CA1203948A - Cross-linkable composition of polyethylene - Google Patents
Cross-linkable composition of polyethyleneInfo
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- CA1203948A CA1203948A CA000427535A CA427535A CA1203948A CA 1203948 A CA1203948 A CA 1203948A CA 000427535 A CA000427535 A CA 000427535A CA 427535 A CA427535 A CA 427535A CA 1203948 A CA1203948 A CA 1203948A
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- copolymer
- composition
- linking
- linked polymer
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Abstract
ABSTRACT OF THE DISCLOSURE
A cross-linkable composition of a partially cross-linked polymer and an organic cross-linking agent is disclosed. The polymer is a copolymer of ethylene and one or more higher alpha-olefins of 3-10 carbon atoms that has a density of less than 0.955 g/cm3 and which has been subjected to a cross-linking process to an extent such that the partially cross-linked polymer so obtained has less than 0.1%
by weight of gel. In a preferred embodiment the copolymer is a linear low density polyethylene, especially a copolymer of ethylene and a higher alpha-olefin having 4-10 carbon atoms.
The composition may be used in a variety of end-uses, especially in the wire coating industry.
A cross-linkable composition of a partially cross-linked polymer and an organic cross-linking agent is disclosed. The polymer is a copolymer of ethylene and one or more higher alpha-olefins of 3-10 carbon atoms that has a density of less than 0.955 g/cm3 and which has been subjected to a cross-linking process to an extent such that the partially cross-linked polymer so obtained has less than 0.1%
by weight of gel. In a preferred embodiment the copolymer is a linear low density polyethylene, especially a copolymer of ethylene and a higher alpha-olefin having 4-10 carbon atoms.
The composition may be used in a variety of end-uses, especially in the wire coating industry.
Description
3~3~3 CROSS-LINKABLE COMPOSITION OF POLYETHYLENE
The present inven-tion relates to a cross-linkable composi-tion of polyethylene in which the polyethylene is in in the form of a partially cross-linked polymer obtained hy subjec-ting an ethylene/higher alpha-olefin copolymer to par-tial cross-linkinq, especially irradiation, and in particular to a cross-linkable composition of such partially cross-linX-ed polymer and an organic cross-linking agen-t. The composi-; -tion may be used in, for instance, -the coating of wire.
Polyethylene is used in a wide varie-ty of end uses especially as a packaging material, as pipe and in the form of moulded articles. In particular, polyethylene may be used in the coating of wire.
Irradiation of polyethylene affects the proper-ties of the polyethylene, especially with regard -to the processing of the polyethylene and the fabrication of ar-ticles there-Erom, and may provide benefits in such processing. Irradia-tion ox polyethylene is known in the art but such irradiation has primarily been conducted on fabricated ar-ticles, e.g., on film to be used as a packaging material, fibre, shee-t or I; moulded articles, and/or at relatively high dosage levels, e.g., at least 2 Mrads of irradiation.
A method for improving melt strength and melt ex-;; tensibility of polyethylene having a density of 0.95 - 0.97 g/cm3 and a melt index, as determined by the procedure of ASTM D-1238 (condi-tion E), of 3-13 dg/min, is disclosed in U.S. Patent 3 563 870 of L.H. Tung et al, which issued 1971 February 16. Toe method involves exposing -the polyethylene to 0.05 - 0.15 Brad of high energy radiation.
An improved process for the irradiation of poly-ethylene, especially a process for the irradiation ox homo-polymers of ethylene and copolymers of ethylene and higher alpha-olefins in the form of granules, is disclosed in European Patent Publication No. 0 047 171 of G. White, published 1982 March 10. In that process, the polyethylene 3~
is irradiated with low levels of electron or gamma irradia-tion in the presence ox an inert atmosphere, especially an atmosphere of steam.
Polyethylene compositions con-taining cross-linking agents are known. For example, U.S. Patent 4 029 729 of R.L.
Rees et al, issued 1977 June l discloses -the use of poly-ethylene compositions comprising an ethylene homopolymer or copolymer having a melt index of at least about 10 dg/min.
and having incorporated therein a cross-linking acetylenic diperoxy compound. Other cross-linkable compositions of polyethylene and organic peroxides are known, for example, compositions in which the peroxide is dicumyl peroxide, as disclosed by F.M. Precopio et al in Canadian Patent 647 ~33, which issued 1962 August 2~.
A composition comprising polyethylene having a density of 0.920-0.970 g/cm3 and a melt index in -the range of 10-35 dg/min., bis(tert.-alkyl peroxyalkyl) benzene, a co-curing agent and anti-oxidants is disclosed by G. White in Canadian Patent Application Jo. 395 824, filed 1982 February 09.
The use of cross-linkable compositions of poly-ethylene and organic peroxides in the coating of wire is known in the art. however, the polyethylene in such cross-linkable compositions has tended to be low density polyethyl-ene made in a high pressure polymerization process. Otherpolyethylenes, especially linear low density polyethylenes, even when cross-linXed using organic peroxides, have been unsatisfactory in such end uses because the resultant cross-linked composition has deficiencies either in the wire coat-ing process or in the properties of the resultant coatedwire.
A cross-linkable composition, especially a composi-tion containing a so-called linear low--densi-ty polyethylene and which is capable of being used in a variety of applica-tions, including the wire coating industry, has now been , 35~
found.
Accordingly, the present invention provides a cross~linkable composition comprising: (a a partially cross-linked polymer obtained from a copolymer of ethylene and one 5or more C3 - Clo alpha-olefin having a density of 0.910-0.955 g/cm3, said copolymer having been subjected to a cross-link-in process to an extent such that the partially cross-linked polymer so obtained has less than 0.1% by weight of gel, and (b) an organic cross-linking agent.
lOIn a preferred embodiment o the composition of the present invention, the copolymer of (a) has been subjected to gamma or electron irradiation, especially less than 2.5 Mrads of irradiation.
In another embodiment, the copolymer of (a) has 15been subjected to cross-linking with an organic cross-linking agent.
In a further embodimen-t of the present invention, the organic cross-linking agent is an acetylenic diperoxy compound, a bis(tert. alkyl peroxy) alkane or a bis(tert.-20alkyl peroxyalkyl)benzene.
In yet another embodiment of the composition, the copolymer is a low-density ethylene/higher alpha-olefin copolymer manufactured by a solution polymerization process, especially a linear low density polyethylene -that is a 25copolymer of ethylene and a higher alpha~olefin having 4-lO
carbon atoms.
The copolymer that may be used in the composition of the present invention is an ethylene/higher alpha-olefin copolymer having a density of less than 0.955 g/cm3, 30especially in the range of 0.910-0.955 g/cm3 and in particular in the range of 0.920-0.930 g/cm3. The density of the copolymer that is used will depend, in particular, on the intended end use for the composition. Such copolymers are copolymers of ethylene and a minor amount of one or more C3-Clo alpha-olefin, especially a C4-Clo alpha-olefin, for , 353~8 example, a copolymer oE ethylene and a minor amount of butene-l, hexene--l and/or octene-l. Techniques for the manufacture oE such copolymers are known in the art. The copolymer may have a mel-t index, before partial crosslinking, in the range of 10-35 dg/min. and especially in the range of 15-25 dg/min.
In particular embodiments of the present invention, the copolymer is a so-called linear low density polyethylene.
Such polymers are copolymers of ethylene and higher alpha-olefins and are known in the art. Linear low density poly-ethylene may be manufactured in, in particular, a solution polymerization process using a co-ordination catalyst or a gas-phase polymerization process.
The partial cross-linking of the copolymer is dis-cussed hereinafter The composition of the present invention also con-tains an organic peroxide cross-linking agent. Organic cross-linking agents are known in the art and are used in the cross-linking of polyethylene. Examples of such cross-link-ing agents include dicumyl peroxide, available from HerculesIncorporated under the trade mark DI-CUP, acetylenic diperoxy compounds, or example, 2,5-dimethyl-~,5-di(tert.-butyl peroxy) hexyne-3 which is available from Wallace and Tiernan under the trade mark LUPE~SOL, bis(-tert.-alkyl peroxy) alkanes and bis(tert. alkyl peroxy alkyl)benzene, for example, bis(tert.-butyl peroxyisopropyl)benzene which is available from ~Iercules Incorporated under the trade mark VULC~P.
The composition of the present invention preferably contains 0.3-7.5 per cent, by weight o the partially cross-linked polymer, of the organic peroxide cross-linking agent, and in particular, 0.3-3.0 per cent, by weight o the poly mer, of the cross-linking agent. The preferred amount of crosslinking agen-t will depend in particular on the intended end use for the composition and on the particular kind of partially cross-linked polymer used in -the composition.
, .
~2~3~
The copolymer used in the composition of the pres-ent invention has been subjected to a cross-linking process to an extent such that the partially cross-linked polymer so obtained has less than 0.1% by weight of gel. As used herein, gel refers to that matter which remains after Soxhlet extraction of partially cross-linked polymer using xylene as solvent and a 200 TYLER* mesh wire screen in the extraction apparatus, although di-fferent definitions may be used in product quality speci-Eications in some industries, as noted in the examples.
One method of partially cross-linking ethylene/-higher alpha-olefin copolymers involves the use of cross-linking agents. Examples of cross-linking agents are the organic cross-linXing agents referred to hereinabove, other organic cross-linking agents e.g. ~,~'-azobisisobutyronit-rile, and silane cross-linking agents e.g. as disclosed in US. Patent 3 075 948 of T.R. Santelli, which issued 1963 January 29 and U.S. Patent 3 646 155 of H.G. Scott, which issued 1972 February 29.
A variety of techniques are known in the art for effecting cross-linking of polyethylene and such techniques may be used in the partial cross-linking of the copolymers hereof. For example the cross-linking agent used to partial-ly cross-link the copolymer may be coated onto and/or impreg-nated into pellets of the copolymer. The pellets are then extruded through an extruder, thereby partially cross-linking the copolymer, and re-pelletized. Alternatively pellets of copolymer may be fed to an extruder and the cross~linking agent, for partial cross-linking, may be metered into molten copolymer in the extruder, after which the copolymer is re-pelletized. The pellets of partially cross~linked polymer thus obtained may then be combined with the organic cross-linking agent to form the compositions of the invention.
An alternative method of partially cross-linking the copolymer is to subjeot the copolymer to electron or gamma irradiation, especially less than 2.5 Mrad of the irradiation. The copolymer is irradiated in the form of, for *denotes trade mark , , .
:~.Z~3~3~
example, granules, and no-t in the form of sheet, film or other fabricated shapes. In particular, the granules may be in the form of pellets, powder or the like. Those are the shapes of -the par-tially cross-linked polymer -that may be fed to processing equipment, Eor example, extruders, used in -the fabrication ox articles from the compositions of the present invention. Techniques for -the irradiation of polyethylene, including ethylene/higher alpha-olefin copolymers, in -this form are known, or example, the techniques disclosed in the aforementioned European Patent Publication No. 0 047 171 of G. White. In the process of White the granules of polyethy-lene are first subjected to an atmosphere of steam at, for example, temperatures o* at least 80C in order to *acilitate reduction of the oxygen content of the granules. Subsequent-ly, the granules are irradiated with electron or garnma irradiation. The granules should remain out of contact with oxygen during the irradiation step. The irradiation is pref-erably carried Ollt in an inert oxygen-free atmosphere, especially an atmosphere of steam.
The amount of irradiation will depend, in particu-lar, on the intended end-use of the compositions of the present invention and especially on the degree of change in properties of the polymer that is desired. High levels of irradiation rnay result in the formation of gel, which in some instances may be undesirable. Irradiation normally does not cause formation of significant amounts of gel until the amount of irradiation exceeds a predetermined level, depend-ent on the particular polyethylene being irradiated, after which gel forms rapidly on further irradiation. As noted hereinbefore, the partially cross-linked polymer hereo* con-tains less than l by weight of gel.
Sources of electron and gamma irradiation are known and any convenient source may be used. The intensity of irradiation may be varied over a wide range. The intensity selected will depend primarily on the availability of a suit-able source of irradiation and the time required to provide 3~8 the require~l amount of irradiation.
The irradiated granules of -the copolymer contain free radicals -that are capable of reacting with oxyyen -there-my affecting the properties of the polymer, especially the properties of articles fabricatec~ therefrom, over a period of time. The patent publication of G. White discloses that the irradiated granules should be main-tained in an inert a-tmos-phere, for example, an atmosphere of steam, for a period of -time after the irradiation has been completed. The period of time selected will depend on whether the irradiation was electron irradiation or gamma irradiation.
The composition of the present invention may con-tain anti-oxidan-ts and other stabilizers, fillers, pigments and the like. preferred antioxidant is 4,4'-thiobis (6-tert. butyl-m-cresol) which is available under the trade marks Santonox R and Santowhite crystals. FIowever, some additives, especially stabilizers, may be affected by irradi-ation or cross-linking and increased levels of such stabiliz-ers may be necessary in the polymer in order that the parti-ally cross-linked polymer will contain the desired level of effective stabilizers. In the al-ternative, the stabilizers may be added to the partially cross-linked polymer after, in particular, irradiation has taken place.
The use of additives to control the rate of cross-linking of polyethylene by organic cross-linking agents is known in the art, for example, Canadian Patent 736 039 of H.R. Larsen, which issued 1966 June 07. In particular, such additives tend to inhibit the premature cross-linking of polyethylene. In a preferred embodiment of the present invention an additive is used to control the rate of cross-linking of the ethylene/alpha-olefin copolymer, especially during the preparation of compositions of partially cross-linked polymer and organic cross-linking agent. Preferrea additives are 2-mercaptobenzthiazole and 4,4'-thiobis (6-tert. butyl-m-cresol).
The compositions of the invention may be wormed by ~3~
techniques known in the art, for example, feecling partially cross-linked polymer in granular form to an extruder, especi-ally an extruder equipped with a suitable mixing screw. Add-itives, particularly the organic cross-linking agent, may be metered into the extruder using a carrier, especially paraf-fin oil, as is disclosed in Canadian Patent 957 473 of H.J.
CooX, which issued 1974 November 12. Alternatively the organic cross-linking agent may be coated onto and/or impreg-nated into pellets of the partially cross linked polymer.
The organic cross linking agent may also be used in the form of a powder e.g. peroxide on a clay support, which may be tumble blended with powdered partially cross-linked polymer prior to extrusion or metered into the polymer in the extruder at a suitable location. The compositions of the present invention may be converted, if necessary, to a form suitable for the in-tended end use by techniques known in the art, for example, by pelletizing or grinding.
The compositions of the present invention Jay be used in the manufacture of a variety of products, especially in the wire-coating industry.
The present invention is further illustrated by the following examples:
Example 1 n ethylene/butene-l copolymer having a density of 0.924 g/cm3, a narrow molecular weight distribution and a melt index of 20 dg/min and containing 50 ppm of a hindered phenolic antioxidant was irradiated in air to 2 Mrad of gamma irradiation to give partially cross-linked polymer. A cross-linkable composition was prepared by admixed 94.5% by weight of the irradiated polyethylene, 5% by weight of Di-Cup dicumyl peroxide on a clay support (2~ by weight of active peroxide) and 0.5% Santonox antioxidant.
A 14 gauge (diameter 0.17 cm) copper wire was coat-ed with the cross-linkable composition at a speed of about 110 m/min. on a laboratory wire-coating apparatus. The melt 3~
. 9 _ temperature of the composition was 166C. The wire was coat-ed to a thickness of about 1.2 mm. No problems were encount-ered ln -the process.
Gel content was measured by the me-thod in Ontario ~ydro Standard Specification M-405SM-78 in which, in essence, 0.3-0.5 g of material is wrapped in 200 mesh wire cloth, boiled in 500 ml of xylene containing a hindered phenolic antioxidant for 5 hours and placed in a vacuum or air-circul-ating oven for at least 12 hours. The amount of insoluble polymer gives the gel content.
The gel con-tent of the composition was 0% after extrusion onto the wire but greater than 75% after subsequent vulcanization at 210C in steam.
Example II
Samples of the cross-linkable composition of Example I met the values required by Ontario Hydro Standard Specification M-405SM-78 with respect to the following tests:
Tensile strength and Elongation (procedure of ASTM
D638);
Retention of -tensile strength and elongation after aging (procedure of ASTM D1870);
Brittle point temperature (procedure of ASTM
D746);
Flexural modulus (procedure oE ASTM D790, method B);
Moisture Absorp-tion after 14 days at 75C
(procedure of ASTM D470).
-
The present inven-tion relates to a cross-linkable composi-tion of polyethylene in which the polyethylene is in in the form of a partially cross-linked polymer obtained hy subjec-ting an ethylene/higher alpha-olefin copolymer to par-tial cross-linkinq, especially irradiation, and in particular to a cross-linkable composition of such partially cross-linX-ed polymer and an organic cross-linking agen-t. The composi-; -tion may be used in, for instance, -the coating of wire.
Polyethylene is used in a wide varie-ty of end uses especially as a packaging material, as pipe and in the form of moulded articles. In particular, polyethylene may be used in the coating of wire.
Irradiation of polyethylene affects the proper-ties of the polyethylene, especially with regard -to the processing of the polyethylene and the fabrication of ar-ticles there-Erom, and may provide benefits in such processing. Irradia-tion ox polyethylene is known in the art but such irradiation has primarily been conducted on fabricated ar-ticles, e.g., on film to be used as a packaging material, fibre, shee-t or I; moulded articles, and/or at relatively high dosage levels, e.g., at least 2 Mrads of irradiation.
A method for improving melt strength and melt ex-;; tensibility of polyethylene having a density of 0.95 - 0.97 g/cm3 and a melt index, as determined by the procedure of ASTM D-1238 (condi-tion E), of 3-13 dg/min, is disclosed in U.S. Patent 3 563 870 of L.H. Tung et al, which issued 1971 February 16. Toe method involves exposing -the polyethylene to 0.05 - 0.15 Brad of high energy radiation.
An improved process for the irradiation of poly-ethylene, especially a process for the irradiation ox homo-polymers of ethylene and copolymers of ethylene and higher alpha-olefins in the form of granules, is disclosed in European Patent Publication No. 0 047 171 of G. White, published 1982 March 10. In that process, the polyethylene 3~
is irradiated with low levels of electron or gamma irradia-tion in the presence ox an inert atmosphere, especially an atmosphere of steam.
Polyethylene compositions con-taining cross-linking agents are known. For example, U.S. Patent 4 029 729 of R.L.
Rees et al, issued 1977 June l discloses -the use of poly-ethylene compositions comprising an ethylene homopolymer or copolymer having a melt index of at least about 10 dg/min.
and having incorporated therein a cross-linking acetylenic diperoxy compound. Other cross-linkable compositions of polyethylene and organic peroxides are known, for example, compositions in which the peroxide is dicumyl peroxide, as disclosed by F.M. Precopio et al in Canadian Patent 647 ~33, which issued 1962 August 2~.
A composition comprising polyethylene having a density of 0.920-0.970 g/cm3 and a melt index in -the range of 10-35 dg/min., bis(tert.-alkyl peroxyalkyl) benzene, a co-curing agent and anti-oxidants is disclosed by G. White in Canadian Patent Application Jo. 395 824, filed 1982 February 09.
The use of cross-linkable compositions of poly-ethylene and organic peroxides in the coating of wire is known in the art. however, the polyethylene in such cross-linkable compositions has tended to be low density polyethyl-ene made in a high pressure polymerization process. Otherpolyethylenes, especially linear low density polyethylenes, even when cross-linXed using organic peroxides, have been unsatisfactory in such end uses because the resultant cross-linked composition has deficiencies either in the wire coat-ing process or in the properties of the resultant coatedwire.
A cross-linkable composition, especially a composi-tion containing a so-called linear low--densi-ty polyethylene and which is capable of being used in a variety of applica-tions, including the wire coating industry, has now been , 35~
found.
Accordingly, the present invention provides a cross~linkable composition comprising: (a a partially cross-linked polymer obtained from a copolymer of ethylene and one 5or more C3 - Clo alpha-olefin having a density of 0.910-0.955 g/cm3, said copolymer having been subjected to a cross-link-in process to an extent such that the partially cross-linked polymer so obtained has less than 0.1% by weight of gel, and (b) an organic cross-linking agent.
lOIn a preferred embodiment o the composition of the present invention, the copolymer of (a) has been subjected to gamma or electron irradiation, especially less than 2.5 Mrads of irradiation.
In another embodiment, the copolymer of (a) has 15been subjected to cross-linking with an organic cross-linking agent.
In a further embodimen-t of the present invention, the organic cross-linking agent is an acetylenic diperoxy compound, a bis(tert. alkyl peroxy) alkane or a bis(tert.-20alkyl peroxyalkyl)benzene.
In yet another embodiment of the composition, the copolymer is a low-density ethylene/higher alpha-olefin copolymer manufactured by a solution polymerization process, especially a linear low density polyethylene -that is a 25copolymer of ethylene and a higher alpha~olefin having 4-lO
carbon atoms.
The copolymer that may be used in the composition of the present invention is an ethylene/higher alpha-olefin copolymer having a density of less than 0.955 g/cm3, 30especially in the range of 0.910-0.955 g/cm3 and in particular in the range of 0.920-0.930 g/cm3. The density of the copolymer that is used will depend, in particular, on the intended end use for the composition. Such copolymers are copolymers of ethylene and a minor amount of one or more C3-Clo alpha-olefin, especially a C4-Clo alpha-olefin, for , 353~8 example, a copolymer oE ethylene and a minor amount of butene-l, hexene--l and/or octene-l. Techniques for the manufacture oE such copolymers are known in the art. The copolymer may have a mel-t index, before partial crosslinking, in the range of 10-35 dg/min. and especially in the range of 15-25 dg/min.
In particular embodiments of the present invention, the copolymer is a so-called linear low density polyethylene.
Such polymers are copolymers of ethylene and higher alpha-olefins and are known in the art. Linear low density poly-ethylene may be manufactured in, in particular, a solution polymerization process using a co-ordination catalyst or a gas-phase polymerization process.
The partial cross-linking of the copolymer is dis-cussed hereinafter The composition of the present invention also con-tains an organic peroxide cross-linking agent. Organic cross-linking agents are known in the art and are used in the cross-linking of polyethylene. Examples of such cross-link-ing agents include dicumyl peroxide, available from HerculesIncorporated under the trade mark DI-CUP, acetylenic diperoxy compounds, or example, 2,5-dimethyl-~,5-di(tert.-butyl peroxy) hexyne-3 which is available from Wallace and Tiernan under the trade mark LUPE~SOL, bis(-tert.-alkyl peroxy) alkanes and bis(tert. alkyl peroxy alkyl)benzene, for example, bis(tert.-butyl peroxyisopropyl)benzene which is available from ~Iercules Incorporated under the trade mark VULC~P.
The composition of the present invention preferably contains 0.3-7.5 per cent, by weight o the partially cross-linked polymer, of the organic peroxide cross-linking agent, and in particular, 0.3-3.0 per cent, by weight o the poly mer, of the cross-linking agent. The preferred amount of crosslinking agen-t will depend in particular on the intended end use for the composition and on the particular kind of partially cross-linked polymer used in -the composition.
, .
~2~3~
The copolymer used in the composition of the pres-ent invention has been subjected to a cross-linking process to an extent such that the partially cross-linked polymer so obtained has less than 0.1% by weight of gel. As used herein, gel refers to that matter which remains after Soxhlet extraction of partially cross-linked polymer using xylene as solvent and a 200 TYLER* mesh wire screen in the extraction apparatus, although di-fferent definitions may be used in product quality speci-Eications in some industries, as noted in the examples.
One method of partially cross-linking ethylene/-higher alpha-olefin copolymers involves the use of cross-linking agents. Examples of cross-linking agents are the organic cross-linXing agents referred to hereinabove, other organic cross-linking agents e.g. ~,~'-azobisisobutyronit-rile, and silane cross-linking agents e.g. as disclosed in US. Patent 3 075 948 of T.R. Santelli, which issued 1963 January 29 and U.S. Patent 3 646 155 of H.G. Scott, which issued 1972 February 29.
A variety of techniques are known in the art for effecting cross-linking of polyethylene and such techniques may be used in the partial cross-linking of the copolymers hereof. For example the cross-linking agent used to partial-ly cross-link the copolymer may be coated onto and/or impreg-nated into pellets of the copolymer. The pellets are then extruded through an extruder, thereby partially cross-linking the copolymer, and re-pelletized. Alternatively pellets of copolymer may be fed to an extruder and the cross~linking agent, for partial cross-linking, may be metered into molten copolymer in the extruder, after which the copolymer is re-pelletized. The pellets of partially cross~linked polymer thus obtained may then be combined with the organic cross-linking agent to form the compositions of the invention.
An alternative method of partially cross-linking the copolymer is to subjeot the copolymer to electron or gamma irradiation, especially less than 2.5 Mrad of the irradiation. The copolymer is irradiated in the form of, for *denotes trade mark , , .
:~.Z~3~3~
example, granules, and no-t in the form of sheet, film or other fabricated shapes. In particular, the granules may be in the form of pellets, powder or the like. Those are the shapes of -the par-tially cross-linked polymer -that may be fed to processing equipment, Eor example, extruders, used in -the fabrication ox articles from the compositions of the present invention. Techniques for -the irradiation of polyethylene, including ethylene/higher alpha-olefin copolymers, in -this form are known, or example, the techniques disclosed in the aforementioned European Patent Publication No. 0 047 171 of G. White. In the process of White the granules of polyethy-lene are first subjected to an atmosphere of steam at, for example, temperatures o* at least 80C in order to *acilitate reduction of the oxygen content of the granules. Subsequent-ly, the granules are irradiated with electron or garnma irradiation. The granules should remain out of contact with oxygen during the irradiation step. The irradiation is pref-erably carried Ollt in an inert oxygen-free atmosphere, especially an atmosphere of steam.
The amount of irradiation will depend, in particu-lar, on the intended end-use of the compositions of the present invention and especially on the degree of change in properties of the polymer that is desired. High levels of irradiation rnay result in the formation of gel, which in some instances may be undesirable. Irradiation normally does not cause formation of significant amounts of gel until the amount of irradiation exceeds a predetermined level, depend-ent on the particular polyethylene being irradiated, after which gel forms rapidly on further irradiation. As noted hereinbefore, the partially cross-linked polymer hereo* con-tains less than l by weight of gel.
Sources of electron and gamma irradiation are known and any convenient source may be used. The intensity of irradiation may be varied over a wide range. The intensity selected will depend primarily on the availability of a suit-able source of irradiation and the time required to provide 3~8 the require~l amount of irradiation.
The irradiated granules of -the copolymer contain free radicals -that are capable of reacting with oxyyen -there-my affecting the properties of the polymer, especially the properties of articles fabricatec~ therefrom, over a period of time. The patent publication of G. White discloses that the irradiated granules should be main-tained in an inert a-tmos-phere, for example, an atmosphere of steam, for a period of -time after the irradiation has been completed. The period of time selected will depend on whether the irradiation was electron irradiation or gamma irradiation.
The composition of the present invention may con-tain anti-oxidan-ts and other stabilizers, fillers, pigments and the like. preferred antioxidant is 4,4'-thiobis (6-tert. butyl-m-cresol) which is available under the trade marks Santonox R and Santowhite crystals. FIowever, some additives, especially stabilizers, may be affected by irradi-ation or cross-linking and increased levels of such stabiliz-ers may be necessary in the polymer in order that the parti-ally cross-linked polymer will contain the desired level of effective stabilizers. In the al-ternative, the stabilizers may be added to the partially cross-linked polymer after, in particular, irradiation has taken place.
The use of additives to control the rate of cross-linking of polyethylene by organic cross-linking agents is known in the art, for example, Canadian Patent 736 039 of H.R. Larsen, which issued 1966 June 07. In particular, such additives tend to inhibit the premature cross-linking of polyethylene. In a preferred embodiment of the present invention an additive is used to control the rate of cross-linking of the ethylene/alpha-olefin copolymer, especially during the preparation of compositions of partially cross-linked polymer and organic cross-linking agent. Preferrea additives are 2-mercaptobenzthiazole and 4,4'-thiobis (6-tert. butyl-m-cresol).
The compositions of the invention may be wormed by ~3~
techniques known in the art, for example, feecling partially cross-linked polymer in granular form to an extruder, especi-ally an extruder equipped with a suitable mixing screw. Add-itives, particularly the organic cross-linking agent, may be metered into the extruder using a carrier, especially paraf-fin oil, as is disclosed in Canadian Patent 957 473 of H.J.
CooX, which issued 1974 November 12. Alternatively the organic cross-linking agent may be coated onto and/or impreg-nated into pellets of the partially cross linked polymer.
The organic cross linking agent may also be used in the form of a powder e.g. peroxide on a clay support, which may be tumble blended with powdered partially cross-linked polymer prior to extrusion or metered into the polymer in the extruder at a suitable location. The compositions of the present invention may be converted, if necessary, to a form suitable for the in-tended end use by techniques known in the art, for example, by pelletizing or grinding.
The compositions of the present invention Jay be used in the manufacture of a variety of products, especially in the wire-coating industry.
The present invention is further illustrated by the following examples:
Example 1 n ethylene/butene-l copolymer having a density of 0.924 g/cm3, a narrow molecular weight distribution and a melt index of 20 dg/min and containing 50 ppm of a hindered phenolic antioxidant was irradiated in air to 2 Mrad of gamma irradiation to give partially cross-linked polymer. A cross-linkable composition was prepared by admixed 94.5% by weight of the irradiated polyethylene, 5% by weight of Di-Cup dicumyl peroxide on a clay support (2~ by weight of active peroxide) and 0.5% Santonox antioxidant.
A 14 gauge (diameter 0.17 cm) copper wire was coat-ed with the cross-linkable composition at a speed of about 110 m/min. on a laboratory wire-coating apparatus. The melt 3~
. 9 _ temperature of the composition was 166C. The wire was coat-ed to a thickness of about 1.2 mm. No problems were encount-ered ln -the process.
Gel content was measured by the me-thod in Ontario ~ydro Standard Specification M-405SM-78 in which, in essence, 0.3-0.5 g of material is wrapped in 200 mesh wire cloth, boiled in 500 ml of xylene containing a hindered phenolic antioxidant for 5 hours and placed in a vacuum or air-circul-ating oven for at least 12 hours. The amount of insoluble polymer gives the gel content.
The gel con-tent of the composition was 0% after extrusion onto the wire but greater than 75% after subsequent vulcanization at 210C in steam.
Example II
Samples of the cross-linkable composition of Example I met the values required by Ontario Hydro Standard Specification M-405SM-78 with respect to the following tests:
Tensile strength and Elongation (procedure of ASTM
D638);
Retention of -tensile strength and elongation after aging (procedure of ASTM D1870);
Brittle point temperature (procedure of ASTM
D746);
Flexural modulus (procedure oE ASTM D790, method B);
Moisture Absorp-tion after 14 days at 75C
(procedure of ASTM D470).
-
Claims (14)
1. A cross-linkable composition comprising: (a) a partially cross-linked polymer obtained from a copolymer of ethylene and one or more C3 - C10 alpha-olefin having a density of 0.910-0.955 g/cm3, said copolymer having been subjected to a crosslinking process to an extent such that the partially crosslinked polymer so obtained has less than 0.1% by weight of gel, and (b) an organic cross-linking agent.
2. The composition of Claim 1 in which the copoly-mer has been partially cross-linked with irradiation in an inert atmosphere.
3. The composition of Claim 2 in which the irradiation is electron irradiation or gamma irradiation.
4. The composition of Claim 1 in which the copoly-mer has been partially cross-linked, in (a), with a cross-linking agent.
5. The composition of Claim 1 in which the organic cross-linking agent, in (b), is selected from the group con-sisting of dicumyl peroxide, acetylenic diperoxy compounds, bis(tert.-alkylperoxy) alkanes and bis(tert.-alkyl peroxy-alkyl)benzenes, said agent being present in an amount of 0.3-7.5% by weight of the partially cross-linked polymer.
6. The composition of any one of Claim 1, Claim 2 and Claim 5 in which the amount of organic cross-linking agent, in (b), is 0.3-3.0% by weight of the partially cross-linked polymer.
7. The composition of any one of Claim 1, Claim 2 and Claim 5 in which the copolymer has a density of 0.920-0.930 g/cm3.
8. The composition of any one of Claim 1, Claim 2 and Claim 5 in which the copolymer is a copolymer of ethylene and a higher alpha-olefin haviny 4-10 carbon atoms,said copolymer having a melt index, before partial cross-linking, in the range of 10-35 dg/min.
9. The composition of any one of Claim 1, Claim 2 and Claim 5 in which the copolymer is a copolymer of ethylene and butene-1.
10. A process for the coating of wire comprising the steps of:
(i) feeding said wire to a wire-coating die on an extruder, (ii) coating said wire with a composition comprising:
(a) a partially cross-linked polymer obtained from a copolymer of ethylene and one or more C3 - C10 alpha-olefin having a density of less than 0.910-0.955 g/cm3, said copolymer having been subjected to a cross-linking process to an extent such that the partially cross-linked polymer so obtained has less than 0.1% by weight of gel, (b) 0.3-7.5%, by weight of the partially cross-linked polymer, of an organic crosslinking agent; and (iii) cross-linking said composition by subject-ing the coated wire so obtained to vulcan-izing conditions.
(i) feeding said wire to a wire-coating die on an extruder, (ii) coating said wire with a composition comprising:
(a) a partially cross-linked polymer obtained from a copolymer of ethylene and one or more C3 - C10 alpha-olefin having a density of less than 0.910-0.955 g/cm3, said copolymer having been subjected to a cross-linking process to an extent such that the partially cross-linked polymer so obtained has less than 0.1% by weight of gel, (b) 0.3-7.5%, by weight of the partially cross-linked polymer, of an organic crosslinking agent; and (iii) cross-linking said composition by subject-ing the coated wire so obtained to vulcan-izing conditions.
11. The process of Claim 10 in which the copolymer is a copolymer of ethylene and a higher alpha-olefin having 4-10 carbon atoms, said copolymer having a melt index, before partial cross-linking, in the range of 10-35 dg/min.
12. The process of Claim 11 in which the amount of organic cross-linking agent is 0.3 - 0.3% by weight of the partially cross-linked polymer.
13. The process of any one of Claim 10, Claim 11 and Claim 12 in which the organic cross-linking agent of (b) is selected from the group consisting of dicumyl peroxide, acetylenic diperoxy compounds, bis(tert.-alkylperoxy)alkanes and bis(tert.-alkyl peroxyalkyl)benzenes.
14. The process of any one of Claim 10, Claim 11 and Claim 12 in which the copolymer has a density of 0.910-0.920 g/cm3.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB82.13513 | 1982-05-10 | ||
| GB8213513 | 1982-05-10 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1203948A true CA1203948A (en) | 1986-04-29 |
Family
ID=10530268
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000427535A Expired CA1203948A (en) | 1982-05-10 | 1983-05-05 | Cross-linkable composition of polyethylene |
Country Status (3)
| Country | Link |
|---|---|
| JP (1) | JPS58208336A (en) |
| AU (1) | AU560760B2 (en) |
| CA (1) | CA1203948A (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6114486A (en) * | 1996-03-05 | 2000-09-05 | The Dow Chemical Company | Rheology-modified polyolefins |
| US6232410B1 (en) | 1997-08-27 | 2001-05-15 | The Dow Chemical Company | Elastomers with improved processability |
-
1983
- 1983-05-05 CA CA000427535A patent/CA1203948A/en not_active Expired
- 1983-05-06 JP JP58078401A patent/JPS58208336A/en active Pending
- 1983-05-09 AU AU14367/83A patent/AU560760B2/en not_active Ceased
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6114486A (en) * | 1996-03-05 | 2000-09-05 | The Dow Chemical Company | Rheology-modified polyolefins |
| US6689851B1 (en) | 1996-03-05 | 2004-02-10 | Dow Global Technologies Inc. | Rheology-modified polyolefins |
| US6232410B1 (en) | 1997-08-27 | 2001-05-15 | The Dow Chemical Company | Elastomers with improved processability |
Also Published As
| Publication number | Publication date |
|---|---|
| AU560760B2 (en) | 1987-04-16 |
| AU1436783A (en) | 1983-11-17 |
| JPS58208336A (en) | 1983-12-05 |
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