EP4110571A1

EP4110571A1 - Container preform made of plastic

Info

Publication number: EP4110571A1
Application number: EP21705573.0A
Authority: EP
Inventors: Christophe Bunel
Original assignee: Sidel Participations SAS
Current assignee: Sidel Participations SAS
Priority date: 2020-02-25
Filing date: 2021-02-22
Publication date: 2023-01-04
Also published as: WO2021170533A1; FR3107468B1; US20230101346A1; FR3107468A1

Abstract

The invention relates to a container preform (1) made of plastic, comprising: - a symmetrical body (3) rotating about a central axis (X); - a base (4) closing the body (3) from one of its ends, the base (4) having an annular bead (8) forming a laying plane of the preform (1), the base (4) having an outer skin oriented towards the outside of the preform (1) and an inner skin oriented towards the inside of the preform (1), characterised in that at least one of the inner skin and the outer skin has, radially from the central axis (X) to the annular bead (8), a profile having a broken curvature.

Description

Title: Plastic container preform

The field of the invention is that of the design and manufacture of plastic containers.

More specifically, the invention relates to a plastic container preform.

Conventionally, a plastic container is obtained by blow molding or stretch blow molding of a preform within a mold in the cavity of the container.

Prior to its blow molding or its stretch blow molding, the preform is heated until its constituent material reaches or exceeds its glass transition temperature. For example, in the case where the container is made of polyethylene terephthalate, the glass transition temperature is between 75 ° C and 80 ° C.

A preform usually includes:

- a body, of substantially cylindrical shape of revolution about a central axis;

a neck, which extends in the extension of the body from a first end thereof, the neck being separated from the body by a collar;

- a bottom, which closes the body at a second end thereof.

By analogy, at the end of the formation of the container:

- the body of the preform becomes the body of the container;

- the neck of the preform remains unchanged during the container forming process;

- the bottom of the preform becomes the bottom of the container.

Whatever the shape of the bottom of the container to be formed, the vast majority of preforms have a convex bottom, hemispherical in shape or more generally convex outward.

However, the great majority of the receptacles have a concave bottom.

It is therefore understood that, during forming, the bottom material must, from a convex profile, turn around to adopt a concave profile.

This reversal induces stresses in the material which can generate microcracks. A relaxation of the blowing constraints (pressure drop) takes place when the formed container is extracted from the mold, tending to cause the bottom of the container to unwind, that is to say its collapse.

Such microcracks are liable to propagate when the container is pressurized, but also when the container is in contact with chemicals such as lubricants which may be found on the conveyor lines existing between two container processing stations.

Cases of rupture of the bottoms of receptacles have even been observed in certain types of funds (ruptures occur in particular in the bottoms of certain receptacles with a petaloid bottom, provided with alternating protruding feet and recessed valleys and intended for drinks. carbonate).

The risk of cracking (and breakage) may be aggravated by the market trend, in search of material savings and reduction of polluting emissions, which tends to impose a reduction in the weight of the preforms, and therefore in the thickness of the preforms. walls of the preforms.

This risk is also aggravated by the increase in production rates (several tens of thousands of containers produced per hour and per machine), which forces a reduction in the individual manufacturing cycle time of a container.

Another factor that can aggravate this risk is the reduction in preform injection cycle times. In fact, this reduction in cycle times results in a large number of residual stresses in the preforms. These stresses, which are released when the container is formed, can cause the bottom of the container to unwind as mentioned above.

The decrease in the individual manufacturing cycle time results in a reduction in the contact time of the container with the mold, and therefore less cooling of the container in the mold.

In addition, certain plastics (this is notably the case of PET, which is widely used in the manufacture of containers) have a "shape memory": in fact, during blowing or stretch-blow molding, these materials undergo changes. internal stresses which tend to relax if the temperature is still too high while the internal pressure has fallen in the container. The relaxation causes a form of axial and radial narrowing of the vessels, which in some way kind, tend to return to their initial shape, namely that of the preform. In fact, the shrinkage ceases quickly after exiting the mold, due to cooling, and a container cannot regain the shape of a preform after stress relieving.

More particularly, for the formed containers, this memory effect induces on the one hand unwanted deformations on the bottoms of the containers, which then become unstable on the laying planes, and on the other hand a reduction in their mechanical strength. The reduction in mechanical strength is for example due to the sagging of the bottom of the container which can cause micro cracks which may subsequently weaken the containers under the effect of mechanical (pressure) or chemical (lubricants) stresses.

An example of unwanted deformation is a sagging of the bottom of the container. In this case, after the manufacture of the container, the concave bottom of the deformed container has an arch of a lower height than expected. Indeed, due to insufficient cooling of the container, and more specifically of the lower part of the container, the concave bottom of the container collapses when it comes out of the mold.

The aim of the invention is in particular to overcome the drawbacks of the prior art.

More precisely, the object of the invention is to provide a preform which makes it possible to obtain containers in which the deformation of the bottom at the exit of the mold is eliminated or, at the very least, limited.

The invention also aims to provide such a preform which makes it possible to obtain containers whose bottoms have sufficient structural mechanical characteristics to withstand the various pressures and / or stresses to which it is subjected.

The invention further aims to provide such a preform which makes it possible to increase the production rates of containers which comply with the desired aesthetic and mechanical criteria.

These objectives, as well as others which will appear subsequently, are achieved by virtue of the invention, which relates to a plastic container preform, comprising: - a symmetrical body of revolution around a central axis;

- a bottom closing the body from one of its ends, the bottom having an annular bead forming a laying plane of the preform, the bottom having an outer skin oriented towards the outside of the preform and an inner skin oriented towards the inside of the preform, characterized in that at least one of the internal skin and of the external skin has, radially from the central axis to the annular bead, a profile having a break in curvature.

By breaking the curvature, the sagging of the bottom of the container, once formed, is limited or even eliminated.

Indeed, the break in curvature of the preform is preserved during the blowing or stretch-blow molding of the container, on the bottom of the formed container.

The break in curvature thus forms a stop to the unwinding of the arch towards the outside of the container. This is further explained by the memory effect offered by PET on the one hand and by the shape geometry of the curvature break on the other hand.

Thus, if the bottom of the container is not cooled enough and the bottom tends to sag, this sag is limited by the break in curvature which forms a mechanical and physical barrier.

The container formed from the preform therefore retains all of its aesthetic and mechanical qualities for use.

Another major advantage is to allow better centering of the preforms during a step of stretching and blowing the preform.

Indeed, a drawing rod can easily come to take position in the bottom of the preform (if necessary via a specific design to cooperate with the bead) and / or the preform can be suitably positioned on a mold base.

Advantageously, the profile comprises, from the central axis to the annular bead:

- a first portion having a first radius of curvature;

- a second portion extending the first portion and having a second radius of curvature;

- a third portion extending the second portion and having a third radius of curvature, the break in curvature being formed by the second radius of curvature presented by the second portion.

These three portions make it possible to clearly mark, visually but also mechanically, the presence of the break in curvature. In the absence of the second portion, the break in curvature would not be marked and the container formed from a preform lacking this second portion would present a greater risk of its bottom collapsing.

Preferably, the second radius is less than 9 mm.

Such a value of the second radius makes it possible to achieve the breaking of curvature in a straightforward manner. A value greater than 9 mm presents a major risk of forming a continuity with the first portion or the third portion, which would promote sagging of the bottom formed.

According to a preferred embodiment, the first portion of the profile has a flat, concave or convex shape.

Thus, the preform can be adapted depending on the structure and design of the container bottom to be manufactured.

Advantageously, the preform has a parting plane at an intersection between the bottom and the body, the parting plane having a thickness EP.

This parting line defines a border between the bottom of the preform and its body.

According to a first design rule, the profile has a maximum height, measured on the central axis, greater than or equal to 5% and less than or equal to 40% of the thickness (EP) of the parting line.

Such a height prevents sagging of the bottom of the containers and limits the increase in injection cycle times.

According to a second design rule, the profile of the internal skin has a maximum height different from the maximum height of the profile of the external skin.

Depending on the shape of the bottom of the container to be manufactured, it is thus possible to provide the preform with a localized surplus of material between the internal skin and the external skin. According to a third design rule, the bottom has a thickness EF greater than or equal to 60% and less than or equal to 100% of the thickness EP of the parting line.

Preferably, the thickness EF of the bottom is greater than or equal to 70% and less than or equal to 90% of the thickness EP of the parting line.

Such a thickness of the bottom makes it possible to facilitate the flow of the material during the manufacture of the container while allowing the bottom of the container to present the desired guarantees in terms of mechanical strength.

According to a fourth design rule, the first portion of the profile has a diameter greater than or equal to 3mm.

Such a diameter facilitates cooperation between the preform and an extension rod in the manufacture of a container by stretch-blow molding.

According to a fifth design rule, the first portion of the profile has a diameter less than or equal to 40% of a diameter of the preform at the parting plane.

This limit on the diameter of the first portion makes it possible to guarantee good flow of the material during the blowing or stretch-blow molding of the preform.

According to a sixth design rule, the profile of the internal skin is parallel to the profile of the external skin.

Such parallelism between the inner skin and the outer skin makes it possible to manufacture a container whose bottom has a constant or almost constant thickness. This then ensures a desired mechanical strength at any point of the bottom.

Of course, several design rules can be combined with each other.

Other characteristics and advantages of the invention will emerge more clearly on reading the following description of various preferred embodiments of the invention, given by way of illustrative and non-limiting examples, and the accompanying drawings, among which:

[Fig. 1] is a perspective view of a preform according to the invention, showing an inset of details on an enlarged scale; [Fig. 2] is a schematic view of a profile of an internal or external skin of a preform according to the invention;

[Fig. 3] is a schematic sectional representation of a preform according to the invention, according to a first embodiment;

[Fig. 4] is a schematic sectional representation of a preform according to the invention, according to a second embodiment;

[Fig. 5] is a schematic sectional representation of a preform, according to a third embodiment;

[Fig. 6] is a schematic sectional view of a preform in a mold during a stretch blow molding phase.

Figure 1 illustrates a plastic preform 1 according to the invention. This preform 1 is used for making plastic containers.

Preform 1 includes:

- a neck 2;

- a body 3;

- a background 4.

More precisely, the body 3 has, at a first end, the neck 2 from which it is separated by a collar 5 and, at a second opposite end, the bottom 4 which closes the preform 1.

As illustrated in FIG. 1, the neck 2 comprises a thread 6 allowing the fixing of a stopper when the preform is transformed into a container and the latter is closed and filled, and a bead 7 forming means of retained by a tamper-evident ring integral with a stopper (not shown).

The preform 1 is substantially cylindrical of revolution about a central axis X.

More particularly, the body 3 and the bottom 4 are advantageously cylindrical of revolution around the central axis X.

The neck 2, meanwhile, is partially symmetrical in revolution around the central axis X, only the thread 6 is not symmetrical.

As illustrated in FIGS. 3, 4 and 5, when it is seen in section, the preform 1 has an internal skin Pi and an external skin Pe. By way of illustrative and non-limiting example, the preform is made of PET, the glass transition temperature of which is around 75 degrees.

Still with reference to Figures 3, 4 and 5, the base 4 has an annular bead 8 forming a laying plane of the preform 1.

More precisely, this annular bead 8 forms a continuous line describing a circle, or exceptionally an ovoid shape depending on the general shape of the preform.

With reference to FIG. 2 which illustrates a skin P of the preform 1, regardless of whether it is an internal skin Pi or an external skin Pe, the skin P presents, radially, from the central axis X up to the annular bead 8, a profile having a break in curvature.

By curvature break, it is designated a break in the profile of the P skin.

In other words, the profile is not made of a line having a single radius of curvature, but includes several lines each having its own radius of curvature.

More precisely, and as is generally done in the prior art, the inner skin Pi or the outer skin Pe defines a generally single curve.

The presence of the break therefore divides this curve into at least two portions each having a different radius.

Still with reference to Figure 2, the profile comprises, from the central axis X to the annular bead 8:

- a first portion 9 having a first radius of curvature;

- a second portion 10 extending the first portion 9 and having a second radius of curvature;

- a third portion 11 extending the second portion 10 and having a third radius of curvature.

The break in the curve is then formed by the second radius of curvature presented by the second portion 10.

According to a preferred embodiment, the second radius of curvature is less than or equal to 9 mm. Such a value makes it possible to create the break in the curve in order to make a real and clear distinction between the first portion 9 and the third portion 11.

More precisely, the second portion 10, by its second radius, makes it possible to prevent a continuity of radius between the first portion 9 and the third portion 11.

More particularly, by extending, in a fictitious manner, the first portion 9 and the third portion 11, it is possible to observe an intersection between their extension. This intersection is unique and not achieved by a collinearity such as would have been the case in the absence of the second portion 10 or by a second portion 10 having a radius of curvature equal to the first radius of curvature and / or to the third radius of curvature, and having a center of radius of curvature identical to the first radius of curvature and / or to the third radius of curvature.

The break in curvature can also be defined by a center of radius of curvature of the second portion 10 distinct from the center of radius of curvature of the first portion 9 and / or of the third portion 11.

Thus, by this distinction of the centers of radii of curvature, it is impossible to have a continuous profile between the first radius of curvature and the third radius of curvature. More precisely, the profile is necessarily marked by a break in the curve thanks to the distinction between the centers of the radii of curvature.

The first portion 9 of the profile has a flat concave or convex shape.

With reference to FIG. 5, the preform has a parting plane 12 at an intersection between the bottom 4 and the body 3, the parting plane 12 having a thickness EP.

Referring to Figure 2, the profile has a maximum height H measured on the central axis, which height H is greater than or equal to 5% of the thickness EP of the parting line 12 and less than or equal to 40% of said thickness EP of the parting line 12.

According to the embodiments illustrated in FIGS. 3 to 5, the profile of the internal skin Pi has a maximum height Hi equal to the maximum height He of the profile of the external skin Pe (in order not to overload the figures, the references He and Hi are only visible in figure 4). As a variant, the profile of the internal skin Pi has a maximum height Hi different from the maximum height He of the profile of the external skin Pe.

Furthermore, the first portion 9 of the profile has a diameter d greater than or equal to 3 mm.

Preferably, and in any event, the diameter d of the first portion 9 of the profile is less than or equal to 40% of a diameter D of the preform 1 at the level of the parting line 12, as illustrated in FIG. figure 5.

In other words, the radius measured between the central axis X and the second portion 10 is preferably greater than or equal to 1.5mm and less than or equal to 20% of the diameter D.

As illustrated in Figures 3 and 5, the profile of the internal skin Pi is parallel to the profile of the external skin Pe.

In other words, the internal skin Pi and the external skin Pe have a degree 1 homothety.

On the other hand, as illustrated in FIG. 4, the internal skin Pi and the external skin Pe are at least partially parallel to each other, the bottom 4 of the preform 1 and more particularly the internal skin Pi and the outer skin Pe then exhibit a degree of homothety greater than degree 1.

According to a first embodiment illustrated in FIG. 3, the first portion 9 of the internal skin Pi and the first portion 9 of the external skin Pe both have a concave shape oriented towards the inside of the preform 1.

According to a second embodiment illustrated in FIG. 4, the first portion 9 of the internal skin Pi and the first portion 9 of the external skin Pe both have a convex shape oriented towards the inside of the preform 1.

According to a third embodiment illustrated in FIG. 5, the first portion 9 of the internal skin Pi and the first portion 9 of the external skin Pe are both flat.

Other embodiments can of course be used. By way of example, the internal skin Pi can have a convex shape on its first portion 9 and the first portion 9 of the outer skin Pe may have a concave shape.

On the contrary, the first portion 9 of the outer skin Pe may have a convex shape and the first portion 9 of the inner skin Pi may have a concave shape.

According to another embodiment not shown, one of the first portion 9 of the outer skin Pe and of the first portion 9 of the inner skin Pi has a flat, concave or convex shape, the other of the first portion 9. of the outer skin Pe and the inner skin Pi have a different shape.

With reference to FIG. 3, the bottom 4 has a thickness EF measured along the central axis X between the internal skin Pi and the external skin Pe, greater than or equal to 60% of the thickness EP of the joint plane 12 and less or equal to 100% of said thickness EP of the parting line 12.

Preferably, the thickness EF of the bottom 4 is greater than or equal to 70% of the thickness EP of the parting line 12 and less than 90% of the thickness EP of the parting line 12.

As illustrated in Figure 5, the bottom 4 of the preform thickens from the annular bead 8 to the parting line 12.

The bottom 4 of the preform according to the invention allows, thanks to its break in curve in particular:

- to avoid sagging of the bottoms of the receptacles at the outlet of the blow mold;

- to optimize the centering of the preform 1 on the bottom of a mold M and / or the centering of a stretching rod T, T 'on the bottom of the preform, during a stretching phase - blowing, as illustrated in Figure 6;

- improve the performance of containers formed under mechanical stresses internal or external to the container;

- to increase the production rates of containers.

With reference to FIG. 6, two variants of stretching rods T, T 'are shown. A first variant (reference T) makes it possible to press the plastic material of the preform 1 against the mold M. A second variant (reference T ') also makes it possible to reinforce the centering of the preform 1 by surrounding the first portion 9, the second portion 10 and at least partially the third portion 11 of the bottom 4.

More particularly, the rupture of curvature forms a reinforcement making it possible to limit the sagging of the bottom of the container, and in particular of the bottom of the vault of the container, which is formed by the first portion 9 of the preform 1. In fact, the rupture of curvature forms a stop in the sagging of the bottom of the container and makes it possible to maintain an arch to the container. This sag limitation is increased with the physical memory of the PET.

Such sagging occurs in particular when the bottom of the container is not sufficiently cooled at the outlet of the mold, such a lack of cooling generally coinciding with too short a contact time between the plastic material and the mold during the manufacture of the container, and more precisely during the blow-molding or stretch-blow molding step.

The release formed by the first portion 9, the second portion 10 and the third portion 11 of the profile of the outer skin Pe with the annular bead 8 of the preform 1, makes it possible to ensure a centering of the preform 1 on the mold base M during the stretch-blow molding phases. For this, the mold M may in particular have a projection at the imprint of the annular bead 8 of the preform 1 or, of the profile of the outer skin Pe of the preform 1, to allow a form cooperation between the preform 1 and the base. of mold M.

Finally, the blowing rates can be increased by virtue of the preform 1 according to the invention since, even in the absence of prolonged contact between the material and the mold during the blowing or the stretch-blow molding, the deformation of the bottom of the container at the outlet of the mold is controlled and / or limited, which allows the container to be used despite a risk of deformation, since the avoidance of sagging of the bottom allows the container to maintain stability on a plane deposit. In addition, the deformation of the bottom may be barely perceptible by the user depending on the value of the radii of curvature of each of the first portion 9, of the second portion 10 and of the third portion 11 of the preform 1.

Claims

1. Plastic container preform (1), comprising:

- a body (3) symmetrical in revolution about a central axis (X);

- a bottom (4) closing the body (3) from one of its ends, the bottom (4) having an annular bead (8) forming a laying plane of the preform (1), the bottom (4) ) having an outer skin (Pe) oriented towards the outside of the preform (1) and an internal skin (Pi) oriented towards the inside of the preform (1), characterized in that at least one of the skin internal (Pi) and of the external skin (Pe) presents, radially from the central axis (X) to the annular bead (8), a profile having a break in curvature the preform having a parting plane (12) at an intersection between the bottom (4) and the body (3), the parting line (12) having a thickness (EP), characterized in that the first portion (9) of the profile has a diameter (d) less than or equal at 40% of a diameter (D) of the preform (1) at the joint plane (12).

2. Preform (1) according to the preceding claim, characterized in that the profile comprises, from the central axis (X) to the annular bead (8):

- a first portion (9) having a first radius of curvature;

- a second portion (10) extending the first portion (9) and having a second radius of curvature;

- a third portion (11) extending the second portion (10) and having a third radius of curvature, the break in curvature being formed by the second radius of curvature presented by the second portion (10).

3. Preform (1) according to the preceding claim, characterized in that the second radius is less than 9 mm.

4. Preform (1) according to claim 2 or claim 3, characterized in that the first portion (9) of the profile has a flat, concave or convex shape.

5. Preform (1) according to any one of the preceding claims, characterized in that the profile has a maximum height (H), measured on the central axis (X), greater than or equal to 5% and less than or equal to 40% of the thickness (EP) of the parting line (12).

6. Preform (1) according to the preceding claim, characterized in that the profile of the internal skin (Pi) has a maximum height (Hi) different from the maximum height (He) of the profile of the external skin (Pe).

7. Preform (1) according to any one of the preceding claims, characterized in that the bottom (4) has a thickness (EF) greater than or equal to 60% and less than or equal to 100% of the thickness (EP) of the parting line (12).

8. Preform (1) according to the preceding claim, characterized in that the thickness (EF) of the bottom (4) is greater than or equal to 70% and less than or equal to 90% of the thickness (EP) of the plane of seal (12).

9. Preform (1) according to any one of the preceding claims, characterized in that the first portion (9) of the profile has a diameter (d) greater than or equal to 3mm.

10. Preform (1) according to any one of the preceding claims, characterized in that the profile of the internal skin (Pi) is parallel to the profile of the external skin (Pe).