MXPA96001866A - A process for extrus - Google Patents

Abstract

A process for the co-extrusion of an inner layer around a conductive medium and an outer layer around the inner layer comprising: (i) introducing into an extrusion apparatus adapted for profile co-extrusion, a conductive medium; internal layer formulation comprising a homogeneous polyethylene having a polydispersity within the range of about 1.5 to about 3.5 and an essentially uniform comonomer distribution, and an organic peroxide, and an outer layer formulation comprising (a) a copolymer of ethylene and unsaturated ester (b) a polyethylene having a polydispersity greater than about 4.0 and a density of at least 0.916 gram per cubic centimeter, the polymer is made by a high pressure process, or (c) a heterogeneous ethylene copolymer and one or more alpha-olefins having a density of less than 0.916 gram per cubic centimeter, a melting index of at least about 4 grams per 10 minutes, and a polydispersity greater than about 4.0, and, optionally, an organic peroxide, and (ii) co-extrude the formulations at a temperature no greater than about 160 degrees.

Description

"A PROCESS FOR EXTRUSION" TECHNICAL FIELD This invention relates to a process for co-extrusion through an electrical conductor or communication means wherein the extruded material is essentially free of melt fracture.

BACKGROUND INFORMATION Polyethylene, during processing operations such as extrusion, is known to experience a phenomenon described as a melt fracture in which, upon exiting the die of the extrusion apparatus, the extruded material has a highly irregular surface. The uneven surface is rough, and does not have a consistent surface to make a finished quality article or to produce an aesthetically pleasing article. Linear polyethylenes such as LLDPE (linear low density polyethylene) and VLDPE (very low density polyethylene), due to an inherent characteristic of the molecular structure / melting rheology, are highly susceptible to melt fracture while highly branched polyethylene such as LDPE (low density polyethylene) has significantly less tendency to fracture by fusion. With linear high molecular weight polyethylene (low melt index), limited molecular weight distribution, limited (uniform) comonomer distribution, the melting fracture phenomenon is especially serious under extrusion conditions at relatively low temperature, such as temperatures lower than 160 degrees C, which vary as low as up to approximately 100 degrees C. Conventional techniques for melt fracture removal are to raise the temperature of the process thereby reducing the viscosity to the polymer, which results in deformation of corresponding minor shear stress in the matrix; decreasing the rate of yield thereby decreasing the rate of shear and the corresponding shear stress in the matrix; or increasing the shear rate of the matrix thereby increasing the viscous energy generation of the polymer to raise the localized melting temperature for an effect similar to raising the process temperature. These techniques reduce the viscosity of the polymer and the resulting melt fracture. However, there are deficiencies in these techniques that make them unacceptable for the processing of materials under low temperature processing conditions, that is, temperatures lower than 160 degrees C. The requirement for 'processing temperatures of less than 160 degrees C is desirable when extruding a resin formulation containing an organic peroxide, a thermally sensitive additive. When extruding a polyethylene formulation containing an organic peroxide, raising the temperature of the process is not a desired option to eliminate the melt fracture in view of the scorching problem, i.e. premature cross-linking caused by the decomposition of the organic peroxide. The decrease in the performance regime is also undesirable because the cost of manufacturing the extruded product increases. Finally, the increase of the shear rate regime of the matrix is similar in effect to the elevation of the temperature of the fusion with the inherent scorching. Another approach to face the phenomenon of fusion fracture is to redesign the process equipment, however, this involves designing equipment for a specific molecular weight resin that limits the usefulness of the equipment and, of course, raises the cost. Incorporating additive processing aids is another approach, but this is expensive and may affect other properties of the product. The mixing of a lower molecular weight polymer with a relatively high molecular weight polymer has the disadvantage that it typically results in a product with properties inferior to the properties of the high molecular weight product. Co-extrusion methods have also been used to overcome fusion fracture, but these methods have generally been applied to tubular blown film processes instead of extruding around wire or glass fibers for example. And these blown film processes have been carried out at temperatures considerably higher than 160 degrees C with resin formulations that do not include peroxides. In addition, the polyethylene resins used in these blown film processes have been of the heterogeneous type, which are not so susceptible to the phenomenon of melt fracture.

EXHIBITION OF THE INVENTION An object of this invention, therefore, is to provide a process for the extrusion of a homogeneous polyethylene formulation containing an organic peroxide around a conductive medium, wherein the extruded material is essentially free of melt fracture. Other objects and advantages will be evident below.

In accordance with the invention, a process has been discovered that fills the aforementioned object. The process is one for the co-extrusion of an inner layer around a conductive medium and an outer layer around the inner layer comprising: (i) introducing into an extrusion apparatus adapted for profile co-extrusion, a conductive medium; an internal layer formulation comprising a homogeneous polyethylene having a polydispersity within the range of about 1.5 to about 3.5, and an essentially uniform comonomer distribution, and an organic peroxide; and an outer layer formulation comprising (a) a copolymer of ethylene and an unsaturated ester; (b) a polyethylene having a polydispersity greater than about 4.0 and a density of at least 0.916 gram per cubic centimeter, the polymer has been produced by a high pressure process; or (c) a copolymer of ethylene and one or more alpha-olefins having a density of less than 0.916 gram per cubic centimeter, a melt index of at least about 4 grams for 10 minutes; and a polydispersity greater than about 4.0, and, optionally, an organic peroxide; and (ii) co-extrude the formulations at a temperature no greater than about 160 degrees C.

DESCRIPTION OF THE PREFERRED MODALITY (S) A profile extrusion process is one in which an extruded material having a structural profile such as wire insulation or cable jacket is prepared. A structural profile typically involves a viscous shaped fusion that leaves a forming matrix followed by cooling. The conductive means may be an electrical conductor, a core consisting of two or more electrical conductors, or an optical fiber communication means consisting of one or more glass fibers formed in a glass core. The extrusion apparatus is described below. The term "extrusion apparatus" in the context of this specification means one or more extrusion apparatuses with the inherent apparatus required for the co-extrusion of the polymer formulations around a conductive medium such as wire or glass fiber. The inner layer extruded around the conductive medium is a homogeneous polyethylene formulation. The thickness of the inner layer usually falls within the range of about 0.762 millimeters to about 7.62 millimeters. The homogeneous polyethylenes are copolymers of ethylene, one or more alpha-olefins, and, optionally, a diene. The alpha-olefins can have from 3 to 12 carbon atoms, and preferably have from 3 to 8 carbon atoms. Examples of alpha-olefins are propylene, 1-butene, 1-hexene, 4-methyl-1-pentene and 1-octene. The dienes may have from about 4 to 20 carbon atoms. Examples of the dienes are 1,4-pentadiene, 1,3-hexadiene, 1/5-hexadiene, 1,4-octadiene, 1,4-hexadiene, dicyclopentadiene, and ethylidene norbornene. As mentioned above, these homogeneous polyethylene have a polydispersity (Mw / Mn) within the range of about 1.5 to about 3.5, and an essentially uniform comonomer distribution. The homogeneous polyethylenes are characterized by relatively low individual melting temperatures and DSC. The heterogeneous polyethylenes (the most common of the two), 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 the weight average molecular weight and Mn is defined as the number average molecular weight. Homogeneous polyethylenes can have a density within the range of 0.860 to 0.930 gram per cubic centimeter, and preferably have a density within the range of 0.870 to about 0.920 gram per cubic centimeter. They may also have a melt index within the range of about 0.5 to about 30 grams per 10 minutes, and preferably have a melt index within the range of about 0.5 to about 5 grams per 10 minutes. Homogeneous polyethylenes can be prepared, for example, with vanadium-based catalysts such as those described in U.S. Patent Nos. 5,332,793 and 5,342,907, and can also be prepared with single-site metallocene catalysts such as those described in U.S. Patent Numbers. 4,937,299 and 5,317,036. The outer layer surrounding the inner layer is a formulation that contains one of three different polymers. The first polymer (a) is an ethylene polymer prepared by conventional high pressure processes. These polymers are highly branched with a large amount of long chain branching. The ethylene polymer can be a copolymer of ethylene and an unsaturated ester, such as vinyl acetate, ethyl acrylate, methyl acrylate, methyl methacrylate, tertiary butyl acrylate, n-butyl acrylate, n-butyl methacrylate, 2-ethylhexyl acrylate, and other alkyl acrylates. The unsaturated ester may have from 4 to 20 carbon atoms, preferably not more than 12 carbon atoms. The unsaturated ester may be present in the copolymer in an amount of about 5 percent to about 40 percent by weight, and preferably from 10 percent to about 35 percent by weight, based on the weight of the copolymer. The density of the copolymer can be within the range of 0.916 to 0.940 gram per cubic centimeter, and preferably falls within the range of 0.925 to 0.935 gram per cubic centimeter. The melt index can be within the range of about 5 to about 100 grams per 10 minutes, and preferably falls within the range of about 8 to about 70 grams per 10 minutes. The outer layer may also be constituted by a formulation containing the polymer (b), a high pressure polyethylene, usually an ethylene homopolymer, prepared for example by the high pressure process described in the Introduction to Polymer Chemistry, Stille , iley and Sons, New York, 1962, pages 149 to 151. The density of the homopolymer may be within the range of 0.916 to 0.930 gram per cubic centimeter, and preferably falls within the range of 0.920 to 0.928 gram per cubic centimeter. The melt index can be within the range of about 1 to about 10 grams per 10 minutes, and preferably falls within the range of about 2 to about 5 grams per 10 minutes. The melt index is determined according to Method D-1238, Condition E, of the American Society for the Testing of Materials, which is measured at 190 degrees C. Finally, the outer layer may be constituted of a formulation containing the polymer (c), which can be referred to as very low density polyethylene (VLDPE). This polymer has a density of less than 0.916 gram per cubic centimeter. The density can be as low as 0.860 gram per cubic centimeter. VLDPE can be produced by conventional low pressure processes such as those mentioned in U.S. Patent Nos. 4,302,565 and 4,508,442. VLDPE is a copolymer of ethylene and one or more alpha-olefins each having from 3 to 12 carbon atoms, and preferably from 3 to 8 carbon atoms. Examples of alpha-olefins are propylene, 1-butene, 1-hexene, 4-methyl-1-pentene and 1-octene. The polydispersity (Mw / Mn) of the polymer of the outer layer may be at least about 4, and preferably falls within the range of about 4.5 to about 10.

The outer layer is generally at least about .127 millimeters thick and for wire and cable applications preferably at least about 381 millimeters thick. The upper thickness limit is just a matter of economy, the lower the upper limit, the more economical it is to provide the same. Conventional additives, which can be introduced into any formulation, are exemplified by antioxidants, coupling agents, ultraviolet light absorbing agents or stabilizers, antistatic agents, pigments, dyes, nucleating agents, fillers or fillers or reinforcing agents or polymer additives, resistivity modifiers such as carbon black, slip agents, plasticizers, processing aids, lubricants, viscosity control agents, tackifiers, anti-blocking agents, surfactants, extender oils, metal deactivators , voltage stabilizers, fillers or fillers and flame retardant additives, crosslinking reinforcers and catalysts, and smoke suppression sub-agents. The filler or filler materials and additives may be added to the formulation of the outer layer in amounts ranging from less than about 0.1 to more than about 200 parts by weight per 100 parts by weight of the base resin. Filler or filler materials and additives may be added for the formulation of the inner layer in amounts ranging from less than about 0.1 no more than about 5 parts by weight per 100 parts by weight of the base resin. Examples of antioxidants are: hindered phenols such as tetrakis [methylene (3,5-di-tert-butyl-4-hydroxyhydrocinnamate)] methane, bis [(beta- (3,5-diter-butyl-4-hydroxybenzyl) - methylcarboxyethyl) sulfide, 4,4'-thiobis (2-methyl-6-tert-butylphenol), 4,4'-thiobis (2-tert-butyl-5-methylphenol), 2'-thiobis (4-methyl) -6-tert-butylphenol), and thioethylene bis (3, 5-di-tert-butyl-4-hydroxy) hydrocinnamate; phosphites and phosphonites such as tris (2,4-di-tert-butylphenyl) phosphite and di-tert-butylphenylphosphonite; thio compounds such as dilauryl thiodipropionate, dimyristyl thiodipropionate, and distearyl thiodipropionate; several siloxanes; and various amines such as polymerized 2, 2, 4-trimethyl-1,2-dihydroquinoline. Antioxidants may be used in amounts of about 0.1 to about 5 parts by weight per 100 parts by weight of the polyethylene. As mentioned above, the low temperature additives, which create the scorch problem at extrusion temperatures above about 160 ° C, are organic peroxides. These organic peroxides can be used to crosslink polyethylene resins. They are a component of the formulation of the inner layer and are an optional component of the formulation of the outer layer. Organic peroxides are conventional and are used in conventional amounts. Examples of organic peroxides are the following (decomposition temperature in degrees C is given in parentheses): succinic acid peroxide (110), benzoyl peroxide (110), tertiary butyl peroxy-2-ethylhexanoate (113), p-chlorobenzoyl peroxide (115), tertiary butyl peroxyisobutyrate (115), tertiary butyl peroxyisopropyl carbonate (135), tertiary butyl peroxylaurate (140), 2,5-dimethyl-2,5-di (peroxybenzoyl) hexane (140), tertiary butyl peroxyacetate (140), tertiary di-t-butyl peroxyphthalate (140), tertiary butyl peroxyalate (140) , cyclohexanone peroxide (145), tertiary butyl peroxybenzoate (145), dicumyl peroxide (150), 2,5-dimethyl-2,5-di (tertiary butyl peroxy) hexane-3 (155), cumyl peroxide of tertiary butyl (155), tertiary butyl hydroperoxide (158), and tertiary di-butyl peroxide (160). Dicumyl peroxide is preferred. The co-extruded material, which is the product of the process of this invention, can be prepared in various types of extrusion apparatus as long as they are adapted for co-extrusion. The mixing can be carried out in the extrusion apparatus or before extrusion in a conventional mixer such as a Brabender ™ mixer or a Banbury ™ mixer. The different extrusion apparatuses and processes for profile extrusion are described in the North American Patents Numbers 4,814,135; 4,857,600; 5,076,988; and 5,153,382. All types of single-screw extruders and twin screws and polymer melt pumps and extrusion processes will generally be suitable for carrying out the process of this invention. A typical extrusion apparatus which is commonly referred to as a manufacturing extrusion apparatus will have a solids feed hopper at its upstream end and a melt forming die at its downstream end. The hopper feeds non-melted plastics to the feeding section of the tubular body containing the processing screw (s) which melt and finally pump the plastic melt through the forming die. At the downstream end, between the end of the screw and the die, there is often a sieve pack and a breaker plate. Manufacturing extrusion devices typically achieve the mechanisms of solid transport and compression, plastic melting, melt mixing and melt pumping even though some two-stage configurations use a separate melt feed extrusion apparatus or a fusion equipment. fusion pumping for the fusion pumping mechanism. The tubular bodies of the extrusion apparatus are removed with tubular body heating and cooling particularities to start up and improved constant state temperature control. Modern equipment usually incorporates multiple heating / cooling zones in the rear feed zone and segmentation of the tubular body and configuration matrix downstream. The length-to-diameter ratio of each tubular body is within the range of about 15: 1 to about 30: 1. In a wire coating process, after passing through the breaker plate, the extruded material is pumped through a melt flow channel to a crosshead which reorients the flow of the polymer typically by 90 degrees in such a way that it is aimed to uniformly coat the driver. In a wire coating extrusion process where multiple layers of material are applied to the conductor, the molten polymer of each extrusion apparatus is pumped independently to a crosshead which is designed to coat the conductive wire in such a way that the different layers of the material are different, that is, the layers of material do not mix in the cross head. The multi-layer cross-head can be designed in such a way that multiple layers of material coat the conductor simultaneously or in a discrete manner. In wire coating applications where the material is cross-linked after extrusion, the cross-head die is fed directly into a heating zone and this zone can be maintained at a temperature within the range of about 145 ° C to about 455 ° C, and preferably within the range of about 200 ° C to about 400 ° C. These temperature scales cover the vaporization vulcanization processes that typically operate at temperature and around 204 ° C and the dry curing vulcanization processes that typically operate at a temperature of around 400 ° C. The advantages of the invention lie in the essential elimination of the melt fracture in the inner layer even when the co-extrusion process is carried out at temperatures of less than about 160 degrees C. and the formulation of the inner layer contains a polyethylene (homogeneous) of limited molecular weight distribution and essentially uniform comonomer distribution. In addition, when a releasable outer layer is provided, the removal or detachment of the outer layer leaves an inner layer, which becomes the outer layer, essentially without melt fracture. Patents that are mentioned in this specification are incorporated by reference herein. The invention is illustrated by the following examples.

Examples 1 to 39 The apparatus used in the examples and their operation will be described as follows. In those examples where there is only a single layer, the internal layer extrusion apparatus is used and the additional apparatus, which is necessary to effect co-extrusion, is not used. The extrusion apparatus used to extrude the inner layer is a single-screw plasticizer extrusion apparatus of 6.35 centimeters, 20: 1 L / D (length to diameter) manufactured by John Royle Company. Contains within its tubular body a short polyethylene screw with a Maddock ™ mixing section to plasticize the polymer. The extrusion apparatus used to extrude the outer layer is a 3.81 centimeter, 24: 1 L / D single screw plasticizer extrusion apparatus manufactured by Sterling Company. This extrusion apparatus also contains within its tubular body a regulated polyethylene supply screw for plasticizing the polymer. The molten polymers of each extrusion apparatus are fed to a cross-sectional head of double layer wire coating manufactured by Canterbury Engineering Company. A wire coating line where a solid copper wire number 14 AG (American Wire Guide) having a diameter of 1.63 millimeters is taken from a loading reel by unwinding wire through a wire regulated supply winch through the cross-head of the double layer wire coating where the wire is coated with molten polymer. The crosshead uses a guide tip with a bore diameter of 1.70 millimeters to guide the wire in contact with the molten polymer coming from a 6.35 centimeter extrusion apparatus followed by contact with the molten polymer from the 3.81 extruder. centimeters. The wire, now coated with internal and external layers of polymer, is attracted through a matrix with an opening of 6.60 millimeters. The polymer-coated wire is then drawn through a downstream vulcanization tube and a water bath by means of an extraction winch. Between the water bath and the winch, a laser micrometer is placed to measure the outer diameter of the coated wire. Fracture fracture is determined by visually examining the coated wire. Each coated wire is provided with a value of 1 to 9 with the value 1 being the worst case of melt fracture and the value 9 representing essentially no melt fracture as follows: 1 = intensely coarse 2 - coarse 3 = skin thick shark 4 = intense shark skin 5 = shark skin 6 = rough surface 7 = slightly rough surface 8 = small imperfection, but acceptable 9 = essentially no fusion fracture Components used in the examples: 1. Polymer A is a homogeneous copolymer of ethylene and 1-octene wherein 1-octene is present in an amount of 24 weight percent based on the weight of the polymer. The polymer has a melt index of 1 gram per 10 minutes; a density of 0.87 gram per cubic centimeter, one Mw / Mn of 2; an essentially uniform comonomer distribution; and is prepared with a metallocene catalyst. 2. Polymer B is a homogeneous copolymer of ethylene and 1-octene wherein 1-octene is present in an amount of 24 weight percent based on the weight of the polymer. The polymer has a melt index of 5 grams per 10 minutes; a density of 0.87 gram per cubic centimeter; one Mw / Mn of 2; an essentially uniform comonomer distribution; and is prepared with a metallocene catalyst. 3. Polymer C is a heterogeneous copolymer of ethylene and 1-hexene, wherein 1-hexene is present in an amount of 16 percent to 20 percent by weight based on the weight of the polymer. The polymer has a melt index of 4 grams per "10 minutes, a density of 0.905 gram per cubic centimeter; one Mw / Mn of 4.5; and prepared with a magnesium / titanium catalyst. 4. Polymer D is an ethylene homopolymer prepared by a high pressure process. The polymer has a melt index of 2 grams per 10 minutes; a density of 0.923 gram per cubic centimeter; one Mw / Mn of 5.2. 5. Polymer E is a copolymer of ethylene and ethyl acrylate wherein ethyl acrylate is present in an amount of 15 percent to 25 percent by weight based on the weight of the copolymer. It is prepared by a high pressure process. The polymer has a melt index of 20 grams per 10 minutes. 6. Polymer F is a copolymer of ethylene and vinyl acetate wherein vinyl acetate is present in an amount of 28 percent to 38 percent by weight based on the weight of the copolymer. It is prepared by a high pressure process. The polymer has an index, melting of 35 grams per 10 minutes. 7. Formulation A is a melt blended mixture of 100 parts by weight of Polymer A; 0.18 part by weight of an antioxidant A; 0.18 part by weight of DSTDP; and 1.8 parts by weight of dicumyl peroxide. 8. Formulation C is a blend mixed by melting per 100 parts by weight of Polymer C; 0.35 part by weight of antioxidant A; 0.35 part by weight of DSTDP; and 1.8 parts by weight of dicumyl peroxide. 9. Formulation D is a melt blended mixture of 100 parts by weight of polymer D; 0.18 part by weight of antioxidant A; and 0.18 part by weight of DSTDP. 10. Formulation E is a melt blended mixture of 100 parts by weight of Polymer E; 30+ parts by weight conductive carbon black; antioxidant B; and dicumyl peroxide. 11. Formulation F is a melt blended mixture of 100 parts by weight of Polymer F; 20+ parts by weight conductive carbon black; antioxidant B; and dicumyl peroxide. It is designed to have a low adhesion to polyethylene in such a way that it can be easily removed from an internal layer of polyethylene. 12. Processing Auxiliary A is a copolymer of vinylidene fluoride and hexafluoropropylene. 13. Processing Assistant B is a mixture containing 80 percent by weight of the Auxiliary Processing A and 20 weight percent polyethylene. 14. The DSTDP is distearyl thiodipropionate. 15. Antioxidant A is thiodiethylene bis (3, 5-di-tert-butyl-4-hydroxyhydrocinnamate). 16. Antioxidant B is a condensation product of acetone-aniline Agerite ™ MA. The variables and the results are indicated in the following Table. The temperature scale for each extrusion apparatus reflects the high and low temperatures of the temperatures measured in each of the four heating zones, the flange, the head and the die. Note: When the polymer is mentioned instead of a formulation, it will be understood that the polymer is being used in the condition "as received" from the manufacturer. This means that the polymer contains calcium stearate and may contain other additives, usually stabilizers. The total amount of additives, however, is not greater than about 1 part per 100 parts of the polymer. In any case, 1.8 parts by weight of dicumyl peroxide per 100 parts by weight of the polymer are present.

Picture example 1 2 3 4 5 6 7 8 9 10 polymer A A A A A A A A A A single layer operating conditions - one layer: scale 123 123 123 123 112 112 112 112 99 99 of temperature a a to a a a a aratio n 143 142 142 141 130 130 128 130 119 120 (° C) revolution- 7 14 14 14 7 14 14 14 7 14 per minute meters 4.57 10.06 6.10 3.05 4.57 10.06 6.10 3.05 4.57 for 10.06 minutes Table (continued) example 1 2 3 4 5 6 7 8 9 10 tempera- 150 154 156 156 138 141 143 144 126 131 fusion temperature (° C) Wall thickness of the extruded material (mm): minimum 1.78 1.75 2.49 3.68 1.57 1.70 2.67 3.71 1.98 1.47 maximum 2.11 2.31 2.62 3.89 2.24 2.39 2.95 3.96 3.96 2.62 Fracture fracture: a layer 2 1 Table (continued) example 11 12 13 14 15 16 17 19 20 polymer A * A * A * A * A * A ** A ** A * A * A * (*) or formulation (**) of a layer or inner layer Operating conditions of a layer or inner layer: scale 99 99 99 99 99 104 104 99 100 99 of a- to a a a a a a a peratu 118 118 118 118 118 118 118 118 119 120 119 ra (° C) revolu- 14 14 14 14 14 13 13 15 15 14 per minute Table (continued) example 11 12 13 14 15 16 17 18 19 20 meters by 6.10 3.05 10.06 10.6 4.57 8.23 10.06 10.06 10.06 10.06 min Tempe- 133 133 132 132 131 134 134 137 137 134 Fusion rate (° C) minimum 2.49 3.68 1.98 2.12 2.31 maximum 2.87 4.01 2.11 2.24 2.39 operating conditions-external layer: scale 99 99 99 107 100 100 of a-a-a-a-peratu 118 118 119 116 115 116 ra (° C) Table (continued) example 11 12 13 14 15 16 17 18 19 20 revolu- 12 18 24 18 24 20 tions / minute tempe- 120 122 123 121 123 126 melting rate (° C) wall .381 .559 .838 from a to a layer .406 .610 .914 external (mm) fracture 1 1 9 9 9 1 1 1 ra by fusion: a layer or internal layer 9 9 9 1 9 9 external (composite) Table (continued) example 21 22 23 24 25 26 27 28 29 30 Polyme- A A A A A B B B B auxiliary B B of pro (500 (500 cessappm ppm A) A) operating conditions - one layer: scale 99 99 99 99 99 99 99 99 99 99 from a to a a a a a a a p erate 119 119 118 118 118 119 119 119 119 ll ll ra (° C) revolu- 14 14 14 14 16 18 24 30 12 13 tions / minute meters 10.06 6.10 3.05 3.05 10.06 10.06 10.06 10.06 10.06 for 10.06 minutes Table (continued) example 21 22 23 24 25 26 27 28 29 30 tempera- 134 136 136 137 137 132 135 138 129 129 fusion temperature (° C) Wall thickness of the extruded material (mm): minimum 1.47 2.67 3.89 3.89 2.39 2.11 2.46 2.82 1.50 1.65 maximum 3.12 3.12 4.27 4.22 2.87 2.13 2.54 2.95 1.63 1.75 fusion fracture: a layer 1 2 Table (continued) example 31 32 33 34 35 36 37 38 39 polymer B * B * B * B * (*) or formulation (**) of a layer or inner layer auxiliary B B of process (500 (500 times ppm ppm A) A) operating conditions of a layer or inner layer: scale 99 99 99 99 99 116 116 116 116 temperature a a a a a a a a a (C) 118 118 119 119 119 127 127 124 124 Table (continued) example 31 32 33 34 35 36 37 38 39 revolu- 14 14 14 14 14 12 12 12 12 per minute meters 10.06 10.06 6.10 3.05 10.06 10.06 10.06 10.06 10.06 per minute melting temperature (° C) 129 129 129 129 127 131 131 131 131 wall thickness of the extruded material (mm): minimum 1.75 1.70 2.39 3.25 2.29 1.98 2.57 2.24 2.44 maximum 1.88 1.83 2.44 3.45 2.36 1.98 1.96 Table (continued) example 31 32 33 34 35 36 37 38 39 F F D formulation of outer layer Operating conditions of external layer: scale of 99 93 107 temperature a a a (° C) 119 116 118 revolutions 24 22 24 per minute melting temperature (°) 127 123 121 Table (continued) example 31 32 33 34 35 36 37 38 39 Fracture fracture: a 9 layer or internal layer 9 9 external (composite) Notes regarding the Table: 1. Examples 1 to 12 seek to avoid melt fracture with respect to Polymer A by varying process conditions such as temperatures, revolutions per minute, and meters per minute, while operating at temperatures below 160 degrees C, without success. 2. Examples 13 to 15 co-extrude the Formulation F through Polymer A under conditions similar to Examples 1 to 12. This essentially eliminates the melt fracture in both the inner layer and the outer layer (composite) 3. Examples 16 and 17 use the same conditions as the inner layer. In Example 17, however, there is a co-extrusion of Formulation D through Formulation A. Example 16 results in intensely thick melt fracture while the outer (or composite) layer of Example 17 is essentially free of fusion fracture. 4. Example 18 is similar in result to the Examples 1 to 12 and 16. Example 19 is a co-extrusion of Formulation E through Polymer A, and the outer layer (or composite) is essentially free of fusion fracture. 5. Example 20 is a co-extrusion of Polymer A through Polymer A. The result is an intensely thick melt fracture. 6. Examples 21 to 23 are similar in results to Examples 1 to 12, 16 and 18. Examples 24 and 25 use a processing aid with little or no improvement. 7. Examples 26 to 30 use Polymer B, which is similar to Polymer A, but with a higher melt index. There is some improvement in melt fracture, but the result is still far from commercial acceptability. 8, Example 31 is similar in result to Examples 26 to 30. Examples 32 to 34 use processing aids with some improvement with Example 34 showing small but acceptable melt fracture. Example 35 is a co-extrusion of Formulation F through polymer B, and essentially there is no melt fracture in the inner or outer layers. 9. Examples 36 and 38 use the heterogeneous Polymer C in Formulation C without coextrusion and the result is essentially that there is no melt fracture. Example 37 co-extrudes Formulation F through Formulation C, and Example 39 co-extrudes Formulation D through Formulation C. The result, again, is essentially that there is no melt fracture. 10. In Examples 13 to 15, 17, 19, 20, 35, 37 and 39 where the temperature scales of the outer layer are provided, the flange, the head and the temperatures of the matrix are not recorded.

Claims (10)

CLAIMS:

1. A process for the co-extrusion of an inner layer around a conductive medium and an outer layer around the inner layer comprising: (i) introducing into an extrusion apparatus adapted for profile co-extrusion, a conductive medium; an internal layer formulation comprising a homogeneous polyethylene having a polydispersity within the range of about 1.5 to about 3.5 and an essentially uniform comonomer distribution and an organic peroxide; and an outer layer formulation comprising (a) a copolymer of ethylene and an unsaturated ester; (b) a polyethylene having a polydispersity greater than about 4.0 and a density of at least 0.916 gram per cubic centimeter, the polymer is produced by a high pressure process; or (c) a heterogeneous copolymer of ethylene and one more alpha-olefins having a density of less than 0.916 gram per cubic centimeter, a melt index of at least about 4 grams per 10 minutes, and a polydispersity greater than about 4.0. and, optionally, an organic peroxide; and (ii) co-extrude the formulations at a temperature no greater than about 160 degrees C.

2. The process according to claim 1, wherein the homogeneous polyethylene is produced with a metallocene catalyst.

3. The process according to claim 2, wherein the homogeneous polyethylene is a copolymer of ethylene, one or more alpha-olefins, each having from 3 to 8 carbon atoms, and, optionally, a diene, and has a melt index within the scale of about 0.5 to about 30 grams per 10 minutes.

4. The process according to claim 1, wherein the polymer of the outer layer is a copolymer of ethylene and vinyl acetate or a methyl or ethyl acrylate or methacrylate wherein the unsaturated ester is present in an amount of about 15. percent to about 38 weight percent based on the weight of the copolymer, or an ethylene homopolymer.

5. A process for the co-extrusion of an inner layer around a conductive medium, and an outer layer around the inner layer comprising: (i) introducing into an extrusion apparatus adapted for profile co-extrusion, a medium driver; an internal layer formulation comprising a homogeneous copolymer of ethylene, one or more alpha-olefins, each having from 3 to 8 carbon atoms, and, optionally, a diene, the copolymer having been produced with a metallocene catalyst, and has a polydispersity within the range of about 1.5 to about 3.5, an essentially uniform comonomer distribution and a melt index within the scale of about 0.5 to about 30 grams per 10 minutes, and an organic peroxide; and an outer layer formulation comprising (a) a copolymer of ethylene and vinyl acetate or of methyl or ethyl acrylate or methacrylate, wherein the unsaturated ester is present in an amount of from about 15 percent to about 38 percent in weight based on the weight of the copolymer; (b) an ethylene homopolymer having a polydispersity greater than about 4.5 and a density of at least 0.916 gram per cubic centimeter; the polymer is made by a high pressure process; or (c) a heterogeneous copolymer of ethylene and one or more alpha-olefins, each alpha-olefin has from 3 to 8 carbon atoms, the copolymer has a density of less than 0.916 gram per cubic centimeter, a melt index of at least about 4 grams per 10 minutes and a polydispersity greater than about 4.5; and (ii) co-extrude the formulations at a temperature no greater than about 160 degrees C.

6. The process according to claim 5, wherein the formulation of the outer layer contains an organic peroxide.

An article of manufacture comprising a conductive medium surrounded by a co-extruded material comprising a cross-linked inner layer of a homogeneous polyethylene having a polydispersity within the range of about 1.5 to about 3.5, and an essentially uniform comonomer distribution and an outer layer comprising (a) a copolymer of ethylene and an unsaturated ester; (b) a polyethylene having a polydispersity greater than about 4.0 and a density of at least 0.916 gram per cubic centimeter, the polymer is made by a high pressure process; or (c) a heterogeneous copolymer of ethylene and one or more alpha-olefins having a density of less than 0.916 gram per cubic centimeter, a melt index of at least about 4 grams per 10 minutes, and a polydispersity greater than about 4.0.

The article of manufacture according to claim 7, wherein the polymer of the outer layer is crosslinked.

9. The article of manufacture according to claim 7, wherein the homogeneous polyethylene is produced with a metallocene catalyst.

10. The article of manufacture according to claim 9, wherein the homogeneous polyethylene is a copolymer of ethylene, one or more alpha-olefins, each having from 3 to 8 carbon atoms, and, optionally, a diene, and has a melt index within the scale of about 0.5 to about 30 grams per 10 minutes. "A PROCESS FOR EXTRUSION" SUMMARY OF THE INVENTION A process for the co-extrusion of an inner layer around a conductive medium and an outer layer around the inner layer comprising: (i) introducing into an extrusion apparatus adapted for profile co-extrusion, a conductive medium; an internal layer formulation comprising a homogeneous polyethylene having a polydispersity within the range of about 1.5 to about 3.5 and an essentially uniform comonomer distribution, and an organic peroxide, and an outer layer formulation comprising (a) a copolymer of ethylene and an unsaturated ester; (b) a polyethylene having a polydispersity greater than about 4.0 and a density of at least 0.916 gram per cubic centimeter, the polymer is made by a high pressure process; or (c) a heterogeneous copolymer of ethylene and one or more alpha-olefins having a density of less than 0.916 gram per cubic centimeter, a melt index of at least about 4 grams per 10 minutes, and a polydispersity greater than approximately 4.0, and, optionally, an organic peroxide; and (ii) co-extrude the formulations at a temperature no greater than about 160 degrees C.