Technical field

The present disclosure relates to the field of plastic films and

compositions and methods for the production thereof. Background

Plastic is the general common term for a wide range of synthetic or semisynthetic organic amorphous solid materials suitable for the manufacture of industrial products. Plastics are typically polymers of high molecular weight, and may contain other substances to improve performance and/or reduce costs.

Many plastic films are manufactured of polyvinylchlohde (PVC) or polyethene (polyethylene) (PE). Plastic films were first made from PVC, which remains the most common material. Non-PVC alternatives are now being sold because of concerns about the risk in transfer of plasticizers from PVC into for example food. It is also problematic to achieve full polymerization of the material, which can contain remains of the vinyl chloride monomer. Further, PVC may generate hydrochloric acid when it is consumed. Also, PVC and PE plastic materials are not biodegradable.

More and more countries over the world are thus concerned about the environmental impact of PVC, as the material is said to be toxic and hard to recycle. Nevertheless, PVC is still often used.

Bioplastics, which are also called organic plastics, are a form of plastics derived from renewable biomass sources, such as vegetable oil, corn starch or microbiota, rather than fossil fuel plastics which are derived from petroleum. Because of their biological degradability, bioplastics are especially popular for disposable items. Biodegradable plastics may however also be produced from petroleum.

Brief description

The inventor has realised that there is a need for a biodegradable plastic that has optical and mechanical properties comparable to the traditional plastics.

It is an object of some aspects of the present disclosure to provide for a composition suitable for forming a cling film. Further, it is an object of some aspects of the present disclosure to provide for a method for forming a cling film.

Further objects of the disclosure in some of its aspects can be gathered by a person skilled in the art after having studied the description below.

The following is a non-limiting and itemized listing of embodiments of the present disclosure, presented for the purpose of providing various features and combinations provided by the invention in certain of its aspects. ITEMS

1. A composition suitable for forming a cling film comprising

a) 75-99 % by weight of a biodegradable, aliphatic-aromatic branched copolyester,

b) 1 -20 % by weight of a biodegradable aliphatic non-branched polyester,

c) a ding-additive and

d) 0-5 % by weight of polylactide. 2. A composition according to item 1 , wherein said biodegradable, aliphatic-aromatic branched copolyester comprises aliphatic and aromatic dicarboxylic acids and an aliphatic dihydroxy compound as monomehc building blocks. 3. A composition according to anyone of the preceding items, wherein said biodegradable, aliphatic-aromatic branched copolyester is comprising monomeric building blocks of

a) an acid component of at least one aliphatic or cycloaliphatic dicarboxylic acid or its ester-forming derivative or a mixture thereof and b) an acid component of at least one aromatic dicarboxylic acid or its ester-forming derivative or a mixture thereof and

c) at least one dihydroxi compound or at least one amino alcohol or a mixture thereof and

d) optionally isocyanurate. 4. A composition according to anyone of the preceding items, wherein said biodegradable, aliphatic-aromatic branched copolyester comprises

monomeric building blocks selected from the group consisting of 1 ,4- butanediol, adipic acid and terephthalic acid.

5. A composition according to anyone of the preceding items, wherein said biodegradable, aliphatic-aromatic branched copolyester is

poly(butyleneadipate terephthalate).

6. A composition according to anyone of the preceding items, wherein said biodegradable, aliphatic-aromatic branched copolyester comprises a monomeric building block selected from the group consisting of mononuclear isocyanurate, binuclear isocyanurate, thnuclear isocyanurate and a mixture thereof.

7. A composition according to anyone of the preceding items, wherein said biodegradable, aliphatic-aromatic branched copolyester comprises

isocyanurate as a monomeric building block.

8. A composition according to anyone of the preceding items, wherein said biodegradable, aliphatic-aromatic branched copolyester comprises

monomeric building blocks of

a) an adipic acid or ester-forming derivatives thereof or a mixture thereof and

b) a terephthalic acid or ester-forming derivatives thereof or a mixture thereof

c) a dihydroxi compound selected from the group consisting of C2-C6- alkanediols and C ₅ -Cio-cycloalkanediols or a mixture thereof and d) optionally a compound containing sulfonate groups.

9. A composition according to anyone of the preceding items, wherein said biodegradable, aliphatic-aromatic branched copolyester comprises epoxide as a monomeric building block. 10. A composition according to anyone of the preceding items, wherein said biodegradable, aliphatic-aromatic branched copolyester has a glass transition temperature of from -35 ^° C to -25 ^° C and a melting range of 105-115 ^° C.

11. A composition according to anyone of the preceding items, wherein said composition is comprising 78-96% by weight, such as 80-95% by weight, such as 85-92% by weight, such as 88-92% by weight, and such as about 90% by weight of the biodegradable aliphatic-aromatic branched copolyester.

12. A composition according to anyone of the preceding items, wherein said biodegradable aliphatic non-branched polyester is selected from a group consisting of polyalkylene succinate adipates and polyalkylene succinates. 13. A composition according to anyone of the preceding items, wherein said biodegradable aliphatic non-branched polyester is selected from a group consisting of polybutylene succinate, polyethylene succinate, polybutylene succinate adipate and polyethylene succinate adipate. 14. A composition according to anyone of the preceding items, wherein said biodegradable aliphatic non-branched polyester is polybutylene succinate.

15. A composition according anyone of the preceding items, wherein said composition is comprising 1 -15% by weight, such as 2-13% by weight, such as 4-11 % by weight, and such as about 5% to about 10% by weight of the biodegradable aliphatic non-branched polyester.

16. A composition according to anyone of the preceding items, wherein said cling additive is selected from mono- and diglycerides.

17. A composition according to anyone of the preceding items, wherein said composition comprises 0.3-1.5% by weight, such as 0.5-1 % by weight, and such as less than 1 % but more than 0.5% by weight of the ding-additive. 18. A composition according to anyone of the preceding items, wherein said composition comprises 1 -5% by weight, such as 1 -3% by weight and such as about 2% by weight of polylactide. 19. Cling film comprising the composition according to any of the preceding items.

20. Use of a cling film according to item 19 for sealing food or food arranged in a tray.

21. Granules comprising the composition according to any one of items 1 - 18.

22. Use of granules according to item 21 for the preparation of a cling film.

23. A process for preparing a composition suitable for forming a cling film, wherein said process comprises mixing of the following components

a) 75-99 % by weight of a biodegradable, aliphatic-aromatic branched copolyester,

b) 0-20 % by weight of a biodegradable aliphatic non-branched polyester,

c) a ding-additive and

d) 0-5 % by weight of polylactide

wherein, during said mixing, said components are subjected to compression of a pressure of 70-200 bar.

24. A process according to item 23, wherein said composition is according to any one of items 1 -18. 25. A process according to items 23-24, wherein the pressure is 80-180 bar, such as 100-150 bar.

26. A process according to anyone of items 23-25, wherein the composition is compressed before the step of film blowing. 27. A process according to anyone of items 23-26, wherein the mixing and compression are carried out using at least one barrier screw. 28. A process according to any one of items 23-27, wherein granules are formed from said composition after said mixing and compression.

29. A method for forming a cling film, comprising blown film extrusion of a composition comprising

a) 80-99 % by weight of a biodegradable, aliphatic-aromatic branched copolyester,

b) 0-20 % by weight of a biodegradable aliphatic non-branched polyester,

c) a ding-additive and

d) 0-5 % by weight of polylactide,

wherein the blow-up ratio in the blown film extrusion is 3-8.

30. A method according to item 29, wherein said composition is according to any one of items 1 -18.

31. A method according to any one of items 29-30, wherein said blow-up ratio is 3-7, such as 4-6, such as 4-4.9.

32. A method according to any one of items 29-31 , wherein the film is stretched by at least 20% in the longitudinal direction after the blown film extrusion.

33. A method according to item 32, wherein said film is stretched by at least 25 %, such as at least 30%, such as at least 40%.

34. A method according to any one of items 32-33, wherein the film is contacted with a first and a second roll, said first roll being arranged upstream the second roll, and the second roll is rotating with a speed which is at least 20% higher than the speed of the first roll, so as to achieve the stretch. 35. A method according to item 34, wherein said speed is at least 25% higher, such as at least 30% higher, such as at least 40% higher. 36. Method according to any one of items 29-35, wherein the components of the composition are mixed and subjected to compression of a pressure of 70-200 bar, such as 80-180 bar, such as 100-150 bar, before the blown film extrusion. 37. Method according to any one of items 29-36, wherein the composition is provided in the form of granules produced according to item 28.

Detailed description

As a first aspect of the present disclosure, there is provided a composition suitable for forming a cling film comprising

a) 75-99 % by weight of a biodegradable, aliphatic-aromatic branched copolyester,

b) 1 -20 % by weight of a biodegradable aliphatic non-branched polyester,

c) a ding-additive and

d) 0-5 % by weight of polylactide.

The cling film may be a thin plastic film which may be used for example for sealing food items in containers to keep them fresh. Cling film, for example sold on rolls in boxes with a cutting edge, clings to many smooth surfaces and can thus remain tight over the opening of a container without the use of adhesive or other devices. Cling film may also be known as cling wrap. The film may have thickness in the range of 5-50 μm.

Biodegradability is the chemical breakdown of materials by a

physiological environment. Biodegradable bioplastics are plastics that can decompose in the natural environment aerobically (e.g. composting) or anaerobically (e.g. landfill). Biodegradation of plastics can be achieved by enabling microorganisms in the environment to degrade the molecular structure of plastic films by metabolism. The plastics may be composed of either bioplastics, which contain components derived from renewable raw materials, or petroleum-based plastics. Under proper conditions

biodegradable plastics may degrade to the point where microorganisms can metabolize them. Degradation of oil-based biodegradable plastics may release previously stored carbon as carbon dioxide.

In the context of the present disclosure, "aliphatic" refers to a compound composed of carbon and hydrogen that do not contain aromatic rings. An aliphatic compound may be cyclic or acyclic and saturated or unsaturated. The carbon atoms can be joined together in straight or branched chains or non-aromatic rings (in this case called alicyclic).

"Polyester" refers to a category of polymers in which the monomeric building blocks are joined together by ester bonds. Further, in the context of the present disclosure, a "copolyester" refers to a polyester which contains more than one type of monomeric building block. The polyester thus becomes a copolyester due to its comonomer content.

"Aliphatic-aromatic copolyester" refers to a compound, in this case a copolyester, which is a compound formed by at least two parts, one aliphatic part which is not containing an aromatic ring and one aromatic part which is containing an aromatic ring. Aliphatic-aromatic copolyesters normally combine the biodegradable properties of aliphatic polyesters with the strength and performance properties of aromatic polyesters.

In the context of the present disclosure, a ding-additive refers to a product which improves the ability of a film to cling to smooth surfaces, such as surfaces of glass, ceramics or plastics. For example, the cling additive may smoothen the surface of the film, thereby improving the cling properties.

Polylactic acid or polylactide (PLA) is a biodegradable, thermoplastic, aliphatic polyester derived from renewable resources, such as corn starch or sugarcanes.

The composition according to the present disclosure is based on the inventor ^' s insight that by combining an aliphatic aromatic branched

copolyester with an aliphatic non-branched polyester together with an addition of a ding-additive and optionally also PLA, a biodegradable composition which is suitable for forming a cling film is produced. The components of the composition have generally been considered not mixable [patent application US 2002/0188071] but the inventor has found that the components are mixable when using certain amounts of the components. Further, the composition of the present disclosure may be used to produce a

biodegradable film of satisfactory optical and mechanical properties. Thus, a composition according to the present disclosure is suitable for forming a film, such as a cling film, which has both high clarity and good cutability.

In the context of the present disclosure, "cutability" refers to how easy it is to tear or cut a film in its latitudinal direction.

In the context of the present disclosure, "clarity" refers to the

transparency to the eye. The "clarity" is thus a visual impression. A clear film is often required to obtain an appetizing impression of food covered by the film.

In an embodiment of the first aspect, the biodegradable, aliphatic- aromatic branched copolyester comprises aliphatic and aromatic dicarboxylic acids and an aliphatic dihydroxy compound as monomehc building blocks. The aliphatic-aromatic branched copolyester may for example contain 95-100 mol% of these three building blocks. In one example, the monomeric building blocks are selected from the group consisting of 1 ,4-butanediol, adipic acid and terephthalic acid. The 1 ,4-butanediol is an aliphatic dihydroxy compound, a diol having the formula HOCH ₂ CH ₂ CH ₂ CH ₂ OH. The adipic acid is an aliphatic dicarboxylic acid having the formula (CH ₂ ) ₄ (CO ₂ H) ₂ . The terephthalic acid is an aromatic dicarboxylic acid with an benzene ring and is having the formula C ₆ H ₄ (CO ₂ H) ₂ .

Copolymerization of aliphatic monomers with aromatic monomers such as terephthalic acid (or diester derivatives such as dimethylterephthalate (DMT)) may be one way to improve the performance properties of aliphatic polyesters. A film containing aliphatic-aromatic branched copolyesters may provide satisfactory transparency, flexibility and anti-fogging performance. The aliphatic-aromatic branched copolyesters are biodegradable.

In one example, the biodegradable, aliphatic-aromatic branched copolyester is poly(butyleneadipate terephthalate).

One example of an aliphatic-aromatic branched copolyester is manufactured by BASF and sold under the trade name Ecoflex. Under this trade name there are a number of different grades. Each grade of polymer has been designed with controlled branching and chain lengthening to possibly match its particular application. Ecoflex is a copolyester comprising 1 ,4-butanediol, adipic acid and dimethylterephthalate (DMT). In some cases, a diisocyanate is used as a chain lengthener.

The structure of Ecoflex is:

Ecoflex is transparent to translucent and has a semi-crystalline structure. The copolyester may used for film extrusion.

By using the new generation product Ecoflex FS BX 7500 (from BASF) instead of the product Ecoflex 7011 (from BASF) in the composition according to the present disclosure, a higher percentage of renewable material may be used. The product Ecoflex 7011 is 100% oil-based whereas the product Ecoflex FS BX 7500 is composed of 38% renewable raw material.

Another aliphatic-aromatic branched copolyester which may be used is manufactured by Eastman Chemical Company and is sold under the trade name Eastar Bio. The copolyester manufactured by Eastman is a copolyester derived from 1 ,4-butanediol, adipic acid and dimethylterephthalate (DMT). Under the trade name Eastar Bio there are a number of different grades. Each grade of polymer has been designed with controlled branching and chain lengthening to possibly match its particular application.

In one embodiment, the biodegradable, aliphatic-aromatic branched copolyester may comprise a monomeric building block selected from the group consisting of mononuclear isocyanurate, binuclear isocyanurate, trinuclear isocyanurate and a mixture thereof. The concentration of such a building block in the polymer may for example be 0.5-5 mol%.

As an example, the biodegradable, aliphatic-aromatic branched copolyester may comprise monomeric building blocks of

a) an acid component of at least one aliphatic or cycloaliphatic dicarboxylic acid or its ester-forming derivative or a mixture thereof and b) an acid component of at least one aromatic dicarboxylic acid or its ester-forming derivative or a mixture thereof and c) at least one dihydroxi compound or at least one amino alcohol or a mixture thereof and

d) optionally isocyanurate.

"Cycloaliphatic" refers to an aliphatic compound containing a cyclic ring. Aliphatic dicarboxylic acids which may used in the present disclosure are generally having 2 to 10 carbon atoms, preferably 4 to 6 carbon atoms. They may be either linear or branched. The cycloaliphatic dicarboxylic acids which can be used in accordance with the present disclosure are for example those having 7 to 10 carbon atoms and, in particular, those having 8 carbon atoms. Specific examples of aliphatic dicarboxylic acids are: malonic acid, succinic acid, sebaic acid, fumaric acid, 2,2-methylglutahc acid, 1 ,3- cyclopentanedicarboxylic acid, adipic acid, glutahc acid, pimelic acid, azelaic acid, maleic acid and suberic acid. It may also be possible to use dicarboxylic acids having a larger number of carbon atoms, for example up to 30 carbon atoms.

Aromatic dicarboxylic acids which may be used in the present disclosure are for example those having 8 to 12 carbon atoms and preferably, those having 8 carbon atoms. Examples of aromatic dicarboxylic acids are:

terephthalic acid, isophtalic acid, 2,6-naphtalic acid and 1 ,5-naphtalic acid. The aromatic dicarboxylic acids or their ester-forming derivatives thereof can be employed singly or as a mixture of two or more thereof.

It is possible in principle to use all diols or amino alcohols able to form esters with the dicarboxylic acids. Examples of suitable alkanediols are:

ethylene glycol, 1 ,2-propanediol, 1 ,5-pentanediol, 1 ,4-butanediol,

cyclopentanediol.

In another embodiment, the biodegradable, aliphatic-aromatic branched copolyester is comprising monomeric building blocks of

a) an adipic acid or ester-forming derivatives thereof or a mixture thereof and

b) a terephthalic acid or ester-forming derivatives thereof or a mixture thereof

c) a dihydroxi compound selected from the group consisting of C ₂ -C ₆ - alkanediols and C ₅ -Cio-cycloalkanediols or a mixture thereof and d) optionally a compound containing sulfonate groups.

The aliphatic-aromatic branched copolyester may thus contain other monomehc building blocks than aliphatic and aromatic dicarboxylic acids and an aliphatic dihydroxy compound. Examples of other components are epoxide, anhydrides, isocyantes and sulfonates. These other components may be used for extending the chain of the molecule.

In one embodiment, the biodegradable, aliphatic-aromatic branched copolyester has a glass transition temperature of from -35 ^° C to -25 ^° C and a melting range of 105-115 ^° C.

In one embodiment, the composition is comprising 78-96% by weight, such as 80-95% by weight, such as 85-92% by weight, such as 88-92% by weight, and such as about 90% by weight of the biodegradable aliphatic- aromatic branched copolyester.

The biodegradable aliphatic non-branched polyester of the present disclosure may be a homopolymer or a copolymer.

In an embodiment of the first aspect, the biodegradable aliphatic non- branched polyester is selected from a group consisting of polyalkylene succinate adipates and polyalkylene succinates. Examples of the

polyalkylene succinate adipates and polyalkylene succinates are polybutylene succinate (PBS), polyethylene succinate (PES), polybutylene succinate adipate (PBSA) and polyethylene succinate adipate. PBS, PES and PBSA are manufactured by Showa High Polymer, LTD, and are sold under the trade name Bionolle. Examples are Bionolle 3001 (PBSA), Bionolle 1001 (PBS) and Bionolle 6000 (PES).

Other examples are polyhydroxybutyrate, copolymers based on polyhydroxybutyrate and polyhydroxyvalerate, poly(hexamethylene glutarate), poly(hexamethylene adipate) and poly(hexamethylenesuccinate). Other examples of aliphatic non-branched polyesters are polyesters from EnPoI and Eastman Chemical. Succinate-based aliphatic polyesters are also

manufactured by Mitsui Toatsu, Nippon Shokubai, Cheil Synthetics, SK Polymers, Misubishi and Sunkyon Industries.

PBS is a biodegradable synthetic aliphatic non-branched polyester. PBS has good mechanical properties and can be applied to a range of end applications via conventional melt processing techniques. PBS is hydro- biodegradable and begins to biodegrade via a hydrolysis mechanism.

Hydrolysis occurs at the ester linkages and this results in a lowering of the polymers ^' s molecular weight, allowing e.g. for further degradation by microorganisms.

In one embodiment, the composition comprises 1 -15% by weight, such as 2-15% by weight, such as 3-13% by weight, such as 4-12% by weight, and such as about 5% to about 10% by weight of the biodegradable aliphatic non- branched polyester. The inventor has produced films using both 5 % and 10 % of the biodegradable aliphatic non-branched polyester with satisfactory results.

In an embodiment of the first aspect, the cling additive is selected from mono- and diglycehdes. Glycehdes, also known as acylglycerols, are esters formed from glycerol and fatty acids. Glycerol has three functional groups, which can be estehfied with one, two or three fatty acids to form

monoglycerides, diglycehdes and triglycerides. The cling additive enhances the stickiness of the film. By producing a film with a sufficient degree of stickiness, the film may for example be used for covering trays or containers with fruits and vegetables.

In one example, the composition comprises 0.3-1.5% by weight, such as

0.5-1 % by weight, and such as less than 1 % but more than 0.5% by weight of the ding-additive. If too much of the cling additive is added, the effect of the addition may be a slippery film. The cling additive may thus become a "slip additive" if its concentration in the film is too high.

In one embodiment, the composition is comprising 1 -5% by weight, such as 1 -3% by weight and such as 2% by weight of polylactide. Polylactide, polylactid acid (PLA) is a linear aliphatic polyester produced by poly- condensation of naturally produced lactid acid or by the catalytic ring opening of the lactide group. PLA tends to be strong but may also be rigid and brittle. Lactic acid may be produced as a co-product of corn wet milling. The ester linkages in PLA is sensitive to both chemical hydrolysis and enzymatic chain cleavage. One company that manufactures PLA is Cargill. As evident from the above, a plastic film, such as a cling film (sometimes referred to as a cling wrap or plastic wrap), comprising the composition is thus provided in the present disclosure. There is also provided a use of such a film for sealing food or food-containing containers. The film may thus be used for sealing fruits or vegetables arranged in trays, which also may be

biodegradable. Consequently, a unit consisting of food arranged in a biodegradable container sealed with a film according to the present invention is biodegradable in its entirety. Consequently, if a piece of food in such a unit is to be disposed, the different components of the unit do not have to be separated from each other before composting. Accordingly, a piece of fruit wrapped in a film according to the present disclosure does not have to be separated from the film before composting.

Another area of use is plastic wrapping of pallets, especially loaded pallets loaded with goods, such as timber pallets.

Granules comprising the composition can also be obtained according to the present disclosure. Granules are particles of a substance. Granules comprising the composition according to the present disclosure may be a convenient way of storing the composition. It is also beneficial to add the composition of the present disclosure in a film making process in the form of granules.

As a second aspect of the present disclosure, there is provided a process for preparing a composition suitable for forming a cling film, wherein said process comprises mixing of the following components

a) 75-99 % by weight of a biodegradable, aliphatic-aromatic branched copolyester,

b) 0-20 % by weight of a biodegradable aliphatic non-branched polyester,

c) a ding-additive and

d) 0-5 % by weight of polylactide,

wherein, during said mixing, said components are subjected to compression at a pressure of 70-200 bar.

The composition used in the second aspect may be the composition according to any one of the embodiments of the first aspect. Thus, components a)-d) may be a)-d) according to any one of the embodiments of the first aspect.

In embodiments of the second aspect, the pressure is 80-180 bar. In other embodiments the pressure is 100-150 bar. The pressure may be measured in the extruder at the end of the barrier screw.

The composition obtained by the above mentioned process may be used for forming a film, such as a cling film, and film forming may be performed by using blown film extrusion.

The composition of the second aspect is thus comprising a

biodegradable aliphatic-aromatic branched copolyester and a ding-additive. Additions of a biodegradable aliphatic non-branched polyester and polylactide are optional.

The mixing and compression is normally performed prior usage in a blown film extrusion process. The components of the second aspect have generally been considered unmixable, at least to such a degree that a clear film may be obtained. However, the inventor has found that by using said degree of compression, a clear film may be obtained. For example, the components may be mixed and compressed at one site and then delivered, e.g. in the form of granules, to another site where blown film extrusion is performed.

Another possibility is to mix the components under compression in connection with the blown film extrusion process. In such cases, components may be added to a hopper connected to an extruder which contains a rotating barrier screw, in which the components are mixed. The extruder may also comprise kneading elements. Inside the extruder, the pressure is increased during the mixing.

Consequently, the blown film extrusion process of the present disclosure may utilize a pre-compressed composition or comprise a step of mixing and compressing the components of the composition.

In a third aspect of the present disclosure, there is provided a method for forming a cling film comprising blown film extrusion of a composition comprising a) 80-99 % by weight of a biodegradable, aliphatic-aromatic branched copolyester,

b) 0-20 % by weight of a biodegradable aliphatic non-branched polyester,

c) a ding-additive and

d) 0-5 % by weight of polylactide,

wherein the blow-up ratio in the blown film extrusion is 3-8.

The composition of the third aspect is thus comprising a biodegradable aliphatic-aromatic branched copolyester and a ding-additive. Additions of a biodegradable aliphatic non-branched polyester and polylactide are optional.

The composition used in the third aspect may be the composition according to any one of the embodiments of the first aspect. Components a)- d) may thus be a)-d) according to any one of the embodiments of the first aspect.

The "blow-up ratio" is the ratio between the diameter of the blown film and the diameter of the outlet of the tool pumping out the molten plastics (i.e. the diameter of the outlet of the die).

In embodiments of the present disclosure, the diameter of the outlet of the die may be 100-500 mm.

The inventor has found that a blow-up ratio of 3 or more results in a film having a satisfactory cutability. Without being limited by any specific theory, the inventor believes such a blow-up ratio orients polymers of the film such that an angle is formed between the extension direction of polymers and the extension direction of the film, which in turn results in increased cutability.

The blow-up ratio may for example be higher than 3, such as higher than 4, such as higher than 5, such as higher than 6

In embodiments of the present disclosure, the blow-up ratio is 3-7. In other embodiments, the ratio is 3-6. In yet other embodiments, the blow-up ratio is 4-6. For example, the blow-up ratio can be higher than 4 and below 5, such as 4-4.9.

In one embodiment of the present disclosure, the film is stretched by at least 20% after the blown film extrusion. In another example, the film is stretched at least 25 %, such as at least 30%, such as at least 40%.

The stretch is also called "pre-stretch". The stretch is performed in the Y- direction, which is the direction of the extension of the film. Sometimes this direction is also referred to as the longitudinal direction or machine direction. The "pre-stretch" in combination with the composition and the blow-up ratio improves the cutabilty and the clarity.

To achieve such stretch, the film may be contacted with a first and a second roll, wherein said first roll is arranged upstream the second roll, and the second roll is rotating with a speed which is at least 20% higher than the speed of the first roll. "Upstream" and "downstream" refer to relative positions along the film-making process.

In one example, the speed is at least 25% higher. In yet another example the speed is at least 30% higher or at least 40% higher.

Blown film extrusion is a process by which many commodity and specialized plastic films are made for the packaging industry. The film blowing process basically consists of extruding a tube of molten thermoplastics and continuously inflating it to above its initial diameter, forming a thin tubular product that can be used directly (for example when forming plastic bags or sacks), or may be slit to form a flat film (for example for forming a sheet).

The components of the thermoplastics (here the components of the "composition") may be added to a hopper arranged at an extruder which may contain at least one barrier screw. The mixing of the components may be performed under compression (see above).

Another possibility is to add a prepared composition, in which the components have already been mixed under compression, to the hopper. In such case, the composition may for example be in a form of granules (see above).

In another example, a mixer/kneader may be employed that operates in conjunction with at least one screw compounding extruder to improve the mixing efficiency. In operation, the at least one kneading element, tooth or pin, moves through the slots of the screw flights to create an efficient mixing action of the melt being pumped there between.

The mixture of the components is heated and conveyed through the extruder to a die. The die is the component on the extruder through which the melt is pushed to form the desired profile. The die may be an upright cylinder with a circular opening. The diameter can be a few centimeters to more than three meters across. The die gap is the width of the gap through which the melted thermoplastics is pushed to form a blown film. In embodiments of the present disclosure, the die gap may be 0.5-2.5 mm, such as 0.9-1.7 mm. An air-ring may be provided around the die. The air-ring may cool the film as it travels upwards. Also, compressed gas, usually air, from an air outlet can be forced into the centre of the extruded circular profile, creating a bubble. This may expand the extruded circular cross section by some ratio (a multiple of the die diameter) to a desired diameter.

The pressure inside the bubble is normally such that the tube stretches, increases its diameter and reduces its wall thickness to desired gauge. The gas may be contained within the bubble by the die and a pair of nip rolls disposed downstream from the die.

Such a pair of nip rolls, e.g. arranged high above the die, may also pull the molten plastics upwards from the die (for example 4 meters to 20 meters or more depending on the amount of cooling required). The nip rolls can provide the force to pull the bubble away from the die in a machine direction at a desired speed. Changing the speed of these nip rolls can change the gauge (wall thickness) of the film.

As the warm, extruded material is drawn up several lengths by nip rolls, the air inside the expanded tube normally has three basic functions. First, the volume and pressure of air blown into the tube causes the material to stretch, thereby determining the overall size of the bubble and the width of the finished sheet. Secondly, the same action, in conjunction with the rate at which the bubble is pulled upward away from the die, determines the thickness of the finished film. Thirdly, the bubble begins the air-cooling process while traveling up to the nip rolls. The rate of the extrusion of the melt, the rate of the speed of the nip rolls, and the degree of inflation of the bubble can together determine the final thickness of the film.

In the next step, nip rolls may flatten the bubble into a double layer of film whose width (called "layflat") is equal to 14 the circumference of the bubble.

Between the die and the nip rolls, the melt can cool, and undergo a phase change to the crystalline state. A so called "frost line" may be observable at the point of the bubble at which the phase change occurs.

The film can thus be cooled down to its crystalline temperature range when it is produced. The film may be cooled on both sides, i.e. on both the outside and the inside of the tubular plastic film during the blown film production. The cooling operation may be carried out with different

temperatures on the two sides of the plastic film. When stretching the film, so called "pre-stretch" (see above), the film can be drawn by rolls rotating at different speeds of rotation such that the sheet is stretched to a desired draw ratio in the longitudinal direction

(machine direction). The draw ratio may be determined by dividing the linear speed of the film exiting the stretching operation by the linear speed of the film entering the stretching operation.

After stretching, the film may optionally be heat-set to stabilize the stretched film.

The film may also be slit and in that case it enters a slitter station. One or both sides of the flat tubular film may be slit.

The film may finally be rolled up on windup rolls. For example, the film take-up speed may be 15-60 m/min. The film produced may have a width of 1100-1500 mm and may have a thickness of 8-20 μm.

It is possible to anneal the plastic film before it is rolled up. The annealing step is optional. For example, annealing can be performed using heat, such as for example infrared heat. Annealing may reduce any internal stresses that may result from the manufacturing process. Annealing may improve the mechanical properties of the film. A result may be that the material will remain dimensionally stable during and after machining. A film subjected to annealing may more easily return to its original position after being exposed to pressure, for example in the form of a pressing thumb, than a film not subjected to annealing.

The processing of the composition on extrusion lines may depend on the composition, the extrusion technology and the processing conditions. Guided by the present disclosure, the skilled person may without undue burden optimize these parameters to achieve a satisfactory quality of the final product.

The concept of the present disclosure has several advantages, of which some are discussed below.

One advantage is the biodegradability. The composition may be biodegraded and only carbon dioxide, water and biomass are produced.

Another advantage is that the permeability of moisture through a film comprising the composition according to the present disclosure may be enhanced compared to other plastics or bioplastics. For example, the sustainability of fruits and vegetables may be enhanced when they are stored covered by a film comprising a composition according to the present disclosure, due to the moisture permeability properties of the film. Another area of use is plastic wrapping of pallets, especially goods loaded pallets, for example timber pallets. A film comprising the composition according to the present disclosure is permeable to moisture and hence, a film according to the present disclosure wrapped around pallets does not need to be perforated in order to prevent condensation.

Another advantage is that it is possible to tear or rip a film according to the present disclosure in the latitudinal direction. This is particularly beneficial in machinery which cuts pieces of the film and wraps food products in such pieces. Consequently, it is generally possible to use the film in conventional packing machines. These packaging machines may be used for packaging fruits and vegetables in trays or containers. Major adjustment of the packaging machine may not be necessary when using this new cling film comprising the composition according to the present disclosure. The tear and rip properties are also beneficial when forming pieces of the film from a roll in box with a cutting edge.

Yet another advantage is that the components of the composition generally do not need to be pre-dhed before mixing.

Brief description of figures

Fig 1 is a schematic representation of a blown film extrusion process.

Detailed description of example embodiments

A non-limiting embodiment of a method of the present disclosure is described in more detail below.

Example 1

In this example, the blown film is prepared by mixing 93 % by weight of

Ecoflex, 5 % by weight of Bionolle and 2 % by weight of a ding-additive (a glycehde). Ecoflex is bought from BASF and Bionolle from Showa High Polymer. The components are mixed and compressed prior the blown film extrusion process.

The composition, in the form of granules, is added to a hopper 1 arranged at an extruder 2 which contains one barrier screw 3 with extrusion elements 4. The barrier screw 3 has a smaller diameter in the end of the extruder 2 where the material is added via the hopper 1 compared to the end where the thermoplastics is leaving the extruder 2. As the diameter of the barrier screw 3 increases along the extruder 2, the pressure inside the extruder 2 increases. The barrier screw 3 rotates with the help of a screw drive motor 5.

In this example, the components of the composition are added to the hopper 1. The material is successively compacted and melted to form a continuous viscous liquid. A pressure is developed on the molten resin inside the extruder 2. The pressure is usually in the range of 70-200 bar. The melted thermoplastics has a temperature in the range of 160-180 ^° C before it leaves the extruder.

The melted material is pumped through a circular, rotating die 6. The die 6 is the component on an extruder 2 affixed to the extruder head 7 through which the melt is pushed out. The die is an upright cylinder with a circular opening. The diameter of the circular opening of the die 6 is about 300 mm. The die gap 8 is 1.3 mm. In this example, the blown film extrusion is carried out vertically upwards.

Around the die an air-ring 9 is arranged. The air-ring 9 cools the film 10 as it travels upwards. The temperature of the air is about 20 ^° C. Also, compressed air from an air outlet is forced into the centre of the extruded circular profile in the beginning of the process and the pressure causes the extruded melt to expand into a bubble. An even and constant pressure is maintained to ensure uniform thickness of the film since the nip rolls 12a and the die 6 prevent leakages.

The extruded circular cross section is expanded by some ratio to a desired diameter. This ratio is called blow up-ratio, which is the ratio between the diameter of the blown film 11 and the diameter of the circular opening of the die. The blow up ratio can be 3-8:1. The polymer angle after the blow-up may be about 45%. The pressure is such that the tube stretches, increasing its diameter and reducing its wall thickness to desired gauge.

The molten plastics is pulled upwards from the die 6 by a pair of nip rolls 12a arranged above the die. The gas is contained within the bubble by the die 6 and by the pair of nip rolls 12a. The nip rolls 12a provide the force to pull the bubble away from the die 6 at a desired speed. Changing the speed of these nip rolls 12a can change the gauge (wall thickness) of the film.

The volume and pressure of air blown into the tube causes the material to stretch, thereby determining the overall size of the bubble and the width of the finished sheet. The volume and pressure of the air blown into the tube and also the rate at which the bubble is pulled upward away from the die 6, determines the thickness of the finished film. The bubble begins the air- cooling process while traveling up to the nip rolls 12a. Between the die 6 and the nip rolls 12a, the melt can cool, and undergo a phase change to the crystalline state.

The film 10 moves into the set of nip rolls 12a which collapse the bubble and flatten the bubble into a double layer of film 13 which width (called "layflat") is equal to 14 the circumference of the bubble.

The film 13 passes through idler rolls 14 during this process to ensure that there is uniform tension in the film 13. When stretching the film, so called "pre-stretch", the film is drawn by a second pair of nip rolls 12b rotating at a higher speed than the first pair of nip rolls 12a such that the sheet is stretched to the desired draw ratio in the longitudinal direction (machine direction). The draw ratio is determined by dividing the linear speed of the film exiting the stretching operation by the linear speed of the film entering the stretching operation. For example, a roll "downstream" rotates with a higher speed than a roll "upstream" and hence a stretching of the film is performed. The film may for example be stretched with 25%, which means that the roll "downstream" rotates with a speed 25% higher than the rotation of the roll "upstream".

The stretching, or pre-stretch ing, of the film increases the clarity of the film. In combination with a large blow-up ratio the stretching improves both mechanical and optical properties of the film, for example the cutability and clarity.

Finally, the film is pulled onto windup rolls 15. The film take-up speed is about 15-60 m/min. Between the nip rolls 12b and the windup rolls 15, the film 13 can pass through a treatment centre depending on the application. During this stage, the film is in this example split to form two films.

The thickness of the film is in the range of 8-20 μm and the width of the film is in the range of 1100-1500 mm.