Surface-treated multi-layered polymer film

Abstract

A sealable polymeric film structure comprising (a) a core layer including a thermoplastic polymer, the core layer having a machine side and a product side that is on a side of the film opposite from the machine side; and (b) a sealable skin layer positioned on the product side of the core layer, the sealable skin layer including a thermoplastic polymer, wherein an exterior surface of the sealable skin layer has a receding Cahn value of at least about 0.48; and wherein in some heat—sealable embodiments, the sealable skin layer sealed to itself has a MST of from about 175° F. to about 220° F., with a jaw pressure of 20 psi for 0.75 seconds and a minimum acceptable seal strength of 200 g / in at 175° F., on a Wrap-Ade™ Crimp Sealer Model J or K.

Description

CROSS-REFERENCE OF RELATED APPLICATIONS [0001] This application claims benefit of priority to Provisional U.S. Application No. 60 / 613,157 filed Sep. 24, 2004 and is incorporated herein by reference.FIELD OF THE INVENTION [0002] This invention relates to polymer films, such as are useful for packaging films. More particularly it relates to heat sealable, biaxially-oriented film structures that are surface treated on the sealing surface. In preferred embodiments, the film is a multilayer film. BACKGROUND OF THE INVENTION [0003] Multilayer polymeric films are commonly used for packaging products such as snack foods, including candies, potato chips, cookies, ice cream bars and dairy products. The versatility and compositional variation of polymer films facilitate usefulness in a variety of packaging applications. A wide array of film compositions are available today due to custom tailoring a multitude of variables related to polymer composition, additives, and method of preparation of t...

AI Technical Summary

Benefits of technology

[0010] This invention provides a film that has functionally useful friction-related properties on both sides of the film to facilitate improved machinability and processability in a relatively high humidity or moist environment, to facilitate improved packaging speed. One side of the film may offer improved processing and packaging machinery interaction while the opposing product side of the film provides advantages for interaction between the film and certain products, such as aqueous-based products. The film exhibits acceptable sealability, desired appearance and optical properties, is substantially non-blocking, and may be useful with moisture-comprising products and in relatively humid conditions, such as with freshly baked confectioneries, dairy products, and water-based products. The film may be suitable for use in packaging relatively low-moisture-content products, such as dry foods, and for use in dry environments. The film may be particularly well suited for use with horizontal form, fill and seal applications (HFFS), vertical, form, fill, and seal applications (VFFS), overwrap applications, pouches, bags, and for use in multilane HFFS packaging applications. The multi-layer film can be used as a coextruded web, or as a component of a laminated film structure. More specifically, the invention provides a film structure that includes a polymer core layer and a heat-sealable polymer skin layer, with the exterior surface of the skin layer possessing sufficient surface-energy to facilitate advantageous film interaction with various products.

[0011] A key aspect of this invention i s that the exterior surface of the sealable skin layer, (typically the product side surface, that is, the surface of the sealable skin layer opposite the core layer side of the sealable skin layer) possesses relatively high energy or is treated to increase the surface energy thereof. If treated to increase the energy, the film is preferably only treated to a limited extent to prevent degradation of the sealability of the sealable skin layer and to prevent treating the opposing side of the film. The relatively high energy or surface treatment may render the product side exterior surface of the film substantially hydrophilic in nature. Additionally, the exterior surface of the film on the side of the core layer opposite the sealable layer, the machine side surface of the film, is either not treated to increase surface energy, or is treated but the surface energy properties are attenuated, such as by printing or coating, such that the surface is substantially low-energy or hydrophobic in nature, as compared to the product side exterior surface. Films according to the present invention comprise the combination of both; (i) the treated or relatively higher-energy, substantially hydrophilic product side surface properties, and (ii) the untreated or relatively low-energy, substantially hydrophobic, machine side surface properties. However, there may be applications for some embodiments w here the machine side surface may be lightly treated, such as for printability, and then at least partially obscured to prevent the machine side from being too hydrophilic.

Problems solved by technology

For example, although polymer films have many desirable properties, untreated or uncoated films may possess certain inherent disadvantages, such as relatively poor water wetability, poor printability, poor barrier properties and / or blocking with adjacent film layers.

The higher the packaging speed, the more difficult this operation becomes.

The performance of a film embodiment, during packaging operations, may vary with changes in environmental conditions and can adversely impact properties on one or both sides of a film.

For example, in a dairy environment where frozen ice cream novelties and frozen water-based pops may be packaged, temperature and humidity conditions may vary widely and inconsistently at various regions within the facility, and within the vicinity of packaging operations, where the packaging equipment and processes are located.

In a humid or wet environment, undesirable friction characteristics may adversely affect the performance of either or both sides of the film.

Friction between packaging equipment surfaces and the film, and / or between the product and the film may cause packaging imperfections and impede high-speed processing.

For example, frozen pops or ice cream bars that are made from a syrup, cream or sugar-based solution may readily adhere and “tack-up” as the product engages the product side of the film, remaining in the proper position and orientation for the packaging process, while a sugar-free version of the product may slide or reorient on the film during packaging operations, resulting in either operational problems and slowing down the packaging line to accommodate the product variations.

A misaligned product may create increased product waste, film waste, machine damage and down-time, due to the product getting caught or chopped in the seals during the packaging process.

As relative humidity increases and condensation forms on equipment, the moisture may adhere to the film creating an excessive staccato movement of the film as the film repeatedly sticks and then releases from the wet machine surfaces.

This staccato movement frequently results in inconsistent package length, film jams, tears, and exaggerated product misalignment problems on the opposing, product side of the film.