EP2084070B1 - Bottom of hollow body obtained by blowing or drawing-blowing of a preform - Google Patents

Abstract

Bottom (3) of hollow body obtained by blowing or drawing-blowing a preform made of thermoplastic material, said bottom (3) comprising a transversal support surface (5), and on either side of said transversal support surface (5) a transversal external edge (6), a concave internal wall with a transversal central part (11) containing a patch (12) made of material of low crystallinity, said patch (12) corresponding to the injection point of the preform; said bottom comprising a peripheral zone around the transversal support surface provided with notches (2) the extreme distal part (23) of which comes near to but does not reach the external edge (6) of the bottom (3), the extreme proximal part (24) of the notches coming in close proximity to the transversal support surface (5).

Description

The invention relates to the technical field of hollow bodies made of thermoplastic material, in particular containers such as pots or bottles.

The invention relates more particularly to hollow bodies obtained by blowing or stretching then blowing a preform injected with thermoplastic material (injection blow molding).

In recent years, the manufacture of plastic containers from pre-injected preforms has grown considerably, especially thanks to the use of polyethylene terephthalate (PET).

Meanwhile, other materials have been envisaged and / or used with more or less success such as, by way of non-limiting examples, polyethylene naphthalate (PEN), polypropylene (PP), polyacrylonitrile (PAN) or mixtures or overlays of various materials.

There remains, in the center of the bottom of the hollow body, a very low crystallinity zone called "pellet" resulting from a portion of the preform that is only very slightly stretched during blow molding or stretch blow molding. The longitudinal axis of the preform corresponds to that of the final container. As a result, during blow molding or stretch blow molding, the stretching of PET is almost zero in the center of the bottom of the container, and increases as one approaches the side wall of the container. .

Whatever their manufacturing process, thermoplastic containers must have good resistance of their bottom.

The bi-oriented PET has good mechanical and thermal resistance. But, as has been said above, the bottom of the containers is much less stretched than the body of the containers, so that the bottom has mechanical and thermal resistance lower than those of the body.

The same problem exists for the collar. The heat treatment of the necks makes it possible to increase their crystallinity. But the heat treatment of the necks (in amorphous PET) leads to isothermal crystallization forming spherulites, thermo hardened PET obtained is therefore no longer translucent. If it is acceptable that the necks of bottles, relatively thick, are not translucent, a bottom of translucent bottle would harm the presentation of the packaged product.

The bottom of the container must withstand shocks, for example when the full container falls.

The container bottom must withstand the internal pressure, especially when the container contains a carbonated beverage. An internal overpressure may result from an increase in the storage temperature of the full bottles and / or the withdrawal of the plastic material from these bottles, this withdrawal generally occurring within two or three weeks of their manufacture and filling.

The bottles are transported in palletized loads and stacked. So that, except for placement of inserts, bottoms of the bottles of the upper layers rest on the caps of the lower bottles and are subject to stresses of depression and punching.

Any deformation of the bottom of the container affects the aesthetics of the product and the stability of the container stored upright.

The container bottom must resist creep.

The container as a whole, and in particular its bottom, must withstand the relatively severe thermal conditions encountered during hot filling or pasteurization.

When hot filling with a liquid at a temperature of at most 94 ° C, the bottom must have a relative aptitude for deformation. It is the same during the subsequent cooling, the bottom having to withstand the vacuum (vacuum compensation).

Pasteurization is carried out for certain flat liquids (non-carbonated fruit juices) or gaseous liquors (beer). During pasteurization, the liquid contained in the closed container may be carried for example at a temperature of between 60 and 80 ° C for about 20 minutes to 2 hours, the temperature being a function of the CO2 content. When the liquid to be pasteurized contains dissolved gas under pressure (carbonated beverage, beer), the bottom material of the container must not only withstand the increase in volume of the hot liquid, but also the increase of the pressure of the hot gas. During cooling, the pasteurized liquid reduces volume, the bottom of the container must also withstand this constraint.

It has been found that some containers have a bottom subject to sag during hot filling. This sinking of the bottom, outwardly, especially in the connection zone between the side wall of the container and the bottom, does not occur regularly around the container. So that the container becomes unstable. This collapse can come from a release of the stresses induced during the final blow of the hot shrunk blank.

Any deformation of the bottom of the container affects the aesthetics of the product and the stability of the container stored upright.

The bottom of the containers must sometimes withstand cleaning agents in the case of reusable containers.

Containers with a thick bottom are also known. In particular, it has been proposed to produce curved bottoms with an inwardly convexity called "champagne" bottoms, the thickness of the convex zone being greater than that of the lateral wall of the container, for example four times larger. . The so-called "champagne" funds offer the advantage of allowing a continuous annular support zone for the standing stored bottle, including a remarkably stable seat. This solution is not satisfactory, the cost of the material forming the container being a preponderant part of the cost price. Between 1979 and 1992, the weight of a PET bottle with a capacity of 2 liters increased from 65 g to 52 g and there is a constant demand for bottles both light and resistant. In addition, the background "champagne" can lose its shape under the action of temperature. Cracks may occur between areas of different thicknesses, specific means to be provided in the molds to cool faster thick areas.

It has been proposed to make the containers with petaloid bottoms. The bottom wall is then generally convex outward and comprises feet, typically four to six feet formed by regularly distributed growths on the bottom, and separated two by two by a portion of the convex bottom wall. These petaloid bottoms are widely used for containers containing carbonated beverages. The radial recesses separating the feet absorb the forces due to the pressurization during filling and maintain the bearing surfaces of the feet in a plane substantially perpendicular to the axis of the container. This solution is not always satisfactory. Under the effect of internal pressure, the petaloid bottoms may burst. The petaloid bottoms can not always withstand the overpressure due to the increase in volume of the contents of the bottle, during a pasteurization.

It has also been proposed to produce bottles with a grooved bottom, where appropriate of the "champagne" rib type. The document FR 2,717,443 describes a bottle in which the ribs depart from the periphery of the bottom and end at the outer limit of a substantially flat annular zone surrounding an amorphous concave central portion. The document FR 2,753,435 of the applicant describes a container whose bottom comprises an undrawn central portion and a peripheral portion connecting the central portion to the side wall of the container, the bottom being provided with ribs extending from the side wall to the theoretical extreme limit from the unstretched central part. This theoretical extreme limit takes into account the slight fluctuations in the shape and dimensions of the central part of the bottom (pellet), from one bottle to another of the same series. No rib ends in the amorphous part.

The document EP 1 099 638 A discloses a hollow body bottom according to the preamble of claim 1.

It turns out that if the funds of the prior art solve only some of the problems posed, none is able, after a fall and a subsequent deformation, to recover its original shape, whether it is filled or not.

The aim of the invention is to provide a new bottle bottom structure whose set of individual characteristics makes it possible to obtain a resistance greater than that of most of the funds currently known, and enables it to recover "naturally" its shape after a constraint. (fall or other) having caused its deformation.

At identical wall thickness, a bottom according to the invention will be more resistant than most previously known bottoms bottoms.

A desired strength, a bottom according to the invention can be made with a material thickness less than most funds previously known.

The invention also aims to provide a bottle having good resistance to hot filling and good resistance to pasteurization.

• un bord externe transversal ;
• une paroi interne concave avec une partie centrale transversale contenant une pastille de matériau à faible cristallinité, cette pastille correspondant au point d'injection de la préforme ;

ce fond de corps creux comprenant une zone périphérique autour de la surface d'appui transversale pourvue d'encoches dont la partie extrême distale vient au voisinage mais n'atteint pas le bord externe du fond, la partie extrême proximale des encoches venant en tangence de la surface d'appui transversal.According to a first aspect, the invention relates to a bottom of a hollow body obtained by blow-molding or stretch-blow molding of a preform made of thermoplastic material, this bottom comprising a transverse bearing surface, and on either side of this transversal support surface:

• a transverse outer edge;
• a concave inner wall with a transverse central portion containing a pellet of low crystallinity material, this pellet corresponding to the injection point of the preform;

this hollow body bottom comprising a peripheral zone around the transverse support surface provided with notches whose distal end portion comes in the vicinity but does not reach the outer edge of the bottom, the proximal end portion of the notches coming in tangency of the transverse support surface.

• la partie extrême proximale des encoches ne débouche pas dans la surface d'appui transversal ;
• les encoches comprennent une paroi de fond et deux ailes latérales et présentent un plan de symétrie ;
• la largeur des encoches est comprise entre 2 et 20 millimètres environ ;
• la profondeur de ces encoches est comprise entre 1 et 5 millimètres environ ;
• la pastille de matériau à faible cristallinité est en saillie en face externe dans la partie centrale transversale ;
• le bord externe est placé à une hauteur h6 par rapport à la surface d'appui transversale, la partie centrale transversale étant placée à une hauteur h11 par rapport à la surface d'appui transversale.

In various embodiments, the background has the following characters, if any combined:

• the proximal end portion of the notches does not open into the transverse bearing surface;
• the notches comprise a bottom wall and two lateral wings and have a plane of symmetry;
• the width of the notches is between 2 and 20 millimeters approximately;
• the depth of these notches is between 1 and 5 millimeters approximately;
• the pellet of low crystallinity material is projecting on the outer face in the transverse central portion;
• the outer edge is placed at a height h6 with respect to the transverse bearing surface, the transverse central portion being placed at a height h11 with respect to the transverse bearing surface.

In an advantageous embodiment, the bottom is in the form of a body of revolution about an axis substantially perpendicular to its transverse bearing surface.

• au voisinage du bord externe, sensiblement tangent à une direction perpendiculaire à la surface d'appui transversale,
• au voisinage de la surface d'appui transversale, sensiblement tangent à cette surface d'appui transversale.

In a particular embodiment, the hollow body bottom has, in vertical radial section, between the outer edge and the transverse bearing surface, a profile which is:

• in the vicinity of the outer edge, substantially tangent to a direction perpendicular to the transverse bearing surface,
• in the vicinity of the transverse bearing surface, substantially tangential to the transverse bearing surface.

Advantageously, the bottom has, in vertical radial section, between the outer edge and the transverse support surface, a substantially parabolic profile.

Advantageously, the bottom has a transverse bearing surface of continuous annular shape, no groove or notch opening into this seating surface.

In one embodiment, starting from the annular seating surface and moving towards the axis of revolution, the bottom presents first an annular step, then a concave profile connecting this step to the transverse central portion.

In one embodiment this bottom comprises reinforcement ribs having an outer edge coming close to the transverse bearing surface, these reinforcing ribs having an inner edge coming close to the transverse central portion, but without reaching this transverse central portion; the reinforcing ribs do not reach the transverse bearing surface.

The invention relates, according to a second aspect, to hollow bodies of thermoplastic material, in particular polyester such as PET, obtained by blow molding or stretch blow molding of a preform, these hollow bodies comprising a side wall and a bottom connected to this side wall. said bottom being as presented above.

• la figure 1 est une vue de dessous d'un fond de corps creux tel que par exemple une bouteille, selon un mode de réalisation de l'invention ;
• la figure 2 est une vue latérale du fond représenté en figure 1 ;
• la figure 3 est une vue en perspective du fond représenté en figures 1 et 2.

Other objects and advantages of the invention will become apparent in the course of the following description of embodiments given by way of non-exclusive examples. this description being made in the light of the appended drawings, in which:

• the figure 1 is a bottom view of a hollow body bottom such as for example a bottle, according to one embodiment of the invention;
• the figure 2 is a side view of the bottom represented in figure 1 ;
• the figure 3 is a perspective view of the bottom represented in Figures 1 and 2 .

The bottom 3 is in the form of a body of revolution about an axis 4 substantially perpendicular to its transverse support surface 5, which is provided essentially with notches 2 (ten notches in the example) near the its outer edge 6, and can be completed at its center by a structure with radial ribs 1.

For this reason, the bottom 3 will be described starting from its outer edge 6 and going radially towards the axis 4 of revolution.

The outer edge 6 is transverse and substantially corresponds to the junction between the bottom 3 and the side wall of the container (not shown). This outer edge 6 is placed at a height h6 relative to the transverse support surface 5 of the bottom 3 (and the bottle comprising the bottom 3, when the bottle is stored upright).

Between the outer edge 6 and the transverse bearing surface 5, the bottom 3 has in vertical radial section a substantially parabolic profile 7. In the vicinity of the outer edge 6, this profile 7 is substantially tangential to a direction 8 perpendicular to the transverse bearing surface 5. In the vicinity of the transverse support surface 5, this profile 7 is substantially tangent to this transverse support surface 5. The profile 7 thus provides a solution of continuity, without breaking bending, between the side wall of the container (not shown) and the surface 5 of transverse support.

The bottom 3 has a transverse support surface 5 of annular and continuous shape. Starting from this annular surface and going towards the axis 4 of revolution, the bottom 3 has an annular step 9 of width (measured radially) substantially equal to the width of the annular surface 5 of transverse support. This annular step 9 allows deformation bottom 3 in the manner of a bellows, under the effect of an overpressure or a vacuum in the hollow body provided with such a bottom.

Starting from this annular step 9 and going towards the axis 4 of revolution, the bottom 3 then has, in vertical radial section, a substantially parabolic profile 10 and then a transverse central portion 11.

The transverse central portion 11 is placed at a height h11 with respect to the transverse support surface 5, this height h11 being any relative to that h6 of the outer edge 6.

An axial pellet 12 protrudes into the transverse central portion 11, this pellet 12 axial projecting downwards, that is to say the outside of the container provided with the bottom 3.

The notches 2, which constitute the soul of the present invention, will now be described.

These notches 2 extend radially. They comprise a bottom wall 20 and two lateral wings 21, 22. Each notch has a radial vertical plane of symmetry. The distal end portion 23 of these notches comes in the vicinity but does not reach the extreme edge 6 of the bottom 3. These notches and have an output close to the vertical but away from the joint plane. Preferably, the proximal end portion 24 of the notches comes close to the seat but does not open into this seat. The width of the notches is typically between 2 and 20 millimeters. The depth of these notches varies according to the capacity of the bottle, and is typically 1.5 millimeters for a bottle of 0.5 liters (3 to 4 millimeters for a bottle of 1.5 liters).

The proximal end portion 24 of the notches comes in tangency of the seat without opening in this seat.

The reinforcing ribs 1 which, in some implementations can complete the notches will now be described.

These reinforcing ribs 1 have an outer edge 13 coming close to the annular step 9 of the bottom 3, but without reaching this annular step 9.

In the illustrated example, these ribs 1 have an inner edge 14 coming close to the transverse central portion 11, but without reaching this transverse central portion 11.

However, it is conceivable that the inner edge 14 of the ribs 1 reaches or even opens into this transverse central portion 11.

Each rib 1 comprises a bottom wall 15 and a flange 16, 17 on either side of the bottom wall 15. The bottom wall 15 is of decreasing width from the outer edge 13 to the inner edge 14 of the rib. As shown in the figures, the bottom wall 15 of a rib does not have a constant curvature over the entire radial length of this rib. In the vicinity of their outer edge 13, the ribs 1 form a more acute angle with the vertical than in the vicinity of their inner edge 14.

Each rib 1 has a vertical plane of symmetry 18 radial.

The ribs 1 come to lean against a central chimney 19 in the center of which protrudes, downwards, the pellet 12, this central chimney 19 being limited upwards by the transverse central portion 11.

The set of individual characteristics of the bottom of the bottle makes it possible to obtain a resistance greater than that of most currently known funds. At identical wall thickness, a bottom according to the invention will be more resistant than most previously known bottoms bottoms. A desired strength, a bottom according to the invention can be made with a material thickness less than most funds previously known.

A bottle comprising a bottom according to the invention has a good resistance to hot filling and good resistance to pasteurization. The central chimney 19 is particularly well reinforced with respect to creep or slump by the presence of reinforcing ribs 1.

A bottle comprising a bottom according to the invention also has good impact resistance on the lower part of the side wall. The presence of the notches reduces the risk of plastic deformation of the bottle in the connection area between the side wall of a container and its seat. The bottom absorbs shocks perfectly and is able to recover "naturally" its initial shape after deformation.

The shape of the bottle bottom allows a reduction of the weight of material and this without weakening the seat or reduce the seating surface compared to conventional bottoms, while maintaining a good resistance to hot filling (vacuum effects when cooling) and shocks. As an indication, a conventional hot-fill bottle of 32 g can be made with 26 g of PET only, using a bottom according to the invention.

In the embodiment shown, the ribs 1 of reinforcement are five in number and substantially identical and equidistant. In other embodiments, the reinforcing ribs are more or less numerous, in particular to take into account the diameter of the bottom. The reinforcing ribs may be of different sizes, a first series may have a bottom wall narrower than the bottom wall of a second series of ribs.

In the embodiment shown, the notches are ten in number and substantially identical and equidistant. In other embodiments, not shown, the ribs extending along radii disposed at mid-distances from adjacent slot locations. By this arrangement, the ribs and notches cooperate best with the reinforcement of the bottom of the hollow body.

Claims (15)

1. Hollow-body bottom (3) obtained by blow moulding or stretch blow moulding a thermoplastic preform, this bottom (3) comprising a transverse support surface (5) and on either side of this transverse support surface (5) :

   - a transverse outer edge (6);

   - a concave inner wall having a transverse central part (11) containing a pellet (12) made of a low-crystallinity material, this pellet (12) corresponding to the point of injection of the preform;

   the bottom (3) comprising around the transverse support surface a peripheral region provided with notches (2), the distal end part (23) of which comes close to but does not reach the outer edge (6) of the bottom (3), characterized in that the proximal end part (24) of the notches comes into tangency with the transverse support surface (5).
2. Hollow-body bottom according to Claim 1, characterized in that the notches (2) comprise a bottom wall (20) and two side wings (21, 22) and have a plane of symmetry.
3. Hollow-body bottom according to Claim 1, characterized in that the proximal end part (24) of the notches does not open into the transverse support surface (5).
4. Hollow-body bottom according to one of Claims 1 to 3, characterized in that the width of the notches is between about 2 and 20 millimetres.
5. Hollow-body bottom according to Claim 4, characterized in that the depth of these notches is between about 1 and 5 millimetres.
6. Hollow-body bottom according to any one of Claims 1 to 5, characterized in that the pellet (12) of low-crystallinity material protrudes from the outer face in the transverse central part (11).
7. Hollow-body bottom according to any one of Claims 1 to 6, characterized in that the outer edge (6) is positioned at a height h6 with respect to the transverse support surface (5), the transverse central part (11) being positioned at a height h11 with respect to the transverse support surface (5).
8. Hollow-body bottom according to any one of the preceding claims, characterized in that it is in the form of a body of revolution about an axis (4) approximately perpendicular to its transverse support surface (5).
9. Hollow-body bottom according to Claim 8, characterized in that, in vertical radial section, between the outer edge (6) and the transverse support surface (5), it has a profile which:

   - near the outer edge (6) is approximately tangent to a direction (8) perpendicular to the transverse support surface (5),

   - near the transverse support surface (5) is approximately tangent to this transverse support surface.
10. Hollow-body bottom according to Claim 9, characterized in that, in vertical radial section, between the outer edge (6) and the transverse support surface (5), it has an approximately parabolic profile (7).
11. Hollow-body bottom according to Claim 9 or 10, characterized in that it has a transverse support surface (5) having a continuous annular form.
12. Hollow-body bottom according to Claim 11, characterized in that, starting from this transverse support surface (5) and in the direction of the axis (4) of revolution, the bottom (2) firstly has an annular step (9), and then a parabolic profile (10) connecting this annular step (9) to the transverse central part (11).
13. Hollow-body bottom according to one of Claims 1 to 12, characterized in that it comprises reinforcing ribs (1) having an outer edge (13) coming close to the transverse support surface (5), these reinforcing ribs (1) having an inner edge (14) coming close to the transverse central part (11) but without reaching this transverse central part (11).
14. Hollow-body bottom according to Claim 13, characterized in that the reinforcing ribs (1) do not reach the transverse support surface (5).
15. Hollow body made of thermoplastic, in particular polyester, such as PET, obtained by blow moulding or stretch blow moulding a preform, this hollow body comprising a side wall and a bottom attached to this side wall, characterized in that said bottom is as presented in any one of the preceding claims.

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