Modified polypropylenes of improved processability

Details Modified polypropylenes of improved processability Modified polypropylenes of improved processability

1998-05-07

2001-03-20

Wu, David W. (Department: 1713)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Polymers from only ethylenic monomers or processes of...

C526S348600, C526S901000, C526S335000, C526S336000, C526S339000, C526S073000, C524S572000

Reexamination Certificate

active

06204348

ABSTRACT:

The invention relates to modified polypropylenes of improved processability, which are produced by the reaction of polypropylene with unsaturated monomers.
In contrast to polyethylenes of low density, which have been produced by high-pressure processes, polypropylenes exhibit a series of disadvantages during thermoplastic processing, such as an increased instability of the melt and the therewith associated smaller processing window. Compared to polyethylene, unmodified polypropylenes permit only a much lower processing speed.
Known methods for improving the processability of polypropylene are the use of blends of polypropylene with LDPE (German patent 32 20 269, WO 94/13460, WO 93/15132), of blends of polypropylene and mixtures of LDPE and hydrogenated vinyltoluene-methylstyrene copolymers (U.S. Pat. No. 4,365,044), of blends of polypropylene and partially cross linked polybutadienes (German patent 29 37 528), ethylene-propylene rubber (EP 505 850), polymethacrylates (European patent 570 221, U.S. Pat. No. 5,506,307), acrylate-grafted polypropylenes (Cruz, C. A., Proc. Polyolefins VIII Intern. Conference Houston, 523, page 147) or EVA (U.S. Pat. No. 4,352,892, British patent 1,400,494).
It is a disadvantage of these methods that the advantageous material properties of polypropylenes, such as nondeformability at elevated temperatures, transparency and modulus, are adversely affected by the high proportion of the modifying components.
An improvement in the processability of polypropylene is also brought about by the treatment of the powder in the solid phase with ionizing radiation (European patent 190 899), peroxides (European patent 384 431) or monomer/peroxide mixtures (EP 437 808). A treatment of polypropylenepolyethylene melts with peroxides for improving the processability (Xanthos, M., Adv. Polym. Techn. 11(1992)4, 295-304) is also known.
Numerous developments of the solid phase modification of polyolefins, including polypropylene, have become known recently. Solid phase grafting is understood to be the coupling of an unsaturated monomeric compound to a free radical site on the polymer molecule, which was produced by a free radical transfer or by high-energy radiation and is present in the solid phase at temperatures below the melting point or the softening point of the polyolefin. For this process, the polyolefins are present in particle form, for example as a powder or granulate, or as a film, sheet or fiber. Compared to the melt modification, the advantage of this method lies, above all, in the lower reaction temperature and therewith drastically reduced degradation and, compared to the solvent modification, the advantage lies in the fact that no organic solvent is used and that such a solvent does not have to be removed after the modification step.
In comparison to the melt modification or solvent modification, it is a disadvantage of the solid phase modification, above all, that the reactions between polymer molecules, as required for the formation of modified polymer structures, proceed very slowly or are strongly hindered in the solid phase.
A series of known solid phase modification methods is characterized by the addition of liquid, unsaturated, monomeric compounds. For example, the German patent 41 23 972 discloses a discontinuous method for producing polar-modified polyethylenes by the free radical coupling of carboxyl monomers and carboxyl monomer mixtures, 50 to 80 parts by weight of carboxyl monomer or carboxyl monomer mixture being added to the polyethylene, in which the free radical-forming agent or a mixture of such agents is then dispersed, after which the polymerization is carried out at temperatures ranging from 60° to 100° C.
In the DD 135 622, a method for coupling styrene to polyolefinic substrates, such as polyethylene, ethylene-propylene diene terpolymers, ethylenevinyl acetate copolymers, polypropylene and chlorinated polyethylene is described, the reaction with styrene or styrene-monomer mixtures taking place below the saturation vapor pressure of the monomers with the dry polymer substrate or with the polymer substrate in the presence of water or a different inert liquid medium. DD 135 621 describes under the same conditions the coupling of butadiene and butadiene-containing monomer mixtures and DD 131 752 describes the coupling of vinyl acetate and vinyl acetate-containing monomer mixtures with the same polymer substrates. Likewise, the addition of swelling agents to increase the yields of the modification reaction of polyolefin particles in the solid phase is known (European patent 0 376 753).
Usually, when liquid, unsaturated monomers are added, they concentrate at the particle surfaces and between the particles. If the free radical-forming agents are decomposed when the monomer distribution is so inhomogeneous, then there is increased homopolymerization of the monomer at the expense of the coupling reaction, that is, there is a reduction in the efficiency of the modification. Moreover, the materials, so produced, have production inhomogeneities and therefore inferior use properties.
One possibility for reducing these disadvantages is indicated in the European patent 0 439 079. A method for producing modified polyolefin copolymers is described, for which the free radical-forming agents and the monomers are added as a liquid phase, either as a pure liquid or as a liquid solution, to the polyolefin particles, the rate of addition of monomer being low and not exceeding 4.5 pph/min. The monomers are added either directly after the whole amount of free radical-forming agent has been added to the polyolefin particles, which are at the temperature required for the decomposition of the initiator, or simultaneously with the addition of the free radical-forming agent, or as a combination of these two methods, in which the addition of free radical-forming agent and of monomer overlaps. However, the significant disadvantages of an inhomogeneous distribution of monomers and of modified regions, which have already been described, also occur with this method.
In the European patent 0 190 889, the solid phase modification of polypropylene for producing branched polypropylene using ionizing radiation is described. One of the disadvantages of this method consists therein that, for deactivating the free radicals in the solid phase, an additional reaction time of 10 minutes to 110 minutes (depending on the temperature), is required.
It is an object of the present invention to develop modified polypropylenes, which have improved processing properties while retaining the strength properties of polypropylene and have been produced by a method, which avoids the disadvantages that have been listed for the known method.
The objects of the present invention accordingly are modified propylene homopolymers and/or modified propylene copolymers of improved processability from propylene homopolymers with melt indexes of 0.05 to 35 g/10 min at 230° C.2.16 kg and/or copolymers of 85.0 to 99.9% by weight of propylene and 0.1 to 15.0% by weight of &agr;-olefins with 2 or 4 to 18 carbon atoms with melt indexes of 0.05 to 45 g/10 min at 230° C. 2.16 kg and ethylenically unsaturated, multifunctional monomers, the modified propylene homopolymers and/or modified propylene copolymers being produced by a continuous method, for which the particulate propylene homopolymers and/or particulate propylene copolymers, in the form of powder, granulate or grit with particle sizes ranging from 0.001 to 7 mm and preferably from 0.05 to 4 mm, optionally with the addition of 0.05 to 3% by weight, based on the propylene homopolymers and/or propylene copolymers used, of acyl peroxides, alkyl peroxides, hydroperoxides, peroxycarbonates and/or peresters as thermally decomposing free radical-forming agents, are reacted with a gas mixture, which consists of 5 to 65% by volume of readily volatile, ethylenically unsaturated, multifunctional monomers, preferably C
4
to C
10
dienes and/or C
7
to C
10
divinyl compounds, and 95 to 35% by volume of inert gas or oxygen or inert gas-oxygen mixtures in any

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