Process for extrusion

a technology of extrusion and process, which is applied in the field of extrusion, can solve the problems of narrow molecular weight distribution, inability to improve the processability of resins into blown films in terms of bubble stability, and resins generally do not achieve a high level of bubble stability

US20020074682A1Inactive Publication Date: 2002-06-20UNION CARBIDE CHEM & PLASTICS TECH CORP
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Patent Information

Authority / Receiving Office
US · United States
Current Assignee / Owner
Publication Date
2002-06-20
Estimated Expiration
Not applicable · inactive patent
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Abstract

A process for the extrusion of polyethylene having a broad molecular weight distribution wherein the polyethylene is prepared in pellet form, said extrusion taking place in a pelletizing extruder having one or more zones essentially filled with polyethylene and two or more zones partially filled with polyethylene including a feed zone comprising (i) introducing the polyethylene into the extruder at a temperature sufficient to melt the polyethylene; (ii) introducing a mixture of an inert gas and oxygen into at least one partially filled zone with the exception of the feed zone, said mixture containing about 1 to about 21 percent by volume oxygen based on the volume of the gaseous mixture; (iii) passing the molten polyethylene through each zone at melt temperature; and (iv) extruding the polyethylene into pellets and cooling same.
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Description

[0001] This application is a continuation-in-part of application Ser. No. 09 / 022,793 filed on Feb. 13, 1998, which is a continuation of application Ser. No. 08 / 671,166 filed on Jun. 26, 1996.

[0002] This invention relates to a process for the extrusion of polyethylene into pellets useful in the production of blown film.BACKGROUND INFORMATION

[0003] Ziegler-type catalysts have undergone development over the years to improve the economy and quality of various polyethylene products. This development has tended towards narrowing the molecular weight distribution of the resin; however, narrow molecular weight distributions are not desirable for blown film resins, i.e., the narrow molecular weight distribution does not improve the processability of the resins into blown film in terms of bubble stability. Rather, bubble stability is a characteristic of broad molecular weight distribution resins.

[0004] A particularly good technique for producing broad molecular weight distribution polyethylen...

Examples

examples 1 to 7

[0081] Ethylene is copolymerized with 1-hexene in each of two fluidized bed reactors. The total pressure in each reactor is 300 psia. Each polymerization is continuously conducted after equilibrium is reached under conditions set forth in Table I. Polymerization is initiated in the first reactor by continuously feeding the above catalyst precursor and cocatalyst triethylaluminum (TEAL) into a fluidized bed of polyethylene granules together with ethylene, 1-hexene, and hydrogen. The TEAL is first dissolved in isopentane (5 percent by weight TEAL). The resulting copolymer mixed with active catalyst is withdrawn from the first reactor and transferred to the second reactor using nitrogen as a transfer medium. The second reactor also contains a fluidized bed of polyethylene granules. Again, ethylene, 1-hexene, and hydrogen are introduced into the second reactor where the gases come into contact with the copolymer and catalyst from the first reactor. Additional cocatalyst is also introduc...