Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
1997-04-04
2001-04-10
Teskin, Fred (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S106000, C108S057250, C108S057280, C296S039100, C296S039200
Reexamination Certificate
active
06214960
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to an ethylene homopolymer which is particularly suitable for the extrusion of heavy gage sheets which can be subsequently thermoformed into very large goods. It also relates to a continuous polymerization process for the production of this ethylene homopolymer. It further relates to a composition consisting essentially of the ethylene homopolymer and to shaped products manufad from this composition, in particular pallets and truck bedliners.
TECHNOLOGY REVIEW
The U.K. Patent Specification GBA-1,501,728 describes polymers, in particular ethylene-hexene copolymers, presenting a melt index measured according to the ASTM D 1238—Condition E standard(at 190° C. under a load of 2.16 kg) from 0.1 to 20 g/10 min and presenting for instance a density from 0.950 to 0.952 g/cm
3
.
Such known ethylene polymers present the drawback that they are not adapted for the manufacture of heavy gage sheets by extrsion, which can subsequently be thermoformed into very large goods. This inconvenience is due to an impropriate combination of melt index and density of the ethylene polymers conferring unadequate mechanical properties such as tensile yield (elongation), tensile impact and fleal modulus.
The invention overcomes this disadvantage by providing a new ethylene polymer which is particulary suitable for the manufacture of very large goods by thermoforming extruded heavy gage sheets. An objective of the invention is to provide an ethylene polymer having simultaneously a particular high load melt index and an elevated density.
SUMMARY OF THE INVENTION
To this end, the invention relates to an ethylene homopolymer having a density of from about 0.956 to about 0.970 g/cm
3
and a high load melt index measured according to the ASTM D 1238—Condition F standard (at 190° C. under a load of 21.6 kg) of frog about 7 to about 21 g/10 min.
One of the essential characteristics of the ethylene homopolymers according to the invention which differentiate them from the commercially available ethylene polymers destnted to the mamnfacture of large goods resides in the absence of comonomer. Furthermore, the ethylene homopolymer according to the invention is characterized by a combination of a particular high load melt index with an elevated density. In general the high load melt index (as defined hereabove) of the ethylene homopolymer is at least 9 g/10 min, most often at least 11 g/10 min; the high load melt index generally does not exceed 17 g/10 min, the values of at most 15 g/10 min being the most advantageous. Good results have been obtained with high load melt indices ranging from about 11 to about 15 g/10 min.
In the mjority of cases the ethylene homopolymer presents a density of at least 0.957 g/cm
3
, in particular at least 0.959 g/cm
3
; the density is usually at most 0.967 g/cm
3
, values of at most 0.965 g/cm
3
being the most r mended. The particularly preferred densities range from about 0.957 to about 0.963 g/cm
3
.
DETAILED DESCRIPTION OF THE INVENTION
The ethylene homopolymers according to the invention can be obtained by any known polymerization process, such as polymerization in gas phase, in suspension or in solution. Furthermore, they can be obtained in a continuous or non continuous process, in a single reactor or in a number of reactors arranged in series, the polymezization conditions (tempeare, optonal hydrogen content, type of polymerization medium) in one reactor being different from those used in the other reactors. A suspension polymerization process is preferred, which is advantageously carried out continuously in a loop reactor.
A suspension polymerization is carried out in a hydrocarbon diluent such as liquid aromatic, cycloaliplatic and aliphatic hydrocarbons at a temperature such that at least 80% (preferably at least 90%) of the polymer formed is insoluble therein. Suitable diluents are linear alkanes such as n-butane, n-hexane and n-heptane or branched alkanes such as isobutane, isopentane, isooctane and 2,2-dimethylpropane or cycloaknes such as cyclopentane and cyclohexane or their mixes. The preferred diluents are n-hexane and isobutane. The best results are obtained with isobutane.
The suspension polymerization temperature is generally at least 20° C., in particular at least 55° C., temperatures of at least 90° C. being recommended. The polymerization temperature is usually at most 200° C., preferably at most 150° C., temperatures of at most 110° C. being advantageous. The particularly preferred temperatures range from about 55 to about 150° C., espey from about 90 to about 110° C.
In a discontinuous suspension polymerzation process, the ethylene pressure, which is advantageously kept constant during polymerization, is most often at least equal to atmospheric pressure, in particular at least 0.4 MPa, pressures of at least 0.6 MPa being preferred. The ethylene pressure is generally at most 5 MPa, in particular at most 2 MPa, ethylene pressures of at most 1.5 MPa being the most common.
In a continuous suspension polymerization process, the ethylene pressure is most often such that the concentration of ethylene in the suspension is at least 0.1 mol %, preferably at least 1 mol %, the values of at least 3 mol % being recommended. The ethylene concentration is in general at most 50 mol %, especially at most 20 mol %, values of at most 10 mol % being the most common. The best results are obtained with an ethylene concentration from about 1 to about 10 mol %, in particular from about 3 to about 10 mol %, for instance approximately 7 mol %.
The ethylene homopolymers according to the invention can be obtained in the presence of a molecular mass regulator such as hydrogen. The hydrogen partial pressure is most often from 0.001 to 2 MPa, in particular from 0.002 to 1.5 MPa and preferably from 0.005 to 1.3 MPa. Nevertheless, the polymerization is advantageously carried out in the absence of hydrogen.
The ethylene homopolymers may be obtained in the presence of any type of catalyst capable of polymerizing ethylene, such as, for example, catalysts based on titanium deposited on a support such as an inorganic support containing magnesium in particular magnesium chloride, catalysts based on chromium deposited on a support, in particular an inorganic support contaig silica, or catalysts based on metallocenes optionally suppoed.
The chromium oxide catalysts deposited on a support are especially preferred. The support can be chosen from polymeric and inorganic supports. The inorganic supports are most suitable. They can be selected from mineral oxides such as oxides of silicon, aluminium, titanium, zirconium, thorium and their mixtures, from mixed oxides of these metals such as aluminium silicate, alumimium phosphate and their mtxtures, and from mineral halogenides such as magnesium chloride. Supports contining silica are suitable. Pure silica is preferred.
In the supported chromium oxide catalysts, the chromium is generally present in a proportion of at least 0.05 wt % based on the total weight of the catalyst, in particular at least 0.1 wt %, values of at least 0.25 wt % being recommended. The chromium proportion is usually at most 10 wt %, especially at most 5 wt %, the values of at most 2 wt % being advantageous. Good results have been obtained with chromium proportions of from about 0.1 to about 5 wt %, preferably of from about 0.25 to about 2 wt %.
The chromium oxide catalysts deposited on a support can be obtained in any way known per se by impregnating the support powder with an aqueous or organic solution of a chromium compound, followed by drying in an oxidizing atmosphere. To this end, it is possible to use a chromium compound chosen from the soluble salts such as the oxides, the acetate, the chloride, the sulphate, the chromate and the bichromate in aqueous solution or such as the acetylacetonate in organic solution. After impregnating the support with the chromium compound, the impregnated support is generally activated by heating it in order to convert at least part of the chromium to hexavalent chromium at a temperature of at least 400°
Fiasse Paul
Mahan Ross M.
Marissal Daniel
Sander Robert E.
Sandstrum Steven D.
Schneller Marina V.
Solvay Polyolefins Europe-Belgium
Teskin Fred
Venable
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