Biodegradable biaxial stretching film, manufacturing method thereof and environment-friendly packaging material comprising film

Abstract

The invention relates to a biodegradable biaxially stretched film, a manufacturing method thereof and an environment-friendly packaging material comprising the film. The biodegradable biaxially stretched film includes: a first outer layer; a second outer layer; and a core layer provided between the first outer layer and the second outer layer, the core layer including a multilayer structure in which first resin layers and second resin layers are alternately laminated, the first resin layers including a first composition containing a polylactic acid-based polymer, the second resin layers including a second composition containing a polylactic acid-based polymer, and the first resin layers including a second composition containing a polylactic acid-based polymer. The second resin layer contains a second composition containing a polyhydroxyalkanoate-based polymer, and the first outer layer and the second outer layer each contain the first composition. The content of the polyhydroxyalkanoate-based polymer is 20% by weight or more based on the total weight of the first composition and the second composition contained in the first outer layer, the second outer layer, and the core layer.

Description

Technical Field

[0001] The present invention relates to a biodegradable biaxially stretched film, a method for manufacturing the same, and an environmentally friendly packaging material including the film. Background Art

[0002] Examples of plastic films widely used for packaging include cellophane, polyvinyl chloride (PVC), polyethylene (PE), polypropylene (PP), nylon, and polyethylene terephthalate (PET).

[0003] However, cellophane films cause serious environmental pollution during the manufacturing process, and their production itself is subject to many regulations. PVC films generate harmful substances such as dioxins when incinerated, and their use is also subject to many regulations. Moreover, PE films lack heat resistance and mechanical properties, so their use is limited except for low-quality packaging applications. Polypropylene, nylon, polyethylene terephthalate, etc. have relatively stable molecular structures and good mechanical properties, but if landfilled without special treatment after being used for packaging, they are difficult to decompose due to their chemical and biological stability and accumulate underground, thus shortening the service life of the landfill soil and causing soil pollution problems.

[0004] To compensate for the drawbacks of non-decomposable plastic films, films using biodegradable resins have recently started to be used. Biodegradable substances refer to substances that can be decomposed by organisms such as bacteria and microorganisms under specified conditions. According to the biodegradability of biodegradable substances, specified composting conditions are required. For example, the composting conditions can be classified into industrial composting conditions, home composting conditions, soil composting conditions, and marine composting conditions, etc., considering factors such as the temperature, humidity, or time required for decomposition.

[0005] Polylactic acid (PLA) films are widely used for the biodegradable resins due to their excellent mechanical properties and optical characteristics. However, due to their unique crystal structure, the PLA films lack flexibility and generate a lot of noise, and since they can be decomposed in industrial composting facilities that require high temperature and humidity, they do not meet the home or soil composting standards, so their use is limited.

[0006] To improve this problem, a method of manufacturing a film by using a biodegradable aliphatic polyester other than polylactic acid alone can be adopted. However, aliphatic polyesters with excellent biodegradability that meet the home or soil composting standards usually have low melting points and glass transition temperatures. Therefore, it is not only difficult to manufacture a film using a biaxial stretching method, but also the final film has low mechanical strength and high thermal shrinkage rate, which may lead to poor processability, productivity, and moldability.

[0007] Therefore, it is necessary to study a biodegradable film that can be biodegraded under home or soil composting conditions, has excellent optical, thermal, and mechanical properties, can be easily manufactured by a biaxial stretching method, and generates less noise.

[0008] Prior art documents

[0009] Patent documents

[0010] Japanese Patent Publication No. 2006-272712 Summary of the invention

[0011] The implementation examples are proposed to solve the problems of the above prior art.

[0012] The implementation examples aim to provide a biodegradable biaxially stretched film that can adjust the composition and constitution of each resin layer included in the biodegradable biaxially stretched film having a multilayer structure, and can have a high biodegradability even under mild composting conditions, and its mechanical properties, flexibility, transparency, and noise level are improved.

[0013] Another implementation example aims to provide a method for manufacturing a biodegradable biaxially stretched film for adjusting the above characteristics of the biodegradable biaxially stretched film to an optimal range.

[0014] Still another implementation example aims to provide a packaging material using the biodegradable biaxially stretched film with improved characteristics, so that it can be biodegraded even under mild composting conditions, and has environmental friendliness and high quality.

[0015] To achieve the above object, an implementation example provides a biodegradable biaxially stretched film, which includes: a first outer layer; a second outer layer; and a core layer disposed between the first outer layer and the second outer layer, the core layer includes a multilayer structure in which a first resin layer and a second resin layer are alternately laminated, the first resin layer contains a first composition containing a polylactic acid-based polymer, the second resin layer contains a second composition containing a polyhydroxyalkanoate-based polymer, the first outer layer and the second outer layer respectively contain the first composition, and based on the total weight of the first composition and the second composition contained in the first outer layer, the second outer layer, and the core layer, the content of the polyhydroxyalkanoate-based polymer is 20% by weight or more.

[0016] Another implementation example provides a method for manufacturing a biodegradable biaxially stretched film, which includes: steps of separately preparing a first composition containing a polylactic acid-based polymer and a second composition containing a polyhydroxyalkanoate-based polymer; separately melt-extruding the first composition and the second composition to obtain a sheet formed by alternately laminating a resin layer containing the first composition and a resin layer containing the second composition; and biaxially stretching and thermally setting the laminated sheet to obtain a biaxially stretched film. Based on the total weight of the first composition and the second composition, the content of the polyhydroxyalkanoate-based polymer is 20% by weight or more.

[0017] Another implementation example provides an environmentally friendly packaging material, which includes a biaxially stretched film. The biaxially stretched film includes: a first outer layer; a second outer layer; and a core layer disposed between the first outer layer and the second outer layer. The core layer includes a multilayer structure formed by alternately laminating a first resin layer and a second resin layer. The first resin layer contains a first composition containing a polylactic acid-based polymer, and the second resin layer contains a second composition containing a polyhydroxyalkanoate-based polymer. The first outer layer and the second outer layer respectively contain the first composition. Based on the total weight of the first composition and the second composition contained in the first outer layer, the second outer layer, and the core layer, the content of the polyhydroxyalkanoate-based polymer is 20% by weight or more.

[0018] The biodegradable biaxially stretched film of the implementation example includes a core layer having a multilayer structure formed by alternately laminating a resin layer containing a first resin composition and a resin layer containing a second resin composition. The first resin composition contains a polylactic acid-based polymer, and the second resin composition contains a polyhydroxyalkanoate-based polymer. An outer layer containing the first resin composition is provided on both sides of the core layer and contains a specified content of the polyhydroxyalkanoate-based polymer. Therefore, the flexibility and transparency can be improved, and the noise reduction effect and biodegradability can be enhanced.

[0019] Moreover, the method for manufacturing the biodegradable biaxially stretched film of the implementation example can further improve the moldability, processability, and productivity.

[0020] Moreover, the biodegradable biaxially stretched film of the implementation example has a multilayer structure. Therefore, each layer can have a relatively thin thickness, which can improve the penetration of organisms such as bacteria and microorganisms, enabling biodegradation even under mild conditions such as household or soil composting standards. When landfilled, it can be completely decomposed and has environmental protection characteristics. Therefore, it can be used as a packaging material in various fields and can provide high-quality environmentally friendly packaging materials. Description of the Drawings

[0021] Figure 1 Brief schematic diagram of the biodegradable biaxially stretched film according to one implementation example of the present invention.

[0022] Figure 2 Brief perspective view of the biodegradable biaxially stretched film according to one implementation example of the present invention.

[0023] Description of reference numerals

[0024] 100: Biodegradable biaxially stretched film

[0025] 105: Core layer

[0026] 110: First resin layer

[0027] 120: Second resin layer

[0028] 130: First outer layer

[0029] 140: Second outer layer Detailed implementation manners

[0030] Hereinafter, the present invention will be described in detail through various implementation examples. The implementation examples are not limited to the content disclosed below, and can be deformed into various forms as long as the gist of the invention is not changed.

[0031] In this specification, the terms referring to each structural element are used to distinguish it from other structural elements, and are not used to limit the implementation examples. Moreover, in this specification, the singular expression includes the singular or plural expression, unless otherwise clearly indicated in the context.

[0032] In this specification, when it is mentioned that a certain part "includes" a certain structural element, this means that other structural elements can also be included, rather than excluding other structural elements, unless there is a contrary description.

[0033] Unless otherwise specified, all numerical ranges representing physical property values, dimensions, etc. of structural elements described in this specification should be understood to be modified by the term "about" in all cases.

[0034] In this specification, terms such as "first" and "second" are used to describe different structural elements, and the structural elements are not limited by the above terms. The purpose of using the terms is to distinguish one structural element from another.

[0035] In this specification, the description that one structural element is formed or disposed above or below another structural element includes directly forming or disposing between these structural elements, or indirectly forming or disposing in such a way that other structural elements are provided in the middle. Moreover, it should be understood that the reference related to above or below each structural element may change according to the direction of the observation object.

[0036] In the numerical ranges that limit the dimensions, physical properties, etc. of structural elements described in this specification, it should also be understood that when numerical ranges that only limit the upper limit value and numerical ranges that only limit the lower limit value are respectively exemplified, the numerical ranges formed by combining these upper limit values and lower limit values are also included in the exemplified ranges.

[0037] Moreover, for ease of explanation, the dimensions of each structural element in the drawings may be exaggerated, which does not represent the dimensions in actual use. Additionally, throughout the specification, the same reference numerals refer to the same structural elements.

[0038] Polylactic acid polymers are a representative biodegradable polymer and have attracted attention as a film material to replace petroleum-based polyester films. However, when polylactic acid polymers are applied to films, a large loud crackling sound is generated during film use, which has been pointed out as a drawback hindering the use of the film as a packaging material. In particular, when a film containing a polylactic acid polymer is used as a food packaging material closely related to daily life, such as a snack bag or a bread bag, this crackling sound may become a noise that gives an unpleasant feeling to users. Since consumers are reluctant to choose products that generate unnecessary noise, it is important to provide a biodegradable film that does not generate unnecessary noise so that the biodegradable film can replace existing petrochemical-based films for environmental protection purposes.

[0039] Moreover, although polylactic acid polymers are biodegradable, they need to undergo a six-month period at a high temperature of around 60 °C and a humidity of 50% RH or more for decomposition, so that they can decompose during industrial composting. Therefore, they are not suitable for use in home or soil composting with milder conditions and have limited applications. To be widely used as a biodegradable film, it is crucial to provide a film that can decompose under normal temperature conditions when landfilled in soil.

[0040] In one implementation example, a biodegradable film can be provided, which includes: a first outer layer; a second outer layer; and a core layer disposed between the first outer layer and the second outer layer. The core layer includes a multi-layer structure in which a first resin layer and a second resin layer are alternately laminated. The first resin layer contains a first composition containing a polylactic acid-based polymer, and the second resin layer contains a second composition containing a polyhydroxyalkanoate-based polymer. The first outer layer and the second outer layer each contain the first composition. Based on the total weight of the first composition and the second composition contained in the first outer layer, the second outer layer, and the core layer, the content of the polyhydroxyalkanoate-based polymer is 20% by weight or more. Therefore, it has excellent flexibility, transparency, and biodegradability, and the noise level is improved.

[0041] [Biodegradable Biaxially Oriented Film]

[0042] Figure 1 It is a schematic diagram of the biodegradable biaxially oriented film according to an implementation example of the present invention.

[0043] In multiple implementation examples of the present invention, the biodegradable biaxially oriented film 100 includes: a first outer layer 130, a second outer layer 140, and a core layer 105 disposed between the first outer layer 130 and the second outer layer 140.

[0044] The first outer layer 130 and the second outer layer 140 can be respectively disposed on two sides of the core layer 105 in a manner facing each other. For example, the first outer layer 130 is formed on one side of the core layer 105, and the second outer layer 140 can be formed on the other side of the core layer 105.

[0045] The core layer 105 includes a multi-layer structure formed by alternately laminating a first resin layer 110 and a second resin layer 120 having different resin components. For example, the core layer 105 can be a laminate in which the first resin layer 110 and the second resin layer 120 are alternately laminated repeatedly.

[0046] The first resin layer 110 contains a first composition, and the second resin layer 120 contains a second composition. The first outer layer 130 and the second outer layer 140 contain the first composition.

[0047] The first composition contains a polylactic acid (PLA)-based polymer. The second composition contains a polyhydroxyalkanoate (PHA)-based polymer.

[0048] Different from petroleum-based resins, the polylactic acid-based polymer is based on biomass, so it can be used as a renewable resource, which helps to inhibit carbon dioxide emissions. Moreover, it has biodegradability and can be decomposed more quickly by moisture, microorganisms, bacteria, etc. than petroleum-based resins, so it can be environmentally friendly.

[0049] The polylactic acid-based polymer may contain L-lactic acid, D-lactic acid, D,L-lactic acid, or a combination thereof. For example, the polylactic acid-based polymer may contain a copolymer of L-lactic acid and D-lactic acid.

[0050] The polylactic acid-based polymer may contain more than 1 mol% of D-lactic acid. For example, it may contain 1 mol% to 12 mol% of D-lactic acid. Specifically, the content of D-lactic acid contained in the polylactic acid-based polymer may be 1 mol% or more, 2 mol% or more, 3 mol% or more, or more than 3 mol%, and may be 12 mol% or less, 10 mol% or less, 9 mol% or less, 8 mol% or less, 7 mol% or less, 6 mol% or less, or 5 mol% or less. For example, the content of D-lactic acid in the polylactic acid-based polymer may be 1 mol% to 10 mol%, 3 mol% to 9 mol%, 3 mol% to 8 mol%, 3 mol% to 7 mol%, 3 mol% to 6 mol%, 3 mol% to 5 mol%, or more than 3 mol% and 5 mol% or less. When manufacturing a film within the above range, the draw processability can be further improved, and the heat resistance characteristics of the film manufactured therefrom can be further enhanced.

[0051] The melt flow index (MI) of the polylactic acid-based polymer may be 5 g / 10 min or more under the conditions of 210 °C and 2.16 kg, may be 8 g / 10 min or more, 10 g / 10 min or more, or 12 g / 10 min or more, and may be 20 g / 10 min or less, 18 g / 10 min or less, 16 g / 10 min or less, or 15 g / 10 min or less. For example, the melt flow index of the polylactic acid-based polymer under the conditions of 210 °C and 2.16 kg may be 5 g / 10 min to 20 g / 10 min, 5 g / 10 min to 18 g / 10 min, 8 g / 10 min to 18 g / 10 min, 10 g / 10 min to 18 g / 10 min, 10 g / 10 min to 16 g / 10 min, 12 g / 10 min to 16 g / 10 min, or 12 g / 10 min to 15 g / 10 min.

[0052] The weight average molecular weight (Mw) of the polylactic acid-based polymer may be 100,000 g / mol to 1,000,000 g / mol. For example, it may be 100,000 g / mol to 800,000 g / mol, 100,000 g / mol to 500,000 g / mol, or 100,000 g / mol to 300,000 g / mol. The weight average molecular weight (Mw) can be measured by gel permeation chromatography (GPC). When the weight average molecular weight (Mw) of the polylactic acid-based polymer is within the above range, the mechanical properties and optical properties of the biodegradable biaxially stretched film 100 can be further enhanced.

[0053] The polyhydroxyalkanoate-based polymer is a thermoplastic natural polyester compound that can be chemically synthesized or produced by microorganisms such as bacteria. The polyhydroxyalkanoate-based polymer has excellent flexibility and biodegradability and can improve noise reduction performance.

[0054] Based on the total weight of the first composition and the second composition included in the first outer layer 130, the second outer layer 140, and the core layer 105, the content of the polyhydroxyalkanoate-based polymer is 20% by weight or more. Moreover, as described later, when the first composition further includes the polylactic acid-based polymer and the polyhydroxyalkanoate-based polymer at the same time, the content of the polyhydroxyalkanoate-based polymer represents the total weight of the polyhydroxyalkanoate-based polymer contained in the first composition and the second composition.

[0055] The biodegradable biaxially stretched film 100 includes the polyhydroxyalkanoate-based polymer satisfying the above content range, thereby enhancing biodegradability. Even under relatively mild conditions, it can be composted, and the flexibility and noise reduction effect of the film can be improved.

[0056] The polyhydroxyalkanoate-based polymer may include one or more repeating units selected from the group consisting of 3-hydroxybutyrate (3HB), 3-hydroxyhexanoate (3HH), 4-hydroxybutyrate (4HB), 3-hydroxypentanoate (3HV), 3-hydroxypropionate (3HP), 5-hydroxypentanoate (5HV), 5-hydroxyhexanoate (5HH), and 6-hydroxyhexanoate (6HH) as polymerization units.

[0057] The polyhydroxyalkanoate-based polymer may include 3-hydroxybutyrate (3HB) repeating units. As the polyhydroxyalkanoate-based polymer includes 3HB repeating units, 3HB residues form the backbone of the polymer, so the polyhydroxyalkanoate-based polymer may have a structure more favorable for biodegradation.

[0058] In another embodiment, the polyhydroxyalkanoate-based polymer may include 3-hydroxybutyrate (3HB) repeating units and one or more additional repeating units selected from the group consisting of 3-hydroxyhexanoate (3HH), 4-hydroxybutyrate (4HB), 3-hydroxypentanoate (3HV), 3-hydroxypropionate (3HP), 5-hydroxypentanoate (5HV), 5-hydroxyhexanoate (5HH), and 6-hydroxyhexanoate (6HH) as polymerization units.

[0059] The polyhydroxyalkanoate-based polymer may include 3-hydroxyhexanoate (3HH) as the additional repeating unit. Specifically, the polyhydroxyalkanoate-based polymer may include a PHBH copolymer (3HB-co-3HH) of 3-hydroxybutyrate (3HB) and 3-hydroxyhexanoate (3HH). Thereby, the stretching properties suitable for the stretching process can be ensured, and the mechanical properties, flexibility, and low-noise property can be improved.

[0060] The polyhydroxyalkanoate-based polymer may include 10 mol% or more of the additional repeating unit, and may also include 11 mol% or more. Moreover, the polyhydroxyalkanoate-based polymer may include 20 mol% or less of the additional repeating unit, and may include 18 mol% or less, 16 mol% or less, 15 mol% or less, 14 mol% or less, 13 mol% or less, or 11 mol% or less. For example, the polyhydroxyalkanoate-based polymer may include 10 mol% to 20 mol% of the additional repeating unit, and may include 10 mol% to 18 mol%, 10 mol% to 16 mol%, 10 mol% to 15 mol%, 10 mol% to 14 mol%, 10 mol% to 13 mol%, or 10 mol% to 11 mol%.

[0061] Specifically, as the PHBH copolymer (3HB-co-3HH), the content of the 3-hydroxyhexanoate (3HH) repeating unit in the polyhydroxyalkanoate-based polymer may be 10 mol% to 20 mol%, 10 mol% to 18 mol%, 10 mol% to 16 mol%, 10 mol% to 15 mol%, 10 mol% to 14 mol%, 10 mol% to 13 mol%, or 10 mol% to 11 mol%. Within the above range, excellent mechanical properties of the film can be maintained, and the flexibility and noise reduction effect can be further improved.

[0062] The melt viscosity of the polyhydroxyalkanoate-based polymer may be 4,000 poise or more at a temperature of 160 °C, and may be 5,000 poise or more, 6,000 poise or more, 7,000 poise or more, 8,000 poise or more, or 9,000 poise or more. The melt viscosity of the polyhydroxyalkanoate-based polymer may be 14,000 poise or less at a temperature of 160 °C, and may be 13,000 poise or less, 12,000 poise or less, or 11,000 poise or less. For example, the melt viscosity of the polyhydroxyalkanoate-based polymer may be 4,000 poise to 14,000 poise, 5,000 poise to 13,000 poise, 6,000 poise to 12,000 poise, 7,000 poise to 11,000 poise, 8,000 poise to 11,000 poise, or 9,000 poise to 11,000 poise at a temperature of 160 °C.

[0063] In one implementation example, the weight-average molecular weight (Mw) of the polyhydroxyalkanoate-based polymer can be from 50,000 g / mol to 400,000 g / mol. For example, it can be from 50,000 g / mol to 300,000 g / mol, from 50,000 g / mol to 200,000 g / mol, or from 50,000 g / mol to 100,000 g / mol. The weight-average molecular weight (Mw) can be measured by gel permeation chromatography (GPC).

[0064] When the polyhydroxyalkanoate-based polymer has the weight-average molecular weight (Mw) within the above range, the compatibility between the polylactic acid-based polymer and / or the first composition is excellent, and the processability of the film can be further improved. Therefore, the biaxially stretched film can maintain appropriate strength, and its flexibility, transparency, and low-noise property can be further improved.

[0065] The biodegradable biaxially stretched film 100 includes a first outer layer 130 and a second outer layer 140 respectively disposed on two sides of the core layer 105, such as on the upper surface and the lower surface.

[0066] The first outer layer 130 and the second outer layer 140 disposed on two sides of the core layer 105 contain the first composition. For example, the first resin layer 110, the first outer layer 130, and the second outer layer 140 can substantially contain the same resin component. The resin layer located outside the biodegradable biaxially stretched film 100 contains the first composition containing the polylactic acid-based polymer, so that the stretching process of the film can become easier, and the moldability, processability, and other manufacturing workabilities can be improved. Moreover, since the first composition is located on the surface of the biodegradable biaxially stretched film 100, the mechanical properties of the biaxially stretched film can be further improved.

[0067] Figure 2 It is a schematic perspective view of the biodegradable biaxially stretched film according to one implementation example of the present invention.

[0068] The sum of the thickness T2 of the first outer layer 130 and the thickness T3 of the second outer layer 140 provided on both sides of the core layer 105 may be 5% to 40% of the total thickness T1 of the biodegradable biaxially stretched film 100. For example, the sum of the thicknesses of the first outer layer 130 and the second outer layer 140 (T2 + T3) may be more than 5%, more than 10%, more than 15%, or more than 20% of the total thickness T1 of the biodegradable biaxially stretched film 100, and may be 40% or less, 35% or less, or 30% or less. Specifically, the sum of the thicknesses of the first outer layer 130 and the second outer layer 140 may be 10% to 40%, 15% to 40%, 20% to 40%, 20% to 35%, or 20% to 30% of the total thickness of the biodegradable biaxially stretched film 100. Within the above range, the stretching process can be easily carried out, and the formability, processability, and productivity can be further improved. Moreover, the mechanical properties such as the surface strength of the biaxially stretched film can be improved, and the anti-slip property, dimensional stability, etc. can also be enhanced.

[0069] The thickness T2 of the first outer layer 130 may be 2% or more, 5% or more, or 10% or more of the total thickness T1 of the biodegradable biaxially stretched film 100, and may be 30% or less, 25% or less, 20% or less, or 15% or less. Moreover, the thickness T3 of the second outer layer 140 may be 2% or more, 5% or more, or 10% or more of the total thickness T1 of the biodegradable biaxially stretched film 100, and may be 30% or less, 25% or less, 20% or less, or 15% or less. Since the thickness T2 of the first outer layer 130 and the thickness T3 of the second outer layer 140 respectively satisfy the above range, the mechanical properties of the biodegradable biaxially stretched film 100 can be further improved, and the stability such as the thermal properties and durability of the film can be further enhanced.

[0070] In one implementation example, the resin layer of the core layer 105 in contact with the first outer layer 130 and the second outer layer 140 may be the second resin layer 120. In another implementation example, the resin layer of the core layer 105 in contact with the first outer layer 130 and the second outer layer 140 may also be the first resin layer 110.

[0071] In one implementation example, the first composition may separately contain the polylactic acid-based polymer as a resin component. For example, the first resin layer 110, the first outer layer 130, and the second outer layer 140 may only contain the polylactic acid-based polymer as a resin component.

[0072] In another implementation example, in addition to the polylactic acid-based polymer, the first composition may further contain other aliphatic polyester-based polymers.

[0073] For example, the first composition may further comprise at least one aliphatic polyester-based polymer such as a polyhydroxyalkanoate (PHA)-based polymer, a polybutylene adipate (PBA)-based polymer, a polybutylene succinate (PBS)-based polymer, a polycaprolactone (PCL)-based polymer, a poly(butylene succinate-co-adipate) (PBSA)-based polymer, or a poly(butylene adipate-co-terephthalate) (PBAT)-based polymer.

[0074] Specifically, the first composition may comprise the polylactic acid-based polymer and at least one aliphatic polyester-based polymer such as a polyhydroxyalkanoate-based polymer, a polycaprolactone-based polymer, a polybutylene succinate-based polymer, or a polybutylene adipate-based polymer. Thereby, the biodegradability of the biodegradable biaxially stretched film 100 can be further improved, and the flexibility can be further enhanced.

[0075] More specifically, the first composition may further comprise the polylactic acid-based polymer and the polyhydroxyalkanoate-based polymer. The polyhydroxyalkanoate-based polymer contained in the first composition and the polyhydroxyalkanoate-based polymer contained in the second composition may be the same polymer. Thereby, the excellent mechanical properties of the biodegradable biaxially stretched film 100 can be maintained, and the noise reduction effect and flexibility can be further improved.

[0076] When the polylactic acid-based polymer and the polyhydroxyalkanoate-based polymer are both contained in the first composition, based on the total weight of the first composition, the content of the polylactic acid-based polymer may be 30 wt% or more, 40 wt% or more, 50 wt% or more, or 60 wt% or more. Moreover, based on the total weight of the first composition, the content of the polylactic acid-based polymer may be 70 wt% or less, 60 wt% or less, or 50 wt% or less.

[0077] Based on the total weight of the first composition, the content of the polylactic acid-based polymer may be 30 wt% to 70 wt%. For example, based on the total weight of the first composition, the content of the polylactic acid-based polymer may be 40 wt% to 60 wt%, 30 wt% to 50 wt%, 40 wt% to 50 wt%, 50 wt% to 70 wt%, or 60 wt% to 70 wt%. Within this range, the excellent mechanical properties and optical properties of the biodegradable biaxially stretched film 100 can be maintained, and the flexibility and biodegradability can be further improved, and the noise level of the film can be further reduced.

[0078] When the poly(lactic acid)-based polymer and the polyhydroxyalkanoate-based polymer are both contained in the first composition, based on the total weight of the first composition, the content of the polyhydroxyalkanoate-based polymer contained in the first composition may be 30% by weight or more, 40% by weight or more, or 50% by weight or more. Alternatively, based on the total weight of the first composition, the content of the polyhydroxyalkanoate-based polymer contained in the first composition may be 70% by weight or less, 60% by weight or less, 50% by weight or less, or 40% by weight or less. For example, based on the total weight of the first composition, the content of the polyhydroxyalkanoate-based polymer may be 30% to 70% by weight, 40% to 60% by weight, 50% to 70% by weight, 50% to 60% by weight, 30% to 50% by weight, or 30% to 40% by weight.

[0079] In one implementation example, based on the total weight of the second composition, the second composition may contain 70% by weight or more, 80% by weight or more, 90% by weight or more, 95% by weight or more, or 97% by weight or more of the polyhydroxyalkanoate-based polymer. Moreover, based on the total weight of the second composition, the content of the polyhydroxyalkanoate-based polymer may be 99% by weight or more or 99.9% by weight or more. For example, the second composition may also contain only the polyhydroxyalkanoate-based polymer as a resin component.

[0080] Based on the total weight of the first composition and the second composition contained in the biodegradable biaxially stretched film 100 (i.e., the core layer 105, the first outer layer 130, and the second outer layer 140), the content of the polyhydroxyalkanoate-based polymer may be 20% by weight or more, 25% by weight or more, 30% by weight or more, 50% by weight or more, or 60% by weight or more, and may be 80% by weight or less, 75% by weight or less, 70% by weight or less, 65% by weight or less, or 60% by weight or less. Within this range, the biodegradable biaxially stretched film 100 can be biodegradable even when landfilled under mild composting conditions such as in soil, and thus can have environmental protection characteristics, and can greatly improve the noise reduction effect and flexibility while maintaining excellent mechanical properties and optical properties.

[0081] Specifically, based on the total weight of the first composition and the second composition contained in the biodegradable biaxially stretched film 100, the content of the polyhydroxyalkanoate-based polymer may be 20% to 80% by weight, 25% to 80% by weight, 25% to 75% by weight, 30% to 70% by weight, 50% to 75% by weight, or 50% to 70% by weight.

[0082] Based on the total weight of the first composition and the second composition contained in the biodegradable biaxially stretched film 100 (i.e., the core layer 105, the first outer layer 130, and the second outer layer 140), the content of the polylactic acid-based polymer can be 20% by weight or more, 25% by weight or more, 30% by weight or more, 35% by weight or more, or 40% by weight or more, and can be 80% by weight or less, 75% by weight or less, 70% by weight or less, 50% by weight or less, or 40% by weight or less.

[0083] Specifically, based on the total weight of the first composition and the second composition contained in the biodegradable biaxially stretched film 100, the content of the polylactic acid-based polymer can be 20% to 80% by weight, 20% to 75% by weight, 25% to 75% by weight, 30% to 70% by weight, 25% to 50% by weight, or 30% to 50% by weight.

[0084] In one implementation example, the content of the polyhydroxyalkanoate-based polymer contained in the biodegradable biaxially stretched film 100 can be higher than the content of the polylactic acid-based polymer. In another implementation example, the content of the polylactic acid-based polymer contained in the biodegradable biaxially stretched film 100 can be higher than the content of the polyhydroxyalkanoate-based polymer.

[0085] The ratio of the total weight of the first composition to the total weight of the second composition contained in the biodegradable biaxially stretched film 100 can be 3:7 to 8:2. For example, based on the total weight of the first composition and the second composition contained in the biodegradable biaxially stretched film 100, the content of the first composition can be 30% to 80% by weight, and the content of the second composition can be 20% to 70% by weight.

[0086] The total weight of the first composition represents the sum of the total weights of the first resin layer 110, the first outer layer 130, and the second outer layer 140. Moreover, the total weight of the second composition represents the total weight of the second resin layer 120. The weights of the first composition and the second composition contained in the biodegradable biaxially stretched film 100 can be adjusted according to the discharge amount during the film manufacturing process.

[0087] In one implementation example, the ratio of the total weight of the first composition contained in the biodegradable biaxially stretched film 100 to the total weight of the second composition may be from 3.5:6.5 to 8:2, from 3.5:6.5 to 7.5:2.5, from 4:6 to 7.5:2.5, from 4:6 to 7:3, from 4.5:5.5 to 7:3, from 5:5 to 7:3, or from 6:4 to 7:3. Within this range, the thicknesses of the first outer layer 130 and the second outer layer 140 can be easily adjusted to the desired range, and the thicknesses of the first resin layer 110 and the second resin layer 120 in the core layer 105 can be appropriately adjusted to further improve the biodegradability and flexibility of the biodegradable biaxially stretched film 100, and excellent low-noise properties and mechanical properties can be maintained.

[0088] In one implementation example, within the range that does not affect the effects of the present invention, the first composition and / or the second composition may further contain common additives. For example, as needed, the additives may include static agents, antistatic agents, antioxidants, heat stabilizers, ultraviolet light blockers, antiblocking agents, and other inorganic lubricants, etc.

[0089] The first composition and the second composition can be separately distinguished and melt-extruded. The first composition and the second composition can be formed into a multilayer film by extrusion or by alternately laminating in a branched sequence. Thus, the first composition can form the first resin layer 110, the first outer layer 130, and the second outer layer 140, and the second composition can form the second resin layer 120.

[0090] Through the first resin layer 110, the overall mechanical properties of the biodegradable biaxially stretched film 100 can be maintained at the desired level, and through the interaction between the second resin layer 120 and the first resin layer 110, the noise generated during the use of the film can be reduced.

[0091] The core layer 105 may have a laminated structure of more than 10 layers. For example, the first resin layer 110 and the second resin layer 120 are alternately laminated more than 10 times to form the core layer 105.

[0092] Since the core layer 105 has a multilayer structure, the biodegradability can be improved and the transparency can be enhanced. For example, the respective different resin layers 110, 120 containing the polylactic acid-based polymer or the polyhydroxyalkanoate-based polymer are laminated with a relatively thin thickness, whereby microorganisms and oxygen can more easily penetrate into the interior of the film and the respective different resin layers, so that the biodegradability can be improved, the haze can be reduced, and the optical properties can be improved.

[0093] Conversely, in the case of a biaxially stretched film having a monolayer structure of a composition containing the polylactic acid-based polymer and the polyhydroxyalkanoate-based polymer, a thicker resin layer containing the polylactic acid-based polymer is formed, thereby reducing the improvement effect on biodegradability, greatly increasing the haze, and reducing the transparency.

[0094] Specifically, the core layer 105 may have a multilayer structure in which the first resin layer 110 and the second resin layer 120 are alternately laminated 10 or more layers, 27 or more layers, 54 or more layers, or 72 or more layers. Moreover, the core layer 105 may have a multilayer structure in which the first resin layer 110 and the second resin layer 120 are alternately laminated 512 layers or less, 256 layers or less, or 144 layers or less. In this case, when the biodegradable biaxially stretched film 100 is applied to a general packaging material such as a snack bag, the generated noise can be reduced, and mechanical properties such as the strength of the film can be maintained above a certain level.

[0095] The thickness of the biodegradable biaxially stretched film 100 may be 1,000 μm or less, 800 μm or less, 600 μm or less, 400 μm or less, 200 μm or less, 100 μm or less, or 60 μm or less. The thickness of the biaxially stretched film may be 10 μm or more, 15 μm or more, or 20 μm or more.

[0096] The haze of the biodegradable biaxially stretched film 100 may be 11% or less, 10% or less, 9.5% or less, 9% or less, 8.5% or less, 8% or less, or 7.5% or less. In one implementation example, the haze of the biodegradable biaxially stretched film 100 may be 2% or more, 4% or more, or 5% or more. Within the haze range, the transparency of the film is excellent and can be used for various purposes. The haze can be measured using a hazemeter (model name: SEP-H) manufactured by Nihon Semitsu Kogaku.

[0097] The average Young's modulus of the biodegradable biaxially stretched film 100 may be 250 kgf / mm 2 or less, 240 kgf / mm 2 or less, 230 kgf / mm 2 or less, 220 kgf / mm 2 or less, 210 kgf / mm 2 or less, 200 kgf / mm 2 or less, 198 kgf / mm 2 or less, 190 kgf / mm 2 or less, 180 kgf / mm 2 or less, or 170 kgf / mm 2Hereinafter. Moreover, the average Young's modulus of the biodegradable biaxially stretched film 100 may be 120 kgf / mm 2 or more, 150 kgf / mm 2 or more, or 160 kgf / mm 2 or more.

[0098] Specifically, the average Young's modulus of the biodegradable biaxially stretched film 100 may be 120 kgf / mm 2 to 250 kgf / mm 2 , 120 kgf / mm 2 to 240 kgf / mm 2 , 120 kgf / mm 2 to 230 kgf / mm 2 , 150 kgf / mm 2 to 230 kgf / mm 2 , 150 kgf / mm 2 to 220 kgf / mm 2 , 160 kgf / mm 2 to 220 kgf / mm 2 , 160 kgf / mm 2 to 210 kgf / mm 2 , 160 kgf / mm 2 to 200 kgf / mm 2 or 160 kgf / mm 2 to 190 kgf / mm 2 . As the biodegradable biaxially stretched film 100 has the average Young's modulus within the above range, its flexibility can be improved, and its processability, formability, and productivity are further enhanced, making it suitable for use as a packaging material.

[0099] The Young's modulus can be measured in accordance with ASTM D882. Specifically, after preparing a test piece by cutting it into a length of 150 mm and a width of 15 mm, the test piece is installed using a tensile testing machine, the chuck spacing is set to 50 mm, an experiment is conducted at a tensile speed of 200 mm / min, and then the linear slope value from the measurement starting point to the time point when the elongation rate reaches 3% is measured. For the average Young's modulus of the biaxially stretched film, the Young's modulus of the film is measured in the MD (machine direction) direction, which is the longitudinal direction of the film, and the TD (transverse direction) direction, which is the transverse direction of the film, respectively, and the average value is obtained.

[0100] The noise level of the biodegradable biaxially stretched film 100 can be measured using a noise analyzer. For example, the length and width of the biodegradable biaxially stretched film 100 are cut into A4 size to prepare a sample for measurement. The long end of the measurement sample is fixed to a bar placed in a box that blocks external noise using a jig, and noise is generated in the sample by rotating the bar. Specifically, the distance between the end of the measurement part where the noise analyzer is placed and the film is set to about 15 cm, and the noise level generated when the bar is rotated 120 degrees at a speed of 400 rpm is measured.

[0101] When the thickness of the biodegradable biaxially stretched film 100 is about 20 μm, the noise level of the biaxially stretched film measured in the evaluation of the film noise level can be 70 dB or less, 65 dB or less, 62 dB or less, 60 dB or less, 58 dB or less, 56 dB or less, 55 dB or less, or 54 dB or less. The biaxially stretched film has a low noise level and can be used as an environmentally friendly packaging material such as a disposable packaging material or a food packaging material in various fields.

[0102] On the other hand, within the range that does not affect the effects of the present invention, a coating or a printing layer can be formed on one side of the surface of the biodegradable biaxially stretched film. For example, an inorganic particle coating or a primer coating for preventing static electricity or adhesion can be formed.

[0103] [Manufacturing method of biodegradable biaxially stretched film]

[0104] In multiple embodiments of the present invention, there is provided a manufacturing method of the biodegradable biaxially stretched film according to the above multiple embodiments, including: a step of separately preparing a first composition containing a polylactic acid-based polymer and a second composition containing a polyhydroxyalkanoate-based polymer (for example, step S10); a step of separately melt-extruding the first composition and the second composition to obtain a sheet formed by alternately laminating a resin layer containing the first composition and a resin layer containing the second composition (for example, step S20); and a step of biaxially stretching and thermally setting the laminated sheet to obtain a biaxially stretched film (for example, step S30). Based on the total weight of the first composition and the second composition, the content of the polyhydroxyalkanoate-based polymer is 20% by weight or more.

[0105] In the step S10, a first composition containing a polylactic acid-based polymer and a second composition containing a polyhydroxyalkanoate-based polymer can be separately prepared. Based on the total weight of the first composition and the second composition, the content of the polyhydroxyalkanoate-based polymer is 20% by weight or more.

[0106] The first composition can be applied to the first resin layer of the biodegradable biaxially stretched film, and the second composition can be applied to the second resin layer of the biodegradable biaxially stretched film.

[0107] For the first composition and the second composition, content that is repetitive of what is described in the biodegradable biaxially stretched film will be omitted, unless there are specifically contrary records.

[0108] The first composition and the second composition can be respectively prepared in the form of chips. Since the compositions are in chip form, they can be easily stored and easily applied to the melting process, for example, step S20.

[0109] The step S10 may further include a drying process of respectively drying the first composition and the second composition.

[0110] The drying process can be carried out at a temperature of 40°C or higher. For example, it can be carried out at a temperature of 50°C or higher, 60°C or higher, or 70°C or higher. Moreover, the drying process can be carried out at a temperature of 80°C or lower or 70°C or lower. For example, the drying process can be carried out at a temperature of 40°C to 90°C, 50°C to 80°C, or 60°C to 80°C.

[0111] The drying process can be carried out for 2 hours to 24 hours. For example, it can be carried out for 3 hours to 12 hours, 6 hours to 12 hours, 6 hours to 10 hours, or 3 hours to 8 hours.

[0112] For example, the drying process can be carried out at a temperature of 60°C to 80°C for 6 hours to 12 hours.

[0113] The drying process can be carried out using a dehumidifying dryer such as a hot air dryer.

[0114] In the step S20, the first composition and the second composition can be respectively melt-extruded. For example, the first composition and the second composition can be melted to form their respective molten resins, and the respective resin layers can be formed from the molten resins.

[0115] The step S20 can be carried out using 2 extruders and a laminating unit with two layers laminated alternately (for example, a multi-layer feed block). The first composition and the second composition can be respectively melt-extruded through the extruders. Moreover, in the laminating unit, after branching the molten resin of the first composition and the molten resin of the second composition, a laminate can be obtained in which a first resin layer derived from the molten resin of the first composition and a second resin layer derived from the molten resin of the second composition are laminated alternately.

[0116] The laminate may have a multilayer structure formed by alternately laminating the first resin layer and the second resin layer for 10 or more layers, 27 or more layers, 54 or more layers, 72 or more layers. In another implementation example, the laminate may have a multilayer structure formed by alternately laminating the first resin layer and the second resin layer for 512 or fewer layers, 256 or fewer layers, or 144 or fewer layers.

[0117] The melt extrusion temperature of the first composition and the melt extrusion temperature of the second composition may be different or may be the same. The difference between the melt extrusion temperature of the first composition and the melt extrusion temperature of the second composition may be less than 30 °C. For example, it may be 25 °C or lower, 20 °C or lower, 15 °C or lower, 10 °C or lower, or 5 °C or lower.

[0118] The melt extrusion temperatures of the first composition and the second composition may each be 200 °C or lower. For example, they may be 190 °C or lower, 180 °C or lower, or 170 °C or lower. Moreover, the melt extrusion temperatures of the first composition and the second composition may each be 120 °C or higher. For example, they may be 130 °C or higher, 140 °C or higher, 150 °C or higher. Specifically, the melt extrusion temperatures of the first composition and the second composition may each be from 120 °C to 200 °C. For example, they may be from 130 °C to 190 °C, from 140 °C to 180 °C, from 140 °C to 170 °C, or from 150 °C to 170 °C.

[0119] Pass the laminate formed by alternately laminating the first resin layer and the second resin layer through a die and closely adhere it to a cooling roll cooled to about 10 °C to 40 °C, thereby obtaining an unstretched multilayer sheet.

[0120] The unstretched multilayer sheet includes a first surface layer and a second surface layer respectively provided on both surfaces of the laminate, for example, the lower surface and the upper surface. The surface layer may be formed by melt-extruding the first composition. The laminate corresponds to the core layer of the biodegradable biaxially stretched film after the stretching process, and the surface layer corresponds to the outer layer of the biodegradable biaxially stretched film after the stretching process. That is, the outer layers on both sides of the sheet may each be a resin layer containing the first composition.

[0121] In one implementation example, the surface layer may be formed together in the step of forming the laminate. For example, the first composition may be melt-extruded on the upper surface and the lower surface of the laminate to form a surface layer containing the first composition on both surfaces of the laminate.

[0122] In the process of manufacturing the unstretched multilayer sheet, the ratio (mass ratio) of the total discharge amount of the first composition to the total discharge amount of the second composition may be from 3:7 to 8:2, from 3.5:6.5 to 8:2, from 3.5:6.5 to 7.5:2.5, from 4:6 to 7.5:2.5, from 4:6 to 7:3, from 4.5:5.5 to 7:3, from 5:5 to 7:3, or from 6:4 to 7:3.

[0123] In the step S30, a biodegradable biaxially stretched film can be manufactured by stretching the unstretched sheet. After the stretching process, the step S30 may further include a heat setting process.

[0124] Specifically, the stretching may be biaxial stretching. For example, it may be sequential biaxial stretching.

[0125] The stretching process may include a step of longitudinal (MD) stretching and a step of transverse (TD) stretching. For example, the stretching process may perform transverse stretching after longitudinally stretching the unstretched sheet.

[0126] Before the stretching process, the step S30 may include a step of preheating the unstretched sheet. In the preheating step, the unstretched sheet may be preheated to a temperature of 50°C to 80°C.

[0127] The longitudinal (MD) stretching may be performed 2 to 4 times at 50°C to 100°C. For example, the longitudinal (MD) stretching may be performed 2.5 to 3.5 times or 2.7 to 3.2 times at 55°C to 85°C or 60°C to 80°C.

[0128] The transverse (TD) stretching may be performed 3 to 5 times at 60°C to 110°C. For example, the transverse (TD) stretching may be performed 3.5 to 5 times or 3.5 to 4.5 times at 65°C to 100°C or 75°C to 95°C.

[0129] By biaxially stretching the unstretched multilayer sheet in two directions, the arrangement and crystallinity of the polymers in the multilayer film can be controlled, thereby further improving the mechanical properties and stability and obtaining a high-quality packaging material.

[0130] The heat setting step may be performed by placing the film at a specified temperature. Through the heat setting step, the mechanical properties and dimensional stability of the biaxially stretched film can be further improved.

[0131] The heat setting step can be carried out at 50°C to 150°C, 70°C to 150°C, 90°C to 140°C, 100°C to 140°C, 110°C to 140°C or 110°C to 130°C. Moreover, the heat setting step can adopt a relaxation rate within 3%, a relaxation rate within 2% or a relaxation rate within 1.5%. The heat setting step can be carried out for more than 1 second, more than 3 seconds or 60 seconds or less, 30 seconds or less, 15 seconds or less.

[0132] In one embodiment, a step of forming a coating and / or a printing layer on one side of the biaxially stretched film can also be carried out.

[0133] In one embodiment, a corona treatment step can also be carried out on the biaxially stretched film. The corona treatment step can be carried out before the coating or printing layer forming step.

[0134] In the corona treatment step, generally, corona discharge treatment can be carried out on the surface of the film in the biaxially stretched film. For example, when a high-frequency high-voltage output is applied between the discharge electrode and the treatment roller, corona discharge will occur. At this time, the corona treatment can be carried out by passing through the surface of the biaxially stretched film.

[0135] Through the corona discharge treatment, the reactive groups on the surface of the biaxially stretched film can be activated, or the surface can be chemically or physically modified to further improve the adhesion, printability, coating and deposition characteristics.

[0136] [Environmentally friendly packaging material]

[0137] In multiple embodiments of the present invention, an environmentally friendly packaging material is provided, which includes a biaxially stretched film. The biaxially stretched film includes: a first outer layer; a second outer layer; and a core layer disposed between the first outer layer and the second outer layer. The core layer includes a multi-layer structure in which a first resin layer and a second resin layer are alternately stacked. The first resin layer contains a first composition containing a polylactic acid-based polymer, and the second resin layer contains a second composition containing a polyhydroxyalkanoate-based polymer. The first outer layer and the second outer layer respectively contain the first composition. Based on the total weight of the first composition and the second composition contained in the first outer layer, the second outer layer and the core layer, the content of the polyhydroxyalkanoate-based polymer is 20% by weight or more.

[0138] The environmentally friendly packaging material includes the biodegradable biaxially stretched film of the above multiple embodiments. For the biodegradable biaxially stretched film, the content repeated with the content described above will be omitted unless there is a particularly contrary record.

[0139] For example, the environmentally friendly packaging material may be in the form of a film or sheet that can be used as an ordinary disposable packaging material and a food packaging material, may be in the form of fibers that can be used as fabrics, knitted fabrics, non-woven fabrics, ropes, etc., and may be in the form of containers that can be used as food packaging containers such as lunch boxes.

[0140] The biodegradable biaxially stretched film can be directly used for the environmentally friendly packaging material or can be used together with a metal foil, a color layer, etc.

[0141] The environmentally friendly packaging material includes a biodegradable biaxially stretched film having excellent flexibility, transparency, and mechanical properties and low haze, and thus can provide excellent physical properties and quality. Moreover, even under the standards of home or soil composting, the biodegradable biaxially stretched film can have high biodegradability and can be completely decomposed when landfilled, having environmental protection characteristics, and thus can be widely used as a packaging material in multiple fields.

[0142] The above content will be described in more detail through the following examples. The following examples are only used to illustrate the present invention, and the scope of the present invention is not limited to these examples.

[0143] [Examples]

[0144] Example 1: Manufacturing a multilayer biodegradable film (1)

[0145] Prepare a first composition containing a polylactic acid (PLA) polymer and a second composition containing a polyhydroxyalkanoate (PHA) polymer.

[0146] Use a polylactic acid copolymer (NatureWorks 3052D) with a D-lactide content of about 3 mol% to 5 mol% and a melt flow index (MI) of about 14.0 g / 10 min at 210 °C and 2.16 kg as the PLA polymer. Use a PHBH (poly(3-hydroxybutylate-co-3-hydroxyhexanoate), 3HB-co-3HH) copolymer with a 3-hydroxyhexanoate (3HH) repeat unit content of 10 to 11 mol% and a melt viscosity of about 9,000 to 11,000 poise at 160 °C as the PHA polymer.

[0147] After removing moisture by drying the first composition at about 70 °C for 4 hours using a dehumidifying dryer and drying the second composition at about 70 °C for 4 hours using a dehumidifying dryer, melt extrusion is performed using 2 extruders and a multilayer feed block with two layers alternately stacked. The first composition uses an extruder at a temperature of 160 °C, and the second composition uses an extruder at a temperature of 160 °C. The discharge ratio of the first composition to the second composition is 70:30.

[0148] In the multi-layer feed block, after dividing the first resin layer containing the first composition into 37 layers and the second resin layer containing the second composition into 36 layers, the first resin layer and the second resin layer are alternately laminated. In this case, the first resin layer is provided on the outer layers of the upper surface / lower surface, and the outer layers each have a thickness of 10% of the total sheet thickness. Then, after passing through a 780 mm die, it is closely adhered to a cooling roll cooled to about 20 °C to obtain an unstretched multi-layer sheet of 73 layers (2 outer layers on both sides and 71 core layers).

[0149] The unstretched multi-layer sheet is longitudinally stretched 3.0 times at about 65 °C, transversely stretched 4.0 times at 85 °C, and then heat-set at 120 °C to give a relaxation rate of 1% to manufacture a biaxially stretched multi-layer film with a thickness of 20 μm.

[0150] Example 2: Manufacturing a multi-layer biodegradable film (2)

[0151] A biaxially stretched multi-layer film is manufactured in the same manner as in Example 1, except that the discharge ratio of the first composition to the second composition is adjusted to 40:60.

[0152] Example 3: Manufacturing a multi-layer biodegradable film (3)

[0153] Prepare a first composition containing 60% by weight of a polylactic acid (PLA) polymer and 40% by weight of a polyhydroxyalkanoate (PHA) polymer, and a second composition containing a PHA polymer. The same copolymer as in Example 1 is used as the PLA polymer and the PHA polymer.

[0154] After removing moisture by drying the first composition at about 70 °C for 4 hours using a dehumidifying dryer and drying the second composition at about 70 °C for 4 hours using a dehumidifying dryer, melt extrusion is performed using 2 extruders and a multi-layer feed block with two layers alternately laminated. The first composition is extruded using an extruder at a temperature of 160 °C, and the second composition is extruded using an extruder at a temperature of 160 °C. The discharge ratio of the first composition to the second composition is 70:30.

[0155] In the multi-layer feed block, after dividing the first resin layer containing the first composition into 37 layers and the second resin layer containing the second composition into 36 layers, the first resin layer and the second resin layer are alternately laminated. In this case, the first resin layer is provided on the outer layers of the upper surface / lower surface, and the outer layers each have a thickness of 10% of the total sheet thickness. Then, after passing through a 780 mm die, it is closely adhered to a cooling roll cooled to about 20 °C to obtain an unstretched multi-layer sheet of 73 layers (2 outer layers on both sides and 71 core layers).

[0156] The unstretched multi-layer sheet is longitudinally stretched 3.0 times at about 65 °C, transversely stretched 4.0 times at 85 °C, and then heat-set at 120 °C with a relaxation rate of 1% to produce a biaxially stretched multi-layer film with a thickness of 20 μm.

[0157] Example 4: Production of a multi-layer biodegradable film (4)

[0158] A biaxially stretched multi-layer film was produced in the same manner as in Example 3, except that the discharge ratio of the first composition to the second composition was adjusted to 50:50.

[0159] Example 5: Production of a multi-layer biodegradable film (5)

[0160] A biaxially stretched multi-layer film was produced in the same manner as in Example 3, except that the first composition contained 40 wt% of a PLA polymer and 60 wt% of a PHA polymer.

[0161] Comparative Example 1: Production of a single-layer biodegradable film (1)

[0162] A composition containing a polylactic acid (PLA) polymer with a D-lactide content of about 1 to 3 mol% and a melt viscosity of about 7,000 to 12,000 poise at 210 °C was prepared. The composition was dried at about 80 °C for about 6 hours by a dehumidifying dryer to remove moisture. Thereafter, the composition was melt-extruded through an extruder at 210 °C, and after passing through a 780 mm die, it was adhered to a cooling roll cooled to 20 °C to obtain a single-layer unstretched sheet. The single-layer unstretched sheet thus obtained was longitudinally stretched 3.0 times at 65 °C and transversely stretched 3.8 times at 120 °C, and then heat-set at 120 °C with a relaxation rate of 1% to produce a biaxially stretched single-layer film with a thickness of 20 μm.

[0163] Comparative Example 2: Production of a single-layer biodegradable film (2)

[0164] The PLA polymer and PHA polymer used in Example 1 were manually stirred in a weight ratio of 40:60, and then mixed in a twin-screw extruder at 160 °C. Then, after drying at about 60 °C for 8 hours by a dehumidifying dryer, melt-extrusion was carried out at 160 °C to produce a single-layer unstretched film with a thickness of 20 μm.

[0165] Comparative Example 3: Production of a single-layer biodegradable film (3)

[0166] The PLA polymer used in Comparative Example 1 and poly(butylene adipate-co-terephthalate) (PBAT) polymer having a melt viscosity of about 7,000 to 12,000 poise at 210 °C and an aliphatic component content of about 50 mol% in the acid component were manually mixed at a weight ratio of 80:20, and then mixed in a twin-screw extruder at 200 °C. Then, after drying for 8 hours at about 60 °C by a dehumidifying dryer, melt extrusion was carried out at 200 °C to produce a single-layer unstretched film with a thickness of 30 μm. After that, melt extrusion was carried out at 200 °C.

[0167] Comparative Example 4: Manufacturing a single-layer biodegradable film (4)

[0168] The PLA polymer and the PHA polymer were manually mixed at a weight ratio of 90:10, and then mixed in a twin-screw extruder at 200 °C. Mixing was carried out in a twin-screw extruder.

[0169] The PLA polymer used in Example 1 was used as the PLA polymer, and poly(3-hydroxybutylate-co-4-hydroxybutylate) (3HB-co-4HB) copolymer with a 4-hydroxybutyrate (4HB) repeat unit content of 30 to 35 mol% was used as the PHA polymer.

[0170] Then, it was dried for 8 hours at about 60 °C by a dehumidifying dryer. The composition was melt-extruded through an extruder at a temperature of 210 °C, passed through a 780 mm die, and then closely adhered to a cooling roll cooled to 20 °C to obtain a single-layer unstretched sheet. The single-layer unstretched sheet thus obtained was longitudinally stretched 3.0 times at 65 °C, transversely stretched 3.8 times at 120 °C, and then heat-set at 120 °C and given a relaxation rate of 1% to manufacture a biaxially stretched single-layer film with a thickness of 20 μm.

[0171] Comparative Example 5: Manufacturing a multi-layer biodegradable film (6)

[0172] A first composition containing the PLA polymer used in Comparative Example 1 and a second composition containing the PBAT polymer used in Comparative Example 3 were prepared.

[0173] After removing moisture by drying the first composition at about 60°C for 8 hours using a dehumidifying dryer and drying the second composition at about 80°C for 2 hours using a dehumidifying dryer, melt extrusion was carried out using 2 extruders and a multi-layer feed block with two layers alternately laminated. The first composition was extruded using an extruder at a temperature of 210°C, and the second composition was extruded using an extruder at a temperature of 210°C. The discharge ratio of the first composition to the second composition was 70:30.

[0174] In the multi-layer feed block, after dividing the first resin layer containing the first composition into 37 layers and the second resin layer containing the second composition into 36 layers, the first resin layer and the second resin layer were alternately laminated. In this case, the first resin layer was provided on the outer layers of the upper surface / lower surface, and the outer layers each had a thickness of 10% of the total sheet thickness. After passing through a 780 mm die, it was closely attached to a cooling roll cooled to about 20°C to obtain an unstretched multi-layer sheet of 73 layers (2 outer layers on both sides and 71 core layers).

[0175] The unstretched multi-layer sheet was longitudinally stretched 3.0 times at about 65°C, transversely stretched 4.0 times at 85°C, and then heat-set at 120°C, giving a relaxation rate of 1% to manufacture a biaxially stretched multi-layer film with a thickness of 20 μm.

[0176] Comparative Example 6: Manufacturing multi-layer biodegradable film (7)

[0177] A first composition containing 95.8 wt% of a PLA polymer and 4.2 wt% of a PHA polymer and a second composition containing a PBAT polymer were prepared.

[0178] The PLA polymer used in Comparative Example 1 was used as the PLA polymer, the PHA polymer (3HB-co-4HB) used in Comparative Example 4 was used as the PHA polymer. The PBAT polymer used in Comparative Example 3 was used as the PBAT polymer.

[0179] Using the first composition and the second composition, a biaxially stretched multi-layer film with a thickness of 20 μm was manufactured in the same manner as in Comparative Example 5.

[0180] Evaluation Example

[0181] Evaluation Example 1: Haze

[0182] For the haze of the biodegradable films manufactured in the examples and comparative examples, it was measured using a hazemeter (SEP-H) of Nihon Semitsu Kogaku in accordance with ASTM D1003 standard.

[0183] Evaluation Example 2: Film Noise Level

[0184] Cut the biodegradable films produced in the examples and comparative examples into A4 size of 210 mm × 297 mm, place them in a box made of polycarbonate with dimensions of 650 (W) mm × 450 (D) mm × 500 (H) mm, and place the biodegradable film 15 cm away from the digital noise analyzer (CR-162C) of Cirrus Research PlC. Clamp both ends of the film with a fixture, rotate it 120 degrees at a speed of 400 rpm to generate noise for more than 30 seconds, measure the noise once per second, and measure a total of 30 times. Measure the average value of the measured values.

[0185] Evaluation Example 3: Average Young's Modulus

[0186] After preparing the biodegradable films produced in the examples and comparative examples according to ASTM D882, cut them into specimens with a length of 150 mm and a width of 15 mm. Then, install the specimens using a tensile testing machine (Instron 5566A), set the chuck spacing to 50 mm, conduct an experiment at a tensile speed of 200 mm / min, and then measure the linear slope value from the measurement starting point to the time point when the elongation rate reaches 3% as the Young's modulus (kgf / mm 2 ). Measure the Young's modulus in the MD direction and TD direction respectively and calculate the average value to obtain the average Young's modulus.

[0187] For the characteristics, compositions, and evaluation results of each layer of the biodegradable films produced in the examples and comparative examples, they are shown in Table 1 and Table 2 below respectively.

[0188]

Table 1

[0189]

[0190]

[0191]

Table 2

[0192]

[0193]

[0194] Referring to Table 1 and Table 2, compared with the single-layer or multi-layer biodegradable sheets and films produced in Comparative Examples 1 to 6, the physical properties such as transparency, noise level, and flexibility of the multi-layer biodegradable films produced in Examples 1 to 5 are overall excellent.

[0195] Specifically, the single-layer biodegradable film of Comparative Example 1 only contains polylactic acid polymer, exhibits a high noise level of 73.8 dB, and has a Young's modulus of 384 kgf / mm 2 and it is confirmed that the flexibility becomes poor. In the single-layer biodegradable films of Comparative Examples 2 to 4, the polylactic acid polymer is mixed with PHA (3HB-co-3HH) polymer, PHA (3HB-co-4HB) polymer, and PBAT polymer respectively and then used, but the haze increases to 15%, 25%, and 11.4% respectively, and the transparency is low. Moreover, it is confirmed that the noise levels of the single-layer biodegradable films of Comparative Examples 3 and 4 are 72.6 dB and 69.2 dB respectively, showing still relatively high noise levels, and the single-layer biodegradable film of Comparative Example 4 has a relatively high average Young's modulus of 330 kgf / mm 2 .

[0196] Moreover, the multi-layer biodegradable films of Comparative Example 5 and Comparative Example 6 exhibit relatively high noise levels of 72.2 dB and 67.5 dB respectively, and the average Young's modulus is 288 kgf / mm 2 and 274 kgf / mm 2 , and the flexibility is still poor.

[0197] On the contrary, regarding flexibility and noise level, it is confirmed that the multi-layer biodegradable films of Examples 1 to 5 have a noise level of 63.5 dB or less and exhibit a Young's modulus of 160 kgf / mm 2 to 220 kgf / mm 2 . Therefore, the flexibility is improved and the noise level becomes lower. Moreover, regarding transparency, it is confirmed that the haze of the multi-layer biodegradable films of multiple examples is measured to be 9.6% or less, the noise level and the average Young's modulus are improved, and excellent transparency is ensured.

[0198] Therefore, the multi-layer biodegradable films of multiple embodiments of the present invention have excellent biodegradability, and the flexibility, noise level, and transparency of the final films are all excellent. Therefore, it can be confirmed that they can be used for various purposes such as packaging, such as food packaging materials, in an environmentally friendly manner.

Claims

1. A biodegradable biaxially stretched film, in, include: First outer layer; a second outer layer; and a core layer, disposed between the first outer layer and the second outer layer, The core layer comprises a multilayer structure in which first resin layers and second resin layers are alternately stacked. The first resin layer comprises a first composition containing a polylactic acid-based polymer, The second resin layer comprises a second composition containing a polyhydroxyalkanoate-based polymer, The first outer layer and the second outer layer respectively comprise the first composition, The content of the polyhydroxyalkanoate-based polymer is 20 wt % or more based on the total weight of the first composition and the second composition included in the first outer layer, the second outer layer and the core layer.

2. The biodegradable biaxially stretched film according to claim 1, wherein: The core layer has a stacked structure of 10 or more layers.

3. The biodegradable biaxially stretched film according to claim 1, wherein: The first composition further comprises at least one aliphatic polyester-based polymer selected from the group consisting of a polyhydroxyalkanoate-based polymer, a polycaprolactone-based polymer, a polybutylene succinate-based polymer, and a polybutylene adipate-based polymer.

4. The biodegradable biaxially stretched film according to claim 3, wherein: The first composition further comprises the polyhydroxyalkanoate-based polymer.

5. The biodegradable biaxially stretched film according to claim 3, wherein: The polylactic acid-based polymer is present in an amount of 30 to 70 wt % based on the total weight of the first composition.

6. The biodegradable biaxially stretched film according to claim 1, wherein: The content of the first composition is 30 wt % to 80 wt % based on the total weight of the first composition and the second composition contained in the biodegradable biaxially stretched film.

7. The biodegradable biaxially stretched film according to claim 1, wherein: The polylactic acid-based polymer is contained in an amount of 20 wt % to 80 wt % based on the total weight of the first composition and the second composition contained in the biodegradable biaxially stretched film.

8. The biodegradable biaxially stretched film according to claim 1, wherein: The polyhydroxyalkanoate-based polymer comprises 3-hydroxybutyrate repeating units.

9. A method for producing a biodegradable biaxially stretched film according to claim 1, in, include: The steps of separately preparing a first composition comprising a polylactic acid-based polymer and a second composition comprising a polyhydroxyalkanoate-based polymer; The first composition and the second composition are melt-extruded separately to obtain a sheet composed of alternately stacked resin layers comprising the first composition and resin layers comprising the second composition; and The stacked sheets are biaxially stretched and heat-set to obtain a biaxially stretched film, The content of the polyhydroxyalkanoate-based polymer is 20 wt % or more based on the total weight of the first composition and the second composition.

10. An environmentally friendly packaging material, wherein: Including biaxially stretched films, The biaxially stretched film comprises: First outer layer; a second outer layer; and a core layer, disposed between the first outer layer and the second outer layer, The core layer includes a multilayer structure in which first resin layers and second resin layers are alternately stacked. The first resin layer comprises a first composition containing a polylactic acid-based polymer, The second resin layer comprises a second composition containing a polyhydroxyalkanoate-based polymer, The first outer layer and the second outer layer respectively comprise the first composition, The content of the polyhydroxyalkanoate-based polymer is 20 wt % or more based on the total weight of the first composition and the second composition included in the first outer layer, the second outer layer and the core layer.

Images