Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Patent
1991-02-13
1992-04-14
Seccuro, Carman J.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
525133, 525194, 525195, 524518, C08L 2326, C08L 3308, C08L 4500, C08K 501
Patent
active
051049406
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to thermoplastic compositions and more particularly thermoplastic elastomeric compositions comprising mixtures of ethylene/acrylate copolymer and of polynorbornene.
Polymers of relatively high molecular weight are generally incompatible with each other. When two polymers of different kind are mixed the mixture generally has mediocre mechanical properties such as tensile strength and elongation at break. A pair of polymers is rarely sufficiently compatible to form a mixture having mechanical properties which are as good as those of the less strong one of the two. However, when two polymers are compatible, the resulting mixture can exhibit an advantageous combination of properties, that is to say that, besides good mechanical properties, it can also have other favorable characteristics.
Thus, U.S. Pat. No. 4,203,884 teaches that compositions comprising the mixture of a thermoplastic crystalline polyolefin, of polynorbornene and of a quantity of plasticizer for polynorbornene which is sufficient to lower its glass transition temperature to the rubber range have advantageous properties. More particularly, this document discloses compositions comprising a mixture of 75 to 10 parts by weight of polyolefin, 25 to 90 parts by weight of polynorbornene and, per 100 parts by weight of polynorbornene, 30 to 400 parts by weight of plasticizer, said compositions being elastoplastic, that is to say that they have elastomeric properties while being processable like thermoplastics. In the molten state, according to this technique, a part of the plasticizer can be present in the thermoplastic polyolefin phase. After cooling, the plasticizer migrates substantially from the crystalline polyolefin phase towards the polynorbornene phase to form part of the latter. In this way the plasticizer improves the thermoplasticity or the processability of the composition. As a general rule, for a given degree of thermoplasticity the composition requires proportionately less polyolefin the greater the quantity of plasticizer.
U.S. Pat. No. 4,203,884 also discloses compositions comprising a mixture of 10 to 90 parts by weight of crystalline polyolefin and of 90 to 10 parts by weight of crosslinked polynorbornene dispersed in the form of particles of small size and of plasticizer in a sufficient quantity to lower the glass transition temperature of the polynorbornene to the rubber range. Thus, the crosslinking of polynorbornene improves the property compromise of the composition, in particular the tensile strength, the solvent resistance and the high-temperature properties. Such compositions are obtained by a dynamic vulcanization process according to which a mixture of polynorbornene, plasticizer, polyolefin and crosslinking agents is kneaded at a sufficient temperature to crosslink the polynorbornene.
Among the thermoplastic crystalline polyolefins which can be employed according to U.S. Pat. No. 4,203,884 there may be mentioned poly-ethylene and polypropylene, the latter being preferred as confirmed by the comparison of the results illustrated by Tables 1 and 2 of the cited document. In fact, this document teaches that compositions comprising from 30 to 60 parts by weight of crosslinked polynorbornene and from 70 to 40 parts by weight of a polyethylene of density 0.960 g/cm.sup.3 have: and for the majority of the applications for thermoplastic elastomers.
The Applicant's experiments have shown, moreover, that these same compositions have a residual compression deformation which is too high and a Shore A hardness which is too high for the majority of the applications for thermoplastic elastomers.
The problem which the present invention is aiming to solve consists, therefore, in choosing from the vast range of ethylene polymers a polymer capable of contributing an advantageous property comprise to an elastoplastic composition based on polynorbornene and plasticizer, making it suitable for the majority of the applications for thermoplastic elastomers and in particular: not higher than 3 MPa, and hours) not exee
REFERENCES:
patent: 3676390 (1972-07-01), Vergne et al.
patent: 4203884 (1980-05-01), Coran et al.
patent: 4990559 (1991-02-01), Shiraki et al.
Dousson Christian
Hert Marius
Atochem
Seccuro Carman J.
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