Patent ID: 11961683
Assignee: OJI HOLDINGS CORPORATION
Field: Other special machines (Mechanical engineering)
Classification: CPC H  B  C | IPC B  H

Claim 0:
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.