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
2000-03-27
2002-01-29
Nutter, Nathan M. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S240000
Reexamination Certificate
active
06342564
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to heterophasic polypropylene copolymers and in particular to heterophasic polypropylene copolymers which are soft, have good impact resistance at low temperatures, good heat sealing properties and good optical properties.
Traditionally, polymers in which low stiffness, and therefore low tensile modulus, as well as good impact at low temperatures are desired properties, have been prepared from soft poly(vinyl chloride) (PVC). However, because PVC products cause environmental problems due to emissions of chlorinated organic compounds during combustion there is currently a trend towards replacing PVC with other polymers. As an alternative to PVC polymers polypropylene polymers have been employed since such polymers are known to have suitable resistance to heat and chemicals as well as attractive mechanical properties.
It is known that certain heterophasic polypropylene copolymers are particularly suitable as soft polymers. When producing soft heterophasic polypropylene copolymers, it is usual to prepare a polypropylene copolymer matrix with a comonomer content to obtain the desired properties. To achieve lower stiffness an amorphous elastomeric component can then be added to the copolymer matrix.
For example, in EP-A-0373660 (Himont Incorporated) a propylene polymer composition is described which has good transparency and improved low temperature impact resistance comprising 70 to 98% crystalline copolymer of propylene with ethylene and/or other &agr;-olefin and an elastomeric propylene-ethylene copolymer.
In EP-A-0416379 (Himont Incorporated) a thermoplastic olefin polymer having elastic properties is disclosed comprising a crystalline polymer fraction comprising for example a copolymer of propylene with at least one &agr;-olefin, a semi-crystalline fraction and 2 to 30% amorphous copolymer fraction of &agr;-olefin and propylene with or without diene.
In the two applications discussed above, for reasons of economy, the initial copolymer matrix can be produced in a slurry reactor rather than in a gas phase reactor. The product of the slurry phase reaction is then flashed to remove unreacted monomers and transferred into a gas phase reactor where further reaction takes place and the elastomeric component is prepared.
However, since the matrix component is prepared in the liquid phase, the comonomer content of the matrix and thus the tensile modulus is limited. Comonomers such as ethylene and other &agr;-olefins cause swelling of the polymers during the reaction in the slurry reactor. When the reaction medium is flashed to remove the monomer reactants after polymerisation of the matrix but before transfer to the gas phase reactor, the morphology of the particles is destroyed and the bulk density of the powder becomes very low. This sticky material agglomerates on the walls in the flash tank and causes problems in transportation into the gas reactor. These problems increase when the proportion of comonomers in the copolymer increases and therefore the softness of the polymer is limited.
Attempts to reduce the stickiness of the material in the flash tank by catalyst manipulation or by reducing the content of xylene-soluble fraction have had limited success and accordingly, in order to obtain soft polypropylene copolymers with a very high comonomer content gas phase polymerisation has traditionally been required.
BRIEF SUMMARY OF THE INVENTION
It has now been surprisingly found that soft polypropylene copolymers can be prepared economically with low tensile modulus values and high comonomer content since the flashing of the matrix mixture prepared in a liquid phase reactor (e.g. a slurry reactor) is unnecessary and transfer of the neat reaction mixture from the liquid phase to the gas phase reactor can be effected directly. Since the flashing step is omitted, there are no problems with the sticky material sticking on the walls of the flash tank and therefore higher comonomer concentrations can be achieved and softness properties improved.
Thus, viewed from one aspect the invention provides a heterophasic polypropylene copolymer having a tensile modulus of 420 MPa or less comprising:
i) a semi-crystalline propylene:ethylene: and optionally other &agr;-olefin copolymer matrix;
ii) an elastomeric propylene:ethylene and optionally other &agr;-olefin copolymer.
Viewed from another aspect the invention provides a process for the preparation of a heterophasic polypropylene copolymer having a tensile modulus of 420 MPa or less comprising:
i) producing a semi-crystalline propylene:ethylene and optionally other &agr;-olefin copolymer matrix in one or more slurry reactors and optionally one or more gas phase reactors;
ii) followed by producing an elastomeric propylene:ethylene and optionally other &agr;-olefin copolymer in the gas phase;
characterised in that the transfer from liquid phase reactor to a subsequent gas phase reactor is effected without flashing to remove unreacted monomer.
DETAILED DESCRIPTION OF THE INVENTION
For the purposes of this application, the term copolymer encompasses polymers comprising two or more comonomers.
The semi-crystalline polypropylene copolymer matrix preferably comprises 0.5 to 10 wt % ethylene and optionally 5 to 12 wt % of other &agr;-olefin. Where the semi-crystalline polypropylene copolymer matrix comprises an &agr;-olefin in addition to ethylene and propylene, ethylene more preferably comprises 1 to 7 wt %, most preferably, 1 to 5 wt % of the matrix and the additional &agr;-olefin 6 to 10 wt % of the matrix.
Where the semi-crystalline matrix component is an ethylene:propylene copolymer only, the ethylene preferably comprises 3.5 to 8.0 wt %, most preferably 4 to 7 wt % by weight of the matrix.
The other &agr;-olefin is may be a C
4-20
mono or diene, and may be linear, branched or cyclic. The other &agr;-olefin is preferably of structure H
2
C═CHR where R represents an alkyl group. Preferably, the &agr;-olefin has between 4 and 8 carbon atoms and is most preferably 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene or 1-octene, especially 1-butene.
The xylene soluble fraction (XS) of the matrix component is preferably in the range 3 to 30%, most preferably 6 to 20% by weight of the matrix component.
The elastomeric propylene:ethylene and optionally other &agr;-olefin copolymer can comprise any suitable ratio of monomers of propylene, ethylene and optionally other &agr;-olefin which results in an amorphous or semicrystalline/amorphous elastomeric copolymer. Preferably, the elastomeric component comprises a copolymer of ethylene and propylene only.
The amount of matrix component in the heterophasic copolymers of the invention is between 20 to 90%, preferably 60 to 90% by weight of the heterophasic copolymer. The amount of elastomeric copolymer may be in the range of 10 to 80%, preferably 10 to 40% by weight of the heterophasic polymer. The elastomer component may comprise 95-5 wt %, preferably 95-20 wt % of crystalline phase and 5-95 wt %, preferably 5-80 wt % amorphous phase.
In one embodiment, 5 to 40% wt of elastomer or plastomer, based on the weight of the heterophasic copolymer may be blended into the heterophasic polymers of the invention. By adding varying amounts of elastomer or plastomer to the heterophasic polymers of the invention, the stiffness of the polymers can be further reduced, optical properties improved and low temperature impact resistance enhanced. Suitable elastomers include ethylene:butene rubber, terpolymer rubber but is preferably ethylene:propylene rubber (EPR). Elastomer may also be added in the form of ethylene:propylene diene monomer (EPDM). These elastomers can be prepared by conventional processes and blended into the heterophasic polymers of the invention by standard mixing techniques.
The tensile modulus of the heterophasic polymer of the invention is 420 MPa or less but preferably should be greater than 80 MPa, preferably greater than 100 MPa. More preferably, the tensile modulus should be in the range 100 to 400 MPa, even more preferably 100 to 35
Alastalo Kauno
Malm Bo
Pitkanen Paivi
Borealis Technology Oy
Liniak, Berenato, Longacre & White, L.L.P.
Nutter Nathan M.
Orzechows Karen Lee
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