POLYESTER-BASED SHRINK FILM
Provided is a heat-shrinkable polyester film which undergoes less change in the physical properties even in a high-humidity environment, has excellent storage stability, and effectively suppresses a breakage phenomenon of the film after heat shrinkage. Disclosed is a heat-shrinkable polyester film derived from a polyester resin, in which when tensile strengths in a main shrinkage direction obtained before and after immersion in water at 23° C. for 168 hours in a tensile test as measured according to JIS K 7127 are designated as C1 (MPa) and C2 (MPa), the following Relational Expression (1) is satisfied: −5.3<( C 2− C 1)<4.2 (1)
1 . A heat-shrinkable polyester film derived from a polyester resin,
wherein in a tensile test measured according to JIS K 7127, when tensile strengths in a main shrinkage direction obtained before and after immersion in water at 23° C. for 168 hours are designated as C1 (MPa) and C2 (MPa), the heat-shrinkable polyester film satisfies the following Relational Expression (1).
−5.3<( C 2− C 1)<4.2 (1)
2 . The heat-shrinkable polyester film according to claim 1 ,
wherein when satisfying the Relational Expression (1) is designated as configuration (a), the heat-shrinkable polyester film not only has the configuration (a) but also has the following configurations (b) and (c):
(b) when the main shrinkage direction is designated as TD direction, and a heat shrinkage rate in the TD direction 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 A1, this A1 is set to a value of 60% or more; and
(c) when a direction orthogonally intersecting the TD direction is designated as MD direction, and a heat shrinkage rate in the MD direction 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 B1, this B1 is set to a value of below 10%.
3 . The heat-shrinkable polyester film according to claim 2 ,
wherein the heat shrinkage rate A1, the heat shrinkage rate B1, the tensile strength C1, and the tensile strength C2 satisfy the following Relational Expression (2).
-
13
≦
C
2
-
C
1
(
1
-
A
1
100
)
×
(
1
-
B
1
100
)
≦
9.5
(
2
)
4 . The heat-shrinkable polyester film according to claim 1 ,
wherein a value of the tensile strength C1 is set to a value within the range of 50 to 75 MPa, and the tensile strength C2 is set to a value within the range of 50 to 75 MPa.
5 . The heat-shrinkable polyester film according to claim 1 ,
wherein the tensile strength C1 and the tensile strength C2 satisfy the following Relational Expression (3).
0.95
≦
C
1
C
2
≦
1.07
(
3
)
6 . The heat-shrinkable polyester film according to claim 2 ,
wherein when a heat shrinkage rate in the TD direction obtained in a case where the heat-shrinkable polyester film is caused to shrink under the conditions of 10 seconds in hot water at 98° C. is designated as A2, this A2 is set to a value of 70% or more, and when a heat shrinkage rate in the MD direction obtained in a case where the heat-shrinkable polyester film is caused to shrink under the conditions of 10 seconds in hot water at 98° C. is designated as B2, this B2 is set to a value of below 10%.
7 . The heat-shrinkable polyester film according to claim 2 ,
wherein the heat shrinkage rate A1 and the heat shrinkage rate A2 satisfy the following Relational Expression (4).
( A 2− A 41)≤5 (4)
8 . The heat-shrinkable polyester film according to claim 1 ,
wherein a haze value of the film before shrinkage as measured according to JIS K 7105 is set to a value of 5% or less.
9 . The heat-shrinkable polyester film according to claim 1 ,
wherein the heat-shrinkable polyester film includes a non-crystalline polyester at a proportion in the range of 90% to 100% by weight of a total amount of resins.