Method of making olefin synthetic resin expansion molded article

Details Method of making olefin synthetic resin expansion molded article Method of making olefin synthetic resin expansion molded article

1992-04-03

1994-12-13

Kuhns, Allan R.

Plastic and nonmetallic article shaping or treating: processes

Pore forming in situ

By mechanically introducing gas into material

264 51, 264DIG16, B29C 6720

Patent

active

053727649

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

The present invention relates to expansion-molded articles of olefin synthetic resins such as ethylene and propylene type synthetic resins and manufacturing method thereof.


PRIOR ART

Expansion molded articles of polystyrene and olefin synthetic resins represented by, for example, polyethylene synthetic resin and polypropylene synthetic resin with their features such as cushioning property, chemical stability, good moldability and lightness have had various uses such as wrapping materials, packing materials and cushioning materials.
The known methods of manufacturing such expansion-molded articles are roughly divided into extrusion molding method and in-mold molding method by the use of pre-expanded beads. With polystyrene expansion-molded articles, for instance, manufacturing methods have roughly been divided into extrusion-type expansion-molding method for heat insulation materials such as building materials, and in-mold expansion-molding method for cushioning materials, packing materials and the like, and each of the manufacturing techniques has almost reached the point of ripening.
With olefin expansion-molded articles represented by, for example, polyethylene and polypropylene synthetic resins, however, there still remain, especially in in-mold expansion-molded articles, many unsolved problems such as method of manufacturing pre-expanded beads and expansion-molding method.
As in-mold expansion-molding type of manufacturing method, there has been known a method of charging pre-expanded beads of synthetic resin into a mold made up of a male member and a female member capable of opening or closing with respect to each other and also capable of forming a cavity when fitted together, introducing water vapor into the mold interior for heating and fusing the pre-expanded beads to form an expansion-molded article and taking the molded article out of the mold after cooling.
The mold used in this method has made therein a large number of water vapor holes for introducing water vapor which heats and fuses the pre-expanded beads charged in the mold, while the pre-expanded beads charged in the mold are subjected to heating by the water vapor introduced through the above-mentioned holes, this giving rise to re-expansion of the pre-expanded beads such that the inter-beads gaps are filled for the beads to be adhered to one another and fused together to form an expansion-molded article.
The technical problems given rise to by such a molding method include, among others: water vapor introduced into the mold, heating progresses from outside of the beads charged in the mold and in contact therewith, this causing a difference in the degree of inter-beads fusing between the outer layer of the molded article and the core portion thereof; and reexpand in such a manner that the inter-beads gaps are filled, the degree of inter-beads fusing is influenced by the presence and the amount of substances which interfere with inter-beads fusion.
In other words, the problem is essentially how the pre-expanded beads charged in the mold can be heated uniformly and how the water vapor can be supplied continuously to the core portion of the mold interior with the drop in temperature minimized. The importance of this problem increases with increasing thickness of the expansion-molded article.
In order to solve the problems for improvement in product quality as well as producibility, continuous efforts have been made for technological improvement mainly about polystyrene expansion-molded articles. For example, there have been proposed a method in which the pressure in a mold is reduced by evacuation (deaeration) to a half-atmospheric level, the air remaining in the mold is further evacuated through replacing with water vapor supplied alternately through water vapor supply pipes and then water vapor is introduced into the mold interior for heating and fusion of the pre-expanded beads (Japanese Patent Publication No. 45940/1986), a method of introducing a large amount of water vapor in a short period of time in the fu

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