EP2051910B1 - Bottom of a hollow body obtained by blowing or stretch-blowing a preform of a thermoplastic material, and hollow body comprising such a bottom - Google Patents

Abstract

A bottom (2) of a hollow body obtained by blowing or stretch-blowing a preform of a thermoplastic material. The bottom (2) includes a transverse support surface (4) and, on either side of the transverse support surface (4), a transverse outer edge (5) and a concave inner wall with a transverse central portion (10) having a pellet (11) of a low-crystallinity material. The pellet corresponds to the injection point of the perform. The bottom (2) has reinforcing ribs (1) having an outer edge (12) adjacent to the outer edge (5) of the bottom (2) as well as an inner edge (13) adjacent to the transverse central portion (10) but not reaching the transverse central portion (10). The reinforcing ribs (1) flare from their outer edge (12) toward their inner edge (13).

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 is usually 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 blowing 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. .

Conventional bi-oriented PET containers exhibit, when they are heated to a temperature above the glass transition temperature, a large shrinkage, by stress release.

To alleviate this problem, it has long been known to carry out a heat treatment called "heat setting" treatment, in which, just after blowing of the preform and while the container is still in contact with the walls of the mold blowing, a temperature of between 120 and 250 ° C is applied to the material for a few seconds. Then the container is cooled while being kept under pressure.

This heat treatment promotes crystal growth. In the amorphous part of the bottle (in particular in the central zone of the bottom corresponding to the injection point of the preform), this heat treatment causes the growth of spherulites, this spherulitic crystallization being slow and isotropic. The material of the "pellet" becomes whitish and opaque. On the other hand, in the other parts of the bottle, which have undergone the orientation, the heat treatment increases the crystallinity without formation of spherulites, and without modifying the transparency of the material.

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 stretched that the body of the containers, so that this 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, the thermo-hardened PET obtained is thus no longer translucent at all. 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 under load palletized and stacked. So that, except for placement of inserts, the bottom 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).

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.

It has been proposed to make the containers with petaloid bottoms. The bottom wall is then generally convex outward and has feet, typically four to six feet formed by excrescences regularly distributed on the bottom, and separated in pairs 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" ribbed 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 a central portion unstretched 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 end limit of the unstretched central portion. 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.

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.

The invention relates, in a first aspect, to a body base with the features of claim 1.

• les nervures de renfort n'atteignent pas le bord externe du fond ;
• au moins une nervure présente un plan de symétrie vertical ;
• les deux ailes latérales de chaque nervure pourvue d'un plan de symétrie sont sensiblement en regard l'une de l'autre en partie extrême distale de ces nervures, et notamment au voisinage de leur bord extérieur ;
• la pastille de matériau à faible cristallinité est en saillie en face externe dans la partie centrale transversale. Cette disposition assure un écartement entre les nervures de renfort et cette pastille ;
• le bord externe est placé à une hauteur h5 par rapport à la surface d'appui transversale, la partie centrale transversale étant placée à une hauteur h10 par rapport à la surface d'appui transversale ;

According to various embodiments, the hollow body bottom has the following characteristics, if necessary combined:

• the reinforcing ribs do not reach the outer edge of the bottom;
• at least one rib has a vertical plane of symmetry;
• the two lateral wings of each rib provided with a plane of symmetry are substantially facing each other at the distal end portion of these ribs, and in particular in the vicinity of their outer edge;
• the pellet of low crystallinity material is projecting on the outer face in the transverse central part. This arrangement ensures a spacing between the reinforcing ribs and this pellet;
• the outer edge is placed at a height h5 with respect to the transverse bearing surface, the transverse central portion being placed at a height h10 with respect to the transverse bearing surface;

In an advantageous embodiment, with the exception of the reinforcing ribs, 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 an advantageous embodiment, the 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 annular shape. Starting from this annular surface and moving towards the axis of revolution, the bottom preferably has first an annular step, then a substantially parabolic profile connecting this step to the central transverse portion.

The invention relates, in a second aspect to a hollow body of thermoplastic material, in particular polyester such as PET, obtained by blow molding or stretch blow molding of a preform, this hollow body 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 emerge during the following description of embodiments, given by way of non-limiting 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 .

With the exception of six radial reinforcing ribs 1, the bottom 2 is in the form of a body of revolution about an axis 3 substantially perpendicular to its transverse support surface 4.

For this reason and for simplicity, the bottom 2 will first be described in isolation from the radial ribs 1, these radial ribs 1 being then described in detail.

The bottom 2 will be described starting from its outer edge 5 and going radially towards the axis 3 of revolution.

The outer edge 5 is transverse and substantially corresponds to the junction between the bottom 2 and the side wall of the container (not shown). This outer edge 5 is placed at a height h5 relative to the transverse bearing surface 4 of the bottom 2 (and the bottle comprising the bottom 2, when the bottle is stored standing).

Between the outer edge 5 and the transverse support surface 4, the bottom has in vertical radial section a substantially parabolic profile. In the vicinity of the outer edge 5, this profile 6 is substantially tangential to a direction 7 perpendicular to the transverse bearing surface 4. In the vicinity of the transverse bearing surface 4, this profile 6 is substantially tangential to the transverse bearing surface 4. The profile 6 thus provides a solution of continuity, without rupture of curvature, between the side wall of the container (not shown) and the transverse bearing surface 4.

The bottom 2 has a transverse bearing surface 4 of annular shape. Starting from this transverse bearing surface 4 and moving towards the axis 3 of revolution, the bottom 2 has an annular step 8 of width (measured radially) substantially equal to the width of the annular transverse bearing surface 4. 8 annular step allows the deformation of the bottom 2 in the manner of a bellows, under the effect of an overpressure or vacuum in the hollow body provided with such a bottom.

Starting from this annular step 8 and going towards the axis 3 of revolution, the bottom 2 then has, in vertical radial section, a substantially parabolic profile 9 and then a transverse central portion 10.

The transverse central portion 10 is placed at a height h 10 relative to the transverse bearing surface 4, this height h10 being greater than that h5 of the outer edge 5.

An axial pellet 11 protrudes into the transverse central portion 10, this pellet 11 axially projecting downwards, that is to say the outside of the container provided with the bottom 2.

The radial reinforcing ribs will now be described.

These radial ribs 1 have an outer edge 12 coming close to the outer edge 5 of the bottom 2. As illustrated, preferably, the outer edge 12 of the radial ribs 1 does not reach this outer edge 5 of the bottom 2, although this is perfectly conceivable and does not change the qualities of the background; it is even possible to alternate ribs reaching the outer edge and others not.

These radial ribs 1 have an inner edge 13 coming close to the transverse central portion 10, but without reaching this transverse central portion 10.

Each radial rib 1 comprises a bottom wall 14 and a flange 15, 16 on either side of this bottom wall 14. The bottom wall 14 is substantially constant width over the entire rib length. Sectional view, each radial rib 1 has a plane 17 of radial vertical symmetry and the bottom wall 14 has a substantially identical contour to that formed by the profile 6, the transverse bearing surface 4, and the profile 9. In view in FIG. a plane perpendicular to its curvature, the bottom wall 14 is substantially flat or slightly curved.

The two lateral wings 15, 16 are substantially facing one another at the distal end of the ribs, and in particular in the vicinity of their outer edge 12.

The two wings 15, 16 laterals deviate from one another and the ribs flare more and more as one approaches the axis 3 of revolution. In the vicinity of their inner edge 13, the reinforcement ribs 1 thus have a very open U-shaped section, when these reinforcing ribs 1 are seen in a plane perpendicular to their bottom wall 14.

The radial ribs 1 thus come to bear against a central chimney 18 in the center of which protrudes, downwards, the pellet 11, this central chimney 18 being limited upwards by the transverse central portion 10.

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 18 is particularly well reinforced with respect to creep or slump by the presence of reinforcement ribs 1 flaring from their distal end (where these ribs have a U-shaped section with substantially parallel and short flanges ) to their proximal end (where these ribs have a very open U-section with longer, curved wings).

A bottle comprising a bottom according to the invention also has good impact resistance on the lower part of the side wall, the ribs projecting over this lower part. The bottom absorbs shocks perfectly and is able to recover "naturally" its initial shape after deformation.

In the embodiment shown, the ribs 1 of reinforcement are six 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.

Claims (12)

1. Bottom (2) of a hollow body obtained by blowing or stretch-blowing a preform made of thermoplastic material, said bottom (2) comprising a transverse support surface (4) and, on either side of said transverse support surface (4):

   - a transverse external edge (5);

   - a concave internal wall with a transverse central portion (10) comprising a pellet (11) of a low-crystallinity material, said pellet (11) corresponding to the injection point of the preform;

   said bottom (2) comprising reinforcing ribs (1) having an outer edge (12) adjacent to the external edge (5) of the bottom (2), said reinforcing ribs (1) having an inner edge (13) adjacent to the transverse central portion (10) but not reaching said transverse central portion (10), characterized in that the reinforcing ribs (1) flare from their outer edge (12) toward their inner edge (13), characterized in that the reinforcing ribs (1) have a bottom wall (14) having a substantially constant width over the entire length of said ribs (1).
2. Bottom of a hollow body according to claim 1, characterized in that the outer edge (12) of the reinforcing ribs (1) does not reach the external edge (5).
3. Bottom of a hollow body according to one of claims 1 to 2, characterized in that at least one rib (1) has a vertical plane of symmetry (17).
4. Bottom of a hollow body according to claim 3, characterized in that the two lateral wings (15, 16) of each reinforcing rib (1) provided with a plane of symmetry are substantially facing one another in the distal end portion of the ribs (1), and particularly in the vicinity of the outer edge (12).
5. Bottom of a hollow body according to any of claims 1 to 4, characterized in that the pellet (11) made of a low-crystallinity material projects at the external surface in the transverse central portion (10).
6. Bottom of a hollow body according to any of claims 1 to 5, characterized in that the external edge (5) is placed at a height h5 with respect to the transverse support surface (4), the transverse central portion (10) being placed at a height h10 with respect to the transverse support surface (4).
7. Bottom of a hollow body according to any of the previous claims, characterized in that, with the exception of the reinforcing ribs (1), the bottom (2) is in the form of a rotating member about an axis (3) that is substantially perpendicular to its transverse support surface (4).
8. Bottom of a hollow body according to claim 7, characterized in that it has, at a vertical radial cross-section, between the external edge (5) and the transverse support surface (4), a profile which is:

   - in the vicinity of the external edge (5), substantially tangent to a direction (7) that is perpendicular to the transverse support surface (4),

   - in the vicinity of the transverse support surface (4), substantially tangent to said transverse support surface (4).
9. Bottom of a hollow body according to claim 8, characterized in that it has, in vertical radial cross-section, between the external edge (5) and the transverse support surface (4), a substantially parabolic profile (6).
10. Bottom of a hollow body according to claim 8 or 9, characterized in that it has a transverse support surface (4) having an annular shape.
11. Bottom of a hollow body according to claim 10, characterized in that, starting from said transverse support surface (4) having an annular shape and in the direction of the axis (3) of revolution, the bottom (2) first has an annular step (8), then a substantially parabolic profile (9) connecting said step (8) to the transverse central portion (10).
12. Hollow body made of thermoplastic material, particularly polyester such as PET, obtained by blowing or stretch-blowing a preform, the hollow body comprising a lateral wall and a bottom connected to the lateral wall, characterized in that said bottom is such as presented in any of the previous claims.

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