Biaxially stretched polypropylene film, metallized film, metallized film roll and film capacitor
A biaxially stretched polypropylene film which has a thickness of from 1.0 μm to 3.5 μm, a tensile fracture stress at 135° C. of 70 MPa or more in a first direction, and a difference between the tensile fracture stress at 125° C. in the first direction and the tensile fracture stress at 135° C. in the first direction of from 0 MPa to 15 MPa (inclusive).
1. A biaxially stretched polypropylene film produced by:
obtaining a cast roll stock sheet produced by melting and extruding a resin;
preheating the cast roll stock sheet using a machine direction (MD) preheating roll group, wherein temperature of the MD preheating roll group during a first stage in said preheating is set to 60-95° C., temperature of the MD preheating roll group during a second stage in said preheating is set to 115-138° C., and contact time with the MD preheating roll group during the second stage of said preheating is set to 5-10 seconds;
stretching the cast roll stock sheet in the MD direction using a MD stretching roll group, wherein a MD stretching ratio is set to 4.5-5.5 times, and temperature of the MD stretching roll group is set to 130-150° C., contact time with the MD stretching roll group is set to 1-2 seconds during said stretching; and
relaxing the cast roll stock sheet using a MD relaxing roll group, wherein temperature of the MD relaxing roll group is set to 120-128° C. and contact time with the MD relaxing roll group is set to 1-2 seconds during said relaxing,
wherein the biaxially stretched polypropylene film has:
a thickness of from 1.0 μm to 3.5 μm;
a tensile fracture stress of 70 MPa or more at 135° C. in a first direction; and
a difference between a tensile fracture stress at 125° C. in the first direction and a tensile fracture stress at 135° C. in the first direction of 0 MPa or more and 15 Mpa or less.
2. The biaxially stretched polypropylene film according to claim 1 , wherein a dimensional change rate at 135° C. in the first direction is −3.2% or more.
3. The biaxially stretched polypropylene film according to claim 1 , wherein a difference between a dimensional change rate at 125° C. in the first direction and a dimensional change rate at 135° C. in the first direction is 0% or more and 1.5% or less.
4. The biaxially stretched polypropylene film according to claim 1 , wherein a crystallite size is 12.20 nm or less.
5. The biaxially stretched polypropylene film according to claim 1 , which is used for a capacitor.
6. A metallized film comprising:
the biaxially stretched polypropylene film according to claim 1 ; and
a metal layer laminated on at least one surface of the biaxially stretched polypropylene film.
7. A metallized film roll formed by winding the metallized film according to claim 6 .
8. A film capacitor comprising the metallized film according to claim 6 , wherein said metallized film is wound or laminated.
9. A method of producing a biaxially stretched polypropylene film, comprising:
obtaining a cast roll stock sheet produced by melting and extruding a resin:
preheating the cast roll stock sheet using a machine direction (MD) preheating roll group, wherein temperature of the MD preheating roll group during a first stage in said preheating is set to 60-95° C., temperature of the MD preheating roll group during a second stage in said preheating is set to 115-138° C., and contact time with the MD preheating roll group during the second stage of said preheating is set to 5-10 seconds:
stretching the cast roll stock sheet in the MD direction using a MD stretching roll group, wherein a MD stretching ratio is set to 4.5-5.5 times, and temperature of the MD stretching roll group is set to 130-150° C., contact time with the MD stretching roll group is set to 1-2 seconds during said stretching;
relaxing the cast roll stock sheet using a MD relaxing roll group, wherein temperature of the MD relaxing roll group is set to 120-128° C. and contact time with the MD relaxing roll group is set to 1-2 seconds during said relaxing,
wherein the biaxially stretched polypropylene film has a tensile fracture stress of 70 MPa or more at 135° C. in a first direction,
wherein a difference between a tensile fracture stress at 125° C. in the first direction of the biaxially stretched polypropylene film and a tensile fracture stress at 135° C. in the first direction of the biaxially stretched polypropylene film is 0-15 MPa.
10. The method of claim 9 , wherein the temperature of the MD preheating roll group during the second stage in said preheating is set to 125-135° C.
11. The method of claim 9 , wherein the contact time with the MD preheating roll group during the second stage in said preheating is set to 5.5-9.5 seconds.
12. The method of claim 9 , wherein the MD stretching ratio in said stretching is set to 4.6-5.5 times.
13. The method of claim 9 , wherein the temperature of the MD stretching roll group in said stretching is set to 135-146° C.
14. The method of claim 9 , wherein the contact time with the MD stretching roll group in said stretching is set to 1.1-1.8 seconds.
15. The method of claim 9 , wherein the contact time with the MD relaxing roll group in said relaxing is set to 1.1-1.8 seconds.
16. The method of claim 9 , wherein the difference between the tensile fracture stress at 125° C. in the first direction of the biaxially stretched polypropylene film and the tensile fracture stress at 135° C. in the first direction of the biaxially stretched polypropylene film is 7-15 MPa.