Stock material or miscellaneous articles – Composite – Of addition polymer from unsaturated monomers
Reexamination Certificate
2000-05-17
2003-05-06
Tarazano, D. Lawrence (Department: 1773)
Stock material or miscellaneous articles
Composite
Of addition polymer from unsaturated monomers
C428S522000
Reexamination Certificate
active
06558809
ABSTRACT:
FIELD OF THE INVENTION
This invention concerns flexible films made from certain polymers that possess two important characteristics. First, they are substantially halogen-free. In other words, current analytical techniques do not reveal the presence of detectable quantities of chemically combined halogen. Second, the polymers yield films that can be activated (bonded or sealed) with high frequency (HF) electromagnetic energy. More particularly, this invention concerns HF or radio frequency (RF) weldable films containing carbon monoxide (CO) copolymers or interpolymers.
BACKGROUND OF THE INVENTION
Products manufactured from flexible polyvinyl chloride (f-PVC) have been used for many years in a multitude of applications. In recent years, however, growing concern about the environmental impact of halogen-containing polymers, from manufacture through disposition, has led to a desire to find alternatives for halopolymers, especially for PVC. Additionally, f-PVC contains a large percentage (typically from 10 to 40 percent (%)) of phthalate plasticizer. Such plasticizers have recently come under scrutiny because of medical and health concerns associated with migration of plasticizer from products that come into intimate contact with the human body, e.g., medical products, food products or toys, or because of leaching to the environment.
Flexible PVC film and sheet is used in many packaging, containment, decorative and protective applications that rely on the physical strength, flexibility, gas impermeability, low cost and HF sealability characteristics of the polymer. With the growing interest in replacing PVC with halogen-free polymers, much attention has been focused on polyolefin polymers such as polypropylene (PP), polyethylene (PE), metallocene polyethylene (mPE), styrenic-olefinic block copolymers and ethylene copolymers like ethylene-vinyl acetate (EVA). Although these polymers duplicate many f-PVC properties, none of them exhibit adequate dielectric properties to permit efficient HF sealability. While films or sheets made from these substitutes for PVC can be thermally welded or heat-sealed, they are not appropriate for HF activation in general or for RF sealing in particular.
Various halogen-free polymers have been described in the literature as exhibiting dielectric properties that permit HF or RF welding or sealing, e.g., thermoplastic polyurethane (TPU), polyamide (nylon) and glycol modified polyester (PETG). However, these polymers cost more than PVC, making direct substitution for f-PVC economically unattractive. In addition, some of the alternate RF active polymers have a significantly higher tensile modulus or stiffness than f-PVC, making the substitution in flexible film packaging or bag applications unfeasible.
Another approach to replace f-PVC with halogen-free polymers, uses copolymers of olefins with acrylate esters or vinyl acetate (VA). By copolymerizing higher levels (generally greater than (>) 15 percent by weight (wt %), based on copolymer weight) of VA or methyl acrylate with ethylene, some measure of RF activity can be achieved. While such olefin copolymers exhibit tensile and modulus properties similar to those of f-PVC and cost less than TPU, nylon and PETG, they have a dielectric loss factor (DLF) that is significantly lower than that of f-PVC. Consequently in RF sealing or welding operations, films made from copolymers of olefins with alkyl acrylates or VA require larger RF generators with a concomitant increase in both capital expenses and power usage, and longer welding times resulting in higher final part costs.
Another approach to incorporating RF activity into a halogen-free polymer is by blending in a RF active inorganic or organic particulate additive, typically at high loading levels. EP 193,902 discloses RF energy sensitized compositions in which inorganic sensitizers such as zinc oxide, bentonite clay, and alkaline earth metal aluminosilicates can be added at 1 to 20 wt % to a composition. WO 92/09415 describes incorporating RF receptors such as phosphonate compounds, phosphate compounds, quaternary ammonium salts, polystyrene sulfonate sodium salt, alkaline earth metal sulfate, and aluminum trihydrate into thermoset compounds and films. U.S. Pat. No. 5,627,223 discloses adding 1 to 50 wt % starch (to impart RF weldability) to a polyolefin blend that also contains a coupling agent. However, incorporation of inorganic or organic particulates will adversely affect film optics and clarity, tensile strength and toughness properties.
Several references teach that CO-containing ethylene copolymers exhibit excellent dielectric properties making them suitable for RF welding. For example, a series of USPs (U.S. Pat. Nos. 4,600,614; 4,601,865; 4,601,948; 4,660,354; 4,671,992; 4,678,713; 4,728,566; 4,766,035; 4,787,194; 4,847,155; and 4,895,457) teaches the use of CO-containing ethylene copolymers, e.g., ethylene-CO (ECO), ethylene-acrylic acid-CO (EAACO) and ethylene-vinyl acetate-CO (EVACO) for applications involving RF weldability and microwave heatability. With high levels of CO, CO-containing copolymers have excellent RF sealability and processability, but the polar nature of the copolymer results in lower interlayer cohesion with adjacent non-polar polyolefin layers in multilayer films. Conversely, with lower levels of CO, the RF activity is not sufficient to allow high speed RF sealing operations. U.S. Pat. No. 4,678,713, along with WO 86/07012, disclose coextruded multi-ply laminates in which at least one ply comprises a CO-containing polymer with RF sealability. Such laminates find use in the construction of multi-wall bags or containers. However, these disclosures are primarily concerned with coextruded multi-ply laminates in which at least one ply is a halopolymer.
WO 96/05056 teaches a thermoplastic polymer blend of a non-polar polyolefin (PO) and a polar ethylene copolymer having CO functionality. The blend contains from 1-90 wt % polar copolymer, based on blend weight. The blend forms a peelable seal layer for an easy opening package rather than a permanent seal. In general, seal strength decreases with increasing polar copolymer content.
EP 0703271 A1 discloses blends of EVA, very low density polyethylene (VLDPE) and, optionally, an EVACO terpolymer that are useful in providing flexible non-halogen containing thermoplastic polyolefin compositions for roof liners.
U.S. Pat. No. 5,029,059 discloses multilayer oriented, heat shrinkable thermoplastic films which may contain ECO copolymers. Halopolymers are recommended as preferred components and RF weldability is not mentioned.
SUMMARY OF THE INVENTION
In a first aspect, the present invention is a multilayer film comprising at least (a) a polar layer having a dielectric loss factor of at least (≧) 0.10 comprising an ethylene copolymer with carbon monoxide (CO) wherein the CO comprises at least 3 percent by weight of the polar layer and (b) a layer comprising a non-polar olefin homopolymer or a non-polar olefin copolymer. The films of the present invention are free of halogen containing polymer and exhibit HF or RF sealability in high speed manufacturing operations.
In a second aspect, the present invention is a halogen-free, HF sealable film comprising a blend of at least two olefin polymers, wherein one olefin polymer is a non-polar homopolymer or a non-polar copolymer and at least one olefin polymer has polymerized therein at least ethylene and CO, the CO being present in an amount sufficient to give the blend a DLF of at least 0.10. The amount of CO is desirably ≧3 wt %, based on total blend weight. The film is preferably a monolayer film, more preferably a substantially phthalate plasticizer-free film. The film of this aspect can, however, function as the polar layer of the multilayer film of the first aspect.
A third aspect of the present invention is an article of manufacture fabricated from the film of either the first aspect or the second aspect. The article of manufacture desirably includes at least one segment wherein the film is sealed to itself, a substrate or both at a
Kelch Robert H.
Pettersson Ing-Mari Gunnel
Tarazano D. Lawrence
The Dow Chemical Company
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