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
1999-11-17
2001-11-06
Lipman, Bernard (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...
C525S308000, C525S309000, C525S320000, C525S322000, C525S329200, C525S330300, C525S333800, C525S387000
Reexamination Certificate
active
06313228
ABSTRACT:
The present invention relates to a process for peroxidic treatment of olefin polymers with di-tert-butyl peroxide in an extruder, in which the olefin polymers together with di-tert-butyl peroxide under an inert gas are fed to an extruder. The present invention further relates to the use of peroxidically treated olefin polymers for producing moldings, fibers, films or nonwoven spunbond fabrics, and also to a process for producing moldings, fibers, films or nonwoven spunbond fabrics.
Olefin polymers are used predominantly in the chemical form in which they are produced during the polymerization. However, for some application sectors it is necessary or advantageous to modify the olefin polymers chemically after the polymerization itself. Peroxides are frequently used here. Examples of reactions in which olefin polymers are treated with peroxides are grafting and crosslinking. Peroxides are also used for molecular-weight degradation.
To be suitable for peroxidic treatment of olefin polymers the peroxides have to satisfy a number of requirements. They must be safe to handle during transport, storage and processing. Their decomposition temperature and decomposition behavior must be such that they decompose only on reaching the desired part of the extruder, and there bring about the chemical modification of the polymer. Neither the peroxides nor their decomposition products may be toxic, and there must not be excessive loss of peroxide due to high volatility during the process.
Examples of peroxides which are used commercially in peroxidic treatment of olefin polymers are dicumyl peroxide, bis(tert-butylperoxyisopropyl)benzene, 2,5-dimethyl-2, 5-di-tert-butylperoxyhexane and di-tert-butyl peroxide (Gächter/Müller, Plastics Additives, 4th Edition, Hanser Publishers, Munich, 1993, Chapter 17 “Organic Peroxides as Cross-linking Agents”, pages 833-962; C.Tzoganakis, J.Vlachopoulos and A. E. Hamielec, Chem. Eng. Prog. 1988, 84(11), “Controlled Degradation of Polypropylene”, pp. 47-49). Di-tert-butyl peroxide has a particularly simple structure and from the commercial point of view is the most advantageous of these peroxides. However, it has high volatility and its use is therefore restricted and only possible in low concentrations, in the form of a master batch with a solid carrier. In addition, its ignition point is between 48 and 55° C., even under nitrogen, and safety aspects of its use are therefore regarded as problematic.
Other compounds of this type which are more expensive but easier to handle are therefore frequently used in industrial applications.
Although the use of di-tert-butyl peroxide is possible if the process is conducted appropriately, this is preferably carried out on laboratory or pilot-plant scale. Here, di-tert-butyl peroxide can be fed as a liquid via metering pumps to the extruder. WO 95/16717 and DE-A 42 20 774 give examples of processes in which di-tert-butyl peroxide is fed into an area of the extruder in which the polymer is molten. However, when the peroxide is added as a liquid to the extruder disadvantages are often encountered in relation to polymer properties and in particular in relation to the film properties of degraded propylene polymers. In addition, there is the danger of explosions within the extruder. Gaseous di-tert-butyl peroxide is quite capable of exploding even in an inert gas atmosphere. If a gas explosion of this type extends to involve liquid peroxide which may be present at the point of injection or also in the vicinity of this point, in particular if mixing into the polyolefin is not immediate, this can damage the extruder.
It is also possible to use di-tert-butyl peroxide as a mixture with the polymer or with a portion of the polymer. For example, U.S. Pat. No. 5,344,886 and U.S. Pat No. 5,344,888 describe processes in which, with the objective of grafting maleic anhydride, a propylene homopolymer in powder form is mixed with a solution of di-tert-butyl peroxide in toluene, a maleic anhydride solution and a coagent in such a way that the solution is absorbed by the polypropylene homopolymer. This mixture is fed to the extruder. However, the preparation of the mixture is a separate and lengthy step requiring provision of additional equipment. This is uneconomic and involves large quantities.
DT-A 25 51 206 describes a process for mixing liquid di-tert-butyl peroxide with a polyolefin, where the liquid di-tert-butyl peroxide is fed into the comminuted polyolefin material in a closed chamber at a significant depth below the surface of the polyolefin material. This, too, is a lengthy process and the di-tert-butyl peroxide is added at relatively low temperatures.
In principle, the peroxide may also be directly introduced into the feed hopper of the extruder together with the olefin polymer. However, for safety reasons it has generally been regarded as necessary here to operate well below 55° C. and to take engineering precautions so that any pressure arising from a possible explosion in the hopper can be released in a controlled manner. For older polymerization processes in particular, the low temperatures are no great disadvantage, since the steps for removing or deactivating the catalyst constituents mean that the polymer is produced at a temperature of this nature.
However, modern processes with high-performance catalysts do not require removal of the catalyst constituents, and the polymer is usually produced at from 70 to 90° C. It is normally also fed at these temperatures to the extruders in which it is pelletized and provided with additives. Equipment serving solely for prior cooling of the polymer in cases where di-tert-butyl peroxide is added to the feed hopper would significantly reduce the cost-effectiveness of the process.
It is an object of the present invention to overcome the disadvantages mentioned and develop a process which permits cost-effective peroxidic treatment of olefin polymers, produces products with good properties and in particular good film properties, and is capable of being carried out simply and safely.
We have found that this object is achieved in that there is no safety hazard using a particular grade of olefin polymers and feeding di-tert-butyl peroxide together with olefin polymers at from 55 to 110° C. directly into the feed hopper of an extruder.
The invention provides a process for peroxidic treatment of olefin polymers with di-tert-butyl peroxide in an extruder, in which the olefin polymers together with di-tert-butyl peroxide under an inert gas are fed to an extruder, which comprises using the olefin polymers in a finely divided form at from 55 to 110° C. The invention also provides the use of peroxidically treated olefin polymers for producing moldings, fibers, films or nonwoven spunbond fabrics, and also a process for producing moldings, fibers, films or nonwoven spunbond fabrics.
For the purposes of the present invention, peroxidic treatment is any reaction in which the olefin polymers are reacted with di-tert-butyl peroxide or with di-tert-butyl peroxide and other reactants. These include grafting or crosslinking reactions, and also degradation reactions.
If ethylenically unsaturated monomers capable of free-radical polymerization, such as maleic anhydride, acrylates or methacrylates, are added alongside di-tert-butyl peroxide to the olefin polymers, the result is graft copolymers in which individual ethylenically unsaturated monomers or polymer chains built up from the ethylenically unsaturated monomers have been grafted onto the olefin polymer chains. If ethylenically unsaturated monomers are added their proportion is usually from 0.1 to 30% by weight, based on the total amount of starting materials. The proportion of the ethylenically unsaturated monomers is preferably from 0.5 to 20% by weight and in particular from 1 to 15% by weight.
In the novel process the di-tert-butyl peroxide may moreover be used together with the olefin polymers with the objective of complete or partial crosslinking of the olefin polymers. Concomitant use of crosslinking auxiliaries, such as triallyl cyanurate or trim
Elser Hermann
Huber Karl
Kagerbauer Karl-Heinz
Klassen Horst
Lehr Klaus
Basell Polyolefine GmbH
Keil & Weinkauf
Lipman Bernard
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