Resin composition, foamed resin using same, and electric wire insulated with foamed resin

1. A foamed resin made of a resin composition having fine bubbles uniformly dispersed therein, wherein

the resin composition comprises a blend of a polyolefin base resin and a polymer material other than the polyolefin base resin, the polymer material being dispersed in the polyolefin base resin;

the bubbles are generated at boundary regions between the base resin and the dispersed polymer material by infusing a foaming gas into the resin composition at a predetermined processing temperature;

the melting point or glass transition temperature of the polymer material is greater than the melting point of the polyolefin base resin and less than the processing temperature; and

the foamed resin is produced by a process comprising blending the polyolefin base resin and the polymer material to provide the resin composition, kneading the resin composition, providing the resin composition in a molding machine, heating the resin composition in the molding machine to provide a molten resin composition, infusing a foaming gas into the molten resin composition in the molding machine at the predetermined processing temperature, molding the resin composition, and foaming the resin composition due to a pressure difference between an inside and outside of the molding machine by generating bubbles at boundary regions between the polyolefin base resin and the dispersed polymer material due to a difference between the melting point or glass transition temperature of the polymer material and the melting point of the polyolefin base resin.

2. The resin composition according to claim 1 , wherein:

content of the polymer material is within a range from 0.1 to 45 parts by mass with regard to 100 parts by mass of total amount of the polvolefin base resin and the polymer material.

3. An electric wire, comprising a metal conductor and an insulator formed on an outer periphery of the metal conductor, wherein the insulator is made of the foamed resin according to claim 1 .

4. The electric wire according to claim 3 , wherein foaming degree of the foamed resin is within a range from 50 to 90%.

5. The electric wire according to claim 3 , wherein the insulator made of the foamed resin has a foaming degree fluctuation of 1.0% or less.

6. The resin composition according to claim 1 , wherein:

the polyolefin base resin comprises at least one member selected from the group consisting of polyethylene, polypropylene, ethylene-propylene copolymer, implant-type thermopolyolefin, ethylene-propylene-butene copolymer, ethylene-butene copolymer, ethylene-octen copolymer, ethylene-hexene copolymer, and ethylene-pentene copolymer.

7. The resin composition according to claim 1 , wherein:

content of the polymer material is within a range from 1 to 25 parts by mass with regard to 100 parts by mass of total amount of the polyolefin base resin and the polymer material.

8. A foamed resin made of a resin composition having fine bubbles uniformly dispersed therein, wherein

the resin composition comprises a blend of a base resin and a polymer material other than the base resin, the polymer material being dispersed in the base resin;

the bubbles are generated at boundary regions between the base resin and the dispersed polymer material by infusing a foaming gas into the resin composition at a predetermined processing temperature;

the melting point or glass transition temperature of the polymer material is greater than the melting point of the base resin and less than about 180 ° C; and

the foamed resin is produced by a process comprising blending the base resin and the polymer material to provide the resin composition, kneading the resin composition, providing the resin composition in a molding machine, heating the resin composition in the molding machine to provide a molten resin composition, infusing a foaming gas into the molten resin composition in the molding machine at the predetermined processing temperature, the predetermined processing temperature being about 180° C. or less, molding the resin composition, and foaming the resin composition due to a pressure difference between an inside and outside of the molding machine by generating bubbles at boundary regions between the base resin and the dispersed polymer material due to a difference between the melting point or glass transition temperature of the polymer material and the melting point of the base resin.

9. The resin composition according to claim 8 , wherein:

content of the polymer material is within a range from 0.1 to 45 parts by mass with regard to 100 parts by mass of total amount of the base resin and the polymer material. A foamed resin made of the resin composition according to claim 1 , having fines bubbles uniformly dispersed therein.

10. An electric wire, comprising a metal conductor and an insulator formed on an outer periphery of the metal conductor, wherein the insulator is made of the foamed resin according to claim 8 .

11. The electric wire according to claim 10 , wherein foaming degree of the foamed resin is within a range from 50 to 90%.

12. The electric wire according to claim 10 , wherein the insulator made of the foamed resin has a foaming degree fluctuation of 1.0% or less.

13. The resin composition according to claim 8 , wherein:

the base resin comprises at least one polyolefin selected from the group consisting of polyethylene, polypropylene, ethylene-propylene copolymer, implant-type thermopolyolefin, ethylene-propylene-butene copolymer, ethylene-butene copolymer, ethylene-octen copolymer, ethylene-hexene copolymer, and ethylene-pentene copolymer.

14. The resin composition according to claim 8 , wherein:

content of the polymer material is within a range from 1 to 25 parts by mass with regard to 100 parts by mass of total amount of the base resin and the polymer material.