Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
1999-05-13
2001-06-05
Zitomer, Fred (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S242000, C526S250000, C526S253000, C526S254000
Reexamination Certificate
active
06242548
ABSTRACT:
DESCRIPTION
1. Field of the Invention
The invention pertains to a melt processable, multimodal, partially crystalline fluoropolymer. More particularly it relates to a multimodal fluoroplastic terpolymer of (i) vinylidene fluoride and (ii) at least two ethylenically unsaturated monomers of the formula CF
2
=CFR
f
where R
f
is F or a perfluoroalkyl of 1 to 8, preferably 1 to 3, carbon atoms.
2. Background
Partially crystalline fluoroplastic terpolymers of tetrafluoroethylene (TFE) vinylidene fluoride (VDF) and hexafluoropropylene (HFP) are available from Dyneon LLC and Dyneon GmbH under the name “Dyneon™ THV”. These fluoroplastic materials and their wide range of uses is described in more detail in “Modem Fluoropolymers”, Wiley, 1997, p. 257. They typically are derived from monomer compositions comprising from 30-70 weight % TFE, 5-40 weight % HFP and 5-55 weight % VDF and have a melting point range of 75° C. to 275° C.
Because of their relatively low melting point, fluoroplastics of this type can be easily coextruded with standard non-fluorinated thermoplastics (i.e., polyethylene, polypropylene, nylon, etc.) using standard extrusion equipment. That means that corrosion-resistant extrusion equipment is generally not needed. This permits the formation of a variety of products, including hose and fuel-line designs such as those disclosed in U.S. Pat. No. 5,804,670 and EP 824059. In such designs, the fluoroplastic provides a chemically resistant permeation barrier.
Very high extrusion speeds are usually used with the standard thermoplastics. However, the commercially available fluoroplastics can usually only be processed at relatively modest or moderate extrusion speeds. At high extrusion speeds, the extrusion process begins to run erratically and the extrudate exhibits regular fluctuations in thickness (the extrudate “breathes”). At even higher extrusion speeds, beginning at a so-called critical shear rate, particularly undesirable surface defects occur which appear in the form of a series of scale-like melt fracture (“sharkskin”). The typical critical shear rate of the standard commercially available fluoroplastics lies between 50 and 100 s
−1
at 265° C. The maximum coextrusion speed of standard thermoplastics with standard fluoroplastics is thus usually limited by the onset of these shear rate related surface defects of the extrudate.
In order to extrude fluoroplastics at the high extrusion speeds typically used with standard thermoplastics, it has been necessary to use low molecular weight fluoroplastics. However, this results in a loss of the mechanical properties (e.g. tensile strength at break, elongation at break, burst pressure of the extrudate.
For these and other reasons, there exists a need for a fluoroplastic terpolymer that can be melt processed at the high extrusion speeds of standard thermoplastics.
SUMMARY OF THE INVENTION
The present invention provides a fluoroplastic terpolymer that can be extruded at the high extrusion speeds of standard polymers without the need to lower the molecular weight of the fluoroplastic. The terpolymer has significantly improved processability as it postpones the onset of melt fracture (“sharkskin”) or other irregularities such as thickness fluctuations. With the polymer of the present invention, the critical shear rate is an order of magnitude higher than it is with the standard types of commercially available fluoroplastics. In some aspects of the invention the critical shear rate 265° C. is increased to more than 1000 s
−1
. Moreover, as the measurement of the melt viscosity before and after extrusion shows, this is achieved without any perceptable degradation of the terpolymer.
The polymer of the invention also offers additional advantages, in the production of thin-wall articles by means of extrusion or coextrusion; in injection molding; in use as an electrostatically dissipative (ESD) fluoroplastic; and in use as a processing additive for melt processable hydrocarbon polymers. The improved injection molding behavior, especially in the case of complicated shapes, and the improved extrusion of hydrocarbon polymers, is particularly noticeable.
With the materials in accordance with the invention, the extrusion of pipes at an increased extrusion throughput is attained as compared to that attained with standard commercially available fluoroplastics. Surprisingly, this is achieved while maintaining the physical properties of the terpolymer. It has also been found that molded objects can be created at lower temperatures so the final products have more dimensional stability and can be more highly loaded. Additionally, the final products can be made under conditions that are less likely to lead to discoloration and/or degradation.
As disclosed above, the polymer of the invention is also useful in the manufacture of ESD fluoroplastics. ESD fluoroplastics are often used in the hoses and fuel lines of motor vehicles. ESD plastics comprise a mixture of carbon and a polymer. As is the case with essentially all of the ESD polymers, the melt viscosity of the starting polymer is substantially increased because of the addition of carbon. Consequently, the ESD polymer becomes more difficult to process. To overcome this difficulty, the melt viscosity of the starting polymer is reduced. See EP 0 312 077 B1, for example, where the molecular weight of the polymer is lowered to reduce the melt viscosity. The reduction of the molecular weight fundamentally worsens the mechanical properties such as elongation at tear and the ultimate tensile strength, for example. As noted above, the molecular weight of the polymer of the invention is not reduced in order to extrude it at higher rates. As a result, the mechanical properties of the extrudate are maintained.
Surprisingly, even as an ESD grade of fluoroplastic, the polymer of the invention can be extruded twice as quickly as commercially available virgin fluoroplastic material without the occurrence of any melt fracture or other surface defects. The resulting smooth surface is beneficial in fuel line applications as it reduces turbulent flow of the fuel through the line and reduces the occurrence of fuel line deposits.
In addition to the advantages disclosed above, the polymer of the invention can be used as a processing additive to provide a melt processable polymer composition. Use of the polymer composition of the invention in this way significantly improves the melt processability of melt processable polymers by either reducing the occurrence of melt defects in a host polymer or by postponing the onset of such defects to higher extrusion rates than is achieved without the use of a processing aid or with the use of other fluoropolymer-based processing aids.
In accordance with the present invention there is provided a multimodal terpolymer derived from interpolymerized units of (i) vinylidene fluoride and (ii) at least two ethylenically unsaturated monomers of the formula CF
2
=CFR
f
where R
f
is fluorine or perfluoroalkyl of 1 to 8, preferably 1 to 3, carbon atoms. As used herein the term multimodal terpolymer means a terpolymer having two or more discrete molecular weight ranges.
The multimodal terpolymer has a relatively low molecular weight component (A), a relatively high molecular weight component (B) and, optionally an ultrahigh molecular weight component (C). Preferably terpolymers contain no more than two to three of the discrete molecular weight components.
Component A of the polymer has a very low molecular weight. The molecular weight of component B lies within the range of molecular weights of the commercially fluoroplastic products such as the THV materials available from Dyneon. The ultrahigh molecular weight component C of the fluoropolymer is such that this component cannot be processed thermoplastically (i.e., melt processed) under normal melt processing conditions without degrading. A measure of the molecular weight is the melt flow index (MFI).
The exact values for MFI
A
, MFI
B
, and MFIc are determined by a number of factors including the way in which t
Dillon Maria P.
Duchesne Denis
Fronek Kirsten J.
Hintzer Klaus
Kaspar Harald
Dyneon LLC
Lilly James V.
Zitomer Fred
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