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
2000-10-10
2002-04-16
Nutter, Nathan M. (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...
C525S240000, C523S113000, C602S041000, C602S042000, C602S048000, C602S052000, C604S006160, C604S008000, C604S019000
Reexamination Certificate
active
06372848
ABSTRACT:
TECHNICAL FIELD
This invention relates to a polymer blend for fabricating medical materials and more particularly, to a blend of ethylene and &agr;-olefin copolymers each having a narrow molecular weight distribution for fabricating medical films and tubings.
BACKGROUND ART
In the medical field, where beneficial agents are collected, processed and stored in containers, transported and ultimately delivered through tubes by infusion to patients, there has been a recent trend toward developing materials useful for fabricating such containers and tubing without the disadvantages of currently used materials such as polyvinyl chloride. These new materials for tubings must have a unique combination of properties, so that the tubing may be used in peritoneal dialysis and I.V. administration sets. Among these are the materials must be optically clear, environmentally compatible, have sufficient yield strength and flexibility, have a low quantity of low molecular weight additives, have good dimensional stability and be compatible with medical solutions.
It is desirable for medical tubing to be optically transparent to allow for visual inspection of fluids in the tubing.
It is also a requirement that the tubing materials be environmentally compatible as a significant quantity of medical tubing is disposed of in landfills and through incineration. Further benefits are realized by using a material that is thermoplastically recyclable so that scrap generated during manufacturing may be incorporated into virgin material and refabricated into other useful articles.
For tubing that is disposed of by incineration, it is necessary to use a material that does not generate or minimizes the formation of by-products such as inorganic acids which may be environmentally harmful, irritating, and corrosive. For example, PVC may generate objectionable amounts of hydrogen chloride (or hydrochloric acid when contacted with water) upon incineration.
To be compatible with medical or dialysis solutions, it is desirable that the tubing material be free from or have a minimal content of low molecular weight additives such as plasticizers, stabilizers and the like. These components could be extracted into the dialysis or therapeutic solutions that come into contact with the material. The additives may react with the solutions or otherwise render the solutions ineffective.
Polyvinyl chloride (“PVC”) has been widely used to fabricate medical tubings as it meets most of these requirements. However, because PVC by itself is a rigid polymer, low molecular weight components known as plasticizers must be added to render PVC flexible. As set forth above, these plasticizers may leach out of the tubing and into the fluid passing through the tubing to contaminate the fluid. For this reason, and because of the difficulties encountered in incinerating PVC, there is a need to replace PVC medical tubing.
Polyolefins have been developed which meet many of the requirements of medical containers and tubing, without the disadvantages associated with PVC. Polyolefins typically are compatible with medical applications because they have minimal extractability to the fluids and contents which they contact. Most polyolefins are environmentally sound as they do not generate harmful degradants upon incineration, and in most cases are capable of being thermoplastically recycled. Many polyolefins are cost effective materials that may provide an economic alternative to PVC. However, there are many hurdles to overcome to replace all the favorable attributes of PVC with a polyolefin.
One particular polyolefin of interest is an ethylene and &agr;-olefin copolymer obtained using a single-site catalyst such as a metallocene catalyst, a vanadium catalyst or the like. Of this group of copolymers those having a density of less than about 0.915 g/cc are most desirable due to their favorable modulus of elasticity and other physical characteristics. These copolymers obtained using a single site catalyst shall be referred to as ultra-low density polyethylene (m-ULDPE). The m-ULDPE copolymers have better clarity and softness, a low level of extractables and also have fewer additives than traditional polyolefins. This is largely due to m-ULDPE having a narrow molecular weight distribution and a narrow composition distribution. The m-ULDPE is a newly commercialized resin that recently has been used in food and some medical applications.
The major technical challenges of using m-ULDPE to fabricate medical tubing or films is to overcome a melt fracture phenomenon that readily occurs in these type of polymers during processing. Melt fracture is typically and easily generated in this family of resins because they display significantly less rheological shear thinning during extrusion when compared to other ULDPE resins obtained using traditional Ziegler-Natta type catalysts. Melt fracture occurs when the surface of the extrudate reaches an unstable flow pattern when the extrusion speed exceeds certain levels. The unstable flow pattern leads to a structural and cosmetic defect in the surface of the finished product which is sometimes referred to as “shark skin” due to its textured finish. The melt fracture phenomenon significantly limits the range of output rates in which these resins can be processed without experiencing melt fracture and in most cases the rate falls outside the desired output rate of commercial extrusion processes. The resin industry has attempted to overcome this challenge by introducing fluoro-polymer based processing aids. The use of such processing aids is undesirable in the medical industry as such additives may leach into the solutions or generate inorganic acids upon incineration.
Currently, there are efforts in dealing with melt fracture without introducing foreign additives into the material formulations. One is to raise the melt temperature, but has a potential drawback of widening the dimensional tolerance due to longer cooling period of the extrudate which in turn can lead to dimensional tolerance problems and slow the extrusion rate. Another is to apply surface coat of fluoro-polymer on the die surface to reduce extrusion friction resistance. Both have been proved not effective for fabricating medical products but may be effective in manufacturing other products. Another effort is to blend a variety of polymers. Blending different polymers to achieve desired product performance is commonly used in the plastics industry. However, the impacts of the miscibility of the resins on the mechanical properties are always one of the major criteria in selecting individual polymers before blending. Products with high haze values are usually generated with mismatched resin densities or refractive indicies.
SUMMARY OF THE INVENTION
The present invention provides a blend of m-ULDPE resins or similar resins with a narrow molecular weight distribution for high speed production of medical products such as tubings or films with no melt fracture, good dimensional control, and high production throughput rate.
The present invention provides a polymer blend for fabricating medical products. The blend has a first ethylene and &agr;-olefin copolymer obtained using a single site catalyst present in an amount by weight of from about 0% to about 99% by weight of the blend and having a melt flow index from fractional, such as about 0.1 g/10 min, to about 5 g/10 min, a second ethylene and &agr;-olefin copolymer obtained using a single site catalyst and being present in an amount by weight of the blend from about 0% to about 99% and having a melt flow index from higher than about 5 g/10 min to about 20 g/10 min; and a third ethylene and &agr;-olefin copolymer obtained using a single-site catalyst and being present in an amount by weight of the blend from about 0% to about 99% and having a melt flow index greater than about 20 g/10 min.
The present invention further provides a polymer blend for fabricating medical products. The blend has a first ethylene and &agr;-olefin copolymer having a molecular weight distribution of less than about 3 and being present in
Ding Samuel
Ling Michael T. K.
Shang Sherwin
Warren Joel
Woo Lecon
Baxter International Inc.
Kelly Paula J. F.
Nutter Nathan M.
Reagen Joseph P.
Wallenstein & Wagner
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