Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Patent
1999-02-26
2000-11-21
Foelak, Morton
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Cellular products or processes of preparing a cellular...
521 57, 521 60, 521142, 521143, C08J 918, C08J 920, C08J 922
Patent
active
061504270
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a foaming propylene-based copolymer, its foaming beads and cellular articles. More precisely, it relates to a foaming propylene-based copolymer of an isotactic propylene-ethylene random copolymer having improved primary foamability and secondary foamability and capable of being foamed into cellular articles having good mechanical properties including rigidity, to foaming beads comprising the copolymer, and to cellular articles as produced by foaming the foaming beads.
DESCRIPTION OF THE BACKGROUND
Crystalline polypropylene resin-based cellular articles are, as being characterized in that (1) their buffer capacity is high, (2) their thermal conductivity is low, and their thermal stability is good as their heat-resisting temperature is much higher than that of polyethylene cellular articles, (3) their chemical resistance is good, (4) their machine workability, press workability and vacuum moldability are good, and (5) they are stiff and have high strength, much used, for example, in buffer materials, wrapping materials, bumper core materials, floating materials, heat-insulating materials, etc.
For producing such crystalline polypropylene resin-based cellular articles, in general, preferably employed is a method comprising dispersing resin beads in an aqueous medium containing a dispersant, then adding a physical foaming agent thereto under heat and pressure to thereby introducing the foaming agent into the resin beads, and thereafter releasing the resin beads along with the aqueous medium into an open space at an atmospheric pressure for primary foaming into foaming beads. In that method, the foaming beads thus prepared are heated in a mold under pressure generally with steam for secondary foaming into a cellular article having a desired shape.
In the foaming method of that type, it is desirable from the viewpoint of industrial advantages to attain the primary foaming and the secondary foaming at temperatures as low as possible for preparing foaming beads having a desired expansion ratio and for finally producing high-quality cellular articles having a high expansion ratio but having few voids.
Crystalline propylene-ethylene random copolymers having a larger ethylene unit content will generally have lower rigidity. Therefore, in order to increase their rigidity, the ethylene unit content of the copolymers must be lowered. However, for conventional crystalline propylene-ethylene random copolymers having a lowered ethylene unit content, the heating temperature for the primary and secondary foaming shall be inevitably high, thereby bringing about some problems with the equipment for the foaming process, and the high heating temperature is disadvantageous for industrial-scale production of cellular articles of the copolymers.
SUMMARY OF THE INVENTION
Given that situation, the object of the present invention is to provide a foaming crystalline polypropylene-based resin of which the primary and secondary foamability is good to give high-quality cellular articles having good mechanical properties including rigidity, and which can be subjected to primary and secondary foaming at lower temperatures than conventional crystalline polypropylene-based resins, and also to provide foaming beads of the resin as well as cellular articles formed from them.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
We, the present inventors have assiduously studied so as to attain the object noted above, and, as a result, have found that a propylene-ethylene random copolymer having specific physical properties has good primary and secondary foamability to give high-quality cellular articles having good mechanical properties including rigidity. On the basis of this finding, we have completed the present invention.
Specifically, the invention provides a foaming propylene-based copolymer of a propylene-ethylene random copolymer, which is characterized in that (1) its ethylene unit content [x (wt. %)] falls between 0.2 and 10% by weight, (2) its melt index [MI (at 230.degree
REFERENCES:
patent: 5346925 (1994-09-01), Sugano et al.
patent: 5468781 (1995-11-01), Sugano et al.
Ito Toshimichi
Seta Yasushi
Tsunori Ryoichi
Foelak Morton
Idemitsu Petrochemical Co. Ltd.
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