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EP-4741448-A1 - HEAT-SHRINKABLE POLYESTER FILM

EP4741448A1EP 4741448 A1EP4741448 A1EP 4741448A1EP-4741448-A1

Abstract

The present invention addresses the problem of providing a heat-shrinkable polyester film having improved shrinkage finish properties without limiting the raw material composition. The present invention is a heat-shrinkable polyester film characterized by containing ethylene terephthalate as a main constituent component and satisfying items (1)-(4) below: (1) A skirt ratio of 1-8% when the film is measured after being fixed in a state of being shrunk by 10% in a main shrinkage direction in 90°C hot air and heat-treated for one minute. (2) A maximum heat shrinkage stress in the main shrinkage direction of 1-10 MPa when the film is fixed in a state of being shrunk by 10% in the main shrinkage direction in 90°C hot air and is measured while being heat-treated for one minute. (3) A shrinkage rate of 20-72% in the main shrinkage direction when the film is immersed in 80°C hot water for 10 seconds. (4) The average refractive index of the film is 1.57-1.585.

Inventors

  • ISHIMARU, Shintaro
  • HARUTA, MASAYUKI

Assignees

  • Toyobo Co., Ltd.

Dates

Publication Date
20260513
Application Date
20240627

Claims (11)

  1. A heat-shrinkable polyester film comprising an ethylene terephthalate unit as a main constituent component, and satisfying the following requirements (1) to (4): (1) a skirt ratio measured after the film is shrunk by 10% in a main shrinkage direction in hot air at 90°C and then heat-treated for one minute while being fixed in the 10% shrunk state is 1% or more and 8% or less; (2) a maximum heat shrinkage stress in the main shrinkage direction is 1 MPa or more and 10 MPa or less, as measured while the film is heat-treated in hot air at 90°C for one minute in a state fixed at a 10% shrinkage after being shrunk by 10% in the main shrinkage direction in hot air at 90°C; (3) a shrinkage rate when the film is immersed in hot water at 80°C for 10 seconds is 20% or more and 72% or less in the main shrinkage direction; and (4) an average refractive index of the film is 1.57 or more and 1.585 or less.
  2. The heat-shrinkable polyester film according to claim 1, wherein a storage elastic modulus at 90°C in a direction orthogonal to the main shrinkage direction of the film is 8 MPa or more and 100 MPa or less.
  3. The heat-shrinkable polyester film according to claim 1, wherein a shrinkage rate when the film is immersed in hot water at 80°C for 10 seconds is -10% or more and 10% or less in a direction orthogonal to the main shrinkage direction.
  4. The heat-shrinkable polyester film according to claim 1, wherein the film contains 1 mol% or more and 30 mol% or less of one or more monomer components selected from the group consisting of isophthalic acid, neopentyl glycol, 1,4-cyclohexanedimethanol, 1,4-butanediol, and diethylene glycol as constituent components of polyester constituting the film.
  5. The heat-shrinkable polyester film according to claim 1, wherein the film contains a mechanically recycled and/or chemically recycled polyester raw material as a raw material constituting the film.
  6. The heat-shrinkable polyester film according to claim 1, wherein a reversible heat capacity difference between before and after a glass transition temperature is 0.2 J/g·K or more and 0.3 J/g·K or less.
  7. The heat-shrinkable polyester film according to claim 1, wherein a glass transition temperature is 50°C or higher and 100°C or lower.
  8. The heat-shrinkable polyester film according to claim 1, wherein the ethylene terephthalate unit is 60 mol% or more with respect to 100 mol% of a polyester-constituting unit.
  9. A heat-shrinkable label using the heat-shrinkable polyester film according to any one of claims 1 to 8 for at least a part thereof.
  10. A package using the heat-shrinkable polyester film according to any one of claims 1 to 8.
  11. A package using the label according to claim 9.

Description

TECHNICAL FIELD The present invention relates to a heat-shrinkable polyester film suitable for label applications and container packaging. More specifically, the present invention is suitably used for labels for beverage bottles, banding of containers such as boxed meals containers, and the like, and is particularly excellent in environmental friendliness and finish property. BACKGROUND ART In recent years, heat-shrinkable films have been widely used for applications such as label packaging serving as both protection of glass bottles or plastic bottles and display of products, cap sealing, bundle packaging, and banding applications for binding boxed meal containers and the like. Among such heat-shrinkable films, polyvinyl chloride-based films have low heat resistance, and further have problems that hydrogen chloride gas is generated at the time of incineration and are a cause of dioxin generation. Polystyrene-based films are inferior in solvent resistance, require use of an ink having a special composition at the time of printing, need to be incinerated at a high temperature, and have a problem that a large amount of black smoke is generated with a strange odor at the time of incineration. For this reason, heat-shrinkable polyester films, which have high heat resistance, are easy to incinerate, and are excellent in solvent resistance, tend to be widely used as shrink labels. Among them, heat-shrinkable polyester films have room for improvement in finish property compared to other materials, and the inventors of the present invention have conducted repeated studies as manufacturers of heat-shrinkable polyester films (for example, Patent Literature 1). Further, Patent Literature 2 discloses a technique capable of improving a sink mark in a case where the film is shrunk on a container having a fixed point such as a square container, regarding shrinkage finish property when used as a label. Patent Literature 2 stipulates a diethylene glycol content of 1 to 20 mol%, and describes that an effect of suppressing the skirt ratio is improved by containing 3 mol% or more. Furthermore, Patent Literature 2 also describes that the skirt ratio can be suppressed in a case where the maximum stress generated by immersion in hot water at 90°C for 10 seconds is 6 N or less. Meanwhile, in recent environmental measures, there exists a method of using a raw material recycled from PET bottles for a heat-shrinkable polyester film in order to reduce load on the environment (for example, Patent Literature 3). In Patent Literature 2, since it is necessary to limit the raw material composition for suppression of the skirt ratio, it has been difficult to increase a content ratio of the recycled material. Further, the skirt ratio of the film described in Examples of Patent Literature 2 is in a range of 10 to 13%, and the outer appearance after shrinkage was not sufficient. CITATION LIST PATENT LITERATURE Patent Literature 1: JP 2011-94159 APatent Literature 2: Japanese Patent No. 5971897Patent Literature 3: Japanese Patent No. 6802535 NON-PATENT LITERATURE Non-Patent Literature 1: F. J. Balta Calleja; M. C. Garcia Gutierrez; D. R. Rueda; S. Piccarolo. Structure development in poly (ethylene terephthalate) quenched from the melt at high cooling rates: X-ray scattering and microhardness study. Polymer. 2000, vol. 41, p. 4143-4148. Non-Patent Literature 2: Atsushi Taniguchi; Miko Cakmak. The suppression of strain induced crystallization in PET through sub-micron TiO2 particle incorporation. Polymer. 2004, vol. 45, p. 6647-6654. SUMMARY OF INVENTION TECHNICAL PROBLEM In view of the above problems, an object of the present invention is to provide a heat-shrinkable polyester film having improved shrinkage finish property without limiting a raw material composition. MEANS FOR SOLVING PROBLEMS The present invention consists of the following configurations. 1. A heat-shrinkable polyester film comprising an ethylene terephthalate unit as a main constituent component, and satisfying the following requirements (1) to (4): (1) a skirt ratio measured after the film is shrunk by 10% in a main shrinkage direction in hot air at 90°C and then heat-treated for one minute while being fixed in the 10% shrunk state is 1% or more and 8% or less;(2) a maximum heat shrinkage stress in the main shrinkage direction is 1 MPa or more and 10 MPa or less, as measured while the film is heat-treated in hot air at 90°C for one minute in a state fixed at a 10% shrinkage after being shrunk by 10% in the main shrinkage direction in hot air at 90°C;(3) a shrinkage rate when the film is immersed in hot water at 80°C for 10 seconds is 20% or more and 72% or less in the main shrinkage direction; and(4) an average refractive index of the film is 1.57 or more and 1.585 or less.2. The heat-shrinkable polyester film according to 1., wherein a storage elastic modulus at 90°C in a direction orthogonal to the main shrinkage direction of the film is 8 MPa or more and 100 MPa or less.3.