Porous film, separator for electric storage device, and electric storage device

A separator for an electric storage device, the separator comprising a porous film having through-pores containing:

• a polyolefin-based resin is a polypropylene resin having a melt flow rate of 4 to 30 g/10 min;
• and
• 70% to 99% by mass of the polypropylene resin having the melt flow rate of 4 to 30 g/10 min and 1% to 30% by mass of a propylene-ethylene copolymer having a melt flow rate of 0.1 to less than 4 g/10 min;
• or
• 80% to 99% by mass of the polypropylene resin having the melt flow rate of 4 to 30 g/10 min and 1% to 20% by mass of an elastomer containing at least propylene or butane as a constituent unit, wherein,
• when a thickness of a circular region having a diameter of 10 mm as an initial thickness t0 after a load of 50 g is applied onto the circular region for 10 seconds, as a thickness t after a load of 500 g is subsequently applied onto the same region for 10 seconds, and as a thickness t1 after 10 seconds has passed after the load applied onto the same region is subsequently changed to 50 g, a thickness change rate (%) of the film as expressed by Equation (1) is 10% to 50%, and a thickness (t1) recovery rate (%) of the film as expressed by Equation (2) is 80% to 99.9%:
• Thickness change rate (%)=[(t0−t)/t0]×100 (1), and
• Thickness (t1) recovery rate (%)−(t1/t0)×100 (2).

An electric storage device comprising a separator for an electric storage, the separator comprising a porous film having through-pores containing:

• a polyolefin-based resin is a polypropylene resin having a melt flow rate of 4 to 30 g/10 min;
• and
• 70% to 99% by mass of the polypropylene resin having the melt flow rate of 4 to 30 g/10 min and 1% to 30% by mass of a propylene-ethylene copolymer having a melt flow rate of 0.1 to less than 4 g/10 min;
• or
• 80% to 99% by mass of the polypropylene resin having the melt flow rate of 4 to 30 g/10 min and 1% to 20% by mass of an elastomer containing at least propylene or butane as a constituent unit, wherein,
• when the thickness of a circular region having a diameter of 10 mm as an initial thickness t0 after a load of 50 g is applied onto the circular region for 10 seconds, as a thickness t after a load of 500 g is subsequently applied onto the same region for 10 seconds, and as a thickness t1 after 10 seconds has passed after the load applied onto the same region is subsequently changed to 50 g, a thickness change rate (%) of the film as expressed by Equation (1) is 10% to 50%, and a thickness (t1) recovery rate (%) of the film as expressed by Equation (2) is 80% to 99.9%:
• Thickness change rate (%)=[(t0−t)/t0]×100 (1), and
• Thickness (t1) recovery rate (%)=(t1/t0)×100 (2).