JP2001192477A - Thermally shrinkable polyester-based film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermally shrinkable polyester-based film which scarcely generates shrinkage irregularity and further defects such as wrinkles, distortion and folds, when shrunk in a hot air shrinkage process, thereby enabling to give a beautiful shrunk finish appearance, especially scarcely deteriorates the shrinkage finish property on storage, and can suitably be used in the uses of full labels and cap seals. SOLUTION: This thermally shrinkable polyester-based film characterized in that the thermal shrinkage rate of the film in the main shrinking direction after a treatment in 80 deg.C hot water for 10 seconds is >=40% and in that the quantity ΔH1 of an endothermic peak which is placed close to the glass transition point of the film and is obtained from an irreversible heat flux curve is >=7.0 J/g.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-shrinkable polyester film suitable mainly for use in labels and cap seals, and more particularly, to shrinkage spots, wrinkles, distortions, and breaks after heat shrinkage of a film in a shrinking step by hot air. The present invention relates to a heat-shrinkable polyester film having extremely low shrinkage, in which the occurrence of intrusion and the like is extremely small, and the storage finish before use is extremely low.

[0002]

2. Description of the Related Art Conventionally, heat shrinkable films have been widely used for shrink wrapping, shrink labels, cap seals, and the like, utilizing the property of shrinking by heating. Above all, a stretched film made of a vinyl chloride resin, a polystyrene resin, a polyester resin, or the like is used as a label for various containers such as a polyethylene terephthalate (PET) container, a polyethylene container, and a glass container.

[0003] However, vinyl chloride resins have problems such as generation of harmful gases such as hydrogen chloride gas when incinerated. When a heat-shrinkable vinyl chloride resin film is used as a shrinkable label for a PET container or the like, it is necessary to separate the label from the container and discard the label when recycling the container. Furthermore, in applications such as full labels that require a high heat shrinkage ratio depending on the shape of the container, there is a problem that the heat shrinkable vinyl chloride resin film cannot be used because the heat shrinkage ratio is low and the shrinkage is insufficient.

[0004] On the other hand, polystyrene-based resin and polyester-based resin films do not generate harmful substances such as hydrogen chloride gas when incinerated, and are expected to be used as shrinkable labels for containers instead of vinyl chloride-based resin films.

However, polystyrene resin films are
Although the finished appearance after shrinkage is good, special ink must be used for printing because of poor solvent resistance. In addition, it requires incineration at a high temperature and generates a large amount of black smoke and an unpleasant odor at the time of incineration. Furthermore, there is a problem that it cannot be used in applications requiring a high heat shrinkage as in the case of the vinyl chloride resin film due to insufficient shrinkage. As a material capable of solving these problems, a polyester resin film is highly expected, and the amount of use thereof is increasing.

However, the above-mentioned conventional heat-shrinkable polyester films are not sufficiently satisfactory in heat-shrink properties. In particular, in the hot air shrinking process, shrinkage spots, wrinkles, distortion, and folds are likely to occur during shrinking, so when coating and shrinking containers such as PET bottles, polyethylene bottles, glass bottles, characters printed on the film before shrinking in advance However, there have been problems such as distortion of the design after shrinkage and insufficient adhesion of the film to the container. In addition, when stored at room temperature for a long period of time, the shrinkage at low temperatures decreases significantly in the shrinking process, so the shrinkage occurs suddenly in the hot air shrinking process, and further defects such as shrinkage spots, wrinkles, distortion and folding occur. There was a problem that it became easy to do.

[0007]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems of the conventional heat-shrinkable polyester film, and produces defects such as shrinkage spots, wrinkles, distortion, and folding during shrinkage in the hot air shrinking step. It is an object of the present invention to provide a heat-shrinkable polyester film which can obtain a beautifully shrink-finished appearance with a very small amount, and in which the shrinkage finish during storage is extremely low, and which is preferably used for full label and cap seal applications. I do.

[0008]

In order to achieve the above object, the heat-shrinkable polyester film of the present invention has a temperature of 80.degree.
The heat shrinkage in the main shrinkage direction after 10 seconds of treatment in warm water is 40
% Or more, the endothermic peak amount ΔH1 near the glass transition of the film obtained from the irreversible heat flux curve is 7.0 J / g or more.

The heat-shrinkable polyester film having the above characteristics has excellent shrink finish even in the hot-air shrinking step. In particular, it is suitably used for full label applications and cap seal applications that require a high shrinkage rate due to the shape of the container used, and can provide a beautiful shrink-finished appearance with very few shrinkage spots, wrinkles, distortions, and folds. . Because of its excellent low-temperature shrinkability, high-speed shrinking process and low-temperature processing become possible, and significant energy savings and productivity improvements are possible. Even if stored for a long period of time, the shrinkage at low temperatures does not decrease, and excellent shrink finish can be maintained. That is, the quality can be maintained for a long period of time even when stored at a higher temperature, for example, a normal temperature, instead of the general low-temperature storage, and the quality holding period can be further extended.

In this case, the heat-shrinkable polyester film preferably has a glass transition temperature obtained from a reversible heat flux curve of less than 65 ° C.

In this case, it is preferable that the change in the enthalpy relaxation amount of the heat-shrinkable polyester film before and after being left in a 40 ° C. atmosphere for 160 hours is less than 1.0 J / g. .

[0012]

Embodiments of the present invention will be described in detail. The heat-shrinkable polyester film of the present invention needs to have a heat-shrinkage rate of 40% or more after a 10-second treatment in hot water at 80 ° C. in the main shrinkage direction. Heat shrinkage 40%
If it is less than 1, in a full label application or a cap seal application in which a film label requires a high shrinkage rate depending on the shape of the container, shrinkage is insufficient, resulting in poor shrink finish.
In order to obtain a more stable shrink finish appearance, the heat shrinkage after treatment in hot water at 80 ° C. for 10 seconds in the main shrinkage direction is 50%.
% Or more, and particularly preferably 60% or more. Although there is no particular limitation on the heat shrinkage in the direction perpendicular to the main shrinkage direction, if the heat shrinkage is large, the shrinkage of the label in the warp direction and the distortion of the pattern occur, so that the heat shrinkage in hot water at 80 ° C. It is preferable that the heat shrinkage after the treatment for 10 seconds is 15% or less.

Further, in the present invention, the endothermic peak amount ΔH1 near the glass transition of the film obtained from the irreversible heat flux curve in the temperature modulation scanning calorimetry is 7.0 J.
/ G or more. When the ΔH1 of the film is less than 7.0 J / g, the amount of enthalpy relaxation during the storage period is large, and the reduction in shrinkage at low temperatures becomes remarkable, and after long-term storage, defects such as uneven spots, wrinkles, distortion, and folding are observed. Are more likely to occur. Furthermore, in order to obtain a stable shrink finish during the storage period, the endothermic peak ΔH1 of the film obtained from the irreversible heat flux curve is preferably 7.5 J / g or more.

Further, in the present invention, it is necessary that the film has a glass transition temperature of less than 65 ° C. obtained from a reversible heat flux curve in a temperature modulation scanning calorimetry. When the glass transition temperature is 65 ° C. or more, defects such as uneven shrinkage, wrinkles, distortion, and folding are likely to occur in the hot air shrinking step in which the film surface temperature tends to be uneven. Further, since the processing temperature becomes high, not only the energy consumption is increased, but also the time for raising the temperature of the film surface is increased, so that the processing speed must be reduced, and the productivity is deteriorated. Therefore, it is not preferable. The lower limit of the glass transition temperature of the film obtained from the reversible heat flux curve is not particularly limited, but is preferably 50 ° C. or more from the viewpoint of the dimensional stability over time of the film.

Further, in the present invention, the film is heated at 40 ° C.
It is necessary that the change in the amount of enthalpy relaxation of the film before and after standing for 160 hours in an atmosphere is 1.0 J / g or less. If the change in the enthalpy relaxation amount of the film is 1.0 J / g or more, when stored at room temperature for a long period of time, the shrinkability at a low temperature in the heat shrinking step is remarkably reduced.
As a result, the film that has been stored for a long period of time begins to shrink at a certain temperature in the heat shrinking step, so that defective rates such as uneven shrinkage, wrinkles, distortion, and breakage increase, causing a problem in industrial production. In particular, in the case of a film having a low glass transition temperature as in the present invention, the tendency is strong.
More preferably, the change in the amount of enthalpy relaxation of the film before and after standing for a time is less than 0.5 J / g.

The thickness of the heat-shrinkable polyester film of the present invention is not particularly limited. For example, the shrinkable film for labels is preferably 10 to 200 μm, more preferably 20 to 100 μm.

The polyester resin used in the heat-shrinkable polyester film of the present invention comprises, as a dicarboxylic acid component, an aromatic dicarboxylic acid or an ester-forming derivative thereof, or an aliphatic dicarboxylic acid, and a polyhydric alcohol component as main components. Is what you do. As an aromatic dicarboxylic acid,
For example, terephthalic acid, isophthalic acid, naphthalene-1,
4- or -2,6-dicarboxylic acid, 5-sodium sulfoisophthalic acid and the like can be mentioned. In addition, examples of these ester derivatives include derivatives such as dialkyl esters and diaryl esters. Examples of the aliphatic dicarboxylic acid include dimer acid, glutaric acid, adipic acid, sebacic acid, azelaic acid, oxalic acid, and succinic acid. Further, an oxycarboxylic acid such as p-oxybenzoic acid and a polyvalent carboxylic acid such as trimellitic anhydride and pyromellitic anhydride may be used in combination, if necessary.

The polyhydric alcohol component of the polyester resin used in the heat-shrinkable polyester film of the present invention includes ethylene glycol, diethylene glycol, dimer diol, propylene glycol, triethylene glycol, 1,4-butanediol, neopentyl glycol. , 1,3-cyclohexanedimethanol, 1,
4-cyclohexanedimethanol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, 2-methyl-1,5-pentanediol, 2,2-diethyl-
1,3-propanediol, 1,9-nonanediol,
Examples thereof include an alkylene glycol such as 1,10-decanediol, an ethylene oxide adduct of a bisphenol compound or a derivative thereof, trimethylolpropane, glycerin, pentaerythritol, polyoxytetramethylene glycol, and polyethylene glycol.
Epsilon caprolactone, which is not a polyhydric alcohol, can also be used.

In the heat-shrinkable polyester film of the present invention, it is preferable to use one or more of the above-described dicarboxylic acid components and polyhydric alcohol components in combination. The type and content of the components of the monomers used in combination can be appropriately determined in consideration of the desired film properties, economy, etc., but it is composed of a composition containing at least one polyester, and Is preferably an ethylene terephthalate unit. More preferably 15 to 70
Mol%. 10 ethylene terephthalate units
If the amount is less than mol%, the rupture resistance and solvent resistance of the film will deteriorate, and if it exceeds 75% by mol, the heat shrinkage will decrease and sufficient shrinkage performance will not be obtained, which is not preferable.

In order to satisfy the above-mentioned changes in the endothermic peak amount, the glass transition temperature, and the enthalpy relaxation amount in the heat-shrinkable polyester film of the present invention, it is necessary to use the above-mentioned constituents of the polyester resin, etc. By combining the film conditions, it is possible to control within the target range of the present invention. The polyesters may be used alone or as a mixture of two or more. When two or more kinds are used in combination, a mixed system of polyethylene terephthalate and a copolymerized polyester may be used, or a combination of copolymerized polyesters may be used. Further, a combination with a homopolyester such as polybutylene terephthalate, polycyclohexylene dimethyl terephthalate, polyethylene naphthalate, or polybutylene naphthalate may be used.

For the purpose of improving the heat resistance such as the degree of coloring and the degree of gelation, the polyester may further contain, in addition to a polymerization catalyst such as antimony oxide, germanium oxide, or a titanium compound, an Mg salt such as magnesium acetate or magnesium chloride; , Ca salts such as calcium chloride, manganese acetate, Mn salts such as manganese chloride, zinc chloride, Zn salts such as zinc acetate,
Co salt such as cobalt chloride and cobalt acetate is not more than 300 ppm as a metal ion with respect to the resulting polyester, and phosphoric acid or a phosphate derivative such as trimethyl phosphate or triethyl phosphate is phosphorous (P)
It is also possible to add 200 ppm or less in conversion.

The total amount of metal ions other than the above-mentioned polymerization catalyst is 300 ppm based on the produced polyester, and the P amount is 200 ppm.
If it exceeds ppm, not only the coloring of the polymer becomes remarkable, but also the heat resistance and hydrolysis resistance of the polymer are remarkably reduced.

At this time, in terms of heat resistance, hydrolysis resistance and the like, the molar atomic ratio (P / M) of the total P amount (P) to the total metal ion amount (M) is 0.4 to 1. It is preferably 0. If the molar atomic ratio (P / M) is less than 0.4 or more than 1.0, the composition of the present invention is not preferable because coloring and generation of coarse particles become remarkable.

The method for producing the polyester is not particularly limited, but a so-called direct polymerization method in which an oligomer obtained by directly reacting a dicarboxylic acid and a glycol is polycondensed,
A so-called transesterification method in which a dimethyl ester of a dicarboxylic acid and a glycol are subjected to transesterification and then polycondensation, and the like, may be used, and an arbitrary production method can be applied.

The timing of adding the metal ions and phosphoric acid and derivatives thereof is not particularly limited. Generally, the metal ions are charged at the time of charging the raw materials, that is, before ester exchange or esterification, and the phosphoric acid is charged before the polycondensation reaction. Is preferably added.

If necessary, fine particles such as silica, titanium dioxide, kaolin, and calcium carbonate may be added. Further, an antioxidant, an ultraviolet absorber, an antistatic agent, a coloring agent, an antibacterial agent and the like may be added. It can also be added. The intrinsic viscosity for forming a film is not particularly limited, but is usually 0.40 to 1.30 dl / g.

The polyester raw material used in the present invention is dried using a drier such as a hopper drier or a paddle drier, or a vacuum drier, and extruded into a film at a temperature of 200 to 300 ° C. Alternatively, the undried polyester raw material is similarly extruded into a film while removing moisture in a vented extruder. When extruding, T-die method
Any existing method such as the tubular method may be adopted. After extrusion, it is quenched to obtain an unstretched film. The stretching process is performed on the unstretched film. However, in order to achieve the object of the present invention, the transverse direction is practical as the main shrinking direction, and hence the film forming method in the case where the main shrinking direction is the transverse direction is described below. Although an example is shown, when the main shrinkage direction is the vertical direction, the film can be formed according to a normal operation, in addition to changing the stretching direction by 90 degrees in the following method.

Further, if attention is paid to making the thickness distribution of the intended heat-shrinkable polyester film uniform,
When the film is stretched in the transverse direction using a tenter, the heat conduction coefficient is set to 0.00 in a preheating process performed prior to the stretching process.
Tg at a low wind speed of 13 calories / cm ² · sec · ° C or less
Heating is preferably performed until the film temperature reaches + 0 ° C. to Tg + 60 ° C. Tg-20 ° C for transverse stretching
The film is stretched 2.3 to 7.3 times, preferably 2.5 to 6.0 times at a temperature of up to Tg + 40 ° C. At this time, the transverse stretching is preferably performed in two or three steps. After a while, 50 ° C ~
At a temperature of 110 ° C., 0-15% elongation or 0-15%
% While relaxing the temperature, if necessary, from 40 ° C
Further heat treatment is performed at a temperature of 100 ° C. to obtain a heat-shrinkable polyester film.

As a stretching method, not only a uniaxial stretching in a transverse direction with a tenter, but also 1.0 to 2.3 times or less in a longitudinal direction.
Preferably, stretching of 1.1 to 1.8 times can be performed. However, if the stretching is performed at a ratio of more than 2.3 times, the heat shrinkage after treatment in hot water at 80 ° C. for 10 seconds in the direction orthogonal to the main shrinkage direction increases, and exceeds 15%, which is not preferable in the present invention. The biaxial stretching may be either sequential biaxial stretching or simultaneous biaxial stretching, and may be performed again if necessary. In the sequential biaxial stretching, the order of stretching is as follows:
Any of vertical, horizontal, vertical, horizontal, vertical, horizontal, vertical, and horizontal may be used. Focusing on suppressing internal heat generation of the film due to stretching and reducing film temperature unevenness in the width direction, the heat transfer coefficient of the stretching step is 0.0009 calories / cm ² · sec.
-° C or higher, preferably 0.0013 to 0.0020 calories / cm ² · sec · ° C. As described above, the present invention is achieved by a combination of a polyester composition of a film raw material and a stretching method.

[0030]

Next, the present invention will be described in more detail with reference to examples and comparative examples. However, the present invention is not limited to the following examples, and may be modified without departing from the spirit of the preceding and following embodiments. All this is included in the technical scope of the present invention. Also,
The methods for measuring and evaluating the physical properties of the films obtained in Examples and Comparative Examples are shown below.

(1) Heat Shrinkage The sample film was cut into a 10 cm × 10 cm square,
After treating in hot water at a predetermined temperature of ± 0.5 ° C. for 10 seconds under no load to cause heat shrinkage, the film was measured in the vertical and horizontal directions, and the heat shrinkage was calculated according to the following equation. The direction in which the heat shrinkage was large was defined as the main shrinkage direction. Heat shrinkage = (length before shrinkage−length after shrinkage) ÷ length before shrinkage × 100 (%)

(2) Endothermic peak amount (ΔH1) The sample film was prepared using a DSC manufactured by TA Instruments
The measurement was performed in a Modulated mode of No. 2920 at a heating rate of 5 ° C./min, a temperature amplitude of ± 1 ° C., and a cycle of 60 seconds. From the obtained irreversible heat flux curve, the endothermic peak calorie near the glass transition temperature was determined as ΔH1. At this time, if the baseline is not clear, the temperature at which the endothermic peak has a maximum value (if there are multiple peaks, the T
1max... Tnmax) as Tmax, and the starting point Tmax−
From 20 ° C. (T1max−20 ° C. when there are multiple peaks) to the end point Tmax + 20 ° C. (If there are multiple peaks, Tnma
x-20 ° C) was calculated as ΔH1. When the minimum value of the endothermic peak falls within the above-mentioned temperature range, ΔH1 was calculated using the minimum value as a start point or an end point. FIG. 1 shows a measurement example.

(3) Glass transition temperature From the reversible heat flux curve obtained by the measurement in the above (2),
The glass transition temperature of the sample film was quantified. The glass transition point referred to here was calculated by analyzing a step-like curve.
Inflection means temperature.

(4) Change in enthalpy relaxation amount before and after aging The film was subjected to a temperature of 40 ° C. ± 1 ° C. and a relative humidity of 30% ± 2%.
After aging for 160 hours in a thermo-hygrostat controlled to take out, take out after aging, and determine the endothermic peak amount before aging as ΔH1 and the endothermic peak amount after aging as ΔH2 according to the measurement method described in (2) above, according to the following equation. The change in the amount of relaxation was determined. Change in enthalpy relaxation amount = △ H2- △ H1

(4) Shrink finish finish Using a steam tunnel (model: SH-1500-L) manufactured by Fuji Astec Inc, a 334 ml glass bottle (used for a commercially available Asahi draft beer water heater manufactured by Asahi Breweries, Ltd.). Returnable bin)
After mounting a heat-shrinkable film label printed in three colors with grass-colored, gold, and white inks manufactured by Toyo Ink Mfg. Co., Ltd. in advance, the tunnel passage time is 10 seconds, and the zone temperature / 2.
The test was carried out by passing under the condition of zone temperature = 80 ° C./90° C., and the shrinkage finish was visually determined. The rank of shrinkage finish was evaluated on a 5-point scale. 5: Best finish 4: Good finish 3: Some defects (within 2 places) 2: Defects (3 to 6 places) 1: Many defects ( 6 or more) and 4 or more were regarded as acceptable levels (number of samples n = 1)
0). Here, the term "defect" refers to a general term for wrinkles, label end folding, color spots, and insufficient shrinkage.

(Synthesis of Polyester) 100 mol% of dimethyl terephthalate (DMT) as a dibasic acid component and 72 of ethylene glycol (EG) as a glycol component were placed in a stainless steel autoclave equipped with a stirrer, a thermometer and a partial reflux condenser. With the composition of mol% and neopentyl glycol (NPG) 28 mol%, the glycol was charged so that the molar ratio was 2.2 times the methyl ester,
0.05 mol of zinc acetate (based on the acid component) as a transesterification catalyst, and 0.1 mol of antimony trioxide as a polycondensation catalyst.
025 mol% (relative to the acid component) was added, and transesterification was carried out while distilling off the generated methanol out of the system. Thereafter, a polycondensation reaction was performed at 280 ° C. under a reduced pressure of 0.2 torr to obtain a polyester (A) having an intrinsic viscosity of 0.68 dl / g.

In the same manner as described above, polyesters shown in Table 1 were obtained.

[0038]

[Table 1]

Note that butanediol (BD) and dimer diol (DIDO) were also used. The intrinsic viscosity of each polyester is (B): 0.70 dl / g,
(C): 1.25 dl / g, (D): 0.60,
(E): 0.68. The reduced viscosity of (F) was 1.30. Reduced viscosity: 0.05 g of a polymer was dissolved in 25 ml of a mixed solution (phenol / tetrachloroethane = 60/40) and measured at 30 ° C. using an Ostwald viscometer.

(Example 1) 50 wt% of polyester A, 30 wt% of B, and 20 wt% of E shown in Table 1 were mixed in a resin state, melt-extruded at 280 ° C, and quenched. An unstretched film was obtained. After pre-heating the unstretched film at 110 ° C. for 8 seconds, it
Stretched 1.3 times at 80 ° C., 1.7 times at 75 ° C., and 1.8 times at 75 ° C., and then cooled to 60 ° C.
A heat treatment was performed for 10 seconds while stretching to obtain a heat-shrinkable polyester film having a thickness of 45 μm. Table 2 shows the physical property values of the obtained film.

Example 2 Polyester F shown in Table 1
Was melt-extruded at 280 ° C. and then rapidly cooled to a thickness of 180 μm.
Was obtained. 110 ° C.
After preheating for 8 seconds, 1.3 times at 85 ° C. in the horizontal direction and 80 times more
The film is stretched 1.7 times at 75 ° C. and 1.8 times at 75 ° C., and then cooled to 60 ° C., and then heat-treated for 10 seconds while being stretched at 70 ° C. for 3% to obtain a heat-shrinkable polyester film having a thickness of 45 μm. Was. Table 2 shows the physical property values of the obtained film.

(Comparative Example 1) 65 wt% of polyester A, 10 wt% of B, and 25 wt% of C shown in Table 1 were mixed in the form of a resin, melt-extruded at 275 ° C., and quenched to obtain a 175 μm thick resin. An unstretched film was obtained. After preheating the unstretched film at 105 ° C. for 10 seconds,
Stretched 3.9 times at 70 ° C, and then fixed at 73 ° C for 10
Heat treatment was performed for 2 seconds to obtain a heat-shrinkable polyester film having a thickness of 45 μm. Table 2 shows the physical property values of the obtained film.

(Comparative Example 2) 50 wt% of polyester A, 25 wt% of B and 25 wt% of C shown in Table 1 were mixed in the form of a resin, melt-extruded at 275 ° C., quenched, and cooled to a thickness of 175 μm. An unstretched film was obtained. After preheating the unstretched film at 105 ° C. for 10 seconds,
Stretched 3.9 times at 70 ° C, and then fixed at 73 ° C for 10
Heat treatment was performed for 2 seconds to obtain a heat-shrinkable polyester film having a thickness of 45 μm. Table 2 shows the physical property values of the obtained film.

Comparative Example 3 55% by weight of polyester A, 35% by weight of B, and 10% by weight of C shown in Table 1 were mixed in the form of a resin, melt-extruded at 275 ° C., quenched, and cooled to a thickness of 175 μm. An unstretched film was obtained. After preheating the unstretched film at 105 ° C. for 10 seconds,
Stretched 3.9 times at 70 ° C, and then fixed at 73 ° C for 10
Heat treatment was performed for 2 seconds to obtain a heat-shrinkable polyester film having a thickness of 45 μm. Table 2 shows the physical property values of the obtained film.

Comparative Example 4 32% by weight of polyester A, 50% by weight of B, 10% by weight of C, and 8% of E shown in Table 1
The mixture was melt-extruded at 280 ° C. and rapidly cooled to obtain an unstretched film having a thickness of 180 μm. The unstretched film was preheated at 110 ° C. for 8 seconds, stretched 4.0 times at 85 ° C. in the transverse direction, and then heat-treated at 75 ° C. for 10 seconds to obtain a heat-shrinkable polyester film having a thickness of 45 μm. Table 2 shows the physical property values of the obtained film.

[0046]

[Table 2]

[0047]

According to the heat-shrinkable polyester film of the present invention, it is possible to obtain a beautiful shrink-finished appearance with extremely few defects such as shrinkage spots, wrinkles, distortion, and folds during shrinkage in the hot air shrinking step. In particular, it is suitable for use in full label and cap seal applications, in which the reduction in shrinkage finish during storage is extremely small.

[Brief description of the drawings]

FIG. 1 is a measurement example of an endothermic peak calorific value ΔH1.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Michio Morishige 2-1-1 Katata, Otsu City, Shiga Prefecture Inside Toyobo Co., Ltd. Address Toyo Spinning Co., Ltd. Inuyama Factory F-term (reference) 4F071 AA44 AA45 AA46 AF43Y AF61 AF61Y AH04 AH06 BB06 BB07 BB08 BC01 BC17 4F210 AA24C AE01 AG01 RC02 RG02 RG04 RG35 RG43

Claims (3)

[Claims] 1. An endothermic peak amount near the glass transition point of a film, which is obtained from an irreversible heat flux curve when the film has a heat shrinkage ratio of 40% or more in a main shrinkage direction after treatment in hot water at 80 ° C. for 10 seconds. A heat-shrinkable polyester film, wherein ΔH1 is 7.0 J / g or more. 2. The heat-shrinkable polyester film according to claim 1, wherein the heat-shrinkable polyester film has a glass transition temperature of less than 65 ° C. obtained from a reversible heat flux curve. the film. 3. The heat-shrinkable polyester film according to claim 1, wherein the change in the amount of enthalpy relaxation of the film before and after standing in a 40 ° C. atmosphere for 160 hours is less than 1.0 J / g. 3. The heat-shrinkable polyester film according to claim 1, wherein: