AU2004202706A1 - Accumulating extrusion blow moulding process - Google Patents

Description

P11643AU01

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT

ORIGINAL

Name of Applicant: Actual Inventor: Address for Service: Invention Title: HOLLYWOOD PLASTICS PTY LTD LESLIE MOSCA HODGKINSON AND McINNES Patent Trade Mark Attorneys Levels 3 and 4, 20 Alfred Street MILSONS POINT NSW 2061 "ACCUMULATING EXTRUSION BLOW MOULDING PROCESS" Details of Associated Provisional Application: 2003903089 filed 18 June 2003 The following statement is a full description of this invention, including the best method of performing it known to us: ACCUMULATING EXTRUSION BLOW MOULDING PROCESS FIELD OF THE INVENTION The present invention relates to a blow moulding process especially suitable for the production of hollow and shaped objects in large quantities from a viscous polymeric material.

BACKGROUND OF THE INVENTION Extrusion blow moulding and injection stretch blow moulding are known moulding processes for the production of hollow and shaped objects in large quantities. However, these processes are not always suitable for the production of hollow or shaped articles from viscous molten polymers where, for example, it is required to incorporate a void in any position on the article, for example, the inclusion of a void space for use as a handle.

Extrusion Blow Moulding Extrusion blow moulding is used for the production of hollow objects in large quantities.

Whilst the obvious application is bottles and similar containers, it is easily adaptable to other items ranging from children's toys to engineering components such as vehicle fuel tanks.

The blow moulding machine is based on a standard extruder barrel and screw assembly to plasticise the polymer. The thermoplastic molten polymer is led through a right angle and through a die to emerge as a hollow (usually circular) pipe section called a parison.

When the parison has reached a sufficient length a hollow mould is closed around it. The mould mates closely at its bottom edge thus forming a seal. The parison is cut at the top by a knife prior to the mould being moved sideways to a second position where air is blown into the parison to inflate it to the shape of the mould.

After a cooling period the mould is opened and the final article is ejected.

To speed production several identical moulds may be fed in cycle by the same extruder unit. The process is not unlike that used for producing glass bottles, in that the molten material is forced into a mould under air pressure.

Injection Stretch Blow Moulding Injection stretch blow moulding is used for the production of high quality containers.

The process is divided into four parts as follows.

a) Injection Molten polymer flows into the injection cavity via the hot runner block, to produce the desired shape of the preform with a mandrel (the core pin) producing the inner diameter and the injection cavity the outer. After a set time the injection moulds and core pins part and the preform held in a neck carrier is rotated 900.

b) Conditioning Because the preform has been cooled in the injection station quickly, it is of varying temperatures throughout its wall thickness. To ensure a good and consistent quality of container, the preform needs a uniform temperature. Heating is employed to achieve this conditioning.

c) Stretching and Blowing Once conditioned to the correct temperature the preform is ready for stretching and blowing to the finished shape. Once the preform is within the blowmould area the moulds close, a stretch rod is introduced to stretch the preform longitudinally and using two levels of air pressure, the preform is blown circumferentially.

d) Discharge After a set time for cooling the moulds open and the preform is removed via drop chutes or robotics. In practice the four stages are carried out concurrently using a revolving carousel of moulds.

However, as indicated above, these known moulding processes are not always suitable for producing moulded articles from viscous molten polymers, such as thermoplastic polyesters including the Polyethylene Terephthalate (PET) family and Polyethylene Terephthalate Glycol copolyester (PETG), for example, PET and/or PETG bottles with a void in any position on the article, to allow the manufacture of articles such as a bottle with a blown handle. Prior art processes have required the production of a composite article wherein the handle portion is fabricated or moulded from a separate plastic material such as PVC.

OBJECTS AND SUMMARY OF THE INVENTION It is an object of this invention to provide a blow moulding process for viscous polymeric materials which goes at least some way towards overcoming or at least minimising the abovementioned prior art problems and/or at least providing a clear alternative choice for manufacturers.

It is another object of this invention to provide a blow moulding process suitable for the production of hollow or shaped articles which is especially suitable for use with viscous molten polymers.

It is a further object of this invention to provide a blow moulding process especially suitable for use with, but not limited to viscous polymers such as PET and/or PETG, which allows the production of articles incorporating a void such as a moulded handle) in any position on the article.

These and other objects will be more apparent from the following description and drawings.

According to one aspect of the present invention there is provided an accumulating extrusion blow moulding process for viscous polymeric materials wherein the molten polymer from an extruder is fed into an accumulator head having an hydraulic ram or piston which forces the molten material at a rate faster than gravity between the mould parts to form an article such as a parison. When the parison has reached a sufficient length a hollow mould is closed around it. The parison is cut at its top or upper end by a knife prior to the mould being moved sideways to a second position where air is blown into the parison to inflate it to the shape of the mould. By rapidly forcing the molten polymer material between the mould parts at a rate faster than gravity, and rapidly closing the mould overcomes problems associated with the normal flow of viscous material in the mould.

In this embodiment of the inventive process, the accumulator head is filled to the shot weight with PET and/or PETG, and the molten polymer is mechanically forced out of the accumulator between the mould parts to form a semi-molten tube or parison. At the same time the mould closes around the parison, forming and cutting the void. A calibration device or blow pin then enters the neck of the mould with the material surrounding it forming the blown article, void and neck area. After a cooling period the mould is opened and the final article is ejected.

The invention also relates to the moulding apparatus used for accumulating extrusion blow moulding of viscous molten polymers from the PET family, and the like, based on a continuous extrusion blow moulding apparatus having an associated accumulator head with a piston or hydraulic ram.

The invention also relates to articles manufactured by the inventive apparatus or by the inventive accumulating extrusion blow moulding process.

BRIEF DESCRIPTION OF THE ACCOMPANYING

DRAWINGS

The invention will be further described with reference to the accompanying non-limiting drawings or illustrations, wherein:- FIGS. 1 and 2 schematically illustrate the main process steps in an accumulating extrusion blow moulding process according to an embodiment of the present invention.

DESCRIPTION OF THE PREFERRED

EMBODIMENT

According to the embodiment of the invention as schematically illustrated in FIGS. 1 and 2, an accumulating extrusion blow moulding process for viscous polymeric materials is illustrated wherein the molten polymer from an extruder is fed into an accumulator head having an hydraulic ram or piston which forces the molten material at a rate faster than gravity between the mould parts to form an article such as a parison. When the parison has reached a sufficient length, a hollow mould is closed around it. The parison is cut at its top or upper end by a knife prior to the mould being moved sideways to a second position where air is blown into the parison to inflate it to the shape of the mould. By rapidly forcing the molten polymer material between the mould parts at a faster rate than gravity, and rapidly closing the mould, overcomes potential problems associated with the normal flow of viscous material in the mould.

The invention is especially applicable to the manufacture of blow moulded semi-rigid containers, such as blow moulded bottles, from viscous molten plastics materials such as PET and/or PETG, but is not limited thereto.

Although an exemplary embodiment of the invention has been shown and described, it will be apparent to those having ordinary skills in the art that a number of changes, modifications or alterations to the invention described herein may be made, none of which depart from the spirit of the present invention. All such changes, modifications and alterations should therefore be seen as being within the scope of the present invention.

It should be apparent that the present invention provides a substantial advance in the field of moulding of semi-rigid containers incorporating a void or the like, providing all of the herein-described advantages without incurring any relative disadvantages.

The term "comprising" as used herein is used in the inclusive sense of "having" or "including", and not in the exclusive sense of "consisting only of'.

Claims (9)

1. An accumulating extrusion blow moulding process for viscous polymers, wherein molten polymer from an extruder is fed into an accumulator head having a hydraulic ram or piston, forcing the molten polymer at a rate raster than gravity between the mould parts to form a moulded article, severing the moulded article at its upper end, moving the mould to a second position, and blowing air into the mould to inflate it to the shape of the mould, and ejecting the moulded article from the mould.

2. An accumulating extrusion blow moulding process according to claim 1, wherein the article produced is a bottle or a parison.

3. A blown moulded product manufactured by a process as claimed in claim 1 or claim 2.

4. A blown moulded product according to claim 3 in the form of a moulded bottle or parison.

A blown moulded product according to claim 3 or claim 4 incorporating a void.

6. A blown moulded product according to claim 5, wherein the void incorporated into the product comprises a carrying handle.

7. A blown moulded article according to any one of claims 3 to 6 fabricated from a viscous polymer such as PET or PETG.

8. An apparatus for manufacturing moulded articles by an accumulating extrusion blow moulding process, said apparatus comprising an extruder for molten plastics material, an accumulator head having a hydraulic ram or piston, a mould of predetermined shape and/or size, means to inject air into the moulded article and means to move the mould from a first position to a second position, and means to eject the moulded article from the mould.

9. An accumulating extrusion blow moulding process according to claim 1, substantially as hereinbefore described with reference to the drawings. An apparatus for manufacturing moulding articles by an accumulating extrusion blow moulding process according to claim 8, substantially as hereinbefore described with reference to the drawings. Dated this 18 th day of June 2004. HOLLYWOOD PLASTICS PTY LTD Patent Attorneys for the Applicant HODGKINSON AND McINNES