FR2843909A1 - PROCESS FOR THE MANUFACTURE OF A PLASTIC MATERIAL HAVING A NUT PROVIDED WITH A DISTRIBUTION ORIFICE TO BE CLOSED BY A PLUG - Google Patents

Abstract

Method for manufacturing, by compression molding, plastic parts having a neck provided with a dispensing orifice comprising a first step of producing a blank (820) of plastic material and a second step of compressing said blank, in which the molding impressions are drawn such that said neck, once molded, has a top wall comprising a breakable zone with a notch whose contour delimits the desired shape of the orifice. The notch has a section typically in the form of a U or V, oriented in a direction substantially parallel to the axis of the neck. The neck, at least at the level of the breakable zone, is shaped by compression molding 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 plastic. Preferably, a direct molding of the neck is carried out on the plug which is intended to close the orifice.

Description

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  PROCESS FOR THE MANUFACTURE OF A PLASTIC MATERIAL HAVING A NUT PROVIDED WITH A DISTRIBUTION ORIFICE TO BE CLOSED BY A PLUG

  s 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 relates more particularly to the conditions of production in high rates of molded objects which have an axisymmetrical neck 10 delimiting a substantially circular orifice, for example flexible plastic tube heads, comprising a neck provided with an 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 to the cylindrical skirt 20. 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 1 324 471). In these two techniques, the skirt is fitted around a punch, one of its ends projecting slightly from the end of the punch, said punch end serving as a mold for producing the internal surface of the tube head (interior shoulder and neck). In these two techniques, a matrix is used which is pressed against the end of the - 2

  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 material in the first case and that it is their mutual approach which causes the 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 denote "punch" the movable part of the compression molding tool, the imprint of which is

  intended to define the interior of the part at least in the vicinity of its neck and "matrix" the movable part of the compression tooling whose imprint is intended to define the exterior of the part at least in the vicinity of its neck .

  Finally punch and die will be called moving parts of the tooling of iS compression molding in the sense that they are movable relative to each other. 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 that are moved continuously, which allowed to obtain, under acceptable economic conditions,

  significantly higher production rates.

  In compression molding, the production of the blank and its positioning in the molding tool present specific problems, the solutions of which have been the subject of numerous patents. The fact remains that, whatever the shape 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 dispensing orifice; 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.

  1o Whatever the form of the blank, these problems are exacerbated when we consider using tools when they are animated by a continuous movement, like those described in French application n 01

03706.

  In French application no. 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 method comprises a first step of producing a plastic blank, a second step of compressing said blank, where the neck thus formed has a top wall provided with a notch whose outline delimits the desired shape of the orifice and a third step in which a mechanical force is applied at a location on the top wall so that a rupture occurs at the level of said notch and that at least part of the wall

  summit detaches thereby freeing 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 mobile parts of the compression tooling and is then compressed by 4

  mutual reconciliation of the moving parts of the tool. The plastic of the blank flows so as to fill the cavities of the impressions of the moving parts until relative immobilization of said moving parts. Said imprints, when the moving 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 10 are a punch - the imprint of which at least partially defines the interior surface of the head of the tube - and a die - whose imprint defines at at least partially the outer surface of the tube head. i5 The notch made has a section through a diametral plane passing through the axis of the neck which, typically in a V or U shape, 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 area, than

  we will call thereafter 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 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 30 generating deformation rates in the order of 103 s-1.

  -5 The small thickness of the breakable zone causes a delicate problem because it is necessary to adjust in an extremely fine manner the air gap existing at the end of travel between the movable parts of the tool, in particular in the vicinity of the cavity used for shaping. the breakable zone. In fact, in order to obtain homogeneous breaking 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 not having to vary.

  no more than 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, to the wear of the active parts, etc ... ). In addition, the tool is subject to a significant risk of breakage in the event of a defect in adjustment, lack of plastic material in the tool, presence of a foreign body, etc. Finally, the tool is also at increased risk

  endurance defect 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 its top wall, in particular in the vicinity of the notch and the breakable zone, is shaped by compression molding 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 impression contributing to the shaping of said breakable zone, in a

  less rigid material than that of said second movable part.

  The association of the two materials - one metallic, the other less rigid, typically a plastic material - allows contact between the two parts -6 molding 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 tool damage.

  s It is thus possible to equip at least locally the imprint of one of the movable parts of the molding tool with an insert made of a less rigid material than that of the other movable 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 as regards the shaping of the part of the neck which includes the breakable zone. is 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 impression for the shaping of 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 by compression of this

part of the neck on the cap.

  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 it is easy to reduce the risk of deterioration of the tools (mechanical stop on the cap, stop of the tools on the shoulder in the event that the plug is not present, etc.). In addition, a part is obtained having a neck fitted directly with its cap 30 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, the cavity can be designed so that the plug meets only local support and that it deforms elastically during 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 regain its initial shape when the compression forces are no longer applied. After demoulding of the part + cap assembly, the cap hoops and / or encloses the neck, which reduces the risk of unscrewing iS after the head is shaped.

  The part of the stopper concerned by the absence of support may 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 wall.

outside 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 over a large part of its surface but it must still ensure the centering of the plug), the compressive forces result in a local expansion of the side wall. The compression force is maintained until stabilization of the -8

  plastic material of the neck. 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 s of the impression: the hooping which will result will be more intense at the base bottleneck.

  The clamping force resulting from this local hooping, substantially proportional to the value of elastic deformation of the part of the stopper concerned, o ensures anti-unscrewing of the stopper after shaping the head, which presents a solution alternative or complementary to the implementation

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 application. PCT / FR02 / 00686 filed by the plaintiff. 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 20 (punch), or to the plug. In the first case, the rupture occurs on the surface

  external but the risk of appearance of burr is low since the steel O-ring allows to impose sharp angles, therefore a high coefficient of multiplication of the stresses prevailing in the breakable zone during the rupture.

  In the other case, the risk of the appearance of burrs is certainly higher, but a possible burr resulting from the rupture of the breakable zone will remain inside.

  bottleneck 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 30 comprising a breakable zone surrounding the dispensing orifice and on the other hand -9 already covered with the plug for closing said dispensing orifice, a

  once this is achieved by tearing the breakable zone.

  The top wall is not necessarily a wall of constant thickness. s 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 that is not necessarily toroidal, with a massive shape that is easier to handle and which also has the following advantages: on the one hand, it is easier to obtain so reproductive in 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 outside the die and not the displacement of a valve 20 sliding in the axial direction inside the die and having to close so

discontinuous 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 of application of the mechanical force, a zone of transmission of the mechanical force intended to be applied to cause the tearing of the rupture zone, a breakable zone and a zone support. 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 U or 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 600. Thus, said bisector makes an angle between 0 and 45, preferably between 0 and 300 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 present

  its branches must be symmetrical around its bisector.

  In general, the desired opening 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 relative to to the axis and whose external 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 a 1s angle less than 55.

  The shape of the notch 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 can 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 cylindrical wall of the neck and having as section (by a plane

  diametral axial) a V whose bisector is perpendicular to the axis of the neck.

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  The rupture of the cover can be carried out subsequently by the user.

  In a preferred form, the molding impressions are drawn such 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 - undercut which is anchored in the cap. 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

  tube violation before 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 an iS matrix whose cavity intended to receive the plug is designed so that the plug 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 plug: in this way the material is somehow extruded through the plug and can be used to fill the top of the plug. While using the same standard cap base, we therefore integrate a personalized decoration on the top of the cap, for example the brand of the product

  the manufacturer's logo, etc ...

  -12 This process proves to be particularly advantageous when molding tools are used in continuous kinematics, such as those described in French application No. 01 03706 filed by the applicant on March 19, 2001. In this application, in addition to their mutual rapprochement resulting in the s compression of a blank, the molding tools are also driven by a continuous general movement having a component not necessarily

  flat but remaining orthogonal to their direction of mutual approximation.

  io FIGURES The figures represent diametral sections of tube heads, parts

  compression molding tools or plugs.

  Figure 1 illustrates the device before overmolding by compression of the head of i5 tube on the cap.

  FIG. 2 illustrates the device after overmolding by compression of the head of the tube on the plug. FIGS. 3, 5 and 7 illustrate the parts of the tool provided with the toric edge which makes it possible to shape the breakable zone (FIG. 3 : punch; figures 5 and 7: plug)

  Figures 4, 6 and 8 detail the tube head + plug assembly obtained after overmolding.

  - 13 EXAMPLE (Figures 1 to 8) The molding of the neck on the cap is carried out by adapting the process described in Example 4 of international application PCT / FR02 / 00686 5 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.

  1o 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 been molded itself shortly before using the same matrix but it can also have been obtained independently on another molding device. Outside i5 of this cavity, the imprint has a shape which defines the outer surface of the shoulder 82 of the tube. The internal surface of the plug 805 defines the surface

  outside 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 805 plug has a thickness

  average 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 cavity 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, the latter then being 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 s roughly and will flow little. The surface imperfections linked to the greater cooling of the plastic material there, the friction and the heterogeneous flow of the resulting material will

  stay 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 mold 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 plug.

  - 15 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 plug 5 (Figure 5 (90 ') and Figure 7 (90 ")). In the first case (Figures 3 and 4), 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 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 therein a protuberance 89 or 89 ′ undercut. In this way, the tube will be i 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 plug 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 to integrate a personalized decoration therein, for example the logo of the manufacturer of the packaged product or

  still the brand of said packaged product.

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BENEFITS

  limitation of the fine adjustment of the air gap (reduction of the adjustment time) s. reduction of the risk of deterioration of the tools (mechanical stop on the stopper, or stop of the tools on the shoulder in the event that the stopper is not present) advantages associated with overmolding: material saving, in particular by appreciable reduction in thicknesses at the level contact surfaces; 10 economy 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 adapting well to the manufacturing conditions in continuous kinematics - 17

Claims (6)

  1) Method of manufacturing by compression molding of plastic parts having a neck (83) provided with a dispensing orifice s comprising a first step of producing a blank (820) of plastic material and a second step of compressing 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 compression tooling and then is 1 compressed by mutual approximation of said 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 once adjoining tools defining the volume of said part, said method being characterized s5 in that a compression tool do nt the 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 movable 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.   - 18 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 said orifice, said plug being positioned 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 breakable zone (86) is shaped using an O-ring (90)   belonging to the punch (835)) Method according to claim 3, in which the breakable zone (86 ', 86 ") is shaped using an O-ring (90', 90") belonging to the plug 15 ( 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 between 20 and 30, preferably between 40 and 50, the bisector of the V making a   angle between 0 and 45, preferably between 0 and 30, with the axis of said neck.   7) Method according to any one of claims 3 to 6 wherein a first movable part is used having a cavity designed so that   said plug (805) meets only a local support and it deforms elastically 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 part of the plug when the compression forces are no longer applied. -19   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 ")   in the plug (805). 9) The method of claim 8 wherein said protrusion (89 ") undercut through the plug, the plastic of the blank   filling the top of the cap.   ) 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.