Transparent oriented polypropylene film with high moisture vapor and oxygen barrier properties

Abstract

Described are transparent oriented polypropylene films with improved barrier properties and methods of making these films. The films and methods include a core layer comprising polypropylene, hydrocarbon resin, and polyethylene wax to improve moisture vapor barrier properties, an optional barrier layer comprising polar polymers to improve oxygen barrier properties, and optional skin layers to improve heat sealing, winding, printing, and / or adhesion.

Description

FIELD OF THE INVENTION[0001]This disclosure relates to an oriented polypropylene transparent film with improved barrier properties. More specifically, this disclosure relates to a multi-layer oriented transparent film that includes a core layer containing polypropylene, hydrocarbon resin, and polyethylene wax and at least one barrier layer containing polar polymers.BACKGROUND OF THE INVENTION[0002]In order to be used in packing applications, biaxially oriented polypropylene (BOPP) films should have excellent mechanical properties, excellent barrier properties (of moisture vapor and / or oxygen gas), and excellent heat sealability among other properties. In addition, BOPP films can include a promoting layer(s) suitable for various laminating, coating, and printing processes.[0003]For some packaging applications, BOPP films should have both good moisture vapor and oxygen gas barrier properties as well as transparency. A high barrier to moisture vapor and oxygen gas can maintain product ...

AI Technical Summary

Benefits of technology

The patent describes a method for improving the barrier properties of transparent BOPP films by using a combination of a polypropylene core layer with hydrocarbon resin and crystalline polyethylene wax, and polar polymeric barrier coatings. The resulting films have high moisture vapor and oxygen barrier properties. The method involves coextruding the core layer with optional barrier layers and optional skin layers, and optionally coextruding the barrier layers with the core layer. The films can be oriented uniaxially or biaxially. The use of polar polymers in the barrier layers can further enhance the barrier properties. The patent also describes a four-layered or five-layered oriented film with improved barrier properties.

Problems solved by technology

Therefore, this technology is not suitable for packaging applications that require transparency.

However, AlOx or SiOx coating is extremely brittle and prone to cracking of the oxide coatings occurring in the downstream processes of converting and packaging applications, such that the high barrier properties of the packaging cannot be maintained due to said cracking.

In addition, the cost of such oxide coating process is comparatively high and uncompetitive to most other high gas barrier OPP film technologies.

Although cast LCP films have good transparency, excellent barrier properties for both moisture vapor and oxygen gas, and excellent mechanical properties, the solvent casting process is very costly and not environmentally friendly.

Melt-extrudable LCPs have been known to present a processing difficulty in making LCP films.

Limitations of LCP film extrusion include high temperature for processing, low melt viscosity, poor adhesion to substrates, broad variations in thickness, opaqueness to light, and uni-axial orientation due to the unique arrangements of LCP chains in the materials.

Thus, the use of LCP packaging films is restricted to the applications of specialty packaging since both materials and processes are relatively expensive for general industrial packaging.

However, the oxygen barrier of the resultant film is only slightly improved over the polyester film of similar thickness.

Most fluoropolymers especially polychlorotrifluoroethylene (PCTFE) exhibit excellent moisture barrier properties (moisture transmission rates in the range of from 0.02 to 0.06 g / 100 in2 / day) and transparency; however, the fluoropolymers usually do not provide significant oxygen gas barrier properties.

Fluoropolymer films are restricted to use in specialty packaging since both fluoropolymers and equipment used for fluoropolymer film production are very expensive.

In addition, fluoropolymer films during incineration generate hydrogen fluoride (HF) which is an environmentally hazardous byproduct.

A costly offline coating process is needed to apply a thick PVdC coating on a BOPP substrate.

Although PVdC coating is a good candidate for moisture vapor and oxygen gas, it also has well-known environmental issues.

Coated BOPP films cannot be recycled into the reclaim streams of BOPP film production due to the intrinsic characteristics of PVdC materials.

Furthermore, PVdC coating in packaging materials decomposes into hazardous substances (for instance hydrogen chloride, HCl) as PVdC coated films are burned by waste incinerators.

Inevitably, the paraffin waxes may migrate onto the surface of the resultant film in downstream processes such as orientation in machine and transverse direction, converting operations, and packaging applications, which may lead to wax plate-out problems and contamination of processing equipment.

In addition, the resultant film showed very limited improvements in oxygen barrier.

In a production line, it is not efficient to add two cap layers onto a single core layer at the stages in-between the two orientation steps.

Although the outer polyolefin cap layers delayed the rate of wax migration, the wax additive in the core layer will continue to migrate through the polyolefin cap layers and form wax crystals on the surface, which may cause processing issues downstream such as wax plate-out or build-up.

In addition, the resulting film showed very limited capability to improve oxygen gas barrier which is required for some food packaging applications.

However, the cavitation of the intermediate layer renders the resulting film opaque and no longer transparent.