- _v l - PACKAGING FILMS

FIELD OF THE INVENTION

The present invention relates to flexible water dispersible films having different water dispersion rates on the two sides of the films .

The term "dispersion" in this context is understood to cover both breakdown of a film into smaller sections, or particulates, on contact with water and also dissolution of a film on contact with water. It should be further understood in this context that when a dispersable film is broken down in water then it is possible for it to breakdown into either particulates that, while invisible to the eye, will eventually settle out giiren the opportunity, or fully. soluble molecules that will not settle out.

BACKGROUND OF THE INVENTION Water dispersible flexible filmέ may be used, for example, for wrapping materials when the materials need to be wrapped securely for an extended period and then released automatically and where flexible 1 film residues would be disadvantageous .

Water soluble flexible films of -many types are known in the art. Polymeric resins such 4s poly vinyl alcohol, polyacrylates , polymethacrylates j and others are disclosed in patent literature for use as {water soluble films.

Applications of such films include, for example, wrapping dry products, as disclosed in US ,7, 005,168, and wrapping low water activity liquids such as detergents or fabric conditioning compositions.

Significant development work has been performed on the use of modifiers to change the rate of dissolution of films and the water activity of dissolution, and to modify films to be insoluble in the presence of certain materials in water, such as selected surfactants.

Another application of water soluble flexible films is as carriers for ingestible pharmaceutical preparations. Polymers for making such films include, for example, poly vinyl alcohol, as disclosed, in US 5,948,430, and Pullulan (Trade Mark), as disclosed in US 7,025,983, as carriers for portable mouthwash compositions.

λ common feature of the art, and a limitation in certain potential applications, is the limited range of solubility properties of the films of the art.

Films of the known art are either slowly soluble, or rapidly soluble, or are only soluble in specific chemical environments.

It is possible to wrap hazardous materials having a high water activity (the ratio of the vapor pressure of the material divided by the vapor pressure of pure water at the same temperature — a high ratio indicates a high level of available water molecules in the _j material) with water insoluble films, such as common commodity polyethylene films, before disposal. This has traditionally been acceptable, for example, in medical waste applications, which are disposed by landfill or incineration .

For more benign waste materials; such as human excreta, the usual final disposal is into, a sewer for biological processing.

An alternative to direct sewer disposal for benign waste materials is portable toilets.

A known issue with most toilets: is the need to carry significant amounts of water for flushing. This is most critical, for example, in aircraft, where a significant weight of water is carried fo± the sole purpose of flushing lavatories, and this weight increases the energy consumption of aircraft.

In the modern world of rising energy pricing, and consciousness of pollution, the use of water for lavatory flushing in aircraft is wasteful. However, no viable alternate system has yet been developed.

The need for water for rinsing can also be an issue in other applications where water mdy be scarce or costly.

Another potential solution for disposal of benign waste materials is to wrap the waste in biodegradable t polymer films that can later be treated by biodegradation with the waste in a conventional water based treatment facility. For example, a lavatory could ba designed to wrap human waste in this way. There would be other applications for this waste disposal system. A desirable film for such application must be highly resistant to warm water contact prior to wrapping waste and!readily dispersible after use.

SUMMARY OF THE INVENTION

The applicant has developed a w^ter dispersible flexible film that includes a water dispersible biodegradable film substrate and a coating on one or both sides of the film that provides differential water resistance on the opposite sides of the film.

In the following disclosure, "water resistance" is understood to mean the elapsed time of contact of pure water at 23 ⁰ C on the surface of a film, substrate or coated film required to reduce the tensile strength of the film, coated film or substrate to less than 10% of its original uncoated tensile strength.

The tensile strength may be determined by any means known in the art .

According to the present invention there is provided a water dispersible flexible film that includes a water dispersible substrate and a coating on one side or a first side of the substrate that provides water resistance that slows water degradation of the film when the first side of the film is contacted by wet substances compared to water degradation of the film that occurs when the other side or second side of the substrate is contacted by wet substances .

The second side of the substrate may be uncoated.

Alternatively, the second side of the substrate has a coating that provides a lower water resistance than the coating on the first side of the substrate. In other words, the rate of degradation when water contacts the second side is less than rate of degradation when water contacts the first side.

According to the present invention there is also provided a package made from the above-described water dispersible flexible film that is designed to retain wet contents within the package for a required period of time and which readily degrades when the film is contacted by wet substances on the outside of the package.

In the above-described package, the first side of the film that has higher water resistance; forms the inside of the package .

According to the present invention there is also provided a method of handling liquid containing materials that includes packaging the materials in packages made from the above-described water dispersiblø flexible film, whereby the film releases the contents of; the packages through wetting the outside of the packages, wherein the packages fail through external and not internal wetting of the packages .

In the simplest form, the water 'dispersible flexible film of the present invention includes a water dispersible substrate that has a water resistance of less than one hour, preferably less than 10 minutes, and most preferably less than 2 minutes , and a hydrophobic coating on one side of the substrate.

The hydrophobic coating may be e^f any composition .

Suitable hydrophobic coatings comprise waxes, polymeric resins, fats and oils, proteins ,or other biologically sourced materials .

The hydrophobic coating is selected to modify the water resistance of the water dispersible Jflexible film on that side of the substrate.

Desirably, the substrate is a flexible biodegradable film according to European Standard EN13432- 2000.

An example of a suitable substrate is a flexible starch based film ("Plantic ^® film") as described in US

patents 5,316,578 and 5,346,936, International applications PCT/AU2005/000794, PCT/AU2005/001507 and PCT/AU2005/001605, US patent application 10/474907 and others in the name of Plantic Limited.

Desirably, the substrate, in the absence of water, has comparable flexibility and tenacity to low density polyethylene (LDPE) . The term "tenacity" in this context is used generically to summarize the resistance of the substrate to tear, puncture or fracture.

It will be understood by those skilled in the art that any biodegradable polymeric film having the required mechanical strength and desirably low water resistance may be used in place of Plantic® film.

Also desirably, the coating is a biodegradable coating. Example coating materials are aliphatic polyesters, although other materials may be suitable.

More preferably, the coating material is degradable according to European Standard EN13432-2000.

Most preferably, the coating material is degradable under aquatic or other environmental conditions, and does not display significant ecotoxicity.

As an example, a preferred watei dispersible flexible film is based on a Plantic® film isubstrate. The Plantic® film is marketed by Plantic® as ^Rl" and comprises chemically modified high amylase starch, native starch, water soluble polymer, a stearatθ, and water, and has a water resistance of less than one minute.

As an example, the film includes a polyester coating on one side of the above-described Plantic® film

substrate that provides a water resistance on the coated side of greater than 6 hours .

A preferred coating is sold as ^Rapidly Biodegradable Hydrophobic Material" (RBHM) by Polymate Ltd of Israel . A coating such as RBHM is preferred due to the certified biodegradation of the coating. Other polyester coatings, or coatings of other chemical nature, either specifically developed for the application or already available in the market are within the scφpe of the present invention .

The applicant found through experiments that a normally rapidly dispersible film such as ' Plantic® Rl film has a water resistance of greater than 6 hours when coated with 3 grams per square metre of the RBHM' coating as described above.

The applicant found through experiments that a coating weight between 1 and 10 grams per j square metre dry weight is suitable where the coating is RBHM.

The applicant found in early experiments that a nominal coating of 3 grains per square metre works well , but other applications may require different coating weights and are within the scope of the present invention.

The selection of preferred coating weights will be understood by those skilled in the art :to be a process of determining the relative performance of proposed coatings at a range of weights to optimize cost and performance .

The coating can be applied by any convenient means .

Should the coating material be thermoplastic, extrusion coating, or even coextrusion with the substrate may be preferred.

If the coating is not thermoplastic, solution coating methods are preferred.

Suitable solution coating methods are roller coating, rod coating, gravure coating, flexographic coating, spray coating, and bath coating.

The choice of coating method is not important to the practice of the present invention, except that an essentially continuous coating is particularly preferred for the practice of the invention

It can be readily appreciated that if the coating is only applied to the inside of a sealed package formed from the water dispersible film of the present invention, the package will have sufficient water resistance not to "disperse" (i.e. break down due to solubilization or mechanical failure of the material in the! liquid - breaking down may lead to total disappearance of the film) within an extended period of contact by a waste having a high water activity that is contained in the package, but wetting the outside of the package, say daring waste management or treatment, will rapidly disperse the packaging film. The coating will not be strong enough to hold the package together once the substrate has been dispersed.

It will be understood by those skilled in the art of material science, which is the relevant technology field for the present invention, that even an intrinsically strong coating material, at a sufficiently thin gauge, will be fragile enough to disperse once the film substrate begins to disperse.

fl ¬

it will also be appreciated by those persons that it should be possible to apply a coating on the other side of the film, with similar or differing water resistance depending the needs of a user .

A film coated on one side with the above coating can be mechanically applied to a solid receptacle, such as a toilet in an aircraft, and accept wastes including liquid of water activity up to 1.0, and remain stable for an extended period. ' i In one embodiment, the water dispersible film of the present invention is indexed through a disposal hatch, sealed if desired, and then severed.

In preparation for later disposal, contact with liquid water on the opposite side of the film weakens and pre-disperses the film, so the waste material can be pumped.

Simple rinsing with water is sufficient to break down any residual film sections to a pumpable consistency.

The use of the water dispersible film of the present invention, as exemplified above, permits the reduction of the cartage of water in aircraft, and allows the final waste product to be treated as a. normal sewer discharge, thus requiring no infrastructure other than the modified lavatory .

The above-described water dispedsible film of the present invention is not intended to be limited by the above description thereof.

For example, other starch polymer blends comprising film modifiers , sugar alcohols ,; polyols , and

ester plasticizers are suitable. Films shpwing acceptable tenacity and flexibility, and having acceptably low native water resistance, are also within the scope of the present invention .

Other water dispersible polymers, based for example on cellulose rather than starch, may also be used.

There may also be other applications which will benefit from a controllable rate of dissolution apart from those as disclosed in the above description of the present invention .

One example is wrapping fresh food by a delicatessen in an edible version of the film, where the food is cooked, heated or otherwise prepared by placing the unopened packaging into cold or hot wφter.

Another example is sterile packaging of small volumes of medical or pharmaceutical products, which are swallowed by the patient.

A further application is the us^ of the film of the present invention in disposable medical applications . Example applications include flushable colostomy bags and vomit collection bags that are currently Constructed from non-dispersible polymers .

The use of coating materials with very long water resistances makes it possible to prepare film-based packaging for carrying liquids of high water activities that are easily disposed by rinsing down & sink once the contents have been removed.

Many modifications may be made tio the embodiments of the present invention described above Without departing from the spirit and scope of the invention.