Method for producing expansion-molded polypropylene-based resin article
View Patent ↗It is an object of the present invention to provide a method for easily and economically producing an expansion-molded polypropylene-based resin article stably with a high porosity, that has continuous voids and that can be used as materials such as a sound absorbing material and a draining material. More specifically, the present invention relates to a method for producing an expansion-molded polypropylene-based resin article, in which a mold is filled with expanded polypropylene-based resin particles, and the expanded particles are heated and fused using water vapor, and then cooled, wherein expanded polypropylene-based resin particles are used in which a polypropylene-based resin having a melt index (MI) of not less than 0.1 g/10 minutes and not more than 9 g/10 minutes is used as a base resin, a cell size is not more than 150 μm, two melting peaks are present on a DSC curve obtained by differential scanning calorimetry, and β/(α+β) is not less than 0.35 and not more than 0.75 when taking a melting calorie at the lower temperature peak as α (J/g) and taking a melting calorie at the higher temperature peak as β (J/g), and a porosity of an obtained molded article is not less than 20% and not more than 50%.
1. A method for producing an expansion-molded polypropylene-based resin article, comprising:
filling a mold with expanded polypropylene-based resin particles;
heating and fusing the expanded particles by using water vapor; and
then cooling the fused and heated expanded particles,
wherein a polypropylene-based resin having a melt index (MI) of not less than 0.1 g/10 minutes and not more than 8 g/10 minutes is used as a base resin for the expanded polypropylene-based resin particles,
a shape of the expanded polypropylene-based resin particles is a pillar shape with an L/D ratio of not less than 1.5 and not more than 3, wherein the pillar shape is a shape in which a maximum diameter (Dmax) and a minimum diameter (Dmin) on a cross section perpendicular to a length direction of the expanded polypropylene-based resin particle are substantially constant along the length direction, and the D in the L/D ratio refers to an average value calculated by a following formula:
D
=
D
max
+
D
min
2
,
a cell size of the expanded polypropylene-based resin particles is not more than 150 μm,
two melting peaks are present on a DSC curve of the expanded polypropylene-based resin particles obtained by differential scanning calorimetry, and β/(α+β) is not less than 0.35 and not more than 0.75 when taking a melting calorie at the lower temperature peak as α(J/g) and taking a melting calorie at the higher temperature peak as β(J/g),
the mold is filled with the expanded polypropylene-based resin particles to which an internal pressure of not less than 0.2 kgf/cm 2 G and not more than 0.7 kgf/cm 2 G is applied,
a porosity of an obtained molded article is not less than 20% and not more than 50%,
the obtained molded article has a peak sound absorption coefficient of no lower than 0.82, and
continuous voids are formed in the obtained molded article.
2. The method for producing an expansion-molded polypropylene-based resin article according to claim 1 ,
wherein when heating and fusing the expanded polypropylene-based resin particles, water vapor at a temperature in a range from 25° C. lower than a melting point of the polypropylene-based resin that is used as the base resin to the melting point thereof is used.
3. The method for producing an expansion-molded polypropylene-based resin article according to claim l,
wherein the porosity of an obtained molded article is not less than 25% and not more than 45%.