WO1991008100A1

WO1991008100A1 - Plastics bottle manufacture

Info

Publication number: WO1991008100A1
Application number: PCT/GB1990/001810
Authority: WO
Inventors: James Butterworth
Original assignee: Lin Pac Plastics International Limited
Priority date: 1989-11-23
Filing date: 1990-11-23
Publication date: 1991-06-13
Also published as: AU6754490A

Abstract

A method of making a plastics bottle comprising a bottle shell (1) and a liner (2) includes the steps of manufacturing a preform, placing it inside a pre-formed bottle shell (1), and blowing the preform using the bottle shell (1) as a mould to provide a continuous liner (2) for the entire inner surface of the bottle. The pre-formed shell (1) not only acts as a mould during the blowing of the liner but subsequently goes on to act as an exo-skeleton for the finished bottle to provide the majority of the strength and barrier characteristics for the bottle. This technique enables the shell to be relined and used repeatedly without risk of contamination. The shell can be made from recycled material.

Description

PLA5TICS BOTTLE MANUFACTURE

Blow moulded bottles especially those made of clear plastics material which is bi-axially oriented during its blow moulding step are nowadays very popular and widely used. They are especially useful for packaging carbonated beverages and capable of resisting the internal pressure generated by the carbonated beverage. ^' Such bottles are also used to contain other liquids ranging from industrial chemicals such as white spirit and methylated spirit to uncarbonated beverages and bottled water.

The majority of such bottles are made from PET (polyethylene terephtalate) or laminates or blends the major constituent of which is PET. PET has a relatively low permeability which both prevents carbon dioxide escaping from carbonated beverage, prevents permeation by the liquid vapour to allow escape of the contents and prevents the ingress of oxygen which can result in oxidation and spoilage of the bottle contents. Its permeability can be reduced still further by including some form of barrier material having an even lower permeability in the form of a layer by or introducing this material as a blend with the PET or as a laminate. PET is expensive and typically 50% cf the manufacturing cost of such a bottle directly results from the material cost of the PET. When barrier materials are included these are typically even more expensive and so increase the material cost still further when blends and laminates are used.

Traditionally such bottles have been arranged to be disposable in the sense that they are only intended to be filled once and then, once their contents have been exhausted, thrown away. Partly as a result of the high material cost and partly because of the recent moves to avoid waste there have been many recent attempts to recycle the materials from such bottles or proposals to reuse them. When the bottles are formed entirely from PET it is possible for them to be recycled but, generally this is not possible if the bottles are formed from a blended or laminated material. However, when recycling the materials from such bottles it is difficult to ensure that the recycled material does not include any contaminants and, to avoid this, each bottle is preferably checked in some way before its material is - recycled. Existing rules prevent recycled material being used for packaging that comes into direct contact with foodstuffs.

One solution to this difficulty is disclosed in GB-A-1600554 where a preform for a plastic bottle is injection moulded or extruded with two layers, an inner layer of virgin plastics material and an outer layer of recycled plastics material. When such a preform is blown to produce a bottle, the resulting bottle is, effectively, lined with virgin plastics material but its outer part can be made from recycled plastics material. Such a technique relies upon the plastics material somehow being returned from the consumer of the contents of the bottle to the preform maker. We are not aware of any commercial use having been made of the technique outlined in this patent specification.

Other proposals for the reuse and refilling of plastics bottles have recently been proposed and are currently being implemented for carbonated soft drinks. For these proposals 1.5L bottles intended to contain a carbonated soft drink are to be formed with a very much greater wall thickness than usual so that, after filling and use they can be returned to the bottle filler. The bottle filler must first remove the remains of a pilfer proof cap from round the neck of the bottle then soak the bottle in a hot caustic bath at a temperature of around 60°C for twenty minutes, wash and rinse the bottle, and then subject each bottle to a sniffing test to try and ensure it is clean and uncontaminated before refilling it with a carbonated beverage and fitting a new closure. The washing and refilling operation is much more complicated than that required for disposable bottles and uses a large amount of energy. Also the hot caustic soak leads to shrinkage and creep of the bottles with resulting changes in their volume. As a result of the very much greater wall thickness and much greater weight of the plastics in each bottle any bottles that not returned also represent a much greater loss of plastics material. Finally, when making preforms by injection moulding the cycle time of the injection moulding machine is exponentially related to the wall thickness of the preform. Thus, while the injection moulding machines can produce preforms on a 18-24 second cycle for disposable bottles, the cycle time is increased to a minute for these recyclable bottles. All of these factors taken together mean that this latest proposal is only attractive economically if, on average, the reusable bottles make twenty round trips before being lost or replaced. In the UK glass milk bottles typically only make seven round trips and, accordingly, is by no means clear that this target will be met.

According to this invention a method of making a plastics bottle comprising a ^'bottle shell and a liner includes the steps of manufacturing a preform, placing it inside a pre-formed bottle shell, and blowing the preform using the bottle shell as a mould to provide a continuous liner for the entire inner surface of the bottle.

The pre-formed shell not only acts as a mould during the blowing of the liner but subsequently goes on to act as an exo-skeleton for the finished bottle to provide the majority of the strength and barrier characteristics for the bottle. However, because the shell is relined before each reuse of the bottle the shell can be made from recycled material and, even if this is somehow contaminated the contamination does not reach the contents of the bottle because of the presence of the liner forming a continuous lining throughout the entire inner surface of the bottle. The plastics material to form the liner represents only a small percentage such as 10-20% of the total weight of the plastics material in the bottle and thus it is always possible to use virgin plastics material for a liner and thus ensure that the liner is always clean, sterile and uncontaminated.

To reuse a bottle made by a method in accordance with this invention the bottle is typically returned to the bottle filling station where the existing liner is removed by applying a vacuum to the neck of the bottle to collapse the liner and allow it to be withdrawn from the shell. The shell is then simply relined before being refilled and recirculated. When the shell is made from the same material as the liner the material from the removed liners may be recycled to produce further shells. Since, in a method in accordance with the present invention the liner is made from a separate preform which is subsequently blown into the shell with the shell acting as a mould during the blowing operation, the bottles can be formed by a very simple blow moulding machine. The machine is so simple that it can be located and form part of the bottle filling plant which considerably enhances the recycling operations. Naturally transport is required to transport the filled bottles from the bottle filling plant to the consumers and the same transport can be used to return empty bottles to the filling plant. Equally, the damaged shells and the used liners can be returned to the manufacturers of the shells and preforms by the same transport used to deliver fresh supplies of preforms and shells.

Preferably the shell includes vent means to allow venting of air displaced from the inside of the shell during blowing of the liner. The vent means also allows air to enter the space between the inner wall of the shell and the outer wall of the liner as the liner is evacuated to collapse it before the shell is reused. The vent means may be formed by corrugations around the internal wall of the side wall of the shell extending up to the neck of the shell when the liner is expanded from the base towards the top. Alternatively the vent means may be formed by a hole in the base of the shell and the liner is expanded from the top downwards during its blowing operation. In the latter case the base of the shell may also include generally radially ^' extending valleys in communication with the hole to ensure that the base of the liner is formed correctly. Particularly when the shell has a waisted configuration it is preferred that vent means are provided at both the top and bottom of the shell.

The centre of the base of an article formed by blow moulding is typically thicker than the side wall of that article. Use can be made of this property by ensuring that the vent in the base of the shell is placed centrally so that, after the liner has been blown into the shell this central thicker region of the liner overlies the vent hole in the base of the shell. This thicker region in the base of the liner may provide sufficient integrity for the whole bottle to compensate for the absence of the shell in the region of the vent hole. Preferably however and, especially when the liner has a thin wall thickness, the shell may include means to seal the vent before the bottle is filled. These means may have the form of a valve with a closure member which is biased into contact with the base of the shell around the vent to seal it. In this case the valve may be held open during the blowing of the liner and merely allowed to close upon completion of the blowing step, for example, by being closed by the base of the liner.

Preferably however the vent includes a removable plug which is inserted after the liner has been blown and before the bottle is filled and, on recycling, is removed before the liner is removed from the shell. In one example the vent means is formed as an internally screw threaded socket which is fixed to the base of the shell and the plug is screwed into this socket to form a gas tight seal. The shell may be formed by a blow stretch moulding process and, in this, the neck of the shell may be removed after the moulding operation but, preferably, the shell is formed by injection moulding. The inside of the shell may be coated with a release agent to ensure that the liner is does not stick to it.

The liner may be made from a material which is chemically similar to that of the shell but which is modified to enable it to be blown without being heated. Typically such materials have a lower intrinsic viscosity and a higher melt flow index. This enables a particularly simple blow moulding machine to be used which requires no heating elements or moulds and this makes it a particularly suitable, machine to be installed at a bottling plant. Whilst such cold blow grades of material are typically different from those used for the shell they are miscible with those used for the shell and can therefore be recycled successfully and reformed into shells.

Particular advantages arise from using material for the liner which can be cold blown in addition to the simplification of the blow moulding machine described above. Less energy is required for the moulding process, and the blowing process can be performed more slowly since it does not have to be finished before the preform has cooled down. Whilst blowing more slowly is not usually an advantage where the shell has a bottom vent this simplifies the design and reduces the capacity of this vent by reducing the speed of venting required. In some circumstances this can offset the disadvantage of reduction in manufacturing capacity resulting from a slower blowing operation. The use of a material with a lower intrinsic viscosity also results in the material forming the liner having a lower structural strength than conventional bottle grade PET. This assists in the subsequent collapse and removal of the liner by the application of a vacuum after use.

Typically the preform of the liner is injection moulded but, particularly when it is made from a material having a lower intrinsic viscosity it may alternatively be vacuum formed- or thermofor ed. When injection moulded from a material having a lower intrinsic viscosity a significant reduction in the injection moulding cycle can be obtained resulting in a greater productivity of the injection moulding machine.

Alternatively the preform for the liner may be made of a conventional bottle grade material and, in this case, the preform is heated before placing it inside the pre-formed bottle shell and blown to provide a continuous liner for the entire inner surface of the bottle.

The liner may be blown by a stretch and blow technique or, especially when the liner has a very thin wall thickness, by a simple blow moulding technique. When the preform is heated preferably it is differentially heated along its length before it is blown. For example, when the preform includes the neck of the completed bottle containing a male screw thread or other feature which co-operates with the bottle closure it is preferred that this portion of the preform is not heated at all whilst the portion of the preform to form the liner of the completed bottle is heated. The portion of the preform to form the liner may itself be -differentially heated to ensure that the preform expands in the required fashion, for example, expands in a direction towards the vent means.

Whilst the liner and the shell are most likely both to be formed of PET they may be formed from different materials particularly when the finished bottle is required to fulfil a particular function. As an example of this, where the finished bottle is intended to be hot filled with a beverage, for example one that has just been pasteurised, it is preferred that the liner is formed of polypropylene since it has a higher thermal stability than PET. When the shell includes the neck of the finished bottle and, for example includes the male screw thread or other fitting on the neck of the bottle which co-operates with the bottle closure and so the shell provides the basic performance characteristics of the finished bottle then the liner may be formed by a safe but cheap plastics material so that it can be discarded after use. This is particularly useful where the preform for the liner can be cold blown.

Particular examples of methods and bottles and resulting from methods in accordance with this invention will now be briefly described with reference to the accompanying drawings which:- Figure 1 is a side elevation of a first example of bottle;

Figure 2 is a side elevation of a second example; Figure 3 is a side elevation of a third example; Figure 4 is a top plan view of the third example; Figure 5 is a side elevation of a fourth example; Figure 6 is a plan of the fourth example; Figure 7 is a side elevation of a fifth example; Figure 8 is a plan of the fifth example; Figures 9 to 12 are all scrap radial sections showing four different neck details;

Figure 13 is a cross section through the base of the shell drawn to a larger scale;

Figure 14 is a radial section through a socket drawn to an even larger scale;

Figure 15 is a radial cross section of a plug; and, Figure 16 is a partially sectioned side elevation of a shell with a liner preform inserted into its neck;

A bottle made by a method in accordance with this invention comprises an outer shell 1 and an inner liner 2. The outer shell can have a variety of forms as shown in Figures 1 to 8.

In the first example shown Figure 1 has the outer shell extending over the entire cylindrical portion and the base of a bottle of generally conventional shape and the liner provides the neck fitting of the bottle and the tapering neck region as well as a lining for all of the shell 1.

In the second example shown in Figure 2 the shell 1 is waisted and extends almost to the neck of the bottle. In this example also the liner forms the entire neck fitting of the bottle.

In the third example shown in Figures 3 and 4 the shell 1 is square in cross section, as illustrated most clearly in Figure 4, and extends right up to a neck support ring 3 formed as part of the neck fitting of the liner 2.

The fourth example shown in Figure 5 and 6 is waisted in shape and the shell 1 extends up to and includes part of the neck fitting.

The fifth example shown in Figures 7 and 8 is generally similar to the third example but the shell 1 extends up to and includes part of the neck fitting.

The form of the neck of the second to fifth examples of bottle may be formed as shown in Figures 9-12. Figure 9 illustrates the situation where the entire neck fitting is formed on the outer shell 1 and the liner 2 extends over the top rim of the neck of the shell 1. Figure 10 illustrates the case where the shell 1 includes the neck support ring 3 whilst the liner 2 includes a male screwthread for attachment of the closure. In the option shown in Figure 11 the shell 1 extends to the base of the neck support ring 3 and the neck support ring 3 and screwthread is formed on the liner 2. Figure 12 corresponds to the arrangement of the second and third examples where the entire neck region of the finished bottle is formed on the liner 2.

Figures 10 to 12 also show in dotted lines the location of venting slots formed on the inside of the shell 1 when the top of the shell 1 requires venting.

The base of these examples may be formed substantially similarly and as shown in Figure 13. Figure 13 illustrates the characteristic thickening in the centre of the base of an article made by a blow moulding process. The base also includes radially extending venting corrugations 5 and a central hole 6. The hole is cut into the centre of the base using a heat piercing system. A female socket 7, shown more clearly in Figure 14, is spin welded into the hole 6 in the base of the shell 1 and includes a frusto-conical sealing surface 8 and a female screw thread 9. A plug 10 having a corresponding frusto-conical sealing surface 11 and male screw thread 12 can be screwed into and out of the socket 7 using a splined tool which co-operates with a correspondingly splined hole 13.

The method of producing bottles in accordance with this invention requires first that the shells 1 are formed by injection moulding or stretch blow moulding and have the sockets 7 spin welded to hole 6 formed in their base. In addition to this a preform to form the liner is injection moulded and, where the liner is to include a neck fitting with screw threads, or interlocking features for use with a bottle closure, and a neck support ring 3, this is also typically formed as part of the injection moulded preform. The shells 1, plugs 10 and preforms for the liner are shipped separately to a bottle filling plant. As part of the processes carried out at the bottle filling plant the preforms for the liner are placed on a heated mandrel or corepin. The mandrel does not heat the neck region of the preform but heats the portion of the preform that is to be blown to form the liner 2. This ensures the integrity of the injection moulded sections which form a seal with the closure. The heated preform is then placed inside the shell 1, as shown in Figure 16, which is either a newly manufactured shell or is a shell which is being reused after having been returned. Alternatively, the preform may be heated after being placed inside the shell 1. The preform is then blown to provide the liner 2 with the shell 1 acting as the blowing mould. By differentially heating the mandrel or corepin it can be ensured that the preform, on inflation expands from the top downwards, bottom upwards or middle outwards to both top and bottom. Whilst the preform is being blown, air that is displaced from inside the shell 1 is vented via the hole 6 and, when provided, the top venting slots. As inflation of the preform proceeds the remaining air is vented via the radially extending valleys 5 in the base of the shell 1. To blow the first example of bottle a metal skirt surrounds the top of the shell 1 to form correctly the shoulder portion of the liner.

Upon completion of the blowing step the plug 10 is screwed into the socket 7 to complete the bottle. The bottle is then rinsed, filled and has a conventional closure applied to its neck. The bottle is then sold at a price including a deposit. After the contents of the bottle have been consumed the bottle can be returned and the deposit reclaimed. The returned bottles are returned to the bottle filling plant where the plugs 10 are unscrewed, either to be reused or to be discarded, and a vacuum is applied to the neck of the liner. This collapses the liner with air being drawn in through the hole 6 and via the radially extending valleys 5 until the liner can be removed from the shell 1. Typically the removed used liners are returned to the shell maker to be granulated and reprocessed tc be made into further shells. Meanwhile, the now empty shell is returned to the bottle blowing machine to have a new liner fitted before it is refilled. Preferably the shell includes a barrier layer of highly impermeable material to enable it to be formed with a lightweight yet still have the required degree of impermeability. -Especially when the shell includes a barrier layer it can be made to an exact size so that the capacity of the resulting bottle is made to a very close tolerance with no fear of subsequent shrinkage or expansion on filling as occurs with conventional refillable bottles during their caustic wash.

Claims

1. A method of making a plastics bottle comprising a bottle shell and a liner characterised by the steps of manufacturing a preform, placing it inside a pre-formed bottle shell, and blowing the preform using the bottle shell as a mould to provide a continuous liner for the entire inner surface of the bottle.

2. A method according to claim 1, in which in an initial stage an existing liner is removed from the pre-formed shell by applying a vacuum to the neck of he bottle to collapse the liner and allow it to be withdrawn before the shell is relined.

3. A method according to claim 2, in which the shell is made from the same material as the liner, and in which the material from the removed liners is recycled to produce further shells.

4. A method in accordance with any one of the preceding claims, in which the shell includes vent means to allow venting of air displaced from the inside of the shell during blowing of the liner.

5. A method according to claim 4, in which the vent means are formed by corrugations around the internal wall of the side wall of the shell extending up to the neck of the shell when the liner, is expanded from the base towards the top, or are formed by a hole in the base of the shell when the liner is expanded from the top downwards during its blowing operation.

6. A method according to claim 4 or 5, in which the vent includes a removable plug which is inserted after the liner has been blown and before the bottle is filled and, on recycling, is removed before the liner is removed from the shell.

7. A method according to any one of the preceding claims, in which the inside of the shell is coated with a release agent to ensure that the liner does not stick to it.

8. A method according to any one of the preceding- claims, in which the preform is cold blown to form the liner.

9. A method according to any one of claims 1 to 1, in which, the preform is heated before -placing it inside the pre-formed bottle shell and blown to provide the liner.

10. A method according to claim 9, in which the preform is differentially heated along its length before it is

^•blown.