HEAT-SHRINKABLE FILM AND PROCESS FOR PREPARING THE SAME
The embodiments relate to a heat-shrinkable film and a process for preparing the same. The heat-shrinkable film comprises a mixed resin, wherein the mixed resin comprises a copolymerized polyester-based resin in which a diol and a dicarboxylic acid are copolymerized; and a polybutylene terephthalate-based resin, and, when a specimen of the heat-shrinkable film having a width of 15 mm, a length of 110 mm, and a thickness of 45 μm is immersed in hot water at 70° C. for 60 seconds to measure shrinkage stress, the development time of the initial shrinkage stress is 20 seconds or shorter. The heat-shrinkable film according to the embodiment comprises a mixed resin having a specific composition, wherein the development time of the initial shrinkage stress is controlled.
1 . A heat-shrinkable film, which comprises a mixed resin, wherein the mixed resin comprises a copolymerized polyester-based resin in which a diol and a dicarboxylic acid are copolymerized; and a polybutylene terephthalate-based resin, and
when a specimen of the heat-shrinkable film having a width of 15 mm, a length of 110 mm, and a thickness of 45 μm is immersed in hot water at 70° C. for 60 seconds to measure shrinkage stress, the development time of the initial shrinkage stress is 20 seconds or shorter.
2 . The heat-shrinkable film of claim 1 , wherein when the heat-shrinkable film specimen is immersed in hot water at 70° C. for 60 seconds to measure shrinkage stress, the maximum shrinkage stress is 2.5 N to 10.0 N.
3 . The heat-shrinkable film of claim 1 , wherein the difference (Tc−Tg) between the crystallization temperature (Tc) and the glass transition temperature (Tg) of the heat-shrinkable film is 10° C. or more.
4 . The heat-shrinkable film of claim 1 , wherein the clumping ratio (CR) is 10% or less as represented by the following Equation 1:
Clumping
ratio
(
CR
,
%
)
=
C
1
9
5
C
2
5
×
1
0
0
[
Equation
1
]
in Equation 1, C 25 is the initial weight (g) of mixed flakes obtained by crushing a polyethylene terephthalate (PET) container provided with the heat-shrinkable film at 25° C., and C 195 is the weight (g) of aggregated flakes that have not been filtered through a 12.5-mm sieve when the mixed flakes obtained by crushing the polyethylene terephthalate (PET) container provided with the heat-shrinkable film are thermally treated at 195° C. for 90 minutes and then filtered.
5 . The heat-shrinkable film of claim 1 , wherein the heat-shrinkable film has a heat shrinkage rate of 45% or more as represented by the following Equation 2:
Heat
shrinkage
rate
(
TS
100
,
%
)
=
x
1
-
x
2
x
1
×
1
0
0
[
Equation
2
]
in Equation 2, x1 is the initial length of the heat-shrinkable film specimen measured at 25° C., and x2 is the length of the heat-shrinkable film specimen, after shrinkage, measured after immersion in hot water at 100° C. for 10 seconds.
6 . The heat-shrinkable film of claim 1 , wherein the thickness deviation (R) is 15 μm or less as represented by the following Equation 3:
Thickness
deviation
(
R
,
µm
)
=
TA
-
TF
[
Equation
3
]
in Equation 3, TA and TF are values calculated using the thicknesses measured with a thickness gauge at intervals of 2 cm in the transverse direction (TD) with the center point in the longitudinal direction (MD) of the heat-shrinkable film specimen having a width of 300 mm and a length of 200 mm as an axis,
TA is the average thickness (μm) of the heat-shrinkable film, and
TF is the thickness (μm) showing the maximum difference from the average thickness among the measured thicknesses.
7 . The heat-shrinkable film of claim 1 , wherein the polybutylene terephthalate-based resin is employed in an amount of 0.5% by weight to 50% by weight based on the total weight of the mixed resin.
8 . The heat-shrinkable film of claim 1 , wherein the diol comprises ethylene glycol, and it comprises at least one comonomer selected from the group consisting of neopentyl glycol and diethylene glycol in an amount of 10% by mole or more based on the total moles of the diol.
9 . The heat-shrinkable film of claim 8 , wherein the diol comprises diethylene glycol in an amount of 2.5% by mole to 10.0% by mole based on the total number of moles of the diol.
10 . The heat-shrinkable film of claim 8 , wherein the comonomer comprises neopentyl glycol and diethylene glycol, and the molar ratio of neopentyl glycol and diethylene glycol is 1:0.10 to 0.40.
11 . The heat-shrinkable film of claim 1 , wherein the copolymerized polyester-based resin is at least one selected from the group consisting of a virgin copolymerized polyester-based resin and a recycled copolymerized polyester-based resin.
12 . A process for preparing the heat-shrinkable film of claim 1 , which comprises:
preparing a copolymerized polyester-based resin in which a diol and a dicarboxylic acid are copolymerized;
mixing the copolymerized polyester-based resin and a polybutylene terephthalate-based resin to prepare a mixed resin;
extruding the mixed resin to prepare an unstretched sheet; and
stretching and heat-setting the unstretched sheet to prepare a heat-shrinkable film.
13 . The process for preparing the heat-shrinkable film according to claim 12 , which further comprises preheating the unstretched sheet at 70° C. to 150° C. before the stretching.
14 . The process for preparing the heat-shrinkable film according to claim 13 , wherein the stretching is carried out at a temperature lower than the preheating temperature by 5° C. or more.