WO2004020168A2

WO2004020168A2 - Method for making a plastic part having a neck provided with a dispensing orifice designed to be closed with a cap

Info

Publication number: WO2004020168A2
Application number: PCT/FR2003/002581
Authority: WO
Inventors: Bertrand Gruau
Original assignee: Cebal S.A.S.
Priority date: 2002-08-27
Filing date: 2003-08-26
Publication date: 2004-03-11
Also published as: AU2003278214A1; EP1534489A2; FR2843909B1; AU2003278214A8; WO2004020168A3; FR2843909A1; WO2004020168A8

Abstract

The invention concerns a method for making by compression moulding plastic parts having a neck provided with a dispensing orifice comprising a first step which consists in producing a plastic blank (820) and a second step which consists in compressing said blank, wherein the moulding cavities are so designed that said neck, once moulded, has a summital wall including a cleavable zone with a notch whereof the outline delimits the desired shape for the orifice. The notch has a typically U-shaped or V-shaped cross-section, oriented in a direction substantially parallel to the neck axis. The neck, at least at the cleavable zone, is shaped by compression moulding of said blank between a first rigid mobile part (835) and a second mobile part (830+805), less rigid than the first mobile part, for example made of plastic material. Preferably, the neck is overmoulded directly on the cap which is designed to close the orifice.

Description

PROCESS FOR MANUFACTURING A PLASTIC MATERIAL HAVING A NUT PROVIDED WITH A DISTRIBUTION ORIFICE TO BE BLOCKED BY

A PLUG

The invention relates to a method of manufacturing by compression molding of plastic parts having a neck provided with a dispensing orifice. These parts are containers or parts of molded containers. The invention is more particularly intended for 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 parts manufactured separately: a cylindrical flexible 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 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 069414) or a compression molding technique for an extruded blank (FR 1 324471.

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 outer surface of the shoulder and the 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 the context of this request, which relates to a process comprising a compression molding step, we will designate "punch" the mobile part of the compression molding tool, the imprint of which is intended to define the interior of the part at at least in the vicinity of its neck and "die" the movable part of the compression tooling whose imprint is intended to define the outside of the part at least in the vicinity of its neck, Finally punch and die will be called movable parts of compression molding tools in the sense that they are movable relative to one another,

In French application no. 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, the solutions have been the subject of numerous patents. The fact remains that, whatever form of the blank used, problems remain:

• either the blank is presented in the form of a massive nut and in this case one cannot avoid the presence of a central veil blocking the dispensing orifice, which requires an additional perforation operation to obtain the orifice of distribution;

• either the blank is produced with a substantially toroidal shape but in this case its handling and its positioning in the molding tool are very delicate. Whatever the form of the blank, these problems are exacerbated when considering the use of tools when they are driven by a continuous movement, such as those described in French application No. 01 03706.

In French application n ° 02 03332, the applicant has developed a method of manufacturing by compression molding of plastic parts provided with a neck having an orifice which solves the problems mentioned above and which can therefore be easily implemented using tools driven by continuous kinematics. This process comprises a first step of producing a plastic blank, typically by extrusion, and a second step of compression molding of said blank, where the neck thus formed has a top wall provided with a notch whose contour delimits the desired shape of the orifice and a third step where a mechanical force is applied at a location on the summit wall so that a rupture occurs at the level of said notch and that at least part of the summit wall detaches, thereby releasing the dispensing orifice.

In the second step of this process, the blank is brought to an appropriate temperature and placed in the space between two moving parts of the compression tooling then is compressed by mutual approximation of the moving parts of the tooling. The mass of the blank, whose shape typically obtained by extrusion is far from the final shape, undergoes significant plastic deformation. The plastic material flows so as to fill the cavities of the impressions of the mobile parts until relative immobilization of said mobile parts. Said imprints, when the movable parts of the tool are joined, delimit the volume of the plastic part provided with its neck, in this case the tube head. In this process, said imprints are drawn so that the neck, once molded, has a top wall which has a notch whose contour delimits the desired shape of the dispensing orifice. When the container is a tube, the moving parts of the compression molding tool are a punch - whose imprint at least partially defines the interior surface of the head of the tube - and a die - whose imprint defines at least partially the outer surface of the tube head.

The notch made has a section through a diametral plane passing through the axis of the neck which, typically in V or U, is 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 °. In line with this notch, the top wall of the neck has a small residual thickness and constitutes a more fragile zone, which we will call hereinafter rupture zone or even breakable zone.

The breakable zone is, by the very presence of the notch, thinner than the neighboring zones. 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 faster than the other parts of the neck, which makes it possible to apply forces causing the rupture less brutal than shocks, that is to say with forces generating deformation rates of the order of 10 ³ s ^-1 .

The small thickness of the breakable zone causes a delicate problem because it is necessary to adjust in an extremely fine way 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, in order to obtain homogeneous rupture conditions on containers or 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 only 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 (misadjustments linked to the expansion of the tools, 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 an increased risk of endurance failure due to its sensitivity to wear.

The Applicant has thought that these various points would be advantageously reduced, or even eliminated, if the neck, at least at the level of its top wall, in particular in the vicinity of the notch and the breakable zone, is shaped by compression molding d 'a blank between a rigid metal element - for example belonging to the punch - and a less rigid element, for example 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. - O

The combination of the two materials - one metallic, the other less rigid, typically a plastic material - allows contact between the two molding parts without risk of damage to one of them. It is thus possible to limit the fine adjustment of the air gap (reduction of the adjustment time) and reduce the risk of deterioration of the tools.

It is thus possible to equip at least locally the imprint of one of the mobile parts of the molding tool with an insert made of a less rigid material than that of the other mobile part. It may for example be a plastic insert placed in a cavity provided for this purpose in the imprint of a movable part of the molding tool. It is also possible to equip the impression of one of the movable parts of the compression tool with the plastic plug intended to close the dispensing orifice and use this plug as part of the molding tool, at least for as regards the shaping of the part of the neck which comprises the breakable zone.

In a preferred embodiment of the invention, a cavity is formed in the matrix and this cavity is filled with a plug intended to close the dispensing orifice. The stopper is placed in such a way that its internal surface at least partially serves as a molding imprint for shaping said neck, at least at its breakable zone. The blank is thus compressed between a punch and a die, the latter being fitted with a plug and a direct overmolding is carried out by compression of this part of the neck on the plug.

Thanks to the overmolding on the cap, the fineness of adjustment of the air gap is limited to the level of the breakable zone and the risk of deterioration of the tools can be easily reduced (mechanical stop on the cap, stop of the tools on the shoulder in the event of a defect in the presence of the cap, etc.). In addition, there is obtained a part having a neck provided directly with its cap with contacting surfaces which correspond perfectly, which ensures a hermetic closure of the container throughout the duration of its use.

The cavity formed in the matrix can be designed so as to fully support the plug during compression, so that said plug does not deform under the effect of compression forces. Conversely, it is possible to design the cavity in such a way that the plug meets only local support and that it deforms elastically during the compression of the blank by imposing a given shape on the external surface of the neck. The latter, once stabilized, is, at least locally, prestressed by a part of the plug which tends to return to its initial shape when the compression forces are no longer applied. After removing the part + cap assembly from the mold, the cap shrouds and / or encloses the neck, which reduces the risk of unscrewing after shaping the head.

The part of the stopper concerned by the lack of support can be for example the bottom of the stopper: the depression of the bottom causes a general deformation of the stopper which results mainly in a longitudinal extension of the side wall. The latter shrinks longitudinally when the stresses are relaxed and traps the reliefs (typically the screw thread (s), the snap-on bead (s), etc.) produced on the external wall of the neck .

The part of the stopper affected by the lack of support can also be the side wall of the stopper: by drawing the stopper and the cavity appropriately (the side wall is not supported by the matrix on a large part of its surface but it must still ensure the centering of the plug), the compression forces result in a local expansion of the side wall. The compression force is maintained until the plastic material of the neck is stabilized. Then the compression force is released and the side wall of the cap retracts by "fretting" the neck. The cavity formed in the matrix can for example have a cylindrical part towards the bottom to ensure the centering of the stopper and a conical part widening towards the surface of the impression: the hooping which will result will be more intense at the base of the neck.

The clamping force resulting from this local hooping, substantially proportional to the value of elastic deformation of the part of the cap concerned, makes it possible to ensure the anti-unscrewing of the cap after shaping the head, which presents an alternative solution. or complementary to the installation of a grain of rice at the end of the fillet.

The example presented below shows the shaping of a tube head provided with a neck by overmolding on a plug according to a process which is adapted from a process described in example 4 of the international application. PCT / FR02 / 00686 filed by the applicant. In this example, the breakable zone is shaped using a molding part which has the shape of a toric edge and this toric edge belongs either to the male tool (punch), or to the plug. In the first case, 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 breakable during rupture. In the other case, the risk of appearance of burrs is certainly higher but any burr resulting from the rupture of the breakable zone will remain inside the neck and will therefore not be visible. Thus this modality of the method according to the invention makes it possible to obtain the container with a neck on the one hand provided with a transverse top wall comprising a breakable zone surrounding the dispensing orifice and on the other hand already covered with the cap intended for close said dispensing orifice once it has been made by tearing the breakable zone.

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 molded part according to the invention has a neck which is not immediately provided with an orifice: the latter is produced in a subsequent step after the first unscrewing of the plug. In this way, the compression can be carried out from a blank which is not necessarily toroidal, with a massive shape which is easier to handle and which also has the following advantages: on the one hand, it is easier to obtain in a reproductive manner by weight (improvement in compression molding conditions) and on the other hand it is subject to less intense, less rapid and less heterogeneous cooling. This shape lends itself in fact 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 blade of shearing external to the die and not the displacement of a sliding valve in the axial direction inside the die and having to seal discontinuously an annular orifice.

The neck is surmounted by a top wall which closes the orifice and part of which - the cover - is partially or entirely detached later. The top wall comprises at least four zones: a zone for applying mechanical force, a zone for transmitting mechanical force intended to be applied to cause tearing of the rupture zone, a zone breakable and a support area. The breakable zone is notched with a notch, the section of which by a diametral plane passing through the axis of the neck has a shape typically in U or in V oriented in a direction slightly inclined with respect to the axis of the neck. For example, if the notch has a V shape, the bisector of the V is slightly inclined relative 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 promotes 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 controlled tearing of the breakable zone. This tolerance is much greater than with an annular notch located for example on lα cylindrical aperture 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 rupture of the cover can be carried out subsequently by the user. In a preferred embodiment, the molding impressions are drawn so that the cover - that is to say the part of the transverse top wall of the neck which is surrounded by the breakable zone - obtained comprises a protuberance in counter skin which is anchored in the cork. Thus, 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.

To avoid untimely unscrewing of the neck until the first use, one can either provide a cover with a protrusion undercut as described above, or provide a slight relief, like grain of rice, at the end of the fillet. screwing or, as also indicated above, use a matrix whose cavity intended to receive the stopper is designed so that the stopper is deformed during compression and that, by elastic loosening, it then comes to grip or shrink the neck.

To facilitate anti-unscrewing of the cap during the entire period of use of the container, a slight relief, such as a grain of rice, can be provided at the end of the screw thread.

The undercut protrusion can also pass through the thickness of the stopper: in this way, the material is somehow extruded through the stopper and can be used to fill the top of the stopper. While using the same standard plug base, we therefore integrate a decor personalized on the top of the cap, for example the brand of the packaged product, the logo of the manufacturer of the said product, etc.

This process proves to be particularly advantageous when using continuous kinematic molding tools, 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 resulting in the compression of 'a draft, the molding tools are also moved in a general continuous movement having a component not necessarily planar but remaining orthogonal to their direction of mutual approach.

FIGURES The figures represent diametrical sections of tube heads, parts of the compression molding tool or plugs.

FIG. 1 illustrates the device before overmolding by compression of the tube head on the plug.

FIG. 2 illustrates the device after overmolding by compression of the tube head on the stopper

Figures 3, 5 and 7 illustrate the parts of the tooling provided with the toric edge which makes it possible to shape the breakable zone (Figure 3: punch; Figures 5 and 7: plug)

Figures 4, 6 and 8 detail the assembly of the tube head + plug obtained after overmolding. EXAMPLE (Figures 1 to 8)

The molding of the neck on the cap is carried out by adapting the method described in Example 4 of international application PCT / FR02 / 00686 filed by the applicant. In this process, it is a matter 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 by compression molding.

We can see in Figure 1 a plug 805 which is placed in a central cavity of the matrix 830. As indicated in the international application PCT / FR02 / 00686, this plug may have itself been molded shortly before using the same matrix but it can also have been obtained independently on another molding device. Outside this cavity, the imprint has a shape which defines the outside 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 protrudes slightly from 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 is taken from the extruder outlet and is deposited on the tooling. This deposit can be made either on the end of the punch or in the imprint of the die 820. It is advantageous to place this blank 820 on the end of the punch 835, for example above the protruding part of the punch 835 , this one being then presented "head up", opposite to what is illustrated in FIG. 1. In such a configuration, the part of the blank which comes into contact with the punch cools - by conduction - a little faster than the rest of the draft and will flow little. The surface imperfections related to the greater cooling of the plastic material at this location, 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.

The blank 820 is compressed by bringing the punch and the matrix together until the target shape of the head is obtained. Under the effect of this translation, the blank 820 is deformed and the flow of the plastic 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. The toric edge 90 imposes the shape of the notch 85 which surmounts 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 which is a tube 81 whose head, comprising a shoulder 82 and a neck 83 closed by a top transverse wall 84, is fitted with a plug 805. 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 toric edge belongs either to the male tool (punch - Figure 3 - 90), or to the plug (Figure 5 (90 ') and Figure 7 (90 ")). In the first case (Figures 3 and 4), the rupture is done on the external surface but the risk of appearance of burr is low since the steel toric edge allows to impose sharp angles, therefore a strong coefficient of multiplication of stresses prevailing in the breakable zone during the rupture In the other cases (FIGS. 5 and 6; FIGS. 7 and 8), a possible burr resulting from the rupture of the breakable zone may remain inside the neck and therefore remain invisible.

The breakable element can be secured to the plug, including a protuberance 89 or 89 ′ undercut therein. In this way, the tube will be effectively opened during the first unscrewing of the stopper and the breaking force, associated with the force of the first unscrewing, guarantees the inviolability of the tube before its first use.

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 "Figures 7 and 8) and the material thus extruded through the stopper can be used to fill the top of the stopper and in particular incorporate a personalized decoration, for example the logo of the manufacturer of the packaged product or the brand of the packaged product. BENEFITS

• limitation of the fineness of adjustment of the air gap (reduction of the adjustment time) • reduction of the risk of deterioration of the tools (mechanical stop on the cap, or stopping of the tools on the shoulder in the event of lack of presence of the plug)

• advantages associated with overmolding: material saving, in particular by appreciable reduction in thicknesses at the level of the contact surfaces; savings in the high-speed manufacturing cycle, by eliminating separate manufacturing steps and automated assembly; perfect tightness of a perfectly intimate contact;

• great flexibility allowing a very large number of variants, with a multitude of geometries made possible by this process. • process that adapts well to manufacturing conditions in continuous kinematics

Claims

1) Method for manufacturing by compression molding of plastic parts having a neck (83) provided with a dispensing orifice comprising a first step of producing a blank (820) of plastic material typically by extrusion and a second step of compression molding of said blank, in which said blank, brought to an appropriate temperature, is placed in the space between a first movable part (830 + 805) and a second movable part (835) of the tool compression then is compressed by mutual approximation of said movable parts of the tool, the plastic material 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 parts mobile tools once attached defining the volume of said part, said method being characterized in that one uses a compression tooling whose imprints are such that said neck, once molded, has a top wall (84) comprising breakable zone (86) associated with a notch (85) whose contour delimits the desired shape of the dispensing orifice , said notch having a section through a diametral plane passing through the axis of the neck, typically in the form of a U or V, oriented in a direction substantially parallel to the axis of the neck (100) and in that said first mobile part (830 + 805) is, 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 mobile part (835).

2) The manufacturing method according to claim 1 in which a compression molding tool is used with a first movable part (830 + 805) which, at least in the part of the imprint contributing to the shaping of said breakable zone (86), is made of plastic while the second movable part (835) is metallic. 3) The manufacturing method according to claim 1 or 2 wherein said first movable part (830 + 805) comprises a cavity provided with a plug (805) intended to close off said orifice, said plug being positioned in such a way

5 so that its internal surface at least partially serves as a molding imprint for shaping said neck (83), at least at its breakable zone (86).

4) Method according to any one of claims 1 to 3, wherein the w breakable zone (86) is shaped using a toric edge (90) belonging to the punch (835)

5) Method according to claim 3, wherein the breakable zone (86 ', 86 ") is shaped using an O-ring (90', 90") belonging to the plug

75 (805)

6) Method according to any one of claims 1 to 5, in which a molding tool is used which shapes said notch (85) using a toric edge (90), the section of which is V-shaped, the angle of the V being 0 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.

7) A method according to any one of claims 3 to 6 wherein one uses a first movable part having a cavity designed so that said plug (805) meets only local support and that it deforms elastically at during compression of the blank by imposing a given shape on the external surface of the neck, the latter, once stabilized, being, at least locally, prestressed by a portion of the plug when the compression forces are no longer applied . 8) Method according to any one of claims 3 to 7 wherein the molding impressions are drawn so that the portion of the transverse top wall (84) of the neck (83) which is surrounded by the breakable zone (86) includes an undercut protrusion (89, 89 ', 89 ")

5 in the plug (805).

9) The method of claim 8 wherein said protuberance (89 ") undercut through the plug, the plastic of the blank filling the top of the plug. W

10) Method according to any one of claims 1 to 9, wherein the compression molding tools (830 and 835) are also moved in a continuous movement orthogonal to their direction of mutual approach.