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
1998-12-21
2001-04-24
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...
C525S321000, C525S324000, C525S314000, C525S315000, C525S247000, C525S268000, C526S073000, C526S125800, C502S132000, C502S134000
Reexamination Certificate
active
06221974
ABSTRACT:
The invention relates to a process for the preparation of rigid polypropylene for e.g. pipe, fiber, profile and moulding applications, containing from 1.0 to 10.0% by weight of ethylene repeating units and having a MFR
2
value of between 0.05 and 0.40 g/10 min, by polymerizing propylene and ethylene or a C
4
-C
10
-&agr;-olefin in the presence of a catalyst system, the procatalyst component of which is a reaction product of at least a tetravalent titanium compound and a magnesium halide compound and the cocatalyst component of which comprises an organoaluminium compound, and hydrogen as a molecular weight regulating agent, to give said polypropylene.
The invention also relates to a process for the preparation of elastomer modified polypropylene for e.g. pipe, fiber, profile and moulding applications, containing from 1.0 to 30% by weight of ethylene or a C
4
-C
10
-&agr;-olefin repeating units and having a MFR
2
value of between 0.05 and 50 g/10 min, by polymerizing propylene and ethylene or a C
4
-C
10
-&agr;-olefin in the presence of a catalyst system, the procatalyst component of which is a reaction product of at least a tetravalent titanium compound and a magnesium halide compound and the cocatalyst component of which comprises an organoaluminium compound, and hydrogen as a molecular weight regulating agent, as well as providing an elastomer component, to give said elastomer modified polypropylene.
Finally, the invention also relates to a creep-resistant polypropylene made by the above processes and its use.
By Melt Flow Rate (MFR) is meant the weight of a polymer extruded through a standard cylindrical die at a standard temperature in a laboratory rheometer carrying a standard piston and load. Thus MFR is a measure of the melt viscosity of a polymer and hence also of its molecular weight. The smaller the MFR, the larger is the molecular weight. It is frequently used for characterizing a polyolefins, e.g. polypropylene, where the standard conditions MFR
mi
are: temperature 230° C.; die dimensions 9.00 mm in length and 2.095 mm in diameter; load of the piston, 2.16 kg (mi=2), 5.0 kg (mi=5), 10.0 kg (mi=10), 21.6 kg (mi=21). See Alger, M. S. M., Polymer Science Dictionary, Elsevier 1990, p. 257. The standard generally used are ISO 1133 C4, ASTM D 1238 and DIN 53735.
By Flow Rate Ratio (FRR) is meant the ratio between the Melt Flow Rate (MFR) measured at a standard temperature and with standard die dimensions using a heavy load and the melt flow rate measured at the same temperature with the same die dimensions using a light load. Usually, for propylene polymers are used nominal loads 10.0 kg and 2.16 kg (ISO 1133 C4). The larger the value of the FRR, the broader the molecular weight distribution.
Polypropylene copolymer has many characteristics which makes it desirable for applications like pipes, fittings, moulded articles, foams etc. Polypropylene as piping material is mainly used in non-pressure applications (pipe and fittings) and profiles. There is a small volume used for pressure pipe, mainly hot water and industrial pipes. The good thermal resistance of polypropylene compared to other polyolefins is utilized for the pipe applications. All three main types of propylene polymer, i.e. homopolymers, random copolymers and block copolymers are used. Homopolymers give the pipe good rigidity but the impact and creep properties are not very good. The block copolymers give good impact properties but the creep properties are like homopolymers due to the homopolymer matrix. Propylene ethylene random copolymers are used for pressure pipe applications for hot water and industrial pipes.
The propylene-ethylene random copolymers for pressure pipes are today produced with high yield Ziegler-Natta catalysts in processes (bulk or gas phase) giving a material having a relatively narrow molecular weight distribution (MWD=M
w
/M
n
) of about 5, corresponding to a FRR (MFR
10
/MFR
2
) of 13-17. The molecular weight (M
w
) of the pipe material with melt flow rate (MFR
2
) of 0.1-0.4 is about 600000-1000000. This high molecular weight and the narrow MWD cause problems in compounding and extrusion of pipes. The processability of such materials is difficult due to the low shear sensitivity causing unwanted degradation of the material and melt fracture, which is seen as uneven surface and thickness variations of the pipes. In addition the conventional propylene random copolymer pipe materials produced in one phase have not strength enough for the short and long term properties (notch resistance and creep) needed for good pressure pipes.
The processability of the conventional propylene random copolymers can be improved by broadening the MWD using multi-stage polymerization processes. In multi-stage polymerization the MWD of the polymer can be broadened by producing different molecular weight polymers in each stage. The MWD of polymer becomes broader when lower molecular weight polymer is reactor-blended into the higher molecular weight polymer adjusting the final MFR by choosing the right molecular weight and the reactor split in each stage. The molecular weight of the polymer in each step can be controlled by hydrogen which acts as a chain transfer agent. Reactor temperature may be also used for controlling the molecular weight of polymer in each step. Multi-stage polymerization is disclosed e.g. in patent application JP-91048214, but the process concerns film grade polypropylene with a final MFR
2
of about 1.5.
When the processability is improved by producing broader MWD propylene random copolymer, also the amount of low molecular fraction is increased if the comonomer feeds are the same in each stage. The taste and odour are adversely affected.
By using a concept invented with high yield TiCl
4
catalyst it is possible to produce pipe material having improved mechanical and pipe properties and also a good extrudability. The improved strength properties of the material come from a very high molecular weight fraction of Mw≧2000000 g/mol and totally novel comonomer distribution together with a broad molecular weight distribution. In another embodiment of the invention, an elastomer is provided within this propylene product for increased impact strength.
The embodiment of the invention relating to a non-elastomeric polypropylene product is essentially characterized by what is said in the characterizing part of claim 1. Thus the invented concept is based on the idea of producing a broad MWD and a high molecular weight propylene random copolymer and improved comonomer distribution using high yield catalysts in two or several reactors at different reaction conditions. The comonomers incorporated in long chains as described in this invention destroy the regularity of the chains leading to the more homogenous distribution of the essential tie-chains and entanglements needed for creep properties and toughness in pipe materials.
The low molecular weight fraction contains no or minimal portion of ethylene repeating units in the polymer. Together with the high molecular weight random copolymer fraction this fraction is improving the processability. The no or low ethylene content fraction gives the total polymer the stiffness needed for rigid materials e.g. pipes, profiles and moulding applications.
A homopolymer or a minirandom copolymer (ethylene<1%) is known to have a stiffness of 1400-1700 MPa when a random copolymer with an ethylene content of ≧2% has a stiffness of <1000 MPa.
The problem with the uneven comonomer distribution with high yield TiCl
4
catalysts is solved in a way that the amount of comonomer is split between the reactors. To the reactor where the high molecular weight propylene polymer is produced is fed more essentially all, comonomer compared to the reactor where the low molecular PP i produced. Higher amounts of comonomer can be fed because the solubility of the high molecular weight polymer is lower. The final comonomer content is adjusted by controlling the comonomer feed into the reactor. The intervals given in this publication al
Harkonen Mika
Malm Bo
Nymark Anders
Birch & Stewart Kolasch & Birch, LLP
Borealis Technology Oy
Wu David W.
Zalukaeva Tanya
LandOfFree
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