Granulated or pelletized compositions of grafting units

Details Granulated or pelletized compositions of grafting units Granulated or pelletized compositions of grafting units

2000-04-25

2002-09-24

Eashoo, Mark (Department: 1732)

Plastic and nonmetallic article shaping or treating: processes

With severing, removing material from preform mechanically,...

To form particulate product

C264S331130, C264S331150

Reexamination Certificate

active

06454980

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to grafted propylene homo and co-polymers and to a process for their preparation. The grafting units are selected from 1,2 polydienes, polyalkenylenes and amorphous elastomers obtained through copolymerization of ethylene-propylene (EPM) or ethylene-propylene with a not conjugated diene monomer (EPDM) Particulary, the present invention concerns a resin suitable to be used as synthetic leather for articles such as, for instance, interior car door panels.
BACKGROUND OF THE INVENTION
The production of interior door panels, dashboard elements, interior trims, consoles and similar parts was usually carried out by coupling a layer of synthetic leather to a supporting element. The two main coupling methods are by glueing the synthetic leather to a rigid support or by pressing and shaping said synthetic leather in a mold together with a heated thermoplastic supporting element.
Recently, the applicant developed a process to produce panels or similar elements by means of co-injection of an outer skin (that represents the synthetic leather) and an inner support layer that gives to the final part the requested rigidity.
One of the problems to be solved using such technology resides in the physical properties of the skin material. The skin material has to join a pleasant-touch (softness) characteristic with a easy-flow behaviour (for injection molding). Polymers having either pleasant-touch or easy-flow behaviour are well known. Polymers with a good pleasant-touch are, e.g., thermoplastic elastomers (TPE) and the polyolefin thermoplastic elastomers (PTE) that are EPM or EPDM blends polyolefin based, whose properties are quite similar to a rubber, or the new TPO (thermoplastic polyolefin) materials which behave themselves as a thermoplastic elastomer.
Unfortunately, while these materials are provided with the pleasant touch characteristic, they are lacking the required easy-flow behaviour; thus, they can not be used in an injection molding process.
The easy flow behaviour is usually achieved via reactive degradation, i.e. a process that reduces the molecular weight (molecular chain length) of the polymer. It is known to carry out selective degradation of propylene homo and co-polymers by means of peroxide or non-peroxide radical initiators.
The use of peroxide radical initiators such as dicumyl peroxide (DCUP), di(tert-butyl) peroxide or of non-peroxide radical initiators such as 2,3-dimethyl-2,3-diphenylethane or 3,4-dimethyl-3,4-diphenylhexane in a concentration between 0.1 to 1.0 by weight, results in an improvement of the Theological properties.(easy-flow) of the propylene polymers. The drawbacks of this method are that the mechanical properties (modulus and impact strength) of the polymers are lowered and that molecules having low weight molecular chains are by-produced. These products have a low melting point and, at low temperature, they become viscous liquids that migrate towards the surface of the molded piece, making it sticky and not suitable to be used.
It is known to modify (grafting) crystalline propylene polymers by treating them at temperatures within the range of 150° to 300° C. with alpha-olefin polymers and co-polymers, for example 1-butene, in the presence of a peroxide radical initiators (European patent 261.786) or of non-peroxide radical initiators (European patent 542.253). In both cases it is not achieved the reorganization of the low weight polymeric chains, hence there is not any reduction of the final piece tackiness even at quite low temperature (<60° C.). Polyalkenylenes grafted on propylene are known as well (Plastic, Rubber and Composite Processing and Application 18, Pg 47-58, 1992 and European Patent EP 642.622). In this case the obtained resins show, in spite of a tackiness reduction, a substantial melt fluidity reduction such as to preclude their processability in injection and co-injection molding.
OBJECT OF THE INVENTION
The aim of the present invention is to solve the above mentioned problems by providing propylene polymers endowed with the properties requested, and a process for their preparation.
SUMMARY OF THE INVENTION
Said object is obtained by means of the present invention that relates to homopolymers and copolymers of propylene. The invention also relates to a process for preparing said (co) polymers, The invention further relates to the use of the above mentioned polymers for producing interior car door panels or other interior elements,. According to a preferred embodiment, the propylene (co)polymers comprise, as grafting units, 5 to 65% of grafted amorphous elastomer obtained through copolymerization of ethylene-cropylene EPM or ethylene-propylene diene monomer (EPDM). EPM and EPDM polymers are known in the relevant art as EPRs, i.e., ethylene/propylene copolymer rubbers, and are practically amorphous. The range of crystallinity for amorphous EPM and EPDM polymers is understood to be from 0 to approximately 10%. Both EPM and EPDM Polymers can be exended with naphtene/paraffin oil.
According to another embodiment, the propylene (co)polymers comprise also from 0.1 to 5% by weight of vinyl polybutadiene as grafting units.
According to a further embodiment of the invention, the (co)polymers are obtained by thermal degradation with the presence of peroxide initiators.
The (co)polymers according to the present invention solve the technical problem above mentioned : thanks to their fluidity they are suitable for injection or co-injection molding process, and the final item thus obtained shows no tackiness. The invention (co)polymers, are also suitable for production of synthetic leather or other items having a good softness, i.e. the pleasant-touch characteristic, with no tackiness. A synthetic leather so obtained could be used to produce car trim panels according to the glueing or hot pressing methods above referred to.
DESCRIPTION OF THE PREFERRED EMBODIMENT
As above mentioned, propylene homo and -copolymers are grafted by using grafting units selected from polyalkenylenes, EPM and EPDM polymers, or mixtures thereof, the amount of polyalkenylenes being within the range from 1 to 30t by weight and the amount of EPM and/or EPDM polymers being within the range, from 5 to 65% by weight of the total composition.
In a preferred embodiment, also vinylbutadienes, i.e. alpha olefins polymers, are added as grafting units to those mentioned above, the amount of vinylpolybutadiene being within the range from 0.01 to 10% by weight.
The preferred starting polymers are propylene polymers, however other starting polymers can:be used. The polymer object of the invention can be prepared by means of reactive transformation (degradation) for example in a extruder or directly during the injection or co-injection molding.
The material fluidity can be kept steady, increased or reduced and in the meantime its softness will be improved making it, in terms of superficial hardness, similar to thermoplastic elastomers.
The process of the invention consists in mixing at a temperature range within 160° to 310° C. propylene polymers with polyalkenylenes and/or amorphous ethylene-propylene copolymers and/or ethylene-propylene-diene terpolymers and optionally, but not necessarily, with alpha-olefins polymers in the presence of radical initators.
Both homopolymers and copolymers of propylene are referred to with the term propylene polymer. In particular the suitable propylene polymers are (co)polymers having an isotactic index higher than 0.1%, copolymers comprising one or more alpha-olefins having 2-10 carbon atoms, for example ethylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-octene; polypropylene compositions obtained through sequential polymerization of propylene and its mixture with ethylene and/or alpha-olefins; blends of propylene (co)polymers with EP(D)M (in this latter case the EP(D)M polymers do not act as grafting units).
The propylene (co)polymers have a Melt-Flow-Index (MFI) comprised in the range from 0.1 to 1000 g/10 min, preferably between 0.2 and 60 at 230° C./21.6N (according to ASTM 1238). Th

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