WO2016081996A1

WO2016081996A1 - Method for manufacturing a container having a fracturable opening arrangement

Info

Publication number: WO2016081996A1
Application number: PCT/AU2015/050740
Authority: WO
Inventors: David John Stevens
Original assignee: Sands Innovations Ltd
Priority date: 2014-11-24
Filing date: 2015-11-24
Publication date: 2016-06-02

Abstract

A method 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 within which a fracture can be initiated and propagated when stress is applied to the fracturable area; the method including; forming the sheet within a forming mould to produce a shell portion, and selectively applying heat to the fracturable area of the shell portion to thereby increase crystallisation of the polymer material within the fracturable area.

Description

METHOD FOR MANUFACTURING A CONTAINER HAVING A 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 the manufacture of containers having a fracturable opening arrangement. While the present invention will be described with respect to the manufacture of such containers in 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, commonly known as (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 or ΆΡΕΤ'. This material is very suitable for thermoforming shapes because it is a thermoplastic in an amorphus state. APET does however have a natural tendency of crystallising 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 crystallisation is kept at below 5%. 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 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 the above noted crystallisation level because the resultant material, known as crystallized PET or '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 its' toughness. CPET is however very heat stable and can typically withstand temperatures of up to 200 degree 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 10% to 40%.

[0005] The heat treatment of APET to form CPET does also result in the material becoming opaque. This is generally not desired for drink containers as this prevents inspection of the contents of the container prior to opening and drinking of the contents. There are however applications where 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, where 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 the 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 such 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.

WO20 2/120344, 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 a 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 has until now been manufactured using polymer materials such as styrene because of the suitability of the material properties of styrene for the above described application. The material properties of APET has however prevented its' use in the production of such containers. While APET has the necessary strength and toughness for the rest of the shell portion, APET does not have sufficient rigidity and 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] 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

[00 0] It is an object of the present invention to provide a method for manufacturing a container having a fracturable opening arrangement using polymer materials that can be crystallised such as APET.

[001 1 ] With this in mind, there is provided a method 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 within which a fracture can be initiated and

propagated when stress is applied to the fracturable area; the method including; forming the sheet within a forming mould to produce a shell portion, and selectively applying heat to the fracturable area of the shell portion to thereby increase crystallisation of the polymer material within the fracturable area.

[0012] 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.

[0013] The heat may be selectively applied by heating a portion of the forming mould in contact with the fracturable area of the formed shell portion so that the fracturable area is heated through heat conduction. The forming mould portion may for example be heated through thermal contact with an external heat source, or through induction heating or high energy excitation heating. Heating of the forming mould portion allows for the simultaneous thermoforming of the shell portion and the selective heating of the fracturable area through heat conduction in a single process step reducing the overall production cycle time.

[00 4] It is however also envisaged that heat may be directly applied to the fracturable area by a direct heat source. The shell portion may be initially thermoformed, and the fracturable area subjected to heat from a separate direct heat source. This heat source may for example be a focused energy radiation source such as a laser, or a heated air stream. The heat source may alternatively be a heated tool for transferring heat by heat conduction to the fracturable area. This may occur at a second station where the moulded shell portion may be transferred to and constrained prior to the heat application.

[0015] The method according to the present invention preferably includes thermoforming of the sheet with the forming mould. This generally requires preheating of the sheet of crystallisable polymer material prior to the

thermoforming of the sheet. This preheating does result in a degree of crystallisation within the sheet. It is preferable to increase the level of

crystallisation of the sheet material during preheating as much as possible, but not enough to negatively effect 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%. Crystallisation levels beyond 25% can excessively thermoset the sheet material such that is is no longer possible to thermoform the sheet. The sheet is preferably preheated to a temperature range of 80 to 130 degree C prior to thermoforming.

[0016] The selective heating of the fracturable area according to the present invention preferably increases the level of crystallisation at the fracturable area at or above 30%. This thereby induces an appropriate degree of brittleness and rigidity at the fracturable area of the shell portion. It is however envisaged that the level of crystallisation of the fracturable area can be as high as 85%.

[0017] The optimal temperature for crystallisation of the fracturable area will be above the glass transition temperature (T_g) of the crystallisable polymer material. This glass transition temperature is typically around 70 degree 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 degree C, and more preferably in the range of 160 to 170 degree C. The temperature may most preferably be 165 degree C.

[00 8] The optimum length of time for the selective heating of the fracturable area can vary depending on whether the selective heating occurs within or after the production cycle of the shell portion. This time period may be from 3 to 5 seconds when the selective heating occurs 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 however also envisaged that the rate of crystallisation can be increased by the addition of nucleating agents within the formulation of the crystallisable polymer material to promote crystallisation. [0019] 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 properties of increased crystallization and mechanical property change when heated over an extended period.

[0020] 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 side of the sheet. That 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 effect the

thermoforming and selective heating of the fracturable area.

[0021] The shell portion of container manufactured 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.

[0022] The method 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 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 the increased brittleness at the fracturable area facilitating fracture generation within that fracturable area.

[0023] 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.

Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:

1 . A method 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 within which a fracture can be initiated and propagated when stress is applied to the fracturable area; the method including; forming the sheet within a forming mould to produce a shell portion, and selectively applying heat to the fracturable area of the shell portion to thereby increase crystallisation of the polymer material within the fracturable area.

2. A method according to claim 1 , wherein the heat is selectively applied by heating a portion of the forming mould in contact with the fracturable area of the formed shell portion so that the fracturable area is heated through heat conduction.

3. A method according to claim 2, wherein the fracturable area of the shell portion is heated through thermal contact of the forming mould with an external heat source.

4. A method according to claim 2, wherein the fracturable area of the shell portion is heated through induction heating or high energy excitation heating of the forming mould.

5. A method according to claim 1 , wherein the heat is directly applied to the fracturable area of the shell portion by a direct heat source.

6. A method according to claim 5, wherein the heat is directly applied by a focused energy radiation source such as a laser, or a heated air stream, or by heat conduction from a heated tool.

7. A method according to any one of the preceding claims, wherein the degree of crystallisation of the sheet during preheating is in the range of 5 to 25%.

8. A method according to any one of the preceding claims, wherein the sheet is thermoformed with the forming mould.

9. A method according to claim 8, wherein the sheet is preheated to a temperature range of 80 to 130 degree C prior to thermoforming.

10. A method according to any one of the preceding claims, wherein the selective heating of the fracturable area increases the level of crystallisation at the fracturable area at or above 35%.

1 1 . A method according to any one of the preceding claims, wherein the selective heating of the fracturable area increases the level of crystallisation at the fracturable area up to 85%.

12. A method according to any one of the preceding claims, wherein the selective heating is applied at a temperature of 130 to 200 degree C.

13. A method according to claim 12, wherein the selective heating is applied at a temperature of 160 to 170 degree C.

14. A method according to claim 12, wherein the selective heating is applied at a temperature of 165 degrees C.

15. A method according to any one of the preceding claims, wherein the selective heating is applied over a time period of from 3 to 5 seconds.

16. A method according to any one of the preceding claims, wherein the crystallisable polymer material is polyethylene terephthalate (PET).

17. A method according to any one of the preceding claims, wherein the sheet is in the form of a laminate of the crystallisable polymer material and a sealant layer or barrier layer of a second polymer material.