US-12617189-B2 - Polypropylene film, laminate, packaging material, and packing body

US12617189B2US 12617189 B2US12617189 B2US 12617189B2US-12617189-B2

Abstract

The present invention addresses the problem of providing a polypropylene film which is structurally stable to heat in deposition when used for packaging, and has appropriate slipperiness without using an anti-blocking agent or particles, and thus has excellent water vapor barrier properties and oxygen barrier properties, in particular, when a transparent deposited layer is laminated. Moreover, the present invention provides a polypropylene film characterized by having at least two types of layers (A layer and B layer) containing a polypropylene-based resin as a main component, wherein the B layer contains a thermoplastic resin incompatible with a polypropylene-based resin, and when the skewnesses Ssk of the A layer and the B layer, as measured through three-dimensional noncontact surface shape measurement, are Ssk (A) and Ssk (B), respectively, the Ssk (B) is at least 5 and the Ssk (A) is less than 5.

Inventors

Yasuyuki Imanishi
Masatoshi Ohkura
Haruki Aono

Assignees

TORAY INDUSTRIES, INC.

Dates

Publication Date: 20260505
Application Date: 20211220
Priority Date: 20201223

Claims (12)

1 . A polypropylene film comprising at least two layers comprising a layer A and a layer B that contain polypropylene based resins as primary components wherein the layer B contains a polymethylpentene based resin having a melting point of 185° C. to 240° C. that is incompatible with the polypropylene based resins and wherein Ssk(B) is 5 or more and Ssk(A) is less than 5 where Ssk(A) and Ssk(B) are the skewness Ssk of the layer A and that of the layer B, respectively, as determined by using a three dimensional noncontact surface profile measuring instrument.
2 . The polypropylene film as set forth in claim 1 , wherein the propylene unit fraction in the resin component present in the layer A is 97.0 mol % or more and 100.0 mol % or less and is equal to or greater than the propylene unit fraction in the resin component present in the entire polypropylene film.
3 . The polypropylene film as set forth in claim 1 , wherein the polypropylene based resin that is the primary component of the layer A has a melting point of 151° C. or more.
4 . The polypropylene film as set forth in claim 1 , wherein Sa(A) and Sa(B) meet the equation 2 where Sa(A) and Sa(B) are the surface roughness Sa of the layer A and that of the layer B, respectively: Sa ( B )/ Sa ( A )>1.0 equation 2.
5 . The polypropylene film as set forth in claim 1 , wherein the layer B is a heat-sealable layer.
6 . The polypropylene film as set forth in claim 1 further comprising a layer C containing a polypropylene based resin as primary component between the layer A and the layer B.
7 . The polypropylene film as set forth in claim 6 , wherein the layer C contains a petroleum resin.
8 . The polypropylene film as set forth in claim 1 that is intended for use as packaging material.
9 . A laminated product comprising a layer, hereafter referred to as a layer D, containing a metal and/or an inorganic compound that altogether account for more than 50 mass % and 100 mass % or less with respect to a total mass of the layer D, wherein the layer D is in contact with the layer A in a polypropylene film as set forth in claim 1 and wherein the layer D has a thickness of 50 nm or less.
10 . The laminated product as set forth in claim 9 , wherein Ssk (D) is less than 5 where Ssk (D) is the skewness Ssk of the layer D as measured with a noncontact type three dimensional surface roughness measuring instrument.
11 . A packaging material comprising a laminated product as set forth in claim 9 .
12 . A package containing contents covered by the packaging material as set forth in claim 11 .

Description

CROSS REFERENCE TO RELATED APPLICATIONS This is the U.S. National Phase application of PCT/JP2021/046933, filed Dec. 20, 2021, which claims priority to Japanese Patent Application No. 2020-213306, filed Dec. 23, 2020, the disclosures of each of these applications being incorporated herein by reference in their entireties for all purposes. FIELD OF THE INVENTION The present invention relates to a polypropylene film, a laminate, a packaging material, and a package that are particularly suitable for the purpose of packaging. BACKGROUND OF THE INVENTION Having high transparency, good mechanical characteristics, and good electric characteristics, polypropylene films have been applied in various fields including packaging materials, tape materials, and electric insulation materials such as wire wrapping and capacitors. For packaging materials that require gas barrier properties, in particular, laminated films produced by vapor-depositing a thin layer of aluminum (hereinafter occasionally referred to as Al) on a polypropylene film have been used widely. However, films obtained by Al vapor deposition are opaque and accordingly, they are not suitable for applications in which the contents have to be visible. Moreover in recent years, there has been a growing movement to recycle packaging plastics, but films containing Al vapor deposition layers are not sufficiently high in recyclability because it is difficult to visually distinguish them from Al-foil laminated films and also because they tend to be colored after recycling, which poses a problem to solve. In view of the above, there is a movement to replace the conventional Al vapor deposition layers with transparent vapor deposition layers of aluminum oxide (hereinafter occasionally referred to as AlOx), silicon oxide, or the like. The use of these transparent vapor deposition layers serves to provide transparent packaging materials and achieve increased recyclability. However, since these transparent vapor deposition layers are generally thinner and more fragile than the Al vapor deposition layers, the vapor deposition layers may be peeled off during the formation of vapor deposition layers or in downstream steps such as for bag making, and defects such as pinholes and cracks may occur in the vapor deposition layers, easily leading to problems such as deterioration in the water vapor barrier property, oxygen barrier property, or the like. A suitable degree of transportability is required during the vapor deposition step, bag making step, etc., and this is now achieved by, for example, adding an anti-blocking agent, particles, etc. to a surface layer of the film, so that the film has a rough surface to ensure high lubricity. In these processed films having vapor deposition layers, however, rigid protrusions result from the addition of an anti-blocking agent or particles described above. Accordingly, problems with defects and damages such as scrapes, pinholes, and cracks can occur in the vapor deposition layers that come in contact with each other during transportation of a product in the form of a wound roll, easily leading to problems such as deterioration in the water vapor barrier property, oxygen barrier property, or the like. To provide polypropylene films suitable for packaging applications, there have been conventional proposals such as films produced by controlling the molecular weight of a polypropylene resin material to increase its rigidity in order to produce a polypropylene film with an increased degree of plane orientation (for example, Patent document 1) and films having improved water vapor barrier property due to an increased degree of plane orientation achieved by adopting a high crystallinity raw material and a high degree of stretching in the length direction or performing a second longitudinal stretching in the length direction after biaxial stretching (for example, Patent document 2). In addition, for the purpose of carrying out suitable vapor deposition and achieving an appropriate transportability in the bag making step during the process for producing a packaging material, there have been other proposals such as films with lubricity developed by forming a rough surface containing particles (for example, Patent document 3) and films with lubricity improved by further controlling the thickness of each layer in a laminated film having particle-containing surface layer (for example, Patent document 4). As compared with this, for the purpose of developing lubricity without adding particles to a polypropylene film designed for release from adhesion, there is proposal of a film that is produced by dispersing a non-polypropylene resin with a high melting point in the surface layer of a polypropylene film (for example, Patent document 5). PATENT DOCUMENTS Patent document 1: Japanese Unexamined Patent Publication (Kokai) No. 2014-055283 Patent document 2: Japanese Unexamined Patent Publication (Kokai) No. 2001-040111 Patent document 3: Japanese Unexa