Heat-shrinkable polyester film, packages, and process for production of heat-shrinkable polyester film

1. A heat-shrinkable polyester film made of a polyester resin comprising 50% by mole or more ethylene terephthalate and containing at least 7 mol % of at least one monomer capable of forming an amorphous component in the whole component of the polyester resin, wherein the following requirements (1) to (5) are satisfied:

(1) a glycerin shrinkage rate in the width direction is not more than 10% when the film is treated for 10 seconds in glycerin at 80° C.;

(2) a glycerin shrinkage rate in the longitudinal direction is not less than 0% and not more than 10% and a glycerin shrinkage rate in the width direction is not less than 20% and not more than 40% when the film is treated for 10 seconds in glycerin at 100° C.;

(3) a glycerin shrinkage rate in the width direction is not less than 40% and not more than 70% when the film is treated for 10 seconds in glycerin at 120° C.;

(4) a shrinkage rate of the film in the width direction after aging for 672 hours under an atmosphere of a temperature of 60° C. and a relative humidity of 40% is not more than 1.5%; and

(5) the number of initial breakages, which is the number of samples are broken at not more than 5% elongation when a tensile test is repeated 10 times in the film longitudinal direction using a tensile tester with a distance between chucks being kept at 100 mm after aging for 672 hours under an atmosphere of a temperature of 60° C. and a relative humidity of 40%, is not more than 2 times,

wherein the heat shrinkable polyester film is prepared by

(a) a lengthwise drawing step of lengthwise drawing a undrawn film so as to provide a total lengthwise draw ratio of not less than 2.8 times and not more than 4.5 times by lengthwise drawing the film in the longitudinal direction at a draw ratio of not less than 2.2 times and not more than 3.0 times at a temperature of not less than Tg and not more than (Tg+30° C.) (first-stage lengthwise drawing) and then lengthwise drawing the film in the longitudinal direction at a draw ratio of not less than 1.2 times and not more than 1.5 times at a temperature of not less than (Tg+10° C.) and not more than (Tg+40° C.);

(b) an annealing step of relaxing the film after lengthwise drawing at a relaxation rate of not less than 10% and not more than 50% in the longitudinal direction while heating the film in the width direction using an infrared heater;

(c) an intermediate heat treatment step of heat-treating the film after annealing for a time period of not less than 1.0 seconds and not more than 9.0 seconds at a temperature of not less than 130° C. and not more than 190° C. with both edges in the width direction being held by clips in a tenter;

(d) a forced cooling step of actively cooling the film after the intermediate heat treatment until the surface temperature becomes a temperature of not less than 80° C. and not more than 120° C.;

(e) a transverse drawing step of drawing the film after forced cooling at a draw ratio of not less than 2.0 times and not more than 6.0 times in the width direction at a temperature of not less than (Tg+10° C.) and not more than (Tg+50° C.); and

(f) a final heat treatment step of heat-treating the film after transverse drawing for a time period of not less than 1.0 seconds and not more than 9.0 seconds at a temperature of the transverse drawing temperature+not less than 15° C. and not more than 40° C. with both edges in the width direction being held by clips in a tenter.

2. The heat-shrinkable polyester film according to claim 1 , wherein a tensile breaking strength in the longitudinal direction is not less than 80 MPa and not more than 300 MPa.

3. The heat-shrinkable polyester film according to claim 2 , wherein a difference is not more than 10% between the glycerin shrinkage rate of the film in the width direction when the film is treated for 10 seconds in glycerin at each of temperatures of 80° C., 100° C. and 120° C. after aging for 672 hours under an atmosphere of a temperature of 60° C. and a relative humidity of 40% and the glycerin shrinkage rate at the same temperature for the film before aging.

4. The heat-shrinkable polyester film according to claim 3 , wherein the polyester resin contains 50 mol % or more of ethylene terephthalate unit, and the monomer capable of forming an amorphous component is at least one selected from neopentyl glycol, 1,4-cyclohexanedimethanol and isophthalic acid and is contained in an amount of not more than 27 mol %.

5. The heat-shrinkable polyester film according to claim 4 , wherein the polyester resin contains 50 mol % or more of ethylene terephthalate unit, and the monomer capable of forming an amorphous component is at least one selected from neopentyl glycol, 1,4-cyclohexanedimethanol and isophthalic acid and is contained in an amount of not more than 27 mol %, and a glass transition point (Tg) is adjusted to 60 to 80° C.

6. The heat-shrinkable polyester film according to claim 3 , wherein the polyester resin contains 50 mol % or more of ethylene terephthalate unit, and the monomer capable of forming an amorphous component is at least one selected from neopentyl glycol, 1,4-cyclohexanedimethanol and isophthalic acid and is contained in an amount of not more than 27 mol %, and a glass transition point (Tg) is adjusted to 60 to 80° C.

7. The heat-shrinkable polyester film according to claim 2 , wherein the polyester resin contains 50 mol % or more of ethylene terephthalate unit, and the monomer capable of forming an amorphous component is at least one selected from neopentyl glycol, 1,4-cyclohexanedimethanol and isophthalic acid and is contained in an amount of not more than 27 mol %.

8. The heat-shrinkable polyester film according to claim 7 , wherein the polyester resin contains 50 mol % or more of ethylene terephthalate unit, and the monomer capable of forming an amorphous component is at least one selected from neopentyl glycol, 1,4-cyclohexanedimethanol and isophthalic acid and is contained in an amount of not more than 27 mol %, and a glass transition point (Tg) is adjusted to 60 to 80° C.

9. The heat-shrinkable polyester film according to claim 2 , wherein the polyester resin contains 50 mol % or more of ethylene terephthalate unit, and the monomer capable of forming an amorphous component is at least one selected from neopentyl glycol, 1,4-cyclohexanedimethanol and isophthalic acid and is contained in an amount of not more than 27 mol %, and a glass transition point (Tg) is adjusted to 60 to 80° C.

10. The heat-shrinkable polyester film according to claim 1 , wherein a difference is not more than 10% between the glycerin shrinkage rate of the film in the width direction when the film is treated for 10 seconds in glycerin at each of temperatures of 80° C., 100° C. and 120° C. after aging for 672 hours under an atmosphere of a temperature of 60° C. and a relative humidity of 40% and the glycerin shrinkage rate at the same temperature for the film before aging.

11. The heat-shrinkable polyester film according to claim 10 , wherein the polyester resin contains 50 mol % or more of ethylene terephthalate unit, and the monomer capable of forming an amorphous component is at least one selected from neopentyl glycol, 1,4-cyclohexanedimethanol and isophthalic acid and is contained in an amount of not more than 27 mol %.

12. The heat-shrinkable polyester film according to claim 11 , wherein the polyester resin contains 50 mol % or more of ethylene terephthalate unit, and the monomer capable of forming an amorphous component is at least one selected from neopentyl glycol, 1,4-cyclohexanedimethanol and isophthalic acid and is contained in an amount of not more than 27 mol %, and a glass transition point (Tg) is adjusted to 60 to 80° C.

13. The heat-shrinkable polyester film according to claim 10 , wherein the polyester resin contains 50 mol % or more of ethylene terephthalate unit, and the monomer capable of forming an amorphous component is at least one selected from neopentyl glycol, 1,4-cyclohexanedimethanol and isophthalic acid and is contained in an amount of not more than 27 mol %, and a glass transition point (Tg) is adjusted to 60 to 80° C.

14. The heat-shrinkable polyester film according to claim 1 , wherein the polyester resin contains 50 mol % or more of ethylene terephthalate unit, and the monomer capable of forming an amorphous component is at least one selected from neopentyl glycol, 1,4-cyclohexanedimethanol and isophthalic acid and is contained in an amount of not more than 27 mol %.

15. The heat-shrinkable polyester film according to claim 14 , wherein the polyester resin contains 50 mol % or more of ethylene terephthalate unit, and the monomer capable of forming an amorphous component is at least one selected from neopentyl glycol, 1,4-cyclohexanedimethanol and isophthalic acid and is contained in an amount of not more than 27 mol %, and a glass transition point (Tg) is adjusted to 60 to 80° C.

16. The heat-shrinkable polyester film according to claim 1 , wherein the polyester resin contains 50 mol % or more of ethylene terephthalate unit, and the monomer capable of forming an amorphous component is at least one selected from neopentyl glycol, 1,4-cyclohexanedimethanol and isophthalic acid and is contained in an amount of not more than 27 mol %, and a glass transition point (Tg) is adjusted to 60 to 80° C.

17. A process for producing a heat-shrinkable polyester film comprising:

(a) a lengthwise drawing step of lengthwise drawing a undrawn film so as to provide a total lengthwise draw ratio of not less than 2.8 times and not more than 4.5 times by lengthwise drawing the film in the longitudinal direction at a draw ratio of not less than 2.2 times and not more than 3.0 times at a temperature of not less than Tg and not more than (Tg 30° C.) (first-stage lengthwise drawing) and then lengthwise drawing the film in the longitudinal direction at a draw ratio of not less than 1.2 times and not more than 1.5 times at a temperature of not less than (Tg+10° C.) and not more than (Tg+40° C.);

(b) an annealing step of relaxing the film after lengthwise drawing at a relaxation rate of not less than 10% and not more than 50% in the longitudinal direction while heating the film in the width direction using an infrared heater;

(c) an intermediate heat treatment step of heat-treating the film after annealing for a time period of not less than 1.0 seconds and not more than 9.0 seconds at a temperature of not less than 130° C. and not more than 190° C. with both edges in the width direction being held by clips in a tenter;

(d) a forced cooling step of actively cooling the film after the intermediate heat treatment until the surface temperature becomes a temperature of not less than 80° C. and not more than 120° C.;

(e) a transverse drawing step of drawing the film after forced cooling at a draw ratio of not less than 2.0 times and not more than 6.0 times in the width direction at a temperature of not less than (Tg+10° C.) and not more than (Tg+50° C.); and

(f) a final heat treatment step of heat-treating the film after transverse drawing for a time period of not less than 1.0 seconds and not more than 9.0 seconds at a temperature of the transverse drawing temperature+not less than 15° C. and not more than 40° C. with both edges in the width direction being held by clips in a tenter,

wherein the heat-shrinkable polyester film made of a polyester resin comprising 50% by mol or more ethylene terephthalate and containing at least 7 mol % of at least one monomer capable of forming an amorphous component in the whole component of the polyester resin, wherein the heat-shrinkable polyester film satisfies the requirements (1) to (5) of claim 1 .

18. A package, wherein the heat-shrinkable polyester film of claim 1 is used as a base material and a label provided with perforations or a pair of notches is attached on at least a part of the outer circumference and heat-shrunk.