Patent Application
20080058449
The fluoroplastics used in the compositions are those that are sufficiently flowable when melted that they can be melt processed, such as extruded, to make products that are strong enough to be useful.
The fluoroplastics include, but are not limited to, melt processable semicrystalline fluoroplastics having a melt point (Tm) above room temperature (RT) or amorphous fluoroplastics having a glass transition temperature (Tg) above room temperature. Representative, non-limiting examples of fluoroplastics can be found in summary articles of this class of materials such as in: “Vinylidene Fluoride-Based Thermoplastics (Overview and Commercial Aspects)”, J. S. Humphrey, Jr., “Tetrafluoroethylene Copolymers (Overview)”, T. Takakura, “Fluorinated Plastics Amorphous”, M. H. Hung, P. R. Resnick, B. E. Smart, W. H. Buck all of Polymeric Material Encylopedia, 1996 Version 1.1, CRC Press, NY; “Fluoropolymers”, K-L. Ring, A. Leder, and M Ishikawa-Yamaki, Chemical Economics Handbook-SRI International 2000, Plastics and Resins 580.0700A all of which are hereby incorporated by reference.
Thus, it is contemplated that the fluoroplastic may be a homopolymer, copolymer, or terpolymer of fluorine-containing monomers including, but not limited to: tetrafluoroethylene, vinylidene difluoride, chlorotrifluoroethylene, and vinyl fluoride. Commercially available examples are illustrated by, but not limited to: poly(vinylidene difluoride), (PVDF); poly(ethylene-tetrafluoroethylene), (E-TEF); hexafluoropropylene/vinylidene fluoride (PVDF/HFP); tetrafluoroethylene/hexafluoropropylene/vinylidene fluoride, (THV); fluorinated ethylene propylene (FEP) and poly(ethylene-chlorotrifluoroethylene), (E-CTFE). It is anticipated that the fluoroplastic can be a mixture of fluoroplastics.
The composition may optionally contain fillers typically used in fluoropolymers. The filler level will be determined by the final application property and cost requirements. Any type of filler or blends of fillers typically used in fluoropolymers or their blends can be used. Suitable fillers include, but are not limited to: extending fillers such as quartz, calcium carbonate, and diatomaceous earth; pigments, such as iron oxide and titanium oxide; fillers, such as silica, carbon black and finely divided metals; heat stabilizers, such as hydrated cerric oxide, calcium hydroxide, magnesium oxide; flame retardants, such as zinc oxide, halogenated hydrocarbons, alumina trihydrate, magnesium hydroxide, wollastonite, organophosphorous compounds and other fire retardant (FR) materials; and other additives known in the art, such as glass fibers, stainless steel, bronze, graphite fiber, graphite, molybdenum disulphide, bronze, thermally conductive fillers, ceramics, polyphenylene sulfones, barium sulphate, magnesium chloride, clays and micas.
The composition includes a silicone hot melt additive. As used herein, the phrase “silicone hot melt additive” means a silicone-containing material which is solid at room temperature (about 25° C.) or the end-use temperature of the final plastic product, whichever is higher, but which melts to form a liquid at temperatures above this. When both the silicone hot melt additive and the fluoroplastic are molten, they are generally not miscible and, thus, the silicone tends to migrate to a surface of, for example, the barrel of the extruder or the surface of a filler, if present.
The transition temperature at which the silicone hot melt additive converts from a solid to a liquid should be lower than or at the temperature at which the fluoroplastic composition is processed As such, its melt transition temperature or a softening temperature is above about 25° C., alternatively in the range of about 50 to about 200° C., or alternatively in the range of about 70 to about 150° C.
The silicone hot melt additive is generally present in an amount of less than about 10 wt %, alternatively less than about 5 wt %, alternatively about 0.1 to 3 wt. %, and alternatively about 1 to about 3 wt %. The optimum level of silicone hot melt additive is system dependant and can be determined by further experimentation by one skilled in the art.
The silicone hot melt additive by its inherent nature does not require additional processing or masterbatching to be effectively incorporated into fluoroplastic, fluorinated thermoplastic and fluoroinated thermoplastic elastomers and will not migrate at room temperature.
The transition temperature of the silicone hot melt additive depends on its composition. Suitable silicone hot melt additives include, but are not limited to, silicone thermoplastics, silicone elastoplastics, silicone solventless adhesives, silicone pressure sensitive adhesives, silicone film adhesives, silicone-resins, silicone-resin/silicone-polymer blends, and silicone copolymers, which all have their melt transition temperature or a softening temperature above about 25° C. Resin polymer blends include, but are not limited to, silicone resins of the MQ-type and silicone gums. These resin polymer blends are described in U.S. Pat. No. 5,708,098, which is incorporated herein by reference. Suitable silicone copolymers include, but are not limited to, copolymers containing only silicone groups and silicone organic copolymers. Suitable silicone organic copolymers include, but are not limited to: silicone amines, such as silicone urethanes, silicone ureas, silicone etherimides, and silicone imides; silicone olefins; silicone polyesters, such as silicone epoxies, silicone acrylics, and silicone methacrylics; silicone aryls, such as silicone styrenes, and silicone biphenylsulphones; and silicone polyethers. Typically, a silicone hot melt additive is selected such that it has an appropriate melt transition temperature for the circumstances and appropriate physical and chemical properties for use in the resultant thermoplastic composition. For example, one can increase or decrease discoloration by selecting more thermally stable materials such as phenyl silicone containing hot melt additives instead of amine containing silicone hot melt additives which are less thermally stable.
The processing temperature for a fluoroplastic composition of the invention is determined by the specific fluoropolymer or fluoropolymer blend melt temperatures. The melt temperature is the initial temperature where the fluoropolymer or fluoropolymer blend starts to deform. The process temperature is typically higher than the melt temperature by about 30-50° C. or more to get good flowability.
When fillers are incorporated in thermoplastic compositions, there is often shear heating during processing which drives the temperatures of the compositions higher. The silicone hot melt additives of the invention can often change the final exit temperatures of such materials. The silicone hot melt additives are believed to compatibilize the filler surface and to migrate to the mixer/extruder surface and lubricate. Silicone hot melt additives behave similarly to traditional silicone additives used in this application. The ability to process the thermoplastic composition at lower temperatures helps to prevent degradation of the thermoplastic.
It should be noted that without the silicone hot melt additive, the melt blend of the filled fluoroplastic may not be uniform; it can have cracks, or unincorporated filler. However, when the silicone hot melt additive is included, the melt blend appears uniform.
Although not wishing to be bound by theory, it is believed that the presence of a small amount of a silicone hot melt additive in the filled fluoroplastic can modify the filler surface in a non-reactive way to treat the surface of the filler in-situ. The silicone hot melt additive is also believed to migrate to the fluoroplastic surface during processing to produce a better extrudate.
The fluoroplastic composition can include other additives or mixtures of additives of the types and in the amounts typically used in processing fluoropolymer compositions. Such additives, include, but are not limited to, compatibilizers, functionalizers, impact modifiers, plasticizers, antioxidants, processing aids, other lubricants, or ultraviolet light stabilizers.
The fluoroplastic composition can be melt blended and made into pellets. The pellets can then be used as the feed for an extruder or other melt processing equipment.
The following examples are presented to further illustrate the compositions and method of this invention, but are not construed as limiting the invention, which is delineated in the appended claims. All parts and percentages in the examples are on a weight basis and all measurements were obtained at approximately 23° C., unless otherwise indicated.
Additive 1 is a silicone hot melt additive with 74 weight percent MQ type resin containing methyl and alkenyl groups and 26 weight percent of a polydimethylsiloxane gum containing terminal and pendant vinyl groups with a total of 650 ppm vinyl and a plasticity of about 150 mm/100.
Additive 2 is a silicone hot melt additive with 71 weight percent MQ type resin containing methyl and alkenyl groups and 29 weight percent of a polydimethylsiloxane gum containing terminal and pendant vinyl groups with a total of 7500 ppm vinyl and a plasticity of about 150 mm/100.
Sample 1B cleanly separated from the mixer surfaces, whereas Sample 1A needed to be scraped off. The cooled slabs were marked with a Sharpie® Permanent Marker. The marker clearly wrote on Sample 1B whereas it did not wet Sample 1A.
Sample 2B cleanly separated from the mixer surfaces, whereas Sample 2A needed to be scraped off. Sample 2A had more unincorporated ZnO than Sample 2B as measured by wiping the surface of the material and noting the amount of filler released.
Sample 3A: NP-3000 (375 g) and ZnO (375 g) were added manually to a 379 ml Haake mixer equipped with banbury-rollers at 300° C. over 8 minutes at low rpm's (revolutions per minute). The rpm's were increased to 120 rpm over 5 minutes. The material was mixed at 120 rpm for 5 minutes. The material end temperature was 370° C.
Sample 4A: Kynar 2750-01 (375 g), ZnO (187.5 g), and NYAD 1250 (187.5 g) were added manually to a 379 ml Haake mixer equipped with banbury-rollers at 200° C. over 15 minutes at low rpm's (revolutions per minute). The rpm's were increased to 120 rpm over 8 minutes. The material was mixed at 120 rpm for 5 minutes.
Sample 4B cleanly released from all the mixer surfaces, whereas Sample 4A needed to be scraped off. Sample 4A (taupe) was discolored compared to Sample 4B (light grey to light tan).
Having described the invention in detail and by reference to specific embodiments thereof, it will be apparent that modifications and variations are possible without departing from the scope of the invention defined in the appended claims. More specifically, although some aspects of the present invention are identified herein as preferred or particularly advantageous, it is contemplated that the present invention is not necessarily limited to these preferred aspects of the invention.
