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DE-112024003155-T5 - Multi-layer structure and packaging material

DE112024003155T5DE 112024003155 T5DE112024003155 T5DE 112024003155T5DE-112024003155-T5

Abstract

A multilayer structure comprising a sealing layer (X) and a substrate layer (Y), wherein the sealing layer (X) comprises a barrier layer (A) comprising as its main component EVOH (a) with an ethylene content of 20 to 50 mol% and a degree of saponification of 90 mol% or more, an adhesive layer (B) comprising as its main component an adhesive resin (b), and a thermal fusion layer (C) comprising as its main component an ethylene-α-olefin copolymer resin (c) having a density of 0.880 to 0.930 g/ cm³ , wherein the substrate layer (Y) is a layer comprising as its main component a polypropylene (y) having a melting point, as measured by a differential scanning calorimeter (DSC), of 150 °C or more, and which is stretched in each of the biaxial directions and has an elastic modulus in each of the biaxial directions under a condition with 23 °C and 50% RH of 2,000 MPa or more, and the thermal fusion layer (C) of the sealing layer (X) is located on an outermost surface.

Inventors

  • Kentaro Yoshida

Assignees

  • KURARAY CO., LTD.

Dates

Publication Date
20260513
Application Date
20240731
Priority Date
20230731

Claims (12)

  1. Multilayer structure comprising a sealing layer (X) and a substrate layer (Y), wherein the sealing layer (X) is a barrier layer (A) comprising as its main component an ethylene-vinyl alcohol copolymer (a) with an ethylene content of 20 to 50 mol% and a degree of saponification of 90 mol% or more, an adhesive layer (B) comprising as its main component an adhesive resin (b), and a thermal fusion layer (C) comprising as its main component an ethylene-α-olefin copolymer resin (c) having a density of 0.880 to 0.930 g/ cm³ , the substrate layer (Y) being a layer comprising as its main component a polypropylene (y) having a melting point, as measured by differential scanning calorimeter (DSC), of 150 °C or more, and being stretched in each of the biaxial directions and having an elastic modulus in each of the biaxial directions under a condition of 23 °C and 50 % RH of 2000 MPa or more, and the thermal fusion layer (C) of the sealing layer (X) is located on an outermost surface.
  2. Multilayer structure according to Claim 1 , where the difference (S - S Y ) between a puncture strength S measured according to JIS Z 1707: 2019 under a condition of 23 °C and 50 % RH and a puncture strength S Y of the substrate layer (Y) measured according to JIS Z 1707: 2019 under a condition of 23 °C and 50 % RH is 3.5 N or more.
  3. Multilayer structure according to Claim 2 , where the puncture resistance is S 12 N or more.
  4. Multilayer structure according to one of the Claims 1 until 3 , wherein, when the substrate layer (Y) is subjected to a temperature increase from 20 °C to 220 °C at 10 °C/min and then a temperature decrease to -50 °C at 10 °C/min using a differential scanning calorimeter (DSC), the difference (T1 - T2) between a maximum endothermic peak temperature (T1) during the temperature increase and a maximum exothermic peak temperature (T2) during the temperature decrease is 56 °C or less.
  5. Multilayer structure according to one of the Claims 1 until 3 , wherein the sealing layer (X) and the substrate layer (Y) are laminated together via an adhesive layer (Z) and the adhesive layer (Z) has a thickness of 2 to 7 µm.
  6. Multilayer structure according to one of the Claims 1 until 3 , wherein the ethylene α-olefin copolymer resin (c) is a linear low-density polyethylene produced by copolymerizing ethylene with an α-olefin having 6 or more carbon atoms.
  7. Multilayer structure according to one of the Claims 1 until 3 , wherein the barrier layer (A) comprises a boron compound at 50 to 400 ppm, expressed as boron element equivalent.
  8. Multilayer structure according to one of the Claims 1 until 3 , wherein the ethylene vinyl alcohol copolymer (a) has an ethylene content of 22 mol% or more and 28 mol% or less.
  9. Multilayer structure according to one of the Claims 1 until 3 , wherein the barrier layer (A) has a thickness of 5 µm or less.
  10. Multilayer structure according to one of the Claims 1 until 3 , which has an oxygen transfer rate of 5 cm 3 /(m 2 · day· atm) or less, as measured according to a method disclosed in JIS K 7126-2: 2006, under a condition of 20 °C and 65 % RH.
  11. Multilayer structure according to one of the Claims 1 until 3 , which has a water vapor transfer rate of 3 g/( m² ·day) or less, as measured according to a method disclosed in JIS K 7129-2: 2019, under a condition of 40 °C and 90% RH.
  12. Packaging material comprising the multi-layer structure according to one of the Claims 1 until 3 .

Description

[TECHNICAL FIELD] The present invention relates to a multilayer structure and a packaging material. [CURRENT STATE OF THE ART] Packaging materials for the long-term preservation of food often need to possess gas barrier properties, such as oxygen barrier properties. Using packaging materials with good gas barrier properties prevents oxidation-related spoilage of food and the proliferation of microorganisms due to oxygen ingress. Commonly used layers to improve gas barrier properties include metal foils, such as aluminum, metal vapor deposition (MVD) coatings, and inorganic MVD coatings, such as silicon dioxide and aluminum oxide. Resin layers with gas barrier properties, such as vinyl alcohol polymers and polyvinylidene chloride, are also widely used. Vinyl alcohol polymers exhibit gas barrier properties through crystallization and densification due to hydrogen bonds between hydroxyl groups in the molecule. Among them, an ethylene-vinyl alcohol copolymer (hereinafter sometimes abbreviated as "EVOH") is suitable for melt forming due to its superior thermal stability, and with the development of coextrusion technology, a multi-layer structure with an EVOH layer in the middle layer is widely used as a gas barrier packaging material. Triggered by environmental and waste problems, there has also been a growing global demand in recent years for the reprocessing of consumer waste, as it is generally known (hereafter perhaps abbreviated to "recycling"), which involves the recovery and reuse of packaging materials consumed on the market. Recycling typically uses a process that includes: shredding the recovered packaging material, separating and washing the shredded material as needed, and then melt-mixing the resulting material using an extruder. In this respect, packaging materials must consist of a single material as far as possible (monomaterialization), which allows for the production of highly pure and high-quality recycled raw materials. For example, from the perspective of superior mechanical strength, a gas barrier packaging material with a polyamide layer and an EVOH layer is generally used. However, this can reduce recyclability because an aggregate(s) can form due to a chemical reaction between the polyamide-based resin and the EVOH. Considering this issue, it is necessary to implement monomaterialization to provide a gas barrier packaging material that is superior in terms of recyclability while maintaining gas barrier properties and mechanical strength. Patent document 1 discloses a multilayer structure comprising: a hard layer with a puncture resistance of at least 40 N/mm and 150 N/mm or less, and (1) a resin composition layer comprising EVOH with a melting point of 170 °C or more and EVOH with a melting point of less than 170 °C, or (2) a resin composition layer comprising modified EVOH containing a modification group with a specific primary hydroxyl group, which is superior in terms of mechanical strength and thermoformability despite the absence of a polyamide layer, and, when the recycled material is melt-formed, prevents the formation of aggregates by resin degradation (gelation) and is also superior in terms of recyclability. [STATE OF THE ART DOCUMENTS] [Patent documents] Patent document 1: International PCT Publication No. 2020/071513 [SUMMARY OF THE INVENTION] [Problems to be solved by the invention] When used as packaging material for a heavy or cumbersome item, a higher resistance to drop impact is generally required, and the multilayer structure described in patent document 1 can sometimes exhibit insufficient drop impact resistance. In particular, when the temperature of the contents is high, for example, in cases of hot filling, heat sterilization, hot boiling, and the like, the container's drop impact resistance is sometimes especially inadequate. The present invention was made to solve the aforementioned problems and it is an object of the invention to provide a multi-layer structure and a packaging material which are superior in terms of gas barrier properties, the breakage resistance of the container in the event of a drop impact and recyclability. [Means of solving the problems] According to the present invention, the problem described above is achieved by providing any one of the following. (1) A multilayer structure comprising a sealing layer (X) and a substrate layer (Y), wherein the sealing layer (X) comprises a barrier layer (A) comprising as its main component an ethylene-vinyl alcohol copolymer (a) (hereinafter possibly referred to as ‘EVOH (a)’) having an ethylene content of 20 to 50 mol% and a degree of saponification of 90 mol% or more, an adhesive layer (B) comprising as its main component an adhesive resin (b), and a thermal fusion layer (C) comprising as its main component an ethylene-α-olefin copolymer resin (c) (hereinafter possibly referred to only as ‘ethylene-α-olefin copolymer resin (c)’) having a density of 0.880 to 0.930 g/ cm³ , wherein the substrate layer (Y)