GB1594464A

GB1594464A - Moulding plastics containers

Info

Publication number: GB1594464A
Application number: GB821077A
Authority: GB
Original assignee: Metal Box PLC
Current assignee: Crown Packaging UK Ltd
Priority date: 1978-05-15
Filing date: 1978-05-15
Publication date: 1981-07-30

Description

(54) MOULDING PLASTICS CONTAINERS (71) We, METAL BOX LIMITED, ob Queens House, Forbury Road, Reading RG1 3JH, Berkshire, England, a British Com- pany, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The invention relates to moulding plastics containers. In particular, but not exclusively, the invention relates to thermoforming from plastics sheet material plastics containers having wide mouths defined by reduced diameter neck portions of the container side wall.

In accordance with the invention from one aspect there is provided a method of moulding a plastics container having a base portion and a tubular side wall portion upstanding from the base portion and terminating in a mouth at its opposite end, wherein the container is moulded by deforming mouldable plastics sheet material into a cavity of a mould having first and second relatively movable parts to form, respectively, the side wall portion and base portion of the container, and after moulding the mould parts are moved and the container is ejected from that end of the first mould part which was adjacent the second mould part.

In accordance with the invention from a second aspect there is provided an apparatus for moulding a plastics container having a base portion and a tubular side wall portion upstanding from the base portion and terminating in a mouth at its opposite end, the apparatus comprising first and second mould parts arranged so as in combination to define a mould cavity into which, for the moulding of the container, mouldable plastics sheet material can be deformed into substantial conformity with the cavity wall, the first mould part providing the part of the mould cavity adapted to form the side wall portion of the container and the second mould part providing the part of the mould cavity adapted to form the container base portion, the first and second mould parts being relatively movable and the apparatus further including mould separation and container ejection means operative after the moulding of the container to effect relative movement of the mould parts in a manner to free the second mould part from the container so that the container can be ejected from that end of the first mould part which was adjacent the second mould part, and thereafter to force the container, base portion first, from the first mould part.

From a third aspect the invention provides a plastics container moulded by a method as defined above.

In order that the invention may be more fully understood an apparatus for thermoforming containers from plastics sheet material and embodying the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Fig. 1 shows the apparatus generally in central vertical section and when in use; Fig. 2 is a scrap view corresponding to Fig. 1 of the apparatus in modification thereof and with the plastics sheet material omitted for clarity; and Fig. 3 is a perspective view of a container produced by the apparatus of Figs.

1 and 2.

Referring 'now to Figs. 1 and 3, a thermoforming machine embodying the invention is arranged for thermoforming wide-mouthed containers 10 (Fig. 3) one at a time. The containers are circular in plan view and comprise a circular base portion 11 and a side wall portion 12 upstanding peripherally from the base portion. Although not apparent from Fig. 3 it is to be understood that the base portion 11 is upwardly domed towards its centre and terminates peripherally in a rounded, downwaally convex bead. The wall portion 12 is joined to the base portion at this bead and comprises, in the upward direction as shown, a first and major right-cylindrical part 14, a short, upwardly and inwardly tapered frustoconical transition part 15, and a second and minor right-cylindrical part 16 od smaller diameter than the part 14 and defining the mouth 17 of the container.

The part 16 includes an outwardly projecting peripheral bead 18 formed closely adjacent its mouth-defining free edge 19 for enabling a suitable plastics closure (not shown) to be snap-engaged onto the container in conventional manner.

It will be appreciated from Fig. 3 that in the container the parts 15 and 16 together form a reduced diameter neck for the container, the remainder of the side wall portion 12 being constituted by the first cylindrical portion 14. This reduced diameter neck provides the container with a pleasing appearance when open, and enables a closure suap-tted over the bead 18 to be arranged with its outer periphery to lie on the cylindrical envelope of the portion 16, further ensuring aesthetic appeal for the closed container.

Referring now to Fig. 1, the apparatus by which the container 10 is made comprises upper and lower platen assemblies 20, 21.

Of the two platen assemblies the upper assembly 20 is essentially fixed in position; the lower assembly, however, is vertically reoiprocable by a cam (not shown) between the raised position shown in which it engages the upper platen assembly to enable a aontainer 10 to be formed in a mould cavity 22 in the lower assembly, and a lowered position in which, as is later to be described, a container so moulded can be ejected for dispatch or further processing.

The upper platen assembly 20 comprises a horizontal platen member 23 which is rigidly carried from the machine frame and which itself serves to mount two downwardly extending and vertical guide rods 24. Centrally between the guide rods 24 the platen member 23 has a vertical through bore through which the push rod 25 of a plug member 26 slidably extends to a contoured plug head 27.

At its upper side the platen member 23 carries apparatus for effecting and controlling vertical reciprocating movement of the plug member. Essentially this apparatus comprises a first, vertioally directed hydraulic or pneumatic ram (not shown) having its cylinder mounted on the platen member 23 and having its piston attached to the push rod 25 at screwthreads 9 of a connection piece 28, and a second, horizontally directed hydraulic or pneumatic ram 29 having its cylinder 30 likewise mounted on the platen member 23 and having a stop member 31 attached to the end of its piston nod 32. The stop member 31 is arranged so as on extension of the ram 29 to project, as shown, under a further stop member 33 fast with the push rod 25 and so define a lower limiting position for the push rod. As will later become apparent, a further lower limiting position for the push rod, at a lower level than the first, applies when the ram 29 is retracted.

In addition to the guide rods 24, the platen member 23 carries on its underside four downwardly extending vertical studs 35 which are screwed into a plate 36 itself secured to the platen member 23 by bolts 60. The studs 35 serve to mount a clamping ring 38 for limited vertical movement in conoentric relation to the plug member 26. The heads 37 of the studs define the lower limit of this movement, the clamping ning being biassed downwardly towards this position by compression springs 39 which are sleeved individually over the studs.

The clamping ring 38 is internally formed with a passage 40 for cooling water. It presents to the lower platen assembly 21, in concentric relation to the plub member 26, a horizontal and annular clamping face 41.

A generally cylindrical knife member 42, likewise arranged in concentric relation to the plug member, is bolted at its top end to the plate 36 by bolts 61 and extends downwardly to a cylindrical portion 43. The portion 43 is slidably received by, and within, the clamping ring 38 and terminates at its free bottom end in a knife edge 44. The length of the studs 35 is such that when the clamping ring 38 is in its lower limiting position as determined by engagement with the stud heads 37, the clamping face 41 is proud of the knife edge 44, and the knife member 42 is accordingly in a retracted, inoperative condition.

The lower platen assembly 21 is formed of two vertically separable parts 50, 51 together capable of forming the mould cavity 22. The upper one 50 of these parts is a bloked assembly of members. It has a vertical through bore 8 defining the side wall for the mould cavity. Around the periphery of the bore 8 the part 50 presents an upwardly facing horizontal and annular clamping face 52 in direct opposition to the clamping face 41 of the upper platen assembly. The lower platen assembly is guided for reciprocating vertical movement towards and away frcim the upper platen assembly by the guide rods 24 which extend downwardly through sleeve bearings 58 on the part 50. Heads 53 on the bottom ends of the guide rods define for the part 50 a lower limiting position to which it is biassed by compression springs 54 sleeved over the guide rods. When the part 50 is in this position a clearance of approximately 1 cm. exists between the clamping faces 43, 52, the overall height of the container 10 to be moulded (and hence the mould cavity 22) being approximately 5 cm.

The underside of the part 50 of the lower platen assembly -is formed with a generally cylindrical recess 55 into the centre of which the bore 8 opens. The lower surface of the part 50 within the recess is particularly denoted 63. The recess is adapted to receive the top end of the second part 51 of the lower platen assembly. As can be seen from Fig. 1, the part 51 is, like the part 50, a bolted assembly of members; it is generally cylindrical.

The uppermost member of the part 51, particularly denoted by the reference numeral 56, is arranged to close the bottom ob the mould cavity 22. Its upper surface 64 is formed with a contoured circular depression 57 conforming to the base portion 11 of a container 10 to be formed. The bore 8 conforms to the side wall portion 12 of a container 10, so that when the parts 50, 51 are together as shown, they combine to form the mould cavity 22.

Features and parts of the apparatus other than those mentioned above will become ap- parent from tbe following description of the manufacture of a container 10 f.rom a sheet 5 (Fig. 1) of a suitable plastics material, for example high density polyethylene, which is drawn from a reel and indexed horizontally through the apparatus in discrete movements by means not shown. The sheet, which is typically 1 mm. thick, is heated prior to its entry into the apparatus by a bank od electrical or hot air heaters (not shown) forming a further part of the thermoforming machine as a whole.

Let it be assumed initially that a previously formed container has just been ejected and the plug member 26 has subsequently been raised to its retracted position in which its head 27 is located above the level of the sheet 5. At this time the lower platen assembly 21 is in its fullly lowered position, that is to say, it has its part 50 lowered onto, and supported by, the heads 53 of the guide rods 24, its part 51 being spaced vertically beneath the part 50 so that a substantial daylight clearance, the function of which will later become apparent, exists between the two parts.

The first stage in the manufacture of Q container 10 is the indexing of the sheet 5 forward (i.e. out of the plane of the paper of Fig. 1) to present fresh but heatYsoftened sheet material 5 over the bore 8. After this, the two parts 50, 51 od the lower platen assembly are dosed together and the lower platen assembly as a whole is raised towards the upper plate assembly. This is effected by the previously-mentioned cam which is located beneath, and effective upon, the part 51, and continuously rotated in synchronism with the indexing of the sheet 5 and the vertical reciprocation of the plug member 26 so that the cam makes one revolution for each container 10.

As it rotates the cam lifts the part 51 into engagement with ;the part 50 at the surfaces 63, 64; initial location of the part 51 within the recess 55 is ensured by engagement of upstanding studs 80 on the part 51 in vertical holes 81 in the undersurface 63 of the part 50 within the recess 55.

Continued lifting movement od the part 51 by the cam then lifts the part 50 off the guide rod heads 53 to clamp the sheet 5 around the mould cavity 22 by co-operation between the clamping faces 41, 52. This movement is accompanied by upward depression of the clamping ring 38 against the springs 39. The depression of the clamping ring may be sufficient to cause the knife edge 44 to stand just proud of the clamping face 41 so as to indent the top surface of the sheet 5, or it may be such that the knife edge 44 is still retracted.

When this limited depression of the clamping ring has been achieved the upward movement of the lower platen assembly is stopped and the lower platen assembly is held by the cam at the top of its travel for a following dwell period. During thais pericd, air under pressure is supplied via a conduit 70 (Fig. 1) to the upper surface of the plastics sheet S over the region defined within the faces 41, 52, it being noted in this respect that the platen member 23, the plate 36, the knife member 42 and the sheet itself together form a substantially airtight chamber for this pressure air. At the same time as the air is admitted the plug member 26 lis lowered by its associated vertical ram from its raised, inoperative position to the upper one of its two lower positions, the ram 29 having been previously extended.

In known manner the air pressure and plug member 26 in combination deform and stretch the clamped region of the sheet downwardly into the mould cavity, so that within the mould cavity there is formed a preform conforming to the cavity walls and accordingly having the shape of the desired container 10.

The position is then as depicted in Fig. 1.

Conduits for cooling water are provided in the lower platen assembly around the mould cavity so that on touching the mould cavity walls the plastics material of the preform is cooled and made rigid. These conduits are indicated in Fig. 1 by the reference numeral.

71A, 71B and 71C.

During the formation of the preform as described above the clamping effected by the clamping faces 41, 52, possibly assisted by indentation of the sheet material by the knife edge 44 as described above, prevents the sheet outside the clamping region from deforming radially inwards towards the mould cavity. Any substantial buckling or crinkling of the material forming the preform is thereby avoided.

After the preform has been formed the cam associated with the lower platen assembly lifts the latter through a small further distance so as by further depressing the clamping ring 38 against the action of the springs 39 to cause the knife edge 44 to sever the preform from its parent sheet 5 and so form the container 10 of Fig. 3. The cam then allows the lower platen assembly to fall under its own weight and under the action od the springs 39 and 54, so that, in sequence, the clamping ring moves to its lowermost position against the heads 37, the part 50 moves to its own lowermost position against the heads 63, and the part 51, which continues to move down after the clamping ring 38 and, later, the part 50 have halted, moves to a position at which the previously mentioned daylight clearance, which has a depth somewhat greater than the depth of the container 10, exists between the parts 50, 51.

The container is lat this time still retained by the part 50, and so has its base 11 open to the daylight clearance.

When the daylight clearance has been achieved the ram 29 is retracted so as to withdraw the stop member 31 from beneath the stop member 33. The vertical ram associated with the plug member 26 is then effective to lower the plug member quickly to its fully lowered position; additionally or al temately a blast of air may be applied to the interior of the container via the oonduit 70. The plug member and/or the air blast strips the container from the part 50 and forces it downwardly into the daylight dear- ance. A generally horizontally directed jet of air generated by means not shown then carries the container away from the thermos forming machine in the forward direction for subsequent printing and any further treatment.

After the stripping and ejection od the container in this way, the plug member 26 is raised to its retracted position above the sheet 5, the sheet 5 is indexed forward, and the process described above is repeated for the manufacture of the following container.

Fig. 2 shows a modification of the thLermo- forming machine of Fig. 1 in which the bore 8 is defined by two members, one of which, denoted 85, provides the part of the bore corresponding to the major night-cylindrical part 14 and the frustocohical part 15 ob the container 10, and the other od which, denoted 86, provides the part of the bore correspond- ing to the minor right-cylindrical part 16 of the container.

The member 86 is secured by bolts 87 to a member 88 which constitutes the body d the part 50 of the lower platen assembly and which accordingly carries the sleeve bearings 58 for the guide rods 24. The member 85 is slideable within the member 88 towards and away from the member 86. It is held captive on the member 88 by studs 89 having heads 90 which are free to move through a limited travel within the member 88. Compression springs 91 sleeved over the studs 89 bias the member 85 downwardly away from the member 86.

The operation of the apparatus of Fig. 2 is identical to that of Fig. 1 except that the stripping of the preform from the bore 8 after moulding is performed in two stages rather than as a single stage operation. Subsequent to the bottoming of the clamping ring 38 on the heads 37 as the lower platen assembly is lowered as previously described, the members 85, 86 and 88 move down in unison until the member 88 bottoms on the heads 53. After this, further lowering of the part 51 Iby the assodated cam frees the member 85 for downward movement away from the members 86, 88 under the action of the springs 91, with the result that the preform is stripped prematurely from the member 86.

Further downward movement of the part 51 then takes up the downward travel available for the member 86, whereupon the stud heads 90 bottom in the member 88 and the parts 85, 86 and 88 thereafter again move down in unison. Stripping of the preform from the member 85 and ejection from the apparatus is later effected as previously described.

The stripping of the container firom the part 50 in two stages rather than only one stage facilitates stripping and is od particular advantage where, as described and shown, the container neck has one or more outwardly projecting formations for attachment of a closure. The invention is not, however, to be considered as limited to the provision of formations on the container neck, and in a modification of the described apparatus the groove 100 provided in the bore 8 for forming the container bead 18 is omitted. The part 16 of the container neck is then plane and suitable for internally receiving the plug portion of a closure of the push-in type.

As with the head 18 of the container of Fig. 3, the one or more formations, where provided, may be "jumped-out" of the mould cavity, that is to say, when the neck is stripped from the mould cavity the natural deform- ability and resilience of the container neck material may be relied upon for enabling the formations to move Out of the complementary formations on the mould. Id desired, however, an apparatus in accordance with rhe invention may employ members arranged for forming part or all -of the container neck and which, subsequent to a moulding operation, are movable generally radially away from the moulded container so as to free one or more formations on the container neck for later ejection of the container. One container for which such an arrangement is proposed has an outwardly projecting flange formed on its neck around the container mouth for providing a plane annular sealing face for a heatisealed diaphragm closure.

A particular feature of a container 10 produced by the described apparatus is the lack of any mould line on at least the portion 16 of its side wall. The portion 16 therefore provides a large and uninterrupted area for print. if desired, the portion 16 may be reverse tapered, that is to say, its diameter may increase towards the base of the container.

In each of the apparatus of Figs. 1 and 2 the parts 50, 51 of the lower platen assembly are separable vertically, that is to say axially of the mould cavity, to enable a container in the mould cavity to be ejected from the apparatus. In a modified arrangement, however, the lower one, 51, of the separable parts 50, 51 is arranged for movement in a transverse direction in relation to the cavity axis, to free the container for ejection. The container may then be stripped from the mould and ejected firom the apparatus downwardly, with a single direction of movement and unimpeded by the mould part 51. The transverse movement of the part 51 is preceded by a small downward movement suffi 'client to bring the part 51 clear of the container bottom to enable the transverse movement to take place.

Although particularly suited for the formation of containers having necked-in mouths as particularly described, the invention is not to be considered as being so limited. It may be applied to containers having unnecked mouths. Moreover, the containers may be of other than circular crosswsection as particularly described.

WHAT WE CLAIM IS: 1. A method of moulding a plastics container having a base portion and a tubular side wall portion upstanding from the base portion and terminating in a mouth at its opposite end, wherein the container is moulded by deforming mouldable plastics sheet matserial into a cavity of a mould having first and second relatively movable parts to form, respectively, the side wall portion and base portion of the container, and after moulding the mould parts are moved and the container is ejected from that end of the first mould part which was adjacent the second mould part.

2. A method as claimed in claim 1, wherein the container is formed from a sheet of mouldable plastics sheet which is presented across the mouth of the mould cavity and subsequently clamped around the periphery of the cavity mouth to define a peripherally clamped region of the sheet, the method including the steps of deforming the said region of the sheet into the cavity and into substantial conformity with the cavity wall to form the container, severing the container from the parent sheet material, effecting relative movement of the mould parts to free the second mould part from the container and enable the container to be ejected from the first mould part, and forcing the container base portion first, from the first mould plart.

3. A method as claimed in claim 1 or claim 2, wherein the deformation of the pllastics sheet material is at least partially effected by pressure mechanically exerted thereon.

4. A method as claimed in any preceding claim, wherein the forcing of the container from the first mould part is at least partially effected by pressure mechanically exerted on the base portion within the container.

5. A method as claimed in any preceding claim, wherein the forcing of the container from the first mould part is at least partially effected by gas pressure exerted on the base portion within the container.

6. Apparatus for moulding a plastics contrainer having a base portion and a tubular side wall portion upstanding from the base portion and terminating in a mouth at its 'opposite end, the apparatus comprising first and second mould parts arranged so as in combination to define a mould cavity into which, for the moulding of the container, mouldabie plastics sheet material can be deformed into substantial conformity with the cavity wall, the first mould part providing the part of the mould cavity adapted to form the side wall portion of the container and the second mould part providing the part of the mould cavity adapted to form the container base portion, the first and second mould parts being relatively movable and the apparatus further including mould separation arid container ejection means operative after the moulding of the container to effect relative movement of the mould parts in a manner to free the second mould part from the container so that the container can be ejected from that end of the first mould part which was adjacent the second mould part, and thereafter to force the container, base portion first, from the first mould part.

7. Apparatus as claimed in claim 6, wherein the first and second mould parts are separable axially of the mould cavity to provide between 'them a daylight clearance greater in depth than the length of the mould cavity and into which the container can be forced, base portion first, from the first mould part.

8. Apparatus as claimed in claim 6, wherein the first and second mould parts are relatively movable firstly longitudinally of the mould cavity to free the second mould part from the container, and latterly transversely of the ,mould cavity; such tnansverse movement enabling the container to be forced, base portion first, from the first mould part and thereafter to leave the apparatus with the same direction of movement and unimpeded by the second mould part.

9. Apparatus as claimed in any claim of claims 6 to 8, which includes a plug member movable axially of the mould cavity and into the same, so as at its free end to mechanically defonm said mouldable plastics sheet material into the mould cavity for the moulding of the container.

10. Apparatus as claimed in claim 9, wherein, subsequent to the moulding of the container, the plug member is further axially

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. may increase towards the base of the container. In each of the apparatus of Figs. 1 and 2 the parts 50, 51 of the lower platen assembly are separable vertically, that is to say axially of the mould cavity, to enable a container in the mould cavity to be ejected from the apparatus. In a modified arrangement, however, the lower one, 51, of the separable parts 50, 51 is arranged for movement in a transverse direction in relation to the cavity axis, to free the container for ejection. The container may then be stripped from the mould and ejected firom the apparatus downwardly, with a single direction of movement and unimpeded by the mould part 51. The transverse movement of the part 51 is preceded by a small downward movement suffi 'client to bring the part 51 clear of the container bottom to enable the transverse movement to take place. Although particularly suited for the formation of containers having necked-in mouths as particularly described, the invention is not to be considered as being so limited. It may be applied to containers having unnecked mouths. Moreover, the containers may be of other than circular crosswsection as particularly described. WHAT WE CLAIM IS:

1. A method of moulding a plastics container having a base portion and a tubular side wall portion upstanding from the base portion and terminating in a mouth at its opposite end, wherein the container is moulded by deforming mouldable plastics sheet matserial into a cavity of a mould having first and second relatively movable parts to form, respectively, the side wall portion and base portion of the container, and after moulding the mould parts are moved and the container is ejected from that end of the first mould part which was adjacent the second mould part.

movable in the same direction as before so as at least partially to force the container from the first mould part.

11. Apparatus as claimed in claim 10, which includes an actuator arranged to effect the required axial movement of the plug member 'and a stop member operable while the container is being moulded to define an intermediate limiting position for the stop member for its deformation of the plastics sheet material, the sto.p member being releasable subsequent to moulding to allow the plug member to be further moved by the actuator so as at least partially to force the container from the first mould part.

12. Apparatus as claimed in any claim of claims 6 to 11, which comprises a first platen assembly, and a second platen assembly having the said first and second mould parts, the platen assemblies being recipnocable towards and away from one another and arranged on engagement to resiliently clamp around the periphery of the cavity mouth a sheet of mouldable plastics material presented across the mouth, the apparatus including -a.

plug member camed by the first platen assembly and movable in relation to the same when the platen assemblies are engaged so as at its free end to mechanically deform the peripherally clamped region of a said plastics sheet into the mould cavity for the moulding of the container, and a tubular knife member mounted on the first platen assembly and operative after moulding to sever the container from the plastics sheet, the first and second mould parts being arranged for relative movement so as to free the second mould part from the moulded container and enable the container to be ejected from the first mould part, and the plug member being arranged for further movement in the same direction as before so as at least partially to force the container, base portion first, from the first mould part.

13. A plastics container made by a method as claimed in any claim of claims 1 to 5 wherein the side wall portion is formed of a minor cylindrical part extending to the mouth of the container, a major cylindrical part having a greater diameter and substantially greater length than the minor cylindrical part and peripherally joined at one end to the base portion, and a transition part connecting the cylindrical parts together so as to extend inwardly d the container in the direction towards the minor cylindrical part.

14. A container as claimed in claim 13, wherein the transition part is frustoconical.

15. A container as maimed in claim 13 or 14, .wherein the base portion has a central dome convex to the container interior, and a rounded peripheral bead convex to the container exterior and joining the dome to the side wall portion.

16. A container as claimed in any claim of claims 13 to 15, wherein the minor cylindrical part includes one or more outwardly projecting formations for engagement with one or more complementary formations od a plastics closure whereby to attach the closure to the container.

17. A container as claimed in any claim of claims 13 to 15, which has an outwardly projecting flange formed at the free end of the minor cylindrical portion around the con miner mouth for providing a plane annular sealing face for a heat~sealed diaphragm closure.

18. A method of moulding a plastics container, substantially as hereinbefore described with reference bo Figs. 1 and 3, or Figs. 2 and 3 of the accompanying drawings.

19. Apparatus, substantially as hereinbefore described with reference to Fig. 1 or Fig. 2 of the accompanying drawings.

20. A plastics container moulded by a method as claimed in any claim of claims 1 to 6 and 18, and substantially as hereinbefore described with reference to Fig. 3 of the accompanying drawings.