Polyolefin foam and polyolefin resin composition

A polyolefin-based crosslinked foam having the following characteristics (a) to (c) obtained by the crosslinked foaming of a foaming polyolefin resin composition comprising a polyolefin resin composition comprising 100 parts by weight of a polyolefin resin having a density of from 0.860 to 0.970 g/cm3 and a weight average molecular weight of 60,000 or more as determined by gel permeation chromatography and from 5 to 50 parts by weight of a low molecular polyolefin wax having a viscosity average molecular weight of from 1,500 to 10,000 as determined by a viscosity method and a melting point of from 100° C. to 160° C. as determined by DSC method, and a foaming agent:

• (a) Gel fraction represented by the residue obtained by extracting with p-xylene at 120° C. for 24 hours, and then immediately drying at 80° C. and 10 mmHg for 24 hours is from 10% to 90%;
• (b) Degree of swelling represented by the following equation (1) is not greater than 30:
• Degree of Swelling = Residue (g) shortly after 24 hours of extraction with p-xylene at 120° C. Residue (g) obtained by extracting with p-xylene at 120° C. for 24 hours, and then immediately drying at 80 C. and 10 mmHg for 24 hours ( 1 )
• and;
• (c) When glass transition point determined from the temperature dependence of dynamic viscoelasticity is represented by the peak of tan δ determined by the measurement of dynamic viscoelasticity at a frequency of 10 Hz, there is observed no peak or one peak, if any, and the ratio α of storage modulus at 0° C. (E′0) to storage modulus at 100° C. (E′100) (α=log E′0/E′100) is from 10 to 30.

A polyolefin-based crosslinked foam having the following characteristics (a) to (c) obtained by the crosslinked foaming of a foaming polyolefin resin composition comprising

• 100 parts by weight of a polyolefin resin composition comprising (i) 100 parts by weight of a straight-chain ethylene homopolymer or a straight-chain ethylene-α-olefin copolymer comprising ethylene and a C3-C12 α-olefin, having a density of from 0.860 to 0.970 g/cm3, a weight average molecular weight of 60,000 or more as determined by gel permeation chromatography, MFR of from 0.1 to 30 g/10 min at 190° C. and a load of 2,160 g, a melt tension of from 50 to 300 mN as determined when stretched at a draw ratio of 50 using a capillary rheometer having a die size L/D of 8/2.095 (mm) and a cylinder temperature of 160° C. and a non-linear parameter of 2 or more as an index of strain hardening of extensional viscosity, and (ii) from 5 to 50 parts by weight of a low molecular polyolefin wax having a viscosity average molecular weight of from 1,500 to 10,000 as determined by a viscosity method and a melting point of from 100° C. to 160° C. as determined by DSC method, and from 2 to 30 parts by weight of a foaming agent:
• (a) Gel fraction represented by the residue obtained by extracting with p-xylene at 120° C. for 24 hours, and then immediately drying at 80° C. and 10 mmHg for 24 hours is from 10% to 90%;
• (b) Degree of swelling represented by the following equation (1) is not greater than 30:
• Degree of Swelling = Residue (g) shortly after 24 hours of Extraction with p-xylene at 120° C. Residue (g) obtained by extracting with p-xylene at 120° C. for 24 hours, and then immediately drying at 80 C. and 10 mmHg for 24 hours ( 1 )
• and;
• (c) When glass transition point determined from the temperature dependence of dynamic viscoelasticity is represented by the peak of tan δ determined by the measurement of dynamic viscoelasticity at a frequency of 10 Hz, there is observed no peak or one peak, if any, and the ratio α of storage modulus at 0° C. (E′0) to storage modulus at 100° C. (E′100) (α=log E′0/E′100) is from 10 to 30.