JPH09239833A - Heat-shrinkable polyester film and production thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a heat-shrinkable polyester film extremely reduced in the occurrence of wrinkles, shrinkage irregularity and strain after shrinkage and excellent in the breakage resistance against an impact. SOLUTION: A stretched film composed of polyester wherein a terephthalic acid component among dicarboxylic acid components is 70mol% or more and an ethylene glycol component among diol components is 70mol% is characterized by that the max. value (σmax) of shrinkage stress in a main shrinkage direction at 90 deg.C is 0.5-1.2kg/mm<2> and a heat shrinkage factor in the main shrinkage direction in hot water is 40% or less at 75 deg.C and 50% or more at 95 deg.C.

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 and a method for producing the same, and more specifically, it has very few wrinkles, shrinkage spots, and distortions after shrinking of the heat-shrinkable film, and has a resistance to rupture against impact. The present invention relates to a heat-shrinkable polyester film having excellent properties and suitable for label applications, and a method for producing the same.

[0002]

2. Description of the Related Art In the field of heat-shrinkable films, particularly shrink films for labels on the body of bottles, films made of polyvinyl chloride, polyethylene, etc. have been mainly used. There is a problem of chlorine-based gas generation during incineration, there is a problem that printing is difficult for polyethylene, and there is also a problem that it is necessary to separate resin labels other than PET when collecting PET bottles. Polyester film has attracted attention. However, many heat-shrinkable polyester films shrink rapidly, and wrinkles, shrinkage spots, and distortions remain after shrinking, and breakage easily occurs due to an external shock after shrinking. It wasn't something that would be done. In order to avoid some of these drawbacks, Japanese Patent Application Laid-Open No. 1-110931 discloses a method of improving shrinkage finish by significantly reducing the breaking elongation in the direction orthogonal to the main shrinkage direction.

[0003]

However, even the shrinkable film obtained by the above method is not only liable to break when tension is applied in the steps of printing, labeling, etc., but also of a bottle filled with contents. If the bottles are transported together in a state that they are contracted in a ring shape on the body, they are likely to be broken by colliding with each other or with the box, which also makes them useful as shrink films for labels. It was a poor film. As described above, in the heat-shrinkable polyester film, it has been an important issue to satisfy both shrink finish property and break resistance before or after shrinkage. The present invention solves the problems of the above conventional heat-shrinkable polyester film, wrinkles after shrinkage, shrinkage unevenness, occurrence of distortion is extremely small, and excellent in break resistance against impact, suitable for label applications. The object is to provide a heat-shrinkable polyester film.

[0004]

In order to achieve the above object, the heat-shrinkable polyester film of the present invention has a terephthalic acid component of 70 mol% or more in the dicarboxylic acid component and an ethylene glycol component of 70 mol% in the diol component. A stretched film made of polyester which is
Maximum value of shrinkage stress (σmax) in the main shrinkage direction that develops from the start of heating in an air oven at 90 ° C for 1 minute
Of 0.5 to 1.2 Kg / mm ² , heat shrinkage in the main shrinkage direction after treatment for 10 seconds in 75 ° C. warm water is 40% or less, 95 ° C.
The heat shrinkage in the main shrinkage direction after treatment in warm water for 10 seconds is 50
% Or more.

The heat-shrinkable polyester film of the present invention having the above-mentioned constitution has stable heat-shrinkability, has very few wrinkles, shrinkage spots, and distortion after shrinkage, and has a high resistance to impact damage. It is an excellent heat-shrinkable film suitable for label use.

Further, the heat shrinkable polyester film production method of the present invention is mainly a polyester unstretched film in which the terephthalic acid component in the dicarboxylic acid component is 70 mol% or more and the ethylene glycol component in the diol component is 70 mol%. When stretching in the shrinking direction, the total stretching ratio is 3.0 times or more, and the stretching temperature in the preceding stage for stretching 40 to 60% of the total stretching ratio is Tg (glass transition point) + 10 to Tg.
It is characterized in that the stretching temperature at the subsequent stage of stretching at + 40 ° C. and 60 to 40% of the total stretching ratio is Tg-15 to Tg + 10 ° C. and lower than the stretching temperature at the preceding stage.

The method for producing a heat-shrinkable polyester film of the present invention having the above-mentioned constitution has a stable heat-shrinkability, has very few wrinkles, shrinkage spots, and distortion after shrinkage, and is resistant to impact. A method of producing a heat-shrinkable film suitable for label use, which is excellent in rupture properties. If the shrinkage properties are set within a certain range by selecting the stretching conditions, the heat shrinkability that achieves both shrink finish and rupture resistance is achieved. Thus, a polyester film can be obtained. The basic idea of the method of the present invention is to improve the shrink finish by maintaining the temperature of the former stage of stretching in the main shrinking direction at high temperature, and to improve the puncture resistance by keeping the latter stage of stretching in the main shrinking direction at low temperature. It is to make it. Further, in the present invention, it is preferable that the main shrinking direction is the width direction (transverse direction) at the time of manufacturing the film in consideration of convenience when using the heat shrinkable film.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be specifically described below. The polyester used in the present invention is a polyester having a terephthalic acid component of 70 mol% or more in the dicarboxylic acid component and an ethylene glycol component of 70 mol% in the diol component, and more specifically, as a dicarboxylic acid component other than terephthalic acid. , Oxalic acid, malonic acid, succinic acid, adipic acid, azelaic acid, sebacic acid, phthalic acid, isophthalic acid, naphthalenedicarboxylic acid, and the like, may be used alone or in combination. Further, as a glycol component other than ethylene glycol, propylene glycol, neopentyl glycol,
Tetramethylene glycol, hexamethylene glycol, trimethylene glycol, diethylene glycol,
One or more known diols such as polyalkylene glycol and 1,4-cyclohexanedimethanol can be used. Further, in order to obtain a heat-shrinkable polyester film having particularly excellent shrink finish, it is preferable to use polyester in which neopentyl glycol is the remaining component of the glycol component. The polyester having a terephthalic acid component of 70 mol% or more in the dicarboxylic acid component and an ethylene glycol component of 70 mol% or more in the diol component used in the present invention means that when two or more polyesters are mixed and used, The proportions of terephthalic acid in the dicarboxylic acid component and the proportion of ethylene glycol in the glycol component in the whole polyester are shown regardless of whether or not transesterification is performed.

In the polyester constituting the heat-shrinkable film of the present invention, the terephthalic acid component in the dicarboxylic acid component is 7
The polyester is 0 mol% or more and the ethylene glycol component in the diol component is 70 mol%, and terephthalic acid and ethylene glycol are dicarboxylic acid components,
When the amount is less than 70 mol in the diol component, the resulting heat-shrinkable film has reduced resistance to breakage after shrinkage.

The heat-shrinkable film of the present invention has the maximum value (σmax) of shrinkage stress in the main shrinkage direction (direction having the maximum shrinkage ratio) developed in the air oven at 90 ° C. for 1 minute after the start of heating. ) Is 0.5 to 1.2 Kg / mm ² . Maximum shrinkage stress of heat shrinkable film (σ
When the (max) exceeds 1.2 Kg / mm ² , shrinkage unevenness and distortion are likely to occur when a packaged object such as a bottle is packaged and passed through a shrink tunnel. On the contrary, when the maximum value of shrinkage stress (σmax) in the main shrinkage direction is less than 0.5 Kg / mm ² , after attaching the label shrinking the heat shrinkable film to the body of the bottle in the shrinking tunnel, When filled with warm contents, the heat of the contents distorts the film after shrinking, and the label tends to sag in the shape of petals at the top of the bottle.

The heat-shrinkable film of the present invention has a heat shrinkage in the main shrinkage direction of 4 after being treated in 75 ° C. hot water for 10 seconds.
0% or less, and 5 hours after treatment for 10 seconds in warm water at 95 ° C
It should be 0% or more. In particular, in order to suppress shrinkage unevenness when packaging a packaged object such as a bottle and passing it through a shrinking tunnel, the heat shrinkage rate in the main shrinking direction after treatment for 10 seconds in hot water at 75 ° C. is 35% or less. Preferably. When the heat shrinkage in the main shrinkage direction at 75 ° C exceeds 40%, when the film is shrunk in the shrink tunnel,
Wrinkles, shrinkage spots, and distortion easily occur. Further, when the thermal shrinkage in the main shrinkage direction at 95 ° C. is less than 50%, insufficient shrinkage is likely to occur in the upper portion of the bottle where the conical diameter is small.

Further, in the method for producing the heat-shrinkable film of the present invention, it is necessary that the total stretching ratio is 3.0 times or more when stretching in the main shrinking direction. When the total draw ratio is less than 3.0 times, the thickness distribution of the obtained heat-shrinkable film is poor and lacks uniformity, and the film-making step and the step of processing the heat-shrinkable film such as printing on the heat-shrinkable film. The productivity of the heat-shrinkable film is also lowered because the operability of the heat-shrinkable film is lowered.

In the method of the present invention, the unstretched film is stretched in the main shrinking direction before the stretching (total stretching ratio of 40 to 60).
%) At a temperature of Tg + 10 to Tg + 40 ° C. If the draw ratio of the previous stage of drawing in the main shrinkage direction is less than 40% of the total draw ratio, or if the draw temperature is Tg.
When the temperature is less than + 10 ° C, the maximum value (σmax) of the shrinkage stress in the main shrinkage direction of the obtained heat-shrinkable film becomes large, and the heat shrinkage rate and the shrinkage stress cannot be made compatible with each other. On the contrary, the stretching ratio before the stretching in the main shrinkage direction is 60% of the total stretching ratio.
% Or the stretching temperature is Tg + 40 ° C. or higher, the maximum value (σmax) of the shrinkage stress in the main shrinkage direction becomes small and the shrinkage stress cannot be controlled.
Since the breaking resistance of the obtained film is lowered, the object of the present invention cannot be obtained, and the thickness distribution of the obtained heat-shrinkable film is deteriorated, so that the commercial value is lowered.

In the method of the present invention, the unstretched film is stretched in the main shrinkage direction after the stretching (40% to 60% of the total stretching ratio).
%) At a temperature of Tg-15 ° C. to Tg + 10 ° C. and a temperature lower than the stretching temperature of the former stage. When the latter-stage draw ratio in the main shrinking direction is less than 40% of the total draw ratio or exceeds Tg + 10 ° C., the resulting heat-shrinkable film has reduced resistance to breakage due to impact force after shrinking. On the contrary, when the stretching ratio in the latter stage of stretching in the main shrinkage direction exceeds 60% or the stretching temperature is Tg-15.
When the temperature is lower than 0 ° C, breakage is likely to occur in the stretching step, and the heat-shrinkable film obtained tends to have poor transparency after heat-shrinking.

The thickness of the heat-shrinkable film of the present invention is not particularly limited.
0 to 200 μm is preferable, and 20 to 100 μm is more preferable.

The heat shrinkage rate of the heat shrinkable film of the present invention in the direction orthogonal to the main shrinkage direction is not particularly limited, but the heat shrinkage rate after treatment in hot water at 95 ° C. for 10 seconds is 1
It is preferably 5% or less, more preferably 10% or less.

Next, the method for producing the heat-shrinkable film of the present invention will be described in more detail, but the production method is not limited to the following. The polyester raw material used in the present invention is dried using a dryer such as a hopper dryer, a paddle dryer or the like, or a vacuum dryer, and extruded into a film at a temperature of 200 to 300 ° C. Any existing method such as a T-die method or a tubular method may be adopted for the extrusion.
After extrusion, it is rapidly cooled to obtain an unstretched film. The unstretched film is subjected to a stretching treatment, but in order to achieve the object of the present invention, the transverse direction is practical as the main shrinkage direction. Therefore, the following is an example of a film forming method in which the main shrinkage direction is the transverse direction. In the case where the main shrinkage direction is the longitudinal direction, the film can be formed according to the usual operation except that the stretching direction in the following method is changed by 90 degrees.

If attention is paid to making the thickness distribution of the desired heat-shrinkable polyester film uniform,
When the film is stretched in the transverse direction using a tenter, the heat transfer coefficient is 0.00 in the preheating step performed prior to the stretching step.
It is preferable to heat at a low wind speed of 13 calories / cm ² · sec · ° C. or lower until the film temperature reaches a predetermined value.
In the transverse stretching, the total stretching ratio is 3.0 times or more, preferably 3.5 times or more, and more preferably 4.0 times or more. Further, the stretching ratio of the former stage is 40 to 60%, preferably 45 to 55% of the total stretching ratio, and Tg + 1.
A temperature of 0 to Tg + 40 ° C., preferably Tg + 15 to Tg
Stretching is carried out at a temperature of + 30 ° C., and then the stretching ratio of the latter stage is 40 to 60%, preferably 45 to 55% of the total stretching ratio, and T
g-15 to Tg + 10 ° C., preferably Tg-10 to Tg
Stretch at a temperature of + 5 ° C. Further, the stretching temperature in the latter stage is lower than the stretching temperature in the former stage, and for example, a low temperature in the range of 1 to 40 ° C. is preferable. Then, if necessary, heat treatment is performed at a temperature of 70 to 100 ° C. to obtain a heat-shrinkable polyester film. The heat transfer coefficient in the stretching process is 0.0009 calories / cm ² · sec, focusing on the point that the internal heat generation of the film during stretching is suppressed and the film temperature unevenness in the width direction is reduced.
-The temperature is not less than 0 ° C, preferably 0.0011 to 0.0017 calories / cm ² · sec · ° C. As for the stretching method, not only transverse uniaxial stretching with a tenter but also a slight stretching in the longitudinal direction is possible. Such 2
The axial stretching may be performed by either a sequential biaxial stretching method or a simultaneous biaxial stretching method, and may be re-stretched in the machine direction or the transverse direction as required.

[0019]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples as long as the gist thereof is not exceeded. In the present invention, the film evaluation method is as follows.

(1) Heat Shrinkage The film was cut into a square of 10 cm × 10 cm, heat treated in unheated water for 10 seconds in warm water having a predetermined temperature of ± 0.5 ° C., and then the lengthwise and longitudinal directions of the film were measured. The dimension in the lateral direction was measured, and the heat shrinkage rate was calculated according to the following formula (1). The direction in which the heat shrinkage rate was large was defined as the main shrinkage direction. Thermal shrinkage = (length before shrinkage-length after shrinkage / length before shrinkage) x 100 (%) (1) Equation

(2) Maximum value of shrinkage stress Using Tensilon (model: UTM-4L) with an air oven manufactured by Toyo Seiki Co., Ltd., 50 mm between chucks, sample shape main shrinkage direction: 10 cm, main shrinkage direction The orthogonal direction: 2 cm, the force developed when heated in an air oven at 90 ° C. for 1 minute was recorded on a recorder, the maximum value was read, and the maximum value of shrinkage stress was determined according to the following formula (2). Maximum shrinkage stress = (reading value / sample cross-section before heating) (Kg / mm ² ) (2) Equation

(3) Shrinkage finish Steam tunnel made by Fuji Astec INC (model: SH-1
500-L), passage time 10 seconds, 1 zone temperature /
2-zone temperature: set to 85 ° C / 90 ° C, 900 cc square PET bottle (height 25.5 cm, central section cross section length 7.1 cm, width 7.1 cm) (commercially available AGF Co., Ltd. blendy The number of samples used was 10 (sample). In addition, the heat shrinkable film,
Three-color printing was performed in advance with grass, gold, and white ink from Toyo Ink Mfg. Co., Ltd. The evaluation was performed visually, and the criteria were as follows. No wrinkles, color spots, or insufficient shrinkage → ○ Color spots → △ Crater-like wrinkles or insufficient shrinkage → ×

(4) Breaking resistance The above-mentioned printing film is subjected to 15 at 30 ° C. and 60% RH atmosphere.
After storage for a day, Tensilon (model: UTM-4L) manufactured by Toyo Seiki Co., Ltd. was used to perform a tensile test according to the method of JIS C2318, and the elongation was 30% in the direction perpendicular to the main shrinkage direction (longitudinal direction). Evaluation by the number of occurrences below (number of samples = 50)
did.

(5) Tg (glass transition point) DSC manufactured by Seiko Instruments Inc. (model: DSC22)
0) was used to draw a tangent line to the endothermic curve obtained when 10 mg of an unstretched film was heated from -40 ° C to 120 ° C at a heating rate of 20 ° C / min, and the intersection was defined as Tg (glass transition point). And

(6) Thickness distribution Contact thickness gauge manufactured by Anritsu Corporation (Model: KG60 / A)
The thickness of a sample of 5 cm in the lengthwise direction and 50 cm in the widthwise direction was measured using (sample number = 20), and the variation in the thickness of each sample was determined by the following equation (3). Also,
The average value of the thickness variations (n = 50) was evaluated according to the following criteria. Thickness variation = (maximum thickness-minimum thickness / average thickness) x 100 (%) (3) Formula Average value: 6% or less → ○ Average value: greater than 6% and less than 10% → △ Average value: 10% or more → ×

The polyesters used in the examples are as follows. Polyester A: Polyethylene terephthalate Polyester B: Polyester consisting of 70 mol% ethylene glycol, 30 mol% neopentyl glycol and terephthalic acid Polyester C: Polybutylene terephthalate Polyester D: 65 mol% terephthalic acid, 10 mol% adipic acid, isophthalic acid Polyester consisting of 25 mol% and butanediol

(Example 1) 35 wt% of polyester A
%, Polyester B 55 wt%, polyester C 1
Extrude polyester mixed with 0 wt% at 280 ° C.
It cooled rapidly and the unstretched film was obtained (Tg: 69 degreeC). A heat transfer coefficient of 0.0008 calories /
The film was preheated to a temperature of 100 ° C. under the condition of cm ² · sec · ° C., and then stretched by a tenter in the transverse direction at a draw ratio of 88 ° C. for 2.6 times and then in the same direction at a temperature of 70 ° C. for a draw ratio of 2.2 times.
Then, it was heat-treated at 80 ° C. for 20 seconds to obtain a heat-shrinkable polyester film having a thickness of 60 μm. (Example 2) A polyester in which 35 wt% of polyester A, 55 wt% of polyester B and 10 wt% of polyester D were mixed was extruded from a T die at 280 ° C and rapidly cooled by a chill roll to obtain an unstretched film (Tg67).
° C). The unstretched film was preheated in the same manner as in Example 1 and then 2.6 in a transverse direction at 85 ° C. with a tenter.
Then, the film was stretched 2.2 times in the same direction at 70 ° C. Then, it was heat-treated at 80 ° C. for 20 seconds to obtain a heat-shrinkable polyester film having a thickness of 60 μm. (Example 3) An unstretched film was stretched in the machine direction at 75 ° C for 1.1
After being double-stretched, a film was formed in the same manner as in Example 2 except that the transverse stretching was performed to obtain a heat-shrinkable polyester film having a thickness of 60 μm. (Example 4) The heat transfer coefficient of the unstretched film obtained by the method of Example 1 was 0.0008 calories / cm ² · sec ·
The film was preheated to a temperature of 91 ° C under the condition of ° C, and then stretched by a tenter in the transverse direction at a draw ratio of 85 ° C for 1.8 times and then in the same direction at a temperature of 68 ° C for a draw ratio of 2.2 times. Then 20 at 80 ℃
It was heat-treated for a second to obtain a heat-shrinkable polyester film having a thickness of 60 μm. (Comparative Example 1) A heat-shrinkable polyester system having a thickness of 60 μm formed by the film formation under the conditions described in Example 1 except that the polyester obtained by mixing 15 wt% of polyester A, 75 wt% of polyester B and 10 wt% of polyester C was used. I got a film. (Comparative Example 2) The unstretched film obtained by the method of Example 1 was stretched 2.6 times in the transverse direction at 70 ° C and then 2.2 times in the same direction at 70 ° C (that is, with a temperature difference. Film was formed by the method described in Example 1 except that the film was stretched only on the low temperature side).
A heat-shrinkable polyester film having a thickness of 60 μm was obtained. (Comparative Example 3) The unstretched film obtained by the method of Example 1 was stretched in the transverse direction by a factor of 2.6 at 88 ° C and then in the same direction by a factor of 2.2 at 88 ° C (that is, with a temperature difference. Film was formed by the method described in Example 1 except that the film was stretched only on the high temperature side.
A heat-shrinkable polyester film having a thickness of 60 μm was obtained. (Comparative Example 4) Later stretching in the transverse direction was conducted at 50 ° C. for 2.2.
A film was formed by the method described in Example 1 except that the number was doubled.
A film could not be obtained due to poor film formation (breakage). (Comparative Example 5) A film was formed by the method described in Example 1 except that the transverse stretching was carried out 3.2 times at 88 ° C and then 1.6 times at 70 ° C in the same direction. A polyester film was obtained. (Comparative Example 6) A film was formed by the method described in Example 4 except that the transverse stretching was performed at 85 ° C by 1.4 times, and subsequently in the same direction at 65 ° C by 2.4 times. A polyester film was obtained. (Comparative Example 7) Heat transfer coefficient of 0.0017 calories / cm
A heat shrinkable polyester film having a thickness of 60 μm was obtained by the method described in Example 1 except that the heat treatment temperature after stretching was ² sec / ° C. and the heat treatment temperature after stretching was 70 ° C. (Comparative Example 8) A thickness of 60 µm was obtained by the method described in Example 1 except that the heat treatment temperature after stretching was 90 ° C.
To obtain a heat-shrinkable polyester film.

Table 1 shows the evaluation results of the films obtained in Examples 1 to 4 and Comparative Examples 1 to 8. As is clear from Table 1, the heat-shrinkable films obtained in Examples 1 to 4 all showed a good shrink finish (no defects such as wrinkles, color spots, insufficient shrinkage, etc.) and excellent break resistance. The thickness distribution was also good. As described above, the heat-shrinkable polyester film of the present invention has high quality and high practicality, and is particularly suitable for shrink labels. On the other hand, the heat-shrinkable film obtained in Comparative Example 1 is inferior in break resistance, the heat-shrinkable film obtained in Comparative Example 2 has wrinkles and color spots, and the heat-shrinkable films obtained in Comparative Examples 3 and 5 The heat-shrinkable film obtained in Comparative Example 6 has color spots, and the heat-shrinkable film obtained in Comparative Example 7 has wrinkles and a thickness distribution. Poorly, the heat shrinkable film obtained in Comparative Example 8 suffered from insufficient shrinkage and was inferior in break resistance. As described above, the heat-shrinkable polyester films obtained in Comparative Examples were inferior in quality and were not practical.

[0029]

[Table 1]

[0030]

EFFECTS OF THE INVENTION The heat-shrinkable polyester film of the present invention according to claim 1 has very few wrinkles, shrinkage spots, and distortions after shrinkage, and is excellent in impact resistance rupture resistance. Further, the method for producing a heat-shrinkable polyester film of the present invention according to claim 2 is a heat-shrinkable polyester film in which wrinkles, shrinkage spots, and distortion are extremely small after shrinkage and which is excellent in break resistance against impact. Is easily obtained.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Shinichiro Okumura 344 Maebata, Kizu, Inuyama City, Aichi Prefecture Inuyama Plant, Toyobo Co., Ltd. (72) Hiroaki Esaki 344 Maebata, Kizu, Inuyama City, Aichi Prefecture Toyobo Co., Ltd. Inuyama Factory (72) Inventor Kiyozo Takabayashi Inuyama City, Aichi Prefecture, Kyuzu, Majihata 344, Toyobo Co., Ltd. Inuyama Factory

Claims (2)

[Claims] 1. A stretched film comprising a polyester having a terephthalic acid component of 70 mol% or more in a dicarboxylic acid component and an ethylene glycol component of 70 mol% in a diol component, which is heated in an air oven at 90 ° C. The maximum value (σmax) of the contraction stress in the main contraction direction that occurs between 1 minute and 1 minute after is 0.5 to 1.2 kg / mm ² , 75
The heat shrinkage in the main shrinkage direction after treatment for 10 seconds in warm water at 4 ℃ is 4
A heat-shrinkable polyester film having a heat-shrinkage rate of 0% or less and a main shrinkage direction of 50% or more after treatment in warm water of 95 ° C. for 10 seconds. 2. When stretching a polyester unstretched film having a terephthalic acid component in the dicarboxylic acid component of 70 mol% or more and an ethylene glycol component in the diol component of 70 mol% in the direction of the main shrinkage direction, the total stretching ratio is A stretching temperature of 3.0 g or more and Tg + 10 to Tg + 40 ° C. in the preceding stage for stretching 40 to 60% of the total stretching ratio, and thereafter,
A method for producing a heat-shrinkable polyester film, which comprises stretching at a stretching temperature of Tg-15 to Tg + 10 ° C. in the latter stage of stretching 60 to 40% of the total stretching ratio and a temperature lower than the stretching temperature of the former stage.