to the dome (7) at their outlet (9d) is equal to 120 degrees.
3. The bottle as claimed in claim 1 or 2, wherein the bottom line (9a) of the grooves has a curved profile with a radius that increases from the skirt (3) to the dome (7).
4. The bottle as claimed in any one of the preceding claims, wherein the grooves (9) emerge in a lower portion (15) of the dome (7) that is vertically delimited, relative to a top portion (16), by the outlet (9d) of the bottom of said grooves, and wherein the lower portion (15) of the dome has a thickness (e15) that is substantially equal to the predetermined thickness (e1), while the top portion (16) of the dome has a minimal thickness (e2) that is significantly greater than said predetermined thickness (e1).
5. The bottle as claimed in claim 4, wherein the minimal thickness (e2) of the top portion (16) of the dome is equal to at least twice the predetermined thickness (e1), and preferably approximately equal to three times said predetermined thickness.
6. The bottle as claimed in claim 4 or 5, wherein, excluding the apex (7a) of the dome corresponding to a point for injection of plastic, the thickness of the top portion (16) of the dome varies in a range from one to three times the minimal thickness (e2).
7. The bottle as claimed in any one of the preceding claims, wherein the apex (7a) of the dome comprises a hollow nipple (17) with a concavity oriented outward.
8. The bottle as claimed in any one of the preceding claims, wherein the height (h) of the grooves (9) at the outlet (9d) in the dome (7) is between 30 and 60% of the height of the dome measured on its outer face, and preferably approximately 40%.
9. The bottle as claimed in any one of the preceding claims, wherein the bearing zone (5) comprises feet (11) having, in radial section, a rounded profile with a radius of curvature that is significantly less than the minimal radius of curvature of the dome and extending circumferentially over a major portion of the periphery of the bearing zone.
10. A method of manufacturing a bottle as claimed in any one of the preceding claims, wherein the following are provided:

    - a standard preform having a cylindrical internal recess terminated by a hemisphere;

    - a mold with a shape corresponding to the external dimensions of the bottle, and

    wherein an operation of blow-molding of the preform is carried out in the mold with a stretch rod in contact with the base of the preform,
    characterized in that the parameters for blow-molding and advancing the stretch rod are adjusted so as to obtain a thickness (e15) in the lower portion (15) of the dome (7) that is substantially equal to the predetermined thickness (e1) of the body (1) of the bottle, and a minimal thickness (e2) of the top portion (16) of the dome that is significantly greater than said predetermined thickness (e1).

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