Plastic and nonmetallic article shaping or treating: processes – With severing – removing material from preform mechanically,... – To form particulate product
Reexamination Certificate
2000-06-01
2003-05-20
Eashoo, Mark (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
With severing, removing material from preform mechanically,...
To form particulate product
C264S211230
Reexamination Certificate
active
06565784
ABSTRACT:
TECHNICAL FIELD
This invention relates to a process for the preparation of compositions useful in the production of jacketing for telecommunications cables or of pipe products.
BACKGROUND INFORMATION
A typical telecommunications cable generally comprises one or more conductors, e.g., copper or glass fiber, in a cable core that is surrounded by at least two layers of polymeric material including an insulating layer and a jacketing layer, which usually contains carbon black.
In order to prepare the jacketing composition, carbon black is generally fed into the feed hopper of a melt/mixer or an extruder along with a resin and other additives. Carbon black, however, is a low bulk density material, which tends to bridge or flood feed hoppers when introduced at typical loadings of, for example, 30 percent by weight at elevated feed rates, i.e., at rates above 2000 pounds per hour (pph) in a 200 millimeter Buss™ co-kneader or 1000 pph in a 140 millimeter Buss™ co-kneader. In addition to bridging or flooding, the high loading can lead to excessive temperatures, which tend to decompose some of the standard additives, and cause degradation of the product. The surge of the feed due to the bridging or flooding can lead to variations in composition viscosity, which, in turn, can lead to excessive power draw fluctuations on the mixer motor, temperature variations at the die plate, and pressure fluctuation upstream of the die pack. The surge also causes a quick build-up of particulates resulting in plugged screen packs and increased pressure, and eventually mixer shut down. Finally, it is found that when the composition is extruded around a wire or core of wires (or glass fibers), the coating is rough rather than smooth.
To solve this problem, a mixture containing the resin, additives, and 30 to 50 percent by weight carbon black is introduced into a high shear mixer, generally off-line, to disperse the carbon black and other additives throughout the resin, and provide what is referred to as a masterbatch. Then, a separate let-down process is carried out in a melt-mixer wherein the masterbatch is diluted with a base resin to provide a homogeneous final product, i.e., a jacketing composition, containing about 2 to 4 percent by weight carbon black. The final product is often in the form of pellets ready for extrusion, storage, or shipping to customers, who will convert the pellets to a cable jacket.
In an attempt to lower costs while improving the quality of the pelleted product, i.e., a product with an improved dispersion of carbon black, industry is looking for an efficient in-line process in which the masterbatch process and let-down process are combined.
DISCLOSURE OF THE INVENTION
An object of this invention, therefore, is to provide a two-in-one process for the preparation of compositions useful in the production of telecommunications jacketing and pipe products and, which, in addition, improves the dispersion of the carbon black throughout the composition. Other objects and advantages will become apparent hereinafter.
According to the invention, a process has been discovered for the preparation of a composition useful in telecommunications jacketing comprising:
(i) introducing a polyolefin into the first mixing zone of a melt/mixer having first and second mixing zones;
(ii) introducing particulate carbon black per se or a premix of said carbon black and polyolefin into the first mixing zone, said carbon black being in an amount of about 2 to about 50 percent based on the weight of the polyolefin introduced into the first mixing zone;
(iii) melting the polyolefin in the presence of the carbon black in the first mixing zone;
(iv) mixing the carbon black and the molten polyolefin in the first mixing zone to provide a molten mixture;
(v) passing the molten mixture from step (iv) into the second mixing zone;
(vi) adding sufficient polyolefin to the molten mixture from step (v) to dilute the carbon black to a level of about 2 to about 3 percent by weight based on the weight of the total polyolefin in the melt/mixer;
(vii) mixing the added polyolefin with the molten mixture in the second mixing zone to provide a molten mixture;
(viii) about simultaneously with step (vii), venting the second mixing zone;
(ix) recovering the mixture from step (vii); and
(x) optionally, pelletizing the mixture from step (ix).
DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
Polyolefin, as that term is used herein, is a thermoplastic resin, which may be crosslinkable. It can be a homopolymer or a copolymer produced from two or more comonomers, or a blend of two or more of these polymers, conventionally used in film, sheet, tubing, and pipe and as jacketing and/or insulating materials in wire and cable applications. The monomers useful in the production of these homopolymers and copolymers can have 2 to 20 carbon atoms, and preferably have 2 to 12 carbon atoms. Examples of these monomers are alpha-olefins such as ethylene, propylene, 1-butene, 1-hexene, 4-methyl-1-pentene, and 1-octene; unsaturated esters such as vinyl acetate, ethyl acrylate, methyl acrylate, methyl methacrylate, t-butyl acrylate, n-butyl acrylate, n-butyl methacrylate, 2-ethylhexyl acrylate, and other alkyl acrylates; diolefins such as 1,4-pentadiene, 1,3-hexadiene, 1,5-hexadiene, 1,4-octadiene, and ethylidene norbornene, commonly the third monomer in a terpolymer; other monomers such as styrene, p-methyl styrene, alpha-methyl styrene, p-chloro styrene, vinyl naphthalene, and similar aryl olefins; nitriles such as acrylonitrile, methacrylonitrile, and alpha-chloroacrylonitrile; vinyl methyl ketone, vinyl methyl ether, vinylidene chloride, maleic anhydride, vinyl chloride, vinylidene chloride, vinyl alcohol, tetrafluoroethylene, and chlorotri-fluoroethylene; and acrylic acid, methacrylic acid, and other similar unsaturated acids.
The homopolymers and copolymers referred to can be non-halogenated, or halogenated in a conventional manner, generally with chlorine or bromine. Examples of halogenated polymers are polyvinyl chloride, polyvinylidene chloride, and polytetrafluoroethylene. The homopolymers and copolymers of ethylene and propylene are preferred, both in the non-halogenated and halogenated form. Included in this preferred group are terpolymers such as ethylene/propylene/diene monomer rubbers.
With respect to polypropylene: homopolymers and copolymers of propylene and one or more other alpha-olefins wherein the portion of the copolymer based on propylene is at least about 60 percent by weight based on the weight of the copolymer can be used to provide the polyolefin of the invention. Polypropylene can be prepared by conventional processes such as the process described in U.S. Pat. No. 4,414,132. Preferred polypropylene alpha-olefin comonomers are those having 2 or 4 to 12 carbon atoms.
Polyethylene, as that term is used herein, is a homopolymer of ethylene or a copolymer of ethylene and a minor proportion of one or more alpha-olefins having 3 to 12 carbon atoms, and preferably 4 to 8 carbon atoms, and, optionally, a diene, or a mixture or blend of such homopolymers and copolymers. The mixture can be a mechanical blend or an in situ blend. Examples of the alpha-olefins are propylene, 1-butene, 1-hexene, 4-methyl-1-pentene, and 1-octene. The polyethylene can also be a copolymer of ethylene and an unsaturated ester such as a vinyl ester, e.g., vinyl acetate or an acrylic or methacrylic acid ester.
The polyethylene can be homogeneous or heterogeneous. The homogeneous polyethylenes usually have a polydispersity (Mw/Mn) in the range of about 1.5 to about 3.5 and an essentially uniform comonomer distribution, and are characterized by single and relatively low DSC melting points. The heterogeneous polyethylenes, on the other hand, have a polydispersity (Mw/Mn) greater than 3.5 and do not have a uniform comonomer distribution. Mw is defined as weight average molecular weight and Mn is defined as number average molecular weight. The polyethylenes can have a density in the range of 0.860 to 0.950 gram per cubic centimeter, and preferably have a density in the
Duffy Sean Gerard
Esseghir Mohamed
Kharazi Alex
Lin Thomas Shiaw-Tong
Wojdyla John Francis
Eashoo Mark
Shipsides Geoffrey P.
Union Carbide Chemicals & Plastics Technology Corporation
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