Extruded propylene polymer resin foam

Details Extruded propylene polymer resin foam Extruded propylene polymer resin foam

1996-06-24

1997-05-13

Foelak, Morton

Stock material or miscellaneous articles

Structurally defined web or sheet

Physical dimension specified

2642107, 2642358, 2642902, 4283044, 521 79, 521 81, 521142, 521143, C08J 900, B32B 326

Patent

active

056290764

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Technical Field
The present invention relates to a novel extruded propylene polymer resin foam. More particularly, the present invention is concerned with a novel extruded propylene polymer resin foam comprising a vast plurality of cells and a matrix constituted by cell walls of the cells and comprised of a propylene polymer resin, wherein said propylene polymer resin has high viscoelasticity characteristics, and wherein the foam has a thickness as large as at least 20 mm, a density as small as 0.03 g/cm.sup.3 or less, an average cell diameter of from 0.4 to 2.0 mm and a closed cell ratio as large as at least 80%. The resin foam of the present invention has not only light weight, but also exhibits high cushioning performance and excellent mechanical strengths, so that, after fabricated into various sizes by cutting, the resultant resin foam articles can be advantageously used in the fields of cushion packaging materials, floating materials, and heat insulating materials.
2. Background Art
Extruded polyethylene resin foams have heretofore been well known, however, have various problems in respect of the properties thereof. On the other hand, propylene polymer resins have high rigidity as compared to polyethylene resins and, therefore, have advantages in that when foams are produced from propylene polymer resins, the foams can exhibit high mechanical strengths with the use of the resin in a reduced amount, so that excellent foams having light weight and excellent mechanical properties can be produced. Accordingly, various attempts have recently been made to improve propylene resin foams.
For example, Unexamined Japanese Patent Application Laid-Open specification No. H4-363227/1992 and Japanese Patent Application prior-to-examination Publication (kohyo) No. H5-506875/1993 (corresponding to International Patent Application Publication No. WO 91/13933) disclose extruded propylene polymer resin foams having a density of 0.03 g/cm.sup.3 or less. However, any of the conventional extruded propylene polymer resin forms having a density of 0.03 g/cm.sup.3 or less does not have a thickness and a closed cell ratio which are sufficient to exert high cushioning performance, so that these forms are unsatisfactory for use as cushion packaging materials.
With a view toward solving the problems accompanying the conventional propylene polymer resin forms, the present inventors have conducted experiments using extruded resin foams having different thicknesses which were produced from olefin polymer resins, such as ethylene polymer resins and propylene polymer resins, in order to find relationships between the thickness of the resin foam and the cushioning performance exerted by the resin foam. Observations have been made using a graph of dynamic impact characteristic curves showing the results of the experiments.
Referring to FIG. 3 of the accompanying drawings, there is shown a graph of dynamic impact characteristic curves, showing the relationships between the static stress generated on the resin foam and the peak acceleration sustained by the weight in the one-time dropping test, with respect to resin foams having different thicknesses. The dynamic impact characteristic curve was obtained by the experiments which were conducted in accordance with the "Testing Methods of Dynamic Compression for Package Cushioning Materials" prescribed in Japanese Industrial Standards (JIS) Z 0235, using extruded polyethylene resin foams each having a density of 0.025 g/cm.sup.3 and respectively having thicknesses of 20, 30 and 40 mm. From FIG. 3 and an explanation thereon (which is given below), not only will the meaning of the "cushioning performance" be made clear, but also it will be understood that for exerting an satisfactory cushioning performance it is necessary for a resin foam to have a thickness of at least 20 mm.
In the graph of FIG. 3 which shows the dynamic impact characteristic curves, the ordinate indicates the peak acceleration J (0-100 G), and the abscissa having a logarithmic scale indicates

REFERENCES:
Chatraei et al., Journal of Rheology, 25(4), 433-443 (1981).
Linster et al., Polymer Bulletin, 16, 187-194 (1986).

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