AU2013206090B2 - Container or Lid Composition and Manufacturing Method - Google Patents

Abstract

A container or container lid for storage of emulsions such as paints is formed of a polymer composition including polyolefin and one or more further components which increase the container surface. The surface may also be post-treated to further increase the surface energy/wettability, at least in the ullage area of the container.

Description

1 Container or lid composition and manufacturing method Cross Reference to Related Application [001] This application is a divisional of International Patent Application No. PCT/AU2006/01972 (W02007/070967), the contents of which are incorporated herein by reference. Field of the invention [002] The invention relates to containers and ids for use with emulsions such as paints detergents and medical products and more particularly products that present the difficulty of forming a "skin" on the ullage areas of a container and its lid when stored therein. Background of the invention 10031 Many product types, such as paints and detergents, and emulsions of oil and water, when packaged in prior art containers can tend to skin or flake on the ullage areas of the container or lid. This limits the ability to package these products in polymers such as polypropylene, polyethylene or high density polyethylene, as the product can be compromised thereby. [004] This problem is particularly noticeable in plastics pails or other containers used for storage of water based emulsion paints, where containers formed from polyolefin materials exhibit quite prominent skinning problems. It is known that in the ullage area of such a container, wet paint that accumulates on the wall in the ullage area forms a skin that is loosely attached to the container wall. This can easily be dislodged and fall back into the bulk of the paint forming lumps. [005] Any reference herein to known prior art does not, unless the contrary indication appears, constitute an admission that such prior art is commonly known by those skilled in the art to which the invention relates, at the priority date of this application. Summary of the invention [006] There is provided a container or container lid when used for storage of a liquid emulsion, the container or container lid formed from a polymer composition comprising 95% to 99.3% by weight polyolefin and 0.7% to 5% by weight humectant, wherein at least a portion of the container or container lid's surface has been treated so as to remove contamination.

2 [007] In one preferred realisation of the invention, the container may be formed of a polymer blend including one or more polyolefins and a further polymer imparting increased surface energy and/or increased wettability to the blend. [008] In another preferred realisation of the invention, the container is formed of a polymer composition including one or more polyolefins and an amount of at least one humectant effective to increase the surface energy and/or wettability of the container surface. [009] In one preferred form, at least part of the container surface adapted has been post-treated to further increase surface energy and/or wettability, for example by abrading, solvent washing, corona treatment or plasma treatment. [010] Other aspects of the invention relate to a method for forming a storage container or lid, a container or lid when used for storage of an emulsion, such as an emulsion paint, and the combination of such a container or lid and the liquid emulsion stored therein. [011] Further forms of the invention are set out in the claims. Polymer Blends [012] In one aspect, the present invention provides a polymer blend comprising two or more polymers, wherein the blend is capable of imparting a relatively high surface energy to a surface of an article formed from the blend, and is capable of imparting a barrier to permeation by water and oxygen to the article. [013] A surface of an article formed from the polymer blend of the present invention will have a relatively high surface energy, and anything that dries on the surface is more likely to remain adhered to the surface when compared to other surfaces having a lower surface energy (for example surfaces formed from HDPE or PP). An article formed from the polymer blend of the present invention also provides a barrier to permeation by oxygen and water, that is, oxygen and water cannot readily permeate through the article. [014] Polymer blends are advantageous because two or more polymers can be combined in order to produce a blend which can be used to form an article that has characteristics imparted by each of the polymers in the blend. For example, one of the polymers in the polymer blend might result in the relatively high surface energy of a surface of an article formed from the blend, and another polymer in the blend might result in the article providing a barrier to permeation by water and/or oxygen. [015] The polymer blend will usually further comprise a compatabiliser in order to increase the miscibility of the polymers in the polymer blend.

3 [016] Typically, the article formed from the polymer blend is a container for the storage of a liquid formulation. In such a container, at least the inner surface of the container has a relatively high surface energy. In some embodiments, the liquid formulation is paint, resin or glue. In embodiments where the liquid formulation is paint, the paint may, for example, be an emulsion paint such as flat, semi-gloss or gloss acrylic paint. [0171 In order for a container to be suitable for the storage of a liquid formulation containing water which sets when exposed to oxygen (for example, an emulsion paint), it is necessary for the container to provide a barrier to permeation by water and oxygen to minimise any premature setting of the liquid formulation in the container. If sufficient water is able to permeate out of the container, the paint around the ullage areas of the container, as well as the surface layer of paint, may prematurely dry. If sufficient oxygen is able to permeate into the container, then oxidative cross-linking of the paint may occur, causing the paint to prematurely dry. [018] Preferably, the surface energy of the surface of the article formed from the polymer blend is, for an emulsion paint, equal to or greater than about 38 dyne/cm. As those skilled in the art will appreciate, the surface energy of a surface is measured based on the specific liquid formulation that is wetting the surface. Thus, when quantifying a surface energy, it is necessary to take into account the specific liquid formulation wetting the surface. The numerical values for surface energy referred to in this specification are with respect to an emulsion paint. [019] As those skilled in the art would realise, however, the relatively high surface energies required to cause different liquid formulations to adhere to the surface typically only vary by small amounts (approximately 5 to 10%). Accordingly, a container having a surface energy of equal to or greater than about 38 dyne/cm, at which point an emulsion paint will wet and start to adhere to the surface, will typically have less skinning than a container having a lower surface energy for any liquid formulation stored in the container. It is within the ability of those skilled in the art to determine the surface energy at which respective liquid formulations will adhere to a surface. [020] Preferably, the polymer blend is processable to form the article using injection moulding, which is the method typically used to manufacture plastic containers for paint, etc. However, containers may also be manufactured from the polymer blend using other techniques, such as injection blow moulding, extrusion blow moulding or injection stretch blow moulding. [021] The polymer blend may, for example, comprise polyethylene terephthalate (PET) and one or more polyolefins. The one or more polyolefins may be selected from the group consisting of: 4 polyethylene (PE), polypropylene (PP), high density polyethylene (HDPE) and low density polyethylene (LDPE). [022] The PET may be provided as recycled PET flake. [023] As noted above, if the polymers in a polymer blend are not compatible (for example they are not miscible), then the polymer blend may further comprise a compatabiliser to increase the miscibility of the polymers. A suitable compatabiliser for a polymer blend comprising PP and PET is maleic anhydride modified styrene ethylene butylene styrene (MAH modified SEBS). [024] In a second aspect, the present invention provides a polymer blend comprising two or more polymers, the blend being processable to form a container for storing a liquid formulation, wherein the blend is capable of imparting a relatively high surface energy to a surface of the container, and capable of imparting a barrier to permeation by water and oxygen to the container. [025] In a third aspect, the present invention provides a polymer blend comprising 10-25% by weight PP, PE, I-IDPE or LDPE, or a mixture of PP and HDPE, or a mixture of two or more of PP, PE, HDPE and LDPE; 5-10% by weight of a compatabiliser; and 65-80% by weight PET. [026] In a fourth aspect, the present invention provides a container for a liquid formulation, the container being formed from a polymer blend according to the first, second or third aspect of the present invention. [027] In a fifth aspect, the present invention provides a container for a liquid formulation, wherein at least part of the inner surface of the container has a relatively high surface energy such that any of the formulation that dries on the surface adheres to the surface, and wherein the container provides a barrier to permeation by water and oxygen. [028] Typically, all of the inner surface of the container has a relatively high surface energy. The liquid formulation is preferably an emulsion paint. Preferably, the surface energy of the inner surface of the container is equal to or greater than about 38 dyne/cm for an emulsion paint. [029] The surface having a high surface energy may be formed from a polymer blend according to the first, second or third aspect of the present invention. [030] In a sixth aspect, the present invention provides a method for forming a container for the storage of a liquid formulation, the method comprising the steps of: - preparing a polymer blend comprising two or more polymers, wherein the blend is capable of imparting to a container formed from the blend (1) a barrier to permeation by water and oxygen through the container, and (2) a relatively high surface energy to the surfaces of the container such that any of the formulation that dries on the surface adheres to the surface; and 5 forming the container from the polymer blend. [031] Preferably, the container is formed using injection moulding. Polymer compositions with additives [032] A further aspect of the present invention provides a container or lid formed from a composition comprising 95 to 99.3% by weight polyolefin and 0.7% to 5% by weight humectant. [033] The polyolefin can be a honopolymer or a copolymer. [034] The polyolefin can be a homopolymer selected from the following: polypropylene, polyethylene, high density polyethylene. [035] The humectant can be selected from one or more than one of the following: poly glycol, polyethylene glycol, propylene glycol, sorbitol, glycerine; glycerol monostearate, glyceryl triacetate, xylitol, maltitol, polymeric polvols, polydextrose, natural extract humectants, quillaia, lactic acid, urea, lithium chloride and common anti-stats such as those based on long-chain aliphatic amines (optionally ethoxylated) and arnides, quaternary ammonium salts (e.g., behentrimonium chloride or cocamidopropyl betaine), esters of phosphoric acid, polyethylene glycol esters, or polyols and anti-fogging agents such as the alkyamines ethoxyates, sorbitol esters, glycerol esters, polyglycerol esters, sorbitan esters, ethoxylated sorbitan esters. [036) The container can be a pail. [037] The container or lid can be used to store a liquid formulation including paint, resin or glue. [038) The liquid formulation can be an emulsion paint [039] The emulsion paint can be one of flat, semi-gloss or gloss acrylic paint. [040] The present invention also provides a method of manufacturing a container or lid, said method comprising forming said container or lid from a composition comprising 95% to 99.5% by weight of polyolefin and 0.5% to 5% of humectant, then subsequently treating at least a portion of the surface of said container or lid which will contact product to be contained by said container or lid so as to remove contamination. [041) The treating can be by means of abrading, solvent washing or burning. [042] The treating can be performed by burning which is effected by means of corona treatment or plasma treatment. [0431 The polyolefin can be a homopolymer or a copolymer.

6 [044] The polyolefin can be selected from one of the following: polypropylene, polyethylene, high density polyethylene. [045] The humectant can be selected from one or more than one of the following: poly glycol, polyethylene glycol, propylene glycol, sorbitol, glycerine; glycerol monostearate, glyceryl triacetate, xylitol, maltitol, polymeric polyols, polydextrose, natural extract humectants, quillaia, lactic acid, urea, lithium chloride and common anti-stats such as those based on long-chain aliphatic amines (optionally ethoxylated) and amides, quaternary ammonium salts (e.g., behentrimonium chloride or cocamidopropyl betaine), esters of phosphoric acid, polyethylene glycol esters, or polyols and anti-fogging agents such as the alkyamines ethoxyates, sorbitol esters, Glycerol esters, Polyglycerol esters, Sorbitan esters, Ethoxylated sorbitan esters [046] The method can include treating the ullage areas of said container or lid. [047] The method can include treating the ullage areas of said container or lid as well as some area of said container which become ullage area once contents are drawn off from said container after use. Detailed description of the embodiment or embodiments [048] The following abbreviations (which are well known to those skilled in the art) will be used throughout the specification: PP - polypropylene PE - polyethylene PA - polyamide PC - polycarbonate HDPE - high density polyethylene LDPE - low density polyethylene UHMWHDPE- ultra high molecular weight high density polyethylene PET - polyethylene terephthalate PEN - polyethylene napthalate APET - amorphous polyethylene terephthalate PETG - polyethylene terephthalate glycol HIPS - high impact polystyrene SEBS - styrene ethylene butylene styrene MAH - maleic anhydride PVC - polyvinyl chloride 7 PVdC - polyvinylidene chloride PCR - post consumer recyclate GMS - glycerol monostearate Polymer Blends [049] The polymer blend of the present invention may be used to form an article that has a surface having a relatively high surface energy and which provides a barrier to permeation by water and oxygen, For example, the blend may be used to form a container for the storage of a liquid formulation such as paint, or part of a container for the storage of a liquid formulation such as paint. [050] A container for the long term storage of a liquid formulation preferably has a number of further properties in addition to providing a barrier to permeation by water and oxygen. For example, the container is preferably strong enough to withstand the rigours of normal use (eg it is not brittle), resistant to degrading when exposed to UV light, and resistant to chemical degradation. [051] A container for the long term storage of a liquid formulation also preferably provides a barrier to any volatile organic compounds that may be in the liquid formulation. For example, gloss paint typically contains aliphatic petroleum solvent and, for a container to be suitable for the storage of gloss paint, that solvent must not be able to escape from the container otherwise the paint stored in the container will prematurely dry. [052] Such properties are typically imparted to a container formed from a polymer blend of the present invention by the polymers in the polymer blend that impart the high surface energy and the barrier to permeation by water and oxygen. However, in some embodiments, additional polymer(s) may be added to the blend which impart these further properties to the container. [053] The surface of a container formed from the polymer blend of the present invention has a relatively high surface energy compared to conventional plastic containers (e.g. containers made from HDPE or PP). As such, any skin of dried liquid formulation which forms on the inner surface of the container (e.g. the lid and ullage areas of the container) more strongly adheres to the surface than it would to a surface having a lower surface energy. In normal use, any formulation that forms a skin on a surface of the container remains adhered to the surface and does not therefore contaminate the bulk liquid formulation.

8 [054] Furthermore, the polymer blend imparts to the container a barrier to water and oxygen which can delay the drying of a liquid formulation stored in the container. The containers formed from the polymer blend of the present invention are therefore even less susceptible to contamination of the liquid formulation due to skinning than conventional plastic containers. [055] Individual components of the polymer blend and the properties they impart to an article formed from the blend will now be described. Polymers that impart high surface energies [056] At least one of the polymers in the polymer blend of the present invention must be capable of imparting a relatively high surface energy to a surface of an article (such as a container) formed from the blend. As discussed above, the surface energy of a surface required to reduce the problem of contamination associated with skinning will depend on the liquid formulation in contact with the surface. [057] The surface energy of a surface is a measure of the wettability of the surface, and may be measured in known ways, for example by the use of a set of 'dyne pens' containing dyne level test inks each graduated to change from a continuous film to droplets when applied to a surface having surface energy below a certain reading corresponding to that test ink. [058] The present inventors have found that when the liquid formulation is a typical emulsion paint, and the surface energy of the surface inside the container is equal to or greater than about 38 dyne/cm, any emulsion paint skin which forms adheres to the inner surface of the container, thereby preventing or reducing contamination of the bulk paint due to skinning. [059] The surface energy of the surface inside the container is therefore preferably greater than about 38 dyne/cm, more preferably greater than about 40 dyne/cm and, more preferably still, greater than 45 dyne/cm. In some embodiments, however, the surface energy may be between 38 and 42 dyne/cm. In other embodiments, the surface energy is between 40 and 42 dyne/cm. [060] Conventional thermoplastics used to form containers for paint are HDPE and PP. Articles formed from such thermoplastics alone have relatively low surface energies of 33 and 29-30 dyne/cm respectively. As such, there is a noted lack of adhesion of emulsion paints to surfaces made from such thermoplastics compared to containers formed from the polymer blends of the present invention. [061] Another commonly available thermoplastic is PET. PET is polar and the surfaces of articles formed from PET alone have a surface energy of 41-42 dyne/cm. However, whilst the oxygen barrier of articles formed from PET alone is high, the barrier to water is relatively low.

9 Accordingly, PET may not be a suitable material for use on its own for forming containers for storing liquid formulations such as paint because the paint may prematurely set as water permeates out of the container. [0621 Furthermore, PET is hygroscopic and must usually be thoroughly dried before processing, otherwise the material can degrade during processing. This polymer can also be quite difficult to process using an injection moulding process (the preferred process for the manufacture of paint containers) and articles formed from PET may be brittle and easily damaged. Accordingly, whilst PET has a number of properties that make it desirable for use in forming containers for storing liquid formulations, it is typically not suitable for use in this respect on its own. [063] PET, being a polar polymer, also provides a barrier to permeation by organic molecules to articles formed from PET. [064] Other polymers that impart high surface energies to an article formed from the polymer include polycarbonate (PC) (46 dyne/cm), polyamides (nylons) (43-46 dyne/cm), polyether etherketone (41 dyne/cm), PVC (39-40 dyne/cm) and PVdC (40 dyne/cm). [065] Whilst some polyamides can also provide an effective barrier to water and oxygen, articles formed only from polyamides tend to be brittle and are therefore unsuitable for use as containers for storing liquid formulations. Polyamides are also quite expensive. [066] The trade name of an exemplary polymer that can be used to impart a high surface energy to a surface of an article is Eastar 9221 (PET). Polymers that impart barriers to permeation of water and oxygen [067] Many liquid formulations start to set upon exposure to the oxygen in the atmosphere due to oxidative cross-linking of the components in the formulation. Furthermore, if water is allowed to escape from a container containing a water based liquid formulation, such as an emulsion paint, the formulation inside the container may start to dry out, potentially exacerbating skinning problems and/or resulting in the formation of a skin on the surface of the paint. It is therefore necessary that containers used to store such liquid formulations provide a barrier to permeation by water and oxygen. [068] It is not necessary for the same polymer in the polymer blend of the present invention to impart to the article formed from the blend the barrier to permeation by both water and oxygen. For example, one polymer in the polymer blend may provide the barrier to permeation by water whilst another polymer provides the barrier to permeation by oxygen.

10 [069] Polymers that can be used to form a container having a barrier to permeation by water include many of the common polyolefins such as PE, PP, HDPE, LDPE or UHMWHDPE. Cross-linked PE or cross-linked PP may also be used, as may TPX polymethyll pentene), but this is relatively expensive. [070] Typically, the polymer blend of the present invention will comprise one or more polyolefins because these polymers are relatively cheap and will impart a number of desirable properties to articles formed from the blend. For example, as noted above, many polyolefins will impart a barrier to permeation by water. In addition, they are also thermoplastic polymers which are well suited to use in injection moulding systems. Furthermore, articles formed from blends comprising appropriate quantities of one or more polyolefins tend to be strong and robust and not easily broken or shattered. [071] In some embodiments, the one or more polyolefins is/are selected from the group consisting of polyethylene (PE), polypropylene (PP), high density polyethylene (HDPE) and low density polyethylene (LDPE). [072] In some embodiments, the one or more polyolefins is/are selected from the group consisting of polyethylene (PE), polypropylene (PP), and high density polyethylene (HDPE). [073] Polymers that can be used to form a container having a barrier to permeation by oxygen include PA, APET, PVC or PEN. [074] Individual polymers that impart a barrier to permeation by both water and oxygen are relatively rare because polymers tend to be either polar (and thus provide a good barrier to oxygen) or non-polar (and thus provide a good barrier to water). An example of a polymer that does impart a barrier to permeation by both water and oxygen is PEN, however, this polymer is relatively expensive. [075] An indication of the barrier which various polymers provide to the permeation of water through an article formed from the polymer is shown below. The units of the measurement are cc.25 microns/m.24 hours.90% humidity. The higher the number, the worse the barrier provided by the polymer to permeation by water. HDPE 5 PEN 5 PP 8 APET 60 PETG 60 HIPS 120 11 PC 150 PVC 150 PA 200 [076] An indication of the barrier which various polymers provide to the permeation of oxygen through an article formed from the polymer is shown below. The units of the measurement are cc.25 microns/m 2 24 hours.atmosphere. Again, the higher the number, the worse the barrier provided by the polymer to the permeation of oxygen. PEN 12 PA 100 APET 150 PVC 150 PETG 400 HDPE 2800 PP 3600 PC 4500 HIPS 5500 [077] The rate of permeation of oxygen and water through an article formed from a polymer blend can readily be measured using standard techniques known in the art. [078] Preferably, the permeation of water through an article formed from a polymer blend of the present invention is less than about 20, more preferably less than about 10 cc.25 microns/m 2 24 hours.90% humidity. [0791 Preferably, the permeation of oxygen through an article formed from a polymer blend of the present invention is less than about 400, more preferably less than about 300 and most preferably less than about 150 cc.25 microns/m 2 24 hoursatmosphere. [080] The trade names of exemplary polymers that can be used to impart a barrier to permeation by water to an article are Basell EP243R (PP) and Quenos GC7260 (HDPE). An exemplary polymer that can be used to impart a barrier to permeation by oxygen to an article is Eastar 9221 (PET). Compatabilisers 12 [081] As discussed above, polymer blends comprising two or more polymers will usually further comprise a compatabiliser. The compatabiliser facilitates the mixing of the polymers in the blend, for example, by increasing the miscibility of two immiscible polymers. [082] The compatabiliser used will depend on the polymers present in the polymer blend. A range of compatabilisers are known to those skilled in the art and can be selected based on the polymers that require compatabilisation. [083] Compatabilisers suitable for use in the present invention include (but are not restricted to) the following: SEBS, MAH modified SEBS (Kraton), MAH modified PP (Equistar), and MAH. Two or more compatabilisers may be used to increase the miscibility of the polymers in the polymer blend. [084] Advantageously, as SEBS is a rubber, if SEBS or MAH modified SEBS is used as a compatabiliser, impact resistance is also imparted to the resultant article. Additional components in the polymer blend [085] The polymer blend may also include additional components. For example, in some embodiments, an initiator may be included in the polymer blend in order to aid in the processability of the blend. For example, a small amount of tale may be added to the blend to aid in processing. [086] The polymer blend may also include a colouring agent in order to provide the article with a colour. Compounds providing a colour to the polymer blend may be dyes or pigments. Blending the polymer blend and forming an article from the blend [087] The polymer blends of the present invention may be prepared by mixing the two or more polymers (and any additional components) using techniques known in the art. [088] For example, each of the components of the polymer blend can be added to a mixing system such as a screw extruder. The components are then thoroughly mixed and heated in the screw such that they melt and become homogeneous. The resultant homogeneous mixture may be injected into a mould by using the screw as a plunger. Once the polymer blend has set, the mould can be opened and the moulded article removed. [089] It is also possible to pre-compound various components of the polymer blend prior to forming the polymer blend. For example, a master-batch comprising one or more polymers and one or more compatabilisers can be prepared and added as a concentrate to an appropriate quantity of one of the base resins (eg. PET) to form the polymer blend.

13 [090] Alternatively, and preferably, a master-batch may be pre-compounded and added to the base resin along with an additional amount of a compatabiliser in order to form the final blend in-situ in the moulding machine. The inventors have found that this method often provides the best miscible mix of the polymer blend and articles which have consistent properties. [091] In a fifth aspect, the present invention provides a container for a liquid formulation, wherein at least part of the inner surface of the container has a relatively high surface energy such that any of the formulation that dries on the surface adheres to the surface, and wherein the container provides a barrier to permeation by water and oxygen. Such a container may be prepared by using a polymer blend to prepare a coating for a standard container for storing liquid formulations (e.g. a metal paint container), where the surface of the coating has a relatively high surface energy. This coating may be applied to the inner surfaces of the container, thus providing the relatively high surface energy to the inner surface of the container. In such embodiments, the barrier to permeation by water and oxygen may be provided by the container itself, so it is not necessary to provide a polymer in the polymer blend that is capable of imparting a barrier to permeation by water and oxygen. [092] In other embodiments of the fifth aspect of the present invention, the container may be prepared by co-injection, two colour moulding, insert moulding or in-mould labelling. In two colour moulding, a first article is moulded and another article is then moulded over the first article. For example, a blend of one or more polymers may be used to form the central portion of a lid (i.e. the portion of the lid which will be exposed to the liquid formulation) and the outside rim that holds the lid on the container is subsequently over-moulded from another material onto the central portion. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE PRESENT INVENTION [093] Preferred embodiments of the present invention will now be described by way of example only, and the preferred embodiments are not to be construed as limiting the scope of the invention in any way. Polymer Blends [094] As discussed above, PP and HDPE are effective materials to provide a moisture barrier, and PET provides an effective oxygen barrier and a high surface energy, to articles formed from these polymers. Accordingly, in a preferred embodiment of the present invention, a container is formed from a polymer blend comprising PP and/or HDPE and PET. PE may be used in place of or in addition to PP.

14 [095] These polymers have significantly different melting points and, in a straight blend, do not form a miscible mix. Accordingly, in order to enable the blend to be processed, a compatabiliser that will combine with all of the polymers is employed or the resultant material would be very brittle. [096] A compatabiliser which the inventors have found to be suitable is MA modified SEBS. The MA modified SEBS is added at about 5-10% by weight of the total weight of the polymers in the polymer blend. [097] For example, the polymer blend may contain (by weight): 10-25% PP; 10% MAH modified SEBS; and 65-80% PET. [0981 Alternatively, the 10-25% PP in the polymer blend may be replaced with 10-25% PE, 10 25% HDPE, or a mixture of PP and HDPE which amounts to 10-25% of the final blend (PP and HDPE have similar specific gravities and can therefore be readily substituted for one another). [099] Advantageously, when using these combinations of polymers and compatabiliser, it is not necessary to dry the PET before preparing the polymer blend, and quite high levels of PET (up to 80% by weight) can be incorporated into the blend. Surprisingly (as PET is usually a brittle plastic when it has not been dried to a very low moisture level), the resultant blend has excellent processability, easily filling a mould over very long flow paths, and containers formed from this blend have excellent toughness and stiffness. [0100] A further beneficial outcome of using the above blend to form a container is that, as it is not necessary to dry the PET, it is possible to use recycled PET flake. The steps of re-pelletising and crystallising the PET, which usually need to be performed, are not necessary. [0 101] Without wishing to be bound by theory, it is believed that the presence of moisture in the undried PET lowers the intrinsic viscosity of the PET (by degrading the polymer and reducing its molecular weight) thereby making it more flowable. The compatabiliser subsequently links the degraded PET fractions to the PP and/or HDPE, thereby avoiding the typical brittleness of materials formed from PET alone. [0102] A preferred method for preparing one of the polymer blends described above involves pre-preparing a blend containing specific proportions of the PP, PET and MA modified SEBS, 15 and adding this pre-blend to specific quantities of PET or a mixture of PP and HDPE in the moulding machine such that the resultant polymer blend in the moulding machine has the appropriate quantities of each of the components. [0103] This method provides optimal mixing conditions and also provides the opportunity to adjust the level of the MA modified SEBS in the final blend in order to control the miscibility and rheology of the final melt. The inventor has found that this method provides a good miscible mix of the polymer blend and that articles prepared using the method tend to be less brittle and have consistent properties. [0104] If desired, other high surface energy resins, such as PC or PA may also be added to the master-batch mix in order to further increase the surface energy of the final product. [0105] As noted above, PET also provides a good barrier for some organic solvents. Accordingly, a container formed from a polymer blend including PET would also have application in storing liquid formulations which contain organic solvents, for example, gloss paint, resin, glue, printing inks, oils, or agricultural chemicals, even though such liquid formulations do not necessarily suffer from skinning problems. [0106] During the formation of articles using the polymer blends described above, the inventors have found that degradation by-products from the polymers may form on the surface of the articles. [0107] Without wishing to be bound by theory, it is believed that the degradation by-products are low molecular weight resins (most likely degraded PET fractions). The presence of such containments on the surface may lower the surface energy of the surface. [0108] The inventors have found that, in some cases, adding an additional 0.5% MAH to the polymer blend before the blend is moulded reduces the surface contamination. [0109] Alternatively, the degradation by-products can be removed from the surface in order to provide higher surface energy levels using a number of techniques known in the art. For example, the contaminated surface can be flamed, or treated using Corona treatment or plasma treatment, etc. Such treatment may provide the article formed from the polymer blend of the present invention with a surface energy of approximately 50 dyne/cm. It is believed that the flame/Corona/plasma treatment physically cleans the surface. [0110] Accordingly, when producing paint containers, all paint contact surfaces are typically treated using Corona or Plasma treatment in order to decontaminate the surfaces (i.e. by burning 16 off the contaminant). The Corona or Plasma treatment will also remove other potential contaminants such as mould, grease etc. [0111] Another way to remove the surface contaminant is to physically abrade the surface by scrubbing. Again, levels of around 50 dyne/cm can be obtained by dry rubbing the surface with a scouring pad. EXAMPLES [0112] A pre-blend was formed from 44% by weight PET, 28% by weight PP and 28% by weight MAH modified SEBS in a twin screw extruder. The pre-blend was then mixed in a ratio of 34% by weight pre-blend to 3% by weight of MAH modified SEBS and 65% by weight undried PET PCR in the barrel of an injection moulding machine. The resultant composition of the polymer blend in the final mixture was about 80% by weight PET, 10% by weight PP and 10% by weight MA modified SEBS. [0113] Two litre pails and lids were made by injecting the molten polymer blend into the cavity of a mould. One of these containers was filled with acrylic emulsion paint and placed in a sealed test chamber containing approximately 30mm of water, and the test chamber was stored at 40*C in an oven for 4 weeks. A control container having a similar pail and lid, but which was moulded from only PP was also placed in the test chamber alongside the container made from the PP/PET blend. [0114] At the end of the 4 week test period, both containers were removed from the oven and allowed to cool. The lids were removed and the contents examined for traces of skin formation. The container made of PP had a noticeable skin formed on the lid and in the headspace above the emulsion paint. This skin was loosely adhered to the container and parts of it had fallen from the wall and lid into the paint as a result of removal of the lid. [0115] The container made from the PP/PET blend had a significantly smaller amount of skin formation. Further, the adhering paint was still mostly wet and the wet paint could be easily incorporated into the bulk of the liquid paint. The light skin that had formed on the surface of the container was also more difficult to remove; it could be wiped with a brush without dislodging it, and could only be removed by use of a hard scraper. Polymer Compositions including Humectants [0116] In order for a container to be suitable for emulsions such as paint emulsions containing water which sets when exposed to oxygen, it is necessary for the container to provide a barrier to permeation by water and oxygen to minimise any premature setting of the liquid formulation in 17 the container. If sufficient water is able to permeate out of the container, the paint around the ullage areas of the container and lid, as well as the surface layer of paint, may prematurely dry. If sufficient oxygen is able to permeate into the container, then oxidative cross-linking of the paint may occur, causing the paint to prematurely dry. This is readily understood by a person skilled in the art of paint container manufacturing. [0117] In general terms the present embodiment of the invention is embodied in a composition for a container or lid comprising a 95% to 99% by weight polyolefin and 0.7% to 5% by weight humectant. The polyolefin can be homopolymer or a copolymer and can be selected from (but not restricted to) - polypropylene, polyethylene, high density polyethylene and low density polyethylene. It will be understood that the 95% to 99.3% by weight of polyolefin may include dry powdered pigment and other compounds. [0118] It is believed that over 5% by weight of humectant will compromise the material properties of the moulded product. Further at levels of greater than 5% humectant it becomes more difficult to feed the polyolefin and humectant mix into the moulding machine. [0119] The concentration of humectant described in the previous paragraph will function well to prevent skinning for a reasonable time. Skinning times can be even longer by removing surface contamination which may be caused by burnt polyolefin or humectant which may occur during the moulding process. Other surface contamination can be present from degraded material eg waxes, burnt material, mould release silicone for mouldability etc and this surface contamination can be removed by abrasion, buying or solvent washing, as described below. [0120] The humectant can be selected from one or more than one of the following: poly glycol, polyethylene glycol, propylene glycol, sorbitol, glycerine; glycerol monostearate, glyceryl triacetate, xylitol, maltitol, or polymeric polyols like polydextrose, polyethylene glycol, or natural extracts like quillaia, or lactic acid, urea or lithium chloride, and common anti-stats such as those based on long-chain aliphatic amines (optionally ethoxylated) and amides. quaternary ammonium salts (e.g., behentrimonium chloride or cocamidopropyl betaine), esters of phosphoric acid, polyethylene glycol esters, or polyols and anti-fogging agents such as the alkyamines ethoxyates, sorbitol esters, Glycerol esters, Polyglycerol esters, Sorbitan esters, Ethoxylated sorbitan esters. [0121] In another embodiment of the invention there is provided a method of manufacturing a container or lid which comprises forming the container or lid from a composition comprising 95% to 99.5% by weight polyolefin and 0.5% to 5% by weight humectant, optionally then 18 treating at least a portion of the surface of said container or lid which will contact product to be contained by said container or lid so as to remove surface contamination. [01221 In a further embodiment a container or lid is provided having one or more internal surfaces formed of a composition comprising 95% to 99.5% by weight polyolefin and 0.5% to 5% by weight humectant, optionally then treating at least a portion of the surface of said container or lid which will contact product to be contained by said container or lid so as to remove surface contamination. [0123] The removal of contaminants is preferably done by means of abrading, solvent washing or burning which can be effected by means of corona treatment or plasma treatment. [0124] The treatment can be of the whole of the surface of said container or lid which will contact product to be contained by said container or lid or in a pattern or in predetermined areas which have a higher probability for product forming a skin thereon. [0125] The surface of the container or lid formed from the composition of the present invention has a relatively high surface energy compared to conventional plastic containers (e.g. containers made from HDPE or PP). As such, any skin of dried liquid formulation which forms on the ullage areas of the container or lid will more strongly adhere to the surface than it would to a surface having a lower surface energy. In normal use, any formulation that forms a skin on a surface of the container remains adhered to the surface and does not therefore contaminate the bulk liquid formulation. [0126] Furthermore, the composition imparts to the container and the lid a barrier to water and oxygen which can delay the drying of a liquid formulation stored in the container. The containers formed from the polymer blend of the present invention are therefore even less susceptible to contamination of the liquid formulation due to skinning than conventional plastic containers. [0127] By surface treating the moulded lid or container by means of abrading, solvent washing or burning which can be effected by means of corona treatment or plasma treatment will remove surface contamination, but in the process will also remove some of the humectant, which may have migrated to the surface of the lid or container. [0128] It is thought that as the humectant is of a lower molecular weight than the polyolefin, the humectant will migrate to the surface of the container or lid. Migration is thought to occur by a diffusion process or by means of capillary forces, once the container or lid is cooled. The presence of the migrated molecules on the container and lid surface will increase the 19 wettability of the these surfaces. The molecules of humectant will continue to migrate after the surface has been treated and will provide higher surface energy levels and thus wettability. [0129] For example, the contaminated surface can be flamed, or treated using Corona treatment or plasma treatment, etc. Such treatment can provide the article formed from the polymer blend of the present invention with a surface energy of approximately 50 dyne/cm. It is believed that the flame/Corona/plasma treatment physically cleans the surface. [0130] Accordingly, when producing paint containers, all paint contact surfaces can be treated using Corona treatment in the preferred method, in order to decontaminate the surfaces (i.e. by burning off the contaminant). The Corona treatment will remove surface contaminants such as mould, grease which may be present at the time of moulding. [0131] Another way to remove the surface contaminant is to physically abrade the surface by scrubbing. Whilst a further means to remove such surface contamination is to solvent wash using a solvent such as xylene. Levels of around 40 dyne/cm can be obtained by dry rubbing the surface with a scouring pad, abrasive or solvent washing. [0132] In the case of paint containers, only the top half of the container's inside surface need be treated in this manner, as once the contents of the container gets below this level, the amount of oxygen contained by the container when it is closed after use, is of sufficient quantity to prematurely dry the paint and thus there is no need to prevent "skinning" in these circumstances with respect to the surfaces of the container or lid, as the paint itself will deteriorate in quality. [0133] In respect of the examples discussed below the master batches are a concentrate of humectant and base polymer (say 10-20% humectant in carrier resin (typically PP or PE) and then added at the appropriate rate to give a final percentage of 0,5%-5% or depending on the characteristics of the additive could be added alone eg. Some material is solid in the form of flakes or powder. COMPARATIVE EXAMPLE 1: [0134] A first master batch was formed from 99.5% by weight PP, 0.5% by weight GMS and fed into the barrel of an injection moulding machine. Pails and lids were made by injecting the molten composition into the cavity of a mould. [0135] Plastic granules are melted and brought to a temperature of 200-300degC and injected under pressure so as to fill an enclosed cavity in the mould. The polymer is then cooled to a 20 temperature below the melting point of the polymer and the solid part is then removed from the mould. Typical temperatures for removal from the mould is 70-120degC. [0136] A second master batch was formed from 99.5% by weight PP, 0.5% by weight GMS and fed into the barrel of an injection moulding machine. Pails and lids were made by injecting the molten composition into the cavity of a mould. After pails and lids have cooled, they are then subjected to the removal of surface contamination by corona treatment. [0137] Containers of the first master batch, were filled with acrylic emulsion paint and closed with lids of the same composition as the container and placed in a sealed test chamber to accelerate the time of skinning - these first master batch containers and lids skinned around the equivalent of 3 months of normal ambient temperature storage conditions. (0138] Test containers are filled with paint to leave a 10% ullage. The container is lidded and inverted so as to wet the lid and ullage area of the container. The container is then returned to an upright position and placed in a sealed test chamber containing approx. 25mm of water. The test samples (in the test chambers) are placed in an oven at 40 degrees centigrade and left for a period of 4 weeks. At the end of the test period the samples are removed and allowed to equilibrate to ambient temperature. The lids are then removed and the exposed surfaces examined for signs of skin formation. Additionally the contents are then poured through a fine mesh sieve (approx. 200mesh). The sieve is washed with running water to expose and skin portions that may have formed. [0139] Containers made from the second master batch were filled with acrylic emulsion paint and closed with lids of the same composition and treatment and placed in a sealed test chamber to accelerate the time of skinning- these second master batch containers and lids skinned around the equivalent of 12 months of normal time. [0140] The 9 month increase in skinning time from first to second master batch samples, renders the second master batch treated composition viable for paint emulsions, taking into the inventory requirements of paint manufacturers and the shelf life of unopened containers of paint emulsion product. [0141] The whole of the ullage area of a filled container is susceptible to skinning. Thus for a pail or container the top 40mm to 50mm may be all that is necessary for treatment by burning or otherwise, with the rest being under the level of the liquid in the container when transported and stored under common/normal conditions of use. It can be beneficial to treat a greater depth ie > 40mm to 50 mm from the top of the container so as to allow some further storage life for a partially filled container after some of the contents have been used.

21 MECHANISM OF ACTION [0142] Without wishing to be bound by theory, it is believed that the present invention works in the following way, with reference to a water-based emulsion paint. [0143] A water based emulsion paint consists of the polymer (acrylic or a vinyl resin for example) suspended in water. As the water evaporates during normal drying of the paint the small droplets come closer together. At a critical point the droplets start to coalesce and by capillary action force out the water between the droplets forming a polymer film. This stage is called the coalescence stage. [0144] It is commonly observed that wet paint that accumulates on lid and the wall of the ullage area of a polyolefin container forms a skin that is loosely attached to the container wall. This can easily be dislodged and fall back into the bulk of the paint forming lumps. [0145] Given the above mechanism for film formation in drying paint, the Applicant believes this observation may be explained by a similar mechanism being established due to surface tension effects. If the container surface is hydrophobic (water repelling) and lipophilic (oil attracting) then a mechanism for separation of the polymer from the water would be established. The water molecules would be repelled from the surface of the container and the polymer droplets would be attracted to the wall. If the conditions allow the coalescence stage to be reached then by capillary action a film would be formed. There would not need to be loss of water by evaporation to set this mechanism going. [0146] With this mechanism for skin formation in mind, it is believed that the present invention works by reducing the hydrophobic and/or lipophilic nature of the polymer container so that the ullage surface is able to be wetted with water, such that the skin forming is reduced. [0147] This mechanism for separation is not restricted to paint. It would also apply to any oil in water emulsion such as yoghurt or mayonnaise. Both these products show a separation when packaged in polyolefin containers. Another similar emulsion is blood. [0148] The present invention is not limited only to emulsion paints, and is intended for use in other applications where similar skinning or separation occurs. [0149] Where ever it is used, the word "comprising" is to be understood in its "open" sense, that is, in the sense of "including", and thus not limited to its "closed" sense, that is the sense of "consisting only of'. A corresponding meaning is to be attributed to the corresponding words "comprise", "comprised" and "comprises" where they appear.

22 [0150] It will be understood that the invention disclosed and defined herein extends to all alternative combinations of two or more of the individual features mentioned or evident from the text. All of these different combinations constitute various alternative aspects of the invention. [0151] While particular embodiments of this invention have been described, it will be evident to those skilled in the art that the present invention may be embodied in other specific forms without departing from the essential characteristics thereof. The present embodiments and examples are therefore to be considered in all respects as illustrative and not restrictive, and all modifications which would be obvious to those skilled in the art are therefore intended to be embraced therein.

Claims (22)

1. A container or container lid when used for storage of a liquid emulsion, the container or container lid formed from a polymer composition comprising 95% to 99.3% by weight polyolefin and 0.7% to 5% by weight humectant, wherein at least a portion of the container or container lid's surface has been treated so as to remove contamination.

2. A container or container lid as claimed in claim 1, wherein said polyolefin is a homopolymer or a copolymer.

3. A container or container lid as claimed in claim 1 or claim 2 wherein said polyolefin is a homopolymer selected from polypropylene and polyethylene.

4. A container or container lid as claimed in any one of claims 1 to 3, wherein said humectant is selected from one or more of the following: polyglycol, polyethylene glycol, propylene glycol, sorbitol, glycerine, glycerol monostearate, glyceryl triacetate, xylitol, maltitol, polymeric polyols, polydextrose, natural extract humectants, quillaia, lactic acid, urea, lithium chloride and common anti-statics such as those based on long-chain aliphatic amines (optionally ethoxylated) and amides, quaternary ammonium salts (e. g. , behentrimonium chloride or cocamidopropyl betaine), esters of phosphoric acid, polyethylene glycol esters, or polyols and anti-fogging agents such as the alkyamines ethoxyates, sorbitol esters, glycerol esters, polyglycerol esters, sorbitan esters, ethoxylated sorbitan esters.

5. A container as claimed in any one of claims 1 to 4, wherein said container is a pail.

6. A container or container lid as claimed in any one of claims 1 to 5 when used to store a liquid formulation including paint, resin or glue.

7. A container or container lid as claimed in claim 6 wherein said liquid is an emulsion paint.

8. A container or container lid as claimed in claim 7 wherein said emulsion paint is one of flat, semi-gloss or gloss acrylic paint. 24

9. A container or container lid as claimed in claim 1, wherein said polymer composition comprises a polymer blend including said at least one polyolefin and polyethylene terephthalate (PET).

10. A container or container lid as claimed in claim 9, wherein the at least one polyolefin is selected from the group consisting of polypropylene (PP), high density polyethylene (HDPE) and low density polyethylene (LDPE).

11. A method of manufacturing a container or container lid, said method comprising forming said container or container lid from a composition comprising 95% to 99.5% by weight of polyolefin and 0.5% to 5% of humectant, then subsequently treating at least a portion of the surface of said container or container lid which will contact product to be contained by said container or container lid so as to remove contamination.

12. A method as claimed in claim 11, wherein said treating is by means of abrading, solvent washing or burning.

13. A method as claimed in claim 12, wherein said treating is performed by burning which is affected by means of corona treatment or plasma treatment.

14. A method as claimed in any one of claims 11 to 13, wherein said polyolefin is homopolymer or a copolymer.

15. A method as claimed in any one of claims 11 to 14, wherein said polyolefin is selected from polypropylene or polyethylene

16. A method as claimed in any one of claims 11 to 15, wherein said humectant is selected from one or more of the following: polyglycol, polyethylene glycol, propylene glycol, sorbitol, glycerine, glycerol monostearate, glyceryl triacetate, xylitol, maltitol, polymeric polyols, polydextrose, natural extract humectants, quillaia, lactic acid, urea, lithium chloride and common anti-stats such as those based on long-chain aliphatic amines (optionally ethoxylated) and amides, quaternary ammonium salts (e. g., behentrimonium chloride or cocamidopropyl betaine), esters of phosphoric acid, polyethylene glycol esters, or polyols and anti-fogging agents such as the alkyamines ethoxyates, sorbitol esters, glycerol esters, polyglycerol esters, sorbitan esters, ethoxylated sorbitan esters. 25

17. A method as claimed in any one of claims 11 to 16, wherein said method includes treating the ullage areas of said container or container lid.

18. A method as claimed in any one of claims 11 to 17, said method further including treating a further area of said container which will become ullage area once contents are drawn off from said container in use.

19. A container or container lid as claimed in claim 9, wherein the PET is provided as recycled PET flake.

20. A container or container lid as claimed in claim 9, wherein the polymer blend comprises: 10-65% by weight PP, PE, HDPE or LDPE, or a mixture of PP and HDPE, or a mixture of two or more of PP, PE, HDPE and LDPE; 5-15% by weight of a compatabiliser; and

25-80% by weight PET. 21. A container or container lid as claimed in claim 20, wherein the polymer blend comprises: 10-25% by weight PP, PE, HDPE or LDPE, or a mixture of PP and HDPE, or a mixture of two or more of PP, PE, HDPE and LDPE; 5-10% by weight of a compatabiliser; and

65-80% by weight PET. 22. A container or container lid as claimed in claim 20 or 21 wherein the compatabiliser is maleic anhydride modified styrene ethylene butylene styrene (MAH modified SEBS). 23. A container or lid as claimed in any one of claims 1-10 and 19-21, when used for storage of an emulsion paint, wherein an inner surface of the container or lid adapted for contact with the emulsion paint has a surface energy of at least 38 dyne/cm. 24. A container or lid as claimed in claim 23, wherein an inner surface of the container or lid adapted for contact with the emulsion paint has a surface energy between 38 dyne/cm and 42 dyne/cm. 26 25. A container or lid as claimed in claim 23, wherein an inner surface of the container or lid adapted for contact with the emulsion paint has a surface energy greater than 45 dyne/cm. VIP PLASTIC PACKAGING PTY LTD WATERMARK PATENT AND TRADE MARKS ATTORNEYS P30679AU02