AU7214600A - Injection moulding - Google Patents

Description

Injection Moulding Page 1 of INJECTION MOULDING The present invention relates to an injection moulding process designed to produce thin walled injection moulded articles such as tubular containers as used in the cosmetics industry.

Tubular containers are currently produced by a combination of extrusion moulding, injection moulding and ultrasonic welding (this combination referred to herein as the "extrusion process"). The body of the tube is extruded in the form of a continuous cylinder which is then cut into the desired length to form the body of the container. In a separate injection moulding process the "head and shoulders" of the tube are produced. The injection moulded "head and shoulders" are then welded to the extruded tube to form the container. Once the container is filled with product the tail end of the container is sealed by a further welding process.

The extrusion process has a number of limitations, these being the high capital investment required for extrusion equipment, an inability to commercially manufacture a variety of tube shapes, an inability to texture surface finishes or emboss the container, and an inability to incorporate attachments such as closures and hooks during the extrusion process.

PCT/AU98/00255 (hereafter referred to as 'The '255 patent') and which is incorporated herein by reference, describes a process and materials for the injection moulding of flexible thin walled articles having thin sections and which provide a number of advantages hitherto unattainable through the extrusion process due to technical constraints. The '255 patent 25 describes a wide variety of polymer types and blends that may be used to injection mould thin 25 walled flexible articles, and a method for selecting suitable blends. The polymers and blends described may be injection moulded using a variety of different injection moulding processes, including such developments as Coralfoam's "Gas-in-Mould" (GIM) system, or Trexel's 'Mucell' process which involves injecting a gas-usually supercritical nitrogen together with the polymer. The use of gas-assisted injection moulding processes such as Mucell may be 30 used to produce foamed thin-walled flexible articles as well as improve the process of injection moulding such articles, the added gas often reducing the effective MFI of the S polymer, thereby making the polymer easier to inject into the mould. The '255 patent also describes means by which the ESCR of many polymer types in particular, relatively high MFI grades of these polymers may be improved in order to increase their utility for the injection moulding of thin walled flexible articles.

Among the polymer types that may be suitable for injection moulding thin walled flexible articles are star, comb and other polymers such as are described in US 6,084,030, which is incorporated herein by reference. This patent describes highly branched polyolefin polymers 40 in the form of a comb, star, nanogel or structural combinations thereof, whereby a plurality of polyolefin arms are linked to a polymeric backbone to provide a highly branched structure in which the properties of the highly branched structure can be conveniently tailored to the application for which the polymer is used. Unlike the prior art it describes, the concepts of the invention described in US 6,084,030 use as the backbone a polymeric structure to which polyolefin arms are linked. Through the use of a polymeric backbone, it is possible to obtain very highly branched polymeric structures in which a relatively high number of branches or arms can be provided on the polymeric backbone. The choice of specific reactive polymeric backbone and/or its manner of preparation controls the branched structure as to comb, star, nanogel or structural combinations thereof. That allows for the preparation of polymers having relatively low viscosities compared to their linear counterparts at the same absolute molecular weight. These polymer types may be particularly suitable for the production of injection mould thin walled flexible articles.

Injection Moulding Page 2 of Other polymer types that may be suitable for injection moulding flexible thin walled articles include polymers that are made up of or include in their structure functional groups and/or monomers that facilitate the breakdown of the polymer molecules into smaller molecules by various means such as the activities of organisms such as bacteria or fungi, the activities of nature such as light, oxidation, etc. Such polymers may include natural components or chemical types such as cellulose, starch, lactic acid and their various derivatives and/or other biologically active moieties in their molecular structure or blends and/or may be polymerised with chemical structures that are designed to make the polymer susceptible to molecular size reduction. Thin walled flexible articles made from such polymers may be particularly advantageous because of their ability to be disposed of more easily than non-degradable polymers, and/or with less environmental impact.

The '255 patent also describes various methods for improving the barrier properties of injection moulded flexible thin walled articles. Amongst the advantages of using various internal coating technologies such as ACTIS (and other chemical vapour deposition methods) as well as barrier lacquers of various types is that by minimising the contact between an injection moulded flexible thin walled article and its contents, it is possible to use suitable grades of recycled polymers for the manufacture of injection moulded flexible thin walled articles that would otherwise not produce commercially acceptable articles. Other methods of modifying the barrier and other properties of injection moulded thin wall flexible articles include incorporating in the polymer blends nanofiller particles, including non-limiting examples such as layered metal oxides or metal oxide salts, to form nanocomposites.

Nanofillers, including functionalised nanofillers, for incorporation into nanocomposites may 25 formed and incorporated into nanocomposites by a variety of means such as those described in WO9947598, WO 0034393, WO 0034378, WO 0034377 and W00034372, all of which are incorporated herein by reference.

The extrusion process disallows the control and variation of wall thickness, while the '255 patent' provides for the manufacture of articles having thin sections capable of controlled and varied thickness. Injection moulding flexible thin walled articles such as tubes allows the area of the tube to be sealed to be aesthetically and/or functionally improved so as to improve the aesthetic appeal, shape and/or effectiveness of the seal and/or to improve the appearance and/or functionality of the tube. For example, the area to be sealed may be fluted so as to increase its surface area for sealing and/or have its wall thickness varied so as to improve the ease of sealing (see Fig. An example of circumstances in which variable wall thickness of the tube is advantageous is cases in which it is desirable for a tube to have thicker-thannormal walls to provide increased stiffness or surface texturing. In such tubes, if the area to be sealed is the same thickness as the wall of the tube the seal time required is increased, as the overall difficulty of effecting a seal. By varying the wall thickness of the end of the tube i to be sealed in order to optimise sealing performance and seal properties, the objectives of improved stiffness of the tube, optimum seal performance and decreased seal time are achieved.

Injection moulding enables the production of tubes with precisely controlled and variable wall thickness as well as dimensions and shapes in the area of the tube to be sealed. Control of the shape, texture and dimensions of a tubes seal allows the attainment of optimum seal strength and performance without the need to vary the wall thickness of the entire tube in order to attain said seal performance improvements (See Figures 1, 2, and 3).

In a further example of the benefits of being to able precisely control and vary the wall thickness of a thin walled article, the area of the thin walled article to be sealed can be Injection Moulding Page 3 of moulded so as to form and/or incorporate 'resealable closures' of various designs such as 'zippers' or seals which can then be 'snap shut', slide-locked, zipped or closed by other means appropriate to the design of the specific zippers. This allows for the production of resealable and/or refillable tubes, bottles or other flexible thin walled article.

At present, flexible thin walled injection moulded packaging products such as tubes are subject to constraints that result in most such products requiring specially designed closure/dispensing means to be affixed or moulded into them in order to enable the dispensing of the product's contents. The cost of such specially designed closure/dispensing means most often adds significantly to the overall cost of the package. In addition most specially designed closure/dispensing means are not suitable for the dispensing of a number of products such as various foods, powders, and so on, thereby rendering the flexible thin walled injection moulded packaging products such as tubes unsuitable or too costly for the packaging of such products. The facility to reseal thin walled articles such as tubes would enable users to refill the article and/or expel the contents of the tube through a larger aperture than is generally provided by the tube, thereby enabling the dispensing of larger-than-normal sized products. Therefore by incorporating various types of seals or zippers into the flexible thin walled injection moulded articles, many of the disadvantages referred to above are overcome. Seals using various types of zipper technology, VelcroTM or magnetic strips could be produced in conjunction with thin walled injection moulded containers (see Figures 9, and 11). The prior art in relation to zippers as pertaining to plastic bags and 'form/fill/seal (FFS) packs is well-developed. However no such prior art exists in relation to the utilization of zippers in thin walled injection moulded articles.

A typical zipper strip has interlocked male and female profiles. Each profile has an interlocking member and a laterally extending web defining a leading flange and a trailing flange on either side :i of the interlocking member (see Figures 5, and For some applications one of the leading flanges is provided with a weak perforation along its length so that it can be separated by pulling S.o the profiles apart resulting in the breaking of the perforation and the disengaging of the interlocking members, as well as the opening of the top seal. As well as simple zipper strips, slide Szippers may be used in conjunction with flexible thin walled injection moulded articles (see Figures 7, and Slide zippers for use with plastic bags are well known in the resealable S fastener art. Examples of zippers that may be used in the present invention can be found in U.S. Pat. Nos. 5,007,143, 5,008,971, 5,131,121, 5,664,299 and 6,112,374, each of which is incorporated by reference.

Resealable articles may be made by various means, such as the incorporation of zippers of various designs and functionality. Various methods for fabricating an article of the present invention with a zipper are proposed. For instances, a method in which an article and a zipper are unitedly formed by an injection molding method; a method in which a zipper is formed on an article by an injection molding method; a method in which a tape previously i formed with a zipper is fused on an article. An illustrative design ofa zipper type that may be incorporated in or moulded into a flexible thin walled article as described in the '255 patent is disclosed in US 5,955,160. Some other known methods, apparatuses and packages illustrative of the background art of manufacturing and/or incorporating zippers into articles are seen for example in U.S. Pat. Nos.: 5,558,613 (assigned to Minigrip, Inc.); 5,557,907 and 5,592,802 (assigned to Illinois Tool Works, Inc.); 4,925,316 (assigned to Minigrip, Inc.); 4,709,398 (assigned to Minigrip, Inc.); 4,691, 372 (assigned to Minigrip, Inc.); 5,330,269 (assigned to Toyo Aluminum Kabushiki Kaisha); 5,067,822 (assigned to Reynolds Consumer Products, Inc.); 4,782,951 (assigned to Oscar Mayer Foods Corp.); and 4,976,811 (assigned to Com-Pac International, Inc.), all of which are hereby incorporated by reference.

Injection Moulding Page 4 of Being able to injection moulding thin walled flexible containers has the potential to significantly reduce the production costs of such articles. For example, being able to injection mould bottles would result in reduced costs for many types and sizes of bottles relative to bottles produced by blow, injection blow or injection stretch processes. In order for flexible thin walled articles as generally described in the '255 patent to function as bottles, the article should preferably be able to stand on its base. However, the open ends of many of the articles described in the '255 patent are most often crimpled and then sealed by heat sealing or other such means, such crimpled seals not being conducive to being able to properly support the article in a stable and upright position. In a further improvement of the invention described in the '255 patent, the open end of the thin walled article may be closed by means of inserting a separate base into the open end of the thin walled article and effecting a seal between the separate base and the thin walled article by means such as 'snap fit', welding by means such as heat or ultrasonic welding, adhesives and the like. If the separate base is designed to enable the resultant thin walled article to stand on said base, the resultant thin walled article can be used as a conventional container such as a bottle. Base inserts can include a threaded ring in their construction which, when attached to the exterior or interior of the tube end, would allow a base to be screwed into or onto the ring. The result of this construction would be a reseal-able screw-in base allowing access to the containers contents (see Figure 26). Similarly, inserts can include legs extending from the insert to form a base for the container, or inserts can connect a number of tubes together by attaching their respective tube ends to a single insert (see Figures 24-30). The addition of threading, a suction cap, or other base inserts would allow their containers to be stored in any position, such as horizontally or upside down when attached to a receptor (see Figure 26 and 29). Base inserts can be used to provide a secondary dispensing capability, thereby allowing the 25 containers contents to be accessed through both ends. Examples of these improvements are shown in Figures 12-15.

As well as the cost, aesthetic, and practical improvements detailed, injection moulding flexible thin walled articles allows for the moulding of an integral appendages If for 30 example, an integral closure is moulded into the thin walled article during the moulding process, the utility of the thin walled article with a base is further improved, and the cost of the complete article is substantially reduced relative to the cost of a similar article with separate closure. Further, including an appendage such as a hook on said base, or inserting tap/s into the article may further improve the functionality of the resultant article. (See Figures 12., 13., 14., and In the case of the addition of a hook, the resultant article may be hung by said hook for convenient storage and/or dispensing of the contents of the article.

An additional cost benefit of such articles is that they can be filled through the large open end prior to the separate base being attached. This opening, being larger than the opening through which most conventional containers such as bottles are filled, enables the more rapid filling of the container of the present invention than most conventional containers. This results in significant improvements in filling times and filling line speeds and corresponding significant reductions in costs for these processes. In a further improvement, the base may be moulded as an integral part of the thin walled article, which would enable the base and the thin walled article to be moulded in one piece and at the same time, thereby eliminating the need to mould a separate base and facilitating the easy application of the base to the thin walled article.

In a further use of the present invention as a bottle, a dual compartment container can be made either by inserting a separate open-base container into the first open-base container, or by injection moulding a dual compartment container with each container having separate or combined access to the exterior by means of a suitable aperture/closure. The two-in-one container thus formed can be filled with two or more separate/different products which can be Injection Moulding Page 5 of separately dispensed, or combined during or just prior to dispensing. The base of the container can be sealed with an insert, thus forming a 2-in-1 upright container.

Because of the generally low draft angles on injection moulded flexible thin walled articles such as tubes as described in the '255 patent, and/or because of certain article designs, difficulties may sometimes be encountered in separating the moulding from conventional moulds at speeds that are beneficial for the commercial production of the tubes. For example, in tool designs that require the withdrawal of the moulded article from the cavity of the tool by holding it on the core while withdrawing the core from the cavity, the moulding can sometimes be separated from the core while the core is being withdrawn from the cavity, thereby leaving the moulding in the cavity. This necessitates the stopping of the production process to remove said moulding from the cavity, thereby slowing down the process and/or risking damage to the moulding and/or mould. This occurrence may be eliminated by holding the moulded article on the fixed half of the mould by various means during the opening of the mould while the mould core and cavity or parts thereof are drawn away from the fixed half of the mould, either simultaneously or sequentially. When the core and cavity have been drawn away a sufficient distance from the moulding to allow the removal of the moulding from the fixed half, the moulding is removed from the fixed half of the mould by various means known to those skilled in the art.

In tool designs such as those described above, the cavity part of the mould may be 'onepiece', in which case it may be moved away from the fixed half as a single piece.

Alternatively the cavity may be 'split', in which case the sections of the split cavity may be separated from the core by moving the cavity sections away from the core separately (see 25 Figure 16, 17, 18, 19, and 20). This 'split cavity' arrangement is particularly suited to the S production of embossed/surface textured mouldings, mouldings with appendages and mouldings of various shapes that preclude the use of a 'one-piece' cavity. The effectiveness of such 'one-piece' or 'split' tool designs, with particular regard to stages of the separation of the core and/or cavity from the moulding while said moulding is attached to the fixed half of 30 the mould, (See Figures 22. and 23.) may be assisted by incorporating a facility to enable the injection of gas between the moulding and the core and/or cavity at particular stages during the moulding cycle. In such arrangements, the injected gas may penetrate between the S moulding and the core and/or cavity, and in doing so may act as a 'cushion' between the core and/or cavity and the moulding, which may assist in the separation of the moulding from the core and/or cavity while the core and/or cavity are separated from the fixed half of the mould.

The gas may be injected from a number of places in the mould, including various points in the core, cavity and fixed half. Particularly advantageous for assisting the retraction of the core from the moulding is to position some or all of the gas injection points around and/or in the tip of the core (see Figures 20 and 21).

In a further improvement of the ejection mechanism of flexible thin walled article tooling, the ejection of the moulded article can be enhanced by constructing the core in such a manner that during the opening of the tool for ejection of the moulded article, and particularly during the withdrawal of the core from the cavity while the moulded article is held on the fixed half of the tool, part or all of the tip of the core can remain against the moulded article while the rest of the core is partially or completely withdrawn. This arrangement, especially in conjunction with the injection of gas to assist with the removal of the moulded article from the mould, acts to hold the moulding onto the fixed half of the tool, thereby assisting with the withdrawal of the core from the moulding. It also assists in the formation of a good seal between the moulding and the fixed half of the tool so that when gas in injected, the loss of gas between the moulding and the fixed half of the tool is minimised, thereby improving the effectiveness of the moulding process. This arrangement is particularly valuable in the Injection Moulding Page 6 of production of flexible thin walled articles that have apertures at their front end, such as thin walled tubes, as in such articles the gas is not naturally prevented from escaping through the aperture, thereby diminishing the effectiveness of the gas in penetrating between the rest of the moulding and the core and/or cavity.

Some polymer formulations used to injection mould flexible thin walled articles such as are described in the '255 patent may be 'sticky' under normal moulding conditions and temperatures, adversely affecting their ability to be removed from the mould under normal moulding conditions. This can significantly increase cycle times by necessitating longer cooling times. In addition, reformulating the formulations with additives to minimise the 'stickiness' of the formulations may be required, such additives often adding to the material costs and/or adversely affecting some other properties of the thin walled articles. Indeed, some otherwise desirable formulations may be so sticky as to preclude their use under normal moulding conditions. In a further improvement to the '255 patent, the use of cooled or cryogenic injected gas may assist with reducing cycle times of such sticky formulations and/or minimise or eliminate the need for various additives as well as improving the barrier properties of the moulding by modifying the molecular arrangement of the polymer(s) due to more rapid cooling than would be the case with the use of gases at temperatures usually encountered in conventional moulding operations. A particular advantage of the injection of cooled or cryogenic gas is that because it rapidly reduces the temperature of the polymer at the interface between the tool and the moulded article, it speeds up the crystallisation and/or 'hardening' of the polymer at said interface, thereby making easier the removal of the moulded article from said surfaces and reducing or eliminating the tendency of the polymer to stick to the mould. This enables the moulded article to be removed from the mould sooner 25 than would otherwise be the case, thereby speeding up the production of the articles. The injection of cooled or cryogenic gas is particularly beneficial in the production of moulded articles that are made from polymers that have a relatively slow rate of 3 crystallisation/hardening and/or have a tendency to stick in tooling due to their tacky characteristics at normal operating temperatures and/or immediately after being moulded.

The injection of cooled or cryogenic gases when moulding such polymers may make possible the moulding of articles from such polymers that would otherwise not be possible, or economic due to prolonged cycle times. Although beneficial for the injection moulding of S articles made from many polymers, this process is particularly beneficial for the moulding of polymers or blends thereof of super-random homo and copolymers of olefins as defined and described in the '255 patent, produced by metallocene or similar catalysts and polymers such as Montell's Catalloy polymers and the like.

The present invention will be further described by the following non-limiting drawings.

Figure 1. Illustrates a cross-section of a conventional flexible tube.

Figure 2. Illustrates a cross-section of a conventional flexible tube with the inner wall of said tube being moulded with flutes to improve sealing area for improved sealing performance.

Figure 3. Illustrates a longitudinal cross-section of a injection moulded tube with controlled wall thickness in order to gain an effective seal while still enabling a stiffer tube through the thickening of the tubes walls. corresponds to the thicker wall and corresponds to the normal or thin wall.

Figure 4. Illustrates a longitudinal cross-section of a conventional flexible tube without varying wall thickness.

Injection Moulding Page 7 of Figure 5. Illustrates a section of a snap zipper, which could be moulded in, or attached to a tube to facilitate the opening and closing of the tubes seal. This particular example has two male profiles and two corresponding female profiles which lock when pressed together.

Figure 6. Illustrates a cross-section of a snap zipper comprising one female and one male profile. As with the zipper illustrated in Figure 5, this zipper may be attached or moulded onto or moulded as an integral part of a thin walled injection moulded product.

Figure 7. Illustrates a cross-section of a sliding zipper where is the female part, is the male part and is the sliding zipper.

Figure 8. Illustrates a three-dimensional sliding zipper which, when placed over the female and male profiles may be dragged up and down them in order to open and close their seal.

Fig 9. Illustrates a longitudinal cross-section of a flexible thin walled article such as a tube to which a snap-zipper has been attached. The article shown is shown in the locked position, with both male and female profiles engaged.

Fig 10. Illustrates a longitudinal cross-section of a flexible thin walled article such as a tube to which a snap-zipper has been attached. The article shown is shown in the open position, with both male and female profiles disengaged from one another.

Figure 11. Illustrates a longitudinal cross-section of a flexible thin walled article such as a tube where no zippers have been attached.

Figure 12. Illustrates a longitudinal cross-section of a thin walled injection moulded article Swith a screw on cap, and a base insert which opens to allow greater access to the product and also allows the container to be stood on its end.

Figure 13. Illustrates a cross-section of a base insert comprising of a sealed end, and a hook upon which the container may be hung upside-down.

Figure 14. Illustrates a cross-section of a base insert comprising of a sealed end, and a hook upon which the container may be hung upside-down.

Figure 15. Illustrates a cross-section of a base insert comprising a cap which opens to give access to the product contained in the container. This insert also allows the container to be stood on its end.

Figure 16. Illustrates a cross section of a tool that can be used for injection moulding thin walled articles such as tubes. The mould comprises of a sliding core, cavity and head, locking guiding pins, hot runner and static headpiece. The mould is shown closed and ready the injection of the polymer.

Figure 17. Illustrates a cross section of a tool that can be used for injection moulding thin walled articles such as tubes. The mould comprises of a sliding core, cavity and head, locking guiding pins, hot runner and static headpiece. The mould is shown with the sliding core and guides as they are retracted the sliding head and cavity holding the mould to the static headpiece. Gas is forced from under the headpiece to facilitate the removal of the moulding.

Figure 18. Illustrates a cross section of a tool that could be used for injection moulding thin walled articles such as tubes. The mould comprises of a sliding core, cavity and head, locking guiding pins, hot runner and static headpiece. The mould is shown with the sliding core, guides, and cavity as they are retracted the sliding head holding the mould to the static headpiece.

Figure 19. Illustrates a cross section of a tool that could be used for injection moulding thin walled articles such as tubes. The mould comprises of a sliding core, cavity and head, locking guiding pins, hot runner and static headpiece. The mould is shown with the sliding core and guides fully retracted the sliding head fully extended.

Figure 20. Illustrates a cross section of the core and sliding head that is in the open position, allowing gas to be forced between the moulding and the core, thus loosening the bond between the two.

Figure 21. Illustrates a cross section of the core and sliding head that is in the closed position.

Figure 22. Illustrates a cross section of the static headpiece with the moulding held in place by a sliding headpiece on the static headpiece.

Figure 23. Illustrates a cross section of the sliding headpiece in the opened position. While the sliding headpiece has remained closed throughout the moulding process, it may be opened to allow the moulding to be ejected from the mould.

S Figure 24. Illustrates a base insert with legs extending from the insert, which has been attached to the container.

Figure 25. Illustrates a base insert which has been produced with an integral hook.

S S Figure 26. Illustrates a base insert with an external thread which may be screwed into the receptor beneath it for storage.

Figure 27. Illustrates a base insert which has been used to connect two containers together.

Figure 28. Illustrates a base insert which allows two containers to be connected together and at the same time allow access to the containers contents through their bases.

S• Figure 29. Illustrates a base insert to which a suction cap has been attached, allowing the container to be stuck to a wall, bench, or other flat surface.

Figure 30. Illustrates a base insert which has been attached to a flexible thin walled container, and allows it to open for access to the containers contents.

Claims (7)

1. A process for the manufacture of flexible, thin-walled articles comprising the steps of: 1) selecting a polymer blend having an ESCR of greater than 10 hours when tested according to the following procedure; i) a plurality (preferably 6 or more) strips of the polymer blend incorporating any post moulding treatment intended for the final article having the cross-sectional dimensions of 0.65 mm in thickness and mmn in width are injection moulded under high shear, long flow length conditions, similar to those intended for use in the manufacture of the flexible thin-walled article.; ii) the strips are bent back upon themselves and stapled 3 mm from the bend; iii) the bent strips are immersed in a solution of a stress crack agent and held at a temperature of iv) the strips are observed for signs of cracking, any signs of cracking are regarded as a failure; and v) the time to failure is when 50% of the strips show signs of cracking; 2) melting said polymer blend; 3) ramming the molten polymer blend into a mould said mould having a cavity which produces a thin-walled article having a thin section 1mm or less in thickness and wherein the thin section is substantially continuous for greater than 50mm in the direction of flow of the molten polymer blend in the mould; and) removing from the mould the thin-walled article formed from the polymer blend.

2. A process according to claim 1 for the manufacture of flexible, thin-walled articles using aerating and polymer-saving processes .i 30

3. A process according to claim 1 for the manufacture of flexible, thin walled articles 0 using polymers capable of degradation by various organisms and/or natural oxidative breakdown.

4. A process according to claim 1 for the manufacture of flexible, thin-walled 00 0 articles using polymers containing nanofiller particles. 35

5. A flexible thin-walled article according to claim 1 wherein the thin-walled tube is of unitary construction and incorporates an integral closure, said integral closure being formed in the mould.

6. A flexible thin-walled article according to claim 1 incorporating resealable 0 :00* zippers.

7. A flexible thin-walled article according to claim 1 which is closed by means of a base of various designs and functionalities. 0