Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2001-03-12
2002-09-17
Woodward, Ana (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S179000, C525S183000
Reexamination Certificate
active
06451912
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to radio frequency (RF) susceptible, film-forming, polymer blend compositions, especially to compositions that are substantially free of halogen-containing polymers such as poly(vinyl chloride) or PVC. In other words, current analytical techniques do not reveal the presence of detectable quantities of chemically combined halogen. The invention particularly relates to mono-layer films fabricated from such compositions and coextruded multi-layer film structures incorporating at least one layer fabricated from such compositions. The invention more particularly relates to such compositions that comprise a copolyamide and an acid-functionalized polyolefin, and their use in such films and structures.
BACKGROUND OF THE INVENTION
Products manufactured from flexible PVC (f-PVC) enjoy a long history of use in a variety of end use applications, including those that rely upon its RF sealing capability, vapor or gas barriers, or flexibility. Concerns about the environmental impact of halogenated polymers such as f-PVC, particularly during their manufacture and disposal, spark efforts to develop halogen-free alternatives. Phthalate plasticizer use in f-PVC, typically at levels of 10-40 percent by weight (wt %), based on composition weight, triggers debates when f-PVC finds its way into medical products, toys for children and food packaging. The debates center upon the tendency of plasticizers to migrate from, or leach out of, f-PVC in use or over time.
Efforts to counter the concerns tend to focus upon olefin polymers such as polypropylene (PP), polyethylene (PE), styrenic block copolymers such as styrene/ethylene butene/styrene or (SEBS), and ethylene copolymers such as ethylene/octene-1 or ethylene/vinyl acetate (EVA) copolymers. The olefin polymers match or approximate many physical properties exhibited by f-PVC and do so at a comparable cost. Films formed from such polymers require heat sealing as they have too low a dielectric loss factor (DLF) to facilitate high frequency (HF) sealing in general or RF sealing in particular.
Literature references describe various halogen-free polymers with dielectric properties that permit HF or RF welding or sealing. Such polymers include, for example, 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 alternate RF active polymers have a significantly higher tensile modulus or stiffness than f-PVC, making substitution in flexible film packaging or bag applications unfeasible.
Copolyamides, known to be RF active, suffer drawbacks in terms of inadequate physical properties and high cost relative to f-PVC. High number average molecular weight (M
n
) polyamides, also known as nylon, generally have a high enough modulus to classify them as stiff relative to f-PVC, and are both difficult to seal and expensive. Low M
n
copolyamides, such as those used in the present invention, typically find use in low viscosity hot melt adhesives. As such, they have low melt strength, low tensile strength, poor processability on conventional extrusion equipment, adhesive type tackiness, and excessive cost.
Another effort to replace f-PVC with halogen-free polymers uses copolymers of olefins with acrylic acid esters (acrylates) or vinyl esters such as vinyl acetate (VA). Copolymers with higher levels (generally greater than (>) 15 wt %, based upon copolymer weight) of VA or methyl acrylate with ethylene, provide some measure of RF activity. While such olefin copolymers exhibit tensile and modulus properties similar to those of f-PVC and are of lower cost than TPU, nylon and PETG, they have a DLF significantly lower than that of f-PVC. The lower DLF effectively requires an increase in RF generator size with a concomitant increase in both capital expenses and power usage. These increases, when coupled with longer welding times, result in a higher final part cost.
An effort to avoid resorting to larger RF generators involves blending RF active inorganic or organic particulate additives, typically at high loading levels, into film-forming olefin polymer compositions. EP 193,902 discloses RF-sensitized compositions that include inorganic additives such as zinc oxide, bentonite clay, and alkaline earth metal aluminosilicates at levels of 1 to 20 wt %, based on composition weight. Patent Cooperation Treaty (PCT) Application Number 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 % of starch (to impart RF weldability) to a polyolefin blend that also contains a coupling agent. Such additives improve RF weldability, but do so while adversely affecting other properties such as film optics and clarity, tensile strength and toughness.
WO 95/13918 discloses multi-layer structures that include a RF susceptible layer based on four components. The components are a propylene-based polymer, a nonpropylene polyolefin, a RF-susceptible polymer, and a polymeric compatibilizing agent. The RF-susceptible polymer may be any of EVA, EMA, ethylene/vinyl alcohol (EVOH), polyamides (including nylons), PVC, vinylidene chloride polymers, vinylidene fluoride polymers, and copolymers of bisphenol A and epichlorohydrins. The compatibilizing agent is a styrene/hydrocarbon block copolymer, preferably an SEBS block copolymer modified by a maleic anhydride (MAH), epoxy or carboxylate functionality.
WO 96/40512 discloses multi-layer structures comprising a skin layer, a barrier layer and a RF-susceptible layer. A combination of four polymers yields the RF-susceptible layer. The polymers are a propylene polymer, a non-propylene polyolefin, a RF-susceptible polymer and a polymeric compatibilizing agent. The RF-susceptible polymer may be an EVA or an EMA copolymer with a sufficient comonomer content, a polyamide, an EVOH copolymer, PVC, vinylidene chloride, a fluoride or a copolymer of bisphenol-A and epichlorohydrin. Styrene/hydrocarbon block copolymers, especially SEBS block copolymers modified with maleic anhydride (MAH), epoxy or carboxylate functionalities, serve as suitable compatibilizing agents.
WO 95/14739 discloses polymeric compositions suitable for use in articles such as medical packaging. The compositions comprise a heat resistant polymer, a RF-susceptible polymer and a compatibilizing polymer. The RF susceptible polymer may be selected from either of two groups of polar polymers. One group includes ethylene copolymers wherein the comonomer is selected from acrylic acid, methacrylic acid, ester derivatives of acrylic acid or methacrylic acid with alcohols having 1-10 carbon atoms (C
1-10
), vinyl acetate and vinyl alcohol. The other group includes copolymers with segments of polyurethane, polyester, polyurea, polyimide, polysulfone or polyamide. The compatibilizer may be a styrenic block copolymer (e.g. SEBS), preferably MAH-fimctionalized.
European Patent Application (EP) 0 688 821 discloses a polyolefin composition that can be formed into sheets and films sealable with RF-generated dielectric heat. The composition comprises a heterophasic olefin polymer and 3-15% of at least one polymer having a dielectric heat loss factor (DHLF or DLF) of at least (>) 0.01. The heterophasic olefin polymer comprises a crystalline propylene homopolymer or copolymer, an optional crystalline ethylene copolymer, and an elastomeric ethylene/propylene (EP) copolymer. The heterophasic olefin polymer may be modified with 0.03 to 0.3% of at least one polar monomer, such as MAH. Polymers meeting the DHLF requirement include polyamides, vinyl polymers, polyesters and polyurethanes. Polyamides, especially those having a M
n
≧1000, are preferred.
SUMMARY OF THE INVENTION
A first aspect of the present invention is a polymeric composition suitable for fabrication
Dow Global Technologies Inc.
Woodward Ana
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