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Method for the preparation of a poly (arylene ether)-polyolefin composition, and composition prepared therebyMethod for the preparation of a poly (arylene ether)-polyolefin composition, and composition prepared thereby description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20060079642, Method for the preparation of a poly (arylene ether)-polyolefin composition, and composition prepared thereby. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS REFERENCE TO RELATED APPLICATION [0001] This application is a division of U.S. Nonprovisional application Ser. No. 10/754,126 filed 9 Jan. 2004. BACKGROUND [0002] Poly(arylene ether)-polyolefin compositions are well known. Many references teach the desirability of preparing these compositions by combining all components in a single mixing step. See, for example, U.S. Pat. No. 4,764,559 to Yamauchi et al.; U.S. Pat. No. 4,772,657 to Akiyama et al.; U.S. Pat. No. 4,863,997 to Shibuya et al.; U.S. Pat. No. 4,985,495 to Nishio et al.; U.S. Pat. No. 4,990,558 to DeNicola, Jr. et al.; U.S. Pat. Nos. 5,071,912, 5,075,376, 5,132,363, 5,159,004, 5,182,151, and 5,206,281 to Furuta et al.; U.S. Pat. No. 5,418,287 to Tanaka et al., and European Patent Application No. 412,787 A2 to Furuta et al. [0003] Alternatively, some references teach the desirability of adding components in order of higher to lower viscosities. See, for example, U.S. Pat. No. 4,764,559 to Yamauchi et al., 4,985,495 to Nishio et al., and U.S. Pat. No. 5,418,287 to Tanaka et al. [0004] In yet another proposed blending method, a polyphenylene ether and a polypropylene-graft-polystyrene copolymer, with or without unmodified polypropylene, are pre-mixed before one or more rubbery substances are added with additional mixing. See, for example, U.S. Pat. Nos. 5,071,912, 5,075,376, 5,132,363, 5,159,004, 5,182,151, and 5,206,281 to Furuta et al.; European Patent Application No. 412,787 A2 to Furuta et al.; and Japanese Unexamined Patent Application 63[1988]-113049 to Shibuya et al. [0005] The above-described methods produce compositions that are inadequate for many commercial uses because they exhibit excessive variability in key properties, including stiffness and impact strength. There remains a need for a method of producing poly(arylene ether)-polyolefin compositions having improved property balances. In particular, there remains a need for a method of producing poly(arylene ether)-polyolefin compositions exhibiting reduced property variability and improved tradeoffs between stiffness, impact strength, and heat resistance. BRIEF SUMMARY [0006] The above described and other drawbacks and disadvantages of the prior art are alleviated by a method of preparing a thermoplastic composition, comprising: melt-blending a poly(arylene ether) and a compatibilizer to form a first intimate blend; and melt-blending the first intimate blend and a polyolefin to form a second intimate blend; wherein the thermoplastic composition is substantially free of at least one component selected from (a) an unhydrogenated block copolymer of an alkenyl aromatic compound and a conjugated diene, and (b) a poly(alkenyl aromatic) resin. [0007] Additional embodiments are described in detail below. BRIEF DESCRIPTION OF THE DRAWING [0008] FIG. 1 is a diagrammatic view of kneading blocks used in high and low intensity upstream and downstream kneading. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [0009] One embodiment is a method comprising: melt-blending a poly(arylene ether) and a compatibilizer to form a first intimate blend; and melt-blending the first intimate blend and a polyolefin to form a second intimate blend; wherein the thermoplastic composition is substantially free of at least one component selected from (a) an unhydrogenated block copolymer of an alkenyl aromatic compound and a conjugated diene, and (b) a poly(alkenyl aromatic) resin. [0010] Extensive experiments by the present inventors have led to the surprising observation that the properties of the composition prepared according to this method are substantially and unexpectedly improved compared to compositions prepared by known methods, especially those methods in which all components are blended simultaneously. [0011] In a preferred embodiment, melt-blending to form the first intimate blend comprises high-energy mixing. The energy of mixing may be expressed in various ways. One factor contributing to the energy of mixing is the extruder addition point. For example, when the composition is compounded on an eleven barrel twin-screw extruder, high-energy mixing of the first-intimate blend may be expressed as addition of first intimate blend components to one of the first four barrels. [0012] Another factor contributing to the energy of mixing is the number of mixing sections, with greater numbers of mixing sections corresponding to higher energy mixing. Each mixing section may comprise at least one mixing element. The first intimate blend and the second intimate blend are each preferably formed using at least one mixing section. Mixing sections and mixing elements are generally well known in the art as components of twin-screw extruders. Each mixing element is disposed non-rotatably on a screw shaft and is used to disperse and distribute components of a thermoplastic composition throughout the blend. The mixing element may or may not advance the composition toward the outlet of the extruder. The present inventors have found that the properties of the composition are improved if the processes of mixing to form the first intimate blend and the second intimate blend each employ at least one mixing section. In a preferred embodiment, mixing to form the first intimate blend and the second intimate blend each employ at least two mixing elements on each screw shaft. [0013] There is no particular limitation on the design of the individual mixing elements. Suitable mixing elements include, for example, mixing elements on each of said shafts which are in radial interwiping relation within the extruder barrel and configured to wipe one another and the cylinder walls, as described in U.S. Pat. No. 4,752,135; mixing element disks having mixing wings as described in U.S. Pat. No. 3,195,868 to Loomans et al. and U.S. Pat. No. 5,593,227 to Scheuring et al.; mixing elements having two opposing lobes wherein one lobe is tapered, as described in U.S. Pat. No. 6,116,770 to Kiani et al.; and the various mixing elements, including those characterized as prior art mixing elements, described in U.S. Pat. No. 5,932,159 to Rauwendaal. [0014] In one embodiment, melt-blending to form a first intimate blend and melt-blending to form a second intimate blend collectively comprise mixing with a mixing energy input of at least about 0.20 kilowatt-hour/kilogram (kW-hr/kg). A mixing energy input of at least about 0.22 kW-hr/kg may be preferred, and an energy input of at least about 0.24 kW-hr/kg may be more preferred. Such quantitative mixing energy input may be determined by measuring the rotation rate of the extruder motor and the extruder motor's current draw. Since a direct current (DC) motor speed is directly proportional to the voltage applied, a previously measured proportionality constant may be used to convert the measured motor speed, in rpm, to a voltage in volts. The energy input may then be calculated as the product of the extruder motor current and voltage, divided by the extruder throughput rate. For example, an extruder operating at 120 volts, 2 amps, and a throughput of 1 kg/hr has an energy input of (120 V)(2 A)/(1 kg/hr)=240 W-hr/kg or 0.240 kW-hr/kg. [0015] In one embodiment, the first intimate blend may be formed and pelletized in one step, then mixed with the polyolefin to form the second intimate blend in another step. [0016] Suitable temperatures for forming the composition are generally about 180.degree. C. to about 400.degree. C. Within this range it may be preferred to form the first intimate blend by exposing the first intimate blend components to a temperature of at least about 200.degree. C., more preferably at least about 250.degree. C., yet more preferably at least about 280.degree. C. Also within the above range, it may be preferred to form the first intimate blend by exposing the first intimate blend components to a temperature of up to about 320.degree. C., more preferably up to about 300.degree. C., yet more preferably up to about 290.degree. C. The same temperatures are also suitable for formation of the second intimate blend. [0017] The method is suitable for preparing the poly(arylene ether)-polyolefin compositions on any scale, from grams to tons. For economical production of commercially significant amounts of the composition, it may preferred that the method have a throughput rate of at least about 10 kilograms per hour (kg/h), more preferably at least about 5,000 kg/h, based on the total weight of the composition. Throughput rates of 100,000 kg/h and higher may be used. [0018] Any known apparatus may be used to carry out the method. Utilization of the method on a laboratory scale may employ a lab-scale mixer such as, for example, a Labo Plastomill available from Toyo Seiki Company, Hyogo, Japan. Preferred apparatuses for conducting the method on a larger scale include single-screw and twin-screw extruders, with twin-screw extruders being more preferred. Extruders for melt blending of thermoplastics are commercially available from, for example, Coperion, Ramsey, N.J. The method may also be carried out using apparatus designed to compound the composition and mold it directly, without an intermediate pelletizing step. Such apparatus is described, for example, in U.S. Pat. No. 6,109,910 to Sekido, and 6,464,910 B1 to Smorgon et al; U.S. Patent Application No. 2003/0021860 A1 to Clock et al; and International Publication No. WO 02/43943 A1 to Adedeji et al. [0019] FIG. 1 illustrates non-limiting examples of extruder configurations useful for conducting the method. The upper half of the figure is a full extruder configuration using high intensity ("+1") upstream kneading ("kneading 1") and low intensity ("-1") downstream kneading ("kneading 2"). High intensity upstream and downstream kneading correspond to use of assemblies of multiple right-handed, left-handed, and neutral kneading elements as depicted in FIG. 1 as Kneading 1 (+1) and Kneading 2 (+1), respectively. Likewise, low intensity upstream and downstream kneading corresponded to the use of assemblies depicted in FIG. 1 as Kneading 1 (-1) and Kneading 2 (-1), respectively. In the screw elements labeled in FIG. 1, RSE stands for right-handed screw element, SFE stands for single flighted element, RKB stands for right-handed kneading block, NKB stands for neutral kneading block, and LKB stands for left-handed kneading block. Each labeled element includes a two-number or three-number designation following the three letter acronyms described above. For conveying elements (i.e., those elements for which the third letter of the three letter acronym is "E"), the first number is the pitch (i.e., the axial length in millimeters required for a flight to make a full revolution). For kneading blocks (i.e., those elements for which the third letter of the three letter acronym is "B"), the first number is the offset angle of each individual disk to its neighbor, and the second number is the total number of disks that make up the screw element. For all screw elements, the last number is the total length of the screw element in millimeters. The numbered sections above the screw elements are known as barrel numbers. Each kneading section is bounded by the first and last kneading blocks within that section. For example, "Kneading 1 +1" is bounded on the left by RKB 45/5/28 and on the right by LKB 45/5/14. It will be understood that the lower half of the figure is meant to show the "opposite" versions of Kneading 1 and Kneading 2 that may be inserted into the corresponding kneading sections in the upper half of the figure. Continue reading about Method for the preparation of a poly (arylene ether)-polyolefin composition, and composition prepared thereby... 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