Biaxially oriented biodegradable film

Abstract

A skin film layer, a sealant film layer, and a combination of a sealant film layer and a skin film layer, wherein the sealant film layer and the skin film layer each contain a blend of 0 to about 80 wt.% polyhydroxyalkanoate (PHA) and about 20 to about 100 weight percent polylactic acid (PLA), and optionally, a small amount of other biopolymers, other polymers, nucleating agents, chain extenders, fatty amides, and fillers; the skin film layer, the sealant film layer, and the combination of the sealant film layer and the skin film layer; and a core film layer containing a blend of about 30 to about 80 wt.% polyhydroxyalkanoate (PHA), about 20 to about 40 wt.% polylactic acid (PLA), and optionally, a small amount of other biopolymers, other polymers, nucleating agents, chain extenders, fatty amides, and fillers; a biaxially stretched industrially or home-compostable film web having at least three coextruded layers selected from the above.

Description

Technical Field

[0001] Related Applications This application is a continuation-in-part of provisional application No. 63 / 369,997, filed on August 1, 2022, which is currently pending.

[0002] Technical Field The present disclosure is directed to biodegradable films, and more specifically, to methods for improving the dimensional stability of poly(hydroxyalkanoate)-based polymer films.

Background Art

[0003] Background and Overview Polymeric films are used in a variety of flexible packaging applications, including food packaging. Polymeric films are typically used in bag-making and heat-sealing processes that are widely used in flexible packaging. The stability of polymeric films is extremely important for maintaining product quality and preventing food quality deterioration during storage. Bag-making and heat-sealing processes are generally carried out at high temperatures. Semi-crystalline polymeric films tend to shrink as they are cooled from high temperatures. The degree of shrinkage depends greatly on the composition of the film material and the processing conditions used in the production of the film. Semi-crystalline materials shrink more than amorphous materials. Dimensional instability or shrinkage of the film during or after cooling from high temperatures plays a significant role in the overall quality of the final product. Significant shrinkage during or after the bag-making or heat-sealing process can contribute to several defects in the final product, including leakage, risk of pinhole formation, and breakage of the seal area.

[0004] Conventional polymer films are typically not industrially or home compostable and, therefore, contribute to environmental waste that must be disposed of. Biodegradable poly(hydroxyalkanoate)-based polymer films can also shrink upon cooling from high temperature to room temperature. The shrinkage characteristics of poly(hydroxyalkanoate)-based films cause significant problems during coating, metallization, lamination, printing, bag making, and sealing processes in which the films are used. In poly(hydroxyalkanoate)-based polymer films obtained from conventional inflation film processes, the shrinkage rate measured in the machine direction (MD) at 110 °C is 45% - 50%. The temperature selected for shrinkage rate measurement is the temperature used in most of the film's post-treatment facilities. The shrinkage rate values of poly(hydroxyalkanoate)-based polymer films are significantly higher compared to other polymer films that are industry standards of less than 5%. Therefore, what is needed is an improved process for making home compostable poly(hydroxyalkanoate)-based polymer films that provide significantly lower shrinkage rates when used in packaging applications.

[0005] Stretched films are produced from plastic granules in which extrusion and stretching are performed by applying uniaxial or biaxial stretching. The film can be stretched in the machine direction (MD) only, the transverse direction (TD) only, simultaneously in MD and TD, or consecutively in MD and TD. Consecutive stretching (i.e., stretching in TD after stretching in MD) is the most common method for commercially producing biaxial stretched films. A typical biaxial stretching process can include one or more of the following steps in the order described: 1. Cast a relatively thick sheet of plastic from a slot die and rapidly cool it on a chill roll. 2. Use heating rollers to stretch the cast sheet of the film in the machine direction (by raising the temperature of the plastic above its glass transition point (Tg)). The rollers consist of a series of nips that rotate at a progressively faster speed than each preceding nip. 3. Stretch the machine direction (MD) sheet of the film in the transverse direction by gripping each edge of the film with clips that circulate on a continuous chain. As the clips pull the sheet forward, the track carrying the clips deviates to pull the plastic in the transverse direction. 4. Pass the now relatively thin film (under uniform MD and TD tension) through a warm oven by means of clips and continuously convey it to anneal the plastic film. 5. After annealing, apply any necessary surface treatment to the film. Cut off the thick edges of the film fixed by the clips gripping the ends and wind back the film. Stretched films can acquire various advantageous properties due to the change in the form of the molecular structure of the film as a result of the stretching process. Examples of such advantageous properties include optimal physical properties (e.g., rigidity and tear strength), good optical characteristics (e.g., transparency or gloss), and enhanced barrier properties. Compared with other packaging materials, stretched films are lightweight and energy-efficient in production.

[0006] The main materials for biaxially stretched films are polypropylene, polyester, and polyamide. Polyethylene and polylactic acid are also biaxially stretched in commercial processes and used in commercial packaging applications. Although there are exceptions for polylactic acid, conventional biaxially stretched films are made from non-biodegradable petroleum-based materials. From the foregoing perspectives, what is needed is an industrially and / or home-compostable biaxially stretched film for use as printable films and barrier films that can be converted into packaging structures meeting the performance requirements of various packaging applications and the necessary end-use certifications.

[0007] From the foregoing perspectives, there is provided an industrially and / or home-compostable biaxially stretched composite film that can be produced using the materials and methods described herein.

[0008] In one embodiment of the present disclosure, there is provided a skin film layer, a sealant film layer, and a core layer, wherein the sealant film layer and the skin film layer each comprise a blend of from 0 to about 80 wt.% polyhydroxyalkanoate (PHA) and from about 20 to about 100 weight percent polylactic acid (PLA), and optionally, small amounts of other biopolymers, other polymers, nucleating agents, chain extenders, fatty amides, and fillers, and a core film layer comprising a blend of from about 30 to about 80 wt.% polyhydroxyalkanoate (PHA), from about 20 to about 40 wt.% polylactic acid (PLA), and optionally, small amounts of other biopolymers, other polymers, nucleating agents, chain extenders, fatty amides, and fillers, and at least three coextruded layers selected from the skin film layer, the sealant film layer, and the core film layer, are provided. The core film layer is disposed between a combination of the skin film layer and the sealant film layer, between two sealant film layers, or between two skin film layers, and the sealant film layer and the skin film layer each contain the same or different amounts of PHA, PLA, and other biopolymers, other polymers, nucleating agents, chain extenders, fatty amides, and fillers.

[0009] In another embodiment, a method for improving the dimensional stability of a biaxially stretched industrially or home-compostable film web comprising at least three coextruded layers is provided. The method includes extruding a composite poly(hydroxyalkanoate)-based polymer film and annealing the composite poly(hydroxyalkanoate) polymer film at a temperature in the range of about 110 °C to about 130 °C during a biaxial stretching process.

[0010] In some embodiments, the biaxially oriented industrially or home-compostable film web comprises at least two sealant film layers comprising a blend of about 0 to about 80 wt.% polyhydroxyalkanoate (PHA) and about 20 to about 100 weight percent polylactic acid (PLA), and optionally other biopolymers, other polymers, nucleating agents, chain extenders, fatty amides, and fillers, wherein the two sealant film layers can each have the same or different amounts of PHA, PLA, and other biopolymers, other polymers, nucleating agents, chain extenders, fatty amides, and fillers; and a core film layer comprising a blend of about 30 to about 80 wt.% polyhydroxyalkanoate (PHA), about 20 to about 40 wt.% polylactic acid (PLA), and optionally small amounts of other biopolymers, other polymers, nucleating agents, chain extenders, fatty amides, and fillers, wherein the core film layer is disposed between the at least two sealant film layers.

[0011] In some embodiments, the biaxially oriented industrially or home-compostable film web comprises at least two skin film layers comprising a blend of about 0 to about 80 wt.% polyhydroxyalkanoate (PHA) and about 20 to about 100 weight percent polylactic acid (PLA), and optionally other biopolymers, other polymers, nucleating agents, chain extenders, fatty amides, and fillers, wherein the two sealant film layers can each have the same or different amounts of PHA, PLA, and other biopolymers, other polymers, nucleating agents, chain extenders, fatty amides, and fillers; and a core film layer comprising a blend of about 30 to about 80 wt.% polyhydroxyalkanoate (PHA), about 20 to about 40 wt.% polylactic acid (PLA), and optionally small amounts of other biopolymers, other polymers, nucleating agents, chain extenders, fatty amides, and fillers, wherein the core film layer is disposed between the at least two skin film layers.

[0012] In some embodiments, the biaxially oriented industrially or home-compostable film web comprises a skin film layer comprising a blend of about 0 to about 80 wt.% polyhydroxyalkanoate (PHA), about 50 to about 70 weight percent polylactic acid (PLA), and optionally small amounts of other biopolymers, other polymers, nucleating agents, chain extenders, fatty amides, and fillers; a core film layer comprising a blend of about 30 to about 80 wt.% polyhydroxyalkanoate (PHA), about 20 to about 40 wt.% polylactic acid (PLA), and optionally small amounts of other biopolymers, other polymers, nucleating agents, chain extenders, fatty amides, and fillers; and a sealant film layer comprising a blend of 0 to about 80 wt.% polyhydroxyalkanoate (PHA) and about 20 to about 100 weight percent polylactic acid (PLA), and optionally small amounts of other biopolymers, other polymers, nucleating agents, chain extenders, fatty amides, and fillers, wherein the core film layer is disposed between the skin film layer and the sealant film layer.

[0013] In some embodiments, the PHA of the core film layer comprises about 2 to about 10 mole percent 3-hydroxyhexanoate and the balance 3-hydroxybutyrate.

[0014] In some embodiments, the PHA of the sealant film layer comprises about 2 to about 10 mole percent 3-hydroxyhexanoate and the balance 3-hydroxybutyrate.

[0015] In some embodiments, the PHA of the skin film layer comprises about 2 to about 10 mole percent 3-hydroxyhexanoate and the balance 3-hydroxybutyrate.

[0016] In some embodiments, the biaxially oriented industrially or home-compostable film has an oven shrinkage rate of 0 to less than about 5% in the machine direction (MD) and 0 to less than about 15% in the transverse direction (TD).

[0017] In some embodiments, the biaxially oriented industrially or home compostable film has a pin puncture resistance of greater than about 700 grams force (gf).

[0018] In some embodiments, a biaxially oriented industrially or home compostable printed film web having a core film layer disposed between a combination of a skin film layer and a sealant film layer is provided.

[0019] In some embodiments, a biaxially oriented industrially or home compostable barrier film web having a core film layer disposed between a combination of a skin film layer and a sealant film layer is provided.

[0020] In some embodiments, the biaxially oriented industrially or home compostable printed film web has an oven shrinkage rate of 0 to less than about 5.0% in the machine direction (MD) and an oven shrinkage rate of 0 to less than about 15% in the transverse direction (TD).

[0021] In some embodiments, the biaxially oriented industrially or home compostable printed film has a pin puncture resistance range of greater than about 700 grams force (gf).

[0022] In some embodiments, the biaxially oriented industrially or home compostable printed film web has a haze value of less than 15%.

[0023] In some embodiments, a biaxially oriented industrially or home compostable barrier film web having a core film layer disposed between two of the sealant film layers is provided.

[0024] In some embodiments, the biaxially oriented barrier film has an oven shrinkage rate of 0 to less than about 5.0% in the machine direction (MD) and an oven shrinkage rate of 0 to less than about 15% in the transverse direction (TD).

[0025] In some embodiments, the biaxially oriented barrier film has a puncture resistance range of greater than about 700 grams force (gf).

[0026] In some embodiments, a biaxially oriented industrially or home-compostable printed film web having a core film layer disposed between two of the skin film layers is provided.

[0027] In some embodiments, prior to or simultaneously with the annealing step, the biaxially oriented industrially or home-compostable film web is relaxed from the draw in the transverse direction (TD) by about 5% to about 25% in the transverse direction (TD).

[0028] In some embodiments, the biaxially oriented industrially or home-compostable film web is annealed at a temperature in the range of about 110°C to about 130°C during the biaxial orientation process, and prior to or simultaneously with the annealing step, the industrially or home-compostable film web is relaxed from the draw in the transverse direction (TD) by about 15% to about 25% in the transverse direction (TD).

[0029] In some embodiments, a coated and / or metallized biaxially oriented barrier web is provided.

[0030] As described in more detail below, certain annealing conditions can provide optimal dimensional stability or minimize the shrinkage rate of poly(hydroxyalkanoate)-based films in the MD and TD directions. When properly annealed, poly(hydroxyalkanoate)-based films do not change in diameter over time or when exposed to high temperatures. Thus, embodiments of the present disclosure provide conditions that can impart biaxial dimensional stability to poly(hydroxyalkanoate)-based films. Dimensionally stable poly(hydroxyalkanoate)-based films made in accordance with the present disclosure can be particularly useful in the food packaging industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0031]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

MODE FOR CARRYING OUT THE INVENTION

[0032] In one aspect, the present disclosure provides a polymer film composition that is particularly suitable for packaging for consumer goods.

[0033] Preferably, the polymer film composition is biodegradable and / or industrially or home compostable. More specifically, the polymer film composition is biodegradable and is also industrially or home compostable.

[0034] As used herein, the term "biodegradable" refers to plastics or polymeric materials that are subject to biodegradation by living organisms (microorganisms) in anaerobic and aerobic environments (determined by ASTM D5511), soil environments (determined by ASTM 5988), freshwater environments (determined by ASTM D5271 (EN29408)), or marine environments (determined by ASTM D6691). The biodegradability of biodegradable plastics can also be determined using ASTM D6868 and European EN13432.

[0035] The polymeric film composition of the present disclosure is preferably also "compostable" as determined by ASTM D6400 with respect to industrial or home compostability.

[0036] Specifically, the biodegradable polymeric film composition includes poly(hydroxyalkanoate) as the biodegradable polymer. The composition generally consists of from about 5 weight percent to about 95 weight percent of poly(hydroxyalkanoate). More preferably, the composition consists of from about 20 weight percent to about 90 weight percent of poly(hydroxyalkanoate). Even more preferably, the polymeric composition includes from about 30 weight percent to about 70 weight percent of poly(hydroxyalkanoate).

[0037] In some cases, the poly(hydroxyalkanoate) used in the production of the biodegradable film is preferably composed of a mixture of monomer units. Thus, the poly(hydroxyalkanoate) contains from about 90 to about 99.9 mole percent of monomer residues of 3-hydroxybutyrate and may contain from about 0.1 to about 10 mole percent of monomer residues of a second 3-hydroxyalkanoate having 5 to 12 carbon atoms. In one embodiment, a poly(hydroxyalkanoate) containing from about 97 to about 99 mole percent of monomer residues of 3-hydroxybutyrate and from about 1 to about 3 mole percent of monomer residues of 3-hydroxyhexanoate can be used in the production of one or more layers of the composite polymer film. Another one or more layers of the composite polymer film may contain a poly(hydroxyalkanoate) containing from about 92 to about 96 mole percent of monomer residues of 3-hydroxybutyrate and from about 4 to about 10 mole percent of monomer residues of 3-hydroxyhexanoate.

[0038] The polymeric composition film may also contain a second biodegradable polymer selected from the group consisting of poly(butylene succinate), poly(butylene succinate-co-adipate), poly(lactic acid), cellulose esters (such as cellulose acetate), thermoplastic starch, and mixtures thereof. The amount of this second biodegradable polymer is typically from about 10 weight percent to about 90 weight percent of the total composition.

[0039] In some embodiments, the second biodegradable polymer may contain poly(butylene succinate) in an amount of from about 5 weight percent to about 50 weight percent of the polymeric film composition. More preferably, the polymeric film composition contains from about 10 weight percent to about 30 weight percent of poly(butylene succinate).

[0040] According to some embodiments, the second biodegradable polymer may comprise poly(butylene succinate)-co-butylene adipate in an amount of about 5 weight percent to about 50 weight percent of the polymeric film composition. More preferably, the polymeric film composition comprises about 10 weight percent to about 30 weight percent of poly(butylene succinate)-co-butylene adipate.

[0041] In some cases, the second biodegradable polymer may comprise poly(lactic acid) in an amount of about 10 weight percent to about 70 weight percent of the polymeric composition. More preferably, the polymeric film composition comprises about 20 weight percent to about 80 weight percent of poly(lactic acid).

[0042] In certain embodiments, the second biodegradable polymer may comprise cellulose acetate or another cellulose ester in an amount of about 5 weight percent to about 50 weight percent of the polymeric film composition. More preferably, the polymeric film composition comprises about 10 weight percent to about 30 weight percent of cellulose acetate or another cellulose ester.

[0043] Generally, poly(hydroxyalkanoate) polymers have a weight average molecular weight of about 50,000 Daltons to about 7.5 million Daltons, more preferably about 300,000 Daltons to about 3 million Daltons, as determined by ASTM D6474-20.

[0044] In certain embodiments, poly(hydroxyalkanoate) and at least one biodegradable polymer are melt blended together in a film extrusion process.

[0045] In some embodiments, a transesterification reaction is carried out by reacting poly(hydroxyalkanoate) and at least one biodegradable polymer with each other in a reactive extrusion process.

[0046] In some embodiments, a nucleating agent may be present in the polymer film composition in an amount of from about 0.1 weight percent to about 5 weight percent. In certain embodiments, the core layer nucleating agent is preferably selected from the group consisting of erythritol, pentaerythritol, dipentaerythritol, artificial sweeteners, stearates, polysaccharides, sorbitol, mannitol, inositol, polyester waxes, nanoclay, behenic acid amide, erucic acid amide, stearic acid amide, oleic acid amide, polyhydroxybutyrate, thymine, cyanuric acid, cytosine, adenine, uracil, guanine, boron nitride, and mixtures thereof.

[0047] The polymer film composition may also include an optional plasticizer material. Materials suitable as plasticizers are typically fatty acid esters of sebacate, citrate, adipic acid, succinic acid, and glucaric acid, lactates, alkyl diesters, citrates, alkyl methyl esters, dibenzoates, propylene carbonate, caprolactone diol having a number average molecular weight of 200 to 10,000 g / mol as determined by ASTM D6474-20, poly(ethylene glycol) having a number average molecular weight of 400 to 10,000 g / mol as determined by ASTM D6474-20, vegetable oils, long chain alkanoic acids, adipates, glycerol, esters of isosorbide derivatives or mixtures thereof, polymeric plasticizers, poly(hydroxyalkanoate) copolymers containing at least 18 mole percent monomer residues of hydroxyalkanoates other than hydroxybutyrate, and mixtures thereof.

[0048] The amount of plasticizer in the polymer film composition can be up to about 15 weight percent. More preferably, the polymer composition is composed of from about 1 weight percent to about 8 weight percent plasticizer.

[0049] Optionally, the polymeric film composition may also include a filler material. Materials suitable as fillers typically include calcium carbonate, talc, nanoclay, nanocellulose, hemp fiber, kaolin, carbon black, wollastonite, glass fiber, carbon fiber, graphite fiber, mica, silica, dolomite, barium sulfate, magnetite, halloysite, zinc oxide, titanium dioxide, montmorillonite, feldspar, asbestos, boron, steel, carbon nanotubes, cellulose fiber, ramie, cotton, starch, polysaccharide, aluminum hydroxide, magnesium hydroxide, modified starch, chitin and chitosan, alginate, gluten, zein, casein, collagen, gelatin, polysaccharide, guar gum, xanthan gum, succinoglycan, natural rubber, rosinic acid, lignin, natural fiber, jute, kenaf, hemp, peanut shell, wood flour, and mixtures thereof.

[0050] The amount of filler in the polymeric film composition can be up to about 50 weight percent. More preferably, the core layer polymeric film composition is composed of about 5 weight percent to about 30 weight percent filler.

[0051] Furthermore, in some cases, the polymeric film composition may contain up to 50 weight percent of one or more additives selected from the group consisting of poly(vinyl alcohol), poly(vinyl acetate), poly(vinyl laurate), poly(ethylene vinyl acetate), poly(glycolic acid), furandicarboxylic acid-based polyester, cellulose, nanocellulose, glucan, and mixtures thereof.

[0052] Generally, at least one poly(hydroxyalkanoate) polymer has a weight average molecular weight of about 50,000 Daltons to about 7.5 million Daltons as determined by ASTM D6474-20, and more preferably, has a weight average molecular weight of about 300,000 Daltons to about 3 million Daltons.

[0053] In another aspect, the present disclosure also provides a product package for consumer product products that utilize the aforementioned polymer composition. Specifically, the product package includes at least one biodegradable package portion that includes the aforementioned polymer composition. The product package can be used for packaging clothing, household items, food, and health and beauty products.

[0054] In certain embodiments, this biodegradable package can be formed by coextrusion. The package is a skin film layer, a sealant film layer, and a combination of the sealant film layer and the skin film layer, where the sealant film layer and the skin film layer each include a blend of 0 to about 80 wt.% polyhydroxyalkanoate (PHA) and about 20 to about 100 weight percent polylactic acid (PLA), and optionally, small amounts of other biopolymers, other polymers, nucleating agents, chain extenders, fatty amides, and fillers, a skin film layer, a sealant film layer, and a combination of the sealant film layer and the skin film layer, and a core film layer that includes a blend of about 30 to about 80 wt.% polyhydroxyalkanoate (PHA), about 20 to about 40 wt.% polylactic acid (PLA), and optionally, small amounts of other biopolymers, other polymers, nucleating agents, chain extenders, fatty amides, and fillers, and can be made by coextruding at least three layers selected from among them. The core film layer is disposed between a combination of the skin film layer and the sealant film layer, between two sealant film layers, or between two skin film layers, and the sealant film layer and the skin film layer each include the same or different amounts of PHA, PLA, and other biopolymers, other polymers, nucleating agents, chain extenders, fatty amides, and fillers.

[0055] For example, with respect to FIG. 1, the barrier film 10 may include one or more core layers 12 between two sealant layers 14, and each of the sealant layers 14 may include one or more sealant layers 14. With respect to FIG. 2, the printed film 16 may include one or more core layers 12 between two skin layers 18, and each of the skin layers 18 may include one or more skin layers 18. The printed film or barrier film 20 may also be made using a core layer(s) 12, a skin layer 18 including one or more skin layers 18, and a sealant layer 14 including one or more sealant layers 14, as shown in FIG. 3. Other variations of the composite biaxially oriented film are illustrated in FIGS. 4-6. In each of FIGS. 4-6, the layer(s) 24 can be any combination of one or more skin layers, barrier layers, other biodegradable layers, metallization layers, coatings, and the like. The core layer(s) 12, the sealant layer(s) 14, and the skin layer(s) 18 are as described above. The structures illustrated in FIGS. 1 and 4 can be heat-sealable barrier film structures. The structures illustrated in FIGS. 2 and 6 can be printed film structures, while the structures illustrated in FIGS. 3 and 5 can be either printed film structures or barrier film structures.

[0056] Degree of crystallinity The volume percent crystallinity (Φ c ) of a semi-crystalline polymer (or copolymer) often determines what kind of end-use properties the polymer has. For example, a highly crystalline (over 50%) polyethylene polymer is strong and rigid and suitable for products such as plastic milk containers. On the other hand, low-crystalline polyethylene is flexible and tough and suitable for products such as food wraps and garbage bags. Crystallinity can be determined by several methods, including x-ray diffraction, differential scanning calorimetry (DSC), density measurement, and infrared absorption. The most appropriate method depends on the material being tested.

[0057] The volume percent crystallinity (Φc) of the poly(hydroxyalkanoate) copolymer can vary depending on the mole percent of poly(3-hydroxyhexanoate) in the poly(hydroxyalkanoate) copolymer. The addition of poly(3-hydroxyhexanoate) increases the flexibility of the poly(hydroxyalkanoate) copolymer while efficiently reducing the volume percent crystallinity, crystallization rate, and melting temperature of the copolymer. The nucleating agents described herein can be used to accelerate the crystallization process of the poly(hydroxyalkanoate) copolymer.

[0058] Generally, the poly(hydroxyalkanoate) described herein for use in the production of composite film structures preferably has a crystallinity of about 0.1% to about 99%, more preferably about 2% to about 80%, and even more preferably about 20% to about 70% when measured by X-ray diffraction.

[0059] When the poly(hydroxyalkanoate) of the present invention is processed into a molded article or film, the amount of crystallinity in such poly(hydroxyalkanoate) is more preferably about 10% to about 80%, more preferably about 20% to about 70%, and even more preferably about 30% to about 60% when measured by X-ray diffraction.

[0060] Melting temperature Preferably, the biodegradable poly(hydroxyalkanoate) of the present invention has a melting temperature (Tm) of about 30°C to about 170°C, more preferably about 90°C to about 165°C, and even more preferably about 130°C to about 160°C.

[0061] Film production method The biaxially oriented industrially or home-compostable films disclosed herein have improved biodegradability and / or compostability and can be processed using conventional procedures for producing single-layer or multilayer films on conventional film-making equipment. The pellets of the poly(hydroxyalkanoate) of the present invention can be dry blended and then melt mixed in a film extruder. Alternatively, if mixing in the film extruder is insufficient, the pellets can be dry blended, melt mixed in a pre-compounding extruder, then re-pelletized and then subjected to film extrusion. Coextrusion of the skin film layer(s) or sealant film layer(s) and the core film layer(s) is a process particularly suitable for producing the barrier webs and print webs described herein.

[0062] Poly(hydroxyalkanoate) can be melt processed into a film using a cast film extrusion method. In the cast film process, the molten polymer mixture is extruded through a slot die. Generally, the flat web from the slot die is cooled on a large moving smooth metal roll. The web is rapidly cooled, peeled from this first roll, passed over one or more auxiliary cooling rolls, then passed through a series of rubber-coated draw rolls or "haul-off" rolls and finally sent to a winder.

[0063] For the production of multilayer films, preferably a coextrusion process is used. In such a process, in addition to a plurality of extruders, either a coextrusion feed block or a multi-manifold die system or a combination of these two is required to achieve a multilayer film structure.

[0064] Quite surprisingly, it has been found that the annealing temperature in the TD oven during the biaxial stretching of the cast film production process can contribute to or minimize the shrinkage rate of the poly(hydroxyalkanoate)-based polymer film. The improved annealing process for poly(hydroxyalkanoate)-based polymer films involves heating the film to a temperature in the range of about 110°C to about 135°C, preferably about 125°C to about 130°C, during the biaxial stretching process, and then relaxing the film by about 5% to about 25% from the draw in the transverse direction (TD). In some embodiments, the film is first relaxed by about 15% to about 25% in the transverse direction (TC) during the biaxial stretching step and then annealed at a temperature in the range of about 110°C to about 120°C. Annealing the semi-crystalline film material at a relatively high temperature is thought to improve the film quality with respect to microstructural and macrostructural features such as crystal morphology, density, and grain size. The improvement in the shrinkage rate of the film as a whole depends on the annealing time, the biaxial stretching temperature, and the amount of relaxation of the film after the annealing step.

[0065] The following non-limiting examples illustrate a process for controlling the shrinkage rate of poly(hydroxyalkanoate)-based polymeric inflation films.

Example

[0066] Example 1 By using a coextrusion process to simultaneously extrude three or more layers, the compounded poly(hydroxyalkanoate)-based polymeric material was converted into a barrier film and a printed film. The experiments were carried out at different annealing roller temperatures using the same extruder. Film samples were prepared at annealing roller temperatures of 60 °C, 80 °C, 100 °C, 110 °C, and 120 °C. Both the machine direction (MD) shrinkage rate and the transverse direction (TD) shrinkage rate were examined using the method described in ASTM D2732. Table 2 shows the film annealing treatment temperature and shrinkage rate data. The shrinkage rate measurement temperature was selected based on a storage temperature of 45 °C for the storage and transportation of the final product, as well as post-processing temperatures (80 °C, 100 °C, and 110 °C) such as coating, metallization, and sealing temperature.

Table 1

[0067] As shown in the above table, the poly(hydroxyalkanoate) film shrinkage rate values at a lower annealing treatment temperature (60 °C) were very high compared to the industry standard of less than 5%. When the annealing treatment temperature was increased above 100 °C, the shrinkage rate values decreased significantly, and at an annealing treatment temperature of 120 °C, the industry standard value of less than 5% was reached.

[0068] The following non-limiting examples illustrate a process for controlling the shrinkage rate of a poly(hydroxyalkanoate)-based polymeric film produced by a biaxially stretched film process.

[0069] Example 2 Poly(hydroxyalkanoate)-based film samples were prepared using the same extruder and MDO profile with different transverse direction (TDO) annealing treatment temperatures. The transverse direction (TD) annealing treatment temperatures used were 60 °C, 93 °C, and 129 °C. The shrinkage rate measurement temperatures were selected based on the maximum temperature expected for the storage / transport of the final product (45 °C) and the maximum temperatures expected for the post-processing processes (such as coating temperature, metallization temperature, and sealing temperature) (80 °C, 100 °C, and 110 °C). Both the machine direction (MD) shrinkage rate and the transverse direction (TD) shrinkage were examined by heating the final film in an oven at 110 °C for 10 minutes. The results are given in the following table.

Table 2

[0070] The poly(hydroxyalkanoate) film shrinkage rate values at the lower annealing treatment temperature (60 °C) were very high compared to the industry standard of less than 5%. Increasing the annealing treatment temperature significantly decreased the shrinkage rate values, and at an annealing treatment temperature of 129 °C, the industry standard value of less than 5% was reached.

[0071] Poly(hydroxyalkanoate)-based polymer films were prepared by modifying poly(hydroxyalkanoate) using a melt strength enhancer, a chain extender, and other processing aids. The poly(hydroxyalkanoate)-based films prepared according to the present disclosure may contain about 50 - 80 weight percent of a poly(hydroxyalkanoate) copolymer and about 20 - about 50 wt.% of a polymer modifier. In some embodiments, the poly(hydroxyalkanoate) copolymer is poly-3-hydroxybutyrate-co-3-hydroxyhexanoate.

[0072] Exemplary formulations that can be used to produce a coextruded biaxially stretched biodegradable film according to the present disclosure. Table 3 below shows the main components of the core film, the sealant film, and the skin film.

Table 3-1

Table 3-2

[0073] In the following table, by using various biaxial annealing treatment temperatures and relaxation rates, the shrinkage rates in the MD direction and the TD direction were determined using the same oven shrinkage temperature. The puncture resistance was determined according to ASTM D-4833. The haze value was determined according to ASTM D1003.

Table 4

Table 5

[0074] Table 6 is an illustration of a printed film made in accordance with the present disclosure having a relatively low haze value.

Table 6

[0075] The foregoing examples for the composite biaxially stretched biodegradable film illustrate that an annealing treatment temperature of about 110 °C to about 130 °C and a TD relaxation rate in the range of 5 to 25% from the stretching in the TD direction can provide a biaxially stretched biodegradable film having a shrinkage rate of less than about 1 to 5% in the machine direction and less than about 6 to 15% in the transverse direction.

[0076] The foregoing description of the preferred embodiments of the present invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obvious modifications or variations are possible in light of the above teachings. The embodiments were chosen and described in order to best illustrate the principles of the invention and its practical application, thereby enabling others skilled in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by the appended claims, provided they are fairly, legally, and equitably within the scope of the granted rights.

Claims

**Claim 1** A biaxially oriented industrially or home-compostable film web comprising a skin film layer, a sealant film layer, and combinations of the sealant film layer and the skin film layer, wherein the sealant film layer and the skin film layer each independently comprise a blend of from 0 to about 80 wt. % polyhydroxyalkanoate (PHA) and from about 20 to about 100 weight percent polylactic acid (PLA), and optionally, minor amounts of other biopolymers, other polymers, nucleating agents, chain extenders, fatty amides, and fillers, the skin film layer, the sealant film layer, and combinations of the sealant film layer and the skin film layer, and a core film layer comprising a blend of from about 30 to about 80 wt. % polyhydroxyalkanoate (PHA), from about 20 to about 40 wt. % polylactic acid (PLA), and optionally, minor amounts of other biopolymers, other polymers, nucleating agents, chain extenders, fatty amides, and fillers, the core film layer being disposed between a combination of the skin film layer and the sealant film layer, between two sealant film layers, or between two skin film layers, the sealant film layer and the skin film layer each independently comprising the same or different amounts of PHA, PLA, and other biopolymers, other polymers, nucleating agents, chain extenders, fatty amides, and fillers, the core film layer A biaxially oriented industrially or home-compostable film web comprising at least three coextruded layers selected from the group consisting of **Claim 2** The biaxially oriented industrially or home-compostable film web of claim 1, wherein the PHA of the core film layer comprises from about 2 to about 10 mole percent 3-hydroxyhexanoate and the balance 3-hydroxybutyrate. **Claim 3** The biaxially oriented industrially or home-compostable film web of claim 1, wherein the PHA of the sealant film layer comprises from about 2 to about 10 mole percent 3-hydroxyhexanoate and the balance 3-hydroxybutyrate. **Claim 4** The PHA of the skin film layer comprises from about 2 to about 10 mole percent 3-hydroxyhexanoate and the balance 3-hydroxybutyrate, the biaxially oriented industrially or home compostable film web of claim 1.

5. The biaxially oriented industrially or home compostable film has an oven shrinkage rate of 0 to less than about 5% in the machine direction (MD) and an oven shrinkage rate of 0 to less than about 15% in the transverse direction (TD), the biaxially oriented industrially or home compostable film web of claim 1.

6. The biaxially oriented industrially or home compostable film has a puncture resistance of greater than about 700 grams force (gf), the biaxially oriented industrially or home compostable film web of claim 1.

7. A biaxially oriented industrially or home compostable printed film web comprising the core film layer disposed between the skin film layer and the sealant film layer combination of claim 1.

8. A biaxially oriented industrially or home compostable barrier film web comprising the core film layer disposed between the skin film layer and the sealant film layer combination of claim 1.

9. The printed film web has an oven shrinkage rate of 0 to less than about 5.0% in the machine direction (MD) and an oven shrinkage rate of 0 to less than about 15% in the transverse direction (TD), the biaxially oriented industrially or home compostable printed film web of claim 8.

10. The biaxially oriented industrially or home compostable printed film web has a puncture resistance range of greater than about 700 grams force (gf), the biaxially oriented industrially or home compostable printed film web of claim 8.

11. The biaxially oriented industrially or home compostable printed film has a haze value of less than 15%, the biaxially oriented industrially or home compostable printed film web of claim 8.

12. A biaxially oriented industrially or home compostable barrier film web comprising the core film layer disposed between two of the sealant film layers of claim 1.

13. The biaxially oriented barrier film web according to claim 12, wherein the biaxially oriented barrier film has an oven shrinkage rate of 0 to less than about 5.0% in the machine direction (MD) and an oven shrinkage rate of 0 to less than about 15% in the transverse direction (TD).

14. The biaxially oriented barrier film web according to claim 12, wherein the biaxially oriented barrier film has a puncture resistance range of greater than about 700 grams force (gf).

15. A biaxially oriented industrially or home-compostable printed film web comprising the core film layer disposed between two of the skin film layers according to claim 1.

16. A method for improving the dimensional stability of a biaxially oriented industrially or home-compostable film web comprising at least three coextruded layers, the method comprising extruding a composite poly(hydroxyalkanoate)-based polymer film and annealing the composite poly(hydroxyalkanoate) polymer film at a temperature in the range of about 110°C to about 130°C during a biaxial stretching process.

17. The method according to claim 16, wherein prior to or simultaneously with the annealing step, the biaxially oriented industrially or home-compostable film web is relaxed from stretching in the transverse direction (TD) by about 5% to about 25% in the transverse direction (TD).

18. The method according to claim 16, wherein the biaxially oriented industrially or home-compostable film web is annealed at a temperature in the range of about 110°C to about 130°C during the biaxial stretching process, and prior to or simultaneously with the annealing step, the industrially or home-compostable film web is relaxed from stretching in the transverse direction (TD) by about 15% to about 25% in the transverse direction (TD).

19. The biaxially oriented industrially or home-compostable film web is At least two sealant film layers, comprising a blend of from about 0 to about 80 wt.% polyhydroxyalkanoate (PHA) and from about 20 to about 100 weight percent polylactic acid (PLA), and optionally other biopolymers, other polymers, nucleating agents, chain extenders, fatty amides, and fillers, wherein the two sealant film layers may each have the same or different amounts of PHA, PLA, and other biopolymers, other polymers, nucleating agents, chain extenders, fatty amides, and fillers, at least two sealant film layers, and a core film layer, comprising a blend of from about 30 to about 80 wt.% polyhydroxyalkanoate (PHA), from about 20 to about 40 wt.% polylactic acid (PLA), and optionally small amounts of other biopolymers, other polymers, nucleating agents, chain extenders, fatty amides, and fillers, wherein the core film layer is disposed between the at least two sealant film layers, the core film layer The method according to claim 16, comprising the above.

20. A biaxially stretched barrier web produced by the method according to claim 19, further comprising coating and / or metallizing the barrier web, the biaxially stretched barrier web.

21. The biaxially stretched industrially or home-compostable film web is At least two skin film layers, comprising a blend of from about 0 to about 80 wt.% polyhydroxyalkanoate (PHA) and from about 20 to about 100 weight percent polylactic acid (PLA), and optionally other biopolymers, other polymers, nucleating agents, chain extenders, fatty amides, and fillers, wherein the two sealant film layers may each have the same or different amounts of PHA, PLA, and other biopolymers, other polymers, nucleating agents, chain extenders, fatty amides, and fillers, at least two skin film layers, and A core film layer comprising from about 30 to about 80 wt. % polyhydroxyalkanoate (PHA), from about 20 to about 40 wt. % polylactic acid (PLA), and optionally a blend of minor amounts of other biopolymers, other polymers, nucleating agents, chain extenders, fatty amides, and fillers, said core film layer being disposed between said at least two skin film layers, the core film layer The method according to claim 16, comprising

22. A biaxially stretched printed web produced by the method according to claim 21, further comprising printing on said printed web, the biaxially stretched printed web

23. The biaxially stretched industrially or home compostable film web is A skin film layer comprising from about 0 to about 80 wt. % polyhydroxyalkanoate (PHA) and from about 50 to about 70 weight percent polylactic acid (PLA), and optionally a blend of minor amounts of other biopolymers, other polymers, nucleating agents, chain extenders, fatty amides, and fillers, the skin film layer A core film layer comprising from about 30 to about 80 wt. % polyhydroxyalkanoate (PHA), from about 20 to about 40 wt. % polylactic acid (PLA), and optionally a blend of minor amounts of other biopolymers, other polymers, nucleating agents, chain extenders, fatty amides, and fillers, and A sealant film layer comprising from 0 to about 80 wt. % polyhydroxyalkanoate (PHA) and from about 20 to about 100 weight percent polylactic acid (PLA), and optionally a blend of minor amounts of other biopolymers, other polymers, nucleating agents, chain extenders, fatty amides, and fillers, said core film layer being disposed between said skin film layer and said sealant film layer, the sealant film layer The method according to claim 16, comprising

24. The method according to claim 16, wherein the biaxially stretched industrially or home compostable film web has a haze value of less than about 15%.

25. The method according to claim 16, wherein the biaxially stretched industrial or home-compostable film web comprising the at least three coextruded layers has an oven shrinkage rate of 0 to less than about 5% in the machine direction (MD) at 120 °C and an oven shrinkage rate of 0 to less than about 15% in the transverse direction (TD). **Claim 26** The method according to claim 16, wherein the biaxially stretched industrial or home-compostable film web has a puncture resistance range of about 700 grams force (gf). **Claim 27** A biaxially stretched industrial or home-compostable film web produced by the method according to claim 16. **Claim 28** A biaxially stretched industrial or home-compostable film web comprising at least three coextruded layers produced by the method according to claim 16.

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