Stock material or miscellaneous articles – Hollow or container type article – Polymer or resin containing
Patent
1991-01-28
1994-07-12
Seccuro, Jr., Carman J.
Stock material or miscellaneous articles
Hollow or container type article
Polymer or resin containing
524528, 525240, 428402, C08L 2308, C08L 2316, C08L 2310, C08J 312
Patent
active
053287347
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a process for reducing the adhesive nature and increasing the crushing resistance of partially crystalline ethylene/alpha-olefins copolymers of very low density, and to non-tacky and crushing-resistant compositions of such copolymers and to a process for preparing the said compositions.
Copolymers of ethylene and of at least one alpha-olefin exhibit an adhesive nature which is proportionately more accentuated the higher their alpha-olefin content. In terms of density, it can be said that the adhesiveness appears when their density is lower than 0.900. Ethylene/alpha-olefins copolymers with a density lower than 0.890 are generally packaged in the form of pellets, granules, blocks or loaves. Their adhesive nature does not present any special problems when they are in the form of blocks or loaves. On the contrary, when they are packaged in the form of small-sized pellets or granules (for example approximately 1 to 5 mm) it is difficult to convey them and to store them in this state, that is to say to avoid their setting solid again after a prolonged storage period, because they exhibit a marked tendency to agglomerate, forming compact blocks. Various means which have been proposed previously to solve this type of problem in the case of various ethylenic elastomers, such as coating the surface of the granules with a silicone oil or with a nonionic surface-active agent such as a copolymer of propylene oxide and ethylene oxide are not wholly satisfactory because, while they reduce the adhesiveness considerably at the time of the treatment, consequently permitting a substantially correct granulation, their effect decreases with time. Furthermore, granules treated with silicone oils or with copolymers of ethylene oxide and propylene oxide do not withstand crushing; after a prolonged period of storage under stress (either the weight of the granules on others in a sack, or the weight of the upper sacks on those of the first layer in storage on a pallet) it is found that the granules tend to flatten, to agglomerate and to form a compact mass which is difficult to handle.
Furthermore, Patent FR-A-2,093,589 describes mixtures of crystalline (co)polymers of alpha-monoolefins and of an amorphous ethylene-propylene or ethylene-propylene-diene rubber, the quantity of the crystalline (co)polymer being from 1 to 30 parts per 100 parts by weight of the rubber. According to the examples in this document an atactic polypropylene or a polypropylene with a melt index equal to 3 may be used as crystalline (co)polymer. The amorphous rubber employed has a Mooney viscosity of between 20 and 120.
For its part, Patent EP-A-037,453 describes a mixture comprising an ethylene-propylene polymer normally subject to flow at room temperature and under storage conditions, and a sufficient quantity (preferably up to 20% by weight of the polymer) of polypropylene to reduce the cold-flow. The ethylene-propylene polymer in question has a Mooney viscosity of 10 to 100 and contains from 40 to 60 mol % of ethylene. The chosen polypropylene preferably has a melt index of 0.5 to 30 dg/min, measured at 230.degree. C. under 2.16 kg.
The solutions recommended by the last two documents referred to, which are suitable for elastomers which are amorphous in most cases, exhibiting a Mooney viscosity and generally having a density lower than 0.86, are not suitable for partially crystalline ethylene/alpha-olefin copolymers exhibiting no Mooney viscosity and having a density of approximately between 0.865 and 0.900. In fact, the addition of an atactic polypropylene or of an isotactic polypropylene of low melt index to these, in the recommended proportions, does not allow a significant reduction in the adhesiveness and increase the crushing resistance.
The present invention proposes to solve this problem by providing a process which, simultaneously, makes it possible to reduce the adhesive nature and to increase the crushing resistance of partially crystalline copolymers of ethylene and of alpha-olefins with a density of approximat
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Coudevylle Urbain
Morese-Seguela Brigitte
Seccuro, Jr. Carman J.
Sofrapocommerciale
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