Gas-barrier multilayer film

Abstract

The gas-barrier multilayer film according to the present invention is biodegradable and possesses excellent gas-barrier properties. When applied to food packaging, its superior gas-barrier properties allow for long-term storage and distribution of food. Furthermore, its ability to biodegrade in soil and marine conditions makes it suitable for use as a biodegradable, environmentally friendly packaging material.

Description

Technical Field

[0001] [Cross - Reference to Related Applications] This application claims the benefit of priority based on Korean Patent Application No. 10 - 2023 - 0094875, filed on July 20, 2023, and all the contents disclosed in the literature of the Korean patent application are incorporated herein by reference as part of this specification.

[0002] The present invention provides a multilayer film that is environmentally friendly and has excellent gas barrier properties.

Background Art

[0003] Recently, due to the frequent occurrence of natural disasters, the severity of environmental pollution and the resulting climate change have come to be recognized as serious problems that must be addressed as a top priority. Among them, reducing the use of disposable plastics is a situation where various countries are implementing policies as a practical environmental pollution improvement activity in daily life.

[0004] As part of such policies, the use of environmentally friendly plastics or biodegradable plastics is recommended, and various plastics that are biodegradable in soil or the ocean are being researched and developed. However, in the case of food packaging, which mostly consists of plastics, materials capable of gas barrier against oxygen and moisture are essential for preventing denaturation and long - term preservation during the food distribution process. In the case of such gas barrier materials, most are non - biodegradable based on petrochemical raw materials. As a result, food packaging companies, etc., generally add a metal layer to add barrier properties for the realization of environmentally friendly food packaging materials applying biodegradable materials, or apply biodegradable plastic materials preferentially to products that do not require barrier properties.

[0005] Therefore, this invention relates to a multilayer film capable of blocking oxygen and moisture based on PGA (Polyglycolic acid), one of the biodegradable polymer materials. We have confirmed that it is possible to realize a biodegradable food packaging material through such a multilayer film, and thus completed this invention. [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] This invention provides a multilayer film that is environmentally friendly and has excellent gas barrier properties. Furthermore, the present invention provides a method for manufacturing a gas-barrier multilayer film. [Means for solving the problem]

[0007] To solve the aforementioned problems, the present invention provides the following gas-blocking multilayer film.

[0008] A gas-barrier multilayer film comprising a base layer (Ts) and a gas-barrier layer (Tb) formed on the base layer, The gas barrier layer (Tb) contains 40 to 60 volume% of poly(glycolic acid; PGA) relative to the total volume of the gas barrier layer (Tb), The aforementioned gas-barrier multilayer film satisfies the following equation 1: Gas-barrier multilayer film. [Formula 1] 0.38 ≤ D(Tb) / D(Ts) < 4.89 In the above formula 1, D(Tb) is the thickness of the gas barrier layer, D(Ts) is the thickness of the substrate layer.

[0009] The gas-barrier multilayer film of the present invention comprises at least two layers: a base layer (Ts) and a gas-barrier layer (Tb) formed on the base layer. The gas-barrier layer (Tb) contains polyglycolic acid PGA, a biodegradable polymer, and is characterized by being biodegradable, environmentally friendly, and exhibiting excellent gas-barrier properties through the mutual complementarity of the gas-barrier layer and the base layer.

[0010] The present invention will be described in detail below.

[0011] In this invention, the term "gas barrier layer (Tb)" refers to a layer containing 40 to 60 volume percent of poly(glycolic acid; PGA) relative to the total volume of the gas barrier layer. The polyglycolic acid is a biodegradable polymer, thereby enabling the gas barrier multilayer film according to the present invention to be used in an environmentally friendly manner. If the polyglycolic acid content in the gas barrier layer is less than 40 volume percent, it is difficult to achieve an effective gas barrier effect, and if the polyglycolic acid content in the gas barrier layer exceeds 60 volume percent, melt processability decreases, and the decomposition phenomenon of polyglycolic acid during processing becomes more severe.

[0012] Preferably, the weight-average molecular weight (Mw) of the polyglycolic acid is 80,000 to 220,000. If the weight-average molecular weight of the polyglycolic acid is less than 80,000, extrusion molding may be difficult due to the low melt viscosity, and there may be problems with the mechanical properties of the molded product, such as a film, being insufficient. If the weight-average molecular weight is higher than 220,000, significant discoloration of the polyglycolic acid may occur, causing problems with the shape of the molded product, such as a film, and more energy may be required for melt processing, making efficient processing difficult. More preferably, the weight-average molecular weight (Mw) of the polyglycolic acid is 100,000 to 200,000.

[0013] Preferably, the molecular weight distribution (Polydispersity Index, PDI) of the polyglycolic acid is 1.5 to 4.5. The molecular weight distribution of the polyglycolic acid is an important factor in the production of polyglycolic acid. If the molecular weight distribution is less than 1.5, precise control of polymer polymerization conditions is required, which may make it difficult to produce economically viable products. Also, if the molecular weight distribution of the polyglycolic acid exceeds 4.5, there is a possibility that the decomposition of the low molecular weight polyglycolic acid will be accelerated during melt processing. More preferably, the molecular weight distribution of the polyglycolic acid is 2.0 to 4.0.

[0014] The gas barrier layer may contain a variety of polymers other than polyglycolic acid, preferably poly(butylene adipate-co-terephthalate) (PBAT). More preferably, the gas barrier layer contains polyglycolic acid and poly(butylene adipate-co-terephthalate), in amounts of 40 to 60% and 60 to 40% by volume, respectively, relative to the total volume of the gas barrier layer. Preferably, the weight-average molecular weight of the poly(butylene adipate-co-terephthalate) is 90,000 to 180,000. If the weight-average molecular weight of the poly(butylene adipate-co-terephthalate) is less than 90,000, a problem may occur in which the mechanical properties of the fabricated film are significantly reduced, and a low melt viscosity may cause difficulties in processes such as film molding. When the weight-average molecular weight of poly(butylene adipate-co-terephthalate) exceeds 180,000, effective resin melting may be difficult in the extrusion molding process.

[0015] In this invention, the term "substrate layer (Ts)" refers to a layer that supports the gas barrier layer, on which the gas barrier layer is formed. Preferably, the substrate layer is made of a biodegradable polyester or a mixture thereof. Examples of biodegradable polyesters include poly(butylene adipate-co-terephthalate) (PABT), polylactic acid (PLA), and polybutylene succinate (PBS). Preferably, the weight-average molecular weight of the poly(butylene adipate-co-terephthalate) is 90,000 to 180,000, the weight-average molecular weight of the polylactic acid is 110,000 to 190,000, and the weight-average molecular weight of the polybutylene succinate is 120,000 to 200,000.

[0016] In particular, the gas-barrier multilayer film according to the present invention is characterized by satisfying formula 1. Formula 1 represents the ratio of the thickness of the gas-barrier layer to the thickness of the base layer and is expressed as "D(Tb) / D(Ts)". If the D(Tb) / D(Ts) value is less than 0.38, there is a possibility that the thickness of the gas-barrier layer will become very thin during melt processing, resulting in a significant decrease in gas-barrier properties. Furthermore, if the D(Tb) / D(Ts) value is 4.89 or higher, the thickness of the base layer will become considerably thinner, leading to a significant decrease in inter-film melt adhesion strength and making it difficult to manufacture packaging materials. In the case of the gas-barrier layer, the problem of thickening may make it difficult to realize an economically appropriate gas-barrier layer.

[0017] On the other hand, the thickness of the gas barrier layer is 10 to 500 μm. The thickness of the substrate layer is 8 to 450 μm.

[0018] Preferably, the gas-barrier multilayer film according to the present invention satisfies the following formula 2. [Formula 2] 0.01 ≤ OTR(Tb) / OTR(Ts) ≤ 0.52 In the above formula 2, OTR(Tb) is the oxygen permeability of the gas barrier layer, OTR(Ts) is the oxygen permeability of the substrate layer.

[0019] The above formula 2 means the ratio of the oxygen permeability of the gas barrier layer to that of the base material layer, and is expressed as "OTR(Tb) / OTR(Ts)". The unit of the oxygen permeability is "cc / m 2 ·day·kPa", and the measurement method is embodied in the following examples. If the OTR(Tb) / OTR(Ts) value is less than 0.01, there is a problem that it is difficult to realize a multilayer film due to the deterioration of the mechanical characteristics of the gas barrier layer. If the OTR(Tb) / OTR(Ts) value exceeds 0.52, there may be a problem that the base material layer peels off during the deformation of the multilayer film due to the thinning of the base material layer, and there is a problem that it is difficult to economically realize an effective gas barrier layer due to the excessive thickening of the gas barrier layer.

[0020] Preferably, the gas barrier multilayer film according to the present invention satisfies the following formula 3. [Formula 3] 0.014≦WVTR(Tb) / WVTR(Ts)≦0.61 In the above formula 3, WVTR(Tb) is the water vapor transmission rate of the gas barrier layer, WVTR(Ts) is the water vapor transmission rate of the base material layer.

[0021] The above formula 3 means the ratio of the water vapor transmission rate of the gas barrier layer to that of the base material layer, and is expressed as "WVTR(Tb) / WVTR(Ts)". The unit of the water vapor transmission rate is "g / m 2 ·day", and the measurement method is embodied in the following examples. If the WVTR(Tb) / WVTR(Ts) value is less than 0.014, there is a problem that it is difficult to realize a multilayer film due to the deterioration of the mechanical characteristics of the gas barrier layer. If the WVTR(Tb) / WVTR(Ts) value exceeds 0.61, there may be a problem that the base material layer peels off during the deformation of the multilayer film due to the thinning of the base material layer as in the case of the above oxygen permeability, and there is a problem that it is difficult to economically realize an effective gas barrier layer due to the excessive thickening of the gas barrier layer.

[0022] On the other hand, the gas-barrier multilayer film according to the present invention may further include various layers as needed, in addition to the base layer and gas-barrier layer described above. In other words, the gas-barrier multilayer film according to the present invention may further include an additional base layer, an additional gas-barrier layer, or an inorganic layer. For example, an additional base layer may be included on a gas-barrier multilayer film including a base layer and a gas-barrier layer to protect the gas-barrier layer, or an additional base layer and gas-barrier layer may be included to further enhance the gas-barrier effect, or an inorganic layer may be added to improve the print visibility of the packaging material or improve the slipperiness of the film and prevent film roll blocking. These examples are shown schematically below. In this case, the base layer and gas-barrier layer are as described above, and the inorganic layer means TiO2, aluminum oxide, or silicon oxide, etc.

[0023] - Substrate layer / Gas barrier layer / Substrate layer - Substrate layer / Gas barrier layer / Inorganic layer / Substrate layer - Substrate layer / Gas barrier layer / Substrate layer / Gas barrier layer - Substrate layer / Gas barrier layer / Substrate layer / Gas barrier layer / Substrate layer Furthermore, the present invention provides a method for manufacturing a gas-barrier multilayer film, comprising the steps of: manufacturing a base layer and a gas-barrier layer film (Step 1); and laminating the films manufactured in Step 1 (Step 2).

[0024] Step 1 can be manufactured by melting the components constituting the base layer and the gas barrier layer to produce a film, and as an example, it can be manufactured in a blown film process. Step 2 can be manufactured by laminating the films produced in Step 1 and then laminating them using a hot press or the like. [Effects of the Invention]

[0025] As described above, the gas-barrier multilayer film according to the present invention is biodegradable and possesses excellent gas-barrier properties. When applied to food packaging, it has the advantage of enabling long-term storage and distribution of food due to its superior gas-barrier properties. Furthermore, its ability to biodegrade in soil and marine conditions allows it to be used as a biodegradable, environmentally friendly packaging material. [Modes for carrying out the invention]

[0026] The embodiments of the present invention will be described in more detail below with reference to the following examples. However, the following examples are merely illustrative of embodiments of the present invention, and the content of the present invention is not limited to the following examples.

[0027] Manufacturing example Each polymer blend was manufactured using a Co-rotating Intermeshing Twin Screw Extruder (BA-19, manufactured by Bautek) consisting of a 19mm screw diameter, an aspect ratio (L / D, length / diameter) of 40, and seven heating barrels, in the ratios listed in Table 1 below.

[0028] Specifically, the barrel temperature was sequentially set from 180°C to 230°C in 20°C increments. Under conditions of 200 rpm and a supply of 3 kg / hr, the extruded strands were cooled in a 20°C water bath, and then polymer blend pellets were produced through a pelletizer. For composition #8, polymer blend pellets were manufactured under the same conditions, except that the barrel temperature was sequentially set from 140°C to 190°C in 20°C increments. In this process, Joncryl ADR 4401 (manufactured by BASF) was used as a compatibilizer to increase the compatibility between the resins. 1.0 phr was added to compositions #1 through #7, #9, and #10, and 0.1 phr was added to composition #8.

[0029] Furthermore, to improve thermal stability, 0.1 phr of PEP 36 (manufactured by ADEKA), a pentaerythritol-based antioxidant, was added to compositions #1 through #7, #9, and #10. In addition, for the production of polymer composites containing inorganic materials, the barrel temperature was sequentially set from 140°C to 190°C in 20°C increments, and 30 wt% TiO2 (manufactured by Sigma Aldrich) was added to poly(butylene adipate-co-terephthalate) (PABT) under the conditions of 200 rpm and a supply rate of 3 kg / hr. [Table 1]

[0030] Examples and Comparative Examples For each composition produced in the previous manufacturing example, a 30 μm thick film was manufactured using a blow film machine (30 mm Air Die, Collin) under the conditions of 230°C, 60 rpm, and a BUR (Blow-up Ratio) of 1.3. However, in the case of composition #8 and the inorganic composite, a 30 μm thick film was manufactured under the conditions of 170°C, 60 rpm, and a BUR (Blow-up Ratio) of 1.3.

[0031] After laminating the aforementioned manufactured films in the configurations shown in Tables 2 and 3 below, a multilayer film was produced using a hot press (Wabash, US) under the conditions of 40°C, 5 MPa, and 6 minutes. The following evaluations were performed on each manufactured multilayer film, and the results are shown in Tables 2 to 4.

[0032] (1) Oxygen permeability (OTR) For each film, the oxygen transmission rate (OTR) was measured for two days at a temperature of 23°C and a ΔP of 1 atm using an OTR (Oxygen Transmission Rate) instrument manufactured by Systech Illinois. (2) Water permeability (WVTR)

[0033] For each film, the water vapor transmission rate (WVTR) was measured for two days under conditions of 37.8°C and 90% relative humidity using a Systech Illinois AquaSense 7101 WVTR (Water Vapor Transmittance Rate) instrument. The oxygen transmission rate of each film was 100 cc / m². 2 When measured at high levels of .day.kPa or higher, water permeability is not measured. [Table 2] [Table 3] [Table 4]

Claims

1. A gas-barrier multilayer film comprising a base layer (Ts) and a gas-barrier layer (Tb) formed on the base layer, The gas barrier layer (Tb) comprises poly(butylene adipate-co-terephthalate) and polyglycolic acid, wherein the polyglycolic acid is present in an amount of 40 to 60 volume% relative to the total volume of the gas barrier layer (Tb). The aforementioned gas-barrier multilayer film satisfies the following equation 1: Gas-barrier multilayer film. [Formula 1] 0.38≦D(Tb) / D(Ts)<4.89 In the above formula 1, D(Tb) is the thickness of the gas barrier layer, D(Ts) is the thickness of the substrate layer.

2. The aforementioned gas-barrier multilayer film satisfies the following equation 2: [Formula 2] 0.01≦OTR(Tb) / OTR(Ts)≦0.52 (In the above formula 2, OTR(Tb) is the oxygen permeability of the gas barrier layer, OTR(Ts) is the oxygen permeability of the substrate layer. The gas-barrier multilayer film according to claim 1.

3. The aforementioned gas-barrier multilayer film satisfies the following equation 3: [Formula 3] 0.014≦WVTR(Tb) / WVTR(Ts)≦0.61 (In the above formula 3, WVTR(Tb) is the moisture permeability of the gas barrier layer, WVTR(Ts) is the moisture permeability of the substrate layer. The gas-barrier multilayer film according to claim 1.

4. The gas barrier layer contains polyglycolic acid and poly(butylene adipate-co-terephthalate) in amounts of 40 to 60% by volume and 60 to 40% by volume, respectively, based on the total volume of the gas barrier layer. The gas-barrier multilayer film according to claim 1.

5. The base layer is made of biodegradable polyester or a mixture thereof. The gas-barrier multilayer film according to claim 1.

6. The biodegradable polyester is poly(butylene adipate-co-terephthalate) (PABT), polylactic acid (PLA), or polybutylene succinate (PBS). The gas-barrier multilayer film according to claim 5.

7. The thickness of the gas barrier layer is 5 to 50 μm. The gas-barrier multilayer film according to claim 1.

8. The thickness of the substrate layer is 5 to 60 μm. The gas-barrier multilayer film according to claim 1.

9. The gas-barrier multilayer film further comprises an additional substrate layer, an additional gas-barrier layer, or an inorganic layer. The gas-barrier multilayer film according to claim 1.

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