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
2000-06-27
2002-04-30
Zitomer, Fred (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C524S380000, C525S199000, C525S231000, C525S240000, C526S247000, C526S255000
Reexamination Certificate
active
06380313
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to fluoropolymer processing additives that employ a vinylether monomer; to a melt processable thermoplastic polymer composition that utilizes this polymer processing additive; and to a method of improving the melt processability of a melt processable thermoplastic polymer.
BACKGROUND
For any melt processable thermoplastic polymer composition, there exists a critical shear rate above which the surface of the extrudate becomes rough and below which the extrudate will be smooth. See, for example, R. F. Westover,
Melt Extruision
, Encyclopedia of Polymer Science and Technology, Vol. 8, pp 573-81 (John Wiley & Sons 1968). The desire for a smooth extrudate surface competes, and must be optimized with respect to, the economic advantages of extruding a polymer composition at the fastest possible speed (i.e. at high shear rates).
Some of the various types of extrudate roughness and distortion observed in melt processable polymers, especially high and low density polyethylenes, are described by A. Rudin, et al., Fluorocarbon Elastomer Aids Polyolefin Extrusion, Plastics Engineering, March 1986, at 63-66. The authors state that for a given set of processing conditions and die geometry, a critical shear stress exists above which polyolefins such as linear low-density polyethylene (LLDPE), high-density polyethylene (BDPE), and polypropylene suffer melt defects. At low shear rates, defects may take the form of “sharkskin”, a loss of surface gloss, that in more serious manifestations appears as ridges running more or less transverse to the extrusion direction. At higher rates, the extrudate can undergo “continuous melt fracture” becoming grossly distorted. At rates lower than those at which continuous melt fracture is first observed, LLDPE and HDPE can also suffer from “cyclic melt fracture”, in which the extrudate surface varies from smooth to rough. The authors state further that lowering the shear stress by adjusting the processing conditions or changing the die configuration can avoid these defects to a limited extent, but not without creating an entirely new set of problems. For example, extrusion at a higher temperature can result in weaker bubble walls in tubular film extrusion, and a wider die gap can affect film orientation.
There are other problems often encountered during the extrusion of thermoplastic polymers. They include a build up of the polymer at the orifice of the die (known as die build up or die drool), increase in back pressure during extrusion runs, and excessive degradation or low melt strength of the polymer due to high extrusion temperatures. These problems slow the extrusion process either because the process must be stopped to clean the equipment or because the process must be run at a lower speed.
Certain fluorocarbon processing aids are known to partially alleviate melt defects in extrudable thermoplastic hydrocarbon polymers and allow for faster, more efficient extrusion. U.S. Pat. No. 3,125,547 to Blatz, for example, first described the use of fluorocarbon polymer process aids with melt-extrudable hydrocarbon polymers wherein the fluorinated polymers are homopolymers and copolymers of fluorinated olefins having an atomic fluorine to carbon ratio of at least 1:2 and wherein the fluorocarbon polymers have melt flow characteristics similar to that of the hydrocarbon polymers.
U.S. Pat. No. 4,904,735 (Chapman, Jr. et al.) describes a fluorinated processing aid for use with a difficultly melt-processable polymer comprising (1) a fluorocarbon copolymer which at the melt-processing temperature of the difficulty melt-processable polymer is either in a melted form if crystalline, or is above its glass transition temperature if amorphous, and (2) at least one tetrafluoroethylene homopolymer or copolymer of tetrafluoroethylene and at least one monomer copolymerizable therewith wherein the mole ratio is at least 1:1, and which is solid at the melt-processable temperature of the difficultly melt-processable polymer.
U.S. Pat. No. 5,397,897 to Morgan at al. describes the use of copolymers of tetrafluoroethylene and hexafluoropropylene having high hexafluoropropylene content as processing aids in polyolefins.
U.S. Pat. Nos. 5,064,594 to Priester et al., and 5,132,368 to Chapman, Jr. et al. describe the use of certain fluoropolymer process aids containing functional polymer chain end groups including —COF, —SO
2
F, SO
3
M, —OSO
3
M, —COOR and —COOM, wherein R is a C
1-3
alkyl group and M is hydrogen, a metal cation, or a quaternary ammonium cation for use with a difficultly melt-processable polymer. The fluoropolymer is selected from the group consisting of (i) irradiated polytetrafluoroethylene, (ii) a partially crystalline copolymer of tetrafluoroethylene and a perfluoro(alkyl vinyl ether) or a perfluoroolefin containing 3-8 carbon atoms, (iii) an elastomeric copolymer of tetrafluoroethylene and a perfluoro(alkyl vinyl ether), (iv) a copolymer of vinylidene fluoride, hexafluoropropylene and tetrafluoroethylene and (v) a copolymer of one or more fluoroolefins and 0.5-40 mole % of a functional-group-containing monomer
wherein Z is —F or —CF
3
, x is 0 or an integer of 1-4, y is 0 or 1, z is an integer of 1-12, and W′ is selected from the functional groups —SO
2
F, —SO
2
Cl, —SO
3
H, —COOR or —COOM, wherein R is C
1-3
alkyl and M is hydrogen, a metal cation, preferably an alkali metal cation, or a quaternary ammonium cation, said fluoropolymer containing at least 100 functional groups W per million carbon atoms. Such functional groups are either thermally unstable or are chemically reactive to basic and/or acidic functionalities present in the extrudable resin or in adjuvants incorporated into the extrudable composition.
U.S. Pat. No. 5,464,904 to Chapman et al. discloses the use of unimodal semicrystalline fluoroplastics such as copolymers of tetrafluoroethylene and hexafluoropropylene and terpolymers of tetrafluoroethylene, hexafluoropropylene and vinylidene fluoride with a polyolefin. The only enhancement of melt-processability described in this patent is shown in Example 25 where a concentration of 1000 ppm of the fluoropolymer in linear low density polyethylene is said to reduce the extrusion pressure of the extrudable composition. There is no showing of a reduction in melt defects.
U.S. Pat. Nos. 5,015,693 and 4,855,013 to Duchesne and Johnson disclose the use of a combination of a poly(oxyalkylene) polymer and a fluorocarbon polymer as a processing additive for thermoplastic hydrocarbon polymers. The poly(oxyalkylene) polymer and the fluorocarbon polymer are used at such relative concentrations and proportions as to reduce the occurrence of melt defects during extrusion. Generally the concentration of the fluoropolymer is present at a level of from 0.005 to 0.2 weight percent of the final extrudate and the poly(oxyalkylene) polymer is present at a level of from 0.01 to 0.8 weight percent of the final extrudate. Preferably, the weight of the fluorocarbon polymer in the extrudate and the weight of the poly(oxyalkylene) polymer in the extrudate are in a ratio of 1:1 to 1:10.
U.S. Pat. No. 5,710,217 to Blong at al. Discloses an extrudable thermoplastic hydrocarbon composition that comprises an admixture of a melt processable hydrocarbon polymer as the major component and an effective amount of a chemically-resistant fluoropolymer process aid. The fluoropolymer contains at least 50% by weight of fluorine and comprises one or more fluoropolymers that are essentially completely ethylenically unsaturated.
While prior processing additives have been useful, there is still a need to provide an improved fluoropolymer processing additive. It is desirable to provide a processing additive that gives improved melt processability as is discussed below. It is also desirable to provide a processing additive that is chemically stable towards aggressive host polymers (e.g., polar non-hydrocarbon host polymers such as nylon, etc.) and/or aggressive adjuvants employed in the host polymer (e.g., antioxidants such as HALS, etc.). Furtherm
Dillon Maria P.
Hintzer Klaus
Hirsch Bernhard
Kaspar Harald
Weilandt Karl-Dieter
Dyneon LLC
Lilly James V.
Zitomer Fred
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