Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Patent
1997-02-24
1997-12-30
Foelak, Morton
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Cellular products or processes of preparing a cellular...
521 59, C08J 918
Patent
active
057031355
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a process for the production of expanded polyolefin beads by impregnating polyolefin particles with volatile blowing agents.
Expanded polyolefin beads are produced industrially by two methods:
In the extrusion method, the polyolefin is melted and the melt mixed with a volatile blowing agent. After extrusion, the expanded polyolefin is granulated.
In the impregnation method (EP-A 53 333), uncrosslinked polyolefin particles are suspended in water and impregnated with a volatile blowing agent under pressure at a temperature in the region of the softening point of the polyolefin. The suspension is then decompressed, whereupon the polyolefin particles expand.
Attempts have also been made to carry out the impregnation in the gas phase (DE-B 1 285 722). However, this requires crosslinking of the polyolefin particles at their surface so that they do not sinter together at the temperatures used, but of course this also makes welding of the foam beads to form moldings more difficult during later processing. In addition, the surface crosslinking requires a separate step.
It is an object of the present invention to produce expanded polyolefin beads by impregnation with volatile blowing agents avoiding the extrusion method, which has high energy consumption, and suspension of the polymer particles in water (which also has high energy consumption and causes effluent problems) and avoiding crosslinking of the bead surface.
We have found that this object is achieved by impregnating particulate propylene or ethylene polymers with gaseous blowing agent in a fluidized bed.
DE-A 33 17 557 describes a process for the production of expandable polyolefin beads in which polyolefin particles kept in the fluid state are impregnated with a blowing agent in the gas phase. The fluid state is achieved by means of rotating vessels or by using stirrers. Fluidization by means of a fluidized bed is not mentioned. Preferred polyolefins are graft polymers of styrene on polyethylene. These polymers, which contain relatively large amounts of polystyrene chains, are capable of keeping volatile blowing agents absorbed for an extended period. However, this is not the case in conventional ethylene and propylene polymers, which means that expandable polyolefin particles cannot be produced by this method.
Although the fluidized-bed method is a common one in chemical technology, it was not obvious that impregnation of polyolefin particles in the region of the softening point can be carried out simply and without sticking. In contrast to conventional impregnation methods, reactor internals are unnecessary.
For the purposes of the present invention, polyolefins are crystalline olefin polymers whose X-ray crystallinity at 25.degree. C. is greater than 25%. Suitable polyolefins for the process are low-density polyethylene (LDPE), medium-density polyethylene (MDPE) and high-density polyethylene (HDPE), polypropylene and ethylene and propylene copolymers containing at least 50 mol % of ethylene and/or propylene units. Examples of suitable comonomers are .alpha.-olefins having up to 12 carbon atoms, such as propylene, butene, pentene, hexene and octene, vinyl esters, such as vinyl acetate, esters of acrylic acid, methacrylic acid, maleic acid or fumaric acid with alcohols containing 1 to 8 carbon atoms, and ionomers. The olefin polymers generally have a melt flow index, MFI (230, 2.16; measured in accordance with DIN 53 735) of from 0.1 to 20, preferably from 0.5 to 15, and a crystallite melting point of from 95.degree. to 170.degree.C. It is also possible to use mixtures of various olefin polymers.
Preference is given to copolymers of propylene with from 0.5 to 15% by weight of ethylene or a C.sub.4 - to C.sub.8 -.alpha.-olefin and copolymers of ethylene with from 3 to 18% by weight of a C.sub.4 - to C.sub.8 -.alpha.-olefin (LLDPE).
Particularly preferred polyolefins are copolymers comprising from 1 to 6% by weight of ethylene and from 94 to 99% by weight of propylene.
The particle size of the polyolefin particles can vary
REFERENCES:
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patent: 5110524 (1992-05-01), Harclerode et al.
patent: 5110836 (1992-05-01), Harclerode et al.
patent: 5580503 (1996-12-01), Hall, III et al.
de Grave Isidoor
Fischer Joachim
Kogel Wolfram
Schweinzer Jurgen
BASF - Aktiengesellschaft
Foelak Morton
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