FR2535681A1 - Device for sealing a lid on thermoplastic containers - Google Patents

Abstract

Device for sealing a lid, having at least one thermoplastic layer, onto the flat horizontal edge of several thermoplastic containers 1. Device of the type comprising a single electrode plate 4 which extends transversely over the entire width of the row of containers and which has, for each corresponding container, a hot annular contact surface 5 whose width is at least equal to that of the edge of the container 15 with which it is associated, and below the edge 15 of the containers 1, a support body 6 which comprises, for each corresponding container 1, a receiving chamber 7 which is open at the top and which is mounted by its lower surface on a press plate 8 which moves vertically and whose upper surface has, around the opening of each receiving chamber 7, a flat annular support surface 9. Each support surface 9 is constituted by the flat top of at least one annular rib 18 whose width at the top is between 0.5 and 2 times the thickness of the edge of the container 15.

Description

Device for sealing a lid on thermoplastic containers
The present invention relates to a device for sealing a lid having at least one thermoplastic layer, on the horizontal plane edge of several thermoplastic containers belonging to at least one row of containers extending transversely to the direction of advance of said containers.

 The sealing device which relates more particularly to the invention is of the type comprising, on the one hand, above the containers, a single electrode plate which extends transversely over the entire width of the row of containers and which presents for each container corresponding to a hot annular contact face whose width is at least equal to that of the container edge with which it is associated3 and 9 on the other hand, below the edge of the containers> a support body which comprises for each corresponding container a room réceprice open upwards, which by its lower face3 is mounted on a press plate vertically movable between a so-called high sealing position and a low position said dégagemment allowing the evacuation and advance of the containers, and whose upper face has around the opening of each receiving chamber an annular flat bearing face intended to bear against the lower face re of the container edge at least in the upper position of the support body.

 Devices of this type are known in particular from French patents 77 33285 (2.421.72Q) and 80 09879 (2.481.641).

 The bearing face known from French patent 2,421,720 and surrounding each receiving chamber has a rounded shape so that this support surface tends to penetrate into the container edge when it heats up in contact with the electrode plate. upper and at least partially cut the container edge by melting or delivery of the thermoplastic material, as cgest the case of the device known from French Patent 7,704,829 (20380.944).

The seal quality obtained with these known devices is not always satisfactory because they often introduce additional tensions or deformations in the lid at the location of the weld zone, which leads to a defective ability to peel the lids .

 Attempts to overcome the aforementioned drawbacks using the sealing device described in French Patent 2,248,641. For this purpose, the lower face of the container edge is preformed with a supporting rib against which the relatively wide flat bearing face of a bearing piece surrounding the opening of the receiving chamber will bear. This design requires the use of large heating means for the container edges in which the support ribs are thermoformed and then these edges must be rapidly cooled to be sufficiently rigid because they will constitute the network of rigid parts of the thermoplastic strip in which one These containers, which will be immediately filled with products, will also be formed. In addition, these support ribs permanently provided on the container edges are not always entirely made, which leads to incomplete and therefore defective sealing beads.

 It is, moreover, practically inevitable that there is at least a slight lack of parallelism between the contact faces of the upper electrode and support faces of the support body, a defect which reduces the quality of a regular seal. from one container to another and even from one place to another in the same sealing bead.

 The object of the invention is to eliminate-or at least to mitigate these disadvantages and to obtain for all the containers of the same row sealing cords which nevertheless allow the consumer to peel the lid without tearing it.

 This object is achieved according to the invention in that each flat bearing face is constituted by the plane top of at least one annular rib whose width at the apex is between 0n5 and 2 times the thickness of the container edge. and that the support body is mounted on the press plate, if necessary, by means of a weakly elastic compensating plate.

 Thanks to this design, the lack of parallelism between the different contact faces of the electrode plate and the bearing faces of the support body can be compensated either with the aid of the narrow support ribs carried by the body. of support and compressing more or less strongly in their area of application the container edges at the time of sealing, or by the combination of the effects of the application of the narrow support ribs and the local compression of the elastic compensating plate .

 Since the reference planes are those defined by the different contact faces of the electrode plate and the flat support ribs of small width with the interposition of a layer of thermoplastic material constituted by the edges of the container. and a thin complex film consisting of the composite material of the lid (eg aluminum foil with a heat-sealing thin film) it is possible to compress very strongly the container-lid edge assembly while applying said assembly to flat against the plane contact face of the electrode plate.It was found that under the effect of the application force acting in a zone of small width, the thermoplastic material located in the immediate vicinity of the electrode plate and in this zone pressure, melts or softens quickly and is driven laterally to neighboring areas where it also solidifies very rapidly. The cover sheet adheres to the container edge not only in the direct compression zone but also in the adjacent areas of indirect compression. In these areas, the container edge is not applied directly against the contact face by the support rib, but only indirectly because of the stiffness of the zones adjacent to the container edge.

 Once the sealing pressure ceases, a sealing bead is obtained which is materialized on the upper face of the container edge by a wide groove of very shallow depth, the bottom of this groove coinciding with the direct compression zone is ie the area of application of the bearing rib against the underside of the container edge. It is also noted that at the location of the sealing bead, the cover sheet is smooth but practically not stretched. It should also be noted that if a small stretch of the cover sheet appeared, this could only occur after sealing and releasing the compressive force.

Other advantages and characteristics of the sealing device will emerge from the following description of an embodiment and some variants illustrated in the accompanying drawing on which
- Figure I is an elevational view of a cross section of a known sealing device
FIG. 2 is a diagrammatic elevational view of a radial section through the upper portion of a container sealed with the device according to FIG. 1;
FIG. 3 is an elevational view of a longitudinal vertical section through the support body of a sealing device according to the invention;
FIG. 4 is a partial plan view of a horizontal section through the support body along the line IV-IV of FIG.
FIG. 5 is a partial view in elevation of a vertical section through the upper part of a variant of the sealing device,
FIG. 6 is a diagrammatic view in a small valley through the sealing bead connecting the container edge to the corresponding part of the cover sheet and obtained with the device according to the invention.
- Figure 7 is an elevational view of a cross section through a variant of the sealing device according to the invention along line Vil-VII of Figure 9
FIG. 8 shows a detail of the device according to FIG.
FIG. 9 is a partial plan view of the device according to FIGS. 8 and 7;
FIG. 10 is an elevational view of a longitudinal section through another variant of the sealing device along line XX of FIG. 11; and
FIG. 11 is a partial plan view of the device according to FIG.

 As can be seen in FIG. 1, a known sealing device comprises, for the planes of receptacles 1 arranged in a row, a row of transverse and thernormal containers from a thermoplastic strip 2, on the one hand above the containers 1 to cover with a cover sheet 3, a single electrode plate 4 which extends transversely over the entire width of the row of containers 1 and which has for each container corresponding 1, a hot annular contact face in the form of an annular rib 5, and, on the other hand, below the edge of the containers 1, a support body 6 which comprises, for each corresponding receptacle, a receiving chamber 7 open towards the top, and which, by its face lower is mounted on a press plate 8 vertically movable between a so-called high sealing position and a low position called release allowing the evacuation and advancement of containers in the perpendicular direction 1 at its upper end, the support body 6 has around the opening of each receiving chamber 7 an annular flat bearing surface 9 intended to bear against the underside of the container edge while at least in the upper position of the support body 6. The press plate 8 is mounted on longitudinal members 10 mechanically connected to lifting devices. The bottom of the containers 1 can be held by the cups 11 of a group of ejectors 12 whose vertical rods 13 pass through the press plate 8 and are fastened, by their lower end, to a stationary frame 14 which, for example, forms part of a packaging installation of the type making it possible to form containers from a thermoplastic strip, filling these thermoformed containers, covering and sealing the filled containers with a lid sheet and, finally, cutting the filled containers and sealed either individually or in groups of containers.

 When ribs 5 are used as contact faces on the electrode 4, a sealing zone 16 is formed on the edge 15 of the container 1 and has on the lid 3 and in the adjacent face of the container edge 15. The cover 3, generally consisting of an aluminum foil, the underside of which is coated with a thin heat-sealing layer 9, is strongly stretched in the sealing zone 16 at the end of the groove 17 so that tears very easily when it is desired to separate the lid 3 from the edge 15 of the container 1 by a peeling movement.

 As can be seen more particularly in FIGS. 3s 5 to 8, 10 and 119, the sealing device according to the invention uses, on the single electrode plate 4, flat hot annular contact faces 4 whose width is at least equal to that On the other hand, each flat bearing face 9 provided at the upper end of the support body 6 is constituted by the plane top of at least one annular rib 1-8 whose width at the apex It is between 0.5 and 2 times the thickness of the edge 15 of a container 1D i.e. the thickness of the thermoplastic strip from which the containers are thermoformed. In addition, it is advantageous to mount the body of the container. support 6 on the press plate 8 by means of a compensating plate 19 which is weakly elastic and is of a sufficient thickness to allow a slight pivoting of the support body 6.

 According to the embodiment shown in FIGS. 3 and 9> the support body 6 comprises two transverse rows of receiving chambers 7 and a bottom 20 which, via a plurality of knobs 21, 22, is fastened to the press plate 8.

The head of the bolts 21,22 is applied against the receiving chamber bottom 7 and the rod of these bolts passes through, with a certain lateral clearance, corresponding bores 23,24 of the bottom 20 of the body 6 and of the plate 19.

Above and in the immediate vicinity of the reflector plate 19, the fastening bolts 21 comprise a low-height flange 25 which has a small amount relative to the inner wall of the corresponding bore 23. The bore 24 has a cross-section of oblong shape so as to allow the support body 6 a slight longitudinal and Z or trans versal movement. This fastening system is a kind of false ball or false pivot allowing the support body 6 to perform pivoting movements of small amplitude.

 To promote the pivoting movements of the support body and in order to adapt these bearing faces 9 to the planes defined by the different contact faces 5 of the electrode plate 4, it is advantageous to subdivide said support body 6 in several juxtaposed support blocks 26,27,28,29, each of which comprises at least one receiving chamber 7 surrounded, at its upper opening, by at least one support rib 18. These support blocks 28 to 29 are juxtaposed transversely to the direction of feed of the containers, but it is also possible to juxtapose two support blocks in the longitudinal direction, that is to say in the direction parallel to the direction of advancement of the containers (see the blocks). 27 and 30, ~ Figure 9).

 It can be seen in particular from FIGS. 7 to 9 that on each side of each support block 26 to 30 is provided a guiding and support guide 31, 32, 33 which extends parallel to the direction of travel of the containers 1 and whose the upper support face 34 is located slightly below the level of the vertices 9 of the support ribs 18 when the press plate 8 occupies the upper sealing position (see FIGS. 7 and 8). These guiding and support rails 31, 32,33 are mounted stationary on a frame of the sealing device Each support block 26 to 30 comprises at least one receiving chamber 7 (see blocks 27 and 30), but may also comprise several receiving chambers and in particular two receiving chambers 7 juxtaposed, preferably, in the direction of advancement of the containers 1 (block 28).

 According to the embodiment shown in Figures 10 and 11D the. Support body 6 is subdivided into longitudinal rails 35 fixedly mounted and transverse support pieces 36 movable relative to longitudinal rails 35 Such an arrangement is known for example from French Patent 11, a12.671. According to this patent, the transverse support pieces are movable transversely and remain at the same level when they deviate laterally to free the passage for the advancement of the containers. The major disadvantage of this arrangement lies in the doubling of the width of the working area of the device relative to the width of a row of containers juxtaposed in the transverse direction of the sealing device. Two transverse support pieces 36 successive and successive in the direction of advancement of the receptacles and two corresponding longitudinal bearing rails 35 and associated with these two support pieces 36 define a receiving chamber 7.

Compared to the state of the art illustrated by the French patent 1,512,671, this embodiment of the sealing device is distinguished by the fact that the transverse support pieces 36 are mounted on the press plate 8 and are steadily movable with it and that, in addition, each of the two longitudinal slideways 39 and the two associated transverse support pieces 36 to define a receiving chamber 7 comprises, on the superficial face, sections of support rib 37,38, 39,40 which, in the sealing position of the press plate 8, complement each other so as to form an annular support rib similar to the support rib 18.

 In a similar manner to the fixing of the support body 6 on the press plate 8 by means of a weakly elastic compensating plate 19, the different support blocks 26 to 30 and the supporting parts 36 arranged between two longitudinal bearing rails 35 are mounted on the press plate 8 by means of at least one elastic compensating plate or elastic compensating cushions 19 and so that they can slightly rotate around their pivots corresponding 21,22 fixed on the press plate 8.When two receiving chambers 7 are provided in the longitudinal direction between two longitudinal rails 35, the support part downstream of the receiving-upstream chamber and the upstream support piece of the receiving chamber downstream can be joined to form a single support piece 41 carrying two sections of support rib 39 and 40. The longitudinal bearing rails 35 are mounted on a fixed frame such as crosspieces 42 of the sealing device, by means of elastic cushions or compensating plates 43. To facilitate the seating of the longitudinal support rails 35 and the support pieces 36 on their mutual supports , namely, the frame or the crosspieces 42 and the press plate 8, said longitudinal guides 35 and the support pieces 36 comprise, at their lower ends, bearing feet 44, 45 traversed by the corresponding fixing pivots or bolts 21 to Z2.

 As can be seen more particularly in FIGS. 5 and 7 to 9, the support rib 18 with its flat support face 9 of relatively small width (0sS to 2 times the thickness of the container edge) makes part of a bearing ring 46 delimiting the opening of a receiving chamber 7 of the support body 6 of a support block 26 to 30. This bearing ring 46 in a manner known per se, is capable of moving a short distance perpendicular to the axis of the receiving chamber 7 and rests by its flat lower face on the flat and horizontal upper face of the support body or a support block. 46 comprises at its base an outer shoulder 47 which is capped with a certain lateral play by several fastening lugs 48 uni necessarily distributed around the opening of the receiving chamber 7 and screwed on the support body or a support block. On the inner side, each bearing ring 46 is provided with a frustoconical self-centering face 49 which connects the inner bearing rib 18 to the inner vertical annular face 50 of the bearing ring 46.

 In some cases and in particular when the thickness of the edge 15 of the container 1 has a thickness of at least one millimeter, the width of the plane top 9 of the annular support rib 18 may be less than the thickness of said container edge 15 .

 As can be seen in FIG. 6, the weld bead 51 connecting the cover sheet 3 to the The container edges 15 are relatively wide and have a small hollow below the weak mark or groove 52 left by the support rib 18 on the underside of the edge 15. The weld or seam 51 has the shape a wide flattened groove whose edges are slightly raised with respect to the upper face of the container edge 15. The width of the sealing bead 51 is greater than the thickness of the container rim 15 and is at least three times that thickness . It will also be appreciated that because of the slightly raised edge of the sealing bead 51D the peeling of the cover sheet 3 is particularly easy.

 The various embodiments described above can undergo a certain number of modifications without, for this reason, departing from the scope of protection defined by the appended claims.

Claims (9)

 1. A device for sealing a lid having at least one thermoplastic layer 5 on the horizontal plane edge of a plurality of thermoplastic containers 1 belonging to at least one and the same row extending transversely to the advance of said containers of the type comprising, firstly, above the containers, a single electrode plate 4 which extends transversely over the entire width of the row of containers and which has for each corresponding container a hot annular contact face 5 whose width is at least equal to that of the container edge 95 with which it is associated7 and on the other hand, below the edge 15 of the containers 1, a support body 6 which comprises for each corresponding container 1 a receiving chamber 7 open upwards which by its underside is mounted on a press plate 8 vertically movable between a so-called high seal position and a low position called release clearance the evacuation and the progress of the containers, and whose upper face has around the opening of each receiving chamber 7 an annular flat bearing face 9 intended to bear against the underside of the container edge At least at an upper position of the support body, characterized in that each flat bearing face 9 is constituted by the plane top of at least one annular rib 18 whose width at the apex is between 0.5 and 2 the thickness of the container edge 15, and that the support body 6 is mounted on the press plate 8, if necessary, by means of a weakly elastic compensating plate 19. 2. Sealing device according to claim 1, characterized in that the support body 5 is subdivided into several juxtaposed support blocks 26 to 3G, each of which comprises at the moiras a reeetracted chamber 7 surrounded at its upper opening by at least one support rib 18 and is mounted on the press plate 8. 3. Sealing device according to any one of claims 1 and 2s characterized in that on each side of each support block 26 to 30 is provided a guide and support rail 31 to 33 which extends parallel to the direction progress of the containers 1 and the upper support surface 34 is located slightly below the level of the vertices 9 of the support ribs 18 when the press plate 8 is in the upper sealing position. 4. A sealing device according to any one of claims 1 and 2, wherein the support body 6 is subdivided into longitudinally fixed rails 35 fixed stationary and transverse support pieces 36 movable relative to the longitudinal rails 35, two transverse support pieces 36 adjacent and successive in the direction of advance of the containers 1 and two corresponding longitudinal bearing rails 35 and associated with these two support parts delimiting a receiving chamber 7, characterized in that the pieces of transverse supports 36 are mounted on the press plate 8 and are vertically movable with it and that cult of the two longitudinal rails 35 and the two associated transverse support parts 36 carry, on their upper faces, sections of support rib 37 to 40 which, in sealing position of the press plate, complement each other so as to form the ego ns an annular support rib 18. 5. Sealer according to any one of claims 1 to 4, characterized in that the support body 6, the support blocks 26 to 30 and the support pieces 36 are mounted on the press plate 8 via the medium of FIG. at least one elastic compensating plate or elastic compensating cushions 19 and tiller so that they or they can slightly rotate around their corresponding pivots 21322 fixed on the pressa plate.  6 sealing device according to any one of claims 1 to 5 characterized in that the guide rails and support. 31 to 33 are mounted stationary on a frame of the device. 7. A sealing device according to any one of claims 1 to 5, characterized in that the longitudinal bearing rails 35 are mounted on a frame 42 of the device via elastic cushions or compensating plates 43. 8. A sealing device according to any one of claims 1 to 7, and having a bearing ring 46 defining the opening of a receiving chamber 7 of the support body 6 or a support block 26 to 30 and capable of moving a short distance perpendicular to the axis of said receiving chamber 7, characterized in that the one or more support ribs 18 are provided on the bearing ring 46 and that a frustoconical self-centering face 49 connects the inner bearing rib 18 to the inner vertical annular face 50 of the bearing ring 46. 9. Sealing device according to any one of claims 1 to. 8, characterized in that the width of the plane top 9 of the annular support rib 18 is less than the thickness of the container edge 15 when the latter has a thickness of at least 1 mm.