EP1485240A2

EP1485240A2 - Method of producing a compression-moulded plastic part comprising a neck which is equipped with a dispensing orifice

Info

Publication number: EP1485240A2
Application number: EP03744402A
Authority: EP
Inventors: Bertrand Gruau; Hervé ZAKRZEWSKI
Original assignee: Cebal SAS
Current assignee: Albea Tubes France SAS
Priority date: 2002-03-18
Filing date: 2003-03-17
Publication date: 2004-12-15
Also published as: MXPA04008940A; BR0308514A; WO2003078126A2; FR2837132B1; JP2005527399A; FR2837132A1; US20050051928A1; US8025825B2; AU2003232291A8; AU2003232291A1; WO2003078126A3; RU2004130495A; CN1638935A; PL370833A1

Abstract

The invention relates to a method for the compression moulding of plastic parts (1) comprising a neck (3) which is equipped with an orifice. The inventive method comprises a first step involving the creation of a blank (20) and a second step involving the compression of said blank. The part is moulded with a neck (3) which is equipped with a top wall (4) comprising: a thin area with a notch (5), the contour of said thin area defining the orifice; and two zones which can withstand the mechanical stress (F) necessary in order to break the top wall (4) at the notch (5). One of said two zones (7) is intended to transmit the aforementioned mechanical stress and the other (8) is used as a support. The section of the notch (5) is slightly inclined in relation to the axis of the neck. According to the invention, after moulding, the mechanical stress (F) is applied to one part of the top wall (91), said part being different to the above-mentioned thin area (6), so that the top wall tears at the notch (5), thereby producing the dispensing orifice.

Description

PROCESS FOR OBTAINING A COMPRESSION MOLDED PLASTIC MATERIAL HAVING A NECK PROVIDED WITH AN ORIFICE

DISTRIBUTION

The invention relates to a method of manufacturing by compression molding of plastic parts having a neck provided with an orifice. These parts are generally containers or parts of containers. The invention relates more particularly to the conditions of production in high rates of molded objects which have an axisymmetric neck delimiting a substantially circular orifice, for example flexible plastic tube heads, comprising a neck provided with a orifice. distribution and a shoulder connecting said neck to a flexible cylindrical skirt. We will use these flexible tube heads to illustrate the present invention.

In general, a flexible tube is produced by assembling two pieces produced separately: a flexible cylindrical skirt of given length (typically 3 to 5 times the diameter) and a head comprising a neck provided with a dispensing orifice and a shoulder connecting said neck with cylindrical skirt. The head made of plastic material (s) can be molded separately and then welded to one end of the skirt, but the latter is advantageously molded and welded autogenously to the skirt using either an injection molding technique (FR 1 069 414) or a compression molding technique for an extruded blank (FR 1 324 471).

In these two techniques, the skirt is fitted around a punch, one of its ends protruding slightly from the end of the punch, said punch end serving as a mold for producing the internal surface of the tube head (inside of shoulder and neck). In these two techniques, a matrix is used which is pressed against the end of the punch, the imprint of this matrix defining the external surface of shoulder and neck. The main difference between these methods lies in the fact that these tools are first pressed firmly against each other before the injection of the plastic in the first case and that it is their mutual approach which causes compression. of an extruded blank in the second case.

In French application n ° 0103706 filed on 19/03/2001, the applicant indicated that a significant increase in production rates (beyond 250-300 units per minute) could be obtained using the technique of molding by compression. In the context of this French application No. 0103706, the Applicant has in fact presented a workshop for manufacturing flexible tubes in which the tube heads were produced by compression molding using tools moved in continuous movement, which allowed to obtain, under acceptable economic conditions, significantly higher production rates.

In compression molding, the production of the blank and its placement in the molding tool present specific problems whose solutions have been the subject of numerous patents. However, these problems are exacerbated when considering the use of tools animated by a continuous movement and the solutions hitherto proposed have proved to be ill-suited to this new constraint.

French application FR 1 324471 (Karl Mâgerle) describes a compression molding process for tube heads in which the lower mold is formed by the end of a mandrel and the end of a skirt fitted around this mandrel, the end of said skirt projecting from the end of said mandrel; the space delimited by the end of the mandrel and the projecting part of the skirt is supplied by injecting plastic material through several orifices regularly distributed in a nozzle; the plastic is distributed around a counter-punch formed at the end of the mandrel and intended to mold the shape of the interior part of the neck. Once the necessary quantity of plastic material has been introduced, the nozzle is removed, the parts of the upper mold are brought together by radial displacement, then the plastic material is compressed by bringing the lower mold closer to the upper mold. The jets are regularly distributed over the circumference and the material thus poured is distributed approximately homogeneously along its circumference before undergoing compression. This gives a substantially uniform thickness around the dispensing orifice.

Applications FR 2460 772 (Karl Mâgerle) and US 4,943,405 (AISA) follow the idea of compressing the plastic material when it is already distributed circumferentially in a substantially regular manner. These requests propose an extruded blank in the form of a torus, which is fitted around a central protuberance linked to one of the mobile parts of the tool. By fitting a toroidal blank around a protrusion, it is authorized that the two parts of the molding tool located at the level of the dispensing orifice come into contact with each other before the plastic material the compressed blank cannot reach this zone; more precisely, the air gap between these two tool parts is so small that no viscous flow of plastic material can occur there. With a toroidal blank, one thus obtains more easily and directly a neck provided with an orifice having a sharp edge.

In FR 2 460 772, the extrusion of the toroidal blank is carried out using an extruder having an annular die, the opening of which is controlled by means of a valve. This closes or not, depending on its position, the annular flow of the plastic and its movement controls the size of the toroidal blank thus obtained. The use of toroidal blanks obtained by discontinuous extrusion of plastic material controlled using a valve is therefore the only means known in the prior art for efficiently and directly obtaining by compression molding a neck provided with an orifice having a sharp edge. However, such a technique is imprecise and does not allow good reproducibility by weight of the toroidal blank, which complicates the conditions of compression molding, the latter not having for example the flexibility of injection molding where all excess material can be more easily removed.

On the other hand, the toroidal blank is cooled relatively quickly by conduction in the tooling. As the contact surface is not regularly distributed, the cooling is heterogeneous and a large part of the advantage provided by the toric geometry of the blank is lost, namely a good distribution of the material before compression. Many solutions such as that proposed in WO96 / 09151 (Karl Mâgerle Lizenz) make it possible to reduce the extent and the heterogeneity of the cooling of the blank before compression but they require the introduction of additional tooling elements (for example the auxiliary support sliding around the central protuberance described in WO96 / 09151) as well as means making it possible to control their movement. Such sophistication makes tooling economically unprofitable, even prohibitive if one wishes to make the moving parts of the tool follow a continuous overall movement.

Finally, the very realization of the toroidal blank and its installation in the air gap between punch and die present significant difficulties when the tools are driven in continuous kinematics, because the extrusion as the injection lend themselves poorly to the continuous movement tools and it is necessary to provide transfer means capable either of displacing the extrusion means themselves which make it possible to obtain the blank or to recover the toroidal blank obtained "statically" and to place it without too much lα deform in the air gap of the compression tools which move in continuous movement.

EP 0 841 258 describes a molding manufacturing process

5 compression of plastic inserts which are introduced into dosing caps. These inserts are provided with a cylindrical dispensing spout and have a veil closing the dispensing orifice, which seems to indicate that the blank used is not necessarily toric, that it can have a massive shape which is easier to produce and that its deposit in the air gap of the tool presents less difficulty. However, this veil must be removed after the insert has been shaped by cutting with a cutting tool. This cutting requires a succession of additional steps and, if such a process can be applied to space-saving inserts, it is difficult to transpose it to the shaping of a tube head by i5 compression molding with autogenous welding of head on the skirt, because the tools involved are more complex and bulky. The problem becomes even more complicated if we want them to follow a continuous overall movement.

The Applicant has therefore sought to develop a process for manufacturing by compression molding of plastic parts provided with a neck having an orifice which is not subject to the problems mentioned above and which can therefore be easily implemented. implemented using tools driven by continuous kinematics.

5 The object according to the invention is a method of manufacturing by compression molding of plastic parts having a neck provided with an orifice comprising a first step of producing a plastic blank and a second step of compressing the said blank, in which said blank, brought to an appropriate temperature, is placed 0 in the air gap comprised between at least two movable parts of the compression tooling is then compressed by mutual approximation of said mobile parts of the tooling, the plastic material of the blank flowing so as to fill the cavities of the impressions of said mobile parts until relative immobilization of said mobile parts, footprints of said movable parts of the tool once joined defining the volume of said piece having a neck, said footprints being drawn so that said neck, once molded, has a top wall which comprises a thinned zone whose outline delimits the desired shape of the orifice, said method being characterized in that said thinned zone is bordered by a notch, the section of which by a diametral plane passing through the axis of the neck is oriented in a direction substantially parallel to the axis of the neck, in that said top wall also includes a zone of application of a mechanical force intended to be app liquified on said top wall with sufficient intensity to break the top wall at the level of said notch, said application zone being distinct from the thinned zone, said top wall also comprising two zones capable of withstanding mechanical force, one of 'between them being intended to transmit said mechanical force and the other to serve as support and in that after opening of said molding tool by relative displacement of its moving parts, said mechanical force is applied in said application zone of such that a rupture occurs at the level of said notch and that at least part of the top wall is detached, thereby releasing the dispensing orifice.

Said notch has a section through a diametral plane passing through the axis of the neck oriented in a direction substantially parallel to the axis of the neck, in that it is made a slight angle with said axis, typically between 0 and 45 °, preferably between 0 ° and 30 °.

Thereafter, we will name rupture zone or even breakable zone the thinned zone of the summit wall located at the level of the notch. The breakable zone is thus a part of the thinned top wall of which one of the faces is provided with a notch. This notch can be located on the underside of the top wall but, preferably, it is located on the top face of the top wall so as to prevent possible deformations of the thinned residual zone resulting from the rupture leading to obtaining geometrical defects accessible to sight or to touch (injurious chips).

The top wall is not necessarily a wall of constant thickness. It can have different parts, some of which can be massive, but it has at least one part that acts as a wall blocking the dispensing orifice.

The molding tool intended to produce the molded part is conventional: it comprises at least two parts which are movable relative to one another. In the case of a tube head, these two parts are the punch and the die. Very often, the neck must have a screw thread on its outer wall, which requires using a matrix itself in several moving parts which move away from each other - for example by means of radial displacements - to facilitate demolding of the threaded part.

The molded part according to the invention has a neck which is not immediately provided with an orifice: the latter is produced in a later stage but without the need to use a cutting tool. In this way, the compression can be carried out with a not necessarily toroidal blank, the massive shape of which on the one hand is easier to obtain in a reproductive manner by weight (improvement of the compression molding conditions) and on the other hand reduces the extent and heterogeneity of cooling. This shape lends itself to better reproducibility by weight since it is possible to extrude a massive extrudate than the shears at the outlet of the die: the amount of material thus obtained depends on the displacement perpendicular to the direction of extrusion of a shear blade external to the die and not of the displacement of a sliding valve in the axial direction inside the die and having to discontinuously close an annular orifice.

The neck is surmounted by a top wall which temporarily plugs the orifice and a part of which - which we will call hereafter the seal - is partially or entirely detached in a later stage of the process using the application of a simple mechanical force applied in a part of the top wall, called the mechanical force application zone and distinct from the breakable zone.

The top wall comprises at least four zones: a zone for applying mechanical force, a zone for transmitting mechanical force, a breakable zone and a support zone. The mechanical force is intended to be applied to said top wall, at the level of the application zone, with sufficient intensity to break said top wall at the level of said notch. The intensity of the force necessary to cause the rupture depends on the direction of said mechanical force and the distance of its point of application from the breakable zone.

In a preferred mode, the cover - that is to say the part of the top wall which detaches partially or entirely after rupture of the breakable zone - is the zone transmitting the forces applied to tear the top wall at the level of the notch and the part corresponding to the attachment of the top wall to the neck is the support zone. The cover has any geometry adapted to the type of mechanical force that must be applied to cause the rupture. It can be in the form of a rod to amplify by leverage a force applied at its end, as illustrated in FIG. 1, or even have a simple shape of veil as illustrated in Figure 4 or have a protuberance whose cross section is in the shape of a non-convex polygon (Figure 5) or whose profile (section through a diametral plane passing through the axis) is T-shaped as illustrated in Figure 3. L 'notch follows any curve, not necessarily flat and not necessarily closed. If it is closed, the rupture of the breakable zone leads to complete detachment of the cover. The latter is advantageously removed, preferably using the residual part of the energy supplied to break the breakable zone. The cut can also follow an open contour. In this case, the rupture of the breakable zone leads to a partial detachment of the cover. The latter is then in the form of a tongue which must be kept folded in an open position so that the orifice is delimited by the outline of the broken breakable zone and the base of the tongue thus obtained and kept folded. In the latter case, it is not necessary to evacuate the partially detached cover.

The breakable zone is notched with a notch, the section of which by a diametral plane passing through the axis of the neck is oriented in a direction that is slightly inclined relative to the axis of the neck. For example, if the notch has a V shape, the bisector of the V is slightly inclined with respect to the axis of the neck and describes a cylinder or a cone having an angle at the center less than 90 °, preferably less than 60 °. Thus, said bisector makes an angle between 0 and 45 °, preferably between 0 ° and 30 ° with the axis of said neck. The angle of the V is between 30 and 90 °, typically between 40 and 50 °. The V does not necessarily have its branches symmetrically around its bisector.

In general, the desired orifice is simply circular and the breakable zone is an annular notch whose section is a V whose internal branch (that is to say the branch closest to the axis) is slightly inclined by relative to the axis and whose outer branch is more strongly inclined. Typically, the internal branch of the V makes an angle with the axis less than 5 °, the bisector makes an angle of 25 ° with the axis of the neck and the external branch makes with said axis an angle less than 55 °.

The shape of the cut locally favors a concentration of the stresses generated by the application of a mechanical force, whether this is a force or a moment applied in a particular place of the cover. The transverse wall may be of small extent, for example limited to the breakable zone, but it must be present to orient the notch so that its axis is substantially parallel to that of the neck.

The Applicant has found that such a geometry concentrates the breaking energy and tolerates a large number of mechanical stresses which can lead to a controlled tearing of the breakable zone. This tolerance is much greater than with an annular notch located for example on the wall of the neck and having as section (by an axial diametral plane) a V whose bisector is perpendicular to the axis of the neck.

The easily breakable area is, by the very presence of the notch, thinner than the neighboring areas. Preferably, the residual thickness under the notch is less than 30% of the overall thickness of the transverse wall outside the notch. Typically, for the geometries of containers envisaged, it is between 0.1 and 0.6 mm. As it is thin, it cools more quickly than the other parts of the neck, which makes it possible to apply forces causing the rupture less brutal than impacts, that is to say with forces generating deformation rates of around 10 ³ s- '. The mechanical force is for example an axial push or traction, a rotation around the axis of the neck, a combination of the two (during the unscrewing - stripping of the head for example), a force applied to the other end of the lid in the form of a stick, etc. In a preferred embodiment of the invention, the rupture of the cover is carried out during the cooling following the molding, as soon as the material stabilizes, which makes it possible to break the cover before the ejection of the part from the molding tools. It is recommended to break the breakable zone as soon as the plastic material reaches, in said breakable zone, a temperature close to the glass transition temperature or then wait for the entire head to cool completely, the zone breakable rising in temperature during the cooling of the molded part due to the thermal inertia of the thicker zones which surround it.

It is also advantageous to place the blank to be compression molded above or directly opposite the end of the protruding part of the molding tool intended to produce the interior surface of the neck. The part of the blank which is in contact with the tool cools a little faster than the rest of the blank by conduction. The surface imperfections linked to the greater cooling of the plastic material there, the friction and the heterogeneous flow of the resulting material will remain on the seal which will then be detached. They will therefore not see each other.

This process proves to be particularly advantageous when molding tools are used in continuous kinematics, such as those described in French application n ° 01 03706 filed by the plaintiff on March 19, 2001. In this application, in addition to their mutual reconciliation causing compression 'a draft, the molding tools are also moved in a general continuous movement having a component not necessarily flat but remaining orthogonal to their direction of mutual approach. Example 2, described below, illustrates an embodiment of the invention applied on the one hand to the production and installation of the blanks on the molding tools in continuous movement and on the other hand to the realization of the orifice while the molded tube head is always fitted on the punch in motion.

Another solution applicable in continuous kinematics consists in giving a part of the cover a rod shape similar to that of Example 1 and in applying a force to the end of the rod as soon as the die is removed from the punch, using, for example, a stationary finger in front of which the punch still fitted with the tube head scrolls. Under the effect of the flexion imposed on the rod and transmitted by it to the transverse wall, the breakable zone is broken and the cover is ejected in a precise and reproducible direction outside the production line in continuous movement.

To obtain a clear and reproducible rupture, the material preferably has a modulus of elasticity in traction at ambient temperature greater than 200 MPa, preferably greater than 500 MPa.

Although developed with the aim of producing continuous kinematics of molded parts having a neck provided with an orifice, this method can be applied to molding methods in which machines are used working step by step. Due to the design of the breakable zone which it implies, the method according to the invention makes it possible to choose from a large number of possible mechanical stresses, that making it possible to obtain, at the lowest cost, a controlled tearing of the breakable zone.

The final stage of the process, in which the cover is torn, can be integrated into the actual production (implemented during the cooling which follows the molding, or just before the output of the manufacturing device in continuous kinematics, etc. .). It can also be deferred until the first use: example 5 illustrates this case, where it is the user who, when he unscrews the cap for the first time, activates the rupture mechanism of the cover. Such a method of the invention thus makes it possible to obtain tube heads provided with a system guaranteeing the absence of violation of the tube before its first use.

FIGURES

All of the figures illustrate the production of flexible tubes. With the exception of FIG. 3, they show diametrical sections of tube heads, parts of the compression molding tool or caps.

FIG. 1a illustrates a particular tube head produced according to the invention, before application of the force intended to break the breakable zone.

FIG. 1 b illustrates a particular shape of the section of the breakable zone according to the invention.

FIG. 2a illustrates, using a diametral section, the positioning of a blank in a compression molding tool

Figure 2b illustrates the molding tool and the molded part at the end of compression. This has a cover whose T-shaped profile causes the presence of an annular groove on the external surface of the cover.

Figure 2c illustrates the distance of the punch provided with the tube head thus molded. Due to the scale used, the annular notch was not shown. Lα 2d illustrates the evacuation of the lid after rupture of the breakable zone, the latter having been caused by the axial displacement imposed by a fork whose fingers come to fit into the annular groove.

FIG. 3 illustrates in perspective a solution in which the tubes of FIGS. 2a to 2d are produced using molding tools which follow a continuous rotational movement and in which the removal of the lids is carried out simply by trapping the ends said movable lids in a static rail not tangent to the path of the tubes.

Figure 4 illustrates another case where the cover is torn and then removed using an axial thrust

FIG. 5 illustrates another case where the cover is torn and then removed using a loosening carried out during the stripping of the matrix.

FIG. 6 illustrates, in three variants, a modality of the invention in which the neck is overmolded by compression on a plug which has been placed beforehand in a cavity of the matrix. Figure 6a) illustrates the device before overmolding by compression of the tube head on the plug; FIG. 6b) illustrates the device after overmolding by compression of the tube head on the stopper; Figures 6c), 6e) and 6g) illustrate the parts of the tooling provided with the toric edge which makes it possible to shape the breakable zone (6c): punch; 6e) and 6g): plug); Figures 6d), 6f) and 6h) detail the assembly of the tube head + plug obtained after overmolding in three different cases.

EXAMPLE 1 (Figures la and 1b) - Tube head designed as part of the method according to the invention

The tube head 1 illustrated in FIG. 1 a has a shoulder 2 and a neck 3 the upper end of which is surmounted by a top wall 4 which has at least one thinned zone 6, the upper face of which is provided with a notch 5, the closed contour of which delimits the desired shape of the orifice. This thinned zone 6, also called breakable zone, is surrounded by two zones 7 and 8 able to resist the mechanical force F which is necessary to break said breakable zone, one of them (7) being intended to transmit said mechanical force and the other (8) to serve as support.

The cover 14 is the part of the top wall 4 which is detached and, in the present case, removed by the application of mechanical force F on the end 91 of the stick 9. The area of application of the force is the end 91 of the stick 9. The zone capable of transmitting the mechanical force comprises the stick 9 and the web 7. The application of the mechanical force F, amplified by the effect of the lever arm which constitutes the stick 9, results in the rupture of the breakable zone and the evacuation of said cover 14.

The breakable zone 6 is notched with a V-shaped notch 5, with an internal branch 61 which forms an angle of 5 ° with the axis of the neck, an external branch 62 which forms an angle of 55 ° with said axis and the bisector 63 of the V which makes an angle of 25 ° with the axis of the neck.

In the particular case of this example, the head is molded with high density polyethylene. Its neck 3 has an external diameter of 11.5 mm and an average thickness of 1.5 mm (excluding screw thread. The transverse web 7, about 1 mm thick, is connected to the top end 8 of the neck 3 , which serves as a support zone The rod 9 has a height of 10 mm, the residual thickness of the veil at the level of the breakable zone is 0.3 mm.

It suffices to apply a force F of the order of 1 newton so that the breakable zone tears and the cover is ejected. Once the cover has been removed, the neck 3 has a 7 mm diameter orifice which does not show any burrs or local deformation.

If, as in Example 2, molding tools are used which move in continuous kinematics, the punch provided with the head 1 of the tube is scrolled in front of a stationary finger. The latter retains the end 91 of the rod 9 in motion and, under the effect of the bending imposed on the rod and transmitted by the latter to the transverse wall 5, the breakable zone 6 is ruptured and the cover is ejected according to a precise and reproducible steering outside the production chain in continuous motion. The Applicant has obtained frank and clear breaks in the breakable zone with a linear speed close to or greater than 0.2 meters per second. Very satisfactory results have been obtained with a speed of 0.8 meters per second with molded heads made of high density polyethylene.

EXAMPLE 2 (Figures 2a, 2b, 2c and 2d, 3) - Method according to the invention applicable to an embodiment of tube heads by compression molding in continuous kinematics

The flexible tube is produced by assembling two parts produced separately: a flexible cylindrical skirt 10 and a head, similar to that described above. The head of high density polyethylene is molded and welded autogenously on one end 11 of the skirt 10 using a compression molding technique of an extruded blank 20.

FIG. 2a illustrates, using a diametral section, the positioning of a blank 20 of high density polyethylene in a compression molding tool. This molding tool comprises a punch assembly 35 and a die assembly 30. Compression is obtained by relative approximation of the punch assembly 35 and the die assembly 30 until relative immobilization of the two parts of the tool. Each of these parts tooling comprises parts (respectively 350 and 351, 300 and 301) which can be movable between them but which are immobile and integral with each other during compression. The relative movement of these parts does not require the introduction of specific control: it is controlled by the relative overall movement between the punch assembly and the die assembly. At the start of compression, the central protuberance 352 is integral with the peripheral portion 351, which forms the punch assembly 35. The portions 300 are adjacent as a result of a radial displacement imposed by a conical fitting and the whole, integral with the upper part 301 forms therewith the matrix assembly 30.

The skirt 10 is fitted around the peripheral part 35 of the punch, one of its ends 11 projecting slightly from the end of this part 35 of the punch, which serves as a mold for producing the internal surface of the tube head (interior shoulder and neck). The end 352 of the central part 350 of the punch is a central protuberance intended to mold the inside of the neck. The moving parts 30 of the die move radially to disengage the screw thread, once it has been molded.

FIG. 2b illustrates the molding tools and the molded part 21 at the end of compression: it is a flexible tube 21 comprising the cylindrical skirt 10, the shoulder 22 and the neck 23 surmounted by a top wall 24. The head has been molded and welded autogenously on the end 11 of the skirt 10. The top wall 24 comprises a transverse wall 25 acting as a seal blocking the dispensing orifice and a protuberance 29 having a T-shaped profile, so that it has an annular groove 28 on its side wall.

FIG. 2c illustrates the distance of the punch assembly from the matrix assembly. The flexible tube thus produced remains integral with the assembly punch and cool. A fork 40 is brought close to the tube head after a few seconds of cooling when the high density polyethylene is stabilized.

FIG. 2d illustrates the evacuation of the top wall 24 after rupture of the breakable zone, this having been caused by the axial displacement imposed by the fork 40 whose fingers come to fit in the annular groove 28. The breakable zone 26 has a geometry with an annular V-shaped notch identical to that of the breakable zone of Example 1. In this way, the head of the finished tube 50 has a cylindrical neck provided with a dispensing orifice.

FIG. 3 illustrates an alternative solution to that illustrated in FIG. 2d: the molding tools, and in particular the punches, follow a continuous rotational movement R, such as that imposed by the device referenced 10 in FIG. 2 of French application no. 01 03706. LesOnce formed, the tubes 50 remain integral with said punches after molding and the removal of the lids is carried out by a simple trapping of the ends of the T-shaped lids, their annular grooves 28 coming to fit in a rail 40 'static and not tangent to the trajectory of the tube heads.

EXAMPLE 3 (Figure 4)

FIG. 4 illustrates another embodiment of a tube in which the head is also compression molded and welded simultaneously to the skirt, in which the top part 64 comprises a simple veil 65 having an annular notch in the vicinity of its attachment to the neck. The veil is torn and then removed using an axial push. The cover may, as illustrated in FIG. 4, have a geometry limited to the veil 65 or else, as illustrated in FIG. 1, include the said veil and also be provided with a rod-shaped part to facilitate gripping and the axial thrust. . EXAMPLE 4 (Figure 5)

FIG. 5 illustrates another embodiment of a tube in which the head is also compression molded and welded simultaneously to the skirt, in which the top wall 74 which comprises a protuberance 75 of non-convex polygonal section (typically a star) and a part bass acting as a seal. The die 30 'does not have radially movable parts (300) and the release of the head with its threaded neck is carried out by unscrewing. As the non-convex polygonal protuberance 75 still occupies the cavity of the mold which formed it, it is blocked in rotation, the breakable zone tears under the effect of the resulting twist, the protuberance is thus detached and then removed during unscrewing.

It is also possible to produce this type of cover on dies with parts with radial displacement (300). In this case, the tube head is removed from the mold after cooling, then the breakable zone is torn and the cover is removed by rotation using a key having the shape complementary to the concave polygonal section.

EXAMPLE 5 (Figures 6a to 6h)

This example makes it possible to solve the delicate problem imposed by the extremely fine adjustment of the air gap existing at the end of the travel between the mobile parts of the tool, in particular in the vicinity of the cavity used to shape the breakable zone. In fact, to obtain homogeneous rupture conditions on these tubes produced at high speed, it is important to make the geometry of the breakable zone as repeatable as possible, the minimum thickness of the breakable zone having to vary at most by a few hundredths of a millimeter. This delicate adjustment of the air gap is long, which limits the production rate, especially since it must be carried out frequently (adjustments linked to the expansion of the tools, to the wear of the active parts, etc.). In addition, the tool is subject to a significant risk of breakage in the event of adjustment failure, lack of plastic material in the tool, presence of a foreign body, etc. Finally, the tool is also exposed at an increased risk of endurance failure due to its sensitivity to wear.

These different points are advantageously reduced, or even eliminated, if the breakable zone is shaped by compression molding of a blank between a rigid metallic element - belonging for example to the punch - and a less rigid element, for example made of plastic . Thus, a compression tooling is used comprising a first movable part and a second movable part, said first movable part being, at least in the part of the imprint contributing to the shaping of said breakable zone, in a less rigid material than that of said second movable part. This can be advantageously achieved if a direct molding of this part of the neck is carried out on the plug which is intended to close the dispensing orifice.

The combination of the two materials - one metallic, the other plastic - allows contact between the two molding parts without risk of damage to one of them. It is thus possible to limit the fineness of adjustment of the air gap (reduction of the adjustment time) and reduce the risk of deterioration of the tools (mechanical stop on the cap, or stopping of the tools on the shoulder in the event of a presence fault plug). In addition, thanks to overmolding, a container + stopper assembly is directly obtained in which the contacting surfaces correspond perfectly, which allows the container to be hermetically sealed for the entire duration of its use. Thus, in the context of this embodiment of the invention, one of the movable parts of the tool, the matrix in this case, can be provided with a plug intended to close said orifice. The latter is positioned so that its internal surface at least partially serves as a molding imprint for shaping said neck, at least at its breakable zone.

The molding of the neck on the stopper can be carried out by proceeding in a similar manner to the process described in Example 4 of international application PCT / FR02 / 00686 filed by the applicant. In this process, it is a question of making a flexible tube. The tube head is molded and welded to a cylindrical skirt obtained by cutting from a sleeve. In this particular case, the head is welded to the skirt simultaneously with its shaping.

We can see in FIG. 6a a plug 805 which is placed in the cavity of the matrix 830. As indicated in the international application PCT / FR02 / 00686, this plug may have been itself molded shortly before using the same matrix but it can also have been obtained independently on another molding device. Outside this cavity, the imprint of the matrix 830 has a shape which defines the outer surface of the shoulder 82 of the tube. The internal surface of the plug 805 defines the external surface of the neck 83 and of the base of the neck.

The punch 835 is provided with a skirt 801. The end 802 of which projects slightly beyond the shoulder 846 of the punch. The stopper 805 has an average thickness of 1 mm. The internal surface of the plug, possibly provided with one or more screw threads, defines the external surface of the neck to be shaped. The part of the imprint of the matrix 830 not covered by the stopper defines the outer surface of the shoulder. The matrix 830 acts as a support tool. A blank 820 made of low density polyethylene taken from the extruder outlet is placed either on the end of the punch or in the cavity of the die 820. It is compressed by bringing the punch and the die together until the intended shape is obtained. of the head. Under the effect of this translation, the blank 820 deforms and the flow of the plastic material is guided by the free surfaces of the residual air gap which gradually decreases in volume. When the punch 835 and the die 830 are joined, they define a molding cavity where the end 802 of the skirt is trapped. Under the effect of compression, the plastic material of the blank flows and fills the various parts of the volume delimited by the imprints of the punch and of the die, thus forming the shoulder 82 and the neck 83, provided with 'a transverse top wall 84 and a breakable zone 86. The plastic material also comes into contact with the end 802 of the skirt. The plastics of the head and the skirt are welded together without further heat or material. They remain welded together after a slight pressure maintenance and after cooling.

We remove the tools and extract the assembly. The assembly is allowed to cool so that there is complete dimensional stabilization of the neck and the stopper.

The breakable zone (86, 86 ', 86 ") is shaped using a molding part which has the shape of a toric edge (90, 90', 90"). This O-ring belongs either to the male tool (punch - Figure 6 c) - 90), or to the plug (Figure 6e) (90 ') and Figure 6g) (90 ")). In the first case (Figure 6c) and 6d)), the rupture is made on the external surface but the risk of appearance of burr is low since the steel toric edge makes it possible to impose sharp angles, therefore a high coefficient of multiplication of the stresses prevailing in the area separable when broken. In other cases, a possible burr resulting from the rupture of the breakable zone may remain invisible inside the neck.

The breakable element can be secured to the plug, including a protuberance 89 or 89 ′ undercut therein. The tube will only be effectively opened during the first unscrewing of the stopper and the rupture force may then be associated with inviolability.

To ensure anti-unscrewing of the cap after shaping the head, a slight relief, such as a grain of rice, can be provided at the end of the screw thread. The undercut protrusion can pass through the thickness of the stopper (89 ") and the material thus extruded through the stopper can be used to fill the top of the stopper and in particular to integrate a personalized decoration, for example a customer logo.

BENEFITS

• simple molding tools;

• elimination of faults associated with previous embodiments of the orifice (burrs, pollution, seizure, etc.); • better reproducibility by weight of the blank which promotes the reliability of compression molding;

• ease of adaptation to a continuous kinematics manufacturing process.

Claims

1) Method for manufacturing by compression molding parts (1) of plastic material having a neck (3) provided with an orifice comprising a first step of producing a blank (20) of plastic material and a second compression step of said blank, in which said blank, brought to an appropriate temperature, is placed in the air gap between at least two movable parts (30 and 35) of the compression tooling and is then compressed by mutual approximation of said w movable parts of the tool, the plastic of the blank flowing so as to fill the cavities of the imprints of said movable parts until relative immobilization of said movable parts, the imprints of said movable parts of the tool once joined defining the volume of said part having a neck, said imprints being drawn so that

Said neck, once molded, has a top wall (4) which comprises a thinned zone (6) whose contour delimits the desired shape of the orifice, said method being characterized in that said thinned zone (6) is bordered by a notch (5), the section of which by a diametral plane passing through the axis of the neck is oriented in a direction substantially parallel to the axis of the neck 0 (100), in that said top wall (4) also comprises an application zone (91) of a mechanical force (F) intended to be applied to said wall with sufficient intensity to break said top wall at the level of said notch, said application zone being distinct from said thinned zone, said top wall also comprising two zones (7 and 58) capable of withstanding said mechanical force (F), one (7) of which is intended to transmit said mechanical force and the other (8) to serve as support, and in that after opening the said tool for molding by relative displacement of its movable parts, said mechanical force is applied in said application zone (91) so that a rupture occurs at said 0 notch and that at least one part (14 ) from the top wall is detached, thereby freeing the dispensing orifice. 2) Method according to claim 1 wherein the rupture of the breakable zone (6) is carried out during the cooling following the molding, as soon as the plastic material reaches the level of the breakable zone its glass transition temperature.

3) Method according to claim 1 or 2 wherein the breakable zone (6) is notched with a V-notch, the angle of the V being between 30 and 90 °, preferably between 40 and 50 °, the bisector of the V making an angle between 0 and 45 °, preferably between 0 ° and 30 °, with the axis of said neck.

4) Method according to any one of claims 1 to 3, wherein the top wall (4) comprises a transverse web (7) and a rod (9) at the end (91) of which a force (F) is applied laterally to cause the breakable zone (6) to rupture.

5) Method according to any one of claims 1 to 3, wherein the top wall (64) comprises a veil (65) which, after molding, is torn and then removed using an axial thrust.

6) Method according to any one of claims 1 to 3, wherein the top wall (24) comprises a transverse wall (25) acting as a cover and a protuberance (29) having a T-shaped profile, such so that it has on its side wall an annular groove (28) serving to grip the fingers of a fork (40) or a rail (40 ') whose relative displacement causes tearing and then removal of said cover.

7) Method according to any one of claims 1 to 3, wherein the top wall (74) is a protuberance (75) of non-convex polygonal section, typically a star, which is torn and then removed using a rotation or unscrewing movement. 8) Method according to any one of claims 1 to 7, wherein the compression molding tools (30 and 35) are also moved in a continuous movement orthogonal to their direction of mutual approach.

9) Method according to claim 1 modified in that one uses a compression tool comprising a first movable part (830 + 805) and a second movable part (835), said first movable part being, at least in the part of the imprint contributing to the shaping of said breakable zone (86), in a less rigid material than that of said second movable part.

10) Method according to claim 9 wherein said first movable part (830 + 805) is, at least in the part of the imprint contributing to the shaping of said breakable zone (86), in plastic material while the second mobile part is metallic.

1 1) The method of claim 10 wherein said first movable part (830 + 805) comprises a cavity provided with a plug (805) intended to close said orifice, said plug being positioned so that its internal surface serves at least partially of molding imprint for shaping said neck (83), at least at its breakable zone (86).

12) A method according to any one of claims 9 to 1 1 wherein the breakable zone (86) is shaped using a toric edge (90) belonging to the punch (835).

13) The method of claim 1 1 wherein the breakable zone (86 ', 86 ") is shaped using an O-ring (90', 90") belonging to the plug (805).