WO2009151290A2

WO2009151290A2 - Heat-shrinkable polyester film

Info

Publication number: WO2009151290A2
Application number: PCT/KR2009/003145
Authority: WO
Inventors: Nam-Ill Kim; Sung Jun Yoon; Taehoung Jeong
Original assignee: SKC Co Ltd
Current assignee: SKC Co Ltd
Priority date: 2008-06-11
Filing date: 2009-06-11
Publication date: 2009-12-17
Anticipated expiration: 2010-12-11
Also published as: JP2011524921A; JP5901969B2; KR20090128743A; WO2009151290A3; KR100987065B1; CN102066465B; CN102066465A

Abstract

A heat-shrinkable polyester film comprising a divalent acid component and a diol component, the diol component containing ethylene glycol in an amount ranging from 10 to 90% by mole, a compound of formula (I) in an amount ranging from 5 to 85% by mole, and at least one material selected from the group consisting of a straight chain diol having a carbon number of 4 or more, diethylene glycol and a polytetramethylene ether glycol in an amount ranging from 5 to 20% by mole, exhibits superior properties suitable for labeling or shrink-wrapping a container.

Description

HEAT-SHRINKABLE POLYESTER FILM

FIELD OF THE INVENTION

The present invention is directed to a heat-shrinkable polyester film having high performance characteristics in terms of uniform heat-shrinkage, minimized rupture or distortion even after secondary thermal shrinkage, which is suitable for labeling or shrink-wrapping a container.

BACKGROUND OF THE INVENTION

Heat-shrinkable films which undergo shrinkage back the pre-drawn form when heated at a predetermined temperature have been extensively used, e.g., for labeling or shrink-wrapping containers, packaging bundled goods and sealing caps.

Such heat-shrinkable films are made of polyvinyl chloride, polystyrene, or polyester. Conventional heat-shrinkable films made of soft polyvinyl chloride are unsuitable for labeling the whole surface of a container due to a limited maximum heat-shrinkage ratio, and have recently become disfavored because they emit toxic pollutants, e.g., dioxin, on combustion. Oriented polystyrene films, on the other hand, have uniform shrinking properties and they can be easily removed from PET bottles for recycling, but they have the problem of poor heat-resistance.

Therefore, heat-shrinkable polyester films formed of polyethylene terephthalate (PET) which have satisfactory heat-resistance and shrinking properties are preferred for labeling the whole surface of a glass bottle. However, the shrinkage stress and shrinkage ratio of the polyester film are generally unacceptably high, which results in non-uniform shrinkage with consequential distortion, end-bending or rupture, especially when it is subjected to a secondary thermal shrinkage process, e.g., a sterilizing or high temperature-filling process.

Korean Patent Publication No. 2004-37126 discloses that the shrinkage uniformity of a polyester film can be improved by incorporating therein neopentyl glycol and 1,4-cyclohexanedimethanol in specific amounts. In addition, Korean Patent Publication No. 2003-84879 discloses a heat-shrinkable polyester film with good cracking-resistance along the oriented direction, which is obtained by controlling the refractive indices of both the longitudinal and transverse direction of the film. Although such heat-shrinkable films show some improvements in terms of uniform shrinkage or good cracking-resistance when subjected to a first thermal shrinkage step for labeling or shrink-wrapping a container, they still suffer from non-uniform shrinkage, distortion or rupture when reheated in a sterilizing or high temperature-filling process after the first labeling step.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide a heat-shrinkable polyester film having high performance characteristics in terms of uniform heat-shrinkage, minimized rupture or distortion even after secondary thermal shrinkage during a sterilizing or high temperature-filling process, processibility, heat-resistance, and mechanical strength. The inventive film can thus be advantageously used for labeling or shrink-wrapping a container. In accordance with the present invention, there is provided a heat-shrinkable polyester film comprising a divalent acid component and a diol component, wherein: the diol component contains ethylene glycol in an amount ranging from 10 to 90% by mole, a compound of formula (I) in an amount ranging from 5 to 85% by mole, and at least one material selected from the group consisting of a straight chain diol having a carbon number of 4 or more, diethylene glycol, and a polytetramethylene ether glycol in an amount ranging from 5 to 20% by mole; and the polyester film has a residual shrinkage stress of 5 N/D or less and a distortion ratio of 5% or less when it has a thickness of 5 μm after being dipped in 90 °C water for 1 min, the distortion ratio calculated by formula (II) is 5% or less, and it has a thermal shrinkage ratio of 40% or more along the main shrinking direction when treated with 90 °C water for 10 seconds:

Rl HO - CH2 - C - CH2 - OH CO

R2 wherein, Ri and R₂ are each independently hydrogen or straight chain C_J-4 alkyl, with the proviso that Ri and R₂ are not simultaneously hydrogen;

(W - ω) / L x 100 (II)

wherein, W is the width (mm) of the film before heat-treatment, ω is the narrowest width (mm) of the film shrunk by said heat-treatment, and L is the length (mm) of the film shrunk after said heat-treatment.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects and features of the present invention will become apparent from the following description of the invention, when taken in conjunction with the accompanying drawings, which respectively show:

FIG. 1 : a schematic diagram illustrating the method for measuring a change in the film length before and after heat-treatment; and FIG. 2: a schematic diagram showing the method for assessing a skirt phenomenon of a film.

DETAILED DESCRIPTION OF THE INVENTION

The heat-shrinkable polyester film in accordance with the present invention comprising a divalent acid component and a diol component may be prepared by copolymerizing a divalent acid component (i.e., a dicarboxylic acid component) such as terephthalic acid and dimethyl terephthalate with a diol component such as ethylene glycol.

The diol component used in the present invention contains ethylene glycol in an amount ranging from 10 to 90% by mole, a compound of formula (I) in an amount ranging from 5 to 85% by mole, preferably from 10 to 25% by mole, and at least one material selected from the group consisting of a straight chain diol having a carbon number of 4 or more, diethylene glycol, and a polytetramethylene ether glycol in an amount ranging from 5 to 20% by mole, preferably from 7 to 15% by mole.

When the amount of the compound of formula (I) is less than 5% by mole, an unsatisfactory shrinkage ratio may result and the resultant film provided around a container as a label may be easily ruptured by an external impact due to excessive generation of oriented crystals during a heat-treatment process after drawing or when thermally shrunk.

In addition, when the amount of the material selected from a straight chain diol, diethylene glycol, a polytetramethylene ether glycol and a mixture thereof is less than 5% by mole, the residual shrinkage stress and the distortion ratio of the resultant film become disadvantageously high, which leads to a riding up or skirt phenomenon of a label. The riding up phenomenon means that a label is rolled up and climbs along the surface of a container. The skirt phenomenon is distortion which is often observed for a label on a non-round shape container. Whereas, when the amount is more than 20% by mole, rupture of a film label as mentioned above frequently occurs, or the shrinkage ratio of the film intends to undesirably gradually increase due to its too low glass transition temperature (Tg). The inventive film has a residual shrinkage stress of 5 N/D or less, preferably 4 N/D or less, and a distortion ratio which is calculated by formula (II) of 5% or less, preferably 4.5% or less, when it has a thickness of 5 μm after being dipped in 90 ^°C water for 1 min. In accordance with one embodiment of the present invention, prior to dipping, the film may be equipped to a fixing holder in which the distance between chucks is 95 mm, the film having the length of 110 mm in the main shrinking direction and a width of 15 mm in the direction perpendicular to the main shrinking direction. When the residual shrinkage stress of the film exceeds 5 N/D, its distortion ratio becomes higher than a desired level, and when the distortion ratio exceeds 5%, cracking-resistance of a film label becomes poor, or a riding up or skirt phenomenon of a film label is observed.

In addition, the inventive film has a thermal shrinkage ratio of 40% or more, preferably 50% or more along the main shrinking direction when treated with 90 ^°C water for 10 seconds. When the thermal shrinkage ratio is less than 40%, satisfactory shrinkage in a concave part such as the neck of a container may be not achieved.

The inventive film may further comprise various divalent acid and diol components besides major components to the extent they do not adversely affect the film properties. For instance, for the purpose of enhancing a glass transition temperature, i.e., heat-resistance of a film, the inventive film may further comprise a divalent acid component selected from the group consisting of naphthalene-2,6-dicarboxylic acid, isophthalic acid, succinic acid, glutaric acid, adipic acid, suberic acid, axelaic acid, sebacic acid, ester derivatives thereof, and a mixture thereof, as well as a diol component selected from the group consisting of 1 ,4-cyclohexane dimethanol, cyclobutanediol, 1,2-propanediol, 1,3-propanediol, and a mixture thereof.

In accordance with the present invention, in order to enhance withdrawing property or processibility after drawn and heat-set, the film may further comprises a runnability enhancing agent, i.e., a slipping agent, which is an organic or inorganic inert particle, in an amount ranging from 0.01 to

1.0% by weight based on the total weight of the film. A preferable runnability enhancing agent that may be used in the present invention is silica gel, calcium carbonate, alumina, or a mixture thereof, having an average particle diameter of 0.01 to 1 Oμm.

The inventive film may further comprise titanium dioxide which acts to enhance a whitening degree of the film preferably in an amount of 0.1 to 1.0% by weight based on the total weight of the film.

The inventive film may be prepared by conventional methods including a blown technique or tenter method. The use of the tenter method results in enhancement of a slipping property of the resultant film and its dimensional stability in a non-shrinking direction.

Especially, in case of a tenter method, it is preferable that the drawing process is performed at a temperature which is 5 to 10^°C higher than a glass transition temperature (Tg) of a undrawn sheet at a total drawing ratio of 3 to 6.

Then, preferably, the drawn film may be heat-set at a temperature which is 2 to 10°C higher than a drawing temperature. The afore-mentioned drawing and heat-setting conditions contribute to uniformity of the resultant film' s thickness.

In order to give an antistatic property to the film, lower a thermal sticking property of the film within a high-temperature shrinking machine, and enhance a slipping property thereof, if necessary, an antistatic, a water-soluble and thermal sticking-resistant polymer, and a slipping agent may be coated on one or both surfaces of the film, respectively. The coating with an antistatic makes the surface resistance of the film below 10¹⁴ Ω, thereby resulting in accurate capping of the upper part of a container with a film label in a sleeve process. In addition, the film does not exhibit a thermal sticking property at 100°C through the coating with the water-soluble and thermal sticking-resistant polymer.

As described above, the inventive heat-shrinkable polyester film has high performance characteristics in terms of uniform heat-shrinkage, minimized rupture or distortion even after secondary thermal shrinkage, processibility, heat-resistance, and mechanical strength, and thus, it can be advantageously used for labeling or shrink-wrapping a container, particularly a glass bottle.

The present invention is further described and illustrated in Examples, which are, however, not intended to limit the scope of the present invention.

Preparation Example 1 (Polymer A)

25 parts by mole of neophentyl glycol, 20 parts by mole of 1,4-butanediol (BDO) and 170 parts by mole of ethylene glycol based on 100 parts by mole of dimethylene terephthalate (DMT) were placed in a stainless steel monomer-preparation reactor equipped with a stirrer, a distillation column and a condenser, and the temperature was raised to 155^°C . Tetrabutylene titanate (TBT) diluted in n-butanol as a catalyst was added thereto in an amount of 0.03% by weight (as TBT) based on the weight of DMT. While continuously removing methanol formed during the reaction, the temperature was raised to 220 °C over a period of 120 min. After the reaction of 1,4-butanediol was complete, manganese acetate diluted in ethylene glycol was added thereto in an amount of 0.03% by weight based pn the weight of DMT. After the reaction was complete, phosphoric acid (a heat stabilizer) was added thereto in an amount of 0.04% by weight based on the weight of DMT and stirred for 10 min, to obtain a monomer. The monomer thus obtained was transferred to a polymerization reactor equipped with a vacuum unit, and it was allowed to undergo polymerization at 280 °C for about 70 min, to obtain a polyester. The resulting polyester was analyzed by NMR, and the result showed that it contained 22% by mole of neophenetyl glycol (NPG) moiety and 21% by mole of butanediol (BDO) moiety based on 100 moles of DMT.

Preparation Example 2 (Polymer B)

22 parts by mole of neophentyl glycol and 170 parts by mole of ethylene glycol based on 100 parts by mole of DMT were placed in the same reactor as that used in Preparation Example 1, and the temperature was raised to 150^°C . Manganese acetate diluted in ethylene glycol was added thereto in an amount of 0.03% by weight based on the weight of DMT. While continuously removing methanol formed during the reaction, the temperature was raised to 220 ^°C over a period of 120 min. After the monomer-preparation reaction was complete, phosphoric acid diluted in ethylene glycol (a heat stabilizer) was added in an amount of 0.04% by weight based on the weight of DMT, and the temperature was raised to 250 °C while stirring for about 10 min. Antimony trioxide diluted in ethylene glycol was added thereto in an amount of 0.04% by weight based on weight of DMT and stirred for about 5 min, to obtain a monomer. The monomer thus obtained was transferred to a polymerization reactor equipped with a vacuum unit, and it was allowed to undergo polymerization at 280 ^°C for about 80 min, to obtain a polyester. The resulting polyester was analyzed by NMR, and the result showed that it contained about 18% by mole of neophenetyl glycol (NPG) moiety based on 100 moles of DMT.

Preparation Example 3 (Polymer C)

25 parts by mole of 2-butyl-2-ethy 1-1, 3 -propanediol and 170 parts by mole of ethylene glycol based on 100 parts by mole of DMT were placed in the same reactor as that used in Preparation Example 1 , and the temperature was raised to 150°C . Manganese acetate diluted in ethylene glycol was added thereto in an amount of 0.03% by weight based on the weight of DMT. While continuously removing methanol formed during the reaction, the temperature was raised to 220 ^°C over a period of 120 min. After the monomer-preparation reaction was complete, phosphoric acid diluted in ethylene glycol (a heat stabilizer) was added in an amount of 0.04% by weight based on the weight of DMT, and the temperature was raised to 250 ^°C while stirring for about 10 min. Antimony trioxide diluted in ethylene glycol was added thereto in an amount of 0.04% by weight based on weight of DMT and stirred for about 5 min, to obtain a monomer. The monomer thus obtained was transferred to a polymerization reactor equipped with a vacuum unit, and it was allowed to undergo polymerization at 280 ^°C for about 80 min, to obtain a polyester. The resulting polyester was analyzed by NMR, and the result showed that it contained about 21% by mole of 2-butyl-2-ethyl-l,3-propanediol (BEPD) moiety based on 100 moles of DMT.

Preparation Example 4 (Polymer D)

LUPOX HV-1010 grade (available from LG Chemicals Inc.) was employed as polybuthylene terephthalate. Preparation Example 5 (Polymer E)

20 parts by mole of neophentyl glycol (NPG), 8 parts by mole of polytetramethylene ether glycol (PTMEG) having an average molecular weight of 210 and 170 parts by mole of ethylene glycol based on 100 parts by mole of DMT were placed in the same reactor as that used in Preparation Example 1 , and the temperature was raised to 150 ^"C . Manganese acetate diluted in ethylene glycol was added in an amount of 0.03% by weight based on the weight of DMT. While continuously removing methanol formed during the reaction, the temperature was raised to 220 ^°C for 120 min. After the monomer-preparation reaction was complete, phosphoric acid diluted in ethylene glycol (a heat stabilizer) was added thereto in an amount of 0.04% by weight based on the weight of DMT, and the temperature was raised to 250 ^°C while stirring for about 10 min. Antimony trioxide diluted in ethylene glycol was added thereto in an amount of 0.04% by weight based on weight of DMT and stirred for about 5 min, to obtain a monomer. The monomer thus obtained was transferred to a polymerization reactor equipped with a vacuum unit, and it was allowed to undergo polymerization at 280 ^°C for about 80 min, to obtain a polyester. The resulting polyester was analyzed by NMR, and the result showed that it contained about 18% by mole of neophentyl glycol (NPG) moiety and 7% by mole of polytetramethylene ether glycol (PTMEG) moiety based on 100 moles of DMT.

Preparation Example 6 (Polymer F)

Inorganic particle master chips (available from SKC Co., Ltd.) which comprise 18,000 ppm of a silica gel having an average particle diameter of 2.7 μm (a slipping agent) were employed as polyethylene terephthalate (PET) prepared by a conventional polymerization method using dimethylene terephthalate and ethylene glycol.

Preparation Example 7 (Polymer G)

The procedure of Preparation Example 2 was repeated except for using 17 parts by mole of diethylene glycol (DEG) and 170 parts by mole of ethylene glycol based on 100 parts by mole of DMT, to obtain a polyester. The resulting polyester was analyzed by NMR, and the result showed that it contained about 16% by mole of diethylene glycol (DEG) moiety based on 100 moles of DMT.

The compositions, glass transition temperatures (Tg; ^°C) and intrinsic viscosities (IV; g/d-β) of the copolymerized polyesters prepared above are shown in Table 1.

Example 1

96% by weight of polymer A pellets obtained in Preparation Example 1 and 4% by weight of polymer F pellets obtained in Preparation Example 6 were mixed and dried for about 6 hours using a dehumidifying dryer. Thereafter, the dried mixture was melted at 245 ^°C , extruded through a T-die, and the extrudate was passed over a casting roller maintained at about 20 °C , to obtain an amorphous sheet. The amorphous sheet was transferred to a tenter and passed through a heated zone thereof maintained at 80 °C , and the preheated sheet thus obtained was drawn in a total draw ratio of 4.0 by performing a first drawing process at about 75 ^°C and a second drawing process at about 70 ^°C, and the resulting drawn film was heat-set at 75 ^°C within the tenter. The heat-set sheet was cooled just before exiting the tender, to obtain a 50 μm-thick and biaxially oriented polyester film. The properties of the film thus obtained are shown in Tables 2 and 3.

Example 2

50% by weight of polymer A pellets obtained in Preparation Example 1, 46% by weight of polymer B pellets obtained in Preparation Example 2 and 4% by weight of polymer F pellets obtained in Preparation Example 6 were mixed and dried with the same method as that described in Example 1. The dried mixture was melted at 260 ^°C, extruded through a T-die, and the extrudate was passed over a casting roller maintained at 20 ^°C , to obtain an amorphous sheet. The amorphous sheet was transferred to a tenter and passed through a heated zone thereof maintained at 95 ^°C , and the preheated sheet thus obtained was drawn in a total draw ratio of 3.8 by performing a first drawing process at about 85 ^°C and a second drawing process at about 80 °C, and the resulting drawn film was heat-set at 75 ^°C within the tenter. The heat-set sheet was cooled just before exiting the tender, to obtain a 50 /M-thick and biaxially oriented polyester film. The properties of the film thus obtained are shown in Tables 2 and 3.

Example 3

The procedure of Example 2 was repeated except for using 80% by weight of polymer B pellets obtained in Preparation Example 2, 16% by weight of polymer D pellets obtained in Preparation Example 4 and 4% by weight of polymer F pellets obtained in Preparation Example 6, to obtain a 50 μm-thick and biaxially oriented polyester film. The properties of the film thus obtained are shown in Tables 2 and 3.

Example 4

The procedure of Example 2 was repeated except for using 60% by weight of polymer B pellets obtained in Preparation Example 2, 36% by weight of polymer G pellets obtained in Preparation Example 7 and 4% by weight of polymer F pellets obtained in Preparation Example 6, to obtain a 50 μm-thick and biaxially oriented polyester film. The properties of the film thus obtained are shown in Tables 2 and 3.

Example 5

The procedure of Example 2 was repeated except for using 60% by weight of polymer A pellets obtained in Preparation Example 1, 36% by weight of polymer G pellets obtained in Preparation Example 7 and 4% by weight of polymer F pellets obtained in Preparation Example 6, to obtain a 50 μm-thick and biaxially oriented polyester film. The properties of the film thus obtained are shown in Tables 2 and 3.

Example 6

The procedure of Example 2 was repeated except for using 11% by weight of polymer A pellets obtained in Preparation Example 1, 85% by weight of polymer E pellets obtained in Preparation Example 5 and 4% by weight of polymer F pellets obtained in Preparation Example 6, to obtain a 50 μm-thick and biaxially oriented polyester film. The properties of the film thus obtained are shown in Tables 2 and 3.

Example 7

The procedure of Example 2 was repeated except for using 80% by weight of polymer C pellets obtained in Preparation Example 3, 16% by weight of polymer D pellets obtained in Preparation Example 4 and 4% by weight of polymer F pellets obtained in Preparation Example 6, to obtain a 50 μm-thick and biaxially oriented polyester film. The properties of the film thus obtained are shown in Tables 2 and 3.

Comparative Example 1

96% by weight of polymer B pellets obtained in Preparation Example 2, and 4% by weight of polymer F pellets obtained in Preparation Example 6 were mixed and dried in the same method as that described in Example 1. The mixture was melted at 260 ^°C , extruded through a T-die, and the extrudate was passed over a casting roller maintained at 20 ^°C , to obtain an amorphous sheet. The amorphous sheet was transferred to a tenter and passed through a heated zone thereof maintained at 95 ^°C , and the preheated sheet thus obtained was drawn in a total draw ratio of 3.8 by performing a first drawing process at about 85 ^°C and a second drawing process at about 80 ^°C, and the resulting drawn film was heat-set at 75 °C within the tenter. The heat-set sheet was cooled just before exiting the tender, to obtain a 50 μm-thick and biaxially oriented polyester film. The properties of the film thus obtained are shown in Tables 2 and 3.

Comparative Example 2

The procedure of Example 2 was repeated except for using 71% by weight of polymer C pellets obtained in Preparation Example 3, 25% by weight of polymer G pellets obtained in Preparation Example 7 and 4% by weight of polymer F pellets obtained in Preparation Example 6, to obtain a 50 μm-thick and biaxially oriented polyester film. The properties of the film thus obtained are shown in Tables 2 and 3.

Comparative Example 3

The procedure of Example 2 was repeated except for using 71% by weight of polymer C pellets obtained in Preparation Example 3, 25% by weight of polymer D pellets obtained in Preparation Example 4 and 4% by weight of polymer F pellets obtained in Preparation Example 6, controlling a pre-heating temperature to 85°C, and controlling respective drawing temperatures to 75 "C and 70 ^"C, to obtain a 50 μm-thick and biaxially oriented polyester film. The properties of the film thus obtained are shown in Tables 2 and 3.

Performance Test

The properties of the polyester films manufactured in Examples 1 to 7 and Comparative Examples 1 to 3 were measured by the following methods.

(1) Thermal (90 °C water) shrinkage ratio (%)

A film sample was cut into a 300 mm (length) x 15 mm (width) piece, put in a water bath maintained at 90 °C for 10 seconds, and the change in the film length after the heat-treatment was measured. Using the following equation, the degree of shrinkage was calculated.

Thermal shrinkage ratio (%) = [(300- Length of the piece after the heat-treatment) / 300] x 100

(2) Residual shrinkage stress

A film sample was cut into a 120 mm (length) x 15 mm (width) piece and indicated at the points of 5 mm far from both sides to the length direction. The 110 mm-long film sample thus obtained was applied to an apparatus having the distance between chucks of 95 mm and equipped with a load cell for sensing a shrinkage stress attached to one of grips thereof {see FIG. 1). Thereafter, the apparatus equipped with the film sample was put in a water bath maintained at 90 °C, followed by heat-treatment for 1 min when the degree of shrinkage of 13.6% was observed. The shrinkage stress value after the heat-treatment was represented as the unit of N/D, wherein the unit D means the film area corresponding to 50μm x 15mm.

(3) Distortion ratio (%) A film sample was applied to an apparatus in accordance with the same method as that described in the afore-mentioned residual shrinkage stress test. The apparatus equipped with the film sample was put in a water bath maintained at 90 °C, followed by heat-treatment for 1 min when the degree of shrinkage of 13.6% was observed. The film sample heat-treated was separated from the apparatus, and a minimum width thereof was measured. The distortion ratio of the film was calculated using formula (II).

(4) Skirt phenomenon

A film sample was subjected to a solvent adhesion to obtain a sleeve of which a lay flat was 105 mm. The sleeve was cut into a 100 mm-long piece. A square woody pole (each of longitudinal and transverse lengths: 50 mm, height: 20 cm) was wrapped with the cut sleeve. The square woody pole thus obtained was put in a water bath maintained at 90 ^°C for about 30 sec. Referring to Fig. 2, a perpendicular distance (mm) from an edge of the square woody pole to the most distorted part of the film was measured, which was represented as the degree of skirt phenomenon.

(5) Cracking-resistance

A film sample was subjected to a solvent adhesion to obtain a sleeve of which a lay flat was 105 mm. The sleeve was cut into a 200 mm-long piece. A "Byul" glass bottle (available from Kuksundang) was wrapped with the cut sleeve. The glass bottle was put in a water bath maintained at 90 ^°C for about 30 sec, and took out thereof to be cooled to an atmosphere temperature. Thereafter, the sleeve was separated from the glass bottle, and cut into a piece of 70 mm (length direction of the bottle corresponding to the main shrinking direction of sleeve before heat-treatment) x 15 mm (width). The sleeve was elongated at a rate of 200 mm/min using Universal Tester (UTM) having the distance between chucks of 50 mm and the degree of elongation at rupture was measured. An average elongation value derived from 3 tests was taken for each sample, as graded according to the following standards.

O: The average elongation value was 100% or more. Δ: The average elongation value was 50% or more and less than 100%. X: The average elongation value was less than 50%.

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.

Claims

WHAT IS CLAIMED IS:

1. A heat-shrinkable polyester film comprising a divalent acid component and a diol component, wherein: the diol component contains ethylene glycol in an amount ranging from 10 to 90% by mole, a compound of formula (I) in an amount ranging from 5 to 85% by mole, and at least one material selected from the group consisting of a straight chain diol having a carbon number of 4 or more, diethylene glycol, and a polytetramethylene ether glycol in an amount ranging from 5 to 20% by mole; and the polyester film has a residual shrinkage stress of 5 N/D or less and a distortion ratio of 5% or less when it has a thickness of 5 μm after being dipped in 90 ^°C water for 1 min, the distortion ratio calculated by formula (II) is 5% or less, and it has a thermal shrinkage ratio of 40% or more along the main shrinking direction when treated with 90 ^°C water for 10 seconds:

Rl

HO - CH2 - c - cm - OH (!)

wherein, Ri and R₂ are each independently hydrogen or straight chain C_1-4 alkyl, with the proviso that Ri and R₂ are not simultaneously hydrogen;

(W - ω) / L x 100 (II)

2. The heat-shrinkable polyester film of claim 1, wherein an antistatic is coated on one or both surfaces of the film.

3. The heat-shrinkable polyester film of claim 1, wherein a water-soluble and thermal sticking-resistant polymer is coated on one or both surfaces of the film.

4. The heat-shrinkable polyester film of claim 2, wherein the surface resistance of the film is below 10¹⁴ Ω.

5. The heat-shrinkable polyester film of claim 3, which does not exhibit a thermal sticking property at 100°C .

6. The heat-shrinkable polyester film of claim 1, wherein the divalent acid component is terephthalic acid or dimethyl terephthalate.

7. The heat-shrinkable polyester film of claim 1, which has a residual shrinkage stress of 4 N/D or less when its thickness is 5 μm.

8. The heat-shrinkable polyester film of claim 1, which has a distortion ratio of 4.5% or less when its thickness is 5 μm.

9. The heat-shrinkable polyester film of claim 1 , wherein the diol component contains at least one material selected from the group consisting of straight chain diol having a carbon number of 4 or more, diethylene glycol and polytetramethylene ether glycol in an amount ranging from 7 to 15% by mole.

10. The heat-shrinkable polyester film of claim 1, wherein the diol component contains the compound of formula (I) in an amount ranging from 10 to 25% by mole.

11. The heat-shrinkable polyester film of claim 1, which further comprise a diol component selected from the group consisting of 1,4-cyclohexane dimethanol, cyclobutanediol, 1 ,2-propanediol, 1,3-propanediol, and a mixture thereof.

12. The heat-shrinkable polyester film of claim 1, which further comprise a divalent acid component selected from the group consisting of naphthalene-2,6-dicarboxylic acid, isophthalic acid, succinic acid, glutaric acid, adipic acid, suberic acid, axelaic acid, sebacic acid, ester derivatives thereof, and a mixture thereof.

13. The heat-shrinkable polyester film of claim 1, which further comprises an organic or inorganic inert particle in an amount ranging from 0.01 to 1.0% by weight based on the total weight of the film.

14. The heat-shrinkable polyester film of claim 13, wherein the organic or inorganic inert particle is silica gel, calcium carbonate, alumina, or a mixture thereof, having an average particle diameter of 0.01 to lOμm.

15. The heat-shrinkable polyester film of claim 1, which further comprises titanium dioxide in an amount of 0.1 to 1.0% by weight based on the total weight of the film.