WO2007070967A1

WO2007070967A1 - Polymer blends

Info

Publication number: WO2007070967A1
Application number: PCT/AU2006/001972
Authority: WO
Inventors: Robert Cecil Mcfadyen
Original assignee: Vip Plastic Packaging Pty Ltd.
Priority date: 2005-12-22
Filing date: 2006-12-22
Publication date: 2007-06-28
Also published as: AU2006326855B2; NZ569305A; AU2006326855A8; AU2006326855A1

Abstract

The present invention relates to 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. The present invention also relates to containers formed from the polymer blend, for example, containers for storing paints.

Description

POLYMER BLENDS

FIELD OF THE INVENTION

The present invention relates to polymer blends for forming containers for the storage of liquid formulations such as paints, and containers for the storage of liquid formulations .

BACKGROUND OF THE IVENTION The storage of liquid formulations such as paint or glue in plastic containers often results in "skinning" of the formulation, in which a dried or partly dried skin forms on the ullage areas of the container and its lid. In paint containers, for example, this skin can become dislodged from the ullage areas of the container or the lid and fall back into the bulk of the paint, resulting in lumps of dried paint contaminating the liquid paint. As the contaminated paint does not have a uniform consistency, when the contaminated paint is applied to a surface, the painted surface may have an unsightly lumpy appearance . The lumps of dried paint in the contaminated paint may also clog spray painting equipment.

SUMMARY OF THE INVENTION The inventor of the invention the subject of the present application has found that the problems associated with skinning may be addressed by improving the adhesion of the skin formed by the liquid formulation to the inner surface of the container in which the liquid formulation is stored. Thus, if any of the liquid formulation forms a skin on the ullage areas of the container and/or its lid, it will remain adhered to the surface of the container and not fall back into the bulk of the liquid formulation. In a first 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.

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.

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.

The polymer blend will usually further comprise a compatabiliser in order to increase the miscibility of the polymers in the polymer blend. 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.

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.

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 . 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.

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.

The polymer blend may, for example, comprise polyethylene terephthalate (PET) and one or more pόlyolefins . The one or more polyolefins may be selected from the group consisting of: polyethylene (PE), polypropylene (PP), high density polyethylene (HDPE) and low density polyethylene (LDPE) .

The PET may be provided as recycled PET flake. 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) .

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.

In a third aspect, the present invention provides a polymer blend comprising 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.

In some embodiments, the polymer blend of the third aspect 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.

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. - S -

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.

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.

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.

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 - forming the container from the polymer blend.

Preferably, the container is formed using injection moulding . DETAILED DESCRIPTION OF THE INVENTION

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 PVdC - polyvinylidene chloride PCR - post consumer recyclate

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. 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.

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.

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.

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.

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.

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

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.

The present inventor has 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. 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.

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.

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. 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.

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.

PET, being a polar polymer, also provides a barrier to permeation by organic molecules to articles formed from PET.

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) .

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.

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

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.

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.

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 (polymethyl pentene) , but this is relatively expensive.

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. 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) .

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) .

Polymers that can be used to form a container having a barrier to permeation by oxygen include PA, APET, PVC or PEN.

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.

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/m².24 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 PC 150 PVC 150 PA 200

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/m².24 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

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.

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/m².24 hours.90% humidity.

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/m².24 hours . atmosphere .

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) .

CompatabiUsers

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 .

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.

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.

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

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 talc may be added to the blend to aid in processing.

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 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.

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 .

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. 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 inventor has found that this method often provides the best miscible mix of the polymer blend and articles which have consistent properties.

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.

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 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.

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.

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.

A compatabiliser which the inventor has found to be suitable is MA modified SEBS. The MA modified SEBS may, for example, be added at about 5-10% by weight of the total weight of the polymer blend. For example, the polymer blend may contain (by weight) :

10-25% PP;

10% MAH modified SEBS; and 65-80% PET.

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) .

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.

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.

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 HDPE₇ thereby- avoiding the typical brittleness of materials formed from PET alone.

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, 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.

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.

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.

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 .

During the formation of articles using the polymer blends described above, the inventor has found that degradation by-products from the polymers may form on the surface of the articles .

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 .

The inventor has found that, in some cases, adding an additional 0.5% MAH to the polymer blend before the blend is moulded reduces the surface contamination.

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 .

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 off the contaminant) . The Corona or Plasma treatment will also remove other potential contaminants such as mould, grease etc.

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 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.

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 4O⁰C 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.

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.

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.

Although the present invention has been described with reference to particular embodiments, it will be appreciated by those skilled in the art that the invention may be embodied in many other forms.

In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary implication, the word "comprise" or variations such as "comprises" or "comprising" is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention.

Claims

1. 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.

2. The polymer blend as claimed in claim 1, wherein the blend further comprises a compatabiliser .

3. The polymer blend as claimed in claim 1 or claim 2, wherein the article formed from the blend is a container for the storage of a liquid formulation.

4. The polymer blend as claimed in claim 3, wherein the liquid formulation is an emulsion paint.

5. The polymer blend as claimed in claim 4, wherein the surface energy of the surface is equal to or greater than about 38 dyne/cm.

6. The polymer blend as claimed in any one of claims 1 to 5, wherein the blend is processable to form the article using injection moulding.

7. The polymer blend as claimed in any one of claims 1 to 6, wherein the blend comprises polyethylene terephthalate (PET) and one or more polyolefins.

8. The polymer blend as claimed in claim 7, wherein 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) .

9. The polymer blend as claimed in claim 7 or claim 8, wherein the PET is provided as recycled PET flake.

10. The polymer blend as claimed in any one of claims 7 to 9, wherein the blend further comprises maleic anhydride modified styrene ethylene butylene styrene (MAH modified SEBS) as a compatabiliser .

11. The polymer blend as claimed in claim 10, wherein the blend comprises about 10 to 25% by weight PP, about 10% by weight MAH modified SEBS and about 65 to 80% by weight PET.

12. 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.

13. A polymer blend comprising:

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.

14. The polymer blend as claimed in claim 13, comprising

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 .

15. The polymer blend as claimed in claim 13 or claim 14, wherein the compatabiliser is NLAH modified SEBS.

16. A container for a liquid formulation, the container being formed from a polymer blend as defined by any one of claims 1 to 15.

17. 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.

18. The container as claimed in claim 17, wherein all of the inner surface of the container has a relatively high surface energy.

19. The container as claimed in claim 17 or claim 18, wherein the surface having a high surface energy is formed from a polymer blend as defined in any one of claims 1 to 15.

20. The container as claimed in any one of claims 17 to 19, wherein the liquid formulation is an emulsion paint .

21. The container as claimed in claim 20, wherein the surface energy of the inner surface of the container is equal to or greater than about 38 dyne/cm.

22. The container as claimed in any one of claims 17 to 21, wherein the container is formed from a polymer blend comprising polypropylene (PP) and/or high density polyethylene (HDPE) , and polyethylene terephthalate (PET) .

23. 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

- forming the container from the polymer blend.

24. The method as claimed in claim 23, wherein the polymer blend comprises one or more polyolefins and polyethylene terephthalate (PET) .

25. The method as claimed in claim 24, wherein 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) .

26. The method as claimed in claim 24 or claim 25, wherein the PET is provided as recycled PET flake.

27. The method as claimed in any one of claims 24 to 26, wherein the blend further comprises maleic anhydride modified styrene ethylene butylene styrene (MAH modified SEBS) as a compatabiliser .

28. The method as claimed in claim 27, wherein the blend comprises about 10 to 25% by weight PP, about 10% by weight MAH modified SEBS and about 65 to 80% by weight PET.

29. The method as claimed in any one of claims 23 to 28, wherein the container is formed using injection moulding.