Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Compositions to be polymerized by wave energy wherein said...
Reexamination Certificate
2003-09-02
2004-08-10
Berman, Susan (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Compositions to be polymerized by wave energy wherein said...
C522S161000, C522S113000
Reexamination Certificate
active
06774156
ABSTRACT:
The present invention relates to a method for the production of propylene copolymers, in particular propylene/ethylene random copolymers or heterophasic (multiple phase) copolymers, for example comprising an ethylene propylene rubber phase in a propylene copolymer matrix phase, having improved properties, in particular high melt strength. In particular, the present invention relates to a process for the production of polypropylene/ethylene random copolymers or heterophasic copolymers having improved properties by irradiating polypropylene/ethylene random or heterophasic copolymers with a high energy electron beam.
Propylene copolymer resins are used in a variety of different applications. However, linear propylene copolymers resins suffer from the problem of having a low melt strength at high melt index, which restricts their use in a number of applications because they are difficult to process. It is known in the art to increase the melt strength of polypropylene, for example by irradiating the propylene copolymer with an electron beam. It is known that electron beam irradiation significantly modifies the structure of a propylene copolymer molecule. The irradiation of propylene copolymers results in chain scission and grafting (or branching) which can occur simultaneously. Up to a certain level of irradiation dose, it is possible to produce from a linear polypropylene copolymers molecule having been produced using a Ziegler-Natta catalyst, a modified polymer molecule having free-end long branches, otherwise known as long chain branching.
It is known that such long chain branching drastically modifies the rheological behaviour of the polypropylene, for example their elongational and shear viscosity.
EP-A-0678527 discloses a process for producing a modified polypropylene in which polypropylene and a cross-linking agent mixture are irradiated with ionising radiation so as to give an absorbed dosage of 1 to 20 kGy, with subsequent heat-treating of the resultant material. In Example 1 it is disclosed that the irradiation conditions have an accelerated voltage of 2 MW and an electric current of 1.0 mA.
WO-A-97/08216 discloses a method for producing diene-modified propylene polymers which are irradiated. It is disclosed that the irradiation is preferably carried out using E-beam or &ggr; radiation at a dose of about 1 to about 20 Mrad for a few seconds. It is disclosed that polypropylene made be modified with a diene and then irradiated to cause chain extension.
EP-A-0634441 discloses a process for making a high melt strength propylene polymer by high energy radiation. The dose range is disclosed as being from 1 to 10,000 Mrads per minute and it is disclosed that the ionising radiation should have sufficient energy to penetrate to the extent desired in the mass of linear, propylene polymer material being radiated. There is also disclosed the use of an accelerating potential (for an electron generator) of 500 to 4000 kV. Following the irradiation step the irradiated material is heated.
EP-A-0190889 discloses a process similar to that of EP-A-0634441 in that it is disclosed that the accelerating potential of an electron generator may be from 500 to 4000 kV.
EP-A-0799839 also has a similar disclosure to EP-A-0634441 and discloses the use of an electron generator having accelerating potential of 500 to 4000 kV.
EP-A-0451804 discloses a method of increasing the molecular weight of syndiotactic polypropylene by irradiation in the absense of oxygen. This specification does not disclose any energy range for the irradiation. The dose of the irradiation may be from 0.1 to 50 Mrad. After irradiation, the polypropylene may be heated.
EP-A-0351866 has a yet further similar disclosure to EP-A-0634441 and discloses the use of an electron generator having an accelerating potential of 500 to 4000 kV.
U.S. Pat. No. 5,554,668 discloses a process for irradiating polypropylene to increase the melt strength thereof. An increase in the melt strength is achieved by decreasing the melt flow rate, otherwise known as the melt index. It is disclosed that a linear propylene polymer material is irradiated with high energy ionising radiation, preferably an electron beam, at a dose rate in the range of from about 1 to 1×10
4
Mrads per minute for a period of time sufficient for a substantial amount of chain scission of the linear, propylene polymer molecule to occur but insufficient to cause gelation of the material. Thereafter, the material is maintained for a period of time sufficient for a significant amount of long chain branches to form. Finally, the material is treated to deactivate substantially all free radicals present in the irradiated material. It is disclosed that for an electron beam, the electrons are beamed from an electron generator having an accelerating potential (i.e. an energy) of from 500 to 4000 kV. Typically, the polypropylene material to be irradiated is in particulate form and is conveyed on a conveyor belt beneath an electron beam generator which continuously irradiates the polypropylene particles as they are translated thereunder by the conveyor belt. The resultant polyethylene has improved melt strength as represented by a decrease in the melt flow rate. A disadvantage of the process disclosed in U.S. Pat. No. 5,554,668 is that the production rate of the irradiated polypropylene is relatively low, because the speed of the conveyor belt is low and only a small volume of material is processed. This results in difficulties in commercial implementation of the process. In addition, the specification discloses the use of a very broad range of dose rates i.e. from 1 to 1×10
4
Mrads per minute. High dose rates of greater than about 40 Mrad can result in a substantially fully cross-linked structure of the polypropylene. Such a cross-linked structure is difficult to process.
EP-A-0520773 discloses an expandable polyolefin resin composition including polypropylene optionally blended with polyethylene. In order to prepare a cross-linked foam, a sheet of expandable resin composition is irradiated with ionising radiation to cross-link the resin. The ionising radiation may include electron rays, at a dose of from 1 to 20 Mrad. It is disclosed that auxiliary cross-linking agents may be employed which include a bifunctional monomer, exemplified by 1,9-nonanediol dimethyacrylate.
U.S. Pat. No. 2,948,666 and U.S. Pat. No. 5,605,936 disclose processes for producing irradiated polypropylene. The latter specification discloses the production of a high molecular weight, non-linear propylene polymer material characterised by high melt strength by high energy irradiation of a high molecular weight linear propylene polymer. It is disclosed that the ionising radiation for use in the irradiation step may comprise electrons beamed from an electron generator having an accelerating potential of 500 to 4000 kV. For a propylene polymer material without a polymerised diene content, the dose of ionising radiation is from 0.5 to 7 Mrad. For propylene polymer material having a polymerised diene content, the dose is from 0.2 to 2 Mrad.
EP-A-0821018 discloses the preparation of cross linkable olefinic polymers which have been subjected to ionising radiation. The specification exemplifies electron beams of relatively low energy and low doses to split polymeric chains in order to graft silane derivatives onto the polymeric chain. The specification does not address the problem of achieving high melt strength of polymers.
EP-A-0519341 discloses the grafting of vinyl monomers on particulate olefin polymers by irradiating the polymer and treating with a grafting monomer. In an example, polypropylene is irradiated with an electron beam having an energy of 2 MeV and subsequently treated with maleic anhydride as a grafting monomer.
U.S. Pat. No. 5,411,994 discloses the production of graft copolymers of polyolefins in which a mass of olefin polymer particles is irradiated and thereafter the mass is treated with a vinyl monomer in liquid form. The ionising radiation dose is about 1 to 12 Mrad and the ionising radiation pr
Debras Guy
Dupire Marc
Michel Jacques
Atofina Research S.A.
Berman Susan
Jackson William D.
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