FRACTURABLE OPENING ARRANGEMENT

FIELD OF THE INVENTION

[0001] The present invention is generally directed to the manufacture of containers for dispensing liquid and powdered products, and in particular to a forming tool for the manufacture of containers having a fracturable opening arrangement. While the present invention will be described with respect to the manufacture of such containers using polyethylene terephthalate (PET), it is to be appreciated that the use of other crystallisable polymer material is also

envisaged, and that the present invention is not restricted to the use of PET.

BACKGROUND TO THE INVENTION

[0002] Environmental and other concerns in relation to plastic containers used in the sale of food, drinks and other products have encouraged the move in the production of containers away from polymers such as styrene to recyclable polymers such as polyethylene terephthalate, (PET). The advantageous material properties of PET are described in an early US patent 2465319 (Whinfield). Such plastics can be readily recycled thereby satisfying environmental concerns. This material is therefore commonly used in the bottled beverages industries to produce recyclable bottles. PET is also used in the thermoforming industry to produce tray and packages such as, for example, strawberry punnet packaging.

[0003] The material currently used for the production of such containers is known as amorphous polyethylene terephthalate (APET). This material is very suitable for thermoforming shapes because it is a thermoplastic in an amorphous state. APET does however have a natural tendency to crystallise when exposed to heat. Processing of APET will result in some crystallising of the material, but the use of thermoplastic properties of this material is maintained if the extent of crystallisation is kept at below 15%. Above this level, the material becomes thermoset and is no longer softened by heat. US Patent 3429854 (Siggel) describes a process for the production of a moulded product by the forming of a preheated sheet of APET using vacuum deep drawing of the sheet onto a mould surface. The moulded sheet is immediately cooled after moulding to limit crystallisation of the polymer and maintain its' amorphous state. The moulded products produced by this process provide improved material properties including toughness a better impact resistance, greater transparency and good electrical properties.

[0004] There are however applications where it is advantageous to increase the level of crystallisation of APET beyond a crystallisation level of about 15% because the resultant material, known as crystallized PET (CPET), has material properties that make it suitable for specific applications. US Patent 3496143 (Siggel) describes a process for producing a moulded product formed by vacuum drawing, where the moulded sheet is subjected to further heat treatment while located on the mould surface to increase the degree of crystallinity higher than 25%. This results in properties including high tensile strength and good dimensional stability at high temperatures. This conversion of APET to CPET can however make the material more brittle such that it loses toughness. CPET is however very heat stable and can typically withstand temperatures of up to 200°C without softening. This makes CPET suitable for containers that must be able to withstand high heat such as plastic oven trays. US Patent 5747127(Prince) describes a dual/ovenable tray manufactured from the thermoforming of thermoplastic resin compositions such as CPET, where the final article has a crystallinity of from about 0% to 40%.

[0005] The heat treatment of APET to form CPET also results in the material becoming opaque. This is generally not desirable for drink containers as it prevents inspection of the contents of the container prior to opening and consumption. There are however applications in which opaqueness is required. US Patent 4179488 (Nishikawa) describes the production of a bottle having an outer milky white colour which is achieved through the application of heat to the outer surface to thereby crystallise the surface material. Other patents describing the production of containers or other articles, in which APET is subjected to heat treatment to form CPET include US Patent 4039641 (Collins), US Patent

4388356 (Hrivnak), US Patent 4878826 (Wendt) and US Patent 5614145

(O'Kane).

[0006] In the bottling of juice bottles, the bottles are filled with heated juice for sterilization. The bottle is generally held by the threaded neck portion of the bottle thereby exposing the bottle neck to very high temperatures as the bottle is being filled. This can result in deformation of the bottle neck. A solution for bottles formed from APET is to heat treat and increase the crystallisation of the neck of the bottle neck. The resultant bottle neck, being now formed from CPET, can better resist deformation by heat during filling. US Patent 4590021 (Funabashi) and US Patent 7981351 (Uesugi) respectively describe processes for forming beverage bottles where the APET is crystallised only at the bottle neck.

Converting the entire bottle from APET to CPET is however not generally preferred. As well as making the entire bottle opaque, CPET is more brittle and less tough than APET. While it is possible to add extra plasticizing agents to the APET such that some flexibility is retained in the CPET once converted, this makes the material more expensive to use.

[0007] The Applicant has developed a container having a fracturable opening arrangement which produces an opening for discharging the contents of that container. This container is described in International Publication No.

WO2012/120344, details of which are incorporated herein by reference. A feature of the Applicant's container is the presence of a fracturable area within a shell portion of the container. The fracturable area is not provided by weakening the material within that fracturable area. Rather, the shell portion at the fracturable area can have a similar strength and toughness as the rest of the container, but must at the same time have sufficient rigidity to fracture when stress is applied to that fracturable area. Stress applied to the container results in a fracture being initiated and propagated through the fracturable area thereby producing an opening for the container. The shell portion is typically formed from a polymer material. The material properties of the polymer material must therefore provide sufficient toughness and strength through the shell portion while still providing sufficient rigidity at the fracturable area of the shell portion to enable a fracture to be generated within that fracturable area.

[0008] The shell portion is generally manufactured from a sheet of polymer material that has been thermoformed into the required shape. This typically involves preheating of the polymer material above the glass transition

temperature (T _g ) of the material. The preheated sheet can then be formed into the required shape within a female cavity of a forming mould. The sheet can be vacuum drawn into the mould cavity by means of a vacuum. Alternatively, or in addition, a matching male mould may be used to push the sheet into the cavity during the forming process. This manufacturing process for producing the shell portion is applicable for polymers such as styrene. This is because this material can provide the necessary rigidity to facilitate the fracture within the fracturable area of the shell portion. The material properties of crystallisable polymer material APET has however restricted its use in the production of such

containers. While APET has the necessary strength and toughness for the rest of the shell portion, APET generally does not have sufficient rigidity or brittleness to make that material readily susceptible to fracture. This therefore makes it unsuitable for use in a container having a fracturable opening arrangement of the type developed by the Applicant.

[0009] Preheating of the polymer sheet will increase the crystallisation level of the polymer material in the formed product. The level of crystallisation in a preheating stage is preferably maintained below a specific amount (i.e. typically equal to or less than 15% by volume) to maintain the sheet in an amorphous polymeric state. Otherwise, it would be difficult to subsequently form the sheet within the forming mould. Heating the forming mould can also increase the crystallisation level of the polymer material in the formed product. Typically a second cooling mould is used to hold and allow the formed product to cool while at the same time preventing warping of the product as it cools. This two step production process increases the production cycle time required to product each formed product thereby reducing the economics of the process. Another problem with this two-step process is that is also requires the polymer in the formed product to be crystallised to the same level throughout.

[0010] For crystallisable polymer materials such as APET to be used in the Applicants' container, it would be advantageous to be able to increase the crystallisation level at and around the fracturable area of a shell portion of the Applicants' container, while at the same time maintaining the level of

crystallisation of the rest of the shell portion. This ensures that the fracturable area has the necessary rigidity as a result of the crystallisation to facilitate fracture propagation, while the flexibility and material toughness of the rest of the shell portion is maintained.

[001 1] It would also be advantageous to be able to selectively increase the level of crystallisation of a part of a formed component made of a crystallisable polymer material such as a shell portion of the Applicant's container within a single production cycle to thereby minimise the production cycle time.

[0012] Any discussion of documents or knowledge in this specification is included to explain the context of the invention. It should not be taken as an admission that any of the material form part of the prior art base or the common general knowledge in the relevant art in Australia or any other country on or before the priority date of the claims herein.

SUMMARY OF THE INVENTION

[0013] According to the present invention, in one aspect there is provided a forming tool for manufacturing a container having a fracturable opening arrangement, the container including a shell portion formed of a sheet of crystallisable polymer material, the shell portion including a fracturable area; the forming tool including; at least one mould cavity for forming the sheet, and a heating tool having a heating surface located within the mould cavity for selectively applying heat to the fracturable area of the shell portion once formed within the mould cavity to thereby increase crystallisation of the polymer material within the fracturable area.

[0014] In another aspect there is provided a container having a fracturable opening arrangement formed in a forming tool; the container including a shell portion formed of a sheet of crystallisable polymer material, the shell portion including a fracturable area; the forming tool including; at least one mould cavity for forming the sheet, and a heating tool having a heating surface located within the mould cavity for selectively applying heat to the fracturable area of the shell portion once formed within the mould cavity to thereby increase crystallisation of the polymer material within the fracturable area.

[0015] The term "fracturable" as used herein means having the capacity to be broken by the propagation of a fracture line within a wall of a container which has been formed by any manufacturing process including but not limited to

thermoforming, injection moulding, blow moulding, extrusion moulding in the case of containers formed from polymer materials, or press forming in the case of containers formed from metal materials such as aluminium.

[0016] The term "crystallisation" as used herein means the induction of a change of the regularly repeating morphology of a polymer material brought about by a combination of molecular mobility and secondary bonding forces over a molecular distance of at least several hundred angstroms. Crystallisation can be visually observed as the point at which a substantially amorphous, unoriented sheet of polymer material changes from a translucent, hazy appearance to a white appearance. As used herein the term ^' crystallisable polymer material' means a polymer material susceptible of crystallisation. [0017] The heating tool may be accommodated within a passage extending through the forming tool to the mould cavity. The heating surface may be positioned to align with and form part of the mould cavity. The heating surface itself may be shaped to form the fracturable area of the shell portion.

[00 8] The forming tool may be typically formed from a machined block of metal, with one or more mould cavities machined into a face of the block. The forming tool may be made from a first material, for example, aluminium. The heating tool may be made of a second material different from the forming tool. The material of the heating tool may preferably have a lower emissivity than the material of the forming tool. The heating tool may be made from material such as brass. The heating tool may provide relatively high heat conductivity at the heating surface of the heating tool compared with the surface of the mould cavity.

[0019] The heating tool may be in contact with the fracturable area of the formed shell portion so that the fracturable area is heated through heat

conduction. The heating tool may be maintained at a temperature of 130 to 200°C. The heating tool may more preferably be maintained at a temperature of between 160 to 170°C. The heating tool may preferably be heated through resistive heating, induction heating or high energy excitation heating. It is also envisaged that the heating tool may be heated through thermal contact with an external heat source. The forming tool may however be maintained a temperature below the glass transition temperature of the polymer material. The term "glass transition temperature" as used herein means that temperature or temperature range at which a change in slope appears in the volume versus temperature curve for a polymer material, below which the polymer exhibits a glassy

characteristic and above which the polymer exhibits a rubbery characteristic. The glass transition temperature (Tg) of amorphous polyethylene terephthalate is about 70°C. The forming tool may for example be maintained at a temperature of around 3 to 25°C. This helps to maintain the degree of crystallisation of the rest of the shell portion by allowing for quick cooling of the shell portion. Insulation may be provided between the heating tool and the body of the forming tool. The insulation may be provided by insulating material, or may be provided by an air gap therebetween.

[0020] Heating of the heating tool allows for the selective heating of the fracturable area through heat conduction at the same time. As only a small part of the shell portion is subjected to heating, this minimises any shrinkage or warping of the shell portion thereby eliminating the need for a second cooling mould to be used. The forming of the shell portion and selective crystallisation of the fracturable area can therefore be achieved in a single process step reducing the overall production cycle time.

[0021] The sheet of crystallisable polymer material is preferably preheated prior to the thermoforming of the sheet. This preheating results in a degree of crystallisation within the sheet. It is preferable to increase the degree of crystallisation of the sheet material during preheating as much as possible, but not enough to negatively affect the thermoforming and the properties of the formed shell portion. The degree of crystallisation of the sheet during preheating is preferably in the range of 5 to 25% by volume. Degrees of crystallisation beyond 25% by volume can excessively thermoset the sheet material such that it is no longer possible to thermoform the sheet. The sheet is preferably preheated to a temperature range of 80 to 130°C prior to thermoforming.

[0022] The selective heating of the fracturable area according to the present invention preferably then increases the degree of crystallisation at the fracturable area to at or above 30% by volume. This thereby induces an appropriate degree of rigidity and brittleness at the fracturable area of the shell portion. It is envisaged that the degree of crystallisation of the fracturable area can be as high as 85% by volume.

[0023] The optimal temperature for crystallisation of the fracturable area will be above the glass transition temperature (Tg) of the crystallisable polymer material. The term "glass transition temperature" as used herein means that temperature or temperature range at which a change in slope appears in the volume versus temperature curve for a polymer material, below which the polymer exhibits a glassy characteristic and above which the polymer exhibits a rubbery characteristic. The glass transition temperature (Tg) of amorphous polyethylene terephthalate is about 70°C. The glass transition temperature is typically around 70°C depending on the formulation of the polymer material. The maximum rate of crystallisation may be reached at a temperature range of 130 to 200°C, and more preferably in the range of 160 to 170°C.

[0024] The optimum length of time for the selective heating of the fracturable area so as to achieve the desired degree of crystallisation may be from 3 to 5 seconds with the selective heating occurring within a standard production cycle. This helps to ensure that the crystallisation rate of the fracturable area is fast enough to not slow the standard production cycle. It is also envisaged that the rate of crystallisation can be increased by the addition of nucleating agents within the formulation of the crystallisable polymer material which promote

crystallisation.

[0025] The crystallisable polymer material used for the method according to the present invention may be polyethylene terephthalate (PET). Alternative crystallisable polymer materials could also be used in the method according to the present invention including polypropylene and or other polymers which exhibit the properties of increased crystallization and mechanical property change when heated.

[0026] It is also envisaged that the sheet may be in the form of a laminate of the crystallisable polymer material and a sealant layer or barrier layer of a second polymer material on one or both sides of the sheet. The sealant or barrier layer may be located on an inner surface of the shell portion once formed. The second polymer material may be selected so as not to detrimentally affect the

thermoforming and selective heating of the fracturable area. [0027] The shell portion of a container manufactured using the forming mould according to the present invention may include a cavity for accommodating a product to be dispensed, and a flange surrounding the periphery of the shell portion. A cover portion may be secured to the shell portion to enclose and retain the product contained within the cavity. The shell and cover portions may together form a container body including a first container portion including the cavity, and a second container portion, an intermediate portion interconnecting the first and second container portions and including the fracturable area, the flange extending about the periphery of the first and second container portions thereof. The container may be opened to allow dispensing of the product by angular displacement of the second container portion relative to the first container portion to thereby produce a container opening formed by a fracture at the fracturable area.

[0028] The forming mould according to the present invention utilises the advantageous material properties of polymer material that has been crystallized by crystallizing the fracturable area of the shell portion thereby increasing the brittleness and rigidity of the plastic at the fracturable area. This therefore enables plastic material such as APET to be utilized for containers having a fracturable opening arrangement of the type developed by the Applicant, with increased brittleness at the fracturable area facilitating fracture generation within that fracturable area.

BRIEF DESCRIPTION OF THE DRAWINGS

[0029] It will be convenient to further describe the invention with respect to the accompanying drawings, which illustrate a preferred embodiment of the forming tool according to the present invention. Other embodiments of the invention are possible, and consequently, the particularity of the accompanying drawings is not to be understood as superseding the generality of the preceding description of the invention. [0030] In the drawings:

[0031 ] Figure 1 is a top perspective view of a forming tool for manufacturing a container having a fracturable opening arrangement according to the present invention;

[0032] Figure 2 is a detailed view of the forming tool of Figure 1 ;

[0033] Figure 3 is a rear perspective exploded view of the forming tool of Figure 1 ;

[0034] Figure 4 is a plan view of a container having a fracturable opening arrangement manufactured using the forming tool of Figure 1 ;

[0035] Figure 5 is a side view of the container of Figure 4; and

[0036] Figure 6 is a detailed view of the container of Figure 4.

DETAILED DESCRIPTION OF THE INVENTION

[0037] Referring initially to Figures 1 to 3, there is shown a forming tool 1 for manufacturing a container 21 having a fracturable opening arrangement 23 according to the present invention. The forming tool 1 shown in Figure 1 includes four mould cavities 3. A heating tool 5 is provided for each mould cavity 3. The heating tool 5 includes a heating surface 7 which forms part of the mould cavity 3. The heating surface 7 also has a profile adapted to form the fracturable area 23 of a shell portion 25 of the container 21 .

[0038] Each heating tool 5 includes a foot portion 9 that is secured to a support tab 1 1 located on the bottom of the forming tool 1 as best shown in Figure 3. The base 9 can be secured to the support tab 11 using fastening means 13. The heating tool 5 further includes an arm member 15 extending from the base 9. The heating surface 7 is provided at the peripheral end of the arm member 15. The arm member 15 is inserted through a passage 17 extending through the forming tool 1 to the mould cavity 3, with the heating surface 7 being positioned to align with and form part of that mould cavity 3.

[0039] It is to be noted that Figure 3 only shows one of the heating tools 5. In the forming tool of Figure 1 , four such heating tools 5 will be provided, one for each mould cavity 3.

[0040] The forming tool 1 is typically formed from a machined block of metal such as aluminium. The heating tool 5 may preferably be formed of a different material from the rest of the forming tool 1. The material of the heating tool should preferably have a lower emissivity than the material of the forming tool 1. Therefore, the heating tool 5 can preferably be formed from brass.

[0041 ] The forming tool 1 may typically include a cooling arrangement (not shown) for maintaining the heating tool at a temperature of preferably around 3 to 5°C. The forming tool 1 may also include a heating arrangement (not shown) for heating the heating tool 5 when supported within the forming tool 1 . The heating tool 5 can preferably be maintained at a temperature of between 130 to 200°C, and more preferably at a temperature of between 160 to 170°C. The forming tool 1 can be adapted for use in vacuum forming sheets of polymer material to form the shell portion 25 of the container 21 . A series of pin holes (not shown) may be located in each of the mould cavities 5, the pin holes being connected through passages to a vacuum source (not shown). This allows the polymer sheet to be vacuumed formed into each of the mould cavities 3 by vacuum drawing.

[0042] Figures 4 to 6 show the container 21 manufactured using the forming tool 1 shown in Figures 1 to 3. Containers of the type shown in Figures 4 to 6 have been developed by the Applicant to provide a fracturable opening

arrangement 23. Such containers are described in International Publication No WO2012/120344. The fracturable opening arrangement 23 includes a fracturable area 27 within the shell portion 25. This fracturable area 27 is configured to facilitate the propagation of a fracture through the fracturable area when a bending stress is applied to the container 21. This may for example be achieved by grasping a main body 29 of the container with one hand while holding a tip portion 31 of the container 21 with the other hand. Angular displacement of the tip portion 31 relative to the main body 29 results in propagation of the fracture through the fracturable area 27. Further information in respect of the

configuration and operation of the fracturable area 27 can be found in the above noted International Publication, details of which are incorporated herein by reference.

[0043] It is preferable for the container 21 to be formed from recyclable material such as APET. However, such material is generally not suitable for use in the Applicant's container in its amorphous state. In order to allow such material to be used for the container 21 having a fracturable opening arrangement 23, it is preferable that the fracturable area 27 of the shell portion have a level of crystallization higher than the rest of the shell portion 25. In the forming tool 1 according to the present invention, the fracturable area 27 is formed by and heated by the heating surface 7 of the heating tool 5 during the forming of the shell portion 25. The cooling of the rest of the forming tool 1 limits the degree of crystallization of the rest of the shell portion 25. The heat selectively applied by the heating tool 5 to the fracturable area 27 raises the level of crystallization, preferably at or above 35% by volume thereby increasing the degree of rigidity at the fracturable area 27. This then facilitates the propagation of a fracture through the fracturable area 27 when stresses are applied to that area.

[0044] The heat is applied to the fracturable area 27 of the shell portion 25 by heat conduction once the shell portion 25 has been formed. The heating tool 5 is separated from the body of the forming tool 1 by an insulating region to prevent heat from conducting into the cooler section of the forming tool 1. This gap can be produced with a traditional insulating material such as ceramic or one effective embodiment is an air gap typically about 0.1 mm wide. This air gap also acts as a venting mechanism during vacuum forming.

[0045] The selective heating of the fracturable area 27 occurs within the production cycle for forming of the shell portion 25. A typical production cycle using the forming tool 1 according to the present invention may be from 3 to 5 seconds. The shell portion 25 having a fracturable area 27 with an increased level of crystallization can therefore be manufactured in a single production cycle without the need for any second production step.

[0046] Modifications and variations as would be deemed obvious to the person skilled in the art are included within the ambit of the present invention as claimed in the appended claims.