Heat-shrinkable polyester film

Abstract

Disclosed is a heat-shrinkable polyester film having a heat shrinkage initiation temperature of 60 C. or lower, a glass transition temperature (Tg) of 77 C. or lower and a heat shrinkage rate of 2% or more at 60 C. which has relatively low glass transition temperature and heat shrinkage initiation temperature, and thus can be useful as a label for a high-density polyethylene (HDPE) container and the like.

Claims

1. A heat-shrinkable polyester film having a heat shrinkage initiation temperature of 60 C. or lower, a glass transition temperature (Tg) of 77 C. or lower and a heat shrinkage rate of 2% or more at 60 C., wherein the film has a heat shrinkage rate of 15% or more at 65 C., 42% or more at 70 C., and 70% or more at 80 C.; wherein the film is prepared by random-copolymerization of one kind of a dibasic acid component with three kinds of diol components; wherein the dibasic acid component (A1) is one of terephthalic acid and dimethyl terephthalate; and wherein the diol components are (B1) ethylene glycol, (B2) one of neopentyl glycol and cyclohexanedimethanol, and (B3) a linear diol component having three or more carbon atoms at a main chain thereof.

2. The heat-shrinkable polyester film of claim 1, wherein the film has a heat shrinkage initiation temperature in a range of 55 C. to 60 C., a glass transition temperature in a range of 70 C. to 77 C., and a heat shrinkage rate of 2% to 10% at 60 C., 15% to 40% at 65 C., 42% to 60% at 70 C., and 70% to 75% at 80 C.

3. The heat-shrinkable polyester film of claim 1, wherein the diol component (B3) is selected from the group consisting of diethylene glycol, 1,3-propanediol, 1,4-butanediol and 1,5-pentanediol.

4. The heat-shrinkable polyester film of claim 1, wherein the amounts of (B1), (B2), and (B3) of the diol components are 60 to 90 mol %, 5 to 30 mol %, and 1 to 20 mol %, respectively, based on the total amount of (B1), (B2), and (B3).

5. The heat-shrinkable polyester film of claim 1, wherein the amounts of (B1), (B2), and (B3) of the diol compounds are 60 to 85 mol %, 10 to 25 mol %, and 1 to 15 mol %, respectively, based on the total amount of (B1), (B2), and (B3).

6. The heat-shrinkable polyester film of claim 1, wherein the heat-shrinkable polyester film is uniaxially stretched in the main contraction direction thereof.

7. A label for container comprising the heat-shrinkable polyester film of claim 1.

8. The label of claim 7, wherein the label for container is used as a label for a high-density polyethylene container.

Description

DETAILED DESCRIPTION OF THE INVENTION

(1) Hereinafter, the present invention will be described in more detail.

(2) The heat-shrinkable polyester film may be prepared by random copolymerization of one kind of dibasic acid component with three kinds of diol components.

(3) In a preferred embodiment of the present invention, the heat-shrinkable polyester film may be prepared by random-copolymerization of (A1) one of terephthalic acid and dimethyl terephthalate as the dibasic acid component with (B1) ethylene glycol, (B2) one of neopentyl glycol and cyclohexanedimethanol and (B3) a linear diol component having three or more carbon atoms at a main chain thereof as the diol components.

(4) In the diol components, the component (B3) may be selected from the group consisting of diethylene glycol, 1,3-propanediol, 1,4-butanediol and 1,5-pentanediol.

(5) Further, in the diol components (B1) to (B3), preferably, the amount of the component (B1) may be 60 to 90 mol %, the amount of the component (B2) may be 5 to 30 mol % and the amount of the component (B3) may be 1 to 20 mol %. More preferably, the amount of the component (B1) may be 60 to 85 mol %, the amount of the component (B2) may be 10 to 25 mol % and the amount of the component (B3) may be 1 to 15 mol %.

(6) As a result, a polymer constituting the heat-shrinkable polyester film may be a random copolymer having the following repetitive units:

(7) ##STR00001##

(8) wherein each of x, y and z is the number of repetitive units.

(9) The heat-shrinkable polyester film of the present invention having the above composition ratio may have a heat shrinkage initiation temperature of 60 C. or lower, and preferably, 55 C. to 60 C. because the glass transition temperature (Tg) of the heat-shrinkable polyester film is lower than that (about 78 C. to 80 C.) of a conventional polyester film. The heat-shrinkable polyester film of the present invention may have a glass transition temperature of 77 C. or lower, preferably 70 C. to 77 C., and more preferably 70 C. to 75 C.

(10) As a result, the heat-shrinkable polyester film of the present invention exhibits a heat shrinkage rate different from that of a conventional polyester film. Specifically, when this heat-shrinkable polyester film was heat-treated in a water tank for 10 seconds, it is preferred that the heat shrinkage rate of the heat-shrinkable polyester film in the main contraction direction is 2% or more at 60 C., 15% or more at 65 C., 42% or more at 70 C., and 70% or more at 80 C. More preferably, the heat shrinkage rate thereof may be 2% to 10% at 60 C., 15% to 40% at 65 C., 42% to 60% at 70 C., and 70% to 75% at 80 C.

(11) The heat-shrinkable polyester film of the present invention may be prepared by a method comprising the steps of: (a) mixing and polymerizing one kind of dibasic acid with three kinds of diols to obtain a random copolymer resin; (b) melting and extruding the random copolymer resin to obtain an unstretched sheet; and (c) stretching the unstretched sheet in the main contraction direction thereof and then thermally fixing the stretched sheet.

(12) In step (b), the melting-extruding temperature of the random copolymer resin may be 260 C. to 285 C.

(13) In step (c), the stretching ratio of the unstretched sheet may be 1:3.5 to 1:4.5, and the thermal fixing temperature of the stretched sheet may be 65 C. to 95 C.

(14) The thickness of the heat-shrinkable polyester film prepared in accordance with the present invention may be 20 m to 90 m.

(15) The present invention provides a label for container comprising the heat-shrinkable polyester film of the present invention.

(16) The label for container may be used as a label for a high-density polyethylene (HDPE) container. In this case, since the shrinkage initiation temperature of the heat-shrinkable polyester film is lower than that of a conventional polyester film, the heat-shrinkable polyester film is thermally contracted and labeled on the HDPE container before the HDPE container is fully expanded, and thus the adhesion between the heat-shrinkable polyester film and the HDPE container can be maintained even after the HDPE container is contracted at room temperature.

(17) Hereinafter, the present invention is described more specifically by the following examples, but these are provided only for illustration purposes and the present invention is not limited thereto.

Examples 1 to 3 and Comparative Examples 1 and 2

Preparation of Heat-Shrinkable Polyester Films

(18) Copolymerized polyester resins were prepared according to the composition ratio given in Table 1 below. The prepared copolymerized polyester resins were melted and extruded, stretched in the main contraction direction thereof, and then thermally fixed to manufacture heat-shrinkable polyester films with thickness of 40 m, respectively. In this process, the polymerization reaction conditions and other process conditions were set in accordance with standard preparation methods for polyester film commonly known and used in the art.

(19) TABLE-US-00001 TABLE 1 Com- Com- Composition ratio Exam- Exam- Exam- parative parative (mol %) ple 1 ple 2 ple 3 Example 1 Example 2 Dibasic TPA 100 100 100 100 100 acid EG 80 75 70 80 75 Diols NPG 15 15 20 CHDM 20 25 DEG 5 10 1,4-BDO 10 TPA: terephthalic acid, EG: ethylene glycol NPG: neopentyl glycol, DEG: diethylene glycol 1,4-BDO: 1,4-butanediol, CHDM: 1,4-cyclohexanedimethanol

(20) The polyester films prepared in Examples 1 to 3 and Comparative Examples 1 and 2 were evaluated using the following test methods, and the results thereof are shown in Table 2 below.

Test Example 1

Heat Shrinkage Rate

(21) Test samples were cut to a size of 300 mm (length)15 mm (width), and then heat-treated in a water bath maintaining a predetermined temperature for 10 seconds, and then the lengths of the heat-treated test samples were measured. The heat shrinkage rate of each of the test samples was calculated by the following equation:
Heat shrinkage rate (%)=[(300test sample length after heat treatment (mm))/300]100

Test Example 2

Evaluation of Defect Rate (Labeling Performance) of HDPE Container

(22) When each of the polyester films prepared in Examples 1 to 3 and Comparative Examples 1 and 2 was labeled on one hundred HDPE containers and then pressure was applied by hand. If the label became loose enough to be folded, the labeled HDPE container was counted as defective. The number of the defective HDPE containers in one hundred HDPE containers was represented by a percentage. Based on this result, the labeling performance of each of the polyester films was evaluated as follows:

(23) Good: defect rate of less than 5%

(24) Poor: defect rate of 5% or more

Test Example 3

Glass Transition Temperature (Tg)

(25) Glass transition temperatures of each of the polyester films were measured using a differential scanning calorimeter (Q100, TA Corporation).

(26) TABLE-US-00002 TABLE 2 Com- Com- parative Exam- Exam- Exam- parative Exam- Categories ple 1 ple 2 ple 3 Example 1 ple 2 Heat 60 C. 2 5 5 0 0 shrinkage 65 C. 23 36 30 0 0 rate 70 C. 45 50 48 25 20 (%) 80 C. 72 73 73 72 72 90 C. 75.5 75.5 75.5 75.5 75.5 100 C. 76.7 76.7 76.7 76.7 76.7 Defect rate of 3 1 1 90 90 container (%) Evaluation of labeling good good good poor poor performance Tg ( C.) 75 72 72 79 84

(27) As shown in Table 2 above, it can be ascertained that each of the heat-shrinkable polyester films of Examples 1 to 3 maintains adhesivity even after it is labeled on a HDPE container because its shrinkage initiation temperature is 60 C. or lower. In contrast, each of the polyester films prepared in accordance with Comparative Examples 1 and 2 becomes loose after it is labeled on the HDPE container due to their high shrinkage initiation temperatures.

(28) While the invention has been described with respect to the above specific embodiments, it should be recognized that various modifications and changes may be made to the invention by those skilled in the art which also fall within the scope of the invention as defined by the appended claims.