Patent Description:
Plastic hollow containers made by means of rotational molding or blow molding techniques, designed to contain a plurality of liquid, solid or gaseous substances belonging to many sectors of industry (food, chemical, pharmaceutical, etc.) are known in the art. For example, included in this type of containers are those designed to contain substances that must not escape uncontrollably and which therefore must be provided with closure systems (screw caps, pressure covers, valves, etc.).

Internally hollow bodies, such as for example the aforementioned containers, and the respective known production techniques present some disadvantages.

The internally hollow bodies of the prior art produced using traditional molding techniques (rotational molding or blow molding), such as bottles, barrels, jerrycans, flasks, bins, tanks, small cisterns have the disadvantage of being difficult to make in square shapes, for example box-shaped or approximable to those of a parallelepiped with slightly rounded edges. In addition, they generally have a worse exterior finish than the aesthetic finish of products manufactured using the injection molding technique.

Moreover, blow molding does not allow the production of details with constant thickness and, consequently, products made with such technology have areas that require a greater amount of plastic material for producing the container, with a consequent greater demand for resources (financial and material). Furthermore, blow-molding technology and, in particular, rotational molding technology are less productive than other technologies, such as injection molding.

Recently, an internally hollow body made of plastic and a related production technique by injection molding were devised, both described in the patent application with publication number <CIT> in the name of the same applicants as the present patent application. The hollow body described in <CIT> is made by the union of two half-shells and the subsequent overmolding by injection of a joining element at the union region of the two half-shells. However, the hollow body and the method of production described in this patent application have some disadvantages. Internally hollow bodies may suffer accidental breakage if subjected to certain load and/or fall tests. In particular, in the event of a fall, it may happen that, as a result of the impulsive impact, one of the two half-shells will detach from the other half-shell and/or the joining element, causing a hole to open and the consequent leakage of the contents.

Moreover, the production times of the hollow bodies according to the prior art are relatively long and produce much waste, limiting the efficiency and effectiveness of production.

One of the objects of the present invention is to improve the robustness of hollow bodies made of plastic, made by molding two half-shells (a main body and a closure body) joined together.

A further object of the present invention is to improve the efficiency and effectiveness of production of such internally hollow bodies.

Such aims are achieved by an internally hollow body, by a method for producing an internally hollow body and by a mold, according to the attached independent claims. The claims dependent on these claims describe further embodiments.

The features and advantages of the present invention will be apparent from the description given below, provided by way of non-limiting example, in accordance with the accompanying figures, wherein:.

In accordance with the accompanying figures, an internally hollow plastic body having an inner cavity <NUM>, preferably adapted to contain liquid, solid or gaseous material is collectively indicated at <NUM>.

The term "internally" means that the cavity <NUM> of the hollow body is internal to the body, which is to say that, for example, the body has an inner surface that defines, at least partially, such cavity and that is in contact with a liquid, solid or gaseous material that flows, or is contained, at least partially, in the cavity, and an outer surface of the hollow body that instead is in contact with the external environment or, for example, with a different or other element with respect to the one contained, or that flows, in the cavity. This type of internally hollow bodies includes, for example conduits, channels, pipes or container bodies.

The internally hollow body <NUM> comprises a main body <NUM> shaped so as to comprise side walls <NUM>, having an inner surface <NUM> which at least partially defines said cavity <NUM> and which ends with a shaped edge <NUM> which delimits an engagement opening <NUM> to the cavity <NUM>. The internally hollow body <NUM> further comprises a closure body <NUM>, comprising side closure walls <NUM> having an inner sealing surface <NUM>. Such inner sealing surface <NUM> is engaged at least partially with the inner surface <NUM> of the side walls <NUM> of the main body <NUM>, and the closure body <NUM> at least partially closes the cavity <NUM> at the engagement opening <NUM>.

According to the invention, for example, such closure body <NUM> is the bottom of a container, as in the embodiment shown in <FIG>, or the cover, as in the embodiment shown in the document <CIT>, or one of the two half-shapes that, when joined, form the entire internally hollow body, or simply a portion of the internally hollow body or an ancillary portion (for example a handle of a container, an inlet mouth and the like).

Additionally, the internally hollow body <NUM> comprises a joining element <NUM>, also made of plastic, having the function of securely joining the main body <NUM> and the closure body <NUM>.

Preferably, the plastic material with which the joining element <NUM> is made is adapted to fuse and weld with the plastic material with which the main body <NUM> or the closure body <NUM> is made. For example, the joining element is made of the same plastic material as the main body <NUM> and/or the closure body <NUM> or with a different plastic but one adapted to fuse with the plastic of the closure body <NUM> and/or of the main body <NUM>.

The term plastic material or plastic means a polymer, for example a synthetic resin, or an elastomer, or a thermoplastic or thermosetting polymer preferably selected from the group of polyethylenes, polypropylenes, methacrylates, polycarbonates or polyamides.

Between the main body <NUM> and the closure body <NUM>, there is an overmolding seat <NUM>, and the joining element <NUM> is overmolded by injection to the main body <NUM> and the closure body <NUM>, covering such overmolding seat <NUM>.

Preferably, the main body <NUM> is joined to the closure body <NUM> at least partially along the shaped edge <NUM> by means of said joining element <NUM> or preferably along the entire shaped edge <NUM>.

The overmolding of the joining element <NUM> on the closure body <NUM> and on the main body <NUM> occurs by injection molding, for example through a step of injection molding of a synthetic resin melted in the overmolding seat <NUM>, when the closure body <NUM> and the main body <NUM> are mutually engaged and inserted in a mold <NUM> for overmolding the joining element <NUM>.

Preferably, the closure body <NUM> is adapted to close completely and sealingly the cavity <NUM>, at the engagement opening <NUM>. In this way, hollow containers are created able to contain, for example, liquid, solid or gaseous substances, such as vials, barrels, jerrycans, flasks, bins, tanks, floats, buoys, lifebuoys, fenders, small cisterns, or bottles, wherein the closure body <NUM> is preferably the bottom or the cover of such containers. In the case of internally hollow bodies for which, once closed, it is not necessary to access the inner cavity again, such as floats, buoys, lifebuoys or fenders, the closure body <NUM> and the main body <NUM> respectively represent each of the two half-shells (preferably equal to each other) to be joined by the joining element to form the buoy, float, lifebuoy or fender.

The closure body <NUM> has, moreover, a mold engagement cavity <NUM> in which a mold <NUM> for injection molding or a part thereof is adapted to counteract the pressure generated in the overmolding seat <NUM> by injection means during an overmolding step of the joining element <NUM> and is at least partially couplable by shape-coupling. This mold engagement cavity <NUM> is preferably formed externally of the cavity <NUM> of the hollow body <NUM>, i.e. it is at least partially delimited from the outer surface of the closure body opposite the inner surface facing the cavity <NUM> of the hollow body <NUM>. In other words, the mold engagement cavity <NUM> is arranged on the opposite side with respect to the inner cavity <NUM> of the hollow body and is defined at least in part (or totally) by the outer surface adapted to be in contact with the external environment or in any case with a different element than that which is contained or flows into the cavity <NUM> (i.e. the mold engagement cavity <NUM> does not face into the cavity <NUM>). For example, such mold engagement cavity <NUM> is delimited by the outer closure surface <NUM> of the side closure walls <NUM> of the closure body, opposite the inner sealing surface <NUM> towards the mold engagement cavity <NUM>. In this way, one avoids that, during the overmolding step, the injection of the resin forming the joining element <NUM>, causes a disengagement between the inner sealing surface <NUM> of the closure body <NUM> and the inner surface <NUM> of the side walls <NUM> the main body <NUM>.

Preferably, as shown for example in <FIG>, the outer closure surface <NUM> that defines the mold engagement cavity <NUM> faces the opposite side with respect to the cavity <NUM>. It follows that the mold <NUM> engages the mold engagement cavity <NUM> externally with respect to the cavity <NUM> of the hollow body <NUM> obtained at the end of the molding step. In this way, the molding steps are reduced, and it is also possible to produce totally closed hollow bodies <NUM>. In effect, if the mold engagement cavity <NUM> were formed in the cavity part <NUM> of the hollow body <NUM>, in the case of totally closed hollow bodies, the mold portion inside the mold cavity <NUM> and the cavity <NUM> would not allow the total closure of the hollow body <NUM>. In effect, in this latter case, it would be necessary to leave an access to the cavity <NUM> free for removing the overmolding mold <NUM> (or part of it, for example, the die or the punch).

The inner sealing surface <NUM> of the closure body <NUM> is engaged at least partially in abutment with the inner surface <NUM> of the main body <NUM> along the engagement portion <NUM>' of such inner surface <NUM> in such a way as to counteract a mechanical stress between the closure body <NUM> and the main body <NUM> along a preferential direction X' (for example a main vertical direction of extension of the hollow body) and in the direction of insertion of the closure body <NUM> in the inner cavity <NUM>. In other words, the engagement between the inner sealing surface <NUM> and the inner surface of the main body <NUM> allows any compressive stress between the closure body <NUM> and the main body <NUM> to be distributed along the side walls <NUM> of the main body. This advantageously allows any impulsive loads acting between the main body <NUM> and the closure body <NUM>, for example, the hollow body accidental falling, to be supported. For example, in the case wherein the hollow body <NUM> is a jerrycan containing liquid, the mechanical stress along the preferential direction X', due to the jerrycan accidently falling with impact on the closure body <NUM>, would be directly distributed by the closure body <NUM> to the side walls <NUM> of the main body <NUM>, ensuring greater impact strength.

Preferably, advantageously, the engagement portion <NUM>' is an engagement surface inclined with respect to the preferential direction X', even more preferably perpendicular to the preferential direction X'. For example, the engagement portion <NUM>' is the rise of a step <NUM> formed on the side walls <NUM> of the main body <NUM>.

Preferably, moreover, the inner sealing surface <NUM> of the closure body <NUM> comprises an abutment portion <NUM>', inclined (preferably perpendicular) with respect to the preferential direction X' and sealingly resting on the engagement portion <NUM>' of the main body <NUM>. This allows both a sealed joint to be obtained between the closure body <NUM> and the main body <NUM> (particularly advantageous in the case of hollow bodies of solid, liquid or gaseous substances) and any mechanical stress to be distributed along an extended contact surface.

In accordance with the invention, the joining element <NUM> is contained along its sides between the side walls <NUM> of the main body and the side closure walls <NUM>. In this way, the joining element remains hidden from the view of an observer looking at the hollow body along a direction perpendicular to the side walls. Moreover, preferably, having defined a transverse plane P perpendicular to the preferential direction X' (for example perpendicular to the side walls <NUM>), the joining element <NUM> is in contact with the external environment only along an outer surface <NUM>, having at least a virtual tangent plane V parallel to said transverse plane P. In other words, for example in the case of a container or a jerrycan, the joining element <NUM> is preferably in contact with the outside only along a surface thereof facing outwards on the opposite side of the bottom of the container or the jerrycan (for example as shown in <FIG>).

Preferably, the outer surface <NUM> of the joining element is in contact with the outside in a discontinuous manner, i.e. only in regions spaced from one another, as shown for example in <FIG>. In other words, the joining element is totally contained between the side walls <NUM> of the main body and the side closure walls <NUM> of the main body, except at such regions spaced apart from one another in contact with the external environment. In particular, these spaced regions of the outer surface <NUM> are preferably located at the entry points of the resin during the overmolding step of the joining element <NUM> inside the mold <NUM>.

In one embodiment (for example shown in <FIG>), the joining element <NUM> is in contact with the external environment only along its outer surface <NUM>, flat and parallel to said transverse plane P.

Furthermore, guide ribs <NUM> are preferably formed on the closure body <NUM>, adapted to guide the closure body <NUM> during the step of coupling with the main body <NUM> towards the inner cavity <NUM>. Preferably, the guide ribs are spaced from one another and protrude from the main body <NUM> towards the inner cavity <NUM>. Moreover, preferably, the guide ribs <NUM> comprise an inclined surface <NUM> adapted to slide along an edge of the side walls <NUM> of the main body during the coupling step. Such inclined surface <NUM> is, for example, connected to the abutment portion <NUM>', so as to facilitate the engagement of the closure body <NUM> during the insertion step in the main body <NUM> until it abuts the abutment portion <NUM>' with the engagement portion <NUM>' of the main body <NUM>.

The internally hollow body <NUM> described up to now may be obtained by means of the mold <NUM> and through a production method according to the continuation of the present description.

Mold <NUM> means a mold for injection molding, for example formed of two or more half-molds, for example a punch <NUM>' and a die <NUM>'', each bearing an impression designed to engage according to shape-coupling with the main body <NUM> or with the closure body <NUM>. For example, the main body <NUM> is inserted in the die <NUM>" of the overmolding mold <NUM> according to shape-coupling and the closure body <NUM> is inserted into the punch <NUM>' of the mold <NUM> according to shape-coupling. Preferably, a part of the walls forming the punch and/or a part of the walls forming the die are adapted to counteract the pressure generated on the overmolding seat <NUM> by the injection means during an overmolding step of the joining element <NUM>.

Preferably, a die wall or only a punch wall 50a (and not both at the same time) is in contact with the synthetic resin during the overmolding step of the joining element, and, in addition to counteracting the pressure during the step of injecting the synthetic resin, such die or punch wall 50a defines an outer closure wall of the overmolding seat of the joining element. In this way, once the overmolded synthetic resin has solidified, at such outer closure wall of the overmolding seat, the outer surface portion <NUM> of the joining element <NUM> is formed. In this way, the joining element <NUM> is contained along its sides between the side walls <NUM> of the main body and the side closure walls <NUM>, avoiding making the structure of the mold <NUM> complex.

In one case, the mold engagement cavity <NUM> comprises an abutment surface <NUM> adapted to receive in abutment a portion of the mold and side walls forming the outer closure surface <NUM> on which the mold walls <NUM> are at least partially engaged to counteract the pressure generated by the injection means during the overmolding step of the joining element <NUM>.

Preferably, the mold engagement cavity <NUM> has an annular shape with a "U" cross-section.

Preferably, the joining element <NUM> completely fills the overmolding seat <NUM>, so as to allow stable welding between the main body <NUM> and the closure body <NUM>.

Preferably, moreover, the overmolding seat <NUM> (and therefore the joining element <NUM>, once molded), is delimited both on the top and on the side by the inner surface <NUM> of the side walls <NUM> of the main body <NUM> and, on the side facing the inner cavity <NUM>, by the side closure walls <NUM>.

Moreover, preferably, the joining element <NUM>, annularly wraps the hollow body <NUM>, creating a sealing welded ring between the main body <NUM> and the closure body <NUM>.

In the case wherein the closure body <NUM> or the main body <NUM> also acts as the bottom of a container, such main body <NUM> or the closure body <NUM> comprises a bottom wall, preferably integral with the side closure walls <NUM>, having an upper bottom surface 15a, which faces the cavity <NUM> of the container and which constitutes the inner bottom surface of the container. The bottom wall <NUM> further comprises an outer bottom surface 15b, opposite the upper bottom surface 15a, not communicating with the cavity <NUM>, but facing the outside of the container.

In one other case, the internally hollow body <NUM> comprises at least one reinforcing wall <NUM>, arranged transversely between two walls 17a, 17b facing each other and defining the mold engagement cavity <NUM>.

According to the present invention, the method for producing the plastic, internally hollow body provides for joining the main body <NUM> and the closure body <NUM> in the same step wherein occurs the molding of a second closure body <NUM>' and/or of a second main body to be used in a subsequent union step to obtain a second internally hollow body.

Preferably, the production of an internally hollow body <NUM> according to the present invention is defined in independent claim <NUM>.

Preferably, the main body <NUM> shaped in plastic and the closure body <NUM> are made by injection molding.

Furthermore, it is provided that in the mold engagement cavity <NUM> of the closure body <NUM> or of the main body <NUM>, the mold <NUM> is inserted at least partially according to shape-coupling with the mold engagement cavity <NUM> of the closure body <NUM> or of the main body <NUM> in such a way that at least one of the walls of the mold counteracts the pressure generated on the overmolding seat <NUM> by the injection of natural or synthetic resin by the injection means during the overmolding step of the joining element <NUM>.

Preferably, the overmolding step of the joining element <NUM>, provides that the molten synthetic resin which, once solidified, constitutes the joining element <NUM>, is injected into the molding seat <NUM> at high temperature, while the main body <NUM> and the closure body <NUM> are inserted into the mold <NUM>. In this step, when the molten resin at high temperature comes into contact with the walls of the overmolding seat <NUM> (for example, the inner sealing surface <NUM> of the side closure walls <NUM>, the inner surface <NUM> of the side walls <NUM>, the shaped edge <NUM>), it causes the onset of fusion on the surface, i.e., a new transition of state from solid to molten form, allowing an effective and complete welding of the joining element <NUM> with the main body <NUM> and with the closure body <NUM> due to the fusion of the materials and the subsequent resolidification step.

Referring now to <FIG>, the internally hollow plastic body <NUM> is made by injection molding in a single mold comprising multiple cavities <NUM>, <NUM>, <NUM>. Each of said multiple cavities <NUM>, <NUM>, <NUM> is formed by the juxtaposition of respective die impressions <NUM>, <NUM>, <NUM> and respective punch impressions <NUM>', <NUM>', <NUM>' obtained respectively on the die <NUM>" and on the punch <NUM>' of the mold <NUM>. The cavities <NUM>, <NUM>, <NUM> are then formed when the mold <NUM> is closed by putting the respective die impressions and the punch impressions together. In each group of <FIG> and <FIG>, a variant embodiment of the die <NUM>" of the mold <NUM>, coupled with respective punch variants <NUM>', shown in <FIG> and <FIG> respectively, is illustrated according to a coupling clearly understandable to the person skilled in the art, executable in a cyclic and continuous way. In other words, <FIG> show the steps of the method on the die <NUM>" side and <FIG> show the steps of the method on the punch <NUM>' side. <FIG> show the steps of the punch <NUM>' side method and <FIG> show the steps of the die side method <NUM>".

The production method of the hollow body <NUM> comprises the steps of:.

As described above, in step d), therefore, the movable shaped element <NUM> forms only a portion of the main impression <NUM>, <NUM>' of the main cavity <NUM>, allowing advantages to be obtained which will be more understood from the continuation of the description.

It is clear that resin is injected into the main cavity <NUM> to generate the main body <NUM> and resin is injected into the closure cavity <NUM> to generate the closure body <NUM>.

In the union cavity <NUM>, the resin is injected into the overmolded seat <NUM> to overmold the joining element <NUM> between the main body <NUM> and the closure body <NUM>.

Moreover, "same step" means that the union between the first closure body <NUM> and the first main body <NUM> takes place without opening the mold before the molding of the second closure body <NUM>' has been completed. In other words, when the mold <NUM> is closed, the plastic resin is injected both to overmold the joining element between the main body <NUM> and the closure body <NUM> in the union cavity <NUM>, and to mold a second closure body <NUM>' in the closure cavity <NUM> to be used in a subsequent union (overmolding) step. For example, this is permitted due to an injection device inside the mold (not shown but known to the person skilled in the art) adapted to inject the polymer resin both into the main cavity <NUM> and into the union cavity <NUM> and into the closure cavity <NUM>. Furthermore, this is also permitted by the use of a bi-injection press if it is decided to join the two half-shells with a different or other colored material.

Preferably, even more advantageously, in step e) it is also envisaged to mold a second main body to be used in the subsequent union (overmolding) step with the second closure body <NUM>'.

Preferably, moreover, the injection of polymer resin for the molding of the second main body, of the second closure body <NUM>' and for the overmolding of the joining element <NUM> between the first main body <NUM> and the first closure body takes place sequentially or simultaneously in the main cavity <NUM>, the closure cavity <NUM> and the union cavity <NUM>.

As previously described, the union of the first main body <NUM> and the first closure body <NUM> takes place by injection overmolding of a joining element <NUM> along the overmolding seat <NUM>.

Preferably, the movement of the movable shaped element <NUM> comprises the step of rotating the shaped element <NUM> about an axis of rotation X and translating such movable shaped element <NUM> along a direction of extraction of the main body <NUM> from the die <NUM>" or from the punch <NUM>'.

Preferably, before step c) the movable shaped element <NUM> is engaged with the die <NUM>" or with the punch <NUM>' so as to form at least partially (and therefore not totally), the main impression <NUM> (as for example illustrated in <FIG> and <FIG>).

Preferably, moreover, the method comprises the step of:
d1) engaging the movable shaped element <NUM> with the die <NUM>" or with the punch <NUM>' of the mold <NUM> so that the movable shaped element <NUM> forms a portion of the union impression <NUM> of the union cavity <NUM> when the mold is closed for molding.

In certain circumstances, step d1) is carried out substantially simultaneously with step d). In other words, the movable shaped element <NUM> engages both with the union cavity <NUM> and with the main cavity <NUM> so as to form a portion of the union impression <NUM> and a portion of the main impression <NUM> when the mold is closed for molding. It is therefore clear that the movable shaped element <NUM> engages both with the union cavity <NUM> and with the main cavity <NUM> in such a way as to form only a portion of the union impression <NUM> and only a portion of the main impression <NUM>, and not the totality of the impression <NUM> and/or of the main impression <NUM>, when the mold is closed for molding.

The punch impressions <NUM>', <NUM>', <NUM>' and the die impressions <NUM>, <NUM>, <NUM> are adapted to come together to form the multiple molding cavities <NUM>, <NUM>, <NUM>, already described above.

The mold <NUM> further comprises a movable shaped element <NUM> movable for transferring the first main body <NUM> from the main impression of the die <NUM> or of the punch <NUM>' to the union impression of the die <NUM> or of the punch <NUM>'. Moreover, such a movable shaped element <NUM> is adapted to engage with the die <NUM>" or with the punch <NUM>' of the mold <NUM> so as to form at least a portion of the main impression of the die <NUM> or of the punch <NUM>'.

Preferably, the movable shaped element <NUM> is adapted to engage with the die <NUM>" or with the punch <NUM>' so as to form at least a portion of the union impression of the die <NUM> or of the punch <NUM>'.

In certain circumstances, the movable shaped element <NUM> comprises a union portion <NUM> and a main portion <NUM> joined together by a connecting portion <NUM>. The union portion <NUM> and the main portion <NUM> are adapted to engage with the union impression of the die <NUM> and with the main impression of the die <NUM> or with the union impression of the punch <NUM>' and with the main impression of the punch <NUM>'.

The movable shaped element <NUM> is adapted to engage with the die <NUM>" or with the punch <NUM>' so as to form only a portion of the union impression of the die <NUM> or the punch <NUM>'.

Preferably, the union portion <NUM> and the main portion <NUM> each comprise a frame <NUM>', <NUM>' which surrounds a housing <NUM>'', <NUM>'' adapted to receive the main body <NUM> therein. Such frame <NUM>', <NUM>'' is adapted to engage with the punch or with the die to form a portion of the union impression and/or the main impression of the punch or the die.

The possibility of moving only a portion of the union impression and/or the main impression of the punch or die allows reduced inertias to be obtained during the movement and therefore higher speeds of movement (for example of rotation), as well as require less power of the movement actuator means.

In one case, the frame <NUM>', <NUM>" comprises an inner side surface <NUM>, which faces the housing <NUM>'', <NUM>''. Such inner side surface <NUM> is shaped in such a way as to engage with the outer side surface <NUM> of the main body <NUM> (for example the outer surface of the side walls <NUM>). Such outer side surface <NUM> is the surface of the main body which faces away from the inner cavity <NUM> of the hollow body <NUM>.

In one case, the shaped movable element <NUM> is rotatable about an axis of rotation X parallel to the direction of movement of the die <NUM>" and of the punch <NUM>' in the closing/opening of the mold <NUM>. Such movable shaped element <NUM> is moreover translatable along the extraction direction of the main body <NUM> from the die or the punch.

In one case, the punch <NUM>' comprises a rotating base <NUM>, rotatable about a base axis of rotation Y. On such rotating base <NUM> are supported the punch union impression <NUM>' and the punch closure impression <NUM>'.

In one case, the rotating base <NUM> is arranged about the main punch impression <NUM>'. Preferably, the base axis of rotation Y passes through the main impression of the punch <NUM>'. Still more preferably, the rotating base <NUM> is in the shape of a circular crown arranged around the main impression of the punch <NUM>'. Moreover, preferably, the base axis of rotation Y coincides with the central axis Z of the mold <NUM>.

With more detailed reference to <FIG>, in order to obtain the internally hollow body <NUM>, it is envisaged to mold first the main body <NUM> and the closure body <NUM> (closing the die in <FIG> on the punch in <FIG>). After having opened the mold, by means of the movable shaped element <NUM>, the main body <NUM> is extracted from the main impression <NUM> (<FIG>), and the main body (<FIG>) is rotated to insert it into the union impression <NUM> (<FIG>). On the punch side <NUM>', the rotating base <NUM> (<FIG>, <FIG>) is moved so as to bring the closure body <NUM> into a position corresponding to the union cavity <NUM> (<FIG>). Subsequently, the mold <NUM> is closed (the die in <FIG> with the punch in <FIG>). The main body <NUM> and the closure body <NUM> engage with each other and the joining element <NUM> is overmolded by injection in the union cavity <NUM> and at the same time a second closure body <NUM>' is molded into the closure cavity <NUM> and a second main body is molded in the main cavity <NUM>; then the mold is opened (<FIG>) and the finished hollow body <NUM> is picked up. At this point, the molding resumes again cyclically with the extraction of the second main body from the main impression <NUM> (<FIG>) and with the movement of the rotating base <NUM> (<FIG>, <FIG>) so as to bring the second closure body <NUM>' into the position corresponding to the union cavity <NUM> (<FIG>) and so on.

In <FIG>, the rotating base <NUM> is arranged adjacent to the main punch impression <NUM>'.

Preferably, the base axis of rotation Y does not pass through the main punch impression <NUM>'.

Preferably, the base axis of rotation Y is spaced with respect to the central axis of the mold <NUM>. In this case, advantageously, by means of a simple rotation, the finished hollow body <NUM> is positioned in a position further from the center of the mold, towards the periphery of the mold, guaranteeing an easier and more convenient pick-up of the finished piece.

With more detailed reference to <FIG>, in order to obtain the internally hollow body <NUM> it is envisaged to mold first the main body <NUM> and the closure body <NUM> (by closing the die in <FIG> on the punch in <FIG>). After having opened the mold, the main body <NUM> is extracted from the main impression <NUM> (<FIG>) by means of the movable shaped element <NUM>, and the main body (<FIG>) is rotated to insert it into the union impression <NUM> (<FIG>). On the punch side <NUM>', the rotating base <NUM> (<FIG>) is moved so as to bring the closure body <NUM> into a position corresponding to the union cavity <NUM> (<FIG>). Preferably, the rotating base <NUM> is moved by means of a first translation movement along the base axis of rotation Y adapted to detach the closure body <NUM> from the closure impression <NUM>' of the punch. Rotating means of the rotating base then move the base about the base axis of rotation Y to bring the closure body <NUM> to correspond with the union cavity <NUM> (<FIG>). Subsequently, translation means of the rotating base <NUM> move the rotating base <NUM> with a second translation movement in the direction opposite to the first translation movement along the base axis of rotation Y (<FIG>).

Contrary to the disclosure of <FIG> wherein the closure impression <NUM>' rotates integrally with the rotating base <NUM>, the closure impression <NUM>' is fixed and integrally supported by a base body <NUM>' of the punch <NUM>', separate from the rotating base. In this case, the rotating base <NUM> acts only as a transport tray for the closure body <NUM>, allowing a reduction of the total mass of the base to be rotated and the relative inertial moments during rotation. Advantageously, this allows the torque that the rotating means must deliver to rotate the rotating base to be reduced, with a consequent reduction of the dimensions of the rotation means, an increase in the speed of variation of the rotation (and of the molding times) and simplification of the mold structure. Subsequently, the mold <NUM> is closed (the die in <FIG> with the punch in <FIG>). The main body <NUM> and the closure body <NUM> engage with each other and the joining element <NUM> is overmolded by injection in the union cavity <NUM> and at the same time a second closure body <NUM>' is molded in the closure cavity <NUM> and a second main body in the main cavity <NUM>; then, the mold is opened (<FIG>). At this point, the molding resumes again cyclically with the extraction of the second main body from the main impression <NUM> (<FIG>) and with the movement of the rotating base <NUM> as already described previously (<FIG>), so as to bring the second closure body <NUM>' into the position corresponding to the union cavity <NUM> (<FIG>) and so on (<FIG>).

Innovatively, the internally hollow body <NUM> due to the particular configuration of engagement between the closure body and the main body and to the disposition of the joining element, allows any impulsive and compression loads acting on the hollow body to be resisted in a more robust manner and at the same time maintains a pleasant overall aesthetic of the product by not showing the unsightly joining element.

Moreover, the production method of the internally hollow body <NUM> described in the preceding paragraphs, allows several types of internally hollow bodies (for example containers) to be made mainly for the food, chemical or petrochemical sectors, or for cleaning or pharmaceutical sectors, or for glues or paints or solvents, or for the boating or gardening sectors.

In particular, the method according to the present disclosure allows internally hollow bodies for injection molding to be made in a more efficient manner, due to the union between the main body and the closure body and to the simultaneous molding of a second closure body, usable in the subsequent union cycle for overmolding.

Advantageously, therefore, the method allows one to combine, on the one hand, the advantages of injection molding techniques with respect to blow molding or rotational molding techniques, and on the other it allows one to speed up the production, increasing efficiency. This allows both the range of shapes and finishes of internally hollow bodies that may be achieved to be expanded and the manufacture process to be improved.

Advantageously, moreover, the production method of internally hollow bodies according to the present disclosure allows the parallelization of the molding process to be increased, due to the possibility of simultaneously molding several internally hollow bodies and at the same time multiple main bodies and closure bodies, eliminating at least the step of withdrawing the closure body (or of the main body) from the mold and the subsequent insertion into the mold intended for overmolding, "replacing it" with rotating operations of a movable shaped element and a rotating base. This makes it possible to move on to the overmolding phase of the joining element in a quicker and more automated manner and, therefore, with an improved productive efficiency.

Claim 1:
Internally hollow plastic body (<NUM>), having a cavity (<NUM>), preferably adapted to contain liquid, solid or gaseous material, comprising:
- a main body (<NUM>) shaped so as to comprise side walls (<NUM>), having an inner surface (<NUM>) that at least partially defines said cavity (<NUM>) and comprising an engagement portion (<NUM>'), said inner surface (<NUM>) delimiting an engagement opening (<NUM>) with the cavity (<NUM>);
- a closure body (<NUM>) comprising side closure walls (<NUM>) having an inner sealing surface (<NUM>), said closure body (<NUM>) closing at least partially the cavity (<NUM>) at the engagement opening (<NUM>);
- a joining element (<NUM>) made of plastic, which joins the main body (<NUM>) to the closure body (<NUM>), said joining element (<NUM>) covering an overmolding seat (<NUM>) between the main body (<NUM>) and the closure body (<NUM>);
wherein the closure body (<NUM>) has a mold engagement cavity (<NUM>) in which a mold (<NUM>) for injection molding can be at least partially coupled by shape-coupling, adapted to counteract the pressure generated in the overmolding seat (<NUM>) by injection means during an overmolding step of the joining element (<NUM>),
and wherein the inner sealing surface (<NUM>) of the closure body (<NUM>) is engaged at least partially in abutment with the inner surface (<NUM>) of the main body (<NUM>) along the engagement portion (<NUM>') in such a way as to counteract a mechanical stress between the closure body (<NUM>) and the main body (<NUM>) along a preferential direction (X') and in the direction of insertion of the closure body (<NUM>) in the inner cavity (<NUM>),
characterized in that the joining element (<NUM>) is contained along its sides between the side walls (<NUM>) of the main body and the side closure walls (<NUM>).