Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Patent
1990-06-19
1992-07-07
Thurlow, Jeffery
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
264205, 526352, C08L 2300
Patent
active
051284154
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a process for preparing articles, such as filaments, tapes, films, tubes, rods and profiles, from high molecular weight polyethylene, with a high tensile strength and a high modulus and low creep.
It is known to prepare articles of high tensile strength and modulus, in particular filaments or tapes, starting from solutions of high molecular weight polyethylene, see U.S. Pat. Nos. 4,344,908; 4,411,854; 4,422,993; 4,430,383 and 4,436,689. In these known processes, a semidilute solution of a linear, high molecular weight polyethylene is converted e.g., spinning to a solvent-containing article, e.g. a filament, which is subsequently converted to an article of high strength and modulus by thermoreversible gelation and drawing. As the strength and modulus of the articles made have been found to increase with increasing molecular weight of the polyethylene used, a polyethylene with a weight-average molecular weight of at least 4.times.10.sup.5, in particular at least 6.times.10.sup.5, and preferably above 1.times.10.sup.6 will generally be started from.
Articles obtained with these known processes have been found to have a relatively high creep.
It has been attempted to lower the creep by for instance irradiation with electron rays. However it appeared that then the tensile strength of the articles strongly decreases. It is also described, see EP-A-205,960, to improve the creep resistance by post-stretching or heat treatment. However this does not appear to be a technical or economical solution due to the very slow stretching and complicated processing steps.
The present invention provides articles with a high modulus, a high tensile strength and low creep, and a process of preparing such articles.
The invention relates to a process for preparing polyethylene articles of high tensile strength, high modulus and low creep, in which a polyethylene feedstock with a viscosity-average molecular weight of at least 500,000 kg/kmole mixed with a solvent or a mixture of solvents for the polyethylene is converted to a shaped, solvent-containing article at a temperature above the dissolving point, this article is cooled to form a solid gel-like article, and this solid article obtained after cooling is drawn at an elevated temperature, whether or not after complete or partial removal of solvent this process being characterized in that a polyethylene feedstock is used which contains 2-20 alkyl side chains per 1000 carbon atoms.
According to one mode of realization of the present invention use is made of a polyethylene copolymer. In that case preferably, a polyethylene copolymer is used which has a viscosity-average molecular weight of more than 6.times.10.sup.5, in particular more than 8.times.10.sup.5 and more in particular more than 1.times.10.sup.6 kg/kmole and which preferably contains 3-12 alkyl side chains per 1000 carbon atoms, which side chains preferably contain at most two carbon atoms.
According to another mode of realization of the present invention use is made of a blend of atoms and atoms, 500,000 Kg/Kmole.
In that case both component (A) and (B) have preferably a viscosity-average molecular weight of more than 6.times.10.sup.5, in particular more than 8.times.10.sup.5 and more in particular 1.times.10.sup.6 Kg/Kmole, while the blend of (A) and (B) preferably contains 2.5-10 and more preferably 4-7 alkyl side chains per 1000 carbon atoms, which side chains preferably contain at most two carbon atoms.
It has been found that when the side chains are too long, e.g. 5, 6 or more carbon atoms, the decrease in creep diminished and moreover also the tensile strength and modulus decrease. If a blend of polyethylene is used the amount of side chains in the component with the highest amount of side chains must be below 100, preferably below 20 per 1000 carbon atoms.
The invention further relates to articles with decreased creep, with a modulus of at least 70 GPa and a tensile strength of at least 2.0 GPa, consisting of an ethylene polymer with a viscosity-average molecular weight of at least 500,00
REFERENCES:
patent: 4344908 (1982-08-01), Smith et al.
patent: 4422993 (1983-12-01), Smith et al.
patent: 4436689 (1984-03-01), Smith et al.
patent: 4455273 (1984-06-01), Harpell et al.
patent: 4536536 (1985-08-01), Kavesh et al.
patent: 4551296 (1985-11-01), Kavesh et al.
patent: 4643865 (1987-02-01), Okada et al.
Bastiaansen Cornelis W. M.
Ohta Yasuo
Sugiyama Hiroshige
Dyneema V.O.F.
Thurlow Jeffery
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