POLYOLEFIN BLENDS CONTAINING REACTIVE AGENTS

Abstract: A polyolefin blend comprising, in physical admixture, a major portion of particles of a first polyethylene and a minor portion of particles of a composition of a second polyethylene, is disclosed. The first polyethylene is selected from the group consisting of homopolymers of ethylene and copolymers of ethylene and at least one C₄ - C₁₀ higher alpha-olefin, and the second polyethylene is a copolymer of ethylene and at least one C₄ - C₁₀ higher alpha-olefin having a density of at least 0.890 g/cm³, especially at least 0.910 g/cm³, and a melt index of at least 40 dg/min. The density of the second polyethylene is at least about 0.005 g/cm³ lower than that of the first polyethylene and the melt index of the second polyethylene is at least 10 dg/min. higher than that of the first polyethylene. The composition of the second polyethylene contains an agent that is capable of reacting with polyolefins that are in a molten state. Such agents are selected from the group consisting of cross-linking agents and modifying agents, and mixtures thereof. In an alternative embodiment, the second polyethylene has a shear viscosity that is not more than 50% of that of the first polyethylene at 200°C and a shear rate of 400 sec⁻¹; in this regard, the first and second polyethylene may be more broadly defined as being homopolymers and copolymers of hydrocarbon alpha-­ olefins having 2-10 carbon atoms. The blends may be used in a wide variety of processes, including blow-moulding pro­ cesses, film and pipe extrusion processes, sheet thermo-­ forming processes and rotational moulding processes.

Description: The present invention relates to polyolefin blends and in particular to a physical admixture of a major portion of particles of an ethylene polymer with a minor portion of particles of a composition of an ethylene polymer and an agent that is capable of reacting with polyolefins in the molten state, such reactive agent being a cross-linking agent and/or a modifying agent and being further defined hereinbelow. Polymers of ethylene, for example, homopolymers of ethylene and copolymers of ethylene and higher alpha-olefins, are used in large volumes for a variety of end-uses, for example, in the form of film, fibres, moulded or thermoformed articles, pipes and coatings. Polyolefin compositions as offered for sale and/or used in such end-uses often contain reactive and/or non-reactive agents to modify or stabilize the polymer during processing or during use of articles fabricated from the compositions. Typical reactive agents include cross-linking agents and certain unsaturated compounds. Typical non-reactive agents include antioxidants and other stabilizers, nucleation agents and additives that affect the slip or blocking characteristics of products or the release of products from moulds used in fabrication processes. It is important that the incorporation of agents into polyolefin compositions be carried out so that the resultant composition has uniform properties. Polymers having properties that are commercially-acceptable in a variety of end-uses are known. In addition, improvements in some polymer properties could lead to improved products and/or use of the polymers in additional end-uses. For instance, one method of improving the end-use characteristics of an article rotationally moulded from polymers of ethylene is to incorporate a cross-linking agent, for example, an organic peroxide, into the polymer composition. In the rotational moulding of a composition containing an organic peroxide, the polymer flows to coat the inside of the mould and then the cross-linking agent causes crosslinking of the polymer so as to increase the molecular weight of the polymer, thereby improving end-use properties of the resultant article. Cross-linkable compositions especially adapted for rotational moulding end-uses are disclosed in EP-A-0 087 210 of G. White. Cross-linkable compositions may also be used in other end-uses to obtain improvements in product properties; the cross-linking of the polymer will tend to affect melt characteristics of the polymer under low shear rate processing conditions. One example of the use of partial cross-linking to obtain an improvement in film properties is disclosed in CA-A-1 123 560 of D.A. Harbourne. Techniques for the incorporation of agents into polyolefins are well known in the art. Non-reactive agents, especially stabilizing agents, are frequently incorporated into molten polymer during the process for the manufacture of the polymer. Reactive and non-reactive agents may also be incorporated into polymers by melt blending techniques in which the agent is metered into or otherwise added to molten polymer during extrusion of the polymer into pellets or a fabricated article. It is important in the addition of agents that the agent be uniformly distributed throughout the polymer. With non-reactive agents, however, the uniformity of the distribution of the agent is normally less critical than with reactive agents. For example, the requirements for a slip agent or a stabilizer may be less critical than for a cross-linking agent. The cross-linking of a polymer increases the molecular weight of the polymer. Thus, in order to obtain a product of uniform properties, especially properties dependent on molecular weight, it is important that the cross-linking of the polymer be carried out in a uniform manner. If the cross-linking is not uniform, the resultant product may, for example, have areas of weakness due to either insufficient or excessive cross-linking of the polymer or have gel particles resulting from excessive cross-linking of the polymer, such gel particles resulting in unacceptable visual appearance and/or areas of weakness in the product. Some fabrication processes, for example blow moulding or bottles and the manufacture of sheet and film, may be more sensitive to non-uniform product properties than other processes. In order to obtain uniform product properties, it has been necessary to use expensive and/or complex processes to incorporate reactive agents into polymers, including special handling facilities and special extruder screw designs. The blending of organic peroxide with molten polyethylene is disclosed in US-A-3 182 033 of R.S. Gregorian and in CA-A-957 473 of H.J. Cook. D.A. Alia disclosed in US-A-4 197 381, that the blending of crystalline polymers and amorphous elastomeric polymers aided in the production of cross-linkable polymers having a homogeneous composition. The blending of reactive agents into polyethylene by means of a physical blend of polyethylene with a different polymer containing the reactive agent is disclosed in EP-A-0 210 306. A blend of polyolefins capable of being used to incorporate reactive agents into polyolefins in a uniform and more economical manner has now been found. Accordingly, the present invention provides a polyolefin blend comprising, in physical admixture, a major portion of particles of a first polyolefin and a minor portion of particles of a composition of a normally solid second polyolefin, the polyolefins being homopolymers and copolymers derived solely from hydrocarbon alpha-olefins having 2-10 carbon atoms, the second polyolefin having a shear viscosity that is not more than 30% of that of the first polyolefin when measured at 200°C and a shear rate of 400 sec⁻¹, said composition being a composition of the second polyolefin and a reactive agent which is a cross-linking agent or modifying agent, or a mixture thereof, the reactive agent being capable of reacting with the polyolefins in a molten state. Both the polyolefins are preferably selected among homopolymers of ethylene and copolymers derived solely from ethylene and at least one C₄₋₁₀ alpha-olefin. The second polyolefin may be copolymer derived solely from ethylene and at least one C₄ - C₁₀ higher alpha-olefin having a density of at least 0.890 g/cm³ and a melt index of at least 40 dg/min, preferably in the range of 40-200 dg/min. The density of the second polyethylene may be at least 0.005 g/cm³, and when that the second polyethylene has a density of at least 0.890 g/cm³, preferably at least 0.008 g/cm³, lower than that of the first polyethylene. The melt index of the second polyethylene may be at least 10 dg/min and when this melt index is in the range of 40-200 dg/min preferably at least 20 dg/min higher than that of the first polyethylene. In a preferred embodiment of the blends of the present invention, the reactive agent is a cross-linking agent which is an organic peroxide. In a further embodiment, the reactive agent is a modifying agent. In another embodiment, the melt index of the second polyethylene is 40-60 dg/min. higher than that of the first polyethylene. In addition, the present invention provides a process for the manufacture of articles from a polyolefin blend as defined above, comprising feeding the blend to melt processing apparatus, melting and admixing said blend and forming an article from the resultant blend. The polyolefin of the blends of the present invention is particularly described herein with reference to such polyolefins being a homopolymer of ethylene and/or a copolymer of ethylene and a minor amount of at least one C₄ - C₁₀ higher alpha-olefin, for example a copolymer of ethylene and a minor amount of butene-1, hexene-1 and/or octene-1. It is to be understood, however, that the polyolefins may be broadly defined as being homopolymers or copolymers of hydrocarbon alpha-olefins having 2-10 carbon atoms. Techniques for the manufacture of such polymers are known in the art. As noted above, the invention is particularly defined with reference to the polyolefins being homopolymers and copolymers of ethylene. The characteristics of the first polyethylene, for example, the density and melt index of the polymer, will depend to a large extend on the intended end-use of the resultant products but, in embodiments, the density may range from 0.890 g/cm³ to 0.970 g/cm³ and the melt index, as measured by the method of ASTM D-1238 (condition E), may range up to 100 dg/min. For example, polymers intended for film and sheet end-uses tend to have melt indices of less than about 10 dg/min whereas polymers intended for moulding end-uses tend to have higher values of melt index. The ranges of density and melt index of polyolefins that are useful for various types of products are known in the trade. The characteristics of the second polyethylene differ from those described above for the first polyethylene. In one embodiment, the density of the second polyethylene is lower than that of the first polyethylene, being at least 0.890 g/cm³, especially at least 0.910 g/cm³, but with the proviso that it is at least 0.005, especially 0.008 g/cm³ lower than the density of the first polyethylene. Secondly, the melt index of the second polyethylene is higher than that of the first polyethylene, being in the range of 40-200, especially 60-150 dg/min., but with the proviso that it is at least 10 dg/min., preferably at least 20 dg/min., higher than the melt index of the first polyethylene. In an alternate embodiment, the second polyethylene has a density of at least 0.890 g/cm³, especially at least 0.910 g/cm³, a melt index of at least 40 dg/min. and has a lower shear viscosity than the first polyethylene; in particular the shear viscosity is not more than 50% of that of the first polyethylene. Preferably, the shear viscosity of the second polyethylene is not more than about 30% of the shear viscosity of the first polyethylene. As used herein, shear viscosity is determined at 200°C at a shear rate of 400 sec⁻¹. In a further embodiment the shear viscosity of the second polyolefin is not more than 15-15% of that of the first polyolefin. The second polyolefin is a normally solid polymer and may include materials frequently referred to as solid waxes but does not include materials that are liquids at ambient temperatures and pressures; the blends of the invention are physical admixtures and are therefore capable of physical separation into the respective components at ambient temperatures. The second polyolefin contains a reactive agent selected from the group consisting of cross-linking agents and modifying agents, and mixtures thereof. As used herein, the expression "reactive agent" refers to an agent that undergoes a chemical reaction at temperatures at which polyethylene is in a molten state. It is to be understood, however, that the rate of chemical reaction may not be significant until the temperature of the molten polyethylene is substantially above the melting point of the polyethylene. For example, it is known that cross-linking agents for polyethylene are usually selected so that the cross-linking reaction occurs above the melting point of the polymer e.g. at or near normal melt processing temperatures. It is preferred that the reaction temperature be such that adequate mixing of polymer and reactive agent may be achieved prior to extensive reaction between polymer and reactive agent; the half-life of a cross-linking agent is usually known over a range of temperatures and may be used to assist in selection of a cross-linking agent suitable for an intended end-use. It is to be understood that the reactive agent may be more than one chemical compound or species and, in that event, part of the composition of the second polyolefin may contain one reactive agent and another part of the composition of the second polyolefin may contain a second reactive agent. It is to be further understood that if the reactive agent is more than one chemical compound or species, then each such reactive agent may be capable of reacting with polyethylene that is in a molten state and/or one such reactive agent may be capable of reacting with another such reactive agent. In the event that the reactive agent is a cross-linking agent e.g. an organic peroxide, the first polyolefin may, but normally will not, contain organic peroxide. However, it may under some circumstances be desirable to incorporate portions of the cross-linking formulation into the first polyolefin. For example, if the cross-linkable composition is to be comprised of both an organic peroxide and a co-curing agent, as is disclosed in the aforementioned EP-A-0 087 210, it might be advantageous to admix the co-curing agent with the first polyolefin and to admix the organic peroxide with the second polyolefin. Such an incorporation of the co-curing agent into the first polyolefin may aid in the fabrication of a uniform product. In any event, the first polyolefin will often contain non-reactive agents known to be incorporated into polyolefin including antioxidants and other stabilizers, and pigments, it being understood that some so-called non-reactive agents useful in polyethylene may have detrimental effects on cross-linking or other reactive agents useful with polyolefin and as such will likely not be used in combination with such cross-linking or other reactive agents. For blends containing cross-linking agents, the preferred cross-linking agent is an organic peroxide, especially a bis(tert. alkyl peroxy alkyl) benzene, dicumyl peroxide or acetylenic diperoxy compound. Other organic peroxides are known to those skilled in the art, including t-butyl hydroperoxide and di-t-butyl peroxide. 2,5-Dimethyl-2,5 bis(tert. butyl peroxyisopropyl)benzene is the preferred organic peroxide and is available commercially under the trade mark Vulcup from Hercules Incorporated. As an alternative, the cross-linking agent may be 2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3 which is available commercially under the trade mark Lupersol 130 from Lucidol Division of Pennwalt Corporation. In an embodiment, the composition of the second polyethylene may be similar to compositions disclosed in the aforementioned publication of G. White EP-A-0 087 210 except that the polyethylene would be selected so as to meet the requirements of the present invention. While the amount of cross-linking agent in the second polyethylene may be varied over a wide range it may be preferable not to have a high concentration of cross-linking agent in the second polyethylene and to then admix only a small amount of the second polythylene with the first polyolefin. In that event, problems may be experienced in mixing the relatively high concentration of cross-linking agent in the second polyolefin in a uniform manner into the first polyolefin. If the cross-linking agent is an organic peroxide, it is preferred that less than 4% by weight of peroxide be present in the second polyolefin and preferably 0.05-1.0% by weight of peroxide. As noted above, a co-curing agent may be incorporated into the first or second polyolefin i.e. either separately from or admixed with cross-linking agent. Examples of co-curing agents include triallyl cyanurate, triallyl isocyanurate and 1,2-polybutadiene. The reactive agent may be a modifying agent, which may be used either alone or, usually, in combination with an initiator. Examples of modifying agents include unsaturated organic acids, and derivatives thereof, e.g. acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, crotonic acid, maleic anhydride, cross-linkable silane compounds e.g. vinyltrimethoxysilane, vinyltriethoxysilane, vinyltris(2-methoxyethoxy) silane and vinylmethyldimethoxysilane, and other compounds capable of being reacted with molten polyethylene. The modifying agents will usually be used in combination with an initiator especially a cross-linking agent e.g. an organic peroxide. With some modifying agents, other initiators are known e.g. styrene acts as an initiator for maleic anhydride. The modifying agent and initiator may be separately admixed with the second polyethylene as compositions thereof. Under some processing conditions, modifying agents may react with polyethylene in the substantial absence of an added initiator. For example, it is known to thermally react maleic anhydride with polyethylene at temperatures of at least about 375°C. The polyethylenes of the blend may contain a stabilizing agent e.g. an antioxidant or an ultra violet stabilizer. Examples of antioxidants are hindered phenolic antioxidants e.g. octadecyl-3,5-di-tert.butyl-4-hydroxy cinnamate and tetrakis-methylene-3-(3',5'ditert.butyl-4-hydroxyphenyl) propionate methane. Hindered phenolic antioxidants may be used in combination with a phosphite antioxidant e.g. di(stearyl)-pentaerythritol diphosphite, tris di-tert.-butyl phenyl phosphite, dilauryl thiodipropionate and bis(2,4-tert.-butylphenyl) pentaerythritol diphosphite. Examples of ultra violet stabilizers are 2-hydroxy-4-n-octoxybenzophenone, 2-(3'-tert butyl-2'-hydroxy-5'-methylphenyl)-5-chlorobenzotriazole and bis-(2,2,6,6,-tetramethyl-4-piperidyl) sebacate. Moreover, the polyethylenes of the blend may contain slip agents, anti-blocking agents, anti-static agents, mould release agents, pigments, nucleating or other processing aids. Examples of slip agents are erucamide and stearamide, of anti-static agents are bis(hydroxyethyl) tallow amine and glycerol monooleate, of anti-blocking agents are silica and mica and of mould release agents are calcium stearate and zinc stearate. Examples of nucleating agents or other processing aids are talc, silica, polyethylene glycol, fluorinated elastomers and polyolefin waxes. As noted above, stabilizing or other so-called non-reactive agents may have detrimental effects on cross-linking or other reactive agents and for that reason it may be preferable not to use certain combinations of agents, as will be understood by those skilled in the art. The ratio of the first polyethylene to the second polyethylene may be varied over a wide range, particularly from 5:1 to 400:1 and especially 50:1 to 100:1. The ratio selected will depend on a variety of factors, including the amount of reactive agent (or of additional reactive agent) to be incorporated into the blend, the type(s) of reactive agent, the need for a uniform product, the type of processing that the resultant blend is to be subjected to and the mixing capabilities of apparatus used therein. With regard to the mixing capabilities of the apparatus, twin-screw extruders may be more effective than single screw extruders. The amount of reactive agent in the blend of the present invention will depend, in particular, on the type of reactive agent and the intended end-use of the blend. Thus, the amount could vary, depending on such other factors, from a few parts per million (ppm) in the blend to in excess of one per cent, by weight. Such amounts will be understood by those skilled in the art. In the event that the reactive agent is a cross-linking agent, the first and second polyolefins may be selected and admixed so that the amount of cross-linking agent in the blend is in the range of 25 ppm to 1000 ppm by weight of the blend. The amount of cross-linking agent in the blend will depend primarily on the intended end-use for the blend. Blends intended for the fabrication of highly cross-linked products will have relatively high levels of cross-linking agents. On the other hand, a small amount of cross-linking agent may be present in the blend so as to effect only a partial crosslinking of the resultant product. The particles of the first and second polyolefins may be any convenient shape and size and may for example be granules, powder, or pellets. Such forms are commercially available forms of polyolefin and/or may be obtained by known techniques e.g. grinding, melt pelletization. However, it is preferred that the particles of the first polyolefin be of substantially the same size as the particles of the composition of the second polyolefin. As the difference in size between the particles increases, so does the possibility that the two types of particles will become separated from one another during storage, transportation or other handling of the blend; such differences may be less critical if the blend is fed to an extruder shortly after preparation thereof. The composition of the second polyolefin may be produced by techniques known in the art for incorporating agents into polyolefin. Such methods include melt blending, coating and extrusion, and injection of the agent into molten polyolefin. If the reactive agent is a modifying agent or especially a cross-linking agent, the reactive agent should be incorporated into the polyolefin in a manner that does not result in premature reaction with the polyolefin, as in known in the art. The resultant blends may be used in a wide variety of end-uses, as is known for polyethylene. Such uses include blow-moulding processes, film and pipe extrusion processes, sheet thermoforming processes and rotational moulding processes. Apparatus used in such processes is referred to herein as melt processing apparatus. In particularly preferred embodiments, the blends are used in the manufacture of film in a blown film process. As is illustrated hereinafter, such a use of the blends can result in substantial increases in the rate of production of film of acceptable quality. However, for any particular combination of apparatus, polymer composition and processing conditions, there may be an optimum level of cross-linking agent above which increases in the rate of film production, if any, may be at the detriment of film quality. The present invention is illustrated by the following examples: Example I A composition of an ethylene/butene-1 copolymer, with 0.55% by weight of Vulcup R organic peroxide and 0.55% by weight of triallyl isocyanurate, was prepared by a melt-blending technique. The copolymer had a density of 0.950 g/cm³ and a melt index of 50 dg/min. The composition was admixed with SCLAIR (Trade Mark) 58A polyethylene, having a density of 0.955 g/cm³ and a melt index of 0.43 dg/min, in a ratio of polyethylene:composition of 100:1, to give a blend of the present invention. The resultant blend was fed to a blow moulding machine equipped with a mould for the fabrication of one gallon bottles. The bottles obtained were of good quality, being free of gel particles. Further details are given below, as Run 1. As a comparison, the corresponding composition having an ethylene homopolymer, with a density of 0.960 g/cm³ and a melt index of 21 dg/min., and the organic peroxide and triallyl isocyanurate was prepared. A blend of this composition and SCLAIR 58A polyethylene (1:100) was prepared and fed to the blow moulding machine. It was found that the polymer contained pellet-sized particles of gel. In addition the polymer melt failed to fill the bottle cavity and the bottles obtained were incomplete and full of holes. Further details are given below as Run 2. Further details are as follows: Example II A composition of an ethylene/butene-1 copolymer with 0.25% by weight of Vulcup R organic peroxide and 0.25% by weight of triallyl isocyanurate was prepared by a melt-blending technique. The copolymer had a density of 0.924 g/cm³ and a melt index of 53 dg/min. The composition was admixed with SCLAIR 13J4 polyethylene, an ethylene/octene-1 copolymer having a density of 0.930 g/cm³ and a melt index of 1.0 dg/min., in a ratio of polyethylene : composition of 50:1, to give a blend of the present invention. The resultant blend was fed to apparatus for the manufacture of film by a blown film technique. The film had a thickness of 25 µm. It was found that a gel-free film could be produced and that the film has a higher melt strength than film produced from SCLAIR 13J4 polyethylene that did not contain the composition of organic peroxide. The higher melt strength permitted an increase in the rate of production of film of 40%. Subsequent testing showed that the impact strength and tensile strength of the film were not adversely affected by the use of the composition of organic peroxide and/or the higher production rate. Example III Dynamic rheological properties of the ethylene/butene-1 and ethylene/octene-1 copolymers of Example II were measured using a Rheometrics (Trade Mark) On-Line rheometer. That rheometer measures the relationship between complex viscosity and angular frequency which, according to the Merz-Cox rule, is equivalent under conditions of linear viscoelasticity to the relationship between shear viscosity and shear rate. The dynamic rheological properties were determined at 200°C under conditions that were equivalent to a shear rate of 400 sec⁻¹. It was found that the shear viscosities of the ethylene/butene-1 and ethylene/octene-1 copolymers were 98 and 800 Pa.s (980 and 8000 poise) respectively. As noted in Example II, film of acceptable properties could be made according to the present invention using the above polymers. Example IV A linear low density polyethylene identified as ESSO (Trade Mark) LPX-1, which has a density of 0.918 g/cm³ and a melt index of 1.0 dg/min., was extruded into film using a blown film process. The film produced had a thickness of 50 µm. It was found that the maximum production rate obtainable with the apparatus and processing conditions being used was 38.6 kg/hr. The production rate was limited by, in particular, stability of the bubble in the blown film process and melt fracture of the polymer at the die lips. A composition of a melt-processing aid and 1000 ppm of Lupersol 130 organic peroxide in an ethylene/butene-1 copolymer having a density of 0.920 g/cm³ and a melt index of 1.40 dg/min. was blended into the above linear low density polymer so as to provide 5% of the composition in the polymer. When film was produced using the method described above, the polymer did not exhibit melt fracture. However, the level of gel in the film was too high to permit an evaluation of any increased stability of the bubble. The above composition was replaced, at a 2% level, with a composition of 2500 ppm of Lupersol 130 organic peroxide in an ethylene/butene-1 copolymer having a density of 0.924 g/cm³ and a melt index of 53 dg/min. On extrusion of the blend into film, it was found that the film obtained was essentially free of gel and that it was possible to increase the production rate by 47%, to 56.7 kg/hr.; melt fracture was not experienced during the trial. Example V In a series of runs, ethylene/alpha-olefin copolymer pellets containing Lupersol 130 organic peroxide were blended with SCLAIR 13J4 polyethylene, an ethylene/octene-1 copolymer having a density of 0.930 g/cm³ and a melt index of 1.0 dg/min. The resultant blends were extruded into film in a blown film process, the apparatus used being equipped with an efficient mixing screw. Further details of the ethylene/alpha-olefin copolymer and the results obtained are shown in Table I. The results show that when the polymer containing the peroxide has a melt viscosity that is about the same as that of major component, film of good quality was not obtained. When the melt viscosity of the polymer containing peroxide was reduced to 50% of the major polymer component, as in Runs 2 and 5, film quality was marginal, being dependent on the amount of peroxide used. However, when the melt viscosity of the polymer containing peroxide was only 20% of that of the major polymer component, good quality film was obtained. In a related series of runs, attempts were made to extrude film from a number of blends using apparatus equipped with a very inefficient mixing screw. It was found that even when the melt viscosity of the polymer containing peroxide was reduced to 5% of that of the major component, the peroxide concentration had to be less than 2500 ppm in order to obtain film of good quality. Thus the present invention will permit the manufacture of film using apparatus having a very inefficient mixing screw, although more efficient mixing screws are preferred. Example VI About 1500g of SCLAIR 2114 polyethylene, an ethylene/butene-1 copolymer having a density of 0.924 g/cm³ and a melt index of 53 dg/min, were ground in an Abbe (Trade Mark) cutter equipped with a 0.48 cm mesh screen. About 45g of sulphur trioxide-trimethylamine complex was dissolved in 600 ml of distilled water at 50°C and, with minimal delay, was distributed on the particles of polyethylene in a Henschel* mixer maintained at 90°C. Nitrogen was continuously passed through the mixer for a period of 20 minutes to remove water vapour. The resultant coated particles, which were still moist, were dried overnight in a vacuum oven at 95°C. A masterbatch was prepared by extruding the thus dried mixture from a 1.90 cm single screw Brabender * extruder, equipped with a mixing screw, at a melt temperature of 182°C. The extrudate was cooled in a water bath, cut in a strand cutter and dried overnight under vacuum. The calculated amount of sulphur trioxide-trimethylamine complex in the masterbatch was 2.9% by weight. A physical admixture of 23g of the masterbatch and 660g of SCLAIR 11K polyethylene, an ethylene/butene-1 copolymer having a density of 0.920 g/cm³ and a melt index of 1.40 dg/min., was prepared. The admixture was extruded from the Brabender extruder, now equipped with a venting screw and a breaker plate, at a melt temperature of 256°C to form cast film having a width of 13.5 cm and a thickness of 50 µm. The hold-up time in the extruder was estimated to be 2.5-5 minutes. The film thus obtained was dyeable, whereas film from either SCLAIR 2114 or SCLAIR 11K polyethylene is not dyeable. In addition, the film did not show evidence of significant amounts of black specks, which are produced if a powder of the complex is reacted with polyethylene. Example VII In a series of runs, pellets of a polymer were coated with 2500 ppm of Lupersol 130 organic peroxide cross-linking agent. The resultant coated pellets were physically admixed, at a 2% level, with SCLAIR 13J4 polyethylene, an ethylene/octene-1 copolymer having a density of 0.930 g/cm³ and a melt index of 1.0 dg/min. to give blends of the present invention. The resultant blends were fed to the extruder of a blown film process; the extruder was equipped with the most efficient mixing screw that was available. The film obtained was inspected for quality. The results obtained are shown in Table II. 1. (i) ethylene/butene/octene terpolymer, density 0.910 g/cm³, melt index 1.7 dg/min. (ii) HPPE = high pressure polyethylene, density 0.918 g/cm³, melt index 7.0 dg/min (iii) polyethylene wax = N-34 Epolene® polymer, density 0.910 g/cm³, Brookfield viscosity 450 mPa.s (450 centipoise) at 125°C. (v) polypropylene = Shell (Trade Mark) 6300, density 0.905 g/cm³, melt flow index 20.0 dg/min. (vi) white concentrate = TiO₂ in a high pressure polyethylene. (vii) black concentrate = carbon black in a linear low density polyethylene. Example VIII A physical admixture of an ethylene/butene-1 copolymer having a density of 0.920 g/cm³ and a melt index of 1.4 dg/min., a concentrate of an organic peroxide cross-linking agent and maleic anhydride was prepared in a Henschel* mixer such that the admixture contained 50 ppm of cross-linking agent and 1% by weight of maleic anhydride. The concentrate of the cross-linking agent was in the form of pellets of an ethylene/butene-1 copolymer having a density of 0.924 g/cm³ and a melt index of 53 dg/min., containing Lupersol 130 organic peroxide. The maleic anhydride was in the form of powder. The mixture was blended in the Henschel mixer for five minutes at a maximum temperature of about 70°C and then extruded through a corotating twin screw extruder, the first two zones of which were at a temperature of 180°C and the remaining zones at a temperature of 200°C. A maleic anhydride-grafted polymer containing 0.56% by weight of maleic anhydride was obtained; the melt index of the polymer was 0.53. Films of the grafted polymer were pressed onto aluminum foil, nylon film and ethylene/vinyl alcohol copolymer film at a temperature of about 180°C. Good adhesion of the grafted polymer to the foil or film substrate was observed in each instance. This example illustrates the use of the present invention with a modifying agent. Example IX An ethylene/butene-1 copolymer having a density of 0.959 g/cm³ and a melt index of 85 dg/min. was blended with 2500 ppm of t-butylhydroperoxide. The resulting blend was physically admixed with pellets of an ethylene/butene-1 copolymer having a density of 0.920 g/cm³ and a melt index of 55 dg/min. in ratios of from 3:97 to 6:94. The admixtures thus obtained were fed to a process for the extrusion coating of paper. The extruded admixture had higher melt strength such that the line speed of the extrusion coating line could be increased from 26 m/minute, in the absence of the peroxide blend, to 46 m/minute. Example X An ethylene/butene-1 copolymer having a density of 0.924 g/cm³ and a melt index of 53 dg/min. was blended with 2500 ppm of Lupersol 130 organic peroxide. The resulting blend was physically admixed, at a 4% and at a 6% level, with SCLAIR 58A ethylene homopolymer which has a density of 0.960 g/cm³ and a melt index of 0.43 dg/min. The resulting blends were extruded into sheet having a thickness of 5 mm. The sheets thus obtained were free of gel, had higher melt strength than the corresponding sheets formed from SCLAIR 58A polyethylene and gave improved performance in the thermoforming process. Example XI Physical admixtures of SCLAIR 11K ethylene/butene-1 copolymer, which has a density of 0.920 g/cm³ and a melt index of 1.4 dg/min, organic peroxide and maleic anhydride were prepared. The organic peroxide (Peroxide Concentrate) was in the form of pellets of a composition of Sclair 2114 polyethylene, an ethylene/butene-1 copolymer having a density of 0.924 g/cm³ and a melt index of 53 dg/min, with 4000 ppm of Lupersol 130 organic peroxide and 4000 ppm of triallyl isocyanurate. The maleic anhydride was either in the form of a powder or a blend in polyethylene, as shown below. The physical admixture was fed to a 1.9 cm Brabender single screw extruder and extruded into a strand using a melt temperature of 225°C. Adhesion tests were conducted by pressing the chopped strand into film between sheets of aluminum at a temperature of 180°C for about 5 seconds. Further details and the results obtained are as follows:

Claims: A polyolefin blend comprising, in physical admixture, a major portion of particles of a first polyolefin and a minor portion of particles of a composition of a normally solid second polyolefin, the polyolefins being homopolymers and copolymers derived solely from hydrocarbon alpha-olefins having 2-10 carbon atoms, the second polyolefin having a shear viscosity that is not more than 30% of that of the first polyolefin when measured at 200°C and a shear rate of 400 sec⁻¹, said composition being a composition of the second polyolefin and a reactive agent which is a cross-linking agent or modifying agent, or a mixture thereof, the reactive agent being capable of reacting with the polyolefins in a molten state. The blend according to Claim 1 in which the first and second polyolefins are selected among homopolymer of ethylene and copolymer derived solely from ethylene and at least one C₄ - C₁₀ alpha-olefin. A polyolefin blend according to Claim 1 wherein the first polyolefin is a first polyethylene and the second polyolefin is a second polyethylene, in which the first polyethylene is a homopolymer of ethylene or a copolymer derived solely from ethylene and at least one C₄ - C₁₀ alpha-olefin, and the second polyethylene is a copolymer of ethylene and at least one C₄ - C₁₀ alpha-olefin having a density of at least 0.890 g/cm³ and a melt index of at least 40 dg/min. The blend according to Claim 3 in which the density of the second polyethylene is at least 0.910 g/cm³. The blend according to Claim 3 or Claim 4 in which the melt index of the second polyethylene is at least 10 dg/min. higher than that of the first polyethylene. The blend according to Claim 5 in which the melt index of the second polyethylene is 40-60 dg/min. higher than that of the first polyethylene. The blend according to any one of Claims 3 to 6 in which the density of the second polyethylene is at least 0.005 g/cm³ lower than that of the first polyethylene. The blend according to Claim 7 in which the density of the second polyethylene is at least 0.008 g/cm³ lower than the density of the first polyethylene. The blend according to any one of Claims 3 to 8 in which the ratio of the first polyethylene to the second polyethylene is in the range of from 10:1 to 100:1. The blend according to Claim 9 in which the ratio of the first polyethylene to the second polyethylene is in the range of from 50:1 to 100:1. The blend according to any of the preceding claims in which the shear viscosity of the second polyolefin is 5-15% of that of the first polyolefin. The blend according to any of the preceding claims in which the reactive agent is a cross-linking agent. The blend according to any of Claims 1 to 11 in which the reactive agent is a modifying agent. The blend according to any of the preceding claims in which the first polyolefin also contains a reactive agent. A process for the manufacture of an article from a polyolefin and a reactive agent capable of reacting with the polyolefin in a molten state, comprising feeding to melt processing apparatus a polyolefin blend according to Claim 1, melting and admixing said blend and forming an article from the resultant blend. The process according to Claim 14 in which the first and second polyolefins are independently a homopolymer of ethylene or a copolymer derived solely from ethylene and at least one C₄ - C₁₀ alpha-olefin. A process for the manufacture of articles from a polyolefin and a reactive agent capable of reacting with the polyolefin in a molten state, comprising feeding to melt processing apparatus a polyolefin blend according to Claim 3, melting and admixing said blend and forming an article from the resultant blend. The process according to Claim 17 in which the shear viscosity of the second polyethylene is 5-15% of that of the first polyethylene. The process according to Claim 17 or Claim 18 in which the density of the second polyethylene is at least 0.910 g/cm³. The process according to any one of Claims 15 to 19 in which the reactive agent is a cross-linking agent. The process according to any one of Claims 15 to 19 in which the reactive agent is a modifying agent. The process according to any one of Claims 15 to 21 in which the ratio of the first polyolefin to the second polyolefin is in the range of 10:1 to 100:1. The process according to any one of Claims 15 to 22 in which the forming is an extrusion and the rate of extrusion of polyolefin is higher than the rate would be for extrusion of the same polyolefin in the absence of the reactive agent or agents. The process according to Claim 22 in which the forming is a blown film extrusion process.

Inventors: WHITE, GEORGE
Applicants: DU PONT CANADA INC.
Application year: 1985
Main classification: C08L23
IPC codes: C08K5, C08L23