Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2000-04-14
2002-02-05
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S053000, C525S324000, C525S232000, C525S236000, C525S315000, C525S319000, C525S240000
Reexamination Certificate
active
06344522
ABSTRACT:
The subject of the present invention is a process for the preparation of a composition containing ethylene polymers, using a number of reactors arranged in series. It relates, in particular, to a process for the preparation of a composition containing ethylene polymers additionally comprising an alpha-olefin.
A process for the preparation of a composition containing ethylene polymers is described in Patent EP-22,376-B1 (Mitsui Petrochemical Industries), according to which at least two reactors are used in series, a first part of the ethylene is polymerized in the presence of a catalyst in a first reactor of the series, a polymer and the catalyst are drawn off from this reactor, these are made to move successively into the other reactors into each of which another part of the ethylene is delivered, which ethylene is polymerized, and a composition containing ethylene polymers is recovered from the last reactor. This known process uses, in each reactor, polymerization conditions different from those used in the other reactors, so that, in each reactor, a polymer is produced which has a different viscosity—and consequently a different melt index—from those produced in the other reactors. In particular, the composition containing ethylene polymers obtained by this known process comprises a first polymer having an intrinsic viscosity of 0.3 to 3 and a second polymer having an intrinsic viscosity of 1 to 12, the ratio between these viscosities being at least equal to 1.5.
This known process does not make it possible to achieve a large difference in the viscosities or the melt indices of the polymers produced in the various reactors, so that it does not make it possible to obtain polymers combining good use properties (characteristic of polymers with high melt indices) and good mechanical properties (characteristic of polymers with low melt indices).
Moreover, this known process is ill-suited to adjusting the molecular weight distribution of the final composition. Consequently, it does not allow access to a final composition suited to the implementation of objects by injection (composition having a molecular weight distribution characterized by an M
w
/M
n
ratio less than 10) nor to compositions which can be used for the manufacture of films by calendering (compositions in which the abovementioned M
w
/M
n
ratio is greater than 40).
This known process additionally has the disadvantage of causing, when the polymer of low viscosity or of high melt index is manufactured in one of the reactors in a hydrocarbon diluent in the presence of hydrogen, rapid saturation of the diluent with hydrogen.
The present invention solves the disadvantages stated above by providing a novel process using a number of reactors which makes it possible to obtain a pronounced difference in the melt indices of the polymers obtained in the various reactors, which shows great flexibility in adjusting the molecular weight distribution of the final polymer composition and which additionally makes it possible to produce a polymer of very high melt index in the presence of a hydrocarbon diluent and hydrogen, without risk of premature saturation of the diluent by the hydrogen.
Consequently, the invention relates to a process for the preparation of a composition containing ethylene polymers comprising a polymer of high melt index and a polymer of low melt index in at least two reactors, according to which part of the ethylene, a catalyst derived from a transition metal chosen from the elements of groups IIIB, IVB, VB and VIB of the periodic table and a cocatalyst are introduced into a first reactor, polymerization of the ethylene is carried out therein, a mixture comprising one of these polymers, the catalyst and the cocatalyst is drawn off from this reactor, the mixture and another part of the ethylene are introduced into a subsequent reactor, which ethylene is polymerized to form the other polymer, the weight ratio of the polymers being equal to (30 to 70):(70 to 30); according to the invention, the catalyst has an intrinsic weight distribution defined by an intrinsic M
w
/M
n
ratio less than or equal to 10 and a deactivation constant less than or equal to 0.5 h
−1
, and the polymer of high melt index has a melt index MI
2
, measured under a load of 2.16 kg at 190° C., of 5 to 1000 g/10 min and the polymer of low melt index has a melt index MI
5
, measured under a load of 5 kg at 190° C., of 0.01 to 2 g/10 min, the ratio between these melt indices being from 500 to 50,000.
Intrinsic molecular weight distribution of a catalyst is understood to denote the molecular weight distribution of a polymer obtained in a single polymerization stage and under constant polymerization conditions in the presence of this catalyst. The intrinsic M
w
/M
n
ratio which characterizes this intrinsic molecular weight distribution denotes the ratio between the weight-average molecular mass (M
w
) of the polymer thus obtained and the number-average molecular mass (M
n
) of this polymer, this ratio being measured by steric exclusion chromatography carried out in 1,2,4-trichlorobenzene at 135° C. on a type 150 C chromatograph from the company Waters.
Deactivation constant of a catalyst is understood to denote the angular coefficient which characterizes the linear relationship between the logarithm of the ratio of the polymerization rate and of the initial polymerization rate, and the polymerization time, the polymerization being carried out in the presence of this catalyst. The angular coefficient is calculated using linear regression.
The melt index MI
2
(respectively MI
5
) of a polymer denotes the flow rate of the molten polymer at 190° C., which flows through a die with a diameter of 2 mm and a length of 8 mm, under the effect of a piston ballasted with a mass of 2.16 kg (respectively 5 kg), this flow rate being expressed in g/10 min according to ASTM standard D 1238.
In the process according to the invention, ethylene is polymerized in the presence of a catalyst. An essential characteristic of the process lies in the properties of the catalyst used. According to the invention, the catalyst has an intrinsic molecular weight distribution defined by an intrinsic M
w
/M
n
ratio at most equal to 10, preferably less than 8, the values less than or equal to 7 being the most advantageous, for example approximately 6.5 or 5. The intrinsic M
w
/M
n
ratio is usually greater than 3, the values greater than 4 being the most common. The catalyst used in the process according to the invention additionally has a deactivation constant less than or equal to 0.5 h
−1
, preferably at most equal to 0.3 h
−1
, the values less than or equal to 0.2 h
−1
, for example of approximately 0.15 h
−1
, being recommended. The deactivation constant is generally greater than 0.05 h
−1
, the values greater than or equal to 0.1 h
−1
being the most common.
The catalyst used in the process according to the invention can be chosen from the Ziegler-type catalysts, in particular those derived from titanium, and from metallocene-type catalysts, metallocene being a cyclopentadienyl derivative of a transition metal, in particular of zirconium.
There may be mentioned, as non-limiting examples of Ziegler-type catalysts, the compounds comprising a transition metal chosen from groups IIIB, IVB, VB or VIB of the periodic table, magnesium and a halogen obtained by mixing a magnesium compound with a compound of the transition metal and a halogenated compound. The halogen can optionally form an integral part of the magnesium compound or of the transition metal compound.
Mention may be made, as examples of metallocene-type catalysts, of metallocenes activated by an aluminoxane and ionic metallocenes activated by an ionizing agent as described, for example, in Patent Application EP-500,944-A1 (Mitsui Toatsu Chemicals).
Ziegler-type catalysts are preferred. Among these, those comprising at least one transition metal chosen from groups IIIB, IVB, VB and VIB, magnesium and at least one halogen are very well suited. Good results are obtained with t
Choi Ling-Siu
Schneller Marina V.
Solvay Polyolefins - Europe Belgium
Venable
Wu David W.
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