JP3448356B2 - Heat shrinkable polyester film - Google Patents

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 used for various packaging materials, and more specifically, it has excellent shrinkage characteristics at high temperature and excellent shrinkage evenness. It is about.

[0002]

2. Description of the Related Art Heat-shrinkable plastic films are used for marking and protecting containers, fishing rods, condensers, rod-shaped fluorescent lamps, etc.
It is used for bundling, improving added value of products, etc., and is also used for integrated packaging and close packaging of books and notebooks. At present, it is expected to develop various applications in many other fields by utilizing the shrinkability and shrinkage stress of the heat-shrinkable film.

Conventionally, as materials for heat-shrinkable films,
Resins such as polyvinyl chloride, polystyrene, and polyolefin have been used. However, such resins have drawbacks in heat resistance, weather resistance, chemical resistance and the like. For example, although polyvinyl chloride film can be used as a heat-shrinkable film having various shrinkage characteristics, fish eyes are likely to occur frequently, and the product printed with this film has a poor aesthetic appearance and a reduced commercial value. It was easy to become what I did. Also, in order to obtain a heat-shrinkable film without fish eyes, excessive quality control is required,
There was a problem that the film production cost increased remarkably. Furthermore, polyvinyl chloride causes pollution problems when incinerated at the time of disposal, and additives such as plasticizers in the polyvinyl chloride resin bleed out over time, causing dirt and other contamination, and It was not preferable in terms of sex.

On the other hand, a heat-shrinkable film obtained from polystyrene has a good finish after shrinkage, but has a low solvent resistance, so that a special ink must be used for printing, and even at room temperature. It had to be stored in a cool place due to spontaneous shrinkage. In addition, there is a big problem in the disposal because it needs to be incinerated at a high temperature and a large amount of black smoke and a strange odor are generated during the incineration. As a material capable of solving these problems, polyester film is highly expected, and its usage amount has been remarkably increasing.

[0005]

Conventionally, heat-shrinkable polyester films have not been sufficiently satisfactory in their heat-shrinkability. In particular, shrinkage unevenness is likely to occur during shrinkage, and when coating and shrinking on containers such as PET bottles, polyethylene bottles, glass bottles, the characters and patterns printed on the film cannot be reproduced well, and the film can be sufficiently adhered to the container. There were problems such as not being there.
In response to such a demand, as described in Japanese Patent Application No. 4-110963 and Japanese Patent Application No. 4-110964, a polyester resin obtained by copolymerizing a specific copolymer component may be used. A heat-shrinkable polyester film or the like has been proposed in which uneven shrinkage is less likely to occur by controlling the shrinkage speed.

[0006] However, such a heat-shrinkable polyester film has shrinkage characteristics at a relatively low temperature, and is suitable for shrink-coating a container such as a glass bottle that shrinks at a high temperature exceeding 100 ° C. Had problems such as uneven shrinkage caused by rapid shrinkage and poor heat resistance. An object of the present invention is to provide an excellent heat-shrinkable polyester film which is excellent in shrinkage characteristics at high temperature and does not cause uneven shrinkage or remain.

[0007]

In view of such circumstances, the inventors of the present invention have arrived at the present invention as a result of earnestly investigating a polyester resin constituting a heat-shrinkable film. That is, the heat-shrinkable polyester film of the present invention comprises a polyester resin comprising an acid component having naphthalene dicarboxylic acid or an ester-forming derivative thereof as a main component and an alcohol component having ethylene glycol as a main component, and cyclohexanediene in the alcohol component. It is characterized by containing 5 to 40 mol% of methanol.

The polyester resin used in the heat-shrinkable polyester film of the present invention comprises an acid component containing naphthalenedicarboxylic acid or its ester-forming derivative as a main component and an alcohol component containing ethylene glycol as a main component. The acid component constituting the polyester resin contains naphthalene dicarboxylic acid such as naphthalene-1,4- or -2,6-dicarboxylic acid or an ester-forming derivative thereof in a proportion of 50 mol% or more in all acid components. And preferably 60 mol% or more,
More preferably, it is 70 mol% or more. This is because when the content of naphthalenedicarboxylic acid is less than 50 mol%, the mechanical strength when formed into a film is lowered, and the glass transition temperature of the polyester resin is lowered to lower the shrinkage characteristics at high temperatures. This is because

Acid components other than naphthalenedicarboxylic acid that can be used in the present invention include aromatic dicarboxylic acids such as terephthalic acid and isophthalic acid, fats such as glutaric acid, adipic acid, sebacic acid, azelaic acid, oxalic acid and succinic acid. Group dicarboxylic acids or their ester-forming derivatives are listed. Among them, the aromatic dicarboxylic acid or its ester-forming derivative is contained in the total acid component in a total amount of 80 or more from the viewpoints of film-forming property, mechanical strength of the film, shrinkage characteristics at high temperature and the like.
It is preferably contained in an amount of not less than mol%, more preferably not less than 85% by mol. The aliphatic dicarboxylic acid or its ester-forming derivative is used for the purpose of increasing the heat shrinkage amount of the film, and is less than 20 mol% in the total acid component.
Preferably, it can be contained in the range of less than 15 mol%. This is because if the content of these aliphatic dicarboxylic acid components is 20 mol% or more, the mechanical strength of the polyester film may decrease.

As the alcohol component constituting the polyester resin, ethylene glycol is contained in a proportion of 50 mol% or more, preferably 60 mol% or more, based on the total alcohol component. This is because when the content of ethylene glycol is less than 50 mol%, the polymerization reactivity tends to decrease during the production of the resin, and the resin having the desired degree of polymerization may not be obtained. is there.

In the present invention, it is important that cyclohexanedimethanol is contained as an alcohol component together with ethylene glycol in a proportion of 5 to 40 mol% in the total alcohol component. This is because if the proportion of the cyclohexanedimethanol component is less than 5 mol%, uneven shrinkage is likely to occur and a sufficient shrinkage amount cannot be obtained. Conversely, if it exceeds 40 mol%, shrinkage starts. This is because when the temperature becomes low and contracts at high temperature, rapid contraction occurs and uneven contraction easily occurs.
It is preferably in the range of 8 to 30 mol%.

Alcohol components other than ethylene glycol and cyclohexanedimethanol that can be used in the present invention include propylene glycol, triethylene glycol, diethylene glycol, neopentyl glycol, polyethylene glycol, polyoxytetramethylene glycol, bisphenol compound or a compound thereof. Examples include ethylene oxide adducts of derivatives. These other alcohol components can be used in a range that does not impair the effects of the present invention, for example, in a range of 20 mol% or less.

In the present invention, the sum of the proportion of acid components other than naphthalenedicarboxylic acid in the total acid components and the proportion of alcohol components other than ethylene glycol in the total alcohol components is in the range of 10 to 50 mol%. Preferably there is. This is because the sum of the ratio of acid components other than naphthalenedicarboxylic acid in the total acid components and the ratio of alcohol components other than ethylene glycol in the total alcohol components is 10 mol%.
Below, there is a tendency that sufficient solvent adhesiveness cannot be obtained,
On the other hand, when it exceeds 50 mol%, the solvent resistance of the film itself tends to be poor, and a resin capable of forming a film tends to be unobtainable, and more preferably in the range of 20 to 40 mol%.

In the present invention, rapid contraction is suppressed,
For the purpose of further reducing shrinkage unevenness, a trivalent or higher polyvalent carboxylic acid or polyhydric alcohol may be used. Specific examples of the trivalent or higher polycarboxylic acid or polyhydric alcohol include polycarboxylic acids such as trimellitic acid, pyromellitic acid and their anhydrides, trimethylolpropane, trimethylolethane, glycerin, diglycerin, Examples include polyhydric alcohols such as pentaerythritol. Among them, trimethylol propane from the viewpoint of the reactivity at the time of thermal stability and polycondensation during film formation, trimellitic acid, pentaerythritol is preferred.

The polyester resin of the present invention can be produced by a known direct polymerization method or transesterification method,
The degree of polymerization is not particularly limited, but the intrinsic viscosity (measured at 25 ° C. in a mixed solution of phenol / tetrachloroethane by weight) is 0.5 because of the moldability of the raw film.
The thing of -1.2 is preferable.

The obtained polyester resin is molded into a heat-shrinkable polyester film by the following method, for example. First, after drying the polyester resin, melt it,
Melt extrusion is performed from a die, and a raw film is formed by a casting method or a calendar method. Next, this raw film was set to 3 from the glass transition temperature (Tg) of the polyester resin.
1.5 to 5.0 times in the longitudinal or transverse direction, preferably 1.0 at a temperature higher than ℃, preferably higher than 5 ℃
The film is stretched to 4.8 times to give a high shrinkage rate to the film. Further, if necessary, it is stretched 1.0 to 1.8 times, preferably 1.0 to 1.5 times in the direction perpendicular to the stretching direction. This is effective in improving the tensile strength of the film and preventing the shrinkage in the stretching direction from shrinking more than necessary.

The stretching of the film is carried out by a method such as simultaneous biaxial stretching, sequential biaxial stretching, uniaxial stretching, etc. Either longitudinal stretching or transverse stretching may be performed first. The stretched heat-shrinkable polyester film can be used as a product as it is, but may be heat-treated at a temperature of 50 to 150 ° C. for several seconds to several tens seconds from the viewpoint of dimensional stability and the like. By performing such heat treatment,
The polyester film of the present invention can exhibit desirable properties such as adjustment of the shrinkage ratio in the shrinking direction, reduction of time-dependent shrinkage of the unshrinked film during storage, and reduction of shrinkage unevenness.

The thickness of the heat-shrinkable polyester film of the present invention is not particularly limited, but it is 1 to 600 μm.
Those in the range of are practically used. 6 to 380 μm for packaging applications, especially packaging of foods, beverages, pharmaceuticals, etc.
Those in the range of are used. When used for labels such as PET bottles, polyethylene bottles and glass bottles, those having a range of 20 to 70 μm are used.

The heat-shrinkable polyester film of the present invention has a shrinkage of 5% or less when it is shrunk in hot air at 80 ° C. for 1 minute without weighting, and it has a shrinkage ratio of 1% in hot air at 120 ° C. without weighting. It is necessary that the contraction rate when contracted for minutes is 20% or more. This is because when the shrinkage ratio at 80 ° C. exceeds 5%, the heat-shrinkable film causes rapid shrinkage and causes uneven shrinkage when shrinked at a high temperature of 120 ° C. or higher, which is preferable. Has a shrinkage of 3 at 80 ° C
% Or less. Also, the shrinkage ratio at 120 ° C. is 20
If it is less than%, a sufficient amount of shrinkage cannot be obtained, the adhesion of the film to the container becomes insufficient, and it becomes difficult to completely cover a container having a particularly complicated shape. Considering the occurrence of shrinkage unevenness due to abrupt shrinkage when the film shrinks, the shrinkage ratio at 120 ° C. is preferably in the range of 20 to 60%.

In the present invention, various conventionally known processing treatments and suitable additives may be added in order to impart more specific performance. Examples of processing treatments include irradiation with ultraviolet rays, α rays, β rays, γ rays or electron beams, corona treatment, plasma irradiation treatment, flame treatment, vinylidene chloride, polyvinyl alcohol, polyamide, polyolefin, etc. Examples thereof include resin coating, laminate, and metal vapor deposition. Examples of additives include polyamide,
Examples thereof include resins such as polyolefin, polymethylmethacrylate and polycarbonate, inorganic particles such as silica, talc, kaolin and calcium carbonate, pigments such as titanium oxide and carbon black, ultraviolet absorbers, release agents and flame retardants.

[0021]

EXAMPLES The present invention will be specifically described below with reference to examples. The shrinkage rate is 80 mm at 120 ° C. with a marked line provided on a polyester film cut into a size of 150 mm in the stretching direction and a size of 20 mm in the direction perpendicular thereto at intervals of 100 mm.
When left unloaded for 1 minute in each hot air of ℃, the length before shrinkage (L) and the length after shrinkage (L ′) were measured in the stretching direction of the film, and calculated by the following formula.

[0022]

Shrinkage (%) = {(L−L ′) / L} × 100 Shrinkage unevenness is 150 mm in the stretching direction and 2 in the direction perpendicular to it.
A polyester film cut into a size of 0 mm
After heat-shrinking in hot air at 120 ° C for 1 minute with no load, uneven appearance of shrinkage on the film was observed. ○: Shrinkage unevenness was hardly observed. △: Shrinkage unevenness was slightly generated. What was done x: Although the shrinkage unevenness was remarkable, it was evaluated in 3 grades.

Example 1 80 mol parts of dimethyl naphthalenedicarboxylate, 20 mol parts of dimethyl terephthalate, 240 mol parts of ethylene glycol and 6 mol% of cyclohexanedimethanol were placed in a reaction vessel, and manganese acetate was used as a transesterification catalyst for all acid components. On the other hand, 400 ppm was added, and the transesterification reaction was sufficiently carried out. Next, 250 ppm of trimethyl phosphate as a stabilizer was added to all acid components, and 400 ppm of antimony trioxide was added as a polymerization catalyst to all acid components, and the temperature in the reaction vessel was maintained at 290 ° C.
Polycondensation reaction was performed for 3 hours under a reduced pressure of Hg or less to obtain a polyester resin. The obtained polyester resin was dried and then melt-extruded from a T die at a resin temperature of 290 ° C. to prepare a raw film. This original film is 110 ℃
Uniaxially stretching 4.5 times in the stretching direction (TD direction),
A heat-shrinkable polyester film having a thickness of 40 μm was obtained.
Table 1 shows the resin composition of the obtained film, the measurement result of the shrinkage ratio, and the evaluation result of the shrinkage unevenness.

Example 2 90 mol parts of dimethyl naphthalene dicarboxylate, 10 mol parts of dimethyl isophthalate, 240 mol parts of ethylene glycol, and 9 mol parts of cyclohexanedimethanol were placed in a reaction vessel, and manganese acetate was used as a transesterification catalyst for all acid components. On the other hand, 400 ppm was added, and the transesterification reaction was sufficiently carried out. Next, 250 ppm of trimethyl phosphate as a stabilizer was added to all acid components, and 400 ppm of antimony trioxide was added as a polymerization catalyst to all acid components, and the temperature in the reaction vessel was maintained at 290 ° C.
Polycondensation reaction was performed for 3 hours under a reduced pressure of Hg or less to obtain a polyester resin. The obtained polyester resin was dried and then melt-extruded from a T die at a resin temperature of 290 ° C. to prepare a raw film. This original film is 110 ℃
Uniaxially stretching 4.5 times in the stretching direction (TD direction),
A heat-shrinkable polyester film having a thickness of 40 μm was obtained.
Table 1 shows the resin composition of the obtained film, the measurement result of the shrinkage ratio, and the evaluation result of the shrinkage unevenness.

Example 3 90 mol parts of dimethyl naphthalenedicarboxylate, 10 mol parts of dimethyl isophthalate, 220 mol parts of ethylene glycol, and 12 mol parts of cyclohexanedimethanol were placed in a reaction vessel, and manganese acetate was used as a transesterification catalyst for all acid components. On the other hand, 400 ppm was added, and the transesterification reaction was sufficiently carried out. Next, 250 ppm of trimethyl phosphate as a stabilizer for all acid components and 400 ppm of antimony trioxide as a polymerization catalyst for all acid components
Add and maintain the temperature in the reaction vessel at 290 ° C,
Polycondensation reaction was performed for 3 hours under reduced pressure of mHg or less to obtain a polyester resin. The obtained polyester resin was dried and then melt-extruded from a T die at a resin temperature of 290 ° C. to prepare a raw film. This original film is 110 ℃
Uniaxially stretching 4.5 times in the stretching direction (TD direction),
A heat-shrinkable polyester film having a thickness of 40 μm was obtained.
Table 1 shows the resin composition of the obtained film, the measurement result of the shrinkage ratio, and the evaluation result of the shrinkage unevenness.

Example 4 90 mol parts of dimethyl naphthalenedicarboxylate, 10 mol parts of dimesyl isophthalate, 210 mol parts of ethylene glycol, and 23 mol parts of cyclohexanedimethanol were placed in a reaction vessel, and manganese acetate was used as an ester exchange catalyst for all acid components. On the other hand, 400 ppm was added, and the transesterification reaction was sufficiently carried out. Next, 250 ppm of trimethyl phosphate as a stabilizer with respect to all acid components and 200 pp of antimony trioxide as a polymerization catalyst with respect to all acid components
m, titanium tetatobutoxide to the total acid component 20
0 ppm was added, the temperature in the reaction vessel was maintained at 290 ° C., and a polycondensation reaction was performed for 3 hours under a reduced pressure of 5 mmHg or less to obtain a polyester resin. The obtained polyester resin was dried and then melt-extruded from a T die at a resin temperature of 290 ° C. to prepare a raw film. This original film,
Uniaxial stretching was performed 4.5 times in the stretching direction (TD direction) at 110 ° C. to obtain a heat-shrinkable polyester film having a thickness of 40 μm. Table 1 shows the resin composition of the obtained film, the measurement result of the shrinkage ratio, and the evaluation result of the shrinkage unevenness.

Example 5 100 mol parts of dimethyl naphthalene dicarboxylate, 210 mol parts of ethylene glycol, and 35 mol parts of cyclohexane dimethanol were placed in a reaction vessel, and 400 ppm of manganese acetate was added as a transesterification catalyst to all acid components to form an ester. The exchange reaction was carried out sufficiently. Then, trimethyl phosphate as a stabilizer is added to the total acid component in an amount of 2
50 ppm, 200 ppm of antimony trioxide as a polymerization catalyst to all acid components, 300 ppm of titanium tetrabutoxide to all acid components, and 250 ppm of cobalt acetate to all acid components were added, and the temperature in the reaction vessel was adjusted to 2
While maintaining at 90 ° C., polycondensation reaction was performed for 3 hours under reduced pressure of 5 mmHg or less to obtain a polyester resin. The obtained polyester resin was dried and then melt-extruded from a T die at a resin temperature of 290 ° C. to prepare a raw film. 3. This raw film was stretched at 110 ° C. in the stretching direction (TD direction).
The film was uniaxially stretched 5 times to obtain a heat-shrinkable polyester film having a thickness of 40 μm. The resin composition of the obtained film,
Table 1 shows the measurement results of the shrinkage ratio and the evaluation results of the shrinkage unevenness.

Example 6 100 mol parts of dimethyl naphthalenedicarboxylate, 210 mol parts of ethylene glycol, and 47 mol parts of cyclohexanedimethanol were placed in a reaction vessel, and 400 ppm of manganese acetate was added as an ester exchange catalyst to the total acid components to form an ester. The exchange reaction was carried out sufficiently. Then, trimethyl phosphate as a stabilizer is added to the total acid component in an amount of 2
50 ppm, 200 ppm of antimony trioxide as a polymerization catalyst to all acid components, 300 ppm of titanium tetrabutoxide to all acid components, and 250 ppm of cobalt acetate to all acid components were added, and the temperature in the reaction vessel was adjusted to 2
While maintaining at 90 ° C., polycondensation reaction was performed for 3 hours under reduced pressure of 5 mmHg or less to obtain a polyester resin. The obtained polyester resin was dried and then melt-extruded from a T die at a resin temperature of 290 ° C. to prepare a raw film. 3. This raw film was stretched at 110 ° C. in the stretching direction (TD direction).
The film was uniaxially stretched 5 times to obtain a heat-shrinkable polyester film having a thickness of 40 μm. The resin composition of the obtained film,
Table 1 shows the measurement results of the shrinkage ratio and the evaluation results of the shrinkage unevenness.

Comparative Example 1 100 mol parts of dimethyl naphthalene dicarboxylate and 240 mol parts of ethylene glycol were placed in a reaction vessel, and manganese acetate was used as a transesterification catalyst in an amount of 500 with respect to all acid components.
ppm was added and the transesterification reaction was sufficiently carried out. Next, 350 ppm of trimethyl phosphate as a stabilizer with respect to all acid components and 500 ppm of antimony trioxide as a polymerization catalyst with respect to all acid components were added, and the temperature in the reaction vessel was maintained at 290 ° C. to 5 mmHg or less. Polycondensation reaction was performed under reduced pressure for 3 hours to obtain a polyester resin. The obtained polyester resin was dried and then melt-extruded from a T die at a resin temperature of 290 ° C. to prepare a raw film. This raw film was uniaxially stretched 4.5 times in the stretching direction (TD direction) at 110 ° C. to obtain a heat-shrinkable polyester film having a thickness of 40 μm. Table 1 shows the resin composition of the obtained film, the measurement result of the shrinkage ratio, and the evaluation result of the shrinkage unevenness.

Comparative Example 2 40 mol parts of dimethyl naphthalene dicarboxylate, 30 mol parts of dimethyl terephthalate, 240 mol parts of ethylene glycol, and 10 mol parts of cyclohexanedimethanol were placed in a reaction vessel, and manganese acetate was used as a transesterification catalyst for all acid components. On the other hand, 500 ppm was added, and the transesterification reaction was sufficiently carried out. Next, trimethyl phosphate as a stabilizer is 350 ppm with respect to all acid components, and antimony trioxide as a polymerization catalyst is 500 ppm with respect to all acid components.
Add and maintain the temperature in the reaction vessel at 290 ° C,
Polycondensation reaction was performed for 3 hours under reduced pressure of mHg or less to obtain a polyester resin. The obtained polyester resin was dried and then melt-extruded from a T die at a resin temperature of 290 ° C. to prepare a raw film. This original film is 110 ℃
The film was uniaxially stretched 4.5 times in the stretching direction (TD direction), but the mechanical strength of the film was weak and the film was broken during the stretching.

Comparative Example 3 100 mol parts of dimethyl naphthalene dicarboxylate, 200 mol parts of ethylene glycol, and 60 mol parts of cyclohexane dimethanol were placed in a reaction vessel, and 400 ppm of manganese acetate was added as an ester exchange catalyst to all acid components to form an ester. The exchange reaction was carried out sufficiently. Then, trimethyl phosphate as a stabilizer is added to the total acid component in an amount of 2
50 ppm, 200 ppm of antimony trioxide as a polymerization catalyst was added to the total acid component, and the temperature in the reaction vessel was adjusted to 2
While maintaining at 90 ° C., polycondensation reaction was performed for 3 hours under reduced pressure of 5 mmHg or less to obtain a polyester resin. The obtained polyester resin was dried and then melt-extruded from a T die at a resin temperature of 290 ° C. to prepare a raw film. 3. This raw film was stretched at 110 ° C. in the stretching direction (TD direction).
The film was uniaxially stretched 5 times to obtain a heat-shrinkable polyester film having a thickness of 40 μm. The resin composition of the obtained film,
Table 1 shows the measurement results of the shrinkage ratio and the evaluation results of the shrinkage unevenness.

Comparative Example 4 30 mol parts of dimethyl naphthalene dicarboxylate, 60 mol parts of dimethyl terephthalate, 10 mol parts of dimethyl isophthalate, 210 mol parts of ethylene glycol, and 5 mol parts of cyclohexanedimethanol were placed in a reaction vessel to serve as an ester exchange catalyst. 400p manganese acetate for all acid components
pm was added and the transesterification reaction was sufficiently carried out. Next, 250 ppm of trimethyl phosphate as a stabilizer was added to all acid components, and 350 ppm of antimony trioxide was added as a polymerization catalyst to all acid components, and the temperature in the reaction vessel was maintained at 290 ° C. to 5 mmHg or less. Polycondensation reaction was performed under reduced pressure for 3 hours to obtain a polyester resin. The obtained polyester resin was dried and then melt-extruded from a T die at a resin temperature of 290 ° C. to prepare a raw film. This raw film was uniaxially stretched 4.5 times in the stretching direction (TD direction) at 110 ° C. to obtain a heat-shrinkable polyester film having a thickness of 40 μm. Table 1 shows the resin composition of the obtained film, the measurement result of the shrinkage ratio, and the evaluation result of the shrinkage unevenness.

[0033]

[Table 1]

The components shown in the table are as follows. NDA: naphthalene dicarboxylic acid component TPA: terephthalic acid component IPA: isophthalic acid component EG: ethylene glycol component CHDM: cyclohexanedimethanol component

[0035]

EFFECT OF THE INVENTION The heat-shrinkable polyester film of the present invention has a high heat-shrinkage ratio even at a relatively high temperature, has excellent shrink adhesion to a container such as a bottle, and can perform shrink coating without uneven shrinkage. Therefore, it is excellent in practicality as various packaging materials, and particularly suitable as a heat shrinkable label for glass bottles.

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-5-245930 (JP, A) JP-A-62-91555 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C08G 63/00-63/91

Claims (2)

(57) [Claims] 1. A polyester resin comprising an acid component containing naphthalenedicarboxylic acid or an ester-forming derivative thereof as a main component and an alcohol component containing ethylene glycol as a main component, wherein cyclohexanedimethanol is contained in an amount of 5 to 40 mol%. A heat-shrinkable polyester film which is characterized by containing. 2. A shrinkage rate of 5% or less when shrunk in hot air of 80 ° C. for 1 minute, and a shrinkage rate of 20% or more when shrunk in hot air of 120 ° C. for 1 minute. A heat-shrinkable polyester film according to claim 1.