JP2007169323A - Heat shrinkable polyester-based film and heat shrinkable label - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a heat shrinkable polyester-based film suitable for a beverage container label while excellent in close adhesion with various inks, exhibiting a good separating property in an aqueous alkaline solution and also excellent in various characteristics such as blocking resistance, sliding property, etc. <P>SOLUTION: This heat shrinkable polyester-based film has ≥50% heat shrinkage in its maximum shrinking direction when a sample obtained by cutting out the film by 10 cm x 10 cm square shape is immersed in warm water at 95°C for 10 sec, pulled up, then immersed in water at 25°C for 10 sec and then pulled up. At an uppermost layer of the first surface of the film, the nitrogen atom content is 0.2-5.0 atomic%, and the dynamic frictional coefficient of the second surfaces of the films with each other is μd ≤0.28. Also, the dynamic frictional coefficient of the second surfaces of the films with each other is μd ≤0.30 after the film is immersed into warm water at 80°C for 20 to have it shrinked by 10% in its maximum shrinking direction, then pulled up and dried naturally under an atmosphere at 23°C and 65% relative humidity for 24 hr. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a heat-shrinkable polyester film, and more particularly, has excellent ink adhesion during printing, and has excellent detachability with respect to ink of a type that is detached with an alkaline aqueous solution, and the film is labeled. Excellent opening after label cutting and good slipping on the outer surface when used as a beverage bottle label film, suitable for vending machine beverage labels, and processing in printing and tubing processes The present invention relates to a heat-shrinkable polyester film having excellent properties.

In recent years, for the purpose of packaging to improve the appearance of packaging, packaging to avoid direct impact of contents, label packaging that protects glass bottles or plastic bottles and displays products, etc.
A heat-shrinkable plastic film having a property of shrinking by heating is widely used. Plastic materials used for these purposes include stretched films such as polyvinyl chloride films, polystyrene films, and polyester films. Labels are used in various containers such as polyethylene terephthalate (PET) containers, polyethylene containers, and glass containers. And used for the purpose of cap seals or integrated packaging.

  In order to produce labels and the like, the following methods are usually employed. That is, the raw polymer is continuously melt extruded to produce an unstretched film. Next, stretching is performed to obtain a film roll. While feeding out the film from this film roll, it is slit to a desired width and wound into a roll again. Subsequently, character information such as various product names and designs are printed. After the printing is finished, the tube is manufactured by overlapping and joining the left and right ends of the film by means such as solvent bonding (tubing process). The slit process and the printing process may be reversed in order. If the obtained tube is cut into a suitable length, it becomes a cylindrical label, and a bag can be manufactured by joining one open end of this cylindrical label.

  And the inside of the shrink tunnel (steam tunnel) of the type that covers the label or bag etc. on the container and blows and heat shrinks by steam, and the shrink tunnel (hot air tunnel) of the type that blows hot air and heat shrinks, A final product (labeled container) is obtained by passing it on a belt conveyor or the like, and heat-shrinking a label, a bag, or the like so as to be in close contact with the container.

By the way, in recent years, labels for PET bottles, etc., have been developed such as inks that are desorbed in an alkaline aqueous solution for the purpose of recycling, and water-based inks that do not reduce or use organic solvents that adversely affect the environment. In order to achieve a predetermined purpose, these inks may have lower performances such as adhesion to a film than conventional types. However, if the adhesion of the ink to the film in the printing process is poor, the ink will drop off, peel off, and the value of the product will be impaired. For this reason, a heat-shrinkable film that has excellent adhesion to these various inks and that exhibits good detachability in an alkaline aqueous solution has been desired.

In order to improve the adhesion with the ink, for example, there is a method of increasing the wetting tension of the film surface by subjecting the film surface to a surface treatment such as a corona treatment in a normal air atmosphere. When the wetting tension on the film surface is increased, the solvent resistance of the film is lowered when the solvent is bonded with tetrahydrofuran or 1,3-dioxolane to form a tube, so that the solvent-bonded portion loses flatness, so-called wakame-like. In some cases, the solvent-adhered portion of the tube may block with other film portions. Moreover, in the process of manufacturing a label by cutting a tube, the upper and lower films may be fused and blocked at the cut portion, and an opening defect may occur when the label is attached to a beverage bottle.

In addition, when used as a label for bottled beverages, when products are transported inside the vending machine, the products may not be able to reach the outlet due to insufficient slipping of the labels, May adhere to the inner surface of the film and may be discharged multiple times.
In order to solve this problem, a method of laminating a layer having good slipperiness on the film surface has been made (see, for example, Patent Document 1).
JP 2004-339734 A

  However, when the process of shrinking and mounting the label with steam is performed, there is a problem that slipperiness is insufficient and variation occurs.

  The present invention aims to provide a heat-shrinkable film that can solve the various problems of the above-mentioned conventional heat-shrinkable film, and specifically, in an alkaline aqueous solution while having excellent adhesion to various inks. An object of the present invention is to provide a heat-shrinkable polyester film that exhibits good detachability and is excellent in various properties such as blocking resistance and slipperiness.

  The heat-shrinkable polyester film of the present invention is pulled up by immersing a sample obtained by cutting the film into a 10 cm × 10 cm square shape in 95 ° C. warm water for 10 seconds and then immersing it in 25 ° C. water for 10 seconds. The thermal contraction rate in the maximum shrinkage direction is 50% or more, the nitrogen atom content of the outermost layer of the first surface of the film is 0.2 to 5.0 atomic%, and the second surfaces of the film are The coefficient of dynamic friction is .mu.d.ltoreq.0.28, and the film is immersed in warm water at 80.degree. C. for 10 seconds in the maximum shrinkage direction, immersed for 20 seconds, then pulled up, and naturally grown for 24 hours in an atmosphere at 23.degree. There is a gist where the coefficient of dynamic friction between the second surfaces of the film after drying is μd ≦ 0.30.

The heat-shrinkable polyester film having the above characteristics has excellent shrinkability, excellent printability for various types of inks, and excellent printability such as adhesion, and is suitable for alkali detachment type inks. Is excellent in alkali detachment. Further, even when the label is cut, the cut portion is not fused or blocked. Furthermore, by satisfying the above requirements for the coefficient of friction, clogging in the vending machine could be prevented when used as a label for a bottled beverage.

  When the wetting tension of the first surface of the film is 40 mN / m or more, the adhesion to the ink is sufficient, and the peel strength after heat sealing the film first surfaces at 75 ° C. is 5 N / 15 mm width or less. Since the blocking resistance is good, both are preferred embodiments of the present invention.

    In the present invention, it is preferable that the first surface and the second surface of the film can be solvent-bonded with 1,3-dioxolane. In the present invention, “solvent adhesion” means that the solvent adhesion strength is 3 N / 15 mm width or more in the measurement methods of the examples described later.

    Furthermore, in the present invention, it is preferable that an easy-slip layer is provided as the outermost layer on the second surface side of the film. The slipping layer preferably contains a silicone component, and the slipping layer is preferably provided by a coating method.

  The present invention also includes a heat-shrinkable label obtained from the heat-shrinkable polyester film.

  The heat-shrinkable film of the present invention is excellent in ink adhesion to various types of ink and has excellent detachability with respect to ink of a type that is desorbed with an alkaline aqueous solution. Moreover, since it is excellent also in blocking resistance, generation | occurrence | production of troubles, such as an opening defect after the label cut at the time of making a film into a label form, can also be suppressed. Moreover, it is excellent in slipperiness and can prevent clogging inside the vending machine when used for beverage labels. Therefore, it is very useful as a label for covering containers such as bottled beverages.

Not only heat-shrinkable polyester film but also various inks by performing corona treatment, flame treatment, plasma treatment, ultraviolet treatment, etc. in air atmosphere on one or both sides of the film surface during film formation or after film formation It has been carried out to improve the adhesion to. Among industrial operations, corona treatment under an air atmosphere is most widely performed as a surface treatment.

When the heat-shrinkable polyester film is also subjected to corona treatment, the surface wetting tension is increased and the adhesion to various types of ink is improved, as with other films. However, when corona treatment is performed, the alkali detachability of the ink that is desorbed with alkali is improved, but fusion and blocking are likely to occur when the heat-shrinkable polyester film is label-cut. There has occurred.

The heat-shrinkable polyester film has strength such as polyethylene terephthalate as the most structural unit, but it reduces the crystallinity of the polymer and has the effect of making it amorphous, and neopentyl glycol. 1,4-butanediol, 1,3-propanediol, etc. for lowering the glass transition temperature (Tg) and expressing the thermal shrinkage at low temperature, etc. Necessary heat shrinkage rate is obtained by using the low Tg monomer component. In particular, due to the effect of the amorphous component, even when the film surface treatment is not performed (untreated state), the adhesion to ink is excellent compared to the untreated PET film.

However, if the heat-shrinkable film is subjected to the corona treatment at the energy level that is practiced for general PET film in order to further improve the adhesion, the film surface is excessively oxidized due to the presence of the amorphous component. It has been found that the wetting tension increases more than necessary. As a result, fusion or blocking occurs when the film is label-cut, the slipperiness of the film surface is reduced and the workability of the film deteriorates, and the film is blocked when the film is stored in a rolled state Troubles such as that occurred.

Therefore, it has been considered to perform a corona treatment (low level treatment) at an energy level lower than that of an ordinary PET film, but this is the case with a corona treatment facility for a normal PET film. It is difficult to perform such low level processing, and it becomes necessary to newly introduce a special power source and electrode equipment for low level processing. In addition, it is possible to improve the adhesion to ink by such a low level of corona treatment. However, if the corona treatment is carried out to the level of ink adhesion necessary for practical use, the film is also melted during label cutting of the film. There was a problem of wearing and blocking, and it was difficult to achieve both characteristics.

In order to secure the ink adhesion and the detachability to the alkali detachment type ink and to prevent the occurrence of fusion or blocking when the film is label-cut, nitrogen atoms are added to the surface of the first surface of the film. It is effective to exist.
The present invention will be described in detail below.

  The heat-shrinkable film of the present invention has a maximum shrinkage when a sample cut into a 10 cm × 10 cm square is immersed in 95 ° C. warm water for 10 seconds and then immersed in 25 ° C. water for 10 seconds. It is a heat-shrinkable film having a direction heat shrinkage of 50% or more. If the film has a heat shrinkage rate of less than 50%, the film does not have sufficient heat shrinkage force, so that when the film is coated and shrunk on a container or the like, it does not adhere to the container and an appearance defect occurs, which is not preferable. A more preferable heat shrinkage rate is 52% or more, and further preferably 55% or more.

Here, the heat shrinkage rate in the maximum shrinkage direction means the heat shrinkage rate in the direction in which the sample shrinks most, and the maximum shrinkage direction is determined by the length of the square in the vertical direction or the horizontal direction. Further, the thermal shrinkage rate (%) was obtained by immersing a sample of 10 cm × 10 cm in warm water at 95 ° C. ± 0.5 ° C. for 10 seconds in a no-load state and then thermally shrinking, and then 25 ° C. ± 0.5 The film was measured in accordance with the following formula after measuring the length in the longitudinal and lateral directions after being immersed in water at 10 ° C. for 10 seconds under no load condition (hereinafter, the heat shrinkage in the maximum shrinkage direction measured under these conditions). The rate is simply abbreviated as “heat shrinkage rate”).
Heat shrinkage rate (%) = 100 × (length before shrinkage−length after shrinkage) ÷ (length before shrinkage)

  Moreover, the nitrogen atom content of the outermost layer of the 1st surface of a film must be 0.2-5.0 atomic% for the film of this invention. This is because, within this range, the alkali detachability of the alkali detachment type ink can be imparted while the adhesion to various inks is enhanced, and the blocking resistance can also be enhanced. This nitrogen atom content is the ratio of nitrogen atoms to the total amount of elements in the film outermost layer (several tens of liters) that can be measured by XPS (X-ray photoelectron spectroscopy). If the content of nitrogen atoms on the film surface is less than 0.2 atomic%, the adhesion to various types of ink will be insufficient. On the other hand, when the nitrogen atom content exceeds 5.0 atomic%, fusion / blocking after label cutting occurs, and slipperiness decreases due to changes in the surface properties of the film. A more preferable lower limit of the nitrogen atom content is 0.25 atomic%, and a further preferable lower limit is 0.3 atomic%. A more preferable upper limit of the nitrogen atom content is 4.9 atomic%, and a further preferable upper limit is 4.8 atomic%.

The form of nitrogen atoms on the first surface of the film may be either a form of nitrogen atoms (N) or a form of nitrogen ions (N ⁺ ). As a method for incorporating nitrogen atoms in the first surface of the film, a method of subjecting the first surface of the film to corona treatment or plasma treatment in a nitrogen atmosphere is preferable. By performing corona treatment or plasma treatment in a nitrogen atmosphere, nitrogen atoms can be present on the film surface in the form of nitrogen atoms (N) or in the form of nitrogen ions (N ⁺ ).

  Moreover, in order to control the amount of nitrogen atoms in the surface layer of the first surface of the film, it is possible to change the equipment and processing conditions in corona treatment or plasma treatment. On the equipment side, for example, the frequency of the power source of the corona treatment equipment, the material and shape of the discharge electrode, the number of materials, the material of the treatment roll, the gap between the discharge electrode and the film treatment surface, the control of the nitrogen gas concentration in a nitrogen atmosphere, In terms of conditions, control of film running speed, atmospheric temperature, roll surface temperature during processing, and the like can be mentioned.

For example, when a preferable facility is exemplified in the corona treatment, the frequency of the power source is preferably in the range of 8 KHz to 60 KHz. The material of the discharge electrode is preferably aluminum or stainless steel, and the shape of the discharge electrode is preferably a knife edge shape, a bar shape, or a wire shape. Further, the number of discharge electrodes is preferably 2 or more in order to uniformly treat the film surface. The treatment roll serves as a counter electrode when corona discharge is performed, but at least the surface material needs to be a dielectric. As the dielectric material, it is preferable to use silicone rubber, hyperon rubber (Hypalon is a registered trademark of DuPont; chlorosulfonated polyethylene), EPT rubber, etc., and coat at least the surface of the treatment roll with a thickness of 1 mm or more. Is preferred. The gap between the discharge electrode and the film processing surface is preferably in the range of about 0.2 mm to 5 mm.

In terms of conditions, the film traveling speed (processing speed) may be processed at an arbitrary speed within the range of the equipment capacity, but the film surface temperature during corona treatment in a nitrogen atmosphere is 20 to 50 ° C. When the oxygen concentration in the nitrogen atmosphere is controlled to 300 ppm or less, the nitrogen atom content on the film surface can be controlled within the above range. The temperature of the surface of the treatment roll is preferably controlled by temperature control equipment, and is preferably adjusted from 30 ° C to 40 ° C. If necessary, a temperature control roll may be arranged before or after the treatment roll.

  Furthermore, if the nitrogen concentration in the atmosphere during corona treatment or plasma treatment varies, it will cause a variation in the nitrogen atom content on the film surface, so a technique that does not vary the atmosphere nitrogen concentration can be adopted. It is preferable. Since the corona treatment is usually performed in an air atmosphere, the corona treatment equipment does not include a sealing means for bringing the nitrogen atmosphere. Therefore, it is necessary to place the corona treatment equipment itself in the chamber in order to put it in a nitrogen atmosphere. At this time, if the air inside the chamber is replaced with nitrogen to form a nitrogen atmosphere and the film is run while corona treatment is performed inside the chamber, the air flows as an accompanying flow of the running film, and the nitrogen concentration in the atmosphere is reduced. It will fluctuate.

  In order to prevent this variation in nitrogen concentration, it is recommended that the gap between the film and the outer periphery of the film entrance in the chamber enclosing the corona treatment equipment be 0.4 mm or less, more preferably 0.3 mm or less. It is also preferable to cut the accompanying flow by covering the gap with a plastic film or cloth. It is also an effective means to make the chamber have a structure of two or more layers and to separately supply nitrogen for cutting the accompanying flow on the outer layer side.

  In addition, oxygen is also present in the corona treatment atmosphere due to the inflow of air, but oxygen may increase the wetting tension of the film more than necessary, so oxygen in the nitrogen atmosphere where corona treatment or plasma treatment is performed. The concentration is preferably controlled to 300 ppm or less. More preferably, it is 250 ppm or less, More preferably, it is 200 ppm or less. In the case of continuously producing a long film roll, it is preferable that the fluctuation range of the oxygen concentration in the nitrogen atmosphere from the start of winding of the roll to the end of winding be an average oxygen concentration of ± 80 ppm or less. More preferably, the average oxygen concentration is ± 60 ppm or less.

  As described above, by setting the nitrogen atom content of the outermost layer of the first surface of the film in a specific range, it was possible to obtain a film that satisfies both the adhesion to the ink and the blocking resistance, The film satisfying both the adhesion to the ink and the blocking resistance can be measured by using the wetting tension. In the present invention, the wetting tension of the first surface of the film is preferably 45 mN / m or more. If the wetting tension on the film surface is less than 45 mN / m, the adhesion to various types of ink will be insufficient. A more preferable lower limit of the wetting tension is 47 mN / m, and a further preferable lower limit is 48 mN / m. Further, the upper limit of the wetting tension of the first surface of the film is not particularly limited, but it is 58 mN / m or less from the viewpoint of suppressing the occurrence of fusion and blocking after the label cut and ensuring the film slipperiness. It is preferable to make it.

  On the other hand, blocking resistance can also be evaluated by the peel strength of the heat seal part. When the first surfaces of the films are heat-sealed at 75 ° C., when the peel strength of the heat-sealed portion is 5 N / 15 mm width or less, various troubles due to film fusion / blocking as described above can be prevented. Furthermore, it is preferable because label cutting can be performed at high speed. A more preferable upper limit of the peel strength (75 ° C.) is 4.5 N / 15 mm width, and a more preferable upper limit is 4 N / 15 mm width. Moreover, in the case of peel strength after heat sealing at 85 ° C., a width of 7 N / 15 mm or less is preferable. More preferably, it is 6 N / 15 mm width or less, More preferably, it is 5 N / 15 mm width or less. In addition, it is preferable that these values are satisfied also in the second surface.

  In terms of slipperiness, the film of the present invention has a coefficient of dynamic friction μd between the second film surfaces of 0.28 or less, and the film is immersed for 20 seconds in a maximum shrinkage direction in warm water at 80 ° C. and then pulled up. The dynamic friction coefficient μd between the second surfaces of the film after being naturally dried for 24 hours in an atmosphere at 23 ° C. and 65% relative humidity should be 0.30 or less. When μd satisfies the above range, it is possible to provide a film having good slipperiness in the vending machine when used as a label for a beverage bottle, for example, the contact area with the inside of the vending machine is large and clogging occurs. Even if it is a square bottle which is easy to do, generation | occurrence | production of clogging can be prevented. Furthermore, the same effect can be obtained also when the shrink fitting process to a bottle is performed using steam. However, if it exceeds this range, the slipperiness becomes insufficient, and troubles such as clogging of containers with vending machines occur. More preferably, the upper limit of μd is that the dynamic friction coefficient μd between the second surfaces of the film is 0.26 or less, and the film is immersed in warm water at 80 ° C. for 10% in the maximum shrinkage direction and then immersed for 20 seconds and then pulled up. The dynamic friction coefficient μd between the second surfaces of the film after being naturally dried for 24 hours in an atmosphere with a relative humidity of 65% is 0.28. The dynamic friction coefficient μd between the second surfaces of the film is a value measured in an environment of 23 ° C. and 65% RH in accordance with JIS K7125.

  The composition and manufacturing method of the heat-shrinkable film of the present invention are not particularly limited as long as each of the above-described characteristics is satisfied. Preferred embodiments will be described below.

  The polyester resin constituting the heat-shrinkable film of the present invention uses, as a dicarboxylic acid component, one or more of aromatic dicarboxylic acids, their ester-forming derivatives, and aliphatic dicarboxylic acids, and polycondensation with a polyhydric alcohol component. The known (copolymerized) polyesters can be used. Examples of the aromatic dicarboxylic acid include terephthalic acid, isophthalic acid, naphthalene-1,4- or -2,6-dicarboxylic acid, and 5-sodium sulfoisophthalic acid. 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 as necessary.

Polyhydric alcohol components include ethylene glycol, diethylene glycol, dimer diol, 1,3-propanediol, triethylene glycol, 1,4-butanediol, neopentyl glycol, 1,4-cyclohexanedimethanol, 1,6-hexane Diol, 3-methyl 1,5-pentanediol, 2-methyl-1,5-pentanediol, 2,2-diethyl-1,3-propanediol, 1,9-nonanediol, 1,10-decanediol, etc. Alkylene glycol, an alkylene oxide adduct of a bisphenol compound or a derivative thereof, trimethylolpropane, glycerin, pentaerythritol, polyoxytetramethylene glycol, polyethylene glycol and the like. Moreover, although it is not a polyhydric alcohol, (epsilon) -caprolactone can also be used.

The polyester raw material which comprises a polyester-type heat-shrinkable film may be individual, and may mix and use 2 or more types. When used alone, homopolyesters other than polyethylene terephthalate such as polybutylene terephthalate, polycyclohexylene dimethyl terephthalate, and polyethylene naphthalate are preferable. This is because polyethylene terephthalate alone does not exhibit heat shrinkability.

However, in consideration of the tear resistance, strength, heat resistance, etc. of the film, the crystalline ethylene terephthalate unit is preferably the main constituent component. Specifically, in 100 mol% of the constituent unit of the polyester raw material, ethylene It is recommended to select the terephthalate unit to be 50 mol% or more. Therefore, it is preferable that 50 mol% or more of the terephthalic acid component in 100 mol% of the dicarboxylic acid component and 50 mol% or more of the ethylene glycol component in 100 mol% of the polyhydric alcohol component. As for an ethylene terephthalate unit, 55 mol% or more is more preferable, and 60 mol% or more is further more preferable. It is recommended that the units other than the ethylene terephthalate unit be 5 mol% or more, more preferably 7 mol% or more, and even more preferably 9 mol% or more in 100 mol% of the constituent unit of the polyester raw material. It is because it becomes possible to ensure the solvent adhesiveness and heat shrinkability of the film by introducing the amorphous improvement component to the above extent. As the amorphous improving component, it is preferable to use at least one of neopentyl glycol, 1,4-cyclohexanedimethanol, and isophthalic acid. In addition, it is more preferable to contain a component that lowers the glass transition temperature (Tg) to ensure the shrinkage property at a low temperature. As the component, at least one of 1,4-butanediol and 1,3-propanediol is preferably contained in an amount of 3 mol% or more, more preferably 5 mol% or more, and further preferably 7 mol% or more. It is preferable.

From the viewpoint of heat shrinkage characteristics and productivity, it is preferable to use a blend of two or more polyesters having different Tg. It is preferable to use a mixture of polyethylene terephthalate and copolymerized polyester (which may be two or more types), but it may be a combination of copolymerized polyesters. Moreover, polybutylene terephthalate, polycyclohexylene dimethyl terephthalate, and polyethylene naphthalate can be combined, or these can be used in combination with other copolyesters. Three types of blends of polyethylene terephthalate, polybutylene terephthalate, a mixed diol component of ethylene glycol and neopentyl glycol, and a copolyester composed of terephthalic acid are most preferable in terms of heat shrinkage characteristics. When two or more polyesters are used in combination, it is preferable from the viewpoint of production efficiency that the respective polymer chips are blended in a hopper.

Polyesters can be produced by melt polymerization in the usual way, but the so-called direct polymerization method in which oligomers obtained by direct reaction of dicarboxylic acids and glycols are polycondensed, dimethyl ester of dicarboxylic acid and glycol are transesterified. Examples include a so-called transesterification method in which polycondensation is performed after the reaction, and any production method can be applied. Moreover, the polyester obtained by another polymerization method may be sufficient. The polymerization degree of polyester is preferably 0.3 to 1.3 dl / g in terms of intrinsic viscosity.

In addition to polymerization catalysts such as antimony oxide, germanium oxide, and titanium compounds, polyester such as magnesium acetate, magnesium chloride and other Mg salts, calcium acetate, calcium chloride, etc. Ca salt, manganese acetate, manganese chloride and other Mn salts, zinc chloride, zinc acetate and other Zn salts, cobalt chloride, cobalt acetate and other Co salts, respectively, with respect to the polyester as 300 ppm or less, phosphoric acid or Phosphoric acid ester derivatives such as phosphoric acid trimethyl ester and phosphoric acid triethyl ester may be added in an amount of 200 ppm or less in terms of phosphorus (P).

If the total amount of metal ions other than the above polymerization catalyst is 300 ppm with respect to the polyester and the amount of P exceeds 200 ppm, not only the coloration of the polymer becomes remarkable, but also the heat resistance and hydrolysis resistance of the polymer are remarkably lowered. .

At this time, in terms of heat resistance, hydrolysis resistance, etc., the molar atomic ratio (P / M) of the total P amount (P) and the total metal ion amount (M) is 0.4 to 1.0. It is preferable. When the molar atomic ratio (P / M) is less than 0.4 or exceeds 1.0, it is not preferable because the film may be colored or coarse particles may be mixed in the film.

The timing of adding the above metal ions, phosphoric acid and derivatives thereof is not particularly limited. Generally, metal ions are added at the time of raw material charging, that is, before transesterification or esterification, and phosphoric acids are added before polycondensation reaction. It is preferable to do this.

In the heat-shrinkable polyester film of the present invention, inorganic particles, organic salt particles and crosslinked polymer particles can be added as a lubricant. Inorganic particles include calcium carbonate, kaolin, talc, magnesium carbonate, barium carbonate, calcium sulfate, barium sulfate, lithium phosphate, calcium phosphate, magnesium phosphate, aluminum oxide, silicon oxide, titanium oxide, zirconium oxide, riotium fluoride, etc. Is mentioned. In particular, in order to obtain a film having a lower haze while obtaining good handling properties, the inorganic particles are preferably aggregated silica particles formed by agglomerating primary particles. Examples of the organic salt particles include terephthalate such as calcium oxalate, calcium, barium, zinc, manganese, and magnesium.

Examples of the crosslinked polymer particles include homopolymers or copolymers of vinyl monomers such as divinylbenzene, styrene, acrylic acid or methacrylic acid. In addition, organic particles such as polytetrafluoroethylene, benzoguanamine resin, thermosetting urea resin, and thermosetting phenol resin may be used.

In addition, when trying to impart lubricity to the film, there is a method of roughening the surface with the above-mentioned lubricant particles and reducing the contact area. However, if too much is added, the transparency of the film is lowered and the commercial value is increased. It may be damaged. For this reason, it is preferable to use the said lubricant particle | grain at the level which suppresses the center surface average roughness in the 2nd surface of a film to 0.03 or less. Within this range, slipperiness can be imparted without impairing the transparency of the label film.

Examples of the method for adding the lubricant include a method in which the lubricant is dispersed in the polymerization step of the polyester used as the film material, or a method in which the polyester after polymerization is melted again and added. In order to disperse the lubricant uniformly over the entire length of the film roll, after dispersing the lubricant in the polyester by any of the methods described above, the shape of the polymer chip in which the lubricant is dispersed is matched and the raw material in the hopper It is preferable to suppress the segregation phenomenon. The polyester is taken out from the polymerization apparatus in the form of a strand in a molten state after polymerization, and immediately cooled with water, and then cut into a chip by a strand cutter. The chip has a cylindrical shape with an elliptical bottom surface. In order to suppress the segregation of raw materials, different types of raw materials in which the average size of the major axis, minor axis, and cylindrical height of the ellipsoidal bottom surface is within the range of the chip size ± 20% of the raw material species with the highest usage ratio A chip is preferably used, and the size is more preferably within ± 15%.

In the raw material composition for producing a film, various known additives may be added as necessary in addition to the polyester and the lubricant. Examples of the additive include an antistatic agent; an antiaging agent; an ultraviolet absorber; and a colorant (dye and the like).
The raw material composition is formed into a film by a known method (for example, an extrusion method or a calendar method). The shape of the film is, for example, a flat shape or a tube shape, and is not particularly limited.

In order to impart heat shrinkability to the unstretched film, a stretching process is performed. As the stretching method, for example, a known method such as a roll stretching method, a long gap stretching method, a tenter stretching method, or a tubular stretching method can be employed. In any of these methods, stretching may be performed by sequential biaxial stretching, simultaneous biaxial stretching, uniaxial stretching, and combinations thereof. In the biaxial stretching, stretching in the vertical and horizontal directions may be performed simultaneously, or one of them may be performed first. The draw ratio is preferably in the range of 1.0 to 7.0 times, and the magnification in one predetermined direction (the maximum shrinkage direction) is preferably 3.5 times or more.

In the stretching step, preheating is preferably performed at a temperature not lower than the glass transition temperature (Tg) of the polymer constituting the film and not higher than Tg + 80 ° C., for example. In the heat setting at the time of stretching, for example, it is recommended to pass the heating zone at 30 to 150 ° C. for about 1 to 30 seconds after stretching. Further, after stretching the film, it may be stretched at a predetermined degree before or after heat setting. Further, after the stretching, a step of cooling while applying a stress to the film while keeping the stretched or tensioned state, or a cooling step after releasing the tensioned state may be added following this treatment.

When producing a label from a heat-shrinkable polyester film, it is preferable to perform tube formation with 1,3-dioxolane. It is because sufficient adhesive force is provided. In forming the tube, 1,3-dioxolane may be applied to one surface of the film and the other surface of the film may be pressure-bonded to the coated surface. When the adhesiveness is insufficient, there is a possibility that the label adhesive part may be peeled off when the label is heat-shrinked or when the beverage bottle is handled.

In order to obtain a film having the above-mentioned dynamic friction coefficient μd, a configuration in which an easy-slip layer is formed on the other side (second surface side) of the film is preferable. As a method for forming the slippery layer, it is sufficient that the slippery layer can be uniformly formed on the surface of the film. However, the slippery layer coating liquid applied during the film formation process (in-line coating), The method of coating (offline coating) is simple, but in particular the cost and the effect of heat treatment during stretching after coating to improve the adhesion between the coating layer and the film are expected. Is preferred. As a coating method, any known method such as a reverse roll method, an air knife method, or a fountain method can be employed. Moreover, it is desirable to contain a lubricant in the coating solution used for coating and to contain a binder resin in order to improve the solvent adhesiveness of the film.

  Inclusion of a binder resin in the coating liquid has an effect of preventing deterioration in printability. With transparent film labels, printing is usually applied to the surface that comes into contact with the container, and especially for the purpose of improving the slipperiness of the beverage container, the easy-slip layer surface is opposite to the surface where the label contacts the container. In many cases, printing is performed on the surface opposite to the slippery layer. Therefore, the printability of the first surface of the film, which is the surface opposite to the easy-slip layer, is important. The cause of hindering the printability of the first surface of the film is the transfer of the slippery layer. This occurs when a film having an easy-sliding layer is rolled up and wound, and the easy-sliding layer is partially or entirely transferred to the opposite surface. The binder resin has the effect of preventing this transfer.

  It should be noted that the use of a particulate lubricant component as a lubricant in the slippery layer may hinder the transparency of the film and may cause the particles to aggregate. Preferred lubricants that do not cause such problems include paraffin wax, microwax, polypropylene wax, polyethylene wax, ethylene-acrylic wax, stearic acid, behenic acid, 12-hydroxystearic acid, stearic acid amide, oleic acid amide, Erucic acid amide, methylene bis stearic acid amide, ethylene bis stearic acid amide, ethylene bis oleic acid amide, butyl stearate, monoglyceride stearate, pentaerythritol tetrastearate, hydrogenated castor oil, stearyl stearate, siloxane, higher alcohol type Molecule, stearyl alcohol, calcium stearate, zinc stearate, magnesium stearate, lead stearate silicone (dimethylsiloxa ) Based low molecular weight compound (oil) or silicone (dimethylsiloxane) -based resins., These other which may be used alone, or may be used in combination of two or more if necessary. Among these, silicone compounds and silicone resins, particularly copolymer resins containing a silicone component are recommended. This is because the dynamic friction coefficient of the film surface is reduced, the change of the friction coefficient before and after the hot water treatment is small, the solvent adhesiveness of the film is hardly hindered, and the effect of preventing the transfer of the slippery layer is great.

  Here, the silicone type refers to organosiloxanes, which are oily, rubbery, and resinous, and are called silicone oil, silicone rubber, and silicone resin, respectively. Since these all have a water repellent effect, a lubrication effect, a release action, etc., inclusion in the outermost layer portion of the film is effective in reducing the surface friction. In addition, when used as a beverage container label, it is often attached by heat-shrinking using steam or hot air. In a slippery layer with low water resistance, the heat-shrinking treatment using steam causes a decrease in slipperiness. Although it is easy, good slipperiness can be maintained even after the steam treatment due to the water repellent effect inherent in silicone.

  Among the silicone-based resins, a copolymer resin containing a silicone component is particularly preferable, and examples thereof include a silicone / acrylate copolymer. When it is formed on the surface of the polyester film as an easy-sliding layer and then wound into a roll, it has a great effect of making it difficult to transfer to the back surface of the film. Further, when used as a beverage label, the film surface is subjected to a printing process, but the printability is hardly hindered.

  The content of the silicone component is preferably from 10 to 80% by weight, more preferably from 20 to 70%, as the existing amount in the slippery layer. If the content is less than 10% by weight, the effect of improving the slipperiness is small, and if it exceeds 80% by weight, the easy-slip layer component is easily transferred to the back surface when rolled.

Furthermore, it is recommended that the easy-slip layer component contains a resin component having a binder function.
Examples of the resin component include polyester resins, polyamide resins, polyurethane resins, epoxy resins, phenol resins, acrylic resins, polyvinyl acetate resins, polyolefin resins such as polyethylene and polypropylene, and copolymers thereof. Or a modified resin, a cellulose resin, etc. are mentioned. When used as a binder of a silicone component-containing copolymer, if a component similar to the copolymer component is used, the effect as a binder is great. Moreover, since the resin used as the binder in the present invention needs water resistance, it is essential that the resin be essentially water-insoluble.

  It is preferable to use water-soluble or water-dispersible lubricants and binder resin components from the viewpoints of safety and environmental friendliness.

The amount of the coating solution is preferably from 0.002~0.5g / m ² as the amount present on the film after stretching (the amount of solid content), more preferably at 0.005~0.4g / m ² Ah. 0.002
If it is less than g / m ² , the slipping property will be small, and if it exceeds 0.5 g / m ² , the transparency of the film will be lowered, the solvent adhesion will be lowered, and wear debris will be generated during processing. Since it becomes easy and may lead to the fall of productivity, it is not preferable.

Since the heat-shrinkable polyester film of the present invention has excellent adhesion to ink, an ink layer can be provided on the first surface side of the film. In particular, it exhibits excellent adhesion to ink having alkali detachability. This type of ink having alkali detachability is, for example, a sample of 1 g obtained by laminating an ink layer on a heat-shrinkable film, cut into 1 cm square, and 30 minutes in 100 cc NaOH 3% aqueous solution (90 ° C.). After stirring, it means an ink having an ink removal rate of 90% by mass or more when washed with water and dried. The reason for the removal is that the ink layer is mainly swollen or dissolved in alkaline hot water. Practically, washing with weak alkaline hot water is usually performed for about 20 to 30 minutes, during which the ink layer is preferably removed.

The method for imparting alkali detachability to the ink layer is not particularly limited. For example, a compound that is soluble or swellable in alkaline hot water is used as a commonly used ink, for example, a colored body or a binder composed of a pigment or a dye. And a method of adding it to an ink containing a volatile organic solvent as a constituent component. Compounds that are soluble or swellable in alkaline hot water include inorganic salts such as sodium chloride, sodium nitrate, potassium nitrate, sodium acetate and ammonium sulfate, organic acids such as ascorbic acid, sebacic acid and azelaic acid or salts thereof, polyethylene oxide, High molecular polyethers such as polytetramethylene oxide, poly (meth) acrylic acid or metal salts thereof, or copolymers thereof (for example, copolymers of styrene and acrylic compounds such as (meth) acrylic acid), etc. Can be mentioned. Examples of the compound include those that are liquid at room temperature. Specifically, alcohols such as methyl alcohol, ethyl alcohol, isopropyl alcohol, tert-butyl alcohol, cyclohexyl alcohol, and benzyl alcohol, ethylene glycol, diethylene glycol, Monoethyl, monopropyl, monobutyl ether or monomethyl, monoethyl, monopropyl, monobutyl ether or monomethyl, monoethyl ester, etc. of polyhydric alcohols such as ethylene glycol and pentaerythritol, etc., dioxane, acetone, methyl ethyl ketone, diacetone alcohol, dimethylformamide , Tetrahydrofuran and the like. Among them, it is preferable that it has a high boiling point because it needs to remain in the ink layer. Specifically, a boiling point of 50 ° C. or higher is preferable, and further, a monoalkyl ether of a polyhydric alcohol due to its solubility in alkaline hot water. Is particularly preferred.

In addition, although the thickness of the heat-shrinkable film of this invention is not specifically limited, For example, as a heat-shrinkable film for labels, 10-200 micrometers is preferable and 20-100 micrometers is more preferable.

  Hereinafter, the present invention will be described in more detail by way of examples. However, the following examples are not intended to limit the present invention, and modifications and implementations within the scope of the present invention are included in the present invention. In addition, the measuring method of the physical property of the film obtained by the Example and the comparative example is as follows.

(1) Thermal contraction rate in the maximum shrinkage direction The film is cut into a 10 cm × 10 cm square along the longitudinal direction and the orthogonal direction, and treated in warm water at 95 ° C. ± 0.5 ° C. for 10 seconds under no load. After heat shrinking, the sample was immediately immersed in water at 25 ° C. ± 0.5 ° C. for 10 seconds, and then the length of the sample in the vertical and horizontal directions was measured and determined according to the following formula. The direction with the largest shrinkage rate was defined as the maximum shrinkage direction.
Heat shrinkage rate (%) = 100 × (length before shrinkage−length after shrinkage) ÷ (length before shrinkage)

(2) Nitrogen atom content on the film surface (atomic%)
Using an X-ray photoelectron spectroscopy measuring apparatus (ESCA spectrometer “ES-200 type”; manufactured by Kokusai Electric Co., Ltd.), the ratio of the amount of nitrogen atoms to the total amount of elements on the first surface of the sample film was determined and determined.

(3) Wetting tension on the film surface The wetting tension of the first surface of the film was measured by the method of JIS K 6768.

(4) Ink adhesion The ink “Daiecolo SRF915 Red” and “SRF Diluting Solvent No. 2” manufactured by Dainichi Seika Kogyo Co., Ltd. were mixed at a weight ratio of 100: 10 and applied to the first surface of the film using Mayer Bar # 5. After coating, it was immediately dried with cold air from a dryer for 15 seconds. After the cellophane tape was applied to the obtained sample, the tape was peeled off, and the occurrence of ink pinholes after peeling was evaluated as follows.
○: No ink pinhole is generated. Δ: Ink pinhole is generated, but the size is less than 1 mm. X: Ink pinhole is generated and the size is 1 mm or more

(5) Alkali detachability of ink After applying the ink to the first surface of the film by the method of (4), a sample was cut out to a size of 2 cm × 20 cm, and the temperature was controlled within the range of 85 ° C. ± 2 ° C. It was immersed in a 1.5% NaOH aqueous solution for 20 minutes. The sample was taken out and immediately immersed in water at 25 ° C. ± 2 ° C. for 20 seconds, and the detached state of the ink layer after taking out was visually judged according to the following criteria.
○: The ink layer is completely detached Δ: The ink layer is partly detached or easily removed by rubbing the ink layer with a cotton swab after removal ×: The ink layer is not detached and the ink layer is removed with a cotton swab after removal Unpeelable by rubbing

(6) Openability after label cutting Slit the heat-shrinkable film, then use a center seal machine to make a tube by solvent bonding with 1,3-dioxolane so that the easy-slip layer coating surface is on the outside, It wound up in a two-fold state. Subsequently, the tube was left for 24 hours in a room controlled at 25 ± 1 ° C. and RH65 ± 2%. Thereafter, the tube was continuously cut with a cutting machine under the same indoor atmosphere conditions (number of cut labels: 200) to produce a heat shrinkable film label. All the labels were opened by hand, and the opening of the cut portion was determined according to the following criteria (full score of 3).
3: Can be opened without resistance 2: There may be light resistance, but opening is possible 1: There is a part where the cutting part cannot be opened

(7) Peeling strength of heat seal part The surface temperature of the seal bar was set in the range of the evaluation temperature ± 0.5 ° C. with a heat sealer, and the film surfaces were heat sealed at a pressure of 40 N / cm ² and a time of 300 seconds. A 15 mm wide sample was cut out from the heat seal portion, and the peel strength was measured with a tensile tester at a peel rate of 200 mm / min. The ambient temperature was 23 ° C.

(8) Friction coefficient The dynamic friction coefficient μd between the second surfaces of the film was measured in an environment of 23 ° C. and 65% RH in accordance with JIS K-7125.
Moreover, about the dynamic friction coefficient after 80 degreeC warm water shrinkage | contraction treatment, fixing a film to the metal frame 10% short in the maximum shrinkage direction with respect to a film, and making it shrink | contract 10% by shrinking in 80 degreeC warm water. After dipping for 20 seconds, the sample was pulled up, naturally dried for 24 hours in an atmosphere of 23 ° C. and 65% relative humidity, and then measured under the same conditions as described above.

(9) Solvent adhesiveness 1,3-dioxolane was applied to one surface of the film, the other surface was pressure-bonded to the coated surface, and joined into a tube shape. The tube was cut into a 15 mm length in the direction perpendicular to the flow direction during processing to obtain a sample, and a T-peel test in the above direction of the joint portion was performed under the condition of a tensile speed of 200 mm / min according to JIS K 6854.

(10) Energy conversion value per film area during surface treatment Energy conversion value per film area (kW / m ² / min) during surface treatment
= High-frequency power device current value (A) x voltage (kV) ÷ electrode width (m) ÷ film travel speed (m / min)
As sought.

Film 1
1) Polyester resin and unstretched film Polyethylene terephthalate 40% by weight, polyester terephthalic acid 100% by mole, neopentyl glycol 30% by mole and ethylene glycol 70% by weight, and polybutylene terephthalate 10% by weight are mixed. The obtained polyester composition was mixed, melt-extruded with a single screw extruder at 280 ° C., and rapidly cooled to obtain an unstretched film having a thickness of 180 μm.

(Preparation of coating solution)
The solid content of an aqueous dispersion of silicone / acrylic acid ester copolymer (Charine NS-626, manufactured by Nissin Chemical Industry Co., Ltd.) is 70% by mass in the total solid content of the coating liquid, and the aqueous dispersion of the acrylic acid ester copolymer is dispersed. The liquid (Vinyl Blanc 2585 Nissin Chemical Industry Co., Ltd.) has a solid content of 20 mass% in the solid content, the acetylene glycol derivative (Surfinol 486 manufactured by Air Products Japan) has a solid content of 10 mass% in the solid content, and isopropyl alcohol 20 mass%. 100 kg of an aqueous solution containing was added to the tank.

The unstretched film is coated with a coating solution by a fountain die coating / smoothing bar method, and then the coating film is preheated at 100 ° C. for 10 seconds with a tenter, and then stretched 4.0 times at 80 ° C. in the transverse direction. For 10 seconds. The thickness of the film was 45 μm, and the coating amount of the slippery layer was 0.01 g / m ² .

Subsequently, the corona treatment in a nitrogen atmosphere was performed on the side opposite to the surface on which the easy-slip layer was formed on the film under the following conditions. The treatment electrode and the treatment portion of the corona treatment apparatus were enclosed by a double chamber, and nitrogen was continuously supplied to replace the nitrogen atmosphere. The corona-treated electrode was a bar electrode made of aluminum, and the treatment roll was made of silicone rubber. The gap between the treatment electrode and the film was 0.5 mm, the gap between the film and the chamber was 0.3 mm, and the gap was covered with a cotton cloth (another). The high frequency power supply used was a device manufactured by Kasuga Electric Co., Ltd., the transmission frequency was 45 ± 3 KHz, the treatment atmosphere temperature and the treatment roll surface temperature were both 40 ° C., and other conditions were subjected to corona treatment as shown in Table 1. The film surface temperature during the treatment was 40 ° C., and the oxygen concentration in the nitrogen atmosphere was 250 ppm. The obtained film is referred to as film 1, and the physical properties of the film are shown in Table 1.

Film 2
As for the coating solution, the solid content of the aqueous dispersion of silicone / acrylate copolymer (Charine FE-230, manufactured by Nissin Chemical Industry Co., Ltd.) is 70% by mass in the total solid content of the coating solution, and water of the copolymerized polyester resin. An aqueous system containing 20% by mass of the solid content of the dispersion (manufactured by AGN709 Toyobo), 10% by mass of the solid content of the acetylene glycol derivative (Surfinol 486 Air Products Japan), and 20% by mass of isopropyl alcohol. A heat-shrinkable film roll was obtained by the same method as film 1 except that the liquid was used as a coating liquid. The obtained film roll is referred to as film 2, and the film physical properties are shown in Table 1.

Film 3
The solid content of dimethyl silicone resin (SE4005 manufactured by Nissin Chemical Laboratory) is 70% by mass in the total solid content of the coating solution, and the solid content of the aqueous dispersion of copolymerized polyester resin (AGN702 manufactured by Toyobo) is 20% by mass. %, Heat shrinkage in the same manner as film 1 except that the solid content of acetylene glycol derivative (Surfinol 486 manufactured by Shin-Etsu Chemical Co., Ltd.) is 10% by weight in solid content and an aqueous solution containing 20% by weight of isopropanol is used as the coating solution. The film roll was obtained. The obtained film roll is referred to as film 3, and the film physical properties are shown in Table 1.

Film 4
Polyester resin aqueous dispersion (TIE51 Takemoto Yushi) solid content is 70 wt% in solid content, polyethylene wax aqueous emulsion (HYTEC E-4BS manufactured by Toho Chemical Industries) is 25 mass% in solid content, antistatic agent (product) The coating solution was an IPA-water solution containing 5% by mass of “TB702” (manufactured by Takemoto Yushi). Other than that, a heat-shrinkable polyester film was obtained in the same manner as Film 1. The obtained film roll is referred to as film 4, and the film physical properties are shown in Table 1.

Film 5
The coating solution is a heat-shrinkable film in the same manner as the film 1 except that an aqueous sulfonate solution (TB214 made by Matsumoto Yushi) and an aqueous solution containing 20% by mass of isopropanol are used as the coating solution and the coating amount is 0.005 g / m ^2. Got a roll. The obtained film roll was used as film 5 and the film physical properties are shown in Table 1.

Film 6
A heat-shrinkable film roll was obtained in the same manner except that the coating solution was not applied to film 1. The obtained film roll was used as film 6 and the film physical properties are shown in Table 1.

Film 7
A heat-shrinkable polyester film having a thickness of 45 μm was obtained in the same manner as in Example 1 except that the film 1 was not subjected to corona treatment. The obtained film was taken as film 7 and the physical properties of the film are shown in Table 1.

Film 8
An unstretched film was obtained in the same manner as film 1. This unstretched film was preheated at 100 ° C. for 10 seconds, stretched 4.0 times in the transverse direction at 80 ° C. with a tenter, and heat treated at 80 ° C. for 10 seconds to obtain a heat-shrinkable polyester film having a thickness of 45 μm. A film was formed. Subsequently, this film was guided to a corona treatment apparatus under an air atmosphere and subjected to corona treatment under the conditions shown in Table 1. The processing equipment at this time was the same as in Example 1. The obtained film was designated as film 8 and the film physical properties are shown in Table 1.

Cylindrical labels were prepared with films 1 to 6 such that a coating layer having a height of 180 mm and a circumference of 220 mm was the outer surface.
Using a steam tunnel made by Fuji Astec Inc (model: SH-1500-L), the above label was passed through for 15 seconds, at a first zone temperature of 70 ° C., a second zone temperature of 75 ° C., and a third zone temperature of 82 ° C., and 500 ml It was heat-shrinked and attached to a PET bottle beverage. When put into the vending machine, out of 400 films 1 to 3, no clogging occurred, 5 out of 400 clogged with film 4, and 8 out of 400 clogged with films 5 and 6 .

  The heat-shrinkable film of the present invention is excellent in ink adhesion to various types of ink and has excellent detachability with respect to ink of a type that is desorbed with an alkaline aqueous solution. Moreover, since it is excellent also in blocking resistance, since generation | occurrence | production of troubles, such as an opening defect after the label cut at the time of making a film into a label form, can also be suppressed, it is excellent in workability and useful on industrial production. Moreover, it is excellent in slipperiness and can prevent clogging inside the vending machine when used for beverage labels. Therefore, it is very useful as a label for covering containers such as bottled beverages.

Claims (8)

  A sample obtained by cutting a film into a 10 cm × 10 cm square shape was dipped in 95 ° C. warm water for 10 seconds, then dipped in water at 25 ° C. for 10 seconds, and then the heat shrinkage rate in the maximum shrinkage direction was 50% or more, the nitrogen atom content of the outermost layer on one side (first side) of the film is 0.2 to 5.0 atomic%, and the dynamic friction between the other side (second side) of the film The coefficient μd is 0.28 or less, the film is dipped for 20 seconds while shrinking 10% in warm water at 80 ° C. in the maximum shrink direction, and then naturally dried for 24 hours in an atmosphere of 23 ° C. and 65% relative humidity. A heat-shrinkable polyester-based film, wherein the coefficient of dynamic friction μd between the second surfaces of the film is 0.30 or less.   The heat-shrinkable polyester film according to claim 1, wherein the wetting tension on the first surface side of the film is 40 mN / m or more.   The heat-shrinkable polyester film according to claim 1 or 2, wherein the first film sides of the coated film have a peel strength after heat sealing at 75 ° C of 5 N / 15 mm width or less.   The heat-shrinkable polyester film according to any one of claims 1 to 3, wherein the first surface and the second surface of the film can be solvent-bonded with 1,3-dioxolane.   The heat-shrinkable polyester film according to any one of claims 1 to 4, wherein an easy-slip layer is provided as an outermost layer on the second surface side of the film.   The heat-shrinkable polyester film according to claim 5, wherein the easy-slip layer contains a silicone component.   The heat-shrinkable polyester film according to claim 5 or 6, wherein the easy-slip layer is provided by a coating method.   A heat-shrinkable label made from the heat-shrinkable polyester film of claim 1-7.