POLYESTER-BASED SHRINK FILM
A heat-shrinkable polyester film that effectively suppresses a breakage phenomenon is provided. Disclosed is a heat-shrinkable polyester film derived from a polyester resin, the heat-shrinkable polyester film satisfying the following configurations (a) to (c): (a) a thermal shrinkage ratio in the TD direction obtainable under the conditions of 10 seconds in hot water at 80° C. as designated A 1 is a value of 25% or greater; (b) when a thermal shrinkage ratio in the TD direction obtainable under the conditions of 10 seconds in hot water at 90° C. as designated A 2 is a value of 40% or greater; and (c) when the upper yield point stress is E 1 and the lower yield point stress is E 2, a numerical value represented by E 1− E 2 is a value of 5 MPa or less.
1 . A heat-shrinkable polyester film derived from a polyester resin, the heat-shrinkable polyester film having the following configurations (a) to (c):
(a) when a main shrinkage direction is designated as TD direction, and a thermal shrinkage ratio in the TD direction obtainable in a case where the heat-shrinkable polyester film is caused to shrink under the conditions of 10 seconds in hot water at 80° C. is designated as A 1 , A 1 is set to a value of 25% or greater;
(b) when a thermal shrinkage ratio in the TD direction obtainable in a case where the heat-shrinkable polyester film is caused to shrink under the conditions of 10 seconds in hot water at 90° C. is designated as A 2 , the A 2 is set to a value of 40% or greater; and
(c) when an upper yield point stress in a stress-strain curve in the TD direction is designated as E 1 , and a lower yield point stress in the stress-strain curve in the TD direction is designated as E 2 , a numerical value represented by E 1 −E 2 is set to a value of 5 MPa or less.
2 . The heat-shrinkable polyester film according to claim 1 , wherein a value of the upper yield point stress E 1 is made greater than a value of the lower yield point stress E 2 , and at the same time, the E 1 is set to a value within the range of 95 to 120 MPa, while the E 2 is set to a value within the range of 90 to 115 MPa.
3 . The heat-shrinkable polyester film according to claim 1 , wherein a numerical value represented by E 2 /E 1 , which is a ratio of the upper yield point stress E 1 and the lower yield point stress E 2 , is set to be above 0.9.
4 . The heat-shrinkable polyester film according to claim 1 , wherein when a direction orthogonally intersecting the TD direction is designated as MD direction, and a thermal shrinkage ratio in the MD direction obtainable in a case where the heat-shrinkable polyester film is caused to shrink under the conditions of 10 seconds in hot water at 80° C. is designated as B1, the B1 is set to a value of 3% or greater.
5 . The heat-shrinkable polyester film according to claim 1 , wherein when a direction orthogonally intersecting the TD direction is designated as MD direction, and a thermal shrinkage ratio in the MD direction obtainable in a case where the heat-shrinkable polyester film is caused to shrink under the conditions of 10 seconds in hot water at 90° C. is designated as B2, the B2 is set to a value of 4% or greater.
6 . The heat-shrinkable polyester film according to claim 1 , wherein when a nominal tensile strain at break in the TD direction as measured according to JIS K 7127/2/200 (1999) is designated as C 1 , the C 1 is set to a value of 40% or greater.
7 . The heat-shrinkable polyester film according to claim 1 , wherein a haze value of the film before shrinkage as measured according to JIS K7105 is set to a value of 5% or less.
8 . The heat-shrinkable polyester film according to claim 1 , wherein a non-crystalline polyester is included at a proportion within the range of 90% to 100% by weight of the total quantity of resins.