GB2104825A - Blow moulding - Google Patents

Abstract

A plastics cup-like container is produced by blow moulding a product 20 which is then severed at 42 or 64 to provide one or two of the containers. The moulding may be shaped so that when the severing takes place the or each resulting cup- like container has an outwardly turned flange by which the container may be sealed by means of a metal or plastics lid. The severing can be effected by a shearing ring 44. The container walls are biaxially orientated which provides enhanced strength and gas barrier properties. A laminated parison can be used, the inner plastics layer having good gas barrier properties. <IMAGE>

Description

SPECIFICATION One piece plastic containers for the holding of carbonated beverages The invention relates to the manufacture of one piece plastic containers for the holding of carbonated beverages.

The containers are what might be described as cup-like containers insofar as they have a base and an outer wall leading to a relatively wide mouth region, as distinguished from bottles which have a bulbous body portion, a base and a relatively narrow neck leading to the mouth.

Conventionally, liquid is poured from bottles in to drinking vessels whereas as liquid beverage may be consumed directly from a cup.

The present invention relates to plastic one piece containers which are however sealed after filling, in order to form packages containing individual quantities of carbonated beverage, in much the same fashion as individual quantities of carbonated beverages are contained in metal cans. As will be clear from the description which follows, the plastic containers according to the invention may be closed by means of metal lids rim rolled to the mouth of the containers, or the said containers may be closed by means of plastics lids which are sealed, for example by spin welding or ultrasonic welding, to the container mouths.

Thus, although the containers are cup-like, they are nevertheless for use in sealed packages holding carbonated beverage, and although in the use of the packages when open, it may be possible to drink the contents directly from the container, in much the same way as one can drink from a bottle, it will be more usual to pour the contents into a separate drinking vessel, and therefore although the designation cup-like has been used herein, that designation is to indicate more the general structure of the plastic container rather than to indicate that a user would of necessity drink from the container.

The only containers produced on a substantial scale for holding carbonated beverage and being of the type which the present invention relates, have been formed by deep drawing hot flat sheet material, and by severing the individually drawn containers from the sheet material, leaving a skeletal waste which can be reprocessed. This method, although it has met with some notable success, still has one or two shortcomings, one of which is that of the sheet material presented to the deep drawing apparatus, only some 25% or so actually is used to form the containers, and 75% has to be recycled. To recycle the material involves processing the skeletal waste into granules or chips, which is energy consuming, and furthermore the recycled material gives subsequent sheet material slightly inferior properties compared to virgin material.

Secondly, the gas barrier properties of the resulting containers, although acceptable in some countries which do not experience extremes of temperature, have shown themselves to be insufficient where wide variations in ambient temperature can be experienced. The gas barrier property of a container is the ability to prevent egress of carbon dioxide from inside the container through the container wall. The shelf life of a sealed container containing carbonated beverage is directly proportional to the gas barrier property, and therefore it is important that the material should have as good a gas barrier as possible.It should be mentioned at this point that when containers according to the invention are filled with carbonated beverage and sealed, normally the carbonated beverage will be in chilled condition which enhances the retention of the maximum carbon dioxide in solution in the drink, but subsequent handling of the container may bring it into a relatively warm environment, and with increase in ambient temperature, the carbon dioxide gas tends to come out of solution, making the internal pressure inside the container rise, and also with increase in internal pressure there will be more tendency for the carbon dioxide to leak through the container wall.

The gas barrier properties of the plastics material, and also its strength to resist increase in internal pressure when used in a container of the type to which the invention relates, is dependent upon the degree of orientation of the material forming the container, and if the material can be bi-axially orientated then much improved strength and gas barrier properties are achieved.With the current method of producing these containers involving deep drawing from sheet material, one can achieve, during the deep drawing process, mono-axial orientation in the direction of drawing of the container, but it is very difficult to obtain any reasonable circumferential orientation (or hoop orientation), during the deep drawing process, and it may well be that it is not possible by deep drawing flat sheet to achieve the necessary degree of bi-axial orientation to give the required gas barrier and strength properties to the finished container.

Plastic blown bottles with acceptable gas barrier properties have been produced by both extrusion blow moulding and injection blow moulding, in that the bottles are formed from a relatively small diameter parison of plastics material which is inflated outwardly to the mould shape, and the blowing process imparts the necessary orientations to the material. The gauge of the blown bottle material is furthermore less than that of the containers formed by the deep drawing process as referred to above, and the residual scrap which must be reprocessed is extremely small.

In the extrusion blow moulding process, a soft hot tubular extrudate of plastics material extends into a split mould, which is closed and the end of the extrudate is sealed, either by the closing of the mould or by other means, and then the tubular extrudate is simply blown outwards to conform to the shape of the mould, and when the plastics material sets, there is formed a blown bottle, complete with a narrow neck which may have screw formations for receiving a cap. In the injection blow moulding process, there is formed in an injection moulding machine a parison which may for example resemble a heavy gauge test tube, but it is formed of plastics material and is provided with the neck formations, such as the screw threads for the bottle top.That parison is fitted in a split mould so th 3t the top end is held firmly, but the tubular portion lies within the mould cavity, extending to say half the depth of the cavity, and being about one third to one fifth of the diameter of the cavity. The parison is heated, and then blown so as to form the bottle body, and the blowing process as can be appreciated effects orientation of the blown material both axially and circumferentially by stretching the material somewhere in the region of 2 to 1 and 3/5 to 1, respectively.

The present invention utilises blow moulding of extrustioor injection moulded parisons for the production of cup-like containers, and the arrangement is that the container is defined by a part of the blow moulded component, and the moulding is subsequently severed to provide the container.

The remainder of the severed moulding may be recycled, in which case care will be taken to ensure that it comprises as small a fraction of the total moulding as possible, and the severing may simultaneously form on the top edge of the container, an outwardly turned flange or rim for the reception of a sealing lid. Alternatively, it is possible to form a rim as described in a subsequent forming operation after the severing of the moulding.

In a particularly suitable example, the mould cavity is provided with a recess in the region of the top of the container part of the moulding, so that the plastics material will deflect into said recess, and in fact define a rim for a sealing lid. When the moulded component is severed, it is severed in the region of the plastics material which deflects into said recess, so that simultaneous with the severing, there is defined the said sealing rim. The mould may be provided with a severing means so that the severing takes place whilst the moulded component is still in the mould cavity proper. The mould cavity may be defined by split mould halves.

The container base may be formed so as to be pressure resisting on the one hand, and on the other hand to be free standing. A suitable construction may comprise a base provided with a plurality of downwardly extending feet, between which extend curved strap portions which lie approximately on a part spherical generatrix.

In a further embodiment, the moulding in fact defines two similar containers arranged back to back in-symmetrical fashion about a centre line so that in cutting the moulding along the centre line, two identical containers result.

Although reference has been made herein to the utilisation of plastics material in the singular, it is to be pointed out that the injection moulded parison or the extruded plastics material parison may in fact be of laminated material, comprising an inner plastics material having particularly good gas barrier properties.

Embodiments of the present invention will now be described, by way of example, with reference to the accompanying diagrammatic drawings, wherein:~ Figs. 1 and 2 illustrate the conventional injection blow moulding process for producing plastics bottles; Figs. 3 and 4 illustrate the conventional extrusion blow moulding process for producing plastics bottles; Figs. 5 and 6 show in accordance with the present invention, the formation of an injection blow moulding from which a container according to the invention is produced; Figs. 7 and 8 show how a moulding can be produced by extrusion blow moulding for the production of a container according to the invention; Fig. 9 illustrates in perspective elevation a container produced by the method of the invention shown in Figs. 5 and 6 or 7 and 8;; Figs. 10 and 1 1 illustrate how two containers can be produced from a single moulding according to the invention; and Fig. 12 is a sectional elevation of a modified form of container according to the present invention.

Referring to the drawings, in Figs. 1 and 2 there is shown a conventional blow moulding mould 10, which is a split mould defining mould halves 12, 14. In the mould cavity 16 in Fig. 1 is shown an injection moulded parison 18 of plastics material which is heated to soften same and of which the closed end is rounded as shown. To produce a bottle of the shape of the mould cavity 16, the parison is blown outwardly until it contacts the mould cavity surface, as shown in Fig. 2. Suitable vent holes (not shown) are provided to enable displaced air to escape from the mould cavity 16, and to allow the blown parison to take up the final bottle shape. It is to be noted that the moulding 20 includes the bottle neck 2? and can be provided with threads to receive a screw top. When the plastics material has set, the mould halves 12, 14 are opened and the moulding 20 is removed. It should be mentioned that the parison undergoes bi-axial orientation in that it is stretched both axially and circumferentially during the blowing operation as indicated by arrows 24, 26.

In the known arrangement shown in Figs. 3 and 4, a tubular extruded parison 30 is located in the mould cavity 16, and the mould 10 is provided with formations for holding and retaining the neck region 22 of the parison, which will in fact form the neck of the bottle in the final moulding. The parison is heated and blown in a fashion similar to that already described, so that the body of the parison contacts and conforms to the shape of the mould cavity surface. When the plastics material has set sufficiently, again the mould 10 is opened and the moulding 20 removed. The body of the bottle is again bi-axially orientated as indicated by arrows 24, 26.

Referring now to Figs. 5 and 6, basically a similar moulding process is illustrated, except that the shape of the mould cavity 1 6 is noticeably different, and in addition the cavity 16 is provided with a recess 40 so that an outwardly formed bead 42 Fig. 6 will result in the finished moulding 20. Additionally, the mould 10 is provided with a shearing ring 44 which can be moved at the appropriate time to shear through the formed bead 42, thereby to serve the resulting moulding 20 and provide a container portion 20A (as shown in Fig. 9) and a residual portion 20B which in fact is scrap and can be recycled. The residual portion 20B should be made as small fraction of the total moulding 20 as possible, so that there will be the minimum of material to be recycled.Fig. 5 shows the injection moulded parison 18 in the mould cavity 16, whilst Fig. 6 shows the parison in blown condition. In the method of the invention the moulding operation may be effected with plug assist as indicated by reference 46 and by dotted lines in Figs. 5 and 6. That is to say a solid plug 46 may be inserted inside the heated injection moulded parison 18 and may be moved downwards towards the bottom of the mould cavity 16 as shown in Fig. 6 in order to prestretch the parison 18 in an axial direction. The plug assist is of course used in conjunction with the blowing of the parison so that it conforms to the cavity shape, thereby to achieve the desired bi-axial orientation.When the moulding 20 has set sufficiently, the cutting ring 44 of the tool is moved in order to shear the moulding 20, to provide the two moulded portions 20A, 20B, so that the container portion 20A in fact takes up the configuration shown in Fig. 9, and it will be seen that the container in this embodiment has a circular cross section, a tapered wall 50, a top rim or flange 51, a pressure resisting base 52 comprising a plurality of feet 54 between which are strap portions 56 of curved configuration. This construction of base 52 has shown itself to be extremely suitably for withstanding internal pressure without everting or extending to such an extent as to make the container incapable being of free standing, but it should be stressed that the configuration of the container can be varied as long a cup-like article results.For example the container can be formed with a cylindrical wall.

In the arrangement shown in Figs. 7 and 8, a similar container 20A is produced, in a similar fashion, except that the starting material is in fact a tubular extruded parison which is blown.

Although reference has been herein to the "blowing" to form the moulding, it is to be appreciated that instead of or in addition to actually pressurising the interior of the parison, the cavity of the mould can be evacuated around the outside of the parison thereby to suck the parison into a shape conforming to the mould surface.

As in the Figs. 5 and 6 embodiment, in the arrangement of Figs. 7 and 8, the plug assist may be used.

In one use of the container for example as shown in Fig. 9, a metal or plastics lid is sealed to the top rim 51 for example by rim rolling after the container contents, carbonated beverage, have been charged into the container, forming a handlable and transportable package. Typically, the container may hold one third of a litre of beverage, so as to form an individual drink, and the lid may be provided with an easy opening device permitting easy access to the interior.

The resulting container is therefore a portion of a blow moulded component which in the blow moulding operation has been bi-axially orientated or in other words has been orientated axially of the container and circumferentially of the container, which is extremely desirable from the strength point of view and from the gas barrier point of view.

Figs. 10 and 11 finally show how, in a single moulding, two similar containers according to the invention may be formed. In this case, the extruded parison 60 is closed at both ends, and therefore it is necessary to use injector needles 62 in the central region for blowing the parison from the position shown in Fig. 10, to the position shown in Fig. 11. It will be clearly appreciated from consideration of the mould configuration shown in Figs. 10 and 11 that two containers 20A identical to that shown in Fig. 9, or according to any other suitable construction, result when the moulding is severed along the central region 64.

The central recess 66 in the mould cavity ensures that each half of the moulding 20 defining a container 20, will be formed with an integral top rim.

Although in the embodiments described, the resulting moulding 20 is provided, by means of the recess in the mould cavity, with an outwardly turned rim, it is not necessary that this should be so, and in another modified method, the rim is formed simultaneously with the cutting of the moulding to sever the container from the remainder, whilst in yet another arrangement, the container is severed from the moulding, and in a subsequent processing step, the said rim is formed.

The container may be formed from a laminated extruded parison or injection moulded parison, and the plastics material or the respective materials when a laminated construction is provided, may be selected from the following, polyester, ethylene vinyl alcohol copolymer, alcrylonitrile, polyvinyl chloride, polyvinylidene.

As regards the construction of the containers, the drawings show a container in tapered form, but this is not essential. Additionally, the drawings show that the container rim extends outwardly from the container wall. In a modified construction, the container at the top may be provided as shown in Fig. 12 with an instepped portion 70 under the said rim 51, so that sealing lids having an outer diameter substantially equal to the diameter of the outer wall can be used for sealing the containers.

In practice there may be a plurality of mould cavities so that a plurality of mouldings may be formed and severed simultaneously.

A suitable plastics material may be used, but is preferred that a polyester plastics material, which exhibits good gas barrier properties when biaxially orientated.

The moulding operation may proceed in a variety of ways. Thus, the extruded parison may be stretched immediately after extrusion and before being placed in the mould. It may be stretched after cutting of the extrudate into individual parisons before being placed in the mould or it may be stretched whilst in the mould by stretching means, before being blown.

Claims (9)

1. A method of producing a plastics container by blow moulding an extrusion or injection or moulded parison wherein the container is defined by a part of the moulding which is bi-axially orientated and which is produced by severing the moulding after the moulding operation, said container having a top which is substantially larger than the size of the parison.

2. A method according to claim 1, wherein the moulding defines two identical containers symmetrically arranged, and the moulding is subsequently severed to define the two containers.

3. A method according to claim 1 or 2, wherein the moulding is formed with shoulder means and when the moulding is severed the said shoulder means defines on the or each container an outwardly turned flange to which a sealing lid may be attached.

4. A method according to claim 1 or 2, wherein the or each container after severing of the mould is processed to provide any outwardly turned rim at the top thereof.

5. A method according to any of claims 1 to 4, wherein the mould has severing means movable to effect the severing of the moulding whilst still in the mould.

6. A method according to claim 5, wherein the severing means is a severing ring movable axially of the mould to sever the moulding across a portion of the moulding which extends into a radial recess.

7. A method according to any preceding claim, wherein the moulding is of polyester plastics material.

8. A method of producing a plastics material container substantially as hereinbefore described with reference to Figs. 5 to 12 of the accompanying drawings.

9. A plastics material container produced by the method of any one of the preceding claims.