Polylactic acid-based resin expanded beads and molded article thereof

Abstract

Polylactic acid-based resin expanded beads of the present invention are obtained by releasing a softened, pressurized foamable resin composition, which comprises a polylactic acid-based resin and a physical blowing agent, to a low pressure atmosphere to foam and expand the resin composition, wherein the polylactic acid-based resin satisfies the conditions (1) to (3) shown below, and exhibits excellent secondary expansion properties and fusion bonding properties. A polylactic acid-based resin expanded beads molded article obtained by in-mold molding of the polylactic acid-based resin expanded beads exhibits excellent mechanical properties. MT≦30 mN  (1) log MT≦0.93 log η−1.75  (2) CT 1/2 ≧600 sec  (3) where MT represents a melt tension [mN] at 190° C., η represents a melt viscosity [Pa·s] at 190° C. and a shear speed of 20 sec −1 , and CT 1/2 represents a half crystallization time [sec] at 110° C.

1 - 5 . (canceled) 
     
     
         6 . Polylactic acid-based resin expanded beads obtained by releasing a softened, pressurized foamable resin composition, which comprises a polylactic acid-based resin and a physical blowing agent, to a low pressure atmosphere to foam and expand the resin composition, wherein the polylactic acid-based resin satisfies the following conditions (1) to (3):
   MT≦30 mN  (1)
     log MT≦0.93 log η−1.75  (2)
     CT 1/2 ≧600 sec  (3)
   where MT represents a melt tension [mN] of the polylactic acid-based resin at 190° C., η represents a melt viscosity [Pa·s] of the polylactic acid-based resin at 190° C. and a shear speed of 20 sec −1 , and CT 1/2  represents a half crystallization time [sec] of the polylactic acid-based resin at 110° C.   
     
     
         7 . The polylactic acid-based resin expanded beads as recited in  claim 6 ,
 wherein the polylactic acid-based expanded resin beads, when measured by the below-mentioned heat flux differential scanning calorimetry, give a first time DSC curve and a second time DSC curve,   wherein the second time DSC curve has a fusion peak having a reference peak top temperature,   wherein the first time DSC curve has both a first fusion peak(s) with a peak top temperature that is on a high temperature side which is higher than the reference peak top temperature and a second fusion peak(s) with a peak top temperature that is on a low temperature side which is not higher than the reference peak top temperature, and   wherein the first and second time DSC curves are measured and defined as follows:   
       (a) a test DSC curve of a test sample of the expanded polylactic acid-based resin beads is measured according to a heat flux differential scanning calorimetry method referenced in JIS K7122 (1987), by heating the test sample at a heating rate of 10° C./minute from 23° C. to a temperature higher by 30° C. than the temperature at which an endothermic peak ends, thereby obtaining the first time DSC curve; 
       (b) the test sample is then maintained for 10 minutes at the temperature higher by 30° C. than the temperature at which the endothermic peak ends in the first time DSC curve; 
       (c) the test sample is then cooled to 30° C. at a cooling rate of 10° C./minute; and 
       (d) the test sample is then measured again by being heated at a heating rate of 10° C./minute to a temperature higher by 30° C. than the temperature at which the endothermic peak ends, thereby obtaining the second time DSC curve. 
     
     
         8 . The polylactic acid-based resin expanded beads as recited in  claim 7 , wherein the first fusion peak(s) with the peak top temperature which is on a higher temperature side which is higher than the reference peak top temperature has a calorific value of 1 to 8 J/g. 
     
     
         9 . The polylactic acid-based resin expanded beads as recited in  claim 6 , wherein the polylactic acid-based resin expanded beads have an apparent density of 24 to 240 g/L. 
     
     
         10 . A polylactic acid-based resin expanded beads molded article obtainable by molding the polylactic acid-based resin expanded beads according to  claim 6  in a mold cavity, said molded article having a density of 15 to 150 g/L and satisfying the following formula:
   (Bending modulus (MPa) of the expanded beads molded article)/(Density (g/L) of the expanded beads molded article)≧0.20 (MPa·L/g).
 
 
     
     
         11 . A polylactic acid-based resin expanded beads molded article obtainable by molding the polylactic acid-based resin expanded beads according to  claim 7  in a mold cavity, said molded article having a density of 15 to 150 g/L and satisfying the following formula:
   (Bending modulus (MPa) of the expanded beads molded article)/(Density (g/L) of the expanded beads molded article)≧0.20 (MPa·L/g).
 
 
     
     
         12 . A polylactic acid-based resin expanded beads molded article obtainable by molding the polylactic acid-based resin expanded beads according to  claim 8  in a mold cavity, said molded article having a density of 15 to 150 g/L and satisfying the following formula:
   (Bending modulus (MPa) of the expanded beads molded article)/(Density (g/L) of the expanded beads molded article)≧0.20 (MPa·L/g).
 
 
     
     
         13 . A polylactic acid-based resin expanded beads molded article obtainable by molding the polylactic acid-based resin expanded beads according to  claim 9  in a mold cavity, said molded article having a density of 15 to 150 g/L and satisfying the following formula:
   (Bending modulus (MPa) of the expanded beads molded article)/(Density (g/L) of the expanded beads molded article)≧0.20 (MPa·L/g).