EP3389987A1

EP3389987A1 - Mould base provided with a central movable insert

Info

Publication number: EP3389987A1
Application number: EP16825520.6A
Authority: EP
Inventors: Pierrick Protais; Mickaël LETESTU; Camille GUITON
Original assignee: Sidel Participations SAS
Current assignee: Sidel Participations SAS
Priority date: 2015-12-16
Filing date: 2016-12-15
Publication date: 2018-10-24
Also published as: CN108367483A; WO2017103494A1; FR3045443B1; FR3045443A1; US20200262128A1; MX2018006698A

Abstract

A method for producing a container (2) provided with a base (8), in a mould (1) that comprises a base (20) with a base block (21) provided with a raised moulding face (22) and a central opening (28), and an insert (29) mounted in the central opening (28), said insert (29) being provided with an end face (30) that has the imprint of a central area (10) of the base (8) of the container (2), and being movable relative to the block (21) between: - a retracted position in which the end face (30) extends in the extension of the moulding face (22) of the block (21), thus completing therewith the imprint of the base (8) of the container (2); - a protruding position in which the insert (29) protrudes relative to the central opening (28) - the method comprising an operation of boxing the central area (10) of the base (8) of the container (2) formed in this way, consisting, during or after the depressurisation phase, of moving the insert (29) to the protruding position of same so as to exert pressure against said central area (10) of the base (8) of the container (2) and increase the clearance of said central area (10) relative to the clearance that it has at the end of the blowing.

Description

Mold bottom with a central mobile insert

The invention relates to the shaping of the containers by blow molding or stretch blow molding of plastic blanks such as polyethylene terephthalate (PET), the term "blank" designating a preform (usually obtained by injection) or an intermediate container having underwent a prior blowing operation from a preform.

A container includes a body, generally cylindrical in shape and extending along a major axis, a shoulder that forms a narrowing from an upper end of the body, an open neck extending the shoulder to allow filling and emptying of the container, and a bottom that closes the body at a lower end thereof.

The forming is generally carried out within a mold delimiting a cavity in the cavity of the container. Such a mold commonly comprises a side wall to the imprint of the body and the shoulder (this side wall being subdivided into two mutually articulated half-molds to allow the introduction of a blank into the mold), and a bottom of mold at the footprint of the container bottom, positioned in an opening between the half-molds.

The preform, after having been heated to a temperature above the glass transition temperature of its material (a PET preform, whose glass transition temperature is about 80 ° C., is usually heated to a temperature greater than 100 ° C. C, typically of the order of 120 ° C), is introduced hot into the mold. A gas under pressure (such as air) is then injected to press the material, made soft by heating, against the wall and the mold base and thus give the preform the impression of the container.

The bottom of the container is a critical zone because its structural stability depends on the stability of the container placed on a surface, whether it be a conveyor during handling operations of the container following its filling, or a table on which a user places the container.

Countless form tips have been devised to stiffen the bottoms of containers, cf. for example patents EP 1 945 518 (in the name of the applicant, describing a petaloid background and its associated mold) and EP 2580132 (also in the name of the applicant, describing a background with star stiffeners). Most, however, have in common:

a peripheral seat which defines a laying plane for the container;

- a central arch, which extends internally to the seat and projecting towards the inside of the container and whose summit part (generally in the center of the arch) extends at a distance from the laying plane, measured axially, called "guard".

Container lightening, imposed by environmental standards, and the quest for economy of material by bottlers tend to weaken the substance and, despite the formalities mentioned above, we observe phenomena of slump in the vault after the container is out of the mold. This phenomenon has even been observed on some petaloid bottoms, yet considered rigid, whose guard gradually decreases, to go to zero (the vault coming to join the laying plan), or even to become negative (the vault forming a protrusion at beyond the laying plane, towards the outside of the container). This results in a lack of stability of the bottom, the container then being likely to fall. An explanation for this phenomenon is the increase in production rates (several thousand containers produced per hour and per mold), which induces a reduction in the manufacturing cycle time of each container, and therefore a reduction in the contact time of the container. with the mold. As a result, the bottom of the container leaving the mold is still very hot and deforms during cooling by freely relaxing the stresses induced by the blowing.

A first objective is to propose a solution to minimize the risk of sagging of the vault.

A second objective is, more precisely, to propose a solution to keep custody at a strictly positive value.

There is provided a method of manufacturing a container having a bottom provided with a seat and a raised central area relative to the seat, by blow molding or stretching, in a mold, of a plastic blank previously heated to a temperature greater than the glass transition temperature of the material, which comprises:

an operation of introducing the blank into said mold, which mold comprises a side wall with the impression of a body of the container and a mold base which completes, with the side wall, the impression of the container to be obtained, this mold base comprising a bottom block which has a relief molding face at the impression of at least the seat of the container and is provided with a central opening, this mold base further comprising an insert, mounted in the central opening and provided with an end face at the footprint of the central zone of the bottom of the container, which insert is movable relative to the block between:

a retracted position in which the end face extends in the extension of the molding face of the block, thus completing with the bottom block the impression of the bottom of the container;

an extended position in which the insert protrudes from the central opening;

which method is characterized in that it further comprises:

a pressurization phase comprising injecting, into the blank, in the retracted position of the insert, a fluid under pressure to form the container;

a depressurization phase comprising placing the container thus formed in communication with the atmosphere, a boxing operation of the central zone of the bottom of the container thus formed consisting, during or after the depressurization phase, in moving the insert towards its position outlet so as to exert a thrust against said central zone of the bottom of the container and to increase the guard of said central zone relative to the guard it has at the end of the blowing.

Such a method makes it possible to obtain a container having an increased guard at the mold outlet. The filling of the container can cause, by creep (in particular under conditions of high temperature and / or pressure), a subsidence of the central zone of the bottom, but the guard, even thus diminished, remains positive, in favor of the stability of the container. Various additional features may be provided, alone or in combination:

the stroke of the insert between its retracted position and its extended position is between 2 mm and 15 mm, and for example about 5 mm; It is proposed, secondly, a mold base for implementing the method according to the invention, in which:

the insert comprises a piston mounted in translation in a liner integral with the bottom block;

the mold base comprises a support on which the bottom block is mounted, and the liner is at least partially formed in said support;

the mold base comprises a fluid circuit, which includes for example a conduit formed in the insert for the circulation of a fluid;

- The insert is provided with radial holes opening the conduit on an outer face of the insert, in the vicinity of the end face; the duct is formed in one piece and comprises an upstream section and a downstream section separated by a web;

the insert is made by additive manufacturing.

Other objects and advantages of the invention will become apparent in the light of the description of an embodiment, given hereinafter with reference to the accompanying drawings, in which:

Figure 1 is a sectional view of a mold for the manufacture of a container according to the method of the invention, which mold bottom is equipped with a movable insert shown in the retracted position;

Figure 2 is a detail view, on a larger scale, of the mold of Figure 1 according to the inset II, with, inset, an additional detail on a larger scale;

Figure 3 is a figure similar to Figure 2, showing the insert in the extended position;

Figure 4 is a sectional view of the bottom of a container formed in the mold illustrated in Figures 1 to 3.

In Figure 1 is shown a mold 1 for forming a container 2 by blow molding or stretching from a blank 3 of plastic material (especially polyethylene terephthalate or PET). The blank 3 may be an intermediate container which has undergone a first blowing operation from a preform. It can still be, as in the illustrated example, a raw injection preform (visible in dashed lines in FIG. 1).

The container 2 comprises a substantially cylindrical body 4 which extends along a main axis X, a shoulder 5 which extends, narrowing, in the extension of the body 4 at an upper end thereof, an open neck 6 at an upper end of the shoulder 5, from which it is separated by a flange 7, and a bottom 8 which closes the body 4 at a lower end thereof. The bottom 8 has a peripheral seat 9 through which the container 2 is intended to rest on a flat surface such as a table, and a central zone 10 (where is particularly an injection pad of the preform 3), raised by relative to the seat 9 and to which it is connected by an arch 11.

According to an embodiment illustrated in the figures, the bottom 8 of the container 2 is petaloid. It comprises an alternation of spaced apart feet 12, terminating in ends which together form (although discretely in the mathematical sense of the term) the seat 9, and valleys 13 with a substantially circular radial section radiating from the area 10 central to the body 4.

The preform 3 comprises a body 14 of substantially tubular shape, intended to form the body 4 and the shoulder 5 of the container 2, a neck 6 which is that of the container 2 and remains unchanged during forming, and a hemispherical bottom 15 intended for form the bottom 8 of the container 2.

The mold 1 comprises a side wall 16 defining a cavity 17 at the impression of the body 4 and the shoulder 5 of the container 2. The side wall 16 extends along a main axis which, when the container 2 is formed, is confused with the main X axis of it. In what follows, the expression "main axis" denotes indifferently the axis of the container or that of the side wall 16.

According to a conventional embodiment, the side wall 16 is subdivided into two half-molds 16A, 16B movable relative to each other, for example by being mutually articulated around a hinge parallel to the main axis X between an open position in which the two half-molds are angularly spaced from one another to allow the introduction of the preform 3 and the evacuation of the container 2, and a closed position in which the two half-molds are pressed against each other to define the cavity 17 together.

The side wall 16 defines an upper opening 18, through which the preform 3 is suspended by its flange 7, and an opposite lower opening 19.

The mold 1 is also equipped with a bottom 20 of mold comprising, firstly, a bottom block 21 (made for example of steel or an aluminum alloy) having a face 22 of embossed molding. imprint of a portion of the bottom 8 comprising the seat 9 and the roof 11, except however the central area.

The bottom block 21 is fixed on a support 23 itself mounted (for example by means of screws 24) on a saddle 25 movable in translation relative to the side wall 16 between a loading / unloading position in which the block 21 is removed from the cavity 17 to allow evacuation of the container 2 formed and the introduction of a preform 3, and a forming position (illustrated in Figures 1, 2 and 3) in which the face 22 of molding comes closing the lower opening 19 to complete, with the cavity 17, the cavity of the container 2 to form.

According to an embodiment illustrated in the figures, where the container

2 is petaloid bottom 8, the bottom molding face 22, at the footprint thereof, comprises an alternation of ribs 26 (at the footprint of the valleys 13) and cavities 27 hollow (each forming a zone seat) to the footprint 12 (for example five in number), which extend between the ribs 26.

As seen in the figures, and more particularly in Figures 2 and 3, the bottom block 21 is provided with a central opening 28 which extends around the main axis X. According to one embodiment, this opening 28 is circular in cross section, but this form is not limiting.

The bottom 20 of the mold comprises, secondly, an insert 29 mounted in translation in the central opening 28. This insert 29 is provided with an end face 30 at the footprint of the central zone 10 of the bottom 8 of the container 2.

The insert 29 is movable (in axial translation, that is to say parallel to the main axis X) relative to the bottom block 21, between: a retracted position (FIGS. 1, 2) in which the end face extends in the extension of the molding face 22 of the block 21, thus completing with it the footprint of the bottom 8 of the container 2, and

an outlet position (FIG. 3) in which the insert 29 protrudes with respect to the central opening 28, axially towards the cavity 17, the end face being offset axially with respect to the central opening towards the central opening; upper opening 18 of the mold. The stroke of the insert 29 between its retracted position and its extended position is advantageously between 2 mm and 15 mm, and is for example about 5 mm.

According to an embodiment illustrated in the figures, the insert 29 incorporates a piston 31 mounted in translation in a jacket 32 secured to the block 21 of bottom. More specifically, in the example illustrated, the liner 32 is formed in the support 23 and is delimited axially, on the one hand upwards (in the direction of the bottom block 21) by an upper wall 33 formed by a spacer interposed between the support 23 and the block 21 of bottom, and secondly downwards by an opposite bottom wall 34 formed in the support 23.

As can be seen in FIG. 2, the insert 29 comprises a cylindrical upper shaft 35 projecting upwardly from the piston 31 and at the end of which is formed the end face. The upper shaft 35 passes through the upper wall 33 through a central opening 36 formed therein.

According to an embodiment illustrated in FIG. 2, the insert 29 further comprises a lower shaft 37 which protrudes downward (i.e. opposite the upper shaft) from the piston 31. The lower shaft 37 passes through the lower wall 34 through a central opening 38 formed therein.

In addition, as also visible in Figure 2, the fifth wheel 25 may be pierced with a bore 39 in which the lower shaft 37 is slidably mounted, a clearance being formed between the bore 39 and the lower shaft 37. The bore 39 advantageously comprises an upper portion 39A and a lower portion 39B insulated from each other by a radially projecting annular shoulder which comes into contact (preferably with the interposition of a seal) of the lower tree 37. The piston 31 delimits in the liner 32 an upper chamber 40, on the side of the upper wall 33, and a lower chamber 41, on the side of the lower wall 34. A primary control fluidic conduit 42 is formed in the support 23 and opens, through the lower wall 34, into the lower chamber 41, for injecting therein a fluid (such as air or oil) under pressure that pushes the piston 31 to the upper wall 33, and thus the insert 29 to its extended position.

The cylinder constituted by the piston 31 and the jacket 32 may be of the simple effect type; in this case, the bottom 20 of the mold comprises one (or more) return spring (s) interposed (s) between the upper wall 33 and the piston 31, which permanently urges it to the lower wall 34 and therefore the insert 29 to its retracted position.

However, as in the example illustrated, the jack constituted by the piston 31 and the jacket 32 may be of the double-acting type: a secondary control fluidic conduit 43 is formed in the support 23 and opens radially into the upper chamber 40, for injecting therein a fluid (such as air or oil) under pressure, which pushes the piston 31 to the lower wall 34 and thus the insert 29 to its retracted position.

Thus, to place the insert 29 in its extended position, it is injected into the lower chamber 41, via the primary control conduit 42 (and by means, for example, of a hose connected to the support 23 by means of a connector), a fluid (such as air or oil) under pressure, which pushes the piston 31 to the upper wall 33 (and thus the insert 29 to its extended position) while the pressure in the chamber 41 lower is simultaneously released.

Conversely, to place the insert 29 in the retracted position, the pressure in the lower chamber 41 is released, while the upper chamber 40 is injected via the secondary control conduit 43 (and by means, for example , a hose connected to the support 23 by means of a connector), a fluid (such as air or oil) under pressure, which pushes the piston 31 towards the lower wall 34 (and therefore the insert 29 to its retracted position).

The tightness between the two chambers 40, 41 is advantageously achieved by means of an annular segment 44 housed in a groove circumferentially formed in the piston 31. Alternatively, the displacement of the insert 29 may be controlled by mechanical means and non-pneumatic (or hydraulic), for example by a cam. For this purpose, a lower end of the insert 29 may carry a cam follower (such as a roller), which cooperates with a cam path, the permanent contact of the cam follower with the cam path being for example ensured by a return spring. The cam path has a high section, which moves the cam follower up (and thus the insert 29 towards its extended position), and a low section that allows the cam follower to lower (and thus to insert 29 to return to its retracted position).

According to a preferred embodiment, the bottom 20 of the mold comprises a circuit 45 of thermal regulation of the insert 29, designed to maintain it at a moderate temperature (typically between 5 ° C. and 30 ° C.) and preferably between 10 ° C and 20 ° C) when the insert 29 must be cooled, or at an elevated temperature (typically between 80 ° C and 120 ° C) when the insert 29 must instead be heated, especially in the case of a heat-fixing of the bottom 8 of the container 2. This circuit 45 is for example of the fluidic type, and then comprises a conduit 46 formed in the insert 29 for the circulation, inside thereof, of a coolant.

As can be seen in particular in FIG. 2, the duct 46 has an upstream section 46A, which opens into the upper portion 39A of the bore 39 via an upstream orifice 47 pierced radially in the insert 29, and a downstream section 46B, which opens in the lower portion 39B of the bore 39 by a downstream orifice 48, also radially pierced in the insert 29.

The thermal control circuit 45 further comprises a feed duct 49 formed (for example by at least one hole) in the fifth wheel 25 and opening into the upper portion 39A of the bore 39, and a discharge duct 50 as well. formed (for example by at least one hole) in the fifth wheel 25 and opening into the lower portion 39B of the bore 39.

To facilitate fluid flow within the insert 29, the duct 46 is advantageously formed in one piece, the upstream section 46A and the downstream section 46B being separated by a web 51. If, as in the illustrated example, the insert 29 is monobloc, this architecture can not be obtained by machining. To obtain it, it is necessary to realize the insert 29 by additive manufacturing. More specifically, to produce the insert 29 in a metal material, for example steel or an aluminum alloy, one can use the technique of three-dimensional printing by laser sintering powder (English "selective laser sintering" or SLS).

As can be seen in FIGS. 2 and 3, the bottom block 21 is mounted, with the interposition of the spacer forming the upper wall 33, on the support 23 in which the insert 29 is previously mounted. As illustrated, a ring 52 centering means provided with a peripheral groove is advantageously mounted on the support 23. The bottom 20 of mold thus formed by assembling the bottom block 21, the spacer forming the upper wall 33 and the insert 29 is, with the support 23 and the ring 52, fixed rigidly on the saddle 25, for example by means of screws 53.

In the closed position of the mold 1, the bottom 20 of the mold is immobilized with respect to the side wall 16 by means of a pair of jaws 54, each integral with a half-mold 16A, 16B, which cooperate with the groove of the ring 52, thus achieving both the maintenance and the centering of the bottom 20 of the mold.

To form the container 2 from the preform 3 (or more generally a blank), the following is carried out:

The insert 29 is in the retracted position, it is first carried out an introduction operation, in the mold 1, the preform 3 (shown in dashed lines in Figure 1) previously heated to a temperature above the glass transition temperature of the material (about 80 ° C for PET).

A pressurization phase comprising injecting, into the preform 3, a gas (such as air) under pressure, preferably while stretching it by means of an elongation rod, is then carried out. The pressure during injection is increased from a pre-blowing pressure of about 7 bars to a blowing pressure greater than or equal to 15 bars, typically of the order of 25 bars to 30 bars (and up to 40 bars). bar). The material then comes to press against the side wall 16, against the molding face 22 and against the end face of the insert 29, thus forming the receptacle 2.

The insert 29 is always in its retracted position when blowing is performed at the pressure greater than 15 bars. In these conditions, the material intimately takes the imprint of the molding face 22 and the end face.

The pressurization phase includes a time delay during which the blowing pressure is maintained to ensure good impression of the material.

Then, during a depressurization phase, the interior volume of the container 2 thus formed is placed in communication with the atmosphere (that is to say, the free air).

The depressurization phase may include a scavenging step, which involves placing the interior volume of the container 2 in communication with a source of fluid at a pressure intermediate the pre-blowing pressure and the blowing pressure, and thus ensuring cooling of the inside of the container 2.

During (or possibly after) the depressurization, a boxing operation is carried out in the central zone 10 of the bottom 8 of the container 2, which consists of moving the insert 29 towards its extended position, as represented in FIG. thrust is exerted against the central zone 10 of the bottom of the container, causing an increase in the guard of said central zone relative to the guard it has at the end of blowing.

In the illustrated example, this operation is performed by pressurizing the lower chamber 41 and simultaneously depressurizing the upper chamber 40, which causes the piston 31 to abut against the upper wall 33 (and thus the insert 29 in its extended position ).

Under the pressure of the insert 29, represented by the arrow in the detail locket of FIG. 3, the bottom 8 of the container deforms from its configuration (shown in solid lines in FIG. 2 and in dashed lines in the figure 3) from the blowing, the central zone 10 going towards the interior of the container 2 (as shown in solid lines in FIG. 3). Cooling (or on the contrary thermofixation) of the container 2 continues, the material, in partial contact with the thermally regulated insert 29, tends to congeal in this deformed configuration.

The insert 29 is held in its extended position for a predetermined duration (for example of the order of a few tenths of a second), then the insert 29 is returned to its lower position (by pressurizing the upper chamber 40 and depressurizing simultaneous lower chamber 41, which causes the piston 31 abuts against the lower wall 34. This replacement of the insert 29 in the lower position can be achieved after the lowering of the mold base 20 accompanying the opening of the mold 1.

As can be seen in FIG. 4, the central zone 8 of the bottom 8 of the container 2 is, at the outlet of the mold 2, in a raised configuration (shown in solid lines) with respect to a conventional configuration (shown in dotted lines) where the forming of the container 2 is performed without the insert 29. Note:

- G1 the guard of the bottom 8 of the container in this elevated configuration (solid line), that is to say the distance, measured axially (parallel to the axis X) between the central zone 10 and the end of the seat 9 (which forms a laying plane for the container 2);

- G0 the guard of a similar background classic (dashed).

Not only the guard G1 of the cooled container 2 is greater than the guard G0, but it has been verified that the guard G1 remains strictly positive after its filling (and its capping), which guarantees its stability not only in the medium term (and in particular during handling operations of the container following its filling: labeling, conveying, wrapping, palletizing) but also in the long term, including when used by a consumer.

Providing numerical values can not be considered as limiting but as speaking. For a container 2 with a petaloid bottom (as illustrated) and a stroke of the insert 29 of 5 mm, the increase of the guard (that is to say the value of G1 - G0) is 1, 5 mm.

Various variants could be adopted without departing from this framework. In particular, it is conceivable for the regulating circuit 45 to fill at least partly a localized blowing function applied to the bottom 8 of the container. For this purpose, the fluid supplying the circuit 45 is preferably a gas, and the insert may be provided with radial bores 55 (optionally inclined) opening the conduit 46 on an outer face of the insert 29, in the vicinity of the terminal face. Such holes are illustrated in dotted lines in the detail medallions of Figures 2 and 3. The injection of fluid during boxing facilitates the detachment of the bottom 8 of the container from the molding face 22 (and therefore its deformation) while minimizing the risk of cracking.

Claims

A method of manufacturing a container (2) having a bottom (8) provided with a seat (9) and a raised central area (10) relative to the seat (9), by blowing or drawing blowing, in a mold (1) of a blank (3) of plastic material previously heated to a temperature above the glass transition temperature of the material, which comprises:

an operation of introducing the blank (3) into said mold (1), which mold comprises a wall (16) lateral to the impression of a body (4) of the container (2) and a bottom (20) of mold which completes, with the wall (16) side, the impression of the container (2) to obtain, the bottom (20) of mold comprising a block (21) having a bottom face (22) of relief molding to the impression of at least the seat (9) of the container (2) and is provided with a central opening (28), the bottom (20) of the mold further comprising an insert (29), mounted in the opening (28) and provided with a face (30) end to the footprint of the central region (10) of the bottom (8) of the container (2), which insert (29) is movable relative to the block (21). ) enter :

- A retracted position in which the end face (30) extends in the extension of the face (22) of the molding block (21), thereby completing with it the footprint of the bottom (8) of the container

(2);

an extended position in which the insert (29) projects from the central opening (28),

characterized in that it further comprises:

a pressurization phase comprising the injection, in the blank

(3), in the retracted position of the insert (29), a fluid under pressure to form the container (2);

- A depressurization phase comprising placing the container (2) thus formed in communication with the atmosphere, a boxing operation of the central zone (10) of the bottom (8) of the container (2) thus formed consisting, during or after the depressurization phase, to move the insert (29) to its extended position so as to exert a thrust against said central zone (10) of the bottom (8) of the container (2) and to increase the guard of said central zone (10) relative to the guard it has at the end of blowing.

2. Method according to claim 1, characterized in that the stroke of the insert (29) between its retracted position and its extended position is between 2 mm and 15 mm.

3. Method according to claim 2, characterized in that the stroke of the insert (29) is about 5 mm.

4. Bottom (20) mold for implementing the method according to one of the preceding claims, characterized in that the insert (29) comprises a piston (31) mounted in translation in a jacket (32) integral with the block (21) bottom.

5. Mold bottom (20) according to claim 4, characterized in that it comprises a circuit (45) for internal thermal regulation.

6. Mold bottom (20) according to claim 5, characterized in that the circuit (45) of thermal regulation comprises a conduit (46) formed in the insert (29) for the circulation of a fluid.

7. Bottom (20) mold according to claim 6, characterized in that the insert (29) is provided with bores (55) radial opening the conduit (46) on an outer face of the insert (29), in the vicinity of the end face (30).

Mold bottom (20) according to claim 6 or claim 7, characterized in that the duct (46) is formed in one piece and comprises an upstream section (46A) and a downstream section (46B) separated by a veil (51).

9. Fondue (20) mold according to claim 8, characterized in that the insert (29) is made by additive manufacturing.