Moulding of containers by using several blowing steps

Abstract: A system for moulding containers in thermoformable and heat-weldable material comprises a heating and welding station (5) and a forming and shape-stabilizing station (6) with at least one welding and forming station (7,8) in-between, producing a progressive forming and shape-stabilizing of the container.

Description: The invention concerns a method and apparatus for moulding containers. US-A-3956441 discloses plastics containers having internal reinforcing ribs formed by a blow-moulding operation including pre-blow and final-blow steps in respective moulds. The pre-blow step includes inflating a parison into contact with concave grooves in the cavity wall of the first mould to form a blown pre-form with ribs on the outside of the pre-form. The final-blow step includes inflating the pre-form to bring the ribs into contact with a substantially smooth cavity wall of the second blow mould. Advantages given for this manner of providing reinforcing ribs are that the ribbing does not interfere with the placing of labels or other decorations on the outside of the container, the ribbing is more concealed than if it were to be on the outside of the container, so that forming the ribbing to be attractive as well as reinforcing is not so necessary, and that "parison wander", which would result in imprecise positioning of the ribbing in the final container can be minimized. US-A-3781395 and BT-A-2704657 disclose blow-moulding operation somewhat similar to that described above. US-A-3423902 discloses a system for blow-thermoforming containers from a pair of webs of thermoformable and heat-weldable material including a station at which vertically cycling pairs of mould halves clamp the webs between them, draw the webs downwards and then release them. When the mould halves clamp the webs between them, they heat the clamped web parts to weld them together about container outlines, inflating air is then introduced between the web parts to form the web parts into the mould recesses of the mould halves and the shape of each container is stabilized before the web parts are released. WO-A-94/08852 discloses a system for blow-thermoforming containers from a pair of webs of thermoformable and heat-weldable material including a preheating station for preheating webs, a heating, forming and welding station for welding the webs and commencing forming of the containers and a final forming and shape-stabilizing station. Mould halves at the heating, forming and welding station are formed with moulding channels whereby forming fluid introduced between the heated webs forms conduits between the sheets. EP-B-0479152 discloses a blow-thermoforming system in which advancement clamps move two mutually facing films along a path on which the following are arranged in sequence: two welding half-moulds, which by mutually welding the two films in preset regions define the outlines of containers which are open toward a longitudinal edge of the films; two half-moulds for heating the welded films and a container-forming station. Air injection nozzles, inserted between two edge flaps at that longitudinal edge of the films, and two forming half-moulds, in which container-forming cavities are provided, operate in the forming station. Divaricators for divaricating the two flaps are provided proximate to the forming station so as to facilitate the insertion of the air injection nozzles. The containers are filled by injecting a product through an open inlet of each container, the inlets being then closed by heat-welding. At the forming station, the external surfaces of the air injection nozzles define the internal surfaces of the inlets and these remain open until after the containers have been filled and thus the interiors of the containers remain accessible to any contaminants present. In the event that the formed containers are transported to other premises for filling, the risk of contamination of their interiors greatly increases. A problem arises in thermoforming larger capacity containers, namely those having a volume greater than about 400 ml., in that there is a tendency towards excessive thinness of the container walls in those areas of the webs subject to considerable stretching, for example in the area of the base of a container with a wide base and tapered neck. Such prior art could be considerably improved with a view to eliminating its various drawbacks. An aim of the present invention is to provide a sheet material thermoforming system that makes it possible to obtain, from webs of thermoformable and heat weldable material, containers of considerable capacity, greater even than 400 ml., having a substantially uniform wall thickness. According to one aspect of the present invention, there is provided a method of moulding a container in thermoformable and heat-weldable sheet material, including heating and welding together in a heating and welding phase at a heating and welding station first and second parts of said material and finally shape stabilizing said first and second parts in a forming and shape-stabilizing phase at a forming and shape-stabilizing station including moulding means, characterized in that between those phases there is at least one welding and forming phase in which said first and second parts are further welded together and a hollow interior formed between said first and second parts by deformation of said first and second parts into mould recess means of further moulding means at at least one welding and forming station. According to another aspect of the present invention, there is provided an apparatus for moulding a container in thermoformable and heat-weldable sheet material, including a heating and welding station at which first and second parts of sheet material are heated and welded together, and a forming and shape-stabilizing station including moulding means and at which said first and second parts are finally shape-stabilized, characterized in that between those stations there is at least one welding and forming station including further moulding means and at which said first and second parts are further welded together and a hollow interior is formed between said first and second parts by deformation of said first and second parts into mould recess means of said further moulding means. Owing to the invention, it is possible to provide a sheet material thermoforming system in which the material from which the container is formed has greater opportunity to flow (for a given rate of production) so as to obtain a substantially uniform wall thickness. The number of welding and forming phases can be varied depending upon the material being thermoformed. For polyvinyl chloride (PVC), polyethylene terephthalate (PET) and high density polyethylene (HDPE), for example, only one welding and forming phase can be used. In a preferred embodiment, more suitable for polypropylene (PP), a thermoforming method for moulding containers from a pair of webs of following phases: a first intermediate phase of heat-welding and forming; a second intermediate phase of heat-welding and forming; the initial phase and the two intermediate phases being carried out at progressively higher temperatures up to the softening temperature of the material; the deformation of said pair of webs in the initial phase, the intermediate phases and the final phase becoming progressively greater up to the final phase. This has the advantage of enabling the formation of containers having uniform wall thickness even in cases of considerable deformation of the pair of webs with respect to their planar undeformed condition. In a particularly advantageous version, the deformation imparted to said webs occurs in a selective manner, such that firstly and mainly middle areas of the containers attain their stabilized shapes and subsequently and mainly end areas of the containers attain their stabilized shapes. This has the further advantage that it is possible to increase significantly the degree of deformation with the same initial thickness of the sheets, or, with the same degree of deformation, to enable significantly thinner webs to be used. It is to be noted as regards this point that the areas destined to be subjected to less deformation, for example, the sides of the container, during their preliminary deformation serve as reservoirs of soft material which subsequently can flow towards the areas subjected to considerable deformation, for example, peripheral areas of the bases of the containers being formed. In a particularly advantageous version the final phase is carried out at a lower temperature than are the preceding phases, at a stabilizing temperature to consolidate the shape of the containers being formed, this temperature being inversely proportional to the specific heat, or proportional to the thermal conductivity, of the material: such a temperature being, for example, from about 20 °C (in the case PVC) to 5-6 °C (in the case of PP). This enables the formed containers to be extracted at the end of the final phase without local structural collapsing taking place. In a particularly advantageous version the following temperature levels are envisaged: the second heat-welding and forming phase is carried out at a temperature close to the softening temperature of the material; the first heat-welding and forming phase is carried out at a temperature that is lower than the softening temperature of the material by an amount that is advantageously between approximately 10 °C and approximately 15 °C; the initial phase is carried out at a temperature that is lower than that of the first heat-welding and forming phase by an amount that is advantageously between approximately 10 °C and approximately 15 °C. Thereby, the temperatures in the thickness of the pair of webs constituting the container can be rendered more uniform, with a consequently improved system. Owing to the thermal inertia of the material, the cooling in the final phase does not cause the material to become so rigid as to make its shaping difficult, but enables the completion of the deformation of the webs and the subsequent stabilization of the deformation obtained. The phases may be performed at respective stations having mould recesses of progressively increasing depths. In particular, the depth of the mould recess forming the intermediate transverse zone of the container in the first welding and forming station is approximately 90% of the depth of the mould recess forming that zone in the final station. It is possible to put transverse grooves in the middle areas of the walls of the mould recesses of the forming and shape-stabilizing station so as to obtain stiffening ribs of the container, without causing dangerous reductions in thickness of the wall of the container. In a further advantageous version, the mould recesses in the intermediate stations have middle wall areas which are curved in three dimensions and joined with end wall areas which are curved in two dimensions, i. e. circularly cylindrical. The curved middle wall areas are preferably convex, that is, curved oppositely to concavities of the formed container and extend from the middle part of the container being formed to one of its ends. This enables the deformation of the material in the areas subject to greatest deformation to be delayed thereby favouring the retention of the material in these areas. In a further advantageous version, at least one of the initial, intermediate or final stations have an injector unit for the forming fluid inserted between the two webs of material: said injector unit having a longitudinal bore for the supply of forming fluid communicating with the inlets of the containers being formed by means of a number of transverse bores. Alternatively, between said longitudinal bore and said inlets there is also a distributor conduit for the forming fluid, to supply all of the containers in a row with said forming fluid. In a further advantageous version, particularly suited to the formation of elastic closing devices of the containers, so that they may be easily forced open elastically by the insertion of injection tubes for filling, especially for applications in which it is necessary to maintain hygienically controlled conditions when filling the containers, there is at least one spacer positioned between said pair of webs and defining therewith the distributor conduit of the forming fluid: said injector unit and/or said spacer having one internal edge that can be received in the corresponding mould and extending parallel to the direction of advance of the sheets, which is preferably vertical for reasons of overall dimensions. The internal edge of said injector unit is aligned with the internal edge of said insert: both edges being of substantially the same shape. To obtain an optimal seal against leakage of the forming fluid from the corresponding mould, that internal edge has a pair of faces converging towards the inside of the corresponding mould so as to form a pair of external flaps of elastic closing devices for the containers. To prevent damaging sliding of the webs in a direction perpendicular to their advance, that internal edge has a pair of longitudinal ribs that limit the transverse sliding of said pair of sheets. It is to be noted, furthermore, that the distributor conduit for the forming fluid in the forming and shape-stabilizing station may be an extension of the corresponding distributor conduit in the preceding intermediate station. Advantageously, downstream of the final station, there is a shearing station to separate the containers from the pair of webs along a perpendicularly transverse plane. In order to optimize the conditions of injection of the forming fluid, the axes of the containers in the forming stations are perpendicularly transverse, the inlets of said containers pointing towards one of the longitudinal edges of the sheets. Furthermore, the containers can be aligned in a single row, or in two opposing parallel rows. In order that the invention may be clearly understood and readly carried into effect, reference will now be made, by, by way of example, to the drawings attached in which: Figure 1 is a diagrammatic longitudinal section through a sheet material thermoforming apparatus at stations where injection of forming fluid occurs; Figure 2 is a section as in Figure 1, but with the moulds open; Figure 3 is a section taken along line III-III of Figure 1, in a version where the containers are to be filled in conditions that are not hygienically controlled; Figure 4 is a section as in Figure 3, but in a version for containers to be filled in a sterile environment; Figure 5 is a transverse section taken along line V-V of Figure 3; Figure 6 is a transverse section taken along VI-VI of Figure 4; Figure 7 is a transverse section taken along VII-VII of Figure 4; Figure 8 is a transverse section taken along VIII-VIII of Figure 3; Figure 9 is a section taken along IX-IX of Figure 3; Figure 10 is a section taken along X-X of Figure 3; Figure 11 is a section taken along XI-XI of Figure 3, but showing a modification; Figure 12 is a schematic side view of a modified version in which the apparatus is fed with a pair of webs of material joined along a longitudinal edge; Figure 13 is a view as in Figure 12, but of a version fed with a single webs folded along a median longitudinal line. Referring to Figures 1 and 2, the moulding apparatus 1 consists of a feed unit 2 for the material in webs 3, advantageously a pair of superimposed sheets, for example, unwound from rolls 4, and of an initial station 5 for heating the webs 3 of material and for welding the outline of the containers 5a, an intermediate station 7 for heat-welding and forming; a successive intermediate station 8 for heat-welding and forming and a forming and shape-stabilizing station 6, said stations being aligned in a forming direction F. The containers 5a are extracted from the forming and shape-stabilizing station 6 joined in groups 9 destined to be separated by shearing the webs 3. The station 5 has mould recesses 10 of areas corresponding to areas of containers 5a and of a depth that is sufficient to keep the webs 3 separate from each other and pressing against the wall of each recess under the pressure of the forming fluid inserted in the closed condition of the corresponding mould halves 11: the depth being, for example, of the order of a couple of millimetres. The station 7 has mould recesses 12 in mould halves 13 and having a depth profile so as to cause the deformation in webs 3 in the areas destined to be subjected to the least amount of overall deformation. The station 8 also has mould recesses 14 in the corresponding mould halves 15 slightly deeper than the recesses 12 to induce further deformation in webs 3 in the areas around the edges of containers 5a. The forming and shape-stabilizing station 6 has recesses 16 in the corresponding mould halves 17 of a shape corresponding to the final shape of containers 5a. Stations 5, 6, 7 and 8 can have injector units 18 for the forming fluid, for example, heated compressed air, each injector unit 18 being inserted between webs 3, having a closed longitudinal bore 19 feeding the compressed air and communicating through a number of transverse bores 20 with each only partially formed container 5a in a group 9. The internal edge of injector unit 18 has a pair of faces 21 (Figure 5) converging towards the inside of the corresponding mould 11, 13, 15, 17 forming a pneumatic seal against webs 3, the faces 21 forming a pair of flaps 21' from the adjacent longitudinal end zones of the webs 3. In the version of Figure 4, 6 and 7, between the transverse bores 20 of injector unit 18 and the inlets of containers 5a being formed, there is a distributor conduit 22 connecting the inlets (in this case spouts) 23 of the containers 5a. The internal edge of injector unit 18 has a pair of longitudinal ribs 24 co-operating with correspoding groves in the mould halves, to ensure sealing and to prevent transverse sliding of webs 3 during forming. It is to be noted that station 6 for stabilizing the shape of containers 5a can be made to operate in conjunction with a spacer 25, of an external shape corresponding to that of the injector unit 18, but without the internal bores: this spacer has the function of preventing air from escaping from inside the containers 5 through the non-welded portion of channel 26 defined by elastic closing devices of containers 5a, the channel 26 being advantageously constituting an extension of the conduits 22 and communicating with it during the injection of the forming fluid. It is to be noted that the conduit 26 can also be obtained, albeit less advantageously as regards stretching of the material, in the station 8 substituting the distributor conduit 22, taking on, in this case, the function of distributing the forming fluid to the containers being formed also in the station 8. Channel 26 is closed at both its longitudinal extremities thereby enabling the inside of each container 2 to be isolated from the outside environment, due to the pressing action exerted on it by mould 17 in the area 27 of pressing elements at the lower extremity of the mould on the extension of channel 26. Mould recesses 10 of station 5 consist mainly of planar surfaces 28 (Figure 8) parallel to each other and joined to the edge of the recesses 10 along the outline of the container 5a being formed. Recesses 12 of welding and second preforming station 7 can have concave portions 29 joined to substantially planar portions 30: alternatively advantageously, they can have convex portions (of which one is shown in broken line and referenced with 29a) having the function of inducing a more pronounced deformation of the material in those areas that are subjected to least deformation, so as to keep the material that is subjected to the greatest deformation substantially undeformed until its introduction into the station 6. Correspondingly, the recesses 14 of the station 8 can have concave wall portions 31 joined to substantially planar wall portions 32; or a convex wall portion 31a. Figure 11 shows protrusions R projecting from the middle of the wall of one mould recess 16 of the station 6 and extending transversely of the container 5a to create, between the protrusions R, stiffening ribs for the formed container 5a. Figure 12 shows how the roll 33 for the supply of material can consist of two superimposed webs 3, possibly obtained from a single folded strip; alternatively, as shown in Figure 13, the webs 3 can be obtained, using deflector element 34 having converging sides 35, that folds a single strip unwound from roll 36. The system also includes a filling station for the formed containers, possibly a conveyor to transfer the containers to the filling station, a punching station to trim the outer edges of the filled containers and a permanent welding station for the spouts of the containers once they have been filled.

Claims: A method of moulding a container in thermoformable and heat-weldable sheet material, including heating and welding together in a heating and welding phase at a heating and welding station (5) first and second parts of said material and finally shape stabilizing said first and second parts in a forming and shape-stabilizing phase at a forming and shape-stabilizing station (6) including moulding means (11, 17), characterized in that between those phases there is at least one welding and forming phase in which said first and second parts are further welded together and a hollow interior formed between said first and second parts by deformation of said first and second parts into mould recess means of further moulding means (13, 15) at at least one welding and forming station (7, 8). A method according to claim 1, wherein between said heating and welding phase (5) and said forming and shape-stabilizing phase (6) there are at least two welding and forming phases at respective welding and forming stations (7, 8). A method according to claim 1, or 2, wherein said heating and welding phase (5) and the welding and forming phase(s) (7, 8) are carried out at progressively higher temperatures up to the softening temperature of said material. A method according to any preceding claim, wherein the container (5a) is made from a pair of webs (3) providing said first and second parts and the deformation of said pair of webs (3) in the heating and welding phase (5), the welding and forming phase(s) (7, 8) and the forming and shape-stabilizing phase (6) becomes progressively greater. A method according to claim 4, wherein the deformation imparted to said webs (3) occurs in a selective manner, such that firstly and mainly middle areas (31) of the container (5a) attain their stabilized shapes and subsequently and mainly end areas (32) of the container (5a) attain their stabilized shapes. A method according to any preceding claim, wherein the forming and shape-stabilizing phase (6) takes place at a stabilizing temperature which substantially is inversely proportional to the specific heat, or proportional to the thermal conductivity, of said material. A method according to claim 6, wherein said stabilizing temperature is in the region of 20 °C and said material is polyvinyl chloride. A method according to claim 6, wherein the stabilizing temperature is in the region of 5-6 °C and said material is polypropylene. A method according to claims 2 and 3, or any one of claims 4 to 8 as appended to claims 2 and 3, wherein the second welding and forming phase (8) is carried out at the softening temperature, the first welding and forming phase (7) is carried out at a differing temperature that is lower than the softening temperature by between approximately 10 °C and approximately 15 °C and said heating and welding phase (5) is carried out at a temperature which is lower than said differing temperature by between approximately 10 °C and approximately 15 °C. A method according to any preceding claim, wherein each phase (5 - 8) is performed for a plurality of such containers simultaneously. A method according to any preceding claim, wherein the container (5a) or a group (9) of containers (5a) produced includes inlet wall portions (21') which are elastic so that an inlet (23) of the container (5a), or a common inlet (23, 26) of the group (9), is self-closing. A method according to claim 11, wherein the inlet wall portions (21') of the container (5a) or group (9) produced comprise respective portions (21') at opposite sides of the inlet (23, 26), and each of the respective portions (21') is of substantially V-shaped section in an axial plane, with the vertices of the respective portions (21') pointing towards each other. A method according to claim 12, wherein said respective portions (21') of the inlet (23, 26)are each of zig-zag section in an axial plane. Apparatus for moulding a container in thermoformable and heat-weldable sheet material, including a heating and welding station (5) at which first and second parts of said material are heated and welded together, and a forming and shape-stabilizing station (6) including moulding means (11, 17) and at which said first and second parts are finally shape-stabilized, characterized in that between those stations (5, 6) there is at least one welding and forming station (7, 8) including further moulding means (13, 15) and at which said first and second parts are further welded together and a hollow interior is formed between said first and second parts by deformation of said first and second parts into mould recess means of said further moulding means (13, 15). Apparatus according to claim 14, wherein between said heating and welding station (5) and said forming and shape-stabilizing station (6) there are at least two welding and forming stations (7, 8) including such further moulding means (13, 15). Apparatus according to claim 14, or 15, wherein the heating and welding station (5), the welding and forming station(s) (7, 8) and the forming and shape-stabilizing station (6) have mould recesses (11, 13 15, 17) of progressively increasing depths. Apparatus according to claim 16, wherein the depth of the middles (31) of the mould recesses of the welding and forming station, or the first welding and forming station (7), as the case may be, is approximately 90% of the depth of the middles of the mould recesses of the forming and shape-stabilizing station (6). Apparatus according to claim 16, or 17, wherein the mould recesses of the forming and shape-stabilizing station (6) have transverse grooves to form stiffening ribs of the container. Apparatus according to any one of claims 16 to 18, wherein the mould recesses of the or each welding and forming station (7, 8), in a plane (IX-IX, X-X) perpendicular to a separation plane (III-III) of the or each moulding means thereof (13, 15) and containing an axis of an entry to each mould recess, have middle wall parts (29, 31) which are curved and end wall parts (23, 30, 32) which are rectilinear. Apparatus according to any one of claims 16 to 18, wherein the mould recesses of the or each welding and forming station (7, 8), in a plane (IX-IX, X-X) perpendicular to a separation plane (III-III) of the or each moulding means thereof (13, 15) and containing an axis of an entry to each mould recess, have middle wall parts (29, 31) which are curved oppositely to adjacent wall parts (29a, 31a). Apparatus according to any one of claims 14 to 20, wherein at least one of the stations (5 - 8) includes forming means (18) arranged to extend along respective adjacent edges of a pair of webs (3) which provide said first and second parts and from which a plurality of such containers (5a) is to be made, the or each forming means (18) including an internal edge serving to co-operate with longitudinal edge zones (21') of said webs to define a conduit (22, 26) interconnecting mouths (23) of said containers (5a). Apparatus according to any one of claims 14 to 21, wherein said forming and shape-stabilizing station (6) includes spacing means (25) including an internal edge serving to space apart respective adjacent longitudinal edge zones (21') of a pair of webs (3) which provide said first and second parts and from which said container (5a) is made and to bound a conduit (26) for forming fluid between said spacing means (25) and said longitudinal edge zones (21'). Apparatus according to claims 21 and 22, wherein the internal edges of said forming means (18) and said spacing means (25) are aligned with one another and of substantially the same cross-sectional outline. Apparatus according to claim 23, or claims 21 and 22, wherein the arrangement is such that said conduit (26) at said forming and shape-stabilizing station (6) communicates with said conduit (22) at the forming and welding station, or the conduit (22) at the forming and welding station (8) immediately preceding said forming and shape-stabilizing station (6), as the case may be. Apparatus according to any one of claims 21 to 24, wherein the internal edge(s) of said forming means (18) and/or said spacing means (25) extend(s) parallelly to an intended path of advance of said webs (3) and is/are receivable in the corresponding moulding means. (11, 13, 15, 17). Apparatus according to any one of claims 21 to 25, wherein provided on said forming means (18) and/or said spacing means (25) at the internal edge(s) is a pair of longitudinal ribs (24) to limit transverse sliding of said webs (3).

Inventors: BARTOLI ANDREA, TABARONI ROBERTO, BARTOLI, ANDREA, TABARONI, ROBERTO
Applicants: UNIFILL INT AG, UNIFILL SPA, UNIFILL INTERNATIONAL A/G, UNIFILL S.P.A.
Application year: 1995
Main classification: B29C49
IPC codes: B29D22, B29C49, B29C69, B29C65, B65D1, B29L22