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EP-4741161-A1 - MULTI-LAYER POLYETHYLENE FILM

EP4741161A1EP 4741161 A1EP4741161 A1EP 4741161A1EP-4741161-A1

Abstract

A multi-layer polyethylene film is a multi-layer polyethylene film comprising at least three layers of a first layer, a second layer, and a third layer in this order, wherein the softening point of the second layer is higher than the softening point of the first layer and higher than the softening point of the third layer, a ratio of the thickness of the second layer to the total thickness of the first layer and the third layer is 1 to 3, a temperature at the maximum of the melting peak observed in differential scanning calorimetry of the multi-layer polyethylene film is more than 129°C and less than 134°C, and an absolute value of the degree of molecular orientation of the multi-layer polyethylene film is less than 1.07.

Inventors

  • KATO RYOJI
  • TAKEI RYO
  • KAMEGAWA Yuki
  • YAMAMURA Takehide
  • YAMASHITA YUKI

Assignees

  • Toppan Holdings Inc.
  • TAMAPOLY CO., LTD.

Dates

Publication Date
20260513
Application Date
20240719

Claims (10)

  1. A multi-layer polyethylene film comprising at least three layers of a first layer, a second layer, and a third layer in this order, wherein the softening point of the second layer is higher than the softening point of the first layer and higher than the softening point of the third layer, a ratio of the thickness of the second layer to the total thickness of the first layer and the third layer is 1 to 3, a temperature at the maximum of the melting peak observed in differential scanning calorimetry of the multi-layer polyethylene film is more than 129°C and less than 134°C, and an absolute value of the degree of molecular orientation of the multi-layer polyethylene film is less than 1.07.
  2. The multi-layer polyethylene film according to claim 1, wherein the melt flow rates at 190°C under a load of 2.16 kg of the polyethylene resins constituting the first layer, the second layer, and the third layer are each 1.5 g/10 min or less.
  3. The multi-layer polyethylene film according to claim 1, wherein when the melt flow rates at 190°C under a load of 2.16 kg of the polyethylene resins constituting the first layer, the second layer, and the third layer are designated as MFR 1 , MFR 2 , and MFR 3 , respectively, MFR 1 - MFR 2 ≤ 0.55 g/10 min and MFR 3 - MFR 2 ≤ 0.55 g/10 min.
  4. The multi-layer polyethylene film according to claim 1, wherein when the melt flow rates at 190°C under a load of 2.16 kg of the polyethylene resins constituting the first layer, the second layer, and the third layer are designated as MFR 1 , MFR 2 , and MFR 3 , respectively, MFR 2 - MFR 1 ≤ 0.55 g/10 min and MFR 2 - MFR 3 ≤ 0.55 g/10 min.
  5. The multi-layer polyethylene film according to any one of claims 1 to 4, wherein the density of the polyethylene resins constituting the first layer and the third layer is less than 0.945 g/cm 3 .
  6. The multi-layer polyethylene film according to any one of claims 1 to 4, wherein the thicknesses of the first layer and the third layer are 1 µm or more and 10 µm or less.
  7. The multi-layer polyethylene film according to any one of claims 1 to 4, wherein the thickness of the second layer is 8 µm or more and 30 µm or less.
  8. The multi-layer polyethylene film according to any one of claims 1 to 4, wherein the softening points of the first layer and the third layer are 120°C or more and 160°C or less.
  9. The multi-layer polyethylene film according to any one of claims 1 to 4, wherein the softening point of the second layer is 125°C or more and 170°C or less.
  10. The multi-layer polyethylene film according to any one of claims 1 to 4, wherein the absolute value of the degree of molecular orientation of the multi-layer polyethylene film is 1 or more.

Description

Technical Field The present invention relates to a multi-layer polyethylene film. Background Art Polyethylene films are excellent in flexibility, transparency, moisture resistance, chemical resistance, and the like, and are inexpensive, so they are used as packaging materials. In recent years, with the growing demand for a recycling-oriented society, attempts have been made to recycle packaging materials. One method for reusing a packaging material in which various materials are composited is to separate it into each material. However, since laminates used for packaging materials are given a predetermined strength, it is necessary to perform thermal, chemical, or mechanical techniques to separate each material, and the separated materials need to be sorted based on specific gravity, spectroscopic differences, etc., which was not efficient. In order to recycle packaging materials more efficiently, mono-materialization, in which a laminate is composed of materials of the same type and the laminate is reused as a single material, is being studied. For example, Patent Literature 1 describes a laminate capable of realizing a packaging material having sufficient strength, heat resistance, and barrier properties applicable as a packaging material and the like, and also being excellent in recyclability, the laminate including a substrate, an adhesive layer, and a heat-seal layer, wherein the substrate and the heat-seal layer are composed of polyethylene, a vapor-deposited film is provided on at least one of between the substrate and the adhesive layer and between the heat-seal layer and the adhesive layer, and the substrate consists of a stretched film. Citation List Patent Literature Patent Literature 1: Japanese Unexamined Patent Publication No. 2020-55157 Summary of Invention Technical Problem When the present inventors studied proceeding with mono-materialization of laminates, there were cases where wrinkles occurred in the polyethylene film depending on the type of polyethylene resin constituting each layer of the polyethylene film and the thickness of each layer, making it difficult to form functional layers such as a vapor-deposited layer and a coating layer. In addition, although stretching the polyethylene film could suppress the occurrence of wrinkles in the polyethylene film, adhesion tended to be inferior when joining with various films such as a sealant film. Therefore, one aspect of the present invention aims to provide a multi-layer polyethylene film in which wrinkles are less likely to occur and adhesion is excellent. Solution to Problem One aspect of the present invention relates to a multi-layer polyethylene film including at least three layers of a first layer, a second layer, and a third layer in this order, wherein the softening point (probe descent temperature) of the second layer is higher than the softening point (probe descent temperature) of the first layer and higher than the softening point (probe descent temperature) of the third layer, a ratio of the thickness of the second layer to the total thickness of the first layer and the third layer is 1 to 3, a temperature at the maximum of the melting peak observed in differential scanning calorimetry of the multi-layer polyethylene film is more than 129°C and less than 134°C, and an absolute value of the degree of molecular orientation of the multi-layer polyethylene film is less than 1.07. The multi-layer polyethylene film has a multi-layer structure, and by adjusting the magnitude relationship of the softening point (probe descent temperature) of each layer and the ratio of the thickness, and adjusting the temperature at the maximum of the melting peak of the multi-layer polyethylene film and the degree of molecular orientation within predetermined ranges, wrinkles are less likely to occur and adhesion is excellent. In the multi-layer polyethylene film, the melt flow rates at 190°C under a load of 2.16 kg of the polyethylene resins constituting the first layer, the second layer, and the third layer may all be 1.5 g/10 min or less from the viewpoint that wrinkles are less likely to occur and adhesion is more excellent. Further, in the multi-layer polyethylene film, when the melt flow rates at 190°C under a load of 2.16 kg of the polyethylene resins constituting the first layer, the second layer, and the third layer are designated as MFR1, MFR2, and MFR3, respectively, MFR1 - MFR2 ≤ 0.55 g/10 min and MFR3 - MFR2 ≤ 0.55 g/10 min may be satisfied. Alternatively, MFR2 - MFR1 ≤ 0.55 g/10 min and MFR2 - MFR3 ≤ 0.55 g/10 min may be satisfied. By using polyethylene resins having a melt flow rate within a specific range as the polyethylene resins constituting each layer of the multi-layer polyethylene film, wrinkles are less likely to occur, and adhesion tends to be more excellent. In the multi-layer polyethylene film, the density of the polyethylene resins constituting the first layer and the third layer may be less than 0.945 g/cm3. By using polye