Search

JP-2026076124-A - Biaxially oriented polypropylene film

JP2026076124AJP 2026076124 AJP2026076124 AJP 2026076124AJP-2026076124-A

Abstract

[Problem] To provide a biaxially oriented polypropylene film and packaging that suppress the drop in heat seal strength after peeling of the sealed portion, thereby enabling more stable peeling of the sealed portion. [Solution] The seal is composed of at least two layers, including a base layer and a seal layer. The base layer is made of a resin material containing polypropylene resin and polyethylene resin. The polypropylene resin in the base layer is a mixture of a propylene homopolymer and a propylene-based elastomer with a melting point of 150°C or higher. When the seal layers are heat-sealed at 130°C, 0.35 MPa, and for 1 second, the heat seal strength is 2.0 N/15 mm or more and 6.0 N/15 mm or less, and the standard deviation of the heat seal strength is 0.45 N/15 mm or less. [Selection Diagram] Figure 1

Inventors

  • 豊田 梨帆
  • 中島 禎彦
  • 濱田 俊一郎
  • 寺本 靖丈

Assignees

  • フタムラ化学株式会社

Dates

Publication Date
20260511
Application Date
20251014
Priority Date
20241023

Claims (9)

  1. A biaxially oriented film for packaging, comprising at least two layers including a base layer and a sealing layer mainly composed of polypropylene resin, wherein the sealing layers are heat-fused together to form an easily openable heat-sealed portion, The aforementioned substrate layer is composed of a resin material containing polypropylene resin and polyethylene resin. The polypropylene resin of the substrate layer is a mixture of a propylene homopolymer and a propylene-based elastomer with a melting point of 150°C or higher. A biaxially oriented polypropylene film characterized in that, when the sealing layers are heat-sealed together under the conditions of 130°C, 0.35 MPa, and for 1 second, the heat seal strength is 2.0 N/15 mm or more and 6.0 N/15 mm or less, and the standard deviation of the heat seal strength is 0.45 N/15 mm or less. Standard deviation of heat seal strength: The standard deviation was calculated from 12 points, which consist of the maximum heat seal strength and the heat seal strength at 1 mm intervals within a range of 5 mm to 15 mm of movement of the chuck of a tensile testing machine, when a test piece with a seal width of 10 mm in the MD direction and 15 mm in the TD direction was fixed to the chuck of a tensile testing machine and peeled off at a speed of 200 mm/min in the MD direction.
  2. The biaxially oriented polypropylene film according to claim 1, wherein the base layer comprises 65 to 90% by weight of the propylene homopolymer, 5 to 15% by weight of the propylene-based elastomer, and 1 to 13% by weight of the polyethylene resin, wherein the proportion of the polyethylene resin is less than or equal to the proportion of the propylene-based elastomer.
  3. The polyethylene resin is a biaxially oriented polypropylene film according to claim 1 or 2 , wherein the MFR measured under conditions of 190°C and a load of 2.16 kg in accordance with JIS K 7210 is 0.01 to 10 g/10 min and the density is 0.900 to 0.970 g/cm³.
  4. The sealing layer is mainly composed of a polypropylene copolymer consisting of one or more of the following: propylene-ethylene copolymer, propylene-ethylene-butene copolymer, or propylene-1/butene copolymer, or a mixture of two or more of these, as described in claim 1 or 2 of the biaxially oriented polypropylene film.
  5. The sealing layer is mainly composed of a polypropylene copolymer consisting of one or more of the following: propylene-ethylene copolymer, propylene-ethylene-butene copolymer, or propylene-1/butene copolymer, or a mixture of two or more of these, as described in claim 3 of the biaxially oriented polypropylene film.
  6. The biaxially oriented polypropylene film according to claim 1 or 2, wherein the haze of the biaxially oriented film is 15% or less.
  7. The biaxially oriented polypropylene film according to claim 3, wherein the haze of the biaxially oriented film is 15% or less.
  8. The biaxially oriented polypropylene film according to claim 4, wherein the haze of the biaxially oriented film is 15% or less.
  9. The biaxially oriented polypropylene film according to claim 5, wherein the haze of the biaxially oriented film is 15% or less.

Description

This invention relates to a biaxially oriented polypropylene film, and more particularly to a biaxially oriented polypropylene film for packaging that forms an easily openable heat-sealable portion. For example, in food packaging, stretched polypropylene film with excellent properties such as transparency and rigidity is preferably used. This packaging is manufactured using methods such as pillow packaging, where the film surfaces are heat-sealed. In recent years, packaging for bread and snacks sold in convenience stores and other retail outlets requires features such as easy opening, allowing for easy removal of the heat-sealed portion. In packaging with easy opening at the seal, an example of a polypropylene film for packaging is a stretched polypropylene film comprising at least two layers, including a sealing layer, wherein the sealing layer is composed of a mixed material of polypropylene resin and low-density polyethylene (see Patent Document 1). In this polypropylene film, the sealing layer is composed of a polypropylene resin manufactured using a single-site catalyst and two types of low-density polyethylene resins with different melt viscosities. The immismatch between the polypropylene and polyethylene resins in the sealing layer leads to a sea-island dispersion structure, resulting in cohesive failure and easy opening. However, the above polypropylene film lacks transparency, making it unsuitable for food packaging where high transparency is required. Furthermore, as a film with good peelability and ease of opening, for example, a stretched polypropylene film containing an anti-fogging agent has been proposed, comprising a base layer and a seal layer laminated to the base layer via an adhesive layer and an intermediate layer. The seal layer is composed of a mixed material of a propylene-based random copolymer and a butene-based elastomer, and the intermediate layer is composed of a mixed material of an amorphous or low-crystalline ethylene-α-olefin copolymer and low-density polyethylene (see Patent Document 2). In this polypropylene film, the intermediate layer of the four-layer structure is composed of 70-95% by weight of ethylene-α-olefin copolymer and 5-30% by weight of low-density polyethylene. When the seal portion is peeled at a speed of 200 mm/min in the TD direction, the maximum heat seal strength is in the range of 2.5-4.5 N/10 mm, and the heat seal strength at the point where the chuck has moved 10 mm is maintained at 60% or more of the maximum heat seal strength. However, although the heat seal strength at a certain distance reached when the seal portion is peeled in the above polypropylene film is maintained at a certain percentage or more of the maximum heat seal strength, the property of a large drop in heat seal strength after peeling has not been improved. Therefore, the stability during peeling is insufficient, and the need for special production equipment for the four-layer structure makes it economically disadvantageous. Furthermore, to prevent the seal from peeling off during transport, a multilayer film has been proposed that achieves both sealing strength and ease of peeling. For example, it comprises an outer layer containing a propylene polymer, an intermediate layer containing 5 to 35% by weight of an ethylene homopolymer and two or more propylene polymers, and a seal layer containing a propylene random copolymer with a melting point of 150°C or lower, wherein at least one of the propylene polymers in the intermediate layer is a propylene homopolymer or a propylene random copolymer, at least one of the propylene polymers is a propylene block copolymer, and the density of the ethylene homopolymer contained in the intermediate layer is 930 kg/ m³ or less (see Patent Document 3). However, this multilayer film is based on the premise of lamination with a surface substrate, and when used as a film for food packaging, the processing costs are high, making it economically disadvantageous. Japanese Patent Publication No. 2021-095162Patent No. 7018794Patent No. 7243462 This is a chart showing the heat seal strength of a biaxially oriented polypropylene film according to one embodiment of the present invention.This is a chart showing the heat seal strength of conventional biaxially oriented polypropylene films. A biaxially oriented polypropylene film according to one embodiment of the present invention is a biaxially oriented film for packaging, comprising at least two layers including a base layer and a sealing layer, both primarily composed of polypropylene resin. During the packaging process, the sealing layers are heat-fused together to form an easily openable heat-sealed section. Packaging made from this biaxially oriented polypropylene film is primarily used as packaging for food products, and is particularly suitable for packaging bread, snacks, and the like. In the biaxially oriented polypropylene film of the present invention, the resin material used in each layer describe