Heat-shrink polyester film for packaging.

Abstract

[Problem] To provide a heat shrinkable polyester film that has sufficient thermal shrinkage characteristics in the main shrinkage direction, which is the longitudinal direction, without containing a large amount of a monomer component that may serve as an amorphous component, while having low thermal shrinkage in the width direction, which is perpendicular to the main shrinkage direction, and low shrinkage stress. [Solution] A heat shrinkable polyester film which contains ethylene terephthalate as a main constituent, while containing from 0 mol% to 5 mol% (inclusive) of a monomer component that may serve as an amorphous component in all polyester resin components, and which is characterized by satisfying the following conditions (1)-(4). (1) The hot water thermal shrinkage in the main shrinkage direction of film is from 15% to 50% (inclusive) in cases where the film is treated in a hot water at 90°C for 10 seconds. (2) The hot water thermal shrinkage in the width direction, which is perpendicular to the main shrinkage direction of film, is from 0% to 12% (inclusive) in cases where the film is treated in a hot water at 90°C for 10 seconds. (3) The maximum shrinkage stress in the main shrinkage direction of film as measured in a hot air at 90°C is from 2 MPa to 10 MPa (inclusive). (4) A constituent unit derived from diethylene glycol is contained in an amount of from 7 mol% to 30 mol% (inclusive) in 100 mol% of all polyester resin components.

Description

Heat-shrinkable polyester film and package The present invention relates to a heat-shrinkable polyester film and a package. Specifically, it is suitable for label applications and bundling applications for binding lunch boxes and the like, and is a film that does not contain a large amount of amorphous components as monomer components constituting polyester. It has a high shrinkage rate in the main shrinkage direction, a low shrinkage rate in the direction orthogonal to the main shrinkage direction, and a low shrinkage stress, so that peeling of the adhesive part of the label and deformation of the container are less likely to occur. It is a heat-shrinkable polyester film. In recent years, stretched films (so-called heat-shrinkable films) made of polyvinyl chloride resins, polystyrene resins, polyester resins, etc. have been widely used for applications such as label packaging, cap sealing, and integrated packaging that combine the protection of glass bottles and PET bottles with product display. Among such heat-shrinkable films, polyvinyl chloride films have problems such as low heat resistance, generation of hydrogen chloride gas during incineration, and being a cause of dioxin. In addition, polystyrene films are inferior in solvent resistance, require the use of inks with special compositions during printing, and need to be incinerated at high temperatures, and there is a problem that a large amount of black smoke is generated with a strange smell during incineration. Therefore, polyester-based heat-shrinkable films with high heat resistance, easy incineration, and excellent solvent resistance have been widely used as shrink labels, and with the increase in the circulation volume of PET containers, the usage amount has been increasing. In addition, as a normal heat-shrinkable polyester film, those that shrink greatly in the width direction are widely used. Such a heat-shrinkable polyester film with the width direction as the main shrinkage direction is stretched at a high magnification in the width direction to exhibit the shrinkage characteristics in the width direction, but in the longitudinal direction orthogonal to the main shrinkage direction, it is often only stretched at a low magnification, and there are also those that are not stretched. Films that are only stretched at a low magnification in the longitudinal direction or films that are only stretched in the width direction have the drawback of inferior mechanical strength in the longitudinal direction. When used as a label film for bottles or a bundling film for bundling lunch boxes and the like, after forming the film into a ring and attaching it to the bottle or lunch box, it must be heat-shrunk in the circumferential direction. Therefore, when attaching a heat-shrinkable film that shrinks in the width direction as a bundling film, an annular body must be formed so that the width direction of the film becomes the circumferential direction, and then the annular body must be cut at predetermined lengths and attached to the bottle or lunch box by hand covering or the like. Therefore, it is difficult to quickly attach a label film or a bundling film made of a heat-shrinkable film that shrinks in the width direction to a bottle or a lunch box. Therefore, recently, there has been a demand for a film that shrinks in the longitudinal direction and can be directly wound around and attached to the periphery of a bottle or a lunch box from a film roll. The center seal process of forming and sealing a film tubular body, and processes such as cutting and hand covering are no longer required, and it is also possible to attach at high speed. In addition, there is a high demand for films that use recycled raw materials for PET bottles from an environmental perspective. Ordinary heat-shrinkable polyester films use raw materials containing a large amount of amorphous components in order to impart heat-shrinkage characteristics. Therefore, there is a limit to the ratio of recycled raw materials that can be mixed, and it has not been possible to provide a heat-shrinkable polyester-based film containing a large amount of recycled raw materials. However, as described in Prior Art Document 1, even without using a large amount of amorphous components, by devising the stretching conditions, it has been found that a heat-shrinkable polyester-based film having high shrinkability in the longitudinal direction, high mechanical strength, and small thickness unevenness in the longitudinal direction can be formed. It has been found that a heat-shrinkable polyester-based film having high shrinkability in the longitudinal direction, high mechanical strength, and small thickness unevenness in the longitudinal direction can be formed. However, in raw materials containing little amorphous component, the drawing stress during drawing increases, so the stress during shrinkage, that is, the shrinkage stress increases. As problems caused by high shrinkage stress, for example, in a bottle label, after winding a film around a bottle and attaching the ends of the label to each other with an adhesive or the like, it is heated and shrink-finished. If the shrinkage stress is high, there will be problems such as the attached part shifting or peeling off. In recent years, for the purpose of weight reduction and waste reduction, containers for box lunches and prepared foods sold at convenience stores and supermarkets may use containers with a thin thickness. In containers with a thin thickness, the strength of the container also decreases. Therefore, if the shrinkage stress of the shrink film for exterior decoration is high, problems such as the container being deformed due to the shrinkage stress will occur. International Publication No. 2014 / 021120 An object of the present invention is to solve the problems of Patent Document 1, and to provide a heat-shrinkable polyester-based film that has sufficient heat shrinkage characteristics in the main shrinkage direction, which is the longitudinal direction, even if it does not contain a large amount of monomer components that can become amorphous components, has a low heat shrinkage rate in the width direction orthogonal to the main shrinkage direction, and has a low shrinkage stress. That is, the present invention has the following configuration. 1. A heat-shrinkable polyester-based film having ethylene terephthalate as a main constituent component and containing 0 mol% or more and 5 mol% or less of monomer components that can become amorphous components in all polyester resin components, and satisfying the following requirements (1) to (4). A heat-shrinkable polyester-based film characterized by the above. (1) The hot water heat shrinkage rate in the main shrinkage direction of the film when treated in hot water at 90°C for 10 seconds is 15% or more and 50% or less. (2) The hot water heat shrinkage rate in the direction orthogonal to the main shrinkage direction of the film when treated in hot water at 90°C for 10 seconds is 0% or more and 12% or less. (3) The maximum shrinkage stress in the main shrinkage direction of the film measured under hot air at 90°C is 2 MPa or more and 10 MPa or less. (4) The constituent unit derived from diethylene glycol is 7 mol% or more and 30 mol% or less in 100 mol% of all polyester resin components. 2. The heat-shrinkable polyester film according to the first aspect, wherein the tensile fracture strength in the direction orthogonal to the main shrinkage direction is 80 MPa or more and 200 MPa or less. 3. The heat-shrinkable polyester film according to the first or second aspect, wherein the film thickness unevenness in the main shrinkage direction of the film is 13% or less. 4. The heat-shrinkable polyester film according to any one of the first to third aspects, wherein in the measurement of the shrinkage stress in the main shrinkage direction of the film under hot air at 90 ° C, the shrinkage stress 30 seconds after the start of measurement is 60% or more and 100% or less of the maximum shrinkage stress. 5. The heat-shrinkable polyester film according to any one of the first to fourth aspects, wherein the main shrinkage direction is the longitudinal direction of the film. 6. A label derived from the heat-shrinkable polyester film according to any one of the first to fifth aspects A package characterized by having at least a part of the outer periphery of the object to be packaged. According to the present invention, the problems of Patent Document 1 are solved, and even if it does not contain a large amount of monomer components that can become amorphous components, it has sufficient heat shrinkage characteristics in the main shrinkage direction that is the longitudinal direction, and in the width direction orthogonal to the main shrinkage direction, the heat shrinkage rate is low and the shrinkage stress is low. It has made it possible to provide a heat-shrinkable polyester film. In addition, since it is not necessary to contain a large amount of monomer components that can become amorphous components in the raw materials, it has made it possible to provide a highly environmentally friendly heat-shrinkable polyester film containing a large amount of PET bottle recycled polyester or polyester using bio-derived raw materials. The heat-shrinkable polyester film of the present invention can be suitably used for film labels for bottles, banding films for lunch boxes, etc., can be very efficiently attached within a short time, and when heat-shrunk after attachment, it is possible to obtain a good finish with extremely little peeling at the bonding part or deformation of the container. Fig. shows a plastic container of a lunch box for evaluating the deformation of the container in the package after shrink finishing. Hereinafter, the heat-shrinkable polyester film of the present invention will be described in detail. The manufacturing method of the heat-shrinkable polyester film will be described in detail later, but the film is usually obtained by transporting and stretching using a roll or the like. At this time, the transport direction of the film is referred to as the longitudinal direction, and the direction orthogonal to the longitudinal direction is referred to as the film width direction. Therefore, the width direction of the heat-shrinkable polyester film shown below is the direction perpendicular to the roll unwinding direction, and the film longitudinal direction refers to the direction parallel to the roll unwinding direction. The main shrinkage direction in the heat-shrinkable polyester films obtained in the examples and comparative examples is the longitudinal direction. As a preferable manufacturing method for continuously manufacturing the heat-shrinkable polyester film according to any one of the above first to third, a polyester-based unstretched film containing ethylene terephthalate as a main constituent component and containing 0 mol% or more and 5 mol% or less of a monomer component that can be an amorphous component in all polyester resin components is stretched in the width direction at a temperature of Tg + 5°C or more and Tg + 40°C or less at a magnification of 3.5 times or more and 6 times or less while gripping both ends in the width direction in the tenter with clips, and then stretched in the longitudinal direction at a temperature of Tg + 5°C or more and Tg + 40°C or less at a magnification of 1.5 times to 2.7 times or less using heated rolls with a speed difference, and then the film is relaxed by 0% or more and 15% or less in the width direction while performing heat treatment at a temperature of Tg or more and Tg + 40°C or less with both ends of the film gripped by clips. As described in Patent Document 1, without using a large amount of amorphous raw materials, the key point in the film-forming conditions for obtaining a shrink film having a high shrinkage rate in the longitudinal direction, high mechanical strength, and small thickness unevenness is to cause orientation crystallization by stretching at a relatively high magnification in the width direction to suppress the shrinkage rate in the direction orthogonal to the main shrinkage direction, and in the subsequent longitudinal stretching, to create a state where the molecules are oriented but the orientation crystallization is small by stretching at a relatively low magnification. However, even at low magnification, the stretching stress during longitudinal stretching becomes high in a raw material system that uses a large amount of crystalline raw material. Also, since the film is stretched at a high magnification in the width direction to generate oriented crystals, the stress during subsequent longitudinal stretching becomes even higher. The stress during stretching is closely related to the shrinkage stress of the film, and in order to reduce the shrinkage stress, it is necessary to reduce the stretching stress. Therefore, the present inventors focused on diethylene glycol as a glycol component that can reduce the stretching stress during longitudinal stretching. When the amount of diethylene glycol increases, the heat resistance deteriorates and the discharge of foreign substances during melt extrusion increases, so it has not been actively used until now. However, the present inventors have found that when diethylene glycol is used, the stretching stress during film stretching decreases, and only the shrinkage stress decreases without a significant decrease in the shrinkage rate. The film of the present invention has ethylene terephthalate as a main constituent component. Here, the main constituent component means that 70 mol% or more of all the polymer constituent components constituting the film is ethylene terephthalate. By using ethylene terephthalate as the main constituent component, excellent mechanical strength and transparency can be obtained. As a polymerization method of polyethylene terephthalate (hereinafter sometimes simply referred to as PET), a direct polymerization method in which terephthalic acid, ethylene glycol, and, if necessary, other dicarboxylic acid components and diol components are directly reacted, and a transesterification method in which dimethyl ester of terephthalic acid (including methyl esters of other dicarboxylic acids if necessary) and ethylene glycol (including other diol components if necessary) are subjected to a transesterification reaction, or any other production method can be used. The intrinsic viscosity of polyethylene terephthalate is preferably in the range of 0.45 to 0.8. If the intrinsic viscosity is lower than 0.45, crystallization occurs due to stretching and the shrinkage property deteriorates, which is not preferable. Also, if it is greater than 0.8, the filter pressure increase becomes large and high-precision filtration becomes difficult, which is not very preferable. The present invention can also use a PET recycling raw material among PETs (hereinafter sometimes simply referred to as a recycling raw material). The recycling raw material generally uses PET as a constituent component in order to improve the moldability when making a PET bottle, but it is common that a small amount of isophthalic acid is contained as a monomer component. In the present invention, although a large amount of a polymer raw material containing a large amount of monomer components that can become amorphous components is not used, since isophthalic acid may be contained in the recycling raw material, the content of the amorphous monomer is expressed as being in the range of 0 mol% or more and 5 mol% or less in 100 mol% of the total polyester resin component. Typical examples of monomers that can become amorphous components are isophthalic acid. For example, neopentyl glycol, 1,4-cyclohexanedimethanol, isophthalic acid, 1,4-cyclohexanedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 2,2-diethyl-1,3-propanediol, 2-n-butyl-2-ethyl-1,3-propanediol, 2,2-isopropyl-1,3-propanediol, 2,2-di-n-butyl-1,3-propanediol, and hexanediol can also be mentioned, and there is no particular problem even if they are contained within the above content range. Here, the interpretation of the above term "capable of becoming an amorphous component" will be explained in more detail. In the present invention, the "amorphous polymer" specifically refers to a case where there is no endothermic peak due to melting in the measurement using a DSC differential scanning calorimeter. The amorphous polymer has not substantially progressed in crystallization and cannot take a crystalline state, or even if it crystallizes, the degree of crystallinity is extremely low. In the present invention, the "crystalline polymer" refers to something other than the above "amorphous polymer", that is, a case where there is an endothermic peak due to melting in the measurement using a DSC differential scanning calorimeter. The crystalline polymer has the property of being crystallizable when the temperature of the polymer is raised, or has already crystallized. Generally, for a polymer in which a large number of monomer units are bonded together, when it has various conditions such as low stereoregularity of the polymer, poor symmetry of the polymer, large side chains of the polymer, many branches of the polymer, and small intermolecular cohesive force between polymers, it becomes an amorphous polymer. However, depending on the state of existence, crystallization may proceed sufficiently and it may become a crystalline polymer. For example, even a polymer with large side chains can become crystalline if the polymer is composed of a single monomer unit. Therefore, even for the same monomer unit, the polymer may become crystalline or amorphous. Thus, in the present invention, the expression "unit derived from a monomer that can become an amorphous component" is used. Here, in the present invention, a monomer unit refers to a repeating unit that constitutes a polymer derived from one polyhydric alcohol molecule and one polyvalent carboxylic acid molecule. When a monomer unit composed of terephthalic acid and ethylene glycol is the main monomer unit constituting the polymer, a monomer unit composed of isophthalic acid and ethylene glycol, a monomer unit composed of terephthalic acid and neopentyl glycol, a monomer unit composed of terephthalic acid and 1,4 - cyclohexanedimethanol, a monomer unit composed of isophthalic acid and butanediol, etc. can be cited as units derived from monomers that can become the above amorphous components. Further, the present invention can use a polyester raw material (hereinafter sometimes simply referred to as a biopolyester raw material) using ethylene glycol produced from a plant - derived raw material as a glycol component. In addition, when the heat - shrinkable polyester - based film of the present invention is treated in hot water at 90 °C for 10 seconds in an unloaded state, the heat shrinkage rate (that is, the hot - water heat shrinkage rate at 90 °C) in the main shrinkage direction of the film calculated by the following formula 1 from the lengths before and after shrinkage is preferably 15% or more and 50% or less. Heat shrinkage rate = { (length before shrinkage - length after shrinkage) / length before shrinkage} × 100 (%) ··· Formula 1 When the hot water heat shrinkage rate in the main shrinkage direction at 90 °C is less than 15%, when used as a label or a bundling film, since the shrinkage amount is small, wrinkles and sagging will occur in the label or bundling film after heat shrinkage, which is not preferable. On the other hand, even if the hot water heat shrinkage rate in the main shrinkage direction at 90 °C exceeds 50%, there is no particular problem. However, in the present invention, usually about 50% is the upper limit of the heat shrinkage rate. The lower limit value of the hot water heat shrinkage rate in the main shrinkage direction at 90 °C is preferably 20%, more preferably 25%, and particularly preferably 30%. In addition, when the heat-shrinkable polyester film of the present invention is treated in hot water at 90 °C for 10 seconds in a no-load state, from the lengths before and after shrinkage, the hot water heat shrinkage rate in the direction orthogonal to the main shrinkage direction of the film calculated by the above formula 1 is preferably 0% or more and 12% or less. When the hot water heat shrinkage rate in the direction orthogonal to the main shrinkage direction at 90 °C exceeds 12%, when used as a label or a bundling film, the length of the film in the direction orthogonal to the shrinkage direction becomes shorter during heat shrinkage, which is not preferable. On the other hand, when it is less than 0%, the label length in the direction orthogonal to the main shrinkage direction becomes longer during heat shrinkage, and sagging occurs and it is likely to wrinkle, which is not preferable. The hot water heat shrinkage rate in the direction orthogonal to the main shrinkage direction at 90 °C is preferably 1% or more and 11% or less, more preferably 2% or more and 10% or less, and even more preferably 3% or more and 9% or less. The heat-shrinkable polyester film of the present invention preferably has a maximum shrinkage stress in the main shrinkage direction measured under a hot air of 90 °C of 2 MPa or more and 10 MPa or less. The measurement of the shrinkage stress shall be carried out by the method described in the examples. When the maximum shrinkage stress at 90 °C in the main shrinkage direction exceeds 10 MPa, lifting or peeling of the label bonding part may occur, or in the case of a thin-walled container, crushing may occur due to shrinkage stress during shrinkage, which is not preferable. The maximum shrinkage stress at 90 °C is more preferably 9 MPa or less, and even more preferably 8 MPa or less. Also, when the maximum shrinkage stress at 90 °C is less than 2 MPa, when used as a label for a container, the label may become loose and not adhere to the container, which is not preferable. The maximum shrinkage stress at 90 °C is more preferably 2.5 MPa or more, and even more preferably 3 MPa or more. Also, the shrinkage stress 30 seconds after the start of measurement in hot air at 90 °C is preferably 60% or more and 100% or less with respect to the above maximum shrinkage stress. That is, the heat-shrinkable polyester-based film of the present invention exhibits a unique heat-shrinkage characteristic that it exhibits a shrinkage stress comparable to the maximum heat-shrinkage stress even 30 seconds after starting to heat-shrink. When the shrinkage stress ratio after 30 seconds / maximum shrinkage stress × 100 (hereinafter referred to as stress ratio) is less than 60%, when covering the container with a label and heating and shrinking it, the followability of the label when the container expands due to heating deteriorates. When the temperature of the container drops after shrinkage and thermal expansion disappears, the label becomes loose and the finish has no tightness, which is not preferable. The above stress ratio is more preferably 75% or more, even more preferably 80% or more, and particularly preferably 90% or more. A larger stress ratio is preferable because the followability is better, but since the shrinkage stress after 30 seconds cannot exceed the maximum shrinkage stress, the upper limit is 100%. The structural unit derived from diethylene glycol as the glycol component contained in the heat-shrinkable polyester-based film of the present invention is preferably 7 mol% or more and 30 mol% or less of the structural unit derived from diethylene glycol in 100 mol% of the total polyester resin component. If it is less than 7 mol%, it is not preferable because it exceeds the above preferable shrinkage stress range. Also, if it exceeds 30 mol%, the heat resistance of the resin decreases and foreign matter generation troubles occur during melt extrusion, which is not preferable. More preferably, it is 8 mol% or more and 29 mol% or less, even more preferably 9 mol% or more and 28 mol%, and particularly preferably 10 mol% or more and 27 mol% or less. The heat-shrinkable polyester film of the present invention preferably has a tensile fracture strength in a direction orthogonal to the main shrinkage direction of the film of 80 MPa or more and 200 MPa or less. The method for measuring the tensile fracture strength will be described in the examples. If the above tensile fracture strength is less than 80 MPa, the "waist" (stiffness) when attaching to a container for label use or banding film use becomes weak, which is not preferable. On the contrary, if the tensile fracture strength exceeds 200 MPa, the cuttability (ease of tearing) at the initial stage when tearing the label or banding film becomes poor, which is not preferable. The lower limit of the tensile fracture strength is more preferably 100 MPa or more, further preferably 110 MPa or more, particularly preferably 120 MPa or more, and the upper limit is more preferably 190 MPa or less, further preferably 180 MPa or less, particularly preferably 170 MPa or less. The heat-shrinkable polyester film of the present invention preferably has a film thickness unevenness in the main shrinkage direction of the film of 13% or less. When the film thickness unevenness of the film in the main shrinkage direction is greater than 13%, printing unevenness is likely to occur during label printing, and shrinkage unevenness after heat shrinkage is likely to occur, which is not preferable. The thickness of the heat-shrinkable polyester film of the present invention is not particularly limited, but is preferably 5 to 100 μm, more preferably 10 to 95 μm as a heat-shrinkable film for label use or banding use. Also, the manufacturing method of the heat-shrinkable polyester film of the present invention is not restricted in any way, but for example, the above-described polyester raw material can be melt-extruded by an extruder to form an unstretched film, and the unstretched film can be obtained by biaxially stretching it by the method shown below. When melt-extruding the raw material resin, it is preferable to dry the polyester raw material using a dryer such as a hopper dryer or paddle dryer, or a vacuum dryer. After drying the polyester raw material in this way, it is melted at a temperature of 200 to 300 °C using an extruder and extruded into a film shape. For such extrusion, any existing method such as the T-die method or the tubular method can be adopted. And an unstretched film can be obtained by rapidly cooling the sheet-like molten resin after extrusion. As a method for rapidly cooling the molten resin, a method of casting the molten resin onto a rotating drum from a die and rapidly cooling and solidifying it to obtain a substantially unoriented resin sheet can be preferably employed. Furthermore, as will be described later, the obtained unstretched film can be stretched in the width direction under predetermined conditions and then stretched in the longitudinal direction under predetermined conditions to obtain the heat-shrinkable polyester-based film of the present invention. Hereinafter, preferred biaxial stretching for obtaining the heat-shrinkable polyester-based film of the present invention will be described. [Preferred stretching method for heat-shrinkable polyester-based film] Ordinary heat-shrinkable polyester-based films are produced by stretching an unstretched film in the direction in which shrinkage is desired. Although the requirements for heat-shrinkable polyester-based films that shrink in the longitudinal direction have been high, simply stretching the unstretched film in the longitudinal direction alone results in a significant decrease in the tensile fracture strength in the width direction and is not preferable in terms of productivity because a wide film cannot be produced. In addition, since ordinary heat-shrinkable polyester films use a raw material containing a large amount of amorphous components to impart heat-shrinkage characteristics, there is a limit to the ratio of recycled raw materials that can be mixed. The stretching method of the heat-shrinkable polyester-based film of the present invention has a contrivance in the stretching ratios in the width direction and the longitudinal direction. The stretching ratios will be described below. [Stretching ratio in the width direction] As a result of research, the inventors have found that for films that do not intentionally use amorphous PET raw materials, the shrinkage rate in the stretching direction becomes high when the stretching ratio is around 2 times. Also, when the stretching ratio is higher than 3 times, the shrinkage rate in the stretching direction decreases and the shrinkage rate in the non-stretching direction becomes high. From these research results, in order to biaxially stretch and shrink in the longitudinal direction, it is preferable to stretch at a temperature of Tg + 5°C or higher and Tg + 40°C or lower and at a transverse stretching ratio of 3.5 times or more and 6 times or less. If it is lower than 3.5 times, it is not sufficient to reduce the shrinkage rate in the width direction. Although there is no particular upper limit for the transverse stretching ratio, if it is higher than 6 times, it becomes difficult to stretch in the longitudinal direction (so-called breakage is likely to occur), which is not preferable. More preferably, it is 3.7 times or more and 5.8 times or less, and even more preferably, it is 3.9 times or more and 5.6 times or less. Since the relationship between the stretching ratio and the shrinkage rate of a film using a PET raw material containing a small amount of amorphous components is as described above, it does not matter whether or not heat treatment is performed after transverse stretching and before longitudinal stretching. [Stretching ratio in the longitudinal direction] In the longitudinal direction, at a temperature of Tg + 5°C or higher and Tg + 40°C or lower, the stretching ratio is preferably 1.5 times or more and 2.7 times or less. If it is lower than 1.5 times, the shrinkage rate is insufficient, and if it is higher than 2.7 times, the shrinkage rate in the width direction becomes high, which is not preferable as a uniaxially shrinkable film in the longitudinal direction. Also, in stretching higher than 2.7 times, the shrinkage stress in the longitudinal direction becomes high, which is not preferable. More preferably, it is 1.6 times or more and 2.6 times or less, and even more preferably, it is 1.7 times or more and 2.5 times or less. Also, if the stretching temperature in the longitudinal direction is less than Tg + 5°C, breakage is likely to occur during stretching, which is not preferable. If it is higher than Tg + 40°C, thermal crystallization of the film progresses and the shrinkage rate decreases, which is not preferable. More preferably, it is Tg + 8°C or higher and Tg + 37°C or lower, and even more preferably, it is Tg + 11°C or higher and Tg + 34°C or lower. As described above, as a preferable stretching method in the present invention, it is exemplified that the stretching ratio in the longitudinal direction is smaller than the stretching ratio in the width direction. [Heat treatment and relaxation in the width direction] It is preferable to perform relaxation in the width direction of 0% or more and 15% or less while performing heat treatment at a temperature of Tg or higher and Tg + 40°C or lower while gripping both ends of the film with clips. If the heat treatment temperature is less than Tg, the meaning of the heat treatment is lost, and the shrinkage over time (so-called natural shrinkage rate) during storage after the product is not preferable as it increases. Also, if it is higher than Tg + 40°C, the thermal crystallization of the molecular chains progresses, and the shrinkage rate decreases not only in the width direction but also in the longitudinal direction, which is not very preferable. More preferably, it is Tg + 3°C or higher and Tg + 37°C or lower, and even more preferably, it is Tg + 6°C or higher and Tg + 34°C or lower. Also, if the relaxation rate in the width direction is lower than 0%, it becomes substantially stretching in the width direction, which is not preferable as relaxation. Also, the relaxation rate may be higher than 15%, but if the relaxation rate is high, the width of the film that finally becomes the product becomes narrow, which is not preferable. More preferably, it is 1% or more and 14% or less, and even more preferably, it is 2% or more and 13% or less. In the present invention, regarding obtaining uniaxial shrinkage property in the longitudinal direction by stretching at a relatively high magnification in the width direction and then stretching at a relatively low magnification in the longitudinal direction, it is considered that the properties of crystalline PET containing not many monomer components that can become amorphous components are related. That is, for crystalline PET, when stretched at a high stretching magnification such as 3.5 times or more in the width direction, for example, the molecular chains are oriented and the crystallization of the molecular chains progresses, and this is presumed to act as a factor for lowering the heat shrinkage rate in the width direction. In this regard, a stretching magnification of about 2.7 times or less in the longitudinal direction is a region where crystallization does not progress much even if the molecular chains are oriented to some extent in the longitudinal direction, and it is estimated that a relatively high heat shrinkage rate can be obtained. Of course, the relaxation heat treatment in the width direction is also considered to make a certain contribution to reducing the heat shrinkage rate in the width direction. The package of the present invention is formed by covering at least a part of the outer periphery of the object to be packaged with a binding film (and label) obtained from the heat-shrinkable polyester film of the present invention and heat-shrinking it. Examples of the object to be packaged include plastic containers such as (PET bottles for beverages, various bottles, cans, snacks, and) bento boxes, paper boxes, and the like. Usually, when covering these objects to be packaged with a label obtained from a heat-shrinkable polyester film by heat-shrinking, the binding film (and label) is heat-shrunk by about 5 to 50% and adhered to the package. Note that the binding film (and label) covering the object to be packaged may or may not be printed. As a method for producing the binding film (and label), a rectangular film is rolled in the longitudinal direction, the ends are overlapped and adhered to form a label shape, or a film wound in a roll shape is rolled in the roll longitudinal direction, the ends are overlapped with the film and adhered to form a tubular body, which is then cut into a label shape. The method of adhering the films to each other can be performed using known methods such as fusion sealing, solvent adhesion, adhesion with a hot melt adhesive, and adhesion with an energy ray curable adhesive. In addition, when an unstretched film is stretched at a ratio of 2.7 times or less, the thickness unevenness in the stretching direction becomes very poor. Therefore, stretching an unstretched film made of PET raw material at a stretching ratio of around 2 times has hardly been performed so far. However, it has been found that when a film once stretched at a high magnification of 3.5 times or more in the width direction is stretched at a ratio of around 2 times in the longitudinal direction, the thickness unevenness in the longitudinal direction is good. This is presumably because, when stretching in the longitudinal direction, unlike stretching an unstretched film, stretching at a high magnification in the width direction once changes the stretching stress and the stress-strain curve when stretching at around 2 times in the longitudinal direction. Hereinafter, the present invention will be described in more detail by way of examples. However, the present invention is not limited to such embodiments, and can be appropriately modified without departing from the spirit of the present invention. The compositions of the raw materials used in the examples and comparative examples, the film production conditions in the examples and comparative examples, and the film evaluation results in the examples and comparative examples are shown in Table 1, Table 2, and Table 3, respectively. Also, the film evaluation method is as follows. [Tg (glass transition temperature)] Using a differential scanning calorimeter (manufactured by Seiko Instruments Inc., DSC220), 5 mg of the unstretched film was placed in a sample pan, the lid of the pan was closed, and the temperature was raised from -40°C to 120°C at a rate of 10°C / min in a nitrogen gas atmosphere for measurement. Tg (°C) was determined based on JIS-K7121-1987. [Intrinsic viscosity (IV)] 0.2 g of polyester was dissolved in 50 ml of a mixed solvent of phenol / 1,1,2,2-tetrachloroethane (60 / 40 (weight ratio)), and measured using an Ostwald viscometer at 30°C. The unit is dl / g. [Thermal shrinkage rate (hot water thermal shrinkage rate)] The film was cut into a 10 cm × 10 cm square, treated in hot water at a predetermined temperature ±0.5°C for 10 seconds in a no-load state to cause thermal shrinkage, and then the dimensions of the longitudinal and transverse directions of the film were measured. According to Equation 1 above, the thermal shrinkage rate was determined for each. The direction with the larger thermal shrinkage rate was defined as the main shrinkage direction. [Shrinkage stress] A strip-shaped film sample with a length of 2000 mm and a width of 20 mm in the main shrinkage direction was cut out from a heat-shrinkable film, and the shrinkage stress was measured using a high-tenacity measuring machine with a heating furnace, the Tensilon universal testing machine PTM-250 (registered trademark of Orientec Co., Ltd.), manufactured by Toyo Baldwin Co., Ltd. (current company name: Orientec). The heating furnace of the high-tenacity measuring machine was preheated to 90 °C inside the furnace, and the distance between the chucks for gripping the film sample was set to 100 mm. When attaching the sample to the chucks of the high-tenacity measuring machine, the air supply to the heating furnace was temporarily stopped, the door of the heating furnace was opened, both ends of the 150-mm-long sample by 25 mm each in the length direction were sandwiched between the chucks, the distance between the chucks was set to 100 mm, and it was fixed tightly so that the distance between the chucks and the length direction of the sample were aligned and the sample was horizontal. After attaching the sample to the chucks, the door of the heating furnace was quickly closed and the air supply was restarted. The time when the door of the heating furnace was closed and the air supply was restarted was defined as the start time of measuring the shrinkage stress, and the shrinkage stress (MPa) after 30 seconds was determined. Also, the maximum value of the shrinkage stress measurement values from the start time of measuring the shrinkage stress to 30 seconds after the start of measurement was defined as the maximum value of the shrinkage stress (maximum shrinkage stress (MPa)). Note that during the measurement of the shrinkage stress, the distance between the chucks was fixed at 100 mm, and the change in the shrinkage stress from the start of measurement to 30 seconds after the start of measurement was measured. Then, the ratio of the shrinkage stress value 30 seconds after the start time of measurement to the maximum value of the shrinkage stress was defined as the shrinkage stress ratio (expressed by the following formula). Shrinkage stress ratio (%) = (Value of shrinkage stress after 30 seconds) ÷ (Maximum value of shrinkage stress) × 100 [Tensile breaking strength] A strip-shaped test piece with a measurement direction (film width direction) of 140 mm and a direction orthogonal to the measurement direction (film longitudinal direction) of 20 mm was prepared. Using a universal tensile testing machine "DSS-100" (manufactured by Shimadzu Corporation), both ends of the test piece were gripped by the chucks by 20 mm on one side each (distance between the chucks: 100 mm), and a tensile test was conducted under the conditions of an ambient temperature of 23 °C and a tensile speed of 200 mm / min, and the strength (stress) at the time of tensile fracture was defined as the tensile breaking strength. [Thickness unevenness in the longitudinal direction] The film was sampled in a long roll shape with a length of 30 m and a width of 40 mm in the longitudinal direction of the film, and measured at a speed of 5 (m / min) using a continuous contact thickness gauge manufactured by Micron Measuring Instrument Co., Ltd. In sampling the above-mentioned roll-shaped film sample, the length direction of the film sample was taken as the main shrinkage direction of the film. The maximum thickness during measurement was designated as Tmax., the minimum thickness as Tmin., and the average thickness as Tave., and the thickness unevenness in the longitudinal direction of the film was calculated from the following formula 2. Thickness unevenness = { (Tmax. - Tmin.) / Tave.} × 100 (%)... Formula 2 [Shrink finishability and container deformation (for use of banding film for bento containers)] For a thin-walled bento container made of polypropylene (side 150 × 150 mm, height 100 mm), the circumferential direction of the container was set as the shrinkage direction of the film so that the body and lid of the container were bound by the film, and after fusing and sealing at 220 °C, it was heat-shrunk in a shrink tunnel at a set temperature of 90 °C. Fig. 1 is a view of the bento container seen from above. Before attaching the film, the length Y from one side to the opposite side was measured at a pitch of 5 mm, and after shrinking and attaching the film, the length Y' at the same location was measured in the same manner, and the absolute value of the difference between Y and Y' was designated as L. The maximum value Lmax of L calculated at a pitch of 5 mm was obtained, and those with a large Lmax were judged to have a large container deformation, and the criteria were as follows. ○: Lmax ≦ 4 mm △: 4 mm < Lmax ≦ 5 mm ×: 5 mm < Lmax [Shrink finishability and peeling of the adhesive part (for use of bottle labels)] A heat-shrinkable film was pre-printed in three colors with grass, gold, and white inks manufactured by Toyo Ink Co., Ltd. Then, both ends of the printed film were adhered with a commercially available ethylene-vinyl acetate-based hot melt adhesive to create a cylindrical label (the main shrinkage direction of the heat-shrinkable film is the circumferential direction, and the outer peripheral length is 1.05 times the outer peripheral length of the bottle to be attached). After that, the cylindrical label was put on a 500-ml PET bottle (body diameter 62 mm, minimum diameter of the neck part 25 mm), and using a steam tunnel (model: SH-1500-L) manufactured by Fuji Astec Inc., it was heat-shrunk at a passing time of 2.5 seconds and a zone temperature of 80°C to attach the label. When attaching, at the neck part, it was adjusted so that the part with a diameter of 55 mm became one end of the label. Labels with peeled adhesive parts after shrinkage were regarded as defective products. 100 labels were created in one sample, and the ratio of defective products among the 100 shrink-finished labels was calculated as the defective rate (%) and evaluated according to the following criteria. ○: 1% or less △: 2% or more and 5% or less ×: 6% or more Also, the polyesters used in the examples and comparative examples are as follows. Into a stainless steel autoclave equipped with a stirrer, a thermometer, and a partial circulation cooler, 100 mol% of dimethyl terephthalate (DMT) as the dicarboxylic acid component and 100 mol% of ethylene glycol (EG) as the glycol component were charged so that the molar ratio of ethylene glycol was 2.2 times that of dimethyl terephthalate. 0.05 mol% of zinc acetate (relative to the acid component) was added as a transesterification catalyst, and 0.225 mol% of antimony trioxide (relative to the acid component) was added as a polycondensation catalyst. The transesterification reaction was carried out while distilling off the generated methanol out of the system. Then, the polycondensation reaction was carried out under a reduced pressure condition of 26.7 Pa at 280°C to obtain polyester A with an intrinsic viscosity of 0.75 dl / g. The composition is shown in Table 1. Synthesis Examples B to D In the same manner as in Synthesis Example A, polyesters B to D shown in Table 1 were obtained. In the production of polyesters B and D, SiO2 (Silicia 266 manufactured by Fuji Silysia Chemical Ltd.; average particle size 1.5 μm) was added as a lubricant to the polyester at a ratio of 7200 ppm. In the table, DEG is diethylene glycol. The intrinsic viscosities of the respective polyesters were B: 0.7 dl / g, C: 0.65 dl / g, and D: 0.65 dl / g. Each polyester was appropriately formed into chips. Note that polyester E is a recycled raw material ("Clear Pellet" manufactured by Yono PET Bottle Recycling Co., Ltd.), and its intrinsic viscosity is 0.63 dl / g. Also, as described in Table 1, this polyester E contains 2 mol% of isophthalic acid with respect to all the dicarboxylic acid components constituting the polyester. Polyester F was prepared by the following production method. Magnesium acetate tetrahydrate was added to a mixture of terephthalic acid purified from a petroleum-derived raw material and ethylene glycol purified from a plant-derived raw material so that the Mg atom concentration in the polyester was 70 ppm, and an esterification reaction was carried out at a temperature of 255°C under normal pressure. Then, antimony trioxide in an amount such that the Sb atom concentration in the polyester was 280 ppm and trimethyl phosphate in an amount such that the P atom concentration in the polyester was 40 ppm were added, and the reaction was further carried out at a temperature of 260°C. Subsequently, the reaction product was transferred to a polycondensation reaction layer, and while heating and raising the temperature, the pressure of the reaction system was gradually reduced, and polycondensation was carried out at 280°C under a reduced pressure of 133 Pa (1 mmHg) by a conventional method to obtain polyester chips with IV = 0.62 dl / g. When the biomass content was measured, the biomass content was 17%. [Example 1] Polyester A, polyester C, and polyester D described above were mixed at a weight ratio of 87:7:6 and charged into an extruder. Thereafter, the mixed resin was melted at 280°C, extruded from a T-die, and wound around a rotating metal roll cooled to a surface temperature of 30°C and rapidly cooled to obtain an unstretched film with a thickness of 162 μm. The Tg of the unstretched film was 72°C. Thereafter, this unstretched film was led to a transverse stretching machine (hereinafter referred to as a tenter). Then, the unstretched film led to the tenter was preheated until the film temperature reached 100°C (Tg + 28°C), and then stretched 4.5 times in the transverse direction at 90°C (Tg + 18°C). Further, the film thus transversely stretched was led to a longitudinal stretching machine in which a plurality of roll groups were continuously arranged, preheated on a preheating roll until it reached 90°C (Tg + 18°C), and then stretched 2 times using the speed difference of the rolls. Thereafter, the longitudinally stretched film was forcibly cooled by a cooling roll set at a surface temperature of 25°C. Then, the cooled film was led to a tenter (second tenter), and in the corresponding second tenter, a 5% relaxation was applied in the film width direction while performing heat treatment for 8 seconds in an atmosphere of 90°C. By cutting and removing both edge portions after the second tenter, a biaxially stretched film of about 18 μm was continuously formed over a predetermined length to obtain a film roll made of a heat-shrinkable polyester-based film. Then, the properties of the obtained film were evaluated by the above method. The evaluation results are shown in Table 3. As a result of the evaluation, it was a film having sufficient shrinkability and a low shrinkage stress, so that there was no peeling of the label adhesion portion or deformation of the container, and good shrinkage finish was obtained. [Example 2] The procedure of Example 1 was repeated except that the draw ratio in the longitudinal direction was 2.5 times and the extrusion amount from the T-die of the molten mixed resin was adjusted so that the thickness of the film after stretching in the longitudinal direction became 18 μm. As a result of the evaluation, it was a film having sufficient shrinkability and a low shrinkage stress, so that there was no peeling of the label adhesion portion or deformation of the container, and good shrinkage finish was obtained. [Example 3] The extrusion amount from the T-die of the mixed resin melted so that the stretching magnification in the longitudinal direction was 2.7 times and the film thickness after stretching in the longitudinal direction became 18 μm was adjusted, and otherwise it was the same as in Example 1. As a result of the evaluation, it was a film having sufficient shrinkability, and good shrink finishing properties were obtained with no peeling of the label adhesion part and no deformation of the container because of the low shrink stress. Example 4 The relaxation during heat treatment, which is a post-stretching process in the longitudinal direction, was set to a relaxation rate of 10%, and otherwise it was the same as in Example 1 except that the extrusion amount from the T-die of the mixed resin melted so that the film thickness became 18 μm was adjusted. As a result of the evaluation, it was a film having sufficient shrinkability, and good shrink finishing properties were obtained with no peeling of the label adhesion part and no deformation of the container because of the low shrink stress. Example 5 The above-mentioned polyester A, polyester C, and polyester D were mixed at a weight ratio of 74:7:19 and charged into an extruder. Subsequently, the mixed resin was melted at 280°C, extruded from a T-die, and wound around a rotating metal roll cooled to a surface temperature of 30°C and rapidly cooled to obtain an unstretched film with a thickness of 162 μm. The Tg of the unstretched film was 65°C. Subsequently, this unstretched film was led into a transverse stretching machine (hereinafter referred to as a tenter). Then, the unstretched film led into the tenter was preheated until the film temperature reached 90°C (Tg + 25°C), and then stretched 4.5 times in the transverse direction at 80°C (Tg + 15°C). Furthermore, the film thus transversely stretched was led into a longitudinal stretching machine in which a plurality of roll groups were continuously arranged, preheated on a preheating roll until it reached 80°C (Tg + 15°C), and then stretched 2 times using the speed difference of the rolls. Subsequently, the longitudinally stretched film was forcibly cooled by a cooling roll set at a surface temperature of 25°C. Then, the cooled film was led into a tenter (second tenter), and in the corresponding second tenter, it was subjected to a relaxation of 8% in the film width direction while being heat-treated for 8 seconds in an atmosphere of 90°C. By cutting and removing both edge portions after the second tenter, a biaxially stretched film of about 18 μm was continuously formed over a predetermined length to obtain a film roll made of a heat-shrinkable polyester-based film. Then, the properties of the obtained film were evaluated by the above method. The evaluation results are shown in Table 3. As a result of the evaluation, it was a film having sufficient shrinkability, a low shrinkage stress, and good shrinkage finish properties without peeling of the label adhesion portion or deformation of the container. [Example 6] The procedure was the same as in Example 5 except that the draw ratio in the longitudinal direction was 2.5 times and the extrusion amount from the T-die of the molten mixed resin was adjusted so that the thickness of the film after stretching in the longitudinal direction became 18 μm. As a result of the evaluation, it was a film having sufficient shrinkability, a low shrinkage stress, and good shrinkage finish properties without peeling of the label adhesion portion or deformation of the container. [Example 7] The longitudinal stretching magnification was set to 2.7 times, and the extrusion amount from the T-die of the mixed resin melted so that the film thickness after stretching in the longitudinal direction became 18 μm was adjusted in the same manner as in Example 5 except for this. As a result of the evaluation, it was a film having sufficient shrinkability and low shrinkage stress, and good shrink finishing properties without peeling of the label adhesion part or deformation of the container. [Example 8] The above-mentioned polyester A, polyester C, and polyester D were mixed at a weight ratio of 55:7:38 and put into an extruder. Thereafter, the mixed resin was melted at 280°C, extruded from a T-die, and wound around a rotating metal roll cooled to a surface temperature of 30°C and rapidly cooled to obtain an unstretched film having a thickness of 162 μm. The Tg of the unstretched film was 55°C. Thereafter, this unstretched film was led to a transverse stretching machine (hereinafter referred to as a tenter). Then, the unstretched film led to the tenter was preheated until the film temperature reached 80°C (Tg + 25°C), and then stretched 4.5 times in the transverse direction at 70°C (Tg + 15°C). Further, the film stretched transversely in this way was led to a longitudinal stretching machine in which a plurality of roll groups were continuously arranged, preheated on a preheating roll until it reached 70°C (Tg + 15°C), and then stretched 2 times using the speed difference of the rolls. Thereafter, the longitudinally stretched film was forcibly cooled by a cooling roll set to a surface temperature of 25°C. Then, the cooled film was led to a tenter (second tenter), and in the corresponding second tenter, a relaxation of 12% was applied in the film width direction while performing heat treatment for 8 seconds in an atmosphere of 90°C. By cutting and removing both edge portions after the second tenter, a biaxially stretched film of about 18 μm was continuously formed over a predetermined length to obtain a film roll made of a heat-shrinkable polyester-based film. Then, the properties of the obtained film were evaluated by the above method. The evaluation results are shown in Table 3. As a result of the evaluation, it was a film having sufficient shrinkability and low shrinkage stress, and good shrink finishing properties without peeling of the label adhesion part or deformation of the container. [Example 9] The longitudinal stretching ratio was set to 2.5 times, and the extrusion amount from the T-die of the mixed resin melted so that the film thickness after stretching in the longitudinal direction became 18 μm was adjusted, and otherwise it was the same as in Example 8. As a result of the evaluation, it was a film having sufficient shrinkability, and due to the low shrinkage stress, there was no peeling of the label adhesion part or deformation of the container, and good shrink finishing properties were obtained. [Example 10] The longitudinal stretching ratio was set to 2.7 times, and the extrusion amount from the T-die of the mixed resin melted so that the film thickness after stretching in the longitudinal direction became 18 μm was adjusted, and otherwise it was the same as in Example 8. As a result of the evaluation, it was a film having sufficient shrinkability, and due to the low shrinkage stress, there was no peeling of the label adhesion part or deformation of the container, and good shrink finishing properties were obtained. [Example 11] It was the same as in Example 10 except that preheating was performed on the preheating roll at 85 °C (Tg + 30 °C) and longitudinal stretching was performed in the longitudinal stretching machine. As a result of the evaluation, it was a film having sufficient shrinkability, and due to the low shrinkage stress, there was no peeling of the label adhesion part or deformation of the container, and good shrink finishing properties were obtained. [Example 12] It was the same as in Example 1 except that the above-mentioned polyester E, polyester C, and polyester D were mixed at a weight ratio of 87:7:6 and charged into an extruder. The Tg of the unstretched film was 72 °C. As a result of the evaluation, it was a film having sufficient shrinkability, and due to the low shrinkage stress, there was no peeling of the label adhesion part or deformation of the container, and good shrink finishing properties were obtained. [Example 13] It was the same as in Example 1 except that the above-mentioned polyester F, polyester C, and polyester D were mixed at a weight ratio of 87:7:6 and charged into an extruder. The Tg of the unstretched film was 72 °C. As a result of the evaluation, it was a film having sufficient shrinkability, and due to the low shrinkage stress, there was no peeling of the label adhesion part or deformation of the container, and good shrink finishing properties were obtained. [Comparative Example 1] The procedure was the same as in Example 1, except that the above-described Polyester A and Polyester B were mixed at a weight ratio of 93:7 and charged into an extruder. The Tg of the unstretched film was 75°C. As a result of the evaluation, although it had sufficient shrinkability, the shrink stress was high, causing peeling at the label adhesion part and deformation of the container, and it was a film that could not obtain good shrink finish properties. [Comparative Example 2] The procedure was the same as in Example 1, except that the above-described Polyester A and Polyester C were mixed at a weight ratio of 93:7 and charged into an extruder. The Tg of the unstretched film was 74°C. As a result of the evaluation, although it had sufficient shrinkability, the shrink stress was high, causing peeling at the label adhesion part and deformation of the container, and it was a film that could not obtain good shrink finish properties. Since the heat-shrinkable polyester-based film of the present invention has excellent properties as described above, it can be suitably used for label applications for bottles and for bundling film applications used for bundling bento lunches, etc. The package in which the film is used as a label or a bundling film has a beautiful appearance. It is a film that has a sufficient heat shrinkage rate in the longitudinal direction even when the content of the monomer component that can become an amorphous component in the polyester is extremely low, so the recycling raw material ratio can be increased, and it is a film suitable for the environment.

Claims

Page 1 of 1 page Claims 1. A group of heat-shrinkable polyester films with ethylene terephthalate as the main structural component and containing monomer components that can be transformed into amorphous components equal to 0 mol% or more than 5 mol% in the total polyester resin composition, and which are heat-shrinkable polyester films that meet the following conditions (1)-(4): (1) In the case of treatment by immersion in hot water at 90 degrees Celsius for 10 seconds, the percentage of shrinkage in hot water of the main shrinkage direction of the film is equal to 15% or more than 50%. (2) In the case of treatment by immersion in hot water at 90 degrees Celsius for 10 seconds, the percentage of shrinkage in hot water of the width direction perpendicular to the main shrinkage direction of the film is equal to 0% or more than 12%. (3) The maximum shrinkage stress of the main shrinkage direction of the film measured under hot air at 90 degrees Celsius is equal to 2 megapascals or more than 10 megapascals. (4) In 100 moles of the total polyester resin composition, the structural unit derived from diethylene glycol is 7 moles or more, and not exceeding 30 moles.

1. A heat-shrinkable polyester film specified in Claim 1, characterized by a tensile strength in the direction perpendicular to the principal shrinkage direction of 80 MPa or more, not exceeding 200 MPa.

2. A heat-shrinkable polyester film specified in Claim 1 or 2, characterized by a film thickness in the principal shrinkage direction not exceeding 13%.

3. A heat-shrinkable polyester film specified in Claim 1-3, characterized by a shrinkage stress measured in the principal shrinkage direction of the film under hot air at 90°C, with a shrinkage stress of 60% or more, not exceeding 100% of the maximum shrinkage stress after 30 seconds of measurement in the principal shrinkage direction.

4. A heat-shrinkable polyester film specified in Claim 1-4, characterized by the principal shrinkage direction being the longitudinal direction of the film.

5. Packaging characterized by at least a portion of the outer surface of the packaged object being a label derived from a heat-shrinkable polyester film specified in Claim 1-5.