Polyamide-based resin expanded beads, molded article of polyamide-based resin expanded beads, and method for producing polyamide-based resin expanded beads
Polyamide-based resin expanded beads contain a polyamide-based resin as a base material resin. The beads have a crystal structure, an intrinsic peak of the polyamide-based resin and a high-temperature peak having a peak top temperature on a higher temperature side than a peak top temperature of the intrinsic peak appear in a DSC curve obtained under a predetermined condition; an amount of heat of fusion of the high-temperature peak is within 5 J/g or more and 50 J/g or less; and a coefficient of variation of the amount of heat of fusion of the high-temperature peak is 20% or less. The beads are produced by in-mold molding. A method for producing the beads includes: impregnating a polyamide-based resin; and releasing expandable polyamide-based resin beads from a sealed container, a temperature in the sealed container is raised at a rate of 0.3° C. or higher and 1.5° C. or lower per 10 minutes.
1 . Polyamide-based resin expanded beads comprising a polyamide-based resin as a base material resin,
wherein:
the polyamide-based resin is a modified polyamide-based resin modified with one or more compounds selected from a group consisting of a carbodiimide compound, and an epoxy compound in an amount of 0.5-3 parts by mass with respect to 100 parts by mass of the polyamide-based resin;
the polyamide-based resin expanded beads have a crystal structure in which a melting peak (intrinsic peak) intrinsic to the polyamide-based resin and a melting peak (high-temperature peak) having a peak top temperature on a higher temperature side than a peak top temperature of the intrinsic peak appear in a DSC curve obtained under the following condition 1;
an amount of heat of fusion of the high-temperature peak is within a range of 7 J/g or more and 20 J/g or less;
a coefficient of variation of the amount of the heat of fusion of the high-temperature peak is about 6% or less;
the polyamide-based resin expanded beads have a closed cell ratio of 85% or more; and
a flexural modulus of the polyamide-based resin is 1000 MPa or more and about 3000 MPa or less:
(Condition 1)
on the basis of heat-flux differential scanning calorimetry of JIS K7122-1987, the polyamide-based resin expanded beads are used as test pieces, and heated and melted at a heating rate of 10° C./min from 30° C. to a temperature higher by 30° C. than that at the end of the melting peak to obtain the DSC curve.
2 . The polyamide-based resin expanded beads according to claim 1 , wherein the polyamide-based resin expanded beads have a closed cell ratio of 90% or more and 97% or less.
3 . The polyamide-based resin expanded beads according to claim 1 , wherein the polyamide-based resin expanded beads do not comprise a thermoplastic elastomer.
4 . A molded article of polyamide-based resin expanded beads obtained by in-mold molding of the polyamide-based resin expanded beads according to claim 1 .
5 . A method for producing the polyamide-based resin expanded beads according to claim 1 , the method comprising:
a dispersion step of dispersing polyamide-based resin beads comprising the modified polyamide-based resin in an aqueous dispersion medium in a sealed container;
an expanding agent applying step of adding an expanding agent to the polyamide-based resin beads;
a crystallization treatment step of heating the polyamide-based resin beads dispersed in the aqueous dispersion medium to form a high-temperature peak; and
an expanding step of releasing the polyamide-based resin beads containing the expanding agent together with the aqueous dispersion medium from the sealed container under a pressure lower than a pressure in the sealed container to expand the polyamide-based resin beads,
wherein in the expanding step, when the polyamide-based resin beads containing the expanding agent are released from the sealed container, a temperature rise adjustment that raises the temperature in the sealed container at a rate of 0.3° C. or higher and 1.5° C. or lower per 10 minutes is performed.
6 . The method for producing the polyamide-based resin expanded beads according to claim 5 , wherein in the crystallization treatment step, the high-temperature peak is formed by holding the polyamide-based resin expanded beads for 1 minute or more and 60 minutes or less at a temperature that is equal to or higher than a temperature lower by 90° C. (Tm−90° C.) than an intrinsic melting point (Tm) of the modified polyamide-based resin and lower than a temperature lower by 50° C. (Tm−50° C.) than the intrinsic melting point (Tm) of the modified polyamide-based resin.