Patent Description:
Surfaces that are difficult to wet are known as hydrophobic surfaces. Such surfaces have a number of commercially important properties. For instance, surfaces that are difficult to wet can be non-stick, self-cleaning and / or resistant to contamination.

Hydrophobic materials are commonly used to form hydrophobic surfaces. Such hydrophobic materials typically include waxes, fluorinated polymers, e.g. polytetrafluoroethylene (PTFE), organosilanes, etc. For instance, silicones, siloxanes and various fluoro-acrylate polymers are the predominant materials used in formulations for water proofing fabric materials. The hydrophobic formulations are generally sprayed onto the surface of a fabric material and, after air curing or drying, provide effective water repellency to rain, moisture, as well as protection against various soils and stains.

However, known hydrophobic materials do not typically adhere well to all surfaces, particularly thermoplastic films.

Moreover, known hydrophobic materials often contain fluorine and these fluorine-containing hydrophobic materials can be toxic.

Accordingly, there is a need for improvement. In particular, there is a need for non-toxic hydrophobic materials which adhere well to surfaces such as thermoplastic films, thereby providing polymeric films that are difficult to wet, self-cleaning and / or resistant to contamination.

<CIT> discloses a superhydrophobic packaging film comprising a mono- or multilayer polymer substrate coated with metal oxide particles which have been modified by a functional group.

Embodiments of the present invention seek to provide polymeric films having WCAs of approximately <NUM>° or greater, in which adhesion between the substrate and the hydrophobic particles is improved when compared to the prior art. Embodiments of the present invention also seek to provide polymeric films which are less toxic when compared to the prior art.

The present invention is as defined in the appended set of claims.

According to a first aspect of the invention, there is provided a polymeric film comprising a substrate at least partially coated with hydrophobic particles, the hydrophobic particles comprising:.

The average diameter of the hydrophobic particles may be less than or equal to approximately <NUM>.

The average diameter of the hydrophobic particles may be less than or equal to approximately <NUM>, e.g. less than or equal to approximately <NUM>.

The average diameter of the hydrophobic particles may be from approximately <NUM> to approximately <NUM>, such as from approximately <NUM> to approximately <NUM>.

The hydrocarbon chain may be straight or branched.

The hydrocarbon chain may have from <NUM> to <NUM> carbons.

The hydrocarbon chain may have from <NUM> to <NUM> carbons, such as from <NUM> to <NUM> carbons.

The hydrocarbon chain may be covalently bound to the metal oxide core via a functional group, e.g. an anionic functional group.

The functional group may comprise any one or a combination of hydroxide, carboxylate, phosphonate, phosphinate, thiolate and thiocarboxylate.

The hydrophobic particles may be free from fluorine.

The substrate may comprise a thermoplastic film. For instance, the substrate may comprise any one or more of a polyolefin, vinyl polymer, polyester and polyacetal film.

The substrate may comprise a co-extruded bilayer or multilayer film. For instance, the co-extruded bilayer or multilayer film may comprise layers of any one or a combination of polyethylene (PE), polypropylene (PP), acetal, acrylic, polyamide, polyvinyl chloride (PVC), ethylene vinyl acetate (EVA), polyvinylidene chloride (PVDC), polystyrene (PS), acrylonitrile butadiene styrene (ABS) and polycarbonate (PC).

The hydrophobic particles may be deposited (e.g. sprayed) onto the substrate. For instance, the hydrophobic particles may be mixed with a carrier, such as a volatile solvent, and the resultant mixture may be sprayed onto the substrate. The mixture of the hydrophobic particles and the carrier may form a solution or suspension. The mixture may have a hydrophobic particle concentration of from approximately <NUM> wt% to approximately <NUM> wt%, such as from approximately <NUM> wt% to approximately <NUM> wt%, such as from approximately <NUM> wt% to approximately <NUM> wt%, e.g. <NUM> wt% or <NUM> wt% or <NUM> wt% or <NUM> wt% or <NUM> wt% or <NUM> wt%.

The hydrophobic particles and the substrate are secured to one another by an adhesive, such as an epoxy resin. For instance, an adhesive may be deposited onto the substrate followed by the hydrophobic particles. Alternatively, the hydrophobic particles may be deposited onto the substrate followed by the adhesive. The hydrophobic particles may become at least partially embedded in the adhesive, which itself provides the bond between the substrate and the hydrophobic particles. When the adhesive is cured, the result is a polymeric film having a hydrophobic three-dimensional surface.

The hydrophobic particles and the adhesive may be mixed and the resultant mixture may be deposited onto the substrate.

The mass ratio of the hydrophobic particles and the adhesive are from <NUM>:<NUM> to <NUM>:<NUM>. Mass ratios of hydrophobic particles and adhesive in this range have been found to produce polymeric films having particularly good hydrophobic surfaces.

The hydrophobic particles or the hydrophobic particle / adhesive mixture may be sprayed onto the substrate using a carrier, e.g. a volatile solvent, as described previously.

In all methods of attaching the hydrophobic particles to the substrate it has been found that the WCAs are not adversely affected even after the polymeric film has been immersed in or exposed to a solvent. Such treatment may result in some of the hydrophobic particles becoming removed from the substrate but the removal has a negligible effect on the WCA.

The hydrophobicity of the polymeric film may be tuned at different regions across the surface thereof. By this it is meant that a first region of the polymeric film may have an associated first WCA measurement and a second region of the polymeric film may have an associated second WCA measurement which differs from the first WCA measurement.

Tuning the hydrophobicity of the polymeric film may be achieved in a number of ways. For instance, more layers of hydrophobic particles may be deposited at the first region than at the second region. Accordingly, the first region will typically have a higher WCA measurement than the second region. Additionally or alternatively, a more concentrated mixture of hydrophobic particles may be deposited at the first region than at the second region. Accordingly, the first region will typically have a higher WCA measurement than the second region. The concentration of hydrophobic particles in the mixture may be adjusted by dilution with the solvent and / or a different species, e.g. a hydrophilic particle and / or an unfunctionalised metal oxide. Additionally or alternatively, different types of hydrophobic particles may be deposited at the respective first and second regions. Accordingly the first and second regions will typically have differing WCA measurements.

The present invention provides self-cleaning polymeric films and processes for producing self-cleaning polymeric films, where the polymeric films have a hydrophobic surface formed by securing hydrophobic particles to a substrate.

The methods of attaching the hydrophobic particles to the substrate result in a polymeric film having a three-dimensional surface structure which can achieve a WCA of approximately <NUM>° or greater. Accordingly, polymeric films of the invention can offer improved self-cleaning properties and / or resistance to contamination.

According to a second aspect of the invention, there is provided use of a polymeric film according to the first aspect of the invention as a food packaging film.

According to a third aspect of the invention, there is provided a food or liquid packaging or container comprising a surface, wherein the polymeric film according to the first aspect of the invention is laminated to the surface.

The surface of the food or liquid packaging or container may comprise metal, alloy, plastics, cardboard and / or glass.

According to a fourth aspect of the invention, there is provided a glass sheet having a polymeric film according to the first aspect of the invention laminated thereto.

The glass sheet may be used in a windscreen, e.g. a windscreen for a vehicle.

According to a fifth aspect of the invention, there is provided a plastics having a polymeric film according to the first aspect of the invention laminated thereto.

According to a sixth aspect of the invention, there is provided a fabric sheet having a polymeric film according to the first aspect of the invention laminated thereto.

According to a seventh aspect of the invention, there is provided an article of clothing or footwear having a polymeric film according to the first aspect of the invention laminated thereto.

Embodiments of the invention will now be described by way of example only with reference to the accompanying drawings, in which:.

Referring to <FIG> there is shown a hydrophobic particle, represented generally at <NUM>. The hydrophobic particle <NUM> comprises a metal oxide core <NUM> and six hydrocarbon chains <NUM>. It is to be appreciated that in other embodiments the hydrophobic particle <NUM> may have greater than or less than six hydrocarbon chains <NUM>. Each hydrocarbon chain <NUM> has from <NUM> to <NUM> carbon atoms. The hydrocarbon chains <NUM> are branched, although they could be straight.

The hydrocarbon chains <NUM> are chemically bound to the metal oxide core <NUM>.

In some embodiments, the hydrocarbon chains <NUM> may be covalently bound to the metal oxide core <NUM> via a functional group <NUM>. Suitable metal oxide cores <NUM> include aluminium oxide, iron oxide, zinc oxide, and silicon oxide.

According to the invention, the hydrophobic particle comprises an aluminium oxide core.

The term "oxide" as used herein is intended to include oxide-hydroxides, hydroxides and also oxides having multiple metal oxidation states. For example, iron oxide may include Fe<NUM>O<NUM> or Fe<NUM>O<NUM> or a combination thereof.

In some embodiments, the hydrophobic particle <NUM> comprises an aluminium oxide core <NUM> having a hydrocarbon chain <NUM> covalently bound thereto by a carboxylate functional group <NUM>. In other embodiments, alternative functional groups may be employed as long as a stable covalent interaction is formed between the metal oxide core <NUM> and the hydrocarbon chain <NUM>. Alternative functional groups <NUM> may comprise any one or a combination of hydroxide, phosphonate, phosphinate, thiolate and thiocarboxylate.

In some embodiments, the hydrocarbon chain <NUM> may be aliphatic. In particular, the hydrocarbon chain <NUM> may be chosen from any suitable alkyl organic group as defined by the formula CxHy, where x and y are whole numbers and x is from <NUM> to <NUM>. In some embodiments, the hydrocarbon chain <NUM> may have from <NUM> to <NUM> carbons, such as from <NUM> to <NUM> carbons.

In some embodiments, the hydrocarbon chain <NUM> may be straight. For instance, the hydrophobic particle <NUM> may be created by reaction of octanoic acid (CH<NUM>(CH<NUM>)<NUM>CO<NUM>H) with the metal oxide core <NUM>.

In some embodiments, the hydrocarbon chain <NUM> may be branched. For instance, the hydrophobic particle <NUM> may be created by reaction of any one of isostearic acid (CH<NUM>(CH<NUM>)<NUM>COOH) and <NUM>-hexyldecanoic acid (CH<NUM>(CH<NUM>)<NUM>CH[(CH<NUM>)<NUM>CH<NUM>]CO<NUM>H) with the metal oxide core <NUM>.

Creation of the hydrocarbon chains <NUM> as described herein can provide the advantage that the resultant hydrophobic particles <NUM> are free from fluorine. This means that the hydrophobic particles <NUM> of the invention have environmental benefits in that they are less toxic when compared to prior art materials.

Referring now to <FIG>, there is shown a polymeric film, indicated generally at <NUM>. The polymeric film <NUM> comprises a substrate <NUM> having the hydrophobic particles <NUM> at least partially embedded therein.

In some embodiments, the polymeric film <NUM> is prepared by depositing, e.g. spraying, the hydrophobic particles <NUM> onto a heated substrate <NUM>. The hydrophobic particles <NUM> may be dissolved or suspended in a solvent. The exposed surface of the substrate <NUM> may be heated until it is softened, followed by deposition of the solution or suspension onto the softened surface. After allowing the solvent to evaporate and the substrate <NUM> to cool the hydrophobic particles <NUM> become at least partially embedded in the substrate <NUM>. The result is a polymeric film <NUM> having a stable, textured and hydrophobic surface. In some embodiments, the substrate <NUM> may be heated by radiation (for example, by infra-red lamps) or by conduction (for example, by placing the substrate <NUM> on a hot plate or by exposing to heated air). It is to be understood that any method that provides sufficient heating to soften the substrate <NUM> without compromising its integrity may be employed.

The choice of solvent is limited only by the need for the solvent to evaporate from the surface of the substrate <NUM>. Suitable solvents include, but are not limited to, isopropanol, toluene and ethanol.

Referring now to <FIG>, there is shown a polymeric film, indicated generally at <NUM>. The polymeric film <NUM> comprises a substrate <NUM>. The hydrophobic particles <NUM> are secured to the substrate <NUM> by an adhesive <NUM>.

In some embodiments, the adhesive <NUM> may be an epoxy resin. The adhesive <NUM> may be applied to the substrate <NUM>, followed by deposition of the solution or suspension containing the hydrophobic particles <NUM>, or vice versa. The adhesive <NUM> is allowed to cure, at which point the hydrophobic particles <NUM> become bonded to the substrate <NUM> by virtue of being at least partially embedded in the adhesive <NUM>.

In some embodiments, the hydrophobic particles <NUM> and the adhesive <NUM> may be mixed and the resultant mixture may be deposited, e.g. sprayed, onto the substrate <NUM>.

Spraying may be effected by dissolving or suspending the mixture in a solvent and utilising a propellant or a compressor as is well known in the industry.

The substrate may comprise a thermoplastic film, e.g. a polyethylene copolymer. The substrate used for all of the subsequent experiments was an EVA/EVA/PVDC/EVA/EVA five layer co-extrusion having a thickness of <NUM> micron.

Aluminium oxide (Al<NUM>O<NUM>) particles having an average diameter of <NUM> were purchased from Sigma-Aldrich.

Iron oxide (Fe<NUM>O<NUM>) particles having an average diameter of from <NUM> - <NUM> were purchased from Sigma-Aldrich.

Isostearic acid was purchased from Nissan Chemical Industries and was used without further purification.

Toluene and isopropanol were supplied by VWR Chemicals.

SP106 Multi-Purpose Epoxy Resin System <NUM> Slow Hardener was purchased from MB Fibreglass.

Spraycraft Universal Airbrush Propellant was used for the spray coating and was purchased from Axminster Tools and Machinery.

WCA measurements were used to study the wettability of the polymeric films.

WCA measurements were obtained by depositing <NUM>µL droplets of H<NUM>O onto the polymeric films. The values of the WCAs that are reported herein are the average of three measurements, recorded at different positions on the surfaces. Standard deviations are used to represent the uncertainties that are associated with these values.

The WCA of the uncoated substrate (i.e. the clean EVA/EVA/PVDC/EVA/EVA five layer co-extruded film) was <NUM>° ±<NUM>°.

The substrate was coated with unfunctionalised Al<NUM>O<NUM> particles. Deposition of the unfunctionalised Al<NUM>O<NUM> particles onto the substrate was achieved through spray coating from <NUM>% wt isopropanolic suspensions at ambient temperature. Three sprays were used to try to achieve maximum coverage of the substrate by the unfunctionalised Al<NUM>O<NUM> particles.

Coating the substrate with the unfunctionalised Al<NUM>O<NUM> particles at ambient temperature resulted in the surface of the polymeric film becoming superhydrophilic. Accordingly, it was not possible to accurately measure the WCA of the resultant polymeric film.

The substrate was coated with unfunctionalised Fe<NUM>O<NUM> particles. Deposition of the unfunctionalised Fe<NUM>O<NUM> particles onto the substrate was achieved through spray coating from <NUM>% wt isopropanolic suspensions at ambient temperature. Three sprays were used to try to achieve maximum coverage of the substrate by the unfunctionalised Fe<NUM>O<NUM> particles.

The WCA of the resultant polymeric film was <NUM>° ±<NUM>°.

Functionalised aluminium oxide (Al<NUM>O<NUM>) particles were synthesised as follows. Aluminium oxide (Al<NUM>O<NUM>) particles (d = <NUM>, <NUM>, <NUM> mmol, <NUM> equiv. ) were refluxed with isostearic acid (<NUM>, <NUM> mmol, <NUM> equiv. ) in toluene (<NUM>) for <NUM> hours. Once the reaction time had elapsed, the reaction mixture was collected and centrifuged at <NUM> rpm for one hour. The solid was then recovered and centrifuged at <NUM> rpm in isopropanol for one hour. Following this, the solid was centrifuged in ethanol at <NUM> rpm for one hour three further times, and then dried at <NUM> for six hours.

The substrate was coated with the functionalised Al<NUM>O<NUM> particles. Deposition of the functionalised Al<NUM>O<NUM> particles onto the substrate was achieved through spray coating from <NUM>% wt isopropanolic suspensions at ambient temperature. Three sprays were used to try to achieve maximum coverage of the substrate by the functionalised Al<NUM>O<NUM> particles.

Functionalised iron oxide (Fe<NUM>O<NUM>) particles were synthesised as follows. Iron oxide (Fe<NUM>O<NUM>) particles (d = <NUM> - <NUM>, <NUM>, <NUM> mmol, <NUM> equiv. ) were refluxed in toluene (<NUM>) with isostearic acid (<NUM>, <NUM> mmol, <NUM> equiv. ) for approximately twenty-four hours, under mechanical stirring. Once the reaction time had elapsed, the mixture was centrifuged at <NUM> rpm for one hour. Following this, the solid was recovered and dried at <NUM> for six hours.

The substrate was coated with the functionalised Fe<NUM>O<NUM> particles. Deposition of the functionalised Fe<NUM>O<NUM> particles onto the substrate was achieved through spray coating from <NUM>% wt isopropanolic suspensions at ambient temperature. Three sprays were used to try to achieve maximum coverage of the substrate by the functionalised Fe<NUM>O<NUM> particles.

The substrate was heated and coated with the functionalised Al<NUM>O<NUM> particles described in Example <NUM>. The functionalised Al<NUM>O<NUM> particles were spray coated onto the substrate once it had been softened as a result of heating. Heating of the substrate was accomplished as follows. First, the substrate was physically attached at its edges to the surface of a glass petri dish. The purpose of this was to secure the substrate in order to limit the extent to which it changed shape during the heating process. Heat was then applied to the petri dish until physical deformation of the substrate was observed. Once physical deformation of the substrate was observed, deposition of the functionalised Al<NUM>O<NUM> particles onto the substrate was achieved through spray coating. The functionalised Al<NUM>O<NUM> particles were spray coated from a <NUM> %wt suspension. Five sprays were used to try to achieve maximum coverage of the substrate by the functionalised Al<NUM>O<NUM> particles. Following each spray, the substrate was continually heated in order to accelerate the removal of the isopropanol. Further spray coating was performed on the substrate when no liquid was observed its surface. The temperature of the substrate was not measured prior to spray coating. However, it was observed that the substrate would start to deform plastically when heated to between <NUM>-<NUM>.

Although this value is slightly lower than when the functionalised Al<NUM>O<NUM> particles were deposited onto the substrate at ambient temperature (Example <NUM>), it is noteworthy that water droplets would readily roll off the polymeric film. Accordingly, this suggests that heating of the substrate during application of the hydrophobic particles does not overly detriment the desired hydrophobic nature of the resultant polymeric film.

In order to determine how well the functionalised Al<NUM>O<NUM> hydrophobic particles bonded to the substrate the polymeric film was sonicated in isopropanol for approximately ten minutes and the WCA was retested.

Following sonication, the WCA of the polymeric film was <NUM>° ±<NUM>°. It is evident that the WCA did not change significantly following sonication which indicates a strong thermal embedding of the functionalised Al<NUM>O<NUM> hydrophobic particles within the substrate.

The substrate was heated and coated with the functionalised Fe<NUM>O<NUM> particles described in Example <NUM> according to the method described in Example <NUM>.

In order to determine how well the functionalised Fe<NUM>O<NUM> hydrophobic particles bonded to the substrate the polymeric film was sonicated in isopropanol for approximately ten minutes and the WCA was retested.

Following sonication, the WCA of the polymeric film was <NUM>° ±<NUM>°. This represents a WCA close to that of the uncoated substrate. This indicates that most of the functionalised Fe<NUM>O<NUM> hydrophobic particles were removed by the sonication. Without being bound to any particular theory, it is understood that functionalised Fe<NUM>O<NUM> hydrophobic particles form relatively large agglomerates on the substrate that are less strongly embedded than, say, functionalised Al<NUM>O<NUM> hydrophobic particles. Accordingly, the functionalised Fe<NUM>O<NUM> hydrophobic particles or more easily removed than the functionalised Al<NUM>O<NUM> hydrophobic particles. However, that is not to say that embodiments incorporating functionalised Fe<NUM>O<NUM> hydrophobic particles are not commercially viable. The sonication test merely seeks to replicate a highly destructive environment to determine the degree of bonding between the hydrophobic particles and the substrate. Hydrophobic films are unlikely to experience such a highly destructive environment in normal use.

Bonding of the functionalised Al<NUM>O<NUM> particles and the substrate by an epoxy resin was studied in examples <NUM> to <NUM>.

In example <NUM>, <NUM> of epoxy resin was added to <NUM> of the functionalised Al<NUM>O<NUM> particles described in Example <NUM> and suspended in <NUM> of isopropanol, such that the mass ratio of functionalised Al<NUM>O<NUM> particles : epoxy resin was approximately <NUM>:<NUM>. Deposition of the mixture onto the substrate was performed through spray coating at ambient temperature, as described previously. Spray coating this suspension onto the substrate resulted in a polymeric film having a WCA of <NUM>° ±<NUM>°.

In examples <NUM> to <NUM>, the ratio of the functionalised Al<NUM>O<NUM> particles and epoxy resin was adjusted.

The functionalised Al<NUM>O<NUM> particle and epoxy resin ratios and the corresponding WCAs for the polymeric films of examples <NUM> to <NUM> are summarised in Table <NUM>. Table <NUM> also shows the WCAs for the polymeric films after they have been sonicated in isopropanol for approximately ten minutes.

Whilst all of examples <NUM> to <NUM> achieved high WCAs, it is clear that polymeric films with the best hydrophobicity were created when the ratio of the functionalised Al<NUM>O<NUM> particles and epoxy resin was from approximately <NUM>:<NUM> (i.e. <NUM> ±<NUM>°) to approximately <NUM>:<NUM> (i.e. <NUM> ±<NUM>°), e.g. <NUM>:<NUM> (i.e. <NUM> ±<NUM>°).

Moreover, as with Example <NUM>, it is evident that the WCAs of Examples <NUM> to <NUM> did not change significantly following sonication. This appears to indicate a strong embedding of the functionalised Al<NUM>O<NUM> hydrophobic particles within the epoxy resin.

Bonding of the functionalised Fe<NUM>O<NUM> particles and the substrate by an epoxy resin was studied in examples <NUM> to <NUM>. The substrate was coated with a mixture of the epoxy resin and the functionalised Fe<NUM>O<NUM> particles described in Example <NUM>. In these examples, epoxy resin was added to the functionalised Fe<NUM>O<NUM> particle suspension. Deposition of the mixture onto the substrate was performed through spray coating at ambient temperature, as described previously.

The functionalised Fe<NUM>O<NUM> particle and epoxy resin ratios and the corresponding WCAs for the polymeric films of examples <NUM> to <NUM> are summarised in Table <NUM>. Table <NUM> also shows the WCAs for the polymeric films after they have been sonicated in isopropanol for approximately ten minutes.

When compared with Examples <NUM> to <NUM>, the WCAs of Examples <NUM> to <NUM> are not as high. However, there is a clear trend that the WCA increases when increasing the ratio functionalised Fe<NUM>O<NUM> particles to epoxy resin. Therefore, it is plausible that the WCA could exceed <NUM>° in embodiments where the functionalised Fe<NUM>O<NUM> particle to epoxy resin ratio exceeds <NUM>:<NUM>.

In summary, the present invention relates to polymeric films that have improved self-cleaning properties by virtue of attaching hydrophobic particles comprising an aluminium oxide core having hydrocarbon chains with from <NUM> to <NUM> carbon atoms to a substrate, such as a thermoplastic film. It has been found that the surface energy of these polymeric films is very low and non-toxic.

Accordingly, the polymeric films can be used in a wide range of applications, including food and liquid packaging. It is also envisaged that the polymeric films can be laminated to a glass, plastics or fabric sheet for improving the hydrophobicity thereof.

It may be useful to tune the WCA at different regions of the polymeric film. In some embodiments, polymeric films may have a first region having an associated WCA measurement and a second region having an associated WCA measurement, whereby the WCA measurements at the first and second regions are different. One way in which this can be achieved is by varying the concentration of hydrophobic particles that are deposited at the first and second regions. For instance, a solution of <NUM> wt% of Al<NUM>O<NUM> hydrophobic particles may be deposited at the first region and a solution of <NUM> wt% Al<NUM>O<NUM> hydrophobic particles may be deposited at the second region. Accordingly, the first region will have a high WCA than the second region due to the high concentration of Al<NUM>O<NUM> hydrophobic particles.

Claim 1:
A polymeric film (<NUM>) comprising a substrate (<NUM>) at least partially coated with hydrophobic particles (<NUM>), the hydrophobic particles (<NUM>) and the substrate (<NUM>) are secured to one another by an adhesive (<NUM>) and wherein the mass ratio of the hydrophobic particles (<NUM>) and the adhesive (<NUM>) is from <NUM>:<NUM> to <NUM>:<NUM>, characterised in that the hydrophobic particles comprise:
an aluminium oxide core (<NUM>); and
a hydrocarbon chain (<NUM>) having from <NUM> to <NUM> carbon atoms,
wherein the hydrocarbon chain (<NUM>) is chemically bound to the aluminium oxide core (<NUM>).