Polyester film, heat-shrinkable label and packaging comprising same
The polyester film according to the embodiment prepared while the crystallinity of a copolymerized polyester film is controlled can be improved in thermal properties and chemical properties. Specifically, the polyester film has not only an excellent shrinkage rate with respect to temperature, but also excellent adhesive strength by a solvent even when applied to gravure printing, UV curing printing, and VSOP printing, making it suitable for a heat shrinkage process and a seaming process. In addition, the polyester film can be applied to a recycling process since it has an appropriate change in crystals during washing with an aqueous solution of NaOH, and the generation of fusion is suppressed even upon prolonged high-temperature drying.
1 . A polyester film, which comprises a polyester resin in which a diol comprising ethylene glycol and diethylene glycol; and a dicarboxylic acid are copolymerized,
wherein the difference between the crystallization temperature (Tc) and the melting temperature (Tm) measured by a differential scanning calorimeter (DSC) is 100° C. or less, and the film has an endothermic peak at 100° C. to 150° C. when measured with a differential scanning calorimeter (DSC) upon treatment with a 1% aqueous solution of NaOH at 85° C. for 15 minutes,
wherein the polyester film has a difference in reversible heat capacity (ΔC0p) of 0.25 J/g·K or more before and after the glass transition temperature (Tg) as measured when it is subjected to first scan by a differential scanning calorimeter (DSC) from room temperature to 300° C. at a temperature elevation rate of 3° C./minute, followed by cooling thereof, and to second scan under the same conditions,
wherein the polyester film has a shrinkage ratio of 74 to 80% in a transverse direction (TD) when heat-treated at a temperature of 80° C. for 10 seconds, and
wherein the difference between the endothermic peak temperature and the melting temperature is 50° C. to 90° C.
2 . The polyester film of claim 1 , wherein the difference between the endothermic peak temperature and the melting temperature is 75° C. to 85° C.
3 . The polyester film of claim 1 , wherein the difference between the crystallization temperature (Tc) and the melting temperature (Tm) measured by a differential scanning calorimeter (DSC) is 65° C. to 100° C.
4 . The polyester film of claim 1 , wherein the difference between the difference (ΔCp) in reversible heat capacity before and after the glass transition temperature (Tg) measured through the first scan and the difference (ΔC0p) in reversible heat capacity before and after the glass transition temperature (Tg) measured through the second scan is 0.01 J/g·K to 0.3 J/g·K.
5 . The polyester film of claim 1 , wherein the polyester film has a maximum peak at a diffraction angle (2θ) of less than 25° in an X-ray diffraction (XRD) spectrum.
6 . The polyester film of claim 1 , wherein the polyester film has a shrinkage rate of 60% to 80% in the main shrinkage direction upon thermal treatment at a temperature of 100° C. for 10 seconds.
7 . The polyester film of claim 1 , wherein, when one sheet of the polyester film is coated with a glycol-based solution and is then adhered with another sheet of the polyester film by 1,3-dioxolane, the peel strength is 500 gf/in or more.
8 . The polyester film of claim 1 , wherein, when the polyester film is crushed to a particle size of 9.5 mm to 12 mm, thermally treated at a temperature of 210° C. under a load of 2.5 kgf for 90 minutes, and passed through a sieve having a hole size of 12.5 mm, the ratio that does not pass may be 5% or less.
9 . The polyester film of claim 1 , wherein the diol further comprises at least one comonomer selected from neopentyl glycol and cyclohexanedimethanol in an amount of 20% by mole to 30% by mole.
10 . The polyester film of claim 1 , wherein the diol further comprises neopentyl glycol in an amount of 20% by mole to 40% by mole.
11 . The polyester film of claim 1 , wherein the diol comprises the diethylene glycol in an amount of 1% by mole to 5% by mole.
12 . A heat shrinkable label, which comprises the polyester film of claim 1 .
13 . A heat shrinkable packaging material, which comprises the polyester film of claim 1 .