Foamed polyolefin resin beads

Abstract

The present invention relates to foamed polyolefin resin beads. Further, the present invention provides foamed resin beads obtained by foaming and expanding composite resin beads which include a core layer constituted by a polyolefin resin and a covering layer which covers the core layer constituted by a polyolefin resin, wherein (a) the polyolefin resin constituting the core layer is a crystalline polyolefin resin, (b) the polyolefin resin constituting the covering layer is a crystalline polyolefin resin which has a lower melting point (B) than a melting point (A) of the polyolefin resin constituting the core layer, wherein a temperature difference [(A)−(B)] between the melting point (B) and the melting point (A) is more than 0° C. and 80° C. or less, or a noncrystalline polyolefin resin which has a softening point (C) lower than the melting point (A) of the polyolefin resin constituting the core layer, wherein a temperature difference [(A)−(C)] between the softening point (C) and the melting point (A) is more than 0° C. and 100° C. or less, and 10% by weight or more and less than 50% by weight of polymer type antistatic agent is contained in the covering layer. The foamed polyolefin resin beads of the present invention provide foamed polyolefin resin beads are excellent in fusion properties between beads at the time of molding in a mold, capable of providing a molded foamed article which is excellent antistatic performance, has no deterioration of the antistatic performance with age, whose antistatic performance is not humidity dependent, does not contaminate packaging products, has a good molded foamed article surface, and has excellent mechanical properties.

Description

BACKGROUND OF THE INVENTION[0001]1. Field of the Invention[0002]The present invention relates to foamed polyolefin resin beads which are excellent in fusion properties between beads at the time of molding in a mold, capable of providing a molded foamed article which is excellent antistatic performance, has no deterioration of the antistatic performance with elapse of the time, whose antistatic performance is not humidity dependent, does not contaminate packaging products, has a good molded foamed article surface, and has excellent mechanical properties. The present invention provides foamed polyolefin resin beads and a molded article obtained by molding the beads in a mold which are used as shock absorbing materials, heat insulating materials, or packaging materials in the electronic or automotive industry or useful for application to returnable boxes.[0003]2. Description of the Related Art[0004]Foamed polyolefin resin beads and a molded foamed article produced by molding the foamed...

AI Technical Summary

Benefits of technology

[0014]According to the present invention, there is provided the foamed polyolefin resin beads, in which shrinkage of the foamed resin beads which is observed when the polymer type antistatic agent is mixed with the foamed polyolefin resin beads is suppressed and fusion bonging properties between foamed resin beads are good.

[0016]In the present invention, it is found that composite resin beads include a core layer constituted by a crystalline polyolefin resin, a covering layer constituted by a crystalline polyolefin resin having a melting point lower than that of the resin constituting the core layer or a covering layer constituted by a noncrystalline polyolefin resin having a softening point lower than the melting point of the resin constituting the core layer and the polymer type antistatic agent is blended with the covering layer, which is foamed and expanded and the obtained foamed polyolefin resin beads can achieve the above-described object.

[0034]The foamed polyolefin resin beads (hereinafter may be referred to as simply “foamed resin beads” or “foamed beads”) of the present invention are foamed resin beads obtained by foaming and expanding composite resin beads including the core layer and the covering layer, the resin constituting the core layer is the crystalline polyolefin resin, the covering layer includes the crystalline polyolefin resin having the melting point lower than that of the crystalline polyolefin resin constituting the core layer or the noncrystalline polyolefin resin having the softening point lower than the melting point of the crystalline polyolefin resin constituting the core layer, and a specific amount of the polymer type antistatic agent is blended with the covering layer. Therefore, there is no shrinkage of foamed resin beads or the shrinkage is small due to the water absorption of the antistatic agent. Further, molding in a mold can be performed without causing damage to the cell structure of the core layer of the foamed resin beads when foamed resin beads are heated at a fusable temperature and foamed resin beads are excellent in fusion bonding properties.

[0036]The foamed resin beads of the present invention have the multilayered structure as described above. When the antistatic agent is blended with the covering layer at a predetermined ratio, the desired antistatic effect can be obtained. Thus, it is not necessarily needed that the antistatic agent is blended with the core layer. Generally, a relatively large amount of the polymer type antistatic agent is necessary to obtain antistatic effects. In the present invention, the desired antistatic performance can be exhibited by having the above-described structure even if the polymer type antistatic agent is not blended with the core layer or the blending amount of the polymer type antistatic agent is small. Therefore, foaming properties of the foamed resin beads are not inhibited and are not greatly shrunk, thereby producing the molded foamed article having the desired mechanical strength. Further, when the blending amount of the antistatic agent is small based on all of the foamed resin beads, sufficient antistatic performance can be exhibited. A step of coating foamed resin beads with the resin containing the antistatic agent after production of the foamed resin beads is not necessary. Thus, foamed resin beads having antistatic properties can be produced at low cost.

Problems solved by technology

Polyolefin resin is easily charged, which causes adhesion of dust and damage to equipment parts.

However, when the antistatic performance is achieved by the surfactant, the surfactant present on the surface of the molded article surface adsorbs moisture in the air.

Therefore, it is difficult to produce the antistatic effect under an environment of low humidity, particularly in winter.

Additionally, there have been problems of contamination due to the adhesion of the surfactant to packaging products and decrease in performance with age.

In the method for applying the surfactant to the surface of the molded article, the surfactant is easily flaked off from the surface of the molded article and the antistatic effect cannot be produced after the separation.

When the expansion ratio is high, the pressure in the cells of the obtained foamed resin beads is reduced by water condensation, which causes the phenomenon of shrinkage of beads in themselves.

When the heating temperature at the time of molding is increased to improve the fusion bonding properties between the foamed resin beads, the foamed resin beads cannot resist the heating temperature.

As a result, the foamed resin beads are shrunk or fused to not only the surface of them but also the inside of them, thereby causing serious damage to the cell structure of the obtained molded foamed article.

On the other hand, when the heating temperature is lowered, fusion bonding properties of foamed resin beads are reduced and the surface condition of the molded foamed article is significantly deteriorated.

Thus, a good molded foamed article cannot be obtained.

A method described in JP-A No. 2002-3634 involves a process of kneading the polymer type antistatic agent with the adhesive resin and coating the surface of foamed resin beads with the adhesive resin containing the polymer type antistatic agent and thus the production step is complicated.

Further, the charging property of the foamed resin beads to a molding cavity may be unstable.

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