GB2642190A

GB2642190A - Improved moulding of plastic containers

Info

Publication number: GB2642190A
Application number: GB2409092.0A
Authority: GB
Inventors: Sideris Michalis; Sideris Loukis
Original assignee: Ipet Tech Ltd
Current assignee: Ipet Tech Ltd
Priority date: 2024-06-25
Filing date: 2024-06-25
Publication date: 2026-01-07
Also published as: GB202409092D0; WO2026002909A1

Abstract

A method of manufacturing a plurality of injection stretch blow moulded containers, comprises injection moulding a first plurality of preforms 12 in a plurality of lines, conditioning the preforms by rotating each preform about a central axis of the preform with respect to one or more heating elements 11 and stretch blowing the preforms which have been conditioned to produce the containers. The preforms may include a neck portion 14, and the method may include shielding 15a, 15b the neck portions from the heating elements whilst rotating each preform. The method may include transferring the preforms from the injection moulding machine into a conditioning station and further to the stretch blowing station, using robotic mechanisms that adjust a pitch distance between each line of preforms. Shields 15a and 15b may have cooling water circulating through channels 18, to prevent them from over-heating. An apparatus for manufacturing a plurality of injection stretch blow moulded containers is also provided.

Description

[0001] Improved Moulding of Plastic Containers The present invention relates to a method and apparatus for improving the injection stretch blow moulding of hollow plastics containers, and in particular to the use of special preform temperature adjustment (conditioning), after injection moulding and before stretch blowing.

[0002] BACKGROUND

[0003] Injection and stretch blow moulding machines and mould sets are commercially available for the injection stretch blow moulding of hollow plastic containers using plastic materials like PET (Polyethylene Terephthalate). In the one-stage process' the two steps of injection moulding test-tube shaped preforms and then stretch-blowing them into containers are achieved within one machine using mould sets with equal number of injection and blow cavities. The preforms are moulded in an injection mould, cooled to about their average stretch-blow temperature in this mould and for the next cycle the injected preforms are transferred to a conditioning station for temperature conditioning. In the next cycle the conditioned preforms are transferred to a stretch-blow station where they are stretched and blown in blow moulds into the final container shape. Some one-stage machines do not provide for preform conditioning and the moulded preforms are transferred directly from injection to stretch blowing. In one-stage machines the number of blowing cavities is equal to the number of injection cavities.

[0004] For the one-stage machines that do not provide for preform conditioning prior to stretch blowing, there is no possibility to adjust the temperature profile of the preform so there is no control on the wall thickness distribution along the height or circumference of the blown container. This makes the design of the preform and its wall thickness very critical because it is the wall thickness of the preform that determines the temperature profile of the preform as it comes out of the injection mould and therefore the material distribution on the blown container. The provision for preform conditioning before stretch blowing enables adjustments to the temperature profile of the preform to be made, which enables better control of the material distribution on the blown container, optimising the container properties for a given weight.

[0005] The conditioning in prior art for 'one-stage' machines, is achieved by placing female shaped metal parts very near the outside surface of the preforms and/or male shaped metal parts very near the inside surface of the preforms. By controlling the temperature at various points of these metal parts and their distance from the preform surface, the preform temperature profile can be adjusted due to the differing rates of heat exchange between the metal parts and the preform. This method of conditioning requires more time to effect temperature adjustments, due to the slow rate of heat transfer. It also gives less control over the temperature profile adjustment because the number of temperature zones that can be used along the length of the preform is very small (usually 3). Such prior art is exemplified by JPH0976338A (NISSEI ASB MACHINE CO LTD).

[0006] In the prior art of one-stage methods, the conditioning is made without the ability of rotating the preforms about their axis, because of the use of fixed means of holding the necks of the preforms. Usually this fixed means is a set of neck cavities, which are used to hold the preforms in the conditioning station, but also to transfer the preforms from injection to conditioning to blowing and to ejection using a rotary indexing movement. This requires the use of several sets (usually 3 or 4) of such gripping means, which are expensive injection mould parts.

[0007] The implementation of one-stage methods is usually done using one line of cavities, which limits the number of cavities and hence the production output of one-stage machines. The use of 2 or 3 lines of cavities is possible, but the increased complexity makes the cost of investment very high. In general the investment cost per unit output for one-stage machines is high.

[0008] There is a need, therefore, for a 'one-stage' method of producing containers, which incorporates better preform temperature adjustment capabilities than the prior art. Such capabilities should include more adjustment zones along the height of the preform and more flexibility in adjustments around the circumference of the preform. Additionally the control on the adjustments should be more accurate.

[0009] Such capabilities will allow finer temperature control on many more points on the preform, which will in turn allow more control on the wall thickness of the blown container, as the container thickness depends on the degree of stretching of the preform, which in turn depends on the preform temperature profile.

[0010] There is a further need of for a 'one-stage' method of producing containers, using a higher number of cavities for high production outputs at a reasonable cost, so that a lower investment cost per unit output can be available to the market.

[0011] An example of a one-stage method on which such capabilities can be applied, is US5206039A (EMERY I VALYI) where it would be possible to use transfer means and preform heating means to achieve fine temperature adjustments, also with many cavities.

[0012] SUMMARY OF THE INVENTION

[0013] According to one aspect, this invention provides a 'one-stage' method for the production of injection stretch blow moulded containers, which includes the step of injection moulding a plurality of preforms and, during said injection moulding step, carrying out in parallel the steps of: conditioning a plurality of preforms injection moulded in the previous cycle, and stretch blowing a plurality of preforms conditioned in the previous cycle, thereby to produce said injection stretch blow moulded containers, where said plurality of injection moulded preforms, said plurality of conditioned injection moulded preforms and said plurality of stretch blow moulded containers are equal in number and where the conditioning step adjusts preform temperature both along the length of the preforms using heating elements and around the circumference of the preforms by rotating each preform around its axis with variable and adjustable speed, while at the same time the necks of the preforms all around their circumference are being shielded from the heating elements.

[0014] According to another aspect this invention provides apparatus for the production of injection stretch blow moulded articles, which includes:-injection mould means defining a plurality of cavities for preforms and being openable to release injection moulded preforms, and closable for injection moulding; means of adjusting the temperature (conditioning) a plurality of injection moulded preforms transferred from said preform cavities; stretch blow moulding means comprising a plurality of cavities for receiving the conditioned preforms and means of stretching and blowing the preforms in the cavities, one or more preform transfer means adapted to take and remove a plurality of preforms from the injection mould, to transfer a plurality of injection moulded preforms from said injection mould to said conditioning means and thence to said stretch blow moulding, and said plurality of injection cavities and said plurality of stretch blow cavities are equal in number, and said conditioning means consisting of - an array of essentially straight heating elements arranged parallel to each other and one above the other to follow the shape along the length of the preforms - one or more such arrays of heating elements to enable conditioning of one or more lines of preforms - means of holding preforms from their necks in one or more straight lines and bringing them near the heating elements - means of rotating each preform around its axis at a variable and controllable speed of rotation -means of shielding the necks of the preforms all around their circumference from the heat of the heating elements - and possibly means of moving the preforms back and forth either parallel to and/or perpendicular to the direction of the heating elements, while the preforms are being rotated near the heating elements In preferred embodiments, the injection moulding, the preform conditioning and the stretch blowing can be located adjacent to each other, allowing for easier preform transfer between process steps, enabling the use of simple and cost effective apparatus for transferring the preforms.

[0015] One benefit of the preferred embodiments is that there is no need to duplicate mould parts for carrying preforms between process steps.

[0016] In the disclosed embodiment of this invention there are provided conditioning means for adjusting the temperature profile of the preforms following their injection moulding and prior to their stretch blow moulding, in one-stage methods.

[0017] Innovatively, the conditioning means consist of an array of heating elements, together with a means of rotating each preform at variable and controllable speed around its axis, offering fine adjustment of temperature both along the height of the preform as well as around the circumference of the preform.

[0018] In the preferred embodiment of the present invention the heating elements used can be economical and easily available straight infra-red lamps, with means of adjusting each lamp's intensity, the lamps placed near each other for finer adjustment of temperature along the preform length.

[0019] In the present embodiment the rotation of each preform around its axis is achieved with a variable speed servo motor, with means of speed variation in a way that the preform rotation speed can be varied within each full circle of rotation of the preform. For example the full circle of 360 degrees can be split into segments, and the speed of rotation can be set at different speeds for each segment. This will provide variable heating around the circumference of the preform, which is particularly advantageous for controlling the thickness of the blown container around its circumference, when the container is not cylindrical or circular.

[0020] An important benefit of the present embodiment is this ability to adjust the degree of preferential heating around the circumference of the preform, enabling fine control of the wall thickness of the blown container when the container shape is oval, square, rectangular or irregular, or when the neck of the container is off-centre from its body.

[0021] Another important benefit of the present embodiment is the possibility to save weight of the blown containers, due to the finer control of the wall thickness of the blown container. This enables the avoidance of thick and thin areas on the container and hence the ability to reduce average wall thickness and hence container weight. This provides substantial environmental benefits, with less use of plastics and less energy required to process the reduced quantity of plastic.

[0022] A further benefit of the present invention is the ability to use many injection and blow cavities, in an economical way, for achieving higher production outputs using a one-step method with reasonable investment.

[0023] BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The invention can be performed in various ways and, by way of example only, specific embodiments thereof will now be described, reference being made to the accompanying drawings.

[0025] Figure 1 is a top view of the machine, illustrating a possible floor layout of the various parts of the machine, to facilitate preform transfers and container removal.

[0026] Figure la is an enlarged top view of the injection mould area of the machine.

[0027] Figure 2a illustrates in cross sectional side view, the use of heating elements and a possible arrangement of their positions, relative to the rotating preforms being heated and the use of shields to protect the necks of the preforms from getting over-heated.

[0028] Figure 2b illustrates in side view one line of preforms in the conditioning station, showing the possible movements that the preform transfer means can achieve when bringing the preforms in and out of the conditioning station, and especially while the preforms are inside the conditioning station.

[0029] Figure 3a illustrates in cross section a possible circumferential segmentation of a preform and an oval container to be blown from that preform.

[0030] Figure 3b illustrates in cross section a possible circumferential segmentation of a preform and a square container to be blown from that preform.

[0031] DESCRIPTION OF PREFERRED EMBODIMENTS

[0032] In one embodiment of the present invention, four lines of twelve cavities each are arranged in the injection and blow moulds, to enable 48 cavity production of containers, for achieving high production outputs. The conditioning of preforms is also done in 4 lines. Figure 1 is a top view of a possible arrangement of the equipment implementing the present invention, while Figure la is an enlarged view of the injection mould area of this arrangement.

[0033] At any given time during the production, there is one set of preforms 1 being moulded in the injection mould 2, which is mounted on the clamping unit 3 of an injection moulding machine 4, while the set of preforms moulded in the previous cycle is having its temperature profile adjusted in conditioning station 5, while the set of preforms that was conditioned in the previous cycle is in the stretch blowing station 6 being stretch blow moulded into containers, while the containers blown in the previous cycle have been ejected into a bin or placed on a conveyor 7.

[0034] To facilitate preform transfers, there are three robotic mechanisms in the preferred embodiment as follows: Robotic mechanism 8 removes preforms from the injection mould by holding them in holding tubes 8a, and carrying out the following tasks: -pick the injection moulded preforms 1 from the injection mould 2, - remove them from the area of the clamping unit 3 so that the clamp can close for the next cycle, - rotate them so that their neck is facing upwards change the distance between the lines of preforms (row pitch adjustment) from the injection row pitch to blow row pitch, which is the same as the conditioning row pitch), and - Release the preforms to the robotic mechanism 9.

[0035] Robotic mechanism 9 transfers preforms to conditioning and then to the blowing station, by carrying out the following tasks: -pick the injection moulded preforms from robotic mechanism 8, - change the distance between each preform within each line (cavity pitch adjustment) from the injection cavity pitch to the conditioning cavity pitch), - Place the preforms vertically downwards inside the conditioning station, rotating them around their axis and possibly moving them parallel and/or perpendicularly to the heating elements of the conditioning station, - after a conditioning time stop rotating and remove the preforms from the conditioning station, change the cavity pitch from the conditioning cavity pitch to the blow cavity pitch, - move the preform and release them to the robotic mechanism 10.

[0036] Robotic mechanism 10 transfers the conditioned preforms to the blow moulds and removes the blown containers from the blow moulds, by carrying out the following tasks: - pick the four lines of conditioned preforms from robotic mechanism 9, - shift them into the open four lines of blow moulds, - After blowing and moulds open, shift blown containers out of blow moulds, -Release blown containers to drop in a bin or guided on a conveyor 7.

[0037] Figure 2a illustrates the use of four arrays of heating elements 11 and a possible arrangement of their positions, relative to the rotating preforms 12 being heated. The heating elements 11 are held on a frame 13 in a way that their horizontal position is adjustable in order to determine the elements' distance from the preforms 12. The necks 14 of preforms 12 are shielded from the heating elements 11, to prevent heating of the necks 14, by using shields 15a and 15b, which can be openable to receive preforms 12 when such preforms 12 have an outward thickness design, where the preform diameter just below the neck is less than the diameter at the preform body. Shields 15a and 15b have cooling water circulating through channels 18, to prevent them from over-heating. Said shields are shaped in a way that they have an essentially circular opening shielding the necks 14 of the preforms 12 all around their circumference, offering very effective protection.

[0038] Figure 2b shows in side view one line of preforms 12 during conditioning, illustrating the possible movements that the robotic mechanism 9 must achieve while holding the preforms 12 using holders 16. Such movements are critical for the required adjustment of the temperature of preforms 12 both along their length and around their circumference. When bringing the preforms 12 in and out of the conditioning station 4, mechanism 9 must make essentially vertical movements according to arrows 17, so that preforms 12 will enter into the circular openings formed by the shields 15a and 15b. Mechanism 9 may start rotating the preforms 12 around their axis just before entering conditioning station 4 and may stop rotating the preforms just after exiting conditioning station 4. In the preferred embodiment the means of rotation is a servo motor, so that not only the speed of rotation can be accurately controlled, but also the position of the preform around its axis can be monitored, in order keep track of the preform rotary orientation, for the cases where a specific orientation of the container neck relative to the container body is required.

[0039] In other preferred embodiments it may be desirable to also have control of the position of the preforms 12 relative to the heating elements 11, in a way that while being rotated and heated, the preforms 12 could be moved back and forth either in a direction parallel to the heating elements axis as shown by arrows 18, or perpendicular to the heating elements axis as shown by arrows 19, or in both directions in combination. A back and forth movement along the directions of arrows 18 for example, can be useful to smooth out any possible variations in heating intensity along the length of the heating element, which would cause one of the preforms 12 to be heated differently than another. Similarly a back and forth movement along the directions of arrows 19 for example, can be useful in cases when a preform 12 has a protrusion moulded on it, which would act as a handle on the blown bottle, which protrusion would hit the heating elements when the preform 12 is rotated, if there was no provision for movement in the directions of arrows 19.

[0040] The control over the speed of rotation is very important for oval, square, rectangular or irregular-shaped containers or containers with their neck not centred with the container body. One full rotation of 360 degrees can be divided into a number of segments, each segment having the same or a different size (number of degrees), and the speed of rotation in each segment can be different, so that slower rotation will provide more heat from the heating elements in the section of the preform circumference corresponding to said segment. In this way the temperature around the circumference of the preforms12 can be controlled in an accurate and flexible manner, according to the shape of the container to be blown.

[0041] Figure 3a illustrates the cross section of a preform 12 destined to be blown into an oval container 20, with the preform 12 circumference separated into 4 segments 21a, 21b, 21c and 21d, with the speed of rotation changing from segment to segment. The angles 22a and 22b that determine the size of the segments can be varied to best suit the degree of ovality of the container 20. A slower rotation speed when the heating elements are facing segments 21b and 21d and a faster rotation speed when the heating elements are facing segments 21a and 21c, will result in a circumferential temperature profile to achieve even wall thickness around the circumference of the blown oval container. Without such temperature profiling, the thickness of the long sides of the oval containers would be thicker than the opposite sides, creating weak parts in the bottle and visual imperfections and wasting plastic material.

[0042] Similarly Figure 3b illustrates the cross section of a preform 12 destined to be blown into a square container 23, with the preform 12 circumference separated into 8 segments 24a -24h, the size of each segment determined by the size of angles 25a and 25b. The speed of rotation can be controlled and changed alternately from one segment to the next, between higher and lower rotation speeds, thus creating a circumferential temperature profile with relatively warmer segments 24a, 24c, 24e, and 24g, resulting in a more even wall thickness between the sides and the corners of the container. Without such temperature profiling, the thickness of the straight sides of the square containers would be thicker than the corners, wasting plastic material.

[0043] In the preferred embodiments, there is provision to change and control the number of the segments into which the full circle of rotation is split, as well as the size of all the segments, as well as the speed of rotation in each segment as well as the transition from one speed of rotation to the next. Such control can be exercised through proper software.

[0044] In the preferred embodiments, there is provision to change and control the intensity of each heating element, thus controlling the preform temperature along the length of the preform

Claims

1. CLAIMS1. A method of manufacturing a plurality of injection stretch blow moulded containers, the method comprising in a first cycle, injection moulding to produce a first plurality of preforms arranged in a plurality of lines and, during the first cycle: conditioning a second plurality of preforms which have been injection moulded in a previous cycle, including rotating each preform about a central axis of the preform with respect to one or more heating elements wherein the speed of rotation of the preforms is varied to produce a plurality of conditioned preforms; and stretch blowing a third plurality of preforms which have been conditioned in the previous cycle, thereby to produce the plurality of injection stretch blow moulded containers.

2. A method according to claim 1, wherein each of the second plurality of preforms is rotated in a circle, wherein the circle is split into segments, and wherein the speed of rotation is set for each segment.

3. A method according to claim 1 or 2, wherein each preform of each plurality of preforms comprises a neck portion having a circumference, and the method includes shielding the circumferences of the neck portions of the preforms from the heating elements whilst rotating each preform.

4. A method according to any preceding claim, wherein prior to conditioning the second plurality of preforms, the method including transferring the first plurality of preforms out of the injection moulding machine using a robotic mechanism, wherein the transferring includes adjusting a pitch distance between each line of preforms and then releasing all of the preforms to a second robotic mechanism.

5. A method according to claim 4, the method including transferring the first plurality of preforms into a conditioning station using the second robotic mechanism, wherein the transferring includes adjusting a pitch distance between all adjacent preforms in each line, and then placing the preforms in the conditioning station.

6. A method according to any preceding claim, wherein conditioning the second plurality of preforms includes moving each preform, while rotating it, in a direction parallel or perpendicular to the heating elements, or in both directions in combination.

7. A method according to any preceding claim, including setting a conditioning time, wherein rotating each preform ceases after the conditioning time.

8. A method according to any preceding claim, wherein after conditioning the second plurality of preforms, the method including transferring the preforms from the conditioning station to the stretch blowing station, wherein the transferring includes adjusting a pitch distance between all adjacent preforms in each line.

9. An apparatus for manufacturing a plurality of injection stretch blow moulded containers, the apparatus comprising: an injection moulding machine comprising an injection mould, the injection mould defining a first plurality of cavities arranged in at least one line for forming a first plurality of preforms; a conditioning station comprising a plurality of arrays of heating elements equal in number to the lines of preforms, each array comprising one or more heating elements, the conditioning station being configured to receive the preforms, and the one or more heating elements being arranged to heat the preforms when received in the conditioning station to form a plurality of conditioned preforms; a stretch blowing station comprising a second plurality of cavities for receiving the plurality of conditioned preforms, the stretch blowing station being configured to stretch and blow the conditioned preforms when received in the cavities to form a plurality of injection stretch blow moulded containers; and one or more robotic mechanisms configured to transfer the plurality of injection moulded preforms from the injection moulding machine to the plurality of preforms in the conditioning station, the robotic mechanisms being further configured to rotate each preform about a central axis of the preform with respect to the one or more heating elements in the conditioning station, and to transfer the conditioned preforms to the second plurality of cavities for stretch blowing into the plurality of injection stretch blow moulded containers.

10. An apparatus according to claim 9, wherein the robotic mechanisms are configured to adjust a pitch distance between each line of preforms as well as to adjust a pitch distance between all adjacent preforms in each line prior to placing the plurality of preforms in the conditioning station, and to adjust a pitch distance between all adjacent preforms in each line after removal from the conditioning station and prior to placing the plurality of conditioned preforms in the stretch blowing station.

11. An apparatus according to claim 9 or 10, wherein the injection moulding machine, the conditioning station and the stretch blowing station are located adjacent one another.

12. An apparatus according to any of claims 9-11, wherein each preform of each plurality of preforms comprises a neck portion, and wherein the conditioning station comprises a shield or plurality of shields arranged between the neck portions of the preforms and the heating elements, wherein each shield comprises at least one channel for flowing a cooling liquid through the shield.

13. An apparatus according to any of claims 9-12, wherein the one or more robotic mechanisms comprises a variable speed servo motor arranged to rotate each preform about its central axis, wherein the speed of rotation is variable.

14. An apparatus according to any of claims 9-13, wherein the one or more robotic mechanisms is configured to move each preform in a vertical, horizontal or oblique direction with respect to the one or more heating elements.

15. An apparatus according to any of claims 9-14, wherein the one or more heating elements comprise at least one array of substantially longitudinal heating elements.

16. An apparatus according to claim 15, wherein the heating elements in each array are arranged in a stack, one above the other.