AU684390B2

AU684390B2 - A stretch blow moulded threaded container

Info

Publication number: AU684390B2
Application number: AU34308/95A
Authority: AU
Inventors: Douglas Smith
Original assignee: ACI ROCKWARE Ltd
Current assignee: ACI ROCKWARE Ltd
Priority date: 1994-10-21
Filing date: 1995-10-18
Publication date: 1997-12-11
Anticipated expiration: 2015-10-18
Also published as: AU3430895A; GB9421279D0; GB2294231A; NZ280288A

Description

AUSTRALIA

Patents Act COMPLETE SPECIFICATION

(ORIGINAL)

Class Int. Class Application Number: Lodged: Complete Specification Lodged: Accepted: Published: Priority Related Art: ft o a Name of Applicant: ACI Rockware Ltd Actual Inventor(s): Douglas Smith Address for Service: PHILLIPS ORMONDE FITZPATRICK Patent and Trade Mark Attorneys 367 Collins Street Melbourne 3000 AUSTRALIA 5 Invention Title: A STRETCH BLOW MOULDED THREADED CONTAINER Our Ref 429414 POF Code: 100/241686 The following statement is a full description of this invention, including the best method of performing it known to applicant(s): -1- -2- A STRETCH BLOW MOULDED THREADED CONTAINER This invention relates to the stretch blow moulding of containers particularly those having a threaded neck or opening. More particularly, it relates to a preform suitable for use in stretch blow moulding such a container and a process for the production of such a container.

Conventional stretch blow moulded containers are usually made by a process including at least the following steps:injection moulding a preform which is closed at one end and open at the other and which has a threaded neck at or near the open end; (ii) adjusting the temperature of the preform to close to its glass transition temperature; (iii) transferring the preform to a blow mould; (iv) stretching the body of the preform in the direction of the axis of the 15 preform in the blow mould using a push rod; and thereafter blowing the body of the preform out axially with air so that the body of the preform conforms to the shape of the mould.

The manufacturing process is generally either "single stage" or "two stage" blow moulding. In single stage blow moulding the preform is cooled after injection S 20 to an appropriate temperature for immediate blow moulding. In two stage blow moulding, the manufactured preform is cooled to room temperature and is thereafter heated to the appropriate temperature and transferred to a blow mould for forming the container.

One problem with the foregoing processes is the high cost, particularly in terms of raw material, in the formation of the injection moulded screw thread finish on the preform. The material thickness at the neck is usually significantly greater than throughout the rest of the container to provide the necessary strength in this unoriented section of the container.

As the injection moulded screw thread is usually formed to cooperate with a closure such as a cap or lid, this part of the preform cannot be heated or stretched during the blow moulding process as it may distort in a manner which renders it ineffective. The thread finish must be kept cool whilst the remainder of the preform is heated. Generally, this means that the preform must be provided

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-3with a transfer flange underneath the thread which extends outwardly from the side walls of the preform. The transfer flange must be of sufficient width and thickness to securely hold the preform whilst the side walls beneath it are heated and stretched to form the container. The presence of such a transfer flange adds significantly to the amount of material needed for the formation of each preform.

To reduce material costs and to simplify the manufacturing process, it is thus desirable to provide a preform which can be moulded to produce both the body of the container and the neck and screw thread finish in a single blow moulding procedure.

In U.S. 4,397,808 there is disclosed a previous method for forming a saturated polyester resin bottle in which the thread is formed in the blowing process. This process involves the stretching of the neck of the preform there S* described to form the neck of the final bottle and thereafter blow moulding the ,.o.,body and neck of the preform. Threads are added to the neck of the bottle by 15 blow moulding the stretched (and hence orientated) neck in a mould having thread forming grooves.

One disadvantage of this prior process is that the threaded neck and body of the container are not formed by a single stretch blow moulding operation (i.e.

the preform must be selectively stretched and then blown). There is thus multiple 20 handling in the stretch blow moulding operation.

It is an object of the present invention to produce a container having a threaded neck by a process which is simple, efficient and which avoids the aforementioned difficulties inherent in previous methods.

However, conventional preform designs are not suitable for stretch blow moulding of a threaded necked container. If a conventional preform is axially stretched from the open end, the neck thins to an unacceptable degree and prevents the formation of a viable screw thread finish. Further, conventional preform design includes a peripheral flange immediately beneath the neck finish for holding the preform during the stretching step and for transfer of the preform from the injection mould to the blow mould. The weight of the transfer flange in conventional preforms is significant relative to the overall weight of the preform.

This upsets uniform heat distribution in the preform in either single stage or two stage blow moulding. In single stage blow moulding the transfer ring is a -4reservoir of heat which pushes heat into adjacent areas on cooling. In two stage blow moulding the flange draws heat away from adjacent areas whilst the preform is being heated. In both cases, the presence of the transfer flange upsets the heat balance of adjacent material (especially in the neck). In stretch blow moulding processes a conventional preform thus thins and stretches in a nonuniform way. Whilst not critical in the production of containers with injected thread finishes, this non-uniformity of heat distribution in the area adjacent the flange would cause significant problems in any process where the thread was to be blown.

The applicants have found that by modifying the preform design it is possible to overcome these difficulties. In particular, if the preform has an upper section which incorporates more material per unit length of preform wall than the lower section then this upper section can provide sufficient heat/elastic energy to the neck to prevent it from thinning excessively during the stretch blow moulding 15 process. This can be conveniently achieved by maintaining uniform preform wall thickness whilst providing an upper portion of increased internal diameter. It will be clear to those skilled in the art that other arrangements of wall thickness and diameter of preform would also adequately achieve the desired material distribution.

20 Further, the applicants have found that if the transfer bead of the preform is formed towards the terminal end of the neck rather than towards the junction of the neck and body of the preform, a smaller bead is required to hold the preform during the stretch blow moulding process. A smaller transfer bead at this position has been found not to upset the heat balance of the material adjacent the transfer bead in a manner which materially effects container production during the stretch blow moulding process. A further advantage of a transfer bead which is smaller than the conventional transfer flange is that material costs are reduced.

Thus, according to the present invention there is provided a process for the manufacture of a plastics container haviig a threaded neck finish which includes at least the following steps:injection moulding a preform which is open at one end and closed at the other which includes a base, a lower side wall portion, an upper side wall portion and a circumferential neck bead disposed at or adjacent the open ~e end of the preform wherein the upper side wall portion comprises more material per unit of preform wall length than does the lower side wall portion; adjusting the temperature of the preform to a temperature at which it may be blow moulded into a container; stretching the lower side wall portion and the upper side wall portion of the preform whilst restraining the open end of the preform by the neck bead; blowing a gas into the open end of the preform, either during or after the stretching step, so to expand it into a blow mould in the shape of the desired container whereby the base forms the bottom of the container, the lower side wall portion forms the side wall portion of the container and the upper side wall of the preform forms at least the neck of the container; the said mould at the position corresponding to the neck of the container comprising thread forming grooves so that when the upper side wall portion is stretched and blown to form the neck of the container a thread is moulded into that portion of the resultant container.

If desired, the circumferential neck bead can be removed after blow moulding and this portion recycled. This is appropriate, particularly in cases where there is a large difference between the diameter of the neck bead and the S. 20 diameter of the thread once blown into the neck portion of the container. In some S: applications, it is also desirable that the outlet opening of the container be large relative to the cap soft drink containers) and in such cases it would be preferable to remove the transfer bead once the container had been blown.

However, preferably the outlet opening has a diameter which is less than 90% of the diameter of the thread. In other applications the material above the threaded area can be utilized if it fulfils a desired functional or design attribute. In particular, the opening through which the contents are dispensed can be restricted whilst still using a large cap.

The profile of the blow mould should be such that the threaded portion in the bottle is of greater external diameter than the transfer bead so that the closure of the container can be properly attached.

There is usually no need to remove the transfer bead in small containers and in bottles where a large cap has been particularly designed. For example, -6the neck bead may conveniently be left in place in a container for a "roll-on applicator" container.

If the desired container is intended to be used on an automated re-heating and filling line or in any other application where the container will be mechanically handled, it is preferred that the shape of the blow mould be such than an additional protuberance be formed in the blow moulding step immediately beneath the moulded thread. The protuberance should be blown to be of a suitable shape so that the container may be held and transferred by mechanical handling means.

It will be appreciated that the strength of the threaded portion of the container neck in a bottle made in accordance with this invention will in part depend on the extent of the orientation imparted during the blow moulding **process. The amount of orientation in the threaded area can be controlled by appropriate design of the initial diameter of the upper side wall portion and the 0 diameter of the threaded portion of the blow mould. Preferably the ratio of the diameter of the diameter of the upper side wall portion of the preform to the diameter of the threaded portion of the blow mould is between 1:1.2 and 1:1.8.

Most preferably it is about 1:1.5.

0°0 0 The invention has application for the manufacture of containers where the 20 diameter of the neck finish and the diameter of the body of the container are approximately the same. Preferably, the neck of the resultant container is at least and most preferably at least 75% of the diameter of the container body.

Thus, the invention is particularly useful in the production of jars and similar such 0 containers.

The invention is particularly applicable when the container intended to be formed has a small outlet opening when compared with the closure thread diameter especially when it is 70% or less of the closure thread diameter.

Examples of such containers include those used for "roll-on" applicators and others such as those which utilize a plug insert in the closure to seal the outlet opening.

According to another aspect of the present invention there is provided a preform suitable for use in the process hereinbefore described. The preform is closed at one end and open at the other and includes a base portion suitable for -7forming the bottom of a container, a lower side wall portion suitable for forming the side walls of a container, an upper side wall portion suitable for forming at least the neck finish of a container and a circumferential neck bead disposed at or adjacent the open end of the preform, wherein said upper side wall portion has an internal diameter greater than the internal diameter of the lower side wall portion and a wall thickness at least as great as the wall thickness of the lower side wall portion; the upper side wall portion comprising more material per unit length of the preform wall than the lower side wall portion.

The wall thickness of the upper side wall portion can be greater than the wall thickness of the lower side wall portion but preferably the wall thickness throughout the preform is substantially uniform. A uniform thickness of the preform wall is most desired as one can thereby avoid problems in manufacture due to uneven heating.

Preferably, the preform has a continuous internal taper in both the upper side wall portion and lower side wall portions so that it can be readily removed from an internal core if formed by injection moulding.

Generally, if a taper is used it is preferably a shallow taper with the upper and lower side wall portions substantially parallel to the axis of the preform and a interconnected by an outwardly flaring transitional portion. In such an S. 20 embodiment, the transitional portion is preferably smoothly curved without sharp S corners bridging the upper and lower side wall portions of the preform.

The neck bead can be of greater diameter than the upper side wall portion but is preferably of slightly smaller diameter to keep material costs at a minimum.

The neck bead is usually formed in the top 3.0 to 5.0 millimetres of the preform.

Preferably, a groove or similar indentation is provided in the upper side wall portion immediately beneath the neck bead so that gripping means may be applied around the bead so to hold it securely during the blow moulding operation. The neck bead can effectively be formed without using a large amount of material and should be of such size that it may readily be cooled in the preform injection mould (in a one stage blow moulding operation) or kept cool (in a two stage blow moulding operation) so that the temperature of the bead is such that it will provide sufficient mechanical strength to withstand the stretching force of the blow moulding operation. A desirable consequence which also flows from using a

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-8small transfer bead is that the small amount of plastic does not upset the heat balance required in the plastic below it to effectively blow mould the container side walls, neck and thread.

The preform of the present invention is particularly suitable for the production of multi-layer preforms by the well known sequential injection techniques using two or more different materials. The absence of the transfer flange lessens the known and troublesome effects of eddy currents caused by the hot flange which generally disturbs the layers during the cooling of the preform.

The invention is hereafter described by reference to a preferred embodiment in which; Figure 1 is a cross sectional view of a preform of the invention and a blow mould for the manufacture of a container; and Figure 2 is a sectional view showing the upper side wall portion of the preform shown in Figure 1 immediately after having been blown so to form a screw thread neck finish.

Figure 1 illustrates a preform 1 having a base 2, a lower side wall portion 3, an upper side wall portion 4, an outwardly flaring transitional portion o 0. interconnecting the upper and lower side wall portions and a circumferential neck bead 6. Apart from the neck bead and the immediately adjacent peripheral 20 groove 7, it will be noted that the wall thickness of the preform is uniform throughout. The neck bead is formed in the top 3 millimetres of the preform.

Blow mould 8 is shown in the shape of a container intended for use as a roll on applicator. Obviously, other suitable container shapes can be used in the 0*0*0* working of this invention.

To manufacture a container, the preform 1 is first injection moulded. After injection moulding the preform is cooled to a temperature close to the glass transition temperature of the plastic material used in the manufacture of the preform. Any suitable orientable plastics material known in the art may be utilized. Preferably, the material is a polyester such as polyethylene terephthalate (PET) or copolymers of PET.

At the same time as cooling for stretch blow moulding, the peripheral bead is cooled off to a lower temperature so to provide adequate strength to restrain the preform from movement during the stretch blow moulding step.

Once the preform has been appropriately cooled, it is stretched in a blow mould (preferably using a push rod) whilst the top of the preform is restrained by appropriate means secured to the peripheral bead 6. Once the preform has been stretched (or during the stretch operation), a suitable gas, such as air, is introduced into the preform to blow it in accordance with conventional methodology. It is blown into the shape of blow mould 8.

With reference to Figure 2, it can be seen that upper side wall portion 4 when stretched and blown forms a neck 10 blown into the shape which includes an appropriate screw thread finish 11.

It will be appreciated from the foregoing that the present invention offers a simple yet effective method in reducing manufacturing costs. With the preform design of the present application, the weight of plastic saved in each preform :against a conventional injected neck finish was 60% with a 15% saving on the total bottle weight. All of the weight saving came out of the neck and removal of the traditional transfer flange. The process of the invention has been achieved by the applicant's departure from conventional preform design and by identifying the need to relocate and minimise the transfer bead.

It should be understood that various modifications and variations may be made to the preform and process as hereinbefore described without departing 20 from the spirit and ambit of the present invention as defined in the following claims.

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Claims

1. A method for the manufacture of a plastics container having a threaded neck finish, said method including at least the following steps:- injection moulding a preform which is open at one end and closed at the other which includes a base, a lower side wall portion, an upper side wall portion and a circumferential neck bead disposed at or adjacent the open end of the preform wherein the upper side wall portion comprises more material per unit of preform wall length than does the lower side wall portion; adjusting the temperature of the preform to a temperature at which it may be blow moulded into a container; S* e stretching the lower side wall portion and the upper side wall portion of the preform whilst restraining the open end of the preform by the neck bead; S S o S blowing a gas into the open end of the preform, either during or after the stretching step, so to expand it into a blow mould in the shape of the desired container whereby the base forms the bottom of the container, the lower side wall portion forms the side wall portion of the container and the O. 4 upper side wall of the preform forms at least the neck of the container; *00. 20 the said mould at the position corresponding to the neck of the container comprising thread forming grooves so that when the upper side wall portion is stretched and blown to form the neck of the container a thread is moulded into that portion of the resultant container.

2. A method as claimed in claim 1 wherein said circumferential neck bead is removed after the container has been formed.

3. A method as claimed in either one of claims 1 or 2 wherein the thread forming grooves of the mould have a diameter greater than that of the transfer bead of the preform.

4. A method as claimed in claim 1 wherein the mould includes an indentation immediately beneath the thread forming grooves adapted to form a protuberance in the resultant container beneath the blow moulded thread.

A preform suitable for use in the manufacture of a plastics container being closed at one end and open at the other which includes a base portion suitable 11 for forming the bottom of a container, a lower side wall portion suitable for forming the side walls of a container, an upper side wall portion suitable for forming at least a neck finish of a container and a circumferential neck bead disposed at or adjacent the open end of the preform, wherein said upper side wall portion has an internal diameter greater than the internal diameter of the lower side wall portion and a wall thickness at least as great as the wall thickness of the lower side wall portion; the upper side wall portion comprising more material per unit length of the preform wall than the lower side wall portion.

6. A preform as claimed in claim 5 wherein the wall thickness of the upper side wall portion is greater than the wall thickness of the lower side wall portion.

7. A preform as claimed in claim 5 wherein the wall thickness throughout the preform is substantially uniform.

8. A preform as claimed in any one of claims 5 to 7 which includes a continuous internal taper in both the upper side wall portion and lower side wall portions.

9. A preform as claimed in any one of claims 5 to 8 being of a multilayer structure incorporating two or more different materials. 20 DATED: 17 October, 1995 PHILLIPS ORMONDE FITZPATRICK Attorneys for: ACI ROCKWARE LIMITED 9927W ABSTRACT A nmehod for the manufacture of a plastics container having a threaded neck finish, said method including at least the following steps:- injection moulding a preform which is open at one end and closed at the other which includes a base, a lower side wall portion, an upper side wall portion and a circumferential neck bead disposed at or adjacent the open end of the preform wherein the upper side wall portion comprises more material per unit of preform wall length than does the lower side wall portion; adjusting the temperature of the preform to a temperature at which it may be blow moulded into a container; stretching the lower side wall portion and the upper side wall portion of the preform whilst restraining the open end of the preform by the neck bead; tape blowing a gas into the open end of the preform, either during or after the ease stretching step, so to expand it into a blow mould in the shape of the desired container whereby the base forms the bottom of the container, the lower side S wall portion forms the side wall portion of the container and the upper side wall of the preform forms at least the neck of the container; too o the said mould at the position corresponding to the neck of the container comprising thread forming grooves so that when the upper side wall portion is stretched and blown to form the neck of the container a thread is moulded into that portion of the Doe.: resultant container. sees*: 0 a I