Heat shrinkable film and preparation method thereof

1. A heat shrinkable film, which comprises a polyester resin,

wherein heat shrinkage characteristics of the heat shrinkable film in a direction perpendicular to a main shrinkage direction satisfy the following Relationships 1 and 2:

−15≤Δ T 70-65 ≤0  [Relationship 1]

0≤Δ T 100-95 ≤5  [Relationship 2]

wherein ΔT X-Y is a value obtained by subtracting a heat shrinkage rate of the heat shrinkable film in the direction perpendicular to the main shrinkage direction after the heat shrinkable film is immersed in a water bath for 10 seconds at Y° C. from a heat shrinkage rate of the heat shrinkable film in the direction perpendicular to the main shrinkage direction after the heat shrinkable film is immersed in a water bath for 10 seconds at X° C.;

wherein the polyester resin comprises a dicarboxylic acid component and a diol component;

wherein the diol component comprises neopentyl glycol in an amount of 10 to 30 mol % based on a total number of moles of the diol component; and

wherein a heat of crystallization (ΔHc) measured by differential scanning calorimetry (DSC) of the heat shrinkable film is 0 to 30 J/g.

2. The heat shrinkable film of claim 1 , wherein the diol component comprises at least one selected from the group consisting of ethylene glycol (EG), diethylene glycol (DEG), and cyclohexanedimethanol (CHDM).

3. The heat shrinkable film of claim 2 , wherein a content of ethylene glycol is 50 to 80% by mole based on the total number of moles of the diol component, and

a content of diethylene glycol is greater than 0 to 20% by mole based on the total number of moles of the diol component.

4. The heat shrinkable film of claim 2 , wherein a sum of contents of neopentyl glycol and cyclohexanedimethanol is 10 to 40% by mole based on the total number of moles of the diol component.

5. The heat shrinkable film of claim 2 , wherein a content of neopentyl glycol is 20 to 30% by mole based on the total number of moles of the diol component.

6. The heat shrinkable film of claim 1 , whose maximum expansion rate in the direction perpendicular to the main shrinking direction is 3 to 15%.

7. The heat shrinkable film of claim 6 , wherein the maximum expansion rate of the heat shrinkable film is present between 70° C. and 90° C. when the heat shrinkage rate of the heat shrinkable film in the direction perpendicular to the main shrinkage direction is measured at an interval of 5° C. between 50° C. and 100° C.

8. The heat shrinkable film of claim 1 , which satisfies that T 75 is −12 to 0%, that T 80 is −15 to 0%, and that T 85 is −10 to 0%, wherein T Z refers to a heat shrinkage rate in the direction perpendicular to the main shrinkage direction after the heat shrinkable film is immersed in a water bath for 10 seconds at Z° C.

9. A process for preparing the heat shrinkable film of claim 1 , which comprises:

preparing a polyester resin composition;

extruding the composition to obtain an unstretched sheet;

preheating the unstretched sheet at a preheating temperature (T1) of 100 to 110° C.;

stretching the preheated unstretched sheet in one direction to obtain a stretched sheet;

thermally treating the stretched sheet at a thermal treatment temperature (T2) of 70 to 98° C.; and

cooling the thermally treated and stretched sheet to prepare the heat shrinkable film,

wherein the polyester resin composition comprises a dicarboxylic acid component and a diol component;

wherein the diol component comprises neopentyl glycol in an amount of 10 to 30 mol % based on a total number of moles of the diol component; and

wherein a heat of crystallization (ΔHc) measured by differential scanning calorimetry (DSC) of the heat shrinkable film is 0 to 30 J/g.

10. The process for preparing a heat shrinkable film of claim 9 , wherein the extrusion is carried out at 260 to 300° C.

11. The process for preparing a heat shrinkable film of claim 9 , wherein T1-T2 is 10 to 40° C.

12. The process for preparing a heat shrinkable film of claim 9 , wherein the preheating is carried out for 0.01 to 1 minute.

13. The process for preparing a heat shrinkable film of claim 9 , wherein the stretching is carried out at a stretching ratio of 3 to 5 times in one direction.

14. The process for preparing a heat shrinkable film of claim 9 , which further comprises printing on the heat shrinkable film.

15. The process for preparing a heat shrinkable film of claim 9 , wherein the heat shrinkage characteristics of the heat shrinkable film in the direction perpendicular to the main shrinkage direction satisfy the following Relationships 1 and 2:

−15≤Δ T 70-65 ≤0  [Relationship 1]

0≤Δ T 100-95 ≤5  [Relationship 2]

wherein ΔT X-Y is a value obtained by subtracting a heat shrinkage rate of the heat shrinkable film in the direction perpendicular to the main shrinkage direction after the heat shrinkable film is immersed in a water bath for 10 seconds at Y° C. from a heat shrinkage rate of the heat shrinkable film in the direction perpendicular to the main shrinkage direction after the heat shrinkable film is immersed in a water bath for 10 seconds at X° C.

16. The process for preparing a heat shrinkable film of claim 9 ,

the diol component further comprises at least one selected from the group consisting of ethylene glycol (EG), diethylene glycol (DEG), and cyclohexanedimethanol (CHDM), and

a sum of contents of neopentyl glycol and cyclohexanedimethanol is 10 to 40% by mole based on the total number of moles of the diol component.