THERMO-SHRINKABLE POLYESTER FILM

Abstract

This disclosure relates to a thermo-shrinkable polyester film with excellent UV absorbance and heat resistance. According to one embodiment of the invention, provided is a thermo-shrinkable polyester film comprising a first resin layer comprising polyester resin comprising residues of dicarboxylic acid components comprising aromatic dicarboxylic acid, and residues of diol components comprising 4-(hydroxymethyl)cyclohexylmethyl 4′-(hydroxymethyl)cyclohexanecarboxylate, and 4,4-(oxybis(methylene)bis)cyclohexane methanol; and a second resin layer comprising the polyester resin and a UV absorber, formed on at least one side of the first layer.

Claims

1. A thermo-shrinkable polyester film comprising a first resin layer comprising polyester resin comprising residues of dicarboxylic acid components comprising aromatic dicarboxylic acid, and residues of diol components comprising 4-(hydroxymethyl)cyclohexylmethyl 4′-(hydroxymethyl)cyclohexanecarboxylate, and 4,4-(oxybis(methylene)bis)cyclohexane methanol; and a second resin layer comprising the polyester resin and a UV absorber, formed on at least one side of the first layer.

2. The thermo-shrinkable polyester film according to claim 1, wherein the contents of 4-(hydroxymethyl)cyclohexylmethyl 4′-(hydroxymethyl)cyclohexanecarboxylate, and 4,4-(oxybis(methylene)bis)cyclohexane methanol are respectively 0.1 to 20 mol %, based on 100 mol % of the dicarboxylic acid component.

3. The thermo-shrinkable polyester film according to claim 1, wherein the residues of diol components further comprise residues of at least one compound selected from the group consisting of 1,4-cyclohexanedimethanol, diethyleneglycol and ethyleneglycol.

4. The thermo-shrinkable polyester film according to claim 3, wherein based on 100 mol % of the dicarboxylic acid component, the content of 1,4-cyclohexanedimethanol is 0.1 to 15 mol %, the content of diethyleneglycol is 1 to 20 mol %, and the content of ethyleneglycol is 30 to 95 mol %.

5. The thermo-shrinkable polyester film according to claim 1, wherein the aromatic dicarboxylic acid includes at least one compound selected from the group consisting of terephthalic acid, dimethyl terephthalate, cycloaliphatic dicarboxylic acid, isophthalic acid, adipic acid, azelaic acid, naphthalenedicarboxylic acid, and succinic acid.

6. The thermo-shrinkable polyester film according to claim 1, wherein the UV absorber includes at least one compound selected from the group consisting of benzotriazole, benzophenone, salycylate, cyanoacrylate, oxanilide, and hindered amine light stabilizer (HALS).

7. The thermo-shrinkable polyester film according to claim 1, wherein the UV absorber is included in the content of 0.1 to 3 wt % in the second resin layer.

8. The thermo-shrinkable polyester film according to claim 1, wherein the second resin layer further comprises at least one additive selected from the group consisting of an antioxidant, a heat stabilizer, a release agent, an agent for applying electrostatic force, an anti-sticking agent and an impact modifier.

9. The thermo-shrinkable polyester film according to claim 1, wherein the film has a thickness of 10 μm to 1 mm.

10. The thermo-shrinkable polyester film according to claim 1, wherein the film has light transmittance of 10% or less at a wavelength of 360 nm or less, and light transmittance of 60% or more at a wavelength of 400 nm, and delta E of 1 or less when exposed to UV (320˜400 nm) wavelength for 500 hours.

11. The thermo-shrinkable polyester film according to claim 1, wherein the film has shrink onset temperature of 65° C. or less, and maximum thermal shrinkage at 65° C. of less than 50% and maximum thermal shrinkage at 90 to 100° C. of 55 to 90%.

12. The thermo-shrinkable polyester film according to claim 1, wherein the film is prepared by extrusion blowing of polyester resin, or stretching 3 to 6 times in a TD (Transverse Direction) using a stretching and extruding machine.

Description

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0055] The present invention will be explained in detail in the following Examples. However, these examples are only to illustrate the invention, and the scope of the invention is not limited thereto.

Preparation Example 1: Preparation of Polyester Resin

[0056] Each 100 moles of dicarboxylic acid component and diol component were introduced into a 3 kg batch reactor and mixed, and temperature was gradually raised to 255° C. to progress esterification reaction. Wherein, as the dicarboyxlic acid component, 100 moles of terephthalic acid was introduced, and as the diol component, 2 moles of 4-(hydroxymethyl) cyclohexanecarboxylic acid, 6 moles of 4,4-(oxybis(methylene)bis) cyclohexane methanol, 5 moles of 1,4-cyclohexanedimethanol, 10 moles of diethyleneglycol, and the remaining amount of ethyleneglycol were introduced.

[0057] Wherein, generated water was discharged outside of the system, and when the generation and discharging of water was finished, the reactant was transferred to a polycondensation reactor equipped with a stirrer, a cooling condenser and vacuum system.

[0058] After adding 0.5 g of tetrabutyl titanate, 0.4 g of triethylphosphate and 0.5 g of cobalt acetate to the esterification product, while the internal temperature of the reactor was raised from 240° C. to 275° C. and the pressure was primarily reduced from atmospheric pressure to 50 mmHg, ethyleneglycol was taken out by low vacuum reaction for 40 minutes, and then, the pressure was gradually reduced again to 0.1 mmHg, polycondensation was progressed under high vacuum until target intrinsic viscosity was achieved, and the product was discharged to prepare polyester resin chip.

Preparation Example 2: Preparation of Polyester Resin Chip

[0059] Polyester resin was prepared by the same method as Example 1, except that as the diol component, 8 moles of 4-(hydroxymethyl) cyclohexane carboxylic acid, 2 moles of 4,4-(oxybis(methylene)bis)cyclohexane methanol, 10 moles of 1,4-cyclohexanedimethanol, 10 moles of diethyleneglycol, and the remaining amount of ethyleneglycol were introduced.

Preparation Example 3: Preparation of Polyester Resin Including UV Absorber

[0060] To the resin prepared according to Preparation Example 1, a UV absorber was melt-mixed in an extruder at 1 to 10 phr, to prepare a polyester resin composition including polyester resin and a UV absorber in the form of a master chip.

Preparation Example 4: Preparation of Polyester Resin Including UV Absorber

[0061] To the resin prepared according to Preparation Example 2, a UV absorber was melt-mixed in an extruder at 1 to 10 phr, to prepare a polyester resin composition including polyester resin and a UV absorber in the form of a master chip

Example 1: Preparation of Bilayered Thermo-Shrinkable Polyester Film

[0062] The master chip of the composition prepared according to Preparation Example 3, and the resin prepared according to Preparation Example 1 were molten at 260 to 290° C. and co-extruded from a T die, and then, quenched in a cooling roller to obtain a non-stretched film. The obtained non-stretched film was stretched 3 to 6 times in a transverse direction at a stretching temperature of 75 to 90° C., at a stretching speed of 60 mm/sec, to obtain a thermo-shrinkable polyester film.

Example 2: Preparation of Bilayered Thermo-Shrinkable Polyester Film

[0063] A thermo-shrinkable polyester film was obtained by the same method as Example 1, except that the master chip of the composition prepared according to Preparation Example 3 and the resin prepared according to Preparation Example 2 were co-extruded.

Example 3: Preparation of Three-Layered Thermo-Shrinkable Polyester Film

[0064] On both side of the resin prepared according to Preparation Example 2, the composition prepared according to Preparation Example 3 were positioned, and they were molten at 260 to 290° C. and co-extruded from a T die, and then, quenched in a cooling roller to obtain a non-stretched film. Thereafter, a stretching process was progressed by the same method as Example 1, to prepare a three-layered thermo-shrinkable film having second resin layers including UV absorber respectively formed on both sides of the first resin layer.

Comparative Example 1

[0065] A thermo-shrinkable polyester film was obtained by the same method as Example 1, except that only the resin prepared according to Preparation Example 1 was extruded.

Comparative Example 2

[0066] A thermo-shrinkable polyester film was obtained by the same method as Example 1, except that only the resin prepared according to Preparation Example 2 was extruded.

Comparative Example 3

[0067] A polyester resin chip was obtained by the same method as Preparation Example 1, except that as the diol components, 10 moles of 1,4-cyclohexanedimethanol, 10 moles of diethyleneglycol, and 80 moles of ethyleneglycol were used.

[0068] The polyester resin chip was molten at 260 to 290° C., and extruded from a T die, and then, quenched in a cooling roller to obtain a non-stretched film. The obtained non-stretched film was stretched 3 to 6 times in a transverse direction at a stretching temperature of 75 to 90° C., at a stretching speed of 60 mm/sec, to obtain a thermo-shrinkable polyester film.

Comparative Example 4

[0069] A polyester resin chip was obtained by the same method as Preparation Example 1, except that as the diol components, 20 moles of 1,4-cyclohexanedimethanol, and 80 moles of ethyleneglycol were used.

[0070] The polyester resin chip was molten at 260 to 290° C., and extruded from a T die, and then, quenched in a cooling roller to obtain a non-stretched film. The obtained non-stretched film was stretched 3 to 6 times in a transverse direction at a stretching temperature of 75 to 90° C., at a stretching speed of 60 mm/sec, to obtain a thermo-shrinkable polyester film.

Experimental Example: Measurement of Properties of Thermo-Shrinkable Polyester Film

[0071] The properties of the thermo-shrinkable films obtained in Examples and Comparative Examples were measured as follows, and the results are shown in the following Table 1.

[0072] (1) Glass Transition Temperature (Tg)

[0073] In order to assess heat resistance, the thermo-shrinkable film was annealed at 300° C. for 5 minutes, and cooled to room temperature, and then, Tg was measured at 2.sup.nd Scan, at a temperature raising rate of 10° C./min.

[0074] (2) Light Transmittance

[0075] Using a UV/Vis spectrometer, maximum light transmittance (%) at a wavelength of 360 nm or less and light transmittance (%) at a wavelength of 400 nm were respectively measured.

[0076] (3) Delta E

[0077] After exposure to UVA (320˜400 nm) wavelength for 500 hours, delta E was measured using a UV/vis spectrometer (Delta E is a measure of color change, and increases as color change is larger).

[0078] (4) Thermal Shrinkage

[0079] The thermo-shrinkable film was cut out to 10 cm×10 cm square, and immersed in hot water of the temperature described in the following Table 1 (65° C. and 95° C.) for 10 seconds under no-load condition to thermally shrink, and then, immersed in hot water of 25° C. for 10 hours. And then, the lengths of the machine direction and transverse direction of the specimen were measured, and thermal shrinkage was calculated according to the following Equation.

Thermal shrinkage (%)=100×(length before shrink−length after shrink)/(length before shrink)

TABLE-US-00001 TABLE 1 Example Example Example Comparative Comparative Comparative Comparative 1 2 3 Example 1 Example 2 Example 3 Example 4 Tg (glass transition 68 69 69 71 71 77 78 temperature, ° C. ) Transmittance at 2 1 2 43 41 42 43 360 nm or less (%) Transmittance at 71 70 69 67 68 67 67 400 nm (%) Delta E 0.5 0.6 0.5 10 13 12 14 (exposure for UVA 500 hours) Thermal MD 3 4 4 3 4 7 10 shrinkage @65° C. (%) TD 32 33 30 25 26 5 4 @65° C. MD 5 5 6 5 6 7 7 @95° C. TD 75 79 78 75 77 60 65 @95° C.

[0080] From the Table 1, it can be seen that the thermo-shrinkable polyester films prepared according to Examples 1 to 3 exhibit glass transition temperature of 65° C. or more, thus having excellent heat resistance. It was also confirmed that the thermo-shrinkable polyester films have shrink onset temperature of 65° C. or less, and exhibit maximum shrinkage at 95° C. of 75% or more, and thus, have very excellent thermal shrinkage.

[0081] Therefore, it is expected that if the thermo-shrinkable polyester film according to the present invention is used as a thermo-shrinkable label, it can be thermally shrunken at low temperature, and thus, is favorable in terms of energy saving, and yet, has high maximum shrinkage of about 70˜90%, affording high degree of freedom of design, and thus, is useful in the industrial application. It is also expected that since the thermo-shrinkable polyester film comprises a resin layer including a UV absorber, it can prevent spoilage of the contents protected by the thermo-shrinkable film due to excellent UV shielding capacity, and has little color change, thus exhibiting excellent appearance.

[0082] Thus, it can be seen that the multilayered thermo-shrinkable polyester film according to the present invention is usefully applied for medical or functional products requiring UV shielding function and prevention of modification or shrinking of films.

[0083] Although specific embodiments of the invention have been described in detail, it would be obvious to one of ordinary knowledge in the art that such specific technologies are only preferable practice embodiments and the scope of the invention is not limited thereto. Thus, the substantive scope of the invention is defined by attached claims and equivalents thereof.